NADPH oxidase 4 over-expression is associated with epithelial ciliary dysfunction in neutrophilic asthma

BACKGROUND: Bronchial epithelial ciliary dysfunction is an important feature of asthma. We sought to determine the role in asthma of neutrophilic inflammation and NADPH oxidases in ciliary dysfunction. METHODS: Bronchial epithelial ciliary function was assessed by video-microscopy in fresh ex vivo epithelial strips from asthmatics stratified by their sputum cell differentials and in cultures from healthy controls and asthmatics. Bronchial epithelial oxidative damage was determined by 8-oxo-dG expression. NOX/DUOX expression was assessed in bronchial epithelial cells by microarrays, with NOX4, DUOX1/2 expression assessed in bronchial biopsies. Ciliary dysfunction following NADPH oxidase inhibition, using GKT137831, was evaluated in fresh epithelial strips from asthmatics and a murine model of ovalbumin sensitisation and challenge. RESULTS: Ciliary beat frequency was impaired in asthmatics with sputum neutrophilia (n=11) versus those without (n=10) (5.8 [0.6] versus 8.8 [0.5]Hz; P=0.003) and was correlated with sputum neutrophil count (r=-0.70; P<0.001). Primary bronchial epithelial cells expressed DUOX1/2 and NOX4. 8-oxo-dG and NOX4, were elevated in neutrophilic versus non-neutrophilic asthmatics, DUOX1 was elevated in both, and DUOX2 was elevated in non-neutrophilic asthma in vivo. In primary epithelial cultures ciliary dysfunction did not persist, although NOX4 expression and reactive oxygen species generation was increased from subjects with neutrophilic asthma. GKT137831 both improved ciliary function in ex vivo epithelial strips (n=13), relative to the intensity of neutrophilic inflammation, and abolished ciliary dysfunction in the murine asthma model without a reduction in inflammation. CONCLUSIONS: Ciliary dysfunction is increased in neutrophilic asthma associated with increased NOX4 expression and is attenuated by NADPH oxidase inhibition.