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NEW ADVANCES ON THE BIOCHEMICAL PATHWAYS IN THE RENINANGIOTENSIN SYSTEM IN HYPERTENSION AND THEIR ROLE IN CARDIAC
STRUCTURE AND FUNCTION BY
AARON J. TRASK
A Dissertation Submitted to the Graduate Faculty of
WAKE FOREST UNIVERSITY GRADUATE SCHOOL OF ARTS AND SCIENCES
in Partial Fulfillment of the Requirements
for the Degree of
DOCTOR OF PHILOSOPHY
Physiology & Pharmacology
December 2008
WinstonSalem, North Carolina
Copyright Aaron J. Trask 2008 Approved by: Carlos M. Ferrario, M.D., Advisor Examining Committee: James E. Jordan, Ph.D., Chairman Mark C. Chappell, Ph.D. Leanne Groban, M.D. E. Ann Tallant, Ph.D. Jasmina Varagic, M.D., Ph.D.
ACKNOWLEDGEMENTS
First and foremost, I want to thank Dr. Nancy Woodley at Ohio Northern
University for encouraging me to attend graduate school. She saw in me a curiosity
that needed an outlet, and graduate school has indeed provided me with a suitable
outlet. Thank you, Nancy. I am forever grateful.
Next, I would like to thank my advisor, Dr. Carlos M. Ferrario for providing
me the opportunities to explore things on my own, for never hovering over me, and
for providing guidance whenever or where ever needed. Your scientific prowess is
a rarity that I hope I can someday acquire. In addition, I would like to thank my
thesis committee without which I would have gone completely crazy in my tenure as
a graduate student. To Jim Jordan – thank you for your insightfulness and guidance
with my experiments when needed. To Mark Chappell – I truly appreciate all of the
help you have been to not only to my thesis experiments, but also as a good scientist.
To Leanne Groban – thank you for helping me understand the intricacies involved in
echocardiography and for our discussions on cardiac diastology. To Ann Tallant –
When I was applying to graduate schools, I came across a school that I had heard
good things about, and then I found your information on the Physiology &
Pharmacology website. I came to Wake Forest because you pushed to get me here. I
am forever grateful. Thank you for all that you and Dr. Gallagher have done for
Channie and I. And last, but not least, to Jasmina Varagic – thank you for your
continued guidance during my time here as a student. Our discussions about
ii
science and life have made me a better person. I truly appreciate our fruitful
discussions!
I would also like to thank the National Institutes of Health and the American
Heart Association for funding these studies.
Next, I would like to acknowledge the great training environment of both the
Department of Physiology & Pharmacology and the Hypertension & Vascular
Research Center. The faculty, staff, and students have made a concerted effort to
make this the best possible place for scientific training. I also want to thank the
Graduate School staff for all of their help throughout my graduate career. They are
truly a superb asset to the Graduate School.
As a first‐generation college graduate, the husband, son, grandson, brother,
and cousin of the hardest‐working people I know, I am truly grateful to my family to
an end at which no words can express. The blue‐collar work ethic instilled in me in
my small hometown of Arcanum, Ohio from a young age has served me well, and I
owe it to my family. To my grandparents, aunts, uncles, cousins – you have always
supported everything that I have wished to do. For that, I am truly appreciative. To
my Dad and Mom, Mark & Peggy – words cannot express how grateful I am for
everything that you have done for me. You have nurtured my curiosity from the
time I was crawling out of my crib at 6 months of age! I hope you will always know
that my curiosity will never die, and I owe it to you. Last, but certainly not least, I
want to thank my wife of five years, Channie. Your constant support through this
beginning of our life together was a driving force in my – our success. I could not
have done it without you.
iii
Four weeks short of my dissertation defense, my maternal grandfather lost
his 20‐year battle with heart disease. His first heart attack at the age of 52, when I
was 8 years old, sparked in me an interest in how the heart works. “What causes
heart attacks? How can they be prevented?,” I remember asking myself. Herman R.
Miller was a hard‐working family man with whom I spent a considerable amount of
time during the course of my childhood and beyond. He taught me many things in
life — how to fish and how to be a craftsman, and more importantly, he taught me
that there was nothing more important in life than family. In short, he helped teach
me how to be a man. After his first heart attack in 1988, he had several other heart
attacks and strokes, was diabetic, hypertensive, hypercholesterolemic — the
epitome of the metabolic syndrome. It was perhaps a medical miracle that he was
able to live quite well for most of his 20 years following his initial heart attack, but I
know that the pharmacy of medications he was taking gave us 20 more years with
him that we would not have had otherwise. It is in that spirit that I hope to be able
to repay what was given to me, more time with a man whom I already dearly miss. I
hope to be able to make further strides in heart research so that other people can be
afforded more time with their loved ones.
With all of that said, I dedicate this entire dissertation to my family without
which I would not be where I am today. Isaac Newton is quoted as once saying, “If I
have seen further, it is by standing on the shoulders of giants.” While quite literally
my generally short‐statured family may not be “giants,” that quote is very befitting
this occasion because they are giants in my life.
iv
TABLE OF CONTENTS
List of Figures ix List of Tables xi List of Abbreviations xii
bstract xvi A
CHAPTER I
GENERAL INTRODUCTION: THE RENINANGIOTENSIN SYSTEM AND THE HEART
(This chapter was published in the Textbook of Nephro‐Endocrinology, Ed. Singh A.
& Williams G. San Diego: Elsevier, 2009. 181‐188.) I.1 Abstract 2 I.2 Introduction 3 I.3 Cardiac RAS: Local vs. Endocrine Origin 4 I.4 RAS Actions at the Cellular Level 7 I.5 RAS and the Coronary Circulation 10 I.6 Significance of the RAS on Cardiac Function 12 I.7 Conclusions 14 References 16
Figures 33
CHAPTER II
GENERAL INTRODUCTION: ANGIOTENSIN(17): PHARMACOLOGY AND NEW CARDIOVASCULAR TREATMPERSPECTIVES IN ENTS
(This chapter was published in Cardiovascular Drug Reviews 2007; 25:162‐174.)
v
II.1 Abstract 38 II.2 Introduction 39 II.3 Angiotensin‐(1‐7)‐Forming Enzymes 40 II.4 Pharmacokinetics 42 II.5 Pharmacodynamics 44 II.6 Conclusions 52 Acknowledgements 53 References 54
Figures 68
CHAPTER III
GENERAL INTRODUCTION: FURTHER EXPANSION OF THE RENIN12) ANGIOTENSIN SYSTEM: ANGIOTENSIN(1
(This chapter is an excerpt from an artice published in the Journal of Molecular
Medicine 2008; 86: 663‐671.)
II.1 I
Angiotensin‐(1‐12) 75
References 77 igures 78 F
CHAPTER IV
RATIONALE AND AIMS
IV.1 Rationale and Aims 82
References 85
CHAPTER V
vi
PRIMARY ROLE OF ANGIOTENSIN CONVERTING ENZYME 2 IN CARDIAC PRODUCTION OF ANGIOTENSIN(17) IN TRANSGENIC REN2 HYPERTENSIVE
RATS
(This chapter was published in the American Journal of Physiology – Heart and Circulatory Physiology 2007; 292:H3019‐H3024.)
V.1 Abstract 88 V.2 Introduction 89 V.3 Materials and Methods 90 V.4 Results 93 V.5 Discussion 95 Acknowledgements 100 References 101 Figures 107
CHAPTER VI
DISRUPTION OF CARDIAC ANGIOTENSIN PEPTIDES BY ANGIOTENSIN CONVERTING ENZYME 2 INHIBITION EXACERBATES CARDIAC HYPERTROPHY
HYPERTENSAND FIBROSIS IN REN2 IVE RATS
(This chapter will be submitted to Hypertension, December, 2008) VI.1 Abstract 118 VI.2 Introduction 120 VI.3 Materials and Methods 121 VI.4 Results 127 VI.5 Discussion 128 Acknowledgements 132
References 134
vii
Tables 144
Figures 148
VII
CHAPTER
ANGIOTENSIN(112) IS AN ALTERNATE SUBSTRATE FOR THE PRODUCTION PEPTIDES IN THE HEART OF ANGIOTENSIN
(This chapter was published in the American Journal of Physiology – Heart and
Circulatory Physiology 2008; 294: H2242‐H2247.) VII.1 Abstract 159 VII.2 Introduction 160 VII.3 Materials and Methods 161 VII.4 Results 164 VII.5 Discussion 167 Acknowledgements 172 References 174 Tables 178
Figures 184
V
CHAPTER III
SUMMARY AND GENERAL DISCUSSION VIII.1 Summary and General Discussion 190 References 200
Figures 208
APPENDIX 212
viii
LIST OF FIGURES CHAPTER I Figure I.1 Current View of the Cardiac Renin‐Angiotensin System 34
igure I.2 The Two Sources of the Cardiac Renin‐Angiotensin System 36 F CHAPTER II Figure II.1 The Chemical Structure of Ang‐(1‐7) 69 Figure II.2 Current View of the Renin‐Angiotensin System 71
igure II.3 Plasma Clearance of Ang‐(1‐7) 73 F CHAPTER III Figure III.1 Ang‐(1‐12) Concentrations in Rat Tissue 79
igure III.2 Immunohistochemical Localization of Ang‐(1‐12) 81 F CHAPTER V Figure V.1 Ang II Degradation in Isolated Rat Hearts 108 Figure V.2 Ang‐(1‐7) Formation in Isolated Rat Hearts 110
erfus te Figure V.3 Immunoreactive Ang‐(1‐7) in Heart P a 112 Figure V.4 Chromatograph of Cardiac Perfusate 114
igure V.5 Angiotensin Converting Enzyme 2 Immunoblots 116 F CHAPTER V
Rate in Ren‐2 Rats
I Figure VI.1 Radiotelemetric Blood Pressure and Heart 149
ix
Figure VI.2 Plasma and Cardiac Angiotensin Peptides 151 Figure VI.3 Brightfield and Polarized Photomicrographs of Collagen Staining 153
Figure VI.4 Photomicrographs Showing Cardiomyocyte Cross‐Sectional Area 155
igure VI.5 Pressure‐Volume Loops in Ren‐2 Rats Treated ± MLN‐4760 157 F CHAPTER V II Figure VII.1 Ang Peptide Production in SD Hearts 185
earts Figure VII.2 Ang Peptide Production in Lewis and Congenic H 187
igure VII.3 Ang Peptide Production in WKY and SHR Hearts 189 F CHAPTER VIII
elin Figure VIII.1 Illustration of the Increasing Role of ACE2 in Cardiac Remod g 209
igure VIII.2 Illustration Relating the Current Studies to the Cardiac RAS 211 F APPENDIX Figure A.1 Ang‐(1‐7) Formation by POP in Isolated Hearts 213 Figure A.2 Ang‐(1‐7) Formation by Serine Proteases in Isolated Hearts 215
x
LIST OF TABLES CHAPTER VI Table VI.1 24‐Hour Radiotelemetric Blood Pressures and Heart Rates 145
able VI.2 Cardiac Functional Parameters 147 T CHAPTER V II Table VII.1 Time Course of Heart Rates in All Strains Studied 179
trains Studied Table VII.2 Time Course of Perfusion Pressures in All S 181 Table VII.3 Pooled Angiotensin Peptide Correlations 183
xi
LIST OF ABBREVIATIONS
2K1C 2 kidney, 1 clip hypertension AALAC nt nd Accreditation of A Association for Assessme a
Laboratory Animal Care ACE angiotensin converting enzyme ACE2 angiotensin converting enzyme 2 ADAM17 tumor necrosis factor α convertase
enzenesulfonyl fluoride AEBSF 4‐(2‐Aminoethyl)b Ang angiotensin ANOVA analysis of variance Aogen angiotensinogen
B r AR angiotensin II type 1 receptor blocke
1
AT angiotensin II type 1 receptor
2
AT angiotensin II type 2 receptor AT(1‐7) angiotensin‐(1‐7) receptor AVE 0991 angiotensin‐(1‐7) analog
uring diastole AWTd anterior wall thickness d BPM beats per minute COX‐2 cyclooxygenase‐2
ker CV‐11974 candesartan, angiotensin receptor bloc D‐Ala7 ng‐(1‐7) angiotensin‐(1‐7) receptor antagonist P/dt rate of change in left ventricular
‐A
d maximummaxpressure
dP/dtmin rate of change in left ventricular
xii
minimumpressure
e′ early mitral annular descent
E/e′ index of left ventricular filling pressures
DT E A ethylenediaminetetraacetic acid
flow velocity Emax maximal early mitral in Eps endopeptidases
g diastole EDDd end‐diastolic dimension durin EDP end‐diastolic pressure
e relationship EDPVR end‐diastolic pressure‐volum EDV end‐diastolic volume
ng diastole ESDd end‐systolic dimenstion duri ESP end‐systolic pressure
e relationship ESPVR end‐systolic pressure‐volum
e ESV end‐systolic volum fmol femtomole
ortening FS fractional sh g gram GFR glomerular filtration rate EPES N Hydroxyethyl)piperazine‐N'‐ethanesulfonic H ‐(2‐
Acid HFBA heptaflurorobutyric acid
liquid chromatography HPLC high performance HR heart rate
Da kilodalton k
xiii
kg kilogram
L‐NAME nitric oxide synthase inhibitor LTP long‐term potentiation LVH left ventricular hypertrophy MAP kinase mitogen activated protein kinase
) receptor mas angiotensin‐(1‐7 MeOH methanol mg milligram μM, μmol/L micromolar mM, mmol/L millimolar mL milliliter
e 2 inhibitor MLN‐4760 angiotensin converting enzym mm Hg millimeters of mercury
genic rat mRen2.Lewis mRen2.Lewis con ng nanogram nM, nmol/L nanomolar NO nitric oxide iNOS inducible nitric oxide synthase PCP lysosomal Pro‐X carboxypeptidase
pg picogram pM, pmol/L picomolar POP prolyl oligopeptidase
P perfusion pressure
xiv
P
Pro(R)R (pro)renin receptor
iastole PWTd posterior wall thickness during d NEP neprilysin, enkephalinase RAS renin‐angiotensin system RIA radioimmunoassay
rting enzyme 2 sACE2 secreted angiotensin conve SD Sprague‐Dawley rat SEM standard error of the mean
ensive rat SHR spontaneously hypert
V S stroke volume t1/2 half‐life
( tau τ) time constant of relaxation
(+ Tg ) [mRen2]27 transgenic rat Tg(‐) non‐transgenic Sprague‐Dawley rat TGF‐β transforming growth factor β TNF‐α tumor necrosis factor α
TOP thimet oligopeptidase
eia unit USP unit United States Pharmacop WFML‐1 rat renin inhibitor WKY wistar‐kyoto rat ZPP z‐pro‐prolinal
xv
ABSTRACT
Aaron J. Trask
NEW ADVANCES ON THE BIOCHEMICAL PATHWAYS IN THE RENIN
ANGIOTENSIN SYSTEM IN HYPERTENSION AND THEIR ROLE IN CARDIAC
STRUCTURE AND FUNCTION
Dissertation under the direction of Carlos M. Ferrario, M.D. Director, Hypertension and Vascular Research Center
Professor of Surgical Sciences and Physiology & Pharmacology
Cardiovascular disease, including heart failure, remains a leading cause of
mortality both in the United States, and worldwide. Two of the most recognized
contributing risk factors to the progression of cardiovascular disease and heart
failure are hypertension and cardiac hypertrophy. Although the incidence of heart
disease has been declining since 1999, it is still the number one killer accounting for
27% of all deaths in the United States in 2005, the latest year for which data are
available. Moreover, hypertension is a critical risk factor contributing to cardiac
hypertrophy and heart disease, and only about one out of every three patients
afflicted with hypertension are actually controlled.
Because the renin‐angiotensin system (RAS) plays a major contributing role
to the pathophysiology of hypertension and heart disease, the studies outlined in
this dissertation traverse the complexities of the biochemical pathways within the
cardiac renin‐angiotensin system in normal and hypertensive rats. My research
showed first that angiotensin converting enzyme 2 (ACE2) directly converts
angiotensin (Ang) II into Ang‐(1‐7) only in hypertrophic hearts isolated from
hypertensive rats. Moreover, chronic in vivo pharmacological blockade of ACE2
xvi
resulted in a disruption of the balance of cardiac Ang II and Ang‐(1‐7), the result of
which was increased cardiac fibrosis and hypertrophy in the absence of functional
changes in the heart. In addition, we showed that a new peptide within the
biochemical cascade of the RAS — called Ang‐(1‐12) — serves as an alternate
substrate for the production of downstream bioactive angiotensin peptides in hearts
isolated from normal and hypertensive rats. Collectively, the studies outlined in this
dissertation provide newer insights into the complexities that exist within the
cardiac RAS. Our data suggest that ACE2 may be a compensatory mechanism in
cardiac hypertrophy attempting to overcome for the deleterious effects of increased
cardiac Ang II activity on cardiac remodeling. Furthermore, our data showing that
both Ang II and Ang‐(1‐7) are produced from Ang‐(1‐12) in a renin‐independent
manner paves the way for the discovery of alternate enzymatic pathways that, in
accounting for the generation of angiotensins, may lead to new therapeutic
approaches for the treatment of hypertension and heart disease.
xvii
CHAPTER I
THE REN HEART INANGIOTENSIN SYSTEM AND THE
Aaron J. Trask and Carlos M. Ferrario
H D ypertension and Vascular Research Centerepart cologyWake icine
ment of Physiology and Pharma Forest Universi y School of MedWinston‐Salem, North Carolina
t
[This chapter was published in the Textbook of NephroEndocrinology (Ed. Singh A. & Williams G. San Diego: Elsevier, 2009. 181188.) and is reprinted with permission. Differences in formatting reflect the requirements of the publisher. Aaron J. Trask prepared the manuscript, while Dr. Carlos M. Ferrario acted in an editorial and advisory capacity.]
1
I.1 ABSTRACT
The existence and physiological importance of the cardiac renin‐angiotensin
system has shaped the ways in which cardiovascular diseases are currently treated.
The actions of two bioactive peptides of the RAS – angiotensin II and angiotensin‐(1‐
7) – on the heart are generally opposing, which provides the system with a counter‐
balancing mechanism that may be altered in pathological states such as
hypertension and heart disease. The current pharmacologic therapies for
hypertension and heart failure, which include angiotensin converting enzyme
inhibitors and angiotensin receptor blockers, may act not only in the systemic
circulation, but they may also act at local tissue sites, including the heart, to correct
the imbalance of the two angiotensin peptides. This chapter encompasses a brief
review of current literature as it pertains to the renin‐angiotensin system in the
heart, and incorporates how current therapies are working toward treatment of
cardiac disorders and heart failure.
Key Words: angiotensin I, angiotensin II, angiotensin‐(1‐7), ACE inhibitor, angiotensin receptor blocker, heart, cardiac RAS
2
I.2 INTRODUCTION
For many years, the renin‐angiotensin system (RAS) was thought to be
mainly a traditional circulating hormonal system whereby renal renin‐dependent
production of angiotensin II (Ang II) occurred in response to a fall in macula densa
sodium concentration, low arterial pressure, or a decrease in circulating blood
volume. Renin could then act upon its circulating substrate, angiotensinogen —
primarily produced in the liver — to produce the inactive precursor decapeptide,
angiotensin I (Ang I). This process served as the starting point for the RAS cascade
in that Ang I could be acted upon by several different enzymes to produce the
biologically active peptide hormones, Ang II and angiotensin‐(1‐7) [Ang‐(1‐7)]. A
diagrammatic figure of the current expanded view of the RAS as primarily
characterized by our laboratories (Ferrario et al., 2005) is shown in Figure I.1.
Recent advances over the last several decades showed that the RAS is not
merely an endocrine system — body tissues harbor local renin‐angiotensin systems,
which can alter physiologic processes by exerting autocrine/paracrine actions.
Local renin‐angiotensin systems (Lee et al., 1993;Paul et al., 2006) have been found
to date in the brain, kidney, vasculature, pancreas, uterus, placenta, the intestine,
and the focus of this chapter, the heart. These local systems are thought to exert
effects on the tissues in which they reside, independent of blood pressure
alterations (Lee et al., 1993;Paul et al., 2006). The local cardiac RAS is no exception.
This chapter will encompass the origin of the cardiac RAS and summarize how it
acts to regulate cardiac processes and coronary blood flow. Most of the
3
experimental findings regarding the cardiac RAS reported in this chapter are
derived from or performed in animal models, including rodents [see Paul et al., 2006
for review]. With the advent and wide use of angiotensin converting enzyme (ACE)
inhibitors and angiotensin receptor blockers (ARBs) for the treatment of
hypertension and heart failure also came clinical data that now begins to
complement years of experimental findings.
I.3 CARDIAC RAS: LOCAL VS. ENDOCRINE ORIGIN
In order for an organ to have a complete RAS, it must possess all of the
necessary components, including the genes leading to the expression of the
precursor protein angiotensinogen, as well as all of the processing enzymes that
determine which biologically‐active peptides will be produced. Using these criteria,
the heart does indeed possess a complete RAS. Angiotensinogen and renin, either
synthesized locally or uptaken from the circulation, serve as the precursors to Ang I,
which can be acted upon by either angiotensin converting enzyme (ACE) or
chymase (Urata et al., 1990) to yield the potent mitogenic vasopressor and growth‐
promoting hormone Ang II. Newer studies (Ferrario et al., 2005) now show that
Ang II can then be hydrolyzed by angiotensin converting enzyme 2 (ACE2) to
produce Ang‐(1‐7) (Trask et al., 2007), an action that allows ACE2 to regulate the
balance of the two biologically‐active arms of the RAS. Ang I can also be acted upon
by the endopeptidases prolyl oligopeptidase (POP), neprilysin (NEP), and thimet
oligopeptidase (TOP) to produce Ang‐(1‐7) (Welches et al., 1993). Although not all
of these activities have been shown to produce Ang‐(1‐7) directly in the heart, all of
4
these enzymes have been shown to hydrolyze Ang I into Ang‐(1‐7) (Chappell et al.,
2000;Yamamoto et al., 1992). Since the heart contains all of these necessary
components to produce Ang‐(1‐7) from Ang I (Cicilini et al., 1994;Fielitz et al.,
2002;Linardi et al., 2004), it is plausible to consider that given the availability of
substrate, Ang‐(1‐7) may also be produced from Ang I in the heart. While this area
of research still requires further investigation, early work from our laboratory
showed the release of Ang‐(1‐7) in canine coronary sinus post induction of acute
myocardial ischemia (Santos et al., 1990). In addition, newer studies showed the
involvement of ACE2 in accounting for the increased formation of Ang‐(1‐7) in
failing human heart ventricles (Zisman et al., 2003b;Zisman et al., 2003a).
As illustrated above, the existence of a RAS that is harbored within the heart
is without question, but the origin of the local cardiac RAS is still somewhat of a
controversy. In support of local production are the following data. First, cardiac
myocytes and fibroblasts have the ability to produce the angiotensin precursor
protein, angiotensinogen, as well as the rate‐limiting enzyme that serves as the
starting point of the RAS cascade, renin. Second, intriguing evidence suggests that
cardiac renin may be synthesized by mast cells, while low in abundance in the
normal heart, may be recruited into the cardiac tissue during pathological processes
such as ischemia (Francis and Tang, 2006;Le and Coffman, 2006;Mackins et al.,
2006;Miyazaki et al., 2006;Reid et al., 2007;Xiao and Bernstein, 2005). Third, some
studies have detected ample amounts of angiotensinogen (Kunapuli and Kumar,
1987;Sawa et al., 1992) in the human heart. In a comparative study of
angiotensinogen and renin, Dzau and colleagues (Dzau et al., 1987) found that
5
angiotensinogen mRNA levels were in far excess of renin in rodent hearts,
suggesting the possibility of excess substrate for the rate‐limiting enzyme, renin.
Fourth, angiotensinogen and renin may be localized only in the atria, but not in the
ventricles (Chernin et al., 1990). These studies provide support that the heart
contain nsin prs the machinery by which to synthesize angiote ecursors.
However, some studies have cast doubt on the de novo production of renin in
the heart. First, there are data that renin is uptaken from the circulation into cardiac
tissue for the processing of angiotensin peptides (Danser, 2003). Second, the
finding that cardiac renin falls to undetectable levels after bilateral nephrectomy is
indeed compelling (Danser et al., 1994), although recent identification of renin in
cardiac mast cells may provide an alternative explanation (Francis and Tang,
2006;Le and Coffman, 2006;Mackins et al., 2006;Miyazaki et al., 2006;Reid et al.,
2007;Xiao and Bernstein, 2005). Third, the transition from a circulating endocrine
to a local autocrine/paracrine system was shown to be mediated by several
different receptors. Both the Ang II AT1 receptor (de Lannoy et al., 1998;van Kats et
al., 1997) and the (pro)renin receptor (Nguyen et al., 2002;Nguyen et al.,
2004;Nguyen and Burckle, 2004) have been reported as mediating their ligand’s
uptake into the heart, respectively. Fourth, Kalinyak et al. (Kalinyak and Perlman,
1987) found that angiotensinogen mRNA was undetectable in the heart. Fifth,
perfused isolated rat hearts required the addition of angiotensinogen and renin into
the perfusate in order to detect angiotensin I formation (de Lannoy et al., 1997).
These data show that components of the renin‐angiotensin system may likely be
uptaken from the circulation for processing by cardiac proteases.
6
In summary, the origin of the cardiac RAS is likely a result of both local
production and uptake from the circulation, both compartments communicating in
endocrine, autocrine, paracrine, and intracrine ways we do not yet understand (see
Figure I.2). Studies that support either the synthesis or uptake of RAS components
in the heart are limited in that both require the isolation of the heart and/or its
components from the organism. While there is no doubt that a wealth of knowledge
has stemmed from these types of studies, including studies from our laboratory,
discovering ways in which to dissect how a particular organ and/or organ system
operates and communicates within the organism is of the utmost importance.
Additional insights into this question may provide a better understanding of the
biological physiology of tissue RAS in general. As previously suggested by Re (Re,
2004), we are in agreement that these two sources of the RAS likely interact via
some mechanism by which we do not yet understand.
I.4 RAS ACTIONS AT THE CELLULAR LEVEL
Two biologically‐active peptides of the RAS exert their effects on cardiac
dynamics and growth at the cellular level. It is now evident that both Ang II and
Ang‐(1‐7) have opposing actions on cardiac myocytes, fibroblasts, and coronary
endothelial cells. Ang II, via the AT1 receptor, facilitates calcium (Ca2+) handling in
the cardiac cells (Baker et al., 1984;Baker et al., 1989;Freer et al., 1976;Kass and
Blair, 1981;Peach, 1981), triggering enhanced cardiac contractility. This occurs via
increases in cytosolic Ca2+ occurring both via increased uptake at the cellular
membrane and by activation of inositol phosphates leading to Ca2+ release from
7
sarcoplasmic reticulum (Baker et al., 1989). In both cardiac myocytes and
fibroblasts, Ang II also exhibits growth‐promoting effects by activating the mitogen‐
activated protein (MAP) kinase cascade, a pathway long recognized to be important
in cellular growth (Booz et al., 1994;Sadoshima et al., 1995;Schorb et al.,
1995;Yamazaki et al., 1995). Solid evidence for Ang II‐mediated cardiac fibrosis was
provided when Villarreal and colleagues (Villarreal et al., 1993) reported that Ang II
could bind AT1 receptors in cardiac fibroblasts. Further studies showed that Ang II
may act through transforming growth factor beta (TGF‐β) to induced increased
collagen deposition (Campbell and Katwa, 1997). Proliferation of fibroblasts leads
to an increased deposition of collagen in the myocardium, which, when combined
with myocyte hypertrophy, leads to left ventricular hypertrophy (LVH) — a major
risk factor for hypertension and heart failure.
The above‐mentioned effects of Ang II have been attributed to the AT1
receptor; however, Ang II also binds to another receptor—the AT2 receptor—with
high affinity (de Gasparo et al., 2000). This receptor is thought to oppose the actions
of Ang II‐induced activation of the AT1 receptor (Carey, 2005;Nakajima et al.,
1995;Yamada et al., 1998). However, more recent evidence purports that cardiac
AT2 receptors can act as constitutive growth‐promoting receptors that do not
antagonize the hypertrophy‐promoting consequences of AT1‐receptor‐mediated
activation by Ang II (D'Amore et al., 2005). As one can easily appreciate, the
underlying void of a complete understanding of these two Ang II receptors and its
implication in the modulation of cardiac function remains to be clarified.
8
In contrast to the cellular effects of Ang II in the heart, Ang‐(1‐7) was recently
shown to inhibit the growth of cardiac myocytes via activation of the mas receptor
(Tallant et al., 2005), which was previously shown to be a functional receptor for
Ang‐(1‐7) (Santos et al., 2003). This finding followed several years of studies that
showed Ang‐(1‐7) could inhibit cellular growth in vascular smooth muscle cells
(Freeman et al., 1996;Strawn et al., 1999;Tallant and Clark, 2003). Moreover, Ang‐
(1‐7) can also mitigate fibrosis under cell culture conditions (Iwata et al., 2005), as
well as fibrosis associated with Ang II‐driven (Grobe et al., 2007) and DOCA‐salt‐
driven (Grobe et al., 2006) cardiac hypertrophy. Indeed, studies from our
laboratory confirmed the existence of Ang‐(1‐7) in the heart and further showed an
increase in Ang‐(1‐7) immunoreactivity in cardiac myocytes, but not in cardiac
fibroblasts in response to coronary artery ligation (Averill et al., 2003). In two
separate studies, Zisman also confirmed that Ang‐(1‐7) could be generated in the
human heart (Zisman et al., 2003b;Zisman et al., 2003a). This local Ang‐(1‐7) may
act on the cells of the heart to improve cardiac function, as will be discussed later in
this chapter. Furthermore, Ang‐(1‐7) augments the threshold to ischemic‐induced
arrhythmias (Ferreira et al., 2001;Ferreira et al., 2002;Santos et al., 2006) as well as
hyperpolarizing the ischemic heart fibers and re‐establishing impulse propagation
(De Mello, 2004). The beneficial effects of Ang (1‐7) are dose‐dependent because at
higher concentrations (10‐7 M) the heptapeptide elicits an appreciable increase of
action potential duration and early‐after depolarizations (De Mello et al., 2007). In
keeping with these findings, progressive conduction and rhythm disturbances with
9
sustained ventricular tachycardia and terminal ventricular fibrillation occurred in
transgenic mice with increased cardiac ACE2 expression (Donoghue et al., 2003).
The intracellular, or “intracrine,” RAS may mediate biological activity on its
own. Very early studies showed that Ang II could be localized to nuclei of both
smooth muscle and cardiac muscle (Robertson, Jr. and Khairallah, 1971) and that
the action of the octapeptide may stimulate intracellular changes in conductance
and calcium handling. Moreover, significant support for intracellular actions of
angiotensin peptides is accumulating. Baker and colleagues (Baker et al., 2004)
found that exogenously‐administered Ang II could cause cardiomyocyte
hypertrophy, as well as stimulate protein synthesis, effects that could not be
reversed by administration of an AT1 receptor antagonist in the extracellular milieu.
These data suggest that intracellular Ang II could promote cardiac hypertrophy
independent of activation of the AT1 receptors on the cellular membrane.
I.5 RAS AND THE CORONARY CIRCULATION
The coronary circulation serves as the supply line to not only the heart, but
largely to the whole organism because if coronary blood flow is interrupted, heart
function is depleted and systemic perfusion can decline. The coronary circulation
also serves as a portal — a portal that allows the exchange of nutrients and
hormones so that the heart can function properly. One of those hormonal systems
that regulates the coronary circulation is the RAS. It is well accepted that blood flow
in any tissue is regulated by both the autonomic nervous system and local effectors.
This heart is no exception. Cardiac blood flow and coronary maintenance can be
10
regulated locally by the production of adenosine, nitric oxide, Ang II, and Ang‐(1‐7),
just to name a few. Reduction of coronary blood flow by Ang II may either be direct,
or it may be mediated by the stimulatory effect of the peptide on the release of
endothelin‐1 (Schaefer et al., 2007). The relevance of the vasoconstrictor effects of
Ang II on the coronary circulation is highlighted by the observation that enalaprilat
improves coronary blood flow post‐angioplasty (Schaefer et al., 2007).
Furthermore, Zhang et al. (Zhang et al., 2005) showed that AT1 receptor‐mediated
coronary constriction is augmented in the prediabetic metabolic syndrome and
contributes to impaired control of coronary blood flow via increases in circulating
Ang II and coronary arteriolar AT receptor density. 1
Evidence for modulation of the coronary circulation by Ang‐(1‐7) was first
discovered by Kumagai and colleagues (Kumagai et al., 1990) in the hamster heart.
These investigators found that Ang‐(1‐7) produced a vasoconstrictor‐like activity,
likely due to the high doses used. Later studies found that Ang‐(1‐7) in fact acted
upon the coronary endothelium to induce nitric oxide release, which produced a
dose‐dependent vasodilatory effect (Almeida et al., 2000;Brosnihan et al., 1996;Li et
al., 1997;Porsti et al., 1994). These findings are consistent with the actions of Ang‐
(1‐7) in other vascular beds (Feterik et al., 2000;Neves et al., 2003;Oliveira et al.,
1999;Ren et al., 2002). Moreover, Ang‐(1‐7) can also modulate the distribution of
blood flow via changes in systemic hemodynamics (Sampaio et al., 2003).
Experimental evidence clearly and directly shows that Ang‐(1‐7) can act as a
vasodilator in not only the coronary circulation, but also other systemic vascular
11
beds. The heptapeptide may also play a role in the distribution of blood flow to
various systemic vascular beds as physiological needs change.
I.6 SIGNIFICANCE OF THE RAS ON CARDIAC FUNCTION
As one can undeniably appreciate given the above‐mentioned consequences
of Ang II and Ang‐(1‐7) at the cellular level of the heart, these biologically‐active
peptides ultimately modulate myocardial performance. Although the effects of the
local cardiac RAS at the cellular level have unveiled potential mediators of heart
disease, the ultimate significance of the local RAS in the heart boils down to its
effects on how the heart performs.
Pathophysiology of RAS in Cardiac Function
The development of angiotensin converting enzyme (ACE) inhibitors and the
later introduction of angiotensin receptor blockers (ARBs) drastically changed the
medical approaches to the management of cardiac pathology, including heart failure.
Both in patients and in experimental animal models of left ventricular dysfunction,
these agents were proven to reverse cardiac hypertrophy (Dahlof et al.,
1992;Dahlof, 1992;Dahlof et al., 2002), correct left ventricular systolic dysfunction
(Braunwald et al., 2004;Buksa, 2000;Kober et al., 1995;Pfeffer et al., 2003;Young et
al., 2004), and ameliorate progression of heart failure (Abdulla et al., 2006;Banerjee
et al., 2003;Giles, 2007;Hedrich et al., 2005;Levine and Levine, 2005;Pfeffer et al.,
2003;Voors and van Veldhuisen, 2005).
Cardioprotection mediated by blockade of increased cardiac expression of
Ang II has been demonstrated in experimental models of induced cardiac pathology,
12
while in humans, direct evidence for a local tissue mechanism is for the most part
inferred from experiments in animals. However, patients with unstable angina
produced Ang II in greater amount than in patients with stable angina; these
changes were associated with increased expression of angiotensinogen, ACE, and
AT1‐receptor genes together with upregulation of tumor necrosis factor (TNF‐α),
interlukin‐6, and iNOS genes (Neri Serneri et al., 2004). Human cardiac Ang II‐
forming activity is increased in autopsied hearts of patients with myocardial
infarction (Ihara et al., 2000), a finding that correlates with studies in the rat
(Ishiyama et al., 2004). Given that changes in cardiac Ang II in infarcted or remnant
myocardium are very limited, it remains to be determined whether blockade of the
octapeptide Ang II in cardiac tissue contributes to the beneficial effects of blockers
of the RAS on cardiac remodeling post‐myocardial infarction.
Contrasting with the functional aspects of Ang II on cardiac performance,
some evidence exists as to whether the heptapeptide Ang‐(1‐7) may be a positive
modulator of cardiac function, counterbalancing the hypertrophic and pro‐fibrotic
actions of Ang II. Initial studies to characterize the functional effects of Ang‐(1‐7) on
the heart showed that its administration could improve both ischemia‐induced
functional impairments and cardiac arrhythmias (Ferreira et al., 2001;Ferreira et al.,
2002). The latter effect may be due to activation of the sodium pump in cardiac
muscle (De Mello, 2004) that may act to hyperpolarize the cell and increase
conduction velocity (De Mello et al., 2007). Additionally, there is accumulating in
vivo evidence of the positive effects of Ang‐(1‐7) in the heart. For example,
administration of Ang‐(1‐7) after coronary artery ligation in rats attenuated the
13
development of heart failure (Loot et al., 2002). Furthermore, plasma Ang‐(1‐7)
was augmented in response to coronary artery ligation in rats, with a corresponding
increase in cardiac ACE2 (Ishiyama et al., 2004). Taken together, these findings
suggest that ACE2 may act to facilitate the conversion of Ang II into Ang‐(1‐7) as
part of a feedforward mechanism as previously described by us, although in cardiac
hypertrophy it appears that the levels of Ang‐(1‐7) are insufficient to
counterbalance the deleterious effects of Ang II (Ferrario et al., 2005). Additional
evidence for this hypothesis stems from severe cardiac functional impairments in
both ACE2‐ and mas‐receptor‐knockout mice (Crackower et al., 2002;Santos et al.,
2006) and the demonstration that ACE2 overexpression is associated with
abrogation of experimentally‐induced cardiac hypertrophy and fibrosis
(Huentelman et al., 2005).
I.7 CONCLUSIONS
As in all biological systems, the integration of the components of various
hormonal systems is required for the proper assessment of physiological and
pathophysiological function. The RAS is no exception. The regulation of the cardiac
RAS is likely not independent of the circulation, although its various components
can undoubtedly exert direct effects on the tissue itself. Nor possibly does the
cardiac RAS operate independent of other tissues, as a very recent report showed
that renal AT1 receptors were required for the development of cardiac hypertrophy
(Crowley et al., 2006). Our understanding of the complexity of the system continues
to evolve. One thing is for sure — the RAS is not solely a circulating endocrine
14
system. Increasing data, much of which is discussed in this chapter, have shown
that the RAS also exerts autocrine, paracrine, and intracrine actions that may work
in concert within the organism to regulate physiological processes that when out of
balance, may induce pathology.
15
REFERENCES
Abdulla, J., Pogue, J., Abildstrom, S.Z., Kober, L., Christensen, E., Pfeffer, M.A., Yusuf,
S., and Torp‐Pedersen, C. (2006). Effect of angiotensin‐converting enzyme inhibition
on functional class in patients with left ventricular systolic dysfunction‐‐a meta‐
analysis. Eur. J. Heart Fail. 8, 90‐96.
Almeida, A.P., Frabregas, B.C., Madureira, M.M., Santos, R.J., Campagnole‐Santos, M.J.,
and Santos, R.A. (2000). Angiotensin‐(1‐7) potentiates the coronary vasodilatatory
effect of bradykinin in the isolated rat heart. Braz. J. Med. Biol. Res. 33, 709‐713.
Averill, D.B., Ishiyama, Y., Chappell, M.C., and Ferrario, C.M. (2003). Cardiac
angiotensin‐(1‐7) in ischemic cardiomyopathy. Circulation 108, 2141‐2146.
Baker, K.M., Campanile, C.P., Trachte, G.J., and Peach, M.J. (1984). Identification and
characterization of the rabbit angiotensin II myocardial receptor. Circ. Res. 54, 286‐
293.
Baker, K.M., Chernin, M.I., Schreiber, T., Sanghi, S., Haiderzaidi, S., Booz, G.W., Dostal,
D.E., and Kumar, R. (2004). Evidence of a novel intracrine mechanism in angiotensin
II‐induced cardiac hypertrophy. Regul. Pept. 120, 5‐13.
Baker, K.M., Singer, H.A., and Aceto, J.F. (1989). Angiotensin II receptor‐mediated
stimulation of cytosolic‐free calcium and inositol phosphates in chick myocytes. J.
Pharmacol. Exp. Ther. 251, 578‐585.
16
Banerjee, A., Talreja, A., Sonnenblick, E.H., and LeJemtel, T.H. (2003). Evolving
rationale for angiotensin‐converting enzyme inhibition in chronic heart failure. Mt.
Sinai J. Med. 70, 225‐231.
Booz, G.W., Dostal, D.E., Singer, H.A., and Baker, K.M. (1994). Involvement of protein
kianse C and Ca2+ in angiotensin II‐induced mitogenesis of cardiac fibroblasts. Am.
J. Physiol 267, C1308‐C1318.
Braunwald, E., Domanski, M.J., Fowler, S.E., Geller, N.L., Gersh, B.J., Hsia, J., Pfeffer,
M.A., Rice, M.M., Rosenberg, Y.D., and Rouleau, J.L. (2004). Angiotensin‐converting‐
enzyme inhibition in stable coronary artery disease. N. Engl. J. Med. 351, 2058‐2068.
Brosnihan, K.B., Li, P., and Ferrario, C.M. (1996). Angiotensin‐(1‐7) dilates canine
coronary arteries through kinins and nitric oxide. Hypertension 27, 523‐528.
Buksa, M. (2000). [Trandolapril in the prevention of the sequelae of left ventricular
systolic dysfunction after acute myocardial infarct]. Med. Arh. 54, 103‐106.
Campbell, S.E. and Katwa, L.C. (1997). Angiotensin II stimulated expression of
transforming growth factor‐beta1 in cardiac fibroblasts and myofibroblasts. J. Mol.
Cell Cardiol. 29, 1947‐1958.
Carey, R.M. (2005). Cardiovascular and renal regulation by the angiotensin type 2
receptor: the AT2 receptor comes of age. Hypertension 45, 840‐844.
17
Chappell, M.C., Gomez, M.N., Pirro, N.T., and Ferrario, C.M. (2000). Release of
angiotensin‐(1‐7) from the rat hindlimb: influence of angiotensin‐converting
enzyme inhibition. Hypertension 35, 348‐352.
Chernin, M.I., Candia, A.F., Stark, L.L., Aceto, J.F., and Baker, K.M. (1990). Fetal
expression of renin, angiotensinogen, and atriopeptin genes in chick heart. Clin. Exp.
Hypertens. A 12, 617‐629.
Cicilini, M.A., Ramos, P.S., Vasquez, E.C., and Cabral, A.M. (1994). Heart prolyl
endopeptidase activity in one‐kidney, one clip hypertensive rats. Braz. J. Med. Biol.
Res. 27, 2821‐2830.
Crackower, M.A., Sarao, R., Oudit, G.Y., Yagil, C., Kozieradzki, I., Scanga, S.E., Oliveira‐
dos‐Santos, A.J., da, C.J., Zhang, L., Pei, Y., Scholey, J., Ferrario, C.M., Manoukian, A.S.,
Chappell, M.C., Backx, P.H., Yagil, Y., and Penninger, J.M. (2002). Angiotensin‐
converting enzyme 2 is an essential regulator of heart function. Nature 417, 822‐
828.
Crowley, S.D., Gurley, S.B., Herrera, M.J., Ruiz, P., Griffiths, R., Kumar, A.P., Kim, H.S.,
Smithies, O., Le, T.H., and Coffman, T.M. (2006). Angiotensin II causes hypertension
and cardiac hypertrophy through its receptors in the kidney. Proc. Natl. Acad. Sci. U.
S. A 103, 17985‐17990.
D'Amore, A., Black, M.J., and Thomas, W.G. (2005). The angiotensin II type 2 receptor
causes constitutive growth of cardiomyocytes and does not antagonize angiotensin
II type 1 receptor‐mediated hypertrophy. Hypertension 46, 1347‐1354.
18
Dahlof, B. (1992). Structural cardiovascular changes in essential hypertension.
Studies on the effect of antihypertensive therapy. Blood Press Suppl 6, 1‐75.
Dahlof, B., Devereux, R.B., Kjeldsen, S.E., Julius, S., Beevers, G., de, F.U., Fyhrquist, F.,
Ibsen, H., Kristiansson, K., Lederballe‐Pedersen, O., Lindholm, L.H., Nieminen, M.S.,
Omvik, P., Oparil, S., and Wedel, H. (2002). Cardiovascular morbidity and mortality
in the Losartan Intervention For Endpoint reduction in hypertension study (LIFE): a
randomised trial against atenolol. Lancet 359, 995‐1003.
Dahlof, B., Pennert, K., and Hansson, L. (1992). Reversal of left ventricular
hypertrophy in hypertensive patients. A metaanalysis of 109 treatment studies. Am.
J. Hypertens. 5, 95‐110.
Danser, A.H. (2003). Local renin‐angiotensin systems: the unanswered questions.
Int. J. Biochem. Cell Biol. 35, 759‐768.
Danser, A.H., van Kats, J.P., Admiraal, P.J., Derkx, F.H., Lamers, J.M., Verdouw, P.D.,
Saxena, P.R., and Schalekamp, M.A. (1994). Cardiac renin and angiotensins. Uptake
from plasma versus in situ synthesis. Hypertension 24, 37‐48.
de Lannoy, L.M., Danser, A.H., Bouhuizen, A.M., Saxena, P.R., and Schalekamp, M.A.
(1998). Localization and production of angiotensin II in the isolated perfused rat
heart. Hypertension 31, 1111‐1117.
de Lannoy, L.M., Danser, A.H., van Kats, J.P., Schoemaker, R.G., Saxena, P.R., and
Schalekamp, M.A. (1997). Renin‐angiotensin system components in the interstitial
19
fluid of the isolated perfused rat heart. Local production of angiotensin I.
Hypertension 29, 1240‐1251.
De Mello, W.C. (2004). Angiotensin (1‐7) re‐establishes impulse conduction in
cardiac muscle during ischaemia‐reperfusion. The role of the sodium pump. J. Renin.
Angiotensin. Aldosterone. Syst. 5, 203‐208.
De Mello, W.C., Ferrario, C.M., and Jessup, J.A. (2007). Beneficial versus harmful
effects of Angiotensin (1‐7) on impulse propagation and cardiac arrhythmias in the
failing heart. J. Renin. Angiotensin. Aldosterone. Syst. 8, 74‐80.
de Gasparo, M., Catt, K.J., Inagami, T., Wright, J.W., and Unger, T. (2000).
International union of pharmacology. XXIII. The angiotensin II receptors. Pharmacol.
Rev. 52, 415‐472.
Donoghue, M., Wakimoto, H., Maguire, C.T., Acton, S., Hales, P., Stagliano, N.,
Fairchild‐Huntress, V., Xu, J., Lorenz, J.N., Kadambi, V., Berul, C.I., and Breitbart, R.E.
(2003). Heart block, ventricular tachycardia, and sudden death in ACE2 transgenic
mice with downregulated connexins. J. Mol. Cell Cardiol. 35, 1043‐1053.
Dzau, V.J., Ellison, K.E., Brody, T., Ingelfinger, J., and Pratt, R.E. (1987). A comparative
study of the distributions of renin and angiotensinogen messenger ribonucleic acids
in rat and mouse tissues. Endocrinology 120, 2334‐2338.
Ferrario, C.M., Trask, A.J., and Jessup, J.A. (2005). Advances in biochemical and
functional roles of angiotensin‐converting enzyme 2 and angiotensin‐(1‐7) in
20
regulation of cardiovascular function. Am. J. Physiol Heart Circ. Physiol 289, H2281‐
H2290.
Ferreira, A.J., Santos, R.A., and Almeida, A.P. (2001). Angiotensin‐(1‐7):
cardioprotective effect in myocardial ischemia/reperfusion. Hypertension 38, 665‐
668.
Ferreira, A.J., Santos, R.A., and Almeida, A.P. (2002). Angiotensin‐(1‐7) improves the
post‐ischemic function in isolated perfused rat hearts. Braz. J. Med. Biol. Res. 35,
1083‐1090.
Feterik, K., Smith, L., and Katusic, Z.S. (2000). Angiotensin‐(1‐7) causes
endothelium‐dependent relaxation in canine middle cerebral artery. Brain Res. 873,
75‐82.
Fielitz, J., Dendorfer, A., Pregla, R., Ehler, E., Zurbrugg, H.R., Bartunek, J., Hetzer, R.,
and Regitz‐Zagrosek, V. (2002). Neutral endopeptidase is activated in
cardiomyocytes in human aortic valve stenosis and heart failure. Circulation 105,
286‐289.
Francis, G.S. and Tang, W.H. (2006). Histamine, mast cells, and heart failure: is there
a connection? J. Am. Coll. Cardiol. 48, 1385‐1386.
Freeman, E.J., Chisolm, G.M., Ferrario, C.M., and Tallant, E.A. (1996). Angiotensin‐(1‐
7) inhibits vascular smooth muscle cell growth. Hypertension 28, 104‐108.
21
Freer, R.J., Pappano, A.J., Peach, M.J., Bing, K.T., McLean, M.J., Vogel, S., and Sperelakis,
N. (1976). Mechanism for the postive inotropic effect of angiotensin II on isolated
cardiac muscle. Circ. Res. 39, 178‐183.
Giles, T.D. (2007). Renin‐Angiotensin system modulation for treatment and
prevention of cardiovascular diseases: toward an optimal therapeutic strategy. Rev.
Cardiovasc. Med. 8 Suppl 2, S14‐S21.
Grobe, J.L., Mecca, A.P., Lingis, M., Shenoy, V., Bolton, T.A., Machado, J.M., Speth, R.C.,
Raizada, M.K., and Katovich, M.J. (2007). Prevention of angiotensin II‐induced
cardiac remodeling by angiotensin‐(1‐7). Am. J. Physiol Heart Circ. Physiol 292,
H736‐H742.
Grobe, J.L., Mecca, A.P., Mao, H., and Katovich, M.J. (2006). Chronic angiotensin‐(1‐7)
prevents cardiac fibrosis in DOCA‐salt model of hypertension. Am. J. Physiol Heart
Circ. Physiol 290, H2417‐H2423.
Hedrich, O., Patten, R.D., and Denofrio, D. (2005). Current Treatment Options for
CHF Management: Focus on the Renin‐Angiotensin‐Aldosterone System. Curr. Treat.
Options. Cardiovasc. Med. 7, 3‐13.
Huentelman, M.J., Grobe, J.L., Vazquez, J., Stewart, J.M., Mecca, A.P., Katovich, M.J.,
Ferrario, C.M., and Raizada, M.K. (2005). Protection from angiotensin II‐induced
cardiac hypertrophy and fibrosis by systemic lentiviral delivery of ACE2 in rats. Exp.
Physiol 90, 783‐790.
22
Ihara, M., Urata, H., Shirai, K., Ideishi, M., Hoshino, F., Suzumiya, J., Kikuchi, M., and
Arakawa, K. (2000). High cardiac angiotensin‐II‐forming activity in infarcted and
non‐infarcted human myocardium. Cardiology 94, 247‐253.
Ishiyama, Y., Gallagher, P.E., Averill, D.B., Tallant, E.A., Brosnihan, K.B., and Ferrario,
C.M. (2004). Upregulation of angiotensin‐converting enzyme 2 after myocardial
infarction by blockade of angiotensin II receptors. Hypertension 43, 970‐976.
Iwata, M., Cowling, R.T., Gurantz, D., Moore, C., Zhang, S., Yuan, J.X., and Greenberg,
B.H. (2005). Angiotensin‐(1‐7) binds to specific receptors on cardiac fibroblasts to
initiate antifibrotic and antitrophic effects. Am. J. Physiol Heart Circ. Physiol 289,
H2356‐H2363.
Kalinyak, J.E. and Perlman, A.J. (1987). Tissue‐specific regulation of angiotensinogen
mRNA accumulation by dexamethasone. J. Biol. Chem. 262, 460‐464.
Kass, R.S. and Blair, M.L. (1981). Effects of angiotensin II on membrane current in
cardiac Purkinje fibers. J. Mol. Cell Cardiol. 13, 797‐809.
Kober, L., Torp‐Pedersen, C., Carlsen, J.E., Bagger, H., Eliasen, P., Lyngborg, K.,
Videbaek, J., Cole, D.S., Auclert, L., and Pauly, N.C. (1995). A clinical trial of the
angiotensin‐converting‐enzyme inhibitor trandolapril in patients with left
ventricular dysfunction after myocardial infarction. Trandolapril Cardiac Evaluation
(TRACE) Study Group. N. Engl. J. Med. 333, 1670‐1676.
23
Kumagai, H., Khosla, M., Ferrario, C., and Fouad‐Tarazi, F.M. (1990). Biological
activity of angiotensin‐(1‐7) heptapeptide in the hamster heart. Hypertension 15,
I29‐I33.
Kunapuli, S.P. and Kumar, A. (1987). Molecular cloning of human angiotensinogen
cDNA and evidence for the presence of its mRNA in rat heart. Circ. Res. 60, 786‐790.
Le, T.H. and Coffman, T.M. (2006). A new cardiac MASTer switch for the renin‐
angiotensin system. J. Clin. Invest 116, 866‐869.
Lee, M.A., Bohm, M., Paul, M., and Ganten, D. (1993). Tissue renin‐angiotensin
systems. Their role in cardiovascular disease. Circulation 87, IV7‐13.
Levine, T.B. and Levine, A.B. (2005). Clinical update: the role of angiotensin II
receptor blockers in patients with left ventricular dysfunction (Part II of II). Clin.
Cardiol. 28, 277‐280.
Li, P., Chappell, M.C., Ferrario, C.M., and Brosnihan, K.B. (1997). Angiotensin‐(1‐7)
augments bradykinin‐induced vasodilation by competing with ACE and releasing
nitric oxide. Hypertension 29, 394‐400.
Linardi, A., Panunto, P.C., Ferro, E.S., and Hyslop, S. (2004). Peptidase activities in
rats treated chronically with N(omega)‐nitro‐L‐arginine methyl ester (L‐NAME).
Biochem. Pharmacol. 68, 205‐214.
24
Loot, A.E., Roks, A.J., Henning, R.H., Tio, R.A., Suurmeijer, A.J., Boomsma, F., and van
Gilst, W.H. (2002). Angiotensin‐(1‐7) attenuates the development of heart failure
after myocardial infarction in rats. Circulation 105, 1548‐1550.
Mackins, C.J., Kano, S., Seyedi, N., Schafer, U., Reid, A.C., Machida, T., Silver, R.B., and
Levi, R. (2006). Cardiac mast cell‐derived renin promotes local angiotensin
formation, norepinephrine release, and arrhythmias in ischemia/reperfusion. J. Clin.
Invest 116, 1063‐1070.
Miyazaki, M., Takai, S., Jin, D., and Muramatsu, M. (2006). Pathological roles of
angiotensin II produced by mast cell chymase and the effects of chymase inhibition
in animal models. Pharmacol. Ther. 112, 668‐676.
Nakajima, M., Hutchinson, H.G., Fujinaga, M., Hayashida, W., Morishita, R., Zhang, L.,
Horiuchi, M., Pratt, R.E., and Dzau, V.J. (1995). The angiotensin II type 2 (AT2)
receptor antagonizes the growth effects of the AT1 receptor: gain‐of‐function study
using gene transfer. Proc. Natl. Acad. Sci. U. S. A 92, 10663‐10667.
Neri Serneri, G.G., Boddi, M., Modesti, P.A., Coppo, M., Cecioni, I., Toscano, T., Papa,
M.L., Bandinelli, M., Lisi, G.F., and Chiavarelli, M. (2004). Cardiac angiotensin II
participates in coronary microvessel inflammation of unstable angina and
strengthens the immunomediated component. Circ. Res. 94, 1630‐1637.
Neves, L.A., Averill, D.B., Ferrario, C.M., Chappell, M.C., Aschner, J.L., Walkup, M.P.,
and Brosnihan, K.B. (2003). Characterization of angiotensin‐(1‐7) receptor subtype
in mesenteric arteries. Peptides 24, 455‐462.
25
Nguyen, G. and Burckle, C.A. (2004). [The (pro)renin receptor: biology and
functional significance]. Bull. Acad. Natl. Med. 188, 621‐628.
Nguyen, G., Burckle, C.A., and Sraer, J.D. (2004). Renin/prorenin‐receptor
biochemistry and functional significance. Curr. Hypertens. Rep. 6, 129‐132.
Nguyen, G., Delarue, F., Burckle, C., Bouzhir, L., Giller, T., and Sraer, J.D. (2002).
Pivotal role of the renin/prorenin receptor in angiotensin II production and cellular
responses to renin. J. Clin. Invest 109, 1417‐1427.
Oliveira, M.A., Fortes, Z.B., Santos, R.A., Kosla, M.C., and de Carvalho, M.H. (1999).
Synergistic effect of angiotensin‐(1‐7) on bradykinin arteriolar dilation in vivo.
Peptides 20, 1195‐1201.
Paul, M., Poyan, M.A., and Kreutz, R. (2006). Physiology of local renin‐angiotensin
systems. Physiol Rev. 86, 747‐803.
Peach, M.J. (1981). Molecular actions of angiotensin. Biochem. Pharmacol. 30, 2745‐
2751.
Pfeffer, M.A., McMurray, J.J., Velazquez, E.J., Rouleau, J.L., Kober, L., Maggioni, A.P.,
Solomon, S.D., Swedberg, K., Van de, W.F., White, H., Leimberger, J.D., Henis, M.,
Edwards, S., Zelenkofske, S., Sellers, M.A., and Califf, R.M. (2003). Valsartan,
captopril, or both in myocardial infarction complicated by heart failure, left
ventricular dysfunction, or both. N. Engl. J. Med. 349, 1893‐1906.
26
Porsti, I., Bara, A.T., Busse, R., and Hecker, M. (1994). Release of nitric oxide by
angiotensin‐(1‐7) from porcine coronary endothelium: implications for a novel
angiotensin receptor. Br. J. Pharmacol. 111, 652‐654.
Re, R.N. (2004). Mechanisms of disease: local renin‐angiotensin‐aldosterone
systems and the pathogenesis and treatment of cardiovascular disease. Nat. Clin.
Pract. Cardiovasc. Med. 1, 42‐47.
Reid, A.C., Silver, R.B., and Levi, R. (2007). Renin: at the heart of the mast cell.
Immunol. Rev. 217, 123‐140.
Ren, Y., Garvin, J.L., and Carretero, O.A. (2002). Vasodilator action of angiotensin‐(1‐
7) on isolated rabbit afferent arterioles. Hypertension 39, 799‐802.
Robertson, A.L., Jr. and Khairallah, P.A. (1971). Angiotensin II: rapid localization in
nuclei of smooth and cardiac muscle. Science 172, 1138‐1139.
Sadoshima, J., Qiu, Z., Morgan, J.P., and Izumo, S. (1995). Angiotensin II and other
hypertrophic stimuli mediated by G protein‐coupled receptors activate tyrosine
kinase, mitogen‐activated protein kinase, and 90‐kD S6 kinase in cardiac myocytes.
The critical role of Ca(2+)‐dependent signaling. Circ. Res. 76, 1‐15.
Sampaio, W.O., Nascimento, A.A., and Santos, R.A. (2003). Systemic and regional
hemodynamic effects of angiotensin‐(1‐7) in rats. Am. J. Physiol Heart Circ. Physiol
284, H1985‐H1994.
27
Santos, R.A., Brum, J.M., Brosnihan, K.B., and Ferrario, C.M. (1990). The renin‐
angiotensin system during acute myocardial ischemia in dogs. Hypertension 15,
I121‐I127.
Santos, R.A., Castro, C.H., Gava, E., Pinheiro, S.V., Almeida, A.P., Paula, R.D., Cruz, J.S.,
Ramos, A.S., Rosa, K.T., Irigoyen, M.C., Bader, M., Alenina, N., Kitten, G.T., and
Ferreira, A.J. (2006). Impairment of in vitro and in vivo heart function in
angiotensin‐(1‐7) receptor MAS knockout mice. Hypertension 47, 996‐1002.
Santos, R.A., Simoes e Silva AC, Maric, C., Silva, D.M., Machado, R.P., de, B., I, Heringer‐
Walther, S., Pinheiro, S.V., Lopes, M.T., Bader, M., Mendes, E.P., Lemos, V.S.,
Campagnole‐Santos, M.J., Schultheiss, H.P., Speth, R., and Walther, T. (2003).
Angiotensin‐(1‐7) is an endogenous ligand for the G protein‐coupled receptor Mas.
Proc Natl. Acad. Sci. U. S. A 100, 8258‐8263.
Sawa, H., Tokuchi, F., Mochizuki, N., Endo, Y., Furuta, Y., Shinohara, T., Takada, A.,
Kawaguchi, H., Yasuda, H., and Nagashima, K. (1992). Expression of the
angiotensinogen gene and localization of its protein in the human heart. Circulation
86, 138‐146.
Schaefer, U., Kurz, T., Bonnemeier, H., Dendorfer, A., Hartmann, F., Schunkert, H., and
Richardt, G. (2007). Intracoronary enalaprilat during angioplasty for acute
myocardial infarction: alleviation of postischaemic neurohumoral and inflammatory
stress? J. Intern. Med. 261, 188‐200.
28
Schorb, W., Conrad, K.M., Singer, H.A., Dostal, D.E., and Baker, K.M. (1995).
Angiotensin II is a potent stimulator of MAP‐kinase activity in neonatal rat cardiac
fibroblasts. J. Mol. Cell Cardiol. 27, 1151‐1160.
Strawn, W.B., Ferrario, C.M., and Tallant, E.A. (1999). Angiotensin‐(1‐7) reduces
smooth muscle growth after vascular injury. Hypertension 33, 207‐211.
Tallant, E.A. and Clark, M.A. (2003). Molecular mechanisms of inhibition of vascular
growth by angiotensin‐(1‐7). Hypertension 42, 574‐579.
Tallant, E.A., Ferrario, C.M., and Gallagher, P.E. (2005). Angiotensin‐(1‐7) inhibits
growth of cardiac myocytes through activation of the mas receptor. Am. J. Physiol
Heart Circ. Physiol 289, H1560‐H1566.
Trask, A.J., Averill, D.B., Ganten, D., Chappell, M.C., and Ferrario, C.M. (2007). Primary
role of angiotensin‐converting enzyme‐2 in cardiac production of angiotensin‐(1‐7)
in transgenic Ren‐2 hypertensive rats. Am. J. Physiol Heart Circ. Physiol 292, H3019‐
H3024.
Trask, A.J. and Ferrario, C.M. (2007). Angiotensin‐(1‐7): pharmacology and new
perspectives in cardiovascular treatments. Cardiovasc. Drug Rev. 25, 162‐174.
Urata, H., Kinoshita, A., Misono, K.S., Bumpus, F.M., and Husain, A. (1990).
Identification of a highly specific chymase as the major angiotensin II‐forming
enzyme in the human heart. J. Biol. Chem. 265, 22348‐22357.
29
van Kats, J.P., de Lannoy, L.M., Jan Danser, A.H., van, M., Jr., Verdouw, P.D., and
Schalekamp, M.A. (1997). Angiotensin II type 1 (AT1) receptor‐mediated
accumulation of angiotensin II in tissues and its intracellular half‐life in vivo.
Hypertension 30, 42‐49.
Villarreal, F.J., Kim, N.N., Ungab, G.D., Printz, M.P., and Dillmann, W.H. (1993).
Identification of functional angiotensin II receptors on rat cardiac fibroblasts.
Circulation 88, 2849‐2861.
Voors, A.A. and van Veldhuisen, D.J. (2005). Pharmacological treatment of chronic
heart failure according to the 2005 guidelines of the European Society of Cardiology.
Minerva Cardioangiol. 53, 233‐239.
Welches, W.R., Brosnihan, K.B., and Ferrario, C.M. (1993). A comparison of the
properties and enzymatic activities of three angiotensin processing enzymes:
angiotensin converting enzyme, prolyl endopeptidase and neutral endopeptidase
24.11. Life Sci. 52, 1461‐1480.
Xiao, H.D. and Bernstein, K.E. (2005). Mast cells: the missing source of cardiac renin?
Mol. Interv. 5, 11‐14.
Yamada, T., Akishita, M., Pollman, M.J., Gibbons, G.H., Dzau, V.J., and Horiuchi, M.
(1998). Angiotensin II type 2 receptor mediates vascular smooth muscle cell
apoptosis and antagonizes angiotensin II type 1 receptor action: an in vitro gene
transfer study. Life Sci. 63, L289‐L295.
30
Yamamoto, K., Chappell, M.C., Brosnihan, K.B., and Ferrario, C.M. (1992). In vivo
metabolism of angiotensin I by neutral endopeptidase (EC 3.4.24.11) in
spontaneously hypertensive rats. Hypertension 19, 692‐696.
Yamazaki, T., Komuro, I., Kudoh, S., Zou, Y., Shiojima, I., Mizuno, T., Takano, H., Hiroi,
Y., Ueki, K., Tobe, K., and . (1995). Angiotensin II partly mediates mechanical stress‐
induced cardiac hypertrophy. Circ. Res. 77, 258‐265.
Young, J.B., Dunlap, M.E., Pfeffer, M.A., Probstfield, J.L., Cohen‐Solal, A., Dietz, R.,
Granger, C.B., Hradec, J., Kuch, J., McKelvie, R.S., McMurray, J.J., Michelson, E.L.,
Olofsson, B., Ostergren, J., Held, P., Solomon, S.D., Yusuf, S., and Swedberg, K. (2004).
Mortality and morbidity reduction with Candesartan in patients with chronic heart
failure and left ventricular systolic dysfunction: results of the CHARM low‐left
ventricular ejection fraction trials. Circulation 110, 2618‐2626.
Zhang, C., Knudson, J.D., Setty, S., Araiza, A., Dincer, U.D., Kuo, L., and Tune, J.D.
(2005). Coronary arteriolar vasoconstriction to angiotensin II is augmented in
prediabetic metabolic syndrome via activation of AT1 receptors. Am. J. Physiol Heart
Circ. Physiol 288, H2154‐H2162.
Zisman, L.S., Keller, R.S., Weaver, B., Lin, Q., Speth, R., Bristow, M.R., and Canver, C.C.
(2003a). Increased angiotensin‐(1‐7)‐forming activity in failing human heart
ventricles: evidence for upregulation of the angiotensin‐converting enzyme
Homologue ACE2. Circulation 108, 1707‐1712.
31
Zisman, L.S., Meixell, G.E., Bristow, M.R., and Canver, C.C. (2003b). Angiotensin‐(1‐7)
formation in the intact human heart: in vivo dependence on angiotensin II as
substrate. Circulation 108, 1679‐1681.
32
Figure I.1. Current view of the cardiac renin angiotensin system enzymes
and peptides. Abbreviations used are: ACE, angiotensin converting enzyme (EC
3.4.15.1); ACE2, angiotensin converting enzyme 2; NEP, neprilysin (EC 3.4.24.11);
POP, prolyl oligopeptidase (EC 3.4.21.26); TOP, thimet oligopeptidase (EC 3.4.24.15)
controlling angiotensin‐(1‐7) [Ang‐(1‐7)] production from angiotensin I or
angiotensin II; Angiotensin receptors are the AT1‐R, the AT2‐R, and the mas‐R.
Adapted from Trask and Ferrario (Trask and Ferrario, 2007).
33
FIGURE I.1
34
Figure I.2. The two possible sources of the cardiac RAS are shown. Ang II
and/or renin may be uptaken from the coronary circulation, or renin and the
precursor angiotensin protein, angiotensinogen (aogen), may be synthesized in the
nuclei of cardiac cells. These two sources of RAS components likely interact via
endocrine, paracrine, autocrine, and even intracrine mechanisms to produce and
regulate the bioactive peptides of the RAS, Ang II and Ang‐(1‐7).
35
FIGURE I.2
36
CHAPTER II
ANGIOTENSIN(17): PHARMACOLOGY & NEW PERSPECTIVES IN CARDIOVASCULAR TREATMENTS
Aaron J. Trask and Carlos M. Ferrario
H D ypertension and Vascular Research Centerepart cologyWake icine
ment of Physiology and Pharma Forest Universi y School of MedWinston‐Salem, North Carolina
t
[This chapter was published in Cardiovascular Drug Reviews (2007; 25:162174.) and is reprinted with permission. Differences in formatting reflect the equirements of the journal. Aaron J. Trask prepared the manuscript, while r. Carlos M. Ferrario acted in an editorial and advisory capacity.]
rD
37
II.1 ABSTRACT
Many advances have been made in the cardiovascular field in the past several
decades. Among them is the progress completed to date on the heptapeptide
member of the renin‐angiotensin system (RAS), angiotensin‐(1‐7) [Ang‐(1‐7)]. The
peptide’s beneficial actions against pathophysiological processes such as cardiac
arrhythmia, heart failure, hypertension, renal disease, preeclampsia, and even
cancer are continuously being uncovered. This review encompasses the
pharmacology of Ang‐(1‐7) and expounds upon the peptide’s potential as a
therapeutic agent against pathological processes both within and outside the
ardiovascular continuum. c
Key Words: Angiotensin‐(1‐7), Hypertension, Cardiac Hypertrophy, Heart Failure, Cardiac Arrhythmia, Cancer
38
II.2 INTRODUCTION
Over the past several decades, many advances have been made regarding the
contribution of the renin‐angiotensin system (RAS) in cardiovascular regulation.
The formation of the biologically active octapeptide, angiotensin II (Ang II) from
angiotensin I (Ang I) has been a significant topic of research, and this has led to
some of the most important treatments in cardiovascular pathologies. For example,
current therapies for hypertension and heart failure include blocking the synthesis
and/or actions of Ang II using angiotensin converting enzyme (ACE) inhibitors or
angiotensin receptor blockers (ARBs), respectively. Undoubtedly, the blockade of
this biologically active peptide has proven very beneficial and has likely increased
not only the quality of life for patients, but also their lifespan (2000; Dahlof et al.,
2002). More recently, the discovery of angiotensin‐(1‐7) [Ang‐(1‐7), Figure II.1] by
our laboratory in 1988 (Schiavone et al., 1988) and the cloning of angiotensin
converting enzyme 2 (ACE2) in 2000 (Donoghue et al., 2000) have led to a new
perception of the intrinsic mechanisms through which the renin angiotensin system
regulates homeostasis. Ang‐(1‐7) is a downstream heptapeptide product of the
system that can regulate blood pressure (Benter et al., 1995b; Ferrario et al., 2005),
cardiac function, and cell growth (Tallant et al., 2005).
Ang II and Ang‐(1‐7) exhibit counterregulatory effects in the systemic
circulation, as well as in tissues important in cardiovascular regulation. It is well
documented that Ang II promotes cell proliferation (Daemen et al., 1991; Su et al.,
1998) and vasoconstriction (Wackenfors et al., 2004), whereas Ang‐(1‐7) has
antiproliferative actions on cardiac myocytes (Tallant et al., 2005) and vascular
39
smooth muscle (Strawn et al., 1999), and is a vasodilator (Ferrario et al., 2005).
These actions have uncovered a new way to think about the RAS, both conceptually
and therapeutically. Indeed, a balance of the two peptides may be required to
circumvent many cardiovascular processes. Both ACE2 and prolyl oligopeptidase
(POP), since they mediate the direct conversion of Ang II into Ang‐(1‐7), may work
to regulate and balance the levels of the two peptides (Figure II.2). Throughout the
history of medicine and pharmacology, few therapeutic possibilities have emerged
that have the potential to truly change the face of a disease without the negative,
compliance‐compromising side effects. The heptapeptide Ang‐(1‐7) may very well
in the near future join those few such drugs in that quest and it emanates from our
own bodies. First discovered by our laboratory in 1988 (Schiavone et al., 1988),
ng‐(1‐7) has been the focus of much current research in the cardiovascular field. A
II.3 ANGIOTENSIN(17)FORMING ENZYMES
Three known enzymes can regulate the formation of Ang‐(1‐7) from Ang I, as
reviewed by Ferrario et al. (Ferrario et al., 1998a). They include neprilysin 24.11
(NEP), thimet oligopeptidase 24.15 (TOP), and prolyl oligopeptidase 21.26 (POP).
Moreover, two known enzymes are known to cleave Ang II into Ang‐(1‐7) – POP,
and the newly discovered angiotensin converting enzyme 2 (ACE2). These enzymes
will be briefly reviewed here.
Neprilysin 24.11
In 1992, studies from our laboratory determined that angiotensin I serves as
a substrate for the enzyme neprilysin (NEP), which produces Ang‐(1‐7) (Yamamoto
40
et al., 1992). Recent studies confirmed that NEP can metabolize Ang I directly into
Ang‐(1‐7), and furthermore, NEP can act upon Ang II to yield Ang‐(1‐4) and Ang‐(3‐
4), but not Ang‐(1‐7) in sheep renal proximal tubular membranes (Shaltout et al.,
2007).
T Oligopeptidase 24.15himet
In a study completed by our group, we showed that Ang‐(1‐7) could be
formed directly from Ang I in the rat hindlimb, which was completely abolished with
the addition of an inhibitor specific to thimet oligopeptidase (Chappell et al., 2000).
The Ang‐(1‐7) formation from Ang I was reduced by NEP inhibition, but it was not
completely abolished. These data confirm the ability of thimet oligopeptidase to
generate Ang‐(1‐7) from Ang I.
Prolyl Oligopeptidase 21.26
In 1971, Walter et al. (Walter et al., 1971) discovered an enzyme found in the
human uterus that cleaved oxytocin at the carboxy‐terminal proline‐leucine bond.
Thus, the enzyme was named post‐proline cleaving enzyme for its action. Since its
discovery, the enzyme was renamed prolyl oligopeptidase 21.26 (POP). Koida and
Walter (Koida and Walter, 1976) discovered that this enzyme cleaved the post‐
proline bond of not only oxytocin and bradykinin, but also Ang II, yielding Ang‐(1‐7).
Later, studies from our laboratory showed that POP can utilize the substrate Ang I to
yield Ang‐(1‐7) in spontaneously hypertensive rats (SHR) (Yamamoto et al., 1992).
Kato and colleagues (Kato et al., 1980) investigated the tissue and brain distribution
of POP and found that POP activity was found in all tissues measured, including, but
not limited to the heart, kidney, lung.
41
Angiotensin Converting Enzyme 2
A reinterpretation of the classical view of the RAS gained favor with the
cloning of ACE2 in 2000 (Donoghue et al., 2000). ACE2 shares 42% sequence
identity to the catalytic domain of ACE (Towler et al., 2004; Vickers et al., 2002);
however it is insensitive to ACE inhibitors. ACE2 mediates the conversion of Ang I
to angiotensin‐(1‐9) [Ang‐(1‐9)] — which can be metabolized into Ang‐(1‐7) by ACE
— as well as the conversion of Ang II into Ang‐(1‐7); however, ACE2 shows a >400‐
fold substrate preference for Ang II than for Ang I (Vickers et al., 2002), reinforcing
the idea that this enzyme is critically important in regulating the levels of
angiotensin peptides in plasma and tissues. Lack of the functional presence of ACE2
resulted in severe cardiac dysfunction associated with the accumulation of cardiac
Ang II (Crackower et al., 2002), and Shaltout and colleagues (Shaltout et al., 2007)
found that ACE2 played a major role in the metabolism of Ang II in the sheep kidney.
We (Trask et al., 2007) recently reported that ACE2 was responsible for most of the
Ang‐(1‐7) formation from exogenously‐added Ang II in isolated hearts from
hypertensive rats, suggesting that ACE2 may serve as a compensatory response to
cardiac remodeling. Additionally, overexpression of ACE2 delivered using lentiviral
methods resulted in the reversal of cardiac hypertrophy and fibrosis in rats
(Huentelman et al., 2005).
I PHARMACOKINETICS
Because Ang‐(1‐7) is a short seven amino acid peptide, it can be readily acted
upon by peptidases, and as such, it has a short half life (t
I.4
1/2). In a vital study by
42
Yamada et. al., (Yamada et al., 1998) the baseline circulating t1/2 of vehicle‐treated
Sprague‐Dawley rats (SD), spontaneously hypertensive rats (SHR), and
hypertensive [mRen2]27 transgenic rats [Tg(+)] was about 10 seconds, although
baseline values of the peptide were much higher in the SHR and Tg(+) compared to
the normotensive SD (377±88 pmol/L, 367±122 pmol/L, and 137±18 pmol/L,
respectively). The t1/2 values were increased 4‐ to 6‐fold with ACE inhibitor
(lisinopril) treatment, whereas the angiotensin receptor blocker (ARB), losartan,
had no significant effect. This result was not entirely unexpected as ACE is
responsible, at least in part, for the metabolism of Ang‐(1‐7) to the inactive
metabolite, Ang‐(1‐5) (Allred et al., 2000; Chappell et al., 1998; Deddish et al., 1998).
Thus, inhibiting this pathway would effectively prolong the t1/2 of the peptide.
Moreover, the plasma clearance of Ang‐(1‐7) was 6.5 ± 0.9 L min‐1 kg‐1 in
normotensive SD rats, whereas the plasma clearance in SHR and Tg(+) rats was
significantly decreased by 39% and 60%, respectively (SHR, 4.0 ± 0.2 L min‐1 kg‐1;
Tg(+), 2.6 ± 0.1 L min‐1 kg‐1) (Yamada et al., 1998), suggesting that the plasma Ang‐
(1‐7) is cleared from the body much slower in the two hypertensive strains (Figure
II.3). Indeed, Chappell and colleagues first found that Ang‐(1‐7) was metabolized
into the inactive fragment Ang‐(1‐5) by ACE in pulmonary tissues (Chappell et al.,
1998). Moreover, Dr. Chappell’s laboratory later found that ACE was responsible for
the breakdown of Ang‐(1‐7) into the inactive metabolite, Ang‐(1‐5) in both
pulmonary and renal tissues (Allred et al., 2000; Chappell et al., 2001).
Indeed, a clinical study by Rodgers and colleagues (Rodgers et al., 2006)
employed increasing subcutaneous doses of Ang‐(1‐7) in human subjects and found
43
a mean plasma t1/2 of 29 minutes and a mean volume of distribution of 3.71 L/kg.
The half life reported in this study is much higher than that reported in rodent
models, likely due not only to the use of higher concentrations of the drug, but also
to its being administered subcutaneously as a slow‐release depot, whereas the
rodent studies employed direct intravenous administration. Taken together, these
studies suggest that Ang‐(1‐7) administered subcutaneously may have a long
enough t1/2 to effectively mediate prolonged biological activity of Ang‐(1‐7),
although the employment of stable analogs of Ang‐(1‐7) may yield a more favorable
harmacologic profile. p
II.5 PHARMACODYNAMICS
The receptor responsible for the observed physiological actions of Ang‐(1‐7)
was not known for some time. However, studies by Tallant et al. (Tallant et al.,
1997) showed that Ang‐(1‐7) bound a non‐AT1, non‐AT2 receptor with high affinity,
which was completely blocked by the addition of the Ang‐(1‐7) antagonist, D‐Ala7‐
Ang‐(1‐7). It was recently discovered that the orphaned mas oncogene bound Ang‐
(1‐7) with high‐affinity (Santos et al., 2003). This G‐protein‐coupled receptor
mediates the current known actions of Ang‐(1‐7), as most of them can be blocked by
its specific inhibitor, D‐Ala7‐Ang‐(1‐7). Activation of the mas receptor triggers the
stimulation of the G‐protein, Gαq, which results in release of nitric oxide (NO) from
the vascular endothelium to mediate vasodilation. Ang‐(1‐7) administration also
decreased the thymidine incorporation in vascular smooth muscle cells (Freeman et
al., 1996; Tallant and Clark, 2003), resulting in a reduction in cellular proliferation
44
and growth. This mechanism was likely due to the receptor’s ability to release
prostaglandins. Moreover, Ang‐(1‐7) inhibits cardiac myocyte growth, which was
mediated by the mas receptor (Tallant et al., 2005). Indeed, mice in which the mas
protein was genetically inactivated exhibit marked cardiac dysfunction (Castro et al.,
2006; Santos et al., 2006).
Although many of the effects of Ang‐(1‐7) can be at least partially attributed
to activation of the mas receptor, Silva et al. (Silva et al., 2006) recently reported
another Ang‐(1‐7) receptor that was sensitive to the Ang‐(1‐7) antagonist D‐Pro7‐
Ang‐(1‐7), but not to another antagonist, D‐Ala7‐Ang‐(1‐7) in aortas from Sprague‐
Dawley rats. There is some bit of discrepancy in this report as the authors have
previously reported that both Ang‐(1‐7) antagonists block the vasodilatory effect in
the mouse aorta (Santos et al., 2003). This adds yet another dimension to the
evolution of the complexity of the RAS that needs to be fully investigated. Two
major questions that need to be addressed are: (1) are the reported effects thus far
on Ang‐(1‐7) due to the activation of the mas receptor, and (2) are the current Ang‐
(1‐7) antagonists solely specific to the mas receptor? Binding studies showed that
Ang‐(1‐7) binds the mas receptor, which was completely blocked with the addition
of D‐Ala7‐Ang‐(1‐7) (Tallant et al., 1997). Therefore, it is known that Ang‐(1‐7)
binds the mas receptor and is a least partially responsible for the physiological
effects reported on Ang‐(1‐7), but given the current data on interactions of the
different angiotensin receptors (Castro et al., 2005; Kostenis et al., 2005), we do not
even come close to understanding the roles of the angiotensin receptor types as it
pertains to their physiological actions and/or interactions. The role of this newly
45
reported Ang‐(1‐7) receptor remains to be elucidated, and its functional significance
may bring scientists to a better understanding of how the system functions not only
within itself, but also with other endogenous physiological systems.
Physiological Actions of Ang(17) on the Heart
One of the first studies to address whether the heart had the machinery to
synthesize Ang‐(1‐7) in vivo was done by Wei and colleagues (Wei et al., 2002) in
the dog heart interstitium. These authors found that Ang‐(1‐7) could be generated
from Ang I, an effect not blocked by the administration of either an AT1 or AT2
receptor blocker. Zisman (Zisman et al., 2003b) later confirmed that Ang‐(1‐7)
could be generated in the human heart from Ang II. Indeed, Averill and colleagues
(Averill et al., 2003) found augmented expression of Ang‐(1‐7) in response to
coronary artery ligation in rat cardiomyocytes, but not cardiac fibroblasts.
Moreover, several studies found that Ang‐(1‐7) improves cardiac function in
response to ischemia/reperfusion. In two separate studies, Ferreira and colleagues
(Ferreira et al., 2001; Ferreira et al., 2002) found that Ang‐(1‐7) was protective
against both ischemia‐induced cardiac functional impairments and ischemia‐
induced cardiac arrhythmias in isolated rat hearts. De Mello (De Mello, 2004) later
reported that Ang‐(1‐7) exerted its antiarrhythmic effects via activation of the
sodium pump. More recently, Ang‐(1‐7) administration caused an improved cardiac
function recovery after 40 minutes of ischemia in isolated hearts from SHR rats
reatedt with the nitric oxide synthase inhibitor, L‐NAME (Benter et al., 2006).
Ang‐(1‐7) also has cardioprotective effects against heart failure and cardiac
hypertrophy. Indeed, chronic Ang‐(1‐7) treatment not only attenuated the
46
development of heart failure in response to coronary artery ligation in rats (Loot et
al., 2002), but it also reversed cardiac hypertrophy and fibrosis in rats (Grobe et al.,
2006a; Grobe et al., 2006b; Iwata et al., 2005; Tallant et al., 2005; Wang et al., 2005).
Ishiyama et al. found that heart failure induced by coronary artery ligation was
associated with an increase in plasma Ang‐(1‐7) levels, which was augmented with
the administration of the AT1 receptor blockers losartan and olmesartan (Ishiyama
et al., 2004). The AT1‐receptor blockade was associated with an upregulation of
cardiac ACE2, suggesting that the increased Ang‐(1‐7) levels may be due to
increased ACE2. Likewise, cardiac Ang‐(1‐7) formation was also increased in
human heart failure when compared to non‐failing hearts (Zisman et al., 2003a).
Taken together, these studies indicate that Ang‐(1‐7) exerts positive effects on the
heart, through both the reduction in cardiac remodeling, and the correction of
cardiac arrhythmias.
Physiological Actions of Ang(17) on the Kidney
Several studies over the past 15 years showed that Ang‐(1‐7) affects the
ways in which the kidney handles water/sodium balance. Ang‐(1‐7) produced
natriuretic and diuretic effects on the kidney, with corresponding increases in
glomerular filtration rate (GFR) (DelliPizzi et al., 1994; Heller et al., 2000; Vallon et
al., 1998), which was explained by inhibition of the Na+‐K+‐ATPase (Handa et al.,
1996). These effects were not dependent upon the AT1 or AT2 receptors, but they
were attenuated by the Ang‐(1‐7) antagonist, D‐Ala7‐Ang‐(1‐7), suggesting
involvement of the mas receptor. Interestingly, Ang‐(1‐7) attenuated the sodium
reabsorption caused by Ang II infusion, but the heptapeptide did not affect the Ang
47
II‐mediated decrease in GFR (Burgelova et al., 2002). Clark et al. (Clark et al., 2003)
later showed that this may be caused by the ability of Ang‐(1‐7) to reduce renal Ang
II receptors. Intrarenal Ang‐(1‐7) blockade caused a decrease in GFR, renal plasma
flow, and sodium excretion in one‐kidney, one‐clip hypertension, as well as salt‐
depleted Sprague‐Dawley and [mRen2]27 transgenic rats, but it had no effect in
salt‐replete or Ang II‐infused rats (Burgelova et al., 2005). These data suggest that
Ang‐(1‐7) only exerts counterregulatory actions on the kidney in response to the
activation of the RAS. In humans, urinary Ang‐(1‐7) was decreased in untreated
essential hypertensive patients when compared to normal, healthy individuals
(Ferrario et al., 1998b). Collectively, these studies show that Ang‐(1‐7) exerts
effects opposite to those of Ang II on the kidney, and that an attenuation of Ang‐(1‐
7) in the kidney may be associate ith human hypertension. d w
ng(1A 7) and Brain Mechanisms
Shortly after its discovery in the hypothalamic‐pituitary explants in 1988
(Schiavone et al., 1988), Ang‐(1‐7) was found to be present in brain areas including
the hypothalamus, medulla oblongata, and amygdala (Chappell et al., 1989). Even
though Ang‐(1‐7) released vasopressin from the hypothalamus (Qadri et al., 1998;
Schiavone et al., 1988), which was not associated with increases in blood pressure
or water intake, there was no increase in the plasma level of the antidiuretic
hormone, suggesting that Ang‐(1‐7) has local effects on the hypothalamus to
modulate vasopressin release.
Since that time, perhaps the most recognized action of Ang‐(1‐7) on the brain
is its alteration of the baroreceptor reflex and neural control of the homeostatic
48
blood pressure. Ang‐(1‐7) also augments the gain of the baroreflex control of heart
rate (Benter et al., 1995a; Campagnole‐Santos et al., 1992; Oliveira et al., 1996)
indicating that loss of the balance between Ang II and Ang‐(1‐7) may explain the
altered regulation of blood pressure in aging individuals (Sakima et al., 2005). One
of the more unexpected actions of Ang‐(1‐7) was data published that it enhanced
long‐term potentiation (LTP) in the hippocampus (Hellner et al., 2005), which is
thought to be the process behind learning and memory. From the data presented
herein, it is obvious that Ang‐(1‐7) has far‐reaching actions on the brain — from the
modulation of vasopressin release to baroreflex function to learning and memory.
A 7) and Pregnancyng(1
During normal pregnancy, bioactive components of the RAS are elevated in
the plasma and urine, including Ang‐(1‐7) (Merrill et al., 2002; Valdes et al., 2001),
and Ang‐(1‐7) and ACE2 are both expressed in the placenta (Valdes et al., 2006).
Preeclampsia, a condition that can occur during pregnancy that is characterized by
high blood pressure and proteinuria, can be detrimental to both the mother and
fetus. Recent studies showed impairment in plasma Ang‐(1‐7) levels during
preeclamptic pregnancies (Merrill et al., 2002), which may be at least partially
responsible for the etiology behind this condition. These initial studies in pregnancy
are in line with what is thought to be impairment in the peptide hormone’s ability to
vasodilate properly.
Vascular effects of Ang(17)
Evidence that Ang‐(1‐7) was produced in the vasculature was first shown by
our laboratory 15 years ago (Santos et al., 1992). It was later shown that Ang‐(1‐7)
49
produced endothelium‐dependent dilation of the coronary arteries of pigs and dogs,
which was mediated by nitric oxide (NO) and bradykinin (Brosnihan et al., 1996;
Porsti et al., 1994). This response was independent of AT1 receptors, AT2 receptors,
and prostaglandins; however ACE inhibition magnified the vasodilatory response of
Ang‐(1‐7). To determine the interaction of Ang‐(1‐7) and NO, studies conducted
from our group confirmed that the vasodilator response was mediated by NO, but it
was discovered that inhibition of nitric oxide synthase in 2‐kidney‐1‐clip (2K1C)
hypertension induced in dogs resulted in a blunted vasodilatory response,
suggesting that an impairment in the nitric oxide system may play a role in the
pathology of hypertension (Nakamoto et al., 1995). Moreover, Ang‐(1‐7)
potentiated the vasodilatory effect of bradykinin administered to conscious rats,
and this response was significantly attenuated by indomethacin, suggesting the
involvement of the prostaglandins (Paula et al., 1995). This effect was later
confirmed by us, and we showed that this effect of Ang‐(1‐7) to potentiate
bradykinin‐induced vasodilation was due to the ability of Ang‐(1‐7) to inhibit ACE
activity and release NO (Li et al., 1997), thereby decreasing the metabolism of
bradykinin and further stimulating vasodilation. More recently, mas receptor
activation by Ang‐(1‐7) improved endothelial function (Faria‐Silva et al., 2005).
Collectively, these data showed that Ang‐(1‐7) acts as a vasodilator through the
release of NO and bradykinin, and it may also improve endothelial function by
otentiating the hypotensive effects of acetylcholine. p
50
A 7) and Growthng(1
The first indication that Ang‐(1‐7) could inhibit growth came in 1996 when
Freeman and colleagues (Freeman et al., 1996) found that Ang‐(1‐7) inhibited the
growth of vascular smooth muscle cells isolated from Sprague‐Dawley rat aortas,
which was later found to be mediated through the release of prostaglandins, with
prostacyclin being the most likely candidate (Tallant and Clark, 2003). In a follow‐
up study from our group, Ang‐(1‐7) administered continuously for 12 days after
carotid artery balloon catheter injury, inhibited neointimal formation compared to
saline‐infused control rats (Strawn et al., 1999). Elevated endogenous Ang‐(1‐7) by
ACE inhibition or angiotensin receptor blockade also yielded similar results. The
data from these studies suggests that Ang‐(1‐7) may be a good candidate for drug‐
coated stent development (Langeveld et al., 2005), and that the ACE inhibitors and
ARBs already on the market may already be facilitating this process. This
suggestion is in keeping with the demonstration of large elevations in plasma Ang‐
(1‐7) in normotensive volunteers administered irbesartan (Schindler, 2007). In
addition, Tallant et al. (Tallant et al., 2005) showed that Ang‐(1‐7) also inhibited the
growth of cardiac myocytes through the activation of the mas receptor, which
further reinforces that Ang‐(1‐7) may be responsible for at least some of the
beneficial outcomes (improved cardiac function and reduced ventricular
remodeling) observed with ACE inhibitor and ARB treatment in heart failure.
In a tireless effort to find a magic bullet for the treatment of various types of
cancers, Ang‐(1‐7) has proven to have high potential as a chemotherapeutic agent.
Building upon the anti‐trophic mechanisms of Ang‐(1‐7), Gallagher and Tallant
51
(Gallagher and Tallant, 2004) showed recently that Ang‐(1‐7) inhibited cancerous
growth in several human lung cancer cell lines, which is in keeping with the
peptide’s antiproliferative effects in the cardiovascular system. Menon et al. (Menon
et al., 2007) recently showed that these results held true in vivo because Ang‐(1‐7)
caused a reduction in the size of lung tumors induced in the flank region of athymic
mice, which was associated with a reduction in cyclooxygenase‐2 (COX‐2).
Likewise, Pantoja et al. (Pantoja et al., 2004) found that Ang‐(1‐7) exerted similar
effects in breast cancer cells, possibly in part due to inhibition of angiogenesis.
Indeed, Ang‐(1‐7) was examined in a Phase I/II clinical trial to determine its
effectiveness and optimal dose against chemotherapy‐induced cytopenias in breast
cancer patients (Rodgers et al., 2006). This study found that the heptapeptide
attenuated cytopenias associated with chemotherapy without any hematologic
toxicity. Collectively, the data on Ang‐(1‐7) and its effects on cancerous growth are
promising. Although still in its infancy, the peptide hormone may provide health
care providers with an alternative treatment regimen with fewer side effects and
ertainly less toxicity. c
II.6 CONCLUSIONS
As indicated in this review, the heptapeptide Ang‐(1‐7) has many beneficial
effects not only on cardiovascular processes, but also in the treatment of cancer, and
an elevation in the peptide associated with current ACE inhibitor and ARB therapy
may account for the favorable outcomes associated with their use. The potential
therapeutic implications of Ang‐(1‐7) indicated that it may be used to treat cardiac
52
hypertrophy, heart failure, hypertension, kidney disease, preeclampsia, and cancer.
Although using the endogenously‐derived peptide for treatments may be on the
horizon, the development of stable Ang‐(1‐7) analogs such as AVE 0991 may prove
to be better pharmacologic effectors of the actions of Ang‐(1‐7) (See Review by
Santos and Ferreira, 2006). In any case, the current data on Ang‐(1‐7) is exciting
and new developments using the peptide are on the horizon.
ACKNOLEDGEMENTS
The authors would like to gratefully acknowledge financial support from the
NIH (HL‐51952), as well as grant support in part provided by Unifi, Inc., Greensboro,
NC, and Farley‐Hudson Foundation, Jacksonville, NC.
53
REFERENCES
(2000) Effects of ramipril on cardiovascular and microvascular outcomes in people
with diabetes mellitus: results of the HOPE study and MICRO‐HOPE substudy.
Heart Outcomes Prevention Evaluation Study Investigators. Lancet 355:253‐
259.
Allred A. J., Diz, D. I., Ferrario, C. M., and Chappell, M. C. (2000) Pathways for
angiotensin‐(1‐‐‐7) metabolism in pulmonary and renal tissues. Am.J.Physiol
Renal Physiol 279:F841‐F850.
Averill D. B., Ishiyama, Y., Chappell, M. C., and Ferrario, C. M. (2003) Cardiac
angiotensin‐(1‐7) in ischemic cardiomyopathy. Circulation 108:2141‐2146.
Benter I. F., Diz, D. I., and Ferrario, C. M. (1995a) Pressor and reflex sensitivity is
altered in spontaneously hypertensive rats treated with angiotensin‐(1‐7).
Hypertension 26:1138‐1144.
Benter I. F., Ferrario, C. M., Morris, M., and Diz, D. I. (1995b) Antihypertensive
actions of angiotensin‐(1‐7) in spontaneously hypertensive rats. Am.J.Physiol
269:H313‐H319.
Benter I. F., Yousif, M. H., Anim, J. T., Cojocel, C., and Diz, D. I. (2006) Angiotensin‐(1‐
7) prevents development of severe hypertension and end‐organ damage in
spontaneously hypertensive rats treated with L‐NAME. Am.J.Physiol Heart
Circ.Physiol 290:H684‐H691.
54
Brosnihan K. B., Li, P., and Ferrario, C. M. (1996) Angiotensin‐(1‐7) dilates canine
coronary arteries through kinins and nitric oxide. Hypertension 27:523‐528.
Burgelova M., Kramer, H. J., Teplan, V., Thumova, M., and Cervenka, L. (2005) Effects
of angiotensin‐(1‐7) blockade on renal function in rats with enhanced
intrarenal Ang II activity. Kidney Int. 67:1453‐1461.
Burgelova M., Kramer, H. J., Teplan, V., Velickova, G., Vitko, S., Heller, J., Maly, J., and
Cervenka, L. (2002) Intrarenal infusion of angiotensin‐(1‐7) modulates renal
functional responses to exogenous angiotensin II in the rat. Kidney Blood
Press Res. 25:202‐210.
Campagnole‐Santos M. J., Heringer, S. B., Batista, E. N., Khosla, M. C., and Santos, R. A.
(1992) Differential baroreceptor reflex modulation by centrally infused
angiotensin peptides. Am.J.Physiol 263:R89‐R94.
Castro C. H., Santos, R. A., Ferreira, A. J., Bader, M., Alenina, N., and Almeida, A. P.
(2005) Evidence for a functional interaction of the angiotensin‐(1‐7)
receptor Mas with AT1 and AT2 receptors in the mouse heart. Hypertension
46:937‐942.
Castro C. H., Santos, R. A., Ferreira, A. J., Bader, M., Alenina, N., and Almeida, A. P.
(2006) Effects of genetic deletion of angiotensin‐(1‐7) receptor Mas on
cardiac function during ischemia/reperfusion in the isolated perfused mouse
heart. Life Sci. 80:264‐268.
55
Chappell M. C., Allred, A. J., and Ferrario, C. M. (2001) Pathways of angiotensin‐(1‐7)
metabolism in the kidney. Nephrol.Dial.Transplant. 16 Suppl 1:22‐26.
Chappell M. C., Brosnihan, K. B., Diz, D. I., and Ferrario, C. M. (1989) Identification of
angiotensin‐(1‐7) in rat brain. Evidence for differential processing of
angiotensin peptides. J.Biol.Chem. 264:16518‐16523.
Chappell M. C., Gomez, M. N., Pirro, N. T., and Ferrario, C. M. (2000) Release of
angiotensin‐(1‐7) from the rat hindlimb: influence of angiotensin‐converting
enzyme inhibition. Hypertension 35:348‐352.
Chappell M. C., Pirro, N. T., Sykes, A., and Ferrario, C. M. (1998) Metabolism of
angiotensin‐(1‐7) by angiotensin‐converting enzyme. Hypertension 31:362‐
367.
Clark M. A., Tallant, E. A., Tommasi, E., Bosch, S., and Diz, D. I. (2003) Angiotensin‐(1‐
7) reduces renal angiotensin II receptors through a cyclooxygenase‐
dependent mechanism. J.Cardiovasc.Pharmacol. 41:276‐283.
Crackower M. A., Sarao, R., Oudit, G. Y., Yagil, C., Kozieradzki, I., Scanga, S. E., Oliveira‐
dos‐Santos, A. J., da, Costa J., Zhang, L., Pei, Y., Scholey, J., Ferrario, C. M.,
Manoukian, A. S., Chappell, M. C., Backx, P. H., Yagil, Y., and Penninger, J. M.
(2002) Angiotensin‐converting enzyme 2 is an essential regulator of heart
function. Nature 417:822‐828.
56
Daemen M. J., Lombardi, D. M., Bosman, F. T., and Schwartz, S. M. (1991) Angiotensin
II induces smooth muscle cell proliferation in the normal and injured rat
arterial wall. Circ.Res. 68:450‐456.
Dahlof B., Devereux, R. B., Kjeldsen, S. E., Julius, S., Beevers, G., de, Faire U., Fyhrquist,
F., Ibsen, H., Kristiansson, K., Lederballe‐Pedersen, O., Lindholm, L. H.,
Nieminen, M. S., Omvik, P., Oparil, S., and Wedel, H. (2002) Cardiovascular
morbidity and mortality in the Losartan Intervention For Endpoint reduction
in hypertension study (LIFE): a randomised trial against atenolol. Lancet
359:995‐1003.
De Mello W. C. (2004) Angiotensin (1‐7) re‐establishes impulse conduction in
cardiac muscle during ischaemia‐reperfusion. The role of the sodium pump.
J.Renin.Angiotensin.Aldosterone.Syst. 5:203‐208.
Deddish P. A., Marcic, B., Jackman, H. L., Wang, H. Z., Skidgel, R. A., and Erdos, E. G.
(1998) N‐domain‐specific substrate and C‐domain inhibitors of angiotensin‐
converting enzyme: angiotensin‐(1‐7) and keto‐ACE. Hypertension 31:912‐
917.
DelliPizzi A. M., Hilchey, S. D., and Bell‐Quilley, C. P. (1994) Natriuretic action of
angiotensin(1‐7). Br.J.Pharmacol. 111:1‐3.
Donoghue M., Hsieh, F., Baronas, E., Godbout, K., Gosselin, M., Stagliano, N., Donovan,
M., Woolf, B., Robison, K., Jeyaseelan, R., Breitbart, R. E., and Acton, S. (2000)
57
A novel angiotensin‐converting enzyme‐related carboxypeptidase (ACE2)
converts angiotensin I to angiotensin 1‐9. Circ.Res. 87:E1‐E9.
Faria‐Silva R., Duarte, F. V., and Santos, R. A. (2005) Short‐term angiotensin(1‐7)
receptor MAS stimulation improves endothelial function in normotensive
rats. Hypertension 46:948‐952.
Ferrario C. M., Chappell, M. C., Dean, R. H., and Iyer, S. N. (1998a) Novel angiotensin
peptides regulate blood pressure, endothelial function, and natriuresis.
J.Am.Soc Nephrol. 9:1716‐1722.
Ferrario C. M., Martell, N., Yunis, C., Flack, J. M., Chappell, M. C., Brosnihan, K. B.,
Dean, R. H., Fernandez, A., Novikov, S. V., Pinillas, C., and Luque, M. (1998b)
Characterization of angiotensin‐(1‐7) in the urine of normal and essential
hypertensive subjects. Am.J.Hypertens. 11:137‐146.
Ferrario C. M., Trask, A. J., and Jessup, J. A. (2005) Advances in biochemical and
functional roles of angiotensin‐converting enzyme 2 and angiotensin‐(1‐7) in
regulation of cardiovascular function. Am.J.Physiol Heart Circ.Physiol
289:H2281‐H2290.
Ferreira A. J., Santos, R. A., and Almeida, A. P. (2001) Angiotensin‐(1‐7):
cardioprotective effect in myocardial ischemia/reperfusion. Hypertension
38:665‐668.
58
Ferreira A. J., Santos, R. A., and Almeida, A. P. (2002) Angiotensin‐(1‐7) improves the
post‐ischemic function in isolated perfused rat hearts. Braz.J.Med.Biol.Res.
35:1083‐1090.
Freeman E. J., Chisolm, G. M., Ferrario, C. M., and Tallant, E. A. (1996) Angiotensin‐(1‐
7) inhibits vascular smooth muscle cell growth. Hypertension 28:104‐108.
Gallagher P. E. and Tallant, E. A. (2004) Inhibition of human lung cancer cell growth
by angiotensin‐(1‐7). Carcinogenesis 25:2045‐2052.
Grobe J. L., Mecca, A. P., Lingis, M., Shenoy, V., Bolton, T. A., Machado, J. M., Speth, R.
C., Raizada, M. K., and Katovich, M. (2006a) Prevention of Angiotensin II‐
Induced Cardiac Remodeling by Angiotensin‐(1‐7). Am.J.Physiol Heart
Circ.Physiol
Grobe J. L., Mecca, A. P., Mao, H., and Katovich, M. J. (2006b) Chronic angiotensin‐(1‐
7) prevents cardiac fibrosis in DOCA‐salt model of hypertension. Am.J.Physiol
Heart Circ.Physiol 290:H2417‐H2423.
Handa R. K., Ferrario, C. M., and Strandhoy, J. W. (1996) Renal actions of angiotensin‐
(1‐7): in vivo and in vitro studies. Am.J.Physiol 270:F141‐F147.
Heller J., Kramer, H. J., Maly, J., Cervenka, L., and Horacek, V. (2000) Effect of
intrarenal infusion of angiotensin‐(1‐7) in the dog. Kidney Blood Press Res.
23:89‐94.
59
Hellner K., Walther, T., Schubert, M., and Albrecht, D. (2005) Angiotensin‐(1‐7)
enhances LTP in the hippocampus through the G‐protein‐coupled receptor
Mas. Mol.Cell Neurosci 29:427‐435.
Huentelman M. J., Grobe, J. L., Vazquez, J., Stewart, J. M., Mecca, A. P., Katovich, M. J.,
Ferrario, C. M., and Raizada, M. K. (2005) Protection from angiotensin II‐
induced cardiac hypertrophy and fibrosis by systemic lentiviral delivery of
ACE2 in rats. Exp.Physiol 90:783‐790.
Ishiyama Y., Gallagher, P. E., Averill, D. B., Tallant, E. A., Brosnihan, K. B., and
Ferrario, C. M. (2004) Upregulation of angiotensin‐converting enzyme 2 after
myocardial infarction by blockade of angiotensin II receptors. Hypertension
43:970‐976.
Iwata M., Cowling, R. T., Gurantz, D., Moore, C., Zhang, S., Yuan, J. X., and Greenberg,
B. H. (2005) Angiotensin‐(1‐7) binds to specific receptors on cardiac
fibroblasts to initiate antifibrotic and antitrophic effects. Am.J.Physiol Heart
Circ.Physiol 289:H2356‐H2363.
Kato T., Okada, M., and Nagatsu, T. (1980) Distribution of post‐proline cleaving
enzyme in human brain and the peripheral tissues. Mol.Cell Biochem. 32:117‐
121.
Koida M. and Walter, R. (1976) Post‐proline cleaving enzyme. Purification of this
endopeptidase by affinity chromatography. J.Biol.Chem. 251:7593‐7599.
60
Kostenis E., Milligan, G., Christopoulos, A., Sanchez‐Ferrer, C. F., Heringer‐Walther, S.,
Sexton, P. M., Gembardt, F., Kellett, E., Martini, L., Vanderheyden, P.,
Schultheiss, H. P., and Walther, T. (2005) G‐protein‐coupled receptor Mas is a
physiological antagonist of the angiotensin II type 1 receptor. Circulation
111:1806‐1813.
Langeveld B., van Gilst, W. H., Tio, R. A., Zijlstra, F., and Roks, A. J. (2005)
Angiotensin‐(1‐7) attenuates neointimal formation after stent implantation
in the rat. Hypertension 45:138‐141.
Li P., Chappell, M. C., Ferrario, C. M., and Brosnihan, K. B. (1997) Angiotensin‐(1‐7)
augments bradykinin‐induced vasodilation by competing with ACE and
releasing nitric oxide. Hypertension 29:394‐400.
Loot A. E., Roks, A. J., Henning, R. H., Tio, R. A., Suurmeijer, A. J., Boomsma, F., and van
Gilst, W. H. (2002) Angiotensin‐(1‐7) attenuates the development of heart
failure after myocardial infarction in rats. Circulation 105:1548‐1550.
Menon, J., Pantoja, D. S., Callahan, M. F., Cline, J. M., Ferrario, C. M., Tallant, E. A., and
Gallagher, P. E. (2007) Angiotensin‐(1‐7) Inhibits Growth of Human Lung
Adenocarcinoma Xenografts in Nude Mice through a Reduction in
Cyclooxygenase‐2. Cancer Research In Press:
Merrill D. C., Karoly, M., Chen, K., Ferrario, C. M., and Brosnihan, K. B. (2002)
Angiotensin‐(1‐7) in normal and preeclamptic pregnancy. Endocrine. 18:239‐
245.
61
Nakamoto H., Ferrario, C. M., Fuller, S. B., Robaczewski, D. L., Winicov, E., and Dean,
R. H. (1995) Angiotensin‐(1‐7) and nitric oxide interaction in renovascular
hypertension. Hypertension 25:796‐802.
Oliveira D. R., Santos, R. A., Santos, G. F., Khosla, M., and Campagnole‐Santos, M. J.
(1996) Changes in the baroreflex control of heart rate produced by central
infusion of selective angiotensin antagonists in hypertensive rats.
Hypertension 27:1284‐1290.
Pantoja, D. S., Tallant, E. A., and Gallagher, P. E. (2004) Inhibition of human breast
cancer cell growth by angiotensin‐(1‐7). 45:
Paula R. D., Lima, C. V., Khosla, M. C., and Santos, R. A. (1995) Angiotensin‐(1‐7)
potentiates the hypotensive effect of bradykinin in conscious rats.
Hypertension 26:1154‐1159.
Porsti I., Bara, A. T., Busse, R., and Hecker, M. (1994) Release of nitric oxide by
angiotensin‐(1‐7) from porcine coronary endothelium: implications for a
novel angiotensin receptor. Br.J.Pharmacol. 111:652‐654.
Qadri F., Wolf, A., Waldmann, T., Rascher, W., and Unger, T. (1998) Sensitivity of
hypothalamic paraventricular nucleus to C‐ and N‐terminal angiotensin
fragments: vasopressin release and drinking. J.Neuroendocrinol. 10:275‐281.
Rodgers K. E., Oliver, J., and diZerega, G. S. (2006) Phase I/II dose escalation study of
angiotensin 1‐7 [A(1‐7)] administered before and after chemotherapy in
62
patients with newly diagnosed breast cancer. Cancer Chemother.Pharmacol.
57:559‐568.
Sakima A., Averill, D. B., Gallagher, P. E., Kasper, S. O., Tommasi, E. N., Ferrario, C. M.,
and Diz, D. I. (2005) Impaired heart rate baroreflex in older rats: role of
endogenous angiotensin‐(1‐7) at the nucleus tractus solitarii. Hypertension
46:333‐340.
Santos R. A., Brosnihan, K. B., Jacobsen, D. W., DiCorleto, P. E., and Ferrario, C. M.
(1992) Production of angiotensin‐(1‐7) by human vascular endothelium.
Hypertension 19:II56‐II61.
Santos R. A., Castro, C. H., Gava, E., Pinheiro, S. V., Almeida, A. P., Paula, R. D., Cruz, J.
S., Ramos, A. S., Rosa, K. T., Irigoyen, M. C., Bader, M., Alenina, N., Kitten, G. T.,
and Ferreira, A. J. (2006) Impairment of in vitro and in vivo heart function in
angiotensin‐(1‐7) receptor MAS knockout mice. Hypertension 47:996‐1002.
Santos R. A. and Ferreira, A. J. (2006) Pharmacological effects of AVE 0991, a
nonpeptide angiotensin‐(1‐7) receptor agonist. Cardiovasc.Drug Rev. 24:239‐
246.
Santos R. A., Simoes e Silva AC, Maric, C., Silva, D. M., Machado, R. P., de, Buhr, I,
Heringer‐Walther, S., Pinheiro, S. V., Lopes, M. T., Bader, M., Mendes, E. P.,
Lemos, V. S., Campagnole‐Santos, M. J., Schultheiss, H. P., Speth, R., and
Walther, T. (2003) Angiotensin‐(1‐7) is an endogenous ligand for the G
protein‐coupled receptor Mas. Proc.Natl.Acad.Sci.U.S.A 100:8258‐8263.
63
Schiavone M. T., Santos, R. A., Brosnihan, K. B., Khosla, M. C., and Ferrario, C. M.
(1988) Release of vasopressin from the rat hypothalamo‐neurohypophysial
system by angiotensin‐(1‐7) heptapeptide. Proc.Natl.Acad.Sci.U.S.A 85:4095‐
4098.
Shaltout H. A., Westwood, B. M., Averill, D. B., Ferrario, C. M., Figueroa, J. P., Diz, D. I.,
Rose, J. C., and Chappell, M. C. (2007) Angiotensin metabolism in renal
proximal tubules, urine, and serum of sheep: evidence for ACE2‐dependent
processing of angiotensin II. Am.J.Physiol Renal Physiol 292:F82‐F91.
Silva D. M., Vianna, H. R., Cortes, S. F., Campagnole‐Santos, M. J., Santos, R. A., and
Lemos, V. S. (2006) Evidence for a new angiotensin‐(1‐7) receptor subtype in
the aorta of Sprague‐Dawley rats. Peptides
Strawn W. B., Ferrario, C. M., and Tallant, E. A. (1999) Angiotensin‐(1‐7) reduces
smooth muscle growth after vascular injury. Hypertension 33:207‐211.
Su E. J., Lombardi, D. M., Siegal, J., and Schwartz, S. M. (1998) Angiotensin II induces
vascular smooth muscle cell replication independent of blood pressure.
Hypertension 31:1331‐1337.
Tallant E. A. and Clark, M. A. (2003) Molecular mechanisms of inhibition of vascular
growth by angiotensin‐(1‐7). Hypertension 42:574‐579.
64
Tallant E. A., Ferrario, C. M., and Gallagher, P. E. (2005) Angiotensin‐(1‐7) inhibits
growth of cardiac myocytes through activation of the mas receptor.
Am.J.Physiol Heart Circ.Physiol 289:H1560‐H1566.
Tallant E. A., Lu, X., Weiss, R. B., Chappell, M. C., and Ferrario, C. M. (1997) Bovine
aortic endothelial cells contain an angiotensin‐(1‐7) receptor. Hypertension
29:388‐393.
Towler P., Staker, B., Prasad, S. G., Menon, S., Tang, J., Parsons, T., Ryan, D., Fisher, M.,
Williams, D., Dales, N. A., Patane, M. A., and Pantoliano, M. W. (2004) ACE2 X‐
ray structures reveal a large hinge‐bending motion important for inhibitor
binding and catalysis. J.Biol.Chem. 279:17996‐18007.
Trask A. J., Averill, D. B., Ganten, D., Chappell, M. C., and Ferrario, C. M. (2007)
Primary Role of Angiotensin Converting Enzyme 2 in Cardiac Production of
Angiotensin‐(1‐7) in Transgenic Ren‐2 Hypertensive Rats. Am.J.Physiol Heart
Circ.Physiol
Valdes G., Germain, A. M., Corthorn, J., Berrios, C., Foradori, A. C., Ferrario, C. M., and
Brosnihan, K. B. (2001) Urinary vasodilator and vasoconstrictor angiotensins
during menstrual cycle, pregnancy, and lactation. Endocrine. 16:117‐122.
Valdes G., Neves, L. A., Anton, L., Corthorn, J., Chacon, C., Germain, A. M., Merrill, D. C.,
Ferrario, C. M., Sarao, R., Penninger, J., and Brosnihan, K. B. (2006)
Distribution of angiotensin‐(1‐7) and ACE2 in human placentas of normal
and pathological pregnancies. Placenta 27:200‐207.
65
Vallon V., Heyne, N., Richter, K., Khosla, M. C., and Fechter, K. (1998) [7‐D‐ALA]‐
angiotensin 1‐7 blocks renal actions of angiotensin 1‐7 in the anesthetized
rat. J.Cardiovasc.Pharmacol. 32:164‐167.
Vickers C., Hales, P., Kaushik, V., Dick, L., Gavin, J., Tang, J., Godbout, K., Parsons, T.,
Baronas, E., Hsieh, F., Acton, S., Patane, M., Nichols, A., and Tummino, P.
(2002) Hydrolysis of biological peptides by human angiotensin‐converting
enzyme‐related carboxypeptidase. J.Biol.Chem. 277:14838‐14843.
Wackenfors A., Pantev, E., Emilson, M., Edvinsson, L., and Malmsjo, M. (2004)
Angiotensin II receptor mRNA expression and vasoconstriction in human
coronary arteries: effects of heart failure and age. Basic
Clin.Pharmacol.Toxicol. 95:266‐272.
Walter R., Shlank, H., Glass, J. D., Schwartz, I. L., and Kerenyi, T. D. (1971)
Leucylglycinamide released from oxytocin by human uterine enzyme. Science
173:827‐829.
Wang L. J., He, J. G., Ma, H., Cai, Y. M., Liao, X. X., Zeng, W. T., Liu, J., and Wang, L. C.
(2005) Chronic administration of angiotensin‐(1‐7) attenuates pressure‐
overload left ventricular hypertrophy and fibrosis in rats. Di
Yi.Jun.Yi.Da.Xue.Xue.Bao. 25:481‐487.
Wei C. C., Ferrario, C. M., Brosnihan, K. B., Farrell, D. M., Bradley, W. E., Jaffa, A. A.,
and Dell'Italia, L. J. (2002) Angiotensin peptides modulate bradykinin levels
66
in the interstitium of the dog heart in vivo. J.Pharmacol.Exp.Ther. 300:324‐
329.
Yamada K., Iyer, S. N., Chappell, M. C., Ganten, D., and Ferrario, C. M. (1998)
Converting enzyme determines plasma clearance of angiotensin‐(1‐7).
Hypertension 32:496‐502.
Yamamoto K., Chappell, M. C., Brosnihan, K. B., and Ferrario, C. M. (1992) In vivo
metabolism of angiotensin I by neutral endopeptidase (EC 3.4.24.11) in
spontaneously hypertensive rats. Hypertension 19:692‐696.
Zisman L. S., Keller, R. S., Weaver, B., Lin, Q., Speth, R., Bristow, M. R., and Canver, C.
C. (2003a) Increased angiotensin‐(1‐7)‐forming activity in failing human
heart ventricles: evidence for upregulation of the angiotensin‐converting
enzyme Homologue ACE2. Circulation 108:1707‐1712.
Zisman L. S., Meixell, G. E., Bristow, M. R., and Canver, C. C. (2003b) Angiotensin‐(1‐
7) formation in the intact human heart: in vivo dependence on angiotensin II
as substrate. Circulation 108:1679‐1681.
67
Figure II.1. The chemical structure of the heptapeptide Ang‐(1‐7).
68
FIGURE II.1
69
Figure II.2. The current view of the RAS shows that Ang‐(1‐7) can be formed
by different enzymes and from different substrates. The actions of the two
biologically active angiotensin peptides, Ang II and Ang‐(1‐7), are mediated by their
respective receptors, the AT1 and mas receptors, respectively. Moreover, a recent
report suggests the existence of another Ang‐(1‐7) receptor, the function of which is
yet to be determined (Silva et al., 2006). The ultimate need for a balance of the two
peptides may lie in the relative activities of the two known enzymes that cleave Ang
II into Ang‐(1‐7) – ACE2 and POP.
70
FIGURE II.2
71
Figure II.3. Plasma clearance of Ang‐(1‐7) in normal SD, and hypertensive
SHR and Tg(+) rats. **P < 0.001. Adapted from Yamada et al., 1998.
72
FIGURE II.3
73
CHAPTER III
FURTHER EXPANSION OF THE COMPLEXITY OF THE RENINANGIOTENSIN SYSTEM: ANGIOTENSIN(112)
Jasmina Varagic, Aaron J. Trask, Mark C. Chappell, Carlos M. Ferrario
H D ypertension and Vascular Research Centerepart cologyWake icine
ment of Physiology and Pharma Forest Universi y School of MedWinston‐Salem, North Carolina
t
[This chapter is an excerpt from an article published in the Journal of Molecular Medicine (2008; 86:663671.) and is reprinted with kind permission from Springer Science+Business Media. Differences in formatting reflect the requirements of the journal. Aaron J. Trask prepared the excerpt, while Drs. Jasmina Varagic, Mark C. Chappell, and Carlos M. Ferrario contributed to the additional components of the article.]
74
III.1 ANGIOTENSIN(112)
In line with expanding data on the newer angiotensin peptide, Ang‐(1‐7),
Nagata and colleagues [3] recently identified another new angiotensin peptide, the
dodecapeptide angiotensin‐(1‐12) [proangiotensin‐12, Ang‐(1‐12)]. The authors
were probing for analogs of Ang II when they discovered an unidentified peak on an
HPLC chromatogram, which the authors found to be a 12‐amino acid derivative of
angiotensinogen, two amino acids larger than the traditional intermediate peptide
Ang I. The dodecapeptide produced pressor responses both in isolated rat aorta and
acutely in intact Wistar rats – a finding that was abrogated by co‐administration of
both an ACE inhibitor or and angiotensin receptor blocker (ARB). These data
suggested that “proangiotensin‐12,” as the authors named it, was exerting its actions
through rapid metabolism into Ang II.
75
Recent data from our laboratory provided further evidence for a biological
role of Ang‐(1‐12) as a new endogenous peptide of the RAS. Because Ang‐(1‐12)
was identified endogenously by RIA in different organs and tissues [3] (Figure III.1),
we first undertook studies that investigated the immunolocalization of the
dodecapeptide in the hearts and kidneys of normal Wistar‐Kyoto (WKY) and
Spontaneously Hypertensive (SHR) rats. Indeed, Jessup et al. [2] found that Ang‐(1‐
12) was localized by immunohistochemistry predominantly in cardiac myocytes,
while staining in the medial and endothelial layers of the coronary arteries
appeared more faint (Figure III.2). The distribution of Ang‐(1‐12) within the hearts
of SHR was more robust than that assessed in WKY. This observation was
confirmed by tissue content analysis, which revealed significantly higher levels of
cardiac Ang‐(1‐12) in SHR compared to WKY. Renal Ang‐(1‐12) was localized to the
proximal and distal tubules, as well as the collecting duct. These data, in accordance
with those from Nagata, show that Ang‐(1‐12) is indeed localized endogenously
within tissues and the distribution of the new angiotensin peptide may reflect the
state of the health of that tissue, as shown by differences in distribution between
WKY and SHR.
Further enhancements towards the understanding for a biological role for
Ang‐(1‐12) were made by studies from both our laboratory and those of our
colleague, Dr. Mark Chappell, which illustrated the metabolic capacity for Ang‐(1‐
12) to yield known downstream bioactive angiotensin peptides. Intriguingly,
Chappell et al. [1] found that Ang‐(1‐12) could be degraded into Ang II via Ang I by
serum and renal ACE, showing that Ang‐(1‐12) is a suitable substrate for ACE
activity, although renin did not participate in the metabolism of the dodecapeptide.
Moreover, we [4] showed that Ang‐(1‐12) could be metabolized into Ang I, Ang II,
and Ang‐(1‐7) in isolated hearts from Sprague‐Dawley rats. Collectively, these data
provide strong evidence that Ang‐(1‐12) may be an alternate precursor substrate
for the formation of bioactive angiotensin peptides in the heart, kidney, and
circulation that may depend on the localization of one of its processing enzymes,
ACE, but not renin.
76
REFERENCES
1. Chappell MC, Westwood BM, Pendergrass KD, Jessup JA, Ferrario CM (2007)
Distinct Processing Pathways for the Novel Peptide Angiotensin‐(1‐12) in the
Serum and Kidney of the Hypertensive mRen2.Lewis Rat. Hypertension
50(4):e139. Abstract.
2. Jessup JA, Chappell MC, Nagata S, Kato J, Kitamura K, Ferrario CM (2007)
Localization of the Novel Angiotensin Peptide, Proangiotensin‐12, in the Heart
and Kidney of Hypertensive and Normotensive Rats. Hypertension 50(4):e101.
Abstract.
3. Nagata S, Kato J, Sasaki K, Minamino N, Eto T, Kitamura K (2006) Isolation and
identification of proangiotensin‐12, a possible component of the renin‐
angiotensin system. Biochem Biophys Res Commun 350:1026‐1031.
4. Trask AJ, Jessup JA, Ferrario CM (2007) Angiotensin‐(1‐12) is a Precursor for
the Processing of Cardiac Tissue Angiotensin Peptides. Hypertension
50(4):e154. Abstract.
77
Figure III.1. Ang‐(1‐12) peptide levels by radioimmunoassay in several
ale Wistar rats. Adapted from Nagata et al. [3] tissues from m
78
Small In
testin
e
Spleen
Kidneys
Liver
Stomach
Lungs
Adrenal
Heart
Brain
Pancre
asAorta
Plasma
0
200
400
600
800
Angi
oten
sin-
(1-1
2)(fm
ol/g
or f
mol
/mL)
FIGURE III.1
79
Figure III.2. Immunohistochemical localization of Ang‐(1‐12) in the heart of
WKY and SHR rats. Note the more robust distribution of Ang‐(1‐12) within the
hearts of SHR than that assessed in WKY. This observation was confirmed by tissue
content analysis, which revealed significantly higher levels of cardiac Ang‐(1‐12) in
SHR compared to WKY. Adapted from Jessup et al. [2]
80
FIGURE III.2
81
CHAPTER IV
IV.1 RATIONALE AND AIMS
Whereas most of the research on the cardioprotective mechanism of cardiac
drugs has focused on reducing the synthesis or activity of cardiac angiotensin II
(Ang II), studies from our group showed first that angiotensin‐(1‐7) [Ang‐(1‐7)] is
important in the regulation of cardiac function and blood pressure by acting as an
endogenous inhibitor of Ang II (5; 10). My present interest in the cardioprotective
effects of Ang‐(1‐7) builds upon previous studies showing that an eight‐week
chronic infusion of Ang‐(1‐7) commencing 2 weeks after myocardial infarction was
associated with restoration of cardiac function and reversal of cardiac hypertrophy
(8). These first studies in Sprague‐Dawley [SD] rats are in keeping with the
demonstration of anti‐arrhythmic actions of Ang‐(1‐7) in ischemia/reperfusion (6;
7) that were found by De Mello (3) to result from activation of the cardiac sodium
pump with consequent re‐establishment of impulse conduction.
New and critical evidence for a role of Ang‐(1‐7) in cardiac remodeling and
function follows the demonstration that a new homologue of ACE, angiotensin
converting enzyme 2 (ACE2), may be critically involved in the regulation of cardiac
function by facilitating conversion of Ang II into Ang‐(1‐7) (1). Interest in the role of
ACE2 in cardiac function has grown since Crackower et al. (1), in collaboration with
us, first demonstrated that ACE2 knockout mice exhibited severe cardiac
dysfunction characterized by thinning of the left ventricular wall, which was
restored when ACE and ACE2 were ablated concurrently. This study suggested that
a balance between ACE and ACE2, mediated by their enzymatic products Ang II and
82
Ang‐(1‐7), respectively, is necessary for normal myocardial function. However, at
the time I commenced my studies, there were no studies in rats that had directly
investigated the role of cardiac ACE2 in hydrolyzing Ang II directly into Ang‐(1‐7),
nor were there studies investigating the role of endogenous ACE2 in cardiac
function.
Based on these observations, and preliminary studies suggesting a
differential role for cardiac ACE2 in producing Ang‐(1‐7) between normal and
hypertensive rats, I evaluated the hypothesis that the metabolic disposition of Ang
II conversion into Ang(17) is significantly shifted in hypertensioninduced
cardiac hypertrophy for the studies outlined in Chapters V and VI. This hypothesis
was evaluated in part by utilizing the Langendorff isolated heart preparation to
ascertain the relative contribution of cardiac ACE2 to Ang‐(1‐7) production from
Ang II between normal and hypertensive rat hearts. Furthermore, an investigation
into the role of cardiac ACE2 in serving as an endogenous balance regulator for local
Ang II and Ang‐(1‐7) was conducted by chronically inhibiting ACE2 in the
[mRen2]27 rat.
Unsuspectingly, an intriguing report from Nagata and colleagues (9) in 2006
provided evidence that a new angiotensin peptide may function as an alternate
substrate for the production of downstream angiotensin peptides, including Ang II
and Ang‐(1‐7). The incubation of “proangiotensin‐12” [Angiotensin‐(1‐12), Ang‐(1‐
12)] with isolated aortas produced a dose‐dependent pressor response, a finding
that was confirmed in intact Wistar rats. The observed pressor actions of Ang‐(1‐
12) were completely abolished by the co‐administration of either the ACE inhibitor
83
captopril or the AT1 receptor antagonist CV‐11974, suggesting to the authors that
Ang‐(1‐12) was being metabolized into Ang II to produce increases in blood
pressure. Evidence exists that angiotensinogen may be synthesized locally (4) or
may be taken up from the circulation (2). Because the presence of the previously‐
undisputed precursor, angiotensinogen, within the heart is controversial, the
findings by Nagata et al. (9) suggested to us that Ang‐(1‐12) may be a true alternate
precursor for the production of angiotensin peptides in the heart. Therefore, we
hypothesized that Ang(112) may serve as an alternate substrate for the
production of angiotensin peptides in the heart in the studies outlined in Chapter
7. The potential for Ang‐(1‐12) to yield bioactive angiotensin peptides may add an
additional level of complexity to the balance between Ang II and Ang‐(1‐7) in the
heart. If Ang‐(1‐12) is a biological substrate for angiotensin peptides, then it may
preferentially be able to produce either Ang II or Ang‐(1‐7) at differing levels, likely
depending in part upon enzyme distributions within the heart. This hypothesis was
evaluated by utilizing the Landendorff isolated heart preparation as previously
discussed.
84
REFERENCES
1. Crackower MA, Sarao R, Oudit GY, Yagil C, Kozieradzki I, Scanga SE, Oliveira‐
dos‐Santos AJ, da CJ, Zhang L, Pei Y, Scholey J, Ferrario CM, Manoukian AS,
Chappell MC, Backx PH, Yagil Y and Penninger JM. Angiotensin‐converting
enzyme 2 is an essential regulator of heart function. Nature 417: 822‐828,
2002.
2. Danser AH, van Kats JP, Admiraal PJ, Derkx FH, Lamers JM, Verdouw PD,
Saxena PR and Schalekamp MA. Cardiac renin and angiotensins. Uptake from
plasma versus in situ synthesis. Hypertension 24: 37‐48, 1994.
3. De Mello WC. Angiotensin (1‐7) re‐establishes impulse conduction in cardiac
muscle during ischaemia‐reperfusion. The role of the sodium pump. J Renin
Angiotensin Aldosterone Syst 5: 203‐208, 2004.
4. Dzau VJ, Ellison KE, Brody T, Ingelfinger J and Pratt RE. A comparative study of
the distributions of renin and angiotensinogen messenger ribonucleic acids in
rat and mouse tissues. Endocrinology 120: 2334‐2338, 1987.
5. Ferrario CM, Chappell MC, Tallant EA, Brosnihan KB and Diz DI.
Counterregulatory actions of angiotensin‐(1‐7). Hypertension 30: 535‐541,
1997.
85
6. Ferreira AJ, Santos RA and Almeida AP. Angiotensin‐(1‐7): cardioprotective
effect in myocardial ischemia/reperfusion. Hypertension 38: 665‐668, 2001.
7. Ferreira AJ, Santos RA and Almeida AP. Angiotensin‐(1‐7) improves the post‐
ischemic function in isolated perfused rat hearts. Braz J Med Biol Res 35: 1083‐
1090, 2002.
8. Loot AE, Roks AJ, Henning RH, Tio RA, Suurmeijer AJ, Boomsma F and van Gilst
WH. Angiotensin‐(1‐7) attenuates the development of heart failure after
myocardial infarction in rats. Circulation 105: 1548‐1550, 2002.
9. Nagata S, Kato J, Sasaki K, Minamino N, Eto T and Kitamura K. Isolation and
identification of proangiotensin‐12, a possible component of the renin‐
angiotensin system. Biochem Biophys Res Commun 350: 1026‐1031, 2006.
10. Nakamura S, Averill DB, Chappell MC, Diz DI, Brosnihan KB and Ferrario CM.
Angiotensin receptors contribute to blood pressure homeostasis in salt‐
depleted SHR. Am J Physiol Regul Integr Comp Physiol 284: R164‐R173, 2003.
86
CHAPTER V
PRIMARY ROLE OF ANGIOTENSIN CONVERTING ENZYME 2 IN CARDIAC PRODUCTION OF ANGIOTENSIN(17) IN TRANSGENIC REN2 HYPERTENSIVE
RATS
Aaron J. Trask1, David B. Averill1, Detlev Ganten2, Mark C. Chappell1, and Carlos M. Ferrario1
tension and Vascular Disease CenterDepartment of Physiology and Pharmacology Wake Forest Universi y School of Medicine
1The Hyper
tWinston‐Salem, North Carolina
2Max‐Delbrück‐Center for Molecular Medicine, Berlin‐Buch, Germany
[This chapter is published in the American Journal of Physiology – Heart and Circulatory Physiology (2007; 292:H3019H3024.) and is reprinted with permission. Differences in formatting reflect the requirements of the journal. Aaron J. Trask prepared the manuscript, while Dr. Carlos M. Ferrario acted in an editorial and advisory capacity. Dr. Detlev Ganten provided the animal model used in these studies. Dr. Averill provided initial assistance with the angendorff isolated heart preparation and Dr. Chappell provided assistance ith the biochemical analysis outlined in this manuscript.]
Lw
87
V.1 ABSTRACT
Angiotensin‐converting enzyme 2 (ACE2) converts angiotensin II (Ang II) to
angiotensin‐(1‐7) [Ang‐(1‐7)] and this enzyme may serve as a key regulatory
juncture in various tissues. Although the heart expresses ACE2, the extent that the
enzyme participates in the cardiac processing of Ang II and Ang‐(1‐7) is equivocal.
Therefore, we utilized the Langendorff preparation to characterize the ACE2
pathway in isolated hearts from male normotensive Sprague‐Dawley [Tg(‐)] and
hypertensive [mRen2]27 [Tg(+)] rats. During a 60‐minute recirculation period with
10 nM Ang II, the presence of Ang‐(1‐7) was assessed in the cardiac effluent. Ang‐
(1‐7) generation from Ang II was similar in both the normal and hypertensive hearts
(Tg(‐): 510 ± 55 pM, n=20 versus Tg(+): 497 ± 63 pM, n=14) with peak levels
occurring at 30 minutes after administration of the peptide. ACE2 inhibition (MLN‐
4760, 1µM) significantly reduced Ang‐(1‐7) production by 83% (57 ± 19 pM, P <
0.01, n=7) in the Tg(+) rats, whereas the inhibitor had no significant effect in the Tg(‐)
rats (285 ± 53 pM, P > 0.05, n=10). ACE2 activity was found in the effluent of
perfused Tg(‐) and Tg(+) hearts and it was highly associated with ACE2 protein
expression (r =0.78). This study is the first demonstration for a direct role of ACE2
in the metabolism of cardiac Ang II in the hypertrophic heart of hypertensive rats.
We conclude that predominant expression of cardiac ACE2 activity in the Tg(+) may
be a compensatory response to the extensive cardiac remodeling in this strain.
Keywords: angiotensin II, hypertension, isolated heart
88
V.2 INTRODUCTION
The involvement of the renin‐angiotensin system (RAS) in the development
of hypertension, cardiac hypertrophy, and subsequent transition to heart failure is
without question. However, newer studies suggest that the hypertrophic and pro‐
fibrotic actions of angiotensin II (Ang II) may be facilitated by a reduced
counterbalancing action of angiotensin‐(1‐7) [Ang‐(1‐7)] since infusion of the
heptapeptide attenuated the cardiac remodeling and the decrease in left ventricular
pumping ability produced by myocardial infarction in rats (14). Ang‐(1‐7) may act
to counterbalance the actions of Ang II by reducing vascular resistance (2),
improving vascular endothelial function (10), reversing cardiac hypertrophy (24),
and cardiac collagen deposition (17), as well as ischemia‐induced cardiac
arrhythmias (8). Indeed, Tallant et al. (27) demonstrated that Ang‐(1‐7) attenuated
the Ang II‐dependent activation of MAPK kinase in isolated cardiomyocytes.
Moreover, the protective actions of Ang‐(1‐7) were blocked by oligonucleotide‐
directed inhibition of the mas protein providing further evidence that the
cardioprotective actions of Ang‐(1‐7) are mediated by the mas receptor (23; 27).
Angiotensin‐converting enzyme 2 (ACE2), a newly discovered enzyme
member of the RAS, links the two functionally opposing arms of the RAS — the Ang
II pressor/hypertrophic path of the RAS to the depressor/anti‐proliferative actions
of Ang‐(1‐7) (14). Zisman et al. (32) recently showed that exogenous Ang‐(1‐7)
formation in human heart tissue was dependent upon Ang II. In ACE2 knockout
mice, Crackower et al. (6) reported significantly higher levels of cardiac Ang II that
were associated with cardiac dilatation. Given the importance that the new studies
89
suggest in terms of the mechanisms that regulate cardiac performance and may
mitigate the hypertrophic actions of Ang II, the current study investigated the role of
ACE2 in the production Ang‐(1‐7) from Ang II in intact hearts from both
normotensive and transgenic hypertensive rats.
V.3 MATERIALS AND METHODS
Animals
Twenty 10 ‐ 12‐week‐old male Sprague‐Dawley [(Tg(‐)), Harlan Laboratories,
Indianapolis, IN] rats and fourteen aged‐matched [mRen2]27 transgenic
hypertensive rats (Tg(+)) bred from our colony at the Hypertension & Vascular
Disease Center were housed in individual cages (12‐hour light/dark cycle) with ad
libitum access to rat chow and tap water. Procedures complied with the policies
implemented by our institutional Animal Care and Use Committee.
Langendorff Procedure
Rats were weighed, placed under deep halothane (2.5 ‐ 3%) anesthesia, and
given heparin (300 USP units) via a catheter inserted into the jugular vein. The
chest was opened down the midline and the heart was excised and immediately
placed in ice‐cold Krebs buffer (NaCl, 118 mM; KCl, 4.7 mM; MgSO4, 3.28 mM;
KH2PO4, 1.18 mM; CaCl2, 2.52 mM; NaHCO3, 25 mM; Glucose, 5.55 mM; Na‐pyruvate,
4.0 mM). Rat hearts were then perfused at a constant flow (10 ‐ 12 mL/min) on a
Langendorff isolated heart perfusion apparatus (Model IH‐SR, Harvard Apparatus,
Holliston, MA). Perfusion pressures (PP) were measured with an ISOTEC force
transducer (Harvard Apparatus, Holliston, MA) and flow rates were monitored
90
using a TS420 flowmeter (Transonic Systems, Inc., Ithaca, NY), both of which were
connected to the Biopac MP100A‐CE hardware (Biopac Systems, Inc., Goleta, CA).
Measurements were recorded using the Biopac AcqKnowledge 3.8.1 computer
software.
After a one‐hour equilibration period, a baseline sample of the cardiac
effluent (2.5 mL) was collected, and then 60 mL of Krebs buffer with 10 nM
angiotensin II (Ang II, Bachem, Torrance, CA) was recirculated through the heart for
60 minutes. All effluent samples were acid‐matched 1:1 (v:v) with 1%
heptafluorobutyric acid (HFBA) to abolish metabolism of the peptides at the
following times: (1) 5 minutes of recirculation, (2) 15 minutes, (3) 30 minutes, (4)
60 minutes. Half of the rats received 1 μM of the ACE2 inhibitor, MLN‐4760
(Millennium Pharmaceuticals, Cambridge, MA), immediately following the collection
of the 15‐minute sample. Previous studies demonstrated that MLN‐4760
specifically inhibits ACE2 at the doses employed here (7). Furthermore, we directly
tested the inhibitory action of MLN‐4760 by assaying the conversion of angiotensin
II into Ang‐(1‐7) in the cardiac effluent by HPLC (see below). Hearts were weighed
at the end of the experiment to calculate the heart weight:body weight ratio.
Biochemical Procedures
Angiotensin peptides were extracted from the acid‐matched samples using
C18 Sep Pak columns (Waters, Milford, MA). Each Sep Pak was activated with 5 mL
of 80% methanol (MeOH)/0.1% HFBA, followed by 5 mL 0.1% HFBA. The 5 mL
samples were then applied to the columns, followed by 10 mL 0.1% HFBA. The
columns were rinsed with 5 mL of MilliQ water, and the peptides were eluted in 3
91
mL 80% MeOH/0.1% HFBA. The eluate was then analyzed by radioimmunoassay
(RIA) for both Ang II and Ang‐(1‐7) as described previously (12; 13), which was
coupled with high performance liquid chromatography (HPLC) analysis of the eluate
to verify the presence of Ang‐(1‐7) as described previously (4). HPLC fraction
numbers 10‐25 were analyzed for immunoreactive Ang‐(1‐7). The minimum
detectable limits of the Ang II and Ang‐(1‐7) RIA assays were 0.8 pg/mL and 2.5
pg/mL, respectively.
ACE2 Activity by HPLC
Effluent collected from the hearts of three Tg(‐) and three Tg(+) rats (without
the ACE2 inhibitor) at the end of the 60‐minute recirculation period were
concentrated using an Amicon Ultra 10,000 molecular weight cut off centrifugal
filters (Millipore, Billerica, MA) and washed twice with 15 mL of HEPES buffer
containing 120 mM NaCl, 10 µM ZnCl2, pH 7.4. ACE2 activity was determined in the
concentrate by quantifying the conversion of 125I‐Ang II to Ang‐(1‐7) for 180 min at
37° C by HPLC as described elsewhere (12).
Immunoblot
ACE2 protein was determined in the Tg(‐) and Tg(+) cardiac effluent by
immunoblot using an N‐terminally directed antibody (AN1212) developed by us
that recognizes ACE2, but not ACE or collectrin (15; 26). We previously confirmed
that this antibody can be blocked by the peptide with which it was raised
(unpublished observations). We applied 25 μL of the concentrated perfusate to
10% SDS polyacrylamide gels (BioRad, Hercules, CA) for one hour at 120 volts in
Tris‐Glycine SDS, transferred onto a PVDF membrane and subsequently blocked for
92
one hour with 5% BioRad Dry Milk and TBS with Tween prior to incubation with the
ACE2 antibody (1:2,000). Immunoblots were then resolved with Pierce Super Signal
West Pico Chemiluminescent substrate (Chicago, IL) as described by the
manufacturer and exposed to Amersham Hyperfilm ECL (Piscataway, NJ).
Statistical Analyses
All values are reported as the mean ± SEM. Student’s t‐test and one‐way
ANOVA were used to determine significant differences at a probability <0.05.
Tukey’s post‐hoc test for multiple comparisons was used following the one‐way
ANOVA. For the RIA, values at or below the minimal detectable limits of the assays
were assigned that value for statistical purposes.
V.4 RESULTS
The heart weight:body weight ratio (mg/g) for the Tg(+) rats (5.13 ± 0.17)
was 26% higher than those determined in the Tg(‐) hearts (4.08 ± 0.12; P < 0.001),
verifying that the hypertensive animals exhibited marked cardiac hypertrophy.
Basal levels of perfusion pressure (PP) and heart rate (HR) were similar between
Tg(‐) and Tg(+) hearts, although the heart rate was slightly lower in the Tg(+) hearts
(PP: Tg(‐), 63.8 ± 2.7 mmHg vs. Tg(+), 60.7 ± 3.2 mmHg, P > 0.05; HR: Tg(‐), 254 ± 6.8
BPM vs P. 219 ± 9.5 BPM, < 0.05).
The overall rate of Ang II degradation in perfused hearts was not different
between the Tg(‐) and Tg(+) rats. The calculated half‐life (t1/2) of the peptide was 42 ±
7 minutes for the Tg(‐) rats and 46 ± 5 minutes (P > 0.05) for the Tg(+) rats (Figure
V.1A and V.1B). Moreover, ACE2 inhibition did not change the Ang II levels in either
93
strain. Ang‐(1‐7) production from exogenous Ang II as determined in the effluent of
hearts perfused with Ang II peaked at 30 minutes to an average of 510 ± 55 pM (P <
0.001 vs. baseline) and 497 ± 63 pM (P < 0.001 vs. baseline) in Tg(‐) and Tg(+) rats,
respectively (Figure V.2A and V.2B). Addition of the ACE2 inhibitor MLN‐4760 in
the Tg(‐) hearts caused no significant changes in Ang‐(1‐7) production at either the
30‐ or 60‐minute time points. In contrast, ACE2 inhibition in the Tg(+) rats resulted
in a sustained reduction in Ang‐(1‐7) averaging 54.7% (P < 0.05) and 83.1% (P <
0.01) at 30 and 60 minutes, respectively.
HPLC analysis of the heart perfusate confirmed the immunoreactive identity
of Ang‐(1‐7) that eluted essentially as a single fraction at 18 minutes (Figure V.3A).
The immunoreactive peak at 24 minutes corresponds to Ang II and most likely
represents the cross reactivity of exogenous Ang II with the Ang‐(1‐7) RIA. Indeed,
HPLC analysis of the buffer containing Ang II revealed a similar peak of Ang II
(Figure V.3B). Finally, the analysis of the Krebs buffer without Ang II demonstrated
no imm vunoreacti e peaks (Figure V.3C).
Although ACE2 is a membrane bound metallopeptidase, we examined
whether ACE2 activity was present in the cardiac effluent. Following the 60‐minute
recirculation period, the perfusate was concentrated 40 fold and incubated with
125I‐Ang II. As illustrated in Figure V.4, the chromatographs reveal significant
conversion to Ang‐(1‐7) in the effluent collected from perfused Tg(‐) (Figure V.4A)
and Tg(+) (Figure V.4B) hearts that was completely abolished by addition of the
ACE2 inhibitor MLN‐4760. The ACE2 activity was significantly higher in the Tg(+)
perfusate (1.97 ± 0.26 fmol/mL/min, n=3) when compared to the normal Tg(‐)
94
perfusate (0.82 ± 0.19 fmol/mL/min, n=3, P < 0.05). Consistent with the presence of
ACE2 activity in the concentrate, we detected an 80‐kilodalton (kDa) band in the
immunoblot of the concentrated effluent from both Tg(‐) hearts (Lanes 3, 4, and 5,
Figure V.5A) and Tg(+) hearts (Lanes 3, 4, and 5, Figure V.5C) using an N‐terminally
directed antibody to rat ACE2. Both the human ACE2 standard and the 80‐kDa band
were blocked in the Tg(‐) and Tg(+) heart effluent by pre‐incubation of the ACE2
immunogenic peptide with the antibody (Figures V.5B and V.5D, respectively),
confirming the presence of endogenous soluble ACE2 (sACE2). Moreover, the
densities of the sACE2 band in pooled samples of the Tg(‐) and Tg(+) heart perfusate
(n=6) were highly associated with ACE2 activity (r=0.78). Immunoreactive bands at
220 kDa and 60 kDa were also evident, but their intensity was not diminished by
blockade with the ACE2 peptide.
V.5 DISCUSSION
Although others have investigated the metabolism of Ang I in the heart (9;
21), the present study in the isolated perfused heart preparation is the first
demonstration, to our knowledge, of a direct contribution of cardiac ACE2 to the
metabolism of Ang II into Ang‐(1‐7) in the hearts of hypertensive rats. In agreement
with previous studies in human heart tissue (32), we now report that cardiac tissue
has a capacity to generate Ang‐(1‐7) from Ang II in normal and hypertensive rat
hearts — albeit the amounts of peptide production are not different in both normal
and hypertrophied hearts. In contrast, our study now reveals a very significant
dependence on ACE2 in the hypertensive heart for Ang‐(1‐7)‐formation, whereas
95
ACE2 had no major role in Ang‐(1‐7) formation in the normal heart. Likewise,
studies by Zisman et al. (31) also demonstrated an increase in ACE2‐mediated Ang‐
(1‐7)‐forming activity in human failing heart tissue. Together, these studies imply
that ACE2 may serve as a compensatory mechanism to preserve Ang‐(1‐7) levels in
response to hypertension‐induced cardiac hypertrophy and progression into heart
failure, although it may not be sufficient to counteract the deleterious effects of Ang
II.
We find that a potent and specific ACE2 inhibitor (7) decreased Ang‐(1‐7)
formation (>80%) from exogenous Ang II in isolated Tg(+) rat hearts. The failure of
this ACE2 inhibitor to reduce cardiac Ang‐(1‐7) formation in Tg(‐) rats suggests that
ACE2 does not contribute to Ang II metabolism in the perfused normal hearts and
that other peptidases may be responsible for the production of Ang‐(1‐7) from Ang
II in Tg(‐) rat hearts. While we did not ascertain the identity of other Ang‐(1‐7)‐
forming enzymes in the heart for normal rats, previous studies suggest that prolyl
oligopeptidase (POP) may be a likely candidate as the enzyme cleaves Ang II to Ang‐
(1‐7) and both soluble and particulate fractions of the Tg(‐) heart exhibit activity (5;
29). POP may prove to be important in the regulation of angiotensin peptides in the
normal heart.
In recently published studies from both our laboratory (19) and others (30),
it was demonstrated that cardiac ACE2 mRNA and activity in heart homogenates
was reduced in rat models of hypertension and cardiac hypertrophy. Studies by
Jessup et al. (19) showed that ACE2 mRNA and activity was blunted in response to
lisinopril or losartan treatment in heart homogenates of mRen2.Lewis rats compared
96
to their normotensive controls. Likewise, Zhong et al. (30) reported a reduction in
both cardiac ACE2 mRNA and protein in SHR rats compared with the normal WKY.
Collectively, these studies indicated an impairment in cardiac homogenate ACE2
activity in the hypertensive heart. The current study investigated the contribution
of coronary artery ACE2 to the metabolism of Ang II into Ang‐(1‐7) ex vivo utilizing
the isolated heart preparation, which is not comparable to ACE2 activity in heart
homogenate. It is indeed likely that even though cardiac ACE2 activity is impaired
in the hypertensive heart, this activity has assumed the role of preserving the Ang‐
(1‐7) levels, as shown by the current study. Since Zisman et al. (31) showed
increased ACE2 activity in failing human heart tissue, it may be that ACE2 increases
as the heart progresses from cardiac hypertrophy into heart failure in an ill‐fated
attempt to protect the heart from demise.
The presence of ACE2 activity in the effluent of the heart suggests that an
active secreted form of the enzyme may act either locally or be released into the
circulation. Immunoblots revealed an 80‐kDa band corresponding to sACE2, as well
as bands of larger and smaller molecular weight (220 kDa and 60 kDa, respectively).
Newton et al. (22) showed the presence of a 72‐kDa form of ACE2 in normal rat
cerebrospinal fluid. In addition, Warner et al. (28) showed that ACE2 can be
secreted from polarized canine kidney epithelial cells, which was blocked by a
metallopeptidase inhibitor, suggesting the secretion was mediated by a
metallosheddase. In a similar study by Lambert et al. (20), the authors identified
tumor necrosis factor‐α convertase (ADAM17) that cleaves ACE2 in human
embryonic kidney cells. The truncated form of ACE2 in this study corresponded to
97
immunoblot bands of 105 or 95 kDa, depending on the glycosylation state of the
enzyme. The ADAM17 protein is present in the human heart, and its expression is
significantly increased in the hearts of patients with cardiomyopathy as compared
to non‐failing hearts (11). Importantly, increased ADAM17 activity was associated
with human heart failure (25), suggesting that a loss of ACE2 (and potential loss of
Ang‐(1‐7) production) from the myocardium is may facilitate the progression of
heart failure. However, ACE2 gene expression was increased in both human and
rodent heart failure (3; 16) and the peptidase activity was elevated in the viable and
border/infarct zones of the heart. Additional studies are required to address the
exact role of ADAM17 in the processing of ACE2 within the heart. It is possible that
the catalytic activity of this secreted form of ACE2 may prove to supplement the
activity of membrane‐bound form, which has been detected in cardiac myocytes, as
well as the vascular endothelium, and the vascular smooth muscle cells of
intracoronary vessels (3). Moreover, the finding that sACE2 activity was higher in
the Tg(+) perfusate suggests that either the rate of ACE2 secretion is higher or the
rate of ACE2 metabolism is lesser in the pathological state of hypertension. In light
of these findings, it may be that the 80‐kDa bands found in our studies (Figure V.5)
correspond to secreted active metabolites of ACE2.
In summary, that ACE2 Ang‐(1‐7)‐forming activity was increased in the Tg(+)
hypertensive strain suggests that this enzyme may constitute an important
compensatory mechanism to pressure and/or RAS‐dependent cardiac hypertrophy
and remodeling, which supports our notion that ACE2 may be a critical feed‐
forward step in the RAS pathway to limit the cardiac effects of Ang II as well as
98
facilitating the vasodilatory and anti‐proliferative actions of Ang‐(1‐7) (14). Albeit
ACE2 was responsible for most of the Ang‐(1‐7)‐forming activity in [mRen2]27 Tg(+)
rats in this study, it may be insufficient to counteract the deleterious actions of Ang
II on the heart. Without the sustained elevated levels of Ang‐(1‐7) to mitigate the
cardiac hypertrophy and fibrosis associated with elevated Ang II, the renin‐
dependent hypertension and cardiac hypertrophy will eventually lead the heart to
failure, which may be more exacerbated in the absence of ACE2. In agreement with
this notion, Crackower et al. (6) showed that genetic deletion of ACE2 resulted in
severe cardiac contractility defects and cardiac dilatation, which was reversed when
ACE and ACE2 were knocked out concomitantly suggesting that the balanced
expression of these two enzymes is critical in maintaining normal heart function.
The discovery of ACE2 and the continual unveiling of its role in the RAS have
elucidated a need for balance between ACE and ACE2 because they work to regulate
the net levels of the known biologically active peptides, Ang II and Ang‐(1‐7). These
peptide levels — both tissue and circulating — may be disrupted in many disease
states, such as hypertension, cardiac fibrosis, and myocardial infarction.
Understanding this balance will be key to unravel the ways in which these disease
tates can be best treated. s
99
ACKNOWLEDGEMENTS
Funding from the NIH (HL‐51952, HL‐56973) provided support for this project.
Additionally, the authors gratefully acknowledge grant support in part provided by
Unifi, Inc., Greensboro, NC, and Farley‐Hudson Foundation, Jacksonville, NC. The
authors would also like to thank Drs. Che‐Ping Cheng, R. Mark Payne, and James
Jordan for their help and counsel in setting up the Langendorff apparatus. The ACE2
inhibitor MLN‐4760 was obtained from Millennium Pharmaceuticals (Cambridge,
A). M
100
R EFERENCES
1. Agirregoitia N, Gil J, Ruiz F, Irazusta J and Casis L. Effect of aging on rat tissue
peptidase activities. J Gerontol A Biol Sci Med Sci 58: B792‐B797, 2003.
2. Benter IF, Ferrario CM, Morris M and Diz DI. Antihypertensive actions of
angiotensin‐(1‐7) in spontaneously hypertensive rats. Am J Physiol 269: H313‐
H319, 1995.
3. Burrell LM, Risvanis J, Kubota E, Dean RG, MacDonald PS, Lu S, Tikellis C, Grant
SL, Lew RA, Smith AI, Cooper ME and Johnston CI. Myocardial infarction
increases ACE2 expression in rat and humans. Eur Heart J 26: 369‐375, 2005.
4. Chappell MC, Brosnihan KB, Diz DI and Ferrario CM. Identification of
angiotensin‐(1‐7) in rat brain. Evidence for differential processing of
angiotensin peptides. J Biol Chem 264: 16518‐16523, 1989.
5. Chappell MC, Tallant EA, Brosnihan KB and Ferrario CM. Processing of
angiotensin peptides by NG108‐15 neuroblastoma x glioma hybrid cell line.
Peptides 11: 375‐380, 1990.
6. Crackower MA, Sarao R, Oudit GY, Yagil C, Kozieradzki I, Scanga SE, Oliveira‐
dos‐Santos AJ, da CJ, Zhang L, Pei Y, Scholey J, Ferrario CM, Manoukian AS,
Chappell MC, Backx PH, Yagil Y and Penninger JM. Angiotensin‐converting
101
enzyme 2 is an essential regulator of heart function. Nature 417: 822‐828,
2002.
7. Dales NA, Gould AE, Brown JA, Calderwood EF, Guan B, Minor CA, Gavin JM,
Hales P, Kaushik VK, Stewart M, Tummino PJ, Vickers CS, Ocain TD and Patane
MA. Substrate‐based design of the first class of angiotensin‐converting
enzyme‐related carboxypeptidase (ACE2) inhibitors. J Am Chem Soc 124:
11852‐11853, 2002.
8. De Mello WC. Angiotensin (1‐7) re‐establishes impulse conduction in cardiac
muscle during ischaemia‐reperfusion. The role of the sodium pump. J Renin
Angiotensin Aldosterone Syst 5: 203‐208, 2004.
9. Erdos EG, Jackman HL, Brovkovych V, Tan F and Deddish PA. Products of
angiotensin I hydrolysis by human cardiac enzymes potentiate bradykinin. J
Mol Cell Cardiol 34: 1569‐1576, 2002.
10. Faria‐Silva R, Duarte FV and Santos RA. Short‐term angiotensin(1‐7) receptor
MAS stimulation improves endothelial function in normotensive rats.
Hypertension 46: 948‐952, 2005.
11. Fedak PW, Moravec CS, McCarthy PM, Altamentova SM, Wong AP, Skrtic M,
Verma S, Weisel RD and Li RK. Altered expression of disintegrin
102
metalloproteinases and their inhibitor in human dilated cardiomyopathy.
Circulation 113: 238‐245, 2006.
12. Ferrario CM, Jessup J, Chappell MC, Averill DB, Brosnihan KB, Tallant EA, Diz DI
and Gallagher PE. Effect of angiotensin‐converting enzyme inhibition and
angiotensin II receptor blockers on cardiac angiotensin‐converting enzyme 2.
Circulation 111: 2605‐2610, 2005.
13. Ferrario CM, Jessup J, Gallagher PE, Averill DB, Brosnihan KB, Ann TE, Smith
RD and Chappell MC. Effects of renin‐angiotensin system blockade on renal
angiotensin‐(1‐7) forming enzymes and receptors. Kidney Int 68: 2189‐2196,
2005.
14. Ferrario CM, Trask AJ and Jessup JA. Advances in biochemical and functional
roles of angiotensin‐converting enzyme 2 and angiotensin‐(1‐7) in regulation
of cardiovascular function. Am J Physiol Heart Circ Physiol 289: H2281‐H2290,
2005.
15. Gallagher PE, Chappell MC, Ferrario CM and Tallant EA. Distinct roles for ANG
II and ANG‐(1‐7) in the regulation of angiotensin‐converting enzyme 2 in rat
astrocytes. Am J Physiol Cell Physiol 290: C420‐C426, 2006.
16. Goulter AB, Goddard MJ, Allen JC and Clark KL. ACE2 gene expression is up‐
regulated in the human failing heart. BMC Med 2: 19, 2004.
103
17. Grobe JL, Mecca AP, Mao H and Katovich MJ. Chronic angiotensin‐(1‐7)
prevents cardiac fibrosis in DOCA‐salt model of hypertension. Am J Physiol
Heart Circ Physiol 290: H2417‐H2423, 2006.
18. Huentelman MJ, Zubcevic J, Katovich MJ and Raizada MK. Cloning and
characterization of a secreted form of angiotensin‐converting enzyme 2. Regul
Pept 122: 61‐67, 2004.
19. Jessup JA, Gallagher PE Chappell MC Ferrario CM. Impaired Counter‐
Regulatory Response of Angiotensin Converting Enzyme
2 (ACE2) and Angiotensin‐(1–7) [Ang‐(1–7)] in the Heart of a New
Congenic Model of Hypertension Derived from [mRen2]27 Transgenic Rats.
Hypertension 48(4), e74‐e75. 2006. Abstract.
20. Lambert DW, Yarski M, Warner FJ, Thornhill P, Parkin ET, Smith AI, Hooper NM
and Turner AJ. Tumor necrosis factor‐alpha convertase (ADAM17) mediates
regulated ectodomain shedding of the severe‐acute respiratory syndrome‐
coronavirus (SARS‐CoV) receptor, angiotensin‐converting enzyme‐2 (ACE2). J
Biol Chem 280: 30113‐30119, 2005.
21. Neves LA, Almeida AP, Khosla MC and Santos RA. Metabolism of angiotensin I
in isolated rat hearts. Effect of angiotensin converting enzyme inhibitors.
Biochem Pharmacol 50: 1451‐1459, 1995.
104
22. Newton, Steven J. Tallant E. Ann Chappell Mark C. Ferrario Carlos M. Gallagher
Patricial E. Evidence of a Secreted and Active Form of ACE2 in Cerebrospinal
Fluid. Hypertension 46, 875‐887. 2005. Abstract.
23. Santos RA, Castro CH, Gava E, Pinheiro SV, Almeida AP, Paula RD, Cruz JS,
Ramos AS, Rosa KT, Irigoyen MC, Bader M, Alenina N, Kitten GT and Ferreira
AJ. Impairment of in vitro and in vivo heart function in angiotensin‐(1‐7)
receptor MAS knockout mice. Hypertension 47: 996‐1002, 2006.
24. Santos RA, Ferreira AJ, Nadu AP, Braga AN, de Almeida AP, Campagnole‐Santos
MJ, Baltatu O, Iliescu R, Reudelhuber TL and Bader M. Expression of an
angiotensin‐(1‐7)‐producing fusion protein produces cardioprotective effects
in rats. Physiol Genomics 17: 292‐299, 2004.
25. Satoh M, Nakamura M, Saitoh H, Satoh H, Maesawa C, Segawa I, Tashiro A and
Hiramori K. Tumor necrosis factor‐alpha‐converting enzyme and tumor
necrosis factor‐alpha in human dilated cardiomyopathy. Circulation 99: 3260‐
3265, 1999.
26. Shaltout HA, Westwood BM, Averill DB, Ferrario CM, Figueroa JP, Diz DI, Rose
JC and Chappell MC. Angiotensin metabolism in renal proximal tubules, urine,
and serum of sheep: evidence for ACE2‐dependent processing of angiotensin II.
Am J Physiol Renal Physiol 292: F82‐F91, 2007.
105
27. Tallant EA, Ferrario CM and Gallagher PE. Angiotensin‐(1‐7) inhibits growth of
cardiac myocytes through activation of the mas receptor. Am J Physiol Heart
Circ Physiol 289: H1560‐H1566, 2005.
28. Warner FJ, Lew RA, Smith AI, Lambert DW, Hooper NM and Turner AJ.
Angiotensin‐converting enzyme 2 (ACE2), but not ACE, is preferentially
localized to the apical surface of polarized kidney cells. J Biol Chem 280: 39353‐
39362, 2005.
29. Wilk S. Prolyl endopeptidase. Life Sci 33: 2149‐2157, 1983.
30. Zhong JC, Huang DY, Yang YM, Li YF, Liu GF, Song XH and Du K. Upregulation of
angiotensin‐converting enzyme 2 by all‐trans retinoic acid in spontaneously
hypertensive rats. Hypertension 44: 907‐912, 2004.
31. Zisman LS, Keller RS, Weaver B, Lin Q, Speth R, Bristow MR and Canver CC.
Increased angiotensin‐(1‐7)‐forming activity in failing human heart ventricles:
evidence for upregulation of the angiotensin‐converting enzyme Homologue
ACE2. Circulation 108: 1707‐1712, 2003.
32. Zisman LS, Meixell GE, Bristow MR and Canver CC. Angiotensin‐(1‐7) formation
in the intact human heart: in vivo dependence on angiotensin II as substrate.
Circulation 108: 1679‐1681, 2003.
106
Figure V.1. Ang II degradation was not different between Tg(‐) hearts (n=10,
Graph A) and Tg(+) hearts (n=7, Graph B) over the course of the recirculation (P >
0.05), and ACE2 inhibition had no effect on the decay of recirculating Ang II in either
strain (P > 0.05).
107
FIGURE V.1
108
Figure V.2. Ang‐(1‐7) formation from Ang II measured by RIA in Tg(‐) (n=10,
Graph A) and Tg(+) (n=7, Graph B) hearts. Ang‐(1‐7) production from Ang II was
significant from baseline values (represented at time=0) in both the Tg(‐) and Tg(+)
rat strains, however there was no difference in Ang‐(1‐7) generation between the
two strains. The Tg(‐) hearts that received the ACE2 inhibitor at 15 minutes
exhibited no significant reduction of Ang‐(1‐7) generation at 30 minutes, but the
Tg(+) Ang‐(1‐7) production at 30 minutes decreased by 54.7%. ACE2 inhibition
reduced Ang‐(1‐7) levels by 83.1% (57.3 ± 18.6 pM, P < 0.01) in the Tg(+) hearts at
60 minutes but had no significant effect in the Tg(‐) hearts. * P < 0.05 vs. baseline, ** P
< 0.001 vs. baseline, † P < 0.05 vs. respective control times, †† P < 0.01 vs. respective
control times.
109
FIGURE V.2
110
Figure V.3. HPLC/RIA analysis of immunoreactive Ang‐(1‐7) in the heart
perfusate. Panel A: immunoreactive peaks corresponding to Ang‐(1‐7) and Ang II
following perfusion of the heart with exogenous Ang II. Panel B: immunoreactive
peak of Ang II in the perfusate buffer containing Ang II. Panel C: absence of
immunoreactive peaks in the perfusion buffer alone.
111
FIGURE V.3
112
Figure V.4. Representative chromatographs of cardiac perfusate
demonstrates that 125I‐Ang‐(1‐7) formation from 125I‐Ang II was abolished by the
ACE2 inhibitor MLN‐4760 in both the Tg(‐) (Panel A) and Tg(+) (Panel B) cardiac
effluent. sACE2 activity was significantly higher in the Tg(+) perfusate when
compared to the normal Tg(‐) perfusate (Tg(+): 1.97 ± 0.26 fmol/mL/min vs. Tg(‐):
0.82 ± 0.19 fmol/mL/min, P < 0.05).
113
FIGURE V.4
114
Figure V.5. ACE2 immunoblots reveals an 80 kDa protein in the cardiac
effluent collected at the end of the 60‐minute recirculation period. Panels A and B
are the Tg(‐) and Tg(+) concentrated perfusates, respectively. Panels C and D are
immunoblots blocked with the immunogenic ACE2 peptide. Lane 1, Magic Markers;
Lane 2, ACE2 standard (20 ng); Lanes 3, 4, and 5, cardiac perfusate (25 μL). The
arrow indicates the 120 kDa ACE2 standard.
115
FIGURE V.5
116
CHAPTER VI
DISRUPTION OF CARDIAC ANGIOTENSIN PEPTIDES BY ANGIOTENSIN CONVERTING ENZYME 2 INHIBITION EXACERBATES CARDIAC HYPERTROPHY
INAND FIBROSIS REN2 HYPERTENSIVE RATS
Aaron J. Trask1,2, Leanne Groban2,3, Brian M. Westwood1, Jasmina Varagic1,2, Detlev Ganten4, Patricia E. Gallagher1,2, Mark C. Chappell1,2, Carlos M. Ferrario1,2
1Hypert Center ension and Vascular Research 2D y epartment of Physiology and Pharmacolog
Wake icine 3Department of Anesthesiology Forest Universi y School of MedWinston‐Salem, North Carolina
t
AND
niversity MediciBerlin, Germany
4Charité‐U ne Berlin
[This chapter will be submitted to Hypertension for publication. Differences in formatting reflect the requirements of the journal. Aaron J. Trask prepared the manuscript, while Dr. Carlos M. Ferrario acted in an editorial and advisory capacity. Dr. Detlev Ganten provided the animal model used in these studies. Drs. Groban and Varagic provided assistance with the cardiac function studies, and Brian Westwood and Drs. Gallagher and Chappell provided assistance with the molecular and biochemical experiments outlined in this manuscript.]
117
VI.1 ABSTRACT
Emerging evidence suggests that cardiac angiotensin converting enzyme 2
(ACE2) may contribute to the regulation of heart function and hypertension‐induced
remodeling. We tested the hypothesis that inhibition of ACE2 in the hearts of
(mRen2)27 hypertensive rats may accelerate progression of cardiac hypertrophy
and fibrosis by preventing conversion of angiotensin II (Ang II) into the anti‐fibrotic
peptide, angiotensin‐(1‐7) [Ang‐(1‐7)]. Fourteen male (mRen2)27 transgenic
hypertensive rats (12 weeks old, 401 ± 7 g) were administered either vehicle (0.9%
saline) or the ACE2 inhibitor, MLN‐4760, subcutaneously via mini‐osmotic pumps
for 28 days (30 mg/kg/day). Chronic administration of the ACE2 inhibitor had no
effect on average 24 h blood pressure throughout the experiment as assessed by
radiotelemetry probes. In contrast, left ventricular (LV) Ang II content was
significantly augmented by 24% in rats chronically treated with the ACE2 inhibitor.
Chronic ACE2 inhibition had no effect on plasma Ang II or Ang‐(1‐7) levels, although
it did reduce cardiac Ang‐(1‐7)/Ang II by 28%. The imbalance in cardiac Ang
peptides was associated with significant increases in both LV anterior and posterior
wall thicknesses, as well as interstitial collagen fraction area and cardiomyocyte
hypertrophy in the transgenic animals chronically treated with the ACE2 inhibitor.
Despite these biochemical and structural changes observed with ACE2 inhibition,
cardiac function was preserved. These studies show that chronic inhibition of ACE2
causes an accumulation of cardiac Ang II, imparting an imbalance in cardiac Ang II
and Ang‐(1‐7), which exacerbates cardiac hypertrophy and fibrosis without
affecting blood pressure or cardiac function.
118
Key Words: angiotensin II, angiotensin‐(1‐7), angiotensin converting enzyme 2, cardiac hypertrophy
119
V INTRODUCTION
According to the most recent Causes of Death Report from the Centers for
Disease Control, heart disease continues to account for the most deaths in the
United States,
I.2
1 and an alarming report from the World Health Organization states
that cardiovascular disease, including heart disease, is the leading cause of mortality
worldwide.2 Hypertension and cardiac hypertrophy are two of the most critical risk
factors contributing to heart disease,3 and the involvement of the renin‐angiotensin
system (RAS) to the pathophysiology of hypertension and cardiac hypertrophy is
undisputed.4, 5 Undeniably, enhanced activity of the mitogenic and pressor peptide,
angiotensin (Ang) II, causes elevations in blood pressure and contributes
significantly to the development of cardiac hypertrophy and fibrosis.6‐8
Contrary to the actions of Ang II on the cardiovascular system, Ang‐(1‐7)
elicits actions that oppose those of the octapeptide,9‐13 lending to our continuing
hypothesis that Ang‐(1‐7) acts to counter‐balance the deleterious actions of
increased Ang II in pathological states.14 In support of this, newer studies show a
compensatory action of Ang‐(1‐7) as an anti‐proliferative, anti‐fibrotic, and anti‐
hypertrophic agent in the heart.15‐19 These Ang‐(1‐7) properties correct cardiac
functional deficits induced by myocardial ischemia.20‐23
An emerging key to the regulation of the balance of Ang II and Ang‐(1‐7) in
the heart is angiotensin converting enzyme 2 (ACE2). This enzyme was identified as
a critical regulator of cardiac function because ACE2 knockout mice exhibited severe
cardiac dysfunction that was associated with thinning of the left ventricular wall.24
ACE2 was discovered by two independent laboratories,25, 26 and Vickers et al.27
120
demonstrated that ACE2 hydrolyzes Ang II into Ang‐(1‐7) with high efficiency.
These studies suggested to us that ACE2 may limit the effects of Ang II by facilitating
its conversion to the anti‐hypertrophic peptide, Ang‐(1‐7).14 Moreover, previous
studies from our laboratory showed a dependence on ACE2 for the cardiac Ang‐(1‐
7) production from Ang II in Ren‐2 hypertensive rats.28 Studies investigating the in
vivo importance of ACE2 on the heart have largely involved genetic knock‐out
mice,24, 29, 30 the results of which may have been dependent upon genetic differences
in the background strains used in those studies.31 Furthermore, ACE2
overexpression in the heart reversed cardiac hypertrophy and fibrosis.32‐35 In
previous studies, no attempt was made to directly assess the effects of ACE2
inhibition or overexpression on plasma and cardiac levels of angiotensin peptides.
Therefore, this study sought to determine whether blockade of endogenous ACE2 in
the Ren‐2 hypertensive rat would shift the balance of cardiac Ang II and Ang‐(1‐7)
towards the pressor Ang II, and to determine whether this shift was associated with
tructural and functional changes within the myocardium. s
VI.3 ALS AND METHODS MATERI
Animals
Fourteen male hemizygous (mRen2)27 transgenic hypertensive rats were
obtained from the colony maintained at the Wake Forest University Hypertension
and Vascular Research Center (Winston‐Salem, NC). All animals were housed paired
in cages until 10 weeks of age (12‐hour light/dark cycle) in an AAALAC‐approved
facility with ad libitum access to rat chow and reverse osmosis (RO) water. After
121
this time, all rats were housed singly for continuous monitoring of arterial pressure
and heart rate using radiotelemetry probes implant at 10 weeks of age (see methods
below). Procedures were approved by our institutional Animal Care and Use
Committee.
Pr Radiotelemetry ocedure
Radiotelemetry probes (Model PhysioTel PA‐C40, Data Sciences
International, St. Paul, MN) were implanted in 14 ten‐week old (mRen2)27
transgenic rats using aseptic surgical techniques in animals anesthetized with
isoflurane (2%) and given atropine sulfate (intramuscular, 0.12 mg). Immediately
prior to probe implantation, animals were medicated with ampicillin (subcutaneous,
150 mg/kg), and buprenorphine (subcutaneous, 0.05 mg/kg). Body temperature
was monitored using a rectal probe and maintained at 37°C. The abdomen was
opened and the catheter tip of the radiotelemetry probe was inserted into the aorta
just superior to the iliac arteries using an angled‐tip 23‐guage needle as an
introducer. A Dacron patch was slipped around the insertion site, and VetBond (<
5μL) was used to seal the catheter in the aorta. The radiotelemetry transmitter
attached to the catheter was secured to the abdominal muscle using 3‐0 silk suture
during closure. The skin was closed using a cruciate knot with 4‐0 stainless steel
suture. Animals were monitored for ambulation and were allowed to recover from
surgery for 14 days prior to the commencement of treatment. Blood pressure and
heart rate data were acquired every 15 minutes continuously until the end of
treatment using Dataquest A.R.T. 4.1 software (Data Sciences International, St. Paul,
MN).
122
Experimental Protocol
Fourteen days after the radiotelemetry probe implant, (mRen2)27
hypertensive rats (401 ± 7 g) were randomly divided into two treatment groups:
one group (n = 7) received vehicle (0.9% saline subcutaneously) and the other
group (n = 7) was administered the ACE2 inhibitor, MLN‐4760 (30 mg/kg/day
subcutaneously) via Alzet mini osmotic pumps (Durect Corporation, Model 2ML4,
Cupertino, CA) implanted in the rats for 28 days. Previous studies showed that
MLN‐4760 specifically inhibits ACE228, 36 and that in vivo treatment at a similar dose
gnificant renal hypertrophy in diabetic mice.and duration resulted in si
37
Echocardiography
Echocardiography was performed by an experienced echocardiographer
(L.G.) who was blinded from the treatment groups. After 28 days of treatment, the
rats were lightly anesthetized with isoflurane (2%) via a nose cone during
spontaneous ventilation. Animals were imaged in a shallow left lateral supine
position using a 12 MHz phased‐array transducer and Philips 5500 (Philips Medical
Systems, Bothell, WA) sector scanner. Real‐time images were stored digitally for
subsequent offline analysis. In short‐axis views, using 2‐D and M‐mode images,
anterior (AWTd) and posterior wall thicknesses (PWTd) during diastole, end‐
systolic (ESDd) and end‐diastolic dimensions (EDDd) during diastole, and %
fractional shortening (FS) were measured and averaged from 5 cardiac cycles. 2‐D
guided pulsed‐wave Doppler spectra of mitral inflow were recorded from an apical
4‐chamber view. Tissue Doppler, an index of diastolic function that is relatively
insensitive to the effects of heart rate and preload,38 was also obtained using the
123
Philips 5500 scanner. Transmitral and tissue Doppler imaging were obtained from
the apical 4‐chamber view to assess early left ventricular filling and septal mitral
annular velocities, respectively. The following Doppler parameters were obtained:
E = transmitral early filling velocity (cm/sec) e′ = early mitral annular descent
(cm/sec), and E/e′ = transmitral early filling to mitral annular descent ratio, which
is an index of left ventricular filling pressure. All data were averaged from 5
consecutive cardiac cycles.
Pressure‐Volume Loop Assessment of Cardiac Function
Direct hemodynamic measures of cardiac function were performed
immediately following echocardiographic analysis as previously described.39‐41
During the experiment, animals were continued on isoflurane anesthesia (2%)
followed by tracheotomy and respired with a positive‐pressure respirator with an
air/O2 mixture (75%/25%). The right jugular vein was cannulated for fluid
administration and a 2F combined conductance catheter‐micromanometer (Model
SPR‐869, Millar Instruments, Houston, TX) connected to a pressure‐conductance
unit (MPVS 300, Millar Instruments, Houston, TX) was inserted into the right carotid
artery and advanced into the left ventricle. The left femoral artery was also
cannulated with a 1.4F cathether tip pressure transducer to monitor blood pressure
simultaneously (Model SPR‐671, Millar Instruments, Houston, TX). Pressure‐
volume loops were recorded off the ventilator for ≤10 seconds at baseline and
during unloading by gently occluding the inferior vena cava with a cotton swab.
Parallel conductance from surrounding structures was calculated by injecting a
small bolus (100 μL) of hypertonic NaCl through the heart via the jugular vein. Data
124
was acquired and analyzed using iox2 (version 2.4) data acquisition and analysis
software (emka TECHNOLOGIES USA, Falls Church, VA). The following parameters
were obtained: end‐systolic pressure (ESP), end‐diastolic pressure (EDP), end‐
systolic volume (ESV), end‐diastolic volume (EDV), stroke volume (SV), maximum
and minimum dP/dt (±dP/dt), tau (τ), end‐systolic PV relation (ESPVR), and end‐
diastoli . c PV relation (EDPVR)
Biochemical Analyses
Immediately following the cardiac catheterization, blood was collected in
pre‐chilled tubes containing peptidase inhibitors (25 mmol/L EDTA, 0.44 mmol/L
1,2‐orthophenanthrolene monohydrate, 1 mmol/L sodium para‐chloro‐
mercuribenzoate (PCMB), and 3 µmol/L of the rat renin inhibitor, WFML‐1) as
described by us previously.42, 43 Blood cells were isolated by centrifugation at
3,000g for 20 minutes, and aliquots of plasma were stored at ‐80°C until
radioimmunoassay (RIA) measurements. Left ventricular (LV) tissues were rapidly
collected and snap frozen in liquid N2 and stored at ‐80°C until assayed. Angiotensin
peptides were extracted from the plasma and tissue samples using C18 Sep Pak
columns (Waters, Milford, MA), and the eluate was analyzed by RIA for Ang II and
Ang‐(1–7) as described.42, 43 The minimum detectable limits of the Ang II and Ang‐
(1‐7) assays were 0.8 pg/mL and 2.5 pg/mL, respectively. The intra‐ and inter‐
assay coefficients of variability were 12% and 22% for Ang II, and 8% and 20% for
Ang‐(1‐7), respectively.
125
Histology
A cross‐section of the heart was collected at the end of treatment and placed
in 4% paraformaldehyde for 24 hours, after which the tissue was transferred to
70% ethanol until paraffin embedding for histological analysis. Picrosirius red
staining was performed as modified from Junqueira et al.44 Briefly, 4 μm heart
sections were deparaffinized and rehydrated prior to placement in filtered 0.1%
picrosirius red for 60 minutes. Sections were washed twice in 0.5% glacial acetic
acid, dehydrated, cleared, and mounted. Eight interstitial and perivascular images
(200x) per section were captured under both bright field and polarized light using
Spot Advanced software 4.0.9 (Diagnostic Instruments, Inc., Sterling Heights, MI)
connected to an Olympus BX60 microscope (Olympus America, Inc., Center Valley,
PA). The polarized RGB color images were converted to grayscale and analyzed by a
blinded individual for both interstitial and perivascular collagen using Adobe
Photoshop CS2 (Adobe Systems, San Jose, CA). Hematoxylin and eosin staining was
also performed using standard methods. Briefly, LV sections were deparaffinized,
rehydrated and stained with Hematoxylin for 5 minutes. After a quick dip in acid
alcohol (0.5% HCl in 70% ethanol), sections were rinsed in water and placed in
eosin for 2 minutes. Sections were dehydrated, cleared and mounted. 100
cardiomyocytes from each section (25 from each of LV anterior wall, posterior wall,
free wall and septum) were analyzed by a blinded individual at 400x magnification
using Simple PCI 6.0 software (Hamamatsu Corporation, Sewickley, PA) connected
to a Leica DM4000B microscope (Leica Microsystems, Bannockburn, IL) for myocyte
cross‐sectional area (mCSA).
126
Statistical Analyses
All data are expressed as mean ± SEM. All statistics were performed using
GraphPad Prism 5.01 software (GraphPad Software, La Jolla, CA). Radiotelemetric
data was analyzed using a 2‐way ANOVA to determine differences between
treatments and over time at a probability < 0.05. All other data was analyzed using
a student’s t‐test at a probability < 0.05. For the RIAs, values at or below the
detectable limits were assigned those values for statistical purposes.
VI.4 RESULTS
Body weights were not different between Vehicle‐ and ACE2 inhibitor‐
treated Ren‐2 rats at the end of treatment (Vehicle: 504 ± 10 g vs. MLN‐4760: 507 ±
6 g, p > 0.05). Administration of the ACE2 inhibitor in Ren‐2 rats did not alter
systolic, diastolic, mean arterial, or pulse pressures at the end of the four‐week
treatment (Figure VI.1 and Table VI.1). ACE2 inhibition for 28 days was
accompanied by mild tachycardia (Figure VI.1 and Table VI.1, p < 0.05).
Circulating plasma Ang II and Ang‐(1‐7) concentrations did not change in the
animals chronically treated with the ACE2 inhibitor (Figure VI.2, Left, p > 0.05).
However, an augmentation in cardiac Ang II (Figure VI.2, Right, p < 0.01) was found
in the ACE2‐inhibitor‐treated animals. Cardiac Ang‐(1‐7) concentrations did not
change (Figure VI.2, Right, p > 0.05). Administration of the ACE2 inhibitor did reveal
a significant reduction in the Ang‐(1‐7)/Ang II ratio (Figure VI.2, Bottom Right, p <
0.05), a finding that was not observed in the circulation (Figure VI.2, Bottom Left, p
127
> 0.05). These data indicate that ACE2 blockade imparts an imbalance in cardiac
angiotensin peptides independent of the circulation.
Because treatment with the ACE2 inhibitor resulted in an accumulation of
cardiac Ang II, heart sections were stained for collagen using picrosirius red. ACE2
blockade resulted in a significant elevation in interstitial collagen fraction area
(Figure VI.3, Left, p < 0.05), but the perivascular collagen/lumen ratio was
unchanged (Figure VI.3, Right, p > 0.05). Likewise, the administration of the ACE2
inhibitor resulted in an increase in cardiomyocyte cross‐sectional area (Figure VI.4,
p < 0.01).
Echocardiographic analysis of heart structure and function revealed
significant increases in both anterior and posterior wall thicknesses during diastole
in the animals chronically treated with the ACE2 inhibitor, while all other
echocardiographic indices of cardiac function were preserved (Table VI.2).
Moreover, cardiac function as measured by direct cardiac catheterization revealed a
tendency for increased intra‐cardiac pressures associated with MLN‐4760
treatment, although the increases in ESP and EDP were not statistically significant
(Table VI.2; p = 0.15 and 0.10, respectively). Other indices of direct cardiac function
were unchanged between vehicle‐ and MLN‐4760‐treated Ren‐2 rats (Table VI.2 and
Figure VI.5).
V DISCUSSION
The current study documents for the first time a contribution of endogenous
cardiac ACE2 to the regulation of tissue and plasma concentrations of angiotensin
I.5
128
peptides and their resultant actions on cardiac structure and function. Chronic
ACE2 blockade in (mRen2)27 hypertensive rats resulted in a significant 24%
augmentation in cardiac Ang II, with associated elevations in LV wall thickness, a
17% increase in the cardiac interstitial collagen fraction area, and a 26% increase in
cardiomyocyte cross‐sectional area. Although cardiac function was preserved
between the two groups, the observed biochemical and structural abnormalities
were independent of changes in blood pressure. The 28% reduction of the Ang‐(1‐
7)/Ang II ratio in the MLN‐4760‐treated rats suggests that cardiac ACE2 contributes
significantly to the balance of cardiac Ang II and Ang‐(1‐7).
Our approach in studying the critical importance of myocardial ACE2 in
regulating cardiac structure and function differs from currently published reports.
While other studies investigating the role of ACE2 in the heart have utilized genetic
knock‐out or overexpression techniques, our current study aimed to investigate the
role of native, endogenous cardiac ACE2 in the regulation of cardiac structure and
function and document the effects of ACE2 inhibition on cardiac Ang II and Ang‐(1‐
7). However, our data are in agreement with previous studies that show a reduction
in cardiac fibrosis and hypertrophy as a result of cardiac ACE2 overexpression32‐35
or vent n n n C c uricular e largeme t i the A E2 kno ko t mice.24, 30
Genetic ablation of ACE2 results in increased cardiac Ang II24, 30 and
enhanced oxidative stress.45 The deleterious actions of elevated cardiac Ang II as
observed in our study on structure and function are well documented. Ang II
promotes cardiac fibrosis and hypertrophy,6‐8, 46 possibly mediated in part by
elevated oxidative stress,47 whereas cardiac Ang‐(1‐7) reverses cardiac fibrosis and
129
hypertrophy.16‐19 Studies by us19 and others48 have shown that the anti‐fibrotic and
anti‐hypertrophic actions of Ang‐(1‐7) are mediated by its binding to the Mas
receptor. Moreover, studies are emerging that Ang‐(1‐7) or ACE2 overexpression
mitigates the Ang II‐induced hypertrophic response. Grobe et al.17 showed that 100
ng/kg/min of Ang‐(1‐7) administration prevented cardiac fibrosis induced by Ang II
in Sprague‐Dawley rats. Likewise, cardiac ACE2 overexpression in Sprague‐Dawley
rats protected hearts from Ang II‐induced cardiac hypertrophy.35 Additionally, Loot
et al.23 showed that chronic administration of Ang‐(1‐7) two weeks after the
induction of myocardial infarction in rats preserved cardiac function. Finally, the
alteration in cardiac Ang II in our study was independent of the circulating system,
as plasma Ang II and Ang‐(1‐7) remained unchanged in response to ACE2 blockade.
This finding adds to the growing body of evidence supporting tissue RAS regulation,
independent or inter‐dependent, upon the circulating system. Shifting the balance
of these two regulatory Ang peptides toward the mitogen Ang II has deleterious
actions on the myocardium.
Because cardiac fibrosis and hypertrophy are associated with impairments in
diastolic function resulting from a stiffening of the myocardium,49 we expected to
find worsening diastolic performance in the rats chronically treated with the ACE2
inhibitor. Although we found significant exaggerated structural changes in the
hearts of Ren‐2 rats chronically treated with the ACE2 inhibitor, we did not observe
any overt functional deficits. While the direction of change for many of our
functional parameters were consistent with diastolic dysfunction (Emax, e′, ESP,
EDP), the insignificant elevation in end‐diastolic pressure in the MLN‐4760‐treated
130
rats was the only close trend of any further diastolic impairment in the Ren‐2 rats.
Cardiac hypertrophy is a pre‐existing compensatory response observed in the
concentric hypertrophic hearts of Ren‐2 rats as shown both in our28 and other
laboratories.39, 50 However, global cardiac function in the hypertrophied hearts of
the (mRen2)27 strain remains normal or slightly improved when compared to
normal age‐matched Sprague‐Dawley rats at 18 weeks of age.39 In our current
study, the mild elevation in heart rate in the absence of cardiac functional deficits
after four weeks of ACE2 blockade suggest that the Ren‐2 hearts are still in a state of
compensated hypertrophy. While ACE2 inhibition had a significant impact on
cardiac Ang peptides and their ratios, it may not have been sufficient to reach a
tipping point transitioning from compensated hypertrophy to diastolic dysfunction
and then to overt heart failure. Although isoflurane is a well‐accepted choice for the
study of cardiac function due to its ease of use and control,41 Janssen et al.51 showed
that isoflurane suppressed cardiac output and heart rate in rodents, although its
cardio‐suppressive actions were relatively less than those of other anesthetic
agents. Therefore, a mild suppression in cardiac function due to isoflurane may
have also hindered our ability to discern minor changes in cardiac function as a
result of ACE2 blockade.
Although beyond the scope of this study, it is important to mention that ACE2
can act on other substrates affecting cardiac function. Apelin can impart
cardioprotective actions on the heart,52 and ACE2 has been shown to inactivate
apelin by cleaving the C‐terminal phenylalanine27 that is required for its binding to
the APJ receptor and physiological responses.53, 54 Chronic pharmacological
131
blockade of ACE2 in our study may have caused an additional accumulation of
apelin, which may compensate for some of the cardiac functional parameters in our
study. Alternatively, ACE2 overexpression has also been shown to downregulate
connexins 40 and 43,55 which are necessary for normal gap junction function and
electrical conduction in the heart. Therefore, a reduction in ACE2 may have
improved electrical conductance, although we did not observe any alterations in
cardiac contractility in our current study. The ultimate role of apelin and connexins
as they relate to ACE2 remain to be clarified.
In conclusion, we show here that chronic ACE2 blockade imparts a significant
accumulation of cardiac Ang II, resulting in an imbalance in the two known bioactive
Ang peptides, Ang II and Ang‐(1‐7). The accumulation of myocardial Ang II in
response to ACE2 blockade was associated with significant interstitial collagen
deposition and cardiomyocyte hypertrophy, while cardiac function was preserved.
These findings show that ACE2 is crucial in maintaining the conversion of Ang II into
Ang‐(1‐7) in the heart. The lack or even a mild reduction in this enzyme may
accelerate the progression of cardiac hypertrophy, which may preclude the
rogre ion to heart failure. p ss
ACKNOWLEDGEMENTS
The authors would like to thank Drs. Michael Callahan and Dawn Delo for their
helpful suggestions for pressure‐volume assessment of cardiac function. The
authors also acknowledge the technical assistance of Ms. Jessica VonCannon. The
132
ACE2 inhibitor MLN‐4760 was obtained from Millennium Pharmaceuticals
(Cambridge, MA).
SOURCES OF FUNDING
This work was supported in part by the American Heart Association Mid‐
Atlantic Affiliate Grants 0715249U (to AJT) and 0765308U (to JV), as well as
National Institutes of Health Grants HL‐51952 (to CMF), HL‐56973 (to MCC), and a
KO8‐AG026764‐04 Paul Beeson Award (to LG). Additionally, the authors gratefully
acknowledge grant support in part provided by Unifi, Inc., Greensboro, NC, and the
Farley‐Hudson Foundation, Jacksonville, NC.
OSURES DISCL
one N
133
REFERENCES 1. Kung HC, Hoyert DL, Xu JQ, Murphy SL. Deaths: Final Data for 2005. 56 ed.
Hyattsville, MD: National Center for Health Statistics; 2008.
2. Preventing Chronic Diseases: A Vital Investment. World Health Organization;
2008.
3. Lloyd‐Jones DM, Larson MG, Leip EP, Beiser A, D'Agostino RB, Kannel WB,
Murabito JM, Vasan RS, Benjamin EJ, Levy D. Lifetime risk for developing
congestive heart failure: the Framingham Heart Study. Circulation.
2002;106:3068‐72.
4. Effects of ramipril on cardiovascular and microvascular outcomes in people
with diabetes mellitus: results of the HOPE study and MICRO‐HOPE substudy.
Heart Outcomes Prevention Evaluation Study Investigators. Lancet.
2000;355:253‐9.
5. Dahlof B, Devereux RB, Kjeldsen SE, Julius S, Beevers G, de FU, Fyhrquist F,
Ibsen H, Kristiansson K, Lederballe‐Pedersen O, Lindholm LH, Nieminen MS,
Omvik P, Oparil S, Wedel H. Cardiovascular morbidity and mortality in the
Losartan Intervention For Endpoint reduction in hypertension study (LIFE): a
randomised trial against atenolol. Lancet. 2002;359:995‐1003.
6. Baker KM, Aceto JF. Angiotensin II stimulation of protein synthesis and cell
growth in chick heart cells. Am J Physiol. 1990;259:H610‐H618.
134
7. Bohm M, Lippoldt A, Wienen W, Ganten D, Bader M. Reduction of cardiac
hypertrophy in TGR(mREN2)27 by angiotensin II receptor blockade. Mol Cell
Biochem. 1996;163‐164:217‐21.
8. Zolk O, Quattek J, Seeland U, El‐Armouche A, Eschenhagen T, Bohm M.
Activation of the cardiac endothelin system in left ventricular hypertrophy
before onset of heart failure in TG(mREN2)27 rats. Cardiovasc Res.
2002;53:363‐71.
9. Chappell MC. Emerging evidence for a functional angiotensin‐converting
enzyme 2‐angiotensin‐(1‐7)‐MAS receptor axis: more than regulation of blood
pressure? Hypertension. 2007;50:596‐9.
10. Ferrario CM, Chappell MC, Tallant EA, Brosnihan KB, Diz DI. Counterregulatory
actions of angiotensin‐(1‐7). Hypertension. 1997;30:535‐41.
11. Santos RA, Ferreira AJ. Angiotensin‐(1‐7) and the renin‐angiotensin system.
Curr Opin Nephrol Hypertens. 2007;16:122‐8.
12. Trask AJ, Ferrario CM. Angiotensin‐(1‐7): pharmacology and new perspectives
in cardiovascular treatments. Cardiovasc Drug Rev. 2007;25:162‐74.
13. Varagic J, Trask AJ, Jessup JA, Chappell MC, Ferrario CM. New angiotensins. J
Mol Med. 2008;86:663‐71.
14. Ferrario CM, Trask AJ, Jessup JA. Advances in biochemical and functional roles
of angiotensin‐converting enzyme 2 and angiotensin‐(1‐7) in regulation of
135
cardiovascular function. Am J Physiol Heart Circ Physiol. 2005;289:H2281‐
H2290.
15. Benter IF, Yousif MH, Anim JT, Cojocel C, Diz DI. Angiotensin‐(1‐7) prevents
development of severe hypertension and end‐organ damage in spontaneously
hypertensive rats treated with L‐NAME. Am J Physiol Heart Circ Physiol.
2006;290:H684‐H691.
16. Grobe JL, Mecca AP, Mao H, Katovich MJ. Chronic angiotensin‐(1‐7) prevents
cardiac fibrosis in DOCA‐salt model of hypertension. Am J Physiol Heart Circ
Physiol. 2006;290:H2417‐H2423.
17. Grobe JL, Mecca AP, Lingis M, Shenoy V, Bolton TA, Machado JM, Speth RC,
Raizada MK, Katovich MJ. Prevention of angiotensin II‐induced cardiac
remodeling by angiotensin‐(1‐7). Am J Physiol Heart Circ Physiol.
2007;292:H736‐H742.
18. Iwata M, Cowling RT, Gurantz D, Moore C, Zhang S, Yuan JX, Greenberg BH.
Angiotensin‐(1‐7) binds to specific receptors on cardiac fibroblasts to initiate
antifibrotic and antitrophic effects. Am J Physiol Heart Circ Physiol.
2005;289:H2356‐H2363.
19. Tallant EA, Ferrario CM, Gallagher PE. Angiotensin‐(1‐7) inhibits growth of
cardiac myocytes through activation of the mas receptor. Am J Physiol Heart
Circ Physiol. 2005;289:H1560‐H1566.
136
20. De Mello WC. Angiotensin (1‐7) re‐establishes impulse conduction in cardiac
muscle during ischaemia‐reperfusion. The role of the sodium pump. J Renin
Angiotensin Aldosterone Syst. 2004;5:203‐8.
21. Ferreira AJ, Santos RA, Almeida AP. Angiotensin‐(1‐7): cardioprotective effect
in myocardial ischemia/reperfusion. Hypertension. 2001;38:665‐8.
22. Ferreira AJ, Santos RA, Almeida AP. Angiotensin‐(1‐7) improves the post‐
ischemic function in isolated perfused rat hearts. Braz J Med Biol Res.
2002;35:1083‐90.
23. Loot AE, Roks AJ, Henning RH, Tio RA, Suurmeijer AJ, Boomsma F, van Gilst
WH. Angiotensin‐(1‐7) attenuates the development of heart failure after
myocardial infarction in rats. Circulation. 2002;105:1548‐50.
24. Crackower MA, Sarao R, Oudit GY, Yagil C, Kozieradzki I, Scanga SE, Oliveira‐
dos‐Santos AJ, da CJ, Zhang L, Pei Y, Scholey J, Ferrario CM, Manoukian AS,
Chappell MC, Backx PH, Yagil Y, Penninger JM. Angiotensin‐converting enzyme
2 is an essential regulator of heart function. Nature. 2002;417:822‐8.
25. Donoghue M, Hsieh F, Baronas E, Godbout K, Gosselin M, Stagliano N, Donovan
M, Woolf B, Robison K, Jeyaseelan R, Breitbart RE, Acton S. A novel angiotensin‐
converting enzyme‐related carboxypeptidase (ACE2) converts angiotensin I to
angiotensin 1‐9. Circ Res. 2000;87:E1‐E9.
137
26. Tipnis SR, Hooper NM, Hyde R, Karran E, Christie G, Turner AJ. A human
homolog of angiotensin‐converting enzyme. Cloning and functional expression
as a captopril‐insensitive carboxypeptidase. J Biol Chem. 2000;275:33238‐43.
27. Vickers C, Hales P, Kaushik V, Dick L, Gavin J, Tang J, Godbout K, Parsons T,
Baronas E, Hsieh F, Acton S, Patane M, Nichols A, Tummino P. Hydrolysis of
biological peptides by human angiotensin‐converting enzyme‐related
carboxypeptidase. J Biol Chem. 2002;277:14838‐43.
28. Trask AJ, Averill DB, Ganten D, Chappell MC, Ferrario CM. Primary role of
angiotensin‐converting enzyme‐2 in cardiac production of angiotensin‐(1‐7) in
transgenic Ren‐2 hypertensive rats. Am J Physiol Heart Circ Physiol.
2007;292:H3019‐H3024.
29. Gurley SB, Allred A, Le TH, Griffiths R, Mao L, Philip N, Haystead TA, Donoghue
M, Breitbart RE, Acton SL, Rockman HA, Coffman TM. Altered blood pressure
responses and normal cardiac phenotype in ACE2‐null mice. J Clin Invest.
2006;116:2218‐25.
30. Yamamoto K, Ohishi M, Katsuya T, Ito N, Ikushima M, Kaibe M, Tatara Y, Shiota
A, Sugano S, Takeda S, Rakugi H, Ogihara T. Deletion of angiotensin‐converting
enzyme 2 accelerates pressure overload‐induced cardiac dysfunction by
increasing local angiotensin II. Hypertension. 2006;47:718‐26.
31. Gurley SB, Coffman TM. Angiotensin‐converting enzyme 2 gene targeting
studies in mice: mixed messages. Exp Physiol. 2008;93:538‐42.
138
32. Der SS, Grobe JL, Yuan L, Narielwala DR, Walter GA, Katovich MJ, Raizada MK.
Cardiac overexpression of angiotensin converting enzyme 2 protects the heart
from ischemia‐induced pathophysiology. Hypertension. 2008;51:712‐8.
33. ez‐Freire C, Vazquez J, Correa de Adjounian MF, Ferrari MF, Yuan L, Silver X,
Torres R, Raizada MK. ACE2 gene transfer attenuates hypertension‐linked
pathophysiological changes in the SHR. Physiol Genomics. 2006;27:12‐9.
34. Grobe JL, Der SS, Stewart JM, Meszaros JG, Raizada MK, Katovich MJ. ACE2
overexpression inhibits hypoxia‐induced collagen production by cardiac
fibroblasts. Clin Sci (Lond). 2007;113:357‐64.
35. Huentelman MJ, Grobe JL, Vazquez J, Stewart JM, Mecca AP, Katovich MJ,
Ferrario CM, Raizada MK. Protection from angiotensin II‐induced cardiac
hypertrophy and fibrosis by systemic lentiviral delivery of ACE2 in rats. Exp
Physiol. 2005;90:783‐90.
36. Dales NA, Gould AE, Brown JA, Calderwood EF, Guan B, Minor CA, Gavin JM,
Hales P, Kaushik VK, Stewart M, Tummino PJ, Vickers CS, Ocain TD, Patane MA.
Substrate‐based design of the first class of angiotensin‐converting enzyme‐
related carboxypeptidase (ACE2) inhibitors. J Am Chem Soc. 2002;124:11852‐
3.
37. Soler MJ, Wysocki J, Ye M, Lloveras J, Kanwar Y, Batlle D. ACE2 inhibition
worsens glomerular injury in association with increased ACE expression in
streptozotocin‐induced diabetic mice. Kidney Int. 2007;72:614‐23.
139
38. Groban L, Pailes NA, Bennett CD, Carter CS, Chappell MC, Kitzman DW, Sonntag
WE. Growth hormone replacement attenuates diastolic dysfunction and
cardiac angiotensin II expression in senescent rats. J Gerontol A Biol Sci Med Sci.
2006;61:28‐35.
39. Connelly KA, Prior DL, Kelly DJ, Feneley MP, Krum H, Gilbert RE. Load‐sensitive
measures may overestimate global systolic function in the presence of left
ventricular hypertrophy: a comparison with load‐insensitive measures. Am J
Physiol Heart Circ Physiol. 2006;290:H1699‐H1705.
40. Connelly KA, Kelly DJ, Zhang Y, Prior DL, Martin J, Cox AJ, Thai K, Feneley MP,
Tsoporis J, White KE, Krum H, Gilbert RE. Functional, structural and molecular
aspects of diastolic heart failure in the diabetic (mRen‐2)27 rat. Cardiovasc Res.
2007;76:280‐91.
41. Pacher P, Nagayama T, Mukhopadhyay P, Batkai S, Kass DA. Measurement of
cardiac function using pressure‐volume conductance catheter technique in
mice and rats. Nat Protoc. 2008;3:1422‐34.
42. Ferrario CM, Jessup J, Gallagher PE, Averill DB, Brosnihan KB, Ann TE, Smith
RD, Chappell MC. Effects of renin‐angiotensin system blockade on renal
angiotensin‐(1‐7) forming enzymes and receptors. Kidney Int. 2005;68:2189‐
96.
43. Ferrario CM, Jessup J, Chappell MC, Averill DB, Brosnihan KB, Tallant EA, Diz
DI, Gallagher PE. Effect of angiotensin‐converting enzyme inhibition and
140
angiotensin II receptor blockers on cardiac angiotensin‐converting enzyme 2.
Circulation. 2005;111:2605‐10.
44. Junqueira LC, Bignolas G, Brentani RR. Picrosirius staining plus polarization
microscopy, a specific method for collagen detection in tissue sections.
Histochem J. 1979;11:447‐55.
45. Oudit GY, Kassiri Z, Patel MP, Chappell M, Butany J, Backx PH, Tsushima RG,
Scholey JW, Khokha R, Penninger JM. Angiotensin II‐mediated oxidative stress
and inflammation mediate the age‐dependent cardiomyopathy in ACE2 null
mice. Cardiovasc Res. 2007;75:29‐39.
46. Villarreal FJ, Kim NN, Ungab GD, Printz MP, Dillmann WH. Identification of
functional angiotensin II receptors on rat cardiac fibroblasts. Circulation.
1993;88:2849‐61.
47. Whaley‐Connell A, Govindarajan G, Habibi J, Hayden MR, Cooper SA, Wei Y, Ma
L, Qazi M, Link D, Karuparthi PR, Stump C, Ferrario C, Sowers JR. Angiotensin
II‐mediated oxidative stress promotes myocardial tissue remodeling in the
transgenic (mRen2) 27 Ren2 rat. Am J Physiol Endocrinol Metab.
2007;293:E355‐E363.
48. Santos RA, Simoes E Silva AC, Maric C, Silva DM, Machado RP, de B, I, Heringer‐
Walther S, Pinheiro SV, Lopes MT, Bader M, Mendes EP, Lemos VS,
Campagnole‐Santos MJ, Schultheiss HP, Speth R, Walther T. Angiotensin‐(1‐7)
141
is an endogenous ligand for the G protein‐coupled receptor Mas. Proc Natl Acad
Sci U S A. 2003;100:8258‐63.
49. Zile MR, Brutsaert DL. New concepts in diastolic dysfunction and diastolic
heart failure: Part II: causal mechanisms and treatment. Circulation.
2002;105:1503‐8.
50. Ohta K, Kim S, Wanibuchi H, Ganten D, Iwao H. Contribution of local renin‐
angiotensin system to cardiac hypertrophy, phenotypic modulation, and
remodeling in TGR (mRen2)27 transgenic rats. Circulation. 1996;94:785‐91.
51. Janssen BJ, De CT, Debets JJ, Brouns AE, Callahan MF, Smith TL. Effects of
anesthetics on systemic hemodynamics in mice. Am J Physiol Heart Circ Physiol.
2004;287:H1618‐H1624.
52. Kuba K, Zhang L, Imai Y, Arab S, Chen M, Maekawa Y, Leschnik M, Leibbrandt A,
Markovic M, Schwaighofer J, Beetz N, Musialek R, Neely GG, Komnenovic V,
Kolm U, Metzler B, Ricci R, Hara H, Meixner A, Nghiem M, Chen X, Dawood F,
Wong KM, Sarao R, Cukerman E, Kimura A, Hein L, Thalhammer J, Liu PP,
Penninger JM. Impaired heart contractility in Apelin gene‐deficient mice
associated with aging and pressure overload. Circ Res. 2007;101:e32‐e42.
53. El MS, Iturrioz X, Fassot C, De MN, Roesch D, Llorens‐Cortes C. Functional
dissociation of apelin receptor signaling and endocytosis: implications for the
effects of apelin on arterial blood pressure. J Neurochem. 2004;90:1290‐301.
142
54. Lee DK, Saldivia VR, Nguyen T, Cheng R, George SR, O'Dowd BF. Modification of
the terminal residue of apelin‐13 antagonizes its hypotensive action.
Endocrinology. 2005;146:231‐6.
55. Donoghue M, Wakimoto H, Maguire CT, Acton S, Hales P, Stagliano N, Fairchild‐
Huntress V, Xu J, Lorenz JN, Kadambi V, Berul CI, Breitbart RE. Heart block,
ventricular tachycardia, and sudden death in ACE2 transgenic mice with
downregulated connexins. J Mol Cell Cardiol. 2003;35:1043‐53.
143
Table VI.1. 24‐hour Average Blood Pressures and Heart Rate Measured by
Radiotelemetry on the last day of Treatment.
144
Table VI.1 Vehicle MLN‐4760 p value Systolic (mm Hg)
Hg)
205 ± 6 207 ± 3 >0.05 Mean Arterial (mm 181 ± 5
153 ± 5
185 ± 2
158 ± 2
>0.05 Diastolic (mm Hg)
g)
>0.05 Pulse Pressure (mmH
eart Rate (mm Hg)
56 ± 2
376 ± 3
53 ± 3
387 ± 2
>0.05
<0.05 H
145
Table VI.2. Echocardiographic and Hemodynamic Analysis of Cardiac
unction in Vehicle‐ and ACE2 inhibitor‐treated Ren‐2 Rats. F
146
Table VI.2 Vehicle MLN‐4760 p value Heart Rate (BPM) 384 ± 11 387 ± 8 0.83 AWTd (cm)
0.224 ± 0.002 0.245 ± 0.006 ** 0.009
03 PWTd (cm) 0.231 ± 0.003 0.257 ± 0.006 ** 0.0 ESDd (cm)
cm)
0.564 ± 0.012
0.009
0.547 ± 0.034
0.031
0.65 EDDd ( 0.885 ± 0.849 ± 0.28 FS (%)
/s)
36 ± 1 36 ± 2 0.86 Emax (cm
/s)
98 ± 4 92 ± 5 0.39 e' (cm 6.13 ± 0.39
28
5.77 ± 0.30
.35
0.47 E/e' 16.24 ± 0.
0
16.35 ± 1
0.94 ESP (mmHg)
Hg)
144 ± 1 164 ± 6 0.15 EDP (mm 17 ± 4 28 ± 5 0.10 ESV (μL)
)
135 ± 16
5
140 ± 19
8
0.87 EDV (μL
)
212 ± 1 209 ± 1 0.88 SV (μL
max
83 ± 7 80 ± 5 0.79 dP/dt (mmHg/s)
/s)
8654 ± 487
06
9177 ± 154
02
0.36 dP/dt min (mmHg
iss, ms)
‐7855 ± 5 ‐8102 ± 3 0.70 tau (We 8.6 ± 0.2 8.2 ± 0.2 0.16 ESPVR
DPVR
0.87 ± 0.27
.13 ± 0.05
1.25 ± 0.31
.14 ± 0.08
0.98
.65 E
0
0
0
147
Figure VI.1. Radiotelemetric blood pressure and heart rate in Vehicle‐ and
MLN‐4760‐treated Ren‐2 rats. Systolic, MAP, diastolic, nor pulse pressures were
altered as a result of ACE2 blockade (p > 0.05). ACE2 blockade did cause a mild
elevation in heart rate (p < 0.05).
148
4 2 0 2 4 6 8 10 12 14 16 18 20 22 24 26 280
100
200
300
400
Control
Systolic
DiastolicMAP
PulsePressure
HeartRate
MLN4760
Treatment Days
Blood Pressure (mmHg) or
Heart Rate (BPM)
FIGURE VI.1
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Figure VI.2. Plasma (left) and cardiac (right) angiotensin peptides. MLN‐
4760 treatment did not change plasma Ang II or Ang‐(1‐7) concentrations, or the
plasma Ang‐(1‐7)/Ang II ratio (p > 0.05). However, ACE2 inhibition did cause a
significant accumulation of myocardial Ang II (Vehicle: 2.11 ± 0.12 fmol/mg protein
vs. MLN‐4760: 2.61 ± 0.09 fmol/mg protein, p < 0.01), while the reduction in cardiac
Ang‐(1‐7) was not statistically significant (Vehicle: 7.19 ± 0.52 fmol/mg protein vs.
MLN‐4760: 6.50 ± 0.56 fmol/mg protein, p > 0.05). Moreover, ACE2 blockade
revealed a significant decrease in the cardiac Ang‐(1‐7)/Ang II ratio (Vehicle: 3.46 ±
0.30 vs. MLN‐4760: 2.49 ± 0.19, p < 0.05).
150
FIGURE VI.2
151
Figure VI.3. Brightfield (top) and polarized (bottom) photomicrographs of
collagen staining by picrosirius red in both treated and untreated Ren‐2 rats. ACE2
inhibition caused a significant elevation in interstitial collagen fraction area (Left,
Vehicle: 1.02 ± 0.03% vs. MLN‐4760: 1.19 ± 0.04%, p < 0.05), whereas the elevation
in perivascular collagen/lumen ratio did not achieve statistical significance (Right,
Vehicle: 1.92 ± 0.15 vs. MLN‐4760: 2.36 ± 0.33, p > 0.05).
152
FIGURE VI.3
153
Figure VI.4. Photomicrographs of cardiac sections showing cardiomyocyte
cross‐sectional area. ACE2 blockade elicited significant cardiomyocyte hypertrophy
(Vehicle: 664 ± 23 μm2 vs. MLN‐4760: 836 ± 33 μm2, p < 0.01). Scalebar represents
50 μm.
154
FIGURE VI.4
155
Figure VI.5. Pressure‐Volume loops of both Vehicle‐ and MLN‐4760‐treated
Ren‐2 rats illustrate that chronic pharmacological ACE2 blockade did not change
cardiac function (numerical data in Table VI.2).
156
FIGURE VI.5
157
CHAPTER VII
ANGIOTENSIN(112) IS AN ALTERNATE SUBSTRATE FOR ANGIOTENSIN PEPTIDE PRODUCTION IN THE HEART
Aaron J. Trask, Jewell A. Jessup, Mark C. Chappell, Carlos M. Ferrario
H D ypertension and Vascular Research Centerepart cologyWake icine
ment of Physiology and Pharma Forest University School of MedWinston‐Salem, North Carolina
[This chapter was published in the American Journal of Physiology – Heart and Circulatory Physiology (2008; 294:H2242H2247.) and is reprinted with permission. Differences in formatting reflect the requirements of the journal. Aaron J. Trask prepared the manuscript, while Dr. Carlos M. Ferrario acted in n editorial and advisory capacity. Dr. Chappell provided assistance with the iochemical analysis outlined in this manuscript.] ab
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VII.1 ABSTRACT
Identification of angiotensin‐(1‐12), as an intermediate precursor derived
directly from angiotensinogen, led us to explore whether the heart has the capacity
to process angiotensin‐(1‐12) into the biologically‐active angiotensin peptides. The
generation of angiotensin I, angiotensin II, and angiotensin‐(1‐7) from exogenous
angiotensin‐(1‐12) was evaluated in the effluent of isolated perfused hearts
mounted on a Langendorff apparatus in three normotensive and two hypertensive
strains – the Sprague‐Dawley, Lewis, congenic mRen2.Lewis, Wistar‐Kyoto, and
Spontaneously Hypertensive rats. Hearts were perfused with Krebs solution for 60
minutes before and after the addition of angiotensin‐(1‐12) (10 nmol/L).
Angiotensin‐(1‐12) caused the rapid appearance of both angiotensin I and
angiotensin II in the perfusate that peaked between 30 and 60 minutes of
recirculation. Production of angiotensin‐(1‐7) from exogenous angiotensin‐(1‐12)
rose steadily over the course of the 60‐minute experiment. These data directly
demonstrate that angiotensin‐(1‐12) is a substrate for the formation of angiotensin
peptides in cardiac tissue. This finding further suggests that this angiotensinogen‐
derived product is a previously unrecognized important precursor peptide to the
renin‐angiotensin system cascade.
Ka
ey Words: angiotensinogen, angiotensin‐(1‐12), angiotensin I, angiotensin II, ngiotensin‐(1‐7), renin, hypertension
159
VII.2 INTRODUCTION
The renin‐angiotensin system (RAS) was originally thought to be a linear
system with the cleavage of angiotensinogen by renin as the first step in the
biochemical cascade leading to the production of biologically‐active peptides.
Studies over the past twenty years have uncovered a more complex processing
cascade primarily from studies that demonstrated a functional role of angiotensin‐
(1‐7) [Ang‐(1‐7)], which can be generated by various peptidases from either
angiotensin I (Ang I) or angiotensin II (Ang II) (1; 15; 17; 18).
In keeping with the idea of a non‐linear RAS, Nagata and colleagues (10)
recently identified a pro‐peptide hormone of the RAS, proangiotensin‐12
[angiotensin‐(1‐12), Ang‐(1‐12)] in plasma and all tissues investigated. Biological
actions of this propeptide as a substrate for Ang II formation were demonstrated by
showing that administration of Ang‐(1‐12) in isolated vessels produced a
vasopressor response that could be blocked by both an angiotensin converting
enzyme (ACE) inhibitor and an angiotensin receptor blocker (ARB). The current
study determined whether Ang‐(1‐12), a peptide upstream of the traditional RAS
cascade, can lead to the generation of Ang II and Ang‐(1‐7) in the isolated hearts of
both normal and genetically‐diverse hypertensive rat strains. To confirm the role of
Ang‐(1‐12) as a suitable substrate for angiotensin peptide formation in the heart,
data were obtained in five different rat strains.
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VII.3 MATERIALS AND METHODS
Animals
To examine whether the rat heart has the capacity to process Ang‐(1‐12) into
the downstream angiotensin peptides Ang I, Ang II, and Ang‐(1‐7), initial studies
focused on employing 11‐ to 12‐week‐old male Sprague‐Dawley (SD, Harlan
Laboratories, Indianapolis, IN, n = 6) rats to the Langendorff isolated heart protocol
outlined below. To determine whether the Ang‐(1‐12) is differentially processed in
the hearts of hypertensive animals versus their normal counterparts, we also
employed both a targeted model of Ang II‐driven hypertension and a genetic model
of hypertension using the Langendorff method in separate experiments.
Normotensive Lewis (Charles River Laboratories, Wilmington, MA, n = 4), and
hypertensive mRen2.Lewis (Congenic, Hypertension & Vascular Research Center,
Wake Forest University School of Medicine, Winston‐Salem, NC, n = 4) rats 11‐ to
12‐week‐old served as the Ang II‐driven hypertensive model. Aged‐matched
Wistar‐Kyoto (WKY, Charles River Laboratories, Wilmington, MA, n = 6) and
Spontaneously‐Hypertensive (SHR, Charles River Laboratories, Wilmington, MA, n =
6) rats served as the genetic model. All animals were housed paired in cages (12‐
hour light/dark cycle) in an AAALAC‐approved facility with ad libitum access to rat
chow and tap water. Procedures were approved by our institutional Animal Care
and Use Committee.
Langendorff Procedure
The isolated heart preparation was performed as previously described by
our laboratory (15). Briefly, rats were weighed, placed under deep isoflurane (2.5‐
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3%) anesthesia, and given heparin (300 USP units) via a catheter inserted into the
jugular vein. The heart was excised and immediately placed in ice‐cold Krebs buffer.
Rat hearts were then perfused at a constant flow (10 ‐ 12 mL/min) on a Langendorff
isolated heart perfusion apparatus. Heart rates, perfusion pressures, and flow rates
were m r d uonito e continuo sly throughout the experiment.
After a one‐hour equilibration period, a baseline sample of the cardiac
effluent (2.5 mL) was collected, and then 60 mL of Krebs buffer with 10 nmol/L
angiotensin‐(1‐12) [Asp1‐Arg2‐Val3‐Tyr4‐Ile5‐His6‐Pro7‐Phe8‐His9‐Leu10‐Leu11‐Tyr12,
Peptide Institute, Inc., Osaka, Japan] was recirculated through the heart for 60
minutes. This dose was chosen based on previous studies from Nagata et al. (10)
who showed that 10 nmol/L of Ang‐(1‐12) was just below the concentration that
elicited marked vasoconstriction in isolated rat aortae. Moreover, previous
experience investigating Ang II metabolism in the isolated heart preparation is in
keeping with the employed dose of Ang‐(1‐12) (15). All effluent samples were acid‐
matched 1:1 (v:v) with 1% heptafluorobutyric acid (HFBA) to abolish metabolism of
the peptides at the following times: (1) 5 minutes of recirculation, (2) 15 minutes,
(3) 30 minutes, (4) 60 minutes. Half of the WKY and SHR rat hearts received 1
μmol/L of the renin inhibitor, WFML‐1 (AnaSpec, San Jose, CA), immediately
following the collection of the 15‐minute sample. Previous studies from our
laboratory demonstrated that WFML‐1 specifically inhibits rat renin (11).
Biochem
162
ical Procedures
Angiotensin peptides were extracted from the acid‐matched samples using
C18 Sep Pak columns (Waters, Milford, MA). Each Sep Pak was conditioned with 5
mL of 80% methanol (MeOH)/0.1% HFBA, followed by 5 mL 0.1% HFBA. The 5 mL
samples were then applied to the columns, followed by 10 mL 0.1% HFBA. The
columns were rinsed with 5 mL of MilliQ water, and the peptides were eluted in 3
mL 80% MeOH/0.1% HFBA. The eluate was then analyzed by radioimmunoassay
(RIA) for Ang I, Ang II and Ang‐(1‐7) as described previously by our laboratory (4;
5). The minimum detectable limits of the Ang I, Ang II and Ang‐(1‐7) assays were
1.0 pg/mL, 0.8 pg/mL and 2.5 pg/mL, respectively. The intra‐ and inter‐assay
coefficients of variability were 18% and 22% for Ang I, 12% and 22% for Ang II, and
8% and 20% for Ang‐(1‐7), respectively.
Renin Assay
Effluent collected from the hearts of WKY and SHR rats (with no renin
inhibitor) was concentrated using Amicon Ultra 10,000 molecular weight cut off
centrifugal filters (Millipore, Billerica, MA) and washed thrice with HEPES buffer (25
mmol/L HEPES, 125 mmol/L NaCl, 10 μmol/L ZnCl2, pH = 7.4). In addition, left
ventricles from both isolated perfused (n = 3) and non‐perfused (n = 3) WKY and
SHR rats were homogenized in 500 μL of HEPES buffer using the Qiagen TissueLyser
for 1 minute at 25 Hz. The homogenate was then centrifuged for 10 minutes at
28,000 x g, and 25 μL of either the resulting supernatant or the concentrated cardiac
effluent was incubated at pH 6.5 in the presence of excess exogenous
angiotensinogen substrate at 37°C for 90 minutes. Renin activity was measured as
the difference in Ang I generated at 37°C minus that present at 0°C. Additional
studies were also conducted in the presence of 3 μmol/L of WFML‐1 to verify that
163
the Ang I‐generating activity in the heart was indeed renin. Ang I was measured by
radioimmunoassay (DiaSorin, Stillwater, MN).
Statistical Analyses
All values are reported as the mean ± SEM. Student’s t‐test and repeated
measures ANOVA followed by a Tukey’s post‐hoc test for multiple comparisons
were used to determine significant differences at a probability <0.05 using
GraphPad Prism 5.0 software (San Diego, CA). For the RIA, values at or below the
minimal detectable limits of the assays were assigned that value for statistical
purposes.
VII.4 RESULTS
Heart rates were not different between normal and hypertensive rat hearts
neither at baseline, nor during the 60‐minute experiment (P > 0.05). Administration
of Ang‐(1‐12) to isolated hearts did not change heart rates throughout the
experiment (Table VII.1) in all but SD hearts; in this strain, mild bradycardia
occurred after 60 minutes (P = 0.02).
Perfusion pressures were not different between normal and hypertensive rat
hearts neither at baseline, nor over the course of the experiment (P > 0.05). Ang‐(1‐
12) caused a small increase in perfusion pressures in SD and WKY hearts only at the
end of the experiment (60 minutes) after the metabolism had stabilized (Table VII.2,
P = 0.004 and P = 0.005, respectively), while perfusion pressures in Lewis, congenic,
or SHR rat hearts did not change over the time course of the experiment (P > 0.05).
164
At baseline, the effluent from the isolated heart of all strains investigated did
not contain detectable concentrations of Ang I, Ang II, or Ang‐(1‐7). The addition of
Ang‐(1‐12) to the perfusate of isolated rat hearts from SD animals was associated
with rapid and sustained increases in the concentrations of Ang I and Ang II;
increases in these peptides were then followed by the slow appearance of Ang‐(1‐7)
[Figure VII.1]. Ang I production from exogenous Ang‐(1‐12) peaked at 28 ± 3
minutes (191 ± 34 pmol/L, P < 0.0001), followed by Ang II at 45 ± 7 minutes (364 ±
81 pmol/L, P < 0.0001), while Ang‐(1‐7) production steadily increased to an average
of 97 ± 31 pmol/L (P = 0.0003) at 55 ± 5 minutes.
In other experiments, addition of Ang‐(1‐12) to the isolated hearts of Lewis
and congenic rats resulted in similar production of Ang I, Ang II, and Ang‐(1‐7) of a
magnitude and time course comparable to those obtained in SD rats (Figure VII.2).
Ang I production in the Lewis and congenic hearts peaked at 26 ± 4 minutes and 30
± 0 minutes (P > 0.05), respectively, followed by Ang II at 53 ± 8 and 53 ± 8 minutes,
respectively (P > 0.05), while Ang‐(1‐7) production again peaked after 60 ± 0
minutes in both strains (P > 0.05).
Correlation analysis of the peptides in SD, Lewis, and congenic cardiac
effluent revealed highly significant correlations between Ang I and Ang II values
(Table VII.3). Moreover, Ang II values were also highly correlated with Ang‐(1‐7)
values in all rat hearts.
165
Evaluation of Renin in the Metabolism of Ang(112)
A final set of experiments in WKY and SHR rat hearts expanded our
characterization of Ang‐(1‐12) metabolism and evaluated a potential role of cardiac
renin in cleaving Ang‐(1‐12) into Ang I. The application of Ang‐(1‐12) to the
perfusate of isolated hearts from WKY and SHR rats resulted in similar and
sustained production of Ang I, Ang II, and Ang‐(1‐7) [Figure VII.3]. Similar to the
previous experiments, Ang I production in the WKY and SHR hearts peaked at 40 ±
10 and 25 ± 5 minutes (P > 0.05), respectively, followed by Ang II at 50 ± 10 minutes
in both strains, respectively (P > 0.05), while Ang‐(1‐7) production peaked after 60
± 0 and 50 ± 10 minutes, respectively (P > 0.05). Addition of the rat renin inhibitor
WFML‐1 to the perfusate did not alter the time‐to‐peak values for any of the
angiotensin peptides (P > 0.05). The addition of the WKY and SHR angiotensin
peptide values to the other strains’ correlation analyses did not significantly alter
the Pearson correlations, although the correlations remained remarkably significant
[Ang I:Ang II, 0.77, P < 0.0001; Ang I:Ang‐(1‐7), 0.61, P < 0.0001; Ang II:Ang‐(1‐7),
0.62, P < 0.0001].
166
Addition of the renin‐specific inhibitor, WFML‐1, to the perfusate did not
alter the production of any of the angiotensin peptides measured in either WKY or
SHR rat hearts (Figure VII.3). Renin activity measured in the effluent of WKY and
SHR rats averaged 1.74 ± 0.15 ng Ang I/mL/hour and 2.24 ± 0.56 ng Ang I/mL/hour
(P > 0.05), verifying its presence in the cardiac effluent. In addition, tissue renin
activity in the perfused WKY and SHR hearts averaged 1.18 ± 0.15 ng Ang I/mg
protein/hour and 4.43 ± 2.79 ng Ang I/mg protein/hour, respectively (P > 0.05);
these values were similar to those measured in freshly homogenized WKY and SHR
hearts (0.656 ± 0.056 ng Ang I/mg protein/hour and 0.716 ± 0.096 ng Ang I/mg
protein/hour, respectively, P > 0.05). Addition of WFML‐1 to the renin assay
completely abolished Ang I‐generating activity from excess exogenous
angiotensinogen, confirming that the activity was indeed due to the presence of
renin in these tissues. Therefore, the failure of endogenous renin inhibition in
altering the pattern and magnitude of peptides generated by the addition of Ang‐(1‐
12) demonstrates that renin has no catalytic activity on Ang‐(1‐12).
VII.5 DISCUSSION
Building upon the initial findings by Nagata et al. (10), as well as our
preliminary observations (3; 6; 16), we report here for the first time that Ang‐(1‐12)
functions as a precursor for the downstream generation of angiotensin peptides in
the hearts of both normal and hypertensive rats. Addition of the dodecapeptide to
the perfusate of isolated hearts from five different rat strains revealed similar
profiles of angiotensin peptide production. Both Ang I and Ang II appeared in
apparent sequence at similar levels in the perfusate. Moreover, the biologically‐
active heptapeptide Ang‐(1‐7) was produced from exogenous Ang‐(1‐12) steadily,
although the overall values of Ang‐(1‐7) found in the perfusate were less than those
found for Ang I and Ang II. The delayed appearance of Ang‐(1‐7) in the perfusate
compared to the pattern of Ang I and Ang II production suggests that Ang‐(1‐7)
formation did not arise directly from Ang‐(1‐12). In agreement with this
167
interpretation, we previously showed that Ang‐(1‐7) is produced from Ang II by
angiotensin converting enzyme 2 (ACE2) in isolated rat hearts (15).
Because baseline levels of Ang I, Ang II, and Ang‐(1‐7) were not detectable in
the perfusate prior to addition of Ang‐(1‐12), endogenous production of these
peptides cannot account for the findings reported here. Lindpaintner et al. (7)
showed non‐detectable levels of Ang I and Ang II in the effluent from the coronary
sinus of isolated perfused rat heart prior to the addition of purified hog renin.
Addition of renin resulted in a time‐dependent generation of Ang I and Ang II.
Therefore, it is not surprising that in our current experiments and in those reported
by us previously (15), baseline levels of angiotensins were not detectable. Their
experiments also argue for the possibility that the effect of Ang‐(1‐12) may be
accounted for by release of pools of preformed (free and/or bound) Ang I, Ang II,
and Ang‐(1‐7). In both situations, either addition of renin or the addition of Ang‐(1‐
12) was required to stimulate the formation of the angiotensins.
In our experiments, a 10 nmol/L dose of Ang‐(1‐12) was required since
Nagata and colleagues (10) found that higher concentrations (≥ 30 nmol/L) of Ang‐
(1‐12) elicited significant vasoconstriction in the isolated rat aorta. Since there
were no differences in any of the angiotensin peptides generated from Ang‐(1‐12)
between Lewis and congenic, nor WKY and SHR hearts, neither targeted nor genetic
hypertension appear to substantially influence the processing of Ang‐(1‐12) in these
isolated hearts when compared to their background strains. The proportionally
similar generation of angiotensin peptides from Ang‐(1‐12) among the tested
168
strains does not negate the possibility that endogenous generation of the peptides
may not differ among various normotensive and hypertensive strains.
The capacity of cardiac tissue to use Ang‐(1‐12) as a substrate for the
production of angiotensin peptides is further illustrated by the existence of highly
significant correlations for Ang I and Ang II values. Indeed, Chappell et al. (3), in a
preliminary report, demonstrated that Ang‐(1‐12) can be metabolized efficiently by
rat serum ACE into Ang I, which can then be sequentially cleaved by ACE to form
Ang II. Furthermore, we observed highly significant correlations between Ang‐(1‐7)
and both Ang I and Ang II in all five rat strain hearts utilized, suggesting that Ang‐(1‐
7) was produced from both Ang I and Ang II. Collectively, these data suggest that in
the heart, Ang‐(1‐12) is processed into Ang I, which can then be processed into both
Ang II and Ang‐(1‐7), although a direct cleavage of Ang‐(1‐12) into Ang II,
particularly in SD hearts, cannot be excluded.
In the study reported by Nagata et al. (10), the cardiac content of Ang‐(1‐12),
Ang I, and Ang II averaged 151 ± 11 pmol/L, 85 ± 8 pmol/L, and 42 ± 7 pmol/L,
respectively. In other words, the content of Ang‐(1‐12) is about twice as large that
of Ang I. We measured peak concentrations of Ang I and Ang II in the coronary
effluent that averaged 531.5 ± 48.4 pmol/L and 594.8 ± 72.6 pmol/L, respectively,
across all strains, which represents no more than 6‐14 fold higher than was found
endogenously by Nagata and colleagues. These data suggest that studies in isolated
hearts reflect to a significant degree what may be the tissue dynamics in vivo.
169
Because others have found that the tetradecapeptide [Ang‐(1‐14)] is cleaved
by renin (8; 9; 13), we administered a rat renin‐specific inhibitor concomitantly
with Ang‐(1‐12) to the perfusate of WKY and SHR isolated hearts to determine
whether Ang‐(1‐12), like Ang‐(1‐14), was a suitable substrate for renin activity. As
indicated above, renin inhibition did not alter the production of any of the
angiotensin peptides, nor did it affect heart rate or perfusion pressures.
Additionally, we verified, in both perfused and non‐perfused hearts, that renin was
present in the heart by measuring its tissue activity as well as the activity in the
cardiac effluent. Therefore, our data show that Ang‐(1‐12), unlike Ang‐(1‐14), is not
cleaved by renin, which corroborates recent studies from our group (3). Renin
specifically cleaves the Leu10‐Leu11 bond of rat angiotensinogen to form Ang I, while
the cleavage between the two aromatic residues Tyr12‐Tyr13 liberates Ang‐(1‐12). A
lack of differential processing of Ang‐(1‐12) between the Lewis and congenic
mRen2.Lewis rats also supports a non‐renin role for the metabolism of Ang‐(1‐12)
in the heart, as the mRen2.Lewis rats express elevated cardiac renin levels (2).
Further support for a biological role of Ang‐(1‐12) in the heart stems from
studies that showed that Ang‐(1‐12) was robustly present in ventricular myocytes
of both WKY and SHR (6). Evidence of functionality is further illustrated by
increased cardiac content of Ang‐(1‐12) in the SHR compared to WKY. That this
peptide was found in most tissues at higher levels than both Ang I and Ang II (10) —
in concert with the findings of the current study — asserts that Ang‐(1‐12) may be a
readily‐available substrate for angiotensin peptide production.
170
LIMITA NTIO S OF STUDY
The data presented herein is a critical first step to understanding the
ultimate role that Ang‐(1‐12) may play in cardiovascular physiology. The purpose
of this initial study was to determine whether the dodecapeptide could serve as a
substrate for the formation of Ang I, Ang II, and Ang‐(1‐7) in the hearts of five
different rat strains, and as such, the enzymatic mechanisms accounting for the
formation of Ang‐(1‐12) from angiotensinogen were outside the scope of the
present study. While not designed to determine enzymatic mechanisms, the current
study undertook steps to exclude renin in the metabolism of Ang‐(1‐12) into any of
the three downstream angiotensin peptides measured. Moreover, based on
preliminary studies from our group (3), the direct enzymatic conversion of Ang‐(1‐
12) into Ang I and Ang‐(1‐7) appears to be mediated by serum ACE and renal NEP,
respectively. Further studies will be required to determine how exactly Ang‐(1‐12)
can be metabolized in not only the heart, but in other tissues critical in physiological
egulation. r
CONCLUSIONS
In the century since Tigerstedt and Bergmann first described renin (14),
many advances have be made regarding the contributions of the renin‐angiotensin
system to the regulation of cardiovascular processes. Indeed, the effective clinical
treatment of hypertension and heart failure arrived almost 100 years after renin’s
discovery — first with the introduction of ACE inhibitors in 1981, later with the
advent of ARBs in 1995, and most currently with the development and arrival of the
171
renin inhibitor, aliskiren, in 2007. The identification of an angiotensin peptide
upstream of Ang I that can serve as a substrate to produce bioactive angiotensin
peptides is a novel and important finding. Although it is not yet known what
enzyme(s) can cleave Ang‐(1‐12) from its parent protein, angiotensinogen, the
possibility that this process may occur in a renin‐independent manner holds high
potential to change our evolving understanding of the renin‐angiotensin system in
the regulation of physiological processes. In support of a renin‐independent
pathway for angiotensin peptide formation, Oparil and colleagues (12) recently
showed that in patients treated with maximal doses of both the renin inhibitor
aliskiren and the AT1 antagonist valsartan, there were additive blood pressure
reductions — an unexpected finding if renin is the sole liberator of angiotensin
peptides. Indeed, we suggest that Ang‐(1‐12) may serve as a “quick‐release”
substrate for the immediate production of the RAS components as necessary, which
may likely be more efficient than the cell making the almost 500‐amino acid
angiotensinogen for the production of angiotensin peptides. The unraveling of the
functional significance of Ang‐(1‐12), as well as the pathways for its formation and
degradation, should bear considerable importance.
ACKNOWLEDGEMENTS
This work was supported by the National Institutes of Health (HL‐51952, HL‐
56973). Aaron J. Trask was supported by an award from the American Heart
Association, Mid‐Atlantic Affiliate (#0715249U). Additionally, the authors gratefully
172
acknowledge grant support in part provided by Unifi, Inc., Greensboro, NC, and
Farley‐Hudson Foundation, Jacksonville, NC.
173
REFERENCES
1. Chappell MC. Emerging evidence for a functional angiotensin‐converting
enzyme 2‐angiotensin‐(1‐7)‐MAS receptor axis: more than regulation of blood
pressure? Hypertension 50: 596‐599, 2007.
2. Chappell MC, Gallagher PE, Averill DB, Ferrario CM and Brosnihan KB. Estrogen
or the AT1 antagonist olmesartan reverses the development of profound
hypertension in the congenic mRen2.Lewis rat. Hypertension 42: 781‐786,
2003.
3. Chappell, M. C., Westwood, B. M., Pendergrass, K. D., Jessup, J. A., and Ferrario,
C. M. Distinct Processing Pathways for the Novel Peptide Angiotensin‐(1‐12) in
the Serum and Kidney of the Hypertensive mRen2.Lewis Rat. Hypertension 50:
e139, 2007. Abstract.
4. Ferrario CM, Jessup J, Chappell MC, Averill DB, Brosnihan KB, Tallant EA, Diz DI
and Gallagher PE. Effect of angiotensin‐converting enzyme inhibition and
angiotensin II receptor blockers on cardiac angiotensin‐converting enzyme 2.
Circulation 111: 2605‐2610, 2005.
5. Ferrario CM, Jessup J, Gallagher PE, Averill DB, Brosnihan KB, Ann TE, Smith
RD and Chappell MC. Effects of renin‐angiotensin system blockade on renal
174
angiotensin‐(1‐7) forming enzymes and receptors. Kidney Int 68: 2189‐2196,
2005.
6. Jessup, J. A., Chappell, M. C., Nagata, S., Kato, J., Kitamura, K., and Ferrario, C. M.
Localization of the Novel Angiotensin Peptide, Proangiotensin‐12, in the Heart
and Kidney of Hypertensive and Normotensive Rats. Hypertension 50: e101,
2007. Abstract.
7. Lindpaintner K, Jin MW, Niedermaier N, Wilhelm MJ and Ganten D. Cardiac
angiotensinogen and its local activation in the isolated perfused beating heart.
Circ Res 67: 564‐573, 1990.
8. Mendelsohn FA and Johnston CI. A radiochemical renin assay. Biochem J 121:
241‐244, 1971.
9. Montague D, Riniker B, Brunner H and Gross F. Synthesis and biological
activities of a tetradecapeptide renin substrate. Am J Physiol 210: 591‐594,
1966.
10. Nagata S, Kato J, Sasaki K, Minamino N, Eto T and Kitamura K. Isolation and
identification of proangiotensin‐12, a possible component of the renin‐
angiotensin system. Biochem Biophys Res Commun 350: 1026‐1031, 2006.
175
11. Nakamura S, Averill DB, Chappell MC, Diz DI, Brosnihan KB and Ferrario CM.
Angiotensin receptors contribute to blood pressure homeostasis in salt‐
depleted SHR. Am J Physiol Regul Integr Comp Physiol 284: R164‐R173, 2003.
12. Oparil S, Yarows SA, Patel S, Fang H, Zhang J and Satlin A. Efficacy and safety of
combined use of aliskiren and valsartan in patients with hypertension: a
randomised, double‐blind trial. Lancet 370: 221‐229, 2007.
13. Skeggs LT, Jr., Lentz KE, Kahn JR and Shumway NP. The synthesis of a
tetradecapeptide renin substrate. J Exp Med 108: 283‐297, 1958.
14. Tigerstedt R. and Bergman P.G. Niere und Kreislauf. Scan Arch Physiol 8, 223‐
271. 1898.
15. Trask AJ, Averill DB, Ganten D, Chappell MC and Ferrario CM. Primary role of
angiotensin‐converting enzyme‐2 in cardiac production of angiotensin‐(1‐7) in
transgenic Ren‐2 hypertensive rats. Am J Physiol Heart Circ Physiol 292:
H3019‐H3024, 2007.
16. Trask, A. J., Jessup, J. A., and Ferrario, C. M. Angiotensin‐(1‐12) is a Precursor
for the Processing of Cardiac Tissue Angiotensin Peptides. Hypertension 50:
e154. 2007. Abstract.
176
17. Welches WR, Brosnihan KB and Ferrario CM. A comparison of the properties
and enzymatic activities of three angiotensin processing enzymes: angiotensin
converting enzyme, prolyl endopeptidase and neutral endopeptidase 24.11.
Life Sci 52: 1461‐1480, 1993.
18. Zisman LS, Meixell GE, Bristow MR and Canver CC. Angiotensin‐(1‐7) formation
in the intact human heart: in vivo dependence on angiotensin II as substrate.
Circulation 108: 1679‐1681, 2003.
177
Table VII.1. Time course of heart rates (BPM) in all strains studied.
178
Table VII.1 5 Min 15 Min 30 Min 60 Min P SD 253 ± 10 210 ± 16 238 ± 10 228 ± 9 * 0.02 Lewis 251 ± 15
234 ± 14
223 ± 10 205 ± 26 0.06 Congenic 219 ± 8
237 ± 24 200 ± 19231 ± 12
212 ± 14 186 ± 17
211 ± 20 181 ± 13
0.69 0.28 WKY
SHR 234 ± 9 206 ± 9 203 ± 15 195 ± 16 0.27
179
Table VII.2. Time course of perfusion pressures (mmHg) in all strains
studied.
180
Table VII.2
5 Min 15 Min 30 Min 60 Min P SD 64 ± 9 83 ± 18 105 ± 27 170 ± 48 † 0.004Lewis 64 ± 4 64 ± 8 74 ± 13 131 ± 48 0.13 Congenic 63 ± 5
66 ± 5 67 ± 8 66 ± 4
74 ± 13 74 ± 6
109 ± 39 113 ± 12
0.22 † 0.005WKY
SHR 72 ± 5 73 ± 7 80 ± 14 110 ± 22 0.09
181
Table VII.3. Pooled angiotensin peptide correlations from SD, Lewis, and
congenic rat cardiac effluent. All Pearson correlation values (r) are P < 0.0001.
182
Table VII.3
Ang I Ang II Ang(17) Ang I ‐ 0.72 0.51 Ang II 0.72 ‐ 0.71 Ang(17) 0.51 0.71 ‐
183
Figure VII.1. Ang I, Ang II, and Ang‐(1‐7) production from exogenous Ang‐
(1‐12) in isolated SD rat hearts (n = 6). Both Ang I and Ang II peaked at 30 minutes
of recirculation (Ang I: 191 ± 34 pmol/L; Ang II: 364 ± 81 pmol/L), while Ang‐(1‐7)
steadily increased until 60 minutes of recirculation (97 ± 31 pmol/L). * P = 0.0003,
and † P < 0.0001 vs. baseline.
184
FIGURE VII.1
185
Figure VII.2. Ang I, Ang II, and Ang‐(1‐7) production from exogenous Ang‐
(1‐12) in isolated Lewis (A, n = 4) and mRen2.Lewis congenic (B, n = 4) rat hearts.
Ang I peaked at 30 minutes of recirculation in both Lewis and congenic (489 ± 112
pmol/L and 625 ± 116 pmol/L, respectively), while both Ang II and Ang‐(1‐7)
steadily increased until 60 minutes of recirculation [Ang II: 493 ± 190 pmol/L
(Lewis), 628 ± 133 pmol/L (congenic); Ang‐(1‐7): 126 ± 39 pmol/L (Lewis), 96 ± 13
pmol/L (congenic)]. There was no statistical difference in any of the angiotensin
peptides between Lewis and congenic rat hearts. * P < 0.01, † P < 0.001, and ‡ P <
0.0001 vs. baseline.
186
FIGURE VII.2
187
Figure VII.3. Ang I (Top panels), Ang II (Middle panels), and Ang‐(1‐7)
[Bottom panels] production from exogenous Ang‐(1‐12) in isolated WKY (Left
panels, n = 6) and SHR (Right panels, n = 6) hearts. Ang I and Ang II both peaked at
30 minutes of recirculation in both WKY and SHR (Ang I: 676 ± 49 pmol/L and 644 ±
68 pmol/L, respectively; Ang II: 620 ± 139 pmol/L and 808 ± 216 pmol/L,
respectively), while Ang‐(1‐7) steadily increased until 60 minutes of recirculation
[228 ± 58 pmol/L (WKY), 204 ± 54 pmol/L (SHR)]. There was no statistical
difference in any of the angiotensin peptides between WKY and SHR hearts, nor did
renin inhibition alter the production of any of the angiotensin peptides measured
(represented by open circles/dotted lines). * P < 0.05 and † P < 0.01 vs. baseline.
188
FIGURE VII.3
189
CHAPTER VIII
VIII.1 SUMMARY AND GENERAL DISCUSSION
Knowledge on the existence of the renin‐angiotensin system (RAS) as a major
physiological regulator has been growing since Tigerstedt and Bergman first
discovered the enzyme renin over a century ago (36). In 1934, Dr. Harry Goldblatt
and colleagues (17), as recounted by Basso and Terragno (3), developed the first
successful experimental model of hypertension by clipping the renal artery in dogs.
Using this experimental model nearly 60 years after the initial discovery of renin,
Irvine Page from the United States and Braun Menendez from Argentina
independently discovered a pressor hormone, “angiotonin” or “hypertensin”, which
was later agreeably called “angiotensin” (Ang) due to its relative ease of
pronunciation in different accents (4). We now know this hormone to be the
octapeptide pressor hormone, Ang II, which is produced from the sequential
cleavage of the protein angiotensinogen into Ang I by renin, and Ang I into Ang II by
angiotensin converting enzyme (ACE).
Knowledge on the expansion of the renin‐angiotensin system has been on the
rise since the discovery of Ang‐(1‐7) in 1988 (33). Twelve years later, the discovery
by two independent laboratories (12; 37) of an enzyme that can directly and
efficiently convert Ang II into Ang‐(1‐7) accelerated acceptance of a critical role of
Ang‐(1‐7) in cardiovascular regulation. Because angiotensin converting enzyme 2
(ACE2) links the two functionally‐opposing arms of the RAS, we evaluated first
190
whether cardiac ACE2 can directly cleave Ang II into Ang‐(1‐7) and to further
determine whether a regulatory shift in the enzyme may disrupt the balance of
these two opposing Ang peptides. Moreover, we also hypothesized that the
inhibition of endogenous cardiac ACE2 would shift the balance between the two
peptides towards the pro‐hypertrophic peptide, Ang II, resulting in the accelerated
progression of cardiac hypertrophy and fibrosis. Unexpectedly, the discovery of a
new angiotensin peptide, Ang‐(1‐12), adds an additional dimension to the
understanding of the biochemical processes leading to the formation of angiotensin
peptides as this substrate may serve as an alternate pathway for the production of
downstream angiotensin peptides, including Ang II and Ang‐(1‐7) (39). The studies
outlined in this dissertation firstly investigated the role of cardiac ACE2 in directly
cleaving Ang II into Ang‐(1‐7), with further examination revealing a shift in the
balance of the two peptides in response to chronic ACE2 inhibition. Furthermore,
additional studies included in this dissertation show that Ang‐(1‐12) can generate
downstream bioactive angiotensin peptides in the heart.
Studies utilizing the isolated heart preparation first showed a differential
role for the production of Ang‐(1‐7) from Ang II by ACE2 (38). In these studies, the
production of Ang‐(1‐7) from exogenous Ang II was not different between normal
Sprague‐Dawley and hypertensive [mRen2]27 transgenic rat hearts; however, the
administration of MLN‐4760, the ACE2‐specific inhibitor, almost completely
abolished Ang‐(1‐7) production in the hypertensive hearts only. These studies were
the first to show that the hypertensive heart is heavily reliant upon ACE2 for the
generation of Ang‐(1‐7) from Ang II. In keeping with these findings, work by others
191
showed increased ACE2 expression and/or activity in human and rodent heart
failure (5; 18; 43). Moreover, Pendergrass et al. (30) found that cardiac ACE2
activity tended to be elevated in the hypertrophic hearts of the congenic rats,
although one other study suggested that ACE2 expression was attenuated in the
hearts of SHR rats (42). Because of the results of our study, together with the
aforementioned findings, we postulated that ACE2 may be part of a compensatory
mechanism by which the heart adapts to allow it to shift the production of
angiotensins from the pro‐hypertrophic and pro‐fibrotic Ang II into the anti‐
hypertrophic and anti‐fibrotic Ang‐(1‐7).
Because ACE2 was critical in maintaining Ang‐(1‐7) production from Ang II
only in the Ren‐2 hypertensive rats, we investigated the direct role of endogenous
ACE2 in mediating the balance of Ang II and Ang‐(1‐7) in the heart and we further
determined its role in cardiac structure and function in this strain. For these
experiments, we administered an ACE2‐specific inhibitor, MLN‐4760, to [mRen2]27
hypertensive rats chronically for 4 weeks. As expected, four‐week treatment with
the ACE2 inhibitor resulted in a significant 28% reduction in the Ang‐(1‐7)/Ang II
ratio—data that show for the first time a direct imbalance of these local cardiac
angiotensin peptides. Of critical importance, the resultant accumulation of cardiac
Ang II observed with chronic ACE2 blockade was associated with marked increases
in left ventricular wall thickness, myocyte cross‐sectional area, and interstitial
fibrosis. Cardiac function remained unchanged. These studies coincide with our
previous observation showing significant dependence on cardiac ACE2 in
metabolizing Ang II into Ang‐(1‐7). However, these studies go a step further and
192
show that the imbalance of these two peptides may facilitate the progression of
cardiac hypertrophy, and eventually the development of heart failure. These studies
illustrate the ability of ACE2 blockade to exacerbate cardiac remodeling in the
absence of changes in blood pressure or cardiac function (illustrated in Figure
VIII.1), although a longer duration of treatment may have expedited the
development of cardiac dysfunction. When interpreted together with other studies,
our research supports an increasing role of cardiac ACE2 in compensated cardiac
hypertrophy through heart failure, although based on these studies and those from
other laboratories, the ability of the enzyme to produce Ang‐(1‐7) may be
insufficient to counteract the deleterious overactivity of Ang II on the heart.
Moreover, the finding that Ang‐(1‐7) is degraded by ACE may suggest a disconnect
between ACE2 and Ang‐(1‐7) because although ACE2 may be increased in cardiac
hypertrophy and heart failure, its efforts may be tempered by elevated ACE activity
to degrade Ang‐(1‐7) in these disease states.
One of the more unexpected findings of our initial study (38) was the
demonstration that ACE2 was secreted from the heart. This secreted form of ACE2
(sACE2), as shown on a western blot at ~80 kDa, appeared to a lesser extent in the
normal Sprague‐Dawley cardiac effluent, whereas sACE2 protein expression
appeared markedly increased in the effluent from the hypertensive rat heart.
Perhaps more importantly, we also showed that this sACE2 was more active in the
effluent from hearts isolated from hypertensive rats. Based on these findings, we
first postulated that the loss of ACE2 from the heart may contribute, at least in part,
to the hypertrophic response seen in the hypertensive rats, and may facilitate the
193
progression to heart failure. This postulate was recently supported by a study that
reported increasing circulating sACE2 in patients with increasing severity of heart
failure (14). Further support for these findings stems from data that showed the
tumor necrosis factor convertase, ADAM17, can shed ACE2 from the membrane
(25), and that the enzyme is increased in human heart failure (15). Collectively,
these studies show that in the stages of compensated cardiac hypertrophy through
later stages of heart failure, the loss of ACE2 by shedding from the heart may have
deleterious effects on the organ in terms of its ability to generate local Ang‐(1‐7) in a
tissue with elevated local Ang II. Future studies may support a role for inhibiting
ADAM17 in heart failure so that the heart may retain ACE2.
The finding that ACE2 blockade in hearts isolated from normal Sprague‐
Dawley rats did not reduce Ang‐(1‐7) production from Ang II (38) led us to
determine what other enzymes may be responsible for Ang‐(1‐7) formation from
Ang II in this strain. In 1971, Walter et al. (40) discovered an enzyme found in the
human uterus that cleaved oxytocin at the carboxy‐terminal proline‐leucine bond.
Thus, the enzyme was named post‐proline cleaving enzyme for its action. Since its
discovery, the enzyme was renamed prolyl oligopeptidase 21.26 (POP). Koida and
Walter (23) later discovered that this enzyme cleaved the post‐proline bond of not
only oxytocin and bradykinin, but also Ang II, yielding Ang‐(1‐7). Furthermore,
studies from our laboratory first showed that POP could produce Ang‐(1‐7) from
Ang I in brain and vascular endothelial cells (32; 41). Kato and colleagues (22)
investigated the tissue and brain distribution of POP and found that POP activity
was found in all tissues, including the heart. Although little is known about POP and
194
its role in the heart, POP activity was higher in normal atria of male Wistar rats
compared to rats with one‐kidney, one‐clip hypertension, providing evidence that
POP may be important in Ang II processing in the heart (8). Based on the above
findings, we perfused normal Sprague‐Dawley hearts with Ang II in the presence
and absence of the POP inhibitor ZPP, on which my advisor holds a patent, (U.S.
Patent Number 5,451,571). In these experiments, we measured Ang‐(1‐7) in the
cardiac effluent before and following inhibition of POP. As expected, Ang‐(1‐7) was
produced from Ang II in the normal heart (Figure A.1) at levels comparable to our
previous study (38). However, the addition of ZPP did not alter the magnitude or
pattern of Ang‐(1‐7) production (Figure A.1). These studies suggest that POP is not
involved in the production of Ang‐(1‐7) from Ang II in hearts isolated from normal
rats.
Because ZPP is not entirely specific to POP (35), and because it is possible
that the lysosomal serine protease Pro‐X carboxypeptidase (PCP, E.C. 3.4.16.2) may
contribute to Ang II metabolism in the arterial circulation (34), we conducted
additional isolated heart studies in the presence and absence of the non‐selective
serine protease inhibitor, 4‐(2‐Aminoethyl)benzenesulfonyl fluoride (AEBSF).
AEBSF did not reduce the level of Ang‐(1‐7) produced from Ang II in the cardiac
effluent (Figure A.2). Collectively, these studies show that ACE2, POP, nor other
serine proteases contribute to the direct formation of Ang‐(1‐7) from Ang II in
hearts isolated from normal Sprague‐Dawley rats. The identity of another enzyme
that may cleave the Pro7‐Phe8 bond of Ang II remains to be clarified. One of the
candidates may be a little‐known enzyme called membrane Pro‐X carboxypeptidase
195
(carboxypeptidase P, EC 3.4.17.16), which can cleave the Pro7‐Phe8 bond of Ang II to
produce Ang‐(1‐7) in vascular smooth muscle cells (28). This membrane‐bound
enzyme is distinct from the lysosomal PCP as described by Dr. Ervin Erdös’
laboratory and above. Although this enzyme is a metallopeptidase that can be
inhibited by ethylenediaminetetraacetic acid (EDTA), its use in isolated heart
studies is not optimal due to the chelation of Ca2+ by EDTA. Further studies are
warranted to investigate the contribution of an unknown enzyme(s) to the
hydroly sis of Ang II into Ang‐(1‐7) in normal hearts.
The potential for an alternate precursor that may yield downstream
bioactive angiotensin peptides is indeed intriguing. Our finding that Ang‐(1‐12)
serves as a biological precursor peptide for downstream angiotensin peptide
production is a novel and exciting piece of a puzzle that has been under
investigation for well over a century. Given the propensity of studies that have
investigated angiotensin peptides within the realm of the heart, there have been
some unexplainable observed phenomena. For example, many studies report that
the cardiac RAS is very minimally expressed based on studies that showed little
angiotensinogen and/or renin mRNA (13; 21). Moreover, some studies have
reported the production of angiotensin peptides from the parent protein
angiotensinogen only when renin was added to the perfusate of isolated rat hearts
(11). There are also studies showing that cardiac angiotensins fall dramatically
after bilateral nephrectomy (6; 10), a maneuver long used to determine the
contribution of renal renin to physiological processes. Collectively, these studies
argue that cardiac angiotensins are derived from the circulation. However, Leenen
196
and colleagues (26) showed that after coronary artery ligation in rats that were
bilaterally‐nephrectomized, local cardiac angiotensin peptides were actually
augmented. This raises the question, “from where did the angiotensin peptides
originate?” If several studies showed that cardiac angiotensins fall in response to
bilateral nephrectomy, the local peptides observed in Dr. Leenen’s study are likely
not der o e nived fr m th circulatio .
Other data involving renin inhibition provide further evidence for a
disconnect in the cardiac renin‐angiotensin system physiology. For example, Oparil
and colleagues (29) found additive reductions in blood pressure in patients
chronically treated with maximal doses of both the angiotensin receptor blocker,
valsartan, and the renin inhibitor, aliskiren, versus each treatment alone. This
finding is unexpected if renin is the sole liberator of angiotensin peptides.
Furthermore, preliminary data from our laboratory show that the acute
administration of the rat renin inhibitor, WFML‐1, to SHR rats reduced blood
pressure and plasma Ang II, but unexpectedly, plasma Ang I was augmented in
response to renin inhibition. Again, if renin is the rate‐limiting step for the
formation of angiotensin peptides, then Ang I should have been reduced in response
to renin inhibition. It is for all of the above unexplained findings that we postulated
that Ang‐(1‐12) may be an intermediate storage depot that is readily available for
the production of downstream Ang II and/or Ang‐(1‐7). In this regard, we showed
(39) that Ang I, Ang II, and Ang‐(1‐7) could be produced from exogenous Ang‐(1‐12)
in hearts isolated from three normotensive and two hypertensive rat strains. One
possibility is that, depending on the tissue distribution of processing enzymes, Ang‐
197
(1‐12) may be able to preferentially produce Ang peptides to either Ang II or Ang‐
(1‐7). For example, Jessup et al. in our laboratory (20) found that Ang‐(1‐12)
concentration and immunolocalization was actually augmented in the hearts of
hypertensive SHR rats compared to normal WKY. In that same study, it was
reported that local cardiac Ang II was augmented in the SHR heart (20). Chappell et
al. (7), in a preliminary report, suggested that ACE rapidly and sequentially cleaves
Ang‐(1‐12) into Ang I and again into Ang II. The finding of elevated cardiac Ang‐(1‐
12) in SHR may contribute, at least in part, to the elevated concentration of local Ang
II in this hypertensive model. Moreover, in the same abstract, Chappell and
colleagues also reported that neprilysin can directly cleave Ang‐(1‐12) into Ang‐(1‐
7) in kidneys (7). Because NEP is higher in kidneys relative to other tissues (27; 31),
this may represent a preferential cleavage of Ang‐(1‐12) to Ang‐(1‐7). Further
studies to address these issues are of the utmost importance as they may provide
better, salternative treatments for hypertension and/or heart disea e.
The findings outlined in this dissertation on the cardiac renin‐angiotensin
system relative to what is known or supported by us and others are highlighted in
blue in Figure VIII.2. We showed that the coronary circulation can process peptides,
including Ang‐(1‐12) and Ang II into bioactive metabolites. This processing is
dependent upon the localization and distribution of the enzymes that arbitrate their
hydrolysis. Moreover, we found that ACE2 and renin can both be secreted from the
heart either from the vasculature directly or from the surrounding cells and/or
interstitial space. Within the local tissue, we also showed that a disruption in the
balance of Ang II and Ang‐(1‐7) results in response to ACE2 blockade. Because we
198
did not observe any changes in circulating Ang II or Ang‐(1‐7), but there was a
significant imbalance in the Ang‐(1‐7)/Ang II ratio within the cardiac tissue itself,
these data suggest that the imbalance was created in an extra‐coronary space, likely
the interstitium, as ACE2 activity is only reported in cardiomyocytes, and not
fibroblasts (16; 19). The augmentation of cardiac Ang II caused significant cardiac
hypertrophy, as indicated by increases in both anterior and posterior wall
thicknesses, as well as increased cardiomyocyte cross‐sectional area. Our finding
that ACE2 blockade resulted in increased collagen expression further suggests that
the mechanism of blockade occurred at cardiomyocytes in the interstitium, as
cardiac fibroblasts lack ACE2 activity (16; 19). It is my belief that the future of the
treatment of heart disease lies in determining the mechanism(s) by which these
different RAS component move and act amongst compartments, i.e. among the
corona n pry circulation, i terstitial s ace, and the intracellular space.
The successes of current treatment regimens for patients diagnosed with
heart failure, as well as in animal models, are focused on blocking the synthesis
and/or actions of Ang II (1; 9), lending to the notion that the action of cardiac Ang II
is elevated in these patients. The studies completed in this dissertation show that
alternative mechanisms may lend to alternative therapeutic approaches. Despite
the successes of ACE inhibitors and ARBs, heart disease remains the number one
cause of mortality in both the United States (24) and worldwide (2). Further strides
on the ultimate role of ACE2 and more recently, Ang‐(1‐12) must be made so that
patients can be afforded longer, high‐quality lives.
199
R EFERENCES
1. Effects of ramipril on cardiovascular and microvascular outcomes in people
with diabetes mellitus: results of the HOPE study and MICRO‐HOPE substudy.
Heart Outcomes Prevention Evaluation Study Investigators. Lancet 355: 253‐
259, 2000.
2. Preventing Chronic Diseases: A Vital Investment. 2008. World Health
Organization. Report.
3. Basso N and Terragno NA. History about the discovery of the renin‐angiotensin
system. Hypertension 38: 1246‐1249, 2001.
4. Braun‐Menendez E and Page IH. Suggested Revision of Nomenclature‐‐
Angiotensin. Science 127: 242, 1958.
5. Burrell LM, Risvanis J, Kubota E, Dean RG, MacDonald PS, Lu S, Tikellis C, Grant
SL, Lew RA, Smith AI, Cooper ME and Johnston CI. Myocardial infarction
increases ACE2 expression in rat and humans. Eur Heart J 26: 369‐375, 2005.
6. Campbell DJ, Kladis A and Duncan AM. Nephrectomy, converting enzyme
inhibition, and angiotensin peptides. Hypertension 22: 513‐522, 1993.
200
7. Chappell, M. C., Westwood, B. M., Pendergrass, K. D., Jessup, J. A., and Ferrario,
C. M. Distinct Processing Pathways for the Novel Peptide Angiotensin‐(1‐12) in
the Serum and Kidney of the Hypertensive mRen2.Lewis Rat. Hypertension
50(4), e139. 2007. Abstract.
8. Cicilini MA, Ramos PS, Vasquez EC and Cabral AM. Heart prolyl endopeptidase
activity in one‐kidney, one clip hypertensive rats. Braz J Med Biol Res 27: 2821‐
2830, 1994.
9. Dahlof B, Devereux RB, Kjeldsen SE, Julius S, Beevers G, de FU, Fyhrquist F,
Ibsen H, Kristiansson K, Lederballe‐Pedersen O, Lindholm LH, Nieminen MS,
Omvik P, Oparil S and Wedel H. Cardiovascular morbidity and mortality in the
Losartan Intervention For Endpoint reduction in hypertension study (LIFE): a
randomised trial against atenolol. Lancet 359: 995‐1003, 2002.
10. Danser AH, van Kats JP, Admiraal PJ, Derkx FH, Lamers JM, Verdouw PD,
Saxena PR and Schalekamp MA. Cardiac renin and angiotensins. Uptake from
plasma versus in situ synthesis. Hypertension 24: 37‐48, 1994.
11. de Lannoy LM, Danser AH, van Kats JP, Schoemaker RG, Saxena PR and
Schalekamp MA. Renin‐angiotensin system components in the interstitial fluid
of the isolated perfused rat heart. Local production of angiotensin I.
Hypertension 29: 1240‐1251, 1997.
201
12. Donoghue M, Hsieh F, Baronas E, Godbout K, Gosselin M, Stagliano N, Donovan
M, Woolf B, Robison K, Jeyaseelan R, Breitbart RE and Acton S. A novel
angiotensin‐converting enzyme‐related carboxypeptidase (ACE2) converts
angiotensin I to angiotensin 1‐9. Circ Res 87: E1‐E9, 2000.
13. Dzau VJ, Ellison KE, Brody T, Ingelfinger J and Pratt RE. A comparative study of
the distributions of renin and angiotensinogen messenger ribonucleic acids in
rat and mouse tissues. Endocrinology 120: 2334‐2338, 1987.
14. Epelman S, Tang WH, Chen SY, Van LF, Francis GS and Sen S. Detection of
soluble angiotensin‐converting enzyme 2 in heart failure: insights into the
endogenous counter‐regulatory pathway of the renin‐angiotensin‐aldosterone
system. J Am Coll Cardiol 52: 750‐754, 2008.
15. Fedak PW, Moravec CS, McCarthy PM, Altamentova SM, Wong AP, Skrtic M,
Verma S, Weisel RD and Li RK. Altered expression of disintegrin
metalloproteinases and their inhibitor in human dilated cardiomyopathy.
Circulation 113: 238‐245, 2006.
16. Gallagher PE, Ferrario CM and Tallant EA. Regulation of ACE2 in Cardiac
Myocytes and Fibroblasts. Am J Physiol Heart Circ Physiol 2008.
202
17. Goldblatt H, Lynch J, Hanzal RF, and Summerville WW. Studies on experimental
hypertension, I: the production of persistent elevation of systolic blood
pressure by means of renal ischemia. J Exp Med 59, 347‐379. 1934.
18. Goulter AB, Goddard MJ, Allen JC and Clark KL. ACE2 gene expression is up‐
regulated in the human failing heart. BMC Med 2: 19, 2004.
19. Grobe JL, Der SS, Stewart JM, Meszaros JG, Raizada MK and Katovich MJ. ACE2
overexpression inhibits hypoxia‐induced collagen production by cardiac
fibroblasts. Clin Sci (Lond) 113: 357‐364, 2007.
20. Jessup JA, Trask AJ, Chappell MC, Nagata S, Kato J, Kitamura K and Ferrario CM.
Localization of the novel angiotensin peptide, angiotensin‐(1‐12), in heart and
kidney of hypertensive and normotensive rats. Am J Physiol Heart Circ Physiol
294: H2614‐H2618, 2008.
21. Kalinyak JE and Perlman AJ. Tissue‐specific regulation of angiotensinogen
mRNA accumulation by dexamethasone. J Biol Chem 262: 460‐464, 1987.
22. Kato T, Okada M and Nagatsu T. Distribution of post‐proline cleaving enzyme
in human brain and the peripheral tissues. Mol Cell Biochem 32: 117‐121, 1980.
23. Koida M and Walter R. Post‐proline cleaving enzyme. Purification of this
endopeptidase by affinity chromatography. J Biol Chem 251: 7593‐7599, 1976.
203
24. Kung HC, Hoyert DL, Xu JQ and Murphy SL. Deaths: Final Data for 2005.
Hyattsville, MD: National Center for Health Statistics, 2008.
25. Lambert DW, Yarski M, Warner FJ, Thornhill P, Parkin ET, Smith AI, Hooper NM
and Turner AJ. Tumor necrosis factor‐alpha convertase (ADAM17) mediates
regulated ectodomain shedding of the severe‐acute respiratory syndrome‐
coronavirus (SARS‐CoV) receptor, angiotensin‐converting enzyme‐2 (ACE2). J
Biol Chem 280: 30113‐30119, 2005.
26. Leenen FH, Skarda V, Yuan B and White R. Changes in cardiac ANG II
postmyocardial infarction in rats: effects of nephrectomy and ACE inhibitors.
Am J Physiol 276: H317‐H325, 1999.
27. Llorens C and Schwartz JC. Enkephalinase activity in rat peripheral organs. Eur
J Pharmacol 69: 113‐116, 1981.
28. Mentlein R and Roos T. Proteases involved in the metabolism of angiotensin II,
bradykinin, calcitonin gene‐related peptide (CGRP), and neuropeptide Y by
vascular smooth muscle cells. Peptides 17: 709‐720, 1996.
29. Oparil S, Yarows SA, Patel S, Fang H, Zhang J and Satlin A. Efficacy and safety of
combined use of aliskiren and valsartan in patients with hypertension: a
randomised, double‐blind trial. Lancet 370: 221‐229, 2007.
204
30. Pendergrass KD, Pirro NT, Westwood BM, Ferrario CM, Brosnihan KB and
Chappell MC. Sex differences in circulating and renal angiotensins of
hypertensive mRen(2).Lewis but not normotensive Lewis rats. Am J Physiol
Heart Circ Physiol 295: H10‐H20, 2008.
31. Ronco P, Pollard H, Galceran M, Delauche M, Schwartz JC and Verroust P.
Distribution of enkephalinase (membrane metalloendopeptidase, E.C.
3.4.24.11) in rat organs. Detection using a monoclonal antibody. Lab Invest 58:
210‐217, 1988.
32. Santos RA, Brosnihan KB, Jacobsen DW, DiCorleto PE and Ferrario CM.
Production of angiotensin‐(1‐7) by human vascular endothelium. Hypertension
19: II56‐II61, 1992.
33. Schiavone MT, Santos RA, Brosnihan KB, Khosla MC and Ferrario CM. Release
of vasopressin from the rat hypothalamo‐neurohypophysial system by
angiotensin‐(1‐7) heptapeptide. Proc Natl Acad Sci U S A 85: 4095‐4098, 1988.
34. Tamaoki J, Sugimoto F, Tagaya E, Isono K, Chiyotani A and Konno K.
Angiotensin II 1 receptor‐mediated contraction of pulmonary artery and its
modulation by prolylcarboxypeptidase. J Appl Physiol 76: 1439‐1444, 1994.
35. Tan F, Morris PW, Skidgel RA and Erdos EG. Sequencing and cloning of human
prolylcarboxypeptidase (angiotensinase C). Similarity to both serine
205
carboxypeptidase and prolylendopeptidase families. J Biol Chem 268: 16631‐
16638, 1993.
36. Tigerstedt R. and Bergman P.G. Niere und Kreislauf. Scan Arch Physiol 8, 223‐
271. 1898.
37. Tipnis SR, Hooper NM, Hyde R, Karran E, Christie G and Turner AJ. A human
homolog of angiotensin‐converting enzyme. Cloning and functional expression
as a captopril‐insensitive carboxypeptidase. J Biol Chem 275: 33238‐33243,
2000.
38. Trask AJ, Averill DB, Ganten D, Chappell MC and Ferrario CM. Primary role of
angiotensin‐converting enzyme‐2 in cardiac production of angiotensin‐(1‐7) in
transgenic Ren‐2 hypertensive rats. Am J Physiol Heart Circ Physiol 292:
H3019‐H3024, 2007.
39. Trask AJ, Jessup JA, Chappell MC and Ferrario CM. Angiotensin‐(1‐12) is an
alternate substrate for angiotensin peptide production in the heart. Am J
Physiol Heart Circ Physiol 294: H2242‐H2247, 2008.
40. Walter R, Shlank H, Glass JD, Schwartz IL and Kerenyi TD. Leucylglycinamide
released from oxytocin by human uterine enzyme. Science 173: 827‐829, 1971.
206
41. Welches WR, Santos RA, Chappell MC, Brosnihan KB, Greene LJ and Ferrario
CM. Evidence that prolyl endopeptidase participates in the processing of brain
angiotensin. J Hypertens 9: 631‐638, 1991.
42. Zhong JC, Huang DY, Yang YM, Li YF, Liu GF, Song XH and Du K. Upregulation of
angiotensin‐converting enzyme 2 by all‐trans retinoic acid in spontaneously
hypertensive rats. Hypertension 44: 907‐912, 2004.
43. Zisman LS, Keller RS, Weaver B, Lin Q, Speth R, Bristow MR and Canver CC.
Increased angiotensin‐(1‐7)‐forming activity in failing human heart ventricles:
evidence for upregulation of the angiotensin‐converting enzyme Homologue
ACE2. Circulation 108: 1707‐1712, 2003.
207
Figure VIII.1. Diagrammatic representation illustrating the increasing role
for ACE2 in cardiac remodeling, but not cardiac function in our studies, as it relates
to blood pressure and different heart conditions from normal through overt heart
failure. DD = diastolic dysfunction.
208
FIGURE VIII.1
209
Figure VIII.2. Diagrammatic representation how the studies outlined in this
dissertation (highlighted in blue) fit into what is known about the cardiac renin‐
angiotensin system. Dotted lines represent unknown potential enzymatic pathways;
Dotted interrupted lines represent the potential movement of proteins and/or
peptides among compartments within the heart.
210
FIGURE VIII.2
211
APPENDIX
Figure A.1. Ang‐(1‐7) formation from Ang II measured by RIA in SD hearts
(n = 8). Ang‐(1‐7) production from Ang II was significant from baseline values
(represented at time=0). The addition of the POP inhibitor, ZPP, at 15 minutes
exhibited no significant reduction of Ang‐(1‐7) generation throughout the 60‐
minute recirculation experiment.
212
0 20 40 600
200
400
600ControlZPP
Recirculation Time (Min)
SD Ang(17) [pM]
FIGURE A.1
213
Figure A.2. Ang‐(1‐7) formation from Ang II measured by RIA in SD hearts
(n = 8). Ang‐(1‐7) production from Ang II was significant from baseline values
(represented at time=0). The addition of the serine protease inhibitor, AEBSF, at 15
minutes exhibited no significant reduction of Ang‐(1‐7) generation throughout the
60‐minute recirculation experiment.
214
0 20 40 600
200
400
600
ControlAEBSF
Recirculation Time (Min)
SD Ang(17) [pM]
FIGURE A.2
215
CURRICULUM VITAE
AARON J. TRASK
April 24, 1980 Richmond, Indiana, U.S.A.
B
ORN:
EDUCATION:
004‐Present e School of Arts and Sciences
ty Graduat2 Wake Forest Universi Winston‐Salem, North Carolina
logy Doctor of Philosophy Graduate Program: Physiology and Pharmaco
Laboratory Advisor: Dr. Carlos M. Ferrario r Research Center
Hypertension and Vascula 999‐2003 1 Ohio Northern University
Ada, Ohio Bachelor of Science, Biology
EMPLOYMENT
004‐Present
:
gram 2 Graduate Fellow
raduate Prof Medicine
Physiology and Pharmacology GWake Forest University School o
orth Carolina Winston‐Salem, N 001‐2003 2 Nurse’s Assistant
Wayne Hospital Greenville, Ohio
R S: ESEARCH SKILL
Isolatean
d vessel ring bath preparations ations
n v L gendorff isolated heart prepar
I ivo cardiac catheterization for measurement of dP/dt, pressure‐volume relationship In vivo blood vessel catheterization (carotid, femoral , jugular) for
d pressure and administration of drugs n of
measurement of bloo Surgical procedure for subcutaneous and intravenous insertio
otic pumps essure surgery, measurements, and
mini‐osm Radiotelemetry blood pr analysis
216
Immunohistochemistry Western blot hybridization Peptide extraction and preparation for HPLC
Radioimmunoassay
FELLOWSHIP
007‐Present l
S: 2 American Heart Association Mid‐Atlantic Affiliate Pre‐Doctora
715249U). Aaron J. Trask, PI. “The ‐(1‐7) Axis in Heart Failure.” Total Award
Fellowship (AHA 0ACE2/Angiotensin
Amount: $40,000
004‐2007 ship, Wake Forest University Graduate School of Arts
Dean’s Fellowand Sciences
2 HONO ARDS: RS AND AW 009 d Professionals 2 Marquis Who’s Who Among Executives an2008 Merck New Investigator Award, American Heart Association
ressure Research el
Council for High Blood P2007 American Heart Association Hypertension Summer School Trav
l Award Award
ol Alumni Trave2006‐2007 Wake Forest University Graduate Scho2000‐2003 Ohio Northern University Arts & Sciences Scholarship
n’s List rship Award
1999‐2003 Ohio Northern University Dea2003 1999‐ Ohio Northern University Achievement/Leade
ship Scholarship
n’s Scholarholarship
1999 Ohio Northern University Dea999 Tiffany Furgason Memorial Sc999 Arcanum Alumni Scholarship 11 PROFESSIONA LIATIONS: L AFFI
rch 2005‐Present American Heart Association
ressure Resea Council for High Blood P2005‐Present American Physiological Society (APS) Cardiovascular Section 2005‐Present Consortium for Southeastern Hypertension Control 001‐Present Beta Beta Beta National Biology Honor Society 001‐Present Omicron Delta Kappa National Leadership Honor Society 22 PROF
ssure
ESSIONAL DEVELOPMENT:
22008 6 nd American Heart Association Council for High Blood Pre
uate Research Annual Meeting, Atlanta, Georgia 2008 3rd Annual National Institutes of Health National Grad
217
Student Research Festival, Bethesda, Maryland 2008 Experimental Biology Meeting, San Diego, California 2007 61st American Heart Association Council for High Blood Pressure
Research Annual Meeting, Tucson, Arizona ool, Fort 2007 6th American Heart Association Hypertension Summer Sch
Collins, Colorado f Hypertension / Consortium for 2007 Inter‐American Society o
Southeast Hypertension Control Annual Meeting, Miami Beach,
006 igh Blood Pressure Florida
60th American Heart Association Council for HResearch Annual Meeting, San Antonio, Texas
2 TEACHING RIENCE:
007‐2008
EXPE
2 Lecturer, Winston‐Salem State University Physical Therapy ‐Salem, North Carolina. Lectures on cardiac ular exercise physiology, hemorrhagic shock,
Program, Winstonoutput, cardiovasc
and heart failure
006 t of Physiology
Graduate Tutor, Wake Forest University Departmen2 and Pharmacology, Winston‐Salem, North Carolina
001‐2003 nterpersonal
Student Tutor, Ohio Northern University ICommunications Skills Center, Ada, Ohio
2 ORGANIZATIONS/ACTIVITIES:
of
t 2006 Student Member, Wake Forest University Departmen Physiology and Pharmacology Curriculum Committee 001‐2003 an, Judicial Board, Ohio Northern University 000‐2003 an, Judicial Committee, Ohio Northern University Student 2 Chairm
ChairmSenate
2 COMMUNIT VICE:
006‐2007 art & Stroke Walk,
Y SER
Team Captain, American Heart Association HeTanglewood Park, Clemmons, North Carolina
2 PUBLICATIONS: BOOK CHAPTERS:
Trask AJ, Varagic J, Ahmad S, Ferrario CM. “Angiotensin‐(1‐7), Angiotensin Converting Enzyme 2, and New Components of the Renin‐Angiotensin System.” Renin‐Angiotensin System and Cardiovascular Disease. Ed. De Mello W.C. & Frohlich E.D. Totowa: Humana Press, Submitted.
218
Trask AJ, Ferrario CM. “The Renin‐Angiotensin System and the Heart.” Textbook of Nephro‐Endocrinology. Ed. Singh A. & Williams G. San Diego:
. Elsevier, 2009. 181‐188
Ferrario CM, Jessup JA, Trask AJ, Varagic J. “Basic Science in Hypertension.” The Year in Hypertension. Ed. Townsend R. Oxford: Clinical Publishing, 2008. 1‐17.
JOURNAL ARTICLES:
Trask AJ, Groban L, Westwood BM, Varagic J, Ganten D, Gallagher PE, Chappell MC, Ferrario CM. Disruption of Cardiac Angiotensin Peptides by Angiotensin Converting Enzyme 2 Inhibition Excacerbates Cardiac Hypertrophy and Fibrosis
Rats. In P in Ren‐2 Hypertensive reparation for Hypertension 2008.
Ferrario CM, Varagic J, Habibi J, Nagata S, Kato J, Chappell MC, Trask AJ, Kitamura K, Whaley‐Connell A, Sowers JR. Differential Regulation of Angiotensin‐(1‐12) in Plasma and Cardiac Tissue in Response to Bilateral Nephrectomy. Submitted to Am J Physiol Heart Circ Physiol 2008.
Jessup JA, Trask AJ, Chappell MC, Nagata S, Kato J, Kitamura K, Ferrario CM. Localization of the Novel Angiotensin Peptide, Angiotensin‐12, in Heart and Kidney of Hypertensive and Normotensive Rats. Am J Physiol Heart Circ Physiol
: H2614‐H2008; 294 2618.
Varagic J, Trask AJ, Jessup JA, Chappell MC, Ferrario CM. New Angiotensins. J Mol Med 2 0 6 ‐0 8; 86: 63 71.
Trask AJ, Jessup JA, Chappell MC, Ferrario CM. Angiotensin‐(1‐12) is an Alternate Substrate for Angiotensin Peptide Production in the Heart. Am J Physiol Heart Circ Physiol 2008; 294: H2242‐H2247.
Trask AJ, Ferrario CM. Angiotensin‐(1‐7): Pharmacology and New Perspectives in Cardiovascular Treatments. Cardiovascular Drug Reviews 2007; 25(2): 162‐174.
Trask AJ, Averill DB, Ganten D, Chappell MC, Ferrario CM. Primary Role of Angiotensin Converting Enzyme 2 in Cardiac Production of Angiotensin‐(1‐7) in Transgenic Ren‐2 Hypertensive Rats. Am J Physiol Heart Circ Physiol 2007; 292:
4. H3019‐H302
Ferrario CM, Trask AJ, Jessup JA. Advances in Biochemical and Functional Roles of Angiotensin‐Converting Enzyme 2 and Angiotensin‐(1–7) in the Regulation of Cardiovascular Function. Am J Physiol Heart Circ Physiol 2005; 289: H2281‐2290. H
219
ABSTRACTS:
Trask AJ, Groban L, Varagic J, Ferrario CM. Inhibition of Angiotensin Converting Enzyme 2 Aggravates Cardiac Hypertrophy in Ren‐2 Hypertensive Rats. 16th Annual Wake Forest University Surgical Sciences Research Day, 2008.
Trask AJ, Groban L, Varagic J, Ferrario CM. Inhibition of Angiotensin Converting Enzyme 2 Aggravates Cardiac Hypertrophy in Ren‐2 Hypertensive Rats. Hypertension 2008; 52(4):e126.
Ferrario CM, Varagic J, Chappell MC, Trask AJ, Nagata S, Kato J. Bilateral Nephrectomy Augments the Cardiac Content of Angiotensin‐(1‐12) and Angiotensin I in Wistar‐Kyoto Rats. Hypertension 2008; 52(4): e126.
Trask AJ, Jessup JA, Tallant EA, Chappell MC, Ferrario CM. Renin‐Independent Processing of Angiotensin‐(1‐12) in the Rat Heart and Isolated Myocytes. Hypertension 2008; 52(4):e45‐e46 (Selected for oral presentation).
Trask AJ, Jessup JA, Tallant EA, Chappell MC, Ferrario CM. Renin‐Independent Processing of Angiotensin‐(1‐12) in the Rat Heart and Isolated Myocytes. Third Annual NIH National Graduate Student Research Festival, Bethesda, Maryland
tation).(Selected for presen
Jessup JA, Habibi J, Trask AJ, Chappell MC, Nagata S, Kato J, Kitamura K, Sowers J, Ferrario CM. Experimental Hypertension is Associated with Differential Expression of Angiotensin‐(1‐12) in Heart of Hypertensive and Normotensive Rats. FASEB, 2008.
Trask AJ, Jessup JA, Ferrario CM. Angiotensin‐(1‐12) is a Precursor for the Processing of Cardiac Tissue Angiotensin Peptides. 8th Annual Wake Forest University G raduate Student Research Day, 2008.
Trask AJ, Jessup JA, Ferrario CM. Angiotensin‐(1‐12) is a Precursor for the Processing of Cardiac Tissue Angiotensin Peptides. 15 Annual Wake Forest University S
th
urgical Sciences Research Day, 2007.
Trask AJ, Jessup JA, Ferrario CM. Angiotensin‐(1‐12) is a Precursor for the Processing of Cardiac Tissue Angiotensin Peptides. Hypertension 2007; 50(4): e154.
Trask AJ, Chappell MC, Ferrario CM. Major Role for Angiotensin Converting Enzyme 2 in Cardiac Angiotensin‐(1‐7) Production in the Congenic Hypertensive mRen2.Lewis Rat. Hypertension 2007; 50(4): e140.
Trask AJ, Averill DB, Chappell MC, Ferrario CM. Predominance of Angiotensin Converting Enzyme 2 to Cardiac Angiotensin‐(1‐7) Production in [mRen2]27
220
Transgenic Hypertensive Rats. Inter‐American Society of Hypertension/COSEHC Annual Scientific Meeting, Miami Beach, Florida, 2007.
Trask AJ, Averill DB, Chappell MC, Ferrario CM. Predominance of Angiotensin Converting Enzyme 2 to Cardiac Angiotensin‐(1‐7) Production in [mRen2]27 Transgenic Hypertensive Rats. Hypertension 2006; 48(4): e72.
Trask AJ, Averill DB, Chappell MC, Ferrario CM. Cardiac Production of Angiotensin‐(1‐7) by Angiotensin Converting Enzyme 2. 13th Annual Wake
ical Sciences Research Day, 2005. Forest University Surg
ORAL PRESENTATIONS:
“New Advances on the Biochemical Pathways in the Renin‐Angiotensin System and their Role in Cardiac Structure and Function.” Nationwide Children’s Hospital, Columbus, Ohio, 2008.
“Renin‐Independent Processing of Angiotensin‐(1‐12) in the Rat Heart and Isolated Myocytes.” 62nd Council for High Blood Pressure Research, Atlanta, Georgia, 2008.
“New Advances on the Biochemical Pathways of the Cardiac Renin‐Angiotensin System.” Wake Forest University Department of Physiology and Pharmacology, Winston‐Salem, North Carolina, 2007.
“The Cardioprotective Effects of the ACE2/Ang‐(1‐7) Axis in Heart Failure.” Wake Forest University Department of Physiology and Pharmacology, Winston‐Salem, North Carolina, 2006.
“The Cardioprotective Effects of the ACE2/Ang‐(1‐7) Axis in Heart Failure.” Wake Forest University Department of Physiology and Pharmacology, Winston‐
006. Salem, North Carolina, 2
POSTER PRESENTATIONS:
“Inhibition of Angiotensin Converting Enzyme 2 Aggravates Cardiac Hypertrophy in Ren‐2 Hypertensive Rats.” 16th Annual Wake Forest University
‐S C 20 8Surgical Sciences Day, Winston alem, North arolina, 0 .
“Inhibition of Angiotensin Converting Enzyme 2 Aggravates Cardiac Hypertrophy in Ren‐2 Hypertensive Rats.” 62nd Council for High Blood Pressure Research, Atlanta, Georgia, 2008.
“Angiotensin‐(1‐12) is a Precursor for the Processing of Cardiac Tissue Angiotensin Peptides.” 8th Annual Wake Forest University Graduate Student Research Day, 2008.
221
“Angiotensin‐(1‐12) is a Precursor for the Processing of Cardiac Tissue Angiotensin Peptides.” 15th Annual Wake Forest University Surgical Sciences Day, Winston‐Salem, North Carolina, 2007.
“Angiotensin‐(1‐12) is a Precursor for the Processing of Cardiac Tissue Angiotensin Peptides.” 61st American Heart Association Council for High Blood Pressure Research, Tucson, Arizona, 2007.
“Major Role for Angiotensin Converting Enzyme 2 in Cardiac Angiotensin‐(1‐7) Production in the Congenic Hypertensive mRen2.Lewis Rat.” 61st American Heart Association Council for High Blood Pressure Research, Tucson, Arizona, 2007.
“Predominance of Angiotensin Converting Enzyme 2 to Cardiac Angiotensin‐(1‐7) Production in [mRen2]27 Transgenic Hypertensive Rats.” Inter‐American Society of Hypertension/COSEHC Annual Scientific Meeting, Miami Beach, Florida, 2007.
“Predominance of Angiotensin Converting Enzyme 2 to Cardiac Angiotensin‐(1‐7) Production in [mRen2]27 Transgenic Hypertensive Rats.” 60th American Heart Association Council for High Blood Pressure Research, San Antonio, Texas, 2006.
“Cardiac Production of Angiotensin‐(1‐7) by Angiotensin Converting Enzyme 2.” 13th Annual Wake Forest University Surgical Sciences Day, Winston‐Salem, North Carolina, 2005.
222