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 (H ₂O₂). 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, H₂O ₂ 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.