Cells preincubated with either different concentrations of NAC or DPI for 1 h received 1 μm fibrillar Aβ1–42. A, after 6 h of incubation, the cells were washed with Hanks’ balanced salt solution and scraped off. Lipids were extracted, and the level of ceramide was measured. After 1 h of incubation, activities of N-SMase (B) and A-SMase (C) were assayed in total cell extracts. Control group served as 100%, and data from other groups were expressed as percent of control. Results are mean ± S.D. of three different experiments. a, p < 0.001; b, p < 0.05 versus Aβ1–42.