Pure Phospholipid Research Articles

Analysis of Intact In Vivo Peroxidized Phospholipids from Bovine Retina via LC-MS/MS and GC-MS/MS Using Autoxidized Retina Reference Standards.

Highly unsaturated fatty acids (HUFAs) are vulnerable to oxygen attack, thus making HUFA-rich, high metabolic rate/reactive oxygen species (ROS)-generating neurological tissue particularly susceptible to increased oxidative stress. Lipid oxidation is a putative early stage marker of neurodegenerative diseases, suggesting that reliable monitoring of oxidized neural lipids in vivo reveals early pathogenesis. Here, we present a novel methodology to detect and quantify intactin vivo ROS-driven peroxidized phospholipids (LPOx-PLs) in bovine retina extract. A protocol for preparing autoxidized pure phospholipids (PLs) and complex retinal extracts served as reference standards and was adapted to enable analytical parameter development. Fatty acid profiles of bovine retinas were first established with routine gas chromatography (GC) methods and used to customize mass spectrometry scanning for major HUFA-carrying PLs in the retinal extract. Targeted multiple reaction monitoring (MRM) scanning via triple quadrupole tandem mass spectrometry detected native (unoxidized) and oxidation-damaged PL regardless of the position of the O or O2 addition along the acyl chains and enabled quantification of relative signals from intact native and oxidized PL (5%-10% CV). MRM-triggered information-dependent acquisition (IDA) spectra confirmed the structure of peroxidized PLs, revealing that peroxidized species (+O-OH) dominated over single O-added species in vitro and in vivo. Positive identification and relative quantification are reported for 12 selected in vivo native and peroxidized phosphatidylcholines and phosphatidylethanolamines. These results enable future studies of the initial peroxidation due to toxins, genetics, or other initiating events influencing in vivo oxidation levels and potentially the effectiveness of strategies to mitigate this mechanism of action.

Critical micellar concentration determination of pure phospholipids and lipid-raft and their mixtures with cholesterol.

Phospholipids in biological membranes establish a chemical equilibrium between free phospholipids in the aqueous phase (CMC) and self-assembled phospholipids in vesicles, keeping the CMC constant. The CMC is different for each phospholipid, depends on the amount of cholesterol, and, according to the lipid-chaperone hypothesis, controls the interaction between free phospholipids and amyloidogenic proteins (such as amylin, amyloid-β, and α-synuclein, all of which are, respectively, associated with a different proteinopathy), which governs the formation of a toxic complex between free lipids and proteins that leads to membrane destruction. Here, we provide quantitative measurements of CMCs and bilayer stability of pure phospholipids, lipid rafts, and their mixture with cholesterol by fluorescence methods (using pyrene as a probe) and light scattering techniques (resonance Rayleigh scattering and fixed-angle light scattering) performed on LUVs, as well as AFM to measure LUV dimensions. Also, we test the lipid-chaperone hypothesis on human IAPP interacting with different mixture of POPC cholesterol. Stated the importance of CMC in membrane stability and protein aggregation processes, these results could be a starting point for the development of a quantitative kinetic model for the lipid chaperone hypothesis.

Changes in free energy barrier for water permeation by stretch-induced phase transitions in phospholipid/cholesterol bilayers

Water permeation through phospholipid/cholesterol bilayers is the key to understanding tension-induced rupture of biological cell membranes. We performed molecular dynamics simulations of stretched phospholipid/cholesterol bilayers to investigate changes in the free energy profile of water molecules across the bilayer and the lipid structure responsible for water permeation. We modeled stretching of the bilayer by applying areal strain. In stretched phospholipid/cholesterol bilayers, the hydrophobic tail of the phospholipids became disordered and the free energy barrier to water permeation decreased. Upon exceeding the critical areal strain, a phase transition to an interdigitated gel phase occurred before rupture, and the hydrophobic tail ordering as well as the free energy barrier were restored. In pure phospholipid bilayers, we did not observe such recoveries. These transient recoveries in the phospholipid/cholesterol bilayer suppressed water permeation and membrane rupture, followed by an increase in the critical areal strain at which the bilayer ruptured. This result agrees with experimental results and provides a reasonable molecular mechanism for the toughness of phospholipid/cholesterol bilayers under tension. Communicated by Ramaswamy H. Sarma

Molecular dynamics simulation of the effect of AQP1 on the transmembrane transport of plasma RONS across cancer cell membranes

In the cold atmospheric plasma (CAP)-assisted cancer treatment, the increase in the concentration of reactive oxygen species (ROS) and reactive nitrogen species (RNS) produced by CAP is believed to be related to the overexpression of aquaporins (AQPs) on cancer cell membranes. In this paper, using classical molecular dynamics simulations, the transmembrane behavior of RNS and ROS on a pure phospholipid bilayer or a AQP1-phospholipid bilayer model was studied. The research shows that hydrophobic RNS tend to be transported through the bilayer of phospholipids. The overexpression of AQP1 can significantly improve the transmembrane efficiency of hydrophilic ROS. Our simulation fills the gap in the research for RNS-related molecular simulation and provides guidance for the precise targeting of cancer cells in CAP therapy.

Studies of some bio-inspired liquid crystals

ABSTRACTThe main phase transition of lipid bilayers corresponds to a defined change from an ordered (gel) to a disordered (fluid liquid crystal) state of hydrocarbon chains, occurring in general at a defined temperature Tm. However, aqueous dispersions of pure anionic phospholipids, and particularly DMPG, may exhibit a ‘melting regime’, from Tmon until Tmoff, over ~10°C. The melting process depends on pH, ionic strength and several details of sample preparation. This paper makes a review on seven papers of the author with different collaborations, with the original proposal of pores in the DMPG melting transition. The focus is on structural results obtained from X-ray scattering, varying concentration and temperature, but integrating with results from other experimental techniques. Initially the effect of salt addition was separated from the effect of DMPG concentration. At DMPG concentrations higher than 70 mM a lamellar phase starts and a detailed study of the temperature variation of 150 mM DMPG allowed arrival to detailed pore model, focused in the surface fractions of pores in the bilayers. The model admits large and small pores in the melting regime and agrees with the new Lamellar Phase with pores (Lp) starting at T3. The large biological relevance is stressed.

Physical and Oxidative Water-in-Oil Emulsion Stability by the Addition of Liposomes from Shrimp Waste Oil with Antioxidant and Anti-Inflammatory Properties.

Liposomes made of partially purified phospholipids (PL) from Argentine red shrimp waste oil were loaded with two antioxidant lipid co-extracts (hexane-soluble, Hx and acetone-soluble, Ac) to provide a higher content of omega-3 fatty acids. The physical properties of the liposomes were characterized by Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS) and Differential Scanning Calorimetry (DSC). The antioxidant and anti-inflammatory activity of the lipid extracts and liposomal suspensions were evaluated in terms of Superoxide and ABTS radical scavenging capacities and TNF-α inhibition. Uni-lamellar spherical liposomes (z-average ≈ 145 nm) with strong negative ζ potential (≈ -67 mV) were obtained in all cases. The high content of neutral lipids in the Hx extract caused structural changes in the bilayer membrane and decreased entrapment efficiency regarding astaxanthin and EPA + DHA contents. The liposomes loaded with the Hx/Ac extracts showed higher antioxidant and anti-inflammatory activity compared with empty liposomes. The liposomal dispersions improved the physical and oxidative stability of water-in-oil emulsions as compared with the PL extract, inducing pronounced close packing of water droplets. The liposomes decreased hydroperoxide formation in freshly made emulsions and prevented thio-barbituric acid-reactive substances (TBARS) accumulation during chilled storage. Liposomes from shrimp waste could be valuable nanocarriers and stabilizers in functional food emulsions.

High-Resolution Ultrasound Spectroscopy for the Determination of Phospholipid Transitions in Liposomal Dispersions.

High-resolution ultrasound spectroscopy (HR-US) is a spectroscopic technique using ultrasound waves at high frequencies to investigate the structural properties of dispersed materials. This technique is able to monitor the variation of ultrasound parameters (sound speed and attenuation) due to the interaction of ultrasound waves with samples as a function of temperature and concentration. Despite being employed for the characterization of several colloidal systems, there is a lack in the literature regarding the comparison between the potential of HR-US for the determination of phospholipid thermal transitions and that of other common techniques both for loaded or unloaded liposomes. Thermal transitions of liposomes composed of pure phospholipids (dimyristoylphosphatidylcholine, DMPC; dipalmitoylphosphatidylcholine, DPPC and distearoylphosphatidylcholine, DSPC), cholesterol and their mixtures were investigated by HR-US in comparison to the most commonly employed microcalorimetry (mDSC) and dynamic light scattering (DLS). Moreover, tramadol hydrochloride, caffeine or miconazole nitrate as model drugs were loaded in DPPC liposomes to study the effect of their incorporation on thermal properties of a phospholipid bilayer. HR-US provided the determination of phospholipid sol-gel transition temperatures from both attenuation and sound speed that are comparable to those calculated by mDSC and DLS techniques for all analysed liposomal dispersions, both loaded and unloaded. Therefore, HR-US is proposed here as an alternative technique to determine the transition temperature of phospholipid membrane in liposomes.

Detection of Bacterial Rhamnolipid Toxin by Redox Liposome Single Impact Electrochemistry

AbstractThe detection of Rhamnolipid virulence factor produced by Pseudomonas aeruginosa involved in nosocomial infections is reported by using the redox liposome single impact electrochemistry. Redox liposomes based on 1,2‐dimyristoyl‐sn‐glycero‐3‐phosphocholine as a pure phospholipid and potassium ferrocyanide as an encapsulated redox content are designed for using the interaction of the target toxin with the lipid membrane as a sensing strategy. The electrochemical sensing principle is based on the weakening of the liposomes lipid membrane upon interaction with Rhamnolipid toxin which leads upon impact at an ultramicroelectrode to the breakdown of the liposomes and the release/electrolysis of its encapsulated redox probe. We present as a proof of concept the sensitive and fast sensing of a submicromolar concentration of Rhamnolipid which is detected after less than 30 minutes of incubation with the liposomes, by the appearing of current spikes in the chronoamperometry measurement.

Detection of Bacterial Rhamnolipid Toxin by Redox Liposome Single Impact Electrochemistry.

The detection of Rhamnolipid virulence factor produced by Pseudomonas aeruginosa involved in nosocomial infections is reported by using the redox liposome single impact electrochemistry. Redox liposomes based on 1,2-dimyristoyl-sn-glycero-3-phosphocholine as a pure phospholipid and potassium ferrocyanide as an encapsulated redox content are designed for using the interaction of the target toxin with the lipid membrane as a sensing strategy. The electrochemical sensing principle is based on the weakening of the liposomes lipid membrane upon interaction with Rhamnolipid toxin which leads upon impact at an ultramicroelectrode to the breakdown of the liposomes and the release/electrolysis of its encapsulated redox probe. We present as a proof of concept the sensitive and fast sensing of a submicromolar concentration of Rhamnolipid which is detected after less than 30 minutes of incubation with the liposomes, by the appearing of current spikes in the chronoamperometry measurement.

Hopanoid Hopene Locates in the Interior of Membranes and Affects Their Properties.

Hopanoids are proposed as sterol surrogates in some bacteria, and it has been proved that some hopanoids are able to induce a liquid-order phase state in lipid membranes. The members of this group of molecules have diverse structures, and not all of them have been studied in detail yet. Here, we study membranes with the hopanoid hopene (hop-22 (29)-ene or diploptene), which is the product of the cycling of squalene by squalene-hopene cyclase, and thus is present in the first step of hopanoid biosynthesis. Hopene is particularly interesting because it lacks a polar head group, which opens the question of how does this molecule accommodate in a lipid membrane, and what are the effects promoted by its presence. In order to get an insight into this, we prepared monolayers and bilayers of a phospholipid with hopene and studied their properties in comparison with pure phospholipid membranes, and with the sterol cholesterol or the hopanoid diplopterol. Film stiffness, shear viscosity, and bending dynamics were very affected by the presence of hopene, while zeta-potential, generalized polarization of Laurdan, and conductivity were affected moderately by this molecule. The results suggest that at very low percentages, hopene locates parallel to the phospholipid molecules, while the excess of the hopene molecules stays between leaflets, as previously proposed using molecular dynamics simulations.

Acetaminophen Interactions with Phospholipid Vesicles Induced Changes in Morphology and Lipid Dynamics

Acetaminophen (APAP) or paracetamol, despite its wide and common use for pain and fever symptoms, shows a variety of side effects, toxic effects, and overdose effects. The most common form of toxic effects of APAP is in the liver where phosphatidylcholine is the major component of the cell membrane with additional associated functionalities. Although this is the case, the effects of APAP on pure phospholipid membranes have been largely ignored. Here, we used 1,2-di-(octadecenoyl)-sn-glycero-3-phosphocholine (DOPC), a commonly found phospholipid in mammalian cell membranes, to synthesize large unilamellar vesicles to investigate how the incorporation of APAP changes the pure lipid vesicle structure, morphology, and fluidity at different concentrations. We used a combination of dynamic light scattering, small-angle neutron and X-ray scattering (SANS, SAXS), and cryo-TEM for structural characterization, and neutron spin-echo (NSE) spectroscopy to investigate the dynamics. We showed that the incorporation of APAP in the lipid bilayer significantly impacts the spherical phospholipid self-assembly in terms of its morphology and influences the lipid content in the bilayer, causing a decrease in bending rigidity. We observe a decrease in the number of lipids per vesicle by almost 28% (0.06 wt % APAP) and 19% (0.12 wt % APAP) compared to the pure DOPC (0 wt % APAP). Our results showed that the incorporation of APAP reduces the membrane rigidity by almost 50% and changes the spherical unilamellar vesicles into much more irregularly shaped vesicles. Although the bilayer structure did not show much change when observed by SAXS, NSE and cryo-TEM results showed the lipid dynamics change with the addition of APAP in the bilayer, which causes the overall decreased membrane rigidity. A strong effect on the lipid tail motion showed that the space explored by the lipid tails increases by a factor of 1.45 (for 0.06 wt % APAP) and 1.75 (for 0.12 wt % APAP) compared to DOPC without the drug.

The Effect of Cholesterol on Membrane-Bound Islet Amyloid Polypeptide.

Islet amyloid polypeptide (IAPP) is a proposed cause of the decreased beta-cell mass in patients with type-II diabetes. The molecular composition of the cell-membrane is important for regulating IAPP cytotoxicity and aggregation. Cholesterol is present at high concentrations in the pancreatic beta-cells, and in-vitro experiments have indicated that it affects the amyloid formation of IAPP either by direct interactions or by changing the properties of the membrane. In this study we apply atomistic, unbiased molecular dynamics simulations at a microsecond timescale to investigate the effect of cholesterol on membrane bound IAPP. Simulations were performed with various combinations of cholesterol, phosphatidylcholine (PC) and phosphatidylserine (PS) lipids. In all simulations, the helical structure of monomer IAPP was stabilized by the membrane. We found that cholesterol decreased the insertion depth of IAPP compared to pure phospholipid membranes, while PS lipids counteract the effect of cholesterol. The aggregation propensity has previously been proposed to correlate with the insertion depth of IAPP, which we found to decrease with the increased ordering of the lipids induced by cholesterol. Cholesterol is depleted in the vicinity of IAPP, and thus our results suggest that the effect of cholesterol is indirect.

Membrane protein density determining membrane fusion revealed by dynamic fluorescence imaging

Membrane fusion is fundamental to biological activity of cells, so disclosingits relevant mechanism is very important for understanding various cell functions. Although artificial model systems have been developed to uncover the mechanism of membrane fusion, key factors determining the mode of membrane fusion remain unclear. Based on the construction of different types of liposome vesicles, we used a dynamic fluorescence imaging method to investigate the effect of membrane protein distribution density on membrane fusion. Time-resolved imaging revealed that protein-free pure phospholipid vesicles themselves occurred full membrane fusion. Moreover, we prepared proteoliposomes with increasing protein-to-lipid ratio to better reflect the characteristic of membrane structure in vivo. Our data showed that pure phospholipid vesicles no longer fused with the proteoliposomes that in a higher protein proportion, indicating dense membrane proteins may hinder membrane fusion. A further comparative analysis of the interactions of pure phospholipid vesicles with the cell membrane / giant plasma membrane vesicles (GPMVs) / protein-free giant unilamellar vesicles (GUVs) confirmed the inhibitory effect of dense membrane proteins on membrane fusion. Our work demonstrates the membrane protein density influences the mode of membrane fusion and lays a foundation for constructing quasi-native membrane fusion models in vitro.

Involvement of a Conserved Intramembrane Acidic Residue in Cholesterol Binding of Mitochondrial VDAC1 Revealed by Microsecond-Scale Simulations

Voltage-dependent anion channel 1 (VDAC1), a β-barrel membrane protein abundant in the mitochondrial outer membrane, mediates the exchange of ions and metabolites between the mitochondrial matrix and the cytosol. Both experimental and previous computational studies suggest that a conserved, membrane-facing residue in VDAC1, glutamate 73 (E73), plays an essential role in the function of the channel, including its oligomerization and interaction with other cytosolic partner proteins. In addition, a recent photoaffinity labeling study identified E73 as a specific binding site for cholesterol, an endogenous membrane lipid that also regulates VDAC functions. However, how cholesterol interacts with E73 and the effects of cholesterol binding at E73 remain poorly understood. Here, we performed an extensive set of microsecond-long atomistic molecular dynamics simulations on both wildtype and mutant forms and in different protonation states (totaling 14 μs) to characterize cholesterol interactions with VDAC1. Analysis of lipid occupancy showed that cholesterol exhibited distinct preferred binding sites from phospholipids on VDAC1. Spontaneous binding and unbinding of cholesterol to E73 in its deprotonated state was captured, a process accompanied by local membrane deformation and water solvation at the E73 side-chain in the middle of the lipid bilayer. Compared to VDAC1 in a pure phospholipid environment, the presence of cholesterol reduces the fluctuations of the β-strands in proximity to E73. Based on our results, we propose a stabilizing role of cholesterol in regulating the VDAC1 dynamics in the region close to E73, which might further modulate VDAC1 function as an ion channel.

Surface-Assisted Formation of Model Protocells from Fatty Acid and Phospholipid Mixtures

Solid substrates have been shown to enhance the formation of prebiotic containers by supporting a spontaneous, multi-step transformation of surface-adhered phospholipid reservoirs to giant unilamellar primitive compartments connected via lipid nanotube networks. It has been previously shown that membranes from mixtures of fatty acids and phospholipids have a selective advantage over the pure phospholipid membranes. Here we show the solid surface-assisted formation of primitive compartments, i.e.

Discerning Membrane Steady-State Oxygen Flux by Monte Carlo Markov Chain Modeling.

Molecular oxygen (O2) permeability coefficients for lipid bilayers have previously been estimated using both electron paramagnetic resonance (EPR) oximetry and molecular dynamics simulation data. Yet, neither technique captures the fluxes that exist physiologically. Here, the dynamic steady state is modeled using a stochastic approach built on atomic resolution molecular dynamics simulation data. A Monte Carlo Markov chain technique is used to examine membrane-level fluxes of oxygen in lipid-water systems. At steady state, the concentration of oxygen is found to be higher inside the model membranes than in surrounding water, consistent with the known favorable partitioning of O2 toward the lipid phase. Pure phospholipid 1-palmitoyl,2-oleoyl-phosphatidylcholine (POPC) bilayers accrue ~40% more O2 molecules at steady state than POPC/cholesterol bilayers (1:1 molecular ratio) mimicking the red blood cell membrane. Steady-state levels of oxygen were reached inside both bilayer types within the same timeframe, but depletion of oxygen from the bilayer interior occurred 17% faster for POPC than for POPC/cholesterol. Likewise, first-order rate constants estimated for accrual to steady state were the same for POPC and POPC/cholesterol, at 190μs-1, while first-order rate constants for depletion of the accrued O2 from the bilayers differed, at 95μs-1 for POPC and 81μs-1 for POPC/cholesterol (lower by 15%). These results are consistent with prior experiments in red blood cells (RBCs) with varying membrane cholesterol content, in which additional cholesterol slowed oxygen uptake and release. Further work is needed to understand whether differences in RBC membrane cholesterol content would affect the delivery of oxygen to tissues.

Emulsification and dilatational surface rheology of ultrasonicated milk fat globule membrane (MFGM) materials

Herein milk fat model emulsions (MFMEs) of infant formulas were prepared with ultrasonication-processed milk fat globule membrane (MFGM) materials (as well as MFGM/Lecithin blend and lecithin). The emulsion stability during storage was determined with a turbiscan. The microstructure of MFMEs was examined with confocal laser scanning microscopy (CLSM) at different pH values. Besides, the adsorption kinetics and linear/nonlinear dilatational rheological properties of oil/water interfaces were measured with a droplet tensiometer. After ultrasonication process, the average particle size of MFGM fragments decreased from 800 ± 100 nm to 230 ± 10 nm. The surface tension (at 100 s) of MFGM-stabilized interfaces was 17.4 mN/m (0.5 g/L), 12.9 mN/m (1.0 g/L and 2.0 g/L) and 11.0 mN/m (4.0 g/L), indicating a good emulsifying capacity of ultrasonicated MFGM materials. At neutral and acidic pH, MFMEs stabilized with MFGM dispersions or MFGM/Lecithin (1:1) at a total concentration of 4.0 g/L showed strong resistance against coalescence (CLSM). MFGM dispersions exhibited different surface rheological behaviour from pure phospholipids, proteins or a simple phospholipid/protein mixture, which suggested a heterogeneous structure of MFGM-stabilized interfaces, mainly consisting of MFGM fragment particles, interspersed with free phospholipids and proteins. These findings could provide a better understanding of emulsifying properties of MFGM materials.

FIX potency of rFIX‐Albumin fusion protein is underestimated by one‐stage methods using silica‐based APTT reagents

Higher potency is obtained with chromogenic substrate (CS) methods and one-stage (OS) method with SynthAFax vs silica-based OS methods on analysis of albutrepenonacog alpha (rFIX fused with albumin, rFIX-FP). Investigation of the effect of contact activator in search for explanation of discrepancy between methods. Chromogenic Rox Factor IX method and OS methods with Pathromtin SL, SynthAFax or new OS method variants using different phospholipid emulsions and addition of either colloidal silica to create APTT reagents or addition of human FXIa together with calcium ions, in the latter case omitting contact activation. The effect of (a) adding different amounts of colloidal silica or (b) mixtures of Pathromtin SL and purified phospholipids immediately before addition of FXIa and calcium chloride was also explored. FIX activation via tissue factor/FVIIa was also made. FIX potency of rFIX-FP when using APTT reagents with pure phospholipid emulsions with added colloidal silica was similar to OS method with Pathromtin SL. In contrast, close to 80% higher FIX potency for rFIX-FP, and similar to OS method with SynthAFax and to the CS method, was obtained when FXIa replaced contact activation. No discrepancies were obtained for plasma-derived FIX. Gradual decrease of colloidal silica or decreasing proportion of Pathromtin SL added just before addition of FXIa raised rFIX-FP potency to that obtained with SynthAFax and Rox Factor IX. Supportive results were obtained with the tissue factor/FVIIa method. Colloidal silica and Pathromtin SL impair activation of rFIX-FP, causing underestimation of rFIX-FP potency.

Influence of Lipid’s Main Transition Temperature on the Stability of Chimeric Liposomal Systems

Background: The incorporation of polymeric components into liposomes promotes structural rearrangement of the lipid bilayers that could affect their properties and their behavior. Therefore, by mixing phospholipids with polymeric compounds the, socalled chimeric liposomal nanosystems are produced and could be advantageous, compared with conventional (e.g. composed of pure phospholipids) liposomal nanostructures. Objective: In this work, we used lipids with different main transition temperature (Tm) i.e 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC, Tm=55°C), L-α-phosphatidylcholine, hydrogenated (Soy) (HSPC, Tm=52 °C) and egg phosphatidylcholine (EggPC, Tm=23 °C) and we studied and compared the physicochemical characteristics and the stability of conventional with that of chimeric liposomes. Methods: Thin-film hydration method (TFH) was used as the preparation protocol for all systems. Dynamic and electrophoretic light scattering (DLS and ELS) were utilized in order to elucidate the physicochemical characteristics of all systems. All liposomal systems exhibited sizes below 100nm while the ζ-potential was around zero, indicating the absence of surface charge. Results: The results revealed that the Tm of each phospholipid influences the biophysical behavior of the lipidic membrane, which contributes to the physicochemical characteristics and affects the physical stability of the liposomal nanosystems. The nature and physicochemical properties of each phospholipid seem to play a key role, regarding the structural characteristics and the formation process of the liposomal nanosystems. Conclusion: : Comparing the physicochemical properties of the conventional liposomes with those of the chimeric liposomal systems, we conclude that the complexity of the latter, due to the incorporation of the polymeric guest into the lipidic bilayer, revealed new properties, which correspond to increased physical stability.

Membrane Tension-Mediated Growth of Liposomes.

Recent years have seen a tremendous interest in the bottom-up reconstitution of minimal biomolecular systems, with the ultimate aim of creating an autonomous synthetic cell. One of the universal features of living systems is cell growth, where the cell membrane expands through the incorporation of newly synthesized lipid molecules. Here, the gradual tension-mediated growth of cell-sized (≈10 µm) giant unilamellar vesicles (GUVs) is demonstrated, to which nanometer-sized (≈30 nm) small unilamellar vesicles (SUVs) are provided, that act as a lipid source. By putting tension on the GUV membranes through a transmembrane osmotic pressure, SUV-GUV fusion events are promoted and substantial growth of the GUV is caused, even up to doubling its volume. Thus, experimental evidence is provided that membrane tension alone is sufficient to bring about membrane fusion and growth is demonstrated for both pure phospholipid liposomes and for hybrid vesicles with a mixture of phospholipids and fatty acids. The results show that growth of liposomes can be realized in a protein-free minimal system, which may find useful applications in achieving autonomous synthetic cells that are capable of undergoing a continuous growth-division cycle.