Inhalation of ambroxol inhibits cigarette smoke-induced acute lung injury in a mouse model by inhibiting the Erk pathway

• Cigarette smoke (CS)-induced airway inflammation and mucus hypersecretion.
• Inhalation of ambroxol decreases inflammatory cells influx into lung.
• Ambroxol inhibits CS-induced proinflammatory factor expression.
• Ambroxol alleviates CS-induced glycosaminoglycans and MUC5AC levels in lung.
• Ambroxol inhibits Erk signaling pathway in human lung epithelial cells.

Oral and injection administration of ambroxol has been clinically used to treat airway disease. However, little is known about its potentials in inhalation therapy. In present studies, we tested the effects of ambroxol by inhalation with intravenous administration, and explored the underlying working mechanism. The mice received 10 cigarettes exposure every day for 4 days. Inhaled solution of ambroxol was aerosolized 20 min before the exposure of cigarette smoke (CS). The effect of ambroxol on the expression of mucoprotein 5AC (MUC5AC) and proinflammatory cytokines in NCI-H292 cells stimulated with cigarette smoke extract (CSE). Four days of daily inhalation of ambroxol at 3.75 or 7.5 mg/ml for 20 min suppressed the accumulation of neutrophils and macrophages in the bronchoalveolar lavage fluid (BALF) and lung tissues, and inhibited increases in the mRNA and protein levels of tumor necrosis factor (TNF)-α, CCL-2 and KC, but not interleukin (IL)-1β in the CS-exposed mice. Moreover, ambroxol at 3.75 or 7.5 mg/ml facilitated airway mucosa cilia clearance, reduced glycosaminoglycans level in BALF and MUC5AC mRNA levels in lung tissues. The effects of ambroxol by inhalation at 7.5 mg/ml was comparable to that of ambroxol at 20 mg/kg i.v. and dexamethasone at 0.5 mg/kg i.p. Using cultured lung epithelial cells, we demonstrated that pretreatment with ambroxol at 2 or 20 μM inhibited the CSE-induced up-regulation of MUC5AC, TNF-α, IL-1β mRNA levels, which was through inhibiting Erk signaling pathway. Our results demonstrate the beneficial effects of ambroxol as an inhalation replace systemic administration for COPD therapy.