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Neuroprotection with Polynitroxylated PEGylated Hemoglobin as a Macromolecular Superoxide Dismutase/Catalase Mimetic Drug for Resuscitation after Traumatic Brain Injury Combined with Hemorrhage Shock

In polynitroxylated PEGylated hemoglobin (PNPH aka SanFlow), polynitroxylation of hemoglobin confers superoxide dismutase/catalase (SOD/CAT) mimetic activities that may directly protect the brain from oxidative stress in addition to facilitating O2 transport. PEGylation of cell‐free hemoglobin also limits extravasation and renal clearance and increases its oncotic pressure, thereby allowing it to be used as a small volume resuscitation fluid in the field. Furthermore, stabilization of PNPH with bound CO prevents metHb formation during storage and permits it to serve as a CO donor that is converted to an oxygen carrier after infusion. We determined whether transfusion of a 4% solution PNPH with bound CO is neuroprotective after traumatic brain injury (TBI) + hemorrhagic shock (HS) as a model of polytrauma. Guinea pigs were used because, like humans, they do not synthesize their own ascorbic acid, which is important in reducing metHb. TBI was produced by a 5‐mm diameter cortical impactor that briefly displaced the dura 3 mm. TBI was followed by 20 mL/kg hemorrhage to a mean arterial pressure (MAP) of 40 mmHg. At 90 min after HS, the guinea pigs were resuscitated with 20 mL/kg lactated Ringer's solution (LR) or 10 mL/kg PNPH over a 90‐min period. Additional doses were infused one and two days later. Compared with animals that received LR, resuscitation with PNPH significantly augmented the early recovery of MAP after HS by 10–18 mmHg (n=12; P <0.001). After infusion of PNPH, total blood metHb and COHb increased by 2% as CO from PNPH equilibrated with the larger erythrocyte hemoglobin pool. At 9 days of recovery, there was no statistical difference in lesion volume or the total volume of the underlying hippocampus among the sham and the two TBI+HS groups. However, accompanying the loss of cerebral cortex, ventricular enlargement as much as three‐fold occurred. In those receiving PNPH, ventricular enlargement was attenuated by 23% (n=12; P <0.05). Most importantly, unbiased stereology analysis revealed that PNPH infusion increased the number of viable neurons in the hippocampus CA1+2 region (Naïve+sham groups = 271,000 ± 39,000; TBI+HS+LR = 159,000 ± 28,000; TBI+HS+PNPH = 235,000 ± 49,000 viable neurons; n=12/group; P <0.05 LR vs PNPH and LR vs Naïve/sham; 6 naïve and 6 sham‐operated guinea pigs did not differ and were combined). In conclusion, resuscitation with PNPH after TBI+HS in guinea pigs provides significant neuroprotection in hippocampus and attenuation of hydrocephalus. These effects may be attributed, in part, to its ability to augment MAP as a hyperoncotic, small volume resuscitation fluid, by its SOD/CAT mimetic activities, and by serving as a CO donor, which at low CO concentrations exerts anti‐apoptotic and anti‐inflammatory effects. PNPH may serve as a multi‐potential resuscitation fluid for polytrauma involving TBI and HS.