Hydrogen peroxide mediates EGCG-induced antioxidant protection in human keratinocytes.

The beneficial health effects of (−)-epigallocatechin-3-gallate (EGCG), the main catechin of green tea, have been attributed to complex interactions with a focus on antioxidative properties. Susceptibility to autoxidation and production of cytotoxic reactive oxygen species (ROS), mostly H2O2, have been suggested to occur in vitro but also in vivo. In this study, we address whether autoxidation-derived H2O2 may be involved in the cytoprotective effects of EGCG. To that end we investigated keratinocyte-derived HaCat and HL-60 promyelocytic leukemia cells with significantly different sensitivities to H2O2 (IC50 117.3 versus 58.3μM, respectively) and EGCG (134.1 versus 84.1μM). HaCat cells significantly resisted cytotoxicity and DNA damage based on enhanced H2O2 clearance, improved DNA repair, and reduced intracellular ROS generation. Cumulative versus bolus EGCG and H2O2 treatment and H2O2 pretreatment before subsequent high-dose EGCG and vice versa significantly reduced DNA damage and cytotoxicity in HaCat cells only. Addition of catalase abolished the protective activities of low-dose H2O2 and EGCG. In summary, our data suggest that autoxidative generation of low-dose H2O2 is a significant player in the cell-type-specific cytoprotection mediated by EGCG and support the hypothesis that regular green tea consumption can contribute as a pro-oxidant to increased resistance against high-dose oxidative stressors.