beta-Amyloid causes apoptosis and death in cultured neurons that may be mediated by generation of reactive oxygen species. Since ascorbic acid concentrations are relatively high in brain, we tested whether and how this antioxidant might protect cultured SH-SY5Y neuroblastoma cells from apoptotic cell death. SH-SY5Y cells did not contain ascorbate in culture but readily took it up to achieve intracellular concentrations several-fold those of GSH. Treatment of cells with 2-10 microM beta-amyloid(25-35) decreased both intracellular ascorbate and GSH without affecting rates of ascorbate transport, which suggests that the peptide induces an oxidant stress in the cells. Overnight culture of cells with 10-20 microM beta-amyloid(25-35) induced apoptosis in SH-SY5Y cells when measured as externalization of phosphatidylserine by annexin V binding, as DNA fragmentation in the TUNEL assay, and as caspase-3 activity in cell lysates. Pre-loading cells with ascorbate substantially prevented apoptosis measured by these assays as well as cell death. In addition to preventing apoptosis, ascorbate loading of SH-SY5Y cells also decreased basal rates of generation of endogenous beta-amyloid. Together, these results support the notion that beta-amyloid induces apoptosis and death in neurons due to oxidant stress and suggest that intracellular ascorbate effectively prevents this toxicity.