Biomedical subjects

L K Curtiss

Publications and source records attributed to L K Curtiss.

At least 55 records · Page 3Linked to original sources

PubMed1997

Dissociation of LPL and LDL: effects of lipoproteins and anti-apoB antibodies.

We have shown previously that the activity of lipoprotein lipase (LPL), the major enzyme responsible for hydrolysis of triglyceride contained in circulating lipoproteins, is associated with lipoproteins in postheparin plasma. In other studies, microtiter plate assays showed that LPL interaction with low density lipoprotein (LDL) and very low density lipoprotein (VLDL) was decreased by antibodies to apolipoprotein (apo)B. To test whether antibodies to apoB affected LPL-LDL association in solution, two types of assays were performed, gel filtration and coprecipitation. First we showed that LPL activity and immunoreactive mass co-eluted during gel filtration of normal postheparin plasma, approximately with the peak of low density lipoproteins. Then LPL was used for gel filtration studies in the presence and absence of LDL and anti-apoB monoclonal antibodies. LPL association with LDL was diminished by antibodies to the amino-terminal region of apoB; antibodies to the carboxyl-terminal LDL receptor binding region of apoB were less effective. LDL binding to LPL containing heparin-agarose was also disrupted by the amino-terminal antibodies to apoB. To determine the LPL-lipoprotein association in situations in which the distribution of plasma lipoproteins was altered, we studied plasma from two types of subjects with dyslipidemias. The addition of 125I-labeled LPL to type 1 postheparin plasma produced two peaks of radioactivity, one peak eluted in the void volume of the column (with the chylomicrons) and a second peak eluted just prior to the normal elution of low density lipoproteins. In postheparin plasma from an abetalipoproteinemic subject, LPL eluted with HDL. We conclude that LPL associates primarily with apoB-containing lipoproteins. The reason for this appears to be that LPL interacts with the apoB.

Antibodies, Monoclonal↗

PubMed1997

Structural determinants for the interaction of lipopolysaccharide binding protein with purified high density lipoproteins: role of apolipoprotein A-I.

The interaction of lipopolysaccharide binding protein (LBP) with apolipoprotein (apo)A-I on high density lipoproteins (HDL) was studied in solid phase ligand binding assays with a biotinylated LBP-specific antibody. The association was dependent on LBP concentration and enhanced in the presence of lipopolysaccharide (LPS). Maximal enhancement was measured at an LPS/LBP molar ratio of 6. To identify regions on apoA-I that participate directly or indirectly in the interaction between LBP and HDL, we attempted to inhibit LBP association with a panel of mapped apoA-I-specific monoclonal antibodies. Whereas some antibodies were effective inhibitors, others were not, even though they bound apoA-I. Furthermore, selected apoA-I synthetic peptides inhibited the antibody-mediated interference of the HDL/LBP interaction. Although no specific mechanism can be defined for the basis of the inhibitory effects of the antibodies on the association of LBP with HDL, we identified a role for three unique regions on apoA-I between residues 1-31, 95-164, and 178-200. These results suggested that apoA-I is a key component in the association of LBP with HDL and may play an important role in the biologic activity of LPS/LBP complexes.

Acute-Phase Proteins↗

PubMed1997

A single copy of apolipoprotein B-48 is present on the human chylomicron remnant.

Individuals homozygous for the e2 allele encoding apolipoprotein E exhibit a remnant removal defect and accumulate substantial levels of intestinally derived particles containing apolipoprotein B-48 (apoB-48). Such lipoproteins were isolated from the plasma of E2/E2 individuals, and further purified by affinity chromatography using a polyclonal antibody specific for selective binding and removal of apoB-100-containing lipoproteins. The unbound lipoproteins, termed chylomicron remnants, were particles with average hydrated diameters of 31.2 nm as determined by dynamic light scattering. They contained apoB-48 and ApoE as their only protein components. The number of apoB-48 molecules on each lipoprotein was assessed by counting the number of antibody molecules bound to the surface of the chylomicron remnants, using either a monoclonal antibody specific for a single epitope on apoB-48 or a mixture of two such monoclonal antibodies specific for widely separated epitopes. The results of this analysis seem unambiguous: no more than one apoB-48 resides on the chylomicron remnant. Because apoB appears to be unable to transfer among lipoprotein particles, it may be inferred that nascent chylomicrons also contain a single copy of apoB-48.

Antibodies, Monoclonal↗

PubMed1996

Cloning of monoclonal autoantibodies to epitopes of oxidized lipoproteins from apolipoprotein E-deficient mice. Demonstration of epitopes of oxidized low density lipoprotein in human plasma.

Many reactive products may be formed when LDL undergoes lipid peroxidation, which in turn can react with lipids, apoproteins, and proteins, generating immunogenic neoepitopes. Autoantibodies recognizing model epitopes of oxidized low density lipoprotein, such as malondialdehydelysine, occur in plasma and in atherosclerotic lesions of humans and animals. Because apo E-deficient mice develop particularly high titers of such autoantibodies, we used their spleens to clone 13 monoclonal antibodies to various epitopes of oxidized LDL ("E0 antibodies"). Binding and competitive RIAs demonstrated significant differences in fine specificity even between E0 antibodies initially selected for binding to the same screening antigen. For example, some E0 antibodies selected for binding to malondialdehyde-LDL also recognized copper oxidized LDL, acrolein-LDL, or LDL modified by arachidonic or linoleic acid oxidation products. Circulating IgG and IgM autoantibodies binding to copper-oxidized LDL, 4-hydroxynonenal-LDL, acrolein-LDL, and LDL modified with arachidonic or linoleic acid oxidation products were found in apo E-deficient mice, suggesting that the respective antigens are formed in vivo. Epitopes recognized by some of the E0 monoclonal antibodies were also found on human circulating LDL. Each of the E0 monoclonal antibodies immunostained rabbit and human atherosclerotic lesions, and some of them yielded distinct staining patterns in advanced lesions. Together, this suggests that the natural monoclonal antibodies recognize different epitopes of complex structures formed during oxidation of lipoproteins, or epitopes formed independently at different lesion sites. Our data demonstrate that a profound immunological response to a large number of different epitopes of oxidized lipoproteins occurs in vivo. The availability of "natural" monoclonal autoantibodies should facilitate the identification of specific epitopes inducing this response.

Acrolein↗

PubMed1996

Antiphospholipid antibodies are directed against epitopes of oxidized phospholipids. Recognition of cardiolipin by monoclonal antibodies to epitopes of oxidized low density lipoprotein.

The optimal clinical management of patients with antiphospholipid antibody syndrome (APS) is uncertain because of a lack of an underlying hypothesis to explain why antiphospholipid autoantibodies (aPL) form to such ubiquitous compounds as phospholipids (PL). In this paper, we demonstrate that many, if not most, aPL are actually directed at neoepitopes of oxidized PL, or neoepitopes generated by adduct formation between breakdown products of oxidized PL and associated proteins. Each cardiolipin (CL) molecule contains four unsaturated fatty acids and is highly susceptible to oxidation, particularly upon exposure to air. Yet, standard anticardiolipin antibodies (aCL) immunoassays routinely bind CL to microtiter wells by evaporation of the ethanol solvent overnight at 4 degrees C. Using a variety of techniques, we demonstrated that rapid oxidation occurs when CL is plated and exposed to air. Sera from apo E-deficient mice, which have high autoantibody titers to oxidized low density lipoprotein, showed a striking time-dependent increase in binding to CL that was exposed to air for increasing periods of time. Monoclonal antibodies to oxidized LDL, cloned from the apo E-deficient mice, also bound to oxidized CL. Both sera and affinity-purified aCL-IgG from APS patients bound to CL progressively as it was oxidized. However, the monoclonal antibodies from apo E-deficient mice, or sera or aCL-IgG from APS patients did not bind to a reduced CL analog that was unable to undergo peroxidation. These data demonstrate that many aPL are directed at neoepitopes of oxidized phospholipids, and suggest that oxidative events may be important in the pathophysiology of APS. In turn, this suggests new therapeutic strategies, possibly including intensive antioxidant therapy.

Animals↗

PubMed1996

Selection of monoclonal antibodies for linear epitopes of an apolipoprotein yields antibodies with comparable affinity for lipid-free and lipid-associated apolipoprotein.

A direct approach is described for generating human apolipoprotein (apo) A-I-specific monoclonal antibodies with defined linear epitopes. The antibodies have comparable binding affinity for delipidated apoA-I and apoA-I on high density lipoproteins (HDL). The antibodies were obtained by immunizing mice with HDL, screening the fusions first for antibodies that bind native HDL and second, for antibodies that bind defined apoA-I synthetic peptides. ApoA-I antibody epitopes assigned on the basis of synthetic peptide binding were confirmed by solid phase and fluid phase antibody competition assays. These antibodies, which bind epitopes that encompass greater than 60% of apoA-I, should prove useful for identifying discrete functional domains of apoA-I on HDL.

Animals↗

PubMed1996

Translocation of apolipoprotein B across the endoplasmic reticulum is blocked in abetalipoproteinemia.

Abetalipoproteinemia (ABL) is an autosomal recessive disease characterized by the inability of the liver and intestine to secrete apolipoprotein B (apoB). Mutations in the microsomal triglyceride transfer protein (MTP) gene, but not the apoB gene, are responsible for the ABL phenotype. It is not clear how loss of MTP in ABL patients leads to a complete, but specific, block in the secretion of apoB. It is to this question that our work is directed. In cultured cells lacking MTP, translocation of apoB is completely arrested, leading to the hypothesis that apoB requires MTP in order to completely enter the lumen of the endoplasmic reticulum, the site of lipoprotein assembly. We examined this hypothesis by determining the presence in plasma of distinct N-terminal apoB peptides, produced exclusively from translocation arrested apoB, in the plasma of six ABL patients and six normal subjects. The data show that N-terminal apoB peptides are present in the plasma of six ABL patients, whereas intact apoB-100 was barely detectable. Moreover, the plasma of all six ABL patients displayed a 2000-fold increase in the amount of an 85 kDa N-terminal apoB peptide relative to apoB-100. These data provide the first in vivo data supporting the essential role that MTP plays in apoB translocation. In normal humans, varied expression of MTP may be responsible for the post-transcriptional regulation of apoB secretion.

Abetalipoproteinemia↗

PubMed1996

Lipoproteins accumulate in immune deposits and are modified by lipid peroxidation in passive Heymann nephritis.

Proteinuria in passive Heymann nephritis is primarily caused by reactive oxygen species that are produced by glomerular cells. Reactive oxygen species apparently exert their damaging effects on the glomerular filter by lipid peroxidation and subsequent adduct formation on matrix proteins of glomerular basement membranes. This raised the question as to the source of polyunsaturated fatty acids required as substrates for lipid peroxidation. Here we have localized by immunocytochemistry rat apolipoprotein E and apolipoprotein B within subepithelial immune deposits. Moreover, apolipoprotein B extracted from isolated glomeruli of proteinuric passive Heymann nephritis rats shows degradation and lipid peroxidation adduct formation, similar to apoproteins of oxidized lipoproteins in atherosclerotic lesions. These data provide evidence that lipoproteins accumulate within immune deposits and suggest that their lipids generate lipid-peroxidation-derived reactive compounds.

Animals↗

PubMed1995

Identification of apolipoprotein B100 polymorphisms that affect low-density lipoprotein metabolism: description of a new approach involving monoclonal antibodies and dynamic light scattering.

Rare mutations in apolipoprotein B (apoB) can cause defective binding of low-density lipoproteins (LDLs) to the LDL receptor, leading to elevated plasma cholesterol levels and premature atherosclerosis. This communication describes a novel approach to study the effects of apoB mutations on LDL metabolism. Monoclonal antibody MB19 identifies a common polymorphism in apoB, an Ile/Thr substitution at residue 71, by binding with a 60-fold higher affinity to apoB(Ile71)-containing LDL. Because each LDL contains a single apoB, a maximum of two LDLs may be bound by the bivalent monoclonal antibody. Thus, at the appropriate concentration, an equivalent amount of MB19 will promote substantial dimer formation of LDL containing the strongly binding apoB(Ile71), but little dimer formation of LDL containing the weakly binding apoB(Thr71). For LDL isolated from heterozygous individuals, the amount of dimer formed, determined by dynamic light scattering, yields an estimate of the allelic ratio of the two forms of LDL. For such individuals, not only the effect of the polymorphism recognized by MB19 but also the effects of other polymorphisms on the LDL allelic ratio can be determined. Examination of six normolipemic MB19 heterozygotes gave percent allelic ratios between 48:52 and 51:49 tight:weak-binding LDL, not significantly different from a 50:50 ratio. These individuals were also heterozygous for six common apoB polymorphisms, allowing calculation of the odds that each of these polymorphisms caused significant alterations in lipid levels. In contrast, the rare mutation at residue 3500 causing defective binding to the LDL receptor and familial defective apoB100 (FDB) resulted in substantial changes (26:74 and 13:87) in LDL allelic ratio in both of two FDB individuals examined.

Alleles↗

PubMed1995

Lipoprotein lipase association with lipoproteins involves protein-protein interaction with apolipoprotein B.

Lipoprotein lipase (LPL) hydrolyzes chylomicron and very low density lipoprotein (VLDL) triglycerides and potentiates the cellular uptake of lipoproteins. These LPL-lipoprotein associations could involve only protein-lipid interaction, or they could be modulated by apolipoproteins (apo). ApoB is the major protein component of chylomicrons, VLDL, and low density lipoprotein (LDL). ApoB100, a large glycoprotein with a molecular mass of 550 kDa, is composed of several functional domains. A carboxyl-terminal region of the protein is the ligand for the LDL receptor. There are several hydrophobic domains that are believed to be important in lipid binding. The relatively hydrophilic amino-terminal region of apoB, however, has no known function. Using solid phase assays we quantified LPL-lipoprotein complex formation. On a molar basis, severalfold greater amounts of LPL bound to LDL and VLDL than to high density lipoprotein at all the concentrations of LPL tested (0.9-55 nM). To assess the roles of LDL protein versus lipid, we performed competition and ligand blotting experiments. LDL and an amino-terminal fragment of apoB competed better for 125I-LPL binding to LDL than did lipid emulsion particles. Delipidation of LDL-coated plates did not alter LPL binding. On ligand blots, LPL bound to amino-terminal fragments of apoB generated by thrombin digestion but not to apoA1, apoE, or carboxyl-terminal fragments of apoB. Further evidence for LPL interaction with the amino-terminal region of apoB was obtained using anti-apoB monoclonal antibodies. Antibodies directed against the amino-terminal regions of apoB blocked LPL interaction with LDL, whereas those against the carboxyl-terminal region of apoB did not inhibit LPL interaction with LDL. Thus, we conclude that a specific interaction between LPL and the amino-terminal region of apoB may facilitate LPL association with circulating lipoproteins.

Antibodies, Monoclonal↗

PubMed1995

Treatment of severe hypercholesterolemia in apolipoprotein E-deficient mice by bone marrow transplantation.

Apo E, a key regulator of cholesterol-rich lipoprotein metabolism, is synthesized by numerous extrahepatic tissues. Although its synthesis in macrophages is documented, the contribution of macrophage-derived apo E to hepatic clearance of serum cholesterol is unknown. To address this issue bone marrow transplantation was performed on hypercholesterolemic apo E-deficient mice with either syngeneic apo E-deficient mouse bone marrow cells (E0-control) or wild-type mouse bone marrow cells expressing apo E (E0-treated). E0-control and E0-treated mice were fed either a regular chow diet or an atherogenic diet (designated E0-control-HF and E0-treated-HF). Serum cholesterol levels dropped dramatically in the E0-treated mice largely due to a reduction in their VLDL cholesterol. No changes were seen in the E0-control mice. After 4 wk serum cholesterol in E0-treated-HF mice was about four-fold lower compared to E0-control-HF animals. Moreover, the extent of atherosclerosis in the E0-treated-HF mice after 14-16 wk was greatly reduced. Wild-type apo E mRNA was detected in the liver, spleen, and brain of the E0-treated mice indicating that apo E gene transfer was successfully achieved through bone marrow transplantation. More importantly, the level of apo E expression was sufficient to reduce the severe hypercholesterolemia of the apo E-deficient mice fed either chow or atherogenic diets.

Alleles↗

PubMed1995

Serum amyloid A (SAA): influence on HDL-mediated cellular cholesterol efflux.

Normal high density lipoprotein (N-HDL) is remodeled during acute phase (AP) reactions by the association of serum amyloid A (SAA) and the depletion of apolipoprotein (apo) A-I. To determine the impact of this remodeling on HDL function, the capacities of N-HDL and AP-HDL to associate with and promote cholesterol efflux from human monocytic THP-1 cells were compared. THP-1 cells preferentially bound AP-HDL compared with N-HDL. Examination of the AP-HDL particles bound to THP-1 cells revealed a disproportionate association of an apoSAA-enriched, apoA-I-depleted subpopulation compared with the composition of the starting material. However, N-HDL and AP-HDL promoted cholesterol efflux from THP-1 cells equally efficiently and in a dose-dependent manner. When N-HDL was experimentally remodeled with apoSAA to achieve an apoprotein composition similar to that of the preferentially bound particles, cellular cholesterol efflux was reduced by 30%. The remodelling of HDL with apoSAA during the acute phase reaction alters cholesterol efflux only when apoSAA constitutes more than 50% of the HDL protein.

Apolipoprotein A-I↗

PubMed1995

Interaction of Lp(a) with plasminogen binding sites on cells.

Lp(a) competes with plasminogen for binding to cells but it is not known whether this competition is due to the ability of Lp(a) to interact directly with plasminogen receptors. In the present study, we demonstrate that Lp(a) can interact directly with plasminogen binding sites on monocytoid U937 cells and endothelial cells. The interaction of Lp(a) with these sites was time dependent, specific, saturable, divalent ion independent and temperature sensitive, characteristics of plasminogen binding to these sites. The affinity of plasminogen and Lp(a) for these sites also was similar (Kd = 1-3 microM), but Lp(a) bound to fewer sites (approximately 10-fold less). Both gangliosides and cell surface proteins with carboxy-terminal lysyl residues, including enolase, a candidate plasminogen receptor, inhibited Lp(a) binding to U937 cells. Additionally, Lp(a) interacted with low affinity lipoprotein binding sites on these cells which also recognized LDL and HDL. The ability of Lp(a) to interact with sites on cells that recognize plasminogen may contribute to the pathogenetic consequences of high levels of circulating Lp(a).

Binding Sites↗

PubMed1995

Structural features of synthetic peptides of apolipoprotein E that bind the LDL receptor.

Apolipoprotein (apo) E, via its receptor binding domain contained in residues 140-150, mediates hepatic and peripheral tissue binding of cholesterol-rich lipoproteins. Previously, we reported that a synthetic peptide representing a linear tandem repeat of amino acids 141-155, the 141-155 dimer, binds the low density lipoprotein (LDL) receptor. To define the structural features essential for LDL receptor binding of the 141-155 dimer, a series of modified peptides were synthesized. The secondary structure content of the modified apoE peptides was assessed by circular dichroism (CD) and the receptor activity was studied in cellular LDL receptor binding assays. alpha-Helix content was necessary but not sufficient for receptor activity because both a 129-162 monomer and the 141-155 dimer peptides had comparable CD spectra and helix contents, but only the 141-155 dimer was receptor active. Deletion of the charged amino terminal residues including arg142 and lys143 in the 145-155 or 144-150 dimers had no effect on alpha-helix content, yet abolished their receptor activities. Helical net models of all receptor active peptides indicated that the LDL-receptor binding activity of the 141-155 dimer is dependent on at least two clusters of basic amino acids present on the hydrophilic face of the amphipathic alpha-helix of the 141-155, 141-150, 141-155 (lys143-->ala) and 141-155 (arg150-->ala) dimer peptides.

Amino Acid Sequence↗

PubMed1995

Immunoelectron microscopy of low density lipoproteins yields a ribbon and bow model for the conformation of apolipoprotein B on the lipoprotein surface.

In the present study, the relative positions of 11 anti-apolipoprotein B monoclonal antibodies have been mapped onto the surface of human low density lipoproteins by electron microscopy. As the epitopes recognized by these antibodies have been previously located on the primary sequence of apoB, these data provide a map of the configuration of the protein on the surface of the LDL. The first 89% of apoB-100 may be modeled as a thick ribbon that wraps once around the LDL, completing the encirclement by about amino acid residue 4050. The thickness of the ribbon is sufficient to penetrate the monolayer, so that it makes contact with the core. There is a kink in the ribbon beginning almost halfway along its length at approximately apoB-48. The C-terminal 11% of apoB constitutes the "bow," an elongated structure of about 480 residues, beginning at 4050 and stretching back into one hemisphere and then crossing the ribbon into the other hemisphere between residues 3000 to 3500, thus bringing sequences in the C-terminal portion of apoB-100 near to the suggested binding site for the LDL receptor. The C-terminal sequences may act as a negative regulator of LDL receptor binding, in agreement with Parhofer et al, 1992. J. Clin. Invest. 89: 1931-1937, who reported the enhanced clearance from plasma of apoB-89-containing lipoproteins. It is proposed that in VLDL the bow could function to inhibit binding to the receptor; during lipolysis to form LDL, it is suggested that these C-terminal inhibitory sequences forming the bow would move sufficiently to allow interaction with the LDL-receptor.

Antibodies, Monoclonal↗

PubMed1994

Expression of human apolipoprotein B90 in transgenic mice. Demonstration that apolipoprotein B90 lacks the structural requirements to form lipoprotein.

Lipoprotein(a) (Lp(a)) is a lipoprotein formed by the disulfide linkage of apolipoprotein(a) (apo(a)) to the apoB100 of a low density lipoprotein particle. Earlier site-directed mutagenesis studies of apo(a) demonstrated that apo(a) cysteine 4057 is required for the disulfide linkage; however, the cysteine residue within apoB100 that is involved in the disulfide bond has not been identified. We previously demonstrated that the apoB100 produced by human apoB transgenic mice binds to apo(a) and forms Lp(a) (Linton, M.F., Farese, R. V., Jr., Chiesa, G., Grass, D. S., Chin, P., Hammer, R. E., Hobbs, H.H., and Young, S.G. (1993) J. Clin. Invest. 92, 3029-3037). To further explore the structural features of human apoB that are required for the formation of Lp(a), we used a transposon-interrupted human apoB gene clone to develop transgenic mice that express high levels of a truncated form of human apoB, apoB90, which contains the amino-terminal 4084 amino acids of apoB. In vitro incubation of apo(a) with the plasma of human apoB90 transgenic mice did not yield Lp(a), as judged by Western blots of SDS-polyacrylamide gels or by a monoclonal antibody-based radioimmunoassay. In contrast, incubation of apo(a) with the plasma of a mouse that expressed an equivalent amount of the full-length apoB100 did yield Lp(a). In addition to these in vitro incubation studies, no Lp(a) could be detected in the plasma of a "double transgenic" mouse expressing both human apoB90 and apo(a). These data indicate that the carboxyl-terminal 10% of apoB100 contains amino acid sequences that are essential for the formation of Lp(a).

Animals↗

PubMed1994

Cellular differences in lipoprotein lipase-mediated uptake of low density lipoproteins.

Lipoprotein lipase (LPL) increases the cellular uptake and degradation of LDL by fibroblasts and macrophages via a heparin-sensitive process. The roles of the LDL receptor, LDL receptor-related protein (LRP), and proteoglycans in this process were studied. In up-regulated human fibroblasts, LPL increased degradation of 125I-low density lipoprotein (LDL) (5 micrograms/ml) only 30% during a 6-h incubation at 37 degrees C. Monoclonal antibody 47 (which interacts with the receptor binding region of apoB) decreased LDL degradation 93% in the absence of LPL, but did not reduce the LPL-mediated increase in degradation. In contrast, addition of the 39-kDa receptor-associated protein (RAP) caused a 43% decrease in the LPL-dependent LDL degradation in non-up-regulated fibroblasts. Monoclonal antibody 47 did not decrease LDL degradation by THP-1 macrophages and RAP caused a < 13% decrease in LPL-mediated LDL degradation. LPL also increased the association of acetyl LDL with the surface of the macrophages but did not increase acetyl LDL degradation. The kinetics of LPL-mediated LDL metabolism in macrophages was then compared with that in fibroblasts. The half-lives of cell surface LDL and LPL during a subsequent 37 degrees C incubation were approximately 1 h in THP-1 cells versus 6 h in fibroblasts. In addition, 50% of the 125I-LDL and 30% of the 125I-LPL were degraded within 3 h. After metabolic labeling of THP-1 proteoglycans with 35SO4, > 30% of pericellular heparan sulfate was lost between 2-4 h of the chase period. Therefore, some of the LPL-mediated LDL degradation in the THP-1 cells could be accounted for by internalization of cell surface proteoglycans. We conclude that LRP, but not the LDL receptor, is involved in LPL-mediated degradation of LDL in fibroblasts. This process is much more rapid in THP-1 cells and in addition to LRP may involve other receptors and internalization of proteoglycans.

Acetylation↗

PubMed1994

Localization of an apolipoprotein A-I epitope critical for lipoprotein-mediated cholesterol efflux from monocytic cells.

The inverse correlation between plasma high density lipoprotein (HDL) levels and the risk for cardiovascular disease has been attributed in part to the role of HDL in facilitating the transport of cholesterol to the liver for catabolism. One component of this reverse cholesterol transport is removal of excess cholesterol from peripheral cells. An immunochemical approach was employed to evaluate the role of human apolipoprotein (apo) A-I in cellular cholesterol efflux and to test the hypothesis that discrete structural domains of the molecule mediate this function. Two apoA-I-specific monoclonal antibodies (AI-11 and AI-14) inhibited in vitro cellular cholesterol efflux from THP-1 monocytic cells to HDL or apoA-I proteoliposomes by approximately 50%. Six other antibodies had no effect although three of these bound significant proportions of the apoA-I proteoliposomes. Antibody AI-11 binds apoA-I amino acid residues 96-111 (Banka, C. L., Bonnet, D. J., Black, A. S., Smith, R. S., and Curtiss, L. K. (1991) J. Biol. Chem. 266, 23886-23892). The AI-14 epitope was localized to residues 74-105. Therefore, the two antibodies that inhibited HDL promotion of cellular cholesterol efflux bound overlapping but distinct regions of the apoA-I molecule.

Amino Acid Sequence↗