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Green Tea Antioxidant
(-)-Epigallocatechin-3-gallate Treatment to Normal Human Epidermal Keratinocytes
Inhibits UVB-induced Oxidative Stress -mediated Phosphorylation of MAPK
and EGFR Signaling Pathways
Katiyar, Santosh1,2,
Afaq, Farrukh1, Perez, Anaibelith1,
Elmets, Craig2 and Mukhtar, Hasan1
Case Western Reserve University, Cleveland, OH 1
University of Alabama at Birmingham, Birmingham, AL2
Abstract-
Ultraviolet (UV) light exposure to mammalian skin induces oxidative
stress, which mediates phosphorylation of cell signaling molecules such
as mitogen activated protein kinase (MAPK) and epidermal growth factor
receptor (EGFR). Phosphorylation of these cell signaling pathways has
been implicated in tumor promotion and progression in mammalian skin.
The molecular mechanisms involved in UV induced oxidative stress-mediated
cell signaling and their inhibition by antioxidants are not well understood.
Exposure of normal human epidermal keratinocytes (NHEK) to physiologic
doses of UV radiation induces intracellular release of hydrogen peroxide
as an oxidant, and phosphorylation of MAPK such as extracellular signal-regulated
kinases (ERK1/2), c-Jun amino-terminal kinases (JNKs) and p38, and EGFR
signaling. In this study we determined whether treatment with (-)-epigallocatechin-3-gallate
(EGCG), a polyphenolic antioxidant from green tea, to NHEK in culture
prevents UVB-induced oxidative stress-mediated cell signaling in NHEK.
Treatment of NHEK with EGCG (5-20 ug/ml) before UVB (30 mJ/cm2)
exposure dose-dependently inhibited UVB-induced intracellular release
of H2O2 (66-88%), which was concomitant with the inhibition of UVB-induced
phosphorylation of ERK1/2 (57-80%), JNK (53-83%), p38 proteins (50-77%)
and EGFR (55-73%) at various time points studied (15-180 min post UVB).
To demonstrate that UVB-induced phosphorylation of MAPK is mediated
via production of H2O2, NHEK were treated with H2O2 (100uM). Treatment
of NHEK with H2O2 resulted in phosphorylation of ERK1/2, JNK and p38.
Using the same <1>in vitro system, when these NHEK were pretreated
with EGCG (20 ug/ml) or with the known antioxidant like ascorbic acid,
H2O2-induced phosphorylation of ERK1/2, JNK and p38 was inhibited. These
observations demonstrate that the antioxidant EGCG may have potential
to inhibit UVB-induced oxidative stress-mediated skin disorders in humans.
Thus, topical use of antioxidants like EGCG could be employed as an
appropriate treatment strategy to prevent human skin disorders caused
by solar UV light exposure.
Keywords: Normal
human epidermal keratinocytes, Ultraviolet light, MAPK & EGFR, Green
tea antioxidant
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