Surface Plasmon Resonance Monitoring of Mono-Rhamnolipid Interaction with Phospholipid-Based Liposomes

Variations in the inner core affect the pharmacokinetics of indomethacin-encapsulated polymeric micelles

Hydrophobic ion pairing (HIP) is a drug encapsulation technology that uses electrostatic interactions between a drug and an additive. However, although polymeric micelles can encapsulate hydrophobic drugs in the core, the encapsulated drug often leaks. Therefore, we designed polymeric micelles with HIP functionalized in a hydrophobic inner core using three diblock copolymers comprising polypeptides with different ratios of polar and hydrophobic amino acids and polyethylene glycol (PEG) to encapsulate indomethacin (IND). The three IND-encapsulated HIP micelles showed different area under the curve (AUC) values as an index of blood retention after intravenous injection in mice. Despite having the same PEG shell, IND-PEG-poly(H/F)n showed a 1.56-fold higher AUC than IND-PEG-poly(D/F)n. PEG interface morphologies were evaluated to determine the differences in pharmacokinetic parameters caused by changes in inner core HIP patterns. The micellarized diblock copolymer was desorbed from IND-PEG-poly(D/F)n due to electrostatic repulsion between IND and the diblock copolymer comprising aspartic acid. Our results suggest that changes in the HIP patterns of the micelle inner core affected the PEG interface morphologies, such as PEG density and diblock copolymer desorption from micelles. These phenomena might lead to changes in the interaction of plasma proteins and drug dispositions.

Liposome bilayer stability: emphasis on cholesterol and its alternatives

Liposomes are spherical lipidic nanocarriers composed of natural or synthetic phospholipids with a hydrophobic bilayer and aqueous core, which are arranged into a polar head and a long hydrophobic tail, forming an amphipathic nano/micro-particle. Despite numerous liposomal applications, their use encounters many challenges related to the physicochemical properties strongly affected by their constituents, colloidal stability, and interactions with the biological environment. This review aims to provide a perspective and a clear idea about the main factors that regulate the liposomes' colloidal and bilayer stability, emphasising the roles of cholesterol and its possible alternatives. Moreover, this review will analyse strategies that offer possible approaches to provide more stable in vitro and in vivo liposomes with enhanced drug release and encapsulation efficiencies.

Curved Membrane Mimics for Quantitative Probing of Protein-Membrane Interactions by Surface Plasmon Resonance

A majority of biomimetic membranes used for current biophysical studies rely on planar structures such as supported lipid bilayer (SLB) and self-assembled monolayers (SAMs). While they have facilitated key information collection, the lack of curvature makes these models less effective for the investigation of curvature-dependent protein binding. Here, we report the development and characterization of curved membrane mimics on a solid substrate with tunable curvature and ease in incorporation of cellular membrane components for the study of protein-membrane interactions. The curved membranes were generated with an underlayer lipid membrane composed of DGS-Ni-NTA and POPC lipids on the substrate, followed by the attachment of histidine-tagged cholera toxin (his-CT) as a capture layer. Lipid vesicles containing different compositions of gangliosides, including GA1, GM1, GT1b, and GQ1b, were anchored to the capture layer, providing fixation of the curved membranes with intact structures. Characterization of the curved membrane was accomplished with surface plasmon resonance (SPR), fluorescence recovery after photobleaching (FRAP), and nano-tracking analysis (NTA). Further optimization of the interface was achieved through principal component analysis (PCA) to understand the effect of ganglioside type, percentage, and vesicle dimensions on their interactions with proteins. In addition, Monte Carlo simulations were employed to predict the distribution of the gangliosides and interaction patterns with single point and multipoint binding models. This work provides a reliable approach to generate robust, component-tuning, and curved membranes for investigating protein interactions more pertinently than what a traditional planar membrane offers.

SPRi analysis of molecular interactions of mApoE-functionalized liposomes as drug delivery systems for brain diseases

The application of liposomes (LPs) to central nervous system disorders could represents a turning point in the therapy and quality of life of patients. Indeed, LPs have demonstrated their ability to cross the blood-brain barrier (BBB) and, as a consequence, to enhance the therapeutics delivery into the brain. Some approaches for BBB crossing involve the modification of LP surfaces with biologically active ligands. Among them, the Apolipoprotein E-modified peptide (mApoE) has been used for several LP-based nanovectors under investigation. In this study, we propose Surface Plasmon Resonance imaging (SPRi) for the characterization of multifunctionalized LPs for Glioblastoma treatment. LPs were functionalized with mApoE and with a metallo-protease sensitive lipopeptide to deliver and guarantee the localized release of an encapsulated drug in diseased areas. The SPRi analysis was optimized in order to evaluate the binding affinity between LPs and mApoE receptors, finding that mApoE-LPs generated SPRi signals referred to interactions between mApoE and receptors mainly present in the brain. Moreover, a significant binding between LPs and VCAM-1 (endothelial receptor) was observed, whereas LPs did not interact significantly with peripheral receptors expressed on monocytes and lymphocytes. SPRi results confirmed not only the presence of mApoE on LP surfaces, but also its binding affinity, thanks to the specific interaction with selected receptors. In conclusion, the high sensitivity and the multiplexing capability associated with the low volumes of sample required and the minimal sample preparation, make SPRi an excellent technique for the characterization of multifunctionalized nanoparticles-based formulations.

Glycolipids improve the stability of liposomes: The perspective of bilayer membrane structure

The storage and thermal stability of liposomes, which are amphiphilic carriers, cause very large challenges. However, glycolipid modification may be a potential method to improve the stability of liposomes. In this study, the mechanism by which tilapia head glycolipids improve the stability of liposomes was studied. The head groups of glycolipids and liposomes have a strong interaction (K_a = 633.650 M^-1), mainly due to hydrogen bonds, which promote the formation of microstructure domains between glycolipids and liposomes. In addition, glycolipids caused the bilayer structure of liposomes to rearrange, resulting in an increase in the phase transition temperature, tight arrangement of membrane molecules, and increase in membrane thickness (from 2.4 nm to 3.5 nm). Novelty, the formation of microstructure domains helped prevent the liposomes membrane structure from being disrupted during storage and heat. Therefore, glycolipid modification improved the stability of liposomes. This study can provide new insights into the development of high-stability liposomes.

Strategies for Surface Design in Surface Plasmon Resonance (SPR) Sensing

Surface plasmon resonance (SPR) comprises several surface-sensitive techniques that enable the trace and ultra-trace detection of various analytes through affinity pairing. Although enabling label-free, sensitive detection and real-time monitoring, several issues remain to be addressed, such as poor stability, non-specific adsorption and the loss of operational activity of biomolecules. In this review, the progress over sensor modification, immobilization techniques and novel 2D nanomaterials, gold nanostructures and magnetic nanoparticles for signal amplification is discussed. The advantages and disadvantages of each design strategy will be provided together with some of the recent achievements.

Mechanisms of Influenza Virus HA2 Peptide Interaction with Liposomes Studied by Dual-Wavelength MP-SPR

A phospholipid-based liposome layer was used as an effective biomimetic membrane model to study the binding of the pH-dependent fusogenic peptide (E4-GGYC) from the influenza virus hemagglutinin HA2 subunit. To this end, a multiparameter surface plasmon resonance approach (MP-SPR) was used for monitoring peptide-liposome interactions at two pH values (4.5 and 8) by means of recording sensorgrams in real time without the need for labeling. Biotinylated liposomes were first immobilized as a monolayer onto the surface of an SPR gold chip coated with a streptavidin layer. Multiple sets of sensorgrams with different HA2 peptide concentrations were generated at both pHs. Dual-wavelength Fresnel layer modeling was applied to calculate the thickness (d) and the refractive index (n) of the liposome layer to monitor the change in its optical parameters upon interaction with the peptide. At acidic pH, the peptide, in its α helix form, entered the lipid bilayer of liposomes, inducing vesicle swelling and increasing membrane robustness. Conversely, a contraction of liposomes was observed at pH 8, associated with noninsertion of the peptide in the double layer of phospholipids. The equilibrium dissociation constant KD = 4.7 × 10-7 M of the peptide/liposome interaction at pH 4.5 was determined by fitting the "OneToOne" model to the experimental sensorgrams using Trace Drawer software. Our experimental approach showed that the HA2 peptide at a concentration up to 100 μM produced no disruption of liposomes at pH 4.5.

Effect of Rhamnolipid Amidation on Biosurfactant Adsorption Loss and Oil-Washing Efficiency

Surfactant adsorption loss seriously hinders the economy of surfactant binary flooding technology for enhancing oil recovery, especially for biosurfactants with higher manufacturing costs. Here, biosurfactant rhamnolipid (RL) is chemically modified to develop a more efficient surfactant, rhamnolipid monoethanol amide (RL-MEA), which is characterized by decreased adsorption loss and increased oil-washing efficiency for enhanced oil recovery at a laboratory scale. Synthesis and characterization of the rhamnolipid monoethanol amide are carried out using high-performance liquid chromatography (HPLC), HPLC/MS, ¹H nuclear magnetic resonance (NMR), and Fourier transform infrared (FTIR) spectroscopy. The aggregation behavior is disclosed by surface tension, dynamic light scattering, and fluorescence spectra with pyrene as the probe. The applied performances of RL-MEA in the simulated enhanced oil recovery are researched, including the efficiency of oil washing, wettability to crude oil, and adsorption isotherms on silicates. Compared with the critical micelle concentration (CMC) of rhamnolipid of 14.23 × 10^-5 M in pure water and 9.02 × 10^-5 M in 0.2 M NaCl solution, the modified RL-MEA shows a significantly lower CMC of 7.15 × 10^-5 M in pure water and 5.34 × 10^-5 M in 0.2 M NaCl solution. More importantly, the modified RL-MEA reduces adsorption loss by 20% and enhanced oil-washing efficiency at higher temperatures and salt concentrations compared with the parent RLs. These findings would provide valuable information for developing efficient surfactant flooding agents for harsh reservoir geological conditions.