Dynamic Activation of Cystic Fibrosis Transmembrane Conductance Regulator by Type 3 and Type 4D Phosphodiesterase Inhibitors

Abstract

The diseases of cystic fibrosis, chronic obstructive pulmonary disease (COPD), and chronic bronchitis are characterized by mucus-congested and inflamed airways. Anti-inflammatory agents that can simultaneously restore or enhance mucociliary clearance through cystic fibrosis transmembrane conductance regulator (CFTR) activation may represent new therapeutics in their treatment. Herein, we report the activation of CFTR-mediated chloride secretion by phosphodiesterase (PDE) 4 inhibitors in T84 monolayer using (125)I anion as tracer. In the absence of forskolin, the iodide secretion was insensitive to PDE4 inhibitor L-826,141 [4-[2-(3,4-bis-difluoromethoxyphenyl)-2-[4-(1,1,1,3,3,3-hexafluoro-2-hydroxypropan-2-yl)phenyl]-ethyl]-3-methylpyridine-1-oxide], roflumilast, or to PDE3 inhibitor trequinsin. However, these inhibitors potently augmented iodide secretion after forskolin stimulation, with efficacy coupled to the activation states of adenylyl cyclase. The iodide secretion from PDE3 or PDE4 inhibition was characterized at first by a prolonged efflux duration, followed by progressively elevated peak efflux rates at higher inhibitor concentrations. Paralleled with an increased phosphor-cAMP response element-binding protein formation, the CFTR activation dissociated from a global cAMP elevation and was blocked by H89 [N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide]. 2-(4-Fluorophenoxy)-N-[(1S)-1-(4-methoxyphenyl)ethyl]nicotinamide, a stereoselective PDE4D inhibitor, augmented iodide efflux more efficiently than its less potent (R)-isomer. The peak efflux from maximal PDE4 and PDE3 inhibition matched that from full adenylyl cyclase activation. These data suggest that PDE3 and PDE4 (mainly PDE4D) form the major cAMP diffusion barrier in T84 cells to ensure a compartmentalized CFTR signaling. Together with their potent anti-inflammatory properties, the potentially enhanced airway mucociliary clearance from CFTR activation may have contributed to the efficacy of PDE4 inhibitors in COPD and asthmatic patients. PDE4 inhibitors may represent new opportunities to combat cystic fibrosis and other respiratory diseases in future.

Cystic Fibrosis Transmembrane Conductance Regulator Activation by Roflumilast Contributes to Therapeutic Benefit in Chronic Bronchitis

“…Alternatively, hypertonic saline, which compensates for CFTR-dependent ASL decrements, also restores ASL volume by osmotic forces (24) and reduces mucus obstruction in a mouse model of chronic bronchitis (32). Because PDE4 inhibitors are known to increase intracellular levels of cAMP and to activate CFTR in airway epithelia (33)(34)(35)(36)(37)(38), we hypothesized that roflumilast could act similarly and ameliorate acquired CFTR dysfunction conferred by CSE. As shown in our studies, roflumilast efficiently activated CFTR in primary HBE cells and in intact human tissues, two models highly faithful to the ion transport properties of human airway epithelia in vivo (2,26).…”

PDE4-inhibitors: A novel, targeted therapy for obstructive airways disease

“…A consequence of reduced sensory input to the central nervous system would be a decrease in parasympathetic outflow to the airways, a reduction in contraction of airway smooth muscle and submucosal gland secretion, both leading to improvements in airflow and symptoms. Alternatively, the activation of the cystic fibrosis transmembrane receptor (CFTR) via elevating the level of cyclic AMP in airway epithelial cells could promote rehydration of the epithelial periciliary layer thereby facilitating mucociliary clearance of mucus and bacteria [33]. Indeed, PDE4 inhibitors can reduce mucus production and increase ciliary beat frequency of airway epithelial cells [34,35].…”

“…This stems from the notion that PDE4-inhibitors per se are relatively poor at inhibiting macrophage function (Table 1), that PDE3 is also present in epithelium and airway smooth muscle and that PDE3-inhibition can produce bronchodilator effects and also promote chloride ion secretion [33]. Mixed PDE-inhibitors can serve to have additive or potentially synergistic actions on cell function [27,33,57] and whilst early mixed PDE3/4 inhibitors evaluated by the inhaled route showed limited activity [58,59] this was attributed to their short retention time within the lung. The development of mixed PDE3/4 inhibitors with long duration of action coupled with anti-inflammatory activity could be of greater utility in COPD [60].…”

Roles of roflumilast, a selective phosphodiesterase 4 inhibitor, in airway diseases

“…Roflumilast has been shown to improve ciliary function in the bronchial epithelium (29). The activation of cystic fibrosis transmembrane receptors (CFTR) via elevating cAMP level in airway epithelial cells could promote epithelial rehydration thereby facilitating mucous clearance (30). These effects may contribute to clinical efficacy PDE4 inhibitor in chronic bronchitis.…”

“…One way is by inhibiting the PDE4D isoform binding site in the brain, causing nausea. Another way is that roflumilast stimulates cystic fibrosis transmembrane conductance regulator (CFRT)-dependent chloride secretion, causing diarrhea (30). However, these side effects typically resolve within 4 weeks after initiating treatment (3).…”