Apolipoprotein B-containing Particles Research Articles

Scavenger receptor BI and cholesterol trafficking.

Scavenger receptor BI (SR-BI) mediates the selective uptake of HDL cholesteryl ester into steroidogenic cells and the liver and is a major determinant of the plasma HDL concentration in the mouse. Recent studies indicate that SR-BI also alters the metabolism of apolipoprotein B-containing particles and influences the development of atherosclerosis in several animal models. These results and the similar pattern of SR-BI expression in humans emphasize that it is important to learn how this receptor influences lipoprotein metabolism and atherosclerosis in people.

An immunoenzymatic procedure for human apo B-containing particles quantification using monoclonal antibodies.

The present report describes a new monoclonal antibody-based enzyme immunoassay (ELISA) for the quantification of apolipoprotein (apo) B-containing particles in plasma. Native low-density lipoprotein (LDL) and a reference serum were utilized to prepare the standard curve. Three different antibodies to apo B-100--4A6E3, 6A10B10, and 2D9--all produced in our laboratory, were examined. The apparent affinity constants of the monoclonal antibodies (MAbs) 4A6E3, 6A10B10, and 2D9 were 2.9 x 10(9), 1.74 x 10(9), and 0.63 x 10(8), respectively. The standard curve was generated for an apo B-LDL range of 0.1 to 4.0 microg/ml. Evaluating the concentration of apo B-containing particles in plasma may allow for a more accurate assessment of the risk of coronary artery disease.

Omega-3 Ethyl Ester Concentrate Decreases Total Apolipoprotein CIII and Increases Antithrombin III in Postmyocardial Infarction Patients

This study investigated whether an ethyl ester preparation of fish oil (w-3) could normalise raised plasma concentrations of triglycerides, apolipoprotein CIII on apolipoprotein B-containing particles (LP CIII:B) found in patients with recent acute myocardial infarction. We also studied the effect of fish oil on antithrombin III levels. Out of 75 patients with a plasma triglyceride value >/=2.0 mmol/L, 22 normalised their triglycerides during diet and were therefore not randomised. The remaining patients were randomly assigned to 12 weeks' treatment with a daily dose of 4g w-3 or placebo. Mean plasma triglyceride concentrations were reduced by 24% from 3.10 +/- 1.15 (SD) to 2.53 +/- 0.94 mmol/L (p < 0.001) on w-3 (p < 0.001 vs placebo). The reduction was due to decreases in very low density lipoprotein concentrations. Total apolipoprotein CIII decreased significantly. This was due to reductions in LP CIII:non B concentrations, but the ratio LP CIII:non B/LP CIII:B was unaffected because of a slight insignificant decrease in LP CIII:B. The plasma triglyceride decreasing effect of w-3 could therefore not be due to redistribution of CIII between lipoproteins. Low density lipoprotein (LDL) cholesterol increased significantly with w-3 by 7%, and antithrombin III increased significantly with fish oil. In conclusion, w-3 had a moderate plasma triglyceride lowering effect and increased LDL cholesterol slightly, while antithrombin III increased in patients with hypertriglyceridaemia who had recently experienced a myocardial infarction.

A monoclonal antibody-based enzyme immunoassay for the measurement of native and glycated apolipoprotein B-containing particles.

We describe the development of sandwich enzyme-linked immunosorbent assays designed to measure native and glycated apolipoprotein B containing particles in plasma. The assays utilize monoclonal antibodies anti native or glycated apo B-LDL for coating and a polyclonal anti apoB-LDL-peroxidase conjugate as the detecting antibody. The method is specific, sensitive and precise. The intra assay coefficient of variation for the plasma native and glycated apolipoprotein B-containing particles was determine to be 7.8% and 7.5%, respectively. The method described can provide specific and reproducible determinations of apoB and glycated-apoB containing particles in plasma; it will be of great interest in the evaluation of atherosclerotic risk in dyslipoproteinemic states in diabetic and non-diabetic subjects.

Low-density lipoprotein apheresis using the Liposorber dextran sulfate cellulose system for patients with hypercholesterolemia refractory to medical therapy.

A subset of patients with familial hypercholesterolemia (FH) have an inadequate lipid-lowering response to diet and drug treatment and should be considered for low-density lipoprotein (LDL)-apheresis therapy. This procedure selectively removes apolipoprotein B-containing particles [LDL, very-low-density lipoprotein, lipoprotein(a)] from plasma independent of diet and drug therapy. Methods for performing LDL-apheresis include dextran sulfate cellulose adsorption, immunoadsorption, and heparin-induced extracorporeal precipitation. The Liposorber Study Group evaluated LDL removal using the Liposorber LA-15 LDL-apheresis System in 64 patients with FH who had not responded adequately to diet and maximal drug therapy. Mean acute reductions in LDL cholesterol (LDL-C) were 76% in heterozygous FH (HtFH) patients and 81% in homozygous FH (HoFH) patients. Time-averaged levels of LDL-C were lowered 41% in HtFH and 53% in HoFH patients. Hypotension was the most frequent side effect, occurring in 3% of procedures. The Liposorber LA-15 System has been approved by the Food and Drug Administration and is recommended for 1) patients with functional homozygous FH (LDL-C level > 500 mg/dL; 2) patients with coronary artery disease (CAD) and LDL-C levels > or = 200 mg/dL; 3) patients without CAD, but an LDL-C level > or = 300 mg/dL.

Fluvastatin reduces levels of plasma apo B-containing particles and increases those of LpA-I

Epidemiologic studies have demonstrated an association between apolipoprotein (apo) B-containing particles (lipoprotein [Lp] E:B; LpC-III:B) and an inverse association between LpA-I and the risk of coronary artery disease (CAD). The effect of 6 weeks of treatment with fluvastatin (20 and 40 mg/day in the evening), a novel competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, on lipoparticle levels was studies in 423 patients with hypercholesterolemia after 14 weeks of standard dietary therapy. The combined data of the European double-blind controlled studies were used for the analysis. Two independent groups of hypercholesterolemic patients receiving fluvastatin (20 and 40 mg every evening) for 6 weeks were compared with a placebo group. For inclusion, patients had to fulfill the following criteria: plasma low-density lipoprotein (LDL) cholesterol levels >160 mg/dL and premature CAD and/or two associated risk factors; LDL cholesterol >190 mg/dL and no CAD; triglycerides <300 mg/dL. All measurements were performed at the Pasteur Institute Central Laboratory. LpE:B and LpC-III:B were measured by double-site ELISA. Lipoprotein A-I and LpA-I:A-II were determined by differential electroimmunodiffusion. Treatment with 20 and 40 mg of fluvastatin was associated with reductions in plasma apo B (median change: −19.3% and −22.8%, respectively; p <0.001), LpE:B (−12.5% and −22.6%, respectively; p <0.001), and LpC-III:B (−3.6% and −36.8%, respectively; p <0.001) particles compared with placebo. Significant increases in plasma apo A-I (1.7% and 4.8%, respectively; p <0.001) and antiatherogenic LpA-I (2.3% and 6.9%, respectively; p <0.001) were also observed. Levels of LpA-I:A-II were not affected by fluvastatin treatment. In conclusion, 6-week treatment with fluvastatin is associated with beneficial antiatherogenic changes in lipoparticle profiles in hypercholesterolemic patients.

Relation of plasma levels and composition of apolipoprotein B-containing lipoproteins to angiographically defined coronary artery disease in young patients with myocardial infarction.

Hypertriglyceridemia is a common metabolic disturbance in men < 45 years old with myocardial infarction. To further investigate the relation between triglyceride-rich lipoproteins and severity of coronary atherosclerosis in this subset of postinfarction patients, apolipoprotein B-containing lipoproteins of 64 consecutive patients were subfractionated in connection with coronary angiography. Density-gradient ultracentrifugation of plasma and coronary angiography were performed 4 to 6 months after the myocardial infarction. Global coronary atherosclerosis and the number and severity of distinct stenoses were evaluated by semiquantitative analysis of 15 proximal coronary segments. The majority of the patients (60%) were hypertriglyceridemic and had higher coronary scores than normotriglyceridemic patients. Of the major plasma lipoproteins, triglycerides and cholesterol in the low-density lipoprotein (LDL) fraction were associated with global coronary atherosclerosis, whereas LDL triglycerides and high-density lipoprotein (HDL) cholesterol correlated directly and inversely, respectively, with the coronary stenosis score. Plasma apolipoprotein B correlated with both coronary scores. The plasma concentrations of lipid and protein in the very-low-density lipoprotein (VLDL) subfractions (VLDL1 through VLDL3) and intermediate-density lipoprotein (IDL) did not correlate with either of the coronary scores, whereas the concentration of triglycerides in dense LDL (density > 1.040 kg/L) was strongly associated with both coronary scores. Compositional analysis of the smallest VLDL particles (VLDL3) and IDL revealed a correlation between the number of cholesteryl ester molecules in small VLDL and global coronary atherosclerosis in hypertriglyceridemic patients. Global coronary atherosclerosis and distinct stenoses in young postinfarction patients are associated with the number of apolipoprotein B-containing particles in plasma and the concentration of LDL triglyceride. Specifically, dense triglyceride-rich LDL particles and, in hypertriglyceridemic patients, small cholesteryl ester-rich VLDL particles relate to coronary artery disease severity.

Immunological properties of apoB-containing lipoprotein particles in human atherosclerotic arteries

In this study, we have documented immunochemical properties of apolipoprotein (apo) B-containing particles (LpB) extracted from human atherosclerotic lesions obtained during vascular reconstructive surgery of patients. These properties were compared to those of particles purified from corresponding atherosclerotic plasma and healthy control plasma. LpB immunoreactivities were tested in solid phase competitive binding radioimmunoassays using five anti-apoB monoclonal antibodies (MAb) for which epitopes have been previously located on the protein. The regions encompassed amino acids 405 to 539 (MAb B1), 1854 to 1879 (MAb B4), 3506 (MAb BA11), and 4355 (MAb BL3). The fifth antibody (MAb BL5) recognizes a conformationally expressed epitope. LpB from lesions presented a significantly decreased immunoreactivity as compared to LpB from respective plasma except for the epitope recognized by MAb BA11 located precisely in the low density lipoprotein (LDL) receptor binding site. The accessibility of the four sequential epitopes was similar on LpB from atherosclerotic and healthy plasma while it was decreased for the conformational one in LpB from atherosclerotic samples. These altered immunoreactivities were not related to changes in chemical composition of LpB as this was quite comparable in all preparations. With regard to electronegativity, apoB fragmentation, immunological accessibility, and size distribution of the particles, changes seem to increase in the following order from healthy plasma, atherosclerotic plasma, and the corresponding lesions. The results confirm some structural characteristics of oxidatively modified particles from human atherosclerotic lesions and to a lesser degree from respective plasma, but more specifically demonstrate a global conformational change in LpB from lesions, this change being perhaps initiated in the plasma.

Synthesis, secretion and immunoelectron microscopic demonstration of apolipoprotein B-containing lipoprotein particles in the visceral rat yolk sac.

Electron microscopic investigations on the involvement of the fetal membranes of the rat (visceral yolk sac) in the lipid metabolism revealed the occurrence of lipoprotein-sized particles located in cisternal Golgi stacks, Golgi vesicles and secretory vesicles of the cells of the visceral yolk sac epithelium as well as in distended areas of the intercellular space between adjacent epithelial cells. Application of the protein A-gold technique with specific anti-apoB antiserum resulted in a specific location of immunogold both over the different compartments of the lipoprotein pathway (RER, Golgi complex, secretory vesicles) as well as over the distended intercellular spaces, thus confirming these particles to be lipoproteins in nature. Isolated visceral epithelial cells prepared by a tryptic digestion method exhibited some ultrastructural alterations, such as a loss of apical brush border, a change from columnar to spherical cell shape, a decrease in phagolysosomes, but an increase in autophagosomal structures after 6 h incubation at a vitality rate of at least 85%. Within this period the epithelial cells secreted measurable amounts of apoB-containing lipoproteins into the medium floating in the density classes d less than 1.006 g/ml, d = 1.006-1.020 g/ml and d = 1.020-1.064 g/ml. The production of the lipoproteins was partly inhibited by cycloheximide indicating the secretion of particles with performed as well as newly synthesized apoB. Negative staining of the particles revealed an average diameter of 34 nm of VLDL, 31 nm of IDL and 24 nm of LDL. In summary, our studies demonstrate that in the feto-placental unit of the rat the fetal membranes are capable of synthesizing and secreting lipoproteins. The cells of the visceral yolk sac epithelium were shown to be the producers of apoB-containing particles.

Plasma lipids, lipoproteins and apolipoproteins in two kindreds of hypobetalipoproteinemia

Plasma lipids and apolipoproteins were quantified in two kindreds of hypobetalipoproteinemia. All affected members were asymptomatic but showed a decrease of 75% in apolipoprotein B and of 69% in LDL-cholesterol. There were no major changes in apo A-I and A-II but all affected family members had reduced levels of apo C-II (by 58%) and C-III (by 59%) without significant decrease in apo C-1 and no specific decrease of apo C-III 1. Apolipoprotein E is decreased in SDS-PAGE. The plasma level and phenotype of Lp(a) are not affected by HBL, suggesting that a catabolic rather than a synthetic mechanism is responsible for the disease. As shown by density gradient ultracentrifugation, HDL 2 particles that contain essentially apolipoprotein A-I, cholesterol and phospholipids represent in affected subjects the major part of HDL. Due to the net reduction of apolipoprotein B-containing particles (VLDL and LDL) as acceptors of lipids in HBL, there is an accumulation of large particles rich in cholesteryl esters.

Interactions of high density lipoproteins with very low and low density lipoproteins during lipolysis.

Interactions of high density lipoproteins (HDL) with very low (VLDL) and low (LDL) density lipoproteins were investigated during in vitro lipolysis in the presence of limited free fatty acid acceptor. Previous studies had shown that lipid products accumulating on lipoproteins under these conditions promote the formation of physical complexes between apolipoprotein B-containing particles (Biochim. Biophys. Acta, 1987. 919: 97-110). The presence of increasing concentrations of HDL or delipidated HDL progressively diminished VLDL-LDL complex formation. At the same time, association of HDL-derived apolipoprotein (apo) A-I with both VLDL and LDL could be demonstrated by autoradiography of gradient gel electrophoretic blots, immunoblotting, and apolipoprotein analyses of reisolated lipoproteins. The LDL increased in buoyancy and particle diameter, and became enriched in glycerides relative to cholesterol. Both HDL2 and HDL3 increased in particle diameter, buoyancy, and relative glyceride content, and small amounts of apoA-I appeared in newly formed particles of less than 75 A diameter. Association of apoA-I with VLDL or LDL could be reproduced by addition of lipid extracts of lipolyzed VLDL or purified free fatty acids in the absence of lipolysis, and was progressively inhibited by the presence of increasing amounts of albumin. We conclude that lipolysis products promote multiple interactions at the surface of triglyceride-rich lipoproteins undergoing lipolysis, including physical complex formation with other lipoprotein particles and transfers of lipids and apolipoproteins. These processes may facilitate remodeling of lipoproteins in the course of their intravascular metabolism.

Influence of triglyceride-rich lipoproteins on nephelometry of apolipoprotein A-I.

Measurement of apolipoprotein A-I in native human sera by endpoint or rate nephelometry may give falsely high results for sera that have a high triglyceride content. Such erroneous determinations of apolipoprotein A-I can be avoided if one instead assays supernates of sera from which apolipoprotein B-containing particles have been precipitated with phosphotungstic acid and MgCl2. A high triglyceride concentration in serum does not impair the completeness of the precipitation of apolipoprotein B-containing lipoproteins or the analytical recovery of apolipoprotein A-I. In a prospective epidemiologic study, by using rate nephelometry we found that there were different mean concentrations for apolipoprotein A-I in supernates of sera from men (1.36 g/L) and women (1.49 g/L). Furthermore, the known risk factors for atherosclerosis showed different correlations with apolipoprotein A-I than with high-density lipoprotein cholesterol.