Encapsulation efficiency Liposomes

As mentioned above, the ability to adsorb to the cornea and an optimal drug release rate have been defined as the two liposomal attributes most responsible for increasing bioavailability after topical ocular administration. A number of factors, including drug encapsulation efficiency, liposome size and charge, distribution of the drug within liposomes, stability of liposomes in the conjunctival sac and ocular tissues, their retention in the conjunctival sac, and most importantly their affinity toward the corneal surface and the rate of release of the encapsulated drug, have... 

Multivesicular Liposomes Kim and his colleages described a method for the preparation of cell size liposomes with high encapsulation efficiency the so-called multivesicular liposomes (Kim et al., 1983). The lipid phase consists of a combination of amphiphatic lipids and a small amount of triglycerides (triolein or trioctanoin) dissolved in chloroform-diethyl ether (1 1). The aqueous phase is slowly added to the organic phase and after vigorous shaking a water-ip-lipid emulsion is formed (Fig. 2A-B). Via a narrow Pasteur pipet the emulsion is subsequently added to a sucrose solution. 

Upon the spontaneous rearrangement of anhydrous phospholipids in the presence of water into a hydrated bilayer structure, a portion of the aqueous phase is entrapped within a continuous, closed bilayer structure. By this process water-soluble compounds are passively entrapped in liposomes. The efficiency of encapsulation varies and depends, for example, on the method of preparation of liposomes and the phospholipid concentration during preparation. Different parameters can be used to describe the encapsulation efficiency ... 

Kirby, C. J., and Gregoriadis, G. (1984). A simple procedure for preparing liposomes capable of high encapsulation efficiency under mild conditions, in Liposome Technology, Vol. 1 (G. Gregoriadis, ed.), CRC Press, Boca Raton, pp. 19-27. 

Probucol, another di-r-butyl phenol, is an anti-atherosclerotic agent that can suppress the oxidation of low-density lipoprotein (LDL) in addition to lowering cholesterol levels. The antioxidant activity of probucol was measured, using EPR, with oxidation of methyl linoleate that was encapsulated in liposomal membranes or dissolved in hexane. Probucol suppressed ffee-radical-mediated oxidation. Its antioxidant activity was 17-fold less than that of tocopherol. This difference was less in liposomes than in hexane solution. Probucol suppressed the oxidation of LDL as efficiently as tocopherol. This work implies that physical factors as well as chemical reactivity are important in determining overall lipid peroxidation inhibition activity (Gotoh et al., 1992). 

Liu JJ, Hong RL, Cheng WF, et al. Simple and efficient liposomal encapsulation of topotecan by ammonium sulfate gradient stability, pharmacokinetic and therapeutic evaluation. Anti-Cancer Drugs 2002 13(7) 709. 

For water-soluble agents, the encapsulation efficiency and thus the internal volume of vesicles which determines the amount of encapsulated material, is a very important factor with regard to the in vitro efficacy. It depends on the liposome size, lipid composition and lamellarity. When the number of liposomes delivered has to be known, the enumeration of the suspension can be performed by multinuclear NMR and photon correlation spectroscopy (110)-... 

Important criteria for the evaluation of liposomal quality are drug-to-lipid ratio, encapsulation efficiency, size, and lamellarity. The higher the drug-to-lipid ratio, the higher is the payload of the carrier and the lower the systemic burden... 

The major obstacle for the use of this type of liposomes in gene delivery was their intrinsically poor encapsulation efficiency of ultra-large payload compounds... 

As phospholipid bilayers form spontaneously when water is added, the important challenge in liposome preparation is not the assembly of simple bilayers (which happens automatically), but in causing the bilayers to form stable vesicles of the desired size, structure and physicochemical properties, with a high drag encapsulation efficiency. There are many different approaches to the preparation of liposomes however, they all have in common that they are based on the hydration of lipids ... 

Plasmids may be incorporated into anionic or neutral liposomes (for further details on liposomes see Section 5.3.1) to ensure protection against in vivo degradation, to control disposition profiles and to enhance intracellular delivery. However, the encapsulation efficiency of plasmids is very low, because of the large dimension of plasmids compared to the internal diameter of the vesicles. 

Drug encapsulation efficiency Active or remote loading [11] Stable liposome encapsulation of drugs at high drug-to-lipid ratios, Many applications in drug delivery... 

Puglisi, G.,Fresta,M.,La Rosa, C., Ventura, C. A., Panic, A. M., and Mazzonne,A. (1992), Liposomes as potential drag carrier for citicoline (CDP-choline) and the effect of formulation conditions on encapsulation efficiency, Pharmazie, 47, 211-215. 

Fresta, M., Villari, A., Puglisi, G., and Cavallaro, G. (1993), 5-Fluorouracil Various kinds of loaded liposomes Encapsulation efficiency, storage stability and fusogenic properties, Int. J. Pharm., 99,145-156. 

Piel, G., Piette, M., Barillaro, V., Castagne, D., Evrard, B., and Delattre, L. (2006), Beta-methasone-in-cyclodextrin-in-liposome The effect of cyclodextrins on encapsulation efficiency and release kinetics, Int. I. Pharm., 312,75-82. 

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