A vesosome is a multi-compartmental structure of lipidic nature used to deliver drugs. They can be considered multivesicular vesicules (MVV) and are, therefore, liposome derived structures.
It consists of one or more bilayers enclosing an aqueous core that contains unilamellar vesicles that function as internal compartments which contain the drug and which can vary in composition from each other. The external bilayer defines the lumen, limits emission of the vesicle contents, and protects the vesicle contents from degradation due to lipolytic enzymes. Its unique properties enable localized drug delivery in specific parts of the body and extend the duration of drug effect. Also, a vesosome is easy to produce and offers the flexibility to deliver multiple drugs within a single carrier, which has been shown to offer important advantages in chemotherapy. Internal vesicle diameters range from 20-500 nm and vesosome diameters range from about 0.1 micron to more than 1.0 micron.
We don’t have to look very far back in history to find the origins of liposomal drug distribution devices. It wasn’t long after liposomes were first described, by British haematologist Dr Alec D Bangham in 1961 (published 1964), at the Babraham Institute, in Cambridge, that scientists first started to contemplate the possibility of employing them as transportation systems in the blood stream. Since then, there have been many advances in this area and as of 2008 there were 11 clinically approved liposomal drugs that target a variety of pathological conditions and illnesses like fungal infections, hepatitis A, influenza or cancer. Now, scientists plan to take full advantage of the 40 years of progress in liposome development to enhance this transportation system by employing vesosomes.
Design and Construction
Vesosome multicompartment structure encapsulates unilamellar liposomes within a second bilayer. For this purpose, it’s necessary to form bilayers that can be opened and closed at will, without disrupting the inner content. This is achieved by adding ethanol to a variety of saturated phospholipids in its gel phase, which drives interdigitation of phospholipids bilayers and subsequent fusion of small vesicles to form flat bilayer sheets. These are steady to removal of the residual ethanol until heated above the lipid chain melting temperature (Tm). The bilayers become flexible, and the sheets spontaneously close on themselves to form unilamellar vesicles. During the closure, the sheets can entrap whatever is around in suspension. By adding the vesicles aggregates including drug-loaded vesicles to the pelleted sheets before heating the mixture, encapsulation is carried out to form vesosomes.
Vesosome structure has taken advantage of the progress in liposome development as steric stabilization, pH loading of drugs (it is loaded by pH gradient), and intrinsic biocompatibility (it can be modified with a variety of agents, for example to specifically target a disease site, or promote adhesion or fusion).
An important variety of molecular structures can be encapsulated in vesosomal vesicles, such as proteins with complex three-dimensional structures or condensed DNA. But the most common use is to fill the vesosome’s vesicles with certain drugs that are going to be delivered in a particular area. Due to the small size of the vesosome and its good protection of the inner vesicles, it can be used in various cases, doing different functions.
Vesosomes are able to locate inflamed areas because of its receptors that are included in the outer lipid bilayer during its construction. Once in the inflamed area, the vesosome will deliver an anti-inflammatory substance from its vesicles though a pH gradient. They are able to locate tumours too. They can even be used to create, in a positioned area, a different nano-environment (considering that vesosome size is about 50 - 200 nanometres) either by altering the pH or the concentration of a particular substance.
To sum up, the use of a vesosome means an easy and simple way for many substances to be encapsulated in lipid bilayer vesicles in order to be transported and delivered safely.