Evidence of surfactant-induced formation of transient pores in lipid bilayers by using magnetic-fluid-loaded liposomes

Harnessing the Therapeutic Potential of Extracellular Vesicles for Biomedical Applications Using Multifunctional Magnetic Nanomaterials

Extracellular vesicles (e.g., exosomes) carrying various biomolecules (e.g., proteins, lipids, and nucleic acids) have rapidly emerged as promising platforms for many biomedical applications. Despite their enormous potential, their heterogeneity in surfaces and sizes, the high complexity of cargo biomolecules, and the inefficient uptake by recipient cells remain critical barriers for their theranostic applications. To address these critical issues, multifunctional nanomaterials, such as magnetic nanomaterials, with their tunable physical, chemical, and biological properties, may play crucial roles in next-generation extracellular vesicles (EV)-based disease diagnosis, drug delivery, tissue engineering, and regenerative medicine. As such, one aims to provide cutting-edge knowledge pertaining to magnetic nanomaterials-facilitated isolation, detection, and delivery of extracellular vesicles and their associated biomolecules. By engaging the fields of extracellular vesicles and magnetic nanomaterials, it is envisioned that their properties can be effectively combined for optimal outcomes in biomedical applications.

Magnetic Nanoparticles as MRI Contrast Agents

Iron oxide nanoparticles (IONPs) have emerged as a promising alternative to conventional contrast agents (CAs) for magnetic resonance imaging (MRI). They have been extensively investigated as CAs due to their high biocompatibility and excellent magnetic properties. Furthermore, the ease of functionalization of their surfaces with different types of ligands (antibodies, peptides, sugars, etc.) opens up the possibility of carrying out molecular MRI. Thus, IONPs functionalized with epithelial growth factor receptor antibodies, short peptides, like RGD, or aptamers, among others, have been proposed for the diagnosis of various types of cancer, including breast, stomach, colon, kidney, liver or brain cancer. In addition to cancer diagnosis, different types of IONPs have been developed for other applications, such as the detection of brain inflammation or the early diagnosis of thrombosis. This review addresses key aspects in the development of IONPs for MRI applications, namely, synthesis of the inorganic core, functionalization processes to make IONPs biocompatible and also to target them to specific tissues or cells, and finally in vivo studies in animal models, with special emphasis on tumor models.

Magnetoliposomes of mixed biomimetic and inorganic magnetic nanoparticles as enhanced hyperthermia agents

Recently, liposomes have been explored as a potential solution to improve the biocompatibility and the colloidal stability of magnetic nanoparticles. Protocols have been developed for producing magnetoliposomes of magnetite nanoparticles obtained inorganically (MNPs). However, the biomimetic synthesis of magnetite using heterologous proteins from magnetotactic bacteria has become a real alternative to produce novel biomimetic magnetic nanoparticles (BMNPs). Among these, the BMNPs obtained in presence of MamC protein from Magnetococcus marinus MC-1 have been proposed as excellent candidates to be potentially used as drug nanocarriers and as hyperthermia agents. However, their colloidal stability still needs to be improved while maintaining their magnetic properties intact. One possibility explored in this manuscript is to form magnetoliposomes that contain BMNPs. Indeed, the protocols developed for producing magnetoliposomes of MNPs need to be tested and modified to be able to include BMNPs. In this context, a protocol has been developed to produce both magnetoliposomes filled with MNPs and/or BMNPs and their potential as hyperthermia agents was tested. In fact, for the first time, these two types of nanoparticles were mixed in different proportions to test the composition that would optimize such as behaviour as hyperthermia agents. Interestingly, it was observed that the hyperthermia behaviour of the magnetoliposomes greatly improved if they were filled with a mixture of MNPs and BMNPs. These results indicate that these magnetoliposomes display optimal characteristics to become a potential agent for hyperthermia and that the opening of those liposomes could be externally controlled by applying an alternate magnetic field.

Surfactants assist in lipid extraction from wet Nannochloropsis sp

An efficient approach involving surfactant treatment, or the modification and utilization of surfactants that naturally occur in algae (algal-based surfactants), was developed to assist in the extraction of lipids from wet algae. Surfactants were found to be able to completely replace polar organic solvents in the extraction process. The highest yield of algal lipids extracted by hexane and algal-based surfactants was 78.8%, followed by 78.2% for hexane and oligomeric surfactant extraction, whereas the lipid yield extracted by hexane and ethanol was only 60.5%. In addition, the saponifiable lipids extracted by exploiting algal-based surfactants and hexane, or adding oligomeric surfactant and hexane, accounted for 78.6% and 75.4% of total algal lipids, respectively, which was more than 10% higher than the lipids extracted by hexane and ethanol. This work presents a method to extract lipids from algae using only nonpolar organic solvents, while obtaining high lipid yields and high selectivity to saponifiables.

Time-course assessment of the aggregation and metabolization of magnetic nanoparticles

To successfully develop biomedical applications for magnetic nanoparticles, it is imperative that these nanoreagents maintain their magnetic properties in vivo and that their by-products are safely metabolized. When placed in biological milieu or internalized into cells, nanoparticle aggregation degree can increase which could affect magnetic properties and metabolization. To evaluate these aggregation effects, we synthesized citric acid-coated iron oxide nanoparticles whose magnetic susceptibility can be modified by aggregation in agar dilutions and dextran-layered counterparts that maintain their magnetic properties unchanged. Macrophage models were used for in vitro uptake and metabolization studies, as these cells control iron homeostasis in the organism. Electron microscopy and magnetic susceptibility studies revealed a cellular mechanism of nanoparticle degradation, in which a small fraction of the particles is rapidly degraded while the remaining ones maintain their size. Both nanoparticle types produced similar iron metabolic profiles but these profiles differed in each macrophage model. Thus, nanoparticles induced iron responses that depended on macrophage programming. In vivo studies showed that nanoparticles susceptible to changes in magnetic properties through aggregation effects had different behavior in lungs, liver and spleen. Liver ferritin levels increased in these animals showing that nanoparticles are degraded and their by-products incorporated into normal metabolic routes. These data show that nanoparticle iron metabolization depends on cell type and highlight the necessity to assess nanoparticle aggregation in complex biological systems to develop effective in vivo biomedical applications.

STATEMENT OF SIGNIFICANCE

Magnetic iron oxide nanoparticles have great potential for biomedical applications. It is however imperative that these nanoreagents preserve their magnetic properties once inoculated, and that their degradation products can be eliminated. When placed in a biological milieu nanoparticles can aggregate and this can affect their magnetic properties and their degradation. In this work, we showed that iron oxide nanoparticles trigger the iron metabolism in macrophages, the main cell type involved in iron homeostasis in the organism. We also show that aggregation can affect nanoparticle magnetic properties when inoculated in animal models. This work confirms iron oxide nanoparticle biocompatibility and highlights the necessity to assess in vivo nanoparticle aggregation to successfully develop biomedical applications.

Magnetic field responsive drug release from magnetoliposomes in biological fluids

The magnetically triggered drug release properties of magnetoliposomes are strongly affected by the presence of serum proteins.

Superparamagnetic-oil-filled nanocapsules of a ternary graft copolymer

Stearic and oleic acid-coated Fe3O4 nanoparticles were dispersed in decahydronaphthalene (DN). This oil phase was dispersed in water using ternary graft copolymer poly(glycidyl methacrylate)-graft-[polystyrene-ran-(methoxy polyethylene glycol)-ran-poly(2-cinnamoyloxyethyl methacrylate)] or PGMA-g-(PS-r-MPEG-r-PCEMA) to yield capsules. The walls of these capsules were composed of PCEMA chains that were soluble in neither water nor DN, and the DN-soluble PS chains stretched into the droplet phase and the water-soluble MPEG chains extended into the aqueous phase. Structurally stable capsules were prepared by photolyzing the capsules with UV light to cross-link the PCEMA layer. Both the magnetite particles and the magnetite-containing capsules were superparamagnetic. The sizes of the capsules increased as they were loaded with more magnetite nanoparticles, reaching a maximal loading of ~0.5 mg of ligated magnetite nanoparticles per mg of copolymer. But the radii of the capsules were always <100 nm. Thus, a novel nanomaterial--superparamagnetic-oil-filled polymer nanocapsules--was prepared. The more heavily loaded capsules were readily captured by a magnet and could be redispersed via shaking. Although the cross-linked capsules survived this capturing and redispersing treatment many times, the un-cross-linked capsules ruptured after four cycles. These results suggest the potential to tailor-make capsules with tunable wall stability for magnetically controlled release applications.

Stabilized magnetic cerasomes for drug delivery

Doxorubicin hydrochloride (DOX)-loaded magnetic cerasomes (DLMCs) were successfully constructed by loading both hydrophobic Fe3O4 nanoparticles (NPs) and antitumor drug DOX into the aqueous interior of cerasomes via facile one-step construction. A possible explanation is that the hydrophobic Fe3O4 NPs can be trapped inside the aqueous core of cerasomes through the formation of an intermediate Fe3O4/micelle complex. It was found that the loading content of Fe3O4 in DLMCs could reach the maximum at a Fe3O4/lipid molar ratio of 4:1. Moreover, DLMCs demonstrated high superparamagnetism and responded strongly to magnetic fields. In addition, DLMCs had a high encapsulation efficiency of 43.4 ± 4.7% and a high drug loading content of 3.2 ± 1.3%. In comparison to drug-loaded liposomes, DLMCs exhibited higher storage stability and better sustained release behavior. A cellular uptake study showed that the use of an external magnetic field enables a rapid and efficient uptake of DLMCs by cancer cells, resulting in higher capability to kill tumor cells than non-magnetic drug-loaded cerasomes. This study suggests that magnetic cerasome offers a potential and effective drug carrier for anticancer applications.

Hybrid nanoparticles for detection and treatment of cancer

There is currently considerable effort to incorporate both diagnostic and therapeutic functions into a single nanoscale system for the more effective treatment of cancer. Nanoparticles have great potential to achieve such dual functions, particularly if more than one type of nanostructure can be incorporated in a nanoassembly, referred to in this review as a hybrid nanoparticle. Here we review recent developments in the synthesis and evaluation of such hybrid nanoparticles based on two design strategies (barge vs. tanker), in which liposomal, micellar, porous silica, polymeric, viral, noble metal, and nanotube systems are incorporated either within (barge) or at the surface of (tanker) a nanoparticle. We highlight the design factors that should be considered to obtain effective nanodevices for cancer detection and treatment.

Interaction of ionic surfactants with cornea-mimicking anionic liposomes

The interaction of surface-active molecules with lipid bilayers is ubiquitous both in biological systems and also in several technological applications. Here we explore the interaction of ionic surfactants with liposomes whose composition mimics the ocular epithelia. In this study, liposomes with a composition mimicking ocular epithelia are loaded with calcein dye above the self-quenching concentration. The liposomes are then exposed to surfactants, and the rate of dye leaked from the liposomes due to the interaction of surfactants is measured. Both cationic and anionic surfactants at various concentrations and ionic strengths are explored. Results show that the liposome bilayer permeability to the dye increases on exposure to the surfactants, leading to the release of the dye trapped in the core. However, the dye release stops after a finite time, suggesting a transient increase in permeability followed by healing. The leakage profiles exhibit two different timescales for the cationic surfactant but only one timescale for the anionic surfactant. The total dye leakage increases with surfactant concentration, and at a given concentration, the dye leakage is significantly higher for the cationic surfactants. The timescale for the healing decreases with increasing surfactant concentration, and increasing ionic strength increases the dye leakage for the anionic surfactant. These results show that the surfactant binding to the lipid bilayer increases the permeability while the bilayers heal likely because of the surfactant jump from the outer to the inner leaflet and/or rearrangement into tighter aggregates.

Interactions between giant unilamellar vesicles and charged core-shell magnetic nanoparticles

This work combined two tools, giant unilamellar vesicles (GUVs) and core-shell magnetic nanoparticles (CSMNs), to develop a simplified model for studying interactions between the cell membrane and nanoparticles. We focused on charged functionalized CSMNs that can be either cationic or anionic. Using optical, electron, and confocal microscopy, we found that giant vesicle-nanoparticle interactions did not result from a simple electrostatic phenomenon because cationic CSMNs tended to bind to positively charged bilayers, whereas anionic CSMNs remained inert.

Interaction of n-octyl β,D-glucopyranoside with giant magnetic-fluid-loaded phosphatidylcholine vesicles: direct visualization of membrane curvature fluctuations as a function of surfactant partitioning between water and lipid bilayer

The present study deals with the morphological modifications of giant dioleoyl phosphatidylcholine vesicles (DOPC GUVs) induced by the nonionic surfactant n-octyl β,D-glucopyranoside at sublytic levels, i.e., in the first steps of the vesicle-to-micelle transition process, when surfactant inserts into the vesicle bilayer without disruption. Experimental conditions were perfected to exactly control the surfactant bilayer composition of the vesicles, in line with former work focused on the mechanical properties of the membrane of magnetic-fluid-loaded DOPC GUVs submitted to a magnetic field. The purpose here was to systematically examine, in the absence of any external mechanical constraint, the dynamics of giant vesicle shape and membrane deformations as a function of surfactant partitioning between the aqueous phase and the lipid membrane, beforehand established by turbidity measurements from small unilamellar vesicles.

Biomimetic silica microspheres in biosensing

Lipid vesicles spontaneously fuse and assemble into a lipid bilayer on planar or spherical silica surfaces and other substrates. The supported lipid bilayers (SLBs) maintain characteristics of biological membranes, and are thus considered to be biomembrane mimetic systems that are stable because of the underlying substrate. Examples of their shared characteristics with biomembranes include lateral fluidity, barrier formation to ions and molecules, and their ability to incorporate membrane proteins into them. Biomimetic silica microspheres consisting of SLBs on solid or porous silica microspheres have been utilized for different biosensing applications. The advantages of such biomimetic microspheres for biosensing include their increased surface area to volume ratio which improves the detection limits of analytes, and their amenability for miniaturization, multiplexing and high throughput screening. This review presents examples and formats of using such biomimetic solid or porous silica microspheres in biosensing.

Long-living intermediates during a lamellar to a diamond-cubic lipid phase transition: a small-angle X-ray scattering investigation

To generate nanostructured vehicles with tunable internal organization, the structural phase behavior of a self-assembled amphiphilic mixture involving poly(ethylene glycol) monooleate (MO-PEG) and glycerol monooleate (MO) is studied in excess aqueous medium by time-resolved small-angle X-ray scattering (SAXS) in the temperature range from 1 to 68 degrees C. The SAXS data indicate miscibility of the two components in lamellar and nonlamellar soft-matter nanostructures. The functionalization of the MO assemblies by a MO-PEG amphiphile, which has a flexible large hydrophilic moiety, appears to hinder the epitaxial growth of a double diamond (D) cubic lattice from the lamellar (L) bilayer structure during the thermal phase transition. The incorporated MO-PEG additive is found to facilitate the formation of structural intermediates. They exhibit greater characteristic spacings and large diffusive scattering in broad temperature and time intervals. Their features are compared with those of swollen long-living intermediates in MO/octylglucoside assemblies. A conclusion can be drawn that long-living intermediate states can be equilibrium stabilized in two- or multicomponent amphiphilic systems. Their role as cubic phase precursors is to smooth the structural distortions arising from curvature mismatch between flat and curved regions. The considered MO-PEG functionalized assemblies may be useful for preparation of sterically stabilized liquid-crystalline nanovehicles for confinement of therapeutic biomolecules.

Interactions of surfactants with lipid membranes

Surfactants are surface-active, amphiphilic compounds that are water-soluble in the micro- to millimolar range, and self-assemble to form micelles or other aggregates above a critical concentration. This definition comprises synthetic detergents as well as amphiphilic peptides and lipopeptides, bile salts and many other compounds. This paper reviews the biophysics of the interactions of surfactants with membranes of insoluble, naturally occurring lipids. It discusses structural, thermodynamic and kinetic aspects of membrane-water partitioning, changes in membrane properties induced by surfactants, membrane solubilisation to micelles and other phases formed by lipid-surfactant systems. Each section defines and derives key parameters, mentions experimental methods for their measurement and compiles and discusses published data. Additionally, a brief overview is given of surfactant-like effects in biological systems, technical applications of surfactants that involve membrane interactions, and surfactant-based protocols to study biological membranes.

Challenges in the development of magnetic particles for therapeutic applications

Certain iron-based particle formulations have useful magnetic properties that, when combined with low toxicity and desirable pharmacokinetics, encourage their development for therapeutic applications. This mini-review begins with background information on magnetic particle use as MRI contrast agents and the influence of material size on pharmacokinetics and tissue penetration. Therapeutic investigations, including (1) the loading of bioactive materials, (2) the use of stationary, high-gradient (HG) magnetic fields to concentrate magnetic particles in tissues or to separate material bound to the particles from the body, and (3) the application of high power alternating magnetic fields (AMF) to generate heat in magnetic particles for hyperthermic therapeutic applications are then surveyed. Attention is directed mainly to cancer treatment, as selective distribution to tumors is well-suited to particulate approaches and has been a focus of most development efforts. While magnetic particles have been explored for several decades, their use in therapeutic products remains minimal; a discussion of future directions and potential ways to better leverage magnetic properties and to integrate their use into therapeutic regimens is discussed.

The effect of magnetic targeting on the uptake of magnetic-fluid-loaded liposomes by human prostatic adenocarcinoma cells

Interactions of magnetic-fluid-loaded liposomes (MFL) with human adenocarcinoma prostatic cell line PC3 were investigated in vitro. MFL consisted of unilamellar phosphatidylcholine vesicles (mean hydrodynamic diameter close to 180 nm) encapsulating 8-nm nanocrystals of maghemite (gamma-Fe(2)O(3)) and sterically stabilized by introducing 5 mol.% of distearylphosphatidylcholine poly(ethylene glycol)(2000) (DSPE-PEG(2000)) in the vesicle bilayer. The association processes with living cells, including binding and effective internalization, were followed versus time at two levels. On one hand, the lipid vesicles labeled by 1 mol.% of rhodamine-marked phosphatidylethanolamine were imaged by confocal fluorescence microscopy. On the other hand, the iron oxide particles associated with cells were independently quantified by magnetophoresis. This allowed modeling of MFL uptake kinetics as a two-step process involving first binding adsorption onto the outer cell membrane followed by subsequent internalization. Capture efficiency was significantly improved by guiding MFL in the near vicinity of the cells by means of a 0.29-T external magnet developing a magnetic field gradient close to 30 mT/mm. Double detection of lipids by fluorescence tracking and of iron oxide by magnetophoresis showed excellent correlation. This demonstrated that MFL associate with tumor cells as intact vesicle structures which conserve their internal content.

Cytokine adsorption/release on uniform magnetic nanoparticles for localized drug delivery

Attachment of cytokines to magnetic nanoparticles has been developed as a system for controlled local drug release in cancer therapy. We studied the adsorption/release of murine interferon gamma (IFN-gamma) on negatively charged magnetic nanoparticles prepared by three different methods, including coprecipitation, decomposition in organic media, and laser pyrolysis. To facilitate IFN-gamma adsorption, magnetic nanoparticles were surface modified by distinct molecules to achieve high negative charge at pH 7, maintaining small aggregate size and stability in biological media. We analyzed carboxylate-based coatings and studied the colloidal properties of the resulting dispersions. Finally, we incubated the magnetic dispersions with IFN-gamma and determined optimal conditions for protein adsorption onto the particles, as well as the release capacity at different pH and as a function of time. Particles prepared by decomposition in organic media and further modified with dimercaptosuccinic acid showed the most efficient adsorption/release capacity. IFN-gamma adsorbed on these nanoparticles would allow concentration of this protein or other biomolecules at specific sites for treatment of cancer or other diseases.

Lipid bilayer elasticity measurements in giant liposomes in contact with a solubilizing surfactant

A new method to probe the modification of the elasticity of phospholipid bilayers is presented. The purpose here concerns the action of a solubilizing surfactant on a vesicle bilayer. This method is based on the measure of the under-field elongation of giant magnetic-fluid-loaded liposomes. The addition of the nonionic surfactant octyl-beta-d-glucopyranoside (OG) to vesicles at sublytic levels increases the elasticity of the membrane, as shown by the value of the bending modulus K(b), which decreases. K(b) measured around 20 kT for a pure 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) bilayer indeed reaches a few kT in the case of the mixed OG-DOPC bilayer. The purpose and interest of this study are to allow the determination of the membrane bending modulus before and after the addition of OG on the same magnetic liposome. Moreover, the experimental conditions used in this work allow the control of lipid and surfactant molar fractions in the mixed aggregates. Then, optical microscopy observation can be performed on samples in well-defined regions of the OG-phospholipid state diagram.

Signatures of clustering in superparamagnetic colloidal nanocomposites of an inorganic and hybrid nature

The individual and co-operative properties of inorganic and hybrid superparamagnetic colloidal nanocomposites that satisfy all the requirements of magnetic carriers in the biosciences and/or catalysis fields are been studied. Essential to the success of this study is the selection of suitable synthetic routes (aerosol and nanocasting) that allow the preparation of materials with different matrix characteristics (carbon, silica, and polymers with controlled porosity). These materials present magnetic properties that depend on the average particle size and the degree of polydispersity. Finally, the analysis of the co-operative behavior of samples allows for the detection of signatures of clustering, which are closely related to the textural characteristics of samples and the methodology used to produce the magnetic carriers.

New noninvasive methodology for real-time monitoring of lipid flip

A new methodology for the detection of lipid flip was developed. This methodology relies on the quenching of the fluorescence of the cascade-blue-labeled lipid through complex formation with a membrane-impermeable cyclen-tetranaphthalenethiourea synthetic receptor for this dye. The high affinity of the receptor to cascade-blue label allows the use of micromolar concentrations of this receptor during the experiment. At these low concentrations, the receptor does not interfere with the membrane integrity and, therefore, renders this new methodology less invasive to the model and cell membranes than commonly utilized 7-nitro-1,2,3-benzoxadiazol-4-yl (NBD)-dithionite methodology. Unlike with the NBD-dithionite assay, where the fluorescence quenching of the NBD group is achieved through its chemical modification, this new assay relies on the noncovalent interactions between cascade-blue label and the receptor. Therefore, the quenching can be reverted by either competitive displacement of the lipid-attached label with a water-soluble substrate or by enzymatic degradation of the receptor leading to the label release and fluorescence dequenching. We demonstrate that this new methodology is suitable for the study of lipid flip in both model spherical bilayer membranes and in-vitro experiments.

Magnetic Targeting of Nanometric Magnetic Fluid–loaded Liposomes to Specific Brain Intravascular Areas: A Dynamic Imaging Study in Mice

PURPOSE

To prospectively determine, by using dynamic imaging, whether a magnet placed over a specific area of the mouse brain could target systemically administered rhodamine-labeled magnetic fluid-loaded liposomes (MFLs) to that brain region.

MATERIALS AND METHODS

Experiments were performed with a French Ministry of Agriculture permit and regional ethics committee authorization. In seven anesthetized C57BL/6 mice, a closed cranial window was implanted above the left parieto-occipital cortex. A laser-scanning confocal fluorescence microscope (LSCFM) was used to track the intravenously injected rhodamine-labeled MFLs within this cortical area, through the cranial window. The MFLs were video monitored for 2 minutes every 15 minutes for 1 hour after injection. A magnet was placed on the cranial window implanted in four mice, while no magnet was placed in three (control) mice. After dynamic in vivo imaging, static in vivo imaging was performed with a different LSCFM. Ex vivo fluorescence histologic analysis was then performed. Paired Student t testing was used to compare the cerebral blood flow and two-dimensional flow values before and 1 hour after MFL injection. For image analysis, intergroup comparisons were performed by using an independent t test.

RESULTS

In vivo video monitoring through the window revealed that the rhodamine-labeled MFLs accumulated in the mouse brain microvasculature exposed to the magnet-first within superficial brain venules and then within intracerebral venules-with no significant change in blood flow (P > .05). MFLs accumulated neither in the arterioles of the mice with a magnet nor in the arterioles of the control mice. Static in vivo imaging findings confirmed the microvascular localization of the rhodamine-labeled MFLs, and histologic findings specified their accumulation on the side of the magnet only.

CONCLUSION

Real-time in vivo imaging of rhodamine-labeled MFLs in the mouse brain cortex revealed that these nanosystems can be magnetically targeted, through microvessels, to selected brain areas.

Interactions of novel, nonhemolytic surfactants with phospholipid vesicles

PEG-12-acyloxystearates constitute a novel class of pharmaceutical solubilizers and are synthesized from polyethylene glycol and 12-hydroxystearic acid, which has been esterified with a second acyl chain. The hemolytic activity of these surfactants decreases drastically with increasing pendant acyloxy chain length, and surfactants with an acyloxy chain of 14 carbon atoms or more are essentially nonhemolytic. In this paper, the interactions of PEG-12-acyloxystearates (acyloxy chain lengths ranging from 8 to 16 carbon atoms) with phosphatidylcholine vesicles, used as a model system for erythrocyte membranes, were studied in search of an explanation for the large variations in hemolytic activity. Surfactant-induced alterations of membrane permeability were investigated by studying the leakage of vesicle-entrapped calcein. It was found that all of the surfactants within the series interact with the vesicle membranes and cause slow leakage at elevated surfactant concentrations, but with large variations in leakage kinetics. The initial leakage rate decreases rapidly with increasing pendant acyloxy chain length. After prolonged incubation, on the other hand, the leakage is not a simple function of acyloxy chain length. The effect of the surfactants on membrane integrity was also investigated by turbidity measurements and cryo-transmission electron microscopy. At a surfactant/lipid molar ratio of 0.4, the vesicle membranes are saturated with surfactant. When the surfactant/lipid molar ratio is further increased, the vesicle membranes are progressively solubilized into mixed micelles. The rate of this process decreases strongly with increasing acyloxy chain length. When comparing the results of the different experiments, it can be concluded that there is no membrane permeabilization below saturation of the vesicle membranes. The large variations in the kinetics suggest that several steps are involved in the mechanism of leakage induced by PEG-12-acyloxystearates and that their relative rates vary with acyloxy chain length. The slow kinetics may in part be explained by the low critical micelle concentrations (CMCs) exhibited by the surfactants. The CMCs were found to be in the range of 0.003-0.025 microM.

The in vitro kinetics of the interactions between PEG-ylated magnetic-fluid-loaded liposomes and macrophages

Binding and uptake kinetics of magnetic-fluid-loaded liposomes (MFL) by endocytotic cells were investigated in vitro on the model cell-line J774. MFL consisted of unilamellar phosphatidylcholine vesicles (mean hydrodynamic diameter close to 200nm) encapsulating 8-nm nanocrystals of maghemite (gamma-Fe(2)O(3)) and sterically stabilized by introducing 5mol% of distearylphosphatidylcholine poly(ethylene glycol)(2,000) (DSPE-PEG(2,000)) in the vesicle bilayer. The association processes with living macrophages were followed at two levels. On one hand, the lipid vesicles were imaged by confocal fluorescence microscopy. For this purpose 1mol% of rhodamine-marked phosphatidylethanolamine was added to the liposome composition. On the other hand, the iron oxide particles associated with cells were independently quantified by magnetophoresis. All the experiments were similarly performed with PEG-ylated or conventional MFL to point out the role of polymer coating. The results showed cell association with both types of liposomes resulting from binding followed by endocytosis. Steric stabilization by PEG chains reduced binding efficiency limiting the amount of MFL internalized by the macrophages. In contrast, PEG coating did not change the kinetics of endocytosis which exhibited the same first-order rate constant for both conventional and PEG-ylated liposomes. Moreover, lipids and iron oxide particle uptakes were perfectly correlated, indicating that MFL vesicle structure and encapsulation rate were preserved upon cell penetration.

An overview of lipid membrane supported by colloidal particles

In recent years, original hybrid assemblies composed of a particle core surrounded by a lipid shell emerged as promising entities for various biotechnological applications. Their broadened bio-potentialities, ranging from model membrane systems or biomolecule screening supports, to substance delivery reservoirs or therapeutic vectors, are furthered by their versatility of composition due to the possible wide variation in the particle nature and size, as well as in the lipid formulation. The synthesis, the characteristics, and the uses of these Lipid/Particle assemblies encountered in the literature so far are reviewed, and classified according to the spherical core size in order to highlight general trends. Moreover, several criteria are particularly discussed: i) the interactions involved between the particles and the lipids, and implicitly the assembly elaboration mechanism, ii) the most suited techniques for an accurate characterization of the entities from structural and physicochemical points of view, and iii) the remarkable properties of the solid-supported lipid membrane obtained.

Sterically stabilized superparamagnetic liposomes for MR imaging and cancer therapy: pharmacokinetics and biodistribution

Pharmacokinetics of magnetic-fluid-loaded liposomes (MFLs) with mean hydrodynamic diameter of 200 nm sterically stabilized by poly(ethylene glycol) (PEG) and labelled by a fluorescent lipid probe, N-(lissamine rhodamine B sulfonyl) phosphatidylethanolamine (Rho-PE) was studied. The loading consisted in an aqueous suspension of maghemite nanocrystals close to 8 nm in size at 1.7 Fe(III)mol/mol total lipids ratio. Double tracking of MFL in blood was performed versus time after intravenous administration in mice. Lipids constituting vesicle membrane were followed by Rho-PE fluorescence spectroscopy while iron oxide was determined independently by relaxometry. MFLs circulating in the vascular compartment conserved their vesicle structure and content. The pharmacokinetic profile was characterized by two first-order kinetics of elimination with distinct plasmatic half-lives of 70 min and 12.5 h. Iron biodistribution and organ histology clearly highlighted preferential MFL accumulation within liver and spleen. The pathway in spleen supported that elimination was governed by the mononuclear phagocyte system (MPS). PEG coating was essential to prolong MFL circulation time whereas iron oxide loading tends to favour uptake by the MPS. Despite partial uptake in the earlier times after administration, MFLs exhibited long circulation behaviour over a 24-h period that, coupled to magnetic targeting, encourages further use in drug delivery.