1
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Yazdani M. Tear film lipid layer and corneal oxygenation: a new function? Eye (Lond) 2023; 37:3534-3541. [PMID: 37138094 PMCID: PMC10686381 DOI: 10.1038/s41433-023-02557-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/22/2023] [Accepted: 04/20/2023] [Indexed: 05/05/2023] Open
Abstract
The classic model of tear film is composed of mucin layer, aqueous layer and the outermost tear film lipid layer (TFLL). The complex mixture of different classes of lipids, mainly secreted by meibomian glands, gives the TFLL unique physicochemical properties. Based on these properties, several functions of TFLL have been found and/or proposed such as the resistance to evaporation and facilitating the formation of a thin film. However, the role of TFLL in the oxygenation of the cornea, a transparent avascular tissue, has never been discussed in the literature. The continuous metabolic activity of the corneal surface and the replenishment of atmospheric gas creates an O2 gradient in the tear film. The molecules of O2 must therefore be transferred from the gas phase to the liquid phase through the TFLL. This process is a function of the diffusion and solubility of the lipid layer as well as interface transfer, which is influenced by alterations in the physical state and lipid composition. In the absence of research on TFLL, the present paper aims to bring the topic into the spotlight for the first time based on existing knowledge on O2 permeability of the lipid membranes and evaporation resistance of the lipid layers. The oxidative stress generated in perturbed lipid layers and the consequent adverse effects are also covered. The function of the TFLL proposed here intends to encourage future research in both basic and clinical sciences, e.g., opening new avenues for the diagnosis and treatment of ocular surface conditions.
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Affiliation(s)
- Mazyar Yazdani
- Department of Medical Biochemistry, Oslo University Hospital, Rikshospitalet, 0027, Oslo, Norway.
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2
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Nagar S, Ajouz L, Nichols KK, Kumar S, Zhao C, Naidoo KK, Robinson MR, Borchman D. Relationship Between Human Meibum Lipid Composition and the Severity of Meibomian Gland Dysfunction: A Spectroscopic Analysis. Invest Ophthalmol Vis Sci 2023; 64:22. [PMID: 37466951 PMCID: PMC10362926 DOI: 10.1167/iovs.64.10.22] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/20/2023] Open
Abstract
Purpose Information on the relationship between meibum lipid composition and severity of meibomian gland dysfunction (MGD) is limited. The purpose of this study was to analyze the molecular components of meibum collected from individuals with no MGD, mild-to-moderate MGD, and severe MGD. Methods Adults with and without MGD were enrolled in a prospective, multicenter, exploratory clinical trial (ClinicalTrials.gov Identifier: NCT01979887). Molar ratios of cholesteryl ester to wax ester (RCE/WE) and aldehyde to wax ester (Rald/WE) in meibum samples were measured with 1H-NMR spectroscopy. Results were evaluated for participants grouped by MGD disease status and severity (non-MGD, mild-to-moderate MGD, and severe MGD), as defined by maximum meibum quality scores, Schirmer test results, and Subject Ocular Symptom Questionnaire responses. Results Sixty-nine meibum samples from 69 individuals were included in the analysis: 24 non-MGD, 24 mild-to-moderate MGD, and 21 severe MGD. Mean RCE/WE was 0.29 in non-MGD, 0.14 in mild-to-moderate MGD (P = 0.038 vs. non-MGD, 51% lower), and 0.07 in severe MGD (P = 0.16 vs. mild-to-moderate MGD, 52% lower; P = 0.002 vs. non-MGD, 76% lower). Mean Rald/WE was 0.00022 in non-MGD, 0.00083 in mild-to-moderate MGD (P = 0.07 vs. non-MGD, 277% higher), and 0.0024 in severe MGD (P = 0.003 vs. mild-to-moderate MGD, 190% higher; P < 0.001 vs. non-MGD, 992% higher). Conclusions RCE/WE was lowest and Rald/WE was highest in the severe MGD cohort, suggesting that these meibum constituent molar ratios may result from the pathophysiology associated with MGD and can impact ocular surface lipid and tear film homeostasis. These findings may potentially help identify targets for MGD treatment.
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Affiliation(s)
- Saumya Nagar
- Allergan, an AbbVie company, Irvine, CA, United States
| | - Layla Ajouz
- Allergan, an AbbVie company, Irvine, CA, United States
| | - Kelly K Nichols
- School of Optometry, University of Alabama at Birmingham, Birmingham, AL, United States
| | - Sandeep Kumar
- Allergan, an AbbVie company, Irvine, CA, United States
| | - Cathy Zhao
- Allergan, an AbbVie company, Irvine, CA, United States
| | - Kugen K Naidoo
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, United States
| | | | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, United States
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3
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Vittitow J, Kissling R, DeCory H, Borchman D. In Vitro Inhibition of Evaporation with Perfluorohexyloctane, an Eye Drop for Dry Eye Disease. CURRENT THERAPEUTIC RESEARCH 2023; 98:100704. [PMID: 37389230 PMCID: PMC10300294 DOI: 10.1016/j.curtheres.2023.100704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Accepted: 05/05/2023] [Indexed: 07/01/2023]
Abstract
Objective Perfluorohexyloctane (PFHO) MIEBOTM, formerly (NOV03) is a single component, water-free eye drop approved by the Food and Drug Administration in the United States for the treatment of dry eye disease. We evaluated the in vitro inhibitory effect of PFHO on the evaporation rate (Revap) of saline. Methods Evaporation rates were measured gravimetrically at 25°C or 35°C. The evaporation rate (Revap) of phosphate-buffered saline (PBS) was measured following the application of 11-200 µL PFHO or 100 µL artificial tears (Soothe XP [Bausch + Lomb, Bridgewater, New Jersey], Systane Balance [Alcon, Fort Worth, Texas], and Systane Ultra [Alcon]). The effect of PFHO on the Revap of PBS was further evaluated following the addition of 50 mg/mL mucin to PBS and compared with that of meibum lipid collected from a 68 year-old White volunteer. Results At 25°C the mean (SEM) Revap of PBS alone or PFHO alone was 4.06 (0.06) and 0.137 (0.004) µm/min, respectively. Layering 100 µL PFHO over PBS inhibited the Revap of PBS by 81% (P < 0.0001), whereas artificial tears had no effect. The presence of mucin attenuated the inhibition of the Revap of PBS by PFHO by 17% (P < 0.0001). At 35°C, the Revap of PBS was inhibited by 88% when layering 100 µL PFHO over PBS and 28% when applying a single 11 µL drop of PFHO (P value < 0.0001 for both). Meibum lipid inhibited the Revap of PBS by 8% at this temperature, whereas the combination of a drop of PFHO plus meibum inhibited the Revap of PBS by 34%. Conclusions PFHO significantly inhibited the Revap of saline in this in vitro model. The data support the idea that PHFO may form an antievaporative layer on the tear film surface and may be a functional substitute for the native tear-film lipid layer in patients with dry eye disease.
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Affiliation(s)
- Jason Vittitow
- Clinical Affairs, Bausch + Lomb, Bridgewater, New Jersey
| | | | - Heleen DeCory
- Medical Affairs, Bausch + Lomb, Bridgewater, New Jersey
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky
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4
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Xu X, Li G, Zuo YY. Effect of Model Tear Film Lipid Layer on Water Evaporation. Invest Ophthalmol Vis Sci 2023; 64:13. [PMID: 36656568 PMCID: PMC9872843 DOI: 10.1167/iovs.64.1.13] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Purpose A majority of in vitro models were incapable of reproducing the evaporation resistance of tear film lipid layer (TFLL) in vivo. The purpose of this research is to develop a novel in vitro model to study the effect of TFLL on water evaporation. Methods A ventilated, closed-chamber, droplet evaporimeter with a constant surface area has been invented to study the evaporation resistance of TFLL. This evaporimeter ensures a rigorous control of environmental conditions, including the temperature, relative humidity, airflow rate, surface area, and surface pressure, thus allowing for reproducible water evaporation measurements over a time period of only 5 minutes. The volumetric evaporation rate of this droplet evaporimeter is less than 2.7 µL/min, comparable to the basal tear production of healthy adults. Together with direct film imaging using atomic force microscopy (AFM), we have studied the effect of a model TFLL on water evaporation, as a function of the lipid composition and surface pressure. Results A model TFLL composed of 40% wax esters, 40% cholesteryl esters, and 20% polar lipids was capable of reducing the water evaporation rate by 11% at surface pressure 47 mN/m. AFM revealed that the model TFLL at high surface pressures consists of discrete droplets/aggregates of the nonpolar lipids residing atop a polar lipid monolayer with phase separation. Conclusions The TFLL may resist water evaporation with a combined mechanism by increasing film compactness of the polar lipid film at the air-water surface, and, to a lesser extent, by increasing film thickness of the nonpolar lipid film.
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Affiliation(s)
- Xiaojie Xu
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, United States
| | - Guangle Li
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, United States
| | - Yi Y. Zuo
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, United States,Department of Pediatrics, John A. Burns School of Medicine, University of Hawaii, Honolulu, Hawaii, United States
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5
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Asiedu K. Candidate Molecular Compounds as Potential Indicators for Meibomian Gland Dysfunction. Front Med (Lausanne) 2022; 9:873538. [PMID: 35685417 PMCID: PMC9170961 DOI: 10.3389/fmed.2022.873538] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Accepted: 04/08/2022] [Indexed: 11/16/2022] Open
Abstract
Meibomian gland dysfunction (MGD) is the leading cause of dry eye disease throughout the world. Studies have shown that several molecules in meibum, including but not limited to interleukins, amino acids, cadherins, eicosanoids, carbohydrates, and proteins, are altered in meibomian gland dysfunction compared with healthy normal controls. Some of these molecules such as antileukoproteinase, phospholipase A2, and lactoperoxidase also show differences in concentrations in tears between meibomian gland dysfunction and dry eye disease, further boosting hopes as candidate biomarkers. MGD is a complex condition, making it difficult to distinguish patients using single biomarkers. Therefore, multiple biomarkers forming a multiplex panel may be required. This review aims to describe molecules comprising lipids, proteins, and carbohydrates with the potential of serving various capacities as monitoring, predictive, diagnostic, and risk biomarkers for meibomian gland dysfunction.
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6
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Acera A, Abad B, Pereiro X, Rodríguez FD, Ruzafa N, Duran JA, Vecino E. Comparative study of the lipid profile of tears and plasma enriched in growth factors. Exp Eye Res 2022; 219:109061. [DOI: 10.1016/j.exer.2022.109061] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2022] [Revised: 03/19/2022] [Accepted: 03/30/2022] [Indexed: 01/05/2023]
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7
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Eftimov P, Ewurum A, Ankem A, Borchman D, Georgiev GA. Correlations between bulk and surface properties of meibomian lipids with alteration of wax-to-sterol esters content. Chem Phys Lipids 2021; 242:105163. [PMID: 34864017 DOI: 10.1016/j.chemphyslip.2021.105163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 11/29/2021] [Accepted: 11/30/2021] [Indexed: 11/03/2022]
Abstract
In a recent study (Ewurum et al., 2021), wax (WE) and sterol esters (CE) from human meibum secretions (MGS) were separated and reconstituted with controlled WE/CE ratios (0%, 20%, 30%, 40%, 50%, 75% and 100% CE weight fractions). It was found that the alterations in the CE content of WE/CE mixtures modified the hydrocarbon chain conformation and packing of the mixture. A major question that emerges is whether the spectroscopic packing parameters determined for bulk meibum translate to a change in the performance of meibomian layers at the air/water interface, as it is the surface film functionality that is crucial for the performance of MGS at the ocular surface. The study of human meibum films with Langmuir surface balance was performed to access the surface properties at blink-like deformations of the film area. Surface pressure (π)-area (A) isocycles and stress relaxations were used to assess the layer's reorganization during area cycling and dilatational elasticity, respectively. The morphology of the films was monitored by Brewster angle microscopy. It was found that the increased order and chain melting temperature of the bulk samples correlated with a raise in the maximum surface pressure attained at minimal surface area and in the transient dilatational modulus of the meibomian layers. Such correlations may allow for development of an improved understanding between the bulk and surface properties of human meibum and of other natural and synthetic tear lipid films.
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Affiliation(s)
- Petar Eftimov
- Department of Cytology, Histology and Embryology, Faculty of Biology, St. Kliment Ohridski University of Sofia, Bulgaria
| | - Anthony Ewurum
- Department of Chemistry, University of Louisville, Louisville, KY, USA
| | - Akhila Ankem
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, USA
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, USA
| | - Georgi As Georgiev
- iBB - Institute for Bioengineering and Biosciences, Interdisciplinary Complex, IST, University of Lisbon, 1649-004 Lisbon, Portugal.
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8
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Abstract
Purpose The purpose of this study was to determine if aging affects meibum lipid composition in non-meibomian gland dysfunction (MGD)/non-dry eye (DE) population. Aging has been repeatedly linked to pathological changes in various tissues and organs, including the onset of MGD and DE, in a number of clinical and population-wide surveys. Both conditions have been associated with abnormal meibum secretion and composition, among other factors. However, the chemical basis for such a connection has not been established yet. Methods To identify and characterize possible changes in the meibum and meibogenesis with aging, lipidomic analyses of meibum samples collected from human subjects of two age groups - young (29 ± 5 years, n = 21) and elderly (68 ± 7 years, n = 29) - with similar male to female ratios in each group were conducted. Intact lipid species from major lipid groups of meibum (such as wax esters, cholesteryl esters, free cholesterol, triacylglycerols, etc.) were compared using lipidome-wide untargeted (such as Principal Component Analysis) and targeted (such as Orthogonal Projections to Latent Structures Discriminant Analysis) approaches, along with focused analyses of specific lipid species in liquid-chromatography mass spectrometry (LC-MS) and tandem mass spectrometry (MS-MS) experiments. Results Extremely high similarities of meibum lipids in the two age groups were observed, with only minor changes in the individual lipid species. The magnitude of the intergroup variability for tested lipid species was comparable to the intragroup variability for the same meibum components. No statistically significant differences in the lipid esterification, elongation, and unsaturation patterns were observed. Conclusions Chronological aging itself seems to have only minor effect on meibogenesis in healthy, non-MGD/non-DE subjects.
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Affiliation(s)
- Igor A. Butovich
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, Texas, United States
- The Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, Dallas, Texas, United States
| | - Tomo Suzuki
- Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan
- Department of Ophthalmology, Kyoto City Hospital Organization, Kyoto, Japan
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9
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Ewurum A, Veligandla SR, Swindle JS, Clark JD, Borchman D. A spectroscopic approach to measuring meibum lipid composition and conformation in donors with Sjӧgren's syndrome. Exp Eye Res 2021; 210:108713. [PMID: 34363797 PMCID: PMC8429180 DOI: 10.1016/j.exer.2021.108713] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2021] [Revised: 06/22/2021] [Accepted: 07/29/2021] [Indexed: 01/15/2023]
Abstract
Patients with Sjӧgren's syndrome (SS) have dry eye associated with meibomian gland dysfunction (MGD). The meibum from donors with dry eye due to MGD but without SS (MMGD) presents with lower levels of cholesteryl ester, less straight chains, and more ordered hydrocarbon chains compared with meibum from donors without MGD (Mn). The aim of the current study was to compare the composition and hydrocarbon chain conformation of meibum from donors with Sjögren's syndrome (Mss) to Mn and MMGD. Meibum was expressed from patients with SS using an ILUX instrument (Alcon Inc., Fort Worth TX). All of the nine meibum donors with SS were female. Meibum composition was characterized using 1H-NMR and meibum hydrocarbon chain conformation was measured using fourier transform infrared spectroscopy. Meibum from every donor with SS measured contained a significantly (P < 0.01) higher cholesteryl ester/wax ester ratio and more straight chains compared with donors without SS or dry eye. None of the nine phase transitional parameters were significantly different, P > 0.05, for Mss compared with Mn. Nor was the CH3/CH2 band height ratio used to estimate the number of hydrocarbon CH3 and CH2 moieties different, P = 0.22, for Mss compared with Mn. In conclusion, the compositional differences between Mss compared with Mn did not result in differences in any of the nine meibum lipid phase transitional parameters measured. The compositional differences observed between Mss and Mn could be markers for or contribute to SS as the differences could lead to tear film lipid packing differences other than conformational differences.
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Affiliation(s)
- Anthony Ewurum
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA
| | - Sravya R Veligandla
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA
| | - Jordan S Swindle
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA
| | - Jeremy D Clark
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA.
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10
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Ewurum A, Ankem A, Georgiev G, Borchman D. A spectroscopic study of the composition and conformation of cholesteryl and wax esters purified from meibum. Chem Phys Lipids 2021; 238:105088. [PMID: 33965419 DOI: 10.1016/j.chemphyslip.2021.105088] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Revised: 04/20/2021] [Accepted: 05/02/2021] [Indexed: 10/21/2022]
Abstract
Elucidating wax ester (WE) and cholesteryl ester (CE) compositional, structural and functional relationships is key to our understanding of how these lipids are involved in natural and pathological processes. Little is known about how CE and WE interact with one another. The focus of the present study is to bridge this gap of knowledge. CE and WE were collected from human meibum as a source of esters with complex hydrocarbon chains. MgO column chromatography was used to separate WE and CE. The esters were characterized using 1H-NMR and Fourier transform infrared spectroscopy. The complexity of the hydrocarbon chains of native WE and CE influenced how changes in the ratio of WE and CE ester influenced some lipid phase transitional parameters but not others. Changes in CE content of WE/CE mixtures undoubtedly modifies the hydrocarbon chain conformation and packing of the mixture. The nature of the change depends on the conformation of the WE and CE. Differences in the complexity of the hydrocarbon chains are likely not to be a major influence on alterations in the order or phase transition temperature when more ordered WE is added to less ordered CE.
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Affiliation(s)
- Anthony Ewurum
- Department of Chemistry, University of Louisville, Louisville, KY, USA
| | - Akhila Ankem
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, USA
| | - Georgi Georgiev
- iBB - Institute for Bioengineering and Biosciences, Interdisciplinary Complex, IST, University of Lisbon, 1649-004, Lisbon, Portugal
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, USA.
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11
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Ziemanski JF, Wilson L, Barnes S, Nichols KK. Triacylglycerol lipidome from human meibomian gland epithelial cells: Description, response to culture conditions, and perspective on function. Exp Eye Res 2021; 207:108573. [PMID: 33848521 DOI: 10.1016/j.exer.2021.108573] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Revised: 03/16/2021] [Accepted: 04/06/2021] [Indexed: 10/21/2022]
Abstract
Preliminary work has shown that select triacylglycerols (TAGs) are upregulated in a preclinical model of MGD, suggesting that TAGs may be an important outcome variable in research involving human meibomian gland epithelial cells (HMGECs). The purpose of this study was to explore the HMGEC TAG lipidome in culture conditions known to influence differentiation. HMGECs were differentiated in DMEM/F12 with 10 ng/ml EGF, FBS (2% or 10%), and rosiglitazone (0, 20, or 50 μM) for two or five days. Following culture, lipids were extracted, processed, and directly infused into a Triple TOF 5600 mass spectrometer (SCIEX, Framingham, MA) with electrospray ionization. MS and MS/MSALL spectra were acquired in the positive ion mode and performed with the SWATH technology. Only the TAGs that were present in all 48 samples were included in the analysis. Multiple regression techniques were utilized to assess the effects of each factor (FBS, rosiglitazone, and culture duration) on each expressed TAG. The HMGEC TAG lipidome consisted of 115 TAGs with 42-62 carbons and zero to 10 double bonds. Fatty acyl chains had 14 to 26 carbons and zero to five double bonds. C18:1 (oleic acid, 25/115, 21.7%) and C16:0 (palmitic acid, 16/115, 13.9%) were the most common fatty acids. FBS, rosiglitazone, and culture duration were significant predictors for 93 TAGs (80.9%) with R2 values ranging from 0.20 to 0.77 (p < 0.05). FBS and rosiglitazone achieved significance (p < 0.05) for 80 (69.6%) and 67 TAGs (58.3%), respectively. Rosiglitazone demonstrated a selective upregulation of TAGs containing 16 or 18 carbons. Culture duration reached significance (p < 0.05) for only 36 TAGs (31.3%). When comparing the 10 most abundant C18:1-containing TAGs in meibum, FBS was a negative predictor for five TAGs (mean standardized coefficient [SC] = -0.58, p < 0.001), rosiglitazone was a positive predictor for six TAGs (mean SC = 0.41, p ≤ 0.03), and culture duration weakly influenced one TAG (SC = 0.27, p = 0.008). FBS and rosiglitazone, unlike culture duration, are powerful modulators of the TAG profile. Rosiglitazone induces changes that could be consistent with fatty acid synthesis, suggesting that quantifying the TAG lipidome could be an indirect measure of lipogenesis. Though both have been described as differentiating agents, FBS and rosiglitazone induce opposing effects on meibum-relevant TAGs. Culturing with rosiglitazone is associated with a TAG profile that is more consistent with the expected outcome of lipogenesis and with the profile observed in normal human meibum.
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Affiliation(s)
- Jillian F Ziemanski
- University of Alabama at Birmingham, School of Optometry, Department of Optometry and Vision Science, Birmingham, AL, USA.
| | - Landon Wilson
- University of Alabama at Birmingham, School of Medicine, Department of Pharmacology and Toxicology, Birmingham, AL, USA
| | - Stephen Barnes
- University of Alabama at Birmingham, School of Medicine, Department of Pharmacology and Toxicology, Birmingham, AL, USA
| | - Kelly K Nichols
- University of Alabama at Birmingham, School of Optometry, Department of Optometry and Vision Science, Birmingham, AL, USA
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12
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Viitaja T, Raitanen JE, Moilanen J, Paananen RO, Ekholm FS. The Properties and Role of O-Acyl-ω-hydroxy Fatty Acids and Type I-St and Type II Diesters in the Tear Film Lipid Layer Revealed by a Combined Chemistry and Biophysics Approach. J Org Chem 2021; 86:4965-4976. [PMID: 33729799 PMCID: PMC8041317 DOI: 10.1021/acs.joc.0c02882] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
![]()
The tear film lipid
layer (TFLL) that covers the ocular surface
contains several unique lipid classes, including O-acyl-ω-hydroxy fatty acids, type I-St diesters, and type II
diesters. While the TFLL represents a unique biological barrier that
plays a central role in stabilizing the entire tear film, little is
known about the properties and roles of individual lipid species.
This is because their isolation from tear samples in sufficient quantities
is a tedious task. To provide access to these species in their pure
form, and to shed light on their properties, we here report a general
strategy for the synthesis and structural characterization of these
lipid classes. In addition, we study the organization and behavior
of the lipids at the air–tear interface. Through these studies,
new insights on the relationship between structural features, such
as number of double bonds and the chain length, and film properties,
such as spreading and evaporation resistance, were uncovered.
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Affiliation(s)
- Tuomo Viitaja
- Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland.,Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, FI-00290 Helsinki, Finland
| | - Jan-Erik Raitanen
- Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland
| | - Jukka Moilanen
- Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, FI-00290 Helsinki, Finland
| | - Riku O Paananen
- Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland.,Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, FI-00290 Helsinki, Finland
| | - Filip S Ekholm
- Department of Chemistry, University of Helsinki, P.O. Box 55, FI-00014 Helsinki, Finland
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13
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Borchman D. Lipid conformational order and the etiology of cataract and dry eye. J Lipid Res 2021; 62:100039. [PMID: 32554545 PMCID: PMC7910524 DOI: 10.1194/jlr.tr120000874] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 06/15/2020] [Indexed: 12/12/2022] Open
Abstract
Lens and tear film lipids are as unique as the systems they reside in. The major lipid of the human lens is dihydrosphingomylein, found in quantity only in the lens. The lens contains a cholesterol to phospholipid molar ratio as high as 10:1, more than anywhere else in the body. Lens lipids contribute to maintaining lens clarity, and alterations in lens lipid composition due to age are likely to contribute to cataract. Lens lipid composition reflects adaptations to the unique characteristics of the lens: no turnover of lens lipids or proteins; the lowest amount of oxygen of any tissue; and contains almost no intracellular organelles. The tear film lipid layer (TFLL) is also unique. The TFLL is a thin (100 nm) layer of lipid on the surface of tears covering the cornea that contributes to tear film stability. The major lipids of the TFLL are wax esters and cholesterol esters that are not found in the lens. The hydrocarbon chains associated with the esters are longer than those found anywhere else in the body (as long as 32 carbons), and many are branched. Changes in the composition and structure of the 30,000 different moieties of TFLL contribute to the instability of tears. The focus of the current review is how spectroscopy has been used to elucidate the relationships between lipid composition, conformational order and function, and the etiology of cataract and dry eye.
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Affiliation(s)
- Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202.
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Ziemanski JF, Wilson L, Barnes S, Nichols KK. Saturation of cholesteryl esters produced by human meibomian gland epithelial cells after treatment with rosiglitazone. Ocul Surf 2020; 20:39-47. [PMID: 33248214 DOI: 10.1016/j.jtos.2020.11.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Revised: 10/29/2020] [Accepted: 11/22/2020] [Indexed: 01/14/2023]
Abstract
PURPOSE The purpose of this study was to compare the cholesteryl ester (CE) profiles expressed from human meibomian gland epithelial cells (HMGECs) in response to rosiglitazone-induced differentiation to that of normal human meibum. METHODS HMGECs were cultured with rosiglitazone (vehicle control, 20 μM, or 50 μM) and fetal bovine serum (FBS, 2% or 10%) for 2 days or 5 days. Following culture, lipid extracts were processed and analyzed by ESI-MSMSALL in positive ion mode. CEs were identified using both LipidView 1.2 and PeakView 2.2 (SCIEX, Framingham, MA) and compared to literature reports of CEs in normal human meibum. RESULTS There were 34 CEs with carbon number ranging from 14 to 34 detected from HMGECs. Across all conditions, HMGECs provided a CE profile that was 14.0% saturated, 60.6% monounsaturated, and 25.4% polyunsaturated. Culturing with 50 μM rosiglitazone and 2% FBS for 2 days resulted in the greatest number of upregulated saturated and monounsaturated CEs and downregulated polyunsaturated CEs. Five CEs were identified as being the most responsive to 50 μM rosiglitazone: CE 24:1, CE 28:1, CE 26:1, CE 18:1, and CE 22:1. CONCLUSION Although differences in the CE profile exist between meibum and HMGECs, rosiglitazone promotes upregulation of highly expressed meibum-relevant CEs and shifts the saturation level toward a more meibum-like profile. The use of rosiglitazone as a differentiating agent is recommended in HMGEC research, and analysis by ESI-MSMSALL is encouraged to differentiate meibum-relevant CEs from other nonpolar distractors detected by vital stains.
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Affiliation(s)
- Jillian F Ziemanski
- University of Alabama at Birmingham, School of Optometry, Department of Optometry and Vision Science, Birmingham, AL, USA.
| | - Landon Wilson
- University of Alabama at Birmingham, School of Medicine, Department of Pharmacology and Toxicology, Birmingham, AL, USA
| | - Stephen Barnes
- University of Alabama at Birmingham, School of Medicine, Department of Pharmacology and Toxicology, Birmingham, AL, USA
| | - Kelly K Nichols
- University of Alabama at Birmingham, School of Optometry, Department of Optometry and Vision Science, Birmingham, AL, USA
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Ramasubramanian A, Ahmed SF, Borchman D. Changes in meibum composition following plaque bachytherapy for choroidal melanoma. BMJ Open Ophthalmol 2020; 5:e000614. [PMID: 33294624 PMCID: PMC7689590 DOI: 10.1136/bmjophth-2020-000614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2020] [Revised: 10/27/2020] [Accepted: 11/12/2020] [Indexed: 11/03/2022] Open
Abstract
Objectives Dry eye is common when external beam radiation is used for the treatment of choroidal melanoma (CM). As meibum structure and composition have been related to dry eye, we determined if plaque bachytherapy for CM alters meibum composition. Design 1H-NMR spectroscopy was used to measure the lipid composition of meibum. Setting The University of Louisville, Kentucky, USA. Participants All 13 participants had CM and one participant had iris melanoma. Main outcome measures Cholesteryl ester (CE) to wax ester (WE) ratio, amount of meibum esters (ME) and meibum lipid saturation were measured. Results ME decreased by 80%±18% (±99% CI) in 11 eyes that were treated compared with the contralateral untreated eye. ME increased by 181% in two eyes that were treated compared with the contralateral untreated eye. The mole % CE/WE for meibum was significantly (p<0.0001) 67% lower in eyes that were irradiated compared with control eyes from donors without CM and were not treated. Plaque brachytherapy induced the de-esterification of CE. The intensity of the meibum cis double bond resonances did not change significantly (p>0.05). Conclusion Eyes that had plaque brachytherapy had a lower amount of expressible meibum and a lower CE/WE ratio compared with meibum from the contralateral eye that received no treatment and eyes that did not have uveal melanoma. Both the quality and quantity of meibum should be considered in designing a therapy for dry eye after plaque brachytherapy.
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Affiliation(s)
| | - Simra Fatima Ahmed
- Department of Ophthtalmology, University of Louisville School of Medicine, Louisville, Kentucky, USA
| | - Douglas Borchman
- Department of Ophthtalmology, University of Louisville School of Medicine, Louisville, Kentucky, USA
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16
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Butovich IA, Suzuki T. Delineating a novel metabolic high triglycerides-low waxes syndrome that affects lipid homeostasis in meibomian and sebaceous glands. Exp Eye Res 2020; 199:108189. [PMID: 32805264 DOI: 10.1016/j.exer.2020.108189] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2020] [Revised: 07/12/2020] [Accepted: 08/07/2020] [Indexed: 10/23/2022]
Abstract
Meibomian glands that are embedded in tarsal plates of human eyelids, and sebaceous glands found in the skin, including that of eyelids, are two related types of holocrine glands that produce lipid-rich secretions called meibum and sebum. Pervasive ocular disorders, such as Meibomian gland dysfunction and dry eye, have been linked to changes in the lipid composition of meibum. However, in most described cases the changes were either small, or random, or insufficiently characterized on the molecular level. Here, we present results of comprehensive lipidomic analyses of meibum, tears and sebum of a patient whose secretions were highly abnormal (abnormal meibum, tears and sebum, or AMTS, patient). The lipidomes were characterized on the level of individual lipid species using ultra-high performance liquid chromatography and high resolution mass spectrometry. The major differences between the AMTS patient and normal age- and gender-matched subjects included, among others, severely diminished pools of normal meibomian lipids such as wax esters and cholesteryl esters in meibum and tears, a 2x increase in total cholesteryl esters to wax esters ratio, their skewed molecular profiles, a ~3x increase in free cholesterol to cholesteryl esters ratio, and, most importantly, a 20x to 30x increase in the triglicerides fraction over the norm. Sebum of the AMTS patient was also highly abnormal lacking major wax esters. Notably, the routine blood lipid panel test of the AMTS patient showed no abnormalities. The data imply that the AMTS patient had a severe, previously unreported, metabolic disorder that affected meibogenesis in Meibomian glands and sebogenesis in sebaceous glands. This is, to the best of our knowledge, a first observation of the condition that we have termed High Triglycerides/Low Waxes (HTLW) syndrome.
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Affiliation(s)
- Igor A Butovich
- Department of Ophthalmology, University of Texas Southwestern Medical Center, Dallas, TX, USA; Graduate School of Biomedical Sciences, University of Texas Southwestern Medical Center, Dallas, TX, USA.
| | - Tomo Suzuki
- Department of Ophthalmology, Kyoto Prefectural University of Medicine, Kyoto, Japan; Department of Ophthalmology, Kyoto City Hospital Organization, Kyoto, Japan
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17
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Hetman ZA, Borchman D. Concentration dependent cholesteryl-ester and wax-ester structural relationships and meibomian gland dysfunction. Biochem Biophys Rep 2020; 21:100732. [PMID: 32042930 PMCID: PMC7000810 DOI: 10.1016/j.bbrep.2020.100732] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Revised: 01/13/2020] [Accepted: 01/14/2020] [Indexed: 01/08/2023] Open
Abstract
Background With dry eye, the ratio of cholesteryl ester (CE) to wax ester (WE) decreases substantially in meibum, but the functional and structural consequences of this change are speculative. The aim of this study is to confirm this finding and to bridge this gap in knowledge by investigating the effect of varying CE/WE ratios on lipid structure and thermodynamics. Methods Infrared spectroscopy was use to quantify CE and WE in human meibum and to measure hydrocarbon chain conformation and thermodynamics in a cholesteryl behenate, stearyl stearate model system. Results The CE/WE molar ratio was 36% lower for meibum from donors with dry eye due to meibomian gland dysfunction compared with meibum from donors without dry eye. CE (5 mol %) dramatically increased the phase transition temperature of pure WE from -0.12 °C to 63 °C in the mixture. Above 5 mol % CB, the phase transition temperature increased linearly, from 68.5 °C to 85 °C. In the ordered state, CE caused an increase in lipid order from about 72% trans rotamers to about 86% trans rotamers. Above 10% CE, the hydrocarbon chains were arranged in a monoclinic geometry. Conclusions The CE/WE is lower in meibum from donors with dry eye due to meibomian-gland dysfunction. Major conformational changes in the hydrocarbon chains of wax and cholesteryl ester mixtures begin to occur with just 5% CB and above. General significance CE-WE interactions may be important for in understanding lipid layer structure and functional relationships on the surface of tears, skin and plants. The CE/WE is lower in meibum from donors with meibomian-gland dysfunction. CE may be important for the tear film lipid layer structure and function. CE-WE interactions may be important on the surface of tears, skin and plants. Conformational changes in WE and CE mixtures begin to occur with just 5% CE. CE, cholesteryl ester; WE, wax ester.
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Affiliation(s)
| | - Douglas Borchman
- Corresponding author. The Kentucky Lions Eye Center, University of Louisville, 301 E. Muhammad Ali Blvd, Louisville, KY, 40202.
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18
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Borchman D, Ramasubramanian A, Foulks GN. Human Meibum Cholesteryl and Wax Ester Variability With Age, Sex, and Meibomian Gland Dysfunction. Invest Ophthalmol Vis Sci 2019; 60:2286-2293. [PMID: 31112994 PMCID: PMC6530518 DOI: 10.1167/iovs.19-26812] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Purpose Relationships between tear film lipid (TFL) layer composition, structure, and function could provide insight into the etiology of dry eye. The molar ratio of cholesteryl ester (CE)/wax ester (WE) was measured in meibum from normal donors (Mn) and compared with meibum from donors with meibomian gland dysfunction (MMGD). Methods CE/WE was measured using nuclear magnetic resonance spectroscopy. Results CE/WE was distributed into two populations with 81% distributed near 0.55 and 19% near 0.3. CE/WE were higher in donors 13 to 19 years old compared with donors 1 to 12 years old and 20 to 88 years old. CE/WE for MMGD was 30% lower, 0.34 ± 0.04, compared with Mn, 0.49 ± 0.04. There were no sex differences in CE/WE. There were no significant racial differences between the CE/WE ratios for Asians and Caucasians. The CE/WE ratio was higher for blacks and lower for Hispanics compared to Caucasians. Due to the small number sampled, confirmation of the later racial results is needed. The packing of CE and WE in the TFL layer was proposed. Conclusions Although MMGD contains much less CE than Mn, factors other than the CE content, such as the levels of saturation and/or proteins, may be responsible for the higher order of MMGD. In addition to saturation, CE could contribute to the increase in order of Mn between 0 and 20 years of age. Observed changes in the meibum content of CE alone is not likely to influence tear film stability.
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Affiliation(s)
- Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States
| | - Aparna Ramasubramanian
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States
| | - Gary N Foulks
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States
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Abstract
PURPOSE Meibum is considered to be a key component of tears that serve to protect the eye, and conformational changes in meibum have not been studied extensively within the population of patients who had hematopoietic stem cell transplantation (HSCT). The aim of this study was to determine possible lipid conformational changes in the meibum of patients who had HSCT. METHODS Participants who had HSCT were randomly sampled for this prospective comparative study. Control participants did not have dry eye or had not undergone allogeneic or autologous stem cell transplantation. Fourier-transform infrared spectroscopy was used to measure meibum phase transition. RESULTS Meibum was collected from both eyes of 36 donors without dry eye (Mc) and from 22 patients who had undergone HSCT (MHSCT). There were no significant differences between the phase transition parameters based on gender or race. The following were the significant differences (P < 0.0001) between the parameters for Mc compared with MHSCT : lipid order (% trans) at 33.4°C increased from 40 (1) to 54 (2), cooperativity decreased from 7.9 (0.4) to 5.4 (0.3), the phase transition temperature (C) increased from 30.3 (0.4) to 34.2 (0.9), and the magnitude of the phase transition (cm) increased from 4.0 (0.1) to 4.7 (0.5) (standard error of the mean). CONCLUSIONS Conformational and thermodynamic differences were observed between Mc and MHSCT. The changes observed in the lipid conformation of meibum from patients receiving HSCTs suggest that meibum composition changes after stem cell transplantation, and clinicians should consider treating the meibomian glands to improve the ocular surface.
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20
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Lipid Saturation and the Rheology of Human Tear Lipids. Int J Mol Sci 2019; 20:ijms20143431. [PMID: 31336861 PMCID: PMC6678947 DOI: 10.3390/ijms20143431] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 06/24/2019] [Accepted: 07/04/2019] [Indexed: 02/03/2023] Open
Abstract
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 % of saturation resulted in thicker, and more elastic films at π = 12 mN/m, with the effects being proportional to the saturation level. At the same time, at lower (≤10 mN/m) π, 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 πmax 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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21
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Borchman D. The optimum temperature for the heat therapy for meibomian gland dysfunction. Ocul Surf 2019; 17:360-364. [PMID: 30794947 PMCID: PMC6529265 DOI: 10.1016/j.jtos.2019.02.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2018] [Revised: 02/06/2019] [Accepted: 02/15/2019] [Indexed: 11/23/2022]
Abstract
PURPOSE Numerous devices have been developed to warm the eyelid as a therapy for Meibomian gland dysfunction. The optimum temperature for such therapy was determined. METHODS Meibum lipid disorder versus temperature was calculated from previously published phase transition parameters measured using infrared spectroscopy. Phase transitions parameters were calculated from meibum obtained from donors with Meibomian gland dysfunction (MMGD), donors who were susceptible to dry eye after hematopoietic stem cell transplantations (MHSCT) and meibum from donors without dry eye (Mn). RESULTS Heating Mn to 40 °C increases the lipid disorder by 20.4%-90%. Heating the meibum another 4° increases the disorder to 95%. MMGD is 73.2% disordered with no heating. Heating MMGD to 41.5 °C increases the disorder by 26.8%-90% disordered. Heating MMGD another 5.1 °C increases the disorder to 95%. As MHSCT is much more ordered, 56.9% disordered compared with Mn and MMGD, a higher temperature above safety limits, 52 and 59 °C is need to disorder MHSCT to 90 and 95% disorder. CONCLUSIONS Heating the eye lid above the phase transition temperature of meibum increases the disorder of meibum lipid which could ameliorate dry eye symptoms. The optimum temperature for disordering Mn and MMGD to 90% maximum disorder is 40 and 41.5 °C, respectively. Safety issues and discomfort should be considered in obtaining an optimal level of disorder, especially for severe cases of dry eye.
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Affiliation(s)
- Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY, 40202, USA.
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22
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Human meibum chain branching variability with age, gender and meibomian gland dysfunction. Ocul Surf 2018; 17:327-335. [PMID: 30553000 DOI: 10.1016/j.jtos.2018.12.005] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Revised: 11/07/2018] [Accepted: 12/11/2018] [Indexed: 12/26/2022]
Abstract
NMR spectroscopy was used to measure hydrocarbon chain branching variability in meibum with age, gender and Meibomian gland dysfuction (MGD). A cohort of 65 meibum donors without dry eye and 31 donors with MGD was studied. Heteronuclear 2D NMR was used to confirm CH3 resonance assignments allowing us to positively identify 23 of the 27 proton resonances of cholesteryl ester and 1H resonances due to straight chain, iso-branched and anteiso-branched hydrocarbons. Meibum from donors without dry eye contained 57 ± 1% straight-chains, 23 ± 1% iso-branched chains and 20 ± 1% anteiso-branched hydrocarbon chains. Compared with meibum from donors without dry eye, meibum from donors with MGD contained less, 50 ± 2% straight-chains, more, 32 ± 2% iso-branched chains and the same amount, 18.0 ± 0.07%, of anteiso-branched hydrocarbon chains. Meibum hydrocarbon chain branching did not change with age between 22 and 68 years of age, nor was it influenced by gender. Based on previous studies, one would expect anteiso-branched chains would contribute to lowering the phase transition temperature of meibum, decrease the elasticity of the tear film lipid layer and increase the molecular area and spreading of meibum on the surface of the eye. Although we speculate that the observed differences in iso-chain branching do not influence tear film stability or rheology, the speculation has yet to be tested.
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23
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Glasgow BJ, Abduragimov AR. Interaction of ceramides and tear lipocalin. Biochim Biophys Acta Mol Cell Biol Lipids 2018; 1863:399-408. [PMID: 29331331 PMCID: PMC5835416 DOI: 10.1016/j.bbalip.2018.01.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Revised: 12/19/2017] [Accepted: 01/06/2018] [Indexed: 10/18/2022]
Abstract
The distribution of lipids in tears is critical to their function. Lipids in human tears may retard evaporation by forming a surface barrier at the air interface. Lipids complexed with the major lipid binding protein in tears, tear lipocalin, reside in the bulk (aqueous) and may have functions unrelated to the surface. Many new lipids species have been revealed through recent mass spectrometric studies. Their association with lipid binding proteins has not been studied. Squalene, (O-acyl) omega-hydroxy fatty acids (OAHFA) and ceramides are examples. Even well-known lipids such as wax and cholesteryl esters are only presumed to be unbound because extracts of protein fractions of tears were devoid of these lipids. Our purpose was to determine by direct binding assays if the aforementioned lipids can bind tear lipocalin. Lipids were screened for ability to displace DAUDA from tear lipocalin in a fluorescence displacement assay. Di- and tri-glycerides, squalene, OAHFA, wax and cholesterol esters did not displace DAUDA from tear lipocalin. However, ceramides displaced DAUDA. Apparent dissociation constants for ceramide-tear lipocalin complexes using fluorescent analogs were measured consistently in the submicromolar range with 3 methods, linear spectral summation, high speed centrifugal precipitation and standard fluorescence assays. At the relatively small concentrations in tears, all ceramides were complexed to tear lipocalin. The lack of binding of di- and tri-glycerides, squalene, OAHFA, as well as wax and cholesterol esters to tear lipocalin is consonant with residence of these lipids near the air interface.
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Affiliation(s)
- Ben J Glasgow
- Departments of Ophthalmology, Pathology and Laboratory Medicine, Jules Stein Eye Institute, University of California, Los Angeles, 100 Stein Plaza Rm. BH 623, Los Angeles, CA 90095, United States.
| | - Adil R Abduragimov
- Departments of Ophthalmology, Pathology and Laboratory Medicine, Jules Stein Eye Institute, University of California, Los Angeles, 100 Stein Plaza Rm. BH 623, Los Angeles, CA 90095, United States
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24
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Abstract
This review contains a compilation of long-standing and more recent relevant information on chronic blepharitis, especially in the context of dry eye disease regarding epidemiology, symptoms, clinical findings and pathophysiology. Chronic blepharitis often represents the underlying cause of dry eye disease but remains undetected and untreated in many cases; however, it can be a result of (hypovolemic) dry eye disease and leads to sometimes severe corneal complications, which are illustrated by material from our own patient archives. Recent findings regarding the lipid composition in the tear film in correlation with that of Meibomian gland secretions and the hypothesis of a biofilm as the basis of chronic blepharitis as a theoretical, not yet proven addition to the previously known pathophysiological factors, are discussed.
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Affiliation(s)
- C Auw-Hädrich
- Klinik für Augenheilkunde, Killianstr. 5, 79106, Freiburg, Deutschland.
| | - T Reinhard
- Klinik für Augenheilkunde, Killianstr. 5, 79106, Freiburg, Deutschland
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25
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Sledge S, Henry C, Borchman D, Yappert MC, Bhola R, Ramasubramanian A, Blackburn R, Austin J, Massey K, Sayied S, Williams A, Georgiev G, Schikler KN. Human Meibum Age, Lipid-Lipid Interactions and Lipid Saturation in Meibum from Infants. Int J Mol Sci 2017; 18:ijms18091862. [PMID: 28846660 PMCID: PMC5618511 DOI: 10.3390/ijms18091862] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 07/25/2017] [Accepted: 08/17/2017] [Indexed: 01/21/2023] Open
Abstract
Tear stability decreases with increasing age and the same signs of instability are exacerbated with dry eye. Meibum lipid compositional changes with age provide insights into the biomolecules responsible for tear film instability. Meibum was collected from 69 normal donors ranging in age from 0.6 to 68 years of age. Infrared spectroscopy was used to measure meibum lipid phase transition parameters. Nuclear magnetic resonance spectroscopy was used to measure lipid saturation. Increasing human meibum lipid hydrocarbon chain unsaturation with age was related to a decrease in hydrocarbon chain order, cooperativity, and in the phase transition temperature. The change in these parameters was most dramatic between 1 and 20 years of age. Meibum was catalytically saturated to determine the effect of saturation on meibum lipid phase transition parameters. Hydrocarbon chain saturation was directly related to lipid order, phase transition temperature, cooperativity, changes in enthalpy and entropy, and could account for the changes in the lipid phase transition parameters observed with age. Unsaturation could contribute to decreased tear film stability with age.
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Affiliation(s)
- Samiyyah Sledge
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Collin Henry
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Marta C Yappert
- Department of Chemistry, University of Louisville, Louisville, KY 40292, USA.
| | - Rahul Bhola
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
- Division of Ophthalmology, Children's Hospital of Orange County, Orange, CA 92868, USA.
| | - Aparna Ramasubramanian
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Ryan Blackburn
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Jonathan Austin
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Kayla Massey
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Shanzeh Sayied
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Aliza Williams
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Georgi Georgiev
- Model Membranes Lab, Department of Biochemistry, Faculty of Biology, St. Kliment Ohridski University of Sofia, Sofia 1164, Bulgaria.
| | - Kenneth N Schikler
- Department of Pediatrics, University of Louisville, Louisville, KY 40202, USA.
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Abstract
The members of the Tear Film Subcommittee reviewed the role of the tear film in dry eye disease (DED). The Subcommittee reviewed biophysical and biochemical aspects of tears and how these change in DED. Clinically, DED is characterized by loss of tear volume, more rapid breakup of the tear film and increased evaporation of tears from the ocular surface. The tear film is composed of many substances including lipids, proteins, mucins and electrolytes. All of these contribute to the integrity of the tear film but exactly how they interact is still an area of active research. Tear film osmolarity increases in DED. Changes to other components such as proteins and mucins can be used as biomarkers for DED. The Subcommittee recommended areas for future research to advance our understanding of the tear film and how this changes with DED. The final report was written after review by all Subcommittee members and the entire TFOS DEWS II membership.
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Mudgil P, Borchman D, Gerlach D, Yappert MC. Sebum/Meibum Surface Film Interactions and Phase Transitional Differences. Invest Ophthalmol Vis Sci 2017; 57:2401-11. [PMID: 27145473 PMCID: PMC5113983 DOI: 10.1167/iovs.16-19117] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Purpose Sebum may contribute to the composition of the tear film lipid layer naturally or as a contaminant artifact from collection. The aims of this study were to determine: if sebum changes the rheology of meibum surface films; if the resonance near 5.2 ppm in the 1H-NMR spectra of sebum is due to squalene (SQ); and if sebum or SQ, a major component of sebum, interacts with human meibum. Methods Human meibum was collected from the lid margin with a platinum spatula. Human sebum was collected using lipid absorbent tape. Langmuir trough technology was used to measure the rheology of surface films. Infrared spectroscopy was used to measure lipid conformation and phase transitions. We used 1H-NMR to measure composition and confirm the primary structure of SQ. Results The NMR resonance near 5.2 ppm in the spectra of human sebum was from SQ which composed 28 mole percent of sebum. Both sebum and SQ lowered the lipid order of meibum. Sebum expanded meibum films at lower concentrations and condensed meibum films at higher concentrations. Sebum caused meibum to be more stable at higher pressures (greater maximum surface pressure). Conclusions Physiological levels of sebum would be expected to expand or fluidize meibum making it spread better and be more surface active (qualities beneficial for tear film stability). Sebum would also be expected to stabilize the tear film lipid layer, which may allow it to withstand the high shear pressure of a blink.
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Affiliation(s)
- Poonam Mudgil
- School of Medicine Western Sydney University, Penrith, New South Wales, Australia
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States
| | - Dylan Gerlach
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, United States
| | - Marta C Yappert
- Department of Chemistry, University of Louisville, Louisville, Kentucky, United States
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28
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Sledge SM, Khimji H, Borchman D, Oliver AL, Michael H, Dennis EK, Gerlach D, Bhola R, Stephen E. Evaporation and Hydrocarbon Chain Conformation of Surface Lipid Films. Ocul Surf 2016; 14:447-459. [PMID: 27395776 DOI: 10.1016/j.jtos.2016.06.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Revised: 05/02/2016] [Accepted: 06/15/2016] [Indexed: 02/01/2023]
Abstract
PURPOSE The inhibition of the rate of evaporation (Revap) by surface lipids is relevant to reservoirs and dry eye. Our aim was to test the idea that lipid surface films inhibit Revap. METHODS Revap were determined gravimetrically. Hydrocarbon chain conformation and structure were measured using a Raman microscope. Six 1-hydroxyl hydrocarbons (11-24 carbons in length) and human meibum were studied. Reflex tears were obtained from a 62-year-old male. RESULTS The Raman scattering intensity of the lipid film deviated by about 7 % for hydroxyl lipids and varied by 21 % for meibum films across the entire film at a resolution of 5 μm2. All of the surface lipids were ordered. Revap of the shorter chain hydroxyl lipids were slightly (7%) but significantly lower compared with the longer chain hydroxyl lipids. Revap of both groups was essentially similar to that of buffer. A hydroxyl lipid film did not influence Revap over an estimated average thickness range of 0.69 to >6.9 μm. Revap of human tears and buffer with and without human meibum (34.4 μm thick) was not significantly different. Revap of human tears was not significantly different from buffer. CONCLUSIONS Human meibum and hydroxyl lipids, regardless of their fluidity, chain length, or thickness did not inhibit Revap of buffer or tears even though they completely covered the surface. It is unlikely that hydroxyl lipids can be used to inhibit Revap of reservoirs. Our data do not support the widely accepted (yet unconfirmed) idea that the tear film lipid layer inhibits Revap of tears.
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Affiliation(s)
- Samiyyah M Sledge
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Hussain Khimji
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA.
| | - Alexandria L Oliver
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Heidi Michael
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Emily K Dennis
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Dylan Gerlach
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Rahul Bhola
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
| | - Elsa Stephen
- Department of Ophthalmology and Visual Sciences, University of Louisville School of Medicine, Louisville, KY 40202, USA
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Intersubject and Interday Variability in Human Tear and Meibum Lipidomes: A Pilot Study. Ocul Surf 2015; 14:43-8. [PMID: 26416436 DOI: 10.1016/j.jtos.2015.08.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Revised: 08/14/2015] [Accepted: 08/27/2015] [Indexed: 11/21/2022]
Abstract
PURPOSE Our aim was to quantitate day-to-day changes in the tear and meibum lipid profile of individual subjects in a pilot study of healthy humans. METHODS Matched tear and meibum samples were obtained from four subjects on three consecutive days. Quantitative lipid profiles of human basal tears and meibum were compared using multivariate analysis by principal components. RESULTS Substantial differences in the lipid profile between subjects were observed, while lipid profiles were steady across the three consecutive days of sampling. Multivariate principal component analysis demonstrated that lysophosphatidylcholine was the largest variant lipid class between subjects in tears, while wax esters comprised the most variation between subjects in meibum secretions. CONCLUSION Interday variability is shown to be much smaller than interpatient variability, suggesting that tears and meibum subjects both have unique profiles in humans.
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Surface Properties of Squalene/Meibum Films and NMR Confirmation of Squalene in Tears. Int J Mol Sci 2015; 16:21813-31. [PMID: 26370992 PMCID: PMC4613282 DOI: 10.3390/ijms160921813] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Revised: 08/28/2015] [Accepted: 08/31/2015] [Indexed: 12/16/2022] Open
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.
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Millar TJ, Schuett BS. The real reason for having a meibomian lipid layer covering the outer surface of the tear film - A review. Exp Eye Res 2015; 137:125-38. [PMID: 25981748 DOI: 10.1016/j.exer.2015.05.002] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 05/05/2015] [Accepted: 05/08/2015] [Indexed: 12/27/2022]
Abstract
This review critically evaluates a broad range of literature in order to show the relationship between meibum, tear lipids and the tear film lipid layer (TFLL). The relationship of meibum composition to dry eye syndrome is briefly discussed. The review also explores the interactions between aqueous and the TFLL by examining the correlations between meibomian lipids and lipids extracted from whole tears, and by considering protein adsorption to the TFLL from the aqueous. Although it is clear to the authors that a normal tear film resists evaporation, an emerging idea from the literature is that the main purpose of the TFLL is to allow the spread of the tear film and to prevent its collapse onto the ocular surface, rather than to be an evaporative blanket. Current models on the possible structure of the TFLL are also examined.
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Affiliation(s)
- Thomas J Millar
- University of Western Sydney, School of Science and Health, Locked Bag 1797, Penrith, NSW 2751, Australia.
| | - Burkhardt S Schuett
- University of Western Sydney, School of Science and Health, Locked Bag 1797, Penrith, NSW 2751, Australia.
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Hunter M, Bhola R, Yappert MC, Borchman D, Gerlach D. Pilot Study of the Influence of Eyeliner Cosmetics on the Molecular Structure of Human Meibum. Ophthalmic Res 2015; 53:131-5. [DOI: 10.1159/000371852] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2014] [Accepted: 01/01/2015] [Indexed: 11/19/2022]
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Borchman D, Yappert MC, Milliner SE, Smith RJ, Bhola R. Confirmation of the Presence of Squalene in Human Eyelid Lipid by Heteronuclear Single Quantum Correlation Spectroscopy. Lipids 2013; 48:1269-77. [DOI: 10.1007/s11745-013-3844-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Accepted: 07/25/2013] [Indexed: 10/26/2022]
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