Intracellular trafficking of beta2-glycoprotein I complexes with lipid vesicles in macrophages: implications on the development of antiphospholipid syndrome

Interaction of antiphospholipid antibodies with endothelial cells in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune disease with arteriovenous thrombosis and recurrent miscarriages as the main clinical manifestations. Due to the complexity of its mechanisms and the diversity of its manifestations, its diagnosis and treatment remain challenging issues. Antiphospholipid antibodies (aPL) not only serve as crucial "biomarkers" in diagnosing APS but also act as the "culprits" of the disease. Endothelial cells (ECs), as one of the core target cells of aPL, bridge the gap between the molecular level of these antibodies and the tissue and organ level of pathological changes. A more in-depth exploration of the relationship between ECs and the pathogenesis of APS holds the potential for significant advancements in the precise diagnosis, classification, and therapy of APS. Many researchers have highlighted the vital involvement of ECs in APS and the underlying mechanisms governing their functionality. Through extensive in vitro and in vivo experiments, they have identified multiple aPL receptors on the EC membrane and various intracellular pathways. This article furnishes a comprehensive overview and summary of these receptors and signaling pathways, offering prospective targets for APS therapy.

Fatal attractions that trigger inflammation and drive atherosclerotic disease

BACKGROUND

Atherosclerosis is the salient, underlying cause of cardiovascular diseases, such as arrhythmia, coronary artery disease, cardiomyopathy, pulmonary embolism and myocardial infarction. In recent years, atherosclerosis pathophysiology has evolved from a lipid-based to an inflammation-centric ideology.

METHODS

This narrative review is comprised of review and original articles that were found through the PubMed search engine. The following search terms or amalgamation of terms were used: "cardiovascular disease," "atherosclerosis," "inflammation," "GRP78," "Hsp60," "oxidative low-density lipoproteins," "aldehyde dehydrogenase," "β2-glycoprotein," "lipoprotein lipase A," "human cytomegalovirus." "SARS-CoV-2," "chlamydia pneumonia," "autophagy," "thrombosis" and "therapeutics."

RESULTS

Emerging evidence supports the concept that atherosclerosis is associated with the interaction between cell surface expression of stress response chaperones, including GRP78 and Hsp60, and their respective autoantibodies. Moreover, various other autoantigens and their autoantibodies have displayed a compelling connection with the development of atherosclerosis, including oxidative low-density lipoproteins, aldehyde dehydrogenase, β2-glycoprotein and lipoprotein lipase A. Atherosclerosis progression is also concurrent with viral and bacterial activators of various diseases. This narrative review will focus on the contributions of human cytomegalovirus as well as SARS-CoV-2 and chlamydia pneumonia in atherosclerosis development. Notably, the interaction of an autoantigen with their respective autoantibodies or the presence of a foreign antigen can enhance inflammation development, which leads to atherosclerotic lesion progression.

CONCLUSION

We will highlight and discuss the complex role of the interaction between autoantigens and autoantibodies, and the presence of foreign antigens in the development of atherosclerotic lesions in relationship to pro-inflammatory responses.

Antioxidative attributes of rice bran extracts in ameliorative effects of atherosclerosis-associated risk factors

Oxidative stress, chronic inflammation, dyslipidemia, hyperglycemia, and shear stress (physical effect) are risk factors associated with the pathogenesis of atherosclerosis. Rice bran, a by-product of rice milling process, is known to house polyphenols and vitamins which exhibit potent antioxidant and anti-inflammatory properties. Through recent emerging knowledge of rice bran in health and wellness, the present study was aimed to assess the ameliorative effects of rice bran extracts (RBE) derived from Japanese colored rice varieties in modulating risk factors of atherosclerosis via in vitro and in vivo study models. Pre-treatment of lipopolysaccharide (LPS)-stimulated murine J774A.1 macrophage-like cells with RBE alleviated nitric oxide (NO) overproduction and downregulated gene expressions of pro-inflammatory modulators: tumor necrosis factor-α (TNF-α), interleukin (IL)-α (IL-1α), IL-1β, IL-6, and inducible nitric oxide synthase (iNOS). In addition, RBE also significantly attenuated LPS-stimulated protein expressions of iNOS, TNF-α, IL-1α, and IL-6 in J774A.1 macrophage-like cells as compared to non-treated LPS control group. In in vivo, 12 weeks of RBE dietary supplementations significantly reduced (p < 0.05) total cholesterol, triglycerides, and pro-atherogenic oxidized LDL/β2-glycoprotein I (oxLDL/β2GPI) complexes at plasma levels, in high fat diet (HFD) induced low density lipoprotein receptor knockout (Ldlr^−/-) mice. En face pathological assessments of murine aortas also revealed significant reductions by 38% (p < 0.05) in plaque sizes of RBE-supplemented HFD mice groups as compared to non RBE-supplemented HFD control mice group. Moreover, gene expressions of aortic (iNOS, TNF-α, IL-1β) and hepatic (TNF-α, IL-1α, IL-1β) pro-inflammatory modulators were also downregulated in RBE-supplemented mice groups. Present study has revealed the potent health attributes and application of RBE as a dietary supplement to attenuate risks of inadvertent oxidative damage and chronic inflammation underlying the pathogenesis of atherosclerosis. Intrinsically, present preliminary findings may provide global health prospects for future dietary implementation of RBE in management of atherosclerosis.

Identification and visualization of oxidized lipids in atherosclerotic plaques by microscopic imaging mass spectrometry-based metabolomics

BACKGROUND AND AIMS

Dysregulated lipid metabolism has emerged as one of the major risk factors of atherosclerosis. Presently, there is a consensus that oxidized LDL (oxLDL) promotes development of atherosclerosis and downstream chronic inflammatory responses. Due to the dynamic metabolic disposition of lipoprotein, conventional approach to purify bioactive lipids for subsequent comprehensive analysis has proven to be inadequate for elucidation of the oxidized lipids species accountable for pathophysiology of atherosclerotic lesions. Herein, we aimed to utilize a novel mass microscopic imaging technology, coupled with mass spectrometry (MS) to characterize oxidized lipids in atherosclerotic lesions.

METHODS

We attempted to use MALDI-TOF-MS and iMScope to identify selected oxidized lipid targets and visualize their respective localizations in study models of atherosclerosis.

RESULTS

Based on the MS analysis, detection of 7-K under positive ionization through product ion peak at m/z 383 [M + H-H₂O] indicated the distinctive presence of targeted lipid within Cu²⁺-oxLDL and Cu²⁺-oxLDL loaded macrophage-like J774A.1 cells, along with other cholesterol oxidation products. Moreover, the application of two-dimensional iMScope has successfully visualized the localization of lipids in aortic atherosclerotic plaques of the Watanabe heritable hyperlipidemic (WHHL) rabbit. Distinctive lipid distribution profiles were observed in atherosclerotic lesions of different sizes, especially the localizations of lysoPCs in atherosclerotic plaques.

CONCLUSIONS

Taken together, we believe that both MALDI-TOF-MS and iMScope metabolomics technology may offer a novel proposition for future pathophysiological studies of lipid metabolism in atherosclerosis.

Rapid and specific detection of oxidized LDL/β2GPI complexes via facile lateral flow immunoassay

β2-Glycoprotein I (β2GPI) forms indissociable complex with oxidized LDL (oxLDL) into proatherogenic oxLDL/β2GPI complex through a specific ligand known as 7-ketocholesteryl-9-carboxynonanoate (oxLig-1). Recent discoveries have demonstrated the atherogenicity of these complexes in patients of both systemic and non-systemic autoimmune diseases. Hence, serological level of oxLDL/β2GPI complexes may represent one crucial clinical parameter for disease prognosis of atherosclerosis-related diseases. Herein, we established a simple, specific and rapid gold nanoparticle (GNP) based lateral flow immunoassay (LFIA) to quantify oxLDL/β2GPI complexes from test samples. Specificities of hybridoma cell-derived monoclonal antibodies against antigen, optimal conditions for conjugation of antibody with GNP, and sensitivity of oxLDL/β2GPI LFIA in comparison to an ELISA-based detection method were assessed accordingly. The established oxLDL/β2GPI LFIA was capable of detecting oxLDL/β2GPI specifically without interference from autoantibodies and solitary components of oxLDL/β2GPI present in test samples. A significant correlation (R² > 0.8) was also obtained with the oxLDL/β2GPI LFIA when compared to the ELISA-based detection. On the whole, the oxLDL/β2GPI LFIA remains advantageous over the oxLDL/β2GPI ELISA. The unnecessary washing step, short developmental and analytical time support facile and rapid detection of oxLDL/β2GPI as opposed to the laborious ELISA system.

Antiphospholipid antibodies can specifically target placental mitochondria and induce ROS production

Women with antiphospholipid antibodies (aPL) have increased risks of pregnancy complications, including a ten-fold increased risk of preeclampsia, which is potentially triggered by the release of placental toxins. Previously, aPL were shown to enter the outer layer of the placenta, the syncytiotrophoblast, associate with mitochondria, and alter mitochondrial function. We hypothesised that aPL may also increase mitochondrial reactive oxygen species (ROS) production, leading to cellular dysfunction and release of toxins. First trimester placental explants were incubated with monoclonal aPL, ID2 and IIC5 (25, 50, and 100 μg/mL), for 3 h at 37 °C and ROS production followed using CellROX Deep Red. In addition, the candidate treatment compounds chloroquine, melatonin, and Mito-Q were tested at therapeutic concentrations for their ability to prevent ROS production. Mitochondria isolated from term placentae were incubated with fluorescently-labelled ID2, IIC5, or control IgG antibodies (2.5, 5, 10, or 20 μg/mL) for 30 min, and mitochondria with bound antibodies were quantified using flow cytometry. In addition, respirometry coupled with fluorimetry was used to interrogate explant mitochondrial respiration and ROS production following incubation with 25, 50, or 100 μg/mL ID2, IIC5, or control IgG for 3 h at 37 °C. ID2 increased explant ROS production in a manner that was completely prevented by the endocytosis inhibitor chloroquine, and partially prevented by the antioxidants melatonin and Mito-Q. Both ID2 and IIC5 displayed a greater ability to bind isolated mitochondria than control antibodies, and increased ROS production attributable to the mitochondrial enzyme glycerol 3-phosphate dehydrogenase (mGPDH). Our evidence supports the hypothesis that aPL interact with syncytiotrophoblast mitochondria, likely via the binding of cardiolipin and β₂ glycoprotein I in mitochondrial membranes, and induce ROS production which contributes to overall oxidative stress and placental dysfunction.

The role of beta-2-glycoprotein I in health and disease associating structure with function: More than just APS

Beta-2-Glycoprotein I (β2GPI) plays a number of essential roles throughout the body. β2GPI, C-reactive protein and thrombomodulin are the only three proteins that possess the dual capability to up and down regulate the complement and coagulation systems depending upon external stimulus. Clinically, β2GPI is the primary antigen in the autoimmune condition antiphospholipid syndrome (APS), which is typically characterised by pregnancy morbidity and vascular thrombosis. This protein is also capable of adopting at least two distinct structural forms, but it has been argued that several other intermediate forms may exist. Thus, β2GPI is a unique protein with a key role in haemostasis, homeostasis and immunity. In this review, we examine the genetics, structure and function of β2GPI in the body and how these factors may influence its contribution to disease pathogenesis. We also consider the clinical implications of β2GPI in the diagnosis of APS and as a potentially novel therapeutic target.

Elevated oxidized lipids, anti-lipid autoantibodies and oxidized lipid immune complexes in active SLE

BACKGROUND

Here, we explore the serum levels of anti-oxidized lipid autoantibodies as well as immune complexes in patients with SLE and determine their correlation with disease.

METHODS

Serum levels of oxidized-LDL immune complexes, autoantibodies to dsDNA, ox-LDL, MDA-LDL, 9-HODE, 13-HODE and POVPC were detected by ELISA in 64 SLE patients and 9 healthy controls.

RESULTS

Active SLE patients exhibited increased serum levels of autoantibodies compared to healthy controls, including anti-MDA-LDL-IgG (p = .003), anti-ox-LDL-IgG (p = .004), anti-9-HODE-IgG (p = .001), anti-13-HODE-IgG (p = .0003), anti-POVPC-IgG (p = .001) and ox-LDL-IC (p = .003). Serum anti-ox-LDL-IgG was positively correlated with SLEDAI (r = 0.34; p = .01), and negatively with C3 (r = -0.40; p = .01). Anti-9-HODE-IgG and anti-POVPC-IgG were positively correlated with SLEDAI and negatively with C4.

CONCLUSIONS

Active SLE patients exhibit significantly increased serum levels of IgG anti-oxidized-lipid autoantibodies. Coordinated elevation of oxidized lipids, autoantibodies to these lipids, and immune complexes of these lipid-antibody components could potentially serve as pathogenic drivers and serum markers of SLE disease activity.

Elevation of serum oxLDL/β2-GPI complexes was correlated with diabetic microvascular complications in Type 2 diabetes mellitus patients

BACKGROUND

High levels of oxLDL/β2-GPI complexes might be a consequence of LDL atherogenic modification mediated by oxidative stress. We aimed to determine whether the levels of serum oxLDL/β2-GPI complexes were correlated with diabetic microvascular complications in type 2 diabetes mellitus (T2DM) patients.

METHODS

Levels of oxLDL/β2-GPI complexes, oxLDL, routine lipid/lipoprotein parameters were measured in 100 healthy controls, 128 T2DM patients without any microvascular complications, and 172 T2DM patients with microvascular complications. Spearman's correlation, multivariable linear regression logistic regression analysis, and receiver operating characteristic (ROC) curve were performed.

RESULTS

Levels of serum oxLDL/β2-GPI complexes and oxLDL were significantly higher in T2DM patients with microvascular complications (oxLDL/β2-GPI complexes: 1.10 ± 0.18 U/mL; oxLDL: 48.12 ± 7.24 mmol/L) than those in T2DM patients without microvascular complications (oxLDL/β2-GPI complexes: 0.98 ± 0.16 U/mL; oxLDL: 41.45 ± 6.81 mmol/L) and controls (oxLDL/β2-GPI complexes: 0.79 ± 0.15 U/mL; oxLDL: 27.85 ± 5.32 mmol/L). Variables that remained significantly associated with oxLDL/β2-GPI complexes were oxLDL (β = 0.568, P < 0.001), TC (β = 0.312, P = 0.013) and microvascular complications (β = 0.205, P = 0.027), which accounted for 58.3% of the variation of the level of oxLDL/β2-GPI complexes in T2DM patients (R² = 0.583). Logistic regression analysis demonstrated that elevation of oxLDL/β2-GPI complexes (OR = 3.14, 95% CI: 1.04-9.46, P = 0.042) and oxLDL levels (OR = 3.02, 95% CI: 1.16-7.83, P = 0.023) were independently associated with occurrence of microvascular complications. Cutoff value of oxLDL/β2-GPI for the presence of microvascular complications was 1.05 U/mL, and AUC area of ROC curve was 0.783 (95%CI: 0.713-0.853), yielding a sensitivity of 86.8% and specificity of 64.9%.

CONCLUSIONS

Elevation of serum oxLDL/β2-GPI complexes was associated with microvascular complications in T2DM patients.

Serum oxLDL-β2GPI complex reflects metabolic syndrome and inflammation in adipose tissue in obese

BACKGROUND/OBJECTIVES

OxLDL-β2GPI complex has been suggested to have a role in the development of atherosclerosis and other inflammatory diseases. The aim of this study was to investigate the possible association of circulating oxLDL-β2GPI with obesity-induced inflammatory state of adipose tissue and related comorbidities as metabolic syndrome development.

SUBJECTS/METHODS

Two cohorts of subjects were examined in the study. Cohort I: 36 women with wide range of body mass index (17-48 kg m^-2) and metabolic status (with or without metabolic syndrome (MS); cohort II: 20 obese women undergoing a dietary intervention (DI) consisting of 1-month very-low-calorie diet, and 5 months of weight-stabilization period. Serum levels of oxLDL-β2GPI were measured by enzyme-linked immunosorbent assay. Insulin sensitivity was evaluated by hyperinsulinemic-euglycemic clamp and homeostasis model assessment of insulin resistance. mRNA expression of macrophage markers was determined in both subcutaneous (SAT) and visceral (VAT) adipose tissue in cohort I and in SAT in cohort II.

RESULTS

Serum oxLDL-β2GPI levels were increased in obese subjects with MS compared to lean or obese without MS (obese with MS: 26.6±5.0 vs lean: 15.17±1.97, P<0.001; vs obese without MS: 16.36±2.89, P<0.05). Serum oxLDL-β2GPI correlated with MS indices (glucose, high-density lipoprotein, triglyceride and ureic acid) and with mRNA expression of macrophage markers in VAT. Weight-reducing DI decreased serum oxLDL-β2GPI levels together with lipid parameters and the mRNA expression of inflammatory markers in SAT.

CONCLUSIONS

OxLDL-β2GPI seems to be an important marker of visceral adipose tissue inflammation and possibly a factor contributing to insulin resistance and metabolic syndrome development in obese patients.

Endosomal Redox Signaling in the Antiphospholipid Syndrome

PURPOSE OF REVIEW

It is well established that the antiphospholipid syndrome (APS) is caused by antiphospholipid antibodies (aPL). While several underlying mechanisms have been described in the past, many open questions remain. Here, we will review data on endosomal signaling and, in particular, redox signaling in APS.

RECENT FINDINGS

Endosomal redox signaling has been implicated in several cellular processes including signaling of proinflammatory cytokines. We have shown that certain aPL can activate endosomal NADPH-oxidase (NOX) in several cell types followed by induction of proinflammatory and procoagulant cellular responses in vitro. Involvement of endosomes in aPL signaling has also been reported by others. In wild-type mice but not in NOX-deficient mice, aPL accelerate venous thrombus formation underscoring the relevance of endosomal NOX. Furthermore, hydroxychloroquine (HCQ) inhibits activation of endosomal NOX and prevents thrombus formation in aPL-treated mice. Endosomal redox signaling is an important novel mechanism involved in APS pathogenesis. This makes endosomes a potential target for future treatment approaches of APS.

The role of iron in the pathogenesis of atherosclerosis

Ferritin and increased iron stores first appeared on the list of cardiovascular risk factors more than 30 years ago and their causal role in the pathogenesis of atherosclerosis has been heavily discussed since the early 1990s. It seems that besides traditional factors such as hyperlipoproteinemia, hypertension, diabetes mellitus, obesity, physical inactivity, smoking and family history, high iron stores represent an additional parameter that could modify individual cardiovascular risk. The role of iron in the pathogenesis of atherosclerosis was originally primarily associated with its ability to catalyze the formation of highly reactive free oxygen radicals and the oxidation of atherogenic lipoproteins. Later, it became clear that the mechanism is more complex. Atherosclerosis is a chronic fibroproliferative inflammatory process and iron, through increased oxidation stress as well as directly, can control both native and adaptive immune responses. Within the arterial wall, iron affects all of the cell types that participate in the atherosclerotic process (monocytes/macrophages, endothelial cells, vascular smooth muscle cells and platelets). Most intracellular iron is bound in ferritin, whereas redox-active iron forms labile iron pool. Pro-inflammatory and anti-inflammatory macrophages within arterial plaque differ with regard to the amount of intracellular iron and most probably with regard to their labile iron pool. Yet, the relation between plasma ferritin and intracellular labile iron pool has not been fully clarified. Data from population studies document that the consumption of meat and lack of physical activity contribute to increased iron stores. Patients with hereditary hemochromatosis, despite extreme iron storage, do not show increased manifestation of atherosclerosis probably due to the low expression of hepcidin in macrophages.

Immunity and early atherosclerosis in the course of systemic lupus erythematosus, mixed connective tissue disease and antiphospholipid syndrome

Atherosclerosis is a chronic inflammatory disease of the arteries associated with various risk factors that promote lipid abnormalities, development and progression of atherosclerotic lesions, plaque rupture, and vascular thrombosis. Atherosclerosis is accelerated in autoimmune diseases. Non-invasive investigations showed increased intima-media thickness (IMT), carotid plaque, and coronary artery calcifications in patients with antiphospholipid syndrome, systemic lupus erythematosus and mixed connective tissue disease compared to controls. The balance between the proinflammatory and anti-inflammatory cytokines allows the immune equilibrium to be maintained. In autoimmune diseases the prevalence of proinflammatory factors leads to premature atherosclerosis. This review presents complementary knowledge on innate and adaptive immunity, cytokines and the role of inflammasomes in progression of early atherosclerosis.

The Role of TLR4 on B Cell Activation and Anti-2GPI Antibody Production in the Antiphospholipid Syndrome

High titer of anti-β₂-glycoprotein I antibodies (anti-β₂GPI Ab) plays a pathogenic role in antiphospholipid syndrome (APS). Numerous studies have focused on the pathological mechanism in APS; however, little attention is paid to the immune mechanism of production of anti-β₂GPI antibodies in APS. Our previous study demonstrated that Toll-like receptor 4 (TLR4) plays a vital role in the maturation of bone marrow-derived dendritic cells (BMDCs) from the mice immunized with human β₂-glycoprotein I (β₂GPI). TLR4 is required for the activation of B cells and the production of autoantibody in mice treated with β₂GPI. However, TLR4 provides a third signal for B cell activation and then promotes B cells better receiving signals from both B cell antigen receptor (BCR) and CD40, thus promoting B cell activation, surface molecules expression, anti-β₂GPI Ab production, and cytokines secretion and making B cell functioning like an antigen presenting cell (APC). At the same time, TLR4 also promotes B cells producing antibodies by upregulating the expression of B-cell activating factor (BAFF). In this paper, we aim to review the functions of TLR4 in B cell immune response and antibody production in autoimmune disease APS and try to find a new way for the prevention and treatment of APS.

Role of apolipoprotein B100 and oxidized low-density lipoprotein in the monocyte tissue factor induction mediated by anti-β2 glycoprotein I antibodies

OBJECTIVE

The objective of this paper is to elucidate the not yet known plasma molecule candidates involved in the induction of tissue factor (TF) expression mediated by β2GPI-dependent anticardiolipin antibody (aCL/β2GPI) on monocytes.

METHODS

Human serum incubated with FLAG-β2GPI was applied for affinity chromatography with anti- FLAG antibody. Immunopurified proteins were analyzed by a liquid chromatography coupled with mass spectrometry (LC-MS). TF mRNA induced by the identified molecules on monocytes was also analyzed.

RESULTS

Apolipoprotein B100 (APOB) was the only identified serum molecule in the MS search. Oxidized LDL, containing APOB as well as ox-Lig1 (a known ligand of β2GPI), was revealed as a β2GPI-binding molecule in the immunoprecipitation assay. TF mRNA was markedly induced by oxidized LDL/β2GPI complexes with either WBCAL-1 (monoclonal aCL/β2GPI) or purified IgG from APS patients. The activities of lipoprotein-associated phospholipase A2, one of the component molecules of oxidized LDL, were significantly higher in serum from APS patients than in those from controls.

CONCLUSION

APOB (or oxidized LDL) was detected as a major β2GPI binding serum molecule by LC-MS search. Oxidized LDL/aCL/β2GPI complexes significantly induced TF expressions on monocytes. These data suggest that complexes of oxidized LDL and aCL/β2GPI may have a crucial role in the pathophysiology of APS.

Elevated beta2-glycoprotein I-low-density lipoprotein levels are associated with the presence of diabetic microvascular complications

AIMS

To investigate serum beta2-glycoprotein I-low-density lipoprotein (β2-GPI-LDL) and oxidized low-density lipoprotein (ox-LDL) levels in type 2 diabetes mellitus (T2DM) patients, and to further evaluate the associations of β2-GPI-LDL with ox-LDL in vivo and with the presence of diabetic microvascular complications.

METHODS

We determined β2-GPI-LDL, ox-LDL and small dense low density lipoprotein cholesterol (sdLDL-C) levels in 236 T2DM patients with or without microvascular complications and 75 controls. The correlation analyses, multiple linear regression analyses and logistic regression analyses were performed, respectively.

RESULTS

Compared with controls, β2-GPI-LDL and ox-LDL levels were significantly elevated in both groups of T2DM patients and those with microvascular complications exhibited the more significant increase than those without complications. Serum β2-GPI-LDL levels were positively correlated with ox-LDL as well as sdLDL-C levels in T2DM patients. Multiple linear regression analyses showed that ox-LDL was one of the independent determinants of β2-GPI-LDL levels. Logistic regression analyses indicated that elevated β2-GPI-LDL and ox-LDL levels had significant predictive values for diabetic microvascular complications.

CONCLUSIONS

Elevated serum β2-GPI-LDL levels may be a serological hallmark of enhanced LDL oxidation in vivo and closely associated with the presence of diabetic microvascular complications.

Fatty acid oxidation changes and the correlation with oxidative stress in different preeclampsia-like mouse models

Background

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) expression is decreased in placenta of some cases of preeclampsia (PE) which may result in free fatty acid (FFA) increased. High FFA level will induce oxidative stress, so abnormal long-chain fatty acid-oxidation may participate in the pathogenesis of PE through oxidative stress pathway.

Methods

PE-like groups were ApoC3 transgenic mice with abnormal fatty acid metabolism, classical PE-like models with injection of Nw-nitro-L-arginine-methyl ester (L-NA) or lipopolysaccharide (LPS) and the antiphospholipid syndrome (APS) mouse model with β2GPI injection (ApoC3+NS, ApoC3+L-NA, L-NA, LPS and β2GPI groups). The control group was wild-type mice with normal saline injection. Except for β2GPI mice, the other mice were subdivided into pre-implantation (Pre) and mid-pregnancy (Mid) subgroups by injection time.

Results

All PE-like groups showed hypertension and proteinuria except ApoC3+NS mice only showed hypertension. Serum FFA levels increased significantly except in LPS group compared to controls (P<0.05). LCHAD mRNA and protein expression in the liver and placenta was significantly higher for ApoC3+NS, ApoC3+L-NA and β2GPI mice and lower for L-NA mice than controls (P<0.05) but did not differ between LPS mice and controls. P47phox mRNA and protein expression in the liver significantly increased in all PE-like groups except LPS group, while P47phox expression in the placenta only significantly increased in L-NA and β2GPI groups.

Conclusions

Abnormal long-chain fatty acid-oxidation may play a different role in different PE-like models and in some cases participate in the pathogenesis of PE through oxidative stress pathway.

Involvement of TLR4 in oxidized LDL/β2GPI/anti-β2GPI-induced transformation of macrophages to foam cells

AIM

It has been reported that oxidized low-density lipoprotein (oxLDL) forms a stable and non-dissociable complex with β2-glycoprotein I (β2GPI) and that IgG anti-β2GPI autoantibodies are able to recognize this complex, thus facilitating macrophage-derived foam cell formation in patients with antiphospholipid syndrome (APS). However, the immunopathological mechanisms of oxLDL/β2GPI complexes in promoting foam cell formation are not fully understood. In this study, we examined the role of toll-like receptor 4 (TLR4) in the oxLDL/β2GPI/anti-β2GPI complex-induced transformation of mouse peritoneal macrophages to foam cells.

METHODS

Oil red O staining and optical density (OD) measurements of intracellular stained oil red O solution were used to monitor the transformation of peritoneal macrophages to foam cells in TLR4-competent C3H/HeN and TLR4-mutant C3H/HeJ mice. During foam cell formation induced by the oxLDL/β2GPI/anti-β2GPI complex, the expression of TLR4 and activation of nuclear factor kappa B (NF-κB) were confirmed by analyzing the protein and mRNA levels of these compounds. Furthermore, the related active molecule expression during foam cell formation induced by the oxLDL/β2GPI/anti-β2GPI complex was examined in the presence or absence of TLR4.

RESULTS

The data showed that treatment with the oxLDL/β2GPI/anti-β2GPI complex markedly increased foam cell formation, the TLR4 expression, NF-κB activation, the tissue factor (TF) expression and tumor necrosis factor-α (TNF-α) and monocyte chemotactic protein-1 (MCP-1) secretion in the C3H/HeN mice. However, the transformation of macrophages to foam cells and the expression levels of phosphorylated NF-κB, TF, TNF-α and MCP-1 were significantly reduced in the C3H/HeJ mice treated with the oxLDL/β2GPI/anti-β2GPI complex. In addition, compared with that achieved by oxLDL alone, the oxLDL/β2GPI complex decreased foam cell formation and the related signaling molecule expression in the C3H/HeN mice.

CONCLUSIONS

Our results indicate that TLR4 plays an important role in the process of oxLDL/β2GPI/anti-β2GPI complex-induced transformation of macrophages to foam cells, which may accelerate the development of atherosclerosis in the setting of APS. However, β2GPI alone functions as an antiatherogenic protein by preventing the foam cell formation induced by oxLDL.

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.

Antiphospholipid antibodies mediate autoimmunity against dying cells

The Antiphospholipid Syndrome (APS) is characterized by thrombosis and pregnancy loss, clinical events mediated by pathogenic anti-phospholipid autoantibodies (aPL). β2-glycoprotein I (β2GPI) is the major autoantigens recognized by aPL. β2GPI is a cationic protein that binds to negatively charged surfaces such as those of apoptotic cells. This feature may lead to two major events: i) immunization with β2GPI fosters the Fc-receptor-mediated uptake by antigen presenting cells of apoptotic material decorated with β2GPI and the activation of β2GPI-specific T cells which in turn provide help to β2GPI-specific B cells for the production of anti-β2GPI; ii) apoptotic bodies decorated with β2GPI can be opsonized by anti-β2GPI and shifted towards a pro-inflammatory clearance by macrophages; epitope spread can occur with the generation of autoimmunity against nuclear autoantigens. In the presence of a predisposing genetic background and of a particular cytokine environment (type I interferons), the sequential emergence of autoantibodies can evolve into overt clinical disease. The spectrum of clinical phenotypes of the patients can be modulated by several factors affecting the pathogenicity of anti-β2GPI (e.g. domain specificity). We conclude that dying cells may play a dual role in APS: (I) as immunogen for the induction of aPL (etiology) and (II) as targets of aPL for the chronification of inflammation and the development of autoimmune diseases (pathology).

Pathophysiological mechanisms in antiphospholipid syndrome

Antiphospholipid syndrome is a systemic autoimmune disease associated with thrombosis and recurrent fetal loss in the setting of detectable antiphospholipid (aPL) antibodies. The major antigenic target has been identifed as β₂-glycoprotein I (β₂GPI), which mediates binding of aPL antibodies to target cells including endothelial cells, monocytes, platelets and trophoblasts, leading to prothrombotic and proinfammatory changes that ultimately result in thrombosis and fetal loss. This article summarizes recent insights into the role of β₂GPI in normal hemostasis, interactions between aPL antibodies, β₂GPI and cell-surface molecules, molecular prothrombotic and proinfammatory changes induced by aPL antibodies and pathogenic changes leading to fetal loss in antiphospholipid syndrome. New directions in therapy using these insights are examined.

Toll-like receptor (TLR)-4 mediates anti-β2GPI/β2GPI-induced tissue factor expression in THP-1 cells

Our previous study demonstrated that annexin A2 (ANX2) on cell surface could function as a mediator and stimulate tissue factor (TF) expression of monocytes by anti-β₂-glycoprotein I/β₂-glycoprotein I complex (anti-β₂GPI/β₂GPI). However, ANX2 is not a transmembrane protein and lacks the intracellular signal transduction pathway. Growing evidence suggests that Toll-like receptor 4 (TLR-4) might act as an 'adaptor' for intracellular signal transduction in anti-β₂GPI/β₂GPI-induced TF expressing cells. In the current study, we investigated the roles of TLR-4 and its related molecules, myeloid differentiation protein 2 (MD-2) and myeloid differentiation factor 88 (MyD88), in anti-β₂GPI/β₂GPI-induced TF expressing human monocytic-derived THP-1 (human acute monocytic leukaemia) cells. The relationship of TLR-4 and ANX2 in this process was also explored. Along with TF, expression of TLR-4, MD-2 and MyD88 in THP-1 cells increased significantly when treated by anti-β₂GPI (10 µg/ml)/β₂GPI (100 µg/ml) complex. The addition of paclitaxel, which competes with the MD-2 ligand, could inhibit the effects of anti-β₂GPI/β₂GPI on TLR-4, MD-2, MyD88 and TF expression. Both ANX2 and TLR-4 in THP-1 cell lysates could bind to β₂GPI that had been conjugated to a column (β₂GPI-Affi-Gel). Furthermore, TLR-4, MD-2, MyD88 and TF expression was remarkably diminished in THP-1 cells infected with ANX2-specific RNA interference (RNAi) lentivirus (LV-RNAi-ANX2), in spite of treatment with a similar concentration of anti-β₂GPI/β₂GPI complex. These results indicate that TLR-4 and its signal transduction pathway contribute to anti-β₂GPI/β₂GPI-induced TF expression in THP-1 cells, and the effects of TLR-4 with ANX2 are tightly co-operative.

Differential trafficking of oxidized LDL and oxidized LDL immune complexes in macrophages: impact on oxidative stress

Background

Oxidized low-density lipoproteins (oxLDL) and oxLDL-containing immune complexes (oxLDL-IC) contribute to formation of lipid-laden macrophages (foam cells). It has been shown that oxLDL-IC are considerably more efficient than oxLDL in induction of foam cell formation, inflammatory cytokines secretion, and cell survival promotion. Whereas oxLDL is taken up by several scavenger receptors, oxLDL-IC are predominantly internalized through the FCγ receptor I (FCγ RI). This study examined differences in intracellular trafficking of lipid and apolipoprotein moieties of oxLDL and oxLDL-IC and the impact on oxidative stress.

Methodology/Findings

Fluorescently labeled lipid and protein moieties of oxLDL co-localized within endosomal and lysosomal compartments in U937 human monocytic cells. In contrast, the lipid moiety of oxLDL-IC was detected in the endosomal compartment, whereas its apolipoprotein moiety advanced to the lysosomal compartment. Cells treated with oxLDL-IC prior to oxLDL demonstrated co-localization of internalized lipid moieties from both oxLDL and oxLDL-IC in the endosomal compartment. This sequential treatment likely inhibited oxLDL lipid moieties from trafficking to the lysosomal compartment. In RAW 264.7 macrophages, oxLDL-IC but not oxLDL induced GFP-tagged heat shock protein 70 (HSP70) and HSP70B', which co-localized with the lipid moiety of oxLDL-IC in the endosomal compartment. This suggests that HSP70 family members might prevent the degradation of the internalized lipid moiety of oxLDL-IC by delaying its advancement to the lysosome. The data also showed that mitochondrial membrane potential was decreased and generation of reactive oxygen and nitrogen species was increased in U937 cell treated with oxLDL compared to oxLDL-IC.

Conclusions/Significance

Findings suggest that lipid and apolipoprotein moieties of oxLDL-IC traffic to separate cellular compartments, and that HSP70/70B' might sequester the lipid moiety of oxLDL-IC in the endosomal compartment. This mechanism could ultimately influence macrophage function and survival. Furthermore, oxLDL-IC might regulate the intracellular trafficking of free oxLDL possibly through the induction of HSP70/70B'.

Oxidized LDL induces in vitro lymphocyte activation in antiphospholipid syndrome

Oxidized low-density lipoprotein (oxLDL) is a key feature of the atheromatosus plaque and plays a critical role in foam cell formation and perpetuation of inflammatory processes. In antiphospholipid syndrome (APS), oxLDL molecules form complexes with beta2GPI and become target antigens for autoantibodies, which are detectable in the sera of these patients. oxLDL takes part in the pathogenesis of APS and in the concomitant accelerated atherosclerosis, yet the exact associated immune mechanisms are not clear in details. The aim of this study was to assess the activation and proliferation response of peripheral blood mononuclear cells (PBMCs) derived from patients with APS in the presence of oxLDL. Thirteen patients with APS and nine healthy individuals were enrolled in the study. Separated PBMCs of these patients were cultured in the presence of immunogenic epitope of oxLDL. Lymphocyte proliferation and cytokine secretion (TNF-alpha, IL-2, IFN-gamma, IL-4, and IL-10) were assessed by ELISA. We found significant PBMC proliferation in APS compared to healthy controls (PI/proliferation index/APS: 1.76 vs. PI control: 0.56; p = 0.032). A significant IL-2 and IFN-gamma secretion were detected upon oxLDL stimulus in patients with APS compared to controls (IL-2 cytokine secretion index (CSI) APS: 278.5, IL-2 CSI controls: 65.1; p = 0.025; IFN-gamma CSI APS: 163.2, IFN-gamma CSI controls: 77.4; p = 0.025). Based on our findings, we assume that oxLDL via Th1-type cytokine production and lymphocyte proliferation may contribute to the perpetuation of immune processes in APS.

Pathophysiology of β2-glycoprotein I in antiphospholipid syndrome

Since β2-glycoprotein I (β2GPI) was described as the major antigenic target for antiphospholipid antibodies, many studies have focused their attention to the physiological role of β2GPI and anti-β2GPI antibodies on autoimmune-mediated thrombosis. Studies reporting the physiological role of β2GPI have been numerous, but the exact mechanism of action(s) has yet to be completely determined. β2GPI’s epitopes for anti-β2GPI autoantibodies have been characterized, however, not all of the heterogeneous anti-β2GPI antibodies are pathogenic. The pathophysiologic role of β2GPI has been reported in the fields of coagulation, fibrinolysis, angiogenesis, and atherosclerosis. Our understanding of the impact of β2GPI, its metabolites and autoantibodies to β2GPI on these physiological functions may contribute to the development of better therapeutic strategies to treat and prevent autoimmune-mediated atherothrombotic vascular disease. Lupus (2010) 19, 379—384.

Autoimmunity, infectious immunity, and atherosclerosis

INTRODUCTION

Vascular inflammation is common in certain systemic autoimmune diseases and contributes to the oxidation of low-density lipoprotein (oxLDL) and oxLDL/beta2-glycoprotein I (beta2GPI) complex formation. These complexes have been implicated as proatherogenic autoantigens that participate in the development of atherosclerotic disease.

DISCUSSION

We have demonstrated that the in vitro macrophage uptake of oxLDL/beta2GPI complexes increases in the presence of IgG anti-beta2GPI antibodies and that IgG immune complexes containing oxLDL/beta2GPI upregulate the expression of both scavenger and Fcgamma receptors to activate beta2GPI specific T cells. Some persistent infections may cause immune responses that promote atherogenesis. Cellular immunity (Th1) against Helicobacter pylori (H. pylori) derived heat shock protein 60 (Hp-HSP60) cross-reacts with endogenous HSP60 to cause cardiovascular disease likely by molecular mimicry.

CONCLUSION

Infectious cellular response may be proatherogenic,while the humoral response (antibody production) maybe protective. We review the recent progress in our understanding of autoimmunity and infectious immunity that promote atherosclerosis.

T cells demonstrate a Th1-biased response to native beta2-glycoprotein I in a murine model of anti-phospholipid antibody induction

Anti-phospholipid syndrome (APS) is an autoimmune disorder characterized by the presence of autoantibody (AAb) to phospholipid (PL)-binding proteins, such as beta2-glycoprotein I (beta2GPI), and clinical manifestations including thrombosis and/or recurrent pregnancy loss. beta2GPI-reactive T cells are clearly implicated in the generation of these AAb, but the mechanism responsible for their activation remains unclear. We hypothesized that immunization of mice with human beta2GPI, in the context of a potent innate immune activator lipopolysaccharide (LPS), would generate not only high titers of anti-PL AAb, but also a strong beta2GPI-specific T cell response. Healthy, nonautoimmune C57BL/6 mice were immunized repeatedly with human beta2GPI in the presence of LPS. High titers of anti-PL to beta2GPI appeared after the second immunization, with T cell reactivity to beta2GPI detectable only after the fourth immunization. Splenic T cells from these mice proliferated in response to native beta2GPI, alone or bound to anionic PL. These T cells produced IL-2 and IFN-gamma, but not IL-4 or IL-10, indicating a Th1 bias of the beta2GPI-specific response. These findings suggest that T cells responsive to beta2GPI may become activated in APS patients by exposure to their cognate Ag in the context of innate immune activation and a pro-inflammatory environment.

Catastrophic antiphospholipid syndrome: treatment, prognosis, and the risk of relapse

The "catastrophic" variant of the antiphospholipid syndrome (APS) is characterized by multiple vascular occlusive events, usually affecting small vessels and developing over a short period of time. Although patients with catastrophic APS represent less than 1% of all patients with APS, they are usually in a life-threatening situation with a 50% mortality rate. The purpose of this paper is to review the treatment strategies and prognostic factors in patients with catastrophic APS. A detailed description of the clinical and laboratory features of the syndrome can be found in the other articles of this issue.

Atherosclerosis in autoimmune diseases

Lipid peroxidation occurs frequently in patients with systemic autoimmune diseases and contributes to autoimmune vascular inflammation. Oxidized low-density lipoprotein (oxLDL) interacts with beta2-glycoprotein I (beta2GPI), forming oxLDL/beta2GPI complexes. Circulating oxLDL/beta2GPI complexes and autoantibodies to these complexes have been demonstrated in patients with systemic lupus erythematosus and antiphospholipid syndrome. These findings suggest an immunogenic nature of the complexes and an active proatherogenic role in autoimmunity. Biochemical characterization of the complexes and immunohistochemical studies of atherosclerotic lesions suggest that most of the complexes originate in the arterial wall and are released into circulation. The in vitro macrophage uptake of oxLDL/beta2GPI complexes increased significantly in the presence of antiphospholipid antibodies (anti-beta2GPI), suggesting that macrophage Fcgamma receptors are involved in the lipid intracellular influx that leads to foam cell formation. These findings provide an immunologic explanation for the accelerated development of atherosclerosis seen in systemic lupus erythematosus and antiphospholipid syndrome.

Autoimmune-mediated atherothrombosis

Autoimmune vascular inflammation and oxidative stress (lipid peroxidation) are common in systemic autoimmune diseases and contribute to the oxidative modification of low-density lipoprotein (oxLDL) and oxLDL/beta2GPI complex formation. Circulating oxLDL/beta2GPI complexes have been detected in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS). The presence of antibodies to oxLDL/beta2GPI complexes indicates that these complexes are immunogenic, and the coexistence of complexes and antibodies has pointed to an active proatherogenic role in the development of autoimmune vascular complications. Immunohistochemical staining of atherosclerotic lesions suggest that these complexes are formed in the arterial wall and released into circulation. The in vitro macrophage uptake of oxLDL/beta2GPI complexes was significantly increased in the presence of antiphospholipid antibodies, either beta2GPI-dependent anticardiolipin or anti-beta2GPI antibodies, suggesting that macrophage Fcgamma receptors are involved in lipid intracellular influx and foam cell formation. These findings provide an explanation for the accelerated development of atherosclerosis seen in SLE and APS. The presence of circulating oxLDL/beta2GPI complexes and IgG antibodies to these complexes indicate significant vascular injury and oxidative stress as well as an active role in autoimmune-mediated atherothrombosis.

The physiopathology of the catastrophic antiphospholipid (Asherson's) syndrome: compelling evidence

Catastrophic antiphospholipid (Asherson's) syndrome (cAPS) was described in the past as a severe variant of the antiphospholipid syndrome (APS). Currently growing evidence suggests it is a unique condition. This statement is based on several clinical and physiopathological features that although not well understood define cAPS by itself. The remarkable features of cAPS are the presence of antiphospholipid antibodies (aPLAs) and microthromboses. Additional physiopathological features are the presence of anemia and thrombocytopenia, which are also often described in similar autoimmune conditions. A strong association with concomitant infection is thought to act as the main trigger of microthromboses in cAPS. Several theories have been proposed to explain these physiopathological features. Some of them suggest the possibility of molecular mimicry between components of infectious microorganisms and natural anticoagulants, which might be involved in the production of cross-reacting aPLAs in cAPS. Some genetic risk factors have also been suggested to be implicated in the onset of cAPS, however they have not been defined yet. Herein, we review the remarkable physiopathological features commonly described in cAPS hitherto. We concluded that although they are not completely understood, it is possible to differentiate them from similar conditions. Nevertheless further studies on these physiopathological mechanisms of the disease are needed.

Predictive, protective, orphan autoantibodies: the example of anti-phospholipid antibodies

Anti-phospholipid antibodies (aPL) are one of the most recent examples of autoantibodies that can appear even long time before any clinical manifestation can be associated with them. There is a general agreement that they may represent a strong risk factor for recurrent thrombosis and/or fetal losses. Anti-phospholipid antibodies represent a necessary but not sufficient factor (first hit) for thrombosis, and require additional triggering factors (second hit) to disclose the thrombogenic activity. Several factors may affect the predictive value of aPL, including titre, immunoglobulin isotype, fine antigenic specificity and affinity binding activity. Their careful evaluation is suggested in order to characterize the true predictive value of aPL.

Pathogenesis of the antiphospholipid syndrome: an additional example of the mosaic of autoimmunity

The antiphospholipid syndrome (APS) is a systemic autoimmune disease characterized by an adaptive immune response against self-PL-binding proteins ending in the production of specific autoantibodies. Antiphospholipid antibodies (aPL; and in particular anti-beta2 glycoprotein I antibodies) are formal diagnostic markers and pathogenic antibodies. Although APS may be considered as an autoantibody-mediated disease, there is now evidence that aPL are necessary but not sufficient to trigger some of the clinical manifestations of the syndrome. For example, additional factors, such as mediators of the innate immunity are now recognized to play a key role as second hits able to induce the thrombotic events in the presence of the autoantibodies. The APS scenario is also supplemented by the influence of genetically determined factors. Finally, environmental agents - in particular infectious ones - were reported to act as triggers for the production of autoantibodies cross-reacting with PL-binding proteins as well as inflammatory stimuli that potentiate the aPL thrombogenic effect. Altogether these findings do support the concept of a mosaic of factors that participate to the pathogenesis of the syndrome at different levels.

Autoantibody explosion in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thrombosis and pregnancy loss in the presence of antiphospholipid antibodies (aPL), mainly anticardiolipin, anti-beta2-glycoprotein I and lupus anticoagulant. However, similar to systemic lupus erythematosus, APS is also characterized by multiple other autoantibodies including 'non-classical' aPL, as well as other antibodies. Herein we describe the autoantigen properties, prevalence and clinical importance of 30 different antibodies in APS. Among the other antibodies characterizing APS are autoantibodies directed to platelets, glycoproteins, various coagulation factors, lamins, mitochondrial antigens and cell surface markers. Few of these autoantibodies are correlated with the presence of other antibodies, and some may have an additive role in the pro-thrombotic tendency of the syndrome. This autoantibody explosion might be important in early identification of the syndrome and its manifestations.