The effect of calcium on the properties of charged phospholipid bilayers

Calcium phosphates enhanced with liposomes - the future of bone regeneration and drug delivery

Effective healing and regeneration of various bone defects is still a major challenge and concern in modern medicine. Calcium phosphates have emerged as extensively studied bone substitute materials due to their structural and chemical resemblance to the mineral phase of bone, along with their versatile properties. Calcium phosphates present promising biological characteristics that make them suitable for bone substitution, but a critical limitation lies in their low osteoinductivity. To supplement these materials with properties that promote bone regeneration, prevent infections, and cure bone diseases locally, calcium phosphates can be biologically and therapeutically modified. A promising approach involves combining calcium phosphates with drug-containing liposomes, renowned for their high biocompatibility and ability to provide controlled and sustained drug delivery. Surprisingly, there is a lack of research focused on liposome-calcium phosphate composites, where liposomes are dispersed within a calcium phosphate matrix. This raises the question of why such studies are limited. In order to provide a comprehensive overview of existing liposome and calcium phosphate composites as bioactive substance delivery systems, the authors review the literature exploring the interactions between calcium phosphates and liposomes. Additionally, it seeks to identify potential interactions between calcium ions and liposomes, which may impact the feasibility of developing liposome-containing calcium phosphate composite materials. Liposome capacity to protect bioactive compounds and facilitate localized treatment can be particularly valuable in scenarios involving bone regeneration, infection prevention, and the management of bone diseases. This review explores the implications of liposomes and calcium phosphate material containing liposomes on drug delivery, bioavailability, and stability, offering insights into their advantages.

Thermodynamic and Structural Study of Budesonide-Exogenous Lung Surfactant System

The clinical benefits of using exogenous pulmonary surfactant (EPS) as a carrier of budesonide (BUD), a non-halogenated corticosteroid with a broad anti-inflammatory effect, have been established. Using various experimental techniques (differential scanning calorimetry DSC, small- and wide- angle X-ray scattering SAXS/WAXS, small- angle neutron scattering SANS, fluorescence spectroscopy, dynamic light scattering DLS, and zeta potential), we investigated the effect of BUD on the thermodynamics and structure of the clinically used EPS, Curosurf®. We show that BUD facilitates the Curosurf® phase transition from the gel to the fluid state, resulting in a decrease in the temperature of the main phase transition (Tm) and enthalpy (ΔH). The morphology of the Curosurf® dispersion is maintained for BUD < 10 wt% of the Curosurf® mass; BUD slightly increases the repeat distance d of the fluid lamellar phase in multilamellar vesicles (MLVs) resulting from the thickening of the lipid bilayer. The bilayer thickening (~0.23 nm) was derived from SANS data. The presence of ~2 mmol/L of Ca2+ maintains the effect and structure of the MLVs. The changes in the lateral pressure of the Curosurf® bilayer revealed that the intercalated BUD between the acyl chains of the surfactant's lipid molecules resides deeper in the hydrophobic region when its content exceeds ~6 wt%. Our studies support the concept of a combined therapy utilising budesonide-enriched Curosurf®.

Phthalocyanine-based glucose-responsive nanocochleates for dynamic prevention of β-cell damage in diabetes

Phthalocyanine is a blue-colored macrocyclic compound with excellent anti-oxidant and lipid-peroxidation abilities due to its intermolecular π-π stacking structure. Antioxidants inhibit intracellular reactive oxygen species formation and decrease oxidation defense ability of the enzymes in diabetes management. The present study aimed to fabricate concanavalin A conjugated phthalocyanine-loaded cochleates (Formulation PhConA) as a glucose-sensitive lipidic system and estimate its efficacy in streptozotocin-induced male Sprague Dawley diabetic rats for 28 days. Thin-film hydration and trapping methods were used in the preparation of liposomes and cochleates, respectively, whereas the surface was modified for concanavalin A conjugation using EDAC: NHS (1:1). Formulation PhConA with rod-shaped structures showed particle size of 415.7 ± 0.46 nm, PdI value of 0.435 ± 0.09, encapsulation efficiency of 85.64 ± 0.34%, and 84.55 ± 0.29% release of phthalocyanine for 56 h. The circular dichroism study displayed a slight deviation after the conjugation effect of concanavalin A to cochleates. The in-vivo studies of the formulation PhConA improved the blood glucose levels along with defensive effect on the liver to overcome the hyperlipidemic effect. The rigid structure of cochleates prolongs the drug elimination from systemic circulation and extends its effect for a longer duration by decreasing the blood glucose level. Thus, the glucose-sensitive formulation PhConA showed significant improvement in diabetic rats within the period of 28 days by improving the oxidative defense and protecting the pancreatic β-cells.

Effects of Ion Concentration and Headgroup Chemistry on Thin Lipid Film Drainage

While the use of lipid nanoparticles in drug delivery applications has grown over the past few decades, much work remains to be done toward the characterization and rational design of the drug carriers. A key feature of delivery is the interaction of the exterior leaflet of the LNP with the outer leaflet of the cell membrane, which relies in part on the fusogenicity of the lipids and the ionic environment. In this paper, we study the interactions between two lipid monolayers using a thin film balance to create lipid thin films and interferometry to measure film evolution. We probe the role of lipid headgroup chemistry and charge, along with ionic solution conditions, in either promoting or hindering film drainage and stability. Specific headgroups phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylserine (PS) are chosen to represent a combination of charge and fusogenicity. We quantify each film's drainage characteristics over a range of capillary numbers. Qualitatively, we find that films transition from drainage via a large dimple to drainage via channels and vortices as the capillary number increases. Additionally, we observe a transition from electrostatically dominated film drainage at low CaCl2 concentrations to fusogenic-dominated film drainage at higher CaCl2 concentrations for anionic fusogenic (PS) films. Understanding the role of headgroup composition, ionic composition, and ionic concentration will pave the way for the design of tunable vesicle and buffer systems that behave desirably across a range of ex vivo and in vivo environments.

Calcium-induced compaction and clustering of vesicles tracked with molecular resolution

Theory and simulations predict the complex nature of calcium interaction with the lipid membrane. By maintaining the calcium concentrations at physiological conditions, herein we demonstrate experimentally the effect of Ca2+ in a minimalistic cell-like model. For this purpose, giant unilamellar vesicles (GUVs) with a neutral lipid DOPC are generated, and the ion-lipid interaction is observed with attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy providing molecular resolution. Firstly, Ca2+ encapsulated within the vesicle binds to the phosphate head groups of the inner leaflets and triggers vesicle compaction. This is tracked by changes in vibrational modes of the lipid groups. As the calcium concentration within the GUV increases, IR intensities change indicating vesicle dehydration and lateral compression of the membrane. Secondly, by inducing a calcium gradient across the membrane up to a ratio of 1:20, interaction between several vesicles occurs as Ca2+ can bind to the outer leaflets leading to vesicle clustering. It is observed that larger calcium gradients induce stronger interactions. These findings with an exemplary biomimetic model reveal that divalent calcium ions not only cause local changes to the lipid packing but also have macroscopic implications to initiate vesicle-vesicle interaction.

Curvature Matters: Modeling Calcium Binding to Neutral and Anionic Phospholipid Bilayers

In this work, the influence of membrane curvature on the Ca²⁺ binding to phospholipid bilayers is investigated by means of molecular dynamics simulations. In particular, we compared Ca²⁺ binding to flat, elastically buckled, or uniformly bent zwitterionic and anionic phospholipid bilayers. We demonstrate that Ca²⁺ ions bind preferably to the concave membrane surfaces in both types of bilayers. We also show that the membrane curvature leads to pronounced changes in Ca²⁺ binding including differences in free ion concentrations, lipid coordination distributions, and the patterns of ion binding to different chemical groups of lipids. Moreover, these effects differ substantially for the concave and convex membrane monolayers. Comparison between force fields with either full or scaled charges indicates that charge scaling results in reduction of the Ca²⁺ binding to curved phosphatidylserine bilayers, while for phosphatidylcholine membranes, calcium binds only weakly for both force fields.

Pro-inflammatory protein S100A9 alters membrane organization by dispersing ordered domains

Pro-inflammatory, calcium-binding protein S100A9 is localized in the cytoplasm of many cells and regulates several intracellular and extracellular processes. S100A9 is involved in neuroinflammation associated with the pathogenesis of Alzheimer's disease (AD). The number of studies on the impact of S100A9 in co-aggregation processes with amyloid-like proteins is increasing. However, there is still a lack of data on how this protein interacts with lipid membranes. We employed atomic force microscopy (AFM), dynamic light scattering (DLS), and fluorescence measurements (Laurdan and Thioflavin-T) to study the interaction between protein and the membrane surface. We used lipid vesicles in bulk and planar tethered lipid bilayers as biomimetic membrane models. We demonstrated that the protein accumulates on negatively charged lipid bilayers but with no further loss of the bilayer's integrity. The most important result is that the initial adsorption and accumulation of apo-form of S100A9 on the lipid membrane surface is lipid phase-sensitive. The breaking down of raft-like and disappearance of gel-like domains indicate that protein incorporates into the hydrophobic part of the lipid bilayer. We observed the most noticeable loss of integrity in lipid bilayers constructed from a lipid mixture (brain total lipid extract). Understanding the function and interactions of these proteins in cellular environments might expand the development of new diagnostic and therapeutic approaches for AD or other related diseases.

Regulation of calcium ions on the interaction between amphotericin B and cholesterol-rich phospholipid monolayer in LE phase and LC phase

Amphotericin B, as a "gold standard", is used to treat invasive fungal infections. The AmB molecule can bind easily to cholesterol and damage cell membranes, so it produces the toxicity on cell membrane, which limits its clinical dose. However, the interaction between AmB and cholesterol-rich membrane is unclear now. The phase state of the membrane and the metal cation outside cell membrane may affect the interaction between AmB and the membrane. In this work, the effects of amphotericin B on the mean molecular area, elastic modulus and stability of mammalian cell membrane rich in cholesterol in the presence of Ca²⁺ ions were studied using DPPC/Chol mixed Langmuir monolayer as a model. The Langmuir-Blodgett method and AFM test were used to study the effects of this drug on the morphology and height of cholesterol-rich phospholipid membrane in the presence of Ca²⁺ ions. The influence of calcium ions on the mean molecular area and the limiting molecular area was similar in LE phase and in LC phase. The calcium ions made the monolayer more condensed. However, calcium ions can weaken the shortening effect of AmB on the relaxation time of the DPPC/Chol mixed monolayer in LE phase but enhance it in LC phase. Interestingly, calcium ions caused a LE-LC coexistence phase to occur in the DPPC/Chol/AmB mixed monolayers at 35mN/m, which was confirmed by atomic force microscopy. The results can help to understand the interaction between amphotericin B and cell membrane rich in cholesterol in the calcium ions environment.

Interactions of Bacterial Quorum Sensing Signals with Model Lipid Membranes: Influence of Membrane Composition on Membrane Remodeling

We report the influence of membrane composition on the multiscale remodeling of multicomponent lipid bilayers initiated by contact with the amphiphilic bacterial quorum sensing signal N-(3-oxo)-dodecanoyl-l-homoserine lactone (3-oxo-C12-AHL) and its anionic headgroup hydrolysis product, 3-oxo-C12-HS. We used fluorescence microscopy and quartz crystal microbalance with dissipation (QCM-D) to characterize membrane reformation that occurs when these amphiphiles are placed in contact with supported lipid bilayers (SLBs) composed of (i) 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) containing varying amounts of cholesterol or (ii) mixtures of DOPC and either 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE, a conical zwitterionic lipid) or 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS, a model anionic lipid). In general, we observe these mixed-lipid membranes to undergo remodeling events, including the formation and subsequent collapse of long tubules and the formation of hemispherical caps, upon introduction to biologically relevant concentrations of 3-oxo-C12-AHL and 3-oxo-C12-HS in ways that differ substantially from those observed in single-component DOPC membranes. These differences in bilayer reformation and their associated dynamics can be understood in terms of the influence of membrane composition on the time scales of molecular flip-flop, lipid packing defects, and lipid phase segregation in these materials. The lipid components investigated here are representative of classes of lipids that comprise both naturally occurring cell membranes and many useful synthetic soft materials. These studies thus represent a first step toward understanding the ways in which membrane composition can impact interactions with this important class of bacterial signaling molecules.

Clarification of the Mechanism of Inhibiting the Maillard Reaction between Phosphatidylethanolamine and Sugars by Adding Fatty Acid Calcium Salts

Lecithin is known to undergo heat induced deterioration by the Maillard reaction between 1 mol of any sugar, except 2-deoxy sugar, and 2 mol of phosphatidylethanolamine (PE). However, we have previously reported that adding fatty acid metal salts can inhibit heat deterioration of soybean lecithin (SL). To clarify the mechanism of inhibition, 1,2-di-O-stearoyl-sn-glycero-3-phosphatidylethanolamine (DSPE), d-glucose, and calcium stearate or calcium decanoate were heated in octane. When DSPE and d-glucose with calcium stearate or calcium decanoate were heated in the octane, the heat deterioration of DSPE was significantly inhibited, and no increase in UV absorption at 350 nm was observed. From these reactant solutions, one compound having a phosphate group and no primary amine was isolated, and NMR spectra confirmed that two molar of stearic acid derived from DSPE were coordinated to the amino group and phosphate group of DSPE. Therefore, we concluded that adding fatty acid metal salts reduced the nucleophilic reactivity of the amino group of PE and inhibited the Maillard reaction with sugars because two molar of fatty acid derived from PE coordinated to the amino group and phosphate group of PE.

The role of ion-lipid interactions and lipid packing in transient defects caused by phenolic compounds

The transient disruption of membranes for the passive permeation of ions or small molecules is a complex process relevant to understanding physiological processes and biotechnology applications. Phenolic compounds are widely studied for their antioxidant and antimicrobial properties, and some of these activities are based on the interactions of the phenolic compound with membranes. Ions are ubiquitous in cells and are known to alter the structure of phospholipid bilayers. Yet, ion-lipid interactions are usually ignored when studying the membrane-altering properties of phenolic compounds. This study aims to assess the role of Ca2+ ions on the membrane-disrupting activity of two phenolic acids and to highlight the role of local changes in lipid packing in forming transient defects or pores. Results from tethered bilayer lipid membrane electrical impedance spectroscopy experiments showed that Ca2+ significantly reduces membrane disruption by caffeic acid methyl ester and caffeic acid. As phenolic acids are known metal chelators, we used UV-vis and fluorescence spectroscopy to exclude the possibility that Ca2+ interferes with membrane disruption by binding to the phenolic compound and subsequently preventing membrane binding. Molecular dynamics simulations showed that Ca2+ but not caffeic acid methyl ester or caffeic acid increases lipid packing in POPC bilayers. The combined data confirm that Ca2+ reduces the membrane-disrupting activity of the phenolic compounds, and that Ca2+-induced changes to lipid packing govern this effect. We discuss our data in the context of ion-induced pores and transient defects and how lipid packing affects membrane disruption by small molecules.

A Comparative Study of Quercetin-Loaded Nanocochleates and Liposomes: Formulation, Characterization, Assessment of Degradation and In Vitro Anticancer Potential

Quercetin, a flavonoid, has antioxidant and anti-inflammatory properties and the potential to inhibit the proliferation of cancer, but its therapeutic efficacy is lowered due to poor solubility and bioavailability. Quercetin-loaded nanocochleates (QN) were developed using a trapping method by the addition of calcium ions into preformed negatively charged liposomes (QL) prepared by a thin-film hydration method. Liposomes were optimized by varying the concentration of Dimyristoyl phosphatidyl glycerol and quercetin by applying D-optimal factorial design using Design-Expert^® software. Stable rods were observed using TEM with an average particle size, zeta potential and encapsulation efficiency of 502 nm, −18.52 mV and 88.62%, respectively, for QN which were developed from spherical QL showing 111.06 nm, −40.33 mV and 74.2%, respectively. In vitro release of quercetin from QN and QL was extended to 24 h. Poor bioavailability of quercetin is due to its degradation in the liver, so to mimic in vivo conditions, the degradation of quercetin released from QL and QN was studied in the presence of rat liver homogenate (S9G) and results revealed that QN, due to its unique structure, i.e., series of rolled up solid layers, shielded quercetin from the external environment and protected it. The safety and biocompatibility of QL and QN were provenby performing cytotoxicity studies on fibroblast L929 cell lines. QN showed superior anticancer activity compared to QL, as seen for human mouth cancerKB cell lines. Stability studies proved that nanocochleates were more stable than liposomal formulations. Thus, nanocochleates might serve as pharmaceutical nanocarriers for the improved efficacy of drugs with low aqueous solubility, poor bioavailability, poor targeting ability and stability.

Dynamic Reconfiguration of Subcompartment Architectures in Artificial Cells

Artificial cells are minimal structures constructed from biomolecular building blocks designed to mimic cellular processes, behaviors, and architectures. One near-ubiquitous feature of cellular life is the spatial organization of internal content. We know from biology that organization of content (including in membrane-bound organelles) is linked to cellular functions and that this feature is dynamic: the presence, location, and degree of compartmentalization changes over time. Vesicle-based artificial cells, however, are not currently able to mimic this fundamental cellular property. Here, we describe an artificial cell design strategy that addresses this technological bottleneck. We create a series of artificial cell architectures which possess multicompartment assemblies localized either on the inner or on the outer surface of the artificial cell membrane. Exploiting liquid-liquid phase separation, we can also engineer spatially segregated regions of condensed subcompartments attached to the cell surface, aligning with coexisting membrane domains. These structures can sense changes in environmental conditions and respond by reversibly transitioning from condensed multicompartment layers on the membrane surface to a dispersed state in the cell lumen, mimicking the dynamic compartmentalization found in biological cells. Likewise, we engineer exosome-like subcompartments that can be released to the environment. We can achieve this by using two types of triggers: chemical (addition of salts) and mechanical (by pulling membrane tethers using optical traps). These approaches allow us to control the compartmentalization state of artificial cells on population and single-cell levels.

3,4,5-Trimethoxybenzoate of Catechin, an Anticarcinogenic Semisynthetic Catechin, Modulates the Physical Properties of Anionic Phospholipid Membranes

3,4,5-Trimethoxybenzoate of catechin (TMBC) is a semisynthetic catechin which shows strong antiproliferative activity against malignant melanoma cells. The amphiphilic nature of the molecule suggests that the membrane could be a potential site of action, hence the study of its interaction with lipid bilayers is mandatory in order to gain information on the effect of the catechin on the membrane properties and dynamics. Anionic phospholipids, though being minor components of the membrane, possess singular physical and biochemical properties that make them physiologically essential. Utilizing phosphatidylserine biomimetic membranes, we study the interaction between the catechin and anionic bilayers, bringing together a variety of experimental techniques and molecular dynamics simulation. The experimental data suggest that the molecule is embedded into the phosphatidylserine bilayers, where it perturbs the thermotropic gel to liquid crystalline phase transition. In the gel phase, the catechin promotes the formation of interdigitation, and in the liquid crystalline phase, it decreases the bilayer thickness and increases the hydrogen bonding pattern of the interfacial region of the bilayer. The simulation data agree with the experimental ones and indicate that the molecule is located in the interior of the anionic bilayer as monomer and small clusters reaching the carbonyl region of the phospholipid, where it also disturbs the intermolecular hydrogen bonding between neighboring lipids. Our observations suggest that the catechin incorporates well into phosphatidylserine bilayers, where it produces structural changes that could affect the functioning of the membrane.

Lipid headgroup and side chain architecture determine manganese-induced dose dependent membrane rigidification and liposome size increase

Metal ion-membrane interactions have gained appreciable attention over the years resulting in increasing investigations into the mode of action of toxic and essential metals. More work has focused on essential ions like Ca or Mg and toxic metals like Cd and Pb, whereas this study investigates the effects of the abundant essential trace metal manganese with model lipid systems by screening zwitterionic and anionic glycerophospholipids. Despite its essentiality, deleterious impact towards cell survival is known under Mn stress. The fluorescent dyes Laurdan and diphenylhexatriene were used to assess changes in membrane fluidity both in the head group and hydrophobic core region of the membrane, respectively. Mn-rigidified membranes composed of the anionic phospholipids, phosphatidic acid, phosphatidylglycerol, cardiolipin, and phosphatidylserine. Strong binding resulted in large shifts of the phase transition temperature. The increase was in the order phosphatidylserine > phosphatidylglycerol > cardiolipin, and in all cases, saturated analogues > mono-unsaturated forms. Dynamic light scattering measurements revealed that Mn caused extensive aggregation of liposomes composed of saturated analogues of phosphatidic acid and phosphatidylserine, whilst the mono-unsaturated analogue had significant membrane swelling. Increased membrane rigidity may interfere with permeability of ions and small molecules, possibly disrupting cellular homeostasis. Moreover, liposome size changes could indicate fusion, which could also be detrimental to cellular transport. Overall, this study provided further understanding into the effects of Mn with biomembranes, whereby the altered membrane properties are consequential to the proper structural and signalling functions of membrane lipids.

Effect of Ionic Strength on Ibuprofenate Adsorption on a Lipid Bilayer of Dipalmitoylphosphatidylcholine from Molecular Dynamics Simulations

In this work, the free energy change in the process of transferring ibuprofenate from the bulk solution to the center of a model of the dipalmitoylphosphatidylcholine bilayer at different NaCl concentrations was calculated. Two minima were found in the free energy profile: a local minimum, located in the vicinity of the membrane, and the global free energy minimum, found near the headgroup region. The downward shift of free energy minima with increasing NaCl concentration is consistent with the results of previous works. Conversely, the upward shift of the free energy maximum with increasing ionic strength is due to the competition of sodium ions and lipids molecules to coordinate with ibuprofenate and neutralize its charge. In addition, normal molecular dynamics simulations were performed to study the effects of the ibuprofenate on the lipid bilayer and in the presence of a high ibuprofenate concentration. The effect of ionic strength on the properties of the lipid bilayer and on lipid-drug interactions was analyzed. The area per lipid shrinking with increasing ionic strength, volume of lipids, and thickness of the bilayer is consistent with the experimental results. At a very high ibuprofenate concentration, the lipid bilayer dehydrates, and it consequently transforms into the gel phase, thus blocking the permeation.

Structural transition of reverse cylindrical micelles to reverse vesicles by mixtures of lecithin and inorganic salts

HYPOTHESIS

The transformation from reverse micelles to reverse vesicles is influenced by electrostatic interactions between lecithin headgroups and inorganic salts. The electrostatic interactions are expected to influence molecular geometry of lecithin, resulting in a reduction in critical packing parameter (p). Hence, it should be possible to drive structural transitions of reverse self-assembled structures by addition of inorganic salts to lecithin solutions.

EXPERIMENTS

Structural transitions of reverse micelles and reverse vesicles were formulated including lecithin and inorganic salts as a function of concentration in cyclohexane. A systematic study was performed using inorganic salts with the different valences of the cations such as Li⁺, Ca²⁺, and La³⁺. To probe the nanodomain structures from the lecithin/salt mixtures, small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used.

FINDINGS

Adding salts to lecithin solutions induced the systematic transformation of reverse self-assembled structures from reverse spherical micelles to reverse cylindrical micelles and finally to reverse vesicles. The transformation was also correlated with interactions between lecithin headgroups and salts, that is, Li⁺ < Ca²⁺ < La³⁺. In addition, a water-soluble dye such as rhodamine B (RB) can be readily encapsulated into reverse micelles and vesicles, indicating that they are potentially useful for controlled solute delivery.

Calcium ion effect on phospholipid bilayers as cell membrane analogues

Ion attachment can modify stability and structure of phospholipid bilayers. Of particular importance is the interaction of phospholipids with divalent cations, such as calcium ions playing an important role in numerous cellular processes. The aim of our study was to determine effects of calcium ions on phospholipid membranes employing two cell membrane analogues, liposomes and planar lipid bilayers, and for the first time the combination of two instrumental setups: gas-phase electrophoresis (nES GEMMA instrumentation) and electrical (capacitance and resistance) measurements. Liposomes and planar lipid bilayers consisted of phosphatidylcholine, cholesterol and phosphatidylethanolamine. Liposomes were prepared from dried lipid films via hydration while planar lipid bilayers were formed using a Mueller-Rudin method. Calcium ions were added to membranes from higher concentrated stock solutions. Changes in phospholipid bilayer properties due to calcium presence were observed for both studied cell membrane analogues. Changes in liposome size were observed, which might either be related to tighter packing of phospholipids in the bilayer or local distortions of the membrane. Likewise, a measurable change in planar lipid bilayer resistance and capacitance was observed in the presence of calcium ions, which can be due to an increased rigidity and tighter packing of the lipid molecules in the bilayer.

Arabidopsis annexin 5 is involved in maintenance of pollen membrane integrity and permeability

In Arabidopsis, a dry stigma surface enables a gradual hydration of pollen grains by a controlled release of water. Occasionally the grains may be exposed to extreme precipitations that cause rapid water influx and swelling, eventually leading to pollen membrane rupture. In metazoans, calcium- and phospholipid-binding proteins, referred to as annexins, participate in the repair of plasma membrane damages. It remains unclear, however, how this process is conducted in plants. Here, we examined whether plant annexin 5 (ANN5), the most abundant member of the annexin family in pollen, is involved in the restoration of pollen membrane integrity. We analyzed the cellular dynamics of ANN5 in pollen grains undergoing hydration in favorable or stress conditions. We observed a transient association of ANN5 with the pollen membrane during in vitro hydration that did not occur in the pollen grains being hydrated on the stigma. To simulate a rainfall, we performed spraying of the pollinated stigma with deionized water that induced ANN5 accumulation at the pollen membrane. Interestingly, calcium or magnesium application affected pollen membrane properties differently, causing rupture or shrinkage of pollen membrane, respectively. Both treatments, however, induced ANN5 recruitment to the pollen membrane. Our data suggest a model in which ANN5 is involved in the maintenance of membrane integrity in pollen grains exposed to osmotic or ionic imbalances.

Biophysical impact of sphingosine and other abnormal lipid accumulation in Niemann-Pick disease type C cell models

Niemann-Pick disease type C (NPC) is a complex and rare pathology, which is mainly associated to mutations in the NPC1 gene. This disease is phenotypically characterized by the abnormal accumulation of multiple lipid species in the acidic compartments of the cell. Due to the complexity of stored material, a clear molecular mechanism explaining NPC pathophysiology is still not established. Abnormal sphingosine accumulation was suggested as the primary factor involved in the development of NPC, followed by the accumulation of other lipid species. To provide additional mechanistic insight into the role of sphingosine in NPC development, fluorescence spectroscopy and microscopy were used to study the biophysical properties of biological membranes using different cellular models of NPC. Addition of sphingosine to healthy CHO-K1 cells, in conditions where other lipid species are not yet accumulated, caused a rapid decrease in plasma membrane and lysosome membrane fluidity, suggesting a direct effect of sphingosine rather than a downstream event. Changes in membrane fluidity caused by addition of sphingosine were partially sustained upon impaired trafficking and metabolization of cholesterol in these cells, and could recapitulate the decrease in membrane fluidity observed in NPC1 null Chinese Hamster Ovary (CHO) cells (CHO-M12) and in cells with pharmacologically induced NPC phenotype (treated with U18666A). In summary, these results show for the first time that the fluidity of the membranes is altered in models of NPC and that these changes are in part caused by sphingosine, supporting the role of this lipid in the pathophysiology of NPC.

Mass Transfer Behavior During Osmotic Dehydration and Vacuum Impregnation of “Phulae” Pineapple and the Effects on Dried Fruit Quality

The influence of osmotic dehydration (OD) in combination with vacuum impregnation (VI) technique on the mass transfer behavior of “Phulae” pineapple was investigated. Pineapple slices of 10 mm thick were immersed in sucrose solution at concentrations of 55 and 65oBrix under atmospheric pressure or vacuum pressures at 250 mmHg (VOD-250) and 450 mmHg (VOD-450). The results deduced that 65o Brix of sucrose solution for 300 min and the vacuum pressure of VI at 450 mmHg were necessitated to increase solute uptake to 14.79 g/100 g when compared to other treatments. Surprisingly, the effect of OD and VI on water loss was not much different. Scanning electron microscope (SEM) showed that the pore sizes of pineapple slices were decreased when the impregnation period increased implying the higher adsorption of sucrose into the fruit structure. Subsequently, calcium lactate (Ca-L) at 2, 4 and 6% (w/w) was incorporated in sucrose solution prior to drying at 60oC in a conventional hot air dryer. It was observed that increasing concentration of Ca-L led to a significant decrease in moisture content (17.74 to 15.53%) and water activity (0.58 to 0.56) whereas calcium content was increased (24.472 to 676.317 mg/100g). However, it should be noted that high concentration of Ca-L had adverse effect on sensory property where overall actability decreased from 7.09 to 5.65 as well as total phenolic content (TPC) (17.74 to 15.53 gGAE/100g), DPPH (223.51 to 159.7 µmol Trolox/100g) and FRAP (380.65 to 291.57 µmol ascorbic acid/100g) values.

Induced fusion and aggregation of bacterial outer membrane vesicles: Experimental and theoretical analysis

Recombinantly engineered bacterial outer membrane vesicles (OMVs) are promising vaccine delivery vehicles. The diversity of exogenous antigens delivered by OMVs can be enhanced by induced fusion of OMV populations. To date there are no reports of induced fusion of bacterial OMVs. Here we measure the pH and salt-induced aggregation and fusion of OMVs and analyze the processes against the Derjaguin-Landau-Verwey-Overbeek (DLVO) colloidal stability model. Vesicle aggregation and fusion kinetics were investigated for OMVs isolated from native E. coli (Nissle 1917) and lipopolysaccharide (LPS) modified E. coli (ClearColi) strains to evaluate the effect of lipid type on vesicle aggregation and fusion. Electrolytes and low pHs induced OMV aggregation for both native and modified LPS constructs, approaching a calculated fusion efficiency of ~25% (i.e. ~1/4 of collision events lead to fusion). However, high fusion efficiency was achieved for Nissle OMVs solely with decreased pH as opposed to a combination of low pH and increased divalent counterion concentration for ClearColi OMVs. The lipid composition of the OMVs from Nissle negatively impacted fusion in the presence of electrolytes, causing higher deviations from DLVO-predicted critical coagulation concentrations with monovalent counterions. The outcome of the work is a defined set of conditions under which investigators can induce OMVs to fuse and make various combinations of vesicle compositions.

Generation of interconnected vesicles in a liposomal cell model

We introduce an experimental method based upon a glass micropipette microinjection technique for generating a multitude of interconnected vesicles (IVs) in the interior of a single giant unilamellar phospholipid vesicle (GUV) serving as a cell model system. The GUV membrane, consisting of a mixture of soybean polar lipid extract and anionic phosphatidylserine, is adhered to a multilamellar lipid vesicle that functions as a lipid reservoir. Continuous IV formation was achieved by bringing a micropipette in direct contact with the outer GUV surface and subjecting it to a localized stream of a Ca²⁺ solution from the micropipette tip. IVs are rapidly and sequentially generated and inserted into the GUV interior and encapsulate portions of the micropipette fluid content. The IVs remain connected to the GUV membrane and are interlinked by short lipid nanotubes and resemble beads on a string. The vesicle chain-growth from the GUV membrane is maintained for as long as there is the supply of membrane material and Ca²⁺ solution, and the size of the individual IVs is controlled by the diameter of the micropipette tip. We also demonstrate that the IVs can be co-loaded with high concentrations of neurotransmitter and protein molecules and displaying a steep calcium ion concentration gradient across the membrane. These characteristics are analogous to native secretory vesicles and could, therefore, serve as a model system for studying secretory mechanisms in biological systems.

Functionally engineered 'hepato-liposomes': Combating liver-stage malaria in a single prophylactic dose

Primaquine continues to remain the gold standard molecule with an incumbent toxicity profile, as far as radical treatment of malaria is concerned. Better molecules are available at experimental level but their targeted delivery is a challenge. The present work identifies 'Decoquinate (DQN)' as a repurposed, safer drug molecule with a potential to function as an appealing replacement for primaquine active against liver-stage malaria. The work focuses on delivering the highly lipophilic DQN (log P ~ 5) in a liposomal carrier system to 'sporozoite infested hepatocytes' using two different in-house synthesized hepatotropic ligands. Functionally engineered 'hepato-liposomes' exhibit differences in their DQN loading capacities but no significant change in morphology or particle size and are also not affected by freeze drying. Two ligands, targeting different receptors on hepatocytes, have been compared for their in vitro and in vivo drug delivery efficiency in liver stage malaria. The studies reveal superior antimalarial efficacy of differently designed DQN loaded liposomes and demonstrate antimalarial efficacy at a low dose of 0.5 mg/kg for a repurposed molecule like DQN. The in vivo studies successfully discriminate the functional efficiency of the carriers and establish the importance of design in liposomal drug delivery for malarial prophylaxis.

Correlations between temperature-dependent rheology and electrostatic interactions in reverse wormlike micelles induced by inorganic salts

Previous studies have shown that the plateau modulus G_p of the wormlike micelles formed in water driven by hydrophobic interactions is a constant upon heating, similar to polymer solutions, and G_p of the reverse worms formed in oils driven by hydrogen bonding decreases with increasing temperature. In this work, we investigated the reverse worms induced by three chloride salts that bind lecithin through different strengths of electrostatic interactions, in the order of LaCl₃ > CaCl₂ > LiCl. We correlated the interaction strengths with the temperature-dependent rheological properties and found that upon heating, G_p for all the reverse worms driven by electrostatic interactions decays slower than that driven by the weak temperature-sensitive hydrogen bonding. Furthermore, the decay rates of G_p follow an order in the inverse relation to the interaction strength, LaCl₃≤ CaCl₂ < LiCl, indicating that the dependence of G_p on temperature can reflect the strength of the driving forces for micellization. We utilized Fourier transform infrared spectroscopy (FTIR) to confirm the weakening of the interaction and the small angle X-ray scattering (SAXS) technique to reveal the decrease in the lengths of the reverse worms as temperature increases, both of which echo the changes in the rheological properties.

Graphene-based sensing of oxygen transport through pulmonary membranes

Lipid-protein complexes are the basis of pulmonary surfactants covering the respiratory surface and mediating gas exchange in lungs. Cardiolipin is a mitochondrial lipid overexpressed in mammalian lungs infected by bacterial pneumonia. In addition, increased oxygen supply (hyperoxia) is a pathological factor also critical in bacterial pneumonia. In this paper we fabricate a micrometer-size graphene-based sensor to measure oxygen permeation through pulmonary membranes. Combining oxygen sensing, X-ray scattering, and Atomic Force Microscopy, we show that mammalian pulmonary membranes suffer a structural transformation induced by cardiolipin. We observe that cardiolipin promotes the formation of periodic protein-free inter-membrane contacts with rhombohedral symmetry. Membrane contacts, or stalks, promote a significant increase in oxygen gas permeation which may bear significance for alveoli gas exchange imbalance in pneumonia.

Transient domains of ordered water induced by divalent ions lead to lipid membrane curvature fluctuations

Cell membranes are composed of a hydrated lipid bilayer that is molecularly complex and diverse, and the link between molecular hydration structure and membrane macroscopic properties is not well understood, due to a lack of technology that can probe and relate molecular level hydration information to micro- and macroscopic properties. Here, we demonstrate a direct link between lipid hydration structure and macroscopic dynamic curvature fluctuations. Using high-throughput wide-field second harmonic (SH) microscopy, we observe the formation of transient domains of ordered water at the interface of freestanding lipid membranes. These domains are induced by the binding of divalent ions and their structure is ion specific. Using nonlinear optical theory, we convert the spatiotemporal SH intensity into maps of membrane potential, surface charge density, and binding free energy. Using an electromechanical theory of membrane bending, we show that transient electric field gradients across the membrane induce spatiotemporal membrane curvature fluctuations.

Hepatitis C Virus p7 Induces Membrane Permeabilization by Interacting with Phosphatidylserine

Hepatitis C virus (HCV) p7 is known to be a nonselective cation channel for HCV maturation. Because the interaction of HCV proteins with host lipids in the endoplasmic reticulum membrane is crucial for the budding process, the identification of p7–lipid interactions could be important for understanding the HCV life cycle. Here, we report that p7 interacts with phosphatidylserine (PS) to induce membrane permeabilization. The interaction of p7 with PS was not inhibited by Gd³⁺ ions, which have been known to interact with negatively charged lipids, but channel activity and p7-induced mitochondrial depolarization were inhibited by Gd³⁺ ions. From the present results, we suggest that the p7–PS interaction plays an essential role in regulating its ion channel function and could be a potential molecular target for anti-HCV therapy.

Rapid functionalisation and detection of viruses via a novel Ca2+-mediated virus-DNA interaction

Current virus detection methods often take significant time or can be limited in sensitivity and specificity. The increasing frequency and magnitude of viral outbreaks in recent decades has resulted in an urgent need for diagnostic methods that are facile, sensitive, rapid and inexpensive. Here, we describe and characterise a novel, calcium-mediated interaction of the surface of enveloped viruses with DNA, that can be used for the functionalisation of intact virus particles via chemical groups attached to the DNA. Using DNA modified with fluorophores, we have demonstrated the rapid and sensitive labelling and detection of influenza and other viruses using single-particle tracking and particle-size determination. With this method, we have detected clinical isolates of influenza in just one minute, significantly faster than existing rapid diagnostic tests. This powerful technique is easily extendable to a wide range of other enveloped pathogenic viruses and holds significant promise as a future diagnostic tool.

Structure and Interactions between Charged Lipid Membranes in the Presence of Multivalent Ions

When aqueous salt solutions contain multivalent ions (like Ca²⁺ or Mg²⁺), strong correlation effects may lead to ion-bridging, net attraction, and tight-coupling between like-charged interfaces. To examine the effects of surface charge density, temperature, salt type, and salt concentration on the structures of tightly coupled charged interfaces, we have used mixed lipid membranes, containing either saturated or unsaturated tails in the presence of multivalent ions. We discovered that tightly coupled membrane lamellar phases, dominated by attractive interactions, coexisted with weakly coupled lamellar phases, dominated by repulsive interactions. To control the membrane charge density, we mixed lipids with negatively charged headgroups, DLPS and DOPS, with their zwitterionic analogue having the same tails, DLPC and DOPC, respectively. Using solution X-ray scattering we measured the lamellar repeat distance, D, at different ion concentrations, temperatures, and membrane charge densities. The multivalent ions tightly coupled the mixed lipid bilayers whose charged lipid molar fraction was between 0.1 and 1. The repeat distance of the tightly coupled phase was about 4 nm for the DLPS/DLPC mixtures and about 5 nm for the DOPS/DOPC mixtures. In this phase, the repeat distance slightly increased with increasing temperature and decreased with increasing charge density. When the molar fraction of charged lipid was 0.1 or 0.25, a less tightly coupled phase coexisted with the tightly coupled phase. The weakly coupled lamellar phase had significantly larger D values, although they were consistently shorter than the D values in monovalent salt solutions with similar screening lengths.

Conformation of Single and Interacting Lipopolysaccharide Surfaces Bearing O-Side Chains

The outer surfaces of Gram-negative bacteria are composed of lipopolysaccharide (LPS) molecules exposing oligo- and polysaccharides to the aqueous environment. This unique, structurally complex biological interface is of great scientific interest as it mediates the interaction of bacteria with antimicrobial agents as well as with neighboring bacteria in colonies and biofilms. Structural studies on LPS surfaces, however, have so far dealt almost exclusively with rough mutant LPS of reduced molecular complexity and limited biological relevance. Here, by using neutron reflectometry, we structurally characterize planar monolayers of wild-type LPS from Escherichia coli O55:B5 featuring strain-specific O-side chains in the presence and absence of divalent cations and under controlled interaction conditions. The model used for the reflectivity analysis is self-consistent and based on the volume fraction profiles of all chemical components. The saccharide profiles are found to be bimodal, with dense inner oligosaccharides and more dilute, extended O-side chains. For interacting LPS monolayers, we establish the pressure-distance curve and determine the distance-dependent saccharide conformation.

Calcium-Induced Lipid Nanocluster Structures: Sculpturing of the Plasma Membrane

The plasma membrane of the cell is a complex, tightly regulated, heterogeneous environment shaped by proteins, lipids, and small molecules. Ca²⁺ ions are important cellular messengers, spatially separated from anionic lipids. After cell injury, disease, or apoptotic events, anionic lipids are externalized to the outer leaflet of the plasma membrane and encounter Ca²⁺, resulting in dramatic changes in the plasma membrane structure and initiation of signaling cascades. Despite the high chemical and biological significance, the structures of lipid-Ca²⁺ nanoclusters are still not known. Previously, we demonstrated by solid-state nuclear magnetic resonance (NMR) spectroscopy that upon binding to Ca²⁺, individual phosphatidylserine lipids populate two distinct yet-to-be-characterized structural environments. Here, we concurrently employ extensive all-atom molecular dynamics (MD) simulations with our accelerated membrane mimetic and detailed NMR measurements to identify lipid-Ca²⁺ nanocluster conformations. We find that major structural characteristics of these nanoclusters, including interlipid pair distances and chemical shifts, agree with observable NMR parameters. Simulations reveal that lipid-ion nanoclusters are shaped by two characteristic, long-lived lipid structures induced by divalent Ca²⁺. Using ab initio quantum mechanical calculations of chemical shifts on MD-captured lipid-ion complexes, we show that computationally observed conformations are validated by experimental NMR data. Both NMR measurements of diluted specifically labeled lipids and MD simulations reveal that the basic structural unit that reshapes the membrane is a Ca²⁺-coordinated phosphatidylserine tetramer. Our combined computational and experimental approach presented here can be applied to other complex systems in which charged membrane-active molecular agents leave structural signatures on lipids.

Do carnitine and extra trace elements change stability of paediatric parenteral nutrition admixtures?

INTRODUCTION

High concentrations of trace elements (TE), in particular zinc and selenium, along with carnitine, are often added to parenteral admixtures in paediatric patients on long-term Parenteral Nutrition (PN). We aim to evaluate whether lipid droplet diameters of these admixtures maintain the recommended range of 0.4-1.0 μm.

MATERIALS AND METHODS

Stability studies were carried out on six parenteral admixtures with carnitine, trace elements and electrolytes added in different amounts. Each admixture was formulated with five different lipid emulsions with or without fish oil. Analyses were performed at time 0 (t = 0) and 24, 48, 72, 96 (t = 96) hours after compounding. Droplet diameters were determined by Light Scattering-Reverse Fourier Optics Technique. Samples, stored at 4 °C, were triple tested for a total of 450 analyses. Regression analyses were performed using panel-data techniques.

RESULTS

During the 4 days, lipid droplet diameters were in the expected range of 0.4-1.0 μm regardless of trace element and carnitine amounts in all admixtures apart from those containing fish-oil based emulsions and calcium concentrations equal to 4.5 mmol/L. In these latter admixtures, 12% of droplet diameters were larger than 1.0 μm and 2% exceeded 5.0 μm immediately after compounding.

CONCLUSION

Carnitine and high concentrations of trace elements do not affect PN admixtures stability and can be safely infused in long-term home-PN paediatric patients and prematures. Only high calcium concentrations in compresence with fish oil based lipid emulsions seem to change PN stability.

Cationic interaction with phosphatidylcholine in a lipid cubic phase studied with electrochemical impedance spectroscopy and small angle X-ray scattering

HYPOTHESIS

Electrochemical Impedance Spectroscopy (EIS) can be used to investigate cationic interaction with the choline headgroup in the ternary system of monoolein/dioleoylphosphatidylcholine/water (MO/DOPC/H₂O).

EXPERIMENTS

EIS was used to estimate the resistance and capacitance of a freestanding membrane of a lipid cubic phase (LCP). The membrane was formed in a small cylindrical aperture separating two compartments, containing one Pt electrode each. The impedance experiments were carried out in a two electrode setup with electrolyte solutions made of KCl, CsCl, MgCl₂ and CaCl₂ filling the compartments at two different ionic strength. Small angle X-ray diffraction (SAXRD) was used to establish the structure and cell unit parameters of the LCP.

FINDINGS

The interpretation of ionic interaction with phosphatidylcholine was based on estimated membrane resistances and capacitances from EIS measurements. The magnitude of cationic interaction with the lipid headgroup in the water channels is correlated to the membrane resistance that increases in the order Cs⁺ < K⁺ < Mg²⁺ < Ca²⁺ following the Hofmeister direct series and also reflecting the order of intrinsic binding constants. The membrane capacitance and SAXRD results are discussed as an effect of cationic interaction and it was possible to observe both swelling and condensing effects. The stability of the cubic phase throughout the experiments was confirmed by SAXRD.

Physiological Calcium Concentrations Slow Dynamics at the Lipid-Water Interface

Phospholipids can interact strongly with ions at physiological concentrations, and these interactions can alter membrane properties. Here, we describe the effects of calcium ions on the dynamics in phospholipid membranes. We used a combination of time-resolved ultrafast two-dimensional infrared spectroscopy and molecular dynamics simulations. We found that millimolar Ca²⁺ concentrations lead to slower fluctuations in the local environment at the lipid-water interface of membranes with phosphatidylserine. The effect was only observed in bilayers containing anionic phosphatidylserine; membranes composed of only zwitterionic phosphatidylcholine did not experience a slowdown. Local water dynamics were measured using the ester groups as label-free probes and were found to be up to 50% slower with 2.5 mM Ca²⁺. Molecular dynamics simulations show that Ca²⁺ primarily binds to the carboxylate group of phosphatidylserines. These findings have implications for apoptotic and diseased cells in which phosphatidylserine is exposed to extracellular calcium and for the biophysical effects of divalent cations on lipid bilayers.

Membrane Remodeling of Giant Vesicles in Response to Localized Calcium Ion Gradients

In a wide variety of fundamental cell processes, such as membrane trafficking and apoptosis, cell membrane shape transitions occur concurrently with local variations in calcium ion concentration. The main molecular components involved in these processes have been identified; however, the specific interplay between calcium ion gradients and the lipids within the cell membrane is far less known, mainly due to the complex nature of biological cells and the difficultly of observation schemes. To bridge this gap, a synthetic approach is successfully implemented to reveal the localized effect of calcium ions on cell membrane mimics. Establishing a mimic to resemble the conditions within a cell is a severalfold problem. First, an adequate biomimetic model with appropriate dimensions and membrane composition is required to capture the physical properties of cells. Second, a micromanipulation setup is needed to deliver a small amount of calcium ions to a particular membrane location. Finally, an observation scheme is required to detect and record the response of the lipid membrane to the external stimulation. This article offers a detailed biomimetic approach for studying the calcium ion-membrane interaction, where a lipid vesicle system, consisting of a giant unilamellar vesicle (GUV) connected to a multilamellar vesicle (MLV), is exposed to a localized calcium gradient formed using a microinjection system. The dynamics of the ionic influence on the membrane were observed using fluorescence microscopy and recorded at video frame rates. As a result of the membrane stimulation, highly curved membrane tubular protrusions (MTPs) formed inside the GUV, oriented away from the membrane. The described approach induces the remodeling of the lipid membrane and MTP production in an entirely contactless and controlled manner. This approach introduces a means to address the details of calcium ion-membrane interactions, providing new avenues to study the mechanisms of cell membrane reshaping.

Structure of Lung-Mimetic Multilamellar Bodies with Lipid Compositions Relevant in Pneumonia

The hierarchical assembly of lipids, as modulated by composition and environment, plays a significant role in the function of biological membranes and a myriad of diseases. Elevated concentrations of calcium ions and cardiolipin (CL), an anionic tetra-alkyl lipid found in mitochondria and some bacterial cell membranes, have been implicated in pneumonia recently. However, their impact on the physicochemical properties of lipid assemblies in lungs and how it impairs alveoli function is still unknown. We use small- and wide-angle X-ray scattering (S/WAXS) and solid-state nuclear magnetic resonance (ssNMR) to probe the structure and dynamics of lung-mimetic multilamellar bodies (MLBs) in the presence of Ca²⁺ and CL. We conjecture that CL overexpressed in the hypophase of alveoli strongly affects the structure of lung-lipid bilayers and their stacking in the MLBs. Specifically, S/WAXS data revealed that CL induces significant shrinkage of the water-layer separating the concentric bilayers in multilamellar aggregates. ssNMR measurements indicate that this interbilayer tightening is due to undulation repulsion damping as CL renders the glycerol backbone of the membranes significantly more static. In addition to MLB dehydration, CL promotes intrabilayer phase separation into saturated-rich and unsaturated-rich lipid domains that couple across multiple layers. Expectedly, addition of Ca²⁺ screens the electrostatic repulsion between negatively charged lung membranes. However, when CL is present, addition of Ca²⁺ results in an apparent interbilayer expansion likely due to local structural defects. Combining S/WAXS and ssNMR on systems with compositions pertinent to healthy and unhealthy lung membranes, we propose how alteration of the physiochemical properties of MLBs can critically impact the breathing cycle.

Cu2+-Directed Liposome Membrane Fusion, Positive-Stain Electron Microscopy, and Oxidation

Natural lipid headgroups contain a few types of metal ligands, such as phosphate, amine, and serine, which interact with metal ions differently. Herein, we studied the binding between Cu²⁺ and liposomes with four types of headgroups: phosphocholine (PC), phosphoglycerol (PG), phosphoserine (PS), and cholinephosphate (CP). Using fluorescently headgroup-labeled liposomes, Cu²⁺ strongly quenched the CP and PS liposomes, whereas quenching of PC and PG was weaker. Dynamic light scattering indicated that all of the four liposomes aggregated at high Cu²⁺ concentrations, and ethylenediaminetetraacetic acid (EDTA) only restored the original size of the PC liposome, implying fusion of the other three types of liposomes. The leakage tests revealed that the integrity of PC liposomes was not affected by Cu²⁺, but the other three liposomes leaked. Under TEM, all of the liposomes show a positive-stain feature in the presence of Cu²⁺ and Cu²⁺-stained individual liposomes with a short incubation time (<1 min). The oxidative catalytic property of Cu²⁺ was also tested, and a tight binding by the PS liposome inhibited the activity of Cu²⁺. Finally, a model of interaction for each liposome was proposed, and each one has a different metal-binding and interaction mechanism.

Sensitivity of peripheral membrane proteins to the membrane context: A case study of phosphatidylserine and the TIM proteins

There is a diverse class of peripheral membrane-binding proteins that specifically bind phosphatidylserine (PS), a lipid that signals apoptosis or cell fusion depending on the membrane context of its presentation. PS-receptors are specialized for particular PS-presenting pathways, indicating that they might be sensitive to the membrane context. In this review, we describe a combination of thermodynamic, structural, and computational techniques that can be used to investigate the mechanisms underlying this sensitivity. As an example, we focus on three PS-receptors of the T-cell Immunoglobulin and Mucin containing (TIM) protein family, which we have previously shown to differ in their sensitivity to PS surface density.

Development of novel biotinylated chitosan-decorated docetaxel-loaded nanocochleates for breast cancer targeting

The motive of study was to develop biotinylated chitosan (BI-CHI) decorated docetaxel (DTX) loaded nanocochleates (BI-CHI-DTX-NC) to achieve controlled drug release, improve bioavailability, targeted delivery and enhanced anticancer potency with the reduced systemic toxicity of DTX. The development involved the loading of DTX to nanocochleates (DTX-NC) through conversion of dimyristoylphosphatidylglycerol-sodium (DMPG-Na) and cholesterol bearing liposome on addition of calcium ions, followed by encapsulated DTX-NC with BI-CHI (BI-CHI-DTX- NC) and compared with DTX and DTX-NC. The release of DTX indicated strong pH dependence and implies strong hydrogen-bonding between nanocochleates and DTX. Formulated BI-CHI-DTX-NC demonstrated higher in-vitro anticancer activity in biotin over expressed human breast cancer MCF-7 cells. The targeting effect for the BI-CHI-DTX-NC was also demonstrated. The concentration of the drug needed for growth inhibition of 50% of cells in a designed time period (GI50) was 1.8 μg/ml for free DTX while it was decreased by 33.34% for the DTX-NC (1.2 μg/ml). Furthermore, the GI50 value of BI-CHI-DTX-NC was 0.2 μg/ml, i.e. an 88.89% decrease was observed as compared to DTX solution. Moreover, bioavailability of DTX from BI-CHI-DTX-NC was increased by 10-folds with longer circulation time and slower plasma elimination with low tissue distribution as compared to DTX solution. The results indicate that the BI-CHI-DTX- NC has the potential to be applied for targeting anticancer drug delivery.

Membrane Tubulation in Lipid Vesicles Triggered by the Local Application of Calcium Ions

Experimental and theoretical studies on ion-lipid interactions predict that binding of calcium ions to cell membranes leads to macroscopic mechanical effects and membrane remodeling. Herein, we provide experimental evidence that a point source of Ca²⁺ acting upon a negatively charged membrane generates spontaneous curvature and triggers the formation of tubular protrusions that point away from the ion source. This behavior is rationalized by strong binding of the divalent cations to the surface of the charged bilayer, which effectively neutralizes the surface charge density of outer leaflet of the bilayer. The mismatch in the surface charge density of the two leaflets leads to nonzero spontaneous curvature. We probe this mismatch through the use of molecular dynamics simulations and validate that calcium ion binding to a lipid membrane is sufficient to generate inward spontaneous curvature, bending the membrane. Additionally, we demonstrate that the formed tubular protrusions can be translated along the vesicle surface in a controlled manner by repositioning the site of localized Ca²⁺ exposure. The findings demonstrate lipid membrane remodeling in response to local chemical gradients and offer potential insights into the cell membrane behavior under conditions of varying calcium ion concentrations.

Changes of membrane fatty acids and proteins of Shewanella putrefaciens treated with cinnamon oil and gamma irradiation

BACKGROUND

In order to detect the antimicrobial mechanism of combined treatment of cinnamon oil and gamma irradiation (GI), the membrane fatty acids and proteins characteristics of Shewanella putrefaciens (S. putrefaciens) treated with cinnamon oil and GI, and the distribution of cinnamon oil in S. putrefaciens were observed in this study.

RESULTS

The membrane lipid profile of S. putrefaciens was notably damaged by treatments of cinnamon oil and the combination of cinnamon oil and GI, with significantly fatty acids decrease in C14:0, C16:0, C16:1, C17:1, C18:1 (p < 0.05). The SDS-PAGE result showed that GI did not have obvious effect on membrane proteins (MP), but GI combined with cinnamon oil changed the MP subunits. Cinnamaldehyde, the main component of cinnamon oil, can not transport into S. putrefaciens obviously. It was transformed into cinnamyl alcohol in the nutrient broth with the action of S. putrefaciens. This indicated that the antimicrobial action of cinnamon oil mainly happened on the membrane of S. putrefaciens.

CONCLUSION

Cinnamon oil could act on the membrane of S. putrefaciens with the damage of fatty acids and proteins, and GI would increase the destructive capability of cinnamon oil on the membrane fatty acids and proteins of S. putrefaciens.