A novel factor IXa-specific enzyme-linked immunosorbent assay detects factor IXa in human plasma.

Background: Factor (F)IXa activity has been detected in human plasma and may impact thrombotic risk. Current FIXa activity assays are complex and cumbersome.

Objectives: To develop a reproducible enzyme-linked immunosorbent assay (ELISA) using a novel monoclonal antibody that detects total FIXa in human plasma.

Therapeutic Anticoagulation with Heparin in Noncritically Ill Patients with Covid-19.

Background: Thrombosis and inflammation may contribute to the risk of death and complications among patients with coronavirus disease 2019 (Covid-19). We hypothesized that therapeutic-dose anticoagulation may improve outcomes in noncritically ill patients who are hospitalized with Covid-19.

Methods: In this open-label, adaptive, multiplatform, controlled trial, we randomly assigned patients who were hospitalized with Covid-19 and who were not critically ill (which was defined as an absence of critical care-level organ support at enrollment) to receive pragmatically defined regimens of either therapeutic-dose anticoagulation with heparin or usual-care pharmacologic thromboprophylaxis.

Phenotype of ribonuclease 1 deficiency in mice.

Biological roles for extracellular RNA (eRNA) have become apparent. For example, eRNA can induce contact activation in blood via activation of the plasma proteases factor XII (FXII) and factor XI (FXI). We sought to reveal the biological role of the secretory enzyme ribonuclease 1 (RNase 1) in an organismal context by generating and analyzing RNase 1 knockout () mice.

Anticoagulant Protein S Targets the Factor IXa Heparin-Binding Exosite to Prevent Thrombosis.

Objective: PS (protein S) is a plasma protein that directly inhibits the coagulation FIXa (factor IXa) in vitro. Because elevated FIXa is associated with increased risk of venous thromboembolism, it is important to establish how PS inhibits FIXa function in vivo. The goal of this study is to confirm direct binding of PS with FIXa in vivo, identify FIXa amino acid residues required for binding PS in vivo, and use an enzymatically active FIXa mutant that is unable to bind PS to measure the significance of PS-FIXa interaction in hemostasis.

Elevated Plasma Factor IXa Activity in Premenopausal Women on Hormonal Contraception.

Objective: Combined oral contraceptives induce a reversible hypercoagulable state with an enhanced risk of venous thromboembolism, but the underlying mechanism(s) remain unclear. Subjects on combined oral contraceptives also demonstrate a characteristic resistance to APC (activated protein C) in the thrombin generation assay. Here, we report the potential role of plasma factor IXa (FIXa) as a mechanism for hormone-induced systemic hypercoagulability.

Tissue factor-factor VIIa complex triggers protease activated receptor 2-dependent growth factor release and migration in ovarian cancer.

Objective: Enhanced tissue factor (TF) expression in epithelial ovarian cancer (EOC) is associated with aggressive disease. Our objective was to evaluate the role of the TF-factor VIIa-protease-activated receptor-2 (PAR-2) pathway in human EOC.

Methods: TCGA RNAseq data from EOC databases were analyzed for PAR expression.

New developments in the management of moderate-to-severe hemophilia B.

Hemophilia B is an X-linked genetic deficiency of coagulation factor IX (FIX) activity associated with recurrent deep tissue and joint bleeding that may lead to long-term disability. FIX replacement therapy using plasma-derived protein or recombinant protein has significantly reduced bleeding and disability from hemophilia B, particularly when used in a prophylactic fashion. Although modern factor replacement has excellent efficacy and safety, barriers to the broader use of prophylaxis remain, including the need for intravenous (IV) access, frequent dosing, variability in individual pharmacokinetics, and cost.

Activation of factor XI by products of prothrombin activation.

The prothrombinase complex converts prothrombin to α-thrombin through the intermediate meizothrombin (Mz-IIa). Both α-thrombin and Mz-IIa catalyze factor (F) XI activation to FXIa, which sustains α-thrombin production through activation of FIX. The interaction with FXI is thought to involve thrombin anion binding exosite (ABE) I.

The regulation of factor IXa by supersulfated low molecular weight heparin.

Supersulfated low molecular weight heparin (ssLMWH) inhibits the intrinsic tenase (factor IXa-factor VIIIa) complex in an antithrombin-independent manner. Recombinant factor IXa with alanine substitutions in the protease domain (K126A, N129A, K132A, R165A, R170A, N178A, R233A) was assessed with regard to heparin affinity in solution and ability to regulate protease activity within the factor IXa-phospholipid (PL) and intrinsic tenase complexes. In a soluble binding assay, factor IXa K126A, K132A, and R233A dramatically (10-20-fold) reduced ssLMWH affinity, while factor IXa N129A and R165A moderately (5-fold) reduced affinity relative to wild type.

Fucosylated chondroitin sulfate inhibits plasma thrombin generation via targeting of the factor IXa heparin-binding exosite.

Depolymerized holothurian glycosaminoglycan (DHG) is a fucosylated chondroitin sulfate with antithrombin-independent antithrombotic properties. Heparin cofactor II (HCII)-dependent and -independent mechanisms for DHG inhibition of plasma thrombin generation were evaluated. When thrombin generation was initiated with 0.

The heparin-binding exosite of factor IXa is a critical regulator of plasma thrombin generation and venous thrombosis.

The role of the factor IXa heparin-binding exosite in coagulation was assessed with mutations that enhance (R170A) or reduce (R233A) stability of the protease-factor VIIIa A2 domain interaction. After tissue factor (TF) addition to reconstituted factor IX-deficient plasma, factor IX R170A supported a 2-fold increase in velocity index (slope) and peak thrombin concentration, whereas factor IX R233A had a 4- to 10-fold reduction relative to factor IX wild-type. In the absence of TF, 5 to 100 pM of factor IXa increased thrombin generation to approach TF-stimulated thrombin generation at 100% factor IX.

The heparin-binding exosite is critical to allosteric activation of factor IXa in the intrinsic tenase complex: the role of arginine 165 and factor X.

Heparin inhibits the intrinsic tenase complex (factor IXa-factor VIIIa) via interaction with a factor IXa exosite. To define the role of this exosite, human factor IXa with alanine substituted for conserved surface residues (R126, N129, K132, R165, N178) was characterized. Chromogenic substrate hydrolysis by the mutant proteases was reduced 20-30% relative to factor IXa wild type.

Depolymerized holothurian glycosaminoglycan and heparin inhibit the intrinsic tenase complex by a common antithrombin-independent mechanism.

Depolymerized holothurian glycosaminoglycan (DHG) is a fucosylated chrondroitin sulfate that possesses antithrombin-independent antithrombotic properties and inhibits factor X activation by the intrinsic tenase complex (factor IXa-factor VIIIa). The mechanism and molecular target for intrinsic tenase inhibition were determined and compared with inhibition by low-molecular-weight heparin (LMWH). DHG inhibited factor X activation in a noncompetitive manner (reduced V(max(app))), with 50-fold higher apparent affinity than LMWH.

The factor IXa heparin-binding exosite is a cofactor interactive site: mechanism for antithrombin-independent inhibition of intrinsic tenase by heparin.

Therapeutic heparin concentrations selectively inhibit the intrinsic tenase complex in an antithrombin-independent manner. To define the molecular target and mechanism for this inhibition, recombinant human factor IXa with alanine substituted for solvent-exposed basic residues (H92, R170, R233, K241) in the protease domain was characterized with regard to enzymatic activity, heparin affinity, and inhibition by low molecular weight heparin (LMWH). These mutations only had modest effects on chromogenic substrate hydrolysis and the kinetics of factor X activation by factor IXa.

Fasting hyperglycemia: etiology, diagnosis, and treatment.

Suboptimal glycemic control in individuals with type 1 and type 2 diabetes mellitus is associated with an increased risk of microvascular and macrovascular complications. Even brief periods of hyperglycemia increase the risk of complications. Fasting hyperglycemia is a phenomenon that has been observed in essentially all individuals with diabetes and may be due to dysregulation of the normal circadian hormonal patterns resulting in increased hepatic glucose output.

Heparin inhibits the intrinsic tenase complex by interacting with an exosite on factor IXa.

The specific molecular target for direct heparin inhibition of factor X activation by intrinsic tenase (factor IXa-factor VIIIa) was investigated. Comparison of size-fractionated oligosaccharides demonstrated that an octasaccharide was sufficient to inhibit intrinsic tenase. Substitution of soluble dihexanoic phosphatidylserine (C6PS) for phospholipid (PL) vesicles demonstrated that inhibition by low-molecular weight heparin (LMWH) was independent of factor IXa-factor VIIIa membrane assembly.

Efficacy, safety, and tolerability of once-daily niacin for the treatment of dyslipidemia associated with type 2 diabetes: results of the assessment of diabetes control and evaluation of the efficacy of niaspan trial.

Background: Diabetic dyslipidemia is characterized by high triglyceride levels; low high-density lipoprotein cholesterol levels; small, dense low-density lipoprotein particles; and high free fatty acid levels. Niacin reduces concentrations of triglyceride-rich and small low-density lipoprotein particles while increasing high-density lipoprotein cholesterol levels. It also lowers levels of free fatty acids and lipoprotein(a).