Decreased susceptibility of liver mitochondria from diabetic rats to oxidative damage and associated increase in α-tocopherol

Abstract

The susceptibility of mitochondria from liver and kidney of diabetic and normal rats to in vitro oxidative damage was assessed. Mitochondria were isolated from diabetic rats 4 weeks after streptozotocin injection and from age-matched, normal rats. Liver mitochondria from diabetic rats were less susceptible to oxidative damage (induced by Fe 3+/adenosine 5′-diphosphate (ADP) xanthine/xanthine oxidase), as assessed by the formation of thiobarbituric acid reacting substances (TBARS) and sulfhydryl loss, than were mitochondria from normal rats. The decreased susceptibility of liver mitochondria from diabetic rats to oxidative damage correlated with a sevenfold increase in mitochondrial α-tocopherol levels. Activities of the antioxidant enzymes, glutathione reductase, glutathione peroxidase, and superoxide dismutase, were lower in liver mitochondria from diabetic compared to normal rats. Manipulation of dietary α-tocopherol, to counteract the increased intake of α-tocopherol due to diabetes-associated polyphagia, failed to lower liver mitochondrial α-tocopherol to the levels found in normal rats. Mitochondria from kidney of diabetic rats were equally as susceptible to in vitro oxidative damage as kidney mitochondrial from normal rats. They had increased levels of superoxide dismutase and glutathione peroxidase but identical levels of α-tocopherol compared to mitochondria from normal rats. Dietary manipulation of α-tocopherol had no effect on kidney mitochondrial levels of the nutrient.