Immobilization of actively thromboresistant assemblies on sterile blood-contacting surfaces.

Rapid one-step modification of thrombomodulin with alkylamine derivatives such as azide, biotin, and PEG is achieved using an evolved sortase (eSrtA) mutant. The feasibility of a point-of-care scheme is demonstrated herein to site-specifically immobilize azido-thrombomodulin on sterilized commercial ePTFE vascular grafts, which exhibit superior thromboresistance compared with commercial heparin-coated grafts in a primate model of acute graft thrombosis.

Reversal of rivaroxaban anticoagulation by haemostatic agents in rats and primates.

Rivaroxaban is an oral, direct factor Xa inhibitor for the management of thromboembolic disorders. Despite its short half-life, the ability to reverse rivaroxaban anticoagulation could be beneficial in life-threatening emergencies. The potential of prothrombin complex concentrate (PCC; Beriplex®), activated PCC (aPCC; FEIBA®) or recombinant activated factor VII (rFVIIa; NovoSeven®) to reverse rivaroxaban in rats and baboons was investigated.

A biologically active surface enzyme assembly that attenuates thrombus formation.

Activation of hemostatic pathways by blood-contacting materials remains a major hurdle in the development of clinically durable artificial organs and implantable devices. We postulate that surface-induced thrombosis may be attenuated by the reconstitution onto blood contacting surfaces of bioactive enzymes that regulate the production of thrombin, a central mediator of both clotting and platelet activation cascades. Thrombomodulin (TM), a transmembrane protein expressed by endothelial cells, is an established negative regulator of thrombin generation in the circulatory system.

Safety and antithrombotic efficacy of moderate platelet count reduction by thrombopoietin inhibition in primates.

Most heart attacks and strokes are caused by blood clots (thrombi) that block the vasculature. Because disease-causing arterial thrombosis depends on blood platelets, platelet inhibitors such as aspirin and clopidogrel effectively decrease the risk of thrombosis; however, they also impair platelet-dependent hemostasis that staunches bleeding from wounds and can therefore produce excessive bleeding. Experimental studies show that a reduction in the number of platelets also inhibits thrombosis, but these treatments also interfere with platelet function.

Inhibition of acute vascular thrombosis in chimpanzees by an anti-human tissue factor antibody targeting the factor X binding site.

Tissue factor (TF) antagonists targeting the factor VII (FVII) binding domain have been shown to interrupt acute vascular thrombus formation without impairing haemostasis in non-human primates. In this study, we evaluate whether a human/mouse chimeric monoclonal antibody (ALT-836, formerly known as Sunol-cH36) blocking the factor X/factor IX (FX/FIX) binding site of tissue factor could achieve similar clinical benefits in an arterial thrombosis model induced by surgical endarterectomy in chimpanzees. In this model, sequential surgical endarterectomies on right and left superficial femoral arteries were performed 30 days apart in five chimpanzees.

Prevention of vascular graft occlusion and thrombus-associated thrombin generation by inhibition of factor XI.

The protease thrombin is required for normal hemostasis and pathologic thrombogenesis. Since the mechanism of coagulation factor XI (FXI)-dependent thrombus growth remains unclear, we investigated the contribution of FXI to thrombus formation in a primate thrombosis model. Pretreatment of baboons with a novel anti-human FXI monoclonal antibody (aXIMab; 2 mg/kg) inhibited plasma FXI by at least 99% for 10 days, and suppressed thrombin-antithrombin (TAT) complex and beta-thromboglobulin (betaTG) formation measured immediately downstream from thrombi forming within collagen-coated vascular grafts.

Capture of flowing endothelial cells using surface-immobilized anti-kinase insert domain receptor antibody.

In humans, self-endothelialization of synthetic grafts is severely limited, but a recent interesting idea is to attract endothelial progenitor cells (EPCs) from peripheral blood onto grafts via antibodies directed at proposed EPC markers. Results with anti-CD34 antibodies have shown some promise, but it is unclear whether CD34 is the best marker for cells with re-endothelializing potential. Much evidence points to kinase insert domain receptor (KDR) as an important indicator of endothelial potential if not a definitive marker.

Procoagulant properties of flow fields in stenotic and expansive orifices.

In the United States, over 125,000 mechanical heart valves (MHVs) are implanted each year. Flow through the MHV hinge can cause thromboemboli formation. The purpose of this study was to examine various orifice geometries representing the MHV hinge region and how these geometries may contribute to platelet activation and thrombin generation.

Fibrinogen gamma' chain carboxy terminal peptide selectively inhibits the intrinsic coagulation pathway.

The minor gammaA/gamma' isoform of fibrinogen contains a high affinity binding site for thrombin exosite II that is lacking in the major fibrinogen isoform, gammaA/gammaA fibrinogen. The biological consequences of gamma' chain binding to thrombin were therefore investigated. Coagulation assays, thrombin activity assays, and a primate thrombosis model were used to characterize the biological effects of the gamma' 410-427 peptide.

Thrombin formation in vitro in response to shear-induced activation of platelets.

Introduction: Thromboembolic events caused by implanted vascular devices present serious medical challenges. In particular bileaflet mechanical heart valves (MHVs) are prone to thrombus formation in the hinge region due to a combination of high shear stress and stagnation regions. Most studies of shear-induced platelet activation and aggregation have been performed using viscometers, parallel plate flow, and other non-physiologic in vitro configurations.

Relative antithrombotic and antihemostatic effects of protein C activator versus low-molecular-weight heparin in primates.

The anticoagulant and anti-inflammatory enzyme, activated protein C (APC), naturally controls thrombosis without affecting hemostasis. We therefore evaluated whether the integrity of primary hemostasis was preserved during limited pharmacological antithrombotic protein C activator (PCA) treatment in baboons. The double-mutant thrombin (Trp215Ala/Glu217Ala) with less than 1% procoagulant activity was used as a relatively selective PCA and compared with systemic anticoagulation by APC and low-molecular-weight heparin (LMWH) at doses that inhibited fibrin deposition on thrombogenic segments of arteriovenous shunts.

Flow and thrombosis at orifices simulating mechanical heart valve leakage regions.

Background: While it is established that mechanical heart valves (MHVs) damage blood elements during leakage and forward flow, the role in thrombus formation of platelet activation by high shear flow geometries remains unclear. In this study, continuously recalcified blood was used to measure the effects of blood flow through orifices, which model MHVs, on the generation of procoagulant thrombin and the resulting formation of thrombus. The contribution of platelets to this process was also assessed.

Factor VIIa inhibitors: chemical optimization, preclinical pharmacokinetics, pharmacodynamics, and efficacy in an arterial baboon thrombosis model.

Highly selective and potent factor VIIa-tissue factor (fVIIa.TF) complex inhibitors were generated through structure-based design. The pharmacokinetic properties of an optimized analog (9) were characterized in several preclinical species, demonstrating pharmacokinetic characteristics suitable for once-a-day dosing in humans.

Soluble thrombomodulin is antithrombotic in the presence of neutralising antibodies to protein C and reduces circulating activated protein C levels in primates.

We studied whether there was a relationship between the anticoagulant effects of recombinant human soluble thrombomodulin (rhsTM) and activation of protein C in a primate model of acute vascular graft thrombosis in 11 baboons (Papio species). Baboons were pretreated with 0.1, 1 and 5 mg/kg of rhsTM, with or without co-injection of a neutralising monoclonal antibody to protein C (HPC4) in the 1 mg/kg rhsTM group.