Dimyristoylphosphatidylcholine Research Articles

Pressure‐dependent adhesion between solid‐supported PC‐lipid bilayers and vesicles under electric fields

AbstractFusion of lipid bilayers in membranes is important in processes from vesicle‐cell interactions (as in drug delivery) to exosome‐cell signaling, while transient transmembrane electric fields are known to occur spontaneously. Two contacting phosphatidylcholine (PC) lipid membranes are known to fuse into one under external electric fields, suggesting that the interaction between them is modified by the field as they approach, prior to the fusion event. Here we measure directly the adhesion energy between dimyristoylphosphatidylcholine (DMPC) and between distearoylphosphatidylcholine (DSPC) surface layers attached to solid substrates both without and with a transmembrane electric field. We find a marked pressure‐dependent adhesion behavior in the electric field, which we attribute to fusion intermediates that are formed, shedding new light on membrane electro‐fusion.

Molecular Dynamics Investigation of Lipid-Specific Interactions with a Fusion Peptide.

The HIV-1 fusion peptide, which is a short hydrophobic peptide from the gp41 coat glycoprotein that participates in the infection of a cell, interacts with model lipid bilayer membranes in a concentration-dependent manner. The interaction of the peptide with the bilayer also strongly depends on the lipid composition. Here, molecular dynamics simulations were performed to investigate lipid-specific interactions that arise shortly after the binding of a less-fusogenic variant of the HIV-1 fusion peptide to a lipid bilayer composed of a mixture of dimyristoyl phosphatidylcholine and dimyristoyl phosphatidylglycerol. The impact of peptide concentration was also studied. An improved understanding was gained of the lipid-specific interactions experienced by the FP. New insight was also gained into how the peptide concentration changes these interactions.

Phonon modes controlled by primary chemical structure of partially fluorinated dimyristoylphosphatidylcholine (DMPC) revealed by multiple-angle incidence resolution spectrometry (MAIRS).

Partially fluorinated dimyristoylphosphatidylcholines (DMPCs) involving double alkyl chains are employed to control the phonon generation in thin films, which is examined by infrared (IR) spectroscopy coupled with multiple-angle incidence resolution spectrometry (MAIRS). technique. Compounds having perfluoroalkyl (Rf) chains are known to exhibit phonon bands in IR spectra because of the strong dipole-dipole interactions. Since the phonon bands of an organic matter have a similar shape to the normal absorption bands, however, recognition of the phonon modes is difficult and confusing for IR spectroscopists. Here, we show that MAIRS works out for finding phonon modes in monolayers: the Berreman shift is readily captured by the MAIRS in-plane and out-of-plane (OP) spectra. By measuring the longitudinal-optic (LO) energy-loss function spectrum of a bulk sample, the degree of molecular aggregation in the monolayer is also revealed by comparing the OP spectrum of the monolayer to the LO one. In addition, partially fluorinated DMPC compounds having both hydrocarbon and Rf chains are prepared, and they are used to obstruct the self-aggregation of the Rf groups in the film. As a result, the phonon characteristics are mostly lost in the MAIRS spectra as expected.

Antimicrobial activity of prophage endolysins against critical Enterobacteriaceae antibiotic-resistant bacteria

Enterobacteriaceae species are part of the 2017 World Health Organization antibiotic-resistant priority pathogens list for development of novel medicines. Multidrug-resistant Klebsiella pneumoniae is an increasing threat to public health and has become a relevant human pathogen involved in life-threatening infections. Phage therapy involves the use of phages or their lytic endolysins as bioagents for the treatment of bacterial infectious diseases. Gram-negative bacteria have an outer membrane, making difficult the access of endolysins to the peptidoglycan. Here, three endolysins from prophages infecting three distinct Enterobacterales species, Kp2948-Lys from K. pneumoniae, Ps3418-Lys from Providencia stuartii, and Kaer26608-Lys from Klebsiella aerogenes, were purified and exhibited antibacterial activity against their specific bacterium species verified by zymogram assays. These three endolysins were successfully associated to liposomes composed of dimyristoyl phosphatidyl choline (DMPC), dioleoyl phosphatidyl ethanolamine (DOPE) and cholesteryl hemisuccinate (CHEMS) at a molar ratio (4:4:2), with an encapsulation efficiency ranging from 24 to 27%. Endolysins encapsulated in liposomes resulted in higher antibacterial activity compared to the respective endolysin in the free form, suggesting that the liposome-mediated delivery system enhances fusion with outer membrane and delivery of endolysins to the target peptidoglycan. Obtained results suggest that Kp2948-Lys appears to be specific for K. pneumoniae, while Ps3418-Lys and Kaer26608-Lys appear to have a broader antibacterial spectrum. Endolysins incorporated in liposomes constitute a promising weapon, applicable in the several dimensions (human, animals and environment) of the One Health approach, against multidrug-resistant Enterobacteriaceae.

Modified styrene-maleic anhydride copolymer-based chromatographic stationary phase for phospholipid separation and analysis

Phospholipids are important signaling molecules, and their metabolism is closely related to various diseases, such as neurodegenerative diseases and cancers. Phospholipids are typically characterized with extreme complexity and structural diversity. For example, phospholipids present in many different forms, such as sn position isomers, double-bond position isomers, double-bond stereochemical isomers, and enantiomers. Therefore, further research on novel separation and analytical techniques for phospholipids is of great importance. As an amphiphilic alternating copolymer, styrene-maleic anhydride copolymer (SMA) can be inserted into the phospholipid bilayer of biofilms to form lipid nanodisks with membrane proteins as the centers, thereby solubilizing membrane proteins and phospholipids. Thus, the introduction of SMA into a chromatographic stationary phase can potentially improve the separation and analysis of phospholipids. In this paper, SMA was successfully grafted onto the surface of silica gel via the "click" reaction and free radical polymerization. After further ring-opening modification of SMA with methyl methionine hydrochloride (MME·HCl), a novel SMA-modified stationary phase material (Sil-SMA-MME) was fabricated. The Sil-SMA-MME stationary phase was characterized using thermogravimetric analysis and Fourier transform infrared spectroscopy (FT-IR), and the results indicated the successful fabrication of the target material. The retention mechanism of the packed Sil-SMA-MME chromatographic column was investigated using hydrophilic nucleosides and nucleic acid bases via high performance liquid chromatography (HPLC) and UV detection. According to the retention characteristics of the nucleosides and nucleic acid bases in different mobile phases, the Sil-SMA-MME chromatographic column exhibited a typical hydrophilic-interaction-based retention mechanism, similar to that of a commercially available amino (SiO2-NH2) column. The separation performance of the Sil-SMA-MME column was evaluated using three types of small-molecule substances, including amides, nucleoside/nucleic acid bases, and phenols. Cyanoacetamide, 2-iodoacetamide, benzamide, p-aminobenzamide, and nicotinamide were used to evaluate the chromatographic performance of the developed Sil-SMA-MME column. When acetonitrile-H2O (96∶4, v/v) was used as the mobile phase, the five compounds exhibited good peak shapes and could be baseline-separated within 8 min. The highest column efficiency achieved was 90900 N/m. By contrast, under the same chromatographic conditions, the test substances were not separated effectively on the SiO2-NH2 column. Regardless of the mobile phase ratio, the peaks of benzamide and 2-iodoacetamide overlapped. These results demonstrate that the developed Sil-SMA-MME column has good separation selectivity. The separation performance of the Sil-SMA-MME column for phospholipid samples was also investigated by HPLC and evaporative light scattering detection (ELSD) to explore its feasibility for phospholipid separation and analysis. Different phospholipid standards were used to evaluate the separation performance of the column. Under certain mobile phase conditions, baseline separation could be achieved for dipalmityl phosphatidyl serine sodium (DPPS), diolyl phosphatidyl choline (DOPC), and dipalmityl phosphatidyl ethanolamine (DPPE), as well as four phosphatidyl choline (PC) standards, namely, lysophosphatidylcholine (LysoPC), dimyristoyl phosphatidyl choline (DMPC), distearyl phosphatidyl choline (DSPC), and dipalmitoyl phosphatidyl choline (DPPC). The separation potential of the developed Sil-SMA-MME column was further evaluated by separating and analyzing phospholipid extracts from Antarctic krill oil and human serum. The results showed that the developed Sil-SMA-MME column has good potential for phospholipid separation and analysis.

Molecular dynamics simulations of an antifreeze protein at the lipid / water interface

The ability of antifreeze proteins (AFP's) and glycoproteins (AFGP's) to prevent damage to certain organisms under cold stress is well established. These molecules have also been shown to prevent chilling damage in some biological membranes and interaction between membranes and AF(G)P's has been observed during chilling events; however, the exact mechanism of membrane stabilization is still not well understood. Molecular modelling is an ideal technique for probing atomistic information in these systems although modelling studies to date have focused on peptide structure and the site and mode, e.g., insertion, of the peptide-membrane interaction. To provide insight into how AF(G)P's may act to stabilize (or destabilize) membranes during phase transitions, we have conducted molecular dynamics (MD) simulations of a solvated dimyristoylphosphatidylcholine (DMPC) lipid bilayer containing an AFP Type I at the lipid/water interface at several temperatures. We present the analysis of several properties of the phospholipid bilayer that are relevant when considering phase transitions. Possible areas for concentrating future research efforts have been highlighted; namely the acyl chain order and the polar headgroups, both of which have been implicated in experimental studies of the stabilization of model membranes by AF(G)P's.

Dual mechanical impact of β-escin on model lipid membranes

Understanding the mechanical behavior of biological membranes is of paramount importance in cell biophysics and in developing new biomaterials for medicine. In this study, we delve into the mechanical impact of β-escin, commonly referred to as escin, a naturally occurring biosurfactant derived from the seeds of the horse chestnut tree. To examine the modulable interaction between escin and dimyristoylphosphatidylcholine (DMPC), which is an archetypical fluid phospholipid and an essential constituent of the cellular fluid membrane, we have used artificial models based on the liquid crystal structure, such as bilayer vesicles and Langmuir monolayers. We have focused on the energetic and kinetic aspects of escin insertion when transversally adsorbed or longitudinally integrated within these model membranes. By employing surface microscopies of epifluorescence and Brewster angle reflectivity, we have elucidated the structural phase behavior of hybrid escin–phospholipid membranes, which exhibit dual mechanical properties characterized by high rigidity and reduced fluidity. Notably, at low temperatures, we observe a soft, glassy rheological behavior reminiscent of liquid crystalline ordered phases, which turns into a fluid-like viscoelasticity resembling more disordered phases at physiological temperatures. The hybrid membranes behave in one way or another as both are driven by an adsorption potential well imposed by escin cohesivity. These intriguing findings are discussed from a physicochemical perspective, highlighting their potential for future pharmacological designs and biomedical applications that exploit the dual mechanical impact of escin on biological membranes.

Amyloid-β Tetramers and Divalent Cations at the Membrane/Water Interface: Simple Models Support a Functional Role.

Charge polarization at the membrane interface is a fundamental process in biology. Despite the lower concentration compared to the abundant monovalent ions, the relative abundance of divalent cations (Ca2+, Mg2+, Zn2+, Fe2+, Cu2+) in particular spaces, such as the neuron synapse, raised many questions on the possible effects of free multivalent ions and of the required protection of membranes by the eventual defects caused by the free forms of the cations. In this work, we first applied a recent realistic model of divalent cations to a well-investigated model of a polar lipid bilayer, di-myristoyl phosphatidyl choline (DMPC). The full atomistic model allows a fairly good description of changes in the hydration of charged and polar groups upon the association of cations to lipid atoms. The lipid-bound configurations were analyzed in detail. In parallel, amyloid-β 1-42 (Aβ42) peptides assembled into tetramers were modeled at the surface of the same bilayer. Two of the protein tetramers' models were loaded with four Cu2+ ions, the latter bound as in DMPC-free Aβ42 oligomers. The two Cu-bound models differ in the binding topology: one with each Cu ion binding each of the monomers in the tetramer; one with pairs of Cu ions linking two monomers into dimers, forming tetramers as dimers of dimers. The models here described provide hints on the possible role of Cu ions in synaptic plasticity and of Aβ42 oligomers in storing the same ions away from lipids. The release of structurally disordered peptides in the synapse can be a mechanism to recover ion homeostasis and lipid membranes from changes in the divalent cation concentration.

Effects of curcumin in the interaction with cardiolipin-containg lipid monolayers and bilayers

Curcumin, a plant polyphenol extracted from the Chinese herb turmeric, has gained widespread attention in recent years because of its multifunctional properties as antioxidant, antinflammatory, antimicrobial, and anticancer agent. Effects of the molecule on mitochondrial membranes properties have also been evidenced. In this work, the interaction of curcumin with models of mitochondrial membranes composed of dimyristoylphosphatidylcholine (DMPC) or mixtures of DMPC and 4 mol% tetramyristoylcardiolipin (TMCL) has been investigated by using biophysical techniques. Spectrophotometry and fluorescence allowed to determine the association constant and the binding energy of curcumin with pure DMPC and mixed DMPC/TMCL aqueous bilayers. The molecular organization of pure DMPC and cardiolipin-containing Langmuir monolayers at the air-water interface were investigated and the morphology of the monolayers transferred into mica substrates were characterized through atomic force microscopy (AFM). It is found that curcumin associates at the polar/apolar interface of the lipid bilayers and the binding is favored in the presence of cardiolipin. At 2 mol%, curcumin is well miscible with lipid monolayers, particularly with mixed DMPC/TMCL ones, where compact terraces formation characterized by a reduction of the surface roughness is observed in the AFM topographic images. At 10 mol%, curcumin perturbs the stability of DMPC monolayers and morphologically are evident terraces surrounded by cur aggregates. In the presence of TMCL, very few curcumin aggregates and larger compact terraces are observed. The overall results indicate that cardiolipin augments the incorporation of curcumin in model membranes highlighting the mutual interplay cardiolipin-curcumin in mitochondrial membranes.

Systemic Protein Delivery via Inhalable Liposomes: Formulation and Pharmacokinetics.

The enormous and thin alveolar epithelium is an attractive site for systemic protein delivery. Considering the excellent biocompatibility of phospholipids with endogenous pulmonary surfactant, we engineered dimyristoylphosphatidylcholine (DMPC)-based liposomes for pulmonary administration, using Cy5.5-labeled bovine serum albumin (BSA-Cy5.5) as a model protein payload. The level of cholesterol (Chol) and surface modification with PEG in inhalable liposomes were optimized iteratively based on the encapsulation efficiency, the release kinetics in the simulated lung fluid, and the uptake in murine RAW 264.7 macrophages. The plasma pharmacokinetics of BSA-Cy5.5-encapsulated liposomes with the composition of DMPC/Chol/PEG at 85:10:5 (molar ratio) was studied in mice following intratracheal aerosolization, in comparison with that of free BSA-Cy5.5 solution. The biodisposition of BSA-Cy5.5 was continuously monitored using whole-body near-infrared (NIR) fluorescence imaging for 10 days. We found that the systemic bioavailability of BSA-Cy5.5 from inhaled liposomes was 22%, which was notably higher than that of inhaled free BSA-Cy5.5. The mean residence time of BSA-Cy5.5 was markedly prolonged in mice administered intratracheally with liposomal BSA-Cy5.5, which is in agreement with the NIR imaging results. Our work demonstrates the great promise of inhalable DMPC-based liposomes to achieve non-invasive systemic protein delivery.

A rhein-huprine hybrid protects erythrocyte membrane integrity against Alzheimer’s disease related Aβ(1-42) peptide

Alzheimer's disease remains largely unknown, and currently there is no complete cure for the disease. New synthetic approaches have been developed to create multi-target agents, such as RHE-HUP, a rhein-huprine hybrid which can modulate several biological targets that are relevant to the development of the disease. While RHE-HUP has shown in vitro and in vivo beneficial effects, the molecular mechanisms by which it exerts its protective effect on cell membranes have not been fully clarified. To better understand RHE-HUP interactions with cell membranes, we used synthetic membrane models and natural models of human membranes. For this purpose, human erythrocytes and molecular model of its membrane built-up of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE) were used. The latter correspond to classes of phospholipids present in the outer and inner monolayers of the human erythrocyte membrane, respectively. X-ray diffraction and differential scanning calorimetry (DSC) results indicated that RHE-HUP was able to interact mainly with DMPC. In addition, scanning electron microscopy (SEM) analysis showed that RHE-HUP modified the normal biconcave shape of erythrocytes inducing the formation of echinocytes. Moreover, the protective effect of RHE-HUP against the disruptive effect of Aβ(1–42) on the studied membrane models was tested. X-ray diffraction experiments showed that RHE-HUP induced a recovery in the ordering of DMPC multilayers after the disruptive effect of Aβ(1–42), confirming the protective role of the hybrid.

Time-domain proton-detected local-field NMR for molecular structure determination in complex lipid membranes.

Proton-detected local-field (PDLF) NMR spectroscopy, using magic-angle spinning and dipolar recoupling, is presently the most powerful experimental technique for obtaining atomistic structural information from small molecules undergoing anisotropic motion. Common examples include peptides, drugs, or lipids in model membranes and molecules that form liquid crystals. The measurements on complex systems are however compromised by the larger number of transients required. Retaining sufficient spectral quality in the direct dimension requires that the indirect time-domain modulation becomes too short for yielding dipolar splittings in the frequency domain. In such cases, the dipolar couplings can be obtained by fitting the experimental data; however ideal models often fail to fit PDLF data properly due to effects of radiofrequency field (RF) spatial inhomogeneity. Here, we demonstrate that by accounting for RF spatial inhomogeneity in the modeling of R-symmetry-based PDLF NMR experiments, the fitting accuracy is improved, facilitating the analysis of the experimental data. In comparison to the analysis of dipolar splittings without any fitting procedure, the accurate modeling of PDLF measurements makes possible three important improvements: the use of shorter experiments that enable the investigation of samples with a higher level of complexity, the measurement of C-H bond order parameters with smaller magnitudes and of smaller variations of caused by perturbations of the system, and the determination of values with small differences from distinct sites having the same chemical shift. The increase in fitting accuracy is demonstrated by comparison with H NMR quadrupolar echo experiments on mixtures of deuterated and non-deuterated dimyristoylphosphatidylcholine (DMPC) and with 1-palmitoyl-2-oleoyl--glycero-3-phosphoethanolamine (POPE) membranes. Accurate modeling of PDLF NMR experiments is highly useful for investigating complex membrane systems. This is exemplified by application of the proposed fitting procedure for the characterization of membranes composed of a brain lipid extract with many distinct lipid types.

A cochleate formulation optimized by D-optimal mixture design enhances oral bioavailability of Revaprazan

A cochleate formulation was developed to enhance the oral bioavailability of revaprazan (RVP). Dimyristoyl phosphatidylcholine (DMPC) liposome containing dicetyl phosphate (DCP) successfully formed a cochleate after treatment with CaCl2, whereas that containing sodium deoxycholate did not. Cochleate was optimised using a D-optimal mixture design with three independent variables—DMPC (X1, 70.58 mol%), cholesterol (X2, 22.54 mol%), and DCP (X3, 6.88 mol%)—and three response variables: encapsulation efficiency (Y1, 76.92%), released amount of free fatty acid at 2 h (Y2, 39.82%), and released amount of RVP at 6 h (Y3, 73.72%). The desirability function was 0.616, showing an excellent agreement between the predicted and experimental values. The cylindrical morphology of the optimised cochleate was visualised, and laurdan spectroscopy confirmed the dehydrated membrane interface, showing an increased generalised polarisation value (approximately 0.5) over small unilamellar vesicle of RVP (RVP-SUV; approximately 0.1). The optimised cochleate showed greater resistance to pancreatic enzyme than RVP-SUV. RVP was released in a controlled manner, achieving approximately 94% release in 12 h. Following oral administration in rats, the optimised cochleate improved the relative bioavailability of RVP by approximately 274%, 255%, and 172% compared to RVP suspension, a physical mixture of RVP and the cochleate, and RVP-SUV, respectively. Thus, the optimised cochleate formulation might be a good candidate for the practical development of RVP.

Dynamic membrane interaction and amyloid fibril formation of glucagon, melittin and human calcitonin

Glucagon is a 29-amino acid peptide hormone secreted by pancreatic α-cells and interacts with specific receptors located in various organs. Glucagon tends to form gel-like fibril aggregates that are cytotoxic. It is important to reveal the glucagon-membrane interaction to understand activity and cytotoxicity of glucagon and glucagon oligomers. In this review, first glucagon-membrane interactions are described as morphological changes in dimyristoylphosphatidylcholine (DMPC) bilayers containing glucagon in acidic and neutral conditions as compared to the case of melittin. Second, fibril formation by glucagon in acidic solution is discussed in light of morphological and structural changes. Third, kinetic analysis of glucagon fibril formation was performed using a two-step autocatalytic reaction mechanism, as investigated in the case of human calcitonin. The first step is a nuclear formation, and the second step is an autocatalytic fibril elongation. Forth, fibril formation of glucagon inside glucagon-DMPC bilayers in neutral solution under near physiological condition is described.

Cholesterol and Melatonin Exert Opposite Effects on the Interaction of Model DMPC Membranes with the SARS‐CoV‐2 S‐Protein: A SANS Study

AbstractAn effect of receptor‐binding domain (RBD) of SARS‐CoV‐2 S‐protein on structural parameters of model lipid membranes presented by dimyristoylphosphatidylcholine (DMPC) systems with cholesterol and melatonin impurities is studied by small angle neutron scattering (SANS). It is shown that an increase in melatonin concentration in the lipid membrane leads to a decrease in the thickness of the lipid bilayer, while an increase in the concentration of cholesterol leads to an increase in its thickness. It is suggested that increasing the concentration of melatonin in a membrane prevents the interaction of coronaviral S‐protein with a lipid membrane of a cell. In the presence of cholesterol in the system, the interaction of a lipid membrane with an active part of S‐protein occurs depending on a phase state of the lipid: in the case of a gel phase, there is no changes in structural parameters, but at higher temperatures in the case of a liquid crystal phase, an addition of RBD SARS‐CoV‐2 to the system causes a reduce in the membrane thickness.

A Biophysical Research on the Determination of Morphological and Structural Properties of Coumarin-Loaded Liposomes

The major goal of this research was to examine how coumarin affects lipid model membranes. For this reason, liposome membranes were formed using dimyristoyl phosphatidylcholine (DMPC) as zwitterionic lipid. The influence of coumarin on the morphology, packing order, fluidity, and hydration state of lipid membranes was specifically investigated by means of microscopic (field emission scanning electron microscopy (FE-SEM)) and spectroscopic (attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy) techniques. Taken into account the results obtained with FE-SEM images and analysis, liposomes without and with coumarin have uniform structures and spherical shapes in appearance. However, coumarin-loaded liposomes are observed with an increase in size when compared to a mean diameter of unloaded-liposomes. Considering ATR-FTIR analysis, the investigation of the vibrational bands which belong to the hydrophobic and hydrophilic parts of DMPC lipid reveals that coumarin alters the physical features of the DMPC liposomes by decreasing the order and increasing the fluidity of the system and making hydrogen bonding with the interfacial and headgroup regions of zwitterionic lipid DMPC. Finally, performing more biophysical studies on the interactions of biologically active compounds with model membranes plays an important role in determining the molecular action mechanisms of these compounds in drug discovery and formulations.

Lipid packing is disrupted in copolymeric nanodiscs compared with intact membranes

Discoidal lipid-protein nanoparticles known as nanodiscs are widely used tools in structural and membrane biology. Amphipathic, synthetic copolymers have recently become an attractive alternative to membrane scaffold proteins for the formation of nanodiscs. Such copolymers can directly intercalate into, and form nanodiscs from, intact membranes without detergents. Although these copolymer nanodiscs can extract native membrane lipids, it remains unclear whether native membrane properties are also retained. To determine the extent to which bilayer lipid packing is retained in nanodiscs, we measured the behavior of packing-sensitive fluorescent dyes in various nanodisc preparations compared with intact lipid bilayers. We analyzed styrene-maleic acid (SMA), diisobutylene-maleic acid (DIBMA), and polymethacrylate (PMA) as nanodisc scaffolds at various copolymer-to-lipid ratios and temperatures. Measurements of Laurdan spectral shifts revealed that dimyristoyl-phosphatidylcholine (DMPC) nanodiscs had increased lipid headgroup packing compared with large unilamellar vesicles (LUVs) above the lipid melting temperature for all three copolymers. Similar effects were observed for DMPC nanodiscs stabilized by membrane scaffolding protein MSP1E1. Increased lipid headgroup packing was also observed when comparing nanodiscs with intact membranes composed of binary mixtures of 1-palmitoyl-2-oleoyl-phosphocholine (POPC) and di-palmitoyl-phosphocholine (DPPC), which show fluid-gel-phase coexistence. Similarly, Laurdan reported increased headgroup packing in nanodiscs for biomimetic mixtures containing cholesterol, most notable for relatively disordered membranes. The magnitudes of these ordering effects were not identical for the various copolymers, with SMA being the most and DIBMA being the least perturbing. Finally, nanodiscs derived from mammalian cell membranes showed similarly increased lipid headgroup packing. We conclude that nanodiscs generally do not completely retain the physical properties of intact membranes.

Interaction of N-acyltaurines with phosphatidylcholines

N-acyltaurines (NATs) are biologically active amphiphilic lipids. They come under the group of compounds known as N-acyl amino acids. NATs were first detected in the brain and other tissues in mice lacking the enzyme fatty acid amide hydrolase FAAH (−/−). N-arachidonoyltaurine (20:4 NAT) acts as an excellent ligand for the subset of transient receptor potential (TRP) channels, especially vanilloid type channels TRPV1 and TRPV4. Also, hydrophobic and hydrophilic regions of NATs enable them to interact with membrane lipids. Here, we have investigated the interaction of NATs, N-myristoyltaurine (NMT), and N-palmitoyltaurine (NPT) with their corresponding diacyl phosphatidylcholines (PCs), dimyristoylphosphatidylcholine (DMPC), and dipalmitoylphosphatidylchoine (DPPC). The miscibility and phase behavior of the hydrated binary mixtures have been investigated by differential scanning calorimetry (DSC). Studies on the interaction of NMT/NPT with DMPC/DPPC revealed that the two amphiphiles mix well up to 50 mol% of NAT and phase separation is observed at higher contents of the NAT. The phase transition of the equimolar mixtures of NAT:PC (50:50) studied by fluorescence, also supported the DSC results. PXRD and FTIR analysis show that the NAT:PC equimolar mixture (50:50) forms different supramolecular structures when compared to that of individual NATs and PCs. From transmission electron microscopic studies it is observed that the equimolar mixtures of NMT and NPT with their corresponding diacylphosphatidylcholines (50:50, mol/mol) forms unilamellar vesicles whose diameter range between 30 and 50 nm.

A Thermodynamic Study on the Interaction between RH-23 Peptide and DMPC-Based Biomembrane Models.

Investigation of the interaction between drugs and biomembrane models, as a strategy to study and eventually improve drug/substrate interactions, is a crucial factor in preliminary screening. Synthesized peptides represent a source of potential anticancer and theragnostic drugs. In this study, we investigated the interaction of a novel synthesized peptide, called RH-23, with a simplified dimyristoylphosphatidylcholine (DMPC) model of the cellular membrane. The interaction of RH-23 with DMPC, organized either in multilamellar vesicles (MLVs) and in Langmuir-Blodgett (LB) monolayers, was assessed using thermodynamic techniques, namely differential scanning calorimetry (DSC) and LB. The calorimetric evaluations showed that RH-23 inserted into MLVs, causing a stabilization of the phospholipid gel phase that increased with the molar fraction of RH-23. Interplay with LB monolayers revealed that RH-23 interacted with DMPC molecules. This work represents the first experimental thermodynamic study on the interaction between RH-23 and a simplified model of the lipid membrane, thus providing a basis for further evaluations of the effect of RH-23 on biological membranes and its therapeutic/diagnostic potential.

Ophthalmic liposomal formulations using synthetic phospholipids for the treatment of dry eye disease

AbstractPurpose: Liposomes composed of soy phosphatidylcholine (PC) have been widely used in artificial tears for the treatment of dry eye disease (DED) due to their ability to supplement the lipid layer of the ocular surface. The disadvantage of PC extracted from natural sources is the difficulty of standardizing its fatty acid composition. Therefore, the use of synthetic phospholipids such as 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) and Dimyristoylphosphatidylcholine (DMPC) allows better characterization and standardization than those from natural sources, being of interest in the preparation of ophthalmic liposomal formulations for DED.Methods: Liposomal formulations comprised of DOPC (F1) and DOPC combined with DMPC (F2) were prepared according to the Bangham technique and dispersed in a borate‐trehalose buffer. Formulations were characterized in terms of pH, size, osmolarity and surface tension. In vitro tolerance was performed in human corneal epithelial cells and compared with soy PC liposomal formulation.Results: Both F1 and F2 synthetic liposomal formulations showed suitable properties for topical ophthalmic administration for DED such as hypotonicity (F1: 244.8 ± 0.74; F2: 252.5 ± 0.08 mOsm/L), neutral pH (F1: 7.52 ± 0.01; F2: 7.54 ± 0.02), low surface tension (F1: 24.53 ± 0.70; F2: 26.93 ± 0.49 mN/m) and a vesicle size of 150.8 ± 59.60 and 181.00 ± 49.83 nm for F1 and F2 respectively. Synthetic phospholipids outperformed soy PC liposomes regarding in vitro tolerance in a very sensitive corneal line, exhibiting cell viability values after 1 hour exposure of 88.71 ± 7.32% and 82.36 ± 8.84% for F1 and F2 respectively compared to soy PC liposomes (73.08 ± 8.74%). After simulated chronic exposure (4 h), cell viability of F1 (78.26 ± 1.65%) and F2 (79.08 ± 1.75%) were higher than the one obtained for PC liposomal formulation (64.53 ± 6.73%).Conclusions: Liposomes composed of synthetic phospholipids are potential candidates for the development of artificial tears for DED treatment.