Liposomes entrapment efficiency

As an example, the liposome-entrapment efficiency of md-LErafAON formulation was found to be greater than 80% in two independent experiments (see Note 7). 

The entrapment efficiency is tested immediately after formulation (0 h postpreparation) and on day 8 post-preparation. The liposome-entrapment efficiency of rafAON is unchanged for up to at least 1 week after formulation. 

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 ... 

Haran G, Cohen R, Bar LK, Barenholz Y. Transmembrane ammonium sulfate gradients in liposomes produce efficient and stable entrapment of amphipathic weak bases. Biochim Biophys Acta 1993 1151 201-215. 

There are several other ways to entrap solutes inside the liposomes, and the entrapping efficiency depends on the structure of liposomes (small unilamellar, large unilamellar, multilamellar, vesicles, etc.) and from the technique for liposome preparation (Roseman etal., 1978 Cullis etal., 1987 Walde and Ishikawa, 2001). 

The liposome-entrapped rafAON is stored at 4°C and used within 3days after preparation. Entrapment efficiency is verified using at least three independent preparations, and each preparation tested in triplicate. 

Self assembly using amphiphilic components to trap drug in solution within a hydrophobic or hydrophilic core has been explored for decades for the delivery of drugs. The most notable example is that of the liposome, which, however, suffered from low entrapment efficiency, leakage, and rapid clearance by the reticuloendothelial system of the liver. This rapid clearance was reduced by the use of PEGylated phospholipids to form of the so-called sterically stabilized or stealth liposomes. ... 

Laham A et al (1988) Intracarotidal administration of liposomally-entrapped ATP Improved efficiency against experimental brain ischemia. Pharmacol Res Commun 20 699-705... 

As mentioned above, it has been reported that by controlling the sugar/lipid mass ratio, during DRV preparation by the conventional DRV technique (1), the entrapment efficiencies and size distribution of the liposomes produced can be controlled (2). 

For calculation of entrapment efficiency of ARSL, the concentration of encapsulated material and liposomal lipid are measured. Calcein and 5,(6) carboxyfluorescein (CF) have been used as encapsulated materials. Initially, the non-encapsulated calcein or CF is separated from ARSL dispersions on Sephadex G-50 chromatography columns (see Note 7) eluted with PBS, pH 7.40, that renders the liposomes osmotically stable (20). The column is presaturated with lipids and therefore the lipid recovery in all cases should be well over 95% (this can be calculated by measuring the lipid concentration in the liposome sample loaded on the column, and the lipid concentration in the liposomal fractions eluted, by a colorimetric assay for phospholipids (21) as described in the following section). 

Among the various methods that can be applied to entrap macromolecules inside liposomes, those methods have to be selected that increase the entrapment efficiency substantially and lead to an entrapment efhciency that is higher than the entrapment yield that results from vesicles prepared by dispersing a lipid hhn with subsequent extrusion (VET method, see Reference 7). Entrapment of macromolecules by the VET method is quite inefficient the likelihood that one liposome could contain enzyme as well as nucleic acid template molecule is very low. 

Laham, A., Claperon, N., Durussel, J. J., Fattal, E., Delattre, J., Puisieux, F., Couvreur, P., and Rossignol, P. (1988) Liposomally entrapped adenosine triphosphate inproved efficiency against experimental brain ischaemia in the rat. J. Chromatogr. 440,455—458. 

The influence of size, the liposome composition, and lamellarity on the entrapment efficiency of EO of Anethum graveolens was studied by Ortan et al. (2009), using multilamellar and unilamellar liposomes prepared by the thin hydration method. They observed a good incorporation of the oil remaining stable for 1 year, and their size distribution showed only slight modifications during the same period. 

Keeping the residual water content of the lyophilized liposomes at minimum may also increase the shelf life of freeze-dried formulation and prevent increases of vesicle size on rehydration [45]. A dehydration-rehydration protocol has been introduced by Kirby and Gregoriadis [46] to produce a mixture of OLVs and MLVs, with entrapment efficiencies between 40% and 50% being reported. Ambisome is an antifungal freeze-dried liposome formulation that is currently available in the maiket for treatment of systemic fungal infections [47]. 

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