The phase behaviour ofl-α-phosphatidylcholine in the presence of chlorpromazine under different experimental conditions

The phase behaviour ofl-α-phosphatidylcholine liposomes has been studied as a function of temperature, pH, ionic strength, etc., in the presence and absence of chlorpromazine by a polarization method using 1,6-diphenyl-1,3,5-hexatriene as a fluorescence probe. The gel crystalline to liquid crystalline (T_c), liquid crystalline to cubic (T_II), and cubic to hexagonal (H_II) transition temperatures in multilayer liposomes have been detected, and are found to be affected by chlorpromazine under different experimental conditions.     

Chromatographic purification steps involved in the synthesis of prodrug-liposome-antibody-complexes

Summary The cytostatic effect of the widely used antitumor drug 1-β-D-arabinofuranosyl cytosine (ara C) can be improved by its chemical derivatization to lipophilic prodrugs. We have incorporated these prodrugs together with lipophilic biotin derivatives into membranes of unilamellar liposomes. Monoclonal antibodies were coupled to the biotin residues of the liposomes via avidin-biotin complexation resulting in prodrug-liposome-antibody complexes whichin vitro preferably bind to cells selectively recognized by the immobilized antibodies. The results open a promising way of drug targeting. The components and liposomal derivatives used for the stepwise preparation of the prodrug-liposome antibody complex are purified by means of preparative liquid chromatography. Lipophilic membrane components are chromatographed on silica gel, antibodies on hydroxylapatite and liposomal derivatives on Ultrogel AcA 22 columns. Concentration and desalting are achieved by ultrafiltration. The purification process can be quantitatively pursued by labelling with radioactive components.     

Cyclodextrins lessen the membrane damaging effect of nonionic tensides

Nonylphenyl-ethyleneoxide polymers containing 5, 9 and 30 ethyleneoxide groups per molecule build into the hydrophobic fatty acid chains of the cell membrane phospholipid dipalmitoyl-phosphatidylcholine (DPPC) resulting in a decreased main transition temperature, a decreased enthalpy of the main transition and in enhanced potassium permeability of DPPC liposomes. The -, - and -cyclodextrins form inclusion complexes with the tenzides lowering their free concentration. The complex formation lessens or sometimes totally prevents the membrane damaging effect of tensides. The effectivity order of cyclodextrins is CD>CD>CD.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K. 20–25 July 1986.     

Lipophilic nucleic acids — A flexible construction kit for organization and functionalization of surfaces

Lipophilic nucleic acids have become a versatile tool for structuring and functionalization of lipid bilayers and biological membranes as well as cargo vehicles to transport and deliver bioactive compounds, like interference RNA, into cells by taking advantage of reversible hybridization with complementary strands. This contribution reviews the different types of conjugates of lipophilic nucleic acids, and their physicochemical and self-assembly properties. Strategies for choosing a nucleic acid, lipophilic modification, and linker are discussed. Interaction with lipid membranes and its stability, dynamic structure and assembly of lipophilic nucleic acids upon embedding into biological membranes are specific points of the review. A large diversity of conjugates including lipophilic peptide nucleic acid and siRNA provides tailored solutions for specific applications in bio- and nanotechnology as well as in cell biology and medicine, as illustrated through some selected examples.     

A Study of the Antioxidant Effect of Flavonic Compounds for Preventing Lipid Oxidation by Using Fluorescence Spectroscopy

In this paper a study of the effect of flavonic compounds in preventing and/or reducing the membrane lipid oxidation due to free radical attack was performed by using fluorescence spectroscopy techniques. Lipid peroxidation was investigated by using liposomes-artificial membrane models, which were prepared by lipid hydration method. Their oxidation was performed with a 15-W ultraviolet germicidal lamp having wavelength radiation 253.7 nm. In the first series of experiments, the protective effect of two synthetic antioxidants (quercetin and caffeic acid) against free radicals was monitored, while in the second series two 70% hydroalcoholic extracts from blueberry and blackcurrant leaves was used. It was determined that natural antioxidants have a much higher antioxidant power against free radicals than synthetic compounds but they degrade after two hours of oxidation. Liposomes are better protected when using natural antioxidants, but their degradation is completed more quickly, than in the case of synthetic antioxidants.     

Fabrication of nano-scale liposomes containing doxorubicin using Shirasu porous glass membrane

Nano-scale liposomes were successfully produced using a Shirasu porous glass (SPG) membrane emulsification technique. Primary liposomes prepared by a film-hydration method were treated using SPG membranes with different pore sizes (2.0, 1.0, 0.7, 0.5, and 0.2 μm) for control over the liposome size. The liposome sizes were evaluated using a dynamic light scattering method and their morphologies were observed by optical microscopy and transmission electron microscopy. As the passage number of liposomes through SPG membrane increased, the size and its distribution of the liposomes gradually decreased. A smaller pore size of the SPG membrane and a higher applied pressure resulted in liposomes with a smaller size. After the preparation of nano-scale liposomes containing ammonium sulfate (AS), doxorubicin (DOX) was encapsulated in the liposomes by a remote loading method, where AS served as a precipitant for DOX. The encapsulation efficiency of the DOX was maximized up to 94% when the concentrations of AS and DOX were 250 and 0.045 mM, respectively. We have obtained the release profiles of the liposomes with different sizes. As shown below, liposomes with smaller size exhibited a faster release profile of drug due to the large surface area. These nano-scale liposomes encapsulating an anti-cancer drug can potentially be employed as drug delivery vehicles for intravenous injection.     

Preparation approaches of the coated capillaries with liposomes in capillary electrophoresis

The use of liposomes as coating materials in capillary electrophoresis has recently emerged as an important and popular research area. There are three preparation methods that are commonly used for coating capillaries with liposomes, namely physical adsorption, avidin–biotin binding and covalent coupling. Herein, the three different coating methods were compared, and the liposome-coated capillaries prepared by these methods were evaluated by studying systematically their EOF characterization and performance (repeatability, reproducibility and lifetime). The amount of immobilized phospholipids and the interactions between liposome or phospholipid membrane and neutral compounds for the liposome-coated capillaries prepared by these methods were also investigated in detail. Finally, the merits and disadvantages for each coating method were reviewed.     

DSC and Raman studies of the side chain length effect of ubiquinones on the thermotropic phase behavior of liposomes

Differential scanning calorimetry and Raman spectroscopy have been used to examine the effects of ubiquinones (UQn) on the thermotropic phase behavior of dipalmitoylphosphatidylcholine (DPPC) in multilamellar vesicles, for UQ/DPPC molar ratios ranging from 0.01 to 0.1. The influence of the side chain length has been investigated by comparing the effect of a series of UQ with 2 (UQ2), 4 (UQ4), 6 (UQ6) and 10 isoprene units (UQ10).In the presence of increasing amount of UQ2 or UQ4, concomitant shift of the gel to liquid crystalline phase transition towards lower temperatures and vanishing of the pretransition are observed. Short-chain ubiquinones are thus inserted parallel to phospholipid chains, their benzoquinone ring being close to the DPPC polar headgroups. In addition, broadening and skewing of the main transition peak support the fact that UQ2 and UQ4 are laterally self-organized in highly concentrated regions located at the boundary of lipid domains. The lipid thermotropic behavior is not affected by the presence of other analogues of the series, UQ6 and UQ10. They remain homogeneously dispersed within the midplane of the phospholipid bilayer. Such a chain length dependence on the location and the organization of ubiquinones analogues may be correlated with their biological activities in biomembranes.     

A comparative study of secondary ion yield from model biological membranes using Aun and C60 primary ion sources

Au_n⁺ and C₆₀⁺ primary ion sources have been used to acquire spectra from phospholipids, symmetric liposomes and asymmetric liposomes. We demonstrate that when using different ion beams different chemical information can be obtained. Symmetric and asymmetric liposomes, with 95% asymmetry, were produced and analysed with Au⁺, Au₃⁺ and C₆₀⁺ primary ion beams. C₆₀⁺ gave the greatest yield from the symmetric liposome but after correcting for the yield effects on the data obtained from the asymmetric liposome it has been shown that C₆₀⁺ is the most surface sensitive, providing the least information from the inner leaflet of the liposome. Au_n⁺ provides the greatest amount of information from the inner leaflet. The results present the possibility of designing ToF-SIMS experiments that selectively probe specific regions of a (bio)molecular surface.