Myocardial insulin resistance and cardiac complications of diabetes

Cardiovascular disease is a major cause of mortality and morbidity in individuals with obesity, type 2 diabetes and the metabolic syndrome. The mechanisms for this are partially understood, but include increased atherosclerosis, hypercoagulability and increased hypertension. Epidemiological data suggests however, that a component of the excess cardiovascular mortality occurs independently of underlying coronary artery disease. Indeed, diabetes is an independent risk factor for the development of heart failure and the mechanisms responsible remain to be clarified. Insulin resistance in skeletal muscle, adipose tissue and the liver are widely recognized features of obesity and type 2 diabetes, and contribute to the pathogenesis of impaired glucose homeostasis. Insulin resistance has also been described in the vasculature, and may contribute to endothelial dysfunction and atherosclerosis. The heart is an insulin responsive organ and less is known about whether or not the heart becomes insulin resistant in diabetes and what the pathogenic consequences of this might be. This review will discuss the currently available evidence from human and animal studies, that the heart may become insulin resistant in obesity and type 2 diabetes. The potential consequences of this on cardiac structure, function and metabolism will be discussed as well as recent data from transgenic mice with perturbed cardiac insulin sensitivity that have shed interesting new insight into potential mechanisms linking cardiac insulin resistance with myocardial dysfunction in diabetes.