A Historical Perspective of Liposomes

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The simplest way to introduce liposomes may be to define them as "lipid vesicles enclosing aqueous space(s)" (New 1990). ... immuno-modulation, diagnosis, drug delivery, cosmetics, genetic ... identified and developments are ongoing.
A Historical Perspective of Liposomes The simplest way to introduce liposomes may be to define them as "lipid vesicles enclosing aqueous space(s)" (New 1990). In another words liposomes are simplified forms of living cells (Figure 1.). Their formation does not require the inclusion of surfactants or emulsifiers; they may be single- or multi-lamellar and vary according to lipid content, surface charge, size, and method of preparation. The properties of these vesicles have been investigated extensively, and ingenious ways have been found to manipulate them to impart behavioural characteristics such as sensitivity to light, heat, pH and magnetic field. Few other areas of research can routinely bring into realisation such a wide range of phenomena. The extensive and ever increasing literature covering the field of liposomology written by researchers with diverse interests is an indication of liposomes being a ubiquitous biochemical tool. Applications of liposomes in the areas of immuno-modulation, diagnosis, drug delivery, cosmetics, genetic engineering and investigations into the origin of life (Pozzi et al 1996; Nomura et al 2001) have been identified and developments are ongoing. In addition, the resemblance of liposomes to cell membranes have made them an ideal system for studying the characteristics of biological membranes.

lipid bilayer

water

water

Figure 1. Cross sectional view of a unilamellar liposome.

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The concept that lamellar structures composed of lipid and water systems might be useful as models for cell membranes has a long history (e.g. see Teitel Bernard 194547, also see Chapman and Arrondo 1981 for a review). However, it was in the early 1960s that much more emphasis was placed upon the study of the properties of lipidwater systems as model biomembranes.

Initially named `Bangosomes`, after being

brought to the attention of the scientific world by A. D. Bangham (Bangham et al 1965), they were later termed `Liposomes`. Bangham himself, however, proposed the name `Amphisome` (Bangham 1981) as a more appropriate term since membrane molecules are characteristically amphiphiles. Pioneers in the field of model biomembranes, Bangham, Chapman, Dervichian, and Luzzati, studied these systems from different view points. The study of the dynamic and sub-microscopic properties of these model membranes, such as fluidity (Chapman et al 1966), and change to other mesomorphic structures, and phase transitions, was for some time carried out distinctively and separately from the study of more macroscopic properties such as their ion trapping and release characteristics (Bangham et al 1965). Some of these investigations have been useful for providing insight into the dynamic structure of biomembranes, such as the fluidity of the lipid matrix and their diffusional properties (e.g. see Chapman 1975), whilst some others have led directly to a potential tool for drug delivery systems (Gregoriadis 1971). Investigations into the role of liposomes as transport vesicles for therapeutic agents have advanced considerably in recent years. Some areas that have attracted attention include the nature of interaction of solutes (proteins, drugs etc.) with liposomes; the factors governing the rate and site of uptake of liposomes after in vivo administration; the mechanism of liposome uptake by cells; and the immunological properties of liposomes. Variations of lipid composition and net charge of liposomal membrane as well as size of liposomes have been recognised as important physical characteristics that may determine the behaviour of the liposome in vitro and in vivo.

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