Liposome dispersion

Liposome size can range from around 20 nm to around 50 pm. To a certain extent, the mean diameter and distribution of the diameters can be controlled by sizing procedures after the formation of the initial liposome dispersion or by a careful selection of the preparation conditions (cf. Sec. II). Several techniques can be used to determine mean particle size and particle size distribution (Groves, 1984). 

An alternative approach is the use of pH-sensitive fluorophores (Lichtenberg and Barenholz, lOSS). These probes are located at the lipid-water interface and their fluorescence behavior reflects the local surface pH, which is a function of the surface potential at the interface. This indirect approach allows the use of vesicles independent of their particle size. Recently, techniques to measure the C potential of Liposome dispersions on the basis of dynamic light scattering became commercially available (Muller et al., 1986). 

The presence of impurities like free fatty acids in egg or soybean phosphatidylcholine, or in the (semi)synthetic phosphatidylcholines (e.g., DMPC, DPPC, DSPC) can be detected by monitoring the electrophoretic behavior of liposome dispersions of these phospholipids in aqueous media with low ionic strength a negative charge will be found on these liposomes when free fatty acids are present in the bilayers. 

Successful attempts to freeze-dry liposome dispersions containing lipophilic compounds were reported. However, after a freeze-... 

Influence of freezing and freeze drying on the stability of liposomes dispersed in aqueous media. Acta Pharmaceut. Technol.. 34. 129-139. 

Kato N, Prime J, Katagiri K, Caruso F (2004) Preparation of J-aggregate liposome dispersions and their chromic transformation. Langmuir 20 5718-5723... 

A solution of DOX (0.5-20 mM) was added to the liposome dispersion (1-120 mM phospholipids) after the creation of an AS gradient. The loading was performed above the Tm of the liposome PC (>65°C for HSPC). The percent loading was followed with incubation time at the desired temperature by mixing an aliquot of the incubation mixture with washed and cleaned Dowex (50mg/per mg total DOX) to remove the free (unloaded) DOX as described below (4). 

Briefly, liposomes (10mM) were incubated for 30minutes at 37°C for egg phosphatidylcholine (EPC) and at 60°C for HSPC-based liposomes with 50 X 10 dpm of methylamine (1 x 10 dpm/mole). At the end of incubation an aliquot of this mixture was passed down a Sephadex G-50 minispin column equilibrated in 10 mM histidine-sucrose buffer 10%, pH 6.7 buffer. Liposomes were eluted at the column void volume and separated from the unencapsulated methylamine. The concentration of liposomes in the original liposomal dispersion and in the void volume fraction was determined from the organic phosphorus (phospholipid) concentration (see section Lipid Quantification and Chemical Stability above) (10,49,53). 

X = ratio between [ C]-methylamine radioactivity (dpm) and phospholipids concentration (mM) in the original liposome dispersion after the incubation and before Sephadex G-50 separation. 

The obtained liposome dispersion was made sterile by filtration through 200-nm pore-sized filters and stored in sterile bottles till usage at 4°C. The liposomes were stable in size for at least 120 days. 

With some molecules, a high concentration results in a lamellar phase but no additional mesophases are formed if the concentration is reduced. The lamellar phase is dispersed in the form of concentric layered particles in an excess of solvent (water or aqueous solution). This results in a vesicular dispersion. If the mesogenic material eonsists of phospholipids, the vesicular dispersion is called a liposomal dispersion... 

Similar to Voltaren" Emulgel, oily droplets of an eutectic mixture of lidocaine and prilocaine are dispersed in a hydrogel to provide local anesthesia to the skin for injections and siugical treatment (Emla cream). A further possibility is the dermal administration of a liposome dispersion as a spray (Heparin PUR ratiopharm Spriih-gel "). After administration, water and isopropylic alcohol evaporate partially resulting in an increase of concentration and in a transition from the initial liposome dispersion into a lamellar liquid crystal [32]. The therapeutic effect appears to be influenced favorably by the presence of lecithins rather than by the degree of liposome dispersion. 

Arakane, K., Hayashi, K., Naito, N., Nagano, T., and Hirobe, M. (1995) pH lowering in liposomal dispersions induced by phospholipid peroxidatio6hem. Pharm. Bull., 43 1755-1758. 

Most of the cationic lipids arrange into bilayers and readily form liposome dispersions in water [16]. At higher electrolyte concentrations, e.g., in physiological solutions, in which electrostatic repulsion is largely screened, and at higher lipid contents bringing the bilayers together, these lipids form well-correlated lamellar... 

Fig. 25 (a) DNA release from EDOPC-DNA lipoplexes after addition of negatively charged lipid dispersion, as monitored by FRET (CM, oleic acid DOPA, dioleoyl phosphatidic acid DOPG, dioleoyl phosphatidylglycerol CL, cardiolipin DOPS, dioleoyl phosphatidylserine PI, phospha-tidylinositol). (b) Fraction of released DNA from EDOPC lipoplexes 10 min after addition of the respective anionic liposomes (c) X-ray diffraction patterns of mixtures of EDOPC and anionic liposome dispersions the respective structures are shown schematically on the left side (reproduced with permission from [98] copyright (2004) Biophysical Society)... 

Talsma, H., van Steenbergen, M.J., Salemink, P.J.M, Crommelin, D.J.A. The cryopreservation of liposomes. 1. A differential scanning calorimetry study of the thermal behavior of a liposome dispersion containing mannitol during freezing/thawing. Pharm. Res. 8, 1021-1026,1991... 

Interaction of Liposomal Dispersions with Molecules Dissolved in Water Through Hydrogen Bonding... 

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