Direct Inhibitory Effect of the PDE4 Inhibitor Roflumilast on Neutrophil Migration in Chronic Obstructive Pulmonary...

Neutrophilic inflammation is characteristic of chronic obstructive pulmonary disease (COPD); yet, there are no effective antiinflammatory therapies. The PDE4 inhibitor roflumilast is approved for use in COPD and suppresses sputum neutrophilia. The mechanism underlying this observation is unclear; therefore, this study addressed whether roflumilast directly affected neutrophil migration. Blood-derived neutrophils were isolated from nonsmokers, smokers, and patients with COPD, and chemotaxis was measured using Boyden chambers. Intracellular calcium ion concentration was measured by fluorimetry, and shape change and CD11b expression were measured by flow cytometry. Neutrophils from patients with COPD showed enhanced chemotactic responses toward both CXCL1 and leukotriene B₄ compared with control cells. Chemotaxis was inhibited by both the active metabolite roflumilast N-oxide and rolipram in a concentration-dependent manner with no difference in responsiveness between subjects. Roflumilast N-oxide and rolipram were less efficacious against CXCL1 and leukotriene B₄-mediated intracellular calcium ion concentration, suggesting that inhibition was not via this pathway. Both PDE4 inhibitors attenuated chemoattractant-mediated shape change and CD11b upregulation, suggesting common mechanisms. The stable cAMP analog 8-bromoadenosine 3',5'-cAMP inhibited chemotaxis, as did the direct Epac1 (exchange protein directly activated by cAMP 1) activator 8-(4-chlorophenylthio)-2'-O-methyladenosine 3',5'-cAMP but not the direct protein kinase A activator N⁶-benzoyladenosine-3',5'-cAMP. These data suggest that roflumilast inhibits neutrophil chemotaxis directly via a cAMP-mediated mechanism requiring activation of Epac1 and that Epac1 activators could reduce COPD neutrophilic inflammation.