Xanthine Oxidase Inhibition and Anti-LDL Oxidation by Prenylated Isoflavones from Flemingia philippinensis Root

Abstract

Xanthine oxidase is a frontier enzyme to produce oxidants, which leads to inflammation in the blood. Prenylated isoflavones from Flemingia philippinens is were found to display potent inhibition against xanthine oxidase (XO). All isolates (1-9) inhibited XO enzyme with IC50 ranging 7.8 similar to 36.4 mu M. The most active isoflavones (2-5, IC50= 7.8 similar to 14.8 mu M) have the structural feature of a catechol motif in B-ring. Inhibitory behaviors were disclosed as a mixed type I mode of inhibition with K-I<K-IS. Binding affinities to XO enzyme were evaluated. Fluorescence quenching effects agreed with inhibitory potencies (IC(50)s). The compounds (2-5) also showed potent anti-LDL oxidation effects in the thiobarbituric acid-reactive substances (TBARS) assay, the lag time of conjugated diene formation, relative electrophoretic mobility (REM), and fragmentation of apoB-100 on copper-mediated LDL oxidation. The compound 4 protected LDL oxidation with 0.7 mu M in TBARS assay, which was 40-fold more active than genistein (IC50 = 30.4 mu M).