A New Global Definition of Acute Respiratory Distress Syndrome.

Background: Since publication of the 2012 Berlin definition of acute respiratory distress syndrome (ARDS), several developments have supported the need for an expansion of the definition, including the use of high-flow nasal oxygen, the expansion of the use of pulse oximetry in place of arterial blood gases, the use of ultrasound for chest imaging, and the need for applicability in resource-limited settings. Methods: A consensus conference of 32 critical care ARDS experts was convened, had six virtual meetings (June 2021 to March 2022), and subsequently obtained input from members of several critical care societies. The goal was to develop a definition that would 1) identify patients with the currently accepted conceptual framework for ARDS, 2) facilitate rapid ARDS diagnosis for clinical care and research, 3) be applicable in resource-limited settings, 4) be useful for testing specific therapies, and 5) be practical for communication to patients and caregivers. Results: The committee made four main recommendations: 1) include high-flow nasal oxygen with a minimum flow rate of ⩾30 L/min; 2) use PaO2:FiO2 ⩽ 300 mm Hg or oxygen saturation as measured by pulse oximetry SpO2:FiO2 ⩽ 315 (if oxygen saturation as measured by pulse oximetry is ⩽97%) to identify hypoxemia; 3) retain bilateral opacities for imaging criteria but add ultrasound as an imaging modality, especially in resource-limited areas; and 4) in resource-limited settings, do not require positive end-expiratory pressure, oxygen flow rate, or specific respiratory support devices. Conclusions: We propose a new global definition of ARDS that builds on the Berlin definition. The recommendations also identify areas for future research, including the need for prospective assessments of the feasibility, reliability, and prognostic validity of the proposed global definition.

Neutrophil reduction attenuates the severity of lung injury in the early phase of pneumococcal pneumonia in mice.

Neutrophils are the first leukocytes to be recruited to sites of inflammation in response to chemotactic factors released by activated macrophages and pulmonary epithelial and endothelial cells in bacterial pneumonia, a common cause of acute respiratory distress syndrome (ARDS). Although neutrophilic inflammation facilitates the elimination of pathogens, neutrophils also may cause bystander tissue injury. Even though the presence of neutrophils in alveolar spaces is a key feature of acute lung injury and ARDS especially from pneumonia, their contribution to the pathogenesis of lung injury is uncertain. The goal of this study was to elucidate the role of neutrophils in a clinically relevant model of bacterial pneumonia. We investigated the effect of reducing neutrophils in a mouse model of pneumococcal pneumonia treated with antibiotics. Neutrophils were reduced with anti-lymphocyte antigen 6 complex locus G6D (Ly6G) monoclonal antibody 24 h before and immediately preceding infection. Mice were inoculated intranasally with Streptococcus pneumoniae and received ceftriaxone 12 h after bacterial inoculation. Neutrophil reduction in mice treated with ceftriaxone attenuated hypoxemia, alveolar permeability, epithelial injury, pulmonary edema, and inflammatory biomarker release induced by bacterial pneumonia, even though bacterial loads in the distal air spaces of the lung were modestly increased as compared with antibiotic treatment alone. Thus, when appropriate antibiotics are administered, lung injury in the early phase of bacterial pneumonia is mediated in part by neutrophils. In the early phase of bacterial pneumonia, neutrophils contribute to the severity of lung injury, although they also participate in host defense.NEW & NOTEWORTHY Neutrophil accumulation is a key feature of ARDS, but their contribution to the pathogenesis is still uncertain. We investigated the effect of reducing neutrophils in a clinically relevant mouse model of pneumococcal pneumonia treated with antibiotics. When appropriate antibiotics were administered, neutrophil reduction with Ly6G antibody markedly attenuated lung injury and improved oxygenation. In the early phase of bacterial pneumonia, neutrophils contribute to the severity of lung injury, although they also participate in host defense.

A TRIFfic perspective on acute lung injury.

Acute lung injury (ALI) is a leading cause of death in people infected with H5N1 avian influenza virus or the SARS-coronavirus. Imai et al. (2008) now report that ALI is triggered by the signaling of oxidized phospholipids through Toll-like receptor 4 (TLR4) and the adaptor protein TRIF. These findings provide insight into the molecular pathogenesis of ALI, a condition for which treatment options are currently very limited.

New Insights into Clinical and Mechanistic Heterogeneity of the Acute Respiratory Distress Syndrome: Summary of the Aspen Lung Conference 2021.

Clinical and molecular heterogeneity are common features of human disease. Understanding the basis for heterogeneity has led to major advances in therapy for many cancers and pulmonary diseases such as cystic fibrosis and asthma. Although heterogeneity of risk factors, disease severity, and outcomes in survivors are common features of the acute respiratory distress syndrome (ARDS), many challenges exist in understanding the clinical and molecular basis for disease heterogeneity and using heterogeneity to tailor therapy for individual patients. This report summarizes the proceedings of the 2021 Aspen Lung Conference, which was organized to review key issues related to understanding clinical and molecular heterogeneity in ARDS. The goals were to review new information about ARDS phenotypes, to explore multicellular and multisystem mechanisms responsible for heterogeneity, and to review how best to account for clinical and molecular heterogeneity in clinical trial design and assessment of outcomes. The report concludes with recommendations for future research to understand the clinical and basic mechanisms underlying heterogeneity in ARDS to advance the development of new treatments for this life-threatening critical illness.

Update on the Features and Measurements of Experimental Acute Lung Injury in Animals: An Official American Thoracic Society Workshop Report.

Advancements in methods, technology, and our understanding of the pathobiology of lung injury have created the need to update the definition of experimental acute lung injury (ALI). We queried 50 participants with expertise in ALI and acute respiratory distress syndrome using a Delphi method composed of a series of electronic surveys and a virtual workshop. We propose that ALI presents as a "multidimensional entity" characterized by four "domains" that reflect the key pathophysiologic features and underlying biology of human acute respiratory distress syndrome. These domains are 1) histological evidence of tissue injury, 2) alteration of the alveolar-capillary barrier, 3) presence of an inflammatory response, and 4) physiologic dysfunction. For each domain, we present "relevant measurements," defined as those proposed by at least 30% of respondents. We propose that experimental ALI encompasses a continuum of models ranging from those focusing on gaining specific mechanistic insights to those primarily concerned with preclinical testing of novel therapeutics or interventions. We suggest that mechanistic studies may justifiably focus on a single domain of lung injury, but models must document alterations of at least three of the four domains to qualify as "experimental ALI." Finally, we propose that a time criterion defining "acute" in ALI remains relevant, but the actual time may vary based on the specific model and the aspect of injury being modeled. The continuum concept of ALI increases the flexibility and applicability of the definition to multiple models while increasing the likelihood of translating preclinical findings to critically ill patients.

Identifying Clinical Research Priorities in Adult Pulmonary and Critical Care. NHLBI Working Group Report.

Preventing, treating, and promoting recovery from critical illness due to pulmonary disease are foundational goals of the critical care community and the NHLBI. Decades of clinical research in acute respiratory distress syndrome, acute respiratory failure, pneumonia, and sepsis have yielded improvements in supportive care, which have translated into improved patient outcomes. Novel therapeutics have largely failed to translate from promising preclinical findings into improved patient outcomes in late-phase clinical trials. Recent advances in personalized medicine, "big data," causal inference using observational data, novel clinical trial designs, preclinical disease modeling, and understanding of recovery from acute illness promise to transform the methods of pulmonary and critical care clinical research. To assess the current state of, research priorities for, and future directions in adult pulmonary and critical care research, the NHLBI assembled a multidisciplinary working group of investigators. This working group identified recommendations for future research, including 1) focusing on understanding the clinical, physiological, and biological underpinnings of heterogeneity in syndromes, diseases, and treatment response with the goal of developing targeted, personalized interventions; 2) optimizing preclinical models by incorporating comorbidities, cointerventions, and organ support; 3) developing and applying novel clinical trial designs; and 4) advancing mechanistic understanding of injury and recovery to develop and test interventions targeted at achieving long-term improvements in the lives of patients and families. Specific areas of research are highlighted as especially promising for making advances in pneumonia, acute hypoxemic respiratory failure, and acute respiratory distress syndrome.

High-density lipoprotein modulates thrombosis by preventing von Willebrand factor self-association and subsequent platelet adhesion.

The ability of von Willebrand factor (VWF) to initiate platelet adhesion depends on the number of monomers in individual VWF multimers and on the self-association of individual VWF multimers into larger structures. VWF self-association is accelerated by shear stress. We observed that VWF self-association occurs during adsorption of VWF onto surfaces, assembly of secreted VWF into hyperadhesive VWF strings on the endothelial surface, and incorporation of fluid-phase VWF into VWF fibers. VWF adsorption under static conditions increased with increased VWF purity and was prevented by a component of plasma. We identified that component as high-density lipoprotein (HDL) and its major apolipoprotein ApoA-I. HDL and ApoA-I also prevented VWF on the endothelium from self-associating into longer strands and inhibited the attachment of fluid-phase VWF onto vessel wall strands. Platelet adhesion to VWF fibers was reduced in proportion to the reduction in self-associated VWF. In a mouse model of thrombotic microangiopathy, HDL also largely prevented the thrombocytopenia induced by injection of high doses of human VWF. Finally, a potential role for ApoA-I in microvascular occlusion associated with thrombotic thrombocytopenic purpura and sepsis was revealed by the inverse relationship between the concentration of ApoA-I and that of hyperadhesive VWF. These results suggest that interference with VWF self-association would be a new approach to treating thrombotic disorders.

Plasma Fibrinogen Qualification as a Drug Development Tool in Chronic Obstructive Pulmonary Disease. Perspective of the Chronic Obstructive Pulmonary Disease Biomarker Qualification Consortium.

The COPD Foundation Biomarker Qualification Consortium (CBQC) is a unique public-private partnership established in 2010 between the COPD Foundation, the pharmaceutical industry, and academic chronic obstructive pulmonary disease (COPD) experts with advisors from the U.S. NHLBI and the Food and Drug Administration (FDA). This was a direct response to the 2009 publication of a guidance on qualification of drug development tools by the FDA. Although data were believed to be available from publicly funded and industry-funded studies that could support qualification of several tools, the necessary data resided in disparate databases. The initial intent of the CBQC was to integrate these data and submit a dossier for the qualification. This led to the FDA qualification of plasma fibrinogen as a prognostic or enrichment biomarker for all-cause mortality and COPD exacerbations in July 2015. It is the first biomarker drug development tool qualified for use in COPD under the FDA's drug development tool qualification program. This perspective summarizes the FDA's qualification process, the formation of the CBQC, and the effort that led to a successful outcome for plasma fibrinogen and discusses implications for future biomarker qualification efforts.

The Fas/FasL pathway impairs the alveolar fluid clearance in mouse lungs.

Alveolar epithelial damage is a critical event that leads to protein-rich edema in acute lung injury (ALI), but the mechanisms leading to epithelial damage are not completely understood. Cell death by necrosis and apoptosis occurs in alveolar epithelial cells in the lungs of patients with ALI. Fas activation induces apoptosis of alveolar epithelial cells, but its role in the formation of lung edema is unclear. The main goal of this study was to determine whether activation of the Fas/Fas ligand pathway in the lungs could alter the function of the lung epithelium, and the mechanisms involved. The results show that Fas activation alters the alveolar barrier integrity and impairs the ability of the lung alveolar epithelium to reabsorb fluid from the air spaces. This result was dependent on the presence of a normal Fas receptor and was not affected by inflammation induced by Fas activation. Alteration of the fluid transport properties of the alveolar epithelium was partially restored by ß-adrenergic stimulation. Fas activation also caused apoptosis of alveolar endothelial cells, but this effect was less pronounced than the effect on the alveolar epithelium. Thus, activation of the Fas pathway impairs alveolar epithelial function in mouse lungs by mechanisms involving caspase-dependent apoptosis, suggesting that targeting apoptotic pathways could reduce the formation of lung edema in ALI.

Th17 cytokines are critical for respiratory syncytial virus-associated airway hyperreponsiveness through regulation by complement C3a and tachykinins.

Respiratory syncytial virus (RSV) infection is associated with serious lung disease in infants and immunocompromised individuals and is linked to development of asthma. In mice, acute RSV infection causes airway hyperresponsiveness (AHR), inflammation, and mucus hypersecretion. Infected cells induce complement activation, producing the anaphylatoxin C3a. In this paper, we show RSV-infected wild-type mice produce Th17 cytokines, a response not previously associated with viral infections. Mice deficient in the C3aR fail to develop AHR following acute RSV infection, and production of Th17 cytokines was significantly attenuated. Tachykinin production also has been implicated in RSV pathophysiology, and tachykinin receptor-null mice were similarly protected from developing AHR. These animals were also deficient in production of Th17 cytokines. Tachykinin release was absent in mice deficient in C3aR, whereas C3a levels were unchanged in tachykinin receptor-null animals. Thus, our data reveal a crucial sequence following acute RSV infection where initial C3a production causes tachykinin release, followed by activation of the IL-17A pathway. Deficiency of either receptor affords protection from AHR, identifying two potential therapeutic targets.

Mechanisms of acute respiratory distress syndrome in children and adults: a review and suggestions for future research.

OBJECTIVES: To provide a current overview of the epidemiology and pathophysiology of acute respiratory distress syndrome in adults and children, and to identify research questions that will address the differences between adults and children with acute respiratory distress syndrome. DATA SOURCES: Narrative literature review and author-generated data. DATA SELECTION: The epidemiology of acute respiratory distress syndrome in adults and children, lung morphogenesis, and postnatal lung growth and development are reviewed. The pathophysiology of acute respiratory distress syndrome is divided into eight categories: alveolar fluid transport, surfactant, innate immunity, apoptosis, coagulation, direct alveolar epithelial injury by bacterial products, ventilator-associated lung injury, and repair. DATA EXTRACTION AND SYNTHESIS: Epidemiologic data suggest significant differences in the prevalence and mortality of acute respiratory distress syndrome between children and adults. Postnatal lung development continues through attainment of adult height, and there is overlap between the regulation of postnatal lung development and inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms. Therefore, there is a different biological baseline network of gene and protein expression in children as compared with adults. CONCLUSIONS: There are significant obstacles to performing research on children with acute respiratory distress syndrome. However, epidemiologic, clinical, and animal studies suggest age-dependent differences in the pathophysiology of acute respiratory distress syndrome. In order to reduce the prevalence and improve the outcome of patients with acute respiratory distress syndrome, translational studies of inflammatory, apoptotic, alveolar fluid clearance, and repair mechanisms are needed. Understanding the differences in pathophysiologic mechanisms in acute respiratory distress syndrome between children and adults should facilitate identification of novel therapeutic interventions to prevent or modulate lung injury and improve lung repair.

The Parker B. Francis Fellowship Program: analysis of 31 years of career development support.

RATIONALE: The Parker B. Francis (PBF) Fellowship Program has supported more than 750 M.D., M.D./Ph.D., and Ph.D. fellows since 1976, but there is little information about the effectiveness of the program in fostering successful careers and producing important research. OBJECTIVES: To survey all past PBF Fellows to obtain information about their productivity and career pathways. METHODS: We obtained e-mail addresses for 526 (74%) of the 712 PBF awardees from 1976 to 2006, then sent an e-mail survey to the 526 past fellows and received 365 replies (69% response rate, 49% overall). Survey questions addressed time in research, areas of research, current position and responsibilities, and research funding. MEASUREMENTS AND MAIN RESULTS: Seventy percent of the 365 respondents spend 25% or greater effort in research and 56% report 50% or more effort in research. Respondents have published an average of 2.7 peer-reviewed publications per year, totaling more than 15,678 peer-reviewed publications, of which 1,875 appeared in high-impact journals. Respondents have received more than $1.8 billion in direct research funding since their PBF Fellowships began. Ph.D. awardees spend more time in research than M.D. awardees, and current research effort did not differ by gender. PBF awardees have become prominent leaders in universities, the National Institutes of Health, health care, and industry. CONCLUSIONS: The PBF Program has been highly successful in producing a large number of scientific and clinical leaders in pulmonary and critical care medicine. The results provide comprehensive data about the success of this career development program and provide a model for programs designed to build the workforce in pulmonary and critical care medicine.

Polymorphonuclear leukocytes mediate Staphylococcus aureus Panton-Valentine leukocidin-induced lung inflammation and injury.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is epidemic in the United States, even rivaling HIV/AIDS in its public health impact. The pandemic clone USA300, like other CA-MRSA strains, expresses Panton-Valentine leukocidin (PVL), a pore-forming toxin that targets polymorphonuclear leukocytes (PMNs). PVL is thought to play a key role in the pathogenesis of necrotizing pneumonia, but data from rodent infection models are inconclusive. Rodent PMNs are less susceptible than human PMNs to PVL-induced cytolysis, whereas rabbit PMNs, like those of humans, are highly susceptible to PVL-induced cytolysis. This difference in target cell susceptibility could affect results of experimental models. Therefore, we developed a rabbit model of necrotizing pneumonia to compare the virulence of a USA300 wild-type strain with that of isogenic PVL-deletion mutant and -complemented strains. PVL enhanced the capacity of USA300 to cause severe lung necrosis, pulmonary edema, alveolar hemorrhage, hemoptysis, and death, hallmark clinical features of fatal human necrotizing pneumonia. Purified PVL instilled directly into the lung caused lung inflammation and injury by recruiting and lysing PMNs, which damage the lung by releasing cytotoxic granule contents. These findings provide insights into the mechanism of PVL-induced lung injury and inflammation and demonstrate the utility of the rabbit for studying PVL-mediated pathogenesis.

Targeting pan-resistant bacteria with antibodies to a broadly conserved surface polysaccharide expressed during infection.

BACKGROUND: New therapeutic targets for antibiotic-resistant bacterial pathogens are desperately needed. The bacterial surface polysaccharide poly-ß-(1-6)-N-acetyl-glucosamine (PNAG) mediates biofilm formation by some bacterial species, and antibodies to PNAG can confer protective immunity. By analyzing sequenced genomes, we found that potentially multidrug-resistant bacterial species such as Klebsiella pneumoniae, Enterobacter cloacae, Stenotrophomonas maltophilia, and the Burkholderia cepacia complex (BCC) may be able to produce PNAG. Among patients with cystic fibrosis patients, highly antibiotic-resistant bacteria in the BCC have emerged as problematic pathogens, providing an impetus to study the potential of PNAG to be targeted for immunotherapy against pan-resistant bacterial pathogens. METHODS: The presence of PNAG on BCC was assessed using a combination of bacterial genetics, microscopy, and immunochemical approaches. Antibodies to PNAG were tested using opsonophagocytic assays and for protective efficacy against lethal peritonitis in mice. RESULTS: PNAG is expressed in vitro and in vivo by the BCC, and cystic fibrosis patients infected by the BCC species B. dolosa mounted a PNAG-specific opsonophagocytic antibody response. Antisera to PNAG mediated opsonophagocytic killing of BCC and were protective against lethal BCC peritonitis even during coinfection with methicillin-resistant Staphylococcus aureus. CONCLUSIONS: Our findings raise potential new therapeutic options against PNAG-producing bacteria, including even pan-resistant pathogens.

Phase 2, randomized, double-blind, placebo-controlled multi-center trial of the clinical and biological effects of anti-CD14 treatment in hospitalized patients with COVID-19 pneumonia.

BACKGROUND: Severe COVID-19 is associated with innate immunopathology, and CD14, a proximal activator of innate immunity, has been suggested as a potential therapeutic target. METHODS: We conducted the COVID-19 anti-CD14 Treatment Trial (CaTT), a Phase II randomized, double-blind, placebo-controlled trial at 5 US-sites between April 12, 2021 and November 30, 2021 (NCT04391309). Hospitalized adults with COVID-19 requiring supplemental oxygen (<30 LPM) were randomized 1:1 to receive 4 daily doses of intravenous IC14, an anti-CD14 monoclonal antibody, or placebo. All participants received remdesivir. The primary outcome was time-to-resolution of illness, defined as improvement on the 8-point NIH-Ordinal COVID-19 Scale to category ≤3. Secondary endpoints were safety and exploratory endpoints were pro-inflammatory and antiviral mediators in serum on days 0-5 & 7. The trial was stopped after 40 patients were randomized and treated due to slow enrollment. FINDINGS: 40 participants were randomized and treated with IC14 (n = 20) or placebo (n = 20). The median time-to-recovery was 6 days (95% CI, 5-11) in the IC14 group vs. 5 days (95% CI, 4-10) in the Placebo group (recovery rate ratio: 0.77 (95% CI, 0.40, 1.48) (log-rank p = 0.435). The number of adverse events was similar in each group, and no IC14-attributable secondary infections occurred. In repeated-measures mixed-effects analyses, IC14 treatment increased serum sCD14 concentrations, an expected pharmacodynamic effect. Pre-planned, exploratory analyses suggested that IC14 treatment decreased the trajectories of circulating MIP-1ß and TNF-α. INTERPRETATION: IC14 treatment did not improve time-to-resolution of illness in hypoxemic patients with COVID-19 in this small trial. Results of exploratory analyses suggested IC14 had biologic effects that warrant future clinical investigation. FUNDING: National Institute of Allergy and Infectious Diseases.

Phenazine content in the cystic fibrosis respiratory tract negatively correlates with lung function and microbial complexity.

Although much is known about how virulence factors affect pathogens and host tissues in vitro, far less is understood about their dynamics in vivo. As a step toward characterizing the chemistry of infected environments, we measured phenazine abundance in the lungs of patients with cystic fibrosis (CF). Phenazines are redox-active small molecules produced by Pseudomonas aeruginosa that damage host epithelia, curb the growth of competing organisms, and play physiologically important roles in the cells that produce them. Here, we quantify phenazines within expectorated sputum, characterize the P. aeruginosa populations responsible for phenazine production, and assess their relationship to CF lung microflora. Chemical analyses of expectorated sputum showed that the concentrations of two phenazines, namely, pyocyanin (PYO) and phenazine-1-carboxylic acid (PCA), were negatively correlated (ρ = -0.68 and -0.57, respectively) with lung function. Furthermore, the highest phenazine concentrations were found in patients whose pulmonary function showed the greatest rates of decline. The constituent P. aeruginosa populations within each patient showed diverse capacities for phenazine production. Early during infection, individual isolates produced more PYO than later during infection. However, total PYO concentrations in sputum at any given stage correlated well with the average production by the total P. aeruginosa population. Finally, bacterial community complexity was negatively correlated with phenazine concentrations and declines in lung function, suggesting a link to the refinement of the overall microbial population. Together, these data demonstrate that phenazines negatively correlate with CF disease states in ways that were previously unknown, and underscore the importance of defining in vivo environmental parameters to better predict clinical outcomes of infections.

Syndecan-4 regulates early neutrophil migration and pulmonary inflammation in response to lipopolysaccharide.

Proteoglycans (PGs) and their associated glycosaminoglycan side chains are effectors of inflammation, but little is known about changes to the composition of PGs in response to lung infection or injury. The goals of this study were to identify changes to heparan sulfate PGs in a mouse model of gram-negative pneumonia, to identify the Toll-like receptor adaptor molecules responsible for these changes, and to determine the role of the heparan sulfate PG in the innate immune response in the lungs. We treated mice with intratracheal LPS, a component of the cell wall of gram-negative bacteria, to model gram-negative pneumonia. Mice treated with intratracheal LPS had a rapid and selective increase in syndecan-4 mRNA that was regulated through MyD88-dependent mechanisms, whereas expression of several other PGs was not affected. To determine the role of syndecan-4 in the inflammatory response, we exposed mice deficient in syndecan-4 to LPS and found a significant increase in neutrophil numbers and amounts of CXC-chemokines and total protein in bronchoalveolar lavage fluid. In studies performed in vitro, macrophages and epithelial cells treated with LPS had increased expression of syndecan-4. Studies performed using BEAS-2B cells showed that pretreatment with heparin and syndecan-4 decreased the expression of CXCL8 mRNA in response to LPS and TNF-α. These findings indicate that the early inflammatory response to LPS involves marked up-regulation of syndecan-4, which functions to limit the extent of pulmonary inflammation and lung injury.