Phosphodiesterase‐4 inhibition improves corticosteroid insensitivity in pulmonary endothelial cells under oxidative stress

Abstract Background Several clinical studies have shown that smoking in asthmatics and chronic obstructive pulmonary disease patients is closely associated with corticosteroid refractoriness. In this work, we have analyzed glucocorticoid insensitivity in human pulmonary artery endothelial cells ( HPAEC s) under cigarette smoke extract ( CSE ) exposure as well as the possible additive effects of the combination therapy with a phosphodiesterase ( PDE )‐4 inhibitor. Methods Interleukin ( IL )‐8 was measured in cell supernatants by ELISA . Histone deacetylase ( HDAC ), histone acetylase ( HAT ), and intracellular c AMP levels were measured by colorimetric assays and enzyme immunoassay, respectively. PDE4 isotypes and glucocorticoid receptor ( GR )‐α and β expression were measured by real‐time RT ‐ PCR . Results The PDE 4 inhibitor rolipram dose dependently inhibited the IL‐8 secretion induced by CSE 5%. In contrast, dexamethasone 1 μM did not show inhibitory effect on IL‐8 secretion. Combination of subeffective rolipram concentrations at 10 nM increased the inhibitory effect of dexamethasone to ~45% of inhibition. Cigarette smoke extract 5% inhibited HDAC activity and increased HAT activity generating glucocorticoid insensitivity. Rolipram did not modify the HDAC activity, however partially inhibited the increase in HAT activity at 1 μM. PDE 4 isotypes were up‐regulated by CSE 5% with the consequent c AMP down‐regulation. Dexamethasone reduced all PDE 4 isotypes expression and showed additive effects with rolipram enhancing c AMP levels. Furthermore, rolipram enhanced GR ‐α expression and inhibited the increase in GR ‐β induced by CSE . Conclusions Combination of rolipram and dexamethasone shows additive properties in HPAEC s under glucocorticoid insensitive conditions. These results may be of potential value in future anti‐inflammatory therapies using combination of PDE 4 inhibitors and glucocorticoids.