title: Surface Properties of Squalene/Meibum Films and NMR Confirmation of Squalene in Tears.
abstract: Squalene (SQ) possesses a wide range of pharmacological activities (antioxidant, drug carrier, detoxifier, hydrating, emollient) that can be of benefit to the ocular surface. It can come in contact with human meibum (hMGS; the most abundant component of the tear film lipid layer) as an endogenous tear lipid or from exogenous sources as eyelid sebum or pharmaceuticals. The aims of this study were to determine (i) if SQ is in tear lipids and (ii) its influence on the surface properties of hMGS films. Heteronuclear single quantum correlation NMR confirmed 7 mol % SQ in Schirmer's strips extracts. The properties of SQ/hMGS pseudo-binary films at the air/water interface were studied with Langmuir surface balance, stress-relaxation dilatational rheology and Brewster angle microscopy. SQ does not possess surfactant properties. When mixed with hMGS squalene (i) localized over the layers' thinner regions and (ii) did not affect the film pressure at high compression. Therefore, tear SQ is unlikely to instigate dry eye, and SQ can be used as a safe and "inert" ingredient in formulations to protect against dry eye. The layering of SQ over the thinner film regions in addition to its pharmacological properties could contribute to the protection of the ocular surface.
authors.affiliation: Department of Biochemistry, Faculty of Biology, St. Kliment Ohridski University of Sofia, 1164 Sofia, Bulgaria. slavyana.plam.ivanova@gmail.com.
authors.forename: Slavyana
authors.initials: S
authors.lastname: Ivanova
authors.affiliation: Institute of Physical Chemistry "R. Kaischew"-BAS, Phase Formation, Crystals and Amorphous Materials Department, 1113 Sofia, Bulgaria. vesselin.tonchev@gmail.com.
authors.forename: Vesselin
authors.initials: V
authors.lastname: Tonchev
authors.affiliation: Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto 602-0841, Japan. nyokoi@koto.kpu-m.ac.jp.
authors.forename: Norihiko
authors.initials: N
authors.lastname: Yokoi
authors.affiliation: Department of Chemistry, University of Louisville, Louisville, KY 40202, USA. mcyappert@louisville.edu.
authors.forename: Marta C
authors.initials: MC
authors.lastname: Yappert
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA. borchman@louisville.edu.
authors.forename: Douglas
authors.initials: D
authors.lastname: Borchman
authors.affiliation: Department of Biochemistry, Faculty of Biology, St. Kliment Ohridski University of Sofia, 1164 Sofia, Bulgaria. ggeorg@biofac.uni-sofia.bg.|Biointerfaces and Biomaterials Laboratory, Department of Optics and Spectroscopy, Faculty of Physics, St. Kliment Ohridski University of Sofia, 1164 Sofia, Bulgaria. ggeorg@biofac.uni-sofia.bg.
authors.forename: Georgi As
authors.initials: GA
authors.lastname: Georgiev
mesh_terms: D066241:Carbon-13 Magnetic Resonance Spectroscopy; D006801:Humans; D009682:Magnetic Resonance Spectroscopy; D008968:Molecular Conformation; D066244:Proton Magnetic Resonance Spectroscopy; D013185:Squalene / Q000737:chemistry*; D013499:Surface Properties; D013666:Tears / Q000737:chemistry*; D028725:Theology
chemical_list: D013185:Squalene
keywords: Langmuir trough; NMR; meibum; sebum; squalene; tear film