Phosphodiesterase 4 inhibitor roflumilast improves the bronchodilative effect of sevoflurane in sensitized airways

Transforming Growth Factor-β1 Decreases β2-Agonist-induced Relaxation in Human Airway Smooth Muscle

Helper T effector cytokines implicated in asthma modulate the contractility of human airway smooth muscle (HASM) cells. We have reported recently that a profibrotic cytokine, transforming growth factor (TGF)-β1, induces HASM cell shortening and airway hyperresponsiveness. Here, we assessed whether TGF-β1 affects the ability of HASM cells to relax in response to β₂-agonists, a mainstay treatment for airway hyperresponsiveness in asthma. Overnight TGF-β1 treatment significantly impaired isoproterenol (ISO)-induced relaxation of carbachol-stimulated, isolated HASM cells. This single-cell mechanical hyporesponsiveness to ISO was corroborated by sustained increases in myosin light chain phosphorylation. In TGF-β1-treated HASM cells, ISO evoked markedly lower levels of intracellular cAMP. These attenuated cAMP levels were, in turn, restored with pharmacological and siRNA inhibition of phosphodiesterase 4 and Smad3, respectively. Most strikingly, TGF-β1 selectively induced phosphodiesterase 4D gene expression in HASM cells in a Smad2/3-dependent manner. Together, these data suggest that TGF-β1 decreases HASM cell β₂-agonist relaxation responses by modulating intracellular cAMP levels via a Smad2/3-dependent mechanism. Our findings further define the mechanisms underlying β₂-agonist hyporesponsiveness in asthma, and suggest TGF-β1 as a potential therapeutic target to decrease asthma exacerbations in severe and treatment-resistant asthma.

Time- and Dose-Dependent Effects of Desflurane in Sensitized Airways

BACKGROUND

Although the bronchodilatory actions of volatile anesthetics, such as halothane, isoflurane, and sevoflurane, have been well documented in previous studies, the properties of desflurane remain controversial. The aim of this study was to investigate the effects of desflurane at different concentrations and durations in an ovalbumin-sensitized guinea pig model of airway hyper-responsiveness.

METHODS

Ovalbumin-sensitized animals (n = 176) were randomly assigned to 5 groups according to the minimum alveolar concentration (MAC) of desflurane they received: 0.0, 0.5, 1.0, 1.5, and 2.0 MAC. Total lung resistance in vivo, airway smooth muscle tension in vitro, and intracellular cyclic adenosine monophosphate (AMP) levels were measured to evaluate the effects of desflurane.

RESULTS

In 5 sensitized groups, total lung resistance increased from baseline to peak at approximately 8 minutes and then decreased slowly until about 17 minutes with extended administration of desflurane. Desflurane dose-dependently increased total lung resistance with or without incremental doses of acetylcholine and reduced muscle tension with increasing concentrations of carbacholine. Cyclic AMP levels were increased by desflurane: at the 60-minute time point, cyclic AMP concentrations (means ± SD) with 0.5 MAC (1.96 ± 0.40) and 1.0 MAC (2.11 ± 0.50) desflurane were higher than those at the 8-minute time point (1.11 ± 0.23 and 1.32 ± 0.32).

CONCLUSIONS

Desflurane exerted time- and dose-dependent effects and could be used at 0.5 and 1.0 MAC concentrations without significant bronchoconstriction in ovalbumin-sensitized guinea pigs. Cyclic AMP-mediated airway smooth muscle relaxation might be one mechanism by which desflurane induces bronchodilation.