The influence of the sample preparation on plasma protein adsorption patterns on polysaccharide-stabilized iron oxide particles and N-terminal microsequencing of unknown proteins

The in vivo organ distribution of i.v. injected drug carriers is strongly influenced by the adsorption of plasma proteins after i.v. injection, e.g. uptake by the mononuclear phagocytic system (MPS). 2-D PAGE could be established to analyze plasma protein adsorption patterns on polysaccharide-stabilized aqueous iron oxide dispersions used as contrast agents in Magnetic Resonance Imaging (MRI). After incubation in human plasma, centrifugation, a washing procedure and a solubilization step were carried out to obtain the proteins adsorbed onto these ultrasmall particles (65 nm in diameter). Patterns of adsorbed proteins were analyzed in dependence on the washing medium used, i.e. highly purified water, phosphate buffered saline and Krebs buffer pH 7.4. Conductivity and composition of the washing medium influenced the adsorption of IgG onto the particles, but had little effect on the other proteins present. IgG was strongly reduced when using the relatively high conductive buffers. The more stabilizing polysaccharide was desorbed the larger was the total amount of adsorbed proteins. Appearance of two unknown chains of spots in the range of appr. 92 kDa, accounting for appr. 10% and 2% of the overall detected protein amount, was observed only when using Krebs buffer during the washing process. Performing N-terminal microsequencing one unknown chain of spots could be identified as a dimer of fibrinogen gamma chains.