Selective antiepileptic effects of N-palmitoylethanolamide, a putative endocannabinoid

PURPOSE: The purpose of this study was to determine whether N-palmitoylethanolamide (PEA), a putative endocannabinoid, would be effective against kindled amygdaloid seizures. For a comparison with earlier work, we also tested the effectiveness of PEA against pentylenetetrazol (PTZ)-induced convulsions. METHODS: Kindling electrodes were implanted bilaterally in the amygdala in 32 Long-Evans rats. After the kindling of generalized (stage 5) seizures, the effects of PEA administration [i.p.; 1, 10, 100 mg/kg in dimethylsulfoxide (DMSO)] were evaluated for anticonvulsant activity. PEA (40 mg/kg, i.p. in DMSO) also was tested for anticonvulsant activity against PTZ-induced convulsions (75 mg/kg, i.p.). RESULTS: After i.p. administration of PEA, kindled rats displayed an increased latency to clonus at the 1-mg/kg dose. No other dose-dependent effects were noted. When tested against PTZ-induced convulsions, PEA protected against tonic convulsions and prolonged the latency between convulsive episodes. CONCLUSIONS: PEA produces antiepileptic effects, but does not completely suppress seizures. The mechanism of action of PEA remains to be defined.     

Topiramate: Preclinical Evaluation of a Structurally Novel Anticonvulsant

Summary: Topiramate [TPM, 2,3:4,5-his-O-(1-methyl-ethylidene)-β-D-fructopyranose sulfamate] (RWJ-17021-000, formerly McN-4853) is a structurally novel antiepileptic drug (AED). The preclinical anticonvulsant profile suggests that TPM acts primarily by blocking the spread of seizures. TPM was highly effective in the maximal electroshock (MES) seizure test in rats and mice. Activity was evident 0.5. h after oral administration and lasted at least 16 h. The ED₅₀ values 4 h after oral dosing were 13.5 and 40.9 mg/kg in rats and mice, respectively. TPM blocked pentylenetetrazol (PTZ)-induced clonic seizures at high doses in mice (ED₅₀= 1,030 mg/kg orally, p.o.). With motor incoordination and loss of righting reflex used as indicators of neurologic impairment, the neuroprotective index (TD₅₀/MES ED₅₀) for TPM was equivalent or superior to that of several approved AEDs. In mice pretreated with SKF-525A (a P450 enzyme inhibitor), the anticonvulsant potency was either increased or unaffected when TPM was tested 0.5, 1, or 2 h after i.p. administration, suggesting that TPM rather than a metabolite was the active agent. In mice pretreated with reserpine or tetrabenazine, the activity of TPM in the MES test was markedly reduced. TPM was inactive in a variety of receptor binding, neurotransmitter uptake, and ion channel tests. TPM weakly inhibited erythrocyte carbonic anhydrase (CA) activity. However, the anticonvulsant activity of TPM appears to differ mechanistically from that of acetazolamide.     

The NMDA antagonist procyclidine,but not ifenprodil,enhances the protective efficacy of common antiepileptics against maximal electroshock-induced seizures in mice

Summary Procyclidine (up to 20mg/kg i.p.) did not influence the electroconvulsive threshold per se, but when given in a dose of 10mg/kg, it potentiated the protective activity of carbamazepine, diphenylhydantoin, phenobarbital and valproate, and in a dose of 20 mg/kg, that of diazepam against maximal electroshock-induced convulsions in mice. Ifenprodil increased the threshold for electroconvulsions when applied at 20 and 40 mg/kg (i.p.), but surprisingly, when combined with all antiepileptics tested, it did not influence their anticonvulsant actions. The chimney test in mice revealed, that application of procyclidine at 10 mg/kg together with phenobarbital and valproate, and procyclidine at 20 mg/kg with diazepam resulted in motor impairment. However, when procyclidine was applied at 10 mg/kg together with carbamazepine or diphenylhydantoin, no motor impairment was noted. The combined treatment of procyclidine (10 mg/kg) with carbamazepine, diphenylhydantoin, phenobarbital or valproate, as well as procyclidine (20 mg/kg) with diazepam caused significant worsening of long-term memory. Finally, procyclidine did not alter the total plasma levels of carbamazepine, diazepam, diphenylhydantoin, phenobarbital and valproate.It may be concluded that not all agents interfering with NMDA receptor complex-mediated events lead to the potentiation of the anticonvulsant activity of antiepileptic drugs.     

Intraction of the Anticonvulsant Ameltolide with standard Anticonvulsants

The newly characterized anticonvulsant ameltolide was studied in mice in combination with the standard antiepileptic drugs (AEDs), phenytoin (PHT), carbamazepine (CBZ), and valproate (VPA). In combination with either PHT or CBZ, ameltolide produced dose-additive effects in the maximal electroshock (MES) test and in the horizontal screen (HS) test for neurologic impairment. The large separation between the doses for the anticonvulsant effects and the neurologically impairing effects (protective index, PI) were maintained as well in the combinations as in the individual compounds. VPA was impotent in the MES test and did not have a clear separation between the doses that produce the anticonvulsant effects and those that are neurologically impairing (low PI). When VPA and ameltolide were combined, the effects were less than additive by isobolographic analysis on both the MES and HS tests. At high oral doses (20 and 40 mg/kg, p.o.), ameltolide produced impairment on the HS test and decreased body temperature. The effects on the HS test were enhanced twofold, whereas the effects on body temperature were not markedly enhanced, by coadministration of the MES ED95 of PHT and CBZ. VPA (MES ED95) appeared to antagonize the temperature-lowering effects of ameltolide. These interaction studies suggest that ameltolide would be safe, with no unexpected effects, when used in epileptic patients concurrently receiving these standard AEDs. These studies also suggest that the effects of ameltolide would be lessened by simultaneous administration of VPA.     

Anticonvulsant activity of the imidazoline 6,7-benzoidazoxan.

The effects of the imidazoline 6,7-benzoidazoxan on seizure threshold were assessed using standard tests of anticonvulsant activity. Benzoidazoxan (10-30 mg/kg i.p.; 100 mg/kg p.o.) prevented tonic, but not clonic, convulsions induced by electroshock in mice. The increase in seizure threshold was of rapid onset, and, although of short duration, was comparable with that obtained using phenytoin and sodium valproate. Moreover, unlike sodium valproate, benzoidazoxan was an efficacious anticonvulsant at doses (20, 30 mg/kg i.p.) which did not impair rotarod performance. The anticonvulsant effects of benzoidazoxan were confirmed using the maximal electroshock test in mice (median effective dose, 13.2 mg/kg i.p.) and rats (anticonvulsant at 30 mg/kg i.p.). In addition, benzoidazoxan (10, 30 mg/kg i.p.) prevented tonic, but not clonic, seizures induced by bicuculline in mice. Thus, the imidazoline benzoidazoxan was found to be a novel anticonvulsant agent against electrically and chemically induced seizures in mice and rats with a profile of action similar to that of phenytoin.     

Amiloride enhances the anticonvulsant action of various antiepileptic drugs in the mouse maximal electroshock seizure model

Accumulating evidence indicates that amiloride (a potassium-sparing diuretic) exerts the anticonvulsant action in various in vivo and in vitro experiments. Therefore, the objective of this study was to assess the influence of amiloride on the protective action of numerous conventional and second-generation antiepileptic drugs [AEDs: carbamazepine (CBZ), lamotrigine (LTG), oxcarbazepine (OXC), phenobarbital (PB), topiramate (TPM), and valproate (VPA)] against maximal electroshock (MES)-induced seizures in mice. Results indicate that amiloride [up to 100 mg/kg, intraperitoneally (i.p.), at 30, 60, and 120 min before the test] neither altered the threshold for electroconvulsions, nor protected the animals against MES-induced seizures in mice. Moreover, amiloride (75 and 100 mg/kg, i.p., 120 min prior to the test) significantly enhanced the anticonvulsant effects of all studied AEDs, except for LTG, by reducing their ED₅₀ values in the MES test. In contrast, amiloride at 50 mg/kg (i.p.) had no significant effect on the antielectroshock action of the tested AEDs in mice. Estimation of total brain AED concentrations revealed that amiloride (75 mg/kg) significantly increased total brain concentrations of CBZ, OXC, and PB, but not those of LTG, TPM, and VPA in mice. In conclusion, one can ascertain that the potentiation of the antiseizure action of TPM and VPA by amiloride in the MES test and lack of any pharmacokinetic interactions between drugs, make the combinations of amiloride with TPM and VPA of pivotal importance for epileptic patients.     

Anticonvulsant 1-phenylcycloalkylamines: two analogues with low motor toxicity when orally administered.

1-Phenylcyclohexylamine (PCA) and its analogues 1-phenylcyclopentylamine (PPA) and 1-(3-fluorophenyl)cyclohexylamine (3-F-PCA) are potent anticonvulsants in the mouse maximal electroshock (MES) seizure test. Unlike the structurally related dissociative anesthetic phencyclidine (PCP), however, which produces motor toxicity at anticonvulsant doses, PCA, PPA, and 3-F-PCA protect against MES seizures at 2.2- to 3.5-fold lower doses than those that cause motor toxicity when administered intraperitoneally (i.p.). In the present study, we evaluated the oral anticonvulsant activity of PCA, PPA, and 3-F-PCA in mice; we also examined 3-F-PCA in rats. All the compounds were orally active in the mouse MES seizure test (ED50 values 14.5, 53.4, and 26.7 mg/kg, respectively). Moreover, 3-F-PCA was especially potent in rats, either when administered i.p. (ED50 0.4 mg/kg vs. 9.4 mg/kg in mice) or orally (ED50 0.8 mg/kg). Surprisingly, however, oral PPA failed to cause motor toxicity in mice even at doses that were many times higher than those that were protective in the MES test (TD50 greater than 300 mg/kg). In rats, 3-F-PCA also showed a strikingly low oral toxicity (TD50 greater than 50 mg/kg) in relation to its potency as an anticonvulsant. Like PCP, PCA analogues block N-methyl-D-aspartate (NMDA)-induced behavioral effects and lethality in mice. Moreover, in vitro studies indicate that the compounds act as uncompetitive antagonists of the NMDA receptor-channel complex. Therefore, their anticonvulsant activity may, at least in part, relate to an interaction with NMDA receptors.     

7-Nitroindazole potentiates the anticonvulsant action of some second-generation antiepileptic drugs in the mouse maximal electroshock-induced seizure model

Summary. The effects of 7-nitroindazole (7NI, a preferential neuronal nitric oxide synthase inhibitor) on the anticonvulsant activity of four second-generation antiepileptic drugs (AEDs: felbamate [FBM], lamotrigine [LTG], oxcarbazepine [OXC] and topiramate [TPM]) were studied in the mouse maximal electroshock-induced seizure (MES) model. Moreover, the influence of 7NI on the acute neurotoxic (adverse-effect) profiles of the studied AEDs, with regard to motor coordination, was determined in the chimney test in mice. Results indicate that 7NI (50 mg/kg; i.p.) significantly potentiated the anticonvulsant activity of OXC, but not that of FBM, LTG and TPM against MES-induced seizures and, simultaneously, it enhanced the acute neurotoxic effects of TPM, but not those of FBM, LTG and OXC in the chimney test in mice. 7NI at the lower dose of 25 mg/kg had no effect on the antiseizure activity and acute neurotoxic profiles of all investigated AEDs. Pharmacokinetic evaluation of interactions between 7NI and LTG, OXC and TPM against MES-induced seizures revealed no significant changes in free (non-protein bound) plasma AED concentrations following 7NI administration. Moreover, none of the examined combinations of 7NI with AEDs from the MES test were associated with long-term memory impairment in mice subjected to the step-through passive avoidance task. Based on our preclinical study, it can be concluded that only the combination of 7NI with OXC was beneficial, when considering its both anticonvulsant and acute neurotoxic effects. Moreover, the lack of impairment of long-term memory and no pharmacokinetic interactions in plasma of experimental animals make the combination of 7NI with OXC worthy of consideration for the treatment of patients with refractory epilepsy. The other combinations tested between 7NI and LTG, FBM and TPM were neutral, when considering their both anticonvulsant effects and acute neurotoxic profiles, therefore, no useful recommendation can be made for their clinical application.     

Furosemide potentiates the anticonvulsant action of valproate in the mouse maximal electroshock seizure model

Accumulating evidence indicates that furosemide (FUR, a loop diuretic) exerts the anticonvulsant action in various in vitro and in vivo experiments. Therefore, the aim of this study was to assess the influence of FUR on the protective action of numerous conventional and newer antiepileptic drugs (carbamazepine [CBZ], lamotrigine [LTG], oxcarbazepine [OXC], phenobarbital [PB], topiramate [TPM] and valproate [VPA]) in the mouse maximal electroshock seizure (MES) model. Results indicate that FUR (up to 100mg/kg, i.p., 30 min before the test) neither altered the threshold for electroconvulsions nor protected the animals against MES-induced seizures in mice. FUR (100 mg/kg, i.p.) enhanced the anticonvulsant effects of VPA in the MES test by reducing its ED(50) value from 230.4 to 185.4 mg/kg (P<0.05). In contrast, FUR at 100 mg/kg had no significant effect on the antielectroshock action of the remaining drugs tested (CBZ, LTG, OXC, PB, and TPM) in mice. Estimation of free plasma and total brain VPA concentrations revealed that the observed interaction between FUR and VPA in the MES test was pharmacodynamic in nature because neither free plasma nor total brain VPA concentrations were altered after i.p. administration of FUR. In conclusion, one can ascertain that the selective potentiation of the antielectroshock action of VPA by FUR and lack of any pharmacokinetic interactions between drugs, make this combination of pivotal importance for epileptic patients treated with VPA and received FUR from other than epilepsy reasons.     

Lacosamide, a novel anti-convulsant drug, shows efficacy with a wide safety margin in rodent models for epilepsy

This paper comprises a series of experiments in rodent models of partial and generalized epilepsy which were designed to describe the anti-convulsant profile of the functionalized amino acid lacosamide. Lacosamide was effective against sound-induced seizures in the genetically susceptible Frings mouse, against maximal electroshock test (MES)-induced seizures in rats and mice, in the rat hippocampal kindling model of partial seizures, and in the 6Hz model of psychomotor seizures in mice. The activity in the MES test in both mice (4.5mg/kg i.p.) and rats (3.9 mg/kg p.o.) fell within the ranges previously reported for most clinically available anti-epileptic drugs. At both the median effective dose for MES protection, as well as the median toxic dose for rotorod impairment, lacosamide elevated the seizure threshold in the i.v. pentylenetetrazol seizure test, suggesting that it is unlikely to be pro-convulsant at high doses. Lacosamide was inactive against clonic seizures induced by subcutaneous administration of the chemoconvulsants pentylenetetrazol, bicuculline, and picrotoxin, but it did inhibit NMDA-induced seizures in mice and showed full efficacy in the homocysteine model of epilepsy. In summary, the overall anti-convulsant profile of lacosamide appeared to be unique, and the drug displayed a good margin of safety in those tests in which it was effective. These results suggest that lacosamide may have the potential to be clinically useful for at least the treatment of generalized tonic-clonic and partial-onset epilepsies, and support ongoing clinical trials in these indications.