Vesicle Suspension Research Articles

Extracellular vesicles derived from mesenchymal stem cells mediate extracellular matrix remodeling in osteoarthritis through the transport of microRNA-29a.

Knee osteoarthritis (KOA) is a common orthopedic condition with an uncertain etiology, possibly involving genetics and biomechanics. Factors like changes in chondrocyte microenvironment, oxidative stress, inflammation, and immune responses affect KOA development. Early-stage treatment options primarily target symptom relief. Mesenchymal stem cells (MSCs) show promise for treatment, despite challenges. Recent research highlights microRNAs (miRNAs) within MSC-released extracellular vesicles that can potentially promote cartilage regeneration and hinder KOA progression. This suggests exosomes (Exos) as a promising avenue for future treatment. While these findings emphasize the need for effective KOA progression management, further safety and efficacy validation for Exos is essential. To explore miR-29a's role in KOA, we'll create miR-29a-loaded vesicles, testing for early treatment in rat models. Extraction of bone marrow MSC-derived extracellular vesicles, preparation of engineered vesicles loaded with miR-29a using ultrasonication, and identification using quantitative reverse transcription polymerase chain reaction; after establishing a rat model of KOA, rats were randomly divided into three groups: Blank control group injected with saline, normal extracellular vesicle group injected with normal extracellular vesicle suspension, and engineered extracellular vesicle group injected with engineered extracellular vesicle suspension. The three groups were subjected to general behavioral observation analysis, imaging evaluation, gross histological observation evaluation, histological detection, and immunohistochemical detection to compare and evaluate the progress of various forms of arthritis. General behavioral observation results showed that the extracellular vesicle group and engineered extracellular vesicle group had better performance in all four indicators of pain, gait, joint mobility, and swelling compared to the blank control group. Additionally, the engineered extracellular vesicle group had better pain relief at 4 wk and better knee joint mobility at 8 wk compared to the normal extracellular vesicle group. Imaging examination results showed that the blank control group had the fastest progression of arthritis, the normal extracellular vesicle group had a relatively slower progression, and the engineered extracellular vesicle group had the slowest progression. Gross histological observation results showed that the blank control group had the most obvious signs of arthritis, the normal extracellular vesicle group showed signs of arthritis, and the engineered extracellular vesicle group showed no significant signs of arthritis. Using the Pelletier gross score evaluation, the engineered extracellular vesicle group had the slowest progression of arthritis. Results from two types of staining showed that the articular cartilage of rats in the normal extracellular vesicle and engineered extracellular vesicle groups was significantly better than that of the blank control group, and the engineered extracellular vesicle group had the best cartilage cell and joint surface condition. Immunohistochemical detection of type II collagen and proteoglycan showed that the extracellular matrix of cartilage cells in the normal extracellular vesicle and engineered extracellular vesicle groups was better than that of the blank control group. Compared to the normal extracellular vesicle group, the engineered extracellular vesicle group had a better regulatory effect on the extracellular matrix of cartilage cells. Engineered Exos loaded with miR-29a can exert anti-inflammatory effects and maintain extracellular matrix stability, thereby protecting articular cartilage, and slowing the progression of KOA.

Comment on "Dynamics and rheology of vesicles under confined Poiseuille flow" by Z. Gou, H. Zhang, A. Nait-Ouhra, M. Abbasi, A. Farutin and C. Misbah, Soft Matter, 2023, 19, 9101.

In a recent paper, [Gou et al., Soft Matter, 2023, 19, 9101-9114] studied numerically the viscosity of a confined suspension of vesicles flowing in a channel as a function of vesicle concentration. In order to discuss the genericity of the observed behaviour, namely a nearly constant effective viscosity at low concentrations, we complement their study by a comparison with the few existing ones in the literature. In particular, we highlight that they fail to reproduce well established results for blood viscosity in microcirculation, thereby suggesting that the conclusions regarding the optimization of cell transport and oxygenation may not apply. We conclude with a quick discussion on potential improvements regarding numerical modeling, as long as physiological relevance is sought.

Measuring the bending rigidity of microbial glucolipid (biosurfactant) bioamphiphile self-assembled structures by neutron spin-echo (NSE): Interdigitated vesicles, lamellae and fibers

Bending rigidity, k, is classically measured for lipid membranes to characterize their nanoscale mechanical properties as a function of composition. Widely employed as a comparative tool, it helps understanding the relationship between the lipid's molecular structure and the elastic properties of its corresponding bilayer. Widely measured for phospholipid membranes in the shape of giant unilamellar vesicles (GUVs), bending rigidity is determined here for three self-assembled structures formed by a new biobased glucolipid bioamphiphile, rather associated to the family of glycolipid biosurfactants than phospholipids. In its oleyl form, glucolipid G-C18:1 can assemble into vesicles or crystalline fibers, while in its stearyl form, glucolipid G-C18:0 can assemble into lamellar gels. Neutron spin-echo (NSE) is employed in the q-range between 0.3 nm−1 (21 nm) and 1.5 nm−1 (4.1 nm) with a spin-echo time in the range of up to 500 ns to characterize the bending rigidity of three different structures (Vesicle suspension, Lamellar gel, Fiber gel) solely composed of a single glucolipid. The low (k = 0.30 ± 0.04 kbT) values found for the Vesicle suspension and high values found for the Lamellar gel (k = 130 ± 40 kbT) and Fiber gel (k = 900 ± 500 kbT) are unusual when compared to most phospholipid membranes. By attempting to quantify for the first time the bending rigidity of self-assembled bioamphiphiles, this work not only contributes to the fundamental understanding of these new molecular systems, but it also opens new perspectives in their integration in the field of soft materials.

Microscopically grounded constitutive model for dense suspensions of soft particles below jamming

Materials made up of soft elastic particles suspended in a fluid form a broad subset of complex fluids, including emulsions, suspensions of microgels, liposomes, or vesicles. Until now, no established model can describe how they flow. Here, we derive from particle-level dynamics a constitutive model describing the rheology of two-dimensional dense soft suspensions below the jamming transition, in a regime where elastic interactions dominate the stress response. Our model successfully captures many observed rheological features, such as shear thinning, normal stresses, and normal stress differences scaling respectively linearly and quadratically with deformation rate in the slow flow limit.

Quantification of Giant Unilamellar Vesicle Fusion Products by High-Throughput Image Analysis.

Artificial cells are based on dynamic compartmentalized systems. Thus, remodeling of membrane-bound systems, such as giant unilamellar vesicles, is finding applications beyond biological studies, to engineer cell-mimicking structures. Giant unilamellar vesicle fusion is rapidly becoming an essential experimental step as artificial cells gain prominence in synthetic biology. Several techniques have been developed to accomplish this step, with varying efficiency and selectivity. To date, characterization of vesicle fusion has relied on small samples of giant vesicles, examined either manually or by fluorometric assays on suspensions of small and large unilamellar vesicles. Automation of the detection and characterization of fusion products is now necessary for the screening and optimization of these fusion protocols. To this end, we implemented a fusion assay based on fluorophore colocalization on the membranes and in the lumen of vesicles. Fluorescence colocalization was evaluated within single compartments by image segmentation with minimal user input, allowing the application of the technique to high-throughput screenings. After detection, statistical information on vesicle fluorescence and morphological properties can be summarized and visualized, assessing lipid and content transfer for each object by the correlation coefficient of different fluorescence channels. Using this tool, we report and characterize the unexpected fusogenic activity of sodium chloride on phosphatidylcholine giant vesicles. Lipid transfer in most of the vesicles could be detected after 20 h of incubation, while content exchange only occurred with additional stimuli in around 8% of vesicles.

Measurement of extracellular volume fraction using magnetic resonance-based conductivity tensor imaging.

Conductivity tensor imaging (CTI) using MRI is an advanced method that can non-invasively measure the electrical properties of living tissues. The contrast of CTI is based on underlying hypothesis about the proportionality between the mobility and diffusivity of ions and water molecules inside tissues. The experimental validation of CTI in both in vitro and in vivo settings is required as a reliable tool to assess tissue conditions. The changes in extracellular space can be indicators for disease progression, such as fibrosis, edema, and cell swelling. In this study, we conducted a phantom imaging experiment to test the feasibility of CTI for measuring the extracellular volume fraction in biological tissue. To mimic tissue conditions with different extracellular volume fractions, four chambers of giant vesicle suspension (GVS) with different vesicle densities were included in the phantom. The reconstructed CTI images of the phantom were compared with the separately-measured conductivity spectra of the four chambers using an impedance analyzer. Moreover, the values of the estimated extracellular volume fraction in each chamber were compared with those measured by a spectrophotometer. As the vesicle density increased, we found that the extracellular volume fraction, extracellular diffusion coefficient, and low-frequency conductivity decreased, while the intracellular diffusion coefficient slightly increased. On the other hand, the high-frequency conductivity could not clearly distinguish the four chambers. The extracellular volume fraction measured by the spectrophotometer and CTI method in each chamber were quite comparable, i.e., (1.00, 0.98 ± 0.01), (0.59, 0.63 ± 0.02), (0.40, 0.40 ± 0.05), and (0.16, 0.18 ± 0.02). The prominent factor influencing the low-frequency conductivity at different GVS densities was the extracellular volume fraction. Further studies are needed to validate the CTI method as a tool to measure the extracellular volume fractions in living tissues with different intracellular and extracellular compartments.

Measurement of extracellular volume fraction using magnetic resonance-based conductivity tensor imaging

Conductivity tensor imaging (CTI) using MRI is an advanced method that can non-invasively measure the electrical properties of living tissues. The contrast of CTI is based on underlying hypothesis about the proportionality between the mobility and diffusivity of ions and water molecules inside tissues. The experimental validation of CTI in both in vitro and in vivo settings is required as a reliable tool to assess tissue conditions. The changes in extracellular space can be indicators for disease progression, such as fibrosis, edema, and cell swelling. In this study, we conducted a phantom imaging experiment to test the feasibility of CTI for measuring the extracellular volume fraction in biological tissue. To mimic tissue conditions with different extracellular volume fractions, four chambers of giant vesicle suspension (GVS) with different vesicle densities were included in the phantom. The reconstructed CTI images of the phantom were compared with the separately-measured conductivity spectra of the four chambers using an impedance analyzer. Moreover, the values of the estimated extracellular volume fraction in each chamber were compared with those measured by a spectrophotometer. As the vesicle density increased, we found that the extracellular volume fraction, extracellular diffusion coefficient, and low-frequency conductivity decreased, while the intracellular diffusion coefficient slightly increased. On the other hand, the high-frequency conductivity could not clearly distinguish the four chambers. The extracellular volume fraction measured by the spectrophotometer and CTI method in each chamber were quite comparable, i.e., (1.00, 0.98 ± 0.01), (0.59, 0.63 ± 0.02), (0.40, 0.40 ± 0.05), and (0.16, 0.18 ± 0.02). The prominent factor influencing the low-frequency conductivity at different GVS densities was the extracellular volume fraction. Further studies are needed to validate the CTI method as a tool to measure the extracellular volume fractions in living tissues with different intracellular and extracellular compartments.

Dynamics and rheology of vesicles under confined Poiseuille flow.

The rheological behavior and dynamics of a vesicle suspension, serving as a simplified model for red blood cells, are explored within a Poiseuille flow under the Stokes limit. Investigating vesicle response has led to the identification of novel solutions that complement previously documented forms like the parachute and slipper shapes. This study has brought to light the existence of alternative configurations, including a fully off-centered form and a multilobe structure. The study unveils the presence of two distinct branches associated with the slipper shape. One branch arises as a consequence of a supercritical bifurcation from the symmetric parachute shape, while the other emerges from a saddle-node bifurcation. Notably, the findings are represented through diagrams that display data collapsing harmoniously based on a combination of independent dimensionless parameters. Delving into the rheological implications, a remarkable observation emerges: the normalized viscosity (i.e. similar to intrinsic viscosity) exhibits a non-monotonic trend as a function of vesicle concentration. Initially, the normalized viscosity diminishes as the concentration increases, followed by a subsequent rise at higher concentrations. Noteworthy is the presence of a minimum value in the normalized viscosity at lower concentrations, aligning well with the concentrations observed in microcirculation scenarios. The intricate behavior of the normalized viscosity can be attributed to a delicate spatial arrangement within the suspension. Importantly, this trend echoes the observations made in a linear shear flow scenario, thereby underscoring the universality of the rheological behavior for confined suspensions.

A Chiral 19F NMR Reporter of Foldamer Conformation in Bilayers.

Understanding and controlling peptide foldamer conformation in phospholipid bilayers is a key step toward their use as molecular information relays in membranes. To this end, a new 19F "reporter" tag has been developed and attached to dynamic peptide foldamers. The (R)-1-(trifluoromethyl)ethylamido ((R)-TFEA) reporter was attached to the C-terminus of α-amino-iso-butyric acid (Aib) foldamers. Crystallography confirmed that the foldamers adopted 310 helical conformations. Variable temperature (VT) NMR spectroscopy in organic solvents showed that the (R)-TFEA reporter had an intrinsic preference for P helicity, but the overall screw-sense was dominated by a chiral "controller" at the N-terminus. The 19F NMR chemical shift of the CF3 resonance was correlated with the ability of different N-terminal groups to induce either an M or a P helix in solution. In bilayers, a similar correlation was found. Solution 19F NMR spectroscopy on small unilamellar vesicle (SUV) suspensions containing the same family of (R)-TFEA-labeled foldamers showed broadened but resolvable 19F resonances, with each chemical shift mirroring their relative positions in organic solvents. These studies showed that foldamer conformational preferences are the same in phospholipid bilayers as in organic solvents and also revealed that phospholipid chirality has little influence on conformation.

Conformational state diagram of DOPC/DPPCd62/cholesterol mixtures.

Raman spectra of aqueous suspensions of vesicles composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), deuterated 1,2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (DPPCd62), and cholesterol (Chol) were studied at room temperature to determine the conformational states of the phospholipid hydrocarbon chains. Deuteration of DPPCd62 allowed us to characterize the conformational states of DOPC and DPPCd62 independently. The parameters of Raman peaks, which are sensitive to the conformational order, were studied in a wide range of compositions. It was found that the DOPC molecules are conformationally disordered for all compositions. The conformational state of the DPPCd62 molecules changes with composition. Their conformational state is influenced by cholesterol-induced partial disordering and DOPC solvation, transforming the DPPC molecules into the disordered state. The conformational state diagram from the Raman experiment was compared with outcomes from the differential scanning calorimetry (DSC) experiment. The Raman spectra also revealed that the DPPC molecules coexist in the disordered and all-trans ordered states for the DOPC/DPPCd62/Chol mixtures except for the pure liquid-disordered phase.

Photo-induced Morphological Changes of Lipid Bilayer Vesicles Enabled by a Visible-Light-Responsive Azo Compound.

Living cells and organelles are separated by a lipid membrane bilayer. It is possible to induce morphological changes in this membrane by disturbing the order of the membrane using external stimuli and understanding the details of this mechanism is expected to be applicable to intracellular transport. DBA (DBAB-BODIPY-aminopropyl), which contains (1) a DBAB (4-[di(biphenyl-4-yl)amino]azobenzene) moiety that undergoes photo-isomerization under visible light irradiation, and (2) a BODIPY (borondipyrromethene) fluorophore was synthesized. The π-π* transition absorptions of both the azo moiety and that of BODIPY moiety in DBA were observed, independently. The photo-isomerization rate constant of the DMSO solution of DBA at 299K is 5.5 ×10-3/s. The structure of the fluorescent group in DBA did not readily influence the isomerization. Upon introducing DBA into the lipid bilayer membranes of a vesicle suspension and irradiating the vesicles with visible light to isomerize the azo group, a morphological change in of the vesicles was observed due to the disturbance of the membrane order. Thus, DBA is a useful molecule for artificial modulation of the lipid membrane morphology.

Dynamic response on a nanometer scale of binary phospholipid-cholesterol vesicles: Low-frequency Raman scattering insight.

Low-frequency Raman spectroscopy was used to study the dynamic response on a nanometer scale of aqueous suspensions of two-component lipid vesicles. Binary mixtures of saturated phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC) and cholesterol are interesting for possible coexistence of solidlike and liquid-ordered phases, while the phase coexistence was not reported for unsaturated phospholipid (1,2-dioleoyl-sn-glycero-3-phosphocholine, DOPC) and cholesterol mixtures. The DOPC-DPPC mixtures represent the well-documented case of coexisting domains of solidlike and liquid-disordered phases. These three series of lipid mixtures are studied here. A broad peak with the maximum in the range of 30-50cm^{-1} and a narrow peak near 10cm^{-1} are observed in the Raman susceptibility of the binary mixtures and attributed to the acousticlike vibrational density of states and layer modes, respectively. Parameters of the broad and narrow peaks are sensitive to lateral and conformational hydrocarbon chain ordering. It was also demonstrated that the low-frequency Raman susceptibility of multicomponent lipid bilayers allows one to determine the phase state of lipid bilayers and distinguish the homogeneous distribution of molecular complexes from coexisting domains with sizes above several nanometers. Thus, the low-frequency Raman spectroscopy provides unique information in studying phase coexistence in lipid bilayers.

A Microfluidic Platform for Sequential Assembly and Separation of Synthetic Cell Models.

Cell-sized vesicles like giant unilamellar vesicles (GUVs) are established as a promising biomimetic model for studying cellular phenomena in isolation. However, the presence of residual components and byproducts, generated during vesicles preparation and manipulation, severely limits the utility of GUVs in applications like synthetic cells. Therefore, with the rapidly growing field of synthetic biology, there is an emergent demand for techniques that can continuously purify cell-like vesicles from diverse residues, while GUVs are being simultaneously synthesized and manipulated. We have developed a microfluidic platform capable of purifying GUVs through stream bifurcation, where a vesicles suspension is partitioned into three fractions: purified GUVs, residual components, and a washing solution. Using our purification approach, we show that giant vesicles can be separated from various residues—which range in size and chemical composition—with a very high efficiency (e = 0.99), based on size and deformability of the filtered objects. In addition, by incorporating the purification module with a microfluidic-based GUV-formation method, octanol-assisted liposome assembly (OLA), we established an integrated production-purification microfluidic unit that sequentially produces, manipulates, and purifies GUVs. We demonstrate the applicability of the integrated device to synthetic biology through sequentially fusing SUVs with freshly prepared GUVs and separating the fused GUVs from extraneous SUVs and oil droplets at the same time.

Correlative imaging using super‐resolution fluorescence microscopy and soft X‐ray tomography at cryogenic temperatures provides a new way to assess virosome solutions for vaccine development

Active virosomes (AVs) are derivatives of viruses, broadly similar to ‘parent’ pathogens, with an outer envelope that contains a bespoke genome coding for four to five viral proteins capable of eliciting an antigenic response. AVs are essentially novel vaccine formulations that present on their surface selected viral proteins as antigens. Once administered, they elicit an initial ‘anti‐viral’ immune response. AVs are also internalised by host cells where their cargo viral genes are used to express viral antigen(s) intracellularly. These can then be transported to the host cell surface resulting in a second wave of antigen exposure and a more potent immuno‐stimulation. A new 3D correlative microscopy approach is used here to provide a robust analytical method for characterisation of Zika‐ and Chikungunya‐derivatised AV populations including vesicle size distribution and variations in antigen loading. Manufactured batches were compared to assess the extent and nature of batch‐to‐batch variations. We also show preliminary results that verify antigen expression on the surface of host cells. We present here a reliable and efficient high‐resolution 3D imaging regime that allows the evaluation of the microstructure and biochemistry of novel vaccine formulations such as AVs.

Structural Organization of Cardiolipin-Containing Vesicles as Models of the Bacterial Cytoplasmic Membrane.

The bacterial cytoplasmic membrane is the innermost bacterial membrane and is mainly composed of three different phospholipid species, i.e., phosphoethanolamine (PE), phosphoglycerol (PG), and cardiolipin (CL). In particular, PG and CL are responsible for the negative charge of the membrane and are often the targets of cationic antimicrobial agents. The growing resistance of bacteria toward the available antibiotics requires the development of new and more efficient antibacterial drugs. In this context, studying the physicochemical properties of the bacterial cytoplasmic membrane is pivotal for understanding drug-membrane interactions at the molecular level as well as for designing drug-testing platforms. Here, we discuss the preparation and characterization of PE/PG/CL vesicle suspensions, which contain all of the main lipid components of the bacterial cytoplasmic membrane. The vesicle suspensions were characterized by means of small-angle neutron scattering, dynamic light scattering, and electron paramagnetic spectroscopy. By combining solution scattering and spectroscopy techniques, we propose a detailed description of the impact of different CL concentrations on the structure and dynamics of the PE/PG bilayer. CL induces the formation of thicker bilayers, which exhibit higher curvature and are overall more fluid. The experimental results contribute to shed light on the structure and dynamics of relevant model systems of the bacterial cytoplasmic membrane.

Understanding charged vesicle suspensions as Wigner glasses: dynamical aspects

Suspensions of charged vesicles in water with added salt are widespread in nature and industrial production. Here we investigate, via Brownian dynamics simulations, a model that grasps the key features of these systems, with bidisperse colloidal beads interacting via a hard-core and an electrostatic double layer potential. Our goal is to focus on a set of interaction parameters that is not generic but measured in recent experiments, and relevant for a class of consumer products, such as liquid fabric softeners. On increasing the volume fraction in a range relevant to real formulation, we show that the dynamics become progressively slower and heterogeneous, displaying the typical signatures of an approaching glass transition. On lowering the salt concentration, which corresponds to increasing the strength and range of the electrostatic repulsion, the emergence of glassy dynamics becomes significantly steeper, and, remarkably, occurs at volume fractions well below the hard-sphere glass transition. The volume fraction dependence of the structural relaxation time at different salt concentration is well described through a functional law inspired by a recently proposed model (Krausser et al 2015 Proc. Natl Acad. Sci. USA 112 13762). According to our results, the investigated system may be thought of as a Wigner glass, i.e. a low-density glassy state stabilized by long-range repulsive interactions. Overall, our study suggests that glassy dynamics plays an important role in controlling the stability of these suspensions.

Molecular Tetrahedrons as Selective and Efficient Ion Transporters via a Two-Station Swing-Relay Mechanism

The traditional approach to utilizing an ion-relay mechanism for ion transport requires three or more ion-relay stations. Herein, we describe a novel strategy, incorporating a swing action to reali...

The SPaCE diagnostic: a pilot study to test the accuracy of a novel point of care sensor for point of care detection of burn wound infection

Wound infection in burn patients is common and has an impact on outcomes. There is no objective method to diagnose infection at point of care (PoC). Early diagnosis prevents progression to sepsis. Diagnostic subjectivity supports over-diagnosis, unnecessary hospitalization, and antibiotic overuse. This pilot study aimed to investigate the accuracy of a novel PoC wound infection diagnostic in burn patients. We produced, and invitro tested, a PoC diagnostic for early wound infection diagnosis. The prototype SPaCE diagnostic uses a patented lipid vesicle suspension into which a clinical swab is placed. The diagnostic delivers a colour-response to Staphylococcus aureus, Pseudomonas aeruginosa, Candida species and Enterococcus faecalis at toxin release. A pilot clinical diagnostic accuracy study was undertaken. The reference standard was a retrospective decision made by an expert clinical panel using routinely available data. Data was available from 33 of 34 patients. Of these, 52% were considered to have a wound infection, 42% not, and two (6%) were equivocal. The diagnostic results showed 24% were infected, 42% were not and 33% produced intermediate results. Agreement between clinical judgement and diagnostic result, assessed using a weighted Kappa, was 0.591 suggesting moderate agreement. If the intermediate results were excluded, 22 sets of data with definitive results achieved a Kappa statistic of 0.81 suggesting 'almost perfect' agreement. Sensitivity and specificity were 57% (8/14) and 71% (12/17), respectively. This pilot study provided evidence that the SPaCE diagnostic could provide valuable and timely data to support clinical decision-making at PoC for wound infection.

Effect of the Hydrocarbon Chain Disorder in Phosphatidylcholine Bilayers on Gigahertz Sound Velocity.

Suspensions of multilamellar vesicles of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and hydrated and dehydrated aligned multilamellar samples of DMPC were studied by Brillouin spectroscopy in the temperature range from 90 to 333 K. The sound velocity of the longitudinal acoustic wave was evaluated from the Brillouin spectra. It was found that phase transition, hydration state, and planar or vesicular form of bilayers affect the gigahertz sound velocity. Usually, the temperature dependence of the sound velocity is weak in solid substances. Amazingly, the sound velocity of hydrated DMPC samples showed significant temperature-induced changes of up to 1.8 times, even within the solid-like gel phase. We explained this effect by temperature-induced excitations of the disordered conformational states of the hydrocarbon chains as well as anharmonic effects. In addition, the relevance of the gigahertz sound velocity to the description of subterahertz Raman features was demonstrated.

The Disordering Effect of Plant Metabolites on Model Lipid Membranes of Various Thickness

This study was focused on the effect of plant metabolites (phloretin, capsaicin, digitonin, diosgenin and betulin) on the model lipid membranes. The methods of assessing the permeability of lipid bilayers based on measuring the leakage of a fluorescent marker (calcein) from liposomes and differential scanning microcalorimetry of vesicle suspension were used. It was found that the release rate of calcein from 1-palmitoyl-2-oleyl-sn-glycero-3-phosphocholine (POPC) liposomes with test compounds added to the suspension at a ratio with lipid 1 : 50 decreased in the order capsaicin > phloretin >> betulin ≈ diosgenin ≈ digitonin. In the case of cholesterol- and ergosterol-containing POPC liposomes, the activity decreased as diosgenin ≈ digitonin > betulin > capsaicin > phloretin. It was demonstrated that phloretin and capsaicin significantly reduce the melting temperature (Tm) and to increase the half-width of the main peak on the endotherm (T1/2) of dipalmitoylphosphocholine (DPPC), distearoylphosphocholine (DSPC) and diarachidoylphosphocholine (DAPC). These results show that the incorporation of these small molecules between the polar “heads” of phosphocholine. It was found that the increase in the length of saturated chains of membrane-forming lipids (from 16 to 20 hydrocarbon units), the absolute values of ΔTm and ΔT1/2 decreased in the presence of phloretin and increased with capsaicin. This may be the result of differences in the localization of phloretin and capsaicin in the membrane. Steroid saponins exhibited a weak effect on the thermotropic behavior of phosphocholines. The absolute values of ΔTm and ΔT1/2 decreased in the order DPPC, DSPC, and DAPC and increased in the order betulin, diosgenin, and digitonin. Steroid saponins are characterized by a more pronounced effect on the thermotropic behavior of the sterol–phospholipid mixture. The findings are consistent with the assumption of a high affinity of the tested saponins for sterol-containing membranes.