Thomas Vanassche

Real-world variability in dabigatran levels in patients with atrial fibrillation.

(Randomized Evaluation of Long-Term Anticoagulation Therapy). J Am Coll Cardiol 2014; 63: 321–8. 9 Douxfils J, Dogne JM, Mullier F, Chatelain B, Ronquist-Nii Y, Malmstrom RE, Hjemdahl P. Comparison of calibrated dilute thrombin time and aPTT tests with LC-MS/MS for the therapeutic monitoring of patients treated with dabigatran etexilate. Thromb Haemost 2013; 110: 543–9. 10 Douxfils J, Mullier F, Robert S, Chatelain C, Chatelain B, Dogne JM. Impact of dabigatran on a large panel of routine or specific coagulation assays. Laboratory recommendations for monitoring of dabigatran etexilate. Thromb Haemost 2012; 107: 985–97. 11 Antovic JP, Skeppholm M, Eintrei J, Boija EE, Soderblom L, Norberg EM, Onelov L, Ronquist-Nii Y, Pohanka A, Beck O, Hjemdahl P, Malmstrom RE. Evaluation of coagulation assays versus LC-MS/MS for determinations of dabigatran concentrations in plasma. Eur J Clin Pharmacol 2013; 69: 1875–81. 12 Skeppholm M, Hjemdahl P, Antovic JP, Muhrbeck J, Eintrei J, Ronquist-Nii Y, Pohanka A, Beck O, Malmstrom RE. On the monitoring of dabigatran treatment in “real life” patients with atrial fibrillation. Thromb Res 2014; 134: 783–9. 13 Hawes EM, Deal AM, Funk-Adcock D, Gosselin R, Jeanneret C, Cook AM, Taylor JM, Whinna HC, Winkler AM, Moll S. Performance of coagulation tests in patients on therapeutic doses of dabigatran: a cross-sectional pharmacodynamic study based on peak and trough plasma levels. J Thromb Haemost 2013; 11: 1493–502. 14 Rao RB. Regarding the effect of dabigatran plasma concentrations. J Am Coll Cardiol 2014; 63: 2885.

Adhesion of Staphylococcus aureus to the vessel wall under flow is mediated by von Willebrand factor-binding protein

Adhesion of Staphylococcus aureus to blood vessels under shear stress requires von Willebrand factor (VWF). Several bacterial factors have been proposed to interact with VWF, including VWF-binding protein (vWbp), a secreted coagulase that activates the hosts prothrombin to generate fibrin. We measured the adhesion of S aureus Newman and a vWbp-deficient mutant (vwb) to VWF, collagen, and activated endothelial cells in a microparallel flow chamber. In vivo adhesion of S aureus was evaluated in the mesenteric circulation of wild-type (WT) and VWF-deficient mice. We found a shear-dependent increase in adhesion of S aureus to the (sub)endothelium that was dependent on interactions between vWbp and the A1-domain of VWF. Adhesion was further enhanced by coagulase-mediated fibrin formation that clustered bacteria and recruited platelets into bacterial microthrombi. In vivo, deficiency of vWbp or VWF as well as inhibition of coagulase activity reduced S aureus adhesion. We conclude that vWbp contributes to vascular adhesion of S aureus through 2 independent mechanisms: shear-mediated binding to VWF and activation of prothrombin to form S aureus-fibrin-platelet aggregates.

Abnormal uterine bleeding in VTE patients treated with rivaroxaban compared to vitamin K antagonists

INTRODUCTION Rivaroxaban is a convenient oral anticoagulant for patients with venous thromboembolism (VTE). The impact of rivaroxaban and vitamin K antagonists (VKAs) on abnormal uterine bleeding (AUB) in real life has not been previously explored. MATERIALS AND METHODS We performed a single-center retrospective study on AUB in female VTE patients of reproductive age who were treated with either rivaroxaban or VKAs. RESULTS Questionnaire results were available for 52 patients in each treatment group. Approximately two thirds of all women reported AUB after initiation of anticoagulant therapy. Patients using rivaroxaban were more likely to experience prolonged (>8days) menstrual bleeding (27 % vs. 8.3%, P=0.017). Rivaroxaban treatment increased the duration of menstrual bleeding from median 5 (IQR 3.5-6.0) days before start of treatment to 6 (IQR 4.1-8.9) days (P<0.001). VKA treatment did not lead to significant prolongation of the menstrual period. Patients on rivaroxaban more frequently reported an unscheduled contact with a physician for AUB than women using VKAs (41% vs. 25%, P=0.096). They also reported increased need for menorrhagia-related medical or surgical intervention (25% vs. 7.7%, P=0.032) and had more adaptations of anticoagulant therapy (15% vs. 1.9%, P=0.031). CONCLUSION AUB is frequent after initiation of anticoagulant therapy for acute symptomatic VTE. Compared to VKAs, rivaroxaban was associated with prolonged menstrual bleeding and more medical interventions and adaptation of anticoagulant treatment for AUB. These data can guide proactive discussion with patients starting anticoagulant therapy.

Inhibition of staphylothrombin by dabigatran reduces Staphylococcus aureus virulence

Summary.  Background: Staphylocoagulase and von Willebrand binding protein (VWbp) bind to prothrombin to form the staphylothrombin complex that converts fibrinogen into fibrin. Objectives: To study the role of staphylothrombin and its inhibition by dabigatran on Staphylococcus aureus virulence. Methods: We studied the effect of staphylothrombin inhibition on bacterial attachment to polystyrene surfaces, leukocyte activation and bactericidal activity for S. aureus ATCC 25923, S. aureus Newman, and staphylocoagulase‐ and VWbp‐negative S. aureus Newman mutants in the presence or absence of prothrombin and fibrinogen. We measured the abscess size after subcutaneous (s.c.) injection of S. aureus ATCC 25923 and S. aureus Newman, as well as an S. aureus Newman mutant strain lacking staphylocoagulase and VWbp, in mice treated with either dabigatran or placebo. Results: Staphylothrombin‐mediated fibrin increased the association of S. aureus to polystyrene surfaces and reduced the bactericidal activity of leukocytes. The absence or inhibition of staphylothrombin decreased the bacterial association, enhanced leukocyte activation and reduced bacterial survival in vitro. Abscess size was smaller in mice treated with dabigatran or infected with a coagulase‐negative mutant. Conclusion: Inhibition or the absence of staphylothrombin reduced S. aureus virulence in in vitro and in vivo models.

Embolic strokes of undetermined source: Prevalence and patient features in the ESUS Global Registry:

Background Recent evidence supports that most non-lacunar cryptogenic strokes are embolic. Accordingly, these strokes have been designated as embolic strokes of undetermined source (ESUS). Aims We undertook an international survey to characterize the frequency and clinical features of ESUS patients across global regions. Methods Consecutive patients hospitalized for ischemic stroke were retrospectively surveyed from 19 stroke research centers in 19 different countries to collect patients meeting criteria for ESUS. Results Of 2144 patients with recent ischemic stroke, 351 (16%, 95% CI 15% to 18%) met ESUS criteria, similar across global regions (range 16% to 21%), and an additional 308 (14%) patients had incomplete evaluation required for ESUS diagnosis. The mean age of ESUS patients (62 years; SD = 15) was significantly lower than the 1793 non-ESUS ischemic stroke patients (68 years, p ≤ 0.001). Excluding patients with atrial fibrillation (n = 590, mean age = 75 years), the mean age of the remaining 1203 non-ESUS ischemic stroke patients was 64 years (p = 0.02 vs. ESUS patients). Among ESUS patients, hypertension, diabetes, and prior stroke were present in 64%, 25%, and 17%, respectively. Median NIHSS score was 4 (interquartile range 2–8). At discharge, 90% of ESUS patients received antiplatelet therapy and 7% received anticoagulation. Conclusions This cross-sectional global sample of patients with recent ischemic stroke shows that one-sixth met criteria for ESUS, with additional ESUS patients likely among those with incomplete diagnostic investigation. ESUS patients were relatively young with mild strokes. Antiplatelet therapy was the standard antithrombotic therapy for secondary stroke prevention in all global regions.

Monitoring and reversal strategies for new oral anticoagulants

Thrombin inhibitor dabigatran and factor Xa inhibitors rivaroxaban, apixaban and edoxaban form a new class of non-vitamin K antagonist oral anticoagulants and have been extensively studied in patients with venous thromboembolism and atrial fibrillation. They offer anticoagulation that is as effective and at least as safe compared to warfarin without the need for routine laboratory monitoring; however, no reversal strategies are currently validated in case of a non-vitamin K antagonist oral anticoagulant-associated bleed. In emergency situations, laboratory drug measurement and well-defined management for non-vitamin K antagonist oral anticoagulant-induced hemorrhage may improve clinical outcome. In this review, the merits and limitations of the routine coagulation tests and some of the more specific laboratory assays are compared. Furthermore, prohemostatic measures are reviewed and the recommended strategies in case of bleeding are summarized. Specific reversal agents are currently under development (idarucizumab for dabigatran, andexanet alfa for Xa inhibitors, and PER977 for both Xa- and thrombin inhibitors), which will facilitate clinical management of severe bleeding and emergency surgery.

Fibrin formation by staphylothrombin facilitates Staphylococcus aureus -induced platelet aggregation

Interactions of Staphylococcus aureus (S. aureus) and platelets play an important role in the pathogenesis of intravascular infections such as infective endocarditis (IE). A typical feature of S. aureus is the ability to generate thrombin activity through the secretion of two prothrombin activating molecules, staphylocoagulase and von Willebrand factor-binding protein (vWbp), which bind to human prothrombin to form the enzymatically active staphylothrombin complex. The role of staphylothrombin in the interaction between S. aureus and platelets has not yet been studied. We found that in contrast with thrombin, staphylothrombin did not directly activate human platelets. However, the staphylothrombin-mediated conversion of fibrinogen to fibrin initiated platelet aggregation and secondary activation and facilitated S. aureus-platelet interactions. Both the genetic absence of staphylocoagulase and vWbp and pharmacological inhibition of staphylothrombin increased the lag time to aggregation, and reduced platelet trapping by S. aureus in high shear stress conditions. The combined inhibition of staphylothrombin and immunoglobulin binding to platelets completely abolished the ability of S. aureus to aggregate platelets in vitro. In conclusion, although staphylothrombin did not directly activate platelets, the formation of a fibrin scaffold facilitated bacteria-platelet interaction, and the inhibition of staphylothrombin resulted in a reduced activation of platelets by S. aureus.

The role of staphylothrombin-mediated fibrin deposition in catheter-related Staphylococcus aureus infections

Staphylococcus aureus (S. aureus) is a frequent cause of catheter-related infections. S. aureus secretes the coagulases staphylocoagulase and von Willebrand factor-binding protein, both of which form a staphylothrombin complex upon binding to prothrombin. Although fibrinogen and fibrin facilitate the adhesion of S. aureus to catheters, the contribution of staphylothrombin-mediated fibrin has not been examined. In this study, we use a S. aureus mutant lacking both coagulases (Δcoa/vwb) and dabigatran, a pharmacological inhibitor of both staphylothrombin and thrombin, to address this question. Genetic absence or chemical inhibition of pathogen-driven coagulation reduced both fibrin deposition and the retention of S. aureus on catheters in vitro. In a mouse model of jugular vein catheter infection, dabigatran reduced bacterial load on jugular vein catheters, as well as metastatic kidney infection. Importantly, inhibition of staphylothrombin improved the efficacy of vancomycin treatment both in vitro and in the mouse model.

Dabigatran Inhibits Staphylococcus aureus Coagulase Activity

ABSTRACT The ability of Staphylococcus aureus to clot plasma through conformational activation of prothrombin by staphylocoagulase is used to distinguish S. aureus from coagulase-negative staphylococci. We show that while the direct thrombin inhibitor dabigatran inhibits staphylocoagulase activity, the clinical use of dabigatran etexilate is not expected to interfere with direct tube coagulase testing.

Role of phenotypic and genetic testing in managing clopidogrel therapy.

The P2Y12 inhibitors, clopidogrel, prasugrel, and ticagrelor, are administered in fixed doses without laboratory monitoring. Randomized trials in acute coronary syndrome have shown that prasugrel and ticagrelor are more effective than standard-dose clopidogrel. Nonetheless, standard-dose clopidogrel remains widely used because it causes less bleeding and is less expensive. Patients treated with standard-dose clopidogrel have substantial variability in platelet inhibition, which is partly explained by genetic polymorphisms encoding CYP2C19, the hepatic enzyme involved in biotransformation of clopidogrel to its active metabolite. Some advocate tailoring P2Y12 inhibitor therapy according to the results of routine laboratory testing. Although there is good evidence for analytic, biological, and clinical validity of several phenotypic and genotypic biomarkers, the benefit of a management strategy that incorporates routine biomarker testing over standard of care without such testing remains unproven. Appropriately designed, adequately powered trials are needed but face the challenges of feasibility, cost, and the progressive switch from clopidogrel to prasugrel or ticagrelor.