Hydrogen peroxide mediates EGCG-induced antioxidant protection in human keratinocytes

Abstract

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 H 2O 2, have been suggested to occur in vitro but also in vivo. In this study, we address whether autoxidation-derived H 2O 2 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 H 2O 2 (IC 50 117.3 versus 58.3 μM, respectively) and EGCG (134.1 versus 84.1 μM). HaCat cells significantly resisted cytotoxicity and DNA damage based on enhanced H 2O 2 clearance, improved DNA repair, and reduced intracellular ROS generation. Cumulative versus bolus EGCG and H 2O 2 treatment and H 2O 2 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 H 2O 2 and EGCG. In summary, our data suggest that autoxidative generation of low-dose H 2O 2 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.