Effect of tea polyphenol on renal function in rats with type 2 diabetes mellitus and the underlying mechanisms

Abstract

Objective To investigate the effect of tea polyphenol(TP)on renal function in rats with type 2 diabetes mellitus(T2DM)and the underlying mechanisms. Methods The combination of high diet feeding with treatment of streptozotocin(30 mg/kg) was used for establishment of rat T2DM model.All rats were randomly divided into normal control group, T2DM control group,low-dose TP-treated group (150 mg/kg), middle-dose TP-treated group(300 mg/kg) and high-doseTP-treated group(600 mg/kg).After TP treatment for 24 weeks, the fasting blood glucose level, renal function and antioxidant effect were observed. Results The fasting blood glucose level(μmol/L), urinary protein excretion rate (μg/min),serum creatinine(μmol/L), blood urea nitrogen level(mmol/L)and the ratio of right to body in low-dose TP-treated groups were 17. 20±10. 01, 212. 46±19. 21, 51. 66±16. 32, 9. 83±3. 18 and 0. 35±0. 02, urinary creatinine(mmol/L)and clearance rate of creatinine(ml/min)were 3. 68±1. 20 and 0. 41±0. 12,superoxide dismutase[SOD, U/(mg·pro)]and catalase[CAT, U/(mg·pro)] were 67. 10 ±5. 93 and 32. 54±2. 98,and malondialdehyde[MDA,nmol/(mg·pro)]was 0. 73±0. 26.These indexes in middle-dose TP-treated group were 14. 37±9. 25, 198. 33±18. 96, 49. 23±16. 78, 8. 52±2. 44, 0. 34±0. 03, 4. 28±1. 37, 0. 49±0. 14, 72. 78±9. 95, 33. 65±3. 26 and 0. 53±0. 23 respectively, and those were 13. 96±9. 85,199. 62±21. 76,41. 51±15. 28,8. 48±2. 42,0. 35±0. 03,4. 07±1. 38,0. 47 ±0. 16, 71. 44±12. 93,33. 78±3. 12 and 0. 54±0. 27 respectively in high-dose TP-treated group.The three TP-treated groups expressed decreased fasting blood glucose level, urinary protein excretion rate, serum creatinine, blood urea nitrogen level and the ratio of right to body(P< 0. 05),and increased urinary creatinine and clearance rate of creatinine(P< 0. 01)as compared with T2DM control group.The three TP-treated groups also showed increased levels of SOD and CAT(P< 0. 05), and decreased MDA level as compared with T2DM control group(P< 0. 01) Conclusion TP showed protective effect on renal function in rats with T2DM possibly by decreasing blood glucose level and increasing antioxidant effect. Key words: Tea polyphenol; Diabetic nephropathy; Antioxidant effect