Surfactant alterations in acute inflammatory lung injury from aspiration of acid and gastric particulates

Role of alveolar nitric oxide in gastroesophageal reflux-associated cough: prospective observational study

BACKGROUND

Fractional exhaled nitric oxide (FeNO) measured at multiple exhalation flow rates can be used as a biomarker to differentiate central and peripheral airway inflammation. However, the role of alveolar nitric oxide (CaNO) indicating peripheral airway inflammation remains unclear in gastroesophageal reflux-associated cough (GERC).

OBJECTIVES

We aimed to characterize the changes in alveolar nitric oxide (CaNO) and determine its clinical implication in GERC.

DESIGN

This is a single-center prospective observational study.

METHODS

FeNOs at exhalation flow rates of 50 and 200 ml/s were measured in 102 patients with GERC and 134 patients with other causes of chronic cough (non-GERC). CaNO was calculated based on a two-compartment model and the factors associated with CaNO were analyzed. The effect of anti-reflux therapy on CaNO was examined in 26 GERC patients with elevated CaNO.

RESULTS

CaNO was significantly elevated in GERC compared with that in non-GERC (4.6 ± 4.4 ppb versus 2.8 ± 2.3 ppb, p < 0.001). GERC patients with high CaNO (>5 ppb) had more proximal reflux events (24 ± 15 versus 9 ± 9 episodes, p = 0.001) and a higher level of pepsin (984.8 ± 492.5 versus 634.5 ± 626.4 pg/ml, p = 0.002) in sputum supernatant than those with normal CaNO. More GERC patients with high CaNO required intensified anti-reflux therapy (χ2 = 3.963, p = 0.046), as predicted by a sensitivity of 41.7% and specificity of 83.3%. Cough relief paralleled a significant improvement in CaNO (8.3 ± 3.0 versus 4.8 ± 2.6 ppb, p < 0.001).

CONCLUSION

Peripheral airway inflammation can be assessed by CaNO measurement in GERC. High CaNO indicates potential micro-aspiration and may predict a necessity for intensified anti-reflux therapy.

Mechanistic Understanding of Lung Inflammation: Recent Advances and Emerging Techniques

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury characterized by an acute inflammatory response in the lung parenchyma. Hence, it is considered as the most appropriate clinical syndrome to study pathogenic mechanisms of lung inflammation. ARDS is associated with increased morbidity and mortality in the intensive care unit (ICU), while no effective pharmacological treatment exists. It is very important therefore to fully characterize the underlying pathobiology and the related mechanisms, in order to develop novel therapeutic approaches. In vivo and in vitro models are important pre-clinical tools in biological and medical research in the mechanistic and pathological understanding of the majority of diseases. In this review, we will present data from selected experimental models of lung injury/acute lung inflammation, which have been based on clinical disorders that can lead to the development of ARDS and related inflammatory lung processes in humans, including ventilation-induced lung injury (VILI), sepsis, ischemia/reperfusion, smoke, acid aspiration, radiation, transfusion-related acute lung injury (TRALI), influenza, Streptococcus (S.) pneumoniae and coronaviruses infection. Data from the corresponding clinical conditions will also be presented. The mechanisms related to lung inflammation that will be covered are oxidative stress, neutrophil extracellular traps, mitogen-activated protein kinase (MAPK) pathways, surfactant, and water and ion channels. Finally, we will present a brief overview of emerging techniques in the field of omics research that have been applied to ARDS research, encompassing genomics, transcriptomics, proteomics, and metabolomics, which may recognize factors to help stratify ICU patients at risk, predict their prognosis, and possibly, serve as more specific therapeutic targets.

Surface mechanical behavior of water-spread poly(styrene)-poly(ethylene glycol) (PS-PEG) micelles at the air-water interface: Effect of micelle size and polymer end/linking group chemistry

HYPOTHESIS

The surface mechanical properties of poly(styrene)-poly(ethylene glycol) (PS-PEG) micelles are influenced by the PEG corona structure. Changes in micelle aggregation number as well as changes in the PEG end group and linking group chemistry of the PS-PEG block copolymer are expected to alter PEG corona characteristics and therefore affect surface mechanical properties of the resulting micelle film.

EXPERIMENTS

Different sized micelles comprised of PS-PEG block copolymer chains were formulated by equilibrating micelles in different ratios of acetone/water mixtures and subsequently removing acetone using dialysis. Additionally, micelles of a similar size and PS-PEG molecular weight but slightly different chemistry were formulated. The micelles were characterized using dynamic light scattering (DLS), transmission electron microscopy (TEM), ¹H NMR, surface pressure-area isotherms and Brewster angle microscopy (BAM).

FINDINGS

The reduction in micelle aggregation number results in the subsequent monolayer having higher compressibility moduli and bending stiffnesses and collapsing at lower surface pressures. Micelle hydrophobicity was shown to improve readsorption of micelles to interface after collapse. Analysis of Brewster angle microscopy images of out-of-plane wrinkle structures which formed upon monolayer collapse indicates the presence of continuous 1 nm thick PEG layer which allows micelle monolayers to bend under high compression.

Hypoxia‐inducible factor (HIF)‐1α‐induced regulation of lung injury in pulmonary aspiration is mediated through NF‐kB

Aspiration‐induced lung injury is a common grievance encountered in the intensive care unit (ICU). It is a significant risk factor for improving ventilator‐associated pneumonia (VAP) and acute respiratory distress syndrome (ARDS). Hypoxia‐inducible factor (HIF)‐1α is one of the primary transcription factors responsible for regulating the cellular response to changes in oxygen tension. Here, we sought to determine the role of HIF‐1α and specifically the role of type 2 alveolar epithelial cells in generating the acute inflammatory response following acid and particles (CASP) aspiration. Previous studies show HIF‐1 α is involved in regulating the hypoxia‐stimulated expression of MCP‐1 in mice and humans. The CASP was induced in C57BL/6, ODD‐Luc, HIF‐1α (+/+) control, and HIF‐1α conditional knockout (HIF‐1α (−/−) mice). Following an injury in ODD mice, explanted organs were subjected to IVIS imaging to measure the degree of hypoxia. HIF‐1α expression, BAL albumin, cytokines, and histology were measured following CASP. In C57BL/6 mice, the level of HIF‐1α was increased at 1 h after CASP. There were significantly increased levels of albumin and cytokines in C57BL/6 and ODD‐Luc mice lungs following CASP. HIF‐1α (+/+) mice given CASP demonstrated a synergistic increase in albumin leakage, increased pro‐inflammatory cytokines, and worse injury. MCP‐1 antibody neutralized HIF‐1α (+/+) mice showed reduced granuloma formation. The NF‐κB expression was increased substantially in the HIF‐1α (+/+) mice following CASP compared to HIF‐1α (−/−) mice. Our data collectively identify that HIF‐1α upregulation of the acute inflammatory response depends on NF‐κB following CASP.

Aspiration syndromes and associated lung injury: incidence, pathophysiology and management

Aspiration is a common condition affecting healthy or sick patients which could create an acute or chronic inflammatory reaction in the lungs. Aspiration syndromes could be categorized according to a content entering the respiratory system into bacterial aspiration pneumonia with the gastric or oropharyngeal bacteria entering, aspiration chemical pneumonitis with bacteria-freegastric acid aspiration, or aspiration of a foreign body which causes an acute pulmonary emergency. There are differences in the clinical presentation of volume-dependent aspirations (microaspiration and macroaspiration): the higher is the volume of aspiration, the greater is the injury to the patient and more serious are the health consequences (with 70 % mortality rate for hospitalized patients). Aspiration syndromes can affect both the airways and pulmonary parenchyma, leading to acute lung injury, increased hospitalization rate and worse outcomes in critically ill patients. Impaired alveolar-capillary permeability, oedema formation, neutrophilic inflammatory response and pulmonary surfactant inactivation lead to reduced lung compliance and loss of aerated lung tissue and give rise to hypoxemia and respiratory failure. This review discusses the effect of aspiration events on the pulmonary tissue. The main focus is to distinguish the differences between bacterial and chemical pneumonia, their clinical presentation and symptoms, risk factors of developing the changes, possibilities of diagnostics and management as well as prevention of aspirations. Because of a risk of serious lung damage after the aspiration, pathophysiology and processes leading to lung tissue injury are discussed in detail. Data sources represent a systematic literature search using relevant medical subject headings.

Strategies to protect surfactant and enhance its activity

The knowledge about surfactant biology is now deeper and recent research has allowed to clarify its role in several human lung disorders. The balance between surfactant production and consumption is better known and the same applies to their regulatory mechanisms. This has allowed to hypothesize and investigate several new and original strategies to protect surfactant and enhance its activity. These interventions are potentially useful for several disorders and particularly for acute respiratory distress syndrome. We here highlight the mechanisms regulating surfactant consumption, encompassing surfactant catabolism but also surfactant injury due to other mechanisms, in a physiopathology-driven fashion. We then analyze each corresponding strategy to protect surfactant and enhance its activity. Some of these strategies are more advanced in terms of research & development pathway, some others are still investigational, but all are promising and deserve a joint effort from clinical-academic researchers and the industry.

Elastin degradation products in acute lung injury induced by gastric contents aspiration

Background

Gastric contents aspiration is a high-risk condition for acute lung injury (ALI). Consequences range from subclinical pneumonitis to respiratory failure, depending on the volume of aspirate. A large increment in inflammatory cells, an important source of elastase, potentially capable of damaging lung tissue, has been described in experimental models of aspiration. We hypothesized that in early stages of aspiration-induced ALI, there is proteolytic degradation of elastin, preceding collagen deposition. Our aim was to evaluate whether after a single orotracheal instillation of gastric fluid, there is evidence of elastin degradation.

Methods

Anesthesized Sprague-Dawley rats received a single orotracheal instillation of gastric fluid and were euthanized 4, 12 and 24 h and at day 4 after instillation (n = 6/group). We used immunodetection of soluble elastin in lung tissue and BALF and correlated BALF levels of elastin degradation products with markers of ALI. We investigated possible factors involved in elastin degradation and evaluated whether a similar pattern of elastin degradation can be found in BALF samples of patients with interstitial lung diseases known to have aspirated. Non-parametric ANOVA (Kruskall-Wallis) and linear regression analysis were used.

Results

We found evidence of early proteolytic degradation of lung elastin. Elastin degradation products are detected both in lung tissue and BALF in the first 24 h and are significantly reduced at day 4. They correlate significantly with ALI markers, particularly PMN cell count, are independent of acidity and have a similar molecular weight as those obtained using pancreatic elastase. Evaluation of BALF from patients revealed the presence of elastin degradation products not present in controls that are similar to those found in BALF of rats treated with gastric fluid.

Conclusions

A single instillation of gastric fluid into the lungs induces early proteolytic degradation of elastin, in relation to the magnitude of alveolar-capillary barrier derangement. PMN-derived proteases released during ALI are mostly responsible for this damage. BALF from patients showed elastin degradation products similar to those found in rats treated with gastric fluid. Long-lasting effects on lung elastic properties could be expected under conditions of repeated instillations of gastric fluid in experimental animals or repeated aspiration events in humans.

Tracheal acid or surfactant instillation raises alveolar surface tension

Whether alveolar liquid surface tension, T, is elevated in the acute respiratory distress syndrome (ARDS) has not been demonstrated in situ in the lungs. Neither is it known how exogenous surfactant, which has failed to treat ARDS, affects in situ T. We aim to determine T in an acid-aspiration ARDS model before and after exogenous surfactant administration. In isolated rat lungs, we combine servo-nulling pressure measurement and confocal microscopy to determine alveolar liquid T according to the Laplace relation. Administering 0.01 N (pH 1.9) HCl solution by alveolar injection or tracheal instillation, to model gastric liquid aspiration, raises T. Subsequent surfactant administration fails to normalize T. Furthermore, in normal lungs, tracheal instillation of control saline or exogenous surfactant raises T. Lavaging the trachea with saline and injecting the lavage solution into the alveolus raises T, suggesting that tracheal instillation may wash T-raising airway contents to the alveolus. Adding 0.01 N HCl or 5 mM CaCl₂-either of which aggregates mucins-to tracheal lavage solution reduces or eliminates the effect of lavage solution on alveolar T. Following tracheal saline instillation, liquid suctioned directly out of alveoli through a micropipette contains mucins. Additionally, alveolar injection of gastric mucin solution raises T. We conclude that 1) tracheal liquid instillation likely washes T-raising mucins to the alveolus and 2) even exogenous surfactant that could be delivered mucin-free to the alveolus might not normalize T in acid-aspiration ARDS. NEW & NOTEWORTHY We demonstrate in situ in isolated lungs that surface tension is elevated in an acid-aspiration acute respiratory distress syndrome (ARDS) model. Following tracheal liquid instillation, also in isolated lungs, we directly sample alveolar liquid. We find that liquid instillation into normal lungs washes mucins to the alveolus, thereby raising alveolar surface tension. Furthermore, even if exogenous surfactant could be delivered mucin-free to the alveolus, exogenous surfactant might fail to normalize alveolar surface tension in acid-aspiration ARDS.

Gastric Aspiration and Its Role in Airway Inflammation

Gastro-Oesophageal Reflux (GOR) has been associated with chronic airway diseases while the passage of foreign matter into airways and lungs through aspiration has the potential to initiate a wide spectrum of pulmonary disorders. The clinical syndrome resulting from such aspiration will depend both on the quantity and nature of the aspirate as well as the individual host response. Aspiration of gastric fluids may cause damage to airway epithelium, not only because acidity is toxic to bronchial epithelial cells but also due to the effect of digestive enzymes such as pepsin and bile salts. Experimental models have shown that direct instillation of these factors to airways epithelia cause damage with a consequential inflammatory response. The pathophysiology of these responses is gradually being dissected, with better understanding of acute gastric aspiration injury, a major cause of acute lung injury, providing opportunities for therapeutic intervention and potentially, ultimately, improved understanding of the chronic airway response to aspiration. Ultimately, clarification of the inflammatory pathways which are related to micro-aspiration via pepsin and bile acid salts may eventually progress to pharmacological intervention and surgical studies to assess the clinical benefits of such therapies in driving symptom improvement or reducing disease progression.

Aspiration Pneumonia in the Dog: A Review

OBJECTIVE

To review the human and veterinary literature pertaining to aspiration pneumonitis and pneumonia.

MATERIAL AND METHODS

Data sources included scientific reviews and original research publications from the human and veterinary literature. All reviews and studies that added to the understanding of aspiration pneumonia were included.

RESULTS

Compared to human medicine, aspiration pneumonia can be difficult to diagnose in the canine patient and is often a diagnosis of presumption. Multiple risk factors exist increasing the likelihood of aspiration pneumonia and a thorough understanding of these can aid in prevention. Treatment recommendations center primarily on supportive care, oxygen therapy and antibiotic administration.

CLINCIAL SIGNIFICANCE

Aspiration pneumonia is a common finding in the canine patient and a thorough understanding of the disease will lead to better treatment outcomes. Further studies on treatment and prevention in veterinary medicine are warranted.

Pneumonitis and pneumonia after aspiration

Aspiration pneumonitis and aspiration pneumonia are clinical syndromes caused by aspiration. These conditions are clinically significant due to their high morbidity and mortality. However, aspiration as a preceding event are often unwitnessed, particularly in cases of asymptomatic or silent aspiration. Furthermore, despite the difference in treatment approaches for managing aspiration pneumonitis and aspiration pneumonia, these two disease entities are often difficult to discriminate from one another, resulting in inappropriate treatment. The use of unclear terminologies hinders the comparability among different studies, making it difficult to produce evidence-based conclusions and practical guidelines. We reviewed the most recent studies to define aspiration, aspiration pneumonitis, and aspiration pneumonia, and to further assess these conditions in terms of incidence and epidemiology, pathophysiology, risk factors, diagnosis, management and treatment, and prevention.

Acute lung injury induced by whole gastric fluid: hepatic acute phase response contributes to increase lung antiprotease protection

Background

Gastric contents aspiration in humans is a risk factor for severe respiratory failure with elevated mortality. Although aspiration-induced local lung inflammation has been studied in animal models, little is known about extrapulmonary effects of aspiration. We investigated whether a single orotracheal instillation of whole gastric fluid elicits a liver acute phase response and if this response contributes to enrich the alveolar spaces with proteins having antiprotease activity.

Methods

In anesthetized Sprague-Dawley rats receiving whole gastric fluid, we studied at different times after instillation (4 h −7 days): changes in blood cytokines and acute phase proteins (fibrinogen and the antiproteases alpha1-antitrypsin and alpha2-macroglobulin) as well as liver mRNA expression of the two antiproteases. The impact of the systemic changes on lung antiprotease defense was evaluated by measuring levels and bioactivity of antiproteases in broncho-alveolar lavage fluid (BALF). Markers of alveolar-capillary barrier derangement were also studied. Non-parametric ANOVA (Kruskall-Wallis) and linear regression analysis were used.

Results

Severe peribronchiolar injury involving edema, intra-alveolar proteinaceous debris, hemorrhage and PMNn cell infiltration was seen in the first 24 h and later resolved. Despite a large increase in several lung cytokines, only IL-6 was found elevated in blood, preceding increased liver expression and blood concentration of both antiproteases. These changes, with an acute phase response profile, were significantly larger for alpha2-macroglobulin (40-fold increment in expression with 12-fold elevation in blood protein concentration) than for alpha1-antitrypsin (2–3 fold increment in expression with 0.5-fold elevation in blood protein concentration). Both the increment in capillary-alveolar antiprotease concentration gradient due to increased antiprotease liver synthesis and a timely-associated derangement of the alveolar-capillary barrier induced by aspiration, contributed a 58-fold and a 190-fold increase in BALF alpha1-antitrypsin and alpha2-macroglobulin levels respectively (p < 0.001).

Conclusions

Gastric contents-induced acute lung injury elicits a liver acute phase response characterized by increased mRNA expression of antiproteases and elevation of blood antiprotease concentrations. Hepatic changes act in concert with derangement of the alveolar capillary barrier to enrich alveolar spaces with antiproteases. These findings may have significant implications decreasing protease burden, limiting injury in this and other models of acute lung injury and likely, in recurrent aspiration.

Altered Lipid Composition of Surfactant and Lung Tissue in Murine Experimental Malaria-Associated Acute Respiratory Distress Syndrome

Malaria-associated acute lung injury (MA-ALI) and its more severe form malaria-associated acute respiratory distress syndrome (MA-ARDS) are common, often fatal complications of severe malaria infections. However, little is known about their pathogenesis. In this study, biochemical alterations of the lipid composition of the lungs were investigated as possible contributing factors to the severity of murine MA-ALI/ARDS. C57BL/6J mice were infected with Plasmodium berghei NK65 to induce lethal MA-ARDS, or with Plasmodium chabaudi AS, a parasite strain that does not induce lung pathology. The lipid profile of the lung tissue from mice infected with Plasmodium berghei NK65 developing MA-ALI/ARDS, but not that from mice without lung pathology or controls, was characterized by high levels of phospholipids -mainly phosphatidylcholine- and esterified cholesterol. The high levels of polyunsaturated fatty acids and the linoleic/oleic fatty acid ratio of the latter reflect the fatty acid composition of plasma cholesterol esters. In spite of the increased total polyunsaturated fatty acid pool, which augments the relative oxidability of the lung membranes, and the presence of hemozoin, a known pro-oxidant, no excess oxidative stress was detected in the lungs of Plasmodium berghei NK65 infected mice. The bronchoalveolar lavage (BAL) fluid of Plasmodium berghei NK65 infected mice was characterized by high levels of plasma proteins. The phospholipid profile of BAL large and small aggregate fractions was also different from uninfected controls, with a significant increase in the amounts of sphingomyelin and lysophosphatidylcholine and the decrease in phosphatidylglycerol. Both the increase of proteins and lysophosphatidylcholine are known to decrease the intrinsic surface activity of surfactant. Together, these data indicate that an altered lipid composition of lung tissue and BAL fluid, partially ascribed to oedema and lipoprotein infiltration, is a characteristic feature of murine MA-ALI/ARDS and possibly contribute to lung dysfunction.

Surfactant

Exogenous pulmonary surfactant, widely used in neonatal care, is one of the best-studied treatments in neonatology, and its introduction in the 1990s led to a significant improvement in neonatal outcomes in preterm infants, including a decrease in mortality. This chapter provides an overview of surfactant composition and function in health and disease and summarizes the evidence for its clinical use.

Recovery of vocal fold immobility following isolated patent ductus arteriosus ligation

OBJECTIVE

Identify laryngoscopic and functional outcomes of infants with vocal fold immobility (VFI) following patent ductus arteriosus (PDA) ligation and identify predictors of recovery.

METHODS

Retrospective review of patients with VFI following PDA ligation from 2001 to 2012 at a single institution. Inclusion criteria were: (1) PDA ligation as only cardiac surgical procedure; (2) left VFI documented by laryngoscopy; (3) minimum follow up 120 days, with at least 2 laryngoscopies performed. Resolution of VFI was determined at follow-up laryngoscopy. Univariate logistic regression models were used to identify variables associated with VFI recovery.

RESULTS

66 subjects were included with median follow up of 3.0 (± 2.1) years. The mean gestational age was 24.5 ± 1.4 weeks, mean birth weight 673 ± 167 g, and mean age at procedure was 18.6 ± 14.3 days. Patients presented with respiratory symptoms (39%), dysphonia (78%) and dysphagia (55%). Resolution of VFI was observed in 2/66 (3%) patients. Recovery was documented at 20 days and 11 months respectively. Respiratory symptoms, dysphagia, and dysphonia persisted at last follow up in 11%, 47%, and 20% of patients.

CONCLUSIONS

VFI associated with ligation of the ductus arteriosus has a low rate of recovery. Clinical symptoms frequently persist, and as such regular follow-up by otolaryngologists to mitigate morbidity is indicated.

Lung mechanical changes following bronchoaspiration in a porcine model: differentiation of direct and indirect mechanisms

Bronchoaspiration results in local deterioration of lung function through direct damage and/or indirect systemic effects related to neurohumoral pathways. We distinguished these effects by selectively intubating the two main bronchi in pigs while a PEEP of 4 or 10cm H2O was maintained. Gastric juice was instilled only into the right lung. Lung mechanical and ventilation defects were assessed by measuring unilateral pulmonary input impedance (ZL,s) and the third phase slope of the capnogram (SIII) for each lung side separately before the aspiration and for 120min thereafter. Marked transient elevations in ZL,s parameters and SIII were observed in the affected lung after aspiration. Elevating PEEP did not affect these responses in the ZL,s parameters, whereas it prevented the SIII increases. None of these indices changed in the intact left lung. These findings furnish evidence of the predominance of the local direct damage over the indirect systemic effects in the development of the deterioration of lung function, and demonstrate the benefit of an initially elevated PEEP following aspiration.

Effect of high advanced glycation end-product diet on pulmonary inflammatory response and pulmonary function following gastric aspiration

It is not clear why some patients with aspiration advance to acute lung injury or acute respiratory distress syndrome, whereas others do not. The Western diet is high in advanced glycation end-products (AGEs), which have been found to be proinflammatory. We hypothesize that dietary AGEs exaggerate the pulmonary inflammatory response following gastric aspiration. CD-1 mice were randomized to receive either a low-AGE (LAGE) or a high-AGE (HAGE) diet for 4 weeks. Five hours after intratracheal instillation of acidified small gastric particles, pulmonary function was determined. Polymorphonuclear neutrophil counts, albumin, cytokine/chemokine, and tumor necrosis factor soluble receptor II concentrations in the bronchoalveolar lavage and lung myeloperoxidase activity were measured. Compared with LAGE-fed animals, those fed a HAGE diet had increased lung tissue resistance (P = 0.017), bronchoalveolar lavage albumin concentration (P < 0.05), pulmonary polymorphonuclear neutrophil counts (P = 0.0045), and lung myeloperoxidase activity (P = 0.002) following aspiration. In addition, the plasma levels of tumor necrosis factor soluble receptor II were significantly elevated (P < 0.05), whereas paradoxically levels of keratinocyte chemoattractant and monocyte chemoattractant protein 1 were decreased in mice with HAGE diet. In conclusion, a diet high in AGEs exacerbates acute lung injury following gastric aspiration as evidenced by increases in neutrophil infiltration, airway albumin leakage, and decreased pulmonary compliance. This is the first evidence implicating exacerbation of acute inflammatory lung injury by dietary AGEs. Targeting AGEs in the circulatory system may offer a therapeutic strategy for limiting lung injury following gastric aspiration.

The effect of gastric juice on interleukin-8 production by cystic fibrosis primary bronchial epithelial cells

CF patients are often treated with proton pump inhibitors (PPIs) to reduce acidic gastro-esophageal reflux (GER) and bronchial aspiration of duodeno-gastric contents is common in CF. We have previously demonstrated that gastric juice (GJ) from patients "on" PPI can induce interleukin-8 (IL-8) production by bronchial epithelial cells in culture. We hypothesized that such effect would be more pronounced in CF patients known to have high inflammatory susceptibility. We aimed to evaluate the effect of GJ on IL-8 production by primary bronchial epithelial cells (PBEC), derived from a CF patient and a healthy subject.

METHODS

PBEC obtained from one donor (normal PBEC) and one receptor (CF-PBEC) for lung transplantation were stimulated with GJ from patients "off" and "on" PPI. IL-8 levels were measured in the supernatant.

RESULTS

GJ from patients "on" PPI provoked a significant higher IL-8 production compared to GJ from patients "off" PPI, both in normal PBEC [462 (200-1468) vs. 11 (4-28) pg/ml, p=0.0001] as in CF-PBEC [1468 (841-2449) vs. 85 (26-131) pg/ml, p<0.0001]. Exposure of the cells to GJ "off" PPI and "on" PPI provoked significantly higher IL-8 production in the CF-PBEC compared to the normal PBEC ["off" PPI 85 (26-131) vs. 11 (4-28) pg/ml, p=0.01; "on" PPI 1468 (841-2449) vs. 462 (200-1468) pg/ml, p=0.01]. Filtration (0.20 μm) of the GJ "on" PPI, to eliminate large particles and bacterial sub-products, resulted in a significant decrease of IL-8 production.

CONCLUSION

Patients with CF, treated with PPIs, have GJ with high pH and high endotoxin levels. These patients often have GER and bronchial aspiration. The aspirated material (GJ "on" PPI) has a significantly enhanced inflammatory effect on CF bronchial epithelial cells in culture. As chronic PPI treatment in CF may result in a paradoxically increased inflammatory effect in the airways, alternative anti-reflux therapies should be considered in CF.

NADPH oxidase and Nrf2 regulate gastric aspiration-induced inflammation and acute lung injury

Recruitment of neutrophils and release of reactive oxygen species are considered to be major pathogenic components driving acute lung injury (ALI). However, NADPH oxidase, the major source of reactive oxygen species in activated phagocytes, can paradoxically limit inflammation and injury. We hypothesized that NADPH oxidase protects against ALI by limiting neutrophilic inflammation and activating Nrf2, a transcriptional factor that induces antioxidative and cytoprotective pathways. Our objective was to delineate the roles of NADPH oxidase and Nrf2 in modulating acute lung inflammation and injury in clinically relevant models of acute gastric aspiration injury, a major cause of ALI. Acid aspiration caused increased ALI (as assessed by bronchoalveolar lavage fluid albumin concentration) in both NADPH oxidase-deficient mice and Nrf2(-/-) mice compared with wild-type mice. NADPH oxidase reduced airway neutrophil accumulation, but Nrf2 decreased ALI without affecting neutrophil recovery. Acid injury resulted in a 120-fold increase in mitochondrial DNA, a proinflammatory and injurious product of cellular necrosis, in cell-free bronchoalveolar lavage fluid. Pharmacologic activation of Nrf2 by the triterpenoid 1-[2-cyano-3-,12-dioxooleana-1,9 (11)-dien-28-oyl]imidazole limited aspiration-induced ALI in wild-type mice and reduced endothelial cell injury caused by mitochondrial extract-primed human neutrophils, leading to the conclusion that NADPH oxidase and Nrf2 have coordinated, but distinct, functions in modulating inflammation and injury. These results also point to Nrf2 as a therapeutic target to limit ALI by attenuating neutrophil-induced cellular injury.

The effects of α-tocopherol on oxidative damage and serum levels of Clara cell protein 16 in aspiration pneumonitis induced by bile acids

Our aim in this study is to examine the effects of α-tocopherol (AT) on rats with aspiration pneumonitis induced with bile acids (BAs). The animals were divided in to four groups, namely saline group ( n = 7), saline + AT group ( n = 7), BA group ( n = 7), and BA + AT group ( n = 7). Saline and BA groups aspirated intratracheally with 1 ml/kg saline and 1 ml/kg bile acids, respectively. AT was given at 20 mg/kg/day dosage for 7 days to the groups. AT group was given 20 mg/kg/day AT for 7 days. Malondialdehyde (MDA), Clara cell protein 16 (CC-16), catalase (CAT), superoxide dismutase (SOD), as well as peribronchial inflammatory cell infiltration, alveolar septal infiltration, alveolar edema, alveolar exudate, alveolar histiocytes, and necrosis were evaluated. The CAT activity of the BA group was significantly lower than the saline group. In the BA + AT group, there was a significant increase in SOD and CAT activities when compared with that of the BA group. The CC-16 and MDA contents in the BA group were significantly higher than in the saline group. The CC-16 and MDA levels of the BA + AT group were significantly lower than BA group. Histopathologic changes were seen in BA group, and there was a significant decrease in the BA + AT group. In conclusion, AT might be beneficial in the treatment of aspiration pneumonitis induced by BAs because AT decreased oxidative damage and resulted in a decrease in CC-16 levels.

Acute lung injury and acute respiratory distress syndrome: experimental and clinical investigations

Acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) can be associated with various disorders. Recent investigation has involved clinical studies in collaboration with clinical investigators and pathologists on the pathogenetic mechanisms of ALI or ARDS caused by various disorders. This literature review includes a brief historical retrospective of ALI/ARDS, the neurogenic pulmonary edema due to head injury, the long-term experimental studies and clinical investigations from our laboratory, the detrimental role of NO, the risk factors, and the possible pathogenetic mechanisms as well as therapeutic regimen for ALI/ARDS.

Increased phospholipase A2 and lyso-phosphatidylcholine levels are associated with surfactant dysfunction in lung contusion injury in mice

OBJECTIVE

Surfactant dysfunction is an important pathologic disturbance in various forms of acute inflammatory lung injury. Previously we reported the presence of marked alterations in the composition and activity of pulmonary surfactant in bilateral lung contusions (LC) injury induced by blunt trauma in rats. This is extended here to a mouse model of unilateral LC with a focus on compositional and functional changes in surfactant associated with permeability injury and increases in activity of secretory phospholipase A2.

RESULTS

Surfactant-associated gene expression was not altered in mice with unilateral LC injury on the basis of Affymetrix analysis. LC mice had significant permeability injury with increased albumin and total protein in bronchoalveolar lavage at 5, 24, 48, and 72 hours after insult compared with uninjured controls. The percent content of large surfactant aggregates was depleted at all postinjury times, and pulmonary pressure-volume (P-V) mechanics and compliance were abnormal during this period. Surfactant dysfunction was evaluated in 24 hours, when permeability injury and P-V changes were most prominent. At this time, activity levels of secretory phospholipase A2 were increased in bronchoalveolar lavage, and chromatographic analysis showed that large surfactant aggregates had decreased levels of phosphatidylcholine and increased levels of lyso-phosphatidylcholine. These changes were accompanied by severe detriments in large aggregate surface activity by pulsating bubble surfactometry. Large aggregates from LC mice at 24 hours had minimum surface tensions of only 12.6 ± 1.1 mN/m after prolonged bubble pulsation (20 min) compared with 0.7 ± 0.03 mN/m for uninjured controls.

CONCLUSION

These results document important detriments in the composition and activity of pulmonary surfactant in LC injury in mice and suggest that active synthetic phospholipase-resistant exogenous surfactants may have utility in treating surfactant dysfunction in this clinically important condition.

Acute respiratory distress syndrome and lung injury: Pathogenetic mechanism and therapeutic implication

To review possible mechanisms and therapeutics for acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). ALI/ARDS causes high mortality. The risk factors include head injury, intracranial disorders, sepsis, infections and others. Investigations have indicated the detrimental role of nitric oxide (NO) through the inducible NO synthase (iNOS). The possible therapeutic regimen includes extracorporeal membrane oxygenation, prone position, fluid and hemodynamic management and permissive hypercapnic acidosis etc. Other pharmacological treatments are anti-inflammatory and/or antimicrobial agents, inhalation of NO, glucocorticoids, surfactant therapy and agents facilitating lung water resolution and ion transports. β-adrenergic agonists are able to accelerate lung fluid and ion removal and to stimulate surfactant secretion. In conscious rats, regular exercise training alleviates the endotoxin-induced ALI. Propofol and N-acetylcysteine exert protective effect on the ALI induced by endotoxin. Insulin possesses anti-inflammatory effect. Pentobarbital is capable of reducing the endotoxin-induced ALI. In addition, nicotinamide or niacinamide abrogates the ALI caused by ischemia/reperfusion or endotoxemia. This review includes historical retrospective of ALI/ARDS, the neurogenic pulmonary edema due to head injury, the detrimental role of NO, the risk factors, and the possible pathogenetic mechanisms as well as therapeutic regimen for ALI/ARDS.

Surfactant therapy for acute lung injury and acute respiratory distress syndrome

This article examines exogenous lung surfactant replacement therapy and its usefulness in mitigating clinical acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS). Surfactant therapy is beneficial in term infants with pneumonia and meconium aspiration lung injury, and in children up to age 21 years with direct pulmonary forms of ALI/ARDS. However, extension of exogenous surfactant therapy to adults with respiratory failure and clinical ALI/ARDS remains a challenge. This article reviews clinical studies of surfactant therapy in pediatric and adult patients with ALI/ARDS, focusing on its potential advantages in patients with direct pulmonary forms of these syndromes.

Neonatal hyperoxia contributes additively to cigarette smoke-induced chronic obstructive pulmonary disease changes in adult mice

The extent by which early postnatal lung injury contributes to the development of chronic obstructive pulmonary disease (COPD) in the adult is unclear. We hypothesized that exposure to hyperoxia during early postnatal life can augment lung changes caused by adult chronic cigarette smoke (CS) exposure. C57BL/6J mice (1 d old) were exposed to hyperoxia (O(2)) for 5 days. At 1 month of age, half of the O(2)-exposed mice and half of the control mice were placed in a CS chamber for 6 months. After exposure to CS, mice underwent quasi-static pressure-volume curve and mean chord length measurements; quantification of pro-Sp-c expression; and measurement of lung IL-8/ KC, CXCR2/IL8Rα, TNF-α, and IL-6 mRNA by real-time PCR. Adult mice exposed to O(2)+CS had significantly larger chord length measurements (P < 0.02) and lung volumes at 35 cm H(2)O (P < 0.05) compared with all other groups. They also had significantly less pro-Sp-c protein and surfactant protein C mRNA expression (P < 0.003). Mice exposed to O(2)+CS and CS-only mice had significantly higher lung resistance and longer mean time constants (P < 0.01), significantly more inflammatory cells in the bronchoalveolar lavage fluid (P < 0.03), and significantly higher levels of lung CXCR2/IL8Rα mRNA compared with mice not exposed to smoke (P < 0.02). We conclude that exposure to early postnatal hyperoxia contributed additively to CS-induced COPD changes in adult mice. These results may be relevant to a growing population of preterm children who sustained lung injury in the newborn period and may be exposed to CS in later life.

Aspiration-induced lung injury

OBJECTIVE

Aspiration of oropharyngeal or gastric contents into the lower respiratory tract is a common event in critically ill patients and can lead to pneumonia or pneumonitis. Aspiration pneumonia is the leading cause of pneumonia in the intensive care unit and is one of the leading risk factors for acute lung injury and acute respiratory distress syndromes. Despite its frequency, it remains largely a disease of exclusion characterized by ill-defined infiltrates on the chest radiograph and hypoxia. An accurate ability to diagnose aspiration is paramount because different modalities of therapy, if applied early and selectively, could change the course of the disease. This article reviews definitions, diagnosis, epidemiology, pathophysiology, including animal models of aspiration-induced lung injury, and evidence-based clinical management. Additionally, a review of current and potential biomarkers that have been tested clinically in humans is provided.

DATA SOURCES

Data were obtained from a PubMed search of the medical literature. PubMed "related articles" search strategies were used.

SUMMARY AND CONCLUSIONS

Aspiration in the intensive care unit is a clinically relevant problem requiring expertise and awareness. A definitive diagnosis of aspiration pneumonitis or pneumonia is challenging to make. Advances in specific biomarker profiles and prediction models may enhance the diagnosis and prognosis of clinical aspiration syndromes. Evidence-based management is supportive, including mechanical ventilation, bronchoscopy for particulate aspiration, consideration of empiric antibiotics for pneumonia treatment, and lower respiratory tract sampling to define pathogenic bacteria that are causative.

Cytotoxicity and induction of inflammation by pepsin in Acid in bronchial epithelial cells

Introduction. Gastroesophageal reflux has been associated with chronic inflammatory diseases and may be a cause of airway remodelling. Aspiration of gastric fluids may cause damage to airway epithelial cells, not only because acidity is toxic to bronchial epithelial cells, but also since it contains digestive enzymes, such as pepsin. Aim. To study whether pepsin enhances cytotoxicity and inflammation in airway epithelial cells, and whether this is pH-dependent. Methods. Human bronchial epithelial cells were exposed to increasing pepsin concentrations in varying acidic milieus, and cell proliferation and cytokine release were assessed. Results. Cell survival was decreased by pepsin exposure depending on its concentration (F = 17.4) and pH level of the medium (F = 6.5) (both P < 0.01). Pepsin-induced interleukin-8 release was greater at lower pH (F = 5.1; P < 0.01). Interleukin-6 induction by pepsin was greater at pH 1.5 compared to pH 2.5 (mean difference 434%; P = 0.03). Conclusion. Pepsin is cytotoxic to bronchial epithelial cells and induces inflammation in addition to acid alone, dependent on the level of acidity. Future studies should assess whether chronic aspiration causes airway remodelling in chronic inflammatory lung diseases.

Long-term morbidities associated with vocal cord paralysis after surgical closure of a patent ductus arteriosus in extremely low birth weight infants

OBJECTIVE

Determine associations between left vocal cord paralysis (LVCP) and poor respiratory, feeding and/or developmental outcomes in extremely low birth weight (ELBW) infants following surgical closure of a patent ductus arteriosus (PDA).

STUDY DESIGN

ELBW infants who underwent PDA ligation between January 2004 and December 2006 were identified. We compared infants with and without LVCP following ligation to determine relationships between LVCP and respiratory morbidities, feeding and growth difficulties and neurodevelopmental impairment at 18 to 22-month follow-up. Student's t-test, Fisher's exact test and multivariable regression analyses were used to determine associations.

RESULT

In all, 60 ELBW infants with a mean gestational age of 25 weeks and mean birth weight of 725 g had a PDA surgically closed. Twenty-two of 55 survivors (40%) were diagnosed with LVCP post-operatively. Infants with LVCP were significantly more likely to develop bronchopulmonary dysplasia (82 vs 39%, P=0.002), reactive airway disease (86 vs 33%, P<0.0001), or need for gastrostomy tube (63 vs 6%, P<0.0001).

CONCLUSION

LVCP as a complication of surgical ductal ligation in ELBW infants is associated with persistent respiratory and feeding problems. Direct laryngoscopy should be considered for all infants who experience persistent respiratory and/or feeding difficulties following PDA ligation.

Predictive modeling and inflammatory biomarkers in rats with lung contusion and gastric aspiration

BACKGROUND

This study uses statistical predictive modeling and hierarchical cluster analyses to examine inflammatory mediators and cells in bronchoalveolar lavage (BAL) as putative biomarkers in rats with blunt trauma lung contusion (LC), gastric aspiration (combined acid and small gastric food particles, CASP), or a combination of the two.

METHODS

Specific parameters assessed in the innate pulmonary inflammatory response were leukocytes, macrophages, and polymorphonuclear neutrophils (PMNs) in BAL; whole lung myeloperoxidase activity; and a series of cytokines or chemokines present in BAL at 5 or 24 hours after injury: tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, interferon-gamma, IL-10, macrophage inflammatory protein-2, cytokine-induced neutrophil chemoattractant-1, and monocyte chemoattractant protein-1.

RESULTS

Rats with LC, CASP, LC + CASP all had severe lung injury compared with uninjured controls based on decreased arterial oxygenation or increased BAL albumin at 5 or 24 hours postinsult. However, the injury groups had distinct overall patterns of inflammation that allowed them to be discriminated accurately by hierarchical cluster analysis (29 of 30 and 35 of 37 rats were correctly classified in hierarchical clusters at 5 and 24 hours, respectively). Moreover, predictive analyses based on an extension of standard receiver-operator characteristic methodology discriminated individual animals and groups with similar high accuracy based on a maximum of two inflammatory parameters per group (29 of 30 and 36 of 37 rats were correctly classified at 5 hours and 24 hours, respectively).

CONCLUSIONS

These results support the possibility that inflammatory biomarker profiles could be developed in the future to improve the diagnosis and management of trauma patients with unwitnessed (occult) gastric aspiration who have an increased risk of clinical acute lung injury or the acute respiratory distress syndrome.

Functional contribution of CXCR2 to lung injury after aspiration of acid and gastric particulates

The effects of individual ELR+ CXC chemokines have been documented in experimental models of acid aspiration. However, aspiration lung injury would be influenced by the combined effects of these chemokines and other factors related to their function. Therefore, the role of the chemokine receptor CXCR2 was examined in lung injury induced by aspiration of acid and acid with gastric particulates. Anesthetized mice were given intratracheal injections of saline, acid solution, or acid containing gastric particles. Within 6 h, bronchoalveolar lavage fluid neutrophils and albumin increased relative to the severity of the insult. Immunohistochemistry and RT-PCR demonstrated striking increases in pulmonary expression of CXCR2 after aspiration. In CXCR2-deficient mice, neutrophil recruitment to airways was significantly reduced after aspiration of either acid or acid with particles. However, lung injury scores were unaffected in Ccr2-/- mice in the acid + particles group. Esterase-stained lung tissue demonstrated that focal aggregates of inflammatory cells contained neutrophils in the Ccr2-/- mice. These studies suggest CXCR2 and its ligands are dominant mediators of neutrophil recruitment to airways after aspiration. However, CXCR2-independent mechanisms recruit neutrophils into areas of cellular aggregation after aspiration of acidified gastric particulates.

Exogenous surfactant instillation attenuates inflammatory response to acid-induced lung injury in rat

The present study was performed to investigate the role of exogenous surfactant on hydrochloric acid (HCL) - induced lung injury in rats. Six-week-old male Sprague-Dawley rats were anesthetized by intraperitoneal injection of pentobarbital sodium (40mg/kg) and HCL (0.1N, 2mL/kg) or normal saline (NS, 2mL/kg) was instilled into the trachea. Thirty minutes after HCL instillation, surfactant at a dose of 60mg (=2mL)/body or NS (2mL) was instilled into the rat lungs. Animals in another experimental group were also treated with the same dose of surfactant supplement 2hours after the first administration. Bronchoalveolar lavage fluid (BALF) was obtained 5hours after HCL instillation. In BALF, increases in total nuclear cell counts, neutrophil counts, optical density at 412nm as an indicator of pulmonary hemorrhage, neutrophil elastase activity, concentrations of albumin and cytokine-induced neutrophil chemoattractant (CINC) induced by HCL instillation were significantly attenuated by surfactant treatment. The wet-to-dry weight (W/D) ratio in the lung and partial oxygen tension (P(O2)) were also estimated; surfactant treatment significantly attenuated the W/D ratio and improved deteriorated P(O2) induced by HCL. Additional surfactant supplementation did not show further beneficial effects on HCL-induced lung injury compared with a single treatment. These results suggest that surfactant shows an anti-inflammatory effect on acid lung injury in rats but the beneficial effects may be dose limited.

Acid aspiration-induced airways hyperresponsiveness in mice

The role of gastroesophageal reflux and micro-aspiration as a trigger of airways hyperresponsiveness (AHR) in patients with asthma is controversial. The role of acid reflux and aspiration as a direct cause of AHR in normal subjects is also unclear. We speculated that aspiration of a weak acid with a pH (1.8) equivalent to the upper range of typical gastric contents would lead to AHR in naive mice. We further speculated that modest reductions in aspirate acidity to a level expected during gastric acid suppression therapy (pH 4.0) would impede aspiration-induced AHR. BALB/c female mice were briefly anesthetized with isoflurane and allowed to aspirate 75 microl of saline with HCl (pH 1.8, 4.0, or 7.4) or underwent sham aspiration. Mice were re-anesthetized 2 or 24 h later, underwent tracheostomy, and were coupled to a mechanical ventilator. Forced oscillations were used to periodically measure respiratory impedance (Zrs) following aerosol delivery of saline and increasing doses of methacholine to measure for AHR. Values for elastance (H), airways resistance (R(N)), and tissue damping (G) were derived from Zrs. Aspirate pH of 1.8 led to a significant overall increase in peak R(N), G, and H compared with pH 4.0 and 7.4 at 2 and 24 h. Differences between pH 7.4 and 4.0 were not significant. In mice aspirating pH 1.8 compared with controls, airway lavage fluid contained more neutrophils, higher protein, and demonstrated higher permeability. We conclude that acid aspiration triggers an acute AHR, driven principally by breakdown of epithelial barrier integrity within the airways.

Blockade of neutrophil responses in aspiration pneumonia via ELR-CXC chemokine antagonism does not predispose to airway bacterial outgrowth

Pneumonia associated with aspiration of bacterial-laden gastric contents is characterized by Glu-Leu-Arg (ELR)-CXC chemokine (e.g., CXC2L1, CXCL8) expression leading to local neutrophil sequestration. This neutrophil response is designed to be protective, but overly aggressive responses can be pathogenic in themselves. Herein we assessed whether blocking neutrophil responses in a guinea pig model of aspiration pneumonia would foster airway bacterial growth. Guinea pigs (n=5) were challenged intranasally with saline, acidified saline or acidified gastric contents (35mg/kg body weight, pH 2.0) and treated subcutaneously with 250mug/kg of the human ELR-CXC chemokine antagonist CXCL8((3-72))K11R/G31P (G31P) or saline. After 20h the animals' airway inflammatory responses and bacterial burdens were assessed. A loss of vascular integrity was apparent in the lungs of the saline-treated aspiration pneumonia animals (12.07+/-1.3% of the pleural surfaces exhibited hemorrhagic consolidation, 4.6x10(6) RBC/ml bronchoalveolar lavage fluid [BALF]), as was a pulmonary neutrophilia. The BAL fluids contained gram-negative and -positive bacteria (total load, 6.3+/-3.2x10(7) CFU/ml BALF) that are associated with nosocomial infections in humans. The G31P-treatments attenuated the pulmonary vascular complications (2.27+/-0.5% pleural surface hemorrhagic consolidation, 0.46x10(6) RBC/ml BALF), and reduced the pulmonary neutrophilia by >/=86%. The G31P-treatments did not lead to significant changes in the airway bacterial loads (total load, 3.46+/-1.8x10(7) CFU/ml BALF). This data indicates that attenuation of the pulmonary neutrophil response in aspiration pneumonia reduces pathology very significantly but does not reduce the efficiency of pulmonary bacterial clearance.

Neonatal oxygen adversely affects lung function in adult mice without altering surfactant composition or activity

Despite its potentially adverse effects on lung development and function, supplemental oxygen is often used to treat premature infants in respiratory distress. To understand how neonatal hyperoxia can permanently disrupt lung development, we previously reported increased lung compliance, greater alveolar simplification, and disrupted epithelial development in adult mice exposed to 100% inspired oxygen fraction between postnatal days 1 and 4. Here, we investigate whether oxygen-induced changes in lung function are attributable to defects in surfactant composition and activity, structural changes in alveolar development, or both. Newborn mice were exposed to room air or 40%, 60%, 80%, or 100% oxygen between postnatal days 1 and 4 and allowed to recover in room air until 8 wk of age. Lung compliance and alveolar size increased, and airway resistance, airway elastance, tissue elastance, and tissue damping decreased, in mice exposed to 60-80% oxygen; changes were even greater in mice exposed to 100% oxygen. These alterations in lung function were not associated with changes in total protein content or surfactant phospholipid composition in bronchoalveolar lavage. Moreover, surface activity and total and hydrophobic protein content were unchanged in large surfactant aggregates centrifuged from bronchoalveolar lavage compared with control. Instead, the number of type II cells progressively declined in 60-100% oxygen, whereas levels of T1alpha, a protein expressed by type I cells, were comparably increased in mice exposed to 40-100% oxygen. Thickened bundles of elastin fibers were also detected in alveolar walls of mice exposed to > or = 60% oxygen. These findings support the hypothesis that changes in lung development, rather than surfactant activity, are the primary causes of oxygen-altered lung function in children who were exposed to oxygen as neonates. Furthermore, the disruptive effects of oxygen on epithelial development and lung mechanics are not equivalently dose dependent.

Surfactant dysfunction in lung contusion with and without superimposed gastric aspiration in a rat model

This study investigates surfactant dysfunction in rats with lung contusion (LC) induced by blunt chest trauma. Rats at 24 h postcontusion had a decreased percent content of large surfactant aggregates in cell-free bronchoalveolar lavage (BAL) and altered large-aggregate composition with decreased phosphatidylcholine (PC), increased lyso-PC, and increased protein compared with uninjured controls. The surface activity of large aggregates on a pulsating bubble surfactometer was also severely impaired at 24 h postcontusion. Decreases in large surfactant aggregate content and surface activity were improved, but still apparent, at 48 and 72 h postcontusion compared with uninjured control rats and returned to normal by 96 h postcontusion. The functional importance of surfactant abnormalities in LC injury was documented in pilot studies showing that exogenous surfactant replacement at 24 h postcontusion improved inflation/deflation lung volumes. Additional experiments investigated a clinically relevant combination of LC plus gastric aspiration (combined acid and small gastric food particles) and found reductions in large surfactant aggregates in BAL similar to those for LC. However, rats given LC + combined acid and small gastric food particles versus LC had more severe surfactant dysfunction based on decreases in surface activity and alterations in large aggregate composition. Combined data for all animal groups had strong statistical correlations between surfactant dysfunction (increased minimum surface tension, decreased large aggregates in BAL, decreased aggregate PC, and increased aggregate lyso-PC) and the severity of inflammatory lung injury (increased total protein, albumin, protein/phospholipid ratio, neutrophils, and erythrocytes in BAL plus increased whole lung myeloperoxidase activity). These results show that surfactant dysfunction is important in the pathophysiology of LC with or without concurrent gastric aspiration and provides a rationale for surfactant replacement therapy in these prevalent clinical conditions.

Superimposed gastric aspiration increases the severity of inflammation and permeability injury in a rat model of lung contusion

INTRODUCTION

Lung contusion (LC) from blunt thoracic trauma is a clinically-prevalent condition that can progress to acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Patients with LC are at risk for gastric aspiration at the time of trauma, but the combined insults have not been well-studied in animal models. This study tests the hypothesis that concurrent gastric aspiration (combined acid and small gastric particles, CASP) at the time of trauma significantly increases permeability injury and inflammation compared with LC alone, and also modifies the inflammatory response to include distinct features compared with the aspiration component of injury.

MATERIALS AND METHODS

Four groups of adult male Long-Evans rats were studied (LC, CASP, LC+CASP, uninjured controls). LC was induced in anesthetized rats at a fixed impact energy of 2.0 J, and CASP (1.2 mL/kg body weight, 40 mg particles/mL, pH=1.25) was instilled through an endotracheal tube. Lung injury and inflammation were assessed by arterial blood gases and levels of albumin, cells, and cytokines/chemokines in bronchoalveolar lavage (BAL) at 5 and 24 h.

RESULTS

Rats with LC+CASP had lower mean PaO(2)/FiO(2) ratios compared with LC alone at 24 h, and higher BAL albumin concentrations compared with either LC or CASP alone. Rats with LC+CASP versus LC had more severe inflammation based on higher levels of PMN in BAL at 5 h, increased whole lung myeloperoxidase (MPO) activity at 5 and 24 h, and increased levels of inflammatory mediators in BAL (TNFalpha, IL-1beta, and MCP-1 at 5 and 24 h; IL-10, MIP-2, and CINC-1 at 5 h). Rats with LC+CASP also had distinct aspects of inflammation compared with CASP alone, i.e., significantly higher levels of IL-10 (5 and 24 h), IL-1beta (24 h), CINC-1 (24 h), and MCP-1 (24 h), and significantly lower levels of MPO (5 h), MIP-2 (5 h), and CINC-1 (5 h).

CONCLUSIONS

Concurrent gastric aspiration can exacerbate permeability lung injury and inflammation associated with LC, and also generates a modified inflammatory response compared with aspiration alone. Unwitnessed gastric aspiration has the potential to contribute to more severe forms of LC injury associated with progression to ALI/ARDS and pneumonia in patients with thoracic trauma.

Surfactant for pediatric acute lung injury

This article reviews exogenous surfactant therapy and its use in mitigating acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) in infants, children, and adults. Biophysical and animal research documenting surfactant dysfunction in ALI/ARDS is described, and the scientific rationale for treatment with exogenous surfactant is discussed. Major emphasis is placed on reviewing clinical studies of surfactant therapy in pediatric and adult patients who have ALI/ARDS. Particular advantages from surfactant therapy in direct pulmonary forms of these syndromes are described. Also discussed are additional factors affecting the efficacy of exogenous surfactants in ALI/ARDS.

Pepsin, a marker of gastric contents, is increased in tracheal aspirates from preterm infants who develop bronchopulmonary dysplasia

OBJECTIVE

The objective of this study was to study the association between pepsin in tracheal aspirate samples and the development of bronchopulmonary dysplasia in preterm infants.

METHODS

Serial tracheal aspirate samples were collected during the first 28 days from mechanically ventilated preterm neonates. Bronchopulmonary dysplasia was defined as the need for supplemental oxygen at 36 weeks' postmenstrual age. An enzymatic assay with a fluorescent substrate was used to detect pepsin. Total protein was measured by the Bradford assay to correct for the dilution during lavage. Immunohistochemistry using antibody against human pepsinogen was performed in 10 lung tissue samples from preterm infants.

RESULTS

A total of 256 tracheal aspirate samples were collected from 59 preterm neonates. Pepsin was detected in 234 (91.4%) of 256 of the tracheal aspirate samples. Twelve infants had no bronchopulmonary dysplasia, 31 infants developed bronchopulmonary dysplasia, and 16 infants died before 36 weeks' postmenstrual age. The mean pepsin concentration was significantly lower in infants with no bronchopulmonary dysplasia compared with those who developed bronchopulmonary dysplasia or developed bronchopulmonary dysplasia/died before 36 weeks' postmenstrual age. Moreover, the mean pepsin level was significantly higher in infants with severe bronchopulmonary dysplasia compared with moderate bronchopulmonary dysplasia. The mean pepsin level in tracheal aspirate samples from the first 7 days was also lower in infants with no bronchopulmonary dysplasia compared with those who developed bronchopulmonary dysplasia or developed bronchopulmonary dysplasia/died before 36 weeks' postmenstrual age. Pepsinogen was not localized in the lung tissues by immunohistochemistry.

CONCLUSION

The concentration of pepsin was increased in the tracheal aspirate of preterm infants who developed bronchopulmonary dysplasia or died before 36 weeks' postmenstrual age. Recovery of pepsin in tracheal aspirate samples is secondary to gastric aspiration, not by hematogenous spread or local synthesis in the lungs. Chronic aspiration of gastric contents may contribute in the pathogenesis of bronchopulmonary dysplasia.

Surfactant dysfunction and lung injury due to the E. coli virulence factor hemolysin in a rat pneumonia model

This study tests the hypothesis that the virulence factor hemolysin (Hly) expressed by extraintestinal pathogenic Escherichia coli contributes to surfactant dysfunction and lung injury in a rat model of gram-negative pneumonia. Rats were instilled intratracheally with CP9 (wild type, Hly-positive), CP9hlyA (Hly-minus), CP9/pEK50 (supraphysiological Hly), or purified LPS. At 6 h postinfection, rats given CP9 had a decreased percentage content of large surfactant aggregates in cell-free bronchoalveolar lavage (BAL), decreased large aggregate surface activity, decreased Pa(O2)/FiO2) ratio, increased BAL albumin/protein levels, and increased histological evidence of lung injury compared with rats given CP9hlyA or LPS. In addition, rats given CP9/pEK50 or CP9 had decreased large aggregate surface activity, decreased Pa(O2)/FiO2) ratios, and increased BAL albumin/protein levels at 2 h postinfection compared with rats given CP9hlyA. The severity of permeability lung injury based on albumin/protein levels in BAL at 2 h was ordered as CP9/pEK50 > CP9 > CP9hlyA > normal saline controls. Total lung titers of bacteria were increased at 6 h in rats given CP9 vs. CP9hlyA, but bacterial titers were not significantly different at 2 h, indicating that increased surfactant dysfunction and lung injury were associated with Hly as opposed to bacterial numbers per se. Further studies in vitro showed that CP9 could directly lyse transformed pulmonary epithelial cells (H441 cells) but that indirect lysis of H441 cells secondary to Hly-induced neutrophil lysis did not occur. Together, these data demonstrate that Hly is an important direct mediator of surfactant dysfunction and lung injury in gram-negative pneumonia.