F10 Gene Expression and Ethnic Disparities Present in Papillary Thyroid Carcinoma

Papillary thyroid carcinoma (PTC) presents a significant health concern, particularly among Hispanic women in the United States, who exhibit a disproportionately higher chance of developing an advanced disease when compared to the non-Hispanic population. Emerging evidence suggests coagulation factor X, encoded by the F10 gene, has a potential role in inhibiting cancer cell migration. However, comprehensive investigations into the differential expression patterns of F10 in Hispanic versus non-Hispanic females remain limited. RNA-sequencing data were acquired from the TCGA database for white female patients, 166 non-Hispanic and 25 Hispanic. A statistically significant (p < 0.05) 2.06-fold increase in F10 expression levels was detected in disease-free tumors compared to recurrent PTC tumors. Furthermore, an increase in F10 gene expression levels was also observed, corresponding to approximately a 1.74-fold increase in non-Hispanic patients compared to Hispanic patients. The probability of tumor recurrence was 1.82 times higher in the cohort with low expression of F10 compared to the high-expression cohort, correlating with the lower disease-free rates observed in the Hispanic patient cohort when compared to non-Hispanics. This finding underscores the relevance of ethnic disparities in molecular profiles for understanding cancer susceptibility. Identifying F10 as a potential prognostic biomarker highlights avenues for targeted interventions and contributes to improving diagnostic and treatment strategies for diverse patient populations.

Dysregulated coagulation system links to inflammation in diabetic kidney disease

Diabetic kidney disease (DKD) is a significant contributor to end-stage renal disease worldwide. Despite extensive research, the exact mechanisms responsible for its development remain incompletely understood. Notably, patients with diabetes and impaired kidney function exhibit a hypercoagulable state characterized by elevated levels of coagulation molecules in their plasma. Recent studies propose that coagulation molecules such as thrombin, fibrinogen, and platelets are interconnected with the complement system, giving rise to an inflammatory response that potentially accelerates the progression of DKD. Remarkably, investigations have shown that inhibiting the coagulation system may protect the kidneys in various animal models and clinical trials, suggesting that these systems could serve as promising therapeutic targets for DKD. This review aims to shed light on the underlying connections between coagulation and complement systems and their involvement in the advancement of DKD.

Coagulation factors II, V, VII, IX, X and XI and mortality - a cohort study

Background

Elevated levels of coagulation factors (F) II (FII), FV, FVII, FIX, FX, and FXI have often been related with coronary heart disease, ischemic stroke, and venous thrombosis (VT). However, there are few studies on their associations with all-cause mortality.

Objective

We explored whether elevated levels of FII, FV, FVII, FIX, FX, and FXI are associated with an increased risk of death in patients who had VT and in individuals from the general population.

Methods

We followed 1919 patients with previous VT and 2800 age- and sex-matched community controls in whom coagulation factor levels were measured. A high coagulation factor was defined as the >90th percentile of normal in the controls. Cox regression analyses were adjusted for age and sex and for being a patient with VT or being a control subject.

Results

The median age at time of enrolment was 48 years for both patients and controls, and slightly more women than men were followed. Over a median follow-up of 6.1 years for patients and 5.0 years for controls, there were 79 and 60 deaths in patient and controls respectively. There was no association of FII, FV, FVII, FIX, FX, and FXI with all-cause mortality in patients or in control individuals.

Conclusions

Elevated levels of FII, FV, FVII, FIX, FX, and FXI levels may not be associated with an increased risk of all-cause mortality. Only for cardiac death, an association with high FX and FXI was found, which confirms the findings of previous studies, but numbers were small.

Structural Model for Factor X Inhibition of IgM and Complement-Mediated Neutralization of Adenovirus

Adenovirus has strong therapeutic potential as an oncolytic virus and gene therapy vector. However, injecting human species C serotype 5 adenovirus, HAdv-C5, into the bloodstream leads to numerous interactions with plasma proteins that affect viral tropism and biodistribution, and can lead to potent immune responses and viral neutralization. The HAdv/factor X (FX) interaction facilitates highly efficient liver transduction and protects virus particles from complement-mediated neutralization after intravenous delivery. Ablating the FX interaction site on the HAdv-C5 capsid leaves the virus susceptible to neutralization by natural IgM followed by activation of the complement cascade and covalent binding of complement components C4b and C3b to the viral capsid. Here we present structural models for IgM and complement components C1, C4b, and C3b in complex with HAdv-C5. Molecular dynamics simulations indicate that when C3b binds near the vertex, multiple stabilizing interactions can be formed between C3b, penton base, and fiber. These interactions may stabilize the vertex region of the capsid and prevent release of the virally encoded membrane lytic factor, protein VI, which is packaged inside of the viral capsid, thus effectively neutralizing the virus. In a situation where FX and IgM are competing for binding to the capsid, IgM may not be able to form a bent conformation in which most of its Fab arms interact with the capsid. Our structural modeling of the competitive interaction of FX and IgM with HAdv-C5 allows us to propose a mechanistic model for FX inhibition of IgM-mediated virus neutralization. According to this model, although IgM may bind to the capsid, in the presence of FX it will likely retain a planar conformation and thus be unable to promote activation of the complement cascade at the virus surface.

Mechanistic Insights of Polyphenolic Compounds from Rosemary Bound to Their Protein Targets Obtained by Molecular Dynamics Simulations and Free-Energy Calculations

Rosemary represents an important medicinal plant that has been attributed with various health-promoting properties, especially antioxidative, anti-inflammatory, and anticarcinogenic activities. Carnosic acid, carnosol, and rosmanol, as well as the phenolic acid ester rosmarinic acid, are the main compounds responsible for these actions. In our earlier research, we carried out an inverse molecular docking at the proteome scale to determine possible protein targets of the mentioned compounds. Here, we subjected the previously identified ligand-protein complexes with HIV-1 protease, K-RAS, and factor X to molecular dynamics simulations coupled with free-energy calculations. We observed that carnosic acid and rosmanol act as viable binders of the HIV-1 protease. In addition, carnosol represents a potential binder of the oncogene protein K-RAS. On the other hand, rosmarinic acid was characterized as a weak binder of factor X. We also emphasized the importance of water-mediated hydrogen-bond networks in stabilizing the binding conformation of the studied polyphenols, as well as in mechanistically explaining their promiscuous nature.

The functional role of the autolysis loop in the regulation of factor X upon hemostatic response

BACKGROUND

The regulation of factor X (FX) is critical to maintain the balance between blood coagulation and fluidity.

OBJECTIVES

To functionally characterize the role of the FX autolysis loop in the regulation of the zymogen and active form of FX.

METHODS

We introduced novel N-linked glycosylations on the surface-exposed loop spanning residues 143-150 (chymotrypsin numbering) of FX. The activity and inhibition of recombinant FX variants was quantified in pure component assays. The in vitro thrombin generation potential of the FX variants was evaluated in FX-depleted plasma.

RESULTS

The factor VIIa (FVIIa)-mediated activation and prothrombin activation was reduced, presumably through steric hinderance. Prothrombin activation was, however, recovered in presence of cofactor factor Va (FVa) despite a reduced prothrombinase assembly. The introduced N-glycans exhibited position-specific effects on the interaction with two FXa inhibitors: tissue factor pathway inhibitor (TFPI) and antithrombin (ATIII). Ki for the inhibition by full-length TFPI of these FXa variants was increased by 7- to 1150-fold, whereas ATIII inhibition in the presence of the heparin-analog Fondaparinux was modestly increased by 2- to 15-fold compared with wild-type. When supplemented in zymogen form, the FX variants exhibited reduced thrombin generation activity relative to wild-type FX, whereas enhanced procoagulant activity was measured for activated FXa variants.

CONCLUSION

The autolysis loop participates in all aspects of FX regulation. In plasma-based assays, a modest decrease in FX activation rate appeared to knock down the procoagulant response even when down regulation of FXa activity by inhibitors was reduced.

Stoichiometric analysis reveals a unique phosphatidylserine binding site in coagulation factor X

BACKGROUND

Cellular trauma or activation exposes phosphatidylserine (PS) and the substantially more abundant phospholipid, phosphatidylethanolamine (PE), on the outer layer of the plasma membrane, thereby allowing binding of many blood clotting proteins. We previously proposed the Anything But Choline (ABC) hypothesis to explain how PS and PE synergize to support binding of clotting proteins with gamma-carboxyglutamate (Gla)-rich domains, which posited that each Gla domain binds to a limited number of PS molecules and multiple PE molecules. However, the minimal number of PS molecules required to stably bind a Gla-domain-containing blood clotting protein in the presence of excess PE was unknown.

OBJECTIVE

To test the ABC hypothesis for factor X by determining the threshold binding requirement of PS molecules under conditions of PS-PE synergy.

METHODS

We used surface plasmon resonance to investigate the stoichiometry of factor X binding to nanoscale membrane bilayers (Nanodiscs) of varying phospholipid composition.

RESULTS AND CONCLUSIONS

We quantified 1.05 ± 0.2 PS molecules per bound factor X molecule in Nanodiscs containing a mixture of 10% PS, 60% PE, and 30% phosphatidylcholine. Hence, there appears to be one truly PS-specific binding site per Gla domain, while the remaining membrane binding interactions can be satisfied by PE.

Major bleeding during oral anticoagulant therapy associated with factor V activation by factor Xa

OBJECTIVE

Plasma thrombin generation (TG) provides important information on coagulation status; however, current TG output parameters do not predict major bleeding of patients on anticoagulants. We recently reported that factor V (FV) activation by factor X (FX)a contributes importantly to the initiation phase of TG. Here we investigated how this pathway varies in the normal population and whether FXa-mediated activation of FV is associated with major bleeding in patients on anticoagulant therapy.

APPROACH

We employed TIX-5, a specific inhibitor of FV activation by FXa, to estimate the contribution of FXa-mediated FV activation to tissue factor (TF)-initiated TG.

RESULTS

We show that the contribution of this pathway to plasma TG varies considerably in the normal population, as measured by the time needed to form the first traces of thrombin (TG lag time; mean prolongation by TIX-5 40%, range 0%-116%). Comparing patients on vitamin K antagonists (VKA) of the BLEED study (263 patients with and 538 patients without major bleeding), showed a marked prolongation in the median TG lag time in the presence of TIX-5 in cases (12.83 versus 11.00 minutes, P = 0.0030), while the TG lag time without TIX-5 only showed a minor although significant difference (5.83 vs. 5.67 minutes, P = 0.0198). The TIX-5 sensitivity (lag time + TIX-5/lag time + vehicle) in the upper quartile was associated with a 1.62-fold (95% confidence interval 1.04-2.52) increased risk of major bleeding compared to the lowest quartile.

CONCLUSION

A greater dependence on FXa-mediated activation of FV of TG is associated with increased risk of major bleeding during VKA therapy.

The rise of factor X level in blood plasma of patients at severe burn injuries

This work is dedicated to the detection of imbalance between the pro- and anti-coagulant branches of hemostasis at severe burn injuries by evaluating the content or activity of individual clotting factors. To select the targets for accurate diagnostics we measured the concentrations of soluble fibrin monomeric complexes and fibrinogen, levels of total prothrombin, factor X, protein C and antithrombin III, and recorded the time of clotting in activated partial thromboplastin time and prothrombin time tests. Factor X level was increased in 26 % of patients on the first day after the burn and it rose further in 62 % patients on the 14 th day of recovery. Increasing factor X level is assumed to be a risk factor of thrombotic complications. We propose to use it as a marker of predisposition to thrombosis at severe burn injury.

Successful Treatment of Factor X Deficiency in a Patient with Lymphoplasmacytic Lymphoma with Bendamustine Plus Rituximab Regimen: A Case Report and Literature Review

Background

Acquired factor X deficiency is an uncommon condition, and affected individuals have severe and spontaneous bleeding. The associated conditions include malignancy, infection, burn, and inflammatory bowel disease. Many previous studies reported association between lymphoproliferative disease and factor X disappearance. Amyloid deposition causing factor X absorption was the most common mechanism. Here, we report a case of stage IV lymphoplasmacytic lymphoma (LPL) with factor X deficiency who was successfully treated with bendamustine plus rituximab (BR) regimen.

Case Presentation

A 52-year-old Thai woman presented with heavy menorrhea, hoarseness, and widespread ecchymosis at her extremities. On physical examination, the patient had bilateral periorbital purpura and vocal cord hematoma. Coagulation testing showed prolonged prothrombin time (PT) and prolonged activated thromboplastin time (aPTT); however, after mixing with 1:1 normal pooled plasma, PT and aPTT were both corrected to normal levels. Factor assays demonstrated markedly decreased factor X levels, but no presence of factor X inhibitor. Bone marrow examination revealed numerous abnormal lymphoplasmacytoid lymphocytes with kappa light chain expression. Serum free light chain assay also showed kappa light chain restriction [kappa 716.16 mg/L, lambda 16.96 mg/L, ratio 42.23 (0.26–1.65)]. The patient was diagnosed as lymphoplasmacytic lymphoma with factor X deficiency. She received chemotherapy with 6 cycles of bendamustine plus rituximab (BR) regimen. The patient responded favorably to treatment, she remains in lymphoma remission at one year after diagnosis, and her factor X level was more than 20%.

Conclusion

We performed a literature review to identify previous case reports about lymphoma-associated factor X deficiency or inhibitor to determine a possible explanation in our patient. It is important to emphasize that when patients present with acquired factor deficiency, including factor X, lymphoproliferative disease is commonly one of the underlying conditions. Furthermore, the recovery of coagulation factor deficiency is possible if successful remission of lymphoma can be achieved.

Characterization of a Missense Mutation in the Catalytic Domain and a Splicing Mutation of Coagulation Factor X Compound Heterozygous in a Chinese Pedigree

Background: Congenital coagulation factor X (FX) deficiency is a rare bleeding disorder with an incidence of one in one million caused by mutations in the FX-coding gene(F10), leading to abnormal coagulation activity and a tendency for severe hemorrhage. Therefore, identifying mutations in FX is important for diagnosing congenital FX deficiency. Results: Genetic analysis of the proband identified two single-base substitutions: c.794T > C: p.Ile265Thr and c.865 + 5G > A: IVS7 + 5G > A. His FX activity and antigen levels were < 1% and 49.7%, respectively; aPTT and PT were prolonged to 65.3 and 80.5 s, respectively. Bioinformatics analysis predicted the two novel variants to be pathogenic. In-vitro expression study of the missense mutation c.794T > C: p.Ile265Thr showed normal synthesis and secretion. Activation of FXs by RVV, FVII/TF, and FVIII/FIX all showed no obvious difference between the variant and the reference. However, clotting activity by PT and aPTT assays and activity of thrombin generation in a TGA assay all indicated reduced activity of the mutant FX-Ile265Thr compared to FX-WT. Minigene assay showed a normal splicing mode c.865 + 5G > A: IVS7 + 5G > A, which is inconsistent with clinical phenotype. Conclusions: The heterozygous variants c.794T > C: p.Ile265Thr or c.865 + 5G > A: IVS7 + 5G > A indicate mild FX deficiency, but the compound heterozygous mutation of the two causes severe congenital FX deficiency. Genetic analysis of these two mutations may help characterize the bleeding tendency and confirm congenital FX deficiency. In-vitro expression and functional study showed that the low activity of the mutant FX-Ile265Thr is caused by decrease in its enzyme activity rather than self-activation. The minigene assay help us explore possible mechanisms of the splicing mutation. However, more in-depth mechanism research is needed in the future.

Activated factor X targeted stored in platelets as an effective gene therapy strategy for both hemophilia A and B

BACKGROUND

Treatment of hemophiliacs with inhibitors remains challenging, and new treatments are in urgent need. Coagulation factor X plays a critical role in the downstream of blood coagulation cascade, which could serve as a bypassing agent for hemophilia therapy. Base on platelet-targeted gene therapy for hemophilia by our and other groups, we hypothesized that activated factor X (FXa) targeted stored in platelets might be effective in treating hemophilia A (HA) and B (HB) with or without inhibitors.

METHODS

To achieve the storage of FXa in platelets, we constructed a FXa precursor and used the integrin αIIb promoter to control the targeted expression of FXa precursor in platelets. The expression cassette (2bFXa) was carried by lentivirus and introduced into mouse hematopoietic stem and progenitor cells (HSPCs), which were then transplanted into HA and HB mice. FXa expression and storage in platelets was examined in vitro and in vivo. We evaluated the therapeutic efficacy of platelet-stored FXa by tail bleeding assays and the thrombelastography. In addition, thrombotic risk was assessed in the recipient mice and the lipopolysaccharide induced inflammation mice.

RESULTS

By transplanting 2bFXa lentivirus-transduced HSPCs into HA and HB mice, FXa was observed stably stored in platelet α-granules, the stored FXa is releasable and functional upon platelet activation. The platelet-stored FXa can significantly ameliorate bleeding phenotype in HA and HB mice as well as the mice with inhibitors. Meanwhile, no FXa leakage in plasma and no signs of increased risk of hypercoagulability were found in transplantation recipients and lipopolysaccharide induced septicemia recipients.

CONCLUSIONS

Our proof-of-principle data indicated that target expression of the FXa precursor to platelets can generate a storage pool of FXa in platelet α-granules, the platelet-stored FXa is effective in treating HA and HB with inhibitors, suggesting that this could be a novel choice for hemophilia patients with inhibitors.

Novel blood coagulation molecules: Skeletal muscle myosin and cardiac myosin

Essentials Striated muscle myosins can promote prothrombin activation by FXa or FVa inactivation by APC. Cardiac myosin and skeletal muscle myosin are pro-hemostatic in murine tail cut bleeding models. Infused cardiac myosin exacerbates myocardial injury caused by myocardial ischemia reperfusion. Skeletal muscle myosin isoforms that circulate in human plasma can be grouped into 3 phenotypes. ABSTRACT: Two striated muscle myosins, namely skeletal muscle myosin (SkM) and cardiac myosin (CM), may potentially contribute to physiologic mechanisms for regulation of thrombosis and hemostasis. Thrombin is generated from activation of prothrombin by the prothrombinase (IIase) complex comprising factor Xa, factor Va, and Ca++ ions located on surfaces where these factors are assembled. We discovered that SkM and CM, which are abundant motor proteins in skeletal and cardiac muscles, can provide a surface for thrombin generation by the prothrombinase complex without any apparent requirement for phosphatidylserine or lipids. These myosins can also provide a surface that supports the inactivation of factor Va by activated protein C/protein S, resulting in negative feedback downregulation of thrombin generation. Although the physiologic significance of these reactions remains to be established for humans, substantive insights may be gleaned from murine studies. In mice, exogenously infused SkM and CM can promote hemostasis as they are capable of reducing tail cut bleeding. In a murine myocardial ischemia-reperfusion injury model, exogenously infused CM exacerbates myocardial infarction damage. Studies of human plasmas show that SkM antigen isoforms of different MWs circulate in human plasma, and they can be used to identify three plasma SkM phenotypes. A pilot clinical study showed that one SkM isoform pattern appeared to be linked to isolated pulmonary embolism. These discoveries enable multiple preclinical and clinical studies of SkM and CM, which should provide novel mechanistic insights with potential translational relevance for the roles of CM and SkM in the pathobiology of hemostasis and thrombosis.

A serine loop in tissue factor mediates substrate selectivity by the tissue factor-factor VIIa complex

Essentials How the tissue factor-factor VIIa complex selects between different substrates is not well understood. We investigated a serine loop in tissue factor and its role in substrate selectivity. The tissue factor serine loop is selective for factor X over factor IX. Substrate selectivity is facilitated by differential regulation of the nearby tissue factor exosite. ABSTRACT: Background The tissue factor-factor VIIa (TF-FVIIa) complex is the physiologic activator of blood clotting and plays a major role in many thrombotic diseases. TF-FVIIa drives clotting through proteolytic cleavage of its major protein substrates, factor IX (FIX) and factor X (FX). However, it remains unclear how TF-FVIIa exhibits selectivity between these substrates. We previously showed that TF residues adjacent to the putative substrate binding site of TF ("exosite") facilitate FX activation, but the role of these residues in substrate selectivity had not been tested. Objectives We hypothesized that a TF serine loop (residues S160-S163) mediates substrate selectivity by the TF-FVIIa complex. Methods We generated TF serine loop and exosite mutants. The mutants were tested in FIX and FX enzyme activation assays as well as thrombin generation assays. Results Changes in the length of the serine loop affected rates of FIX and FX activation very differently. FX activation was decreased by up to 200-fold when the loop length was changed by just one residue. In contrast, FIX activation was largely unaffected. Substrate selectivity was also detected in thrombin generation assays. Activation assays with TF serine loop and exosite double mutants revealed that the serine loop has no effect on the exosite during FIX activation. In contrast, the serine loop regulates the exosite during FX activation. Conclusions Our results provide new insights into how the TF-FVIIa complex actively selects between its major protein substrates, which is mediated by a TF serine loop.

The Potential Role of Coagulation Factor Xa in the Pathophysiology of COVID-19: A Role for Anticoagulants as Multimodal Therapeutic Agents

SARS-CoV-2 infection (COVID-19) results in local and systemic activation of inflammation and coagulation. In this review article, we will discuss the potential role of coagulation factor Xa (FXa) in the pathophysiology of COVID-19. FXa, a serine protease, has been shown to play a role in the cleavage of SARS-CoV-1 spike protein (SP), with the inhibition of FXa resulting in the inhibition of viral infectivity. FX is known to be primarily produced in the liver, but it is also expressed by multiple cells types, including alveolar epithelium, cardiac myocytes, and macrophages. Considering that patients with preexisting conditions, including cardiopulmonary disease, are at an increased risk of severe COVID-19, we discuss the potential role of increased levels of FX in these patients, resulting in a potential increased propensity to have a higher infectious rate and viral load, increased activation of coagulation and inflammation, and development of fibrosis. With these observations in mind, we postulate as to the potential therapeutic role of FXa inhibitors as a prophylactic and therapeutic treatment for high-risk patients with COVID-19.

Exosite binding drives substrate affinity for the activation of coagulation factor X by the intrinsic Xase complex

Factor X activation by the intrinsic Xase complex, composed of factor IXa bound to factor VIIIa on membranes, is essential for the amplified blood coagulation response. The biological significance of this step is evident from bleeding arising from deficiencies in factors VIIIa or IXa in hemophilia. Here, we assess the mechanism(s) that enforce the distinctive specificity of intrinsic Xase for its biological substrate. Active-site function of IXa was assessed with a tripeptidyl substrate (PF-3688). The reversible S1 site binder, 4-aminobenzamidine (pAB), acted as a classical competitive inhibitor of PF-3688 cleavage by Xase. In contrast, pAB acted as a noncompetitive inhibitor of factor X activation. This disconnect between peptidyl substrate and protein substrate cleavage indicates a major role for interactions between factor X and extended sites on Xase in determining substrate affinity. Accordingly, an uncleavable factor X variant, not predicted to engage the active site of IXa within Xase, acted as a classical competitive inhibitor of factor X activation. Fluorescence studies confirmed the binding of factor X to Xase assembled with IXa with a covalently blocked active site. Our findings suggest that the recognition of factor X by the intrinsic Xase complex occurs through a multistep "dock-and-lock" pathway in which the initial interaction between factor X and intrinsic Xase occurs at exosites distant from the active site, followed by active-site docking and bond cleavage.

Partial rescue of naturally occurring active site factor X variants through decreased inhibition by tissue factor pathway inhibitor and antithrombin

BACKGROUND

Activated coagulation factor X (FXa) is the serine protease component of prothrombinase, the physiological activator of prothrombin. Factor X Nottingham (A404T) and Taunton (R405G) are two naturally occurring mutations, identified in families with a bleeding phenotype.

OBJECTIVE

To characterize these FX variants functionally.

METHODS

The activity and inhibition of recombinant FX variants were quantified in plasma-based and pure component assays.

RESULTS

The prothrombin times in FX-depleted plasma supplemented with FX Nottingham and Taunton were greatly increased compared to that of wild-type (WT) FX. Kinetic investigations of activated variants in the prothrombinase complex showed kcat /Km reduced ~50-fold and ~5-fold, respectively, explaining the prolonged prothrombin time (PT). The substituted residues are located in the protease domain Na+ -binding loop, important for the activity of FXa, as well as its inhibition. Both FXa Nottingham and Taunton showed reduced affinity for Na+ . Plasma-based thrombin generation assays triggered with 1 pmol/L tissue factor (TF) demonstrated only small differences in activities compared to WT FX, but large reductions at 10 pmol/L TF. Severely reduced inhibition of both FXa Nottingham and Taunton by tissue factor pathway inhibitor (TFPI) and antithrombin (AT), was shown in pure-component FXa inhibition assays. Factor Xa Nottingham and Taunton produced higher amounts of thrombin than WT FXa in pure-component prothrombinase assays in the presence of TFPI and AT, explaining the results from the plasma-based assay.

CONCLUSIONS

Factor X Nottingham and Taunton both display decreased proteolytic activity. However, their reduced activity in plasma triggered by low TF can be rescued by decreased inhibition by the natural FXa inhibitors, TFPI and AT.

Immunoglobulin Light Chain Amyloidosis with Severe Liver Dysfunction Accompanied by Factor X Deficiency

Severe hepatic failure is rarely a cause of death in patients with immunoglobulin light chain (AL) amyloidosis. We herein report a case of AL amyloidosis involving a bleeding tendency due to factor X deficiency and marked hepatic involvement of amyloidosis. The patient died due to severe liver dysfunction two weeks after admission. The diagnosis was confirmed histologically by AL-λ amyloidosis, with the liver and spleen as the main lesions, on an autopsy. As treatment-related toxicity is strong in advanced cases, appropriate treatments are required to improve the prognosis of AL amyloidosis with severe liver dysfunction.

The direct oral anticoagulants rivaroxaban and dabigatran do not inhibit orthotopic growth and metastasis of human breast cancer in mice

Essentials Factor Xa (FXa)-targeting direct oral anticoagulants (DOACs) reduce venous thromboembolism (VTE) The effects of FXa-targeting DOACs on cancer progression remain to be studied In xenograft models, a FXa-targeting DOAC did not inhibit breast cancer growth and metastasis A thrombin-targeting DOAC, dabigatran, also did not inhibit breast cancer growth and metastasis ABSTRACT: Background Factor Xa-targeting DOACs were recently found to reduce recurrent VTE efficiently in cancer patients when compared to the standard treatment with low-molecular-weight heparins (LMWHs). While the anticancer effects of LMWHs have been extensively studied in preclinical cancer models, the effects of FXa-targeting DOACs on cancer progression remain to be studied. Objective We investigated whether the FXa-targeting DOAC rivaroxaban and the thrombin-targeting DOAC dabigatran etexilate (DE) affected human breast cancer growth and metastasis in orthotopic xenograft models. Methods/results Mice that were put on a custom-made chow diet supplemented with rivaroxaban (0.4 or 1.0 mg/g diet) or dabigatran etexilate (DE) (10 mg/g diet) showed prolonged ex vivo coagulation times (prothrombin time [PT] and activated partial thromboplastin time [aPTT] assay, respectively). However, rivaroxaban and DE did not inhibit MDA-MB-231 tumor growth and metastasis formation in lungs or livers of 7-week-old fully immunodeficient NOD/SCID/ƴC-/- (NSG) mice. Comparable data were obtained for rivaroxaban-treated mice when using NOD-SCID mice. Rivaroxaban and DE treatment also did not significantly inhibit tumor growth and metastasis formation when using another human triple negative breast cancer (TNBC) cell line (HCC1806) in NOD-SCID mice. The FXa and thrombin-induced gene expression of the downstream target CXCL8 in both cell lines, but FXa and thrombin, did not significantly stimulate migration, proliferation, or stemness in vitro. Conclusion Although effectively inhibiting coagulation, the DOACs rivaroxaban and DE did not inhibit orthotopic growth and metastasis of human TNBC. It remains to be investigated whether DOACs exert antitumorigenic effects in other types of cancer.

Co-localization of Coagulation Factor X and its Inhibitory System, PZ/ZPI, in Human Endometrial Cancer Tissue

BACKGROUND/AIM

Hemostatic system components contribute to cancer progression independently from their roles in hemostasis. It has been shown that protein Z (PZ)/protein Z-dependent protease inhibitor (ZPI) inhibit coagulation factor X (FX). The aim of the study was to analyze the expression of PZ/ZPI in relation to the main coagulation factor - FX in human endometrial cancer tissue.

MATERIALS AND METHODS

Immunohistochemical analysis was performed on 21 endometrial cancer specimens employing antibodies against ZPI, PZ and FX.

RESULTS

Endometrial cancer cells showed a strong expression of ZPI and PZ and medium expression of FX. Normal endometrial tissue showed no expression of ZPI, PZ or FX.

CONCLUSION

Strong expression of PZ and ZPI in endometrial cancer cells suggests a role of these proteins in endometrial cancer.

Detection and Extraction of Heparin from Camel Lungs

BACKGROUND

Heparin is an essential drug used as an anticoagulant. Access to raw material suitable for heparin extraction is critical for creating a viable business opportunity. In Saudi Arabia, large amounts of raw material with potential for heparin extraction are wasted.

OBJECTIVE

To extract heparin and low-molecular-weight heparin (LMWH) from the camel lung, and measure its potency and activity.

METHODS

Heparin preparation included three steps: extraction, electrophoretic identification, and activity measurement. Fresh lung tissue (100 g) was minced and homogenized in a blender. Crude heparin extracts were prepared using Charles's or Volpi's method with slight modifications. Heparin was purified by electrophoresis using high-purity agarose gels in barium acetate buffer. The heparin activity of purified samples was assayed spectrophotometrically using commercial heparin kits.

RESULTS

Charles's and Volpi's extraction methods were simple and easy to establish. The yield was 90 mg crude heparin per 100 g of camel lung tissue following Volpi's extraction protocol, whereas Charles's method did not yield any heparin. The separation of heparin and LMWH by gel electrophoresis resulted in sharp and clear product bands using material prepared according to Volpi's method. The heparin preparation had an anti-factor Xa activity of 37 IU/mg, indicating weak potency.

CONCLUSION

Preparation of active heparin from camel lung tissue is a technology applicable in manufacturing. Further method development is needed to increase heparin purity and potency.

New functional test for the TFPIα cofactor activity of Protein S working in synergy with FV-Short

Essentials Protein S and FV-Short are synergistic cofactors to Tissue Factor Pathway Inhibitor α (TFPIα). An assay for the TFPIα synergistic cofactor activity of protein S with FV-Short was developed. The assay was specific for the synergistic TFPIα-cofactor activity of free protein S. Protein S deficient individuals with known mutations were correctly distinguished from controls. SUMMARY: Background Protein S is an anticoagulant cofactor to both activated protein C and tissue factor pathway inhibitor (TFPIα). The TFPIα-cofactor activity of protein S is stimulated by a short isoform of factor V (FV-Short), the two proteins functioning in synergy. Objective Using the synergistic TFPIα-cofactor activity between protein S and FV-Short to develop a functional test for plasma protein S. Patients/Methods TFPIα-mediated inhibition of FXa in the presence of FV-Short, protein S and negatively charged phospholipid vesicles was monitored in time by synthetic substrate S2765. TFPIα, FXa and FV-Short were purified proteins, whereas diluted plasma from protein S deficient patients or controls were used as source for protein S. Results The assay was specific for free protein S demonstrating good correlation to free protein S plasma levels (r = 0.92) with a Y-axis intercept of -5%. Correlation to concentrations of total protein S (free and C4BPβ+-bound) was lower (r = 0.88) and the Y-axis intercept was +46%, which is consistent with the specificity for free protein S. The test distinguished protein S-deficient individuals from 6 families with known ProS1 mutations from family members having no mutation. Protein S levels of warfarin-treated protein S deficient cases were lower than protein S in cases treated with warfarin for other causes. Conclusions We describe a new assay measuring the TFPIα-cofactor activity of plasma protein S. The test identifies type I/III protein S deficiencies and will be a useful tool to detect type II protein S deficiency having defective TFPIα-cofactor activity.

Inhibition of activated factor X; a new pathway in ameliorating carbon tetrachloride-induced liver fibrosis in rats

Activated factor X has a central role in the coagulation activation and also contributes to chronic inflammation and tissue fibrosis. In this study, rivaroxaban, a direct factor X inhibitor, attenuates liver fibrosis induced by carbon tetrachloride (CCl₄ ). Male rats were randomly allocated into three groups: a control group, CCl ₄ fibrotic group, and CCl ₄ +rivaroxaban (5 mg/kg) group. Liver fibrosis was induced by subcutaneous injection of CCl ₄ twice a week for 6 weeks. Rivaroxaban significantly restored the biochemical parameter including inflammatory and fibrosis markers with histopathological evidence using routine and Masson trichrome staining. It reduced also the expression of tissue factor, fibrin, transforming growth factor and α-smooth muscle actin in the liver tissues. This concludes that rivaroxaban attenuates liver injury caused by CCl ₄ , at least in part by inhibiting coagulation and proinflammatory activation. In conclusion, rivaroxaban may be used for the management of liver fibrosis.

4-O-Methylhonokiol Influences Normal Cardiovascular Development in Medaka Embryo

Although 4-O-Methylhonokiol (MH) effects on neuronal and immune cells have been established, it is still unclear whether MH can cause a change in the structure and function of the cardiovascular system. The overarching goal of this study was to evaluate the effects of MH, isolated from Magnolia grandiflora, on the development of the heart and vasculature in a Japanese medaka model in vivo to predict human health risks. We analyzed the toxicity of MH in different life-stages of medaka embryos. MH uptake into medaka embryos was quantified. The LC₅₀ of two different exposure windows (stages 9–36 (0–6 days post fertilization (dpf)) and 25–36 (2–6 dpf)) were 5.3 ± 0.1 μM and 9.9 ± 0.2 μM. Survival, deformities, days to hatch, and larval locomotor response were quantified. Wnt 1 was overexpressed in MH-treated embryos indicating deregulation of the Wnt signaling pathway, which was associated with spinal and cardiac ventricle deformities. Overexpression of major proinflammatory mediators and biomarkers of the heart were detected. Our results indicated that the differential sensitivity of MH in the embryos was developmental stage-specific. Furthermore, this study demonstrated that certain molecules can serve as promising markers at the transcriptional and phenotypical levels, responding to absorption of MH in the developing embryo.

The perils of inhibiting deficient factors

Essentials Anticoagulation in patients with factor X deficiency is an evidence-poor area. A patient with factor X deficiency was anticoagulated with warfarin followed by rivaroxaban. Warfarin may be a safer anticoagulant option than rivaroxaban in hereditary factor X deficiency. A baseline coagulation screen should be performed prior to commencement of anticoagulation.

SUMMARY

We report a case of a previously undiagnosed factor X deficiency in an 83-year-old man who had no previous bleeding history despite multiple hemostatic challenges. He was anticoagulated with warfarin for atrial fibrillation without bleeding complications; however, major hemorrhage occurred soon after a switch to rivaroxaban.

Distinct Pathogenesis of Pancreatic Cancer Microvesicle-Associated Venous Thrombosis Identifies New Antithrombotic Targets In Vivo

OBJECTIVE

Cancer patients are at high risk of developing deep venous thrombosis (DVT) and venous thromboembolism, a leading cause of mortality in this population. However, it is largely unclear how malignant tumors drive the prothrombotic cascade culminating in DVT.

APPROACH AND RESULTS

Here, we addressed the pathophysiology of malignant DVT compared with nonmalignant DVT and focused on the role of tumor microvesicles as potential targets to prevent cancer-associated DVT. We show that microvesicles released by pancreatic adenocarcinoma cells (pancreatic tumor-derived microvesicles [pcMV]) boost thrombus formation in a model of flow restriction of the mouse vena cava. This depends on the synergistic activation of coagulation by pcMV and host tissue factor. Unlike nonmalignant DVT, which is initiated and propagated by innate immune cells, thrombosis triggered by pcMV was largely independent of myeloid leukocytes or platelets. Instead, we identified externalization of the phospholipid phosphatidylethanolamine as a major mechanism controlling the prothrombotic activity of pcMV. Disrupting phosphatidylethanolamine-dependent activation of factor X suppressed pcMV-induced DVT without causing changes in hemostasis.

CONCLUSIONS

Together, we show here that the pathophysiology of pcMV-associated experimental DVT differs markedly from innate immune cell-promoted nonmalignant DVT and is therefore amenable to distinct antithrombotic strategies. Targeting phosphatidylethanolamine on tumor microvesicles could be a new strategy for prevention of cancer-associated DVT without causing bleeding complications.

Blood Coagulation Factor X Exerts Differential Effects on Adenovirus Entry into Human Lymphocytes

It has been proposed that blood coagulation factors, principally factor X (FX), enhance the uptake of human adenovirus type 5 (Ad5) into cultured epithelial cells by bridging the viral hexon capsid protein and cell-surface heparan sulphate proteoglycans (HSPGs). We studied the effects of FX on Ad transduction of lymphoid cell lines (NK92MI, a natural killer cell line; Daudi, a B-cell line and Jurkat, a T-cell line) as well as primary peripheral blood lymphocytes (PBL) and HeLa epithelial cells using either replication-deficient Ad5, or a derivative in which the Ad5 fiber was replaced with that of another Ad type, Ad35, termed Ad5F35. PBL and NK92MI were resistant to Ad5 transduction. Transduction of Jurkat and Daudi cells by Ad5 was reduced by FX but without discernible effects on cell-surface Ad5 binding. FX reduced virus binding and transduction of all lymphoid cell lines by Ad5F35, as well as transduction of the T- and Natural Killer (NK)-cell populations of PBL. Flow cytometry analysis showed that all lymphoid cell lines were negative for HSPG components, in contrast to HeLa cells. FX reduced transduction of an HSPG-negative mutant Chinese hamster ovary cell line (CHOpgsA745) by Ad5 and Ad5F35, with Ad5F35 binding also being reduced by FX. These results point to fiber-dependent differences (Ad5 versus Ad35 fiber) in Ad binding to and transduction of human lymphoid and epithelial cells in the presence of FX.

Factor V-short and protein S as synergistic tissue factor pathway inhibitor (TFPIα) cofactors

BACKGROUND

FV-Short is a normal splice variant of Factor V (FV) having a short B domain, which exposes a high affinity-binding site for tissue factor pathway inhibitor α (TFPIα). FV-Short and TFPIα circulate in complex in plasma.

OBJECTIVES

The aim was to elucidate whether FV-Short affects TFPIα as inhibitor of coagulation FXa and to test whether the TFPIα-cofactor activity of protein S is influenced by FV-Short.

METHODS

Recombinant FV, wild-type FV-Short and a FV-Short thrombin-cleavage resistant variant were expressed and purified. The influence of FV and FV-Short variants and/or protein S on the FXa inhibitory activity of TFPIα was monitored both in a purified system and in a plasma-based thrombin generation assay.

RESULTS

FV-Short had intrinsically weak TFPIα-cofactor activity but with protein S present, FV-Short yielded efficient inactivation of FXa. Protein S alone did not promote full TFPIα-activity. Intact FV was inefficient at low protein S concentrations and had 10-fold lower activity compared to FV-Short at physiological protein S levels. Activation of FV-Short by thrombin resulted in the loss of the TFPIα-cofactor activity. The synergistic TFPIα-cofactor activity of FV-Short and protein S was also demonstrated in plasma using a thrombin generation assay.

CONCLUSIONS

FV-Short and protein S are highly efficient, synergistic cofactors to TFPIα in the regulation of FXa activity, whereas full length FV has lower activity. Our results suggest the formation of an efficient FXa-inhibitory complex between FV-Short, TFPIα and protein S on the surface of negatively charged phospholipids.

Factor X Friuli Coagulation Disorder: Almost 50 Years Later

The story of factor X (FX) Friuli. Factor X Friuli was discovered in 1969 to 1970. However, the story of that disease was an international event since patients with this defect were studied in France and in Italy, and different diagnoses were reached-FVII; FX; combined prothrombin complex; and combined FII, FVII, and FX deficiencies. The diagnostic difficulties were due to the peculiar clotting pattern presented by these patients, namely, prolonged partial thromboplastin time, prolonged prothrombin time but normal Russell viper venom clotting time. Only suitable anti-FX antisera clarified the pattern. Altogether 12 homozygotes and 102 heterozygotes have been followed during 4 decades. Six homozygotes died, 2 of them due to HIV infection and 1 due to hepatitis B liver cirrhosis. The other 3 died of nontransfusion-related morbidity. Bleeding tendency has been moderate in agreement with the extrinsic or intrinsic system assay results-FX level of 4% to 5% is considered normal. Heterozygotes may present occasional bleeding manifestations usually during surgery or delivery. Molecular analysis have shown that the mutation responsible for the defect is a Pro343Ser substitution in exon 8. Chimeric FX Friuli mice have been useful in studying the effect of FX levels on embryonic or natal mortality of these animals. No new homozygote but several heterozygotes have been recently seen. The study of FX Friuli has revolutionized the diagnostic approach to FX deficiencies. The FX should be assayed by all assay systems. The FX Friuli has never been described in any other country, and all patients studied come from the Friuli Meduna River Valley.

Local Regulation of Thrombin Activity by Factor Xa in Peripheral Nerve Schwann Cells

Thrombin through its receptor plays an important role in the peripheral nervous system (PNS) but the pathways leading to its generation there are not known. In the blood, activated factor X (FXa) which is formed from factor X (FX) by tissue factor (TF) and factor VII (FVII), cleaves prothrombin into thrombin. We here studied these factors in vivo in mouse sciatic nerve and in vitro in a Schwannoma cell line and provide mRNA, immunoblot and immunohistochemistry evidence that FX and FXa are expressed in the normal and injured peripheral nerve and in Schwannoma cells. Furthermore, TF and FVII were localized histologically to the node of Ranvier in the sciatic nerve. Adding exogenous FXa increased the thrombin levels in sciatic nerve (11.6 ± 1.6 mU/ml compared to 35.2 ± 6 mU/ml p = 0.02) and in Schwannoma cell line (4.5 ± 0.2 mU/ml compared to 18.1 ± 0.5 mU/ml p < 0.001), indicating a large reserve of prothrombin. In the injured nerve, FX mRNA was upregulated 1 day after injury compared to normal nerve (103 ± 38 versus 1 ± 0.3 FOI p < 0.001). FXa protein levels increased 1 h after the injury and then decreased significantly at 1 and 2 days following injury despite an increase in its precursor, FX. Injecting the selective FXa inhibitor apixaban immediately upon injury decreased thrombin activation and improved motor function after nerve injury. The results localize the extrinsic coagulation pathway and FXa to the PNS, suggesting a critical role for FXa in PNS thrombin formation and the possible therapeutic use of selective FXa inhibitors in nerve injuries.

Bispecific antibody mimicking factor VIII

There are some issues in the current factor (F)VIII replacement therapy for severe hemophilia A. One is mental and physical burden for the multiple intravenous infusions, and the other is difficulty in the hemostatic treatment for the patients with FVIII inhibitor. The development of novel drug with fully hemostatic effect, simply procedure, and long-acting reaction has been expected. Recently, FVIIIa-mimicking humanized recombinant bispecific antibody (ACE910) against FIXa and FX was developed. In the non-human clinical study, primate model of acquired hemophilia A demonstrated that the ACE910 was effective on both on-going and spontaneous bleedings. A phase I clinical study was conducted in healthy adults by single subcutaneous infusion of ACE910, followed by the patients' part study, Japanese patients with severe hemophilia A without or with inhibitor were treated with once-weekly subcutaneous injection of ACE910 at three dose levels for 12 successive weeks. There was no significant adverse event related to ACE910 in the clinical and laboratorial findings, and t1/2 of ACE910 was ∼30 days. The median annual bleeding rates were reduced very markedly dose-dependently, independently of inhibitor. Furthermore, among the patients with dose escalation, bleeding rate was decreased as ACE910 dose was increased. In conclusion, ACE910 would have a number of promising features: its high subcutaneous bioavailability and long half-life make the patients possible to be injected subcutaneously with a once-a-week or less frequency. In addition, ACE910 would provide the bleeding prophylactic efficacy, independently of inhibitor.

Inactivation of human coagulation factor X by a protease of the pathogen Capnocytophaga canimorsus

Essentials Capnocytophaga canimorsus causes severe dog bite related blood stream infections. We investigated if C. canimorsus contributes to bleeding abnormalities during infection. The C. canimorsus protease CcDPP7 causes factor X dysfunction by N-terminal cleavage. CcDPP7 inhibits coagulation in vivo, which could promote immune evasion and trigger hemorrhage.

SUMMARY

Background Capnocytophaga canimorsus is a Gram-negative bacterium that is present in the oral flora of dogs and causes fulminant sepsis in humans who have been bitten, licked, or scratched. In patients, bleeding abnormalities, such as petechiae, purpura fulminans, or disseminated intravascular coagulation (DIC), occur frequently. Objective To investigate whether C. canimorsus could actively contribute to these bleeding abnormalities. Methods Calibrated automated thrombogram and clotting time assays were performed to assess the anticoagulant activity of C. canimorsus 5 (Cc5), a strain isolated from a fatal human infection. Clotting factor activities were measured with factor-deficient plasma. Factor X cleavage was monitored with the radiolabeled zymogen and western blotting. Mutagenesis of Cc5 genes encoding putative serine proteases was performed to identify the protease that cleaves FX. Protein purification was performed with affinity chromatography. Edman degradation allowed the detection of N-terminal cleavage of FX. Tail bleeding times were measured in mice. Results We found that Cc5 inhibited thrombin generation and increased the prothrombin time and the activated partial thromboplastin time of human plasma via FX cleavage. A mutant that was unable to synthesize a type 7 dipeptidyl peptidase (DPP7) of the S46 serine protease family failed to proteolyse FX. The purified protease (CcDPP7) cleaved FX heavy and light chains from the N-terminus, and was active in vivo after intravenous injection. Conclusions This is, to our knowledge, the first study demonstrating a detailed mechanism for FX inactivation by a bacterial protease, and it is the first functional study associating DPP7 proteases with a potentially pathogenic outcome.

Biorheology of platelet activation in the bloodstream distal to thrombus formation

Thrombus growth at the site of vascular injury is mediated by the sequential events of platelet recruitment, activation and aggregation concomitant with the initiation of the coagulation cascade, resulting in local thrombin generation and fibrin formation. While the biorheology of a localized thrombus formation has been well studied, it is unclear whether local sites of thrombin generation propagate platelet activation within the bloodstream. In order to study the physical biology of platelet activation downstream of sites of thrombus formation, we developed a platform to measure platelet activation and microaggregate formation in the bloodstream. Our results show that thrombi formed on collagen and tissue factor promote activation and aggregation of platelets in the bloodstream in a convection-dependent manner. Pharmacological inhibition of the coagulation factors (F) X, XI or thrombin dramatically reduced the degree of distal platelet activation and microaggregate formation in the bloodstream without affecting the degree of local platelet deposition and aggregation on a surface of immobilized collagen. Herein we describe the development and an example of the utility of a platform to study platelet activation and microaggregate formation in the bloodstream (convection-limited regime) relative to the local site of thrombus formation.

The carboxyl-terminal region is NOT essential for secreted and functional levels of coagulation factor X

BACKGROUND

The homologous coagulation factor X (FX), VII (FVII), IX (FIX) and protein C (PC) display striking differences in the carboxyl-terminus, with that of FX being the most extended. This region is essential for FVII, FIX and PC secretion.

OBJECTIVES

To provide experimental evidence for the role of the FX carboxyl-terminus.

METHODS

Recombinant FX (rFX) variants were expressed in multiple eukaryotic cell systems. Protein and activity levels were evaluated by ELISA, coagulant and amidolytic assays.

RESULTS AND DISCUSSION

Expression of a panel of progressively truncated rFX variants in HEK293 cells revealed that the deletion of up to 21 residues in the carboxyl-terminus did not significantly affect secreted protein levels, as confirmed in HepG2 and BHK21 cells. In contrast, chimeric rFX-FVII variants with swapped terminal residues showed severely reduced levels. The truncated rFX variants revealed normal amidolytic activity, suggesting an intact active site. Intriguingly, these variants, which included that resembling the activated FXβ form once cleaved, also displayed remarkable or normal pro-coagulant capacity in PT- and aPTT-based assays. This supports the hypothesis that subjects with nonsense mutations in the FX carboxyl-terminus, so far never identified, would be asymptomatic.

CONCLUSIONS

For the first time we demonstrate that the FX carboxyl-terminal region downstream of residue K467 is not essential for secretion and provides a modest contribution to pro-coagulant properties. These findings, which might suggest an involvement of the carboxyl-terminal region in the divergence of the homologous FX, FVII, FIX and PC, help to interpret the mutational pattern of FX deficiency.

Near fatal spontaneous intraperitoneal bleeding: A rare manifestation in a congenital factor X deficiency carrier

Congenital factor X (FX) deficiency is a rare coagulation disorder of autosomal recessive inheritance, characterized by bleeding of variable severity. Bleeding severity generally correlates with the level of FX functional activity and severe bleeding usually occurs in moderate and severe deficiency, when FX coagulant activity is <5%. FX activity above 10% is infrequently associated with severe bleeding. Here we report the rare occurrence of life-threatening massive spontaneous intraperitoneal bleeding with hypovolemic shock, resulting from spontaneous rupture of an ovarian luteal cyst in a 25-year-old FX deficiency carrier woman, with a FX activity of 26%. She was managed successfully conservatively, with fresh frozen plasma and packed red blood cell transfusions and she showed gradual improvement. The case is being reported to discuss the diagnosis and management of this rare inherited coagulation disorder.

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.

Hemorrhagin VaH4, a covalent heterodimeric P-III metalloproteinase from Vipera ammodytes ammodytes with a potential antitumour activity

In the envenomation caused by a bite of Vipera ammodytes ammodytes, the most venomous snake in Europe, hemorrhage is usually the most severe consequence in man. Identifying and understanding the hemorrhagic components of its venom is therefore particularly important in optimizing medical treatment of patients. We describe a novel high molecular mass hemorrhagin, VaH4. The isolated molecule is a covalent dimer of two homologous subunits, VaH4-A and VaH4-B. Complete structural characterization of A and partial characterization of B revealed that both belong to the P-III class of snake venom metalloproteinases (SVMPs), comprising a metalloproteinase, a disintegrin-like domain and a cysteine-rich domain. However, neither VaH4-A nor VaH4-B possess the Cys174 involved in the inter-subunit disulphide bond of P-III SVMPs. A three-dimensional model of the VaH4 dimer suggests that Cys132 serves this function. This implies that dimers in the P-III class of SVMPs can be formed either between their Cys132 or Cys174 residues. The proteolytic activity and stability of VaH4 depend on Zn²⁺ and Ca²⁺ ions and the presence of glycosaminoglycans, which indicates physiological interaction of VaH4 with the latter element of the extracellular matrix (ECM). The molecular mass of VaH4, determined by MALDI/TOF mass spectrometry, is 110.2 kDa. N-deglycosylation reduced the mass of each monomer by 8.7 kDa. The two possible N-glycosylation sites in VaH4-A are located at completely different positions from those in homodimeric P-IIIc VaH3 from the same venom, however, without any evident functional implications. The hemorrhagic activity of this slightly acidic SVMP is ascribed to its hydrolysis of components of the ECM, particularly fibronectin and nidogen, and of some blood coagulation proteins, in particular the α-chain of fibrinogen. VaH4 is also significant medically as we found it cytotoxic against cancer cells and due to its substantial sequence similarity to ADAM/ADAMTS family of physiologically very important human proteins of therapeutic potential.

The international normalized ratio according to Owren in liver disease: interlaboratory assessment and determination of international sensitivity index

INTRODUCTION

The international normalized ratio (INR) is used to prioritize liver disease patients for transplantation. Previous studies have shown high interlaboratory variability in Quick-based INR determinations in samples of patients with liver disease. We assessed Owren-based INR reagents for analyzing INR in patients with liver disease. Further, we determined the difference between international sensitivity index (ISI) for patients on vitamin K antagonists (ISIVKA) and ISI for patients with liver disease (ISIliver).

PATIENTS AND METHODS

Twenty patients with liver disease were included, 10 with INR 1.8-3.6 (group A1) and 10 with INR 1.2-1.5 (group C1). Plasma from these patients was analyzed for Owren-based INR in eight Swedish laboratories using either of following reagents: SPA+, Owrens PT or Nycotest PT. To determine ISI liver, the reference thromboplastin RBT/05 and additional 41 patients with liver disease and 20 normal controls were included. ISIVKA was determined according to the WHO procedure. The difference between the ISIVKA and ISIliver was calculated.

RESULTS

The coefficients of variance for the Owren based INR methods were 6.2% in group A1, 3.9 % in group C1 and 5.3% for all patients. The difference between ISIVKA and ISIliver were -0.4%, -0.7% and -0.2% for SPA+, Owrens PT and Nycotest PT respectively.

CONCLUSIONS

Interlaboratory variation in INR analyses according to Owren in patients with liver disease is low and the difference between ISIVKA and ISIliver is below 10% with this method. ISIVKA can therefore be used in the INR calibration, for the Owren reagents studied, when analyzing plasma from patients with liver disease.

Procoagulant adaptation of a blood coagulation prothrombinase-like enzyme complex in australian elapid venom

The macromolecular enzyme complex prothrombinase serves an indispensable role in blood coagulation as it catalyzes the conversion of prothrombin to thrombin, a key regulatory enzyme in the formation of a blood clot. Interestingly, a virtually identical enzyme complex is found in the venom of some Australian elapid snakes, which is composed of a cofactor factor Va-component and a serine protease factor Xa-like subunit. This review will provide an overview of the identification and characterization of the venom prothrombinase complex and will discuss the rationale for its powerful procoagulant nature responsible for the potent hemostatic toxicity of the elapid venom.