AM-36

This study determined the antihyperalgesic effect of CNSB002, a sodium channel blocker with antioxidant properties given alone and in combinations with morphine in rat models of inflammatory and neuropathic pain.

Dose response curves for nonsedating doses of morphine and CNSB002 given intraperitoneally alone and together in combinations were constructed for antihyperalgesic effect using paw withdrawal from noxious heat in two rat pain models: carrageenan-induced paw inflammation and streptozotocin (STZ)-induced diabetic neuropathy.

The maximum nonsedating doses were: morphine, 3.2 mg/kg; CNSB002 10.0 mg/kg; 5.0 mg/kg CNSB002 with morphine 3.2 mg/kg in combination. The doses calculated to cause 50% reversal of hyperalgesia (ED50) were 7.54 (1.81) and 4.83 (1.54) in the carrageenan model and 44.18 (1.37) and 9.14 (1.24) in the STZ-induced neuropathy model for CNSB002 and morphine, respectively (mg/kg; mean, SEM). These values were greater than the maximum nonsedating doses. The ED50 values for morphine when given in combination with CNSB002 (5 mg/kg) were less than the maximum nonsedating dose: 0.56 (1.55) in the carrageenan model and 1.37 (1.23) in the neuropathy model (mg/kg; mean, SEM). The antinociception after morphine (3.2 mg/kg) was increased by co-administration with CNSB002 from 28.0 and 31.7% to 114.6 and 56.9% reversal of hyperalgesia in the inflammatory and neuropathic models, respectively (P < 0.01; one-way analysis of variance-significantly greater than either drug given alone).

The maximum antihyperalgesic effect achievable with nonsedating doses of morphine may be increased significantly when the drug is used in combination with CNSB002.

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 IC50 of 0.28 microM. Veratridine (100 microM)-induced neurotoxicity in murine cerebellar granule cells was completely inhibited by AM-36 (1.7 microM) compared to only partial inhibition by sipatrigine (26 microM). 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 microM). 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.