Background: Patients with severe asthma are less sensitive to oral or inhaled corticosteroids. Relative corticosteroid insensitivity has been shown in peripheral blood mononuclear cells and alveolar macrophages in these patients. Aims and objectives: Determine the response of corticosteroids in airway smooth muscle cells (ASMCs) of severe asthma, in terms of suppression of cytokine-induced chemokine release and mRNA expression, and investigate the underlying mechanisms. Methods: ASMCs of non-asthmatics (NA; 12), patients with non-severe (NSA; 10) or severe asthma (SA; 10) were pretreated with dexamethasone (Dex; 10 -10 -10 -6 M) followed by stimulation with TNF-α at 10 ng/mL. IL-8 and eotaxin release determined by ELISA; mRNA quantified by RT-PCR. p65 NF-κB recruitment to gene promoters measured by ChIP assay; p38, JNK, and ERK expression measured by Western blot. Results: Baseline and TNF-α induced eotaxin release and mRNA were higher in NSA, but not SA, compared to NA, while no differences were observed for IL-8. p65 recruitment to gene promoters did not differ. Dex (10 -6 M) suppressed induced eotaxin release by 36.7% vs 16.7% ( p <0.05) in NSA and SA, respectively. Dex (10 -6 M) suppressed induced IL-8 release by 49.8% vs 25.7% ( p <0.01) in NA and SA, respectively. Induced IL-8 and eotaxin mRNA was significantly inhibited by Dex (10 -7 M) in NA and NSA ( p <0.05) but not in SA. Induced phosphorylated p38 and JNK were significantly higher in SA compared to NA, respectively ( p <0.05). Conclusions: Corticosteroid insensitivity exists in ASMCs of severe asthma, which may be associated with enhanced p38 and JNK activity.
Chang et al. (Thu,) studied this question.