Role of 8-isoprostane as an oxidative stress marker in streptozotocin induced diabetic nephropathy in male rats and its correlation with angiotensin II

To evaluate the role of 8-isoprostane as a contributor of diabetic nephropathy [DN], its usefulness as an early marker of oxidative stress, and its correlation with serum and intrarenal angiotensin II [Ang II] production. The study was conducted on 40 age and weight [250-300 g] matched male albino rats. Ten rats were vehicle treated and served as controls, they constituted group I. The remaining 30 rats were made diabetic for 4 weeks by single intravenous streptozotocin [STZ] injection [50 mg/kg]. The diabetic rats were subdivided into 3 groups. Group II: untreated diabetic rats [n=10], group Ill: insulin treated diabetic rats [n=10], they received subcutaneous insulin injections [3 U/rat/day] for 4 weeks. Group IV diabetic rats [n=10], received combined subcutaneous insulin [3 U/rat/day] and intraperitoneal vitamin E [alpha-tocopherol 20 mg/day] for 4 weeks starting from the first day of the experiment. Blood and 24 hours urine samples were collected from all rats at the end of the 1[st], 2[nd], 3[rd] and 4[th] weeks of the study for determination of serum urea, and urinary excretion rates of proteins and 8-isoprostane. At the end of the study period [4 weeks], blood samples were obtained from all rats by cardiac puncture under ether anesthesia. The rats were sacrificed and kidneys were removed for determination of Ang II in kidney tissue homogenates. Final serum glucose, Ang II, and 8-isoprostane were measured. Untreated diabetic rats showed progressive increase in serum urea, proteinuria, and urinary 8-isoprostane excretion rate throughout the whole study, as compared to control ones. Moreover, serum glucose, 8-isoprostane, Ang II, and kidney tissue Ang II were significantly higher in untreated diabetic rats. Insulin treatment significantly reduced the measured parameters in group III rats as compared to group II. A further decrease of the measured parameters was observed after combined insulin and vitamin E treatment in group IV rats. However, the values did not reach basal levels. Increased serum 8-isoprostane and intrarenal Ang II levels as a result of oxidative stress may contribute to the development of DN in hyperglycemic rats. Insulin in combination with vitamin E may exert a more beneficial effect in reducing or retarding the rate of deterioration of diabetic kidney than insulin alone. The advances in the understanding of the 8-isoprostane pathway not only as an early marker of oxidative stress but also as a culprit in the genesis of target organ damage, may lead to novel therapeutic approaches for several diseases resulting from oxidative stress