Diabetic cardiomyopathy and its prevention by metallothionein: experimental evidence, possible mechanisms and clinical implications.

Cardiac failure is a leading cause for the mortality of diabetic patients, in part due to a specific cardiomyopathy, referred to as diabetic cardiomyopathy, which occurs with or without co-existence of vascular diseases. Although several mechanisms responsible for diabetic cardiomyopathy have been proposed, oxidative stress is widely considered as one of the major causes for the pathogenesis of the disease. Thus, a few laboratories are trying to develop antioxidants used to prevent diabetic cardiomyopathy. Metallothioneins (MTs) are cysteine-rich metal-binding proteins with several biological roles including antioxidant property. We and others have indicated the significant cardiac protection of MT against diabetes using cardiac-specific MT-overexpressing transgenic mice and OVE26MT mice (cross-bred of cardiac MT transgenic mice with genetically engineered diabetic OVE26 mice). Several possible mechanisms responsible for MT's cardiac protection from diabetes were revealed. These include MT's important roles in calcium regulation, zinc homeostasis, insulin sensitization, and antioxidant action. Since MT is ubiquitously expressed in mammalian tissues and is highly inducible by a variety of reagents such as zinc, the clinical potential for inducing cardiac MT as an antioxidant by zinc supplementation to prevent various diabetic complications, including cardiomyopathy, has been explored in diabetic animal models and patients. Since zinc has been therapeutically used for several other non-diabetic diseases in clinics, it provides further potential use of zinc for diabetic patients. Therefore, this review will briefly introduce the biochemical features of MT along with its critical roles in redox homeostasis and antioxidant function in the heart, and then discuss the current research on the prevention of diabetic cardiomyopathy by MT with an emphasis on experimental evidence, possible mechanisms, and clinical implications.