Restoration of the interfacial properties of lung surfactant with a newly designed hydrocarbon/fluorocarbon lipid

Serum proteins, especially fibrinogen, inactivate the lung surfactant mixture by adsorbing quickly and irreversibly to the alveolar air/aqueous interface. As a consequence of the inactivation, the surfactant becomes dysfunctional, and respiration cannot be maintained properly. Preventing the adsorption of surface active serum proteins to the air/water interface is important because this phenomenon causes fatal diseases such as acute respiratory distress syndrome (ARDS). Although some treatments exist, improvements in synthetic surfactants that can resist this inactivation are still expected. In this context, a novel ion pair lipid (IPL, CF3(CF2)7SO3−(CH2CH3)3N+(CH2OCH2)10(CH2)15CH3) has been designed and synthesized. This surfactant reduces the inhibitory effect of fibrinogen by selectively interacting with DPPC (dipalmitoylphosphatidylcholine) and mimicking some of the interfacial properties of the pulmonary surfactant protein B (SP-B). Surface pressure–area isotherms and fluorescence microscopy images demonstrate that IPL can mix and interact synergistically with DPPC due to its unique molecular structure. Hysteresis behaviors of the monolayers, which are composed of mixtures of DPPC and IPL at different molar ratios, indicate that with increasing amounts of IPL, the lipid losses from the interface induced by the presence of fibrinogen significantly decrease. It is also found that IPL is able to adsorb to monolayers formed in the presence of fibrinogen, whereas fibrinogen cannot penetrate the monolayers formed in the presence of IPL. These results indicate that by mimicking some of the interfacial properties of SP-B, this novel hybrid molecule is promising in terms of preventing fibrinogen adsorption and therefore resisting surfactant inactivation.