Synthesis and characterization of recombinant factor VIIa-conjugated magnetic iron oxide nanoparticles for hemophilia treatment

Maghemite (γ-Fe₂O₃) nanoparticles of 15.0 ± 2.1 nm in diameter were prepared by nucleation, followed by controlled growth of magnetic iron oxide thin films onto gelatin nuclei. Functionalization of these magnetic nanoparticles with activated double bonds was accomplished by interacting divinyl sulfone with the gelatin coating of the γ-Fe ₂O₃ nanoparticles. The activated double bonds were then used for covalent binding, via Michael addition reaction, of recombinant factor VIIa and human serum albumin to the surface of these nanoparticles. Recombinant factor VIIa was also physically bound to the magnetic nanoparticles by interacting this factor with the human serum albumin conjugated γ-Fe ₂O₃ nanoparticles. The influence of factor VIIa concentration on the immobilization yield has been elucidated. Leakage of the bound factor VIIa into PBS containing 4% albumin was insignificant. The coagulant activity of the physically adsorbed recombinant factor VIIa was similar to that of the free one and was significantly better than that of the covalently bound. The blood half-life of free factor VIIa is short, about 2-3 h, because of digestion by proteolytic enzymes and inhibitory effects. Stabilization of factor VIIa against trypsin (a model proteolytic enzyme) and chloromethyl ketone-type inhibitor was accomplished by conjugation of the factor to the γ-Fe₂O₃ nanoparticles. This stabilization may extend the blood half-life of factor VIIa. Therefore, IV injection of factor VIIa conjugated γ-Fe₂O₃ nanoparticles instead of free factor may avoid the frequent dosing and reduce the cost of hemophilia treatment.