Polar Headgroup Region Research Articles

Structural basis for the access and binding of resolvin D1 (RvD1) to formyl peptide receptor 2 (FPR2/ALX), a class A GPCR.

Inflammation is essential to the body's defense against tissue injury and microbial invasion. However, uncontrolled inflammation is highly detrimental and can result in chronic inflammatory diseases such as asthma, cancer, obesity, and diabetes. An increasing body of evidence suggests that specialized pro-resolving lipid mediators (SPMs), such as resolvins, are actively involved in critical cellular events that drive the resolution of inflammation and a return to homeostasis. An imbalance caused by insufficient SPMs can result in the unsuccessful resolution of inflammation. The D-series resolvins (metabolites of docosahexaenoic acid), such as resolvin D1 (RvD1) and resolvin D2 (RvD2), carry out their pro-resolving functions by directly binding to class A G protein-coupled receptors FPR2/ALXR and GPR32, and GPR18, respectively. We recently demonstrated that RvD1 and RvD2 preferentially partition and accumulate at the polar headgroup regions of the membrane. However, the mechanistic detail of how RvD1 gains access to the FPR2 binding site from a surrounding membrane environment remains unknown. In this study, we used classical MD and well-tempered metadynamics simulations to examine the structural basis for the access and binding of RvD1 to its target receptor from aqueous and membrane environments. The results offer valuable insights into the access path, potential binding pose, and key residue interactions essential for the access and binding of RvD1 to FPR2/ALXR and may help in identifying small molecule therapeutics as a possible treatment for inflammatory disorders.

Reorientation of interfacial water molecules during melting of brain sphingomyelin is associated with the phase transition of its C24:1 sphingomyelin lipids

Melting of brain sphingomyelin (bSM) manifests as a broad feature in the DSC curve that encompasses the temperature range of 25 – 45 °C, with two distinguished maxima originating from the phase transitions of two the most abundant components: C24:1 (Tm,1) and C18:0 (Tm,2). While C24:1/C18:0 sphingomyelin transforms from the gel/ripple phase to the fluid/fluid phase, the dynamics of water molecules in the interfacial layer remain completely unknown. Therefore, we carried out a calorimetric (DSC), spectroscopic (temperature-dependent UV-Vis and fluorescence) and MD simulation study of bSM in the absence/presence of Laurdan® (bSM ± L) suspended in Britton-Robinson buffer with three different pH values, 4 (BRB4), 7 (BRB7) and 9 (BRB9), and of comparable ionic strength (I = 100 mM). According to DSC, T̅m, 1 (≈ 34.5 °C/≈ 32.1 °C) and T̅m, 2 (≈ 38.0 °C/≈ 37.2 °C) of bSM suspended in BRB4, BRB7, and BRB9 in the absence/presence of Laurdan® are found to be practically pH-independent. Turbidity-based data (UV-Vis) detected both qualitative and quantitative differences in the response of bSM suspended in BRB4/BRB7/BRB9 (T̅m: ∼ 35 °C/32.0 ± 0.2 °C/36.4 ± 0.4), suggesting an intricate interplay of weakening of van der Waals forces between their hydrocarbon chains and of increased hydration in the polar headgroups region during melting. The temperature-dependent response of Laurdan® reported a discontinuous, pH-dependent change in the reorientation of interfacial water molecules that coincides with the melting of C24:1 lipids (on average, T̅m (LTC/HTC): ≈ 31.8 °C/30.6 °C/30.5 °C). MD simulations elucidated the impact of Laurdan® on a change in the physicochemical properties of bSM lipids and characterized the hydrogen bond network at the interface at 20 °C and 50 °C.

Exploring the Properties of Curved Lipid Membranes: Comparative Analysis of Atomistic and Coarse-Grained Force Fields.

Curvature emerges as a fundamental membrane characteristic crucial for diverse biological processes, including vesicle formation, cell signaling, and membrane trafficking. Increasingly valuable insights into atomistic details governing curvature-dependent membrane properties are provided by computer simulations. Nevertheless, the underlying force field models are conventionally calibrated and tested in relation to experimentally derived parameters of planar bilayers, thereby leaving uncertainties concerning their consistency in reproducing curved lipid systems. In this study we compare the depiction of buckled phosphatidylcholine (POPC) and POPC-cholesterol membranes by four popular force field models. Aside from agreement with respect to general trends in curvature dependence of a number of parameters, we observe a few qualitative differences. Among the most prominent ones is the difference between atomistic and coarse grained force fields in their representation of relative compressibility of the polar headgroup region and hydrophobic lipid core. Through a number of downstream effects, this discrepancy can influence the way in which curvature modulates the behavior of membrane bound proteins depending on the adopted simulation model.

Archaea membranes in response to extreme acidic environments

Bipolar tetraether lipids (BTL), such as glycerol dialkyl calditol tetraether (GDNT) and glycerol dialkyl glycerol tetraether (GDGT), are the dominating lipid species in thermoacidophiles that inhabit at pH ≤ 4 and temperatures ≥65°C. BTL containing archaea membranes respond to environmental pH changes by varying the number of cyclopentane rings in the isoprenoids, the amount of GDNT relative to GDGT, the ratio of tetraethers to diethers, and the level of glycosylation in polar headgroups. These structural and compositional adjustments can alter the hydrogen bond networks in the membrane polar headgroup regions and the packing tightness and rigidity in the membrane hydrophobic core. It is likely that these changes in non-covalent interactions among archaea lipids are made to retain low membrane volume fluctuations and their low sensitivity to temperature, as illustrated in the case of liposomes made of the polar lipid fraction E (PLFE) of Sulfolobus acidocaldarius. As such, a low passive proton permeability and a near neutral intracellular pH can be maintained, and, as a result, optimal activities of soluble and membrane-bound proteins in thermoacidophiles can be retained in acidic growth conditions at elevated growth temperatures.

Abstract 16947: Sotagliflozin, a Dual SGLT 1 and 2 Inhibitor, Has High Membrane Affinity and Hydrocarbon Core Location Compared With Empagliflozin

Background: The dual SGLT-1 and 2 inhibitor sotagliflozin (sota) reduced atherothrombotic events and hospitalization for worsening heart failure in patients with diabetes in clinical trials (SCORED, SOLOIST). Unlike selective SGLT2 inhibitors such as empagliflozin (empa), sota binds with higher affinity to SGLT1, which is located in the intestine, kidney, heart, brain, and vascular endothelial cells. To elucidate the physico-chemical basis for differences in tissue distribution and receptor affinity, we compared the effects of these drugs on membrane binding and molecular location. Methods: Membranes reconstituted from cardiac phospholipid and cholesterol were used to measure drug partitioning across a range of cholesterol concentrations. Multilamellar vesicles were prepared as mixtures of cardiac phospholipid (CPL), cholesterol, and each agent at 30 μM or vehicle. Drug-membrane partitioning was determined by rapid centrifugation and UV/Vis spectrophotometry. In parallel experiments, we used small angle x-ray scattering (SAXS) to identify drug location in model membranes containing phosphatidylcholine and cholesterol. Results: Sota had a membrane partition coefficient (8590 ± 2078) that was 16-fold higher than empa (519 ± 195, p<0.001) in CPL membranes. This high membrane affinity was preserved over a range of cholesterol levels compared to empa (p<0.001). Consistent with high membrane affinity, SAXS analysis showed that sota had a location evidenced by a broad increase in electron density in the hydrocarbon core extending to approximately 20 Å from the membrane center. By contrast, empa had a location limited to the polar headgroup region, consistent with its lower lipophilicity and tissue penetration. Conclusions: Sota had high membrane affinity and distinct location in the hydrocarbon core compared to empa. This may contribute to the effect of its dual SGLT-1 and 2 inhibition in vivo across various tissues including the heart. These distinct membrane interactions may also partially explain the reduced atherothrombotic risk as demonstrated in outcome trials with sota but not selective SGLT-2 inhibitors.

Investigation of the Membrane Localization and Interaction of Selected Flavonoids by NMR and FTIR Spectroscopy.

In this report, we discuss the effects of undescribed flavone derivatives, HZ4 and SP9, newly isolated from the aerial parts of Hottonia palustris L. and Scleranthus perennis L. on membranes. Interaction of flavonoids with lipid bilayers is important for medicinal applications. The experiments were performed with FTIR and NMR techniques on liposomes prepared from DPPC (dipalmitoylphosphatidylcholine) and EYPC (egg yolk phosphatidylcholine). The data showed that the examined polyphenols incorporate into the polar head group region of DPPC phospholipids at both 25 °C and 45 °C. At the lower temperature, a slight effect in the spectral region of the ester carbonyl group is observed. In contrast, at 45 °C, both compounds bring about the changes in the spectral regions attributed to antisymmetric and symmetric stretching vibrations of CH2 and CH3 moieties. Similarly, as in DPPC lipids, the tested compounds interact with the fingerprint region of the polar head groups of the EYPC lipids and cause its reorganization. The outcomes obtained by NMR analyses confirmed the localization of both flavonoids in the polar heads zone. Unraveled effects of HZ4 and SP9 in respect to lipid bilayers can partly determine their biological activities and are crucial for their usability in medicine as disease-preventing phytochemicals.

Nucleoside Analog Reverse-Transcriptase Inhibitors in Membrane Environment: Molecular Dynamics Simulations.

The behavior of four drugs from the family of nucleoside analog reverse-transcriptase inhibitors (zalcitabine, stavudine, didanosine, and apricitabine) in a membrane environment was traced using molecular dynamics simulations. The simulation models included bilayers and monolayers composed of POPC and POPG phospholipids. It was demonstrated that the drugs have a higher affinity towards POPG membranes than POPC membranes due to attractive long-range electrostatic interactions. The results obtained for monolayers were consistent with those obtained for bilayers. The drugs accumulated in the phospholipid polar headgroup region. Two adsorption modes were distinguished. They differed in the degree of penetration of the hydrophilic headgroup region. Hydrogen bonds between drug molecules and phospholipid heads were responsible for adsorption. It was shown that apricitabine penetrated the hydrophilic part of the POPC and POPG membranes more effectively than the other drugs. Van der Waals interactions between S atoms and lipids were responsible for this.

Statin Action Targets Lipid Rafts of Cell Membranes: GIXD/PM-IRRAS Investigation of Langmuir Monolayers.

Lipid rafts are condensed regions of cell membranes rich in cholesterol and sphingomyelin, which constitute the target for anticholesterolemic drugs - statins. In this work, we use for the first time a combined grazing-incidence X-ray diffraction (GIXD)/polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS)/Brewster angle microscopy (BAM) approach to show the statin effect on model lipid rafts and its components assembled in Langmuir monolayers at the air-water interface. Two representatives of these drugs, fluvastatin (FLU) and cerivastatin (CER), of different hydrophobicity were chosen, while cholesterol (Chol) and sphingomyelin (SM), and their 1:1 mixture were selected to form condensed monolayers of lipid rafts. The effect of statins on the single components of lipid rafts indicated that both the hydrophobicity of the drugs and the organization of the layer determined the drug-lipid interaction. For cholesterol monolayers, only the most hydrophobic CER was effectively changing the film structure, while for the less organized sphingomyelin, the biggest effect was observed for FLU. This drug affected both the polar headgroup region as shown by PM-IRRAS results and the 2D crystalline structure of the SM monolayer as evidenced by GIXD. Measurements performed for Chol/SM 1:1 models proved also that the statin effect depends on the presence of Chol-SM complexes. In this case, the less hydrophobic FLU was not able to penetrate the binary layer at all, while exposure to the hydrophobic CER resulted in the phase separation and formation of ordered assemblies. The changes in the membrane properties were visualized by BAM images and GIXD patterns and confirmed by thermodynamic parameters of hysteresis in the Langmuir monolayer compression-decompression experiments.

Comparative analysis of a POPC bilayer and a DPC micelle comprising an interfacial anchored peptide using all-atom MD simulations

Abstract Biological membranes are complex systems due to their composition and dynamics. Therefore, membrane mimetics are widely used to investigate lipid properties and interactions between molecules and membrane lipids. Using all-atom molecular dynamics simulations, within this study two systems composed of different membrane mimetics are compared: a 1-palmitoyl-2-oleoyl-3-glycero-phosphatidylcholine (POPC) bilayer or a dodecylphosphocholine (DPC) micelle and a nonapeptide (V94-T-K-Y-W-F-Y-R-L102). Previous 1H-NMR experiments have demonstrated that, in the presence of DPC micelles, this peptide folds as a stable amphipathic helix located in the polar head group region with the tryptophan residue pointing toward the inside of the micelle. The present comparison reveals a hydrophobic surface twice as large for the micelle as for the bilayer and a different arrangement of the acyl chains. The peptide secondary structure is not strongly affected by the membrane mimetics whereas the peptide is more deeply inserted in the bilayer than in the micelle. The contacts between the peptide and the DPC or POPC molecules are analysed and although the distances and lifetimes of these contacts are very different in the micelle and the bilayer, similar specific interactions were found that mainly involved the side chains of the residues R101 and L102.

Phase transfer mechanisms of fluorophore-labeled cell-penetrating peptide ε-poly-l-α-lysine at liquid|liquid interfaces

The transfer reaction of a novel cell-penetrating peptide, ε-poly-l-α-lysine (εPL) as a bacterial polycationic isopeptide, was investigated at the water|1,2-dichloroethane (DCE) interface. Spectroelectrochemical analysis elucidated the interfacial reaction mechanism of covalently carboxyfluorescein (FAM)-labeled εPL (FAM-εPL) in detail. FAM-εPL showed the concentration-dependent interfacial mechanisms in the positive potential region, i.e., the adsorption from the aqueous side of the interface was occurred at the low concentration of FAM-εPL, while the ion transfer across the interface accompanied by the adsorption process at the organic side proceeded further as the concentration increased. The facilitated ion transfer of FAM-εPL was observed at the biomimetic interface with a phospholipid layer. The transfer process of FAM-εPL was accelerated by the specific interaction at the aqueous side of the biomimetic interface, that is, the polar headgroup region of the phospholipid layer. The interfacial and membrane permeation mechanisms of εPL were elucidated through the spectroelectrochemical measurements by the fluorescent FAM modification and the phase transfer of a membrane impermeable FAM was also achieved by forming the conjugate with εPL.

L-Phenylalanine Partitioning Mechanisms in Model Biological Membranes.

Time-resolved fluorescence spectroscopy in combination with differential scanning calorimetry (DSC) was used to study the chemical interactions that occur when l-phenylalanine is introduced to solutions containing phosphatidylcholine vesicles. Studies reported in this work address open questions about l-Phe's affinity for lipid vesicle bilayers, the effects of l-Phe partitioning on bilayer properties, l-Phe's solvation within a lipid bilayer, and the amount of l-Phe within that local solvation environment. DSC data show that l-Phe reduces the amount of heat necessary to melt saturated phosphatidylcholine bilayers from their gel to liquid-crystalline state but does not change the transition temperature (Tgel-lc). Time-resolved emission shows only a single l-Phe lifetime at low temperatures corresponding to l-Phe remaining solvated in aqueous solution. At temperatures close to Tgel-lc, a second, shorter lifetime appears that is assigned to l-Phe already embedded within the membrane that becomes hydrated as water starts to permeate the lipid bilayer. This new lifetime is attributed to a conformationally restricted rotamer in the bilayer's polar headgroup region and accounts for up to 30% of the emission amplitude. Results reported for dipalmitoylphosphatidylcholine (DPPC, 16:0) lipid vesicles prove to be general, with similar effects observed for dimyristoylphosphatidylcholine (DMPC, 14:0) and distearoylphosphatidylcholine (DSPC, 18:0) vesicles. Taken together, these results create a complete and compelling picture of how l-Phe associates with model biological membranes. Furthermore, this approach to examining amino acid partitioning into membranes and the resulting solvation forces points to new strategies for studying the structure and chemistry of membrane-soluble peptides and selected membrane proteins.

Polar localization of new flavonoids from aerial parts of Scleranthus perennis and Hottonia palustris and their modulatory action on lipid membranes properties

The aim of this study was to characterize, for the first time, the interactions, location, and influence of flavonoids isolated from aerial parts of Scleranthus perennis (Caryophyllaceae) and Hottonia palustris (Primulaceae) on the properties of model lipid membranes prepared from dipalmitoylphosphatidylcholine (DPPC) and egg yolk phosphatidylcholine (EYPC). The tested compounds incorporated into liposomes into the region of the polar heads or at the water/membrane interface of DPPC phospholipids. Spectral effects accompanying the presence of polyphenols revealed their effect on ester carbonyl groups apart from SP8. All polyphenols brought about reorganization of the polar zone of liposomes as it was observed by FTIR technique. Additionally, fluidization effect was noted in the region of symmetric and antisymmetric stretching vibrations of the CH2 and CH3 groups with exception to HZ2 and HZ3. Similarly, in EYPC liposomes, they interacted mainly with the regions of the choline heads of the lipids and had various effects on the carbonyl ester groups with exception to SP8. The region of polar head groups is restructured due to the presence of the additives in liposomes. The outcomes obtained using the NMR technique confirmed the locations of all of the tested compounds in the polar zone and indicated a flavonoid-dependent modifying effect towards lipid membranes. HZ1 and SP8 raised motional freedom in this region whereas opposite effect was revealed for HZ2 and HZ3. In the hydrophobic region restricted mobility was noted. In this report we discuss the mechanism of previously undescribed flavonoids in terms of their actions on membranes.

Ethosome as a potential transdermal drug delivery system

Ethosomes are elastic nanovesicles with phospholipid bases that are noninvasive delivery vehicles and have a high ethanol concentration (20–45%). As transdermal drug delivery confers poor penetration, the major obstacle is the low diffusion rate of drugs across the stratum corneum. The sophisticated ethosomal delivery systems enable drugs to reach the deep skin layers and/or the systemic circulation. The development of these new carriers involves the employment of several preparatory processes. Ethosomal dispersions are added to gels, patches, and creams for ease of use and stability. Ethanol is known as an efficient permeation enhancer and has been added in the vesicular systems to prepare elastic nanovesicles. It has the potential to interact with the polar head group region of lipid molecules, lowering the melting point of the stratum corneum lipid and raising lipid fluidity and cell membrane permeability as a result. Ethosomes' special structure allows them to enclose and transmit through the skin highly lipophilic substances like propranolol and trihexyphenidil as well as cationic medicines like testosterone and minoxidil. This article provides a detailed review of the ethosomal structure, mechanism of penetration along with various methods of preparation. Also, the article focuses on the applications of ethosomal carriers and opportunities for the research and future development of novel improved therapies.

In vivo targeting of a tumor-antigen encoded DNA vaccine to dendritic cells in combination with tumor-selective chemotherapy eradicates established mouse melanoma.

Despite remarkable progress during the past decade, eradication of established tumors by targeted cancer therapy and cancer immunotherapy remains an uphill task. Herein, we report on a combination approach for eradicating established mouse melanoma. Our approach employs the use of tumor selective chemotherapy in combination with in vivo dendritic cell (DC) targeted DNA vaccination. Liposomes of a newly synthesized lipopeptide containing a previously reported tumor-targeting CGKRK-ligand covalently grafted in its polar head-group region were used for tumor selective delivery of cancer therapeutics. Liposomally co-loaded STAT3siRNA and WP1066 (a commercially available inhibitor of the JAK2/STAT3 pathway) were used as cancer therapeutics. In vivo targeting of a melanoma antigen (MART-1) encoded DNA vaccine (p-CMV-MART1) to dendritic cells was accomplished by complexing it with a previously reported mannose-receptor selective in vivo DC-targeting liposome. Liposomes of the CGKRK-lipopeptide containing encapsulated FITC-labeled siRNA, upon intravenous administration in B16F10 melanoma bearing mice, showed remarkably higher accumulation in tumors 24 h post i.v. treatment, compared to their degree of accumulation in other body tissues including the lungs, liver, kidneys, spleen and heart. Importantly, the findings in tumor growth inhibition studies revealed that only in vivo DC-targeted genetic immunization or only tumor-selective chemotherapy using the presently described systems failed to eradicate the established mouse melanoma. The presently described combination approach is expected to find future applications in combating various malignancies (with well-defined surface antigens).

The Influence of Cationic Nitrosyl Iron Complex with Penicillamine Ligands on Model Membranes, Membrane-Bound Enzymes and Lipid Peroxidation.

This paper shows the biological effects of cationic binuclear tetranitrosyl iron complex with penicillamine ligands (TNIC-PA). Interaction with a model membrane was assessed using a fluorescent probes technique. Antioxidant activity was studied using a thiobarbituric acid reactive species assay (TBARS) and a chemiluminescence assay. The catalytic activity of monoamine oxidase (MAO) was determined by measuring liberation of ammonia. Antiglycation activity was determined fluometrically by thermal glycation of albumine by D-glucose. The higher values of Stern-Volmer constants (KSV) obtained for the pyrene located in hydrophobic regions (3.9 × 104 M-1) compared to KSV obtained for eosin Y located in the polar headgroup region (0.9 × 104 M-1) confirms that TNIC-PA molecules prefer to be located in the hydrophobic acyl chain region, close to the glycerol group of lipid molecules. TNIC-PA effectively inhibited the process of spontaneous lipid peroxidation, due to additive contributions from releasing NO and penicillamine ligand (IC50 = 21.4 µM) and quenched luminol chemiluminescence (IC50 = 3.6 μM). High activity of TNIC-PA in both tests allows us to assume a significant role of its radical-scavenging activity in the realization of antioxidant activity. It was shown that TNIC-PA (50-1000 μM) selectively inhibits the membrane-bound enzyme MAO-A, a major source of ROS in the heart. In addition, TNIC-PA is an effective inhibitor of non-enzymatic protein glycation. Thus, the evaluated biological effects of TNIC-PA open up the possibility of its practical application in chemotherapy for socially significant diseases, especially cardiovascular diseases.

Anticancer drugs tamoxifen and 4hydroxytamoxifen as effectors of phosphatidylethanolamine lipid polymorphism

The interaction of tamoxifen (TMX) and its metabolite 4-hydroxytamoxifen (HTMX) with a biomimetic membrane model system composed of 1,2-dielaidoylphosphatidylethanolamine (DEPE) has been studied using a biophysical approach. Incorporation of TMX into DEPE bilayers gives rise to a progressive broadening of the Lβ/Lα phase transition and a downward temperature shift. The Lβ/Lα phase transition presents multiple endotherms, indicating a lateral segregation of TMX/DEPE domains within the plane of the bilayer. TMX and HTMX also widen and shift the Lα to hexagonal-HII transition toward lower values, the phase diagrams showing that both compounds facilitate formation of the HII phase. TMX increases motional disorder of DEPE acyl chains in the Lβ, Lα and HII phases, whereas the effect of HTMX is clearly different. In addition, neither TMX nor HTMX significantly perturb the hydration state of the polar headgroup region of DEPE. Molecular dynamics (MD) simulations indicate that these drugs do not affect membrane thickness, area per lipid, or the conformation of DEPE molecules. As a general rule, the interaction of HTMX with DEPE is qualitatively similar to TMX but less intense. However, a significant difference shown by MD is that HTMX is mainly placed around the center of each monolayer while TMX is located mainly at the center of the membrane, also having a greater tendency to cluster formation. These results are discussed to understand the modulation of phosphatidylethanolamine lipid polymorphism carried out by these drugs, which could be of relevance to explain their effects on enzyme activity or membrane permeabilization.

Transfer Mechanism of Anthracycline Antibiotics and Their Ion Association with PAMAM Dendrimer at Liquid|Liquid Interfaces**

AbstractThe transfer reaction of anthracycline antibiotics, daunorubicin (DNR) and doxorubicin (DOX), was investigated at the water|1,2‐dichloroethane (DCE) interface. Spectroelectrochemical analysis demonstrated significant changes in the transfer mechanism of anthracycline cations with a slight structural difference across the bare water|DCE interface and the biomimetic interface with a phospholipid layer. The facilitated ion transfer feature was found for both HDNR+ and HDOX+ at the biomimetic interface, where the adsorption process of HDOX+ was observed over a wide potential range at the aqueous side of the interface, that is, the polar headgroup region of the phospholipid layer. The molecular association between the carboxylate‐terminated generation 3.5 polyamidoamine (G3.5 PAMAM) dendrimer and anthracycline derivatives occurred preferentially under neutral pH conditions. The negatively charged G3.5 PAMAM dendrimer induced positive shifts of the transfer potential of anthracycline cations at the water|DCE interface, indicating its ability as potential‐ and pH‐responsive drug carriers.

Inulin-Modified Liposomes as a Novel Delivery System for Cinnamaldehyde.

Cinnamaldehyde as an antioxidant was encapsulated in inulin-modified nanoliposomes in order to improve its physical and antioxidant stability. The microstructure, particle size and volume distribution of cinnamaldehyde liposomes were characterized by atomic force microscopy (AFM) and dynamic light scattering (DLS). The particle size and polydispersion index (PDI) values of the inulin modified liposomes were 72.52 ± 0.71 nm and 0.223 ± 0.031, respectively. The results showed that the liposomes after surface modification with inulin remained spherical. Raman and Fourier transform infrared (FTIR) spectra analysis showed that hydrogen bonds were formed between the inulin and the liposome membrane. Inulin binding also restricted the freedom of movement of lipid molecules and enhanced the order of the hydrophobic core of the membrane and the polar headgroup region in lipid molecules. Therefore, the addition of different concentrations of inulin influenced the permeability of the liposome bilayer membrane. However, when inulin was excessive, the capacity of the bilayer membrane to load the cinnamaldehyde was reduced, and the stability of the system was reduced. Additionally, the encapsulation efficiency (EE) and retention rate (RR) of cinnamaldehyde from inulin-modified liposomes during storage were determined. The EE value of the inulin modified liposomes was 70.71 ± 0.53%. The liposomes with 1.5% inulin concentration had the highest retention rate (RR) and the smallest particle size during storage at 4 °C. The addition of inulin also enhanced the thermal stability of the liposomes. Based on the results, the surface modification improved the oxidation stability of liposomes, especially the DPPH scavenging ability. In conclusion, these results might help to develop inulin as a potential candidate for the effective modification of the surface of liposomes and provide data and conclusions for it.

Membrane Potentials Trigger Molecular-Scale Rearrangements in the Outer Membrane of Gram-Negative Bacteria.

The structural complexity of the cell envelope of Gram-negative bacteria limits the fabrication of realistic models of bacterial cell membranes. A vertical Langmuir-Blodgett withdrawing was used to deposit a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) monolayer on the Au(111) surface. The second leaflet composed of di[3-deoxy-D-manno-octulosonyl]-lipid A (KLA) was deposited using Langmuir-Schaefer transfer. The use of an electrode material as a support for the POPE-KLA bilayer allowed electrochemical control of the membrane's stability, compactness, and structure. Capacitance-potential curves showed a typical pattern for the supported lipid bilayers electrochemical characteristic. The minimum membrane capacitance was ∼4 μF cm-2 and did not change in the following desorption-adsorption cycles, indicating the presence of a stable bilayer structure with an asymmetric composition of both leaflets. However, at a molecular scale, as elucidated in spectroelectrochemical experiments, large differences in the response of both leaflets to electric potentials were observed. The acyl chains in POPE and KLA existed in a liquid state. The quantitative analysis of the CH stretching modes indicated potential-driven reorientations in the hydrophobic fragment of the bilayer, already in the adsorbed state. To assign observed rearrangements to POPE and KLA lipids in both leaflets, per-deuterated d31-POPE was transferred into the inner leaflet. Since no potential-dependent changes of the CD2 stretching modes in the d31-POPE-KLA bilayer were observed, reorientations in the acyl chain region were assigned to the KLA molecules. Mg2+ ions were bound to the polar head groups of KLA. The strength of electrostatic interactions in the polar head group region of KLA was dependent on the direction of the electric field. At negative electric potentials, the binding of divalent cations weakened, which gave the KLA molecules increased orientational flexibility. This behavior in electric fields is peculiar for the outer membrane and indicates that the microbial cell membranes have different electrochemical properties than phospholipid bilayers.

Therapeutic lithium alters polar head-group region of lipid bilayer and prevents lipid peroxidation in forebrain cortex of sleep-deprived rats

Lithium is regarded as a unique therapeutic agent for the management of bipolar disorder (BD). In efforts to explain the favourable effects of lithium in BD, a wide range of mechanisms was suggested. Among those, the effect of clinically relevant concentrations of lithium on the plasma membrane was extensively studied. However, the biophysical properties of brain membranes isolated from experimental animals exposed to acute, short-term and chronic lithium have not been performed to-date. In this study, we compared the biophysical parameters and level of lipid peroxidation in membranes isolated from forebrain cortex (FBC) of therapeutic lithium-treated and/or sleep-deprived rats. Lithium interaction with FBC membranes was characterized by appropriate fluorescent probes. DPH (1,6-diphenyl-1,3,5-hexatriene) and TMA-DPH (1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene p-toluenesulphonate) were used for characterization of the hydrophobic lipid core and Laurdan (6-dodecanoyl-2-dimethylaminonaphthalene) for the membrane-water interface. Lipid peroxidation was determined by immunoblot analysis of 4-HNE-(4-hydroxynonenal)-protein adducts. The organization of polar head-group region of FBC membranes, measured by Laurdan generalized polarization, was substantially altered by sleep deprivation and augmented by lithium treatment. Hydrophobic membrane interior characterized by steady-state anisotropy of DPH and TMA-DPH fluorescence was unchanged. Chronic lithium had a protective effect against peroxidative damage of membrane lipids in FBC. In summary, lithium administration at a therapeutic level and/or sleep deprivation as an animal model of mania resulted in changes in rat FBC membrane properties.