Effects of Synthetic Sphingosine-1-Phosphate Analogs on Cytosolic Phospholipase A₂α–Independent Release of Arachidonic Acid and Cell Toxicity in L929 Fibrosarcoma Cells: the Structure–Activity Relationship

Abstract

Sphingolipid metabolites including ceramide, sphingosine, and their phosphorylated products [sphingosine-1-phosphate (S1P) and ceramide-1-phosphate] regulate cell functions including arachidonic acid (AA) metabolism and cell death. The development of analogs of S1P may be useful for regulating these mediator-induced cellular responses. We synthesized new analogs of S1P and examined their effects on the release of AA and cell death in L929 mouse fibrosarcoma cells. Among the analogs tested, several compounds including DMB-mC11S [dimethyl (2S,3R)-2-tert-butoxycarbonylamino-3-hydroxy-3-(3'-undecyl)phenylpropyl phosphate] and DMB-mC9S [dimethyl (2S,3R)-2-tert-butoxycarbonylamino-3-hydroxy-3-(3'-nonyl)phenylpropyl phosphate] released AA within 1 h and caused cell death 6 h after treatment. The release of AA was observed in C12 cells [a L929 variant lacking a type α cytosolic phospholipase A₂ (cPLA₂α)] and L929-cPLAα–siRNA cells (L929 cells treated with small interference RNA for cPLA₂α). Treatment with pharmacological inhibitors of secretory and Ca²⁺-independent PLA₂s decreased the DMB-mC11S–induced release of AA. The effect of the S1P analogs tested on the release of AA was comparable to that on cell death in L929 cells, and a high correlation coefficient was observed. Two analogs lacking a butoxycarbonyl moiety [DMAc-mC11S (dimethyl (2S,3R)-2-acetamino-3-hydroxy-3-(3'-undecyl)phenylpropyl phosphate] and DMAm-mC11S [dimethyl (2S,3R)-2-amino-3-hydroxy-3-(3'-undecyl)phenylpropyl phosphate)] had inhibitory effects on the release of AA and cell toxicity induced by DMB-mC11S. Synthetic phosphorylated lipid analogs may be useful for studying PLA₂ activity and its toxicity in cells.
[Supplementary Fig. 1: available only at http://dx.doi.org/10.1254/jphs.08284FP]