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Prabhu J, Singh AP, Vanni S. An in silico osmotic pressure approach allows characterization of pressure-area isotherms of lipid monolayers at low molecular areas. SOFT MATTER 2023; 19:3377-3385. [PMID: 37102755 PMCID: PMC10170484 DOI: 10.1039/d2sm01419j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Surface pressure-area isotherms of lipid monolayers at the air-water interface provide essential information about the structure and mechanical behaviour of lipid membranes. These curves can be readily obtained through Langmuir trough measurements and, as such, have been collected for decades in the field of membrane biochemistry. However, it is still challenging to directly observe and understand nanoscopic features of monolayers through such experiments, and molecular dynamics (MD) simulations are generally used to provide a molecular view of such interfaces. In MD simulations, the surface pressure-area (Π-A) isotherms are generally computed using the Kirkwood-Irving formula, that relies on the evaluation of the pressure tensor. This approach, however, has intrinsic limitations when the molecular area in the monolayer is low (typically < 60 Å2 per lipid). Recently, an alternative method to compute Π-A isotherms of surfactants, based on the calculation of the three-dimensional osmotic pressure via the implementation of semipermeable barriers was proposed. In this work, we investigate the feasibility of this approach for long-chain surfactants such as phospholipids. We identify some discrepancies between the computed values and experimental results, and we propose a semi-empirical correction based on the molecular structure of the surfactants at the monolayer interface. To validate the potential of this new approach, we simulate several phosphatidylcholine and phosphatidylethanolamine lipids at various temperatures using all-atom and coarse-grained force fields, and we compute the corresponding Π-A isotherms. Our results show that the Π-A isotherms obtained using the new method are in very good agreement with experiments and far superior to the canonical pressure tensor-based method at low molecular areas. This corrected osmotic pressure method allows for accurate characterization of the molecular packing in monolayers in various physical phases.
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Affiliation(s)
- Janak Prabhu
- Department of Biology, University of Fribourg, Chemin du Musée 10, 1700 Fribourg, Switzerland.
| | - Akhil Pratap Singh
- Department of Biology, University of Fribourg, Chemin du Musée 10, 1700 Fribourg, Switzerland.
| | - Stefano Vanni
- Department of Biology, University of Fribourg, Chemin du Musée 10, 1700 Fribourg, Switzerland.
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2
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Viitaja T, Raitanen JE, Moilanen J, Paananen RO, Ekholm FS. Biophysical profiling of synthetic ultra-long tear film lipids. Colloids Surf B Biointerfaces 2023; 223:113145. [PMID: 36701899 DOI: 10.1016/j.colsurfb.2023.113145] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2022] [Revised: 01/04/2023] [Accepted: 01/11/2023] [Indexed: 01/15/2023]
Abstract
The tear film lipid layer (TFLL) is a unique biological membrane of importance to the maintenance of ocular surface health. The underlying factors at play, e.g. the ability to retard evaporation and offer protection from the environment, are all closely connected to the properties of individual lipid components and their interplay. The TFLL contains unique ultra-long polar lipid species such as O-acyl-ω-hydroxy fatty acids, type I-St diesters and type II diesters, which are considered important for its proper function. Herein, we have synthesized model compounds from these categories and studied their biophysical and surface rheological properties at the aqueous interface. Altogether, we provide insights on the distinct biophysical profiles of these lipid classes and discuss how their interplay may affect the structure and function of the TFLL.
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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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3
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Keramatnejad M, DeWolf C. A biophysical study of tear film lipid layer model membranes. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184102. [PMID: 36535341 DOI: 10.1016/j.bbamem.2022.184102] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2022] [Revised: 11/22/2022] [Accepted: 12/12/2022] [Indexed: 12/23/2022]
Abstract
The tear film lipid layer (TFLL), the final layer of the human tear film is responsible for surface tension reduction while blinking, water evaporation retardation and maintaining the stability of the tear film. The study of the composition-structure-function relationship of TFLL is paramount, as a compromised structure of TFLL leads to the emergence of dry eye disease (DED) which is one the most prevalent ophthalmic surface diseases of the modern world, associated with chronic pain and reduced visual capability. In this model membrane study, a systematic approach is used to study the biophysical properties of TFLL model membranes as a function of composition. Three mixed-lipid model membranes are studied along with their individual components comprising cholesteryl oleate (CO), glyceryl trioleate (GT), L-α-phosphatidylcholine (egg PC) and a free fatty acid mixture. The models become progressively more complex from binary to quaternary mixtures, allowing the role of each individual lipid to be derived. Langmuir balance, Brewster Angle Microscopy (BAM) and Profile Analysis Tensiometer (PAT) are used to study the surface activity and compression-expansion cycles, morphology, and rheological behaviour of the model membranes, respectively. Evidence of multilayering is observed with inclusion of CO and a reversible collapse is associated with the GT phase transition. An initially more coherent film is observed due to the addition of polar PC. Notably, these individual behaviours are retained in the mixed films and suggest a possible role for each physiological component of TFLL.
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Affiliation(s)
- Mahshid Keramatnejad
- Department of Chemistry & Biochemistry, Centre for Nanoscience Research, Concordia University,7141 Sherbrooke Street west, H4B1R6 Montreal, Canada.
| | - Christine DeWolf
- Department of Chemistry & Biochemistry, Centre for Nanoscience Research, Concordia University,7141 Sherbrooke Street west, H4B1R6 Montreal, Canada.
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Keramatnejad M, DeWolf C. Impact of Pollutant Ozone on the Biophysical Properties of Tear Film Lipid Layer Model Membranes. MEMBRANES 2023; 13:165. [PMID: 36837668 PMCID: PMC9964828 DOI: 10.3390/membranes13020165] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 01/17/2023] [Accepted: 01/25/2023] [Indexed: 06/18/2023]
Abstract
Ozone exposure from environmental smog has been implicated as a risk factor for developing dry eye disease (DED). The tear film lipid layer (TFLL), which is the outermost layer of the tear film and responsible for surface tension reduction while blinking, is in direct contact with the environment and serves as the first line of defense against external aggressors such as environmental pollution. The impact of exposure to ozone on the biophysical properties of three TFLL model membranes was investigated. These model membranes include a binary mixture of cholesteryl oleate (CO) and L-α-phosphatidylcholine (egg PC), a ternary mixture of CO, glyceryl trioleate (GT) and PC, as well as a quaternary mixture of CO, GT, a mixture of free fatty acids palmitic acid and stearic acid (FFAs) and PC. Biophysical impacts were evaluated as changes to the surface activity, respreadability, morphology and viscoelastic properties of the films. Expansion to higher molecular areas was observed in all the TFLL model membrane films which is attributable to the accommodation of the cleaved chains in the film. Significant morphological changes were observed, namely fluidization and the disruption of the phase transition behaviour of GT, and multilayer formation of CO. This fluidization reduces the hysteresis loops for the model membranes. On the other hand, the viscoelastic properties of the films exhibited differential impacts from ozone exposure as a function of composition. These findings are correlated to chemical changes to the lipids determined using ESI-MS.
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Atkova EL, Yartsev VD, Ekaterinchev MA, Shkolyarenko NY. [Biometric characteristics of the lacrimal passages in healthy individuals and in patients with nasolacrimal duct obstruction]. Vestn Oftalmol 2023; 139:20-26. [PMID: 37942593 DOI: 10.17116/oftalma202313905120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2023]
Abstract
Despite an obvious interest in the processes occurring in the lacrimal passages in their obstruction, there is few articles analyzing their biometric parameters. PURPOSE The study investigates the biometric characteristics of the lacrimal passages in healthy individuals and in patients with nasolacrimal duct obstruction. MATERIAL AND METHODS The study included 81 cases of partial nasolacrimal duct obstruction and 38 cases without tear drainage insufficiency. All patients underwent computed tomography with dacryocystography. Analysis of the biometric parameters involved calculation of the length, volume, and average sectional area of the nasolacrimal duct and the nasolacrimal bony canal. The ratio R4/16l was calculated (where R is the radius of the nasolacrimal duct; l is the length of the nasolacrimal duct). The normality of values was assessed using the Shapiro-Wilk test. Intergroup differences were assessed using the Mann-Whitney test and t-statistics for independent samples. Correlation analysis was performed according to the Spearman method. ROC analysis was carried out. Differences were considered significant at p≤0.05. RESULTS There were significant differences in the volume (p=0.004) and the average sectional area of the nasolacrimal duct (p=0.014), as well as in the length of the nasolacrimal canal (p=0.034). Relationships were established between the age of patients without tear drainage insufficiency and the length of the nasolacrimal canal (p=0.042); the length of the nasolacrimal canal and the volume of the nasolacrimal duct (p=0.034), as well as the volume of the nasolacrimal duct and the nasolacrimal canal in partial nasolacrimal duct obstruction (p=0.017). The AUC of the R4/16l ratio in the ROC analysis was 0.653 (p=0.007). CONCLUSION In addition to the obvious differences, it was found that the length of the nasolacrimal bony canal significantly differed in the subjects of both study groups. We considered the tear ducts as a hydrodynamic system obeying Poiseuille's law, so we calculated the ratio R4/16l. The value of this ratio varied (p=0.016), and the ROC analysis showed high sensitivity and specificity of the criterion. This makes it possible to use this ratio as a diagnostic criterion for partial nasolacrimal duct obstruction.
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Affiliation(s)
- E L Atkova
- Krasnov Research Institute of Eye Diseases, Moscow, Russia
| | - V D Yartsev
- Krasnov Research Institute of Eye Diseases, Moscow, Russia
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Marrink SJ, Monticelli L, Melo MN, Alessandri R, Tieleman DP, Souza PCT. Two decades of Martini: Better beads, broader scope. WIRES COMPUTATIONAL MOLECULAR SCIENCE 2022. [DOI: 10.1002/wcms.1620] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Siewert J. Marrink
- Groningen Biomolecular Sciences and Biotechnology Institute & Zernike Institute for Advanced Materials University of Groningen Groningen The Netherlands
| | - Luca Monticelli
- Molecular Microbiology and Structural Biochemistry (MMSB ‐ UMR 5086) CNRS & University of Lyon Lyon France
| | - Manuel N. Melo
- Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa Oeiras Portugal
| | - Riccardo Alessandri
- Pritzker School of Molecular Engineering University of Chicago Chicago Illinois USA
| | - D. Peter Tieleman
- Centre for Molecular Simulation and Department of Biological Sciences University of Calgary Alberta Canada
| | - Paulo C. T. Souza
- Molecular Microbiology and Structural Biochemistry (MMSB ‐ UMR 5086) CNRS & University of Lyon Lyon France
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7
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The lung surfactant activity probed with molecular dynamics simulations. Adv Colloid Interface Sci 2022; 304:102659. [PMID: 35421637 DOI: 10.1016/j.cis.2022.102659] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Revised: 03/18/2022] [Accepted: 03/31/2022] [Indexed: 01/17/2023]
Abstract
The surface of pulmonary alveolar subphase is covered with a mixture of lipids and proteins. This lung surfactant plays a crucial role in lung functioning. It shows a complex phase behavior which can be altered by the interaction with third molecules such as drugs or pollutants. For studying multicomponent biological systems, it is of interest to couple experimental approach with computational modelling yielding atomic-scale information. Simple two, three, or four-component model systems showed to be useful for getting more insight in the interaction between lipids, lipids and proteins or lipids and proteins with drugs and impurities. These systems were studied theoretically using molecular dynamic simulations and experimentally by means of the Langmuir technique. A better understanding of the structure and behavior of lung surfactants obtained from this research is relevant for developing new synthetic surfactants for efficient therapies, and may contribute to public health protection.
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Viitaja T, Raitanen JE, Hynynen A, Moilanen J, Svedström K, Paananen RO, Ekholm FS. On the importance of chain branching in tear film lipid layer wax and cholesteryl esters. Colloids Surf B Biointerfaces 2022; 214:112429. [PMID: 35278859 DOI: 10.1016/j.colsurfb.2022.112429] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2022] [Revised: 02/22/2022] [Accepted: 02/23/2022] [Indexed: 11/30/2022]
Abstract
The tear film lipid layer (TFLL) is important to the maintenance of ocular surface health. Surprisingly, information on the individual roles of the myriad of unique lipids found therein is limited. The most abundant lipid species are the wax esters (WE) and cholesteryl esters (CE), and, especially their branched analogs. The isolation of these lipid species from the TFLL has proved to be tedious, and as a result, insights on their biophysical profiles and role in the TFLL is currently lacking. Herein, we circumvent these issues by a total synthesis of the most abundant iso-methyl branched WEs and CEs found in the TFLL. Through a detailed characterization of the biophysical properties, by the use of Langmuir monolayer and wide-angle X-ray scattering techniques, we demonstrate that chain branching alters the behavior of these lipid species on multiple levels. Taken together, our results fill an important knowledge gap concerning the structure and function of the TFLL on the whole.
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Affiliation(s)
- Tuomo Viitaja
- Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland; Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, Helsinki FI-00290, Finland
| | - Jan-Erik Raitanen
- Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland
| | - Antti Hynynen
- Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland
| | - Jukka Moilanen
- Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, Helsinki FI-00290, Finland
| | - Kirsi Svedström
- Department of Physics, University of Helsinki, P.O. Box 64, Helsinki FI-00014, Finland
| | - Riku O Paananen
- Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland; Ophthalmology, University of Helsinki and Helsinki University Hospital, Haartmaninkatu 8, Helsinki FI-00290, Finland.
| | - Filip S Ekholm
- Department of Chemistry, University of Helsinki, P.O. Box 55, Helsinki FI-00014, Finland.
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9
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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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10
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Sofińska K, Lupa D, Chachaj-Brekiesz A, Czaja M, Kobierski J, Seweryn S, Skirlińska-Nosek K, Szymonski M, Wilkosz N, Wnętrzak A, Lipiec E. Revealing local molecular distribution, orientation, phase separation, and formation of domains in artificial lipid layers: Towards comprehensive characterization of biological membranes. Adv Colloid Interface Sci 2022; 301:102614. [PMID: 35190313 DOI: 10.1016/j.cis.2022.102614] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2021] [Revised: 01/28/2022] [Accepted: 02/01/2022] [Indexed: 01/01/2023]
Abstract
Lipids, together with molecules such as DNA and proteins, are one of the most relevant systems responsible for the existence of life. Selected lipids are able to assembly into various organized structures, such as lipid membranes. The unique properties of lipid membranes determine their complex functions, not only to separate biological environments, but also to participate in regulatory functions, absorption of nutrients, cell-cell communication, endocytosis, cell signaling, and many others. Despite numerous scientific efforts, still little is known about the reason underlying the variability within lipid membranes, and its biochemical significance. In this review, we discuss the structural complexity of lipid membranes, as well as the importance to simplify studied systems in order to understand phenomena occurring in natural, complex membranes. Such systems require a model interface to be analyzed. Therefore, here we focused on analytical studies of artificial systems at various interfaces. The molecular structure of lipid membranes, specifically the nanometric thickens of molecular bilayer, limits in a major extent the choice of highly sensitive methods suitable to study such structures. Therefore, we focused on methods that combine high sensitivity, and/or chemical selectivity, and/or nanometric spatial resolution, such as atomic force microscopy, nanospectroscopy (tip-enhanced Raman spectroscopy, infrared nanospectroscopy), phase modulation infrared reflection-absorption spectroscopy, sum-frequency generation spectroscopy. We summarized experimental and theoretical approaches providing information about molecular structure and composition, lipid spatial distribution (phase separation), organization (domain shape, molecular orientation) of lipid membranes, and real-time visualization of the influence of various molecules (proteins, drugs) on their integrity. An integral part of this review discusses the latest achievements in the field of lipid layer-based biosensors.
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Xu X, Li G, Zuo YY. Biophysical properties of tear film lipid layer I. Surface tension and surface rheology. Biophys J 2022; 121:439-450. [PMID: 34958775 PMCID: PMC8822608 DOI: 10.1016/j.bpj.2021.12.033] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2021] [Revised: 12/04/2021] [Accepted: 12/22/2021] [Indexed: 02/03/2023] Open
Abstract
Tear film lipid layer (TFLL) is the outmost layer of the tear film. It plays a crucial role in stabilizing the tear film by reducing surface tension and retarding evaporation of the aqueous layer. Dysfunction of the TFLL leads to dysfunctional tear syndrome, with dry eye disease (DED) being the most prevalent eye disease, affecting 10%-30% of the world population. To date, except for treatments alleviating dry eye symptoms, effective therapeutic interventions in treating DED are still lacking. Therefore, there is an urgent need to understand the biophysical properties of the TFLL with the long-term goal to develop translational solutions in effectively managing DED. Here, we studied the composition-function correlations of an artificial TFLL, under physiologically relevant conditions, using a novel experimental methodology called constrained drop surfactometry. This artificial TFLL was composed of 40% behenyl oleate and 40% cholesteryl oleate, representing the most abundant wax ester and cholesteryl ester in the natural TFLL, respectively, and 15% phosphatidylcholine and 5% palmitic-acid-9-hydroxy-stearic-acid (PAHSA), which represent the two predominant polar lipid classes in the natural TFLL. Our study suggests that the major biophysical function of phospholipids in the TFLL is to reduce the surface tension, whereas the primary function of PAHSA is to optimize the rheological properties of the TFLL. These findings have novel implications in better understanding the physiological and biophysical functions of the TFLL and may offer new translational insight to the treatment of DED.
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Affiliation(s)
- Xiaojie Xu
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu
| | - Guangle Li
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu
| | - Yi Y. Zuo
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu,Department of Pediatrics, John A. Burns School of Medicine, University of Hawaii, Honolulu,Corresponding author
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Galor A, Sanchez V, Jensen A, Burton M, Maus K, Stephenson D, Chalfant C, Mandal N. Meibum sphingolipid composition is altered in individuals with meibomian gland dysfunction-a side by side comparison of Meibum and Tear Sphingolipids. Ocul Surf 2022; 23:87-95. [PMID: 34861426 PMCID: PMC8792295 DOI: 10.1016/j.jtos.2021.11.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2021] [Revised: 11/23/2021] [Accepted: 11/24/2021] [Indexed: 01/21/2023]
Abstract
PURPOSE Sphingolipids (SPL) play a role in cell signaling, inflammation, and apoptosis. The purpose of this study was to examine meibum and tear SPL composition in individuals with poor versus good meibum quality. METHODS Individuals were grouped by meibum quality (n = 25 with poor quality, case group and n = 25 with good quality, control group). Meibum and tears were analyzed with liquid chromatography-mass spectrometry (LC-MS) to quantify SPL classes. Semiquantitative and relative composition (mole percent) of SPL and major classes, Ceramide (Cer), Hexosyl-Ceramide (Hex-Cer), Sphingomyelin (SM), Sphingosine (Sph), and sphingosine 1-phosphate (S1P) were compared between groups. RESULTS Demographic characteristics were similar between the two groups. Overall, individuals with poor meibum quality had more SPL pmole in meibum and tears than controls. Relative composition analysis revealed that individuals with poor meibum quality had SPL composed of less Cer, Hex-Cer, and Sph and more SM compared to individuals with good quality meibum. This pattern was not reproduced in tears as individuals with poor meibum quality had SPL composed of a similar amount of Cer, but more Hex-Cer, Sph and SM compared to controls. In meibum, SPL pmole and relative composition most strongly correlated with MG metrics while in tears, SPL pmole and relative composition most strongly correlated with tear production. SPL in both compartments, specifically Cer pmole in meibum and S1P% in tears, correlated with DE symptoms. CONCLUSION SPL composition differs in meibum and tears in patients with poor vs good meibum quality. These findings may be translated into therapeutic targets for disease.
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Affiliation(s)
- Anat Galor
- Miami Veterans Administration Medical Center, 1201 NW 16th St, Miami, FL 33125,Bascom Palmer Eye Institute, University of Miami, 900 NW 17th Street, Miami, FL 33136
| | - Victor Sanchez
- New York University Grossman School of Medicine, New York, NY 10016
| | - Andrew Jensen
- Miami Veterans Administration Medical Center, 1201 NW 16th St, Miami, FL 33125
| | - Madeline Burton
- Department of Ophthalmology, University of Tennessee Health Sciences Center, Hamilton Eye Institute, 930 Madison Avenue, Memphis, TN 38163
| | - Kenneth Maus
- Departments of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, FL 33620
| | | | - Charles Chalfant
- Departments of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, FL 33620,The Moffitt Cancer Center, Tampa, FL 33620,Research Service, James A. Haley Veterans Hospital, Tampa, FL 33612
| | - Nawajes Mandal
- Department of Ophthalmology, University of Tennessee Health Sciences Center, Hamilton Eye Institute, 930 Madison Avenue, Memphis, TN 38163,Departments of Anatomy and Neurobiology, and Pharmaceutical Sciences, University of Tennessee Health Sciences Center, 930 Madison Avenue, Memphis, TN 38163,Memphis VA Medical Center, 1030 Jefferson Avenue, Memphis, TN 38104.,Corresponding Author: Nawajes Mandal, PhD, 930 Madison Avenue, Suite 718, Memphis, TN 38163;
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13
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Xavier P, Viswanath P. The Role of Molecular Packing in Dictating the Miscibility of Some Cholesteryl n-Alkanoates at Interfaces. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:11203-11211. [PMID: 34525810 DOI: 10.1021/acs.langmuir.1c01025] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Cholesteryl n-alkanoates of saturated fatty acids and their mixtures are widely studied in different physical states and also due to their significance in biology. Here, we address the miscibility of some homologues of cholesteryl n-alkanoates at interfaces, which are known to exhibit different (cholesteryl octanoate, ChC8, and cholesteryl stearate, ChC18) or the same (cholesteryl nonanoate, ChC9, and cholesteryl laurate, ChC12) molecular packing in bulk. Surface manometry and Brewster angle microscopy studies on ChC8 (cholesteryl-cholesteryl interaction, referred to as m-i packing)/ChC9 (cholesteryl-chain interaction, referred to as m-ii packing) and also on ChC18 (chain-chain interactions, referred to as the crystalline bilayer)/ChC9 mixtures reveal phase separation at the air-water (A-W) interface plausibly due to the difference in the molecular packing. In contrast, ChC12/ChC9 (both m-ii packing) mixtures form a homogeneous phase and exhibit a higher collapse pressure (almost twice) than that of ChC9 indicating higher stability. At the air-solid (A-S) interface, the height profiles extracted from the surface topography images using an atomic force microscope yielded thicknesses of 3.6 ± 0.1 and 5.6 ± 0.1 nm for ChC18/ChC9 mixtures (at 0.66 and 0.5 mole fractions (MF)) corresponding to individual assembly, whereas a uniform thickness of 3.5 ± 0.2 nm is obtained for the case of ChC12/ChC9 mixtures (at 0.2, 0.5, and 0.8 MF) corresponding to m-ii packing. Ellipsometry studies reveal that the desorption temperature increases with the mole fraction of ChC9 and attains a maximum at 406.8 ± 4.8 K for 0.4 MF of ChC9, beyond which it decreases. Raman spectroscopy studies are carried out for ChC12/ChC9 mixtures in the homogeneous phase and in the collapsed state. Here, the dependency of peak positions on different physical states was assessed. Our studies offer new insights into the compatibility of molecular packing influencing the phase behavior and may be of relevance to tear film studies and on the formation of crystals in atherosclerosis.
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Affiliation(s)
- Pinchu Xavier
- Centre for Nano and Soft Matter Sciences, Shivanapura, Bengaluru 562 162, India
- Manipal Academy of Higher Education, Madhav Nagar, Manipal 576 104, India
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Torrent-Burgués J, Hoyo J, Tzanov T. Lipid artificial tears at a mimetic ocular interface. Chem Phys Lipids 2021; 238:105087. [PMID: 33964291 DOI: 10.1016/j.chemphyslip.2021.105087] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Revised: 04/26/2021] [Accepted: 04/28/2021] [Indexed: 10/21/2022]
Abstract
We studied the behaviour of three lipid tear products, commercialised by the same brand, as Langmuir films at the air/liquid interface to simulate the ocular environment. No significant differences were observed in the surface behaviour of two of them disclosing the same composition, but commercialised for different applications. The interaction of several subphases, namely sodium chloride, glucose, albumin and lysozyme present in the natural tear, with the lipid films was assessed at room temperature and the temperature of human tear using surface pressure-area isotherms and elastic modulus plots. There is a notable influence of sodium chloride and the proteins albumin and lysozyme on the surface pressure-area isotherm of the lipid Langmuir films. Albumin shifted this isotherm to lower areas while an opposite shift was caused by lysozyme. These studies could be useful for the formulation of new lipid-containing artificial tears, and for increasing the confidence of the customers in commercial eye care formulations.
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Affiliation(s)
- Juan Torrent-Burgués
- Grup de Biotecnologia Molecular i Industrial, Department of Chemical Engineering, Universitat Politècnica de Catalunya, Rambla Sant Nebridi 22, 08222, Terrassa, Spain.
| | - Javier Hoyo
- Grup de Biotecnologia Molecular i Industrial, Department of Chemical Engineering, Universitat Politècnica de Catalunya, Rambla Sant Nebridi 22, 08222, Terrassa, Spain
| | - Tzanko Tzanov
- Grup de Biotecnologia Molecular i Industrial, Department of Chemical Engineering, Universitat Politècnica de Catalunya, Rambla Sant Nebridi 22, 08222, Terrassa, Spain
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15
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Svitova TF, Lin MC. Evaporation retardation by model tear-lipid films: The roles of film aging, compositions and interfacial rheological properties. Colloids Surf B Biointerfaces 2021; 197:111392. [DOI: 10.1016/j.colsurfb.2020.111392] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 09/22/2020] [Accepted: 09/28/2020] [Indexed: 01/07/2023]
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16
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Mixed polar-nonpolar lipid films as minimalistic models of Tear Film Lipid Layer: A Langmuir trough and fluorescence microscopy study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183300. [PMID: 32243884 DOI: 10.1016/j.bbamem.2020.183300] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 03/11/2020] [Accepted: 03/29/2020] [Indexed: 12/11/2022]
Abstract
The Tear Film Lipid Layer (TFLL) covering the surface of the aqueous film at human cornea forms a first barrier between the eye and environment. Its alterations are related to dry eye disease. TFLL is formed by a complex mixture of lipids, with an excess of nonpolar components and a minor fraction of polar molecules. Its thickness is up to 160 nm, hence a multilayer-like structure of TFLL is assumed. However, details of TFLL organization are mostly unavailable in vivo due to the dynamic nature of the human tear film. To overcome this issue, we employ a minimalistic in vitro lipid model of TFLL. We study its biophysical characteristics by using a combination of the Langmuir trough with fluorescence microscopy. The model consists of two-component polar-nonpolar lipid films with a varying component ratio spread on the aqueous subphase at physiologically relevant temperature. We demonstrate that the model lipid mixture undergoes substantial structural reorganization as a function of lateral pressure and polar to nonpolar lipid ratio. In particular, the film is one-molecule-thick and homogenous under low lateral pressure. Upon compression, it transforms into a multilayer structure with inhomogeneities in the form of polar-nonpolar lipid assemblies. Based on this model, we hypothesize that TFLL in vivo has a duplex polar-nonpolar structure and it contains numerous mixed lipid aggregates formed because of film restructuring. These findings, despite the simplified character of the model, seem relevant for TFLL physiology as well as for understanding pathological conditions related to the lipids of the tear film.
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17
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Dokouhaki M, Prime EL, Qiao GG, Kasapis S, Day L, Gras SL. Structural-rheological characteristics of Chaplin E peptide at the air/water interface; a comparison with β-lactoglobulin and β-casein. Int J Biol Macromol 2020; 144:742-750. [PMID: 31837361 DOI: 10.1016/j.ijbiomac.2019.12.075] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2019] [Revised: 12/10/2019] [Accepted: 12/10/2019] [Indexed: 11/27/2022]
Abstract
The Chaplin E peptide is a surface-active agent that can adsorb to the air/water interface and form interfacial films that display distinct interfacial properties as a function of pH. The ~2 nm thick homogeneous Chaplin E film formed under acidic conditions contains ordered structures that give a high dilatational elasticity. In contrast, the heterogeneous film formed under basic conditions contained fibrils resulting in a rough ~17 nm thick film with predominantly viscoelastic properties, probably due to the reduced intermolecular interactions. These fibrils were also susceptible to breakage, fragmenting into shorter fibrils, which gave a greater elasticity. The fibrils also lead to a greater shear viscosity compared to the ordered structures aligned within the Chaplin E film at pH 3.0. A higher stability was observed for the foam formed by the Chaplin E compared to the foam formed by β-lactoglobulin, consistent with the greater rheological properties observed for the Chaplin E film at the interface. Our findings suggest that Chaplin E has potential to provide long time stability to dispersions in food, consumer goods or pharmaceutical applications, forming films with greater rheological properties and at least similar thickness to those formed by other surface-active proteins such as β-casein and β-lactoglobulin.
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Affiliation(s)
- Mina Dokouhaki
- School of Science, RMIT University, Bundoora West Campus, VIC 3083, Australia.
| | - Emma L Prime
- Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia
| | - Greg G Qiao
- The Department of Chemical Engineering, The University of Melbourne, Parkville, VIC 3010, Australia
| | - Stefan Kasapis
- School of Science, RMIT University, Bundoora West Campus, VIC 3083, Australia
| | - Li Day
- AgResearch Ltd., Grasslands Research Centre, Tennent Drive, Palmerston North 4442, New Zealand
| | - Sally L Gras
- The Department of Chemical Engineering, The University of Melbourne, Parkville, VIC 3010, Australia; The Bio21 Molecular Science and Biotechnology Institute and The ARC Dairy Innovation Hub, The University of Melbourne, Parkville, Vic 3010, Australia.
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18
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Bai X, Xu L, Tang JY, Zuo YY, Hu G. Adsorption of Phospholipids at the Air-Water Surface. Biophys J 2019; 117:1224-1233. [PMID: 31519299 DOI: 10.1016/j.bpj.2019.08.022] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 08/03/2019] [Accepted: 08/19/2019] [Indexed: 11/15/2022] Open
Abstract
Phospholipids are ubiquitous components of biomembranes and common biomaterials used in many bioengineering applications. Understanding adsorption of phospholipids at the air-water surface plays an important role in the study of pulmonary surfactants and cell membranes. To date, however, the biophysical mechanisms of phospholipid adsorption are still unknown. It is challenging to reveal the molecular structure of adsorbed phospholipid films. Using combined experiments with constrained drop surfactometry and molecular dynamics simulations, here, we studied the biophysical mechanisms of dipalmitoylphosphatidylcholine (DPPC) adsorption at the air-water surface. It was found that the DPPC film adsorbed from vesicles showed distinct equilibrium surface tensions from the DPPC monolayer spread via organic solvents. Our simulations revealed that only the outer leaflet of the DPPC vesicle is capable of unzipping and spreading at the air-water surface, whereas the inner leaflet remains intact and forms an inverted micelle to the interfacial monolayer. This inverted micelle increases the local curvature of the monolayer, thus leading to a loosely packed monolayer at the air-water surface and hence a higher equilibrium surface tension. These findings provide novel insights, to our knowledge, into the mechanism of the phospholipid and pulmonary surfactant adsorption and may help understand the structure-function correlation in biomembranes.
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Affiliation(s)
- Xuan Bai
- Department of Engineering Mechanics, Zhejiang University, Hangzhou, China; The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China; School of Engineering Science, University of Chinese Academy of Sciences, Beijing, China
| | - Lu Xu
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii
| | - Jenny Y Tang
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii
| | - Yi Y Zuo
- Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii; Department of Pediatrics, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, Hawaii.
| | - Guoqing Hu
- Department of Engineering Mechanics, Zhejiang University, Hangzhou, China.
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Enkavi G, Javanainen M, Kulig W, Róg T, Vattulainen I. Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance. Chem Rev 2019; 119:5607-5774. [PMID: 30859819 PMCID: PMC6727218 DOI: 10.1021/acs.chemrev.8b00538] [Citation(s) in RCA: 173] [Impact Index Per Article: 34.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2018] [Indexed: 12/23/2022]
Abstract
Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.
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Affiliation(s)
- Giray Enkavi
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Matti Javanainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy
of Sciences, Flemingovo naḿesti 542/2, 16610 Prague, Czech Republic
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Waldemar Kulig
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
| | - Tomasz Róg
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
| | - Ilpo Vattulainen
- Department
of Physics, University of
Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland
- Computational
Physics Laboratory, Tampere University, P.O. Box 692, FI-33014 Tampere, Finland
- MEMPHYS-Center
for Biomembrane Physics
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20
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Cucina A, Filali S, Risler A, Febvay C, Salmon D, Pivot C, Pelandakis M, Pirot F. Dual 0.02% chlorhexidine digluconate - 0.1% disodium EDTA loaded thermosensitive ocular gel for Acanthamoeba keratitis treatment. Int J Pharm 2019; 556:330-337. [PMID: 30553004 DOI: 10.1016/j.ijpharm.2018.12.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Revised: 11/30/2018] [Accepted: 12/03/2018] [Indexed: 10/27/2022]
Abstract
Poor bioavailability and low residence time limit the efficiency of conventional biguanide-based eye drops against Acanthamoeba keratitis. The aim of this work was to formulate an original anti-amoebic thermoreversible ocular gel combining biguanide and metalloproteases inhibitor - chelating agent. Chlorhexidine digluconate (CHX)-ethylenediaminetetraacetic acid disodium salt (Na2EDTA) were compounded in poloxamer 407 saline solution. 0.02% CHX - 0.1% Na2EDTA loaded thermosensitive ocular gel exhibited appropriate pH (5.73 ± 0.06), iso-osmolality (314 ± 5 mOsm/kg), viscosity (ranged between 15 and 25 mPa.s) and thermal gelation (26.5 °C and 33 °C) properties. Bioadhesion of gel was successfully tested onto isolated bovine eyes as well as the assessment of CHX penetration into the cornea. Intracorneal CHX concentration was found greater than trophozoite minimum amoebicidal concentration and minimal cysticidal concentration after 15-min and 2-h ocular exposure, respectively, while any CHX permeation through the cornea was detected (<51 ng/cm2/h). Improvement of CHX ocular bioavailability was attributed to probable solubilization of tear film lipid layer by poloxamer. In vitro efficiency of CHX-Na2EDTA ocular gel was confirmed from the drastic reduction of trophozoite and cyst survival (to 25% and 2%, respectively), confirming the potential of the multicomponent pharmaceutical material strategy for the treatment of Acanthamoeba keratitis.
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Affiliation(s)
- Annamaria Cucina
- Service Pharmaceutique, Plateforme Fripharm, Groupe Hospitalier Centre Edouard Herriot, Hospices Civils de Lyon, 5, Place d'Arsonval, F-69437 Lyon Cedex 03, France; Université de Lyon, Laboratoire de Pharmacie Galénique Industrielle, UMR-CNRS 5305, Plateforme Fripharm, ISPB-Faculté de Pharmacie, Université Claude Bernard Lyon 1, 8, Avenue Rockefeller, F-69373 Lyon Cedex 08, France
| | - Samira Filali
- Service Pharmaceutique, Plateforme Fripharm, Groupe Hospitalier Centre Edouard Herriot, Hospices Civils de Lyon, 5, Place d'Arsonval, F-69437 Lyon Cedex 03, France; Université de Lyon, Laboratoire de Pharmacie Galénique Industrielle, UMR-CNRS 5305, Plateforme Fripharm, ISPB-Faculté de Pharmacie, Université Claude Bernard Lyon 1, 8, Avenue Rockefeller, F-69373 Lyon Cedex 08, France
| | - Arnaud Risler
- Laboratoire Lorrain de Chimie Moléculaire, Faculté des Sciences et Techniques, Université de Lorraine, Boulevard des Aiguillettes, F-54506 Vandoeuvre les Nancy, France
| | - Camille Febvay
- Service d'Ophtalmologie, Groupement Hospitalier Edouard Herriot, 5, Place d'Arsonval, F-69437 Lyon Cedex 03, France
| | - Damien Salmon
- Service Pharmaceutique, Plateforme Fripharm, Groupe Hospitalier Centre Edouard Herriot, Hospices Civils de Lyon, 5, Place d'Arsonval, F-69437 Lyon Cedex 03, France; Université de Lyon, Laboratoire de Pharmacie Galénique Industrielle, UMR-CNRS 5305, Plateforme Fripharm, ISPB-Faculté de Pharmacie, Université Claude Bernard Lyon 1, 8, Avenue Rockefeller, F-69373 Lyon Cedex 08, France
| | - Christine Pivot
- Service Pharmaceutique, Plateforme Fripharm, Groupe Hospitalier Centre Edouard Herriot, Hospices Civils de Lyon, 5, Place d'Arsonval, F-69437 Lyon Cedex 03, France
| | - Michel Pelandakis
- Université de Lyon, Laboratoire de Microbiologie, Adaptation et Pathogénie, UMR 5240, ISPB-Faculté de Pharmacie Laboratoire L3, 8, avenue Rockefeller - 69373 Lyon Cedex 08, France
| | - Fabrice Pirot
- Service Pharmaceutique, Plateforme Fripharm, Groupe Hospitalier Centre Edouard Herriot, Hospices Civils de Lyon, 5, Place d'Arsonval, F-69437 Lyon Cedex 03, France; Université de Lyon, Laboratoire de Pharmacie Galénique Industrielle, UMR-CNRS 5305, Plateforme Fripharm, ISPB-Faculté de Pharmacie, Université Claude Bernard Lyon 1, 8, Avenue Rockefeller, F-69373 Lyon Cedex 08, France. http://fripharm.com
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21
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Dursch TJ, Li W, Taraz B, Lin MC, Radke CJ. Tear-Film Evaporation Rate from Simultaneous Ocular-Surface Temperature and Tear-Breakup Area. Optom Vis Sci 2018; 95:5-12. [PMID: 29252906 DOI: 10.1097/opx.0000000000001156] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
SIGNIFICANCE A corneal heat-transfer model is presented to quantify simultaneous measurements of fluorescein tear-breakup area (TBA) and ocular-surface temperature (OST). By accounting for disruption of the tear-film lipid layer (TFLL), we report evaporation rates through lipid-covered tear. The modified heat-transfer model provides new insights into evaporative dry eye. PURPOSE A quantitative analysis is presented to assess human aqueous tear evaporation rate (TER) through intact TFLLs from simultaneous in vivo measurement of time-dependent infrared OST and fluorescein TBA. METHODS We interpret simultaneous OST and TBA measurements using an extended heat-transfer model. We hypothesize that TBAs are ineffectively insulated by the TFLL and therefore exhibit higher TER than does that for a well-insulting TFLL-covered tear. As time proceeds, TBAs increase in number and size, thereby increasing the cornea area-averaged TER and decreasing OST. Tear-breakup areas were assessed from image analysis of fluorescein tear-film-breakup video recordings and are included in the heat-transfer description of OST. RESULTS Model-predicted OSTs agree well with clinical experiments. Percent reductions in TER of lipid-covered tear range from 50 to 95% of that for pure water, in good agreement with literature. The physical picture of noninsulating or ruptured TFLL spots followed by enhanced evaporation from underlying cooler tear-film ruptures is consistent with the evaporative-driven mechanism for local tear rupture. CONCLUSIONS A quantitative analysis is presented of in vivo TER from simultaneous clinical measurement of transient OST and TBA. The new heat-transfer model accounts for increased TER through expanding TBAs. Tear evaporation rate varies strongly across the cornea because lipid is effectively missing over tear-rupture troughs. The result is local faster evaporation compared with nonruptured, thick lipid-covered tear. Evaporative-driven tear-film ruptures deepen to a thickness where fluorescein quenching commences and local salinity rises to uncomfortable levels. Mitigation of tear-film rupture may therefore reduce dry eye-related symptoms.
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Affiliation(s)
- Thomas J Dursch
- Chemical and Biomolecular Engineering Department, University of California, Berkeley, Berkeley, California.,Clinical Research Center, School of Optometry, University of California, Berkeley, Berkeley, California
| | - Wing Li
- Clinical Research Center, School of Optometry, University of California, Berkeley, Berkeley, California
| | - Baseem Taraz
- Chemical and Biomolecular Engineering Department, University of California, Berkeley, Berkeley, California
| | - Meng C Lin
- Clinical Research Center, School of Optometry, University of California, Berkeley, Berkeley, California.,Vision Science Group, University of California, Berkeley, Berkeley, California *
| | - Clayton J Radke
- Chemical and Biomolecular Engineering Department, University of California, Berkeley, Berkeley, California.,Clinical Research Center, School of Optometry, University of California, Berkeley, Berkeley, California
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22
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Mudgil P, Borchman D, Ramasubramanian A. Insights into Tear Film Stability from Babies and Young Adults: A Study of Human Meibum Lipid Conformation and Rheology. Int J Mol Sci 2018; 19:ijms19113502. [PMID: 30405031 PMCID: PMC6275043 DOI: 10.3390/ijms19113502] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2018] [Revised: 10/31/2018] [Accepted: 11/02/2018] [Indexed: 11/22/2022] Open
Abstract
Babies have the most stable tears and people with dry eye have the least stable tears. Meibum may contribute to tear film stability, so in this study, the hydrocarbon chain conformation and rheology of meibum from babies was studied for the first time. Infrared spectroscopy was used to measure lipid phase transitions. Rheology was measured using Langmuir film technology. Meibum from 25 donors 1 to 13 years old was compared with meibum from 18 donors 13 to 25 years old. The phase transition temperature and lipid order (stiffness) increased with increasing age from 1 to 25 years. The increase in meibum lipid order from 1 to 25 years of age may contribute to the instability of the tear film with age and contribute to films with a higher reciprocal compressibility modulus that are not as compressible and not as viscoelastic. Changes in the lipid phase transition parameters of meibum lipid with dry eye are an exacerbation of the changes observed with age. The lower reciprocal compressibility moduli of meibum films from children and babies compared with meibum from adults reiterates higher stability in their films which spread better, resist deformation, and facilitates their ability to be quickly restored after blinking.
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Affiliation(s)
- Poonam Mudgil
- School of Medicine, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia.
| | - Douglas Borchman
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
| | - Aparna Ramasubramanian
- Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, KY 40202, USA.
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23
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Bock U, Deylen D V, M J, M D, C S, S R. Development of In Vitro Methodologies to Investigate Binding by Sodium Hyaluronate in Eye Drops to Corneal Surfaces. Open Ophthalmol J 2018; 12:226-240. [PMID: 30159097 PMCID: PMC6080064 DOI: 10.2174/1874364101812010226] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 06/05/2018] [Accepted: 07/12/2018] [Indexed: 01/03/2023] Open
Abstract
PURPOSE To develop in vitro methods to assess binding by sodium hyaluronate in eye drops to corneal surfaces. METHODS Two different, complementary corneal binding set-ups were developed. In a dynamic in vitro model, confluent corneal epithelial cells (HCE-T) were assembled in chamber slides and a declining channel. A static model was constructed with ex vivo porcine corneas clamped in Franz cells. To test the predictive capacity of models, four different eye drops containing sodium hyaluronate were spiked with tritium-labeled sodium hyaluronate to standardize quantification. In both settings, eye drops were applied for 5 min and physiological conditions were mimicked by flushing with artificial tear fluid. Spreading experiments on HCE-T next to synthetic membranes were used for further characterization. RESULTS Binding was more pronounced in dynamic HCE-T model. Three of the four eye drops demonstrated sigmoidal elution of sodium hyaluronate, suggesting pronounced binding. One solution eluted distinctly faster, likewise the buffer control. The static method produced a similar ranking but at lower levels. When eye drops in which phosphate buffer was replaced by citrate buffer (i.e., to prevent calcification) were used, binding was not influenced. All eye drops spread immediately when placed on HCE-T and at the same order of magnitude on glass and polyethylene terephthalate surfaces. CONCLUSION Dynamic and static models performed on different corneal sources were used to determine sodium hyaluronate binding kinetics in solutions under physiological conditions. These methodologies resulted in a ranking of the capacity of sodium hyaluronate to bind in vitro to corneal surfaces.
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Affiliation(s)
- Udo Bock
- Bock Project Management, Tawern, Germany
| | - Von Deylen D
- Technische Universität Carolo-Wilhelmina zu Braunschweig, Institut für Pharmazeutische Technologie, Braunschweig, Germany
| | - Jochner M
- Technische Universität Carolo-Wilhelmina zu Braunschweig, Institut für Pharmazeutische Technologie, Braunschweig, Germany
| | - Doerr M
- Bayer Vital GmbH, Scientific Affairs Consumer Health, Leverkusen, Germany
| | - Stäbler C
- Bayer Vital GmbH, Scientific Affairs Consumer Health, Leverkusen, Germany
| | - Reichl S
- Technische Universität Carolo-Wilhelmina zu Braunschweig, Institut für Pharmazeutische Technologie, Braunschweig, Germany
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24
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Javanainen M, Lamberg A, Cwiklik L, Vattulainen I, Ollila OHS. Atomistic Model for Nearly Quantitative Simulations of Langmuir Monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2018; 34:2565-2572. [PMID: 28945973 DOI: 10.1021/acs.langmuir.7b02855] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Lung surfactant and a tear film lipid layer are examples of biologically relevant macromolecular structures found at the air-water interface. Because of their complexity, they are often studied in terms of simplified lipid layers, the simplest example being a Langmuir monolayer. Given the profound biological significance of these lipid assemblies, there is a need to understand their structure and dynamics on the nanoscale, yet there are not many techniques able to provide this information. Atomistic molecular dynamics simulations would be a tool fit for this purpose; however, the simulation models suggested until now have been qualitative instead of quantitative. This limitation has mainly stemmed from the challenge to correctly describe the surface tension of water with simulation parameters compatible with other biomolecules. In this work, we show that this limitation can be overcome by using the recently introduced four-point OPC water model, whose surface tension for water is demonstrated to be quantitatively consistent with experimental data and which is also shown to be compatible with the commonly employed lipid models. We further establish that the approach of combining the OPC four-point water model with the CHARMM36 lipid force field provides nearly quantitative agreement with experiments for the surface pressure-area isotherm for POPC and DPPC monolayers, also including the experimentally observed phase coexistence in a DPPC monolayer. The simulation models reported in this work pave the way for nearly quantitative atomistic studies of lipid-rich biological structures at air-water interfaces.
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Affiliation(s)
- Matti Javanainen
- Laboratory of Physics, Tampere University of Technology , 33101 Tampere, Finland
| | | | - Lukasz Cwiklik
- J. Heyrovský Institute of Physical Chemistry of the Czech Academy of Sciences , 182 23 Prague 8, Czech Republic
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences , 166 10 Prague 6, Czech Republic
| | - Ilpo Vattulainen
- Laboratory of Physics, Tampere University of Technology , 33101 Tampere, Finland
- MEMPHYS - Center for Biomembrane Physics, www.memphys.dk
| | - O H Samuli Ollila
- Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences , 166 10 Prague 6, Czech Republic
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25
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Wizert A, Iskander DR, Cwiklik L. Interaction of lysozyme with a tear film lipid layer model: A molecular dynamics simulation study. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2017; 1859:2289-2296. [DOI: 10.1016/j.bbamem.2017.08.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2017] [Revised: 08/07/2017] [Accepted: 08/23/2017] [Indexed: 01/07/2023]
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26
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Garrigue JS, Amrane M, Faure MO, Holopainen JM, Tong L. Relevance of Lipid-Based Products in the Management of Dry Eye Disease. J Ocul Pharmacol Ther 2017; 33:647-661. [PMID: 28956698 PMCID: PMC5655476 DOI: 10.1089/jop.2017.0052] [Citation(s) in RCA: 73] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2017] [Accepted: 08/15/2017] [Indexed: 12/23/2022] Open
Abstract
Components of the ocular surface synergistically contribute to maintaining and protecting a smooth refractive layer to facilitate the optimal transmission of light. At the air-water interface, the tear film lipid layer (TFLL), a mixture of lipids and proteins, plays a key role in tear surface tension and is important for the physiological hydration of the ocular surface and for ocular homeostasis. Alterations in tear fluid rheology, differences in lipid composition, or downregulation of specific tear proteins are found in most types of ocular surface disease, including dry eye disease (DED). Artificial tears have long been a first line of treatment in DED and aim to replace or supplement tears. More recently, lipid-containing eye drops have been developed to more closely mimic the combination of aqueous and lipid layers of the TFLL. Over the last 2 decades, our understanding of the nature and importance of lipids in the tear film in health and disease has increased substantially. The aim of this article is to provide a brief overview of our current understanding of tear film properties and review the effectiveness of lipid-based products in the treatment of DED. Liposome lid sprays, emulsion eye drops, and other lipid-containing formulations are discussed.
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Affiliation(s)
| | | | | | - Juha M. Holopainen
- Helsinki Eye Lab, Ophthalmology, Helsinki University Hospital, University of Helsinki, Helsinki, Finland
| | - Louis Tong
- Singapore Eye Research Institute, Singapore
- Yong Loo Lin School of Medicine, National University of Singapore, Singapore
- Duke-NUS Medical School, Singapore
- Singapore National Eye Center, Singapore
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27
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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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Patterson M, Vogel HJ, Prenner EJ. The effect of repeated lateral compression and expansions mimicking blinking on selected tear film polar lipid monofilms. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:319-330. [PMID: 27993563 DOI: 10.1016/j.bbamem.2016.12.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2016] [Revised: 11/17/2016] [Accepted: 12/15/2016] [Indexed: 10/20/2022]
Abstract
The tear film lipid layer is formed on the anterior surface of the eye, functioning as a barrier to excess evaporation and foreign particles, while also providing stability to the tear film. The lipid layer is organized into a polar lipid layer consisting of phospholipids, ceramides, and free fatty acids that act as a surfactant to a non-polar multilayer of wax and cholesterol esters. Due to shear forces from eye movement and the compression and expansion of blinking, the tear lipids are under constant stress. However, tear film is able to resist immediate rupture and remains intact over multiple blinks. This work aimed to better understand the lateral organization of selected tear film polar lipids. The polar lipid biomimetic studied here consisted of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl glucosylceramide (PGC), and palmitoyl sphingomyelin (PSM). Surface pressure-area isocycles mimicked blinking and films were visualized by Brewster angle microscopy (BAM). All lipid systems formed relatively reversible films as indicated by limited hysteresis. However, pure DPPC and PSM films experienced greater changes in lipid packing upon compression and expansion compared to pure PGC and DPPE. This suggests that the driving force behind maintaining the lateral organization of the polar lipids from tear film may be the hydrogen bonding propensities of the head groups. Additionally, isocycles of films containing DPPC, DPPE, and PGC mixtures exhibited evidence for reversible multilayer formation or folding. This was supported by 3D analysis of structures that formed during compression but reintegrated back into the bulk lipid film during expansion near the in vitro tear film surface pressure of the open eye. Therefore, the polar lipids of tear film may be directly involved in preventing film rupture during a blink.
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Affiliation(s)
- Matthew Patterson
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Hans J Vogel
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada
| | - Elmar J Prenner
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
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Olżyńska A, Cwiklik L. Behavior of sphingomyelin and ceramide in a tear film lipid layer model. Ann Anat 2016; 210:128-134. [PMID: 27837653 DOI: 10.1016/j.aanat.2016.10.005] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2016] [Revised: 10/13/2016] [Accepted: 10/16/2016] [Indexed: 11/27/2022]
Abstract
Tear film lipid layer is a complex lipid mixture forming the outermost interface between eye and environment. Its key characteristics, such as surface tension and structural stability, are governed by the presence of polar lipids. The origin of these lipids and exact composition of the mixture are still elusive. We focus on two minor polar lipid components of the tear film lipid later: sphingomyelin and ceramide. By employing coarse grain molecular dynamics in silico simulations accompanied by Langmuir balance experiments we provide molecular-level insight into behavior of these two lipids in a tear film lipid layer model. Sphingomyelin headgroups are significantly exposed at the water-lipids boundary while ceramide molecules are incorporated between other lipids frequently interacting with nonpolar lipids. Even though these two lipids increase surface tension of the film, their molecular-level behavior suggests that they have a stabilizing effect on the tear film lipid layer.
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Affiliation(s)
- Agnieszka Olżyńska
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, Prague 18223, Czech Republic
| | - Lukasz Cwiklik
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, Prague 18223, Czech Republic; Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, Prague 16610, Czech Republic.
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Bunker A, Magarkar A, Viitala T. Rational design of liposomal drug delivery systems, a review: Combined experimental and computational studies of lipid membranes, liposomes and their PEGylation. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2334-2352. [DOI: 10.1016/j.bbamem.2016.02.025] [Citation(s) in RCA: 103] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2015] [Revised: 02/09/2016] [Accepted: 02/10/2016] [Indexed: 01/22/2023]
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Svitova TF, Lin MC. Dynamic interfacial properties of human tear-lipid films and their interactions with model-tear proteins in vitro. Adv Colloid Interface Sci 2016; 233:4-24. [PMID: 26830077 DOI: 10.1016/j.cis.2015.12.009] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 12/15/2015] [Accepted: 12/15/2015] [Indexed: 11/16/2022]
Abstract
This review summarizes the current state of knowledge regarding interfacial properties of very complex biological colloids, specifically, human meibum and tear lipids, and their interactions with proteins similar to the proteins found in aqueous part of human tears. Tear lipids spread as thin films over the surface of tear-film aqueous and play crucial roles in tear-film stability and overall ocular-surface health. The vast majority of papers published to date report interfacial properties of meibum-lipid monolayers spread on various aqueous sub-phases, often containing model proteins, in Langmuir trough. However, it is well established that natural human ocular tear lipids exist as multilayered films with a thickness between 30 and 100nm, that is very much disparate from 1 to 2nm thick meibum monolayers. We employed sessile-bubble tensiometry to study the dynamic interfacial and rheological properties of reconstituted multilayered human tear-lipid films. Small amounts (0.5-1μg) of human tear lipids were deposited on an air-bubble surface to produce tear-lipid films in thickness range 30-100nm corresponding to ocular lipid films. Thus, we were able to overcome major Langmuir-trough method limitations because ocular tear lipids can be safely harvested only in minute, sub-milligram quantities, insufficient for Langmuir through studies. Sessile-bubble method is demonstrated to be a versatile tool for assessing conventional synthetic surfactants adsorption/desorption dynamics at an air-aqueous solution interface. (Svitova T., Weatherbee M., Radke C.J. Dynamics of surfactant sorption at the air/water interface: continuous-flow tensiometry. J. Colloid Interf. Sci. 2003;261:1170-179). The augmented flow-sessile-bubble setup, with step-strain relaxation module for dynamic interfacial rheological properties and high-precision syringe pump to generate larger and slow interfacial area expansions-contractions, was developed and employed in our studies. We established that this method is uniquely suitable for examination of multilayered lipid-film interfacial properties. Recently it was compellingly proven that chemical composition of human tear lipids extracted from whole tears is substantially different from that of meibum lipids. To be exact, healthy human tear lipids contain 8-16% of polar lipids, similar to lung lipids, and they are mostly double-tailed phospholipids, with C16 and longer alkyl chains. Rationally, one would assume that the results obtained for meibum lipids, devoid of surface-active components such as phospholipids, and, above all, in a form of monolayers, are not pertinent or useful for elucidating behavior and stability of an averaged 60-nm thick ocular tear-lipid films in vivo. The advantage of sessile-bubble technique, specifically, using a small amount of lipids required to attain multilayered films, unlocks the prospect of evaluating and comparing the interfacial properties of human tear lipids collected from a single individual, typically 100-150μg. This is in sharp contrast with several milligrams of lipids that would be required to build equally thick films for Langmuir-trough experiments. The results of our studies provided in-depth understanding of the mechanisms responsible for properties and stability of human tear-lipid films in vivo. Here we summarize recent publications and our latest findings regarding human tear-lipid interfacial properties, their chemical composition, and their interaction with model proteins mimicking the proteins found in human tear-aqueous phase.
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Affiliation(s)
- Tatyana F Svitova
- University of California, Berkeley, School of Optometry, Clinical Research Center, United States
| | - Meng C Lin
- University of California, Berkeley, School of Optometry, Clinical Research Center, United States; University of California, Vision Science Program, United States
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Baoukina S, Tieleman DP. Computer simulations of lung surfactant. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2431-2440. [PMID: 26922885 DOI: 10.1016/j.bbamem.2016.02.030] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2015] [Revised: 02/21/2016] [Accepted: 02/23/2016] [Indexed: 01/26/2023]
Abstract
Lung surfactant lines the gas-exchange interface in the lungs and reduces the surface tension, which is necessary for breathing. Lung surfactant consists mainly of lipids with a small amount of proteins and forms a monolayer at the air-water interface connected to bilayer reservoirs. Lung surfactant function involves transfer of material between the monolayer and bilayers during the breathing cycle. Lipids and proteins are organized laterally in the monolayer; selected species are possibly preferentially transferred to bilayers. The complex 3D structure of lung surfactant and the exact roles of lipid organization and proteins remain important goals for research. We review recent simulation studies on the properties of lipid monolayers, monolayers with phase coexistence, monolayer-bilayer transformations, lipid-protein interactions, and effects of nanoparticles on lung surfactant. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Svetlana Baoukina
- Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada.
| | - D Peter Tieleman
- Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, 2500 University Dr. NW, Calgary, AB T2N 1N4, Canada.
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Cwiklik L. Tear film lipid layer: A molecular level view. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2421-2430. [PMID: 26898663 DOI: 10.1016/j.bbamem.2016.02.020] [Citation(s) in RCA: 107] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 02/13/2016] [Accepted: 02/16/2016] [Indexed: 11/15/2022]
Abstract
Human cornea is covered by an aqueous tear film, and the outermost layer of the tear film is coated by lipids. This so-called tear film lipid layer (TFLL) reduces surface tension of the tear film and helps with the film re-spreading after blinks. Alterations of tear lipids composition and properties are related to dry eye syndrome. Therefore, unveiling structural and functional properties of TFLL is necessary for understanding tear film function under both normal and pathological conditions. Key properties of TFLL, such as resistance against high lateral pressures and ability to spread at the tear film surface, are directly related to the chemical identity of TFLL lipids. Hence, a molecular-level description is required to get better insight into TFLL properties. Molecular dynamics simulations are particularly well suited for this task and they were recently used for investigating TFLL. The present review discusses molecular level organization and properties of TFLL as seen by these simulation studies. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Lukasz Cwiklik
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic.
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Biophysical characterization of monofilm model systems composed of selected tear film phospholipids. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1858:403-14. [PMID: 26657693 DOI: 10.1016/j.bbamem.2015.11.025] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2015] [Revised: 11/13/2015] [Accepted: 11/21/2015] [Indexed: 02/06/2023]
Abstract
The tear film protects the eye from foreign particles and pathogens, prevents excess evaporation, provides lubrication, and maintains a high quality optical surface necessary for vision. The anterior layer of tear film consists of polar and non-polar lipid layers. The polar lipids form a monolayer on the aqueous subphase, acting as surfactants for the non-polar lipid multilayer. A tear film polar lipid biomimetic consisting of dipalmitoyl phosphatidylcholine (DPPC), dipalmitoyl phosphatidylethanolamine (DPPE), palmitoyl glucosylceramide (PGC), and palmitoyl sphingomyelin (PSM) was characterized using Langmuir monolayers and Brewster angle microscopy (BAM). Lipid combinations formed very stable monolayers, especially those containing DPPC or PSM. Surface experiments and elasticity analyses revealed that PGC resulted in more condensed and rigid mixed monolayers. DPPE provided resistance to large changes in lipid ordering over a wide surface pressure range. Ternary mixtures containing DPPE and PGC with either DPPC or PSM experienced the greatest lipid ordering within the natural tear film surface pressure range suggesting that these lipids are important to maintain tear film integrity during the inter-blink period. Finally, BAM images revealed unique structures within monolayers of DPPC, DPPE, and PGC at the natural tear film surface pressure. 3D analysis of these domains suggested either the formation of multilayers or outward protrusions at surface pressures far below the point of irreversible collapse as seen on the isotherm. This entails that the polar lipids of tear film may be capable of multilayer formation or outward folding as a mechanism to prevent rupture of the tear film during a blink.
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Gartia MR, Misra SK, Ye M, Schwartz-Duval A, Plucinski L, Zhou X, Kellner D, Labriola LT, Pan D. Point-of-service, quantitative analysis of ascorbic acid in aqueous humor for evaluating anterior globe integrity. Sci Rep 2015; 5:16011. [PMID: 26525715 PMCID: PMC4630616 DOI: 10.1038/srep16011] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Accepted: 10/07/2015] [Indexed: 02/07/2023] Open
Abstract
Limited training, high cost, and low equipment mobility leads to inaccuracies in decision making and is concerning with serious ocular injuries such as suspected ruptured globe or post-operative infections. Here, we present a novel point-of-service (POS) quantitative ascorbic acid (AA) assay with use of the OcuCheck Biosensor. The present work describes the development and clinical testing of the paper-based biosensor that measures the changes in electrical resistance of the enzyme-plated interdigitated electrodes to quantify the level of AA present in ocular fluid. We have demonstrated the proof-of-concept of the biosensor testing 16 clinical samples collected from aqueous humor of patients undergoing therapeutic anterior chamber paracentesis. Comparing with gold standard colorimetric assay for AA concentration, OcuCheck showed accuracy of >80%, sensitivity of >88% and specificity of >71%. At present, there are no FDA-approved POS tests that can directly measures AA concentration levels in ocular fluid. We envisage that the device can be realized as a handheld, battery powered instrument that will have high impact on glaucoma care and point-of-care diagnostics of penetrating ocular globe injuries.
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Affiliation(s)
- Manas R Gartia
- Department of Bioengineering, University of Illinois at Urbana-Champaign.,Carle Foundation Hospital, 611 West Park Street, Urbana, IL, USA.,Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign
| | - Santosh K Misra
- Department of Bioengineering, University of Illinois at Urbana-Champaign.,Carle Foundation Hospital, 611 West Park Street, Urbana, IL, USA
| | - Mao Ye
- Department of Bioengineering, University of Illinois at Urbana-Champaign.,Carle Foundation Hospital, 611 West Park Street, Urbana, IL, USA
| | - Aaron Schwartz-Duval
- Department of Bioengineering, University of Illinois at Urbana-Champaign.,Carle Foundation Hospital, 611 West Park Street, Urbana, IL, USA
| | - Lisa Plucinski
- Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign
| | - Xiangfei Zhou
- Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign
| | - David Kellner
- Research Park, University of Illinois at Urbana Champaign, IL
| | - Leanne T Labriola
- Carle Foundation Hospital, 611 West Park Street, Urbana, IL, USA.,Department of Surgery, University of Illinois College of Medicine, Urbana IL, USA
| | - Dipanjan Pan
- Department of Bioengineering, University of Illinois at Urbana-Champaign.,Beckman Institute of Advanced Science and Technology, University of Illinois at Urbana-Champaign.,Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign.,Carle Foundation Hospital, 611 West Park Street, Urbana, IL, USA
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36
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Stratification of Tear Components During Tear Microdesiccation on Vertical Glass Surfaces. Cornea 2015; 34:959-66. [DOI: 10.1097/ico.0000000000000467] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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37
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Shaali M, Lara-Avila S, Dommersnes P, Ainla A, Kubatkin S, Jesorka A. Nanopatterning of mobile lipid monolayers on electron-beam-sculpted Teflon AF surfaces. ACS NANO 2015; 9:1271-1279. [PMID: 25541906 DOI: 10.1021/nn5050867] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Direct electron-beam lithography is used to fabricate nanostructured Teflon AF surfaces, which are utilized to pattern surface-supported monolayer phospholipid films with 50 nm lateral feature size. In comparison with unexposed Teflon AF coatings, e-beam-irradiated areas show reduced surface tension and surface potential. For phospholipid monolayer spreading experiments, these areas can be designed to function as barriers that enclose unexposed areas of nanometer dimensions and confine the lipid film within. We show that the effectiveness of the barrier is defined by pattern geometry and radiation dose. This surface preparation technique represents an efficient, yet simple, nanopatterning strategy supporting studies of lipid monolayer behavior in ultraconfined spaces. The generated structures are useful for imaging studies of biomimetic membranes and other specialized surface applications requiring spatially controlled formation of self-assembled, molecularly thin films on optically transparent patterned polymer surfaces with very low autofluorescence.
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Affiliation(s)
- Mehrnaz Shaali
- Department of Chemical and Biological Engineering and ‡Quantum Device Physics Laboratory, Chalmers University of Technology , 41296 Gothenburg, Sweden
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Nagashima T, Uematsu S. Water-binding phospholipid nanodomains and phase-separated diacylglycerol nanodomains regulate enzyme reactions in lipid monolayers. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:1479-1488. [PMID: 25565217 DOI: 10.1021/la503906m] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Phospholipid 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) nanodomains covered with bound water as well as diacylglycerol 1-palmitoyl-2-oleoyl-sn-glycerol (POG) nanodomains separated from a lipid membrane were studied, using monolayer surfaces of POPC hydrolyzed by phospholipase C (PLC). The investigation was based on the analysis of compression isotherms and on atomic force microscope (AFM) observations of Langmuir-Blodgett (LB) films and Langmuir-Schaefer (LS) films. The results included reaction rate constants obtained by kinetic analysis of phosphocholine at surface pressures from 0.1 to 31 mN/m and determined by a luminol-enhanced chemiluminescence method. Monolayer elastic modulus values and fluorescence microscopic images confirmed that hydrolysis by PLC progressed in the intermediate monolayer between a liquid-expanded (L1) film and a liquid-condensed (L2) film at 2-17 mN/m. Furthermore, the intermediate film was confirmed to consist of L1 film and the POPC nanodomains in the L2 state are covered with bound water, conclusions based on the following AFM results: (1) nanodomains in POPC LS films were catalyzed by PLC, (2) POG nanodomains extended out from LB films of mixed POPC/POG 9/1 (mol/mol) monolayers, and (3) POPC LS films were covered with bound water, as indicated by cross-sectional analysis. At the optimal surface pressure of 10 mN/m, when POPC nanodomains (L2), with internal diameters of ∼75 nm, were hydrolyzed by PLC, they shrank down into pockets of the same size as those that appeared with POG. The resulting pocket sizes on LS films were in agreement with POG nanodomain sizes on LB films. This study demonstrated that PLC reacted with POPC nanodomains (L2) dispersed in L1/L2 mixed phase monolayers selectively and that POG nanodomains were phase-separated from the monolayer as hydrolysis proceeded.
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Affiliation(s)
- Teruyoshi Nagashima
- Department of Physical Biochemistry, Graduate School of Pharmaceutical Sciences, University of Shizuoka , 52-1 Yada, Suruga Ward, Shizuoka City, Shizuoka 422-8526, Japan
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Nisoh N, Karttunen M, Monticelli L, Wong-ekkabut J. Lipid monolayer disruption caused by aggregated carbon nanoparticles. RSC Adv 2015. [DOI: 10.1039/c4ra17006g] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Carbon nanoparticles (CNP) have significant impact on the Pulmonary Surfactant (PS), the first biological barrier in the respiratory system.
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Affiliation(s)
- Nililla Nisoh
- Department of Physics
- Faculty of Science
- Kasetsart University
- Bangkok
- Thailand
| | - Mikko Karttunen
- Department of Chemistry and Waterloo Institute for Nanotechnology
- University of Waterloo
- Waterloo
- Canada
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40
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Lens-care-solution-induced alterations in dynamic interfacial properties of human tear-lipid films. Cont Lens Anterior Eye 2014; 37:368-76. [DOI: 10.1016/j.clae.2014.05.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2013] [Revised: 05/15/2014] [Accepted: 05/22/2014] [Indexed: 11/23/2022]
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Dwivedi M, Backers H, Harishchandra RK, Galla HJ. Biophysical investigations of the structure and function of the tear fluid lipid layer and the effect of ectoine. Part A: natural meibomian lipid films. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2708-15. [PMID: 24841755 DOI: 10.1016/j.bbamem.2014.05.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 05/02/2014] [Accepted: 05/05/2014] [Indexed: 11/27/2022]
Abstract
The tear fluid lipid layer is the outermost part of the tear film on the ocular surface which protects the eye from inflammations and injuries. We investigated the influence of ectoine on the structural organization of natural meibomian lipid films using surface activity analysis and topographical studies. These films exhibit a continuous pressure-area isotherm without any phase transition. With the addition of ectoine, the isotherm is expanded towards higher area per molecule values suggesting an increased area occupied by the interfacial lipid molecules. The AFM topology scans of natural meibomian lipid films reveal a presence of fiber-like structures. The addition of ectoine causes an appearance of droplet-like structures which are hypothesized to be tri-acyl-glycerols and other hydrophobic components excluded from the lipid film. Further the material properties of the droplet-like structure with respect to the surrounding were determined by using the quantitative imaging mode of the AFM technique. The droplet-like structures were found to be comparatively softer than the surrounding. Based on the observations a preliminary hypothesis is proposed explaining the mechanism of action of ectoine leading to the fluidization of meibomian lipid films. This suggests the possibility of ectoine as a treatment for the dry eye syndrome.
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Affiliation(s)
- Mridula Dwivedi
- NRW International Graduate School of Chemistry and Institute of Biochemistry, Germany; Institute of Biochemistry, Westfälische Wilhelms Universität, Wilhelm-Klemm-Str.2, 48149 Münster, Germany
| | - Hannes Backers
- Institute of Biochemistry, Westfälische Wilhelms Universität, Wilhelm-Klemm-Str.2, 48149 Münster, Germany
| | - Rakesh Kumar Harishchandra
- Institute of Biochemistry, Westfälische Wilhelms Universität, Wilhelm-Klemm-Str.2, 48149 Münster, Germany
| | - Hans-Joachim Galla
- Institute of Biochemistry, Westfälische Wilhelms Universität, Wilhelm-Klemm-Str.2, 48149 Münster, Germany.
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42
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Wizert A, Iskander DR, Cwiklik L. Organization of lipids in the tear film: a molecular-level view. PLoS One 2014; 9:e92461. [PMID: 24651175 PMCID: PMC3961367 DOI: 10.1371/journal.pone.0092461] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2013] [Accepted: 02/21/2014] [Indexed: 01/03/2023] Open
Abstract
Biophysical properties of the tear film lipid layer are studied at the molecular level employing coarse grain molecular dynamics (MD) simulations with a realistic model of the human tear film. In this model, polar lipids are chosen to reflect the current knowledge on the lipidome of the tear film whereas typical Meibomian-origin lipids are included in the thick non-polar lipids subphase. Simulation conditions mimic those experienced by the real human tear film during blinks. Namely, thermodynamic equilibrium simulations at different lateral compressions are performed to model varying surface pressure, and the dynamics of the system during a blink is studied by non-equilibrium MD simulations. Polar lipids separate their non-polar counterparts from water by forming a monomolecular layer whereas the non-polar molecules establish a thick outermost lipid layer. Under lateral compression, the polar layer undulates and a sorting of polar lipids occurs. Moreover, formation of three-dimensional aggregates of polar lipids in both non-polar and water subphases is observed. We suggest that these three-dimensional structures are abundant under dynamic conditions caused by the action of eye lids and that they act as reservoirs of polar lipids, thus increasing stability of the tear film.
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Affiliation(s)
- Alicja Wizert
- Institute of Biomedical Engineering and Instrumentation, Wroclaw University of Technology, Wroclaw, Poland
| | - D. Robert Iskander
- Institute of Biomedical Engineering and Instrumentation, Wroclaw University of Technology, Wroclaw, Poland
| | - Lukasz Cwiklik
- J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Prague, Czech Republic
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, v.v.i., Prague, Czech Republic
- Department of Physics, Tampere University of Technology, Tampere, Finland
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43
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Racial variations in interfacial behavior of lipids extracted from worn soft contact lenses. Optom Vis Sci 2014; 90:1361-9. [PMID: 24270592 DOI: 10.1097/opx.0000000000000098] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
PURPOSE To explore interfacial behaviors and effects of temperature and dilatation on dynamic properties of multilayered human tear lipids extracted from silicone hydrogel (SiH) lenses worn by asymptomatic Asian and white subjects. METHODS Interfacial properties of lipids extracted from Focus N&D lenses worn by 14 subjects continuously for 1 month were studied. The lipids were deposited on an air bubble immersed in a model tear electrolyte (MTE) solution to form 100 ± 20-nm-thick films. Surface pressure was recorded during slow expansion/contraction cycles to evaluate compressibility and hysteresis of lipid films. Films were also subjected to fast step-strain dilatations at temperatures of 22 to 45°C for their viscoelastic property assessment. RESULTS Isocycles for Asian and white lipids were similar at low surface pressures but had distinctly different compressibility and hysteresis at dynamic pressures exceeding 30 mN/m. Rheological parameters of reconstituted lipids were also dissimilar between Asian and white. The elastic modulus E∞ for white lipids was 1.5 times higher than that for Asian lipids, whereas relaxation time (t) was on average 1.3 times higher for Asian. No significant changes were observed in rheological properties of both Asian and white lipids when temperature increased from 22.0 to 36.5°C. However, for white lipids, E∞ reduced considerably at temperatures higher than 42.0°C, whereas t remained unchanged. For Asian lipids, both E∞ and t started to decline as temperature increased to 38°C and higher. CONCLUSIONS Higher elastic modulus of white lipids and elasticity threshold at certain deformations indicate stronger structure and intermolecular interactions as compared with more viscous Asian lipids. The differences in interfacial behaviors between Asian and white lipids may be associated with the differences in their chemical compositions.
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Gagnon BP, Meli MV. Effects on the self-assembly of n-alkane/gold nanoparticle mixtures spread at the air-water interface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:179-185. [PMID: 24359253 DOI: 10.1021/la4037937] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Nanoparticle films formed at the air-water interface readily form rigid films, where the nanoparticles irreversibly associate into floating "islands", often riddled with voids and defects, upon solvent evaporation. Improving the nanoparticle mobility in these films is key to achieving control over the nanoparticle packing parameters, which is attractive for a variety of applications. In this study, a variety of n-alkanes were mixed with tetradecanethiol-capped 2 nm gold nanoparticles and studied as Langmuir films at 18 and 32 °C. Pressure-area isotherms at 18 °C reveal a mixed liquid-expanded phase of nanoparticles and alkane at the air-water interface, but only for n-alkanes that are equal to or exceed the nanoparticle capping ligand in carbon chain length. Transmission electron microscopy images of the corresponding films suggest that the nanoparticles are mixed with a continuous hydrocarbon phase at 0 mN/m and that the hydrocarbon is squeezed out of the nanoparticle film during compression.
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Affiliation(s)
- Brandon P Gagnon
- Department of Chemistry and Biochemistry, Mount Allison University , 63C York Street, Sackville NB, Canada
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Koivuniemi A, Sysi-Aho M, Orešič M, Ollila S. Interfacial properties of high-density lipoprotein-like lipid droplets with different lipid and apolipoprotein A-I compositions. Biophys J 2013; 104:2193-201. [PMID: 23708359 DOI: 10.1016/j.bpj.2013.02.058] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Revised: 02/06/2013] [Accepted: 02/14/2013] [Indexed: 01/22/2023] Open
Abstract
The surface properties of high-density lipoproteins (HDLs) are important because different enzymes bind and carry out their functions at the surface of HDL particles during metabolic processes. However, the surface properties of HDL and other lipoproteins are poorly known because they cannot be directly measured for nanoscale particles with contemporary experimental methods. In this work, we carried out coarse-grained molecular dynamics simulations to study the concentration of core lipids in the surface monolayer and the interfacial tension of droplets resembling HDL particles. We simulated lipid droplets composed of different amounts of phospholipids, cholesterol esters (CEs), triglycerides (TGs), and apolipoprotein A-Is. Our results reveal that the amount of TGs in the vicinity of water molecules in the phospholipid monolayer is 25-50% higher compared to the amount of CEs in a lipid droplet with a mixed core of an equal amount of TG and CE. In addition, the correlation time for the exchange of molecules between the core and the monolayer is significantly longer for TGs compared to CEs. This suggests that the chemical potential of TG is lower in the vicinity of aqueous phase but the free-energy barrier for the translocation between the monolayer and the core is higher compared to CEs. From the point of view of enzymatic modification, this indicates that TG molecules are more accessible from the aqueous phase. Further, our results point out that CE molecules decrease the interfacial tension of HDL-like lipid droplets whereas TG keeps it constant while the amount of phospholipids varies.
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Benlloch-Navarro S, Franco I, Sánchez-Vallejo V, Silvestre D, Romero FJ, Miranda M. Lipid peroxidation is increased in tears from the elderly. Exp Eye Res 2013; 115:199-205. [DOI: 10.1016/j.exer.2013.07.011] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2013] [Revised: 06/22/2013] [Accepted: 07/12/2013] [Indexed: 10/26/2022]
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Robciuc A, Hyötyläinen T, Jauhiainen M, Holopainen JM. Ceramides in the pathophysiology of the anterior segment of the eye. Curr Eye Res 2013; 38:1006-16. [PMID: 23885886 DOI: 10.3109/02713683.2013.810273] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
PURPOSE Sphingolipid (SL) research reached a peak in the past years. Yet this positive trend was not evident for eye research as the relative number of studies centered on SLs is decreasing. Our aim is to encourage the inclusion of SL metabolites in studies of ocular pathophysiology by summarizing recent findings and current awareness concerning ceramides in the anterior segment of the eye. METHODS Review of literature relating to ceramides as bioactive lipids and the extent to which their particular nature was investigated in ocular pathophysiology. RESULTS Ceramides are rare but indispensable lipids that influence cellular responses through their effects on membrane biophysical properties or direct interaction with target proteins. Their biological significance is increased by variability and adaptability as there are tens of enzymes designed to modulate their function. The eye offers a set of unique environments where ceramides or other SLs have not been extensively studied. Not surprisingly, ceramides were associated with apoptosis in the metabolically active tissues, while little is known about its effects on the biophysical properties of the tears or lens lipids. More so, there are still aspects of the ocular homeostasis control where SLs contribution has not been investigated to date (e.g. pathogen aggression). CONCLUSIONS Ceramides and SL metabolism still receive increasing attention and have proven to be a significant metabolite in many research fields (e.g. cancer, stress response and inflammation) and there are yet many questions that they will aid answer. With the present work, we seek to increase awareness of these lipids also in eye research and to highlight their importance as common regulators of various diseases.
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Affiliation(s)
- Alexandra Robciuc
- Department of Ophthalmology, University of Helsinki, Helsinki Eye Lab, Helsinki, Finland
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Schuett BS, Millar TJ. An investigation of the likely role of (O-acyl) ω-hydroxy fatty acids in meibomian lipid films using (O-oleyl) ω-hydroxy palmitic acid as a model. Exp Eye Res 2013; 115:57-64. [PMID: 23792170 DOI: 10.1016/j.exer.2013.06.016] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Revised: 04/23/2013] [Accepted: 06/10/2013] [Indexed: 10/26/2022]
Abstract
(O-acyl) ω-hydroxy fatty acids (OAHFAs) are a recently found group of polar lipids in meibum. Since these lipids can potentially serve as a surfactant in the tear film lipid layer, the surface properties of a molecule of this lipid class was investigated and compared with a structurally related wax ester and a fatty acid. (O-oleyl) ω-hydroxy palmitic acid was synthesized and used as the model OAHFA. It was spread either alone or mixed with human meibum on an artificial tear buffer in a Langmuir trough, and pressure-area isocycle profiles were recorded at different temperatures and compared with those of palmityl oleate and oleic acid. These measurements were accompanied by fluorescence microscopy of meibum mixed films during pressure-area isocycles. The pressure area curves indicated that pure films of the model OAHFA are as surface active as oleic acid films, cover a much larger surface area than either palmityl oleate or oleic acid and show a distinct biphasic pressure-area isocycle profile. The OAHFAs appeared to remain on the aqueous surface and show only a minor re-arrangement into multi-layered structures during repetitive pressure area isocycles. All these properties can be explained by OAHFAs binding weakly to the aqueous surface via an ester group and strongly via a carboxyl group. By contrast, the pressure area profiles of palmityl oleate films indicate that they form multi-layers and oleic acid presumably forms micelles and desorbs into the subphase. When mixed with meibum, similar features as for pure films were observed. In addition, meibum-OAHFA films appeared very homogeneous; a feature not seen with other mixtures. In conclusion these data support the notion that the tested OAHFA is a very potent surfactant which is important in spreading and stabilising meibomian lipid films.
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Affiliation(s)
- Burkhardt S Schuett
- School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia
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Abstract
A lipid monolayer lining a boundary between two immiscible phases forms a complex interface with inhomogeneous distribution of forces. Unlike lipid bilayers, monolayers are formed in asymmetric environment and their properties depend strongly on lipid surface density. The monolayer properties are also affected significantly by the representation of the pure interface. Here we give a brief theoretical introduction and describe methods to simulate lipid monolayers starting from force-fields and system setup to reproducing state points on the surface tension (pressure)-area isotherms and transformations between them.
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Affiliation(s)
- Svetlana Baoukina
- Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.
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