The J-elongated conformation of ß2-glycoprotein I predominates in solution: implications for our understanding of antiphospholipid syndrome.

ß2-Glycoprotein I (ß2GPI) 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 ß2GPI to that in solution. ß2GPI 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, ß2GPI 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 ß2GPI 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 ß2GPI 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 ß2GPI provides a strategy to block pathogenic aPLs in APS.

Antiphospholipid Syndrome and Renal Allograft Thrombosis.

Renal allograft thrombosis is the most frequent and devastating complication in the early postrenal transplantation period. Several risk factors to develop graft thrombosis depending on donors and recipients are well known. Antiphospholipid syndrome (APS) is well recognized as an important cause of kidney injury, with specific clinical and histological features that may lead to renal injury caused by thrombosis at any location within the renal vasculature. There are 3 forms of APS, primary (the most common form), associated to other systemic autoimmune diseases (SAD-APS), and catastrophic. Nevertheless, patients with SAD-APS and renal failure only represent 2% to 5% in hemodialysis or transplantation. The presence of pretransplant antiphospholipid antibodies increases risk of graft thrombosis. A new form of APS based on IgA anti-ß-2-glycoprotein-I (B2GPI) antibodies, representing up to 30% of patients in end-stage renal disease and renal transplantation, is the main independent risk factor for graft thrombosis and early graft loss after renal transplantation. In addition, B2GP1 bound to IgA aB2GP1 immunocomplexes have been described as a marker to predict thrombosis after renal transplantation in patients with antiphospholipid antibodies. Anticoagulation remains the main treatment to prevent renal allograft thrombosis, although new preventive strategies are coming. Future studies may help to identify better therapeutic targets.

Síndrome antifosfolípido catastrófico / Catastrophic antiphospholipid syndrome

El síndrome antifosfolípido está definido por la combinación de manifestaciones clínicas trombóticas y/u obstétricas y un título persistentemente alto y significativo de anticuerpos antifosfolípidos. La presencia de múltiples trombos en lechos vasculares pequeños que lleva a falla multiorgánica, simultáneamente o en menos de 1 semana, define al síndrome antifosfolípido catastrófico el cual conlleva alta mortalidad; sin embargo, la sospecha diagnóstica y la institución temprana del tratamiento, definitivamente inciden en el pronóstico de éstos pacientes(AU)

Antiphospholipid syndrome is defined by the combination of thrombotic and/or obstetric clinical manifestations and a persistently high and significant title of antiphospholipid antibodies. The presence of multiple thrombi in small vascular beds leading to multi-organ failure that occurs simultaneously or in less than 1 week, and defines the catastrophic antiphospholipid syndrome which carries high mortality, The suspected diagnosis and early treatment affects the prognosis of these patients(AU)

Antiphospholipid antibodies promote tissue factor-dependent angiogenic switch and tumor progression.

Progression to an angiogenic state is a critical event in tumor development, yet few patient characteristics have been identified that can be mechanistically linked to this transition. Antiphospholipid autoantibodies (aPLs) are prevalent in many human cancers and can elicit proangiogenic expression in several cell types, but their role in tumor biology is unknown. Herein, we observed that the elevation of circulating aPLs among breast cancer patients is specifically associated with invasive-stage tumors. By using multiple in vivo models of breast cancer, we demonstrated that aPL-positive IgG from patients with autoimmune disease rapidly accelerates tumor angiogenesis and consequent tumor progression, particularly in slow-growing avascular tumors. The action of aPLs was local to the tumor site and elicited leukocytic infiltration and tumor invasion. Tumor cells treated with aPL-positive IgG expressed multiple proangiogenic genes, including vascular endothelial growth factor, tissue factor (TF), and colony-stimulating factor 1. Knockdown and neutralization studies demonstrated that the effects of aPLs on tumor angiogenesis and growth were dependent on tumor cell-derived TF. Tumor-derived TF was essential for the development of pericyte coverage of tumor microvessels and aPL-induced tumor cell expression of chemokine ligand 2, a mediator of pericyte recruitment. These findings identify antiphospholipid autoantibodies as a potential patient-specific host factor promoting the transition of indolent tumors to an angiogenic malignant state through a TF-mediated pathogenic mechanism.

NF-κB is activated from endosomal compartments in antiphospholipid antibodies-treated human monocytes.

BACKGROUND: The antiphospholipid antibody syndrome (APS) is an autoimmune disease associated with arterial or venous thrombosis and/or recurrent fetal loss and is caused by pathogenic antiphospholipid antibodies (aPLA). We recently demonstrated that Toll-like receptor 2 (TLR2) and CD14 contribute to monocyte activation of aPLA. OBJECTIVE: To study the mechanisms of cell activation by aPLA, leading to pro-coagulant and pro-inflammatory responses. METHODS AND RESULTS: For this study, we used purified antibodies from the plasmas of 10 different patients with APS and healthy donors. We demonstrate that aPLA, but not control IgG, co-localizes with TLR2 and TLR1 or TLR6 on human monocytes. Blocking antibodies to TLR2, TLR1 or TLR6, but not to TLR4, decreased TNF and tissue factor (TF) responses to aPLA. Pharmacological and siRNA approaches revealed the importance of the clathrin/dynamin-dependent endocytic pathway in cell activation by aPLA. In addition, soluble aPLA induced NF-κB activation, while bead-immobilized aPLA beads, which cannot be internalized, were unable to activate NF-κB. Internalization of aPLA in monocytes and NF-κB activation were dependent on the presence of CD14. CONCLUSION: We show that TLR2 and its co-receptors, TLR1 and TLR6, contribute to the pathogenicity of aPLA, that aPLA are internalized via clathrin- and CD14-dependent endocytosis and that endocytosis is required for NF-κB activation. Our results contribute to a better understanding of the APS and provide a possible therapeutic approach.

Progress in detection and structural characterization of glycosphingolipids in crude lipid extracts by enzymatic phospholipid disintegration combined with thin-layer chromatography immunodetection and IR-MALDI mass spectrometry.

In order to proceed in detection and structural analysis of glycosphingolipids (GSLs) in crude lipid extracts, which still remains a challenge in glycosphingolipidomics, we developed a strategy to structurally characterize neutral GSLs in total lipid extracts prepared from in vitro propagated human monocytic THP-1 cells, which were used as a model cell line. The procedure divides into (1) extraction of total lipids from cellular material, (2) enzymatical disintegration of phospholipids by treatment of the crude lipid extract with phospholipase C, (3) subsequent multiple thin-layer chromatography (TLC) overlay detection of individual GSLs with a mixture of various anti-GSL antibodies, and (4) structural analysis of immunostained GSLs directly on the TLC plate using infrared matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometry (IR-MALDI-o-TOF MS) in combination with collision-induced dissociation (CID). Whereas GSLs were mostly undetectable in untreated crude lipid extracts, pretreatment with phospholipase C resulted in clear-cut mass spectra. MS(1) and MS(2) analysis gave similar results when compared to those obtained with a highly purified neutral GSL preparation of THP-1 cells, which served as a control. We could demonstrate in this study the feasibility of simultaneous multiple immunodetection of individual neutral GSLs in one and the same TLC run and their structural characterization in crude lipid extracts after phospholipase C treatment, thereby avoiding laborious and long-lasting sample purification. This powerful combinatorial technique allows for efficient structural characterization of GSLs in small tissue samples and takes a step forward in the emerging field of glycosphingolipidomics.

Role of the coagulation system in development.

The generation of knock out mice urged researchers, not always voluntarily, to newly define developmental functions of the gene knocked out. Among others, this has led to the establishment of the field of developmental haemostasis. The work in this field identified a role of coagulation proteases and their regulators independent of haemostasis in the embryo proper. Rather, coagulation proteases regulate cellular function through receptor dependent signalling in the embryo proper, both within and outside the vasculature. Likewise, coagulation proteases modulate placental development independent of haemostasis through mechanisms involving the activation of maternal myeloid derived cells. The following review summarizes the current knowledge in the field of developmental haemostasis and pinpoints open questions within this evolving field.

Unusual association between Budd-Chiari syndrome secondary to antiphospholipid syndrome and relapsing polychondritis: a case report and review of the literature.

Relapsing polychondritis is a rare immune-mediated condition, characterized by episodic inflammation of the cartilaginous tissue, in particular the ears, nose, and eyes, and involvement of joints and respiratory tract. Nearly one third of patients showed other associated diseases, such as systemic vasculitides, connective tissue diseases, or myelodysplastic syndromes. Antiphospholipid antibodies can be found in relapsing polychondritis in patients with no clinical thrombotic disease. However, when antiphospholipid syndrome is present, its clinical manifestations can be severe and life threatening. We describe the case of a patient with relapsing polychondritis associated to Budd-Chiari syndrome due to antiphospholipid syndrome. The present clinical observations together with the updated review of the literature suggest a search for antiphospholipid antibodies in all patients with relapsing polychondritis.

Measurement of lupus anticoagulants: an update on quality in laboratory testing.

Lupus anticoagulants (LAs) are antiphospholipid antibodies that interfere with in vitro phospholipid-dependent clotting tests, but are associated in vivo with significant clinical manifestations such as recurrent pregnancy loss and venous and arterial thrombosis. Although their detection is important for the diagnosis of thrombotic disorders such as the antiphospholipid syndrome, laboratory identification has historically been fraught with many issues. These have included variability in the sensitivity of assays and reagents; high false-negative and false-positive detection rates; a lack of consensus for the use of mixing tests; and, to some extent, lack of compliance with guidelines published by the Lupus Anticoagulant/Antiphospholipid Antibody Scientific Standardization Committee of the International Society on Thrombosis and Haemostasis (ISTH). Since the most recently updated guidelines in 2009, external quality assurance (EQA) programs have conducted surveys to provide a "snapshot" of laboratory practices related to the investigation of LA and to identify problems and monitor improvements in testing for LA. This article will review the impact of the most recently updated ISTH guidelines for LA testing and discuss the findings of recent EQA surveys.

Lupus anticoagulant: a marker for stroke and venous thrombosis in primary Sjögren's syndrome.

Antiphospholipid antibodies (aPL) and antiphospholipid syndrome (APS) have been described in primary Sjögren's syndrome (pSS) with controversial findings regarding aPL prevalence and their association with thrombotic events. We evaluated 100 consecutive pSS patients (American-European criteria) and 89 age-gender-ethnicity-matched healthy controls for IgG/IgM anticardiolipin (aCL), IgG/IgM anti-beta2-glycoprotein-I (aß2GPI), and lupus anticoagulant (LA) (positivity according to APS Sydney's criteria). Clinical analysis followed standardized interview and physical examination assessing thrombotic and nonthrombotic APS manifestations and thrombosis risk factors. aPLs were detected in 16 % patients and 5.6 % controls (p = 0.035). LA was the most common aPL in patients (9 %), followed by aß2GPI (5 %) and aCL (4 %). Thrombotic events occurred in five patients [stroke in two, myocardial infarction in one and deep-vein thrombosis (DVT) in four], but in none of controls (p = 0.061). Mean age at time of stroke was 35 years. Three patients with thrombotic events (including the two with stroke) had APS (Sydney's criteria) and were positive exclusively for LA. Comparison of patients with (n = 16) and without (n = 84) aPL revealed similar mean age, female predominance, and ethnicity (p > =0.387). Frequencies of livedo reticularis (25 vs. 4.8 %, p = 0.021), stroke (12.5 vs. 0 %, p = 0.024), and DVT (18.8 vs. 1.2 %, p = 0.013) were significantly higher in APL + patients. Conversely, frequencies of hypertension, dyslipidemia, diabetes, obesity, smoking, sedentarism, and hormonal contraception were similar in patients with or without aPL (p ≥ 0.253). Our study identified LA as an important marker for APS in pSS, particularly for stroke in young patients, warranting routine evaluation of these antibodies and rigorous intervention in modifiable risk factors.

Use of monoclonal antibodies to dissect specificity and pathogenesis of antiphospholipid antibodies.

Monoclonal antiphospholipid antibodies (aPL) have been utilized to dissect the relationship between their sequence, structure, binding and biological properties relevant to the pathogenesis of the antiphospholipid syndrome. In particular, sequence analysis of aPL has highlighted the clustering of certain amino acid residues in the antigen contact sites of their heavy and light chains. Therefore, these sequence motifs are likely to be important in determining aPL binding properties and their pathogenic effects. Experiments, however, using monoclonal aPL engineered to contain specific point mutations in their sequence which alter their ability to bind relevant antigens have shown that these alterations in binding are not directly mirrored by their pathogenic effects. In this review we focus on work carried out by others and ourselves using monoclonal antibodies with specific binding properties to extend our knowledge of the non-linear structure-binding-function relationship of aPL.

Hydroxychloroquine directly reduces the binding of antiphospholipid antibody-beta2-glycoprotein I complexes to phospholipid bilayers.

Treatment with the antimalarial drug hydroxychloroquine (HCQ) has been associated with reduced risk of thrombosis in the antiphospholipid (aPL) syndrome (APS) and, in an animal model of APS, with reduction of experimentally induced thrombosis. Recognition of beta2-glycoprotein I (beta2GPI) by aPL antibodies appears to play a major role in the disease process. We therefore used the techniques of ellipsometry and atomic force microscopy (AFM) to investigate whether HCQ directly affects the formation of aPL IgG-beta2GPI complexes on phospholipid bilayers. HCQ, at concentrations of 1 mug/mL and greater, significantly reduced the binding of aPL-beta2GPI complexes to phospholipid surfaces and THP-1 (human acute monocytic leukemia cell line) monocytes. The drug also reduced the binding of the individual proteins to bilayers. This HCQ-mediated reduction of binding was completely reversed when the HCQ-protein solutions were dialyzed against buffer. HCQ also caused modest, but statistically significant, reductions of clinical antiphospholipid assays. In conclusion, HCQ reduces the formation of aPL-beta2GPI complexes to phospholipid bilayers and cells. This effect appears to be due to reversible interactions between HCQ and the proteins and may contribute to the observed reduction of thrombosis in human and experimental APS. These results support the possibility that HCQ, or analogous molecules, may offer novel nonanticoagulant therapeutic strategies for treating APS.

Platelet and coagulation activation markers in myeloproliferative diseases: relationships with JAK2 V6I7 F status, clonality, and antiphospholipid antibodies.

BACKGROUND AND OBJECTIVES: Patients with myeloproliferative disease (MPD) have an increased risk of thrombosis. We studied markers of platelet and coagulation activation in a large cohort of patients with MPD (n = 118) and related this to Janus Kinase 2 (JAK2) V617 F mutation status, a marker of clonality, and the presence of antiphospholipid antibodies (APA), all of which have been associated with thrombosis in MPD. METHODS: D-dimer, thrombin-antithrombin complexes (TAT), prothrombin fragments 1 + 2 (F(1+2)), soluble E-selectin (sE-selectin), and soluble P-selectin (sP-selectin) levels were compared between patients and hypertensive controls (n = 127). Assays for lupus anticoagulant (LA), anticardiolipin antibodies (ACA), antibeta2 glycoprotein 1 antibodies (anti-beta(2)GP1), and antiprothrombin antibodies (alpha-Pro) were also performed. The JAK2 V617F mutation status was determined in the cohort using amplification refractory mutation system (ARMS) polymerase chain reaction. Disease clonality was determined in 54 patients using the HUMARA assay. RESULTS: sP-selectin was significantly increased in patients with MPD (P

Prothrombotic coagulation abnormalities in patients with newly diagnosed multiple myeloma.

Prothrombotic coagulation abnormalities were analyzed in patients with untreated multiple myeloma. Increases in factor VIII, in von Willebrand factor (vWF) and a decrease in protein S were observed and these changes were strongly associated with disease stage. No difference in baseline coagulation parameters was found between patients with and without subsequent venous thromboembolism.

Abnormalities of homocysteine and B vitamins in the nephrotic syndrome.

INTRODUCTION: The nephrotic syndrome is associated with heightened risk for arterial and venous thrombosis. Multiple derangements of hemostasis and acquired risk factors such as hyperlipidemia and hypertension contribute to this risk. The prevalence in the nephrotic syndrome of high circulating levels of homocysteine and of low levels of the B vitamins that are involved in its metabolism, which may play a role in thrombosis, is not well defined. MATERIALS AND METHODS: In 84 patients with nephrotic syndrome and 84 sex- and age-matched controls, hemostasis variables and the circulating levels of total homocysteine (tHcy), vitamin B(6), B(12) and folates were measured. RESULTS: tHcy levels were higher, vitamin B(6) and vitamin B(12) levels were lower in nephrotic patients than in controls. The association of low vitamin B(6) levels with the nephrotic syndrome was independent of any other alteration associated with the disease. Eighty-two percent of patients with the nephrotic syndrome had vitamin B(6) levels falling in the lowest quartile of the normal distribution. Antithrombin deficiency, factor V Leiden, antiphospholipid antibodies, hypertension, dyslipidemia, were more frequent in patients with the nephrotic syndrome than in controls. CONCLUSIONS: Patients with the nephrotic syndrome have multiple risk factors for thrombosis. We report that they frequently have low circulating levels of vitamin B(6), which associate with a heightened risk for venous and arterial thrombosis.