Plasma protein adsorption patterns on liposomes: establishment of analytical procedure.

After intravenous (i.v.) injection, colloidal drug carriers such as liposomes, emulsions, polymeric or solid lipid nanoparticles immediately interact with plasma proteins. The adsorbed plasma protein patterns depend on physico-chemical characteristics of the carriers' surface and are regarded as a key factor for the in vivo behavior of the carriers. The comprehension of the correlation between protein adsorption and in vivo organ distribution can be utilized to obtain drug targeting to different tissues. Carriers with different protein adsorption patterns will interact with different tissue-specific receptors or will be recognized by different macrophage subpopulations. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was applied to determine the protein adsorption patterns on polystyrene particles as model carriers. To transfer this analytical method to i.v. injectable colloidal carriers such as liposomes, a new sample preparation method was developed. The separation of liposomes from plasma after incubation was achieved by gel filtration using a Sepharose 2B column. This technique allowed a mild separation independent from eluent composition and only according to size differences. Possible protein desorption from the liposomes and adsorption onto the gel were minimized by using an eluent with a sufficiently high ionic strength. To estimate the efficiency of separation, the content of liposomes and plasma in each fraction being eluted was determined by ultraviolet (UV) spectroscopy. With this new separation method plasma protein adsorption patterns on liposomes could be analyzed for the first time. The sample preparation by gel filtration seemed to have no influence on liposome stability as far as size distribution is concerned.