Model Lipid Membranes Research Articles

Fast Estimation of the Blood-Brain Barrier Permeability by Pulling a Ligand through a Lipid Membrane.

The blood–brain barrier (BBB) is a physical barrier that regulates the homeostasis of the neural microenvironment. A relative estimate of the BBB permeability, which is important for drug design, may be experimentally provided by the logBB (the blood–brain concentration ratio) and the logPS (permeability–surface-area product), while many computational methods aim to identify key properties that correlate well with these quantities. Although currently existing computational methods (e.g., quantitative structure activity relation) have made a significant contribution in screening various compounds that could potentially translocate through the BBB, they are unable to provide a physical explanation of the underlying processes and they can often be computationally demanding. Here, we use steered molecular dynamics simulation to estimate the BBB permeability of various compounds on the basis of simple lipid–membrane models by computing the nonequilibrium work, Wneq, produced by pulling the compounds through the membrane. We found that the values of Wneq correlate remarkably well with logBB and logPS for a range of compounds and different membrane types and pulling speeds, independently of the choice of force field. Moreover, our results provide insight into the role of hydrogen bonds, the energetic barriers, and the forces exerted on the ligands during their pulling. Our method is computationally easy to implement and fast. Therefore, we anticipate that it could provide a reliable prescreening tool for estimating the relative permeability of the BBB to various substances.

Flavonol clustering in model lipid membranes: DSC, AFM, force spectroscopy and MD simulations study

We here report on flavonols (myricetin (MCE) and its glycoside myricitrin (MCI)) – 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) membrane interactions focusing on the effects of flavonol clustering on the membrane thermotropic and nanomechanical properties.Atomic force microscopy (AFM), force spectroscopy (FS) and differential scanning calorimetry (DSC) together with molecular dynamics (MD) simulations provided a consistent picture of flavonol - DMPC membrane interactions. DMPC membrane as a supported lipid bilayer preserved its integrity even at higher flavonol molar fraction x. When present at x = 0.1 – 0.3, MCE and MCI both slightly improve DMPC bilayer fluidity which is evidenced by the decrease in the main phase transition temperature Tm. MCE is found within the interior of the bilayer, while MCI incorporates in the head group-water interface region. AFM and FS confirmed clusters as protrusions with an average height of 0.012 μm and average diameters of 0.60 and 0.24 μm for MCE and MCI clusters, respectively. The average membrane thickness in DMPC fluid phase decreases for 7% at xMCE = 0.30, while only 4% at xMCI = 0.27.The induced membrane changes are dependent on the chemical and physical properties of inserted flavonols. The hypothesis regarding the tendency of flavonol to clustering in membranes by increasing flavonol molar fraction has been confirmed.

Dewatering of Nannochloropsis Sp Via Forward Osmosis: A Molecular Dynamics Study

Microalgal biomass is an essential source of renewable energy and the production of high-valued bio-products. Nannochloropsis sp. is a marine microalgae which contains high valued bio-compounds. However, it contains elevated moisture which hinders extraction of important significant bio-compounds. A dewatering process of Nannochloropsis sp via forward osmosis is proposed. The objective of the study is to evaluate the effect of salinity on the lipid membrane of microalgae Nannochloropsis sp by inducing osmotic pressure difference. A microalgae lipid membrane model was developed using molecular dynamics and evaluated through relative structural changes and water dynamics by varying the salinity. The results revealed at elevated salinity, compression occurs to the lipid membrane based on the tail order and area per head groups. The dynamics of water molecules showed that water migration happens as early as 20 ns. Despite membrane compression, a total of 5 water molecules migrated within the 150 ns. This suggests that forward osmosis is a promising alternative for microalgal dewatering.

Elasticity and phase behaviour of biomimetic membrane systems containing tetraether archaeal lipids

Archaeal single-cell microorganisms are characterised by particularly strong resistance to harsh environments at extreme temperature ranges, pH values, high pressure and salinity. The recognition of molecules rendering the archaeal membranes stable in such conditions represents an important step towards understanding the molecular mechanisms, which underlie the cellular survival, in order to effectively exploit them in biomedicine and bionanotechnology. Here we report on the bending elasticity and phase behaviour of model lipid membranes containing tetraether archaeal lipids. The bending elasticity modulus of membranes composed of palmitoyl-oleoyl phosphatidylcholine and glycerol dialkyl glycerol tetraether extract from the archaeon Thermoplasma acidophilum’s plasma membrane is measured by analysis of the thermal shape fluctuations of nearly spherical giant unilamellar vesicles (tens of micrometers in size). The bending rigidity is reported to non-monotonically depend on the archaeal lipids’ concentration in the bilayer. At 50 wt% of tetraether lipids in the membrane we measure around 20% decrease of the bending modulus compared to the studied single-component phosphocholine bilayer. The membrane resistance to bending increases at archaeal lipids’ content higher than 70 wt%. These findings support the hypothesis about a probable looping conformation at very low amounts of bipolar lipids in the membrane and prevailing spanning tetraether molecules at higher concentrations. Fluorescence microscopy reveals structural phase coexistence at low temperatures (6 °C) for 75 wt% of bolalipids in the bilayer. Laurdan spectroscopy measurements of large unilamellar vesicles (hundreds of nanometers in size) provide evidences for increased lipid ordering at the glycerol level induced by the presence of up to 90 wt% of bolalipid in the bilayer. At this archaeal lipid content we measure increased bending rigidity of the membrane. The fatty acyl chain mobility probed by DPH fluorescence spectroscopy is significantly reduced in the presence of bolalipids. The lipid ordering decreases with increasing the temperature to an extent depending on the bolalipid content in the membrane. The presence of bipolar lipids in the bilayer affects the lipid packing more strongly at the glycerol level compared to the hydrophobic core of the membrane. By elucidating the effect of tetraether lipids on the structural and mechanical properties of the bilayer, the reported results are expected to help in advancing on liposome-based pharmaceuticals and biomedical applications as well as for developments in sensorics and nanotechnology.

The Structural Integrity of the Model Lipid Membrane during Induced Lipid Peroxidation: The Role of Flavonols in the Inhibition of Lipid Peroxidation.

The structural integrity, elasticity, and fluidity of lipid membranes are critical for cellular activities such as communication between cells, exocytosis, and endocytosis. Unsaturated lipids, the main components of biological membranes, are particularly susceptible to the oxidative attack of reactive oxygen species. The peroxidation of unsaturated lipids, in our case 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), induces the structural reorganization of the membrane. We have employed a multi-technique approach to analyze typical properties of lipid bilayers, i.e., roughness, thickness, elasticity, and fluidity. We compared the alteration of the membrane properties upon initiated lipid peroxidation and examined the ability of flavonols, namely quercetin (QUE), myricetin (MCE), and myricitrin (MCI) at different molar fractions, to inhibit this change. Using Mass Spectrometry (MS) and Fourier Transform Infrared Spectroscopy (FTIR), we identified various carbonyl products and examined the extent of the reaction. From Atomic Force Microscopy (AFM), Force Spectroscopy (FS), Small Angle X-Ray Scattering (SAXS), and Electron Paramagnetic Resonance (EPR) experiments, we concluded that the membranes with inserted flavonols exhibit resistance against the structural changes induced by the oxidative attack, which is a finding with multiple biological implications. Our approach reveals the interplay between the flavonol molecular structure and the crucial membrane properties under oxidative attack and provides insight into the pathophysiology of cellular oxidative injury.

Fluorescence Mapping of α-Tocopherol Redox Activity in Supported Lipid Bilayers

Lipid membranes have gained wide attention as assembly scaffolds, owing to their ability to self-assemble into well-defined fluid structures, allowing the compartmentalization and direct assembly of components of interest in a fluid platform. Model lipid membranes offer the opportunity to mimic and study processes occurring across these fluid mosaics such as respiration, transport and signaling.Armed with a spectroelectrochemistry microscopy setup, in this study we have explored redox reactions within lipid membranes, proof of concept experiments intended to address the response of membrane embedded redox systems. Experimentally, a supported lipid bilayer was formed on top on an indium tin oxide (ITO)-coated glass. H4BPMHC, a redox sensitive fluorogenic probe bearing the chromanol moiety of α-tocopherol (Vitamin E), and a BODIPY tail segment was incorporated within the lipid membrane. The electrochemical and optical properties were next studied using our total internal reflection fluorescence (TIRF) microscopy based spectro-electrochemical (SEC) setup, that enables monitoring emission while minimizing background by virtue of sampling a small ~ 300 nm region above the glass water interface, while also controlling the redox potential at the basal leaflet of the lipid membrane.Our results are consistent with oxidation of the chromanol moiety of the probe into a chromanone moiety through an irreversible process that elicits fluorescence, and further thermally induced rearrangement of the newly formed chromanone into a chromoquinone. We will discuss the general methodology, results, and implications of the work in the context of electron transport through relay redox systems.

Synergistic Biophysical Techniques Reveal Structural Mechanisms of Engineered Cationic Antimicrobial Peptides in Lipid Model Membranes.

In the quest for new antibiotics, two novel engineered cationic antimicrobial peptides (eCAPs) have been rationally designed. WLBU2 and D8 (all 8 valines are the d-enantiomer) efficiently kill both Gram-negative and -positive bacteria, but WLBU2 is toxic and D8 nontoxic to eukaryotic cells. We explore protein secondary structure, location of peptides in six lipid model membranes, changes in membrane structure and pore evidence. We suggest that protein secondary structure is not a critical determinant of bactericidal activity, but that membrane thinning and dual location of WLBU2 and D8 in the membrane headgroup and hydrocarbon region may be important. While neither peptide thins the Gram-negative lipopolysaccharide outer membrane model, both locate deep into its hydrocarbon region where they are primed for self-promoted uptake into the periplasm. The partially α-helical secondary structure of WLBU2 in a red blood cell (RBC) membrane model containing 50 % cholesterol, could play a role in destabilizing this RBC membrane model causing pore formation that is not observed with the D8 random coil, which correlates with RBC hemolysis caused by WLBU2 but not by D8.

Synchronous, Crosstalk-free Correlative AFM and Confocal Microscopies/Spectroscopies

Microscopies have become pillars of our characterization tools to observe biological systems and assemblies. Correlative and synchronous use of different microscopies relies on the fundamental assumption of non-interference during images acquisitions. In this work, by exploring the correlative use of Atomic Force Microscopy and confocal-Fluorescence-Lifetime Imaging Microscopy (AFM-FLIM), we quantify cross-talk effects occurring during synchronous acquisition. We characterize and minimize optomechanical forces on different AFM cantilevers interfering with normal AFM operation as well as spurious luminescence from the tip and cantilever affecting time-resolved fluorescence detection. By defining non-interfering experimental imaging parameters, we show accurate real-time acquisition and two-dimensional mapping of interaction force, fluorescence lifetime and intensity characterizing morphology (AFM) and local viscosity (FLIM) of gel and fluid phases separation of supported lipid model membranes. Finally, as proof of principle by means of synchronous force and fluorescence spectroscopies, we precisely tune the lifetime of a fluorescent nanodiamond positioned on the AFM tip by controlling its distance from a metallic surface. This opens up a novel pathway of quench sensing to image soft biological samples such as membranes since it does not require tip-sample mechanical contact in contrast with conventional AFM in liquid.

Effects of fluidity and charge density on the morphology of a bicellar mixture – A SANS study

The spontaneously formed structures of physiologically relevant lipid model membranes made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol) and 1,2-hexanoyl-sn-glycero-3-phosphocholine have been evaluated in depth using small angle neutron scattering. Although a common molar ratio of long- to short- chain phospholipids (~4) as reported in many bicellar mixtures was used, discoidal bicelles were not found as the major phase throughout the range of lipid concentration and temperature studied, indicating that the required condition for the formation of bicelle is the immiscibility between the long- and short- chain lipids, which were in the gel and Lα phases, respectively, in previous reports. In this study, all lipids are in the Lα phase. The characterization outcome suggests that the spontaneous structures tie strongly with the physical parameters of the system such as melting transition temperature of the long-chain lipid, total lipid concentration and charge density of the system. Multilamellar vesicles, unilamellar vesicles, ribbons and perforated lamellae can be obtained based on the analysis of the small angle neutron scattering results, leading to the construction of structural diagrams. This report provides the important map to choose suitable lipid systems for the structural study of membrane-associated proteins, design of theranostic nanocarriers or other related research fields.

Effect of Cholesterol on the Structure of Networked Water at the Surface of a Model Lipid Membrane.

Using all-atom molecular dynamics simulations and network analysis, we investigated the effect of membrane cholesterol level on the structure of organized water at the interface between bulk water and a model lipid membrane. Irrespective of membrane cholesterol content, interfacial water structure is largely perturbed by the presence of the membrane surface due to water-phospholipid interactions, which deplete the chance of hydrogen bonding among water molecules. In contrast, the addition of cholesterol suppresses the disturbing effect of the membrane on water-water hydrogen bonding as cholesterol provides a more bulklike environment for the interfacial water molecules, as evidenced by enhancement of local water density, a reduction in their orientational bias, and increases in both the number of hydrogen bonds and the topological complexity of the hydrogen bond network.

Equilibria in DPPC-Diosgenin and DPPC-Diosgenin Acetate Bilayer Lipid Membranes: Interfacial Tension and Microelectrophoretic Studies

Interactions between components of model lipid membranes (spherical lipid bilayers and liposomes) are investigated here. Parameters characterizing equilibria in the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-diosgenin (Dio) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC)-diosgenin acetate (DAc) membrane systems have been determined. The interfacial tension measurement of spherical lipid bilayers was based on the Young-Laplace’s equation using a homemade computer-controlled device. We assume a 1:1 complex in the DPPC-Dio and DPPC-DAc membrane systems. The parameters A 3 − 1 , the surface concentration of lipid membranes formed from these complexes, γ 3 , the interfacial tension of such membranes, and, K, the constant stability of these complexes were calculated. Microelectrophoresis was used for examinations of the surface charge density of lipid membranes. The values were obtained here from electrophoretic mobility data applying Smoluchowsky’s equation. The effect of pH (pH ranged of 2 to 10) on the electrolyte solution and the compositions of the membranes was analyzed. The obtained results indicate that the modification of DPPC membranes with both Dio and DAc causes changes in surface charge density values and shifts of the isoelectric point.

A way to introducing a hydrophilic bioactive agent into model lipid membranes. The role of cetyl palmitate in the interaction of curcumin with 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine monolayers

Abstract The interfacial behavior of curcumin, a model anti-inflammatory drug was studied upon interaction with cetyl palmitate and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine. Cetyl palmitate finds applications for topical delivery in nanostructured lipid carriers, while the phosphatidylcholine was used both as a component of the carrier and as a model membrane lipid. Here, surface pressure, thermodynamics, Brewster angle microscopy, molecular dynamics and polarization modulation infrared reflection-absorption spectroscopy were used to better our understanding of the interaction between the components of the delivery systems and, on the other hand, of their interaction with biological membranes. Moreover, thermodynamics was used to analyze the effect of curcumin on the lipid systems and, in particular, on the model membranes. The results obtained indicate that mixtures of curcumin and cetyl palmitate form Langmuir films, while none of the two pure components does. This effect was interpreted in terms of formation of a complex between curcumin and the hydrophobic, water insoluble cetyl palmitate. The hydrophilic-hydrophobic balance of the complex allows its penetration into the monolayer and mixing with the phospholipid phase. This finding may be of interest for further design of phytolipids for drug delivery applications.

Membrane Stability in the Presence of Methacrylate Esters.

Bioproduction of poly(methyl methacrylate) is a fast growing global industry that is limited by cellular toxicity of monomeric methacrylate intermediates to the producer strains. Maintaining high methacrylate concentrations during biofermentation, required by economically viable technologies, challenges bacterial membrane stability and cellular viability. Studying the stability of model lipid membranes in the presence of methacrylates offers unique molecular insights into the mechanisms of methacrylate toxicity, as well as into the fundamental structural bases of membrane assembly. We investigate the structure and stability of model membranes in the presence of high levels of methacrylate esters using solid-state nuclear magnetic resonance (NMR) and small-angle X-ray scattering (SAXS). Wide-line 31P NMR spectroscopy shows that butyl methacrylate (BMA) can be incorporated into the lipid bilayer at concentrations as high as 75 mol % without significantly disrupting membrane integrity and that lipid acyl chain composition can influence membrane tolerance and ability to accommodate BMA. Using high resolution 13C magic angle spinning (MAS) NMR, we show that the presence of 75 mol % BMA lowers the lipid main transition temperature by over 12 degrees, which suggests that BMA intercalates between the lipid chains, causing uncoupling of collective lipid motions that are typically dominated by chain trans-gauche isomerization. Potential uncoupling of the bilayer leaflets to accommodate a separate BMA subphase was not supported by the SAXS experiments, which showed that membrane thickness remained unchanged even at 80% BMA. Reduced X-ray scattering contrast at the polar/apolar interface suggests BMA localization in that region between the lipid molecules.

Development of lipid membrane based assays to accurately predict the transfection efficiency of cell-penetrating peptide-based gene nanoparticles.

Successful gene therapy requires the development of vectors that enable efficient delivery of genetic materials (e.g., pDNA or siRNA) to targeted cells, without degradation of the genetic materials. We have shown that nanoparticles formed by combining cell-penetrating peptide and pDNA (CPP-pDNA) into complexes and condensing them with calcium chloride can provide gene nanoparticles with high transfection efficiency and low cytotoxicity. In this work, we compare in situ measurements of the membrane insertion potential of three arginine-based gene nanoparticles (RW9-NPs, R9-NPs, and RH9-NPs) using four lipid compositions and two types of model membrane (Langmuir monolayers vs. supported bilayers) with their transfection efficiency in two human cancer cell lines. Using a Langmuir trough, we measured the membrane insertion potential of our gene nanoparticles to model membrane monolayers. A Quartz Crystal Microbalance with Dissipation (QCM-D) technique was used to monitor the adsorption of these nanoparticles to lipid bilayers of various compositions. Finally, gene expression using these nanoparticles was measured in breast cancer and cervical cancer cell lines. Our cell culture studies indicate that although R9-NPs and RW9-NPs show a significant increase in transfection efficiency compared to free pDNA, RH9-NPs do not show any significant difference. Both the Langmuir monolayer and QCM-D bilayer studies show that these results are best reflected in the in situ measurement assays when lipid systems containing a mixture of phospholipids, cholesterol, and sphingolipids are used. It is important to note that the mechanism of penetration is expected to differ for RW9 vs. R9; however, gene nanoparticles containing either of these CPPs show similar transfection efficiency. Our results therefore demonstrate that the design of predictive assays for gene therapy using CPPs must involve carefully chosen model lipid membrane systems that accurately represent the varying compositions of cell membranes.

Primary and Secondary Hydration Forces between Interdigitated Membranes Composed of Bolaform Microbial Glucolipids.

To better understand lipid membranes in living organisms, the study of intermolecular forces using the osmotic pressure technique applied to model lipid membranes has constituted the ground knowledge in the field of biophysics since four decades. However, the study of intermolecular forces in lipid systems other than phospholipids, like glycolipids, has gained a certain interest only recently. Even in this case, the work generally focuses on the study of membrane glycolipids, but little is known on new forms of non-membrane functional compounds, like microbial bolaform glycolipids. This work explores, through the osmotic stress method involving an adiabatic humidity chamber coupled to neutron diffraction, the short-range (<2 nm) intermolecular forces of membranes entirely composed of interdigitated glucolipids. Experiments are performed at pH 6 when the glucolipid is partially negatively charged and for which we explore the effect of low (16 mM) and high (100 mM) ionic strength. We find that this system is characterized by primary and secondary hydration regimes insensitive and sensitive to ionic strength, respectively, and with typical decay lengths of λH1 = 0.37 ± 0.12 nm and λH2 = 1.97 ± 0.78 nm.

Regulation of Lipid Membrane Partitioning of Tamoxifen by Ionic Strength and Cholesterol.

The purpose of this study was to inspect the interactions between an anti-breast cancer, TAM, with model of lipid membranes composed of either zwitterionic DPPC LUVs or anionic DPPG LUVs and how they depend on ionic strength and cholesterol. The Kp of TAM into DPPC and DPPG LUVs were determined at three different NaCl concentrations by second derivative UV-Vis spectrophotometry. The effect of cholesterol incorporated into these LUVs on TAM's Kp was also assessed. The ATR-FTIR measurements were carried out to verify structural changes within the acyl chain and head group regions of the liposomes upon TAM partitioning. Increasing salt concentration produced negligible impact on the partitioning of TAM into DPPC bilayer as its Kp remained unaffected whilst induced outstanding reduction of TAM's Kp into DPPG liposomes. Furthermore, TAM was found to disorder the lipids' acyl chains, which could result in an increase in the membrane fluidity, a necessary piece of information to refer to when prescribing TAM dosage for administration. Additionally, cholesterol showed astoundingly opposite contribution to the partitioning of TAM into the LUVs, as its Kp value reduced in DPPC/Chol bilayer yet increased in DPPG/Chol liposomes. Ionic strength and cholesterol play a noteworthy role in regulation of TAM partitioning into lipid membranes as they could obstruct or promote such action.

Interaction of Alpha-Synuclein with Raft Containing Model Lipid Membranes: Morphology and Structure

Interaction of Alpha-Synuclein with Raft Containing Model Lipid Membranes: Morphology and Structure

Lipid Bilayers Influenced by Taurin and Betain

We studied the influence of natural osmolytes Taurin and Betain on the stability and fluidity of lipid model membranes. They components of daily products aim at our well-being, such as energy drinks or baby creams. We used a combination of simultaneous SAXS/WAXS/DSC measurements, being able to identify the structures, their dimensions and the phase transition temperatures. Thermal scans show morphologies similar to aqueous solution of the pure lipids, although with different dimensions and transition temperatures. In POPE, we observe structures with high curvature, and upon temperature cycling, the induction of possible cubic phases. Fully hydrated POPE hydrated with solutions of such osmolytes surprisingly lacks anomalous diffraction patterns over a wide temperature range on cooling from the hexagonal phase. The diffraction peaks in the last patterns are much less intense than at the beginning of the scan. The DSC shows a higher phase transition temperature on heating than for pure aqueous POPE, while during cooling this is not seen. DSC of POPE in on these samples shows a transition at a different temperature than purely hydrated POPE. The SAXS scan indicates a less organized stack of bilayers and the hexagonal phase, normally following the lamellar upon heating, could not be clearly seen up to 85oC. Moreover, no well-organized structure was formed during cooling. On combining SAXS/WAXS and DSC results obtained from dispersions of POPE in either aqueous solution of Taurin and Betain, one can see their effect from a structural perspective, that is, their influence on the macro organization of the self-assembled mesogenic units. Both osmolytes seem to require high temperatures (weaker interactions between headgroups of neighbouring lipids) to effectively interact with the POPE (headgroups) and influence the dispersion.

Effect of Melatonin on Lipid Membrane Structure and Membrane Interactions with Amyloid. An NMR and LSPR Study

Alzheimer's Disease (AD) is a neurodegenerative disease and leading cause of dementia resulting in memory loss and cognition decline. The molecular mechanism of AD is not well understood, which has delayed the development of effective treatments. Amyloid-ß (Aß) is the suspected cause of AD, as nonspecific interactions of toxic amyloid oligomers with the plasma membrane cause neuronal cell death. Melatonin is a hormone produced by pineal gland to regulate sleep cycle and has been shown to be protective against Aß in cellular and animal studies, but the molecular mechanism is not well understood. Melatonin can partition into lipid membranes and has remarkable effects on their biophysical properties; this may be important in explaining its protective effects. In this study, we aimed to determine the effect of melatonin on the phase behaviour of model lipid membranes and its ability to inhibit amyloid interaction with lipid bilayers, using nuclear magnetic resonance (NMR) and localized surface plasmon resonance (LSPR), respectively. We used a tertiary mixture of DPPC, POPC, and cholesterol bilayers as a lipid model. Fully hydrated multilamellar lipid stacks were used in solid-state ²H-NMR experiments, showing that melatonin competes with cholesterol to associate with certain lipids and promotes the coexistence of liquid ordered and liquid disordered phases in a temperature-dependent manner. We studied membrane interactions with Aß (1-42) using LSPR and determined that the incorporation of melatonin into the lipid bilayer leads to a decrease in the nonspecific binding of Aß to the supported lipid bilayer. Combining the results from both techniques, we conclude that melatonin's protective effect against amyloid toxicity in lipid membranes is due to its ability to change the structural properties of the membrane and to reduce amyloid affinity to such membranes.

Effects of omega-O-acylceramide structures and concentrations in healthy and diseased skin barrier lipid membrane models

Ceramides (Cers) with ultralong (∼32-carbon) chains and ω-esterified linoleic acid, composing a subclass called omega-O-acylceramides (acylCers), are indispensable components of the skin barrier. Normal barriers typically contain acylCer concentrations of ∼10 mol%; diminished concentrations, along with altered or missing long periodicity lamellar phase (LPP), and increased permeability accompany an array of skin disorders, including atopic dermatitis, psoriasis, and ichthyoses. We developed model membranes to investigate the effects of the acylCer structure and concentration on skin lipid organization and permeability. The model membrane systems contained six to nine Cer subclasses as well as fatty acids, cholesterol, and cholesterol sulfate; acylCer content-namely, acylCers containing sphingosine (Cer EOS), dihydrosphingosine (Cer EOdS), and phytosphingosine (Cer EOP) ranged from zero to 30 mol%. Systems with normal physiologic concentrations of acylCer mixture mimicked the permeability and nanostructure of human skin lipids (with regard to LPP, chain order, and lateral packing). The models also showed that the sphingoid base in acylCer significantly affects the membrane architecture and permeability and that Cer EOP, notably, is a weaker barrier component than Cer EOS and Cer EOdS. Membranes with diminished or missing acylCers displayed some of the hallmarks of diseased skin lipid barriers (i.e., lack of LPP, less ordered lipids, less orthorhombic chain packing, and increased permeability). These results could inform the rational design of new and improved strategies for the barrier-targeted treatment of skin diseases.