Recent aspects in the use of liposomes in biotechnology and medicine

Mechanical Stability of Lipid Membranes Decorated with Dextran Sulfate

Lipid vesicles decorated with polysaccharides have been proposed as vehicles for drug delivery because the polymers confer to the vesicles an enhanced stability, increasing the probability of the drug for reaching the target cell. Here, we first test the affinity of dextran sulfate (DS) for two different vesicle composition, and afterward, we study the effect of DS on the liposome mechanical properties. We found that DS binds to both tested membrane compositions. The interaction of DS with the anionic membranes studied here is mediated by the metal ions present in the aqueous solution (Na⁺ and Ca²⁺), being higher in the presence of Ca²⁺. Binding occurs preferentially in regions of closely packed lipids. Strikingly, DS did not affect the stability against detergent and the membrane rigidity of none of the vesicles. Thus, the proposed stability increase induced by this kind of polymers in drug delivery systems is not related with a modulation of the membrane thermodynamic properties but to other biochemical factors.

Partitioning of Ganglioside-Reconstituted Liposomes in Aqueous Two-Phase Systems

The partitioning of ganglioside (GM3,GD1a, GD1b or GT1b)-reconstituted liposomes was investigated in an aqueous poly(ethylene oxide)/dextran two-phase system to evaluate the carbohydrate–carbohydrate interactions in water. The partitioning of the ganglioside-reconstituted liposome was strongly affected by the buffer employed. As the concentration of sodium phosphate decreased, the ganglioside-reconstituted liposomes were partitioned to the bottom, dextran-rich, phase. In 10 mM sodium phosphate containing 150 mM sodium chloride, the conventional liposome without ganglioside were located mostly at the interface between the two phases. On the other hand, the ganglioside-reconstituted liposomes were significantly partitioned to the bottom dextran-rich phase, which was related to the ganglioside density on the liposomal surface. This partitioningto the dextran-rich phase also depended on the chemical structure of the ganglioside on the liposomal surface. The affinity of liposomal ganglioside being on the liposomal surface to dextran was the following sequence; GT1b>GD1a>GD1b>GM3. Partitioning of liposomes to the top poly(ethylene oxide)-rich phase was negligible irrespective of the characteristics of the liposomal surface.

Cell Specificity of Macromolecular Assembly of Cholesteryl and Galactoside Groups-Conjugated Pullulan

Galactose or lactose groups were conjugated to cholesterol-bearing pullulan (CHP). The CHP derivatives obtained formed monodisperse nanoparticles upon self-aggregation in water. Nanoparticles of galactoside-conjugated CHP self-aggregates were specifically internalized by rat hepatocytes and HepG2 cells. Galactoside-bearing CHP-coated liposome or oil droplet of O/W-emulsion was also taken up by HepG2 cells. Tissue distribution of the nanoparticle CHP self-aggregates changed dramatically with chemical conjugation of the galactose moiety. Galactoside-bearing nanoparticles were specifically accumulated in the liver.

Direct Fusion between Poly(ethylene oxide)-lipid Modified Liposomes and Murine Mitotic B16 Melanoma Cells

The interactions between the poly(ethylene oxide)-bearing lipid (PEO-lipid) were investigated with the average number of ethylene oxide units of 5, 15 and 32-reconstituted egg PC liposomes and murine mitotic B16 melanoma cells. Water-soluble FITC-dextran (20kDa) and lipophilic octadecyl rhodamine B (OD-RhoB) were encapsulated in liposomes to study the interaction modes with these cells by fluorescence microscopic techniques. Both fluorescent probes loaded in the PEO-lipid (n 32, 20mol%)-reconstituted liposome were specifically transferred to the mitotic cells. This process was not inhibited at 4°C or after the treatment of endocytosis inhibitor cytochalasin B or D. Confocal fluorescence microscopic observation of the cells treated with the liposome at 4°C revealed that FITC-dextran and OD-RhoB were transferred to the cytosol and the plasma membrane, respectively. In addition, when the mitotic cells were treated with the PEO-lipid (n 32, 20mol%)-reconstituted liposome encapsulated diphtheria toxin fragment A (DTA), approximately 30% of the cells were killed by the DTA-dependent cytotoxicity. These data indicate that the PEO-lipid (n 32, 20mol%)-reconstituted liposome directly fused with the plasma membrane of the murine mitotic B16 melanoma cells.

Superparamagnetic iron oxide nanoparticles (SPIONs): development, surface modification and applications in chemotherapy

At present, nanoparticles are used for various biomedical applications where they facilitate laboratory diagnostics and therapeutics. More specifically for drug delivery purposes, the use of nanoparticles is attracting increasing attention due to their unique capabilities and their negligible side effects not only in cancer therapy but also in the treatment of other ailments. Among all types of nanoparticles, biocompatible superparamagnetic iron oxide nanoparticles (SPIONs) with proper surface architecture and conjugated targeting ligands/proteins have attracted a great deal of attention for drug delivery applications. This review covers recent advances in the development of SPIONs together with their possibilities and limitations from fabrication to application in drug delivery. In addition, the state-of-the-art synthetic routes and surface modification of desired SPIONs for drug delivery purposes are described.

Stavudine-loaded mannosylated liposomes: in-vitro anti-HIV-I activity, tissue distribution and pharmacokinetics

Cells of the mononuclear phagocyte system (MPS) are important hosts for human immunodeficiency virus (HIV). Lectin receptors, which act as molecular targets for sugar molecules, are found on the surface of these cells of the MPS. Stavudine-loaded mannosylated liposomal formulations were developed for targeting to HIV-infected cells. The mannose-binding protein concanavalin A was employed as model system for the determination of in-vitro ligand-binding capacity. Antiretroviral activity was determined using MT-2 cell line. Haematological changes, tissue distribution and pharmacokinetic studies of free, liposomal and mannosylated liposomal drug were performed following a bolus intravenous injection in Sprague-Dawley rats. The entrapment efficiency of mannosylated liposomes was found to be 47.H ± 1.57%. Protein-carbohydrate interaction has been utilized for the effective delivery of mannosylated formulations. Cellular drug uptake was maximal when mannosylated liposomes were used. MT2 cells treated continuously with uncoated liposomal formulation had p24 levels 8–12 times lower than the level of free drug solution. Further, the mannosylated liposomes have shown p24 levels that were 14–20 and 1.42.3 times lower than the level of free drug and uncoated liposomal formulation treatment, respectively. Similar results were observed when infected MT2 cells were treated overnight. Stavudine, either given plain or incorporated in liposomes, led to development of anaemia and leucocytopenia while mannosylated liposomes overcame these drawbacks. These systems maintained a significant level of stavudine in the liver, spleen and lungs up to 12 h and had greater systemic clearance as compared with free drug or the uncoated liposomal formulation. Mannosylated liposomes have shown potential for the site-specific and ligand-directed delivery systems with desired therapeutics and better pharmacological activity.

Nanovehicular intracellular delivery systems

This article provides an overview of principles and barriers relevant to intracellular drug and gene transport, accumulation and retention (collectively called as drug delivery) by means of nanovehicles (NV). The aim is to deliver a cargo to a particular intracellular site, if possible, to exert a local action. Some of the principles discussed in this article apply to noncolloidal drugs that are not permeable to the plasma membrane or to the blood-brain barrier. NV are defined as a wide range of nanosized particles leading to colloidal objects which are capable of entering cells and tissues and delivering a cargo intracelullarly. Different localization and targeting means are discussed. Limited discussion on pharmacokinetics and pharmacodynamics is also presented. NVs are contrasted to micro-delivery and current nanotechnologies which are already in commercial use. Newer developments in NV technologies are outlined and future applications are stressed. We also briefly review the existing modeling tools and approaches to quantitatively describe the behavior of targeted NV within the vascular and tumor compartments, an area of particular importance. While we list "elementary" phenomena related to different level of complexity of delivery to cancer, we also stress importance of multi-scale modeling and bottom-up systems biology approach.

Formulation and optimization of piroxicam proniosomes by 3-factor, 3-level Box-Behnken design

The aim of this study was to investigate the combined influence of 3 independent variables in the preparation of piroxicam proniosomes by the slurry method. A 3-factor, 3-level Box-Behnken design was used to derive a second-order polynomial equation and construct contour plots to predict responses. The independent variables selected were molar ratio of Span 60:cholesterol (X(1)), surfactant loading (X(2)), and amount of drug (X(3)). Fifteen batches were prepared by the slurry method and evaluated for percentage drug entrapment (PDE) and vesicle size. The transformed values of the independent variables and the PDE (dependent variable) were subjected to multiple regression to establish a full-model second-order polynomial equation. F was calculated to confirm the omission of insignificant terms from the full-model equation to derive a reduced-model polynomial equation to predict the PDE of proniosome-derived niosomes. Contour plots were constructed to show the effects of X(1), X(2) and X(3) on the PDE. A model was validated for accurate prediction of the PDE by performing checkpoint analysis. The computer optimization process and contour plots predicted the levels of independent variables X(1), X(2), and X(3) (0, -0.158 and -0.158 respectively), for maximized response of PDE with constraints on vesicle size. The Box-Behnken design demonstrated the role of the derived equation and contour plots in predicting the values of dependent variables for the preparation and optimization of piroxicam proniosomes.

Vertical and directional insertion of helical peptide into lipid bilayer membrane

A novel helical hexadecapeptide carrying a poly(ethylene glycol) (PEG) chain at the N terminal was synthesized. The N and C terminals of the compound are labeled with a fluorescein isothiocyanate (FITC) group and an N-ethylcarbazolyl group (ECz), respectively. An octapeptide carrying the same groups and a hexadecapeptide without a PEG chain were also synthesized and used as control. A mixture of the peptide and dimyristoylphosphatidylcholine was sonicated in a buffer to prepare the liposome. The orientation as well as direction of the helical segment in the lipid bilayer were analyzed by quenching experiments of the FITC and the ECz fluorescence. The results clearly indicated that the helical segment of the peptide penetrated into the lipid bilayer with vertical orientation in both the gel and liquid crystalline states of the lipid bilayer. Notably, the bulky N terminal was left behind in the outer aqueous phase of liposome, meaning that the C terminal of the peptide points to the inner aqueous phase of liposome. The insertion mode of the helical peptide into a bilayer membrane is therefore well-regulated in terms of the orientation and the directionality by designing the balance between the PEG chain and the helix length. The methodology presented here will initiate a way to construct artificial functional molecular systems that can induce vectorial transport phenomena as seen in biological systems.

Stability study of stavudine-loaded O-palmitoyl-anchored carbohydrate-coated liposomes

The purpose of this study was to evaluate the physicochemical stability of carbohydrate-anchored liposomes. In the present study, carbohydrate (galactose, fucose, and mannose) was palmitoylated and anchored on the surface of positively charged liposomes (PL). The stabilities of plain neutral liposomes (NL), PL, and O-palmitoyl carbohydrate-anchored liposomes were determined. The effects of storage conditions (4 degrees C +/- 2 degrees C, 25 degrees C +/- 2 degrees C/60% +/- 5% relative humidity [RH], or 40 degrees C +/- 2 degrees C/75% +/- 5% RH for a period of 10, 20, and 30 days) were observed on the vesicle size, shape, zeta potential, drug content, and in vitro ligand agglutination assay by keeping the liposomal formulations in sealed amber-colored vials (10-mL capacity) after flushing with nitrogen. The stability of liposomal formulations was found to be temperature dependent. All the liposomal formulations were found to be stable at 4 degrees C +/- 2 degrees C up to 1 month. Storage at 25 degrees C +/- 2 degrees C/60% +/- 5% RH and 40 degrees C +/- 2 degrees C/75% +/- 5% RH adversely affected uncoated liposomal formulations. Carbohydrate coating of the liposomes could enhance the stability of liposomes at 25 degrees C +/- 2 degrees C/60% +/- 5% RH and 40 degrees C +/- 2 degrees C/75% +/- 5% RH.

Molecular recognition on the supported and on the air/water interface-spread protein monolayers

Targeting of proteins at interfaces via affinity ligands or specific antibodies is important for the understanding of protein functioning in biological membranes. This review brings together a great number of research works accomplished in this field in the past decade by a variety of analytical methods. It highlights two simple in situ techniques of monitoring molecular recognition processes at interfaces recently developed in the author's laboratory. The first of these techniques is based on the measurements of surface pressure increments of a protein monolayer spread at the air/water interface at a constant area resulting from the interaction with its specific ligands injected into the aqueous subphase beneath the preformed protein monolayer. The second technique takes advantage of the feature of [(14)C]-labeled proteins that enable in situ measurements of surface density changes of adsorbed protein molecules on a solid support resulting from the interaction with its specific antibody.

Functionalized nanocompartments (Synthosomes): Limitations and prospective applications in industrial biotechnology

Synthosomes are mechanically stable vesicles with a block copolymer membrane and an engineered transmembrane protein acting as selective gate. The polymer vesicles are nanometer-sized (50-1000 nm) and functionalized by loading them with enzymes for bioconversions or encapsulating charged macromolecules for selective compound recovery/release. The Synthosome system might become a novel technology platform for biocatalysis and selective product recovery. Progress in Synthosome research comprises employed block copolymers, transmembrane channel engineering, and functionalizations, which are discussed here in detail. The challenges in transmembrane protein engineering, as well as cost-effective production, in block copolymer design and the state of the art in Synthosome characterization comprising quantification of encapsulated protein, translocation efficiency, number of transmembrane channels per vesicle, and enzyme kinetics are also presented and discussed. An assessment of the Synthosome technology platform for prospective applications in industrial (white) biotechnology concludes this review.

Gene Transfer by DNA/mannosylated Chitosan Complexes into Mouse Peritoneal Macrophages

Chitosan is a biodegradable and biocompatible polymer and is useful as a non-viral vector for gene delivery. In order to deliver pDNA/chitosan complex into macrophages expressing a mannose receptor, mannose-modified chitosan (man-chitosan) was employed. The cellular uptake of pDNA/man-chitosan complexes through mannose recognition was then observed. The pDNA/man-chitosan complexes showed no significant cytotoxicity in mouse peritoneal macrophages, while pDNA/man-PEI complexes showed strong cytotoxicity. The pDNA/man-chitosan complexes showed much higher transfection efficiency than pDNA/chitosan complexes in mouse peritoneal macrophages. Observation with a confocal laser microscope suggested differences in the cellular uptake mechanism between pDNA/chitosan complexes and pDNA/man-chitosan complexes. Mannose receptor-mediated gene transfer thus enhances the transfection efficiency of pDNA/chitosan complexes.

Liposome fluidization and melting point depression by pressurized CO2 determined by fluorescence anisotropy

The influence of CO2 on the bilayer fluidity of liposomes, which are representative of model cellular membranes, was examined for the first time at the elevated pressures (up to 13.9 MPa) associated with CO2-based processing of liposomes and microbial sterilization. Fluidization and melting point depression of aqueous dipalmitoylphosphatidylcholine (DPPC) liposomes by pressurized CO2 (present as an excess phase) were studied by steady-state fluorescence anisotropy using the membrane probe 1,6-diphenyl-1,3,5-hexatriene (DPH). Isothermal experiments revealed reversible, pressure-dependent fluidization of DPPC bilayers at temperatures corresponding to near-gel (295 K) and fluid (333 K) phases at atmospheric pressure, where the gel-to-fluid phase transition (Tm) occurs at approximately 315 K. Isobaric measurements (PCO2 =1.8, 7.0, and 13.9 MPa) of DPH anisotropy demonstrate substantial melting point depression (DeltaTm = -4.8 to -18.5 K) and a large broadening of the gel-fluid phase transition region, which were interpreted using conventional theories of melting point depression. Liposome fluidity is influenced by CO2 accumulation in the hydrocarbon core and polar headgroup region, as well as the formation of carbonic acid and/or the presence of buffering species under elevated CO2 pressure.

Design of vesicles of 1,2-di-O-acyl-3-O-(β-d-sulfoquinovosyl)-glyceride bearing two stearic acids (β-SQDG-C18), a novel immunosuppressive drug

The immunosuppressive effects of synthetic sulfo-glycolipids in the class of sulfoquinovosyl-diacylglycerols (SQDG), including stereoisomers, were interesting in development of a promising clinical drug. Especially, 1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-beta-D-glucopyranosyl)-sn-glycerol (beta-SQDG-C18) was thought to be a valuable candidate because of the preliminary observations of its high inhibitory activities in spite of low toxicities. The problem of using this material is to find an applicable way avoiding its low solubility in water. The vesicle formation of beta-SQDG-C18 is advantageous to i.v. administration in its chemico-structural character. With preparation in water, beta-SQDG-C18 was hard to form vesicles, because its hydrophilicity was strong. We examined the suitable parameter of the vesicle forming condition. It was possible to take a balance between the hydrophilicity and the hydrophobicity of the beta-SQDG-C18 molecule to be optimized to form vesicles in 150 mM PBS. In addition, we demonstrated the strong immunosuppressive activity of beta-SQDG-C18 vesicles. This is the first report of the preparation method of beta-SQDG-C18 vesicles, which should facilitate in vitro and in vivo application.

Strings of vesicles: flow behavior in an unusual type of aqueous gel

This is a study of 10 asymmetric gemini surfactants that self-assemble into vesicles which, in turn, self-assemble into gels. The geminis have the following general structure: long-chain/phosphate/2-carbon spacer/quaternary nitrogen/short-chain. Dynamic light scattering and transmission electron microscopy (TEM) demonstrate that in dilute aqueous systems these compounds self-assemble into vesicles. The vesicles are cohesive as proven by cryo-high resolution electron microscopy (cryo-HRSEM) images that reveal a "pearls on a string" morphology. These strings of vesicles create a complex network that rigidifies the water. The one gemini in the study that does not form a gel is also the only vesicle system that, according to cryo-HRSEM and TEM, assembles into clumps rather than chains. It is proposed that the vesicles are cohesive owing to protrusion of short chains from the vesicle surfaces, thereby creating hydrophobic "patches" whose intervesicular overlap supersedes the normal membrane/membrane repulsive forces. Analogous geminis having two long chains, neither of which are thought capable of departing from their bilayers, also form vesicles, but they are noncohesive (as expected from the model). Rheological experiments carried out on the gels show that gelation is mechanically reversible. Thus, if an applied torque breaks a string, the string can rapidly mend itself as long as the temperature exceeds its calorimetrically determined T(m) value. Gel strength, as manifested by the yield stress of the soft material, was shown to be particularly sensitive to the structure of the gemini. All three individual components of the systems (geminis, vesicles, and gels) have widespread practical applications.

Selective in vitro labeling of white blood cells using 99mTc-labeled liposomes

We describe a method by which endocytosis-based radiolabeling of WBC is achieved using 99mTc-liposomes of optimal size and charge, and of a composition that assures both in vitro (whole blood) and intracellular stability of the radiopharmaceutical. In our study, excellent in vitro stability of 99mTc-liposomes with 95% labeling efficiency was observed with >90% stability up to 6 h and a minimum of 85% after 24 h of incubation either in normal saline or serum. Total WBC labeling efficiency using 99mTc-liposomes determined by radio-thin layer chromatographic analysis was 30.6 +/- 2.21%, 20.89 +/- 1.31% for monocytes and 9.7 +/- 1.74% for polymorphonuclears. Negligible activity was bound to red blood cells. The procedure did not affect the cell viability and the separation of the free 99mTc-liposomes from the cells was done by centrifugation.

Polysaccharide coated liposomes for oral immunization--development and characterization

Polysaccharide coated liposomes were prepared, characterized and evaluated for their potential use in oral immunization. Liposomes were prepared by reverse phase evaporation method. Bovine serum albumin (BSA) was chosen as the model antigen. Pulluan, a naturally occurring polysaccharide produced by a yeast like fungus, was chemically modified into its palmitoyl derivative (O-palmitoylpullulan; OPP) and was used for coating of the liposomes. The synthesized OPP was characterized by IR and NMR spectroscopy. The liposomes prepared were characterized for their size, shape, surface charge, encapsulation efficiency and stability in simulated gastric fluid. The immune stimulating activity was studied by measuring the serum IgA and IgG following oral administration of the prepared polysaccharide coated liposomes. Similarly, other formulations were studied and the results were compared. BSA loaded liposomes coated with OPP and plain polysaccharide could produce better IgG and IgA titre levels as compared to plain alum adsorbed BSA. The plain liposomes containing BSA could however produce significantly higher IgG and IgA levels as compared to equivalent BSA-alum based oral immunization. The results indicate that chemically modified polysaccharide coated liposomes can be used as a potential adjuvants for effective oral immunization.

Antitumour activity of cytotoxic liposomes equipped with selectin ligand SiaLe(X), in a mouse mammary adenocarcinoma model

The overexpression of lectins by malignant cells compared with normal ones can be used for the targeting of drug-loaded liposomes to tumours with the help of specific carbohydrate ligands (vectors). Recently we have shown that liposomes bearing specific lipid-anchored glycoconjugates on a polymeric matrix bind in vitro to human malignant cells more effectively and, being loaded with a lipophilic prodrug of merphalan, reveal higher cytotoxic activity compared with unvectored liposomes. In this study, carbohydrate-equipped cytotoxic liposomes were tested in vivo in a mouse breast cancer model, BLRB-Rb (8.17)1Iem strain with a high incidence of spontaneous mammary adenocarcinoma (SMA). Firstly, a cell line of the SMA was established which was then used to determine the specificity of the tumour cell lectins. After screening of the lectin specificity of a number of fluorescent carbohydrate probes, SiaLe(X) was shown to be the ligand with the most affinity, and a lipophilic vector bearing this saccharide was synthesised. Then different liposomal formulations of the synthetic merphalan lipid derivative and SiaLe(X) vector were prepared and applied in the treatment of mice with grafted adenocarcinomas. The results of the tumorigenesis data show that the therapeutic efficacy of merphalan increases sharply after its insertion as a lipophilic prodrug into the membrane of SiaLe(X)-vectored liposomes.

The in vivo effect of liposomes on hematopoiesis

The influence of liposome structure on hematopoiesis in vivo was assessed in relation to the different contents and origins of phospholipids that make up their membrane structures. Changes within different hematopoietic cells and serum tumor necrosis factor alpha (TNF-alpha) levels were estimated up to 14 days following intravenous administration of liposomes made of either pure egg yolk phosphatidylcholine (LEY) or a soybean phospholipid preparation (LSB) into normal CBA mice. In peripheral blood, only transient changes within white blood cells were observed. In bone marrow, a persistent decline in the number of mature granulocytes, monocytes, and lymphocytes was found. The changes within femoral granulocytic proliferative compartments in various stages of differentiation and a maturation compartment pointed out that, parallel with the depletion of the granulocyte-storage pool, stimulation of de novo production of granulocytic cells occurred. Although both types of tested liposomes induced similar cellular changes, only liposomes made of pure egg yolk phosphatidylcholine induced a transient increase in serum TNF-alpha levels.

Liposomes coated with chemically modified dextran interact with human endothelial cells

Some liposomal formulations are now in clinical use. New applications in biology and medicine using targeted liposomes remain an intensive research area. In this context, liposomes constituted of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (70/10/20 mol %) were prepared by detergent dialysis and coated with dextran (Dx) or functionalized dextran (FDx), both hydrophobized by a cholesterol anchor which penetrates the lipid bilayer during the vesicle formation. The coating of liposomes with these polysaccharides was performed because chemically modified dextran but not native Dx interacted with vascular cells. The liposome uptake by human endothelial cells was followed using uncoated and coated liposomes radiolabeled with a neutral lipid (3H-cholesterol) and a polar phospholipid (14C-PC). The results indicated for both radiolabels a preferential uptake by endothelial cells of FDx-coated liposomes compared to uncoated or Dx-coated liposomes. Addition to the culture medium of calcium up to 10 mM further enhanced the level and rate of incorporation of FDx-coated liposomes, whereas interaction of endothelial cells with uncoated liposomes or liposomes coated with Dx was poorly affected. Liposome membranes were then labeled with N-(lissamine rhodamine B sulfonyl)diacyl-PE and liposome uptake by endothelial cells was observed by fluorescence microscopy. The punctate intracellular fluorescence of cells incubated at 37 degrees C with fluorolabeled liposomes is indicative of the liposome localization within the endocytotic pathway of the cells. Altogether, these data demonstrate that coating of liposomes with FDx enable specific interactions with human endothelial cells in culture. Consequently, these liposomes coated with bioactive polymers represent an attractive approach as materials for use as drug delivery vehicles targeting vascular cells.

Receptor-Ck controls the expression of Bcl-2 and cyclin d genes

By making use of receptor-Ck positive lymphocytes (from normal human subjects) as well as receptor-Ck negative lymphocytes (from untreated chronic myeloid leukemic (CML) patients) as cellular models, we were able to show that receptor-Ck-dependent signalling is involved in the regulation of genes coding for Bcl-2 and cyclin D. Further, experiments directed to resolve the mechanism by which this receptor regulates these genes revealed that receptor-Ck, upon activation by cholesterol, initiates the cleavage of a 125 kDa cytoplasmic protein leading to the generation of a 47 kDa factor having specific affinity for genomic sterol regulatory element (SRE)/SRE-like sequence present in the promoter region of genes coding for Bcl-2 and cyclin D. Based upon these observations, we propose that the inability of leukemic cells to express receptor-Ck is responsible for the deregulated over-expression of genes coding for Bcl-2 and cyclin D and this phenomenon may be of importance in understanding leukemic haematopoiesis.

Synthesis of a new neoglycolipid (AgH-1) and its effect upon the properties of dipalmitoylphosphatidylcholine: cholesterol liposomes

A new neoglycolipid (AgH-1) bearing carbohydrate units that mimics the antigenic determinant of the O-blood group was synthesized and the effect of its incorporation in dipalmitoylphosphatidylcholine (DPPC): cholesterol liposomes was evaluated. The results obtained show that AgH-1 is readily incorporated into DPPC:cholesterol liposomes. The conditions leading to the optimal incorporation are the result of a compromise between incorporation efficiency and incorporation extent. The presence of AgH-1 produces liposomes of smaller size, with only small changes in the properties of the bilayer. However, the data obtained employing diphenylhexatriene and laurodan as fluorescence probes and merocyanine 540 as optical probe suggest that AgH-1 incorporation leads to a small rigidization of the liposomes at temperatures lower than ca. 42 degrees C.

Aging of soya-PC liposomes containing vitamin E reverses the stimulating effects of freshly prepared liposomes on growth of fibroblasts in culture

Extruded soya-PC liposomes (VET) averaging 80.4 +/- 24.3 nm in diameter and containing 0 to 25% vitamin E were added to human fibroblasts in culture immediately after preparation or after a 4 month cold storage period (aged liposomes). Following 8 days of incubation, the effect on the growth, membrane permeability, and protein content of the fibroblasts was determined. The freshly prepared liposomes induced a proliferative effect on cell growth at low phospholipid concentrations (10 and 50 microM). This effect was lost as the phospholipid concentration increased, and at concentrations exceeding 100 microM the toxic effects of liposomes became apparent. The incorporation of vitamin E into the liposomes reduced this toxicity. Aged liposomes showed a loss of proliferative activity at phospholipid levels of 10 and 50 microM. The age of the liposomes also influenced the protective effect of vitamin E on the cultures. Liposomes containing the vitamin and stored prior to use showed no proliferative effect, and cell toxicity increased with the percentage of vitamin initially present in the liposomes. The results suggest that vitamin E, incorporated into freshly prepared liposomes, is able to protect fibroblasts in culture from the toxic effects shown by phospholipid concentrations above 100 muM. This protective effect was lost when liposomes were stored prior to use.

Receptor-Ck-dependent regulation of genes in HL-60 cell line

The selective and conspicuous absence of a novel receptor-Ck (having affinity for cholesterol moiety in lipoproteins and intrinsic tyrosine kinase activity) in various leukemic cell lines/patients, prompted us to explore the nature of interrelationship between receptor-Ck deficiency and over-expression of genes coding for bcl-2, cyclin 'D', chimeric bcr-abl, c-myc and LDL-receptor in the human promyelocytic leukemic cell line (HL-60). This study revealed unambiguously that deregulated expression of these genes is primarily due to the inability of these cells to express the receptor-Ck gene. Based upon the observations we propose that 'receptor-Ck' deficiency may be responsible for the initiation of chronic myeloid leukemia.

99mTc-labelled diphytanoylphosphatidylcholine liposomes: in vitro and in vivo studies

The uniquely structured diphytanoylphosphatidylcholine (DphPC) forms liposomes more stable than conventional straight chain phospholipids. In this study DphPC and pegylated DphPC (DphPC-PEG) liposomes were radiolabelled and evaluated in vitro and in vivo. 99mTc-DphPC liposomes were found to be nontoxic to human white blood cells in vitro. In addition 99mTc labelled DphPC-PEG liposomes were evaluated as a nonspecific infection imaging agent in a mouse model. Infection sites were imaged within 30 min postinjection, and the radiopharmaceutical exhibited a remarkable in vivo stability. As their biodistribution and pharmacokinetic patterns can be size-modulated, DphPC-based lipsomes are excellent candidates for diagnostic and therapeutic applications.

An interfacial tension model of the interaction of water-soluble polymers with phospholipid composite monolayers

The axi-symmetric drop-shape analysis-pendant drop technique has been used to measure interfacial tension at the chlorobenzene-water interface in the presence of adsorbed films of dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine (DPPC), DMPC-cholesterol, DPPC-cholesterol, DMPC-cholesterol-dicetyl phosphate (DCP) and DPPC-cholesterol-DCP. A surface-pressure function, pi * = pi lipid-polymer -pi lipid (where pi lipid is the surface pressure of the mono-layer without polymer and pi lipid-polymer is the surface pressure of the lipid mono-layer and adsorbed polymer at equilibrium at the chlorobenzene-water interface) was used to characterize the interaction of eight water-soluble polymers with the lipid films. The equation, delta pi * = pi II*-pi I* (where the subscripts II and I denote the higher and lower lipid composites, respectively) was used to determine the differential effect of cholesterol and DCP on mono-layer characteristics in the presence of 1% w/v polymer. Cholesterol or polymer individually condensed DMPC films and expanded DPPC films. However, composite films of DMPC-cholesterol-DCP and carboxymethylchitin (CM-chitin), poly(acrylic acid) (PAA) or poly(vinyl alcohol) (PVA) were more expanded than DMPC films whereas composite films of DPPC were neither more condensed nor expanded than DPPC films. A polymer impact ratio, P* = pi lipid-polymer/pi lpolymer was calculated and the polymers were ranked in order of their impact on the lipid film. PVA and polysaccharides gave low and high P* values, respectively, corresponding to high and low levels of film interaction, whereas PAA and hydrophobized polysaccharides gave intermediate values, indicating their affinity for and penetration of interfacial films with little disruption of the mono-layer. The results show that measurement of interfacial pressures at the chlorobenzene-water interface might be advantageous for evaluating the action of polymers on biological membranes.

Fusion between Jurkat cell and PEO-lipid modified liposome

Direct fusion between Jurkat cell and a liposome modified with poly(ethylene oxide)-bearing lipid (PEO-lipid) was examined using diphtheria toxin fragment A (DTA) as the probe. Only the DTA-loaded liposome modified with PEO-lipid(n = 32) (n is the number of ethylene oxide units) exerted significant cytotoxicity against Jurkat cells, while liposomes lacking either the PEO-lipid or DTA did not. Liposomes modified by the PEO-lipid with shorter PEO chain(n = 5 or 15) did not show any cytotoxicity, irrespective of their DTA-loading. The cytotoxicity was observed even in the presence of cytochalasin B, an inhibitor of endocytosis. Judging from these results, we concluded that the PEO-lipid(n = 32)-modified liposome directly fused with plasma membrane of Jurkat cell.

Vesicles made of glycophospholipids with homogeneous (two fluorocarbon or two hydrocarbon) or heterogeneous (one fluorocarbon and one hydrocarbon) hydrophobic double chains

The vesicle-forming ability of the new anionic double chain glycophospholipids 1-4, with either two hydrocarbon or two perfluorocarbon chains, or a mixed double chain (one fluorinated, one hydrogenated), was investigated. When dispersed in water, 1a-c,e, 2b,c and 4b,c readily gave heat-sterilizable vesicles, 30-70 nm in diameter. The galactose and mannose-based fluorinated vesicles were also highly stable on aging. The 6-substituted glucose derivatives 3 formed tubules that reversibly interconverted into vesicles, depending on temperature. The leakage rate in buffer of carboxyfluorescein or calcein from vesicles made from 1a-c,e 2b,c and 4b,c depended on the sugar (t1/2 galactose > mannose > glucose). It decreased significantly with increasing fluorination and length of the hydrophobic tails. The mixed perfluorocarbon/hydrocarbon-tailed amphiphiles were found to be miscible with both the two fluorocarbon chains and the two hydrocarbon chains derivatives. Such admixing tended, however, to increase the small unilamellar vesicles' permeability. In buffered serum, all the vesicles investigated were highly permeable, but incorporation of cholesterol or DSPC in vesicles made of 1e significantly reduced their permeability in serum. The new vesicle and membrane components have i.v. maximum tolerated doses as high as 500 mg/kg body weight in mice; hemolytic activity sharply decreases with increasing degree of fluorination.