Inhibition of xanthine oxidase by liquiritigenin and isoliquiritigenin isolated from Sinofranchetia chinensis

The methanol extract of the stem of Sinofranchetia chinensis inhibited the activity of xanthine oxidase in vitro. Bioassay-guided purification led to the isolation of liquiritigenin and isoliquiritigenin as the main xanthine oxidase inhibitors. This inhibition of enzyme activity was found to be dose dependent, with an IC50 value of approximately 49.3 mu M for liquiritigenin and 55.8 mu M for isoliquiritigenin. Lineweaver-Burk transformation of the inhibition data indicated that the inhibition was of a mixed type for both liquiritigenin and isoliquiritigenin. For liquiritigenin, the K-i and K-I were determined to be 14.0 mu M and 151.6 mu M, respectively. For isoliquiritigenin, the K-i and K-I were determined to be 17.4 mu M and 81.9 mu M, respectively. These results suggest that these natural products could be used to treat conditions where the inhibition of xanthine oxidase is warranted.