|Voss, Kenneth - Ken|
|Merrill, jr, Alfred|
Submitted to: Molecular Nutrition and Food Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/22/2007
Publication Date: 8/29/2007
Citation: Seiferlein, M., Humpf, H., Voss, K.A., Sullards, C.M., Allegood, J.C., Wang, E., Merrill, Jr, A.H. 2007. Hydrolyzed fumonisins HFB1 and HFB2 are acylated in vitro and in vivo by ceramide synthase to form cytotoxic N-acyl-metabolites. Molecular Nutrition and Food Research 51:1120-1130. Interpretive Summary: Fumonisins B1 (FB1) and B2 (FB2) are fungal toxins found in corn and in corn-based foods. When corn is cooked by nixtamalization, the process for making masa for tortillas and other foods, FB1 and FB2 are converted to the hydrolyzed forms, HFB1 and HFB2, also known as AP1 and AP2, respectively. Results of rat feeding studies indicated that HFB1 and other hydrolyzed fumonisins were toxic whereas, in contrast, HFB1 was not toxic when fed to mice. While there is no evidence that FB1 of FB2 are metabolized by animals, it has been shown that HFB1 can be metabolically combined with a fatty acid by enzymes found in rat liver to form a compound known as N-acyl AP1. We have done additional experiments to further define the metabolism of HFB1 and HFB2 and found that the rate at which the N-acyl AP1 and N-acyl AP2 compounds were formed depended on the type of fatty acid present in the incubation mixture. Other experiments showed that the N-acyl AP1 and N-acyl AP2 metabolites of HFB1 and HFB2 were toxic to cells. When the livers of rats given HFB1 for five days were analyzed, it was converted to a series of N-acyl AP1 compounds that differed from one another by the composition of their fatty acid component. This is the first report of the metabolism of HFB1 in animals. Because metabolism affects biological activity, improved understanding of the metabolism and biological effects of hydrolyzed fumonisins and their metabolites will be important for understanding the potential implications of these compounds for human health.
Technical Abstract: Fumonisins are produced by Fusarium verticillioides and other Fusarium species. They are found in corn and corn-based foods. Fumonisins B1 (FB1) and B2 (FB2), the most abundant fumonisins, are toxic to animals and disrupt sphingolipid metabolism by inhibiting the enzyme ceramide synthase. Their hydrolyzed forms, HFB1 and HFB2 (also known as aminopentols, AP1 and AP2) are found in foods prepared from nixtamalized corn. HFB1 inhibits ceramide synthase and is cytotoxic in vitro, but conflicting reports have been obtained from rodent feeding studies regarding the in vivo toxicity of hydrolyzed fumonisins. Hepatic metabolism of FB1 or FB2 has not been demonstrated, however, when incubated with rat liver microsomes in the presence of the fatty acid cosubstrates palmitoyl coenzyme A or ner¬vonoyl coenzyme A in vitro, HFB1 and HFB2 were converted to their respective N-acylated metabolites, palmitoyl- and nervonoyl-AP1/2. The formation of the nervonoyl compounds (C24:1-AP1/2) occurred faster than the formation of the palmitoyl compounds, C16-AP1/2. Vmax was 156.5 pmol/min/mg protein when HFB1 was incubated with nervonoyl coenzyme A and 8.7 pmol/min/mg protein when incubated with palmitoyl coenzyme A. The acylation products inhibited ceramide synthase in vitro at 1 and 10 'molar concentrations and were also cytotoxic to the human colonic cell line (HT29) in vitro (MTT assay). Furthermore, HPLC-MS/MS analysis of tissue samples from rats given intraperitoneal doses of HFB1 for five days demonstrated the in vivo formation of a mixture of N-acylated AP1 metabolites having fatty acids of various chain lengths. This is the first demonstration of the in vivo metabolism of hydrolyzed fumonisins to compounds that have cytotoxic and ceramide inhibitory properties. Further investigations on the metabolism of hydrolyzed fumonisins and the potential toxicity of the metabolites in vivo are warranted.