Acute lung injury secondary to hydrochloric acid instillation induces small airway hyperresponsiveness

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a severe form of respiratory failure characterized by altered lung mechanics and poor oxygenation. Bronchial hyperresponsiveness has been reported in ARDS survivors and animal models of acute lung injury. Whether this hyperreactivity occurs at the small airways or not is unknown.

OBJECTIVE

To determine ex-vivo small airway reactivity in a rat model of acute lung injury (ALI) by hydrochloric acid (HCl) instillation.

METHODS

Twelve anesthetized rats were connected to mechanical ventilation for 4-hour, and randomly allocated to either ALI group (HCl intratracheal instillation; n=6) or Sham (intratracheal instillation of 0.9% NaCl; n=6). Oxygenation was assessed by arterial blood gases. After euthanasia, tissue samples from the right lung were harvested for histologic analysis and wet-dry weight ratio assessment. Precision cut lung slice technique (100-200 μm diameter) was applied in the left lung to evaluate ex vivo small airway constriction in response to histamine and carbachol stimulation, using phase-contrast video microscopy.

RESULTS

Rats from the ALI group exhibited hypoxemia, worse histologic lung injury, and increased lung wet-dry weight ratio as compared with the sham group. The bronchoconstrictor responsiveness was significantly higher in the ALI group, both for carbachol (maximal contraction of 84.5±2.5% versus 61.4±4.2% in the Sham group, P<0.05), and for histamine (maximal contraction of 78.6±5.3% versus 49.6±5.3% in the Sham group, P<0.05).

CONCLUSION

In an animal model of acute lung injury secondary to HCL instillation, small airway hyperresponsiveness to carbachol and histamine is present. These results may provide further insight into the pathophysiology of ARDS.

Case report of tracheobronchial injuries after acid ingestion: CT findings with serial follow-up: Airway complication after acid ingestion

RATIONALE

Tracheobronchial injury from acid ingestion is a less reported clinical presentation than injury of the gastrointestinal tract, but it can occur due to direct exposure from acid aspiration and cause fatal complications.

PATIENT CONCERNS

A 43-year-old man presented to the emergency department after ingesting nitric acid complaining of chest pain and dyspnea.

DIAGNOSES

The initial chest computed tomography (CT) images revealed an acute lung injury related to acid aspiration. The follow-up chest CT showed acute and late tracheobronchial injures.

INTERVENTIONS

Bronchoscopy showed deep caustic airway injuries consisting of hemorrhage, sloughing of the mucosa, and ulceration of the trachea and left-side bronchial tree.

OUTCOMES

Progressive narrowing of the left main bronchus with total collapse of the left lung occurred as a late complication of acid ingestion.

LESSONS

Tracheobronchial injury should be considered in cases of aspiration pneumonia after acid ingestion; chest CT can be used to detect and assess acute and late complications of tracheobronchial injuries.

The proteomic response is linked to regional lung volumes in ventilator-induced lung injury

It is unclear how acid-induced lung injury alters the regional lung volume response to mechanical ventilation (MV) and how this impacts protein expression. Using a mouse model, we investigated the separate and combined effects of acid aspiration and MV on regional lung volumes and how these were associated with the proteome. Adult BALB/c mice were divided into four groups: intratracheal saline, intratracheal acid, saline/MV, or acid/MV. Specific tidal volume (sVt) and specific end-expiratory volume (sEEV) were measured at baseline and after 2 h of ventilation using dynamic high-resolution four-dimensional computed tomography (4DCT) images. Lung tissue was dissected into 10 regions corresponding to the image segmentation for label-free quantitative proteomic analysis. Our data showed that acid aspiration significantly reduced sVt and caused further reductions in sVt and sEEV after 2 h of ventilation. Proteomic analysis revealed 42 dysregulated proteins in both Saline/MV and Acid/MV groups, and 37 differentially expressed proteins in the Acid/MV group. Mapping of the overlapping proteins showed significant enrichment of complement/coagulation cascades (CCC). Analysis of 37 unique proteins in the Acid/MV group identified six additional CCC proteins and seven downregulated proteins involved in the mitochondrial respiratory chain (MRC). Regional MRC protein levels were positively correlated with sEEV, while the CCC protein levels were negatively associated with sVt. Therefore, this study showed that tidal volume was associated with the expression of CCC proteins, while low end-expiratory lung volumes were associated with MRC protein expression, suggesting that tidal stretch and lung collapse activate different injury pathways.NEW & NOTEWORTHY This study provides novel insights into the regional response to mechanical ventilation in the setting of acid-induced lung injury and highlights the complex interaction between tidal stretch and low-end-expiratory lung volumes; both of which caused altered regulation of different injury pathways.

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.

Dendriform Pulmonary Ossification in the Absence of Usual Interstitial Pneumonia: CT Features and Possible Association With Recurrent Acid Aspiration

OBJECTIVE

Dendriform pulmonary ossification (DPO) is a rare lung disease in which mature bone is present in the peripheral interstitium of the lung. It typically occurs in patients with usual interstitial pneumonia (UIP). We assessed patients with CT findings of DPO without UIP to determine possible causative factors and to assess the clinical and CT course. We hypothesized that DPO without UIP would be a unique entity.

MATERIALS AND METHODS

We retrospectively reviewed CT reports for the word "ossification." Two observers reviewed each examination for micronodules 1-5 mm in diameter in the peripheral interstitium (subpleural and perifissural spaces and interlobular septa), some of which had high attenuation on mediastinal windows, presence of contiguous clusters of nodules resulting in a branching pattern, and lack of findings of UIP or focal lung disease. We reviewed the electronic medical records and follow-up CT and clinical information in all eligible patients.

RESULTS

The study population consisted of 52 men with a median age of 79 years old. Seventy-five percent of the patients had gastroesophageal reflux disease, obstructive sleep apnea, or a chronic neurologic disorder. No progressive pulmonary symptoms were attributed directly to DPO, and no patient developed pulmonary fibrosis or suffered clinical decline from DPO. CT showed minimal progression or remained stable at follow-up (77% for at least 1 year, 25% for over 4 years).

CONCLUSION

DPO in the absence of UIP occurs in elderly men and appears to be associated with chronic aspiration of gastric acid. The course is indolent.

Inhibition of TNF Receptor p55 By a Domain Antibody Attenuates the Initial Phase of Acid-Induced Lung Injury in Mice

BACKGROUND

Tumor necrosis factor-α (TNF) is strongly implicated in the development of acute respiratory distress syndrome (ARDS), but its potential as a therapeutic target has been hampered by its complex biology. TNF signals through two receptors, p55 and p75, which play differential roles in pulmonary edema formation during ARDS. We have recently shown that inhibition of p55 by a novel domain antibody (dAb™) attenuated ventilator-induced lung injury. In the current study, we explored the efficacy of this antibody in mouse models of acid-induced lung injury to investigate the longer consequences of treatment.

METHODS

We employed two acid-induced injury models, an acute ventilated model and a resolving spontaneously breathing model. C57BL/6 mice were pretreated intratracheally or intranasally with p55-targeting dAb or non-targeting "dummy" dAb, 1 or 4 h before acid instillation.

RESULTS

Acid instillation in the dummy dAb group caused hypoxemia, increased respiratory system elastance, pulmonary inflammation, and edema in both the ventilated and resolving models. Pretreatment with p55-targeting dAb significantly attenuated physiological markers of ARDS in both models. p55-targeting dAb also attenuated pulmonary inflammation in the ventilated model, with signs that altered cytokine production and leukocyte recruitment persisted beyond the very acute phase.

CONCLUSION

These results demonstrate that the p55-targeting dAb attenuates lung injury and edema formation in models of ARDS induced by acid aspiration, with protection from a single dose lasting up to 24 h. Together with our previous data, the current study lends support toward the clinical targeting of p55 for patients with, or at risk of ARDS.

The effect of matrix metalloproteinase-3 deficiency on pulmonary surfactant in a mouse model of acute lung injury

The acute respiratory distress syndrome (ARDS) is characterized by arterial hypoxemia accompanied by severe inflammation and alterations to the pulmonary surfactant system. Published data has demonstrated a protective effect of matrix metalloproteinase-3 (Mmp3) deficiency against the inflammatory response associated with ARDS; however, the effect of Mmp3 on physiologic parameters and alterations to surfactant have not been previously studied. It was hypothesized that Mmp3 deficient (Mmp3(-/-)) mice would be protected against lung dysfunction associated with ARDS and maintain a functional pulmonary surfactant system. Wild type (WT) and Mmp3(-/-) mice were subjected to acid-aspiration followed by mechanical ventilation. Mmp3(-/-) mice maintained higher arterial oxygenation compared with WT mice at the completion of ventilation. Significant increase in functional large aggregate surfactant forms were observed in Mmp3(-/-) mice compared with WT mice. These findings further support a role of Mmp3 as an attractive therapeutic target for drug development in the setting of ARDS.

Soluble Receptor for Advanced Glycation End-Products Predicts Impaired Alveolar Fluid Clearance in Acute Respiratory Distress Syndrome

RATIONALE

Levels of the soluble form of the receptor for advanced glycation end-products (sRAGE) are elevated during acute respiratory distress syndrome (ARDS) and correlate with severity and prognosis. Alveolar fluid clearance (AFC) is necessary for the resolution of lung edema but is impaired in most patients with ARDS. No reliable marker of this process has been investigated to date.

OBJECTIVES

To verify whether sRAGE could predict AFC during ARDS.

METHODS

Anesthetized CD-1 mice underwent orotracheal instillation of hydrochloric acid. At specified time points, lung injury was assessed by analysis of blood gases, alveolar permeability, lung histology, AFC, and plasma/bronchoalveolar fluid measurements of proinflammatory cytokines and sRAGE. Plasma sRAGE and AFC rates were also prospectively assessed in 30 patients with ARDS.

MEASUREMENTS AND MAIN RESULTS

The rate of AFC was inversely correlated with sRAGE levels in the plasma and the bronchoalveolar fluid of acid-injured mice (Spearman's ρ = -0.73 and -0.69, respectively; P < 10(-3)), and plasma sRAGE correlated with AFC in patients with ARDS (Spearman's ρ = -0.59; P < 10(-3)). Similarly, sRAGE levels were significantly associated with lung injury severity, and decreased over time in mice, whereas AFC was restored and lung injury resolved.

CONCLUSIONS

Our results indicate that sRAGE levels could be a reliable predictor of impaired AFC during ARDS, and should stimulate further studies on the pathophysiologic implications of RAGE axis in the mechanisms leading to edema resolution. Clinical trial registered with www.clinicaltrials.gov (NCT 00811629).

Synergy between acid and endotoxin in an experimental model of aspiration-related lung injury progression

Aspiration is a common cause of lung injury, but it is unclear why some cases are self-limited while others progress to acute respiratory distress syndrome (ARDS). Sporadic exposure to more than one insult could account for this variable progression. We investigated whether synergy between airway acid and endotoxin (LPS) amplifies injury severity in mice and whether LPS levels in human patients could corroborate our experimental findings. C57BL/6 mice aspirated acid (pH 1.3) or normal saline (NS), followed by LPS aerosol or nothing. Bronchoalveolar lavage fluid (BALF) was obtained 2 to 49 h later. Mice were injected with FITC-dextran 25 h after aspiration and connected to a ventilator, and lung elastance (H) measured periodically following deep inflation (DI). Endotracheal and gastric aspirates were also collected from patients in the intensive care unit and assayed for pH and LPS. Lung instability (ΔH following DI) and pressure-volume hysteresis in acid- or LPS-exposed mice was greater than in controls but markedly greater in the combined acid/LPS group. BALF neutrophils, cytokines, protein, and FITC-dextran in the acid/LPS mice were geometrically higher than all other groups. BALF from acid-only mice markedly amplified LPS-induced TNF-α production in cultured macrophages. Human subjects had variable endotracheal LPS levels with the highest burden in those at higher risk of aspiration. Acid aspiration amplifies LPS signaling in mice to disrupt barrier function and lung mechanics in synergy. High variation in airway LPS and greater airway LPS burden in patients at higher risk of aspiration could help explain the sporadic progression of aspiration to ARDS.

Localized acid instillation by a wedged-catheter method reveals a role for vascular gap junctions in spatial expansion of acid injury

Acid aspiration is a major cause of acute lung injury. However, the mechanisms that underlie this spatial expansion of the injury remain undefined. In current animal models of acid injury, intratracheal acid instillation replicates the lung injury. However intratracheal instillation causes a global effect, precluding studies of how the injury spreads. Here, we report an airway catheter-based method for localized acid delivery in the isolated blood-perfused rat lung. We co-instilled hydrochloric acid with evans blue through the catheter into one lung and determined blood-free extravascular lung water in tissue samples from regions that either received, or did not receive the instilled acid. Tissue samples from the noncatheterized contralateral lung were used as controls. Lung water increased both in the regions that received acid, as well as in adjacent regions that did not. Pretreating the lung with vascular infusions of the gap junctional blocker, glycerrhetinic acid, blunted the acid-induced lung water increase at the adjacent regions. These findings indicate that endothelial gap junction communication causes spread of lung injury from regions that were directly acid injured, to adjacent sites that did not directly receive acid. Our new method for establishing localized acid injury provides evidence for a novel role for vascular gap junctions in the spatial expansion of acid injury.

Effects of pentoxifylline on TNF-alpha and lung histopathology in HCL-induced lung injury

OBJECTIVE

To evaluate the effects of pentoxifylline on hydrochloric acid-induced lung lesions in rats subjected to mechanical ventilation.

METHODS

Twenty male, adult Wistar-EPM-1 rats were anesthetized and randomly grouped (n=5 animals per group) as follows: control-MV (mechanical ventilation, MV group); bilateral instillation of HCl (HCl group); bilateral instillation of HCl followed by pentoxifylline (50 mg/kg bw) infusion (HCl+PTX group) and pentoxifylline infusion followed by bilateral instillation of HCl (PTX+HCl group). At 20, 30, 90 and 180 min after treatments, the blood partial pressures of CO2 and O2 were measured. The animals were euthanized, and bronchoalveolar lavages were taken to determine the contents of total proteins, corticosterone [corrected] and TNF-alpha. Samples of lung tissue were used for histomorphometric studies and determining the wet-to-dry (W/D) lung weight ratio.

RESULTS

In the MV group, rats had alveolar septal congestion, and, in the HCl group, a remarkable recruitment of neutrophils and macrophages into the alveoli was noticed; these events were reduced in the animals with PTX+HCl. The partial pressure of oxygen increased in PTX+HCl animals (121+/-5 mmHg) as compared with the HCl (62+/-6 mmHg) and HCl+PTX (67+/-3 mmHg) groups within 30 minutes. TNF-alpha levels in bronchoalveolar lavage were significantly higher in the HCl group (458+/-50 pg/mL), reduced in the HCl+PTX group (329+/-45 pg/mL) and lowest in the PTX+HCl group (229+/-41 pg/mL). The levels of corticosterone [corrected] in bronchoalveolar lavage were significantly lower in the HCl (8+/-1.3 ng/mL) and HCl+PTX group (16+/-2 ng/mL) and were highest in the PTX+HCl (27+/-1.9 ng/mL).

CONCLUSION

Pretreatment with PTX improves oxygenation, reduces TNF-alpha concentration and increases the concentration of corticosterone [corrected] in bronchoalveolar lavage upon lung lesion induced by HCl.

Switching between intravenous and oral pantoprazole

Proton pump inhibitors (PPIs) are the most effective antisecretory drugs available for controlling gastric acid acidity and volume. They are the drugs of choice in the treatment of moderate-to-severe gastroesophageal reflux disease, hypersecretory disorders, and peptic ulcers. Currently in the United States, they are only available in an oral formulation. However, pantoprazole will soon be available in an intravenous formulation and will extend the power of PPIs to inpatient hospital settings. Intravenous pantoprazole has been shown to be effective and safe in clinical trials. Intravenous pantoprazole is indicated for the treatment of patients who require PPI therapy but who are unable to take oral medication. Intravenous pantoprazole has been shown to maintain acid suppression in patients switched from oral PPIs, so no change in dosage is required when switching from one formulation to the other. Potential hospital-based uses for intravenous PPI therapy include perioperative use as prophylaxis for acid aspiration syndrome during induction of anesthesia, prophylaxis for stress-related mucosal disease, and management of gastrointestinal bleeding from stress or acid peptic disease.