Fumonisin-induced tumor necrosis factor-alpha expression in a porcine kidney cell line is independent of sphingoid base accumulation induced by ceramide synthase inhibition

Previous studies have shown that fumonisin B-1 (FB1) inhibits ceramide synt hase, resulting in accumulation of free sphinganine and sphingosine. Tumor necrosis factor-alpha (TNF alpha) plays an important role in FB1 toxicity a nd the expression of TNF alpha mRNA in liver and kidney is increased follow ing FB1 exposure in mice. The objective of the current study was to investi gate whether these two events (sphingoid bases accumulation and TNF alpha i nduction) are dependent on each other. An increase in expression of TNF alp ha mRNA was detected in LLC-PK1 cells as early as 4 h after FB, treatment b ut decreased to the control levels after 8 h. A positive linear correlation was observed between the expression of TNF alpha mRNA and FB1 concentratio n. Increases of intracellular sphingoid bases were also detected after 4 h of FB1 treatment and progressively increased until 24 h. Exposure of the ce lls to sphinganine or sphingosine did not significantly alter the expressio n of TNF alpha. Inhibition of sphingoid base biosynthesis by ISP-1, a speci fic inhibitor of serine palmitoyltransferase, the first enzyme in de novo s phingolipid biosynthesis, efficiently blocked the accumulation of free sphi ngoid bases in response to FB1, but it did not prevent the induction of TNF alpha expression. Results indicate that FB1-induced increase in TNF alpha expression is independent of sphingoid base accumulation-induced by ceramid e synthase inhibition in LLC-PK1 cells. (C) 2001 Academic Press.