Role of Impaired CFTR Function in Pathogenesis of Pneumonia Among Alcohol Users

Abstract

INTRODUCTIONImpairment of mucociliary clearance (MCC) increases the risk of respiratory infections among excessive alcohol users. The mechanisms underlying this impact of alcohol on MCC are not currently understood. Our previous in vitro studies indicated that alcohol decreases ion transport via CFTR channels, the defective protein that causes cystic fibrosis. Here, we have attempted to validate these findings in vivo and test the hypothesis that alcohol‐induced CFTR dysfunction reduces airway surface hydration and mucus transport thereby impairing airway defense against inhaled bacterial pathogens, in particular Klebsiella pneumoniae, to which alcohol users are disproportionately susceptible. Since CFTR dysfunction correlates with reduced PKA‐dependent CFTR phosphorylation and channel gating due to increased cAMP degradation by phosphodiesterase‐4B (PDE4B) enzymes, we also tested the effects of PDE4 inhibitor, roflumilast, on CFTR function and bacterial clearance in alcohol‐fed rats.METHODSAge and gender‐matched rats (CFTR+/+) were pair‐fed with Lieber‐DeCarli alcohol diet or isocaloric control diet for 4 weeks and with K. pneumoniae (KP, ATCC 43816). Subsets of rats were randomly treated with vehicle/roflumilast (5mg/kg/day) by oral gavage starting 7 days before the end of the alcohol diet. CFTR activity was measured with nasal potential difference (NPD) and MCC was assayed with radiographic clearance of Tc99. Airway surface liquid (ASL), periciliary layer (PCL), and ciliary beat frequency (CBF) of excised trachea were quantified with micro‐optical coherence tomography (μOCT).RESULTSAlcohol administration reduced CFTR ion transport by NPD. Clearance of Tc99 label in 30 min indicated delayed MCC in alcohol‐treated rats. Trachea excised from alcohol‐treated rats exhibited significantly decreased PCL depth, but no meaningful differences in ASL or CBF. Roflumilast treatment significantly increased CFTR activity in both control and alcohol‐administered rats. Increased CFTR activation by roflumilast resulted in augmented PCL depth, reduced mucus viscosity and significantly accelerated MCT rate. Compared to controls, histopathological examination of lung sections from alcohol‐treated animals exhibited more severe evidence of multifocal pneumonia with edema, fibrin deposition and numerous bacteria in alveolar spaces. Ongoing studies are determining the impact of roflumilast treatment on bacterial clearance and severity of pneumonia by K. pneumoniae.CONCLUSIONSAlcohol‐induced defects in CFTR ion transport resulted in reduced airway surface hydration and delayed mucus clearance in rat airways that was associated with diminished ability to clear bacterial pathogens. Acquired (non‐genetic) CFTR dysfunction may be a suitable pharmacologic target to improve mucus clearance impaired by chronic alcohol use. Administration of roflumilast may boost lung host defense against bacterial pathogens and improve pneumonia outcomes in individuals affected by excessive alcohol use.Support or Funding InformationNIH 1R01AA027528