Lipid Bilayer Structure Research Articles

A NARRATIVE REVIEW ON TRANSFERSOMES: VESICULAR TRANSDERMAL DELIVERY SYSTEM FOR ENHANCED DRUG PERMEATION

Transdermal administration of drug is generally limited by the barrier function of the skin vascular system are one of the most controversial method for transdermal delivery of active substance. transdermal drug delivery system is designed to deliver biological active agents through the skin, principally by diffusion for local internal if not systemic effects. The transdermal delivery system was relaunched after the discovery of elastic vesicles like transfersome, ethosome, cubosome, phytosome etc. Transfersomes are a form of elastic or deformable vesicle, which were introduced in the early 1990s. Elasticity is generated by incorporation of edge activator in lipid bilayer structure. Drug absorbed and distributed into organs and tissue and eliminated from the body it must pass through one or more biological membranes at various locations such movement of drug across the membrane is called as drug transport for the drug delivery to cross the body it should pass through the membrane barrier. This concept of drug delivery system was designed in attempt to concentrate the amount of drug in the remaining drug; therefore, the phospholipid-based carrier system is of considerable interest in the era.

Mimicking Thylakoid Membrane with Chlorophyll/TiO2/Lipid Co-Assembly for Light-Harvesting and Oxygen Releasing.

There is a growing interest in the design and construction of artificial photosythetic materials for solar energy utilization and conversion. Inspired by the structure of thylakoid membrane, we present here a hybrid construct for light-harvesting and oxygen releasing. Our design conjugates chlorophyll to TiO2 in a native-like membrane environment. The natural bilayer structure of lipids is utilized to localize the amphiphilic chlorophyll a and hydrophobic tetrabutyl titanate TBOT in the liposomal membrane during hydration process. The coassembled structure, which mimics the essential organization of the thylakoid membrane, is characterized using a combination of field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometer (EDS), Ramam spectra, pressure (π)-area (Α) isotherms, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) analysis. Our results demonstrate successful insertation of chlorophyll a in the membrane and confirm the in situ formation of TiO2 nanoshell confined at the lipid bilayer/water interface. We further show that the hybrid liposomes exhibit unambiguous photoactivity in visible light-harvesting and oxygen release, likely resulting from a larger specific surface area of the TiO2 shell, an efficient interfacial conjugation of the chlorophyll molecules with the thin TiO2 layer. The density functional theory (DFT) calculations were in accordance with the eletron injection processes.We expect that the present work will open a new insight into interfacial recombination between light-harvesting pigments and their sensitized photocatalysis, and develop a new kind of artificial photosynthetic materials with zero-cost of environmental degradation and high efficiency for the photocatalytic O2 production.

Membrane Protein Structures in Lipid Bilayers; Small-Angle Neutron Scattering With Contrast-Matched Bicontinuous Cubic Phases.

This perspective describes advances in determining membrane protein structures in lipid bilayers using small-angle neutron scattering (SANS). Differentially labeled detergents with a homogeneous scattering length density facilitate contrast matching of detergent micelles; this has previously been used successfully to obtain the structures of membrane proteins. However, detergent micelles do not mimic the lipid bilayer environment of the cell membrane in vivo. Deuterated vesicles can be used to obtain the radius of gyration of membrane proteins, but protein-protein interference effects within the vesicles severely limits this method such that the protein structure cannot be modeled. We show herein that different membrane protein conformations can be distinguished within the lipid bilayer of the bicontinuous cubic phase using contrast-matching. Time-resolved studies performed using SANS illustrate the complex phase behavior in lyotropic liquid crystalline systems and emphasize the importance of this development. We believe that studying membrane protein structures and phase behavior in contrast-matched lipid bilayers will advance both biological and pharmaceutical applications of membrane-associated proteins, biosensors and food science.

Presence of SARS-CoV-2 RNAs in Exosomes from COVID‐19 Patients: Their Characterization and Prognostic Potential

Aim: Exosomes are frequently used for characterization of diseases, e.g., viral infections, but have not been reported for COVID-19. The aims of our study were to determine exosomes’ novel applications for SARS-CoV-2 RNA infection and prognosis of COVID-19 disease.Methods: From 15 COVID-19 patients and five healthy controls, 32 serum samples were collected by clinicians in Wuhan, China. Exosomes were purified, their RNAs (exoRNAs) were isolated and analyzed using RT-PCR for the presence of the N and/or ORF1ab viral genes, and the human RNaseP gene as reference.Results: Exosomes showed their typical lipid bilayer structure between 30 to 150 nm in size. No viral RNAs were detected from the 5 healthy controls. From 4 patients (26.67% of the patients), only the viral N but not the ORF1ab genes was detected. However, intact viral particles were not observed in exosome samples from the four positive patients. Importantly, expression of the N gene was detected during the active or early-stages of the disease, and the expression levels gradually decreased from the critical to the mild patients (in reverse to their CT values): Patient 1 /critical/ progress/ (CT-value: 34.74), Patient 9/severe/progress (CT-value: 37.65), Patient 11/severe /progress (CT-value: 37.16), and Patient 15/mild/early stage (CT-value: 38.44). Among them, only patient 1 had received stem cell transfusion. Patients 9 and 11 demonstrated recurrence of SARS-CoV-2. Patient 15 was the earliest phase patient with the N gene.Conclusion: SARS-CoV-2 RNAs were detected in exosomes which came only from the 15 COVID-19 patients but not from the 5 healthy controls. In addition, the presence of the viral N gene showed association with severity in the disease. Our novel discovery indicates that SARS-CoV-2 RNAs in serum exosomes can be used to complement existing assays for characterization of the SARS-CoV-2 infection and for prognosis of the COVID-19 disease.Funding Statement: This study was funded by National Natural Science Foundation of China (Grant No. 81702273), the Key Project for Anti-2019 Novel Coronavirus Pneumonia from the National Key Research and Development Program of China (Grant No. 2020YFC0845500), the National Key Research and Development Program of China (Grant No. 2018YFE0204500), Science and technology key project of Guangdong Province: Study on the source and epidemiology of COVID-19 (No.2020B111107001), the Scientific research project of COVID-19 epidemic prevention and control in Guangdong universities (No.2020KZDZX1087), and the Zhongnan Hospital of Wuhan University Science, Technology and Innovation Seed Fund, Project znpy2018117 and znpy2019064.Declaration of Interests: We declare no competing interests.Ethics Approval Statement: The study was reviewed and approved by Medical Ethics Committee Zhongnan Hospital of Wuhan University in the Scientific Research project No 2020066.

Structure and Interaction of Lipid Bilayers in the Presence of ATP

Even in the absence of membrane receptors, adenosine triphosphate (ATP) has been shown to interact with lipid membranes and to affect their interactions. Measurements of zeta potentials by dynamic light scattering (DLS) show that ATP creates a positive zeta potential of phosphatidylcholine (PC) lipid vesicles. A similar effect is seen on phosphatidylserine (PS) bilayers in that the negative zeta potential of PS diminishes in magnitude in the presence of ATP. We further investigate the effect of ATP on lipid bilayers by 2H NMR spectroscopy which gives us an order parameter profile for the carbon-deuterium bonds along lipid acyl chains.

Olive Oil Restores Functionality of Intracellularly Retained Mutant CNG Channel

Membrane lipids regulate structure and function of transmembrane proteins through different mechanisms, which depend on the context of the cell type and the inherent characteristics of the protein. For instance, mechanisms that underlie lipid regulation of ion channels depend upon specific lipid-protein interactions required to maintain the proper orientation of channel domains relative to each other. Perturbations of the lipid bilayer structure and packing may have a significant impact on the channel structure and function.

A New Standard for Membrane Structure? Investigating Factors that Influence Measured Bilayer Thickness in Cryo-EM Images

Cryogenic electron microscopy (cryo-EM) is a promising tool for the analysis of lipid bilayer structure. We recently showed that cryo-EM can be used to measure the bilayer thickness of lipid vesicles and biological membranes with sub-angstrom precision (Heberle et al. 2020 PNAS 117:19943). Despite the great potential of cryo-EM for bilayer structural studies, factors that influence the primary data have not been systematically evaluated. Here, we investigate the influence of energy filtering, contrast transfer function corrections, and instrument defocus length on the primary image data. We report on how these parameters influence such measurements as distributions of membrane thickness, average radial intensity profiles across the bilayer, and spatial autocorrelation of the bilayer thickness. Experimental measurements were correlated with images calculated from two-dimensional projections of atomistic molecular simulations of lipid bilayers, convolved with a contrast transfer function to mimic primary cyro-EM data. This approach yields insights into the molecular origins of measurements quantified from images. We also explored the influence of membrane curvature on thickness using DOPC vesicles of varying diameter prepared via sonication or extrusion through pore sizes ranging from 30-200 nm in diameter. The smallest vesicles exhibited bilayer thinning consistent with curvature stress. The practical implications of instrument settings on the analysis of single and multicomponent lipid membranes and how membrane curvature differs depending on observed size are discussed. These efforts demonstrate how data collection can be systematically optimized to maximize the potential of cryo-EM for resolving variation in membrane thickness within biological membranes.

Coarse-Grained Force Fields from the Perspective of Statistical Mechanics: Better Understanding of the Origins of a MARTINI Hangover

The popular MARTINI coarse-grained model is used as a test case to analyze the adherence of top-down coarse-grained molecular dynamics models (i.e., models primarily parametrized to match experimental results) to the known features of statistical mechanics for the underlying all-atom representations. Specifically, the temperature dependence of various pair distribution functions, and hence their underlying potentials of mean force via the reversible work theorem, are compared between MARTINI 2.0, Dry MARTINI, and all-atom simulations mapped onto equivalent coarse-grained sites for certain lipid bilayers. It is found that the MARTINI models do not completely capture the lipid structure seen in atomistic simulations as projected onto the coarse-grained mappings and that issues of accuracy and temperature transferability arise due to an incorrect enthalpy–entropy decomposition of these potentials of mean force. The potential of mean force for the association of two amphipathic helices in a lipid bilayer is also calculated, and especially at shorter ranges, the MARTINI and all-atom projection results differ substantially. The former is much less repulsive and hence will lead to a higher probability of MARTINI helix association in the MARTINI bilayer than occurs in the actual all-atom case. Additionally, the bilayer height fluctuation spectra are calculated for the MARTINI model, and compared to the all-atom results, it is found that the magnitude of thermally averaged amplitudes at intermediate length scales are quite different, pointing to a number of possible consequences for realistic modeling of membrane processes. Taken as a whole, the results presented here show disagreement in the enthalpic and entropic driving forces driving lateral structure in lipid bilayers as well as quantitative differences in association of embedded amphipathic helices, which can help direct future efforts to parametrize CG models with better agreement to the all-atom systems they aspire to represent.

Statins as inhibitors of voltage-gated potassium channels Kv1.3 in cancer cells

Voltage-gated potassium channels are integral membrane proteins selectively permeable for potassium ions and activated upon change of membrane potential. Voltage-gated potassium channels of the Kv1.3 type were discovered both in plasma membrane and in inner mitochondrial membrane (mito Kv1.3 channels). For some time Kv1.3 channels located both in plasma membrane and in mitochondria are considered as a potentially new molecular target in several pathologies including some cancer disorders. Lipophilic nontoxic organic inhibitors of Kv1.3 channels may potentially find a clinical application to support therapy of some cancer diseases such as breast, pancreas and lung cancer, melanoma or chronic lymphocytic leukaemia (B-CLL). Inhibition of T lymphocyte Kv1.3 channels may be also important in treatment of chronic and acute respiratory diseases including severe pulmonary complication in corona virus disease Covid 19, however further studies are needed to confirm this supposition.Statins are small-molecule organic compounds, which are lipophilic and are widely used in treatment of hypercholesterolemia and atherosclerosis. Electrophysiological studies performed in our laboratory showed that statins: pravastatin, mevastatin and simvastatin are effective inhibitors of Kv1.3 channels in cancer cells of human T cell line Jurkat. We showed that application of the statins in the concentration range from 1.5 μM to 50 μM inhibited the channels in a concentration-dependent manner. The inhibitory effect was the most potent in case of simvastatin and the least potent in case of pravastatin. The inhibition was partially irreversible in case of simvastatin and fully reversible in case of pravastatin and mevastatin. It was accompanied by a significant acceleration of the current inactivation rate without any significant change of the activation rate. Mechanism of the inhibition is probably complex, including a direct interaction with the channel protein and perturbation of lipid bilayer structure, leading to stabilization of the inactivated state of the channels.

Structural and mechanical parameters of lipid bilayer membranes using a lattice refined self-consistent field theory

The self-consistent field theory of Scheutjens and Fleer is implemented on a grid with (lattice) sites that are smaller than the segment size. In this quasi lattice-free implementation we consider united atom-like molecular models and study bilayer self-assembly of phospholipids in a selective solvent (water). We find structural as well as mechanical parameters for these bilayers. The mean (κ) and Gaussian ([small kappa, Greek, macron]) bending moduli, as well as the spontaneous curvature of the monolayer (Jm0), are computed for the first time following a grand canonical ensemble route. Results are in line with previous estimates for mechanical parameters that at the time could not be made following this correct route. This proves that the mean bending modulus is only a very weak function of the membrane tension. We performed a systematic study on the effects of model parameter variations. The mean bending modulus generally grows with increasing bilayer thickness. As expected Jm0 and [small kappa, Greek, macron] behave oppositely with respect to each other and for classical phospholipids assumes values near zero. As an example, an increase in the lipophilic to hydrophilic ratio in the lipids, may cause the Gaussian bending rigidity to switch sign from negative to positive, while - not necessarily at the same point - the spontaneous curvature of the monolayer may switch sign from positive to negative. Together with other investigated trends, these results point to mechanisms of how topological phase transitions of the lipid bilayer membranes may be regulated in the biological context, which correlates with known lipid phase behaviour.

Mimicking the Mammalian Plasma Membrane: An Overview of Lipid Membrane Models for Biophysical Studies.

Cell membranes are very complex biological systems including a large variety of lipids and proteins. Therefore, they are difficult to extract and directly investigate with biophysical methods. For many decades, the characterization of simpler biomimetic lipid membranes, which contain only a few lipid species, provided important physico-chemical information on the most abundant lipid species in cell membranes. These studies described physical and chemical properties that are most likely similar to those of real cell membranes. Indeed, biomimetic lipid membranes can be easily prepared in the lab and are compatible with multiple biophysical techniques. Lipid phase transitions, the bilayer structure, the impact of cholesterol on the structure and dynamics of lipid bilayers, and the selective recognition of target lipids by proteins, peptides, and drugs are all examples of the detailed information about cell membranes obtained by the investigation of biomimetic lipid membranes. This review focuses specifically on the advances that were achieved during the last decade in the field of biomimetic lipid membranes mimicking the mammalian plasma membrane. In particular, we provide a description of the most common types of lipid membrane models used for biophysical characterization, i.e., lipid membranes in solution and on surfaces, as well as recent examples of their applications for the investigation of protein-lipid and drug-lipid interactions. Altogether, promising directions for future developments of biomimetic lipid membranes are the further implementation of natural lipid mixtures for the development of more biologically relevant lipid membranes, as well as the development of sample preparation protocols that enable the incorporation of membrane proteins in the biomimetic lipid membranes.

Site-specific peroxidation modulates lipid bilayer mechanics

Peroxidation of plasma membranes, characterized by oxidative attack of lipidic carbon–carbon double-bonds in unsaturated fatty acids, has been identified as an important biochemical event in multiple pathological conditions, including neurodegenerative diseases, atherosclerosis, diabetes, preeclampsia, aging, cancer, etc. Changes to the lipid bilayer structure as a result of lipid peroxidation may lead to lipid membrane malfunction, and consequently initiate further downstream biochemical cascades. However, how lipid peroxidation modulates the mechanical properties of lipid membranes remains largely controversial. In this study, we investigate the peroxidation of lipids with polyunsaturated fatty acid tails using molecular dynamics simulations. By systematically varying the oxidation site, we find that lipid peroxidation alters the biophysical properties of bilayer membrane in a peroxidation site-specific manner. Specifically, our results suggest that peroxidation at sites in the bilayer interior disturbs and softens the membrane, whereas peroxidation at sites near the membrane–water interface results in a more ordered and stiffer membrane. Such a peroxidation site-specific modulation of lipid membrane mechanics provides an explanation for the contradictory results obtained in previous experiments. Our study paves the way for an improved understanding of the initiation of the downstream cellular dysfunction caused by lipid peroxidation.

The exosomes role in pathogenesis of cardiovascular diseases

According to World Health Organization, annually cardiovascular diseases cause 17,5 billion deaths in the developed world. This is the reason why the study of molecular mechanisms of these pathologies has a huge importance for the development of new diagnostic and therapeutic strategies. One of the strategies on this matter is the research of the small extracellular vesicles or exosomes and its role in pathogenesis of cardiovascular diseases. Exploring their transporting and signaling functions in the development of acute coronary syndrome, stable angina, heart valve diseases, hypertrophic cardiomyopathy, vascular atherosclerosis has a great importance.Exosomes are spherical vesicles of 30–100 nm, expressed by almost all human cells. Their cytoplasmic membrane has lipid bilayer structure with tetraspanins CD9, CD63, CD81 and CD82 as the markers. Exosomes act as effectors transferring microRNA, mRNA, cytokines and growth factors between varies cells.The aim of this review is to analyze the literature data of exosomal role in the development of main cardiologic syndrome’s and evaluation of existed literature on exosomes potential as therapeutic target.

Encapsulation of Graphene in the Hydrophobic Core of a Lipid Bilayer.

Theoretical simulations have predicted that a lipid bilayer forms a stable superstructure when a sheet of graphene is inserted in its hydrophobic core. We experimentally produced for the first time a lipid–graphene–lipid assembly by combining the Langmuir–Blodgett and the Langmuir–Schaefer methods. Graphene is sandwiched and remains flat within the hydrophobic core of the lipid bilayer. Using infrared spectroscopy, ellipsometry, and neutron reflectometry, we characterized the superstructure at every fabrication step. The hybrid superstructure is mechanically stable and graphene does not disturb the natural lipid bilayer structure.

2D and 3D Control of Lipid Bilayer Membranes for Molecular Sensors

The lipid bilayer structure is the main component of cell membranes, therefore, the physical properties of such structure have been studied for many years. Recently, the applications of lipid bilayers have been studied, in addition to fundamental studies. For instance, a transistor-like device was developed (Ma et al., ACS Omega, 2019).As a part of such studies, we show the 2D and 3D control of lipid bilayer membranes. The first one is the effect of local anesthetics, Dibucaine hydrochloride molecules, on the phase behavior of ternary lipid membranes, which corresponds to the 2D control of lipid bilayer membranes (Yoshida et al., MedChemComm, 2015). The lipid membranes composed of a saturated phospholipid, unsaturated phospholipid, and cholesterol induce lateral phase separation. We revealed that the phase behavior is affected by the insertion of local anesthetic molecules into bilayer structures. Another one is the effect of toxic polar molecules, acetonitrile molecules, on the shape of lipid bilayer vesicles, which corresponds to the 3D control of lipid bilayer membranes (Yoshida et al., Colloids Interfaces, 2018). Insertion of acetonitrile molecules induces the membrane deformation.We are trying to utilize such behaviors for soft and bio-inspired molecular sensors. We show the trials for such applications.

DDRE-14. HEMP DERIVED EXTRACELLULAR VESICLES (EVS): A POTENTIAL ANTI-GLIOMA THERAPY

Abstract INTRODUCTION Extracellular vesicles (EVs) have been harvested from many plant sources, some of which have anti-cancer effects and some could be used as therapeutic nanodelivery vectors. Hemp plant is a natural source of cannabinoids, of which delta 9-tetrahydroxicannabinol (THC) and cannabidiol (CBD) have proven anti-cancer proprieties. HYPOTHESIS We hypothesized that hemp EVs are enriched in cannabinoids and their application will reduce glioblastoma (GBM) tumor progression. APPROACH EVs were isolated from the hemp plant using ultracentrifugation. Nanotracking analysis, electron microscopy and liquid chromatography tandem mass spectrometry (LC-MS/MS) were utilized to characterize EVs. GBM cell lines were cultured in the neuropshere assay to evaluate hemp EVs anti-glioma effects. Fluorescent-labelled EVs were used to evaluate their brain tissue distribution in orthotopic patient-derived GBM xenografts. RESULTS Hemp EVs have a median diameter of 112.6nm with a typical lipid-bilayer structure. LC-MS/MS have shown that while cannabidiolic, cannabigerolic, and tetrahydroxicannabinolic acids represent 69.1 ± 2.1%, 19.1 ± 1.6%, 6.5 ± 0.54% of the total cannabinoids in hemp EVs, CBD and THC only make 4.75 ± 0.26%, and 0.5 ± 0.3%. Hemp EVs are potent anti-glioma agents with a 7-day LD-50 of 1.04µM and 2.4µM [based on EVs total cannabinoid content] for KR-158 and L0 GBM lines, respectively. Compared to the vehicle, overnight incubation of L0 cells with 1µM hemp EVs significantly reduced GBM cell migration (630.3 ± 61.43 vs 143.7 ± 8.7). Intranasal administration of hemp EVs led to a widespread distribution in tumor bearing brain including GBM tumor core. CONCLUSION Based on these results, hemp EVs with enriched cannabinoid content exert antiglioma effect in-vitro and when delivered intranasally, are widely distributed throughout the brain and within the tumor of PDX animals. Further experiments are ongoing to address the impact of nasally-delivered hemp EVs on tumor progression and compare to the application of purified acidic cannabinoids.

Halogenation-Dependent Effects of the Chlorosulfolipids of Ochromonas danica on Lipid Bilayers.

The chlorosulfolipids are amphiphilic natural products with stereochemically complex patterns of chlorination and sulfation. Despite their role in toxic shellfish poisoning, potential pharmacological activities, and unknown biological roles, they remain understudied due to the difficulties in purifying them from natural sources. The structure of these molecules, with a charged sulfate group in the middle of the hydrophobic chain, appears incompatible with the conventional lipid bilayer structure. Questions about chlorosulfolipids remain unanswered partly due to the unavailability of structural analogues with which to conduct structure-function studies. We approach this problem by combining enantioselective total synthesis and membrane biophysics. Using a combination of Langmuir pressure-area isotherms of lipid monolayers, fluorescence imaging of vesicles, mass spectrometry imaging, natural product isolation, small-angle X-ray scattering, and cryogenic electron microscopy, we show that danicalipin A (1) likely inserts into lipid bilayers in the headgroup region and alters their structure and phase behavior. Specifically, danicalipin A (1) thins the bilayer and fluidizes it, allowing even saturated lipid to form fluid bilayers. Lipid monolayers show similar fluidizing upon insertion of danicalipin A (1). Furthermore, we show that the halogenation of the molecule is critical for its membrane activity, likely due to sterically controlled conformational changes. Synthetic unchlorinated and monochlorinated analogues do not thin and fluidize lipid bilayers to the same extent as the natural product. Overall, this study sheds light on how amphiphilic small molecules interact with lipid bilayers and the importance of stereochemistry and halogenation for this interaction.

Advanced spray dried proliposomes of amphotericin B lung surfactant-mimic phospholipid microparticles/nanoparticles as dry powder inhalers for targeted pulmonary drug delivery

The purpose of this study was to design, develop and characterize inhalable proliposomal microparticles/nanoparticles of Amphotericin B (AmB) with synthetic phospholipids, dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) which are lung surfactant-mimic phospholipids. Organic solutions of AmB and phospholipids, were co-spray dried using an advanced closed-mode system and a high performance cyclone. Scanning electron microscopy (SEM) was employed to visualize the surface structure, morphology, and particles size. The residual water content of the proliposomes was quantified by Karl Fisher coulometric titration (KFT). Degree of crystallinity/non-crystallinity was measured by X-ray powder diffraction (XRPD). Phase behavior was measured by differential scanning calorimetry. The chemical composition by molecular fingerprinting was established using attenuated total reflectance (ATR)-Fourier-transform infrared (FTIR) spectroscopy. The amount of AmB loaded into the proliposomes was quantified using UV-VIS spectroscopy. The in vitro aerosol dispersion performance was conducted using the Next Generation Impactor (NGI) and the human dry powder inhaler (DPI) (Handihaler®) that is FDA-approved. Different human lung cell lines were employed to demonstrate in vitro safety as a function of dose and formulation. Smooth, spherical microparticles/nanoparticles were formed at medium and high spray drying pump rates and had low residual water content. A characteristic peak in the XRPD diffraction pattern as well as an endotherm in DSC confirmed the presence of the lipid bilayer structure characteristic in the DPPC/DPPG proliposomal systems. Superior in vitro aerosol performance was achieved with engineered microparticles/nanoparticles demonstrating suitability for targeted pulmonary drug delivery as inhalable dry powders. The in vitro cellular studies demonstrated that the formulated proliposomes are safe. These AmB proliposomes can be a better option for targeted treatment of severe pulmonary fungal infections.

Time-Dependent Lipid Dynamics, Organization and Peptide-Lipid Interaction in Phospholipid Bilayers with Incorporated β-Amyloid Oligomers.

Nonfibrillar β-amyloid (Aβ) oligomers are considered as major neurotoxic species in the pathology of Alzheimer's disease. The presence of Aβ oligomers was shown to cause membrane disruptions in a broad range of model systems. However, the molecular basis of such a disruption process remains unknown. We previously demonstrated that membrane-incorporated 40-residue Aβ (Aβ40) oligomers could form coaggregates with phospholipids. This process occurred more rapidly than the fibrillization of Aβ40 and led to more severe membrane disruption. The present study probes the time-dependent changes in lipid dynamics, bilayer structures, and peptide-lipid interactions along the time course of the oligomer-induced membrane disruption, using solid-state NMR spectroscopy. Our results suggest the presence of certain intermediate states with phospholipid molecules entering the C-terminal hydrogen-bonding networks of the Aβ40 oligomeric cores. This work provides insights on the molecular mechanisms of Aβ40-oligomer-induced membrane disruption.

Confinement in Nanodiscs Anisotropically Modifies Lipid Bilayer Elastic Properties.

Lipid nanodiscs are small synthetic lipid bilayer structures that are stabilized in solution by special circumscribing (or scaffolding) proteins or polymers. Because they create native-like environments for transmembrane proteins, lipid nanodiscs have become a powerful tool for structural determination of this class of systems when combined with cryo-electron microscopy or nuclear magnetic resonance. The elastic properties of lipid bilayers determine how the lipid environment responds to membrane protein perturbations, and how the lipid in turn modifies the conformational state of the embedded protein. However, despite the abundant use of nanodiscs in determining membrane protein structure, the elastic material properties of even pure lipid nanodiscs (i.e., without embedded proteins) have not yet been quantitatively investigated. A major hurdle is due to the inherently nonlocal treatment of the elastic properties of lipid systems implemented by most existing methods, both experimental and computational. In addition, these methods are best suited for very large “infinite” size lipidic assemblies, or ones that contain periodicity, in the case of simulations. We have previously described a computational analysis of molecular dynamics simulations designed to overcome these limitations, so it allows quantification of the bending rigidity (KC) and tilt modulus (κt) on a local scale even for finite, nonperiodic systems, such as lipid nanodiscs. Here we use this computational approach to extract values of KC and κt for a set of lipid nanodisc systems that vary in size and lipid composition. We find that the material properties of lipid nanodiscs are different from those of infinite bilayers of corresponding lipid composition, highlighting the effect of nanodisc confinement. Nanodiscs tend to show higher stiffness than their corresponding macroscopic bilayers, and moreover, their material properties vary spatially within them. For small-size MSP1 nanodiscs, the stiffness decreases radially, from a value that is larger in their center than the moduli of the corresponding bilayers by a factor of ∼2–3. The larger nanodiscs (MSP1E3D1 and MSP2N2) show milder spatial changes of moduli that are composition dependent and can be maximal in the center or at some distance from it. These trends in moduli correlate with spatially varying structural properties, including the area per lipid and the nanodisc thickness. Finally, as has previously been reported, nanodiscs tend to show deformations from perfectly flat circular geometries to varying degrees, depending on size and lipid composition. The modulations of lipid elastic properties that we find should be carefully considered when making structural and functional inferences concerning embedded proteins.