Green Tea Polyphenols Induce Differentiation and Proliferation

The most abundant green tea polyphenol, epigallocatechin-3-gallate (EGCG), was found to induce differential effects be-tween tumor cells and normal cells. Nevertheless, how normal epithelial cells respond to the polyphenol at concentrations for which tumor cells undergo apoptosis is undefined. The current study tested exponentially growing and aged primary human epidermal keratinocytes in response to EGCG or a mixture of the four major green tea polyphenols. EGCG elicited cell differ-entiation with associated induction of p57/KIP2 within 24 h in growing keratinocytes, measured by the expression of keratin 1, filaggrin, and transglutaminase activity. Aged keratinocytes, which exhibited low basal cellular activities after culturing in growth medium for up to 25 days, renewed DNA synthesis and activated succinate dehydrogenase up to 37-fold upon expo-sure to either EGCG or the polyphenols. These results suggest that tea polyphenols may be used for treatment of wounds or certain skin conditions characterized by altered cellular activi-ties or metabolism. Green tea polyphenols (referred to as GTPPs, to include the four major polyphenols: epicatechin, epigallocatechin, ep-catechin-3-gallate, and epigallocatechin-3-gallate (EGCG) have been identified to possess chemopreventive and apopto-tic activity against certain cancers, whereas normal epider-mal keratinocytes follow a survival pathway that has not been fully elucidated (Chen et al., 1998; Paschka et al., 1998;