Examination of the anti-oxidative effect in renal tubular cells and apoptosis by oxidative stress

The incidence of urolithiasis has increased in the industrialized nations. However, both the pathogenesis and methods for its prevention remain to be clarified. We demonstrate that the antioxidative effect of green tea decreases the formation of calcium oxalate stones, OPN (osteopontin) expression, and apoptosis, and increases SOD (superoxide dismutase) activity in rat kidney tissues. The inhibitory effect of green tea on calcium oxalate urolithiasis is most likely due to its antioxidative effects. Therefore, we examined oxidative stress in vivo applied to Madin-Darby canine kidney (MDCK) cells, to which catechin, an antioxidant, was added. To evaluate the effects of oxidative stress on MDCK cells, we use a hypoxic condition because hypoxia is known to lead to oxidative stress. Confluent cultures of MDCK cells were exposed to (-)epigallocatechin 3 gallate (EGCG) (0, 0.1, 0.5, 5.0 mg/ml) for 2, 4, 8 or 16 h to determine changes in protein secretion and apoptosis. OPN protein expression was observed in MDCK cells of all 16 groups. The levels of expression of OPN protein were the same among all groups. In all groups, SOD protein expression was observed. In the groups exposed to EGCG 0.5, 5.0 mg/ml, SOD staining was more enhanced than in the EGCG 0 and 0.1 mg/ml groups. No deposits were detected in any of the 16 groups. RT-PCR was performed to detect sequences from OPN (979 bp) and SOD (447 bp). Quantitative analyses showed that SOD activity decreased gradually in all groups. Only in the EGCG 0 mg/ml 16 h group were TUNEL-positive cells observed. In the other groups, TUNEL-positive cells were not detected. EGCG used as an antioxidant protects renal tubular cell from cellular injury caused by oxidative stress through SOD protein expression.