Marijke Peetermans

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.

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.

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.

Staphylokinase Control of Staphylococcus aureus Biofilm Formation and Detachment Through Host Plasminogen Activation

Staphylococcus aureus biofilms, a leading cause of persistent infections, are highly resistant to immune defenses and antimicrobial therapies. In the present study, we investigated the contribution of fibrin and staphylokinase (Sak) to biofilm formation. In both clinical S. aureus isolates and laboratory strains, high Sak-producing strains formed less biofilm than strains that lacked Sak, suggesting that Sak prevents biofilm formation. In addition, Sak induced detachment of mature biofilms. This effect depended on plasminogen activation by Sak. Host-derived fibrin, the main substrate cleaved by Sak-activated plasminogen, was a major component of biofilm matrix, and dissolution of this fibrin scaffold greatly increased susceptibility of biofilms to antibiotics and neutrophil phagocytosis. Sak also attenuated biofilm-associated catheter infections in mouse models. In conclusion, our results reveal a novel role for Sak-induced plasminogen activation that prevents S. aureus biofilm formation and induces detachment of existing biofilms through proteolytic cleavage of biofilm matrix components.

Idarucizumab for dabigatran overdose.

Abstract Context: An overdose of oral anticoagulants represents a challenging scenario for emergency physicians. Dabigatran, an oral direct thrombin inhibitor, is increasingly used in place of warfarin. The lack of an antidote is a concern in patients who overdose on dabigatran, even though the drug can be eliminated with hemodialysis. Idarucizumab is an antibody fragment that binds dabigatran with high affinity. It reverses the anticoagulant effect of dabigatran within minutes and is approved for the reversal of dabigatran during emergency situations. Case details: We describe the use of idarucizumab in the management of a 68-year-old woman who was taking dabigatran 150 mg twice daily and ingested 125 capsules. Despite gastric lavage and administration of activated charcoal within two hours of drug intake, the activated partial thromboplastin time (aPTT) and prothrombin time (PT) remained prolonged. The administration of 5 g of intravenous idarucizumab promptly and completely reversed the anticoagulant activity of dabigatran as assessed by routine and specific coagulation assays (aPTT from to 75 to 26 s, PT from 26 to 11 s and diluted thrombin time from 92 to 27 s). The initially planned emergency hemodialysis was canceled. Discussion: This case highlights the potential use of idarucizumab for the management of massive dabigatran overdoses.

Plasminogen activation by staphylokinase enhances local spreading of S. aureus in skin infections

BackgroundStaphylococcus aureus (S. aureus) is a frequent cause of skin and soft tissue infections. A unique feature of S. aureus is the combined presence of coagulases that trigger fibrin formation and of the plasminogen activator staphylokinase (SAK). Whereas the importance of fibrin generation for S. aureus virulence has been established, the role of SAK remains unclear.We studied the role of plasminogen activation by SAK in a skin infection model in mice and evaluated the impact of alpha-2-antiplasmin (α2AP) deficiency on the spreading and proteolytic activity of S. aureus skin infections. The species-selectivity of SAK was overcome by adenoviral expression of human plasminogen. Bacterial spread and density was assessed non-invasively by imaging the bioluminescence of S. aureus Xen36.ResultsSAK-mediated plasmin activity increased the local invasiveness of S. aureus, leading to larger lesions with skin disruption as well as decreased bacterial clearance by the host. Even though fibrin and bacterial surfaces protected SAK-mediated plasmin activity from inhibition by α2AP, the deficiency of α2AP resulted in increased bacterial spreading. SAK-mediated plasmin also induced secondary activation of gelatinases, shown both in vitro and in lesions from the in vivo model.ConclusionSAK contributes to the phenotype of S. aureus skin infections by enhancing bacterial spreading as a result of fibrinolytic and proteolytic activation.

Shear-Resistant Binding to von Willebrand Factor Allows Staphylococcus lugdunensis to Adhere to the Cardiac Valves and Initiate Endocarditis

BACKGROUND Staphylococcus lugdunensis is an emerging cause of endocarditis. To cause endovascular infections, S. lugdunensis requires mechanisms to overcome shear stress. We investigated whether platelets and von Willebrand factor (VWF) mediate bacterial adhesion to the vessel wall and the cardiac valves under flow. METHODS S. lugdunensis binding to VWF, collagen, and endothelial cells was studied in a parallel flow chamber in the absence and presence of platelets. In vivo adhesion of S. lugdunensis was evaluated in a mouse microvasculature perfusion model and a new mouse model of endocarditis. RESULTS Contrary to other coagulase-negative staphylococci, S. lugdunensis bound to VWF under flow, thus enabling its adhesion to endothelial cells and to the subendothelial matrix. In inflamed vessels of the mesenteric circulation, VWF recruited S. lugdunensis to the vessel wall. In a novel endocarditis mouse model, local inflammation and the resulting release of VWF enabled S. lugdunensis to bind and colonize the heart valves. CONCLUSIONS S. lugdunensis binds directly to VWF, which proved to be vital for withstanding shear forces and for its adhesion to the vessel wall and cardiac valves. This mechanism explains why S. lugdunensis causes more-aggressive infections, including endocarditis, compared with other coagulase-negative staphylococci.

Clumping factor A, von Willebrand factor-binding protein and von Willebrand factor anchor Staphylococcus aureus to the vessel wall.

Essentials Staphylococcus aureus (S. aureus) binds to endothelium via von Willebrand factor (VWF). Secreted VWF‐binding protein (vWbp) mediates S. aureus adhesion to VWF under shear stress. vWbp interacts with VWF and the Sortase A‐dependent surface protein Clumping factor A (ClfA). VWF‐vWbp‐ClfA anchor S. aureus to vascular endothelium under shear stress.

Coagulase Activity by Staphylococcus aureus: A Potential Target for Therapy?

Staphylococcus aureus is a leading cause of skin and soft tissue infections, foreign body infections, and infective endocarditis. In case of endovascular infection with S. aureus, higher rates of cardiac valve destruction, embolic complications, severe sepsis, and death occur. The unique capacity of S. aureus to induce clotting has been known for over a century; however, its role in virulence has long been controversial. S. aureus secretes two coagulases, staphylocoagulase and von Willebrand factor binding protein that both activate prothrombin to generate fibrin. A better understanding of the molecular mechanisms as well as the new strategies to target the coagulases have highlighted their importance in S. aureus virulence. Coagulase activity is essential for the formation of S. aureus-fibrin-platelet microaggregates and for the homing of S. aureus to the vascular wall under flow. Absence or inhibition of S. aureus coagulase activity improved outcome in disease models of skin infection, sepsis, catheter infection, and endocarditis. Here, we review how the manipulation of the hosts hemostatic system contributes to the disease-causing potential of S. aureus and discuss the S. aureus coagulases as promising targets for novel therapeutic strategies.