Altered Glutamate Metabolism Research Articles

Glutamate chemical exchange saturation transfer (GluCEST) MRI to evaluate the relationship between demyelination and glutamate content in depressed mice

Glutamatergic alteration is one of the potential mechanisms of depression. However, there is no consensus on whether glutamate metabolism changes affect the myelin structure of depression in mouse models. Glutamate chemical exchange saturation transfer (GluCEST) is a novel and powerful molecular imaging technique that can visualize glutamate distribution. In this study, we used the GluCEST imaging technique to look at glutamate levels in mice under chronic unpredictable mild stress (CUMS) and how they relate to demyelination. The CUMS mice were exposed to different stress factors for 6 weeks. Evaluated of depression in CUMS mice by behavioral tests. MRI scans were then performed, including T2-mapping, GluCEST, and diffusion tensor imaging (DTI) sequences. Brain tissues were collected for Luxol Fast Blue staining and immunofluorescence staining to analyze the changes in the myelin sheath. Artificially sketched regions of interest (ROI) (corpus callosum, hippocampus, and thalamus) were used to calculate the GluCEST value, fractional anisotropy (FA), and T2 value. Compared with the control group, the GluCEST value in the ROIs of CUMS mice significantly decreased. Similarly, the FA value in ROIs was lower in the CUMS group than in the CTRL group, but the T2 value did not differ significantly between the two groups. The histological results showed that ROIs in the CUMS group had demyelination compared with the CTRL group, indicating that DTI was more sensitive than T2 mapping in detecting myelin abnormalities. Furthermore, the GluCEST value in the ROIs correlates positively with the FA value. These findings suggest that altered glutamate metabolism may be one of the important factors leading to demyelination in depression, and GluCEST is expected to serve as an imaging biological marker for the diagnosis of demyelination in depression.

Medial prefrontal cortex neurotransmitter abnormalities in posttraumatic stress disorder with and without comorbidity to major depression.

Posttraumatic stress disorder (PTSD) is a chronic psychiatric condition that follows exposure to a traumatic stressor. Though previous in vivo proton (1H) MRS) research conducted at 4 T or lower has identified alterations in glutamate metabolism associated with PTSD predisposition and/or progression, no prior investigations have been conducted at higher field strength. In addition, earlier studies have not extensively addressed the impact of psychiatric comorbidities such as major depressive disorder (MDD) on PTSD-associated 1H-MRS-visible brain metabolite abnormalities. Here we employ 7 T 1H MRS to examine concentrations of glutamate, glutamine, GABA, and glutathione in the medial prefrontal cortex (mPFC) of PTSD patients with MDD (PTSD+MDD+; N= 6) or without MDD (PTSD+MDD-; N= 5), as well as trauma-unmatched controls without PTSD but with MDD (PTSD-MDD+; N= 9) or without MDD (PTSD-MDD-; N= 18). Participants with PTSD demonstrated decreased ratios of GABA to glutamine relative to healthy PTSD-MDD- controls but no single-metabolite abnormalities. When comorbid MDD was considered, however, MDD but not PTSD diagnosis was significantly associated with increased mPFC glutamine concentration and decreased glutamate:glutamine ratio. In addition, all participants with PTSD and/or MDD collectively demonstrated decreased glutathione relative to healthy PTSD-MDD- controls. Despite limited findings in single metabolites, patterns of abnormality in prefrontal metabolite concentrations among individuals with PTSD and/or MDD enabled supervised classification to separate them from healthy controls with 80+% sensitivity and specificity, with glutathione, glutamine, and myoinositol consistently among the most informative metabolites for this classification. Our findings indicate that MDD can be an important factor in mPFC glutamate metabolism abnormalities observed using 1H MRS in cohorts with PTSD.

Maternal sleep deprivation disrupts glutamate metabolism in offspring rats.

Maternal sleep deprivation (MSD) has emerged as a significant public health concern, yet its effects on offspring metabolism remain poorly understood. This study investigated the metabolomic implications of MSD on offspring cognitive development, with a particular focus on alterations in glutamate metabolism. Pregnant rats were subjected to sleep deprivation during late gestation. Plasma and brain samples from their offspring were collected at different postnatal days (P1, P7, P14, and P56) and analyzed using untargeted metabolomics with liquid chromatography-mass spectrometry. Metabolomic analysis revealed significant differences in various amino acids, including L-glutamate, L-phenylalanine, L-tyrosine, and L-tryptophan, which are crucial for cognitive function. Subsequent differential analysis and partial least squares discriminant analysis (sPLS-DA) demonstrated a gradual reduction in these metabolic differences in the brain as the offspring underwent growth and development. KEGG pathway analysis revealed differential regulation of several pathways, including alanine, aspartate, and glutamate metabolism, glutathione metabolism, arginine biosynthesis, aminoacyl-tRNA biosynthesis, histidine metabolism, and taurine and hypotaurine metabolism, at different developmental stages. Mantel and Spearman analyses indicated that the observed changes in metabolites in MSD progeny may be related to various gut microbes, Ruminococcus_1, Ruminococcaceae_UCG-005, and Eubacterium_coprostanoligenes_group. Biochemical assays further demonstrated developmental changes in the L-glutamate metabolic pathway. Collectively, these findings suggest that MSD not only affects maternal well-being but also has enduring metabolic consequences for offspring, particularly impacting pathways linked to cognitive function. This highlights the importance of addressing maternal sleep health to mitigate potential long-term consequences for offspring.

Neuronal Hyperactivity in the Hippocampus during the Early Stage of Streptozotocin-Induced Type 1 Diabetes in Mice

Introduction: Cognitive dysfunction due to reduced neuronal transmission in the brain is a major emerging complication in diabetes. However, recent neuroimaging studies have demonstrated non-linear changes including hyperactivity in the hippocampus during the early stage of diabetes. This study aimed to determine the changes in neuronal activity at a single-cell level in hippocampal CA1 pyramidal neurons in the early stage of streptozotocin-induced type 1 diabetes in mice. Methods: Whole-cell patch-clamp recordings from acute brain slices were performed in mice over 4 consecutive weeks following the induction of hyperglycaemia using streptozotocin. In addition, microdialysate was collected from CA1 area while the mice were in an arousal state. The concentrations of glutamate and GABA in the microdialysate were then measured using ultra-performance liquid chromatography with mass spectrometry. Results: CA1 neurons in streptozotocin-induced diabetic mice exhibited higher membrane potentials (p = 0.0052), higher frequency of action potentials (p = 0.0052), and higher frequency of spontaneous excitatory post-synaptic currents (p = 0.037) compared with controls during the second week after hyperglycaemia was established. No changes in electrophysiological parameters were observed during the first, the third, and the fourth week. Moreover, the diabetic mice had higher extracellular glutamate concentration in CA1 area compared with controls (p = 0.021) during the second week after the initiation of diabetes. No change in the extracellular GABA concentration was observed. Conclusion: Our study demonstrated a temporary state of neuronal hyperactivity at the single-cell level in the hippocampal CA1 region during the early stage of diabetes. This neuronal hyperactivity might be related to altered glutamate metabolism and provide clues for future brain-target intervention.

Conduct disorder and hyperprolinemia type I: A case report

IntroductionHyperprolinemia is defined by high proline levels of blood and its primary type consists on a metabolic disorder that is the result of a number of different genetic defects affecting the degradation of proline. The complex relationship between this disease and different psychiatric phenotypes has been an important subject of study in recent years, suggesting a “common psychiatric phenotype” (Namavar et al. Am J Med Genet B Neuropsychiatr Genet 2021; 186(5), 289-317), though its exact characteristics are yet to be determined. A higher prevalence of psychotic disorders (Guo et al. Metab Brain dis 2018; 33 89-97) explained through altered glutamate metabolism, autism spectrum disorders, developmental delay and intellectual disability has been proposed.ObjectivesTo describe the case of a patient, recently diagnosed of hyperprolinemia type I, presenting a conduct disorder alongside with ADHD, oppositional defiant disorder and an unspecified pervasive developmental disorder.MethodsWe present the case of a 15-year-old male that has received follow-up care by our mental health services. The patient was born preterm (35+5 weeks) and required reanimation, oxygen therapy, antiretroviral therapy (biological mother was HIV positive) and pharmacological therapy with phenobarbital (in order to treat methadone withdrawal syndrome). It was adopted nationally when he was 18-month-old and experimented an adequate development during his first years, only highlighting slight psychomotor restlessness and distinctive facial features. During the next years, he receives diagnosis of ADHD (with little to no registered response to amphetamine derivatives), oppositional defiant disorder, social pragmatic communication disorder and fetal alcohol syndrome.ResultsDuring his first hospital admission, a neuropediatrician was contacted to study the patient and recommended for a metabolic screening to be done, where high blood levels of proline were detected (940.1μmol/L). After this, a procedure of massive exome sequencing of genes that were known to be related to alterations in the metabolism of proline was conducted, finding the mutation c.[1357C>T] in the gen PRODH. This translates to an amino acid replacement in the protein proline dehydrogenase (p.[Arg453Cys]; [Arg453Cys]), which has been studied (Bender et al. Am J Hum Genet 2005; 76 409–420) that it reduced its activity in a 70%, making it a very probable cause of the hyperprolinemia.ConclusionsThere is still scarce evidence of the psychiatric phenotypes presented in patients with hyperprolinemia. Further research is needed in order to accurately define the complex relationship between this metabolic disorder and its effect on the central nervous system.Disclosure of InterestNone Declared

Exploring the Role of Neurotransmitters in Multiple Sclerosis: An Expanded Review

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease of the central nervous system (CNS). Although emerging evidence has shown that changes in neurotransmitter levels in the synaptic gap may contribute to the pathophysiology of MS, their specific role has not been elucidated yet. In this review, we aim to analyze preclinical and clinical evidence on the structural and functional changes in neurotransmitters in MS and critically discuss their potential role in MS pathophysiology. Preclinical studies have demonstrated that alterations in glutamate metabolism may contribute to MS pathophysiology, by causing excitotoxic neuronal damage. Dysregulated interaction between glutamate and GABA results in synaptic loss. The GABAergic system also plays an important role, by regulating the activity and plasticity of neural networks. Targeting GABAergic/glutamatergic transmission may be effective in fatigue and cognitive impairment in MS. Acetylcholine (ACh) and dopamine can also affect the T-mediated inflammatory responses, thereby being implicated in MS-related neuroinflammation. Also, melatonin might affect the frequency of relapses in MS, by regulating the sleep-wake cycle. Increased levels of nitric oxide in inflammatory lesions of MS patients may be also associated with axonal neuronal degeneration. Therefore, neurotransmitter imbalance may be critically implicated in MS pathophysiology, and future studies are needed for our deeper understanding of their role in MS.

Glutamate blunts cell-killing effects of neutrophils in tumor microenvironment.

Neutrophils are the first defenders of the innate system for injury and infection. They have gradually been recognized as important participants in tumor initiation and development due to their heterogeneity and plasticity. In the tumor microenvironment (TME), neutrophils can exert antitumor and protumor functions, depending on the surroundings. Tumor cells systemically alter intracellular amino acid (AA) metabolism and extracellular AA distribution to meet their proliferation need, leading to metabolic reprogramming and TME reshaping. However, the underlying mechanisms that determine how altered AAs affect neutrophils in TME are less‐explored. Here, we identified that abundant glutamate releasing from tumor cells blunted neutrophils’ cell‐killing effects toward tumor cells in vitro and in vivo. Mass spectrometric detection, flow cytometry, and western blot experiments proved that increased levels of pSTAT3/RAB10/ARF4, mediated by glutamate, were accompanied with immunosuppressive phenotypes of neutrophils in TME. We also discovered that riluzole, an FDA‐approved glutamate release inhibitor, significantly inhibited tumor growth by restoring neutrophils’ cell‐killing effects and decreasing glutamate secretion from tumor cells. These findings highlight the importance of tumor‐released glutamate on neutrophil transformation in TME, providing new possible cancer treatments targeting altered glutamate metabolism.

Acute effects of ketamine on the pregenual anterior cingulate: linking spontaneous activation, functional connectivity, and glutamate metabolism

Ketamine exerts its rapid antidepressant effects via modulation of the glutamatergic system. While numerous imaging studies have investigated the effects of ketamine on a functional macroscopic brain level, it remains unclear how altered glutamate metabolism and changes in brain function are linked. To shed light on this topic we here conducted a multimodal imaging study in healthy volunteers (N = 23) using resting state fMRI and proton (1H) magnetic resonance spectroscopy (MRS) to investigate linkage between metabolic and functional brain changes induced by ketamine. Subjects were investigated before and during an intravenous ketamine infusion. The MRS voxel was placed in the pregenual anterior cingulate cortex (pgACC), as this region has been repeatedly shown to be involved in ketamine’s effects. Our results showed functional connectivity changes from the pgACC to the right frontal pole and anterior mid cingulate cortex (aMCC). Absolute glutamate and glutamine concentrations in the pgACC did not differ significantly from baseline. However, we found that stronger pgACC activation during ketamine was linked to lower glutamine concentration in this region. Furthermore, reduced functional connectivity between pgACC and aMCC was related to increased pgACC activation and reduced glutamine. Our results thereby demonstrate how multimodal investigations in a single brain region could help to advance our understanding of the association between metabolic and functional changes.

The central role of the glutamate metabolism in long-term antiretroviral treated HIV-infected individuals with metabolic syndrome.

Metabolic syndrome (MetS) is a significant factor for cardiometabolic comorbidities in people living with HIV (PLWH) and a barrier to healthy aging. The long-term consequences of HIV-infection and combination antiretroviral therapy (cART) in metabolic reprogramming are unknown. In this study, we investigated metabolic alterations in well-treated PLWH with MetS to identify potential mechanisms behind the MetS phenotype using advanced statistical and machine learning algorithms.We included 200 PLWH from the Copenhagen Comorbidity in HIV-infection (COCOMO) study. PLWH were grouped into PLWH with MetS (n = 100) defined according to the International Diabetes Federation (IDF) consensus worldwide definition of the MetS or without MetS (n = 100). The untargeted plasma metabolomics was performed using ultra-high-performance liquid chromatography/mass spectrometry (UHPLC/MS/MS) and immune-phenotyping of Glut1 (glucose transporter), xCT (glutamate/cysteine transporter) and MCT1 (pyruvate/lactate transporter) by flow cytometry. We applied several conventional approaches, machine learning algorithms, and linear classification models to identify the biologically relevant metabolites associated with MetS in PLWH.Of the 877 identified biochemicals, 9% (76/877) differed significantly between PLWH with and without MetS (false discovery rate < 0.05). The majority belonged to amino acid metabolism (43%). A consensus identification by combining supervised and unsupervised methods indicated 11 biomarkers of MetS phenotype in PLWH. A weighted co-expression network identified seven communities of positively intercorrelated metabolites. A single community contained six of the potential biomarkers mainly related to glutamate metabolism. Transporter expression identified altered xCT and MCT in both lymphocytic and monocytic cells. Combining metabolomics and immune-phenotyping indicated altered glutamate metabolism associated with MetS in PLWH, which has clinical significance.

Therapeutic potentiality of a new flavonoid against ketamine induced glutamatergic dysregulation in schizophrenia: In vivo and in silico approach

Glutamate and dopamine hypotheses are leading theories of the pathophysiology of schizophrenia. Multiple lines of evidence suggest that dopaminergic and glutamatergic dysfunction is an underlying mechanism in schizophrenia. Since currently available antipsychotic drugs have significant untoward side effects, identification of new neuroprotective compounds from the medicinal plants may prove beneficial in neurodegenerative disorders. In our previous investigation we have isolated, characterized and reported a novel bioactive compound viz. 3-(3, 4-dimethoxy phenyl)-1-(4-methoxy phenyl) prop-2-en-1-one from the Celastrus paniculatus (CP) is used for the current clinical intervention of schizophrenia disease. The present study is mainly aimed to evaluate the neuroprotective potential of the above bioactive compound against ketamine-induced schizophrenia with particular reference to glutamate metabolism using in vivo and in silico methods. The decrease in glutamine content and the activity levels of glutamate dehydrogenase, glutamine synthetase, and glutaminase in different regions of the rat brain suggests lowered oxidative deamination and lowered mobilization of glutamate towards glutamine formation during ketamine-induced schizophrenia. Pre-treatment with the plant compound reversed the alterations in glutamate metabolism and restored the normal glutamatergic neurotransmission akin to the reference drug, clozapine. In addition, the compound has shown strong interaction and exhibited the highest binding energies against selected NMDA receptors with the lowest inhibition constant than the reference drug. Recoveries of these parameters during anti-schizophrenic treatment suggest that administration of plant compound might offer neuroprotection by interrupting the pathological cascade of glutamatergic neurotransmission that occurs during schizophrenia.

Evidence That Cannabis Exposure, Abuse, and Dependence Are Related to Glutamate Metabolism and Glial Function in the Anterior Cingulate Cortex: A 1H-Magnetic Resonance Spectroscopy Study.

There is evidence that long-term cannabis use is associated with alterations to glutamate neurotransmission and glial function. In this study, 26 long-term cannabis users (males=65.4%) and 47 non-cannabis using healthy controls (males=44.6%) underwent proton magnetic resonance spectroscopy (1H-MRS) of the anterior cingulate cortex (ACC) in order to characterize neurometabolite alterations in cannabis users and to examine associations between neurometabolites, cannabis exposure, and cannabis use behaviors. Myo-inositol, a marker of glial function, and glutamate metabolites did not differ between healthy controls and cannabis users or cannabis users who met criteria for DSM5 cannabis use disorder (n=17). Lower myo-inositol, a putative marker of glial function, was related to greater problematic drug use (F1,22 = 11.95, p=.002; Cohen’s f=0.59, large effect; Drug Abuse Screening Test) and severity of cannabis dependence (F1,22 = 6.61, p=.17; Cohen’s f=0.44, large effect). Further, past-year cannabis exposure exerted different effects on glutamate and glutamate+glutamine in males and females (glutamate: F1,21 = 6.31, p=.02; glutamate+glutamine: F1,21 = 7.20, p=.014), such that greater past-year cannabis exposure was related to higher concentrations of glutamate metabolites in male cannabis users (glutamate: F1,14 = 25.94, p=.00016; Cohen’s f=1.32, large effect; glutamate+glutamine: F1,14 = 23.24, p=.00027, Cohen’s f=1.24, large effect) but not in female cannabis users (glutamate: F1,6 = 1.37, p=0.78; glutamate+glutamine: F1,6 = 0.001, p=.97). The present results extend existing evidence of altered glial function and glutamate metabolism with cannabis use by providing evidence linking problematic drug use behaviors with glial function as measured with myo-inositol and recent chronic cannabis exposure to alterations in glutamate metabolism. This provides novel directions for the interrogation of the impact of cannabis use on brain neurochemistry.

Glutamate Transporters and Mitochondria: Signaling, Co-compartmentalization, Functional Coupling, and Future Directions.

In addition to being an amino acid that is incorporated into proteins, glutamate is the most abundant neurotransmitter in the mammalian CNS, the precursor for the inhibitory neurotransmitter γ-aminobutyric acid, and one metabolic step from the tricarboxylic acid cycle intermediate α-ketoglutarate. Extracellular glutamate is cleared by a family of Na+-dependent transporters. These transporters are variably expressed by all cell types in the nervous system, but the bulk of clearance is into astrocytes. GLT-1 and GLAST (also called EAAT2 and EAAT1) mediate this activity and are extremely abundant proteins with their expression enriched in fine astrocyte processes. In this review, we will focus on three topics related to these astrocytic glutamate transporters. First, these transporters co-transport three Na+ ions and a H+ with each molecule of glutamate and counter-transport one K+; they are also coupled to a Cl- conductance. The movement of Na+ is sufficient to cause profound astrocytic depolarization, and the movement of H+ is linked to astrocytic acidification. In addition, the movement of Na+ can trigger the activation of Na+ co-transporters (e.g. Na+-Ca2+ exchangers). We will describe the ways in which these ionic movements have been linked as signals to brain function and/or metabolism. Second, these transporters co-compartmentalize with mitochondria, potentially providing a mechanism to supply glutamate to mitochondria as a source of fuel for the brain. We will provide an overview of the proteins involved, discuss the evidence that glutamate is oxidized, and then highlight some of the un-resolved issues related to glutamate oxidation. Finally, we will review evidence that ischemic insults (stroke or oxygen/glucose deprivation) cause changes in these astrocytic mitochondria and discuss the ways in which these changes have been linked to glutamate transport, glutamate transport-dependent signaling, and altered glutamate metabolism. We conclude with a broader summary of some of the unresolved issues.

Gabapentin Attenuates Oxidative Stress and Apoptosis in the Diabetic Rat Retina.

Neurodegeneration in diabetic retina has been widely considered as initiating factor that may lead to vascular damage, the classical hallmark of diabetic retinopathy. Diabetes induced altered glutamate metabolism in the retina, especially through glutamate excitotoxicity might play a major role in the neurodegeneration. Increased level of branched chain amino acids (BCAAs) measured in diabetic retina might cause an increase in the neurotoxic level of glutamate by transamination of citric acid cycle intermediates. In order to analyze the transamination of BCAAs and their influence on neurodegenerative factors, we treated streptozotocin-induced diabetic rats with gabapentin, a leucine analogue and an inhibitor of branched chain amino transferase (BCATc). Interestingly, gabapentin lowered the retinal level of BCAAs in diabetic rats. Furthermore, gabapentin treatments ameliorated the reduced antioxidant glutathione level and increased malondialdehyde (MDA), the marker of lipid peroxidation in diabetic rat retinas. In addition, gabapentin also reduced the expression of proapoptotic caspase-3, a marker of apoptosis and increased anti-apoptotic marker Bcl-2 in diabetic retinas. Thus, these results suggest that gabapentin stimulates glutamate disposal, and ameliorates apoptosis and oxidative stress in diabetic rat retina. The influence of gabapentin may be due to its capacity to increase the ratio of BCKA to BCAA which in turn would reduce glutamate excitotoxicity in diabetic retina.

Ethanol normalizes glutamate-induced elevation of intracellular sodium in olfactory neuroepithelial progenitors from subjects with bipolar illness but not nonbipolar controls: Biologic evidence for the self-medication hypothesis.

Alcohol use disorders are quite common in bipolar patients with a prevalence of comorbidity that exceeds all other primary psychiatric diagnoses other than other substance use disorders1; over 60% of people with bipolar disorder type I (BD I) have comorbid alcohol dependence at some point in their lives.1 This intimate relationship has served as the basis of the proposed idea of “self-medication.”2 However, biological confirmation of “self-medication,” specifically, the correction of an abnormal biologic marker with alcohol, has never been demonstrated. Recently, we have succeeded in utilizing olfactory neuroepithelium biopsy to produce permanent cell lines of olfactory neuroepithelial progenitors (ONPs) from patients with BD and matched nonbipolar controls.3 These cells possess the genetic heritage of BD I and can be used for investigation of differential biological responses to ethanol. Ionic regulatory abnormalities have repeatedly been documented in patients with BD I.4 Most notably, intracellular sodium and calcium are elevated during both mania and depression, this distribution of cations alters transmembrane potential of lymphocytes—a phenomenon which may be a useful diagnostic marker (reviewed in references 4). Both pharmacologic and genetic animal models which inhibit the sodium pump to elevate intracellular sodium and calcium concentrations create mania-like behaviors (reviewed in 4). Similarly, altered-glutamate metabolism is a consistent finding in BD (reviewed in 4). Importantly, brain glutamate and glutamine are elevated in most brain areas in patients with bipolar illness during mania, depression, and euthymia. By extension, treating ONP cells with glutamate to increase both intracellular sodium and calcium may be a cellular model of bipolar illness, mania, and/or bipolar depression.

Acyl-CoA synthetase 6 enriches the neuroprotective omega-3 fatty acid DHA in the brain

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is highly abundant in the brain and confers protection against numerous neurological diseases, yet the fundamental mechanisms regulating the enrichment of DHA in the brain remain unknown. Here, we have discovered that a member of the long-chain acyl-CoA synthetase family, Acsl6, is required for the enrichment of DHA in the brain by generating an Acsl6-deficient mouse (Acsl6-/-). Acsl6 is highly enriched in the brain and lipid profiling of Acsl6-/- tissues reveals consistent reductions in DHA-containing lipids in tissues highly abundant with Acsl6. Acsl6-/- mice demonstrate motor impairments, altered glutamate metabolism, and increased astrogliosis and microglia activation. In response to a neuroinflammatory lipopolysaccharide injection, Acsl6-/- brains show similar increases in molecular and pathological indices of astrogliosis compared with controls. These data demonstrate that Acsl6 is a key mediator of neuroprotective DHA enrichment in the brain.

Glutamate Dehydrogenase-Deficient Mice Display Schizophrenia-Like Behavioral Abnormalities and CA1-Specific Hippocampal Dysfunction.

Brain imaging has revealed that the CA1 subregion of the hippocampus is hyperactive in prodromal and diagnosed patients with schizophrenia (SCZ), and that glutamate is a driver of this hyperactivity. Strikingly, mice deficient in the glutamate synthetic enzyme glutaminase have CA1 hypoactivity and a SCZ-resilience profile, implicating glutamate-metabolizing enzymes. To address this further, we examined mice with a brain-wide deficit in the glutamate-metabolizing enzyme glutamate dehydrogenase (GDH), encoded by Glud1, which should lead to glutamate excess due to reduced glutamate metabolism in astrocytes. We found that Glud1-deficient mice have behavioral abnormalities in the 3 SCZ symptom domains, with increased baseline and amphetamine-induced hyperlocomotion as a positive symptom proxy, nest building and social preference as a negative symptom proxy, and reversal/extradimensional set shifting in the water T-maze and contextual fear conditioning as a cognitive symptom proxy. Neuroimaging of cerebral blood volume revealed hippocampal hyperactivity in CA1, which was associated with volume reduction. Parameters of hippocampal synaptic function revealed excess glutamate release and an elevated excitatory/inhibitory balance in CA1. Finally, in a direct clinical correlation using imaging-guided microarray, we found a significant SCZ-associated postmortem reduction in GLUD1 expression in CA1. These findings advance GLUD1 deficiency as a driver of excess hippocampal excitatory transmission and SCZ symptoms, and identify GDH as a target for glutamate modulation pharmacotherapy for SCZ. More broadly, these findings point to the likely involvement of alterations in glutamate metabolism in the pathophysiology of SCZ.

Neurotrophic, Cytoprotective, and Anti-inflammatory Effects of St. John's Wort Extract on Differentiated Mouse Hippocampal HT-22 Neurons.

Introduction: Since ancient times Hypericum perforatum L. named St. John's wort (SJW), has been used in the management of a wide range of applications, including nervous disorders. Development of mood disorders are due to alterations in glutamate metabolism, initiation of inflammatory pathways, and changes of the neuronal plasticity. Previous studies suggest that the glutamatergic system contributes to the pathophysiology of depression. Extracts of SJW have been recommended for the treatment of depression. The aim of the present in vitro study was to evaluate the action of STW3-VI, a special SJW extract in differentiated mouse hippocampal HT-22 neurons. We evaluated the stimulation of neurogenesis, the protective effect against glutamate or N-methyl-D-aspartate receptor induced-excitotoxicity and its anti-inflammatory properties in LPS-activated human macrophages.Results: After 48 h treatment, STW3-VI stimulated the neurite formation by 25% in comparison with the control and showed protective effects against glutamate- or NMDA-induced cytotoxicity by significantly increasing the viability about +25 or +50%. In conjunction with these effects, after pretreatment with STW3-VI, the intracellular reduced glutathione content was significantly 2.3-fold increased compared with the neurons incubated with glutamate alone. Additionally, pre-treatment of human macrophages with STW3-VI showed anti-inflammatory effects after 24 or 48 h concerning inhibition of LPS-induced TNF release by −47.3 and −53.8% (24 h) or −25.0 to −64.8% (48 h).Conclusions: Our data provide new evidence that STW3-VI protects hippocampal cells from NMDA- or glutamate-induced cytotoxicity. Moreover, our results indicate a morphological remodeling by increasing neurite outgrowth and activation of the anti-inflammatory defense by inhibition of the cytokine production in human macrophages after STW3-VI treatment. These protective, neurotrophic and anti-inflammatory properties may be beneficial in the treatment of depressive disorders.

Altered glutamate metabolism contributes to antiepileptogenic effects in the progression from focal seizure to generalized seizure by low-frequency stimulation in the ventral hippocampus.

As a promising method for treating intractable epilepsy, the inhibitory effect of low-frequency stimulation (LFS) is well known, although its mechanisms remain unclear. Excessive levels of cerebral glutamate are considered a crucial factor for epilepsy. Therefore, we designed experiments to investigate the crucial parts of the glutamate cycle. We evaluated glutamine synthetase (GS, metabolizes glutamate), glutaminase (synthesizes glutamate), and glutamic acid decarboxylase (GAD, a γ-aminobutyric acid [GABA] synthetase) in different regions of the brain, including the dentate gyrus (DG), CA3, and CA1 subregions of the hippocampus, and the cortex, using western blots, immunohistochemistry, and enzyme activity assays. Additionally, the concentrations of glutamate, GABA, and glutamine (a product of GS) were measured using high-performance liquid chromatography (HPLC) in the same subregions. The results indicated that a transiently promoted glutamate cycle was closely involved in the progression from focal to generalized seizure. Low-frequency stimulation (LFS) delivered to the ventral hippocampus had an antiepileptogenic effect in rats exposed to amygdaloid-kindling stimulation. Simultaneously, LFS could partly reverse the effects of the promoted glutamate cycle, including increased GS function, accelerated glutamate-glutamine cycling, and an unbalanced glutamate/GABA ratio, all of which were induced by amygdaloid kindling in the DG when seizures progressed to stage 4. Moreover, glutamine treatment reversed the antiepileptic effect of LFS with regard to both epileptic severity and susceptibility. Our results suggest that the effects of LFS on the glutamate cycle may contribute to the antiepileptogenic role of LFS in the progression from focal to generalized seizure.

Altered Expression of Human Mitochondrial Branched Chain Aminotransferase in Dementia with Lewy Bodies and Vascular Dementia

Cytosolic and mitochondrial human branched chain aminotransferase (hBCATc and hBCATm, respectively) play an integral role in brain glutamate metabolism. Regional increased levels of hBCATc in the CA1 and CA4 region of Alzheimer’s disease (AD) brain together with increased levels of hBCATm in frontal and temporal cortex of AD brains, suggest a role for these proteins in glutamate excitotoxicity. Glutamate toxicity is a key pathogenic feature of several neurological disorders including epilepsy associated dementia, AD, vascular dementia (VaD) and dementia with Lewy bodies (DLB). To further understand if these increases are specific to AD, the expression profiles of hBCATc and hBCATm were examined in other forms of dementia including DLB and VaD. Similar to AD, levels of hBCATm were significantly increased in the frontal and temporal cortex of VaD cases and in frontal cortex of DLB cases compared to controls, however there were no observed differences in hBCATc between groups in these areas. Moreover, multiple forms of hBCATm were observed that were particular to the disease state relative to matched controls. Real-time PCR revealed similar expression of hBCATm mRNA in frontal and temporal cortex for all cohort comparisons, whereas hBCATc mRNA expression was significantly increased in VaD cases compared to controls. Collectively our results suggest that hBCATm protein expression is significantly increased in the brains of DLB and VaD cases, similar to those reported in AD brain. These findings indicate a more global response to altered glutamate metabolism and suggest common metabolic responses that might reflect shared neurodegenerative mechanisms across several forms of dementia.

Conceptual convergence: increased inflammation is associated with increased basal ganglia glutamate in patients with major depression.

Inflammation and altered glutamate metabolism are two pathways implicated in the pathophysiology of depression. Interestingly, these pathways may be linked given that administration of inflammatory cytokines such as interferon-α to otherwise non-depressed controls increased glutamate in the basal ganglia and dorsal anterior cingulate cortex (dACC) as measured by magnetic resonance spectroscopy (MRS). Whether increased inflammation is associated with increased glutamate among patients with major depression is unknown. Accordingly, we conducted a cross-sectional study of 50 medication-free, depressed outpatients using single-voxel MRS, to measure absolute glutamate concentrations in basal ganglia and dACC. Multivoxel chemical shift imaging (CSI) was used to explore creatine-normalized measures of other metabolites in basal ganglia. Plasma and cerebrospinal fluid (CSF) inflammatory markers were assessed along with anhedonia and psychomotor speed. Increased log plasma C-reactive protein (CRP) was significantly associated with increased log left basal ganglia glutamate controlling for age, sex, race, body mass index, smoking status and depression severity. In turn, log left basal ganglia glutamate was associated with anhedonia and psychomotor slowing measured by the finger-tapping test, simple reaction time task and the Digit Symbol Substitution Task. Plasma CRP was not associated with dACC glutamate. Plasma and CSF CRP were also associated with CSI measures of basal ganglia glutamate and the glial marker myoinositol. These data indicate that increased inflammation in major depression may lead to increased glutamate in the basal ganglia in association with glial dysfunction and suggest that therapeutic strategies targeting glutamate may be preferentially effective in depressed patients with increased inflammation as measured by CRP.