O2- and pneumonia-induced lung injury. I. Pathological and morphometric studies

Differential changes in expression of inflammatory mRNA and protein after oleic acid-induced acute lung injury

Background: Acute Respiratory Distress syndrome (ARDS) is a clinical syndrome of noncardiac pulmonary edema and inflammation leading to acute respiratory failure. We used the oleic acid infusion pig model of ARDS resembling human disease to explore cytokine changes in white blood cells (WBC) and plasma proteins, comparing baseline to ARDS values. Methods: Nineteen juvenile female swine were included in the study. ARDS defined by a PaO2/FiO2 ratio < 300 was induced by continuous oleic acid infusion. Arterial blood was drawn before and during oleic acid infusion, and when ARDS was established. Cytokine expression in WBC was analyzed by RT-qPCR and plasma protein expression by ELISA. Results: The median concentration of IFN-γ mRNA was estimated to be 59% (p = 0.006) and of IL-6 to be 44.4% (p = 0.003) of the baseline amount. No significant changes were detected for TNF-α, IL-17, and IL-10 mRNA expression. In contrast, the concentrations of plasma IFN-γ and IL-6 were significantly higher (p = 0.004 and p = 0.048 resp.), and TNF-α was significantly lower (p = 0.006) at ARDS compared to baseline. Conclusions: The change of proinflammatory cytokines IFN-γ and IL-6 expression is different comparing mRNA and plasma proteins at oleic acid-induced ARDS compared to baseline. The migration of cells to the lung may be the cause for this discrepancy.

Alveolar Hyperoxia and Exacerbation of Lung Injury in Critically Ill SARS-CoV-2 Pneumonia

Acute hypoxic respiratory failure (AHRF) is a prominent feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) critical illness. The severity of gas exchange impairment correlates with worse prognosis, and AHRF requiring mechanical ventilation is associated with substantial mortality. Persistent impaired gas exchange leading to hypoxemia often warrants the prolonged administration of a high fraction of inspired oxygen (FiO2). In SARS-CoV-2 AHRF, systemic vasculopathy with lung microthrombosis and microangiopathy further exacerbates poor gas exchange due to alveolar inflammation and oedema. Capillary congestion with microthrombosis is a common autopsy finding in the lungs of patients who die with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome. The need for a high FiO2 to normalise arterial hypoxemia and tissue hypoxia can result in alveolar hyperoxia. This in turn can lead to local alveolar oxidative stress with associated inflammation, alveolar epithelial cell apoptosis, surfactant dysfunction, pulmonary vascular abnormalities, resorption atelectasis, and impairment of innate immunity predisposing to secondary bacterial infections. While oxygen is a life-saving treatment, alveolar hyperoxia may exacerbate pre-existing lung injury. In this review, we provide a summary of oxygen toxicity mechanisms, evaluating the consequences of alveolar hyperoxia in COVID-19 and propose established and potential exploratory treatment pathways to minimise alveolar hyperoxia.

Supplemental Oxygen Alters the Airway Microbiome in Cystic Fibrosis

Features of the airway microbiome in persons with cystic fibrosis (pwCF) are correlated with disease progression. Microbes have traditionally been classified for their ability to tolerate oxygen. It is unknown whether supplemental oxygen, a common medical intervention, affects the airway microbiome of pwCF. We hypothesized that hyperoxia significantly impacts the pulmonary microbiome in cystic fibrosis. In this study, we cultured spontaneously expectorated sputum from pwCF in artificial sputum medium under 21%, 50%, and 100% oxygen conditions using a previously validated model system that recapitulates microbial community composition in uncultured sputum. Culture aliquots taken at 24, 48, and 72 h, along with uncultured sputum, underwent shotgun metagenomic sequencing with absolute abundance values obtained with the use of spike-in bacteria. Raw sequencing files were processed using the bioBakery pipeline to determine changes in taxonomy, predicted function, antimicrobial resistance genes, and mobile genetic elements. Hyperoxia reduced absolute microbial load, species richness, and diversity. Hyperoxia reduced absolute abundance of specific microbes, including facultative anaerobes such as Rothia and some Streptococcus species, with minimal impact on canonical CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. The effect size of hyperoxia on predicted functional pathways was stronger than that on taxonomy. Large changes in microbial cooccurrence networks were noted. Hyperoxia exposure perturbs airway microbial communities in a manner well tolerated by key pathogens. Supplemental oxygen use may enable the growth of lung pathogens and should be further studied in the clinical setting. IMPORTANCE The airway microbiome in persons with cystic fibrosis (pwCF) is correlated with lung function and disease severity. Supplemental oxygen use is common in more advanced CF, yet its role in perturbing airway microbial communities is unknown. By culturing sputum samples from pwCF under normal and elevated oxygen conditions, we found that increased oxygen led to reduced total numbers and diversity of microbes, with relative sparing of common CF pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. Supplemental oxygen use may enable the growth of lung pathogens and should be further studied in the clinical setting.

Hyperoxia and Lungs: What We Have Learned From Animal Models

Although oxygen (O₂) is essential for aerobic life, it can also be an important source of cellular damage. Supra-physiological levels of O₂ determine toxicity due to exacerbated reactive oxygen species (ROS) production, impairing the homeostatic balance of several cellular processes. Furthermore, injured cells activate inflammation cascades, amplifying the tissue damage. The lung is the first (but not the only) organ affected by this condition. Critically ill patients are often exposed to several insults, such as mechanical ventilation, infections, hypo-perfusion, systemic inflammation, and drug toxicity. In this scenario, it is not easy to dissect the effect of oxygen toxicity. Translational investigations with animal models are essential to explore injuring stimuli in controlled experimental conditions, and are milestones in understanding pathological mechanisms and developing therapeutic strategies. Animal models can resemble what happens in critical care or anesthesia patients under mechanical ventilation and hyperoxia, but are also critical to explore the effect of O₂ on lung development and the role of hyperoxic damage on bronchopulmonary dysplasia. Here, we set out to review the hyperoxia effects on lung pathology, contributing to the field by describing and analyzing animal experimentation's main aspects and its implications on human lung diseases.

Effects of long term normobaric hyperoxia exposure on lipopolysaccharide-induced lung injury

Purpose/Aim of the study: Prolonged exposure to hyperoxia can cause injury to normal lung tissue. However, patients with acute hypoxic respiratory failure are frequently exposed to very high oxygen levels. This study investigated the effects of long term normobaric hyperoxia exposure in a mouse model of acute severe lung injury (SLI).Meterials and Methods: C57BL/6J mice were injected intratracheally with lipopolysaccharide (LPS, 4 mg/kg) to induce acute lung injury. After 2 h, mice were divided into two groups, and then exposed to room air or hyperoxic conditions for 48 h. Animals in the hyperoxia group were placed within their cages in a Plexiglass chamber with an atmosphere of 95% O₂ maintained constant using an oxygen analyzer. After exposure to normoxia (N) or hyperoxia (H) for 48 h, the left lungs were collected for tissue paraffin block or oxidative stress assay. One lobe of the right lung was collected for lung/body weight ratio. The lung injury score and the mean linear intercept were evaluated in hematoxylin and eosin -stained lungs. The biochemical tests were performed by using ELISA assay.Results: Lung injury scoring, lung/body weight, and mean linear intercept were not significantly different between the N + LPS (NLPS) and H + LPS (HLPS) groups. Similar trends were observed in hydroxyproline and transforming growth factor-β (TGF-β) levels. Total cell and neutrophil counts in bronchoalveolar lavage fluid showed no significant differences between NLPS and HLPS groups. Histological analyses demonstrated more severe lung injury and fibrosis in the NLPS group than in the HLPS group. In addition, interleukin (IL)-1β was significantly decreased in the HLPS group compared to the NLPS group. Other inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and IL-6, showed similar trends. The malondialdehyde (MDA) level was significantly lower in the HLPS group than in the NLPS group.Conclusions: Exposure to hyperoxia did not augment lung injury in the LPS-induced lung injury model, and some indicators even showed better outcomes. These results suggest that long-term high-oxygen therapy in patients with SLI has low risk of lung injury.

Ascorbic Acid Attenuates Hyperoxia-Compromised Host Defense against Pulmonary Bacterial Infection

Supraphysiological concentrations of oxygen (hyperoxia) can compromise host defense and increase susceptibility to bacterial infections, causing ventilator-associated pneumonia. The phagocytic activity of macrophages is impaired by hyperoxia-induced increases in the levels of reactive oxygen species (ROS) and extracellular high-mobility group box protein B1 (HMGB1). Ascorbic acid (AA), an essential nutrient and antioxidant, has been shown to be beneficial in various animal models of ROS-mediated diseases. The aim of this study was to determine whether AA could attenuate hyperoxia-compromised host defense and improve macrophage functions against bacterial infections. C57BL/6 male mice were exposed to hyperoxia (≥98% O₂, 48 h), followed by intratracheal inoculation with Pseudomonas aeruginosa, and simultaneous intraperitoneal administration of AA. AA (50 mg/kg) significantly improved bacterial clearance in the lungs and airways, and significantly reduced HMGB1 accumulation in the airways. The incubation of RAW 264.7 cells (a macrophage-like cell line) with AA (0-1,000 μM) before hyperoxic exposure (95% O₂) stabilized the phagocytic activity of macrophages in a concentration-dependent manner. The AA-enhanced macrophage function was associated with significantly decreased production of intracellular ROS and accumulation of extracellular HMGB1. These data suggest that AA supplementation can prevent or attenuate the development of ventilator-associated pneumonia in patients receiving oxygen support.

The thioredoxin reductase-1 inhibitor aurothioglucose attenuates lung injury and improves survival in a murine model of acute respiratory distress syndrome

AIMS

Inflammation and oxygen toxicity increase free radical production and contribute to the development of acute respiratory distress syndrome (ARDS), which is a significant cause of morbidity and mortality in intensive care patients. We have previously reported increased glutathione (GSH) levels in lung epithelial cells in vitro and attenuated adult murine hyperoxic lung injury in vivo after pharmacological thioredoxin reductase-1 (TrxR1) inhibition. Using a murine ARDS model, we tested the hypothesis that aurothioglucose (ATG) treatment increases pulmonary GSH levels, attenuates lung injury, and decreases mortality in a GSH-dependent manner.

RESULTS

Adult mice received a single intratracheal dose of 0.375 μg/g lipopolysaccharide (LPS) 12 h before a single intraperitoneal injection of 25 mg/kg ATG. Control mice received intratracheal and/or intraperitoneal saline. Mice were then exposed to room air or hyperoxia (>95% O2). Lung injury was assessed by bronchoalveolar lavage protein concentrations. Expression of glutamate-cysteine ligase modifier subunit (GCLM), GSH, cytokines, and chemokines was determined. Exposure to LPS/hyperoxia induced inflammation and lung injury. ATG treatment significantly attenuated lung injury, increased lung GCLM expression and GSH levels, and decreased mortality. GSH depletion completely prevented the protective effects of ATG in LPS/hyperoxia-exposed mice.

INNOVATION

ATG treatment significantly attenuates lung injury and enhances survival in a clinically relevant murine model of ARDS. The protective effects of ATG are GSH dependent.

CONCLUSION

Augmentation of GSH systems by TrxR1 inhibition could represent a promising therapeutic approach to attenuate oxidant-mediated lung injury and improve patient outcomes.

Structure and composition of pulmonary arteries, capillaries, and veins

The pulmonary vasculature comprises three anatomic compartments connected in series: the arterial tree, an extensive capillary bed, and the venular tree. Although, in general, this vasculature is thin-walled, structure is nonetheless complex. Contributions to structure (and thus potentially to function) from cells other than endothelial and smooth muscle cells as well as those from the extracellular matrix should be considered. This review is multifaceted, bringing together information regarding (i) classification of pulmonary vessels, (ii) branching geometry in the pulmonary vascular tree, (iii) a quantitative view of structure based on morphometry of the vascular wall, (iv) the relationship of nerves, a variety of interstitial cells, matrix proteins, and striated myocytes to smooth muscle and endothelium in the vascular wall, (v) heterogeneity within cell populations and between vascular compartments, (vi) homo- and heterotypic cell-cell junctional complexes, and (vii) the relation of the pulmonary vasculature to that of airways. These issues for pulmonary vascular structure are compared, when data is available, across species from human to mouse and shrew. Data from studies utilizing vascular casting, light and electron microscopy, as well as models developed from those data, are discussed. Finally, the need for rigorous quantitative approaches to study of vascular structure in lung is highlighted.

Assessment of pulmonary oxygen toxicity: relevance to professional diving; a review

When breathing oxygen with partial oxygen pressures PO₂ of between 50 and 300 kPa pathological pulmonary changes develop after 3-24h depending on the PO₂. This kind of injury (known as pulmonary oxygen toxicity) is not only observed in ventilated patients but is also considered an occupational hazard in oxygen divers or mixed gas divers. To prevent these latter groups from sustaining irreversible lesions adequate prevention is required. This review summarizes the pathophysiological effects on the respiratory tract when breathing oxygen with PO₂ of 50-300 kPa (hyperoxia). We discuss to what extent the most commonly used lung function parameters change after exposure to hyperoxia and its role in monitoring the onset and development of pulmonary oxygen toxicity in daily practice. Finally, new techniques in respiratory medicine are discussed with regard to their usefulness in monitoring pulmonary oxygen toxicity in divers.

High Mobility Group Box-1 mediates hyperoxia-induced impairment of Pseudomonas aeruginosa clearance and inflammatory lung injury in mice

Mechanical ventilation with supraphysiological concentrations of oxygen (hyperoxia) is routinely used to treat patients with respiratory distress. However, a significant number of patients on ventilators exhibit enhanced susceptibility to infections and develop ventilator-associated pneumonia (VAP). Pseudomonas aeruginosa (PA) is one of the most common species of bacteria found in these patients. Previously, we demonstrated that prolonged exposure to hyperoxia can compromise the ability of alveolar macrophages (AMs), an essential part of the innate immunity, to phagocytose PA. This study sought to investigate the potential molecular mechanisms underlying hyperoxia-compromised innate immunity against bacterial infection in a murine model of PA pneumonia. Here, we show that exposure to hyperoxia (≥ 99% O2) led to a significant elevation in concentrations of airway high mobility group box-1 (HMGB1) and increased mortality in C57BL/6 mice infected with PA. Treatment of these mice with a neutralizing anti-HMGB1 monoclonal antibody (mAb) resulted in a reduction in bacterial counts, injury, and numbers of neutrophils in the lungs, and an increase in leukocyte phagocytic activity compared with mice receiving control mAb. This improved phagocytic function was associated with reduced concentrations of airway HMGB1. The correlation between phagocytic activity and concentrations of extracellular HMGB1 was also observed in cultured macrophages. These results indicate a pathogenic role for HMGB1 in hyperoxia-induced impairment with regard to a host's ability to clear bacteria and inflammatory lung injury. Thus, HMGB1 may provide a novel molecular target for improving hyperoxia-compromised innate immunity in patients with VAP.

Acute lung injury and acute respiratory distress syndrome

Every year, more information accumulates about the possibility of treating patients with acute lung injury or acute respiratory distress syndrome with specially designed mechanical ventilation strategies. Ventilator modes, positive end-expiratory pressure settings, and recruitment maneuvers play a major role in these strategies. However, what can we take from these experimental and clinical data to the clinical practice? In this article, we discuss substantial options of mechanical ventilation together with some adjunctive therapeutic measures, such as prone positioning and inhalation of nitric oxide.

Moderate oxygen augments lipopolysaccharide-induced lung injury in mice

Despite the associated morbidity and mortality, underlying mechanisms leading to the development of acute lung injury (ALI) remain incompletely understood. Frequently, ALI develops in the hospital, coinciding with institution of various therapies, including the use of supplemental oxygen. Although pathological evidence of hyperoxia-induced ALI in humans has yet to be proven, animal studies involving high oxygen concentration reproducibly induce ALI. The potentially injurious role of lower and presumably safer oxygen concentrations has not been well characterized in any species. We hypothesized that in the setting of a preexisting insult to the lung, the addition of moderate-range oxygen can augment lung injury. Our model of low-dose intratracheal LPS (IT LPS) followed by 60% oxygen caused a significant increase in ALI compared with LPS or oxygen alone with increased alveolar neutrophils, histological injury, and epithelial barrier permeability. In the LPS plus oxygen group, regulatory T cell number was reduced, and macrophage activation markers were increased, compared with LPS alone. Antibody-mediated depletion of neutrophils significantly abrogated the observed lung injury for all measured factors. The enhanced presence of alveolar neutrophils in the setting of LPS and oxygen is due, at least in part, to elevated chemokine gradients signaling neutrophils to the alveolar space. We believe these results strongly support an effect of lower concentrations of oxygen to augment the severity of a mild preexisting lung injury and warrants further investigation in both animals and humans.

Animal models of acute lung injury

Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury.

Antioxidants improve antibacterial function in hyperoxia-exposed macrophages

Hyperoxia and pulmonary infections are well known to increase the risk of acute and chronic lung injury in newborn infants, but it is not clear whether hyperoxia directly increases the risk of pneumonia. The purpose of this study was to examine: (1) the effects of hyperoxia and antioxidant enzymes on inflammation and bacterial clearance in mononuclear cells and (2) developmental differences between adult and neonatal mononuclear cells in response to hyperoxia. Mouse macrophages were exposed to either room air or 95% O2 for 24 h and then incubated with Pseudomonas aeruginosa. After 1 h, bacterial adherence, phagocytosis, and macrophage inflammatory protein (MIP)-1alpha production were analyzed. Bacterial adherence increased 5.8-fold (p < 0.0001), phagocytosis decreased 60% (p < 0.05), and MIP-1alpha production increased 49% (p < 0.05) in response to hyperoxia. Overexpression of MnSOD or catalase significantly decreased bacterial adherence by 30.5%, but only MnSOD significantly improved bacterial phagocytosis and attenuated MIP-1alpha production. When monocytes from newborns and adults were exposed to hyperoxia, phagocytosis was impaired in both groups. However, adult monocytes were significantly more impaired than neonatal monocytes. Data indicate that hyperoxia significantly increases bacterial adherence while impairing function of mononuclear cells, with adult cells being more impaired than neonatal cells. MnSOD reduces bacterial adherence and inflammation and improves bacterial phagocytosis in mononuclear cells in response to hyperoxia, which should minimize the development of oxidant-induced lung injury as well as reducing nosocomial infections.

Hyperoxia induces macrophage cell cycle arrest by adhesion-dependent induction of p21Cip1 and activation of the retinoblastoma protein

Hyperoxia induces growth arrest, apoptosis, necrosis, and morphological changes (spreading and adhesion) in various types of cells. The mechanism of hyperoxia-induced cell growth arrest has not been well elucidated, especially in macrophages. One possible mechanism is a role of cell adhesion in hyperoxia-induced cell cycle arrest. To evaluate this finding, macrophages were cultured in normoxia (21% O2) or hyperoxia (95% O2) in adhesion or low adhesion conditions. Incubation of macrophages in hyperoxia induced cell cycle arrest. The hyperoxia-induced cell cycle arrest was prevented by low adhesion conditions. To evaluate pathways potentially involved in hyperoxia-induced growth arrest, we measured extracellular regulated kinase and retinoblastoma protein activation and p21Cip1 and p53 accumulation. Hyperoxia strongly induced activation of extracellular regulated kinase and retinoblastoma protein as well as up-regulation of p21Cip1. These effects of hyperoxia were attenuated under low adhesion conditions, suggesting a role for integrin-dependent signaling. The induction of p21Cip1 and activation of retinoblastoma protein occurred via a p53-independent mechanism. These results suggest that adhesion-dependent pathways are required for hyperoxia-induced cell cycle arrest in macrophages.

Lethal systemic capillary leak syndrome associated with severe ventilator-induced lung injury: an experimental study

OBJECTIVE

We report the evolution of severe ventilator-induced lung injury associated with lethal systemic capillary leak syndrome, when sheep were ventilated at a peak inspiratory pressure of 50 cm H2O, at a respiratory rate of 8 breaths.min, with an inspiratory time of 2.5 secs.

DESIGN

A prospective laboratory animal study.

SETTING

Experimental animal research laboratory.

SUBJECTS

Mixed breed sheep.

INTERVENTIONS

Sheep were anesthetized, paralyzed, and mechanically ventilated.

MEASUREMENTS AND MAIN RESULTS

This sheep model was characterized by a rapidly evolving massive anasarca, hemoconcentration, cardiac dysfunction, multiple system organ failure, and severe ventilator-induced lung injury. Cardiovascular changes and profound hemoconcentration developed within 6 hrs from the start of mechanical ventilation, along with a major decline in pulmonary compliance and deterioration in arterial blood gases. When total static lung compliance decreased to 0.15 mL (cm H2O)(-1) x kg(-1) (7-30 hrs), the sheep were randomized to two groups. Group I received high (recruitive) positive end-expiratory pressure (9-20 cm H2O), adjusted as needed; group II received low (supportive) positive end-expiratory pressure (2-6 cm H2O). Sheep in both groups progressively deteriorated and died with cardiocirculatory failure and multiple system organ failure within 12-24 hrs from start of treatment.

CONCLUSIONS

This model of lethal systemic capillary leak syndrome with multiple system organ failure differs greatly from our previous sheep model of acute ventilator-induced lung injury in which sheep were ventilated with a peak inspiratory pressure of 50 cm H2O, a respiratory rate of 4 breaths x min(-1), and an inspiratory time of 1.35 secs, without inducing capillary leak syndrome. The mere change of respiratory rate from 4 to 8 breaths x min(-1), with a near doubling of the inspiratory time to 2.5 secs, although maintaining eucapnia, resulted in lethal systemic capillary leak syndrome and multiple system organ failure with both gross and microscopic pathology of lungs greatly different from our previous model of mechanical ventilation-induced acute respiratory distress syndrome.

High frequency percussive ventilation and conventional ventilation after smoke inhalation: a randomised study

Inhalation injury and bacterial pneumonia represent some of the most important causes of mortality in burn patients. Thirty-five severely burned patients were randomised on admission for conventional ventilation (CV; control group) versus high frequency percussive ventilation (HFPV; study group). HFPV is a ventilatory mode, introduced 10 years ago which combines the advantages of CV with some of those of high frequency ventilation. Arterial blood gases, ventilatory and hemodynamic variables were recorded for 5 days at 2h intervals. Incident complications were classically managed. A statistical analysis (Student's t-test and Wilcoxon signed rank test) demonstrated a significant higher PaO(2)/FiO(2) from days 0 to 3 in the HFPV group. No significant differences were observed for the other parameters. Our findings suggest that HFPV can improve blood oxygenation during the acute phase following inhalation injury allowing reduction of FiO(2). No significant differences were observed between groups for mortality nor incidence of infectious complications in this study.

Alveolar type II cell abnormalities and peroxide formation in lungs of rats given IL-1 intratracheally

Acute lung injury (ALI) is characterized by increased lung levels of proinflammatory cytokines, inflammation, oxidative stress, edema, and impaired gas exchange. Notably, ALI patients also exhibit pulmonary surfactant abnormalities, including increased levels of phospholipids in their lung lavages. In the present study, to assess early alterations of the lung surfactant system in ALI, we induced inflammation and acute lung injury in rats by administering interleukin-1alpha (IL-1) intratracheally. Five h after IL-1 instillation, we examined lung tissue ultrastructure by electron microscopy using both routine staining methods and cerium chloride staining to localize hydrogen peroxide (H2O2) histologically. We also measured lung lavage phospholipid levels, lung tissue gamma-glutamyl transpeptidase (GGT) activities (a marker of oxidative stress), and arterial blood oxygen tensions. We observed that lungs of rats given IL-1 intratracheally had increased neutrophil accumulation, increased H2O2 production, and increased alveolar type II (ATII) pneumocyte ultrastructural abnormalities compared to rats given saline intratracheally. Intratracheal instillation of IL-1 also increased phospholipid levels in the bronchoalveolar lavage (BAL), possibly as a consequence of the abnormal discharge of lamellar bodies into the alveolar lumen. In addition, IL-1-insuffated rats had increased lung GGT levels and impaired blood oxygenation compared to saline-insufflated rats. Treatment with mepacrine decreased lung neutrophil accumulation, ultrastructural lung abnormalities, lung lavage phospholipid levels, lung tissue GGT levels, and blood oxygenation impairment in rats given IL-1 intratracheally, suggesting a possible relationship between these events. Our results indicate that IL-1-induced acute lung injury in rats is marked by neutrophil-dependent oxidative stress, ATII cell defects, abnormal discharge of lamellar body phospholipids, and impaired blood oxygenation.

Hepatocyte growth factor is elevated in chronic lung injury and inhibits surfactant metabolism

Adult respiratory distress syndrome may incorporate in its pathogenesis the hyperplastic proliferation of alveolar epithelial type II cells and derangement in synthesis of pulmonary surfactant. Previous studies have demonstrated that hepatocyte growth factor (HGF) in the presence of serum is a potential mitogen for adult type II cells (R. J. Panos, J. S. Rubin, S. A. Aaronson, and R. J. Mason. J. Clin. Invest. 92: 969-977, 1993) and that it is produced by fetal mesenchymal lung cells (J. S. Rubin, A. M.-L. Chan, D. P. Botarro, W. H. Burgess, W. G. Taylor, A. C. Cech, D. W. Hirschfield, J. Wong, T. Miki, P. W. Finch, and S. A. Aaronson. Proc. Natl. Acad. Sci. USA 88: 415-419, 1991). In these studies, we expand on this possible involvement of HGF in chronic lung injury by showing the following. First, normal adult lung fibroblasts transcribe only small amounts of HGF mRNA, but the steady-state levels of this message rise substantially in lung fibroblasts obtained from animals exposed to oxidative stress. Second, inflammatory cytokines produced early in the injury stimulate the transcription of HGF in isolated fibroblasts, providing a plausible mechanism for the increased amounts of HGF seen in vivo. Third, HGF is capable of significantly inhibiting the synthesis and secretion of the phosphatidylcholines of pulmonary surfactant. Fourth, HGF inhibits the rate-limiting enzyme in de novo phosphatidylcholine synthesis, CTP:choline-phosphate cytidylyltransferase (EC 2.7.7.15). Our data indicate that fibroblast-derived HGF could be partially responsible for the changes in surfactant dysfunction seen in adult respiratory distress syndrome, including the decreases seen in surfactant phosphatidylcholines.

Respiratory mechanics and surfactant in the acute respiratory distress syndrome

1. Although abnormalities in pulmonary surfactant were initially implicated in the pathogenesis of the acute respiratory distress syndrome (ARDS) 30 years ago, most subsequent research has focused on mediators of the parenchymal acute lung injury (ALI) and the associated increase in alveolocapillary permeability. 2. Surfactant is essential for normal breathing and the severity of ALI correlates with surfactant dysfunction and abnormalities in surfactant composition; however, no relationship has been shown with respiratory system compliance. In neonates and most animal models, respiratory system compliance will directly reflect the elastic properties of the lung. However, the greater vertical height of the chest wall in adults, in combination with the increase in lung density due to ALI, results in dependent collapse of alveoli. Because simple, global measurement of compliance is strongly influenced by the volume of aerated lung, alternative measures of respiratory mechanics may reflect surfactant dysfunction. 3. Using a dynamic, volume-dependent model of respiratory mechanics to indirectly reflect this heterogeneous inflation, we have found direct relationships with surfactant composition in patients with ARDS. A failure of surfactant to increase surface tension in large alveoli may also explain why lung overdistension occurs at relatively low pressures. Furthermore, surfactant dysfunction will exaggerate heterogeneous lung inflation, augmenting regional overinflation, and is essential for ALI secondary to repetitive opening and closing of alveoli during tidal ventilation. 4. Ventilation-induced ALI has also been shown to result in massive increases in pro-inflammatory cytokines within the lung. Because ALI itself fails to compartmentalize cytokines, with spillover into the systemic circulation resulting in distant organ dysfunction, surfactant dysfunction may have widespread implications.

The usefulness of combined high-frequency percussive ventilation during acute respiratory failure after smoke inhalation

Inhalation injury and bacterial pneumonia represent some of the most important causes of mortality in burn patients. We describe 11 severely burned patients with acute respiratory failure due to inhalation injury who did not respond adequately to conventional respiratory support. High-frequency percussive ventilation (HFPV) is a recent ventilatory mode, which combines the advantages of conventional ventilation with some of those of high-frequency ventilation. Seven patients developed pulmonary infection during the acute phase; one patient died of multiple organ failure on day 25. All the other patients survived; two developed bronchiolitis obliterans symptoms before discharge. No side-effects were noted and haemodynamic tolerance of HFPV was excellent. Our findings suggest that HFPV can improve pulmonary function and gas exchange in these catastrophic pulmonary failures following inhalation injury.

Effects of continuous bed rotation and prolonged mechanical ventilation on healthy, adult baboons

OBJECTIVE

To study, in a model of prolonged mechanical ventilation, the role of continuous bed rotation on lung function and pathology.

DESIGN

Prospective animal study.

SETTING

Animal research laboratory.

SUBJECTS

Healthy adult baboons (Papio cynocephalus), anesthetized with ketamine, sedated, paralyzed, mechanically ventilated for 11 days, and monitored with pulmonary and peripheral arterial catheters.

INTERVENTIONS

Animals were divided into two experimental groups: a) mechanical ventilation alone (control, n = 7); and b) mechanical ventilation with continuous bed rotation therapy to 45 degrees (continuous rotation group, n = 5). Mechanical ventilation was provided for 11 days with an FIO2 of 0.21 and tidal volume of 12 mL/ kg. Bronchoalveolar lavage was performed through a fiberoptic bronchoscope. Nursing care procedures, antacids, enteral feeding, and prophylactic antibiotics were administered.

MEASUREMENTS AND MAIN RESULTS

Measurements of hemodynamics, pulmonary functions, lung volumes, arterial blood gases, and chest radiographs were done daily. Bronchoalveolar lavage was performed at days 0, 7, and 11. There were no significant changes in hemodynamics, gas exchange, or pulmonary functions during the study period in either group. Microbiological surveillance cultures were negative in both experimental groups. In the control group after 7 days, six of seven animals developed patchy atelectasis; by day 11, two of seven animals demonstrated persistent radiologic abnormalities. Bronchoalveolar lavage neutrophils were significantly increased in control animals at days 7 and 11. Lung pathology in the control group showed areas of bronchiolitis, with surrounding bronchopneumonia in five of seven animals. None of the continuous rotation animals showed any radiologic or morphologic abnormalities.

CONCLUSIONS

Prolonged mechanical ventilation in the control group resulted in atelectasis, increased concentrations of bronchoalveolar lavage neutrophils, and mild pneumonitis. These effects were not associated with changes in lung volumes, oxygenation, or hemodynamic parameters. Continuous bed rotation helped to prevent these abnormalities.

Drug-induced pulmonary disease

Drug-induced disease of any system or organ can be associated with high morbidity and mortality, and it is tremendously costly to the health care of our country. More than 100 medications are known to affect the lungs adversely, including the airways in the form of cough and asthma, the interstitium with interstitial pneumonitis and noncardiac pulmonary edema, and the pleura with pleural effusions. Patients commonly do not even know what medications they are taking, do not bring them to the physician's office for identification, and usually do not relate over-the-counter medications with any problems they have. They assume that all nonprescription drugs are safe. Patients also believe that if they are taking prescription medications at their discretion, meaning on an as-needed basis, then these medications are also not important. This situation stresses just how imperative it is for the physician to take an accurate drug history in all patients seen with unexplained medical situations. Cardiovascular drugs that most commonly produce a pulmonary abnormality are amiodarone, the angiotensin-converting enzyme inhibitors, and beta-blockers. Pulmonary complications will develop in 6% of patients taking amiodarone and 15% taking angiotensin-converting enzyme inhibitors, with the former associated with interstitial pneumonitis that can be fatal and the latter associated with an irritating cough that is not associated with any pathologic or physiologic sequelae of consequence. The beta-blockers can aggravate obstructive lung disease in any patient taking them. Of the antiinflammatory agents, acetylsalicyclic acid can produce several different airway and parenchymal complications, including aggrevation of asthma in up to 5% of patients with asthma, a noncardiac pulmonary edema when levels exceed 40 mg/dl, and a pseudosepsis syndrome. More than 200 products contain aspirin. Low-dose methotrexate is proving to be a problem because granulomatous interstitial pneumonitis develops in 5% of those patients receiving it. This condition occurs most often in patients receiving the drug for rheumatoid arthritis, but it has been reported in a few patients receiving it for refractory asthma. Chemotherapeutic drug-induced lung disease is almost always associated with fever, thus mimicking opportunistic infection, which is the most common cause of pulmonary complications in the immunocompromised host. However, in 10% to 15% of patients, the pulmonary infiltrate is due to an adverse effect from a chemotherapeutic agent. This complication is frequently fatal even when recognized early.(ABSTRACT TRUNCATED AT 400 WORDS)

Acute lung injury during bacterial or fungal sepsis

We compared physiological and ultrastructural indices of acute lung injury (ALI) during septic shock caused by taxonomically diverse pathogens to distinguish ALI due to endogenous inflammatory mediators vs. microbial exotoxins or other factors. Conscious rats were infected i.v. with gram-negative Escherichia coli (EC, serotype 055:B5), exotoxin-C producing gram-positive Staphylococcus aureus (SA), or yeast-phase Candida albicans (CA, a clinical isolate). Viable inocula of 10(10) EC, 10(10) SA, or 10(9) CA caused lethal shock in < 24 h, but distinct types of ALI were noted after bacteria vs. fungi. Within 0.5 h of EC infection, leukocytes marginated in the lung vasculature; by death at 6-14 h, animals were hyperoxemic but not acidemic, and showed slight interstitial edema with increased wet/dry weight ratios (W/D = 5.22 +/- 0.10, mean +/- SE, vs. 4.86 +/- 0.07 in controls, P < 0.05). Similarly mild ALI occurred after 10(10) SA. In contrast, within 0.5 h of CA infection, yeast were visible within lung intravascular leukocytes. By death at 6-12 h, CA animals showed hyperoxic acidemia and moderate ALI with capillary obstruction, interstitial hemorrhage, and elevated lung W/D (5.52 +/- 0.13, P < 0.01 vs. controls) associated with yeast-mycelial transformation. Prior neutropenia accelerated mortality and worsened ALI after CA, with hypoxemic acidemia, increased lung W/D (7.23 +/- 0.34, P < 0.05 vs. other groups), capillary occlusion, perivascular and alveolar hemorrhage, and septal disruption by mycelia. Bacteremia induced large increases in serum tumor necrosis factor-alpha (TNF) and interleukin-1 alpha within 1.5 h, but these cytokines remained low in CA animals, even at death. Neither survival nor ALI after EC or CA was altered by pentoxifylline, which attentuated TNF production, or by cyclooxygenase inhibition with ibuprofen. Thus, overall ALI severity correlated with physiological indices of pulmonary function, but ultrastructural changes correlated better with pathogen type than circulating cytokine or eicosanoid mediators. Whereas lethal bacteremia induced early cytokinemia and mild ALI with or without bacterial exotoxins, moderate ALI apparently was mediated by fungal exotoxins during lethal candidemia, which worsened during neutropenia due to enhanced mycelial proliferation.

Decreased surfactant protein A in patients with bacterial pneumonia

Abnormalities have been previously noted in the lipid content of the lavage fluid of patients with bacterial pneumonia. In order to determine if these changes were also seen in surfactant apoproteins, we studied levels of surfactant protein A (SP-A) in patients with bacterial pneumonia. Patients without human immunodeficiency virus who were being evaluated for pulmonary infiltrates underwent bronchoscopy with bronchoalveolar lavage (BAL). Twenty-two patients with pneumonia, 12 caused by gram-positive organisms (Gm+ PNEU) and 10 caused by gram-negative organisms (Gm- PNEU), were compared with 10 patients with idiopathic pulmonary fibrosis (IPF) and 11 control subjects (CON). The percentage of neutrophils in the BAL was significantly higher in the patients with IPF and the pneumonia groups than in the control group (CON: mean, 1; range, 0 to 3. IPF: mean, 26; range, 13 to 42). Gm+ PNEU: mean, 33; range, 8 to 99. Gm- PNEU: mean, 64; range, 10 to 92; p < 0.0001). The amount of SP-A in the BAL fluid was similar for the CON and the IPF groups (CON: mean, 15; range, 5.75 to 26.5 micrograms/ml BAL. IPF: mean, 18.4; range, 6.49 to 45.64 micrograms/ml), whereas both pneumonia groups had significantly less SP-A (Gm- PNEU: mean, 5.54; range, 0.58 to 12.7. G+ PNEU: mean, 1.93; range, 0.47 to 6.74; p < 0.001). There was significantly less SP-A in the Gm+ PNEU group than in the Gm- PNEU group (p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Surfactant and the adult respiratory distress syndrome

ARDS includes a complex series of events leading to alveolar damage, high permeability pulmonary edema, and respiratory failure. The endogenous pulmonary surfactant system is crucial to maintaining normal lung function, and only recently has it been appreciated that alterations in the surfactant system significantly contributed to the pathophysiology of the lung injury of patients with ARDS. Through a combination of analyzing BAL samples from patients with ARDS and extensive animal studies, there have been significant insights into the variety of surfactant abnormalities that can occur in injured lungs. These include altered surfactant composition and pool sizes, abnormal surfactant metabolism, and inactivation of alveolar surfactant by serum proteins present within the airspace. Positive effects of exogenous surfactant administration on acute lung injury have been reported. There is now a prospective, randomized clinical trial evaluating the efficacy of aerosolized exogenous surfactant in patients with ARDS. This trial has demonstrated improvements in gas exchange and a trend toward decreased mortality in response to the surfactant. Despite these encouraging results, there are multiple factors requiring further investigation in the development of optimal surfactant treatment strategies for patients with ARDS. Such factors include the development of optimal surfactant delivery techniques, determining the ideal time for surfactant administration during the course of injury, and the development of optimal exogenous surfactant preparations that will be used to treat these patients. With further clinical trials and continued research efforts, exogenous surfactant administration should play a useful role in the future therapeutic approach to patients with ARDS.

Prophylactic use of high-frequency percussive ventilation in patients with inhalation injury

Death and the incidence of pneumonia are significantly increased in burn patients with inhalation injury, despite application of conventional ventilatory support techniques. The effect of high-frequency percussive ventilation on mortality rate, incidence of pulmonary infection, and barotrauma were studied in 54 burn patients with documented inhalation injury admitted between March 1987 and September 1990 as compared to an historic cohort treated between 1980 and 1984. All patients satisfied clinical criteria for mechanical ventilation. High-frequency percussive ventilation was initiated within 24 hours of intubation. The patients' mean age and burn size were 32.2 years and 47.8%, respectively (ranges, 15 to 88 years; 0% to 90%). The mean number of ventilator days was 15.3 +/- 16.7 (range, 1 to 150 days), with 26% of patients ventilated for more than 2 weeks. Fourteen patients (25.9%) developed pneumonia compared to an historic frequency of 45.8% (p less than 0.005). Mortality rate was 18.5% (10 patients) with an expected historic number of deaths of 23 (95% confidence limits of 17 to 28 deaths). The documented improvement in survival rate and decrease in the incidence of pneumonia in patients treated with prophylactic high-frequency ventilation (HFV), as compared to a cohort of patients treated in the 7 years before the trial, indicates the importance of small airway patency in the pathogenesis of inhalation injury sequelae and supports further use and evaluation of HFV.

Changes in pulmonary surfactant during bacterial pneumonia

In pneumonia, bacteria induce changes in pulmonary surfactant. These changes are mediated by bacteria directly on secreted surfactant or indirectly through pulmonary type II epithelial cells. The bacterial component most likely responsible is endotoxin since gram-negative bacteria more often induce these changes than gram-positive bacteria. Also, endotoxin and gram-negative bacteria induce similar changes in surfactant. The interaction of bacteria or endotoxin with secreted surfactant results in changes in the physical (i.e. density and surface tension) properties of surfactant. In addition, gram-negative bacteria or endotoxin can injure type II epithelial cells causing them to produce abnormal quantities of surfactant, abnormal concentrations of phospholipids in surfactant, and abnormal compositions (i.e. type and saturation of fatty acids) of PC. The L/S ratio, the concentration of PG, and the amount of palmitic acid in PC are all significantly lower. The changes in surfactant have a deleterious effect on lung function characterized by significant decreases in total lung capacity, static compliance, diffusing capacity, and arterial PO2 and a significant increase in mean pulmonary arterial pressure. Also decreased concentrations of surfactant or an altered surfactant composition can result in the anatomic changes commonly seen in pneumonia such as pulmonary edema, hemorrhage, and atelectasis.