Acquired cystic fibrosis transmembrane conductance regulator dysfunction in the lower airways in COPD

Abstract

Background: Cigarette smoke and smoking-induced inflammation decrease cystic fibrosis transmembrane conductance regulator (CFTR) activity and mucociliary transport in the nasal airway and cultured bronchial epithelial cells. This raises the possibility that lower airway CFTR dysfunction may contribute to the pathophysiology of COPD. We compared lower airway CFTR activity in current and former smokers with COPD, current smokers without COPD, and lifelong nonsmokers to examine the relationships between clinical characteristics and CFTR expression and function.

Methods: Demographic, spirometry, and symptom questionnaire data were collected. CFTR activity was determined by nasal potential difference (NPD) and lower airway potential difference (LAPD) assays. The primary measure of CFTR function was the total change in chloride transport (Δchloride-free isoproterenol). CFTR protein expression in endobronchial biopsy specimens was measured by Western blot.

Results: Compared with healthy nonsmokers (n = 11), current smokers (n = 17) showed a significant reduction in LAPD CFTR activity (Δchloride-free isoproterenol, -8.70 mV vs -15.9 mV; P = .003). Similar reductions were observed in smokers with and without COPD. Former smokers with COPD (n = 7) showed a nonsignificant reduction in chloride conductance (-12.7 mV). A similar pattern was observed for CFTR protein expression. Univariate analysis demonstrated correlations between LAPD CFTR activity and current smoking, the presence of chronic bronchitis, and dyspnea scores.

Conclusions: Smokers with and without COPD have reduced lower airway CFTR activity compared with healthy nonsmokers, and this finding correlates with disease phenotype. Acquired CFTR dysfunction may contribute to COPD pathogenesis.

Figure 1.

Bronchoscopic placement of the lower airway potential difference catheter. A, Supraglottic view. B, View from position in the lingual outlet.

Figure 2.

Lower airway potential difference in smokers with and without COPD. Representative lower airway potential difference tracings for each disease group. The start of each perfusion solution is marked with an arrow. Stable potential difference achieved after chloride-free isoproterenol perfusion is denoted with a red bar. High-frequency (0.2-0.5 Hz) noise most visible at the end of the tracing represents artifact caused by respiration. CFS = COPD former smoker; CS = COPD smoker; HNS = healthy nonsmoker; HS = healthy smoker.

Figure 3.

Ion transport activity in smokers with and without COPD. A, Cystic fibrosis transmembrane conductance regulator (CFTR) activity estimated in the lower airway by the change in PD following perfusion with chloride-free isoproterenol. **P < .005; ^***P = .054. B, Baseline potential difference as determined by the stable PD following perfusion with Ringer solution. Baseline PD was lower in both healthy smokers (−7.71 ± 0.88) and COPD smokers (−7.33 ± 1.30) than in healthy nonsmokers (−12.61 ± 1.94). *P < .05. C, Amiloride-sensitive PD determined by the change in PD with amiloride perfusion. Amiloride-sensitive PD was lower in healthy smokers (4.04 ± 0.78 mV) and COPD smokers (2.49 ± 0.72 mV) than in healthy nonsmokers (8.79 ± 2.09 mV); COPD former smokers again were intermediate but not statistically different from healthy control patients (5.08 ± 1.50). *P < .05; **P < .005. PD = potential difference.

Figure 4.

CFTR expression in the lower airway as determined by Western blot analysis. A, Representative blot demonstrating CFTR C-band expression compared with tubulin loading control. The densitometry ratio for each respective lane is shown. B, Summary data of that shown in A. *P < .05. See Figure 2 and 3 legends for expansion of abbreviations.

Figure 5.

Correlation of CFTR function as estimated by NPD and LAPD. Each parameter was calculated as the Δchloride-free isoproterenol perfusion compared with the respective value in the normal control population. A, Correlation between NPD and LAPD. No significant correlation was observed between CFTR-dependent chloride transport measured by NPD compared with LAPD in the overall population (r = 0.17, P = .34) or in healthy nonsmokers (r = −0.13, P = .70). B, Number of patients with a discordantly low LAPD compared with NPD vs the number of patients with a concordant or high LAPD. Discordantly low LAPD was defined as an LAPD below the mean (eg, < 100% of normal) when the NPD was equal to or above the mean (eg, ≥ 100% of normal). *P < .05 by Fisher exact test. LAPD = lower airway potential difference; NPD = nasal potential difference. See Figure 2 and 3 legends for expansion of other abbreviations.

Figure 6.

HNE levels in BAL samples. A, Mean HNE concentration in BAL samples (three 50-μL aliquots/sample) measured by fluorogenic substrate cleavage assay compared with purified substrate. *P < .05. B, Correlation between CFTR activity measured by LAPD (Δchloride-free plus isoproterenol perfusion) and BAL HNE concentration. The regression line was not statistically significant. HNE = human neutrophil elastase. See Figure 3 and 5 legends for expansion of other abbreviations.