title: Role of neutral lipids in tear fluid lipid layer: coarse-grained simulation study.
abstract: Tear fluid lipid layer (TFLL) residing at the air-water interface of tears has been recognized to play an important role in the development of dry eye syndrome. Yet, the composition, structure, and mechanical properties of TFLL are only partly known. Here, we report results of coarse-grained simulations of a lipid layer comprising phospholipids, free fatty acids, cholesteryl esters, and triglycerides at the air-water interface to shed light on the properties of TFLL. We consider structural as well as dynamical properties of the lipid layer as a function of surface pressure. Simulations revealed that neutral lipids reside heterogeneously between phospholipids at relatively low pressures but form a separate hydrophobic phase with increasing surface pressure, transforming the initial lipid monolayer to a two-layered structure. When the model of TFLL was compared to a one-component phospholipid monolayer system, we found drastic differences in both structural and dynamical properties that explain the prominent role of neutral lipids as stabilizers of the TFLL. Based on our results, we suggest that neutral lipids are able to increase the stability of the TFLL by modulating its dynamical and structural behavior, which is important for the proper function of tear film.
authors.affiliation: Department of Applied Physics, Aalto University School of Science, Finland.
authors.forename: Jelena
authors.initials: J
authors.lastname: Telenius
authors.forename: Artturi
authors.initials: A
authors.lastname: Koivuniemi
authors.forename: Pipsa
authors.initials: P
authors.lastname: Kulovesi
authors.forename: Juha M
authors.initials: JM
authors.lastname: Holopainen
authors.forename: Ilpo
authors.initials: I
authors.lastname: Vattulainen
mesh_terms: D000388:Air; D002788:Cholesterol Esters / Q000737:chemistry*; D003198:Computer Simulation; D004058:Diffusion; D005230:Fatty Acids, Nonesterified / Q000737:chemistry*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D008956:Models, Chemical; D010743:Phospholipids / Q000737:chemistry*; D011312:Pressure; D012212:Rheology; D013499:Surface Properties; D013666:Tears / Q000737:chemistry*; D013816:Thermodynamics; D014280:Triglycerides / Q000737:chemistry*; D014867:Water
chemical_list: D002788:Cholesterol Esters; D005230:Fatty Acids, Nonesterified; D010743:Phospholipids; D014280:Triglycerides; D014867:Water