Exposure to polymers reverses inhibition of pulmonary surfactant by serum, meconium, or cholesterol in the captive bubble surfactometer

Dysfunction of pulmonary surfactant in the lungs is associated with respiratory pathologies such as acute respiratory distress syndrome or meconium aspiration syndrome. Serum, cholesterol, and meconium have been described as inhibitory agents of surfactant's interfacial activity once these substances appear in alveolar spaces during lung injury and inflammation. The deleterious action of these agents has been only partly evaluated under physiologically relevant conditions. We have optimized a protocol to assess surfactant inhibition by serum, cholesterol, or meconium in the captive bubble surfactometer. Specific measures of surface activity before and after native surfactant was exposed to inhibitors included i), film formation, ii), readsorption of material from surface-associated reservoirs, and iii), interfacial film dynamics during compression-expansion cycling. Results show that serum creates a steric barrier that impedes surfactant reaching the interface. A mechanical perturbation of this barrier allows native surfactant to compete efficiently with serum to form a highly surface-active film. Exposure of native surfactant to cholesterol or meconium, on the other hand, modifies the compressibility of surfactant films though optimal compressibility properties recover on repetitive compression-expansion cycling. Addition of polymers like dextran or hyaluronic acid to surfactant fully reverses inhibition by serum. These polymers also prevent surfactant inhibition by cholesterol or meconium, suggesting that the protective action of polymers goes beyond the mere enhancement of interfacial adsorption as described by depletion force theories.