Activated protein C, protein S, and tissue factor pathway inhibitor cooperate to inhibit thrombin activation

INTRODUCTION

Thrombin, the enzyme which converts fibrinogen into a fibrin clot, is produced by the prothrombinase complex, composed of factor Xa (FXa) and factor Va (FVa). Down-regulation of this process is critical, as excess thrombin can lead to life-threatening thrombotic events. FXa and FVa are inhibited by the anticoagulants tissue factor pathway inhibitor alpha (TFPIα) and activated protein C (APC), respectively, and their common cofactor protein S (PS). However, prothrombinase is resistant to either of these inhibitory systems in isolation.

MATERIALS AND METHODS

We hypothesized that these anticoagulants function best together, and tested this hypothesis using purified proteins and plasma-based systems.

RESULTS

In plasma, TFPIα had greater anticoagulant activity in the presence of APC and PS, maximum PS activity required both TFPIα and APC, and antibodies against TFPI and APC had an additive procoagulant effect, which was mimicked by an antibody against PS alone. In purified protein systems, TFPIα dose-dependently inhibited thrombin activation by prothrombinase, but only in the presence of APC, and this activity was enhanced by PS. Conversely, FXa protected FVa from cleavage by APC, even in the presence of PS, and TFPIα reversed this protection. However, prothrombinase assembled on platelets was still protected from inhibition, even in the presence of TFPIα, APC, and PS.

CONCLUSIONS

We propose a model of prothrombinase inhibition through combined targeting of both FXa and FVa, and that this mechanism enables down-regulation of thrombin activation outside of a platelet clot. Platelets protect prothrombinase from inhibition, however, supporting a procoagulant environment within the clot.

SARS-CoV-2 Spike Proteins and Cell-Cell Communication Induce P-Selectin and Markers of Endothelial Injury, NETosis, and Inflammation in Human Lung Microvascular Endothelial Cells and Neutrophils: Implications for the Pathogenesis of COVID-19 Coagulopathy

COVID-19 progression often involves severe lung injury, inflammation, coagulopathy, and leukocyte infiltration into pulmonary tissues. The pathogenesis of these complications is unknown. Because vascular endothelium and neutrophils express angiotensin-converting enzyme-2 and spike (S)-proteins, which are present in bodily fluids and tissues of SARS-CoV-2-infected patients, we investigated the effect of S-proteins and cell-cell communication on human lung microvascular endothelial cells and neutrophils expression of P-selectin, markers of coagulopathy, NETosis, and inflammation. Exposure of endothelial cells or neutrophils to S-proteins and endothelial-neutrophils co-culture induced P-selectin transcription and expression, significantly increased expression/secretion of IL-6, von Willebrand factor (vWF, pro-coagulant), and citrullinated histone H3 (cit-H3, NETosis marker). Compared to the SARS-CoV-2 Wuhan variant, Delta variant S-proteins induced 1.4-15-fold higher P-selectin and higher IL-6 and vWF. Recombinant tissue factor pathway inhibitor (rTFPI), 5,5'-dithio-bis-(2-nitrobenzoic acid) (thiol blocker), and thrombomodulin (anticoagulant) blocked S-protein-induced vWF, IL-6, and cit-H3. This suggests that following SARS-CoV-2 contact with the pulmonary endothelium or neutrophils and endothelial-neutrophil interactions, S-proteins increase adhesion molecules, induce endothelial injury, inflammation, NETosis and coagulopathy via the tissue factor pathway, mechanisms involving functional thiol groups, and/or the fibrinolysis system. Using rTFPI, effectors of the fibrinolysis system and/or thiol-based drugs could be viable therapeutic strategies against SARS-CoV-2-induced endothelial injury, inflammation, NETosis, and coagulopathy.

Platelet tissue factor pathway inhibitor-α dampens cardiac thrombosis and associated fibrosis in mice

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is the primary inhibitor of events initiating the blood coagulation pathway. Tfpi-/- mice die during embryonic development. The absence of protease-activated receptor (PAR) 4, the major thrombin receptor on mouse platelets, rescues Tfpi-/-mice to adulthood. Among the 3 TFPI isoforms in mice, TFPIα is the only isoform within platelets (pltTFPIα) and the only isoform that inhibits prothrombinase, the enzymatic complex that converts prothrombin to thrombin.

OBJECTIVES

To determine biological functions of pltTFPIα.

METHODS

Tfpi-/-/Par4-/- mice were irradiated and transplanted with bone marrow from mice lacking or containing pltTFPIα. Thus, PAR4 expression was restored in the recipient mice, which differed selectively by the presence or absence of pltTFPIα and lacked other forms of TFPI.

RESULTS

Recipient mice lacking pltTFPIα had reduced survival over the 200-day posttransplant period. Necropsy revealed radiation injury associated with large intraventricular platelet-rich thrombi, whereas other organs were not affected. Thrombi were associated with fibrotic presentations, including increased collagen deposition, periostin-positive activated fibroblasts, myofibroblasts, and macrophage infiltrates. Recipient mice containing pltTFPIα showed evidence of radiation injury but lacked heart pathology.

CONCLUSIONS

Tfpi-/-/Par4-/- mice develop severe cardiac fibrosis following irradiation and transplantation with bone marrow lacking pltTFPIα. This pathology is markedly reduced when the mice are transplanted with bone marrow containing pltTFPIα. Thus, in this model system pltTFPIα has an important physiological role in dampening pathological responses mediated by activated platelets within the heart tissue.

Tissue factor pathway inhibitor is a potential modifier of bleeding risk in factor XI deficiency

BACKGROUND

Factor (F) XI deficiency is associated with increased bleeding risk in some individuals. Neither FXI levels nor clinical clotting assays predict the bleeding risk. Compared with controls, FXI-deficient bleeders have reduced clot formation, decreased fibrin network density, and increased susceptibility to fibrinolysis. Tissue factor pathway inhibitor (TFPI) was recently implicated as a modifying factor in individuals with bleeding of unknown cause.

OBJECTIVES

To determine the potential of TFPI in modifying the bleeding risk in FXI-deficient individuals.

METHODS

The effects of TFPI on thrombin generation and clot formation, structure, and fibrinolysis in FXI-deficient plasma were measured in vitro in the absence or presence of inhibitory anti-TFPI antibody or exogenous recombinant TFPIα. Total plasma TFPI concentration was measured in 2 independent cohorts of controls and FXI-deficient individuals classified as bleeders or nonbleeders (cohort 1: 10 controls and 16 FXI-deficient individuals; cohort 2: 48 controls and 57 FXI-deficient individuals) and correlated with ex vivo plasma clot formation and fibrinolysis parameters associated with bleeding risk.

RESULTS

In an in vitro FXI deficiency model, inhibition of TFPI enhanced thrombin generation and clot formation, increased the network density, and decreased fibrinolysis, whereas an increase in TFPI had the opposite effects. Compared with controls, plasma from FXI-deficient bleeders had higher TFPI concentration. Total plasma TFPI concentrations correlated with parameters from ex vivo clotting and fibrinolysis assays that differentiate FXI-deficient bleeders and nonbleeders.

CONCLUSION

Coagulation and fibrinolysis parameters that differentiate FXI-deficient nonbleeders and bleeders were altered by plasma TFPIα. Total plasma TFPI was increased in FXI-deficient bleeders. TFPI may modify the bleeding risk in FXI-deficient individuals.

SARS-CoV-2 Spike Proteins and Cell-Cell Communication Inhibits TFPI and Induces Thrombogenic Factors in Human Lung Microvascular Endothelial Cells and Neutrophils: Implications for COVID-19 Coagulopathy Pathogenesis

In SARS-CoV-2-infected humans, disease progression is often associated with acute respiratory distress syndrome involving severe lung injury, coagulopathy, and thrombosis of the alveolar capillaries. The pathogenesis of these pulmonary complications in COVID-19 patients has not been elucidated. Autopsy study of these patients showed SARS-CoV-2 virions in pulmonary vessels and sequestrated leukocytes infiltrates associated with endotheliopathy and microvascular thrombosis. Since SARS-CoV-2 enters and infects target cells by binding its spike (S) protein to cellular angiotensin-converting enzyme 2 (ACE2), and there is evidence that vascular endothelial cells and neutrophils express ACE2, we investigated the effect of S-proteins and cell-cell communication on primary human lung microvascular endothelial cells (HLMEC) and neutrophils expression of thrombogenic factors and the potential mechanisms. Using S-proteins of two different SARS-CoV-2 variants (Wuhan and Delta), we demonstrate that exposure of HLMEC or neutrophils to S-proteins, co-culture of HLMEC exposed to S-proteins with non-exposed neutrophils, or co-culture of neutrophils exposed to S-proteins with non-exposed HLMEC induced transcriptional upregulation of tissue factor (TF), significantly increased the expression and secretion of factor (F)-V, thrombin, and fibrinogen and inhibited tissue factor pathway inhibitor (TFPI), the primary regulator of the extrinsic pathway of blood coagulation, in both cell types. Recombinant (r)TFPI and a thiol blocker (5,5'-dithio-bis-(2-nitrobenzoic acid)) prevented S-protein-induced expression and secretion of Factor-V, thrombin, and fibrinogen. Thrombomodulin blocked S-protein-induced expression and secretion of fibrinogen but had no effect on S-protein-induced expression of Factor-V or thrombin. These results suggests that following SARS-CoV-2 contact with the pulmonary endothelium or neutrophils and endothelial-neutrophil interactions, viral S-proteins induce coagulopathy via the TF pathway and mechanisms involving functional thiol groups. These findings suggest that using rTFPI and/or thiol-based drugs could be a viable therapeutic strategy against SARS-CoV-2-induced coagulopathy and thrombosis.

TFPI and FXIII negatively and S100A8/A9 and Cystatin C positively correlate with D-dimer in COVID-19

D-dimer is an established biomarker of thromboembolism and severity in COVID-19. We and others have recently reported the dysregulation of tissue factor pathway inhibitor (TFPI), FXIII, fibrinolytic pathway, inflammatory markers, and tissue injury markers, particularly in severe COVID-19. However, association of these markers with thromboembolism in COVID-19 remains elusive. The correlation analyses between these markers in patients with moderate (non-ICU) and severe COVID-19 (ICU) were performed to delineate the potential pathomechanisms and impact of thromboembolism. We observe a negative correlation of plasma TFPI (r² = 0.148, P = 0.035), FXIII (r² = 0.242, P = 0.006), and plasminogen (r² = 0.27, P = 0.003) with D-dimer, a biomarker of thromboembolism, levels in these patients. Further analysis revealed a strong positive correlation between fibrinolytic markers tissue plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1) (r² = 0.584, P < 0.0001). Interestingly, a significant positive correlation of PAI-1, but not tPA, was observed with platelets and endothelial cells dysfunction markers P-selectin (r² = 0.184, P = 0.01) and soluble CD40 ligand (sCD40 L) (r² = 0.163, P = 0.02). Moreover, calprotectin (S100A8/A9) and cystatin C (CST3), previously linked with thromboembolism, exhibited positive correlations with each other (r² = 0.339, P = 0.0007) and with the level of D-dimer independently in COVID-19. Finally, the tissue injury marker myoglobin demonstrated a strong positive correlation with D-dimer (r² = 0.408, P = 0.0001). Taken together, inverse correlations of TFPI and FXIII with D-dimer suggest the TF pathway activation and aberrant fibrin polymerization in COVID-19 patients. The elevated level of PAI-1 is potentially contributed by activated platelets and endothelial cells. S100A8/A9 may also play roles in impaired fibrinolysis and thromboembolism, in part, through regulating the CST3. These findings strengthen the understanding of thromboembolism and tissue injury and may help in better management of thromboembolic complications in COVID-19 patients.

TFPI inhibits breast cancer progression by suppressing ERK/p38 MAPK signaling pathway

BACKGROUND

Tissue factor pathway inhibitor-1 (TFPI) is a serine protease inhibitor, which is responsible for inactivating TF-induced coagulation. Recently, increasing studies revealed that TFPI was lowly expressed in tumor cells and exhibited the antitumor activity.

OBJECTIVE

The aim of this study was to explore the role and underlying molecular mechanisms of TFPI in breast cancer.

METHODS

The expression and prognostic value of TFPI were analyzed using UALCAN and Kaplan-Meier plotter website. The expression level of TFPI in breast cancer tissues and cells was examined by immunohistochemistry (IHC) and western blot analysis, respectively. Cellular proliferation was evaluated by CCK-8 and colony formation assays. Cell migration and invasion were determined by transwell assay. The methylation level of TFPI promoter was determined by methylation-specific PCR.

RESULTS

TFPI expression was significantly lower in breast cancer tissues and cells compared to normal breast tissues and normal breast cells. Patients with low TFPI levels showed worse overall survival (OS). Furthermore, overexpression of TFPI significantly inhibited the proliferation, migration and invasion of breast cancer cells. Conversely, knockdown of TFPI promoted the proliferation, migration and invasion of breast cancer cells. Mechanistically, TFPI inhibited the ERK/p38 MAPK signaling pathway in breast cancer. Moreover, DNA hypermethylation of TFPI promoter was responsible for the downregulation of TFPI in breast cancer cells.

CONCLUSION

TFPI inhibited breast cancer cell proliferation, migration and invasion through inhibition of the ERK/p38 MAPK signaling pathway, suggesting that TFPI may serve as a novel prognostic biomarker and therapeutic target for breast cancer.

Anti-TFPI for hemostasis induction in patients with rare bleeding disorders, an ex vivo thrombin generation (TG) guided pilot study

BACKGROUND

Rare bleeding disorders (RBD) are inherited coagulopathies, whose hemostatic control is based upon replacement therapy. Marstacimab (PF-06741086) is a human monoclonal IgG that targets the Kunitz2 domain of tissue factor pathway inhibitor [TFPI]. Marstacimab is currently in development for bleeding prophylaxis in patients with hemophilia.

OBJECTIVES

To assess the potential impact of Marstacimab upon thrombin generation (TG) in RBD patients' plasma samples.

RESULTS

Our cohort included 18 RBD patients, with severe deficiencies: 5 Von Willebrand Disease (VWD) type 3, 4 FVII, 3 FXI, 2 FXIII deficiency and 1 patient with: FX, FV + FVIII, Fibrinogen, combined vitamin K dependent factors' deficiency. Citrated samples from RBD patients were collected and spiked with Marstacimab, TG was measured by calibrated automated thrombogram. Among all patients a reduced baseline TG was observed as compared to controls. Improvement of median (lag time, peak and ETP was observed in Marstacimab spiked samples from 8 min, 99 nM, 1116 nMx min to 5.5 min, 194 nM,1614 nMx min, respectively. None of the values measured among RBD patients exceeded normal controls.

CONCLUSION

These in vitro data suggest that Marstacimab may serve as a promising approach for restoring the hemostatic balance in various RBD, though potential clinical implications should be further investigated.

Case Report and Literature Review: Behçet's Disease With a Novel TFPI Gene Mutation

We report a case of Behçet's disease (BD) with a newly identified tissue factor pathway inhibitor (TFPI) gene mutation. The patient suffered from recurrent deep vein thrombosis and dural sinus thrombosis which could not be relieved by constant anticoagulation therapy. Slight relapsing oral lesion was the initial manifestation of BD but was neglected. Genital ulcers and ocular symptoms were manifest 8-month later than vascular involvement. The patient was diagnosed with BD at last and a novel mutation in TFPI was identified simultaneously. After administration with azathioprine and dexamethasone, the clinical symptoms were quickly gone and no relapse was found during 7-month follow-up.

Effects of human TFPI and CD47 expression and selectin and integrin inhibition during GalTKO.hCD46 pig lung perfusion with human blood

BACKGROUND

Loss of barrier function when GalTKO.hCD46 porcine lungs are perfused with human blood is associated with coagulation pathway dysregulation, innate immune system activation, and rapid sequestration of human formed blood elements. Here, we evaluate whether genetic expression of human tissue factor pathway inhibitor (hTFPI) and human CD47 (hCD47), alone or with combined selectin and integrin adhesion pathway inhibitors, delays GalTKO.hCD46 porcine lung injury or modulates neutrophil and platelet sequestration.

METHODS

In a well-established paired ex vivo lung perfusion model, GalTKO.hCD46.hTFPI.hCD47 transgenic porcine lungs (hTFPI.hCD47, n = 7) were compared to GalTKO.hCD46 lungs (reference, n = 5). All lung donor pigs were treated with a thromboxane synthase inhibitor, anti-histamine, and anti-GPIb integrin-blocking Fab, and were pre-treated with Desmopressin. In both genotypes, one lung of each pair was additionally treated with PSGL-1 and GMI-1271 (P- and E-selectin) and IB4 (CD11b/18 integrin) adhesion inhibitors (n = 6 hTFPI.hCD47, n = 3 reference).

RESULTS

All except for two reference lungs did not fail within 480 min when experiments were electively terminated. Selectin and integrin adhesion inhibitors moderately attenuated initial pulmonary vascular resistance (PVR) elevation in hTFPI.hCD47 lungs. Neutrophil sequestration was significantly delayed during the early time points following reperfusion and terminal platelet activation was attenuated in association with lungs expressing hTFPI.hCD47, but additional adhesion pathway inhibitors did not show further effects with either lung genotype.

CONCLUSION

Expression of hTFPI.hCD47 on porcine lung may be useful as part of an integrated strategy to prevent neutrophil adhesion and platelet activation that are associated with xenograft injury. Additionally, targeting canonical selectin and integrin adhesion pathways reduced PVR elevation associated with hTFPI.hCD47 expression, but did not significantly attenuate neutrophil or platelet sequestration. We conclude that other adhesive mechanisms mediate the residual sequestration of human formed blood elements to pig endothelium that occurs even in the context of the multiple genetic modifications and drug treatments tested here.

Effect of Revascularization on Exercise-Induced Changes in Cardiac and Prothrombotic Biomarkers in Patients with Coronary Artery Disease

We examined whether resting levels and exercise-induced changes during exercise ECG stress test (EST) of cardiac Troponin T (cTnT), NT-proBNP and prothrombotic markers were affected by revascularization in patients with coronary artery disease (CAD).

EST1 was performed before coronary angiography and revascularization, and patients (n  =  20) with confirmed CAD, performed another EST (EST2) 9 weeks later. Blood samples were drawn at rest and within five min after termination of ESTs.

cTnT and NT-proBNP increased during exercise at both ESTs (p < 0.001, all). Resting cTnT levels at EST2 versus EST1 were significantly higher (p  =  0.02) whereas NT-proBNP did not differ. At both visits, increased D-dimer (p  =  0.008 and <0.001), pro-thrombin fragment 1  +  2 (p  =  0.009 and 0.001) and tissue factor pathway inhibitor (TFPI) (p < 0.001 and 0.001) during exercise were demonstrated. Resting levels of endogenous thrombin potential (ETP) and TFPI were reduced at EST2 versus EST1 (p < 0.01).

Revascularization did not affect exercise-induced release of cardiac and prothrombotic biomarkers and did not reduce resting levels of cTnT or NT-proBNP, suggesting revascularization per se not to prevent secretion of biomarkers. The lower resting levels of ETP and TFPI after revascularization may however, be indicative of reduced thrombin generation and endothelial activation.

Clinicaltrials.gov, CADENCE, NCT01495091 https://clinicaltrials.gov/ct2/show/NCT01495091?term = 01495091&draw = 2&rank = 1.

Androgen-dependent tissue factor pathway inhibitor regulating protein: a review of its peripheral actions and association with cardiometabolic diseases

The first genome-wide association study on coronary artery disease (CAD) in the Han Chinese population identified C6orf105 as a susceptibility gene. The C6orf105 gene was later found to encode for a protein that regulates tissue factor pathway inhibitor (TFPI) expression in endothelial cells in an androgen-dependent manner, and the novel protein was thus termed androgen-dependent TFPI-regulating protein (ADTRP). Since the identification of ADTRP, there have been several studies associating genetic variants on the ADTRP gene with CAD risk, as well as research providing mechanistic insights on this novel protein and its functional role. ADTRP is a membrane protein, whose expression is upregulated by androgen, GATA-binding protein 2, oxidized low-density lipoprotein, peroxisome proliferator-activated receptors, and low-density lipoprotein receptors. ADTRP regulates multiple downstream targets involved in coagulation, inflammation, endothelial function, and vascular integrity. In addition, ADTRP functions as a fatty acid esters of hydroxy fatty acid (FAHFA)-specific hydrolase that is involved in energy metabolism. Current evidence suggests that ADTRP may play a role in the pathogenesis of atherosclerosis, CAD, obesity, and metabolic disorders. This review summarizes the current literature on ADTRP, with a focus on the peripheral actions of ADTRP, including expression, genetic variations, signaling pathways, and function. The evidence linking ADTRP and cardiometabolic diseases will also be discussed.

Resistance to activated protein C and impaired TFPI activity in women with previous hormone-induced venous thromboembolism

INTRODUCTION

Hormonal contraception is a well-known risk factor for venous thromboembolism (VTE). APC resistance and impaired functions of protein S and TFPI are thought to play an important role in the pathogenesis of hormone-related VTE. It is unknown, whether women, who develop VTE during hormonal contraception possess a vulnerability in these pathways, making them susceptible to thrombosis.

MATERIALS AND METHODS

Plasma samples were obtained from 57 premenopausal women in average 15.3 years after hormone-associated VTE and from 31 healthy controls. Thrombin generation at high tissue factor (TF) in the absence and in the presence of activated protein C (APC) and at low TF without and with inhibiting anti-protein S- and anti-TFPI-antibodies was measured via calibrated automated thrombography.

RESULTS

Women with previous hormone-related thrombosis had higher thrombin generation at low TF, higher APC resistance, protein S- and TFPI ratios, differences: 219.9 nM IIa.min (95%CI:90.4 to 349.3); 1.88 (95%CI:0.71 to 3.05); 0.13 (95%CI:0.01 to 0.26) and 0.19 (95%CI:0.08 to 0.30), respectively. Thrombin generation at high TF without APC did not differ between the groups. Smoking decreased thrombin generation at low TF by -222.6 nM IIa.min (95%CI: -381.1 to -64.1), the APC sensitivity ratio by -2.20 (95%CI: -3.63 to -0.77) and the TFPI ratio by -0.16 (95%CI: -0.29 to -0.03), but did not influence thrombin generation at high TF.

DISCUSSION

We demonstrated impairment of the protein S/TFPI system and increased APC resistance in women with previous hormone-induced VTE. Smoking decreased thrombin generation at assay conditions, dependent on the function of the TFPI system.

Natural anticoagulants: A missing link in mild to moderate bleeding tendencies

Introduction

There is a growing interest in natural anticoagulants as a cause of mild to moderate bleeding disorders (MBDs), particularly in patients with bleeding of unknown cause (BUC), which is defined as having a mild to moderate bleeding phenotype without a definite diagnosis despite exhaustive and repeated laboratory investigations. Recently, abnormalities in two natural anticoagulant pathways, thrombomodulin (TM), and tissue factor pathway inhibitor (TFPI), were identified in single patients or families as the underlying cause for a bleeding tendency.

Aim

The objective of this review is to discuss the current understanding of the role of natural anticoagulants in MBDs using available clinical and translational data.

Methods

A Cochrane Library and PubMed (MEDLINE) search focusing on selected natural anticoagulants and their role in MBDs was conducted.

Results

Data on the influence of natural anticoagulants including protein C, protein S, antithrombin, TM, and TFPI or factors with anticoagulant properties like fibrinogen gamma prime (γ’) on MBDs are scarce. Observations from sepsis treatment and from translational research highlight their importance as regulators of the haemostatic balance, especially via the activated protein C‐related pathway, and suggest a role in some MBDs.

Conclusion

Similar to the distinct genetic variants of natural anticoagulants linked to thrombosis, we hypothesize that novel variants may be associated with a bleeding tendency and could be identified using next generation sequencing.

Intrauterine lethality in Tfpi gene disrupted mice is differentially suppressed during mid- and late-gestation by platelet TFPIα overexpression

BACKGROUND

Tissue factor pathway inhibitor (TFPI) is an anticoagulant protein required for murine embryonic development. Intrauterine lethality of Tfpi-/- mice occurs at mid- and late gestation, the latter of which is associated with severe cerebrovascular defects. Megakaryocytes produce only the TFPIα isoform, which is stored within platelets and released upon activation.

OBJECTIVES

To examine biological activities of platelet TFPIα (pTFPIα) by characterizing effects of pTFPIα overexpression in Tfpi-/- mice.

METHODS

Transgenic mice overexpressing pTFPIα were generated and crossed onto the Tfpi-/- background. Genetic and histological analyses of embryos were performed to investigate the function of pTFPIα during embryogenesis.

RESULTS

The transgene (Tg) increased pTFPIα 4- to 5-fold without altering plasma TFPI in adult Tfpi+/+ and Tfpi+/- mice but did not rescue Tfpi-/- mice to wean. Analyses of the impact of pTFPIα overexpression on Tfpi-/- survival, however, were complicated by linkage between the Tg integration site and the endogenous Tfpi locus on chromosome 2. Strain-specific genetic interactions also modulated Tfpi-/- embryonic survival. After accounting for these underlying genetic factors, pTFPIα overexpression completely suppressed mid-gestational lethality of Tfpi-/- embryos but had no effect on development of cerebrovascular defects during late gestation resulting in their lack of survival to wean.

CONCLUSIONS

pTFPIα overexpression rescued Tfpi-/- embryos from mid-gestational but not late gestational lethality. The prevalence of underlying genetic factors complicating analyses within our study illustrates the importance of meticulously characterizing transgenic mouse models to avoid spurious interpretation of results.

Target-mediated drug disposition modeling of an anti-TFPI antibody (MG1113) in cynomolgus monkeys to predict human pharmacokinetics and pharmacodynamics

BACKGROUND

MG1113 is a human monoclonal antibody of tissue factor pathway inhibitor (TFPI) under development for prophylaxis for hemophilia patients with or without inhibitors against factor VIII products, which have been used for the treatment of hemophilia. Because TFPI is a negative regulator in the extrinsic coagulation pathway, neutralization of TFPI function by MG1113 can potentially increase coagulation activity by bypassing the intrinsic coagulation pathway, which factor VIII activates.

OBJECTIVES

This study aims to determine the correlation between pharmacokinetics (PK) and pharmacodynamics (PD) after administering MG1113 to monkeys and to predict the PK and PD of MG1113 in humans by the Target-Mediated Drug Disposition (TMDD) model using the results from monkeys.

METHODS

The PK profile of MG1113 and the PD effect on the free TFPI level were evaluated after intravenous (IV) and subcutaneous (SC) administrations of MG1113 (2.5, 5, and 10 mg/kg) to male cynomolgus monkeys. After setting up the PK/PD model on monkeys, PK parameters on humans were calculated using allometric scaling, and then clinically effective doses were predicted applying the TMDD model.

RESULTS AND CONCLUSIONS

MG1113 showed nonlinear PK after both IV and SC administrations at the dosing range from 2.5 to10 mg/kg. The concentrations of MG1113 versus TFPI could be characterized a dose-response relationship using a TMDD model. The TMDD modeling and simulation built in this study were used to simulate various dosage regimens of MG1113 to apply to the first-in-human study design, and moreover expected to be referred to establish the dose for further clinical trials.

Imbalance in Coagulation/Fibrinolysis Inhibitors Resulting in Extravascular Thrombin Generation in Gliomas of Varying Levels of Malignancy

Neoplastic processes are integrally related to disturbances in the mechanisms regulating hemostatic processes. Brain tumors, including gliomas, are neoplasms associated with a significantly increased risk of thromboembolic complications, affecting 20-30% of patients. As gliomas proliferate, they cause damage to the brain tissue and vascular structures, which leads to the release of procoagulant factors into the systemic circulation, and hence systemic activation of the blood coagulation system. Hypercoagulability in cancer patients may be, at least in part, a result of the inadequate activity of coagulation inhibitors. The aim of the study was to evaluate the expression of the inhibitors of the coagulation and fibrinolysis systems (tissue factor pathway inhibitor, TFPI; tissue factor pathway inhibitor-2 TFPI-2; protein C, PC; protein S, PS, thrombomodulin, TM; plasminogen activators inhibitor, PAI-1) in gliomas of varying degrees of malignancy. Immunohistochemical studies were performed on 40 gliomas, namely on 13 lower-grade (G2) gliomas (8 astrocytomas, 5 oligodendrogliomas) and 27 high-grade gliomas (G3-12 anaplastic astrocytomas, 4 anaplastic oligodendrogliomas; G4-11 glioblastomas). A strong expression of TFPI-2, PS, TM, PAI-1 was observed in lower-grade gliomas, while an intensive color immunohistochemical (IHC) reaction for the presence of TFPI antigens was detected in higher-grade gliomas. The presence of PC antigens was found in all gliomas. Prothrombin fragment 1+2 was observed in lower- and higher-grade gliomas reflecting local activation of blood coagulation. Differences in the expression of coagulation/fibrinolysis inhibitors in the tissues of gliomas with varying degrees of malignancy may be indicative of their altered role in gliomas, going beyond that of their functions in the hemostatic system.

Insights into the Functional Role of ADTRP (Androgen-Dependent TFPI-Regulating Protein) in Health and Disease

The novel protein ADTRP, identified and described by us in 2011, is androgen-inducible and regulates the expression and activity of Tissue Factor Pathway Inhibitor, the major inhibitor of the Tissue Factor-dependent pathway of coagulation on endothelial cells. Single-nucleotide polymorphisms in ADTRP associate with coronary artery disease and myocardial infarction, and deep vein thrombosis/venous thromboembolism. Some athero-protective effects of androgen could exert through up-regulation of ADTRP expression. We discovered a critical role of ADTRP in vascular development and vessel integrity and function, manifested through Wnt signaling-dependent regulation of matrix metalloproteinase-9. ADTRP also hydrolyses fatty acid esters of hydroxy-fatty acids, which have anti-diabetic and anti-inflammatory effects and can control metabolic disorders. Here we summarize and analyze the knowledge on ADTRP and try to decipher its functions in health and disease.

Expression analysis of tissue factor pathway inhibitors TFPI-1 and TFPI-2 in Paralichthys olivaceus and antibacterial and anticancer activity of derived peptides

Tissue factor pathway inhibitors (TFPI), including TFPI-1 and TFPI-2, are Kunitz-type serine protease inhibitors that mainly inhibit the blood coagulation induced by tissue factors. Previous reports on teleost proved TFPI play important roles in innate immunity. In this study, two TFPI (PoTFPI-1 and PoTFPI-2) molecules from Japanese flounder (Paralichthys olivaceus) were analyzed and characterized for their expression patterns, antibacterial and anticancer activities of the C-terminal derived peptides. Quantitative real time RT-PCR analysis shows that constitutive PoTFPI-1 expression occurred, in increasing order, in the brain, muscle, spleen, gills, head kidney, blood, intestine, heart, and liver; PoTFPI-2 was expressed, in increasing order, in the brain, gills, head kidney, muscle, intestine, spleen, liver, heart, and blood. Under the stimulation of fish pathogens, both PoTFPI-1 and PoTFPI-2 expressions increased significantly in a manner that depended on the pathogens, tissue type, and infection stage. Furthermore, C-terminal peptides TP25 and TP26, derived from PoTFPI-1 and PoTFPI-2, respectively, were synthesized and proved to be active against Micrococcus luteus (for TP25 and TP26) and Staphylococcus aureus (for TP25) via retardation effects on bacterial nucleic acids. In addition, TP25 and TP26 also displayed significant inhibitory effects on human colon cancer cell line HT-29. These results reveal that both PoTFPI-1 and PoTFPI-2 play important roles in host innate immunity. The antibacterial activity and anticancer cells function of TP25 and TP26 will add new insights into the roles of teleost TFPI.

ADTRP regulates TFPI expression via transcription factor POU1F1 involved in coronary artery disease

Genomic variants in both ADTRP and TFPI genes are associated with risk of coronary artery disease (CAD). ADTRP regulates TFPI expression and endothelial cell functions involved in the initiation of atherosclerotic CAD. ADTRP also specifies primitive myelopoiesis and definitive hematopoiesis by upregulating TFPI expression. However, the underlying molecular mechanism is unknown. Here we show that transcription factor POU1F1 is the key by which ADTRP regulates TFPI expression. Luciferase reporter assays, chromatin-immunoprecipitation (ChIP) and electrophoretic mobility shift assay (EMSA) in combination with analysis of large and small deletions of the TFPI promoter/regulatory region were used to identify the molecular mechanism by which ADTRP regulates TFPI expression. Genetic association was assessed using case-control association analysis and phenome-wide association analysis (PhenGWA). ADTRP regulates TFPI expression at the transcription level in a dose-dependent manner. The ADTRP-response element was localized to a 50 bp region between -806 bp and -756 bp upstream of TFPI transcription start site, which contains a binding site for POU1F1. Deletion of POU1F1-binding site or knockdown of POU1F1 expression abolished ADTRP-mediated transcription of TFPI. ChIP and EMSA demonstrated that POU1F1 binds to the ADTRP response element. Genetic analysis identified significant association between POU1F1 variants and risk of CAD. PhenGWA identified other phenotypic traits associated with the ADTRP-POU1F1-TFPI axis such as lymphocyte count (ADTRP), waist circumference (TFPI), and standing height (POU1F1). These data identify POU1F1 as a transcription factor that regulates TFPI transcription in response to ADTRP, and link POU1F1 variants to risk of CAD for the first time.

Neutralizing Antibody Assay Development with High Drug and Target Tolerance to Support Clinical Development of an Anti-TFPI Therapeutic Monoclonal Antibody

Immunogenicity is a major challenge for protein therapeutics which can potentially reduce drug efficacy and safety and is often being monitored by anti-drug antibody (ADA) and neutralizing antibody (NAb) assays. Circulating targets and residual drugs in matrices can have significant impacts on accuracy of results from ADA and NAb assays, and sufficient drug and target tolerance for these assays are necessary. Here, we report the development of a competitive ligand binding (CLB) NAb assay for an anti-TFPI (tissue factor pathway inhibitor) monoclonal antibody (PF-06741086) with high drug and target tolerance to support ongoing clinical studies. A double acid affinity capture elution approach was used to mitigate drug interference, and a robust target removal strategy was employed to enhance target tolerance. The validated NAb assay has sensitivity of 313 ng/mL, drug tolerance of 50 μg/mL, and target tolerance of 1200 ng/mL. A step-by-step tutorial of assay development is described in this manuscript along with the rationale for using a high drug/target tolerant NAb assay. The NAb assay cut point factor obtained was 0.78. Other assay performance characteristics, e.g., precision and selectivity, are also discussed. This validated method demonstrated a superior drug and target tolerance to warrant specific and precise characterization of the NAb responses in support of ongoing clinical studies.

Bioequivalence of a biosimilar enoxaparin sodium to Clexane® after single 100 mg subcutaneous dose: results of a randomized, double-blind, crossover study in healthy volunteers

Purpose

To demonstrate the pharmacokinetic/pharmacodynamic (PK/PD) equivalence of a biosimilar enoxaparin to the reference drug, and to assess its safety and tolerability in healthy volunteers.

Patients and methods

A randomized, double-blind, crossover, 2-sequence, single-dose study was conducted in healthy volunteers of both sexes. Participants were sequentially and randomly administered single subcutaneous injections of enoxaparin 100 mg manufactured by Rovi (test; Madrid, Spain) and Clexane^® (enoxaparin 100 mg manufactured by Sanofi, reference) separated by a 1-week washout period. The primary PK/PD variables were maximum activity (A_max) and area under the effect curve from time 0 to the last measured activity (T) (AUEC_0–T) and AUEC from time 0 to infinity (AUEC_0–inf) of anti-FXa activity, and A_max and AUEC_0–T of anti-FIIa activity. Secondary variables were A_max and AUEC_0–T, AUEC_0–inf of tissue factor pathway inhibitor, and the ratio of AUEC_0–T anti-FXa to anti-FIIa activity. Biosimilarity would be shown when the 95% CI of the ratio of geometric least squares means (95% CI RGLSMs) of primary PK/PD parameters fell within the standard range of bioequivalence, ie, 80%–125%.

Results

The study sample consisted of 46 volunteers (33 males) aged 18–44 years and with body mass index ranging from 19.0 to 31.1 kg/m². Three subjects did not complete the study. The curves of anti-FXa, anti-FIIa and tissue factor pathway inhibitor activities corresponding to administration of the test and reference products were comparable. The 95% CI RGLSMs of A_max, AUEC_0–T and AUEC_0–inf for anti-FXa activity were 94.6%–105.9%, 99.8%–108.0% and 100.0%–108.6% respectively; A_max and AUEC_0–T for anti-FIIa activity were 94.7%–112.6% and 90.9%–117.9% respectively. In addition, the 95% CI RGLSMs of all secondary variables fell within the range 80%–125%. The incidence and types of adverse events after administration of the test and reference drugs were similar.

Conclusion

The results conclusively showed that the enoxaparin manufactured by Rovi is equivalent to the reference enoxaparin in all primary and secondary PK/PD parameters, as required by the European Medicines Agency to grant marketing authorization to a biosimilar low molecular-weight heparin.

Translational Pharmacokinetic/Pharmacodynamic Characterization and Target-Mediated Drug Disposition Modeling of an Anti-Tissue Factor Pathway Inhibitor Antibody, PF-06741086

Tissue factor pathway inhibitor (TFPI) exhibits multiple isoforms, which are known to present in multiple locations such as plasma, endothelium, and platelets. TFPI is an endogenous negative modulator of the coagulation pathway, and therefore, neutralization of TFPI function can potentially increase coagulation activity. A human monoclonal antibody, PF-06741086, which interacts with all isoforms of TFPI is currently being tested in clinic for treating hemophilia patients with and without inhibitors. To support clinical development of PF-06741086, pharmacokinetics (PK) and pharmacodynamics of PF-06741086 were characterized in monkeys. In addition, a mechanistic model approach was used to estimate PK parameters in monkeys and simulate PK profiles in human. The results show that PF-06741086 exhibited target-mediated drug disposition and had specific effects on various hemostatic markers including diluted prothrombin time, thrombin generation, and thrombin-antithrombin complex in monkeys after administration. The model-predicted and observed human exposures were compared retrospectively, and the result indicates that the exposure prediction was reasonable within less than 2-fold deviation. This study demonstrated in vivo efficacy of PF-06741086 in monkeys and the utility of a rational mechanistic approach to describe PK for a monoclonal antibody with complex target binding.

Emicizumab, A Bispecific Antibody to Factors IX/IXa and X/Xa, Does Not Interfere with Antithrombin or TFPI Activity In Vitro

Emicizumab is a humanized bispecific antibody that binds simultaneously to factor (F) IXa and FX replacing the cofactor function of FVIIIa. Because emicizumab recognizes FIX/FIXa and FX/FXa, a question may arise whether emicizumab competes with antithrombin (AT) and/or tissue factor pathway inhibitor (TFPI), thereby enhancing overall hemostatic potential by blocking their antihemostatic effects. To address this question, we performed enzymatic assays using purified coagulation factors to confirm whether emicizumab interferes with the action of AT on FIXa or FXa, or with the action of TFPI on FXa. In those assays, we found no interference of emicizumab on the actions of AT and TFPI. We next assessed emicizumab's influences on the anticoagulation actions of AT or TFPI in thrombin generation assays triggered with FXIa or tissue factor (TF) in AT-depleted or TFPI-depleted plasma supplemented with AT or TFPI in vitro. In those assays, we employed anti-FIXa and anti-FX monospecific one-armed antibodies derived from emicizumab instead of emicizumab itself so as to prevent emicizumab's FVIIIa cofactor activity from boosting thrombin generation. Consequently, we found that neither anti-FIXa, anti-FX monospecific antibody, nor the mixture of the two interfered with the anticoagulation actions of AT or TFPI in plasma. Although emicizumab can bind to FIXa and FXa, our results showed no interference of emicizumab with the action of AT or TFPI on FIXa or FXa. This indicates that the presence of emicizumab is irrelevant to the action of AT and TFPI, and thus should not alter the coagulant/anticoagulant balance related to AT and TFPI.

Correlates of plasma and platelet tissue factor pathway inhibitor, factor V, and Protein S

Background

Plasma Tissue Factor Pathway Inhibitor (TFPI) circulates bound to factor V (fV) and Protein S (PS). Estrogen therapy decreases plasma TFPI and PS. TFPI, fV, and PS circulate within platelets, and are released upon activation to modulate thrombus formation.

Objective

Identify factors affecting the concentrations of plasma and platelet TFPI, fV, and PS.

Methods

Blood samples were obtained from 435 healthy individuals. Plasma total TFPI, TFPIɑ, fV, and PS, and platelet TFPI, fV, and PS were quantified. Correlations between these protein concentrations and age, gender, race, and estrogen use were established.

Results

In males, only plasma fV increased with age, while in females, all plasma analytes increased with age. Males had higher plasma total TFPI, TFPIα, and PS than females. The platelet proteins in either sex remained relatively stable with increasing age. Platelet TFPI and PS were comparable in both sexes, while platelet fV was higher in females. Estrogen use was associated with decreased plasma total TFPI and TFPIα, and platelet PS, but not with platelet TFPI concentration. Racial differences in plasma and platelet proteins were observed, some of which were larger than inter-individual differences observed within racial groups. TFPI, fV and PS concentrations correlated in plasma, while only fV and PS correlated in platelets.

Conclusions

Plasma and platelet TFPI, fV and PS differ in their: (i) in vivo association; (ii) demographic correlates; and (iii) alteration by estrogen therapies. Therefore, the plasma and platelet pools of these proteins may modulate hemostasis and thrombosis via different biochemical pathways.

Tissue factor pathway inhibitor attenuates ER stress-induced inflammation in human M2-polarized macrophages

Endoplasmic reticulum (ER) stress has been shown to play a key role during the initiation and clinical progression of the cardiovascular diseases, such as atherosclerosis. We have recently shown that expression of tissue factor pathway inhibitor (TFPI) in human monocyte-derived macrophages (MDMs) was induced by cholesterol crystals (CC). In the present study we aimed to determine the role of TFPI under ER stress conditions using human MDMs. qRT-PCR and immunohistochemistry analysis were performed to determine the presence of the ER stress marker CCAAT/enhancer binding protein homologous protein (CHOP) and TFPI in human carotid plaque material and also in human MDMs polarized into pro-inflammatory M1 or anti-inflammatory M2 populations. CHOP mRNA levels were upregulated in the plaques compared to healthy vessels, and CHOP protein was localized in the same area as TFPI in the plaques. Both CHOP and TFPI mRNA levels were upregulated after CC treatment, especially in the M2 phenotype, and the ER stress inhibitor 4-phenylbutyric acid (PBA) reversed this effect. Furthermore, CC treatment increased the levels of the pro-inflammatory cytokines TNF-α, IL-6, and IL-8, which for TNF-α and IL-8 was inhibited by PBA, and reduced the levels of the anti-inflammatory cytokine IL-10 in M2-polarized macrophages. Knockdown of TFPI prior to CC treatment exacerbated TNF-α and IL-6 levels, but reduced IL-8 and IL-10 levels. Our results show that CC induce TFPI and cytokine expression in M2-polarized macrophages through activation of the ER stress pathway and that TFPI has a protective effect against TNF-α and IL-6 mediated inflammation. These mechanisms may have implications for the pathogenesis of atherosclerosis.

Inhibition of microRNA-500 has anti-cancer effect through its conditional downstream target of TFPI in human prostate cancer

PURPOSE

We investigated the prognostic potential and regulatory mechanism of microRNA-500 (miR-500), and human gene of tissue factor pathway inhibitor (TFPI) in prostate cancer.

METHODS

MiR-500 expression was assessed by qRT-PCR in prostate cancer cell lines and primary tumors. Cancer patients' clinicopathological factors and overall survival were analyzed according to endogenous miR-500 level. MiR-500 was downregulated in DU145 and VCaP cells. Its effect on prostate cancer proliferation, invasion in vitro, and tumorigenicity in vivo, were probed. Possible downstream target of miR-500, TFPI was assessed by luciferase assay and qRT-PCR in prostate cancer cells. In miR-500-downregulated DU145 and VCaP cells, TFPI was silenced to see whether it was directly involved in the regulation of miR-500 in prostate cancer. TFPI alone was either upregulated or downregulated in DU145 and VCaP cells. Their effect on prostate cancer development was further evaluated.

RESULTS

MiR-500 is upregulated in both prostate cancer cells and primary tumors. In prostate cancer patients, high miR-500 expression is associated with poor prognosis and overall survival. In DU145 and VCaP cells, miR-500 downregulation inhibited cancer proliferation, invasion in vitro, and explant growth in vivo. TFPI was verified to be associated with miR-500 in prostate cancer. Downregulation of TFPI reversed anti-cancer effects of miR-500 downregulation in prostate cancer cells. However, neither TFPI upregulation nor downregulation alone had any functional impact on prostate cancer development.

CONCLUSION

MiR-500 may be a potential biomarker and molecular target in prostate cancer. TFPI may conditionally regulate prostate cancer in miR-500-downregualted prostate cancer cells.

Coagulation factor and protease pathways in thrombosis and cardiovascular disease

The biochemical characterisation of the proteolytic pathways that constitute blood coagulation was one of the most relevant achievements in biomedical research during the second half of the 20th century. Understanding these pathways was of crucial importance for improving global health through application in haemostasis and thrombosis pathologies. Immediately after the cloning of the genes corresponding to these proteins, mutations were discovered in them that were associated with imbalances in haemostasis. Later, the importance of coagulation pathways in other pathological processes was demonstrated, such as in atherosclerosis and inflammation, both essential processes involved in vascular disease. In the present review we evaluate the concepts that have allowed us to reach the integrated vision on coagulation that we have today. The thrombo-inflammation model encompassing these aspects includes a pivotal role for the proteases of the coagulation pathway as well as the regulatory proteins thereof. These concepts illustrate the importance of the coagulation cascade in cardiovascular pathology, not only in thrombotic processes, but also in atherosclerotic processes and in the response to ischaemia-reperfusion injury, making it a central mechanism in cardiovascular disease.

Interaction of factor V B-domain acidic region with its basic region and with TFPI/TFPI2: Structural insights from molecular modeling studies

BACKGROUND

Factor V (FV) B-domain contains an acidic region (FV-AR2) and a basic region (FV-BR), which interact with each other and maintain FV in a procofactor form; removal of either region via deletion/proteolysis results in an active FVa molecule. Tissue factor pathway inhibitor type-1 (TFPI) and type-2 (TFPI2) each contain a C-terminus basic segment homologous to FV-BR; this region in TFPI (and predicted in TFPI2) binds to FV-AR2 in platelet FVa (that lacks FV-BR) with high affinity and inhibits FVa function.

OBJECTIVES

To understand molecular interactions between FV-AR2 with FV-BR, TFPI-BR and TFPI2-BR.

METHODS

Circular dichroism (CD) and molecular modeling approaches.

RESULTS AND CONCLUSIONS

CD experiments reveal the presence of ∼20% helical content in both FV-AR2 and FV-BR but each lacks beta-sheet. Predicted structures of FV-AR2 and FV-BR, obtained using threading (I-TASSER), are consistent with the CD data and have compact folds with hydrophobic residues in the interior and charged residues on the surface. Scores from QMEAN and ModFOLD servers indicate a very high probability for each structure to be native. Predicted models of Kunitz domain-3 of TFPI and TFPI2 each with C-terminal basic tail are consistent with known homologous structures. Docking experiments using ClusPro indicate that the acidic groove of FV-AR2 has high shape complementarity to accommodate the conserved basic residues in FV-BR (1002-RKKKK-1006), TFPI-BR (256-RKRKK-260) or TFPI2-BR (191-KKKKK-195). Further, similar electrostatic interactions occur in each case. These models, in the absence of experimentally determined structures, provide a guiding point for proper mutagenesis studies in FV, TFPI and TFPI2.

Factor V has an anticoagulant cofactor activity that targets the early phase of coagulation

Tissue factor pathway inhibitor (TFPI), the main inhibitor of initiation of coagulation, exerts an important anticoagulant role through the factor Xa (FXa)-dependent inhibition of tissue factor/factor VIIa. Protein S is a TFPI cofactor, enhancing the efficiency of FXa inhibition. TFPI can also inhibit prothrombinase assembly by directly interacting with coagulation factor V (FV), which has been activated by FXa. Because full-length TFPI associates with FV in plasma, we hypothesized that FV may influence TFPI inhibitory function. Using pure component FXa inhibition assays, we found that although FV alone did not influence TFPI-mediated FXa inhibition, it further enhanced TFPI in the presence of protein S, resulting in an ∼8-fold reduction in K_i compared with TFPI alone. A FV variant (R709Q/R1018Q/R1545Q, FV^ΔIIa) that cannot be cleaved/activated by thrombin or FXa also enhanced TFPI-mediated inhibition of FXa ∼12-fold in the presence of protein S. In contrast, neither activated FV nor recombinant B-domain-deleted FV could enhance TFPI-mediated inhibition of FXa in the presence of protein S, suggesting a functional contribution of the B domain. Using TFPI and protein S variants, we show further that the enhancement of TFPI-mediated FXa inhibition by protein S and FV depends on a direct protein S/TFPI interaction and that the TFPI C-terminal tail is not essential for this enhancement. In FXa-catalyzed prothrombin activation assays, both FV and FV^ΔIIa (but not activated FV) enhanced TFPI function in the presence of protein S. These results demonstrate a new anticoagulant (cofactor) function of FV that targets the early phase of coagulation before prothrombinase assembly.

Targeting TFPI for hemophilia treatment

Hemophilia is a severe bleeding disorder treated by infusion of the missing blood coagulation protein, factor VIII or factor IX. The discovery and characterization of the anticoagulant protein tissue factor pathway inhibitor (TFPI) led to the realization that inhibition of TFPI activity could restore functional hemostasis through the extrinsic blood coagulation pathway in a manner that does not require the activity of factors VIII or IX. There are currently several therapeutic agents that inhibit TFPI in development for treatment of hemophilia. A comprehensive understanding of TFPI structure, biochemistry, and cellular expression is necessary to understand how it modulates bleeding in hemophilia and the physiological impact of therapeutic agents targeting TFPI.

Rethinking events in the haemostatic process: role of factor V and TFPI

Regulatory mechanisms responsible for limiting blood clot formation are critical for maintaining normal haemostasis. Dysregulation can lead to bleeding (e.g. haemophilia) or thrombosis. New findings showing that tissue factor pathway inhibitor-alpha (TFPIα) binds coagulation factor V(a) and inhibits prothrombinase assembly highlights that our understanding of the initiation of coagulation is evolving. Work over the past decade on the biochemistry of FV activation has laid the groundwork for deciphering the mechanistic bases that may underpin how TFPIα mediates these anticoagulant effects. Collectively, these new findings are re-shaping our thinking about how coagulation is initiated at the site of injury. These ideas could have important clinical implications and help identify new ways to bias the coagulation response for the treatment of haemophilia and other disorders of the haemostatic process.

Increased circulating procoagulant and anticoagulant factors as TF and TFPI according to severity or infecting serotypes in human dengue infection

Tissue Factor (TF) is the initiator of coagulation and Tissue Factor Inhibitor (TFPI) is the physiological inhibitor of the TF/FVIIa complex. Circulating levels of TF and TFPI were quantified in dengue patients and the relationships with disease severity and infecting serotype analysed. A significant decrease in TF and TPFI plasma levels was observed in mild DF patients compared with severe dengue. Furthermore, both factors were associated with haemorrhagic manifestations. Finally, TF levels were significantly increased in DENV-1/2 infected patients as compared with DENV-4. These findings suggest that activation of TF-pathway is an important component of DENV -related coagulation disorders.

The role of microRNA-27a/b and microRNA-494 in estrogen-mediated downregulation of tissue factor pathway inhibitor α

Essentials Estrogens are known to influence the expression of microRNAs in breast cancer cells. We looked at microRNAs in estrogenic regulation of tissue factor pathway inhibitor α (TFPIα). Estrogen upregulated microRNA-27a/b and microRNA-494 through the estrogen receptor α. MicroRNA-27a/b and microRNA-494 are partly involved in estrogenic downregulation of TFPIα.

SUMMARY

Background Tissue factor pathway inhibitor (TFPI) has been linked to breast cancer pathogenesis. We have recently reported TFPI mRNA levels to be downregulated by estrogens in a breast cancer cell line (MCF7) through the estrogen receptor α (ERα). Accumulating evidence also indicates that activation of ERα signaling by estrogens may modulate the expression of target genes indirectly through microRNAs (miRNAs). Objectives To examine if miRNAs are involved in the estrogenic downregulation of TFPIα. Methods Computational analysis of the TFPI 3'-untranslated region (UTR) identified potential binding sites for miR-19a/b, miR-27a/b, miR-494, and miR-24. Transient overexpression or inhibition of the respective miRNAs was achieved by transfection of miRNA mimics or inhibitors. Direct targeting of TFPI 3'-UTR by miR-27a/b and miR-494 was determined by luciferase reporter assay in HEK293T cells. Effects of 17α-ethinylestradiol (EE2) and fulvestrant on relative miR-27a/b, miR-494, and TFPI mRNA levels in MCF7 cells were determined by qRT-PCR and secreted TFPIα protein by ELISA. Transient knockdown of ERα was achieved by siRNA transfection. Results EE2 treatment lead to a significant increase in miR-19a, miR-27a/b, miR-494, and miR-24 mRNA levels in MCF7 cells through ERα. miR-27a/b and miR-494 mimics lead to reduced TFPI mRNA and protein levels. Luciferase assay showed direct targeting of miR-27a/b and miR-494 on TFPI mRNA. Impaired estrogen-mediated downregulation of TFPI mRNA was detected in anti-miR-27a/b and anti-miR-494 transfected cells. Conclusions Our results provide evidence that miR-27a/b and miR-494 regulate TFPIα expression and suggest a possible role of these miRNAs in the estrogen-mediated downregulation of TFPIα.

Pro- and anticoagulant properties of factor V in pathogenesis of thrombosis and bleeding disorders

Factor V (FV) serves an important role in the regulation of blood coagulation, having both pro- and anticoagulant properties. The circulating high molecular weight single-chain FV molecule undergoes a series of proteolytic cleavages during both activation of coagulation and during anticoagulant regulation of coagulation by activated protein C (APC). It is noteworthy that mutations in the factor V gene (F5) either cause thrombosis or bleeding. New insights into the importance and complexity of FV functions have been generated from elucidation of the pathogenic mechanisms of two familial mutations in the F5 gene. The first mutation was identified as a result of the discovery of APC resistance as the most common risk factor for venous thrombosis. The mutation (FV Leiden) predicts the Arg(506) Gln replacement, which impairs the normal regulation of FVa by APC, as the Arg506 site is an important APC cleavage site. In addition, elucidation of APC resistance resulted in the discovery of the anticoagulant APC cofactor activity of FV. The second FV mutation (FV(A2440G) ), identified in a family with an autosomal dominant bleeding disorder, has led to the discovery of an alternative splicing generating a previously unidentified FV isoform (FV-Short), which inhibits coagulation via an unexpected and intriguing mechanism involving the coagulation inhibitor TFPI-α. These are naturally occurring mutations in the F5 gene that have generated new knowledge on the role of FV in regulation of coagulation and the importance of genetic risk factors for thrombosis and bleeding.

Development, Maintenance, and Reversal of Multiple Drug Resistance: At the Crossroads of TFPI1, ABC Transporters, and HIF1

Early detection and improved therapies for many cancers are enhancing survival rates. Although many cytotoxic therapies are approved for aggressive or metastatic cancer; response rates are low and acquisition of de novo resistance is virtually universal. For decades; chemotherapeutic treatments for cancer have included anthracyclines such as Doxorubicin (DOX); and its use in aggressive tumors appears to remain a viable option; but drug resistance arises against DOX; as for all other classes of compounds. Our recent work suggests the anticoagulant protein Tissue Factor Pathway Inhibitor 1α (TFPI1α) plays a role in driving the development of multiple drug resistance (MDR); but not maintenance; of the MDR state. Other factors; such as the ABC transporter drug efflux pumps MDR-1/P-gp (ABCB1) and BCRP (ABCG2); are required for MDR maintenance; as well as development. The patient population struggling with therapeutic resistance specifically requires novel treatment options to resensitize these tumor cells to therapy. In this review we discuss the development, maintenance, and reversal of MDR as three distinct phases of cancer biology. Possible means to exploit these stages to reverse MDR will be explored. Early molecular detection of MDR cancers before clinical failure has the potential to offer new approaches to fighting MDR cancer.

New insights into the biology of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) dampens the initiation of blood coagulation by inhibiting two potent procoagulant complexes, tissue factor-factor VIIa (TF-FVIIa) and early forms of prothrombinase. TFPI isoforms, TFPIα and TFPIβ, result from alternative splicing of mRNA, producing distinct C-terminal ends of the two proteins. Both isoforms inhibit TF-FVIIa, but only TFPIα can inhibit early forms of prothrombinase by binding of its positively charged C-terminus with high affinity to the acidic B-domain exosite of FVa, which is generated upon activation by FXa. TFPIα and TFPIβ are produced in cultured human endothelial cells, while platelets contain only TFPIα. Knowledge of the anticoagulant mechanisms and tissue expression patterns of TFPIα and TFPIβ have improved our understanding of the phenotypes observed in different mouse models of TFPI deficiency, the east Texas bleeding disorder, and the development of pharmaceutical agents that block TFPI function to treat hemophilia.

Placental vascular pathology and increased thrombin generation as mechanisms of disease in obstetrical syndromes

Obstetrical complications including preeclampsia, fetal growth restriction, preterm labor, preterm prelabor rupture of membranes and fetal demise are all the clinical endpoint of several underlying mechanisms (i.e., infection, inflammation, thrombosis, endocrine disorder, immunologic rejection, genetic, and environmental), therefore, they may be regarded as syndromes. Placental vascular pathology and increased thrombin generation were reported in all of these obstetrical syndromes. Moreover, elevated concentrations of thrombin-anti thrombin III complexes and changes in the coagulation as well as anticoagulation factors can be detected in the maternal circulation prior to the clinical development of the disease in some of these syndromes. In this review, we will assess the changes in the hemostatic system during normal and complicated pregnancy in maternal blood, maternal–fetal interface and amniotic fluid, and describe the contribution of thrombosis and vascular pathology to the development of the great obstetrical syndromes.

Inhibition of tissue factor:factor VIIa-catalyzed factor IX and factor X activation by TFPI and TFPI constructs

BACKGROUND

TFPI is a Kunitz-type protease inhibitor that downregulates the extrinsic coagulation pathway by inhibiting factor Xa (FXa) and FVIIa. All three Kunitz domains (KD1, KD2, and KD3) and protein S are required for optimal inhibition of FXa and FVIIa. There is limited information on Kunitz domain requirements of the inhibition of TF:FVIIa-catalyzed FIX and FX activation by TFPI.

AIM

To investigate the role of the Kunitz domains of TFPI and protein S in the inhibition of FX and FIX activation.

METHODS

Inhibition of TF:FVIIa-catalyzed FX and FIX activation by full-length TFPI (TFPIFL ) and TFPI constructs was quantified from progress curves of FXa and FIXa generation measured with chromogenic substrates.

RESULTS AND CONCLUSIONS

TFPIFL inhibited TF:FVIIa-catalyzed FIX activation with a Ki of 16.7 nmol L(-1) . Protein S reduced the Ki to 1.0 nmol L(-1) . TFPI1-150 and KD1-KD2 had 10-fold higher Ki values and were not stimulated by protein S. Single Kunitz domains were poor inhibitors of TF:FVIIa-catalyzed FIX activation (Ki >800 nm). FX activation was measured at limiting FVIIa and excess TF or vice versa. At both conditions, TFPIFL , TFPI1-150 , and KD1-KD2 showed similar inhibition of FX activation. However, at low phospholipid concentrations, TFPIFL was ~ 15-fold more active than TFPI1-150 or KD1-KD2. Apparently, excess phospholipids act as a kind of sink for TFPIFL , limiting its availability for TF:FVIIa inhibition. Preformed FXa:TFPIFL/1-150 complexes rapidly and stoichiometrically inhibited FIX and FX activation by TF:FVIIa, indicating that binary TFPI:FXa complex formation is the limiting step in TF:FVIIa inhibition. Protein S also enhanced inhibition of TF:FVIIa-catalyzed FX activation by TFPI.

Pharmacokinetics of an anti-TFPI monoclonal antibody (concizumab) blocking the TFPI interaction with the active site of FXa in Cynomolgus monkeys after iv and sc administration

INTRODUCTION

Concizumab (mAb 2021) is a monoclonal IgG4 antibody (mAb) that binds to the Kunitz-type protease inhibitor (KPI) 2 domain of TFPI thereby blocking the interaction of this domain with the active site of FXa. The objective of the present study was to characterize the pharmacokinetics of concizumab in Cynomolgus monkeys after intravenous (iv) and subcutaneous (sc) administration.

METHODS

Data from two studies were included in the modelling, all in all data from 52 monkeys distributed into 9 groups. Three groups received three escalating sc doses of concizumab with a one week dosing interval, two groups were administered a single dose, and four groups received multiple doses over 13 weeks of concizumab. The plasma concentration was measured using a standard ELISA, and pharmacokinetic data were analysed using NONMEM.

RESULTS

The pharmacokinetics of concizumab were characterised by a high bioavailability (93%) after sc administration. The time course of the elimination of concizumab from the circulation was well described by the proposed target mediated drug disposition (TMDD) model. The clearance of concizumab was estimated to be 0.14 ml/h/kg, the target clearance was characterized by a 50% saturation level of 0.54 μg/ml (Km), and the clearance at target saturation was estimated to be 11 μg/h/kg.

CONCLUSION

Concizumab displays a typical TMDD profile with important implications for a putative treatment regime in haemophilia patients. Compared to current standard haemophilia treatment, concizumab has a high bioavailability after sc administration and may provide a viable alternative to intravenous dosing for the treatment of haemophilia.

Tissue factor pathway inhibitor prevents airway obstruction, respiratory failure and death due to sulfur mustard analog inhalation

Sulfur mustard (SM) inhalation causes airway injury, with enhanced vascular permeability, coagulation, and airway obstruction. The objective of this study was to determine whether recombinant tissue factor pathway inhibitor (TFPI) could inhibit this pathogenic sequence.

METHODS

Rats were exposed to the SM analog 2-chloroethyl ethyl sulfide (CEES) via nose-only aerosol inhalation. One hour later, TFPI (1.5mg/kg) in vehicle, or vehicle alone, was instilled into the trachea. Arterial O2 saturation was monitored using pulse oximetry. Twelve hours after exposure, animals were euthanized and bronchoalveolar lavage fluid (BALF) and plasma were analyzed for prothrombin, thrombin-antithrombin complex (TAT), active plasminogen activator inhibitor-1 (PAI-1) levels, and fluid fibrinolytic capacity. Lung steady-state PAI-1 mRNA was measured by RT-PCR analysis. Airway-capillary leak was estimated by BALF protein and IgM, and by pleural fluid measurement. In additional animals, airway cast formation was assessed by microdissection and immunohistochemical detection of airway fibrin.

RESULTS

Airway obstruction in the form of fibrin-containing casts was evident in central conducting airways of rats receiving CEES. TFPI decreased cast formation, and limited severe hypoxemia. Findings of reduced prothrombin consumption, and lower TAT complexes in BALF, demonstrated that TFPI acted to limit thrombin activation in airways. TFPI, however, did not appreciably affect CEES-induced airway protein leak, PAI-1 mRNA induction, or inhibition of the fibrinolytic activity present in airway surface liquid.

CONCLUSIONS

Intratracheal administration of TFPI limits airway obstruction, improves gas exchange, and prevents mortality in rats with sulfur mustard-analog-induced acute lung injury.

Human platelets do not express tissue factor

BACKGROUND

The controversy about the expression of tissue factor (TF) in platelet after de novo synthesis prevail despite many groups recognize that platelet isolation, assays and reagents, particularly non-specific antibodies, may account for the diversity. In this study the potential of TF expression was evaluated using immune-purified human platelets and employing a very sensitive and highly specific TF activity assay.

METHODS

Isolated platelets in plasma anti-coagulated with Fragmin were subjected to stimulation by LPS plus PMA, IgG antibody or TRAP and tested for TF activity.

RESULTS

Platelets stimulated with LPS plus PMA for 4 hours expressed trace amounts of TF like activity (PCA), not inhibited by anti-TF antibody (0.2±0.1 mU/ml blood). Platelets, not immune-adsorbed to remove monocytes, showed significant TF activity (2.0±0.9 mU/ml blood) that was nearly abolished by anti-TF antibody. IgG antibody from patient with lupus anticoagulant failed to enhance the trace amount of PCA as compared to the control in contrast to high TF activity induced in monocytes (0.4±0.1 mU/ml blood versus 27.5±10.5 mU/10(6) cells) showing that activation of complement is not mediating TF expression. Platelet subjected to TRAP activation for 10 min possessed only trace amounts of PCA that was not inhibited by anti-TF antibody and slightly enhanced by anti-TFPI antibody.

CONCLUSIONS

It is concluded that platelets free of monocytes do not express TF activity when stimulated by LPS or activated complement factors, implying no role for Toll like receptor (TLR4) as suggested recently. There is no evidence of TF activity associated with platelets as a result of rapid and dynamic process.