Effects of elastase inhibitor on the epithelial cell apoptosis in bleomycin-induced pulmonary fibrosis

Abstract

Alveolar epithelial cell injury and apoptosis is consistent findings in human idiopathic pulmonary fibrosis (IPF). Epithelial cell apoptosis is known to be induced by leukocyte elastase in vitro. The authors hypothesized that synthetic neutrophil elastase inhibitor, sivelestat (ONO-5046), can inhibit the bleomycin-induced pulmonary fibrosis in rats by blocking the apoptotic pathways in epithelial cells. Adult rats were injected with intratracheal bleomycin. Sivelestat was given for 13 days intraperitoneally after bleomycin treatments. Similar experiments were carried out in which A549 cells, a human alveolar type II epithelial cell line, were treated with bleomycin or neutrophil elastase. In rats, sivelestat decreased neutrophil counts and the cytokine-induced neutrophil chemoattractant (CINC)-1 in the bronchoalveolar lavage (BAL) fluid of bleomycin-treated rats. Sivelestat also decreased the bleomycin-induced lung inflammatory cell apoptosis by decreasing caspase-3 and -9 activities. In A549 cells, sivelestat decreased the elastase-induced epithelial cell apoptosis but not the bleomycin-induced epithelial cell apoptosis. Similarly, sivelestat inhibited the elastase-induced cell death but not the bleomycin-induced cell death in MTT assays. Sivelestat also inhibited the elastase-induced caspase-3 and -9 activities and cytochrome c release from the mitochondria but did not inhibit the bleomycin-induced caspase activities in A549 cells. In conclusion, bleomycin caused the lung inflammatory cell apoptosis through the caspase-9 and -3 pathways in rats. Sivelestat inhibited pulmonary fibrosis by blocking these mitochondria-mediated apoptotic pathways in bleomycin-treated rats and in elastase-treated A549 cells. These findings suggest that sivelestat can suppress the bleomycin-induced pulmonary fibrosis by blocking neutrophil chemotaxis and by inhibiting the neutrophil elastase-induced lung cell apoptosis in rats.