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

Abstract

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.