Nitric Oxide and the Diabetic Heart

Introduction and aim: The concept of diabetic cardiomyopathy, i. e. ventricular dysfunction in patients with diabetes without atherosclerotic coronary artery disease, has gained much credence in recent years. In these patients, myocardial contractility is impaired and diastolic inflow abnormal, resulting in a particularly high risk for heart failure. The radical nitric oxide (NO) plays a crucial role in coronary and cardiac physiology and appears to be important in diabetic cardiomyopathy as well. A dysregulation of cardiac myocyte endothelial NO synthase (eNOS) in the course of diabetes and/or a reduced bioavailability of NO due to oxidative stress factors have been suggested. However, studies using NO donor drugs or NOS inhibitors have yielded equivocal results. Therefore, many aspects of NO function in diabetic hearts need to be clarified, including the respective importance of eNOS and inducible NOS, the mechanisms of altered eNOS regulation, and the functions of NO metabolites (specifically peroxynitrite). The aim of this project is to study the role of NO in the cardiac complications of diabetes in a novel transgenic mouse model overexpressing eNOS exclusively in cardiomyocytes. Methods: eNOS transgenic mice and control littermates will be treated with the ß-cell toxin streptozotocin, resulting in hyperglycaemia and catabolic weight loss within several weeks (type I diabetes model). Four weeks after treatment, heart function will be determined in vitro in normoxia and following ischaemia/reperfusion stress that is known to generate oxygen free radicals. To complement the functional studies, a number of biochemical variables that depend on, or are affected by, NO and oxidative stress will be studied, including eNOS transcription and expression, NO and NO metabolite formation, and myocardial Ca2+ regulation. Specific goals: The project comprises 3 sections: The first objective is to evaluate the contractile performance and to determine how supplemental endogenous NO affects contractile diabetic cardiomyopathy. The second objective is to test the hypothesis that altered myocardial NO metabolism (oxidative stress, peroxynitrite generation) plays a causal role in diabetes-induced contractile dysfunction. The third objective is to determine the role of eNOS in the regulation of cellular Ca2+ homeostasis in diabetes. The proposed work is expected to provide new insights into the molecular mechanisms underlying the pathophysiological role of the cardiomyocyte NO system in diabetes. The results may have important implications for the development of NO-related drugs for the treatment of diabetic cardiomyopathy.

Introduction and aim: The concept of diabetic cardiomyopathy, i. e. ventricular dysfunction in patients with diabetes without atherosclerotic coronary artery disease, has gained much credence in recent years. In these patients, myocardial contractility is impaired and diastolic inflow abnormal, resulting in a particularly high risk for heart failure. The radical nitric oxide (NO) plays a crucial role in coronary and cardiac physiology and appears to be important in diabetic cardiomyopathy as well. A dysregulation of cardiac myocyte endothelial NO synthase (eNOS) in the course of diabetes and/or a reduced bioavailability of NO due to oxidative stress factors have been suggested. However, studies using NO donor drugs or NOS inhibitors have yielded equivocal results. Therefore, many aspects of NO function in diabetic hearts need to be clarified, including the respective importance of eNOS and inducible NOS, the mechanisms of altered eNOS regulation, and the functions of NO metabolites (specifically peroxynitrite). The aim of this project is to study the role of NO in the cardiac complications of diabetes in a novel transgenic mouse model overexpressing eNOS exclusively in cardiomyocytes. Methods: eNOS transgenic mice and control littermates will be treated with the ß-cell toxin streptozotocin, resulting in hyperglycaemia and catabolic weight loss within several weeks (type I diabetes model). Four weeks after treatment, heart function will be determined in vitro in normoxia and following ischaemia/reperfusion stress that is known to generate oxygen free radicals. To complement the functional studies, a number of biochemical variables that depend on, or are affected by, NO and oxidative stress will be studied, including eNOS transcription and expression, NO and NO metabolite formation, and myocardial Ca2+ regulation. Specific goals: The project comprises 3 sections: The first objective is to evaluate the contractile performance and to determine how supplemental endogenous NO affects contractile diabetic cardiomyopathy. The second objective is to test the hypothesis that altered myocardial NO metabolism (oxidative stress, peroxynitrite generation) plays a causal role in diabetes-induced contractile dysfunction. The third objective is to determine the role of eNOS in the regulation of cellular Ca2+ homeostasis in diabetes. The proposed work is expected to provide new insights into the molecular mechanisms underlying the pathophysiological role of the cardiomyocyte NO system in diabetes. The results may have important implications for the development of NO-related drugs for the treatment of diabetic cardiomyopathy.