Pre-treatment with the NMDA receptor glycine-binding site antagonist L-701,324 improves pharmacosensitivity in a mouse kindling model

Association of UGT2B7 and CaMK4 with response of valproic acid in Chinese children with epilepsy

AIM OF THE STUDY

Valproic acid (VPA) is a widely used antiepileptic drug for epilepsy. However, approximately 30% of patients with epilepsy do not respond to this therapy even when it was appropriately used. In order to explore the potential genetic factors related to the VPA response, this pharmacogenetics study was conducted.

METHODS

A total of one hundred and fifty-seven Chinese children with epilepsy who were administered with by VPA for at least one year were enrolled. Thirteen single-nucleotide polymorphisms (SNPs) located in eight genes involving targets and metabolic enzymes of VPA were genotyped. The frequencies of these polymorphisms and the effect of genotypes on the efficacy of VPA were analyzed.

RESULTS

The frequencies of two SNPs, rs7668258 (uridine diphosphate glucuronosyltransferase-2B7, UGT2B7) and rs306104 (calmodulin-kinase 4, CaMK4) were associated with VPA responses. However, no association was found for the other SNPs. Furthermore, the polymorphism of UGT2B7 influenced the adjusted concentration (AC) in the responders rather than in the non-responders.

CONCLUSION

Two SNPs (UGT2B7 and CaMK4) were associated with VPA response, which may explain the pharmacological mechanism of VPA resistance to some extent.

RNA-seq analysis of blood of valproic acid-responsive and non-responsive pediatric patients with epilepsy

Epilepsy is the most common chronic neurological disorder, affecting ~70 million individuals worldwide. However, approximately one-third of the patients are refractory to epilepsy medication. Of note, 100% of patients with genetic epilepsy who are resistant to the traditional drug, valproic acid (VPA), are also refractory to the other anti-epileptic drugs. The aim of the present study was to compare the transcriptomes in VPA responders and non-responders, to explore the mechanism of action of VPA and identify possible biomarkers to predict VPA resistance. Thus, RNA-seq was employed for transcriptomic analysis, differentially expressed genes (DEGs) were analyzed using Cuffdiff software and the DAVID database was used to infer the functions of the DEGs. A protein-protein interaction network was obtained using STRING and visualized with Cytoscape. A total of 389 DEGs between VPA-responsive and non-responsive pediatric patients were identified. Of these genes, 227 were upregulated and 162 were downregulated. The upregulated DEGs were largely associated with cytokines, chemokines and chemokine receptor-binding factors, whereas the downregulated DEGs were associated with cation channels, iron ion binding proteins, and immunoglobulin E receptors. In the pathway analysis, the toll-like receptor signaling pathway, pathways in cancer, and cytokine-cytokine receptor interaction were mostly enriched by the DEGs. Furthermore, three modules were identified by protein-protein interaction analysis, and the potential hub genes, chemokine (C-C motif) ligand 3 and 4, chemokine (C-X-C motif) ligand 9, tumor necrosis factor-α and interleukin-1β, which are known to be closely associated with epilepsy, were identified. These specific chemokines may participate in processes associated with VPA resistance and may be potential biomarkers for monitoring the efficacy of VPA.

Anticonvulsant effect of minocycline on pentylenetetrazole-induced seizure in mice: involvement of nitric oxide and N-methyl-d-aspartate receptor

Anticonvulsant effects of minocycline have been explored recently. This study was designed to examine the anticonvulsant effect of acute administration of minocycline on pentylenetetrazole-induced seizures in mouse considering the possible role of the nitric oxide/N-methyl-d-aspartate (NMDA) pathway. We induced seizure using intravenous administration of pentylenetetrazole. Our results showed that acute administration of minocycline increased the seizure threshold. Furthermore, co-administration of subeffective doses of the nonselective nitric oxide synthase (NOS) inhibitor NG-l-arginine methyl ester (10 mg/kg) and the neuronal NOS inhibitor 7-nitroindazole (40 mg/kg) enhanced the anticonvulsant effect of subeffective doses of minocycline (40 mg/kg). We found that inducible NOS inhibitor aminoguanidine (100 mg/kg) had no effect on the antiseizure effect of minocycline. Moreover, l-arginine (60 mg/kg), as a NOS substrate, reduced the anticonvulsant effect of minocycline. We also demonstrated that pretreatment with the NMDA receptor antagonists ketamine (0.5 mg/kg) and MK-801 (0.05 mg/kg) increased the anticonvulsant effect of subeffective doses of minocycline. Results showed that minocycline significantly decreased the hippocampal nitrite level. Furthermore, co-administration of a neuronal NOS inhibitor like NMDA receptor antagonists augmented the effect of minocycline on the hippocampal nitrite level. In conclusion, we revealed that anticonvulsant effect of minocycline might be, at least in part, due to a decline in constitutive hippocampal nitric oxide activity as well as inhibition of NMDA receptors.

Knockout of P-glycoprotein does not alter antiepileptic drug efficacy in the intrahippocampal kainate model of mesial temporal lobe epilepsy in mice

Pharmacoresistance to antiepileptic drugs (AEDs) is a major challenge in epilepsy therapy, affecting at least 30% of patients. Thus, there is considerable interest in the mechanisms responsible for such pharmacoresistance, with particular attention on the specific cellular and molecular factors that lead to reduced drug sensitivity. Current hypotheses of refractory epilepsy include the multidrug transporter hypothesis, which posits that increased expression or function of drug efflux transporters, such as P-glycoprotein (Pgp), in brain capillaries reduces the local concentration of AEDs in epileptic brain regions to subtherapeutic levels. In the present study, this hypothesis was addressed by evaluating the efficacy of six AEDs in wildtype and Pgp deficient Mdr1a/b(-/-) mice in the intrahippocampal kainate model of mesial temporal lobe epilepsy. In this model, frequent focal electrographic seizures develop after an initial kainate-induced status epilepticus. These seizures are resistant to major AEDs, but the mechanisms of this resistance are unknown. In the present experiments, the focal nonconvulsive seizures were resistant to carbamazepine and phenytoin, whereas high doses of valproate and levetiracetam exerted moderate and phenobarbital and diazepam marked anti-seizure effects. All AEDs suppressed generalized convulsive seizures. No significant differences between wildtype and Pgp-deficient mice were observed in anti-seizure drug efficacies. Also, the individual responder and nonresponder rates in each experiment did not differ between mouse genotypes. This does not argue against the multidrug transporter hypothesis in general, but indicates that Pgp is not involved in the mechanisms explaining that focal electrographic seizures are resistant to some AEDs in the intrahippocampal mouse model of partial epilepsy. This was substantiated by the finding that epileptic wildtype mice do not exhibit increased Pgp expression in this model.

N-methyl-d-aspartate receptor coagonist d-serine suppresses intake of high-preference food

d-Serine is abundant in the forebrain and physiologically important for modulating excitatory glutamatergic neurotransmission as a coagonist of synaptic N-methyl-d-aspartate (NMDA) receptor. NMDA signaling has been implicated in the control of food intake. However, the role of d-serine on appetite regulation is unknown. To clarify the effects of d-serine on appetite, we investigated the effect of oral d-serine ingestion on food intake in three different feeding paradigms (one-food access, two-food choice, and refeeding after 24-h fasting) using three different strains of male mice (C57Bl/6J, BKS, and ICR). The effect of d-serine was also tested in leptin signaling-deficient db/db mice and sensory-deafferented (capsaicin-treated) mice. The expression of orexigenic neuropeptides [neuropeptide Y (Npy) and agouti-related protein (Agrp)] in the hypothalamus was compared in fast/refed experiments. Conditioned taste aversion for high-fat diet (HFD) was tested in the d-serine-treated mice. Under the one-food-access paradigm, some of the d-serine-treated mice showed starvation, but not when fed normal chow. HFD feeding with d-serine ingestion did not cause aversion. Under the two-food-choice paradigm, d-serine suppressed the intake of high-preference food but not normal chow. d-Serine also effectively suppressed HFD intake but not normal chow in db/db mice and sensory-deafferented mice. In addition, d-serine suppressed normal chow intake after 24-h fasting despite higher orexigenic gene expression in the hypothalamus. d-Serine failed to suppress HFD intake in the presence of L-701,324, the selective and full antagonist at the glycine-binding site of the NMDA receptor. Therefore, d-serine suppresses the intake of high-preference food through coagonism toward NMDA receptors.