Xanthine oxidase-inhibitory and hypouricemic action of Black poplar bud extract

Our study aimed to investigate the effect of the extract from Black poplar (Populus nigra L.) buds on xanthine oxidase (XO) activity in vitro and its hypouricemic action in rats. Poplars have been traditionally used in gout- and arthritis-treatment practices in medieval Europe. Besides, phenolic-rich resins from poplar buds are usually the main costituents of honey bee propolis that has a wide traditional use.

After preliminary in vitro evaluation, extract was administered for 3 consecutive days to potassium oxonate-induced hyperuricemic rats in concentrations of 100 and 500mg/kg. Allopurinol (10mg/kg), was used as a reference drug. Uric acid/serum urate, urea, creatinine and electrolytes Na⁺, K⁺, Cl^- were determined in daily collected urine and in serum at the end of the experiment. ALT, AST activities in serum and XO activities in the liver homogenate were determined.

The extract inhibited XO activity in vitro, showing a mixed-mode inhibitory action and IC₅₀ value of 8.2µg/mL. In rats, poplar extract at 500mg/kg significantly (P<0.05) reduced serum urate levels by 27% compared to hyperuricemic control group which the effect similar to that of allopurinol at a dose 10mg/kg. The mode of action still needs to be further elucidated as it did not exhibit effect on liver XO but the observed effect on Na⁺, K⁺, and Cl^- excretion suggest the uricosuric action.

Further research is needed to fully elucidate the potential of poplar extract in management of hyperuricemia.

Keywords: Xanthine oxidase, hypouricemic effect, hyperuricemia, gout, enzyme inhibition, Populus nigra, black poplar extract

Acknowledgement: This research was supported by MSM 6046070901 and GACR 525/08/P503