Precision of metabolite-selective MRS measurements of glutamate, GABA and glutathione: A review of human brain studies

Single-voxel proton magnetic resonance spectroscopy (SV 1 H-MRS) is an in vivo noninvasive imaging technique used to detect neurotransmitters and metabolites. It enables repeated measurements in living participants to build explanatory neurochemical models of psychiatric symptoms and testing of therapeutic approaches. Given the tight link among glutamate, gamma-amino butyric acid (GABA), glutathione and glutamine within the cellular machinery, MRS investigations of neurocognitive and psychiatric disorders must quantify a network of metabolites simultaneously to capture the pathophysiological states of interest. Metabolite-selective sequences typically provide improved metabolite isolation and spectral modelling simplification for a single metabolite at a time. Non-metabolite-selective sequences provide information on all detectable human brain metabolites, but feature many signal overlaps and require complicated spectral modelling. Although there are short-echo time (TE) MRS sequences that do not use spectral editing and are optimised to target either glutamate, GABA or glutathione, these approaches usually imply a precision tradeoff for the remaining two metabolites. Given the interest in assessing psychiatric and neurocognitive diseases that involve excitation-inhibition imbalances along with oxidative stress, there is a need to survey the literature on the quantification precision of current metabolite-selective MRS techniques. In this review, we locate and describe 17 studies that report on the quality of simultaneously acquired MRS metabolite data in the human brain. We note several factors that influence the data quality for single-shot acquisition of multiple metabolites of interest using metabolite-selective MRS: (1) internal in vivo references; (2) brain regions of interests; (3) field strength of scanner; and/or (4) optimised acquisition parameters. We also highlight the strengths and weaknesses of various SV spectroscopy techniques that were able to quantify in vivo glutamate, GABA and glutathione simultaneously. The insights from this review will assist in the development of new MRS pulse sequences for simultaneous, selective measurements of these metabolites and simplified spectral modelling.

Evaluation of GABA Production by Alginate-Microencapsulated Fresh and Freeze-Dried Bacteria Enriched with Monosodium Glutamate during Storage in Chocolate Milk

Two strains of γ-aminobutyric acid (GABA) producing bacteria, L. brevis Y1 and L. plantarum LM2, were microencapsulated in sodium alginate with two concentrations (1% and 2%) of monosodium glutamate (MSG) by using vibrating technology. The mix of both species was microencapsulated both in fresh and freeze-dried form. After 0, 1, 2, and 4 weeks of storage at 4 °C in quarter strength Ringer's solution, the microcapsules were subjected to cell viable counting and sub-cultured in MRS at 37° for 24 h. The MRS cultures were analyzed for the GABA content. The amount of GABA produced per CFU of MRS inoculum was then calculated. Only the 4-week-old microcapsules were used to inoculate a chocolate milk drink with the aim of obtaining a functionalized drink containing viable probiotic cells and GABA after a 1-week incubation at 4 °C. Therefore, the GABA production in chocolate milk per CFU of the probiotic culture after the incubation time was calculated. Results of the GABA analysis by liquid chromatography mass spectrometry of the MRS sub-cultures showed no significant difference (p > 0.05) in GABA yield between 1% and 2% MSG for the microcapsules containing fresh cells. On the contrary, a significant difference (p < 0.05) in productivity along the storage was registered. Microcapsules containing freeze-dried cells showed significant differences (p < 0.05) in GABA yield between 1% and 2% MSG only after 2 and 4 weeks of storage. A significant difference (p < 0.05) in GABA yield between the storage time was found only for the trials with 2% MSG for freeze-dried cells. The synthesis of GABA in chocolate milk significantly decreased (p < 0.05) only for fresh cells when comparing 2% with 1% MSG. In conclusion, a 1-month storage of microcapsules containing both culture forms, fresh and freeze-dried, did not affect GABA production.

Gamma-Aminobutyric Acid-Producing Levilactobacillus brevis Strains as Probiotics in Litchi Juice Fermentation

Levilactobacillus brevis strains can be isolated from traditional Chinese pickles and used as the starter cultures to improve the nutritional profiles of fermented juices. Three L. brevis strains (LBG-29, LBG-24, LBD−14) that produce high levels of gamma-aminobutyric acid (GABA; >300 mg/L) were isolated from traditional Chinese pickles. The strains showed tolerance to low pH and high bile salts and exhibited safety in vitro. Litchi juice was fermented using each strain at 37 °C for 48 h. The litchi juice was determined to be a good substrate for fermentation as the process enhanced its functional profile. Overall, cell vitality increased (above 8.7 log10 CFU/mL), the antioxidant activities of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric ion-reducing antioxidant power (FRAP) were significantly increased, and the antioxidant capacity of the 2,2′-amino-di(3-ethyl-benzothiazoline sulphonic acid-6)ammonium salt (ABTS) was decreased. There was also a significant increase in the GABA and acetic acid content after LBG-29 and LBG-24 fermentation. It was thus determined that the LBG-29 and LBG-24 strains could be used to improve beverage functionality and aid in the development of new products. This is the first report of litchi fermentation using L. brevis as a starter culture. Further research is required to elucidate the functional benefits for the human body and the nutritional and functional properties during its shelf life.

Gamma-amino butyric acid (GABA) supplementation alleviates dexamethasone treatment-induced oxidative stress and inflammation response in broiler chickens

This experiment was conducted to investigate the effect of Gamma-amino butyric acid (GABA) on growth performance, serum and liver antioxidant status, inflammation response and hematological changes, in male broiler chickens under experimentally induced stress via in-feed dexamethasone (DEX). A total of 300 male chicks (Ross 308) on day 7 after hatching, were randomly selected into four groups which were positive control group (PC, without any treatment), negative control (NC, with 1 mg/kg DEX), a third group received 1 mg/kg DEX and 100 mg/kg GABA (DG ⁺) and the last one was (DG ⁺⁺) which received 1 mg/kg DEX and 200 mg/kg GABA. Each group has five replicates (15 birds/replicate). Dietary GABA modulated DEX-induced adverse effects on body weight, feed intake, and feed conversion ratio. The DEX-induced effect of serum levels of IL-6 and IL-10 was reduced by dietary GABA supplementation. The activity of serum and liver superoxide dismutase, catalase, glutathione peroxidase were enhanced and malondialdehyde was reduced by GABA supplementation. The serum levels of total cholesterol & triglyceride were higher while low-density lipoprotein & high-density lipoprotein were lower in GABA groups than NC group. GABA supplementation also significantly decreased the heterophil, heterophil/lymphocyte ratio and elevated the activities of aspartate aminotransferase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) than NC group. In conclusion, dietary GABA supplementation can alleviate DEX stress-induced oxidative stress and inflammation response.

United States Pharmacopeia (USP) Safety Review of Gamma-Aminobutyric Acid (GABA)

Gamma-amino butyric acid (GABA) is marketed in the U.S. as a dietary supplement. USP conducted a comprehensive safety evaluation of GABA by assessing clinical studies, adverse event information, and toxicology data. Clinical studies investigated the effect of pure GABA as a dietary supplement or as a natural constituent of fermented milk or soy matrices. Data showed no serious adverse events associated with GABA at intakes up to 18 g/d for 4 days and in longer studies at intakes of 120 mg/d for 12 weeks. Some studies showed that GABA was associated with a transient and moderate drop in blood pressure (<10% change). No studies were available on effects of GABA during pregnancy and lactation, and no case reports or spontaneous adverse events associated with GABA were found. Chronic administration of GABA to rats and dogs at doses up to 1 g/kg/day showed no signs of toxicity. Because some studies showed that GABA was associated with decreases in blood pressure, it is conceivable that concurrent use of GABA with anti-hypertensive medications could increase risk of hypotension. Caution is advised for pregnant and lactating women since GABA can affect neurotransmitters and the endocrine system, i.e., increases in growth hormone and prolactin levels.

Succinic Semialdehyde Dehydrogenase Deficiency: An Update

Succinic semialdehyde dehydrogenase deficiency (SSADH-D) is a genetic disorder that results from the aberrant metabolism of the neurotransmitter γ-amino butyric acid (GABA). The disease is caused by impaired activity of the mitochondrial enzyme succinic semialdehyde dehydrogenase. SSADH-D manifests as varying degrees of mental retardation, autism, ataxia, and epileptic seizures, but the clinical picture is highly heterogeneous. So far, there is no approved curative therapy for this disease. In this review, we briefly summarize the molecular genetics of SSADH-D, the past and ongoing clinical trials, and the emerging features of the molecular pathogenesis, including redox imbalance and mitochondrial dysfunction. The main aim of this review is to discuss the potential of further therapy approaches that have so far not been tested in SSADH-D, such as pharmacological chaperones, read-through drugs, and gene therapy. Special attention will also be paid to elucidating the role of patient advocacy organizations in facilitating research and in the communication between researchers and patients.

Pharmacological Intervention through Dietary Nutraceuticals in Gastrointestinal Neoplasia

Neoplastic conditions associated with gastrointestinal (GI) tract are common worldwide with colorectal cancer alone accounting for the third leading rate of cancer incidence. Other GI malignancies such as esophageal carcinoma have shown an increasing trend in the last few years. The poor survival statistics of these fatal cancer diseases highlight the need for multiple alternative treatment options along with effective prophylactic strategies. Worldwide geographical variation in cancer incidence indicates a correlation between dietary habits and cancer risk. Epidemiological studies have suggested that populations with high intake of certain dietary agents in their regular meals have lower cancer rates. Thus, an impressive embodiment of evidence supports the concept that dietary factors are key modulators of cancer including those of GI origin. Preclinical studies on animal models of carcinogenesis have reflected the pharmacological significance of certain dietary agents called as nutraceuticals in the chemoprevention of GI neoplasia. These include stilbenes (from red grapes and red wine), isoflavones (from soy), carotenoids (from tomatoes), curcuminoids (from spice turmeric), catechins (from green tea), and various other small plant metabolites (from fruits, vegetables, and cereals). Pleiotropic action mechanisms have been reported for these diet-derived chemopreventive agents to retard, block, or reverse carcinogenesis. This review presents a prophylactic approach to primary prevention of GI cancers by highlighting the translational potential of plant-derived nutraceuticals from epidemiological, laboratory, and clinical studies, for the better management of these cancers through consumption of nutraceutical rich diets and their intervention in cancer therapeutics.

Psychosis effect on hippocampal reduction in schizophrenia

INTRODUCTION

In schizophrenia, disruption of the neurodevelopmental processes may lead to brain changes and subsequent clinical manifestations of the illness. Reports of the progressive nature of these morphological brain changes raise questions about their causes. The possible toxic effects of repeated stressful psychotic episodes may contribute to the disease progression.

OBJECTIVES

To analyze the influence of illness duration and previous psychotic episodes on hippocampal gray matter volume (GMV) in schizophrenia.

METHODS

We performed an analysis of hippocampal GMV correlations with illness duration, number of previous psychotic episodes, and age in 24 schizophrenia patients and 24 matched healthy controls.

RESULTS

We found a cluster of GMV voxels in the left hippocampal tail that negatively correlated with the number of previous psychotic episodes, independent from the effect of age. On the other hand we found no effect of illness duration independent of age on the hippocampal GMV. Finally, we found a cluster of significant group-by-age interaction in the left hippocampal head.

CONCLUSIONS

We found an additive adverse effect of psychotic episodes on hippocampal morphology in schizophrenia. Our findings support toxicity of psychosis concept, together with etiological heterogeneity of brain changes in schizophrenia.

Expression of mitochondrial branched-chain aminotransferase and α-keto-acid dehydrogenase in rat brain: implications for neurotransmitter metabolism

In the brain, metabolism of the essential branched chain amino acids (BCAAs) leucine, isoleucine, and valine, is regulated in part by protein synthesis requirements. Excess BCAAs are catabolized or excreted. The first step in BCAA catabolism is catalyzed by the branched chain aminotransferase (BCAT) isozymes, mitochondrial BCATm and cytosolic BCATc. A product of this reaction, glutamate, is the major excitatory neurotransmitter and precursor of the major inhibitory neurotransmitter γ-aminobutyric acid (GABA). The BCATs are thought to participate in a α-keto-acid nitrogen shuttle that provides nitrogen for synthesis of glutamate from α-ketoglutarate. The branched-chain α-keto acid dehydrogenase enzyme complex (BCKDC) catalyzes the second, irreversible step in BCAA metabolism, which is oxidative decarboxylation of the branched-chain α-keto acid (BCKA) products of the BCAT reaction. Maple Syrup Urine Disease (MSUD) results from genetic defects in BCKDC, which leads to accumulation of toxic levels of BCAAs and BCKAs that result in brain swelling. Immunolocalization of BCATm and BCKDC in rats revealed that BCATm is present in astrocytes in white matter and in neuropil, while BCKDC is expressed only in neurons. BCATm appears uniformly distributed in astrocyte cell bodies throughout the brain. The segregation of BCATm to astrocytes and BCKDC to neurons provides further support for the existence of a BCAA-dependent glial-neuronal nitrogen shuttle since the data show that BCKAs produced by glial BCATm must be exported to neurons. Additionally, the neuronal localization of BCKDC suggests that MSUD is a neuronal defect involving insufficient oxidation of BCKAs, with secondary effects extending beyond the neuron.

Prefrontal cortical gamma-aminobutyric Acid levels in panic disorder determined by proton magnetic resonance spectroscopy

BACKGROUND

Panic disorder (PD) is hypothesized to be associated with altered function of the major inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). Previous proton magnetic resonance spectroscopy (MRS) studies found lower GABA concentrations in the occipital cortex of subjects with PD relative to healthy control subjects. The current study is the first MRS study to compare GABA concentrations between unmedicated PD subjects and control subjects in the prefrontal cortex (PFC).

METHODS

Unmedicated subjects with PD (n = 17) and age- and sex-matched healthy control subjects (n = 17) were scanned on a 3 Tesla scanner using a transmit-receive head coil that provided a sufficiently homogenous radiofrequency field to obtain spectroscopic measurements in the dorsomedial/dorsal anterolateral and ventromedial areas of the PFC.

RESULTS

The prefrontal cortical GABA concentrations did not differ significantly between PD subjects and control subjects. There also was no statistically significant difference in glutamate/glutamine (Glx), choline, or N-acetyl aspartate concentrations.

CONCLUSIONS

The previously reported finding of reduced GABA concentrations in the occipital cortex of PD subjects does not appear to extend to the PFC.