Additional laboratory tests to improve on the diagnosis of antiphospholipid syndrome

Whether additional tests to improve on the diagnosis of antiphospholipid syndrome are useful is a matter of debate. New tests exploring the presence of antiphospholipid antibodies are now available and comprise subgroups of antibodies directed to β2-glycoprotein I, namely anti-Domain 1 and anti-Domain 4/5, and anti-phosphatidylserine/prothrombin antibodies. The aim of this article is to discuss in a forum with the scientific community on the possible utility of additional test for the diagnosis of antiphospholipid syndrome, especially in incomplete antiphospholipid antibody profiles.

Prothrombin is a binding partner of the human receptor of advanced glycation end products

The receptor for advanced glycation end products (RAGE) plays a key role in mammal physiology and in the etiology and progression of inflammatory and oxidative stress-based diseases. In adults, RAGE expression is normally high only in the lung where the protein concentrates in the basal membrane of alveolar Type I epithelial cells. In diseases, RAGE levels increase in the affected tissues and sustain chronic inflammation. RAGE exists as a membrane glycoprotein with an ectodomain, a transmembrane helix, and a short carboxyl-terminal tail, or as a soluble ectodomain that acts as a decoy receptor (sRAGE). VC1 domain is responsible for binding to the majority of RAGE ligands including advanced glycation end products (AGEs), S100 proteins, and HMGB1. To ascertain whether other ligands exist, we analyzed by MS the material pulled down by VC1 from human plasma. Twenty of 295 identified proteins were selected and associated to coagulation and complement processes and to extracellular matrix. Four of them contained a γ-carboxyl glutamic acid (Gla) domain, a calcium-binding module, and prothrombin (PT) was the most abundant. Using MicroScale thermophoresis, we quantified the interaction of PT with VC1 and sRAGE in the absence or presence of calcium that acted as a competitor. PT devoid of the Gla domain (PT des-Gla) did not bind to sRAGE, providing further evidence that the Gla domain is critical for the interaction. Finally, the presence of VC1 delayed plasma clotting in a dose-dependent manner. We propose that RAGE is involved in modulating blood coagulation presumably in conditions of lung injury.

A Retrospective Comparison of 3-Factor Prothrombin Complex Concentrate Products for Warfarin Reversal

Background and Purpose

Current guidelines suggest that 3-factor prothrombin complex concentrate is a possible alternative to 4-factor products for the emergent reversal of bleeding secondary to warfarin. While multiple observational studies have evaluated various forms of 3-factor prothrombin complex concentrate individually, no study has compared the efficacy of the 2 products. The purpose of this study is to compare the efficacy and safety of Bebulin™ and Profilnine™ for the emergent reversal of warfarin-associated major bleeding.

Methods

We conducted a retrospective cohort study of patients receiving both Bebulin™ and Profilnine™ at an urban, academic medical center with comprehensive stroke center designation and a neurosurgical center of excellence. All patients were treated at a single center that utilized a fixed, weight-based dosing protocol. The primary outcome was the percentage of patients in each group achieving a goal international normalization ratio of 1.4 or less.

Results

There was a significant difference in goal international normalization ratio achieved favoring Bebulin™ (85.5% vs 27.3%; P < .001) over Profilnine™. Median dose per kilogram of actual body weight was the same between the groups. When we assessed results by baseline™ international normalization ratio subgroup, more patients in the Bebulin™ group achieved goal when baseline values were 6 or less. No thrombotic events were documented in either group.

Conclusions

We found that patients treated with Bebulin™ experienced significantly higher rates of successful international normalization ratio reversal when compared to those who received Profilnine™. Further research is needed to determine the comparative efficacy between the 2 agents.

Tetra positive thrombotic antiphospholipid syndrome: Major contribution of anti-phosphatidyl-serine/prothrombin antibodies to lupus anticoagulant activity

BACKGROUND

The concurrent presence of lupus anticoagulant, anticardiolipin, and anti β2-glycoprotein I antibodies (triple positive profile) identifies patients at high risk of thromboembolic events. These patients are also positive for anti-phosphatidyl-serine/prothrombin antibodies (tetra-positive profile).

OBJECTIVE

Understand which antibody among anti-β2-glycoprotein I and anti-phosphatidyl-serine/prothrombin is responsible for lupus anticoagulant activity.

PATIENTS/METHODS

Affinity purified anti-β2-glycoprotein I antibodies from plasma of 14 tetra-positive patients spiked into normal pooled plasma were tested.

RESULTS AND CONCLUSIONS

Anti-β2-glycoprotein I antibodies did not prolong the diluted Russell viper venom time and silica clotting time (median ratio 0.98, interquartile ratio [IQR] 0.9-1.06; and 1.0, IQR 0.91-1.03, respectively). Anticoagulant activity remained in the flow-through that was deprived of anti-β2 glycoprotein I antibodies (median ratio 1.88, IQR 1.58-2.77; and 1.75, IQR 1.17-2.9, respectively). This material was loaded on size-exclusion chromatography Sephacryl S-300 column and showed that anticoagulant activity and anti-phosphatidyl-serine/prothrombin antibodies coeluted in the same fractions. Besides, the flow through was poured into a prothrombin affinity column. Protein yield in three patients ranged from 54 to 91 μg/mL and showed strong positivity in phosphatidyl-serine/prothrombin ELISA. The affinity purified material prolonged the coagulation time of normal pooled plasma: the diluted Russell viper venom ratio in the three patients was 2.09, 1.21, and 1.35; that of silica clotting time was 2.05, 1.5, and 2.13. In conclusion, under the assay conditions used, anticoagulant activity in tetra-positive antiphospholipid syndrome patients may largely be attributable to anti-phosphatidyl-serine/prothrombin antibodies.

Specificity and affinity of the N-terminal residues in staphylocoagulase in binding to prothrombin

In Staphylococcus aureus-caused endocarditis, the pathogen secretes staphylocoagulase (SC), thereby activating human prothrombin (ProT) and evading immune clearance. A previous structural comparison of the SC(1-325) fragment bound to thrombin and its inactive precursor prethrombin 2 has indicated that SC activates ProT by inserting its N-terminal dipeptide Ile1-Val2 into the ProT Ile16 pocket, forming a salt bridge with ProT's Asp194, thereby stabilizing the active conformation. We hypothesized that these N-terminal SC residues modulate ProT binding and activation. Here, we generated labeled SC(1-246) as a probe for competitively defining the affinities of N-terminal SC(1-246) variants preselected by modeling. Using ProT(R155Q,R271Q,R284Q) (ProTQQQ), a variant refractory to prothrombinase- or thrombin-mediated cleavage, we observed variant affinities between ∼1 and 650 nm and activation potencies ranging from 1.8-fold that of WT SC(1-246) to complete loss of function. Substrate binding to ProTQQQ caused allosteric tightening of the affinity of most SC(1-246) variants, consistent with zymogen activation through occupation of the specificity pocket. Conservative changes at positions 1 and 2 were well-tolerated, with Val1-Val2, Ile1-Ala2, and Leu1-Val2 variants exhibiting ProTQQQ affinity and activation potency comparable with WT SC(1-246). Weaker binding variants typically had reduced activation rates, although at near-saturating ProTQQQ levels, several variants exhibited limiting rates similar to or higher than that of WT SC(1-246). The Ile16 pocket in ProTQQQ appears to favor nonpolar, nonaromatic residues at SC positions 1 and 2. Our results suggest that SC variants other than WT Ile1-Val2-Thr3 might emerge with similar ProT-activating efficiency.

Prothrombin Is Responsible for the Lupus Cofactor Phenomenon in a Patient with Lupus Anticoagulant/Hypoprothrombinemia Syndrome

Lupus anticoagulant is a misnomer as it is commonly associated with thromboembolic events. In few cases, the name retains its literal meaning when it characterizes patients with a bleeding disorder. We describe a patient with lupus anticoagulant, hypoprothrombinemia, and major bleeding (lupus anticoagulant/hypoprothrombinemia syndrome). Immunological studies revealed a huge amount of circulating monoclonal immunoglobulin M lambda (IgMλ) antiphosphatidylserine/prothrombin antibodies (14,400 U/mL). Affinity purified monoclonal antibodies (440 U/mL) prolonged the coagulation time of normal plasma by 12.2 seconds (diluted Russell viper venom time) and 25.5 seconds (silica clotting time). The original patient's plasma mixed 1:1 with normal plasma showed a marked prolongation of coagulation times (lupus cofactor) from a ratio of 2.94 to 5.23 in diluted Russel viper venom time and from 2.30 to 3.00 using the silica clotting time. Human prothrombin added to original patient's plasma caused a marked prolongation of coagulation times in diluted Russell viper venom test thus unequivocally explaining the lupus cofactor phenomenon. In conclusion, we have shown that lupus anticoagulant/hypoprothrombinemia syndrome is attributable to monoclonal IgMλ antibodies directed to phosphatidylserine/prothrombin and that prothrombin is the protein responsible for the observed lupus cofactor phenomenon.

TLR8 and complement C5 induce cytokine release and thrombin activation in human whole blood challenged with Gram-positive bacteria

We recently showed that TLR8 is critical for the detection of Gram-positive bacteria by human monocytes. Here, we hypothesized that TLR8 and complement together regulate antibacterial responses in human blood. Anticoagulated blood was treated with selective inhibitors of TLR8 and/or complement C5, and then challenged with live Streptococcus agalactiae (Group B streptococcus, GBS), Staphylococcus aureus, or Escherichia coli. Cytokine production, plasma membrane permeability, bacterial survival, phagocytosis, and activation of coagulation was examined. GBS and S. aureus, but not E. coli, triggered TLR8-dependent production of IL-12p70, IL-1β, TNF, and IL-6 in fresh human whole blood. In purified polymorphonuclear neutrophils (PMN), GBS and S. aureus induced IL-8 release in part via TLR8, whereas PMN plasma membrane leakage and extracellular DNA levels increased independently of TLR8. TLR8 was more important than C5 for bacteria-induced production of IL-12p70, IL-1β, and TNF in blood, whereas IL-8 release was more C5 dependent. Both TLR8 and C5 induced IL-6 release and activation of prothrombin cleavage, and here their combined effects were additive. Blocking of C5 or C5aR1 attenuated phagocytosis and increased the extracellular growth of GBS in blood, whereas TLR8 inhibition neither reduced phagocytosis nor intracellular killing of GBS and S. aureus. In conclusion, TLR8 is more important than C5 for production of IL-12p70, IL-1β, and TNF upon GBS and S. aureus infection in blood, whereas C5 is central for IL-8 release and phagocytosis. Both TLR8 and C5 mediate IL-6 release and activation of coagulation during challenge with Gram-positive bacteria in blood.

Prothrombin Arg541Trp Mutation Leads to Defective PC (Protein C) Pathway Activation and Constitutes a Novel Genetic Risk Factor for Venous Thrombosis

OBJECTIVE

Defective PC (protein C) pathway predisposes patients to venous thromboembolism (VTE) and is mostly, but not exclusively, attributed to hereditary PC or PS (protein S) deficiencies and activated PC resistance caused by factor V Leiden mutation. Approach and Results: In a patient with acute mesenteric venous thrombosis and positive family history of VTE associated with the impaired PC pathway function determined by thrombin generation test, we identified a novel heterozygous prothrombin mutation p.Arg541Trp. Two more patients with positive family history of VTE carrying the same mutation were identified in a cohort of another 373 unrelated patients, making an overall prevalence of 0.8%. Family investigation revealed 11 individuals in the 3 pedigrees harboring the heterozygous prothrombin p.Arg541Trp mutation, and 8 of them (72%) had experienced episodes of VTE. Functional studies indicated the mutation moderately decreased procoagulant activity of prothrombin and had mild impact on the inactivation of thrombin by its inhibitor antithrombin. However, the amino acid residue substitution significantly compromised PC activation by thrombin, both in the absence and presence of soluble thrombomodulin, and thus rendered prothrombin function procoagulant biased.

CONCLUSIONS

In summary, the prothrombin p.Arg541Trp mutation constitutes a new genetic risk factor of VTE by impairing function of PC pathway and tilting thrombin's procoagulant activity over anticoagulant function.

Severity of Anaemia Has Corresponding Effects on Coagulation Parameters of Sickle Cell Disease Patients

Sickle cell disease (SCD) is an inherited condition characterized by chronic haemolytic anaemia. SCD is associated with moderate to severe anaemia, hypercoagulable state and inconsistent platelet count and function. However, studies have yielded conflicting results with regards to the effect of anaemia on coagulation in SCD. The purpose of this study was to determine the effect of anaemia severity on selected coagulation parameters of SCD patients. Four millilitres of venous blood samples were taken from the participants (SCD and non-SCD patients) and used for analysis of full blood count and coagulation parameters. Data was analysed using SPSS version-16. From the results, it was seen that individuals with SCD had a prolonged mean PT, APTT and high platelet count compared to the controls. There was also significant difference in the mean PT (p = 0.039), APTT (p = 0.041) and platelet count (p = 0.010) in HbSS participants with severe anaemia. Mean APTT also showed significant difference (p = 0.044) with severe anaemia in HbSC participants. It can be concluded that SCD patients have prolonged PT, APTT and increased platelet count which might predispose them to bleeding episodes and thrombocytosis. Significant difference was also seen between severity of anaemia and mean PT, APTT and platelet count in HbSS individuals.

Prothrombin 3'end Gene Variants in Patients With Sporadic Colon Adenocarcinoma

BACKGROUND/AIM

Thrombin plays significant roles in various types of cancer. However, the expression levels of prothrombin, the thrombin precursor, in cancer remain unclear. Variants of the 3'end of the prothrombin gene lead to increased prothrombin expression. This study aimed to analyze prothrombin 3'end gene variants in colon tumor and adjacent normal tissue samples.

MATERIALS AND METHODS

The study group consisted of 93 patients suffering from colon adenocarcinoma. The 3'end of the prothrombin gene was analyzed by DNA sequencing.

RESULTS

Three variants, all previously associated with increased prothrombin expression were detected. Frequency of the FII 19911G allele was 46.77% and 47.85% in tumor and normal tissue, respectively. For the FII 20210A allele, the detected frequencies were 2.15% and 1.61%, respectively. The frequency of the FII c.1824T allele was 0.54% in both tissues. Four patients showed different genotypes in tumor and normal tissue.

CONCLUSION

Prothrombin 3' end gene variants may play a role in colorectal cancer.

Inherited thrombophilia and portal vein thrombosis in cirrhosis: A systematic review and meta-analysis

BACKGROUND

Portal vein thrombosis (PVT) is common in cirrhosis. PVT is associated with high morbidity and mortality. Individual reports suggest that PVT occurs more frequently in patients with cirrhosis and inherited thrombophilia. The relationship between cirrhosis, PVT development, and inherited thrombophilia was explored in this study. The aim of the study was to determine whether cirrhotic patients with nontumoral PVT have an increased rate of inherited thrombophilia.

METHODS

Studies were identified by searching electronic databases up to October 2017 with English language and human subject restrictions. Two independent reviewers screened citations and extracted data. Magnitude of effect was calculated to obtain aggregate estimates of effect size and 95% confidence intervals (CIs). Between-study variability and heterogeneity were assessed.

RESULTS

Of 2893 citations identified, 9 studies composed of 1929 subjects with cirrhosis were included. The overall prevalence of PVT was 6.5% (n = 125). Both prothrombin G20210A mutation (odds ratio [OR], 2.43; 95% CI, 1.07-5.53; P = 0.03) and factor V Leiden (FVL) (OR, 1.98; 95% CI, 1.06-3.68; P = 0.03) were significantly associated with PVT risk. Methyltetrahydrofolate reductase C677T mutation was not associated with increased PVT risk. No heterogeneity or publication bias was observed. One important study with opposite findings could not be included due to lack of primary data.

CONCLUSIONS

FVL and PTG20210A mutation were associated with increased PVT risk in patients with cirrhosis. This finding reframes the role of inherited thrombophilia in PVT development in patients with cirrhosis. Future prospective studies investigating screening for inherited thrombophilia in all cirrhosis patients with PVT seem warranted.

Chronic testosterone administration improves cardiac contractility and has a beneficial effect on the haemostatic system by enhancing fibrinolytic activity and inducing hypocoagulation in healthy rats

This study investigated the effects of chronic supraphysiological dose of testosterone propionate administration cardiovascular function in rats from the perspective of haemostatic function including platelet functions, coagulation, and fibrinolysis. Testosterone significantly enhanced cardiac contractility by enhancing LVSP (10%), dp/dt_max (36.7%), dp/dt_min (14.6%) without altering heart rate, diastolic function, and serum lipid profile. While it has no effect on platelets count, thromboxane B2 levels, and platelet aggregation, testosterone significantly enhanced bleeding time and increased circulatory and thoracic aorta mRNA and protein levels of tPA (46.5%, 58.2%, and 74.3%, respectively) and significantly decreased those of PAI-1 (29.3%, 26.4%, and 32.8%, respectively). While there were no significant changes in PT and aPTT, mRNA and protein levels of prothrombin and factor VII were downregulated in the livers of the testosterone-treated rats (57.7% and 64.9%, respectively). Overall, chronic testosterone administration in rats may act as a cardio-protective agent by modulating haemostasis in rats.

Effects of microbubble-enhanced ultrasound combined with prothrombin on microwave ablation in rabbit VX2 liver tumor

OBJECTIVE

This study aimed to investigate effects of microbubble-enhanced ultrasound (MEUS) combined with prothrombin on microwave ablation (MWA) on VX2 liver tumors in a rabbit model.

METHODS

80 rabbits with VX2 liver tumors were randomly divided into Group A (sham + NS), Group B (sham + NS + P), Group C (MEUS), and Group D (PMEUS). After treatment, targeted liver tumors were ablated with MWA. On 0, 3, 7 and 14 d, volume of coagulated area was measured. Tissues in ablated area, transition area and surrounding area were collected.

RESULTS

On 0, 3, 7 and 14 d, coagulated volume in Group D was larger than remaining three groups (P<0.05). On 7 d and 14 d, tumor volume in Group D was smaller than remaining three groups (P<0.05). Fibrotic band in Group D was wider than in remaining three groups (P<0.05). Cellular ultrastructure injury in ablated area on 0 d and mitochondrial injury in transition area on 7 d were more severe in Group D than in remaining three groups. On 0, 3, 7 and 14 d, proliferative cellular nuclear antigen-positive index in transition area in Group C and Group D was lower than Group A and Group B (P<0.05). On 0, 3 and 7 d, apoptosis index in transition area in Group D was higher than remaining three groups (P<0.05).

CONCLUSIONS

MEUS combined with prothrombin on MWA can significantly expand ablation volume, enhance the necrosis of ablated tissues, inhibit tumor growth/metastasis and improve therapeutic effect of MWA on rabbit VX2 liver tumors.

Increased Activated Protein C Response Rates Reduce the Thrombotic Risk of Factor V Leiden Carriers But Not of Prothrombin 20210G>A Carriers

RATIONALE

Carriers of the most common prothrombotic mutations FVL (factor V Leiden) and FII (prothrombin) 20210G>A show a highly variable clinical phenotype. Using standardized in vivo coagulation activation followed by activity pattern analysis we have recently shown, that the FVL mutation accelerates thrombin and APC (activated protein C) formation in carriers without a history of venous thromboembolism (VTE).

OBJECTIVE

The aim of this prospective cohort study was to investigate, if the FII 20210G>A mutation induces a similar reaction pattern, and if the response rates differ in FVL and FII 20210G>A mutation carriers with prior VTE (VTE+).

METHODS AND RESULTS

We comparatively analyzed 30 FVL carriers, 28 FII 20210G>A carriers (thereof 13 VTE+ each) and 15 healthy controls. Changes in plasma levels of thrombin, prothrombin activation fragment 1+2 (F1+2), TAT (thrombin-antithrombin complex), APC, and D-dimer were monitored over 8 hours after infusion of recombinant factor VIIa (15 µg/kg). An increase of F1+2 and TAT levels was observed, that did neither differ between FVL and FII 20210G>A carriers nor between asymptomatic and VTE+ carriers of these mutations. Median plasma levels of APC increased more (P=0.008) in FVL carriers (from 1.39 to 7.79 pmol/L) than in FII 20210G>A carriers (from 1.03 to 5.79 pmol/L), and more in FII 20210G>A carriers (P=2×10^-4) than in healthy controls (from 0.86 to 3.00 pmol/L). Most importantly, however, the APC response was greater (P=0.015) in asymptomatic (n=13) than in VTE+ (n=12) heterozygous FVL carriers, with an increase of APC levels from 1.44 to 8.11 pmol/L versus 1.27 to 5.62 pmol/L.

CONCLUSIONS

These in vivo data demonstrate that the FII 20210G>A and FVL mutations share an intermediate phenotype that is characterized by increased thrombin formation after coagulation activation. Furthermore, our data support the conclusion that the APC activating capacity of FVL carriers modifies the thrombotic risk of this common prothrombotic mutation.

Protein Z-dependent protease inhibitor (ZPI) is a physiologically significant inhibitor of prothrombinase function

Current thought holds that factor Xa (FXa) bound in the prothrombinase complex is resistant to regulation by protein protease inhibitors during prothrombin activation. Here we provide evidence that, contrary to this view, the FXa-specific serpin inhibitor, protein Z-dependent protease inhibitor (ZPI), complexed with its cofactor, protein Z (PZ), functions as a physiologically significant inhibitor of prothrombinase-bound FXa during prothrombin activation. Kinetics studies showed that the rapid rate of inhibition of FXa by the ZPI-PZ complex on procoagulant membrane vesicles (k_{a (app)} ∼10⁷ m^-1 s^-1) was decreased ∼10-fold when FXa was bound to FVa in prothrombinase and a further ∼3-4-fold when plasma levels of S195A prothrombin were present (k_{a (app)} 2 × 10⁵ m^-1 s^-1). Nevertheless, the ZPI-PZ complex produced a major inhibition of thrombin generation during prothrombinase-catalyzed activation of prothrombin under physiologically relevant conditions. The importance of ZPI-PZ complex anticoagulant regulation of FXa both before and after incorporation into prothrombinase was supported by thrombin generation assays in plasma. These showed enhanced thrombin generation when the inhibitor was neutralized with a PZ-specific antibody and decreased thrombin generation when exogenous ZPI-PZ complex was added whether prothrombin was activated directly by FXa or through extrinsic or intrinsic pathway activators. Moreover, the PZ antibody enhanced thrombin generation both in the absence and presence of activated protein C (APC) anticoagulant activity. Taken together, these results suggest an important anticoagulant role for the ZPI-PZ complex in regulating both free FXa generated in the initiation phase of coagulation as well as prothrombinase-bound FXa in the propagation phase that complement prothrombinase regulation by APC.

Effect of Genetic Factors on the Etiopathogenesis of Thrombosed Hemorrhoidal Disease

OBJECTIVE

The aim of this study is to investigate whether genetic factors known to increase thrombosis risk play a role in the etiopathogenesis of thrombosed hemorrhoidal disease. Methods: Genomic DNA from patients with thrombosed hemorrhoidal disease was analyzed for the presence of factor V Leiden, prothrombin G20210A, methylenetetrahydrofolate reductase C677T, and methylenetetrahydrofolate reductase A1298C mutations. Results: No significant differences were found in the allele frequencies of factor V Leiden, prothrombin G20210A, methylenetetrahydrofolate reductase C677T, and methylenetetrahydrofolate reductase A1298C mutations between patients with thrombosed hemorrhoidal disease and controls (p 0.05). Moreover, there were no significant differences in the genotype (heterozygous and homozygous mutations) of factor V Leiden, prothrombin G20210A, methylenetetrahydrofolate reductase C677T and A1298C mutations between patients with thrombosed hemorrhoidal disease and controls (p 0.05). Conclusions: Our findings indicate that mutations associated with venous thromboembolism do not play a role in the etiopathogenesis of thrombosed hemorrhoidal disease; however, several environmental, mechanical, and hemodynamic factors may contribute to the etiopathogenesis of hemorrhoidal disease.

Common Variations in Prothrombotic Genes and Susceptibility to Ischemic Stroke in Young Patients: A Case-Control Study in Southeast Iran

Background and Objective: Evidence indicates that genetic factors may be involved in the risk of ischemic stroke (IS). The aim of this study was to assess the effect of genetic polymorphisms located in exons or untranslated regions of MTHFR as well as FV genes on ischemic stroke. Materials and Methods: In this case-control study, 106 patients with IS and 157 healthy volunteers (age <50 years) were genotyped for MTHFR C677T, A1298C, C2572A and C4869G, FVL, and prothrombin G20210A polymorphisms. Results: The MTHFR 677CT genotype was more frequent in patients and increased risk of IS with Odds Ratio = 1.9. The MTHFR A1298C and C2572A polymorphisms were not associated with IS in dominant and recessive models. Our findings showed a significant decrease in the MTHFR4869CG genotype in IS patients, and this variant was associated with a decreased risk of IS in the dominant model. The CAAT haplotype was associated with increased risk, and the GAAC haplotype was associated with decreased risk of IS compared to other haplotypes. There was no relation between FVL G1691A polymorphism and IS risk. Conclusions: The present study showed that the MTHFR 677CT genotype was more frequent and the MTHFR 4869CG genotype was less frequent in young IS patients.

Structure of Coagulation Factor II: Molecular Mechanism of Thrombin Generation and Development of Next-Generation Anticoagulants

Coagulation factor II, or prothrombin, is a multi-domain glycoprotein that is essential for life and a key target of anticoagulant therapy. In plasma, prothrombin circulates in two forms at equilibrium, “closed” (~80%) and “open” (~20%), brokered by the flexibility of the linker regions. Its structure remained elusive until recently when our laboratory solved the first X-ray crystal structure of the zymogen locked in the predominant closed form. Because of this technical breakthrough, fascinating aspects of the biology of prothrombin have started to become apparent, and with this, novel and important questions arise. Here, we examine the significance of the “closed”/“open” equilibrium in the context of the mechanism of thrombin generation. Further, we discuss the potential translational opportunities for the development of next-generation anticoagulants that arise from this discovery. By providing a structural overview of each alternative conformation, this minireview also offers a relevant example of modern structural biology and establishes a practical workflow to elucidate the structural features of analogous clotting and complement factors.

Infection-induced thrombin production: a potential novel mechanism for preterm premature rupture of membranes (PPROM)

BACKGROUND

Preterm premature rupture of membranes is a leading contributor to maternal and neonatal morbidity and death. Epidemiologic and experimental studies have demonstrated that thrombin causes fetal membrane weakening and subsequently preterm premature rupture of membranes. Although blood is suspected to be the likely source of thrombin in fetal membranes and amniotic fluid of patients with preterm premature rupture of membranes, this has not been proved. Ureaplasma parvum is emerging as a pathogen involved in prematurity, which includes preterm premature rupture of membranes; however, until now, prothrombin production that has been induced directly by bacteria in fetal membranes has not been described.

OBJECTIVE

This study was designed to investigate whether Ureaplasma parvum exposure can induce prothrombin production in fetal membranes cells.

STUDY DESIGN

Primary fetal membrane cells (amnion epithelial, chorion trophoblast, and decidua stromal) or full-thickness fetal membrane tissue explants from elective, term, uncomplicated cesarean deliveries were harvested. Cells or tissue explants were infected with live Ureaplasma parvum (1×10⁵, 1×10⁶ or 1×10⁷ colony-forming units per milliliter) or lipopolysaccharide (Escherichia coli J5, L-5014; Sigma Chemical Company, St. Louis, MO; 100 ng/mL or 1000 ng/mL) for 24 hours. Tissue explants were fixed for immunohistochemistry staining of thrombin/prothrombin. Fetal membrane cells were fixed for confocal immunofluorescent staining of the biomarkers of fetal membrane cell types and thrombin/prothrombin. Protein and messenger RNA were harvested from the cells and tissue explants for Western blot or quantitative reverse transcription polymerase chain reaction to quantify thrombin/prothrombin protein or messenger RNA production, respectively. Data are presented as mean values ± standard errors of mean. Data were analyzed using 1-way analysis of variance with post hoc Dunnett's test.

RESULTS

Prothrombin production and localization were confirmed by Western blot and immunostainings in all primary fetal membrane cells and tissue explants. Immunofluorescence observations revealed a perinuclear localization of prothrombin in amnion epithelial cells. Localization of prothrombin in chorion and decidua cells was perinuclear and cytoplasmic. Prothrombin messenger RNA and protein expression in fetal membranes were increased significantly by Ureaplasma parvum, but not lipopolysaccharide, treatments in a dose-dependent manner. Specifically, Ureaplasma parvum at a dose of 1×10⁷ colony-forming units/mL significantly increased both prothrombin messenger RNA (fold changes in amnion: 4.1±1.9; chorion: 5.7±4.2; decidua: 10.0±5.4; fetal membrane: 9.2±3.0) and protein expression (fold changes in amnion: 138.0±44.0; chorion: 139.6±15.1; decidua: 56.9±29.1; fetal membrane: 133.1±40.0) compared with untreated control subjects. Ureaplasma parvum at a dose of 1×10⁶ colony-forming units/mL significantly up-regulated prothrombin protein expression in chorion cells (fold change: 54.9±5.3) and prothrombin messenger RNA expression in decidua cells (fold change: 4.4±1.9).

CONCLUSION

Our results demonstrate that prothrombin can be produced directly by fetal membrane amnion, chorion, and decidua cells. Further, prothrombin production can be stimulated by Ureaplasma parvum exposure in fetal membranes. These findings represent a potential novel underlying mechanism of Ureaplasma parvum-induced rupture of fetal membranes.

Prothrombin: Another Clotting Factor After FV That Is Involved Both in Bleeding and Thrombosis

Clotting factor defects are usually associated with bleeding. About 2 decades ago, 2 polymorphisms, one of FII (G20210A) and another of FV (Arg506Gln), have been shown to be associated with prothrombotic state and venous thrombosis. As a consequence, FII and FV could be considered both as prohemorrhagic factors and prothrombotic conditions. Recently, it has been shown that missense mutations in the prothrombin gene of amino acid Arg596 of exon 14 to Leu596, Gln596, or Trp596 caused the appearance of a thrombophilic state and venous thrombosis. These mutated FII are not associated with bleeding, but only with venous thrombosis. Furthermore, they are all heterozygotes for the mutations. No missense mutation associated with thrombosis has been discovered so far for FV. As a consequence, the prothrombotic activity of FII is the result of a polymorphism and of a missense mutation, whereas that of FV derives only from a polymorphism. The observation that a clotting factor defect may be associated with both bleeding or venous thrombosis depending on the site of the mutation has caused an extensive reevaluation of the blood clotting mechanism.

Frequency and characteristics associated with inherited thrombophilia in patients with intracranial dural arteriovenous fistula

OBJECTIVEThe pathogenesis of dural arteriovenous fistulas (DAVFs) remains poorly defined. Prior studies on thrombophilia as a risk factor for DAVF development are limited by small sample sizes and poor generalizability.METHODSIn this longitudinal observational study, all patients with intracranial DAVFs evaluated at the University of California, San Francisco from December 1994 through April 2014 were identified. After obtaining patient consent, 3 thrombophilic mutations, factor V Leiden (rs6025), MTHFR (rs1801133), and prothrombin G20210A, were genotyped. The authors evaluated the association of thrombophilia status (presence of any thrombophilic mutation) and clinical and angiographic characteristics using either a 2-sample t-test or Fisher's exact test.RESULTSA total of 116 patients with diagnosed intracranial DAVFs were included in the study. Twenty-five (22%) patients met criteria for thrombophilia. Focal neurological deficits tended to occur more frequently in the thrombophilia group (78% vs 57%, p = 0.09). Angiographic characteristics of DAVFs, including high-risk venous flow pattern, multiplicity of DAVF, and the presence of venous sinus thrombosis, did not differ significantly between the 2 groups but tended to be more common in the thrombophilic than in the nonthrombophilic group.CONCLUSIONSThis study is one of the largest of thrombophilia and DAVF to date. The frequency of mutations associated with thrombophilia in this study was higher than that in the general population.

Optimisation of antithrombin resistance assay as a practical clinical laboratory test: Development of prothrombin activator using factors Xa/Va and automation of assay

INTRODUCTION

Antithrombin resistance (ATR) is a novel thrombotic risk in abnormal prothrombins. A manual ATR assay using Oxyuranus scutellatus (Ox) venom as a prothrombin activator was established for detecting antithrombin-resistant prothrombin. However, this assay was limited because of Ox snake venom availability and its throughput capacity. Here, we have improved the ATR assay using bovine factors Xa and Va (FXa/Va) as prothrombin activators and have optimised assay conditions for an automated instrument (ACL TOP 500).

METHODS

Diluted plasma was incubated with a prothrombin activator mix (phospholipids, CaCl₂ , and bovine FXa/Va), followed by inactivation with antithrombin for 10, 20 and 30 minutes. We added a chromogenic substrate S-2238, and assessed changes in absorbance/min at 405 nm. We also adapted assay conditions for ACL TOP 500.

RESULTS

Optimum conditions for FXa/Va treatment were 6.25% phospholipids, 5 mM CaCL₂ , 0.01 μg/mL FXa and 0.1 μg/mL FVa. ATR assay kinetics with the FXa/Va activator was comparable with that with the Ox activator in heterozygous reconstituted plasma with the recombinant wild-type or antithrombin-resistant prothrombin. Using ACL TOP 500, optimum conditions for the FXa/Va treatment were 10.0% phospholipids, 5 mM CaCl₂ , 0.02 μg/mL FXa and 0.2 μg/mL FVa. The automated ATR assay with the FXa/Va activator demonstrated good detectability for antithrombin-resistant prothrombin in plasma from a heterozygous carrier with prothrombin Yukuhashi or Belgrade.

CONCLUSION

We optimised the ATR assay with the FXa/Va activator and adapted the assay for ACL TOP 500; the assay showed the ability to clearly detect antithrombin-resistant prothrombin in manual and automated procedures.

Association of Factor V Leiden and Prothrombin G20210A Polymorphisms in Women with Recurrent Pregnancy Loss in Isfahan Province, Iran

Background:

Maternal thrombophilia has been identified as a risk factor for recurrent pregnancy loss (RPL). The aim of this study was to investigate the association between prothrombin G20210A and factor V Leiden (FVL) polymorphisms in women with RPL and a control group of parous women in Isfahan province of Iran.

Methods:

We studied 250 women with idiopathic RPL and 116 control cases. Prothrombin and FVL different genotypes were determined using polymerase chain reaction and reverse hybridization technique.

Results:

The frequencies of heterozygous mutation prothrombin G20210A were 6% and 0.9%, respectively (P = 0.025), in cases compared to the control group. The frequencies of homozygous mutation prothrombin G20210A were 0.4% and 0%, respectively, in cases compared to controls (P = 0.02). The prothrombin mutation was significantly higher in cases compared to the control group (odds ratio 8.81; 95% confidence interval: 1.16–66.62). There was no significant difference between the FVL mutation and pregnancy loss.

Conclusions:

The results indicated a significant higher frequency of prothrombin G20210A in women with RPL in comparison with controls. Our data suggest that the prothrombin G20210A mutation, but not the FVL mutation, may be an unrecognized cause of RPL in our population.

Screening and functional exploration of prothrombin Arg596 related mutations in Chinese venous thromboembolism patients

AIMS

Dysfunctional prothrombin residue Arg596 associated mutation has been found to precipitate venous thromboembolism (VTE). In the current study we investigated the prevalence of Arg596 associated mutations in Chinese patients with VTE and explored the functional impact of Arg596Gln mutation on coagulation function in affected patients.

METHODS

Prothrombin clotting activity was measured in 267 unrelated patients with unprovoked VTE. Patients with moderately decreased activities underwent further analysis of the F2 gene. Prothrombin amidolytic activity and antigen levels were detected in mutation carriers. Specific family members were investigated about their VTE histories and clinical phenotypes. The thrombin generation test (TGT) was used to evaluate thrombin function and antithrombin resistance assay was applied to assess the extent of impaired antithrombin inhibition of mutation carriers.

RESULTS

Two heterozygous mutation carriers of prothrombin Arg596Gln were identified, both of whom had moderately decreased clotting activities but normal amidolytic activities and antigen levels. Among the families of the two probands, nine out of 13 mutation carriers experienced episodes of VTE. TGTs showed that patients had elevated endogenous thrombin potential and prolonged start tail time. Thrombin generation could be inhibited in the presence of thrombomodulin. The thrombin Arg596Gln variant in patients' plasma presented strong resistance to antithrombin inhibition.

CONCLUSION

Prothrombin Arg596Gln mutation is a risk factor for Chinese patients with VTE due to its moderately decreased clotting activity but strong resistance to antithrombin inhibition. Prothrombin clotting activity screening and its encoding gene sequencing should be considered in patients with VTE when other established risk factors are absent.

Clinical outcome of patients with a vitamin K antagonist-associated bleeding treated with prothrombin complex concentrate

BACKGROUND

Vitamin K antagonists (VKA) are used for the treatment of thromboembolism. Patients with severe VKA-associated bleeding require immediate restoration of haemostasis. Clinical studies on the effect of prothrombin complex concentrate (PCC) are heterogeneous with respect to outcome of bleeding.

OBJECTIVE

To evaluate the clinical outcome of patients treated with PCC for VKA-associated bleeding.

METHODS

We performed a cohort study of consecutive patients who received PCC for VKA-related bleeding in five Dutch hospitals. Data were collected by chart review on the bleeding event, international normalized ratio (INR), haemostatic efficacy, thromboembolic (TE) complications, and mortality. The primary outcome was effective haemostasis, assessed by an adaptation of the Sarode criteria with a surrogate outcome for patients with ICH without repeat CT.

RESULTS

One hundred patients were included. Mean age was 74 years, 54% were male and 79% received VKA for atrial fibrillation. Most patients presented with ICH (41%) or GI bleeding (36%). Effective haemostasis was achieved in 67/98 (68%) patients using the adapted classification. Surrogate outcomes were applied for 32 patients and data for two patients was missing. Median pre-treatment INR was 3.9 (IQR 2.9-5.8). One hour after PCC infusion, the INR was available for 50 patients and of these, 35 (70%) had an INR ≤1.4. TE complications occurred in five patients and 22 died (60% bleeding-related) within 30 days.

CONCLUSION

PCC achieved effective haemostasis in 68% of evaluable patients with VKA-associated bleeding. TE complication rates were low, but mortality rates were high, due to the large number of patients with ICH.

Effect of propeptide amino acid substitution in γ-carboxylation, activity and expression of recombinant human coagulation factor IX

The production of recombinant vitamin K dependent (VKD) proteins for therapeutic purposes is an important challenge in the pharmaceutical industry. These proteins are primarily synthesized as precursor molecules and contain pre-propeptide sequences. The propeptide is connected to γ-carboxylase enzyme through the γ-carboxylase recognition site for the direct γ-carboxylation of VKD proteins that has a significant impact on their biological activity. Propeptides have different attitudes toward γ-carboxylase and certain amino acids in propeptide sequences are responsible for the differences in γ-carboxylase affinity. By aiming to replace amino acids in hFIX propeptide domain based on the prothrombin propeptide, pMT-hFIX-M14 expression cassette, containing cDNA of hFIX with substituted -14 residues (Asp to Ala) was made. After transfection of Drosophila S2 cells, expression of the active hFIX was analyzed by performing ELISA and coagulation test. A 1.4-fold increase in the mutant recombinant hFIX expression level was observed in comparison with that of a native recombinant hFIX. The enhanced hFIX activity and specific activity of the hFIXD-14A (2.2 and 1.6 times, respectively) were further confirmed by comparing coagulation activity levels of substituted and native hFIX. Enrichment for functional, fully γ-carboxylated hFIX species via barium citrate adsorption demonstrated 2-fold enhanced recovery in the S2-expressing hFIXD-14A relative to that expressed native hFIX. These results show that changing -14 residues leads to a decrease in the binding affinity to substrate, increase in γ-carboxylation and activity of recombinant hFIX. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:515-520, 2018.

Preclinical evaluation of point-of-care prothrombin time as a biomarker test to guide prothrombin replacement therapy in coagulopathic bleeding

BACKGROUND

Hemorrhage is still a common cause of death in trauma. Central lab measured prothrombin time (lab PT) is predictive of low prothrombin concentration and clinical outcome in trauma patients, however, treatment guidance is limited by slow turnaround times. Here, we have preclinically evaluated the potential of a point-of-care prothrombin time test (POC PT) as a faster alternative to identify patients with low prothrombin concentration.

METHODS

Human whole blood was serially diluted and prothrombin time measured by POC PT (CoaguChek XS Pro, Roche) and lab PT. Recombinant human prothrombin (MEDI8111) was added to human whole blood with or without depletion of prothrombin by pretreatment with prothrombin neutralizing antibodies.

RESULTS

There was no observable difference in the sensitivity of either test to dilution at blood volumes of 60-100%. At blood volumes of ≤55% (equivalent to 47 mg/L prothrombin), PT sharply increased, with greater dilutional sensitivity observed in the POC test. Both tests were insensitive to prothrombin up to 194 mg/L added MEDI8111 (equivalent to 328 mg/L prothrombin versus endogenous concentration of 129 mg/L). Depletion of endogenous prothrombin inversely correlated with an increase in PT which returned to baseline following addition of 97 mg/L MEDI8111 or above. Both assays correlated well above 48.5 mg/L added MEDI8111 (65.9 mg/L prothrombin).

CONCLUSIONS

Our data supports that POC PT tests, such as the CoaguChek XS Pro, are fit for purpose to confirm a coagulopathic threshold for prothrombin and provide a fast, simple, and mobile method to guide MEDI8111 therapy in bleeding trauma patients.

Multiplexed silicon photonic sensor arrays enable facile characterization of coagulation protein binding to nanodiscs with variable lipid content

Interactions of soluble proteins with the cell membrane are critical within the blood coagulation cascade. Of particular interest are the interactions of γ-carboxyglutamic acid-rich domain-containing clotting proteins with lipids. Variability among conventional analytical methods presents challenges for comparing clotting protein-lipid interactions. Most previous studies have investigated only a single clotting protein and lipid composition and have yielded widely different binding constants. Herein, we demonstrate that a combination of lipid bilayer nanodiscs and a multiplexed silicon photonic analysis technology enables high-throughput probing of many protein-lipid interactions among blood-clotting proteins. This approach allowed direct comparison of the binding constants of prothrombin, factor X, activated factor VII, and activated protein C to seven different binary lipid compositions. In a single experiment, the binding constants of one protein interacting with all lipid compositions were simultaneously determined. A simple surface regeneration then facilitated similar binding measurements for three other coagulation proteins. As expected, our results indicated that all proteins exhibit tighter binding (lower K_d ) as the proportion of anionic lipid increases. Interestingly, at high proportions of phosphatidylserine, the K_d values of all four proteins began to converge. We also found that although k_off values for all four proteins followed trends similar to those observed for the K_d values, the variation among the proteins was much lower, indicating that much of the variation came from the kinetic binding (k_on) of the proteins. These findings indicate that the combination of silicon photonic microring resonator arrays and nanodiscs enables rapid interrogation of biomolecular binding interactions at model cell membrane interfaces.

Effect of sorafenib on des-γ-carboxyprothrombin secretion by a human hepatocellular carcinoma cell line

Patients with hepatocellular carcinoma (HCC) who respond to sorafenib have been reported to exhibit an increase in the level of des-γ-carboxyprothrombin (DCP) in the blood, subsequent to the initiation of sorafenib treatment. In the present study, the levels of secretion of DCP and DCP with more γ-carboxyglutamic residues (NX-DCP) and the effects of hypoxic conditions were examined in 13 liver cancer cell lines, and the presence of vitamin K and sorafenib, in the KYN-2 cell line, which resulted in confirmed DCP and NX-DCP secretion. DCP, NX-DCP and prothrombin secretion were confirmed in 2/13 cell lines, KYN-2 and KIM-1. The level of secretions increased under hypoxic conditions. The addition of vitamin K suppressed cell proliferation, and DCP expression decreased to below detectable levels, however the level of prothrombin expression increased. Sorafenib treatment increased the level of apoptosis and suppressed cell proliferation, and decreased DCP and NX-DCP. In contrast, levels of prothrombin and vascular endothelial growth factor (VEGF) expression exhibited a slight increase. When the same experiment was conducted under hypoxic conditions, DCP secretion significantly decreased in the presence of sorafenib. The level of DCP secretion increased by several fold in the sorafenib-treated and non-treated cells compared with the normoxic conditions. Prothrombin and VEGF values with normoxic conditions remained almost similar with hypoxic conditions. Under hypoxic conditions, NX-DCP significantly decreased below the control values for the first 48 h subsequent to sorafenib treatment, but significantly increased at 72 h. In vivo experiments demonstrated that sorafenib inhibited angiogenesis and tumor proliferation, but the levels of DCP and NX-DCP did not differ significantly from the controls. These findings indicate that the suppression of neovascularization by sorafenib promotes blood vessel ischemia, producing hypoxic conditions whereby vitamin K uptake and utilization efficiency is reduced.

Non-canonical proteolytic activation of human prothrombin by subtilisin from Bacillus subtilis may shift the procoagulant-anticoagulant equilibrium toward thrombosis

Blood coagulation is a finely regulated physiological process culminating with the factor Xa (FXa)-mediated conversion of the prothrombin (ProT) zymogen to active α-thrombin (αT). In the prothrombinase complex on the platelet surface, FXa cleaves ProT at Arg-271, generating the inactive precursor prethrombin-2 (Pre2), which is further attacked at Arg-320-Ile-321 to yield mature αT. Whereas the mechanism of physiological ProT activation has been elucidated in great detail, little is known about the role of bacterial proteases, possibly released in the bloodstream during infection, in inducing blood coagulation by direct proteolytic ProT activation. This knowledge gap is particularly concerning, as bacterial infections are frequently complicated by severe coagulopathies. Here, we show that addition of subtilisin (50 nm to 2 μm), a serine protease secreted by the non-pathogenic bacterium Bacillus subtilis, induces plasma clotting by proteolytically converting ProT into active σPre2, a nicked Pre2 derivative with a single cleaved Ala-470-Asn-471 bond. Notably, we found that this non-canonical cleavage at Ala-470-Asn-471 is instrumental for the onset of catalysis in σPre2, which was, however, reduced about 100-200-fold compared with αT. Of note, σPre2 could generate fibrin clots from fibrinogen, either in solution or in blood plasma, and could aggregate human platelets, either isolated or in whole blood. Our findings demonstrate that alternative cleavage of ProT by proteases, even by those secreted by non-virulent bacteria such as B. subtilis, can shift the delicate procoagulant-anticoagulant equilibrium toward thrombosis.

Coexistence of anti-β2-glycoprotein I domain I and anti-phosphatidylserine/prothrombin antibodies suggests strong thrombotic risk

BACKGROUND

Highly specific assays for measuring antiphospholipid antibodies (aPLs) are required for accurate assessment of thrombotic risk. aPLs against β2-glycoprotein I domain I (anti-β2GPIdI) and against prothrombin complexed with phosphatidylserine (anti-PS/PT) have been recently identified as being associated with a hypercoagulable state. This study evaluated the synergism between anti-β2GPIdI and anti-PS/PT for predicting thrombotic events.

METHODS

A total of 180 patients with clinical suspicion of hypercoagulability were evaluated. The plasma levels of lupus anticoagulant (LA) and antibodies against anticardiolipin (anti-CL) (IgG and IgM), β2GPI (IgG and IgM), PS/PT (IgG and IgM), and β2GPI dI (IgG) were measured.

RESULTS

IgG anti-β2GPIdI and LA were highly associated with thrombosis. Mean values and positivity rates of IgG anti-β2GPI dI and IgG anti-PS/PT were significantly higher in the triple-positive group (LA+, IgG anti-CL+, IgG anti-β2GPI+) than in the other groups. Interestingly, the thrombotic risk [odds ratio (OR) 24.400, 95% confidence interval (CI) 1.976-63.273, p<0.001] of the newly defined triple positive group (LA+, IgG anti-CL+, IgG anti-β2GPIdI+; OR 11.182, 95% CI 1.976-63.273, p=0.006) was more than twice that of the triple-positive group (LA+, IgG anti-CL+, IgG anti-β2GPI+). Double positivity for IgG anti-PS/PT and IgG anti-β2GPI also indicated significant thrombotic risk (OR 7.467, 95% CI 2.350-23.729, p=0.001). Furthermore, the thrombotic risk associated with double positivity for IgG anti-PS/PT and IgG anti-β2GPIdI was markedly elevated (OR 33.654, 95% CI 6.322-179.141, p<0.001).

CONCLUSIONS

Our data suggest that simultaneous measurement of IgG anti-β2GPIdI and IgG anti-PS/PT may improve clinical decision-making for aPL-positive patients.

Clinical and biochemical characterization of the prothrombin Belgrade mutation in a large Serbian pedigree: new insights into the antithrombin resistance mechanism

Essentials Prothrombin Belgrade mutation leads to antithrombin resistance. Clinical and biochemical phenotypes in a large family with this mutation were investigated. In carriers, we detected decreased factor II activity and increased endogenous thrombin potential. Prothrombin Belgrade mutation represents a strong prothrombotic risk factor.

SUMMARY

Background The recently reported c.1787G>A mutation in the prothrombin gene leads to Arg596Gln replacement in the protein molecule (prothrombin Belgrade). This substitution impairs binding of antithrombin to thrombin and results in inherited thrombophilia, known as antithrombin resistance. Objectives We aimed to elucidate the clinical and biochemical characteristics of thrombophilia associated with antithrombin resistance in a large Serbian family with the prothrombin Belgrade mutation. Patients and methods Nineteen family members were investigated, among whom 10 were carriers of the c.1787G>A mutation. In all subjects the clinical phenotype was determined and laboratory investigations of hemostatic parameters were performed. Results Six out of the 10 mutation carriers developed thromboembolic events, mainly deep venous and mesenteric vein thrombosis. The median age of the first thrombotic event was 26.5 (12-41) years, whereas the incidence rate of first thrombosis was 2.2% per year. In all mutation carriers prothrombin activity was significantly decreased in comparison with non-carriers, clearly distinguishing each group. However, the presence of the mutation did not affect the prothrombin antigen level in plasma. The endogenous thrombin potential was significantly increased in all carriers in comparison with non-carriers, indicating the presence of blood hypercoagulability. Interestingly, levels of D-dimer and the F1+2 fragment were similar in both groups. Conclusions Although rare, the prothrombin Belgrade mutation represents strong thrombophilia with early onset of thrombosis in the investigated family. According to our results, decreased prothrombin activity may be a simple screening test for detection of this mutation in thrombotic patients.

Time in the Therapeutic Range (TTR): An Overly Simplified Conundrum

Anticoagulation with warfarin has been used for over 60 years; however, its administration is fraught with difficulty since many factors can affect warfarin dosing. The concept of time in therapeutic range (TTR) has become a popular way to report warfarin management and compare anticoagulation management across clinical trials. However, TTR is a much more complex concept than most clinicians and trialists recognize. This manuscript attempts to discuss some of the important factors underlying this complexity and presents a suggestion to improve reports on TTR.

Prothrombin Loading of Vascular Smooth Muscle Cell-Derived Exosomes Regulates Coagulation and Calcification

OBJECTIVE

The drug warfarin blocks carboxylation of vitamin K-dependent proteins and acts as an anticoagulant and an accelerant of vascular calcification. The calcification inhibitor MGP (matrix Gla [carboxyglutamic acid] protein), produced by vascular smooth muscle cells (VSMCs), is a key target of warfarin action in promoting calcification; however, it remains unclear whether proteins in the coagulation cascade also play a role in calcification.

APPROACH AND RESULTS

Vascular calcification is initiated by exosomes, and proteomic analysis revealed that VSMC exosomes are loaded with Gla-containing coagulation factors: IX and X, PT (prothrombin), and proteins C and S. Tracing of Alexa488-labeled PT showed that exosome loading occurs by direct binding to externalized phosphatidylserine (PS) on the exosomal surface and by endocytosis and recycling via late endosomes/multivesicular bodies. Notably, the PT Gla domain and a synthetic Gla domain peptide inhibited exosome-mediated VSMC calcification by preventing nucleation site formation on the exosomal surface. PT was deposited in the calcified vasculature, and there was a negative correlation between vascular calcification and the levels of circulating PT. In addition, we found that VSMC exosomes induced thrombogenesis in a tissue factor-dependent and PS-dependent manner.

CONCLUSIONS

Gamma-carboxylated coagulation proteins are potent inhibitors of vascular calcification suggesting warfarin action on these factors also contributes to accelerated calcification in patients receiving this drug. VSMC exosomes link calcification and coagulation acting as novel activators of the extrinsic coagulation pathway and inducers of calcification in the absence of Gla-containing inhibitors.

Association of conventional haemostasis and coagulation tests with the risk of acute upper gastrointestinal bleeding in liver cirrhosis: a retrospective study

OBJECTIVE

A retrospective study was performed to compare the difference in platelet count (PLT), prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (APTT), between cirrhotic patients with and without acute upper gastrointestinal bleeding (AUGIB) or acute oesophageal variceal bleeding (AEVB).

METHODS

Between January 2012 and June 2014, a total of 1734 cirrhotic patients were enrolled and were classified into 'AUGIB' (n = 497) and 'no AUGIB' (n = 1237) groups according to their disease history. They were further divided into 'AEVB' (n = 297) and 'no AEVB' (n = 1259) groups according to the endoscopic findings. Additionally, 178 patients with AUGIB were not assigned to either the 'AEVB' or 'no AEVB' groups due to the absence of any endoscopic findings.

RESULTS

Compared with the 'no AUGIB' group, the 'AUGIB' group had similar PLT (99.99 ± 89.90 vs.101.47 ± 83.03; P = 0.734) and APTT (42.96 ± 15.20 vs.43.77 ± 11.01; P = 0.219), but significantly higher PT (17.30 ± 5.62 vs.16.03 ± 4.68; P < 0.001) and INR (1.45 ± 0.69 vs.1.31 ± 0.59; P < 0.001). A lower PT was independently associated with the absence of AUGIB (OR = 0.968; 95% CI: 0.942-0.994). Compared with the 'no AEVB' group, the 'AEVB' group had significantly lower PLT (86.87 ± 62.14 vs.101.74 ± 83.62; P = 0.004) and APTT (40.98 ± 7.9 vs.43.72 ± 10.97; P < 0.001), but similar PT (16.53 ± 3.71 vs.16.04 ± 4.68; P = 0.088) and INR (1.35 ± 0.41 vs.1.31 ± 0.59; P = 0.225). A higher PLT was independently associated with the absence of AEVB (OR = 1.004; 95% CI: 1.002-1.006; P = 0.001).

CONCLUSIONS

PLT was associated with the occurrence of portal hypertension-related bleeding in liver cirrhosis.

Coagulation disorders and their cutaneous presentations: Pathophysiology

Hypercoagulable states are inherited or acquired predispositions to venous or arterial thromboses that are best understood in the context of the coagulation cascade. Dermatologists can play a critical role in diagnosing and treating patients with hypercoagulable states because cutaneous symptoms may be a presenting manifestation, thereby reducing morbidity and mortality related to these conditions. This review focuses on the epidemiology and pathophysiology of hypercoagulable states, while the accompanying article iterates the basic clinical features, diagnostic testing, and management of patients who have these conditions.

Dual effect of histone H4 on prothrombin activation

Essentials Prothrombin converts slowly to thrombin upon interaction with histone H4. Histone H4 may also affect the reactivity of prothrombin toward factor Xa. Histone H4 enhances or inhibits activation by factor Xa depending on cofactor Va. The results reveal an unanticipated dual effect of histone H4 on prothrombin activation by factor Xa.

SUMMARY

Background Recent studies have documented the ability of prothrombin to convert to the mature protease thrombin upon interaction with histone H4. The effect is abrogated by mutation of the catalytic Ser and requires the Gla domain. Objectives To explore the effect of histone H4 on the reactivity of prothrombin to its physiological activator factor (F) Xa, free or assembled in the prothrombinase complex. Methods The effect of histone H4 on prothrombin activation by FXa and prothrombinase is studied with kinetic assays. The potential epitope of prothrombin recognizing histone H4 is explored with electrostatic calculations using recent crystal structures. Results and Conclusions Binding of histone H4 has a dual effect on prothrombin activation by FXa that is of mechanistic significance: it enhances the reaction > 10-fold in the absence of cofactor Va, but produces complete inhibition in the presence of cofactor. Histone H4 binding to prothrombin produces very slow autoactivation independent of the coagulation cascade and promotes slow thrombin generation by FXa in the absence of phospholipids. In addition, histone H4 has a rapid and drastic inhibitory effect on prothrombin activation by prothrombinase that is likely to dominate pathophysiology.

Genetic risk factors for venous thrombosis in the elderly in a case-control study

Essentials Risk of venous thrombosis (VT) related to common genetic variants in those aged 70+ is unknown. We studied Factor V Leiden, prothrombin mutation, non-O blood group and family history (FH) of VT. Risk of VT was increased 2.2-, 1.4-, 1.3- and 2.1-fold respectively. FH is easy to obtain and can be implemented in clinical decision rules of VT risk in the elderly. Click to hear Prof. Reitsma discuss genetic risk factors of arterial and venous thrombosis

SUMMARY

Background As the incidence of venous thrombosis (VT) increases steeply with age and the number of elderly people is on the rise, studies of VT in this age group are important. Objectives We aimed to study the associations of common genetic risk factors (i.e. the factor V Leiden and prothrombin G20210A mutations, non-O blood group and family history of VT) with risk of a first VT in older age (> 70 years). Methods Four hundred and one consecutive cases with a first-time thrombosis and 431 controls (all ≥ 70 years) were included in the AT-AGE case-control study. Information on risk factors for VT, including family history of VT in first-degree relatives, was obtained by interview. Unprovoked VT was defined as thrombosis not related to surgery, fracture, plaster cast or immobility within 3 months prior to VT. Results The risk of VT was 2.2-fold increased in factor V Leiden carriers (95% confidence interval [CI], 1.2-3.9), 1.4-fold increased in prothrombin mutation carriers (95% CI, 0.5-3.9), and 1.3-fold increased in those with non-O blood group (95% CI, 1.0-1.8). Positive family history of VT was associated with a 2.1-fold increased risk of VT (95% CI, 1.5-3.1). The highest risk of VT was found in individuals who had both a positive family history and were carriers of one of the two prothrombotic mutations. Conclusions Genetic factors clearly related to VT in younger populations were also risk factors in older age and a positive family history was also important in this age group.

Structural Architecture of Prothrombin in Solution Revealed by Single Molecule Spectroscopy

The coagulation factor prothrombin has a complex spatial organization of its modular assembly that comprises the N-terminal Gla domain, kringle-1, kringle-2, and the C-terminal protease domain connected by three intervening linkers. Here we use single molecule Förster resonance energy transfer to access the conformational landscape of prothrombin in solution and uncover structural features of functional significance that extend recent x-ray crystallographic analysis. Prothrombin exists in equilibrium between two alternative conformations, open and closed. The closed conformation predominates (70%) and features an unanticipated intramolecular collapse of Tyr(93) in kringle-1 onto Trp(547) in the protease domain that obliterates access to the active site and protects the zymogen from autoproteolytic conversion to thrombin. The open conformation (30%) is more susceptible to chymotrypsin digestion and autoactivation, and features a shape consistent with recent x-ray crystal structures. Small angle x-ray scattering measurements of prothrombin wild type stabilized 70% in the closed conformation and of the mutant Y93A stabilized 80% in the open conformation directly document two envelopes that differ 50 Å in length. These findings reveal important new details on the conformational plasticity of prothrombin in solution and the drastic structural difference between its alternative conformations. Prothrombin uses the intramolecular collapse of kringle-1 onto the active site in the closed form to prevent autoactivation. The open-closed equilibrium also defines a new structural framework for the mechanism of activation of prothrombin by prothrombinase.

Vitamin K-Dependent Protein Activity and Incident Ischemic Cardiovascular Disease: The Multi-Ethnic Study of Atherosclerosis

OBJECTIVE

Vitamin K-dependent proteins (VKDPs), which require post-translational modification to achieve biological activity, seem to contribute to thrombus formation, vascular calcification, and vessel stiffness. Whether VKDP activity is prospectively associated with incident cardiovascular disease has not been studied.

APPROACH AND RESULTS

VKDP activity was determined by measuring circulating des-γ-carboxy prothrombin concentrations in a random sample of 709 multiethnic adults free of cardiovascular disease drawn from the Multi-Ethnic Study of Atherosclerosis (MESA). Lower des-γ-carboxy prothrombin concentrations reflect greater VKDP activity. Subjects were followed up for the risk of ischemic cardiovascular disease (coronary heart disease, stroke, and fatal cardiovascular disease) for 11.0 years of follow-up. A total of 75 first ischemic CVD events occurred during follow-up. The incidence of ischemic cardiovascular disease increased progressively across des-γ-carboxy prothrombin quartiles, with event rates of 5.9 and 11.7 per 1000 person-years in the lowest and highest quartiles. In analyses adjusted for traditional cardiovascular risk factors and measures of vitamin K intake, a doubling of des-γ-carboxy prothrombin concentration was associated with a 1.53 (95% confidence interval, 1.09-2.13; P=0.008) higher risk of incident ischemic cardiovascular disease. The association was consistent across strata of participants with diabetes mellitus, hypertension, renal impairment, and low vitamin K nutritional intake.

CONCLUSIONS

In this sample of middle-aged and older adults, VKDP activity was associated with incident ischemic cardiovascular events. Further studies to understand the role of this large class of proteins in cardiovascular disease are warranted.

The Fragment 1 Region of Prothrombin Facilitates the Favored Binding of Fragment 12 to Zymogen and Enforces Zymogen-like Character in the Proteinase

Thrombin is produced from the C-terminal half of prothrombin following its proteolytic activation. The N-terminal half, released as the propiece Fragment 12 (F12), is composed of an N-terminal γ-carboxyglutamate domain (Gla) followed by two kringles (K1 and K2). The propiece plays essential roles in regulating prothrombin activation and proteinase function. The latter results from the ability of F12 to reversibly bind to the (pro)catalytic domain through K2 with high affinity and highly favorable thermodynamic constants when it is a zymogen in comparison to proteinase. Such discrimination is lost for K2 binding after proteolytic removal of the N-terminal Gla-K1 region of F12. The Ca(2+)-stabilized structure of the Gla domain is not required for F12 to bind the zymogen form more favorably. Enhanced binding to zymogen versus proteinase correlates with the ability of the propiece to enforce zymogen-like character in the proteinase. This is evident in variants of meizothrombin, an intermediate of prothrombin activation that contains the propiece covalently attached. This phenomenon is also independent of the Gla domain. Thus, the presence of K1 in covalent linkage with K2 in the propiece governs the ability of K2 to bind the (pro)catalytic domain in favor of zymogen, thereby enforcing zymogen-like character in the proteinase.

Ribophorin II is involved in the tissue factor expression mediated by phosphatidylserine-dependent antiprothrombin antibody on monocytes

OBJECTIVE

Phosphatidylserine-dependent, also called aPS-PT, recognizes the phosphatidylserine-prothrombin complex, which is associated with APS. We have previously reported that aPS-PT induces tissue factor (TF) expression on monocytes through the p38 mitogen-activated protein kinase pathway. However, the cell surface interaction between prothrombin and aPS-PT, which is involved in the activation of cell-signalling pathways, has remained unknown. The objective of this study was to identify membrane proteins involved in the binding of prothrombin and aPS-PT to monocyte surfaces as well as the induction of TF expression.

METHODS

RAW264.7 cells with FLAG-tagged prothrombin were incubated and separated using affinity chromatography with anti-FLAG antibody-conjugated Sepharose beads. Immunopurified proteins were then analysed by an online nano-liquid chromatography-tandem mass spectrometry. The binding between prothrombin and the identified protein, ribophorin II (RPN2), was analysed by ELISA and surface plasmon resonance. To elucidate the role of RPN2 in TF expression, the TF mRNA level in RAW264.7 cells treated with RPN2 small interfering RNA was determined by quantitative real-time PCR (qPCR).

RESULTS

RPN2 was identified as a candidate molecule involved in the binding of prothrombin to the cell surface. The binding between prothrombin and RPN2 was confirmed by ELISA and surface plasmon resonance. RAW264.7 cells treated with RPN2 small interfering RNA showed significant reduction of the TF expression mediated by prothrombin and a mouse monoclonal aPS-PT.

CONCLUSION

We identified that RPN2 is one of the prothrombin-binding proteins on monocyte surfaces, suggesting that RPN2 is involved in the pathophysiology of thrombosis in patients with APS.

Thrombophilic risk of individuals with rare compound factor V Leiden and prothrombin G20210A polymorphisms: an international case series of 100 individuals

The risk of thrombosis in individuals with rare compound thrombophilias, homozygous factor V Leiden (FVL) plus heterozygous prothrombin G20210A (PTM), homozygous PTM plus heterozygous FVL, and homozygous FVL plus homozygous PTM, is unknown. We identified, worldwide, individuals with these compound thrombophilias, predominantly through mailing members of the International Society on Thrombosis and Haemostasis. Physicians were sent a clinical questionnaire. Confirmatory copies of the genetic results were obtained. One hundred individuals were enrolled; 58% were female. Seventy-one individuals had a venous thrombosis (includes superficial and deep vein thrombosis, and pulmonary embolism), 4 had an arterial thrombosis and 6 had both. Nineteen individuals had never had a thrombotic event. Thrombosis-free survival curves demonstrated that 50% of individuals had experienced a thrombotic event by 35 yrs of age, while 50% had a first venous thromboembolic event (VTE; includes all venous thrombosis except superficial thrombosis) by 41 yrs of age; 38.2% of first VTEs were unprovoked. 37% of patients had at least one VTE recurrence. Seventy percent of first pregnancies carried to term and not treated with anticoagulation were thrombosis-free. In conclusion, patients with these rare compound thrombophilias are not exceedingly thrombogenic, even though they have a substantial risk for VTE.

The Dual Regulatory Role of Amino Acids Leu480 and Gln481 of Prothrombin

Prothrombin (FII) is activated to α-thrombin (IIa) by prothrombinase. Prothrombinase is composed of a catalytic subunit, factor Xa (fXa), and a regulatory subunit, factor Va (fVa), assembled on a membrane surface in the presence of divalent metal ions. We constructed, expressed, and purified several mutated recombinant FII (rFII) molecules within the previously determined fVa-dependent binding site for fXa (amino acid region 473-487 of FII). rFII molecules bearing overlapping deletions within this significant region first established the minimal stretch of amino acids required for the fVa-dependent recognition exosite for fXa in prothrombinase within the amino acid sequence Ser(478)-Val(479)-Leu(480)-Gln(481)-Val(482). Single, double, and triple point mutations within this stretch of rFII allowed for the identification of Leu(480) and Gln(481) as the two essential amino acids responsible for the enhanced activation of FII by prothrombinase. Unanticipated results demonstrated that although recombinant wild type α-thrombin and rIIa(S478A) were able to induce clotting and activate factor V and factor VIII with rates similar to the plasma-derived molecule, rIIa(SLQ→AAA) with mutations S478A/L480A/Q481A was deficient in clotting activity and unable to efficiently activate the pro-cofactors. This molecule was also impaired in protein C activation. Similar results were obtained with rIIa(ΔSLQ) (where rIIa(ΔSLQ) is recombinant human α-thrombin with amino acids Ser(478)/Leu(480)/Gln(481) deleted). These data provide new evidence demonstrating that amino acid sequence Leu(480)-Gln(481): 1) is crucial for proper recognition of the fVa-dependent site(s) for fXa within prothrombinase on FII, required for efficient initial cleavage of FII at Arg(320); and 2) is compulsory for appropriate tethering of fV, fVIII, and protein C required for their timely activation by IIa.

The Importance of Thrombin in Cerebral Injury and Disease

There is increasing evidence that prothrombin and its active derivative thrombin are expressed locally in the central nervous system. So far, little is known about the physiological and pathophysiological functions exerted by thrombin in the human brain. Extra-hepatic prothrombin expression has been identified in neuronal cells and astrocytes via mRNA measurement. The actual amount of brain derived prothrombin is expected to be 1% or less compared to that in the liver. The role in brain injury depends upon its concentration, as higher amounts cause neuroinflammation and apoptosis, while lower concentrations might even be cytoprotective. Its involvement in numerous diseases like Alzheimer’s, multiple sclerosis, cerebral ischemia and haemorrhage is becoming increasingly clear. This review focuses on elucidation of the cerebral thrombin expression, local generation and its role in injury and disease of the central nervous system.

Actions of thrombin in the interstitium

Thrombin is a pleiotropic enzyme best known for its contribution to fibrin formation and platelet aggregation during vascular hemostasis. There is increasing evidence to suggest a role for thrombin in the development of interstitial fibrosis, but interstitial thrombin has not been demonstrated by the direct determination of activity. Rather its presence is inferred by products of thrombin action such as fibrin and activated fibroblasts. This review will focus on possible mechanisms of thrombin formation in the interstitial space, the possible actions of thrombin, processes regulating thrombin activity in the interstitial space, and evidence supporting a role for thrombin in fibrosis.

Association of factor V Leiden, Janus kinase 2, prothrombin, and MTHFR mutations with primary Budd-Chiari syndrome in Egyptian patients

BACKGROUND AND AIM

Budd-Chiari syndrome (BCS) is defined as obstruction of hepatic venous outflow anywhere from the small hepatic veins to the suprahepatic inferior vena cava. The pathogenesis of BCS is still not fully understood. This study aimed to evaluate the association of factor V Leiden (FVL), Janus kinase 2 (JAK2), prothrombin, and methylene tetrahydrofolate reductase (MTHFR) mutations with primary BCS.

METHODS

The study was carried out on 35 patients with primary BCS and 15 age and gender matched healthy individuals as a control group. Genotyping of FVL, prothrombin, and MTHFR mutations was determined by GENEQUALITY AB-THROMBO TYPE kit based on the reverse hybridization principle. JAK2 mutation was determined by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

There was a statistically significant difference between patients and controls regarding FVL, MTHFR C677T, and MTHFR A1298C mutations with odds ratio of 1.83, 2.0, and 1.79, respectively. Hetero MTHFR C677T, hetero FVL, and hetero MTHFR A1298C were the most common etiological factors being responsible for 57.1, 42.9, and 42.9% of primary BCS cases, respectively.

CONCLUSION

It could be concluded that BCS is a multifactorial disease; in the current study, MTHFR C677T mutation was the most common cause of disease. Identification of one cause of BCS should not eliminate investigations for detection of other etiological factors.

Factor V Leiden, Prothrombin and MTHFR Mutation in Patients with Preeclamsia, Intrauterine Growth Restriction and Placental Abruption

BACKGROUND

Factor V Leiden, Prothrombin and MTHFR gene mutation, could have an influence in pregnancy with adverse outcome Preeclamsia, IUGR and Placental abruption.

AIM

The aim of this study is to investigate the presence of above mentioned inherited thrombophilias and its statistical significance, distribution among the complicated and normal pregnancy, and relative risk for carrier of mutation to develop preeclampsia, IUGR and placental abruption.

MATERIAL AND METHODS

Prospective cohort study is implemented at University Clinic for Obstetric and Gynecology in Skopje, Republic of Macedonia. The study included 109 delivered patients: 40 with preeclapmsia, 22 with IUGR, 17 with placental abruption and 30 as control group with normal pregnancy. The amount of 3 ml venous blood has been used for detection of these point mutations using ThromboStrip -Opegen, QIAGEN kit manufactured for thrombotic risk.

RESULTS

The highest frequency was found: in the group with preeclampsia 35% were MTHFR homozygous, IUGR -MTHFR heterozygous 45%, Placental abruption- 52.9% MTHFR heterozygous, and in the control group without thrombophilia 56.7%. There were combined thrombophilia in 3 patients. There aren`t statistical significance in presence of thrombophilia among groups (p > 0.05). Statistical significance (p < 0.05) was found between carriers of MTHFR homozygous in preeclampsia and group with placental abruption and control group. Relative risk in IUGR group for MTHFR homozygous was 5.54 (1.37

CONCLUSION

The presence of mutation MTHFR homozygous could increase the risk for development of IUGR and mutation of Factor V Leiden for placental abruption. Further investigations with more patients are warranted.

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Key Words

• IUGR
• MTHFR
• factor V Leiden
• placental abruption
• preeclampsia
• prothrombin

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MESH Headings Collapse

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Recombinant human prothrombin (MEDI8111) prevents bleeding in haemophilia A and B mice

BACKGROUND

Haemophilia A and B are treated with FVIII and FIX replacement therapy. Treatment may be complicated by inhibitory antibodies that require bypass therapy such as FEIBA(®) in which prothrombin (FII) is suggested to be the main active component.

METHODS

To evaluate the effect of FII on haemophilia recombinant human (rh) FII (MEDI8111) or plasma-derived human FII (pdhFII) was given as single doses to anaesthetized haemophilia A and B mice 3 min before tail transection and rhFVIII or rhFIX was used for comparison. After tail transection, automatic bleeding registration was used to continuously measure blood loss (BL) and bleeding time (BT). Thrombin generation and plasma concentrations of human FVIII, FIX, FII and thrombin-antithrombin complex (TAT) were measured.

RESULTS

Blood loss and BT were dose-dependently decreased by rhFVIII or rhFIX. The concentrations that decreased BL and BT for rhFVIII by 50% (EC50) were 0.06 and 0.01 IU mL(-1) and for rhFIX 0.07 and 0.07 IU mL(-1) , respectively. Administration of rhFVIII and rhFIX dose-dependently increased thrombin generation potential but did not affect TAT. MEDI8111 and pdhFII dose-dependently decreased BL and BT in haemophilia A mice, EC50 37 and 87 and 100 and 155 mg L(-1) respectively. In haemophilia B mice given MEDI8111 EC50 was for BL 56 mg L(-1) and for BT 67 mg L(-1) . TAT and thrombin generation increased dose-dependently for MEDI8111 and pdhFII.

CONCLUSION

MEDI8111 dose-dependently decreased bleeding and increased procoagulant activity in haemophilia A and B mice and suggest that MEDI8111 may be useful for preventing bleeding in patients with haemophilia A and B.