In vivo modification of GABAA receptor with a high dose of pyridoxal phosphate induces tonic-clonic convulsion in immature mice

Pyridoxamine Supplementation Effectively Reverses the Abnormal Phenotypes of Zebrafish Larvae With PNPO Deficiency

Neonatal epileptic encephalopathy (NEE), as a result of pyridoxine 5′-phosphate oxidase (PNPO) deficiency, is a rare neural disorder characterized by intractable seizures and usually leads to early infant death. The clinical phenotypes do not respond to antiepileptic drugs but are alleviated in most cases by giving large doses of pyridoxal 5′-phosphate (PLP). PLP is the active form of vitamin B6 participating in more than 100 enzymatic pathways. One of the causes of NEE is pathogenic mutations in the gene for human PNPO (hPNPO). PNPO is a key enzyme in converting pyridoxine (PN), the common dietary form of vitamin B6, and some other B6 vitamers to PLP. More than 25 different mutations in hPNPO, which result in reduced catalytic activity, have been described for PNPO-deficiency NEE. To date, no animal model is available to test new therapeutic strategies. In this report, we describe using zebrafish with reduced activity of Pnpo as an animal model. Knocking down zPnpo resulted in developmental anomalies including brain malformation and impaired locomotor activity, similar to the clinical features of PNPO-deficiency NEE. Other anomalies include a defective circulation system. These anomalies were significantly alleviated by co-injecting either zpnpo or hPNPO mRNAs. As expected from clinical observations in humans, supplementing with PLP improved the morphological and behavioral anomalies. PN only showed marginal positive effects, and only in a few anomalies. Remarkably, pyridoxamine (PM), another dietary form of vitamin B6, showed rescue effects even at a lower concentration than PLP, presenting a possible new therapeutic treatment for PNPO-deficiency NEE. Finally, GABA, a neurotransmitter whose biosynthesis depends on a PLP-dependent enzyme, showed some positive rescue effect. These results suggest zebrafish to be a promising PNPO-deficiency model for studying PLP homeostasis and drug therapy in vivo.

Brain mitochondrial proteome alteration driven by creatine deficiency suggests novel therapeutic venues for creatine deficiency syndromes

Creatine (Cr) is a small metabolite with a central role in energy metabolism and mitochondrial function. Creatine deficiency syndromes are inborn errors of Cr metabolism causing Cr depletion in all body tissues and particularly in the nervous system. Patient symptoms involve intellectual disability, language and behavioral disturbances, seizures and movement disorders suggesting that brain cells are particularly sensitive to Cr depletion. Cr deficiency was found to affect metabolic activity and structural abnormalities of mitochondrial organelles; however a detailed analysis of molecular mechanisms linking Cr deficit, energy metabolism alterations and brain dysfunction is still missing. Using a proteomic approach we evaluated the proteome changes of the brain mitochondrial fraction induced by the deletion of the Cr transporter (CrT) in developing mutant mice. We found a marked alteration of the mitochondrial proteomic landscape in the brain of CrT deficient mice, with the overexpression of many proteins involved in energy metabolism and response to oxidative stress. Moreover, our data suggest possible abnormalities of dendritic spines, synaptic function and plasticity, network excitability and neuroinflammatory response. Intriguingly, the alterations occurred in coincidence with the developmental onset of neurological symptoms. Thus, cerebral mitochondrial alterations could represent an early response to Cr deficiency that could be targeted for therapeutic intervention.

Pyridox(am)ine-5-Phosphate Oxidase Deficiency Treatable Cause of Neonatal Epileptic Encephalopathy With Burst Suppression: Case Report and Review of the Literature

Pyridox(am)ine-5-phosphate oxidase deficiency is an autosomal recessive disorder of pyridoxine metabolism. Intractable neonatal epileptic encephalopathy is the classical presentation. Pyridoxal-5-phosphate or pyridoxine supplementation improves symptoms. We report a patient with myoclonic and tonic seizures at the age of 1 hour. Pyridoxal-5-phosphate was started on the first day of life and seizures stopped at the age of 3 days, but encephalopathy persisted for 4 weeks. She had normal neurodevelopmental outcome at the age of 12 months on pyridoxal-5-phosphate monotherapy. She had novel homozygous pathogenic frameshift mutation (c.448_451del;p.Pro150Argfs*27) in the PNPO gene. Long-lasting encephalopathy despite well-controlled clinical seizures does neither confirm nor exclude pyridox(am)ine-5-phosphate oxidase deficiency. Normal neurodevelopmental outcome of our patient emphasizes the importance of pyridoxal-5-phosphate treatment. Pyridox(am)ine-5-phosphate oxidase deficiency should be included in the differential diagnosis of Ohtahara syndrome and neonatal myoclonic encephalopathy as a treatable underlying cause. In addition, we reviewed the literature for pyridox(am)ine-5-phosphate oxidase deficiency and summarized herein all confirmed cases.

Vitamin B-6 Metabolism and Interactions with TNAP

Two observations stimulated the interest in vitamin B-6 and alkaline phosphatase in brain: the marked increase in plasma pyridoxal phosphate and the occurrence of pyridoxine responsive seizures in hypophosphatasia. The increase in plasma pyridoxal phosphate indicates the importance of tissue non-specific alkaline phosphatase (TNAP) in transferring vitamin B-6 into the tissues. Vitamin B-6 is involved in the biosynthesis of most of the neurotransmitters. Decreased gamma-aminobutyrate (GABA) appears to be most directly related to the development of seizures in vitamin B-6 deficiency. Cytosolic pyridoxal phosphatase/chronophin may interact with vitamin B-6 metabolism and neuronal development and function. Ethanolaminephosphate phospholyase interacts with phosphoethanolamine metabolism. Extracellular pyridoxal phosphate may interact with purinoceptors and calcium channels. In conclusion, TNAP clearly influences extracellular and intracellular metabolism of vitamin B-6 in brain, particularly during developmental stages. While effects on GABA metabolism appear to be the major contributor to seizures, multiple other intra- and extra-cellular metabolic systems may be affected directly and/or indirectly by altered vitamin B-6 hydrolysis and uptake resulting from variations in alkaline phosphatase activity.

Epilepsy due to PNPO mutations: genotype, environment and treatment affect presentation and outcome

The first described patients with pyridox(am)ine 5'-phosphate oxidase deficiency all had neonatal onset seizures that did not respond to treatment with pyridoxine but responded to treatment with pyridoxal 5'-phosphate. Our data suggest, however, that the clinical spectrum of pyridox(am)ine 5'-phosphate oxidase deficiency is much broader than has been reported in the literature. Sequencing of the PNPO gene was undertaken for a cohort of 82 individuals who had shown a reduction in frequency and severity of seizures in response to pyridoxine or pyridoxal 5'-phosphate. Novel sequence changes were studied using a new cell-free expression system and a mass spectrometry-based assay for pyridoxamine phosphate oxidase. Three groups of patients with PNPO mutations that had reduced enzyme activity were identified: (i) patients with neonatal onset seizures responding to pyridoxal 5'-phosphate (n = 6); (ii) a patient with infantile spasms (onset 5 months) responsive to pyridoxal 5'-phosphate (n = 1); and (iii) patients with seizures starting under 3 months of age responding to pyridoxine (n = 8). Data suggest that certain genotypes (R225H/C and D33V) are more likely to result in seizures that to respond to treatment with pyridoxine. Other mutations seem to be associated with infertility, miscarriage and prematurity. However, the situation is clearly complex with the same combination of mutations being seen in patients who responded and did not respond to pyridoxine. It is possible that pyridoxine responsiveness in PNPO deficiency is affected by prematurity and age at the time of the therapeutic trial. Other additional factors that are likely to influence treatment response and outcome include riboflavin status and how well the foetus has been supplied with vitamin B6 by the mother. For some patients there was a worsening of symptoms on changing from pyridoxine to pyridoxal 5'-phosphate. Many of the mutations in PNPO affected residues involved in binding flavin mononucleotide or pyridoxal 5'-phosphate and many of them showed residual enzyme activity. One sequence change (R116Q), predicted to affect flavin mononucleotide binding and binding of the two PNPO dimers, and with high residual activity was found in Groups (ii) and (iii). This sequence change has been reported in the 1000 Genomes project suggesting it could be a polymorphism but alternatively it could be a common mutation, perhaps responsible for the susceptibility locus for genetic generalized epilepsy on 17q21.32 (close to rs72823592). We believe the reduction in PNPO activity and B6-responsive epilepsy in the patients reported here indicates that it contributes to the pathogenesis of epilepsy.

Enhanced pyridoxal 5'-phosphate synthetic enzyme immunoreactivities do not contribute to GABAergic inhibition in the rat hippocampus following pilocarpine-induced status epilepticus

To comprehend the role of pyridoxal 5'-phosphate (PLP) in epilepsy or seizure, we investigated whether the expressions of two PLP synthetic enzymes (pyridoxal kinase, PLK; pyridoxine-5'-phosphate oxidase, PNPO) are altered in the hippocampus and whether changes in paired-pulse responses in the hippocampus are associated with altered PLP synthetic enzyme expressions following status epilepticus (SE). PLK and PNPO immunoreactivities were significantly increased in the rat hippocampus accompanied by reductions in paired-pulse inhibition at 1 day and 1 week after SE. Four weeks after SE, PLK and PNPO immunoreactivities in dentate granule cells were similar to those in control animals, while their immunoreactivities were markedly reduced in Cornu Ammonis 1 (CA1) pyramidal cells due to neuronal loss. Linear regression analysis identified a direct proportional relationship between PLK/PNPO immunoreactivity and normalized population spike amplitude ratio in the dentate gyrus and the CA1 region as excluded the data obtained from 4 weeks after SE. These findings indicate that the upregulation of PLK and PNPO immunoreactivities in principal neurons may not be involved in gamma-aminobutyric acid (GABA)ergic inhibition, but rather in enhanced excitability during epileptogenic periods.

Potential role of pyridoxal-5'-phosphate phosphatase/chronopin in epilepsy

Changes in actin dynamics and pyridoxal-5'-phosphate (PLP) metabolisms are closely related to the pathophysiological profiles of the epileptic hippocampus. Recently, it has been reported that PLP phosphatase/chronophin (PLPP/CIN) directly dephosphorylates actin-depolymerizing factor (ADF)/cofilin as well as PLP. In the present study, therefore, we have investigated whether PLPP/CIN is linked to the dynamics of actin filament assembly and the excitability in the rat hippocampus. In control animals, pyridoxine chloride (PNP) treatment increased PLPP/CIN immunoreactivity only in astrocytes, which did not affect electrophysiological properties. Following status epilepticus, the PLPP/CIN protein level increased in granule cells and reactive astrocytes. These changes in PLPP/CIN protein level showed an inverse correlation with phospho-ADF (pADF)/cofilin levels and F-actin content. These changes were also accompanied by alterations in the excitability ratio and paired-pulse inhibition. Transduction of PLPP/CIN by Tat-PLPP/CIN showed similar effects on pADF/cofilin levels, F-actin content and excitability ratio in normal animals. These findings suggest that PLPP/CIN-mediated actin dynamics may play an important role in the changes of morphological properties and excitability of the epileptic hippocampus.

Anticonvulsant characteristics of pyridoxyl-gamma-aminobutyrate, PL-GABA

GABA is the major inhibitory neurotransmitter in the central nervous system, and its concentration in the brain in associated with a variety of neurological disorders, including seizures, convulsions, and epilepsy. The concentration of GABA is modulated by the pyridoxal-5'-phosphate (PLP)-dependent enzymes, GAD and GABA-T. In this study, we generated pyridoxyl-gamma-aminobutyrate (PL-GABA), a novel GABA analogue composed of pyridoxyl and GABA, and have also characterized its anticonvulsant and pharmacological functions in vitro. The results of biodistribution studies revealed that PL-GABA is capable of crossing the blood-brain barrier. PL-GABA evidenced anticonvulsant activity in a wide range of epilepsy models, some of which were electrically-based (MES seizures) and some chemically-based (bicuculline, pentylenetetrazol (PTZ), picrotoxine, 3-mercaptopropionic acid). Following a timed subcutaneous administration of PTZ to mice, PL-GABA consistently increased the latencies to first twitch and clonus. In addition, PL-GABA displayed no signs of tolerance after subchronic (10 day) treatment. PL-GABA appears to exert its anticonvulsant effects by influencing seizure spread and by raising the seizure threshold. Therefore, our results indicate that PL-GABA exerts a broad-spectrum anticonvulsant effect, and identify the potential for reduced PL-GABA tolerance as an additional positive profile for novel antiepileptic drugs.

Tat-mediated protein transduction of human brain pyridoxal kinase into PC12 cells

Pyridoxal kinase (PK) catalyses the phosphorylation of vitamin B6 to pyridoxal-5'-phosphate (PLP). A human brain PK gene was fused with a gene fragment encoding the HIV-1 Tat protein transduction domain (RKKRRQRRR) in a bacterial expression vector to produce a genetic in-frame Tat-PK fusion protein. The expressed and purified Tat-PK fusion proteins transduced efficiently into PC12 cells in a time- and dose-dependent manner when added exogenously in culture media. Once inside the cells, the transduced Tat-PK proteins showed catalytic activity and are stable for 48 h. The intracellular concentration of PLP, which is known as a biologically active form of vitamin B6, was increased by pre-treatment of Tat-PK to the PC12 cells. Those results suggest that the transduction of Tat-PK fusion protein can be one of the ways to regulate the PLP level and to replenish this enzyme in the various neurological disorders related to vitamin B6.

Changes in pyridoxal kinase immunoreactivity in the gerbil hippocampus following spontaneous seizure

To identify the roles of pyridoxal kinase (PLK) in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of PLK expression in the gerbil hippocampus was conducted. PLK immunoreactivity in a pre-seizure group of seizure sensitive (SS) gerbils was more strongly detected than that in a seizure resistant (SR) group. The density of PLK immunoreactivity in a 30-min postictal group was significantly lower than that of a pre-seizure group. In a 12 h postictal group, PLK immunodensity recovered to pre-seizure level. The over-expression of PLK in the hippocampus of pre-seizure SS gerbils suggests that PLP play an important role in the modulation of GAD activity and GABA reuptake as mediated by membrane transporter via neurons.

Chronological changes in pyridoxine-5'-phosphate oxidase immunoreactivity in the seizure-sensitive gerbil hippocampus

To identify the roles of pyridoxine-5'-phosphate (PNP) oxidase in epileptogenesis and the recovery mechanisms in spontaneous seizure, a chronological and comparative analysis of PNP oxidase expression was conducted. PNP oxidase immunoreactivity in a preseizure group of seizure-sensitive (SS) gerbils was detected more strongly than that in a seizure-resistant (SR) group. The density of PNP oxidase immunoreactivity in a 30 min postictal group was significantly lower than that in a preseizure group. In a 12 hr postictal group, PNP oxidase immunodensity had recovered to a preseizure level. The overexpression of PNP oxidase in the hippocampus of preseizure SS gerbils suggests that PNP or pyridoxal 5'-phosphate plays an important role in the modulation of glutamic acid decarboxylase activity and gamma-aminobutyric acid reuptake as mediated by membrane transporter via neurons. In addition, this change in the PNP oxidase immunoreactivity following seizure may be a compensatory response designed to reduce epileptic activity in this animal.

Age-specific N-methyl-D-aspartate-induced seizures: perspectives for the West syndrome model

PURPOSE

With intraperitoneal N-methyl-D-aspartate (NMDA; 15-200 mg/kg) administration, we attempted to develop an animal model of age-specific West syndrome to serve for testing of putative anticonvulsant drugs and to determine the mechanisms of this disorder.

METHODS

Experiments were performed in 12-, 18-, and 60-day-old (adult) rats. The effects of systemic pretreatment with hydrocortisone (5-25 mg/kg), pyridoxine (20-250 mg/kg), and sodium valproate (VPA; 200 and 400 mg/kg) against the NMDA-induced automatisms, emprosthotonic (hyperflexion), and clonic-tonic seizures were determined. NMDA-induced EEG changes and alterations of the performance in horizontal bar, rotorod, open field, and elevated plus-maze tests were recorded.

RESULTS

In young rats, hydrocortisone had proconvulsant effects. High doses of pyridoxine induced epileptiform activity independent of and distinct from that induced by NMDA. Only VPA had moderate effects against the NMDA-induced syndrome. EEG consisted of periods of suppression mixed with ictal activity of serrated waves and high-voltage chaotic EEG activity. In adult rats, EEG alterations involved spike and spike-and-wave activity. NMDA also deteriorated performance of young rats in the open field, rotorod, and elevated plus maze tests.

CONCLUSIONS

NMDA syndrome in rats fulfills some, but not all, criteria of the West syndrome model, such as occurrence of flexion seizures, nonspecific diffuse EEG changes, refractoriness to antiepileptic therapy (but a response to VPA), as well as long-term alteration of behavioral tasks. However, NMDA-induced seizures represent an acute model without the occurrence of spontaneous seizures, whereas in the clinical situation, both the seizures and neurologic deterioration are chronic. Further, in the West syndrome and the NMDA seizure model, there is an incongruent response to therapy with antiepileptic drugs.

Proconvulsant effects induced by pyridoxine in young rats

High doses of pyridoxine (vitamin B6) can be neurotoxic in adults. Effects of intraperitoneally administered B6 (100, 250 and 400 mg/kg) were studied in 7, 12, 18 and 60 day old rats. B6 elicited epileptiform EEG discharges without any motor correlate in all age groups. In contrast, motor seizures were rare, seen only in 18 day old rats (250 mg/kg of B6). Data indicate that in young rats, B6 may have proconvulsant effects in doses relevant to those sometimes used in pediatric neurology.