Inhaled ozone induces distinct alterations in pulmonary function in models of acute and episodic exposure in female mice

Abstract

Ozone is an urban air pollutant known to cause lung injury and altered function. Using established models of acute (0.8 ppm, 3 h) and episodic (1.5 ppm, 2 h, 2 times/wk, 6 wk) inhalation exposure, we observed distinct structural changes in the lung; whereas acutely, ozone primarily disrupts the bronchiolar epithelial barrier, episodic exposure causes airway remodeling. Herein we examined how these responses altered pulmonary function. A SCIREQ small animal ventilator was used to assess lung function; impedance was used to conditionally model resistance and elastance. Episodic, but not acute ozone exposure reduced the inherent and frequency-dependent tissue recoil (elastance) of the lung. Episodic ozone also increased central and high-frequency resistance relative to air control after methacholine challenge, indicating airway hyperresponsiveness. Pressure-volume (PV)-loops showed that episodic ozone increased maximum lung volume, whereas acute ozone decreased lung volume. Episodic ozone-induced functional changes were accompanied by increases in alveolar circularization; conversely, minimal histopathology was observed after acute exposure. However, acute ozone exposure caused increases in total phospholipids, total surfactant protein D (SP-D), and low-molecular weight SP-D in bronchoalveolar lavage fluid. Episodic ozone exposure only increased total SP-D. These findings demonstrate that acute and episodic ozone exposure caused distinct alterations in surfactant composition and pulmonary function. Whereas loss in PV-loop area following acute ozone exposure is likely driven by increases in SP-D and inflammation, emphysematous pathology and airway hyperresponsiveness after episodic ozone appear to be the result of alterations in lung structure.

Keywords: lung lipids; ozone; pulmonary mechanics; surfactant protein.