Carboxyfluorescein-5,6 liposomal encapsulation

Secondly, we investigated the effect of coating with these polysaccharides on the barrier function of liposomal membrane. The spontaneous release of carboxyfluorescein (CF) encapsulated in the interior of liposomes as a function of time was investigated at 50.0 °C (Fig. 3). Coating the outer surface of liposomes with these polysaccharides brought about several fold decrease in the permeability for CF. The substitution degree of acyl residues to behave as an anchor rather than the molecular weight of polysaccharide seems more important to coat conveniently the surface of liposomes. 

Woolfrey, S. G. Taylor, G. Kellaway, 1. W. Smith, A. Pulmonary absorption of liposome-encapsulated 6-carboxyfluorescein. J. Controlled Release 1988,5, 203-209. 

Truneh, A. Machy, R Barbet, J. Mishal, Z. Lemoimier, F. A. Leserman, L. D. Endocytosis of HI. A and H-2 molecules on transformed murine cells measured by fluorescence dequenching of liposome-encapsulated carboxyfluorescein. EMBO J. 1983, 2, 2285-2291. 

Similarly comb-like copolymers of vinyl pyrollidone and vinyl alkyl amines were shown [446] to influence the permeability of negatively charged phospholipid liposomes containing encapsulated carboxyfluorescein. At a pH of approximately 7, the copolymers allowed permeability and solute release due to polymer/liposome complex formation and disruption of the phospholipid membrane. 

Membrane permeabilization activity of peptides is currently measured by the use of artificial membrane bilayers, such as liposomes or erythrocytes. The hposome leakage assay can be performed by using spectrofluorimetry with a concentration-dependent quenching of a dye (calcein, carboxyfluorescein) encapsulated in liposomes. Disruption of hposomes in the presence of peptide-inducing leakage will lead to an increase in the fluorescence intensity of the liposome solution. Erythrocyte lysis assay is based on the absorption of hemoglobin, which can be measured once released into the extracellular medium upon erythrocyte lysis in the presence of peptide. 

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). 

Fig. 3. Spontaneous release of carboxyfluorescein (200 mM) encapsulated in the interior core of liposomes with and without artificial cell wall as a function of time at 50 C and y = 0.20 M (NaCl) in 20 mM Tris-HCl (pH 8.6) top, small single-walled liposomes (30 mg, 2.4 x 10" M as lecithin in the cuvette) without polysaccharides ( —O- ) and as coated with 5 mg of OPP-50(5.6) ( ), OPP-50(1.8)...

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