Targeting the contact system in a rabbit model of extracorporeal membrane oxygenation

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.

Neutrophils: a key component in ECMO-related acute organ injury

Extracorporeal membrane oxygenation (ECMO), as an extracorporeal life support technique, can save the lives of reversible critically ill patients when conventional treatments fail. However, ECMO-related acute organ injury is a common complication that increases the risk of death in critically ill patients, including acute kidney injury, acute brain injury, acute lung injury, and so on. In ECMO supported patients, an increasing number of studies have shown that activation of the inflammatory response plays an important role in the development of acute organ injury. Cross-cascade activation of the complement system, the contact system, and the coagulation system, as well as the mechanical forces of the circuitry are very important pathophysiological mechanisms, likely leading to neutrophil activation and the production of neutrophil extracellular traps (NETs). NETs may have the potential to cause organ damage, generating interest in their study as potential therapeutic targets for ECMO-related acute organ injury. Therefore, this article comprehensively summarized the mechanism of neutrophils activation and NETs formation following ECMO treatment and their actions on acute organ injury.

Factor XII promotes the thromboinflammatory response in a rat model of venoarterial extracorporeal membrane oxygenation

BACKGROUND

Factor XII (FXII) is a multifunctional protease capable of activating thrombotic and inflammatory pathways. FXII has been linked to thrombosis in extracorporeal membrane oxygenation (ECMO), but the role of FXII in ECMO-induced inflammatory complications has not been studied. We used novel gene-targeted FXII- deficient rats to evaluate the role of FXII in ECMO-induced thromboinflammation.

METHODS

FXII-deficient (FXII-/-) Sprague-Dawley rats were generated using CRISPR/Cas9. A minimally invasive venoarterial (VA) ECMO model was used to compare wild-type (WT) and FXII-/- rats in 2 separate experimental cohorts: rats placed on ECMO without pharmacologic anticoagulation and rats anticoagulated with argatroban. Rats were maintained on ECMO for 1 hour or until circuit failure occurred. Comparisons were made with unchallenged rats and rats that underwent a sham surgical procedure without ECMO.

RESULTS

FXII-/- rats were maintained on ECMO without pharmacologic anticoagulation with low resistance throughout the 1-hour experiment. In contrast, WT rats placed on ECMO without anticoagulation developed thrombotic circuit failure within 10 minutes. Argatroban provided a means to maintain WT and FXII-/- rats on ECMO for the 1-hour time frame without thrombotic complications. Analyses of these rats demonstrated that ECMO resulted in increased neutrophil migration into the liver that was significantly blunted by FXII deficiency. ECMO also resulted in increases in high molecular weight kininogen cleavage and complement activation that were abrogated by genetic deletion of FXII.

CONCLUSIONS

FXII initiates hemostatic system activation and key inflammatory sequelae in ECMO, suggesting that therapies targeting FXII could limit both thromboembolism and inopportune inflammatory complications in this setting.

Bivalirudin-hydrogel coatings of polyvinyl chloride on extracorporeal membrane oxygenation for anticoagulation

Introduction

Thromboembolic events associated with extracorporeal membrane oxygenation (ECMO) in clinical treatment are typical. Heparin coating has been widely employed as a surface modification strategy for ECMO tubes. However, its clinical application is often accompanied by unavoidable complications due to its mechanism of action. As a direct thrombin inhibitor with a single target, Bivalirudin (BV) has exhibited a lower incidence of adverse events and superior pharmacokinetic performance compared to heparin.

Methods

A gelatin methacrylate hydrogel (GelMA) coating layer with BV was successfully synthesized on polyvinyl chloride, and the drug release ratio was close to complete release within 7 days.

Results and discussion

Simulated extracorporeal circulation experiments using roller pumps in vitro and jugular arteriovenous bypass experiments in rabbits demonstrated its outstanding anticoagulant efficacy. The systemic anticoagulant assay proved that BV hydrogel coating does not affect the coagulation level, and reduces the risk of complications such as systemic bleeding compared to intravenous injection. BV-Coating GelMA hydrogel tube has exhibited good biocompatibility and significantly improved anticoagulant performance, making it an optimal choice for surface materials used in blood-contacting medical devices.

Novel strategies in antithrombotic therapy: targeting thrombosis while preserving hemostasis

Antithrombotic therapy is a delicate balance between the benefits of preventing a thrombotic event and the risks of inducing a major bleed. Traditional approaches have included antiplatelet and anticoagulant medications, require careful dosing and monitoring, and all carry some risk of bleeding. In recent years, several new targets have been identified, both in the platelet and coagulation systems, which may mitigate this bleeding risk. In this review, we briefly describe the current state of antithrombotic therapy, and then present a detailed discussion of the new generation of drugs that are being developed to target more safely existing or newly identified pathways, alongside the strategies to reverse direct oral anticoagulants, showcasing the breadth of approaches. Combined, these exciting advances in antithrombotic therapy bring us closer than we have ever been to the "holy grail" of the field, a treatment that separates the hemostatic and thrombotic systems, preventing clots without any concurrent bleeding risk.

Polyphosphate as an antithrombotic target and hemostatic agent

Polyphosphate (PolyP) is a polymer comprised of linear phosphate units connected by phosphate anhydride bonds. PolyP exists in a diverse range of eukaryotes and prokaryotes with varied chain lengths ranging from six to thousands of phosphate units. Upon activation, human platelets and neutrophils release short-chain PolyP, along with other components, to initiate the coagulation pathway. Long-chain PolyP derived from cellular or bacterial organelles exhibits higher proinflammatory and procoagulant effects compared to short-chain PolyP. Notably, PolyP has been identified as a low-hemorrhagic antithrombotic target since neutralizing plasma PolyP suppresses the thrombotic process without impairing the hemostatic functions. As an inorganic polymer without uniform steric configuration, PolyP is typically targeted by cationic polymers or recombinant polyphosphatases rather than conventional antibodies, small-molecule compounds, or peptides. Additionally, because of its procoagulant property, PolyP has been incorporated in wound-dressing materials to facilitate blood hemostasis. This review summarizes current studies on PolyP as a low-hemorrhagic antithrombotic target and the development of hemostatic materials based on PolyP.

Development of new anticoagulant in 2023: Prime time for anti-factor XI and XIa inhibitors

Thrombosis remains one of the leading causes of death in the world. The history of anticoagulation has evolved considerably from non-specific drugs (i.e., heparins and vitamin K antagonists, VKA) to agents that directly target specific coagulation factors (i.e., argatroban, fondaparinux and direct oral anticoagulants, DOAC). Since the last decade, DOAC are widely used in clinical practice because of their ease to use with favorable pharmacological profile and not requiring monitoring, particularly for venous thromboembolism treatment and prevention and stroke prevention in atrial fibrillation. However, despite having a better safety profile than VKA, their bleeding risk is not negligible. Therefore, research is underway to develop new anticoagulant therapies with a better safety profile. One of these news approaches to reduce the risk of bleeding is to target the coagulation in the intrinsic pathway, in particular the contact activation, with the ultimate goal of preventing thrombosis without impairing hemostasis. Based on epidemiological data with patients with inherited factor XI (FXI) deficiency and preclinical studies, FXI emerged as the most promising candidate target separating hemostasis from thrombosis. This review summaries the role of FXI and FXIa in hemostasis, provides evidence of initial success with FXI pathway inhibitors in clinical trials (such as IONIS-FXI_Rx, fesomersen, osocimab, abelacimab, milvexian, asundexian or xisomab 3G3) and highlights the opportunities and challenges for this next generation of anticoagulants.