Cholesterol secoaldehyde (ChSeco or 3 beta-hydroxy-5-oxo-5,6-secocholestan-6-al) has been shown to induce A beta aggregation and apoptosis in GT1-7 hypothalamic neurons. The present study was undertaken to evaluate the effects of ChSeco on rat primary cortical neuronal cells. ChSeco was cytotoxic at concentrations ranging from 5 to 20 mu M, while cholesterol of comparable concentrations showed little or no toxicity. In ChSeco-exposed neuronal cells, there was an increased formation of intracellular peroxide or peroxide-like substance(s), the levels of which were comparable to those found in typical menadione exposures. There was a loss in the mitochondrial transmembrane potential, the extent of which was dependent on concentration of ChSeco employed. Pre-treatment with N-acetyl-L-cysteine (5 mM: 1 h) offered protection against the cytotoxicity and the generation of intracellular oxidants. Cytotoxicity of ChSeco was evidenced by the loss of axonal branches and also condensed apoptotic nuclei in these cells. Immunohistochemical analysis revealed a decreased intracellular A beta 42 staining proportional to the loss in the axonal out growth and dendritic branches. The observed decrease in A beta 42 has been suggested to be due to loss of integrity of dendrites and the plasma membrane, possibly resulting from increased production of reactive oxygen species. (C) 2009 Elsevier Inc. All rights reserved.