Formation of an intact liposome layer adsorbed on oxidized gold confirmed by three complementary techniques: QCM-D, AFM and confocal fluorescence microscopy

Regulation of Nanoliposome Rigidity and Bioavailability of Oligomeric Proanthocyanidin with Phytosterols Containing Different C3 Branches

The rigidity of nanoliposomes significantly influences their physical stability and in vitro and in vivo behaviors (e.g., cellular uptake, blood circulation, biodistribution, etc.). This study aimed to quantify the rigidity of the nanoliposomes composed of phytosterol with varying C3 branches and phospholipids (DPPC, DOPC) using atomic force microscopy. Young's modulus, determined by the Shell model, effectively differentiated between mechanical differences in nanoliposomes with varying components and component structure and phase states. FTIR results indicated that P-SG exhibited the highest Young's modulus (175.98 ± 10.53 MPa) due to the hydrogen bond between the glucose residue of steryl glycosides (SGs) and the phospholipid polar head. However, the rigidity of DOPC nanoliposomes was not significantly different due to the unsaturated bond. The addition of oligomeric proanthocyanidin (OPC) did not change the order of rigidity among the nanoliposomes, with P-SG-OPC having the highest Young's modulus (126.27 ± 2.06 MPa). In the simulated gastrointestinal tract experiment, P-SG-OPC exhibited the greatest stability, with minimal particle aggregation. Cellular uptake experiments revealed that DPPC nanoliposomes with high rigidity had optimal endocytosis, while DOPC nanoliposome uptake was independent of rigidity. In melanin production inhibition tests, the inhibitory effect correlated directly with Young's modulus and P-SG-OPC had the best inhibitory effect on melanin generation. Our findings in this study provide valuable insights into the design and optimization of nanoliposomes for the efficient delivery of active substances, offering potential solutions for improving the efficacy of drug delivery systems.

Supported Lipid Bilayer Platform for Characterizing the Membrane-Disruptive Behaviors of Triton X-100 and Potential Detergent Replacements

Triton X-100 (TX-100) is a widely used detergent to prevent viral contamination of manufactured biologicals and biopharmaceuticals, and acts by disrupting membrane-enveloped virus particles. However, environmental concerns about ecotoxic byproducts are leading to TX-100 phase out and there is an outstanding need to identify functionally equivalent detergents that can potentially replace TX-100. To date, a few detergent candidates have been identified based on viral inactivation studies, while direct mechanistic comparison of TX-100 and potential replacements from a biophysical interaction perspective is warranted. Herein, we employed a supported lipid bilayer (SLB) platform to comparatively evaluate the membrane-disruptive properties of TX-100 and a potential replacement, Simulsol SL 11W (SL-11W), and identified key mechanistic differences in terms of how the two detergents interact with phospholipid membranes. Quartz crystal microbalance-dissipation (QCM-D) measurements revealed that TX-100 was more potent and induced rapid, irreversible, and complete membrane solubilization, whereas SL-11W caused more gradual, reversible membrane budding and did not induce extensive membrane solubilization. The results further demonstrated that TX-100 and SL-11W both exhibit concentration-dependent interaction behaviors and were only active at or above their respective critical micelle concentration (CMC) values. Collectively, our findings demonstrate that TX-100 and SL-11W have distinct membrane-disruptive effects in terms of potency, mechanism of action, and interaction kinetics, and the SLB platform approach can support the development of biophysical assays to efficiently test potential TX-100 replacements.

Adsorption Behavior of Arabinogalactan-Proteins (AGPs) from Acacia senegal Gum at a Solid-Liquid Interface

Adsorption of five different hyperbranched arabinogalactan-protein (AGP) fractions from Acacia senegal gum was thoroughly studied at the solid-liquid interface using a quartz crystal microbalance with dissipation monitoring (QCM-D), surface plasmon resonance (SPR), and atomic force microscopy (AFM). The impact of the protein/sugar ratio, molecular weight, and aggregation state on the adsorption capacity was investigated by studying AGP fractions with different structural and biochemical features. Adsorption on a solid surface would be primarily driven by the protein moiety of the AGPs through hydrophobic forces and electrostatic interactions. Increasing ionic strength allows the decrease in electrostatic repulsions and, therefore, the formation of high-coverage films with aggregates on the surface. However, the maximum adsorption capacity was not reached by fractions with a higher protein content but by a fraction that contains an average protein quantity and presents a high content of high-molecular-weight AGPs. The results of this thorough study highlighted that the AGP surface adsorption process would depend not only on the protein moiety and high-molecular-weight AGP content but also on other parameters such as the structural accessibility of proteins, the molecular weight distribution, and the AGP flexibility, allowing structural rearrangements on the surface and spreading to form a viscoelastic film.

The role of positively charged sites in the interaction between model cell membranes and γ-Fe2O3 NPs

The various applications of iron oxide nanoparticles (NPs) in clinical care and wastewater treatment are rapidly developing, thus their biological safety is worth attention. The electrostatic interaction between cell membranes and NPs is the key mechanism behind membrane damage and membrane penetration. Cell membranes are generally negatively charged with a few positively charged domains. The role of the positively charged sites in the NP-membrane interaction needs further investigation. In this study, the ratio of the positively charged sites was adjusted in two model cell membranes: giant and small unilamellar vesicles (GUVs and SUVs). After exposure to negatively charged γ-Fe₂O₃ NPs, the adhesion of NPs on the membranes and the induced membrane disruption were studied by microscopic observation and quartz crystal microbalance (QCM) monitoring. γ-Fe₂O₃ NPs adhered to and disrupted the membranes containing even few positively charged sites, although the whole membrane exhibited a negative zeta potential and hence electrostatically repels the NPs. The number of adhered γ-Fe₂O₃ NPs increased remarkably on membranes with overall positive zeta potential, but more serious disruption happened to membranes with higher ratios of positively charged sites. Therefore, the membrane rupture was more correlated to the number of positively charged sites than to the zeta potential of the whole membrane. In addition, exposure to γ-Fe₂O₃ NPs decreased the order of the lipid molecules and hence increased the fluidity of the membrane phase, and the most significant phase change occurred in the negatively charged membrane with the highest ratio of positively charged sites. Infrared spectra indicated that γ-Fe₂O₃ NPs probably interact with the membranes via the phosphodiester and trimethylamine groups in the lipid head groups. Our research furthers our knowledge of the electrostatic interaction between NPs and cell membranes, which should help to predict the biological effects of γ-Fe₂O₃ NPs.

Silver Nanoparticles on Cellulose Surfaces: Quantitative Measurements

In this work, cellulose films pre-activated with carbonyldiimidazole (CDI) and grafted with 1,6-hexanediamine, were decorated with silver nanoparticles (AgNPs). The generation of AgNPs was followed by quartz crystal microbalance (QCM). The obtained films were characterized by X-Ray Photoelectron Spectroscopy (XPS) and imaged by atomic force microscopy (AFM). XPS confirmed the synthesis in situ of AgNPs on the film attesting their oxidation state. The results from the three techniques were compared showing how sound the quantitative treatment of the results issued from these techniques can be. The main objective of this work is exactly to show that the quantitative exploration of the results of different characterization techniques can and should be practiced systematically instead of just comparing them qualitatively.

Engineering the interface between lipid membranes and nanoporous gold: A study by quartz crystal microbalance with dissipation monitoring

Nanoporous gold (np-Au) is a nanostructured metal with many desirable attributes. Despite the growing number of applications of nanoporous materials, there are still open questions regarding their fabrication and subsequent surface functionalization. For example, the hydrophobic nature of gold surfaces makes the formation of planar supported lipid layers challenging. Here, the authors engineer the interface between np-Au and 1,2-dioleoyl-sn-glycero-3-phosphocholine lipid layers using well-differentiated approaches based on vesicle adsorption and solvent exchange methods. The results reveal that the nanotopography of the np-Au surface plays a clear role in the vesicle adsorption process. Compared to vesicle adsorption, the solvent exchange method proves successful in the formation of planar supported lipid bilayers in both np-Au and planar Au surfaces, being less sensitive to the surface morphological features. The influence of nanostructured surfaces on lipid layer formation is determined by the driving mechanisms behind each process, i.e., the balance of adhesion and cohesion forces in vesicle adsorption and lyotropic lipid phase transitions in solvent exchange, respectively. A better understanding of such interactions will contribute to the development of a variety of applications, from electrochemical biosensors to drug screening and delivery systems, using nanoporous gold coated with stimuli-responsive lipid layers.

Effects of Flow and Bulk Vesicle Concentration on Supported Lipid Bilayer Formation

Supported lipid bilayers (SLBs) have been used extensively in a variety of biotechnology applications and fundamental studies exploring lipid behavior. Despite their widespread use, various physicochemical parameters have yet to be thoroughly investigated for their impact on SLB formation. In this work, we have studied the importance of flow in inducing the rupture of surface adsorbed chicken egg-derived l-α-phosphatidylcholine (egg PC) vesicles on silica and gold surfaces via quartz crystal microbalance with dissipation monitoring (QCM-D). On silica at 25 °C, egg PC vesicles were found to adsorb in a flattened configuration (∼13 nm thick, compared to bulk vesicle diameters of ∼165 nm) but only undergo a transition to a stable SLB under flow conditions. In the absence of flow, an increase in system temperature to 37 °C was able to promote vesicle rupture and SLB formation on silica with a 10 times lower rupture time, compared to rupture under continuous flow (175 μL/min flow rate). Gold surfaces, with their increased hydrophobicity, led to less vesicle flattening once adsorbed (structures ∼60 nm thick), and did not support vesicle rupture or SLB formation, even at flow rates of up to 650 μL/min. We also showed that, under continuous flow conditions, vesicle adsorption rates on silica surfaces follow Langmuir kinetics, with an inverse dependence on bulk vesicle concentration, while an empirical power law dependence of vesicle rupture time on bulk vesicle concentration was observed. Ultimately, this work elicits fundamental insight into the importance of flow and bulk vesicle concentration in the adsorbed vesicle rupture process during SLB formation using QCM-D.

pH-dependent lipid vesicle interactions with plasma polymerized thin films

Model lipid vesicle and supported lipid bilayer (SLB) systems are used in a variety of applications including biosensing, cell membrane mimics, and drug delivery. Exposure of a surface to a vesicle solution provides a straightforward method for creating such systems via vesicle adsorption and collapse. However, this process is complex and the relationship between the surface physicochemical properties and vesicle collapse is poorly understood. Plasma polymers are thin conformal films that can be applied to a variety of materials to modify surface properties. This paper uses quartz crystal microbalance with dissipation and fluorescence recovery after photobleaching (FRAP) to explore lipid vesicle interactions with plasma polymerized acrylic acid (ppAAc), allylamine (ppAAm), and ppAAc/ppAAm micropatterns. Vesicle interactions were dependent on plasma polymer chemistry and pH of the buffer solution. Vesicles readily and stably adsorbed to ppAAm over a wide pH range. ppAAc demonstrated limited interactions at pH 7 and vesicle adsorption at pH 4. Vesicle collapse and SLB formation could be induced using a pH change. FRAP was used to explore the fluidity of the lipid structures on both the patterned and unpatterned plasma polymer films. On ppAAm/ppAAc micropatterns, pH transitions combined with the presence of chemically distinct regions on the same substrate enabled immobile lipid islands on ppAAc to be surrounded by fluid lipid regions on ppAAm. This work demonstrates that plasma polymer films could enable spatially controlled vesicle adsorption and SLB formation on a wide variety of different substrates.

Physicochemical characterizations of functional hybrid liposomal nanocarriers formed using photo-sensitive lipids

With recent advances in the field of diagnostics and theranostics, liposomal technology has secured a fortified position as a potential nanocarrier. Specifically, radiation/photo-sensitive liposomes containing photo-polymerizable cross-linking lipids are intriguing as they can impart the vesicles with highly interesting properties such as response to stimulus and improved shell stability. In this work, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphoethanolamine (DTPE) is used as a photo-polymerizable lipid to form functional hybrid-liposomes as it can form intermolecular cross-linking through the diacetylenic groups. Hybrid-liposomes were formulated using mixtures of DTPE and saturated lipids of different chain lengths (dipalmitoylphosphatidylcholine (DPPC) and dimirystoilphosphatidylcholine (DMPC)) at different molar ratios. The physico-chemical characteristics of the liposomes has been studied before and after UV irradiation using a combination of techniques: DSC, QCM-D and solid-state NMR. The results signify the importance of a subtle modification in alkyl chain length on the phase behavior of the hybrid-liposomes and on the degree of crosslinking in the shell.

Washless Method Enables Multilayer Coating of an Aggregation-Prone Nanoparticulate Drug Delivery System with Enhanced Yields, Colloidal Stability, and Scalability

Aggregation is frequently encountered during coating nanoparticles, especially when the core is not solid and the coating polyelectrolytes are weak. Here, the coating of a nanoliposome with two weak polyelectrolytes, alginate and chitosan, is investigated. First, quartz crystal microbalance with dissipation, atomic force microscopy, scanning electron microscopy, and energy dispersive spectroscopy analyses confirm the feasibility of firm adsorption of up to 16 layers of weak polyelectrolytes to the liposomal surface. Titrations are then performed to identify the lowest amounts of polyelectrolytes required to make eight saturated coating layers using the washless method. Significantly improved yields and reproducibility (almost 100%) are achieved, in addition to control over layer thickness. Attenuated total reflectance Fourier transform infrared spectroscopy studies confirm the success of layering. This is special since scientists always attempt to reduce nanoparticle aggregation by substituting the soft core, using one strong polyelectrolyte, or contending with lower yields or numbers of coating layers.

Nanoviscosity Measurements Revealing Domain Formation in Biomimetic Membranes

Partitioning of lipid molecules in biomimetic membranes is a model system for the study of naturally occurring domains, such as rafts, in biological membranes. The existence of nanometer scale membrane domains in binary lipid mixtures has been shown with microscopy methods; however, the nature of these domains has not been established unequivocally. A common notion is to ascribe domain separation to thermodynamic phase equilibria. However, characterizing thermodynamic phases of single bilayer membranes has not been possible due to their extreme dimensions: the size of the domains falls to the order of tens to hundreds of nanometers whereas the membrane thickness is only a few nanometers. Here, we present direct measurements of phase transitions in single bilayers of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) phospholipid mixtures using quartz crystal microbalance-based nanoviscosity measurements. Coexisting thermodynamic phases have been successfully identified, and a phase diagram was constructed for the single bilayer binary lipid system. It was demonstrated that domain separation only takes place in planar membranes, and thus, it is absent in liposomes and not detectable in calorimetric measurements on liposome suspensions. On the basis of energetic analysis, the main transition was identified as the breaking of van der Waals interactions between the acyl chains.

Interactions of Aqueous Imidazolium-Based Ionic Liquid Mixtures with Solid-Supported Phospholipid Vesicles

Despite the environmentally friendly reputation of ionic liquids (ILs), their safety has been recently questioned given their potential as cytotoxic agents. The fundamental mechanisms underlying the interactions between ILs and cells are less studied and by far not completely understood. Biomimetic films are here important biophysical model systems to elucidate fundamental aspects and mechanisms relevant for a large range of biological interaction ranging from signaling to drug reception or toxicity. Here we use dissipative quartz crystal microbalance QCM-D to examine the effect of aqueous imidazolium-based ionic liquid mixtures on solid-supported biomimetic membranes. Specifically, we assess in real time the effect of the cation chain length and the anion nature on a supported vesicle layer of the model phospholipid DMPC. Results indicate that interactions are mainly driven by the hydrophobic components of the IL, which significantly distort the layer and promote vesicle rupture. Our analyses evidence the gradual decrease of the main phase transition temperature upon increasing IL concentration, reflecting increased disorder by weakening of lipid chain interactions. The degree of rupture is significant for ILs with long hydrophobic cation chains and large hydrophobic anions whose behavior is reminiscent of that of antimicrobial peptides.

Graphene Oxide and Lipid Membranes: Size-Dependent Interactions

We have investigated the interaction of graphene oxide (GO) sheets with supported lipid membranes with focus on how the interaction depends on GO sheet size (three samples in the range of 90-5000 nm) and how it differs between small and large liposomes. The layer-by-layer assembly of these materials into multilamellar structures, as discovered in our previous research, is now further explored. The interaction processes were monitored by two complementary, real time, surface-sensitive analytical techniques: quartz crystal microbalance with dissipation monitoring (QCM-D, electroacoustic sensing) and indirect nanoplasmonic sensing (INPS, optical sensing). The results show that the sizes of each of the two components, graphene oxide and liposomes, are important parameters affecting the resulting multilayer structures. Spontaneous liposome rupture onto graphene oxide is obtained for large lateral dimensions of the graphene oxide sheets.

Minimal synthetic cells to study integrin-mediated adhesion

To shed light on cell-adhesion-related molecular pathways, synthetic cells offer the unique advantage of a well-controlled model system with reduced molecular complexity. Herein, we show that liposomes with the reconstituted platelet integrin αIIb β3 as the adhesion-mediating transmembrane protein are a functional minimal cell model for studying cellular adhesion mechanisms in a defined environment. The interaction of these synthetic cells with various extracellular matrix proteins was analyzed using a quartz crystal microbalance with dissipation monitoring. The data indicated that integrin was functionally incorporated into the lipid vesicles, thus enabling integrin-specific adhesion of the engineered liposomes to fibrinogen- and fibronectin-functionalized surfaces. Then, we were able to initiate the detachment of integrin liposomes from these surfaces in the presence of the peptide GRGDSP, a process that is even faster with our newly synthesized peptide mimetic SN529, which specifically inhibits the integrin αIIb β3 .

Ionic liquids affect the adsorption of liposomes onto cationic polyelectrolyte coated silica evidenced by quartz crystal microbalance

The worldwide use of ionic liquids (ILs) is steadily increasing, and even though they are often referred to as "green solvents" they have been reported to be toxic, especially toward aquatic organisms. In this work, we thoroughly study two phosphonium ILs; octyltributylphosphonium chloride ([P8444]Cl) and tributyl(tetradecyl)phosphonium chloride ([P14444]Cl). Firstly, the critical micelle concentrations (CMCs) of the ILs were determined with fluorescence spectroscopy and the optical pendant drop method in order to gain an understanding of the aggregation behavior of the ILs. Secondly, a biomimicking system of negatively charged unilamellar liposomes was used in order to study the effect of the ILs on biomembranes. Changes in the mechanical properties of adsorbed liposomes were determined by quartz crystal microbalance (QCM) measurements with silica coated quartz crystal sensors featuring a polycation layer. The results confirmed that both ILs were able to incorporate and alter the biomembrane structure. The membrane disrupting effect was emphasized with an increasing concentration and alkyl chain length of the ILs. In the extreme case, the phospholipid membrane integrity was completely compromised.

Soft landing of cell-sized vesicles on solid surfaces for robust vehicle capture/release

Based on a concept of a smooth and steady landing of fragile objects without destruction via a soft cushion, we have developed a model for the soft landing of deformable lipid giant unilamellar vesicles (GUVs) on solid surfaces. The foundation for a successful soft landing is a solid substrate with a two-layer coating, including a bottom layer of positively charged lysozymes and an upper lipid membrane layer. We came to a clear conclusion that anionic GUVs when sedimented on a surface, the vesicle rupture occurs upon the direct contact with the positively charged lysozyme layer due to the strong coulombic interactions. In contrast, certain separation distances was achieved by the insertion of a soft lipid membrane cushion between the charged GUVs and the lysozyme layer, which attenuated the coulombic force and created a mild buffer zone, ensuring the robust capture of GUVs on the substrate without their rupture. The non-covalent bonding facilitated a fully reversible stimuli-responsive capture/release of GUVs from the biomimetic solid surface, which has never been demonstrated before due to the extreme fragility of GUVs. Moreover, the controllable capture/release of cells has been proven to be of vital importance in biotechnology, and similarity the present approach to capture/release cells is expected to open the previously inaccessible avenues of research.

Effect of cholesterol on the phase behavior of solid-supported lipid vesicle layers

The interest in solid-supported biomimetic membranes stems from their utility in nanotechnology and biosensing. In particular, supported lipid vesicles (SLVs) have become popular in both fundamental biophysical studies and pharmaceutical screening applications. It is thus essential to gain information on the structural properties and phase behavior of SLVs. Here we report on a study on the influence of cholesterol on the phase behavior of SLVs of saturated phospholipids by using quartz crystal microbalance with dissipation monitoring, a label-free and nonintrusive surface-sensitive technique. Two complementary approaches have been used, a Voigt-based viscoelastic model yielding shear viscosity temperature profiles and the first-order derivative of the frequency (mass-sensitive) shifts. Anomalies in the shear viscosity and extrema in the first-order derivative frequency curves stand as a token of the main phase transition and provide information on its gradual suppression upon addition of cholesterol. This method proves convenient for its small sample volume needed, its short temperature equilibration time and the non-necessity of external labels. This work can be regarded as a starting point for further studies on more rare lipid systems and different geometries, such as tethered SLVs or biologically relevant vesicles produced by living cells.

Single molecule FRET reveals pore size and opening mechanism of a mechano-sensitive ion channel

The mechanosensitive channel of large conductance, which serves as a model system for mechanosensitive channels, has previously been crystallized in the closed form, but not in the open form. Ensemble measurements and electrophysiological sieving experiments show that the open-diameter of the channel pore is >25 Å, but the exact size and whether the conformational change follows a helix-tilt or barrel-stave model are unclear. Here we report measurements of the distance changes on liposome-reconstituted MscL transmembrane α-helices, using a ‘virtual sorting’ single-molecule fluorescence energy transfer. We observed directly that the channel opens via the helix-tilt model and the open pore reaches 2.8 nm in diameter. In addition, based on the measurements, we developed a molecular dynamics model of the channel structure in the open state which confirms our direct observations.

DOI:http://dx.doi.org/10.7554/eLife.01834.001

Bacterial cells are full of fluid, and they will burst if they are not able to respond to a build up of pressure. Fortunately, the membrane of a bacterial cell contains channels that can detect the increased mechanical stress on the cell membrane and then open to relieve the pressure.

In many bacterial cells, the last defence against the cell exploding is called the mechanosensitive channel of large conductance (MscL). This is made of five proteins, each of which consists of TM1 and TM2 helixes, which are responsible for opening and closing the channel. Two models have been proposed to explain how the channels are opened. In the barrel-stave model, the TM1 helix moves, while the TM2 helix remains stationary. This results in an open pore that is lined with TM1 and TM2 helixes in the same way that wooden staves line a barrel. In the helix-tilt model, both helixes tilt towards the membrane to open the channel.

Wang et al. have now used a technique called single-molecule fluorescence resonance energy transfer (FRET) to explore the structure of the open channel in E. coli in order to determine which model is correct. In this technique an individual channel is labeled with two different fluorescent molecules. By illuminating the channel with light of a wavelength that excites the first fluorescent molecule, and measuring the strength of the fluorescence from the second molecule, it is possible to work out the distance between the two molecules. From this, the structure of the channel and how it opens and closes can be explored.

Previous attempts to measure the diameters of open channels using fluorescence techniques have suffered from issues caused by the use of large numbers of fluorescent molecules. This has made it necessary to use computational modeling to extract the required data. By looking at a series of individual proteins, Wang et al. overcame these problems and found that the diameter of the fully open pore is 2.8 nm. The result provides strong support for the helix-tilt model.

DOI:http://dx.doi.org/10.7554/eLife.01834.002

Assessment of the antigen-specific antibody response induced by mucosal administration of a GnRH conjugate entrapped in lipid nanoparticles

Vaccines administered parenterally have been developed against gonadotrophin-releasing hormone (GnRH) for anti-fertility and anti-cancer purposes. The aim of this study was to demonstrate whether mucosal delivery using GnRH immunogens entrapped in lipid nanoparticles (LNP) could induce anti-GnRH antibody titers. Immunogens consisting of KLH (keyhole limpet hemocyanin) conjugated to either GnRH-I or GnRH-III analogues were entrapped in LNP. Loaded non-ionic surfactant vesicles (NISVs) were administered subcutaneously, while nasal delivery was achieved using NISV in xanthan gum and oral delivery using NISV containing deoxycholate (bilosomes). NISV and bilosomes had similar properties: they were spherical, in the nanometre size range, with a slightly negative zeta potential and surface properties that changed with protein loading and inclusion of xanthan gum. Following immunization in female BALB/c mice, systemic antibody responses were similar for both GnRH-I and GnRH-III immunization. Only nasal delivery proved to be successful in terms of producing systemic and mucosal antibodies.

FROM THE CLINICAL EDITOR

The main research question addressed in this study was whether mucosal delivery using gonadotrophin-releasing hormone immunogens entrapped in lipid nanoparticles could induce anti-GnRH antibody titers. Only nasal delivery proved to be successful in terms of producing systemic and mucosal antibodies with this approach.

Sirolimus encapsulated liposomes for cancer therapy: physicochemical and mechanical characterization of sirolimus distribution within liposome bilayers

Sirolimus has recently been introduced as a therapeutic agent for breast and prostate cancer. In the current study, conventional and Stealth liposomes were used as carriers for the encapsulation of sirolimus. The physicochemical characteristics of the sirolimus liposome nanoparticles were investigated including the particle size, zeta potential, stability and membrane integrity. In addition atomic force microscopy was used to study the morphology, surface roughness and mechanical properties such as elastic modulus deformation and deformation. Sirolimus encapsulation in Stealth liposomes showed a high degree of deformation and lower packing density especially for dipalmitoyl-phosphatidylcholine (DPPC) Stealth liposomes compared to unloaded. Similar results were obtained by differential scanning calorimetry (DSC) studies; sirolimus loaded liposomes were found to result in a distorted state of the bilayer. X-ray photon electron (XPS) analysis revealed a uniform distribution of sirolimus in multilamellar DPPC Stealth liposomes compared to a nonuniform, greater outer layer lamellar distribution in distearoylphosphatidylcholine (DSPC) Stealth liposomes.

Non-labeled monitoring of targeted liposome interactions with a model receptor surface: effect of flow rate and water content

In this study, we present a novel in vitro approach that utilizes two surface-sensitive and label-free techniques, i.e. surface plasmon resonance (SPR) and quartz crystal microbalance (QCM), to study the interfacial events during liposome-target surface interactions. The flow channels of SPR and QCM devices were first synchronized via hydrodynamic modeling. Biotin-streptavidin was used as a model pair and self-assembled monolayers (SAMs) were utilized as model surfaces for targeted liposome-surface interaction studies. The interactions between biotin-liposomes and the streptavidin-biotin-SAM surfaces were investigated under controlled shear flows using the synchronized SPR and QCM devices. The response of the liposome interaction was monitored as a function of the flow rate. The affinity and the amount of bound liposome indicated that the increased flow rate improved the binding of the targeted liposomes to the model membrane surfaces. The combined use of the synchronized SPR and QCM devices for nanoparticle interaction studies clearly demonstrates the effect of the flow rate (or the shear stress) on the liposome binding. Our results suggest that the binding of liposomes to the model membranes is flow rate and shear stress regulated. Thus, the flow rate (or the shear stress), which is usually neglected, should be taken into account during the development and optimization of targeted liposome formulations. In addition, the water content within the liposome layer (including the water inside the liposomes and the water between the liposomes) had a significant influence on the visco-elasticity and the binding kinetics to the SAM surfaces.

Adsorption kinetics of DPPG liposome layers: a quantitative analysis of surface roughness

Roughness of a positively charged poly(allylamine hydrochloride) (PAH) polyelectrolyte surface was shown to strongly influence the adsorption of 1.2-dipalmitoyl-sn-3-glycero-[phosphorrac-(1-glycerol)] (DPPG) liposomes on it. The adsorption kinetic curves of DPPG liposomes onto a low-roughness PAH layer reveal an adsorbed amount of 5 mg/m², pointing to liposome rupture, whereas a high-roughness surface leads to adsorbed amounts of 51 mg/m², signifying adsorption of intact liposomes. The adsorption kinetic parameters calculated from adsorption kinetic curves allow us to conclude that the adsorption process is due to electrostatic interactions and also depends on processes such as diffusion and reorganization of lipids on the surface. Analysis of the roughness kinetics enabled us to calculate a growth exponent of 0.19 ± 0.07 and a roughness exponent of around 0.84, revealing that DPPG liposomes adsorbed onto rough surfaces follow the Villain self-affine model. By relating self-affine surfaces with hydrophobicity, the liposome integrity was explained by the reduction in the number of water molecules on the PAH surface, contributing to counterion anchorage near PAH ionic groups, reducing the liposome/PAH layer electrostatic forces and, consequently, avoiding liposome rupture.

Anesthetics interacting with lipid rafts

The exact mechanism by which anesthetics induce cell membrane-mediated modifications is still an open question. Although the fluidization effect of the anesthetic molecules on the cellular membrane is widely recognized, it is not known if anesthetics show any preference for specific membrane domains, namely the lipid rafts. The importance of these membrane micro-domains derives from the fact that they have been associated with cell signaling pathways, as well as with specific drug interactions. The objective of this work is to contribute for the elucidation of this question through the comparison of the anesthetic interactions with membranes of various lipid compositions. Liposomes prepared with an equimolar mixture of POPC, sphingomyelin and cholesterol, were chosen as models for lipid rafts. The interactions of these liposomes with two local anesthetics, tetracaine and lidocaine, and one general anesthetic, propofol, were studied. The effect of cholesterol was investigated by comparing anesthetic interactions with POPC/SM liposomes and POPC/SM/CHOL liposomes. The following experimental techniques were used: quartz crystal microbalance with dissipation, differential scanning calorimetry and phosphorus nuclear magnetic resonance. Although the liposomes investigated by the different techniques are not in the same conditions, it is possible to assemble the information obtained from all experimental techniques employed to reach a general conclusion. Tetracaine interacts more with raftlike domains, lidocaine induces stronger modifications on POPC/SM liposomes and the results for propofol are not fully conclusive but it seems to be the least prone to lipid interactions. The results were compared with those obtained with DMPC-containing liposomes, reported in a previous work.