scholarly journals Lipid Saturation and the Rheology of Human Tear Lipids

2019 ◽  
Vol 20 (14) ◽  
pp. 3431 ◽  
Author(s):  
Georgi As. Georgiev ◽  
Douglas Borchman ◽  
Petar Eftimov ◽  
Norihiko Yokoi
Keyword(s):  
Phase Transition ◽  
Surface Properties ◽  
Acyl Chain ◽  
Tear Film ◽  
Meibomian Gland ◽  
Lipid Phase ◽  
Strong Impact ◽  
Brewster Angle Microscopy ◽  
Lipid Phase Transitions ◽  
Pressure Area

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

scholarly journals Effects of Lipid Saturation on the Surface Properties of Human Meibum Films

2018 ◽  
Vol 19 (8) ◽  
pp. 2209 ◽  
Author(s):  
Yana Nencheva ◽  
Aparna Ramasubramanian ◽  
Petar Eftimov ◽  
Norihiko Yokoi ◽  
Douglas Borchman ◽  
...  
Keyword(s):  
Surface Properties ◽  
Acyl Chain ◽  
Tear Film ◽  
Meibomian Gland ◽  
Film Structure ◽  
Strong Impact ◽  
Heterogeneous Structure ◽  
Brewster Angle Microscopy ◽  
Chain Order ◽  
Compression Isotherms

Elevated levels of acyl chain saturation of meibomian lipids are associated with vastly different effects: from enhanced tear film (TF) stability in infants to shortened TF breakup time in meibomian gland disease patients. Thus it is important to study the effect of saturation on the surface properties of human meibum (MGS). Therefore, MGS films (1, 2, 3, 4, 5, 10, 25, 50, 67, and 100% saturation) were spread at the air/water interface of a Langmuir surface balance. The layers’ capability to reorganize during dynamic area changes was accessed via the surface pressure (π)-area (A) compression isotherms and step/relaxation dilatational rheology studies. Film structure was monitored with Brewster angle microscopy. The raise in the % (at ≥10%) of saturation resulted in the formation of stiffer, thicker, and more elastic films at π ≥ 12 mN/m with the effects being proportional to the saturation level. At the same time, at low (≤10 mN/m) π the raise in saturation resulted in altered spreading and heterogeneous structure of MGS layers. The strong impact of saturation on MGS surface properties correlates with our recent spectroscopy study, which demonstrated that saturation induced increase of MGS acyl chain order, phase transition temperature, and cooperativity.

scholarly journals Insights into Tear Film Stability from Babies and Young Adults: A Study of Human Meibum Lipid Conformation and Rheology

2018 ◽  
Vol 19 (11) ◽  
pp. 3502 ◽  
Author(s):  
Poonam Mudgil ◽  
Douglas Borchman ◽  
Aparna Ramasubramanian
Keyword(s):  
Phase Transition ◽  
Dry Eye ◽  
Tear Film ◽  
Hydrocarbon Chain ◽  
Lipid Phase ◽  
Film Stability ◽  
Lipid Order ◽  
Lipid Phase Transitions ◽  
Tear Film Stability ◽  
Lipid Conformation

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.

Fatty acyl chain structure, orientational order, and the lipid phase transition in Acholeplasma laidlawii B membranes. A review of recent 19F nuclear magnetic resonance studies

1984 ◽  
Vol 62 (11) ◽  
pp. 1134-1150 ◽  
Author(s):  
P. M. Macdonald ◽  
B. D. Sykes ◽  
R. N. McElhaney
Keyword(s):  
Phase Transition ◽  
Fatty Acids ◽  
Nuclear Magnetic Resonance ◽  
Acyl Chain ◽  
Orientational Order ◽  
Membrane Lipid ◽  
Fatty Acyl ◽  
Fatty Acyl Chain ◽  
Lipid Phase ◽  
Lipid Phase Transition

The orientational order parameters of monofluoropalmitic acids biosynthetically incorporated into membranes of Acholeplasma laidlawii B in the presence of a large excess of a variety of structurally diverse fatty acids have been determined via 19F nuclear magnetic resonance (19F NMR) spectroscopy. It is demonstrated that these monofluoropalmitic acids are relatively nonperturbing membrane probes based upon physical (differential scanning calorimetry), biochemical (membrane lipid analysis), and biological (growth studies) criteria. 19F NMR is shown to convey the same qualitative and quantitative picture of membrane lipid order provided by 2H-NMR techniques and to be sensitive to the structural characteristics of the membrane fatty acyl chains, as well as to the lipid phase transition. Representatives of each naturally occurring class of fatty acyl chain structures, including straight-chain saturated, methyl-branched, monounsaturated, and alicyclic-ring-substituted fatty acids, were studied and the 19F-NMR order parameters were correlated with the lipid phase transitions (determined calorimetrically). The lipid phase transition was the prime determinant of overall orientational order regardless of fatty acid structure. Effects upon orientational order attributable to specific structural substituents were discernible, but were secondary to the effects of the lipid phase transition. In the gel state, relative overall order was directly proportional to the temperature of the particular lipid phase transition. Not only the overall order, but also the order profile across the membrane was sensitive to the presence of particular structural substituents. In particular, in the gel state specific fatty acyl structures demonstrated a characteristic disordering effect in the membrane order profile. These various observations can be merged to provide a unified picture of the manner in which fatty acyl chain chemistry modulates the physical state of membrane lipids.

scholarly journals Effects of Curcumin on Lipid Membranes: an EPR Spin-label Study

2020 ◽  
Vol 78 (2) ◽  
pp. 139-147
Author(s):  
Mariusz Duda ◽  
Kaja Cygan ◽  
Anna Wisniewska-Becker
Keyword(s):  
Phase Transition ◽  
Lipid Membranes ◽  
Acyl Chain ◽  
Protective Role ◽  
Lipid Phase ◽  
Therapeutic Effects ◽  
Structural Effects ◽  
Spectral Parameters ◽  
Paramagnetic Resonance ◽  
Lipid Order

Abstract Curcumin is a yellow–orange dye widely used as a spice, food coloring and food preservative. It also exhibits a broad range of therapeutic effects against different disorders such as cancer, diabetes, or neurodegenerative diseases. As a compound insoluble in water curcumin accumulates in cell membranes and due to this location it may indirectly lead to the observed effects by structurally altering the membrane environment. To exert strong structural effects on membrane curcumin needs to adopt a transbilayer orientation. However, there is no agreement in literature as to curcumin’s orientation and its structural effects on membranes. Here, we investigated the effects of curcumin on lipid order, lipid phase transition, and local polarity in a model liposome membranes made of DMPC or DSPC using electron paramagnetic resonance (EPR) spin labeling technique. Curcumin affected lipid order at different depths within the membrane: it slightly increased the phospholipid polar headgroup mobility as monitored by spectral parameters of T-PC, while along the acyl chain the ordering effect was observed in terms of order parameter S. Also, rotational correlation times τ2B and τ2C of 16-PC in the membrane center were increased by curcumin. Polarity measurements performed in frozen suspensions of liposomes revealed enhancement of water penetration by curcumin in the membrane center (16-PC) and in the polar headgroup region (T-PC) while the intermediate positions along the acyl chain (5-PC and 10-PC) were not significantly affected. Curcumin at a lower concentration (5 mol%) shifted the temperature of the DMPC main phase transition to lower values and increased the transition width, and at a higher concentration (10 mol%) abolished the transition completely. The observed effects suggest that curcumin adopts a transbilayer orientation within the membrane and most probably form oligomers of two molecules, each of them spanning the opposite bilayer leaflets. The effects are also discussed in terms of curcumin’s protective activity and compared with those imposed on membranes by other natural dyes known for their protective role, namely polar carotenoids, lutein and zeaxanthin.

Pressure-jump X-ray studies of liquid crystal transitions in lipids

2006 ◽  
Vol 364 (1847) ◽  
pp. 2635-2655 ◽  
Author(s):  
John M Seddon ◽  
Adam M Squires ◽  
Charlotte E Conn ◽  
Oscar Ces ◽  
Andrew J Heron ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Lipid Membranes ◽  
Cubic Phase ◽  
Lipid Phase ◽  
Pressure Jump ◽  
X Ray Diffraction ◽  
X Ray ◽  
Lipid Phase Transitions ◽  
Cubic Phases

In this paper, we give an overview of our studies by static and time-resolved X-ray diffraction of inverse cubic phases and phase transitions in lipids. In §1 , we briefly discuss the lyotropic phase behaviour of lipids, focusing attention on non-lamellar structures, and their geometric/topological relationship to fusion processes in lipid membranes. Possible pathways for transitions between different cubic phases are also outlined. In §2 , we discuss the effects of hydrostatic pressure on lipid membranes and lipid phase transitions, and describe how the parameters required to predict the pressure dependence of lipid phase transition temperatures can be conveniently measured. We review some earlier results of inverse bicontinuous cubic phases from our laboratory, showing effects such as pressure-induced formation and swelling. In §3 , we describe the technique of pressure-jump synchrotron X-ray diffraction. We present results that have been obtained from the lipid system 1 : 2 dilauroylphosphatidylcholine/lauric acid for cubic–inverse hexagonal, cubic–cubic and lamellar–cubic transitions. The rate of transition was found to increase with the amplitude of the pressure-jump and with increasing temperature. Evidence for intermediate structures occurring transiently during the transitions was also obtained. In §4 , we describe an IDL-based ‘ AXcess ’ software package being developed in our laboratory to permit batch processing and analysis of the large X-ray datasets produced by pressure-jump synchrotron experiments. In §5 , we present some recent results on the fluid lamellar– Pn 3 m cubic phase transition of the single-chain lipid 1-monoelaidin, which we have studied both by pressure-jump and temperature-jump X-ray diffraction. Finally, in §6 , we give a few indicators of future directions of this research. We anticipate that the most useful technical advance will be the development of pressure-jump apparatus on the microsecond time-scale, which will involve the use of a stack of piezoelectric pressure actuators. The pressure-jump technique is not restricted to lipid phase transitions, but can be used to study a wide range of soft matter transitions, ranging from protein unfolding and DNA unwinding and transitions, to phase transitions in thermotropic liquid crystals, surfactants and block copolymers.

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