Cytotoxicity of nonreduced and reduced sphingolipid messengers
| Treatment | DNA damage | Cell death | Clonogenicity |
|---|---|---|---|
| % Vehicle control | |||
| Vehicle | 3 ± 1 | 3 ± 1 | 100 ± 4 |
| Ceramide | 56 ± 52-a | 42 ± 72-a | 37 ± 92-b |
| Dihydroceramide | 4 ± 1 | 2 ± 12-a | 98 ± 1 |
| Sphingosine | 88 ± 92-a | 74 ± 102-a | 3 ± 22-b |
| Dihydrosphingosine | 83 ± 112-a | 79 ± 122-a | 4 ± 22-b |
U937 cells were exposed to nonreduced (ceramide, sphingosine) and reduced (dihydroceramide, dihydrosphingosine) sphingolipid analogs at equimolar levels (10 μm). Cells were withdrawn after 6 hr and prepared for visualization of DNA damage by fluorescence microscopy after staining with FITC-dUTP in the presence of TdT or visualization of apoptotic cell death by light microscopy after staining with conventional Wright-Giemsa. Values are expressed as percentage of vehicle-treated controls and reflect mean ± standard error of apoptotic cells (125 cells scored per treatment).