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    Lipid Saturation and the Rheology of Human Tear Lipids

    Year: 2019

    Journal: Int. J. Mol. Sci., Volume 20, JUL 2

    Authors: Georgiev, Georgi As.; Borchman, Douglas; Eftimov, Petar; Yokoi, Norihiko

    Organizations: National Institutes of Health, USAUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USA [R01EY026180]; Research to Prevent Blindness Inc. New York, NY, USAResearch to Prevent Blindness (RPB) [GN151619B]; Ministry of Education and Science of Bulgaria grant [P(sic)-22-876/8.04.2019]; NATIONAL EYE INSTITUTEUnited States Department of Health & Human ServicesNational Institutes of Health (NIH) - USANIH National Eye Institute (NEI) [R01EY026180] Funding Source: NIH RePORTER

    Keywords: human meibum; acyl chain saturation; Langmuir films; tear film stability; surface properties

    Elevated levels of acyl chain saturation of meibomian lipids are associated with enhanced tear film (TF) stability in infants to shortened TF breakup time with meibomian gland dysfunction. Thus, the effect of saturation on the surface properties of human TF lipids (TFLs) using a Langmuir surface balance and Brewster angle microscopy was studied. Lipid phase transitions were measured using infrared spectroscopy. The raise in the `)/c. of saturation resulted in thicker, and more elastic films at pi = 12 mN/m, with the effects being proportional to the saturation level. At the same time, at lower (<= 10 mN/m) pi, the raise in saturation resulted in an altered spreading and modified structure of TFL layers. The strong impact of saturation on TFL surface properties correlated with a saturation induced increase of the TFL acyl chain order, phase transition temperature, and lipid lipid interactions. The native TFL order and pi(max) were significantly greater, compared with native meibum collected from the same individual. Aggregation of lipids on the tear surface due to saturation was not as significant as it was for meibum. Although the surface pressure/area isotherms for TFL were similar for meibum, differences in rheology and phase transition parameters warrant the study of both.
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