Dual mechanisms of green tea extract‐induced cell survival in human epidermal keratinocytes

Abstract

Beneficial effects attributed to green tea, such as its anticancer and antioxidant properties, may be mediated by (-)-epigallocatechin-3-gallate (EGCG). In this study, the effects of EGCG on cell proliferation and UV-induced apoptosis were investigated in normal epidermal keratinocytes. When topically applied to aged human skin, EGCG stimulated the proliferation of epidermal keratinocytes, which increased the epidermal thickness. In addition, this topical application also inhibited the UV-induced apoptosis of epidermal keratinocytes. EGCG was found to increase the phosphorylation of Bad protein at the Ser112 and Ser136. Moreover, EGCG-induced Erk phosphorylation was found to be critical for the phosphorylation of Ser112 in Bad protein, and the EGCG-induced activation of the Akt pathway was found to be involved in the phosphorylation of Ser136. Furthermore, EGCG increased Bcl-2 expression but decreased Bax expression, causing an increase in the Bcl-2-to-Bax ratio. In addition, we demonstrate the differential growth inhibitory effects of EGCG on cancer cells. In conclusion, this study demonstrates that EGCG promotes keratinocyte survival and inhibits the UV-induced apoptosis via two mechanisms: by phosphorylating Ser112 and Ser136 of Bad protein through Erk and Akt pathways, respectively, and by increasing the Bcl-2-to-Bax ratio. Moreover, these two proposed mechanisms of EGCG-induced cell proliferation may differ kinetically to promote keratinocyte survival.

Antimicrobial activity of green tea extract against isolates of methicillin–resistant Staphylococcus aureus and multi–drug resistant Pseudomonas aeruginosa

“…Another possible mechanism is green tea extract may affect the activity of dihydrofolate reductase, an enzyme that is needed by pathogenic bacteria to synthesize purine and pyrimidine as well as increase the thickness of the epidermis [33] .…”

Essential role of caspases in epigallocatechin-3-gallate-mediated inhibition of nuclear factor kappaB and induction of apoptosis

“…A significant reason for the great interest in EGCG is because of its remarkable effects in many in vitro and in vivo tumor model systems Singh et al, 2002;Chung et al, 2003;Gupta et al, 2003;Hastak et al, 2003). Part of this effect of EGCG appears to be because, at physiologically attainable concentrations, it induces apoptosis in cancer cells without affecting normal cells (Ahmad et al, 1997, 2000; Chen et al, 1998).…”

“…Epigallocatechin-3-gallate (EGCG), the major polyphenolic constituent present in green tea, has received much attention over the last few years, as a potential cancerchemopreventive and cancer-chemotherapeutic agent, possibly because of its wide range of effects on a number of cellular processes and efficacy in many tumor model systems (Singh et al, 2002;Chung et al, 2003;Gupta et al, 2003;Hastak et al, 2003). Our previous studies have shown that EGCG, at pharmacologically attainable concentrations, results in inhibition of cell growth, arrest of the cell cycle in G0/G1 phase and induction of apoptosis in some human carcinoma cells (Ahmad et al, 1997).…”

Inhibitory Activity of Fresh Green Tea and Black Tea Extracts (Camellia Sinensis) on Intestinal Pathogens Isolated From Diarrheal Sample

“…The phytochemical constituents of green tea extracts were able to prevent the adherence of microbes with the intestinal walls and interfere with the cell division thus inhibiting growth and multiplication of microbes 31 . The green tea extract may affect the purine and pyrimidine synthesis in bacteria 32 . In addition to these reports are available that both green and black tea produced larger zone of inhibition (400 µg / ml) which supports our study 33 .…”