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Perez-Salas U, Garg S, Gerelli Y, Porcar L. Deciphering lipid transfer between and within membranes with time-resolved small-angle neutron scattering. CURRENT TOPICS IN MEMBRANES 2021; 88:359-412. [PMID: 34862031 DOI: 10.1016/bs.ctm.2021.10.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This review focuses on time-resolved neutron scattering, particularly time-resolved small angle neutron scattering (TR-SANS), as a powerful in situ noninvasive technique to investigate intra- and intermembrane transport and distribution of lipids and sterols in lipid membranes. In contrast to using molecular analogues with potentially large chemical tags that can significantly alter transport properties, small angle neutron scattering relies on the relative amounts of the two most abundant isotope forms of hydrogen: protium and deuterium to detect complex membrane architectures and transport processes unambiguously. This review discusses advances in our understanding of the mechanisms that sustain lipid asymmetry in membranes-a key feature of the plasma membrane of cells-as well as the transport of lipids between membranes, which is an essential metabolic process.
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Affiliation(s)
- Ursula Perez-Salas
- Physics Department, University of Illinois at Chicago, Chicago, IL, United States.
| | - Sumit Garg
- Physics Department, University of Illinois at Chicago, Chicago, IL, United States
| | - Yuri Gerelli
- Department of Life and Environmental Sciences, Universita` Politecnica delle Marche, Ancona, Italy
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2
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Steck TL, Lange Y. Transverse distribution of plasma membrane bilayer cholesterol: Picking sides. Traffic 2018; 19:750-760. [PMID: 29896788 DOI: 10.1111/tra.12586] [Citation(s) in RCA: 88] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2018] [Revised: 06/04/2018] [Accepted: 06/05/2018] [Indexed: 12/23/2022]
Abstract
The transverse asymmetry (sidedness) of phospholipids in plasma membrane bilayers is well characterized, distinctive, actively maintained and functionally important. In contrast, numerous studies using a variety of techniques have concluded that plasma membrane bilayer cholesterol is either mostly in the outer leaflet or the inner leaflet or is fairly evenly distributed. Sterols might simply partition according to their differing affinities for the asymmetrically disposed phospholipids, but some studies have proposed that it is actively transported to the outer leaflet. Other work suggests that the sterol is enriched in the inner leaflet, driven by either positive interactions with the phosphatidylethanolamine on that side or by its exclusion from the outer leaflet by the long chain sphingomyelin molecules therein. This uncertainty raises three questions: is plasma membrane cholesterol sidedness fixed in a given cell or cell type; is it generally the same among mammalian species; and does it serve specific physiological functions? This review grapples with these issues.
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Affiliation(s)
- Theodore L Steck
- Department of Biochemistry and Molecular Biology, University of Chicago, Chicago, Illinois
| | - Yvonne Lange
- Department of Pathology, Rush University Medical Center, Chicago, Illinois
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Wah B, Breidigan JM, Adams J, Horbal P, Garg S, Porcar L, Perez-Salas U. Reconciling Differences between Lipid Transfer in Free-Standing and Solid Supported Membranes: A Time-Resolved Small-Angle Neutron Scattering Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2017; 33:3384-3394. [PMID: 28300412 DOI: 10.1021/acs.langmuir.6b04013] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Maintaining compositional lipid gradients across membranes in animal cells is essential to biological function, but what is the energetic cost to maintain these differences? It has long been recognized that studying the passive movement of lipids in membranes can provide insight into this toll. Confusingly the reported values of inter- and, particularly, intra-lipid transport rates of lipids in membranes show significant differences. To overcome this difficulty, biases introduced by experimental approaches have to be identified. The present study addresses the difference in the reported intramembrane transport rates of dimyristoylphosphatidylcholine (DMPC) on flat solid supports (fast flipping) and in curved free-standing membranes (slow flipping). Two possible scenarios are potentially at play: one is the difference in curvature of the membranes studied and the other the presence (or not) of the support. Using DMPC vesicles and DMPC supported membranes on silica nanoparticles of different radii, we found that an increase in curvature (from a diameter of 30 nm to a diameter of 100 nm) does not change the rates significantly, differing only by factors of order ∼1. Additionally, we found that the exchange rates of DMPC in supported membranes are similar to the ones in vesicles. And as previously reported, we found that the activation energies for exchange on free-standing and supported membranes are similar (84 and 78 kJ/mol, respectively). However, DMPC's flip-flop rates increase significantly when in a supported membrane, surpassing the exchange rates and no longer limiting the exchange process. Although the presence of holes or cracks in supported membranes explains the occurrence of fast lipid flip-flop in many studies, in defect-free supported membranes we find that fast flip-flop is driven by the surface's induced disorder of the bilayer's acyl chain packing as evidenced from their broad melting temperature behavior.
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Affiliation(s)
- Benny Wah
- Physics Department, University of Illinois at Chicago , Chicago, Illinois 60607, United States
| | - Jeffrey M Breidigan
- Physics Department, University of Illinois at Chicago , Chicago, Illinois 60607, United States
| | - Joseph Adams
- Physics Department, University of Illinois at Chicago , Chicago, Illinois 60607, United States
| | - Piotr Horbal
- Physics Department, University of Illinois at Chicago , Chicago, Illinois 60607, United States
| | - Sumit Garg
- Physics Department, University of Illinois at Chicago , Chicago, Illinois 60607, United States
- Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States
| | - Lionel Porcar
- Large Scale Structure Group, Institut Laue-Langevin , Grenoble F-38042, France
- Department of Chemical Engineering, Colburn Laboratory, University of Delaware , Newark, Delaware 19716, United States
| | - Ursula Perez-Salas
- Physics Department, University of Illinois at Chicago , Chicago, Illinois 60607, United States
- Materials Science Division, Argonne National Laboratory , Lemont, Illinois 60439, United States
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4
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Beck Z, Matyas GR, Alving CR. Detection of liposomal cholesterol and monophosphoryl lipid A by QS-21 saponin and Limulus polyphemus amebocyte lysate. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:775-80. [DOI: 10.1016/j.bbamem.2014.12.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/02/2014] [Revised: 11/26/2014] [Accepted: 12/05/2014] [Indexed: 11/16/2022]
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5
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Noninvasive neutron scattering measurements reveal slower cholesterol transport in model lipid membranes. Biophys J 2011; 101:370-7. [PMID: 21767489 DOI: 10.1016/j.bpj.2011.06.014] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Revised: 05/24/2011] [Accepted: 06/02/2011] [Indexed: 01/12/2023] Open
Abstract
Proper cholesterol transport is essential to healthy cellular activity and any abnormality can lead to several fatal diseases. However, complete understandings of cholesterol homeostasis in the cell remains elusive, partly due to the wide variability in reported values for intra- and intermembrane cholesterol transport rates. Here, we used time-resolved small-angle neutron scattering to measure cholesterol intermembrane exchange and intramembrane flipping rates, in situ, without recourse to any external fields or compounds. We found significantly slower transport kinetics than reported by previous studies, particularly for intramembrane flipping where our measured rates are several orders of magnitude slower. We unambiguously demonstrate that the presence of chemical tags and extraneous compounds employed in traditional kinetic measurements dramatically affect the system thermodynamics, accelerating cholesterol transport rates by an order of magnitude. To our knowledge, this work provides new insights into cholesterol transport process disorders, and challenges many of the underlying assumptions used in most cholesterol transport studies to date.
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Vrins C, Vink E, Vandenberghe KE, Frijters R, Seppen J, Groen AK. The sterol transporting heterodimer ABCG5/ABCG8 requires bile salts to mediate cholesterol efflux. FEBS Lett 2007; 581:4616-20. [PMID: 17825296 DOI: 10.1016/j.febslet.2007.08.052] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2007] [Revised: 08/24/2007] [Accepted: 08/24/2007] [Indexed: 11/16/2022]
Abstract
The ATP binding cassette transporters ABCG5 and ABCG8 are indispensable for hepatobiliary cholesterol transport. In this study, we investigated the specificity of the heterodimer for cholesterol acceptors. Dog gallbladder epithelial cells were mono- or double-transfected with lentiviral mouse Abcg5 and Abcg8 vectors. Double-transfected cells showed increased efflux to different bile salt (BS) species, while mono-transfected cells did not show enhanced efflux. The efflux was initiated at micellar concentrations and addition of phosphatidylcholine increased efflux. Cholesterol secretion was highly BS dependent, whereas other cholesterol acceptors such as ApoAI, HDL or methyl-beta-cyclodextrin did not elicit Abcg5/g8 dependent cholesterol secretion.
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Affiliation(s)
- Carlos Vrins
- Academic Medical Center, Department of Medical Biochemistry, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands
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7
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John K, Kubelt J, Müller P, Wüstner D, Herrmann A. Rapid transbilayer movement of the fluorescent sterol dehydroergosterol in lipid membranes. Biophys J 2002; 83:1525-34. [PMID: 12202377 PMCID: PMC1302250 DOI: 10.1016/s0006-3495(02)73922-2] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
This study establishes a new assay for measuring the transbilayer movement of dehydroergosterol (DHE) in lipid membranes. The assay is based on the rapid extraction of DHE by methyl-beta-cyclodextrin (M-CD) from liposomes. The concentration of DHE in the liposomal membrane was measured by using fluorescence resonance energy transfer (FRET) from DHE to dansyl-phosphatidylethanolamine, which is not extracted from liposomes by M-CD. The method was applied to small (SUV) and large (LUV) unilamellar vesicles of different compositions and at various temperatures. From the kinetics of FRET changes upon extraction of DHE from membranes, rates of M-CD mediated extraction and flip-flop of DHE could be deduced and were found to be dependent on the physical state of the lipid phase. For egg phosphocholine and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine in the liquid-crystalline state, halftimes of extraction and transbilayer movement were <5 s and approximately 20-50 s, respectively, at 10 degrees C. For 1,2-dimyristoyl-sn-glycero-3-phosphocholine-SUV being in the gel state at 10 degrees C, the respective halftimes were 28 s and 5-8 min. Surprisingly, DHE could not be extracted from LUV consisting of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. This might be an indication of specific interactions between DHE molecules in membranes depending on the phospholipid composition of the membrane.
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Affiliation(s)
- Karin John
- Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, Institut für Biologie, D-10115 Berlin, Germany
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Leventis R, Silvius JR. Use of cyclodextrins to monitor transbilayer movement and differential lipid affinities of cholesterol. Biophys J 2001; 81:2257-67. [PMID: 11566796 PMCID: PMC1301697 DOI: 10.1016/s0006-3495(01)75873-0] [Citation(s) in RCA: 173] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
In view of the demonstrated cholesterol-binding capabilities of certain cyclodextrins, we have examined whether these agents can also catalyze efficient transfer of cholesterol between lipid vesicles. We here demonstrate that beta- and gamma-cyclodextrins can dramatically accelerate the rate of cholesterol transfer between lipid vesicles under conditions where a negligible fraction of the sterol is bound to cyclodextrin in steady state. beta- and gamma-cyclodextrin enhance the rate of transfer of cholesterol between vesicles by a larger factor than they accelerate the transfer of phospholipid, whereas, for alpha- and methyl-beta-cyclodextrin, the opposite is true. Analysis of the kinetics of cyclodextrin-mediated cholesterol transfer between large unilamellar vesicles composed mainly of 1-stearoyl-2-oleoyl phosphatidylcholine (SOPC) or SOPC/cholesterol indicates that transbilayer flip-flop of cholesterol is very rapid (halftime < 1-2 min at 37 degrees C). Using beta-cyclodextrin to accelerate cholesterol transfer, we have measured the relative affinities of cholesterol for a variety of different lipid species. Our results show strong variations in cholesterol affinity for phospholipids bearing different degrees of chain unsaturation and lesser, albeit significant, effects of phospholipid headgroup structure on cholesterol-binding affinity. Our findings also confirm previous suggestions that cholesterol interacts with markedly higher affinity with sphingolipids than with common membrane phospholipids.
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Affiliation(s)
- R Leventis
- Department of Biochemistry, McGill University, Montréal, Québec H3G 1Y6, Canada
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Woodford JK, Colles SM, Myers-Payne S, Billheimer JT, Schroeder F. Sterol carrier protein-2 stimulates intermembrane sterol transfer by direct membrane interaction. Chem Phys Lipids 1995; 76:73-84. [PMID: 7788802 DOI: 10.1016/0009-3084(95)02436-m] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
It is unclear how the cytosolic sterol carrier protein-2 (SCP-2) binds sterols and enhances sterol transfer between membranes. Therefore, human recombinant SCP-2 was used in conjunction with phase fluorometry, dialysis, and chemical labeling techniques to show if a direct membrane effect accounted for this activity. SCP-2 directly interacted with L-cell fibroblast plasma membrane vesicles as determined by increased fluorescence anisotropy of coumarin-labeled protein (CPM-SCP-2). Furthermore, a new fluorescence lifetime component due to plasma membrane-bound CPM-SCP-2 was observed. Dialysis studies with 3H- cholesterol loaded plasma membranes indicated that SCP-2, added to the donor compartment, stimulated sterol transfer whether or not the dialysis membrane was permeable to SCP-2. Nevertheless, ligand-binding experiments indicated that chemically blocking the SCP-2 sterol binding site inhibited the ability of SCP-2 to enhance sterol transfer between plasma membrane vesicles. SCP-2 did not stimulate plasma membrane fusion. Addition of SCP-2 to plasma membranes increased the anisotropy plasma membrane proteins covalently reacted with CPM, but not that of lipids labeled with the fatty acid analogue octadecyl rhodamine B. In conclusion, the data are consistent with SCP-2 stimulating intermembrane sterol transfer by direct interaction with sterol in the membrane and enhancing its desorption from the membrane.
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Affiliation(s)
- J K Woodford
- Department of Physiology and Pharmacology, Texas A & M University, TVMC College Station 77843-4466, USA
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Woodford JK, Hapala I, Jefferson JR, Knittel JJ, Kavecansky J, Powell D, Scallen TJ, Schroeder F. Mechanistic studies of sterol carrier protein-2 effects on L-cell fibroblast plasma membrane sterol domains. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1189:52-60. [PMID: 8305459 DOI: 10.1016/0005-2736(94)90279-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The factors which regulate intermembrane sterol domains and exchange in biomembranes are not well understood. A new fluorescent sterol exchange assay allowed correlation of changes in polarization to sterol transfer. Analysis of spontaneous sterol exchange between L-cell plasma membranes indicated two exchangeable and one very slowly or nonexchangeable sterol domain. The exchangeable domains exhibited half-times of 23 and 140 min with fractional contributions of 5 and 30%, respectively. Sterol carrier protein-2 (SCP-2) enhanced sterol exchange between L-cell plasma membranes and altered sterol domain size in a concentration dependent manner. Previous model membrane studies indicate that SCP-2 alters sterol domains and exchange through interaction with anionic phospholipids. In contrast to these observations, the ionic shielding agents KCl, low pH, or neomycin were either totally or partially ineffective inhibitors of SCP-2 action in L-cell plasma membrane exchanges. Thus the mechanism of SCP-2 in sterol transfer appears to be less charge dependent in L-cell plasma membranes than in model membranes. The cholesterol lowering drug probucol was also capable of altering the sterol exchange kinetics.
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Affiliation(s)
- J K Woodford
- Department of Pharmacology and Cell Biophysics, University of Cincinnati Medical Center, OH 45267-0004
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11
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Robins SJ, Fasulo JM, Robins VF, Patton GM. Utilization of different fatty acids for hepatic and biliary phosphatidylcholine formation and the effect of changes in phosphatidylcholine molecular species on biliary lipid secretion. J Lipid Res 1991. [DOI: 10.1016/s0022-2275(20)41995-9] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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12
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Schroeder F, Butko P, Nemecz G, Scallen TJ. Interaction of fluorescent delta 5,7,9(11),22-ergostatetraen-3 beta-ol with sterol carrier protein-2. J Biol Chem 1990. [DOI: 10.1016/s0021-9258(19)40208-1] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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13
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Nemecz G, Fontaine RN, Schroeder F. A fluorescence and radiolabel study of sterol exchange between membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 943:511-21. [PMID: 3415992 DOI: 10.1016/0005-2736(88)90384-7] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The fluorescent sterols delta 5,7,9(11),22-ergostatetraen-3 beta-ol (dehydroergosterol) and delta 5,7,9,(11)-cholestatrien-3 beta-ol (cholestatrienol) as well as [1,2-3H]cholesterol were utilized as cholesterol analogues to examine spontaneous exchange of sterol between 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) small unilamellar vesicles (SUV). Exchange of fluorescent sterols was monitored at 24 degrees C by release from self-quenching of polarization from the time of mixing without separation of donor and acceptor vesicles. The polarization curve for 35 mol% sterol in POPC best fitted a two-exponential function, with a fast-exchange rate constant k1 = 0.0217 min-1, 1t1/2 = 32 min, size pool 1 = 12%, and a slow rate constant k2 = 2.91.10(-3) min-1, 2t1/2 = 238 min, size pool 2 = 88%. In addition to the above two exchangeable pools of sterol, the data were consistent with the presence of a slowly or nonexchangeable pool, 42% of total sterol, that was highly dependent on sterol content. These results were confirmed by simultaneous monitoring of [1,2-3H]cholesterol radioactivity and dehydroergosterol fluorescence intensity after separation of donor and acceptor vesicles by ion-exchange column chromatography. Thus, dehydroergosterol or cholestatrienol exchange as measured by fluorescence parameters (polarization and/or intensity) provides two new methods to follow cholesterol spontaneous exchange. These methods allow resolution and quantitation of a shorter exchange t1/2 near 30 min previously not reported. Thus, the cholesterol desorption rate from membranes may be faster than previously believed. In addition, the presence of a slowly non-exchangeable pool was confirmed.
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Affiliation(s)
- G Nemecz
- Division of Pharmacology and Medicinal Chemistry, College of Pharmacy, University of Cincinnati Medical Center, OH 45267-0004
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14
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Stein O, Oette K, Haratz D, Halperin G, Stein Y. Sphingomyelin liposomes with defined fatty acids: metabolism and effects on reverse cholesterol transport. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 960:322-33. [PMID: 3382678 DOI: 10.1016/0005-2760(88)90040-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Small unilamellar liposomes prepared from sphingomyelins with defined 14C-labeled fatty acids were studied after injection into rats. The liposomes contained trace amounts of [3H]cholesteryl linoleyl ether (CLE), which served as a nonexchangeable and nonhydrolyzable marker. The liposomes were cleared from the circulation with an initial t1/2 of about 90 min. [14C]18:0- and [14C]18:1-containing sphingomyelins were cleared at a similar rate, but [14C]18:2-sphingomyelin disappeared much faster. The liver accounted for up to 70% of [3H]cholesteryl ether injected with 18:0-sphingomyelin liposomes, and for up to 50% with liposomes prepared from 18:1 or 18:2-sphingomyelin. The initial uptake of the liver appeared to be of the entire particle, and the loss of 14C label with time indicated metabolism of the sphingomyelins. With [14C]18:0-sphingomyelin liposomes, up to 8% of liver radioactivity was recovered in neutral lipids 6 h after injection, and this value was 17 and 22% with [14C]18:2- and [14C]18:1-sphingomyelins, respectively. The recovery in 'carcass' of [3H]cholesteryl ether 3 h after injection of [14C]18:2-sphingomyelin liposomes was 33% and of 14C label, 21%. Injection of 18:1- or 18:2-sphingomyelin liposomes (5.4 mumol/100 g body weight) resulted in a 2-fold increase of plasma unesterified cholesterol; a 30% increase was seen with 18:0 liposomes (2.63 mumol/100 g body weight). In experiments with cultured cells, the unsaturated sphingomyelin liposomes alone enhanced cholesterol efflux more extensively than the saturated ones, but their efficacies became similar when mixed with apoprotein (apo) A-I. At equimolar concentration, apo C-III1 or C-III2 had a smaller effect than apo A-I. It is concluded that 18:1- or 18:2-sphingomyelin tends to form small unilamellar liposomes which may reach also extrahepatic tissues. The liposomes able to enhance cholesterol release in vitro and in vivo. Since they are not a substrate for lecithin-cholesterol acyltransferase, they should be able to deliver the free cholesterol to the liver, where they are also rapidly metabolized.
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Affiliation(s)
- O Stein
- Department of Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel
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15
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Brasaemle DL, Robertson AD, Attie AD. Transbilayer movement of cholesterol in the human erythrocyte membrane. J Lipid Res 1988. [DOI: 10.1016/s0022-2275(20)38521-7] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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16
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Thomas PD, Poznansky MJ. Cholesterol transfer between lipid vesicles. Effect of phospholipids and gangliosides. Biochem J 1988; 251:55-61. [PMID: 3390160 PMCID: PMC1148963 DOI: 10.1042/bj2510055] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The effect of lipid composition on the rate of cholesterol movement between cellular membranes is investigated using lipid vesicles. The separation of donor and acceptor vesicles required for rate measurement is achieved by differential centrifugation so that the lipid effect can be quantified in the absence of a charged lipid generally used for ion-exchange-based separation. The rate of cholesterol transfer from small unilamellar vesicles (SUVs) containing 50 mol% cholesterol to a common large unilamellar vesicle (LUV) acceptor containing 20 mol% cholesterol decreases with increasing mol% of sphingomyelin in the SUVs, while phosphatidylethanolamine and phosphatidylserine have no appreciable effect at physiologically relevant levels. There is a large decrease in rate when phosphatidylethanolamine constitutes 50 mol% of donor phospholipids. Interestingly, gangliosides which have the same hydrocarbon moiety as sphingomyelin exert an opposite effect. The effect of spingomyelin seems to be mediated by its ability to decrease the fluidity of the lipid matrix, while that of gangliosides may arise from a weakening of phosphatidylcholine-cholesterol interactions or from a more favourable (less polar) microenvironment for the desorption of cholesterol provided by the head-group interactions involving sugar residues. If the effect of asymmetric transbilayer distribution of lipids is taken into consideration, the observed composition-dependent rate changes could partly account for the large difference in the rates of cholesterol desorption from the inner and outer layers of plasma membrane. Such rate differences may be responsible for an unequal steady-state distribution of cholesterol among various cellular membranes and lipoproteins.
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Affiliation(s)
- P D Thomas
- Department of Physiology, University of Alberta, Edmonton, Canada
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17
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Phillips MC, Johnson WJ, Rothblat GH. Mechanisms and consequences of cellular cholesterol exchange and transfer. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 906:223-76. [PMID: 3297153 DOI: 10.1016/0304-4157(87)90013-x] [Citation(s) in RCA: 452] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
It is apparent from consideration of the reactions involved in cellular cholesterol homeostasis that passive transfer of unesterified cholesterol molecules plays a role in cholesterol transport in vivo. Studies in model systems have established that free cholesterol molecules can transfer between membranes by diffusion through the intervening aqueous layer. Desorption of free cholesterol molecules from the donor lipid-water interface is rate-limiting for the overall transfer process and the rate of this step is influenced by interactions of free cholesterol molecules with neighboring phospholipid molecules. The influence of phospholipid unsaturation and sphingomyelin content on the rate of free cholesterol exchange are known in pure phospholipid bilayers and similar effects probably occur in cell membranes. The rate of free cholesterol clearance from cells is determined by the structure of the plasma membrane. It follows that the physical state of free cholesterol in the plasma membrane is important for the kinetics of cholesterol clearance and cell cholesterol homeostasis, as well as the structure of the plasma membrane. Bidirectional flux of free cholesterol between cells and lipoproteins occurs and rate constants characteristic of influx and efflux can be measured. The direction of any net transfer of free cholesterol is determined by the relative free cholesterol/phospholipid molar ratios of the donor and acceptor particles. Cholesterol diffuses down its gradient of chemical potential generally partitioning to the phospholipid-rich particle. Such a surface transfer process can lead to delivery of cholesterol to cells. This mechanism operates independently of any lipoprotein internalization by receptor-mediated endocytosis. The influence of enzymes such as lecithin-cholesterol acyltransferase and hepatic lipase on the direction of net transfer of free cholesterol between lipoproteins and cells can be understood in terms of their effects on the pool sizes and the rate constants for influx and efflux. Excess accumulation of free cholesterol in cells stimulates the rate of cholesteryl ester formation and induces deposition of cholesteryl ester inclusions in the cytoplasm similar to the situation in the 'foam' cells of atherosclerotic plaque. Clearance of cellular cholesteryl ester requires initial hydrolysis to free cholesterol followed by efflux of this free cholesterol. The rate of clearance of cholesteryl ester from cytoplasmic droplets is influenced by the physical state of the cholesteryl ester; liquid-crystalline cholesteryl ester is removed more slowly than cholesteryl ester in a liquid state.(ABSTRACT TRUNCATED AT 400 WORDS)
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18
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Leduc R, Patton GM, Atkinson D, Robins SJ. Influence of different molecular species of phosphatidylcholine on cholesterol transport from lipoprotein recombinants in the rat. J Biol Chem 1987. [DOI: 10.1016/s0021-9258(18)47621-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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19
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Dawidowicz EA. Lipid Exchange: Transmembrane Movement, Spontaneous Movement, and Protein-Mediated Transfer of Lipids and Cholesterol. CURRENT TOPICS IN MEMBRANES AND TRANSPORT 1987. [DOI: 10.1016/s0070-2161(08)60046-5] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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20
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Murgatroyd JE, Green C. Cholesterol transfer from rat, human and sheep erythrocytes. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1987; 88:23-6. [PMID: 3677603 DOI: 10.1016/0305-0491(87)90073-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
1. The spontaneous transfer of cholesterol out of sheep, rat and human erythrocyte membranes was measured. 2. The rates of cholesterol transfer did not correlate with the very different levels of sphingomyelin in the membranes. 3. Cholesterol transferred at similar rates out of vesicles made of lipids extracted from the three types of erythrocyte. 4. The results are discussed in relation to the proposal that cholesterol and sphingomyelin are closely associated in cell surface membranes.
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Bar LK, Barenholz Y, Thompson TE. Fraction of cholesterol undergoing spontaneous exchange between small unilamellar phosphatidylcholine vesicles. Biochemistry 1986; 25:6701-5. [PMID: 3790552 DOI: 10.1021/bi00369a056] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The kinetics of the spontaneous exchange of [3H]cholesterol between small unilamellar vesicles of phosphatidylcholine has been reexamined. Although first-order exchange kinetics were observed (k = 0.0117 min-1), in good agreement with previous studies, about 20% of the total cholesterol was found to be nonexchangeable in the 8-h time frame of the experiments. The size of this nonexchangeable pool was found to depend on the type of phospholipid and the temperature. It seems probable that the two pools of cholesterol defined in these experiments reflect the complex phase structure of the cholesterol-phosphatidylcholine vesicles.
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Heath TD, Lopez NG, Papahadjopoulos D. The effects of liposome size and surface charge on liposome-mediated delivery of methotrexate-gamma-aspartate to cells in vitro. BIOCHIMICA ET BIOPHYSICA ACTA 1985; 820:74-84. [PMID: 3876848 DOI: 10.1016/0005-2736(85)90217-2] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
We have studied the liposome-mediated delivery of methotrexate-gamma-aspartate to five cell lines. The sensitivity of the cells to encapsulated drug varies widely in accordance with their ability to take up the liposomes. CV1-P cells can be 150-times more sensitive to encapsulated methotrexate-gamma-aspartate than to free drug, while AKR/J SL2 cells are only twice as sensitive to the encapsulated drug. Negatively-charged liposomes are much more efficient for delivery than are neutral liposomes, and cholesterol is an essential component of the liposome membrane for optimal drug delivery. The optimal liposome size for drug delivery is 0.1 micron, although the amount of cell-associated lipid is the same for all liposome sizes. The effect of the encapsulated drug is inhibited by NH4Cl, suggesting an endocytic mechanism for delivery. The potency of the encapsulated drug is not affected by wide variations in the drug: lipid ratio.
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Child P, op den Kamp JA, Roelofsen B, van Deenen LL. Molecular species composition of membrane phosphatidylcholine influences the rate of cholesterol efflux from human erythrocytes and vesicles of erythrocyte lipid. BIOCHIMICA ET BIOPHYSICA ACTA 1985; 814:237-46. [PMID: 3978102 DOI: 10.1016/0005-2736(85)90441-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The efflux of [3H]cholesterol from prelabelled human erythrocytes having modified phosphatidylcholine compositions was measured during 24-h incubations in the presence of unlabelled acceptor liposomes composed of equimolar amounts of egg phosphatidylcholine and cholesterol. The cells were modified by replacement of part of the native phosphatidylcholine with either dipalmitoylphosphatidylcholine, palmitoyloleoylphosphatidylcholine or dilinoleoylphosphatidylcholine catalyzed by phosphatidylcholine-specific transfer protein from bovine liver. The results indicated that the efflux of [3H]cholesterol was faster from erythrocytes in which the dipalmitoylphosphatidylcholine content was increased from 7 to 25% of the total, than from cells enriched in palmitoyloleoylphosphatidylcholine or dioleoylphosphatidylcholine. Incorporation of dilinoleoylphosphatidylcholine to a level of 13% of the total phosphatidylcholine slowed the rate of efflux of [3H]sterol. The phosphatidylcholine replacements produced no significant differences in cholesterol/phospholipid ratio before or after 24 h of incubation with the acceptor egg phosphatidylcholine-cholesterol vesicles. Using vesicles prepared from erythrocyte lipid, modified to reflect the changes in the phosphatidylcholine composition induced in the whole cells, the same influence of composition on the rate of cholesterol exchange was evident. Enhancement of the dipalmitoylphosphatidylcholine content from 7 to 25% of the total phosphatidylcholine pool increased the rate of [3H]cholesterol efflux, while the addition of the same amount of dilinoleoylphosphatidylcholine slowed it compared to controls. The magnitude of the effect was comparable in intact cells and erythrocyte lipid vesicles enriched in dipalmitoylphosphatidylcholine, while the influence of dilinoleoylphosphatidylcholine was more marked in the intact cells. These results demonstrate that changes in the molecular species composition of the phosphatidylcholine pool can influence the rate of exchange of cholesterol but not necessarily the cellular content of sterol in the human erythrocyte. The influence of this phospholipid appears to be expressed independently of the presence of membrane protein or an underlying cytoskeleton.
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Fugler L, Clejan S, Bittman R. Movement of cholesterol between vesicles prepared with different phospholipids or sizes. J Biol Chem 1985. [DOI: 10.1016/s0021-9258(18)89236-5] [Citation(s) in RCA: 74] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Chapter 6 Cholesterol and biomembrane structures. ACTA ACUST UNITED AC 1985. [DOI: 10.1016/s0167-7306(08)60682-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Bruckdorfer KR, Crowe J, Sherry MK. Evidence for a water-soluble intermediate in exchange of cholesterol between membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 778:489-96. [PMID: 6509049 DOI: 10.1016/0005-2736(84)90398-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The mechanism of inter-membrane cholesterol exchange has been a matter of some debate. Evidence from kinetic studies indicates that cholesterol must transfer to and from membranes in a water-soluble form. In this study attempts have been made to demonstrate that this occurs using either dialysis membranes or a barrierless multiphase polymer system to physically separate the membranes. In both systems small amounts of cholesterol were seen to transfer from one membrane pool to another using both liposomes and erythrocyte membranes as donors or acceptors. The cholesterol transfer was shown to be independent of the movement of other membrane components. The amount of transfer observed was limited by the physical properties of the systems employed. The barrier to cholesterol transfer in the dialysis membrane system is primarily the pore size of the membrane, while in the multiphase polymer system the transfer was limited by the viscosity of the medium and the distance between the lower and upper phases containing the membranes. Nevertheless, the results provide evidence that cholesterol transfer is by a dissociation of molecules from membranes into the aqueous medium and does not require the formation of a collision complex between the membranes.
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Bellini F, Phillips MC, Pickell C, Rothblat GH. Role of the plasma membrane in the mechanism of cholesterol efflux from cells. BIOCHIMICA ET BIOPHYSICA ACTA 1984; 777:209-15. [PMID: 6487625 DOI: 10.1016/0005-2736(84)90422-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
In order to investigate the role of the plasma membrane in determining the kinetics of removal of cholesterol from cells, the efflux of [3H]cholesterol from intact cells and plasma membrane vesicles has been compared. The release of cholesterol from cultures of Fu5AH rat hepatoma and WIRL-3C rat liver cells to complexes of egg phosphatidylcholine (1 mg/ml) and human high-density apolipoprotein is first order with respect to concentration of cholesterol in the cells, with half-times (t 1/2) for at least one-third of the cell cholesterol of 3.2 +/- 0.6 and 14.3 +/- 1.5 h, respectively. Plasma membrane vesicles (0.5-5.0 micron diameter) were produced from both cell lines by incubating the cells with 50 mM formaldehyde and 2 mM dithiothreitol for 90 min. The efflux of cholesterol from the isolated vesicles follows the same kinetics as the intact, parent cells: the t 1/2 values for plasma membrane vesicles of Fu5AH and WIRL cells are 3.9 +/- 0.5 and 11.2 +/- 0.7 h, respectively. These t 1/2 values reflect the rate-limiting step in the cholesterol efflux process, which is the desorption of cholesterol molecules from the plasma membrane into the extracellular aqueous phase. The fact that intact cells and isolated plasma membranes release cholesterol at the same rates indicates that variations in the plasma membrane structure account for differences in the kinetics of cholesterol release from different cell types. In order to investigate the role of plasma membrane lipids, the kinetics of cholesterol desorption from small unilamellar vesicles prepared from the total lipid isolated from plasma membrane vesicles of Fu5AH and WIRL cells were measured. Half-times of cholesterol release from plasma membrane lipid vesicles of Fu5AH and WIRL cells were the same, with values of 3.1 +/- 0.1 and 2.9 +/- 0.2 h, respectively. Since bilayers formed from isolated plasma membrane lipids do not reproduce the kinetics of cholesterol efflux observed with the intact plasma membranes, it is likely that the local domain structure, as influenced by membrane proteins, is responsible for the differences in t 1/2 values for cholesterol efflux from these cell lines.
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Ramsammy LS, Chauhan VP, Box LL, Brockerhoff H. Interactions in the hydrogen belts of membranes: cholesterol leaving phosphatidylcholine bilayers. Biochem Biophys Res Commun 1984; 118:743-6. [PMID: 6704105 DOI: 10.1016/0006-291x(84)91457-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Cholesterol transfer from sonicated liposomes of phosphatidylcholine containing 10 or 30 mole percent cholesterol was measured with erythrocytes as acceptor. The activation energies of the (rate-limiting) bilayer-cholesterol dissociation were determined. In parallel experiments, phosphatidylcholine was replaced by an analog lacking the carbonyl oxygens, diether-phosphatidylcholine. The activation energies for dissociation of cholesterol from this phospholipid were three Cal/mole smaller than those for cholesterol-phosphatidylcholine dissociation, at both concentrations of cholesterol. These results demonstrate the involvement of the carbonyl oxygen in cholesterol-phospholipid bonding and support the hypothesis of lipid-lipid hydrogen bonding in the hydrogen belts of membranes.
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Kelusky EC, Dufourc EJ, Smith IC. Direct observation of molecular ordering of cholesterol in human erythrocyte membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 735:302-4. [PMID: 6688740 DOI: 10.1016/0005-2736(83)90306-1] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The first observation of the orientation and order of cholesterol in a natural membrane is reported. The 2H-NMR spectrum of [2,2,3,4,4,6-2H6]cholesterol incorporated into human erythrocyte ghosts demonstrates that the orientation and anisotropic motion of cholesterol is very similar in natural and model membranes.
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Ray TK, Nandi J, Dannemann A, Gordon GB. Role of cholesterol in the structure and function of gastric microsomal vesicles. J Cell Biochem 1983; 21:141-50. [PMID: 6309874 DOI: 10.1002/jcb.240210205] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Digitonin was used as a tool to investigate the organization and function of cholesterol in gastric microsomes. Microsomal vesicles were treated with digitonin for different time at 0-4 degrees C under isotonic conditions. The effects of digitonin treatment of the vesicles on removal of cholesterol, ultrastructural changes, (H+ + K+)-ATPase activity, and gastric ATPase-dependent H+ uptake ability were investigated. Microsomal cholesterol was extracted in an exponential manner with a t1/2 of 32 min. There was no release of microsomal phospholipids by digitonin treatment during the same period. Digitonin treatment (30 min) produced visible "holes" in the vesicles; at the same time (H+ + K+)-ATPase-dependent H+ uptake was abolished. Under the same conditions the K+-stimulated ATPase activity, however, was moderately (about 35%) reduced, although the response of K+ stimulation to valinomycin was obliterated. Longer digitonin treatment resulted in gradual diffusion and eventual disappearance of the "holes" with the generation of distorted cup-shaped microsomes. The data strongly suggest that membrane lipids are freely mobile and that there is a certain degree of specialization in the organization of gastric microsomal cholesterol for the proper maintenance of the membrane structure and function.
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Bhat SG, Brockman HL. The role of cholesteryl ester hydrolysis and synthesis in cholesterol transport across rat intestinal mucosal membrane: a new concept. Biochem Biophys Res Commun 1982; 109:486-92. [PMID: 7181929 DOI: 10.1016/0006-291x(82)91747-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Dresdner G, Hammarström L, Smith CI. Binding and incorporation of lecithin-cholesterol vesicles to lymphocytes: a spin-label study. J Membr Biol 1982; 64:155-66. [PMID: 6276552 DOI: 10.1007/bf01870881] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
When lecithin-cholesterol vesicles, containing the membrane-bound spin probe 3-doxyl-cholestane, were set in contact with mouse lymphocytes, the vesicles adsorbed to the cell and vesicle-membrane components were transferred to it. The spin probe was enzymatically reduced at the inside of the cell membrane. The spin-label method provided a means to determine quantitatively the extent of vesicles adsorption and vesicle-cell fusion by measuring the transfer of vesicles membrane material to the cell. This method, together with the reduction of spin label by the cell, allowed also a quantitative estimate to the extent of endocytosis during cell-liposome interaction.
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Parkes JG, Watson HR, Joyce A, Phadke RS, Smith IC. Cholesterol-phospholipid interactions. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 1982. [DOI: 10.1016/0005-2736(82)90209-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Hale JE, Schroeder F. Asymmetric transbilayer distribution of sterol across plasma membranes determined by fluorescence quenching of dehydroergosterol. EUROPEAN JOURNAL OF BIOCHEMISTRY 1982; 122:649-61. [PMID: 7060596 DOI: 10.1111/j.1432-1033.1982.tb06488.x] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
A new method for measurement of transbilayer distribution of sterol in plasma membranes is reported. The procedure utilized a fluorescent sterol, dehydroergosterol, and a chemical quenching agent, trinitrobenzenesulfonic acid. Dehydroergosterol was useful as a probe molecule for sterols for the following reasons, (a) Dehydroergosterol contained no bulky side chains as reporter groups. (b) Dehydroergosterol structurally resembled cholesterol and desmosterol, the primary sterol synthesized by LM fibroblasts. (c) Dehydroergosterol interacted with digitonin, filipin, and served as a substrate for cholesterol oxidase. (d) The phase transition of dipalmitoylglycerophosphocholine was completely abolished by dehydroergosterol. (e) The native sterol of LM fibroblasts, desmosterol, was completely replaced by dehydroergosterol without effect on LM cell growth, cell doubling time, plasma membrane (Na+, K+)-ATPase and 5'-nucleotidase activity, microsomal NADPH-dependent cytochrome c reductase activity, and mitochondrial succinate-dependent cytochrome c reductase activity. (f) Neither the phospholipid composition nor the sterol/phospholipid ratio of LM fibroblasts were altered by supplementation with dehydroergosterol. The trinitrophenyl group of trinitrophenylglycine or of surface membranes of LM fibroblasts or red blood cells treated with trinitrobenzenesulfonic acid was an excellent quencher of dehydroergosterol fluorescence. Fluorescence in mouse very-low-density lipoproteins, LM fibroblasts plasma membranes, red blood cell surface membranes, and in rat red blood cell membranes was quenched 95 +/- 3%, 20 +/- 2%, 75 +/- 4%, and 69 +/- 4% respectively when the quenching agent was present on only the extracellular site of the membrane. Trinitrophenyl residues effectively quenched the dehydroergosterol fluorescence in the plasma membrane of LM cells by 20% when dehydroergosterol was present from 1-85 mol/100 ml of the membrane sterol. When both sides of the plasma membrane were trinitrophenylated, greater than 95% of the dehydroergosterol fluorescence was quenched. In addition, when LM cells were cultured with dehydroergosterol, exposed latex beads, and the endocytosed particles isolated as phagosomes and treated with trinitrobenzenesulfonic acid under non-penetrating conditions, the fluorescence of the dehydroergosterol was quenched nearly 64%. From these and other results we deduced that the inner monlayer of the LM fibroblasts plasma membrane was enriched with dehydroergosterol. In contrast, the distribution of the sterol in red blood cell membranes indicated an enrichment in the outer monolayer.
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Poznansky MJ, Czekanski S. Cholesterol movement between human skin fibroblasts and phosphatidylcholine vesicles. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 685:182-90. [PMID: 7059600 DOI: 10.1016/0005-2736(82)90096-7] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Cholesterol readily exchanges between human skin fibroblasts and unilamellar phospholipid vesicles. Only a fraction of the exchangeable cholesterol and only 10-15% of the total cellular free cholesterol is available for net movement or depletion to cholesterol-free phosphatidylcholine vesicles. [14C]Cholesterol introduced into the fibroblast plasma membrane by exchange from lipid vesicles does not readily equilibrate with fibroblast cholesterol labelled endogenously from [3H]mevalonic acid. While endogenously-synthesized [3H]cholesterol readily becomes incorporated into a pool of esterified cholesterol, little, if any, of the [14C]cholesterol introduced into the fibroblast membrane by exchange from lipid vesicles becomes available for esterification. We interpret these findings as suggesting that: (1) net cholesterol movement from fibroblasts to an acceptor membrane is limited to a small percentage of the plasma membrane cholesterol, and (2) separate pools of cholesterol exist in human skin fibroblasts, one associated with the plasma membrane and the second associated with intracellular membranes, and equilibration of cholesterol between the two pools is a very limited process.
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Rottem S, Shinar D, Bittman R. Symmetrical distribution and rapid transbilayer movement of cholesterol in Mycoplasma gallisepticum membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1981; 649:572-80. [PMID: 7317418 DOI: 10.1016/0005-2736(81)90161-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The exchange of cholesterol between [14C]cholesterol-labeled Mycoplasma gallisepticum cells and an excess of sonicated egg phosphatidylcholine/cholesterol vesicles (molar ratio of 0.9) was measured. More than 90% of the radioactive cholesterol underwent transfer from intact cells to the vesicles. The kinetics of the transfer was biphasic. About 50% of the radioactive cholesterol was exchanged with a half-time of about 4 h. The residual was exchanged at a slower rate with a half-time of about 9 h at 37 degrees C. Bovine serum albumin had a pronounced effect in enhancing both the fast and slow rates of cholesterol exchange, but did not affect the pool sizes significantly. The half-time for equilibration of the two pools in the presence of 2% albumin, calculated using a reversible two-pool method of analysis, was 6.2 h. The effect of albumin was also obtained with isolated membrane preparations and with cells treated with growth inhibitors, suggesting that this effect is independent of albumin preservation of cell viability. The rate enhancement of albumin was concentration dependent with maximal effects observed with greater than or equal to 2%, where the rates of exchange of both the rapidly and slowly exchanging pools were twice as fast. The mechanism by which albumin may affect the exchange rates is discussed.
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Steele JA, Poznansky MJ, Eaton DC, Brodwick MS. Lipid vesicle-mediated alterations of membrane cholesterol levels: effects on Na+ and K+ currents in squid axon. J Membr Biol 1981; 63:191-8. [PMID: 7310857 DOI: 10.1007/bf01870980] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
We demonstrate that cholesterol can exchange from sonicated lipid vesicles to a perfused squid axon membrane and that vesicles with varying cholesterol/phospholipid (C/P) mole ratios can be used to achieve either net loading or net depletion of axon membrane cholesterol. Two types of evidence were obtained which show that net loading or depletion of cholesterol was achieved: (i) changes in the cholesterol/phospholipid (C/P) mole ratios of axons, and (ii) visualization of cholesterol depleted from the preparation by cholesterol-free vesicles by thin-layer chromatography. The C/P mole ratios indicate that cholesterol levels in the preparation were increased or decreased by 30-40%. Increasing or decreasing membrane cholesterol levels were ineffective in altering the Na+ or K+ occurrents in voltage-clamped axons. In addition, we determined that cholesterol "flip-flop" across the axonal membrane occurred with a t 1/2 of 7.3 to 15.3 min.
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Noordam P, Van Echteld C, De Kruijff B, De Gier J. Rapid transbilayer movement of phosphatidylcholine in unsaturated phosphatidylethanolamine containing model membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 1981. [DOI: 10.1016/0005-2736(81)90319-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Abstract
The kinetics of cholesterol exchange between two populations of small unilamellar vesicles has been investigated. There is no change in the initial rate of this exchange process over a 100-fold change in the acceptor vesicle concentration at a constant donor concentration. These results are not consistent with a collision-dependent exchange mechanism. In support of transfer via the aqueous phase, the inclusion of a negatively charged lipid into the vesicles did not affect the exchange rate. Evidence for a water-soluble pool of cholesterol that had partitioned ut of the vesicle was obtained. Finally, cholesterol exchange was observed when donor and acceptor membranes were separated by a barrier through which neither could pass. These data together support our contention that the exchange of cholesterol between these vesicles involves a water-soluble intermediate.
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McLean LR, Phillips MC. Mechanism of cholesterol and phosphatidylcholine exchange or transfer between unilamellar vesicles. Biochemistry 1981; 20:2893-900. [PMID: 7195733 DOI: 10.1021/bi00513a028] [Citation(s) in RCA: 285] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
The mechanism of cholesterol and phosphatidylcholine exchange has been investigated by following the transfer of radiolabeled cholesterol and phosphatidylcholine from negatively charged, unilamellar cholesterol-egg yolk phosphatidylcholine donor vesicles to neutral acceptor vesicles of similar composition. Vesicles were incubated in the absence of protein and were stable to fusion over the course of the experiment. At intervals, donor and acceptor vesicles were separated by passage through a column of DEAE-Sepharose; less than 1% of the charged and 80-95% of the neutral vesicles were recovered in the eluate. Over 12 h at 37 degrees C, 90% of the donor vesicle [4-14C]cholesterol was transferred to the acceptor vesicles in a first-order process whose half-time was 2.3 +/- 0.3 h. This indicates that transfer of cholesterol molecules from the inner to outer monolayer of the vesicle bilayer is not rate limiting in exchange. In contrast to cholesterol exchange, the half-time for 1-palmitoyl-2-oleoyl[1-14C]phosphatidylcholine exchange was 48 +/- 5 h so that more than six molecules of cholesterol were transferred for each molecule of phosphatidylcholine. The interfacial flux of cholesterol from the donor bilayer is 5.3 x 10(-15) mol cm-2 s-1 (approximately 3 molecules/min for an average vesicle) and is similar to fluxes observed in other systems where phosphatidylcholine or cholesterol ester exchange is catalyzed by an exchange protein. When the acceptor vesicle concentration was increased 20-fold in cholesterol exchange experiments or 9-fold in phosphatidylcholine exchange experiments, the rate of label transfer was not affected. The activation energy of cholesterol exchange between 15 and 37 degrees C was 73 +/- 5 kJ mol-1. Transfer of cholesterol across a dialysis membrane is shown to be a slow process whose rate may be predicted by application of Fick's first law of diffusion. These results are only consistent with a mechanism of lipid exchange in which cholesterol and phosphatidylcholine diffuse through the aqueous phase; the experimental activation energy is associated with desorption of lipid from the donor bilayer into the aqueous phase.
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Kimura T. ACTH stimulation on cholesterol side chain cleavage activity of adrenocortical mitochondria. Transfer of the stimulus from plasma membrane to mitochondria. Mol Cell Biochem 1981; 36:105-22. [PMID: 6264282 DOI: 10.1007/bf02354909] [Citation(s) in RCA: 69] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Adrenocortical mitochondrial cholesterol side chain cleavage reactions are regulated by the influence of pituitary ACTH. The mechanism of the stimulation involves adenyl cyclase, cAMP-dependent protein kinase, cholesterol esterase, and ribosomal labile protein synthesis. Through these reactions the stimulus reaches the mitochondrial side chain cleavage enzyme system. In this review article, the current implications on the stimulus transfer from the plasma membrane to the mitochondrial inner membrane are summarized. In particular the availability of cholesterol to P-450scc was discussed in terms of the distribution of cholesterol molecules in the membranes.
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Quinn PJ. The fluidity of cell membranes and its regulation. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1981; 38:1-104. [PMID: 7025092 DOI: 10.1016/0079-6107(81)90011-0] [Citation(s) in RCA: 237] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
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Etemadi AH. Membrane asymmetry. A survey and critical appraisal of the methodology. II. Methods for assessing the unequal distribution of lipids. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 604:423-75. [PMID: 7008848 DOI: 10.1016/0005-2736(80)90579-9] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In the companion paper, I have reviewed the techniques employed for assessment of the asymmetric distribution and orientation of membrane proteins. This article deals with methods applicable to the investigation of the unequal distribution of lipids between the two membrane leaflets. Among the techniques I will discuss are the use of immunological techniques and lectins, chemical reagents, enzymatic isotopic labeling and degradation of membrane lipids, exchange proteins and physical techniques. Whenever appropriate, problems of crypticity and non-availability of lipids to interact with the appropriate ligands, reagents, modifying enzymes or exchange proteins have been envisaged. It appears that in many case, highly discordant results, sometimes with the same biological material, have been obtained. Some of the difficulties encountered presumably stem from the reported existence of non-bilayer arrangements and isotropic movement of lipids as evidenced by freeze-fracture and NMR studies. Other problems may be related to the induction of such arrangements, especially the inverted micellar arrangement, by the modifying agents, particularly degradation enzymes or exchange proteins when they cause severe unilateral modification of the lipids of the exposed leaflet. In addition, the situation is complicated by the role of the induced increase in the flip-flop rate under different experimental conditions and by modification of the rearrangement of lipid molecules as a result of the metabolic state of the cell or ghost preparation and of the reactivity of lipids as a consequence of temperature changes. Here, more so than with proteins, one must be cautious in interpreting experimental results. Moreover, it would appear that the use of different techniques in conjunction and the consequent comparison of results should be recommended. It has been emphasized that 'general rules' do not hold and that each new material should be assay again. To give one example, it is not pertinent to state that proteins enhance the flip-flop rate in lipid vesicles (and hence in membranes). This holds true for glycophorin from erythrocyte membrane, but could not be proved when mitochondrial cytochrome oxidase was used. There seems to be no rule for the distribution of lipids between the two leaflets of different membranes. For example, even for different strains of the same bacterial species, highly divergent results have been reported. It is generally (and probably under the influence of different studies with erythrocytes) believed that in mammalian plasma membranes, choline phospholipids are enriched in the outer leaflet and aminophospholipids in the inner leaflet. Though this contention may prove to be correct, different instances of contradictory results have been given in the text. This shows that if rules do exist, they remain to be discovered or established...
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Gerritsen WJ, Henricks PA, de Kruijff B, van Deenen LL. The transbilayer movement of phosphatidylcholine in vesicles reconstituted with intrinsic proteins from the human erythrocyte membrane. BIOCHIMICA ET BIOPHYSICA ACTA 1980; 600:607-19. [PMID: 7407133 DOI: 10.1016/0005-2736(80)90464-2] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Vesicles have been prepared from 18 : 1c/18 : 1c-phosphatidylcholine with or without purified glycophorin or partially purified band 3 (obtained by organomercurial gel chromatography). The vesicles have been characterized by freeze-fracture electron microscopy, binding studies to DEAE-cellulose, 31P-NMR and K+ trap measurements. Pools of phosphatidylcholine available for exchange have been investigated using phosphatidylcholine exchange protein from bovine liver. The protein-containing vesicles both exhibit exchangeable pools larger than the fraction of phosphatidylcholine in the outer monolayer, whereas in the protein-free vesicles the exchangeable pool is consistent with the outer monolayer. The results indicate that both glycophorin and the partially purified band 3 preparation enhance the transbilayer movement of phosphatidylcholine.
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Abstract
Efflux of contents from small unilamellar vesicles of various compositions, conaining a highly quenched fluorescent compound (calcein, 175 mM) was determined as a function of temperature in the presence and absence of human serum. Efflux of calcein from the liposomes was monitored as an increase in fluorescence as calcein became dequenched upon release from the liposomes. The presence of serum significantly increased liposome leakage in all cases. Incorporation of increasing molar ratios of cholesterol into liposomes reduced leakage of calcein from liposomes incubated with buffer and with serum. Leakage was significantly faster from liposomes with an osmotic gradient across the membrane (higher inside) than from equiosmolar liposomes. The leakage of [14C]sucrose from egg lecithin liposomes at 37 degrees C was also dramatically increased in the presence of serum.
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47
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Etemadi AH. [Organizational tendencies of the constituents of biological membrane and problems of their distributional asymetry]. Biochimie 1980; 62:111-34. [PMID: 6990997 DOI: 10.1016/s0300-9084(80)80188-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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48
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Kido T, Kimura T. The formation of binary and ternary complexes of cytochrome P-450scc with adrenodoxin and adrenodoxin reductase.adrenodoxin complex. The implication in ACTH function. J Biol Chem 1979. [DOI: 10.1016/s0021-9258(19)86389-5] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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49
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Lange Y, D'Alessandro JS, Small DM. The affinity of cholesterol for phosphatidylcholine and sphingomyelin. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 556:388-98. [PMID: 486469 DOI: 10.1016/0005-2736(79)90127-5] [Citation(s) in RCA: 85] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Erythrocyte ghosts were incubated with sonicated vesicles and the uptake of cholesterol by vesicles allowed to proceed to equilibrium. The experiments were carried out for a series of phospholipids at different temperatures. The equilibrium partition of cholesterol between ghosts and single shelled vesicles provided a measure of the relative affinities of cholesterol for the different phospholipids studied. It was found that the affinity of cholesterol for dipalmitoyl phosphatidylcholine was the same as that for N-palmitoyl sphingomyelin both at temperatures above and below the gel to liquid crystalline transition temperature of these phospholipids.
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50
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Giraud F, Claret M. A study of cholesterol transfers between erythrocytes and lipid vesicles: possible involvement of interparticular collisions. FEBS Lett 1979; 103:6-91. [PMID: 582437 DOI: 10.1016/0014-5793(79)81278-8] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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