Liposome properties

Liposomes are stable microscopic vesicles formed by phospholipids and similar amphipathic lipids. Liposome properties vary substantially with lipid composition, size, surface charge, and the method of preparation. They are therefore divided into three classes based on their size and number of bilayers. 

The liposomes are formed from bilayers by applying energy during the mixing process. In liposomes the core, an aqueous interior is separated by one or more phospholipid bilayers from the aqueous exterior. The size of the liposomes depends upon the manufacturing techniqne, intensity of mixing, etc. and is stable for a defined period of time. Liposomal properties and functionality depend on external parameters, such as pH and ionic strength of the medium. ... 

Uses Carrier, emulsifier, choline enrichment for pharmaceuticals and liposomes Properties 95% cone. 

Uses For use in membrane protein solubilization, enzymology and enzyme production, analytical applies, (chromatography), electrophoresis, molecular biology, antigen and vaccine preparations, drug delivery, liposomes Properties Wh, cryst, complete sol, in water m,w, 288,38 99% purity Storage Store under cover R,T,... 

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. 

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

Liposomes have been widely used as model membranes and their physicochemical properties have therefore been studied extensively. More recently, they have become important tools for the study of membrane-mediated processes (e.g., membrane fusion), catalysis of reactions occurring at interfaces, and energy conversion. Besides, liposomes are currently under investigation as carrier systems for drugs and as antigen-presenting systems to be used as vaccines. 

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. 

In vivo reproducible results can only be achieved if the liposome-drug or -antigen combinations are thoroughly characterized upon preparation in terms of their physical and chemical properties and, besides, if the stability during storage is ensured. In this chapter both the pharmaceutical (preparation, characterization, and stability) aspects and the therapeutic potentials and limitations of drug and antigen delivery with liposomes will be discussed. 

The behavior of liposomes in vivo can be influenced to a considerable extent by varying chemical composition and physical properties. Parameters affecting rate of clearance from the blood and tissue distribution include size, composition, dose, and surface characteristics (e.g., charge, hydrophobicity, presence of homing devices such as antibodies). 

Thus, liposomes—with or without adjuvants—have a potential as antigen delivery systems. No clear insights exist on how to prepare liposome-based vaccines with optimum immunological properties by rationale instead of by trial and error. Therefore, much basic work is needed to unravel the mechanisms involved. 

A notable property of liposomes, which has not been appreciated enough, is the presence of water inside liposomes. This makes them an excellent delivery system for biotechnologically engineered proteins with tertiary and quanternary structures which are sensitive to irreversible damage induced by dehydration, as often occurs with alternative, particulate carrier systems. 

Allen, T. M., and Everest, J. M. (1983). Effect of liposome size and di ug release properties on pharmacokinetics of liposome-encapsulated drugs in rats, J. Pharmacol. Exp. Ther.. 226, 539-544. 

Browning, J. L. (1981). NMR studies of the structural and motional properties of phospholipids in membranes, in Liposomes From Physical Structure to Therapeutic Applications (C. G. Knight, ed.), Elsevier, Amsterdam, pp. 189-242. 

Szoka, F., and Papahadjopoulos, D. (1980). Comparative properties and methods of preparation of lipid vesicles (liposomes), Ann. 

Numerous experimental therapeutics have shown potency in vitro however, when they are tested in vivo, they often lack significant efficacy. This is often attributed to unfavorable pharmacokinetic properties and systemic toxicity, which limit the maximum tolerated dose. These limitations can be overcome by use of drug carriers. Two general types of carrier systems have been designed drug conjugation to macromolecular carriers, such as polymers and proteins and drug encapsulation in nanocarriers, such as liposomes, polymersomes and micelles. 

There has been considerable discussion regarding the mode of action of the sea cucumber and starfish saponins. Both the triterpene and steroidal glycosides inhibit both Na/K ATPase and Ca/Mg ATPase 06) possibly as a result of their aglycone structures. However, their detergent properties cause membrane disruption which will influence the activity of membrane-bound enzymes such as the ATPases. In investigating the actions of saponins on multilamellar liposomes, it was found that cholesterol serves as the binding site for such saponins and that cholesterol-free lip-somes are not lysed by saponins 107). 

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. 

Frostell-Karlsson, A., Widegren, H., Green, C. E., Hamalainen, M. D., Westerlund, L., Karlsson, R., Fenner, K., Van De Waterbeemd, H. Biosensor analysis of the interaction between drug compounds and liposomes of different properties a two-dimensional characterization tool for estimation of membrane absorption. /. Pharm. Sci. 2005, 94, 25-37. 

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