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Jigoranu RA, Roca M, Costache AD, Mitu O, Oancea AF, Miftode RS, Haba MȘC, Botnariu EG, Maștaleru A, Gavril RS, Trandabat BA, Chirica SI, Haba RM, Leon MM, Costache II, Mitu F. Novel Biomarkers for Atherosclerotic Disease: Advances in Cardiovascular Risk Assessment. Life (Basel) 2023; 13:1639. [PMID: 37629496 PMCID: PMC10455542 DOI: 10.3390/life13081639] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2023] [Revised: 07/19/2023] [Accepted: 07/24/2023] [Indexed: 08/27/2023] Open
Abstract
Atherosclerosis is a significant health concern with a growing incidence worldwide. It is directly linked to an increased cardiovascular risk and to major adverse cardiovascular events, such as acute coronary syndromes. In this review, we try to assess the potential diagnostic role of biomarkers in the early identification of patients susceptible to the development of atherosclerosis and other adverse cardiovascular events. We have collected publications concerning already established parameters, such as low-density lipoprotein cholesterol (LDL-C), as well as newer markers, e.g., apolipoprotein B (apoB) and the ratio between apoB and apoA. Additionally, given the inflammatory nature of the development of atherosclerosis, high-sensitivity c-reactive protein (hs-CRP) or interleukin-6 (IL-6) are also discussed. Additionally, newer publications on other emerging components linked to atherosclerosis were considered in the context of patient evaluation. Apart from the already in-use markers (e.g., LDL-C), emerging research highlights the potential of newer molecules in optimizing the diagnosis of atherosclerotic disease in earlier stages. After further studies, they might be fully implemented in the screening protocols.
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Affiliation(s)
- Raul-Alexandru Jigoranu
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Department of Cardiology, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Mihai Roca
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Clinical Rehabilitation Hospital, 700661 Iasi, Romania
| | - Alexandru-Dan Costache
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Clinical Rehabilitation Hospital, 700661 Iasi, Romania
| | - Ovidiu Mitu
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Department of Cardiology, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Alexandru-Florinel Oancea
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Department of Cardiology, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Radu-Stefan Miftode
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Department of Cardiology, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Mihai Ștefan Cristian Haba
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Department of Cardiology, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Eosefina Gina Botnariu
- Department of Internal Medicine II, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania;
- Department of Diabetes, Nutrition and Metabolic Diseases, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Alexandra Maștaleru
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Clinical Rehabilitation Hospital, 700661 Iasi, Romania
| | - Radu-Sebastian Gavril
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Clinical Rehabilitation Hospital, 700661 Iasi, Romania
| | - Bogdan-Andrei Trandabat
- Department of Surgery II, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania;
- Department of Orthopedics and Trauma, Clinical Rehabilitation Hospital, 700661 Iasi, Romania
| | - Sabina Ioana Chirica
- Faculty of General Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (S.I.C.); (R.M.H.)
| | - Raluca Maria Haba
- Faculty of General Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (S.I.C.); (R.M.H.)
| | - Maria Magdalena Leon
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Clinical Rehabilitation Hospital, 700661 Iasi, Romania
| | - Irina-Iuliana Costache
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Department of Cardiology, “St. Spiridon” Emergency County Hospital, 700111 Iasi, Romania
| | - Florin Mitu
- Department of Medical Specialties I, Faculty of Medicine, University of Medicine and Pharmacy “Grigore T. Popa”, 700115 Iasi, Romania; (R.-A.J.); (O.M.); (A.-F.O.); (R.-S.M.); (M.Ș.C.H.); (A.M.); (R.-S.G.); (M.M.L.); (I.-I.C.); (F.M.)
- Clinical Rehabilitation Hospital, 700661 Iasi, Romania
- Romanian Academy of Medical Sciences, 030167 Bucharest, Romania
- Romanian Academy of Scientists, 050045 Bucharest, Romania
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2
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Öörni K, Kovanen PT. Aggregation Susceptibility of Low-Density Lipoproteins-A Novel Modifiable Biomarker of Cardiovascular Risk. J Clin Med 2021; 10:1769. [PMID: 33921661 PMCID: PMC8074066 DOI: 10.3390/jcm10081769] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 03/31/2021] [Accepted: 04/13/2021] [Indexed: 01/07/2023] Open
Abstract
Circulating low-density lipoprotein (LDL) particles enter the arterial intima where they bind to the extracellular matrix and become modified by lipases, proteases, and oxidizing enzymes and agents. The modified LDL particles aggregate and fuse into larger matrix-bound lipid droplets and, upon generation of unesterified cholesterol, cholesterol crystals are also formed. Uptake of the aggregated/fused particles and cholesterol crystals by macrophages and smooth muscle cells induces their inflammatory activation and conversion into foam cells. In this review, we summarize the causes and consequences of LDL aggregation and describe the development and applications of an assay capable of determining the susceptibility of isolated LDL particles to aggregate when exposed to human recombinant sphingomyelinase enzyme ex vivo. Significant person-to-person differences in the aggregation susceptibility of LDL particles were observed, and such individual differences largely depended on particle lipid composition. The presence of aggregation-prone LDL in the circulation predicted future cardiovascular events in patients with atherosclerotic cardiovascular disease. We also discuss means capable of reducing LDL particles' aggregation susceptibility that could potentially inhibit LDL aggregation in the arterial wall. Whether reductions in LDL aggregation susceptibility are associated with attenuated atherogenesis and a reduced risk of atherosclerotic cardiovascular diseases remains to be studied.
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Affiliation(s)
- Katariina Öörni
- Wihuri Research Institute, 00290 Helsinki, Finland;
- Molecular and Integrative Biosciences Research Programme, Faculty of Biological and Environmental Sciences, University of Helsinki, 00014 Helsinki, Finland
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A trimeric Rab7 GEF controls NPC1-dependent lysosomal cholesterol export. Nat Commun 2020; 11:5559. [PMID: 33144569 PMCID: PMC7642327 DOI: 10.1038/s41467-020-19032-0] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 09/18/2020] [Indexed: 12/26/2022] Open
Abstract
Cholesterol import in mammalian cells is mediated by the LDL receptor pathway. Here, we perform a genome-wide CRISPR screen using an endogenous cholesterol reporter and identify >100 genes involved in LDL-cholesterol import. We characterise C18orf8 as a core subunit of the mammalian Mon1-Ccz1 guanidine exchange factor (GEF) for Rab7, required for complex stability and function. C18orf8-deficient cells lack Rab7 activation and show severe defects in late endosome morphology and endosomal LDL trafficking, resulting in cellular cholesterol deficiency. Unexpectedly, free cholesterol accumulates within swollen lysosomes, suggesting a critical defect in lysosomal cholesterol export. We find that active Rab7 interacts with the NPC1 cholesterol transporter and licenses lysosomal cholesterol export. This process is abolished in C18orf8-, Ccz1- and Mon1A/B-deficient cells and restored by a constitutively active Rab7. The trimeric Mon1-Ccz1-C18orf8 (MCC) GEF therefore plays a central role in cellular cholesterol homeostasis coordinating Rab7 activation, endosomal LDL trafficking and NPC1-dependent lysosomal cholesterol export. Lysosomes play an important role in cellular LDL-cholesterol uptake. Here, the authors perform a genome-wide genetic screen for cholesterol regulators and identify C18orf8 as a conserved subunit of a trimeric Rab7 GEF that controls LDL trafficking and NPC1-dependent lysosomal cholesterol export.
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4
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Abstract
Cholesterol homeostasis is of central importance for life. Therefore, cells have developed a divergent set of pathways to meet their cholesterol needs. In this review, we focus on the direct transfer of cholesterol from lipoprotein particles to the cell membrane. More molecular details on the transfer of lipoprotein-derived lipids were gained by recent studies using phospholipid bilayers. While amphiphilic lipids are transferred right after contact of the lipoprotein particle with the membrane, the transfer of core lipids is restricted. Amphiphilic lipid transfer gains special importance in genetic diseases impairing lipoprotein metabolism like familial hypercholesterolemia. Taken together, these data indicate that there is a constant exchange of amphiphilic lipids between lipoprotein particles and the cell membrane.
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5
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Ahmad F, Leake DS. Antioxidants inhibit low density lipoprotein oxidation less at lysosomal pH: A possible explanation as to why the clinical trials of antioxidants might have failed. Chem Phys Lipids 2018. [PMID: 29518380 PMCID: PMC5989656 DOI: 10.1016/j.chemphyslip.2018.03.001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Oxidised low density lipoprotein (LDL) was considered to be important in the pathogenesis of atherosclerosis, but the large clinical trials of antioxidants, including the first one using probucol (the PQRST Trial), failed to show benefit and have cast doubt on the importance of oxidised LDL. We have shown previously that LDL oxidation can be catalysed by iron in the lysosomes of macrophages. The aim of this study was therefore to investigate the effectiveness of antioxidants in preventing LDL oxidation at lysosomal pH and also establish the possible mechanism of oxidation. Probucol did not effectively inhibit the oxidation of LDL at lysosomal pH, as measured by conjugated dienes or oxidised cholesteryl esters or tryptophan residues in isolated LDL or by ceroid formation in the lysosomes of macrophage-like cells, in marked contrast to its highly effective inhibition of LDL oxidation at pH 7.4. LDL oxidation at lysosomal pH was inhibited very effectively for long periods by N,N'-diphenyl-1,4-phenylenediamine, which is more hydrophobic than probucol and has been shown by others to inhibit atherosclerosis in rabbits, and by cysteamine, which is a hydrophilic antioxidant that accumulates in lysosomes. Iron-induced LDL oxidation might be due to the formation of the superoxide radical, which protonates at lysosomal pH to form the much more reactive, hydrophobic hydroperoxyl radical, which can enter LDL and reach its core. Probucol resides mainly in the surface monolayer of LDL and would not effectively scavenge hydroperoxyl radicals in the core of LDL. This might explain why probucol failed to protect against atherosclerosis in various clinical trials. The oxidised LDL hypothesis of atherosclerosis now needs to be re-evaluated using different and more effective antioxidants that protect against the lysosomal oxidation of LDL.
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Affiliation(s)
- Feroz Ahmad
- Institute of Cardiovascular and Metabolic Research, University of Reading, Reading, United Kingdom.
| | - David S Leake
- Institute of Cardiovascular and Metabolic Research, University of Reading, Reading, United Kingdom
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6
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Melchior JT, Street SE, Andraski AB, Furtado JD, Sacks FM, Shute RL, Greve EI, Swertfeger DK, Li H, Shah AS, Lu LJ, Davidson WS. Apolipoprotein A-II alters the proteome of human lipoproteins and enhances cholesterol efflux from ABCA1. J Lipid Res 2017; 58:1374-1385. [PMID: 28476857 DOI: 10.1194/jlr.m075382] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2017] [Revised: 04/25/2017] [Indexed: 12/25/2022] Open
Abstract
HDLs are a family of heterogeneous particles that vary in size, composition, and function. The structure of most HDLs is maintained by two scaffold proteins, apoA-I and apoA-II, but up to 95 other "accessory" proteins have been found associated with the particles. Recent evidence suggests that these accessory proteins are distributed across various subspecies and drive specific biological functions. Unfortunately, our understanding of the molecular composition of such subspecies is limited. To begin to address this issue, we separated human plasma and HDL isolated by ultracentrifugation (UC-HDL) into particles with apoA-I and no apoA-II (LpA-I) and those with both apoA-I and apoA-II (LpA-I/A-II). MS studies revealed distinct differences between the subfractions. LpA-I exhibited significantly more protein diversity than LpA-I/A-II when isolated directly from plasma. However, this difference was lost in UC-HDL. Most LpA-I/A-II accessory proteins were associated with lipid transport pathways, whereas those in LpA-I were associated with inflammatory response, hemostasis, immune response, metal ion binding, and protease inhibition. We found that the presence of apoA-II enhanced ABCA1-mediated efflux compared with LpA-I particles. This effect was independent of the accessory protein signature suggesting that apoA-II induces a structural change in apoA-I in HDLs.
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Affiliation(s)
- John T Melchior
- Department of Pathology and Laboratory Medicine, Center for Lipid and Arteriosclerosis Science, University of Cincinnati, Cincinnati, OH 45237
| | - Scott E Street
- Department of Pathology and Laboratory Medicine, Center for Lipid and Arteriosclerosis Science, University of Cincinnati, Cincinnati, OH 45237
| | - Allison B Andraski
- Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA 02115
| | - Jeremy D Furtado
- Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA 02115
| | - Frank M Sacks
- Department of Nutrition, Harvard T. H. Chan School of Public Health, Boston, MA 02115; Department of Genetics & Complex Diseases, Harvard T. H. Chan School of Public Health, Boston, MA 02115
| | - Rebecca L Shute
- Department of Pathology and Laboratory Medicine, Center for Lipid and Arteriosclerosis Science, University of Cincinnati, Cincinnati, OH 45237
| | - Emily I Greve
- Department of Pathology and Laboratory Medicine, Center for Lipid and Arteriosclerosis Science, University of Cincinnati, Cincinnati, OH 45237
| | - Debi K Swertfeger
- Division of Biomedical Informatics Cincinnati Children's Hospital Research Foundation, Cincinnati, OH 45229
| | - Hailong Li
- Division of Biomedical Informatics Cincinnati Children's Hospital Research Foundation, Cincinnati, OH 45229
| | - Amy S Shah
- Division of Endocrinology, Department of Pediatrics, Cincinnati Children's Hospital Research Foundation, Cincinnati, OH 45229
| | - L Jason Lu
- Division of Biomedical Informatics Cincinnati Children's Hospital Research Foundation, Cincinnati, OH 45229
| | - W Sean Davidson
- Department of Pathology and Laboratory Medicine, Center for Lipid and Arteriosclerosis Science, University of Cincinnati, Cincinnati, OH 45237.
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Kornmueller K, Lehofer B, Meindl C, Fröhlich E, Leitinger G, Amenitsch H, Prassl R. Peptides at the Interface: Self-Assembly of Amphiphilic Designer Peptides and Their Membrane Interaction Propensity. Biomacromolecules 2016; 17:3591-3601. [PMID: 27741400 PMCID: PMC5111122 DOI: 10.1021/acs.biomac.6b01089] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
![]()
Self-assembling
amphiphilic designer peptides have been successfully
applied as nanomaterials in biomedical applications. Understanding
molecular interactions at the peptide–membrane interface is
crucial, since interactions at this site often determine (in)compatibility.
The present study aims to elucidate how model membrane systems of
different complexity (in particular single-component phospholipid
bilayers and lipoproteins) respond to the presence of amphiphilic
designer peptides. We focused on two short anionic peptides, V4WD2 and A6YD, which are structurally
similar but showed a different self-assembly behavior. A6YD self-assembled into high aspect ratio nanofibers at low peptide
concentrations, as evidenced by synchrotron small-angle X-ray scattering
and electron microscopy. These supramolecular assemblies coexisted
with membranes without remarkable interference. In contrast, V4WD2 formed only loosely associated assemblies over
a large concentration regime, and the peptide promoted concentration-dependent
disorder on the membrane arrangement. Perturbation effects were observed
on both membrane systems although most likely induced by different
modes of action. These results suggest that membrane activity critically
depends on the peptide’s inherent ability to form highly cohesive
supramolecular structures.
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Affiliation(s)
- Karin Kornmueller
- Institute of Biophysics, Medical University of Graz , BioTechMed-Graz, Harrachgasse 21/VI, 8010 Graz, Austria
| | - Bernhard Lehofer
- Institute of Biophysics, Medical University of Graz , BioTechMed-Graz, Harrachgasse 21/VI, 8010 Graz, Austria
| | - Claudia Meindl
- Center for Medical Research, Core Facility Imaging, Medical University of Graz , Stiftingtalstraße 24, 8010 Graz, Austria
| | - Eleonore Fröhlich
- Center for Medical Research, Core Facility Imaging, Medical University of Graz , Stiftingtalstraße 24, 8010 Graz, Austria
| | - Gerd Leitinger
- Institute of Cell Biology, Histology and Embryology, Research Unit Electron Microscopic Techniques, Medical University of Graz , Harrachgasse 21, 8010 Graz, Austria
| | - Heinz Amenitsch
- Institute of Inorganic Chemistry, Graz University of Technology , Stremayrgasse 9/4, 8010 Graz, Austria
| | - Ruth Prassl
- Institute of Biophysics, Medical University of Graz , BioTechMed-Graz, Harrachgasse 21/VI, 8010 Graz, Austria
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Bairaktari ET, Seferiadis KI, Elisaf MS. Evaluation of Methods for the Measurement of Low-Density Lipoprotein Cholesterol. J Cardiovasc Pharmacol Ther 2016; 10:45-54. [PMID: 15821838 DOI: 10.1177/107424840501000106] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A high concentration of low-density lipoprotein cholesterol (LDL-C) in plasma is one of the strongest risk factors for atherosclerotic cardiovascular disease and mortality. The most common approach to determining LDL-C in the clinical laboratory is the Friedewald calculation. There is an increased interest to improve the accuracy of LDL-C estimated by this equation. The expert panel convened by National Cholesterol Education Program has recommended the development of accurate direct methods to measure LDL-C. Several homogeneous and fully automated methods have been introduced in recent years that show improved precision and accuracy over earlier methods, especially the Friedewald calculation. Each of the atherogenic particles in plasma—very-low, intermediate-, and low-density lipoprotein—as well as lipoprotein (a), contain one molecule of apolipoprotein B (apoB) and thus, plasma total concentration of apoB reflects the number of atherogenic particles. Several studies suggested that the measurement of apoB could improve the prediction of risk of coronary artery disease. Thus, in addition to the newly developed direct assays, alternative calculation procedures have been proposed that also take into consideration total serum apoB concentration for the estimation of LDL-C and the presence of small, dense LDL particles. The new generation of homogenous methods for the measurement of LDL-C and the use of serum apoB concentration for the estimation of LDL-C can contribute to the accurate LDL-C determination.
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Affiliation(s)
- Eleni T Bairaktari
- Laboratory of Clinical Chemistry, Medical School, University of Ioannina, Ioannina, Greece
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9
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Okazaki M, Yamashita S. Recent Advances in Analytical Methods on Lipoprotein Subclasses: Calculation of Particle Numbers from Lipid Levels by Gel Permeation HPLC Using “Spherical Particle Model”. J Oleo Sci 2016; 65:265-82. [DOI: 10.5650/jos.ess16020] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
| | - Shizuya Yamashita
- Rinku General Medical Center
- Department of Community Medicine & Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine
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10
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Wade KR, Hotze EM, Briles DE, Tweten RK. Mouse, but not human, ApoB-100 lipoprotein cholesterol is a potent innate inhibitor of Streptococcus pneumoniae pneumolysin. PLoS Pathog 2014; 10:e1004353. [PMID: 25188225 PMCID: PMC4154877 DOI: 10.1371/journal.ppat.1004353] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2014] [Accepted: 07/18/2014] [Indexed: 11/19/2022] Open
Abstract
Streptococcus pneumoniae produces the pore-forming toxin pneumolysin (PLY), which is a member of the cholesterol-dependent cytolysin (CDC) family of toxins. The CDCs recognize and bind the 3β-hydroxyl group of cholesterol at the cell surface, which initiates membrane pore formation. The cholesterol transport lipoproteins, which carry cholesterol in their outer monolayer, are potential off-pathway binding targets for the CDCs and are present at significant levels in the serum and the interstitial spaces of cells. Herein we show that cholesterol carried specifically by the ApoB-100-containing lipoprotein particles (CH-ApoB-100) in the mouse, but not that carried by human or guinea pig particles, is a potent inhibitor of the PLY pore-forming mechanism. Cholesterol present in the outer monolayer of mouse ApoB-100 particles is recognized and bound by PLY, which stimulates premature assembly of the PLY oligomeric complex thereby inactivating PLY. These studies further suggest that the vast difference in the inhibitory capacity of mouse CH-ApoB-100 and that of the human and the guinea pig is due to differences in the presentation of cholesterol in the outer monolayer of their ApoB-100 particles. Therefore mouse CH-ApoB-100 represents a significant innate CDC inhibitor that is absent in humans, which may underestimate the contribution of CDCs to human disease when utilizing mouse models of disease.
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Affiliation(s)
- Kristin R. Wade
- Department of Microbiology and Immunology, The University of Oklahoma Sciences Center, Oklahoma City, Oklahoma, United States of America
| | - Eileen M. Hotze
- Department of Microbiology and Immunology, The University of Oklahoma Sciences Center, Oklahoma City, Oklahoma, United States of America
| | - David E. Briles
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama, United States of America
| | - Rodney K. Tweten
- Department of Microbiology and Immunology, The University of Oklahoma Sciences Center, Oklahoma City, Oklahoma, United States of America
- * E-mail:
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11
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Chetty PS, Ohshiro M, Saito H, Dhanasekaran P, Lund-Katz S, Mayne L, Englander W, Phillips MC. Effects of the Iowa and Milano mutations on apolipoprotein A-I structure and dynamics determined by hydrogen exchange and mass spectrometry. Biochemistry 2012; 51:8993-9001. [PMID: 23066790 DOI: 10.1021/bi300926j] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The Iowa point mutation in apolipoprotein A-I (G26R) leads to a systemic amyloidosis condition, and the Milano mutation (R173C) is associated with hypoalphalipoproteinemia, a reduced plasma level of high-density lipoprotein. To probe the structural effects that lead to these outcomes, we used amide hydrogen-deuterium exchange coupled with a fragment separation/mass spectrometry analysis (HX MS). The Iowa mutation inserts an arginine residue into the nonpolar face of an α-helix that spans residues 7-44 and causes changes in structure and structural dynamics. This helix unfolds, and other helices in the N-terminal helix bundle domain are destabilized. The segment encompassing residues 116-158, largely unstructured in wild-type apolipoprotein A-I, becomes helical. The helix spanning residues 81-115 is destabilized by 2 kcal/mol, increasing the small fraction of time it is transiently unfolded to ≥1%, which allows proteolysis at residue 83 in vivo over time, releasing an amyloid-forming peptide. The Milano mutation situated on the polar face of the helix spanning residues 147-178 destabilizes the helix bundle domain only moderately, but enough to allow cysteine-mediated dimerization that leads to the altered functionality of this variant. These results show how the HX MS approach can provide a powerful means of monitoring, in a nonperturbing way and at close to amino acid resolution, the structural, dynamic, and energetic consequences of biologically interesting point mutations.
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Affiliation(s)
- Palaniappan Sevugan Chetty
- Lipid Research Group, Gastroenterology, Hepatology and Nutrition Division, Children's Hospital of Philadelphia, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, Pennsylvania 19104-4318, United States
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12
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Strong A, Ding Q, Edmondson AC, Millar JS, Sachs KV, Li X, Kumaravel A, Wang MY, Ai D, Guo L, Alexander ET, Nguyen D, Lund-Katz S, Phillips MC, Morales CR, Tall AR, Kathiresan S, Fisher EA, Musunuru K, Rader DJ. Hepatic sortilin regulates both apolipoprotein B secretion and LDL catabolism. J Clin Invest 2012; 122:2807-16. [PMID: 22751103 DOI: 10.1172/jci63563] [Citation(s) in RCA: 169] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2012] [Accepted: 05/21/2012] [Indexed: 01/05/2023] Open
Abstract
Genome-wide association studies (GWAS) have identified a genetic variant at a locus on chromosome 1p13 that is associated with reduced risk of myocardial infarction, reduced plasma levels of LDL cholesterol (LDL-C), and markedly increased expression of the gene sortilin-1 (SORT1) in liver. Sortilin is a lysosomal sorting protein that binds ligands both in the Golgi apparatus and at the plasma membrane and traffics them to the lysosome. We previously reported that increased hepatic sortilin expression in mice reduced plasma LDL-C levels. Here we show that increased hepatic sortilin not only reduced hepatic apolipoprotein B (APOB) secretion, but also increased LDL catabolism, and that both effects were dependent on intact lysosomal targeting. Loss-of-function studies demonstrated that sortilin serves as a bona fide receptor for LDL in vivo in mice. Our data are consistent with a model in which increased hepatic sortilin binds intracellular APOB-containing particles in the Golgi apparatus as well as extracellular LDL at the plasma membrane and traffics them to the lysosome for degradation. We thus provide functional evidence that genetically increased hepatic sortilin expression both reduces hepatic APOB secretion and increases LDL catabolism, providing dual mechanisms for the very strong association between increased hepatic sortilin expression and reduced plasma LDL-C levels in humans.
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Affiliation(s)
- Alanna Strong
- Institute for Translational Medicine and Therapeutics, Cardiovascular Institute, and Institute for Diabetes, Obesity and Metabolism, Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA, USA
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13
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Gauthamadasa K, Vaitinadin NS, Dressman JL, Macha S, Homan R, Greis KD, Silva RAGD. Apolipoprotein A-II-mediated conformational changes of apolipoprotein A-I in discoidal high density lipoproteins. J Biol Chem 2012; 287:7615-25. [PMID: 22235130 DOI: 10.1074/jbc.m111.291070] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
It is well accepted that HDL has the ability to reduce risks for several chronic diseases. To gain insights into the functional properties of HDL, it is critical to understand the HDL structure in detail. To understand interactions between the two major apolipoproteins (apos), apoA-I and apoA-II in HDL, we generated highly defined benchmark discoidal HDL particles. These particles were reconstituted using a physiologically relevant phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) incorporating two molecules of apoA-I and one homodimer of apoA-II per particle. We utilized two independent mass spectrometry techniques to study these particles. The techniques are both sensitive to protein conformation and interactions and are namely: 1) hydrogen deuterium exchange combined with mass spectrometry and 2) partial acetylation of lysine residues combined with MS. Comparison of mixed particles with apoA-I only particles of similar diameter revealed that the changes in apoA-I conformation in the presence of apoA-II are confined to apoA-I helices 3-4 and 7-9. We discuss these findings with respect to the relative reactivity of these two particle types toward a major plasma enzyme, lecithin:cholesterol acyltransferase responsible for the HDL maturation process.
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Affiliation(s)
- Kekulawalage Gauthamadasa
- Department of Pathology and Laboratory Medicine, Center for Lipids and Atherosclerosis Sciences, University of Cincinnati, Cincinnati, Ohio 45267, USA
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14
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Gauthamadasa K, Rosales C, Pownall HJ, Macha S, Jerome WG, Huang R, Silva RAGD. Speciated human high-density lipoprotein protein proximity profiles. Biochemistry 2010; 49:10656-65. [PMID: 21073165 DOI: 10.1021/bi1015452] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
It is expected that the attendant structural heterogeneity of human high-density lipoprotein (HDL) complexes is a determinant of its varied metabolic functions. To determine the structural heterogeneity of HDL, we determined major apolipoprotein stoichiometry profiles in human HDL. First, HDL was separated into two main populations, with and without apolipoprotein (apo) A-II, LpA-I and LpA-I/A-II, respectively. Each main population was further separated into six individual subfractions using size exclusion chromatography (SEC). Protein proximity profiles (PPPs) of major apolipoproteins in each individual subfraction was determined by optimally cross-linking apolipoproteins within individual particles with bis(sulfosuccinimidyl) suberate (BS(3)), a bifunctional cross-linker, followed by molecular mass determination by MALDI-MS. The PPPs of LpA-I subfractions indicated that the number of apoA-I molecules increased from two to three to four with an increase in the LpA-I particle size. On the other hand, the entire population of LpA-I/A-II demonstrated the presence of only two proximal apoA-I molecules per particle, while the number of apoA-II molecules varied from one dimeric apoA-II to two and then to three. For most of the PPPs described above, an additional population that contained a single molecule of apoC-III in addition to apoA-I and/or apoA-II was detected. Upon composition analyses of individual subpopulations, LpA-I/A-II exhibited comparable proportions for total protein (∼58%), phospholipids (∼21%), total cholesterol (∼16%), triglycerides (∼5%), and free cholesterol (∼4%) across subfractions. LpA-I components, on the other hand, showed significant variability. This novel information about HDL subfractions will form a basis for an improved understanding of particle-specific functions of HDL.
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Affiliation(s)
- Kekulawalage Gauthamadasa
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237, United States
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15
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Vuorela T, Catte A, Niemelä PS, Hall A, Hyvönen MT, Marrink SJ, Karttunen M, Vattulainen I. Role of lipids in spheroidal high density lipoproteins. PLoS Comput Biol 2010; 6:e1000964. [PMID: 21060857 PMCID: PMC2965744 DOI: 10.1371/journal.pcbi.1000964] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2010] [Accepted: 09/17/2010] [Indexed: 01/25/2023] Open
Abstract
We study the structure and dynamics of spherical high density lipoprotein (HDL) particles through coarse-grained multi-microsecond molecular dynamics simulations. We simulate both a lipid droplet without the apolipoprotein A-I (apoA-I) and the full HDL particle including two apoA-I molecules surrounding the lipid compartment. The present models are the first ones among computational studies where the size and lipid composition of HDL are realistic, corresponding to human serum HDL. We focus on the role of lipids in HDL structure and dynamics. Particular attention is paid to the assembly of lipids and the influence of lipid-protein interactions on HDL properties. We find that the properties of lipids depend significantly on their location in the particle (core, intermediate region, surface). Unlike the hydrophobic core, the intermediate and surface regions are characterized by prominent conformational lipid order. Yet, not only the conformations but also the dynamics of lipids are found to be distinctly different in the different regions of HDL, highlighting the importance of dynamics in considering the functionalization of HDL. The structure of the lipid droplet close to the HDL-water interface is altered by the presence of apoA-Is, with most prominent changes being observed for cholesterol and polar lipids. For cholesterol, slow trafficking between the surface layer and the regimes underneath is observed. The lipid-protein interactions are strongest for cholesterol, in particular its interaction with hydrophobic residues of apoA-I. Our results reveal that not only hydrophobicity but also conformational entropy of the molecules are the driving forces in the formation of HDL structure. The results provide the first detailed structural model for HDL and its dynamics with and without apoA-I, and indicate how the interplay and competition between entropy and detailed interactions may be used in nanoparticle and drug design through self-assembly.
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Affiliation(s)
- Timo Vuorela
- Department of Physics, Tampere University of Technology, Tampere, Finland
| | - Andrea Catte
- Department of Physics, Tampere University of Technology, Tampere, Finland
- Department of Medicine and Center for Computational and Structural Biology, University of Alabama, Birmingham, Alabama, United States of America
| | | | - Anette Hall
- Department of Physics, Tampere University of Technology, Tampere, Finland
| | | | - Siewert-Jan Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen, Groningen, The Netherlands
| | - Mikko Karttunen
- Department of Applied Mathematics, The University of Western Ontario, London, Ontario, Canada
| | - Ilpo Vattulainen
- Department of Physics, Tampere University of Technology, Tampere, Finland
- Department of Applied Physics, Aalto University School of Science and Technology, Espoo, Finland
- MEMPHYS–Center of Biomembrane Physics, Physics Department, University of Southern Denmark, Odense M, Denmark
- * E-mail:
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16
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Alexander ET, Tanaka M, Kono M, Saito H, Rader DJ, Phillips MC. Structural and functional consequences of the Milano mutation (R173C) in human apolipoprotein A-I. J Lipid Res 2009; 50:1409-19. [PMID: 19318685 DOI: 10.1194/jlr.m800578-jlr200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Carriers of the apolipoprotein A-I(Milano) (apoA-I(M)) variant, R173C, have reduced levels of plasma HDL but no increase in cardiovascular disease. Despite intensive study, it is not clear whether the removal of the arginine or the introduction of the cysteine is responsible for this altered functionality. We investigated this question using two engineered variations of the apoA-I(M) mutation: R173S apoA-I, similar to apoA-I(M) but incapable of forming a disulfide bond, and R173K apoA-I, a conservative mutation. Characterization of the lipid-free proteins showed that the order of stability was wild type approximately R173K>R173S>R173C. Compared with wild-type apoA-I, apoA-I(M) had a lower affinity for lipids, while R173S apoA-I displayed intermediate affinity. The in vivo effects of the apoA-I variants were measured by injecting apoA-I-expressing adeno-associated virus into apoA-I-null mice. Mice that expressed the R173S variant again showed an intermediate phenotype. Thus, both the loss of the arginine and its replacement by a cysteine contribute to the altered properties of apoA-I(M). The arginine is potentially involved in an intrahelical salt bridge with E169 that is disrupted by the loss of the positively charged arginine and repelled by the cysteine, destabilizing the helix bundle domain in the apoA-I molecule and modifying its lipid binding characteristics.
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Affiliation(s)
- Eric T Alexander
- Gastroenterology/Nutrition/Hepatology Division, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4318, USA
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17
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Massey JB, Pownall HJ, Macha S, Morris J, Tubb MR, Silva RAGD. Mass spectrometric determination of apolipoprotein molecular stoichiometry in reconstituted high density lipoprotein particles. J Lipid Res 2009; 50:1229-36. [PMID: 19179308 DOI: 10.1194/jlr.d800044-jlr200] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Plasma HDL-cholesterol and apolipoprotein A-I (apoA-I) levels are strongly inversely associated with cardiovascular disease. However, the structure and protein composition of HDL particles is complex, as native and synthetic discoidal and spherical HDL particles can have from two to five apoA-I molecules per particle. To fully understand structure-function relationships of HDL, a method is required that is capable of directly determining the number of apolipoprotein molecules in heterogeneous HDL particles. Chemical cross-linking followed by SDS polyacrylamide gradient gel electrophoresis has been previously used to determine apolipoprotein stoichiometry in HDL particles. However, this method yields ambiguous results due to effects of cross-linking on protein conformation and, subsequently, its migration pattern on the gel. Here, we describe a new method based on cross-linking chemistry followed by MALDI mass spectrometry that determines the absolute mass of the cross-linked complex, thereby correctly determining the number of apolipoprotein molecules in a given HDL particle. Using well-defined, homogeneous, reconstituted apoA-I-containing HDL, apoA-IV-containing HDL, as well as apoA-I/apoA-II-containing HDL, we have validated this method. The method has the capability to determine the molecular ratio and molecular composition of apolipoprotein molecules in complex reconstituted HDL particles.
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Affiliation(s)
- John B Massey
- Section of Atherosclerosis and Vascular Medicine, Department of Medicine, Baylor College of Medicine, Houston, TX 77030, USA
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18
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Molecular structure of low density lipoprotein: current status and future challenges. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2008; 38:145-58. [DOI: 10.1007/s00249-008-0368-y] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2008] [Accepted: 08/28/2008] [Indexed: 01/01/2023]
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19
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Kumpula LS, Kumpula JM, Taskinen MR, Jauhiainen M, Kaski K, Ala-Korpela M. Reconsideration of hydrophobic lipid distributions in lipoprotein particles. Chem Phys Lipids 2008; 155:57-62. [PMID: 18611396 DOI: 10.1016/j.chemphyslip.2008.06.003] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2008] [Revised: 05/25/2008] [Accepted: 06/03/2008] [Indexed: 11/29/2022]
Abstract
Lipoprotein particles are commonly known as micellar aggregates with hydrophobic lipids located within the core and amphipathic molecules in the surface. Using a new structural model for optimizing the distribution of hydrophobic lipids, namely triglyceride (TG) and cholesterol ester (CE) molecules, we reveal that particle size-dependent proportion of these 'core lipids' may locate in the surface of lipoprotein particles. The composition of the particles also strongly influences the actual molecular content of the surface. For example, in high-density lipoprotein (HDL) particles the percentage of CEs of all surface lipids is between 13% and 27% due to the high tendency of CEs to locate in the surface and the high concentration of CEs in the particles. Conversely, although the percentage of TG molecules in the surface of HDL particles is also high, approximately 60% as for CE, the percentage of TGs of all surface lipids is low, only up to 5%, because HDL particles have a low-TG concentration. These structural models provide an intuitive and coherent structural rationale for various metabolic cascades in lipoprotein metabolism with the catalytic enzyme action and molecular binding for transport proteins taking place at the surface of the particles.
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Affiliation(s)
- Linda S Kumpula
- Computational Medicine Research Group, Department of Biomedical Engineering and Computational Science, Helsinki University of Technology, P.O. Box 9203, FI-02015 HUT, Finland
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20
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Vedhachalam C, Ghering AB, Davidson WS, Lund-Katz S, Rothblat GH, Phillips MC. ABCA1-induced cell surface binding sites for ApoA-I. Arterioscler Thromb Vasc Biol 2007; 27:1603-9. [PMID: 17478755 DOI: 10.1161/atvbaha.107.145789] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
OBJECTIVE The purpose of this study was to understand the interactions of apoA-I with cells expressing ABCA1. METHODS AND RESULTS The binding of wild-type (WT) and mutant forms of human apoA-I to mouse J774 macrophages was examined. Analysis of total binding at 37 degrees C of 125I-WT apoA-I to the cells and specifically to ABCA1, as determined by covalent cross-linking, revealed saturable high affinity binding in both cases. Determination of the level of cell-surface expression of ABCA1 showed that only about 10% of the apoA-I associated with the cell surface was bound directly to ABCA1. Furthermore, when 125I -apoA-I was cross-linked to ABCA1-upregulated cells and examined by SDS-PAGE, the major (approximately 90%) band migrated as monomeric apoA-I. In contrast to WT apoA-I, the C-terminal deletion mutants delta190 to 243 and delta223 to 243 that have reduced lipid affinity, exhibited marked reductions (50 and 70%, respectively) in their abilities to bind to the surface of ABCA1-upregulated cells. However, these C-terminal deletion mutants cross-linked to ABCA1 as effectively as WT apoA-I. CONCLUSIONS This study demonstrates that ABCA1 activity creates 2 types of high affinity apoA-I binding sites at the cell surface. The low capacity site formed by direct apoA-I/ABCA1 interaction functions in a regulatory role, whereas the much higher capacity site generated by apoA-I/lipid interactions functions in the assembly of nascent HDL particles.
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Affiliation(s)
- Charulatha Vedhachalam
- Division of GI/Nutrition, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4318, USA
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21
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Silva RAGD, Schneeweis LA, Krishnan SC, Zhang X, Axelsen PH, Davidson WS. The structure of apolipoprotein A-II in discoidal high density lipoproteins. J Biol Chem 2007; 282:9713-9721. [PMID: 17264082 DOI: 10.1074/jbc.m610380200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
It is well accepted that high levels of high density lipoproteins (HDL) reduce the risk of atherosclerosis in humans. Apolipoprotein A-I (apoA-I) and apoA-II are the first and second most common protein constituents of HDL. Unlike apoA-I, detailed structural models for apoA-II in HDL are not available. Here, we present a structural model of apoA-II in reconstituted HDL (rHDL) based on two well established experimental approaches: chemical cross-linking/mass spectrometry (MS) and internal reflection infrared spectroscopy. Homogeneous apoA-II rHDL were reacted with a cross-linking agent to link proximal lysine residues. Upon tryptic digestion, cross-linked peptides were identified by electrospray mass spectrometry. 14 cross-links were identified and confirmed by tandem mass spectrometry (MS/MS). Infrared spectroscopy indicated a beltlike molecular arrangement for apoA-II in which the protein helices wrap around the lipid bilayer rHDL disc. The cross-links were then evaluated on three potential belt arrangements. The data clearly refute a parallel model but support two antiparallel models, especially a "double hairpin" form. These models form the basis for understanding apoA-II structure in more complex HDL particles.
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Affiliation(s)
- R A Gangani D Silva
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237
| | - Lumelle A Schneeweis
- Departments of Pharmacology, Biochemistry, and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - Srinivasan C Krishnan
- Mass Spectrometry Application Laboratory, Applied Biosystems, Framingham, Massachusetts 01701
| | - Xiuqi Zhang
- Department of Chemistry, University of Illinois, Chicago, Illinois 60607
| | - Paul H Axelsen
- Departments of Pharmacology, Biochemistry, and Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania 19104
| | - W Sean Davidson
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45237.
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22
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Duong PT, Collins HL, Nickel M, Lund-Katz S, Rothblat GH, Phillips MC. Characterization of nascent HDL particles and microparticles formed by ABCA1-mediated efflux of cellular lipids to apoA-I. J Lipid Res 2006; 47:832-43. [PMID: 16418537 DOI: 10.1194/jlr.m500531-jlr200] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The nascent HDL created by ABCA1-mediated efflux of cellular phospholipid (PL) and free (unesterified) cholesterol (FC) to apolipoprotein A-I (apoA-I) has not been defined. To address this issue, we characterized the lipid particles released when J774 mouse macrophages and human skin fibroblasts in which ABCA1 is activated are incubated with human apoA-I. In both cases, three types of nascent HDL containing two, three, or four molecules of apoA-I per particle are formed. With J774 cells, the predominant species have hydrodynamic diameters of approximately 9 and 12 nm. These discoidal HDL particles have different FC contents and PL compositions, and the presence of acidic PL causes them to exhibit alpha-electrophoretic mobility. These results are consistent with ABCA1 located in more than one membrane microenvironment being responsible for the production of the heterogeneous HDL. Activation of ABCA1 also leads to the release of apoA-I-free plasma membrane vesicles (microparticles). These larger, spherical particles released from J774 cells have the same PL composition as the 12 nm HDL and contain CD14 and ganglioside, consistent with their origin being plasma membrane raft domains. The various HDL particles and microparticles are created concurrently, and there is no precursor-product relationship between them. Importantly, a large fraction of the cellular FC effluxed from these cells by ABCA1 is located in microparticles. Collectively, these results show that the products of the apoA-I/ABCA1 interaction include discoidal HDL particles containing different numbers of apoA-I molecules. The cellular PLs and cholesterol incorporated into these nascent HDL particles originate from different cell membrane domains.
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Affiliation(s)
- Phu T Duong
- Division of GI/Nutrition, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-4318, USA
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23
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Davidson WS, Ghering AB, Beish L, Tubb MR, Hui DY, Pearson K. The biotin-capture lipid affinity assay: a rapid method for determining lipid binding parameters for apolipoproteins. J Lipid Res 2005; 47:440-9. [PMID: 16267343 DOI: 10.1194/jlr.d500034-jlr200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The lipid affinity of plasma apolipoproteins is an important modulator of lipoprotein metabolism. Mutagenesis techniques have been widely used to modulate apolipoprotein lipid affinity for studying biological function, but the approach requires rapid and reliable lipid affinity assays to compare the mutants. Here, we describe a novel method that measures apolipoprotein binding to a standardized preparation of small unilamellar vesicles (SUVs) containing trace biotinylated and fluorescent phospholipids. After a 30 min incubation at various apolipoprotein concentrations, vesicle-bound protein is rapidly separated from free protein on columns of immobilized streptavidin in a 96-well microplate format. Vesicle-bound protein and lipid are eluted and measured in a fluorescence microplate reader for calculation of a dissociation constant and the maximum number of potential binding sites on the SUVs. Using human apolipoprotein A-I (apoA-I), apoA-IV, and mutants of each, we show that the assay generates binding constants that are comparable to other methods and is reproducible across time and apolipoprotein preparations. The assay is easy to perform and can measure triplicate binding parameters for up to 10 separate apolipoproteins in 3.5 h, consuming only 120 microg of apolipoprotein in total. The benefits and potential drawbacks of the assay are discussed.
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Affiliation(s)
- W Sean Davidson
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, OH 45237-0507, USA.
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24
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Abstract
Dietary sphingomyelin (SM) is hydrolyzed by intestinal alkaline sphingomyelinase and neutral ceramidase to sphingosine, which is absorbed and converted to palmitic acid and acylated into chylomicron triglycerides (TGs). SM digestion is slow and is affected by luminal factors such as bile salt, cholesterol, and other lipids. In the gut, SM and its metabolites may influence TG hydrolysis, cholesterol absorption, lipoprotein formation, and mucosal growth. SM accounts for approximately 20% of the phospholipids in human plasma lipoproteins, of which two-thirds are in LDL and VLDL. It is secreted in chylomicrons and VLDL and transferred into HDL via the ABCA1 transporter. Plasma SM increases after periods of large lipid loads, during suckling, and in type II hypercholesterolemia, cholesterol-fed animals, and apolipoprotein E-deficient mice. SM is thus an important amphiphilic component when plasma lipoprotein pools expand in response to large lipid loads or metabolic abnormalities. It inhibits lipoprotein lipase and LCAT as well as the interaction of lipoproteins with receptors and counteracts LDL oxidation. The turnover of plasma SM is greater than can be accounted for by the turnover of LDL and HDL particles. Some SM must be degraded via receptor-mediated catabolism of chylomicron and VLDL remnants and by scavenger receptor class B type I receptor-mediated transfer into cells.
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Affiliation(s)
- Ake Nilsson
- Department of Medicine, University of Lund, University Hospital, S-22185 Lund, Sweden.
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25
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Boyle-Roden E, Walzem RL. Integral apolipoproteins increase surface-located triacylglycerol in intact native apoB-100-containing lipoproteins. J Lipid Res 2005; 46:1624-32. [PMID: 15930523 DOI: 10.1194/jlr.m400434-jlr200] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
High-resolution NMR was used to measure the presence and quantity of triacylglycerol (TAG) in the surface of intact native apolipoprotein B-100-containing lipoprotein particles that are made by chickens in response to estrogen treatment and that in hens are deposited in yolk follicles (VLDLy). Integration of 13C NMR resonances shows that intact VLDLy particles contain more surface TAG (5.1 +/- 0.6 mol%, 6.7 +/- 0.8 weight %) than predicted by apolipoprotein-free models using similarly acyl-heterogenous TAG. Change in downfield chemical shift values of surface to core TAG in VLDLy was 0.8 ppm compared with 1.3 ppm in vesicles prepared with purified egg phosphatidylcholine and TAG isolated from the VLDLy, indicating that reduced surface TAG hydration may contribute to the resistance to lipase hydrolysis characteristic of this lipoprotein species. Apolipoprotein-mediated changes in surface lipid composition and lipid hydration provide possible general mechanisms for selectivity in lipoprotein substrate characteristics.
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Affiliation(s)
- Elizabeth Boyle-Roden
- Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA.
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26
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Vedhachalam C, Liu L, Nickel M, Dhanasekaran P, Anantharamaiah GM, Lund-Katz S, Rothblat GH, Phillips MC. Influence of ApoA-I structure on the ABCA1-mediated efflux of cellular lipids. J Biol Chem 2004; 279:49931-9. [PMID: 15383537 DOI: 10.1074/jbc.m406924200] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The influence of apolipoprotein (apo) A-I structure on ABCA1-mediated efflux of cellular unesterified (free) cholesterol (FC) and phospholipid (PL) is not well understood. To address this issue, we used a series of apoA-I mutants to examine the contributions of various domains in the molecule to ABCA1-mediated FC and PL efflux from mouse J774 macrophages and human skin fibroblasts. Irrespective of the cell type, deletion or disruption of the C-terminal lipid-binding domain of apoA-I drastically reduced the FC and PL efflux ( approximately 90%), indicating that the C-terminal amphipathic alpha-helix is required for high affinity microsolubilization of FC and PL. Deletion in the N-terminal region of apoA-I also reduced the lipid efflux ( approximately 30%) and increased the K(m) about 2-fold compared with wild type apoA-I, whereas deletion of the central domain (Delta123-166) had no effect on either K(m) or V(max). These results indicate that ABCA1-mediated lipid efflux is relatively insensitive to the organization of the apoA-I N-terminal helix-bundle domain. Alterations in apoA-I structure caused parallel changes in its ability to bind to a PL bilayer and to induce efflux of FC and PL. Overall, these results are consistent with a two-step model for ABCA1-mediated lipid efflux. In the first step, apoA-I binds to ABCA1 and hydrophobic alpha-helices in the C-terminal domain of apoA-I insert into the region of the perturbed PL bilayer created by the PL transport activity of ABCA1, thereby allowing the second step of lipidation of apoA-I and formation of nascent high density lipoprotein particles to occur.
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Affiliation(s)
- Charulatha Vedhachalam
- Division of GI/Nutrition, The Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA
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27
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Liu L, Bortnick AE, Nickel M, Dhanasekaran P, Subbaiah PV, Lund-Katz S, Rothblat GH, Phillips MC. Effects of apolipoprotein A-I on ATP-binding cassette transporter A1-mediated efflux of macrophage phospholipid and cholesterol: formation of nascent high density lipoprotein particles. J Biol Chem 2003; 278:42976-84. [PMID: 12928428 DOI: 10.1074/jbc.m308420200] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mechanism of formation of high density lipoprotein (HDL) particles by the action of ATP-binding cassette transporter A1 (ABCA1) is not defined completely. To address this issue, we monitored efflux to apoA-I of phosphatidylcholine (PC), sphingomyelin (SM), and unesterified (free) cholesterol (FC) from J774 macrophages, in which ABCA1 is up-regulated, and investigated the nature of the particles formed. The various apoA-I/lipid particles appearing in the extracellular medium were separated by gel filtration chromatography. The presence of apoA-I in the extracellular medium led to the simultaneous formation of more than one type of poorly lipidated apoA-I-containing particle: there were 9- and 12-nm diameter particles containing approximately 3:1 and 1:1 phospholipid/FC (mol/mol), respectively, which were present together with 6-nm monomeric apoA-I. Removal of the C-terminal alpha-helix (residues 223-243) of apoA-I reduced phospholipid and FC efflux and prevented formation of the 9- and 12-nm HDL particles; the apoA-I variant formed larger particles that eluted in the void volume. FC loading of the J774 cells also led to the formation of larger apoA-I-containing particles that were highly enriched in FC. Besides creating HDL particles, ABCA1 mediated release of larger (20-450-nm diameter) FC-rich particles that were not involved in HDL formation and that are probably membrane vesicles. These particles contained 1:1 PC/SM in contrast to the HDL particles, which contained 2:1 PC/SM. This is consistent with lipid raft and non-raft plasma membrane domains being involved primarily in ABCA1-mediated vesicle release and nascent HDL formation, respectively.
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Affiliation(s)
- Lijuan Liu
- Gastrointestinal/Nutrition Division, Children's Hospital of Philadelphia, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-4318, USA
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28
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Davidson WS, Hilliard GM. The spatial organization of apolipoprotein A-I on the edge of discoidal high density lipoprotein particles: a mass specrometry study. J Biol Chem 2003; 278:27199-207. [PMID: 12724319 DOI: 10.1074/jbc.m302764200] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The three-dimensional structure of human apoA-I on nascent, discoidal HDL particles has been debated extensively over the past 25 years. Recent evidence has demonstrated that the alpha-helical domains of apoA-I are arranged in a belt-like orientation with the long axis of the helices perpendicular to the phospholipid acyl chains on the disc edge. However, experimental information on the spatial relationships between apoA-I molecules on the disc is lacking. To address this issue, we have taken advantage of recent advances in mass spectrometry technology combined with cleavable cross-linking chemistry to derive a set of distance constraints suitable for testing apoA-I structural models. We generated highly homogeneous, reconstituted HDL particles containing two molecules of apoA-I. These were treated with a thiol-cleavable cross-linking agent, which covalently joined Lys residues in close proximity within or between molecules of apoA-I in the disc. The cross-linked discs were then exhaustively trypsinized to generate a discrete population of peptides. The resulting peptides were analyzed by liquid chromatography/mass spectrometry before and after cleavage of the cross-links, and resulting peaks were identified based on the theoretical tryptic cleavage of apoA-I. We identified at least 8 intramolecular and 7 intermolecular cross-links in the particle. The distance constraints are used to analyze three current models of apoA-I structure. The results strongly support the presence of the salt-bridge interactions that were predicted to occur in the "double belt" model of apoA-I, but a helical hairpin model containing the same salt-bridge docking interface is also consistent with the data.
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Affiliation(s)
- W Sean Davidson
- Department of Pathology and Laboratory Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0529,
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29
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Cushley RJ, Okon M. NMR studies of lipoprotein structure. ANNUAL REVIEW OF BIOPHYSICS AND BIOMOLECULAR STRUCTURE 2002; 31:177-206. [PMID: 11988467 DOI: 10.1146/annurev.biophys.31.101101.140910] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Early NMR structural studies of serum lipoproteins were based on (1)H, (13)C, (31)P, and (2)H studies of lipid components. From the early studies information on composition, lipid chain dynamics and order parameters, and monolayer organization resulted. More recently, selective or complete isotopic labeling techniques, combined with multidimensional NMR spectroscopy, have resulted in structural information of apoprotein fragments. Finally, use of heteronuclear three- and four-dimensional experiments have yielded solution structures and protein-lipid interactions of intact apolipoproteins C-I, C-II, and A-I.
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Affiliation(s)
- Robert J Cushley
- Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby V5A 1S6, British Columbia, Canada.
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30
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Segrest JP, Jones MK, De Loof H, Dashti N. Structure of apolipoprotein B-100 in low density lipoproteins. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)30267-4] [Citation(s) in RCA: 359] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
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31
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Chanson NF, Lontie JF, Carpentier YA, Motta C. Incubation of lipid emulsions with plasma lipoproteins modifies the fluidity of each particle. Lipids 2001; 36:819-25. [PMID: 11592733 DOI: 10.1007/s11745-001-0790-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
Lipid emulsions (LE) contain triglyceride (TG)-rich particles (TGRP) and phospholipid-rich particles (PLRP). Various lipid and protein exchanges take place during in vitro incubations of LE with lipoproteins. These composition changes affect physical properties of particles. The aim of this study was to determine the role of different LE particles and the effect of TG composition on physical modifications. Low density lipoproteins (LDL: 1.025 < d < 1.040 g/mL) or high density lipoproteins (HDL: 1.085 < d< 1.150 g/mL) were incubated with the following four LE or their TGRP or PLRP, which were manufactured with the same phospholipid emulsifier: long-chain triglycerides (LCT): 100% soybean oil; medium-chain triglycerides (MCT)/LCT (MCT/LCT, 5:5, w/w); FO (100% fish oil); and MLF541 (MCT/LCT/FO, 5:4:1, by wt). After incubation, modified LE particles and lipoproteins were analyzed by fluorescence polarization. Observed physical modifications were significant in emulsion particles (ordering effect) but not in lipoproteins and also were significant for TG composition effect. Since intact emulsion contained a large excess of TGRP over PLRP, it is not surprising that intact emulsion had the same behavior as TGRP alone, and that PLRP had the same physical characteristics as lipoproteins. TG loss and cholesterol and protein acquisitions by emulsion particles rigidify their envelope. The two emulsions containing FO were less ordered after incubation. In conclusion, incubation of LE with lipoproteins changes physical properties of each kind of particle, and TG composition of the emulsion affects emulsion particle changes but has no effect on LDL and HDL. These order modifications induce more effective exchanges between LE particles and lipoproteins and modify their metabolism; HDL changes may increase the reverse cholesterol transport.
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Affiliation(s)
- N F Chanson
- L. Deloyers Laboratory for Experimental Surgery, Université Libre de Bruxelles, Brussels, Belgium
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32
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Lusa S, Blom TS, Eskelinen EL, Kuismanen E, Månsson JE, Simons K, Ikonen E. Depletion of rafts in late endocytic membranes is controlled by NPC1-dependent recycling of cholesterol to the plasma membrane. J Cell Sci 2001; 114:1893-900. [PMID: 11329376 DOI: 10.1242/jcs.114.10.1893] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
In mammalian cells, cholesterol is thought to associate with sphingolipids to form lateral membrane domains termed rafts. Increasing evidence suggests that rafts regulate protein interactions, for example, during signalling, intracellular transport and host-pathogen interactions. Rafts are present in cholesterol-sphingolipid-enriched membranes, including early and recycling endosomes, but whether rafts are found in late endocytic organelles has not been analyzed. In this study, we analyzed the association of cholesterol and late endosomal proteins with low-density detergent-resistant membranes (DRMs) in normal cells and in cells with lysosomal cholesterol-sphingolipid accumulation. In normal cells, the majority of [(3)H]cholesterol released from [(3)H]cholesterol ester-LDL associated with detergent-soluble membranes, was rapidly transported to the plasma membrane and became increasingly insoluble with time. In Niemann-Pick C1 (NPC1) protein-deficient lipidosis cells, the association of LDL-cholesterol with DRMs was enhanced and its transport to the plasma membrane was inhibited. In addition, the NPC1 protein was normally recovered in detergent-soluble membranes and its association with DRMs was enhanced by lysosomal cholesterol loading. Moreover, lysosomal cholesterol deposition was kinetically paralleled by the sequestration of sphingolipids and formation of multilamellar bodies in late endocytic organelles. These results suggest that late endocytic organelles are normally raft-poor and that endocytosed LDL-cholesterol is efficiently recycled to the plasma membrane in an NPC1-dependent process. The cholesterol-sphingolipid accumulation characteristic to NPC disease, and potentially to other sphingolipidoses, causes an overcrowding of rafts forming lamellar bodies in the degradative compartments.
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Affiliation(s)
- S Lusa
- Dept of Molecular Medicine, National Public Health Institute, Helsinki, Finland
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33
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Safi W, Maiorano JN, Davidson WS. A proteolytic method for distinguishing between lipid-free and lipid-bound apolipoprotein A-I. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)31649-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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34
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Effect of acylglyceride content on the structure and function of reconstituted high density lipoprotein particles. J Lipid Res 2001. [DOI: 10.1016/s0022-2275(20)32338-5] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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35
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36
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Hevonoja T, Pentikäinen MO, Hyvönen MT, Kovanen PT, Ala-Korpela M. Structure of low density lipoprotein (LDL) particles: basis for understanding molecular changes in modified LDL. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1488:189-210. [PMID: 11082530 DOI: 10.1016/s1388-1981(00)00123-2] [Citation(s) in RCA: 271] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Low density lipoprotein (LDL) particles are the major cholesterol carriers in circulation and their physiological function is to carry cholesterol to the cells. In the process of atherogenesis these particles are modified and they accumulate in the arterial wall. Although the composition and overall structure of the LDL particles is well known, the fundamental molecular interactions and their impact on the structure of LDL particles are not well understood. Here, the existing pieces of structural information on LDL particles are combined with computer models of the individual molecular components to give a detailed structural model and visualization of the particles. Strong evidence is presented in favor of interactions between LDL lipid constituents that lead to specific domain formation in the particles. A new three-layer model, which divides the LDL particle into outer surface, interfacial layer, and core, and which is capable of explaining some seemingly contradictory interpretations of molecular interactions in LDL particles, is also presented. A new molecular interaction model for the beta-sheet structure and phosphatidylcholine headgroups is introduced and an overall view of the tertiary structure of apolipoprotein B-100 in the LDL particles is presented. This structural information is also utilized to understand and explain the molecular characteristics and interactions of modified, atherogenic LDL particles.
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Affiliation(s)
- T Hevonoja
- Wihuri Research Institute, Kalliolinnantie 4, FIN-00140 Helsinki, Finland
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37
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Lund-Katz S, Zaiou M, Wehrli S, Dhanasekaran P, Baldwin F, Weisgraber KH, Phillips MC. Effects of lipid interaction on the lysine microenvironments in apolipoprotein E. J Biol Chem 2000; 275:34459-64. [PMID: 10921925 DOI: 10.1074/jbc.m005265200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lysines in apolipoprotein (apo) E are key factors in the binding of apoE to the low density lipoprotein receptor, and high affinity binding requires that apoE be associated with lipid. To gain insight into this effect, we examined the microenvironments of the eight lysines in the 22-kDa fragment of apoE3 (residues 1-191) in the lipid-free and lipid-associated states. As shown by (1)H,(13)C heteronuclear single quantum coherence nuclear magnetic resonance, lysine resonances in the lipid-free fragment were poorly resolved over a wide pH range, whereas in apoE3.dimyristoyl phosphatidylcholine (DMPC) discs, the lysine microenvironments and protein conformation were significantly altered. Sequence-specific assignments of the lysine resonances in the spectrum of the lipidated 22-kDa fragment were made. In the lipid-free protein, six lysines could be resolved, and all had pK(a) values above 10. In apoE3.DMPC complexes, however, all eight lysines were resolved, and the pK(a) values were 9.2-11.1. Lys-143 and Lys-146, both in the receptor binding region in helix 4, had unusually low pK(a) values of 9.5 and 9.2, respectively, likely as a result of local increases in positive electrostatic potential with lipid association. Shift reagent experiments with potassium ferricyanide showed that Lys-143 and Lys-146 were much more accessible to the ferricyanide anion in the apoE3.DMPC complex than in the lipid-free state. The angle of the nonpolar face of helix 4 is smaller than the angles of helices 1, 2, and 3, suggesting that helix 4 cannot penetrate as deeply into the DMPC acyl chains at the edge of the complex and that its polar face protrudes from the edge of the disc. This increased exposure and the greater positive electrostatic potential created by interaction with DMPC may explain why lipid association is required for high affinity binding of apoE to the low density lipoprotein receptor.
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Affiliation(s)
- S Lund-Katz
- Joseph Stokes Jr. Research Institute, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania 19104-4318, USA.
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38
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Aggregation, fusion, and vesicle formation of modified low density lipoprotein particles: molecular mechanisms and effects on matrix interactions. J Lipid Res 2000. [DOI: 10.1016/s0022-2275(20)31964-7] [Citation(s) in RCA: 180] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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39
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Orlova EV, Sherman MB, Chiu W, Mowri H, Smith LC, Gotto AM. Three-dimensional structure of low density lipoproteins by electron cryomicroscopy. Proc Natl Acad Sci U S A 1999; 96:8420-5. [PMID: 10411890 PMCID: PMC17531 DOI: 10.1073/pnas.96.15.8420] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Human low density lipoproteins (LDL) are the major cholesterol carriers in the blood. Elevated concentration of LDL is a major risk factor for atherosclerotic disease. Purified LDL particles appear heterogeneous in images obtained with a 400-kV electron cryomicroscope. Using multivariate statistical and cluster analyses, an ensemble of randomly oriented particle images has been subdivided into homogeneous subpopulations, and the largest subset was used for three-dimensional reconstruction. In contrast to the general belief that below the lipid phase-transition temperature (30 degrees C) LDL are quasi-spherical microemulsion particles with a radially layered core-shell organization, our three-dimensional map shows that LDL have a well-defined and stable organization. Particles consist of a higher-density outer shell and lower-density inner lamellae-like layers that divide the core into compartments. The outer shell consists of apolipoprotein B-100, phospholipids, and some free cholesterol.
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Affiliation(s)
- E V Orlova
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, Houston, TX 77030, USA
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40
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Rodrigueza WV, Thuahnai ST, Temel RE, Lund-Katz S, Phillips MC, Williams DL. Mechanism of scavenger receptor class B type I-mediated selective uptake of cholesteryl esters from high density lipoprotein to adrenal cells. J Biol Chem 1999; 274:20344-50. [PMID: 10400657 DOI: 10.1074/jbc.274.29.20344] [Citation(s) in RCA: 155] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Despite extensive studies and characterizations of the high density lipoprotein-cholesteryl ester (HDL-CE)-selective uptake pathway, the mechanisms by which the hydrophobic CE molecules are transferred from the HDL particle to the plasma membrane have remained elusive, until the discovery that scavenger receptor BI (SR-BI) plays an important role. To elucidate the molecular mechanism, we examined the quantitative relationships between the binding of HDL and the selective uptake of its CE in the murine adrenal Y1-BS1 cell line. A comparison of concentration dependences shows that half-maximal high affinity cell association of HDL occurs at 8.7 +/- 4.7 micrograms/ml and the Km of HDL-CE-selective uptake is 4.5 +/- 1.5 micrograms/ml. These values are similar, and there is a very high correlation between these two processes (r2 = 0.98), suggesting that they are linked. An examination of lipid uptake from reconstituted HDL particles of defined composition and size shows that there is a non-stoichiometric uptake of HDL lipid components, with CE being preferred over the major HDL phospholipids, phosphatidylcholine and sphingomyelin. Comparison of the rates of selective uptake of different classes of phospholipid in this system gives the ranking: phosphatidylserine > phosphatidylcholine approximately phosphatidylinositol > sphingomyelin. The rate of CE-selective uptake from donor particles is proportional to the amount of CE initially present in the particles, suggesting a mechanism in which CE moves down its concentration gradient from HDL particles docked on SR-BI into the cell plasma membrane. The activation energy for CE uptake from either HDL3 or reconstituted HDL is about 9 kcal/mol, indicating that HDL-CE uptake occurs via a non-aqueous pathway. HDL binding to SR-BI allows access of CE molecules to a "channel" formed by the receptor from which water is excluded and along which HDL-CE molecules move down their concentration gradient into the cell plasma membrane.
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Affiliation(s)
- W V Rodrigueza
- Department of Biochemistry, MCP Hahnemann University, Philadelphia, Pennsylvania 19129, USA
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41
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Zarev S, Thérond P, Bonnefont-Rousselot D, Beaudeux JL, Gardès-Albert M, Legrand A. Major differences in oxysterol formation in human low density lipoproteins (LDLs) oxidized by *OH/O2*- free radicals or by copper. FEBS Lett 1999; 451:103-8. [PMID: 10371147 DOI: 10.1016/s0014-5793(99)00564-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The aim of our study was to determine the oxysterol formation in low density lipoproteins (LDLs) oxidized by defined oxygen free radicals (*OH/O2*-). This was compared to the oxysterol produced upon the classical copper oxidation procedure. The results showed a markedly lower formation of oxysterols induced by *OH/O2*- free radicals than by copper and thus suggested a poor ability of these radicals to initiate cholesterol oxidation in LDLs. Moreover, the molecular species of cholesteryl ester hydroperoxides produced by LDL copper oxidation seemed more labile than those formed upon *OH/O2*(-)-induced oxidation, probably due to their degradation by reaction with copper ions.
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Affiliation(s)
- S Zarev
- Laboratoire de Biochimie Métabolique et Clinique, Faculté de Pharmacie, Paris, France
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42
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Gillotte KL, Zaiou M, Lund-Katz S, Anantharamaiah GM, Holvoet P, Dhoest A, Palgunachari MN, Segrest JP, Weisgraber KH, Rothblat GH, Phillips MC. Apolipoprotein-mediated plasma membrane microsolubilization. Role of lipid affinity and membrane penetration in the efflux of cellular cholesterol and phospholipid. J Biol Chem 1999; 274:2021-8. [PMID: 9890960 DOI: 10.1074/jbc.274.4.2021] [Citation(s) in RCA: 154] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lipid-free apolipoprotein (apo) A-I contributes to the reverse transport of cholesterol from the periphery to the liver by solubilizing plasma membrane phospholipid and cholesterol. The features of the apolipoprotein required for this process are not understood and are addressed in the current study. Membrane microsolubilization of human fibroblasts is not specific for apo A-I; unlipidated apos A-II, C, and E incubated with the fibroblast monolayers at a saturating concentration of 50 micrograms/ml are all able to release cholesterol and phospholipid similarly. To determine the properties of the apolipoprotein that drive the process, apo A-I peptides spanning the entire sequence of the protein were utilized; the peptides correspond to the 11- and 22-residue amphipathic alpha-helical segments, as well as adjacent combinations of the helices. Of the 20 helical peptides examined, only peptides representing the N-and C-terminal portions of the protein had the ability to solubilize phospholipid and cholesterol. Cholesterol efflux to the most effective peptides, 44-65 and 209-241, was approximately 50 and 70%, respectively, of that to intact apo A-I. Deletion mutants of apo E and apo A-I were constructed that have reduced lipid binding affinities as compared with the intact molecule. The proteins, apo A-I (Delta222-243), apo A-I (Delta190-243), apo E3 (Delta192-299) and apo E4 (Delta192-299) all exhibited a decreased ability to remove cellular cholesterol and phospholipid. These decreases correlated with the reduced ability of these proteins to penetrate into a phospholipid monomolecular film. Overall, the results indicate that insertion of amphipathic alpha-helices between the plasma membrane phospholipid molecules is a required step in the mechanism of apolipoprotein-mediated cellular lipid efflux. Therefore the lipid binding ability of the apolipoprotein is critical for efficient membrane microsolubilization.
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Affiliation(s)
- K L Gillotte
- Department of Biochemistry, MCP Hahnemann University, Philadelphia, Pennsylvania 19129, USA
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43
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Pregetter M, Prassl R, Schuster B, Kriechbaum M, Nigon F, Chapman J, Laggner P. Microphase separation in low density lipoproteins. Evidence for a fluid triglyceride core below the lipid melting transition. J Biol Chem 1999; 274:1334-41. [PMID: 9880504 DOI: 10.1074/jbc.274.3.1334] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The structural organization of the neutral lipid core in human low density lipoproteins (LDL) was investigated in physicochemically defined, distinct human LDL subspecies in the density range of 1. 0244-1.0435 g/ml by evaluation of the core lipid transition temperature, chemical composition, and the behavior of spin-labeled core lipids. Calorimetric studies were performed on more than 60 LDL preparations, and the transition temperature, which varied between 19 and 32 degreesC, was correlated to the chemical composition and revealed a discontinuity at a critical cholesteryl ester to triglyceride ratio of approximately 7:1. For electron spin resonance studies, several LDL preparations were probed with spin-labeled cholesteryl esters and triglycerides, respectively. In LDL with a high triglyceride content, both labels exhibited similar mobility behavior. In contrast, in LDL with only small concentrations of triglycerides, the behavior of labeled cholesteryl esters and labeled triglycerides differed distinctly. The cholesteryl esters were strongly immobilized below the transition temperature, whereas the triglycerides remained fluid throughout the measured temperatures. These results suggest that the critical cholesteryl ester to triglyceride mass ratio of 7:1 corresponds to two concentric compartments with a radial ratio of 2:1, where the liquid triglycerides occupy the core, and the cholesteryl esters form the frozen shell. At higher triglyceride contents, the triglyceride molecules insert into the cholesteryl ester shell and depress the peak transition temperature of the LDL core, whereas at lower triglyceride contents, excess cholesteryl esters are dissolved in the core.
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Affiliation(s)
- M Pregetter
- Institut für Biophysik und Röntgenstrukturforschung, Osterreichische Akademie der Wissenschaften, A-8010 Graz, Austria
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44
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45
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Abstract
Plasma lipoprotein surface properties are important but poorly understood determinants of lipoprotein catabolism. To elucidate the relation between surface properties and surface reactivity, the physical properties of surface monolayers of native lipoproteins and lipoprotein models were investigated by fluorescent probes of surface lipid fluidity, surface lateral diffusion, and interfacial polarity, and by their reactivity to Naja melanoleuca phospholipase A2 (PLA2). Native lipoproteins were human very low, low-, and subclass 3 high-density lipoproteins (VLDL, LDL, and HDL3); models were 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) or its ether analog in single-bilayer vesicles, large and small microemulsions of POPC and triolein, and reassembled HDL (apolipoprotein A-I plus phospholipid). Among lipoproteins, surface lipid fluidity increased in the order HDL3 < LDL < VLDL, varying inversely with their (protein + cholesterol)/phospholipid ratios. Models resembled VLDL in fluidity. Both lateral mobility in the surface monolayer and polarity of the interfacial region were lower in native lipoproteins than in models. Among native lipoproteins and models, increased fluidity in the surface monolayer was associated with increased reactivity to PLA2. Addition of cholesterol (up to 20 mol%) to models had little effect on PLA2 activity, whereas the addition of apolipoprotein C-III stimulated it. Single-bilayer vesicles, phospholipid-triolein microemulsions, and VLDL have surface monolayers that are quantitatively similar, and distinct from those of LDL and HDL3. Surface property and enzymatic reactivity differences between lipoproteins and models were associated with differences in surface monolayer protein and cholesterol contents. Thus differences in the surface properties that regulate lipolytic reactivity are a predictable function of surface composition.
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Affiliation(s)
- J B Massey
- Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA
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46
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Rodrigueza WV, Mazany KD, Essenburg AD, Pape ME, Rea TJ, Bisgaier CL, Williams KJ. Large versus small unilamellar vesicles mediate reverse cholesterol transport in vivo into two distinct hepatic metabolic pools. Implications for the treatment of atherosclerosis. Arterioscler Thromb Vasc Biol 1997; 17:2132-9. [PMID: 9351382 DOI: 10.1161/01.atv.17.10.2132] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Phospholipid liposomes are synthetic mediators of "reverse" cholesterol transport from peripheral tissue to liver in vivo and can shrink atherosclerotic lesions in animals. Hepatic disposal of this cholesterol, however, has not been examined. We compared hepatic effects of large (approximately equal to 120-nm) and small (approximately equal to 35-nm) unilamellar vesicles (LUVs and SUVs), both of which mediate reverse cholesterol transport in vivo but were previously shown to be targeted to different cell types within the liver. On days 1, 3, and 5, rabbits were intravenously injected with 300 mg phosphatidylcholine (LUVs or SUVs) per kilogram body weight or with the equivalent volume of saline. After each injection, LUV- and SUV-injected animals showed large increases in plasma concentrations of unesterified cholesterol, indicating mobilization of tissue stores. After hepatic uptake of this cholesterol, however, SUV-treated animals developed persistently elevated plasma LDL concentrations, which by day 6 had increased to more than four times the values in saline-treated controls. In contrast, LUV-treated animals showed normal LDL levels. By RNase protection assay, SUVs suppressed hepatic LDL receptor mRNA at day 6 (to 61 +/- 4% of control, mean +/- SEM), whereas LUVs caused a statistically insignificant stimulation. Hepatic HMG-CoA reductase message was also significantly suppressed with SUV, but not LUV treatment, and hepatic 7 alpha-hydroxylase message showed a similar trend. These data on hepatic mRNA levels indicate that SUVs, but not LUVs, substantially perturbed liver cholesterol homeostasis. We conclude that LUVs and SUVs mobilize peripheral tissue cholesterol and deliver it to the liver, but to distinct metabolic pools that exert different regulatory effects. The effects of one of these artificial particles, SUVs, suggest that reverse cholesterol transport may not always be benign. In contrast, LUVs may be a suitable therapeutic agent, because they mobilize peripheral cholesterol to the liver without suppressing hepatic LDL receptor mRNA and without provoking a subsequent rise in plasma LDL levels.
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Affiliation(s)
- W V Rodrigueza
- Department of Biochemistry, Medical College of Pennsylvania, Philadelphia, USA
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Murphy HC, Ala-Korpela M, White JJ, Raoof A, Bell JD, Barnard ML, Burns SP, Iles RA. Evidence for distinct behaviour of phosphatidylcholine and sphingomyelin at the low density lipoprotein surface. Biochem Biophys Res Commun 1997; 234:733-7. [PMID: 9175784 DOI: 10.1006/bbrc.1997.6634] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
This study demonstrates that the use of high field 1H NMR spectroscopy permits individual detection of phosphatidylcholine and sphingomyelin molecules at the surface of native low density lipoprotein (LDL) particles. Distinct behaviour was observed for the choline head group -N(CH3)3 resonances of these different phospholipids revealing preferential immobilisation for phosphatidylcholine. This suggests the existence of reversible and irreversible phosphatidylcholine-apolipoprotein B interactions and is consistent with microdomain formation at the surface monolayer of LDL. The novel resonance assignment and results show that 1H NMR can provide efficient and practical means for future studies on the structure and dynamics at the LDL surface.
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Affiliation(s)
- H C Murphy
- Medical Unit (Cellular and Molecular Mechanisms Research Group), St. Bartholomew's and The Royal London School of Medicine and Dentistry, United Kingdom
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Ettelaie C, Haris PI, James NJ, Wilbourn B, Adam JM, Bruckdorfer KR. Alterations in the structure of apolipoprotein B-100 determine the behaviour of LDL towards thromboplastin. BIOCHIMICA ET BIOPHYSICA ACTA 1997; 1345:237-47. [PMID: 9150244 DOI: 10.1016/s0005-2760(96)00185-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Apolipoprotein B-100 acts as an inhibitor of thromboplastin activity independently of the tissue factor pathway inhibitor (TFPI) associated with plasma lipoproteins. Analysis of the primary structure of Apo B-100 showed a higher than expected occurrence of lysine groups in the receptor-binding region. In order to demonstrate the participation of lysine groups of Apo B-100 in the inhibition of thromboplastin, thromboplastin and Apo B-100 were incubated together in the presence of poly-L-lysine, poly-L-arginine, lysine and arginine monomers. The inhibition of thromboplastin by Apo B-100 was completely suppressed in the presence of poly-L-lysine. Poly-L-arginine was found to be less effective and neither lysine or arginine monomers had any significant effect on the inhibitory effect of Apo B-100. Alterations in the structure of Apo B-100 reconstituted in lipid vesicles resembling LDL, brought about by lipid peroxidation and lipid loading were examined by means of Fourier transform infra-red spectroscopy. It was found that, upon oxidation without the addition of cupric ions, the apolipoprotein attains a more exposed conformation with an increase in alpha-helical structure. This increase occurred at the expense of beta-structure. On lipid loading, an increase in beta-structure at the expense of the alpha-helix, was demonstrated. It is therefore proposed that the variable action of LDL towards thromboplastin derives from alterations in the secondary structure of the Apo B-100, particularly the receptor-binding region.
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Affiliation(s)
- C Ettelaie
- Department of Biochemistry and Molecular Biology, Royal Free Hospital Medical School, London, UK.
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Nishida HI, Nishida T. Phospholipid transfer protein mediates transfer of not only phosphatidylcholine but also cholesterol from phosphatidylcholine-cholesterol vesicles to high density lipoproteins. J Biol Chem 1997; 272:6959-64. [PMID: 9054384 DOI: 10.1074/jbc.272.11.6959] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Phospholipid transfer protein (PLTP) purified from human plasma was found to enhance the transfer of cholesterol from single bilayer vesicles containing phosphatidylcholine and cholesterol to high density lipoprotein-3. The rate of cholesterol transfer was greatly influenced by the cholesterol content of the donor vesicles. The maximal rate was observed with the vesicles containing 20-25 mol % cholesterol. This was in contrast to a progressive decline in the rate of phosphatidylcholine transfer with an increase in the cholesterol content. To determine the binding of cholesterol and phosphatidylcholine to PLTP, the mixtures of PLTP and the vesicles containing 3H-labeled phosphatidylcholine and 14C-labeled cholesterol were incubated and subjected to sucrose density gradient centrifugation. Determination of the label profiles showed that cholesterol as well as phosphatidylcholine were transferred from the vesicles to PLTP. The reversible nature of the binding was shown by the transfer of labeled cholesterol and phosphatidylcholine bound to PLTP to the acceptor vesicles or low density lipoprotein. Isothermal equilibrium binding of PLTP for cholesterol and phosphatidylcholine showed that PLTP possessed a considerably higher affinity and binding capacity for phosphatidylcholine than for cholesterol. The phosphatidylcholine binding affinity and capacity were greater when PLTP was incubated with phosphatidylcholine vesicles without cholesterol. A possible importance of PLTP-mediated cholesterol transfer in the circulation was described.
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Affiliation(s)
- H I Nishida
- Burnsides Research Laboratory, Department of Food Science and Human Nutrition, University of Illinois, Urbana, Illinois 61801, USA
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Rodrigueza WV, Williams KJ, Rothblat GH, Phillips MC. Remodeling and shuttling. Mechanisms for the synergistic effects between different acceptor particles in the mobilization of cellular cholesterol. Arterioscler Thromb Vasc Biol 1997; 17:383-93. [PMID: 9081695 PMCID: PMC5021317 DOI: 10.1161/01.atv.17.2.383] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
In normal physiology, cells are exposed to cholesterol acceptors of different sizes simultaneously. The current study examined the possible interactions between two different classes of acceptors, one large (large unilamellar phospholipid vesicles, LUVs) and one small (HDL or other small acceptors), added separately or in combination to Fu5AH rat hepatoma cells. During a 24-hour incubation, LUVs of palmitoyl-oleoyl phosphatidylcholine at 1 mg phospholipid (PL) per milliliter extracted approximately 20% of cellular unesterified cholesterol (UC) label and mass in a slow, continuous fashion (half-time [t1/2] for UC efflux was approximately 50 hours) and human HDL3 at 25 micrograms PL per milliliter extracted approximately 15% cellular UC label with no change in cellular cholesterol mass (t1/2 of approximately 8 hours). In contrast, the combination of LUVs and HDL3 extracted over 90% of UC label (t1/2 of approximately 4 hours) and approximately 50% of the UC mass, indicating synergy. To explain this synergy, specific particle interactions were examined, namely, remodeling, in which the two acceptors alter each other's composition and thus the ability to mobilize cellular cholesterol, and shuttling, in which the small acceptor ferries cholesterol from cells to the large acceptor. To examine remodeling, LUVs and HDL were coincubated and reisolated before application to cells. This HDL became UC depleted, PL enriched, and lost a small amount of apolipoprotein A-I. Compared with equivalent numbers of control HDL particles; remodeled HDL caused faster efflux (t1/2 approximately 4 hours) and exhibited a greater capacity to sequester cellular cholesterol over 24 hours (approximately 38% versus approximately 15% for control HDL), consistent with their enrichment in PL. Remodeled LUVs still extracted approximately 20% of cellular UC. Thus, remodeling accounted for some but not all of the synergy between LUVs and HDL. To examine shuttling, several approaches were used. First, reisolation of particles after an 8-hour exposure to cells revealed that HDL contained very little of the cellular UC label. The label was found almost entirely with the LUVs, suggesting that LUVs continuously stripped the HDL of cellular UC. Second, bidirectional flux studies demonstrated that LUVs blocked the influx of HDL UC label into cells, while the rate of efflux of cellular UC was maintained. These kinetic effects explained the massive net loss of cellular UC to LUVs with HDL. Third, cyclodextrin, an artificial small acceptor that does not acquire PL and hence does not become remodeled, exhibited substantial synergy with LUVs, supporting shuttling. Thus, the presence of large and small acceptors together can overcome intrinsic deficiencies in each. Small acceptors are efficient at extracting cellular cholesterol because they approach cell surfaces easily but have a low capacity, whereas large acceptors are inefficient but have a high capacity. When present simultaneously, where the small acceptor can transfer cholesterol quickly to the large acceptor, high efficiency and high capacity are achieved. The processes responsible for this synergy, namely, remodeling and shuttling, may be general phenomena allowing cooperation both during normal physiology and after therapeutic administration of acceptors to accelerate tissue cholesterol efflux in vivo.
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Affiliation(s)
- W V Rodrigueza
- Department of Biochemistry, MCP Hahnemann School of Medicine, Allegheny University of the Health Sciences, Philadelphia, PA, USA
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