the potential role of vanadyl sulfate as an anti-diabetic agent used to treat non- insulin-dependent...

The Potential Role of Vanadyl Sulfate As An Anti-diabetic Agent

Used to Treat Non-Insulin-Dependent Diabetes Mellitus

Presented ByChristopher Theberge, B.S.

NIDDM Statistics90%-95% of diabetes diagnoses15.7 million Americans inflicted About 800,000 new diagnoses per yearIncreases risk of other life-threatening

diseasesCosts taxpayers $105 billion dollars per

year

VanadiumShellfish, mushrooms, and parsley rich

in the elementUpper limit 1.8 mg/day of elemental

vanadium set for adults 19 years and older

Most diets supply ~15 ug/dayNeeded for normal growth and

development but exact role undefined

Why Vanadium?

• Inhibit Phosphotyrosine Phosphatases leading to enhanced receptor Phosphorylation and tyrosine kinase activity (IRTK)• Stimulate glucose uptake without any change in IRTK activity

High doses In Vivo and In Vitro:

•Insulin mimetic-effects

Previous Animal Studies

Vanadium Salts Shown To

Hexose Transport

Lipogenesis

Glucose Oxidation

Glycogen synthase

Fasting and FedGlucose Levels

Improve OGT

Restore Early Insulin Secretion

Mimic Insulin

Previous Human Studies

Vanadium Salts Shown To

Glycolysis

Glycogen synthesis

Lipogenesis

Gluconeogenesis

Liver Skeletal Muscle

Augment glucose uptake by

Glycogen Formation

Some Reasoning Behind the Following Studies

•Takes at least 4 weeks to exert its effects

•VOSO4 most active intracellular form

•Sample sizes of 8 or less subjects

•Conflicting results

•Safety and efficacy of Vanadium unknown

•VOSO4 dose dependent

Metabolic Effects of Vanadyl Sulfate Metabolic Effects of Vanadyl Sulfate in Humans With Non-Insulin -in Humans With Non-Insulin -

Dependent Diabetes Mellitus: In Vivo Dependent Diabetes Mellitus: In Vivo and In Vitro Studiesand In Vitro Studies

Metabolism, Vol 49, No 3 (March), 2000: pp 400-410Metabolism, Vol 49, No 3 (March), 2000: pp 400-410

Goldfine et al.Goldfine et al.

Goldfine et al.

Investigated efficacy and mechanism of action of VOSO4 as an oral hypoglycemic agent

Subjects • 16 Type II diabetics (11 Males, 5

Females)• Age 45.9 +/- 10.2 years

• Not using Vanadium supplementation• BMI 33.8 +/- 8.1 kg/m2

Goldfine et al. Self-Controlled Study Design

12 weeks

Weeks 4-10: VOSO4 ingested at 25, 50, or 100 mg doses 3x/day

75, 150, and 300 mg/day

Weeks 10-12: Insulin sensitivity with 2-step euglycemic clamp

Week 1: Baseline lab testing

Weeks 2 & 3: Placebo 3x/day

Week 4: Insulin sensitivity with 2-step euglycemic clamp

Goldfine et al.

Methods/Measurements

• Hepatic glucose production (HGP)

• Oxidative vs nonoxidative glucose disposal

• Serum levels of thiobarbituric acid-reactive substances (TBARS)

•Serum triglyceride (TG) Apo A & B

Goldfine et al.

Methods/Measurements (cont.)

•Muscle biopsy to test effect of VOSO4 on insulin-sensitive cellular enzymes

• Phosphatidylinositol 3-kinase (PI 3-K) & Insulin Receptor Substrate 1 (IRS-1) • Glycogen synthase • Phosphotyrosine phosphatase

Goldfine et al.

GI disturbances with 150 mg VOSO4/day in some subjects

Cramping, abdominal discomfort, or diarrhea in all with 300 mg VOSO4/day

Peak serum levels and time to achieve them varied greatly between subjects

Linear correlation between peak serum level and VOSO4 dose

Results

Goldfine et al.

Effect of VOSO4 on HbA1c

6

7

8

9

Placebo Vanadyl

150 mg

300 mg

P<0.05

P=0.05

HbA1c (%)

Adapted from Goldfine et al. Metabolic Effects of Vanadyl in Human NIDDM. Metabolism, 2000.

Goldfine et al.

Mean fasting glucose significantly only in 300 mg group

Insulin sensitivity improved in several subjects at 150 mg and 300 mg doses only.

Results (cont.)

Goldfine et al.

Basal HGP and suppression from insulin at all doses

Oxidative and nonoxidative glucose metabolism

TBARS @ 300 mg/dayGlycogen synthase Phosphotyrosine phosphataseSubject weightSerum TG Apo A or Apo B

Results (cont.)

No Significant Changes In:

Effect of 150 mg/day VOSO4 on PI 3-K, insulin receptor, IRS-1 and Shc

0

1

2

3

4

5

6

- + - + - + - + - + - + - + - +

PI 3-K

InsulinPre-V Post-V Pre-V Post-V Pre-V Post-VPre-V Post-V

InsulinReceptor

IRS-1

Shc

FoldStimulation

*p=0.02**p<0.01 vs basal

*

**

*

**

**

Adapted from Goldfine et al. Metabolic Effects of Vanadyl in Human NIDDM. Metabolism, 2000.

Results/Conclusions

•Vanadyl may act at other steps of insulin action

•Tissue Phosphatases may not accurately reflect tissue target for VOSO4 to enhance insulin signaling

•Serum Vanadium levels hardly detectable after 2 weeks

Limitations Small sample size (More

Males)

Significant distribution of age and BMI

Meal content and inconsistent meal timings

Absorption rates and GI side effects

Lower levels of peak serum could not be assessed by pill count or patient adherence

<5% of ingested Vanadium normally absorbed

Peak serum levels may not reflect levels achieved at cellular site of action

VOSO4 relatively weak Ptase inhibitor

Vanadyl Sulfate Improves Vanadyl Sulfate Improves Hepatic and Muscle Insulin Hepatic and Muscle Insulin

Sensitivity in Type 2 DiabetesSensitivity in Type 2 Diabetes

JCE & M, Vol. 86, Np. 3, 2001: pp 1410-1417JCE & M, Vol. 86, Np. 3, 2001: pp 1410-1417

Cusi et al.Cusi et al.

Cusi et al.

Reexamine effects of VOSO4on glycemic control, insulin secretion, EGP, and

insulin-mediated whole body glucose disposal.

Subjects

Cusi et al.

• 11 poorly controlled Type II diabetics (7 Males, 4 Females)

•Ages 59 +/- 2 years

•BMI 28.9 +/- 1.1 kg/m2

•6 subjects being treated with sulfonylurea

•5 Non-diabetics (3 Males, 2 Females)

Study DesignCusi et al.

Non-diabetics received euglycemic clamp and served as control group

Study Design (cont.)

Cusi et al.

1. Instructed on weight-maintaining ADA diet

2. 75-g Oral Glucose Tolerance Test (OGTT) after 12 hour fast

3. Euglycemic clamp at interval of 3-7 days

Baseline Testing in Treatment Group

Study Design (cont.)

Cusi et al.

2 week titration period with 25 mg VOSO4 2x/day

4 weeks-50 mg doses 3x/day

Total Daily Dose: 150 mg/day

Plasma Vanadium levels determined before and after 6 week treatment and 6 weeks thereafter

Methods/MeasurementsCusi et al.

•Fasting Plasma Glucose (FPG) during OGTT

•Endogenous Glucose Production (EGP)

•Whole body insulin-mediated glucose disposal

•Treatment response to FPG, HbA1c & fructosamine

Euglycemic Clamp:

150

160

170

180

190

200

210

Cusi et al.

0 2 4 6 Week

(mg/dL)

FPG After 6 Weeks of VOSO4 Treatment

* *

* P<0.01

Adapted from Cusi et al. VOSO4 Improves Hepatic and Muscle Sensitivity In NIDDM. JCE &M, 2001.

ResultsPlasma fructosamine significantly decreased at 4

weeks and HbA1c at 6 weeks

Diarrhea (n=4) & abdominal discomfort (n=2)

Plasma glucose concentration reduced about 30 mg/dL during OGTT

Plasma insulin lower during OGTT suggesting improved insulin sensitivity

Cusi et al.

Cusi et al.

Results (cont.)No Change in:

Subject Weights

Basal EGP Before and After VOSO4 Treatment

0

1

2

3

4

5

BeforeTreatment

VOSO4 Non-DiabeticControls

EGP(mg/kg LBM.min)

Diabetics

P<0.01

Adapted from Cusi et al. VOSO4 Improves Hepatic and Muscle Sensitivity In NIDDM. JCE &M, 2001.

*

*P<0.01

Whole Body Insulin-Mediated Glucose Disposal Before and After VOSO4 Treatment

0

2

4

6

8

10

BeforeTreatment

VOSO4 Non-DiabeticControls

Insulin-Mediated Glucose Uptake

(mg/kg LBM.min)

Diabetics

P<0.03*

* P<0.01

Adapted from Cusi et al. VOSO4 Improves Hepatic and Muscle Sensitivity In NIDDM. JCE &M, 2001.

Conclusions Close correlation between basal EGP reduction and

improved FPG suggesting VOSO4 has an impact on liver

Insulin sensitivity did not correlate with the decline in FPG after treatment with skeletal muscle

VOSO4 did not stimulate insulin secretion

Serum Vanadium levels returned to normal after 6 weeks discontinuation

Cusi et al.

Limitations

Small sample size (Again, more males)

Changing diet for study may have affected results

Subjects had poorly controlled diabetes

Sulfonylureas and diet or alone

Cusi et al.

ConclusionsVOSO4 appears to be effective on lowering

glucose levels through improved insulin sensitivity in muscle tissue without change in weight

Appears to be relatively well-tolerated and safe short-term

Vanadium reduced basal EGP suggesting has ability to ameliorate hepatic insulin resistance

ConclusionsVOSO4 did not correlate with overall muscle tissue

phosphatases

Activity of specific phosphatases hard to isolate may be affected by VOSO4

Phosphatases in specific tissues differentially affected

Inhibition in vivo is lost in vitro

Conclusions

Finally:

VOSO4 is capable of becoming oxidized to vanadate in vivo, leading to less activating potential

Effects may be different in non-Caucasian population

Future ImplicationsLong term effects of Vanadium must

be assessed More studies needed on humans

(Races?)Effects are minimal to consider it a

pharmacological optionNewer and more effective Vanadium

analogues are under development