Effect of black and green tea polyphenols on c-jun phosphorylation and H2O2 production in transformed and non-transformed human bronchial cell lines:possible mechanisms of cell growth inhibition and apoptosis induction

The biological activities of theaflavin (TF), theaflavin gallate (TFG) and theaflavin digallate (TFdiG) from black tea and (-)-epigallocatechir1 3-gal late (EGCG) acid (-)-epigallocatechin (EGC) from green tea were investigate d using SV40-immortalized (33BES) and Ha-ras gene transformed (21BES) human bronchial epithelial cell lines. Growth inhibition and cell viability were measured by trypan blue dye exclusion assay following 24 h treatment with the tea polyphenols. TFdiG, EGC and EGCG displayed comparable inhibitory ef fects on the growth of 21BES cells, with estimated IC50 values of 22-24 muM . TFG exhibited a lower inhibitory activity (IC50 37 muM, and TF was even l ess effective (IC50 47 muM) in this cell line. A similar effect was also ob served in 33BES cells. These results suggest that the gallate structure of theaflavins is important for growth inhibition. Exposure of 21BES cells to 25 muM TFdiG, EGC and EGCG for 24 h led to induction of cell apoptosis/deat h as determined by the Annexin V apoptosis assay. With TFdiG treatment cell death occurred early, and quickly peaked at 8-12 h, Morphological observat ions showed that TFdiG-treated cells appeared irregular in shape, with cyto plasmic granules, suggesting a cytotoxic effect, On the other hand, EGC and EGCG showed a lag phase before a rapid increase in apoptosis between 16 an d 24 h, without any marked morphological changes, which was similar to that induced by H2O2. TFdiG, EGC and EGCG induced similar amounts of N2O2 forma tion in 21BES cells. Exogenously added catalase significantly prevented EGC - and EGCG-induced cell apoptosis, but did not prevent TFdiG-induced cell d eath, suggesting that H2O2 is involved in the apoptosis induced by EGCG and ECC, but not in TFdiG-induced cell death. EGCG and TFdiG were shown to dec rease c-jun protein phosphorylation in 21BES cells, such inhibition is expe cted to result in lowered AP-1 activity, which may contribute to the growth inhibitory activity of tea polyphenols.