Hemoglobin-based artificial blood: new polymeric derivatives of hemoglobin with low oxygen affinity.

To make stroma-free hemoglobin (SFHb) capable of carrying oxygen satisfactorily in vivo it is necessary both to improve its intravascular persistence and to reduce its affinity for oxygen. The method used up to now has consisted of chemical modification of SFHb to lower its oxygen affinity (fixation of permanent effector inside the phosphate binding site or intramolecular cross-linking of the deoxy form of SFHb), then polymerization or substitution with polymers. We have designed new functionalized polymers (from dextran and polyoxyethylene), capable of mimicking the effect of the natural intraerythrocyte effector, 2,3-disphosphoglycerate, i.e. of decreasing its affinity for oxygen, and we have linked these polymers chemically to oxyHb. All the resulting conjugates have lower oxygen affinity than SFHb and, when injected into rats, do not lead to hemoglobinuria. Preliminary in vivo tests also showed that these conjugates possess no acute toxicity. Further experiments with rats are now under way (60% and 80% hemorrhagic shocks) with the aim of evaluating whether these new products can be regarded as potential candidates for blood substitution.