Induction of apoptosis by sphingosine, sphinganine, and C ₂-ceramide in human colon cancer cells, but not by C ₂-dihydroceramide

Complex dietary sphingolipids such as sphingomyelin and glycosphingolipids have been reported to inhibit the development of colon cancer. This protective role may be the result of the conversion of complex sphingolipids to bioactive metabolites including sphingoid bases (sphingosine and sphinganine) and ceramide, which inhibit proliferation and stimulate apoptosis. In the current study, we evaluated the significance of the 4,5-trans double bond by comparing the effects of sphingosine and the cell permeable short-chain ceramide analog C₂-ceramide to those of sphinganine and C₂- dihydroceramide, which lack this structural feature. The effects of the sphingoid bases, C₂-ceramide, and C₂-dihydroceramide on apoptosis were determined by detecting 200-bp DNA ladders or hypodiploid areas (sub-G₀/G₁), indicative of apoptosis, in HCT-116 human colon cancer cells. In addition, the effects of the sphingoid bases at an apoptotic concentration for 12 hours on cell cycle distribution were determined by flow cytometry. The results indicated that the sphingoid bases and C ₂-ceramide induced apoptosis, whereas C₂-dihydroceramide had no effects. Sphingoid bases arrested the cell cycle at the G₂/M phase. The present study provides evidence that the 4,5-trans double bond is necessary for the apoptotic effect of C₂-ceramide, but not for that of sphingoid bases.