Strategy of Chemical Modification to Free Radical Scavengers for Suppression of Hydrogen Peroxide-Induced Cytotoxicity

Hydrogen peroxide (H2O2) has been implicated as a mediator of cellular injuries in a variety of clinical conditions including cancer and acquired immunodeficiency syndrome (AIDS). We assessed effects of free radical scavengers on H2O2-induced damages by an SOS chromotest with bacterial cells and by a colony formation assay and a DNA precipitation assay with mammalian cells. We found that certain plant polyphenols (e.g., caffeic acid esters and quercetin) suppressed H2O2-induced cytotoxicity and H2O2-induced DNA damage in mammalian and bacterial cells. In contrast, neither α-tocopherol nor ascorbic acid showed any effects in these assays. The structure-activity relation in these studies revealed that the presence of an o-dihydroxy structure (or its equivalent p-dihydroxy structure) and affinity for the cell membranes proved essential to the protection. Chemical modification (e.g., esterification of caffeic acid and demethylation of curcumin) based on the above structure-activity relation made these compounds effective in the protection against H2O2-induced cell damages.