Influence of block copolymers on the adsorption of plasma proteins to microspheres

Surface modification of poly(lactide-co-glycolide) nanospheres by biodegradable poly(lactide)-poly(ethylene glycol) copolymers

The modification of surface properties of biodegradable poly(lactide-co- glycolide) (PLGA) and model polystyrene nanospheres by poly(lactide)-poly(ethylene glycol) (PLA:PEG) copolymers has been assessed using a range of in vitro characterization methods followed by in vivo studies of the nanospheres biodistribution after intravenous injection into rats. Coating polymers with PLA:PEG ratio of 2:5 and 3:4 (PEG chains of 5000 and 2000 Da. respectively) were studied. The results reveal the formation of a PLA:PEG coating layer on the particle surface resulting in an increase in the surface hydrophilicity and decrease in the surface charge of the nanospheres. The effects of addition of electrolyte and changes in pH on stability of the nanosphere dispersions confirm that uncoated particles are electrostatically stabilized, while in the presence of the copolymers, steric repulsions are responsible for the stability. The PLA:PEG coating also prevented albumin adsorption onto the colloid surface. The evidence that this effect was observed for the PLA:PEG 3:4 coated nanospheres may indicate that a poly(ethylene glycol) chain of 2000 Da can provide an effective repulsive barrier to albumin adsorption. The in vivo results reveal that coating of PLGA nanospheres with PLA:PEG copolymers can alter the biodistribution in comparison to uncoated PLGA nanospheres. Coating of the model polystyrene nanospheres with PLA:PEG copolymers resulted in an initial high circulation level, but after 3 hours the organ deposition data showed values similar to uncoated polystyrene spheres. The difference in the biological behaviour of coated PLGA and polystyrene nanospheres may suggest a different stability of the adsorbed layers on these two systems.(ABSTRACT TRUNCATED AT 250 WORDS)

Polystyrene-poly (ethylene glycol) (PS-PEG2000) particles as model systems for site specific drug delivery. 2. The effect of PEG surface density on the in vitro cell interaction and in vivo biodistribution

The effect of differing densities of poly (ethylene glycol-2000) (PEG2000) at the particle surface of polystyrene-poly (ethylene glycol-2000) (PS-PEG2000) particles was assessed in terms of hydrophobic interaction chromatography (HIC) and the in vitro and in vivo behaviour of the particles. The particles, with different surface densities of PEG, were prepared by varying the copolymerizing reaction of styrene with a PEG macromonomer. There is a clear relationship between the surface density of PEG as determined by X-ray photoelectron spectroscopy and surface hydrophobicity as assessed by hydrophobic interaction chromatography (HIC). Similarly, the interaction of the particles with non-parenchymal liver cells in in vitro studies was shown to decrease as the surface density of PEG increases. The in vivo study investigating the biodistribution of the PS-PEG particles after intravenous injection into rats reveals that a relationship exists between the surface density of PEG and the extent to which the particles remain in the circulation, avoiding recognition by the reticuloendothelial system. Particles with the higher surface densities show increased circulatory times which compared well with data for particles prepared with the surface adsorbed PEO-PPO block copolymer, Poloxamine 908.

Internalization of poly(D,L-lactic acid) nanoparticles by isolated human leukocytes and analysis of plasma proteins adsorbed onto the particles

The objective of this work was to investigate the interactions of poly(D,L-lactic acid) nanoparticles prepared by a recently developed salting-out process, with lymphocytes and monocytes isolated from healthy human donors. Nanoparticles were labeled with a hydrophobic fluorescent dye and incubated with lymphocytes and monocytes, and their uptake was followed by flow cytometry in the presence and absence of plasma. Plasma protein adsorption increased nanoparticle uptake by monocytes, whereas a decrease of cellular binding of the nanoparticles to lymphocytes was noted. The cellular uptake for both cell types consisted in a passive adsorption and in an energy-requiring process, because the cells became 2-3 times more fluorescent when the incubation temperature was increased from 4 to 37 degrees C. When nanoparticles were coated with polyethylene glycol 20,000, uptake by monocytes decreased by 43 and 78% in phosphate-buffered saline and plasma, respectively; a similar decrease in nanoparticle uptake was observed for lymphocytes. Two-dimensional gel electrophoresis was performed to identify the plasma opsonins adsorbed onto the nanoparticle surface. Protein mappings for uncoated and polyethylene glycol-coated nanoparticles differed for two spot series. These spots, not yet clearly identified, may represent specific apolipoproteins involved in the metabolism of human lipoproteins, indicating the possible involvement of specific receptors in the uptake of the nanoparticles.