Endothelium and oxidised lipoproteins (original) (raw)
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Arteriosclerosis, Thrombosis, and Vascular Biology, 2001
Autoantibodies to oxidation-specific epitopes of low density lipoprotein (LDL), such as malondialdehydemodified LDL (MDA-LDL), occur in plasma and atherosclerotic lesions of humans and animals. Plasma titers of such antibodies are correlated with atherosclerosis in murine models, and several such autoantibodies have been cloned. However, human-derived monoclonal antibodies to epitopes of oxidized LDL (OxLDL) have not yet been reported. We constructed a phage display antibody library from a patient with high plasma anti-MDA-LDL titers and isolated 3 monoclonal IgG Fab antibodies, which specifically bound to MDA-LDL. One of these, IK17, also bound to intact OxLDL as well as to its lipid and protein moieties but not to those of native LDL. IK17 inhibited the uptake of OxLDL by macrophages and also bound to apoptotic cells and inhibited their phagocytosis by macrophages. IK17 strongly immunostained necrotic cores of human and rabbit atherosclerotic lesions. When 125 I-IK17 was injected intravenously into LDL receptor-deficient mice, its specific uptake was greatly enriched in atherosclerotic plaques versus normal aortic tissue. Human autoantibodies to OxLDL have important biological properties that could influence the natural course of atherogenesis. (Arterioscler Thromb Vasc Biol. 2001;21:1333-1339.)
Defective Catabolism of Oxidized LDL by J774 Murine Macrophages
Medical Science Symposia Series, 1993
In 5774 murine macrophages, chemically oxidized LDL (OxLDL) and biologically oxidized LDL (BioOxLDL) have similar metabolic fates, characterized by a relatively poor degradation when compared with acetylated LDL (AcLDL), and a modest ability to activate acyl-CoA:cholesterol acyltransferase (ACAT) (850 and 754 pmol [**C]oleate/mg cell protein in OxLDL-and BioOxLDL-incubated cells, versus 425 and 7070 pmol [W]cholesteryl oleate/mg cell protein in control and AcLDL-incubated cells) with a massive increase of cellular free cholesterol. Therefore, OxLDL were used to investigate the cellular processing of oxidatively modified LDL. Binding and fluorescence microscopy studies demonstrated that OxLDL are effectively bound and internalized by macrophages and accumulate in organelles with density properties similar to those of endo/lysosomes. Although the overall metabolism of OxLDL is modestly affected by 100 PM chloroquine, owing to the poor cellular degradation of the substrate, the drug can further depress OxLDL degradation, indicating that this process takes place in an acidic compartment. Failure to detect products of extensive degradation of OxLDL in the medium is due to their relative resistance to enzymatic hydrolysis, as demonstrated also by in vitro experiments with partially purified lysosomal enzymes, rather than to the intracellular accumulation of degradation products (degraded intracellular protein is, at most, 8.5% of total). This sluggish degradation process is not due to a cytotoxic effect since OxLDL do not affect the intracellular processing of other ligands like AcLDL or 1gG.m The accumulation of OxLDL-derived products within macrophages may elicit cellular responses, the relevance of which in the atherosclerotic process remains to be addressed.
Phospholipids in oxidized LDL not adducted to apoB are recognized by the CD36 scavenger receptor
Free Radical Biology and Medicine, 2003
Previous studies have shown that oxidation of low-density lipoprotein (oxLDL) results in its recognition by scavenger receptors on macrophages. Whereas blockage of lysyl residues on apoB-100 of oxLDL by lipid peroxidation products appears to be critical for recognition by the scavenger receptor class A (SR-A), modification of the lipid moiety has been suggested to be responsible for recognition by the scavenger class B receptor, CD36. We studied the recognition by scavenger receptors of oxidized LDL in which lysyl residues are blocked prior to oxidation through methylation [ox(m)LDL]. This permits us to minimize any contribution of modified apoB-100 to the recognition of oxLDL, but does not disrupt the native configuration of lipids in the particle. We found that ox(m)LDL was recognized by receptors on mouse peritoneal macrophages (MPM) almost as well as oxLDL. Ox(m)LDL was recognized by CD36-transfected cells but not by SR-A-transfected cells. Oxidized phospholipids (oxPC) transferred from oxLDL or directly from oxPC to LDL, conveyed recognition by CD36-transfected cells, confirming that CD36 recognized unbound oxidized phospholipids in ox(m)LDL. Collectively, these results suggest that oxPC not adducted to apoB within the intact oxLDL particle are recognized by the macrophage scavenger receptor CD36, that these lipids are not recognized by SR-A, and that they can transfer from oxidized to unoxidized LDL and induce CD36 recognition.
Biochimica et Biophysica Acta (BBA) - Molecular Basis of Disease, 1997
. To define the structural and chemical criteria governing recognition of oxidized LDL oxLDL by mouse peritoneal Ž . macrophages MPM , we exposed LDL to novel chemical modification agents that induce defined neutralizing and non-neutralizing alterations of lysine as models for distinct apoB adducts present in oxLDL. We found some exceptions to the usual notion that neutralization of lysine positive charges is the principal determinant governing MPM recognition. In addition, competitive binding experiments using chemically modified 125 I-LDL preparations revealed that, whereas some Ž . modifications engendered recognition principally by the classical scavenger receptor class A SRA , as seen for acetylated Ž . LDL acLDL , chemical models of advanced aldehydic modifications of LDL led instead to MPM uptake mainly by oxLDL receptors distinct from SRA. q 1997 Elsevier Science B.V.
Journal of Lipid Research, 2001
 2-Glycoprotein I ( 2-GPI) is a major antigen for antiphospholipid antibodies (Abs) present in patients with the antiphospholipid syndrome (APS). We previously reported that  2-GPI specifically binds to oxidized low density lipoprotein (oxLDL), but not to native low density lipoprotein (LDL). In the present study, a ligand specific for  2-GPI, oxLig-1, was purified from the extracted lipids of oxLDL. The structure of oxLig-1 was shown to be identical to that of synthesized 7-ketocholesteryl-9-carboxynonanoate by mass spectroscopy and nuclear magnetic resonance analyses. Both purified and synthesized oxLig-1 were recognized by  2-GPI and subsequently by anti- 2-GPI auto-Abs, either in enzyme-linked immunosorbent assay (ELISA) or in ligand blot analysis. Binding of liposomes containing oxLig-1 (oxLig-1-liposomes) to mouse macrophages, J774A.1 cells, was relatively low, as compared with that of phosphatidylserine (PS)-liposomes. In contrast, binding of oxLig-1liposomes was enhanced more than 10-fold in the presence of both  2-GPI and an anti- 2-GPI auto-Ab (WB-CAL-1), derived from (NZW x BXSB) F1 mouse, an animal APS model. Anti- 2-GPI auto-Abs derived from APS patients with episodes of arterial thrombosis were detected in ELISA, using a solid phase oxLig-1 complexed with  2-GPI. We suggest that autoimmune atherogenesis linked to  2-GPI interaction with oxLDL and Abs may be present in APS.
The Journal of Lipid Research, 2004
This study tests the hypothesis that autoantibodies to oxidation epitopes on oxidized LDL (OxLDL) promote the clearance of OxLDL from the plasma. Human LDL (hLDL) was injected into immune-competent apolipoprotein E-deficient (apoE ؊ / ؊ ) mice and immune-deficient apoE ؊ / ؊ /recombination-activating gene-deficient mice that lack mature T and B cells and thus antibodies. There was a progressive decrease in human apoB-100 in the plasma in all mice, but the rate of clearance was not greater in the immune-competent mice than in the immune-deficient mice. Interestingly, oxidized phospholipid (OxPL) epitopes as detected by the EO6 antibody on the hLDL increased over time, suggesting de novo oxidation of the LDL or transfer of OxPL to the particles. Because the native LDL was not extensively modified, we also examined the clearance of copper OxLDL. Although the extensively OxLDL was cleared faster than the native LDL, there was no difference in the rate of clearance as a function of immune status. There appeared to be some transfer of OxPL to the endogenous murine LDL. Together, these results suggest that oxidation-specific antibodies do not participate to any great extent in the clearance of OxLDL from plasma. However, it is possible that such antibodies may bind to oxidation epitopes and modulate lesion formation within the vessel wall. -Reardon, C. A., E. R. Miller, L. Blachowicz, J. Lukens, C. J. Binder, J. L. Witztum, and G. S. Getz. Autoantibodies to OxLDL fail to alter the clearance of injected OxLDL in apolipoprotein E-deficient mice. J. Lipid Res. 2004. 45: 1347-1354.
Antibodies against oxidized LDL--theory and clinical use
Physiological research / Academia Scientiarum Bohemoslovaca, 2001
Modification of low density lipoprotein (LDL) particles due to oxidation, glycation and binding of advanced glycation end-products (AGEs) or malondialdehyde (MDA, a final product of lipid peroxidation) is considered most important in the process of atherogenesis. Oxidatively modified LDL are distinguished by another receptor type, which was discovered on the surface of macrophages and was called the scavenger receptor. Uncontrolled intake of LDL converts macrophages to foam cells; their accumulation under the vascular endothelium is considered as the first stage of atherosclerosis. Oxidation of LDL is a complex process taking place in both the extra- and intracellular space. At the end of this oxidative process, modified LDL particles show chemotactic, cytotoxic and immunogenic properties. Oxidized LDL express a large number of epitopes and cause production of polyclonal autoantibodies against these products, especially against apoB100 modified by MDA and 4-hydroxynonenal. IgoxLDL (...
Inhibition of macrophage metabolism by oxLDL
2012
Intracellular oxidative stress is induced by oxidised low density lipoprotein (oxLDL) in macrophages. In the atherosclerotic lesions, this oxLDL dependent oxidative stress appears to cause macrophage cell death, a key process in the development of the necrotic core within the complex plaque. Macrophages are activated by γ-interferon to synthesise
The FASEB Journal
The immediate effects of oxidized low density lipoprotein (OxLDL) on the metabolic activity of cultured macrophages (RAW 264.7) were studied using a microphysiometer. Administration of OxLDL acutely induced a concentration-dependent increase in metabolic activity, with an EC 50 of 16 { 3 mg/ml OxLDL and a maximal effect of 35% { 4% (mean { SEM; nÅ5). A biphasic response was measured after administration of 75 or 100 mg/ml OxLDL consisting of an initial sharp increase, followed by the induction of a long-lasting hypoactivity of 80% of the control value. Incubation of cells with polyinosinic acid (polyI; 100 mg/ml) for 30 min prior to OxLDL administration could completely block the effect of 25 mg/ml OxLDL. In addition, polyI acted as a full antagonist on the decrease of the biphasic response of cells generated by 75 and 100 mg/ml OxLDL. Macrophages used in this study possessed a specific binding site for OxLDL, with a dissociation constant (K D ) of 9 { 2 mg/ml and a maximal binding of 610 { 32 ng 125 I-OxLDL/mg cell protein. Binding of 125 I-OxLDL to macrophages could be completely competed for by unlabeled OxLDL, by polyI for 58%, and by AcLDL for 46%. In conclusion, OxLDL can acutely activate the metabolic state of macrophages by a receptor-mediated process in a concentration-dependent fashion, which could be antagonized by polyI. Metabolic responses to OxLDL may underlie the changes observed in macrophages in the early atherosclerotic plaque.-de VriesAcute effects of oxidized low density lipoprotein on metabolic responses in macrophages. FASEB J. 12, 111-118 (1998)