Tea pigments induce cell-cycle arrest and apoptosis in HepG2 cells

AIM: To investigate the molecular mechanisms by which tea pigments exert preventive effects on liver carcinogenesis. METHODS: HepG2 cells were seeded at a density of 5x10(5)/well in six-well culture dishes and incubated overnight. The cells then were treated with various concentrations of tea pigments over 3 d, harvested by trypsinization, and counted using a hemocytometer. Flow cytometric analysis was performed by a flow cytometer after propidium iodide labeling. Bcl-2 and p21(WAF1) proteins were determined by Western blotting. In addition, DNA laddering assay was performed on treated and untreated cultured HepG2 cells. RESULTS: Tea pigments inhibited the growth of HepG2 cells in a dose-dependent manner. Flow-cytometric analysis showed that tea pigments arrested cell cycle progression at G(1) phase. DNA laddering was used to investigate apoptotic cell death, and the result showed that 100 mg/L of tea pigments caused typical DNA laddering. Our study also showed that tea pigments induced upregulation of p21(WAF1) protein and downregulation of Bcl-2 protein. CONCLUSION: Tea pigments induce cell-cycle arrest and apoptosis. Tea pigments may be used as an ideal chemopreventive agent. (C) 2005 The WJG Press and Elsevier Inc. All rights reserved.