Hemoglobin-vesicles for a Transfusion Alternative and Targeted Oxygen Delivery

Hb-vesicles (HbV) are artificial oxygen carriers that encapsulate purified Hb solution (35 g/dl) in unilamellar phospholipid vesicles (liposomes). The dispersion stability of HbV is attained using surface-modification with polyethylene glycol (PEG), so that the deoxygenated HbV can be stored at room temperature for years. Moreover, the intravenously injected HbV does not induce aggregation when contacted with blood components. Animal experiments have verified the safety and efficacy of HbV as a transfusion alternative. One advantage of HbV is that the O₂ affinity (P₅₀) of HbV can be regulated easily to that of RBC (28 torr) and to other values by manipulating the amount of the allosteric effectors, such as pyridoxal 5′-phosphate, coencapsulated in HbV. It is possible that HbV with a lower P₅₀ (higher O₂ affinity) would retain O₂ in the normal tissue while unloading O₂ to a targeted hypoxic tissue. Small HbV (250–280 nm diameter) is distributed homogeneously in the plasma phase, and HbV would transport oxygen through collateral arteries in the ischemic tissues. Results of in vitro and in vivo experiments of the domestic and international collaborations have confirmed the possibility of targeted O₂ delivery by HbV.