Differential effects of fumonisin B-1 on cell death in cultured cells: thesignificance of the elevated sphinganine

Fumonisins are specific inhibitors of ceramide synthase in sphingolipid met abolism. An alteration in sphingolipid metabolism as a result of fumonisin exposure is related to cell death (Yoo et al., 1992). The objective of this study was to investigate whether elevated free sphinganine levels are rela ted to the sensitivity of cultured cells to fumonisin exposure. Fumonisin B -1 elevated the intracellular free sphinganine concentraions in both LLC-PK 1 and Chinese hamster ovary (CHO) cells. However, CHO cells are resistant t o fumonisin cytotoxicity at 50 muM, while LLC-PK1 cells are sensitive at co ncentrations greater than 35 muM. The intracellular concentration of free s phinganine in LLC-PK1 cells treated at 50 muM fumonisin B-1 for 72 h was ap proximately 1450 pmol/mg protein relative to the 37 pmol observed in the co ntrol culture. Under the same conditions, the population of apoptotic cells in the 50 muM fumonisin B-1-treated culture was approximately 37% of the t otal compared to 12% in the control. The caspase Ill-like activity after 72 h in the 50 CIM fumonisin B-1-exposed culture increased to approximately 5 0 pmol/mg protein/hr compared to 6 pmol/mg protein/hr in the control. L-cyc loserine, a serine palmitoyltransferase inhibitor, reduced the fumonisin B- 1-stimulated caspase Ill-like activity down to the control level. Under the same culture conditions, the intracellular concentration of free sphingani ne after L-cycloserine plus fumonisin B1 treatment was 140 pmol/mg protein compared to 1450 pmol/mg protein in fumonisin B1 alone. The intracellular c oncentration of free sphinganine in CHO cells treated with 50 CIM fumonisin B-1 for 72 h was approximately 460 pmol/mg protein, indicating that the ma ss amount of elevated free sphinganine in the CHO cells was about 32% of th at in LLC-PK1 cells. Adding exogenous sphinganine to the CHO cells along wi th 50 muM fumonisin B-1 treatment for 72 h caused both necrosis and apoptos is. in conclusion, the elevated endogenous sphinganine acts as a contributi ng factor to the fumonisin-induced cell death.