Effect of nitrogen dioxide on ovalbumin-induced allergic airway disease in a murine model

The National Environmental Respiratory Center (NERC) experiment in multi-pollutant air quality health research: II. Comparison of responses to diesel and gasoline engine exhausts, hardwood smoke and simulated downwind coal emissions

The NERC Program conducted identically designed exposure-response studies of the respiratory and cardiovascular responses of rodents exposed by inhalation for up to 6 months to diesel and gasoline exhausts (DE, GE), wood smoke (WS) and simulated downwind coal emissions (CE). Concentrations of the four combustion-derived mixtures ranged from near upper bound plausible to common occupational and environmental hotspot levels. An "exposure effect" statistic was created to compare the strengths of exposure-response relationships and adjustments were made to minimize false positives among the large number of comparisons. All four exposures caused statistically significant effects. No exposure caused overt illness, neutrophilic lung inflammation, increased circulating micronuclei or histopathology of major organs visible by light microscopy. DE and GE caused the greatest lung cytotoxicity. WS elicited the most responses in lung lavage fluid. All exposures reduced oxidant production by unstimulated alveolar macrophages, but only GE suppressed stimulated macrophages. Only DE retarded clearance of bacteria from the lung. DE before antigen challenge suppressed responses of allergic mice. CE tended to amplify allergic responses regardless of exposure order. GE and DE induced oxidant stress and pro-atherosclerotic responses in aorta; WS and CE had no such effects. No overall ranking of toxicity was plausible. The ranking of exposures by number of significant responses varied among the response models, with each of the four causing the most responses for at least one model. Each exposure could also be deemed most or least toxic depending on the exposure metric used for comparison. The database is available for additional analyses.

A dynamic system for single and repeated exposure of airway epithelial cells to gaseous pollutants

In vitro models are promising approaches to investigate the adverse effects and the mode of action of air pollutants on the respiratory tract. We designed a dynamic system that allows the single or repeated exposure of cultured cells to two major indoor air gaseous pollutants, formaldehyde (HCHO) and nitrogen dioxide (NO2), alone or as a mixture. In this system, the Calu-3 human bronchial epithelial cell line was exposed at the air-liquid interface (ALI) or submerged by culture medium to synthetic air or to target concentrations of HCHO and/or NO2 once or on 4 consecutive days before assessment of cell viability and necrosis, IL-6 and IL-8 release and trans-epithelial electrical resistance. Our data showed that whereas the ALI method can be used for single short-term exposures only, the submerged method provides the possibility to expose Calu-3 cells in a repeated manner. As well, we found that repeated exposures of the cells to HCHO and NO2 at concentrations that can be found indoors triggered a significant decrease in cell metabolism and an increase in IL-8 release that were not evoked by a single exposure. Thus, our work highlights the fact that the development of systems and methods that allow repeated exposures of cultured cells to gaseous compounds in mixtures is of major interest to evaluate the impact of air pollution on the respiratory tract.

Effect of formaldehyde on asthmatic response to inhaled allergen challenge

BACKGROUND

Exposure to formaldehyde may lead to exacerbation of asthma.

OBJECTIVES

Our aim in this study was to investigate whether exposure to a low level (500 microg/m(3)) of formaldehyde enhances inhaled allergen responses.

METHODS

Twelve subjects with intermittent asthma and allergy to pollen were exposed, at rest, in a double-blind crossover study to either formaldehyde or purified air for 60 min. The order of exposure to formaldehyde and air-only was randomized, and exposures were separated by 2 weeks. We also performed an allergen inhalation challenge after each exposure. Airway responsiveness to methacholine and lower airway inflammation (induced sputum) were assessed 8 hr after allergen challenge.

RESULTS

The median dose of allergen producing a 15% decrease in forced expiratory volume in 1 sec (PD(15)FEV(1)) was 0.80 IR (index of reactivity) after formaldehyde exposure compared with 0.25 IR after air-only exposure (p = 0.06). Formaldehyde exposure did not affect allergen-induced increase in responsiveness to methacholine (p = 0.42). We found no formaldehyde-associated effect on the airway inflammatory response, in particular the eosinophilic inflammatory response, induced by the allergen challenge 8 hr before.

CONCLUSION

In this study, exposure to 500 microg/m(3) formaldehyde had no significant deleterious effect on airway allergen responsiveness of patients with intermittent asthma; we found a trend toward a protective effect.

Effects of nitrogen dioxide on allergic airway responses in subjects with asthma

OBJECTIVE

We sought to determine whether nitrogen dioxide (NO2) can enhance airway inflammation after allergen challenge in asthmatic subjects.

METHODS

Fifteen house-dust-mite (HDM)-sensitive asthmatic subjects were exposed for 3 hours to filtered air or 0.4 ppm NO2, followed by inhalational challenge with HDM allergen. Markers of inflammation were measured in sputum at 6 hours and 26 hours after allergen challenge.

RESULTS

After exposure to NO2, eosinophil concentration decreased significantly in the 6-hour postallergen sputum. No significant NO2-related difference was observed for other variables.

CONCLUSIONS

Our results suggest that, in most asthmatic individuals, multi-hour exposure to a high ambient concentration of NO2 does not enhance the inflammatory response to subsequent inhaled allergen as assessed by cell distribution in induced sputum. Because the decrease in airway eosinophils has been reported in previous animal studies, future research should be directed toward the mechanism of this effect.

Nitrogen dioxide enhances allergic airway inflammation and hyperresponsiveness in the mouse

In addition to being an air pollutant, NO2 is a potent inflammatory oxidant generated endogenously by myeloperoxidase and eosinophil peroxidase. In these studies, we sought to determine the effects of NO2 exposure on mice with ongoing allergic airway disease pathology. Mice were sensitized and challenged with the antigen ovalbumin (OVA) to generate airway inflammation and subsequently exposed to 5 or 25 ppm NO2 for 3 days or 5 days followed by a 20-day recovery period. Whereas 5 ppm NO2 elicited no pathological changes, inhalation of 25 ppm NO2 alone induced acute lung injury, which peaked after 3 days and was characterized by increases in protein, LDH, and neutrophils recovered by BAL, as well as lesions within terminal bronchioles. Importantly, 25 ppm NO2 was also sufficient to cause AHR in mice, a cardinal feature of asthma. The inflammatory changes were ameliorated after 5 days of inhalation and completely resolved after 20 days of recovery after the 5-day inhalation. In contrast, in mice immunized and challenged with OVA, inhalation of 25 ppm NO2 caused a marked augmentation of eosinophilic inflammation and terminal bronchiolar lesions, which extended significantly into the alveoli. Moreover, 20 days postcessation of the 5-day 25 ppm NO2 inhalation regimen, eosinophilic and neutrophilic inflammation, pulmonary lesions, and AHR were still present in mice immunized and challenged with OVA. Collectively, these observations suggest an important role for NO2 in airway pathologies associated with asthma, both in modulation of degree and duration of inflammatory response, as well as in induction of AHR.