In vivo influence of ceramide accumulation induced by treatment with a glucosylceramide synthase inhibitor on ischemic neuronal cell death

It has been shown that exogenous ceramide induces delayed neuronal death (DND) of cultured hippocampal neurons. To evaluate the role of endogenous ceramide in ischemic DND, the glucosylceramide synthase inhibitor, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), was used to generate ceramide in gerbil hippocampi in vivo. The trimethylsilylated derivatives of ceramide were analyzed directly by gas chromatography mass spectrometry, after separation with high-performance thin-layer chromatography. The ceramide compositions in vehicle hippocampus consisted mainly of C18:0 fatty acyl sphingosine (87.9%), with C16:0 and C20:0 ceramides being minor components (7.1% and 5.1%, respectively). Ceramide level in the hippocampi from gerbils subjected to D-PDMP treatment was 1.5-fold higher than those from vehicle-treated gerbils. In spite of the accumulation of ceramide observed in the D-PDMP group, the histological studies did not reveal any ischemic neuronal death in hippocampal CA1 neurons with the gerbils that had been subjected to a sham operation (2-min sublethal ischemia). These results suggest that the ceramide accumulation induced by blocking the de novo synthesis of glucosylceramide with D-PDMP may be independent of the metabolic pathway underlying ischemic DND.