Purpose: Oxidative stress has long been recognized as an important mediator of apoptosis in lens epithelial cells and also plays an important role in the pathogenesis of cataracts. (-)-Epigallocatechin gallate (EGCG), the most abundant component in green tea, has potent antioxidant activity. The goals of this study were to determine the protective effect of EGCG against H(2)O(2)-induced apoptotic death and the possible mechanisms involved in human lens epithelial (HLE) cells.
Methods: HLEB-3, a human lens epithelial cell line, was exposed to various concentrations of H(2)O(2) and EGCG and subsequently monitored for cell death by the MTT assay and flow cytometric analysis using Annexin V and PI. The effect of EGCG in protecting HLE cells from cell death was determined by various assays after the cells were exposed to H(2)O(2). The ability of EGCG to block the accumulation of intracellular reactive oxygen species and the loss of mitochondrial membrane potential (Deltapsim) induced by H(2)O(2) was examined with dichlorofluorescein (DCF) fluorescence and 5,5',6,6'-tetrachloro-1,1',3,3'-tetrathylbenzimidazol carbocyanine iodide (JC-1). The expression of cytochrome c, caspase-9, caspase-3, and Bcl-2 family proteins was measured by western blotting. The changed expression of the mitogen activated protein kinase (MAPK) and Akt pathways was also detected by western blot.
Results: In the present study, EGCG protected against cell death caused by H(2)O(2) in HLEB-3 cells. EGCG reduced the H(2)O(2)-induced generation of reactive oxygen species (ROS), the loss of mitochondrial membrane potential (Deltapsim), and the release of cytochrome c from the mitochondria into the cytosol. EGCG inhibited the H(2)O(2)-stimulated increase of caspase-9 and caspase-3 expression and the decrease of the Bcl-2/Bax ratio. Moreover, EGCG attenuated the reduced activation and expression of ERK, p38 MAPK, and Akt induced by H(2)O(2).
Conclusions: These findings suggest that EGCG protects HLE cells from the mitochondria-mediated apoptosis induced by H(2)O(2) through the modulation of caspases, the Bcl-2 family, and the MAPK and Akt pathways.