Green Tea Attenuates Oxidative Stress and Downregulates the Expression of Angiotensin II AT(1) Receptor in Renal and Hepatic Tissues of Streptozotocin-Induced Diabetic Rats

This study investigates the potential of green tea to modulate oxidative stress and angiotensin II AT(1) receptor expression in renal and hepatic tissues of diabetic rats. Three groups of rats were studied after 8 weeks following diabetes induction: normal, streptozotocin-induced diabetic (diabetic control), and green-tea-treated diabetic rats. Total antioxidant, catalase, and malondialdehyde levels were assayed by standard procedures. Levels of AT(1) receptor labeling, in renal and hepatic tissues of the three rat groups, were immunohistochemically investigated using an anti-AT(1) receptor antibody. Levels of total antioxidant and catalase were significantly reduced, whereas malondialdehyde levels and AT(1) receptor labeling were significantly increased in renal and hepatic tissues of diabetic control rats compared to normal rats. Compared to diabetic control rats, total antioxidant and catalase levels were significantly increased, whereas malondialdehyde levels and AT(1) receptor labeling in the green-tea-treated diabetic group were significantly reduced throughout hepatic lobules and renal cortical and medullary vascular and tubular segments to levels comparable to those observed in normal rats. The capacity of green tea to modulate diabetes-induced oxidative stress and AT(1) receptor upregulation may be beneficial in opposing the deleterious effects of excessive angiotensin II signaling, manifested by progressive renal and hepatic tissue damage.