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 (H(2)O(2)) production and H(2)O(2)-mediated phosphorylation of MAPK signaling pathways. We found that treatment of EGCG (20 microg/ml of media) to NHEK before UVB (30 mJ/cm(2)) exposure inhibited UVB-induced H(2)O(2) 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 H(2)O(2) (oxidative stress) production, NHEK were treated with the oxidant H(2)O(2). Treatment of H(2)O(2) 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), H(2)O(2)-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.