| Abstract
| - Hemoglobin (Hb) vesicles have been developed as cellular-type Hb-based O2 carriers in which a purified andconcentrated Hb solution is encapsulated with a phospholipid bilayer membrane. Ferrous Hb molecules within anHb vesicle were converted to ferric metHb by reacting with reactive oxygen species such as hydrogen peroxide(H2O2) generated in the living body or during the autoxidation of oxyHb in the Hb vesicle, and this leads to theloss of O2 binding ability. The prevention of metHb formation by H2O2 in the Hb vesicle is required to prolongthe in vivo O2 carrying ability. We found that a mixed solution of metHb and l-tyrosine (l-Tyr) showed aneffective H2O2 elimination ability by utilizing the reverse peroxidase activity of metHb with l-Tyr as an electrondonor. The time taken for the conversion of half of oxyHb to metHb (T50) was 420 min for the Hb vesiclescontaining 4 g/dL (620 μM) metHb and 8.5 mM l-Tyr ((metHb/l-Tyr) Hb vesicles), whereas the time of conversionfor the conventional Hb vesicles was 25 min by stepwise injection of H2O2 (310 μM) in 10 min intervals.Furthermore, in the (metHb/l-Tyr) Hb vesicles, the metHb percentage did not reach 50% even after 48 h undera pO2 of 40 Torr at 37 °C, whereas T50 of the conventional Hb vesicles was 13 h under the same conditions.Moreover, the T50 values of the conventional Hb vesicles and the (metHb/l-Tyr) Hb vesicles were 14 and 44 h,respectively, after injection into rats (20 mL/kg), confirming the remarkable inhibitory effect of metHb formationin vivo in the (metHb/l-Tyr) Hb vesicles.
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