Exosite crosstalk in thrombin.

Thrombin is the central mediator of hemostasis, where it converts fibrinogen to fibrin, activates upstream factors to promote coagulation, activates factor XIII and thrombin-activatable fibrinolysis inhibitor to stabilize fibrin, mediates anticoagulation, and modulates cellular activity via cell surface receptors. Thus, regulation of thrombin activity is essential to the hemostatic balance. Thrombin is regulated by positively charged surface domains that surround the active site.

Abelacimab versus Rivaroxaban in Patients with Atrial Fibrillation.

Background: Abelacimab is a fully human monoclonal antibody that binds to the inactive form of factor XI and blocks its activation. The safety of abelacimab as compared with a direct oral anticoagulant in patients with atrial fibrillation is unknown.

Methods: Patients with atrial fibrillation and a moderate-to-high risk of stroke were randomly assigned, in a 1:1:1 ratio, to receive subcutaneous injection of abelacimab (150 mg or 90 mg once monthly) administered in a blinded fashion or oral rivaroxaban (20 mg once daily) administered in an open-label fashion.

Antithrombotic Strategies for Patients With Peripheral Artery Disease: JACC Scientific Statement.

Patients with peripheral artery disease (PAD) experience major cardiovascular and limb events. Antithrombotic strategies including antiplatelets and anticoagulants remain a cornerstone of treatment and prevention. Recent trials have shown heterogeneity in the response to antithrombotic therapies in patients presenting primarily with PAD when compared to those presenting primarily with coronary artery disease.

Reversal of direct oral anticoagulants: guidance from the SSC of the ISTH.

The currently approved direct oral anticoagulants (DOACs) are increasingly used in clinical practice. Although serious bleeding risks are lower with DOACs than with vitamin K antagonists, bleeding remains the most frequent side effect. Andexanet alfa and idarucizumab are the currently approved specific reversal agents for oral factor (F)Xa inhibitors and dabigatran, respectively.

Prothrombin complex concentrate for emergency surgery in patients on oral Xa-inhibitors.

Background: It is uncertain whether prothrombin complex concentrate (PCC) improves hemostasis in patients on treatment with oral factor Xa-inhibitors (XaI) who require emergency surgery.

Objectives: To evaluate whether, in patients with therapeutic levels of oral XaI, preoperative PCC prevents excessive bleeding during and after emergency surgery and is not associated with thrombotic complications.

Methods: We conducted a prospective cohort study wherein a fixed 2000 IU dose of 4-factor PCC was given to patients taking oral XaI with plasma XaI levels of at least 75 ng/mL before the emergency surgery with an expected blood loss of at least 50 mL.

Histidine-Rich Glycoprotein Modulates the Toxic Effects of High-Dose Polyphosphate in Mice.

Background: Polyphosphate (polyP), a procoagulant released from platelets, activates coagulation via the contact system and modulates cardiomyocyte viability. High-dose intravenous polyP is lethal in mice, presumably because of thrombosis. Previously, we showed that HRG (histidine-rich glycoprotein) binds polyP and attenuates its procoagulant effects.

Optimization of plasma-based BioID identifies plasminogen as a ligand of ADAMTS13.

ADAMTS13, a disintegrin and metalloprotease with a thrombospondin type 1 motif, member 13, regulates the length of Von Willebrand factor (VWF) multimers and their platelet-binding activity. ADAMTS13 is constitutively secreted as an active protease and is not inhibited by circulating protease inhibitors. Therefore, the mechanisms that regulate ADAMTS13 protease activity are unknown.

Human platelets contain a pool of free zinc in dense granules.

Background: Activated platelets release procoagulant factors that include Ca and Zn. Releasable Ca stores have been identified in platelet dense granules and the dense tubular system, but similar stores of free Zn have not been identified.

Objectives: Guided by studies of platelet Ca, we employed minimally disruptive methods to identify and localize concentrated free Zn in human platelets.

Current Gaps in the Provision of Safe and Effective Anticoagulation in Atrial Fibrillation and the Potential for Factor XI-Directed Therapeutics.

The global prevalence of atrial fibrillation is rapidly increasing, in large part due to the aging of the population. Atrial fibrillation is known to increase the risk of thromboembolic stroke by 5 times, but it has been evident for decades that well-managed anticoagulation therapy can greatly attenuate this risk. Despite advances in pharmacology (such as the shift from vitamin K antagonists to direct oral anticoagulants) that have increased the safety and convenience of chronic oral anticoagulation in atrial fibrillation, a preponderance of recent observational data indicates that protection from stroke is poorly achieved on a population basis.

When Direct Oral Anticoagulants Should Not Be Standard Treatment: JACC State-of-the-Art Review.

For most patients, direct oral anticoagulants (DOACs) are preferred over vitamin K antagonists for stroke prevention in atrial fibrillation and for venous thromboembolism treatment. However, randomized controlled trials suggest that DOACs may not be as efficacious or as safe as the current standard of care in conditions such as mechanical heart valves, thrombotic antiphospholipid syndrome, and atrial fibrillation associated with rheumatic heart disease. DOACs do not provide a net benefit in conditions such as embolic stroke of undetermined source.

Thrombin-activatable fibrinolysis inhibitor and sex modulate thrombus stability and pulmonary embolism burden in a murine model.

Background: Thrombin-activatable fibrinolysis inhibitor (TAFI) levels are positively correlated with the risk of thrombosis. The mechanism of how TAFI affects venous thromboembolism (VTE) remains uncertain. In addition, the role of sex on the risk of VTE has also been studied.

PAR4 Inhibition Reduces Coronary Artery Atherosclerosis and Myocardial Fibrosis in SR-B1/LDLR Double Knockout Mice.

Background: SR-B1 (scavenger receptor class B type 1)/LDLR (low-density lipoprotein receptor) double knockout mice fed a high-fat, high-cholesterol diet containing cholate exhibit coronary artery disease characterized by occlusive coronary artery atherosclerosis, platelet accumulation in coronary arteries, and myocardial fibrosis. Platelets are involved in atherosclerosis development, and PAR (protease-activated receptor) 4 has a prominent role in platelet function in mice. However, the role of PAR4 on coronary artery disease in mice has not been tested.

Study of Rivaroxaban for Cerebral Venous Thrombosis: A Randomized Controlled Feasibility Trial Comparing Anticoagulation With Rivaroxaban to Standard-of-Care in Symptomatic Cerebral Venous Thrombosis.

Background: Emerging data suggest that direct oral anticoagulants may be a suitable choice for anticoagulation for cerebral venous thrombosis (CVT). However, conducting high-quality trials in CVT is challenging as it is a rare disease with low rates of adverse outcomes such as major bleeding and functional dependence. To facilitate the design of future CVT trials, SECRET (Study of Rivaroxaban for Cerebral Venous Thrombosis) assessed (1) the feasibility of recruitment, (2) the safety of rivaroxaban compared with standard-of-care anticoagulation, and (3) patient-centered functional outcomes.

New Therapeutic Targets for the Prevention and Treatment of Venous Thromboembolism With a Focus on Factor XI Inhibitors.

FXI (factor XI) and FXII (factor XII) have emerged as targets for new anticoagulants that have the potential to be both more efficacious and safer than the currently available direct oral anticoagulants for the prevention and treatment of venous thromboembolism. In this review, we discuss the role of FXI and FXII in the pathogenesis of venous thromboembolism, explain why FXI is a better target, and explain why FXI inhibitors have potential advantages over currently available anticoagulants. Finally, we describe the FXI inhibitors under development and discuss their potential to address unmet needs in venous thromboembolism management.

Warfarin faring better: vitamin K antagonists beat rivaroxaban and apixaban in the INVICTUS and PROACT Xa trials.

Although guidelines give preference to direct oral anticoagulants (DOACs) over vitamin K antagonists (VKAs) for stroke prevention in most patients with atrial fibrillation (AF), DOACs are not recommended in those with rheumatic heart disease or mechanical heart valves. The results of the INVICTUS trial (Investigation of Rheumatic AF Treatment Using Vitamin K Antagonists, Rivaroxaban or Aspirin Studies), which compared rivaroxaban with a VKA in patients with rheumatic heart disease-associated AF, and the PROACT Xa trial (A Trial to Determine if Participants with an On-X Aortic Valve Can be Maintained Safely on Apixaban), which compared apixaban with warfarin in patients with an On-X valve in the aortic position, support the use of VKAs for these indications. In this paper, we review the results of these trials, provide perspective on why VKAs were superior to DOACs, and discuss future directions for anticoagulation in these disorders.

Treatment of Cancer-Associated Thrombosis: Recent Advances, Unmet Needs, and Future Direction.

Cancer-associated thrombosis, with the incidence rising over the years, is associated with significant morbidity and mortality in patients with cancer. Recent advances in the treatment of cancer-associated venous thromboembolism (VTE) include the introduction of direct oral anticoagulants (DOACs), which provide a more convenient and effective option than low-molecular-weight heparin (LMWH). Nonetheless, important unmet needs remain including an increased risk of bleeding in certain patient subgroups such as those with gastroesophageal cancer, concerns about drug-drug interactions, and management of patients with severe renal impairment.

News at XI: moving beyond factor Xa inhibitors.

Oral anticoagulants are a mainstay for the prevention and treatment of arterial and venous thrombosis. Direct oral anticoagulants (DOACs) have replaced vitamin K antagonists for many indications. Currently available DOACs include dabigatran, which inhibits thrombin, and apixaban, edoxaban, and rivaroxaban, which inhibit factor (F) Xa.

Histidine-rich glycoprotein attenuates catheter thrombosis.

Factor XII (FXII) knockdown attenuates catheter thrombosis in rabbits. Because histidine-rich glycoprotein (HRG) modulates FXIIa activity, we hypothesized that HRG depletion would promote catheter thrombosis. To test this, rabbits were given either antisense oligonucleotides (ASOs) against HRG or FXII, a control ASO, or saline.

Reversal agents for current and forthcoming direct oral anticoagulants.

Over the past 20 years, there has been a shift from vitamin K antagonists to direct oral anticoagulants (DOACs), which include the thrombin inhibitor dabigatran and the factor Xa inhibitors apixaban, edoxaban, and rivaroxaban. Although DOACs are associated with less serious bleeding than vitamin K antagonists, bleeding still occurs with DOACs, particularly in the elderly and in those with comorbidities. Reversal of the anticoagulant effects of the DOACs may be needed in patients with serious bleeding and in those requiring urgent surgery or intervention.