Oxidized low-density lipoprotein and autoimmune antibodies in patients with antiphospholipid syndrome with a history of thrombosis

Limited Association between Antibodies to Oxidized Low-Density Lipoprotein and Vascular Affection in Patients with Established Systemic Lupus Erythematosus

Patients with systemic lupus erythematosus (SLE) are at an increased risk of cardiovascular disease. We aimed to evaluate whether antibodies to oxidized low-density lipoprotein (anti-oxLDL) were associated with subclinical atherosclerosis in patients with different SLE phenotypes (lupus nephritis, antiphospholipid syndrome, and skin and joint involvement). Anti-oxLDL was measured by enzyme-linked immunosorbent assay in 60 patients with SLE, 60 healthy controls (HCs) and 30 subjects with anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). Intima-media thickness (IMT) assessment of vessel walls and plaque occurrence were recorded using high-frequency ultrasound. In the SLE cohort, anti-oxLDL was again assessed in 57 of the 60 individuals approximately 3 years later. The levels of anti-oxLDL in the SLE group (median 5829 U/mL) were not significantly different from those in the HCs group (median 4568 U/mL), while patients with AAV showed significantly higher levels (median 7817 U/mL). The levels did not differ between the SLE subgroups. A significant correlation was found with IMT in the common femoral artery in the SLE cohort, but no association with plaque occurrence was observed. The levels of anti-oxLDL antibodies in the SLE group were significantly higher at inclusion compared to 3 years later (median 5707 versus 1503 U/mL, p < 0.0001). Overall, we found no convincing support for strong associations between vascular affection and anti-oxLDL antibodies in SLE.

Lipid Metabolism Profiles in Rheumatic Diseases

Rheumatic diseases are a group of chronic autoimmune disorders that involve multiple organs or systems and have high mortality. The mechanisms of these diseases are still ill-defined, and targeted therapeutic strategies are still challenging for physicians. Recent research indicates that cell metabolism plays important roles in the pathogenesis of rheumatic diseases. In this review, we mainly focus on lipid metabolism profiles (dyslipidaemia, fatty acid metabolism) and mechanisms in rheumatic diseases and discuss potential clinical applications based on lipid metabolism profiles.

Oxidized low-density lipoprotein in inflammation-driven thrombosis

Thrombosis is the defining feature of the most prevalent causes of cardiovascular mortality, such as myocardial infarction, stroke, and pulmonary artery embolism. Although platelet activation and activation of the plasmatic coagulation system are the hallmarks of thrombus formation, inflammatory processes and the cellular responses involved are increasingly being recognized as critical modulators of thrombosis. In the context of many chronic inflammatory diseases that are associated with a high thrombotic risk, oxidized lipoproteins represent a prominent sterile trigger of inflammation. Oxidized low-density lipoprotein and its components play a central role in the initiation and progression of atherosclerotic plaques, but also in other processes that lead to thrombotic events. Moreover, dying cells and microvesicles can be decorated with some of the same oxidized lipid components that are found on oxidized lipoproteins, and thereby similar mechanisms of thromboinflammation may also be active in venous thrombosis. In this review, we summarize the current knowledge on how oxidized lipoproteins and components thereof affect the cells and pathways involved in thrombosis.

Autoantibodies to posttranslational modifications in rheumatoid arthritis

Autoantibodies have been associated with human pathologies for a long time, particularly with autoimmune diseases (AIDs). Rheumatoid factor (RF) is known since the late 1930s to be associated with rheumatoid arthritis (RA). The discovery of anticitrullinated protein antibodies in the last century has changed this and other posttranslational modifications (PTM) relevant to RA have since been described. Such PTM introduce neoepitopes in proteins that can generate novel autoantibody specificities. The recent recognition of these novel specificities in RA provides a unique opportunity to understand human B-cell development in vivo. In this paper, we will review the three of the main classes of PTMs already associated with RA: citrullination, carbamylation, and oxidation. With the advancement of research methodologies it should be expected that other autoantibodies against PTM proteins could be discovered in patients with autoimmune diseases. Many of such autoantibodies may provide significant biomarker potential.

Immune response to lipoproteins in atherosclerosis

Atherosclerosis, the underlying cause of cardiovascular disease, is characterized by chronic inflammation and altered immune response. Cholesterol is a well-known risk factor associated with the development of cardiovascular diseases. Elevated serum cholesterol is unique because it can lead to development of atherosclerosis in animals and humans even in the absence of other risk factors. Modifications of low-density lipoproteins mediated by oxidation, enzymatic degradation, and aggregation result in changes in their function and activate both innate and adaptive immune system. Oxidized low-density lipoprotein (LDL) has been identified as one of the most important autoantigens in atherosclerosis. This escape from self-tolerance is dependent on the formation of oxidized phospholipids. The emerging understanding of the importance of immune responses against oxidized LDL in atherosclerosis has focused attention on the possibility of development of novel therapy for atherosclerosis. This review provides an overview of immune response to lipoproteins and the fascinating possibility of developing an immunomodulatory therapy for atherosclerosis.

Anti-apoA-1 IgG and oxidized LDL are raised in rheumatoid arthritis (RA): potential associations with cardiovascular disease and RA disease activity

OBJECTIVE

To determine whether emerging cardiovascular risk factors such as anti-apolipoprotein A-1 (anti-apoA-1) immunoglobulin (Ig)G and oxidized low density lipoprotein (oxLDL) are associated with cardiovascular disease (CVD), carotid intima-media thickness (IMT), and disease activity in rheumatoid arthritis (RA).

METHOD

We determined the aforementioned associations in 69 RA patients with disease duration of 5 years and 46 controls matched by age, sex, and smoking status. Anti-apoA-1 IgG and oxLDL were measured by enzyme-linked immunosorbent assay (ELISA). Carotid arteries were examined by ultrasound. Disease Activity Score calculated on 28 joints (DAS28) was used to assess disease activity.

RESULTS

CVD prevalence was higher among RA patients than controls (17% vs. 2%, p = 0.01) but there was no difference in IMT (median: 0.67 vs. 0.66, p = 0.33). RA patients had a higher anti-apoA-1 IgG prevalence than controls (20% vs. 0%, p = 0.001). Anti-apoA-1 IgG and oxLDL levels were higher in cases than controls [median: 0.33 vs. 0.175 optical density (OD), p = 0.03; and 121 vs. 37.2 U/L, p = 0.0001, respectively]. Anti-apoA-1 IgG-positive patients had higher levels of oxLDL (median: 140.5 vs. 112 U/L, p = 0.01) than those tested negative. Receiver operating characteristic (ROC) curve analysis showed that only anti-apoA-1 IgG was a modest but significant predictor of CVD [area under the curve (AUC) = 0.65, p = 0.03] in RA patients. oxLDL was significantly associated with RA disease activity, whereas anti-apoA-1 IgG was not.

CONCLUSIONS

Anti-apoA-1 IgG could be a marker of CVD in RA, whereas oxLDL levels seem to reflect RA disease activity. Other causes of CVD than a general increase in atherosclerosis (as determined by IMT measurements) including plaque stability may therefore be of importance to explain the increased incidence of CVD in RA.

The role of innate and adaptive immunity to oxidized low-density lipoprotein in the development of atherosclerosis

Atherosclerosis is a chronic inflammatory process of the arterial wall associated with systemic and local immune responses to various antigens, oxidized low-density lipoprotein (oxLDL) being the most significant. Both IgM and IgG antibodies to oxLDL are produced during atherosclerosis. Some studies have shown that elevated levels of antibody to oxLDL correlate with the degree of atherosclerosis. Other studies reported that immunization of experimental animals with oxLDL induces high levels of antibodies to oxLDL, with decreased atherosclerosis, suggesting that the immune response to oxLDL may be antiatherogenic. The accelerated development of atherosclerosis has been observed in patients with systemic autoimmune diseases. In patients with antiphospholipid syndrome (APS), beta2-glycoprotein I (beta2GPI) is a major antigenic target for anticardiolipin antibodies (aCLs). We recently reported that oxLDL interacts with beta2GPI via oxLDL-derived specific ligands, such as 7-ketocholesteryl-9-carboxynonanoate (oxLig-1) to form complexes. In vitro, anti-beta2GPI autoantibodies bind to oxLDL/beta2GPI complexes that are actively taken up by macrophages via Fcgamma receptors. Circulating oxLDL/beta2GPI complexes were detected in patients with systemic lupus erythematosus (SLE) and APS, at higher levels than in healthy individuals. Autoantibodies against these complexes were also present; however, IgG anti-oxLig-1/beta2GPI antibody levels in SLE patients with APS were significantly higher than those in SLE patients without APS and those in healthy individuals.

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.