Nasal potential difference in cystic fibrosis considering severe CFTR mutations

Personalized medicine with drugs targeting the underlying protein defect in cystic fibrosis: is monitoring of treatment response necessary?

Cystic fibrosis (CF) is caused by two mutations in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) gene. In the last years, drugs targeting the underlying protein defect like lumacaftor/ivacaftor (LUM/IVA) or tezacaftor/ivacaftor (TEZ/IVA) and more recently elexacaftor/tezacaftor/ivacaftor (ELX/TEZ/IVA) were admitted. Outcome parameters evaluating therapy response like forced expiratory pressure in 1 s (FEV₁), body mass index (BMI) or the efficacy of CFTR function in sweat glands showed improvement in several cases. Other, CFTR biomarkers were analysed rarely. This prospective observational study was aimed at evaluating CFTR function in patients treated with different CFTR modulators together with common valid clinical outcome parameters at standardized appointments (day 0, week 2, 4, 16). We followed four patients with the same mutation (F508del-CFTR), sex, age and disease severity. Monitoring focused on lung function, gastrointestinal aspects and CFTR function of sweat glands, nasal and intestinal epithelium. Sweat tests were performed by pilocarpine iontophoresis. Nasal potential difference (NPD) measured transepithelial voltage in vivo and potential increased when CFTR function improved. Rectal biopsies were obtained for intestinal current measurements (ICM) ex vivo. Intestinal CFTR function was assessed by stimulating chloride secretion with different reagents. Response to CFTR modulators regarding clinical outcome parameters was rather variable. A sweat chloride reduction of 35.3 mmol/L, nasal CFTR rescue of 4.4% and fivefold higher CFTR function in the intestine was seen at week 16 post-LUM/IVA. Due to our monitoring, we identified a non-responder to LUM/IVA and TEZ/IVA. In case of ELX/TEZ/IVA, clinical parameters and CFTR bioassays improved and were concordant. Although our cohort is small, results emphasize that non-responders exist and conclusions could not be drawn if patients were not monitored. Data on CFTR function can confirm or disprove ongoing CFTR dysfunction and might be helpful selectively. Non-responders need other alternative therapy options as demonstrated with ELX/TEZ/IVA.

Chloride and sodium ion concentrations in saliva and sweat as a method to diagnose cystic fibrosis

OBJECTIVE

Cystic fibrosis diagnosis is dependent on the chloride ion concentration in the sweat test (≥60mEq/mL - recognized as the gold standard indicator for cystic fibrosis diagnosis). Moreover, the salivary glands express the CFTR protein in the same manner as sweat glands. Given this context, the objective was to verify the correlation of saliva chloride concentration and sweat chloride concentration, and between saliva sodium concentration and sweat sodium concentration, in patients with cystic fibrosis and healthy control subjects, as a tool for cystic fibrosis diagnosis.

METHODS

There were 160 subjects enrolled: 57/160 (35.70%) patients with cystic fibrosis and two known CFTR mutations and 103/160 (64.40%) healthy controls subjects. Saliva ion concentration was analyzed by ABL 835 Radiometer^® equipment and, sweat chloride concentration and sweat sodium concentration, respectively, by manual titration using the mercurimetric procedure of Schales & Schales and flame photometry. Statistical analysis was performed by the chi-squared test, the Mann-Whitney test, and Spearman's correlation. Alpha=0.05.

RESULTS

Patients with cystic fibrosis showed higher values of sweat chloride concentration, sweat sodium concentration, saliva chloride concentration, and saliva sodium concentration than healthy controls subjects (p-value<0.001). The correlation between saliva chloride concentration and sweat chloride concentration showed a positive Spearman's Rho (correlation coefficient)=0.475 (95% CI=0.346 to 0.587). Also, the correlation between saliva sodium concentration and sweat sodium concentration showed a positive Spearman's Rho=0.306 (95% CI=0.158 to 0.440).

CONCLUSIONS

Saliva chloride concentration and saliva sodium concentration are candidates to be used in cystic fibrosis diagnosis, mainly in cases where it is difficult to achieve the correct sweat amount, and/or CFTR mutation screening is difficult, and/or reference methods for sweat test are unavailable to implement or are not easily accessible by the general population.

Sweat test and cystic fibrosis: overview of test performance at public and private centers in the state of São Paulo, Brazil

Objective:

The sweat test (ST) measures chloride levels in sweat and is considered the gold standard for the diagnosis of cystic fibrosis (CF). However, the reliability of a ST depends on their being performed by experienced technicians and in accordance with strict guidelines. Our aim was to evaluate how sweat stimulation, sweat collection, and chloride measurement are performed at 14 centers (9 public centers and 5 private centers) that routinely perform STs in the state of São Paulo, which has the highest frequency of CF in Brazil.

Methods:

This was a cross-sectional cohort study, using a standardized questionnaire administered in loco to the staff responsible for conducting STs.

Results:

No uniformity regarding the procedures was found among the centers. Most centers were noncompliant with the international guidelines, especially regarding the collection of sweat (the samples were insufficient in 10-50% of the subjects tested); availability of stimulation equipment (which was limited at 2 centers); modernity and certification of stimulation equipment (most of the equipment having been used for 3-23 years); and written protocols (which were lacking at 12 centers). Knowledge of ST guidelines was evaluated at only 1 center.

Conclusions:

Our results show that STs largely deviate from internationally accepted guidelines at the participating centers. Therefore, there is an urgent need for standardization of STs, training of qualified personnel, and acquisition/certification of suitable equipment. These are essential conditions for a reliable diagnosis of CF, especially with the increasing demand due to newborn screening nationwide, and for the assessment of a possible clinical benefit from the use of modulator drugs.

Thirty Years of Sweat Chloride Testing at One Referral Center

OBJECTIVE

To conduct a descriptive analysis of the sweat test (ST), associating ST results with epidemiological data, CFTR (cystic fibrosis transmembrane conductance regulator) mutations and reasons to indicate the ST, as well as correlating sweat sodium and sweat chloride concentrations in subjects.

METHODS

Retrospective survey and descriptive analysis of 5,721 ST at a university referral center.

RESULTS

The inclusion of the subjects was based on clinical data related with cystic fibrosis (CF) phenotype. The samples were grouped by (i) sweat chloride concentrations (mEq/L): <30: 3,249/5,277 (61.6%); ≥30 to <60: 1,326/5,277 (25.1%); ≥60: 702/5,277 (13.3%) and (ii) age: (Group A--GA) 0 to <6 months; (Group B--GB) ≥6 months to <18 years; (Group C--GC) ≥18 years. Digestive symptoms showed higher prevalence ratio for the CF diagnosis as well as association between younger age and higher values of sweat chloride, sweat sodium, and chloride/sodium ratio. The indication of ST due to respiratory symptoms was higher in GB and associated with greater age, lower values of sweat chloride, sweat sodium, and chloride/sodium ratio. There was higher prevalence of ST with sweat chloride levels <30 mEq/L in GB, ≥60 mEq/L in GC, and with borderline level in GB. There was positive correlation between sweat sodium and sweat chloride. Sweat chloride/sweat sodium and sweat sodium-sweat chloride indexes showed association with sex, reason for ST indication, and CFTR mutations. Sex alters some values presented in the ST. The number of ST/year performed before and after the newborn screening implementation was the same; however, we observed a higher number of borderlines values. A wide spectrum of CFTR mutation was found. Severe CFTR mutations and F508del/F508del genotype were associated with highest probability of ST chloride levels ≥60 mEq/L, and the absence of CFTR mutations identified was associated with borderline ST and respiratory symptoms.

CONCLUSIONS

ST data showed wide variability dependent on age, sex, reason for examination indication, CFTR mutations, and weight of the collected sweat sample. Sweat sodium concentration is directly correlated with sweat chloride levels and it could be used as a quality parameter.

Changes in the inner ear structures in cystic fibrosis patients

OBJECTIVE

Although prolonged use of antibiotics is very common in cystic fibrosis (CF) patients, no studies have assessed the changes in both cochlear and peripheral vestibular systems in this population.

METHODS

We used human temporal bones to analyze the density of vestibular dark, transitional, and hair cells in specimens from CF patients who were exposed to several types of antibiotics, as compared with specimens from an age-matched control group with no history of ear disease or antibiotic use. Additionally, we analyzed the changes in the elements of the cochlea (hair cells, spiral ganglion neurons, and the area of the stria vascularis). Data was gathered using differential interference contrast microscopy and light microscopy.

RESULTS

In the CF group, 83% of patients were exposed to some ototoxic drugs, such as aminoglycosides. As compared with the control group, the density of both type I and type II vestibular hair cells was significantly lower in all structures analyzed; the number of dark cells was significantly lower in the lateral and posterior semicircular canals. We noted a trend toward a lower number of both inner and outer cochlear hair cells at all turns of the cochlea. The number of spiral ganglion neurons in Rosenthal's canal at the apical turn of the cochlea was significantly lower; furthermore, the area of the stria vascularis at the apical turn of the cochlea was significantly smaller.

CONCLUSIONS

Deterioration of cochlear and vestibular structures in CF patients might be related to their exposure to ototoxic antibiotics. Well-designed case-control studies are necessary to rule out the effect of CF itself.

Quality of sweat test (ST) based on the proportion of sweat sodium (Na) and sweat chloride (Cl) as diagnostic parameter of cystic fibrosis: are we on the right way?

BACKGROUND

To assess the quality of sweat test (ST) based on the proportion of sweat sodium and sweat chloride as diagnostic parameter of cystic fibrosis (CF).

METHODS

A retrospective study of 5,721 sweat samples and subsequent descriptive analysis were carried out. The test was considered "of good quality" (correct) when: (i) sweat chloride was lower than 60 mEq/L, and sweat sodium was higher than sweat chloride; (ii) sweat chloride was higher than 60 mEq/L, and sweat sodium was lower than sweat chloride.

RESULTS

The study included 5,692/5,721 sweat samples of ST which had been requested due to clinical presentations compatible with CF and/or neonatal screenings with altered immunoreactive trypsinogen values. Considering the proportion of sweat sodium and sweat chloride as ST quality parameter, the test was performed correctly in 5,023/5,692 (88.2 %) sweat samples. The sweat chloride test results were grouped into four reference ranges for chloride (i) chloride < 30 mEq/L: 3,651/5,692 (64.1 %); (ii) chloride ≥ 30 mEq/L to < 40 mEq/L: 652/5,692 (11.5 %); (iii) ≥ 40 mEq/L to < 60 mEq/L: 673/5,692 (11.8 %); (iv) ≥ 60 mEq/L: 716/5,692 (12.6 %). In the comparative analysis, there was no association between ST quality and: (i) symptoms to indicate a ST [respiratory (p = 0.084), digestive (p = 0.753), nutritional (p = 0.824), and others (p = 0.136)], (ii) sweat weight (p = 0.416). However, there was a positive association with: (i) gender, (ii) results of ST (p < 0.001), (iii) chloride/sodium ratio (p < 0.001), (iv) subject's age at the time of ST [grouped according to category (p < 0.001) and numerical order (p < 0.001)]. For the subset of 169 patients with CF and two CFTR mutations Class I, II and/or III, in comparative analysis, there was a positive association with: (i) sweat chloride/sodium ratio (p < 0.001), (ii) sweat chloride values (p = 0.047), (iii) subject's age at the time of the ST grouped by numerical order (p = 0.001).

CONCLUSIONS

Considering that the quality of ST can be assessed by levels of sweat sodium and sweat chloride, an increasing number of low-quality tests could be observed in our sweat samples. The quality of the test was associated with important factors, such as gender, CF diagnosis, and subjects' age.