The role of voltage-gated and ligand-gated ion channels in epileptogenesis of both genetic and acquired epilepsies, and as targets in the development of new antiepileptic drugs (AEDs) is reviewed. Voltage-gated Na+ channels are essential for action potentials, and their mutations are the substrate for generalised epilepsy with febrile seizures plus and benign familial neonatal infantile seizures; Na+ channel inhibition is the primary mechanism of carbamazepine, phenytoin and lamotrigine, and is a probable mechanism for many other classic and novel AEDs. Voltage-gated K+ channels are essential in the repolarisation and hyperpolarisation that follows paroxysmal depolarisation shifts (PDSs), and their mutations are the substrate for the benign neonatal epilepsy and episodic ataxia type 1; they are new targets for AEDs such as retigabine. Voltage-gated Ca2+ channels are involved in neurotransmitter release, in the sustained depolarisation-phase of PDSs, and in the generation of absence seizures; their mutations are a substrate for juvenile myoclonic epilepsy and the absence-like pattern seen in some mice; the antiabsence effect of ethosuximide is due to the inhibition of thalamic T-type Ca2+ channels. Voltage-gated Cl- channels are implicated in GABA(A) transmission, and mutations in these channels have been described in some families with juvenile myoclonic epilepsies, epilepsy with grand mal seizures on awakening or juvenile absence epilepsy. Hyperpolarisation-activated cation channels have been implicated in spike-wave seizures and in hippocampal epileptiform discharges. The Cl- ionophore of the GABA(A) receptor is responsible for the rapid post-PDS hyperpolarisation, it has been involved in epileptogenesis both in animals and humans, and mutations in these receptors have been found in families with juvenile myoclonic epilepsy or generalised epilepsy with febrile seizures plus; enhancement of GABA(A) inhibitory transmission is the primary mechanism of benzodiazepines and phenobarbital and is a mechanistic approach to the development of novel AEDs such as tiagabine or vigabatrin. Altered GABA(B)-receptor function is implicated in spike-wave seizures. Ionotropic glutamate receptors are implicated in the sustained depolarisation phase of PDS and in epileptogenesis both in animals and humans; felbamate, phenobarbital and topiramate block these receptors, and attenuation of glutamatergic excitatory transmission is another new mechanistic approach. Mutations in the nicotinic acetylcholine receptor are the substrates for the nocturnal frontal lobe epilepsy. The knowledge of the role of the ion channels in the epilepsies is allowing the design of new and more specific therapeutic strategies.
Lamotrigine (LTG) is metabolized by UGT1A4 but UGT2B7 also contributes to its glucuronidation. The aim of this study was to determine whether UGT2B7_- 161C>T and UGT2B7_372A>G polymorphisms contribute to the intersubject variability in LTG concentration-to-dose ratio (LTG-CDR) in epileptic patients. Fifty-three white epileptic patients attending the Neuropediatric and Neurology Services at the Marqués de Valdecilla University Hospital, in whom LTG serum concentration was to be measured for pharmacokinetic monitoring, were selected according to predefined criteria for LTG-CDR evaluation. All patients had at least one steady-state LTG serum concentration obtained before the first dose in the morning. Patients were classified in 3 groups of comedication: (1) LTG in combination with metabolism-inducer anticonvulsants (n = 22), (2) LTG in combination with valproate (n = 13), and (3) LTG as monotherapy (n = 16) or in combination with valproate and inducers (n = 2). Genotypes were determined by Applied Biosystems Genotyping Assays with TaqMan probes. A significant association was found between LTG-CDR and UGT2B7_-161C>T polymorphism (P = 0.021) when patient age and concomitant antiepileptic drugs were taken into account. Comedication explained 70% of the LTG-CDR variability, patient age 24%, and UGT2B7_-161C>T 12%. In contrast, a significant association between LTG-CDR and this polymorphism was not found in the bivariate study when age and comedication groups were not considered. A significant association between UGT2B7_372A>G and LTG-CDR was not found in the bivariate or the multivariate studies. UGT2B7_-161C>T polymorphism is significantly associated with LTG-CDR when comedication with other antiepileptic drugs and patient age are taken into account in a multivariate analysis.
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