Core-Shell Structured Hemoglobin Nanoparticles as Artificial O2 Carriers

This paper describes the synthesis and O-2 binding properties of core-shell structured hemoglobin (Hb) nanoparticles (NPs), artificial O-2 carriers of five types, as designed for use as red blood cell (RBC) substitutes. Human adult Hbs were polymerized using alpha-succinimidyl-omega-maleimide and dithiothreitol in spheroidal shapes to create parent particles. Subsequent covalent wrapping of the sphere with human serum albumin (HSA) yielded 100 nm-diameter Hb nanoparticles (HbNPs). The HbNP showed higher O-2 affinity than that of RBC, but NPs prepared under a N-2 atmosphere exhibited low O-2 affinity. Entirely synthetic particles comprising recombinant human adult Hb and recombinant HSA were also fabricated. Using a recombinant Hb (rHb) variant in which Leu-beta 28 of the heme pocket had been replaced with Phe, we found somewhat low O-2 affinity of rHb(beta L28F)NP. Particles made of stroma-free Hb (SFHb) containing natural antioxidant enzyme catalase (SFHbNP) formed a very stable O-2 complex, even in aqueous H2O2 solution. The SFHbNP showed good blood compatibility and did not affect the blood cell component functionality. The circulation half-life of SFHbNP in rats was considerably longer than that of naked Hb. All results indicate these Hb-based NPs as useful alternative materials for RBC and as a useful O-2 therapeutic reagent in diverse medical scenarios.