Tissue factor in antiphospholipid antibody-induced pregnancy loss: a pro-inflammatory molecule

Expression of tissue factor and tissue factor pathway inhibitors during ovulation in rats: a relevance to the ovarian hyperstimulation syndrome

BACKGROUND

Blood coagulation has been associated with ovulation and female infertility. In this study, the expression of the tissue factor system was examined during ovulation in immature rats; the correlation between tissue factor and ovarian hyperstimulation syndrome (OHSS) was evaluated both in rats and human follicular fluids.

METHODS

Ovaries were obtained at various times after human chorionic gonadotropin (hCG) injection to investigate the expression of tissue factor system. Expression levels of ovarian tissue factor, tissue factor pathway inhibitor (Tfpi)-1 and Tfpi-2 genes and proteins were determined by real-time quantitative polymerase chain reaction (qPCR), and Western blot and immunofluorescence analyses, respectively. Expression levels of tissue factor system were also investigated in ovaries of OHSS-induced rats and in follicular fluid of infertile women.

RESULTS

The expression of tissue factor in the preovulatory follicles was stimulated by hCG, reaching a maximum at 6 h. Tissue factor was expressed in the oocytes and the preovulatory follicles. Tfpi-2 mRNA levels were mainly increased by hCG in the granulosa cells whereas the mRNA levels of Tfpi-1 were decreased by hCG. Human CG-stimulated tissue factor expression was inhibited by the progesterone receptor antagonist. The increase in Tfpi-2 expression by hCG was decreased by the proliferator-activated receptor γ (PPARγ) antagonist. Decreased expression of the tissue factor was detected in OHSS-induced rats. Interestingly, the tissue factor concentrations in the follicular fluids of women undergoing in vitro fertilization were correlated with pregnancy but not with OHSS.

CONCLUSIONS

Collectively, the results indicate that tissue factor and Tfpi-2 expression is stimulated during the ovulatory process in rats; moreover, a correlation exists between the levels of tissue factor and OHSS in rats but not in humans.

Antiphospholipid antibodies in women with severe preeclampsia and placental insufficiency: a case-control study

Objective Preterm delivery for preeclampsia or placental insufficiency (PREPI) is a clinical criterion for antiphospholipid syndrome (APS), but no prior prospective studies have used the international classification criteria for APS. Our objective is to determine the proportion of women with PREPI who test positive for aPL using international criteria for antiphospholipid antibody (aPL) assays. Methods We conducted a prospective, case-control study of 148 women delivered < 36 weeks because of PREPI compared to 148 controls. PREPI cases delivered < 36 weeks were compared to matched controls. Cases and controls were tested for aPL. Demographic variables were compared with chi-squared and Wilcoxon-rank-sum statistics. Rates of + aPL were compared using adjusted odds ratios (aORs) for maternal body mass index (BMI) and Caucasian race. Positive aPL (+aPL) was defined as lupus anticoagulant (LA), anticardiolipin (aCL) immunoglobulin G (IgG) (GPL) or immunoglobulin M (IgM) (MPL) ≥ 40, or anti-β2-glycoprotein I (aβ2GPI) IgG (SGU) or IgM (SMU) ≥ 40. Results Controls were more likely to be Caucasian (87% vs 70%, p = 0.006) and had lower BMIs (BMI 26 vs 33, p < 0.001). Positive aPL were found more commonly in cases than controls (11.5% vs 1.4%, aOR 8.9 (95% CI 1.9-41.4)). In + aPL cases, 76% had + LA, 41% had + aCL, and 24% had + aβ2GPI. Conclusion Women requiring early delivery for PREPI are more likely to have aPL (and thus APS) than controls. This is the first prospective study using both obstetric definitions and laboratory criteria in accordance with APS international criteria.

Complement-coagulation connections

: Complement and coagulation are evolutionarily related proteolytic cascades in the blood that are critical for effecting an appropriate innate response to injury that limits bleeding and infection, while promoting healing. Although often viewed as distinct, it has long been recognized that cross-talk likely exists between these pathways. Only recently have molecular links been established. These are providing insights that are revealing opportunities for the development of novel therapeutic strategies to better treat a wide range of thrombotic, inflammatory, immune, infectious, and malignant diseases. In this brief review, the complex relationship between complement and coagulation is highlighted, underlining some of the newly uncovered interactions, in the hopes of stimulating innovative research that will yield improvements in patient outcomes.

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.

The physiologic anticoagulant and anti-inflammatory role of heparins and their utility in the prevention of pregnancy complications

Accumulating evidence supports the concept of increased thrombin generation, placental vascular lesions, and inflammation as crucial points in the development of the great obstetrical syndromes [preeclampsia, intrauterine growth restriction (IUGR), preterm labor (PTL), preterm prelabor rupture of membranes (PROM), fetal demise and recurrent abortions]. In light of this, the role of heparins for primary or secondary prevention of these syndromes is becoming more and more apparent, mainly due to the antithrombotic and anti-inflammatory effects of heparins. There is agreement regarding the use of heparin in the prevention of gestational complications in patients with antiphospholipid syndrome, while its use for other obstetrical complications is under debate. In the present review we will describe the physiologic role of heparins on coagulation and inflammation and we will discuss current evidence regarding the use of heparins for the prevention/ treatment of obstetrical syndromes.

Pre-eclampsia as a manifestation of antiphospholipid syndrome: assessing the current status

The presence of antiphospholipid antibodies is considered a risk factor for pre-eclampsia. Two meta-analyses and a number of case-control and cohort studies have found associations between pre-eclampsia and lupus anticoagulant, anticardiolipin, and/or anti-β2 glycoprotein I. However, existing literature is inconsistent, with varying severity of pre-eclampsia phenotype examined, differing aPL titer cutoffs used to define positive status, and an overwhelming lack of repeat confirmatory aPL testing. This calls into question the link between aPLs and pre-eclampsia, or at least makes it less well defined. There is evidence for a mechanistic pathway between aPLs and adverse pregnancy outcomes (APOs) including pre-eclampsia via the complement pathway. Complement appears to be overactive in pregnancies affected by APOs. A mouse model has show that the fetal wastage caused by treatment with human aPLs can be salvaged by either creating genetic knockouts along the complement, TNF-alpha, and tissue factor pathways or be treating mice with monoclonal antibodies blocking key complement factors. Thus, this is worth further investigation to clarify the likely association of aPLs and pre-eclampsia in humans, as well is to further evaluate the interaction with complement in human pregnancies.

Reincarnation of ancient links between coagulation and complement

Throughout evolution, organisms have developed means to contain wounds by simultaneously limiting bleeding and eliminating pathogens and damaged host cells via the recruitment of innate defense mechanisms. Disease emerges when there is unchecked activation of innate immune and/or coagulation responses. A key component of innate immunity is the complement system. Concurrent excess activation of coagulation and complement - two major blood-borne proteolytic pathways - is evident in numerous diseases, including atherosclerosis, diabetes, venous thromboembolic disease, thrombotic microangiopathies, arthritis, cancer, and infectious diseases. Delineating the cross-talk between these two cascades will uncover novel therapeutic insights.

Eculizumab reduces complement activation, inflammation, endothelial damage, thrombosis, and renal injury markers in aHUS

Atypical hemolytic uremic syndrome (aHUS) is a genetic, life-threatening disease characterized by uncontrolled complement activation, systemic thrombotic microangiopathy (TMA), and vital organ damage. We evaluated the effect of terminal complement blockade with the anti-C5 monoclonal antibody eculizumab on biomarkers of cellular processes involved in TMA in patients with aHUS longitudinally, during up to 1 year of treatment, compared with in healthy volunteers. Biomarker levels were elevated at baseline in most patients, regardless of mutational status, plasma exchange/infusion use, platelet count, or lactate dehydrogenase or haptoglobin levels. Eculizumab reduced terminal complement activation (C5a and sC5b-9) and renal injury markers (clusterin, cystatin-C, β2-microglobulin, and liver fatty acid binding protein-1) to healthy volunteer levels and reduced inflammation (soluble tumor necrosis factor receptor-1), coagulation (prothrombin fragment F1+2 and d-dimer), and endothelial damage (thrombomodulin) markers to near-normal levels. Alternative pathway activation (Ba) and endothelial activation markers (soluble vascular cell adhesion molecule-1) decreased but remained elevated, reflecting ongoing complement activation in aHUS despite complete terminal complement blockade. These results highlight links between terminal complement activation and inflammation, endothelial damage, thrombosis, and renal injury and underscore ongoing risk for systemic TMA and progression to organ damage. Further research regarding underlying complement dysregulation is warranted. This trial was registered at www.clinicaltrials.gov as #NCT01194973.

Platelets are required for enhanced activation of the endothelium and fibrinogen in a mouse thrombosis model of APS

Antiphospholipid syndrome (APS) is defined by thrombosis, fetal loss, and the presence of antiphospholipid antibodies, including anti-β2-glycoprotein-1 autoantibodies (anti-β2GP1) that have a direct role in the pathogenesis of thrombosis in vivo. The cellular targets of the anti-β2GP1 autoantibody/β2GP1 complex in vivo were studied using a laser-induced thrombosis model of APS in a live mouse and human anti-β2GP1 autoantibodies affinity-purified from APS patients. Cell binding of fluorescently labeled β2GP1 and anti-β2GP1 autoantibodies revealed their colocalization on the platelet thrombus but not the endothelium. Anti-β2GP1 autoantibodies enhanced platelet activation, monitored by calcium mobilization, and endothelial activation, monitored by intercellular adhesion molecule-1 expression. When eptifibatide was infused to block platelet thrombus formation, enhanced fibrin generation and endothelial cell activation were eliminated. Thus, the anti-β2GP1 autoantibody/β2GP1 complex binds to the thrombus, enhancing platelet activation, and platelet secretion leads to enhanced endothelium activation and fibrin generation. These results lead to a paradigm shift away from the concept that binding of the anti-β2GP1 autoantibody/β2GP1 complex activates both endothelial cells and platelets toward one in which activation of platelets in response to anti-β2GP1 autoantibody/β2GP1 complex binding leads to subsequent enhanced endothelium activation and fibrin generation.

Study on the pathogenesis of autoimmune-type recurrent spontaneous abortion by establishing a new mouse model

OBJECTIVE

To establish a new mouse model for autoimmune-type recurrent spontaneous abortion (AI-RSA) and demonstrate the potential role of intrauterine immunization with β2GP-1-like antigen in AI-RSA, we performed an intrauterine injection of human β2GP-1 in BALB/c mice and unrelated protein, adjuvants, and normal saline (NS) as controls. The mean number of embryos implanted (MNEI), embryo loss rate (ELR), mean embryo bulk (MEB), and mean placental weight (MPW) were analyzed. Compared with the control mice, BALB/c mice injected with human β2GP-1 showed increased anti-β2GP-1 and MPW. Moreover, BALB/c mice immunized with human β2GP-1 exhibited hypercoagulability and vascular thrombus formation in the placenta. Electron microscopy confirmed the existence of platelet aggregation, mitochondrial swelling, and endothelial cell necrosis in the placentas of BALB/c mice immunized with human β2GP-1. These finding indicated that intrauterine immunization with β2GP-1 successfully induced AI-RSA in mice. Increased anti-β2GP-1 antibody could independently induce hypercoagulability, vascular endothelial injury, and vascular thrombus formation in the placenta, which led to AI-RSA.

Polyphosphate suppresses complement via the terminal pathway

Polyphosphate, synthesized by all cells, is a linear polymer of inorganic phosphate. When released into the circulation, it exerts prothrombotic and proinflammatory activities by modulating steps in the coagulation cascade. We examined the role of polyphosphate in regulating the evolutionarily related proteolytic cascade complement. In erythrocyte lysis assays, polyphosphate comprising more than 1000 phosphate units suppressed total hemolytic activity with a concentration to reduce maximal lysis to 50% that was 10-fold lower than with monophosphate. In the ion- and enzyme-independent terminal pathway complement assay, polyphosphate suppressed complement in a concentration- and size-dependent manner. Phosphatase-treated polyphosphate lost its ability to suppress complement, confirming that polymer integrity is required. Sequential addition of polyphosphate to the terminal pathway assay showed that polyphosphate interferes with complement only when added before formation of the C5b-7 complex. Physicochemical analyses using native gels, gel filtration, and differential scanning fluorimetry revealed that polyphosphate binds to and destabilizes C5b,6, thereby reducing the capacity of the membrane attack complex to bind to and lyse the target cell. In summary, we have added another function to polyphosphate in blood, demonstrating that it dampens the innate immune response by suppressing complement. These findings further establish the complex relationship between coagulation and innate immunity.

Management of women with recurrent pregnancy losses and antiphospholipid antibody syndrome

Antiphospholipid antibodies (aPL) have been associated with recurrent pregnancy losses (RPL) and other obstetrical complications. The diagnostic criteria for the classical antiphospholipid antibody syndrome (APS) have been utilized for the detection of obstetrical APS in women with RPL. However, laboratory findings and immunopathology of obstetrical APS are significantly different from those of classical APS. In addition, many women with RPL who have positive aPL do not have symptoms consistent with the current APS criteria. The induction of a proinflammatory immune response from trophoblasts and complement activation by aPL rather than thromboembolic changes has been reported as a major immunopathological feature of obstetrical APS. Heparin treatment has been reported to be effective in prevention of early pregnancy loss with APS but not for the late pregnancy loss or complications. The complex effects of heparin may explain the limited efficacy of heparin treatment in RPL. New diagnostic criteria for obstetrical APS are needed urgently, and new therapeutic approaches should be explored further.

Antiphospohlipid syndrome in obstetrics

Antiphospholipid syndrome is characterised by a variety of clinical and immunological manifestations. The clinical hallmarks of this syndrome are thrombosis and poor obstetric outcomes, including miscarriages, fetal loss and severe pre-eclampsia. The main antiphospholipid antibodies include lupus anticoagulant, anticardiolipin and anti-β2-glycoprotein I. The combination of aspirin and heparin is considered the standard of care for women with antiphospholipid syndrome and embryo-fetal losses; however, aspirin in monotherapy may have a place in women with recurrent early miscarriage. A good benefit-risk ratio of low-molecular-weight heparin in pregnancy thrombosis treatment has been reported. Warfarin must be avoided if possible throughout the first trimester of pregnancy. Adequate pregnancy management of women with antiphospholipid syndrome should include co-ordinated medical-obstetrical care, a close follow-up protocol and a good neonatal unit. Close blood pressure control and early detection of proteinuria, together with Doppler studies of the utero-placental circulation should be included in the management protocol.

Thrombophilias and stillbirth

It is often postulated that both inherited and acquired thrombophilias increase the risk of stillbirth. In an attempt to reduce this theoretical risk, pregnant patients with prior fetal losses and thrombophilias are anticoagulated. However, there is no definitive proof that thrombophilias are causally linked to stillbirth. Prospective studies have failed to establish a definitive link between inherited thrombophilias and stillbirth. The extant literature suggests that only high concentrations of antiphospholipid antibodies are associated with stillbirth. Moreover, when pregnant women with prior fetal losses even in these cases are placed on anticoagulation, it is unclear that their recurrence risk of stillbirth decreases.

New therapeutic targets for the antiphospholipid syndrome

IMPORTANCE OF THE FIELD

The antiphospholipid syndrome (APS) is an autoimmune condition whereby pathogenic antiphospholipid antibodies (aPL) cause vascular thrombosis and/or recurrent miscarriage, and carries a high burden of morbidity and mortality. Currently the only proven treatment is long-term anticoagulation, which is not effective in all patients and carries risk of haemorrhage.

AREAS COVERED IN THIS REVIEW

Novel therapeutic targets that are currently being explored for APS in order to address the unmet needs of better, safer and ideally targeted therapy. These include B cell depletion, new-generation anticoagulants, interfering with aPL cell-mediated activation of endothelial cells and platelets both at the cell surface level and intracellularly, targeting components of the complement system and the novel concept of using decoy peptides to target only the pathogenic sub-population of aPL.

WHAT THE READER WILL GAIN

An overview of the potential targets and rationale underpinning them.

TAKE HOME MESSAGE

Though current options remain limited for the treatment of APS, the future holds much promise with the identification of multiple targets, many of which are currently being explored. The challenge will be to undertake carefully designed prospective multi-centre trials to generate the evidence necessary to support integration of such candidates into clinical practice.

Role of tissue factor in thrombosis in antiphospholipid antibody syndrome

Antiphospholipid syndrome (APS) is an acquired autoimmune disorder defined by the presence of an antiphospholipid antibody (aPL) and the occurrence of at least one associated clinical condition that includes venous thrombosis, arterial thrombosis or pregnancy morbidity. The aPL detected in APS have long been thought to have a direct prothrombotic effect in vivo. However, the pathophysiology underlying their coagulopathic effect has not been defined. Emerging data suggest a role for the procoagulant protein tissue factor (TF). In this review we provide an overview of TF, describe mouse models used in the evaluation of the role of TF in thrombosis, as well as summarize recent work on TF and APS.

Antiphospholipid antibody-mediated reproductive failure in antiphospholipid syndrome

The association of elevated titers of circulating antiphospholipid (anti-PL) Abs in antiphospholipid syndrome (APS) and reproductive failure is well established in the literature. The clinical features include recurrent abortions at various stages, including implantation, placentation in the first trimester, miscarriages in the second and third trimesters, intrauterine growth retardation, preeclampsia with placental insufficiency and growth restrictions, arterial and venous thrombosis, and possibly also infertility. APS-mediated recurrent pregnancy loss and other features of reproductive failure might result from diverse autoimmune factors, inflammation, involving different mechanisms, which encompass pathogenic anti-PL Abs. Herein, we discuss the association of anti-PL Abs with reproductive failure with special emphasis on antiphospholipid autoantibodies characterizing APS. This association is evident from either human studies or murine models.

Dysregulated complement activation as a common pathway of injury in preeclampsia and other pregnancy complications

The complement system protects the host against invading organisms, initiates inflammation and dispose of immune complexes and the products of inflammatory injury. The complement system provides an important link between the innate and adaptive immune systems. Experimental observations suggest that increased complement activation causes and/or perpetuates inflammation during pregnancy. Recent studies suggest a link between complement activation and preeclampsia. Excessive activation or insufficient regulation of complement recruits leukocytes and unleashes potent inflammatory and anti-angiogenic mediators associated with placental insufficiency and maternal endothelial dysfunction characteristic of preeclampsia. We review the animal and human studies that link complement activation and pathogenic events in preeclampsia, present evidence that activation of the complement system is associated with the development of preeclampsia and provides new targets to prevent its complications.