Structural modification of plasma HDL by phospholipids promotes efficient ABCA1-mediated cholesterol release

It has been suggested that ABCA1 interacts preferentially with lipid-poor apolipoprotein A-I (apoA-I). Here, we show that treatment of plasma with dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles generates preβ1-apoA-I-containing lipoproteins (LpA-I)-like particles similar to those of native plasma. Isolated preβ1-LpA-I-like particles inhibited the binding of 125I-apoA-I to ABCA1 more efficiently than HDL3 (IC50 = 2.20 ± 0.35 vs. 37.60 ± 4.78 μg/ml). We next investigated the ability of DMPC-treated plasma to promote phospholipid and unesterified (free) cholesterol efflux from J774 macrophages stimulated or not with cAMP. At 2 mg DMPC/ml plasma, both phospholipid and free cholesterol efflux were increased (∼50% and 40%, respectively) in cAMP-stimulated cells compared with unstimulated cells. Similarly, both phospholipid and free cholesterol efflux to either isolated native preβ1-LpA-I and preβ1-LpA-I-like particles were increased significantly in stimulated cells. Furthermore, glyburide significantly inhibited phospholipid and free cholesterol efflux to DMPC-treated plasma. Removal of apoA-I-containing lipoproteins from normolipidemic plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. Finally, treatment of Tangier disease plasma with DMPC affected the amount of neither preβ1-LpA-I nor free cholesterol efflux.These results indicate that DMPC enrichment of normal plasma resulted in the redistribution of apoA-I from α-HDL to preβ-HDL, allowing for more efficient ABCA1-mediated cellular lipid release. Increasing the plasma preβ1-LpA-I level by either pharmacological agents or direct infusions might prevent foam cell formation and reduce atherosclerotic vascular disease. It has been suggested that ABCA1 interacts preferentially with lipid-poor apolipoprotein A-I (apoA-I). Here, we show that treatment of plasma with dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles generates preβ1-apoA-I-containing lipoproteins (LpA-I)-like particles similar to those of native plasma. Isolated preβ1-LpA-I-like particles inhibited the binding of 125I-apoA-I to ABCA1 more efficiently than HDL3 (IC50 = 2.20 ± 0.35 vs. 37.60 ± 4.78 μg/ml). We next investigated the ability of DMPC-treated plasma to promote phospholipid and unesterified (free) cholesterol efflux from J774 macrophages stimulated or not with cAMP. At 2 mg DMPC/ml plasma, both phospholipid and free cholesterol efflux were increased (∼50% and 40%, respectively) in cAMP-stimulated cells compared with unstimulated cells. Similarly, both phospholipid and free cholesterol efflux to either isolated native preβ1-LpA-I and preβ1-LpA-I-like particles were increased significantly in stimulated cells. Furthermore, glyburide significantly inhibited phospholipid and free cholesterol efflux to DMPC-treated plasma. Removal of apoA-I-containing lipoproteins from normolipidemic plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. Finally, treatment of Tangier disease plasma with DMPC affected the amount of neither preβ1-LpA-I nor free cholesterol efflux. These results indicate that DMPC enrichment of normal plasma resulted in the redistribution of apoA-I from α-HDL to preβ-HDL, allowing for more efficient ABCA1-mediated cellular lipid release. Increasing the plasma preβ1-LpA-I level by either pharmacological agents or direct infusions might prevent foam cell formation and reduce atherosclerotic vascular disease. HDL is believed to be a potent physiological protective system against atherosclerotic vascular disease. Although it has become generally accepted that this protective effect of HDL is attributable to its pivotal role in the reverse cholesterol transport (RCT) process (1Brewer Jr., H.B. Santamarina-Fojo S. New insights into the role of the adenosine triphosphate-binding cassette transporters in high-density lipoprotein metabolism and reverse cholesterol transport.Am. J. Cardiol. 2003; 91: 3E-11EGoogle Scholar, 2Tall A.R. Plasma cholesteryl ester transfer protein.J. Lipid Res. 1993; 34: 1255-1274Google Scholar), structural determinants of molecular interactions between circulating HDL particles and key cell proteins governing the RCT process are complex and not well understood. A growing body of evidence indicates that ABCA1 is a critical cell surface protein required for the transfer of cellular lipid and the maintenance of HDL levels in plasma and is likely important for the first step of RCT from peripheral tissues, including macrophages in the vessel wall (3Joyce C.W. Amar M.J. Lambert G. Vaisman B.L. Paigen B. Najib-Fruchart J. Hoyt Jr., R.F. Neufeld E.D. Remaley A.T. Fredrickson D.S. et al.The ATP binding cassette transporter A1 (ABCA1) modulates the development of aortic atherosclerosis in C57BL/6 and apoE-knockout mice.Proc. Natl. Acad. Sci. USA. 2002; 99: 407-412Google Scholar, 4Marcil M. Bissonnette R. Vincent J. Krimbou L. Genest J. Cellular phospholipid and cholesterol efflux in high-density lipoprotein deficiency.Circulation. 2003; 107: 1366-1371Google Scholar). Furthermore, Brewer and colleagues (5Basso F. Freeman L. Knapper C.L. Remaley A. Stonik J. Neufeld E.B. Tansey T. Amar M.J. Fruchart-Najib J. Duverger N. et al.Role of the hepatic ABCA1 transporter in modulating intrahepatic cholesterol and plasma HDL cholesterol concentrations.J. Lipid Res. 2003; 44: 296-302Google Scholar) have documented that hepatic ABCA1 is a key protein for the formation and maintenance of plasma HDL levels. Moreover, the importance of ABCA1 in the lipidation of apolipoprotein A-I (apoA-I) is highlighted by the finding that >50 mutations in the ABCA1 gene have been associated with a variety of clinically distinct HDL deficiency diseases, including Tangier disease (TD) and familial HDL deficiency (6Marcil M. Brooks-Wilson A. Clee S.M. Roomp K. Zhang L.H. Yu L. Collins J.A. Dam M. van Molhuizen H.O. Loubster O. et al.Mutations in the ABC1 gene in familial HDL deficiency with defective cholesterol efflux.Lancet. 1999; 354: 1341-1346Google Scholar, 7Singaraja R.R. Brunham L.R. Visscher H. Kastelein J.J. Hayden M.R. Efflux and atherosclerosis: the clinical and biochemical impact of variations in the ABCA1 gene.Arterioscler. Thromb. Vasc. Biol. 2003; 23: 1322-1332Google Scholar). These patients are characterized by extremely low HDL-cholesterol levels, caused by defective transport of cellular cholesterol and phospholipids to the extracellular space, leading to hypercatabolism of lipid-poor nascent HDL particles (8Batal R. Tremblay M. Krimbou L. Mamer O. Davignon J. Genest Jr., J. Cohn J.S. Familial HDL deficiency characterized by hypercatabolism of mature apoA-I but not proapoA-I.Arterioscler. Thromb. Vasc. Biol. 1998; 18: 655-664Google Scholar). Earlier studies by Fielding and colleagues (9Castro G.R. Fielding C.J. Early incorporation of cell-derived cholesterol into pre-beta-migrating high-density lipoprotein.Biochemistry. 1988; 27: 25-29Google Scholar, 10Kawano M. Miida T. Fielding C.J. Fielding P.E. Quantitation of pre beta-HDL-dependent and nonspecific components of the total efflux of cellular cholesterol and phospholipid.Biochemistry. 1993; 32: 5025-5028Google Scholar) have documented that a minor subspecies of human HDL that migrates with preβ mobility on agarose gels can remove free cholesterol from cultured fibroblasts at a faster rate than α-migrating HDL, which constitutes the bulk of plasma HDL. Furthermore, it was documented that preβ-HDL particles were present in the peripheral lymph of dogs (11Lefevre M. Sloop C.H. Roheim P.S. Characterization of dog prenodal peripheral lymph lipoproteins. Evidence for the peripheral formation of lipoprotein-unassociated apoA-I with slow pre-beta electrophoretic mobility.J. Lipid Res. 1988; 29: 1139-1148Google Scholar), suggesting a key role for these particles in the initial removal of cholesterol. This is consistent with the concept of Hara and Yokoyama (12Hara H. Yokoyama S. Interaction of free apolipoproteins with macrophages. Formation of high density lipoprotein-like lipoproteins and reduction of cellular cholesterol.J. Biol. Chem. 1991; 266: 3080-3086Google Scholar) that lipid-free or lipid-poor apoA-I interacts with a site on the cell membrane, removes cellular lipids, and generates nascent preβ-HDL particles. Subsequently, preβ-HDL particles become mature, spherical, and α-migrating HDL by the action of LCAT, which converts free cholesterol to cholesteryl ester. Moreover, this concept is supported by studies demonstrating that preβ-HDL particles act as an initial acceptor of cellular cholesterol and shuttle it into a series of larger preβ particles and ultimately to α-migrating particles (13Francone O.L. Gurakar A. Fielding C. Distribution and functions of lecithin:cholesterol acyltransferase and cholesteryl ester transfer protein in plasma lipoproteins. Evidence for a functional unit containing these activities together with apolipoproteins A-I and D that catalyzes the esterification and transfer of cell-derived cholesterol.J. Biol. Chem. 1989; 264: 7066-7072Google Scholar, 14Huang Y. Eckardstein A. von Assmann G. Cell-derived unesterified cholesterol cycles between different HDLs and LDL for its effective esterification in plasma.Arterioscler. Thromb. 1993; 13: 445-458Google Scholar). In spite of the importance of preβ1-apoA-I-containing lipoproteins (LpA-I) particles in RCT, very little is known about their contribution to the human plasma ABCA1-dependent cholesterol efflux pathway. This is likely because of the low amount of these particles and the difficulty of isolating them. These problems were circumvented in the present study by increasing the plasma level of preβ1-LpA-I using dimyristoyl phosphatidylcholine (DMPC) multilamellar vesicles (MLVs). Therefore, our experiments were directed at determining the affinity of these newly formed preβ1-LpA-I-like particles for ABCA1 and monitoring their ability to promote cholesterol efflux from a macrophage cell culture model. Blood samples were obtained from normolipidemic male with an Blood was from the into containing were on experiments in which plasma was with was as the at a of Plasma was from cells by and was on treatment with phospholipids or electrophoretic of apoA-I-containing particles. This study was by the of the Plasma from was by von Eckardstein from the of containing phosphatidylcholine or were as B. M. L. G. O. of the cholesterol efflux of human by enrichment with Lipid Res. Scholar). Plasma from of either normolipidemic or was with phospholipids at their for in the of 2 to the samples were by agarose or At the DMPC-treated plasma samples were from lipoprotein by with as L. M. H. Genest J. and functional of human plasma high lipoprotein containing Lipid Res. 2003; 44: Scholar), phospholipid and free cholesterol efflux of and apolipoprotein in normolipidemic and apolipoprotein Tangier disease. in a apolipoprotein Tangier disease. particles were by as L. M. Davignon J. Genest J. Interaction of lecithin:cholesterol acyltransferase complex with low density lipoprotein protein Evidence for an system in Biol. Chem. Scholar). samples were in the first to their by agarose and in the to the by high molecular protein was as a on samples were particles were by the with native plasma preβ1-LpA-I or preβ1-LpA-I-like particles were isolated from normolipidemic plasma or not with DMPC as M. B. M. M. Krimbou L. Genest J. and cellular of apolipoprotein A-I lipidation by the cassette transporter A1 Biol. Chem. Scholar), with the Plasma samples were or not with DMPC for at in the of 2 DMPC-treated plasma or plasma was to a human were and were by agarose and the was containing the were at the of as L. Tremblay M. H. Davignon J. Cohn J.S. In the of in human Lipid Res. 1998; Scholar). of apoA-I-containing lipoproteins by was as a to which is from the gels by particles were by molecular to lipid-free apoA-I or of isolated preβ1-LpA-I and preβ1-LpA-I-like particles was by the of a apoA-I free of 2 native preβ1-LpA-I was obtained from of normolipidemic plasma, preβ1-LpA-I-like particles was obtained from of DMPC-treated plasma, with an of for both native preβ1-LpA-I and preβ1-LpA-I-like particles. plasma apoA-I was in and against and apoA-I was binding were as M. B. M. M. Krimbou L. Genest J. and cellular of apolipoprotein A-I lipidation by the cassette transporter A1 Biol. Chem. Scholar, L. M. B. M. M. Genest J. interactions between and impact on Lipid Res. Scholar). apoA-I was with by to a of fibroblasts were on and were stimulated with and for were at with 125I-apoA-I in in the of increasing of either native preβ1-LpA-I-like or apoA-I for 2 cells were with and with and with amount of was by experiments were to the in cell binding of the apoA-I be attributable to the 125I-apoA-I binding to different particles of the cells. Therefore, an was in which either preβ1-LpA-I-like particles or HDL3 particles were with 125I-apoA-I similar for the apoA-I binding and the HDL3 was by amount of 125I-apoA-I was associated with the because of between lipid-free 125I-apoA-I and preβ1-LpA-I in our lipid-free 125I-apoA-I was from the using a with a This system between lipid-free apoA-I and particles with molecular lipid-free 125I-apoA-I was associated with preβ1-LpA-I-like particles by as by In we show that both the and the isolated preβ1-LpA-I with an molecular of J774 macrophages were cultured in with At cells were with or for a the cells were and with in with or for Plasma or not with DMPC was of lipoproteins with and Plasma samples of were with cAMP-stimulated or unstimulated cells for at In glyburide was to the together with the Cellular lipid efflux was as in in in results are as of total phospholipid or cholesterol. and were on an HDL-cholesterol was by cholesterol in the of lipoproteins with from the by Plasma apoA-I and were by or by in total plasma was by of apoA-I was by with M. B. M. M. Krimbou L. Genest J. Characterization of human ATP binding cassette transporter for determining the of nascent high density lipoprotein Biol. Chem. Scholar). phospholipid was in native preβ1-LpA-I or preβ1-LpA-I-like particles by the of and L. to phospholipid of cells with and variations of cellular Biol. Scholar). were with are as ± was for between studies by and colleagues B. M. L. G. O. of the cholesterol efflux of human by enrichment with Lipid Res. Scholar) and et A.R. L. Interaction of plasma high density lipoproteins with multilamellar Scholar) have documented that enrichment of human with phospholipid the formation of the effect of DMPC treatment on the redistribution of apoA-I HDL the of apoA-I-containing HDL were by as by and colleagues Roheim P.S. M. Distribution of apoA-I-containing HDL in patients with Thromb. Vasc. Biol. Scholar). Plasma samples from normolipidemic or not with were by and different HDL were by of to the of apoA-I associated with HDL in DMPC treatment of plasma significantly increased the of preβ1-LpA-I the of the particles were significantly At the were in or DMPC treatment of plasma with was a of α-migrating HDL preβ Furthermore, of plasma from a normolipidemic with DMPC preβ1-LpA-I particles in a as by of to the of apoA-I associated with preβ1-LpA-I by newly formed preβ-HDL have and similar to those of native plasma preβ1-LpA-I preβ1-LpA-I-like In we that of plasma with either or not significantly plasma preβ1-LpA-I levels. of isolated preβ1-LpA-I and preβ1-LpA-I-like particles by a in the apoA-I Furthermore, with of isolated native preβ1-LpA-I and preβ1-LpA-I-like particles that both of these particles apoA-I not the the total of isolated native preβ1-LpA-I and preβ1-LpA-I-like particles with but the of of phospholipid in both of these particles. preβ1-LpA-I and preβ1-LpA-I-like particles and of phospholipid of both of these particles or of as by that a of apoA-I-containing particles were as preβ1-LpA-I-like particles in DMPC-treated plasma, the was these newly formed particles with the ABCA1 were to the ability of isolated preβ1-LpA-I-like as well as native preβ1-LpA-I and HDL particles to for the binding of 125I-apoA-I to normal fibroblasts in which ABCA1 was with and in isolated preβ1-LpA-I-like particles inhibited the binding of 125I-apoA-I to ABCA1 more efficiently than HDL3 (IC50 = 2.20 ± 0.35 vs. 37.60 ± 4.78 lipid-free apoA-I was to have a to ABCA1 compared with particles (IC50 = ± vs. 2.20 ± 0.35 At the of binding to ABCA1 were between isolated native preβ1-LpA-I and particles (IC50 = ± vs. 2.20 ± 0.35 experiments were to the in cell binding of the apoA-I be attributable to the 125I-apoA-I binding to different particles of the as in and amount of 125I-apoA-I was associated with either preβ1-LpA-I-like particles or the results in Furthermore, we have documented that the binding of 125I-apoA-I to unstimulated fibroblasts was very low and in ABCA1 fibroblasts M. B. M. M. Krimbou L. Genest J. and cellular of apolipoprotein A-I lipidation by the cassette transporter A1 Biol. Chem. Scholar). native plasma preβ1-LpA-I has been to be the first acceptor of cellular cholesterol (9Castro G.R. Fielding C.J. Early incorporation of cell-derived cholesterol into pre-beta-migrating high-density lipoprotein.Biochemistry. 1988; 27: 25-29Google Scholar), the was the newly formed preβ1-LpA-I-like particles the cholesterol efflux of plasma and to this effect is mediated by the ABCA1 treatment of normolipidemic plasma with increasing of as in and plasma was of lipoproteins with and plasma samples of were for with either or J774 macrophages stimulated or not with cAMP. cell culture has been by to ABCA1-mediated lipid efflux. it was documented that J774 macrophages low levels of ABCA1 and and cholesterol to extracellular by with ABCA1-mediated cholesterol efflux M. L. G. F. F. of density lipoprotein by human cassette transporter but not lipid efflux to high density Biol. Chem. Scholar). in by the of DMPC to plasma, we that DMPC can the ability of plasma to promote both phospholipid and free cholesterol efflux in either stimulated or unstimulated cells in a At 2 mg DMPC/ml plasma DMPC phospholipid efflux to DMPC-treated plasma from cAMP-stimulated cells was increased by compared with unstimulated cells ± vs. ± Similarly, free cholesterol efflux to DMPC-treated plasma was increased significantly compared with unstimulated cells ± vs. ± Similarly, both phospholipid and free cholesterol efflux from stimulated cells to either isolated native preβ1-LpA-I or preβ1-LpA-I-like particles was increased and respectively) compared with unstimulated cells In we show that free cholesterol efflux to of free cholesterol efflux to DMPC-treated plasma Furthermore, were in free cholesterol efflux to between cAMP-stimulated and unstimulated cells not and cholesterol efflux from J774 macrophages to either isolated native preβ1-apoA-I-containing lipoproteins (LpA-I) or preβ1-LpA-I-like particles. J774 cells were with or and stimulated or not with as in and Isolated native preβ1-LpA-I or preβ1-LpA-I-like particles were for with J774 cells. and cholesterol efflux were as of total in the and ± from that preβ1-LpA-I-like particles present in DMPC-treated plasma were for the ABCA1-mediated we the ability of either DMPC-treated or plasma to promote phospholipid and free cholesterol efflux from cAMP-stimulated J774 cells in the or of glyburide an of ABCA1 efflux from stimulated cells to DMPC-treated plasma was reduced by ± vs. ± free cholesterol efflux was reduced by ± vs. ± In phospholipid efflux to plasma was reduced by ± vs. ± free cholesterol efflux was reduced by ± vs. ± in the of Furthermore, treatment of J774 cells with glyburide for not or as by the of apoA-I-containing particles in the of cholesterol efflux of DMPC-treated plasma, plasma from a normolipidemic was from apoA-I-containing lipoproteins by as in and and with DMPC cholesterol efflux in removal of apoA-I-containing lipoproteins from plasma drastically reduced free cholesterol efflux mediated by DMPC-treated plasma. the role of apoA-I-containing particles in the increased ability of DMPC-treated plasma to promote free cholesterol plasma from either patients with or was or not with 2 mg DMPC/ml plasma, and samples were by particles were as in the of a amount of preβ1-LpA-I in plasma of that in DMPC treatment not preβ1-LpA-I levels compared with those in Similarly, DMPC treatment of plasma not promote cholesterol efflux from cAMP-stimulated cells of of plasma from patients with on preβ1-apoA-I-containing lipoproteins (LpA-I) level and efflux from cAMP-stimulated J774 cells. Plasma from of normolipidemic and was or not for with 2 mg plasma at in the of 2 to LCAT, and plasma samples were by samples were together on the for and were for associated with preβ1-LpA-I was by of ± = are plasma samples from and were for with J774 cells stimulated with efflux was as a of total cholesterol in the of ± = are A growing body of evidence indicates that lipid-poor apoA-I not a role in the RCT process but has as a for to the development of atherosclerotic vascular disease T. C.J. M. C.L. et of apoA-I on atherosclerosis in patients with a 2003; Scholar). lipid-poor as plasma has that it more effective than mature α-HDL in or atherosclerosis is a of In the present we of a study by and colleagues B. M. L. G. O. of the cholesterol efflux of human by enrichment with Lipid Res. Scholar) demonstrating that enrichment of human with phospholipid to the formation of HDL This to the affinity of these newly formed particles for ABCA1 and their ability to promote cholesterol efflux. Although the structural of HDL have not been the present study that at 2 mg DMPC/ml plasma, a of particles were to preβ1-LpA-I-like particles and similar to those of native plasma preβ1-LpA-I particles both apoA-I and HDL apoA-I but not M. R. M. L. Roheim P.S. with low HDL cholesterol levels have HDL Thromb. Vasc. Biol. Scholar), it is that the of lipid-poor apoA-I from particles DMPC studies that the lipid of preβ1-LpA-I as well as the of apoA-I these particles from those of HDL C.J. Fielding P.E. of reverse cholesterol Lipid Res. Scholar, high density of apolipoprotein A-I to Scholar). Furthermore, preβ1-LpA-I is to be an initial acceptor of cell-derived consistent with the that lipid-poor apoA-I interacts preferentially with the ABCA1 transporter M. B. M. M. Krimbou L. Genest J. and cellular of apolipoprotein A-I lipidation by the cassette transporter A1 Biol. Chem. Scholar, M. B. M. M. Krimbou L. Genest J. Characterization of human ATP binding cassette transporter for determining the of nascent high density lipoprotein Biol. Chem. Scholar). This concept is supported by our results that both isolated native preβ1-LpA-I and preβ1-LpA-I-like particles have an to ABCA1 compared with HDL3 This is consistent with our results that the of either lipid-free apoA-I or with lipid their affinity for ABCA1 M. B. M. M. Krimbou L. Genest J. and cellular of apolipoprotein A-I lipidation by the cassette transporter A1 Biol. Chem. Scholar, L. M. B. M. M. Genest J. interactions between and impact on Lipid Res. Scholar). studies have documented that efflux to plasma that of the cholesterol from cells is associated with preβ-HDL, it of total plasma apoA-I Y. Eckardstein A. von Assmann G. Cell-derived unesterified cholesterol cycles between different HDLs and LDL for its effective esterification in plasma.Arterioscler. Thromb. 1993; 13: 445-458Google Scholar). We that in preβ1-LpA-I-like particles treatment of plasma with DMPC be associated with a in the ability of DMPC-treated plasma to promote cholesterol efflux the ABCA1 transporter pathway. is supported by the DMPC-treated plasma stimulated phospholipid and free cholesterol efflux from cAMP-stimulated cells compared with unstimulated cells phospholipid and free cholesterol efflux from stimulated cells to isolated native preβ1-LpA-I and preβ1-LpA-I-like particles was increased by compared with that of unstimulated and glyburide inhibited both phospholipid and free cholesterol efflux to DMPC-treated plasma compared with plasma in cAMP-stimulated cells. on these we have that preβ1-LpA-I-like particles significantly to the of cholesterol the ABCA1 in our cAMP-stimulated macrophage cell culture model. it be that in this cholesterol efflux as the or plasma is as an This is in with a study by and colleagues M. L. G. F. F. of density lipoprotein by human cassette transporter but not lipid efflux to high density Biol. Chem. Scholar) that the of the ABCA1-dependent cholesterol efflux be by increasing the of preβ-HDL phospholipid transfer protein or by it Although evidence has been demonstrating that preβ1-LpA-I-like particles with ABCA1 and promote cholesterol efflux the of the it apolipoproteins known to with as be in the of the cholesterol efflux of DMPC-treated plasma. it has been that particles a role in RCT by together with preβ1-LpA-I as initial of cell-derived cholesterol Y. Eckardstein A. von S. Assmann G. of the apolipoprotein on and transfer of cell-derived cholesterol in Scholar). Furthermore, we have documented that the ABCA1 transporter the lipidation of lipid-free in a cell culture L. M. B. M. M. Genest J. interactions between and impact on Lipid Res. Scholar). we that DMPC enrichment of plasma increased the level of plasma in a not It is that particles to the ability of DMPC-treated plasma to promote cholesterol efflux. an in the of DMPC enrichment of plasma, cholesterol from cAMP-stimulated cells was It is likely that the present in plasma of as we have documented L. M. H. Genest J. and functional of human plasma high lipoprotein containing Lipid Res. 2003; 44: Scholar), was to DMPC the of a DMPC effect on preβ1-LpA-I is attributable to the total of α-migrating apoA-I-containing particles in plasma L. M. H. Genest J. and functional of human plasma high lipoprotein containing Lipid Res. 2003; 44: Scholar, Eckardstein A. Y. S. H. G. Assmann G. cholesterol transport in plasma of patients with different of familial HDL Thromb. Vasc. Biol. Scholar). This is consistent with our that removal of apoA-I-containing lipoproteins from normal plasma free cholesterol efflux mediated by DMPC-treated plasma These the of apoA-I-containing particles in the of the cholesterol efflux of DMPC-treated plasma. Earlier studies by and colleagues A.R. L. Interaction of plasma high density lipoproteins with multilamellar Scholar) have documented that of isolated HDL with a of or multilamellar both and HDL3 into lipoproteins of density and increased Furthermore, the formation of was by It is likely that lipoproteins were formed as a of the interactions of with from HDL. This is consistent with our results that both preβ1-LpA-I and particles were increased by DMPC enrichment of plasma. Although the of plasma preβ1-LpA-I has and its role in atherosclerosis is at this C.J. Fielding P.E. of reverse cholesterol Lipid Res. Scholar), preβ1-LpA-I levels have been in disease T. Y. K. T. T. T. M. lipoprotein in Chem. Scholar). a study by and colleagues S. lipoprotein and disease in male of the Thromb. Vasc. Biol. Scholar) documented that preβ1-LpA-I level was not significantly associated with disease and levels a with disease. it was by and colleagues N. and ABCA1-mediated cholesterol efflux to from patients with Lipid Res. Scholar) that preβ1-LpA-I level with ABCA1-mediated and with cell cholesterol efflux. Furthermore, it has been that of into plasma preβ1-LpA-I which can RCT C.J. R. F. G. in and reverse cholesterol transport in Lipid Res. Scholar). This is supported by a study by and colleagues T. C.J. M. C.L. et of apoA-I on atherosclerosis in patients with a 2003; Scholar) demonstrating that complex a of atherosclerosis as by results of the present consistent with the concept that preβ1-LpA-I particles or lipid-poor apoA-I are the for the ABCA1 transporter in the structural of plasma HDL by DMPC resulted in the redistribution of plasma apoA-I in of the lipid-poor apoA-I allowing for more efficient ABCA1-mediated cholesterol release. Although this have it an lipid-poor apoA-I as preβ1-LpA-I has that in than plasma von Eckardstein for plasma. This was supported by from the of and by the and of the in

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