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

: 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 µM, whereas l‐PDMP was stimulatory over the same concentration range, and the maximal effect was observed at 10–15 µM. Rat neocortical explants were doubly labeled with [14C]serine and [3H]galactose at 15 µMl‐ 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.