In order to study the
biological activities of
tea preparations and purified
tea polyphenols, their growth inhibitory effects were investigated using four human
cancer cell lines. Growth inhibition was measured by [3H]
thymidine incorporation after 48 h of treatment. The
green tea catechins (-)-epigallocatechin-3-gallate (EGCG) and (-)-
epigallocatechin (EGC) displayed strong growth inhibitory effects against lung tumor cell lines H661 and H1299, with estimated IC50 values of 22 microM, but were less effective against
lung cancer cell line H441 and
colon cancer cell line HT-29 with IC50 values 2- to 3-fold higher. (-)-Epicatechin-3-gallate, had lower activities, and (-)-
epicatechin was even less effective. Preparations of
green tea polyphenols and theaflavins had higher activities than extracts of
green tea and decaffeinated
green tea. The results suggest that the growth inhibitory activity of
tea extracts is caused by the activities of different
tea polyphenols. Exposure of H661 cells to 30 microM EGCG, EGC or theaflavins for 24 h led to the induction of apoptosis as determined by an
annexin V apoptosis assay, showing apoptosis indices of 23, 26 and 8%, respectively; with 100 microM of these compounds, the apoptosis indices were 82, 76 and 78%, respectively. Incubation of H661 cells with EGCG also induced a dose-dependent formation of H2O2. Addition of H2O2 to H661 cells caused apoptosis in a manner similar to that caused by EGCG. The EGCG-induced apoptosis in H661 cells was completely inhibited by exogenously added
catalase (50 units/ml). These results suggest that
tea polyphenol-induced production of H2O2 may mediate apoptosis and that this may contribute to the growth inhibitory activities of
tea polyphenols in vitro.