Sodium channel blocking activity of AM-36 and sipatrigine (BW619C89): in vitro and in vivo evidence

Sodium channel blockers are neuroprotective against cerebral ischemia in animal models. A novel neuroprotective compound AM-36, when screened for activity at the most common receptor and ion channel binding sites, revealed activity at site 2 Na + channels. Studies then investigated this Na + channel blocking activity in vitro and in vivo relative to other Na + channel blockers, including the neuroprotective agent sipatrigine (BW619C89). AM-36 inhibited batrachotoxinin (BTX)-sensitive Na + channel binding in rat brain homogenates with an IC 50 of 0.28 μM. Veratridine (100 μM)-induced neurotoxicity in murine cerebellar granule cells was completely inhibited by AM-36 (1.7 μM) compared to only partial inhibition by sipatrigine (26 μM). Veratridine-stimulated glutamate release, as measured through a microdialysis probe in the cortex of anesthetised rats, was inhibited by 90% by superfusion of AM-36 (1000 μM). In the endothelin-1 (ET-1) model of middle cerebral artery occlusion (MCAo) in conscious rats, both AM-36 (6 mg/kg i.p.) and sipatrigine (10 mg/kg i.p.) 30 min post-MCAo significantly reduced cortical, but not striatal infarct volume. As the refractiveness of the striatum is likely to be dependent on the route and time of drug administration, AM-36 (1 mg/kg i.v.) was administered 3 or 5 h after MCAo and significantly reduced both cortical and striatal infarct volumes. The present studies demonstrate Na + channel blocking activity of AM-36 both in vitro and in vivo, together with significant neuroprotection when administration is delayed up to 5 h following experimental stroke.