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.

Background: Tetracyclines are broad-spectrum antibiotics that are also used to induce gene expression using the reverse tetracycline transactivator / tetracycline operator system (rtTA/tetO system). The system assumes that tetracyclines have no effects on mammals. However, a number of studies suggest that tetracyclines may have powerful anti-inflammatory effects. We report that the tetracycline, doxycycline, inhibits neutrophil (PMN) influx into the lungs of mice treated with bacterial endotoxin (LPS). Methods: Mice were challenged with intratracheal LPS in the presence or absence of doxycyline. bronchoalveolar lavage cell counts and differential, total bronchoalveolar lavage protein, lung homogenate caspase-3 and tissue imaging were used to assess lung injury. In addition, PMN chemotaxis was measured in vitro and syndecan-1 was measured in bronchoalveolar lavage fluid. Results: The administration of doxycycline resulted in a significant decrease in the number of bronchoalveolar lavage PMNs in LPS-treated mice. Doxycycline had no effect on other markers of lung injury such as total bronchoalveolar lavage protein and whole lung caspase-3 activity. However, doxycycline resulted in a decrease in shed syndecan-1 in bronchoalveolar lavage fluid. Conclusion: We conclude that doxycycline has an important anti-inflammatory effect that can potentially confound the experiments in which the rtTA/tetO system is being used to study the immune response.

The cellular communication network factor 1 (CCN1) is a matricellular protein that can modulate multiple tissue responses including inflammation and repair. We have previously shown that adenoviral overexpression of Ccn1 is sufficient to cause acute lung injury in mice. We hypothesized that CCN1 is present in the airspaces of lungs during the acute phase of lung injury and higher concentrations are associated with acute respiratory distress syndrome (ARDS) severity. We tested this hypothesis by measuring: 1) CCN1 in bronchoalveolar lavage fluid (BALF) and lung homogenates from mice subjected to ventilation-induced lung injury (VILI); 2) Ccn1 gene expression and protein levels in MLE-12 cells (alveolar epithelial cell line) subjected to mechanical stretch; 3) CCN1 in BALF from mechanically-ventilated humans with and without ARDS. BALF CCN1 concentrations and whole lung CCN1 protein levels were significantly increased in mice with VILI (n = 6) vs. non-injured controls (n = 6). Ccn1 gene expression and CCN1 protein levels were increased in MLE-12 cells cultured under stretch conditions. Subjects with ARDS (n = 77) had higher BALF CCN1 levels compared with mechanically-ventilated subjects without ARDS (n = 45) (p<0.05). In subjects with ARDS, BALF CCN1 concentrations were associated with higher total protein, sRAGE, and worse P_aO₂/F_iO₂ ratios (all p<0.05). CCN1 is present in the lungs of mice and humans during the acute inflammatory phase of lung injury and concentrations are higher in patients with increased markers of severity. Alveolar epithelial cells may be an important source of CCN1 under mechanical stretch conditions.

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 β-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.

Physical and psychological symptoms are the hallmark of patients’ subjective perception of their illness. The purpose of this analysis was to determine if patients with COPD have distinctive symptom profiles and to examine the association of symptom profiles with systemic biomarkers of inflammation. We conducted latent class analyses of three physical (dyspnea, fatigue, and pain) and two psychological symptoms (depression and anxiety) in 302 patients with moderate to severe COPD using baseline data from a longitudinal observational study of depression in COPD. Systemic inflammatory markers included IL1, IL8, IL10, IL12, IL13, INF, GM-CSF, TNF-α (levels >75thcentile was considered high); and CRP (levels >3 mg/L was considered high). Multinominal logistic regression models were used to examine the association between symptom classes and inflammation while adjusting for key socio-demographic and disease characteristics. We found that a 4-class model best fit the data: 1) low physical and psychological symptoms (26%, Low-Phys/Low-Psych), 2) low physical but moderate psychological symptoms (18%, Low-Phys/Mod Psych), 3) high physical but moderate psychological symptoms (25%, High-Phys/Mod Psych), and 4) high physical and psychological symptoms (30%, High-Phys/High Psych). Unadjusted analyses showed associations between symptom class with high levels of IL7, IL-8 (p ≤ .10) and CRP (p < .01). In the adjusted model, those with a high CRP level were less likely to be in the High-Phys/Mod-Psych class compared to the Low-Phys/Low-Psych (OR: 0.41, 95%CI 0.19, 0.90) and Low-Phys/Mod-Psych classes (OR: 0.35, 95%CI 0.16, 0.78); elevated CRP was associated with in increased odds of being in the High-Phys/High-Psych compared to the High-Phys/Mod-Psych class (OR: 2.22, 95%CI 1.08, 4.58). Younger age, having at least a college education, oxygen use and depression history were more prominent predictors of membership in the higher symptom classes. Patients with COPD can be classified into four distinct symptom classes based on five commonly co-occurring physical and psychological symptoms. Systemic biomarkers of inflammation were not associated with symptom class. Additional work to test the reliability of these symptom classes, their biological drivers and their validity for prognostication and tailoring therapy in larger and more diverse samples is needed. Clinicaltrials.gov, NCT01074515 .