Liposomes

Abstract

Liposomes are synthetic vesicles consisting of one or more phospholipid bilayers, able to accommodate water‐ and lipid‐soluble molecules. They are used as a delivery system for drugs, genes and vaccines in therapeutics. Liposomes may be formulated with a range of characteristics including different size, charge and drug retention, which can be tailored for a given drug and target site. There is a range of clinical products approved for use which exploit liposomes to passively target drugs or vaccines to the appropriate site of action thereby improving specificity and reducing toxicity. Liposomes can also be actively targeted to specific cells or subcellular regions using targeting ligands attached to their surface, or by modification of the bilayer to give triggered release under appropriate conditions.

Key concepts:

  • Liposomes are bilayer constructs formed when amphiphiles are exposed to water.

  • Liposomes can be formulated in different sizes, with different bilayer melting points and with different surface charges allowing for optimization to suit a given drug and target site.

  • The lipid head‐group dictates the surface charge of the liposomes and the acyl tail influences the melting point of the lipid bilayer and its permeability and therefore influences the drug release rates from liposomes.

  • The presence of cholesterol within the bilayers can reduce their permeability and drug leakage.

  • In commercial products, phosphatidylcholines in combination with cholesterol are commonly used to formulate the liposomes.

  • Drugs can be loaded within the aqueous compartment of the liposomes or within the lipophilic region of the bilayers depending on the lipophilicity of the drug. Through electrostatic interactions, molecules can also be adsorbed on the surface of liposomes.

  • Currently, liposomes are used for the delivery of drugs, for example cancer chemotherapy, systemic fungal infections and vaccines.

  • Cationic liposomes are being investigated as potential delivery systems for a range of nucleic acid therapies and for subunit vaccines.

Keywords: liposomes; lipids; drug delivery; drug targeting; nanotechnology

Figure 1.

Schematic representation of a lipid, which can form bilayer vesicles with drug entrapped in the aqueous phase or within the bilayer. With appropriate electrostatic interactions, drugs can also be adsorbed onto the surface.

close

References

Allison AG and Gregoriadis G (1974) Liposomes as immunological adjuvants. Nature 252: 252.

Bangham AD, Standish MM and Watkins JC (1965) Diffusion of univalent ions across the lamellae of swollen phospholipids. Journal of Molecular Biology 13: 238–252.

Brewer JM and Alexander J (1992) The adjuvant activity of non‐ionic surfactant vesicles (niosomes) on the BALB/c humoral response to bovine serum albumin. Immunology 75: 570–575.

Christensen D, Agger EM, Andreasen LV et al. (2009) Liposome‐based cationic adjuvant formulations (CAF): past, present and future. Journal of Liposome Research 19(1): 2–11.

Christie JG and Kompella UB (2008) Ophthalmic light sensitive nanocarrier systems. Drug Discovery Today 13: 124–134.

Demel RA, Geurts vanKessel WSM and van Deenen LLM (1972) The properties of polyunsaturated lecithins in monolayers and liposomes and the interactions of these lecithins with cholesterol. Biochimica et Biophysica Acta: Biomembranes 266: 26–40.

Felgner PL and Ringold GM (1989) Cationic liposomes‐mediated transfection. Nature 337: 387–388.

Gregoriadis G (2006) Liposome Technology, 3rd edn, vol. 1. New York: Informa Healthcare.

Gregoriadis G, Bacon A, McCormack B et al. (2007) Liposome‐based DNA/protein vaccines: procedures for entrapment and immunisation studies. In: Gregoriadis G (ed.) Liposome Technology, 3rd edn, vol. 2, pp. 233–244. New York: Informa Healthcare.

Gregoriadis G and Ryman BE (1972) Fate of protein‐containing liposomes injected into rats. An approach to the treatment of storage diseases. European Journal of Biochemistry 24: 485–491.

Mann FS, Scales HE, Shakir E et al. (2006) Oral delivery of tetanus toxoid using vesicles containing bile salts (bilosomes) induces significant systemic and mucosal immunity. Methods 38: 90–95.

Perrie Y, Frederik PM and Gregoriadis G (2001) Liposome‐mediated DNA vaccination: the effect of vesicle composition. Vaccine 19: 3301–3310.

Senior J and Gregoriadis G (1982) Is half life of circulating liposomes determined by changes in their permeability? FEBS Letters 145: 109–114.

Tseng Y‐C, Mozumdar S and Huang L (2009) Lipid‐based systemic delivery of siRNA. Advanced Drug Delivery Reviews 61: 721–731.

Vangala A, Kirby D, Rosenkrands I et al. (2006) A comparative study of cationic liposome and niosome‐based adjuvant systems for protein subunit vaccines: characterisation, environmental scanning electron microscopy and immunisation studies in mice. Journal of Pharmacy and Pharmacology 58: 787–799.

Wilschut J (2009) Influenza vaccines: the virosome concept. Immunology Letters 122: 118–121.

Further Reading

Bangham AD, Hill MW and Miller NGA (1974) Preparation and use of liposomes as models of biological membrane. In: Korn ED (ed.) Methods in Membrane Biology, vol. 1, pp. 1–68. New York: Plenum Press.

Gregoriadis G (1976) The carrier potential of liposomes in biology and medicine. New England Journal of Medicine 295: 704–710.

Gregoriadis G (1995) Engineering targeted liposomes: progress and problems. Trends in Biotechnology 13: 527–537.

Gregoriadis G (ed.) (2007) Liposome Technology, 3rd edn, vols I–III. New York: Informa Healthcare.

Gregoriadis G (2003) Liposomes in drug and vaccine delivery. Drug Delivery Systems and Sciences 2: 91–97.

Lasic DD and Papahadjopoulos D (eds) (1998) Medical Applications of Liposomes. Amsterdam: Elsevier.

Perrie Y and McNeil SE (2006) Gene delivery using cationic liposomes. Expert Opinion in Therapeutic Patents 16(10): 1271–1382.

Contact Editor close
Submit a note to the editor about this article by filling in the form below.

* Required Field

How to Cite close
Gregoriadis, Gregory, and Perrie, Yvonne(Jan 2010) Liposomes. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0002656.pub2]