[Investigation of a novel mechanism of diabetic complications: impacts of mitochondrial reactive oxygen species].

Large, prospective, clinical trials have confirmed the efficacy of intensive blood-glucose control to prevent the onset and progression of diabetic complications. However, since it is difficult to maintain blood glucose concentrations close to the normal range, the effect of intensive therapy to prevent diabetic complications may be limited. Other approaches are therefore required to prevent the progression of diabetic complications based on the elucidation of the biological mechanisms. In this review, the impacts of mitochondrial reactive oxygen species (ROS) on diabetes-related complications are described. In endothelial cells, high glucose levels increase mitochondrial ROS, and the normalization of mitochondrial ROS production by inhibitors of mitochondrial metabolism, or by the overexpression of UCP-1 or MnSOD, prevents the glucose-induced accumulation of sorbitol, activation of protein kinase C, and formation of advanced glycation end products, all of which are believed to be major molecular mechanisms of diabetic complications. We also demonstrated that 8-hydroxydeoxyguanosine, which represents mitochondrial oxidative damage, was elevated in patients with either retinopathy, albuminuria, or the increased intima-media thickness of carotid arteries compared to patients without diabetic vascular complications. In addition, to investigate the impact of mitochondrial ROS on diabetic retinopathy in vivo, we established a novel transgenic mouse, which specifically expressed MnSOD in endothelial cells. By the introduction of diabetes, levels of urinary 8-hydroxydeoxyguanosine and expressions of VEGF and fibronectin mRNA in retinas were increased in wild type littermates; however, these observations were ameliorated in transgenic mice. Taking the results together, hyperglycemia could induce mitochondrial ROS production, associating it with the pathogenesis of diabetic vascular complications.