Neuroprotection (focal ischemia) and neurotoxicity (electroencephalographic) studies in rats with AHN649, a 3-amino analog of dextromethorphan and low-affinity N-methyl-D-aspartate antagonist.

AHN649, an analog of dextromethorphan (DM) and a relatively selective low-affinity N-methyl-D-aspartate antagonist, was evaluated for neuroprotective effects using the rat intraluminal filament model of temporary middle cerebral artery occlusion. Rats were subjected to 2 h of focal ischemia followed by 72 h of reperfusion. In vehicle-treated rats, middle cerebral artery occlusion resulted in neurological deficits and severe infarction measuring 232 +/- 25 mm(3), representing approximately 25% contralateral hemispheric infarction. Post-treatment with AHN649 (0.156-20 mg/kg i.v.) or DM (0.156-10 mg/kg i.v.) significantly reduced cortical infarct volume by 40 to 60% compared with vehicle-control treatments. AHN649 neuroprotection was linear and dose dependent (ED(50) = 0.80 mg/kg), whereas DM neuroprotection (ED(50) = 1.25 mg/kg) was nonlinear and less effective at the higher doses (2.5-10 mg/kg). Although impaired neurological function scores improved in all groups by 24 to 72 h, the most dramatic improvement was associated with AHN649 treatments. In a rat electroencephalographic model of brain function, separate neurotoxicity experiments revealed that acute i.v. doses of DM caused seizures (ED(50) = 19 mg/kg) and death (LD(50) = 27 mg/kg). In contrast, AHN649 failed to induce seizure activity at doses up to 100 mg/kg (LD(50) = 79 mg/kg). Collectively, AHN649 is described as a potent, efficacious neuroprotective agent devoid of serious central nervous system neurotoxicity and possessing potential therapeutic value as antistroke treatment. Furthermore, the feasibility of targeting low-affinity N-methyl-D-aspartate-site ligands as postinjury therapy for ischemic brain injury has been confirmed.