Pulmonary surfactant-associated proteins and inflammatory factors in obstructive sleep apnea

Pulmonary surfactant (PS) plays roles in promoting the removal of the liquid, host defense, and immune regulation in the tracheal, bronchial, and alveoli epithelium. PS protein expression level can be regulated by oxygen levels and related free radicals. Obstructive sleep apnea (OSA) is featured with oxygen free radical production for damaging epithelial tissues and thus may affect PS production. The study was to explore the relationship between PS protein and OSA severity. We collected serum and bronchoalveolar lavage fluid (BALF) samples from 35 OSA patients and 22 healthy subjects. PS-associated proteins and inflammatory factors, including surfactant proteins, HIF-1 alpha, NF-kappa B, and IL-6, were analyzed. Regression analysis was performed to reveal the relationship between biochemical factors and clinical indexes recorded during PSG monitor. Lower BALF and surfactant protein (except surfactant protein C or SPC) levels occurred in OSA patients (all p < 0.05 compared to control group). A strongly negative correlation was found between surfactant protein with apnea-hypopnea index (AHI) and other sleeping indexes including ODI3 and ODI4. Similar patterns were found in serum samples, which were strongly correlated with BALF counterparts. Surfactant proteins were further found to have negative regression with inflammatory factors such as HIF-1 alpha, NF-kappa B, and IL-6. This study established the relationship between PS-related protein with severity of OSA, plus their relationship with inflammatory factors. Our results provided possibly novel markers in general circulation for disease evaluation of OSA.