Carbocisteine inhibits oxidant-induced apoptosis in cultured human airway epithelial cells

Background and objective: Increased oxidant levels have been associated with exacerbations of COPD, and L‐carbocisteine, a mucolytic agent, reduces the frequency of exacerbations. The mechanisms underlying the inhibitory effects of L‐carbocisteine on oxidant‐induced COPD exacerbations were examined in an in vitro study of human airway epithelial cells. Methods: In order to examine the antioxidant effects of L‐carbocisteine, human tracheal epithelial cells were treated with L‐carbocisteine and exposed to hydrogen peroxide (H₂O₂). Cell apoptosis was assessed using a cell death detection ELISA, and the pathways leading to cell apoptosis were examined by measurement of caspase‐3 and caspase‐9 by western blot analysis with fluorescent detection. Results: The proportion of apoptotic cells in human tracheal epithelium was increased in a concentration‐ and time‐dependent manner, following exposure to H₂O₂. Treatment with L‐carbocisteine reduced the proportion of apoptotic cells. In contrast, H₂O₂ did not increase the concentration of LDH in supernatants of epithelial cells. Exposure to H₂O₂ activated caspase‐3 and caspase‐9, and L‐carbocisteine inhibited the H₂O₂‐induced activation of these caspases. L‐carbocisteine activated Akt phosphorylation, which modulates caspase activation, and the inhibitors of Akt, LY294002 and wortmannin, significantly reversed the inhibitory effects of L‐carbocisteine on H₂O₂‐induced cell apoptosis. Conclusions: These findings suggest that in human airway epithelium, L‐carbocisteine may inhibit cell damage induced by H₂O₂ through the activation of Akt phosphorylation. L‐carbocisteine may have antioxidant effects, as well as mucolytic activity, in inflamed airways.