No description available.

To review the literature on treatment of venous thromboembolism (VTE) and prevention of cardioembolic stroke with direct-acting oral anticoagulants (DOACs) in low- and high-body-weight patients and to make recommendations regarding agent selection and dosing in these patient populations. Summary: The selection and optimal dosing of DOACs in low- and high-body-weight patients has not yet been fully elucidated by clinical trials; however, evidence suggests that issues of both safety and efficacy in patients at the extremes of body weight may warrant careful consideration when selecting a DOAC for such patients. This review provides a thorough discussion of the use of DOACs in the treatment of VTE and prevention of cardioembolic stroke in patients at the extremes of body weight and provides guidance regarding agent selection. Conclusion: While the published evidence on use of DOACs in patients at extremes of body weight is sparse, apixaban and rivaroxaban appear to have the most favorable safety and efficacy profiles. Edoxaban and dabigatran should be avoided.

Introduction : L'hémophilie est une maladie génétique de la coagulation due à un déficit en facteur VIII ou en facteur IX. Ces déficits sont responsables d'un déficit du complexe ténase intrinsèque (VIIIa-IXa). De plus, le complexe ténase extrinsèque (facteur tissulaire - VIIa) est physiologiquement rapidement inhibé par le TFPI lié au facteur Xa. Nous avons évalué la capacité d'une forme tronquée du facteur Xa (GDXa), dépourvue de domaine Gla à se lier au TFPI et à soulager l'inhibition physiologique du complexe ténase extrinsèque. Matériel et Méthodes : Dans une première partie, nous avons évalué la capacité du GDXa à restaurer la génération de thrombine de plasmas d'hémophiles A et B sévères sans et avec inhibiteurs. Nous avons également comparé les profils de génération de thrombine obtenus après addition du GDXa à ceux obtenus en présence d'anticorps neutralisants anti-TFPI ou anti-antithrombine. Enfin, nous avons comparé les cinétiques enzymatiques de neutralisation du facteur Xa et du GDXa par le TFPI et l'antithrombine. Dans une seconde partie, nous avons étudié in silico les interactions entre la chaîne lourde du facteur Xa et le TFPI pour détecter les zones d'interaction défavorables. Cette étude a identifié des acides aminés du facteur Xa qui pourraient être substitués pour optimiser l'interaction avec le TFPI. Les résultats in silico ont orienté nos choix de mutagenèse dirigée pour concevoir différents variants moléculaires du GDXa (R138F, R138G, R138I) où l'arginine 138 est substituée. Ces variants protéiques ont été produits de façon recombinante dans des cellules HEK293E. La capacité des différents variants à restaurer la génération de thrombine de plasmas d'hémophiles a été testée avec les surnageants de culture cellulaires correspondants. Résultats : Dans la première partie, nous avons montré que le GDXa est capable de restaurer la génération de thrombine de plasmas d'hémophiles A et B sans et avec inhibiteurs. Comparativement au facteur Xa, le GDXa montre une affinité moindre pour le TFPI tandis que les affinités du GDXa et du facteur Xa pour l'antithrombine sont identiques. Enfin, malgré une demi-vie courte, l'effet du GDXa sur la génération de thrombine est maintenu pendant au moins une heure. Dans la seconde partie, nous avons produit les différents variants R138F, R138G et R138I en cellules HEK293E et montré que les surnageants de culture cellulaire étaient capables de restaurer la génération de thrombine de plasmas d'hémophiles de façon plus efficace que le GDXa. Conclusion : Comme le GDXa est capable de restaurer la génération de thrombine de plasmas d'hémophiles, nos résultats suggèrent que le GDXa pourrait être une alternative efficace aux thérapeutiques hémostatiques court-circuitantes actuelles chez les hémophiles sans ou avec inhibiteurs. Les résultats obtenus renforcent l'hypothèse que l'activité pro-coagulante du GDXa serait liée à la formation d'un complexe GDXa-TFPI limitant la formation du complexe Xa-TFPI nécessaire à l'inhibition physiologique du complexe ténase extrinsèque. De plus, notre approche rationnelle basée sur une étude in silico visant à augmenter l'affinité du TFPI pour le GDXa a permis de produire différents variants moléculaires du GDXa dont l'activité procoagulante in vitro est augmentée par rapport au GDXa. / Background: Hemophilia is caused by deficiencies in coagulation factor VIII or IX, resulting in direct blockade of the intrinsic tenase complex and indirect blockade of the extrinsic tenase complex which is rapidly inhibited upon binding of factor Xa to tissue factor pathway inhibitor (TFPI). We evaluated the ability of Gla-domainless factor Xa (GDXa), a truncated form of factor Xa devoid of procoagulant properties, to bind to TFPI and to alleviate the physiological inhibition of the extrinsic tenase. Design and Methods: In the first part of this work, we evaluated the ability of GDXa to restore coagulation in plasmas from hemophilia A and B patients without and with inhibitors, using a thrombin generation assay triggered by a low concentration of tissue factor. We then compared its efficacy to generate thrombin to depletion of antithrombin or TFPI by specific antibodies. Finally, we compared the kinetics of neutralization of factor Xa and GDXa by antithrombin and TFPI. In the second part of this work, we realized an in silico study of the interactions between factor Xa heavy chain and TFPI. The aim was to detect unfavorable interactions and to identify amino-acid candidates for mutagenesis in order to increase affinity for TFPI. Taking into account the results of this in silico study, we produced by genic engienering different molecular variants of GDXa (R138F, R138G, R138I) where Arg138 was substituted by site directed mutagenesis. Proteins were produced in HEK293E cells. We tested dialyzed cell culture supernatants containing each variant to restore thrombin generation in plasmas from severe hemophilia patients. Results: In the first part of this work, we showed that GDXa was able to restore thrombin generation in plasma samples from hemophiliacs. This effect was observed for plasma from hemophilia A patients without or with inhibitors and for plasma from hemophilia B patients. GDXa had a lower affinity than factor Xa for TFPI whereas the affinities of both proteins for antithrombin were similar. Finally, despite a short half-life in plasma, the effect of GDXa on thrombin generation was sustained for at least one hour. In the second part of this work, we produced the different variants R138F, R138G et R138I in HEK293E cells and showed that cell culture supernatants were able to restore thrombin generation in a more efficient way than GDXa. Conclusions: As GDXa was able to restore thrombin generation in plasma from hemophilia patients, our results suggest that it may be an effective alternative to current treatments for hemophilia with or without inhibitors. Results sustained the hypothesis that GDXa coagulant activity is through TFPI binding and competition with factor Xa to bind TFPI resulting in limiting factor Xa-TFPI formation, which is essential for inhibition of extrinsic tenase complex. Furthermore, rational design of GDXa variants based on an in silico study lead to production of proteins whose coagulant activity is increased compared to GDXa."

The serine protease factor Xa (FXa) plays an integral role in the coagulation cascade and has recently been implicated in a variety of proinflammatory roles, establishing it as a link between coagulation and inflammatory processes. In this thesis, I elaborate on previous literature by characterizing further the response of primary human T lymphocytes to FXa. Building on previous literature that describes the effect of FXa on whole T cell populations, I describe here the effect of FXa on both antigen-independent and antigen-dependent proliferation and costimulation of primary CD4+ and CD8+ T cells, thereby establishing an immunological role for FXa. Further, I show that FXa elicits an immediate and direct effect on T cells demonstrated by the rapid upregulation of the signalling cascade kinases, ERK1 and ERK2. Lastly, I demonstrate that the protease activated receptor 2 (PAR2) is involved in the mediation of this direct FXa effect.

The serine protease factor Xa (FXa) plays an integral role in the coagulation cascade and has recently been implicated in a variety of proinflammatory roles, establishing it as a link between coagulation and inflammatory processes. In this thesis, I elaborate on previous literature by characterizing further the response of primary human T lymphocytes to FXa. Building on previous literature that describes the effect of FXa on whole T cell populations, I describe here the effect of FXa on both antigen-independent and antigen-dependent proliferation and costimulation of primary CD4+ and CD8+ T cells, thereby establishing an immunological role for FXa. Further, I show that FXa elicits an immediate and direct effect on T cells demonstrated by the rapid upregulation of the signalling cascade kinases, ERK1 and ERK2. Lastly, I demonstrate that the protease activated receptor 2 (PAR2) is involved in the mediation of this direct FXa effect.

No description available.

Study Objective Although data from the Regulation of Coagulation in Orthopedic Surgery to Prevent Deep Venous Thrombosis and Pulmonary Embolism (RECORD) 1-4 trials have shown a similar postoperative bleeding risk between rivaroxban and enoxaparin in patients undergoing total hip arthroplasty (THA) and total knee arthroplasty (TKA), anecdotal observations from local institutions have suggested that postoperative bleeding rates seemed higher in patients who received rivaroxaban than those reported in the RECORD trials. Thus, the objective of this pilot study was to assess postoperative bleeding events observed in clinical practice in patients receiving rivaroxaban after undergoing THA and TKA and to compare their results with those published in the RECORD trials. Design Retrospective cohort study with a comparator group of patients from the RECORD 1-4 trials. Setting Two institutions within a regional health care system. Patients Four hundred forty adults who received at least one dose of rivaroxaban 10 mg daily after undergoing THA or TKA in the two institutions between August 2011 and October 2013 (cohort group), and 6183 patients who received rivaroxaban in the RECORD 1-4 trials (comparator group). Measurements and Main Results Postoperative bleeding was assessed in the cohort patients versus the patients in the RECORD trials. The primary outcome, occurrence of any postoperative bleeding, was a composite of major and clinically relevant nonmajor bleeding as defined in the RECORD trials. Any postoperative bleeding occurred in 6.8% of the cohort patients versus 3.2% of the RECORD trial patients (p<0.0001); 1.4% of the cohort patients versus 0.38% of the RECORD trial patients suffered a major bleed (p=0.013). Within defined major bleeding, bleeding leading to reoperation and clinically overt extrasurgical site bleeding resulting in either a hemoglobin level decrease of at least 2 g/dl or transfusion of 2 units or greater of packed red blood cells were reported in 0.68% versus 0.19% (p=0.073) and 0.68% versus 0.13% (p=0.032), respectively, of the cohort patients versus the RECORD trial patients. Conclusion Overall, any postoperative bleeding in the cohort patients occurred significantly more frequently than that observed in the RECORD trial patients. The major bleeding rate was also significantly higher in the cohort patients, influenced by higher rates of bleeding leading to reoperation and clinically overt extrasurgical site bleeding resulting in either a hemoglobin decrease of at least 2 g/dl or transfusion of two units or greater of packed red blood cells. These findings from our pilot study are thought provoking and, thus, invite further investigation.

Intrinsic structural and conformational mechanisms regulate the functional specificity of the coagulation system. The study of these structure-function relationships is important for understanding the strategies used in the management of clinical thrombosis. Previous studies have shown that the central enzyme in clotting, thrombin, is sequestered inside of a clot, and protected from the natural downregulator antithrombin (AT). This is problematic for anticoagulants like heparin which depend on AT. Subsequently, it was found that the key upstream propagator of thrombin, the prothrombinase enzyme complex, is also resistant to the AT-heparin. Our data show that further upstream of prothrombinase, the intrinsic tenase is only moderately protected, while there is no protection at the level of the initiator complex, extrinsic tenase. This protection phenomenon possibly reflects steric and allosteric mechanisms that ensure maximal activation of the coagulation system once a threshold stimulus is achieved. These mechanisms likely evolved as a result of conformational rearrangement, as evidenced by the proteolytic activation of thrombin activity following proteolysis of prothrombin. Indeed, subtle differences in the structural interaction of ligands with the active site can lead to substantial differences in enzyme activity. The binding of rivaroxaban and apixaban to factor Xa is nearly identical; both interact with the active site with comparable affinity. Despite this, a 3-fold faster rate of the rivaroxaban on-rate yields significantly greater prolongation of the prothrombin time (PT) and activated partial thromboplastin time (aPTT), global tests of coagulation. These small differences in ligand interaction also have allosteric consequences. Structural differences between the direct thrombin inhibitors dabigatran and argatroban yield divergent exosite-mediated thrombin binding to physiologic ligands like yA-fibrin, y'-fibrin, factor Va, and factor VIII, interactions that govern clot-mediated protection from AT inhibition, and the various functions of thrombin. These divergent effects were robust and ligand-dependent, suggesting conserved energetic scaffolds within the thrombin molecule that govern allosteric changes throughout the molecule. Because proteolysis of prothrombin yields significant allosteric and structural rearrangement that capacitates the active site for substrate recognition amd catalytic ability, we investigated the role of Ser195, a key residue in the thrombin catalytic triad in also regulating thrombin allostery. Site directed mutagenesis of Ser195 to Ala yielded a significant increase in the flexibility of the entire thrombin molecule, as evidenced by increased potency of dabigatran and argatroban in terms of their capacity to modulate exosite binding through the active site, and increased interexosite cooperative and competitive allostery. Together, these studies represent an advance in our understanding of the consequences of both small molecule ligation of coagulation proteases, as well as the consequences of subtle structural modification for overall allosteric function. / Thesis / Doctor of Philosophy (PhD)

Direct factor Xa inhibitors (FXaI) account for most oral anticoagulant use. FXaI-associated bleeding events are common and are associated with substantial morbidity and mortality. Nonspecific hemostatic therapies such as prothrombin complex concentrates (PCC) are often administered for FXaI-associated bleeding. The mechanism by which these agents improve hemostasis in the setting of direct oral anticoagulation is unclear. Thrombin generation assays may effectively measure the effect of anticoagulation reversal among FXaI-treated patients when bleeding cessation would otherwise be challenging to measure. To build a research program on the utility of thrombin generation assays to measure both the impact of direct oral anticoagulation and anticoagulation reversal, we completed a review of the literature with narrative synthesis and carried out a pilot study to determine the feasibility of a full scale prospective observational study of TGA responses among patients receiving PCC for FXaI-associated major bleeding or needing urgent surgery.

The influences of posttranslational modifications on the functions of the versatile serpin protein C inhibitor (PCI) were studied. PCI is a serine protease inhibitor that is expressed in many tissues and secreted to various fluids in human, including blood plasma, seminal plasma, and urine. PCI in blood can act both as an anticoagulant and a procoagulant and is believed to play a role in pathogen defence. PCI in reproductive tissues is believed to regulate human reproduction at several steps, including the fertilization process. Due to the broad protease specificity and the contradictory activities, the physiological role of PCI is elusive. In this work the inhibitor was purified from blood and seminal plasma by immunoaffinity chromatography. Blood-derived PCI was found to be highly heterogeneous, due to variations in posttranslational modifications. The occupancy and structures of N- and O-glycans attached to blood plasma PCI and N-glycans of seminal plasma PCI were determined by mass spectrometry. An O-glycosylation site at Thr 20 was identified in PCI derived from blood. N-glycan structures of PCI isolated from blood and seminal plasma differed markedly, demonstrating that they are expressed in a tissue-specific manner. Proteolytic processing also appeared to be tissue-specific, since N-terminally cleaved PCI was found in PCI isolated both from blood and seminal plasma, but the length of the lacking segment differed. The effects of the N-linked glycans and the N-terminus of PCI on protease inhibition were determined using enzymatic measurements with chromogenic substrates. The N-glycans and the N-terminus had different effects on the inhibition of thrombin, factor Xa and prostate specific antigen, demonstrating that posttranslational modifications of PCI affect its functional specificity. These findings enhance the understanding of the regulation of the various functions of PCI and may potentially be used for the production of specialized PCI variants for medical purposes.