Pre-Exposure of Pulmonary Surfactant to Hyaluronic Acid Alters its Structure and Interfacial Properties

Abstract

Pulmonary surfactant is a complex mixture of lipids and proteins lining the alveolar air-water interface. By lowering the surface tension, pulmonary surfactant stabilizes the respiratory epithelium against physical forces tending to collapse it. Dysfunction of surfactant is associated with respiratory pathologies such as acute respiratory distress syndrome (ARDS) or meconium aspiration syndrome (MAS), where naturally occurring inhibitory agents reach the lung. We have already confirmed the higher resistance to inhibition of preparations combining pulmonary surfactant and polymers such as hyaluronan (HA) and the potential use of these additives to design new therapeutic surfactant preparations. In the present study we have analysed the effect of HA on the structure and surface behaviour of pulmonary surfactant complexes, in order to investigate the possible mechanism for HA-promoted reactivation. We have observed significant effects of HA on structural properties such as aggregation of surfactant membranes, or size, distribution and packing of segregated ordered lipid domains. We have also observed that HA promotes refining of surfactant composition, i.e. enrichment of pelletable large surfactant complexes in saturated phospholipids. Surprisingly, we have detected no apparent direct interaction between surfactant complexes and HA even though we have observed 100% of transfer of surfactant complexes into the interface only in the presence of this polymer. All of these irreversible changes in surfactant structure and activity are observed only upon pre-exposure of surfactant to polymer concentrations at which the polymer forms an entangled meshwork. We propose that the polymer meshwork is responsible for entropy-mediated changes in surfactant structure, which may enhance surfactant function and thus resistance to inactivation.