Anti-hyperuricemic and nephroprotective effects of Smilax china L

Smilax china L., popularly known as "Jin Gang Ten", has been widely used as a traditional herbal medicine for the treatment of gout, rheumatoid arthritis and other diseases for a long time in China.

The present study was carried out to investigate the effect of Smilax china L. on hyperuricemia and renal dysfunction in induced hyperuricemic animals.

Five fractions (petroleum ether, chloroform, ethyl acetate, n-butanol and residual ethanol fraction) of Smilax china L. were orally administered to potassium oxonate-induced hyperuricemic mice for three days. The xanthine oxidase inhibitory activities and modes of action of nine compounds isolated from ethyl acetate fraction (EAF) were then examined in vitro. Finally, different dosages of EAF were administered to 10% fructose-induced hyperuricemic rats.

EAF (250 mg/kg) exhibited stronger anti-hyperuricemic activity in hyperuricemic mice compared with the other four fractions. Caffeic acid, resveratrol, rutin and oxyresveratrol isolated from EAF showed different inhibitory activities on xanthine oxidase in vitro, with the IC(50) values of 42.60, 37.53, 42.20 and 40.69 μM, respectively, and exhibited competitive or mixed inhibitory actions. Moreover, EAF (125, 250 and 500 mg/kg) markedly reversed the serum uric acid level (p<0.05, p<0.01 and p<0.001, respectively), fractional excretion of urate (p<0.05, p<0.01 and p<0.01, respectively) and blood urea nitrogen (p<0.05, p<0.01 and p<0.01, respectively) to their normal states, and prevented the renal damage against tubulointerstitial pathologies in hyperuricemic rats.

These findings show that Smilax china L. exhibits anti-hyperuricemic and nephroprotective activity in hyperuricemic animals.