Preventive effects of green tea on renal stone formation and the role of oxidative stress in nephrolithiasis

Purpose: Urinary stones are similar to arteriosclerosis in epidemiology, mechanism, calcification composition and age at frequent occurrence. The calcification that occurs in arteriosclerosis is inhibited by antioxidants. Green tea leaves contain approximately 13% catechins, which have been shown to have antioxidant effects. We investigated the inhibitory, antioxidative effects of green tea on calcium urinary stone formation. Materials and Methods: A total of 120 Wistar rats were divided into 4 groups, namely group 1-control rats receiving saline, group 2-stone group rats administered ethylene glycol (EG) and vitamin D3, group 3-drink group rats administered EG, vitamin D3 and green tea given as drinking water, and group 4-powder group rats administered EG, vitamin D3 and 2.5% powdered green tea leaves mixed in a powder diet. Pooled 24-hour urine samples and blood samples were collected and the 2 kidneys were excised 7, 14 and 21 days after administration, respectively. One kidney was used for immunohistological examination of osteopontin, superoxide dismutase (SOD), p65, p53 and bcl-2 expression, in situ hybridization of osteopontin and detection of apoptosis, while the other was used for quantitative analysis of SOD activity. Results: Green tea treatment decreased urinary oxalate excretion and calcium oxalate deposit formation. Green tea treatment increased SOD activity compared with the stone group. The degree of apoptosis in the stone group was significantly increased compared with the drink and powder groups. Conclusions: The inhibitory effect of green tea on calcium oxalate urolithiasis is most likely due to antioxidative effects.