Delayed treatment with AM-36, a novel neuroprotective agent, reduces neuronal damage after endothelin-1-induced middle cerebral artery occlusion in conscious rats

Background and Purpose-AM-36 is a novel arylalkylpiperazine with combined a ntioxidant and Na+ channel blocking actions. Individually, these properties have been shown to confer neuroprotection in a variety of in vitro and in vivo animal models of stroke. Preliminary studies have shown that AM-36 is neuroprotective in vivo. The purpose of the present study was to assess the neuroprotective and behavioral outcome after delayed administration of AM- 36 in an endothelin-1-induced, middle cerebral artery model of cerebral isc hemia in conscious rats. Methods-Conscious male hooded Wistar rats were subjected to middle cerebral artery occlusion by perivascular microinjection of endothelin-1 via a prev iously implanted cannula. AM-36 (6 mg/kg IP) or vehicle was administered in traperitoneally 30, 60, or 180 minutes after middle cerebral artery occlusi on. Functional outcome was determined 24, 48, and 72 hours after stroke by neurological deficit score, motor performance, and sensory hemineglect test s. Rats were killed at 72 hours, and infarct area and volume were determine d by histology and computerized image analysis. Results-Endothelin-1-induced middle cerebral artery occlusion resulted in m arked functional deficits and neuronal damage. AM-36 significantly reduced cortical damage when administration was delayed until 30, 60, or 180 minute s after stroke. Interestingly, neuronal damage was time-dependently reduced , with the greatest protection found when AM-36 was administered 180 minute s after stroke. Striatal damage was significantly reduced after treatment w ith AM-36 at 180 minutes after stroke. Functional outcome paralleled histop athology. Rota-rod performance, sensory hemineglect, and neurological defic it scores returned to preischemia levels in AM-36-treated rats by 72 hours after stroke when administration was delayed by 180 minutes after stroke. Conclusions-AM-36 potently protects against both neuronal damage and functi onal deficits even when administered up to 180 minutes after induction of s troke. In fact, the greatest protection was found when administration was d elayed by 180 minutes after stroke. The possible mechanisms of action of AM -36 are discussed. The present findings suggest that AM-36 may have great p romise in the acute treatment of human stroke.