Antioxidant defense system in diabetic kidney: A time course study

Oxygen free radicals (OFRs) have been suggested to be a contributory factor in complications of diabetes mellitus. In the present study, we investigated the lipid peroxide level measured as thiobarbituric acid reactive substances (TBARS) and activities of antioxidant enzymes viz., [superoxide dismutase (SOD), catalase (CAT) and glutathione-peroxidase (GSH-Px)] in the kidney of streptozotocin induced diabetic rats at various stages of development of diabetes. Sprague Dawley rats were divided into two groups: group I, control (n = 42) and group II, diabetic (n = 42). Each group was further subdivided into seven groups each consisting of six rats. Rats in subgroups were studied at weekly intervals (0 to 6 weeks). Blood glucose levels were estimated at the time of sacrifice. TBARS levels and activity of antioxidant enzymes were measured in kidney. The levels of TEARS in the diabetic group increased initially, dropped to baseline level after 2 weeks and then progressively increased at 5(th) and 6(th) week (p < 0.05). There was an increase in catalase activity at first week after that it decreased as compared to control group. However, GSH-Px activity in the diabetic group increased after 1 week and then remained at the same level except a small drop in the 2nd week. Total SOD and CuZn-SOD activity increased significantly in diabetic kidney as compared to controls at all time intervals, while Mn-SOD activity showed no change. The present findings suggest that oxidative stress accompanies at early onset of diabetes mellitus and the susceptibility of the kidney to oxidative stress during the early stages may be an important factor in the development of diabetic nephropathy.