Airway ion transport impacts on disease presentation and severity in cystic fibrosis

A systematic review of animal and human data comparing the nasal potential difference test between cystic fibrosis and control

The nasal potential difference test (nPD) is an electrophysiological measurement which is altered in patients and animal models with cystic fibrosis (CF). Because protocols and outcomes vary substantially between laboratories, there are concerns over its validity and precision. We performed a systematic literature review (SR) of the nPD to answer the following review questions: A. Is the nasal potential difference similarly affected in CF patients and animal models?", and B. "Is the nPD in human patients and animal models of CF similarly affected by various changes in the experimental set-up?". The review protocol was preregistered on PROSPERO (CRD42021236047). We searched PubMed and Embase with comprehensive search strings. Two independent reviewers screened all references for inclusion and extracted all data. Included were studies about CF which described in vivo nPD measurements in separate CF and control groups. Risk of bias was assessed, and three meta-analyses were performed. We included 130 references describing nPD values for CF and control subjects, which confirmed substantial variation in the experimental design and nPD outcome between groups. The meta-analyses showed a clear difference in baseline nPD values between CF and control subjects, both in animals and in humans. However, baseline nPD values were, on average, lower in animal than in human studies. Reporting of experimental details was poor for both animal and human studies, and urgently needs to improve to ensure reproducibility of experiments within and between species.

On the Corner of Models and Cure: Gene Editing in Cystic Fibrosis

Cystic fibrosis (CF) is a severe genetic disease for which curative treatment is still lacking. Next generation biotechnologies and more efficient cell-based and in vivo disease models are accelerating the development of novel therapies for CF. Gene editing tools, like CRISPR-based systems, can be used to make targeted modifications in the genome, allowing to correct mutations directly in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. Alternatively, with these tools more relevant disease models can be generated, which in turn will be invaluable to evaluate novel gene editing-based therapies for CF. This critical review offers a comprehensive description of currently available tools for genome editing, and the cell and animal models which are available to evaluate them. Next, we will give an extensive overview of proof-of-concept applications of gene editing in the field of CF. Finally, we will touch upon the challenges that need to be addressed before these proof-of-concept studies can be translated towards a therapy for people with CF.

Chloride Conductance, Nasal Potential Difference and Cystic Fibrosis Pathophysiology

PURPOSE

Cystic fibrosis (CF) is a multisystem genetic disease caused by dysfunction of the epithelial anionic channel Cystic Fibrosis Transmembrane conductance Regulator (CFTR). Decreased mucociliary clearance because of thickened mucus is part of the pulmonary disease pathophysiology. It is controversial if the thickened airway surface liquid (ASL) is caused by the deficient chloride secretion and excessive sodium (through ENaC) and water hyperabsorption from the periciliar fluid or by the lack of bicarbonate secretion with relative acidification of the ASL. Correlations between the magnitude of in vivo chloride conductance with phenotypic characteristics and CF genotype can help to elucidate these mechanisms and direct to new treatments.

METHODS

Nasal potential difference was measured in 28 CF patients (age from 0.3 to 28 year) and correlated with pulmonary function, pancreatic phenotype, pulmonary colonization and genotype severity.

RESULTS

The CFTR-chloride conductance was better in older patients (r = 0.40; P = 0.03), in patients with better pulmonary function (r = 0.48; P = 0.01), and was associated with genotype severity. Higher chloride diffusion in the presence of a favorable chemical gradient was associated with Pseudomonas aeruginosa negativity (P < 0.05). More negative NPDmax was associated with pancreatic insufficiency (P < 0.01) as well with genotype severity, but not with the pulmonary function.

CONCLUSIONS

The anion permeability through CFTR, mainly chloride, but bicarbonate as well, is the most critical factor in CF airway pathophysiology. Treatments primarily directed to correct CFTR function and/or airway acidity are clearly a priority.

Repeatability and Diagnostic Value of Nasal Potential Difference in a Genetically Admixed Population

BACKGROUND

The genetic diversity of the Brazilian population results from three ethnic groups admixture: Europeans, Africans and Amerindians, thus increasing the difficulty of performing cystic fibrosis (CF) diagnosis. The nasal potential difference (NPD) evaluates the cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial sodium channel (ENaC) activity. Despite being a useful CF diagnostic test and a biomarker of CFTR-modulator drugs, it is also highly operator dependent. Therefore, it may be difficult to get accurate results and to interpret them. Wilschanski and Sermet scores were proposed to address these issues. This study aimed to evaluate repeatability and diagnostic value of NPD parameters and Wilschanski and Sermet scores in a CF center in Rio de Janeiro.

METHODS

NPD was performed in 78 subjects. Maximal PD, amiloride response, total chloride response, and Wilschanski and Sermet scores were explored as means (confidence interval, CI). One-way ANOVA was used to compare mean differences and Scheffe test was used to pair-wise comparisons. Repeatability was evaluated by scatter and Bland-Altman plots. The Ethics Committee of the CF Center has approved the study protocol. Parents and adult participants signed an informed consent form.

RESULTS

Forty-eight healthy-volunteers, 19 non-CF and 11 CF patients were enrolled in this study. Significant differences were found when comparing CF patients' NPD parameters to the other two groups (P = 0.000). Moreover, no significant differences were found when parameters from non-CF patients were compared with those from healthy volunteers (P > 0.05). The means of NPD parameters and diagnostic scores of each group were in concordance with disease/non-disease conditions. The repeatability data - Wilschanski and Sermet and NPD - allow NPD to be performed in this Brazilian CF Center.

CONCLUSIONS

The present study gathered consistent data for Bland-Altman plots. The results of Wilschanski and Sermet diagnostic scores suggest that they were concordant with CF/non-CF conditions. More NPD tests should be performed in the Rio de Janeiro CF dynamic cohort to contribute to international NPD validation studies and to provide NPD as a biomarker in Brazil.

Nasal potential difference: Best or average result for CFTR function as diagnostic criteria for cystic fibrosis?

BACKGROUND

The current practice of averaging the nasal potential difference (NPD) results of right and left nostril measurements reduce inter-individual variability but may underestimate individual CFTR function.

METHODS

Best NPD response to Cl(-)-free and isoproterenol perfusion (=largest ΔPD(0Cl/Iso)) from the right and left nostril was compared to the average result in 13 cystic fibrosis (CF), 78 query-CF patients and 22 healthy controls from 2 cohorts.

RESULTS

Despite moderate to good correlation (p<0.001) between right and left measured ΔPD(0Cl/Iso), we observed large differences in some individuals. A comparison of average versus best ΔPD(0Cl/Iso) showed only moderate agreement (Giessen κ=0.538; Toronto κ=0.607). Averaging ΔPD(0Cl/Iso) showed a lower composite chloride response compared to best ΔPD(0Cl/Iso) and altered diagnostic NPD interpretation in 30 of 113 (27%) subjects.

CONCLUSIONS

The current practice of averaging the NPD results of right and left nostril measurements leads to an underestimation of the individual CFTR function and should be reconsidered.

Intestinal current measurement versus nasal potential difference measurements for diagnosis of cystic fibrosis: a case-control study

Background

Nasal potential difference (NPD) and intestinal current measurement (ICM) are functional CFTR tests that are used as adjunctive diagnostic tools for cystic fibrosis (CF). Smoking has a systemic negative impact on CFTR function. A diagnostic comparison between NPD and ICM and the impact of smoking on both CFTR tests has not been done.

Methods

The sweat chloride test, NPD, and ICM were performed in 18 patients with CF (sweat chloride >60 mmol/l), including 6 pancreatic sufficient (PS) patients, and 13 healthy controls, including 8 smokers. The NPD CFTR response to Cl-free and isoproterenol perfusion (Δ0Cl^- + Iso) was compared to the ICM CFTR response to forskolin/IBMX, carbachol, and histamine (ΔI_{sc, forskolin/IBMX+ carbachol+histamine}).

Results

The mean NPD CFTR response and ICM CFTR response between patients with CF and healthy controls was significantly different (p <0.001), but not between patients with CF who were PS and those who were pancreatic insufficient (PI). Smokers have a decreased CFTR response measured by NPD (p = 0.049). For ICM there is a trend towards decreased CFTR response (NS). Three healthy control smokers had NPD responses within the CF-range. In contrast to NPD, there was no overlap of the ICM response between patients with CF and controls.

Conclusions

ICM is superior to NPD in distinguishing between patients with CF who have a sweat chloride > 60 mmol/l and healthy controls, including smokers. Neither NPD nor ICM differentiated between patients with CF who were PS from those who were PI. Smoking has a negative impact on CFTR function in healthy controls measured by NPD and challenges the diagnostic interpretation of NPD, but not ICM.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2466-14-156) contains supplementary material, which is available to authorized users.

Optimizing nasal potential difference analysis for CFTR modulator development: assessment of ivacaftor in CF subjects with the G551D-CFTR mutation

Nasal potential difference (NPD) is used as a biomarker of the cystic fibrosis transmembrane conductance regulator (CFTR) and epithelial sodium channel (ENaC) activity. We evaluated methods to detect changes in chloride and sodium transport by NPD based on a secondary analysis of a Phase II CFTR-modulator study. Thirty-nine subjects with CF who also had the G551D-CFTR mutation were randomized to receive ivacaftor (Kalydeco™; also known as VX-770) in four doses or placebo twice daily for at least 14 days. All data were analyzed by a single investigator who was blinded to treatment assignment. We compared three analysis methods to determine the best approach to quantify changes in chloride and sodium transport: (1) the average of both nostrils; (2) the most-polarized nostril at each visit; and (3) the most-polarized nostril at screening carried forward. Parameters of ion transport included the PD change with zero chloride plus isoproterenol (CFTR activity), the basal PD, Ringer's PD, and change in PD with amiloride (measurements of ENaC activity), and the delta NPD (measuring CFTR and ENaC activity). The average and most-polarized nostril at each visit were most sensitive to changes in chloride and sodium transport, whereas the most-polarized nostril at screening carried forward was less discriminatory. Based on our findings, NPD studies should assess both nostrils rather than a single nostril. We also found that changes in CFTR activity were more readily detected than changes in ENaC activity, and that rigorous standardization was associated with relatively good within-subject reproducibility in placebo-treated subjects (±2.8 mV). Therefore, we have confirmed an assay of reasonable reproducibility for detecting chloride-transport improvements in response to CFTR modulation.

[Mucoviscidosis: CFTR mutation-specific therapy: a ray of sunshine in a cloudy sky]

There is a need to find a cure for pulmonary disease in cystic fibrosis (CF), though full benefit of this approach will be restricted to those patients with well-preserved lungs. The most promising route is currently that of a pharmacological mutation-specific approach aiming at correcting the mechanism by which mutations lead to impairment of chloride conductance across respiratory epithelial cells. In the past 14years, 7 candidate drugs (CPX, 4PBA, gentamicin, PTC124, VX-770 or Ivacaftor, VX-809 or Lumacaftor, and Miglustat) have been investigated in CF patients. A postulate of 14 out of the 15 published studies has been that an effective agent had to improve total chloride secretion as assessed in vivo by nasal potential difference measurements. The present review casts a critical look at these studies. Apparent inconsistencies are discussed as well as possible limitations of nasal potential difference measurements as outcome parameters in these trials. Primarily targeting a mutation carried by less than 2% of French CF patients, the 2 Ivacaftor studies could well be a milestone on the long road toward a cure for CF. However, further data on safety and long-term efficacy are obviously needed and the current price of this medication in the US would make it unaffordable for European patients.

Modular microfluidic system as a model of cystic fibrosis airways

A modular microfluidic airways model system that can simulate the changes in oxygen tension in different compartments of the cystic fibrosis (CF) airways was designed, developed, and tested. The fully reconfigurable system composed of modules with different functionalities: multichannel peristaltic pumps, bubble traps, gas exchange chip, and cell culture chambers. We have successfully applied this system for studying the antibiotic therapy of Pseudomonas aeruginosa, the bacteria mainly responsible for morbidity and mortality in cystic fibrosis, in different oxygen environments. Furthermore, we have mimicked the bacterial reinoculation of the aerobic compartments (lower respiratory tract) from the anaerobic compartments (cystic fibrosis sinuses) following an antibiotic treatment. This effect is hypothesised as the one on the main reasons for recurrent lung infections in cystic fibrosis patients.

A randomized placebo-controlled trial of miglustat in cystic fibrosis based on nasal potential difference

BACKGROUND

Preclinical data suggest that miglustat could restore the function of the cystic fibrosis transmembrane conductance regulator gene in cystic fibrosis cells.

METHODS

Single-center, randomized, double-blind, placebo-controlled, crossover Phase II study in 11 patients (mean±SD age, 26.3±7.7 years) homozygous for the F508del mutation received oral miglustat 200 mgt.i.d. or placebo for two 8-day cycles separated by a 14-day washout period. The primary endpoint was the change in total chloride secretion (TCS) assessed by nasal potential difference.

RESULTS

No statistically significant changes in TCS, sweat chloride values or FEV(1) were detected. Pharmacokinetic and safety were similar to those observed in patients with other diseases exposed to miglustat.

CONCLUSIONS

There was no evidence of a treatment effect on any nasal potential difference variable. Further studies with miglustat need to adequately address criteria for assessment of nasal potential difference.

Airway delivery of low-dose miglustat normalizes nasal potential difference in F508del cystic fibrosis mice

RATIONALE

N-butyldeoxynojyrimicin (NB-DNJ, miglustat [Zavesca]) an approved drug for treating Gaucher disease, was reported to be able to correct the defective trafficking of the F508del-CFTR protein.

OBJECTIVES

To evaluate the efficacy of in vivo airway delivery of miglustat for restoring ion transport in cystic fibrosis (CF).

METHODS

We used nasal transepithelial potential difference (PD) as a measure of sodium and chloride transport. The effect of nasal instillation of a single dose of miglustat was investigated in F508del, cftr knockout and normal homozygous mice. The galactose iminosugar analog N-butyldeoxygalactonojirimycin (NB-DGJ) was used as a placebo.

MEASUREMENTS AND MAIN RESULTS

In F508del mice, sodium conductance (evaluated by basal hyperpolarization) and chloride conductance (evaluated by perfusing the nasal mucosa with chloride-free solution in the presence of amiloride and forskolin) were normalized 1 hour after an intranasal dose of 50 picomoles of miglustat. Chloride conductance in the presence of 200 microM 4-4'-diisothiocyanostilbene-2,2'-disulphonic acid (DIDS), an inhibitor of alternative chloride channels, was much higher after miglustat than after placebo. In cftr knockout mice, a normalizing effect was observed on sodium but not on chloride conductance.

CONCLUSIONS

Our results provide clear evidence that nasal delivery of miglustat, at picomolar doses, normalizes sodium and Cftr-dependent chloride transport in F508del transgenic mice; they highlight the potential of topical miglustat as a therapy for CF.