Acylation of Naturally Occurring and Synthetic 1-Deoxysphinganines by Ceramide Synthase

Abstract

Fumonisin B 1 (FB 1 ) 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 1 . Both FB 1 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 1 , 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 1 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.Fumonisins are mycotoxins produced by Fusarium moniliforme (Sheldon) and related fungi that are common contaminants of maize and certain other foods (1). Fumonisin B 1 (FB 1 ) 1 is comprised of a long chain aminopentol (AP 1 ) with two of the side chain hydroxyls esterified to tricarballylic acids ( Fig. 1) (2, 3). Although numerous fumonisins have been characterized (1-4), FB 1 is usually the most abundant in contaminated food, except when corn has been treated with base to produce masa flour for tortillas, which hydrolyzes FB 1 to AP 1 (1).Fumonisins are responsible for at least two diseases, equine leukoencephalomalacia and porcine pulmonary edema (5, 6). Studies with these and other animals have uncovered a wide spectrum of toxicologic effects, which include hepatotoxicity, nephrotoxicity, neurotoxicity, developmental toxicity, and immunosuppression (and immunostimulation under some conditions) (for reviews, see Refs. 1, 7, and 8). Fumonisins are also hepatocarcinogenic in rats (1) and have been implicated in esophageal cancer in humans in South Africa and China (9 -11).The diverse effects of these mycotoxins appear to be due to inhibition of ceramide synthase, the enzyme that catalyzes the acylation of sphinganine, sphingosine, and other sphingoid bases (12, 13). Inhibition has been shown in vitro with intact cells and for animals exposed to fumonisins (7) and is manifested by up to several hundredfold incre...

Ceramide Synthase Inhibition by Fumonisin B1 Causes Accumulation of 1-Deoxysphinganine

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