MECHANISMS OF MYOCARDIAL ISCHEMIC INJURY IN DIABETES

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DESCRIPTION: (Verbatim from the application): The long term objective of this proposal is to determine if impairment of cardioprotective signal transduction and increased oxidative stress are mechanisms responsible for the exacerbation of myocardial ischemic injury in diabetes and hyperglycemia, using an integrated cellular and physiological approach. Coronary artery disease is the leading cause of death in diabetic patients, and hyperglycemia has been described as one of the strongest predictors of death after acute myocardial infarction in both diabetic and non-diabetic patients. Recent findings from this laboratory have demonstrated that acute hyperglycemia abolishes the protection afforded by the early phase of ischemic preconditioning, an endogenous cardioprotective mechanism mediated by activation of adenosine receptors, protein kinase C (PKC) and adenosine triphosphate-regulated potassium (KATP) channels. Experiments conducted to meet Specific Aim 1 will address the hypotheses that acute hyperglycemia (dosedependently) and acute (3 weeks) and chronic (6 months) diabetes (alloxan/streptozotocin) exacerbate myocardial injury during ischemia and abolish the protection afforded by early and late ischemic preconditioning in canine myocardium. Specific Aim 2 will address the hypotheses that hyperglycemia and diabetes attenuate cardioprotective signal transduction via inhibition of adenosine receptor (A1 and A3), PKC, and KATP channel activation. In vivo canine experiments measuring the reduction in myocardial infarct size in response to specific agonists will be complemented by in vitro experiments. Sarcolemmal KATP channel activity will be assessed using patch clamp techniques, mitochondrial KATP channel activity measured with flavoprotein fluorescence, interstitial adenosine concentrations determined with HPLC, and PKC isoforms quantified in control, hyperglycemic and diabetic dogs. The hypothesis that oxygen-derived free radicals contribute to enhanced myocardial injury via interactions with adenosine and KATP channels will be further investigated during Specific Aim 3. Experiments wifi be conducted in animals after chronic treatment with the antioxidants, tempol or dimethyithiourea, to reverse the deleterious effects of increased oxidant stress on the extent of ischemia and reperfusion injury, interstitial adenosine concentration and KATP channel activity induced by diabetes and hyperglycemia. The duration and severity of diabetes and hyperglycemia will be specifically examined as determinants of degree of oxidant stress. Thus, this proposal will delineate mechanisms responsible for the adverse consequences of diabetes and hyperglycemia during myocardial ischemia using an integrated approach of in vivo and cellular techniques.