Factor XI Inhibition for the Prevention of Catheter-Associated Thrombosis in Patients With Cancer Undergoing Central Line Placement: A Phase 2 Clinical Trial.

BACKGROUND: Despite the ubiquitous utilization of central venous catheters in clinical practice, their use commonly provokes thromboembolism. No prophylactic strategy has shown sufficient efficacy to justify routine use. Coagulation factors FXI (factor XI) and FXII (factor XII) represent novel targets for device-associated thrombosis, which may mitigate bleeding risk. Our objective was to evaluate the safety and efficacy of an anti-FXI mAb (monoclonal antibody), gruticibart (AB023), in a prospective, single-arm study of patients with cancer receiving central line placement. METHODS: We enrolled ambulatory cancer patients undergoing central line placement to receive a single dose of gruticibart (2 mg/kg) administered through the venous catheter within 24 hours of placement and a follow-up surveillance ultrasound at day 14 for evaluation of catheter thrombosis. A parallel, noninterventional study was used as a comparator. RESULTS: In total, 22 subjects (n=11 per study) were enrolled. The overall incidence of catheter-associated thrombosis was 12.5% in the interventional study and 40.0% in the control study. The anti-FXI mAb, gruticibart, significantly prolonged the activated partial thromboplastin time in all subjects on day 14 compared with baseline (P<0.001). Gruticibart was well tolerated and without infusion reactions, drug-related adverse events, or clinically relevant bleeding. Platelet flow cytometry demonstrated no difference in platelet activation following administration of gruticibart. T (thrombin)-AT (antithrombin) and activated FXI-AT complexes increased following central line placement in the control study, which was not demonstrated in our intervention study. CRP (C-reactive protein) did not significantly increase on day 14 in those who received gruticibart, but it did significantly increase in the noninterventional study. CONCLUSIONS: FXI inhibition with gruticibart was well tolerated without any significant adverse or bleeding-related events and resulted in a lower incidence of catheter-associated thrombosis on surveillance ultrasound compared with the published literature and our internal control study. These findings suggest that targeting FXI could represent a safe intervention to prevent catheter thrombosis. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04465760.

Ibrutinib Inhibits BMX-Dependent Endothelial VCAM-1 Expression In Vitro and Pro-Atherosclerotic Endothelial Activation and Platelet Adhesion In Vivo.

Introduction: Inflammatory activation of the vascular endothelium leads to overexpression of adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), contributing to the pro-thrombotic state underpinning atherogenesis. While the role of TEC family kinases (TFKs) in mediating inflammatory cell and platelet activation is well defined, the role of TFKs in vascular endothelial activation remains unclear. We investigated the role of TFKs in endothelial cell activation in vitro and in a nonhuman primate model of diet-induced atherosclerosis in vivo. Methods and Results: In vitro, we found that ibrutinib blocked activation of the TFK member, BMX, by vascular endothelial growth factors (VEGF)-A in human aortic endothelial cells (HAECs). Blockade of BMX activation with ibrutinib or pharmacologically distinct BMX inhibitors eliminated the ability of VEGF-A to stimulate VCAM-1 expression in HAECs. We validated that treatment with ibrutinib inhibited TFK-mediated platelet activation and aggregation in both human and primate samples as measured using flow cytometry and light transmission aggregometry. We utilized contrast-enhanced ultrasound molecular imaging to measure platelet GPIbα and endothelial VCAM-1 expression in atherosclerosis-prone carotid arteries of obese nonhuman primates. We observed that the TFK inhibitor, ibrutinib, inhibited platelet deposition and endothelial cell activation in vivo. Conclusion: Herein we found that VEGF-A signals through BMX to induce VCAM-1 expression in endothelial cells, and that VCAM-1 expression is sensitive to ibrutinib in vitro and in atherosclerosis-prone carotid arteries in vivo. These findings suggest that TFKs may contribute to the pathogenesis of atherosclerosis and could represent a novel therapeutic target.

Platelet reactivity and platelet count in women with iron deficiency treated with intravenous iron.

Background: Iron deficiency anemia (IDA) and heavy menstrual bleeding are prevalent, interrelated issues impacting over 300 million premenopausal women worldwide. IDA is generally associated with increased platelet counts; however, the effects of IDA and its correction on platelet function in premenopausal women remain unknown. Objectives: We sought to determine how IDA and intravenous iron affect platelet count and platelet function in premenopausal women. Methods: Hematologic indices were assessed in a multicenter, retrospective cohort of 231 women repleted with intravenous iron. Pre- and postinfusion blood samples were then obtained from a prospective cohort of 13 women to analyze the effect of intravenous iron on hematologic parameters as well as platelet function with flow cytometry and platelet aggregation assays under physiologic shear. Results: Following iron replacement, anemia improved, and mean platelet counts decreased by 26.5 and 16.0 K/mm3 in the retrospective and prospective cohorts, respectively. Replacement reduced baseline platelet surface P-selectin levels while enhancing platelet secretory responses to agonists, including collagen-related peptide and ADP. Platelet adhesion and aggregation on collagen under physiologic shear also significantly increased following repletion. Conclusion: We find that intravenous iron improves anemia while restoring platelet counts and platelet secretory responses in premenopausal women with iron deficiency. Our results suggest that iron deficiency as well as iron replacement can have a range of effects on platelet production and function. Consequently, platelet reactivity profiles should be further examined in women and other groups with IDA where replacement offers a promising means to improve anemia as well as quality of life.

Severe thrombocytopenia in adults undergoing extracorporeal membrane oxygenation is predictive of thrombosis.

Extracorporeal membrane oxygenation (ECMO) provides lifesaving circulatory support and gas exchange, although hematologic complications are frequent. The relationship between ECMO and severe thrombocytopenia (platelet count <50 × 109/L) remains ill-defined. We performed a cohort study of 67 patients who received ECMO between 2016 and 2019, of which 65.7% received veno-arterial (VA) ECMO and 34.3% received veno-venous (VV) ECMO. All patients received heparin and 25.4% received antiplatelet therapy. In total, 23.9% of patients had a thrombotic event and 67.2% had a hemorrhagic event. 38.8% of patients developed severe thrombocytopenia. Severe thrombocytopenia was more common in patients with lower baseline platelet counts and increased the likelihood of thrombosis by 365% (OR 3.65, 95% CI 1.13-11.8, P = .031), while the type of ECMO (VA or VV) was not predictive of severe thrombocytopenia (P = .764). Multivariate logistic regression controlling for additional clinical variables found that severe thrombocytopenia predicted thrombosis (OR 3.65, CI 1.13-11.78, P = .031). Over a quarter of patients requiring ECMO developed severe thrombocytopenia in our cohort, which was associated with an increased risk of thrombosis and in-hospital mortality. Additional prospective observation is required to clarify the clinical implications of severe thrombocytopenia in the ECMO patient population.

The efficacy and safety of thrombopoietin receptor agonists in patients with chronic liver disease undergoing elective procedures: a systematic review and meta-analysis.

Thrombopoietin receptor agonists (TPO-RAs) can mitigate preprocedural thrombocytopenia in patients with chronic liver disease (CLD) however their effects on procedural outcomes is unclear. In this meta-analysis, we aimed to better define the efficacy, thrombotic risk and bleeding mitigation associated with the use of preoperative TPO-RAs in patients with CLD. We performed a systematic review and meta-analysis of randomized placebo-controlled clinical trials to assess the use of preprocedural TPO-RAs in patients with CLD, searching MEDLINE, EMBASE and the Cochrane library database. Six publications comprising eight randomized trials (1229 patients; 717 received TPO-RAs, 512 received placebo) and three unique TPO-RAs were retrieved. The majority of the included procedures were endoscopic. TPO-RAs were significantly more likely to result in a preoperative platelet count greater than 50 x 109/L (72.1% vs 15.6%, RR 4.8, 95% CI 3.6-6.4 p < .00001. NNT 1.8) and reduced the incidence of platelet transfusions (22.5% vs 67.8%, RR 0.33, 95% CI 0.3-0.4 p < .00001. NNT 2.2). Total periprocedural bleeding was decreased in patients who received TPO-RAs (11.6% vs 15.6%, RR 0.64, 95% CI 0.5-0.9 p = .01. NNT 24.7) and there was no increase in the rate of thrombosis (2.2% vs 1.8% RR 1.25, 95% CI 0.6-2.9 p = .60. NNH 211.1). In patients with CLD the use of preprocedural TPO-RAs resulted in significant increased platelet counts, and decreased the incidence of platelet transfusions as compared to placebo. TPO use likewise decreased the incidence of total periprocedural bleeding without increasing the rate of thrombosis.

The contact activation inhibitor AB023 in heparin-free hemodialysis: results of a randomized phase 2 clinical trial.

End-stage renal disease (ESRD) patients on chronic hemodialysis have repeated blood exposure to artificial surfaces that can trigger clot formation within the hemodialysis circuit. Dialyzer clotting can lead to anemia despite erythropoietin and iron supplementation. Unfractionated heparin prevents clotting during hemodialysis, but it is not tolerated by all patients. Although heparin-free dialysis is performed, intradialytic blood entrapment can be problematic. To address this issue, we performed a randomized, double-blind, phase 2 study comparing AB023, a unique antibody that binds factor XI (FXI) and blocks its activation by activated FXII, but not by thrombin, to placebo in 24 patients with ESRD undergoing heparin-free hemodialysis. Patients were randomized to receive a single predialysis dose of AB023 (0.25 or 0.5 mg/kg) or placebo in a 2:1 ratio, and safety and preliminary efficacy were compared with placebo and observations made prior to dosing within each treatment arm. AB023 administration was not associated with impaired hemostasis or other drug-related adverse events. Occlusive events requiring hemodialysis circuit exchange were less frequent and levels of thrombin-antithrombin complexes and C-reactive protein were lower after AB023 administration compared with data collected prior to dosing. AB023 also reduced potassium and iron entrapment in the dialyzers, consistent with less blood accumulation within the dialyzers. We conclude that despite the small sample size, inhibition of contact activation-induced coagulation with AB023 was well tolerated and reduced clotting within the dialyzer. This trial was registered at www.clinicaltrials.gov as #NCT03612856.

Thrombosis and Bleeding in Extracorporeal Membrane Oxygenation (ECMO) Without Anticoagulation: A Systematic Review.

Extracorporeal membrane oxygenation (ECMO) causes both thrombosis and bleeding. Major society guidelines recommend continuous, systemic anticoagulation to prevent thrombosis of the ECMO circuit, though this may be undesirable in those with active, or high risk of, bleeding. We aimed to systematically review thrombosis and bleeding outcomes in published cases of adults treated with ECMO without continuous systemic anticoagulation. Ovid MEDLINE, Cochrane CENTRAL and CDSR, and hand search via SCOPUS were queried. Eligible studies were independently reviewed by two blinded authors if they reported adults (≥18 years) treated with either VV- or VA-ECMO without continuous systemic anticoagulation for ≥24 hours. Patient demographics, clinical data, and specifics of ECMO technology and treatment parameters were collected. Primary outcomes of interest included incidence of bleeding, thrombosis of the ECMO circuit requiring equipment exchange, patient venous or arterial thrombosis, ability to wean off of ECMO, and mortality. Of the 443 total publications identified, 34 describing 201 patients met our inclusion criteria. Most patients were treated for either acute respiratory distress syndrome or cardiogenic shock. The median duration of anticoagulant-free ECMO was 4.75 days. ECMO circuity thrombosis and patient thrombosis occurred in 27 (13.4%) and 19 (9.5%) patients, respectively. Any bleeding and major or "severe" bleeding was reported in 66 (32.8%) and 56 (27.9%) patients, respectively. Forty patients (19%) died. While limited by primarily retrospective data and inconsistent reporting of outcomes, our systematic review of anticoagulant-free ECMO reveals an incidence of circuity and patient thrombosis comparable to patients receiving continuous systemic anticoagulation while on ECMO.

Factor XII plays a pathogenic role in organ failure and death in baboons challenged with Staphylococcus aureus.

Activation of coagulation factor (F) XI promotes multiorgan failure in rodent models of sepsis and in a baboon model of lethal systemic inflammation induced by infusion of heat-inactivated Staphylococcus aureus. Here we used the anticoagulant FXII-neutralizing antibody 5C12 to verify the mechanistic role of FXII in this baboon model. Compared with untreated control animals, repeated 5C12 administration before and at 8 and 24 hours after bacterial challenge prevented the dramatic increase in circulating complexes of contact system enzymes FXIIa, FXIa, and kallikrein with antithrombin or C1 inhibitor, and prevented cleavage and consumption of high-molecular-weight kininogen. Activation of several coagulation factors and fibrinolytic enzymes was also prevented. D-dimer levels exhibited a profound increase in the untreated animals but not in the treated animals. The antibody also blocked the increase in plasma biomarkers of inflammation and cell damage, including tumor necrosis factor, interleukin (IL)-1ß, IL-6, IL-8, IL-10, granulocyte-macrophage colony-stimulating factor, nucleosomes, and myeloperoxidase. Based on clinical presentation and circulating biomarkers, inhibition of FXII prevented fever, terminal hypotension, respiratory distress, and multiorgan failure. All animals receiving 5C12 had milder and transient clinical symptoms and were asymptomatic at day 7, whereas untreated control animals suffered irreversible multiorgan failure and had to be euthanized within 2 days after the bacterial challenge. This study confirms and extends our previous finding that at least 2 enzymes of the contact activation complex, FXIa and FXIIa, play critical roles in the development of an acute and terminal inflammatory response in baboons challenged with heat-inactivated S aureus.

Heparin Resistance Is Common in Patients Undergoing Extracorporeal Membrane Oxygenation but Is Not Associated with Worse Clinical Outcomes.

Extracorporeal membrane oxygenation (ECMO) protocols generally require systemic anticoagulation with heparin to prevent circuit thrombosis. The prevalence, risk factors, and outcomes of heparin resistance in this setting are ill-defined. To better understand the prevalence and clinical consequences of heparin resistance in this population, we conducted a retrospective analysis of all patients treated with ECMO at a single academic medical center between 2016 and 2019. Univariate and multivariate analyses were used to evaluate predictors and outcomes of heparin resistance. Of 67 patients in our study, 50.7% met the threshold for heparin resistance for at least 1 day, which was managed in all cases with increases in heparin dose. Patients with heparin resistance were more likely to be male (82.4% vs. 48.5%, p = 0.005) and to have a higher mean platelet count (132 vs. 104 × 103/mL, p = 0.027) compared with those without heparin resistance. Multivariate logistic regression found no significant association between the development of heparin resistance and rates of thrombosis, hemorrhage, or overall survival. Additional prospective studies are required to clarify the clinical implications of heparin resistance in this population.

Anticoagulation strategies in extracorporeal circulatory devices in adult populations.

Extracorporeal circulatory devices such as hemodialysis and extracorporeal membrane oxygenation can be lifesaving; however, they are also prone to pathologic events including device failure, venous and arterial thrombosis, hemorrhage, and an accelerated risk for atherosclerotic disease due to interactions between blood components and device surfaces of varying biocompatibility. While extracorporeal devices may be used acutely for limited periods of time (eg, extracorporeal membrane oxygenation, continuous venovenous hemofiltration, therapeutic apheresis), some patients require chronic use of these technologies (eg, intermittent hemodialysis and left ventricular assist devices). Given the substantial thrombotic risks associated with extracorporeal devices, multiple antiplatelet and anticoagulation strategies-including unfractionated heparin, low-molecular-weight heparin, citrate, direct thrombin inhibitors, and direct oral anticoagulants, have been used to mitigate the thrombotic milieu within the patient and device. In the following manuscript, we outline the current data on anticoagulation strategies for commonly used extracorporeal circulatory devices, highlighting the potential benefits and complications involved with each.

Design of a Microfluidic Bleeding Chip to Evaluate Antithrombotic Agents for Use in COVID-19 Patients.

INTRODUCTION: Interventions that could prevent thrombosis, clinical decompensation, and respiratory compromise in patients with novel coronavirus disease (COVID-19) are key to decrease mortality rate. Studies show that profound cytokine release and excessive activation of blood coagulation appear to be key drivers of COVID-19 associated mortality. Since limited in vitro methods exist for assessing the effects of anticoagulants on hemostasis, the development of novel therapies to safely prevent thrombosis in COVID-19 patients relies on preclinical animal models and early phase human trials. Herein we present the design of a microfluidic "bleeding chip" to evaluate the effects of antithrombotic therapies on hemostatic plug formation in vitro. METHODS: The design of the microfluidic device consists of two orthogonal channels: an inlet that serves as a model blood vessel, and a bleeding channel to model hemostatic plug formation at sites of compromised endothelial barrier function. This is achieved by placing a series of 3 pillars spaced 10 µm apart at the intersection of the two channels. The pillars and bleeding channel are coated with the extracellular matrix protein collagen. RESULTS: Perfusion of human whole blood through the microfluidic bleeding chip led to initial platelet adhesion and aggregation at the pillars followed by hemostatic plug formation and occlusion of the bleeding channel. CONCLUSIONS: Safe and effective mitigating agents are needed for treatment and prevention of thrombotic complications in COVID-19 patients. This simple microfluidic device holds potential to be developed into a tool for assessing the effects of anticoagulant therapy on hemostasis.

Evaluation of the Antihemostatic and Antithrombotic Effects of Lowering Coagulation Factor VII Levels in a Non-human Primate.

INTRODUCTION: Tissue factor (TF) and factor (F) VII, components of the extrinsic pathway of blood coagulation, are essential for hemostatic plug formation in response to injury; less clear are their roles in propagating thrombosis, as observational data in humans with congenital FVII deficiency suggests persistent thrombotic and bleeding risk even at significantly decreased FVII levels. We aimed to define the contribution of FVII to thrombus formation and hemostasis using a non-human primate model. METHODS: We treated baboons with a FVII antisense oligonucleotide (ASO) and measured platelet and fibrin deposition inside and distal to collagen- or TF-coated vascular grafts. We assessed hemostasis by measuring bleeding time (BT) and prothrombin time (PT). Enoxaparin and vehicle treatments served as controls. RESULTS: FVII-ASO treatment reduced FVII levels by 95% and significantly increased both the PT and BT. Lowering FVII levels did not decrease platelet deposition in collagen- or TF-coated grafts, in thrombi distal to the grafts, or fibrin content of either collagen- and TF-coated grafts. Lowering FVII levels were associated with a modest 25% reduction in platelet deposition at 60 min in the distal thrombus tail of TF-coated grafts only. CONCLUSIONS: FVII inhibition by way of ASO is feasible yet significantly impairs hemostasis while only exhibiting antithrombotic effects when thrombosis is initiated by vessel wall surface-associated TF exposure.

When to consider targeted therapies in thrombotic microangiopathies in the modern era: walking the tightrope between cost, safety, and efficacy.

Thrombotic Microangiopathy (TMA) is a heterogeneous collection of syndromes that encompasses TTP, HUS, and other processes characterized by thrombocytopenia, microangiopathic hemolytic anemia, and, if untreated, organ failure and death. Novel therapies have recently been approved for the management of certain thrombotic microangiopathies, including caplacizumab for immune-mediated TTP, and eculizumab for atypical HUS. These options have complicated the standard workflow, which includes initiation of plasma exchange until ADAMTS13 testing can be resulted. Given such results may take several days, there is indecision regarding the appropriate initial management of TMA. Decisions regarding caplacizumab and eculizumab are complex, and include considerations over costs, side effects, and efficacy. In the following forum, we discuss the current data and pose possible management strategies in patients with TMA before final diagnosis can be obtained.

Diagnosis and management of hereditary haemochromatosis.

Hereditary haemochromatosis, one of the most common genetic disorders in the United States, can produce systemic iron deposition leading to end-organ failure and death if untreated. The diagnosis of this condition can be challenging as elevated serum ferritin may be seen in a variety of conditions, including acute and chronic liver disease, a range of systemic inflammatory states, and both primary and secondary iron overload syndromes. Appropriate and timely diagnosis of haemochromatosis is paramount as simple interventions, such as phlebotomy, can prevent or reverse organ damage from iron overload. The recognition of other aetiologies of elevated ferritin is also vital to ensure that appropriate intervention is provided and phlebotomy only utilized in patients who require it. In this review, we summarize the existing data on the work up and management of hereditary haemochromatosis and present a practical algorithm for the diagnosis and management of this disease.

The contact pathway and sepsis.

The contact pathway factors XI (FXI) and XII (FXII) have been demonstrated to be largely dispensable for hemostasis, as their absence results in a mild to absent bleeding diathesis. A growing body of literature, however, suggests that the contact pathway contributes to the pathologic host response to certain infectious organisms that produces the often-fatal syndrome known as sepsis. The contact pathway factors serve as a central node connecting inflammation to coagulation, and may offer a potentially safe therapeutic target to mitigate the morbidity and mortality associated with sepsis. Herein, we summarize published in vivo and in vitro data that have explored the roles of the contact pathway in sepsis, and discuss potential clinical applications of novel FXI- and FXII-inhibiting drugs currently under investigation.

Asymptomatic "breakthrough" thrombosis and anticoagulant "failure": Keep calm and carry on.

Despite therapeutic anticoagulation, patients with venous thromboembolism (VTE) not uncommonly present with findings of progressive thrombosis, sometimes within the first several weeks of treatment. While the prevailing strategy in these scenarios is to assume the current anticoagulant is ineffective and to switch to a different drug class, this practice may be unnecessary. Numerous trials of heparins and vitamin K antagonists for VTE have demonstrated that asymptomatic thrombus propagation despite therapeutic anticoagulation is common. While similar, serial imaging studies after initial VTE have not been replicated in trials of the direct oral anticoagulants, we reason that asymptomatic thrombus propagation detected within the first month of VTE diagnosis can be managed with continuation of the current anticoagulant strategy and close follow-up for worsening or recurrent symptoms.

The Safety and Efficacy of Novel Agents Targeting Factors XI and XII in Early Phase Human Trials.

Although anticoagulation without hemorrhage is a primary aim, this vision has remained as yet out of reach. Even despite the superior safety profile of the direct oral anticoagulants, hemorrhage remains a major risk of anticoagulation. Selective inhibition of the contact pathway of coagulation, specifically coagulation factor XI (FXI) and/or factor XII (FXII), has now substantial epidemiologic and preclinical data supporting the notion that these factors contribute to pathologic thrombosis and are yet primarily dispensable for in vivo hemostasis. In this way, targeting FXI and FXII may revolutionize the future anticoagulation landscape. Several drugs are under development for this purpose, including: ISIS 416858, a FXI antisense oligonucleotide which impairs hepatic synthesis of FXI; MAA868, a monoclonal antibody that binds the procoagulant enzymatic site of both zymogen and activated FXI (FXIa); BAY 1213790, a monoclonal antibody that binds the procoagulant enzymatic site of FXIa only; and AB023, a monoclonal antibody that inhibits activated FXII-mediated activation of FXI, along with two small molecules in clinical trials. Each of these drugs have demonstrated favorable safety profiles in their phases 1 and 2 studies to date, with preclinical data also supporting efficacy of abrogating thrombosis in various animal models. Other benefits of some of these drugs include once-monthly dosing and safety in patients with renal or hepatic impairment, while others offer quickly metabolized parenteral options, thus providing more convenient and widely available anticoagulation options. Though still far from the marketplace, drugs targeting FXI and FXII have the potential to usher in a new era of anticoagulation therapy.