Examination of the electrophoretic behavior of liposomes

Rosehip Extract-Loaded Liposomes for Potential Skin Application: Physicochemical Properties of Non- and UV-Irradiated Liposomes

In the present study, rosehip (Rosa canina L.) extract was successfully encapsulated in phospholipid liposomes using a single-step procedure named the proliposome method. Part of the obtained liposomes was subjected to UV irradiation and non-treated (native) and UV-irradiated liposomes were further characterized in terms of encapsulation efficiency, chemical composition (HPLC analysis), antioxidant capacity, particle size, PDI, zeta potential, conductivity, mobility, and antioxidant capacity. Raman spectroscopy as well as DSC analysis were applied to evaluate the influence of UV irradiation on the physicochemical properties of liposomes. The encapsulation efficiency of extract-loaded liposomes was higher than 90%; the average size was 251.5 nm; the zeta potential was -22.4 mV; and the conductivity was found to be 0.007 mS/cm. UV irradiation did not cause a change in the mentioned parameters. In addition, irradiation did not affect the antioxidant potential of the liposome-extract system. Raman spectroscopy indicated that the extract was completely covered by the lipid membrane during liposome entrapment, and the peroxidation process was minimized by the presence of rosehip extract in liposomes. These results may guide the potential application of rosehip extract-loaded liposomes in the food, pharmaceutical, or cosmetic industries, particularly when liposomal sterilization is needed.

Quality Control of Bacterial Extracellular Vesicles with Total Protein Content Assay, Nanoparticles Tracking Analysis, and Capillary Electrophoresis

Extracellular vesicles (EVs) were isolated from Pectobacterium zantedeschiae culturing media using direct ultracentrifugation (UC), iodixanol cushion ultracentrifugation (ICUC), and iodixanol density gradient ultracentrifugation (IDGUC) techniques. The isolates were characterized with total protein content assay (bicinchoninic acid assay, BCA), nanoparticles tracking analysis (NTA), and capillary electrophoresis (CE). A satisfactory correlation (R2 > 0.94) between quantitative results obtained with BCA, NTA and CE was achieved only for isolates obtained with the IDGUC. The correlation between protein content and CE was proved to be related to the isolates’ purity. The NTA was found unable to provide reliable information on EVs quantity in samples isolated with UC and ICUC, due to the co-isolated particulate impurities. Moreover, the work reports polysaccharides, used as culturing media components, as a potential source of bias of quantitation with total protein content assay and NTA. The study demonstrates the advantageous selectivity of CE in quality control of EVs and its ability to differentiate subpopulations of EVs of Pectobacterium.

Interplay of Interfacial Viscosity, Specific-Ion, and Impurity Adsorption Determines Zeta Potentials of Phospholipid Membranes

Ion-specific induced changes of the ζ-potential of phospholipid vesicles are commonly used to quantify the affinity of different ions to the lipid interface. The negative ζ-potential of zwitterionic net-neutral phospholipid vesicles in neat water, which changes sign and increases in solutions of NaCl or KCl, is a phenomenon consistently observed in experiments but not fully understood theoretically. Using atomistic molecular dynamics simulations in the presence of applied electric fields which drive electroosmotic flows, in combination with an electrostatic continuum model based on the modified Poisson-Boltzmann and Helmholtz-Smoluchowski equations, we study the electrokinetic and electrostatic properties as well as the specific ion affinities to the phospholipid-water interface, in order to resolve these puzzling observations. Our modified continuum equations account for the dielectric profile at the lipid-water interface, ion-specific interactions between ions and the lipid-water interface, and the interfacial viscosity profile, which are all extracted from our atomistic simulations and rather accurately predict ion-density and electrostatic-potential distributions as well as ζ-potentials in comparison with our atomistic simulations. Our continuum model can explain experimental ζ-potentials only when we assume minute amounts of surface-active anionic impurities in the aqueous solution. In fact, the amount of impurities needed to explain the experimental data increases linearly with the salt concentration, suggesting that surface-active species, which might be already present in the lab water or lipid samples, could further be introduced through the added salt.

Investigation of selected parameters of capillary zone electrophoresis method for analysis of isolates of outer membrane vesicles

The capillary zone electrophoresis (CZE) has recently been proposed by our group as a novel technique for outer membrane vesicles (OMVs) characterization (J. Chromatography 1621 (2020) 461047). In present work the impact of selected parameters of CZE method on OMVs isolates analysis was assessed. It was shown that the extension of sample injection plug length significantly improves the detectability of macromolecular aggregates in CZE. Moreover, a negligible adsorption of OMVs to both uncoated and polymer-modified (poly(DMA-GMA-MAPS)) capillary walls was proven. Finally, the relaxation effect as well as deformation/polarization of vesicles were demonstrated to affect OMVs electrophoretic mobility. The significance of these findings was discussed.

Simultaneous measurement of individual mitochondrial membrane potential and electrophoretic mobility by capillary electrophoresis

Mitochondrial membrane potential varies, depending on energy demand, subcellular location, and morphology and is commonly used as an indicator of mitochondrial functional status. Electrophoretic mobility is a heterogeneous surface property reflective of mitochondrial surface composition and morphology, which could be used as a basis for separation of mitochondrial subpopulations. Since these properties are heterogeneous, methods for their characterization in individual mitochondria are needed to better design and understand electrophoretic separations of subpopulations of mitochondria. Here we report on the first method for simultaneous determination of individual mitochondrial membrane potential and electrophoretic mobility by capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). Mitochondria were isolated from cultured cells, mouse muscle, or liver, and then polarized, labeled with JC-1 (a ratiometric fluorescent probe, which indicates changes in membrane potential), and separated with CE-LIF. Red/green fluorescence intensity ratios from individual mitochondria were used as an indicator of mitochondrial membrane potential. Reproducible distributions of individual mitochondrial membrane potential and electrophoretic mobility were observed. Analysis of polarized and depolarized regions of interest defined using red/green ratios and runs of depolarized controls allowed for the determination of membrane potential and comparison of electrophoretic mobility distributions in preparations containing depolarized mitochondria. Through comparison of these regions of interest, we observed dependence of electrophoretic mobility on membrane potential, with polarized regions of interest displaying decreased electrophoretic mobility. This method could be applied to investigate mitochondrial heterogeneity in aging or disease models where membrane potential is an important factor.

Remotely controlled diffusion from magnetic liposome microgels

The reversible, temperature-dependent change in the permeability of a phospholipid bilayer has been used for controlling the diffusion rate of encapsulated molecular payload from liposomes. Liposomes were preloaded with a fluorescent dye and immobilized in calcium alginate hydrogel microparticles that also contained iron oxide nanoparticles. The composite microparticles were produced by a drop-on-demand inkjet method. The ability of iron oxide nanoparticles to locally dissipate heat upon exposure to a radio-frequency (RF) alternating magnetic field was used to control the local temperature and therefore diffusion from the liposomes in a contactless way using an RF coil. Several different release patterns were realized, including repeated on-demand release. The internal structure of the composite alginate-liposome-magnetite microparticles was investigated, and the influence of microparticle concentration on the heating rate was determined. In order to achieve a temperature rise required for the liposome membrane melting, the concentration of alginate beads should be at least 25% of their maximum packing density for the nanoparticle concentration and specific absorption rate used.

Predicting isoelectric points of nonfunctional mitochondria from Monte Carlo simulations of surface compositions

Mitochondria are heterogeneous organelles involved in energy production, metabolism, and cellular signaling that oftentimes are isolated from cells for chemical characterization (e.g., proteomic analysis). The chemical composition of the mitochondrial outer membrane is one of the factors defining the mitochondrial isoelectric point (pI), which is a property useful for the analysis and characterization of isolated mitochondria. We previously used capillary isoelectric focusing (cIEF) with laser-induced-fluorescence detection to determine the experimental pI of individual mitochondria after their isolation under depolarizing conditions. This technique revealed that, when kept nonfunctional, mitochondrial pI is heterogeneous as displayed by the observed distributions of pI. To model the effect of surface composition on pI heterogeneity of these mitochondria, we devised a method to predict mitochondrial pI values using simulated surface compositions. The method was initially validated by predicting the pI values of known mitochondrial outer membrane proteins and was then extended to isolated mitochondria, in which both ionizable amino acids and phospholipids contribute to mitochondrial pI. After using a Monte Carlo method to generate a library of over 2 million possible mitochondrial surface compositions, sufficient compositions to match the frequency of occurrence of experimental mitochondrial pI values were randomly selected. This comparison allows for association of a given individual mitochondrial pI with thousands of randomly chosen compositions. The method predicts significant changes in the percentages of some amino acids and phospholipids for observed pI differences between individual mitochondria, which is an important advancement toward explaining the observed heterogeneity of mitochondrial pI.

Hybrid capillary-microfluidic device for the separation, lysis, and electrochemical detection of vesicles

The primary method for neuronal communication involves the extracellular release of small molecules that are packaged in secretory vesicles. We have developed a platform to separate, lyse, and electrochemically measure the contents of single vesicles using a hybrid capillary-microfluidic device. This device incorporates a sheath-flow design at the outlet of the capillary for chemical lysis of vesicles and subsequent electrochemical detection. The effect of sheath-flow on analyte dispersion was characterized using confocal fluorescence microscopy and electrochemical detection. At increased flow rates, dispersion was minimized, leading to higher separation efficiencies but lower detected amounts. Large unilamellar vesicles (diameter approximately 200 nm), a model for secretory vesicles, were prepared by extrusion and loaded with an electroactive molecule. They were then separated and detected using the hybrid capillary-microfluidic device. Determination of size from internalized analyte concentration provides a method to characterize the liposomal suspension. These results were compared to an orthogonal size measurement using dynamic light scattering to validate the detection platform.

Fast determination of mitochondria electrophoretic mobility using micro free-flow electrophoresis

Fast, continuous separation of mitochondria from rat myoblasts using micro free-flow electrophoresis (muFFE) with online laser-induced fluorescence detection (LIF) is reported. Mitochondrial electrophoretic profiles were acquired in less than 30 s. In comparison to macroscale FFE instruments, muFFE devices consumed approximately 100-fold less sample, used 10-fold less buffer, and required a 15-fold lower electric field. Mitochondrial electrophoretic mobility distributions measured using muFFE were compared to those measured with a capillary electrophoresis instrument with laser-induced fluorescence detection (CE-LIF). There was high similarity between the two distributions with CE-LIF distribution being offset by 1.8 x 10(-4) cm(2) V(-1) s(-1) with respect to the microFFE distribution. We hypothesize that this offset results from the differences in electric field strength used in the techniques. In comparison to CE-LIF, analysis of mitochondria using muFFE greatly decreased separation time and required less separation voltage, while maintaining low sample (125 nL) and buffer (250 microL) volumes. These features together with the potential for collecting separated organelle fractions for further characterization make microFFE a very attractive tool for the high-throughput analysis of organelle subpopulations as well as investigating the fundamentals of the electrophoretic mobility of biological particles.

Evaluation of asymmetric liposomal nanoparticles for encapsulation of polynucleotides

Conventional lipid bilayer liposomes have similar inner and outer leaflet compositions; asymmetric liposomes have different lipid leaflet compositions. The goal of this work is to place cationic lipids in the inner leaflet to encapsulate negatively charged polynucleotides and to place neutral/anionic lipids on the outer leaflet to decrease nonspecific cellular uptake/toxicity. Inverse emulsion particles have been developed with a single lipid leaflet of cationic and neutral lipids surrounding an aqueous core containing a negatively charged 21-mer DNA oligo. The particles are accelerated through an oil-water interface, entrapping a second neutral lipid to form oligo encapsulated unilamellar liposome nanoparticles. Inverse emulsion particles can be consistently produced to encapsulate an aqueous environment containing negatively charged oligo. The efficiency of encapsulated liposome formation is low and depends on the hydrocarbon used as the oil phase. Dodecane, mineral oil, and squalene were tested, and squalene, a branched hydrocarbon, yielded the highest efficiency.

Recent advances in the analysis of biological particles by capillary electrophoresis

This review covers research papers published in the years 2005-2007 that describe the application of capillary electrophoresis to the analysis of biological particles such as whole cells, subcellular organelles, viruses and microorganisms.

Electrophoretic and Dielectrophoretic Field Gradient Technique for Separating Bioparticles

We describe a new device for separation of complex biological particles and structures exploiting many physical properties of the biolytes. The device adds a new longitudinal gradient feature to insulator dielectrophoresis, extending the technique to separation of complex mixtures in a single channel. The production of stronger local field gradients along a global gradient allows particles to enter, initially transported through the channel by electrophoresis and electroosmosis, and to be isolated according to their characteristic physical properties, including charge, polarizability, deformability, surface charge mobility, dielectric features, and local capacitance. In this work, the separation mechanism is described in terms of the relevant electromechanical principles, and proof-of-principle is demonstrated using various bacteria cells as model systems. The results demonstrate the selectivity of the technique and suggest that it may form the foundation for a versatile and useful tool for separating mixtures of complex biological particles and structures.

Individual electrophoretic mobilities of liposomes and acidic organelles displaying pH gradients across their membranes

This report focuses on measuring the individual electrophoretic mobilities of liposomes with different pH gradients across their membrane using capillary electrophoresis with laser-induced fluorescence detection (CE-LIF). The results from the individual analysis of liposomes show that, using surface electrostatic theories and the electrokinetic theory as the first approximation, zeta potential contributes more significantly to the electrophoretic mobility of liposomes than liposomal size. For liposomes with an outer pH 7.4 (pH(o) 7.4) and a net negative outer surface charge, the most negative electrophoretic mobilities occur when the inner pH (pH(i)) is 6.8; at higher or lower pH(i), the electrophoretic mobilities are less negative. The theories mentioned above cannot explain these pH-induced electrophoretic mobility shifts. The capacity theory, predicting an induced electrical charge on the surface of liposomes, can only explain the results at pH(i) > 6.8. In this report, we hypothesize that there is a flip-flop process of phospholipids, which refers to the exchange of phospholipids between the outer and inner layers of the membrane. This flip-flop is caused by the pH gradient and membrane instability and results in the observed electrophoretic mobility changes when pH(i) is <6.8. Furthermore, it is found that the mobilities of acidic organelles are consistent with the predictions of liposome models we used here.

Resolution of small molecules by passage through an open capillary

When a solute passes through an open capillary, in which a laminar flow is established, different peak profiles can be obtained according to its diffusion property under a working condition, i.e., the radius and length of the capillary and the flow rate of the carrier solution. If a solute diffuses over the entire cross section of the capillary before it is eluted, a Gaussian-shaped diffusion peak appears, which has an apex at the travel time of the average flow. Insufficient solute diffusion, which is realized, e.g., by increasing flow rates or capillary radius, produces a new peak having an apex at the travel time of the maximum flow. This implies that two solutes can be resolved simply by passing through a capillary. However, our previous study indicated that the diffusion coefficients of two solutes should be at least one order different for their resolution based on this principle, suggesting that its applicability is highly restricted. In the present paper, this concept has been extended to the resolution between dissolved solutes that have similar intrinsic diffusion properties. The incorporation of molecular aggregates in the carrier makes a solute less diffusive according to the extent of their interaction and allows the resolution of a dissolved molecule from other ones differing in the affinity to the molecular aggregates. Several examples of peak resolution for phenols, aromatic hydrocarbons, and inorganic anions are shown and discussed on the basis of the modification of the diffusion natures due to their interactions with micelles or vesicles.

Examination of nonendocytotic bulk transport of nanoparticles across phospholipid membranes

Nonendocytotic transport is believed to play a role in the transmigration of particles less than 100 nm within biological systems. Determining the fundamental mechanism of this transport across cell membranes is essential if nanotechnology is to be utilized in general medical practice and may lead to methods of treating the deleterious internalization of ambient, possibly pollutant, nanoparticles. In order to gain a broader understanding of nonendocytotic transmembrane transport, it becomes essential to devise a method which allows the isolation of fundamental modes of transport such as passive Brownian diffusion through a membrane, as opposed to effusion-like transport of particles through transmembrane channels. The passive Brownian diffusion contribution was investigated using gold nanoparticles and mimetic biomembranes. Specifically, gold nanoparticle dispersions consisting of 7, 10, and 15 nm diameter particles were captured in giant unilamelar vesicles composed of phosphatidylcholine, phosphatidic acid, and cholesterol. Nonendocytotic transmembrane transport was modeled as the time derivative of the appearance of nanoparticles in the phosphate buffer outside the vesicles at 37 degrees C. The results show the transport rate to be zero; hence, a simple diffusive process of transmembrane transport is not supported.

Capillary electrophoresis of liposomes functionalized for protein binding

CE enabled assessing the attachment of hexa-histidine-tagged proteins to functionalized phospholipid liposomes. The liposomes were made of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, phosphatidyl-ethanolamine, cholesterol and distearoyl-glycero-3-phosphoethanolamine-N-methoxy(polyethylene glycol) in a molar ratio of 29:26:40:5. The unilamellar vesicles, which had an average diameter of 170 nm, were labelled by inclusion of FITC-dextran for fluorescence detection. CE was carried out in poly(vinyl alcohol) (PVA)-coated capillaries at 25 degrees C with a BGE consisting of Tris-HCl (50 mM, pH 8.0). For conjugation of the liposomes with the proteins (soluble synthetic receptor fragments with molecular mass of 60 and 70 kDa, respectively), Ni(2+) was implanted into the vesicle surface by an anchor lipid containing a nitrilotriacetate acid (NTA) group as complexation agent for the metal ions. The difference in surface charge enabled the separation of the different species of interest by CE: plain vesicles, vesicles functionalised with Ni-NTA, vesicle-protein complexes and the species formed upon removal of the Ni-ions by complexation with EDTA. Loss of the Ni-ions resulted in the release of the proteins and the reappearance of the plain Ni-free NTA-liposome species in the electropherograms.

Analysis of liposomes by capillary electrophoresis and their use as carrier in electrokinetic chromatography

This contribution reviews work about liposomes in the context of electrically driven separation methods in the capillary format. The discussion covers four topics. The one broaches the application of liposomes as pseudo-stationary phases or carriers in vesicle or liposome electrokinetic chromatography (EKC) in the way as microemulsions and micelles are used; it includes the chromatographic use of liposomal bilayers as stationary phases attached to the wall for capillary electrochromatography (CEC). The second topic is the characterization and separation of liposomes as analytes by capillary electrophoresis (CE). Then the determination of distribution coefficients and binding constants between liposomes and ligands is discussed, and finally work dealing with peptides and proteins are reviewed with lipid bilayers as constituents of the electrically driven separation system.

Physico-chemical characterization and transfection efficacy of cationic liposomes containing the pEGFP plasmid

Cationic liposomes-DNA complexes (lipoplexes) are largely used in gene delivery. Deciphering specific chemical and physical properties of lipoplexes is a necessary step to unravel the mechanisms underlying transfection and to improve transfection efficacy in each experimental model. In the present paper we investigated the physico-chemical features of lipoplexes containing a plasmid encoding for the GFP protein, in order to correlate these results with transfection efficacy. Cationic unilamellar vesicles (mean diameter 100 nm) were prepared, from the cationic DC-Chol lipid and the zwitterionic phospholipid DOPE. The two components of the liposome bilayer were used at molar ratio close to unity. ESR spectra were recorded and zeta potential zeta was measured on liposomes complexed with the plasmid. One of the main points of interest in this paper resided in the fact that both kinds of measurements were carried out in the same conditions (i.e. lipid concentration, medium composition, and pH) employed for cell transfection experiments. Transfection was performed on CHO cells; the percentage of fluorescent cells was evaluated and compared with the above physico-chemical features. It emerged that the composition and pH of the medium, the lipoplex/cell ratio, as well as the amount of lipoplex added to the cell culture were critical parameters for transfection efficacy. Finally, lipoplex surface charge played a fundamental role to achieve a high transfection level.

Adsorption equilibria between liposome membrane formed of phosphatidylcholine and aqueous sodium chloride solution as a function of pH

The effect has been studied of the adsorption of ions (H(+), Na(+), OH(-), Cl(-)) which are present in solution upon the electric charge of the liposome membrane formed of phosphatidylcholine (PC). The surface charge density of the membrane was determined as a function of pH and electrolyte concentration from electrophoretic mobility measurements. The measurements were carried out by the laser-Doppler microelectrophoresis method. A four-equilibria model has been proposed to describe the phenomena occurring on the membrane surface. The equilibria in which the adsorption of other ions on the liposome membrane surface was involved were assumed to exist beside the equilibria in which the H(+) and OH(-) ions were engaged. The idea was confirmed by mathematical calculations. Association constants of the liposome membrane surface with ions of solution (K(AH), K(ANa), K(BOH), K(BCl)) were determined. The proposed model has been proved to be correct by comparing the resulting theoretic charge variation curves of the lecithin membrane with the experimental data.

Capillary electrophoresis-based analysis of phospholipid and glycosaminoglycan binding by human beta2-glycoprotein I

Human beta2-glycoprotein I (beta2gpI) is a phospholipid and heparin binding plasma glycoprotein involved in autoimmune diseases characterized by blood clotting disturbances (thrombosis) together with the occurrence of autoantibodies against beta2gpI. With the final goal of assessing autoantibody influence on binding interactions of beta2gpI we have studied the development of capillary electrophoresis (CE)-based assays for interactions of negatively charged ligands with beta2gpI. In the development of suitable conditions for analysis at neutral pH of this basic protein (pI about 8) we found the pH hysteresis behavior of fused silica surfaces useful since the protonated surface after an acid pre-wash counteracted protein adsorption efficiently in contrast to more laborious procedures including acrylamide/dimethylacrylamide coatings that did not permit analysis of this particular protein. This simple approach made estimates of heparin-beta2gpI interactions possible and the principle was shown also to work for detection of betagpI binding to anionic phospholipids. Utilizing the pH hysteresis effect may be a simple solution to the adsorption problems often encountered in analyses of proteins by CE.

Effects of deformability, uneven surface charge distributions, and multipole moments on biocolloid electrophoretic migration

Liposomes have been widely used as cellular and bioparticle mimics due to their lipid bilayer structure and relative ease of production and manipulation. Such biocolloids are frequently characterized by capillary electrophoresis (CE), which promises a wealth of information about such properties as surface charge, composition, and rigidity. The applicability of this information is somewhat limited, however, since it is interpreted with colloidal theories that do not account for the unique properties of biocolloids. In this work, the effects of deformability, mobile surface charges, intrinsic polarizability, and uneven surface charge distributions are incorporated into colloidal theories in order to better model the electrophoretic behaviors of liposomes.

Lipid vesicles in capillary electrophoretic techniques: characterization of structural properties and associated membrane-molecule interactions

This paper reviews the use of lipid vesicles as model membranes in capillary electrophoresis (CE). The history and utility of CE in the characterization of microparticles is summarized, focusing on the application of colloidal electromigration theories to lipid vesicles. For instance, CE experiments have been used to characterize the size, surface properties, enclosed volumes, and electrophoretic mobilities of lipid vesicles and of lipoprotein particles. Several techniques involving small molecules or macromolecules separated in the presence of lipid vesicles are discussed. Interactions between the analytes and the lipid vesicles - acting as a pseudostationary phase or coated stationary phase in electrokinetic chromatography (EKC) - can be used to obtain additional information on the characteristics of the vesicles and analytes, and to study the biophysical properties of membrane-molecule interactions in lipid vesicles and lipoproteins. Different methods of determining binding constants by EKC are reviewed, along with the relevant binding constant calculations and a discussion of the application and limitations of these techniques as they apply to lipid vesicle systems.