Several dietary flavonoids such as quercetin, luteolin and genistein have been suggested to have cancer chemopreventive effects, although the mechanisms are not fully understood. In the present study, the effects of these flavonoids as antioxidants were investigated in the following systems: (1) production of hydrogen peroxide (H 2 O 2 ) and superoxide anion (O 2 − ), (2) lipid peroxidation induced by FeCl 2 in rat liver, and (3) formation of 8-hydroxy-2′-deoxyguanosine (8-OHdG) induced by either UV or Fenton reaction in calf thymus DNA. The results showed that quercetin and luteolin were equally potent in scavenging H 2 O 2 , with genistein having a moderate effect. Quercetin and luteolin had a potent inhibitory effect on (O 2 − ) generation by xanthine/xanthine oxidase while genistein had a moderate effect. Quercetin and luteolin were potent in inhibiting lipid peroxidation induced by FeCl 2 in rat liver while genistein had a very weak inhibitory effect. All the test compounds had a potent quenching effect on 8-OHdG formation induced by UV light irradiation, with the order of effects being genistei-n > luteolin > quercetin. Of the test compounds, luteolin exhibited the most potent quenching effect on Fenton-induced 8-OHdG formation. The scavenging of oxygen free radicals, the inhibitory effect on lipid peroxidation and the quenching effect on 8-OHdG formation by quercetin, luteolin and genistein may, at least in part, be responsible for their anticarcinogenic effects.
