Behavioral effects of a neurotoxic compound isolated from Clibadium surinamense L (Asteraceae)

Clibadium surinamense L, popularly known as cunambi, is a native plant from the Northern region of Brazil illegally used for predatory fishing. Previous results from our laboratory have demonstrated that the oral treatment of mice with the ethanolic extract (EE) of the leaves of the plant induced generalized tonic-clonic seizures followed by death within 30 min. The aims of the present paper were to characterize the convulsant effect of the hexanic extract (HE) of the stems and leaves of C. surinamense and, by bioguided purification, to identify the active principle and its mechanism of action. The leaves and stems were extracted with hexane (100 g/L) in Soxhlet for 36 h (yield of 2.4%), the solvent was evaporated and the powder dissolved in 1.5% saline/Tween 80. Male mice (30-35 g) treated with HE (22.5-360 mg/kg, p.o.) showed behavioral alterations consistent with CNS stimulation. The intensity and duration of the effect were proportional to the administered doses. The behavioral alterations, measured with a graded score of seizure severity, revealed that pretreatment with carbamazepine (30 mg/kg, i.p., 60 min) or phenytoin (50 mg/kg, i.p., 30 min) did not alter the HE convulsive effect. In contrast, phenobarbital (30 mg/kg, i.p., 60 min) or diazepam (2 mg/kg, i.p., 30 min) reduced the HE effect, increasing the ED(50) for clonic seizures from 64.4 to 89.8 mg/kg and 168.9 mg/kg, respectively. Purification of the HE in a silica gel column eluted with a hexane/ethyl acetate gradient yielded a single fraction with convulsant effect in which cunaniol acetate was identified by (1)H NMR as the main active compound. These results indicated that inhibition of GABAergic transmission by cunaniol acetate might be responsible for the convulsant effects of C. surinamense L in mice, but do not exclude a direct cunaniol action labilizing neuronal excitability.