lipid metabolism hanley n. abramson, ph.d

1

Lipid Metabolism

Hanley N. Abramson, Ph.D.Professor, Department of Pharmaceutical Sciences

Wayne State UniversityOctober 2010

2

Fatty AcidsCH3(CH2)nCH2CO2H

O

OCH3(CH2)nCH2C-O-R

CH3(CH2)nCH2C-OH H-O-R

O

O

CH3(CH2)nCH2C-OH H-S-R

CH3(CH2)nCH2C-S-R

Ester Thioester

3

Fatty Acids as Stored Energy

• Fatty acids are the body’s principal form of stored energy

• Carbon almost completely reduced as CH2

• Very closely packed in storage tissues - not hydrated as sugars are

4

Dietary Fatty Acids

• Comprise 30-60% of caloric intake in average American diet

• Triacylglycerols, phospholipids, sterol esters

• Principal sources: dairy products, meats

5

Digestion of Dietary Triacylglycerols

• Occurs in duodenum• Facilitated by

• Bile salts (emulsification)• Alkaline medium (pancreatic juice)

Pancreaticlipases

OH

OH

TAG MAG

Intestinallipases Glycerol

+Fatty Acids

Blocked by Orlistat (“Fat Blocker”) - Xenical/Alli

6

Epithelial Cell (Intestinal Wall)

Intestinal lumenMAG Glycerol Fatty Acids

TAG

Lipoprotein

ChylomicronsLymphatics

Blood (bound to albumin)Adipose TissueAnd Muscle

7

Adipocytes

8

Fat Storage

• Mainly as triacylglycerols (triglycerides) in adipose cells

• Constitute 84% of stored energy• Protein - 15%• Carbohydrate (glucose or glycogen) - <1%

9

Processing of Lipid Reserves: Overview

1. Lipid Mobilization:In adipose tissue TAGs hydrolyzed to

fatty acids plus glycerol

2. Transport of Fatty Acids in BloodTo Tissues

3. Activation of Fatty Acids as CoA Ester

4. Transport into Mitochondria

5. Metabolism to Acetyl CoA

Release of Fatty Acids from Triacylglycerols

O

O

O

O O O+

HOC-R3 HOC-R2 HOC-R1

Triacylglycerol Glycerol

Lipases

CH2OH

CHOH

CH2OHCH2OC-R1

CHOC-R2

CH2OC-R3

11Adipose Cell

Hormone(Adrenalin, Glucagon, ACTH)

Receptor (7TM)

ATP c-AMPAdenylylCyclase

Activates

Activates lipase

Triacylglycerols Glycerol + Fatty acids Blood

Lipolysis

Insulinblocks thisstep

12

ATP c-AMP AMP

Inactive Kinase Activated Kinase

Inactive Lipase Activated LipaseP

Triacyl-glycerol

Glycerol +Fatty Acids

Phosphatase(Hormone-sensitiveLipase)

Insulin favors formationof the inactive lipase

Adenylyl cyclase Phosphodiesterase

Enhanced by insulinEnhanced by glucagon

13

Acylglycerol Lipases

TriacylglycerolLipase

DiacylglycerolLipase

OH

OH

OH

MonoacylglycerolLipase

OH

OH

OH

Triacylglycerol (TAG)

Diacylglycerol (DAG)

Monoacylglycerol(MAG)

Glycerol

14

Fate of Glycerol

OH

OH

OH

Glycerol

In Liver:

DihydroxyacetonePhosphate

Pyruvate

Glucose

Glycolysis

Gluconeogenesis

15

Beta Oxidation

• Cleavage of fatty acids to acetate in tissues

• Occurs in mitochondria

9 CH3COSCoACO2H

[O] [O] [O] [O] [O][O] [O] [O]

16

Steps in Beta Oxidation• Fatty Acid Activation by Esterification

with CoASH• Membrane Transport of Fatty Acyl CoA

Esters• Carbon Backbone Reaction Sequence

• Dehydrogenation• Hydration• Dehydrogenation• Carbon-Carbon Cleavage (Thiolase Reaction)

17

Fatty Acid Activation by Esterification with CoASH

CoASH + RCO2H + ATP RCOSCoA + AMP + PPi AcylCoA

Synthetase

2 Pi

Pyrophos-phatase

Occurs in outer mitochondrialmembrane for long chain fatty acids

ATP AMP + PPi -32.3CoASH + RCO2H RCOSCoA +31.5PPi 2 Pi -33.6

G0’(KJ/mole)

-34.4

18

Membrane Transport of Fatty Acyl CoA Esters

Transported across inner mitochondrial

membrane by translocase

(CH3)3NO

O -OH

(CH3)3NO

O -O2CR

Carnitineacyltransferase II(matrix side of inner mitochondrialmembrane)

Carnitineacyltransferase I(outer part of mitochondrial inner membrane)

O-Acylcarnitine

Carnitine

+

+RCOSCoA +

19Source: http://cellbio.utmb.edu/cellbio/mitochondria_1.htm

Carnitine acyltransferase I Carnitine acyltransferase II

Translocase

20

Beta Oxidation Reaction Sequence

Occurs in Mitochondria

Repeat Sequence

H H

H H

H

H

H

H

HO HO

H

O

H

O

Enoyl CoA Hydratase

R-CH2-C-C-COSCoA R-CH2-C=C-COSCoA

R-CH2-C-C-COSCoAR-CH2-C-C-COSCoA

R-CH2-C-SCoA CH3-C-SCoA

Acyl CoADehydrogenase

FAD FADH 2trans-2-enoyl CoA

H2O

L--Hydroxyacyl CoA

L--Hydroxyacyl CoADehydrogenase

NAD+NADH + H+

CoASH

+

Thiolase

-Ketoacyl CoA

(-ketothiolase)

21

Complete Beta Oxidation of Palmitoyl CoA

CH3CH2--CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2COSCoA

7 Cycles

8 CH3COSCoA + 7 FADH2 + 7 NADH + 7 H+

22

Energetics of Complete Oxidation of Fatty Acids

Palmitic Acid Palmitoyl CoA -2

CH3COSCoA CO2 + H2O 108

High Energy PhosphateBonds Generated

Net 106

TCA Cycle

106 High Energy Phosphate Bonds G0’ = 3,233 KJ/Mole

For Palmitic Acid CO2:G0’ = - 9,790 KJ/Mole

Efficiencyof -Oxidation = 33%

23

Complete Oxidation

Fatty Acids: 9 kcal/g

Carbohydrates: 4 kcal/g

Protein: 4 kcal/g

24

American Golden Plover

25

Arctic Tern

26

Camel

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Beta Oxidation of Odd Carbon Fatty Acids

CH3CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2COSCoA

5 Cycles

5 CH3COSCoA + CH3CH2COSCoAPropionyl CoA

CO2H

COSCoA

H-C-CH3

CO2H

COSCoA

CH3-C-HHO2CCH 2CH2COSCoA

D-MethylmalonylCoA

L-MethylmalonylCoA

Succinyl CoA

TCA Cycle

Propionyl CoA CarboxylaseATP/CO2

EpimeraseMutase

Vit. B12

28

Beta Oxidation of Unsaturated Fatty Acids

H HCH3(CH2)7-C=C-CH2(CH2)6COSCoA

H HCH3(CH2)7-C=C-CH2COSCoA

H

H

CH3(CH2)7-CH2-C=C-COSCoA

Oleoyl CoABeta Oxidation(3 Cycles)

cis-3

Isomerase

trans-2

Continuation of Beta Oxidation

29

Ketogenesis: Formation of Ketone Bodies

2 CH3COSCoA CH3COCH2COSCoAThiolase

CH3COSCoA

Acetoacetyl CoA

HO2C-CH2-C-CH2COSCoA

OH

CH3

-Hydroxy--methylglutaryl CoA(HMG CoA)

HMG CoASynthase

Cholesterol(in cytosol)

Severalsteps

Ketogenesis(in liver: mitochon-

drial matrix)

See Slide 78

30

Ketogenesis: Formation of Ketone Bodies (Cont’d.)

HO2C-CH2-C-CH2COSCoA

OH

CH3

HMG CoAAcetoacetate

HMG CoAlyase

- CH3COSCoA

- CO2

CH3COCH3

Acetone(volatile)

CH3CHCH2CO2

OH

-Hydroxybutyrate

NADH + H+

NAD+Dehydrogenase

Ketone bodies are important sources of energy, especially in starvation

CH3COCH2CO2

31

-Hydroxybutyrate Acetoacetate Succinyl CoA

SuccinateAcetoacetyl CoA

-Ketoacyl CoAtransferase

2 Acetyl CoAThiolase

TCA Cycle

Ketone Bodies As Energy SourcesIn liver

Acetoacetate is major energysource in cardiac muscle andrenal cortex; also in brain instarvation and diabetes

Not found in liver

Combines with oxaloacetate

32

Ketones in Diabetes MellitusIn presence of insulin:

• Enhanced glucose uptake by tissues• Decreased mobilization of lipids by

adipocytes

In absence of insulin:• Decreased glucose uptake by tissues• Increased mobilization of lipids by adipocytes

33

Ketones in Diabetes MellitusBiochemical consequences of decreased insulin production:

• Glucose not taken up by liver• Decreased oxaloacetate to combine with

acetyl CoA to enter TCA

• Adipocytes release fatty acids into blood• Increased production of ketone bodies in liver

34

CH3COCH2CO2H pKa = 3.6 Acetoacetic Acid

CH3CHCH2CO2H pKa = 4.7 -Hydroxybutyric acid

OH

Concentration of acetoacetic acid can result in metabolicacidosis (pH 7.1) affinity of Hb for O2.

Metabolic Acidosis in Untreated Diabetes Mellitus

35

Fatty Acid Biosynthesis

36

Fatty Acid Synthesis vs. Degradation

Intermediates

Site

Enzymes

RedoxCoenzymes

Synthesis DegradationLinked to SH in Linked to CoASHProteins (Acyl Carrier Proteins)

Cytosol Mitochondria

Components of Separate PolypeptidesSingle Peptide

NADP+ / NADPH NAD+ / NADH

37

Fatty Acid Biosynthesis

• Occurs in cytosol• Starts with acetyl CoA

• Problem:» Most acetyl CoA produced in mitochondria» Acetyl CoA unable to traverse mitochondrial

membrane

38Mitochondrial

membrane

Cytosol Mitochondria

Glucose Pyruvate Pyruvate Acetyl CoA

Oxalo-acetate

Citrate

Citrate

Acetyl CoA

PyruvateDehydrogenase

ATP-CitrateLyase

Malate

Oxaloacetate

Malic enzyme

Malate dehydrogenase

Note: Acetyl CoAcannot be convertedto glucose

Citrate As Carrier of Acetate Groups

39

Fatty Acid Biosynthesis: Formation of Malonyl CoA

CH3COSCoA + ATP + HCO3- -O2CCH2COSCoA

Acetyl CoACarboxylase

+ ADP + Pi + H+

Malonyl CoA

• Committed step in fatty acid synthesis• Reaction is irreversible• Regulation of acetyl CoA carboxylase activity:

by palmitoyl CoA by citrate (feed-forward allosteric activation)

by insulin by epinephrine and glucagon

• Malonyl CoA inhibits carnitine acyl transferase I • Blocks beta oxidation

40

Fatty Acid Biosynthesis:Role of Acyl Carrier Proteins

CH3COSCoA CH3CO-S-ACP

-O2CCH2COSCoA -O2CCH2CO-S-ACP

AcetylTransferase

MalonylTransferase

Acetyl ACP

Malonyl ACP

ACP = Acyl carrier protein

41

Fatty Acid Biosynthesis:Formation of Acetoacetyl ACP

CH3CO-S-ACP + -O2CCH2CO-S-ACP

CH3COCH2CO-S-ACP + CO2Acetoacetyl ACP

-Ketoacyl ACPSynthetase

42

Fatty Acid Biosynthesis:Formation of Butyryl ACP

CH3COCH2CO-S-ACP CH3CCH2CO-S-ACPOH

HAcetoacetyl ACP-D-Hydroxybutyryl ACP

-Ketoacyl ACPreductase

NADPH+ H+

NADP+

CH3C=C-CO-S-ACP

H

H

-Hydroxyacyl ACPdehydratase- H2O

Crotonyl ACPCH3CH2CH2CO-S-ACP

Butyryl ACP2,3-trans-Enoyl ACPreductase

NADPH+ H+

NADP+

43

Fatty Acid Biosynthesis:Sources of NADPH

Pentose Phosphate Pathway:CHO

OH

OHOHOP

HO

CO2-

OH

OHOHOP

HONADP+

NADPH+ H+ NADP+

NADPH+ H+

CO2

OH

OHOHOP

O

Ribulose-5-phosphate6-Phospho-

gluconateGlucose-6-phosphate

Malic Enzyme:

HO-CH-CO2-

CH2CO2-Malate

CO2

NADP+

NADPH+ H+

Malic Enzyme

CH3CCO2-

O

Pyruvate

44

Fatty Acid Biosynthesis:Chain Elongation

CH3CH2CH2CO-S-ACP -O2CCH2CO-S-ACP+

CH3CH2CH2COCH2CO-S-ACP

CH2CH2CH2CHCH2CO-S-ACP CH3CH2CH2C=CCO-S-ACP

H

H

OH

45

Fatty Acid Biosynthesis:Chain Elongation (Cont’d)

CH3(CH2)3CH2CO-S-ACPCH3CH2CH2C=CCO-S-ACP

H

H

NADPH+ H+

NADP+

CH3(CH2)13CH2CO-S-ACP

5 Cycles

Palmitoyl ACPCH3(CH2)13CH2CO2

-

PalmitateThioesterase

46

Fatty Acid Biosynthesis:Fatty Acid Synthase

in Animals• Consists of a single polypeptide containing seven distinct domains

• Conducts all steps in fatty acid synthesis except function of acyl CoA carboxylase

• Fatty acid synthase expression normally very low in most cells

47

Orlistat: A Fatty Acid Synthase (FAS) Inhibitor

Anti-obesity (Inhibitspancreatic lipase in git)

Inhibits thioesterase domain of FAS

Anti-cancer (experimental): FAS overexpressed in several tumor types; inhibition induces apoptosis

48

The Crystal Structureof a Mammalian Fatty Acid SynthaseTimm Maier, Marc Leibundgut, Nenad Ban*

Sept. 5, 2008

49

Further Processing of Fatty Acids: ElongationCH3(CH2)13CH2COSCoA

Palmitoyl CoA

CH3(CH2)13CH2COCH2COSCoA

CH3(CH2)13CH2CCH2COSCoA

OH

H

NADH + H+

NAD+

Thiolase

Dehydrogenase

L- Configuration

CH3COSCoA

In mitochondria andat surface of endoplasmic reticulum

50

Further Processing of Fatty Acids: Elongation (Cont’d)

CH3(CH2)13CH2CCH2COSCoAOH

H

CH3(CH2)13CH2C=CCOSCoAH

H

- H2O Hydratase

CH3(CH2)13CH2CH2CH2COSCoAStearoyl CoA

NADPH + H+

NADP+

Dehydrogenase

51

Further Processing of Fatty Acids: UnsaturationCH3(CH2)13CH2CH2CH2COSCoA

CH3(CH2)7C=C(CH2)7COSCoA + H2OH H

Stearoyl CoA

Oleoyl CoA

This reaction occurs in eukaryotesEndoplasmic reticulum membrane

Stearoyl CoADesaturase

O2

52

Further Processing of Fatty Acids: Polyunsaturation

CH3(CH2)7C=C(CH2)7CO2H

H HOleic acid

Plants: Further unsaturationoccurs primarily in this region

Animals: Further unsaturationoccurs primarily in this region

CO2H

(18:19)

9

Linoleic acid (18:29, 12)

12 9

Linolenic acid (18:312, 15)

15 12 9

Essential dietaryfatty acids in mammals

CO2H

53

Formation of Arachidonate in Mammals

Linoleic acid

CO2H14 11 8 5

Arachidonic acid (20:48, 11, 14)(Eicosa-5,-8,11,14-tetraenoic acid)

As CoA ester:1) Elongation2) Desaturation x 2

Prostaglandins

CO2H

54

Omega-3 Fatty AcidsCO2H

CO2H

-3 double bond Eicosapentaenoic acid (20:58, 11, 14, 17)

Docahexaenoic acid (22:67, 10, 13, 16, 19)

• Found in fish oils, esp. cold water fish• Important in:

Growth regulationModulation of inflammationPlatelet activationLipoprotein metabolism

55

Metabolite Regulation of Fatty Acid Synthesis and Breakdown

Pyruvate Acetyl CoA Malonyl CoA

Palmitoyl CoA

Citrate

Inhibits

Stimulates

BetaOxidation

Blocks

Glucose

56

Hormonal Regulation of Fatty Acid Synthesis and Breakdown

ATP cAMP AMPAdenylyl cyclase

Glucagon andepinephrine

Stimulates

Phosphodiesterase

Insulin

Stimulates

Activates Protein Kinase

Inactivates ACC byphosphorylation

Inhibition offatty acidsynthesis

Activates triacyl-glycerollipase

Inactivateslipase

57

Synthesis of Phosphatidate

O-

O

O-

O

O

O

O

CH2OC-R1

CHOC-R2

CH2OC-R3

CHO2C-R2

CH2O2C-R1

CH2OH

CH2O-P-O-

CH2O2C-R1

CHO2C-R2C=O

CH2OH

CH2O-P-O-CH2OH

CHOH

CH2OHDihydroxyacetone

Phosphate(from glycolysis)

Glycerol

Phosphatidate (formed in endoplasmic reticulum)

Diacylglycerol(important incell signaling)

R3COSCoA

Diacylglycerolacyltransferase(liver)

Triacylglycerol(transported toadipocytes andmuscle)

58

Synthesis of Glycerophospholipids

CH2OH

CH2O2C-R1

CHO2C-R2

N

N

NH2

O

O

OHOH

R3NCH2CH2OPOPO+

R=H; CDP ethanolamineR=CH3; CDP cholineCDP = cytidine diphosphate

Diacylglycerol

+ Transferase

R3=NH3; Phosphatidylethanolamine

R3=N(CH3)3; Phosphatidylcholine

O-

O

CO2-

CH2O-P-O-CH2CHNH 3

CH2O2C-R1

CHO2C-R2

+

+

CO 2-

HOCH 2CHNH3

HOCH 2CH2NH3+ Serine

Ethanolamine

O-

O

CHO2C-R2

CH2O2C-R1

CH2O-P-O-CH2CH2R3

+

+

Phosphatidylserine

59

Respiratory Distress Syndrome

Most frequently seen in premature infants

Also called hyaline membrane disease

Failure to produce sufficient dipalmitoyl phosphatidylcholine,which normally is found in the extracellular fluid surroundingalveoli; decreases surface tension of fluid to prevent lungcollapse

Treatment in infants born before 30 weeks includes administration of artificial lung surfactant (e.g., Exosurf orPumactant)

60

Synthesis of Glycero-phospholipids (Cont’d)

O-

O

CHO2C-R2

CH2O2C-R1

CH2O-P-O- CH2O-CDP

CH2O2C-R1

CHO2C-R2

Phosphatidate Cytidine diphosphate (CDP) diacylglycerol

Phosphatidyl-inositol

O-

O

OH

OHHO

OH OH

CH2O-P-O

CH2O2C-R1

CHO2C-R2

OH

OPO3H2H2O3PO

OH OH

OPO3H2

CH2OH

CH2O2C-R1

CHO2C-R2+

Diacylglycerol (DAG)

Phospholipase C(plasma membrane)

Both IP3 and DAG are important second messengersin cell signaling pathways

Inositol-1,4,5-triphosphate (IP3)

Phosphorylationof 4 & 5 OH groups

61

Synthesis of Glycero-phospholipids (Cont’d)

O-

O O

O-OH

CHO2C-R3

CH2O2C-R4

CH2O-P-O-CH2CHCH2-O-P-O-CH2

CH2O2C-R1

CHO2C-R2

CH2O-CDP

CH2O2C-R1

CHO2C-R2

Cytidine diphosphate (CDP) diacylglycerol

Cardiolipin: formed in innermitochondrial membrane;plays role in oxidativephosphorylation

62

Synthesis of Glycero-phospholipids (Cont’d)

O-

OCH2O-P-O-

CH2OH

C=O

Dihydroxyacetone Phosphate(from glycolysis)

O-

OCH2O-P-O-CH2CH2NH3

CH2-O-CH=CHR1

CHO2C-R2

+

Plasmalogens(Abundant in cardiactissue and CNS)

63

Synthesis of Sphingolipids+

CO 2-

HOCH 2CHNH3CH3(CH2)14COSCoA +

HCO3-2 CoASH

3-Ketosphingosine synthase

CH3(CH2)14CO-CHCH2OH

NH3+ 2S,3-Ketosphinganine

3 Steps

CH3(CH2)12CH=CH-CH-CH-CH2OH

OH

Ceramide

Palmitoyl CoA

Serine

trans

CH3(CH2)nCONH

64

Synthesis of Sphingolipids(Cont’d)

CH3(CH2)12CH=CH-CH-CH-CH2OH

CH3(CH2)nCONH

OH

CeramideO-

O +CH2O-P-O-CH2CH2N(CH3)3

CH2O2C-R1

CHO2C-R2

Phosphatidylcholine

Diacylglycerol

CH3(CH2)12CH=CH-CH-CH-CH2O-P-OCH2CH2N(CH3)3

CH3(CH2)nCONH

OH O

O-

+

Sphingomyelin

CerebrosidesGangliosides

trans

trans

65

Synthesis of Gangliosides

CH3(CH2)12CH=CH-CH-CH-CH2OH

CH3(CH2)nCONH

OH

Ceramide

CH3(CH2)12CH=CH-CH-CH-CH2O-Sugar

CH3(CH2)nCONH

OH

Cerebroside

Ganglioside

trans

transGlucose orgalactose

Ceramide - Sugar - Sugar - GalNAc - Gal

NANNAN = N-acetylneuraminateGalNAc = N-acetylgalactose

66

Lipid Storage Diseases(Gangliosidoses)

67

Tay-Sachs Disease

Ceramide - O - Glucose - Galactose - N-Acetylgalactose

Hexoseaminidase Acatalyzes cleavage of this glycoside linkage

GM2 (a ganglioside):

Autosomal recessive disorder characterized by deficiencyof hexoseaminidase A; accumulation of gangliosides in brainMost prevalent in Jews from Eastern EuropeFor further information see: http://www.marchofdimes.com/professionals/681_1227.asp

68

Other GangliosidosesGaucher’s disease:

Fabry’s disease:

Nieman-Pick disease:

Ceramide - O - Glucose

Ceramide - O - Glucose - O - Galactose - O - Galactose

Ceramide - Phosphate - Choline

-glucosidase

-galactosidase

sphingomyelinase

69

Synthesis of Eicosanoids

O-

O +CH2O-P-O-CH2CH2NR'3

CH2O2C-R

CHO2C

R’= H or CH3

In cell membrane

Hydrolysis of sn-2 ester bondby phospholipase A2 (PLA2)

-O2C

Arachidonate

70

Synthesis of Eicosanoids:PLA2 Activation

Various stimuli: Activation ofHormones, autacoids, etc. Membrane-bound

Receptors PLA2

Activity

Ca+2

Arachidonate release and eicosanoid synthesisare important mediators of tissue injury and inflammation

71

Synthesis of Eicosanoids:Prostaglandin Synthesis

CO2-O

O

CO2-

HO=O

O

O

Cyclicendoperoxide

Hydroperoxide

Prostaglandinendoperoxidesynthetase

(Cyclooxygenase)

Cyclooxygenase

Hydroperoxidase

Prostaglandin endoperoxide synthetase (also called cyclooxygenase) possesses both cyclooxygenase and hydroperoxidase activityTwo forms of cyclooxygenase: COX -1 - constitutively expressed COX -2 - inducible

PGH2

PGG2

CO2-

O-O-H

O

O

CO2-

OH

O

O

72

Cyclooxygenase (COX) InhibitorsNonsteroidal antiinflammatory drugs:

OCOCH3

CO2H

Acetylsalicylic acid(aspirin)

O - CCH3

CO2H

O

HOH2C

COX

Ser-530 CH2OCOCH3

COX

Irreversible inhibition of COX by acetylationof the active site

Actions of Aspirin:Antiinflammatory (COX-2 inhibition)GI injury (COX-1 inhibition)

73

COX-2 Selective Inhibitors

O

O

SO2CH3

Rofecoxib (Vioxx)

N

N

SO2NH2

CH3

F3C

Celecoxib (Celebrex)

Glucocorticoids block COX-2 expression

74

ProstaglandinsO

HO

CO2H

OH

HO

O

CO2H

OHHO

HO

CO2H

OH

CO2-

OH

O

O

PGH2

PGE2

PGD2

PGF2

Prostaglandins exhibit a varietyof actions on different tissues

75

Prostacyclin and Thromboxanes

O

HO2C OH

OH

CO2-

OH

O

O

PGH2 Prostacyclin (PGI2):Blocks platelet aggregation

Prostacyclinsynthase

O

O CO2-

OH

Thromboxane synthase

Thromboxane A2 (TxA2):Promotes platelet aggregation (t1/2 = 30 sec.)

O

OH

HO

CO2-

OH

Non-Enzymatic

Thromboxane B2 (TxB2):inactive

76

Leukotriene BiosynthesisCO2H

Arachidonic acid

CO2HOOH

5-Hydroperoxyeicosa-6,8,11,14-tetraenoic acid(5-HPETE)

5-Lipoxygenase

OCO2H

Leukotriene A4 (LTA4)

5-Lipoxygenase

OHCO2H

Cys

Gly Glu

S

GlutathioneLTC4 synthase

Leukotriene C4 (LTC4)OH

CO2H

CysS

Leukotriene E4 (LTE4)

- Glu- Gly

CO2HOH

LTA

Hydrolase

Leukotriene B4 (LTB4)

Leukotrienes areimportant mediatorsof inflammation

Cysteinyl leukotrienes

77

Leukotriene Biosynthesis (Cont’d)

CO2H

Arachidonic acid

HOO

CO2H12-Lipoxygenase

12-Hydroperoxyeicosa-5,8,10,14-tetraenoic acid(12-HPETE)

HO

CO2H

12-Hydroxyeicosa-5,8,10,14-tetraenoic acid(12-HETE)

78

Leukotriene Biosynthesis Inhibition

SCH-N-CONH2

CH3

OH

Zileuton (Zyflo)

An inhibitor of 5-lipoxygenaseUsed in the treatment of asthma

79

Cholesterol Biosynthesis: Formation of Mevalonate

2 CH3COSCoA CH3COCH2COSCoAThiolase

CH3COSCoA

Acetoacetyl CoA

HO2C-CH2-C-CH2COSCoA

OH

CH3

-Hydroxy--methyl-glutaryl CoA (HMG CoA)

HMG CoASynthase

HO2C-CH2-C-CH2CH2OH

OH

CH3

3R-Mevalonic acid

HMGCoAreductase

CoASH NADP + NADPH + H+

Key control stepin cholesterolbiosynthesis

Liver is primary site of cholesterol biosynthesis

80

Cholesterol Biosynthesis: Processing of Mevalonate

-O2C-CH2-C-CH2CH2OH

OH

CH3

Mevalonate

-O2C-CH2-C-CH2CH2OPOPCH3

OH

2 Steps

ATP5-Pyrophospho-mevalonate

CH2=C-CH2CH2OPOP

CH3

- CO2

- H2O

Isopentenylpyrophosphate

CH3-C=CH2CH2OPOPCH3

Dimethylallylpyrophosphate

Isomerase

81

Cholesterol Biosynthesis:Isoprenoid Condensation

H

OPOP

OPOP

Head

TailHead

Tail

IsopentenylPyrophosphate (IPP)

Dimethylallylpyrophosphate Head to tail

CondensationOPOP

Geranyl Pyrophosphate (GPP)

OPOP

Farnesyl Pyrophosphate (FPP)

Head to tailcondensationof IPP and GPP

Tail to tailcondensationof 2 FPPs

Squalene

Head Tail

Head Tail

Isoprenes

Geranyl transferase

Geranyl transferase

Squalene synthase

82

Isoprenoids• Widely distributed in nature• Generally contain multiple of 5 carbons:

• Monoterpene; 10 carbons• Sesquiterpene: 15 carbons• Diterpene: 20 carbons

OHOH

Menthol: a monoterpene

Lycopene: a tetraterpene

83

Conversion of Squalene to Cholesterol

OH +

CH3H3C

CH3

HO

CH3

CH3

CH3

HO

CH3

CH3

RCO2

Squalene

Squalenemonooxygenase

2,3-Oxidosqualenecyclase

Lanosterol

20 Steps

Cholesterol

Acyl-CoA:cholesterolacyltransferase Cholesterol esters

(principal transport form in blood)

O2

Squalene-2,3-epoxide

84

Inhibition of Cholesterol Biosynthesis

COSCoA

HOCO2

-CH3

C -S -CoA

HOCO2

-CH3

H

OH

][ HOCO2

-CH3

OH

HOCO2

-H

OH

CH2CH2

NF

C6H5NHCO

Atorvastatin (Lipitor):resembles intermediate

HMG CoA MevalonateIntermediate

HMGCoAreductase

85

Transformations of Cholesterol: Bile Salts

CO2-

HO

CH3

HO OHH

CH3

CONHCH2RCH3

CH3

HO

CH3

Cholesterol Cholic acid

R = CH2SO3- Taurocholate

R = CO2- Glycocholate

Detergents

86

Transformations of Cholesterol: Steroid Hormones

O

O

O

OH

OHHO

O

CH3

HO

CH3

Cholesterol

Estradiol

ProgesteroneCortisol

O

OH

TestosteroneHO

OH

CH2

HO

OH

OH Vitamin D