Prothrombin C20209T mutation in deep vein thrombosis: a case report

Thrombophilias is a recognized risk factor for thrombotic events. The prothrombin variant G20210A gene mutation has been commonly examined using polymerase chain reaction (PCR). Currently, in many clinical laboratories, performing the PCR in real-time technique, which, in addition to identifying the G20210A mutation, makes possible the detection of other mutations in the 3'UTR of the prothrombin gene by melting curve analysis, due to the ability of this analysis to be amplicon-dependent (e.g., C20209T, C20221T and A20218G). We report the first case in Chile that describes the atypical prothrombin C20209T mutation, in a 50-year-old male patient diagnosed with deep vein thrombosis in the lower limb and family history of thrombophilia. In the literature, there are few studies of the prevalence and functionality of this mutation; its association with thrombotic events is controversial.

Thrombophilic genes alterations as risk factor for recurrent pregnancy loss

OBJECTIVE

The important polymorphisms leading to inherited thrombophilia are Factor V Leiden (FVL), Prothrombin G20210A and MTHFR C677T and A1298C. The frequencies also the correlation among these polymorphisms and RPL have been reported controversially in various populations. Our clinic is one of the referral centers in reproductive biomedicine in which patients in all over Iran refer to; thus the results of this study could be considered clinically beneficial. Besides, in the present study, not only the frequency of specific but also multiple thrombophilic gene alterations were compared in Iranian women with RPL and a control group.

METHODS

The patients group comprised 330 women with three or more consecutive RPLs. The control population included 350 women with at least one child and no history of pregnancy loss. FVL, Prothrombin G20210A and MTHFR C677T polymorphisms were analyzed by Strip assay kit. MTHFR A1298C was genotyped by PCR-RFLP.

RESULTS

The frequencies of FVL, Prothrombin G20210A, MTHFR C677T and MTHFR A1298C mutations in patients were 8.48, 4.24, 45.45 and 59.39%, and in controls were 2.86, 2.86, 34.28 and 6%, respectively.

CONCLUSIONS

The present data showed that FVL, MTHFR polymorphisms also combined with thrombophilic gene mutations have a strong association with RPL.

Effects of recombinant human prothrombin on thrombin generation in plasma from patients with hemophilia A and B

BACKGROUND

The present study was carried out to investigate the impact of FII levels, and their increase, on the hemostatic potential in plasma from hemophilia A and B patients with and without inhibitors.

METHOD

Recombinant human factor (F) II (rhFII) was added ex vivo to plasma from 68 patients with hemophilia A and B, with or without inhibitors. The hemostatic potential as measured by thrombin generation (calibrated automated thrombogram [CAT]) was focused on the endogenous thrombin potential (ETP) as it has been shown to correlate with the clinical phenotype of bleeding in hemophilia patients and has also been used to guide bypassing therapy in hemophilia patients with inhibitors before elective surgery. The factor eight inhibitor bypassing agent (FEIBA(®) ) was used as a reference to the clinical situation.

RESULTS

The study shows that rhFII concentration-dependently increased ETP by a similar magnitude in hemophilia A and B, both with and without inhibitors. Compared with FEIBA, rhFII showed a shallower concentration-response curve. In both types of hemophilia 100 mg L(-1) of rhFII roughly doubled the ETP. A corresponding response was obtained by 0.5 U mL(-1) of FEIBA.

CONCLUSION

These data support the theory that FII is one of the major components responsible for the efficacy of FEIBA. The data also indicate that rhFII may be useful, alone or in combination with other coagulation factors, in some of the conditions for which FEIBA is used today, although more data are needed to substantiate this.

Synthesis of Phospholipid-Protein Conjugates as New Antigens for Autoimmune Antibodies

Copper(I)-catalyzed azide-alkyne cycloaddition, or CuAAC click chemistry, is an efficient method for bioconjugation aiming at chemical and biological applications. Herein, we demonstrate how the CuAAC method can provide novel phospholipid-protein conjugates with a high potential for the diagnostics and therapy of autoimmune conditions. In doing this, we, for the first time, covalently bind via 1,2,3-triazole linker biologically complementary molecules, namely phosphoethanol amine with human β2-glycoprotein I and prothrombin. The resulting phospholipid-protein conjugates show high binding affinity and specificity for the autoimmune antibodies against autoimmune complexes. Thus, the development of this work might become a milestone in further diagnostics and therapy of autoimmune diseases that involve the production of autoantibodies against the aforementioned phospholipids and proteins, such as antiphospholipid syndrome and systemic lupus erythematosus.

The balance of pro- and anticoagulant processes underlying thrombin generation

BACKGROUND

The generation of thrombin in time is the combined effect of the processes of prothrombin conversion and thrombin inactivation. Measurement of prothrombin consumption used to provide valuable information on hemostatic disorders, but is no longer used, due to its elaborate nature.

OBJECTIVES

Because thrombin generation (TG) curves are easily obtained with modern techniques, we developed a method to extract the prothrombin conversion curve from the TG curve, using a computational model for thrombin inactivation.

METHODS

Thrombin inactivation was modelled computationally by a reaction scheme with antithrombin, α(2) Macroglobulin and fibrinogen, taking into account the presence of the thrombin substrate ZGGR-AMC used to obtain the experimental data. The model was validated by comparison with data obtained from plasma as well as from a reaction mixture containing the same reactants as plasma.

RESULTS

The computational model fitted experimental data within the limits of experimental error. Thrombin inactivation curves were predicted within 2 SD in 96% of healthy subjects. Prothrombin conversion was calculated in 24 healthy subjects and validated by comparison with the experimental consumption of prothrombin during TG. The endogenous thrombin potential (ETP) mainly depends on the total amount of prothrombin converted and the thrombin decay capacity, and the peak height is determined by the maximum prothrombin conversion rate and the thrombin decay capacity.

CONCLUSIONS

Thrombin inactivation can be accurately predicted by the proposed computational model and prothrombin conversion can be extracted from a TG curve using this computational prediction. This additional computational analysis of TG facilitates the analysis of the process of disturbed TG.

Lupus anticoagulant-hypoprothrombinemia syndrome: report of two cases and review of the literature

Lupus anticoagulant-hypoprothrombinemia syndrome (LA-HPS) is a rare acquired disorder caused by prothrombin antibodies. The disease is most common in the pediatric age group (<16 years), and more prevalent in women. There are well-established clinical diseases associated with LA-HPS, most notably systemic lupus erythematosus (SLE) and viral infections. The clinical manifestation of LA-HPS varies greatly in severity and it may cause severe life-threatening bleeding diathesis. LA-HPS is to be suspected when a patient presents with bleeding and a prolonged activated partial thromboplastin and prothrombin time, in combination with a lupus anticoagulant. The diagnosis is confirmed in the laboratory by identification of reduced prothrombin levels. There are no standardized recommendations for treatment of the hemorrhage associated with the syndrome; corticosteroids are used as first-line treatment. This review summarizes what is currently known about the pathogenesis, clinical features, diagnosis, treatment and prognosis of LA-HPS, and presents two case reports.

Prothrombin structure: unanticipated features and opportunities

The structure of prothrombin has eluded investigators for decades but recent efforts have succeeded in revealing the architecture of this important clotting factor. Unanticipated features have emerged outlining the significant flexibility of the zymogen due to linker regions connecting the γ carboxyglutamic domain, kringles and protease domain. A new, structure-based framework helps in defining a molecular mechanism of prothrombin activation, rationalizes the severe bleeding phenotypes of several naturally occurring mutations and identifies targets for drug design.

The effect of recombinant and plasma-derived prothrombin on prothrombin time in human plasma

INTRODUCTION

When investigating coagulation assays to measure the effect of infused prothrombin (FII) in in vivo coagulopathy models, we found that addition of FII, plasma-derived human FII (pd-hFII) or recombinant human FII (r-hFII), to normal plasma resulted in a concentration-dependent increase in prothrombin time (PT) initiated with Innovin(®) .

METHODS

The effect on PT by addition to plasma of either pd-hFII or r-hFII, using different commercial PT reagents, was studied both by turbidimetry and viscometry.

RESULT

Addition of FII to plasma resulted in increased PT when initiated with Innovin(®) : PT increased with 20% by doubling the concentration. The prolongation of PT became more pronounced with 2-6000 times diluted Innovin(®) . However, by adjustment of the final free Ca(2+) concentration in the assay with diluted Innovin(®) from 8.3 to 1.3 mmol/L, no FII-dependent increase in PT was found. In contrast, no prolongation of PT was found with other commercial PT reagents. A KM = 3 nmol/L was obtained with pd-hFII, respectively, r-hFII with FII-depleted plasma using Thromborel(®) to initiate PT.

CONCLUSION

At normal plasma concentration of FII, addition of FII should not have an effect on PT. The prolonged PT with Innovin(®) , but not with other PT reagents, at supranormal FII concentration is an artefact.

Prevalence of thrombophilic gene polymorphisms in an azari population of iran

There is several evidence suggests that thrombophilic gene polymorphisms may influence susceptibility to thromboembolic events. The prevalence of these polymorphisms is different in various races and ethnics. Accordingly, we studied the prevalence of Factor V (G1691A and A4070G), prothrombin G20210A and PAI-1 4G/5G in healthy northwest population of Iran. In this prospective study, 500 healthy individuals, who had no history of both personal and family history of thromboembolic disorders, were selected as a sample of healthy population in northwestern Iran. Genotyping of these polymorphisms was performed using the amplification refractory mutation system-polymerase chain reaction method. No significant differences were detected between the expected and observed frequencies of FV G1691A and A4070G, prothrombin G20210A polymorphisms (P>0.05), while the expected frequency of 4G allele was significantly more than observed frequency in the studied population (P<0.01). These findings were compared with other reports from various populations. In conclusion, the allele frequency for FV G1691A and PAI-1 4G/5G polymorphisms showed relative consistency compared to those of previous studies, while the incidence pattern of FV A4070G polymorphism in Northwestern population of Iran showed conflicting results regarding other studied population. The prothrombin G20210A polymorphism was observed at a higher frequency than other studied populations.

A deep vein thrombosis caused by 20209C>T mutation in homozygosis of the prothrombin gene in a Caucasian patient

Introduction:

Additional nucleotide substitutions in the 3′-untranslated region of prothrombin gene could explain some thrombotic events and also adverse pregnancy outcomes. We describe the first case of a homozygous 20209C>T mutation as the cause of deep vein thrombosis in a Spanish patient.

Case and methods:

The 56-year-old male patient with a partial tear of the Achilles tendon developed calf (tibial) deep vein thrombosis after immobilization and was treated with an anticoagulant. To determine if the deep vein thrombosis was of genetic origin, a peripheral blood DNA sample was analysed for the presence of the three most frequent mutations associated with thrombotic events: factor V Leiden (1691G>A), prothrombin (20210G>A) and methylene tetrahydrofolate reductase (677C>T). The presence or absence of the normal allele of prothrombin could not be determined using the PTH-FV-MTHFR StripAssay (Vienna Lab).

Results:

Comprehensive analysis showed that the patient had a variant interfering with the polymerase chain reaction product, we sequenced the entire prothrombin gene and found that the patient had a homozygous C>T mutation at position 20209; this interfered with the polymerase chain reaction product, which needs a C at this position to be able to bind to the wild-type probe present in the test strip.

Conclusion:

The homozygous 20209C>T mutation and the presence of the mutation 677C>T in heterozygosity explained the patient’s deep vein thrombosis because the combination of mutations would increase the risk of thrombosis. Suitable genetic counselling should be provided to the patient and first-degree relatives as it important to detect prothrombin gene variants that could increase risk for thrombotic events.

Bilateral renal artery thrombosis in inherited thrombophilia: a rare cause of acute kidney injury

We describe the case of a 47-year-old man who developed significant acute, and subsequently chronic, kidney injury due to bilateral renal infarction. This occurred in the context of a combined inherited thrombophilia including antithrombin III deficiency and a prothrombin gene mutation. Bilateral renal artery thrombosis developed despite prophylactic treatment for thromboembolism. Arterial thrombosis is rare in the context of inherited thrombophilia and bilateral renal infarction is an unusual cause of acute kidney injury. Bilateral renal infarction due to primary renal artery thrombosis has not been previously described in antithrombin III deficiency, either as an isolated defect or in combination with other hereditary thrombophilia.

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 transition of prothrombin to thrombin

The proteolytic conversion of prothrombin to thrombin catalyzed by prothrombinase is one of the more extensively studied reactions of blood coagulation. Sophisticated biophysical and biochemical insights into the players of this reaction were developed in the early days of the field. Yet, many basic enzymological questions remained unanswered. I summarize new developments that uncover mechanisms by which high substrate specificity is achieved, and the impact of these strategies on enzymic function. Two principles emerge that deviate from conventional wisdom that has otherwise dominated thinking in the field. (i) Enzymic specificity is dominated by the contribution of exosite binding interactions between substrate and enzyme rather than by specific recognition of sequences flanking the scissile bond. Coupled with the regulation of substrate conformation as a result of the zymogen to proteinase transition, novel mechanistic insights result for numerous aspects of enzyme function. (ii) The transition of zymogen to proteinase following cleavage is not absolute and instead, thrombin can reversibly interconvert between zymogen-like and proteinase-like forms depending on the complement of ligands bound to it. This establishes new paradigms for considering proteinase allostery and how enzyme function may be modulated by ligand binding. These insights into the action of prothrombinase on prothrombin have wide-ranging implications for the understanding of function in blood coagulation.

Elevated prothrombin promotes venous, but not arterial, thrombosis in mice

OBJECTIVE

Individuals with elevated prothrombin, including those with the prothrombin G20210A mutation, have increased risk of venous thrombosis. Although these individuals do not have increased circulating prothrombotic biomarkers, their plasma demonstrates increased tissue factor-dependent thrombin generation in vitro. The objectives of this study were to determine the pathological role of elevated prothrombin in venous and arterial thrombosis in vivo, and distinguish thrombogenic mechanisms in these vessels.

APPROACH AND RESULTS

Prothrombin was infused into mice to raise circulating levels. Venous thrombosis was induced by electrolytic stimulus to the femoral vein or inferior vena cava ligation. Arterial thrombosis was induced by electrolytic stimulus or ferric chloride application to the carotid artery. Mice infused with prothrombin demonstrated increased tissue factor-triggered thrombin generation measured ex vivo, but did not have increased circulating prothrombotic biomarkers in the absence of vessel injury. After venous injury, elevated prothrombin increased thrombin generation and the fibrin accumulation rate and total amount of fibrin ≈ 3-fold, producing extended thrombi with increased mass. However, elevated prothrombin did not accelerate platelet accumulation, increase the fibrin accumulation rate, or shorten the vessel occlusion time after arterial injury.

CONCLUSIONS

These findings reconcile previously discordant findings on thrombin generation in hyperprothrombinemic individuals measured ex vivo and in vitro, and show elevated prothrombin promotes venous, but not arterial, thrombosis in vivo.

The thrombophilic network of autoantibodies in celiac disease

BACKGROUND

Celiac disease is a life-long autoimmune condition, affecting genetically susceptible individuals that may present with thromboembolic phenomena. This thrombophilia represents a puzzle with multiple constituents: hyperhomocysteinemia, B12 and\or folate deficiency, methylenetetrahydrofolate reductase mutations, and protein C and S deficiency due to vitamin K deficiency. However, the well known thrombogenic factors, antiphosphatidylserine/prothrombin and antiprothrombin have never been explored in celiac disease.

METHODS

The serum autoantibody levels were determined in 248 individuals, classified into three groups. Group 1 comprised 70 children with definitive celiac disease (age: 7.04 ±4.3 years, male to female ratio 1.06) and group 2 comprised 88 normal children (age: 6.7 ±4.17 years, male to female ratio 0.87), representing controls. The pediatric populations were compared to group 3, which included 90 adults who were family members (parents) of group 1 (age: 34.6 ±11.35 years, male to female ratio 1.2). Antibodies were checked by enzyme-linked immunosorbent assay.

RESULTS

Mean optical density levels of serum antiphosphatidylserine/prothrombin immunoglobulin G antibodies were 32.4 ±19.4, 3.6 ±2.5 and 16.1 ±15.8 absorbance units in groups 1, 2 and 3 respectively (P <0.0001), with 45.7%, 0% and 7.8% of groups 1, 2 and 3 respectively positive for the antibody (P <0.01). Mean optical density levels of serum antiphosphatidylserine/prothrombin immunoglobulin M antibodies were 14.2 ±8.7, 6.7 ±6.4 and 12.4 ±15.5 absorbance units in groups 1, 2 and 3 respectively (P <0.0001), with 7.1%, 3.4% and 9.9% of groups 1, 2 and 3 positive for the antibody. Mean optical density levels of serum antiprothrombin and antiphospholipid immunoglobulin G antibodies were higher in groups 1 and 3 compared with 2 (P <0.005) and in groups 1 and 2 compared with 3 (P <0.01), respectively. Groups 1, 2 and 3 were positive for antiphospholipid immunoglobulin G antibodies (groups 1 and 2 compared with 3) . Celiac disease sera harbor a higher antiprothrombin immunoglobulin G level compared with controls.

CONCLUSIONS

It is suggested that the intestinal injury, endothelial dysfunction, platelet abnormality and enhanced apoptosis recently described in celiac disease are at the origin of the increased exposure of phospholipids or new epitopes representing autoantigens. Those autoantibodies might play a pathogenic role in the thrombophilia associated with celiac disease and represent markers for potential anticoagulant preventive therapy.

GAPSS: the Global Anti-Phospholipid Syndrome Score

OBJECTIVE

To develop and validate a risk score [global APS score (GAPSS)] derived from the combination of independent risk for thrombosis and pregnancy loss (PL), taking into account the aPL profile, conventional cardiovascular risk factors and the autoimmune antibody profile.

METHODS

This cross-sectional study included 211 consecutive SLE patients. Data on clinical manifestations, conventional cardiovascular risk factors, aPL profile, ANAs, ENA and anti-dsDNA were collected. Long-term low-dose aspirin, oral anticoagulant and HCQ treatment were also included in the analysis. Patients were randomly divided into two sets by a computer-generated randomized list. We developed GAPSS in the first set of patients (n = 106), assigning the risk factors identified by multivariate analysis weighted points proportional to the β-regression coefficient values. GAPSS was validated in the second set of patients (n = 105). The relationship between GAPPS and thrombosis and/or PL was analysed.

RESULTS

In the first set, higher values of GAPSS were seen in patients who experienced thrombosis and/or PL compared with those without clinical events [GAPSS 9.3 (4.8) (range 1-19) and 5.3 (4) (range 0-16), P < 0.001]. Also taken separately, patients who experienced thrombosis or PL showed higher GAPSS compared with those without clinical events [GAPSS 9.6 (4.8) (range 1-19) vs 4.9 (5) (range 0-14), P = 0.027 for thrombosis; 7.3 (5) vs 3.9 (5.1) (range 0-16), P = 0.024 for PL, respectively]. In the second set, the results were similar, with statistically higher values of GAPSS in patients with a clinical history of thrombosis and/or PL compared with those without events [GAPSS 9.5 (5.6) (range 0-20) and 3.9 (4.1) (range 0-17), P < 0.001). Higher values were also seen when subclassifying the patients according to the clinical manifestation, thrombosis or PL [GAPSS 9.5 (5.6) (range 0-20) vs 4.8 (5.4) (range 0-17), P = 0.036 for thrombosis; 7.9 (3.3) vs 3.8 (5.4) (range 0-16), P = 0.037 for PL, respectively).

CONCLUSION

These data propose a substantial improvement in risk prediction of thrombosis or PL in SLE based on assessment of the GAPSS, a quantitative scoring system.

Congenital factor II deficiency: moroccan cases

BACKGROUND

Clotting factor II, or prothrombin, is a vitamin K-dependent proenzyme that functions in the blood coagulation cascade. Inherited factor II deficiency is an extremely rare autosomal recessive disorder affecting both genders: clinical bleeding can vary widely in homozygous individuals, and heterozygotes often remain clinically asymptomatic. This study highlights the rarity of inherited factor II deficiency and the importance of coagulation testing in the diagnosis of this condition.

METHODS

We report four cases of factor II deficiency at our institution.

RESULTS

At diagnosis, two patients were 3 days old, whereas the other two patients were 13 and 40 years of age. Three patients were female, and one was male. Symptoms of factor II deficiency were reported at referral in three patients; the deficiency was an incidental finding in the remaining case. The parents of all four patients were consanguineous (first degree). Factor II enzymatic activity was 1% in 3 cases and 5% in the incidental case. The treatment consisted of transfusion with fresh frozen plasma in all cases.

CONCLUSIONS

The congenital deficiency of factor II is a rare inherited disorder. The diagnosis is mainly based on coagulation tests. However, the prognosis of this disease and access to medication are associated with the risk of occurrence of severe bleeding.

Pharmacogenetic typing for oral anti-coagulant response among factor V Leiden mutation carriers

CONTEXT

Factor V Leiden mutation is the most common inherited predisposition for hypercoagulability and thereby a common genetic cause for initiation of oral anti-coagulation therapy. There is a dearth of knowledge of coumarin response profile in such thrombophilic population.

AIMS

The current pilot study aims to estimate coumarin sensitivity in an Indian cohort with an inherited thrombophilia risk factor (Factor V Leiden mutation carriers) based on the observed frequency of CYP2C9 (*)2, (*)3 and VKORC1-1639G >A genotype combinations.

SETTINGS AND DESIGN

A retrospective study carried out in a tertiary health care center in India.

MATERIALS AND METHODS

Carriers of FVL mutation were genotyped for CYP2C9 ((*)2, F(*)3) and VKORC1 (-1639G >A) variants by PCR-RFLP technique.

STATISTICAL ANALYSIS USED

Chi-square test to analyze difference in expected and observed genotype frequency.

RESULTS

Sixty-one (n = 61) unrelated carriers of FVL mutation were observed in the 13 years study period. The allele frequency of CYP2C9 (*)2, CYP2C9 (*)3, and VKORC1-1639A in this cohort was 0.06, 0.11, and 0.16, respectively. Six (9.7%) individuals had two of the three variant alleles (heterozygous or homozygous), and 28 (45.9%) were heterozygous for at least one polymorphism.

CONCLUSIONS

Pre-prescription genotyping for coumarin drugs, if introduced in Indians with inherited thrombophilia (in whom oral anti-coagulant therapy may be necessary), is likely to identify 9.7% (hypersensitive) subjects in whom the optimum anti-coagulation may be achieved with reduced dosages, 44.3% (normal sensitivity) who may require higher dose and also 55.6% (hyper and moderate sensitivity) subjects who are likely to experience bleeding episodes.

A high affinity, antidote-controllable prothrombin and thrombin-binding RNA aptamer inhibits thrombin generation and thrombin activity

BACKGROUND

The conversion of prothrombin to thrombin is one of two non-duplicated enzymatic reactions during coagulation. Thrombin has long been considered an optimal anticoagulant target because it plays a crucial role in fibrin clot formation by catalyzing the cleavage of fibrinogen, upstream coagulation cofactors and platelet receptors. Although a number of anti-thrombin therapeutics exist, it is challenging to use them clinically due to their propensity to induce bleeding. Previously, we isolated a modified RNA aptamer (R9D-14) that binds prothrombin with high affinity and is a potent anticoagulant in vitro.

OBJECTIVES

We sought to explore the structure of R9D-14 and elucidate its anticoagulant mechanism(s). In addition to designing an optimized aptamer (RNA(R9D-14T)), we also explored whether complementary antidote oligonucleotides can rapidly modulate the optimized aptamer's anticoagulant activity.

METHODS AND RESULTS

RNA(R9D-14T) binds prothrombin and thrombin pro/exosite I with high affinity and inhibits both thrombin generation and thrombin exosite I-mediated activity (i.e. fibrin clot formation, feedback activity and platelet activation). RNA(R9D-14T) significantly prolongs the aPTT, PT and TCT clotting assays, and is a more potent inhibitor than the thrombin exosite I DNA aptamer ARC-183. Moreover, a complementary oligonucleotide antidote can rapidly (< 2 min) and durably (>2 h) reverse RNA(R9D-14T) anticoagulation in vitro.

CONCLUSIONS

Powerful anticoagulation, in conjunction with antidote reversibility, suggests that RNA(R9D-14T) may be ideal for clinical anticoagulation in settings that require rapid and robust anticoagulation, such as cardiopulmonary bypass, deep vein thrombosis, stroke or percutaneous coronary intervention.

Polyphosphate binds with high affinity to exosite II of thrombin

BACKGROUND

Polyphosphate (a linear polymer of inorganic phosphate) is secreted from platelet dense granules, and we recently showed that it accelerates factor V activation by thrombin.

OBJECTIVE

To examine the interaction of polyphosphate with thrombin.

METHODS AND RESULTS

Thrombin, but not prothrombin, altered the electrophoretic migration of polyphosphate in gel mobility assays. Thrombin binding to polyphosphate was influenced by ionic strength, and was evident even in plasma. Two positively charged exosites on thrombin mediate its interactions with other proteins and accessory molecules: exosite I (mainly with thrombin substrates), and exosite II (mainly with certain anionic polymers). Free thrombin, thrombin in complex with hirudin's C-terminal dodecapeptide and gamma-thrombin all bound polyphosphate similarly, excluding exosite I involvement. Mutations within exosite II, but not within exosite I, the Na(+)-binding site or hydrophobic pocket, weakened thrombin binding to polyphosphate as revealed by NaCl dependence. Surface plasmon resonance demonstrated tight interaction of polyphosphate with thrombin (K(d) approximately 5 nm) but reduced interaction with a thrombin exosite II mutant. Certain glycosaminoglycans, including heparin, only partially competed with polyphosphate for binding to thrombin, and polyphosphate did not reduce heparin-catalyzed inactivation of thrombin by antithrombin.

CONCLUSION

Polyphosphate interacts with thrombin's exosite II at a site that partially overlaps with, but is not identical to, the heparin-binding site. Polyphosphate interactions with thrombin may be physiologically relevant, as the polyphosphate concentrations achievable following platelet activation are far above the approximately 5 nM K(d) for the polyphosphate-thrombin interaction.

Prothrombin gene G20210A mutation in acute deep venous thrombosis patients with poor response to warfarin therapy

AIM

The pathogenesis of deep venous thrombosis (DVT) involves an interaction between hereditary and acquired factors. Prothrombin gene mutation is one of the hereditary risk factors. We evaluated the frequency of the prothrombin gene mutation in patients with DVT and its relation to oral warfarin anticoagulant therapy response.

METHODS

Prothrombin gene mutation was looked for in 40 DVT patients with poor response to warfarin. The results were compared with 40 DVT patients with a normal response to warfarin and 30 healthy blood donors. Blood samples were also assessed for protein C, protein S, anti-thrombin III and anticardiolipin antibodies (ACA) levels.

RESULTS

Prothrombin gene mutation was found in normal and poor DVT responders (6/40 and 13/40, respectively; p = NS) as well as in healthy controls (1/30). Patients with recurrent DVT or a family history of DVT were significantly (p<0.0001) more likely to have the prothrombin mutation than other DVT patients. Non prothrombin abnormalities (protein C, anti-thrombin III and ACA) were more common in poor responders than controls (p<0.0037) as were ACA (p<0.034).

CONCLUSIONS

Prothrombin gene mutation is present in several DVT patients, especially those with recurrent DVT or a family history of DVT. This mutation may contribute to a poor response to warfarin.

Prothrombin amino terminal region helps protect coagulation factor Va from proteolytic inactivation by activated protein C

The hypothesis that prothrombin (FII) protects coagulation factor Va (FVa) from proteolytic inactivation by activated protein C (APC) was tested using purified proteins. FII dose-dependently protected FVa from APC proteolysis under conditions where competition of proteins for binding to negatively-charged phospholipid surface was not relevant (i.e. either at high phospholipid vesicle concentrations or using soluble dicaproylphosphatidylserine at levels below its critical micellar concentration). Cleavages in FVa at both Arg(506) and Arg(306) by APC were inhibited by FII. FII did not alter the amidolytic activity of APC towards chromogenic oligopeptide substrates or inhibit FVIIIa inactivation by APC, implying that the FII-mediated protection of FVa from APC proteolysis was due to the ability of FII to inhibit protein-protein interactions between FVa and APC. FII also protected FVa from inactivation by Gla-domainless APC, ruling out a role for the APC Gla domain for these observations. To identify domains of FII responsible for the observed phenomenon, various forms or fragments of FII were employed. Biotin-Phe-ProArg-CMK-inhibited meizothrombin and fII-fragment 1*2 protected FVa from proteolysis by APC. In contrast, no significant protection of FVa from APC cleavage was observed for Gladomainless-FII, prethrombin-1, prethrombin-2, FII fragment 1 or active site inhibited-thrombin (DEGR-thrombin). Overall, these data demonstrate that the Gla domain of FII linked to kringle 1 and 2 is necessary for the ability of FII to protect FVa from APC cleavage and support the general concept that assembly of the FII activation complex (FXa*FVa*FII*lipid surface) protects FVa from APC inactivation so that the procoagulant, thrombin generating pathway can act unhindered by APC. Only following FII activation and dissociation of the FII Gla domain fragments from the FII-ase complex, can APC inactivate FVa and down-regulate thrombin generation.

Etiology of hypercoagulable state in women with recurrent fetal loss without other causes of miscarriage from Southern Italy: new clinical target for antithrombotic therapy

BACKGROUND

Recurrent fetal loss (RPL) is one of the most common cause of sterility. Several studies identified thrombophilia as the principal cause of recurrent pregnancy loss. However, reported studies often do not evaluate other causes of miscarriages in their inclusion and exclusion criteria. So the aim of our study was to investigate the role of inherited thrombophilia in patients with RPL and without other causes of RPL.

PATIENTS AND METHODS

Patients with 2 or more first trimester abortion or with 1 or more late pregnancy loss were considered for this study. In order to evaluate the causes of RPL we looked for chromosomal, endocrine, chronic inflammatory, and infectious alterations. 90 patients affected by unexplained RPL were enrolled and tested for hemostatic alterations. These women were tested for inherited and/or acquired thrombophilia by MTHFR C677T gene polymorphism, factor V Leiden gene polymorphism, PTHRA20210G gene polymorphism, protein S deficiency, protein C deficiency, antithrombin III deficiency, lupus anticoagulant, and anticardiolipin antibodies Ig G and Ig M.

RESULTS

Acquired and/or inherited thrombophilia are strongly associated with RPL when other common causes of miscarriage were excluded. 78% of tested women showed hemostatic abnormalities. Several women with combined thrombophilic defects were also identified by our data.

CONCLUSION

After a thorough evaluation of other causes of miscarriage women affected by RPL should be tested for thrombophilia. Our data demonstrated 78% of women with one or combined thrombophilic conditions. Differences with previous studies should be related to difference in the inclusion and exclusion criteria and ethnic background. Because these patients often also show a hypercoagulable state, it an antithrombotic treatment before and during pregnancy may improve their clinical outcome (ie, secondary prevention of miscarriage and primary thromboprophylaxis).

Exosites in the substrate specificity of blood coagulation reactions

The specificity of blood coagulation proteinases for substrate, inhibitor, and effector recognition is mediated by exosites on the surfaces of the catalytic domains, physically separated from the catalytic site. Some thrombin ligands bind specifically to either exosite I or II, while others engage both exosites. The involvement of different, overlapping constellations of exosite residues enables binding of structurally diverse ligands. The flexibility of the thrombin structure is central to the mechanism of complex formation and the specificity of exosite interactions. Encounter complex formation is driven by electrostatic ligand-exosite interactions, followed by conformational rearrangement to a stable complex. Exosites on some zymogens are in low affinity proexosite states and are expressed concomitant with catalytic site activation. The requirement for exosite expression controls the specificity of assembly of catalytic complexes on the coagulation pathway, such as the membrane-bound factor Xa*factor Va (prothrombinase) complex, and prevents premature assembly. Substrate recognition by prothrombinase involves a two-step mechanism with initial docking of prothrombin to exosites, followed by a conformational change to engage the FXa catalytic site. Prothrombin and its activation intermediates bind prothrombinase in two alternative conformations determined by the zymogen to proteinase transition that are hypothesized to involve prothrombin (pro)exosite I interactions with FVa, which underpin the sequential activation pathway. The role of exosites as the major source of substrate specificity has stimulated development of exosite-targeted anticoagulants for treatment of thrombosis.

Genetic thrombophilia has pleiotropic effects in pregnancy

Genetic thrombophilia has been established as a risk factor for pregnancy-associated disorders, such as thrombosis, early and late miscarriage, and pre-eclampsia. Associations between the factor V (F5) Leiden G1691A and the prothrombin/factor II (F2) G20210A SNPs and pre-eclampsia have been evaluated in over 50 association studies. A pooled analysis of 23 and 11 studies demonstrates that carriage of the F5 Leiden G1691A (p < 0.001; odds ratio [OR] 2.0; 95% confidence interval [CI] 1.6-2.5) and the F2 G20210A (p < 0.001; OR 1.8; 95% CI 1.1-2.9) SNPs is significantly associated with pre-eclampsia. Besides pre-eclampsia, genotyping for the F5 Leiden G1691A and the F2 G20210A SNPs is also useful for individual risk assessment regarding pregnancy-associated thrombosis. Carriers of the F5 Leiden G1691A SNP will develop this condition in 6.4% of heterozygotes and in 8.9-16.7% of homozygotes. A total of 6.2% of women with the F2 G20210A SNP and 17.8% of women with simultaneous carriage of the F5 Leiden G1691A and F2 G20210A SNPs will develop pregnancy-associated thrombosis. Both the F5 Leiden G1691A and F2 G20210A SNPs are also risk factors of early recurrent, late recurrent and late spontaneous miscarriage based on a published meta-analysis of 31 studies. These women may benefit from prophylactic heparinization. Six case-control and cohort studies of 687 women with genetic thrombophilia document live birth rates of 82% (181/221) using low-molecular-weight heparin or fractionated heparin compared with 20% (95/466) without therapy (p < 0.001, OR 17.7; 95% CI 12.2-25.5). Based on the data in the literature, including association studies and meta-analyses of these association studies, it can be concluded that genetic thrombophilia due to carriage of the F5 Leiden G1691A and F2 G20210A SNPs is a significant and clinically relevant risk factor for pre-eclampsia, pregnancy-associated thrombosis, and early and late miscarriages.