N-oleoylethanolamine inhibits glucosylation of natural ceramides in CHP-100 neuroepithelioma cells: Possible implications for apoptosis

We report that N-oleoylethanolamine (NOE), widely employed as a ceramidase inhibitor, also inhibits glucosylation of naturally occurring ceramides. When CHP-100 neuroepithelioma cells were exposed for 18 h to non-toxic NOE concentrations (i.e. up to 70 μM), basal incorporation of labelled hexose into glucosylceramide (GlcCer) and higher order neutral glycosphingolipids was significantly inhibited. In cells treated with 30 μM N-hexanoylsphingosine C₆-Cer), NOE affected only marginally short-chain glucocerebroside accumulation, but markedly decreased accumulation of glucocerebrosides originating from glucosylation of a long-chain ceramide (Lc-Cer) pool produced upon C₆-Cer treatment. Evidence is provided that NOE effects neither are mediated by their effects on ceramidase nor are due to enhanced long-chain GlcCer (Lc-GlcCer) conversion to higher order glycosylated derivatives. NOE inhibition of Lc-GlcCer generation was accompanied by enhanced accumulation of Lc-Cer and by potentiation of apoptosis induced by C₆-Cer; the possible causal relationships between these two phenomena are discussed.