Effects of anti-cardiolipin antibodies and IVIg on annexin A5 binding to endothelial cells: implications for cardiovascular disease

Systemic lupus erythematosus and cardiovascular disease

The prognosis in systemic lupus erythematosus (SLE) has improved due to better treatment and care, but cardiovascular disease (CVD) still remains an important clinical problem, since the risk of CVD in SLE is much higher than among controls. Atherosclerosis is the main cause of CVD in the general population, and in SLE, increased atherosclerosis, especially the prevalence of atherosclerotic plaques, has been demonstrated. Atherosclerosis is an inflammatory condition, where immunity plays an important role. Interestingly, oxidized low-density lipoprotein, defective clearance of dead cells, and inflammation, with a pro-inflammatory T-cell profile are characteristics of both atherosclerosis and SLE. In addition to atherosclerosis as an underlying cause of CVD in SLE, there are also other non-mutually exclusive mechanisms, and the most important of these are antiphospholipid antibodies (aPL) leading to the antiphospholipid antibody syndrome with both arterial and venous thrombosis. aPL can cause direct pro-inflammatory and prothrombotic effects on endothelial and other cells and also interfere with the coagulation, for example, by inhibiting annexin A5 from its antithrombotic and protective effects. Antibodies against phosphorylcholine (anti-PC) and other small lipid-related epitopes, sometimes called natural antibodies, are negatively associated with CVD and atherosclerosis in SLE. Taken together, a combination of traditional risk factors such as hypertension and dyslipidemia, and nontraditional ones, especially aPL, inflammation, and low anti-PC are implicated in the increased risk of CVD in SLE. Close monitoring of both traditional risk factors and nontraditional ones, including treatment of disease manifestations, not lest renal disease in SLE, is warranted.

Low Levels of Antibodies Against Oxidized but not Nonoxidized Cardiolipin and Phosphatidylserine Are Associated with Atherosclerotic Plaques in Systemic Lupus Erythematosus

Objective.

We have reported that the prevalence of atherosclerotic plaques and their echolucency was increased in systemic lupus erythematosus (SLE). We here study antibodies against oxidized cardiolipin (anti-OxCL) and phosphatidylserine (anti-OxPS) in SLE and in relation to atherosclerosis measures.

Methods.

Patients with SLE (n = 114) were compared with age- and sex-matched population-based controls (n = 122). Common carotid intima-media thickness and plaque occurrence were determined by B-mode ultrasonography. Plaques were graded according to echogenicity as 1–4, with 1 being echolucent. Antibodies were determined by ELISA.

Results.

In the SLE group, the prevalence of low IgM anti-OxPS and low total IgM levels (below 33rd percentile) was increased compared to controls (p = 0.045 and p = 0.0079, respectively). Among SLE patients with atherosclerotic plaques, the prevalence of low IgM anti-OxPS (p = 0.0019) and anti-OxCL (p = 0.031) was increased. Only IgM anti-OxPS remained significant (p = 0.019) after adjusting for other significant factors. Echolucent plaques (total, or left side) were more prevalent among SLE patients with low IgM anti-OxCL and anti-OxPS when controlled for other significant factors (p < 0.05). Low total IgM was independently associated with echolucent plaque on left side (p < 0.05), but not other atherosclerosis measures. IgM anticardiolipin antibodies (aCL) and antiphosphatidylserine antibodies (anti-PS) were higher among SLE patients with cardiopulmonary disease, including arterial, valvular, and venous disease (p < 0.05). There were no associations between antibodies and other disease manifestations or activity. Both anti-OxCL and anti-OxPS, in contrast to aCL, and anti-PS, were cofactor−β2-glycoprotein I (β2-GPI)-independent.

Conclusion.

The prevalence of low levels of IgM anti-OxCL and anti-OxPS (both cofactor-β2-GPI-independent) is associated with the presence of plaques and echolucent plaques in SLE.

Auto-antibodies as emergent prognostic markers and possible mediators of ischemic cardiovascular diseases

During the last 15 years, a growing body of evidence supported the fact that auto-antibodies represent not only emergent markers but also active mediators of cardiovascular disease (CVD), clinically represented mostly by acute coronary syndrome (ACS) and stroke. There is a contrasted relationship between auto-antibodies and CVD, some being protective, while others acting as potential risk factors. Therefore, we performed a review of the literature on the respective cardiovascular prognostic value of the most relevant auto-antibodies in ACS and stroke, and their putative pathophysiological properties in atherogenesis. This review highlights auto-antibodies as active modulators of the innate immune system in atherogenesis (either toward a pro- or anti-inflammatory response), or by affecting basal heart rate regulation (anti-apoA-1 IgG). Given their apparent prognostic independency towards traditional cardiovascular risk factors, the data available in the literature indicates that some of those auto-antibodies could be of valuable help for cardiovascular risk stratification in the future, especially because their deleterious effects have been shown to be potentially abrogated in vivo and in vitro by existing therapeutic modalities. Although evidence in humans is currently lacking, these studies may open innovative therapeutic perspectives for CVD in the future.

Seronegative antiphospholipid syndrome

APS is an autoimmune disease that leads to arterial and/or venous thrombosis, recurrent pregnancy loss and persistently positive aPLs. Patients with clinical manifestations highly suggestive of APS but persistently negative conventional aPLs are classified as having seronegative APS. Ongoing research has revealed the existence of non-criteria antibodies proposed to be relevant to APS and that can be potentially included in the disease's classification criteria. We present a literature review on the most promising antibodies of this heterogeneous aPL family, which includes antibodies to a zwitterionic phospholipid, namely phosphatidylethanolamine, phospholipid-binding plasma proteins, phospholipid-protein complexes and anionic phospholipids other than cardiolipin. Although these molecules can increase the diagnostic yield of APS, their clinical relevance is still debatable and needs to be confirmed by interlaboratory efforts toward standardizing diagnostic tools, in addition to experimental data and larger longitudinal studies.

Annexin A5 inhibits atherogenic and pro-inflammatory effects of lysophosphatidylcholine

OBJECTIVE

Atherosclerosis is an inflammatory condition, and rupture of atherosclerotic plaques is a major cause of cardiovascular disease (CVD). Lysophosphatidylcholine (LPC) is generated in low-density lipoprotein (LDL) during oxidation and/or enzymatic modification and has been implicated in atherosclerosis. Annexin A5 (ANXA5) is an antithrombotic and atheroprotective plasma protein. Here, we demonstrate novel pro-inflammatory and atherogenic properties of LPC, and inhibitory effects of ANXA5.

METHODS

Endothelial cells and macrophages (differentiated from, THP-1 a monocytic cell line) were co-cultured. Expression of MMP-9 and OxLDL uptake by macrophages were studied by flow cytometry. The effect of LPC on leukotriene B4 (LTB4) synthesis in macrophages was studied by enzyme immunoassay (EIA). Chemotactic properties of LPC were investigated using a mouse intra-peritoneal recruitment model.

RESULTS

Co-culture of macrophages and endothelial cells enhanced MMP-9 expression in both cell types. This effect was increased by LPC and diminished by ANXA5. Likewise, LPC induced LTB4 production by macrophages, whereas native LDL or phosphatidylcholine (PTC) had no effect. ANXA5 inhibited uptake of OxLDL in macrophages. LPC induced cell infiltration in vivo, as determined by increased cell count in mouse peritoneal exudates, and this effect was inhibited by ANXA5.

CONCLUSIONS

ANXA5 could potentially play an important protective role in both atherogenesis and atherosclerotic plaque rupture by reducing pro-inflammatory effects of OxLDL and LPC as well as inhibiting OxLDL binding and uptake by macrophages. The possibility that ANXA5 could be developed into a novel therapy against CVD deserves further study.

Surface plasmon resonance shows a gender difference in circulating annexin A5 in human

The level of circulating anxA5 is correlated to various diseases such as acute myocardial infarction, trauma, thrombosis, inflammation and in some cancers. Our aim was to assess whether a direct approach using surface plasmon resonance (SPR) could be easily used to provide a rapid and cheap alternative to detect anxA5 in blood samples in human. Our results indicate that SPR permits to detect and quantify circulating anxA5 in serum with a minimum time of manipulation. Furthermore, we report here, for the first time, that the level of circulating anxA5 is significantly higher in male than in female (5.43 (± 0.02) and 4.41 (± 0.2)ng/ml, respectively). In conclusion, we found that SPR can be used to rapidly quantify anxA5 in patients and that a gender difference has to be taken into account to explain gender differences in the prevalence of some diseases.

Cardiovascular co-morbidity in patients with rheumatic diseases

During recent years atherosclerosis, the major cause of cardiovascular disease (CVD), has been recognised as a chronic inflammatory condition in which rupture of atherosclerotic lesions appears to play a major role. The risk of CVD is raised in many rheumatic diseases. This risk is high in systemic lupus erythematosus - as much as a 50-times increase among middle-aged women has been reported. Studies on CVD and atherosclerosis in rheumatic disease could thus provide interesting information about CVD and atherosclerosis in addition to being an important clinical problem. A combination of traditional and nontraditional risk factors accounts for the increased risk of CVD and atherosclerosis in rheumatic disease. One interesting possibility is that atherosclerotic lesions in rheumatic disease are more prone to rupture than normal atherosclerotic lesions. It is also likely that increased risk of thrombosis may play an important role, not least in systemic lupus erythematosus. Further, it is not clear whether an increased risk of CVD is a general feature of rheumatic disease, or whether this only occurs among subgroups of patients. It should be emphasised that there is an apparent lack of treatment studies where CVD in rheumatic disease is the end point. Control of disease activity and of traditional risk factors, however, appears to be well founded in relation to CVD in rheumatic disease. Further studies are needed to determine the exact role of lipid-lowering drugs as statins. Hopefully novel therapies can be developed that target the causes of the inflammation in atherosclerotic lesions both in rheumatic patients and in the general population.