Lipidic drug carriers liposomes

The phase transition of lipid bilayers which comprise phospholipid mixtures, or phospholipids with different lengths of acyl chains, are of great importance due to their similarities with biomembranes or with lipid drug carriers such as liposomes, it is important to study the phase transitions and to detennine the exact crystalline mesophases of the mixed system. Thermal analysis studies indicated that the mi.xed lipids provide higher melting temperatures compared to those of pure lipids. This phenomenon occurrs w hen the lengths of the acyl chains are substantially different. 

Phospholipids e.g. form spontaneously multilamellar concentric bilayer vesicles73 > if they are suspended e.g. by a mixer in an excess of aqueous solution. In the multilamellar vesicles lipid bilayers are separated by layers of the aqueous medium 74-78) which are involved in stabilizing the liposomes. By sonification they are dispersed to unilamellar liposomes with an outer diameter of 250-300 A and an internal one of 150-200 A. Therefore the aqueous phase within the liposome is separated by a bimolecular lipid layer with a thickness of 50 A. Liposomes are used as models for biological membranes and as drug carriers. 

An excellent carrier is needed to deliver a sufficient amount of prostaglandins to the diseased site. Liposomes have been studied for a long time as possible drug carriers. However, the clinical use of liposomes has delayed because of some difficulties in mass production, sterilization, stability and safety. Since 1980 we have attempted to use lipid microspheres (lipid emulsions) instead of liposomes as a better carrier for lipophilic drugs (7). 

In the previous chapters it has been shown that stable cell membrane models can be realized via polymerization of appropriate lipids in planar monolayers at the gas-water interface as well as in spherical vesicles. Moreover, initial experiments demonstrate that polymeric liposomes carrying sugar moieties on their surface can be recognized by lectins, which is a first approach for a successful targeting of stabilized vesicles being one of the preconditions of their use as specific drug carriers in vivo. 

Cullis PR, Chonn A, Semple SC. Interactions of liposomes and lipid-based carrier systems with blood proteins Relation to clearance behaviour in vivo. Adv Drug Deliv Rev 1998 32 3. 

Liposomes are colloidal particles that can be prepared with (phospho)-lipid molecules derived from either natural sources or chemical synthesis (recently reviewed by Lian and Ho [14]). The potential application of liposomes as biodegradable or biocompatible drug carriers to enhance the potency and reduce the toxicity of therapeutic agents was recognized in 1960. In the 1960s and 1970s various methods for liposome preparation were developed as... 

FIGURE 9.5 Schematic representation of phospholipids distribution in lipid emulsions and liposomes. Both drug carrier systems show similar surface. The main differences between liposomes and lipid droplets are related to the mean diameter and nature of the inner contents. (From dos Santos, 2005.)... 

Cevc, G. 1996. Transfersomes, liposomes and other lipid suspensions on the skin Permeation vesicle penetration and transdermal drug delivery. Crit Rev Ther Drug Carrier Syst 13 257. 

In the wake of the commercial success of several liposome dmg products, lipid-based carriers are on the verge of becoming an accepted and versatile tool in drug delivery. Porter and Charman (Chapter 4) add an entirely new dimension to the usefulness of lipid-based carriers by showing that the systemic distribution... 

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