|SULLARDS, M. CAMERON|
Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2008
Publication Date: 2/20/2009
Citation: Zitomer, N.C., Mitchell, T.R., Voss, K.A., Bondy, G.S., Pruett, S.T., Garnier-Amblard, E.C., Liebeskind, L.S., Park, H., Wang, E., Sullards, M., Merrill, A.H., Riley, R.T. 2009. Ceramide synthase inhibition by fumonisin B1 causes accumulation of 1-deoxy-sphinganine: a novel category of bioactive 1-deoxy-sphingoid bases and 1-deoxy-dihydroceramides biosynthesized by mammalian cell lines and animals. Journal of Biological Chemistry. 284(8):4786-4795.
Interpretive Summary: Fumonisin B1 (FB1) is a chemical produced by a mold commonly found on corn. In animals and plants it prevents the formation of a group of fats known as sphingolipids and disrupts the metabolism of sphingolipids and other fats. As a result of disrupting sphingolipid metabolism, fumonisin causes kidney and liver toxicity and other disease. Disruption of sphingolipid metabolism in cultured cells causes the accumulation of a chemical called sphinganine (Sa), its metabolite Sa 1-phosphate and a previously unidentified metabolite. Sophisticated chemical analysis of the latter showed that the unidentified metabolite was a novel compound known as 1-deoxysphinganine (1-deoxySa). This novel compound arises from condensation of the amino acid alanine with the fatty acid palmitoyl-CoA via an enzyme known as serine palmitoyltransferase (SPT). The 1-deoxySa was found to be toxic to the cells and it was also detected in mouse liver and kidney, therefore, this compound is likely to contribute to pathologies associated with fumonisins. Interestingly, in the absence of FB1, substantial amounts of 1-deoxySa are made and enzymatically modified by the addition of fatty acids (acylation) on the primary amino group of the 1-deoxySa. This new group of acylated 1-deoxySa was also detected in cultured cells and mouse liver and kidney. Thus, these compounds are an underappreciated category of bioactive sphingolipids that might play important roles in cell regulation.
Technical Abstract: Fumonisin B1 (FB1) is a mycotoxin that inhibits ceramide synthases (CerS) and causes kidney and liver toxicity and other disease. Inhibition of CerS by FB1 increases sphinganine (Sa), Sa 1-phosphate and a previously unidentified metabolite. Analysis of the latter by quadrupole-time-of-flight mass spectrometry assigned a m/z = 286.3123 in positive ionization mode, consistent with the molecular formula for deoxy-sphinganine (C18H40NO). Comparison with a synthetic standard using liquid chromatography, electrospray tandem mass spectrometry identified the metabolite as 1-deoxysphinganine (1-deoxySa) based on LC mobility and production of a distinctive fragment ion (m/z 44, CH3CH=NH2+) upon collision induced dissociation. This novel sphingoid base arises from condensation of alanine with palmitoyl-CoA via serine palmitoyltransferase (SPT) as evidenced by incorporation of [U-13C]-L-alanine into 1-deoxySa by Vero cells; inhibition of its production in LLC-PK1 cells by myriocin, an SPT inhibitor; and the absence of incorporation of [U-13C]palmitate into [13C]1-deoxySa in LY-B cells, which lack SPT activity, whereas, LY-B-LCB1 cells, in which SPT has been restored by stable transfection, produce large amounts of [13C]1-deoxySa. 1-deoxySa was elevated in FB1-treated cells and mouse liver and kidney, and its cytotoxicity was > that of Sa for LLC-PK1 and DU-145 cells, therefore, this compound is likely to contribute to pathologies associated with fumonisins. In the absence of FB1, substantial amounts of 1-deoxySa are made and acylated to N-acyl-1-deoxySa (i.e., 1-deoxy-dihydroceramides) by mammalian cells and tissues. Thus, these compounds are an underappreciated category of bioactive sphingoid bases and “ceramides” that might play important roles in cell regulation.