Indispensable amino acid deficiency and increased seizure susceptibility in rats

Cytokine Pattern of Peripheral Blood Mononuclear Cells Isolated from Children Affected by Generalized Epilepsy Treated with Different Protein Fractions of Meat Sources

The objective of the present study was the evaluation of cytokine patterns in terms of TNF-α, IL-10, IL-6, and IL-1β secretion in peripheral blood mononuclear cell (PBMC) supernatants isolated from blood of children affected by generalized epilepsy and treated in vitro with myofibrillar, sarcoplasmic, and total protein fractions of meat and fish sources. Children with generalized epilepsy (EC group, n = 16) and children without any clinical signs of disease, representing a control group (CC group n = 16), were recruited at the Complex Structure of Neuropsychiatry Childhood-Adolescence of Policlinico Riuniti (Foggia, Italy). Myofibrillar (MYO), sarcoplasmic (SA), and total (TOT) protein fractions were obtained from longissimus thoracis muscle of beef (BF) and lamb (LA); from pectoralis muscle of chicken (CH); and from dorsal white muscle of sole (Solea solea, SO), European hake (Merluccius merluccius, EH), and sea bass fish (Dicentrarchus labrax, SB), respectively. PBMCs were isolated from peripheral blood of EC and CC groups, and an in vitro stimulation in the presence of 100 μg/mL for each protein fraction from different meat sources was performed. Data were classified according to three different levels of cytokines produced from the EC group relative to the CC group. TNF-α, IL-10, and IL-6 levels were not affected by different meat fractions and meat sources; on the contrary, IL-1β levels were found to be significantly affected by the tested proteins fractions, as well as different meat sources, in high-level cytokine group. On average, the protein fractions obtained from LB, BF, and CH meat sources showed a higher level of IL-1β than the protein fractions obtained from EH and SB fish samples. When all cytokine classes were analyzed, on average, a significant effect was observed for IL-10, IL-1β, and TNF-α. Data obtained in the present study evidence that the nutritional strategy based on protein from fish and meat sources may modulate the immunological cytokine pattern of infants with generalized epilepsy.

Association between EEG Paroxysmal Abnormalities and Levels of Plasma Amino Acids and Urinary Organic Acids in Children with Autism Spectrum Disorder

Abnormalities in the plasma amino acid and/or urinary organic acid profile have been reported in autism spectrum disorder (ASD). An imbalance between excitatory and inhibitory neuronal activity has been proposed as a mechanism to explain dysfunctional brain networks in ASD, as also suggested by the increased risk of epilepsy in this disorder. This study explored the possible association between presence of EEG paroxysmal abnormalities and the metabolic profile of plasma amino acids and urinary organic acids in children with ASD. In a sample of 55 children with ASD (81.8% male, mean age 53.67 months), EEGs were recorded, and 24 plasma amino acids and 56 urinary organic acids analyzed. EEG epileptiform discharges were found in 36 (65%) children. A LASSO regression, adjusted by age and sex, was applied to evaluate the association of plasma amino acids and urinary organic acids profiles with the presence of EEG epileptiform discharges. Plasma levels of threonine (THR) (coefficient = −0.02, p = 0.04) and urinary concentration of 3-Hydroxy-3-Methylglutaric acid (HMGA) (coefficient = 0.04, p = 0.02) were found to be associated with the presence of epileptiform discharges. These results suggest that altered redox mechanisms might be linked to epileptiform brain activity in ASD.

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.

Indispensable Amino Acid-Deficient Diets Induce Seizures in Ketogenic Diet-Fed Rodents, Demonstrating a Role for Amino Acid Balance in Dietary Treatments for Epilepsy

Background

Low protein amounts are used in ketogenic diets (KDs), where an essential (indispensable) amino acid (IAA) can become limiting. Because the chemically sensitive, seizurogenic, anterior piriform cortex (APC) is excited by IAA limitation, an imbalanced KD could exacerbate seizure activity.

Objective

We questioned whether dietary IAA depletion worsens seizure activity in rodents fed KDs.

Methods

In a series of 6 trials, male rats or gerbils of both sexes (6-8/group) were given either control diets (CDs) appropriate for each trial, a KD, or a threonine-devoid (ThrDev) diet for ≥7 d, and tested for seizures using various stimuli. Microchip analysis of rat APCs was also used to determine if changes in transcripts for structures relevant to seizurogenesis are affected by a ThrDev diet. Glutamate release was measured in microdialysis samples from APCs during the first meal after 7 d on a CD or a ThrDev diet.

Results

Adult rats showed increased susceptibility to seizures in both chemical (58%) and electroshock (doubled) testing after 7 d on a ThrDev diet compared with CD (each trial, P ≤ 0.05). Seizure-prone Mongolian gerbils had fewer seizures after receiving a KD, but exacerbated seizures (68%) after 1 meal of KD minus Thr (KD-T compared with CD, P < 0.05). In kindled rats fed KD-T, both counts (19%) and severities (77%) of seizures were significantly elevated (KD-T compared with CD, P < 0.05). Gene transcript changes were consistent with enhanced seizure susceptibility (7-21 net-fold increases, P = 0.045-0.001) and glutamate release into the APC was increased acutely (4-fold at 20 min, 2.6-fold at 60 min, P < 0.05) after 7 d on a ThrDev diet.

Conclusion

Seizure severity in rats and gerbils was reduced after KDs and exacerbated by ThrDev, both in KD- and CD-fed animals, consistent with the mechanistic studies. We suggest that a complete protein profile in KDs may improve IAA balance in the APC, thereby lowering the risk of seizures.

A Spontaneous Missense Mutation in Branched Chain Keto Acid Dehydrogenase Kinase in the Rat Affects Both the Central and Peripheral Nervous Systems

A novel mutation, causing a phenotype we named frogleg because its most obvious characteristic is a severe splaying of the hind limbs, arose spontaneously in a colony of Sprague-Dawley rats. Frogleg is a complex phenotype that includes abnormalities in hind limb function, reduced brain weight with dilated ventricles and infertility. Using micro-satellite markers spanning the entire rat genome, the mutation was mapped to a region of rat chromosome 1 between D1Rat131 and D1Rat287. Analysis of whole genome sequencing data within the linkage interval, identified a missense mutation in the branched-chain alpha-keto dehydrogenase kinase (Bckdk) gene. The protein encoded by Bckdk is an integral part of an enzyme complex located in the mitochondrial matrix of many tissues which regulates the levels of the branched-chain amino acids (BCAAs), leucine, isoleucine and valine. BCAAs are essential amino acids (not synthesized by the body), and circulating levels must be tightly regulated; levels that are too high or too low are both deleterious. BCKDK phosphorylates Ser293 of the E1α subunit of the BCKDH protein, which catalyzes the rate-limiting step in the catabolism of the BCAAs, inhibiting BCKDH and thereby, limiting breakdown of the BCAAs. In contrast, when Ser293 is not phosphorylated, BCKDH activity is unchecked and the levels of the BCAAs will decrease dramatically. The mutation is located within the kinase domain of Bckdk and is predicted to be damaging. Consistent with this, we show that in rats homozygous for the mutation, phosphorylation of BCKDH in the brain is markedly decreased relative to wild type or heterozygous littermates. Further, circulating levels of the BCAAs are reduced by 70-80% in animals homozygous for the mutation. The frogleg phenotype shares important characteristics with a previously described Bckdk knockout mouse and with human subjects with Bckdk mutations. In addition, we report novel data regarding peripheral neuropathy of the hind limbs.

Effects of essential amino acid deficiency: down-regulation of KCC2 and the GABAA receptor; disinhibition in the anterior piriform cortex

The anterior piriform cortex (APC) is activated by, and is the brain area most sensitive to, essential (indispensable) amino acid (IAA) deficiency. The APC is required for the rapid (20 min) behavioral rejection of IAA deficient diets and increased foraging, both crucial adaptive functions supporting IAA homeostasis in omnivores. The biochemical mechanisms signaling IAA deficiency in the APC block initiation of translation in protein synthesis via uncharged tRNA and the general amino acid control kinase, general control nonderepressing kinase 2. Yet, how inhibition of protein synthesis activates the APC is unknown. The neuronal K(+) Cl(-) cotransporter, neural potassium chloride co-transporter (KCC2), and GABAA receptors are essential inhibitory elements in the APC with short plasmalemmal half-lives that maintain control in this highly excitable circuitry. After a single IAA deficient meal both proteins were reduced (vs. basal diet controls) in western blots of APC (but not neocortex or cerebellum) and in immunohistochemistry of APC. Furthermore, electrophysiological analyses support loss of inhibitory elements such as the GABAA receptor in this model. As the crucial inhibitory function of the GABAA receptor depends on KCC2 and the Cl(-) transmembrane gradient it establishes, these results suggest that loss of such inhibitory elements contributes to disinhibition of the APC in IAA deficiency. The circuitry of the anterior piriform cortex (APC) is finely balanced between excitatory (glutamate, +) and inhibitory (GABA, -) transmission. GABAA receptors use Cl(-), requiring the neural potassium chloride co-transporter (KCC2). Both are rapidly turning-over proteins, dependent on protein synthesis for repletion. In IAA (indispensable amino acid) deficiency, within 20 min, blockade of protein synthesis prevents restoration of these inhibitors; they are diminished; disinhibition ensues. GCN2 = general control non-derepressing kinase 2, eIF2α = α-subunit of the eukaryotic initiation factor 2.

The anterior piriform cortex is sufficient for detecting depletion of an indispensable amino acid, showing independent cortical sensory function

Protein synthesis requires a continuous supply of all of the indispensable (essential) amino acids (IAAs). If any IAA is deficient, animals must obtain the limiting amino acid by diet selection. Sensing of IAA deficiency requires an intact anterior piriform cortex (APC), but does it act alone? Shortly after rats begin eating an IAA-deficient diet, the meal ends and EPSPs are activated in the APC; from there, neurons project to feeding circuits; the meal ends within 20 min. Within the APC in vivo, uncharged tRNA activates the general amino acid control non-derepressing 2 (GCN2) enzyme system increasing phosphorylation of eukaryotic initiation factor (P-eIF2α), which blocks general protein synthesis. If this paleocortex is sufficient for sensing IAA depletion, both neuronal activation and P-eIF2α should occur in an isolated APC slice. We used standard techniques for electrophysiology and immunohistochemistry. After rats ate IAA-devoid or -imbalanced diets, their depleted slices responded to different stimuli with increased EPSP amplitudes. Slices from rats fed a control diet were bathed in artificial CSF replete with all amino acids with or without the IAA, threonine, or a tRNA synthetase blocker, l-threoninol, or its inactive isomer, d-threoninol. Thr depletion in vitro increased both EPSP amplitudes and P-eIF2α. l (but not d)-threoninol also increased EPSP amplitudes relative to control. Thus, we show independent excitation of the APC with responses parallel to those known in vivo. These data suggest a novel idea: in addition to classical processing of peripheral sensory input, direct primary sensing may occur in mammalian cortex.

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.