The role of tissue factor in the antiphospholipid syndrome

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.

Antiphospholipid syndrome and tissue factor: a thrombotic couple

The antiphospholipid syndrome (APS) is characterized by thrombosis and/or pregnancy morbidity in the presence of antiphospholipid antibodies (aPL). Among the thrombogenic mechanisms proposed, it has been suggested that aPL can stimulate tissue factor (TF) expression by endothelial cells (ECs) and monocytes. Moreover, our in vivo studies have shown that APS patients (particularly those with thrombosis) have increased monocyte TF expression. Yet, the molecular mechanism(s) by which aPL induce TF expression has not been completely underscored. In a recent study, we have demonstrated that aPL induces TF expression in monocytes from APS patients by activating, simultaneously and independently, the phosphorylation of MEK-1/ERK proteins, and the p38 MAP kinase-depenent nuclear translocation and activation of NFκB/Rel proteins. Understanding the intracellular mechanism(s) of aPL-mediated monocyte activation may help to establish new therapeutic approaches, such as selective inhibition of MAP kinases, to reverse the prothrombotic state in APS. Furthermore, the contribution of TF to a protrombotic state in the APS provides a renewed focus on antithrombotic therapies in current use, including the oral anticoagulation and, more recently, the use of statins, which have been proven to be effective in the inhibition of EC and monocyte TF-expression.

'Atherothrombosis-associated microRNAs in Antiphospholipid syndrome and Systemic Lupus Erythematosus patients'

MicroRNAs markedly affect the immune system, and have a relevant role in CVD and autoimmune diseases. Yet, no study has analyzed their involvement in atherothrombosis related to APS and SLE patients. This study intended to: 1) identify and characterize microRNAs linked to CVD in APS and SLE; 2) assess the effects of specific autoantibodies. Six microRNAs, involved in atherothrombosis development, were quantified in purified leukocytes from 23 APS and 64 SLE patients, and 56 healthy donors. Levels of microRNAs in neutrophils were lower in APS and SLE than in healthy donors. Gene and protein expression of miRNA biogenesis-related molecules were also reduced. Accordingly, more than 75% of identified miRNAs by miRNA profiling were underexpressed. In monocytes, miR124a and -125a were low, while miR-146a and miR-155 appeared elevated. Altered microRNAs’ expression was linked to autoimmunity, thrombosis, early atherosclerosis, and oxidative stress in both pathologies. In vitro treatment of neutrophils, monocytes, and ECs with aPL-IgG or anti-dsDNA-IgG antibodies deregulated microRNAs expression, and decreased miRNA biogenesis-related proteins. Monocyte transfections with pre-miR-124a and/or -125a caused reduction in atherothrombosis-related target molecules. In conclusion, microRNA biogenesis, significantly altered in neutrophils of APS and SLE patients, is associated to their atherothrombotic status, further modulated by specific autoantibodies.

Circulating levels of tissue factor and proinflammatory cytokines in patients with primary antiphospholipid syndrome or leprosy related antiphospholipid antibodies

The antiphospholipid syndrome (APS) is characterized by the presence of antiphospholipid antibodies (aPL) in patients with thromboembolic complications. In APS, most aPL are autoantibodies to β2-glycoprotein I and prothrombin, which play a major role in the APS pathogenesis. Nevertheless, antibodies with the same antigen specificity are also found in aPL patients with leprosy, in whom thromboembolic complications are uncommon. The in vivo upregulation of the tissue factor (TF) pathway and the imbalance of cytokines have been proposed as potential mechanisms of thrombosis in the APS. We measured the circulating levels of TF, interleukin 6 (IL-6), IL-6 receptor (sIL-6R), tumor necrosis factor (TNF-a) and interferon g (IFN-g) in 83 patients with autoimmune aPL (42 with and 41 without clinical features of definite primary APS), 48 leprosy patients (33 with aPL) and 48 normal controls. There was a trend (P = 0.06) to higher median sTF in patients with autoimmune aPL (139 pg/mL) compared with leprosy patients (103.5 pg/mL) and controls (123 pg/mL). In addition, the frequency of raised sTF levels (.187 pg/mL) was significantly higher in the group with autoimmune aPL [22.9% (APS 21.4%, non-APS 24.4%)] but not in leprosy (10.4%) compared with controls (4.2%). Elevated levels of IL-6 and TNF-a and a trend to lower IFN-g were found in patients with definite APS. Leprosy patients with aPL, however, had increased TNF-a and IFN-g but normal IL-6 levels. Levels of sIL-6R did not differ between controls and either patients with autoimmune aPL or leprosy. The different cytokine profiles as well as differences in circulating levels of TF might contribute to the high thrombotic risk found in patients with autoimmune aPL but not in leprosy related aPL patients.

Antiphospholipid-Mediated Thrombosis: Interplay Between Anticardiolipin Antibodies and Vascular Cells

The antiphospholipid syndrome (APS) is characterized by thrombosis or pregnancy morbidity in the presence of antiphospholipid autoantibodies (aPL). aPL are a heterogeneous family of autoantibodies with diverse cross-reactivities whose origin and role have not been fully elucidated. Many of the autoantibodies associated with APS are directed against phospholipid-binding plasma proteins, such as β2-GPI and prothrombin, or phospholipid-protein complexes. The mechanisms by which aPL cause thrombosis are not completely understood. There is no unique mechanism able to explain all symptoms associated with the presence of aPL. Different theories have been proposed, including the effect of aPL on endothelial cells, monocytes, and platelets. aPL are able to recognize, injure, or activate cultured vascular endothelial cells. Cultured endothelial cells incubated with aPL express increased levels of cell adhesion molecules and tissue factor (TF), an effect mediated by β2-GPI, and may promote inflammation and thrombosis. Overexpression of TF has been also shown in monocytes in vitro and ex vivo. TF is the major initiator of coagulation in vivo; thus, its dysregulation may be one of the most important contributors to thrombosis. Effects of aPL upon platelets are not completely elucidated. aPL bind anionic phospholipid but they are normally in the inner side of cell membranes. When platelets are activated by different agonists, anionic phospholipids are exposed. There is some evidence showing that activated platelets are present in aPL-positive patients. Increased levels of β-thrombomodulin, and microvesicle formation seem to support this hypothesis. Activated platelets may contribute to thrombosis by persistent exposure of a procoagulant surface.

Accelerated rejection, thrombosis, and graft failure with angiotensin II type 1 receptor antibodies

BACKGROUND

Angiotensin II type 1 receptor antibodies (AT1R-Abs) have been implicated in renal transplant rejection and failure; however, the mechanism of allograft damage, patterns of clinical presentation, and response to desensitization of AT1R-Abs have not been clearly established.

CASE DIAGNOSIS/TREATMENT

We present the case of a 7-year-old boy with preformed AT1R-Abs who developed accelerated vascular and cellular rejection and renal allograft thrombosis despite desensitization and treatment with angiotensin receptor blockade. Although an association between AT1R-Abs and microvascular occlusion has been previously described, we are the first to describe an association between AT1R-Abs and renal artery thrombosis, leading to devastating early allograft failure.

CONCLUSIONS

This case highlights the risk of allograft thrombosis associated with AT1R-Abs and illustrates that previous treatments utilized for AT1R-Abs may not always be effective. Further studies are needed to better characterize the mechanisms of AT1R-Ab pathogenesis and to establish safe levels of AT1R-Abs both pre- and post-transplantation. Given the outcome of this patient and the evidence of pro-coagulatory effects of AT1R-Abs, we suggest that the presence of AT1R-Ab may be a risk factor for thrombosis. The role of treatment with anti-coagulation and novel immunomodulatory agents such as tocilizumab and bortezomib require further investigation.

Immunotherapy in antiphospholipid syndrome

Antiphospholipid syndrome (APS) is a disorder characterized by the association of arterial or venous thrombosis and/or pregnancy morbidity with the presence of antiphospholipid antibodies (anticardiolipin antibodies, lupus anticoagulant antibodies, and/or anti-β2-glycoprotein I antibodies). Thrombosis is the major manifestation in patients with aPLs, but the spectrum of symptoms and signs associated with aPLs has broadened considerably, and other manifestations, such as thrombocytopenia, non-thrombotic neurological syndromes, psychiatric manifestations, livedo reticularis, skin ulcers, hemolytic anemia, pulmonary hypertension, cardiac valve abnormality, and atherosclerosis, have also been related to the presence of those antibodies. Several studies have contributed to uncovering the basis of antiphospholipid antibody pathogenicity, including the targeted cellular components, affected systems, involved receptors, intracellular pathways used, and the effector molecules that are altered in the process. Therapy for thrombosis traditionally has been based on long-term oral anticoagulation; however, bleeding complications and recurrence despite high-intensity anticoagulation can occur. The currently accepted first-line treatment for obstetric APS (OAPS) is low-dose aspirin plus prophylactic unfractionated or low-molecular-weight heparin (LMWH). However, in approximately 20% of OAPS cases, the final endpoint, i.e. a live birth, cannot be achieved. Based on all the data obtained in different research studies, new potential therapeutic approaches have been proposed, including the use of new oral anticoagulants, statins, hydroxychloroquine, coenzyme Q10, B-cell depletion, platelet and TF inhibitors, peptide therapy or complement inhibition among others. Current best practice in use of these treatments is discussed.

Cardiovascular risk in systemic autoimmune diseases: epigenetic mechanisms of immune regulatory functions

Autoimmune diseases (AIDs) have been associated with accelerated atherosclerosis (AT) leading to increased cardio- and cerebrovascular disease risk. Traditional risk factors, as well as systemic inflammation mediators, including cytokines, chemokines, proteases, autoantibodies, adhesion receptors, and others, have been implicated in the development of these vascular pathologies. Yet, the characteristics of vasculopathies may significantly differ depending on the underlying disease. In recent years, many new genes and signalling pathways involved in autoimmunity with often overlapping patterns between different disease entities have been further detected. Epigenetics, the control of gene packaging and expression independent of alterations in the DNA sequence, is providing new directions linking genetics and environmental factors. Epigenetic regulatory mechanisms comprise DNA methylation, histone modifications, and microRNA activity, all of which act upon gene and protein expression levels. Recent findings have contributed to our understanding of how epigenetic modifications could influence AID development, not only showing differences between AID patients and healthy controls, but also showing how one disease differs from another and even how the expression of key proteins involved in the development of each disease is regulated.

Differential expression of protease-activated receptors in monocytes from patients with primary antiphospholipid syndrome

OBJECTIVE

To investigate the expression of protease-activated receptors (PARs), their potential regulation by anticardiolipin antibodies (aCL), and their association with the expression of other molecules relevant to thrombosis in monocytes obtained from 62 patients with primary antiphospholipid syndrome (APS).

METHODS

Monocytes were isolated from peripheral blood mononuclear cells by magnetic depletion of nonmonocytes. Expression of tissue factor (TF) and PARs 1-4 genes was measured by quantitative real-time reverse transcription-polymerase chain reaction. Cell surface TF and PARs 1-4 expression was analyzed by flow cytometry. For in vitro studies, purified normal monocytes were incubated with purified APS patient IgG, normal human serum IgG, or lipopolysaccharide, in the presence or absence of specific monoclonal antibodies anti-PAR-1 (ATAP2) or anti-PAR-2 (SAM11) to test the effect of blocking the active site of PAR-1 or PAR-2.

RESULTS

Analysis of both mRNA and protein for the 4 PARs revealed significantly increased expression of PAR-2 as compared with the control groups. PAR-1 was significantly overexpressed in APS patients with thrombosis and in the control patients with thrombosis but without APS. PAR-3 expression was not significantly altered. PAR-4 expression was absent in all groups analyzed. In addition, we demonstrated a correlation between the levels of PAR-2 and the titers of IgG aCL, as well as parallel behavior of TF and PAR-2 expression. In vitro, IgG from APS patients significantly increased monocyte expression of PAR-1 and PAR-2. Inhibition studies suggested that there was direct cross-talk between TF and PAR-2, such that inhibition of PAR-2 prevented the aCL-induced expression of TF.

CONCLUSION

These results provide the first demonstration of increased expression of PARs in monocytes from patients with APS. Thus, PAR antagonists might have therapeutic potential as antithrombotic agents in APS.

Vasoactive Intestinal Peptide and pituary adenylate cyclase-activating polypeptide inhibit tissue factor expression in monocyte in vitro and in vivo

Tissue factor (TF), which is expressed on the surface of activated monocytes, is the major procoagulant that initiates thrombus formation in sepsis. Two endogenous neuropeptides, vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP), are attractive candidates for the development of therapies against septic shock. The purpose of this study was to examine whether VIP or PACAP inhibit the LPS-induced TF expression in monocytes. Treatment of freshly isolated human monocytes or cultured monocytic THP-1 cells with VIP or PACAP leads to reduced LPS-induced TF protein, mRNA expression and activity, as demonstrated by Western blot, real-time polymerase chain reaction, and TF activity assay, respectively. In an endotoxemic model, VIP blunts the increase of LPS-induced TF expression in blood cells at the transcriptional level, as demonstrated by real-time polymerase chain reaction. However, neither neuropeptide affects the expression of TF pathway inhibitor in monocytes. In vitro, LPS increases the migration of c-Rel/p65 into the nucleus and the phosphorylation of p38 and JNK, all of which are essential for LPS-induced TF expression. In addition, interestingly, VIP and PACAP block both the migration of c-Rel/p65 and the phosphorylation of p38 and JNK, as demonstrated by Western blot analysis. These data indicate that VIP and PACAP inhibit LPS-induced TF expression in monocytes in vitro and in vivo, confirming these peptides as candidates for the multitarget therapy of septic shock.

Annexin A2: biology and relevance to the antiphospholipid syndrome

Antiphospholipid antibodies (aPL), the majority of which are directed against beta(2)-glycoprotein I (beta(2)GPI), are associated with an increased incidence of venous and arterial thrombosis. The pathogenesis of antiphospholipid/anti-beta(2)GPI-associated thrombosis has not been defined, and is likely multifactorial. However, accumulating evidence suggests an important role for endothelial cell activation with the acquisition of a procoagulant phenotype by the activated endothelial cell. Previous work demonstrated that endothelial activation by antiphospholipid/anti-beta(2)GPI antibodies is beta(2)GPI-dependent. We extended these observations by defining annexin A2 as an endothelial beta(2)GPI binding site. We also observed that annexin A2 plays a critical role in endothelial cell activation induced by anti-beta(2)GPI antibodies, and others have described direct endothelial activation by anti-annexin A2 antibodies in patients with aPL . Similar findings have been reported using human monocytes, which also express annexin A2. Because annexin A2 is not a transmembrane protein, how binding of beta(2)GPI/anti-beta(2)GPI antibodies, or anti-annexin A2 antibodies, to endothelial annexin A2 causes cellular activation is unknown. Recent studies, however, suggest an important role for the Toll-like receptor family, particularly TLR4. In this article, we review the role of these interactions in the activation of endothelial cells by aPL . The influence of these antibodies on the ability of annexin A2 to enhance t-PA-mediated plasminogen activation is also discussed.

Humoral responses directed against non-human leukocyte antigens in solid-organ transplantation

Antibody-mediated mechanisms have a major impact on allograft function and survival. During the last decade, improved immunohistochemical and serologic diagnostic procedures have been developed to monitor antibody responses against human leukocyte antigens (HLA). Acute and chronic allograft rejection can occur in HLA-identical sibling transplants implicating the importance of immune response against non-HLA targets. Non-HLA, complement and noncomplement-fixing antibodies may be responsible for a variety of allograft injuries, reflecting the complexity of their acute and chronic actions. Non-HLA antibodies may occur as alloantibodies or autoantibodies. Their antigenic targets described, thus, far include various minor histocompatibility antigens, vascular receptors, adhesion molecules, and intermediate filaments. An analysis of the subtle mechanistic differences in the individual antibody responses directed against non-HLA may help to identify patients at particular risk for irreversible acute or chronic allograft injuries and improve overall outcomes. This review summarizes the current state of research, development in diagnostic and therapeutic strategies, discusses some emerging problems, and provides perspectives in the area of humoral response against non-HLA in solid-organ transplantation.

Genomics and proteomics: a new approach for assessing thrombotic risk in autoimmune diseases

Several systemic autoimmune conditions, including rheumatoid arthritis, systemic lupus erythematosus and antiphospholipid syndrome, are characterised by enhanced atherosclerosis and, consequently, higher cardiovascular morbidity and mortality rates. The association of these diseases with atherosclerosis suggests a common pathogenic mechanism. Genomic and proteomic studies performed on atherosclerotic plaques have further confirmed the presence of a gene and protein profile similar to that observed in autoimmune diseases with cardiovascular risks. Human sera and body fluids have been analysed and have resulted in the identification of auto-antibodies that can be used as diagnostic markers in specific autoimmune diseases, and proteomic fingerprints of blood cells, tissues and body fluids have resulted in the identification of individual proteins or patterns of protein expression that are deregulated. The information provided by these proteomic studies is of diagnostic and therapeutic potential. In this review, we discuss new approaches available for assessing thrombotic risk in autoimmune diseases, focusing in the genomic and proteomic methods now available to deep into the origin of the mechanisms associated with vascular involvement in systemic autoimmune diseases. The increasing data available suggests that when treating patients with these autoimmune disorders, paying attention to the increased risk of cardiovascular disease is essential.

Anti-beta2-glycoprotein I antibodies induce monocyte release of tumor necrosis factor alpha and tissue factor by signal transduction pathways involving lipid rafts

OBJECTIVE

To investigate the association of beta(2)-glycoprotein I (beta(2)GPI) with lipid rafts in monocytic cells and to evaluate the proinflammatory and procoagulant effects of anti-beta(2)GPI binding to its target antigen on the monocyte plasma membrane.

METHODS

Human monocytes were fractionated by sucrose density-gradient centrifugation and analyzed by Western blotting. Immunoprecipitation experiments were performed to analyze the association of beta(2)GPI with lipid rafts and the possible interaction of beta(2)GPI with annexin A2 and Toll-like receptor 4 (TLR-4). Monocytes were then stimulated with affinity-purified anti-beta(2)GPI antibodies from patients with the antiphospholipid syndrome (APS). Interleukin-1 receptor-associated kinase (IRAK) phosphorylation and NF-kappaB activation were evaluated by immunoprecipitation and transcription factor assay, respectively. Supernatants from monocytes were tested for tumor necrosis factor alpha (TNFalpha) and tissue factor (TF) levels by enzyme-linked immunosorbent assay.

RESULTS

We found beta(2)GPI and its putative receptor annexin A2 in lipid raft fractions of human monocytes. Moreover, there was an association between beta(2)GPI and TLR-4, suggesting that it was partially dependent on raft integrity. Triggering with anti-beta(2)GPI antibodies induced IRAK phosphorylation and consequent NF-kappaB activation, which led to the release of TNFalpha and TF.

CONCLUSION

Anti-beta(2)GPI antibodies react with their target antigen, likely in association with annexin A2 and TLR-4, in lipid rafts in the monocyte plasma membrane. Anti-beta(2)GPI binding triggers IRAK phosphorylation and NF-kappaB translocation, leading to a proinflammatory and procoagulant monocyte phenotype characterized by the release of TNFalpha and TF, respectively. These findings provide new insight into the pathogenesis of APS, improving our knowledge of valuable therapeutic targets.

The role of angiotensin II type 1 receptor-activating antibodies in renal allograft vascular rejection

Acute rejection with vascular involvement remains a challenging problem in renal allotransplantation. Fibrinoid necrosis of the arteries with secondary thrombotic occlusions is C4d negative in 50% of cases and has the worst prognosis among all allograft vascular lesions. Nonhuman leukocyte antigen (HLA) non-complement-fixing antibodies reacting to artery-specific antigens have been speculated to be responsible for causing severe vascular injury. We recently reported the presence of agonistic antibodies against the angiotensin II type 1 receptor (AT(1)R-AA) in 16 recipients of renal allografts who had severe vascular rejection and malignant hypertension but who did not have anti-HLA antibodies. AT(1)R-AA stimulate AT(1)R and induce mediators of inflammation and thrombosis. Removal of AT(1)R-AA by plasmapheresis in combination with pharmacologic AT(1)R blockade leads to improved renal function and graft survival in AT(1)R-AA-positive patients. We have shown that the analysis of the subtle diagnostic and mechanistic differences may help to identify patients at particular risk and improve outcome of rejections with vascular pathology.

The catastrophic antiphospholipid (Asherson's) syndrome and malignancies

The catastrophic antiphospholipid syndrome is characterised by the rapid chronological development of fulminant thrombotic complications that predominantly affect small vessels. It has been reported as frequently occurring in patients with underlying malignancies. We analysed the web site-based international registry of patients with catastrophic APS. The clinical characteristics of patients with CAPS and an underlying malignancy were evaluated. Of the 262 patients included in the CAPS registry, information on associated malignancies was available in 23 (9%) cases. Haematological malignancies were present in 6 (26%) patients. Four of the patients suffered from lung carcinoma (17%), and two patients (9%) from colon carcinoma. In most of the patients (61%), malignancy was the precipitating factor for CAPS. In 4 patients (17%), however, surgical procedures related to the carcinoma were noted as precipitating factors. In one patient CAPS occurred during allogenic stem cell transplantation after diagnosis of acute lymphoblastic leukemia (ALL). Cerebral manifestations were most common and consisted mainly of cerebral infarcts and encephalopathy. Recovery occurred in 9/23 (39%) patients. Malignancy may be an important risk factor for CAPS. 9% of patients with CAPS presented with an underlying malignancy. In most of these patients, the malignancy and/or surgical procedures were the precipitating factors for CAPS.

Vascular endothelial growth factor expression in monocytes from patients with primary antiphospholipid syndrome

BACKGROUND

One of the described mechanisms leading to thrombosis in antiphospholipid syndrome (APS) is overexpression of tissue factor (TF) in the monocytes and endothelial cells of patients with antiphospholipid antibodies (aPL). Vascular endothelial growth factor (VEGF) may stimulate monocyte TF expression through its receptor, the tyrosine kinase Flt-1.

OBJECTIVES

This study aimed to analyze the following in monocytes of 55 primary APS patients: VEGF and Flt-1 expression levels, their potential regulation by aPL, and the association of VEGF and Flt-1 expression with the increased TF expression found in APS patients.

RESULTS

Purified monocytes from APS patients showed higher levels of VEGF and Flt-1 than healthy donors, which further correlated with immunoglobulin G (IgG) anticardiolipin titers and TF expression rank. Moreover, monocyte VEGF and Flt-1 levels were significantly higher in patients with than in patients without previous thrombosis. In vitro, IgG from APS patients increased monocyte VEGF and Flt-1 expression in a dose-dependent manner. VEGF and Flt-1 expression was significantly inhibited by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580; this suggests the involvement of this kinase in the aPL-induced VEGF and Flt-1 upregulation.

CONCLUSIONS

Our data show, for the first time in vivo, that monocytes from primary APS patients have an increased expression of VEGF and Flt-1. Furthermore, in vitro results indicated that this cytokine is produced by monocytes when treated with aPL, and that the p38 MAPK signaling pathway plays an important role. Thus, VEGF might act as a regulatory factor in aPL-mediated monocyte activation and TF expression, thereby contributing to the proinflammatory-prothrombotic phenotype of APS patients.

Complement-fixing activity of anticardiolipin antibodies in patients with and without thrombosis

We have analysed in vitro the complement-fixing activity of anticardiolipin antibodies (C-fix aCL) from patients with persistent and moderate/high titres IgG aCL antibodies: 21 with thrombosis and 11 without thrombosis. Titre and C-fix ability of aCL were measured by ELISA. APS and non-APS patients were similar with regard to mean levels of IgG aCL (46 +/- 24 versus 51 +/- 30 GPL, P = 0.7), frequency of IgM aCL (P = 0.7) and a comparable predominance of IgG2 aCL reactivity on ELISA (95% versus 100%, respectively, P = 1.0). Remarkably, a high frequency of C-fix aCL (71% versus 92%, P = 0.35) was observed in both groups. Similarly, no difference was observed in the mean level of C-fix aCL in APS and non-APS patients (7 +/- 6 versus 9 +/- 8 SDunits, P = 0.3). Analysis of 10 primary and 11 secondary APS also revealed a comparable IgG aCL mean titre (57 +/- 29 versus 37 +/- 11, P = 0.06), frequency of IgM aCL (P = 0.6) and of C-fix aCL (70% versus 73%, P = 0.99). Among APS patients six had exclusive arterial events and seven exclusive venous events. The IgG aCL mean titre (36 +/- 10 versus 36 +/- 11 GPL, P = 0.9) and the frequency of IgM aCL antibodies (P = 0.56) in these subgroups of patients were comparable. There was a trend of higher frequency of C-fix aCL in patients with exclusive venous events (100%) compared to 50% of those with exclusive arterial events (p = 0.07). Importantly, C-fix aCL titre was higher in the former group compared to the later one (8 +/- 5 SDunits versus 2 +/- 2 SDunits, P = 0.016). Our data support the notion of a high frequency of C-fix aCL in APS. Although it does not discriminate those patients without thrombotic events with persistent moderate/high levels of aCL, this property seems to be more relevant in venous events and may provide the basis for further understanding the distinct pathogenic mechanisms underlying arterial and venous occlusive disorders of APS.

Antiphospholipid antibodies from patients with the antiphospholipid syndrome induce monocyte tissue factor expression through the simultaneous activation of NF-kappaB/Rel proteins via the p38 mitogen-activated protein kinase pathway, and of the MEK-1/ERK pathway

OBJECTIVE

Antiphospholipid syndrome (APS) is characterized by thrombosis and the presence of antiphospholipid antibodies (aPL). In patients with primary APS, expression of tissue factor (TF) on the surface of monocytes is increased, which may contribute to thrombosis in these patients. However, the intracellular mechanisms involved in aPL-mediated up-regulation of TF on monocytic cells are not understood. This study was undertaken to investigate the intracellular signals induced by aPL that mediate TF activation in monocytes from APS patients.

METHODS

We analyzed, both in vivo and in vitro, aPL interactions with proteins that have signaling functions, including mitogen-activated protein kinases (MAP kinases) and NF-kappaB/Rel proteins.

RESULTS

In vivo studies demonstrated significantly higher levels of both TF messenger RNA and TF protein in monocytes from APS patients compared with controls. At the molecular level, increased proteolysis of IkappaBalpha and activation of NF-kappaB were observed. Constitutive activation of both p38 and ERK-1 MAP kinases was also found. Treatment of normal monocytes with aPL activated ERK-1 and p38 MAP kinases, as well as the IkappaB/NF-kappaB pathway, in a dose-dependent manner. NF-kappaB activation and IkappaBalpha degradation induced by aPL were inhibited by the NF-kappaB inhibitor SN50 and the p38 MAP kinase inhibitor SB203580, thus suggesting crosstalk between these pathways. However, the MEK-1/ERK inhibitor PD98059 did not affect aPL-induced NF-kappaB binding activity. TF expression induced by aPL was significantly inhibited by combined treatment with the 3 inhibitors.

CONCLUSION

Our results suggest that aPL induces TF expression in monocytes from APS patients by activating, simultaneously and independently, the phosphorylation of MEK-1/ERK proteins, and the p38 MAP kinase-dependent nuclear translocation and activation of NF-kappaB/Rel proteins.

Autoantibodies against the fibrinolytic receptor, annexin 2, in antiphospholipid syndrome

The association of thrombosis and gestational morbidity with antiphospholipid antibodies is termed antiphospholipid syndrome (APS). Annexin 2 (A2) is a profibrinolytic endothelial cell surface receptor that binds plasminogen, its tissue activator (tPA), and beta(2)-glycoprotein I (beta2GPI), the main antigen for antiphospholipid antibodies. Here, we evaluate A2 as a target antigen in APS. Serum samples from 434 individuals (206 patients with systemic lupus erythematosus without thrombosis, 62 with APS, 21 with nonautoimmune thrombosis, and 145 healthy individuals) were analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoblot for antiphospholipid and A2 antibodies. Anti-A2 antibodies (titer > 3 SDs) were significantly more prevalent in patients with APS (22.6%; venous, 17.5%; arterial, 34.3%; and mixed thrombosis, 40.4%) than in healthy individuals (2.1%, P < .001), patients with nonautoimmune thrombosis (0%, P = .017), or patients with lupus without thrombosis (6.3%, P < .001). Anti-A2 IgG enhanced the expression of tissue factor on endothelial cells (6.4-fold +/- 0.13-fold SE), blocked A2-supported plasmin generation in a tPA-dependent generation assay (19%-71%) independently of beta2GPI, and inhibited cell surface plasmin generation on human umbilical vein endothelial cells (HUVECs) by 34% to 83%. We propose that anti-A2 antibodies contribute to the prothrombotic diathesis in antiphospholipid syndrome.

Thrombotic manifestations of the antiphospholipid syndrome in patients with malignancies

The presence of antiphospholipid antibodies has been reported in a large variety of patients with malignancies. Many case reports and reviews have appeared indicating that the presence of the antiphospholipid antibodies is related to thrombotic associations with the antiphospholipid syndrome (APS) in a proportion of these patients. We investigated the frequency of the thrombotic manifestations in 58 patients demonstrating antiphospholipid antibodies and with a history of neoplasia, including haematologic and lymphoproliferative malignancies. Antiphospholipid antibodies were detected by clotting assay [lupus anticoagulant (LAC)] or by enzyme-linked immunosorbent assay [anticardiolipin antibodies (aCL)] according to the Sapporo criteria. Patients, 39/58, suffered from solid tumours and 19/58 patients from malignant haematologic or lymphoproliferative diseases. One patient was suffering simultaneously from two solid tumours and a malignant lymphoma. Among the patients with solid tumours, 18/39 (46%) patients had thromboembolic complications of the antiphospholipid syndrome. Among the patients with haematologic and lymphoproliferative malignancies, only 6/19 (32%) suffered from thromboembolic complications. There was, however, no relation between the titres of aCL antibodies and the clinical manifestations. The presence, but not the titres, of antiphospholipid antibodies may identify a subset of cancer patients with a high risk of developing thrombotic complications. The frequency of thrombosis, however, is lower in aPL-positive patients with lymphoproliferative and haematological malignancies.

Predictive role of hs-C-reactive protein in patients with antiphospholipid syndrome

High-sensitive C-reactive protein (hs-CRP) is a marker of inflammation which has been shown in several prospective studies to independently predict myocardial infarction, stroke and peripheral artery disease. Patients with antiphospholipid antibodies (aPL) are at increased risk of recurrent thromboembolic events, but the possibility of predicting this risk seems rather limited. Similarities were recently found between aPL and CRP in the pathology of thrombosis. The current study investigated the predictive role of hs-CRP in a cohort of patients with neurological manifestations. A follow-up investigation was done in a cohort of 55 aPL-positive patients with acute manifestations of neurological disease. hs-CRP levels were measured in all patients at enrollment and were compared to the patients' condition after a median period of 32 months. Lupus anticoagulants were detected according to the Standardization of Lupus Anticoagulants (SSC) of the ISTH. Anticardiolipin tests were performed by a beta2-glycoprotein I-dependent enzyme-linked immunsorbent assay (Pharmacia ELISA). hs-CRP was measured by latex-enhanced turbidometry (dimension RXL, Dade Behring). Cerebral infarctions and transient ischemic attacks were the most frequent cerebral events. In patients with aPL, elevated levels of hs-CRP were closely associated with an increased rate of recurrent or residual symptoms (OR, 12.5; 95% CI, 3.72-41.94) and were not related to other risk factors, except smoking (p<0.05). The rate at which a given patient's condition deteriorated was also related to the level of hs-CRP. In patients with antiphospholipid syndrome (APS), elevated levels of hs-CRP may identify a group of patients which is at high risk of recurrent or residual neurological symptoms and which may benefit from more careful follow-up and from antithrombotic therapy.

Annexin A2 mediates endothelial cell activation by antiphospholipid/anti-β2 glycoprotein I antibodies

Patients with antiphospholipid antibodies (APLAs) are at increased risk for arterial and venous thrombosis. Many APLAs associated with these events react with β2 glycoprotein I (β2GPI), and endothelial cell reactive antibodies that activate endothelial cells in a β2GPI-dependent manner occur commonly in these patients. We previously reported that β2GPI binds with high affinity to annexin A2 on the endothelial surface, though the relevance of this interaction to APLA/anti-β2GPI antibody–induced endothelial activation has not been determined. In this report, we confirm that anti-β2GPI antibodies activate endothelial cells in the presence of β2GPI, and demonstrate that anti–annexin A2 antibodies directly cause endothelial cell activation of a similar magnitude and with a similar time course. Moreover, bivalent anti–annexin A2 F(ab′)2 fragments also caused endothelial cell activation, whereas monomeric Fab fragments not only did not cause activation, but blocked activation induced by anti–annexin A2 antibodies and F(ab′)2 fragments, as well as that caused by anti-β2GPI antibodies in the presence of β2GPI. These observations suggest a novel pathway for endothelial activation induced by APLA/anti-β2GPI antibodies that is initiated by cross-linking or clustering of annexin A2 on the endothelial surface.

Angiotensin II type 1-receptor activating antibodies in renal-allograft rejection

BACKGROUND

Antibodies against HLA antigens cause refractory allograft rejection with vasculopathy in some, but not all, patients.

METHODS

We studied 33 kidney-transplant recipients who had refractory vascular rejection. Thirteen had donor-specific anti-HLA antibodies, whereas 20 did not. Malignant hypertension was present in 16 of the patients without anti-HLA antibodies, 4 of whom had seizures. The remaining 17 patients had no malignant hypertension. We hypothesized that activating antibodies targeting the angiotensin II type 1 (AT1) receptor might be involved.

RESULTS

Activating IgG antibodies targeting the AT1 receptor were detected in serum from all 16 patients with malignant hypertension and without anti-HLA antibodies, but in no other patients. These receptor-activating antibodies are subclass IgG1 and IgG3 antibodies that bind to two different epitopes on the second extracellular loop of the AT1 receptor. Tissue factor expression was increased in renal-biopsy specimens from patients with these antibodies. In vitro stimulation of vascular cells with an AT1-receptor-activating antibody induced phosphorylation of ERK 1/2 kinase and increased the DNA binding activity of the transcription factors activator protein 1 (AP-1) and nuclear factor-kappaB. The AT1 antagonist losartan blocked agonistic AT1-receptor antibody-mediated effects, and passive antibody transfer induced vasculopathy and hypertension in a rat kidney-transplantation model.

CONCLUSIONS

A non-HLA, AT1-receptor-mediated pathway may contribute to refractory vascular rejection, and affected patients might benefit from removal of AT1-receptor antibodies or from pharmacologic blockade of AT1 receptors.

Fluvastatin inhibits up-regulation of tissue factor expression by antiphospholipid antibodies on endothelial cells

BACKGROUND

Mechanisms of thrombosis induced by antiphospholipid (aPL) antibodies include up-regulation of tissue factor (TF) expression on endothelial cells (ECs). Statins have been shown to reduce levels of TF induced by tumor necrosis factor (TNF-alpha) and lipopolysaccharide (LPS) on ECs. In a recent study, fluvastatin inhibited thrombogenic and proinflammatory properties of aPL antibodies in in vivo models. The aim of this study was to determine whether fluvastatin has an effect on aPL-induced expression of TF on ECs.

METHODS

IgGs were purified from four patients with APS (IgG-APS) and from control sera (IgG-NHS). Cultured human umbilical vein endothelial cells (HUVEC) were treated with IgG-APS or IgG-NHS or with medium alone or with phorbol myristate acetate (PMA), as a positive control. In some experiments, cells were pretreated with fluvastatin (2.5, 5 or 10 micro m) with and without mevalonate (100 micro m). TF expression on HUVECs was measured by ELISA.

RESULTS

PMA and the four IgG-APS preparations increased the expression of TF on EC significantly (4.9-, 2.4-, 4.2-, 3.5- and 3.1-fold, respectively), in a dose-dependent fashion. Fluvastatin (10 micro m) inhibited the effects of PMA and the four IgG-APS on TF expression by 70, 47, 65, 22 and 68%, respectively, and this effect was dose-dependent. Mevalonate (100 micro m) completely abrogated the inhibitory effects of fluvastatin on TF expression induced by aPL.

CONCLUSION

Because of the suggested pathogenic role of aPL on induction of TF on ECs, our data provide a rationale for using statins as a therapeutic tool in treatment of thrombosis in APS.

Type 1 and type 2 cytokine-producing CD4+ and CD8+ T cells in primary antiphospholipid syndrome

Antiphospholipid syndrome (APS) is an autoimmune condition characterized by thrombosis and/or recurrent fetal loss as well as the presence of autoantibodies against epitopes present on phospholipid-binding proteins. The role of cellular immunity in the pathogenesis of the syndrome remains unclear. We studied the cellular phenotype and the production of type 1 [interferon (IFN)-gamma, interleukin (IL)-2] and type 2 (IL-4, IL-10) cytokines by CD4+ and CD8+ T-lymphocyte subsets in 13 patients with untreated primary APS (PAPS) and in 32 healthy controls. The production of cytokines was determined in T cells after a 5-h culture with or without mitogenic stimulation using a flow cytometric method of intracellular cytokine staining. In six of the patients these studies were repeated 6 months later. In PAPS patients we found a reduced percentage of circulating CD4+CD45RA+ and an increased percentage and absolute number of CD8+HLA-DR+ cells. A type 1 response was observed in the patients' unstimulated cells, indicated by an increase in IFN-gamma-producing CD8+, IL-2-producing CD4+ T cells, and a decrease in IL-4-producing CD4+ and CD8+ T cells. Similar results were obtained in the patients at follow-up. Taken together, these results suggest a chronic in vivo stimulation of CD4+ and CD8+ T cells in PAPS patients exhibiting a type 1 polarization. Changes of cellular immunity may contribute to the pathogenesis of the clinical manifestations of the syndrome and might be proven to be useful targets for therapeutic interventions in the future.

Intracellular signaling triggered by antiphospholipid antibodies in platelets and endothelial cells: a pathway to targeted therapies

Understanding the intracellular events triggered by antiphospholipid (aPL) antibodies in platelets and endothelial cells (ECs) is important in designing new modalities of targeted therapies for the treatment of thrombosis in Antiphospholipid Syndrome (APS). A recent study showed a significant increase in the expression of GPIIb/IIIa on platelets treated with aPL antibodies and a thrombin receptor peptide agonist (TRAP), and these effects were abrogated by hydroxychloroquine (HQ). Hydroxychloroquine has also been shown to reduce in vivo aPL-induced thrombus formation. Furthermore, aPL-enhanced thrombosis in vivo can be abrogated by infusions of a GPIIb/IIIa antagonist (1B5) monoclonal antibody, and aPL-mediated thrombophilia is not observed in GPIIb/IIIa-deficient mice. Treatment of platelets with aPL antibodies has resulted in a significant increase in p38 mitogen-activated protein kinase (p38MAPK) phosphorylation and aPL-induced platelet aggregation and thromboxane B2 (TXB2) production was abrogated by SB203580 (a p38MAPK inhibitor). aPL antibodies induce increased expression, function and transcription of tissue factor (TF) on EC. Activation of ECs and thrombogenicity of aPL in vivo can be reversed by treatment of the animals with statins. Upregulation of TF on ECs can also be abrogated by treatment of the cells with fluvastatin. There is also indication of activation of nuclear factor kappa B (NFkappaB), increase in phosphorylation of p38MAPK in ECs by aPL antibodies that can be reversed by specific inhibitors MG132 and SB203580, respectively. The data open the possibility to new treatment modalities that may include the use of hydroxychloroquine, statins, specific antagonists of GPIIb/IIIa (such as abciximab or equivalent) and specific p38MAPK inhibitors, after the completion of well-designed clinical studies.

Inhibition of the thrombogenic and inflammatory properties of antiphospholipid antibodies by fluvastatin in an in vivo animal model

OBJECTIVE

Antiphospholipid antibodies (aPL) have thrombogenic properties in vivo, through their interactions with soluble coagulation factors and their ability to modulate the functions of cells involved in coagulation homeostasis. These antibodies have also been shown to enhance the adhesion of leukocytes to endothelial cells (ECs) in vivo. New lipophilic statins such as fluvastatin have antiinflammatory and antithrombogenic effects. This study uses an in vivo mouse model to investigate whether fluvastatin has an effect on decreasing both the adhesion of leukocytes to ECs and the thrombus formation induced by aPL.

METHODS

Two groups of CD-1 male mice, each comprising approximately 18 mice, were fed either normal saline solution or 15 mg/kg fluvastatin for 15 days. Each of the 2 groups was further subdivided to receive either purified IgG from patients with the antiphospholipid syndrome (IgG-APS) or normal IgG from healthy subjects. Analysis of thrombus dynamics was performed in treated and control mice, using a standardized thrombogenic injury procedure, and the area (size) of the thrombus was measured. Adhesion of leukocytes to ECs was analyzed with a microcirculation model of exposed cremaster muscle. Baseline and posttreatment soluble intercellular adhesion molecule 1 (sICAM-1) levels were determined by enzyme-linked immunosorbent assay.

RESULTS

IgG-APS mice treated with fluvastatin showed significantly smaller thrombi, a reduced number of adherent leukocytes, and decreased levels of sICAM-1 compared with IgG-APS animals treated with placebo.

CONCLUSION

These findings indicate that fluvastatin significantly diminishes aPL-mediated thrombosis and EC activation in vivo. These results may have important implications for the design of new treatment strategies aimed at preventing recurrent thrombosis in patients with APS.

Autoimmune antiphospholipid antibodies impair the inhibition of activated factor X by protein Z/protein Z-dependent protease inhibitor

The hemostatic process is tightly regulated by several antithrombotic mechanisms. Among them, protein Z (PZ)-dependent protease inhibitor (ZPI) potently inhibits factor (F)Xa in a manner dependent on calcium ions, phospholipids and PZ. Autoimmune antiphospholipid antibodies (aPL) are mainly directed against phospholipid-binding plasma proteins such as beta2-glycoprotein I (beta2GPI) and prothrombin, and are known to interfere with phospholipid-dependent hemostatic pathways. In this study, we investigated whether purified aPL are able to interfere with inhibition of FXa by PZ/ZPI. beta2GPI modestly delayed the FXa inactivation by PZ/ZPI and most isolated aPL-IgGs were found to further increase the inhibitory potential of beta2GPI on PZ/ZPI activity. Without beta2GPI, the PZ/ZPI activity was unaffected by the addition of aPL-IgG. As PZ deficiency is hypothesized to lead to a prothrombotic state, we performed a case-control study to measure plasma levels of PZ and ZPI in 66 patients with autoimmune aPL and 152 normal controls. The prevalence of low PZ levels (below the 5th percentile of controls) was significantly greater in the 37 patients with definite antiphospholipid syndrome (APS) (24.3%) but not in the 29 aPL patients not fulfilling the criteria for APS (10.3%) compared with the normal group (4.6%, P < 0.001 vs. APS). ZPI antigen levels were similar in patients with aPL and normal controls. Concomitant PZ deficiency increased by approximately sevenfold the risk of arterial thrombosis in aPL patients. Taken together, these data suggest that the PZ/ZPI system is commonly impaired in aPL patients thus probably increasing the thrombotic risk.

Treatment and monitoring of patients with antiphospholipid antibodies and thrombotic history (Hughes syndrome)

Patients with Hughes (antiphospholipid) syndrome who develop an initial thrombosis have an increased risk of subsequent thrombotic events. Current therapy to prevent recurrent thrombosis is controversial. While it seems clear that anticoagulant treatment is a better option than anti-aggregants alone, there is no consensus regarding the duration and intensity of oral anticoagulation. The risk of bleeding, the main complication of anticoagulant treatment, and the need for frequent monitoring of the International Normalized Ratio to measure the anticoagulant effect of warfarin concern patients and physicians. In addition, there is some debate about the validity of the International Normalized Ratio in patients with lupus anticoagulant activity. The development of new therapies that target more specific pathogenic mechanisms is highly warranted.