Preferential sphingosine-1-phosphate enrichment and sphingomyelin depletion are key features of small dense HDL3 particles -: Relevance to antiapoptotic and antioxidative activities

Objective - The purpose of this study was to define heterogeneity in the molecular profile of lipids, including sphingomyelin and sphingosine-1-phosphate, among physicochemically-defined HDL subpopulations and potential relevance to antiatherogenic biological activities of dense HDL3. Methods and Results - The molecular profile of lipids (cholesteryl esters, phospholipids, sphingomyelin, and sphingosine-1- phosphate) in physicochemically-defined normolipidemic HDL subpopulations was determined by high-performance liquid chromatography and gas chromatography. As HDL particle size and molecular weight decreased with increment in density, molar lipid content diminished concomitantly. On a % basis, sphingomyelin abundance diminished in parallel with progressive increase in HDL density from HDL2b (12.8%) to HDL3c (6.2%; P < 0.001); in contrast, sphingosine-1- phosphate was preferentially enriched in small HDL3 ( 40 to 50 mmol/mol HDL) versus large HDL2 (15 to 20 mmol/mol HDL; P < 0.01). Small HDL3c was equally enriched in LpA-I particles relative to LpA-I: A-II. The sphingosine-1-phosphate/sphingomyelin ratio correlated positively with the capacities of HDL subspecies to attenuate apoptosis in endothelial cells ( r = 0.73, P = 0.001) and to retard LDL oxidation ( r = 0.58, P = 0.01). Conclusions - An elevated sphingosine-1- phosphate/sphingomyelin ratio is an integral feature of small dense HDL3, reflecting enrichment in sphingosine-1- phosphate, a key antiapoptotic molecule, and depletion of sphingomyelin, a structural lipid with negative impact on surface fluidity and LCAT activity. These findings further distinguish the structure and antiatherogenic activities of small, dense HDL.