Ceramide Synthase Inhibition by Fumonisin B1 Causes Accumulation of 1-Deoxysphinganine A NOVEL CATEGORY OF BIOACTIVE 1-DEOXYSPHINGOID BASES AND 1-DEOXYDIHYDROCERAMIDES BIOSYNTHESIZED BY MAMMALIAN CELL LINES AND ANIMALS

Fumonisin B-1 (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 an m/z = 286.3123 in positive ionization mode, consistent with the molecular formula for deoxysphinganine (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 indicated by incorporation of L-[U-C-13] 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-C-13] palmitate into 1-[C-13] deoxySa in LY-B cells, which lack SPT activity. LY-B-LCB1 cells, in which SPT has been restored by stable transfection, however, produce large amounts of 1-[C-13] deoxySa. 1-DeoxySa was elevated in FB1-treated cells and mouse liver and kidney, and its cytotoxicity was greater than or equal to 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-deoxydihydroceramides). Thus, these compounds are an underappreciated category of bioactive sphingoid bases and ceramides that might play important roles in cell regulation.