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Preparation and in vitro characteristics of polymerized pyridoxylated hemoglobin

Stroma‐free hemoglobin solutions have been the subject of extensive studies as potential acellular oxygen carriers. Oncotic pressure considerations limit the hemoglobin concentration of the solutions (6–8 g/dl) to one‐half the normal whole blood values. Furthermore, the free hemoglobin has a short plasma half‐life (2–4 hours). In principle, polymerization offers a means of normalizing the oxygen‐carrying capacity as well as extending the plasma half‐life. Pyridoxylation of hemoglobin prior to polymerization provides an acceptable P50. Pyridoxylated hemoglobin (14–16 g/dl) was polymerized with a 12.5 percent glutaraldehyde solution. Since the goal was to obtain a 15 g per dl solution iso‐oncotic with plasma, the polymerization reaction was monitored by the drop in colloid osmotic pressure. The reaction was quenched with 1.3 M lysine when the colloid osmotic pressure reached normal values (20–25 torr). The polymerization yield was 80 percent, with molecular weights ranging from 120,000 to 600,000 Dalton. The polymerized hemoglobin had a binding coefficient of 1.32, a Pso of 16 torr, a Bohr coefficient of –0.12, and a Hill coefficient of 1.7. The viscosity of the solution was 4.5 centipoise. The methemoglobin levels were comparable to that of unpolymerized stroma‐free hemoglobin. Polymerized hemoglobin solutions provide a normal oxygen‐carrying capacity with a P50 comparable to that of unpolymerized stroma‐free hemoglobin solutions.