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

Exposure of normal human epidermal keratinocytes (NHEK) to UVB radiation in duces intracellular release of hydrogen peroxide (oxidative stress) and pho sphorylation of mitogen-activated protein kinase cell signaling pathways. H ere, we demonstrate that pretreatment of NHEK with (-)-epigallocatechin-3-g allate (EGCG), an antioxidant from green tea, inhibits UVB-induced hydrogen peroxide (H2O2) production and H2O2-mediated phosphorylation of MAPK signa ling pathways. We found that treatment of EGCG (20 mug/ml of media) to NHEK before UVB (30 mJ/cm(2)) exposure inhibited UVB-induced H2O2 production (6 6-80%) concomitant with the inhibition of UVB-induced phosphorylation of ER K1/2 (57-80%), JNK (53-83%), and p38 (50-77%) proteins. To demonstrate whet her UVB-induced phosphorylation. of MAPK occurs via UVB-induced H2O2 (oxida tive 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 wi th the known antioxidant ascorbic acid (as positive control), H2O2-induced phosphorylation of ERK1/2, JNK, and p38 was found to be significantly inhib ited. These findings demonstrate that EGCG has the potential to inhibit UVB -induced oxidative stress-mediated phosphorylation of MAPK signaling pathwa ys, suggesting that EGCG could be useful in attenuation of oxidative stress -mediated and MAPK-caused skin disorders in humans. (C) 2001 Academic Press .