Autoantibodies against malondialdehyde-modified lipoprotein(a) in antiphospholipid syndrome

Primary Antiphospholipid Syndrome with and Without Acute Myocardial Infarction/Angina: A Cross-Sectional Study

Introduction

Acute myocardial infarct/angina (AMI-A) is a possible complication in primary antiphospholipid syndrome (pAPS) patients. This study compares data obtained from pAPS patients with and without AMI-A.

Methods

This cross-sectional study of 66 (85.2% female) pAPS patients (Sidney criteria). Demographics, clinical data, medication use, and antiphospholipid antibodies were evaluated. Patients were divided into two groups: pAPS with AMI-A and pAPS without AMI-A.

Results

Sixty-six patients with primary APS (six with AMI-A and 60 without AMI-A) were selected. They were similar for demographics, disease duration, and anthropometrics (p > 0.05). Patients with AMI-A compared to those patients without AMI-A had more frequently dyslipidemia (66 vs. 28%, p = 0.05), systemic hypertension (83 vs. 37%, p = 0.02), and increased levels of lipoprotein (a) (116 ± 67 vs. 36 ± 35 mg/dl, p = 0.0002). Interesting, current physical activity (66.7 vs. 23%, p = 0.04) was more seen in the first group when compared to the second one. Patients with AMI-A used more statins (66 vs. 22%, p = 0.017) and acetylsalicylic (100 vs. 28%, p = 0.05). Higher median levels of IgM anticardiolipin antibodies [70 (0–120) vs. 9 (0–120), p = 0.03] were observed in the first group.

Conclusions

pAPS patients and AMI-A have distinct clinical and laboratory spectra from those without AMI-A. It is characterized by dyslipidemia and hypertension, hyper lipoprotein(a), and a lower IgM anticardiolipin frequency.

Lipoprotein(a) and its role in inflammation, atherosclerosis and malignancies

Lipoprotein (a) (Lp(a)) is a modified low-density lipoprotein (LDL) particle with an additional specific apolipoprotein (a), covalently attached to apolipoprotein B‑100 of LDL by a single thioester bond. Increased plasma Lp(a) level is a genetically determined, independent, causal risk factor for cardiovascular disease.

The precise quantification of Lp(a) in plasma is still hampered by mass-sensitive assays, large particle variation, poor standardization and lack of assay comparability.

The physiological functions of Lp(a) include wound healing, promoting tissue repair and vascular remodeling. Similarly to other lipoproteins, Lp(a) is also susceptible for oxidative modifications, leading to extensive formation of pro-inflammatory and pro-atherogenic oxidized phospholipids, oxysterols, oxidized lipid-protein adducts in Lp(a) particles, that perpetuate atherosclerotic lesion progression and intima-media thickening through induction of M1-macrophages, inflammation, autoimmunity and apoptosis. The oxidation-specific epitopes of modified lipoproteins are major targets of pre-immune, natural IgM antibodies, that may attenuate the pro-inflammatory and pro-atherogenic effects of Lp(a).

Although the data are still insufficient, recent studies suggest a potential anti-neoplastic role of Lp(a).

Anticardiolipin Antibodies as a Risk Factor of Atherosclerosis in Intermittent Claudication

Anticardiolipin antibodies have been associated as a risk factor of atherosclerosis. The aim of this study was to evaluate the association between anticardiolipin antibodies and intermittent claudication. Forty consecutive patients (33 men, 7 women; age range: 45-84 years, mean 65.5) who were seen in the angiology and vascular surgery department with intermittent claudication were evaluated. Exclusion criteria included prior revascularization, angioplasty, or a history of thrombosis of a lower limb. Forty individuals (23 men, 17 women; age range: 58-82 years, mean 67.1) who attended a support group for senior citizens and who were apparently healthy formed the control group. Anticardiolipin antibodies were evaluated by means of enzyme-linked immunosorbent assay (ELISA) for quantitative measurement of immunoglobulin G (IgG) and IgM antibodies against cardiolipins in serum. IgG levels were considered normal when <7, borderline from 7 to 10, and elevated at >10 GPL units/mL; IgM levels were normal when <4, borderline from 4 to 7, and elevated at >7 MPL, as recommended by the test manufacturers. Statistical analysis used the relative risk test with a confidence interval of 95%. Twenty-three patients from the study group and 6 individuals from the control group were found to have elevated levels of anticardiolipin antibodies giving a relative risk of 3.833 (ranging from 1.749 to 8.4; p value <0.0001). In conclusion, patients who have elevated levels of anticardiolipin antibodies present a 3.8 times greater risk of developing intermittent claudication.

A Systematic Literature Review of the Association of Lipoprotein(a) and Autoimmune Diseases and Atherosclerosis

Objective. To investigate the association of lipoprotein(a) and atherosclerosis-related autoimmune diseases, to provide information on possible pathophysiologic mechanisms, and to give recommendations for Lp(a) determination and therapeutic options. Methods. We performed a systematic review of English language citations referring to the keywords "Lp(a)" AND "autoimmune disease" AND "atherosclerosis," "Lp(a)" AND "immune system" OR "antiphospholipid (Hughes) syndrome (APS)" OR "rheumatoid arthritis" OR "Sjögren's syndrome" OR "systemic lupus erythematosus" OR "systemic sclerosis" OR "systemic vasculitis" published between 1991 and 2011 using Medline database. Results. 22 out of 65 found articles were identified as relevant. Lp(a) association was highest in rheumatoid arthritis (RA), followed by systemic lupus erythematosus (SLE), moderate in APS and lowest in systemic sclerosis (SSc). There was no association found between Lp(a) and systemic vasculitis or Sjögren's syndrome. Conclusion. Immune reactions are highly relevant in the pathophysiology of atherosclerosis, and patients with specific autoimmune diseases are at high risk for CVD. Elevated Lp(a) is an important risk factor for premature atherosclerosis and high Lp(a) levels are also associated with autoimmune diseases. Anti-Lp(a)-antibodies might be a possible explanation. Therapeutic approaches thus far include niacin, Lp(a)-apheresis, farnesoid x-receptor-agonists, and CETP-inhibitors being currently under investigation.

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.

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.

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.

‘Not only…but also’: factors that contribute to accelerated atherosclerosis and premature coronary heart disease in systemic lupus erythematosus

Premature coronary heart disease (CHD) has emerged as a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). Overall SLE patients have a 5-6-fold increased risk of CHD and this excess risk is especially pronounced in younger women where the excess risk may be >50-fold. Studies from our group and others have also demonstrated that SLE patients have a higher prevalence of subclinical atherosclerosis compared with controls, with approximately 30% having evidence of subclinical involvement. It is important to consider what factors may underlie this excess risk. We have found that certain 'classic' risk factors, i.e. hypertension and diabetes mellitus, are more prevalent in SLE and that persistent hypercholesterolaemia independently predicts patients who will develop CHD. These risk factors alone do not completely explain the excess risk observed, and after adjusting for classic risk factors SLE remains independently associated with both clinical and subclinical outcomes. Certain other metabolic changes also occur more frequently in SLE, namely premature menopause, renal impairment, high triglycerides and higher plasma homocysteine. In addition, insulin resistance is more pronounced in patients with SLE, and approximately 18% have the metabolic syndrome. It is also increasingly accepted that atherosclerosis is a chronic inflammatory condition, and in SLE systemic complement activation as well as immune complex formation can result in changes that promote the development of atheroma. Similarly, autoantibody production, especially antibodies directed against lipoprotein subtypes and those in the antiphospholipid (APLA) family, are gaining increasing attention. The role of the latter are particularly controversial as different subtypes have been shown to both promote and protect against atherogenesis. In a study looking at carotid plaque in SLE, we found that APLA was independently associated with the presence of plaque; this study also found that patients with plaque had higher white cell counts, suggesting ongoing chronic inflammation. We have also noted a negative correlation between activation of transforming growth factor beta-1 and carotid intima-medial thickness. This cytokine, which is known to be a potent anti-inflammatory molecule, has also been shown to be protective against atherogenesis. With regard to therapy, steroids may be a true double-edged sword, with low doses exerting a beneficial anti-inflammatory role whereas higher doses may be detrimental through exacerbation of metabolic risk factors. In contrast, we have found that antimalarials have a beneficial effect on lipids especially when co-prescribed with steroids, and this, along with anti-inflammatory and proposed antiplatelet effects, may confer protection against CHD in lupus. The risk of premature CHD in SLE is therefore mediated by a number of factors that involve not only classic risk factors but also a range of factors associated with SLE itself. Preventative strategies will therefore need to address all potential risk factors of relevance. A more through understanding of the interplay between autoimmunity and atherogenesis should be possible by the study of SLE, and this may not only benefit lupus patients but also may have implications for our understanding of atherosclerosis in general.

Cardiovascular disease in lupus patients: Should all patients be treated with statins and aspirin?

Premature coronary heart disease (CHD) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus (SLE). In certain age groups, the risk can be >50 times that of an age-matched population. This population also has an increased prevalence of several key classic risk factors that contribute to the CHD development. Chronic inflammation, anti-phospholipid antibodies and exposure to steroid therapy are also likely to have an impact. We have adopted a proactive approach to classic risk factor management with 'ideal targets' based on viewing SLE as a CHD equivalent condition. In this context, a significant proportion of SLE patients (approximately 30%) will require statins and the majority would be treated with aspirin prophylaxis. Better control of the underlying inflammatory disease is also likely to play an important role and the relative safety of anti-malarials allows their consideration as an adjunct in a large proportion of patients. Well-conducted clinical trials are now needed to advance beyond these initial recommendations.

Autoantibody explosion in systemic lupus erythematosus: more than 100 different antibodies found in SLE patients

OBJECTIVE

Description of the various autoantibodies that can be detected in patients with systemic lupus erythematosus (SLE).

METHODS

A literature review, using the terms "autoantibody" and "systemic lupus erythematosus", was conducted to search for articles on autoantibodies in SLE, their target antigens, association with disease activity, or other clinical associations.

RESULTS

One hundred sixteen autoantibodies were described in SLE patients. These include autoantibodies that target nuclear antigens, cytoplasmic antigens, cell membrane antigens, phospholipid-associated antigens, blood cells, endothelial cells, and nervous system antigens, plasma proteins, matrix proteins, and miscellaneous antigens. The target of autoantibody, the autoantigen properties, autoantibody frequencies in SLE, as well as clinical associations, and correlation with disease activity are described for all 116 autoantibodies.

CONCLUSIONS

SLE is the autoimmune disease with the largest number of detectable autoantibodies. Their production could be antigen-driven, the result of polyclonal B cell activation, impaired apoptotic pathways, or the outcome of idiotypic network dysregulation.

Current debates in antiphospholipid syndrome: the acquired antibody-mediated thrombophilia

Antiphospholipid (APL) syndrome is the most common form of acquired thrombophilia. It can cause significant morbidity and even mortality. The term "APL antibodies" represents a heterogeneous group of antibodies associated with this disorder. Currently no single assay can identify every APL antibody. Clinically relevant APL antibodies are mainly anticardiolipin antibodies (ACA) detected by solid phase enzyme-linked immunosorbent assay (ELISA) and lupus anticoagulants (LA) demonstrated by in vitro coagulation assay. However, there are some other antibodies associated with the APL syndrome (i.e., subgroup APL antibodies). ACAs, LAs, and subgroup APL antibodies represent intersecting, but non-identical, subsets of autoantibodies. Thus, those autoantibodies may coexist or may occur independently. Any organ system and any size of vessel can be affected during the clinical course of the disease. Therefore, the APL syndrome can manifest itself in a wide variety of clinical thrombotic features. Fetal loss and pregnancy morbidity represent a specific challenge. Despite tremendous advances in the understanding of the pathogenesis of APL syndrome during the past decade, the mainstay of management is still anticoagulation. However, there is no general agreement regarding the duration and intensity of anti-coagulant therapy. In this review, we focused on the current dilemmas and their present clarifications in the wide clinicopathologic spectrum of APL syndrome and APL antibody-related distinct pathologic conditions.

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

BACKGROUND

LDL-immune complexes (IC) have a powerful pathogenic role for inducing foam cell formation in vitro more efficiently than any other known mechanism. Studies have also shown that plasma LDL-IC concentration is a powerful marker for the development of atherosclerosis. The structure, fatty acid composition and antioxidant concentrations of Lp(a) and LDL are quite similar. The same oxidation pattern has also been described for both lipoproteins. Modified forms of Lp(a), some resembling oxidized Lp(a), have been identified in human atheromatous lesions. The existence of autoantibodies against MDA-Lp(a) in vivo is also presented. Therefore, we suppose that Lp(a) might trigger an immune response leading to the production of autoantibodies and subsequently to the formation of immune complexes. This study examined the existence of IgG-bound Lp(a)-IC and investigated its value as a risk factor for the development of atherosclerosis.

METHODS

We developed two "sandwich" ELISAs for measuring plasma Lp(a)-IC and LDL-IC concentrations, using anti-human IgG(Fab) as the capture antibody, and quantitating with monoclonal anti-apo(a) or anti-apoB enzyme conjugate. Their concentrations were studied in 160 patients with coronary heart disease (CHD) and 290 control subjects.

RESULTS

Plasma TC, LDL-C, TG and apoB concentrations in CHD patients were all significantly increased, whereas HDL-C and apoAI concentrations were decreased. The Lp(a) concentrations in the patients with CHD were also significantly different from those of control (262.4+/-220.0 vs. 211.3+/-199.4 mg/l, P<0.005). Plasma Lp(a)-IC (2.24+/-1.71 vs. 1.62+/-1.50 AU, P<0.0001) and LDL-IC (2.77+/-1.29 vs. 1.40+/-0.92 AU, P<0.0001) concentrations in patients with CHD were both significantly higher than those of control. The relationships between Lp(a)-IC, LDL-IC concentrations and other lipid traits in all the studied subjects (n=450) were carried out. LDL-IC concentrations were positively correlated with LDL-C, apoB, TC, TG and Lp(a) concentrations, while negatively correlated with HDL-C and apoAI concentrations, respectively. Similarly, Lp(a)-IC concentrations were positively correlated with Lp(a), LDL-C, apoB and TC concentrations, while negatively correlated with HDL-C and apoAI concentrations, respectively. Furthermore, a significantly positive relation between LDL-IC and Lp(a)-IC concentrations was also found (r=0.313, P<0.0001).

CONCLUSIONS

We report the existence of Lp(a)-IC in both the plasma of patients with CHD and control subjects. Lp(a)-IC concentration increases in the CHD patients.

Atherosclerosis and connective tissue diseases

Large increases in mortality related to premature atherosclerosis with coronary artery disease and stroke have been reported in patients with systemic lupus erythematosus (SLE), antiphospholipid syndrome (APLS), or rheumatoid arthritis (RA). Studies found relative risks of 5 for myocardial infarction, 6 to 10 for stroke in SLE patients, and 3.6 for cardiovascular deaths in RA patients. The main risk factors for atherosclerosis included not only the classic factors identified in epidemiological studies such as the Framingham study (advanced age, high cholesterol levels, hypertension, diabetes mellitus, and obesity), but also prolonged glucocorticoid therapy, long duration of SLE, postmenopausal status, and heart failure. SLE per se is an independent risk factor. The current pathogenic hypothesis for atherosclerosis involves an inflammatory response (erythrocyte sedimentation rate, C-reactive protein, and fibrin), autoantibodies, immune complexes (containing antibodies to phospholipids, to oxidized LDLs, and to endothelial cells), cytokine-producing activated T cells, and bacterial or viral infections responsible for an immune response against heat shock proteins (endogenous HSP60 and its equivalent, bacterial HSP65). Early risk factor intervention and effective control of inflammation should be incorporated into the management of connective tissue disease with the goal of protecting patients against atherosclerosis.

Atherosclerosis and autoimmunity

Novel risk factors for the progression of atherosclerosis such as C-reactive protein (CRP) and adhesion molecules have stimulated much recent interest in the role of inflammation in atherosclerotic disease. There is also evidence emerging that autoimmunity may have a role in the pathogenesis of atherosclerosis. In this article we explore the evidence for the role of autoimmunity in human atherosclerosis, both in the general population and in the context of the antiphospholipid syndrome. In particular we will focus on several autoantigens, review the evidence for their role in the process of atherosclerosis and the nature of the immune responses.

Coronary artery disease in systemic lupus erythematosus: A review of the literature

CONTEXT

Coronary artery occlusive disease is a common though underappreciated complication of systemic lupus erythematosus (SLE), typically a disease of young women. A case of a premenopausal patient with SLE and an acute myocardial infarction is presented, and the etiology and management of coronary artery disease in SLE reviewed.

OBJECTIVES

To review the incidence, risk factors, pathology and treatment of coronary artery disease in systemic lupus erythematosus.

DATA SOURCES

MEDLINE search of articles in English-language journals from 1980 to 2000. The index words "systemic lupus erythematosus" and the following co-indexing terms were used: "coronary artery disease," "atherosclerosis," "vasculitis," "anticardiolipin antibodies," "antiphospholipid syndrome." SELECTION SYNTHESIS AND ABSTRACTION: Papers identified were reviewed and abstracted by the authors with a presentation of a summary.

RESULTS

The prevalence of coronary artery disease among women with SLE between the ages of 35 and 44 years is at least 50-fold greater than among age-matched control subjects. Of these, coronary atherosclerosis accounts for the vast majority of cases; vasculitis of the coronary arteries and other causes generally believed to be more typical of SLE are comparatively rare.

CONCLUSIONS

The evidence suggests that SLE is a significant risk factor for coronary atherosclerosis independent of the classic risk factors of hypertension, tobacco use, and hyperlipidemia.

Anti-malondialdehyde antibodies in MRL+/+ mice treated with trichloroethene and dichloroacetyl chloride: possible role of lipid peroxidation in autoimmunity

Trichloroethene (TCE) and one of its metabolites dichloroacetyl chloride (DCAC) are known to induce/accelerate autoimmune (AI) response in MRL+/+ mice as evident from anti-nuclear, anti-ssDNA, anti-cardiolipin, and DCAC-specific antibodies in the serum (Khan et al., Toxicol. Appl. Pharmacol. 134, 155-160, 1995). In the present study, we measured anti-malondialdehyde antibodies (AMDA) in the serum of TCE- or DCAC-treated mice in order to understand the contribution of lipid peroxidation to this AI response. Female MRL+/+ mice (5 weeks old) received ip injections of 10 mmol/kg TCE or 0.2 mmol/kg of DCAC in corn oil (100 microl) every 4(th) day for 6 weeks, while controls received an equal volume of vehicle only, and AMDA was measured in the sera of these animals by an ELISA established in our laboratory. While TCE treatment caused only marginal induction of AMDA, DCAC treatment elicited a significant AMDA response. Furthermore, a time-response study of DCAC (0.2 mmol/kg, every 4(th) day, for 2, 4, 6, or 8 weeks) showed an induction of AMDA (3/4) after 4 weeks of treatment, which was even greater at both 6 and 8 weeks of DCAC treatment (5/5). These findings were further substantiated by the presence of AMDA in systemic lupus erythematosus-prone MRL-lpr/lpr mice as early as 6 weeks of age. Presence of AMDA, as observed in this study, not only indicates increased lipid peroxidation (oxidative stress), but also suggests a putative role of oxidative stress in inflammatory autoimmune diseases.

Update on antiphospholipid antibodies

The association of antibodies with an apparent specificity for anionic phospholipids with thrombosis, fetal loss, thrombocytopenia, and certain other clinical manifestations is now well-recognized as the antiphospholipid syndrome (APS). Recent advances in our understanding of the antibodies and antigens involved include discovery of the crystal structure of beta2-glycoprotein I, (beta2GPI), genetic studies of beta2GPI polymorphisms, and the development of anti-beta2GPI and antiprothrombin immunoassays as clinical laboratory tests. The identification of antigen-specific T cells in APS patients has stimulated interest in the role of the cellular immune response in the syndrome. Clinical research in APS will also benefit from the development of preliminary classification criteria.

Antiphospholipid syndrome: antibodies and antigens

Elucidation of the antibodies and antigens involved in the antiphospholipid syndrome has provided many new insights and research opportunities. The major autoantibodies associated with the syndrome and detected in clinical laboratory assays for antiphospholipid antibodies are directed against prothrombin and beta2-glycoprotein I beta2GPI), a phospholipid-binding plasma protein whose physiological function is unknown. Recent advances in our understanding of these antibodies and antigens include discovery of the crystal structure of beta2GPI, identification of a plasmin cleavage site in beta2GPI, genetic studies of beta2GPI polymorphisms, development of clinical laboratory assays using purified protein antigens, and the identification of antigen specific T cells.

Lipoprotein(a) oxidation and autoantibodies: a new path in atherothrombosis

Lipoprotein(a) (Lp(a)) is considered a vascular pathogen of outstanding importance. High plasma levels of this lipoprotein are associated with premature arterial disease; however, the mechanisms involved have not been clarified. The atherosclerotic process is increasingly regarded as a chronic inflammatory reaction in the arterial wall where oxidation-mediated endothelial injury involving modified forms of low-density lipoprotein (LDL) seems to be a key event. Autoimmune pathways are involved in the progression of atherosclerosis and humoral response to oxidatively modified LDL can be considered among these pathways. A number of factors can be encountered in the pathogenesis of the accelerated arterial disease seen in patients with antiphospholipid (Hughes) syndrome (APS) and systemic lupus erythematosus (SLE). Among these, high levels of Lp(a) have been described in both and increasing evidence indicates that patients with antiphospholipid antibodies (aPL) are under oxidative stress. Recent studies suggest that the so-called 'oxidation theory of atherosclerosis' may also be applied to Lp(a). This fact makes this lipoprotein potentially suitable as a target of the immune system and antibodies reacting against oxidatively-modified Lp(a) by malondialdehyde have been recently described in APS and SLE. It is therefore likely that an immune response to the oxidized moiety of Lp(a) might be influential in the pathogenicity of this lipoprotein and, subsequently, of atherosclerosis.