Detection of IgG-bound lipoprotein(a) immune complexes in patients with coronary heart disease

Preparation of LDL , Oxidation , Methods of Detection, and Applications in Atherosclerosis Research

The concept of lipid peroxidation has been known for a long time. It is now well established that LDL plays a major role in atherosclerosis. Oxidized low-density lipoprotein (Ox-LDL) has been studied for over 35 years. Numerous pro- and anti-atherogenic properties have been attributed to Ox-LDL. Component composition of Ox-LDL is complex due to the influence of various factors, including the source, method of preparation, storage and use. Hence, it is very difficult to clearly define and characterize Ox-LDL. It contains unoxidized and oxidized fatty acid derivatives both in the ester and free forms, their decomposition products, cholesterol and its oxidized products, proteins with oxidized amino acids and cross-links, polypeptides with varying extents of covalent modification with lipid oxidation products and many others. The measurement of lipid oxidation has been a great boon, not only to the understanding of the process but also in providing numerous serendipitous discoveries and methodologies. In this chapter, we outline the methodologies for the preparation and testing of various lipoproteins for oxidation studies.

Proatherogenic Sialidases and Desialylated Lipoproteins: 35 Years of Research and Current State from Bench to Bedside

This review summarizes the main achievements in basic and clinical research of atherosclerosis. Focusing on desialylation as the first and the most important reaction of proatherogenic pathological cascade, we speak of how desialylation increases the atherogenic properties of low density lipoproteins and decreases the anti-atherogenic properties of high density lipoproteins. The separate sections of this paper are devoted to immunogenicity of lipoproteins, the enzymes contributing to their desialylation and animal models of atherosclerosis. In addition, we evaluate the available experimental and diagnostic protocols that can be used to develop new therapeutic approaches for atherosclerosis.

Differential Role for Activating FcγRIII in Neointima Formation After Arterial Injury and Diet-Induced Chronic Atherosclerosis in Apolipoprotein E-Deficient Mice

Atherogenesis and arterial remodeling following mechanical injury are driven by inflammation and mononuclear cell infiltration. The binding of immune complexes (ICs) to immunoglobulin (Ig)-Fc gamma receptors (FcγRs) on most innate and adaptive immune cells induces a variety of inflammatory responses that promote atherogenesis. Here, we studied the role of FcγRIII in neointima formation after arterial injury in atherosclerosis-prone mice and compared the outcome and mechanism to that of FcγRIII in diet-induced “chronic” atherosclerosis. FcγrIII^–/–/Apoe^–/– and control Apoe^–/– mice were subjected to wire-induced endothelial denudation of the carotid artery while on high-fat diet (HFD). FcγrIII deficiency mitigated neointimal plaque formation and lesional macrophage accumulation, and enhanced neointimal vascular smooth muscle cell (VSMC) numbers. This went along with a reduced expression of tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1/CCL2), and vascular cell adhesion molecule-1 (VCAM-1) in the neointimal lesions. Interestingly, in a chronic model of diet-induced atherosclerosis, we unraveled a dichotomic role of FcγRIII in an early versus advanced stage of the disease. While FcγrIII deficiency conferred atheroprotection in the early stage, it promoted atherosclerosis in advanced stages. To this end, FcγrIII deficiency attenuated pro-inflammatory responses in early atherosclerosis but promoted these events in advanced stages. Analysis of the mechanism(s) underlying the athero-promoting effect of FcγrIII deficiency in late-stage atherosclerosis revealed increased serum levels of anti-oxidized-LDL immunoglobulins IgG2c and IgG2b. This was paralleled by enhanced lesional accumulation of IgGs without affecting levels of complement-activated products C5a or C5ar1, FcγRII, and FcγRIV. Moreover, FcγrIII-deficient macrophages expressed more FcγrII, Tnf-α, and Il-1β mRNA when exposed to IgG1 or oxLDL-IgG1 ICs in vitro, and peripheral CD4+ and CD8+ T-cell levels were altered. Collectively, our data suggest that deficiency of activating FcγRIII limits neointima formation after arterial injury in atherosclerosis-prone mice as well as early stage chronic atherosclerosis, but augments late-stage atherosclerosis suggesting a dual role of FcγRIII in atherogenic inflammation.

Apolipoprotein(a), an enigmatic anti-angiogenic glycoprotein in human plasma: A curse or cure?

Angiogenesis is a finely co-ordinated, multi-step developmental process of the new vascular structure. Even though angiogenesis is regularly occurring in physiological events such as embryogenesis, in adults, it is restricted to specific tissue sites where rapid cell-turnover and membrane synthesis occurs. Both excessive and insufficient angiogenesis lead to vascular disorders such as cancer, ocular diseases, diabetic retinopathy, atherosclerosis, intra-uterine growth restriction, ischemic heart disease, stroke etc. Occurrence of altered lipid profile and vascular lipid deposition along with vascular disorders is a hallmark of impaired angiogenesis. Among lipoproteins, lipoprotein(a) needs special attention due to the presence of a multi-kringle protein subunit, apolipoprotein(a) [apo(a)], which is structurally homologous to many naturally occurring anti-angiogenic proteins such as plasminogen and angiostatin. Researchers have constructed different recombinant forms of apo(a) (rhLK68, rhLK8, RHACK2, KV-11, and AU-6) and successfully exploited its potential to inhibit unwanted angiogenesis during tumor metastasis and retinal neovascularization. Similar to naturally occurring anti-angiogenic proteins, apo(a) can directly interfere with angiogenic signaling pathways. Besides this, apo(a) can also exert its anti-angiogenic effect indirectly by inducing endothelial cell apoptosis, by inhibiting endothelial progenitor cell functions or by upregulating nuclear factors in endothelial cells via apo(a)-bound oxPLs. However, the impact of the anti-angiogenic potential of native apo(a) during physiological angiogenesis in embryos and wounded tissues is not yet explored. In this context, we review the studies so far done to demonstrate the anti-angiogenic activity of apo(a) and the recent developments in using apo(a) as a therapeutic agent to treat impaired angiogenesis during vascular disorders, with emphasis on the gaps in the literature.

The Atherogenic Role of Circulating Modified Lipids in Atherosclerosis

Lipid accumulation in the arterial wall is a crucial event in the development of atherosclerotic lesions. Circulating low-density lipoprotein (LDL) is the major source of lipids that accumulate in the atherosclerotic plaques. It was discovered that not all LDL is atherogenic. In the blood plasma of atherosclerotic patients, LDL particles are the subject of multiple enzymatic and non-enzymatic modifications that determine their atherogenicity. Desialylation is the primary and the most important atherogenic LDL modification followed by a cascade of other modifications that also increase blood atherogenicity. The enzyme trans-sialidase is responsible for the desialylation of LDL, therefore, its activity plays an important role in atherosclerosis development. Moreover, circulating modified LDL is associated with immune complexes that also have a strong atherogenic potential. Moreover, it was shown that antibodies to modified LDL are also atherogenic. The properties of modified LDL were described, and the strong evidence indicating that it is capable of inducing intracellular accumulation of lipids was presented. The accumulated evidence indicated that the molecular properties of modified LDL, including LDL-containing immune complexes can serve as the prognostic/diagnostic biomarkers and molecular targets for the development of anti-atherosclerotic drugs.

Inflammation and the pathogenesis of atherosclerosis in systemic lupus erythematosus

Atherosclerosis is a complicated inflammatory process characterized by the interactions of numerous different moieties including lipids, enzymes, endothelial cells, cytokines, chemokines, leukocytes, adhesion molecules, complement and antibodies. As in the pathogenesis of many lupus disease processes, the increased risk of atherosclerosis seen in systemic lupus erythematosus (SLE) is likely due to the complex interplay of many of these inflammatory mediators. Expanding our understanding of the pathogenesis of atherosclerosis in SLE is critical if we are to improve the quality of care and reduce mortality in this vulnerable population.

Immunopathology of desialylation: human plasma lipoprotein(a) and circulating anti-carbohydrate antibodies form immune complexes that recognize host cells

Human plasma lipoprotein(a) [Lp(a)], the dominant lipoprotein in atherosclerotic plaques, contains an apo(a) subunit of variable size linked to the apoB subunit of a low-density lipoprotein (LDL) molecule. Circulating lipoprotein immune complexes (ICs) assayed by ELISA using microplate-coated anti-apo(a) or anti-apoB antibody for capture and peroxidase-labelled anti-human immunoglobulins as probe consisted mostly of Lp(a) despite several-fold excess of LDL over Lp(a) in plasma. Microplate coating of plasma lipoprotein IC and probing with antibodies to apo(a) and apoB also revealed negligible presence of LDL compared to Lp(a). Peanut agglutinin specific to desialylated O-glycans bound significantly more to Lp(a) recovered after urea dissociation of IC than to free Lp(a). Plasma lipoproteins separated by ultracentrifugation and desialylated by neuraminidase formed IC with naturally occurring antibodies in normal plasma. These de novo ICs agglutinated desialylated but not normal human RBC in proportion to the polyagglutinin antibody titre of plasma used, suggesting availability of multiple unoccupied binding sites on the participating antibodies even after IC formation. Agglutination was inhibitable by galactosides and decreased 4-8 fold if precursor lipoprotein was selectively depleted of Lp(a), showing agglutinating ICs were contributed mainly by desialylated Lp(a) and galactose-specific antibodies. IC was 2 fold more agglutinating if lipoproteins used contained smaller rather than larger Lp(a) molecules of the same number. Small size/high plasma concentration Lp(a) phenotype and neuraminidase-releasing diseases including diabetes are risk factors for vascular disorders. Results suggest a possible route of Lp(a) attachment to vascular cells that offer terminal galactose on surface glycans following desialylation.

Human plasma anti-α-galactoside antibody forms immune complex with autologous lipoprotein(a)

Anti-α-galactoside antibody (anti-Gal) from human plasma that bound to α-galactoside-bearing guar galactomannan gel and was eluted with specific sugar (affinity-purified anti-Gal ; APAG) invariably contained apo(a) and apo B subunits in a proportion close to that in plasma lipoprotein(a) [Lp(a)]. Since LDL does not contain apo(a), result suggested Lp(a) as a component of APAG. Lp(a) in APAG was complexed with anti-Gal since plate-coated anti-apo(a) captured Lp(a) along with the antibody. Association of Lp(a) with anti-Gal in APAG was considerably lower in presence of anti-Gal-specific sugar, suggesting that Lp(a) occupied the sugar-binding site of anti-Gal. Content of Lp(a)-bound anti-Gal in APAG, though a minor fraction of total antibody, increased steadily with total Lp(a) content of plasma. Further, Lp(a) released from immune complex-rich fraction of plasma by anti-Gal- specific sugar was proportional to total plasma Lp(a). Anti-Gal titre decreased with increasing Lp(a) concentration among 114 plasma samples. Results indicate the potential of anti-Gal molecules with its binding site partially occupied by Lp(a) molecule(s) to a) use the remaining binding site(s) to recognize other macromolecules or cells and b) transport Lp(a) across Fc receptor-bearing cells.

Hypolipidemic and antioxidant properties of a polysaccharide fraction from Enteromorpha prolifera

A polysaccharide fraction (EPF2) was obtained from the crude polysaccharides of Enteromorpha prolifera by a series isolation procedure. Monosaccharide components analysis indicated that EPF2 was composed of rhamnose, xylose, mannose, galactose and glucose in a molar ratio of 3.64:1.08:0.21:0.75:0.27. Hypolipidemic and antioxidant properties of EPF2 were investigated. The results showed that the hypolipidemic effect of EPF2 was in a concentration-dependent fashion and the prior oral administration of EPF2 (300 mg/kg body weight) exhibited considerable effect which could bear comparison with that of simvastatin. Moreover, administration of EPF2 could significantly enhance the activities of endogenous antioxidant enzymes and lowered the content of maleic dialdehyde (MDA) in serum. The results suggested that EPF2 had a high hypolipidemic activity and this activity might be attributed to its antioxidant potential.

Development of immunoassays for anti-electronegative LDL autoantibodies and immune complexes

BACKGROUND

Electronegative low-density lipoprotein (LDL-) promotes atherosclerosis through inflammatory and immunologic mechanisms that lead to the production of anti-LDL(-) autoantibodies and to the subsequent formation of immune complexes (IC) and macrophage foam cells. We described the development and validation of an ELISA for the quantification of free anti-LDL(-) autoantibodies and an ELISA for the quantification of IC consisting of LDL(-)-bound IgG in human plasma.

METHODS

LDL(-) purified from human plasma, and anti-LDL(-) monoclonal antibody Fab fragments were adsorbed onto ELISA plates to capture anti-LDL(-) autoantibodies and IC-LDL(-), respectively. The performance characteristics of both ELISAs, including the limits of detection and quantification, accuracy and inter- and intra-assay precision were evaluated. Linearity, interference and stability tests were also performed.

RESULTS

The calibration range of the anti-LDL(-) assay was 0.004-0.125 mU/l and plasma demonstrated a dilutional linearity when diluted 1:100, 1:200, 1:400 and 1:800. The calibration range of the IC-LDL(-) assay was 0.06-4 U/l, and plasma demonstrated a dilutional linearity when diluted 1:12.5, 1:25, 1:50 and 1:100. Both ELISAs showed intra- and inter-assay precision and recovery within the required limits for immunoassays.

CONCLUSION

These ELISAs can be used in clinical studies and for the biochemical investigation of atherosclerosis. In addition, they will enable the comprehensive evaluation of the importance of bound or free autoantibodies against LDL(-) in this disease.

Percutaneous coronary intervention results in acute increases in native and oxidized lipoprotein(a) in patients with acute coronary syndrome and stable coronary artery disease

OBJECTIVE

To investigate possible changes of native and oxidized lipoprotein(a) [ox-Lp(a)] levels after percutaneous coronary intervention (PCI).

DESIGN AND METHODS

Lp(a), ox-Lp(a), and Lp(a) immune complexes (IC) and autoantibody levels were studied in 111 patients with acute coronary syndrome (ACS) and 68 patients with stable coronary artery disease (CAD) before and after PCI.

RESULTS

Compared with pre-PCI, Lp(a), ox-Lp(a), and Lp(a)-IC levels acutely increased, while the autoantibody decreased in both the ACS and stable CAD patients. They all returned toward baseline by 1 to 2 days. The absolute change of ox-Lp(a) was found positively related with both the diameter of stenosis (R=0.273, P=0.004) and the number of vessel disease (R=0.312, P=0.001) in the ACS patients, while not in the stable CAD patients.

CONCLUSION

PCI results in acute plasma increases of ox-Lp(a) and Lp(a). Ox-Lp(a) may be present in ruptured or permeable plaques and be released into the circulation by PCI.

The Role of Immune Complexes in Atherogenesis

Atherosclerosis is now recognized as a chronic inflammatory disease and is characterized by features of inflammation at all stages of its development. It also appears to display elements of autoimmunity, and several autoantibodies including those directed against oxidized low-density lipoprotein (ox-LDL) and heat shock proteins (Hsps) have been identified in atherosclerosis. Immune complexes (ICs) may form between these antigens and autoantibodies and via Fc receptor signaling and complement activation may modulate the inflammation in atherosclerosis. Antibody isotype may direct the role that ICs play in atherogenesis, immunoglobulin G (IgG) being potentially pro-atherogenic and immunoglobulin M (IgM) playing a protective role. Therapeutic options targeting complement activation and those which are potentially Fc-receptor mediated have been investigated in animal models, though targeting Fc receptor signaling is an area that needs further investigation.

Oxidized low-density lipoprotein

Oxidized low-density lipoprotein (Ox-LDL) has been studied for over 25 years. Numerous pro- and anti-atherogenic properties have been attributed to Ox-LDL. Yet, Ox-LDL has neither been defined nor characterized, as its components and composition change depending on its source, method of preparation, storage, and use. It contains unoxidized and oxidized fatty acid derivatives both in the ester and free forms, their decomposition products, cholesterol and its oxidized products, proteins with oxidized amino acids and cross-links, and polypeptides with varying extents of covalent modification with lipid oxidation products, and many others. It seems to exist in vivo in some form not yet fully characterized. Until its pathophysiological significance, and how it is generated in vivo are determined, the nature of its true identity will be only of classical interest. In this review, its components, their biological actions and methods of preparation will be discussed.

The level of malondialdehyde-modified LDL and LDL immune complexes in patients with rheumatoid arthritis

OBJECTIVES

To explore possible associations of malondialdehyde-modified low-density lipoprotein (MDA-LDL) and LDL-immune complexes (LDL-IC) with atherosclerosis in rheumatoid arthritis (RA).

DESIGN AND METHODS

Plasma MDA-LDL, LDL-IC levels and mechanisms of the changes were investigated in RA patients with or without coronary artery disease (CAD), simple CAD patients and control.

RESULTS

MDA-LDL and LDL-IC levels were found increased in all the studied patients, the RA patients with CAD exhibited the most significant changes. MDA-LDL levels were higher in the RA patients with CAD than those both in the simple RA and CAD patients. Multiple linear regression analysis showed that CAD, LDL-IC and erythrocyte sedimentation rate accounted for 36.5% of the variation in MDA-LDL levels; and age, activity, MDA-LDL and rheumatoid factors accounted for 34.5% of the variation in LDL-IC.

CONCLUSIONS

High levels of MDA-LDL and LDL-IC are risk factors for increased risk of atherosclerosis in RA patients and are associated with inflammation.

Elevated concentrations of oxidized lipoprotein(a) are associated with the presence and severity of acute coronary syndromes

OBJECTIVE

To investigate possible mechanisms and association of increased oxidized Lp(a) [ox-Lp(a)] levels with presence and extent of acute coronary syndromes (ACS).

METHODS

Ox-Lp(a) levels were studied in 96 patients with ACS, 89 patients with stable coronary artery disease (CAD), and 100 control subjects.

RESULTS

Compared to control, ox-Lp(a) levels increased in stable CAD patients (P<0.001), and especially in ACS (P<0.001) (ACS, 16.29+/-13.80 microg/ml; stable CAD, 10.04+/-10.32 microg/ml; control, 7.10+/-9.16 microg/ml). The ratio of ox-Lp(a) to Lp(a) was higher in the ACS than those in the stable CAD (P<0.05) and control (P<0.001). Ox-Lp(a) levels were found associated with a graded increase in extent of angiographically documented CAD in the ACS (R=0.275, P=0.007), while not in the stable CAD (R=0.090, P=0.402). Multiple linear regression analysis found ox-Lp(a) (beta=0.271, P=0.019), age (beta=0.244, P=0.038) and TG (beta=0.213, P=0.070) accounted for 11.1% of the variation in the extent of angiographically documented CAD in ACS patients; Lp(a) (beta=0.415, P=0.000) and extent of CAD (beta=0.193, P=0.071) accounted for 21.5% of that in ox-Lp(a) levels.

CONCLUSION

Elevated ox-Lp(a) levels are associated with presence and severity of ACS, and may be useful for identification of patients with ACS.

Plasma oxidized lipoprotein(a) and its immune complexes are present in newborns and children

BACKGROUND

Oxidized Lp(a) [ox-Lp(a)] has been reported to play more potent roles than native Lp(a) in atherosclerosis. We investigated the distribution characteristics of plasma ox-Lp(a) and Lp(a) immune complex [Lp(a)-IC] levels in newborns and children.

METHODS

Plasma ox-Lp(a) and Lp(a)-IC levels were measured in 747 children and 30 cord blood by ELISAs.

RESULTS

The mean levels of Lp(a), ox-Lp(a) and Lp(a)-IC were much lower in newborns than in children (P<0.001), and increased rapidly to that in children after birth. The distributions of Lp(a), ox-Lp(a) and Lp(a)-IC were skewed toward low values in children, no difference of their levels was found in each of the 13year groups. The levels of ox-Lp(a) correlated positively with total and LDL cholesterol, Lp(a) and Lp(a)-IC; Lp(a)-IC correlated positively with sex, total and LDL cholesterol, Lp(a) and ox-Lp(a), respectively. Multiple linear regression analysis showed Lp(a) and Lp(a)-IC accounted for 42% of the variation in ox-Lp(a) levels, and ox-Lp(a) accounted for 30% of that in Lp(a)-IC.

CONCLUSIONS

The fact that ox-Lp(a) and Lp(a)-IC are present in newborns and children suggests that oxidized lipoproteins play an initiating role in atherosclerotic process.

Native, oxidized lipoprotein(a) and lipoprotein(a) immune complex in patients with active and inactive rheumatoid arthritis: plasma concentrations and relationship to inflammation

BACKGROUND

Several studies suggest that lipoprotein (a) [Lp(a)] act as acute phase reactant and be associated with early atherosclerosis in rheumatoid arthritis (RA). Oxidized Lp(a) [ox-Lp(a)] and Lp(a) immune complex (IC) concentrations both increased in patients with coronary heart disease. We investigated Lp(a), ox-Lp(a) and Lp(a)-IC concentrations in RA patients and to explore the relationships with inflammatory disease activity markers.

METHODS

Plasma Lp(a), ox-Lp(a) and Lp(a)-IC concentrations, and inflammatory markers were analyzed in 54 patients with RA, including 23 active and 21 inactive RA, and 60 control subjects.

RESULTS

Lp(a) and ox-Lp(a) concentrations in active RA were higher than those in both inactive RA and control; Lp(a)-IC concentrations in active RA were also higher than inactive RA, while no difference was found in Lp(a), ox-Lp(a) and Lp(a)-IC concentrations between inactive RA and control. Lp(a) concentrations were found positively correlated with ox-Lp(a) and Lp(a)-IC concentrations, respectively; ox-Lp(a) concentrations were also related with Lp(a)-IC. Lp(a), ox-Lp(a) and Lp(a)-IC were all found positively related with C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), respectively.

CONCLUSIONS

Native, oxidized Lp(a) and Lp(a)-IC concentrations increased in active RA patients. Inflammation may induce the changes of Lp(a), resulting in increased ox-Lp(a) and Lp(a)-IC, and may play an important role in atherosclerosis.

Development of new enzyme-linked immunosorbent assay for oxidized lipoprotein(a) by using purified human oxidized lipoprotein(a) autoantibodies as capture antibody

BACKGROUND

Oxidized Lp(a) [ox-Lp(a)] has been reported to play more potent role than native Lp(a) in atherosclerosis. Ox-Lp(a), autoantibodies, and Lp(a) immune complexes have all been detected in vivo. Thus, the isolation of its autoantibodies and the investigation of ox-Lp(a) may provide a new means to explore the exact pathogenic role of ox-Lp(a). We isolated and identified human autoantibodies against ox-Lp(a) and developed a new ELISA for ox-Lp(a) by using autoantibodies as capture antibody.

METHODS

Ox-Lp(a) autoantibodies were isolated and identified from healthy subjects by affinity chromatography. 2 "sandwich" ELISAs were developed for measuring ox-Lp(a) level, using autoantibodies against ox-Lp(a) or rabbit antiserum against ox-LDL as the capture antibody and quantitating with monoclonal anti-apo(a) enzyme conjugate, respectively. Ox-Lp(a) levels were studied by both the ELISAs in 100 patients with coronary heart disease (CHD) and 100 control subjects.

RESULTS

The isolated ox-Lp(a) autoantibodies reacted with both apo(a) and apoB epitopes of Ox-Lp(a). Compared to control, plasma ox-Lp(a) levels in patients with CHD were significantly increased (ELISA using human autoantibodies: 24.3+/-33.4 vs. 8.4+/-9.3 microg/ml, P<0.0001; ELISA using antibodies against ox-LDL: 13.0+/-13.8 vs. 7.3+/-9.7 microg/ml, P<0.0001, respectively). Furthermore, a significantly positive relationship between ox-Lp(a) levels detected by 2 ELISAs was also found (R=0.78, P<0.0001).

CONCLUSION

We isolated human autoantibodies against ox-Lp(a), which can recognize both apo(a) and apoB epitopes of ox-Lp(a). The developed ELISA for ox-Lp(a) by using human auoantibodies may more accurately reflect the state of Lp(a) oxidation in vivo. Ox-Lp(a) levels increase in patients with CHD.

A microtiter assay for quantifying protein-protein interactions associated with cell-cell adhesion

Cell-cell adhesions are a hallmark of epithelial tissues, and the disruption of these contacts plays a critical role in both the early and late stages of oncogenesis. The interaction between the transmembrane protein E-cadherin and the intracellular protein beta-catenin plays a crucial role in the formation and maintenance of epithelial cell-cell contacts and is known to be downregulated in many cancers. The authors have developed a protein complex enzyme-linked immunosorbent assay (ELISA) that can quantify the amount of beta-catenin bound to E-cadherin in unpurified whole-cell lysates with a Z' factor of 0.74. The quantitative nature of the E-cadherin:beta-catenin ELISA represents a dramatic improvement over the low-throughput assays currently used to characterize endogenous E-cadherin:beta-catenin complexes. In addition, the protein complex ELISA format is compatible with standard sandwich ELISAs for parallel measurements of total levels of endogenous E-cadherin and beta-catenin. In 2 case studies closely related to cancer cell biology, the authors use the protein complex ELISA and traditional sandwich ELISAs to provide a detailed, quantitative picture of the molecular changes occurring within adherens junctions in vivo. Because the E-cadherin: beta-catenin protein complex plays a crucial role in oncogenesis, this protein complex ELISA may prove to be a valuable quantitative prognostic marker of tumor progression.

Differences in human antioxidized LDL autoantibodies in patients with stable and unstable angina

BACKGROUND

Autoantibodies to oxidized LDL (anti-oxLDL) have been found in the serum of patients with coronary artery disease (CAD). This study was designed to compare the differences in anti-oxLDL titers and isotypes in unstable and stable angina patients and to correlate these results with known markers of active inflammation in CAD.

METHODS

Thirty patients from a tertiary referral general hospital with documented CAD were studied. Anti-oxLDL IgG titers and its isotypes, high sensitivity C-reactive protein (hsCRP) and serum amyloid A (SAA) were measured.

RESULTS

The anti-oxLDL IgG titer was lower (p=0.03) in the unstable angina group compared to the stable angina patients (0.084+/-0.102 OD versus 0.195+/-0.149 OD, respectively). The predominant IgG isotype in both groups was IgG2. IgG4 was significantly higher (0.270+/-0.146 OD, p=0.04) in the unstable angina group versus patients with stable angina (0.198+/-0.019 OD). There was a significant inverse correlation between anti-oxLDL and hsCRP and SAA in this sample population (R=0.37, p<0.05 and R=0.36, p<0.05, respectively).

CONCLUSION

Patients with unstable angina have lower levels of anti-oxLDL IgG in the acute setting of CAD. Plaque instabilization does not seem to acutely modify the isotype subsets of anti-oxLDL IgG in these patients.

Lipoprotein (a) and its immune complexes in dyslipidemic subjects

OBJECTIVES

To investigate plasma levels of lipoprotein (a) [Lp(a)] and low-density lipoprotein (LDL)-circulating immune complexes (IC) in subjects with various dyslipidemias.

METHODS

Plasma Lp(a), Lp(a)-IC, and LDL-IC levels were determined by enzyme-linked immunosorbent assays (ELISAs) in 198 subjects with various dyslipidemias and 34 control subjects.

RESULTS

Hypertriglyceridemic subjects exhibited the lowest plasma Lp(a) levels, while hypercholesterolemic subjects exhibited the highest levels. Subjects with mixed hyperlipidemia had intermediate plasma Lp(a) concentrations, which were significantly lower than those of subjects with normal lipid levels. Interestingly, we also found that hypertriglyceridemic subjects had the lowest plasma Lp(a)-IC and LDL-IC levels, while hypercholesterolemic subjects exhibited the highest levels. Triglyceride (TG) levels were negatively correlated with Lp(a) (r = -0.15, P < 0.05), Lp(a)-IC (r = -0.20, P < 0.01), and LDL-IC (r = -0.214, P < 0.01) concentrations. Furthermore, significantly positive relationships were found between Lp(a)-IC and Lp(a) levels (r = 0.65, P < 0.001) and between LDL-IC and LDL-C levels (r = 0.43, P < 0.001).

CONCLUSIONS

The results argue for a regulatory role of TG on plasma Lp(a) and its circulating immune complexes in subjects with various dyslipidemias. The circulating levels of these immune complexes levels are likely to change with different concentrations of Lp(a) and LDL.

Positive correlation between in vivo oxidized LDL and LDL immune complexes

OBJECTIVES

To investigate the possible relationship between oxidized low-density lipoprotein (ox-LDL) and LDL immune complexes (IC).

METHODS

Both LDL-IC and ox-LDL were detected by sandwich ELISA. The levels were also studied in 60 patients with coronary heart disease (CHD) and 50 control subjects.

RESULTS

Compared to controls, both the plasma ox-LDL concentrations (595.5 +/- 194.8 vs. 440.3 +/- 175.0 microg/l, P < 0.001) and LDL-IC levels (2.74 +/- 0.73 vs. 1.38 +/- 0.78 AU, P < 0.001) in the patients with CHD were significantly increased. The relationships between LDL-IC, ox-LDL levels, and other lipid parameters in all the studied subjects (n = 100) were analyzed. LDL-IC levels were positively correlated with TC, TG, LDL-C, lipoprotein(a) [Lp(a)], and apolipoprotein B (apoB) concentration, while negatively correlated with apoA1 concentration, respectively. Similarly, ox-LDL levels were also found positively correlated with TC, LDL-C, and apoB concentrations, respectively. Furthermore, a significantly positive correlation between ox-LDL and LDL-IC levels was found (r = 0.313, P < 0.005).

CONCLUSION

In vivo oxidized LDL positively correlates with circulating levels of LDL immune complexes.