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.

The Effect of Ambient Ozone on Unsaturated Tear Film Wax Esters

“…14,35 Due to this, an approach of using multiple compression-expansion cycles has been adopted in studies using Langmuir films. 30,[35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51] However, this approach relies on the assumption that the lipid films remain chemically stable for the duration of the experiment, which is not the case for unsaturated WEs in ambient air. Also, measurements on unsaturated CEs have shown time-dependent changes in the isotherms due to autoxidation.…”

“…However, such effect was not observed in tightly packed BO films. Tear film is also known to contain water soluble antioxidants like ascorbate, urate and glutathione, 26,27 antioxidant proteins like superoxide dismutase, 28 and lipid soluble antioxidants like vitamin E, 29 squalene, 30 and plasmalogens. 12 It is likely that the antioxidant systems in tear fluid protect the TFLL from ozonolysis.…”

Surface properties and exponential stress relaxations of mammalian meibum films

“…The fitting of the curves to a sum of decaying exponents allows identification of the number of processes involved in the reorganization of the heterogeneous film constituents and their characteristic times and how these depend on the temperature (Georgiev et al 2011(Georgiev et al , 2012Tschoegl 1989;van Hunsel and Joos 1989). The results are discussed in the context of the data on the surface properties and viscoelasticity of human meibum reported previously (Georgiev et al 2010(Georgiev et al , 2011(Georgiev et al , 2012(Georgiev et al , 2013(Georgiev et al , 2014Ivanova et al 2015;Leiske et al 2010). …”

“…In order to facilitate the comparison of the surface properties and structure of canine and feline meibum films with those of human meibum (hMGS) layers and the corresponding discussion, representative reference data are taken from our previous studies (Georgiev et al 2010(Georgiev et al , 2012(Georgiev et al , 2013(Georgiev et al , 2014Ivanova et al 2015). These data are presented as insets in Figs.…”

“…Experiments were performed at two temperatures: 25 and 35 °C. The consensus mean temperature of the central cornea in humans, as obtained by infrared thermography, is 34-35.11 °C (Abreau et al 2016) and 35 °C was implemented as aqueous subphase temperature in numerous studies of human meibum films Georgiev et al 2012Georgiev et al , 2013Georgiev et al , 2014Ivanova et al 2015;Leiske et al 2012;Mudgil and Millar 2011;Raju et al 2013;Shrestha et al 2011). It was shown (Biondi et al 2015;Maggs 2008;Rysa and Sarvaranta 1974;Schwartz and Feller 1962) that although the body temperature of small mammals like dogs and cats is higher than in humans, the corneal surface temperature of these animals varies greatly depending on the environmental conditions and the location of measurement over the cornea; in a room with still air, it does not exceed 35.6 °C, which is very close to that of humans.…”