Submitted to: Toxicologist
Publication Type: Abstract Only
Publication Acceptance Date: January 15, 2001
Publication Date: March 1, 2001
Interpretive Summary: No Interpretive Summary Required. Abstract presented at the 40th Annual Meeting of the Society of Toxicology, San Francisco, California, March 25-29, 2001.
Technical Abstract: Fumonisin B1 (FB1) is a toxic and carcinogenic fungal metabolite produced on corn by Fusarium verticillioides. It inhibits ceramide synthase, a key enzyme in the biosynthesis and turnover of sphingolipids. It has been proposed that disruption of sphingolipid metabolism by FB1 is the underlying cause of its toxicity. We previously reported that N-acetylation of FB1 prevents the inhibitory effect of FB1 on ceramide synthase. Researchers at another laboratory arrived at the opposite conclusion, and reported that FA1 inhibits ceramide synthase, and therefore that the primary amino group is not necessary for activity. We now report that FA1 spontaneously rearranges to O-acetylated analogs, even under frozen and desiccated conditions, and that rearrangement products but not FA1 itself are inhibitors of ceramide synthase. Liver slices exposed for 20 hr to 0.5 micro-M "contaminated" FA1 containing unknown amounts of O-acetylated FB1 had sphinganine:sphingosine (Sa:So) ratios of 1.15-1.64. Control slices had Sa:So ratios of 0.07-0.24. Clean-up of the contaminated FA1 to remove the O-acetylated FB1 yielded 99% FA1, which produced Sa:So ratios in liver slices of 0.08-0.18. After 2 yrs storage, the purified FA1 contained 8% O-acetylated FB1, and was again capable of ceramide synthase inhibition. Subsequent experiments showed that in neutral solution, FA1 is the most stable form and predominates. In acidic solution, the equilibrium shifts toward the O-acetylated forms. FA1 in solid form also rearranges, but more slowly than in acid solution. Since FA1 is considerably less cytotoxic than FB1, these results support the hypothesis that a primary amino group is necessary for both ceramide synthase inhibition and toxicity.