ACYLATION OF NATURALLY-OCCURRING AND SYNTHETIC 1-DEOXYSPHINGANINES BYCERAMIDE SYNTHASE - FORMATION OF N-PALMITOYL-AMINOPENTOL PRODUCES A TOXIC METABOLITE OF HYDROLYZED FUMONISIN, AP(1), AND A NEW CATEGORY OF CERAMIDE SYNTHASE INHIBITOR

Fumonisin B-1 (FB1) is the predominant member of a family of mycotoxin s produced by Fusarium moniliforme (Sheldon) and related fungi. Certai n foods also contain the aminopentol backbone (AP(1)) that is formed u pon base hydrolysis of the ester-linked tricarballylic acids of FB,. B oth FB, and, to a lesser extent, AP(1) inhibit ceramide synthase due t o structural similarities between fumonisins (as 1-deoxy-analogs of sp hinganine) and sphingoid bases. To explore these structure-function re lationships further, erythro- and threo-2-amino, 3-hydroxy- (and 3, 5- dihydroxy-) octadecanes were prepared by highly stereoselective synthe ses. All of these analogs inhibit the acylation of sphingoid bases by ceramide synthase, and are themselves acylated with V-max/K-m of 40-12 5 for the erythro-isomers (compared with approximately 250 for D-eryth ro-sphinganine) and 4-6 for the threo-isomers. Ceramide synthase also acylates AP(1) (but not FB,, under the conditions tested) to N-palmito yl-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 sphi nganine accumulation as an inhibitor of ceramide synthase. These studi es demonstrate that: the 1-hydroxyl group is not required for sphingoi d bases to be acylated; both erythro- and threo isomers are acylated w ith 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 a s well as a toxic metabolite that may play a role in the diseases caus ed by fumonisins.