Liposome ethanol concentration

Figure 2 Encapsulation as a function of ethanol concentration. Oligonucleotides were added to distearoyl-phosphatidyl-choline/cholesterol/l-0-(2 -(co-methoxy-poly-ethylene-glycol)succinoyl)-2-iV-myristoyl-sphingosine /1,2-dioleoyl-3-dimethylam-monium propane liposomes in varying concentrations of ethanol at an initial oligonucleotide-to-lipid ratio of 0.24mg/mg. Abbreviations AS, antisense oligonucleotide %EtOH(v/v), percentage of ethanol in volume/volume.

The DFT H-NMR spectra of DPPC/GMi (1.0 M 0.1 M) liposomes in the presence of ethanol-de are shown in Figure 3. At low ethanol concentrations, a small decrease in the choline methyl resonance is detected, indicative of surface ordering. The methylene resonance decreases markedly above - 1% ethanol. Above 2% ethanol, the choline methyl begins to increase. 

Perhaps the simplest solvent dispersion method is that developed by Batzri and Korn (1973). Phospholipids and other lipids to be a part of the liposomal membrane are first dissolved in ethanol. This ethanolic solution then is rapidly injected into an aqueous solution of 0.16M KC1 using a syringe, resulting in a maximum concentration of no more than 7.5 percent ethanol. Using this method, single bilayer liposomes of about 25 nm diameter can be created that are... 

Figure 5.28 Circular dichroism spectra of DC8 9PC tubules prepared in (a) ethanol-water (7 3), (b) methanol-ethanol-water (35 35 20), and (c) methanol-water (70 30) and (d) DCj PC liposomes above melting temperature. All samples were prepared at lipid concentration of 2.0 mg/ml and spectra for tubules were recorded at 25°C. Liposome spectrum was recorded at 40°C and peak intensity is about 104 smaller than that from tubules.

Foradada and Estelrich [3.63] studied the encapsulation of thioguanine (TG) in three types of liposomes produced by extrusion, ethanol injection and dehydration-rehydration vesicles. The entrapment has been examined at three different concentrations (1, 0.1 and 0.01 mM) and at three different pH values (4.7,7.4 and 9.2). The dehydration-rehydration vesicles were found to be the optimum method to encapsulate TG, independent of the pH value. At pH 4.7, 12 mmol/mol of lipid were entrapped, while with the other methods a maximum of 3 mmol/mol of lipid has been achieved. The authors related this behavior to the formation of hydrogen bridges between the TG and the liposomes. 

The procedure chosen for the preparation of lipid complexes of AmB was nanoprecipitation. This procedure has been developed in our laboratory for a number of years and can be applied to the formulation of a number of different colloidal systems liposomes, microemulsions, polymeric nanoparticles (nanospheres and nanocapsules), complexes, and pure drug particles (14-16). Briefly, the substances of interest are dissolved in a solvent A and this solution is poured into a nonsolvent B of the substance that is miscible with the solvent A. As the solvent diffuses, the dissolved material is stranded as small particles, typically 100 to 400 nm in diameter. The solvent is usually an alcohol, acetone, or tetrahydrofuran and the nonsolvent A is usually water or aqueous buffer, with or without a hydrophilic surfactant to improve colloid stability after formation. Solvent A can be removed by evaporation under vacuum, which can also be used to concentrate the suspension. The concentration of the substance of interest in the organic solvent and the proportions of the two solvents are the main parameters influencing the final size of the particles. For liposomes, this method is similar to the ethanol injection technique proposed by Batzii and Korn in 1973 (17), which is however limited to 40 mM of lipids in ethanol and 10% of ethanol in final aqueous suspension. 

An even more striking effect is observed by addition of the surfactant sodiumdodecyl sulfate (SDS) to vesicles (Fig. 23). While monomeric vesicles of (19) and dipalmitoylle-cithin are destroyed by low SDS concentrations, the polymerized vesicles are stable up to 2 - 10 3 mol/1 SDS25). Polymerized vesicle dispersions can be diluted with ethanol without precipitation.231 Polymeric liposomes of (20) are stable in 80% ethanol for weeks. This could also be shown by Regen et al. for polymerized vesicles of the methacryloylic lipids (4) and (6)13141 (Fig. 24) by monitoring the turbidity (absor-... 

Transfersomes, deformable liposomes, were introduced by Cevc et al. in the early 1990s [66-69]. The main components of these systems are phospholipids, a surfactant edge activator (such as sodium cholate), water and sometimes very low concentrations of ethanol (<7%) [66]. Transfersomes are prepared by the same methods as liposomes. The preparation process is usually followed by homogenization, sonication, or other mechanical means to reduce the size of the lipid vesicles. 

FIGURE 13.5 (a) Visualization of a typical multilamellar ethosome containing 2% PL, 30% ethanol, and water by TEM (b) Entrapment of fluorescent probes by phopholipid vesicles as visualized by CSLM. Liposomes (a-c) or ethosomes (d-f) were prepared with one of three fluorescent probes rhodamine red (a, d), D-289 (b, e), or calceine (c, f). White represents the highest concentration of probe. (Reproduced from Touitou, E. et al., J. Control. Release, 65, 403, 2000. With permission from Elsevier.)... 

Unfortunately, there are only few data available describing the effects of ethanol on conventional liposomes composed of molecules with mixed-chain fatty acids, such as POPC. The few permeability studies seem to demonstrate that the effect of ethanol on such liposomes might be low. And with GVs, there is (to the best of my knowledge) only one study that has been published demonstrating the effect of ethanol on the GV bilayers. In this study it was shown that high concentrations of ethanol induce shape transformations of GV formed by electroformation and it was assumed that the stability of these GVs might be negatively influenced. 

Solvent-based prohposomes are also referred to as alcohol- or ethanol-based proliposomes when ethanol is used as the solvent. Ethanol-based proliposomes are concentrated ethanohc solutions comprising phospholipid, ethanol, and aqueous phase (5 4 10 w/w/w). This proliposome mixture generates liposomes on dilution with aqueous medium [49]. The coexistence of ethanol and aqueous phase with phospholipids in this ratio has been shown to form stacked (precipitated) bilayers which generate liposomes when more aqueous phase is added [49]. 

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