U937 cells were exposed to ceramide or sphingosine at equimolar levels (10 μm) in the presence of the ceramide acylhydrolase inhibitor oleoylethanolamine (100 μm) or the ceramide synthase inhibitor fumonisin B₁ (100 μm). Cells exhibiting apoptotic DNA damage were visualized by fluorescence microscopy in fixed preparations after staining with FITC-dUTP in the presence of TdT as described in Materials and Methods. Values are expressed as percent untreated controls and reflect mean ± standard error of apoptotic cells (100 cells scored per treatment).

• ↵3-a Increased vs.vehicle-treated controls (p < 0.01).