Scientific Publications by FDA Staff

Biochem J 2006 Nov 1;399(3):513-24

Ascorbate removes key precursors to oxidative damage by cell free hemoglobin in vitro and in vivo.

Dunne J, Caron A, Menu P, Alayash AI, Buehler PW, Wilson MT, Silaghi-Dumitrescu R, Faivre B, Cooper CE

Cooper CE (reprint author), Univ Essex, Dept Biol Sci, Wivenhoe Pk, Colchester, Essex CO4 3SQ England Univ Essex, Dept Biol Sci, Colchester, Essex CO4 3SQ England Univ Henri Poincare, Fac Pharm, Lab Hematol Physiol, Nancy, F-54001 France US FDA, Ctr Biol Evaluat & Res, Div Hematol, Lab Biochem & Vasc Biol, Bethesda, MD 20892 USA

Hemoglobin initiates free radical chemistry. In particular the interactions of peroxides with the ferric(met) species of hemoglobin generate two strong oxidants: ferryl iron and a protein-bound free radical. We studied the endogenous defences to this reactive chemistry in a rabbit model following 20% exchange transfusion with cell free hemoglobin stabilized in tetrameric form (via crosslinking with bis(3,5-dibromosalicyl)fumarate). The transfusate contained 95- oxyhemoglobin, 5% methemoglobin and 25 muM free iron. Electron paramagnetic resonance spectroscopy revealed that the free iron in the transfusate was rendered redox inactive by rapid binding to transferrin. Methemoglobin was reduced to oxyhemoglobin by a slower process (t 1/2 = 1 hour). No globin-bound free radicals were detected in the plasma. These redox defences could be fully attributed to a novel multifunctional role of plasma ascorbate in removing key precursors of oxidative damage. Ascorbate is able to effectively reduce plasma methemoglobin, ferryl hemoglobin and globin radicals. The ascorbyl free radicals formed are efficiently re-reduced by the erythrocyte membrane-bound reductase (which itself uses intraerythrocyte ascorbate as electron donor). As well as relating to the toxicity of hemoglobin-based oxygen carriers, these findings have implications for situations where heme proteins exist outside the protective cell environment e.g. hemolytic anemias, subarachnoid hemorraghe, rhabdomyolysis.