Phosphodiesterase 4 inhibitors delay human eosinophil and neutrophil apoptosis in the absence and presence of salbutamol

Abstract

In asthma and chronic obstructive pulmonary disease (COPD), the number of eosinophils and neutrophils in the lung is increased. One described mechanism leading to the impaired clearance of these cells from the lung is the delay in their programmed cell death (apoptosis). Selective inhibitors of phosphodiesterases (PDEs) are under development for the treatment of lung diseases because of their anti-inflammatory and bronchodilator activity. The aim of the present study was to establish whether inhibitors of PDE3, PDE4 and PDE5 modulate human eosinophil or neutrophil apoptosis or β 2-adrenoceptor agonist- or cytokine-afforded survival. We also evaluated whether a PDE4 inhibitor could modulate the effect of a corticosteroid on eosinophil and neutrophil apoptosis. Apoptosis was measured by using the relative DNA fragmentation assay and Annexin-V binding. Inhibitors of PDE4 (rolipram; 0.1–10 μM) and PDE3 (cilostazol; 0.1–10 μM) delayed spontaneous eosinophil apoptosis maximally by 25% and 15%, respectively. A combination of a PDE4 or PDE3 inhibitor (10 μM) with salbutamol (100 nM) further delayed eosinophil apoptosis maximally by 42–49%. In neutrophils, rolipram (10 μM) also decreased apoptosis with a maximal inhibition of 13%. The combination of rolipram (10 μM) and salbutamol (100 nM) produced a 27% inhibition of neutrophil apoptosis. Inhibitor of cGMP-specific PDE5 (zaprinast; 0.1–10 μM) did not affect eosinophil apoptosis and only slightly increased spontaneous neutrophil apoptosis. The effect of budesonide on apoptosis was not significantly modulated by a PDE4 inhibitor in eosinophils or neutrophils. The present results show that selective inhibitors of cAMP-hydrolyzing PDEs (PDE3 and PDE4) delay eosinophil apoptosis and, thus, increase their survival in vitro. Furthermore, β 2-adrenoceptor agonists enhance the anti-apoptotic effects of PDE3 and PDE4 inhibitors, suggesting that such drug combinations may prolong eosinophil and neutrophil longevity in the lung.