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 KI and KIS 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.