Lipid bilayers liposomes

C. Evaluation of Membrane Affinity In Vitro Interaction with Liposomal Lipid Bilayer... 

Support has been obtained in experiments with natural thermo-zeaxanthin (22) containing mixed acyl residues [47] and with the pure z so-C15 0 acylated thermozeaxanthin (23), prepared by total synthesis, on a liposomal lipid bilayer [48]. 

Scattered within the transport literature are a handful of reports on the possibility of using liposomes (lipid bilayer vesicles) in separations (25,29). There are a number of attractive features associated with liposome membrane systems (i) the bilayer constituents are highly biocompatible phospholipids, organic solvents are essentially eliminated (ii) liposomes have a small size (100 nm diameter) and a very large surface area, while the walls are very thin (3 nm), thus transport rates can be very rapid (iii) the technology and economics associated with manufacturing and storing liposomes has improved dramatically over the past ten years 30). 

Category III—Supramolecular (Exo-) those assemblies involving amphiphilic monomers that lead to medium-large supramolecular structures. These assemblies tend to function as transport entities, barriers, membranes, and container-type structures (i.e., micelles, liposomes, lipid bilayers, etc.) and... 

Lipid-anchor-dextran Liposome capture Liposomes (lipid bilayer)... 

The in situ method using rat living intestine was simple and qualitative. However, it was difficult to evaluate the weak interaction between polymers and cell membranes quantitatively. Therefore, the lipid bilayer of liposome was used as a model of cell membranes for the quantitative evaluation for the affinity of the hydrophobized polymers (15). 

Phospholipids e.g. form spontaneously multilamellar concentric bilayer vesicles73 > if they are suspended e.g. by a mixer in an excess of aqueous solution. In the multilamellar vesicles lipid bilayers are separated by layers of the aqueous medium 74-78) which are involved in stabilizing the liposomes. By sonification they are dispersed to unilamellar liposomes with an outer diameter of 250-300 A and an internal one of 150-200 A. Therefore the aqueous phase within the liposome is separated by a bimolecular lipid layer with a thickness of 50 A. Liposomes are used as models for biological membranes and as drug carriers. 

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Liposomes are members of a family of vesicular structures which can vary widely in their physicochemical properties. Basically, a liposome is built of one or more lipid bilayers surrounding an aqueous core. The backbone of the bilayer consists of phospholipids the major phospholipid is usually phosphatidylcholine (PC), a neutral lipid. Size, number of bilayers, bilayer charge, and bilayer rigidity are critical parameters controlling the fate of liposomes in vitro and in vivo. Dependent on the preparation procedure unilamellar or multilamellar vesicles can be produced. The diameter of these vesicles can range from 25 nm up to 50 ym—a 2000-fold size difference. 

The enormous size of these liposomes enables measurements to be made on a single lipid bilayer. However, the conditions required for their preparation, their fragility, and their size preclude their use in therapy. 

S-layer protein was crystallized on lipid monolayers lipid bilayer membranes and liposome. 

TH Tien, A Ottova-Leitmannova. Membrane Biophysics as Viewed from Experimental Bilayer Lipid Membranes Planar Lipid Bilayers and Spherical Liposomes. New York Elsevier Science, 2000. 

Artificial membrane systems can be prepared by appropriate techniques. These systems generally consist of mixtures of one or more phospholipids of natural or synthetic origin that can be treated (eg, by using mild sonication) to form spherical vesicles in which the lipids form a bilayer. Such vesicles, surrounded by a lipid bilayer, are termed liposomes. 

Biochemical studies with purified preparations incorporated into liposomes have also been performed [32,33,96-98]. Reconstituted receptors from skeletal muscle bound DHPs, PAAs and diltiazem with high affinity and in a 1 1 1 stoichiometry [97], In general, the reconstituted proteins exhibit the characteristic pharmacological properties expected for these channels. In recent studies, our laboratory has reconstituted partially purified channels into liposomes containing the Ca -sensitive fluorescent dye, fluo-3 [33,96]. These channels exhibit Ca influx that is sensitive to activation by Ca channel activators and inhibitors with affinities similar to those observed in intact cells, and the Ca influx is dependent on the establishment of a gradient in the presence of valinomycin [132]. This assay provides a convenient and rapid approach to obtaining a macroscopic picture of the activity of the channels under different conditions, while the more complex studies in lipid bilayers provide a more complete analysis of the single channel behavior. 

Using the reconstitution approaches described above, we have demonstrated that phosphorylation of the skeletal muscle Ca channels by PKC results in activation of the channels [108], In the fluo 3-containing liposomes, channels phosphorylated by PKC exhibited a two-fold increase in the rate and extent of Ca " influx [108], Using the lipid bilayer-T-tubule membrane reconstitution system we are currently analyzing the effects of PKC-catalyzed phosphorylation at the single channel level [133], The demonstration that these channels undergo phosphorylation as a result of activation of PKC in intact skeletal muscle cells has not yet been achieved. 

Concerning the mechanism of action of catechins, studies carried out on S. aureus and E. coli cells by Ikigai et al. [72] reported that their bactericidal effect is primarily involved in the damage of bacterial membranes catechins induce a rapid leakage of small molecules entrapped in the intraliposomal space, determining the aggregation of the liposomes. These actions cause damage in the membrane lipid bilayer and cell death (Table 1). 

Liposomes, which are lipid bilayer vesicles prepared from mixtures of lipids, also provide a useful tool for studying passive permeability of molecules through lipid. This system has, for example, been used to demonstrate the passive nature of the absorption mechanism of monocarboxylic acids [131]. Liposome partitioning of... 

Liposomes are vesicles with an aqueous core surrounded by lipid bilayer walls. Drugs may be encapsulated into the liposomes, either in the bilayers or into the aqueous core of the liposomes. Liposomes have been widely investigated by systemic and local drug delivery in different cavities of the body. 

Interaction of the liposomal lipids with cellular lipid bilayers or other lipid bilayers in the body (e.g. skin lipids) depends on the nature of the lipids in the liposome. In order to... 

Effect of Cholesterol. Cholesterol inclusion into the lipid bilayers composed of DPPC or DSPC, eliminates apparent Tc and reduces permeability at and above the usual Tc. On the other hand, cholesterol inclusion increases packing of fluid bilayer composed of lipids with unsaturated fatty acyl chains. Since cholesterol rich liposomes are stable in plasma, cholesterol is commonly used as a liposomal component. 

Other methods for preparing liposomes have been developed, such as hydration of lipids from an organic phase, and detergent removal methods. A lipid bilayer is formed in an aqueous solution of lipids dissolved in an organic solvent... 

The half-life of liposomes administered in the blood stream is affected by the composition, size, charge, and fluidity. Liposomes with a small size or with a rigid lipid bilayer have a longer half-life (38 9). Large liposomes administered iv tend to accumulate at a lymph node near the injected site. This tendency can be useful for preventing metastases. Liposomes which pass through the lymph node have a tendency to accumulate in the RES, such as the liver and spleen (40,41). The disposition of liposomes is altered by the dose of liposomes as well as size or lipid composition of liposomes. Cholesterol rich liposomes are cleared slower due to... 

Figure 2. Liposomes with a specific character a), temperature-sensitive liposome b). target-sensitive liposome c). pH-sensitive liposome. Closed triangles and rectangles in lipid bilayer indicate amphiphiles which change the liposome s hydration with pH changes.

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