Chronic ozone exposure in mice mimics clinical asthma-COPD overlap syndrome and is attenuated by tiotropium

Environmental air pollutants including ozone cause severe irritation and respiratory diseases. Here, we report that 6 week's ozone exposure in mice (1.5 ppm, twice weekly) causes airway hyperreactivity, eosinophil and neutrophil recruitment, Th2 immune response, respiratory barrier disruption with inflammation, fibrosis and emphysema reminiscent of COPD, more rapidly than cigarette smoke exposure. This model features important aspects of asthma-COPD overlap syndrome (ACOS) as recently described in patients. Since Tiotropium (TTP), an anticholinergic receptor antagonist, blocks smooth muscle cell contraction and mucus secretion with a prolonged bronchodilator effect in patients with asthma or COPD, we asked whether its effect is limited to bronchodilation. We report here that Tiotropium not only reduced airways hyperreactivity, but also drastically diminished eosinophil recruitment, Th2 cell response and ozone-induced lung inflammatory pathology including emphysema. Therefore, chronic O₃-induced lung pathology in mice mimics ACOS in patients and is attenuated by TTP treatment. The mechanisms of TTP protective effect on respiratory barrier disruption and chronic inflammation need to be further explored.