| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Cholesterol effects on the phospholipid condensation and packing in the bilayer: a molecular simulation study Rog, T. and M. Pasenkiewicz-Gierula (2001), FEBS Lett 502(1-2): 68-71. Abstract: A 15-ns molecular dynamics simulation of the fully hydrated liquid-crystalline dimyristoylphosphatidylcholine-cholesterol (DMPC-Chol) bilayer containing approximately 22 mol% Chol was carried out. The generated trajectory was analysed to investigate the mechanism of the Chol condensing effect on DMPC hydrocarbon chains and the influence of Chol on the chain packing in the membrane. Chol was found to induce stronger van der Waals interactions among the chains, whereas its interactions with the chains were weak. In the DMPC-Chol bilayer, as in the DMPC bilayer, DMPC chains were regularly packed around a chosen chain but around a Chol molecule they were not. DMPC gamma chains made closer contacts with Chol than the beta chains. |
| Cholesterol efflux alters lipid raft stability and distribution during capacitation of boar spermatozoa Shadan, S., P. S. James, et al. (2004), Biol Reprod 71(1): 253-65. Abstract: A reduction in plasma membrane cholesterol is one of the early events that either triggers or is closely associated with capacitation of mammalian spermatozoa. In this investigation, we have examined the effects of cholesterol efflux on tyrosine phosphorylation, lipid diffusion, and raft organization in boar spermatozoa. Results show that a low level of cholesterol efflux, mediated by 5 mM methyl-beta-cyclodextrin (MBCD), enhances capacitation and induces phosphorylation of two proteins at 26 and 15 kDa without affecting sperm viability. Lipid diffusion rates under these conditions are largely unaffected except when cholesterol efflux is excessive. Low-density Triton X100-insoluble complexes (lipid rafts) were isolated from spermatozoa and found to have a restricted profile of proteins. Capacitation-associated cholesterol efflux has no effect on raft composition, but cholesterol depletion destabilizes them completely and phosphorylation is suppressed. During MBCD-mediated capacitation, the distribution of GM1 gangliosides on spermatozoa changes in a sequential manner from overlying the sperm tail to clustering on the sperm head. It is concluded that there is a safe window for removal of plasma membrane cholesterol from spermatozoa within which protein phosphorylation and polarized migration of lipid rafts take place. A preferential loss of cholesterol from the nonraft pool may be the stimulus that promotes raft clustering over the anterior sperm head. |
| Cholesterol efflux as a critical component of Alzheimer's disease pathogenesis Rebeck, G. W. (2004), J Mol Neurosci 23(3): 219-24. Abstract: The risk of Alzheimer's disease and the levels of amyloid deposition are altered by factors associated with high cholesterol levels. When cells have high levels of cholesterol, they induce an efflux system of to maintain a proper cholesterol equilibrium. In the brain, cholesterol is converted to 24S hydroxycholesterol by the enzyme Cyp46. 24S hydroxycholesterol promotes gene transcription through interactions with LXR. We have found that in cells derived from the brain, two proteins important for cholesterol efflux, ABCA1 and apoE, are induced by this system. Furthermore, we have found that pharmacologic induction of LXR also induced secreted Abeta levels, particularly levels of Abeta42. We suggest that the risk of amyloid deposition associated with high cholesterol may be through induction of the LXR system. |
| Cholesterol efflux by acute-phase high density lipoprotein: role of lecithin: cholesterol acyltransferase Khovidhunkit, W., J. K. Shigenaga, et al. (2001), J Lipid Res 42(6): 967-75. Abstract: HDL plays an initial role in reverse cholesterol transport by mediating cholesterol removal from cells. During infection and inflammation, several changes in HDL composition occur that may affect the function of HDL; therefore, we determined the ability of acute-phase HDL to promote cholesterol removal from cells. Acute-phase HDL was isolated from plasma of Syrian hamsters injected with lipopolysaccharide. Cholesterol removal from J 774 murine macrophages by acute-phase HDL was less efficient than that by control HDL because of both a decrease in cholesterol efflux and an increase in cholesterol influx. LCAT activity of acute-phase HDL was significantly lower than that of control HDL. When LCAT activity of control HDL was inactivated, cholesterol efflux decreased and cholesterol influx increased to the level observed in acute-phase HDL. Inactivation of LCAT had little effect on acute-phase HDL. In GM 3468A human fibroblasts, the ability of acute-phase HDL to remove cholesterol from cells was also lower than that of normal HDL. The impaired cholesterol removal, however, was primarily a result of an increase in cholesterol influx without changes in cholesterol efflux. When control HDL in which LCAT had been inactivated was incubated with fibroblasts, cholesterol influx increased to a level comparable to that of acute-phase HDL, without any change in cholesterol efflux. These results suggest that the ability of acute-phase HDL to mediate cholesterol removal was impaired compared with that of control HDL and the lower LCAT activity in acute-phase HDL may be responsible for this impairment. The decreased ability of acute-phase HDL to remove cholesterol from cells may be one of the mechanisms that account for the well-known relationship between infection/inflammation and atherosclerosis. |
| Cholesterol efflux capacity in vitro predicts the severity and extent of coronary artery disease in patients with and without type 2 diabetes Pajunen, P., M. Syvanne, et al. (2001), Scand Cardiovasc J 35(2): 96-100. Abstract: OBJECTIVE: To investigate the relation between severity and extent of coronary artery disease (CAD) and in vitro cholesterol efflux capacity. DESIGN: This study consisted of 46 type 2 diabetic, and 42 nondiabetic men undergoing coronary angiography. Quantitative coronary angiography was used to estimate the severity, extent, and overall "atheroma burden" of CAD. The capacity of patient plasma to induce cholesterol efflux from cultured Fu5AH rat hepatoma cells was measured in vitro. RESULTS: In the combined study population (n = 88), there was a significant inverse correlation between efflux and global atheroma burden (r = -0.23, p < 0.05). In the diabetic group, the global atheroma burden index was independently associated both with cholesterol efflux and with LpA-I levels. However, in the nondiabetic CAD group this association was lost when efflux and LpA-I levels were included in the same model. CONCLUSION: The present study demonstrated that efflux capacity was inversely associated with the severity and extent of CAD. In the diabetic group this association was independent of LpA-I levels, suggesting impaired antiatherogenic potential of these particles in type 2 diabetic patients. |
| Cholesterol efflux effect of high density lipoprotein is impaired by whole cigarette smoke extracts through lipid peroxidation Ueyama, K., M. Yokode, et al. (1998), Free Radic Biol Med 24(1): 182-90. Abstract: It has been reported that high density lipoprotein (HDL) plays an anti-atherogenic role by stimulating cholesterol efflux from the foam cells in the atheromatous lesion. In this study, we prepared a novel modified form of HDL (CS-HDL) by incubating HDL with whole cigarette smoke (CS) extracts containing both particulate matter and gas-phase smoke, and examined its effect on cholesterol efflux. CS-HDL showed a marked increase of conjugated dienes and denaturation of apoA-I, a major protein component of HDL. The cholesterol efflux effect of CS-HDL was remarkably reduced to the same level as that of oxidatively modified HDL induced by copper ion (Ox-HDL). Addition of 20 microg/ml superoxide dismutase (SOD) during the CS-modification of HDL caused retrieval of cholesterol efflux activity by 53% and a remarkable decrease in the conjugated dienes level. SOD, however, had no ameliorative effect on apoA-I denaturation. When HDL was incubated only with gas-phase smoke (gasCS-HDL), neither increase of conjugated dienes nor impairment of the cholesterol efflux effect was observed, whereas apoA-I was denaturated to the same extent as seen in CS-HDL. These results indicate that whole CS-extracts, but not gas-phase smoke, reduces cholesterol efflux effect of HDL and that lipid peroxidation associated with superoxide anion is involved in this functional impairment. |
| Cholesterol efflux from adipose cells is coupled to diacylglycerol production and protein kinase C activation Theret, N., C. Delbart, et al. (1990), Biochem Biophys Res Commun 173(3): 1361-8. Abstract: Apolipoprotein A-I (apo A-I)*/DMPC complexes have been previously shown to promote cholesterol efflux from cholesterol-preloaded adipose cells whereas apo A-II/DMPC complexes, which bind to the same cell surface binding sites, were ineffective. Addition of apo A-I/DMPC complexes led to a rapid and transient formation of diacylglycerol. However, in contrast to PGF2 alpha (Doglio et al., Proc. Natl. Acad. Sci. USA, 1989, 86, 1148), no accumulation of inositol phosphates was observed. Apo A-II/DMPC complexes had no effect on diacylglycerol formation. Stimulation by apo A-I/DMPC complexes or native HDL3 of cells prelabelled with (2-palmitoyl 9,103H)phosphatidylcholine induced also the formation of labelled diacylglycerol whereas apo A-II/DMPC complexes and HDL3 treated with tetranitromethane showed no effect. Direct activation of protein kinase C(s) by PMA promoted cholesterol efflux providing that DMPC liposomes were present as cholesterol acceptor. It is proposed that lipoprotein particles have two separate effects, i.e. a ligand-induced effect leading to cholesterol translocation from intracellular stores to the cell surface and a bilayer-induced effect allowing cholesterol efflux from the cell surface to the acceptor. |
| Cholesterol efflux from cells to immunopurified subfractions of human high density lipoprotein: LP-AI and LP-AI/AII Johnson, W. J., E. P. Kilsdonk, et al. (1991), J Lipid Res 32(12): 1993-2000. Abstract: Using immunoaffinity chromatography, we separated human high density lipoprotein (HDL) into two subfractions: LP-AI, in which all particles contain apolipoprotein A-I (apoA-I) but no apoA-II, and LP-AI/AII, in which all particles contain both apoA-I and apoA-II. To compare LP-AI and LP-AI/AII as acceptors of cell cholesterol, the isolated subfractions were diluted to 50 micrograms phospholipid/ml, and then incubated with monolayer cultures of cells in which whole-cell and lysosomal cholesterol has been labeled with 14C and 3H, respectively. We used three cell types (Fu5AH rat hepatoma cells, normal human skin fibroblasts, and rabbit aortic smooth muscle cells). When these cells were prepared to contain normal physiological quantities of cholesterol (20-35 micrograms/mg protein), LP-AI and LP-AI/AII were nearly equally efficient in promoting efflux of both whole-cell and lysosomal cholesterol. For whole-cell cholesterol, the rate constants for efflux to LP-AI and LP-AI/AII were: 0.050/h and 0.053/h, respectively, with Fu5AH cells; 0.0063/h and 0.0074/h with GM3468 human skin fibroblasts; and 0.0076/h and 0.0079/h with rabbit aortic smooth muscle cells. When cholesterol in hepatoma cells or fibroblasts was elevated two- to threefold above normal, there was still not difference in efflux of whole-cell cholesterol to LP-AI and LP-AI/AII. In longterm incubations, the net depletion of cholesterol mass from cholesterol-enriched cells was either identical with the two HDL subfractions, or somewhat greater with LP-AI/AII.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Cholesterol efflux from fibroblasts to discoidal lipoproteins with apolipoprotein A-I (LpA-I) increases with particle size but cholesterol transfer from LpA-I to lipoproteins decreases with size Agnani, G. and Y. L. Marcel (1993), Biochemistry 32(10): 2643-9. Abstract: To understand the role of different discoidal lipoproteins in cellular cholesterol efflux, defined discoidal lipoproteins containing 2, 3, or 4 apolipoproteins (apo) A-I per particle (Lp2A-I, Lp3A-I, and Lp4A-I) were prepared from mixtures of apoA-I and phospholipids with or without cholesterol. Each particle had a slow pre beta migration on agarose gel electrophoresis which further decreased as the number of apoA-I increased. Incubation of cholesterol-labeled human fibroblasts with the different LpA-I at an equimolar concentration in apoA-I showed that the best acceptors of cellular cholesterol were Lp4A-I, followed by Lp3A-I and Lp2A-I. Cholesterol efflux to these particles was positively correlated to the number of apoA-I, to the ratio of phospholipids to apoA-I, and to the size of particles, three interrelated parameters. To follow the subsequent movement of cellular cholesterol after it became associated with LpA-I, cholesterol- and apoA-I-labeled LpA-I were incubated with plasma which resulted in parallel modifications of each labels electrophoretic migration with time. However, 3Hcholesterol-labeled LpA-I transferred from pre beta to alpha migration with a precursor-product relationship while 125I-LpA-I progressively shifted from pre beta to alpha migration. The change in electrophoretic migration of 125I-LpA-I is independent of cholesterol and appears related only to a modification of apoA-I charge. Lp2A-I was fastest in changing its electrophoretic migration to alpha, followed by Lp3A-I and then Lp4A-I.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Cholesterol efflux from Fu5AH cells to the serum of patients with Alagille syndrome. Importance of the hdl-phospholipids/free cholesterol ratio and of the hdl size distribution Davit-Spraul, A., V. Atger, et al. (1999), J Lipid Res 40(2): 328-35. Abstract: We have previously described the lipoprotein abnormalities in cholestatic children with paucity of interlobular bile ducts (PILBD), and we have shown that two different profiles emerged among these patients, depending on the level of lecithin:cholesterol acyltransferase (LCAT) activity. Reduced LCAT activity was associated with hypo-alpha-lipoproteinemia (group I) whereas normal LCAT activity was associated with hyper-alpha-lipoproteinemia (group II). In both groups, high density lipoproteins (HDL) were enriched with phospholipids and LpA-I particles were predominant. Here, we have investigated the ability of serum and of isolated HDL, obtained from PILBD and control subjects, to promote cellular cholesterol efflux, from Fu5AH rat hepatoma cells. The mean fractional efflux to 5% serum in each group was, on average, following the differences in HDL concentrations (control: 30.1 +/- 4.2%; group I: 23.7 +/- 7.9%, ns; group II: 44.2 +/- 6.5%, P < 0.001). The variations in efflux values in group II were positively correlated to the variations in HDL-PL concentrations (P < 0.0001) and in HDL-PL to serum apo-AI ratio (P < 0.003). By contrast, the variation in efflux in group I was only positively related to the large range of HDL-PL to free cholesterol (FC) ratio values (P < 0.0004). Fractional efflux to isolated HDL, measured at a constant HDL-PL amount, confirmed this relationship (P < 0.0001). Two-dimensional gel electrophoresis of the HDL size and apo A-I distribution in serum, revealed that small size HDL(3) and pre-beta HDL were predominant in the serum of patients from group I, especially those exhibiting low HDL-PL to FC ratio, whereas in the serum of patients from group II, both small HDL(3) and large HDL2 were present.These results suggest that a combination of an imbalance between phospholipids and free cholesterol in the HDL particles and a deficit in large acceptors of cholesterol will be responsible for an impairment of cellular cholesterol efflux in PILBD patients with reduced lecithin:cholesterol acyltransferase activity.-Davit-Spraul, A., V. Atger, M. L. Pourci, M. Hadchouel, A. Legrand, and N. Moatti. Cholesterol efflux from Fu5AH cells in the serum of patients with Alagille syndrome: importance of the HDL-phospholipids/free cholesterol ratio and of the HDL size distribution. |
| Cholesterol efflux from Fu5AH hepatoma cells induced by plasma of subjects with or without coronary artery disease and non-insulin-dependent diabetes: importance of LpA-I:A-II particles and phospholipid transfer protein Syvanne, M., G. Castro, et al. (1996), Atherosclerosis 127(2): 245-53. Abstract: We measured the capacity of human plasma to induce cholesterol efflux from Fu5AH rat hepatoma cells in four groups of men with or without non-insulin-dependent diabetes mellitus (NIDDM) and coronary artery disease (CAD). Plasma from men with both NIDDM and CAD (n = 47) had the lowest efflux capacity (17.3 +/- 3.6%) whereas healthy control subjects with neither diabetes nor CAD (n = 25) had the highest capacity (19.8 +/- 3.4%). The groups with CAD but no diabetes (n = 44) and with NIDDM but no CAD (n = 35) had intermediate efflux values (18.5 +/- 3.8 and 18.5 +/- 3.9%, respectively). In a 2 x 2 factorial ANOVA, the differences were significant with respect to the presence of CAD (P = 0.038) and NIDDM (P = 0.041), with no interaction between the factors. The concentration of HDL particles containing apolipoprotein (apo) A-I but no apo A-II (LpA-I) was not related to efflux capacity in univariate or multivariate analyses. A multivariate regression analysis showed that when controlled for the presence of NIDDM and CAD, the concentration of particles containing both apo A-I and apo A-II (LpA-I:A-II) and plasma phospholipid transfer protein activity were both positively, independently, and significantly (P < 0.001) related to cholesterol efflux capacity. |
| Cholesterol efflux from human monocyte-derived macrophages in the presence of LpA-I:A-II Skarlatos, S. I., N. Duverger, et al. (1995), Biochim Biophys Acta 1270(1): 19-25. Abstract: Previous epidemiological studies have suggested that the LpA-I subfraction of HDL is more protective than the LpA-I:A-II subfraction against the development of cardiovascular disease. A possible basis for a specific anti-atherogenic function of LpA-I emerged from studies of cholesterol efflux from cultured mouse adipocytes. LpA-I efficiently removed excess cholesterol from the mouse adipocytes, while LpA-I:A-II was ineffective. On the other hand, LpA-I:A-II was able to stimulate cholesterol efflux from a number of other cell types including rodent macrophages. Because of previously reported differences in HDL stimulation of cholesterol clearance from macrophages of different origins, we determined whether LpA-I:A-II could induce cholesterol efflux from cultured human monocyte-macrophages. Our findings showed that LpA-I:A-II and HDL3 effectively stimulated cholesterol efflux from human monocyte-macrophages enriched with cholesterol by incubation with AcLDL. LpA-I:A-II also decreased by one-half the amount of cholesterol accumulated when macrophages were incubated with AcLDL and LpA-I:A-II together. Thus, it would appear that the differential anti-atherogenic effects of LpA-I:A-II and LpA-I do not derive from their effects on macrophage cholesterol efflux. Possibly these HDL subfractions differentially affect other biologic processes that modulate the development of cardiovascular disease. |
| Cholesterol efflux from macrophages and other cells von Eckardstein, A. (1996), Curr Opin Lipidol 7(5): 308-19. Abstract: Foam cell formation by lipid accumulation in macrophages is a prominent finding in atherosclerotic plaques. Since macrophages cannot limit the uptake of lipids, cholesterol efflux is probably essential to inhibit progression and cause regression of atherosclerosis. Cholesterol efflux is generally attributed to HDL in the extracellular space. Slow bidirectional fluxes of cholesterol occur between plasma membrane and lipid-rich HDL subclasses. Esterification of cholesterol in HDL by lecithin: cholesterol acyltransferase causes net cholesterol efflux. In contrast, some lipid-free apolipoproteins (especially apolipoprotein A-I) and lipid-poor HDL subclasses such as prebeta 1-apolipoprotein A-I containing lipoprotein mediate rapid and unidirectional cholesterol efflux from specific cholesterol domains in the plasma membrane. Extracellular presence of HDL or apolipoprotein A-I moreover facilitates the translocation of cholesterol from intracellular pools to the plasma membrane, probably via signal transduction. The activated transfer machinery appears to involve the Golgi apparatus and diverts cholesterol from the shuttle between acylcoenzyme A: cholesterol acyltransferase and neutral cholesteryl ester hydrolase (cholesteryl ester cycle). Endogenously synthesized apolipoprotein E facilitates HDL-mediated cholesterol efflux from macrophages. Moreover, at least in human monocyte-derived macrophages, apolipoprotein E appears to be involved in the export of cholesterol independently from extracellular acceptors. Cholesterol efflux can be inhibited by some oxysterols that are found in macrophages of atherosclerotic plaques and macrophages that are loaded in vitro with oxidized LDL. |
| Cholesterol efflux from macrophages mediated by high-density lipoprotein subfractions, which differ principally in apolipoprotein A-I and apolipoprotein A-II ratios von Hodenberg, E., S. Heinen, et al. (1991), Biochim Biophys Acta 1086(2): 173-84. Abstract: High-density lipoprotein (HDL) was fractionated by preparative isoelectric focussing into six distinct subpopulations. The major difference between the subfractions was in the molar ratio of apolipoprotein A-I to apolipoprotein A-II, ranging from 2.1 to 0.5. The least acidic particles had little apolipoprotein A-II, were larger and contained the most lipid. The efflux capacity of the HDL subfractions was tested with mouse peritoneal macrophages and a mouse macrophage cell line (P388D1), either fed with acetylated low-density lipoprotein or free cholesterol. All the HDL subfractions were equally able to efflux cholesterol. The efflux was concentration dependant and linear for the first 6 h. The HDL subfractions bound with high affinity (Kd = 6.7-7.9 micrograms/ml) at 4 degrees C to the cell surface of P388D1 cells (211,000-359,000 sites/cell). Ligand blotting showed that all the HDL subfractions bound to membrane polypeptides at 60, 100, and 210 kDa. These HDL binding proteins may represent HDL receptors. In summary HDL particles, which differed principally in ratio of apolipoprotein A-I to apolipoprotein A-II behaved in a similar manner for both cholesterol efflux and cell surface binding. |
| Cholesterol efflux from normal and Tangier disease fibroblasts into normal, high-density lipoprotein-deficient, and apolipoprotein E-deficient plasmas Schuler-Luttmann, S., Y. Zhu, et al. (2000), Metabolism 49(6): 770-7. Abstract: Tangier disease (TD) fibroblasts have defective cholesterol release in the presence of lipid-free apolipoproteins. We compared normolipidemic probands and patients with apolipoprotein A-I (apoA-I) deficiency, apoE deficiency, or TD in terms of the plasma capacity to induce the efflux of 3H-cholesterol from normal and TD fibroblasts and to esterify this cell-derived cholesterol. Compared with normal fibroblasts, TD fibroblasts released a significantly smaller fraction of 3H-cholesterol into normal, high-density lipoprotein (HDL)-deficient, and apoE-deficient plasmas. Supplementation of apoE-deficient plasma with exogenous apoE normalized the cholesterol efflux from normal cells but did not fully restore the reduced cholesterol efflux from TD fibroblasts. Compared with control plasma, HDL- and apoE-deficient plasmas had a significantly reduced activity to esterify cell-derived cholesterol. Cholesterol derived from TD fibroblasts was less available for esterification in either patient or normal plasmas than cholesterol derived from normal cells. The esterification defect of TD cell-derived cholesterol was more pronounced in patient plasmas than in control plasma. We conclude that (1) apoA-I and, to a lesser degree, apoE are important determinants of the cholesterol efflux and esterification capacity of plasma, (2) TD fibroblasts have a reduced capacity to release cholesterol into the plasma, and (3) TD cell-derived cholesterol is less available for esterification in plasma than cholesterol from normal fibroblasts. The absence of distinct apoA-I- or apoE-containing subclasses aggravates the defective efflux and esterification of cholesterol derived from TD cells. |
| Cholesterol efflux in vivo from a depot of cationized LDL injected into a thigh muscle of small rodents Stein, O., Y. Dabach, et al. (1997), Atherosclerosis 133(1): 15-22. Abstract: We have developed a model system to measure quantitatively removal of cholesterol from a well-defined depot in vivo. To that end, lipoproteins were injected into the rectus femoris muscle of small rodents, using a 25 microliters Hamilton syringe and a 27-gauge needle. In most experiments, the injected volume was 10 microliters containing 200 micrograms of cholesterol. The lipoproteins tested were native or modified LDL labeled with trace amounts of 3Hfree cholesterol (3HFC). The amount of label or of cholesterol mass recovered at various time intervals after injection was normalized to that found after 10 min (designated time 0). In mice, the highest recovery of the 3Hcholesterol 24 h after injection was found with cationized LDL, and ranged between 78% and 84%, whereas retention of native LDL did not exceed 24%. Based on results of 9 experiments with cationized LDL, the loss of 3HFC was mono-exponential between 1 and 14 days and the t1/2 was about 4 days. The disappearance curve of cholesterol mass showed an initial slow and a later more rapid component, the latter with a t1/2 of 4 days. The initial lag is most probably due to the presence of cholesteryl ester, which needs to be hydrolyzed prior to egress. This assumption was verified by injection of cat-LDL labeled with 3Hcholesteryl oleate and finding a similar lag as well as evidence of 3Hcholesteryl ester hydrolysis. Histological examination of the injected muscle 1-4 days after injection of cat LDL showed infiltration with mononuclear cells in an area limited to the site of injection. The presently described model system, which mimics to some extent events occurring during atherogenesis, permits quantitative evaluation of egress of deposited cholesterol and may allow to study the role of HDL in such a process. |
| Cholesterol efflux is defective in macrophages from atherosclerosis-susceptible White Carneau pigeons relative to resistant show racer pigeons Yancey, P. G. and R. W. St Clair (1992), Arterioscler Thromb 12(11): 1291-304. Abstract: White Carneau (WC) pigeons are susceptible to the development of aortic atherosclerosis, whereas Show Racer (SR) pigeons are resistant, even though there are no differences in the known risk factors, including plasma cholesterol levels, lipoproteins, blood pressure, etc. Although this suggests that the difference in atherosclerosis susceptibility between WC and SR pigeons may be mediated at the level of the arterial wall, we have yet to identify a mechanism that can account for this difference. In pigeons as in other species (including humans), macrophages play a major role in the pathogenesis of atherosclerosis. Pigeon macrophages have multiple mechanisms for the uptake of lipoproteins and the accumulation of cholesteryl esters. To date, however, no differences in lipoprotein uptake between macrophages of WC and SR pigeons have been identified that could explain the difference in atherosclerosis susceptibility. In the present study we explored the alternative hypothesis that there are differences in the rate of cholesteryl ester clearance from peritoneal macrophages isolated from the two breeds of pigeons. Cholesterol efflux studies were conducted with elicited pigeon peritoneal macrophages that were loaded with cholesteryl ester either in vitro by incubation with rabbit beta-very low density lipoprotein or in vivo by isolation of macrophages from birds fed a cholesterol-containing diet. Using these techniques we were able to load WC and SR macrophages consistently with cholesteryl esters to levels typical of arterial foam cells (150-1,150 micrograms/mg cell protein). Under these cholesterol loading conditions there was no net efflux of cholesterol from either WC or SR macrophages when incubated for up to 24 hours in the presence of pigeon or human high density lipoprotein (HDL), fetal bovine serum, or lipoprotein-deficient serum. Under the same conditions, efflux of cholesterol from mouse peritoneal macrophages was stimulated by human and pigeon HDL. Despite the inability of HDL, lipoprotein-deficient serum, or fetal bovine serum to promote net cholesterol efflux, apoprotein (apo) HDL/phosphatidylcholine (PC) vesicles stimulated cholesteryl ester clearance from both WC and SR pigeon macrophages but at a significantly slower rate from WC pigeon macrophages. When incubated in the presence of excess apoHDL/PC (400 micrograms/ml), the rate of depletion of cellular cholesteryl esters was log-linear for at least 48 hours. WC macrophages cleared an average of only 9% of their cholesteryl esters in 24 hours when incubated with excess apoHDL/PC, whereas SR macrophages reduced their cholesteryl ester content by an average of 42%.(ABSTRACT TRUNCATED AT 400 WORDS) |
| Cholesterol efflux mediated by apolipoproteins is an active cellular process distinct from efflux mediated by passive diffusion Mendez, A. J. (1997), J Lipid Res 38(9): 1807-21. Abstract: It is becoming increasingly accepted that removal of cellular cholesterol occurs by at least two pathways, one involving the well-described aqueous diffusion mechanism and another promoted by lipid-free apolipoproteins. We compared the contribution of apolipoprotein-dependent and -independent pathways, taking into consideration the influence of cellular metabolism, on cholesterol efflux promoted by different extracellular acceptor types. The acceptors used were assumed to participate in only passive efflux by lipid-dependent mechanisms (phospholipid vesicles and trypsin-modified high density lipoproteins) or to stimulate efflux by apolipoprotein-dependent pathways (purified apolipoprotein A-I and high density lipoproteins). Apolipoprotein-mediated cholesterol efflux was only apparent in growth-arrested or cholesterol-enriched cells and required metabolic energy. In contrast, cholesterol efflux by apolipoprotein-depleted acceptors did not depend on cell growth state, cholesterol enrichment, or metabolic energy. Apolipoprotein-mediated efflux was not observed at temperatures below 22 degrees C, while apolipoprotein-independent efflux was only reduced by 50% at 4 degrees C compared with incubations at 37 degrees C. Additionally, apolipoproteins promoted a more rapid and larger decrease in intracellular cholesteryl esters when measured by changes in cholesteryl ester radioactivity, mass, or the pool of cholesterol available for esterification by acyl coenzyme A:cholesterol acyltransferase. Efflux of excess cellular cholesterol by an apolipoprotein-dependent pathway appears to involve specific cellular events consistent with the properties of an active transport pathway and distinguishable from cholesterol efflux by apolipoprotein-depleted acceptors through passive mechanisms. |
| Cholesterol efflux potential of sera from mice expressing human cholesteryl ester transfer protein and/or human apolipoprotein AI Atger, V., M. de la Llera Moya, et al. (1995), J Clin Invest 96(6): 2613-22. Abstract: The ability of whole serum to promote cell cholesterol efflux and the relationships between apoprotein and lipoprotein components of human serum efflux have been investigated previously (de la Llera Moya, M., V. Atger, J.L. Paul, N. Fournier, N. Moatti, P. Giral, K.E. Friday, and G.H. Rothblat. 1994. Arterioscler. Thromb. 14:1056-1065). We have now used this experimental system to study the selective effects of two human lipoprotein-related proteins, apoprotein AI (apo AI) and cholesteryl ester transfer protein (CETP) on cell cholesterol efflux, when these proteins are expressed in transgenic mice. The percent efflux values for cholesterol released in 4 h from Fu5AH donor cells to 5% sera from the different groups of mice were in the order: background = human apo AI transgenic (HuAITg) > human CETP transgenic (HuCETPTg) > human apo AI and CETP transgenic (HuAICETPTg) >> apo AI knockout mice. In each group of mice a strong, positive correlation (r2 ranging from 0.64 to 0.76) was found between efflux and HDL cholesterol concentrations. The slopes of these regression lines differed between groups of mice, indicating that the cholesterol acceptor efficiencies of the sera differed among groups. These differences in relative efficiencies can explain why cholesterol efflux was not proportional to the different HDL levels in the various groups of mice. We can conclude that: (a) HDL particles from HuAITg mice are less efficient as cholesterol acceptors than HDL from the background mice; (b) despite a lower average efflux due to lower HDL cholesterol concentrations, HDL particles are more efficient in the HuCETPTg mice than in the background mice; and (c) the coexpression of both human apo AI and CETP improves the efficiency of HDL particles in the HuAICETPTg mice when compared with the HuAITg mice. We also demonstrated that the esterification of the free cholesterol released from the cells by lecithin cholesterol acyltransferase in the serum was reduced in the HuAITg and AI knockout mice, whereas it was not different from background values in the two groups of mice expressing human CETP. |
| Cholesterol efflux promotes acrosome reaction in goat spermatozoa Iborra, A., M. Companyo, et al. (2000), Biol Reprod 62(2): 378-83. Abstract: Cholesterol efflux and membrane destabilization play an important role in sperm capacitation and membrane fusion in the acrosome reaction (AR). In this study we establish the effect of cholesterol removal from spermatozoa on acrosomal responsiveness. Mature goat spermatozoa were incubated in BSA-free medium in the presence of beta-cyclodextrin (betaCD) as cholesterol acceptor. After incubation with 8 mM betaCD, 50-60% of cholesterol was released from sperm membranes with no loss in the phospholipid content, and 35% of AR was induced. However, when 30% of cholesterol was lost, this moderate cholesterol decrease was unable to initiate AR. Cholesterol desorption was very rapid, following an exponential kinetics with a half-time of around 10 min, which is in contrast with the slow sigmoidal kinetics of acrosomal responsiveness: around 2 h was required for maximal AR. Our results suggest that cholesterol efflux has a direct influence on the onset of the AR, that is, merely removing cholesterol would trigger the AR. |