Suppression of hydroperoxide-induced cytotoxicity by polyphenols.

A variety of synthetic and dietary polyphenols protect mammalian and bacterial cells from cytotoxicity induced by hydroperoxides, especially hydrogen peroxide (H2O2). Cytotoxicity of H2O2 on Chinese hamster V79 cells was assessed with a colony formation assay. Cytotoxicity and mutagenicity of H2O2 on Salmonella TA104 were assessed with the Ames test. SOS response induced by H2O2 was investigated in the SOS chromotest with Escherichia coli PQ37. The polyphenol-bearing o-dihydroxy (catechol) structure, i.e., nordihydroguaiaretic acid, caffeic acid ester, gallic acid ester, quercetin, and catechin, were effective for suppression of H2O2-induced cytotoxicity in these assay systems. In contrast, neither ferulic acid ester-bearing o-methoxyphenol structure nor alpha-tocopherol were effective, indicating that o-dihydroxy or its equivalent structure in flavonoids is essential for the protection. There are many reports describing that polyphenols act as prooxidants in the presence of metal ions. Our results suggest, however, that they act as antioxidants in the cells, when no metal ions are added to the medium.