Protective effects of liquiritin apioside on cigarette smoke-induced lung epithelial cell injury

Cigarette smoking is associated with an increased incidence of chronic obstructive pulmonary disease (COPD). In this study, we hypothesized that liquiritin apioside (LA), a main flavonoid component from Glycyrrhiza uralensis, had antioxidant properties by inducing glutathione (GSH) biosynthesis via the inhibition of cytokines and protected lung epithelial cells against cigarette smoke-mediated oxidative stress. A549 cells were treated with cigarette smoke extract (CSE) and/or LA. ICR mice were exposed to cigarette smoke (CS) for four days with increasing exposure time for up to 6 h per day to elicit epithelial cells injury. One hour before smoke exposure, mice were treated with LA by gavage; 18 h after the last CS exposure all examinations were performed. Treatment with LA concentration-dependently prevented CSE-induced cytotoxicity, increase of TGF-β and TNF-α mRNA expression, depletion of GSH and apoptosis in A549 cells. LA at doses 3, 10 and 30 mg/kg dose-dependently inhibited pulmonary neutrophil and macrophage inflammation. Lung sections of the CS-exposed LA treated mice showed an apparently reduced pulmonary inflammation and a significant inhibitory effect on mucus containing goblet cells in the large airways. Furthermore, the CS-induced pulmonary release of TGF-β, TNF-α and myeloperoxidase activity was reduced, and superoxide dismutase activity was enhanced.These results indicate that protective roles of LA on CS-induced the lung epithelial cell injury are mediated by inhibiting TGF-β and TNF-α expression and increasing anti-oxidative levels of GSH, suggesting that LA might be effective as protective agent against epithelial injury in COPD.