Effect of subchronic in vivo exposure to nitrogen dioxide on lung tissue inflammation, airway microvascular leakage, and in vitro bronchial muscle responsiveness in rats

Short-Term Exposure to Air Pollution and Epiglottitis: A Nested Case-Control Study

OBJECTIVES/HYPOTHESIS

This study investigated the impacts of air pollution and meteorological factors on the occurrence of epiglottitis.

STUDY DESIGN

A nested case-control study.

METHODS

Participants ≥40 years old in the Korean National Health Insurance Service-Health Screening Cohort were analyzed. A total of 2,615 epiglottitis patients and 10,460 matched control participants were analyzed. The odds ratios (ORs) for epiglottitis associated with meteorological and air pollution factors, including sulfur dioxide (SO₂ , ppb), nitrogen dioxide (NO₂ , ppb), ozone (O₃ , ppb), and carbon monoxide (CO, ppm), after 3, 7, 15, and 30 days of exposure were analyzed using conditional logistic regression adjusted for total cholesterol, blood pressure, fasting blood glucose, obesity, smoking, alcohol consumption, prior upper respiratory infection, tonsillectomy, immunocompromise, autoimmune disease, and the Charlson comorbidity index.

RESULTS

The daily temperature range and NO₂ exposure after 3 days were associated with increased rates of epiglottitis (OR = 1.03, 95% confidence interval [CI] = 1.02-1.05 for temperature range and OR = 1.78, 95% CI = 1.14-2.77 for NO₂ , respectively). These results were generally consistent at 7, 15, and 30 days.

CONCLUSIONS

The temperature range and NO₂ exposure for 3, 7, 15, and 30 days were positively related to the occurrence of adult epiglottitis.

LEVEL OF EVIDENCE

3 Laryngoscope, 2021.

Effects of nitrous acid exposure on baseline pulmonary resistance and Muc5ac in rats

We examined the baseline pulmonary resistance (RLung), baseline dynamic lung compliance (Cdyn), cytokine inductions, and histological alterations in rats exposed to nitrous acid (HONO) with secondary products of nitrogen dioxide (NO₂) and nitric oxide (NO) to assess its biological effects. We exposed three groups of nine male F344 rats to different doses of HONO for six weeks (24 h/day). The cumulative values of HONO concentration were measured twice. The average concentrations of nitrogen oxide for each group were 5.8 parts per million (ppm) HONO with secondary products of 0.7 ppm NO₂ and 2.3 ppm NO, 4.1 ppm HONO with 0.1 ppm NO₂ and 0.6 ppm NO, and a clean air control. We measured baseline RLung and baseline Cdyn using tracheal cannulation. A tracheal tube was inserted into the trachea by tracheostomy, and lung function measurements (baseline RLung and baseline Cdyn) were conducted in mechanically ventilated rats. We measured mRNA levels of Cxcl-1, TNF-α, and Muc5ac in the right lung using quantitative RT-PCR, and observed histological alterations and the alveolar mean linear intercept (Lm) on the left lung. Our results demonstrated that HONO exposure significantly increased baseline RLung, Lm and Muc5ac expression, but did not affect baseline Cdyn or expression of Cxcl-1 and TNF-α. Further, we identified bronchial smooth muscle hypertrophy, pulmonary emphysema-like alterations in the alveolar duct centriacinar regions, and increased goblet cells in HONO-exposed rats. The present results suggest that HONO (with secondary products) adversely affects respiratory function, but that these pathologies may be unrelated to inflammation.

Phenotypical and functional characterization of alveolar macrophage subpopulations in the lungs of NO2-exposed rats

Background

Alveolar macrophages (AM) are known to play an important role in the regulation of inflammatory reactions in the lung, e.g. during the development of chronic lung diseases. Exposure of rats to NO₂ has recently been shown to induce a shift in the activation type of AM that is characterized by reduced TNF-α and increased IL-10 production. So far it is unclear, whether a functional shift in the already present AM population or the occurrence of a new, phenotypically different AM population is responsible for these observations.

Methods

AM from rat and mice were analyzed by flow cytometry for surface marker expression and in vivo staining with PKH26 was applied to characterize newly recruited macrophages. Following magnetic bead separation, AM subpopulations were further analyzed for cytokine, inducible NO synthase (iNOS) and matrix metalloproteinase (MMP) mRNA expression using quantitative RT-PCR. Following in vitro stimulation, cytokines were quantitated in the culture supernatants by ELISA.

Results

In untreated rats the majority of AM showed a low expression of the surface antigen ED7 (CD11b) and a high ED9 (CD172) expression (ED7^-/ED9^high). In contrast, NO₂ exposure induced the occurrence of a subpopulation characterized by the marker combination ED7⁺/ED9^low. Comparable changes were observed in mice and by in vivo labeling of resident AM using the dye PKH26 we could demonstrate that CD11b positive cells mainly comprise newly recruited AM. Subsequent functional analyses of separated AM subpopulations of the rat revealed that ED7⁺ cells showed an increased expression and production of the antiinflammatory cytokine IL-10 whereas TNF-α production was lower compared to ED7^- AM. However, iNOS and IL-12 expression were also increased in the ED7⁺ subpopulation. In addition, these cells showed a significantly higher mRNA expression for the matrix metalloproteinases MMP-7, -8, -9, and -12.

Conclusion

NO₂ exposure induces the infiltration of an AM subpopulation that, on the one hand may exert antiinflammatory functions by the production of high amounts of IL-10 but on the other hand may contribute to the pathology of NO₂-induced lung damage by selective expression of certain matrix metalloproteinases.

Comparison of effects ofin vivo nitrogen dioxide exposure starting from different periods on alveolar macrophage activity, assessed by a chemiluminescence technique in Brown-Norway rats

Nitrogen dioxide (NO2) has been extensively studied for its immune modulating effects on pulmonary cells. Alveolar macrophages (AMs) play an important role in pulmonary immunity. The Brown-Norway (BN) rat has been studied as a high-risk model of allergic diseases. In this study, BN rats were exposed to NO2 from the embryonic or weanling period (EP or WP, respectively). To evaluate the effects of NO2 exposure on pulmonary immunity, the activity levels of rat AMs were assessed as reactive oxygen species-generating capacity, measured by a chemiluminescence (CL) technique, and as cytokine-producing ability. Except for 0.2 ppm of NO2 exposure, the CL responses of AMs obtained from the WP group at 12 weeks old were suppressed significantly. Changes of the cytokine-producing levels suggest that inflammatory reactions are terminated at 12 weeks in the EP group. Correlations between the CL responses and the cytokine levels reveal that NO2 exposure may modulate the direction of AM activation. The CL technique is thought to be useful to evaluate changes in AM activity. In this study, the results suggest that, using the high-risk model of allergic diseases, NO2 exposure from the weanling period has stronger effects on AM activity.

NO2-induced airway inflammation is associated with progressive airflow limitation and development of emphysema-like lesions in C57BL/6 mice

The major features of chronic obstructive pulmonary disease (COPD) comprise a not fully reversible airflow limitation associated with an abnormal inflammatory response, increased mucus production and development of emphysema-like lesions. Animal models that closely mimic these alterations represent an important issue for the investigation of pathophysiological mechanisms. Since most animal models in this area have focused on specific aspects of the disease, we aimed to investigate whether exposure of C57BL/6 mice to nitrogen dioxide (NO2) may cause a more complex phenotype covering several of the characteristics of the human disease. Therefore, mice were exposed to NO2 for 14h each day for up to 25 days. Initial dose response experiments revealed the induction of a significant inflammatory response at a dose of 20 ppm NO2. Mice developed progressive airway inflammation together with a focal inflammation of the lung parenchyma characterized by a predominant influx of neutrophils and macrophages. In addition, goblet cell hyperplasia was detected in the central airways and increased collagen deposition was found in the lung parenchyma. NO2-exposed mice developed emphysema-like lesions as indicated by a significantly increased mean linear intercept as compared to control mice. Finally, the assessment of lung functional parameters revealed the development of progressive airway obstruction over time. In conclusion, our data provide evidence that the inflammatory response to NO2 exposure is associated with increased mucus production, development of airspace enlargement and progressive airway obstruction. Thus, NO2-exposed mice may serve as a model to investigate pathophysiological mechanisms that contribute to the development of human COPD.

Impaired superoxide radical production by bronchoalveolar lavage cells from NO(2)-exposed rats

Production of superoxide radicals is a central property of professional phagocytes used to combat invading microorganisms. Even though the number of macrophages and neutrophils is often increased in the lungs of patients with chronic lung diseases, these patients frequently suffer from bacterially induced exacerbations. To understand the underlying mechanisms, we investigated the production of superoxide radicals by bronchoalveolar lavage (BAL) cells in a rat NO(2) exposure model (10 ppm NO(2) for 1, 3, or 20 days). We showed that cells from NO(2)-exposed animals display a significantly impaired superoxide radical release after zymosan stimulation. The use of specific inhibitors (antimycin or diphenyleneiodonium [DPI]) revealed that the major enzyme systems, NADPH oxidase and complex III of the respiratory chain, are affected. In addition, we investigated gene expression and enzyme activities of antioxidant enzymes. mRNA expression was significantly enhanced for glutathione peroxidase (GPx)-3 and CuZn-superoxide dismutase (SOD) in BAL cells from animals exposed 3 and 20 days, and GPx and SOD enzyme activities were increased in BAL cells from rats exposed 20 days. In conclusion, concomitant occurrence of reduced production and increased scavenging of superoxide radicals resulted in the drastically impaired release of these radicals from BAL cells of NO(2)-exposed rats.

Shift toward an alternatively activated macrophage response in lungs of NO2-exposed rats

Inflammatory mechanisms are thought to play an important role in the pathogenesis of acute and chronic obstructive pulmonary diseases. In a rat inhalation model using continuous exposure to 10 ppm nitrogen dioxide for 1, 3, and 20 d, we investigated the inflammatory response with particular focus on the activation state of alveolar macrophages. Whereas the number of inflammatory cells and total protein concentration were increased in the bronchoalveolar lavage (BAL), the amount of the proinflammatory cytokine tumor necrosis factor-alpha was markedly reduced with increasing exposure time. In contrast, interleukin (IL)-10 and IL-6 were found at elevated levels and intracellular amounts of suppressor of cytokine signaling-3 protein increased in BAL cells. Upon in vitro lipopolysaccharide stimulation, BAL cells revealed reduced capability to produce the proinflammatory mediators tumor necrosis factor-alpha, IL-1 beta, and nitric oxide, but showed markedly increased transcription and protein release for IL-10. In addition, elevated levels of IL-6, scavenger receptor B, and suppressor of cytokine signaling-3 mRNA were detected in BAL cells from exposed animals. Analyses of highly purified alveolar macrophages indicated that changes in the activation state of these cells were responsible for the observed effects. In conclusion, a priming toward development of the alternatively activated macrophage phenotype occurred in the lungs of rats following nitrogen dioxide inhalation.

Bronchopulmonary inflammation and airway smooth muscle hyperresponsiveness induced by nitrogen dioxide in guinea pigs

We investigated whether acute exposure to nitrogen dioxide (NO2) causes major inflammatory responses (inflammatory cell recruitment, oedema and smooth muscle hyperresponsiveness) in guinea pig airways. Anaesthetised guinea pigs were exposed to 18 ppm NO2 or air for 4 h through a tracheal cannula. Bronchoalveolar lavage was performed and airway microvascular permeability and in vitro bronchial smooth muscle responsiveness were measured. Exposure to NO2 induced a significant increase in eosinophils and neutrophils in bronchoalveolar lavage fluid, microvascular leakage in the trachea and main bronchi (but not in peripheral airways), and a significant in vitro hyperresponsiveness to acetylcholine, electrical field stimulation, and neurokinin A, but not to histamine. Thus, this study shows that in vivo exposure to high concentrations of NO2 induces major inflammatory responses in guinea pig airways that mimic acute bronchitis induced by exposure to irritant gases in man.