Contact Activation Inhibitor, AB023, in Heparin-Free Hemodialysis: Results of a Randomized Phase 2 Clinical Trial

The third-generation anticoagulants: factors XI, XII, and XIII inhibitors

BACKGROUND

Arterial or venous thromboembolic events are responsible for one-fourth of all deaths worldwide. Anticoagulants are the mainstay for the prevention and treatment of venous thromboembolic events (VTE). Heparin and vitamin K antagonists were the first non-specific medications used in anticoagulant therapy, followed by safer alternatives, such as fondaparinux, argatroban, and direct oral anticoagulants. However, the latter bear the risk of potentially lethal internal bleeding. Novel drugs inhibiting various coagulation factors, such as factors XIa, XIIa, and XIIIa, appear to have a lesser risk of bleeding and are in the spotlight. This review aims to consolidate findings from published clinical trials of newer drugs inhibiting factors XIa, XIIa, and XIIIa.

MAIN BODY

Factor XI inhibitors have been researched more extensively as compared to factor XII and factor XIII inhibitors. Phase 2 study results of factor XI inhibitors indicated their superiority over enoxaparin for reduction of VTE incidence and better safety profile in terms of bleeding. Factor XII inhibitors also hold the promise of lowering the risk of bleeding, as indicated in animal studies. Further human studies would ensure their safety and applicability in the human population. Numerous laboratory researches have revealed, the potent antithrombotic profile of factor XIII inhibition with limited bleeding risks.

CONCLUSION

Larger statistically powered studies could supplement data to establish the role of FXI inhibitors in the prevention of both arterial and venous thromboembolic events in high-risk populations. While early results of factor XII and factor XIII inhibitors look promising, they still have a long road ahead before their therapeutic efficacy in humans is established.

Substrates, Cofactors, and Cellular Targets of Coagulation Factor XIa

Coagulation factor XI (FXI) has increasingly been shown to play an integral role in several physiologic and pathological processes. FXI is among several zymogens within the blood coagulation cascade that are activated by proteolytic cleavage, with FXI converting to the active serine protease form (FXIa). The evolutionary origins of FXI trace back to duplication of the gene that transcribes plasma prekallikrein, a key factor in the plasma kallikrein-kinin system, before further genetic divergence led to FXI playing a unique role in blood coagulation. While FXIa is canonically known for activating the intrinsic pathway of coagulation by catalyzing the conversion of FIX into FIXa, it is promiscuous in nature and has been shown to contribute to thrombin generation independent of FIX. In addition to its role in the intrinsic pathway of coagulation, FXI also interacts with platelets, endothelial cells, and mediates the inflammatory response through activation of FXII and cleavage of high-molecular-weight kininogen to generate bradykinin. In this manuscript, we critically review the current body of knowledge surrounding how FXI navigates the interplay of hemostasis, inflammatory processes, and the immune response and highlight future avenues for research. As FXI continues to be clinically explored as a druggable therapeutic target, understanding how this coagulation factor fits into physiological and disease mechanisms becomes increasingly important.

Ten tips to manage oral anticoagulation in hemodialysis patients with atrial fibrillation

Patients with chronic kidney disease (CKD) have a high incidence and prevalence of atrial fibrillation (AF). While general treatment strategies for AF may largely be transferred to patients with mild to moderate CKD, patients with advanced CKD-particularly hemodialysis (HD) patients-with AF pose substantial therapeutical challenges to cardiologists and nephrologists. The arguably greatest dilemma is the very limited evidence on appropriate strategies for prevention of stroke and systemic embolism in HD patients with AF, since the risk for both thromboembolic events without oral anticoagulation and severe bleeding events with oral anticoagulation are substantially increased in advanced CKD, compared with the general population. Thus, the benefit to risk ratio of either vitamin K antagonists or direct oral anticoagulants is less evident in HD than in non-CKD patients with AF. As a multidisciplinary panel of clinicians, we here propose 10 tips that may help our colleagues to navigate between the risk of undertreatment-exposing CKD patients with AF to a high stroke risk-and overtreatment-exposing the very same patients to a prohibitively high bleeding risk. These tips include ideas on alternative risk stratification strategies and novel treatment approaches that are currently in clinical studies-such as factor XI inhibitors or left atrial appendage closure-and may become game-changers for HD patients with AF.

Novel horizons in anticoagulation: the emerging role of factor XI inhibitors across different settings

Anticoagulants have long been fundamental in preventing and treating thromboembolic disorders, with a recent shift of focus towards direct oral anticoagulants, thanks to their ease of use, efficacy, and safety. Despite these advancements, bleeding complications remain a major concern with any anticoagulant, highlighting the need for safer drugs. Factor XI (FXI) inhibitors have emerged as promising agents in this regard, offering a novel approach by targeting upstream factors in the coagulation system. Phase II trials have shown encouraging outcomes, indicating a reduced bleeding risk compared to that associated with traditional anticoagulants, particularly in the context of cardiovascular disease management when combined with antiplatelet therapy. However, the variability in findings and limited efficacy data call for a cautious interpretation pending insights from phase III trials. These trials are essential for validating the potential of FXI inhibitors to balance bleeding risk reduction and maintain anticoagulant efficacy. This review explores the pharmacology, potential indications, clinical data, and future directions of FXI inhibitors, providing a perspective on their evolving role in anticoagulant therapy. It also provides a detailed analysis of data from published clinical trials on FXI inhibitors in various indications. Preliminary data from ongoing trials are also outlined. As the field moves forward, a cautiously optimistic outlook can be expected, focusing on comprehensive data from phase III trials to define the role of FXI inhibitors in various clinical scenarios.

The first-in-human study to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of the factor XI monoclonal antibody SHR-2004 in healthy subjects

BACKGROUND

Inhibiting the coagulation factor XI (FXI) is a novel strategy for prevention and treatment of thromboembolism without affecting extrinsic coagulation pathways. SHR-2004 is a humanized monoclonal antibody that selectively binds to FXI and factor XIa (FXIa).

RESEARCH DESIGN & METHODS

This randomized, double-blind, dose-escalation, placebo-controlled study evaluated SHR-2004 administered either intravenously (i.v.; Part A) or subcutaneously (s.c.; Part B). In Part A, 24 subjects received a single i.v. dose of SHR-2004 (0.1, 0.3, or 1.0 mg/kg) or placebo. In Part B, 40 subjects received a single s.c. dose of SHR-2004 (0.5, 1.0, 3.0, or 4.5 mg/kg) or placebo.

RESULTS

SHR-2004 was well tolerated. Plasma exposure to SHR-2004 increased in a dose-dependent manner. The geometric mean half-time ranged from 11.6 to 13.0 days. FXI activity decreased, and the activated partial thromboplastin time (APTT) was prolonged after i.v. and s.c. administration in a dose- and time-dependent manner. FXI activity was nearly completely abolished immediately after administering the highest i.v. dose, with the average APTT prolonged to nearly three times of baseline.

CONCLUSION

SHR-2004 is a promising candidate for further development as an anticoagulant drug that exerts effective anticoagulation with minimal risk of bleeding.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov identifier is NCT05369767.

Hemostasis and complement in allogeneic hematopoietic stem cell transplantation: clinical significance of two interactive systems

Hematopoietic stem cell transplantation (HCT) represents a curative treatment option for certain malignant and nonmalignant hematological diseases. Conditioning regimens before HCT, the development of graft-versus-host disease (GVHD) in the allogeneic setting, and delayed immune reconstitution contribute to early and late complications by inducing tissue damage or humoral alterations. Hemostasis and/or the complement system are biological regulatory defense systems involving humoral and cellular reactions and are variably involved in these complications after allogeneic HCT. The hemostasis and complement systems have multiple interactions, which have been described both under physiological and pathological conditions. They share common tissue targets, such as the endothelium, which suggests interactions in the pathogenesis of several serious complications in the early or late phase after HCT. Complications in which both systems interfere with each other and thus contribute to disease pathogenesis include transplant-associated thrombotic microangiopathy (HSCT-TMA), sinusoidal obstruction syndrome/veno-occlusive disease (SOS/VOD), and GVHD. Here, we review the current knowledge on changes in hemostasis and complement after allogeneic HCT and how these changes may define clinical impact.

Progress towards permanent respiratory support

PURPOSE OF REVIEW

Although lung transplantation stands as the gold standard curative therapy option for end-stage lung disease, the scarcity of available organs poses a significant challenge in meeting the escalating demand. This review provides an overview of recent advancements in ambulatory respiratory assist systems, selective anticoagulation therapies that target the intrinsic pathway, and innovative surface coatings to enable permanent respiratory support as a viable alternative to lung transplantation.

RECENT FINDINGS

Several emerging ambulatory respiratory assist systems have shown promise in both preclinical and clinical trials. These systems aim to create more biocompatible, compact, and portable forms of extracorporeal membrane oxygenation that can provide long-term respiratory support. Additionally, innovative selective anticoagulation strategies, currently in various stages of preclinical or clinical development, present a promising alternative to currently utilized nonselective anticoagulants. Moreover, novel surface coatings hold the potential to locally prevent artificial surface-induced thrombosis and minimize bleeding risks.

SUMMARY

This review of recent advancements toward permanent respiratory support summarizes the development of ambulatory respiratory assist systems, selective anticoagulation therapies, and novel surface coatings. The integration of these evolving device technologies with targeted anticoagulation strategies may allow a safe and effective mode of permanent respiratory support for patients with chronic lung disease.

Targeting the Contact Pathway of Coagulation for the Prevention and Management of Medical Device-Associated Thrombosis

Hemorrhage remains a major complication of anticoagulants, with bleeding leading to serious and even life-threatening outcomes in rare settings. Currently available anticoagulants target either multiple coagulation factors or specifically coagulation factor (F) Xa or thrombin; however, inhibiting these pathways universally impairs hemostasis. Bleeding complications are especially salient in the medically complex population who benefit from medical devices. Extracorporeal devices-such as extracorporeal membrane oxygenation, hemodialysis, and cardiac bypass-require anticoagulation for optimal use. Nonetheless, bleeding complications are common, and with certain devices, highly morbid. Likewise, pharmacologic prophylaxis to prevent thrombosis is not commonly used with many medical devices like central venous catheters due to high rates of bleeding. The contact pathway members FXI, FXII, and prekallikrein serve as a nexus, connecting biomaterial surface-mediated thrombin generation and inflammation, and may represent safe, druggable targets to improve medical device hemocompatibility and thrombogenicity. Recent in vivo and clinical data suggest that selectively targeting the contact pathway of coagulation through the inhibition of FXI and FXII can reduce the incidence of medical device-associated thrombotic events, and potentially systemic inflammation, without impairing hemostasis. In the following review, we will outline the current in vivo and clinical data encompassing the mechanism of action of drugs targeting the contact pathway. This new class of inhibitors has the potential to herald a new era of effective and low-risk anticoagulation for the management of patients requiring the use of medical devices.

Catheter-related deep vein thrombosis: Where are we at and where are we going? Updates and ongoing unmet clinical needs

BACKGROUND

Catheter-related thrombosis (CRT) is one of the major complications affecting patients with indwelling venous catheters, usually involving the upper extremity deep venous system. This condition can lead to potentially life-threatening complications such as pulmonary embolism and sepsis. The risk of developing CRT varies depending on type of catheters and patient characteristics. Despite advances in materials and technologies, the actual incidence of CRT is still considerable. Available evidence on CRT management remains controversial, and clinical guidelines base their recommendations on data from non-catheter related upper extremity or lower extremity deep venous thromboses.

AIMS

This narrative review aims to describe the epidemiology of CRT, to review the available evidence on its management and to highlight the current unmet needs.

METHODS

No formal search strategy was applied for the revision of the literature. The main sources of information used were Medline and guidelines from international societies.

CONTENT

The management of CRT requires a careful balance between the risk of thrombus progression, recurrent events, and systemic embolization and the increased bleeding risk in often fragile patients. Open issues include the optimal management of the catheter and the type and duration of anticoagulant therapy. Direct oral anticoagulants are increasingly prescribed, representing an important alternative to the standard of care low molecular weight heparins in selected cases. The development of new anticoagulant drugs such as factors XI and XII inhibitors may offer further advantages in this context.

CONCLUSIONS

The management of CRT is still challenging with constant need for updated evidence to support tailored approaches.

Anticoagulant therapy in renal insufficiency theme: Anticoagulation in complex situations

Many patients with impaired renal function have concurrent indications for anticoagulant therapy, including atrial fibrillation and venous thromboembolism. For mild chronic kidney disease, data from clinical trials and existing guidelines can be applied to clinical management. The benefits and harms of anticoagulation therapy in patients with more advanced renal impairment are nuanced, as both thrombotic and bleeding risk are increased. Until recently, data regarding anticoagulants in severe renal impairment were primarily observational, but emerging evidence includes a few small clinical trials and the emergence of novel agents hypothesized to have improved efficacy and safety in this population. In this review, we summarize existing data on anticoagulation in patients with chronic kidney disease. We suggest a framework for anticoagulation decision-making in the burgeoning worldwide population of patients with chronic kidney disease.

Will Factor XI Inhibitors Replace Current Anticoagulants for Stroke Prevention in Atrial Fibrillation?

PURPOSE OF REVIEW

This review provides an overview of the factor XI (FXI) inhibitor hypothesis for the development of novel anticoagulants which may be safer to those currently used in clinical practice and describes preliminary clinical data from phase 2 dose-ranging studies of patients with atrial fibrillation.

RECENT FINDINGS

Recent data from phase 2 dose ranging studies demonstrate substantial reductions in bleeding with FXI pathway inhibition compared with currently approved anticoagulants. However, larger studies are necessary to demonstrate efficacy of FXI inhibition for stroke prevention in atrial fibrillation. FXI pathway inhibition holds great promise for revolutionizing the landscape of anticoagulation for atrial fibrillation, primarily by reducing bleeding risk; however, further data are necessary to demonstrate efficacy.

Milvexian: An Oral, Bioavailable Factor XIa Inhibitor

Direct oral anticoagulants have a dose-dependent increased bleeding risk which limits use in certain populations. Studies in both animals and humans with inherited variations in factor XI levels provide a theoretical basis for a drug target capable of addressing current unmet needs. Milvexian is an oral factor XIa inhibitor that has the potential to provide robust anticoagulant effect without increased bleeding compared with current standard of care. Several key studies in the preclinical, phase I, and phase II stages have reported promising safety data in venous thromboembolism and stroke prevention without compromising hemostasis. The planned phase III trials will examine the efficacy of milvexian for prevention of thrombotic events in patients with acute stroke, acute coronary syndrome, and atrial fibrillation.

Hallmarks for Thrombotic and Hemorrhagic Risks in Chronic Kidney Disease Patients

Chronic kidney disease (CKD) is a global health issue causing a significant health burden. CKD patients develop thrombotic and hemorrhagic complications, and cardiovascular diseases are associated with increased hospitalization and mortality in this population. The hemostatic alterations are multifactorial in these patients; therefore, the results of different studies are varying and controversial. Endothelial and platelet dysfunction, coagulation abnormalities, comorbidities, and hemoincompatibility of the dialysis membranes are major contributors of hypo- and hypercoagulability in CKD patients. Due to the tendency of CKD patients to exhibit a prothrombotic state and bleeding risk, they require personalized clinical assessment to understand the impact of antithrombotic therapy. The evidence of efficacy and safety of antiplatelet and anticoagulant treatments is limited for end-stage renal disease patients due to their exclusion from major randomized clinical trials. Moreover, designing hemocompatible dialyzer membranes could be a suitable approach to reduce platelet activation, coagulopathy, and thrombus formation. This review discusses the molecular mechanisms underlying thrombotic and hemorrhagic risk in patients with CKD, leading to cardiovascular complications in these patients, as well as the evidence and guidance for promising approaches to optimal therapeutic management.

Thrombogenicity of biodegradable metals

Biodegradable metals offer a promising means to ameliorate many of the long-term risks associated with vascular devices made of conventional biostable stent metals. While numerous biodegradable metal alloys have been developed and characterized in animal models, knowledge of their blood reactivity and thrombogenicity remains unknown. Metal hemocompatibility is particularly valuable because current generation drug-eluting stents pose a significant long-term thrombosis risk. In this study, four pure metals, widely used as degradable base materials (Fe, Zn, Mg, and Mo), and three alloys commonly used in cardiovascular devices [NiTi, CoCr, and stainless steel (SS)] were evaluated. This work examined how each of these metals activate platelets, coagulation factors, and inflammation using in vitro hemocompatibility assays and a clinically relevant ex vivo non-human primate arteriovenous shunt model. Testing found that while all metals promoted a downstream activation of platelets and coagulation in flowing whole blood, platelet and fibrin attachment to Mg was markedly reduced. Additionally, Fe and Mo trended toward higher platelet attachment and contact pathway activation. Overall, the results suggest that Mg may delay clot initiation, but not eliminate clot formation, indicating the importance of understanding thrombosis in Mg alloys that are currently being developed for clinical use as biodegradable stents.

Treatment strategies of the thromboembolic risk in kidney failure patients with atrial fibrillation

The incidence and prevalence of atrial fibrillation (AF) in patients affected by kidney failure, i.e. glomerular filtration rate <15 ml/min/1.73 m2, is high and probably underestimated. Numerous uncertainties remain regarding how to prevent thromboembolic events in this population because both cardiology and nephrology guidelines do not provide clear recommendations. The efficacy and safety of oral anticoagulant therapy (OAC) in preventing thromboembolism in patients with kidney failure and AF has not been demonstrated for either vitamin K antagonists (VKAs) or direct anticoagulants (DOACs). Moreover, it remains unclear which is more effective and safer, because estimated creatinine clearance <25-30 ml/min was an exclusion criterion in the randomized controlled trials (RCTs). Three RCTs comparing DOACs and VKAs in kidney failure failed to reach the primary endpoint, as they were underpowered. The left atrial appendage is the main source of thromboembolism in the presence of AF. Left atrial appendage closure (LAAC) has recently been proposed as an alternative to OAC. RCTs comparing the efficacy and safety of LAAC versus OAC in kidney failure were terminated prematurely due to recruitment failure. A recent prospective study showed a reduction in thromboembolic events in haemodialysis patients with AF and undergoing LAAC compared with patients taking or not taking OAC. We review current treatment standards and discuss recent developments in managing the thromboembolic risk in kidney failure patients with AF. The importance of shared decision-making with the multidisciplinary team and the patient to consider individual risks and benefits of each treatment option is underlined.

Safety and tolerability of the protein C activator AB002 in end-stage renal disease patients on hemodialysis: a randomized phase 2 trial

BACKGROUND

The protein C system regulates blood coagulation, inflammation, and vascular integrity. AB002 is an injectable protein C activating enzyme under investigation to safely prevent and treat thrombosis. In preclinical models, AB002 is antithrombotic, cytoprotective, and anti-inflammatory. Since prophylactic use of heparin is contraindicated during hemodialysis in some end-stage renal disease (ESRD) patients, we propose using AB002 as a short-acting alternative to safely limit blood loss due to clotting in the dialysis circuit.

METHODS

This phase 2, randomized, double-blind, placebo-controlled, single-dose study evaluates the safety and tolerability of AB002 administered into the hemodialysis line of ESRD patients during hemodialysis at one study center in the United States (ClinicalTrials.gov: NCT03963895). In this study, 36 patients were sequentially enrolled into two cohorts and randomized to AB002 or placebo in a 2:1 ratio. In cohort 1, patients received 1.5 µg/kg AB002 (n = 12) or placebo (n = 6); in cohort 2, patients received 3 µg/kg AB002 (n = 12) or placebo (n = 6). Patients underwent five heparin-free hemodialysis sessions over 10 days and were dosed with AB002 or placebo during session four.

RESULTS

Here we show that AB002 is safe and well-tolerated in ESRD patients, with no treatment-related adverse events. Clinically relevant bleeding did not occur in any patient, and the time to hemostasis at the vascular access sites is not affected by AB002.

CONCLUSIONS

As far as we are aware, this proof-of-concept study is the first clinical trial assessing the therapeutic potential of protein C activation. The results herein support additional investigation of AB002 to safely prevent and treat thrombosis in at-risk populations.

Plasma kallikrein supports FXII-independent thrombin generation in mouse whole blood

ABSTRACT

Plasma kallikrein (PKa) is an important activator of factor XII (FXII) of the contact pathway of coagulation. Several studies have shown that PKa also possesses procoagulant activity independent of FXII, likely through its ability to directly activate FIX. We evaluated the procoagulant activity of PKa using a mouse whole blood (WB) thrombin-generation (TG) assay. TG was measured in WB from PKa-deficient mice using contact pathway or extrinsic pathway triggers. PKa-deficient WB had significantly reduced contact pathway-initiated TG compared with that of wild-type controls and was comparable with that observed in FXII-deficient WB. PKa-deficient WB supported equivalent extrinsic pathway-initiated TG compared with wild-type controls. Consistent with the presence of FXII-independent functions of PKa, targeted blockade of PKa with either small molecule or antibody-based inhibitors significantly reduced contact pathway-initiated TG in FXII-deficient WB. Inhibition of activated FXII (FXIIa) using an antibody-based inhibitor significantly reduced TG in PKa-deficient WB, consistent with a PKa-independent function of FXIIa. Experiments using mice expressing low levels of tissue factor demonstrated that persistent TG present in PKa- and FXIIa-inhibited WB was driven primarily by endogenous tissue factor. Our work demonstrates that PKa contributes significantly to contact pathway-initiated TG in the complex milieu of mouse WB, and a component of this contribution occurs in an FXII-independent manner.

Factor XI as a new target for prevention of thromboembolism in cardiovascular disease: a meta-analysis of randomized controlled trials

Anticoagulant therapy is a mainstay in the management of patients with cardiovascular disease. The use of conventional anticoagulants carries potential side effects, mainly bleeding. Drugs targeting Factor XI (FXI) have been investigated in randomized controlled trials as a new option with more favorable outcomes. A comprehensive literature search was conducted to identify relevant studies comparing FXI inhibitors to placebo or standard therapy. The primary outcomes were incidence of all bleeding events, major bleeding, and thromboembolism. Secondary outcomes included incidence of all adverse events (AE), serious AE, and all-cause mortality. A total of 11 studies involving 10,536 patients were included. FXI inhibitors were associated with a trend toward reduction of bleeding events and incidence of thromboembolism compared to the control group (placebo/standard therapy). There was no statistically significant difference between both groups in terms of adverse events and all-cause mortality. When compared to enoxaparin, FXI inhibitors significantly reduced the risk of bleeding events (RR = 0.42, 95% CI: 0.23-0.76, P = 0.004) and thromboembolism (RR = 0.59, 95% CI: 0.44-0.77, P = 0.001). On the other hand, when compared to DOACs, FXI inhibitors were associated with a significant reduction in bleeding events but not thromboembolism. Whereas, compared to placebo, FXI inhibitors did not increase the risk of bleeding events, adverse events, or all-cause mortality (P > 0.05). FXI inhibitors could be a safer and more potent option for prevention of thromboembolism than conventional therapy.

Pharmacological and clinical appraisal of factor XI inhibitor drugs

The evolution of anticoagulation therapy, from vitamin K antagonists to the advent of direct oral anticoagulants (DOACs) almost two decades ago, marks significant progress. Despite improved safety demonstrated in pivotal trials and post-marketing observations, persistent concerns exist, particularly regarding bleeding risk and the absence of therapeutic indications in specific subgroups or clinical contexts. Factor XI (FXI) has recently emerged as a pivotal contributor to intraluminal thrombus formation and growth, playing a limited role in sealing vessel wall injuries. Inhibiting FXI presents an opportunity to decouple thrombosis from haemostasis, addressing concerns related to bleeding events while safeguarding against thromboembolic events. Notably, FXI inhibition holds promise for patients with end-stage renal disease or cancer, where clear indications for DOACs are currently lacking. Various compounds have undergone design, testing, and progression to phase 2 clinical trials, demonstrating a generally favourable safety and tolerability profile. However, validation through large-scale phase 3 trials with sufficient power to assess both safety and efficacy outcomes is needed. This review comprehensively examines FXI inhibitors, delving into individual classes, exploring their pharmacological properties, evaluating the latest evidence from randomized trials, and offering insights into future perspectives.

Pharmacologic targeting of coagulation factors XII and XI by monoclonal antibodies reduces thrombosis in nitinol stents under flow

BACKGROUND

Cardiovascular implantable devices, such as vascular stents, are critical for the treatment of cardiovascular diseases. However, their success is dependent on robust and often long-term antithrombotic therapies. Yet, the current standard-of-care therapies often pose significant bleeding risks to patients. Coagulation factor (F)XI and FXII have emerged as potentially safe and efficacious targets to safely reduce pathologic thrombin generation in medical devices.

OBJECTIVES

To study the efficacy of monoclonal antibody-targeting FXII and FXI of the contact pathway in preventing vascular device-related thrombosis.

METHODS

The effects of inhibition of FXII and FXI using function-blocking monoclonal antibodies were examined in a nonhuman primate model of nitinol stent-related thrombosis under arterial and venous flow conditions.

RESULTS

We found that function-blocking antibodies of FXII and FXI reduced markers of stent-induced thrombosis in vitro and ex vivo. However, FXI inhibition resulted in more effective mitigation of thrombosis markers under varied flow conditions.

CONCLUSION

This work provides further support for the translation of contact pathway of coagulation inhibitors for their adjunctive clinical use with cardiovascular devices.

The foundation for investigating factor XI as a target for inhibition in human cardiovascular disease

Anticoagulant therapy is a mainstay in the management of patients with cardiovascular disease and related conditions characterized by a heightened risk for thrombosis. Acute coronary syndrome, chronic coronary syndrome, ischemic stroke, and atrial fibrillation are the most common. In addition to their proclivity for thrombosis, each of these four conditions is also characterized by local and systemic inflammation, endothelial/endocardial injury and dysfunction, oxidative stress, impaired tissue-level reparative capabilities, and immune dysregulation that plays a critical role in linking molecular events, environmental triggers, and phenotypic expressions. Knowing that cardiovascular disease and thrombosis are complex and dynamic, can the scientific community identify a common pathway or specific point of interface susceptible to pharmacological inhibition or alteration that is likely to be safe and effective? The contact factors of coagulation may represent the proverbial "sweet spot" and are worthy of investigation. The following review provides a summary of the fundamental biochemistry of factor XI, its biological activity in thrombosis, inflammation, and angiogenesis, new targeting drugs, and a pragmatic approach to managing hemostatic requirements in clinical trials and possibly day-to-day patient care in the future.

Targeting factor XI and factor XIa to prevent thrombosis

ABSTRACT

Direct oral anticoagulants (DOACs) that inhibit the coagulation proteases thrombin or factor Xa (FXa) have replaced warfarin and other vitamin K antagonists (VKAs) for most indications requiring long-term anticoagulation. In many clinical situations, DOACs are as effective as VKAs, cause less bleeding, and do not require laboratory monitoring. However, because DOACs target proteases that are required for hemostasis, their use increases the risk of serious bleeding. Concerns over therapy-related bleeding undoubtedly contribute to undertreatment of many patients who would benefit from anticoagulation therapy. There is considerable interest in the plasma zymogen factor XI (FXI) and its protease form factor XIa (FXIa) as drug targets for treating and preventing thrombosis. Laboratory and epidemiologic studies support the conclusion that FXI contributes to venous and arterial thrombosis. Based on 70 years of clinical observations of patients lacking FXI, it is anticipated that drugs targeting this protein will cause less severe bleeding than warfarin or DOACs. In phase 2 studies, drugs that inhibit FXI or FXIa prevent venous thromboembolism after total knee arthroplasty as well as, or better than, low molecular weight heparin. Patients with heart disease on FXI or FXIa inhibitors experienced less bleeding than patients taking DOACs. Based on these early results, phase 3 trials have been initiated that compare drugs targeting FXI and FXIa to standard treatments or placebo. Here, we review the contributions of FXI to normal and abnormal coagulation and discuss results from preclinical, nonclinical, and clinical studies of FXI and FXIa inhibitors.

Biology of factor XI

ABSTRACT

Unique among coagulation factors, the coagulation factor XI (FXI) arose through a duplication of the gene KLKB1, which encodes plasma prekallikrein. This evolutionary origin sets FXI apart structurally because it is a homodimer with 2 identical subunits composed of 4 apple and 1 catalytic domain. Each domain exhibits unique affinities for binding partners within the coagulation cascade, regulating the conversion of FXI to a serine protease as well as the selectivity of substrates cleaved by the active form of FXI. Beyond serving as the molecular nexus for the extrinsic and contact pathways to propagate thrombin generation by way of activating FIX, the function of FXI extends to contribute to barrier function, platelet activation, inflammation, and the immune response. Herein, we critically review the current understanding of the molecular biology of FXI, touching on some functional consequences at the cell, tissue, and organ level. We conclude each section by highlighting the DNA mutations within each domain that present as FXI deficiency. Together, a narrative review of the structure-function of the domains of FXI is imperative to understand the etiology of hemophilia C as well as to identify regions of FXI to safely inhibit the pathological function of activation or activity of FXI without compromising the physiologic role of FXI.

Pharmacokinetics, pharmacodynamics, and safety of frunexian in healthy Chinese volunteer adults: A randomized dose-escalation phase I study

The purpose of this study was to evaluate the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of frunexian (formerly known as EP-7041 and HSK36273) injection, a small molecule inhibitor of activated coagulation factor XI (FXIa), in healthy Chinese adult volunteers. This study was a randomized, placebo- and positive-controlled, sequential, ascending-dose (0.3/0.6/1.0/1.5/2.25 mg/kg/h) study of 5-day continuous intravenous infusions of frunexian. Frunexian administration exhibited an acceptable safety profile with no bleeding events. Steady state was rapidly reached with a median time ranging from 1.02 to 1.50 h. The mean half-life ranged from 1.15 to 1.43 h. Frunexian plasma concentration at a steady state and area under the concentration-time curve exhibited dose-proportional increases. The dose-escalation study of frunexian demonstrated its progressively enhanced capacities to prolong activated partial thromboplastin time (aPTT) and inhibit FXIa activity. The correlations between PK and PD biomarkers (aPTT/baseline and FXI clotting activity/baseline) were described by the two Emax models, with the EC50 values of 8940 and 1300 ng/mL, respectively. Frunexian exhibits good safety and PK/PD properties, suggesting it is a promising candidate for anticoagulant drug.

New Directions in Infection-Associated Ischemic Stroke

The relationship between infections and stroke has not been fully characterized, probably delaying the development of specific treatments. This narrative review addresses mechanisms of stroke linked to infections, including hypercoagulability, endothelial dysfunction, vasculitis, and impaired thrombolysis. SARS-CoV-2, the virus that causes COVID-19, may promote the development of stroke, which may represent its most severe neurological complication. The development of specific therapies for infection-associated stroke remains a profound challenge. Perhaps the most important remaining issue is the distinction between infections that trigger a stroke versus infections that are truly incidental. This distinction likely requires the establishment of appropriate biomarkers, candidates of which are elevated levels of fibrin D-dimer and anticardiolipin/antiphospholipid antibodies. These candidate biomarkers might have potential use in identifying pathogenic infections preceding stroke, which is a precursor to establishing specific therapies for this syndrome.

Milvexian: A Focus on a New Oral Anticoagulant that Targets Factor XIa for Thromboembolism Prophylaxis

Drugs that target factor XI and/or XIa have been evaluated as alternatives to existing anticoagulants, in light of studies that indicate that a decrease in Factor XI/XIa levels or activity may result in a lower risk of thrombosis without a significant increase in bleeding risk. Milvexian is an investigational small-molecule factor XIa inhibitor that has recently completed phase 2 clinical trials. Preclinical studies were suggestive of its potential to prevent arterial and venous thrombosis. It was well-tolerated in healthy participants, as well as in participants with mild or moderate hepatic impairment and moderate or severe renal impairment. Notably, patients who received milvexian after knee arthroplasty had a dose-proportional lower incidence of venous thromboembolism compared to patients who received postoperative enoxaparin, and they had a lower incidence of clinically relevant bleeding. A separate phase 2 trial was conducted that assessed the use of milvexian for secondary stroke prevention in patients who had ischemic stroke or transient ischemic attack. It failed its primary objective of establishing a dose-response relationship between milvexian and a composite endpoint of symptomatic ischemic stroke or covert brain infarction. The trial did, however, show a reduction in the relative risk of symptomatic ischemic stroke across most of the treatment groups receiving various dosages of milvexian compared to placebo. The efficacy of milvexian in secondary stroke prevention will be further assessed in an upcoming phase 3 trial. Additional upcoming phase 3 trials will also assess its efficacy in stroke prevention in patients with atrial fibrillation as well as in event reduction in patients with acute coronary syndrome.

Factor XI/XIa inhibitors for the prevention and treatment of venous and arterial thromboembolism: A narrative review

During the past decade, direct oral anticoagulants (DOACs) have advanced and simplified the prevention and treatment of venous thromboembolism (VTE). However, there remains a high incidence of bleeds, which calls for agents that have a reduced risk of bleeding. Factor XI (FXI) deficiency is associated with lower rates of venous thrombosis and stroke compared to the general population with a lower risk of bleeding. In conjunction with this, phase 2 studies have demonstrated safety and the potential for reduced thrombotic events with FXI inhibitors as compared to currently available medications. The aim of this review is to summarize key data on the clinical pharmacology of FXI, the latest developments in clinical trials of FXI inhibitors, and to describe the efficacy and safety profiles of FXI inhibitors for the prevention of venous and arterial thromboembolism.

Left Atrial Appendage Occlusion and Post-procedural Antithrombotic Management

Left atrial appendage occlusion (LAAO) is an established alternative to oral anticoagulation for stroke prevention in atrial fibrillation. Antithrombotic therapy is used in the post-procedural period to prevent device-related thrombosis (DRT). The risk of DRT is considered highest in the first 45-90 days after device implantation, based on animal studies of the device healing process. Clinically applied antithrombotic regimens vary greatly across studies, continents, and centers. This article gives an overview of the evidence behind current antithrombotic regimens, ongoing randomized trials, and future post-procedural management.

Anticoagulation for people receiving long-term haemodialysis

BACKGROUND

Haemodialysis (HD) requires safe and effective anticoagulation to prevent clot formation within the extracorporeal circuit during dialysis treatments to enable adequate dialysis and minimise adverse events, including major bleeding. Low molecular weight heparin (LMWH) may provide a more predictable dose, reliable anticoagulant effects and be simpler to administer than unfractionated heparin (UFH) for HD anticoagulation, but may accumulate in the kidneys and lead to bleeding.

OBJECTIVES

To assess the efficacy and safety of anticoagulation strategies (including both heparin and non-heparin drugs) for long-term HD in people with kidney failure. Any intervention preventing clotting within the extracorporeal circuit without establishing anticoagulation within the patient, such as regional citrate, citrate enriched dialysate, heparin-coated dialysers, pre-dilution haemodiafiltration (HDF), and saline flushes were also included.

SEARCH METHODS

We searched the Cochrane Kidney and Transplant Register of Studies up to November 2023 through contact with the Information Specialist using search terms relevant to this review. Studies in the Register are identified through searches of CENTRAL, MEDLINE, and EMBASE, conference proceedings, the International Clinical Trials Registry Platform (ICTRP) Search Portal and ClinicalTrials.gov.

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-randomised controlled studies (quasi-RCTs) evaluating anticoagulant agents administered during HD treatment in adults and children with kidney failure.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the risk of bias using the Cochrane tool and extracted data. Treatment effects were estimated using random effects meta-analysis and expressed as relative risk (RR) or mean difference (MD) with 95% confidence intervals (CI). Evidence certainty was assessed using the Grading of Recommendation, Assessment, Development and Evaluation approach (GRADE).

MAIN RESULTS

We included 113 studies randomising 4535 participants. The risk of bias in each study was adjudicated as high or unclear for most risk domains. Compared to UFH, LMWH had uncertain effects on extracorporeal circuit thrombosis (3 studies, 91 participants: RR 1.58, 95% CI 0.46 to 5.42; I2 = 8%; low certainty evidence), while major bleeding and minor bleeding were not adequately reported. Regional citrate anticoagulation may lower the risk of minor bleeding compared to UFH (2 studies, 82 participants: RR 0.34, 95% CI 0.14 to 0.85; I2 = 0%; low certainty evidence). No studies reported data comparing regional citrate to UFH on risks of extracorporeal circuit thrombosis and major bleeding. The effects of very LMWH, danaparoid, prostacyclin, direct thrombin inhibitors, factor XI inhibitors or heparin-grafted membranes were uncertain due to insufficient data. The effects of different LMWH, different doses of LMWH, and the administration of LMWH anticoagulants using inlet versus outlet bloodline or bolus versus infusion were uncertain. Evidence to compare citrate to another citrate or control was scant. The effects of UFH compared to no anticoagulant therapy or different doses of UFH were uncertain. Death, dialysis vascular access outcomes, blood transfusions, measures of anticoagulation effect, and costs of interventions were rarely reported. No studies evaluated the effects of treatment on non-fatal myocardial infarction, non-fatal stroke and hospital admissions. Adverse events were inconsistently and rarely reported.

AUTHORS' CONCLUSIONS

Anticoagulant strategies, including UFH and LMWH, have uncertain comparative risks on extracorporeal circuit thrombosis, while major bleeding and minor bleeding were not adequately reported. Regional citrate may decrease minor bleeding, but the effects on major bleeding and extracorporeal circuit thrombosis were not reported. Evidence supporting clinical decision-making for different forms of anticoagulant strategies for HD is of low and very low certainty, as available studies have not been designed to measure treatment effects on important clinical outcomes.

Factor XI as a therapeutic target in neuroinflammatory disease

PURPOSE OF REVIEW

This review summarizes the pathophysiology and potential therapeutic options for treatment of multiple sclerosis, a common neuronal demyelinating disorder affecting 2.2 million people worldwide. As an autoimmune disorder, multiple sclerosis is associated with neuroinflammation and increased permeability of the blood-brain barrier (BBB), although the cause linking multiple sclerosis with compromised barrier function remains ill-defined. It has been previously shown that coagulation factors, including thrombin and fibrin, exacerbate the inflammatory processes and permeability of the BBB.

RECENT FINDINGS

Increased levels of the coagulation factor (F) XII have been found in patients presenting with relapsing-remitting multiple sclerosis, with a deleterious role for FXII being validated in murine model of multiple sclerosis, experimental autoimmune encephalitis (EAE). Recent work has uncovered a role for the major substrate activated by FXII and thrombin, FXI, in the disorder of EAE. The study found that pharmacological targeting of FXI decreased clinical symptoms, lymphocyte invasion, and white matter destruction in a multiple sclerosis model.

SUMMARY

This review emphasizes the role of FXII and FXI in regulating barrier function and the immune response in neuroinflammation. These new findings broaden the potential for therapeutic utility of FXI inhibitors beyond thrombosis to include neuroinflammatory diseases associated with compromised BBB function, including multiple sclerosis.

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.

Activation of coagulation FXI promotes endothelial inflammation and amplifies platelet activation in a nonhuman primate model of hyperlipidemia

Background

Hyperlipidemia is associated with chronic inflammation and thromboinflammation. This is an underlying cause of several cardiovascular diseases, including atherosclerosis. In diseased blood vessels, rampant thrombin generation results in the initiation of the coagulation cascade, activation of platelets, and endothelial cell dysfunction. Coagulation factor (F) XI represents a promising therapeutic target to reduce thromboinflammation, as it is uniquely positioned at an intersection between inflammation and thrombin generation.

Objectives

This study aimed to investigate the role of FXI in promoting platelet and endothelial cell activation in a model of hyperlipidemia.

Methods

Nonhuman primates (NHPs) were fed a standard chow diet (lean, n = 6) or a high-fat diet (obese, n = 8) to establish a model of hyperlipidemia. Obese NHPs were intravenously administered a FXI blocking antibody (2 mg/kg) and studied at baseline and at 1, 7, 14, 21, and 28 days after drug administration. Platelet activation and inflammatory markers were measured using fluorescence-activated cell sorting or enzyme-linked immunosorbent assay. Molecular imaging was used to quantify vascular cell adhesion molecule 1 (VCAM-1) expression at the carotid bifurcation.

Results

Obese NHPs demonstrated increased sensitivity for platelet P-selectin expression and phosphatidylserine exposure in response to platelet GPVI or PAR agonists compared with lean NHPs. Obese NHPs exhibited elevated levels of C-reactive protein, cathepsin D, and myeloperoxidase compared with lean NHPs. Following pharmacological inhibition of FIX activation by FXIa, platelet priming for activation by GPVI or PAR agonists, C-reactive protein levels, and endothelial VCAM-1 levels were reduced in obese NHPs.

Conclusion

FXI activation promotes the proinflammatory phenotype of hyperlipidemia by priming platelet activation and inciting endothelial cell dysfunction.

Factor XI Inhibition With Heparin Reduces Clot Formation in Simulated Pediatric Extracorporeal Membrane Oxygenation

Extracorporeal membrane oxygenation (ECMO) supplies circulatory support and gas exchange to critically ill patients. Despite the use of systemic anticoagulation, blood exposure to ECMO surfaces causes thromboembolism complications. Inhibition of biomaterial surface-mediated activation of coagulation factor XI (FXI) may prevent device-associated thrombosis. Blood was collected from healthy volunteers (n = 13) following the U.S. Army Institute of Surgical Research standard operating procedure for testing in an ex vivo ECMO circuit. A roller-pump circuit circulated either 0.5 U/ml of unfractionated heparin alone or in combination with the anti-FXI immunoglobulin G (IgG) (AB023) for 6 hours or until clot formation caused device failure. Coagulation factor activity, platelet counts, time to thrombin generation, peak thrombin, and endogenous thrombin potential were quantified. AB023 in addition to heparin sustained circuit patency in all tested circuits (5/5) after 6 hours, while 60% of circuits treated with heparin alone occluded (3/8), log-rank p < 0.03. AB023 significantly prolonged the time to clot formation as compared to heparin alone (15.5 vs . 3.3 minutes; p < 0.01) at the 3-hour time point. AB023 plus heparin significantly reduced peak thrombin compared to heparin alone (123 vs . 217 nM; p < 0.01). Inhibition of contact pathway activation of FXI may be an effective adjunct to anticoagulation in extracorporeal life support.

Anticoagulants in adult extracorporeal membrane oxygenation: alternatives to standardized anticoagulation with unfractionated heparin

BACKGROUND

Extracorporeal membrane oxygenation (ECMO) is a vital technique for severe respiratory or heart failure patients. Bleeding and thrombotic events are common during ECMO and negatively impact patient outcomes. Unfractionated heparin is the primary anticoagulant, but its adverse effects limit its use, necessitating alternative anticoagulants.

OBJECTIVE

Review available alternative anticoagulants for adult ECMO patients. Explore potential novel anticoagulants for future ECMO use. Aim to reduce complications (bleeding and thrombosis) and improve safety and efficacy for critically ill ECMO patients.

METHODS

Comprehensive literature review of existing and emerging anticoagulants for ECMO.

RESULTS

Identified a range of alternative anticoagulants beyond unfractionated heparin. Evaluated their potential utility in mitigating ECMO-related complications.

CONCLUSION

Diverse anticoagulant options are available and under investigation for ECMO. These alternatives may enhance patient safety and outcomes during ECMO support. Further research and clinical studies are warranted to determine their effectiveness and safety profiles.

Factor XI Inhibitors: Potential Role in End-Stage Kidney Disease

Patients with end-stage kidney disease (ESKD) experience a high thrombotic risk but are also at increased risk of bleeding. There is an unmet need for safer antithrombotic therapy in patients with ESKD on hemodialysis. Factor XI (FXI) represents an attractive therapeutic target for anticoagulation because of the potential to mitigate the bleeding risks associated with currently approved anticoagulants, especially in patients at high risk of bleeding. FXI inhibition is also an attractive option in settings where coagulation is activated by exposure of the blood to artificial surfaces, including the extracorporeal circuit during hemodialysis. Therapies targeting FXI that are in the most advanced stages of clinical development include antisense oligonucleotides, monoclonal antibodies, and synthetic small molecules, which serve either to lower FXI levels or block its physiological effects. This review article presents the most recent pharmacological data with FXI inhibitors, briefly describes phase 2 and 3 clinical trials with these agents, and critically examines the potential future use of FXI inhibitors for extracorporeal circuit anticoagulation in patients with ESKD. In addition, laboratory monitoring and reversal of FXI inhibitors are briefly discussed.

Clotting of the Extracorporeal Circuit in Hemodialysis: Beyond Contact-Activated Coagulation

Thrombotic complications in patients with end-stage kidney disease are frequent. While being a lifesaving treatment for these patients, hemodialysis introduces a thromboinflammatory environment. Additionally, the extracorporeal hemodialysis circuit itself is prone to clotting because of an interaction between different activation mechanisms of the coagulation system, platelets, and the immune system. Anticoagulation of the patient and the machine is frequently complicated by bleeding. We discuss the factors important in this balancing act and touch on potential strategies that are on the horizon to target thromboinflammation.

Implementation of a coagulation component into a phosphate kinetics model in haemodialysis therapy: A tool for detection of clotting problems?

A coagulation component should be considered in phosphate kinetics modelling because intradialytic coagulation of the extracorporeal circuit and dialyser might reduce phosphate removal in haemodialysis. Thus, the objective of this study was to add and evaluate coagulation as an individual linear clearance reduction component to a promising three-compartment model assuming progressive intradialytic clotting. The model was modified and validated on intradialytic plasma and dialysate phosphate samples from 12 haemodialysis patients collected during two treatments (HD1 and HD2) at a Danish hospital ward. The most suitable clearance reduction in each treatment was identified by minimizing the root mean square error (RMSE). The model simulations with and without clearance reduction were compared based on RMSE and coefficient of determination (R2 ) values. Improvements were found for 17 of the 24 model simulations when clearance reduction was added to the model. The slopes of the clearance reduction were in the range of 0.011-0.632/h. Three improvements were found to be statistically significant (|observed z value| > 1.96). A very significant correlation (R2  = 0.708) between the slopes for HD1 and HD2 was found. Adding the clearance reduction component to the model seems promising in phosphate kinetics modelling and might be explained, at least in part, by intradialytic coagulation. In future studies, the model might be developed further to serve as a potentially useful tool for the quantitative detection of clotting problems in haemodialysis. NEW FINDINGS: What is the central question of this study? The aim was to add an intradialytic coagulation component to a modified version of a promising three-compartment phosphate kinetics model. The hypothesis was that circuit and dialyser clotting can be modelled by an individual linear phosphate clearance reduction component during haemodialysis treatment. What is the main finding and its importance? Improvements were found for 17 of 24 model simulations when clearance reduction was added to the model. Thus, the kinetics model seems promising and could be a useful tool for the quantitative detection of clotting problems in haemodialysis patients.

A new strategy for anticoagulation: The factor XI inhibitors

Direct oral anticoagulants (DOACs) are currently the first-choice therapy for the prevention of cardioembolic events in patients with atrial fibrillation and for the treatment of venous thromboembolism (VTE) due to their more favorable efficacy to safety profile in comparison to vitamin K antagonists (VKA). DOACs did not show a clinical benefit when used for in stroke prevention in patients with mechanic or rheumatic valves or in those who underwent transcatheter aortic valve implantation (TAVI), in the treatment of VTE in patients with antiphospholipid antibody syndrome and in prevention of VTE in medically ill patients. There are some concerns for bleeding excess at the gastrointestinal site for some, but not all, DOACs. In recent years, in order to overcome the limitations of the available DOACs and to explore the advantages of anticoagulation in additional clinical settings, the development of factor XI and factor XII inhibitors as anticoagulant agents has been proposed. Emerging data show that factor XI has a minor role in the physiological process of hemostasis and an important role in the development of thrombosis. Bleeding has been viewed for several years as an unavoidable side effect of anticoagulant therapy. The aim of factor XI inhibitors is to challenge this dogma by favoring the uncoupling between hemostasis and thrombosis. This paper provides an update on the rationale for the use of factor XI inhibitors, their pharmacological properties and the preliminary clinical findings.

Pharmacological targeting of coagulation factor XI attenuates experimental autoimmune encephalomyelitis in mice

Multiple sclerosis (MS) is the most common causes of non-traumatic disability in young adults worldwide. MS pathophysiologies include the formation of inflammatory lesions, axonal damage and demyelination, and blood brain barrier (BBB) disruption. Coagulation proteins, including factor (F)XII, can serve as important mediators of the adaptive immune response during neuroinflammation. Indeed, plasma FXII levels are increased during relapse in relapsing-remitting MS patients, and previous studies showed that reducing FXII levels was protective in a murine model of MS, experimental autoimmune encephalomyelitis (EAE). Our objective was to determine if pharmacological targeting of FXI, a major substrate of activated FXII (FXIIa), improves neurological function and attenuates CNS damage in the setting of EAE. EAE was induced in male mice using murine myelin oligodendrocyte glycoprotein peptides combined with heat-inactivated Mycobacterium tuberculosis and pertussis toxin. Upon onset of symptoms, mice were treated every other day intravenously with anti-FXI antibody, 14E11, or saline. Disease scores were recorded daily until euthanasia for ex vivo analyses of inflammation. Compared to the vehicle control, 14E11 treatment reduced the clinical severity of EAE and total mononuclear cells, including CD11b+CD45high macrophage/microglia and CD4+ T cell numbers in brain. Following pharmacological targeting of FXI, BBB disruption was reduced, as measured by decreased axonal damage and fibrin(ogen) accumulation in the spinal cord. These data demonstrate that pharmacological inhibition of FXI reduces disease severity, immune cell migration, axonal damage, and BBB disruption in mice with EAE. Thus, therapeutic agents targeting FXI and FXII may provide a useful approach for treating autoimmune and neurologic disorders.

Factor XIa Inhibitors as a Novel Anticoagulation Target: Recent Clinical Research Advances

BACKGROUND

While current clinically administered anticoagulant medications have demonstrated effectiveness, they have also precipitated significant risks: severe bleeding complications including, but not limited to, gastrointestinal hemorrhaging and intracranial and other life-threatening major bleedings. An ongoing effort is being made to identify the best targets for anticoagulant-targeted drugs. Coagulation factor XIa (FXIa) is emerging as an important target of current anticoagulant treatment.

OBJECTIVE

This review will summarize the development of anticoagulants and recent advances in clinical trials of experimental factor XI inhibitors from a clinical application perspective.

RESULTS

As of 1 January 2023, our search screening included 33 clinical trials. We summarized the research progress of FXIa inhibitors from seven clinical trials that evaluated their efficacy and safety. The results showed no statistically meaningful distinction in the primary efficacy between patients receiving FXIa inhibitors compared to controls (RR = 0.796; 95% CI: 0.606-1.046; I² = 68%). The outcomes did not indicate a statistical difference in the occurrence of any bleeding between patients receiving FXIa inhibitors compared to controls (RR = 0.717; 95% CI: 0.502-1.023; I² = 60%). A subgroup analysis found significant differences in severe bleeding and clinically relevant hemorrhaging in subjects receiving FXIa inhibitors compared to Enoxaparin (RR = 0.457; 95% CI: 0.256-0.816; I² = 0%).

CONCLUSIONS

Clinical trials to date have indicated that factor XIa is a potential anticoagulation target, and factor XIa inhibitors may play an important role in the development of anticoagulants.

Potential anticoagulant of traditional chinese medicine and novel targets for anticoagulant drugs

BACKGROUND

Anticoagulants are the main drugs used for the prevention and treatment of thrombosis. Currently, anticoagulant drugs are primarily multitarget heparin drugs, single-target FXa inhibitors and FIIa inhibitors. In addition, some traditional Chinese drugs also have anticoagulant effects, but they are not the main direction of treatment at present. But the anticoagulant drugs mentioned above, all have a common side effect is bleeding. Many other anticoagulation targets are under investigation. With further exploration of coagulation mechanism, how to further determine new anticoagulant targets and how to make traditional Chinese medicine play anticoagulant role have become a new field of exploration.

PURPOSE

The purpose of the study was to summarize the recent research progress on coagulation mechanisms, new anticoagulant targets and traditional Chinese medicine.

METHODS

A comprehensive literature search was conducted using four electronic databases, including PubMed, Embase, CNKI, Wanfang database and ClinicalTrials.gov, from the inception of the study to 28 Feb 2023. Key words used in the literature search were "anticoagulation", "anticoagulant targets", "new targets", "coagulation mechanisms", "potential anticoagulant", "herb medicine", "botanical medicine", "Chinese medicine", "traditional Chinese medicine", "blood coagulation factor", keywords are linked with AND/OR. Recent findings on coagulation mechanisms, potential anticoagulant targets and traditional Chinese medicine were studied.

RESULTS

The active components extracted from the Chinese medicinal herbs, Salvia miltiorrhiza, Chuanxiong rhizoma, safflower and Panax notoginseng have obvious anticoagulant effects and can be used as potential anticoagulant drugs, but the risk of bleeding is unclear. TF/FVIIa, FVIII, FIX, FXI, FXII, and FXIII have all been evaluated as targets in animal studies or clinical trials. FIX and FXI are the most studied anticoagulant targets, but FXI inhibitors have shown stronger advantages.

CONCLUSION

This review of potential anticoagulants provides a comprehensive resource. Literature analysis suggests that FXI inhibitors can be used as potential anticoagulant candidates. In addition, we should not ignore the anticoagulant effect of traditional Chinese medicine, and look forward to more research and the emergence of new drugs.

New pharmacotherapeutic options for oral anticoagulant treatment in atrial fibrillation patients aged 65 and older: factor XIa inhibitors and beyond

INTRODUCTION

Although much progress has been made using anticoagulation for stroke prevention in patients with non-valvular atrial fibrillation, bleeding is still a major concern.

AREAS COVERED

This article reviews current pharmacotherapeutic options in this setting. Particular emphasis is placed on the ability of the new molecules to minimize the bleeding risk in elderly patients. A systematic search of PubMed, Web of Science, and the Cochrane Library up to March 2023 was carried out.

EXPERT OPINION

Contact phase of coagulation is a possible new target for anticoagulant therapy. Indeed, congenital or acquired deficiency of contact phase factors is associated with reduced thrombotic burden and limited risk of spontaneous bleeding. These new drugs seem particularly suitable for stroke prevention in elderly patients with non-valvular atrial fibrillation in whom the hemorrhagic risk is high. Most of anti Factor XI (FXI) drugs are for parenteral use only. A group of small molecules are for oral use and therefore are candidates to substitute direct oral anticoagulants (DOACs) for stroke prevention in elderly patients with atrial fibrillation. Doubts remain on the possibility of impaired hemostasis. Indeed, a fine calibration of inhibition of contact phase factors is crucial for an effective and safe treatment.

Titanium is a potent inducer of contact activation: implications for intravascular devices

BACKGROUND

Titanium (Ti) and its alloys are widely used in manufacturing medical devices because of their strength and resistance to corrosion. Although Ti compounds are considered compatible with blood, they appear to support plasma contact activation and may be thrombogenic.

OBJECTIVES

The objective of this study was to compare Ti and titanium nitride (TiN) with known activators of contact activation (kaolin and silica) in plasma-clotting assays and to assess binding and activation of factor XII, (FXII), factor XI (FXI), prekallikrein, and high-molecular-weight kininogen (HK) with Ti/TiN.

METHODS

Ti-based nanospheres and foils were compared with kaolin, silica, and aluminum in plasma-clotting assays. Binding and activation of FXII, prekallikrein, HK, and FXI to surfaces was assessed with western blots and chromogenic assays.

RESULTS

Using equivalent surface amounts, Ti and TiN were comparable with kaolin and superior to silica, for inducing coagulation and FXII autoactivation. Similar to many inducers of contact activation, Ti and TiN are negatively charged; however, their effects on FXII are not neutralized by the polycation polybrene. Antibodies to FXII, prekallikrein, or FXI or coating Ti with poly-L-arginine blocked Ti-induced coagulation. An antibody to FXII reduced FXII and PK binding to Ti, kallikrein generation, and HK cleavage.

CONCLUSION

Titanium compounds induce contact activation with a potency comparable with that of kaolin. Binding of FXII with Ti shares some features with FXII binding to soluble polyanions but may have unique features. Inhibitors targeting FXII or FXI may be useful in mitigating Ti-induced contact activation in patients with titanium-based implants that are exposed to blood.

Insights in the Prothrombotic Changes After Implantation of a Left Ventricular Assist Device in Patients With End-Stage Heart Failure: A Longitudinal Observational Study

Thrombus formation is a common complication during left ventricular assist device (LVAD) therapy, despite anticoagulation with vitamin K antagonists (VKA) and a platelet inhibitor. Plasma levels of markers for primary and secondary hemostasis and contact activation were determined before LVAD implantation and 6 and 12 months thereafter in 37 adults with end-stage heart failure. Twelve patients received a HeartMate 3, 7 patients received a HeartWare, and 18 patients received a HeartMate II. At baseline, patients had elevated plasma levels of the platelet protein upon activation, β-thromboglobulin, and active von Willebrand factor in thrombogenic state (VWFa), which remained high after LVAD implantation. Von Willebrand factor levels and VWF activity were elevated at baseline but normalized 12 months after LVAD implantation. High D -dimer plasma levels, at baseline, remained elevated after 12 months. This was associated with an increase in plasma thrombin-antithrombin-complex levels and plasma levels of contact activation marker-cleaved H-kininogen after LVAD implantation. Considering these results it could be concluded that LVAD patients show significant coagulation activation despite antithrombotic therapy, which could explain why patients are at high risk for LVAD-induced thrombosis. Continuous low-grade systemic platelet activation and contact activation may contribute to prothrombotic effects of LVAD.