Carbon Monoxide Releasing Molecule-2-Upregulated ROS-Dependent Heme Oxygenase-1 Axis Suppresses Lipopolysaccharide-Induced Airway Inflammation

The up-regulation of heme oxygenase-1 (HO-1) is mediated through nicotinamaide adenine dinucleotide phosphate (NADPH) oxidases (Nox) and reactive oxygen species (ROS) generation, which could provide cytoprotection against inflammation. However, the molecular mechanisms of carbon monoxide-releasing molecule (CORM)-2-induced HO-1 expression in human tracheal smooth muscle cells (HTSMCs) remain unknown. Here, we found that pretreatment with CORM-2 attenuated the lipopolysaccharide (LPS)-induced intercellular adhesion molecule (ICAM-1) expression and leukocyte count through the up-regulation of HO-1 in mice, which was revealed by immunohistochemistrical staining, Western blot, real-time PCR, and cell count. The inhibitory effects of HO-1 by CORM-2 were reversed by transfection with HO-1 siRNA. Next, Western blot, real-time PCR, and promoter activity assay were performed to examine the HO-1 induction in HTSMCs. We found that CORM-2 induced HO-1 expression via the activation of protein kinase C (PKC)α and proline-rich tyrosine kinase (Pyk2), which was mediated through Nox-derived ROS generation using pharmacological inhibitors or small interfering ribonucleic acids (siRNAs). CORM-2-induced HO-1 expression was mediated through Nox-(1, 2, 4) or p47^phox, which was confirmed by transfection with their own siRNAs. The Nox-derived ROS signals promoted the activities of extracellular signal-regulated kinase 1/2 (ERK1/2). Subsequently, c-Fos and c-Jun-activator protein-1 (AP-1) subunits-were up-regulated by activated ERK1/2, which turned on transcription of the HO-1 gene by regulating the HO-1 promoter. These results suggested that in HTSMCs, CORM-2 activates PKCα/Pyk2-dependent Nox/ROS/ERK1/2/AP-1, leading to HO-1 up-regulation, which suppresses the lipopolysaccharide (LPS)-induced airway inflammation.

Hydrogen sulfide exposure triggers chicken trachea inflammatory injury through oxidative stress-mediated FOS/IL8 signaling

Hydrogen sulfide (H₂S) is well known to cause irritation and damage to airway following inhalation, but the mechanism by which H₂S contributes to airway toxicity is unclear. In order to assess the respiratory toxicity of H₂S inhalation in chicken trachea, we investigated the change of oxidative stress parameters, tracheal tissue structure and transcriptome profiles of chicken trachea exposed to H₂S for 42 days. The results showed H₂S exposure induced oxidative stress and inflammation in trachea. The ultrastructural analysis revealed loss of cilia and accumulation of mucus in tracheal epithelium. Differentially expressed genes (DEGs) analysis indicated 454 genes were significantly changed, including 136 genes upregulated and 318 genes downregulated. Gene ontology and KEGG analysis showed many genes involved in response to oxidative stress, inflammatory and immune response, which might contribute to H₂S-induced tracheal inflammatory injury. Among those genes, N-acetyl-L-cysteine (NAC) treatment blocked the H₂S-triggered expression of FOS and IL8. Silencing FOS by siRNA inhibited H₂S-induced expression of IL8. Taken together, we concluded that H₂S induced oxidative stress leads to tracheal inflammation through FOS/IL8 signaling, leading to excessive mucus secretion and absence of cilia. These results provide new insights for unveiling the biological effects of H₂S in vivo and in vitro.

Staphylococcal alpha-toxin causes increased tracheal epithelial permeability

Staphylococcus aureus is an important cause of pulmonary infections. The role of S. aureus alpha-toxin as a virulence factor is unclear. We hypothesized that airway epithelium is a target of S. aureus alpha-toxin and that exposure of airway epithelium to alpha-toxin results in damage to the airway epithelium. To examine the hypothesis that alpha-toxin is capable of independently producing airway epithelium damage as measured by permeability and morphometry, an isolated whole mouse trachea test apparatus was developed. In vitro epithelial permeability (P) was calculated and digital micrographs were analyzed morphometrically. Purified S. aureus alpha-toxin produced a significant increase in tracheal epithelial P (P < 0.05). Morphometric analysis revealed the ratio of adherent tracheal epithelium attached to the basement membrane divided by the total length of the basement membrane decreased in a dose-dependent manner with 1 microg/ml alpha-toxin and 10 microg/ml alpha-toxin (P < 0.05). We developed a novel isolated whole mouse trachea test apparatus for the measurement of tracheal epithelium damage. Increased P and separation of the tracheal epithelium from the basement membrane occurred after S. aureus alpha-toxin exposure. We conclude that mammalian airway epithelium is a target of S. aureus alpha-toxin.

Production of pro-inflammatory polypeptides by airway mucous glands and its potential significance

Burn patients often develop respiratory distress and ARDS several days after injury. An ovine model allows experimental study of this problem. In sheep the injury is characterized by intense acute inflammation in the trachea and bronchi from 3 to 48h after injury, with accumulation of neutrophils, fibrin and other plasma proteins, and mucus in airway lumens. We have carried out immunostaining for multiple cytokines in this model, including interleukin-8 (IL-8), Interleukin-1 beta (IL-1beta), interleukin-1 alpha (IL-1alpha), tumor necrosis factor-alpha (TNF-alpha), and vascular endothelial growth factor (VEGF). All of these show intense immunostaining in airway mucous glands. IL-1beta and VEGF show substantial constitutive staining in the serous cells of mucous glands, while IL-8, IL-1alpha, and TNF-alpha show substantially increased expression after injury. This pattern of expression of cytokines in mucous glands, and the apparent release of cytokines into the lumen after injury, are considered potentially highly significant in the progression of injury in this model. In addition, a proinflammatory function of mucous glands might prove to be important in chronic lung diseases such as chronic bronchitis and asthma.

Assessing the effects of racemic and single-enantiomer albuterol on airway secretions in long-term intubated patients

OBJECTIVE

In vitro data suggest that the S-enantiomer of albuterol can induce mucociliary dysfunction. This clinical study assesses the clinical significance of standard doses of the S-enantiomer on airway secretions in long-term intubated patients by comparing a racemic formulation of albuterol, an R-enantiomer formulation, and normal saline solution.

DESIGN

A placebo-controlled crossover study.

PATIENTS

Fourteen stable intubated patients with a median duration of intubation of 21 months and a median age of 72 years.

SETTING

Long-term ventilator unit in skilled nursing facility.

INTERVENTIONS

Following a 2-week washout period during which regularly scheduled beta2-agonists were discontinued, tracheal aspirates were collected for 4 h/d for a 5-day period to establish baseline values, and the patients were then randomized in crossover manner to each of three nebulized treatments: normal saline solution, racemic albuterol, and R-albuterol. Each treatment was administered three times daily for 5 days, followed by a 2-day washout.

MEASUREMENTS

Tracheal aspirates were analyzed for volume, sodium, chloride, bicarbonate, interleukin (IL)-8, IL-1beta, soluble intercellular adhesion molecule, and tumor necrosis factor-alpha.

RESULTS

There were no consistent significant differences among the three treatment periods either in terms of volume of secretions or in the concentrations of the electrolytes or the inflammatory indexes. However, all three treatments, including saline solution, were associated with increased secretion volume after the first dose, but this effect was not apparent on subsequent doses.

CONCLUSION

There were no significant differences between racemic albuterol and R-albuterol observed in this study for any of the parameters studied, suggesting that the S-enantiomer does not adversely affect airway secretions at recommended doses. In addition, the routine administration of nebulized beta(2)-sympathomimetic agonists to stable patients undergoing prolonged intubation, for the sole purpose of changing the volume and composition of secretions of airway secretions, is not supported by the results of this study.

Elevated Tissue Kallikrein Activity in Airway Secretions from Patients with Tracheobronchitis Associated with Prolonged Mechanical Ventilation

The clinical course of patients undergoing prolonged mechanical ventilation is often complicated by the development of purulent tracheobronchitis. The purpose of this study was to assess whether ventilator-associated hypersecretion is associated with elevated levels of tissue kallikrein (TK) activity. TK can induce marked bronchial inflammation in animal models and TK activity is increased in the airway secretions of symptomatic asthmatics. It has not been studied in conditions with predominantly neutrophilic bronchial secretions, although animal data indicate that neutrophil elastase may stimulate TK activity. We measured TK activity in airway secretions of patients undergoing mechanical ventilation for more than 4 weeks (PMV group) and in two comparator groups: patients with cystic fibrosis, who were colonized with Pseudomonas aeruginosa (CF group) and patients undergoing mechanical ventilation for less than one week who did not have clinical evidence of purulent airway secretions (acute mechanical ventilation, AMV group). We also compared the level of neutrophil elastase (NE) activity, an index of neutrophil activation, in the three patient groups. TK and NE activity in the sol phase were measured by the degradation of chromogenic substrates (DL Val-Leu-Arg pNA and N-Methoxy Succinyl Ala-Ala-Pro-Val pNA, respectively). Intergroup differences in cell counts were not significant. However, TK activity was significantly less in the AMV group than in the PMV and cystic fibrosis patients (Kruskal-Wallis ANOVA, p < 0.05). Elastase activity was significantly greater in the CF group (p < 0.05) than in the other two groups. Compared to patients undergoing short-term mechanical ventilation (AMV group), TK activity was elevated in patients with purulent tracheobronchitis associated with prolonged mechanical ventilation (PMV group). The elevation in TK activity in these patients is comparable to levels in sputum from patients with cystic fibrosis (CF group), although the latter had a significantly higher level of NE activity. The observation of increased TK activity in patients with neutrophilic airway inflammation suggests that TK may play a role in modulating inflammation in ventilator-associated tracheobronchitis and may be worthy of further study to determine its source and significance.

Mucin-producing elements and inflammatory cells

Airway goblet cells and submucosal glands form the major sources of human respiratory mucins. In the adult, mucus-secreting glands occupy about one-third of the inner airway wall wherever there is supportive cartilage (i.e. from the larynx to small bronchi). In hypersecretory conditions such as chronic bronchitis, asthma and cystic fibrosis, glands are considered to be the major source of tracheobronchial mucus, especially that which is expectorated abnormally as sputum. In contrast, goblet cells are regularly found throughout the tracheobronchial tree. Normally sparse or absent in bronchioles (i.e. small airways of less than 1 mm diameter), goblet cells appear and increase in number in airway hypersecretory conditions: their secretions likely contribute to airflow obstruction and early closure of bronchioles, especially during expiration. The increase in gland mass has been considered to be the histological correlate of mucus-hypersecretion in conditions such as chronic bronchitis. However, there appears to be a better association of sputum production with scores of airway wall inflammation than with gland size per se. Thus, while the absolute mass of mucus-secreting tissue is important, it is likely that the release of inflammatory cell secretions (e.g. neutrophil elastase, mast cell chymotryptase), mediators of inflammation (e.g. interleukin 4, 13) and products of the metabolism of arachidonic acid (such as 15-HETE) contribute more than previously realized to the hypersecretion of mucus in chronic bronchitis. New data discussed herein provide supportive evidence for this hypothesis and identify a newly reported link between plasma cells and mucus-hypersecretion by submucosal glands. These considerations demonstrate the complexity of targets that need to be considered for the treatment of mucus hypersecretion.

Dendritic cell influx differs between the subglottic and glottic mucosae during acute laryngotracheitis induced by a broad spectrum of stimuli

Clinically, the subglottic and glottic mucosae may react differently, eg, during acute laryngotracheitis. In healthy rats, we showed previously that the composition of the mucosal immune system of the larynx also differs between these areas. Neutrophils, lymphocytes, and dendritic cells (DCs) are part of this mucosal immune system. In particular, DCs occupy a key function. They migrate into inflamed mucosae during the early phase of the immune response, which is normally characterized by an influx of neutrophils. Thus, they help to overcome the time lag between the innate and the adaptive immune responses. In the present study, the influx of DCs, neutrophils, and T lymphocytes into the subglottic and glottic mucosae of rats was examined at different time points after challenge with a broad spectrum of stimuli such as dead Moraxella catarrhalis, viable Bordetella pertussis, viable Sendai virus, and the soluble protein ovalbumin. The number of DCs increased rapidly after the application of the antigens. This increase was as rapid as the increase in neutrophils. Depending on the kind of antigen, their number in the mucosa increased up to 1,000 cells per 0.1 mm2 (Sendai virus). The comparison of different mucosal areas shows that an overwhelming number of immunocompetent cells entered the subglottic mucosa, whereas only a few cells migrated into the adjacent glottic mucosa. In conclusion, after inhalation of different kinds of antigens, the subset of immunocompetent cells investigated in this study entered the laryngeal mucosa in high numbers. The number of DCs entering the laryngeal mucosa was higher than the numbers of the other immune cells investigated. This finding underlines their function as first-line sentinels of the mucosal immune system of the larynx. The observation that the number of cells entering the laryngeal mucosa is location-dependent indicates the ability of adjacent laryngeal regions to react differently. This is similar to the clinical observation of a selective subglottic reaction during acute laryngotracheitis.

Plasma extravasation in the rat trachea induced by cold air is mediated by tachykinin release from sensory nerves

Cold air was delivered to anesthetized, artificially ventilated, pathogen-free F344 rats via a tracheal cannula. Inhalation of cold air increased Evans blue dye extravasation in the trachea in a time-dependent (1 to 10 min) manner. Plasma extravasation increased after 3 min exposure to cold air and reached a maximum after 10 min exposure. The neutral endopeptidase inhibitor, phosphoramidon (2.5 mg/kg, intravenously), increased by 84% the plasma extravasation induced by inhalation of cold air for 1 min. The plasma extravasation evoked by 5 min exposure to cold air was abolished by the NK1 tachykinin receptor antagonist, CP-99,994 (4 mg/kg, intravenously); was reduced 30% by the B2 bradykinin receptor antagonist, HOE140 (0.1 mumol/kg, intravenously); and was not affected by H1 (pyrilamine, 10 mg/kg, intraperitoneally) or H2 (cimetidine, 10 mg/kg, intraperitoneally) histamine receptor antagonists or the cyclooxygenase inhibitor indomethacin (5 mg/kg, intravenously). In rats infected with Sendai virus, plasma extravasation evoked by inhalation of cold air was greater than in pathogen-free rats. Pretreatment with CP-99,994 (4 mg/kg, intravenously) inhibited completely the plasma extravasation induced by cold air in virus-infected rats. These findings indicate that cold air increases plasma extravasation in the rat trachea by a neurogenic mechanism that involves the release of tachykinins from sensory nerves. Kinin release may also play a role in this neurogenic inflammatory response.

Hydrogen peroxide-induced epithelial damage increases terbutaline transport in guinea-pig tracheal wall: implications for drug delivery

An isolated vagus nerve-tracheal tube preparation from guinea-pig was treated intraluminally with hydrogen peroxide (H2O2) at various concentrations. Exposure to, 100 mmol/L H2O2 for 20 min was chosen for further experiments since it appeared to cause selective damage to the epithelium. Thus the subepithelial layers of the tracheal wall appeared intact as judged by light microscopic examination. The response to nerve stimulation (increase in intratracheal pressure) was attenuated by only about 20%. Terbutaline administration into the tracheal lumen caused a concentration-dependent inhibition of the response to nerve stimulation. In tracheal preparations pretreated with 100 mmol/L H2O2 there was a 20-fold decrease in the EC50 for terbutaline. The EC50 for terbutaline added to the external medium was not changed by the H2O2 pretreatment. The efflux of 3H-terbutaline from the tracheal lumen into the external medium was three times higher in H2O2-treated than in control preparations. It is concluded that in the H2O2-damaged epithelium the absorption of terbutaline is enhanced resulting in a better availability of the drug in the smooth muscle layer after intraluminal administration.

Growth of Bacteroides fragilis in rabbit tracheal organ culture: anaerobiosis and tissue respiration

Rabbit tracheal explants supporting growth of inoculated Bacteroides fragilis in air were shown to keep low oxygen tension. Treating the explants with sodium azide induced high oxygen tension and arrested reversibly the growth of B. fragilis.