Metabolic disturbances in diabetic cardiomyopathy.

It has been established that diabetes results in a cardiomyopathy, and increasing evidence suggests that an altered substrate supply and utilization by cardiac myocytes could be the primary injury in the pathogenesis of this specific heart muscle disease. For example, in diabetes, glucose utilization is insignificant, and energy production is shifted almost exclusively towards beta-oxidation of free fatty acids (FFA). FFA's are supplied to cardiac cells from two sources: lipolysis of endogenous cardiac triglyceride (TG) stores, or from exogenous sources in the blood (as free acid bound to albumin or as TG in lipoproteins). The approximate contribution of FFA from exogenous or endogenous sources towards beta-oxidation in the diabetic heart is unknown. In an insulin-deficient state, adipose tissue lipolysis is enhanced, resulting in an elevated circulating FFA. In addition, hydrolysis of the augmented myocardial TG stores could also lead to high tissue FFA. Whatever the source of FFA, their increased utilization may have deleterious effects on myocardial function and includes the abnormally high oxygen requirement during FFA metabolism, the intracellular accumulation of potentially toxic intermediates of FFA, a FFA-induced inhibition of glucose oxidation, and severe morphological changes. Therapies that target these metabolic aberrations in the heart during the early stages of diabetes could potentially delay or impede the progression of more permanent sequelae that could ensue from otherwise uncontrolled derangements in cardiac metabolism.