Role of lipophilicity and hydrogen peroxide formation in the cytotoxicity of flavonols

We compared the lipophilicity and toxicity of the four flavonols, galangin, kaempferol, quercetin and myricetin, which respectively have no, one, two and three hydroxyl groups on the B-ring. The lipophilicity was in the order of myricetin < quercetin < kaempferol < galangin. The cytotoxicity determi ned by a colony-formation assay with Chinese hamster lung fibroblast V79 ce lls was in the order of quercetin < kaempferol < galangin < myricetin. Apar t from myricetin, the order of lipophilicity was the same as that of cytoto xicity, implying that the cytotoxicity was attributable to the lipophilicit y. The cytotoxicity of myricetin was attributable to the hydrogen peroxide formed by autoxidation.