Effect of ACEA--a selective cannabinoid CB1 receptor agonist on the protective action of different antiepileptic drugs in the mouse pentylenetetrazole-induced seizure model

Endogenous cannabinoid ligands and cannabinoid CB1 receptor agonists have been shown to exert anticonvulsant effects in various experimental models of epilepsy. The purpose of this study was to determine the effects of arachidonyl-2'-chloroethylamide (ACEA-a highly selective cannabinoid CB1 receptor agonist) on the protective action of clonazepam, ethosuximide, phenobarbital, and valproate against pentylenetetrazole (PTZ)-induced clonic seizures in mice. To ascertain any pharmacokinetic contribution of ACEA to the observed interactions between tested drugs, free (non-protein bound) plasma and total brain concentrations of the antiepileptic drugs were estimated. Additionally, acute adverse-effect profiles of the combination of ACEA and different classical antiepileptic drugs (clonazepam, ethosuximide, phenobarbital and valproate) with respect to motor performance, long-term memory and skeletal muscular strength were measured. Results indicated that ACEA (10mg/kg, i.p.) co-administered with phenylmethylsulfonyl fluoride (PMSF-a substance protecting ACEA against degradation by the fatty-acid hydrolase; 30mg/kg, i.p.) significantly potentiated the anticonvulsant activity of ethosuximide, phenobarbital and valproate in the mouse PTZ-induced clonic seizure model by reducing their median effective doses (ED(50) values) from 122.8mg/kg to 71.7mg/kg (P<0.01; for ethosuximide), from 13.77mg/kg to 5.26mg/kg (P<0.05; for phenobarbital), and from 142.7mg/kg to 87.3mg/kg (P<0.05; for valproate), respectively. In contrast, ACEA (10mg/kg, i.p.) in combination with PMSF (30mg/kg, i.p.) had no impact on the protective action of clonazepam against PTZ-induced seizures in mice. However, ACEA (10mg/kg)+PMSF (30mg/kg) considerably increased free plasma and total brain concentrations of ethosuximide and valproate in mice suggesting a pharmacokinetic nature of interaction between drugs. In contrast, free plasma and total brain concentrations of clonazepam and phenobarbital remained unchanged after ACEA+PMSF administration and thus, indicating pharmacodynamic interactions. Moreover, none of the examined combinations of ACEA (10mg/kg, i.p.)+PMSF (30mg/kg, i.p.) with clonazepam, ethosuximide, phenobarbital, and valproate (at their ED(50) values from the PTZ-induced seizure test) affected motor coordination in the chimney test, long-term memory in the passive avoidance task, and muscular strength in the grip-strength test in mice, indicating no possible acute adverse effects in animals. In conclusion, pharmacodynamic enhancement of the anticonvulsant potency of phenobarbital by ACEA+PMSF is worthy of recommendation for further clinical settings. Pharmacokinetic interactions of ACEA+PMSF with ethosuximide and valproate seem to be responsible for a significant suppression of PTZ-induced seizures in mice. The combination of ACEA+PMSF with clonazepam seems to be neutral from a preclinical viewpoint.

Effects of WIN 55,212-2 mesylate (a synthetic cannabinoid) on the protective action of clonazepam, ethosuximide, phenobarbital and valproate against pentylenetetrazole-induced clonic seizures in mice

The aim of this study was to determine the effect of WIN 55,212-2 mesylate (WIN - a non-selective cannabinoid CB1 and CB2 receptor agonist) on the protective action of four classical antiepileptic drugs (AEDs: clonazepam [CZP], ethosuximide [ETS], phenobarbital [PB], and valproate [VPA]) in the mouse pentylenetetrazole (PTZ)-induced clonic seizure model. WIN (15 mg/kg, i.p.) significantly enhanced the anticonvulsant action of ETS, PB and VPA, but not that of CZP against PTZ-induced clonic seizures. The ED(50) values of ETS, PB and VPA were reduced from 148.0, 13.9 and 137.1mg/kg to 104.0, 8.3 and 85.6 mg/kg, respectively (P<0.05). WIN (5 and 10mg/kg, i.p.) had no impact on the anticonvulsant action of all studied AEDs against PTZ-induced clonic seizures. WIN (15 mg/kg, i.p.) significantly elevated total brain concentrations of ETS and VPA, but not those of CZP and PB in mice. Moreover, WIN combined with CZP, ETS, PB and VPA significantly impaired motor performance, long-term memory and muscular strength in mice subjected to the chimney, passive avoidance and grip-strength tests, respectively. Pharmacodynamic enhancement of the anticonvulsant action of PB by WIN against PTZ-induced clonic seizures is favorable from a preclinical viewpoint. Advantageous effects of WIN in combination with ETS and VPA against PTZ-induced seizures were pharmacokinetic in nature. However, WIN combined with CZP, ETS, PB and VPA impaired motor coordination and long-term memory as well as reduced skeletal muscular strength in the experimental animals.