Nebulized antithrombin limits bacterial outgrowth and lung injury in Streptococcus pneumoniae pneumonia in rats

Experimental and clinical perspectives on glycocalyx integrity and its relation to acute respiratory distress syndrome

The development of microcirculation imaging devices has significantly advanced our comprehension of the capillary environment's dynamics. Early research suggested that erythrocytes did not contact the vessel's inner surface due to the Fåhraeus effect, implying the presence of a covering on the endothelial cell surface. Subsequent electron microscopy studies revealed this layer to be a complex part of the vessel wall, now known as the endothelial glycocalyx (EG). The EG is a network of proteoglycans and glycoproteins bound to the endothelial membrane, incorporating soluble molecules from the endothelium and plasma. Over time, studies have elucidated the structure, function, and therapeutic targets of the glycocalyx, underscoring its pivotal role in vascular biology. The presence of cellular extensions of lung tissue cells in both vascular and nonvascular areas demonstrates the pivotal role of the glycocalyx in pulmonary vascular leak, surfactant dysfunction, impaired lung compliance and gas exchange abnormalities, which are hallmarks of acute respiratory distress syndrome (ARDS). It is of the utmost importance to elucidate the mechanisms underlying alveolocapillary glycocalyx degradation to develop efficacious treatments for ARDS, which has a mortality rate of 35 %. An understanding of the glycocalyx's role in vascular integrity provides a foundation for exploring new therapeutic avenues to mitigate lung injury and improve clinical outcomes in ARDS patients.

Arterial Thrombosis in Acute Respiratory Infections: An Underestimated but Clinically Relevant Problem

During the COVID-19 pandemic, there was increased interest in the issue of thrombotic complications of acute respiratory infections. Clinical reports and pathological studies have revealed that thrombus formation in COVID-19 may involve the venous and arterial vasculature. As thrombotic complications of infectious respiratory diseases are increasingly considered in the context of COVID-19, the fact that thrombosis in lung diseases of viral and bacterial etiology was described long before the pandemic is overlooked. Pre-pandemic studies show that bacterial and viral respiratory infections are associated with an increased risk of thrombotic complications such as myocardial infarction, ischemic stroke, pulmonary embolism, and other critical illnesses caused by arterial and venous thrombosis. This narrative review article aims to summarize the current evidence regarding thrombotic complications and their pathogenesis in acute lower respiratory tract infections.

Inhaled heparin: Past, present, and future

While heparin has traditionally served as a key anticoagulant in clinical practice for nearly a century, recent years have witnessed a growing interest in its role as a potent antiinflammatory and antiviral agent, as well as an anticancer agent. To address challenges with injection-based delivery, exploring patient-friendly routes such as oral and pulmonary delivery is crucial. This review specifically highlights the multiple therapeutic benefits of inhaled heparin. In summary, this review serves as a valuable source of information, providing deep insights into the diverse therapeutic advantages of inhaled heparin and its potential applications within clinical contexts.

Acute respiratory distress syndrome heterogeneity and the septic ARDS subgroup

Acute respiratory distress syndrome (ARDS) is an acute diffuse inflammatory lung injury characterized by the damage of alveolar epithelial cells and pulmonary capillary endothelial cells. It is mainly manifested by non-cardiogenic pulmonary edema, resulting from intrapulmonary and extrapulmonary risk factors. ARDS is often accompanied by immune system disturbance, both locally in the lungs and systemically. As a common heterogeneous disease in critical care medicine, researchers are often faced with the failure of clinical trials. Latent class analysis had been used to compensate for poor outcomes and found that targeted treatment after subgrouping contribute to ARDS therapy. The subphenotype of ARDS caused by sepsis has garnered attention due to its refractory nature and detrimental consequences. Sepsis stands as the most predominant extrapulmonary cause of ARDS, accounting for approximately 32% of ARDS cases. Studies indicate that sepsis-induced ARDS tends to be more severe than ARDS caused by other factors, leading to poorer prognosis and higher mortality rate. This comprehensive review delves into the immunological mechanisms of sepsis-ARDS, the heterogeneity of ARDS and existing research on targeted treatments, aiming to providing mechanism understanding and exploring ideas for accurate treatment of ARDS or sepsis-ARDS.

Serine Protease Inhibitors Restrict Host Susceptibility to SARS-CoV-2 Infections

The coronavirus disease 2019, COVID-19, is a complex disease with a wide range of symptoms from asymptomatic infections to severe acute respiratory syndrome with lethal outcome. Individual factors such as age, sex, and comorbidities increase the risk for severe infections, but other aspects, such as genetic variations, are also likely to affect the susceptibility to SARS-CoV-2 infection and disease severity. Here, we used a human 3D lung cell model based on primary cells derived from multiple donors to identity host factors that regulate SARS-CoV-2 infection. With a transcriptomics-based approach, we found that less susceptible donors show a higher expression level of serine protease inhibitors SERPINA1, SERPINE1, and SERPINE2, identifying variation in cellular serpin levels as restricting host factors for SARS-CoV-2 infection. We pinpoint their antiviral mechanism of action to inhibition of the cellular serine protease, TMPRSS2, thereby preventing cleavage of the viral spike protein and TMPRSS2-mediated entry into the target cells. By means of single-cell RNA sequencing, we further locate the expression of the individual serpins to basal, ciliated, club, and goblet cells. Our results add to the importance of genetic variations as determinants for SARS-CoV-2 susceptibility and suggest that genetic deficiencies of cellular serpins might represent risk factors for severe COVID-19. Our study further highlights TMPRSS2 as a promising target for antiviral intervention and opens the door for the usage of locally administered serpins as a treatment against COVID-19. IMPORTANCE Identification of host factors affecting individual SARS-CoV-2 susceptibility will provide a better understanding of the large variations in disease severity and will identify potential factors that can be used, or targeted, in antiviral drug development. With the use of an advanced lung cell model established from several human donors, we identified cellular protease inhibitors, serpins, as host factors that restrict SARS-CoV-2 infection. The antiviral mechanism was found to be mediated by the inhibition of a serine protease, TMPRSS2, which results in a blockage of viral entry into target cells. Potential treatments with these serpins would not only reduce the overall viral burden in the patients, but also block the infection at an early time point, reducing the risk for the hyperactive immune response common in patients with severe COVID-19.

Role of lungs in the hemostasis system (review of literature)

The lung tissue contains various hemostatic system elements, which can be released from the lungs, both under physiological and pathological conditions. The COVID-19 pandemic has led to an increase in the number of patients with acute respiratory distress syndrome (ARDS) in intensive care units worldwide. When the lungs are damaged, coagulation disorders are mediated by tissue factor (TF) - factor VIIa (F VIIa), and inhibition of this pathway completely eliminates intrapulmonary fibrin deposition. A tissue factor pathway inhibitor TFPI also contributes to pulmonary coagulationdisturbance in ARDS. Pulmonary coagulationdisturbance caused by pneumonia can worsen the damage to the lungs and thus contribute to the progression of the disease. Cytokines are the main linking factors between inflammation and changes in blood clotting and fibrinolysis. The sources of proinflammatory cytokines in the lungs are probably alveolar macrophages. The activation of alveolar macrophages occurs through the nuclear factor kappa-bi (NF-κB), which controls thetranscription of the expression of immune response genes, cell apoptosis, which leads to the development of inflammation and autoimmune diseases as a result of direct stimulation of TF activation. Conversely,coagulation itself can affect bronchoalveolar inflammation. Coagulation leads to the formation of proteases that interact with specific cellular receptors, activating intracellular signaling pathways. The use of anticoagulant therapy, which also has an anti-inflammatory effect, perhaps one of the therapeutic targets for coronavirus infection.The difficulty here is that it seems appropriate to study anticoagulant interventions' influence on clinically significant cardio-respiratory parameters.

Antithrombin and Its Role in Host Defense and Inflammation

Antithrombin (AT) is a natural anticoagulant that interacts with activated proteases of the coagulation system and with heparan sulfate proteoglycans (HSPG) on the surface of cells. The protein, which is synthesized in the liver, is also essential to confer the effects of therapeutic heparin. However, AT levels drop in systemic inflammatory diseases. The reason for this decline is consumption by the coagulation system but also by immunological processes. Aside from the primarily known anticoagulant effects, AT elicits distinct anti-inflammatory signaling responses. It binds to structures of the glycocalyx (syndecan-4) and further modulates the inflammatory response of endothelial cells and leukocytes by interacting with surface receptors. Additionally, AT exerts direct antimicrobial effects: depending on AT glycosylation it can bind to and perforate bacterial cell walls. Peptide fragments derived from proteolytic degradation of AT exert antibacterial properties. Despite these promising characteristics, therapeutic supplementation in inflammatory conditions has not proven to be effective in randomized control trials. Nevertheless, new insights provided by subgroup analyses and retrospective trials suggest that a recommendation be made to identify the patient population that would benefit most from AT substitution. Recent experiment findings place the role of various AT isoforms in the spotlight. This review provides an overview of new insights into a supposedly well-known molecule.

Targeting coagulation activation in severe COVID-19 pneumonia: lessons from bacterial pneumonia and sepsis

Novel coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2), has rapidly spread throughout the world, resulting in a pandemic with high mortality. There are no effective treatments for the management of severe COVID-19 and current therapeutic trials are focused on antiviral therapy and attenuation of hyper-inflammation with anti-cytokine therapy. Severe COVID-19 pneumonia shares some pathological similarities with severe bacterial pneumonia and sepsis. In particular, it disrupts the haemostatic balance, which results in a procoagulant state locally in the lungs and systemically. This culminates in the formation of microthrombi, disseminated intravascular coagulation and multi-organ failure. The deleterious effects of exaggerated inflammatory responses and activation of coagulation have been investigated in bacterial pneumonia and sepsis and there is recognition that although these pathways are important for the host immune response to pathogens, they can lead to bystander tissue injury and are negatively associated with survival. In the past two decades, evidence from preclinical studies has led to the emergence of potential anticoagulant therapeutic strategies for the treatment of patients with pneumonia, sepsis and acute respiratory distress syndrome, and some of these anticoagulant approaches have been trialled in humans. Here, we review the evidence from preclinical studies and clinical trials of anticoagulant treatment strategies in bacterial pneumonia and sepsis, and discuss the importance of these findings in the context of COVID-19.

Nebulised heparin as a treatment for COVID-19: scientific rationale and a call for randomised evidence

Nebulised unfractionated heparin (UFH) has a strong scientific and biological rationale and warrants urgent investigation of its therapeutic potential, for COVID-19-induced acute respiratory distress syndrome (ARDS). COVID-19 ARDS displays the typical features of diffuse alveolar damage with extensive pulmonary coagulation activation resulting in fibrin deposition in the microvasculature and formation of hyaline membranes in the air sacs. Patients infected with SARS-CoV-2 who manifest severe disease have high levels of inflammatory cytokines in plasma and bronchoalveolar lavage fluid and significant coagulopathy. There is a strong association between the extent of the coagulopathy and poor clinical outcomes.The anti-coagulant actions of nebulised UFH limit fibrin deposition and microvascular thrombosis. Trials in patients with acute lung injury and related conditions found inhaled UFH reduced pulmonary dead space, coagulation activation, microvascular thrombosis and clinical deterioration, resulting in increased time free of ventilatory support. In addition, UFH has anti-inflammatory, mucolytic and anti-viral properties and, specifically, has been shown to inactivate the SARS-CoV-2 virus and prevent its entry into mammalian cells, thereby inhibiting pulmonary infection by SARS-CoV-2. Furthermore, clinical studies have shown that inhaled UFH safely improves outcomes in other inflammatory respiratory diseases and also acts as an effective mucolytic in sputum-producing respiratory patients. UFH is widely available and inexpensive, which may make this treatment also accessible for low- and middle-income countries.These potentially important therapeutic properties of nebulised UFH underline the need for expedited large-scale clinical trials to test its potential to reduce mortality in COVID-19 patients.

"War to the knife" against thromboinflammation to protect endothelial function of COVID-19 patients

In this viewpoint, we summarize the relevance of thromboinflammation in COVID-19 and discuss potential mechanisms of endothelial injury as a key point for the development of lung and distant organ dysfunction, with a focus on direct viral infection and cytokine-mediated injury. Entanglement between inflammation and coagulation and resistance to heparin provide a rationale to consider other therapeutic approaches in order to preserve endothelial function and limit microthrombosis, especially in severe forms. These strategies include nebulized heparin, N-acetylcysteine, plasma exchange and/or fresh frozen plasma, plasma derivatives to increase the level of endogenous anticoagulants (tissue factor pathway inhibitor, activated protein C, thrombomodulin, antithrombin), dipyridamole, complement blockers, different types of stem cells, and extracellular vesicles. An integrated therapy including these drugs has the potential to improve outcomes in COVID-19.

Effects of nebulized antithrombin and heparin on inflammatory and coagulation alterations in an acute lung injury model in rats

BACKGROUND

During acute respiratory distress syndrome, proinflammatory mediators inhibit natural anticoagulant factors, which alter the normal balance between coagulation and fibrinolysis leading to a procoagulant state. We hypothesize that pulmonary administration of anticoagulants might be beneficial to treat acute respiratory distress syndrome for their anticoagulant and antiinflammatory effects and reduce the risk of systemic bleeding.

OBJECTIVES

Our aim is to study the effects of nebulized antithrombin (AT) and combined AT and heparin in an animal model of acute lung injury.

METHODS

Acute lung injury was induced in rats by the intratracheal administration of hydrochloric acid and lipopolysaccharide. AT alone (500 IU/kg body weight) or combined with heparin (1000 IU/kg body weight) were nebulized after the injury. Control groups received saline instead. Blood, lung tissue, bronchoalveolar lavage, and alveolar macrophages (AM) isolated from bronchoalveolar lavage were collected after 48 hours and analyzed.

RESULTS

Nebulized anticoagulant treatments reduced protein concentration in the lungs and decreased injury-mediated coagulation factors (tissue factor, plasminogen activator inhibitor-1, plasminogen, and fibrinogen degradation product) and inflammation (tumor necrosis factor α and interleukin 1β) in the alveolar space without affecting systemic coagulation and no bleeding. AT alone reduced fibrin deposition and edema in the lungs. Heparin did not potentiate AT coagulant effect but promoted the reduction of macrophages infiltration into the alveolar compartment. Anticoagulants reduced nuclear factor-kB downstream effectors in AM.

CONCLUSIONS

Nebulized AT and heparin attenuate lung injury through decreasing coagulation and inflammation without altering systemic coagulation and no bleeding. However, combined AT and heparin did not produce a synergistic effect.

Factor XI deficiency is not associated with an increased risk of pneumonia and pneumonia-related mortality

INTRODUCTION

Drugs targeting factor XI (FXI) shows promising results in reducing postoperative VTE. Recently, researchers have shown that FXI knockout mice had a worse outcome when infected with pathogens for pneumonia, raising concerns about the safety of these drugs.

AIM

To investigate the effect of FXI deficiency on the incidence of pneumonia and outcomes of pneumonia in humans.

METHODS

Using the computerized database of the largest healthcare provider in Israel, we identified adults who were tested for FXI activity between January of 2002 and December of 2014 (n = 10 193). Patients were followed up until December of 2016 for the occurrence of pneumonia and pneumonia requiring hospitalization as a proxy of severe pneumonia.

RESULTS

A total of 8958 (87.9%) had normal FXI activity, 804 (7.9%) had partial deficiency and 431 (4.2%) had severe deficiency; 722 individuals had pneumonia during 70 881 person-years of follow-up (incidence rate: 10.2 per 1000 person-years). Compared to those with normal FXI activity, the adjusted HR for pneumonia was 0.87 (95% CI, 0.67-1.14), and 0.95 (0.69-1.30) for those with partial and severe FXI deficiency, respectively. Overall, 256 individuals were hospitalized for pneumonia during 72 209 person-years of follow-up (incidence rate: 3.5 per 1000 person-years). The corresponding HR for severe pneumonia was 1.0 (0.70-1.48) and 0.86 (0.53-1.40) in those with partial and severe FXI deficiency, respectively. FXI deficiency was not significantly associated with 30-day and 90-day mortality among patients with pneumonia.

CONCLUSION

FXI deficiency was not associated with an increased risk of pneumonia, pneumonia severity or short-term mortality among patients with pneumonia.

Anticoagulant therapy in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) presents a complex pathophysiology characterized by pulmonary activated coagulation and reduced fibrinolysis. Despite advances in supportive care of this syndrome, morbidity and mortality remains high, leading to the need of novel therapies to combat this disease. Focus these therapies in the inhibition of ARDS development pathophysiology is essential. Beneficial effects of anticoagulants in ARDS have been proved in preclinical and clinical trials, thanks to its anticoagulant and anti-inflammatory properties. Moreover, local administration by nebulization in the alveolar compartment increases local efficacy and does not produce systemic bleeding. In this review the coagulation and fibrinolytic pathway and its pharmacological targets to treat ARDS are summarized.

Nebulized Heparin Attenuates Pulmonary Coagulopathy and Inflammation through Alveolar Macrophages in a Rat Model of Acute Lung Injury

Objective  Alveolar macrophages play a key role in the development and resolution of acute respiratory distress syndrome (ARDS), modulating the inflammatory response and the coagulation cascade in lungs. Anti-coagulants may be helpful in the treatment of ARDS. This study investigated the effects of nebulized heparin on the role of alveolar macrophages in limiting lung coagulation and inflammatory response in an animal model of acute lung injury (ALI).

Methods  Rats were randomized to four experimental groups. In three groups, ALI was induced by intratracheal instillation of lipopolysaccharide (LPS) and heparin was nebulized at constant oxygen flow: the LPS/Hep group received nebulized heparin 4 and 8 hours after injury; the Hep/LPS/Hep group received nebulized heparin 30 minutes before and 4 and 8 hours after LPS-induced injury; the LPS/Sal group received nebulized saline 4 and 8 hours after injury. The control group received only saline. Animals were exsanguinated 24 hours after LPS instillation. Lung tissue, bronchoalveolar lavage fluid (BALF) and alveolar macrophages isolated from BALF were analysed.

Results  LPS increased protein concentration, oedema and neutrophils in BALF as well as procoagulant and proinflammatory mediators in lung tissue and alveolar macrophages. In lung tissue, nebulized heparin attenuated ALI through decreasing procoagulant (tissue factor, thrombin–anti-thrombin complexes, fibrin degradation products) and proinflammatory (interleukin 6, tumour necrosis factor alpha) pathways. In alveolar macrophages, nebulized heparin reduced expression of procoagulant genes and the effectors of transforming growth factor beta (Smad 2, Smad 3) and nuclear factor kappa B (p-selectin, CCL-2). Pre-treatment resulted in more pronounced attenuation.

Conclusion  Nebulized heparin reduced pulmonary coagulopathy and inflammation without producing systemic bleeding, partly by modulating alveolar macrophages.

Nebulized anticoagulants in lung injury in critically ill patients-an updated systematic review of preclinical and clinical studies

Pneumonia, inhalation trauma and acute respiratory distress syndrome (ARDS), typical causes of lung injury in critically ill patients, are all three characterized by dysregulated inflammation and coagulation in the lungs. Nebulized anticoagulants are thought to have beneficial effects as they could attenuate pulmonary coagulopathy and maybe even affect pulmonary inflammation. A systematic search of the medical literature was performed using terms referring to aspects of the condition ('pneumonia', 'inhalation trauma' and 'ARDS'), the intervention ('nebulized', 'vaporized', and 'aerosolized') and anticoagulants limited to agents that are commercially available and frequently given or tested in critically ill patients ['heparin', 'danaparoid', 'activated protein C' (APC), 'antithrombin' (AT) and 'tissue factor pathway inhibitor' (TFPI)]. The systematic search identified 16 articles reporting on preclinical studies and 11 articles reporting on human trials. All nebulized anticoagulants attenuate pulmonary coagulopathy in preclinical studies using various models for lung injury, but the effects on inflammation are less consistent. Nebulized heparin, danaparoid and TFPI, but not APC and AT also reduced systemic coagulation. Nebulized heparin in lung injury patients shows contradictory results, and there is concern over systemic side effects of this strategy. Future studies need to focus on the way to nebulize anticoagulants, as well as on efficient but safe dosages, and other side effects.

Nebulized Recombinant Human Tissue Factor Pathway Inhibitor Attenuates Coagulation and Exerts Modest Anti-inflammatory Effects in Rat Models of Lung Injury

BACKGROUND

Critically ill patients are at a constant risk of direct (e.g., by pneumonia) or indirect lung injury (e.g., by sepsis). Excessive alveolar fibrin deposition is a prominent feature of lung injury, undermining pulmonary integrity and function.

METHODS

We examined the effect of local administration of recombinant human tissue factor pathway inhibitor (rh-TFPI), a natural anticoagulant, in two well-established models of lung injury in rats. Rats received intratracheal instillation of Pseudomonas aeruginosa, causing direct lung injury, or they received an intravenous injection of Escherichia coli lipopolysaccharide (LPS), causing indirect lung injury. Rats were randomized to local treatment with rh-TFPI or placebo through repeated nebulization.

RESULTS

Challenge with P. aeruginosa or LPS was associated with increased coagulation and decreased fibrinolysis in bronchoalveolar lavage fluid (BALF) and plasma. Rh-TFPI levels in BALF increased after nebulization, whereas plasma rh-TFPI levels remained low and systemic TFPI activity was not affected. Nebulization of rh-TFPI attenuated pulmonary and systemic coagulation in both models, without affecting fibrinolysis. Nebulization of rh-TFPI modestly reduced the inflammatory response and bacterial growth of P. aeruginosa in the alveolar compartment.

CONCLUSIONS

Local treatment with rh-TFPI does not alter systemic TFPI activity; however, it attenuates both pulmonary and systemic coagulopathy. Furthermore, nebulized rh-TFPI modestly reduces the pulmonary inflammatory response and allows increased bacterial clearance in rats with direct lung injury caused by P. aeruginosa.

Feasibility and Safety of Local Treatment with Recombinant Human Tissue Factor Pathway Inhibitor in a Rat Model of Streptococcus pneumoniae Pneumonia

Pulmonary coagulopathy is intrinsic to pulmonary injury including pneumonia. Anticoagulant strategies could benefit patients with pneumonia, but systemic administration of anticoagulant agents may lead to suboptimal local levels and may cause systemic hemorrhage. We hypothesized nebulization to provide a safer and more effective route for local administration of anticoagulants. Therefore, we aimed to examine feasibility and safety of nebulization of recombinant human tissue factor pathway inhibitor (rh-TFPI) in a well-established rat model of Streptococcus (S.) pneumoniae pneumonia. Thirty minutes before and every 6 hours after intratracheal instillation of S. pneumonia causing pneumonia, rats were subjected to local treatment with rh-TFPI or placebo, and sacrificed after 42 hours. Pneumonia was associated with local as well as systemic activation of coagulation. Nebulization of rh-TFPI resulted in high levels of rh-TFPI in bronchoalveolar lavage fluid, which was accompanied by an attenuation of pulmonary coagulation. Systemic rh-TFPI levels remained undetectable, and systemic TFPI activity and systemic coagulation were not affected. Histopathology revealed no bleeding in the lungs. We conclude that nebulization of rh-TFPI seems feasible and safe; local anticoagulant treatment with rh-TFPI attenuates pulmonary coagulation, while not affecting systemic coagulation in a rat model of S. pneumoniae pneumonia.

Antimicrobial effects of helix D-derived peptides of human antithrombin III

Antithrombin III (ATIII) is a key antiproteinase involved in blood coagulation. Previous investigations have shown that ATIII is degraded by Staphylococcus aureus V8 protease, leading to release of heparin binding fragments derived from its D helix. As heparin binding and antimicrobial activity of peptides frequently overlap, we here set out to explore possible antibacterial effects of intact and degraded ATIII. In contrast to intact ATIII, the results showed that extensive degradation of the molecule yielded fragments with antimicrobial activity. Correspondingly, the heparin-binding, helix D-derived, peptide FFFAKLNCRLYRKANKSSKLV (FFF21) of human ATIII, was found to be antimicrobial against particularly the Gram-negative bacteria Escherichia coli and Pseudomonas aeruginosa. Fluorescence microscopy and electron microscopy studies demonstrated that FFF21 binds to and permeabilizes bacterial membranes. Analogously, FFF21 was found to induce membrane leakage of model anionic liposomes. In vivo, FFF21 significantly reduced P. aeruginosa infection in mice. Additionally, FFF21 displayed anti-endotoxic effects in vitro. Taken together, our results suggest novel roles for ATIII-derived peptide fragments in host defense.

Influenza Virus H1N1 inhibition by serine protease inhibitor (serpin) antithrombin III

Endogenous serine protease inhibitors (serpins) are anti-inflammatory mediators with multiple biologic functions. Serpins are also part of the early innate immune response to viral infection that includes mannose binding lectins, soluble CD14, defensins and antimicrobial peptides. Recently, serpin antithrombin III (ATIII) was shown to have broad-spectrum antiviral activity against HIV, HSV and HCV. We tested ATIII's antiviral activity against a variety of influenza virus strains. In our studies we found strong in vitro inhibition of influenza virus A H1N1 isolates. Our data also demonstrate that ATIII potency was more than 100-fold that of ribavirin. We also found that inhibition was dependent on viral hemagglutinin with decreasing efficacy in the order of H1N1 > H3N2 > H5N1 >> Flu B. In vivo efficacy is currently still lacking demonstrating need for more advanced delivery methods for this biomolecule. Understanding how ATIII regulates influenza virus inhibition may reveal new avenues for therapeutic interventions.

Antithrombin attenuates vascular leakage via inhibiting neutrophil activation in acute lung injury

OBJECTIVE

To test the hypothesis that restoration of antithrombin plasma concentrations attenuates vascular leakage by inhibiting neutrophil activation through syndecan-4 receptor inhibition in an established ovine model of acute lung injury.

DESIGN

Randomized controlled laboratory experiment.

SETTING

University animal research facility.

SUBJECTS

Eighteen chronically instrumented sheep.

INTERVENTIONS

Following combined burn and smoke inhalation injury (40% of total body surface area, third-degree flame burn; 4 × 12 breaths of cold cotton smoke), chronically instrumented sheep were randomly assigned to receive an IV infusion of 6 IU/kg/hr recombinant human antithrombin III or normal saline (n = 6 each) during the 48-hour study period. In addition, six sham animals (not injured, continuous infusion of vehicle) were used to obtain reference values for histological and immunohistochemical analyses.

MEASUREMENTS AND MAIN RESULTS

Compared to control animals, recombinant human antithrombin III reduced the number of neutrophils per hour in the pulmonary lymph (p < 0.01 at 24 and 48 hr), alveolar neutrophil infiltration (p = 0.04), and pulmonary myeloperoxidase activity (p = 0.026). Flow cytometric analysis revealed a significant reduction of syndecan-4-positive neutrophils (p = 0.002 vs control at 24 hr). Treatment with recombinant human antithrombin III resulted in a reduction of pulmonary nitrosative stress (p = 0.002), airway obstruction (bronchi: p = 0.001, bronchioli: p = 0.013), parenchymal edema (p = 0.044), and lung bloodless wet-to-dry-weight ratio (p = 0.015). Clinically, recombinant human antithrombin III attenuated the increased pulmonary transvascular fluid flux (12-48 hr: p ≤ 0.001 vs control each) and the deteriorated pulmonary gas exchange (12-48 hr: p < 0.05 vs control each) without increasing the risk of bleeding.

CONCLUSIONS

The present study provides evidence for the interaction between antithrombin and neutrophils in vivo, its pathophysiological role in vascular leakage, and the therapeutic potential of recombinant human antithrombin III in a large animal model of acute lung injury.

Protein C and acute inflammation: a clinical and biological perspective

The protein C system plays an active role in modulating severe systemic inflammatory processes such as sepsis, trauma, and acute respiratory distress syndrome (ARDS) via its anticoagulant and anti-inflammatory properties. Plasma levels of activated protein C (aPC) are lower than normal in acute inflammation in humans, except early after severe trauma when high plasma levels of aPC may play a mechanistic role in the development of posttraumatic coagulopathy. Thus, following positive results of preclinical studies, a clinical trial (PROWESS) with high continuous doses of recombinant human aPC given for 4 days demonstrated a survival benefit in patients with severe sepsis. This result was not confirmed by subsequent clinical trials, including the recently published PROWESS-SHOCK trial in patients with septic shock and a phase II trial with patients with nonseptic ARDS. A possible explanation for the major difference in outcome between PROWESS and PROWESS-SHOCK trials is that lung-protective ventilation was used for the patients included in the recent PROWESS-SHOCK, but not in the original PROWESS trial. Since up to 75% of sepsis originates from the lung, aPC treatment may not have added enough to the beneficial effect of lung-protective ventilation to show lower mortality. Thus whether aPC will continue to be used to modulate the acute inflammatory response in humans remains uncertain. Because recombinant human aPC has been withdrawn from the market, a better understanding of the complex interactions between coagulation and inflammation is needed before considering the development of new drugs that modulate both coagulation and acute inflammation in humans.

Bronchoalveolar hemostasis in lung injury and acute respiratory distress syndrome

Enhanced intrapulmonary fibrin deposition as a result of abnormal broncho-alveolar fibrin turnover is a hallmark of acute respiratory distress syndrome (ARDS), pneumonia and ventilator-induced lung injury (VILI), and is important to the pathogenesis of these conditions. The mechanisms that contribute to alveolar coagulopathy are localized tissue factor-mediated thrombin generation, impaired activity of natural coagulation inhibitors and depression of bronchoalveolar urokinase plasminogen activator-mediated fibrinolysis, caused by the increase of plasminogen activator inhibitors. There is an intense and bidirectional interaction between coagulation and inflammatory pathways in the bronchoalveolar compartment. Systemic or local administration of anticoagulant agents (including activated protein C, antithrombin and heparin) and profibrinolytic agents (such as plasminogen activators) attenuate pulmonary coagulopathy. Several preclinical studies show additional anti-inflammatory effects of these therapies in ARDS and pneumonia.

Nebulized anticoagulants for acute lung injury - a systematic review of preclinical and clinical investigations

Background

Data from interventional trials of systemic anticoagulation for sepsis inconsistently suggest beneficial effects in case of acute lung injury (ALI). Severe systemic bleeding due to anticoagulation may have offset the possible positive effects. Nebulization of anticoagulants may allow for improved local biological availability and as such may improve efficacy in the lungs and lower the risk of systemic bleeding complications.

Method

We performed a systematic review of preclinical studies and clinical trials investigating the efficacy and safety of nebulized anticoagulants in the setting of lung injury in animals and ALI in humans.

Results

The efficacy of nebulized activated protein C, antithrombin, heparin and danaparoid has been tested in diverse animal models of direct (for example, pneumonia-, intra-pulmonary lipopolysaccharide (LPS)-, and smoke inhalation-induced lung injury) and indirect lung injury (for example, intravenous LPS- and trauma-induced lung injury). Nebulized anticoagulants were found to have the potential to attenuate pulmonary coagulopathy and frequently also inflammation. Notably, nebulized danaparoid and heparin but not activated protein C and antithrombin, were found to have an effect on systemic coagulation. Clinical trials of nebulized anticoagulants are very limited. Nebulized heparin was found to improve survival of patients with smoke inhalation-induced ALI. In a trial of critically ill patients who needed mechanical ventilation for longer than two days, nebulized heparin was associated with a higher number of ventilator-free days. In line with results from preclinical studies, nebulization of heparin was found to have an effect on systemic coagulation, but without causing systemic bleedings.

Conclusion

Local anticoagulant therapy through nebulization of anticoagulants attenuates pulmonary coagulopathy and frequently also inflammation in preclinical studies of lung injury. Recent human trials suggest nebulized heparin for ALI to be beneficial and safe, but data are very limited.

Transfusion-related acute lung injury in cardiac surgery patients is characterized by pulmonary inflammation and coagulopathy: a prospective nested case-control study

OBJECTIVE

Transfusion-related acute lung injury is the leading cause of transfusion-related morbidity and mortality. Clinical data on the pathogenesis of transfusion-related acute lung injury are sparse. The objective of the present study was to determine inflammation and coagulation pathways involved in the onset of transfusion-related acute lung injury.

DESIGN

Nested case-control study.

SETTING

Operating theatre and intensive care department of a tertiary referral hospital.

PATIENTS

Elective cardiac surgery patients requiring postsurgery intensive care admission.

INTERVENTIONS

None.

MEASUREMENTS

Cardiac surgery patients (n=668) were prospectively screened for the onset of transfusion-related acute lung injury. Transfusion-related acute lung injury cases (n=16) were randomly assigned to transfused and nontransfused cardiac surgery controls in a 1:2 ratio. Blood samples were taken pre- and postoperatively and at onset of transfusion-related acute lung injury. In addition, at onset of transfusion-related acute lung injury, bronchoalveolar lavage fluid was obtained. In plasma and bronchoalveolar lavage fluid, levels of interleukin-6, interleukin-8, elastase-α1-antitrypsin complexes, thrombin-antithrombin complexes, plasminogen activator activity, and plasminogen activator inhibitor-1 were determined by means of enzyme-linked immunosorbent assay.

MAIN RESULTS

In all patients, cardiac surgery was associated with systemic inflammation, evidenced by an increase in plasma levels of interleukin-6, interleukin-8, and elastase-α1-antitrypsin complexes compared with presurgery levels (p<.001). Prior to onset of transfusion-related acute lung injury, systemic interleukin-8 and interleukin-6 levels were higher compared with nontransfused controls (p<.01). In transfusion-related acute lung injury cases, bronchoalveolar lavage fluid levels of interleukin-8, interleukin-6, and elastase-α1-antitrypsin complexes were elevated compared with control groups (p<.05). Both plasma and bronchoalveolar lavage fluid levels of thrombin-antithrombin complexes were enhanced in transfusion-related acute lung injury cases compared with control groups (p<.01). Bronchoalveolar lavage fluid levels of plasminogen activator activity were decreased due to an increase in plasminogen activator inhibitor-1 levels in transfusion-related acute lung injury cases compared with control groups (p<.01), indicating suppressed fibrinolysis.

CONCLUSIONS

Prior to onset of transfusion-related acute lung injury, there is systemic inflammation and neutrophil sequestration. Transfusion-related acute lung injury is characterized by both systemic and pulmonary inflammation and activation of neutrophils, as well as enhanced coagulation and suppressed fibrinolysis.

Enhanced thrombin generation and depressed anticoagulant function in children with pneumonia

AIMS

To clarify the status of the coagulation system in children with community-acquired pneumonia.

METHODS

Coagulation activation markers (prothrombin fragment F1 + 2, thrombin-antithrombin complexes, D-dimer), the natural anticoagulants (antithrombin, protein C and S) and tissue factor were measured in 28 consecutive children with pneumonia on admission to the hospital. Patients were divided into those with either bacterial-type pneumonia (at least two of the following three criteria: plasma C-reactive protein (CRP) >80 mg/L, white blood cell count >15 × 10(9) /L and alveolar infiltrates on the chest radiograph) or viral-type pneumonia.

RESULTS

The majority of the patients (79%) showed elevation of at least one of the three coagulation activation markers. Plasma CRP concentration correlated with F1 + 2 (R = 0.44, p < 0.05) and D-dimer (R = 0.71, p < 0.0001). Patients with bacterial-type pneumonia (n = 17) had higher D-dimer levels (p < 0.05) and lower levels of antithrombin (p = 0.005) and protein C (p = 0.08) than the patients with viral-type pneumonia.

CONCLUSIONS

Children with community-acquired bacterial-type pneumonia show distinctive changes in their coagulation system. The finding of coagulation system activation and depressed function of natural anticoagulants in uncomplicated pneumonia helps to understand the rapid and unpredictable changes observed in the coagulation status in patients with more severe forms of disease.

Plasma-derived human antithrombin attenuates ventilator-induced coagulopathy but not inflammation in a Streptococcus pneumoniae pneumonia model in rats

BACKGROUND

Mechanical ventilation exaggerates pneumonia-associated pulmonary coagulopathy and inflammation. We hypothesized that the administration of plasma-derived human antithrombin (AT), one of the natural inhibitors of coagulation, prevents ventilator-induced pulmonary coagulopathy, inflammation and bacterial outgrowth in a Streptococcus pneumoniae pneumonia model in rats.

METHODS

Forty-eight hours after induction of S. pneumoniae pneumonia rats were subjected to mechanical ventilation (tidal volume 12 mL kg(-1), positive end-expiratory pressure 0 cmH(2)O and inspired oxygen fraction 40%). Rats were randomized to systemic treatment with AT (250 IU administered intravenously (i.v.) before the start of mechanical ventilation) or placebo (saline). Non-ventilated, non-infected rats and non-ventilated rats with pneumonia served as controls. The primary endpoints were pulmonary coagulation and inflammation in bronchoalveolar lavage fluid (BALF).

RESULTS

Pneumonia was characterized by local activation of coagulation and inhibition of fibrinolysis, resulting in increased levels of fibrin degradation products and fibrin deposition in the lung. Mechanical ventilation exaggerated pulmonary coagulopathy and inflammation. Systemic administration of AT led to supra-normal BALF levels of AT and decreased ventilator-associated activation of coagulation. AT neither affected pulmonary inflammation nor bacterial outgrowth from the lungs or blood.

CONCLUSIONS

Plasma-derived human AT attenuates ventilator-induced coagulopathy, but not inflammation and bacterial outgrowth in a S. pneumoniae pneumonia model in rats.

The effect of heparin administration in animal models of sepsis: a prospective study in Escherichia coli-challenged mice and a systematic review and metaregression analysis of published studies

INTRODUCTION

If thrombosis contributes to sepsis, heparin titrated using activated partial thromboplastin times may be efficacious. We investigated heparin in preclinical models.

METHODS AND MAIN RESULTS

In unchallenged mice (n = 107), heparin at 100, 500, or 2500 units/kg produced activated partial thromboplastin time levels less than, within, or greater than a prespecified therapeutic range (1.5-2.5 times control), respectively. In animals (n = 142) administered intratracheal Escherichia coli challenge, compared to placebo treatment, heparin at 100, 500, or 2500 units/kg were associated with dose dependent increases in the hazard ratios of death (hazard ratio [95% confidence interval]: 1.08 [0.66, 1.76]; 1.34 [0.80, 2.24]; 3.02 [1.49, 6.10], respectively) (p = .001 for the dose effect). Compared to normal saline challenge, E. coli without heparin (i.e., with placebo) increased the activated partial thromboplastin time (p = .002) close to the therapeutic range. While heparin at 100 and 500 units/kg with E. coli further increased activated partial thromboplastin time (p < .0001 vs. placebo) within or above the therapeutic range, respectively, these did not decrease inflammatory cytokines or lung injury. In metaregression analysis of published preclinical studies, heparin improved survival with lipopolysaccharide (n = 23, p < .0001) or surgically induced infection (n = 14, p < .0001) but not monobacterial (n = 7, p = .29) challenges.

CONCLUSION

Coagulopathy with sepsis or other variables, such as type of infectious source, may influence the efficacy of heparin therapy for sepsis.

Nebulized heparin is associated with fewer days of mechanical ventilation in critically ill patients: a randomized controlled trial

Introduction

Prolonged mechanical ventilation has the potential to aggravate or initiate pulmonary inflammation and cause lung damage through fibrin deposition. Heparin may reduce pulmonary inflammation and fibrin deposition. We therefore assessed whether nebulized heparin improved lung function in patients expected to require prolonged mechanical ventilation.

Methods

Fifty patients expected to require mechanical ventilation for more than 48 hours were enrolled in a double-blind randomized placebo-controlled trial of nebulized heparin (25,000 U) or placebo (normal saline) 4 or 6 hourly, depending on patient height. The study drug was continued while the patient remained ventilated to a maximum of 14 days from randomization.

Results

Nebulized heparin was not associated with a significant improvement in the primary end-point, the average daily partial pressure of oxygen to inspired fraction of oxygen ratio while mechanically ventilated, but was associated with improvement in the secondary end-point, ventilator-free days amongst survivors at day 28 (22.6 ± 4.0 versus 18.0 ± 7.1, treatment difference 4.6 days, 95% CI 0.9 to 8.3, P = 0.02). Heparin administration was not associated with any increase in adverse events.

Conclusions

Nebulized heparin was associated with fewer days of mechanical ventilation in critically ill patients expected to require prolonged mechanical ventilation. Further trials are required to confirm these findings.

Trial registration

The Australian Clinical Trials Registry (ACTR-12608000121369).

Supernatant of stored platelets causes lung inflammation and coagulopathy in a novel in vivo transfusion model

Transfusion-related acute lung injury is suggested to be a "2-hit" event resulting from priming and activation of pulmonary neutrophils. Activation may result from infusion of lysophosphatidylcholines (LysoPCs), which accumulate during storage of blood products. In the present study, we developed a syngeneic in vivo transfusion model to test whether storage of platelet concentrates (PLTs) results in lung injury in healthy rats as well as in a "2-hit" model using lipopolysaccharide-pretreated rats. In addition, the effect of washing of platelets was studied. In healthy rats, transfusion of aged PLTs caused mild lung inflammation. In LPS-pretreated rats, transfusion of aged PLTs, but not fresh PLTs, augmented pulmonary systemic coagulopathy. When PLTs components were transfused separately, supernatant of aged PLTs, but not washed aged platelets, induced pulmonary injury in the "2-hit" model. Supernatants of aged PLTs contained increased concentrations of LysoPCs compared with fresh PLTs, which enhanced neutrophil priming activity in vitro. We conclude that transfusion of aged PLTs induces lung inflammation in healthy rats. In a "2-hit" model, aged PLTs contribute to pulmonary and systemic coagulopathy, which may be mediated by LysoPCs, which accumulate in the supernatant of PLTs during storage.