Objective: The concentration-dependent nephroprotective effects of orally-administered aqueous green tea extract (AGTE) were studied. Materials and Methods: Forty rats of both sexes (weighing ٢٠٠-٢٥٠g) with various concentrations {٠.٦٢٥%, ١.٢٥% and ٢.٥% of aqueous green tea extract (AGTE)} as their main source of drinking fluid ٧ days before and ٥ days after administration of methotrexate (MTX). The parameters of oxidative stress, malondialdehyde (MDA) and reduced glutathione (GSH) were daily measured in kidney homogenate in addition to histopathological examinations after killing. Results: Analysis of data revealed significant amelioration of oxidative stress in groups of animals treated with different concentrations of AGTE compared to MTX-treated group as evidenced by lowering MDA contents and elevation of GSH levels in kidney tissue homogenate but the levels still significantly different compared to controls. Furthermore, increasing concentrations of AGTE produce no concentration-dependent improvement of the damage induced by MTX in kidney tissue, as observed in kidney rats sections in concentrations ٠.٦٢٥% and ٢.٥% AGTE, while improvement in renal morphological changes was observed in group of animals treated with ١.٢٥% AGTE + MTX. Conclusion: The concentration-dependent protective effects of AGTE against MTXinduce kidney damage were not evidenced, where higher concentration of AGTE (٢.٥%) used in this study resulted in deterioration in the renal functions and morphology, which may be due to its pro-oxidant effect; while renal protective effects was evidenced in a concentration of ١.٢٥% AGTE, an effect that could be related to its antioxidant properties at this concentration.
