الفهرس 
Definition and Structure of Liposomes
Liposomes in treatment of alopeciaOnly 14 pages are availabe for public view
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Abstract
Skin is the largest organ in the human body and functions as a protective barrier. The large surface area and easy accessibility of skin make it one of the attractive routes for drug delivery in the treatment of skin diseases and systemic diseases. These include various types of formulations delivery systems such as powders, solutions, sprays, suspensions, emulsions, ointments, creams, pastes, gels, and patches (Torchilin, 2006). The rate and extent of drug penetration into different layers of skin and into systemic circulation are governed by drug properties and formulation characteristics. The recent emergence of nanotechnology has opened up new opportunities to develop nanosystems for topical and transdermal applications .One of the lipid-based nanosystem is liposomes (Fang et al., 2006).
Liposomes are microscopic vesicles formed from phospholipids as biological membranes. A fundamental feature of cell membranes is the organization of lipids into bi-bilayer, providing permeability barriers between exterior and interior compartments (Dreher et al., 2003).
The ability of phospholipids to form a bi-layer structure is because of the presence of a polar or hyDROPhilic (water-attracting) head-group region and a non-polar, lipophilic (water-repellent) tail. Therefore, liposomes contain a lipophilic compartment within the bi-layer membranes and hyDROPhilic compartments between the membranes (De Leeuw et al., 2009).
The liposomes are classified into natural and artificial liposomes.
I. Natural liposomes:
They are nano-sized vesicles which are water soluble on the outside and carry the fat soluble nutrient on the inside. These are called nano-vesicles micelles and liposomes (Kim et al., 2002).
II. The artificial liposomes:
The artificial liposomes are concentric bilayered vesicles in which an aqueous volume is entirely enclosed by a membraneous lipid bilayer mainly composed of natural or synthetic phospholipids which are used to increase drug transport across the skin and loaded with great variety of molecules such as small drug molecules, proteins, nucleotides and even plasmids (Samad et al., 2007).
The mechanisms of the penetration of liposomes into the skin: This can be mediated through one or more methods including; diffusion, transepidermal osmotic gradient, pilosebaceous unit, endocytosis, intercellular penetration (Katare et al., 2010).
Application of liposomes in medicine:
a) Diagnostic applications:
Diagnostic imaging requires that appropriate intensity of signal from an area of interest is achieved to differentiate certain structures from surrounding tissues. So, they are used in diagnostic imaging including gamma-scintigraphy, magnetic resonance, computed tomography and ultrasonography. (Vanbree et al., 2000).
b) Therapeutic applications:
1. Topical uses:
Topical application of liposomes has great potential in dermatology. Liposomes have been used successfully to enhance the clinical efficacy of several drugs in treatment of acne, atopic eczema, vetilig, psoariasis fungal infection skin cancer (Mozafari, 2005).
2. Systemic applications:
Liposomes are used in treatment of many diseases as in cancer therapy, AIDS, respiratory diseases, ocular diseases, thrombophelibitis, infections and allergic diseases. Also it can be used in drug delivery system as in brain drug delivery, gene delivery and vaccine delivery.
Advantage of liposomes:
It act not only as “drug transporters” through the skin but also as “drug localizers” within the skin. This allows therapeutically effective concentrations to be achieved at the site of action at a controlled rate and also eliminate or minimize side effects such as systemic toxicity and cutaneous irritation (Franklin, 2010).
Disadvantages of liposomes:
Liposomes disadvantages are minimal as production cost is high, leakage and fusion of encapsulated drug may occur and sometimes phospholipid undergoes oxidation and hydrolysis like reaction (Banerjee et al., 2002).