Effects of Type II diabetes on coronary vasodilation.

• By Matthew Cozier

Research Project 3003MSC

• Supervisor: Roselyn Rose'Meyer• Lab partners; Lynette Burges & Katie Crane

Overview

1. Aims & Hypothesis

2. Introduction– Epidemiology of diabetes, – Effects of hyperglycemia – Coronary heart disease & pathological mechanisms

3. Materials & Methods

4. Results

5. Discussion & Conclusion

Hypothesis

Type II diabetes affects the mechanism of ischemia induced vasodilation, and potentiates the risk of coronary heart disease.

(Cozier et al., 2008)(Cozier et al., 2008)

AimsTo measure

Coronary vasodilatory mechanisms

Fasting blood glucose levels,

Blood pressure,

Heart and body weight,

Coronary flow rate

Potassium levels in adipose and skeletal muscle tissues.

Between groups consisting of male Wistar rats with or without 3

weeks dietary intervention of 5% glucose, and age-matched Zucker

obsese rats

Introduction

• Diabetes Melitus (DM) is a 'metabolic syndrome'.• DM associated with the onset & progression of

coronary heart disease (CHD)†

• Accounts for 10% of the global expenditure of health care.*

† Hanley AJ, Williams K, Stern MP, Haffner SM (2002): Homeostasis model assessment of insulin resistance in relation to the incidence of cardiovascular disease: the San Antonio Heart Study. Diabetes Care 25: 1177–1184, 2002.* Diabetes Atlas. Gan D, Ed. Brussels, Belgium, International Diabetes Federation, 2003

Worldwide mortality of diabetes

Wild SH., Roglic G., Green a., Sicree R., King H., Global Prevalence of Diabetes. Estimates for the year 2000 and projections for 2030. Diabetes Care 27;(5)1047-1053

(Wild et al., 2000)(Wild et al., 2000)

<3%<3%

<3%<3%

3-5%3-5%

3-5%3-5%

3-5%3-5%

6-8%6-8%

6-8%6-8%>8%>8%

Suboptimal Suboptimal provision of health provision of health care for diabeticscare for diabetics

High prevalence of High prevalence of type II diabetes high type II diabetes high –associated with –associated with increased obesityincreased obesity

Diabetes Epidemiology & Projections

• Worldwide by 2010; 218.3 Million people 97% will have Type II Diabetes.

2 out of 3 patients with type II diabetes will suffer from cardiovascular disease... 141.9 Million people

Diabetes is the greatest risk factor for CHD*

* de Courten M, Zimmet P (1997) Screening for non-insulin-dependent diabetes mellitus: where to draw the line. Diabet Med 14: 95±98 Danaei G., Lawes C.M., Vander Hoorn S., et al., Global and regional mortality from ischaemic heart disease and stroke attribute to higher-than-optimum blood glucose concentration: Comparative risk assessment. Lancet. 2006; 368:1651-1659.

Type II Diabetes

• Resistance to insulin and hyperglycemia.• Attributed to obesity, poor diet and lack of

exercise.• Progresses from a state of ’pre-diabetes.’

– Pre-diabetes; Similar symptoms exist – yet glucose levels considered sub-acute

• Signs & Symptoms; – increased thirst, – increased hunger,– fatigue, – increased urination, especially at night, – weight loss, blurred vision, – sores that do not heal.

The pathobiology of diabetes Type II

• Affects physiology– Hyperglycemia– Dehydration– Hypokalemia– Ketoacidosis

The pathobiology of diabetes Type II

• Affects cell biology– Cell metabolism → produciton of O

2 radicals

– Cell signalling - intracellular signalling cascades.– Cell function (tissue specific)

• -->> Vasodilatory mechanisms << --

Cardiovascular complications.

Mechanisms of ischemia induced Vasodilation

• 2 main Pathways– NO induced

• Nitric oxide is derived from many tissues end product of arginine catabolism, catalysed by NOS.

Mechanism of Action. NO → NO receptor → cGMP → PKG → Relaxation of Smooth muscle.

Nitroprusside - NO receptor Agonists;

Mechanisms of ischemia induced Vasodilation

• Adenosine Mediated• Adenosine is the end product of ATP

dephosphorylation

Adenosine → A2 Adenosine Receptors

→ cAMP → PKA → K-ATP channel activation → Hyperpolarisation of the cell membrane → vasodilation.

A link between metabolic state of the heart and function of the cardiac vasculature.

NECA; Adenosine AnalogueDiazoxide; K-ATP channel opener

The Downward Spiral.

Myocardial Myocardial InfarctionInfarction

Myocardial Myocardial IschemiaIschemia

Poor Poor PerfusionPerfusion

Tissue Tissue Necrosis & Necrosis & Tissue Tissue DamageDamage

Cardiac Cardiac DysfunctionDysfunction

DeathDeath

BadBad

Much

Much Badness

Badness

ReperfusionReperfusion

Tissue Tissue RecoveryRecovery

Normal Normal Function of Function of the heartthe heart

Green = VasodilationGreen = Vasodilation

Red = No VasodilationRed = No Vasodilation

Materials & Methods

• Animal Models;– 12 Male Wistar Rats

• 6 Control• 6 rats Glucose treated - fed upon a diet consisting of 5%

– 6 Male Zucker obese Rats

The Zucker Rat

Materials & Methods

Langendorf reperfusion apparatus...

• Heart Rates• Coronary pressure• LVDP• Rate of ventricular systole• Rate of ventricular diastole

Results

* P < 0.05 vs Control† P < 0.05 vs Glucose treated

Results

* P < 0.05 vs Control† P < 0.05 vs Glucose treated

Results

* P < 0.05 vs Control† P < 0.05 vs Glucose treated

Results

* P < 0.05 vs Control

Results

**

* P < 0.05 vs Control

Results

* P < 0.05 vs Control

Results

* P < 0.05 vs Control

Results

* P < 0.05 vs Control

Results

[Nitroprusside][Nitroprusside]

Conclusions• Both glucose treated and Zucker obese rats are

pre-diabetic. – Insulin resistance observed– Hyperglycemia– Exhibited some degree of resistance to the diazoxide,

NECA and nitroprusside.

• Type II diabetes attenuates the coronary vasodilatory response to myocardial ischemia. – May explain the reduced recovery rates in those

suffering from both diabetes and cardiovascular heart disease.

All aims have been achieved; experiment successful.

Future Directions

• Determine how diabetes affects the actions of endogenous and exogenous vasodilatory compounds

• Determine the diabetic rat hearts sensitivity to numerous vasoconstrictors, and new drugs that have not yet been considered such as glibenclamide.

• Identify how the body handles potassium in type II diabetes and determine how this may impact upon vasodilation.

• Use the Zucker lean rats may as a more suitable candidate for further experimentation in order to reduce genetic variability between populations and yield more precise data.

• Take advantage of novel methods of observing the ‘energetics’ of the heart in order to observe the effects of diabetes at a metabolic level.

• Investigate protein modification and levels of expression in myocytes, vascular endothelium and many other cell types isolated from rats with II diabetes.

Roselyn Rose’MeyerRoselyn Rose’Meyer

Lynette Burges & Katie Crane