Role of cyclo-oxygenase-2 induction in interleukin-1β induced attenuation of cultured human airway smooth muscle cell cyclic AMP generation in response to isoprenaline

Abstract

1. Airway smooth muscle (ASM) in human asthma shows reduced relaxation and cyclic AMP generation in response to β-adrenoceptor agonists. IL-β attenuates cyclic AMP generation but the underlying mechanism is unclear. We have reported that IL-1β induces cyclo-oxygenase-2 (COX-2) in human ASM cells and results in a marked increase in prostanoid generation with PGE₂ and PGI₂ as the major products.

2. We investigated the role of COX-2 induction and prostanoid release (measured as PGE₂) in IL-1β induced attenuation of cyclic AMP generation in response to the β-adrenoceptor agonist isoprenaline (ISO).

3. Pre-treatment of human ASM cells with IL-1β significantly attenuated cyclic AMP generation in response to high concentrations of ISO (1.0–10.0 μM) in a time- and concentration-dependent manner. The effect was accompanied by a high concentration of PGE₂ release. The non-selective COX inhibitor indomethacin (Ind), the selective COX-2 inhibitor NS-398, the protein synthesis inhibitors cycloheximide (CHX) and actinomycin D and the steroid dexamethasone (Dex) all abolished the PGE₂ release and prevented the attenuated cyclic AMP generation.

4. COX substrate arachidonic acid time- and concentration-dependently mimicked IL-1β induced attenuation and the effect was prevented by the non-selective COX inhibitors Ind and flurbiprofen, but not by NS-398, CHX and Dex.

5. In contrast to IL-1β, TNFα and IFNγ, which are ineffective in inducing COX-2 and releasing PGE₂ from human ASM cells, did not affect the cyclic AMP formation.

6. Our study demonstrates that COX-2 induction and the consequent release of prostanoids plays a crucial role in IL-1β induced attenuation of human ASM cell cyclic AMP response to ISO.

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