Prolonging the circulation time and modifying the body distribution of intravenously injected polystyrene nanospheres by prior intravenous administration of poloxamine-908. A 'hepatic-blockade' event or manipulation of nanosphere surface in vivo?

Intravenously injected uncoated small (60 nm) and large (250 nm) size model polystyrene particles (which are cleared rapidly from the blood by macrophages of the reticuloendothelial system) can be converted to long-circulatory and splenotropic particles in vivo, respectively, if such particles are injected shortly (up to 3 h) after an appropriate dose of the block polymer non-ionic surfactant, poloxamine-908. Evidence indicates that small and large size polystyrene beads can acquire a coating of poloxamine-908 and/or poloxamine-protein complexes in vivo. The adsorption of such complexes on to the bead surface could explain their altered body distribution since small and large size polystyrene beads that were precoated with poloxamine-908 exhibit similar biodistribution following i.v. injection.