Inhibition of Xanthine Oxidase by Acacia confusa Extracts and Their Phytochemicals

Acacia confusa Merr. (Leguminosae) is traditionally used as a medicinal plant in Taiwan. In the present study, the XOD-inhibitory activity of ethanolic extracts from A. confusa was investigated for the first time. Results demonstrated that the ethanolic extract of A. confusa heartwood had a strong XOD-inhibitory activity. Among all fractions derived from heartwood extracts, the EtOAc fraction exhibited the best inhibitory activity. Following column chromatography and reverse-phase high-performance liquid chromatography, eight specific phytochemicals including melanoxetin, 7,8,3′,4′-tetrahydroxyflavone, transilitin, okanin, 3,7,8,3′-tetrahydroxy-4′-methoxyflavone, 7,8,3′-trihydroxy-3,4′-dimethoxyflavone, 7,3′,4′-trihydroxyflavone, and 7,3′,4′-trihydroxy-3-methoxyflavone were isolated and identified from the EtOAc fraction. In addition, the IC50 values indicated that okanin showed the strongest XOD-inhibitory effect (IC50 value of 0.076 μM), followed by melanoxetin (0.274 μM) and allopurinol (4.784 μM). The present study revealed that okanin and melanoxetin showed excellent inhibition on XOD in noncompetitive and competitive mode, respectively, and their inhibitory activity is better than that of allopurinol. This is the first study that demonstrates the XOD-inhibitory performance of okanin and melanoxetin.