Toll-like receptor and antiphospholipid mediated thrombosis: in vivo studies

Pregnancy in antiphospholipid syndrome: what should a rheumatologist know?

This review focuses on the management of reproductive issues in women who have antiphospholipid syndrome (APS) or are carriers of antiphospholipid antibodies (aPL). The importance of aPL detection during preconception counselling relies on their pathogenic potential for placental insufficiency and related obstetric complications. The risk of adverse pregnancy outcomes can be minimized by individualized risk stratification and tailored treatment aimed at preventing placental insufficiency. Combination therapy of low-dose acetylsalicylic acid and heparin is the mainstay of prophylaxis during pregnancy; immunomodulation, especially with hydroxychloroquine, should be considered in refractory cases. Supplementary ultrasound surveillance is useful to detect fetal growth restriction and correctly tailor the time of delivery. The individual aPL profile must be considered in the stratification of thrombotic risk, such as during assisted reproduction techniques requiring hormonal ovarian stimulation or during the follow-up after pregnancy in order to prevent the first vascular event.

Lipid-binding antiphospholipid antibodies: significance for pathophysiology and diagnosis of the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is an autoimmune disease characterized by the presence of pathogenic antiphospholipid antibodies (aPL). Since approximately 30 years ago, lipid-binding aPL, which do not require a protein cofactor, have been regarded as irrelevant for APS pathogenesis even though anticardiolipin are a diagnostic criterion of APS. In this review, we will summarize the available evidence from in vitro studies, animal models, and epidemiologic studies, which suggest that this concept is no longer tenable. Accordingly, we will only briefly touch on the role of other aPL in APS. This topic has been amply reviewed in detail elsewhere. We will discuss the consequences for laboratory diagnostics and future research required to resolve open questions related to the pathogenic role of different aPL specificities.

Natural supplements in antiphospholipid syndrome: A case for further study

Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by thrombotic events and/or pregnancy complications in the presence of persistently positive antiphospholipid antibodies (aPL). Although long-term anticoagulation with vitamin K antagonists is considered standard of care, there is an unmet need for safe therapeutics as primary thromboprophylaxis or adjuncts to standard of care in APS. APS is driven by oxidative stress, procoagulant, proinflammatory and angiogenic pathways. For these reasons there has been an increased interest into the investigation of antithrombotic, anti-inflammatory and anti-oxidant properties of natural supplements in APS. The objective of this review is to summarize the mechanistic, epidemiologic and clinical evidence behind the use of natural supplements in APS, with a specific focus on vitamin D, omega-3 fatty acids, coenzyme Q10, gingerol, and isoquercetin. This review should serve as a compelling argument for the future study of natural supplements in APS.

Low-grade endotoxemia and risk of recurrent thrombosis in primary antiphospholipid syndrome. The multicenter ATHERO-APS study

INTRODUCTION

Low-grade endotoxemia is associated with systemic inflammation, enhanced oxidative stress and cardiovascular events in different clinical settings, but its possible role as "second hit" in patients with primary antiphospholipid syndrome (PAPS) has never been investigated.

PURPOSE

To evaluate the relationship between plasma lipopolysaccharide (LPS) levels, oxidative stress markers and risk of thrombosis in the prospective multicenter ATHERO-APS study.

METHODS

Baseline LPS, soluble NADPH-oxidase 2-derived peptide (sNOX-dp), H2O2 production, hydrogen peroxide breakdown activity (HBA), and nitric oxide (NO) bioavailability were compared in 97 PAPS, 16 non-thrombotic aPL carriers and 21 controls (CTRL) matched for age and sex. Correlations among laboratory variables were explored by Rho Spearman's correlation (rS). Cox-regression analysis was performed to assess the association between LPS and risk for a composite outcome of cardiovascular death, venous and arterial thromboembolism.

RESULTS

In the whole cohort (median age 51 years (IQR 43-60), 72 % female), PAPS demonstrated higher levels of LPS, sNOX-dp and H2O2 and lower levels of NO and HBA compared to non-thrombotic aPL carriers and CTRL. LPS levels were inversely correlated with HBA (rS: -0.295, p = 0.001) and NO (rS: -0.322, p < 0.001) and directly correlated with sNOX-dp (rS:0.469, p < 0.001) and H202 (rS:0.282, p < 0.001). PAPS showed higher levels of LPS, sNOX-dp and H2O2 and lower levels of NO and HBA compared to aPL carriers and CTRL. After a 4.7 years follow-up of, 11 composite outcomes were reported in PAPS (2.5 per 100 patient-years) while none was observed in aPL carriers. On Cox-regression analysis, patients with LPS above the median (>23.1 pg/ml) had a 5-fold increased risk of composite outcome compared to those with LPS below the median, after adjustment for sex, age, diabetes, and global antiphospholipid syndrome score.

CONCLUSION

Low-grade endotoxemia is associated with an increased oxidative stress and a higher risk of thrombosis in PAPS. Its prognostic value in carriers needs to be investigated in larger cohorts.

An Emerging Role for Type I Interferons as Critical Regulators of Blood Coagulation

Type I interferons (IFNs) are central mediators of anti-viral and anti-bacterial host defence. Detection of microbes by innate immune cells via pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and cGAS-STING, induces the expression of type I IFN-stimulated genes. Primarily comprising the cytokines IFN-α and IFN-β, type I IFNs act via the type I IFN receptor in an autocrine or exocrine manner to orchestrate rapid and diverse innate immune responses. Growing evidence pinpoints type I IFN signalling as a fulcrum that not only induces blood coagulation as a core feature of the inflammatory response but is also activated by components of the coagulation cascade. In this review, we describe in detail recent studies identifying the type I IFN pathway as a modulator of vascular function and thrombosis. In addition, we profile discoveries showing that thrombin signalling via protease-activated receptors (PARs), which can synergize with TLRs, regulates the host response to infection via induction of type I IFN signalling. Thus, type I IFNs can have both protective (via maintenance of haemostasis) and pathological (facilitating thrombosis) effects on inflammation and coagulation signalling. These can manifest as an increased risk of thrombotic complications in infection and in type I interferonopathies such as systemic lupus erythematosus (SLE) and STING-associated vasculopathy with onset in infancy (SAVI). We also consider the effects on coagulation of recombinant type I IFN therapies in the clinic and discuss pharmacological regulation of type I IFN signalling as a potential mechanism by which aberrant coagulation and thrombosis may be treated therapeutically.

Genetic variation in toll-like receptor 4 gene with primary antiphospholipid syndrome susceptibility: a cohort of Egyptian patients

Background

As toll-like receptor 4 (TLR4) plays important roles in cellular immunity and TLR4 polymorphisms have been shown to be associated with susceptibility to a range of diseases, the present study aimed to investigate the association between TLR4 gene polymorphisms and the incidence of primary antiphospholipid syndrome (PAPS).

Methods

Two TLR4 single nucleotide polymorphisms (rs4986790 and rs4986791) were assessed in 110 subjects of Egyptian ethnicity, including 65 female patients with PAPS and 45 matched healthy controls, using polymerase chain reaction-restriction fragment length polymorphism. Results were verified using automated sequencing.

Results

The homozygous wild-type (AA, aspartic acid) rs4986790 variant and (CC, threonine) rs4986791 variant were the predominant genotypes in the control and PAPS groups.

Conclusion

The results of this preliminary study of TLR4 gene variants among patients with PAPS in an Egyptian population found no association between the rs4986790 and rs4986791 variants and susceptibility to PAPS.

Mechanisms of immunothrombosis and vasculopathy in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune thrombophilia propelled by circulating antiphospholipid antibodies that herald vascular thrombosis and obstetrical complications. Antiphospholipid antibodies recognize phospholipids and phospholipid-binding proteins and are not only markers of disease but also key drivers of APS pathophysiology. Thrombotic events in APS can be attributed to various conspirators including activated endothelial cells, platelets, and myeloid-lineage cells, as well as derangements in coagulation and fibrinolytic systems. Furthermore, recent work has especially highlighted the role of neutrophil extracellular traps (NETs) and the complement system in APS thrombosis. Beyond acute thrombosis, patients with APS can also develop an occlusive vasculopathy, a long-term consequence of APS characterized by cell proliferation and infiltration that progressively expands the intima and leads to organ damage. This review will highlight known pathogenic factors in APS and will also briefly discuss similarities between APS and the thrombophilic coagulopathy of COVID-19.

Therapeutic Potential and Immunomodulatory Role of Coenzyme Q10 and Its Analogues in Systemic Autoimmune Diseases

Coenzyme Q₁₀ (CoQ₁₀) is a mitochondrial electron carrier and a powerful lipophilic antioxidant located in membranes and plasma lipoproteins. CoQ₁₀ is endogenously synthesized and obtained from the diet, which has raised interest in its therapeutic potential against pathologies related to mitochondrial dysfunction and enhanced oxidative stress. Novel formulations of solubilized CoQ₁₀ and the stabilization of reduced CoQ₁₀ (ubiquinol) have improved its bioavailability and efficacy. Synthetic analogues with increased solubility, such as idebenone, or accumulated selectively in mitochondria, such as MitoQ, have also demonstrated promising properties. CoQ₁₀ has shown beneficial effects in autoimmune diseases. Leukocytes from antiphospholipid syndrome (APS) patients exhibit an oxidative perturbation closely related to the prothrombotic status. In vivo ubiquinol supplementation in APS modulated the overexpression of inflammatory and thrombotic risk-markers. Mitochondrial abnormalities also contribute to immune dysregulation and organ damage in systemic lupus erythematosus (SLE). Idebenone and MitoQ improved clinical and immunological features of lupus-like disease in mice. Clinical trials and experimental models have further demonstrated a therapeutic role for CoQ₁₀ in Rheumatoid Arthritis, multiple sclerosis and type 1 diabetes. This review summarizes the effects of CoQ₁₀ and its analogs in modulating processes involved in autoimmune disorders, highlighting the potential of these therapeutic approaches for patients with immune-mediated diseases.

B cells in primary antiphospholipid syndrome: Review and remaining challenges

It is now widely accepted that antiphospholipid antibodies (aPL) have direct pathogenic effects and that B cells, notably through aPL production, play a key role in the development of antiphospholipid syndrome (APS). Recent findings strengthened the implication of B cells with the description of specific B cell phenotype abnormalities and inborn errors of immunity involving B cell signaling in APS patients. In addition, it has been shown in preclinical models that cross-reactivity between APS autoantigens and mimotopes expressed by human gut commensals can lead to B cell tolerance breakdown and are sufficient for APS development. However, B cell targeting therapies are surprisingly not as effective as expected in APS compared to other autoimmune diseases. Elucidation of the B cell tolerance breakdown mechanisms in APS patients may help to develop and guide the use of novel therapeutic agents that target B cells or specific immune pathway.

OxLDL/β2GPI/anti‑β2GPI Ab complex induces inflammatory activation via the TLR4/NF‑κB pathway in HUVECs

Patients with antiphospholipid syndrome have been identified to have higher incidence rates of atherosclerosis (AS) due to the elevated levels of anti-β2-glycoprotein I (β2GPI) antibody (Ab). Our previous studies revealed that the anti-β2GPI Ab formed a stable oxidized low-density lipoprotein (oxLDL)/β2GPI/anti-β2GPI Ab complex, which accelerated AS development by promoting the accumulation of lipids in macrophages and vascular smooth muscle cell. However, the effects of the complex on endothelial cells, which drive the initiation and development of AS, remain unknown. Thus, the present study aimed to determine the proinflammatory roles of the oxLDL/β2GPI/anti-β2GPI Ab complex in human umbilical vein endothelial cells (HUVECs) in an attempt to determine the underlying mechanism. Reverse transcription-quantitative PCR, enzymy-linked immunosorbent assay, western blotting and immunofluorescence staining were performed to detect the expressions of inflammation related factors and adhesion molecules. Monocyte-binding assay was used to investigate the effects of oxLDL/β2GPI/anti-β2GPI Ab complex on monocyte adhesion to endothelial cells. The results demonstrated that the oxLDL/β2GPI/anti-β2GPI Ab complex upregulated the expression of Toll-like receptor (TLR)4 and the levels of NF-κB phosphorylation in HUVECs, and subsequently enhanced the expression levels of inflammatory cytokines, including TNF-α, IL-1β and IL-6, as well as those of adhesion molecules, such as intercellular adhesion molecule 1 and vascular adhesion molecule 1. In addition, the complex facilitated the recruitment of monocytes by promoting the secretion of monocyte chemotactic protein 1 in HUVECs. Notably, the described effects of the oxLDL/β2GPI/anti-β2GPI Ab complex in HUVECs were abolished by either TLR4 or NF-κB blockade. In conclusion, these findings suggested that the oxLDL/β2GPI/anti-β2GPI Ab complex may induce a hyper-inflammatory state in endothelial cells by promoting the secretion of proinflammatory cytokines and monocyte recruitment, which was discovered to be largely dependent on the TLR4/NK-κB signaling pathway.

Genetic Factors in Antiphospholipid Syndrome: Preliminary Experience with Whole Exome Sequencing

As in many autoimmune diseases, the pathogenesis of the antiphospholipid syndrome (APS) is the result of a complex interplay between predisposing genes and triggering environmental factors, leading to a loss of self-tolerance and immune-mediated tissue damage. While the first genetic studies in APS focused primarily on the human leukocytes antigen system (HLA) region, more recent data highlighted the role of other genes in APS susceptibility, including those involved in the immune response and in the hemostatic process. In order to join this intriguing debate, we analyzed the single-nucleotide polymorphisms (SNPs) derived from the whole exome sequencing (WES) of two siblings affected by APS and compared our findings with the available literature. We identified genes encoding proteins involved in the hemostatic process, the immune response, and the phospholipid metabolism (PLA2G6, HSPG2, BCL3, ZFAT, ATP2B2, CRTC3, and ADCY3) of potential interest when debating the pathogenesis of the syndrome. The study of the selected SNPs in a larger cohort of APS patients and the integration of WES results with the network-based approaches will help decipher the genetic risk factors involved in the diverse clinical features of APS.

NETs in APS: Current Knowledge and Future Perspectives

PURPOSE OF REVIEW

Antiphospholipid syndrome (APS) is a thrombo-inflammatory disease that is primarily treated with anticoagulation. Better understanding the inflammatory aspects of APS could lead to safer, more effective, and more personalized therapeutic options. To this end, we sought to understand recent literature related to the role of neutrophils and, in particular, neutrophil extracellular traps (NETs) in APS.

RECENT FINDINGS

Expression of genes associated with type I interferons, endothelial adhesion, and pregnancy regulation are increased in APS neutrophils. APS neutrophils have a reduced threshold for NET release, which likely potentiates thrombotic events and perhaps especially large-vein thrombosis. Neutrophil-derived reactive oxygen species also appear to play a role in APS pathogenesis. There are new approaches for preventing and disrupting NETs that could potentially be leveraged to reduce the risk of APS-associated thrombosis. Neutrophils and NETs contribute to APS pathophysiology. More precisely understanding their roles at a mechanistic level should help identify new therapeutic targets for inhibiting NET formation, enhancing NET dissolution, and altering neutrophil adhesion. Such approaches may ultimately lead to better clinical management of APS patients and thereby reduce the chronic burden of this disease.

The J-elongated conformation of β2-glycoprotein I predominates in solution: implications for our understanding of antiphospholipid syndrome

β₂-Glycoprotein I (β₂GPI) is an abundant plasma protein displaying phospholipid-binding properties. Because it binds phospholipids, it is a target of antiphospholipid antibodies (aPLs) in antiphospholipid syndrome (APS), a life-threatening autoimmune thrombotic disease. Indeed, aPLs prefer membrane-bound β₂GPI to that in solution. β₂GPI exists in two almost equally populated redox states: oxidized, in which all the disulfide bonds are formed, and reduced, in which one or more disulfide bonds are broken. Furthermore, β₂GPI can adopt multiple conformations (i.e. J-elongated, S-twisted, and O-circular). While strong evidence indicates that the J-form is the structure bound to aPLs, which conformation exists and predominates in solution remains controversial, and so is the conformational pathway leading to the bound state. Here, we report that human recombinant β₂GPI purified under native conditions is oxidized. Moreover, under physiological pH and salt concentrations, this oxidized form adopts a J-elongated, flexible conformation, not circular or twisted, in which the N-terminal domain I (DI) and the C-terminal domain V (DV) are exposed to the solvent. Consistent with this model, binding kinetics and mutagenesis experiments revealed that in solution the J-form interacts with negatively charged liposomes and with MBB2, a monoclonal anti-DI antibody that recapitulates most of the features of pathogenic aPLs. We conclude that the preferential binding of aPLs to phospholipid-bound β₂GPI arises from the ability of its preexisting J-form to accumulate on the membranes, thereby offering an ideal environment for aPL binding. We propose that targeting the J-form of β₂GPI provides a strategy to block pathogenic aPLs in APS.

Role of microRNAs in the Development of Cardiovascular Disease in Systemic Autoimmune Disorders

Rheumatoid Arthritis (RA), Systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) are the systemic autoimmune diseases (SADs) most associated with an increased risk of developing cardiovascular (CV) events. Cardiovascular disease (CVD) in SADs results from a complex interaction between traditional CV-risk factors, immune deregulation and disease activity. Oxidative stress, dyslipidemia, endothelial dysfunction, inflammatory/prothrombotic mediators (cytokines/chemokines, adipokines, proteases, adhesion-receptors, NETosis-derived-products, and intracellular-signaling molecules) have been implicated in these vascular pathologies. Genetic and genomic analyses further allowed the identification of signatures explaining the pro-atherothrombotic profiles in RA, SLE and APS. However, gene modulation has left significant gaps in our understanding of CV co-morbidities in SADs. MicroRNAs (miRNAs) are emerging as key post-transcriptional regulators of a suite of signaling pathways and pathophysiological effects. Abnormalities in high number of miRNA and their associated functions have been described in several SADs, suggesting their involvement in the development of atherosclerosis and thrombosis in the setting of RA, SLE and APS. This review focusses on recent insights into the potential role of miRNAs both, as clinical biomarkers of atherosclerosis and thrombosis in SADs, and as therapeutic targets in the regulation of the most influential processes that govern those disorders, highlighting the potential diagnostic and therapeutic properties of miRNAs in the management of CVD.

Increased Adhesive Potential of Antiphospholipid Syndrome Neutrophils Mediated by β2 Integrin Mac-1

OBJECTIVE

While the role of antiphospholipid antibodies in activating endothelial cells has been extensively studied, the impact of these antibodies on the adhesive potential of leukocytes has received less attention. This study was undertaken to investigate the extent to which antiphospholipid syndrome (APS) neutrophils adhere to resting endothelial cells under physiologic flow conditions and the surface molecules required for that adhesion.

METHODS

Patients with primary APS (n = 43), patients with a history of venous thrombosis but negative test results for antiphospholipid antibodies (n = 11), and healthy controls (n = 38) were studied. Cells were introduced into a flow chamber and perfused across resting human umbilical vein endothelial cells (HUVECs). Surface adhesion molecules were quantified by flow cytometry. Neutrophil extracellular trap release (NETosis) was assessed in neutrophil-HUVEC cocultures.

RESULTS

Upon perfusion of anticoagulated blood through the flow chamber, APS neutrophils demonstrated increased adhesion as compared to control neutrophils under conditions representative of either venous (n = 8; P < 0.05) or arterial (n = 15; P < 0.0001) flow. At the same time, APS neutrophils were characterized by up-regulation of CD64, CEACAM1, β2 -glycoprotein I, and activated Mac-1 on their surface (n = 12-18; P < 0.05 for all markers). Exposing control neutrophils to APS plasma or APS IgG resulted in increased neutrophil adhesion (n = 10-11; P < 0.0001) and surface marker up-regulation as compared to controls. A monoclonal antibody specific for activated Mac-1 reduced the adhesion of APS neutrophils in the flow-chamber assay (P < 0.01). The same monoclonal antibody reduced NETosis in neutrophil-HUVEC cocultures (P < 0.01).

CONCLUSION

APS neutrophils demonstrate increased adhesive potential, which is dependent upon the activated form of Mac-1. In patients, this could lower the threshold for neutrophil-endothelium interactions, NETosis, and possibly thrombotic events.

Genetics of Antiphospholipid Syndrome

PURPOSE OF REVIEW

Antiphospholipid syndrome (APS) is a rare heterogenous disorder associated with the presence of antiphospholipid antibodies and can present in a wide variety of clinical manifestations including thrombosis and pregnancy complications. Although the etiology of APS remains poorly understood, there is strong support for considering APS as a complex genetic disease in which multiple genetic risk factors, in conjunction with environmental factors, affect its onset, progression, and severity. Here, we provide a comprehensive review of the current knowledge of the genetic basis of APS, which remains in its infancy.

RECENT FINDINGS

Most genetic studies to date in APS were performed in small cohorts of patients. As a result, only few genetic associations reported are convincing. Several reports suggested genetic associations with HLA class II alleles in APS, and only two genetic loci outside of the HLA region (STAT4 and C1D) reached the threshold for genome-wide level of significance (P < 5 × 10^-8). In this review, we also shed light on the genetic differences among the diverse clinical subsets of APS and briefly discuss the role that DNA methylation changes might play in the pathophysiology of this disease. The genetic basis of APS remains poorly characterized. Larger collaborative multicenter studies using well-characterized patients are needed to comprehensively understand the role of genetic susceptibility in APS.

Mechanisms of Antiphospholipid Syndrome Induction: Role of NKT Cells

The review discusses the mechanisms of participation of natural killer T cells (NKT cells) in the induction of antiphospholipid antibodies (APA) that play a major pathogenetic role in the formation of antiphospholipid syndrome (APS), summarizes the data on APS pathogenesis, and presents modern concepts on the antibody formation involving follicular helper type II NK cells.

Amniotic fluid antiphospholipid antibodies: potential role in antiphospholipid syndrome-independent aberrant implantation process

BACKGROUND

The direct role of antiphospholipid antibodies (aPL) at maternal-fetal interface has not been fully investigated, especially whether they are involved in physiological and pathological implantation conditions, in an antiphospholipid syndrome (APS)-independent manner. In fact, trophoblast cells and placental endothelial cells at the implantation site express potential aPL targeted-phospholipid antigens (PL Ags); thus, the local production and presence of their specific antibodies, not related to APS (characterized by aPL presence in the peripheral blood), could be a potential marker of aberrant invasion, implantation and fetal-maternal immune tolerance processes.

METHODS

Anti-Beta₂glycoprotein I (anti-β₂GPI) and anticardiolipin (aCL Ab) antibodies (the most clinically relevant aPL) were detected by immunoenzymatic assay (ELISA), in the amniotic fluid (AF) of 167 women with physiological and complicated common pregnancy conditions, sharing an aberrant implantation process, such as recurrent pregnancy loss (RPL), autoimmune hypothyroidism (ahT) and smoking. All women included in the study were negative to peripheral blood aPL.

RESULTS

aCL and anti-β₂GPI antibodies were detectable in all the AF samples. RPL, ahT and smoking patients had higher level of anti-β₂GPI Abs (IgM) compared to women with physiological pregnancies (p < 0.0001). Since IgM cannot cross the placenta, their local production in response to maternal-fetal interface stimuli, could be hypothesized.

CONCLUSIONS

The presence of aPL in the AF (not related to APS) could reveal a potential clinical significance at maternal-fetal interface in selected pregnancy complications, in which an aberrant implantation process, and in turn an impaired fetal-maternal immune tolerance cross-talk, could occur.

New Biomarkers for Atherothrombosis in Antiphospholipid Syndrome: Genomics and Epigenetics Approaches

Antiphospholipid Syndrome (APS) is an autoimmune disorder, characterized by pregnancy morbidity and/or a hyper coagulable state involving the venous or the arterial vasculature and associated with antiphospholipid antibodies (aPL), including anti-cardiolipin antibodies (aCL), anti-beta2-glycoprotein I (anti-ß2GPI), and Lupus anticoagulant (LA). In recent years there have been many advances in the understanding of the molecular basis of vascular involvement in APS. APS is of multifactorial origin and develops in genetically predisposed individuals. The susceptibility is determined by major histocompatibility complex (MHC). Different HLA-DR and HLA-DQ alleles have been reported in association with APS. Moreover, MHC II alleles may determine the autoantibody profile and, as such, the clinical phenotype of this disease. Besides, polymorphisms in genes related to the vascular system are considered relevant factors predisposing to clinical manifestations. Antiphospholipid antibodies (aPL) induce genomic and epigenetic alterations that support a pro- thrombotic state. Thus, a specific gene profile has been identified in monocytes from APS patients -related to aPL titres in vivo and promoted in vitro by aPL- explaining their cardiovascular involvement. Regarding epigenetic approaches, we previously recognized two miRNAs (miR-19b/miR-20a) as potential modulators of tissue factor, the main receptor involved in thrombosis development in APS. aPLs can further promote changes in the expression of miRNA biogenesis proteins in leukocytes of APS patients, which are translated into an altered miRNA profile and, consequently, in the altered expression of their protein targets related to thrombosis and atherosclerosis. MicroRNAs are further released into the circulation, acting as intercellular communicators. Accordingly, a specific signature of circulating miRNAs has been recently identified in APS patients as potential biomarkers of clinical features. Genomics and epigenetic biomarkers might also serve as indices for disease progression, clinical pharmacology, or safety, so that they might be used to individually predict disease outcome and guide therapeutic decisions. In that way, in the setting of a clinical trial, novel and specific microRNA–mRNA regulatory networks in APS, modified by effect of Ubiquinol treatment, have been identified. In this review, current and previous studies analyzing genomic/epigenetic changes related to the clinical profile of APS patients, and their modulation by effect of specific therapies, are discussed.

Role of TLR‑4 in anti‑β2‑glycoprotein I‑induced activation of peritoneal macrophages and vascular endothelial cells in mice

Anti‑phospholipid syndrome (APS) is a systematic autoimmune disease that is associated with presence of antiphospholipid antibodies (aPL), recurrent thrombosis, and fetal morbidity in pregnancy. Toll‑like receptor‑4 (TLR‑4), a member of TLR family, is known to have a fundamental role in pathogen recognition and activation of innate immunity. The β2‑glycoprotein I (β2GPI), a protein circulating in the blood at a high concentration, is able of scavenging lipopolysaccharide (LPS) and clear unwanted anionic cellular remnants, such as microparticles, from the circulation. Our previous study demonstrated that TLR‑4 and its signaling pathways contribute to the upregulation of pro‑coagulant factors and pro‑inflammatory cytokines in monocytes induced by anti‑β2GPI in vitro. The present study aimed to define the roles of TLR‑4 in vivo. C3H/HeN mice (TLR‑4 intact) and C3H/HeJ mice (TLR‑4 defective) were stimulated with an intraperitoneal injection with anti‑β2GPI‑immunoglobulin G(IgG), then peritoneal macrophages and vascular endothelial cells (VECs) were extracted from treated mice, and analyses were conducted on the expression profiles of pro‑inflammatory cytokines and adhesion molecules. The results demonstrated that the expression of pro‑inflammatory cytokines, including tumor necrosis factor‑α (TNF‑α), interleukin (IL)‑1β and IL‑6, in the peritoneal macrophages, and adhesion molecules, including intercellular cell adhesion molecule‑1 (ICAM‑1), vascular cell adhesion molecule‑1 (VCAM‑1) and E‑selectin, in VECs of C3H/HeN mice (TLR‑4 intact) were significantly higher than those of C3H/HeJ mice (TLR‑4 defective). The phosphorylation levels of p38 mitogen‑activated protein kinase (MAPK) and nuclear factor‑κB (NF‑κB) p65 in peritoneal macrophages and VECs from C3H/HeN mice stimulated with anti‑β2GPI‑IgG were significantly increased compared with those from C3H/HeJ mice (TLR‑4 defective). The isotype control antibody (NR‑IgG) had no such effects on peritoneal macrophages and VECs. Furthermore, the inhibitors of TLR‑4, p38 MAPK and NF‑κB may significantly reduce the anti‑β2GPI‑IgG‑induced TNF‑α, IL‑1β and IL‑6 mRNAs expression in the peritoneal macrophages from TLR‑4 intact mice. The results indicated that a TLR‑4 signal transduction pathway is involved in anti‑β2GPI‑IgG‑induced activation of peritoneal macrophages and VECs. This study has provided a basis for subsequent investigations to elucidate the pathological mechanisms underlying anti‑phospholipid syndrome.

Antiphospholipid Antibodies Overlapping in Isolated Neurological Syndrome and Multiple Sclerosis: Neurobiological Insights and Diagnostic Challenges

Antiphospholipid syndrome (APS) is characterized by arterial and venous thrombosis, pregnancy morbidity and fetal loss caused by pathogenic autoantibodies directed against phospholipids (PL) and PL-cofactors. Isolated neurological APS may represent a significant diagnostic challenge, as epidemiological, clinical and neuroimaging features may overlap with those of multiple sclerosis (MS). In an open view, MS could be considered as an organ-specific anti-lipid (phospholipid and glycosphingolipid associated proteins) disease, in which autoreactive B cells and CD8+ T cells play a dominant role in its pathophysiology. In MS, diverse autoantibodies against the lipid-protein cofactors of the myelin sheath have been described, whose pathophysiologic role has not been fully elucidated. We carried out a review to select clinical studies addressing the prevalence of antiphospholipid (aPL) autoantibodies in the so-called MS-like syndrome. The reported prevalence ranged between 2% and 88%, particularly aCL and aβ2GPI, with predominant IgM isotype and suggesting worse MS prognosis. Secondarily, an updated summary of current knowledge on the pathophysiological mechanisms and events responsible for these conditions is presented. We draw attention to the clinical relevance of diagnosing isolated neurological APS. Prompt and accurate diagnosis and antiaggregant and anticoagulant treatment of APS could be vital to prevent or at least reduce APS-related morbidity and mortality.

Elevated plasma level of soluble triggering receptor expressed on myeloid cells-1 is associated with inflammation activity and is a potential biomarker of thrombosis in primary antiphospholipid syndrome

Background

Soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) is an innate-immune receptor found in blood. Its presence reflects innate immune cell activation. We sought to investigate plasma sTREM-1 levels in patients with primary antiphospholipid syndrome (PAPS).

Methods

A cross-sectional, case-control design was used. Plasma sTREM-1 levels were analyzed by enzyme-linked immunosorbent assay (ELISA) in consecutive patients diagnosed with PAPS or asymptomatic antiphospholipid antibody (APLA) carriers and controls.

Results

The study cohort included 33 patients with PAPS, 10 asymptomatic APLA carriers, and 73 controls. Mean plasma sTREM-1 levels were significantly higher in patients with PAPS (299.2 ± 146.7 pg/ml) and thrombotic PAPS-ever (current and past thrombotic event) (327.2 ± 151.3 pg/ml) compared with controls (230.2 ± 85.5 pg/ml; p = 0.006 and p = 0.003, respectively), patients with thrombotic PAPS compared with patients with past obstetric APS (195.12 ± 58.52 pg/ml, p = 0.01) and APLA carriers (215.8 ± 51.6 pg/ml, p = 0.02), patients with current thrombotic PAPS (429.5 ± 227.5 pg/ml) compared with patients with past thrombotic PAPS (289.5 ± 94.65 pg/ml, p = 0.01), and patients with PAPS who had ever had a stroke or venous thromboembolic event compared with patients who had not (p = 0.007 and p = 0.02, respectively). On receiver operator characteristic curve analysis, plasma sTREM-1 levels differentiated patients with current thrombotic PAPS from asymptomatic APLA carriers and controls, with an area under the curve of 0.7292 (p = 0.0014) and 0.88 (p < 0.0001), respectively. Multivariate regression analysis to identify sTREM-1 predictors (thrombotic PAPS-ever, age, and sex) yielded an independent association of sTREM-1 levels with thrombotic PAPS (p < 0.0001).

Conclusions

Plasma sTREM-1 levels are significantly elevated in patients with thrombotic PAPS. Levels of sTREM-1 might serve as a biomarker for thrombosis in patients with PAPS.

New insight into antiphospholipid syndrome: antibodies to β2glycoprotein I-domain 5 fail to induce thrombi in rats

Clinical studies have reported different diagnostic/predictive values of antibodies to domain 1 or 4/5 of β₂glycoproteinI in terms of risk of thrombosis and pregnancy complications in patients with antiphospholipid syndrome. To obtain direct evidence for the pathogenic role of anti-domain 1 or anti-domain 4/5 antibodies, we analyzed the in vivo pro-coagulant effect of two groups of 5 sera IgG each reacting selectively with domain 1 or domain 5 in lipopolysaccharide (LPS)-treated rats. Antibody-induced thrombus formation in mesenteric vessels was followed by intravital microscopy, and vascular deposition of β₂glycoproteinI, human IgG and C3 was analyzed by immunofluorescence. Five serum IgG with undetectable anti-β₂glycoproteinI antibodies served as controls. All the anti-domain 1-positive IgG exhibited potent pro-coagulant activity while the anti-domain 5-positive and the negative control IgG failed to promote blood clot and vessel occlusion. A stronger granular deposit of IgG/C3 was found on the mesenteric endothelium of rats treated with anti-domain 1 antibodies, as opposed to a mild linear IgG staining and absence of C3 observed in rats receiving anti-domain 5 antibodies. Purified anti-domain 5 IgG, unlike anti-domain 1 IgG, did not recognize cardiolipin-bound β₂glycoproteinI while being able to interact with fluid-phase β₂glycoproteinI. These findings may explain the failure of anti-domain 5 antibodies to exhibit a thrombogenic effect in vivo, and the interaction of these antibodies with circulating β₂glycoproteinI suggests their potential competitive role with the pro-coagulant activity of anti-domain 1 antibodies. These data aim at better defining “really at risk” patients for more appropriate treatments to avoid recurrences and disability.

Insights into the diagnosis and pathogenesis of the antiphospholipid syndrome

The Antiphospholipid syndrome (APS), formerly known as Anticardiolipin or Hughes syndrome, is a systemic autoimmune disorder characterized by obstetrical complications and thrombotic events affecting almost every organ-system in patients persistently testing positive for antiphospholipid antibodies (aPL). The contribution of the extra-criteria aPL to the pathogenesis of APS have exceeded the expectations of a simple, direct pathologic 'hit' leading to thrombogenesis or obstetrical complications, and more pathologic pathways are being linked directly or indirectly to aPL. The value of extra-criteria aPL is on the rise, and these antibodies are nowadays evaluated as markers for risk assessment in the diagnostic approach to APS. A diagnosis of APS should be considered in pediatric patients with suggestive clinical and laboratory picture. Management of APS remains mostly based on anticoagulation, while other drugs are being tested for efficacy and side effects. Low-dose aspirin may have a role in the management of thrombotic and obstetric APS. Due to the high variability in disease severity and complication recurrence outcomes, new tools are being developed and validated to assess the damage index and quality of life of APS patients.

Obstetric Anti-phospholipid Syndrome: State of the Art

PURPOSE OF REVIEW

This review focuses on new pathogenesis and clinical-therapeutic aspects of obstetric anti-phospholipid syndrome (ob-APS) in the last 5 years.

RECENT FINDINGS

The pathogenesis of ob-APS is multifactorial, including placental infarctions, infiltration of inflammatory cells that cause acute and chronic inflammation, leading to uncontrolled inflammation and poor pregnancy outcomes. A preconception counseling and a patient-tailored treatment are fundamental to improve maternal and fetal outcomes. Thanks to conventional treatment, based on low-dose aspirin and heparin, 70% of women with ob-APS can have successful pregnancies. Women with positive anti-phospholipid antibodies (aPL) without clinical manifestations ("aPL carriers") or with obstetric manifestation not fulfilling ob-APS criteria need to be further investigated in order to assess their best management. Great interest has been given to drugs that could interact in the pathophysiological mechanisms, such as hydroxychloroquine, statins, and eculizumab. These drugs could be considered for patients refractory to conventional therapy.

Clinical Risk Assessment in the Antiphospholipid Syndrome: Current Landscape and Emerging Biomarkers

PURPOSE OF REVIEW

Laboratory criteria for the classification of antiphospholipid syndrome include the detection of a lupus anticoagulant and/or anticardiolipin and anti-β2-glycoprotein I antibodies. However, the majority of patients who test positive in these assays do not have thrombosis. Current risk-stratification tools are largely limited to the antiphospholipid antibody profile and traditional thrombotic risk factors.

RECENT FINDINGS

Novel biomarkers that correlate with disease activity and potentially provide insight into future clinical events include domain 1 specific anti-β₂GPI antibodies, antibodies to other phospholipids or phospholipid/protein antigens (such as anti-PS/PT), and functional/biological assays such as thrombin generation, complement activation, levels of circulating microparticles, and annexin A5 resistance. Clinical risk scores may also have value in predicting clinical events. Biomarkers that predict thrombosis risk in patients with antiphospholipid antibodies have been long sought, and several biomarkers have been proposed. Ultimately, integration of biomarkers with established assays and clinical characteristics may offer the best chance of identifying patients at highest risk of APS-related complications.

Antiphospholipid syndrome: an update for clinicians and scientists

PURPOSE OF REVIEW

Antiphospholipid syndrome (APS) is a leading acquired cause of thrombosis and pregnancy loss. Upon diagnosis (which is unlikely to be made until at least one morbid event has occurred), anticoagulant medications are typically prescribed in an attempt to prevent future events. This approach is not uniformly effective and does not prevent associated autoimmune and inflammatory complications. The goal of this review is to update clinicians and scientists on mechanistic and clinically relevant studies from the past 18 months, which have especially focused on inflammatory aspects of APS pathophysiology.

RECENT FINDINGS

How antiphospholipid antibodies leverage receptors and signaling pathways to activate cells is being increasingly defined. Although established mediators of disease pathogenesis (like endothelial cells and the complement system) continue to receive intensive study, emerging concepts (such as the role of neutrophils) are also receiving increasing attention. In-vivo animal studies and small clinical trials are demonstrating how repurposed medications (hydroxychloroquine, statins, and rivaroxaban) may have clinical benefit in APS, with these concepts importantly supported by mechanistic data.

SUMMARY

As anticoagulant medications are not uniformly effective and do not comprehensively target the underlying pathophysiology of APS, there is a continued need to reveal the inflammatory aspects of APS, which may be modulated by novel and repurposed therapies.

Low molecular weight heparin and aspirin exacerbate human endometrial endothelial cell responses to antiphospholipid antibodies

PROBLEM

Women with antiphospholipid antibodies (aPL) are at risk for pregnancy complications despite treatment with low molecular weight heparin (LMWH) or aspirin (ASA). aPL recognizing beta2 glycoprotein I can target the uterine endothelium, however, little is known about its response to aPL. This study characterized the effect of aPL on human endometrial endothelial cells (HEECs), and the influence of LMWH and ASA.

METHOD OF STUDY

HEECs were exposed to aPL or control IgG, with or without low-dose LMWH and ASA, alone or in combination. Chemokine and angiogenic factor secretion were measured by ELISA. A tube formation assay was used to measure angiogenesis.

RESULTS

aPL increased HEEC secretion of pro-angiogenic VEGF and PlGF; increased anti-angiogenic sFlt-1; inhibited basal secretion of the chemokines MCP-1, G-CSF, and GRO-α; and impaired angiogenesis. LMWH and ASA, alone and in combination, exacerbated the aPL-induced changes in the HEEC angiogenic factor and chemokine profile. There was no reversal of the aPL inhibition of HEEC angiogenesis by either single or combination therapy.

CONCLUSION

By aPL inhibiting HEEC chemokine secretion and promoting sFlt-1 release, the uterine endothelium may contribute to impaired placentation and vascular transformation. LMWH and ASA may further contribute to endothelium dysfunction in women with obstetric APS.

Mechanisms of thrombosis in systemic lupus erythematosus and antiphospholipid syndrome

The presence of antiphospholipid antibodies is one of the most common acquired risk factors for thrombosis. Antiphospholipid antibodies is a collective term for a set of autoantibodies with closely related but different specificity. Experiments in which isolated patient antibodies were injected into mice have shown that a specific subset of autoantibodies, those directed against the first domain of plasma protein β₂-glycoprotein I, can explain the increased risk of thrombosis. Experiments performed with these mice have shown that autoantibodies against β₂-glycoprotein I bind to and activate cells such as endothelial cells, monocytes, and platelets. Activation of these cells, all involved in the regulation of hemostasis, results in a shift towards a prothrombotic state. How this process is regulated, whether this is the only mechanism involved, and whether this is the only subpopulation responsible for the increased thrombotic risk is unknown. In this review, we will critically discuss what is known and what is debatable on the pathophysiology of antiphospholipid syndrome.

Activated signature of antiphospholipid syndrome neutrophils reveals potential therapeutic target

Antiphospholipid antibodies, present in one-third of lupus patients, increase the risk of thrombosis. We recently reported a key role for neutrophils - neutrophil extracellular traps (NETs), in particular - in the thrombotic events that define antiphospholipid syndrome (APS). To further elucidate the role of neutrophils in APS, we performed a comprehensive transcriptome analysis of neutrophils isolated from patients with primary APS. Moreover, APS-associated venous thrombosis was modeled by treating mice with IgG prepared from APS patients, followed by partial restriction of blood flow through the inferior vena cava. In patients, APS neutrophils demonstrated a proinflammatory signature with overexpression of genes relevant to IFN signaling, cellular defense, and intercellular adhesion. For in vivo studies, we focused on P-selectin glycoprotein ligand-1 (PSGL-1), a key adhesion molecule overexpressed in APS neutrophils. The introduction of APS IgG (as compared with control IgG) markedly potentiated thrombosis in WT mice, but not PSGL-1-KOs. PSGL-1 deficiency was also associated with reduced leukocyte vessel wall adhesion and NET formation. The thrombosis phenotype was restored in PSGL-1-deficient mice by infusion of WT neutrophils, while an anti-PSGL-1 monoclonal antibody inhibited APS IgG-mediated thrombosis in WT mice. PSGL-1 represents a potential therapeutic target in APS.

Diagnosis and management of the antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy complications in the presence of persistent antiphospholipid antibodies (APLA). Laboratory diagnosis of APLA depends upon the detection of a lupus anticoagulant, which prolongs phospholipid-dependent anticoagulation tests, and/or anticardiolipin (aCL) and anti-β2-glycoprotein-1 (β2GPI) antibodies. APLA are primarily directed toward phospholipid binding proteins. Pathophysiologic mechanisms underlying thrombosis and pregnancy loss in APS include APLA induced cellular activation, inhibition of natural anticoagulant and fibrinolytic systems, and complement activation, among others. There is a high rate of recurrent thrombosis in APS, especially in triple positive patients (patients with lupus anticoagulant, aCL and anti-β2GPI antibodies), and indefinite anticoagulation with a vitamin K antagonist is the standard of care for thrombotic APS. There is currently insufficient evidence to recommend the routine use of direct oral anticoagulants (DOAC) in thrombotic APS. Aspirin with low molecular weight or unfractionated heparin may reduce the incidence of pregnancy loss in obstetric APS. Recent insights into the pathogenesis of APS have led to the identification of new potential therapeutic interventions, including anti-inflammatory and immunomodulatory therapies. Additional research is needed to better understand the effects of APLA on activation of signaling pathways in vascular cells, to identify more predictive biomarkers that define patients at greatest risk for a first or recurrent APLA-related clinical event, and to determine the safety and efficacy of DOACs and novel anti-inflammatory and immune-modulatory therapies for refractory APS.

In Vivo Role of Neutrophil Extracellular Traps in Antiphospholipid Antibody-Mediated Venous Thrombosis

OBJECTIVE

Antiphospholipid syndrome (APS) is a leading acquired cause of thrombotic events. Although antiphospholipid antibodies have been shown to promote thrombosis in mice, the role of neutrophils has not been explicitly studied. The aim of this study was to characterize neutrophils in the context of a new model of antiphospholipid antibody-mediated venous thrombosis.

METHODS

Mice were administered fractions of IgG obtained from patients with APS. At the same time, blood flow through the inferior vena cava was reduced by induction of stenosis. Resulting thrombi were characterized for size and neutrophil content. Circulating factors and the vessel wall were also assessed.

RESULTS

As measured by both thrombus weight and thrombosis frequency, mice treated with IgG from patients with APS (APS IgG) demonstrated exaggerated thrombosis as compared with control IgG-treated mice. Thrombi in mice treated with APS IgG were enriched for citrullinated histone H3 (a marker of neutrophil extracellular traps [NETs]). APS IgG-treated mice also demonstrated elevated levels of circulating cell-free DNA and human IgG bound to the neutrophil surface. In contrast, circulating neutrophil numbers and markers of vessel wall activation were not appreciably different between APS IgG-treated mice and control mice. Treatment with either DNase (which dissolves NETs) or a neutrophil-depleting antibody reduced thrombosis in APS IgG-treated mice to the level in control mice.

CONCLUSION

These data support a mechanism whereby circulating neutrophils are primed by antiphospholipid antibodies to accelerate thrombosis. This line of investigation suggests new, immunomodulatory approaches for the treatment of APS.

Dimerized Domain V of Beta2-Glycoprotein I Is Sufficient to Upregulate Procoagulant Activity in PMA-Treated U937 Monocytes and Require Intact Residues in Two Phospholipid-Binding Loops

Upregulation of the procoagulant activity of monocytes by antibodies to beta2- glycoprotein I (β2GPI) is one of the mechanisms contributing to thrombosis in antiphospholipid syndrome. Current knowledge about receptors responsible for the upregulation of procoagulant activity by β2GPI/anti-β2GPI complexes and their binding sites on β2GPI is far from complete. We quantified the procoagulant activity expressed by phorbol 12-myristate 13-acetate (PMA)- differentiated U937 cells by measuring clotting kinetics in human plasma exposed to stimulated cells. Cells stimulated with anti-β2GPI were compared to cells treated with dimerized domain V of β2GPI (β2GPI-DV) or point mutants of β2GPI-DV. We demonstrated that dimerized β2GPI-DV is sufficient to induce procoagulant activity in monocytes. Using site-directed mutagenesis, we determined that the phospholipid-binding interface on β2GPI is larger than previously thought and includes Lys308 in β2GPI-DV. Intact residues in two phospholipid-binding loops of β2GPI-DV were important for the potentiation of procoagulant activity. We did not detect a correlation between the ability of β2GPI-DV variants to bind ApoER2 and potentiation of the procoagulant activity of cells. The region on β2GPI inducing procoagulant activity in monocytes can now be narrowed down to β2GPI-DV. The ability of β2GPI-DV dimers to come close to cell membrane and attach to it is important for the stimulation of procoagulant activity.

Patient-derived anti-β2GP1 antibodies recognize a peptide motif pattern and not a specific sequence of residues

Antiphospholipid antibody syndrome is an autoimmune disease characterized by the presence of so-called antiphospholipid antibodies and clinical manifestations such as recurrent thromboembolic or pregnancy complications. Although the main antigenic determinant for antiphospholipid antibodies has been identified as the β-2-glycoprotein 1 (β2GP1), the precise epitope recognized by antiphospholipid antibodies still remains largely unknown. In the study herein, we wanted to identify a sequence in domain I of β2GP1 able to induce the proliferation of CD4⁺ T cells isolated from antiphospholipid antibody syndrome patients, but not from healthy donors, and to interact with antiphospholipid antibodies. We have characterized a sequence in domain I of β2GP1 that triggers CD4⁺ T-cell proliferation. A comparison of this sequence with the previously reported binding of antiphospholipid antibodies to discontinuous epitope R39-R43 reveals the presence of an indeterminate motif in β2GP1, in which the polarity determines the characteristics and specificity of antiphospholipid antibodies-interacting motifs. Using point mutations, we characterized the main antiphospholipid antibodies-interacting motif as ϕϕϕζζFxC, but also established ϕϕϕζζFxϕ-related motifs as potential antiphospholipid antibodies epitopes, in which ϕ represents nonpolar residues and ζ polar residues, with charges of the residues not being involved. Of specific importance, these different motifs are present at least once in all antiphospholipid antibodies-related receptors described so far. We have further demonstrated, in vitro, that peptides and domains of β2GP1 containing these motifs were able to interact with antiphospholipid antibodies and inhibit their monocyte activating activity. These results established that the antiphospholipid antibodies-interacting motifs are determined by the polarity, but not by the sequence or charge, of amino acids. These data could also contribute to the future development of more sensitive and specific diagnostic tools for antiphospholipid antibody syndrome determination and potential peptide- or β2GP1 domain-based clinical therapies.

Recent advances in understanding antiphospholipid syndrome

Antiphospholipid syndrome (APS), also known as Hughes Syndrome, is a systemic autoimmune disease characterized by thrombosis and/or pregnancy morbidity in the presence of persistently positive antiphospholipid antibodies. A patient with APS must meet at least one of two clinical criteria (vascular thrombosis or complications of pregnancy) and at least one of two laboratory criteria including the persistent presence of lupus anticoagulant (LA), anticardiolipin antibodies (aCL), and/or anti-b2 glycoprotein I (anti-b2GPI) antibodies of IgG or IgM isotype at medium to high titres in patient’s plasma. However, several other autoantibodies targeting other coagulation cascade proteins (i.e. prothrombin) or their complex with phospholipids (i.e. phosphatidylserine/prothrombin complex), or to some domains of β2GPI, have been proposed to be also relevant to APS. In fact, the value of testing for new aPL specificities in the identification of APS in thrombosis and/or pregnancy morbidity patients is currently being investigated.

TNF-alpha and annexin A2: inflammation in thrombotic primary antiphospholipid syndrome

Antiphospholipid syndrome (APS) is characterized by thromboses and/or pregnancy losses. Laboratory criterion for the diagnosis of APS is the presence of antiphospholipid antibodies (anticardiolipin, anti-beta2-glycoprotein I (aβ2gpI) and lupus anticoagulant). On the one hand, the latest classification criteria for the diagnosis of APS emphasized that thrombotic manifestations of the syndrome should be without any signs of an inflammatory process, while on the other hand, some recent reports have suggested that APS is a "pro-inflammatory state." This article is focused on the importance of TNF-alpha and annexin A2 (anxA2) for patients with vascular (thrombotic) manifestations of the primary APS. The classic antithrombotic and antiplatelet therapy does not protect APS patients from the development of recurrent thrombosis. Therefore, an urgent need for the introduction of new therapeutic approaches in the treatment of APS patients is obvious. This review provides a rationale for the necessity for the use of immunomodulatory medications that could interfere with β2gpI binding to its receptor(s), such as anxA2, and/or inhibit TNF-alpha activity.

Anti-apolipoprotein A-1 auto-antibodies as active modulators of atherothrombosis

Humoral autoimmune-mediated inflammation plays a role in atherogenesis, and potentially in arterial thrombosis. Anti-apolipoprotein A-1 (apoA-1) IgG have been reported to represent emergent mediators of atherogenesis through Toll-like receptors (TLR) 2, 4 and CD14 signalling. We investigated the role of anti-apoA-1 IgG on tissue factor (TF) expression and activation, a key coagulation regulator underlying atherothrombosis. Atherothrombosis features were determined by immunohistochemical TF staining of human carotid biopsies derived from patients with severe carotid stenosis undergoing elective surgery (n=176), and on aortic roots of different genetic backgrounds mice (ApoE-/-; TLR2-/-ApoE-/- and TLR4-/-ApoE-/-) exposed to passive immunisation with anti-apoA-1 IgG. Human serum levels of anti-apoA-1 IgG were measured by ELISA. In vitro, on human-monocyte-derived-macrophages (HMDM) the anti-apoA-1 IgG increased TF expression and activity were analysed by FACS and chromogenic assays in presence of different pharmacological inhibitors. Human serum anti-apoA-1 IgG levels significantly correlated to intraplaque TF expression in carotid biopsies (r=0.31, p<0.001), which was predictive of clinically symptomatic lesions. On HMDM, anti-apoA-1 IgG induced a TLR2, 4 and CD14-dependent increase in TF expression and activity, involving NF-kappaB and a c-Jun N-terminal kinase-dependent AP-1 transcription factors. In ApoE-/- mice, anti-apoA-1 IgG passive immunisation significantly enhanced intraplaque TF expression when compared to control IgG. This effect was lost in both TLR2-/-ApoE-/- and TLR4-/-ApoE-/- mice. These results demonstrate that anti-apoA-1 IgG are associated with TF expression in human atherosclerotic plaques, induce TF expression in vitro and in vivo through TLR2 and 4 signalling, supporting a possible causal relationship between anti-apoA-1 IgG and atherothrombosis.

Soluble analog of ApoER2 targeting beta2-glycoprotein I in immune complexes counteracts hypertension in lupus-prone mice with spontaneous antiphospholipid syndrome

Essentials (NZWxBXSB)F1 male mice develop antibodies beta2-glycoprotein I (β2GPI) and hypertension. A1-A1 is a soluble analogue of ApoE receptor 2 with a high affinity for β2GPI/antibody complexes. A1-A1 improved blood pressure and arterial elastance in (NZWxBXSB)F1 male mice. A1-A1 had no adverse effects on the hemodynamics of healthy mice.

SUMMARY

Background Antiphospholipid syndrome (APS) is diagnosed based on the presence of antiphospholipid antibodies and clinical thrombosis or fetal loss during pregnancy. Lupus-prone (NZWxBXSB)F1 male mice are the mouse model of spontaneous APS. They develop anti-β2GPI antibodies, microinfarcts and hypertension. ApoER2 is a receptor that contributes to anti-β2GPI-dependent thrombosis in APS by down-regulating endothelial nitric oxide synthase activation. Objectives A1-A1 is a small protein constructed from two identical ligand-binding modules from ApoER2, containing the binding site for β2GPI. We studied how treatment with A1-A1 affects the development of hypertension in (NZWxBXSB)F1 male mice. Methods We treated (NZWxBXSB)F1 male mice with A1-A1 for up to 4 weeks and examined changes in hemodynamics by left ventricular pressure-volume loop measurements. Results We observed improvements in blood pressure in the A1-A1 treated mice. A1-A1 prevented the deterioration of arterial elastance by decreasing systemic resistance and improving vessel compliance. We did not detect any adverse effects of the treatment in either male mice or in apparently healthy female (NZWxBXSB)F1 mice. Conclusions We demonstrated that A1-A1, which is a soluble analog of ApoER2 that binds pathological β2GPI/anti-β2GPI complexes, has a positive impact on hemodynamics in lupus-prone mice with spontaneous anti-β2GPI antibodies and hypertension.

Modulation of endothelial function by Toll like receptors

Endothelial cells (EC) are able to actively control vascular permeability, coagulation, blood pressure and angiogenesis. Most recently, a role for endothelial cells in the immune response has been described. Therefore, the endothelium has a dual role controlling homeostasis but also being the first line for host defence and tissue damage repair thanks to its ability to mount an inflammatory response. Endothelial cells have been shown to express pattern-recognition receptors (PRR) including Toll-like receptors (TLR) that are activated in response to stimuli within the bloodstream including pathogens and damage signals. TLRs are strategic mediators of the immune response in endothelial cells but they also regulate the angiogenic process critical for tissue repair. Nevertheless, endothelial activation and angiogenesis can contribute to some pathologies. Thus, inappropriate endothelial activation, also known as endothelial dysfunction, through TLRs contributes to tissue damage during autoimmune and inflammatory diseases such as atherosclerosis, hypertension, ischemia and diabetes associated cardiovascular diseases. Also TLR induced angiogenesis is required for the growth of some tumors, atherosclerosis and rheumatoid arthritis, among others. In this review we discuss the importance of various TLRs in modulating the activation of endothelial cells and their importance in immunity to infection and vascular disease as well as their potential as therapeutic targets.

Ribophorin II is involved in the tissue factor expression mediated by phosphatidylserine-dependent antiprothrombin antibody on monocytes

OBJECTIVE

Phosphatidylserine-dependent, also called aPS-PT, recognizes the phosphatidylserine-prothrombin complex, which is associated with APS. We have previously reported that aPS-PT induces tissue factor (TF) expression on monocytes through the p38 mitogen-activated protein kinase pathway. However, the cell surface interaction between prothrombin and aPS-PT, which is involved in the activation of cell-signalling pathways, has remained unknown. The objective of this study was to identify membrane proteins involved in the binding of prothrombin and aPS-PT to monocyte surfaces as well as the induction of TF expression.

METHODS

RAW264.7 cells with FLAG-tagged prothrombin were incubated and separated using affinity chromatography with anti-FLAG antibody-conjugated Sepharose beads. Immunopurified proteins were then analysed by an online nano-liquid chromatography-tandem mass spectrometry. The binding between prothrombin and the identified protein, ribophorin II (RPN2), was analysed by ELISA and surface plasmon resonance. To elucidate the role of RPN2 in TF expression, the TF mRNA level in RAW264.7 cells treated with RPN2 small interfering RNA was determined by quantitative real-time PCR (qPCR).

RESULTS

RPN2 was identified as a candidate molecule involved in the binding of prothrombin to the cell surface. The binding between prothrombin and RPN2 was confirmed by ELISA and surface plasmon resonance. RAW264.7 cells treated with RPN2 small interfering RNA showed significant reduction of the TF expression mediated by prothrombin and a mouse monoclonal aPS-PT.

CONCLUSION

We identified that RPN2 is one of the prothrombin-binding proteins on monocyte surfaces, suggesting that RPN2 is involved in the pathophysiology of thrombosis in patients with APS.

Release of neutrophil extracellular traps by neutrophils stimulated with antiphospholipid antibodies: a newly identified mechanism of thrombosis in the antiphospholipid syndrome

OBJECTIVE

Antiphospholipid antibodies (aPL), especially those targeting β2 -glycoprotein I (β2 GPI), are well known to activate endothelial cells, monocytes, and platelets, with prothrombotic implications. In contrast, the interaction of aPL with neutrophils has not been extensively studied. Neutrophil extracellular traps (NETs) have recently been recognized as an important activator of the coagulation cascade, as well as an integral component of arterial and venous thrombi. This study was undertaken to determine whether aPL activate neutrophils to release NETs, thereby predisposing to the arterial and venous thrombosis inherent in the antiphospholipid syndrome (APS).

METHODS

Neutrophils, sera, and plasma were prepared from patients with primary APS (n = 52) or from healthy volunteers and characterized. No patient had concomitant systemic lupus erythematosus.

RESULTS

Sera and plasma from patients with primary APS had elevated levels of both cell-free DNA and NETs, as compared to healthy volunteers. Freshly isolated neutrophils from patients with APS were predisposed to high levels of spontaneous NET release. Further, APS patient sera, as well as IgG purified from APS patients, stimulated NET release from control neutrophils. Human aPL monoclonal antibodies, especially those targeting β2 GPI, also enhanced NET release. The induction of APS NETs was abrogated with inhibitors of reactive oxygen species formation and Toll-like receptor 4 signaling. Highlighting the potential clinical relevance of these findings, APS NETs promoted thrombin generation.

CONCLUSION

Our findings indicate that NET release warrants further investigation as a novel therapeutic target in APS.

Genetic aspects of the antiphospholipid syndrome: An update

Studies on the immunogenetic predisposition to antiphospholipid syndrome (APS) and on other non-genetic and epigenetic factors are summarised and discussed. Family studies suggest a genetic predisposition to APS. It appears that this genetic predisposition is in part accounted for by the HLA system, the most consistent associations being those with DR4 and DRw53. Furthermore, it appears that lupus anticoagulant (LA) and anticardiolipin (aCL) antibodies are both associated with the same HLA antigens. Population studies suggest that HLA genes have a role in conferring susceptibility to develop primary APS, with some differences in different ethnic groups. Other genes, outside the MHC, give their contribution to the development of this autoimmune syndrome, such as IRF5, STAT4 and those related to inherited thrombophilia--factor V Leiden and G20210A prothrombin polymorphisms. Finally, post-transcriptional modifications of anti-beta2GPI antibodies could be implicated too.

Antiphospholipid antibody-mediated effects in an arterial model of thrombosis are dependent on Toll-like receptor 4

Patients with antiphospholipid syndrome (APS) produce antiphospholipid antibodies (aPL) and develop vascular thrombosis that may occur in large or small vessels in the arterial or venous beds. On the other hand, many individuals produce aPL and yet never develop thrombotic events. Toll-like receptor 4 (TLR4) appears to be necessary for aPL-mediated prothrombotic effects in venous and microvascular models of thrombosis, but its role in arterial thrombosis has not been studied. Here, we propose that aPL alone are insufficient to cause thrombotic events in an arterial model of APS, and that a concomitant trigger of innate immunity (e.g. TLR4 activation) is required. We show specifically that anti-β2-glycoprotein I (anti-β2GPI) antibodies, a subset of aPL, accelerated thrombus formation in C57BL/6 wild-type, but not TLR4-deficient, mice in a ferric chloride-induced carotid artery injury model. These aPL bound to arterial and venous endothelial cells, particularly in the presence of β2GPI, and to human TLR4 by enzyme-linked immunoassay. Arterial endothelium from aPL-treated mice had enhanced leukocyte adhesion, compared to control IgG-treated mice. In addition, aPL treatment of mice enhanced expression of tissue factor (TF) in leukocytes induced by the TLR4 ligand lipopolysaccharide (LPS). aPL also enhanced LPS-induced TF expression in human leukocytes in vitro. Our findings support a mechanism in which aPL enhance TF expression by leukocytes, as well as augment adhesion of leukocytes to the arterial endothelium. The activation of TLR4 in aPL-positive individuals may be required to trigger thrombotic events.

Delineating the deranged immune system in the antiphospholipid syndrome

The antiphospholipid syndrome (APS) is a systemic autoimmune disease that is characterized serologically by the presence of antiphospholipid antibodies (aPL) and clinically by vascular thrombosis and obstetric complications. The protein β2 glycoprotein I (β2GPI) is identified as the most important autoantigen in this syndrome. Activation of endothelial cells, thrombocytes and placental tissue by anti-β2GPI antibodies relates to the clinical manifestations of APS. This review describes genetic and environmental factors in relation to APS and summarizes the current knowledge on abnormalities in components of both the innate and adaptive immune system in APS. The role of dendritic cells, T-cells, B-cells, monocytes, neutrophils and NK-cells as well as the complement system in APS are discussed. Several gaps in our knowledge on the pathophysiology of APS are identified and a plea is made for future extensive immune cell profiling by a systems medicine approach in order to better unravel the pathogenesis of APS, to gain more insight in the role of the immune system in APS as well as having the potential to reveal biomarkers or novel therapeutic targets.

Elevated expression of platelet-derived chemokines in patients with antiphospholipid syndrome

OBJECTIVE

Platelet factor 4 tetramers (CXCL4 chemokine) form complexes with β2glycoprotein I (β2GPI), recognized by anti-β2GPI antibodies leading to platelet activation in antiphospholipid syndrome (APS), either primary (PAPS) or secondary (SAPS). Increased plasma levels of CXCL4 may favor this process; therefore we measured plasma levels of CXCL4, a CXCL4 variant (CXCL4L1) and as controls, platelet-derived chemokines CXCL7 (NAP-2) and CCL5 (RANTES), in APS, and disease controls such as patients with systemic lupus erythematosus (SLE) coronary artery disease (CAD) and healthy donors (HDs).

METHODS

Plasma samples and platelets were isolated from patients with APS (n = 87), SLE (n = 29), CAD (n = 14) and 54 HDs. Plasma levels of CXCL4, CXCL4L1, CXCL7 and CCL5 as well as intracellular platelet CXCL4 and CXCL4L1 were measured using ELISA. Platelet CXCL4 and CXCL4L1 RNA levels were determined by RT-PCR.

RESULTS

CXCL4, CXCL7 (NAP-2) and CCL5 (RANTES) plasma levels were significantly higher in patients with APS compared to both control groups (SLE, CAD) and HDs. CXCL4L1 plasma levels were also significantly higher in APS than in SLE and HDs, but lower from that of CAD patients. Statistically significant concordance was detected between CXCL4 and CXCL7 (p < 0.0001) or CCL5 (p < 0.0001) plasma levels in patients with APS, either PAPS or SAPS. CXCL4L1 plasma levels were inversely correlated with CXCL4 (P = 0.0027), CXCL7 (p = 0.012) and CCL5 (p = 0.023) in PAPS and positively with CXCL4 (p = 0.0191), CCL5 (p < 0.0001) and CXCL7 (P < 0.0001), in SAPS. Levels of CXCL4, CXCL4L1, CXCL7 and CCL5 were divided in "high" (exceeding a level defined as the mean of HDs and 3 SD) and "low" (below this level); The "CXCL4L1 high" group was characterized by increased IgG aCL, (p = 0.0215), double antibody positivity (either aCL or anti-β2GPI plus LA), (p = 0.0277), triple antibody positivity (aCL plus anti-β2GPI plus LA), (p = 0.0073) and thrombocytopenia (p = 0.0061), as well as with at least 1 thrombotic event or the last 5 years (p = 0.0001), or more than 3 thrombotic events ever (p = 0.0151).

CONCLUSIONS

Chemokines associated with platelet activation and immune cell chemotaxis were found to be elevated in APS patients' plasma and may contribute to the pathogenesis of the syndrome. High CXCL4L1 plasma levels are associated with the clinical expression of APS and should be prospectively evaluated as a biomarker.