Protective Effect of Transfusion of Carbon Monoxide‐Bound PEGylated Hemoglobin (PEG‐COHb) after Transient Focal Cerebral Ischemia

Abstract

Transfusion of acellular PEG‐COHb at 20 min of middle cerebral artery occlusion (MCAO) maintains pial arteries in a dilated state and reduces infarct volume. We investigated whether the decrease in infarct volume could be attributed to improved oxygenation and to known anti‐inflammatory effects of moderate levels of CO. Anesthetized rats underwent MCAO for 2 h by the intraluminal filament technique. Transfusion of 10 ml/kg of a 4% solution of PEG‐COHb at 20 min of MCAO decreased Hif‐1a protein expression in the ischemic hemisphere by 83 (11)% (SE) at 2 h after onset of MCAO, consistent with improved intraischemic oxygenation. Next, we examined the effect of delaying transfusion until reperfusion. Infarct volume in cerebral cortex was significantly decreased from 36 (5)% in controls to 17 (6)%, 15 (5)%, and 17 (5)% in groups transfused with PEG‐COHb at 20 min, 2 h, and 4 h after MCAO, respectively. PEG‐COHb transfusion at reperfusion decreased TNFa and IL‐1b gene expression by 69% and 74%, respectively, in cortex 24 h after MCAO. To test for the direct effect of CO, another group received an injection of the CO‐releasing molecule‐3 (6.63 mg/kg, iv) at reperfusion; gene expression was significantly decreased by 84% for TNFa and by 83% for IL‐1b. These data indicate a significant therapeutic time window for transfusion of small amounts of PEG‐COHb after ischemic stroke. The protective effect of PEG‐COHb transfused at reperfusion appears to be related to the CO donor effect of PEG‐COHb and an associated suppression of neuroinflammation. In addition, the benefit of transfusion during the period of vascular occlusion may be related to its ability to improve tissue oxygenation via collateral vessels. (Supported by NIH NS038684.)