Synergistic Inhibition by β2-Agonists and Corticosteroids on Tumor Necrosis Factor- α –Induced Interleukin-8 Release from Cultured Human Airway Smooth-Muscle Cells

Abstract

We have previously reported that human airway smooth-muscle (ASM) cells produce abundant interleukin (IL)-8, a major neutrophil chemoattractant involved in asthma exacerbations. Here, we tested the effects of the beta(2)-agonists salbutamol (Salbu) and salmeterol (Salme) on IL-8 release and tumor necrosis factor (TNF)-alpha-induced IL-8 release from ASM cells. We found that TNF-alpha strongly enhanced IL-8 release in a time- and concentration-dependent manner, whereas Salbu, Salme, the direct adenylyl cyclase activator forskolin (FSK), and the cyclic monophosphate (cAMP) analogue 8-bromoadenosine 3',5'-cAMP (8-Br-cAMP) alone weakly stimulated IL-8 release. TNF-alpha (10 ng/ml)-induced IL-8 release was markedly inhibited by the steroids dexamethasone (Dex) (0.1 to 10 microM) and fluticasone (Flut) (0.01 to 1 microM) but unaffected by Salbu, Salme, FSK, or 8-Br-cAMP. However, a combination of Dex (1 microM) or Flut (0.1 microM) with Salbu (10 microM), Salme (1 microM), FSK (10 microM), or 8-Br-cAMP (10 and 100 microM) significantly enhanced the inhibition by Dex or Flut alone. Experiments with KT5720, a selective inhibitor of cAMP-dependent protein kinase A; rolipram, a selective inhibitor of type IV phosphodiesterase; and ICI-118,551, a beta(2)-receptor antagonist, suggested that the synergistic inhibition was mediated by beta(2)-receptor in a cAMP-dependent manner. This novel synergistic interaction of beta(2)-agonists and steroids may partly explain the benefits that result when these agents are combined to treat asthma.