Induction of Ganglioside Biosynthesis and Neurite Outgrowth of Primary Cultured Neurons by l-threo-1-Phenyl-2-Decanoylamino-3-Morpholino-1-Propanol

Abstract: We reported previously that stereoisomers of 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), the d - threo and l - threo forms, exerted inhibitory and stimulatory effects on glycosphingolipid (GSL) biosynthesis in B16 melanoma cells, respectively. In the present study, the primary cultured rat neocortical explants were treated with l - or d - threo -PDMP. These isomers exhibited opposite effects on neurite outgrowth: d -PDMP was inhibitory at concentrations ranging from 5 to 20 µ M , whereas l -PDMP was stimulatory over the same concentration range, and the maximal effect was observed at 10–15 µ M . Rat neocortical explants were doubly labeled with ¹⁴C]serine and ³H]galactose at 15 µ M l - or d -PDMP. l -PDMP increased the incorporations of both labels into sphinganine, sphingosine, ceramide, sphingomyelin, neutral GSLs, and gangliosides, whereas d -PDMP inhibited the glucosylation of ceramide resulting in a reduction of ganglioside biosynthesis and accumulation of precursors of glucosylceramide, ceramide, and sphingomyelin. To clarify the stimulatory effect of l -PDMP on GSL biosynthesis, serine palmitoyltransferase, sphingosine N -acyltransferase, glucosylceramide synthase, lactosylceramide synthase, GM3 synthase, and GD3 synthase were quantified in cell lysates of explants pretreated with this agent. Serine palmitoyltransferase was fully activated up to 150% of the control. Furthermore, marked increases in the activities of lactosylceramide synthase (200%), GM3 synthase (240%), and GD3 synthase (300%) were observed. These results suggest that the neurotrophic action of l -PDMP may be ascribable to its stimulatory effect on the biosynthesis of GSLs, especially that of gangliosides.