Modulation of absence seizures by branched-chain amino acids: correlation with brain amino acid concentrations

The therapeutic potential of a polyunsaturated fatty acid-enriched high-fat diet in Leigh syndrome: Insights from a preclinical model

INTRODUCTION

Leigh syndrome is often caused by Ndufs4 mutations. The Ndufs4 knockout (KO) mouse model recapitulates key disease features, including systemic inflammation, neurodegeneration, and motor deficits. While dietary interventions such as the ketogenic diet show promise in mitigating mitochondrial dysfunction, conflicting results highlight uncertainties regarding its efficacy. Here, we evaluate the therapeutic potential of a polyunsaturated fatty acid (PUFA)-enriched high-fat diet (HFD) in Ndufs4 KO mice.

METHODS

Dietary intervention began at postnatal day 23, with mice receiving either a normal diet (ND) or a HFD enriched with PUFAs. Phenotypic evaluation, including locomotor function, clasping behaviour, and survival, continued until natural death. In a second group of animals, biochemical analyses were conducted after three weeks on the diets, using Western blot to evaluate neurometabolic and inflammatory regulators, flow cytometry to quantify serum inflammation markers, and metabolic profiling to identify alterations in neurometabolism and the neurolipidome.

RESULTS

The HFD significantly extended lifespan and improved clasping behaviour in Ndufs4 KO mice but had no effect on locomotor activity or grip strength decline. While whole-brain mTOR (p70S6K1, 4E-BP1) and SIRT1 (PGC1-α, TNF-α) signalling pathways remained unaffected, the diet significantly reduced serum pro-inflammatory markers TNF and IL-6. Furthermore, the PUFA-enriched HFD partially restored disruptions in TCA cycle, ketone body, branched-chain amino acid, and lipid metabolism, indicating potential metabolic reprogramming.

CONCLUSION

Dietary interventions, such as a PUFA-enriched HFD, may alleviate systemic inflammation, partially correct metabolic imbalances, and mitigate specific disease phenotypes in Leigh syndrome, warranting further investigation into the underlying mechanisms and broader therapeutic applications.

Association between Branched-Chain amino acids and Epilepsy: A Mendelian randomized study

BACKGROUND

Branched-chain amino acids (BCAAs) have been affected epilepsy, yet conclusions remain inconclusive, lacking causal evidence regarding whether BCAAs affect epilepsy. Systematic exploration of the causal relationship between BCAAs and epilepsy could hand out new ideas for the treatment of epilepsy.

METHODS

Utilizing bidirectional Mendelian randomization (MR) study, we investigated the causal relationship between BCAA levels and epilepsy. BCAA levels from genome-wide association studies (GWAS), including total BCAAs, leucine levels, isoleucine levels, and valine levels, were employed. Causal relationships were explored applying the method of inverse variance-weighted (IVW) and MR-Egger, followed by sensitivity analyses of the results to evaluate heterogeneity and pleiotropy.

RESULTS

Through strict genetic variant selection, we find some related SNPs, total BCAA levels (9), leucine levels (11), isoleucine levels (7), and valine levels (6) as instrumental variables for our MR analysis. Following IVW and sensitivity analysis, total BCAAs levels (OR = 1.14, 95 % CI = 1.019 ∼ 1.285, P = 0.022) and leucine levels (OR = 1.15, 95 % CI = 1.018 ∼ 1.304, P = 0.025) had significant correlation with epilepsy.

CONCLUSIONS

There exists a causal relationship between the levels of total BCAAs and leucine with epilepsy, offering the new ideas into epilepsy potential mechanisms, holding significant implications for its prevention and treatment.

Branched-chain amino acids as adjunctive-alternative treatment in patients with autism: a pilot study

The branched-chain amino acid (BCAA) is a group of essential amino acids that are involved in maintaining the energy balance of a human being as well as the homoeostasis of GABAergic, glutamatergic, serotonergic and dopaminergic systems. Disruption of these systems has been associated with the pathophysiology of autism while low levels of these amino acids have been discovered in patients with autism. A pilot open-label, prospective, follow-up study of the use of BCAA in children with autistic behaviour was carried out. Fifty-five children between the ages of 6 and 18 participated in the study from May 2015 to May 2018. We used a carbohydrate-free BCAA-powdered mixture containing 45·5 g of leucine, 30 g of isoleucine and 24·5 g of valine in a daily dose of 0·4 g/kg of body weight which was administered every morning. Following the initiation of BCAA administration, children were submitted to a monthly psychological examination. Beyond the 4-week mark, BCAA were given to thirty-two people (58·18 %). Six of them (10·9 %) discontinued after 4-10 weeks owing to lack of improvement. The remaining twenty-six children (47·27 %) who took BCAA for longer than 10 weeks displayed improved social behaviour and interactions, as well as improvements in their speech, cooperation, stereotypy and, principally, their hyperactivity. There were no adverse reactions reported during the course of the treatment. Although these data are preliminary, there is some evidence that BCAA could be used as adjunctive treatment to conventional therapeutic methods for the management of autism.

Leucine Reduced Blood-Brain Barrier Disruption and Infarct Size in Early Cerebral Ischemia-Reperfusion

A disruption of the blood-brain barrier (BBB) is a crucial pathophysiological change that can impact the outcome of a stroke. Ribosomal protein S6 (S6) and protein kinase B (Akt) play significant roles in early cerebral ischemia-reperfusion injury. Studies have suggested that branched-chain amino acids (BCAAs) may have neuroprotective properties for spinal cord or brain injuries. Therefore, we conducted research to investigate if leucine, one of the BCAAs, could offer neuroprotection and alter BBB disruption, along with its effects on the phosphorylation of S6 and Akt during the early phase of cerebral ischemia-reperfusion, specifically within the thrombolytic therapy time window. In rats, ten min after left middle cerebral artery occlusion (MCAO), 5 µL of 20 mM L-leucine or normal saline was injected into the left lateral ventricle. After two hours of reperfusion following one hour of MCAO, we determined the transfer coefficient (Ki) of 14C-α-aminoisobutyric acid to assess the BBB disruption, infarct size, and phosphorylation of S6 and Akt. Ischemia-reperfusion increased the Ki (+143%, p < 0.001) and the intra-cerebroventricular injection of leucine lowered the Ki in the ischemic-reperfused cortex (-34%, p < 0.001). Leucine reduced the percentage of cortical infarct (-42%, p < 0.0001) out of the total cortical area. Ischemia-reperfusion alone significantly increased the phosphorylation of both S6 and Akt (p < 0.05). However, the administration of leucine had no further effect on the phosphorylation of S6 or Akt in the ischemic-reperfused cortex. This study suggests that an acute increase in leucine levels in the brain during early ischemia-reperfusion within a few hours of stroke may offer neuroprotection, possibly due to reduced BBB disruption being one of the major contributing factors. Leucine did not further increase the already elevated phosphorylation of S6 or Akt by ischemia-reperfusion under the current experimental conditions. Our data warrant further studies on the effects of leucine on neuronal survival and its mechanisms in the later stages of cerebral ischemia-reperfusion.

Circulating Metabolites as Biomarkers of Disease in Patients with Mesial Temporal Lobe Epilepsy

A major challenge in the clinical management of patients with mesial temporal lobe epilepsy (MTLE) is identifying those who do not respond to antiseizure medication (ASM), allowing for the timely pursuit of alternative treatments such as epilepsy surgery. Here, we investigated changes in plasma metabolites as biomarkers of disease in patients with MTLE. Furthermore, we used the metabolomics data to gain insights into the mechanisms underlying MTLE and response to ASM. We performed an untargeted metabolomic method using magnetic resonance spectroscopy and multi- and univariate statistical analyses to compare data obtained from plasma samples of 28 patients with MTLE compared to 28 controls. The patients were further divided according to response to ASM for a supplementary and preliminary comparison: 20 patients were refractory to treatment, and eight were responsive to ASM. We only included patients using carbamazepine in combination with clobazam. We analyzed the group of patients and controls and found that the profiles of glucose (p = 0.01), saturated lipids (p = 0.0002), isoleucine (p = 0.0001), β-hydroxybutyrate (p = 0.0003), and proline (p = 0.02) were different in patients compared to controls (p < 0.05). In addition, we found some suggestive metabolites (without enough predictability) by multivariate analysis (VIP scores > 2), such as lipoproteins, lactate, glucose, unsaturated lipids, isoleucine, and proline, that might be relevant to the process of pharmacoresistance in the comparison between patients with refractory and responsive MTLE. The identified metabolites for the comparison between MTLE patients and controls were linked to different biological pathways related to cell-energy metabolism and pathways related to inflammatory processes and the modulation of neurotransmitter release and activity in MTLE. In conclusion, in addition to insights into the mechanisms underlying MTLE, our results suggest that plasma metabolites may be used as disease biomarkers. These findings warrant further studies exploring the clinical use of metabolites to assist in decision-making when treating patients with MTLE.

Aberrant BCAA and glutamate metabolism linked to regional neurodegeneration in a mouse model of Leigh syndrome

The dysfunction of respiratory chain complex I (CI) is the most common form of mitochondrial disease that most often presents as Leigh syndrome (LS) in children - a severe neurometabolic disorder defined by progressive focal lesions in specific brain regions. The mechanisms underlying this region-specific vulnerability to CI deficiency, however, remain elusive. Here, we examined brain regional respiratory chain enzyme activities and metabolic profiles in a mouse model of LS with global CI deficiency to gain insight into regional vulnerability to neurodegeneration. One lesion-resistant and three lesion-prone brain regions were investigated in Ndufs4 knockout (KO) mice at the late stage of LS. Enzyme assays confirmed significantly decreased (60-80%) CI activity in all investigated KO brain regions, with the lesion-resistant region displaying the highest residual CI activity (38% of wild type). A higher residual CI activity, and a less perturbed NADH/NAD⁺ ratio, correlate with less severe metabolic perturbations in KO brain regions. Moreover, less perturbed BCAA oxidation and increased glutamate oxidation seem to distinguish lesion-resistant from -prone KO brain regions, thereby identifying key areas of metabolism to target in future therapeutic intervention studies.

Neuroanesthesiology Update

This review is intended to provide a summary of the literature pertaining to the perioperative care of neurosurgical patients and patients with neurological diseases. General topics addressed in this review include general neurosurgical considerations, stroke, neurological monitoring, and perioperative disorders of cognitive function.

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.

Effects of Branched-Chain Amino Acid Supplementation on Spontaneous Seizures and Neuronal Viability in a Model of Mesial Temporal Lobe Epilepsy

BACKGROUND

The essential branched-chain amino acids (BCAAs) leucine, isoleucine, and valine have recently emerged as a potential novel treatment for medically refractory epilepsy. Blood-derived BCAAs can readily enter the brain, where they contribute to glutamate biosynthesis and may either suppress or trigger acute seizures. However, the effects of BCAAs on chronic (ie, spontaneous recurrent) seizures and epilepsy-associated neuron loss are incompletely understood.

MATERIALS AND METHODS

Sixteen rats with mesial temporal lobe epilepsy were randomized into 2 groups that could drink, ad libitum, either a 4% solution of BCAAs in water (n=8) or pure water (n=8). The frequency and relative percent of convulsive and nonconvulsive spontaneous seizures were monitored for a period of 21 days, and the brains were then harvested for immunohistochemical analysis.

RESULTS

Although the frequency of convulsive and nonconvulsive spontaneous recurrent seizures over a 3-week drinking/monitoring period were not different between the groups, there were differences in the relative percent of convulsive seizures in the first and third week of treatment. Moreover, the BCAA-treated rats had over 25% fewer neurons in the dentate hilus of the hippocampus compared with water-treated controls.

CONCLUSIONS

Acute BCAA supplementation reduces seizure propagation, whereas chronic oral supplementation with BCAAs worsens seizure propagation and causes neuron loss in rodents with mesial temporal lobe epilepsy. These findings raise the question of whether such supplementation has a similar effect in humans.

d-Leucine: Evaluation in an epilepsy model

BACKGROUND

Current medicines do not provide sufficient seizure control for nearly one-third of patients with epilepsy. New options are needed to address this treatment gap. We recently found that the atypical amino acid d-leucine protected against acutely-induced seizures in mice, but its effect in chronic seizures has not been explored. We hypothesized that d-leucine would protect against spontaneous recurrent seizures. We also investigated whether mice lacking a previously-described d-leucine receptor (Tas1R2/R3) would be protected against acutely-induced seizures.

METHODS

Male FVB/NJ mice were subjected to kainic acid-induced status epilepticus and monitored by video-electroencephalography (EEG) (surgically implanted electrodes) for 4weeks before, during, and after treatment with d-leucine. Tas1R2/R3 knockout mice and controls underwent the maximal electroshock threshold (MES-T) and 6-Hz tests.

RESULTS

There was no difference in number of calendar days with seizures or seizure frequency with d-leucine treatment. In an exploratory analysis, mice treated with d-leucine had a lower number of dark cycles with seizures. Tas1R2/R3 knockout mice had elevated seizure thresholds in the MES-T test but not the 6-Hz test.

CONCLUSIONS

d-Leucine treatment was ineffective against chronic seizures after kainic acid-induced status epilepticus, but there was some efficacy during the dark cycle. Because d-leucine is highly concentrated in the pineal gland, these data suggest that d-leucine may be useful as a tool for studying circadian patterns in epilepsy. Deletion of the Tas1R2/R3 receptor protected against seizures in the MES-T test and, therefore, may be a novel target for treating seizures.

A review of traditional and novel treatments for seizures in autism spectrum disorder: findings from a systematic review and expert panel

Despite the fact that seizures are commonly associated with autism spectrum disorder (ASD), the effectiveness of treatments for seizures has not been well studied in individuals with ASD. This manuscript reviews both traditional and novel treatments for seizures associated with ASD. Studies were selected by systematically searching major electronic databases and by a panel of experts that treat ASD individuals. Only a few anti-epileptic drugs (AEDs) have undergone carefully controlled trials in ASD, but these trials examined outcomes other than seizures. Several lines of evidence point to valproate, lamotrigine, and levetiracetam as the most effective and tolerable AEDs for individuals with ASD. Limited evidence supports the use of traditional non-AED treatments, such as the ketogenic and modified Atkins diet, multiple subpial transections, immunomodulation, and neurofeedback treatments. Although specific treatments may be more appropriate for specific genetic and metabolic syndromes associated with ASD and seizures, there are few studies which have documented the effectiveness of treatments for seizures for specific syndromes. Limited evidence supports l-carnitine, multivitamins, and N-acetyl-l-cysteine in mitochondrial disease and dysfunction, folinic acid in cerebral folate abnormalities and early treatment with vigabatrin in tuberous sclerosis complex. Finally, there is limited evidence for a number of novel treatments, particularly magnesium with pyridoxine, omega-3 fatty acids, the gluten-free casein-free diet, and low-frequency repetitive transcranial magnetic simulation. Zinc and l-carnosine are potential novel treatments supported by basic research but not clinical studies. This review demonstrates the wide variety of treatments used to treat seizures in individuals with ASD as well as the striking lack of clinical trials performed to support the use of these treatments. Additional studies concerning these treatments for controlling seizures in individuals with ASD are warranted.

Beneficial effects of l-leucine and l-valine on arrhythmias, hemodynamics and myocardial morphology in rats

Branched chain amino acids (BCAA) have been shown to have a general protective effect on the heart in different animal models as well as in humans. However, so far no attempt has been made to specifically elucidate their influence on arrhythmias. Our study was performed to evaluate whether an infusion of either l-leucine or l-valine in a dose of 1mgkg(-1)h(-1) 10min before a 7-min period of left anterior descending artery occlusion followed by 15min of reperfusion, had an effect on arrhythmias measured during the reperfusion phase in the ischemia- and reperfusion-induced arrhythmias model in rats in vivo. The effect of the infusion of these substances on mean arterial blood pressure was monitored throughout the experiment. Both of the tested amino acids exhibited significant antiarrhythmic properties. l-Leucine reduced the duration of ventricular fibrillation (P<0.05) and l-valine decreased the duration of ventricular fibrillation (P<0.001) and ventricular tachycardia (P<0.05). The two amino acids were generally hypotensive. l-Valine lowered blood pressure in all phases of the experiment (P<0.05) while l-leucine lowered this parameter mainly towards the end of occlusion and reperfusion (P<0.05). In addition, 30min infusion of the amino acids in the used dose did not produce any apparent adverse histological changes that were remarkably different from control. In summary, the results of our study suggest that l-leucine and l-valine in the dose that was used attenuates arrhythmias and are hypotensive in their influence. Our findings lend support to the many ongoing investigations into the benefit of the application of l-leucine and l-valine in cardiology like their addition to cardioplegic solutions.

Branched chain amino acids as adjunctive therapy to ketogenic diet in epilepsy: pilot study and hypothesis

A pilot prospective follow-up study of the role of the branched chain amino acids as additional therapy to the ketogenic diet was carried out in 17 children, aged between 2 and 7 years, with refractory epilepsy. All of these patients were on the ketogenic diet; none of them was seizure free, while only 13 had more or less benefited from the diet. The addition of branched chain amino acids induced a 100% seizure reduction in 3 patients, while a 50% to 90% reduction was noticed in 5. Moreover, in all of the patients, no reduction in ketosis was recorded despite the change in the fat-to-protein ratio from 4:1 to 2.5:1. Although our data are preliminary, we suggest that branched chain amino acids may increase the effectiveness of the ketogenic diet and the diet could be more easily tolerated by the patients because of the change in the ratio of fat to protein.

Glutamatergic alterations in the cortex of genetic absence epilepsy rats

BACKGROUND

In absence epilepsy, the neuronal hyper-excitation and hyper-synchronization, which induce spike and wave discharges in a cortico-thalamic loop are suspected to be due to an imbalance between GABA and glutamate (GLU) neurotransmission. In order to elucidate the role played by GLU in disease outcome, we measured cortical and thalamic extracellular levels of GLU and GABA. We used an in vivo quantitative microdialysis approach (no-net-flux method) in an animal model of absence epilepsy (GAERS). In addition, by infusing labelled glutamate through the microdialysis probe, we studied in vivo glutamate uptake in the cortex and thalamus in GAERS and non-epileptic control (NEC) rats. Expression of the vesicular glutamate transporters VGLUT1 and VGLUT2 and a synaptic component, synaptophysin, was also measured.

RESULTS

Although extracellular concentrations of GABA and GLU in the cortex and thalamus were not significantly different between GAERS and NEC rats, cortical GLU uptake was significantly decreased in unrestrained awake GAERS. Expression of VGLUT2 and synaptophysin was increased in the cortex of GAERS compared to NEC rats, but no changes were observed in the thalamus.

CONCLUSION

The specific decrease in GLU uptake in the cortex of GAERS linked to synaptic changes suggests impairment of the glutamatergic terminal network. These data support the idea that a change in glutamatergic neurotransmission in the cortex could contribute to hyperexcitability in absence epilepsy.

Chronic levetiracetam treatment early in life decreases epileptiform events in young GAERS, but does not prevent the expression of spike and wave discharges during adulthood

PURPOSE

In Genetic Absence Epilepsy Rats from Strasbourg (GAERS), age-related absence seizures start to appear from postnatal day (PN) 30 concomitant with 'spike and wave discharges' (SWDs) appearing on cortical EEG recordings. The aim of this study was to investigate the effect of early chronic levetiracetam (LEV) treatment on the development of SWDs in young and adult GAERS.

METHODS

From PN 23 until PN 60, LEV (54 mg/kg, i.p.) was administered once daily to GAERS (n=8), while control GAERS (n=7) received saline (0.9% NaCl, i.p.). All animals were implanted with four epidural EEG electrodes at PN 51. EEG was recorded for 3h daily, during the last 4 days of the treatment (PN 57-PN 60) and during 4 additional days after treatment had been terminated (PN 61-PN 64). The animals were monitored again at the age of 4 months (PN 120-PN 124), about 2 months after the last administration of LEV.

RESULTS

During treatment, epileptiform events in the LEV group were significantly reduced (62%, P<0.05) in comparison with the control group. During the following 4 days, epileptiform events were reduced in the LEV group, with an average difference of 53% (P=0.064). Once the animals had reached adult age, there was no difference in epileptiform events between the LEV group and controls.

CONCLUSION

In this study, chronic LEV administration induced a reduction in epileptiform events in young GAERS. This effect persisted to some extent after treatment cessation (PN 61-PN 64), which might indicate a slowing down of epileptogenic processes. However, at the age of 4 months all animals revealed a similar expression of epileptiform discharges.

The Acute and Chronic Effect of Vagus Nerve Stimulation in Genetic Absence Epilepsy Rats from Strasbourg (GAERS)

PURPOSE

The aim of this study was to evaluate the efficacy of acute and chronic vagus nerve stimulation (VNS) in genetic absence epilepsy rats from Strasbourg (GAERS). This is a validated model for absence epilepsy, characterized by frequent spontaneous absences concomitant with spike and wave discharges (SWD) on the EEG. Although absences are a benign form of seizures, it is conceptually important to investigate the efficacy of VNS in a controlled study by using this chronic epilepsy model.

METHODS

Both control and stimulated GAERS were implanted with five epidural EEG electrodes and a stimulation electrode around the left vagus nerve. In the first experiment, VNS was given when SWD occurred in the EEG; this was repeated the next day. A randomized crossover design (n = 8) was used. In the chronic experiment, GAERS underwent EEG monitoring during a first baseline week. During the second week, the treated group (n = 18) received VNS; controls (n = 13), on the other hand, only underwent EEG recordings.

RESULTS

On day 1 of the acute VNS experiment, the mean duration of the SWD when VNS was applied was higher than in baseline conditions (p < 0.05). However, on day 2, there was no difference in mean duration of the SWD. In the chronic VNS experiment, no statistically significant differences were found between control and stimulated GAERS.

CONCLUSIONS

Acute VNS applied shortly after the onset of SWD prolonged the mean duration of SWD in GAERS at least during the first day of VNS. Chronic stimulation hardly affected SWD in GAERS.

The ketogenic diet; fatty acids, fatty acid-activated receptors and neurological disorders

This review outlines the molecular sensors that reprogram cellular metabolism in response to the ketogenic diet (KD). Special emphasis is placed on the fasting-, fatty acid- and drug-activated transcription factor, peroxisome proliferator-activated receptor alpha (PPARalpha). The KD causes a switch to ketogenesis that is coordinated with an array of changes in cellular lipid, amino acid, carbohydrate and inflammatory pathways. The role of both liver and brain PPARalpha in mediating such changes will be examined, with special reference to the anti-epileptic effects not only of the KD but a range of synthetic anti-epileptic drugs such as valproate. Finally, the implications of the KD and activated brain PPARalpha will be discussed in the context of their potential involvement in a range of disorders of neuro-degeneration and neuro-inflammation.

Expression of monocarboxylic acid transporters (MCT) in brain cells. Implication for branched chain alpha-ketoacids transport in neurons

The alpha-ketoisocaproic acid (KIC) is a short branched-chain monocarboxylate, which accumulates in neural cells. It plays an important role in maintaining nitrogen balance in the brain, a process of a great importance for shuttling of glutamine and glutamate between astrocytes and neurons. Higher accumulation of KIC in isolated cerebral cortex neurons at lower external pH, as well as sensitivity of this process to alpha-cyano-4-hydroxycinnamate indicate an involvement of a transporter, belonging to the family of monocarboxylate transporters (MCT).The expression of MCT1 and MCT2 isoforms in the brain cells was studied using reverse transcriptase-polymerase chain reaction (RT-PCR) method. The mRNA coding MCT1 was detected in astrocytes, brain endothelial cells, tumour cells (neuroblastoma and glioma) and in cortex neurons of newborn rats, but not in adult ones. MCT2, which is less abundant isoform than MCT1, was expressed in astrocytes, in brain endothelial cells and at low level in newborn rats' neurons, being absent in neurons from adult brain.The observed sensitivity of KIC accumulation towards SH-groups reagents did not fit to the known characteristics of MCT1 and MCT2. Therefore, the change of MCT expression during brain development, as well as lack of MCT1 and MCT2 in neurons of adults, point to another MCT isoform being involved in alpha-ketoisocaproic acid accumulation. This could be either one of other known MCT isoforms or a new member of family MCT, specific towards branched chain alpha-ketoacids.

Disturbance of cultured rat neuronal network activity depends on concentration and ratio of leucine and alpha-ketoisocaproate: implication for acute encephalopathy of maple syrup urine disease

Increased concentrations of leucine and its respective ketoacid alpha-ketoisocaproate (KIC) in plasma and cerebrospinal fluid are related to acute and reversible encephalopathy in patients with maple syrup urine disease. We studied electrophysiological properties of primary dissociated rat neurons at increased extracellular concentrations of leucine and KIC (1-10 mM). Spontaneous neuronal network activity was reversibly reduced or blocked by leucine as well as by KIC in a dose-dependent manner. Simultaneous incubation with both substances led to a minor inhibition compared to the effect of each substance alone. Neuronal resting potential, voltage dependent Na(+) (I(Na)) and K(+) (I(K)) currents, the GABA- and glycine-elicited membrane currents, and glutamate-induced intracellular Ca(2+) increase of single neurons, however, were unaffected by both substances. We conclude that acute neuronal network dysfunction in maple syrup urine disease is mainly based on an imbalance of the presynaptic glutamatergic/GABAergic neurotransmitter concentrations or their release.

Effects of topiramate in two models of genetically determined generalized epilepsy, the GAERS and the Audiogenic Wistar AS

PURPOSE

The antiepileptic effects of topiramate (TPM) were assessed in two models of genetically determined generalized epilepsy. The model of nonconvulsive epilepsy used was a model of absence seizures, the GAERS (Genetic Absence Epilepsy Rat from Strasbourg); and the model of convulsive seizures was an audiogenic rat model, the Wistar Audiogenic Sensitive (AS) rat.

METHODS

GAERS were equipped with four cortical electrodes over the frontoparietal cortex, and the duration of spike-and-wave discharges (SWDs) on the EEG was recorded for periods of 20 to 120 or 300 min. In Wistar AS, the occurrence of, latency to, and duration of one or two wild running episodes and tonic seizures were recorded.

RESULTS

In the 16 GAERS studied, TPM (10, 30, and 60 mg/kg) dose-dependently reduced the expression of SWD that almost totally disappeared at the two highest doses between 40 and 120 min. SWD duration returned to control levels by 180 and 280 min after the injection of 30 and 60 mg/kg TPM, respectively. In Wistar AS, 10 mg/kg TPM induced the occurrence of a second running episode not present in control rats, indicative of a decrease in sensitivity of the rats to the stimulus and increased by 330% the latency to the tonic seizure that still occurred in the eight rats studied. At 30 and 60 mg/kg, the latency to wild running increased by 140%; the second running episode was suppressed in six and seven rats, respectively, whereas the tonic seizure occurred only in one of the eight rats studied at these two doses.

CONCLUSIONS

These results support the broad spectrum of antiepileptic activity of TPM, confirming its efficacy in primary generalized seizures of both tonic-clonic and of the absence type.