Stilbene compounds are specific inhibitors of the superoxide anion generation catalyzed by xanthine oxidase

The inhibitory effect of xanthine oxidase (XO) reactions with stilbene compounds, 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging by stilbene compounds and superoxide anion (O(2)-) scavenging activity were examined. The inhibition of the O(2)- generation catalyzed by XO by stilbene compounds is stronger than the effect on uric acid formation. The suppression of the O(2)- generation with resveratrol was diminished by the addition of flavin adenine dinucleotide (FAD). The water-solubility and visible spectra (VIS) of the stilbene compounds in the presence of water-soluble flavin compounds indicated a π-π interaction between the stilbene compounds and the isoalloxazine in flavin compounds. These results indicate that stilbene compounds specifically bind the FAD site in XO so as to inhibit the O(2)- generation. In the case of piceatannol, it is deduced that the suppression of O(2)- generation is induced by this specific binding to the FAD site and the subsequent reduction of XO.