Inhibitory Capacity of Xanthine Oxidase in Antigout Therapy by Indonesian Medicinal Plants

The traditional medicine has been used in Indonesia since the days of the Ancient Mataram Kingdom (about 12 centuries ago). Indonesia is rich in medicinal plants. For this reason, it is necessary to inform the broader community regarding medicinal plants in Indonesia that have the potential as antigout. The prevalence of gout in Indonesia is in the range of 1.6−13.6 per 100,000 people and will increase with age. There are 25 species of Indonesian plants that have more than 50% xanthine oxidase (XO) enzyme inhibitory activity. XO is responsible for catalyzing hypoxanthine to xanthine then producing uric acid, accompanied by the formation of reactive oxygen species (ROS) during catalysis. The magnitude of the inhibitory power to XO ranged from 50.00±1.16% to 97.53%. The lowest inhibitory power of 50.00±1.16% was in Phaleria macrocarpa, while Orthosiphon aristatus had the highest inhibitory power of 97.53%. The major compounds that inhibit xanthine oxidase are flavonoids. The structural similarity of flavonoids in rings A and C with xanthine as a substrate causes hydrophobic interactions, hydrogen bonds, and van der Waals forces between flavonoids and XO. It means that flavonoids bind to the XO active site, thereby preventing the formation of uric acid. The type of inhibitory kinetics that occurs between flavonoids and XO is competitive inhibition. Five plants with competitive inhibition kinetics against XO are Sida rhombifolia, Syzygium polyanthum, Cyperus rotundus, Ruellia tuberosa and Phaleria macrocarpa.