Elevated sphingoid bases and complex sphingolipid depletion as contributing factors in fumonisin-induced cytotoxicity

Fumonisin B1 is an inhibitor of ceramide synthase, a key enzyme in de novo sphingolipid biosynthesis and reacylation of free sphingosine. The purpose of this study was to determine the contribution of increased intracellular free sphinganine and decreased complex sphingolipids on cell growth and cell death induced by fumonisin B1 in pig kidney LLC-PK1 cells. Fumonisin B1 caused an increase in intracellular free sphinganine which preceded depletion of complex sphingolipids, inhibition of cell growth, and cell death. The effects on cell growth and cell death were well correlated with the increase in free sphingoid bases and depletion of complex sphingolipids. Exogenously added sphinganine mimicked the effects of fumonisin, but beta-chloroalanine, an inhibitor of serine palmitoyltransferase which is the first enzyme in de novo sphingolipid biosynthesis, also inhibited cell growth and increased cell death. When added simultaneously, beta-chloroalanine reduced the fumonisin-induced sphinganine increase by approximately 90%; however, it exacerbated the decrease in more complex sphingolipids. The effects of fumonisin on cell growth and cell death were only partially prevented by beta-chloroalanine (approximately 50 to 60%). The results suggest that both the elevation of free sphingoid bases and the decrease in complex sphingolipids contribute to the decreased cell growth and cytolethality of fumonisin B1 in pig kidney LLC-PK1 cells.