ApoA-I induces a preferential efflux of monounsaturated phosphatidylcholine and medium chain sphingomyelin species from a cellular pool distinct from HDL3 mediated phospholipid efflux

Electrospray ionization tandem mass spectrometry (ESI-MS/MS) was used for a detailed analysis of cellular phospholipid and cholesterol efflux in free cholesterol (FC) loaded human primary fibroblasts and human monocyte-derived macrophages (HMDM) loaded with enzymatically modified LDL (E-LDL). Although both cell models differed significantly in their cellular lipid composition, a higher apoA-I specific efflux was found for monounsaturated phosphatidylcholine (PC) species together with a decreased contribution of polyunsaturated PC species in both cell types. Moreover, medium chain sphingomyelin (SPM) species SPM 14:0 and SPM 16:1 were translocated preferentially to apoA-I in both cell types. in contrast to fibroblasts, HMDM displayed a considerable proportion of cholesteryl esters (CE) in basal and apoA-I specific efflux media, most likely due to secretion of CE associated to apoE. Analysis of HDL3 mediated lipid efflux from HMDM using D-9-choline and C-13(3)-FC stable isotope labeling revealed significantly different D-9-PC and D-9-SPM species pattern for apoA-I and HDL3 specific efflux media, which indicates a contribution of distinct cellular phospholipid pools to apoA-I and HDL3 mediated efflux. Together with a partial loading of fibroblasts and HMDM with HDL3-derived CE species, these data add further evidence for retroendocytosis of HDL. In summary, analysis of apoA-I/ABCA1 and HDL3 mediated lipid efflux by ESI-MS/MS demonstrated a preferential efflux of monounsaturated PC and medium chain SPM to apoA-I. Moreover, this is the first study, which provides evidence for distinct cellular phospholipid pools used for lipid transfer to apoA-I and HDL3 from the analysis of phospholipid species pattern in HMDM. (c) 2007 Elsevier B.V. All rights reserved.