Effects of ozone repeated short exposures on the airway/lung inflammation, airway hyperresponsiveness and mucus production in a mouse model of ovalbumin-induced asthma

Objective: The purpose of this study is to explore the influence of ozone repeated short exposures on airway/lung inflammation, airway hyperresponsiveness (AHR) and airway hypersecretion in ovalbumin (OVA) sensitized/challenged asthmatic mouse model. Methods: OVA sensitization was performing by intraperitoneal injection. Ozone exposures (3ppm for 3hours) were given one hour after aerosolized OVA challenges (once every other day, 4 times totally). Methacholine (MCH) bronchial provocation tests, Liu's staining of BALF cell smears, hematoxylin-eosin (HE) staining and Periodic Acid-Schiff (PAS) staining of lung tissue were performed. Interleukins (ILs; IL-4, IL-13, IL-1 beta, and IL-18) protein (ELISA) and mRNA expression levels (RT-qPCR) in murine lung, 8-hydroxy-2'-deoxyguanosine (8-OHdG, ELISA), malondialdehyde (MDA, thiobarbituric acid assay), reduced glutathione (GSH, spectrophotometric method) in bronchoalveolar lavage fluid (BALF), and GSH1 mRNA relative expression levels (RT-qPCR) in lung tissue were analyzed. Result: Repeated ozone exposures down-regulated the AHR to MCH in mice undergoing OVA sensitization and challenge, however not all parameters associated with asthma were decreased since obvious mucus hypersecretion was induced and airway inflammation increased slightly, especially around small airways. Following ozone co-exposure, the increase of IL-4 and IL-13 levels in murine lung caused by OVA sensitization/challenge were reversed. Instead, levels of IL-1 beta in BALF remained, higher than negative control group. Ozone repeated short exposures also induced significant increase of 8-OHdG in BALF in OVA sensitized and challenged mice. Conclusion: For asthmatic mice undergoing ozone exposures, AHR is not an accurate indicator of the severity of asthma. Repeated short ozone exposures increase mucus hypersecretion, possibly via an increase in oxidative stress and immune dysregulation.