bis(3-5-dibromosalicyl)fumarate and mono(3-5-dibromosalicyl)fumarate

One approach to the development of an effective red cell substitute has been chemical modification of human hemoglobin to optimize oxygen transport and plasma half-life. Human hemoglobin A0 and two of these modified hemoglobins, one prepared from the cross-linking of the alpha-chains at lysine residue 99 by bis(3,5-dibromosalicyl)fumarate (Hb-DBBF) and the other by acylation of lysine residue 82 of the beta-chain by mono-(3,5-dibromosalicyl)fumarate (Hb-FMDA), were tested by HPLC for their susceptibility to oxidative damage caused by H2O2. Such oxidative insult may occur during ischemia and reperfusion of tissues after transfusion of red cell substitutes to patients with hypovolemic shock and trauma. Hb-DBBF was extremely susceptible to damage of its heme and protein moieties with stoichiometric amounts of H2O2, whereas Hb-FMDA was highly resistant, even at 10-fold molar excess and at an acidic pH of 4.7. Hemoglobin A0 was of intermediate susceptibility, exhibiting alteration of heme and protein moieties at acidic but not neutral pH. Since the degradation of heme can release the potentially toxic agent iron, Hb-FMDA may be a more promising candidate than Hb-DBBF for development as a red cell substitute. A similar approach may be used to assess the susceptibility of other hemoglobin-based red cell substitutes to oxidative damage in order to determine the molecular basis of heme and protein alteration.

Topics: Aspirin; Biological Transport; Blood Substitutes; Cross-Linking Reagents; Drug Design; Erythrocytes; Heme; Hemoglobins; Humans; Hydrogen Peroxide; Oxidation-Reduction; Oxygen

We have examined the interactions between nitric oxide (NO) and oxidized human hemoglobin, comparing the behavior of unmodified HbA0 with that of two chemically modified hemoglobins. The latter are promising red cell substitute candidates due to their lower oxygen affinity and greater stability as tetramers. The modified forms examined were HbA-DBBF, cross-linked between the alpha chains with bis(3,5-dibromosalicyl) fumarate, and HbA-FMDA, modified between the beta chains with fumaryl monodibromoaspirin. NO binding to the oxidized forms of these hemoglobins is biphasic, due to the differing reactivities of alpha and beta chains. The structural modifications result in altered rate constants for NO binding to both alpha and beta chains. The affinity of the ferric hemes for NO is not correlated with their oxygen affinities in the ferrous state. In a much slower first-order process, the ferric hemes of HbA become reduced. Faster and more heterogeneous kinetics are observed for reduction of the modified hemoglobins. These results may have physiological relevance, since endogenously produced NO is now recognized to play an important role in the relaxation of vascular smooth muscles. If present in vivo, cell-free hemoglobins exposed to NO become rapidly oxidized. Our results show that subsequent interactions of NO with ferrihemoglobin can result in redox cycling. This has the potential of depleting NO and further altering vascular tone with rates dependent on structural parameters of the ferrihemoglobin that are not determined by oxygen affinity.

Topics: Aspirin; Cross-Linking Reagents; Drug Stability; Humans; Kinetics; Macromolecular Substances; Methemoglobin; Nitric Oxide; Oxidation-Reduction; Oxygen; Spectrophotometry