Post-ischemic RSR13 amplifies the effect of dizocilpine on outcome from transient focal cerebral ischemia in the rat

In a recent study of focal cerebral ischemia in rats, pre-ischemic administration of the synthetic allosteric hemoglobin modifier RSR13 (2-[4-[[3,5-dimethylanilino) carbonyl] methyl] phenoxy]-2-methylproprionic acid) reduced cerebral infarct size when combined with the NMDA receptor antagonist dizocilpine (MK-801) but not when given alone. We hypothesized that post-ischemic RSR13 administration would enhance neuroprotection afforded by NMDA receptor antagonism in a rat model of transient middle cerebral artery occlusion (MCAO). Fasted normothermic Wistar rats underwent 75 min of temporary MCAO. At onset of reperfusion, rats randomly received: (1) 0.9% NaCl (vehicle) i.v. alone ( n=16); (2) 0.9% NaCl+dizocilpine (0.25 mg/kg) i.v. ( n=16); or (3) RSR13 (150 mg/kg)+dizocilpine (0.25 mg/kg) i.v. ( n=17). Seven days later, neurologic deficit and cerebral infarct size were determined. Dizocilpine alone compared to vehicle reduced mean±S.D. subcortical (52±24 mm 3 vs. 122±64 mm 3, P=0.003) and cortical (35±35 mm 3 vs. 125±72 mm 3, P=0.00074) infarct volumes. When compared to dizocilpine alone, the combination of RSR13+dizocilpine further reduced subcortical (37±14 mm 3 vs. 52±24 mm 3, P=0.034) and cortical (8±19 mm 3 vs. 35±35 mm 3, P=0.018) infarct size. RSR13+dizocilpine improved neurologic scores vs. either dizocilpine alone ( P=0.0014) or vehicle ( P=10 −7). The combination of NMDA receptor antagonism and a RSR13 mediated rightward shift of the oxy-hemoglobin dissociation curve improved outcome from MCAO. Because this occurred after reperfusion, our results suggest that the post-ischemic brain continues to suffer from hypoperfusion defects, which are amenable to therapy by enhanced O 2 delivery. The results also support the concept that neuroprotective strategies, which combine drugs with different mechanisms of action, may yield cumulative benefits.