Oxidation of cod phospholipids in liposomes: Effects of salts, pH and zeta potential

Development of novel lipoplex formulation methodologies to improve large-scale transient transfection for lentiviral vector manufacture

Large-scale transient transfection has advanced significantly over the last 20 years, enabling the effective production of a diverse range of biopharmaceutical products, including viral vectors. However, a number of challenges specifically related to transfection reagent stability and transfection complex preparation times remain. New developments and improved transfection technologies are required to ensure that transient gene expression-based bioprocesses can meet the growing demand for viral vectors. In this paper, we demonstrate that the growth of cationic lipid-based liposomes, an essential step in many cationic lipid-based transfection processes, can be controlled through adoption of low pH (pH 6.40 to pH 6.75) and in low salt concentration (0.2× PBS) formulations, facilitating improved control over the nanoparticle growth kinetics and enhancing particle stability. Such complexes retain the ability to facilitate efficient transfection for prolonged periods compared with standard preparation methodologies. These findings have significant industrial applications for the large-scale manufacture of lentiviral vectors for two principal reasons. First, the alternative preparation strategy enables longer liposome incubation times to be used, facilitating effective control in a good manufacturing practices setting. Second, the improvement in particle stability facilitates the setting of wider process operating ranges, which will significantly improve process robustness and maximise batch-to-batch control and product consistency.

Preparation and in vivo evaluation of an intravenous emulsion loaded with an aprepitant-phospholipid complex

In present, there was no detailed report on the formulation optimization and quality evaluation of aprepitant (APT) injectable lipid emulsion (APT-IE). The aim of the present investigation was to prepare and evaluate its properties of APT-IE loaded with an APT phospholipid complex (APT-PC) in vitro and in vivo. APT-PC was obtained by solvent evaporation with APT and phospholipids, then analyzed by X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry. Lipid emulsions are a new formulation that can reduce side effects and improve drug loading.APT-IE prepared by High-pressure homogenization and optimized by response surface methodology (RSM). The proportion of sodium oleate, poloxamer 188 and soybean oil were selected as variables for the optimization. The optimal formulation of ATP-IE had the following characteristics: particle size, 82.83 ± 1.89 nm; polydispersity index, 0.243 ± 0.008; zeta potential, -59.0 ± 2.54 mV; encapsulation efficiency, 98.84%±1.43%; drug loading, 7.08 ± 0.16 mg/mL; and osmotic pressure, 301 ± 2.15 mOsmol/kg. Transmission electron microscopy images indicated that the particle diameter of APT-IE was approximately 100 nm, with a morphology of spheroidal or spherical. APT-IE exhibited sufficient stability after storage at 4 ± 2 °C for more than 6 months. The results of the pharmacokinetic study demonstrated that APT-IE had the advantages of better safety, higher bioavailability, and obvious liver targeting than APT solution (APT-SL). The area under the curve (AUC) of APT-IE was 3-fold enhanced compared with APT-SL. The targeted enhancement multiple of APT-IE to liver tissue was greater than that of APT-SL. These results suggested that APT-IE has broad clinical application and industrial production potential.

Recent Trends in Improving the Oxidative Stability of Oil-Based Food Products by Inhibiting Oxidation at the Interfacial Region

In recent years, new approaches have been developed to limit the oxidation of oil-based food products by inhibiting peroxidation at the interfacial region. This review article describes and discusses these particular approaches. In bulk oils, modifying the polarity of antioxidants by chemical methods (e.g., esterifying antioxidants with fatty alcohol or fatty acids) and combining antioxidants with surfactants with low hydrophilic–lipophilic balance value (e.g., lecithin and polyglycerol polyricinoleate) can be effective strategies for inhibiting peroxidation. Compared to monolayer emulsions, a thick interfacial layer in multilayer emulsions and Pickering emulsions can act as a physical barrier. Meanwhile, high viscosity of the water phase in emulsion gels tends to hinder the diffusion of pro-oxidants into the interfacial region. Furthermore, applying surface-active substances with antioxidant properties (such as proteins, peptides, polysaccharides, and complexes of protein-polysaccharide, protein-polyphenol, protein-saponin, and protein-polysaccharide-polyphenol) that adsorb at the interfacial area is another novel method for enhancing oil-in-water emulsion oxidative stability. Furthermore, localizing antioxidants at the interfacial region through lipophilization of hydrophilic antioxidants, conjugating antioxidants with surfactants, or entrapping antioxidants into Pickering particles can be considered new strategies for reducing the emulsion peroxidation.

Model systems for studying lipid oxidation associated with muscle foods: Methods, challenges, and prospects

Lipid oxidation is a complex process in muscle-based foods (red meat, poultry and fish) causing severe quality deterioration, e.g., off-odors, discoloration, texture defects and nutritional loss. The complexity of muscle tissue -both composition and structure- poses as a formidable challenge in directly clarifying the mechanisms of lipid oxidation in muscle-based foods. Therefore, different in vitro model systems simulating different aspects of muscle have been used to study the pathways of lipid oxidation. In this review, we discuss the principle, preparation, implementation as well as advantages and disadvantages of seven commonly-studied model systems that mimic either compositional or structural aspects of actual meat: emulsions, fatty acid micelles, liposomes, microsomes, erythrocytes, washed muscle mince, and muscle homogenates. Furthermore, we evaluate the prospects of stem cells, tissue cultures and three-dimensional printing for future model system development. Based on this reviewing of oxidation models, tailoring correct model to different study aims could be facilitated, and readers are becoming acquainted with advantages and shortcomings. In addition, insight into recent technology developments, e.g., stem cell- and tissue-cultures as well as three-dimensional printing could provide new opportunities to overcome the current bottlenecks of lipid oxidation studies in muscle.

Does membrane curvature elastic energy play a role in mediating oxidative stress in lipid membranes?

The effects of oxidative stress on cells are associated with a wide range of pathologies. Oxidative stress is predominantly initiated by the action of reactive oxygen species and/or lipoxygenases on polyunsaturated fatty acid containing lipids. The downstream products are oxidised phospholipids, bioactive aldehydes and a range of Schiff base by-products between aldehydes and lipids, or other biomacromolecules. In this review we assess the impact of oxidative stress on lipid membranes, focusing on the changes that occur to the curvature preference (lipid spontaneous curvature) and elastic properties of membranes, since these biophysical properties modulate phospholipid homeostasis. Studies show that the lipid products of oxidative stress reduce stored curvature elastic energy in membranes. Based upon this observation, we hypothesize that the effects of oxidative stress on lipid membranes will be reduced by compounds that increase stored curvature elastic energy. We find a strong correlation appears across literature studies that we have reviewed, such that many compounds like vitamin E, Curcumin, Coenzyme Q10 and vitamin A show behaviour consistent with this hypothesis. Finally, we consider whether age-related changes in lipid composition represent the homeostatic response of cells to compensate for the accumulation of in vivo lipid oxidation products.

Impact of pH, ferrous ions, and tannic acid on lipid oxidation in plant-based emulsions containing saponin-coated flaxseed oil droplets

The influence of pH (pH 3, 5 and 7), ferrous ions (0 or 100 μM Fe²⁺), and tannic acid (0 to 0.1% TA) on the rate of lipid oxidation in plant-based emulsions containing quillaja saponin-coated flaxseed oil droplets was studied. Tannic acid formed complexes with Fe²⁺ whose properties depended on TA:Fe²⁺ ratio and pH. Emulsions were incubated at 37 °C in the dark, and changes in their particle size, surface potential, appearance, microstructure, and lipid oxidation status were monitored over time. The initial ζ-potential and mean particle diameter of the emulsions were -68 mV and 0.18 μm, respectively. In the absence of TA, the particle size increased appreciably during storage due to droplet coalescence, as rapid oxidation occurred. In the presence of TA, the emulsions were more resistant to both droplet aggregation and lipid oxidation, as a result of its strong ferrous ion-binding properties. The lipid oxidation rate increased with decreasing pH, which was attributed to an increase in ferrous ion's water-solubility and activity in acidic solutions. The addition of Fe²⁺ greatly accelerated lipid oxidation, but the oxidation rate was decreased by also adding TA. These results suggest that tannic acid is an effective antioxidant in emulsions, which can be attributed to its ferrous ion-chelation properties.

Oxidation of Polyunsaturated Lipid Membranes by Photocatalytic Titanium Dioxide Nanoparticles: Role of pH and Salinity

In the present study, UV-induced membrane destabilization by TiO₂ (anatase) nanoparticles was investigated by neutron reflectometry (NR), small-angle X-ray scattering (SAXS), quartz crystal microbalance with dissipation (QCM-D), dynamic light scattering (DLS), and ζ-potential measurements for phospholipid bilayers formed by zwitterionic palmitoyloleoylphosphatidylcholine (POPC) containing biologically relevant polyunsaturations. TiO₂ nanoparticles displayed pH-dependent binding to such bilayers. Nanoparticle binding alone, however, has virtually no destabilizing effects on the lipid bilayers. In contrast, UV illumination in the presence of TiO₂ nanoparticles activates membrane destabilization as a result of lipid oxidation caused by the generation of reactive oxygen species (ROS), primarily ^•OH radicals. Despite the short diffusion length characterizing these, the direct bilayer attachment of TiO₂ nanoparticles was demonstrated to not be a sufficient criterion for an efficient UV-induced oxidation of bilayer lipids, the latter also depending on ROS generation in bulk solution. From SAXS and NR, minor structural changes were seen when TiO₂ was added in the absence of UV exposure, or on UV exposure in the absence of TiO₂ nanoparticles. In contrast, UV exposure in the presence of TiO₂ nanoparticles caused large-scale structural transformations, especially at high ionic strength, including gradual bilayer thinning, lateral phase separation, increases in hydration, lipid removal, and potential solubilization into aggregates. Taken together, the results demonstrate that nanoparticle-membrane interactions ROS generation at different solution conditions act in concert to induce lipid membrane destabilization on UV exposure and that both of these need to be considered for understanding the performance of UV-triggered TiO₂ nanoparticles in nanomedicine.

Following the Fate of Dye-Containing Liposomes In Vitro

The rather limited success of translation from basic research to clinical application has been highlighted as a major issue in the nanomedicine field. To identify the factors influencing the applicability of nanosystems as drug carriers and potential nanomedicine, we focused on following their fate through fluorescence-based assays, namely flow cytometry and imaging. These methods are often used to follow the nanocarrier internalization and targeting; however, the validity of the obtained results strictly depends on how much the nanosystem’s fate can be inferred from the fate of fluorescent dyes. To evaluate the parameters that affect the physicochemical and biological stability of the labeled nanosystems, we studied the versatility of two lipid dyes, TopFluor^®-PC and Cy5-DSPE, in conventional liposomes utilizing well-defined in vitro assays. Our results suggest that the dye can affect the major characteristics of the system, such as vesicle size and zeta-potential. However, a nanocarrier can also affect the dye properties. Medium, temperature, time, fluorophore localization and its concentration, as well as their interplay, affect the outcome of tracing experiments. Therefore, an in-depth characterization of the labeled nanosystem should be fundamental to understand the conditions that validate the results within the screening process in optimization of nanocarrier.

Plant-Based Nanoparticles Prepared from Proteins and Phospholipids Consisting of a Core-Multilayer-Shell Structure: Fabrication, Stability, and Foamability

Gliadin-phospholipid hybrid nanoparticles with a core-multilayered-shell internal structure were fabricated using a coassembly approach based on antisolvent coprecipitation. The mean particle diameters of the nanoparticles depended on their composition, increasing from 78 to 145 nm as the mass ratio of gliadin to phospholipid (G/P) increased from 7:3 to 3:7. The hybrid nanoparticles had better pH, salt, and thermal stabilities than simple gliadin nanoparticles. Hybrid nanoparticles with the highest phospholipid fraction (G/P 3:7) had the best pH, salt, and thermal stabilities, remaining stable from pH 3 to 8, from 0 to 300 mmol/L NaCl, and when boiled at pH 4 or 5 for 90 min. Hybrid nanoparticles also had better foam-formation and stability characteristics than gliadin nanoparticles, particularly at the highest phospholipid level. The structured nanoparticles developed in this study may therefore be useful for application in commercial products, for example, as delivery systems, emulsifiers, or foaming agents.

Lyophilization of a triply unsaturated phospholipid: effects of trace metal contaminants

As liquid liposomal formulations are prone to chemical degradation and aggregation, these formulations often require freeze drying (e.g., lyophilization) to achieve sufficient shelf-life. However, liposomal formulations may undergo oxidation during lyophilization and/or during prolonged storage. The goal of the current study was to characterize the degradation of 1,2-dilinolenoyl-sn-glycero-3-phosphocholine (DLPC) during lyophilization and to also probe the influence of metal contaminants in promoting the observed degradation. Aqueous sugar formulations containing DLPC (0.01 mg/ml) were lyophilized, and DLPC degradation was monitored using HPLC/UV and GC/MS methods. The effect of ferrous ion and sucrose concentration, as well as lyophilization stage promoting lipid degradation, was investigated. DLPC degradation increased with higher levels of ferrous ion. After lyophilization, 103.1 ± 1.1%, 66.9 ± 0.8%, and 28.7 ± 0.7% DLPC remained in the sucrose samples spiked with 0.0 ppm, 0.2 ppm, and 1.0 ppm ferrous ion, respectively. Lipid degradation predominantly occurs during the freezing stage of lyophilization. Sugar concentration and buffer ionic strength also influence the extent of lipid degradation, and DLPC loss correlated with degradation product formation. We conclude that DLPC oxidation during the freezing stage of lyophilization dramatically compromises the stability of lipid-based formulations. In addition, we demonstrate that metal contaminants in sugars can become highly active when lyophilized in the presence of a reducing agent.

Oxidative stability of marine phospholipids in the liposomal form and their applications

Marine phospholipids (MPL) have attracted a great deal of attention recently as they are considered to have a better bioavailability, a better resistance towards oxidation and a higher content of eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) than oily triglycerides (fish oil) from the same source. Due to their tight intermolecular packing conformation at the sn-2 position and their synergism with α-tocopherol present in MPL extracts, they can form stable liposomes which are attractive ingredients for food or feed applications. However, MPL are still susceptible to oxidation as they contain large amounts polyunsaturated fatty acids and application of MPL in food and aquaculture industries is therefore a great challenge for researchers. Hence, knowledge on the oxidative stability of MPL and the behavior of MPL in food and feed systems is an important issue. For this reason, this review was undertaken to provide the industry and academia with an overview of (1) the stability of MPL in different forms and their potential as liposomal material, and (2) the current applications and future prospects of MPL in both food and aquaculture industries with special emphasis on MPL in the liposomal form.

The role of iron in peroxidation of polyunsaturated fatty acids in liposomes

This work investigated iron-catalyzed lipid oxidation in marine phospholipid liposomes. Oxygen consumption was used as a method to study lipid oxidation at pH 5.5 and 30 degrees C. The relationship between consumed oxygen and amount of peroxides (PV) and thiobarbituric reactive substances (TBARS) formed showed that both Fe2+ and Fe3+ catalyzed lipid oxidation. When Fe2+ was added to liposomes at a concentration of approximately 10 microM, an initial drop in dissolved oxygen (oxygen uptake rate >258 microM/min), followed by a slower linear oxygen uptake (oxygen uptake rate 4-6 microM/min), was observed. Addition of Fe3+ induced only the linear oxygen uptake. The initial fast drop in dissolved oxygen was due to oxidation of Fe2+ to Fe3+ by preexisting lipid peroxides (rate 79 microM Fe2+/min). Fe3+ is reduced by peroxides to Fe2+ at a slow rate (0.25 microM Fe3+/min at 30 degrees C) in a pseudo-first-order reaction. The redox cycling between Fe2+ and Fe3+ leads to an equilibrium between Fe2+ and Fe3+ resulting in a linear oxygen uptake. During the linear oxygen uptake, the interaction of Fe (3+) with lipid peroxide is the rate-limiting factor. Both alkoxy and peroxy radicals are formed by breakdown of peroxides by Fe2+ and Fe3+. These radicals react with fatty acids giving lipid radicals reacting with oxygen.