Ozone Inhalation Attenuated the Effects of Budesonide on Aspergillus fumigatus-Induced Airway Inflammation and Hyperreactivity in Mice

Abstract

Inhaled glucocorticoids form the mainstay of asthma treatment because of their anti-inflammatory effects in the lung. Exposure to the air pollutant ozone (O3) exacerbates chronic airways disease. We and others showed that presence of the epithelial-derived surfactant protein-D (SP-D) is important in immunoprotection against inflammatory changes including those induced by O3 inhalation in the airways. SP-D synthesis requires glucocorticoids. We hypothesized here that O3 exposure impairs glucocorticoid responsiveness (including SP-D production) in allergic airway inflammation. The effects of O3 inhalation and glucocorticoid treatment were studied in a mouse model of allergic asthma induced by sensitization and challenge with Aspergillus fumigatus (Af) in vivo. The role of O3 and glucocorticoids in regulation of SP-D expression was investigated in A549 and primary human type II alveolar epithelial cells in vitro. Budesonide inhibited airway hyperreactivity, eosinophil counts in the lung and bronchoalveolar lavage (BAL) and CCL11, IL-13, and IL-23p19 release in the BAL of mice sensitized and challenged with Af (p < 0.05). The inhibitory effects of budesonide were attenuated on inflammatory changes and were completely abolished on airway hyperreactivity after O3 exposure of mice sensitized and challenged with Af. O3 stimulated release of pro-neutrophilic mediators including CCL20 and IL-6 into the airways and impaired the inhibitory effects of budesonide on CCL11, IL-13 and IL-23. O3 also prevented budesonide-induced release of the immunoprotective lung collectin SP-D into the airways of allergen-challenged mice. O3 had a bi-phasic direct effect with early (<12 h) inhibition and late (>48 h) activation of SP-D mRNA (sftpd) in vitro. Dexamethasone and budesonide induced sftpd transcription and translation in human type II alveolar epithelial cells in a glucocorticoid receptor and STAT3 (an IL-6 responsive transcription factor) dependent manner. Our study indicates that O3 exposure counteracts the effects of budesonide on airway inflammation, airway hyperreactivity, and SP-D production. We speculate that impairment of SP-D expression may contribute to the acute O3-induced airway inflammation. Asthmatics exposed to high ambient O3 levels may become less responsive to glucocorticoid treatment during acute exacerbations.

Oxidative Stress Promotes Corticosteroid Insensitivity in Asthma and COPD

“…Patients with severe asthma and COPD often exhibit greater levels of oxidative stress biomarkers, with increased levels correlating with worsened symptoms, decreased lung function, and corticosteroid insensitivity [37,75,[78][79][80][81][82][83]. This oxidative burden is achieved by exposure to environmental and cellular sources of RONS.…”

“…Increases in pollutant levels contribute to disease pathogenesis and exacerbations in asthma and COPD [80,81,102]. Ozone is an oxidant that induces Th17-mediated neutrophilic airway inflammation and is associated with decreased corticosteroid sensitivity [79,103,104]. Exposure to other environmental pollutants, such as diesel exhaust and <2.5 µm particulate matter (PM 2.5 ), also induces high levels of oxidative stress in the lung [82,83,105].…”

Ozone-Induced Oxidative Stress, Neutrophilic Airway Inflammation, and Glucocorticoid Resistance in Asthma

“…O 3 exposure results in accumulation of reactive oxygen species (ROS) most likely through lipid peroxidation processes of the pulmonary surfactant phospholipids (60) and cell membranes (126)(127)(128). ROS in turn rapidly activate the release of alarmins IL-1b, IL-6, IL-23, IL-33, TNF-a, and TSLP (Figure 1A) leading to a cascade of proinflammatory changes in structural and immune cells in the respiratory mucosal tissue (106,116,122,129,(131)(132)(133)(134)(135)(136). Activation of the RORgt proinflammatory signaling pathway leads to mRNA transcription of the IL-17A and IL-22 genes (Figure 1B) (131,(137)(138)(139)(140)(141)(142)(143)(144)(145)(146).…”

“…Because asthmatic patients respond to O 3 with an enhanced airway neutrophilic influx compared with non-asthmatic controls (155), the observation that neutrophils are poorly responsive to glucocorticoids ( 15) raises a serious concern related to asthma treatment. Indeed, recent studies demonstrated that O 3 impaired the effects of glucocorticoid treatment in a mouse model of allergen-induced asthma in vivo as well as in human cell lines and primary epithelial cells in vitro (58,122,156). What are the underlying molecular mechanisms of O 3 -induced glucocorticoid resistant neutrophilic airway inflammation in asthma?…”

“…Against O 3 -induced inflammatory injury, the lung mounts immuno-protective mechanisms such as production of the epithelial-cell derived collectin, surfactant protein D (SP-D) (101). Constitutive expression of this molecule in airway epithelial cells is promoted by glucocorticoid dependent transcription (120)(121)(122). O 3 -induced oxidative stress not only destroys the biologically active tertiary molecular structure of SP-D (91,(123)(124)(125) but it also diminishes glucocorticoid responsiveness and SP-D expression in airway epithelial cells in vivo and in vitro (122).…”