Role of oxygen derived radicals for vascular dysfunction in the diabetic heart: Prevention by α-tocopherol?

The evidence that the generation of reactive oxygen intermediates (ROI) plays an important role for the increased cardiovascular risk in diabetes is summarised. In addition to the well known parameters of oxidative stress as lipid hydroperoxides and thiobarbituric acid substances (TBARS), recent observations indicate that isoprostanes which can be taken as a more specific parameter of oxidative stress, are generated in higher amounts by diabetic patients. This increased formation of isoprostanes can be inhibited by an instalment of a close metabolic control or the supplementation with tocopherol. The cause for the elevated oxidative stress is not yet fully understood, however the autoxidation of glucose, the formation of advanced glycation endproducts and the activation of NADPH-oxidase seem to be relevant processes. Since ROI are able to quench nitric oxide and to inhibit the synthesis of prostacyclin, the antithrombotic, vasodilating and antiatherosclerotic properties of endothelium are impaired in diabetes. Additionally, the balance of endothelial mediators released by endothelium is shifted to angiotensin II and endothelin, compounds which enhance the proliferation of smooth muscle cells and may limit the coronary reserve of myocardium. The activation of the transcription factor NF-κB by glucose and its autoxidative products is regarded as a key event in the transformation of the vasculature in diabetes. Epidemiological observations and very recent clinical studies underlie the impact of ROI for the development of cardiovascular complications in diabetes and suggest that an antioxidative treatment might be helpful to reduce the cardiac risk in diabetes.