Suppression of active oxygen-induced cytotoxicity by flavonoids.

The flavonoids quercetin, kaempferol, catechin and taxifolin suppressed cytotoxicity of active oxygen species (O2- and H2O2) on Chinese hamster V79 cells. Cytotoxicity of active oxygen species was assessed with a colony formation assay. The flavonoids prevented the decrease in the number of colonies caused by H2O2 or O2- at concentrations which were not themselves cytotoxic. There was a very substantial difference in the dose-dependency of the protective effects brought about by quercetin and kaempferol in contrast to catechin and taxifolin. The structure-activity relationship revealed that either the o-dihydroxy structure in the B ring or certain structures in the A and C rings of the flavonoids are necessary for the protective activities.