The Effects of the Contact Activation System on Hemorrhage

Revisiting the significance of natural protease inhibitors: A comprehensive review

Protease inhibitors (PIs) function as a natural adversary to proteolytic enzymes. They can diminish or inhibit the catalytic properties of proteases, which are crucial for various tasks in the physiology and metabolism of cellular forms. Protease Inhibitors are low molecular weight (5-25 kDa) stable proteins. Plants are a fair source of PIs, so foods containing PIs remarkably influence human health. PIs are usually present in storage tissues of the plant, although they are present in other aerial parts as well. In plants, protease inhibitors participate in vital functions such as maintaining physiological homeostasis, mobilization of storage proteins, defense systems, apoptosis, and other processes. In recent years, plant-derived PIs have shown promising results in treating various diseases including inflammatory conditions, osteoporosis, cardiovascular issues, and brain disorders. The primary goal of this review is to provide a comprehensive understanding of the characteristics, applications, and challenges associated with natural protease inhibitors in plants, which draws insights from an extensive examination of 80+ research papers with a focus on their potential in agriculture and medicine. By synthesizing findings from an extensive literature review, this work aims to guide future research directions and innovations in leveraging plant-based PIs for sustainable agricultural practices and advanced therapeutic interventions.

Aprotinin (II): Inhalational Administration for the Treatment of COVID-19 and Other Viral Conditions

Aprotinin is a broad-spectrum inhibitor of human proteases that has been approved for the treatment of bleeding in single coronary artery bypass surgery because of its potent antifibrinolytic actions. Following the outbreak of the COVID-19 pandemic, there was an urgent need to find new antiviral drugs. Aprotinin is a good candidate for therapeutic repositioning as a broad-spectrum antiviral drug and for treating the symptomatic processes that characterise viral respiratory diseases, including COVID-19. This is due to its strong pharmacological ability to inhibit a plethora of host proteases used by respiratory viruses in their infective mechanisms. The proteases allow the cleavage and conformational change of proteins that make up their viral capsid, and thus enable them to anchor themselves by recognition of their target in the epithelial cell. In addition, the activation of these proteases initiates the inflammatory process that triggers the infection. The attraction of the drug is not only its pharmacodynamic characteristics but also the possibility of administration by the inhalation route, avoiding unwanted systemic effects. This, together with the low cost of treatment (≈2 Euro/dose), makes it a good candidate to reach countries with lower economic means. In this article, we will discuss the pharmacodynamic, pharmacokinetic, and toxicological characteristics of aprotinin administered by the inhalation route; analyse the main advances in our knowledge of this medication; and the future directions that should be taken in research in order to reposition this medication in therapeutics.

Circulating Blood Prognostic Biomarker Signatures for Hemorrhagic Cerebral Cavernous Malformations (CCMs)

Cerebral cavernous malformations (CCMs) are a neurological disorder characterized by enlarged intracranial capillaries in the brain, increasing the susceptibility to hemorrhagic strokes, a major cause of death and disability worldwide. The limited treatment options for CCMs underscore the importance of prognostic biomarkers to predict the likelihood of hemorrhagic events, aiding in treatment decisions and identifying potential pharmacological targets. This study aimed to identify blood biomarkers capable of diagnosing and predicting the risk of hemorrhage in CCM1 patients, establishing an initial set of circulating biomarker signatures. By analyzing proteomic profiles from both human and mouse CCM models and conducting pathway enrichment analyses, we compared groups to identify potential blood biomarkers with statistical significance. Specific candidate biomarkers primarily associated with metabolism and blood clotting pathways were identified. These biomarkers show promise as prognostic indicators for CCM1 deficiency and the risk of hemorrhagic stroke, strongly correlating with the likelihood of hemorrhagic cerebral cavernous malformations (CCMs). This lays the groundwork for further investigation into blood biomarkers to assess the risk of hemorrhagic CCMs.

Bradykinin release following trauma and hemorrhagic shock causes pulmonary alveolar leak in a rodent model

BACKGROUND

Hemorrhage accounts for 40% of the preventable death following severe injury. Activation of systemic coagulation produces bradykinin (BK), which may cause leak from the plasma to the extravascular space and to the tissues, which is part of the complex pathophysiology of trauma-induced end-organ injury. We hypothesize that BK, released during activation of coagulation in severe injury, induces pulmonary alveolar leak.

METHODS

Isolated neutrophils (PMNs) were pretreated with a specific BK receptor B2 antagonist HOE-140/icatibant and BK priming of the PMN oxidase was completed. Rats underwent tissue injury/hemorrhagic shock (TI/HS), TI/icatibant/HS, and controls (no injury). Evans blue dye was instilled, and the percentage leak from the plasma to the lung was calculated from the bronchoalveolar lavage fluid (BALF). CINC-1 and total protein were measured in the BALF, and myeloperoxidase was quantified in lung tissue.

RESULTS

The BK receptor B2 antagonist HOE140/icatibant inhibited (85.0 ± 5.3%) BK priming of the PMN oxidase ( p < 0.05). The TI/HS model caused activation of coagulation by increasing plasma thrombin-antithrombin complexes ( p < 0.05). Versus controls, the TI/HS rats had significant pulmonary alveolar leak: 1.46 ± 0.21% versus 0.36 ± 0.10% ( p = 0.001) and increased total protein and CINC-1 in the BALF ( p < 0.05). Icatibant given after the TI significantly inhibited lung leak and the increase in CINC-1 in the BALF from TI/icatibant/HS rats versus TI/HS ( p < 0.002 and p < 0.05) but not the total protein. There was no PMN sequestration in the lungs. Conclusions: This mixed injury model caused systemic activation of hemostasis and pulmonary alveolar leak likely due to BK release.

CONCLUSION

This mixed injury model caused systemic activation of hemostasis and pulmonary alveolar leak likely due to BK release.

LEVEL OF EVIDENCE

Original Article, Basic Science.

Human plasma kallikrein: roles in coagulation, fibrinolysis, inflammation pathways, and beyond

Human plasma kallikrein (PKa) is obtained by activating its precursor, prekallikrein (PK), historically named the Fletcher factor. Human PKa and tissue kallikreins are serine proteases from the same family, having high- and low-molecular weight kininogens (HKs and LKs) as substrates, releasing bradykinin (Bk) and Lys-bradykinin (Lys-Bk), respectively. This review presents a brief history of human PKa with details and recent observations of its evolution among the vertebrate coagulation proteins, including the relations with Factor XI. We explored the role of Factor XII in activating the plasma kallikrein-kinin system (KKS), the mechanism of activity and control in the KKS, and the function of HK on contact activation proteins on cell membranes. The role of human PKa in cell biology regarding the contact system and KSS, particularly the endothelial cells, and neutrophils, in inflammatory processes and infectious diseases, was also approached. We examined the natural plasma protein inhibitors, including a detailed survey of human PKa inhibitors' development and their potential market.

Factor XII deficiency: a clinical and molecular genetic study

Factor XII deficiency is a rare inherited disorder caused by clotting factor XII (FXII, F12) deficiency. It is often asymptomatic but can have both thrombotic and haemorrhagic symptoms. The aim of this study was to describe the spectrum of F12 gene mutations in a Russian population and learn more about the relationship between F12 variants and clinical phenotypes. We obtained and analysed genetic and clinical data from 33 apparently unrelated patients with FXII plasma levels below 60% and genetic data from 26 healthy controls with no history of FXII deficiency. Forty mutant alleles and six different deleterious substitutions were identified. Of these substitutions, three were major in the Russian population (c.-62C > T, c.-57G > C and c.1532-1G > A, total frequency 92.5%) and the three others (p.615 del C, c.1180_1181delCA, and CD218 TAT- > CAT p.Tyr218His) were rare and novel in the world population. Eight patients with mild FXII deficiency were found to be homozygous for a hypomorphic variant of functional polymorphism C46T and have no other deleterious substitutions in the F12 gene. Contrary to data in the literature, our study showed that mild haemorrhagic manifestations are common among patients with FXII deficiency.

Synthesis of cross-linked polymer based on purified Sterculia foetida L. gum as a potential hemostatic agent

A method for purifying the polysaccharides from Sterculia foetida L. gum was developed. The effects of purifying conditions were also studied. Results have shown that the conditions of pH 0.5, temperature of 80°C, and 2.5-h reaction duration gave the best polysaccharides yield. The mineral content and the molecular weight of the obtained polysaccharides were measured for characterization. The cross-linking of the polysaccharides with citric acid in order to achieve a desired polymer was performed successfully. The obtained polymers under different conditions were evaluated for the potential application as a hemostatic agent, including tests of swelling behavior in different fluids, whole-blood clotting time and enzymatic bio-degradation. Results have shown that the citric acid/polysaccharides ratio of 0.01 produced a comparative yield of polymer flakes with increased swelling properties, as well as shortened in vitro blood clotting time and gradual biodegradability in three experimental days. Therefore, the citric acid/polysaccharides ratio of 0.01 was selected for the subsequent experiment to obtain the polymer after 1.5 h of purification, which gave the best swelling properties, 20 times the initial weight, reduced the whole-blood clotting time by 50% and showed a rapid bio-degradation. The results obtained from this study provide essential knowledge on the research of the use of S. foetida gum polysaccharides as a passive hemostatic agent, thereby extending the potential pharmaceutical applications of natural polysaccharides in Vietnam.

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.

Plant Kunitz Inhibitors and Their Interaction with Proteases: Current and Potential Pharmacological Targets

The action of proteases can be controlled by several mechanisms, including regulation through gene expression; post-translational modifications, such as glycosylation; zymogen activation; targeting specific compartments, such as lysosomes and mitochondria; and blocking proteolysis using endogenous inhibitors. Protease inhibitors are important molecules to be explored for the control of proteolytic processes in organisms because of their ability to act on several proteases. In this context, plants synthesize numerous proteins that contribute to protection against attacks by microorganisms (fungi and bacteria) and/or invertebrates (insects and nematodes) through the inhibition of proteases in these organisms. These proteins are widely distributed in the plant kingdom, and are present in higher concentrations in legume seeds (compared to other organs and other botanical families), motivating studies on their inhibitory effects in various organisms, including humans. In most cases, the biological roles of these proteins have been assigned based mostly on their in vitro action, as is the case with enzyme inhibitors. This review highlights the structural evolution, function, and wide variety of effects of plant Kunitz protease inhibitors, and their potential for pharmaceutical application based on their interactions with different proteases.

Thromboinflammation in Brain Ischemia: Recent Updates and Future Perspectives

Despite decades of promising preclinical validation and clinical translation, ischemic stroke still remains as one of the leading causes of death and disability worldwide. Within its complex pathophysiological signatures, thrombosis and inflammation, that is, thromboinflammation, are highly interconnected processes leading to cerebral vessel occlusion, inflammatory responses, and severe neuronal damage following the ischemic event. Hence, we here review the most recent updates on thromboinflammatory-dependent mediators relevant after stroke focusing on recent discoveries on platelet modulation, a potential regulation of the innate and adaptive immune system in thromboinflammation, utterly providing a thorough up-to-date overview of all therapeutic approaches currently undergoing clinical trial.

Review of evidence implicating the plasminogen activator system in blood-brain barrier dysfunction associated with Alzheimer's disease

Elucidating the pathogenic mechanisms of Alzheimer’s disease (AD) to identify therapeutic targets has been the focus of many decades of research. While deposition of extracellular amyloid-beta plaques and intraneuronal neurofibrillary tangles of hyperphosphorylated tau have historically been the two characteristic hallmarks of AD pathology, therapeutic strategies targeting these proteinopathies have not been successful in the clinics. Neuroinflammation has been gaining more attention as a therapeutic target because increasing evidence implicates neuroinflammation as a key factor in the early onset of AD disease progression. The peripheral immune response has emerged as an important contributor to the chronic neuroinflammation associated with AD pathophysiology. In this context, the plasminogen activator system (PAS), also referred to as the vasculature’s fibrinolytic system, is emerging as a potential factor in AD pathogenesis. Evolving evidence suggests that the PAS plays a role in linking chronic peripheral inflammatory conditions to neuroinflammation in the brain. While the PAS is better known for its peripheral functions, components of the PAS are expressed in the brain and have been demonstrated to alter neuroinflammation and blood-brain barrier (BBB) permeation. Here, we review plasmin-dependent and -independent mechanisms by which the PAS modulates the BBB in AD pathogenesis and discuss therapeutic implications of these observations.

Plasma Kallikrein Contributes to Intracerebral Hemorrhage and Hypertension in Stroke-Prone Spontaneously Hypertensive Rats

Plasma kallikrein (PKa) has been implicated in contributing to hemorrhage following thrombolytic therapy; however, its role in spontaneous intracerebral hemorrhage is currently not available. This report investigates the role of PKa on hemorrhage and hypertension in stroke-prone spontaneously hypertensive rats (SHRSP). SHRSP were fed with a high salt-containing stroke-prone diet to increase blood pressure and induce intracerebral hemorrhage. The roles of PKa on blood pressure, hemorrhage, and survival in SHRSP were examined in rats receiving a PKa inhibitor or plasma prekallikrein antisense oligonucleotide (PK ASO) compared with rats receiving control ASO. Effects on PKa on the proteolytic cleavage of atrial natriuretic peptide (ANP) were analyzed by tandem mass spectrometry. We show that SHRSP on high-salt diet displayed increased levels of PKa activity compared with control rats. Cleaved kininogen was increased in plasma during stroke compared to SHRSP without stroke. Systemic administration of a PKa inhibitor or PK ASO to SHRSP reduced hemorrhage and blood pressure, and improved neurological function and survival compared with SHRSP receiving control ASO. Since PKa inhibition was associated with reduced blood pressure in hypertensive rats, we investigated the effects of PKa on the cleavage of ANP. Incubation of PKa with ANP resulted in the generation fragment ANP_5-28, which displayed reduced effects on blood pressure lowering compared with full length ANP. PKa contributes to increased blood pressure in SHRSP, which is associated with hemorrhage and reduced survival. PKa-mediated cleavage of ANP reduces its blood pressure lowering effects and thereby may contribute to hypertension-induced intracerebral hemorrhage.

[Spontaneous fibrinolysis and possibilities of its acceleration in pulmonary embolism]

This review contains the data concerning the mechanisms of spontaneous fibrinolysis in pulmonary vessels and possibilities of its acceleration in pulmonary embolism. The spontaneous fibrinolysis system is known to be sequential and multifactorial, with the interaction of accelerators (t-PA and u-PA) and inhibitors (alpha-2-antiplasmin, PAI-1, TAFI). The fibrinolytic processes take place in case of prevailing reactions of accelerating factors over inhibiting ones. The endothelium of pulmonary vessels possesses pronounced antithrombogenic and profibrinolytic properties, therefore, the processes of fibrinolysis in the pulmonary vascular bed normally occur more intensively than in the vessels of the systemic circulation. The membrane proteins of the endothelium annexins A2 activate plasminogen, whereas thrombomodulin inhibits the activity of PAI-1. The main approaches to increase the fibrinolysis intensity in conditions of pulmonary embolism may be aimed at elevating the activity of fibrinolytic enzymes (enhancing the synthesis of annexins A2, the use of NMDA-receptor antagonists) and suppressing its inhibitors (the use of monoclonal antibodies to alpha-2-antiplasmin, as well as plasminogen activator inhibitor-1 (PAI-1) and thrombin-activatable fibrinolysis inhibitor (TAFI). Promising directions for future research can be the synthesis of a new generation of tissue-type plasminogen activators, and investigations of the possibility of clinical application of antithrombin and thrombomodulin, angiotensin converting enzyme inhibitors and cortisol antagonists. To meet these challenges, it is necessary to develop new models of venous thrombosis and acute pulmonary embolism in different animal species, with the assessment of the changes in the venous haemodynamics and pulmonary microcirculation on the background of administration of a new class of fibrinolytic agents.

Trauma-induced coagulopathy

Uncontrolled haemorrhage is a major preventable cause of death in patients with traumatic injury. Trauma-induced coagulopathy (TIC) describes abnormal coagulation processes that are attributable to trauma. In the early hours of TIC development, hypocoagulability is typically present, resulting in bleeding, whereas later TIC is characterized by a hypercoagulable state associated with venous thromboembolism and multiple organ failure. Several pathophysiological mechanisms underlie TIC; tissue injury and shock synergistically provoke endothelial, immune system, platelet and clotting activation, which are accentuated by the 'lethal triad' (coagulopathy, hypothermia and acidosis). Traumatic brain injury also has a distinct role in TIC. Haemostatic abnormalities include fibrinogen depletion, inadequate thrombin generation, impaired platelet function and dysregulated fibrinolysis. Laboratory diagnosis is based on coagulation abnormalities detected by conventional or viscoelastic haemostatic assays; however, it does not always match the clinical condition. Management priorities are stopping blood loss and reversing shock by restoring circulating blood volume, to prevent or reduce the risk of worsening TIC. Various blood products can be used in resuscitation; however, there is no international agreement on the optimal composition of transfusion components. Tranexamic acid is used in pre-hospital settings selectively in the USA and more widely in Europe and other locations. Survivors of TIC experience high rates of morbidity, which affects short-term and long-term quality of life and functional outcome.

[Hereditary angioedema]

Hereditary angioedema (HAE) encompasses a heterogeneous group of diseases with similar phenotypes but different underlying genotypes. Specific clinical signs may point to HAE as opposed to histaminergic angioedema: the typical prolonged development of angioedema over time, positive family history, a lack of response to antihistamines and steroids and response to bradykinin antagonists are typical signs of HAE. The different types of HAE may be associated with a severe clinical course. They are life-long conditions and are still potentially life-threatening. The quality of life of patients with HAE may be considerably impaired. Management plans should be individualized, which is facilitated by the variety of specific medicastions available.

Impact of Bradykinin Generation During Thrombolysis in Ischemic Stroke

Ischemic stroke is one of the leading causes of death and disability worldwide. Current medical management in the acute phase is based on the activation of the fibrinolytic cascade by intravenous injection of a plasminogen activator (such as tissue-type plasminogen activator, tPA) that promotes restauration of the cerebral blood flow and improves stroke outcome. Unfortunately, the use of tPA is associated with deleterious effects such as hemorrhagic transformation, symptomatic brain edema, and angioedema, which limit the efficacy of this therapeutic strategy. Preclinical and clinical evidence suggests that intravenous thrombolysis generates large amounts of bradykinin, a peptide with potent pro-inflammatory, and pro-edematous effects. This tPA-triggered generation of bradykinin could participate in the deleterious effects of thrombolysis and is a potential target to improve neurological outcome in tPA-treated patients. The present review aims at summarizing current evidence linking thrombolysis, bradykinin generation, and neurovascular damage.

Improving the understanding of plasma kallikrein contribution to arterial thrombus formation using two plant protease inhibitors

The purpose of antithrombotic therapy is the prevention of thrombus formation and/or its extension with a minimum risk of bleeding. The inhibition of a variety of proteolytic processes, particularly those of the coagulation cascade, has been reported as a property of plant protease inhibitors. The role of trypsin inhibitors (TIs) from Delonix regia (Dr) and Acacia schweinfurthii (As), members of the Kunitz family of protease inhibitors, was investigated on blood coagulation, platelet aggregation, and thrombus formation. Different from Acacia schweinfurthii trypsin inhibitor (AsTI), Delonix regia trypsin inhibitor (DrTI) is a potent inhibitor of FXIa with a K_iapp of 1.3 × 10^-9 M. In vitro, both inhibitors at 100 µg corresponding to the concentrations of 21 μM and 15.4 μM of DrTI and AsTI, respectively, increased approximately 2.0 times the activated partial thromboplastin time (aPTT) in human plasma compared to the control, likely due to the inhibition of human plasma kallikrein (huPK) or activated factor XI (FXIa), in the case of DrTI. Investigating in vivo models of arterial thrombus formation and bleeding time, DrTI and AsTI, 1.3 µM and 0.96 µM, respectively, prolonged approximately 50% the time for total carotid artery occlusion in mice compared to the control. In contrast to heparin, the bleeding time in mice treated with the two inhibitors did not differ from that of the control group. DrTI and AsTI inhibited 49.3% and 63.8%, respectively, ex vivo murine platelet aggregation induced by adenosine diphosphate (ADP), indicating that these protein inhibitors prevent arterial thrombus formation possibly by interfering with the plasma kallikrein (PK) proteolytic action on the intrinsic coagulation pathway and its ability to enhance the platelet aggregation activity on the intravascular compartment leading to the improvement of a thrombus.

The Plasma Kallikrein-Kininogen Pathway Is Critical in the Pathogenesis of Colitis in Mice

The kallikrein-kinin system (KKS) consists of two serine proteases, prekallikrein (pKal) and factor XII (FXII), and a cofactor, high-molecular-weight kininogen (HK). Upon activation of the KKS, HK is cleaved to release bradykinin. Although the KKS is activated in humans and animals with inflammatory bowel disease (IBD), its role in the pathogenesis of IBD has not been characterized. In the present study, we determined the role of the KKS in the pathogenesis of IBD using mice that lack proteins involved in the KKS. In two colitis models, induced by dextran sulfate sodium (DSS) or 2,4,6-trinitrobenzene sulfonic acid (TNBS), mice deficient in HK, pKal, or bradykinin receptors displayed attenuated phenotypes, including body weight loss, disease activity index, colon length shortening, histological scoring, and colonic production of cytokines. Infiltration of neutrophils and inflammatory monocytes in the colonic lamina propria was reduced in HK-deficient mice. Reconstitution of HK-deficient mice through intravenous injection of HK recovered their susceptibility to DSS-induced colitis, increased IL-1β levels in the colon tissue and bradykinin concentrations in plasma. In contrast to the phenotypes of other mice lacking other proteins involved in the KKS, mice lacking FXII had comparable colonic inflammation to that observed in wild-type mice. The concentration of bradykinin was significantly increased in the plasma of wild-type mice after DSS-induced colitis. In vitro analysis revealed that DSS-induced pKal activation, HK cleavage, and bradykinin plasma release were prevented by the absence of pKal or the inhibition of Kal. Unlike DSS, TNBS-induced colitis did not trigger HK cleavage. Collectively, our data strongly suggest that Kal, acting independently of FXII, contributes to experimental colitis by promoting bradykinin release from HK.