Active Oxygens Generation by Flavonoids

Abstract

The hydrogen peroxide (H₂O₂)-generating effects of 14 flavonoids were investigated. Seven out of 14 flavonoids tested were found to generate H₂O₂ in an acetate buffer of pH 7.4. The H₂O₂-generating abilities of flavonoids decrease in the order of myricetin>baicalein>quercetin>(-)-epicatechin>(+)-catechin>fisetin=7, 8-dihydroxy flavone. This ability was observed in flavonoids with either a pyrogallol or catechol structure, and the pyrogallol-type flavonoids generated more H₂O₂ than the catechol-types. The amount of H₂O₂ generated by myricetin (pyrogallol-type flavonoid) was proportional to its concentration and to the reaction time until about 4 h. In addition, H₂O₂ generation by myricetin was dependent on the amount of dissolved oxygen in the buffer, and it was inhibited by the addition of superoxide dismutase.These results suggest that the flavonoids generate H₂O₂ by donating a hydrogen from their pyrogallol or catechol structure to oxygen, through a superoxide anion radical.It was also found that flavonoids which generated more H₂O₂ were more powerful antioxidants in the NADPH-dependent lipid peroxidation of rat microsomes.