jeudi 3 juin 2010

The Antifolate Activity of Tea Catechins

A naturally occurring gallated polyphenol isolated from green tea leaves, ( )-epigallocatechin gallate (EGCG), has been shown to be an inhibitor of dihydrofolate reductase (DHFR) activity in vitro at concentrations found in the serum and tissues of green tea drinkers (0.1-1.0 Mmol/L). These data
provide the first evidence that the prophylactic effect of green tea drinking on certain forms of cancer, suggested by epidemiologic studies, is due to the inhibition of DHFR by EGCG and could also explain why tea extracts have been traditionally used in ‘‘alternative medicine’’ as anticarcinogenic/antibiotic agents or in the treatment of conditions such
as psoriasis. EGCG exhibited kinetics characteristic of a slow, tight-binding inhibitor of 7,8-dihydrofolate reduction with bovine liver DHFR (KI = 0.109 Mmol/L), but of a classic, reversible, competitive inhibitor with chicken liver DHFR (KI = 10.3 MAmol/L). Structural modeling showed that EGCG can bind to human DHFR at the same site and in a similar orientation to that observed for some structurally characterized DHFR inhibitor complexes. The responses of lymphoma cells to EGCG and known antifolates were similar, that is, a dose-dependent inhibition of cell growth (IC50 = 20 Mmol/L for EGCG), G0-G1 phase arrest of the cell cycle, and induction of apoptosis. Folate depletion increased the sensitivity of these cell lines to antifolates and EGCG. These effects were attenuated by growing the cells in a medium containing hypoxanthine-thymidine, consistent with DHFR being the site of action for EGCG.

Our data may also explain why neural tube defects such as anencephaly and spina bifida, which are usually associated with folic acid deficiency, have been linked to high levels of maternal green tea consumption during the periconceptional

Journal Reference:
Enma Navarro-Pera´n et al. The Antifolate Activity of Tea Catechins. Cancer Res 2005; 65(6): 2059-64

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