Mechanisms and Structural Specificity of Hydrogen Peroxide Formation during Oxidation of Catechins

Abstract

Hydrogen peroxide (H₂O₂) formed in aqueous solutions of tea catechins such as epicatechin (EC), epicatechin gallate (ECg), epigallocatechin (EGC), and epigallocatechin gallate (EGCg) was measured by an HPLC method. The amount of H₂O₂ formed depended on their chemical structures, pH, temperature and incubation time. The gallyl moiety in the B-ring of the gallocatechins, namely EGC and EGCg, mainly contributed to the H₂O₂ formation. Superoxide dismutase inhibited oxidation of the gallocatechins and, consequently, the H₂O₂ formation. Cytotoxic effects were investigated by a colony formation assay with Chinese hamster V79 cells, and the effects of the gallocatechins were stronger than those of EC and ECg. The cytotoxic effects of the gallocatechins were inhibited completely by catalase and partially by superoxide dismutase. These results indicate that the gallocatechins were oxidized by superoxide, accompanied by the formation of H₂O₂, and their cytotoxic effects were ascribed to the H₂O₂ formation.