Received for publication January 12, 2005.
Revised April 29, 2005.
Accepted for publication April 29, 2005.

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 CFTR activation may represent new therapeutics in their treatment. Herein we report the activation of CFTR-mediated chloride secretion by PDE4 inhibitors in T84 monolayer using ¹²⁵I anion as tracer. In the absence of forskolin, the iodide secretion was insensitive to PDE4 inhibitor L-826,141, Roflumilast or to PDE3 inhibitor Trequinsin. However, these inhibitors potently augmented iodide secretion following 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-CREB formation, the CFTR activation dissociated from a global cAMP elevation and was blocked by H89. 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 AC-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.

Key words: CFTR, PDE3, PDE4, PDE4D, T84, cAMP

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