Cysteinyl-leukotrienes are potent mediators involved in various inflammatory diseases and lung disorders such as asthma. However, their precise role in the pathogenesis of pulmonary fibrosis is unknown. In the present study, we investigated the effect of montelukast, a cysteinyl-leukotriene type 1 receptor antagonist, on bleomycin-induced pulmonary fibrosis in mice. Montelukast (10mg/kg/day) was orally administered to the bleomycin-induced pulmonary fibrosis mice for 3days before and 14days after intratracheal instillation of bleomycin. We evaluated the effects of montelukast on the development of pulmonary fibrosis in these mice and investigated the expression of various cytokines and two cysteinyl-leukotriene receptors. Treatment with montelukast significantly attenuated the increased fibrotic area and hydroxyproline content in the fibrotic lungs of bleomycin-instilled mice. Montelukast treatment also decreased mRNA levels of IL-6, IL-10, IL-13, and TGF-β1, all of which were elevated in fibrotic lungs. In fibrotic lungs, TNF-α and IL-1β mRNA levels were increased and IFN-γ mRNA levels were decreased, but montelukast did not affect these mRNA levels. Furthermore, cysteinyl-leukotriene type 1 receptor mRNA levels were increased, whereas cysteinyl-leukotriene type 2 receptor mRNA levels were decreased in fibrotic lungs. Montelukast treatment induced the recovery of cysteinyl-leukotriene type 2 receptor mRNA levels to normal control levels but did not change cysteinyl-leukotriene type 1 receptor mRNA levels. These results suggest that montelukast exhibits its beneficial effects by inhibiting the overexpression of IL-6, IL-10, IL-13, and TGF-β1 and by modulating the homeostatic balance between the cysteinyl-leukotriene type 1 and type 2 receptors.
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