Metabolism of brain amino acids following pentylenetetrazole treatment

Comprehensive characterization of amino acids and water-soluble vitamins in a pentylenetetrazole-induced seizures rat model

Epilepsy is a complex neurological disease characterized by spontaneous recurrent seizures that affect around 1% of the global population. Despite the significant progress in the mechanisms of epileptogenesis, there is still about 60% of cases in which the cause is unknown. Thus, revealing the molecular mechanisms of epileptogenesis will greatly improve the development of epilepsy treatment. Since the comprehensive characterization of amino acids and water-soluble vitamins is important in understanding the underlying mechanisms of epilepsy or seizures, we developed two liquid chromatography-tandem mass spectrometry methods to quantify 17 water-soluble vitamins and 46 amino acids and applied them to our pentylenetetrazole-induced kindling rat model. All water-soluble vitamins were detected with a linearity of r > 0.992 and limits of quantitation between 0.1 and 5 ng/ml except for nicotinic acid. For amino acids, the linearities obtained were good with correlation coefficients higher than 0.99, and matrix effects were between 85.3% and 110%. To handle the multidimensional data more effectively, multivariate statistical analysis approaches used in non-targeted metabolomics were creatively exploited in the visualization, interpretation, and exploration of the results.

Insights into the development of pentylenetetrazole-induced epileptic seizures from dynamic metabolomic changes

Epilepsy is often considered to be a progressive neurological disease, and the nature of this progression remains unclear. Understanding the overall and common metabolic changes of epileptic seizures can provide novel clues for their control and prevention. Herein, a chronic kindling animal model was established to obtain generalized tonic-clonic seizures via the repeated injections of pentylenetetrazole (PTZ) at subconvulsive dose. Dynamic metabolomic changes in plasma and urine from PTZ-kindled rats at the different kindling phases were explored using NMR-based metabolomics, in combination with behavioral assessment, brain neurotransmitter measurement, electroencephalography and histopathology. The increased levels of glucose, lactate, glutamate, creatine and creatinine, together with the decreased levels of pyruvate, citrate and succinate, ketone bodies, asparagine, alanine, leucine, valine and isoleucine in plasma and/or urine were involved in the development and progression of seizures. These altered metabolites reflected the pathophysiological processes including the compromised energy metabolism, the disturbed amino acid metabolism, the peripheral inflammation and changes in gut microbiota functions. NMR-based metabolomics could provide brain disease information by the dynamic plasma and urinary metabolic changes during chronic epileptic seizures, yielding classification of seizure stages and profound insights into controlling epilepsy via targeting deficient energy metabolism.

Revealing the Antiepileptic Effect of α-Asaronol on Pentylenetetrazole-Induced Seizure Rats Using NMR-Based Metabolomics

α-Asaronol from Acorus tatarinowii (known as "Shichangpu" in Traditional Chinese medicine) has been proved to possess more efficient antiepileptic activity and lower toxicity than α-asarone (namely "Xixinnaojiaonang" as an antiepileptic drug in China) in our previous study. However, the molecular mechanism of α-asaronol against epilepsy needs to be known if to become a novel antiepileptic medicine. Nuclear magnetic resonance (NMR)-based metabolomics was applied to investigate the metabolic patterns of plasma and the brain tissue extract from pentylenetetrazole (PTZ)-induced seizure rats when treated with α-asaronol or α-asarone. The results showed that α-asaronol can regulate the metabolomic level of epileptic rats to normal to some extent, and four metabolic pathways were associated with the antiepileptic effect of α-asaronol, including alanine, aspartate, and glutamate metabolism; synthesis and degradation of ketone bodies; glutamine and glutamate metabolism; and glycine, serine, and threonine metabolism. It was concluded that α-asaronol plays a vital role in enhancing energy metabolism, regulating the balance of excitatory and inhibitory neurotransmitters, and inhibiting cell membrane damage to prevent the occurrence of epilepsy. These findings are of great significance in developing α-asaronol into a promising antiepileptic drug derived from Traditional Chinese medicine.

Animal Models of Metabolic Epilepsy and Epilepsy Associated Metabolic Dysfunction: A Systematic Review

Epilepsy is a serious neurological disorder affecting around 70 million people globally and is characterized by spontaneous recurrent seizures. Recent evidence indicates that dysfunction in metabolic processes can lead to the alteration of neuronal and network excitability, thereby contributing to epileptogenesis. Developing a suitable animal model that can recapitulate all the clinical phenotypes of human metabolic epilepsy (ME) is crucial yet challenging. The specific environment of many symptoms as well as the primary state of the applicable neurobiology, genetics, and lack of valid biomarkers/diagnostic tests are the key factors that hinder the process of developing a suitable animal model. The present systematic review summarizes the current state of available animal models of metabolic dysfunction associated with epileptic disorders. A systematic search was performed by using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) model. A range of electronic databases, including google scholar, Springer, PubMed, ScienceDirect, and Scopus, were scanned between January 2000 and April 2020. Based on the selection criteria, 23 eligible articles were chosen and are discussed in the current review. Critical analysis of the selected literature delineated several available approaches that have been modeled into metabolic epilepsy and pointed out several drawbacks associated with the currently available models. The result describes available models of metabolic dysfunction associated with epileptic disorder, such as mitochondrial respiration deficits, Lafora disease (LD) model-altered glycogen metabolism, causing epilepsy, glucose transporter 1 (GLUT1) deficiency, adiponectin responsive seizures, phospholipid dysfunction, glutaric aciduria, mitochondrial disorders, pyruvate dehydrogenase (PDH) α-subunit gene (PDHA1), pyridoxine dependent epilepsy (PDE), BCL2-associated agonist of cell death (BAD), Kcna1 knock out (KO), and long noncoding RNAs (lncRNA) cancer susceptibility candidate 2 (lncRNA CASC2). Finally, the review highlights certain focus areas that may increase the possibilities of developing more suitable animal models and underscores the importance of the rationalization of animal models and evaluation methods for studying ME. The review also suggests the pressing need of developing precise robust animal models and evaluation methods for investigating ME.

Branched-Chain Amino Acids and Seizures: A Systematic Review of the Literature

BACKGROUND

Up to 40% of patients with epilepsy experience seizures despite treatment with antiepileptic drugs; however, branched-chain amino acid (BCAA) supplementation has shown promise in treating refractory epilepsy.

OBJECTIVES

The purpose of this systematic review was to evaluate all published studies that investigated the effects of BCAAs on seizures, emphasizing therapeutic efficacy and possible underlying mechanisms.

METHODS

On 31 January, 2017, the following databases were searched for relevant studies: MEDLINE (OvidSP), EMBASE (OvidSP), Scopus (Elsevier), the Cochrane Library, and the unindexed material in PubMed (National Library of Medicine/National Institutes of Health). The searches were repeated in all databases on 18 February, 2019. We only included full-length preclinical and clinical studies that were published in the English language that examined the effects of BCAA administration on seizures.

RESULTS

Eleven of 2045 studies met our inclusion criteria: ten studies were conducted in animal models and one study in human subjects. Seven seizure models were investigated: the strychnine (one study), pentylenetetrazole (two studies), flurothyl (one study), picrotoxin (two studies), genetic absence epilepsy in rats (one study), kainic acid (two studies), and methionine sulfoximine (one study) paradigms. Three studies investigated the effect of a BCAA mixture whereas the other studies explored the effects of individual BCAAs on seizures. In most animal models and in humans, BCAAs had potent anti-seizure effects. However, in the methionine sulfoximine model, long-term BCAA supplementation worsened seizure propagation and caused neuron loss, and in the genetic absence epilepsy in rats model, BCAAs exhibited pro-seizure effects.

CONCLUSIONS

The contradictory effects of BCAAs on seizure activity likely reflect differences in the complex mechanisms that underlie seizure disorders. Some of these mechanisms are likely mediated by BCAA's effects on glucose, glutamate, glutamine, and ammonia metabolism, activation of the mechanistic target of rapamycin signaling pathway, and their effects on aromatic amino acid transport and neurotransmitter synthesis. We propose that a better understanding of mechanisms by which BCAAs affect seizures and neuronal viability is needed to advance the field of BCAA supplementation in epilepsy.

Effect of newer anti-epileptic drugs (AEDs) on the cognitive status in pentylenetetrazol induced seizures in a zebrafish model

Epilepsy is marked by seizures that are a manifestation of excessive brain activity and is symptomatically treatable by anti-epileptic drugs (AEDs). Unfortunately, the older AEDs have many side effects, with cognitive impairment being a major side effect that affects the daily lives of people with epilepsy. Thus, this study aimed to determine if newer AEDs (Zonisamide, Levetiracetam, Perampanel, Lamotrigine and Valproic Acid) also cause cognitive impairment, using a zebrafish model. Acute seizures were induced in zebrafish using pentylenetetrazol (PTZ) and cognitive function was assessed using the T-maze test of learning and memory. Neurotransmitter and gene expression levels related to epilepsy as well as learning and memory were also studied to provide a better understanding of the underlying processes. Ultimately, impaired cognitive function was seen in AED treated zebrafish, regardless of whether seizures were induced. A highly significant decrease in γ-Aminobutyric Acid (GABA) and glutamate levels was also discovered, although acetylcholine levels were more variable. The gene expression levels of Brain-Derived Neurotrophic Factor (BDNF), Neuropeptide Y (NPY) and Cyclic Adenosine Monophosphate (CAMP) Responsive Element Binding Protein 1 (CREB-1) were not found to be significantly different in AED treated zebrafish. Based on the experimental results, a decrease in brain glutamate levels due to AED treatment appears to be at least one of the major factors behind the observed cognitive impairment in the treated zebrafish.

Effect of saponin fraction from Ficus religiosa on memory deficit, and behavioral and biochemical impairments in pentylenetetrazol kindled mice

In our previous study, the saponin-rich fraction (SRF) of adventitious root extract of Ficus religiosa L. (Moraceae) was shown to have an anticonvulsant effect in acute animal models of convulsions. The present study was envisaged to study the effect of SRF in the pentylenetetrazol (PTZ) kindling mouse model and its associated depression and cognition deficit. Treatment with the SRF (1, 2 and 4 mg/kg; i.p.) for 15 days in kindled mice significantly decreased seizure severity on days 5, 10 and 15 when challenged with PTZ (35 mg/kg; i.p.). Marked protection against kindling-associated depression was also observed on days 10 and 15 in the SRF-treated groups when tested using the tail-suspension test. However, the SRF treatment failed to protect kindling-associated learning and memory impairments in the passive shock avoidance paradigm. The observed behavioral effects were corroborated with modulation in the levels of noradrenaline, dopamine, serotonin, GABA and glutamate in discrete brain regions.

Dietary supplementation with acetyl-l-carnitine in seizure treatment of pentylenetetrazole kindled mice

In spite of the availability of new antiepileptic drugs a considerable number of epilepsy patients still have pharmacoresistant seizures, and thus there is a need for novel approaches. Acetyl-l-carnitine (ALCAR), which delivers acetyl units to mitochondria for acetyl-CoA production, has been shown to improve brain energy homeostasis and protects against various neurotoxic insults. To our knowledge, this is the first study of ALCAR's effect on metabolism in pentylenetetrazole (PTZ) kindled mice. ALCAR or the commonly used antiepileptic drug valproate, was added to the drinking water of mice for 25days, and animals were injected with PTZ or saline three times a week during the last 21 days. In order to investigate ALCAR's effects on glucose metabolism, mice were injected with [1-(13)C]glucose 15 min prior to microwave fixation. Brain extracts from cortex and the hippocampal formation (HF) were studied using (1)H and (13)C NMR spectroscopy and HPLC. PTZ kindling caused glucose hypometabolism, evidenced by a reduction in both glycolysis and TCA cycle turnover in both brain regions investigated. Glutamatergic and GABAergic neurons were affected in cortex and HF, but the amount of glutamate was only reduced in HF. Slight astrocytic involvement could be detected in the cortex. Interestingly, the dopamine content was increased in the HF. ALCAR attenuated the PTZ induced reduction in [3-(13)C]alanine and the increase in dopamine in the HF. However, TCA cycle metabolism was not different from that seen in PTZ kindled animals. In conclusion, even though ALCAR did not delay the kindling process, it did show some promising ameliorative effects, worthy of further investigation.

Reduced astrocytic contribution to the turnover of glutamate, glutamine, and GABA characterizes the latent phase in the kainate model of temporal lobe epilepsy

The occurrence of spontaneous seizures in mesial temporal lobe epilepsy (MTLE) is preceded by a latent phase that provides a time window for identifying and treating patients at risk. However, a reliable biomarker of epileptogenesis has not been established and the underlying processes remain unclear. Growing evidence suggests that astrocytes contribute to an imbalance between excitation and inhibition in epilepsy. Here, astrocytic and neuronal neurotransmitter metabolism was analyzed in the latent phase of the kainate model of MTLE in an attempt to identify epileptogenic processes and potential biomarkers. Fourteen days after status epilepticus, [1-(13)C]glucose and [1,2-(13)C]acetate were injected and the hippocampal formation, entorhinal/piriform cortex, and neocortex were analyzed by (1)H and (13)C magnetic resonance spectroscopy. The (13)C enrichment in glutamate, glutamine, and γ-aminobutyric acid (GABA) from [1-(13)C]glucose was decreased in all areas. Decreased GABA content was specific for the hippocampal formation, together with a pronounced decrease in astrocyte-derived [1,2-(13)C]GABA and a decreased transfer of glutamine for the synthesis of GABA. Accumulation of branched-chain amino acids combined with decreased [4,5-(13)C]glutamate in hippocampal formation could signify decreased transamination via branched-chain aminotransferase in astrocytes. The results point to astrocytes as major players in the epileptogenic process, and (13)C enrichment of glutamate and GABA as potential biomarkers.

Effects of pentylenetetrazole-induced seizures on metabolomic profiles of rat brain

Epilepsy is one of the most common neurological disorders and approximately one-third of patients with epilepsy are resistant to treatment. In order to develop our understanding of the metabolic changes occurring during seizure a metabolomic approach was employed. Using a pentylenetetrazole (PTZ) kindling model of epilepsy metabolomic analysis of brain extracts from the cerebellum, brain stem, prefrontal cortex and hippocampus was performed. Principal component analysis (PCA) of the (1)H NMR derived data revealed a distinct metabolic profile for each brain region. In order to assess the changes occurring following seizure partial least square discriminant analysis (PLS-DA) models for each brain region for PTZ-kindled and control animals were constructed. For all the brain regions good predictive models were built and the discriminating metabolites were identified. Results following one injection of PTZ indicated that the changes observed in the cerebellum and hippocampus were mainly due to seizure. In the hippocampus of PTZ-kindled animals the metabolites changing included lactate, succinate, GABA, NAA, choline and taurine. Analysis of the cerebellum of PTZ-kindled animals revealed changes in lactate, myo-inositol, choline, GABA, creatine, succinate, phosphocholine and GPC. Overall, the results indicate that seizure may be associated with an increase in energy demand, altered neurotransmitter balance and an increase in neuronal loss and gliosis.

Quinolinic Acid-induced Seizures Stimulate Glutamate Uptake into Synaptic Vesicles from Rat Brain: Effects Prevented by Guanine-based Purines

Glutamate uptake into synaptic vesicles is a vital step for glutamatergic neurotransmission. Quinolinic acid (QA) is an endogenous glutamate analog that may be involved in the etiology of epilepsy and is related to disturbances on glutamate release and uptake. Guanine-based purines (GBPs) guanosine 5'-monophosphate (GMP and guanosine) have been shown to exert anticonvulsant effects against QA-induced seizures. The aims of this study were to investigate the effects of in vivo administration of several convulsant agents on glutamate uptake into synaptic vesicles and investigate the role of MK-801, guanosine or GMP (anticonvulsants) on glutamate uptake into synaptic vesicles from rats presenting QA-induced seizures. Animals were treated with vehicle (saline 0.9%), QA 239.2 nmoles, kainate 30 mg/kg, picrotoxin 6 mg/kg, PTZ (pentylenetetrazole) 60 mg/kg, caffeine 150 mg/kg or MES (maximal transcorneal electroshock) 80 mA. All convulsant agents induced seizures in 80-100% of animals, but only QA stimulated glutamate uptake into synaptic vesicle. Guanosine or GMP prevented seizures induced by QA (up to 52% of protection), an effect similar to the NMDA antagonist MK-801 (60% of protection). Both GBPs and MK-801 prevented QA-induced glutamate uptake stimulation. This study provided additional evidence on the role of QA and GBPs on glutamatergic system in rat brain, and point to new perspectives on seizures treatment.

Impaired growth and neurological abnormalities in branched-chain alpha-keto acid dehydrogenase kinase-deficient mice

The BCKDH (branched-chain alpha-keto acid dehydrogenase complex) catalyses the rate-limiting step in the oxidation of BCAAs (branched-chain amino acids). Activity of the complex is regulated by a specific kinase, BDK (BCKDH kinase), which causes inactivation, and a phosphatase, BDP (BCKDH phosphatase), which causes activation. In the present study, the effect of the disruption of the BDK gene on growth and development of mice was investigated. BCKDH activity was much greater in most tissues of BDK-/- mice. This occurred in part because the E1 component of the complex cannot be phosphorylated due to the absence of BDK and also because greater than normal amounts of the E1 component were present in tissues of BDK-/- mice. Lack of control of BCKDH activity resulted in markedly lower blood and tissue levels of the BCAAs in BDK-/- mice. At 12 weeks of age, BDK-/- mice were 15% smaller than wild-type mice and their fur lacked normal lustre. Brain, muscle and adipose tissue weights were reduced, whereas weights of the liver and kidney were greater. Neurological abnormalities were apparent by hind limb flexion throughout life and epileptic seizures after 6-7 months of age. Inhibition of protein synthesis in the brain due to hyperphosphorylation of eIF2alpha (eukaryotic translation initiation factor 2alpha) might contribute to the neurological abnormalities seen in BDK-/- mice. BDK-/- mice show significant improvement in growth and appearance when fed a high protein diet, suggesting that higher amounts of dietary BCAA can partially compensate for increased oxidation in BDK-/- mice. Disruption of the BDK gene establishes that regulation of BCKDH by phosphorylation is critically important for the regulation of oxidative disposal of BCAAs. The phenotype of the BDK-/- mice demonstrates the importance of tight regulation of oxidative disposal of BCAAs for normal growth and neurological function.

Branched-chain [corrected] amino acid metabolism: implications for establishing safe intakes

There are several features of the metabolism of the indispensable BCAAs that set them apart from other indispensable amino acids. BCAA catabolism involves 2 initial enzymatic steps that are common to all 3 BCAAs; therefore, the dietary intake of an individual BCAA impacts on the catabolism of all 3. The first step is reversible transamination followed by irreversible oxidative decarboxylation of the branched-chain alpha-keto acid transamination products, the branched chain alpha-keto acids (BCKAs). The BCAA catabolic enzymes are distributed widely in body tissues and, with the exception of the nervous system, all reactions occur in the mitochondria of the cell. Transamination provides a mechanism for dispersing BCAA nitrogen according to the tissue's requirements for glutamate and other dispensable amino acids. The intracellular compartmentalization of the branched-chain aminotransferase isozymes (mitochondrial branched-chain aminotransferase, cytosolic branched-chain aminotransferase) impacts on intra- and interorgan exchange of BCAA metabolites, nitrogen cycling, and net nitrogen transfer. BCAAs play an important role in brain neurotransmitter synthesis. Moreover, a dysregulation of the BCAA catabolic pathways that leads to excess BCAAs and their derivatives (e.g., BCKAs) results in neural dysfunction. The relatively low activity of catabolic enzymes in primates relative to the rat may make the human more susceptible to excess BCAA intake. It is hypothesized that the symptoms of excess intake would mimic the neurological symptoms of hereditary diseases of BCAA metabolism.

Pentylenetetrazole affects metabolism of astrocytes in culture

Cortical and cerebellar astrocytes were cultured in medium containing pentylenetetrazole (PTZ), a gamma-aminobutyric acid (GABA)(A) receptor antagonist, for 3 weeks (up to 6 mM) or 2 hr (10 mM). Cells were incubated in medium containing [U-(13)C]glutamate (0.5 mM) and unlabeled glucose (3 mM) for 2 hr and cell extracts and media were analyzed by (13)C magnetic resonance (MR) spectroscopy and high-performance liquid chromatography (HPLC). When cerebellar astrocytes were incubated with PTZ for 2 hr, the amount of glucose removed from the medium and glucose and [U-(13)C]glutamate oxidation were decreased. Metabolism in cortical astrocytes was affected only slightly; amounts of glutathione and aspartate were decreased. When cerebellar and cortical cells were cultured in the presence of PTZ for 3 weeks, the amount of glucose removed from the medium and lactate formed were increased, indicating increased glycolytic activity. Despite the increased intracellular [U-(13)C]glutamate concentration in both types of astrocytes cultured with PTZ, labeled glutamine and glutathione were unchanged, indicating intracellular compartmentation. The amount of cellular protein was decreased at 6 mM PTZ for cerebellar astrocytes and 1 mM for cortical astrocytes, indicating a differential sensitivity to the effects of PTZ. In conclusion, mitochondrial metabolism and glycolysis were decreased by short-term incubation with PTZ in cerebellar astrocytes, whereas long-term incubation affected both types of astrocytes, leading to increased glycolysis.