Properties of Lipid Models of Lung Surfactant Containing Cholesterol and Oxidized Lipids: A Mixed Experimental and Computational Study.

We introduce and study a multicomponent lipid film mimicking lipid composition of the human lung surfactant. It consists of phospholipids with various lipid headgroups and tail saturation. Furthermore, it includes cholesterol and oxidized lipids. Langmuir trough and fluorescence microscopy experiments are combined with fully atomistic molecular dynamics simulations. The considered lipid mixtures form complex interfacial films with properties modulated by lateral compression. Cholesterol laterally condenses, and oxidized lipids laterally expand the films; both types of molecules increase film miscibility. Oxidized lipids also alter the lipid-water interface enhancing film hydration; this effect can be partially reversed by cholesterol. Regarding presentation of different chemical moieties toward the aqueous subphase, the zwitterionic phosphatidylcholine groups dominate at the lipid-water interface, while both the negatively charged phosphatidylglycerol and hydroxyl group of cholesterol are less exposed. The investigated synthetic lipid-only mimic of the lung surfactant may serve as a basis for further studies involving nonlipid pulmonary surfactant components.