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.

Procoagulant Activity of Blood and Microvesicles Is Disturbed by Pneumococcal Pneumolysin, Which Interacts with Coagulation Factors

The coagulation and contact systems are parts of the innate immune system as they prevent bleeding and dissemination of pathogens and also contribute to microbial killing by inflammatory reactions and the release of antimicrobial peptides. Here, we investigated the influence of Streptococcus pneumoniae on the coagulation and contact system. S. pneumoniae (pneumococci), but no other investigated streptococcal species, impairs coagulation of blood by autolysis and release of pneumolysin. Defective blood coagulation results from the lysis of tissue factor-producing mononuclear cells and their procoagulant microvesicles, which are the main trigger for blood coagulation during sepsis. In addition, pneumolysin binds coagulation and contact system factors, but this does not result in activation. Thus, pneumococci modulate activation of the coagulation system by releasing pneumolysin, which could potentiate lung injury during pneumonia.

Contact system activation in disseminated intravascular coagulation: activities of prekallikrein and high-molecular-weight kininogen are significant risk factors

The contact system activation can play a role in microthrombus formation of disseminated intravascular coagulation (DIC). This study investigated whether the activity of prekallikrein and high-molecular-weight kininogen (HMWK) correlated DIC progression. Contact system factors (prekallikrein, HMWK, activated factor XII), coagulation factors (IX, XI, XII) and tissue factor were measured in 140 patients who clinically suspected of having DIC. Prekallikrein and HMWK activity levels showed significant linear relationships with DIC score and antithrombin level, whereas prekallikrein and HMWK antigen levels did not. The activated factor XII, factor XII, factor XI and tissue factor were significant risk factors of overt-DIC. This finding suggests that consumption of prekallikrein and HMWK contributes to microvascular thrombosis in DIC. Measurements of prekallikrein and HMWK activity could be used as potential diagnostic markers for overt-DIC.

New Biomarkers in Anaphylaxis (Beyond Tryptase)

Purpose of Review

The purpose of this review is to provide a better understanding of anaphylaxis pathophysiology and describe the underlying mechanisms, effector cells, and the potential biomarkers involved depending on the anaphylaxis endotypes.

Recent Findings

New insight into the potential relevance of pathways others than IgE-dependent anaphylaxis has been unraveled, as well as other biomarkers than tryptase, such as the role of platelet activation factor, basogranulin, dipeptidyl peptidase I, CCL-2, and other cytokines.

Summary

Gaining knowledge of all the mediators and cellular activation/communication pathways involved in each endotype of anaphylaxis will allow the application of precision medicine in patients with anaphylactic reactions, providing insights to the most appropriate approach in each case and helping to stratify severity and risk prediction.

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.

An update on factor XII-driven vascular inflammation

The plasma protein factor XII (FXII) is the liver-derived zymogen of the serine protease FXIIa that initiates an array of proteolytic cascades. Zymogen activation, enzymatic FXIIa activity and functions are regulated by interactions with cell receptors, negatively charged surfaces, other serine proteases, and serpin inhibitors, which bind to distinct protein domains and regions in FXII(a). FXII exerts mitogenic activity, while FXIIa initiates the pro-inflammatory kallikrein-kinin pathway and the pro-thrombotic intrinsic coagulation pathway, respectively. Growing evidence indicates that FXIIa-mediated thrombo-inflammation plays a crucial role in various pathological states besides classical thrombosis, such as endothelial dysfunction. Consistently, increased FXIIa levels are associated with hypercholesterolemia and hypertriglyceridemia. In contrast, FXII deficiency protects from thrombosis but is otherwise not associated with prolonged bleeding or other adverse clinical manifestations. Here, we review current concepts for FXII(a)-driven vascular inflammation focusing on endothelial hyperpermeability, receptor signaling, atherosclerosis and immune cell activation.

C1-Inhibitor: Structure, Functional Diversity and Therapeutic Development

Human C1-Inhibitor (C1INH), also known as C1-esterase inhibitor, is an important multifunctional plasma glycoprotein that is uniquely involved in a regulatory network of complement, contact, coagulation, and fibrinolytic systems. C1INH belongs to a superfamily of serine proteinase inhibitor (serpins) and exhibits its inhibitory activities towards several target proteases of plasmatic cascades, operating as a major anti-inflammatory protein in the circulation. In addition to its inhibitory activities, C1INH is also involved in non-inhibitory interactions with some endogenous proteins, polyanions, cells and infectious agents. While C1INH is essential for multiple physiological processes, it is better known for its deficiency with regards to Hereditary Angioedema (HAE), a rare autosomal dominant disease clinically manifested by recurrent acute attacks of increased vascular permeability and edema. Since the link was first established between functional C1INH deficiency in plasma and HAE in the 1960s, tremendous progress has been made in the biochemical characterization of C1INH and its therapeutic development for replacement therapies in patients with C1INH-dependent HAE. Various C1INH biological activities, recent advances in the HAE-targeted therapies, and availability of C1INH commercial products have prompted intensive investigation of the C1INH potential for treatment of clinical conditions other than HAE. This article provides an updated overview of the structure and biological activities of C1INH, its role in HAE pathogenesis, and recent advances in the research and therapeutic development of C1INH; it also considers some trends for using C1INH therapeutic preparations for applications other than angioedema, from sepsis and endotoxin shock to severe thrombotic complications in COVID-19 patients.

The contact system in liver injury

Coagulation is controlled by a delicate balance of prothrombotic and antithrombotic mechanisms, to prevent both excessive blood loss from injured vessels and pathologic thrombosis. The liver plays a pivotal role in hemostasis through the synthesis of plasma coagulation factors and their inhibitors that, in addition to thrombosis and hemostasis, orchestrates an array of inflammatory responses. As a result, impaired liver function has been linked with both hypercoagulability and bleeding disorders due to a pathologic balance of pro- and anticoagulant plasma factors. At sites of vascular injury, thrombus propagation that finally may occlude the blood vessel depends on negatively charged biopolymers, such as polyphosphates and extracellular DNA, that provide a physiological surface for contact activation of coagulation factor XII (FXII). FXII initiates the contact system that drives both the intrinsic pathway of coagulation, and formation of the inflammatory mediator bradykinin by the kallikrein–kinin system. Moreover, FXII facilitates receptor-mediated signalling, thereby promoting mitogenic activities, angiogenesis, and neutrophil stimulation with implications for liver diseases. Here, we summarize current knowledge on the FXII-driven contact system in liver diseases and review therapeutic approaches to target its activities during impaired liver function.

Does hereditary angioedema make COVID-19 worse?

The coronavirus disease 2019 (COVID-19) pandemic has spread rapidly worldwide. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the causative agent for COVID-19, enters host cells via angiotensin-converting enzyme 2 (ACE2) and depletes ACE2, which is necessary for bradykinin metabolism. The depletion of ACE2 results in the accumulation of des-Arg (9)-bradykinin and possible bradykinin, both of which bind to bradykinin receptors and induce vasodilation, lung injury, and inflammation. It is well known that an overactivated contact system and excessive production of bradykinin comprise the key mechanisms that drive the pathogenesis of hereditary angioedema (HAE). It is reasonable to speculate that COVID-19 may increase disease activity in patients with HAE and vice versa. In this review, we explore the potential interactions between COVID-19 and HAE in terms of the contact system, the complement system, cytokine release, increased T helper 17 cells, and hematologic abnormalities. We conclude with the hypothesis that comorbidity with HAE might favor COVID-19 progression and may worsen its outcomes, while COVID-19 might in turn aggravate pre-existing HAE and prompt the onset of HAE in asymptomatic carriers of HAE-related mutations. Based on the pathophysiologic links, we suggest that long-term prophylaxis should be considered in patients with HAE at risk of SARS-CoV-2 infection, especially the prophylactic use of C1 inhibitor and lanadelumab and that HAE patients must have medications for acute attacks of angioedema. Additionally, therapeutic strategies employed in HAE should be considered for the treatment of COVID-19, and clinical trials should be performed.

A Review: Does Complement or the Contact System Have a Role in Protection or Pathogenesis of COVID-19?

INTRODUCTION

COVID-19 presentation may include a profound increase in cytokines and associated pneumonia, rapidly progressing to acute respiratory distress syndrome (ARDS). This so-called cytokine storm often leads to refractory edema, respiratory arrest, and death. At present, anti-IL-6, antiviral therapy, convalescent plasma, hydroxychloroquine, and azithromycin among others are being investigated as potential treatments for COVID-19. As the disease etiology and precise therapeutic interventions are still not definitively defined, we wanted to review the roles that complement and the contact system may have in either the treatment or pathogenesis of the disease.

METHODS

We searched the recent literature (PubMed) on complement and coronavirus; contact system and coronavirus; bradykinin and coronavirus; and angiotensin receptor and coronavirus. The manuscript complies with ethics guidelines and was deemed exempt from institutional review board approval according to Human Subjects Protection Office guidelines.

RESULTS

Mouse models are available for the study of coronavirus and complement. Although complement is effective in protecting against many viruses, it does not seem to be protective against coronavirus. C3 knockout mice infected with SARS-CoV had less lung disease than wild-type mice, suggesting that complement may play a role in coronavirus pathogenesis. Some evidence suggests that the observed pulmonary edema may be bradykinin-induced and could be the reason that corticosteroids, antihistamines, and other traditional interventions for edema are not effective. Angiotensin-converting enzyme 2 (ACE2) is a co-receptor for SARS-CoV-2, and studies thus far have not concluded a benefit or risk associated with the use of either ACE-inhibitors or angiotensin receptor antagonists. Activation of complement and the contact system, through generation of bradykinin, may play a role in the SARS-CoV-2-induced pulmonary edema, and our search suggests that further work is necessary to confirm our suspicions.

Elevated extracellular trap formation and contact system activation in acute leukemia

Leukemic cells release their nuclear contents into the extracellular space upon activation. The released nuclear contents, called extracellular traps, can activate the contact system of coagulation. This study accessed the extent of contact system activation, the levels of extracellular traps, and coagulation activation in hematologic malignancies including acute leukemia. In 154 patients with hematologic malignancies (acute leukemia, n = 29; myelodysplastic syndrome, n = 20; myeloproliferative neoplasms, n = 69; plasma cell myeloma, n = 36) and 48 normal controls, the levels of coagulation factors (fibrinogen and factor VII, VIII, IX, and XII), D-dimer, thrombin generation, extracellular trap markers (histone-DNA complex, cell-free dsDNA, leukocyte elastase), and contact system markers (activated factor XII [XIIa], high-molecular-weight kininogen, prekallikrein, bradykinin) were measured. Patients with acute leukemia showed the highest levels of peak thrombin, extracellular trap markers, and factor XIIa. Factor XIIa level was significantly associated with the presence of acute leukemia. The histone-DNA complex and cell-free dsDNA were revealed as significant associated factors with the factor XIIa level. Three markers of extracellular traps and two markers of thrombin generation significantly contributed to the hemostatic abnormalities in hematologic malignancies. Contact system was activated in acute leukemia and its activation was significantly associated with the extent of extracellular trap formation. This finding suggests that extracellular traps might be a major source of contact system activation and therapeutic strategies targeting extracellular trap formation or contact system activation may be beneficial in acute leukemia.

Introducing the pro-coagulant contact system in the numerical assessment of device-related thrombosis

Thrombosis is a major concern in blood-coated medical devices. Contact activation, which is the initial part of the coagulation cascade in device-related thrombosis, is not considered in current thrombus formation models. In the present study, pro-coagulant reactions including the contact activation system are coupled with a fluid solver in order to evaluate the potential of the contact system to initiate thrombin production. The biochemical/fluid model is applied to a backward-facing step configuration, a flow configuration that frequently appears in medical devices. In contrast to the in vivo thrombosis models in which a specific thrombotic zone (injury region) is set a priori by the user to initiate the coagulation reaction, a reactive surface boundary condition is applied to the whole device wall. Simulation results show large thrombin concentration in regions related to recirculation zones without the need of an a priori knowledge of the thrombus location. The numerical results align well with the regions prone to thrombosis observed in experimental results reported in the literature. This approach could complement thrombus formation models that take into account platelet activity and thrombus growth to optimize a wide range of medical devices.

The role of contact system in septic shock: the next target? An overview of the current evidence

BACKGROUND

Septic shock remains challenging to intensive care units worldwide, despite recent documented improvement in mortality over the years. Multiple new therapies have been attempted without success in large clinical trials. Evidence concerning the role of the contact system and bradykinin on septic shock physiological manifestations is shown by this article.

OBJECTIVES

The objective of the study is to review the current evidence linking contact system activation and septic shock, as well as efficacy of available therapies targeting this pathophysiological pathway and to evaluate the potential of further researching the matter.

RESULTS

Multiple animal studies are already available and suggestive of a meaningful role of contact system activation on septic shock. However, human trials are still scarce, and the ones available are not enough to establish such a strong connection. Furthermore, attempted therapies have been successful across multiple species, but not as much in humans. Therefore, contact system and septic shock relationship remains plentiful in questions to be answered in the coming years or decades.

CONCLUSIONS

Whether the contact system is not as relevant in humans as it is in animals or there is only lack of evidence remains to be explained. The subject is an attractive open field for further research aiming to aid in tackling such a burdensome condition.

Contact pathway of coagulation and inflammation

The contact system, also named as plasma kallikrein-kinin system, consists of three serine proteinases: coagulation factors XII (FXII) and XI (FXI), and plasma prekallikrein (PK), and the nonenzymatic cofactor high molecular weight kininogen (HK). This system has been investigated actively for more than 50 years. The components of this system and their interactions have been elucidated from in vitro experiments, which indicates that this system is prothrombotic by activating intrinsic pathway, and proinflammatory by producing bioactive peptide bradykinin. Although the activation of the contact system have been implicated in various types of human disease, in only a few instances is its role clearly defined. In the last 10 years, our understanding of the contact system, particularly its biology and (patho)physiology has greatly increased through investigations using gene-modified animal models. In this review we will describe a revitalized view of the contact system as a critical (patho)physiologic mediator of coagulation and inflammation.

The role and regulation of complement activation as part of the thromboinflammation elicited in cell therapies

Cell therapies in which the cells come into direct contact with blood and other body fluids are emerging treatment procedures for patients with various diseases, such as diabetes mellitus, liver insufficiency, and graft-versus-host disease. However, despite recent progress, these procedures are associated with tissue loss caused by thromboinflammatory reactions. These deleterious reactions involve the activation of the complement and coagulation cascades and platelet and leukocyte activation, ultimately resulting in clot formation and damage to the implanted cells. In this concept review, we discuss the basic mechanisms underlying the thrombininflammatory process, with special reference to the engagement of complement and emerging strategies for the therapeutic regulation of these reactions that include the use of selective systemic inhibitors and various procedures to coat the surfaces of the cells. The coating procedures may also be applied to other treatment modalities in which similar mechanisms are involved, including whole organ transplantation, treatment with biomaterials in contact with blood, and extracorporeal procedures.