Liposome hydrophilic coating

Sterically stabilized ( stealth ) liposomes, which carry hydrophilic coatings, are used to obtain prolonged circulation times. 

The liposome biodistribution profile changes significantly when the vesicle surface [227-229] is coated with polymers, usually PEG. Longer blood circulation, lower liver uptake, and higher accumulation in tumors have been reported. The presence of the hydrophilic groups of PEG on the liposome surface provides electrostatic and steric repulsion between PEG-grafted liposomes. PEG molecules neutralize the surface charge of vesicles and thus prevent their opsonization. Also, liposome opsonization is reduced due to inability of opsonins to bind to hydrophilic surfaces. Moreover, the thickness of the PEG layer influences the interaction of the liposomes... 

Takeuchi, H., Kojima, H., Yamamoto, H., and Kawashima, Y. (2001), Evaluation of circulation profiles of liposomes coated with hydrophilic polymers having different molecular weights in rats, J. Controlled Release, 75, 83-91. 

In addition to PEGylation, polyvinyl pyrolidone (PVP) nanoparticles modified with hydrophilic polaxa-mine have been reported to adsorb less protein than the unmodified particles, conventional liposomes, and stealth liposomes.Polystyrene microspheres coated with lecithin and particles coated with Pluronic were also observed to adsorb less protein and demonstrate a prolonged blood circulation time without adversely affecting the safety profile of the drug. 

Sterically stabilized liposomal doxorubicin (pegylated liposomal doxorubicin Caelyx/Doxil) is coated with polyethylene glycol (3), which results in so-called stealth liposomes. In liposomal daunorubicin the liposome consists of a lipid bilayer of distearoylphosphati-dylcholine and cholesterol in a 2 1 molar ratio (4). Both formulations have a hydrophilic outer layer, which attracts a coating of water around the liposomal shell. This increases the circulation time by making the formulation virtually invisible to the reticuloendothelial system. 

Nonviral vectors are mostly liposomes of one type or another. Liposomal envelopes can transport substances across cell membranes which would otherwise be repelled by the hydrophilicity of the gene construct. Liposomes may be constructed that are either anionic or cationic. Complex liposomes, coated with antibodies that will target specific antigen presenting cells, can also be designed. 

Senior J, Delgado C, Fisher D, et al. (1991). Influence of surface hydrophilicity of liposomes on their interaction with plasma protein and clearance from the circulation studies with poly(ethylene glycol)-coated vesicles. Biochim. Biophys. Acta. 1062 77-82. 

Partial to complete 3-0-octadecylated polysaccharides exhibited characteristic solution and solid properties based on hydrophilic-hydrophobic structures. These polymers are suggested to form micellar conformations in water and in chloroform polysaccharide-coated liposomes, polymeric membranes, and thermotropic liquid-crystalline mesophase, depending on the octadecyl content. Hydrolysis of 3-deoxygenat-ed, 3-0-methylated, and 3-0-octadecylated dextrans by an endo-acting dextrans is compared. The possibility of a combshaped branched polysaccharide toward cell-specific biomedical materials is discussed. 

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