Hindawi Publishing Corporation
Oxidative Medicine and Cellular Longevity
Volume 2013, Article ID 254069, 14 pages
http://dx.doi.org/10.1155/2013/254069
Research Article
Exacerbated Airway Toxicity of Environmental Oxidant
Ozone in Mice Deficient in Nrf2
Hye-Youn Cho,
1
Wesley Gladwell,
1
Masayuki Yamamoto,
2
and Steven R. Kleeberger
1
1
Laboratory of Respiratory Biology, National Institute of Environmental Health Sciences, National Institutes of Health,
Research Triangle Park, NC 27709, USA
2
Tohoku University Graduate School of Medicine, Sendai 980-8575, Japan
Correspondence should be addressed to Hye-Youn Cho; cho2@niehs.nih.gov
Received 11 January 2013; Accepted 29 March 2013
Academic Editor: Mi-Kyoung Kwak
Copyright © 2013 Hye-Youn Cho et al. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Ozone (O
3
) is a strong oxidant in air pollution that has harmful effects on airways and exacerbates respiratory disorders. e
transcription factor Nrf2 protects airways from oxidative stress through antioxidant response element-bearing defense gene
induction. e present study was designed to determine the role of Nrf2 in airway toxicity caused by inhaled O
3
in mice. For
this purpose, Nrf2-deficient (2
−/−
) and wild-type (2
+/+
) mice received acute and subacute exposures to O
3
. Lung injury
was determined by bronchoalveolar lavage and histopathologic analyses. Oxidation markers and mucus hypersecretion were
determined by ELISA, and Nrf2 and its downstream effectors were determined by RT-PCR and/or Western blotting. Acute and sub-
acute O
3
exposures heightened pulmonary inflammation, edema, and cell death more severely in 2
−/−
mice than in 2
+/+
mice. O
3
caused bronchiolar and terminal bronchiolar proliferation in both genotypes of mice, while the intensity of compensatory
epithelial proliferation, bronchial mucous cell hyperplasia, and mucus hypersecretion was greater in 2
−/−
mice than in 2
+/+
mice. Relative to 2
+/+
,O
3
augmented lung protein and lipid oxidation more highly in 2
−/−
mice. Results suggest that Nrf2
deficiency exacerbates oxidative stress and airway injury caused by the environmental pollutant O
3
.
1. Introduction
Ozone (O
3
) is a highly reactive gaseous oxidant air pollutant.
Elevated levels of ambient O
3
have been associated with
increased hospital visits and respiratory symptoms including
chest discomfort, breathing difficulties, coughing, and lung
function decrement [1, 2]. Moreover, subjects with preexist-
ing asthma and rhinitis are known to be particularly vulner-
able to O
3
and are at risk of exacerbations [3]. Controlled
O
3
exposure studies in healthy volunteers found oxidant
generation and temporal antioxidant depletion in fluid lining
compartments of the airways or sputum [4]. Inhaled O
3
in experimental animal models causes airway inflammation
and hyperresponsiveness, reactive oxygen species (ROS)
production, mucus overproduction, and epithelial damage
and compensatory proliferation predominantly in ciliated
cells of the upper respiratory tract and Clara cells in terminal
bronchioles. Long-term exposure of O
3
may cause lung
tumors in certain strains of mice [5].
Many studies have investigated the roles of inflamma-
tory mediators in the pathogenic airway response to O
3
.
Infiltration of neutrophils into the interstitium and airways
contributes to O
3
-induced nasal mucous cell metaplasia and
airway hyperreactivity [6, 7], although some studies demon-
strated uncoupling of airway inflammation and hyperreactiv-
ity [8, 9]. Tumor-necrosis-factor- (TNF-) , a susceptibility
gene for O
3
toxicity in mice [10], has a significant role in O
3
-
induced inflammation and airway hyperreactivity in rodent
lungs mediated through nuclear factor-B and activator
protein-1 [10–13]. Toll-like receptor 4 and inflammasome
proteins (e.g., Nlrp3) also contribute to O
3
-induced airway
hyperpermeability and hyperreactivity, respectively, in mice
[14–16].
O
3
is thought to initiate toxicity by oxidation of bio-
molecules including proteins and lipids in epithelial lining