Vitamin K-dependent Coagulation Factors Research Articles

Protocolized warfarin reversal with 4-factor prothrombin complex concentrate versus 3-factor prothrombin complex concentrate with recombinant factor VIIa

IntroductionLife-threatening bleeding can complicate warfarin therapy. Rapid anticoagulant reversal via replacement of vitamin-K dependent clotting factors is essential for hemostasis. We compare two methods of rapid factor replacement for warfarin reversal. MethodsA retrospective cohort study of warfarin-treated patients experiencing life-threatening bleeding who received a reversal protocol comprised of 4F PCC or 3F PCC and rFVIIa was performed. Demographic, clinical and anticoagulant reversal information, and all adverse events attributed to warfarin reversal were recorded. Results195 patients were included in final analysis. While baseline demographics were similar between groups, the 3F-PCC group had a longer ICU LOS and higher in-hospital mortality (p < .01, .01).Pre-reversal INR was similar between both groups, but post-reversal INR was significantly lower in the 3F-PCC group, 0.8 versus 1.3 (p < .01). Significantly more patients experienced thromboembolic complications in the 3F-PCC group than the 4F-PCC group (p < .01). Receipt of rFVIIa was significantly associated with thromboembolic complications. DiscussionA 4F PCC reversal strategy is efficacious in INR reversal and provides lower thromboembolic risk as compared to 3F PCC with rFVIIa.

Coagulation Factor Plasma Levels Following Administration of a 4-Factor Prothrombin Complex Concentrate for Rapid Vitamin K Antagonist Reversal in Japanese Patients

BackgroundFour-factor prothrombin complex concentrates (4F-PCCs) have been approved for urgent vitamin K antagonist reversal in Western countries for many years. Ethnicity and genetic variations between populations may influence the pharmacokinetic profile of 4F-PCC treatments.ObjectiveTo report plasma levels of vitamin K-dependent coagulation factors and proteins C and S in Japanese patients following administration of a 4F-PCC approved recently in Japan.MethodsThis was a subanalysis of a prospective, open-label, Phase IIIb study in Japanese patients requiring rapid vitamin K antagonist reversal owing to major bleeding (n = 6) or need for urgent surgery (n = 5). International normalized ratio and plasma levels of factors II, VII, IX, and X, and proteins C and S were measured before PCC infusion and at specific time points for the next 24 hours. Adverse events and serious adverse events were recorded up to Day 14 and 45, respectively.ResultsRapid increases in plasma concentrations 30 minutes following 4F-PCC infusion were seen for all factors and proteins C and S, with median concentrations compared with baseline increasing by ≥100% and 70% in the bleeding and surgical groups, respectively. A concurrent decrease in international normalized ratio was observed. Plasma levels for each factor and protein remained within physiologic levels throughout the assessment period. No relationship between thromboembolic events and elevated plasma levels was identified.ConclusionsAdministration of 4F-PCC in Japanese patients receiving vitamin K antagonist anticoagulation therapy resulted in rapid and sustained increases in plasma levels and was well tolerated, indicating that this treatment is effective for the urgent reversal of vitamin K antagonist therapy in this population.

Combined deficiency of vitamin K-dependent coagulation factors and extensive hemorrhage

Combined deficiency of vitamin K-dependent coagulation factors and extensive hemorrhage

Hypoprothrombinemia and severe perioperative haemorrhagic complications in cardiac surgery patients treated with high-dose cefazolin for infective endocarditis

Endocarditis is a serious and common disease that requires prolonged antimicrobial therapy. The recent shortage of oxacillin has led to the use of other antimicrobial agents such as cefazolin to treat endocarditis due to methicillin-sensitive Staphylococcus aureus. We describe four cases of life-threatening haemorrhagic complications (fatal in two cases) in patients treated with high-dose cefazolin. All of these patients with major bleeding presented with hypoprothrombinemia secondary to hypovitaminosis K. This adverse event may be due to inhibition of vitamin K epoxide reductase and/or gamma-glutamyl-carboxylase by the 2-methyl-1,2,3-thiadiazol-5-thiol group of cefazolin. This inhibition may result in hypoprothrombinemia by altering the synthesis of vitamin K-dependent coagulation factors. The increasing use of cefazolin, especially at a high dose and for a prolonged period of time, should be accompanied by regular monitoring of coagulation, including prothrombin index, and vitamin K supplementation.

Finding the optimal dose of vitamin K1 to treat vitamin K deficiency and to avoid anaphylactoid reactions.

Vitamin K1 injection induces severe dose-related anaphylactoid reactions and overdose for the treatment of vitamin K deficiency. We aimed to find an optimal and small dose of vitamin K1 injection to treat vitamin K deficiency and avoid anaphylactoid reactions in animal. Rats were administered a vitamin K-deficient diet and gentamicin to establish vitamin K deficiency model. Behaviour tests were performed in beagle dogs to observe anaphylactoid reactions. The results showed an increased protein induced by vitamin K absence or antagonist II (PIVKA-II) levels, a prolonging of prothrombin time (PT) and activated partial thromboplastin time (APTT) and a decrease in vitamin K-dependent coagulation factor (F) II, VII, IX and X activities in the model group. In vitamin K1 0.01 mg/kg group, the liver vitamin K1 levels increased fivefold and the liver vitamin K2 levels increased to the normal amount. Coagulation markers PT, APTT, FVII and FIX activities returned to normal. Both in the 0.1 and 1.0 mg/kg vitamin K1 groups, coagulation functions completely returned to normal. Moreover, the amount of liver vitamin K1 was 40 (0.1 mg/kg) or 100 (1.0 mg/kg) times as in normal. Vitamin K2 was about 4 (0.1 mg/kg) or 5 (1.0 mg/kg) times as the normal amount. There was no obvious anaphylactoid symptom in dogs with the dose of 0.03 mg/kg, which is equivalent to the dose of 0.01 mg/kg in rats. These results demonstrated that a small dose of vitamin K1 is effective to improve vitamin K deficiency and to prevent anaphylactoid reactions, simultaneously.

A Joint Model for Vitamin K-Dependent Clotting Factors and Anticoagulation Proteins.

Warfarin acts by inhibiting the reduction of vitamin K (VK) to its active form, thereby decreasing the production of VK-dependent coagulation proteins. The aim of this research is to develop a joint model for the VK-dependent clotting factors II, VII, IX and X, and the anticoagulation proteins, proteins C and S, during warfarin initiation. Data from 18 patients with atrial fibrillation who had warfarin therapy initiated were available for analysis. Nine blood samples were collected from each subject at baseline, and at 1-5, 8, 15 and 29days after warfarin initiation and assayed for factors II, VII, IX and X, and proteins C and S. Warfarin concentration-time data were not available. The coagulation proteins data were modelled in a stepwise manner using NONMEM® Version 7.2. In the first stage, each of the coagulation proteins was modelled independently using a kinetic-pharmacodynamic model. In the subsequent step, the six kinetic-pharmacodynamic models were combined into a single joint model. One patient was administered VK and was excluded from the analysis. Each kinetic-pharmacodynamic model consisted of two parts: (1) a common one-compartment pharmacokinetic model with first-order absorption and elimination for warfarin; and (2) an inhibitory E max model linked to a turnover model for coagulation proteins. In the joint model, an unexpected pharmacodynamic lag was identified and the estimated degradation half-life of VK-dependent coagulation proteins were in agreement with previously published values. The model provided an adequate fit to the observed data. The joint model represents the first work to quantify the influence of warfarin on all six VK-dependent coagulation proteins simultaneously. Future work will expand the model to predict the influence of exogenously administered VK on the time course of clotting factor concentrations after warfarin overdose and during perioperative warfarin reversal procedures.

Autosomal recessive inherited bleeding disorders in Pakistan: a cross-sectional study from selected regions

BackgroundAutosomal recessive bleeding disorders (ARBDs) include deficiencies of clotting factors I, II, V, VII, X, XI, XIII, vitamin K dependent clotting factors, combined factor V & VIII, Von Willebrand Disease (vWD) type 3, Glanzmann’s thrombasthenia (GT) and Bernard–Soulier syndrome. Patients with primary bleeding disorders from all the major provincial capitals of Pakistan were screened for ARBDs. Prothrombin (PT), activated partial thromboplastin time (APTT), bleeding time (BT) and fibrinogen levels were measured. Cases with isolated prolonged APTT were tested for factors VIII and IX using factor assays This was followed by FXI:C level assessment in cases with normal FVIII and FIX levels. vWD was screened in patients with low FVIII levels. Factors II, V and X were tested in patients with simultaneous prolongation of PT and APTT. Peripheral blood film examination and platelet aggregation studies were performed to assess platelet disorders. Urea clot solubility testing was done to detect Factor XIII levels where platelet function tests were normal. Descriptive analysis was done using SPSS version 16.ResultsOf the 429 suspected bleeding disorder patients, 148 (35%) were diagnosed with hemophilia A and 211 (49.1%) patients had ARBDs. 70 patients (16.3%) remained undiagnosed. Out of 211 patients with ARBD; 95 (33.8%) had vWD type 3. Fibrinogen deficiency was found in 34 patients (12%), GT in 27 (9.6%), factor XIII deficiency in 13 (4.6%), factor VII deficiency in 12 (4.3%), factor V deficiency in 9 (3.2%). Eight patients (2.8%) had vitamin K-dependent clotting factor deficiency, Bernard–Soulier syndrome was diagnosed in seven patients (2.5%), factor X deficiency in 2 (0.7%), factor II deficiency in 2 (0.7%), factor XI deficiency and combined factor V and VIII deficiency in 1 (0.4%) patient each.ConclusionvWD type 3 was the most common ARBD found in our sample of patients in Pakistan, followed by fibrinogen deficiency and GT in respective order.

Dietary and genetic influences on hemostasis in a Yup'ik Alaska Native population.

Fish and marine animals are important components of the subsistence diet of Alaska Native people, resulting in a high ω3 PUFA intake. The historical record for circumpolar populations highlights a tendency for facile bleeding, possibly related to ω3 PUFA effects on platelet activation and/or vitamin K-dependent clotting factors. To evaluate these two scenarios in Yup’ik people of southwestern Alaska, we examined the association between dietary ω3 PUFA intake and activities of clotting factor II, V, fibrinogen, PT, INR, PTT, and sP-selectin in 733 study participants, using the nitrogen isotope ratio of red blood cells as a biomarker of ω3 PUFA consumption. sP-selectin alone correlated strongly and inversely with ω3 PUFA consumption. Approximately 36% of study participants exhibited PIVKA-II values above the threshold of 2 ng/ml, indicative of low vitamin K status. To assess genetic influences on vitamin K status, study participants were genotyped for common vitamin K cycle polymorphisms in VKORC1, GGCX and CYP4F2. Only CYP4F2*3 associated significantly with vitamin K status, for both acute (plasma vitamin K) and long-term (PIVKA-II) measures. These findings suggest: (i) a primary association of ω3 PUFAs on platelet activation, as opposed to vitamin K-dependent clotting factor activity, (ii) that reduced CYP4F2 enzyme activity associates with vitamin K status. We conclude that high ω3 PUFA intake promotes an anti-platelet effect and speculate that the high frequency of the CYP4F2*3 allele in Yup’ik people (~45%) evolved in response to a need to conserve body stores of vitamin K due to environmental limitations on its availability.

Identification of the blood coagulation factor interacting sequences in staphylococcal superantigen-like protein 10

Staphylococcal superantigen-like proteins (SSLs) are a family of exoproteins of Staphylococcus aureus. We have shown that SSL10 binds to vitamin K-dependent coagulation factors and inhibits blood coagulation induced by recalcification of citrated plasma. SSL10 was revealed to bind to coagulation factors via their γ-carboxyglutamic acid (Gla) domain. In this study we attempted to identify the responsible sequence of SSL10 for the interaction with coagulation factors. We prepared a series of domain swap mutants between SSL10 and its paralog SSL7 that does not interact with coagulation factors, and examined their binding activity to immobilized prothrombin using ELISA-like binding assay. The domain swap mutants that contained SSL10β1-β3 (23MEMKN ISALK HGKNN LRFKF RGIKI QVL60) bound to immobilized prothrombin, and mutants that contained SSL10β10-β12 (174SFYNL DLRSK LKFKY MGEVI ESKQI KDIEV NLK207) also retained the binding activity. On the other hand, mutants that lacked these two regions did not bind to prothrombin. These sequences, each alone, bound to prothrombin as 33 amino acid length polypeptides. These results suggest that SSL10 has two responsible sequences for the binding to prothrombin. These prothrombin-binding peptides would contribute to the development of new anticoagulants.

Basic concept for evaluating coagulation and fibrinolysis data.

"Fibrin is insoluble in blood" is the most important concept to accept the coagulation system. Essentially, blood coagulation is a process to convert blood from soluble to insoluble. Fibrinolysis is another process to convert insoluble protein to soluble protein again. The blood coagulation cascade requires calcium ion and efficiently acts on platelet phospholipid membranes. On the other hand, the fibrinolysis system efficiently acts on fibrin. Unlike other vitamin K-dependent coagulation factors, thrombin can be released from the coagulation site to the systemic circulation and has multiple biological effects regulated through thrombin receptors. Thrombin is captured by thrombomodulin on endothelial cells or anti-thrombin. Low level of coagulation and fibrinolysis idling are always working even under healthy conditions because of shear stress on injured vessels. Measurement of coagulation times, such as PT and APTT, is the basic method used by numerous clinics in coagulation-related examinations. Measurement of coagulation factor activity by one method is based on the concept that excess amounts of coagulation factors circulate in the blood. Under DIC conditions, excess pathological protease activity yields a huge amount of peptides in the blood in addition to coagulation and fibrinolysis markers.

GGCX-Associated Phenotypes: An Overview in Search of Genotype-Phenotype Correlations.

Gamma-carboxylation, performed by gamma-glutamyl carboxylase (GGCX), is an enzymatic process essential for activating vitamin K-dependent proteins (VKDP) with important functions in various biological processes. Mutations in the encoding GGCX gene are associated with multiple phenotypes, amongst which vitamin K-dependent coagulation factor deficiency (VKCFD1) is best known. Other patients have skin, eye, heart or bone manifestations. As genotype–phenotype correlations were never described, literature was systematically reviewed in search of patients with at least one GGCX mutation with a phenotypic description, resulting in a case series of 47 patients. Though this number was too low for statistically valid correlations—a frequent problem in orphan diseases—we demonstrate the crucial role of the horizontally transferred transmembrane domain in developing cardiac and bone manifestations. Moreover, natural history suggests ageing as the principal determinant to develop skin and eye symptoms. VKCFD1 symptoms seemed more severe in patients with both mutations in the same protein domain, though this could not be linked to a more perturbed coagulation factor function. Finally, distinct GGCX functional domains might be dedicated to carboxylation of very specific VKDP. In conclusion, this systematic review suggests that there indeed may be genotype–phenotype correlations for GGCX-related phenotypes, which can guide patient counseling and management.

During warfarin induction, the Fiix‐prothrombin time reflects the anticoagulation level better than the standard prothrombin time

Background The prothrombin time (PT) is equally prolonged by reduction of each of the vitamin K-dependent (VKD) factors (F) II, VII and X. The Fiix-PT is only affected by FII and FX, the main contributors to thrombin generation (TG). Objective To test the hypothesis that variability in warfarin anticoagulation is reduced early during monitoring with the normalized PT-ratio calculated from Fiix-PT (Fiix-International Normalized Ratio [INR]) compared with traditional PT-INR monitoring. Also, that because of its insensitivity to FVII, Fiix-PT more accurately reflects TG when Fiix-INR and PT-INR are discrepant. Methods Samples from Fiix-trial participants monitored with either Fiix-PT or PT were used. VKD coagulation factors and TG were measured in samples from 40 patients during stable anticoagulation and in serial samples obtained from 26 patients during warfarin induction. TG was assessed in relation to selective reduction in single VKD factors. Results During Fiix-warfarin induction full anticoagulation measured as FII or FX activity was achieved at a similar rate to that with PT-warfarin but subsequently stabilized better. Fiix-INR but not PT-INR mirrored total TG during initiation. During induction, FII (R2 = 0.66) and FX (R2 = 0.52) correlated better with TG and with a steeper slope than did FIX (R2 = 0.37) and in particular FVII (R2 = 0.21). In vitro, FII and FX were the main determinants of TG at concentrations observed during VKA anticoagulation, whereas FVII and FIX had little influence. Conclusions Fiix-PT monitoring reduces anticoagulation variability, suggesting that monitoring FVII has a limited role during VKA management. TG is better reflected by Fiix-PT.

Role of Thromboelastography Platelet Mapping and International Normalized Ratio in Defining "Normocoagulability" During Anticoagulation for Mechanical Circulatory Support Devices: A Pilot Retrospective Study.

Thromboembolic (TE) events and hemorrhagic complications continue to remain as frequent adverse events and causes of death after mechanical circulatory support device (MCSD) implantation. To counterbalance this postimplant multifactorial hypercoagulable state, antithrombotic therapy given postimplant must be individually tailored to keep patient adequately anticoagulated yet normocoagulable. Prior studies describing different anticoagulation protocols do not define normocoagulability for patients on MCSDs. We evaluated the role of thromboelastography platelet mapping (TEG PM) in defining "normocoagulability" for MCS patients on anticoagulant (warfarin) and antiplatelet agents. Ninety-eight MCSD patients who underwent TEG PM assay at our institution from 2012 to 2014 were included for retrospective analysis. Eleven (11.2%) subjects developed at least one TE event during the study period. Of the 13 TE events, 8 occurred in patients with total artificial heart (TAH). TEG parameters closest to the event or when patient was clinically adequately anticoagulated and corresponding international normalized ratio (INR) were measured. Thromboelastography coagulation index (CI) appears to be the single most statistically significant parameter that can be used to designate a patient as normocoagulable. Based on our results, patients with HeartMate II (HM II) and Heart Ware (HW) devices should be maintained at a CI value of less than or equal to 1.5 whereas patients with TAH devices should be maintained at a CI less than or equal to 1.2. The CI should be correlated with the degree of Vitamin K-dependent coagulation factor inhibition that is achieved using device-specific goal INR ranges. A recent modification, TEG PM assesses the effects of antiplatelet drug. Maximal amplitude arachidonic acid (MA-AA) < 50 and maximal amplitude adenosine diphosphate (MA-ADP) < 50 are desired for normocoagulable state.

Reversing vitamin K antagonists: making the old new again.

Vitamin K antagonists (VKAs) are commonly used for the prevention and treatment of thrombotic disorders. The response to VKAs is highly variable due to their specific interaction with the vitamin K cycle, and hence interference with hepatic synthesis of vitamin K-dependent coagulation factors. Monitoring the anticoagulant effect of VKAs by assessing the patient's international normalized ratio (INR) is essential because complications are closely related to the intensity of anticoagulation. Treatment with VKAs contains a substantial risk of bleeding with a high case fatality rate. Reversal of VKAs is required in case of bleeding or a supratherapeutic INR, but also prior to high-risk surgery or interventions. Choice of methods to reverse VKAs depends on whether or not the patient is bleeding or is in need of an urgent procedure, and has to be based on the pharmacokinetic and pharmacodynamic properties of the VKA. Reversal strategies include withholding the VKA, administration of vitamin K1, and substitution of vitamin K-dependent procoagulant factors, and need to be combined with measures according to general bleeding management.

Coagulative safety of epidural catheters after major upper gastrointestinal surgery: advanced and routine coagulation analysis in 38 patients.

BackgroundThe risk of spinal haematoma in patients receiving epidural catheters is estimated using routine coagulation tests, but guidelines are inconsistent in their recommendations on what to do when results indicate slight hypocoagulation. Postoperative patients are prone to thrombosis, and thromboelastometry has previously shown hypercoagulation in this setting. We aimed to better understand perioperative haemostasis by comparing results from routine and advanced tests, hypothesizing that patients undergoing major upper gastrointestinal surgery would be deficient in vitamin K-dependent coagulation factors because of malnutrition, or hypocoagulative because of accumulation of low molecular weight heparin (LMWH).MethodsThirty-eight patients receiving epidural analgesia for major upper gastrointestinal surgery were included. We took blood at the time of preoperative epidural catheterization and at catheter withdrawal. Prothrombin time-international normalized ratio (PT-INR), activated partial thromboplastin time (aPTT) and platelet count (Plc) were analysed, and also albumin, proteins induced by vitamin K absence (PIVKA-II), rotational thromboelastometry (ROTEM®), multiple electrode aggregometry (Multiplate®) and activities of factors II, VII, IX, X, XI, XII and XIII.ResultsPostoperative coagulation was characterized by thrombocytosis and hyperfibrinogenaemia. Mean PT-INR increased significantly from 1.0 ± 0.1 to 1.2 ± 0.2 and mean aPTT increased significantly from 27 ± 3 to 30 ± 4 s. Activity of vitamin K-dependent factors did not decrease significantly: FIX and FX activity increased. FXII and FXIII decreased significantly. Mean Plc increased from 213 ± 153 × 106/L while all mean ROTEM-MCFs (maximal clot firmnesses) especially FIBTEM-MCF increased significantly to above the reference interval. All mean ROTEM® clotting times were within their reference intervals both before and after surgery. ROTEM® (HEPTEM minus INTEM) results were spread around 0. There were significant correlations between routine tests and the expected coagulation factors, but not any of the viscoelastic parameters or PIVKA-II. Multiplate® area under curve and EXTEM-MCF correlated significantly to Plc as did EXTEM-MCF to fibrinogen, FIX, FX and FXIII; and FIBTEM-MCF to Plc, FII, FXI and FXIII.ConclusionsThe increase in PT-INR may be caused by decreased postoperative FVII while the elevated aPTT may be caused by low FXII. The mild postoperative hypocoagulation indicated by routine tests is not consistent with thromboelastometry. The relevance of ROTEM® and Multiplate® in the context of moderately increased routine tests remains unclear.Trial registration number is not applicable since this is not a clinical trial.Electronic supplementary materialThe online version of this article (doi:10.1186/s13741-016-0053-0) contains supplementary material, which is available to authorized users.

Pseudoxanthome élastique variant avec déficit en facteurs de coagulation vitamine K-dépendants et perte d’élasticité cutanée

Pseudoxanthoma elasticum (PXE)-like syndrome is characterized by the association of PXE and cutis laxa (CL) features with a deficiency of vitamin K-dependent clotting factors. It was first described in 1971 and was identified as a distinct genetic entity in 2007 with analysis of the GGCX (γ-glutamyl carboxylase) gene, which is involved in congenital deficiency in vitamin K-dependent clotting factors. Here we report a new case of this extremely rare syndrome. A 23-year-old female patient was seen for the emergence of loose and redundant skin following extensive weight loss. She also presented a deficiency of vitamin K-dependent clotting factors. Physical examination revealed excessive, leathery skin folds in the axillary and neck regions. A skin biopsy revealed polymorphous and fragmented elastic fibers in the reticular dermis. These were mineralized, as was demonstrated by Von Kossa staining. The clinical features of CL associated with the histopathological features of PXE and vitamin K-dependent clotting factor deficiency led us to a diagnosis of PXE-like syndrome. A molecular study of the GGCX gene showed compound heterozygosity. The GGCX gene is usually responsible for PXE-like syndrome. GGCX encodes a γ-glutamyl carboxylase necessary for activation of gla-proteins. Gla-proteins are involved both in coagulation factors in the liver and in the prevention of ectopic mineralization of soft tissues. Uncarboxylated forms of gla-proteins in fibroblast would thus enable mineralization and fragmentation of elastic fibers.

Reversing the Effect of Oral Anticoagulant Drugs: Established and Newer Options.

The vitamin K antagonists (VKAs) have been the standard (and only) oral anticoagulants used for the long-term treatment or prevention of venous thromboembolism or stroke in patients with atrial fibrillation. The coagulopathy induced by VKAs can be reversed with vitamin K, and in urgent situations, the vitamin K-dependent coagulation factors can be replaced by transfusion. In the last decade, a new class of oral anticoagulants has been developed, direct oral anticoagulants that bind to a specific coagulation factor and neutralize it. These compounds were shown to be effective and safe compared with the VKAs and were licensed for specific indications, but without a specific reversal agent. The absence of a reversal agent is a barrier to more widespread use of these agents. Currently, for the management of major life-threatening bleeding with the direct oral anticoagulants, most authorities recommend the use of four factor prothrombin complex concentrates. There are now three reversal agents in development and poised to enter the market. Idarucizumab is a specific antidote targeted to reverse the direct thrombin inhibitor, dabigatran, which was recently approved for use in the USA. Andexanet alfa is an antidote targeted to reverse the oral direct factor Xa inhibitors as well as the indirect inhibitor enoxaparin. Ciraparantag is an antidote targeted to reverse the direct thrombin and factor Xa inhibitors as well as the indirect inhibitor enoxaparin.

Origin of the gender differences of the natural resistance to antivitamin K anticoagulants in rats.

Vitamin K antagonists (VKA) are used either in human medicine to prevent thromboembolic disorders or as rodenticides for pest control management. In rodents, female rats are described to be more tolerant to the action of vitamin K antagonists than males. Nevertheless, the mechanism of this greatest tolerance is still unknown and this study aims to identify the origin of this greatest tolerance after VKA administration. Therefore, difethialone, one of the most powerful VKA was used in this study. A possible difference in the pharmacokinetics of difethialone between males and females was first investigated. The determination of the pharmacokinetic parameters allowed to exclude a pharmacokinetic origin of the greatest tolerance of females to VKA. Thus, a natural resistance to difethialone of the liver VKOR activity, which is the target of VKA, was thus explored in females. The determination of Ki towards difethialone in liver microsomes allowed to also exclude this hypothesis. Therefore, equipment in vitamin K-dependent clotting factors and properties of vitamin K-dependent clotting factors were explored. Basal activity of clotting factors VII and X were found significantly higher in females of respectively 43% and 21%. Moreover, after VKA administration, half-lives of clotting factors II and X were found significantly longer in females of respectively 27% and 10% and a lag time of 4h before the beginning of the decay of factor VII was observed only in females after difethialone administration. The greater tolerance of female rats to VKA is thus due a stronger basal pool of vitamin K-dependent clotting factors VII and X and to a slower decline of vitamin K-dependent clotting factors II, VII and X after VKA administration.

経口抗凝固療法に関連する二大合併症（頭蓋内出血，血栓症／血栓弁）の治療，及び併発時の管理

Warfarinによる経口抗凝固薬療法には，効果不足に起因する血栓性合併症と，効果過剰に起因する出血性合併症という双方のリスクが伴う．後者の中で特に重大な合併症である頭蓋内出血の死亡率は50％を超える．予後改善には早急かつ完全なWarfarin拮抗が必須である．新鮮凍結血漿が第一選択だが，Vitamin K依存性凝固因子の含有量が製剤間で異なり必要量が一概に予測できない，拮抗に時間を要する，容量負荷が大きいという側面を有する．緊急時には血液凝固第IX因子複合体が有用だが，適応外使用である．Warfarin拮抗の際には同時に血栓塞栓症の予防も念頭に置かなければならず，特に機械弁挿入患者では完全な止血を確認後，早期からヘパリンを併用し，発症1～2週間でWarfarin再開を考慮する．また機械弁不全をみた場合，血栓溶解療法を行うか否かには血栓弁とパンヌスの鑑別が重要である．さらに頭蓋内出血既往例が血栓弁を生じた場合，血栓溶解療法は禁忌に準じると考えるべきである．

Prothrombin Membrane Binding and Gla-Dependent Function Are Not Required for Effective Hemostasis In Vivo

Prothrombin, like other vitamin K-dependent coagulation factors, undergoes γ-carboxylation of its Gla domain, a posttranslational modification critical for membrane binding. In patients on anticoagulant treatment with warfarin, the INR has historically been correlated with the degree of des-gamma-carboxy-prothrombin (DCP or PIVKA-II). PIVKA-II can be measured readily and used as a marker for vitamin K deficiency or warfarin therapy and is thought to be useful in detecting subclinical disease. Long-standing dogma suggests prothrombin γ-carboxylation is necessary for prothrombin membrane binding facilitating engagement with prothrombinase leading to rapid thrombin generation and effective hemostasis. However, recent studies indicate that despite an inability to bind membranes, uncarboxylated (desGla) full-length prothrombin demonstrated an unexpected modest decrease in the rate of thrombin generation (J Biol Chem 2013, 288:27789-800). Thus, it is possible loss of prothrombin γ-carboxylation, and thereby membrane binding, is far less significant for prothrombin activation than previously appreciated. Instead warfarin's effect on other coagulation factors (FX, FIX, and FVII) may be the primary causative determinant impairing hemostasis in these anticoagulated patients.To test these ideas, we first analyzed thrombin generation using recombinant full-length fully carboxylated and desGla prothrombin in vitro. Human prothrombin deficient plasma (Factor II activity <4%) was reconstituted to normal levels (100 μg/mL) with desGla or carboxylated prothrombin. DesGla prothrombin generated approximately half the amount of thrombin observed in carboxylated prothrombin plasma and normal human plasma controls.We next analyzed full-length desGla prothrombin's in vivo hemostatic function. A prothrombin anti-sense oligonucleotide (ASO) was administered to hemostatically normal mice to knock down endogenous murine prothrombin expression (<0.1-1μg/mL, 0.1-1%) and confirmed by ELISA analysis. Hemostasis was analyzed by the ferric chloride (FeCl3) carotid artery injury model. In mice treated with an ASO control, vessel occlusion occurred at approximately 8 minutes while mice treated with the prothrombin ASO did not clot during the 30-minute post injury observation period. In additional experiments two minutes following injury, prothrombin ASO treated mice were administered either carboxylated or desGla recombinant prothrombin to restore plasma concentrations to the normal range (100 μg/mL). Remarkably, administration of either desGla or carboxylated prothrombin restored vessel occlusion to ASO control findings, with minimal variability observed between desGla and carboxylated prothrombin treated mice (Figure 1).Warfarin treatment results in impaired prothrombin γ-carboxylation. However, if prothrombin γ-carboxylation, is, in fact, not necessary for prothrombin activation, fully carboxylated Factor Xa (FXa) should reverse the effects of warfarin by efficiently activating the un/under-carboxylated prothrombin thereby bypassing the other warfarin-affected factors. To study this, we used a "zymogen-like" factor Xa (FXaI16L) molecule previously developed by our group (Nat. Biotech 2011, 29:1028-33) that has a greater half-life than the wild-type protein. In thrombin generation assays, addition of 1nM FXaI16L to plasma from patients anticoagulated with warfarin, irrespective on INR (2.8, 4,4 7.1), resulted in thrombin generation comparable to that of normal human plasma. Importantly, similar results were obtained in vivo in warfarin-anticoagulated mice (INR 2-3). Administration of 3 mg/kg FXaI16L to 8 out of 8 warfarin mice corrected the time to carotid artery occlusion in the FeCl3 injury model.In two separate in vitro and in vivo model systems, we demonstrated that prothrombin membrane binding is not absolutely required for thrombin generation. Thrombin is unique among the coagulation serine proteases in that it does not have a Gla domain once fully processed by prothrombinase; thus, the absence of a Gla domain in the protease (thrombin) may explain the lack of a requirement for membrane binding by the zymogen (prothrombin) precursor. Our findings may also have clinical relevance, since they suggest that FXa (or a variant) could be used as a novel warfarin bypass strategy to rapidly achieve hemostasis in the setting of warfarin anticoagulation. [Display omitted] DisclosuresGreene:Baxter: Research Funding. Camire:Spark Therapeutics: Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Patents & Royalties, Research Funding; NovoNordisk: Research Funding.