In vitro evaluation of xanthine oxidase inhibitory activity of aqueous extract of seven medicinal herbs

Over production of uric acid by xanthine oxidase (XO) causes gout. XO inhibitors for example allopurinol are the most important available anti gout drugs. Medicinal herbs are available natural sources that may be useful for the treatment of gout. In this study the inhibitory activity of aqueous extracts of Matricaria chamomilla L., Hypericum perforatum L., Fraxinus excelsior L., Zea mays L., Trachyspermum copticum (L.) Link, Cynara scolymus L. and Hedera helix L. were measured. In these experiments, under controlled conditions xanthine turns into uric acid by XO. Uric acid absorbance was measured at 295 nm using a UV spectrophotometer. Adding allopurinol (as positive control) or aqueous extracts to the solution containing XO, can decrease uric acid production by inhibition of this enzyme. At first, XO inhibitory activity of allopurinol and reproducibility of the method was evaluated by conducting three experiments. The results showed an EC50= 0.43 μg/ml for allopurinol. Then, XO inhibitory activity of aqueous extracts at 0.1, 0.5, 1, 1.5, 2 and 3 mg/ml were measured. Matricaria chamomilla could inhibit enzyme up to 68% (P< 0.001) while maximum XO inhibitory activities of Hypericum perforatum and Cynara scolymus were 36% (P< 0.001) and 21% (P< 0.001) respectively. Other extracts did not have any significant effect on XO. Our obtained results showed that part of anti gout effects of Matricaria chamomilla, Hypericum perforatum and Cynara scolymus is due to XO inhibition.