Hepatic inflammatory responses to alphaalpha-cross-linked hemoglobin infusion in rats

First-generation blood substitutes: what have we learned? Biochemical and physiological perspectives

Chemically modified or recombinant hemoglobin (Hb)-based oxygen carriers (HBOCs) have been developed as oxygen therapeutics or 'blood substitutes' for use in a variety of clinical settings. Oxidative and nitrosative reactions of acellular Hb can limit the effectiveness and compromise the safety of HBOCs. The reactions between Hb and biologically relevant redox active molecules may also perturb redox sensitive signaling pathways. In recent years, systematic in vitro and in vivo structural and functional evaluation of several HBOCs has been carried out and, in some cases, delineated the 'structural' origin of their toxicity. This enables potential protective strategies against Hb-mediated side reactions to be rationally suggested. Here the authors provide an overview of their research experiences, novel insights into the molecular basis of toxicities of these products and some lessons learned.

Interactions of hemoglobin with hydrogen peroxide alters thiol levels and course of endothelial cell death

We investigated cellular injury and death induced by ultrapure human Hb (HbA(0)) and its diaspirin cross-linked derivative DBBF-Hb in normal and glutathione (GSH)-depleted bovine aortic endothelial cells subjected to hydrogen peroxide (H(2)O(2)). HbA(0) underwent extensive degradation and heme loss, whereas DBBF-Hb persisted longer in its ferryl (Fe(4+)) form. The formation of ferryl HbA(0) or ferryl DBBF-Hb was associated with a significant decrease in endothelial cell GSH compared with the addition of H(2)O(2) or Hbs alone. This effect was inhibited by catalase, but not by superoxide dismutase or deferoxamine mesylate. The presence of HbA(0) and DBBF-Hb reduced H(2)O(2)-induced apoptosis, as measured by cell morphology, annexin V binding assay, and caspase inhibition, consistent with the ability to consume H(2)O(2) in an enzyme-like fashion. However, the pattern of cell death and injury produced by HbA(0) and DBBF-Hb appeared to be distinctly different among proteins as well as among cells with and without GSH. These findings may have important implications for the use of cell-free Hb as oxygen therapeutics in patients with coexisting pathologies who may lack antioxidant protective mechanisms.

Site-specific modifications and toxicity of blood substitutes. The case of diaspirin cross-linked hemoglobin

Safe and effective hemoglobin-based blood substitutes may be advantageous over conventional therapies for certain clinical settings requiring short term blood replacement such as emergency resuscitation and hemodilution in surgery. Many advances have been made in developing these oxygen therapeutics, however safety concerns continue to slow their clinical progress. An important and often overlooked consideration in evaluating the safety of modified hemoglobins is the impact of chemical and/or genetic modifications on the redox chemistry of these proteins. Diaspirin cross-linked hemoglobin (DBBF-Hb) has been extensively evaluated in vitro and in animal models, and thus represents a useful model to explore possible correlations between structural-functional alterations and toxicity of hemoglobin-based blood substitutes.