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Interleukin-1ß, Transforming Growth Factor-ß₁, and Bradykinin Attenuate Cyclic AMP Production by Human Pulmonary Artery Smooth Muscle Cells in Response to Prostacyclin Analogues and Prostaglandin E₂ by Cyclooxygenase-2 Induction and Downregulation of Adenylyl Cyclase Isoforms 1, 2, and 4

From the Division of Respiratory Medicine, University of Nottingham, City Hospital, Nottingham, UK.

Correspondence to Prof Alan J. Knox, Division of Respiratory Medicine, University of Nottingham, Clinical Science Building, City Hospital, Nottingham, NG5 1PB, England. E-mail alan.knox{at}nottingham.ac.uk

Increased levels of inflammatory cytokines contribute to the pathophysiology of pulmonary hypertension. Prostacyclin (PGI₂) analogues, which relax pulmonary vessels mainly through cAMP elevation, have a major therapeutic role. In this study, we show that prolonged incubation with bradykinin (BK), interleukin-1ß (IL-1ß), and transforming growth factor-ß₁ (TGF-ß₁) markedly impairs cAMP accumulation in human pulmonary artery smooth muscle cells in response to short-term incubation with prostaglandin E₂ (PGE₂) and the PGI₂ analogues iloprost and carbaprostacyclin. A similar reduction in cAMP accumulation in response to a direct adenylyl cyclase activator, forskolin, suggested that the effect was attributable to downregulation of adenylyl cyclase. Reverse transcriptase–polymerase chain reaction studies showed downregulation of adenylyl cyclase isoforms 1, 2, and 4. The effect of IL-1ß, BK, and TGF-ß₁ on cAMP levels was abrogated by the selective COX-2 inhibitor NS398. Furthermore, it was mimicked by prolonged incubation with the COX-2 product PGE₂ and PGI₂ analogues or the COX substrate arachidonic acid, suggesting that it was mediated by endogenous prostanoids produced by COX-2. Consistent with this, IL-1ß, BK, and TGF-ß₁ all induced COX-2 and PGE₂ release. These results show that BK, IL-1ß, and TGF-ß₁ downregulate adenylyl cyclase in human pulmonary artery smooth muscle cells via COX-2 induction and prostanoid release. This suggests a novel mechanism whereby mediators and cytokines produced in pulmonary hypertension may impair the therapeutic effects of prostacyclin analogues such as iloprost and carbaprostacyclin.

Key Words: interleukin-1ß • transforming growth factor-ß₁ • bradykinin • cAMP • adenylyl cyclase

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