J Biol Chem, Vol. 273, Issue 30, 19060-19064, July 24, 1998

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

Hans-Ulrich Humpf, Eva-Maria Schmelz^¶, Filmore I. Meredith, Hubert Vesper^¶, Teresa R. Vales^¶, Elaine Wang^¶, David S. Menaldino^¶, Dennis C. Liotta^¶, and Alfred H. Merrill Jr.^¶

From the  Lehrstuhl für Lebensmittelchemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany, ^¶ Departments of Chemistry and Biochemistry, Emory University School of Medicine, Atlanta, Georgia 30322, and  Toxicology & Mycotoxin Research Unit, United States Department of Agriculture, Agricultural Research Service, Athens, Georgia 30613

Fumonisin B₁ (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 (AP₁) that is formed upon base hydrolysis of the ester-linked tricarballylic acids of FB₁. Both FB₁ and, to a lesser extent, AP₁ 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 AP₁ (but not FB₁, under the conditions tested) to N-palmitoyl-AP₁ (PAP₁) with a V_max/K_m of approximately 1. The toxicity of PAP₁ was evaluated using HT29 cells, a human colonic cell line. PAP₁ was at least 10 times more toxic than FB₁ or AP₁ 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 AP₁ is acylated to PAP₁, a new category of ceramide synthase inhibitor as well as a toxic metabolite that may play a role in the diseases caused by fumonisins.