Liposomes: A short Review

Liposomes have a vast range of uses that have always been widened and improved upon since it was first noted that it was able to selfassemble into vesicles. These arrangements are found in many different shapes as well as sizes depending on the lipid composition. Liposomes are often being used to transport molecular cargos such as deoxyribose nucleotide for therapeutic benefits. Due to varied scientific applications of liposomes, they are under extensive investigation as drug carriers for enhancing the delivery of therapeutical agents. As a result of new developments in liposome technology, many liposomebased drug formulations are being investigated, and lately some of them have been approved for clinical use. INTRODUCTION Liposomes were first described by British haematologist Dr Alec D Bangham [1][2][3] FRS at the Babraham Institute, in Cambridge when they were discovered by him and R. W. Horne, who were testing the institute's new electron microscope by adding negative stain to dry phospholipids. The name liposome is derived from two Greek words: 'Lipos' meaning fat and 'Soma' meaning body. A liposome is a tiny bubble (vesicle), made out of the same material as a cell membrane. They are usually made of phospholipids, which are molecules that comprise a tail and a head group. The head is hydrophobic, whereas the tail which is made of a long hydrocarbon chain is hydrophilic. Normally, phospholipids can be found as a bilayer. [4][5] When in contact with water, the head will line up to face the water. In cells, one layer of hydrophilic heads faces the external environment of cell while another layer faces the internal environment of cell. The hydrophobic tails of both layers then face each other to form a bilayer. [6] Liposomes are vesicular structures that can be formed with the accumulation of lipids that interacts with one another in a specific manner. [7] Depending upon the composition and the structure, liposomes can separate hydrophobic or hydrophilic molecules from the solution. [8][9] These vesicles are not strong formations but rather are fluid entities that are complex supramolecular assemblies. Because of their dynamic properties and relatively easy manipulative ability, liposomes have been used widely in the analytical sciences as well as for drug and gene delivery. When the structural layer of phospholipid is disrupted, they are able to realign themselves into smaller structures. [10] These reassembled bilayer structures are known as liposomes while a monolayer is called micelle. [11] A liposome can be formed at a variety of sizes. Liposomes which can be filled with drugs, are used in delivering specific drugs in the treatment for cancer and other diseases. [12] Liposomes can be classified into multilamellar vesicle, unilamellar vesicle, and the cochleate vesicle. [3] Moreover, they are composite structures made of phospholipids and may contain small amounts of other molecules. Though liposomes can vary in sizes, unilamellar liposomes are generally smaller in size with various targeting ligands attached to their surface that allows an increase in their surface-attachment area that enhances its efficiency in the treatment of various diseases . [13] Schematic diagram of a liposome that is formed by phospholipids in an aqueous solution. Source: www.liposome.com Source: www.enzymatic.com Liposome is known to have an artificially-prepared vesicle made of a lipid bilayer, which can be prepared by altering biological membranes. As a result, it can be used as a means of administering nutrients and drugs. Liposomes can be classified into multilamellar vesicle, unilamellar vesicle, and the cochleate vesicle. [14] Thus a liposome blueprint enables surface ligands to get attached to unhealthy tissues. Anna Jone/J. Pharm. Sci. & Res. Vol.5(9), 2013, 181 183