Inhibition of xanthine oxidase by phenolic phytochemicals from Broussonetia papyrifera

The roots of Broussonetia papyrifera were extracted into four different polar solvents: chloroform, 50% ethanol in water, ethanol, and water. The ethanol extract showed the most potent inhibition (72.3% at 20 g/mL) against xanthine oxidase (XOD). Chromatography of EE yielded nine phenolic phytochemicals, which were confirmed as broussochalcone A (1), broussochalcone B (2), 3,4-dihydroxyisolonchocarpin (3), 4-hydroxyisolonchocarpin (4), 3-′(3-methylbut-2-enyl)-3′,4′,7-trihydroxyflavane (5), kazinol A (6), kazinol B (7), kazinol E (8), and broussoflavan A (9). All isolated compounds (19) possessed potent antioxidant activities against 2,2-diphenyl-l-picrylhydrazyl and 2,2′-azino-bis-ethylbenzthiazoline-6-sulfonic acid (ABTS) radicals with IC50 values ranging from 5.8 to 252.8M. Although most compounds exhibited potent inhibition with IC50 values ranging 0.6–164 M against XOD, compounds 1 and 3 were found to be the principal contributors to the XOD inhibition in ethanol extract. The analysis of K I and K IS values proved that the two most promising compounds (1 and 3), present at high concentrations in the root barks as analyzed by using high-performance liquid chromatography analysis, were reversible mixed type I inhibitors.