Inflammation and oxidative stress in the sputum of patients with cystic fibrosis: correlations with lung function, aerobic fitness, and morbidity

OBJECTIVE: The aim of this study was to compare the sputum inflammatory profile of children and adolescents with cystic fibrosis (CF) to that of healthy saliva controls and to assess the association between these markers and key clinical variables. METHODS: This is an observational study comparing a group of CF patients with a healthy control group, including sputum samples from patients aged 6-18 years, followed up at a CF referral center. All procedures were performed on the same day, including spirometry, cardiopulmonary exercise testing, and sputum collection and processing. Demographic and clinical data were collected from patient records. RESULTS: A total of 12 CF patients were included with a mean age of 13.0±2.8 years, a mean forced expiratory volume in one second of 86.4±20.8%, and a peak oxygen consumption (VO2peak) of 35.4±4.6 mL kg -1 min-1. A predominance of neutrophils was found in the sputum. The median (interquartile range) of interleukin-8 (IL-8) was 386.8 (310.5) pg/g of protein, and thiobarbituric acid-reactive substances (TBARS) had a median of 2.2 (0.9) μM/g of protein. When comparing CF patients and healthy individuals, the CF group showed higher IL-8 concentrations (p<0.001) and increased TBARS levels (p=0.01). A correlation was found between IL-6 concentration and the number of days on antibiotics (rho=0.71; p=0.009), and an inverse moderate correlation was found between IL-8 and forced expiratory flow between 25 and 75% (FEF25-75%) (rho=-0.62; p=0.033). CONCLUSIONS: Individuals with CF exhibited increased sputum inflammation compared with healthy controls, which correlated with lung function and morbidity but not with aerobic fitness.