Interactions of serum with lung surfactant extract in the bronchiolar and alveolar airway models

Lung surfactant (LS) a lipid–protein mixture is secreted by type-II pneumocytes and prevents alveolar collapse as well as maintains upper airway patency. In certain lung pathophysiology dysfunction of the LS occurs due to leakage of serum derived materials interacting with surfactant at the respiratory air–water interface. Bovine lipid extract surfactant (BLES) with and without foetal calf serum (FCS) were studied as models of bronchiolar airway patency using a capillary surfactometer, and in alveolar (terminal) airway using adsorbed Langmuir films in a surface balance. About 5 wt.% of serum was found to maximally decrease airway patency of BLES by 90%, as well as the surface films ability to reach low surface tension below 25 mN/m. In fact, FCS was found to be about 200-fold more potent inhibitor of the surfactant extract compared to a major serum component, albumin. Also serum but not albumin significantly reduced the gel-phase structures found in BLES films under compression at low amounts (5–10 wt.%), and eventually abolished these organized structures as imaged by fluorescence and atomic force microscopy. This fact suggests that serum caused complete molecular re-organization of the surfactant lipids in films at an air–water interface, and the ability of such films to reduce surface tension or maintain airway patency. The study may provide a novel structure–function disruption model for lung surfactant inactivation in the airways in pathophysiology.