Low oxygen affinity derivatives of human hemoglobin by fixation of polycarboxylic dextran to the oxyform

Purification and chemical modifications of hemoglobin in developing hemoglobin based oxygen carriers

The efficacy of blood substitutes, as a whole, has been readily demonstrated, in animals as well as clinical studies. It is well known that stroma free hemoglobin (SF-Hb) is very toxic, due to effects on renal and coagulation functions and vascular tone. Several modifications have been made to the hemoglobin tetramer in an attempt to eliminate its toxicity. Conjugation, cross-linking, polymerization, and recombinant technology have all been used to reduce toxicity, while aiming to optimize the therapeutic value of hemoglobin based blood substitutes. The remaining issue seems to be the hypertensive response seen in many hemoglobin solutions. The cause of the hypertensive response, and hence what chemical modifications are suitable to alleviate it are still under debate.

New support for the affinity chromatography of hemoglobin

A new support for affinity chromatography of hemoglobin was synthesised from EAH Sepharose-4B containing a hexamethylamine spacer. Benzenetetracarboxylic (BTC) or benzenehexacarboxylic (BHC) acids were covalently bound to the spacer arm. At pH close to the pI of the protein, the biospecificity of the support due to the interactions of the allosteric site of hemoglobin with immobilised polyanionic ligands was proved. When the allosteric site was blocked by covalently linked pyridoxalphosphate, the protein showed no more affinity for the support. Further investigations were done on the BHC support; the association constants between BHC support and the hemoglobin forms, oxyhemoglobin and deoxyhemoglobin, were determined. The deoxyhemoglobin affinity was ten times higher than that of oxyhemoglobin, both for fixed and for free ligand. The following values of binding constants K(PX) and K(PL) (1 mol(-1)) with fixed or free ligand respectively were found: for oxyhemoglobin, K(PX)=8.0x10(2), K(PL)=1.4x10(4); for deoxyhemoglobin, K(PX)=9.7x10(4), K(PL)=2.3x10(5). The BHC support capacity was about 4.7x10(-5) mol hemoglobin g(-1) of dry gel corresponding to 1.5x10(-6) mol hemoglobin g(-1) of hydrated gel or 0.1 g hemoglobin g(-1) of hydrated gel.