Comparative HPLC-MSn analysis of canine and human meibomian lipidomes: many similarities, a few differences

The aim of this study was to evaluate the lipidome of meibomian gland secretions in canines (cMGS) – a common pet and laboratory animal – and to compare it with that of human MGS (hMGS), to determine whether canines could be used as a valid experimental animal model in studies of the biochemistry and physiology of the human ocular surface in general, and of the Meibomian glands in particular. The MGS of both species were evaluated using HPLC in combination with atmospheric pressure chemical ionization ion trap mass spectrometry. The main lipid classes found in cMGS were very long chain cholesteryl esters, wax esters, (O-acyl)-omega-hydroxy fatty acids (OAHFA), and cholesteryl esters of OAHFA. The lipidomes of cMGS and hMGS were found to be qualitatively similar, which implies similar biosynthetic and biodegradation pathways in canines and humans. However, some quantitative differences between the two were observed

Comparative HPLC-MSn analysis of canine and human meibomian lipidomes: many similarities, a few differences

The aim of this study was to evaluate the lipidome of meibomian gland secretions in canines (cMGS) – a common pet and laboratory animal – and to compare it with that of human MGS (hMGS), to determine whether canines could be used as a valid experimental animal model in studies of the biochemistry and physiology of the human ocular surface in general, and of the Meibomian glands in particular. The MGS of both species were evaluated using HPLC in combination with atmospheric pressure chemical ionization ion trap mass spectrometry. The main lipid classes found in cMGS were very long chain cholesteryl esters, wax esters, (O-acyl)-omega-hydroxy fatty acids (OAHFA), and cholesteryl esters of OAHFA. The lipidomes of cMGS and hMGS were found to be qualitatively similar, which implies similar biosynthetic and biodegradation pathways in canines and humans. However, some quantitative differences between the two were observed

Evaluation and Quantitation of Intact Wax Esters of Human Meibum by Gas-Liquid Chromatography-Ion Trap Mass Spectrometry

PURPOSE. Wax esters (WE) of human meibum are one of the largest group of meibomian lipids. Their complete characterization on the level of individual intact lipid species has not been completed yet. We obtained detailed structural information on previously uncharacterized meibomian WE. METHODS. Intact WE were separated and analyzed by means of high-temperature capillary gas-liquid chromatography (GLC) in combination with low voltage (30 eV) electron ionization ion trap mass spectrometry (ITMS). 3D (mass-to-charge ratio [m/z] versus lipid sample weight versus signal intensity) calibration plots were used for quantitation of WE. RESULTS. We demonstrated that GLC-ITMS was suitable for analyzing unpooled/underivatized WE collected from 14 individual donors. More than 100 of saturated and unsaturated WE (SWE and UWE, respectively) were detected. On average, UWE represented about 82% of the total WE pool. About 90% of UWE were based on oleic acid, while less than 10% were based on palmitoleic acid. The amounts of poly-UWE were <3% of their mono-UWA counterparts. SWE were based primarily on C 16 -C 18 fatty acids (FA) in overall molar ratios of 22:65:13. A pool of C 16:0 -FA was comprised of a 20:80 (mol/ mol) mixture of straight chain and iso-branched isomers, while the corresponding ratio for C 18:0 -FA was 43:57. Interestingly, C 17:0 -FA was almost exclusively branched, with anteiso-and isoisomers found in a ratio of 93:7. CONCLUSIONS. GLC-ITMS can be used successfully to analyze more than 100 individual species of meibomian WE, which were shown to comprise 41 6 8% (wt/wt) of meibum, which made them the largest group of lipids in meibum. (Invest Ophthalmol Vis Sci. 2012;53:3766-3781 1 This secretion has a critical role in protecting the surface of the human eye from desiccation by mixing with aqueous tears (produced by lacrimal glands) and forming the outermost part of the tear film layer, the tear film lipid layer. This lipid-rich layer ''seals'' the underlaying aqueous layer of the tear film, keeping the ocular surface moist, which is critical for its health and good vision. 2,3 Over a period of more than four decades, meibomian WE have been evaluated in a number of studies of animals and humans (for comprehensive reviews of earlier findings, see the most recent reviews on the topic 4-7 ). However, for the purpose of our study, only information related directly to human meibum will be discussed. Earlier, human meibomian WE from normal (nondry eye) and dry eye subjects were studied using gas (or gasliquid) chromatography with flame ionization detection (GC-FID and GLC-FID), and GC-and GLC-mass spectrometry (GCand GLC-MS). MATERIALS AND METHODS Samples of meibum were collected using a protocol described previously 13 and the amounts of collected meibum were measured gravimetrically. All sample collection procedures that involved human subjects were approved by the UT Southwestern Institutional Review Board, and were conducted in accordance with the Declaration of From th

Meibum Lipid Composition in Asians with Dry Eye Disease

10.1371/journal.pone.0024339PLoS ONE610

Adsorption of Human Tear Lipocalin to Human Meibomian Lipid Films

PURPOSE. Tear lipocalin (Tlc) is a major lipid binding protein in tears and is thought to have an important role in stabilizing the Meibomian lipid layer by transferring lipids to it from the aqueous layer or ocular surface, or by adsorbing to it directly. These possible roles have been investigated in vitro using human Tlc. METHODS. Tlc was purified from human tears by size exclusion chromatography followed by ion exchange chromatography. Three additional samples of the Tlc were prepared by lipidation, delipidation, and relipidation. The lipids extracted from the purified Tlc were analyzed by HPLC-MS followed by fragmentation. Adsorption of these different forms of Tlc to a human Meibomian lipid film spread on the surface of an artificial tear buffer in a Langmuir trough were observed by recording changes in the pressure with time (⌸-T profile) and monitoring the appearance of the film microscopically. These results were compared with similar experiments using a bovine Meibomian lipid film. RESULTS. The results indicated that Tlc binds slowly to a human Meibomian lipid film compared with lysozyme or lactoferrin, even at 37°C. The adsorption of Tlc to a human Meibomian lipid film was very different from its adsorption to a bovine Meibomian lipid film, indicating the nature of the lipids in the film is critical to the adsorption process. Similarly, the different forms of Tlc had quite distinct adsorption patterns, as indicated both by changes in ⌸-T profiles and the microscopic appearance of the films. CONCLUSIONS. It was concluded that human Tlc was capable of adsorbing to and penetrating into a Meibomian lipid layer, but this process is very complex and depends on both the types of lipids bound to Tlc and the lipid complement comprising the Meibomian lipid film. (Invest Ophthalmol Vis Sci. 2009;50: 140 -151

Meibomian gland lipid alterations and ocular surface sequela in Awat2 knockout murine model of meibomian gland dysfunction and evaporative dry eye disease

PurposeThere is an urgent need for animal models of meibomian gland dysfunction (MGD) and evaporative dry eye disease (EDED) to understand their pathophysiology and investigate novel therapeutics. This study sought to further define the acyl-CoA: wax alcohol acyltransferase 2 knockout (Awat2 KO) mouse as a model of EDED using a combination of novel clinical, biochemical, and biophysical endpoints.MethodsWildtype and Awat2 KO mice between 1 and 18 months of age were used. Ocular examinations and advanced imaging were performed. The lipidomic composition and in situ melting temperature of meibum were determined. qPCR was performed to define ocular surface gene and pro-inflammatory transcript expression. Dynamic contact angle goniometry was performed to assess the adherence capability of the ocular surface.ResultsAwat2 KO mice have mild, white, hyperreflective corneal opacities of the anterior stroma and significantly enlarged apical epithelial cells (P = 0.0004). In Awat2 KO meibum, wax esters were 9-10 times lower than in wildtype meibum. Additionally, meibum melting temperature increased from 32° to 47 °C (P < 0.0001), leading to impaired meibum secretion and dilation of the central duct. Awat2 KO corneal epithelia had significantly decreased mucin expression (Muc1 and Muc4, P = 0.0043) and increased interferon-γ production (P = 0.0303). Awat2 KO globes have a significantly shortened time of droplet adherence to their ocular surface (P = 0.0053), indicating a decreased tear film adherence capacity. Wildtype corneal epithelia does not express Awat2, indicating that the EDED phenotype is secondary to the loss of Awat2 from the meibomian glands.ConclusionsAwat2 KO mice recapitulate many of features of human MGD and EDED, representing a model to test novel therapeutics

Automated surface sampling of lipids from worn contact lenses coupled with tandem mass spectrometry

The deposition of biological material (biofouling) onto polymeric contact lenses is thought to be a major contributor to lens discomfort and hence discontinuation of wear. We describe a method to characterize lipid deposits directly from worn contact lenses utilizing liquid extraction surface analysis coupled to tandem mass spectrometry (LESA-MS/MS). This technique effected facile and reproducible extraction of lipids from the contact lens surfaces and identified lipid molecular species representing all major classes present in human tear film. Our data show that LESA-MS/MS is a rapid and comprehensive technique for the characterization of lipid-related biofouling on polymer surfaces