Azithromycin inhibits mucin secretion, mucous metaplasia, airway inflammation, and airways hyperresponsiveness in mice exposed to house dust mite extract.

Excessive production, secretion, and retention of abnormal mucus is a pathological feature of many obstructive airways diseases including asthma. Azithromycin is an antibiotic that also possesses immunomodulatory and mucoregulatory activities, which may contribute to the clinical effectiveness of azithromycin in asthma. The current study investigated these nonantibiotic activities of azithromycin in mice exposed daily to intranasal house dust mite (HDM) extract for 10 days. HDM-exposed mice exhibited airways hyperresponsiveness to aerosolized methacholine, a pronounced mixed eosinophilic and neutrophilic inflammatory response, increased airway smooth muscle (ASM) thickness, and elevated levels of epithelial mucin staining. Azithromycin (50 mg/kg sc, 2 h before each HDM exposure) attenuated HDM-induced airways hyperresponsiveness to methacholine, airways inflammation (bronchoalveolar lavage eosinophil and neutrophils numbers, and IL-4, IL-5, IL-6, IL-10, IL-12, IL-13, and RANTES levels), and epithelial mucin staining (mucous metaplasia) by at least 50% (compared with HDM-exposed mice, P < 0.05). Isolated tracheal segments of HDM-exposed mice secreted Muc5ac and Muc5b (above baseline levels) in response to exogenous ATP. Moreover, ATP-induced secretion of mucins was attenuated in segments obtained from azithromycin-treated, HDM-exposed mice ( P < 0.05). In additional ex vivo studies, ATP-induced secretion of Muc5ac (but not muc5b) from HDM-exposed tracheal segments was inhibited by in vitro exposure to azithromycin. In vitro azithromycin also inhibited ATP-induced secretion of Muc5ac and Muc5b in tracheal segments from IL-13-exposed mice. In summary, azithromycin inhibited ATP-induced mucin secretion and airways inflammation in HDM-exposed mice, both of which are likely to contribute to suppression of airways hyperresponsiveness.