Neuroprotective effect of epigallocatechin-3-gallate against beta-amyloid-induced oxidative and nitrosative cell death via augmentation of antioxidant defense capacity.

beta-Amyloid (Abeta) peptide, a major component of senile plaques has been regarded to play a crucial role in the development and neuropathogenesis of Alzheimer's disease (AD). Increasing data from in vitro and in vivo studies indicate that Abeta-induced damages in neurons and glia are mediated via nitrosative as well as oxidative stress. Therefore, recent researches have been focused on searching for dietary and herbal manipulations to protect against the Abeta-induced oxidative and/or nitrosative cell death. Epigallocatechin-3-gallate (EGCG), one of these candidates is a major polyphenolic compound present in green tea and has been reported to exhibit potent antioxidant and anti-inflammatory properties. In the present study, we have investigated the effect of EGCG against Abeta-induced oxidative and/or nitrosative cell death in BV2 microglia. Abeta treatment led to apoptosis in BV2 cells as revealed by DNA fragmentation, perturbation of mitochondrial transmembrane potential, and alterations in the expression of apoptosis-regulator Bcl-2 family proteins. EGCG pretreatment effectively ameliorated Abeta-induced cytotoxicity and manifestation of proapoptotic signals. Furthermore, BV2 cells exposed to Abeta underwent nitrosative stress as shown by the increased expression of inducible nitric oxide synthase (iNOS) and subsequent production of nitric oxide (NO) and peroxynitrite, which were effectively suppressed by EGCG pretreatment. To elucidate a molecular mechanism underlying the neuroprotective effect of EGCG, we have examined the cellular metabolism of reduced glutathione (GSH) with antioxidant properties. EGCG treatment fortified cellular GSH pool through elevated mRNA expression of gamma-glutamylcysteine ligase (GCL), the rate limiting enzyme in the glutathione biosynthesis. These results suggest that EGCG may have preventive and/or therapeutic potential in AD patients by augmenting cellular antioxidant defense capacity and attenuating Abeta-mediated oxidative and/or nitrosative cell death.