Diabetic cardiomyopathy is related directly to hyperglycemia. Cell death such as apoptosis plays a critical role in cardiac pathogenesis. Whether hyperglycemia induces myocardial apoptosis, leading to diabetic cardiomyopathy, remains unclear. We tested the hypothesis that apoptotic cell death occurs in the diabetic myocardium through mitochondrial cytochrome c-mediated caspase-3 activation pathway. Diabetic mice produced by streptozotocin and H9c2 cardiac myoblast cells exposed to high levels of glucose were used. In the hearts of diabetic mice, apoptotic cell death occurred as detected by terminal deoxynucleotidyl transferasemediated dUTP nick-end labeling (TUNEL) assay. Correspondingly, caspase-3 activation as determined by enzymatic assay and mitochondrial cytochrome c release detected by Western blotting analysis were observed. Supplementation of insulin inhibited diabetesinduced myocardial apoptosis as well as suppressed hyperglycemia. To explore whether apoptosis in diabetic hearts is related directly to hyperglycemia, we exposed cardiac myoblast H9c2 cells to high levels of glucose (22 and 33 mmol/l) in cultures. Apoptotic cell death was detected by TUNEL assay and DAPI nuclear staining. Caspase-3 activation with a concomitant mitochondrial cytochrome c release was also observed. Apoptosis or activation of caspase-3 was not observed in the cultures exposed to the same concentrations of mannitol. Inhibition of caspase-3 with a specific inhibitor, Ac-DEVD-cmk, suppressed apoptosis induced by high levels of glucose. In addition, reactive oxygen species (ROS) generation was detected in the cells exposed to high levels of glucose. These results suggest that hyperglycemia directly induces apoptotic cell death in the myocardium in vivo. Hyperglycemiainduced myocardial apoptosis is mediated, at least in part, by activation of the cytochrome c-activated caspase-3 pathway, which may be triggered by ROS derived from high levels of glucose.

These results suggest that attenuation of early-phase cardiac cell death by MT results in a significant prevention of the development of diabetic cardiomyopathy. This process is mediated by MT suppression of mitochondrial oxidative stress.

Diabetes is a serious public health problem. Improvements in the treatment of noncardiac complications from diabetes have resulted in heart disease becoming a leading cause of death in diabetic patients. Several cardiovascular pathological consequences of diabetes such as hypertension affect the heart to varying degrees. However, hyperglycemia, as an independent risk factor, directly causes cardiac damage and leads to diabetic cardiomyopathy. Diabetic cardiomyopathy can occur independent of vascular disease, although the mechanisms are largely unknown. Previous studies have paid little attention to the direct effects of hyperglycemia on cardiac myocytes, and most studies, especially in vitro, have mainly focused on the molecular mechanisms underlying pathogenic alterations in vascular smooth-muscle cells and endothelial cells. Thus, a comprehensive understanding of the mechanisms of diabetic cardiomyopathy is urgently needed to develop approaches for the prevention and treatment of diabetic cardiac complications. This review provides a survey of current understanding of diabetic cardiomyopathy. Current consensus is that hyperglycemia results in the production of reactive oxygen and nitrogen species, which leads to oxidative myocardial injury. Alterations in myocardial structure and function occur in the late stage of diabetes. These chronic alterations are believed to result from acute cardiac responses to suddenly increased glucose levels at the early stage of diabetes. Oxidative stress, induced by reactive oxygen and nitrogen species derived from hyperglycemia, causes abnormal gene expression, altered signal transduction, and the activation of pathways leading to programmed myocardial cell deaths. The resulting myocardial cell loss thus plays a critical role in the development of diabetic cardiomyopathy. Advances in the application of various strategies for targeting the prevention of hyperglycemia-induced oxidative myocardial injury may be fruitful.