Background In a mouse model of mild chronic asthma, both inflammation and remodelling can be suppressed by dexamethasone (a glucocorticoid) and roflumilast (a selective phosphodiesterase-4 inhibitor).
Objective To better understand the underlying molecular mechanisms, we investigated the effects of treatment on airway expression of inflammation-related cytokines, as well as on epithelial expression of growth factors.
Methods BALB/c mice systemically sensitized to ovalbumin were challenged with aerosolized antigen for 6 weeks and treated with roflumilast or dexamethasone during the final 2 weeks. Expression of mRNA, for a variety of cytokines and growth factors, was assessed in selectively dissected proximal airways or in airway epithelium obtained by laser capture microdissection.
Results In the airway wall of vehicle-treated challenged animals, there was significantly elevated expression of mRNA for a variety of pro-inflammatory and T helper type 2 cytokines, as well as for IFN-γ. All these cytokines were suppressed by dexamethasone. Treatment with roflumilast reduced expression of IL-17A, TNF-α, granulocyte-macrophage colony-stimulating factor and IL-6, but did not inhibit other cytokines. Both drugs suppressed the enhanced expression of mRNA for growth factors such as TGF-β1 and FGF-2 in airway epithelium.
Conclusions Whereas dexamethasone non-specifically inhibits numerous mediators involved in inflammation and the immune response, roflumilast selectively inhibits a subset of pro-inflammatory cytokines and growth factors. These mediators and/or the cells that produce them may have critical roles in the pathogenesis of the lesions of chronic asthma.