| For medical practitioners and the general public - Cholesterol Journal Article Catalog. |
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| Modulation of cholesterol levels in broiler meat by dietary garlic and copper Konjufca, V. H., G. M. Pesti, et al. (1997), Poult Sci 76(9): 1264-71. Abstract: Male Ross x Ross 208 chickens were fed from hatching to 21 d of age either a control diet (based on corn and soybean meal) or the control diet supplemented with 0, 1.5, 3.0, and 4.5% of a commercial garlic powder in Experiments 1 and 2. Once the dose-response relationship was established, 3% garlic powder or 63 or 180 mg/kg copper as cupric citrate or cupric sulfate pentahydrate were supplemented to the diet (Experiments 3, 4, 5, and 6). In the first two experiments, reductions of plasma cholesterol (P = 0.006) and triacylglycerols (P = 0.013) and liver (P = 0.012) and breast muscle (P = 0.165) cholesterol were observed in garlic-supplemented birds. Feeding either garlic powder or copper (63 and 180 mg/kg) resulted in reduced levels of plasma cholesterol, liver cholesterol, blood reduced glutathione, and breast and thigh muscle cholesterol. Differences were significant at P < 0.05 in at least one experiment. 3-Hydroxy-3-methylglutaryl reductase activity was decreased due to dietary garlic (P = 0.0369), but not by pharmacological levels of dietary copper (P = 0.982). The activity of fatty acid synthetase was decreased in birds fed copper (P = 0.035). Both garlic and copper supplements decreased cholesterol 7 alpha-hydroxylase activity (P = 0.024 and P = 0.022, respectively). The results of these trials confirm the findings that garlic and copper alter lipid and cholesterol metabolism. However, they do not work by the same mechanism. Feeding dietary garlic or copper for 21 d reduced cholesterol levels of broiler meat without altering growth of the chickens or feed efficiency. |
| Modulation of cholesterol metabolism affects tumor growth in hamsters Kishinaka, M., S. Kuroki, et al. (1998), Fukuoka Igaku Zasshi 89(1): 11-9. Abstract: To investigate the effects of cholesterol and cholesterol-lowering agents on cholesterol metabolism and tumor growth, 0.5% cholesterol, 2% cholestyramine, or 0.01% simvastatin was fed to hamsters with transplanted Simian virus40 transformed tumor cells. Tumor weight, tissue cholesterol and DNA concentrations, and HMG-CoA reductase activities were determined. Cholesterol or cholestyramine feeding did not affect the tumor growth, however, the tumor weight and DNA concentration were decreased and tumor HMG-CoA reductase activity was increased in the simvastatin group. In conclusion, simvastatin may inhibit the DNA synthesis and growth of the Simian virus40 transformed tumor cells possibly through the inhibition of cholesterol and isoprenoids synthesis in the hamster. |
| Modulation of coronavirus-mediated cell fusion by homeostatic control of cholesterol and fatty acid metabolism Cervin, M. and R. Anderson (1991), J Med Virol 35(2): 142-9. Abstract: Cellular susceptibility to fusion mediated by murine coronavirus (mouse hepatitis virus, MHV strain A59) was separated into lipid-dependent and lipid-independent mechanisms with the use of subclones and selected mutants of mouse L-2 fibroblasts. Fusion-resistant L-2 cell mutants had similar cholesterol and fatty acid composition as did their fusion-susceptible parent subclone, and were presumably deficient in a genetically mutable non-lipid, host cell factor (e.g., fusion protein receptor). On the other hand, cellular sensitivity to virus fusion, which is known to be influenced by cell cholesterol content Daya et al., 1988, was shown further to be modulated by homeostatic alterations in fatty acid metabolism. Cholesterol supplementation of mouse L-2 fibroblasts or of peritoneal macrophages from MHV-susceptible mice elevated susceptibility to viral fusion. Increased fusion susceptibility occurred in cholesterol-supplemented L-2 cells in the absence of any detectable alterations in host cell fatty acid composition, thus demonstrating fusion enhancement by cholesterol alone. L-2 cells cloned by limiting dilution in normal (not cholesterol-supplemented) medium were found to be heterogeneous in cholesterol content. Interestingly, high cholesterol-containing subclones had increased levels of C-18:0, C-18:2, C-20:4, and C-22:6 and markedly reduced levels of C-18:1 fatty acids when compared to low cholesterol-containing subclones. High cholesterol-containing subclones did not show enhanced susceptibility to viral fusion, suggesting that homeostatic alteration of fatty acid metabolism compensated for the increased cholesterol levels and countered the normally fusion-enhancing effect of cholesterol alone.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Modulation of endoplasmic reticulum-bound cholesterol regulatory enzymes by iron/ascorbate-mediated lipid peroxidation Brunet, S., L. Thibault, et al. (2000), Free Radic Biol Med 28(1): 46-54. Abstract: Mammalian sterol regulatory enzymes are integral membrane proteins of the endoplasmic reticulum. They play a critical role in liver cholesterol homeostasis and the maintenance of overall cholesterol balance in different species. Because lipid peroxidation has been implicated in hepatic dysfunction and atherosclerosis, we hypothesized that its occurrence could alter the composition and properties of the bilayer lipid environment, and thereby affect the functions of these membrane proteins. Preincubation of rat liver microsomes with iron (Fe)/ascorbate (50 microM/200 microM), known to induce peroxidation, resulted in a significant inhibition of (i) the rate-limiting enzyme in cholesterol biosynthesis, HMG-CoA reductase (46%, p <.01), (ii) the crucial enzyme controlling the conversion of cholesterol in bile acids, cholesterol 7alpha-hydroxylase (48%, p <.001), and (iii) the central enzyme for cholesterol esterification: Acyl-CoA:cholesterol acyltransferase (ACAT, 80%, p <.0001). The disturbances of these key enzymes took place concomitantly with the high production of malondialdehyde (350%, p <.007) and the loss of polyunsaturated fatty acids (36.19 +/- 1.06% vs. 44.24 +/- 0.41 in controls, p <.0008). While alpha-tocopherol simultaneously neutralized lipid peroxidation, preserved microsomal fatty acid status, and restored ACAT activity, it was not effective in preventing Fe/ascorbate-induced inactivation of both HMG-CoA reductase (44%, p <.01) and cholesterol 7alpha-hydroxylase (71%, p <.0001). These results indicate that Fe/ascorbate alters the activity of the rate-determining steps in liver cholesterol metabolism, either directly or via lipid peroxidation, capable of modifying their membrane environment. The present data also suggest that the three regulatory enzymes respond differently when exposed to Fe/ascorbate or antioxidants, which may be due to dissimilar mechanisms. |
| Modulation of endosomal cholesteryl ester metabolism by membrane cholesterol Wang, Y., A. B. Castoreno, et al. (2005), J Biol Chem 280(12): 11876-86. Abstract: Cells acquire cholesterol in part by endocytosis of cholesteryl ester containing lipoproteins. In endosomes and lysosomes cholesteryl ester is hydrolyzed by acidic cholesteryl ester hydrolase producing cholesterol and fatty acids. Under certain pathological conditions, however, such as in atherosclerosis, excessive levels of cholesteryl ester accumulate in lysosomes for reasons that are poorly understood. Here, we have studied endosomal and lysosomal cholesteryl ester metabolism in cultured mouse macrophages and with cell-free extracts. We show that net hydrolysis of cholesteryl ester is coupled to the transfer of cholesterol to membranes. When membrane cholesterol levels are low, absorption of cholesterol effectively drives cholesteryl ester hydrolysis. When cholesterol levels in acceptor membranes approach saturation or when cholesterol export is blocked, cholesterol is re-esterified in endosomes. These results reveal a new facet of cellular cholesterol homeostasis and provide a potential explanation for cholesteryl ester accumulation in lysosomes of atherosclerotic cells. |
| Modulation of endothelial inward-rectifier K+ current by optical isomers of cholesterol Romanenko, V. G., G. H. Rothblat, et al. (2002), Biophys J 83(6): 3211-22. Abstract: Membrane potential of aortic endothelial cells under resting conditions is dominated by inward-rectifier K(+) channels belonging to the Kir 2 family. Regulation of endothelial Kir by membrane cholesterol was studied in bovine aortic endothelial cells by altering the sterol composition of the cell membrane. Our results show that enriching the cells with cholesterol decreases the Kir current density, whereas depleting the cells of cholesterol increases the density of the current. The dependence of the Kir current density on the level of cellular cholesterol fits a sigmoid curve with the highest sensitivity of the Kir current at normal physiological levels of cholesterol. To investigate the mechanism of Kir regulation by cholesterol, endogenous cholesterol was substituted by its optical isomer, epicholesterol. Substitution of approximately 50% of cholesterol by epicholesterol results in an early and significant increase in the Kir current density. Furthermore, substitution of cholesterol by epicholesterol has a stronger facilitative effect on the current than cholesterol depletion. Neither single channel properties nor membrane capacitance were significantly affected by the changes in the membrane sterol composition. These results suggest that 1) cholesterol modulates cellular K(+) conductance by changing the number of the active channels and 2) that specific cholesterol-protein interactions are critical for the regulation of endothelial Kir. |
| Modulation of entry of enveloped viruses by cholesterol and sphingolipids (Review) Rawat, S. S., M. Viard, et al. (2003), Mol Membr Biol 20(3): 243-54. Abstract: Enveloped animal viruses infect host cells by fusion of viral and target membranes. This crucial fusion event occurs either with the plasma membrane of the host cells at the physiological pH or with the endosomal membranes at low pH and is triggered by specific glycoproteins in the virus envelope. Both lipids and proteins play critical and co-operative roles in the fusion process. Interactions of viral proteins with their receptors direct which membranes fuse and viral fusion proteins then drive the process. These fusion proteins operate on lipid assemblies, whose physical and mechanical properties are equally important to the proper functioning of the process. Lipids contribute to the viral fusion process by virtue of their distinct chemical structure, composition and/or their preferred partitioning into specific microdomains in the plasma membrane called 'rafts'. An involvement of lipid rafts in viral entry and membrane fusion has been examined recently. However, the mechanism(s) by which lipids as dynamic raft components control viral envelope-glycoprotein-triggered fusion is not clear. This paper will review literature findings on the contribution of the two raft-associated lipids, cholesterol and sphingolipids in viral entry. |
| Modulation of hepatic and pulmonary drug-metabolizing enzyme activities of rabbits by dietary cholesterol Nakahama, T., M. Fukuhara, et al. (1992), Res Commun Chem Pathol Pharmacol 75(1): 57-68. Abstract: Modulation of the activities of drug-metabolizing enzymes by dietary cholesterol was studied in rabbits. In male rabbits fed a 1.5% cholesterol-diet, an elevated levels of serum cholesterols and triglycerides were observed from the early phase of cholesterol-feeding. At 12 weeks after the onset of cholesterol feeding, a marked increase was observed in the wet weights of livers but not of lungs, while total contents of lipids and cholesterols were elevated in both tissues in cholesterol-fed animals. The content of collagen was increased significantly in livers, but not in lungs and the phase I drug-metabolizing enzyme activities were significantly reduced in livers but remained unchanged in lungs by cholesterol feeding. On the other hand, the phase II drug-metabolizing enzyme activities varied depending on the enzymes in both tissues. The results demonstrate that dietary cholesterol induces different effects on rabbit liver and lung and that the modulation of the hepatic enzymes by dietary cholesterol in rabbits differs from that in rats, mice and guinea pigs in which the activity of the enzymes are elevated by dietary cholesterol. |
| Modulation of intrahepatic cholesterol trafficking: evidence by in vivo antisense treatment for the involvement of sterol carrier protein-2 in newly synthesized cholesterol transport into rat bile Puglielli, L., A. Rigotti, et al. (1996), Biochem J 317 (Pt 3): 681-7. Abstract: Biliary cholesterol represents one of the two major excretory pathways for sterol elimination from the body and plays a central role in cholesterol gallstone formation. Biliary cholesterol originates from a precursor pool of preformed and newly synthesized free cholesterol. Although it has been suggested that newly synthesized and preformed biliary cholesterol are secreted by independent pathways, the specific cellular and molecular mechanisms are unknown. We used male Wistar rats to study the time-course of the appearance of newly synthesized cholesterol, phosphatidylcholine and protein into bile. The specific role of sterol carrier protein-2 (SCP-2) in the transport of newly synthesized biliary cholesterol was evaluated by an in vivo antisense oligonucleotide approach. In contrast to 14Cphosphatidylcholine and 35Sproteins, the time-course of 14Ccholesterol appearance into bile was rapid, and microtubule- and Golgi-independent. In vivo SCP-2 antisense treatment reduced and delayed the appearance of biliary 14Ccholesterol. Furthermore, hepatic SCP-2 expression increased more than 3-fold over control values in rats that had been treated with diosgenin to increase biliary secretion of newly synthesized cholesterol. These results suggest that SCP-2 is necessary for the rapid transport of newly synthesized cholesterol into bile and that hepatocytes can induce SCP-2 expression according to the rate of biliary secretion of newly synthesized cholesterol. |
| Modulation of lipoprotein(a) atherogenicity by high density lipoprotein cholesterol levels in middle-aged men with symptomatic coronary artery disease and normal to moderately elevated serum cholesterol. Regression Growth Evaluation Statin Study (REGRESS) Study Group Cobbaert, C., J. W. Jukema, et al. (1997), J Am Coll Cardiol 30(6): 1491-9. Abstract: OBJECTIVES: This study sought to examine whether lipoprotein(a) levels predict coronary artery lumen changes in patients with symptomatic coronary artery disease (CAD) and normal to moderate hypercholesterolemia. BACKGROUND: Recent conflicting reports have confirmed or refuted the association of lipoprotein(a) with clinical events or angiographically verified disease progression. METHODS: The association between serum lipoprotein(a) and changes in coronary artery lumen was studied in 704 men entered into the Regression Growth Evaluation Statin Study (REGRESS), a double-blind, placebo-controlled, quantitative angiographic study that assessed the effect of 2 years of pravastatin treatment. The primary end points were changes in average mean segment diameter (MSD) and average minimal obstruction diameter (MOD). Pravastatin- and placebo-treated patients were classified as having progressing, regressing or stable CAD, and median lipoprotein(a) concentrations were compared. Bivariate and multivariate regression analyses were performed in the overall patient group and in high risk subgroups. RESULTS: Pravastatin treatment did not affect serum apolipoprotein(a) levels. Median in-trial (sampled at 24 months) apolipoprotein(a) levels for regressing, stable and progressing CAD were, respectively, 130, 162 and 251 U/liter in placebo-treated patients and 143, 224 and 306 U/liter in pravastatin-treated patients. Predictors of MSD and MOD changes were baseline MSD and MOD, in-trial apolipoprotein(a), in-trial high density lipoprotein (HDL) cholesterol and baseline use of long-acting nitrates. The multivariate models predicted 14% of MSD changes and 12% of MOD changes; apolipoprotein(a) predicted only 2.6% and 4.8%, respectively. However, in patients with in-trial HDL cholesterol levels <0.7 mmol/liter, apolipoprotein(a) predicted up to 37% of the arteriographic changes. CONCLUSIONS: Serum lipoprotein(a) levels predict coronary artery lumen changes in normal to moderately hypercholesterolemic white men with CAD; its atherogenicity is marked in the presence of concomitant hypoalphalipoproteinemia. |
| Modulation of membrane cholesterol levels: effects on endothelial cell function Broadley, C., E. Dawidowicz, et al. (1991), Exp Cell Res 193(1): 144-50. Abstract: The endothelial cell lining of blood vessels is now recognized as an active interface between blood and the underlying tissue. Modulation of cholesterol levels in several cell types has resulted in altered cell function. We have removed cholesterol from the endothelial cell membrane and have observed corresponding alterations in endothelial cell function. Following depletion of cholesterol from the endothelial cells, polymorphonuclear leukocyte adhesion to the cells was decreased. Angiotensin-converting enzyme activity of the endothelial cells was increased following removal of cholesterol from the endothelial cell membranes. The results of fluorescence polarization measurements suggest that these changes may be partially explained by altered membrane order. |
| Modulation of membrane function by cholesterol Yeagle, P. L. (1991), Biochimie 73(10): 1303-10. Abstract: The molecular basis for the essential role of cholesterol in mammalian (and other cholesterol-requiring) cells has long been the object of intense interest. Cholesterol has been found to modulate the function of membrane proteins critical to cellular function. Current literature supports two mechanisms for this modulation. In one mechanism, the requirement of 'free volume' by integral membrane proteins for conformational changes as part of their functional cycle is antagonized by the presence of high levels of cholesterol in the membrane. In the other mechanism, the sterol modulates membrane protein function through direct sterol-protein interactions. This mechanism provides an explanation for the stimulation of the activity of important membrane proteins and for the essential requirement of a structurally-specific sterol for cell viability. In some cases, these latter membrane proteins exhibit little or no activity in the absence of the specific sterol required for growth of that cell type. The specific sterol required varies from one cell type to another and is unrelated to the ability of that sterol to affect the bulk properties of the membrane. |
| Modulation of metarhodopsin formation by cholesterol-induced ordering of bilayer lipids Mitchell, D. C., M. Straume, et al. (1990), Biochemistry 29(39): 9143-9. Abstract: The effect of lipid ordering on the kinetics and extent of metarhodopsin II (meta II) formation was evaluated in bovine rhodopsin which had been reconstituted into phosphatidylcholine vesicles containing 0, 15, and 30 mol% cholesterol. The rate of establishment of the dynamic equilibrium between metarhodopsin I (meta I) and the two kinetically distinguished forms of meta II in the branched meta II model meta IIfast and meta IIslow; Straume, M., Mitchell, D. C., Miller, J. L., & Litman, B. J. (1990) Biochemistry (preceding paper in this issue) is derived from kinetic measurements of rhodopsin photolysis in these vesicle systems at several temperatures. Values of the meta I in equilibrium with meta IItotal equilibrium constant, Keq, are calculated from the derived model-dependent rate constants, and are shown to be equivalent to those derived from rapidly acquired absorbance spectra. The presence of 30 mol% cholesterol reduces Keq by approximately 50% between 10 and 37 degrees C. Analysis of the model-dependent parameters in terms of delta H and delta S reveals that cholesterol raises the free energy of meta IIslow, relative to meta I, by increasing delta H whereas it raises the relative free energy of meta IIfast by making delta S meta IIfast relative to meta I less positive. The reduction in Keq by both temperature and cholesterol is found to be directly correlated with a parameter that reflects the free volume available for molecular motion in the hydrophobic core of the bilayer Straume, M., & Litman, B. J. (1988) Biochemistry 27, 7723-7733.(ABSTRACT TRUNCATED AT 250 WORDS) |
| Modulation of Na,K-ATPase and Na-ATPase activity by phospholipids and cholesterol. I. Steady-state kinetics Cornelius, F. (2001), Biochemistry 40(30): 8842-51. Abstract: The effects of phospholipid acyl chain length (n(c)), degree of acyl chain saturation, and cholesterol on Na,K-ATPase reconstituted into liposomes of defined lipid composition are described. The optimal acyl chain length of monounsaturated phosphatidylcholine in the absence of cholesterol was found to be 22 but decreased to 18 in the presence of 40 mol % cholesterol. This indicates that the hydrophobic matching of the lipid bilayer and the transmembrane hydrophobic core of the membrane protein is a crucial parameter in supporting optimal Na,K-ATPase activity. In addition, the increased bilayer order induced by both cholesterol and saturated phospholipids could be important for the conformational mobility of the Na,K-ATPase changing the distribution of conformations. Lipid fluidity was important for several parameters of reconstitution, e.g., the amount of protein inserted and the orientation in the liposomes. The temperature dependence of the Na,K-ATPase as well of the Na-ATPase reactions depends both on phospholipid acyl chain length and on cholesterol. Cholesterol increased significantly both the enthalpy of activation and entropy of activation for Na,K-ATPase activity and Na-ATPase activity of Na,K-ATPase reconstituted with monounsaturated phospholipids. In the presence of cholesterol the free energy of activation was minimum at a lipid acyl chain length of 18, the same that supported maximum turnover. In the case of ATPase reconstituted without cholesterol, the minimum free energy of activation and the maximum turnover both shifted to longer acyl chain lengths of about 22. |
| Modulation of Na,K-ATPase by phospholipids and cholesterol. II. Steady-state and presteady-state kinetics Cornelius, F., N. Turner, et al. (2003), Biochemistry 42(28): 8541-9. Abstract: The effects of phospholipid acyl chain length (n(c)) and cholesterol on several partial reactions of Na,K-ATPase reconstituted into liposomes of defined lipid composition are described. This regards the E(1)/E(2) equilibrium, the phosphoenzyme level, and the K(+)-deocclusion reaction. In addition, the lipid effects on some steady-state properties were investigated. Finally, the effects of cholesterol on the temperature sensitivity of the phosphorylation and spontaneous dephosphorylation reactions were investigated. The fatty acid and cholesterol composition of the native Na,K-ATPase membrane preparation showed a remarkable similarity to the lipid composition known to support maximum hydrolytic capacity as determined from in vitro experiments. The main rate-determining step of the Na,K-ATPase reaction, the E(2) --> E(1) reaction, as well as several other partial reactions were accelerated by cholesterol. This regards the phosphorylation by ATP as well as the E(1) - P --> E(2)-P reaction. Moreover, cholesterol shifted the E(1)/E(2) equilibrium toward the E(1) conformation and increased the K(+)-deocclusion rate. Finally, cholesterol significantly affected the temperature sensitivity of the spontaneous dephosphorylation reaction and the phosphorylation by ATP. The effects of cholesterol were not completely equivalent to those induced by increasing the phospholipid acyl chain length, indicating that the cholesterol effects are not entirely caused by increasing the hydrophobic bilayer thickness, which indicates an additional mechanism of action on the Na,K-ATPase. |
| Modulation of Na+,K+-pump activity and Na+,Li+-exchange in rabbit erythrocytes at various stages of cholesterol feeding Makarov, V. L. (1995), Biokhimiia 60(9): 1468-76. Abstract: The activities of the Na+,K(+)-pump and the Na+/Li(+)-exchange and the intracellular concentration of Na+ in erythrocytes of rabbits with experimental hypercholesterolemia have been studied at different stages of cholesterol (Ch) feeding as well as at different intervals after stopping of cholesterol-rich diets. After sufficiently long periods of feeding the animals with Ch (1.5-2 months), a significant activation of the Na+,K(+)-pump, reduction of the Na+/Li(+)-exchange rate and lowering of the intracellular sodium content in erythrocytes of rabbits from experimental groups were observed. Several months after stopping Ch-rich diets there was a partial normalization of the parameters under study. However, at the initial stage of the experiment (20 days after the beginning of Ch feeding) as well as two weeks after Ch feeding had been stopped, there occurred no changes in the activities of the ion transport systems or in Na+i despite substantial changes in the plasma Ch level. It is suggested that the observed effect of dietary Ch on the activity of ion carriers may be mediated by affecting the expression of the corresponding genes. |
| Modulation of Na-H antiporter activity in human lymphoblasts by altered membrane cholesterol Poli de Figueiredo, C. E., L. L. Ng, et al. (1991), Am J Physiol 261(6 Pt 1): C1138-42. Abstract: The effects of changes in membrane cholesterol on Na-H antiporter activity in culture human lymphoblasts are described. Lymphoblast cholesterol alteration was achieved with liposomes of phosphatidylcholine (cholesterol depletion) or phosphatidylcholine plus cholesterol (cholesterol enrichment). Lymphoblast intracellular pH (pHi) was examined by fluorimetry using cells loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)5(6)-carboxyfluorescein, and the Na-dependent proton efflux rate at a pHi of 6.0 was taken as the maximum velocity of the Na-H antiporter. Lymphoblast membrane cholesterol depletion activated the Na-H antiporter, and enrichment of membrane cholesterol caused inhibition of the antiporter activity. This study demonstrates that in situ modification of membrane cholesterol can modulate the activity of the Na-H antiporter. |
| Modulation of particulate nitric oxide synthase activity and peroxynitrite synthesis in cholesterol enriched endothelial cell membranes Deliconstantinos, G., V. Villiotou, et al. (1995), Biochem Pharmacol 49(11): 1589-600. Abstract: Endothelium-derived relaxing factor/nitric oxide (EDRF/NO) is produced by the vascular wall and is a key modulator of vascular tone and blood pressure. Since reduced EDRF/NO release from the endothelium is a major key event in the development of atherosclerosis, we investigated the effect of cholesterol on endothelial cell particulate (membrane-bound) NO synthase activity. Low concentrations (up to 0.2 mM) of liposomal cholesterol progressively activated plasma membrane-bound NO synthase. Increasing cholesterol concentration above that which maximally stimulated enzyme activity produced a progressive inhibition with respect to the control value. In time course experiments using endothelial cell plasma membranes enriched with cholesterol, changes in NO production were followed by analogous changes in soluble guanylate cyclase activity (sGC). N-Monomethyl-L-arginine (L-NMMA) (1 mM) inhibited particulate NO synthase activity at all cholesterol concentrations used with subsequent decreases in cGMP production. Egg lecithin liposomes (free of cholesterol) had no effect on NO synthase activity. A three-fold increase in superoxide (O2-) and a 2.5-fold increase in NO formation followed by an eight-fold increase in peroxynitrite (ONOO-) production by cholesterol-treated microsomes isolated from endothelial cells was observed, one which rose further up to eight-fold in the presence of superoxide dismutase (SOD) (10 U/mL). Cholesterol had no effect on Lubrol-PX solubilized membrane-bound NO synthase or on cytosolic (soluble) NO synthase activities of endothelial cells. Cholesterol modulated lipid fluidity of plasma membranes labelled with 1,6-diphenyl-1,3,5-hexatriene (DPH) as indicated by the steady state fluorescence anisotropy (ro/r)-1-1. Arrhenius plots of (ro/r)-1-1 indicated that the lipid phase separation of the membranes at 26.2 +/- 1.5 degrees was elevated to 34.4 +/- 1.9 degrees in cholesterol-enriched membranes, consistent with a general decrease in membrane fluidity. Cholesterol-enriched plasma membranes treated with egg lecithin liposomes showed a lipid phase separation at 27.5 +/- 1.6 degrees, indicating the reversible effect of cholesterol on membrane lipid fluidity. Arrhenius plots of NO synthase activity exhibited break point at 26.9 +/- 1.8 degrees which rose to 35.6 +/- 2.1 degrees in 0.5 mM cholesterol-treated plasma membranes and decreased to 21.5 +/- 1.4 degrees in plasma membranes treated with 0.2 mM cholesterol. The allosteric properties of plasma membrane-bound NO synthase inhibited by Mn2+ (as reflected by changes in the Hill coefficient) were changed by cholesterol, consistent with modulations of the fluidity of the lipid microenvironment of the enzyme.(ABSTRACT TRUNCATED AT 400 WORDS) |
| Modulation of phosphoinositide 3-kinase activation by cholesterol level suggests a novel positive role for lipid rafts in lysophosphatidic acid signalling Peres, C., A. Yart, et al. (2003), FEBS Lett 534(1-3): 164-8. Abstract: Methyl-beta-cyclodextrin (MbetaCD) was used to explore a role for cholesterol-enriched plasma membrane microdomains in coupling lysophosphatidic acid (LPA) stimulation to phosphoinositide 3-kinase (PI3K) activation. Cholesterol depletion strongly inhibited the production of phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,4,5-trisphosphate in Vero cells stimulated with LPA. In agreement, the phosphorylation of Akt/protein kinase B, but not of Erk kinases, was suppressed by MbetaCD. MbetaCD did not interfere with the overall phospholipid metabolism, and its effects were reversed in cholesterol add-back experiments. Finally, PI3K was detected in lipid rafts prepared from control but not MbetaCD-treated cells, suggesting that these microdomains contribute to LPA signalling by compartmentalising component(s) of the PI3K pathway. |
| Modulation of phospholipid acyl chain order by cholesterol. A solid-state 2H nuclear magnetic resonance study Sankaram, M. B. and T. E. Thompson (1990), Biochemistry 29(47): 10676-84. Abstract: The effect of cholesterol on the acyl chain order of three glycerophosphocholines with 14, 16, and 18 carbons per acyl chain, namely, di(14:0)PC, di(16:0)PC, and di(18:0)PC, above the gel to liquid-crystalline phase transition temperature was investigated by using 2H nuclear magnetic resonance spectroscopy. Average acyl chain lengths were calculated from the segmental order parameters (Smol) for the sn-1 and the sn-2 chains in the absence of cholesterol and at 3:1, 2:1, and 1:1 mole ratios of phospholipid-cholesterol. The three binary mixtures of cholesterol with phosphatidylcholines are in the liquid-ordered (lo) phase. For all the three phosphatidylcholine-cholesterol systems, the distance from the carbonyl groups to the terminal methyl groups is shorter than the length of the cholesterol molecule. A molecular model for the lo phase consistent with these observations has in a statistical sense a part of each cholesterol molecule in one monolayer extending into the other monolayer. This results in a packing arrangement akin to that in interdigitated systems. On the basis of the effect of cholesterol on phospholipid acyl chain orientational order, it is suggested that the liquid-disordered (ld) phase at low cholesterol concentrations corresponds to a packing mode in which the cholesterol molecule spans the entire transbilayer hydrophobic region. A molecular mechanism is proposed in which increasing the concentration of cholesterol has the effect of stretching the acyl chains of phospholipids by increasing the population of trans conformers up to a stage where the hydrophobic length is considerably longer than the cholesterol molecule. Beyond this concentration, the partially interdigitated phase forms.(ABSTRACT TRUNCATED AT 250 WORDS) |