Protection from Transient Focal Cerebral Ischemia by Transfusion of Polynitroxylated Pegylated Hemoglobin

Polynitroxylation of hemoglobin (Hb) confers superoxide dismutase and catalase mimetic activity and can protect neurons from native Hb and glutamate. Here, we determined if transfusion of polynitroxylated pegylated Hb (PNPH) is protective in the rat filament model of 2 h of middle cerebral artery occlusion (MCAO). Transfusion of 10 ml/kg of PNPH at 20 min of MCAO reduced the median infarct volume in cerebral cortex from 40% (37-47% interquartile range; n=10) in controls to 3% (0-7%; n=10; P<0.001) with PNPH and in striatum from 78% (66-88%) to 34% (0-37%; P<0.001). The therapeutic window was evaluated in a second experiment. Compared to the control median hemispheric infarct volume of 22% (13-34%; n=15), infarct volume was reduced to 7% (3-13%; n=14; P<0.05) when PNPH was transfused at 4 h after MCAO (2 h of reperfusion) but not significantly when transfused at 6 h (8%; 3-35%; n=14) or at 8 h (12%; 10-25%; n=14) after MCAO. To determine whether PNPH might act by promoting vasodilation, pial arteriolar diameter in the distal MCA border region was measured in closed cranial windows during MCAO. With no transfusion, MCAO induced an initial dilation (36±5%; ±SD; n=8) that subsided by 2 h (5±11%). With PNPH transfusion at 20 min of MCAO, the initial dilation (31±8%; n=7) was better maintained at 2 h (21±11%; P<0.02). To determine whether delaying PNPH transfusion until 90 min of MCAO would improve penumbral perfusion, laser-Doppler flow (LDF) was measured in the ischemic border region where the reduction in LDF was less severe than in the core. LDF significantly increased from 48±18% of the pre-ischemic baseline to 67±21% (P<0.005). Thus, PNPH transfusion has a significant therapeutic window for protection from transient MCAO and may act, in part, by stabilizing vascular function and improving collateral blood flow.