Agonist-induced β2-adrenoceptor desensitization and downregulation enhance pro-inflammatory cytokine release in human bronchial epithelial cells

It is not clear whether increased asthma severity associated with long-term use of beta(2)-adrenoceptor (beta(2)-AR) agonists can be attributed to receptor degradation and increased inflammation. We investigated the cross-talk between beta-AR agonist-mediated effects on beta(2)-AR function and expression and cytokine release in human bronchial epithelial cells. In 16HBE14o(-) cells grown in the presence and absence of beta-AR agonists and/or antagonists, the beta(2)-AR density was assessed by radioligand binding; the receptor protein and mRNA was determined using laser scanning cytometer and RT-PCR; cAMP generation, the cytokines IL-6 and IL-8 release were determined using AlphaScreen Assay and ELISA, respectively. Isoprenaline (ISO) and salbutamol (Salbu) induced a concentration- and time-dependent significant decrease in beta(2)-AR density. Both Salbu and ISO reduced cAMP generation in a concentration-dependent manner while in same cell culture the IL-6 and IL-8 release was significantly enhanced. These effects were antagonized to a greater extent by ICI 118.551 than by propranolol, but CGP 20712A had no effect. Reduction of the beta(2)-AR protein and mRNA could be seen when cells were treated with ISO for 24 h. Our findings indicate a direct link between cytokine release and altered beta(2)-AR expression and function in airway epithelial cells. beta(2)-AR desensitization and downregulation induced by long-term treatment with beta(2)-AR agonists during asthma may account for adverse reactions also due to enhanced release of pro-inflammatory mediators and should, thus, be considered in asthma therapy. (C) 2014 Elsevier Ltd. All rights reserved.