Xanthine oxidase inhibitory effect of formula Er-miao tang combined with inhibitory and antioxidant activities of Phyllanthus amarus L. and Orthosiphon stamineus Benth.

Abstract

This study aimed to evaluate the xanthine oxidase (XO) a modified traditional formula, Er-miao tang, combined with Phyllanthus amarus L. and Orthosiphon stamineus Benth. The goal was to explore a complementary approach utilising locally available medicinal plants. XO inhibitory activity was assessed using Noro’s spectrophotometric method, while antioxidant capacity was evaluated via the DPPH radical scavenging assay. Both water decoction and 40% ethanol extracts of the combined formula were tested. The combined formula showed stronger XO inhibition than Er-miao tang alone. The 40% ethanol extract exhibited the highest activity (IC₅₀=88.61 μg/ml), followed by the water decoction (IC₅₀=93.78 μg/ml), compared to Er-miao tang alone (IC₅₀=110.97 μg/ml). Both the water extract and the 40% ethanol extract of the formulation demonstrated antioxidant activity, with IC₅₀ values of 65.33 and 53.25 μg/ml against DPPH radicals, respectively. The combination of Er-miao tang with P. amarus and O. stamineus enhances XO inhibitory and antioxidant activities, supporting further investigation of the formulation as a potential source of inhibitory constituents.