Green Tea Attenuates Oxidative Stress and Downregulates the Expression of Angiotensin II AT₁Receptor in Renal and Hepatic Tissues of Streptozotocin-Induced Diabetic Rats

Abstract

This study investigates the potential of green tea to modulate oxidative stress and angiotensin II AT1 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 AT1 receptor labeling, in renal and hepatic tissues of the three rat groups, were immunohistochemically investigated using an anti-AT1 receptor antibody. Levels of total antioxidant and catalase were significantly reduced, whereas malondialdehyde levels and AT1 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 AT1 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 AT1 receptor upregulation may be beneficial in opposing the deleterious effects of excessive angiotensin II signaling, manifested by progressive renal and hepatic tissue damage.

Anti-hypertensive Herbs and their Mechanisms of Action: Part I

“…Catechins, the major flavonoids in tea, include (−)-epicatechin (EC), (−)-epicatechin-3-gallate (ECG), (−)-epigallocatechin (EGC), and (−)-epigallocatechin-3-gallate (EGCG; Deka and Vita, 2011 ). EGCG constitutes the primary component of tea's total catechins (Babu and Liu, 2008 ; Faria et al, 2012 ; Slevin et al, 2012 ; Thomson et al, 2012 ). Constituents of tea lessen the risk of hypertension through several mechanisms, such as attenuation of oxidative stress (Table 1 ).…”

“…Constituents of tea lessen the risk of hypertension through several mechanisms, such as attenuation of oxidative stress (Table 1 ). Green tea has been reported to increase CAT antioxidant enzyme while simultaneously blocking AT 1 receptors in streptozotocin-treated rats (Thomson et al, 2012 ). It has also been reported to upregulate the expression of antioxidants genes such as SOD1 and GST in C57BL/6 mice (Newsome et al, 2014 ).…”

Effects of kolaviron on hepatic oxidative stress in streptozotocin induced diabetes

“…An elevated level of liver MDA, a product of lipid peroxidation, has been reported in diabetic rats [ 20 – 23 ]. Results from our study corroborate these observations.…”

Effects and Mechanisms of Tea for the Prevention and Management of Diabetes Mellitus and Diabetic Complications: An Updated Review

“…In apparently healthy individuals, green tea extract could reduce oxidative stress and reduce the risk of diabetic liver diseases by lowering the malondialdehyde level and increasing the glutathione level [126]. In addition, green tea could ameliorate liver inflammation and damage caused by diabetes mellitus by lowering angiotensin II receptors [130]. Further, black tea extract protected the liver by increasing cellular antioxidant capacity and reducing membrane lipid peroxidation, inhibiting oxidative stress in diabetic and obese rats caused by alloxan and high cholesterol diets [17].…”