Acylation of naturally occurring and synthetic 1-deoxysphinganines by ceramide synthase -: Formation of N-palmitoyl-aminopentol produces a toxic metabolite of hydrolyzed fumonisin, AP1, and a new category of ceramide synthase inhibitor

Fumonisin B-1 (FB1) is the predominant member of a family of mycotoxins produced by Fusarium moniliforme (Sheldon) and related fungi. Certain foods also contain the aminopentol backbone (AP(1)) that is formed upon base hydrolysis of the ester-linked tricarballylic acids of FB,. Both FB, and, to a lesser extent, AP(1) inhibit ceramide synthase due to structural similarities between fumonisins (as 1-deoxy-analogs of sphinganine) and sphingoid bases. To explore these structure-function relationships further, erythro- and threo-2-amino, 3-hydroxy- (and 3, 5-dihydroxy-) octadecanes were prepared by highly stereoselective syntheses. All of these analogs inhibit the acylation of sphingoid bases by ceramide synthase, and are themselves acylated with V-max/K-m of 40-125 for the erythro-isomers (compared with approximately 250 for D-erythro-sphinganine) and 4-6 for the threo-isomers. Ceramide synthase also acylates AP(1) (but not FB,, under the conditions tested) to N-palmitoyl-AP(1) (PAP(1)) with a V-max/K-m of approximately 1. The toxicity of PAP(1) was evaluated using HT29 cells, a human colonic cell line. PAP(1) was at least 10 times more toxic than FB, or AP(1) and caused sphinganine accumulation as an inhibitor of ceramide synthase. These studies demonstrate that: the 1-hydroxyl group is not required for sphingoid bases to be acylated; both erythro- and threo isomers are acylated with the highest apparent V-max/K-m for the erythro-analogs; and AP(1) is acylated to PAP(1), a new category of ceramide synthase inhibitor as well as a toxic metabolite that may play a role in the diseases caused by fumonisins.