Inhibition of UVB-Induced Oxidative Stress-Mediated Phosphorylation of Mitogen-Activated Protein Kinase Signaling Pathways in Cultured Human Epidermal Keratinocytes by Green Tea Polyphenol (−)-Epigallocatechin-3-gallate

Abstract

Exposure of normal human epidermal keratinocytes (NHEK) to UVB radiation induces intracellular release of hydrogen peroxide (oxidative stress) and phosphorylation of mitogen-activated protein kinase cell signaling pathways. Here, we demonstrate that pretreatment of NHEK with (−)-epigallocatechin-3-gallate (EGCG), an antioxidant from green tea, inhibits UVB-induced hydrogen peroxide (H2O2) production and H2O2-mediated phosphorylation of MAPK signaling pathways. We found that treatment of EGCG (20 μg/ml of media) to NHEK before UVB (30 mJ/cm2) exposure inhibited UVB-induced H2O2 production (66–80%) concomitant with the inhibition of UVB-induced phosphorylation of ERK1/2 (57–80%), JNK (53–83%), and p38 (50–77%) proteins. To demonstrate whether UVB-induced phosphorylation of MAPK occurs via UVB-induced H2O2 (oxidative stress) production, NHEK were treated with the oxidant H2O2. Treatment of H2O2 to NHEK resulted in phosphorylation of ERK1/2, JNK, and p38. Using the same in vitro system, when these cells were pretreated with EGCG or with the known antioxidant ascorbic acid (as positive control), H2O2-induced phosphorylation of ERK1/2, JNK, and p38 was found to be significantly inhibited. These findings demonstrate that EGCG has the potential to inhibit UVB-induced oxidative stress-mediated phosphorylation of MAPK signaling pathways, suggesting that EGCG could be useful in attenuation of oxidative stress-mediated and MAPK-caused skin disorders in humans.