Membrane permeability and stability of liposomes made from highly fluorinated double-chain phosphocholines derived from diaminopropanol, serine or ethanolamine

Entropic effects enable life at extreme temperatures

Maintaining membrane integrity is a challenge at extreme temperatures. Biochemical synthesis of membrane-spanning lipids is one adaptation that organisms such as thermophilic archaea have evolved to meet this challenge and preserve vital cellular function at high temperatures. The molecular-level details of how these tethered lipids affect membrane dynamics and function, however, remain unclear. Using synthetic monolayer-forming lipids with transmembrane tethers, here, we reveal that lipid tethering makes membrane permeation an entropically controlled process that helps to limit membrane leakage at elevated temperatures relative to bilayer-forming lipid membranes. All-atom molecular dynamics simulations support a view that permeation through membranes made of tethered lipids reduces the torsional entropy of the lipids and leads to tighter lipid packing, providing a molecular interpretation for the increased transition-state entropy of leakage.

Liposome: composition, characterisation, preparation, and recent innovation in clinical applications

In the last decades, pharmaceutical interested researches aimed to develop novel and innovative drug delivery techniques in the medical and pharmaceutical fields. Recently, phospholipid vesicles (Liposomes) are the most known versatile assemblies in the drug delivery systems. The discovery of liposomes arises from self-forming enclosed phospholipid bilayer upon coming in contact with the aqueous solution. Liposomes are uni or multilamellar vesicles consisting of phospholipids produced naturally or synthetically, which are readily non-toxic, biodegradable, and are readily produced on a large scale. Various phospholipids, for instance, soybean, egg yolk, synthetic, and hydrogenated phosphatidylcholine consider the most popular types used in different kinds of formulations. This review summarises liposomes composition, characterisation, methods of preparation, and their applications in different medical fields including cancer therapy, vaccine, ocular delivery, wound healing, and some dermatological applications.

Egg Yolk Extracts as Potential Liposomes Shell Material: Composition Compared with Vesicles Characteristics

Our aim was to propose simple extraction process to obtain phospholipids along with yolk-derived vitamins and fats. Five extracts marked as ethanol/acetone, methanol-chloroform/acetone, hot ethanol, hexane, and cold ethanol were developed and compared. Extracts' compositions were analyzed in terms of phospholipid, polar and nonpolar fraction, cholesterol, carotenoids, and tocopherols content. Further, liposomes prepared from extracts were characterized. The highest extraction efficiency was achieved by a one-step hexane procedure. However, that sample, in contrast to the other four extracts, revealed distinctively lower permeability when used for liposomes membrane formation. Principal component analysis proved that major components contents were decisive for liposomes membranes permeability, whereas minor constituents' content controlled zeta potential and Z-average size.

PRACTICAL APPLICATION

Liposomes are nanocarriers widely used in pharmaceutical industry. Due to intravenous route of administration, they have to be produced from phospholipids of very fine purity. On the other hand, there is increasing interest in nanoencapsulation of labile, bioactive substances for manufacturing of health promoting food. Unfortunately, high-price pure phospholipids are prohibitive for food applications. The use of raw material obtained by simple extraction procedure instead of highly purified phospholipids could be an attractive alternative for food industry.

Near-Infrared Activated Release of Doxorubicin from Plasmon Resonant Liposomes

Precise control of drug release from nanoparticles can improve efficacy and reduce systemic toxicity associated with administration of certain medications. Here, we combined two phenomena, photothermal conversion in plasmon resonant gold coating and thermal sensitivity of liposome compositions, to achieve a drug delivery system that rapidly releases doxorubicin in response to external stimulus.

Methods: Thermosensitive liposomes were loaded with doxorubicin and gold-coated to produce plasmon resonant drug delivery system. Plasmon resonance facilitates release of contents upon near-infrared laser illumination, thus providing spatial and temporal control of the process. This controlled delivery system was compared to thermosensitive liposomes without gold coating and to the FDA-approved Doxil that was gold-coated to create a plasmon resonant coating. Release of doxorubicin from the gold-coated thermosensitive liposomes was further confirmed by tests of cell viability.

Results: Upon laser illumination at 760 nm and 88 mW/cm² power density, permeability of plasmon resonant liposomes increased by three orders of magnitude, from 70×10^-12 to 60,000x10^-12 cm/s. In control experiments, mild hyperthermia (42°C) increased permeability of these thermosensitive liposomes to just 3,700×10^-12 cm/s. Neither hyperthermia nor laser illumination elicit content release from Doxil or plasmon resonant Doxil obtained by gold coating. Laser-induced release of doxorubicin from plasmon resonant thermosensitive liposomes resulted in the loss of cell viability significantly greater than in any of the control groups.

Conclusion: Combination of thermosensitive liposomes with plasmon resonant coating enables rapid, controlled release, not currently available in pharmaceutical formulations of anticancer drugs.

Copying of Mixed-Sequence RNA Templates inside Model Protocells

The chemical replication of RNA inside fatty acid vesicles is a plausible step in the emergence of cellular life. On the primitive Earth, simple protocells with the ability to import nucleotides and short oligomers from their environment could potentially have replicated and retained larger genomic RNA oligonucleotides within a spatially defined compartment. We have previously shown that short 5'-phosphoroimidazolide-activated "helper" RNA oligomers enable the nonenzymatic copying of mixed-sequence templates in solution, using 5'-phosphoroimidazolide-activated mononucleotides. Here, we report that citrate-chelated Mg2+, a catalyst of nonenzymatic primer extension, enhances fatty acid membrane permeability to such short RNA oligomers up to the size of tetramers, without disrupting vesicle membranes. In addition, selective permeability of short, but not long, oligomers can be further enhanced by elevating the temperature. The ability to increase the permeability of fatty acid membranes to short oligonucleotides allows for the nonenzymatic copying of RNA templates containing all four nucleotides inside vesicles, bringing us one step closer to the goal of building a protocell capable of Darwinian evolution.

Progress in the synthesis of fluorinated phosphatidylcholines for biological applications

Fluorinated phospholipids have attracted a lot of interest over the past 40 years. While mono- and polyfluorinated analogs are mostly designed to be used as ¹⁹F NMR probes, highly fluorinated phospholipids are mainly developed as drug delivery devices and oxygen carriers. This review describes their synthetic pathways, their properties and potential applications.

Permeability across lipid membranes

Molecular permeation through lipid membranes is a fundamental biological process that is important for small neutral molecules and drug molecules. Precise characterization of free energy surface and diffusion coefficients along the permeation pathway is required in order to predict molecular permeability and elucidate the molecular mechanisms of permeation. Several recent technical developments, including improved molecular models and efficient sampling schemes, are illustrated in this review. For larger penetrants, explicit consideration of multiple collective variables, including orientational, conformational degrees of freedom, are required to be considered in addition to the distance from the membrane center along the membrane normal. Although computationally demanding, this method can provide significant insights into the molecular mechanisms of permeation for molecules of medical and pharmaceutical importance. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.

Hexanoyl-Chitosan-PEG Copolymer Coated Iron Oxide Nanoparticles for Hydrophobic Drug Delivery

Nanoparticle (NP) formulations may be used to improve in vivo efficacy of hydrophobic drugs by circumventing solubility issues and providing targeted delivery. In this study, we developed a hexanoyl-chitosan-PEG (CP6C) copolymer coated, paclitaxel (PTX)-loaded, and chlorotoxin (CTX) conjugated iron oxide NP (CTX-PTX-NP) for targeted delivery of PTX to human glioblastoma (GBM) cells. We modified chitosan with polyethylene glycol (PEG) and hexanoyl groups to obtain the amphiphilic CP6C. The resultant copolymer was then coated onto oleic acid-stabilized iron oxide NPs (OA-IONP) via hydrophobic interactions. PTX, a model hydrophobic drug, was loaded into the hydrophobic region of IONPs. CTX-PTX-NP showed high drug loading efficiency (>30%), slow drug release in PBS and the CTX-conjugated NP was shown to successfully target GBM cells. Importantly, the NPs showed great therapeutic efficacy when evaluated in GBM cell line U-118 MG. Our results indicate that this nanoparticle platform could be used for loading and targeted delivery of hydrophobic drugs.

Synthesis and self-assembly of an amino-functionalized hybrid hydrocarbon/fluorocarbon double-chain phospholipid

In this article, we designed and synthesized an amino-functionalized hybrid hydrocarbon/fluorocarbon double-chain phospholipid (ACFPC) containing one chain with the hydrophobic fluorocarbon chain and terminal amino, amide, and ether linkages and one chain with the hydrocarbon chain. The novel reactive phospholipid was fully characterized with Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), and mass spectrometry (MS). Then the self-assembly behaviors of the hybrid double-chain phospholipid in aqueous and acidic media were investigated with transmission electron microscopy (TEM), the critical micelle concentration (cmc), dynamic light scattering (DLS), and the hydrocarbon double-chain phospholipid (ACCPC) for comparison. Moreover, their self-assembled structures in aqueous and acidic media were simulated using the dissipative particle dynamics (DPD) method. These results suggest that the fluorocarbon/hydrocarbon hybrid-chain phospholipid can self-assemble into a more stable microstructure compared to the double hydrocarbon chain phospholipid, which will have the potential ability to self-assemble into a more stable minicking biomembrane structure onto material surfaces to inhibit protein adsorption under complicated physiological conditions.

Characterization of dynamically prepared phospholipid-modified reversed-phase columns

We have modified a reversed-phase (RP8) column by passing through it an aqueous solution of phosphatidylcholine-based liposomes. The phospholipids from the liposomes adsorb onto the octyl chain of the stationary phase, thus altering the nature of the stationary phase and of the chromatographic interactions. The properties of the phospholipid-modified column were investigated using solutes belonging to several chemical classes. We found that the retention factors of negatively and positively charged solutes decreased as the amount of phospholipid in the column was increased. For the solutes studied here the extent of the decrease was smaller for the positive solutes. With neutral solutes, the retention factors of some (benzenediols) increased markedly while with others (ketones) the retention factors decreased. The selectivities between the various solutes on the phospholipid-modified column were different than on the original reversed-phase column. The retention behavior of the solutes can be explained in terms of (1) effective shielding of the hydrophobic part of the stationary phase by the polar head groups of the phospholipids and (2) hydrogen bond formation between the solutes and the carbonyl oxygens as well as the non-ester phosphate oxygens in the polar head groups of the phospholipids.

Effect of fluorine substitution on the interaction of lipophilic ions with the plasma membrane of mammalian cells

The effects of the anionic tungsten carbonyl complex [W(CO)(5)SC(6)H(5)](-) and its fluorinated analog [W(CO)(5)SC(6)F(5)](-) on the electrical properties of the plasma membrane of mouse myeloma cells were studied by the single-cell electrorotation technique. At micromolar concentrations, both compounds gave rise to an additional antifield peak in the rotational spectra of cells, indicating that the plasma membrane displayed a strong dielectric dispersion. This means that both tungsten derivatives act as lipophilic ions that are able to introduce large amounts of mobile charges into the plasma membrane. The analysis of the rotational spectra allowed the evaluation not only of the passive electric properties of the plasma membrane and cytoplasm, but also of the ion transport parameters, such as the surface concentration, partition coefficient, and translocation rate constant of the lipophilic anions dissolved in the plasma membrane. Comparison of the membrane transport parameters for the two anions showed that the fluorine-substituted analog was more lipophilic, but its translocation across the plasma membrane was slower by at least one order of magnitude than that of the parent hydrogenated anion.

Phase behavior of fluorocarbon and hydrocarbon double-chain hydroxylated and galactosylated amphiphiles and bolaamphiphiles. Long-term shelf-stability of their liposomes

This paper describes the morphological characterization, by freeze-fracture electron microscopy, and the thermotropic phase behavior, by differential scanning calorimetry and/or X-ray scattering, of aqueous dispersions of various hydroxylated and galactosylated double-chain amphiphiles and bolaamphiphiles, several of them containing one or two hydrophobic fluorocarbon chains. Colloidal systems are observed in water with the hydroxylated hydrocarbon or fluorocarbon bolaamphiphiles only when they are dispersed with a co-amphiphile such as rac-1,2-dimyristoylphosphatidylcholine (DMPC) or rac-1,2-distearoylphosphatidylcholine (DSPC). Liposomes are formed providing the relative content of bolaamphiphiles does not exceed 20% mol. Most of these liposomes can be thermally sterilized and stored at room temperature for several months without any significant modification of their size and size distribution. The hydrocarbon galactosylated bolaamphiphile HO[C24][C12]Gal forms in water a lamellar phase (the gel to liquid-crystal phase transition is complete at 45 degrees C) and a Im3m cubic phase above 47 degrees C. The fluorocarbon HO[C24][F6C5]Gal analog displays a more complex and metastable phase behavior. The fluorinated non-bolaform galactosylated [F8C7][C16]AEGal and SerGal amphiphiles form lamellar phases in water. Low amounts (10% molar ratio) of the HO[C24][F6C5]Gal or HO[C24][C12]Gal bolaamphiphiles or of the single-headed [F8C7][C16]AEGal improve substantially the shelf-stability of reference phospholipon/cholesterol 2/1 liposomes. These liposomes when co-formulated with a single-headed amphiphile from the SerGal series are by far less stable.

Improved stability of highly fluorinated phospholipid-based vesicles in the presence of bile salts

The stability of fluorinated phospholipid-based vesicles in terms of detergent-induced release of encapsulated carboxyfluorescein has been evaluated. The fluorinated liposomes are substantially more resistant towards the lytic action of sodium taurocholate than conventional DSPC or even DSPC/CH 1/1 liposomes. Concerning structure/permeability relationships, the larger the fluorination degree of the membrane, the higher the resistance of the fluorinated liposomes to their destruction by the detergent. These results show that fluorinated liposomes have a promising potential as drug carrier and delivery systems for oral administration.

Transmembrane pH-driven Na+ permeability of fluorinated phospholipid-based membranes

The permeability to the H+/Na+ exchange of fluorinated phospholipid-based membranes has been evaluated by measuring the dissipation rate of a liposomal transmembrane pH gradient in the presence of Na+. The fluorinated liposomes are made from fluorocarbon/hydrocarbon or fluorocarbon/fluorocarbon double-chain ether-connected glycerophosphocholines or amido-connected phosphocholines deriving from diaminopropanol or serine. The fluorocarbon/hydrocarbon mixed-chain phospholipids, as compared to the fluorocarbon/fluorocarbon ones, form membranes that are substantially more able to maintain a transmembrane pH gradient in the presence of NA+ and display a lower Na+ permeability. However, these membranes are more permeable to the H+/Na/ exchange than conventional DSPC (1,2-distearoylphosphatidylcholine) ones. Our results indicate a detrimental impact of the membrane fluorination degree on H+/Na+ permeability: the lower the fluorination degree of the membrane, the lower its H+/Na+ permeability. Concerning structure/permeability relationships, it appears that the replacement of the ester connecting bond in their fluorinated phosphatidylcholine analogues for an ether or amide one lowers the transmembrane H+/Na+ exchange.