Protective effects of S-nitrosoglutathione against amyloid beta-peptide neurotoxicity

Amyloid beta-peptide (Abeta) is a major constituent of senile plaques in the brains of Alzheimer's disease (AD) patients. We have previously demonstrated ceramide production secondary to Abeta-induced activation of neutral sphingomyelinase (nSMase) in cerebral endothelial cells and oligodendrocytes, which may contribute to cellular injury during progression of AD. In this study, we first established the "Abeta --> nSMase --> ceramide --> free radical --> cell death" pathway in primary cultures of fetal rat cortical neurons. We also provided experimental evidence showing that S-nitrosoglutathione (GSNO), a potent endogenous antioxidant derived from the interaction between nitric oxide (NO) and glutathione, caused dose-dependent protective effects against Abeta/ceramide neurotoxicity via inhibition of caspase activation and production of reactive oxygen species (ROS). This GSNO-mediated neuroprotection appeared to involve activation of cGMP-dependent protein kinase (PKG), phosphatidylinositol 3-kinase (PI3K), and extracellular signal-regulated kinase (ERK). Activation of the cGMP/PKG pathway induced expression of thioredoxin and Bcl-2 that were beneficial to cortical neurons in antagonizing Abeta/ceramide toxicity. Consistently, exogenous application of thioredoxin exerted remarkable neuroprotective efficacy in our experimental paradigm. Results derived from the present study establish a neuroprotective role of GSNO, an endogenous NO carrier, against Abeta toxicity via multiple signaling pathways.