Irritant-induced asthma to hypochlorite in mice due to impairment of the airway barrier.

After a recovery period of 14 days an intranasal (i.n.) challenge with 0.003% active chlorine (in ClO-) or vehicle (distilled water, H2O) was given, followed by assessment of the breathing frequency. One day later, pulmonary function, along with pulmonary inflammation was determined. Lung permeability was assessed by means of total broncho-alveolar lavage (BAL) protein content and plasma surfactant protein (SP)-D levels. In vivo micro-CT imaging revealed enlargement of the lungs and airways early after NA treatment, with a return to normal at day 14. When challenged i.n. with ClO-, NA-pretreated mice immediately responded with a sensory irritant response. Twenty-four hours later, NA/ClO- mice showed airway hyperreactivity (AHR), accompanied by a neutrophilic and eosinophilic inflammation. NA administration followed by ClO- induced airway barrier impairment, as shown by increased BAL protein and plasma SP-D concentrations; histology revealed epithelial denudation. These data prove that NA-induced lung impairment renders the lungs of mice more sensitive to an airway challenge with ClO-, confirming the hypothesis that incomplete barrier repair, followed by irritant exposure results in airway hypersensitivity.