title: Biophysical characterization of monofilm model systems composed of selected tear film phospholipids.
abstract: The tear film protects the eye from foreign particles and pathogens, prevents excess evaporation, provides lubrication, and maintains a high quality optical surface necessary for vision. The anterior layer of tear film consists of polar and non-polar lipid layers. The polar lipids form a monolayer on the aqueous subphase, acting as surfactants for the non-polar lipid multilayer. A tear film polar lipid biomimetic consisting of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl glucosylceramide (PGC), and palmitoyl sphingomyelin (PSM) was characterized using Langmuir monolayers and Brewster angle microscopy (BAM). Lipid combinations formed very stable monolayers, especially those containing DPPC or PSM. Surface experiments and elasticity analyses revealed that PGC resulted in more condensed and rigid mixed monolayers. DPPE provided resistance to large changes in lipid ordering over a wide surface pressure range. Ternary mixtures containing DPPE and PGC with either DPPC or PSM experienced the greatest lipid ordering within the natural tear film surface pressure range suggesting that these lipids are important to maintain tear film integrity during the inter-blink period. Finally, BAM images revealed unique structures within monolayers of DPPC, DPPE, and PGC at the natural tear film surface pressure. 3D analysis of these domains suggested either the formation of multilayers or outward protrusions at surface pressures far below the point of irreversible collapse as seen on the isotherm. This entails that the polar lipids of tear film may be capable of multilayer formation or outward folding as a mechanism to prevent rupture of the tear film during a blink.
authors.affiliation: Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Matthew
authors.initials: M
authors.lastname: Patterson
authors.affiliation: Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
authors.forename: Hans J
authors.initials: HJ
authors.lastname: Vogel
authors.affiliation: Biochemistry Research Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada. Electronic address: eprenner@ucalgary.ca.
authors.forename: Elmar J
authors.initials: EJ
authors.lastname: Prenner
mesh_terms: D008567:Membranes, Artificial; D010743:Phospholipids / Q000737:chemistry*; D013666:Tears / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D010743:Phospholipids
keywords: Brewster angle microscopy; Compression modulus; Langmuir monolayer; Tear film; Tear film polar lipid