Diabetic retinopathy: Mitochondrial dysfunction and retinal capillary cell death

Oxidative stress is increased in the retina in diabetes; the levels of oxidatively modified DNA and nitrosylated proteins are elevated, and antioxidant defense enzymes are impaired. The levels of superoxides are elevated in the retina, and the mitochondria become dysfunctional with proapoptotic protein, Bax, translocating from the cytosol into the mitochondria, and cytochrome c leaking out from the mitochondria. This is accompanied by increased retinal capillary cell apoptosis, and the formation of acellular capillaries and pericyte ghosts, the early signs of retinopathy in animal models of diabetic retinopathy. Inhibition of superoxides inhibits glucoseinduced mitochondrial dysfunction, activation of caspase-3, and cell death in retinal capillary cells. In animal models, long-term administration of lipoic acid or other antioxidants inhibits the development of diabetic retinopathy via inhibition of accumulation of oxidatively modified DNA and nitrotyrosine and capillary cell apoptosis in the retina. Understanding the role of mitocbondria in the development of retinopathy in diabetes should help identify therapies that can neutralize superoxides and inhibit their dysfunction and, ultimately, the development of retinopathy.