DIFFERENTIAL SUSCEPTIBILITIES OF THE PROSTHETIC HEME OF HEMOGLOBIN-BASED RED-CELL SUBSTITUTES - IMPLICATIONS IN THE DESIGN OF SAFER AGENTS

One approach to the development of an effective red cell substitute ha s been chemical modification of human hemoglobin to optimize oxygen tr ansport and plasma half-life. Human hemoglobin A(0) and two of these m odified hemoglobins, one prepared from the cross-linking of the alpha- chains at lysine residue 99 by bis(3,5-dibromosalicyl)fumarate (Hb-DBB F) and the other by acylation of lysine residue 82 of the beta-chain b y mono-(3,5-dibromosalicyl)fumarate (Hb-FMDA), were tested by HPLC for their susceptibility to oxidative damage caused by H2O2. Such oxidati ve insult may occur during ischemia and reperfusion of tissues after t ransfusion of red cell substitutes to patients with hypovolemic shock and trauma. Hb-DBBF was extremely susceptible to damage of its heme an d protein moieties with stoichiometric amounts of H2O2, whereas Hb-FMD A was highly resistant, even at 10-fold molar excess and at an acidic pH of 4.7. Hemoglobin A(0) was of intermediate susceptibility, exhibit ing alteration of heme and protein moieties at acidic but not neutral pH. Since the degradation of heme can release the potentially toxic ag ent iron, Hb-FMDA may be a more promising candidate than Hb-DBBF for d evelopment as a red cell substitute. A similar approach may be used to assess the susceptibility of other hemoglobin-based red cell substitu tes to oxidative damage in order to determine the molecular basis of h eme and protein alteration.