Dietary antioxidants fail in protection against oxidative genetic damage in in vitro evaluation

Carcinogenesis is believed to be induced through the oxidative damage of DN A, and antioxidants are expected to suppress it. So, the polyphenolic antio xidants in daily foods were investigated to see whether they protect agains t genetic damage by active oxygen. In the evaluation, we used a bioassay an d a chemical determination, a Salmonella mutagenicity test for mutation by a N-hydroxyl radical from one of the dietary carcinogens 3-amino-1-methyl-5 H-pyrido[4,3-b]indole and the formation of 8-hydroxyl (8-OHdG) from 2'-deox yguanosine (2'-dG) in a Fenton OH-radical generating system. Thirty-one ant ioxidants including flavonoids were compared in terms of radical-trapping a ctivity with bacterial DNA and 2'-dG. Antioxidants inhibited the mutation b ut the IC50 values were in the mM order. Against 8-OHdG formation, only alp ha -tocopherol had a suppressive effect with an IC50 Of 1.5 muM. Thus, exce pt a-tocopherol, the dietary antioxidants did not scavenge the biological r adicals faster than bacterial DNA and intact 2'-dG, indicating that they fa iled to prevent oxidative gene damage and probably carcinogenesis.