Introduction:
Cystic fibrosis (CF) involves chronic inflammation and decreased pulmonary function, which increase caloric demand. Yet, sufficient energy provision is hindered by reduced appetite and fat malabsorption. Brain-derived neurotrophic factor (BDNF), leptin, and neuropeptide Y (NPY) belong to energy balance-regulating factors. We aimed to assess their concentrations in CF patients in order to search for potential clinical correlates.

Material and methods:
This was an exploratory, cross-sectional study. Patients’ weight and height Z-scores, forced expiratory volume in 1 s (FEV₁%), exocrine pancreatic status (fecal elastase-1), genotypes, and other characteristics were assessed. Serum concentrations of BDNF, leptin, NPY, IL-6, and TNF-α were measured using ELISA.

Results:
The study enrolled 56 patients, of whom 29 (52%) were female and 17 (30%) were younger than 16 years. Median (1st–3rd quartile) mass Z-score was –0.85 (–1.56–(–0.36)); median FEV1 was 70.5% (45.0–89.5); 48 (86%) patients had exocrine pancreatic insufficiency and 8 (14%) diabetes. Overall, median concentrations were: BDNF: 33.91 ng/ml (26.40–40.43), leptin: 12.05 ng/ml (8.93–17.77), NPY: 2.86 ng/ml (1.75–4.42). None of these factors correlated with mass Z-score, FEV₁%, IL-6 or TNF-α. Leptin and NPY correlated negatively (ρ = –0.62, p = 3 × 10^–7); BDNF/NPY ratio was associated with leptin (ρ = 0.54, p = 2 × 10^–5), BDNF/leptin ratio correlated with NPY (ρ = 0.60, p = 1 × 10^–6). In a multivariable regression analysis NPY was weakly, but independently, associated with FEV1%, and leptin with age.

Conclusions:
BDNF and leptin were not associated with weight Z-score or FEV₁%. Serum NPY concentrations seemed to be lower in CF patients with reduced pulmonary function independently of malnutrition and inflammation.