Na(+) channel effects of remacemide and desglycinyl-remacemide in rat cortical synaptosomes

The NMDA receptor complex as a therapeutic target in epilepsy: a review

A substantial amount of research has shown that N-methyl-D-aspartate receptors (NMDARs) may play a key role in the pathophysiology of several neurological diseases, including epilepsy. Animal models of epilepsy and clinical studies demonstrate that NMDAR activity and expression can be altered in association with epilepsy and particularly in some specific seizure types. NMDAR antagonists have been shown to have antiepileptic effects in both clinical and preclinical studies. There is some evidence that conventional antiepileptic drugs may also affect NMDAR function. In this review, we describe the evidence for the involvement of NMDARs in the pathophysiology of epilepsy and provide an overview of NMDAR antagonists that have been investigated in clinical trials and animal models of epilepsy.

Isobolographic analysis of interactions between remacemide and conventional antiepileptic drugs in the mouse model of maximal electroshock

Using the mouse maximal electroshock-induced seizure model, indicative of tonic-clonic seizures in humans, the present study was aimed at characterizing the interaction between remacemide and valproate, carbamazepine, phenytoin, and phenobarbital. Isobolographic analysis indicated additive interactions between remacemide and valproate, carbamazepine, and phenytoin (for all fixed ratios of tested drugs: 1:3, 1:1, and 3:1). Additivity was also observed between remacemide and phenobarbital applied in proportions of 1:1 and 3:1. In contrast, the combination of remacemide and phenobarbital at the fixed-ratio of 1:3 resulted in antagonism. Neither motor performance nor long-term memory was impaired by remacemide or by carbamazepine, phenobarbital, phenytoin, and valproate whether or not these drugs were administered singly or in combination. In combination with remacemide, brain concentrations of carbamazepine, phenobarbital, and phenytoin were increased by 71, 21, and 16%, respectively. Although brain valproate concentrations were unaffected by remacemide co-administration, brain concentrations of remacemide and its active metabolite, desglycinyl-remacemide, were increased by 68 and 162%, respectively. In contrast, phenobarbital co-administration was associated with decreases in brain remacemide (27%) and desglycinyl-remacemide (9%) concentrations, whereas only remacemide concentrations (increased by 131%) were affected by carbamazepine co-administration. In conclusion, significant and desirable pharmacodynamic interactions were observed between remacemide and valproate, carbamazepine, phenytoin, and phenobarbital. However, the concurrent pharmacokinetic interactions associated with remacemide complicate these observations and do not make remacemide a good candidate for adjunctive treatment of epilepsy.

Effects of carbamazepine, phenytoin, lamotrigine, oxcarbazepine, topiramate and vinpocetine on Na+ channel-mediated release of [3H]glutamate in hippocampal nerve endings

Several of the most effective antiepileptic drugs are believed to stop the paroxysmal neuronal activity acting as Na(+) channel blockers. However, no single study comparing in parallel the potency and efficacy of the most commonly used antiepileptic drugs on brain Na(+) channel-mediated responses is available. In the present study the effects of increasing concentrations of carbamazepine, phenytoin, lamotrigine, oxcarbazepine and topiramate, which are among the most frequently used antiepileptic drugs, and of the new putative antiepileptic drug, vinpocetine, on the release of glutamate (Glu) elicited by the Na(+) channel opener, veratridine were investigated in hippocampal isolated nerve endings preloaded with the labeled excitatory amino acid neurotransmitter. The present results show that carbamazepine, phenytoin, lamotrigine and oxcarbazepine, in the range from 150 to 1500 microM, progressively inhibit [(3)H]Glu release induced by veratridine. Also vinpocetine progressively inhibits the veratridine-induced response, but in a much lower range of concentrations (from 1.5 to 15 microM), whereas topiramate only exerts a modest inhibition (20%) of Glu release to veratridine at the highest dose tested (1500 microM). These results indicate that the mechanism of action of several of the most widely used antiepileptic drugs involves reduction in cerebral presynaptic voltage sensitive Na(+) channels permeability. Considering that the high doses of antiepileptic drugs required to control seizures are frequently accompanied by adverse secondary effects, the higher potency of vinpocetine to reduce Na(+) channels permeability might be advantageous.

The antiepileptic drug carbamazepine affects sodium transport in toad epithelium

The present work investigates the effects of the antiepileptic drug carbamazepine (CBZ) on sodium transport in the isolated skin of the toad Pleurodema thaul. A submaximal concentration of the drug (0.2 mM) applied to the outer surface of the epithelium increased the electrical parameters short-circuit current (Isc) and potential difference (PD) by over 28%, whereas only a higher concentration (1 mM) induced over a 45% decrease in these parameters when applied to the inner surface. The amiloride test showed that the outer surface stimulatory effect was accompanied by an increase and the inner surface inhibitory effect by a decrease in the sodium electromotive force (ENa). Exploration of these effects of CBZ on the outer surface showed that 0.2 mM increased net Na+ (22Na) influx by 20% and 0.6 mM CBZ decreased Na+ mucosa-serosa flux by 19%, a result in agreement with the finding that higher concentrations of CBZ applied to the inner surface not only decreased ENa but also sodium conductance (GNa).

The antiepileptic drug phenytoin affects sodium transport in toad epithelium

The effects of phenytoin on isolated Pleurodema thaul toad skin were investigated. Low (micromolar) concentrations of the antiepileptic agent applied to the outside surface of the toad epithelium increased the electrical parameters (short-circuit current and potential difference) by over 40%, reflecting stimulation of Na(+) transport, whereas higher (millimolar concentrations, outside and inside surface) decreased both electric parameters, the effect being greater at the inside surface (40% and 80% decrease, respectively). The amiloride test showed that the stimulatory effect was accompanied by an increase and the inhibitory effect by a decrease in the sodium electromotive force (ENa). It is concluded that the drug interaction with membrane lipid bilayers might result in a distortion of the lipid-protein interface contributing to disturbance of Na(+) epithelial channel activity. After applying the Na(+)-K(+)-ATPase blocker ouabain and replacing the Na(+) ions in the outer Ringer's solution by choline, it was concluded that both active and passive transport are involved in sodium absorption, although active transport predominates.

Influence of cytochrome P450 induction on the pharmacokinetics and pharmacodynamics of remacemide hydrochloride

Remacemide hydrochloride (RMD) is a putative anticonvulsant agent with an active metabolite, desglycinyl-remacemide (DGR) and a broad spectrum of activity in experimental seizure models. In clinical trials, however, the efficacy of RMD is questionable. In the case of add-on studies, the inconclusive findings may be related to pharmacokinetic interactions between RMD and established antiepileptic drugs. We have investigated the influence of cytochrome P450 (CYP(450)) induction following repeated treatment with phenobarbital (PB) on the pharmacokinetics and pharmacodynamics of RMD in mice. Pre-treatment with PB (80 mg/kg; once daily for 4 days) significantly increased CYP(450) content and activity in mouse liver. This was associated with a consistent reduction in the brain concentrations of both RMD and DGR and attenuation of the anticonvulsant effects of RMD in the maximal electroshock model. Pharmacokinetic analysis suggested that DGR was proportionately more susceptible to CYP(450) induction than the parent compound. As the principal active moiety, the selectively enhanced metabolism of DGR under induced conditions may underlie the debatable findings of add-on trials with RMD in refractory epilepsy. However, this hypothesis does not explain the similarly questionable efficacy of RMD monotherapy in newly diagnosed epilepsy, an observation that may have wider pharmacological implications.