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

Association of anti-factor Xa-guided anticoagulation with hemorrhage during ECMO support: A systematic review and meta-analysis

BACKGROUND

The use of extracorporeal membrane oxygenation (ECMO) is associated with complex hemostatic changes. Systemic anticoagulation is initiated to prevent clotting in the ECMO system, but this comes with an increased risk of bleeding. Evidence on the use of anti-Xa-guided monitoring to prevent bleeding during ECMO support is limited. Therefore, we aimed to analyze the association between anti-factor Xa-guided anticoagulation and hemorrhage during ECMO.

METHODS

A systematic review and meta-analysis was performed (up to August 2023).

PROSPERO

CRD42023448888.

RESULTS

Twenty-six studies comprising 2293 patients were included in the analysis, with six works being part of the meta-analysis. The mean anti-Xa values did not show a significant difference between patients with and without hemorrhage (standardized mean difference -0.05; 95% confidence interval [CI]: -0.19; 0.28, p = .69). We found a positive correlation between anti-Xa levels and unfractionated heparin dose (UFH; pooled estimate of correlation coefficients 0.44; 95% CI: 0.33; 0.55, p < .001). The most frequent complications were any type of hemorrhage (pooled 36%) and thrombosis (33%). Nearly half of the critically ill patients did not survive to hospital discharge (47%).

CONCLUSIONS

The most appropriate tool for anticoagulation monitoring in ECMO patients is uncertain. Our analysis did not reveal a significant difference in anti-Xa levels in patients with and without hemorrhagic events. However, we found a moderate correlation between anti-Xa and the UFH dose, supporting its utilization in monitoring UFH anticoagulation. Given the limitations of time-guided monitoring methods, the role of anti-Xa is promising and further research is warranted.

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.

Design, synthesis and biological evaluation of 6-chloro-quinolin-2-one derivatives as novel FXIa inhibitors

A series of 6-chloro-quinolin-2-one derivatives were designed and synthesized as FXIa inhibitors by exploration of P1, P1 prime and P2 prime groups. Each compound was accessed for inhibitory effect on FXIa and some of them were evaluated in the clotting assay. 14c demonstrated excellent in-vitro potency (FXIa IC50: 15 nM, 2 x aPTT: 6.8 μM) and good in-vivo efficacy (prolonged in-vivo aPTT by more than 1-fold but not PT). Moreover, the pharmacokinetics property of 14c were evaluated following intravenous administration in rats, which indicated that 14c probably will be a clinical candidate for intravenous administration.

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.

Design, expression and biological evaluation of DX-88mut as a novel selective factor XIa inhibitor for antithrombosis

Thrombotic diseases, such as myocardial infarction, stroke, and deep vein thrombosis, severely threaten human health, and anticoagulation is an effective way to prevent such illnesses. However, most anticoagulant drugs in the clinic have different bleeding risks. Previous studies have shown that coagulation factor XI is an ideal target for safe anticoagulant drug development. Here, we designed the FXIa inhibitory peptide DX-88mut by replacing Loop1 (DGPCRAAHPR) and Loop2 (IYGGC) in DX-88, which is a clinical drug targeting PKa for the treatment of hereditary angioedema, using Loop1 (TGPCRAMISR) and Loop2 (FYGGC) in the FXIa inhibitory peptide PN2KPI, respectively. DX-88mut selectively inhibited FXIa against a panel of serine proteases with an IC50 value of 14.840 ± 0.453 nM, dose-dependently prolonged APTT in mouse, rat and human plasma, and potently inhibited FeCl3-induced carotid artery thrombosis in mice at a dose of 1 µmol/kg. Additionally, DX-88mut did not show a significant bleeding risk at a dose of 5 µmol/kg. Taken together, these results show that DX-88mut is a potential candidate for the development of a novel antithrombotic agent.

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.

The Journey Through the Pathogenesis and Treatment of Venous Thromboembolism in Inflammatory Bowel Diseases: A Narrative Review

Inflammatory bowel diseases (IBDs) are chronic inflammatory disorders of the gastrointestinal tract including Crohn's disease and ulcerative colitis, which may result in several extraintestinal complications (∼20-30% of cases), such as increased risk of venous thromboembolism (VTE). The main pathophysiological mechanism of VTE is an inflammation-induced hypercoagulable state, and recent data have shown that endothelial dysregulation due to gut and systemic inflammation may also lead to a prothrombotic state. Several prothrombotic alterations have been described, such as the activation of the coagulation system, platelet abnormalities, and dysregulation of fibrinolysis. Furthermore, the dysregulation of the gut microbiome seems to play a vital role in increasing systemic inflammation and thus inducing a procoagulant state. Our review aims to examine the main correlations between IBD and VTE, the underlying pathophysiology, and current therapeutic options.

Thromboinflammatory challenges in stroke pathophysiology

Despite years of encouraging translational research, ischemic stroke still remains as one of the highest unmet medical needs nowadays, causing a tremendous burden to health care systems worldwide. Following an ischemic insult, a complex signaling pathway emerges leading to highly interconnected thrombotic as well as neuroinflammatory signatures, the so-called thromboinflammatory cascade. Here, we thoroughly review the cell-specific and time-dependent role of different immune cell types, i.e., neutrophils, macrophages, T and B cells, as key thromboinflammatory mediators modulating the neuroinflammatory response upon stroke. Similarly, the relevance of platelets and their tight crosstalk with a variety of immune cells highlights the relevance of this cell-cell interaction during microvascular dysfunction, neovascularization, and cellular adhesion. Ultimately, we provide an up-to-date overview of therapeutic approaches mechanistically targeting thromboinflammation currently under clinical translation, especially focusing on phase I to III clinical trials.

aPTT-guided anticoagulation monitoring during ECMO support: A systematic review and meta-analysis

INTRODUCTION

The initiation of the extracorporeal membrane oxygenation (ECMO) is associated with complex coagulatory and inflammatory processes and consequently needed anticoagulation. Systemic anticoagulation bears an additional risk of serious bleeding, and its monitoring is of immense importance. Therefore, our work aims to analyze the association of anticoagulation monitoring with bleeding during ECMO support.

MATERIAL AND METHODS

Systematic literature review and meta-analysis, complying with the PRISMA guidelines (PROSPERO-CRD42022359465).

RESULTS

Seventeen studies comprising 3249 patients were included in the final analysis. Patients experiencing hemorrhage had a longer activated partial thromboplastin time (aPTT), a longer ECMO duration, and higher mortality. We could not find strong evidence of any aPTT threshold association with the bleeding occurrence, as less than half of authors reported a potential relationship. Finally, we identified the acute kidney injury (66%, 233/356) and hemorrhage (46%, 469/1046) to be the most frequent adverse events, while almost one-half of patients did not survive to discharge (47%, 1192/2490).

CONCLUSION

The aPTT-guided anticoagulation is still the standard of care in ECMO patients. We did not find strong evidence supporting the aPTT-guided monitoring during ECMO. Based on the weight of the available evidence, further randomized trials are crucial to clarify the best monitoring strategy.

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.

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.

Factor XIa Inhibitors in Anticoagulation Therapy: Recent Advances and Perspectives

Factor XIa (FXIa) in the intrinsic pathway of the coagulation process has been proven to be an effective and safe target for anticoagulant discovery with limited or no bleeding. Numerous small-molecule FXIa inhibitors (SMFIs) with various scaffolds have been identified in the early stages of drug discovery. They have served as the foundation for the recent discovery of additional promising SMFIs with improved potency, selectivity, and pharmacokinetic profiles, some of which have entered clinical trials for the treatment of thrombosis. After reviewing the coagulation process and structure of FXIa, this perspective discusses the rational or structure-based design, discovery, structure-activity relationships, and development of SMFIs disclosed in recent years. Strategies for identifying more selective and druggable SMFIs are provided, paving the way for the design and discovery of more useful SMFIs for anticoagulation therapy.

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.

Thrombotic Events Develop in 1 Out of 5 Patients Receiving ECMO Support: An 11-Year Referral Centre Experience

BACKGROUND

The use of extracorporeal membrane oxygenation (ECMO) for critically ill patients is growing rapidly given recent developments in technology. However, adverse events are frequently reported that have potentially devastating impacts on patient outcomes. The information on predictors and risk factors for thrombotic events, especially that focusing on the comparison of veno-arterial and veno-venous ECMO configurations, are still inconsistent and sparse; therefore, we aimed to close this gap.

METHODS

We performed a retrospective analysis of all patients on extracorporeal life support admitted to the intensive care units of a tertiary university center in Europe.

RESULTS

From 645 patients, 417 who received extracorporeal life support due to cardiogenic shock (290, 70%), respiratory failure (116, 28%) or hypothermia (11, 3%) were included. In total, 22% (92) of the patients experienced thrombotic events with a similar incidence in both ECMO configurations. Anticoagulation consisted of unfractionated heparin (296, 71%) and argatroban (70, 17%). Univariate Cox analyses identified hemoconcentration and increased maximal clot firmness (thromboelastometry) as risk factors for thrombosis. Moreover, the patients experiencing thrombosis had longer ECMO duration and intensive care stays.

CONCLUSIONS

ECMO is a specialized life-support modality with a high risk of complications. A longer ECMO duration is associated with thrombosis occurrence in patients receiving ECMO support. Following hemorrhage, thromboembolic complications are common adverse events. However, in contrast to major bleeding, no impact on mortality was observed. The question arises if a protocol with less anticoagulation may have a role to play in the future.

Pharmacological reduction of coagulation factor XI reduces macrophage accumulation and accelerates deep vein thrombosis resolution in a mouse model of venous thrombosis

BACKGROUND

Deep vein thrombosis (DVT) and post-thrombotic syndrome (PTS) remain highly prevalent despite modern medical therapy. Contact activation is a promising target for safe antithrombotic anticoagulation. The anti-factor XI (FXI) monoclonal antibody 14E11 reduces circulating levels of FXI without compromising hemostasis. The human recombinant analog, AB023, is in clinical development. The role of FXI in mediation of inflammation during DVT resolution is unknown.

OBJECTIVES

Investigate the effects of pharmacological targeting of FXI with 14E11 in an experimental model of venous thrombosis.

METHODS

Adult wild-type CD1 mice were treated with subcutaneous anti-FXI antibody (14E11, 5 mg/kg) versus saline prior to undergoing surgical constriction of the inferior vena cava (IVC). Mice were evaluated at various time points to assess thrombus weight and volume, as well as histology analysis, ferumoxytol enhanced magnetic resonance imaging (Fe-MRI), and whole blood flow cytometry.

RESULTS

14E11-treated mice had reduced thrombus weights and volumes after IVC constriction on day 7 compared to saline-treated mice. 14E11 treatment reduced circulating monocytes by flow cytometry and macrophage content within thrombi as evaluated by histologic staining and Fe-MRI. Collagen deposition was increased at day 3 while CD31 and smooth muscle cell actin expression was increased at day 7 in the thrombi of 14E11-treated mice compared to saline-treated mice.

CONCLUSION

Pharmacologic targeting of FXI enhances the early stages of experimental venous thrombus resolution in wild-type CD1 mice, and may be of interest for future clinical evaluation of the antibody in DVT and PTS.

Anticoagulation Strategies during Extracorporeal Membrane Oxygenation: A Narrative Review

The development of extracorporeal life support technology has added a new dimension to the care of critically ill patients who fail conventional treatment options. Extracorporeal membrane oxygenation (ECMO)—specialized temporary life support for patients with severe cardiac or pulmonary failure—plays a role in bridging the time for organ recovery, transplant, or permanent assistance. The overall patient outcome is dependent on the underlying disease, comorbidities, patient reaction to critical illness, and potential adverse events during ECMO. Moreover, the contact of the blood with the large artificial surface of an extracorporeal system circuit triggers complex inflammatory and coagulation responses. These processes may further lead to endothelial injury and disrupted microcirculation with consequent end-organ dysfunction and the development of adverse events like thromboembolism. Therefore, systemic anticoagulation is considered crucial to alleviate the risk of thrombosis and failure of ECMO circuit components. The gold standard and most used anticoagulant during extracorporeal life support is unfractionated heparin, with all its benefits and disadvantages. However, therapeutic anticoagulation of a critically ill patient carries the risk of clinically relevant bleeding with the potential for permanent injury or death. Similarly, thrombotic events may occur. Therefore, different anticoagulation strategies are employed, while the monitoring and the balance of procoagulant and anticoagulatory factors is of immense importance. This narrative review summarizes the most recent considerations on anticoagulation during ECMO support, with a special focus on anticoagulation monitoring and future directions.

Contact pathway in surgical and transcatheter aortic valve replacement

Background

Aortic valve replacement is the gold standard treatment for severe symptomatic aortic stenosis, but thrombosis of bioprosthetic valves (PVT) remains a concern.

Objective

To analyze the factors involved in the contact pathway during aortic valve replacement and to assess their impact on the development of thromboembolic complications.

Methods

The study was conducted in 232 consecutive patients who underwent: transcatheter aortic valve replacement (TAVR, N = 155), and surgical valve replacement (SAVR, N = 77) (MUVITAVI project). Demographic and clinical data, outcomes including a combined end point (CEP) of thrombotic events, and imaging controls were recruited. Samples were collected 24 h before and 48 h after valve replacement. FXII, FXI and (pre)kallikrein were evaluated by Western Blot and specific ELISA with nanobodies.

Results

The CEP of thrombotic events was reached by 19 patients: 13 patients presented systemic embolic events and 6 patients subclinical PVT. Valve replacement did not cause FXII activation or generation of kallikrein. There was a significant reduction of FXI levels associated with the procedure, which was statistically more pronounced in SAVR than in TAVR. Cases with reductions of FXI below 80% of basal values had a lower incidence of embolic events during the procedure than patients in whom FXI increased above 150%: 2.7 vs. 16.7%; p: 0.04.

Conclusion

TAVR or SAVR did not significantly activate the contact pathway. A significant reduction of FXI, was observed, particularly in SAVR, associated with lower incidence of thrombotic events. These results encourage evaluating the usefulness and safety of FXI-directed antithrombotic treatments in these patients.

Fibrinogen and Factor XIII in Venous Thrombosis and Thrombus Stability

As the third most common vascular disease, venous thromboembolism is associated with significant mortality and morbidity. Pathogenesis underlying venous thrombosis is still not fully understood. Accumulating data suggest fibrin network structure and factor XIII-mediated crosslinking are major determinants of venous thrombus mass, composition, and stability. Understanding the cellular and molecular mechanisms mediating fibrin(ogen) and factor XIII production and function and their ability to influence venous thrombogenesis and resolution may inspire new anticoagulant strategies that target these proteins to reduce or prevent venous thrombosis in certain at-risk patients. This article summarizes fibrinogen and factor XIII biology and current knowledge of their function during venous thromboembolism.

Extracorporeal Membrane Oxygenation in Critically Ill Children

Neonatal and pediatric extracorporeal membrane oxygenation (ECMO) has evolved over the past 50 years. Advances in technology, expertise, and application have increased the number of centers providing ECMO with expanded indications for use. However, increasing the use of ECMO in recent years to more medically complex critically ill children has not changed overall survival despite increased experience and improvements in technology. This review focuses on ECMO history, circuits, indications and contraindications, management, complications, and outcome data. The authors highlight important areas of progress, including unintubated and awake patients on ECMO, application during the COVID-19 pandemic, and future directions.

The Role of Excessive Anticoagulation and Missing Hyperinflammation in ECMO-Associated Bleeding

Extracorporeal membrane oxygenation (ECMO) is increasingly used in carefully selected patients with cardiac or respiratory failure. However, complications are common and can be associated with worse outcomes, while data on risk factors and outcomes are inconsistent and sparse. Therefore, we sought to investigate potential risk factors and predictors of haemorrhage and adverse events during ECMO and its influence on mortality. We retrospectively reviewed all patients on ECMO support admitted to intensive care units of a tertiary university centre in Austria. In a period of ten years, ECMO support was used in 613 patients, with 321 patients meeting the inclusion criteria of this study. Haemorrhage, occurring in more than one third of the included patients (123, 38%), represented the most common and serious ECMO complication, being associated with an increased one year mortality (51% vs. 35%, p = 0.005). The main risk factors for haemorrhage were severity of the disease (hazard ratio (HR) = 1.01, p = 0.047), a prolonged activated partial thromboplastin time (HR = 1.01, p = 0.007), and lower values of C-reactive protein (HR = 0.96, p = 0.005) and procalcitonin (HR = 0.99, p = 0.029). In summary, haemorrhage remained the main ECMO complication with increased mortality. Moreover, we reported a possible association of lower inflammation and bleeding during ECMO support for the first time. This generated a new hypothesis that warrants further research. Finally, we recommend stricter monitoring of anticoagulation especially in patients without hyperinflammation.

Pharmacokinetics and pharmacodynamics of Abelacimab (MAA868), a novel dual inhibitor of Factor XI and Factor XIa

BACKGROUND

Factor XI (FXI) inhibition offers the promise of hemostasis-sparing anticoagulation for the prevention and treatment of thromboembolic events. Abelacimab (MAA868) is a novel fully human monoclonal antibody that targets the catalytic domain and has dual activity against the inactive zymogen Factor XI and the activated FXI.

OBJECTIVES

To investigate the safety, pharmacokinetics (PK), and pharmacodynamics (PD) of single dose intravenous and multiple dose subcutaneous administration of abelacimab in healthy volunteers and patients with atrial fibrillation, respectively.

PATIENTS/METHODS

In study ANT-003, healthy volunteers were administered single intravenous doses of abelacimab (30-150 mg) or placebo. The ANT-003 study also included a cohort of obese but otherwise healthy subjects. In study ANT-004, patients with atrial fibrillation were administered monthly subcutaneous doses of abelacimab (120 mg and 180 mg), or placebo, for 3 months. Key PK and PD parameters, including activated partial thromboplastin time (aPTT) and free FXI levels, as well as anti-drug antibodies (ADA) were assessed.

RESULTS

Following intravenous administration of abelacimab, the terminal elimination half-life ranged from 25 to 30 days. One hour after the start of the intravenous infusion greater than 99% reductions in free FXI levels were observed. Following once monthly subcutaneous administration, marked reductions from baseline in free FXI levels were sustained. Parenteral administration of abelacimab demonstrated a favorable safety profile with no clinically relevant bleeding events.

CONCLUSIONS

Intravenous and multiple subcutaneous dose administration of abelacimab were safe and well tolerated. The safety, PK, and PD data from these studies support the clinical development of abelacimab.

The versatile role of the contact system in cardiovascular disease, inflammation, sepsis and cancer

The human contact system consists of plasma proteins, which - after contact to foreign surfaces - are bound to them, thereby activating the zymogens of the system into enzymes. This activation mechanism gave the system its name - contact system. It is considered as a procoagulant and proinflammatory response mechanism, as activation finally leads to the generation of fibrin and bradykinin. To date, no physiological processes have been described that are mediated by contact activation. However, contact system factors play a pathophysiological role in numerous diseases, such as cardiovascular diseases, arthritis, colitis, sepsis, and cancer. Contact system factors are therefore an interesting target for new therapeutic options in different clinical conditions.

Crosstalk between the renin-angiotensin, complement and kallikrein-kinin systems in inflammation

During severe inflammatory and infectious diseases, various mediators modulate the equilibrium of vascular tone, inflammation, coagulation and thrombosis. This Review describes the interactive roles of the renin–angiotensin system, the complement system, and the closely linked kallikrein–kinin and contact systems in cell biological functions such as vascular tone and leakage, inflammation, chemotaxis, thrombosis and cell proliferation. Specific attention is given to the role of these systems in systemic inflammation in the vasculature and tissues during hereditary angioedema, cardiovascular and renal glomerular disease, vasculitides and COVID-19. Moreover, we discuss the therapeutic implications of these complex interactions, given that modulation of one system may affect the other systems, with beneficial or deleterious consequences.

The renin–angiotensin, complement and kallikrein–kinin systems comprise a multitude of mediators that modulate physiological responses during inflammatory and infectious diseases. This Review investigates the complex interactions between these systems and how these are dysregulated in various conditions, including cardiovascular diseases and COVID-19, as well as their therapeutic implications.

Venous thromboembolism: Recent advancement and future perspective

Clinicians have been more and more often encountering patients with venous thromboembolism (VTE), including pulmonary embolism and deep vein thrombosis, leading to the increased importance of VTE in daily clinical practice. VTE is becoming a common issue in Asian countries including Japan. The management strategies of VTE have changed dramatically in the past decade including the introduction of direct oral anticoagulants (DOACs). In addition, there have been several landmark clinical trials assessing acute treatment strategies including thrombolysis and inferior vena cava (IVC) filter. The current VTE guidelines do not recommend the routine use of thrombolysis or IVC filters based on recent evidence; Nevertheless, the prevalence of thrombolysis and IVC filter use in Japan was strikingly high. The novel profiles of DOACs with rapid onset of action and potential benefit of a lower risk for bleeding compared with vitamin K antagonist could make home treatment feasible and is safer even with extended anticoagulation therapy. One of the most clinically relevant issues for VTE treatment is optimal duration of anticoagulation for the secondary prevention of VTE. Considering recent evidence, optimal duration of anticoagulation should be determined based on the risk for recurrence as well as the risk for bleeding in an individual patient. Despite the recent advances for VTE management, there are still a number of uncertain issues that challenge clinicians in daily clinical practice, such as cancer-associated VTE and minor VTE including subsegmental pulmonary embolism and distal deep vein thrombosis, warranting future research. Several clinical trials are now ongoing for these issues, globally as well as in Japan. The current review is aimed to overview the recent advances in VTE management, describe the current status including some domestic issues in Japan, and discuss the future perspective of VTE.

Biomaterial and cellular implants:foreign surfaces where immunity and coagulation meet

Exposure of blood to a foreign surface in the form of a diagnostic or therapeutic biomaterial device or implanted cells or tissues, elicits an immediate, evolutionarily conserved thrombo-inflammatory response by the host. Primarily designed to protect against invading organisms following an injury, this innate response features instantaneous activation of several blood-borne, highly interactive and well-orchestrated cascades and cellular events that limit bleeding, destroy and eliminate the foreign substance/cells, and promote healing and a return to homeostasis via delicately balanced regenerative processes. In the setting of blood-contacting synthetic or natural biomaterials and implantation of foreign cells/tissues, innate responses are robust, albeit highly context-specific. Unfortunately, they tend to be less than adequately regulated by the host's natural anti-coagulant/anti-inflammatory pathways, thereby jeopardizing the functional integrity of the device, as well as the health of the host. Strategies to achieve biocompatibility with a sustained return to homeostasis, particularly while the device remains in situ and functional, continue to elude scientists and clinicians. In this review, some of the complex mechanisms by which biomaterials and cellular transplants provide a "hub" for activation and amplification of coagulation and immunity - thrombo-inflammation - will be discussed, with a view toward the development of innovative means of overcoming the innate challenges.

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.

Microscale Parallel Synthesis of Acylated Aminotriazoles Enabling the Development of Factor XIIa and Thrombin Inhibitors

Herein we report a microscale parallel synthetic approach allowing for rapid access to libraries of N‐acylated aminotriazoles and screening of their inhibitory activity against factor XIIa (FXIIa) and thrombin, which are targets for antithrombotic drugs. This approach, in combination with post‐screening structure optimization, yielded a potent 7 nM inhibitor of FXIIa and a 25 nM thrombin inhibitor; both compounds showed no inhibition of the other tested serine proteases. Selected N‐acylated aminotriazoles exhibited anticoagulant properties in  vitro influencing the intrinsic blood coagulation pathway, but not extrinsic coagulation. Mechanistic studies of FXIIa inhibition suggested that synthesized N‐acylated aminotriazoles are covalent inhibitors of FXIIa. These synthesized compounds may serve as a promising starting point for the development of novel antithrombotic drugs.

Biomarkers in cancer patients at risk for venous thromboembolism: data from the AVERT study

BACKGROUND

The mechanisms surrounding cancer-associated venous thromboembolism (VTE) are not well characterized. AVERT, a randomized placebo controlled thromboprophylaxis study in ambulatory cancer patients, provides a unique opportunity to gain insights into thrombotic mechanism(s).

METHODS

All available citrated platelet-free plasma samples collected at the point of randomization from individuals enrolled in the AVERT study were evaluated for the expression of D-dimer, soluble P-selectin (sP- selectin), active plasminogen activator inhibitor 1 (aPAI-1), clot lysis time (CLT) and activated factor XIa-C1 inhibitor complex (FXIa-C1). We compared the differential expression of sP-selectin, aPAI-1, CLT and FXIa-C1 among individual tumor types with normal controls. We evaluated the impact of disease type (hematologic versus solid organ malignancy) and stage (metastatic versus non-metastatic) on individual biomarker expression.

RESULTS

We included 449 AVERT participants in this analysis. Baseline expression of the selected thrombosis biomarkers differed significantly by individual tumor type compared with normal controls. Levels of aPAI-1, CLT, FXIa-C1 and sP-selectin were significantly elevated in individuals with lymphoma compared to individuals with non-metastatic solid organ malignancies (p<0.05). Individuals with metastatic solid organ disease had elevated levels of D-dimer and sP-selectin compared to those with non-metastatic disease (p<0.05).

CONCLUSION

Among a cohort of ambulatory patients at intermediate to high risk of VTE, these exploratory findings suggest that baseline activation of coagulation and fibrinolysis pathways vary significantly by tumor type and disease stage.

The rebirth of the contact pathway: a new therapeutic target

PURPOSE OF REVIEW

Anticoagulation with vitamin-K antagonists or direct oral anticoagulants is associated with a significant risk of bleeding. There is a major effort underway to develop antithrombotic drugs that have a smaller impact on hemostasis. The plasma contact proteins factor XI (FXI) and factor XII (FXII) have drawn considerable interest because they contribute to thrombosis but have limited roles in hemostasis. Here, we discuss results of preclinical and clinical trials supporting the hypothesis that the contact system contributes to thromboembolic disease.

RECENT FINDINGS

Numerous compounds targeting FXI or FXII have shown antithrombotic properties in preclinical studies. In phase 2 studies, drugs-targeting FXI or its protease form FXIa compared favorably with standard care for venous thrombosis prophylaxis in patients undergoing knee replacement. While less work has been done with FXII inhibitors, they may be particularly useful for limiting thrombosis in situations where blood comes into contact with artificial surfaces of medical devices.

SUMMARY

Inhibitors of contact activation, and particularly of FXI, are showing promise for prevention of thromboembolic disease. Larger studies are required to establish their efficacy, and to establish that they are safer than current therapy from a bleeding standpoint.

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.

Dual inhibition of factor XIIa and factor XIa as a therapeutic approach for safe thromboprotection

Clinical practice shows that a critical unmet need in the field of medical device-associated thrombosis prevention is the availability of an anticoagulant therapy without hemorrhagic risk. In the quest for new drugs that are at least as effective as those currently available, while avoiding bleeding complications, molecules that target nearly every step of the coagulation pathway have been developed. Among these molecules, inhibitors of factor XII (FXII) or factor XI (FXI) are promising alternatives as deficiencies in these factors protect against thrombosis without causing spontaneous hemorrhage, as revealed by epidemiological and preclinical data. Ixodes ricinus-contact phase inhibitor (Ir-CPI), a new anticoagulant candidate with an innovative mechanism of action could be this ideal anticoagulant agent for safe prevention from clotting on medical devices. This protein, which selectively binds to FXIIa, FXIa, and plasma kallikrein and inhibits the reciprocal activation of FXII, prekallikrein, and FXI in human plasma, was shown to prevent thrombosis in an ovine cardiopulmonary bypass system associated with cardiac surgeries. Furthermore, as opposed to unfractionated heparin, Ir-CPI appears to be devoid of bleeding risk. This review outlines the rationale for targeting upstream coagulation factors in order to prevent medical device-associated thrombosis; examines the novel approaches under development; and focuses on Ir-CPI, which shows promising properties in the field of thrombosis prevention.

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.

Pharmacokinetic-Pharmacodynamic Analysis' Role in Design of Phase ⅠClinical Trials of Anticoagulant Agents: A Systematic Review

INTRODUCTION

There remains an unmet need for better anticoagulants. The phase I clinical trial is of great significance in the development of anticoagulants, and the design is special. This system review aims to provide insights for the design of future phase I clinical trials of anticoagulants.

AREAS COVERED

We searched the database PubMed and ClinicalTrail.gov website, to collate the phase I clinical trial of anticoagulants in healthy people. The study protocol, inclusion-exclusion criteria, safety, and pharmacodynamic indexes were reviewed.

EXPERT OPINION

New anticoagulants under development focused on inhibiting one or more than one serine proteases within the coagulation cascade. Agents targeting intrinsic factors are in the pipeline of the drug development. The enrollment eligibility criteria have more restrictions on laboratory tests, medical history, or medication history related to bleeding and coagulation; more precautions were taken to assess and minimize the risk of hemorrhagic events. Pharmacodynamics markers were evaluated as a surrogate marker of anticoagulation potency to guide further dose selection in drug's development. In future, the positive control study can be applied in phase I studies of new anticoagulants with appropriate pharmacodynamics markers, which can provide more favorable information on making 'go/no' decision in drug development.

Camelid-derived single-chain antibodies in hemostasis: Mechanistic, diagnostic, and therapeutic applications

Hemostasis is a complex process involving the concerted action of molecular and vascular components. Its basic understanding as well as diagnostic and therapeutic aspects have greatly benefited from the use of monoclonal antibodies. Interestingly, camelid-derived single-domain antibodies (sdAbs), also known as VHH or nanobodies, have become available during the previous 2 decades as alternative tools in this regard. Compared to classic antibodies, sdAbs are easier to produce and their small size facilitates their engineering and functionalization. It is not surprising, therefore, that sdAbs are increasingly used in hemostasis-related research. In addition, they have the capacity to recognize unique epitopes unavailable to full monoclonal antibodies. This property can be used to develop novel diagnostic tests identifying conformational variants of hemostatic proteins. Examples include sdAbs that bind active but not globular von Willebrand factor or free factor VIIa but not tissue factor-bound factor VIIa. Finally, sdAbs have a high therapeutic potential, exemplified by caplacizumab, a homodimeric sdAb targeting von Willebrand factor that is approved for the treatment of thrombotic thrombocytopenic purpura. In this review, the various applications of sdAbs in thrombosis and hemostasis-related research, diagnostics, and therapeutic strategies will be discussed.

EP-7041, a Factor XIa Inhibitor as a Potential Antithrombotic Strategy in Extracorporeal Membrane Oxygenation: A Brief Report

Objectives:

Current approaches to systemic antithrombotic therapy in support of extracorporeal membrane oxygenation are limited and are hampered by both thrombotic and hemorrhagic complications. An alternative approach is needed.

Design:

Inhibition of coagulation factor XI/activated factor XI is an appealing pathway for antithrombotic support of extracorporeal membrane oxygenation. Selective inhibition of the contact pathway of coagulation could reduce bleeding risk, and because factor XI is linked with the inflammatory and complement systems, it can also be viewed as a biologically plausible target for the prevention of abnormal thrombosis during extracorporeal membrane oxygenation.

Conclusions:

We introduce initial information on EP-7041, a parenteral, potent, and selective, small-molecule activated factor XIa inhibitor with pharmacodynamic and pharmacokinetic characteristics that appear well suited for use in a critical care environment.

Thromboinflammation in COVID-19 acute lung injury

Since the initial description in 2019, the novel coronavirus SARS-Cov-2 infection (COVID-19) pandemic has swept the globe. The most severe form of the disease presents with fever and shortness of breath, which rapidly deteriorates to respiratory failure and acute lung injury (ALI). COVID-19 also presents with a severe coagulopathy with a high rate of venous thromboembiolism. In addition, autopsy studies have revealed co-localized thrombosis and inflammation, which is the signature of thromboinflammation, within the pulmonary capillary vasculature. While the majority of published data is on adult patients, there are parallels to pediatric patients. In our experience as a COVID-19 epicenter, children and young adults do develop both the coagulopathy and the ALI of COVID-19. This review will discuss COVID-19 ALI from a hematological perspective with discussion of the distinct aspects of coagulation that are apparent in COVID-19. Current and potential interventions targeting the multiple thromboinflammatory mechanisms will be discussed.

Increased Levels of Coagulation Factor XI in Plasma Are Related to Alzheimer's Disease Diagnosis

BACKGROUND

Alzheimer's disease is a complex disorder of unclear etiology that develops in the elderly population. It is a debilitating, progressive neurodegeneration for which disease-modifying therapies do not exist. Previous studies have suggested that, for a subset of patients, dysregulation in hemostasis might be one of the molecular mechanisms that ultimately leads to the development of neurodegeneration resulting in cognitive decline that represents the most prominent symptomatic characteristic of Alzheimer's disease.

OBJECTIVE

To examine a relationship between factors that are part of coagulation and anticoagulation pathways with cognitive decline that develops during Alzheimer's disease.

METHODS

SOMAscan assay was used to measure levels of coagulation/anticoagulation factors V, VII, IX, X, Xa, XI, antithrombin III, protein S, protein C, and activated protein C in plasma samples obtained from three groups of subjects: 1) subjects with stable cognitively healthy function, 2) subjects with stable mild cognitive impairment, and 3) subjects diagnosed with probable Alzheimer's disease.

RESULTS

Our results show that protein levels of coagulation factor XI are significantly increased in patients who are diagnosed with probable Alzheimer's disease compared with cognitively healthy subjects or patients diagnosed with mild cognitive impairment. Furthermore, our results demonstrate that significant predictors of Alzheimer's-type diagnosis are factors IX and XI-an increase in both factors is associated with a reduction in cognitive function.

CONCLUSION

Our study justifies further investigations of biological pathways involving coagulation/anticoagulation factors in relation to dementia, including dementia resulting from Alzheimer's-type neurodegeneration.

Pulmonary embolism: update on management and controversies

Pulmonary embolism is a common and potentially fatal cardiovascular disorder that must be promptly diagnosed and treated. The diagnosis, risk assessment, and management of pulmonary embolism have evolved with a better understanding of efficient use of diagnostic and therapeutic options. The use of either clinical probability adjusted or age adjusted D-dimer interpretation has led to a reduction in diagnostic imaging to exclude pulmonary embolism. Direct oral anticoagulation therapies are safe, effective, and convenient treatments for most patients with acute venous thromboembolism, with a lower risk of bleeding than vitamin K antagonists. These oral therapeutic options have opened up opportunities for safe outpatient management of pulmonary embolism in selected patients. Recent clinical trials exploring the use of systemic thrombolysis in intermediate to high risk pulmonary embolism suggest that this therapy should be reserved for patients with evidence of hemodynamic compromise. The role of low dose systemic or catheter directed thrombolysis in other patient subgroups is uncertain. After a diagnosis of pulmonary embolism, all patients should be assessed for risk of recurrent venous thromboembolism to guide duration of anticoagulation. Patients with a venous thromboembolism associated with a strong, transient, provoking risk factor can safely discontinue anticoagulation after three months of treatment. Patients with an ongoing strong risk factor, such as cancer, or unprovoked events are at increased risk of recurrent events and should be considered for extended treatment. The use of a risk prediction score can help to identify patients with unprovoked venous thromboembolism who can benefit from extended duration therapy. Despite major advances in the management of pulmonary embolism, up to half of patients report chronic functional limitations. Such patients should be screened for chronic thromboembolic pulmonary hypertension, but only a small proportion will have this as the explanation of their symptoms. In the remaining patients, future studies are needed to understand the pathophysiology and explore interventions to improve quality of life.

New Antithrombotic Drugs in Acute Coronary Syndrome

In recent years, much progress has been made in the field of antithrombotic drugs in acute coronary syndrome (ACS) treatment, as reflected by the introduction of the more potent P2Y12-inhibitors prasugrel and ticagrelor, and novel forms of concomitant anticoagulation, such as fondaparinux and bivalirudin. However, despite substantial improvements in contemporary ACS treatment, there remains residual ischemic risk in this group and hence the need for even more effective antithrombotic drugs, while balancing antithrombotic efficacy against bleeding risk. This review discusses recently introduced and currently developed antiplatelet and anticoagulant drugs in ACS treatment.

The contact activation system as a potential therapeutic target in patients with COVID-19

Coronavirus disease 2019 (COVID-19) is predicted to overwhelm health care capacity in the United States and worldwide, and, as such, interventions that could prevent clinical decompensation and respiratory compromise in infected patients are desperately needed. Excessive cytokine release and activation of coagulation appear to be key drivers of COVID-19 pneumonia and associated mortality. Contact activation has been linked to pathologic upregulation of both inflammatory mediators and coagulation, and accumulating preclinical and clinical data suggest it to be a rational therapeutic target in patients with COVID-19. Pharmacologic inhibition of the interaction between coagulation factors XI and XII has been shown to prevent consumptive coagulopathy, pathologic systemic inflammatory response, and mortality in at least 2 types of experimental sepsis. Importantly, inhibition of contact activation also prevented death from Staphylococcus aureus-induced lethal systemic inflammatory response syndrome in nonhuman primates. The contact system is likely dispensable for hemostasis and may not be needed for host immunity, suggesting it to be a reasonably safe target that will not result in immunosuppression or bleeding. As a few drugs targeting contact activation are already in clinical development, immediate clinical trials for their use in patients with COVID-19 are potentially feasible for the prevention or treatment of respiratory distress.