Activation of the Cystic Fibrosis Transmembrane Conductance Regulator by the Flavonoid Quercetin Potential Use as a Biomarker of ΔF508 Cystic Fibrosis Transmembrane Conductance Regulator Rescue

Therapies to correct the Delta F508 cystic fibrosis transmembrane conductance regulator (CFTR) folding defect require sensitive methods to detect channel activity in vivo. The beta(2) adrenergic receptor agonists, which provide the CFTR stimuli commonly used in nasal potential difference assays, may not overcome the channel gating defects seen in Delta F508 CFTR after plasma membrane localization. In this study, we identify an agent, quercetin, that enhances the detection of surface Delta F508 CFTR, and is suitable for nasal perfusion. A screen of flavonoids in CFBE41o(-) cells stably transduced with Delta F508 CFTR, corrected to the cell surface with low temperature growth, revealed that quercetin stimulated an increase in the short-circuit current. This increase was dose-dependent in both Fisher rat thyroid and CFBE41o(-) cells. High concentrations inhibited Cl(-) conductance. In CFBE41o(-) airway cells, quercetin (20 mu g/ml) activated Delta F508 CFTR, whereas the beta(2) adrenergic receptor agonist isoproterenol did not. Quercetin had limited effects on cAMP levels, but did not produce detectable phosphorylation of the isolated CFTR R-domain, suggesting an activation independent of channel phosphorylation. When per-fused in the nares of Cftr(+) mice, quercetin (20 mu g/ml) produced a hyperpolarization of the potential difference that was absent in Cftr(-/-) mice. Finally, quercetin-induced, dose-dependent hyperpolarization of the nasal potential difference was also seen in normal human subjects. Quercetin activates CFTR-mediated anion transport in respiratory epithelia in vitro and in vivo, and may be useful in studies intended to detect the rescue of Delta F508 CFTR by nasal potential difference.