Correlation between plasma levels of glutamate, alanine and serine with severity of depression

Metabolic Perturbations Associated with both PFAS Exposure and Perinatal/Antenatal Depression in Pregnant Individuals: A Meet-in-the-Middle Scoping Review

PURPOSE OF REVIEW

Depression during the perinatal or antenatal period affects at least 1 in 10 women worldwide, with long term health implications for the mother and child. Concurrently, there is increasing evidence associating maternal exposure to per- and poly-fluoroalkyl substances (PFAS) to adverse pregnancy outcomes. We reviewed the body of evidence examining both the associations between PFAS exposure and perturbations in the maternal metabolome, and the associations between the maternal metabolome and perinatal/antenatal depression. Through this, we sought to explore existing evidence of the perinatal metabolome as a potential mediation pathway linking PFAS exposure and perinatal/antenatal depression.

RECENT FINDINGS

There are few studies examining the metabolomics of PFAS exposure-specifically in pregnant women-and the metabolomics of perinatal/antenatal depression, let alone studies examining both simultaneously. Of the studies reviewed (N = 11), the majority were cross sectional, based outside of the US, and conducted on largely homogenous populations. Our review identified 23 metabolic pathways in the perinatal metabolome common to both PFAS exposure and perinatal/antenatal depression. Future studies may consider findings from our review to conduct literature-derived hypothesis testing focusing on fatty acid metabolism, alanine metabolism, glutamate metabolism, and tyrosine metabolism when exploring the biochemical mechanisms conferring the risk of perinatal/antenatal depression due to PFAS exposure. We recommend that researchers also utilize heterogenous populations, longitudinal study designs, and mediation approaches to elucidate key pathways linking PFAS exposures to perinatal/antenatal depression.

Determining of 18 amino acids in plasma of pregnant women with sleep disorders by UHPLC-MS/MS

Many pregnant women experience sleep disorders, and amino acid levels could play a crucial role in affecting maternal sleep. To explore this potential relationship, an accurate and effective UHPLC-MS/MS method has been developed to monitor 18 amino acids in the plasma samples of pregnant women. This method aims to assess how plasma amino acid levels might be linked to sleep disorders during pregnancy. Plasma samples were precipitated with acetonitrile containing 0.2% formic acid. We used 5% seralbumin as the surrogate matrix to establish quantitative curves for amino acid determination in human plasma. The method was validated in both the surrogate matrix and human plasma. The optimized UHPLC-MS/MS method was validated, showing that that the analytes had comparable recovery and negligible matrix effects in both 5% seralbumin and human plasma. The linearity, lower limit of quantification, precision, accuracy, and stability all met the acceptance criteria. The validated method was successfully applied to determination of the plasma levels of 18 amino acids in pregnant women with or without sleep disorders, indicating that alanine, lysine, tryptophan, glutamic acid, and phenylalanine levels had significant changes which may be related to sleep disorders during early pregnancy. An accurate, reliable, and efficient UHPLC-MS/MS method was successfully developed and support to find the specific amino acids as potential biomarkers for sleep disorders in pregnant women.

Adolescent male rats show altered gut microbiota composition associated with depressive-like behavior after chronic unpredictable mild stress: Differences from adult rats

Accumulating evidence reveals the metabolism and neurotransmitter systems are different in major depressive disorder (MDD) between adolescent and adult patients; however, much is still unknown from the gut microbiome perspective. To minimize confounding factors such as geographical location, ethnicity, diet, and drugs, we investigated the gut microbial differences between adolescent and adult male Sprague-Dawley rats. We exposed the adolescent rats to chronic unpredictable mild stress (CUMS) for 3 weeks and assessed their behavior using the sucrose preference test (SPT), open field test (OFT), and forced swimming test (FST). We collected and sequenced fecal samples after the behavioral tests and compared them with our previous data on adult rats. Both adolescent and adult CUMS rats exhibited reduced sucrose preference in SPT, reduced total distance in OFT, and increased immobility time in FST. Moreover, compared to their respective controls, the adolescent CUMS rats had distinct amplicon sequence variants (ASVs) mainly in the Muribaculaceae family, Bacteroidetes phylum, while the adult CUMS rats had those in the Lachnospiraceae family, Firmicutes phylum. In the adolescent group, the Muribaculaceae negatively correlated with FST and positively correlated with SPT and OFT. In the adult group, the different genera in the Lachnospiraceae showed opposite correlations with FST. Furthermore, the adolescent CUMS rats showed disrupted microbial functions, such as "Xenobiotics biodegradation and metabolism" and "Immune system", while the adult CUMS rats did not. These results confirmed the gut microbiota differences between adolescent and adult rats after CUMS modeling and provided new insight into the age-related influence on depression models.

Alzheimer Disease-Link With Major Depressive Disorder and Efficacy of Antidepressants in Modifying its Trajectory

Alzheimer disease (AD) is a devastating neurodegenerative disorder that affects millions of individuals worldwide, with no effective cure. The main symptoms include learning and memory loss, and the inability to carry out the simplest tasks, significantly affecting patients' quality of life. Over the past few years, tremendous progress has been made in research demonstrating a link between AD and major depressive disorder (MDD). Evidence suggests that MDD is commonly associated with AD and that it can serve as a precipitating factor for this disease. Antidepressants such as selective serotonin reuptake inhibitors, which are the first line of treatment for MDD, have shown great promise in the treatment of depression in AD, although their effectiveness remains controversial. The goal of this review is to summarize current knowledge regarding the association between AD, MDD, and antidepressant treatment. It first provides an overview of the interaction between AD and MDD at the level of genes, brain regions, neurotransmitter systems, and neuroinflammatory markers. The review then presents current evidence regarding the effectiveness of various antidepressants for AD-related pathophysiology and then finally discusses current limitations, challenges, and future directions.

Arginine metabolomics in mood disorders

Alterations of nitric oxide (NO) homeostasis have been described in mood disorders. However, the analytical challenges associated with the direct measurement of NO have prompted the search for alternative biomarkers of NO synthesis. We investigated the published evidence of the association between these alternative biomarkers and mood disorders (depressive disorder or bipolar disorder). Electronic databases were searched from inception to the June 30, 2023. In 20 studies, there was a trend towards significantly higher asymmetric dimethylarginine (ADMA) in mood disorders vs. controls (p = 0.072), and non-significant differences in arginine (p = 0.29), citrulline (p = 0.35), symmetric dimethylarginine (SDMA; p = 0.23), and ornithine (p = 0.42). In subgroup analyses, the SMD for ADMA was significant in bipolar disorder (p < 0.001) and European studies (p = 0.02), the SMDs for SDMA (p = 0.001) and citrulline (p = 0.038) in European studies, and the SMD for ornithine in bipolar disorder (p = 0.007), Asian (p = 0.001) and American studies (p = 0.005), and patients treated with antidepressants (p = 0.029). The abnormal concentrations of ADMA, SDMA, citrulline, and ornithine in subgroups of mood disorders, particularly bipolar disorder, warrant further research to unravel their pathophysiological role and identify novel treatments in this group (The protocol was registered in PROSPERO: CRD42023445962).

Effects of Chaihu Shugan San on Brain Functional Network Connectivity in the Hippocampus of a Perimenopausal Depression Rat Model

In this study, we used Chaihu Shugan San (CSS), a traditional Chinese herbal formula, as a probe to investigate the involvement of brain functional network connectivity and hippocampus energy metabolism in perimenopausal depression. A network pharmacology approach was performed to discover the underlying mechanisms of CSS in improving perimenopausal depression, which were verified in perimenopausal depression rat models. Network pharmacology analysis indicated that complex mechanisms of energy metabolism, neurotransmitter metabolism, inflammation, and hormone metabolic processes were closely associated with the anti-depressive effects of CSS. Thus, the serum concentrations of estradiol (E2), glutamate (Glu), and 5-hydroxytryptamine (5-HT) were detected by ELISA. The brain functional network connectivity between the hippocampus and adjacent brain regions was evaluated using resting-state functional magnetic resonance imaging (fMRI). A targeted metabolomic analysis of the hippocampal tricarboxylic acid cycle was also performed to measure the changes in hippocampal energy metabolism using liquid chromatography-tandem mass spectrometry (LC-MS/MS). CSS treatment significantly improved the behavioral performance, decreased the serum Glu levels, and increased the serum 5-HT levels of PMS + CUMS rats. The brain functional connectivity between the hippocampus and other brain regions was significantly changed by PMS + CUMS processes but improved by CSS treatment. Moreover, among the metabolites in the hippocampal tricarboxylic acid cycle, the concentrations of citrate and the upregulation of isocitrate and downregulation of guanosine triphosphate (GTP) in PMS + CUMS rats could be significantly improved by CSS treatment. A brain functional network connectivity mechanism may be involved in perimenopausal depression, wherein the hippocampal tricarboxylic acid cycle plays a vital role.

Association of Blood Metabolomics Biomarkers with Brain Metabolites and Patient-Reported Outcomes as a New Approach in Individualized Diagnosis of Schizophrenia

Given its polygenic nature, there is a need for a personalized approach to schizophrenia. The aim of the study was to select laboratory biomarkers from blood, brain imaging, and clinical assessment, with an emphasis on patients' self-report questionnaires. Metabolomics studies of serum samples from 51 patients and 45 healthy volunteers, based on the liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS/MS), led to the identification of 3 biochemical indicators (cortisol, glutamate, lactate) of schizophrenia. These metabolites were sequentially correlated with laboratory tests results, imaging results, and clinical assessment outcomes, including patient self-report outcomes. The hierarchical cluster analysis on the principal components (HCPC) was performed to identify the most homogeneous clinical groups. Significant correlations were noted between blood lactates and 11 clinical and 10 neuroimaging parameters. The increase in lactate and cortisol were significantly associated with a decrease in immunological parameters, especially with the level of reactive lymphocytes. The strongest correlations with the level of blood lactate and cortisol were demonstrated by brain glutamate, N-acetylaspartate and the concentrations of glutamate and glutamine, creatine and phosphocreatine in the prefrontal cortex. Metabolomics studies and the search for associations with brain parameters and self-reported outcomes may provide new diagnostic evidence to specific schizophrenia phenotypes.

The possible place for psychedelics in pharmacotherapy of mental disorders

Since its emergence in the 1960s, the serotonergic theory of depression bore fruit in the discovery of a plethora of antidepressant drugs affecting the lives of millions of patients. While crucial in the history of drug development, recent studies undermine the effectiveness of currently used antidepressant drugs in comparison to placebo, emphasizing the long time it takes to initiate the therapeutic response and numerous adverse effects. Thus, the scope of contemporary pharmacological research shifts from drugs affecting the serotonin system to rapid-acting antidepressant drugs. The prototypical representative of the aforementioned class is ketamine, an NMDA receptor antagonist capable of alleviating the symptoms of depression shortly after the drug administration. This discovery led to a paradigm shift, focusing on amino-acidic neurotransmitters and growth factors. Alas, the drug is not perfect, as its therapeutic effect diminishes circa 2 weeks after administration. Furthermore, it is not devoid of some severe side effects. However, there seems to be another, more efficient, and safer way to target the glutamatergic system. Hallucinogenic agonists of the 5-HT2A receptor, commonly known as psychedelics, are nowadays being reconsidered in clinical practice, shedding their infamous 1970s stigma. More and more clinical studies prove their clinical efficacy and rapid onset after a single administration while bearing fewer side effects. This review focuses on the current state-of-the-art literature and most recent clinical studies concerning the use of psychedelic drugs in the treatment of mental disorders. Specifically, the antidepressant potential of LSD, psilocybin, DMT, and 5-MeO-DMT will be discussed, together with a brief summary of other possible applications.

Protective Effects of Lacticaseibacillus rhamnosus IDCC3201 on Motor Functions and Anxiety Levels in a Chronic Stress Mouse Model

Growing evidence indicates a crucial role of the gut microbiota in physiological functions. Gut-brain axis imbalance has also been associated with neuropsychiatric and neurodegenerative disorders. Studies have suggested that probiotics regulate the stress response and alleviate mood-related symptoms. In this study, we investigated the effects of the probiotic Lacticaseibacillus rhamnosus IDCC3201 (L3201) on the behavioral response and fecal metabolite content in an unpredictable chronic mild stress (UCMS) mouse model. Our study shows that chronic stress in mice for three weeks resulted in significant changes in behavior, including lower locomotor activity, higher levels of anxiety, and depressive-like symptoms, compared to the control group. Metabolomic analysis demonstrated that disrupted fecal metabolites associated with aminoacyl-tRNA biosynthesis and valine, leucine, and isoleucine biosynthesis by UCMS were restored with the administration of L3201. Oral administration of the L3201 ameliorated the observed changes and improved the behavioral alterations along with fecal metabolites, suggesting that probiotics play a neuroprotective role.

Towards Novel Potential Molecular Targets for Antidepressant and Antipsychotic Pharmacotherapies

Depression and schizophrenia are two highly prevalent and severely debilitating neuropsychiatric disorders. Both conventional antidepressant and antipsychotic pharmacotherapies are often inefficient clinically, causing multiple side effects and serious patient compliance problems. Collectively, this calls for the development of novel drug targets for treating depressed and schizophrenic patients. Here, we discuss recent translational advances, research tools and approaches, aiming to facilitate innovative drug discovery in this field. Providing a comprehensive overview of current antidepressants and antipsychotic drugs, we also outline potential novel molecular targets for treating depression and schizophrenia. We also critically evaluate multiple translational challenges and summarize various open questions, in order to foster further integrative cross-discipline research into antidepressant and antipsychotic drug development.

Gut microbiota-based metabolites of Xiaoyao Pills (a typical Traditional Chinese medicine) ameliorate depression by inhibiting fatty acid amide hydrolase levels in brain

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicines (TCMs) are often prepared in oral dosage forms, making TCMs interact with gut microbiota after oral administration, which could affect the therapeutic effect of TCM. Xiaoyao Pills (XYPs) are a commonly used TCM in China to treat depression. The biological underpinnings, however, are still in its infancy due to its complex chemical composition.

AIM OF THE STUDY

The study aims to explore XYPs' underlying antidepressant mechanism from both in vivo and in vitro.

MATERIALS AND METHODS

XYPs were composed of 8 herbs, including the root of Bupleurum chinense DC., the root of Angelica sinensis (Oliv.) Diels, the root of Paeonia lactiflora Pall., the sclerotia of Poria cocos (Schw.) Wolf, the rhizome of Glycyrrhiza uralensis Fisch., the leaves of Mentha haplocalyx Briq., the rhizome of Atractylis lancea var. chinensis (Bunge) Kitam., and the rhizome of Zingiber officinale Roscoe, in a ratio of 5:5:5:5:4:1:5:5. The chronic unpredictable mild stress (CUMS) rat models were established. After that, the sucrose preference test (SPT) was carried out to evaluate if the rats were depressed. After 28 days of treatment, the forced swimming test and SPT were carried out to evaluate the antidepressant efficacy of XYPs. The feces, brain and plasma were taken out for 16SrRNA gene sequencing analysis, untargeted metabolomics and gut microbiota transformation analysis.

RESULTS

The results revealed multiple pathways affected by XYPs. Among them, the hydrolysis of fatty acids amide in brain decreased most significant via XYPs treatment. Moreover, the XYPs' metabolites which mainly derived from gut microbiota (benzoic acid, liquiritigenin, glycyrrhetinic acid and saikogenin D) were found in plasma and brain of CUMS rats and could inhibit the levels of FAAH in brain, which contributed to XYPs' antidepressant effect.

CONCLUSIONS

The potential antidepressant mechanism of XYPs by untargeted metabolomics combined with gut microbiota-transformation analysis was revealed, which further support the theory of gut-brain axis and provide valuable evidence of the drug discovery.

Plausible Role of Stem Cell Types for Treating and Understanding the Pathophysiology of Depression

Major Depressive Disorder (MDD), colloquially known as depression, is a debilitating condition affecting an estimated 3.8% of the population globally, of which 5.0% are adults and 5.7% are above the age of 60. MDD is differentiated from common mood changes and short-lived emotional responses due to subtle alterations in gray and white matter, including the frontal lobe, hippocampus, temporal lobe, thalamus, striatum, and amygdala. It can be detrimental to a person’s overall health if it occurs with moderate or severe intensity. It can render a person suffering terribly to perform inadequately in their personal, professional, and social lives. Depression, at its peak, can lead to suicidal thoughts and ideation. Antidepressants manage clinical depression and function by modulating the serotonin, norepinephrine, and dopamine neurotransmitter levels in the brain. Patients with MDD positively respond to antidepressants, but 10–30% do not recuperate or have a partial response accompanied by poor life quality, suicidal ideation, self-injurious behavior, and an increased relapse rate. Recent research shows that mesenchymal stem cells and iPSCs may be responsible for lowering depression by producing more neurons with increased cortical connections. This narrative review discusses the plausible functions of various stem cell types in treating and understanding depression pathophysiology.

NMDA receptors as therapeutic targets for depression treatment: Evidence from clinical to basic research

Ketamine, functioning as a channel blocker of the excitatory glutamate-gated N-methyl-d-aspartate (NMDA) receptors, displays compelling fast-acting and sustained antidepressant effects for treatment-resistant depression. Over the past decades, clinical and preclinical studies have implied that the pathology of depression is associated with dysfunction of glutamatergic transmission. In particular, the discovery of antidepressant agents modulating NMDA receptor function has prompted breakthroughs for depression treatment compared with conventional antidepressants targeting the monoaminergic system. In this review, we first summarized the signalling pathway of the ketamine-mediated antidepressant effects, based on the glutamate hypothesis of depression. Second, we reviewed the hypotheses of the synaptic mechanism and network of ketamine antidepressant effects within different brain areas and distinct subcellular localizations, including NMDA receptor antagonism on GABAergic interneurons, extrasynaptic and synaptic NMDA receptor-mediated antagonism, and ketamine blocking bursting activities in the lateral habenula. Third, we reviewed the different roles of NMDA receptor subunits in ketamine-mediated cognitive and psychiatric behaviours in genetically-manipulated rodent models. Finally, we summarized the structural basis of NMDA receptor channel blockers and discussed NMDA receptor modulators that have been reported to exert potential antidepressant effects in animal models or in clinical trials. Integrating the cutting-edge technologies of cryo-EM and artificial intelligence-based drug design (AIDD), we expect that the next generation of first-in-class rapid antidepressants targeting NMDA receptors would be an emerging direction for depression therapeutics. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

A role of GABAA receptor α1 subunit in the hippocampus for rapid-acting antidepressant-like effects of ketamine

Ketamine can produce rapid-acting antidepressant effects in treatment-resistant patients with depression. Although alterations in glutamatergic and GABAergic neurotransmission in the brain play a role in depression, the precise molecular mechanisms in these neurotransmission underlying ketamine's antidepressant actions remain largely unknown. Mice exposed to FSS (forced swimming stress) showed depression-like behavior and decreased levels of GABA (γ-aminobutyric acid), but not glutamate, in the hippocampus. Ketamine increased GABA levels and decreased glutamate levels in the hippocampus of mice exposed to FSS. There was a correlation between GABA levels and depression-like behavior. Furthermore, ketamine increased the levels of enzymes and transporters on the GABAergic neurons (SAT1, GAD67, GAD65, VGAT and GAT1) and astrocytes (EAAT2 and GAT3), without affecting the levels of enzymes and transporters (SAT2, VGluT1 and GABA_AR γ2) on glutamatergic neurons. Moreover, ketamine caused a decreased expression of GABA_AR α1 subunit, which was specifically expressed on GABAergic neurons and astrocytes, an increased GABA synthesis and metabolism in GABAergic neurons, a plasticity change in astrocytes, and an increase in ATP (adenosine triphosphate) contents. Finally, GABA_AR antagonist bicuculline or ATP exerted a rapid antidepressant-like effect whereas pretreatment with GABA_AR agonist muscimol blocked the antidepressant-like effects of ketamine. In addition, pharmacological activation and inhibition of GABA_AR modulated the synthesis and metabolism of GABA, and the plasticity of astrocytes in the hippocampus. The present data suggest that ketamine could increase GABA synthesis and astrocyte plasticity through downregulation of GABA_AR α1, increases in GABA, and conversion of GABA into ATP, resulting in a rapid-acting antidepressant-like action. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Metabolome-wide association study on physical activity

The underlying mechanisms linking physical activity to better health are not fully understood. Here we examined the associations between physical activity and small circulatory molecules, the metabolome, to highlight relevant biological pathways. We examined plasma metabolites associated with self-reported physical activity among 2217 participants from the Airwave Health Monitoring Study. Metabolic profiling was conducted using the mass spectrometry-based Metabolon platform (LC/GC-MS), measuring 828 known metabolites. We replicated our findings in an independent subset of the study (n = 2971) using untargeted LC-MS. Mendelian randomisation was carried out to investigate potential causal associations between physical activity, body mass index, and metabolites. Higher vigorous physical activity was associated (P < 0.05/828 = 6.03 × 10-5) with circulatory levels of 28 metabolites adjusted for age, sex and body mass index. The association was inverse for glutamate and diacylglycerol lipids, and direct for 3-4-hydroxyphenyllactate, phenyl lactate (PLA), alpha-hydroxy isovalerate, tiglylcarnitine, alpha-hydroxyisocaproate, 2-hydroxy-3-methylvalerate, isobutyrylcarnitine, imidazole lactate, methionine sulfone, indole lactate, plasmalogen lipids, pristanate and fumarate. In the replication panel, we found 23 untargeted LC-MS features annotated to the identified metabolites, for which we found nominal associations with the same direction of effect for three features annotated to 1-(1-enyl-palmitoyl)-2-oleoyl-GPC (P-16:0/18:1), 1-(1-enyl-palmitoyl)-2-linoleoyl-GPC (P-16:0/18:2), 1-stearoyl-2-dihomo-linolenoyl-GPC (18:0/20:3n3 or 6). Using Mendelian randomisation, we showed a potential causal relationship between body mass index and three identified metabolites. Circulatory metabolites are associated with physical activity and may play a role in mediating its health effects.

Differentially regulated targets in the fast-acting antidepressant effect of (R)-ketamine: A systems biology approach

Approximately two-thirds of patients with major depressive disorder (MDD) fail to respond to conventional antidepressants, suggesting that additional mechanisms are involved in the MDD pathophysiology. In this scenario, the glutamatergic system represents a promising therapeutic target for treatment-resistant depression. To our knowledge, this is the first study using semantic approach with systems biology to identify potential targets involved in the fast-acting antidepressant effects of ketamine and its enantiomers as well as identifying specific targets of (R)-ketamine. We performed a systematic review, followed by a semantic analysis and functional gene enrichment to identify the main biological processes involved in the therapeutic effects of these agents. Protein-protein interaction networks were constructed, and the genes exclusively regulated by (R)-ketamine were explored. We found that the regulation of α-Amino-3-Hydroxy-5-Methyl-4-Isoxazolepropionic Acid (AMPA) receptor and N-methyl-d-aspartate (NMDA) receptor subunits-Postsynaptic Protein 95 (PSD-95), Brain Derived Neurotrophic Factor (BDNF), and Tyrosine Receptor Kinase B (TrkB) are shared by the three-antidepressant agents, reinforcing the central role of the glutamatergic system and neurogenesis on its therapeutic effects. Differential regulation of Transforming Growth Factor Beta 1 (TGF-β1) receptors-Mitogen-Activated Protein Kinases (MAPK's), Receptor Activator of Nuclear Factor-Kappa Beta Ligand (RANKL), and Serotonin Transporter (SERT) seems to be particularly involved in (R)-ketamine antidepressant effects. Our data helps further studies investigating the relationship between these targets and the mechanisms of (R)-ketamine and searching for other therapeutic compounds that share the regulation of these specific biomolecules. Ultimately, this study could contribute to improve the fast management of depressive-like symptoms with less detrimental side effects than ketamine and (S)-ketamine.

The Utility of Amino Acid Metabolites in the Diagnosis of Major Depressive Disorder and Correlations with Depression Severity

Major depressive disorder (MDD) is a highly prevalent and disabling condition with a high disease burden. There are currently no validated biomarkers for the diagnosis and treatment of MDD. This study assessed serum amino acid metabolite changes between MDD patients and healthy controls (HCs) and their association with disease severity and diagnostic utility. In total, 70 MDD patients and 70 HCs matched in age, gender, and ethnicity were recruited for the study. For amino acid profiling, serum samples were analysed and quantified by liquid chromatography-mass spectrometry (LC-MS). Receiver-operating characteristic (ROC) curves were used to classify putative candidate biomarkers. MDD patients had significantly higher serum levels of glutamic acid, aspartic acid and glycine but lower levels of 3-Hydroxykynurenine; glutamic acid and phenylalanine levels also correlated with depression severity. Combining these four metabolites allowed for accurate discrimination of MDD patients and HCs, with 65.7% of depressed patients and 62.9% of HCs correctly classified. Glutamic acid, aspartic acid, glycine and 3-Hydroxykynurenine may serve as potential diagnostic biomarkers, whereas glutamic acid and phenylalanine may be markers for depression severity. To elucidate the association between these indicators and clinical features, it is necessary to conduct additional studies with larger sample sizes that involve a spectrum of depressive symptomatology.

Pharmacological and Physiological Correlates of the Bidirectional Fear Phenotype of the Carioca Rats and Other Bidirectionally Selected Lines

The Carioca rat lines originated from the selective bidirectional breeding of mates displaying extreme defense responses to contextual conditioned fear. After three generations, two distinct populations could be distinguished: the Carioca High- and Low-conditioned Freezing rats, CHF, and CLF, respectively. Later studies identified strong anxiety-like behaviors in the CHF line, while indications of impulsivity and hyperactivity were prominent in the CLF animals. The present review details the physiological and pharmacological-related findings obtained from these lines. The results discussed here point towards a dysfunctional fear circuitry in CHF rats, including alterations in key brain structures and the serotoninergic system. Moreover, data from these animals highlight important alterations in the stress-processing machinery and its associated systems, such as energy metabolism and antioxidative defense. Finally, evidence of an alteration in the dopaminergic pathway in CLF rats is also debated. Thus, accumulating data gathered over the years, place the Carioca lines as significant animal models for the study of psychiatric disorders, especially fear-related ones like anxiety.

Gut microbiome-wide association study of depressive symptoms

Depression is one of the most poorly understood diseases due to its elusive pathogenesis. There is an urgency to identify molecular and biological mechanisms underlying depression and the gut microbiome is a novel area of interest. Here we investigate the relation of fecal microbiome diversity and composition with depressive symptoms in 1,054 participants from the Rotterdam Study cohort and validate these findings in the Amsterdam HELIUS cohort in 1,539 subjects. We identify association of thirteen microbial taxa, including genera Eggerthella, Subdoligranulum, Coprococcus, Sellimonas, Lachnoclostridium, Hungatella, Ruminococcaceae (UCG002, UCG003 and UCG005), LachnospiraceaeUCG001, Eubacterium ventriosum and Ruminococcusgauvreauiigroup, and family Ruminococcaceae with depressive symptoms. These bacteria are known to be involved in the synthesis of glutamate, butyrate, serotonin and gamma amino butyric acid (GABA), which are key neurotransmitters for depression. Our study suggests that the gut microbiome composition may play a key role in depression.

Are mGluR2/3 Inhibitors Potential Compounds for Novel Antidepressants?

Depression is the most common mental illness characterized by anhedonia, avolition and loss of appetite and motivation. The majority of conventional antidepressants are monoaminergic system selective inhibitors, yet the efficacies are not sufficient. Up to 30% of depressed patients are resistant to treatment with available antidepressants, underscoring the urgent need for development of novel therapeutics to meet clinical needs. Recent years, compounds acting on the glutamate system have attracted wide attention because of their strong, rapid and sustained antidepressant effects. Among them, selective inhibitors of metabotropic glutamate receptors 2 and 3 (mGluR2/3) have shown robust antidepressant benefits with fewer side-effects in both preclinical and clinical studies. Thus, we here attempt to summarize the antidepressant effects and underlying mechanisms of these inhibitors revealed in recent years as well as analyze the potential value of mGluR2/3 selective inhibitors in the treatment of depression.

Exploration for biomarkers of postpartum depression based on metabolomics: A systematic review

BACKGROUND

Postpartum depression (PPD) is the most frequent psychiatric complication during the postnatal period and its mechanisms are not fully understood. Metabolomics, can quantitatively measure metabolites in a high-throughput method, and thus uncover the underlying pathophysiology of disease.

OBJECTIVES

In this study, we reviewed metabolomics studies conducted on PPD, aiming to understand the changes of metabolites in PPD patients and analyze the potential application of metabolomics in PPD prediction and diagnosis.

METHODS

Relevant articles were searched in PubMed, Google scholar, and Web of Science databases from January 2011 to July 2022. The metabolites involved were systematically examined and compared. MetaboAnalyst online software was applied to analyze metabolic pathways.

RESULTS

A total of 14 papers were included in this study. There were several highly reported metabolites, such as kynurenine, kynurenic acid, and eicosapentaenoic acid. Dysregulation of metabolic pathways involved amino acids metabolism, fatty acids metabolism, and steroids metabolism.

LIMITATIONS

The included studies are relatively inadequate, and further work is needed.

CONCLUSIONS

This study summarized significant metabolic alterations that provided clues for the prediction, diagnosis, and pathogenesis of PPD.

Possible involvement of NO-cGMP signaling in the antidepressant like Effect of Amantadine in mice

In the present study, antidepressant like effect of amantadine was studied in mice using tail suspension test (TST) and forced swim test (FST). Further the effect of amantadine treatment on the brain nitrite, glutamate and serotonin levels was also determined. Amantadine (AMT) (50, 100 and 150 mg/kg, i.p.) was administered to the mice and after 30 min of administration the mice were subjected to TST and FST. It was observed that the administration of AMT (100 and 150 mg/kg, i.p.) decreased the immobility period of mice in TST and FST significantly as compared to control. The findings from the whole brain neurochemical assay suggested that the AMT (100 and 150 mg/kg, i.p.) treatment decreased the brain nitrite and glutamate level but increased the brain serotonin significantly as compared to control. Further the influence of NO-cGMP signaling in the antidepressant like effect of amantadine was also determined. It was observed that the NO donor (i.e. L-Arginine (50 mg/kg, i.p.)) potentiated the effect elicited by AMT (50 mg/kg, i.p.) in FST and decreased the brain serotonin level of AMT (50 mg/kg, i.p.) treated mice. Further the pretreatment of cGMP modulator (i.e. Sildenafil (1 mg/kg, i.p.)) potentiated the behavioral effect elicited by AMT (50 mg/kg, i.p.) in TST and FST and decreased the brain nitrite and glutamate level of AMT (50 mg/kg, i.p.) treated mice. In conclusion, amantadine exerted antidepressant like effect in mice and NO-cGMP signaling influences the antidepressant like effect of amantadine in mice.

Therapeutic effect of fecal microbiota transplantation on chronic unpredictable mild stress-induced depression

Background and objective

Depression is a complex neuropsychiatric disease with extensive morbidity. Its pathogenesis remains unclear, and it is associated with extremely low rates of cure and complete remission. It is vital to study the pathogenesis of depression to develop effective treatments. This study aimed to explore the therapeutic effects and mechanisms of fecal microbiota transplantation (FMT) for the treatment of depression in rats.

Methods

Thirty Sprague-Dawley (SD) rats were randomly divided into three groups: control, chronic unpredictable mild stress (CUMS) to model depression, and CUMS+FMT. For the CUMS and CUMS+FMT groups, after CUMS intervention (four weeks), the rats were given normal saline or FMT (once/week for three weeks), respectively. Behavior, colonic motility, 16S rDNA amplicon sequencing, and untargeted metabolomics on fecal samples were compared between the three rat groups. The following markers were analyzed: 5-hydroxytryptamine (5-HT), gamma-aminobutyric acid (GABA), glutamate (Glu), and brain-derived neurotrophic factor (BDNF) levels in the hippocampus; glucagon-like peptide 1 (GLP-1), lipopolysaccharide (LPS), and interleukin (IL)-6 levels in the serum; and GLP-1, GLP-1 receptor (GLP-1R), and serotonin 4 receptor (5-HT₄R) levels in colonic tissues.

Results

FMT improved symptoms of depression and colonic motility in rats exposed to CUMS. The expression levels of 5-HT, GABA, BDNF, and other biochemical indices, significantly differed among the three groups. Meanwhile, the intestinal microbiota in the CUMS+FMT group was more similar to that of the control group with a total of 13 different fecal metabolites.

Conclusion

FMT exerted antidepressant effects on CUMS-induced depression in rats, and the mechanism involved various neurotransmitters, inflammatory factors, neurotrophic factors, and glucagon-like peptides.

The influence of a tomato food matrix on the bioavailability and plasma kinetics of oral gamma-aminobutyric acid (GABA) and its precursor glutamate in healthy men

Gamma-aminobutyric acid (GABA) and its precursor glutamate play signaling roles in a range of tissues. Both function as neurotransmitters in the central nervous system, but they also modulate pancreatic and immune functioning, for example. Besides endogenous production, both compounds are found in food products, reaching relatively high levels in tomatoes. Recent studies in rodents suggest beneficial effects of oral GABA on glucose homeostasis and blood pressure. However, the bioavailability from food remains unknown. We studied the bioavailability of GABA and glutamate from tomatoes relative to a solution in water. After a fasting blood sample was taken, eleven healthy men randomly received 1 liter of 4 different drinks in a cross-over design with a one-week interval. The drinks were a solution of 888 mg L^-1 GABA, a solution of 3673 mg L^-1 glutamate, pureed fresh tomatoes and plain water as the control. Following intake, 18 blood samples were taken at intervals for 24 hours. Plasma GABA and glutamate concentrations were determined by ultra-pressure liquid chromatography coupled with tandem mass spectrometry (UPLC-MS/MS). Fasting plasma GABA and glutamate concentrations were found to be 16.71 (SD 2.18) ng mL^-1 and 4626 (SD 1666) ng mL^-1, respectively. Fasting GABA levels were constant (5.8 CV%) between individuals, while fasting glutamate levels varied considerably (23.5 CV%). GABA from pureed tomatoes showed similar bioavailability to that of a solution in water. For glutamate, the absorption from pureed tomatoes occurred more slowly as seen from a longer t_max (0.98 ± 0.14 h vs. 0.41 ± 0.04 h, P = 0.003) and lower C_max (7815 ± 627 ng mL^-1vs. 16 420 ± 2778 ng mL^-1, P = 0.006). These data suggest that GABA is bioavailable from tomatoes, and that food products containing GABA could potentially induce health effects similar to those claimed for GABA supplements. The results merit further studies on the bioavailability of GABA from other food products and the health effects of GABA-rich diets. The clinical trial registry number is NCT04086108 (https://clinicaltrials.gov/ct2/show/NCT04303468).

Dysregulation of adult hippocampal neuroplasticity in major depression: pathogenesis and therapeutic implications

Major depressive disorder (MDD) was previously hypothesized to be a disease of monoamine deficiency in which low levels of monoamines in the synaptic cleft were believed to underlie depressive symptoms. More recently, however, there has been a paradigm shift toward a neuroplasticity hypothesis of depression in which downstream effects of antidepressants, such as increased neurogenesis, contribute to improvements in cognition and mood. This review takes a top-down approach to assess how changes in behavior and hippocampal-dependent circuits may be attributed to abnormalities at the molecular, structural, and synaptic level. We conclude with a discussion of how antidepressant treatments share a common effect in modulating neuroplasticity and consider outstanding questions and future perspectives.

Glutamate Efflux across the Blood–Brain Barrier: New Perspectives on the Relationship between Depression and the Glutamatergic System

Depression is a significant cause of disability and affects millions worldwide; however, antidepressant therapies often fail or are inadequate. Current medications for treating major depressive disorder can take weeks or months to reach efficacy, have troubling side effects, and are limited in their long-term capabilities. Recent studies have identified a new set of glutamate-based approaches, such as blood glutamate scavengers, which have the potential to provide alternatives to traditional antidepressants. In this review, we hypothesize as to the involvement of the glutamate system in the development of depression. We identify the mechanisms underlying glutamate dysregulation, offering new perspectives on the therapeutic modalities of depression with a focus on its relationship to blood–brain barrier (BBB) permeability. Ultimately, we conclude that in diseases with impaired BBB permeability, such as depression following stroke or traumatic brain injury, or in neurogenerative diseases, the glutamate system should be considered as a pathway to treatment. We propose that drugs such as blood glutamate scavengers should be further studied for treatment of these conditions.

Plasma Amino Acid Concentrations in Patients with Alcohol and/or Cocaine Use Disorders and Their Association with Psychiatric Comorbidity and Sex

(1) Background: Co-occurrence of mental and substance use disorders (SUD) is prevalent, but complicates their clinical courses, and specific biomarkers are required. Amino acids are altered in primary mental disorders; however, little is known about SUD and psychiatric comorbidity. Because most psychiatric disorders and biomarkers show sex differences, we investigated amino acids in men and women with alcohol and/or cocaine use disorders (AUD and/or CUD) and psychiatric comorbidity. (2) Methods: A cross-sectional study was conducted in 295 participants, who were divided into four groups (AUD, n = 60; CUD, n = 41; AUD + CUD, n = 64; and control, n = 130). Participants were clinically assessed, and plasma amino acid concentrations were analyzed in relation to sex, diagnosis of SUD and psychiatric comorbidity (3) Results: In the total sample, there were sex differences, and women showed lower Iso, Leu, Gln and Glu than men. While patients with CUD and AUD + CUD had higher Glu, Gly, Orn and Ser than controls, patients with AUD showed no differences. In SUD, patients with psychiatric comorbidity had lower Orn and higher Ala than non-comorbid patients in the AUD group. (4) Conclusions: There was a dysregulation of plasma amino acids in abstinent patients with SUD. However, our results suggest the importance of considering the clinical characteristics and sex in the validity of amino acids as potential biomarkers for SUD.

A Preliminary Nuclear Magnetic Resonance Metabolomics Study Identifies Metabolites that Could Serve as Diagnostic Markers of Major Depressive Disorder

BACKGROUND

The evaluation of metabolites that are directly involved in the physiological process, few steps short of phenotypical manifestation, remains vital for unravelling the biological moieties involved in the development of the (MDD) and in predicting its treatment outcome.

METHODOLOGY

Eight (8) urine and serum samples each obtained from consenting healthy controls (HC), twenty-five (25) urine and serum samples each from first episode treatment naïve MDD (TNMDD) patients, and twenty (22) urine and serum samples each s from treatment naïve MDD patients 2 weeks after SSRI treatment (TWMDD) were analysed for metabolites using proton nuclear magnetic resonance (1HNMR) spectroscopy. The evaluation of patients' samples was carried out using Partial Least Squares Discriminant Analysis (PLS-DA) and Orthogonal Partial Least Square- Discriminant Analysis (OPLSDA) models.

RESULTS

In the serum, decreased levels of lactate, glucose, glutamine, creatinine, acetate, valine, alanine, and fatty acid and an increased level of acetone and choline in TNMDD or TWMDD irrespective of whether an OPLSDA or PLSDA evaluation was used were identified. A test for statistical validations of these models was successful.

CONCLUSION

Only some changes in serum metabolite levels between HC and TNMDD identified in this study have potential values in the diagnosis of MDD. These changes included decreased levels of lactate, glutamine, creatinine, valine, alanine, and fatty acid, as well as an increased level of acetone and choline in TNMDD. The diagnostic value of these changes in metabolites was maintained in samples from TWMDD patients, thus reaffirming the diagnostic nature of these metabolites for MDD.

The comparison of nucleotide metabolites and amino acids patterns in patients with eating disorders, with and without symptoms of depression

Purines, pyrimidines, and amino acid level have gained attention recently as potential determinants of mental disorders. However, eating disorders patients (ED) have not been yet appropriately studied, especially subjects with coexisting mood disorders. This paper examines the serum level of nucleotide catabolites and plasma amino acids in eating disorders with hyperphagia, with and without Major Depressive Disorder (MDD). Samples were taken from adult persons suffering from eating disorders (two forms: simple obesity and binge eating disorder) with MDD (n = 20) and without (n = 17). Serum nucleotides and plasma amino acids concentrations were analyzed with high-performance liquid chromatography-mass spectrometry. The nucleotides metabolite in MDD patients had a significantly (p < 0.05) lower uridine. Among MDD patients with ED significantly (p < 0.05) higher levels of asparagine, glutamine, proline, and arginine were found as compared to the control group. This study demonstrated differences in nucleotide metabolite and amino acid pattern in depression patients with eating disorders. This may be relevant to the mechanisms and may help identify biomarkers.

Blood Glutamate Scavenging With Pyruvate as a Novel Preventative and Therapeutic Approach for Depressive-Like Behavior Following Traumatic Brain Injury in a Rat Model

Depression is a common and serious complication following traumatic brain injury (TBI). Both depression and TBI have independently been associated with pathologically elevated extracellular brain glutamate levels. In the setting of TBI, blood glutamate scavenging with pyruvate has been widely shown as an effective method to provide neuroprotection by reducing blood glutamate and subsequent brain glutamate levels. Here we evaluate pyruvate as a novel approach in the treatment and prevention of post-TBI depression-like behavior in a rat model. Rats were divided into five groups: (1) sham-operated control with pyruvate, (2) sham-operated control with placebo, (3) post-TBI with placebo, (4) post-TBI given preventative pyruvate, and (5) post-TBI treated with pyruvate. These groups had an equal number of females and males. Rats were assessed for depressive-like behavior, neurological status, and glutamate levels in the blood and brain. Post-TBI neurological deficits with concurrent elevations in glutamate levels were demonstrated, with peak glutamate levels 24 h after TBI. Following TBI, the administration of either prophylactic or therapeutic pyruvate led to reduced glutamate levels, improved neurologic recovery, and improved depressive-like behavior. Glutamate scavenging with pyruvate may be an effective prophylactic and therapeutic option for post-TBI depression by reducing associated elevations in brain glutamate levels.

Effect of Coriander Plants on Human Emotions, Brain Electrophysiology, and Salivary Secretion

Simple Summary

This research aims to investigate the effects of coriander plants on human emotions and physiological activities. The results showed coriander plants could significantly reduce the angry sub-scores, alpha amylase and amino acids (arginine, proline, histidine, and taurine) concentrations in saliva. Theta (4–8 Hz) band activity of the cerebral cortex was significantly enhanced. Moreover, taurine significantly positively correlated with anger and negatively correlated with vigor. All the results signified that coriander plant could influence the activity of brain electrophysiological and salivary secretion through its VOCs to improve people’s negative emotions. This study will provide a theoretical basis for the living coriander plants have some therapeutic effect on the human psychological state.

Abstract

Coriander is a popular herb with versatile applications. However, the current research about coriander medicinal values have been mainly focusing on its extracts while lacking in the relationship between living coriander plants and emotion. Therefore, this study aims to investigate the effects of coriander plants on human emotions and physiological activities. The results showed that the main Volatile organic compounds (VOCs) of coriander plants were 2-ethyl-1-hexanol, d-limonene, eucalyptol, benzyl alcohol, Isophorone, dimethyl glutarate, α-terpineol, styrene, methyl methacrylate, α-pinene. Coriander plants could significantly reduce the angry sub-scores, alpha amylase and amino acids (arginine, proline, histidine, and taurine) concentrations in saliva. Theta (4–8 Hz) band activity of the cerebral cortex was significantly enhanced. Moreover, taurine significantly positively correlated with anger and negatively correlated with vigor. All the results signified that coriander plant could influence the activity of brain electrophysiological and salivary secretion through its VOCs to improve people’s negative emotions.

Prospective study on the association between serum amino acid profiles and depressive symptoms among the Japanese working population

Objective

Accumulating evidence suggests that amino acids, particularly tryptophan and glutamate, play an important role in the pathology of depression, but prospective epidemiologic data on this issue is scarce. We examined the association between circulating amino acids and the risk of depressive symptoms in a Japanese working population.

Methods

Participants were 841 workers who were free from depressive symptoms and provided blood at baseline and completed 3-yr follow-up survey. 30 varieties of amino acid concentrations in serum were measured using liquid chromatography/mass spectrometry. Depressive symptoms were defined using the Center for Epidemiologic Studies Depression Scale. Logistic regression was used to calculate the odds ratios of depressive symptoms according to serum amino acids with adjustment for lifestyle factors.

Results

A total of 151 (18.0%) workers were newly identified as having depressive symptoms at the follow-up. Baseline tryptophan and glutamate concentrations in serum were not appreciably associated with the risk of depressive symptoms. Risk of depressive symptoms tended to increase with increasing arginine concentrations; the multivariable-adjusted odds ratio for the highest versus lowest tertile of serum arginine was 1.65 (95% confidence interval: 0.96–2.83; P for trend = 0.07). No clear association was found for other amino acids.

Conclusions

Results of the present study do not support a significant role of circulating amino acids in the development of depressive symptoms among Japanese.

Metabolomics-based discrimination of patients with remitted depression from healthy controls using 1H-NMR spectroscopy

The aim of the study was to investigate differences in metabolic profiles between patients with major depressive disorder (MDD) with full remission (FR) and healthy controls (HCs). A total of 119 age-matched MDD patients with FR (n = 47) and HCs (n = 72) were enrolled and randomly split into training and testing sets. A 1H-nuclear magnetic resonance (NMR) spectroscopy-based metabolomics approach was used to identify differences in expressions of plasma metabolite biomarkers. Eight metabolites, including histidine, succinic acid, proline, acetic acid, creatine, glutamine, glycine, and pyruvic acid, were significantly differentially-expressed in the MDD patients with FR in comparison with the HCs. Metabolic pathway analysis revealed that pyruvate metabolism via the tricarboxylic acid cycle linked to amino acid metabolism was significantly associated with the MDD patients with FR. An algorithm based on these metabolites employing a linear support vector machine differentiated the MDD patients with FR from the HCs with a predictive accuracy, sensitivity, and specificity of nearly 0.85. A metabolomics-based approach could effectively differentiate MDD patients with FR from HCs. Metabolomic signatures might exist long-term in MDD patients, with metabolic impacts on physical health even in patients with FR.

Fecal Microbial and Metabolomic Change during treatment course for depression: An Observational Study

BACKGROUND

There is growing evidence regarding the connection between alterations in gut microbiota and their metabolites in patients with depressive disorders, suggesting a potential role in pathophysiology. Our study aimed to investigate the relationship between microbial, metabolomic features and the course of treatment for depression in a real-world clinical setting.

METHODS

Patients diagnosed with depressive disorders were recruited, and their stool was collected at three time points during their depression treatments. Patients were divided into three groups: non-responders, responders, and stable remitters. Gut microbiomes were analyzed using 16S rRNA gene sequencing, and gut metabolomes were analyzed by a mass spectrometry approach. Microbiomes/metabolomes were compared between groups cross-sectionally and longitudinally.

RESULTS

A total of 33 patients were recruited and divided into non-responders (n = 16), responders (n = 11), and stable remitters (n = 6). Non-responders presented lower alpha diversity in the Phylogenic Diversity index compared to responders during the treatment course (p = 0.003). Non-responders presented increased estimated glutamate synthesis functions by the microbiota compared to responders and stable remitters (p = 0.035). There were no specific microbiota or metabolome that differentiated the three groups.

LIMITATIONS

Small sample size with no healthy controls.

CONCLUSIONS

Our results indicate that both cross-sectional microbial features and longitudinal microbial transitions are different depending on the treatment course of depression. Controlled studies, as well as animal studies, are needed in the future to elucidate the causal relationship between microbiota and depression.

Glutamate and depression: Reflecting a deepening knowledge of the gut and brain effects of a ubiquitous molecule

The versatility of glutamate as the brain’s foremost excitatory neurotransmitter and modulator of neurotransmission and function is considered common knowledge. Years of research have continued to uncover glutamate’s effects and roles in several neurological and neuropsychiatric disorders, including depression. It had been considered that a deeper understanding of the roles of glutamate in depression might open a new door to understanding the pathological basis of the disorder, improve the approach to patient management, and lead to the development of newer drugs that may benefit more patients. This review examines our current understanding of the roles of endogenous and exogenous sources of glutamate and the glutamatergic system in the aetiology, progression and management of depression. It also examines the relationships that link the gut-brain axis, glutamate and depression; as it emphasizes how the gut-brain axis could impact depression pathogenesis and management via changes in glutamate homeostasis. Finally, we consider what the likely future of glutamate-based therapies and glutamate-based therapeutic manipulations in depression are, and if with them, we are now on the final chapter of understanding the neurochemical milieu of depressive disorders.

Novel rapid-acting glutamatergic modulators: Targeting the synaptic plasticity in depression

Major depressive disorder (MDD) is severely prevalent, and conventional monoaminergic antidepressants gradually exhibit low therapeutic efficiency, especially for patients with treatment-resistant depression. A neuroplasticity hypothesis is an emerging advancement in the mechanism of depression, mainly expressed in the glutamate system, e.g., glutamate receptors and signaling. Dysfunctional glutamatergic neurotransmission is currently considered to be closely associated with the pathophysiology of MDD. Biological function, pharmacological action, and signal attributes in the glutamate system both regulate the neural process. Specific functional subunits could be therapeutic targets to explore the novel glutamatergic modulators, which have fast-acting, and relatively sustained antidepressant effects. Here, the present review summarizes the pathophysiology of MDD found in the glutamate system, exploring the role of glutamate receptors and their downstream effects. These convergent mechanisms have prompted the development of other modulators targeting on glutamate system, including N-methyl-d-aspartate receptor antagonists, selective GluN2B-specific antagonists, glycine binding site agents, and regulators of metabotropic glutamate receptors. Relevant researches underly the putative mechanisms of these drugs, which reverse the damage of depression by regulating glutamatergic neurotransmission. It also provides further insight into the mechanism of depression and exploring potential targets for novel agent development.

Disrupting the α7nAChR-NR2A protein complex exerts antidepressant-like effects

Major depressive disorder (MDD) is associated with significant morbidity and mortality. Most antidepressant medications target the serotonin and norepinephrine transporters, but a significant minority of patients do not respond to treatment and novel therapeutic targets are needed. We previously identified a protein complex composed of the α7 nicotinic acetylcholine receptor (nAChR) and NMDA glutamate receptors (NMDARs), through which α7nAChR upregulates NMDAR function. Disruption of the α7nAChR-NMDAR complex with an interfering peptide blocked α7nAChR-mediated upregulation of NMDAR function and cue-induced reinstatement of nicotine seeking in rat models of relapse. Here we report that disrupting the α7nAChR-NMDAR complex with the interfering peptide also has antidepressant-like effects in the forced swim test (FST), a common rat behaviour screening test for antidepressant effects. Furthermore, the interfering peptide significantly increases extracellular signal-regulated kinase (ERK) activity in the animals subjected to the FST. Our results provide a novel potential therapeutic target for the development of new antidepressant medications.

Targeting metabotropic glutamate receptors for the treatment of depression and other stress-related disorders

The discovery of robust antidepressant effects of ketamine in refractory patients has led to increasing focus on agents targeting glutamatergic signaling as potential novel antidepressant strategy. Among the agents targeting the glutamatergic system, compounds acting at metabotropic glutamate (mGlu) receptors are among the most promising agents under studies for depressive disorders. Further, the receptor diversity, distinct distribution in the CNS, and ability to modulate the glutamatergic neurotransmission in the brain areas implicated in mood disorders make them an exciting target for stress-related disorders. In preclinical models, antidepressant and anxiolytic effects of mGlu₅ negative allosteric modulators (NAMs) have been reported. Interestingly, mGlu_2/3 receptor antagonists show fast and sustained antidepressant-like effects similar to that of ketamine in rodents. Excitingly, they can also induce antidepressant effects in the animal models of treatment-resistant depression and are devoid of the side-effects associated with ketamine. Unfortunately, clinical trials of both mGlu₅ and mGlu_2/3 receptor NAMs have been inconclusive, and additional trials using other compounds with suitable preclinical and clinical properties are needed. Although group III mGlu receptors have gained less attention, mGlu₇ receptor ligands have been shown to induce antidepressant-like effects in rodents. Collectively, compounds targeting mGlu receptors provide an alternative approach to fill the outstanding clinical need for safer and more efficacious antidepressants. This article is part of the special Issue on "Glutamate Receptors - mGluRs".

The role of the excitation:inhibition functional balance in the mPFC in the onset of antidepressants

Currently available antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs), generally require weeks to months to produce a therapeutic response, but the mechanism of action underlying the delayed onset of antidepressant-like action remains to be elucidated. The balance between excitatory glutamatergic pyramidal neurons and inhibitory γ-aminobutyric acid (GABA) interneurons, i.e., the excitation:inhibition functional (E:I) balance, in the medial prefrontal cortex (mPFC) is critical in regulating several behaviors and might play an important mediating role in the mechanism of rapid antidepressant-like action reported by several studies. In the present study, the multichannel electrophysiological technique was used to record the firing activities of pyramidal neurons and interneurons and investigate the effects of a single dose of fluoxetine and ketamine (both 10 mg/kg, i.p.) on the E:I functional balance in the rat mPFC after 90 min or 24 h, and the forced swimming test (FST) was used to evaluate the antidepressant-like effects of fluoxetine and ketamine. The present study also explored the effects of chronic treatment with fluoxetine (10 mg/kg, i.g.) for 7 d or 21 d on the E:I functional balance in the mPFC. The present results suggested that a single dose of ketamine could both significantly increase the firing activities of pyramidal neurons and significantly decrease the firing activities of interneurons in the mPFC and exerted significant antidepressant-like action on the FST after 90 min and 24 h, but fluoxetine had no such effects under the same conditions. However, chronic treatment with fluoxetine for 21 d (but not 7 d) could significantly affect the firing activities of pyramidal neurons and interneurons in the mPFC. Taken together, the present results indicated that rapid regulation of the E:I functional balance in the mPFC might be an important common mechanism of rapid-acting antidepressants and the delayed onset of SSRIs might be partly attributed to their inability to rapidly regulate the E:I functional balance in the mPFC. The present study provided a new entry point to the development of rapid-acting antidepressants.

Genetic Variations of Ionotropic Glutamate Receptor Pathways on Interferon-α-induced Depression in Patients with Hepatitis C Viral Infection

IMPORTANCE

The most supportive evidence of the inflammation theory of depression is that up to one-third of patients with Hepatitis C virus infection (HCV) develop clinical depressive episodes during interferon-α (IFN-α) therapy. As glutamate-mediated excitotoxicity has been found to be a consequence of excessive inflammation and a pathogenic mechanism of depression, it is plausible to investigate genes on ionotropic glutamate receptor pathways.

OBJECTIVE

To identify the at-risk genetic variations on ionotropic glutamate receptor pathways for interferon-α-induced depression.

METHOD

We assessed 291 patients with chronic HCV undergoing IFN-α therapy and analyzed the single nucleotide polymorphisms (SNPs) in genes related to ionotropic glutamate receptors in this prospective case-control study. Patients who developed IFN-α-induced depression anytime during the treatment were defined as the case group, while those who did not were defined as the control group. Genomic DNA was extracted from peripheral blood and analyzed by Affymetrix TWB array. Allelic and haplotype association tests were conducted using χ2 tests to assess the difference in allele and haplotype frequencies between cases and controls. Additionally, we performed 5000 permutations to control gene-wide family-wise error rates and create empirical p-values. Stratified analyses were then done to control for confounders and adjust odds ratios for our significant SNPs. We also did an additional stratified analysis to re-assess genes with near-significant SNPs (empirical p-value=0.05-0.10), employing Bonferroni correction with the effective number of independent tests to control gene-wide family-wise error rates.

RESULTS

The minor and major allele frequencies of rs7542 (empirical p-value=0.0310) in MAPK3, rs3026685 (empirical p-value=0.0378) in PICK1, rs56005409 (empirical p-value=0.0332) in PRKCA, rs12914792 (empirical p-value=0.0096), rs17245773 (empirical p-value=0.0340) in RASGRF1, and rs78387863 (empirical p-value=0.0086), rs74365480 (empirical p-value=0.0200) in RASGRF2 were found significantly different between cases and controls. Haplotype association tests also revealed one significant haplotype in PRKCA (empirical p-value=0.0200) and one in RASGRF1 (empirical p-value=0.0048). Stratified analyses showed no signs of confounders for most of our significant SNPs, except for rs78387863 in RASGRF2. After a re-assessment of our near-significant genes by stratified analyses, two SNPs in GRIN2B turned significant.

CONCLUSIONS

This study provided supportive evidence of the involvement of the RAS/RAF/mitogen-activated protein kinase (MAPK) signaling pathway and glutamate ionotropic receptor AMPA type subunit 2(GluR2) transportation in the pathogenesis of IFN-α-induced depression.

Modulation of DNA Methylation and Gene Expression in Rodent Cortical Neuroplasticity Pathways Exerts Rapid Antidepressant-Like Effects

BACKGROUND

Stress increases DNA methylation, primarily a suppressive epigenetic mechanism catalyzed by DNA methyltransferases (DNMT), and decreases the expression of genes involved in neuronal plasticity and mood regulation. Despite chronic antidepressant treatment decreases stress-induced DNA methylation, it is not known whether inhibition of DNMT would convey rapid antidepressant-like effects.

AIM

This work tested such a hypothesis and evaluated whether a behavioral effect induced by DNMT inhibitors (DNMTi) corresponds with changes in DNA methylation and transcript levels in genes consistently associated with the neurobiology of depression and synaptic plasticity (BDNF, TrkB, 5-HT1A, NMDA, and AMPA).

METHODS

Male Wistar rats received intraperitoneal (i.p.) injection of two pharmacologically different DNMTi (5-AzaD 0.2 and 0.6 mg/kg or RG108 0.6 mg/kg) or vehicle (1 ml/kg), 1 h or 7 days before the learned helplessness test (LH). DNA methylation in target genes and the correspondent transcript levels were measured in the hippocampus (HPC) and prefrontal cortex (PFC) using meDIP-qPCR. In parallel separate groups, the antidepressant-like effect of 5-AzaD and RG108 was investigated in the forced swimming test (FST). The involvement of cortical BDNF-TrkB-mTOR pathways was assessed by intra-ventral medial PFC (vmPFC) injections of rapamycin (mTOR inhibitor), K252a (TrkB receptor antagonist), or vehicle (0.2 μl/side).

RESULTS

We found that both 5-AzaD and RG108 acutely and 7 days before the test decreased escape failures in the LH. LH stress increased DNA methylation and decreased transcript levels of BDNF IV and TrkB in the PFC, effects that were not significantly attenuated by RG108 treatment. The systemic administration of 5-AzaD (0.2 mg/kg) and RG108 (0.2 mg/kg) induced an antidepressant-like effect in FST, which was, however, attenuated by TrkB and mTOR inhibition into the vmPFC.

CONCLUSION

These findings suggest that acute inhibition of stress-induced DNA methylation promotes rapid and sustained antidepressant effects associated with increased BDNF-TrkB-mTOR signaling in the PFC.

Platelet-derived growth factor BB: A potential diagnostic blood biomarker for differentiating bipolar disorder from major depressive disorder

Bipolar disorder (BD) is frequently misdiagnosed as major depressive disorder (MDD) due to overlapping depressive symptoms. This study investigated whether serum platelet-derived growth factor BB (PDGF-BB) is a differential diagnostic biomarker for BD and MDD. An initial SOMAscan proteomics assay of 1311 proteins in small samples from patients with BD and MDD and healthy controls (HCs) suggested that serum levels of PDGF-BB differed between BD and MDD. We then conducted a two-step, exploratory, cross-sectional, case-control study at our institute and five sites that included a total of 549 participants (157 with BD, 144 with MDD, and 248 HCs). Clinical symptoms were assessed using the Hamilton Depression Rating Scale and the Young Mania Rating Scale. In the initial analysis at our institute, serum PDGF-BB levels in the MDD group (n = 36) were significantly lower than those in the BD (n = 39) and HC groups (n = 36). In the multicenter study, serum PDGF-BB levels in the MDD group were again significantly lower than those in the BD and HC groups, with no significant difference between the BD and HC groups. Treatment with sodium valproate was associated with significantly lower serum PDGF-BB levels in patients with BD. After controlling for confounding factors (sex, age, body mass index, clinical severity, and valproate medication), serum PDGF-BB levels were lower in the MDD group than in the BD group regardless of mood state. Our findings suggest that serum PDGF-BB may be a potential biomarker to differentiate BD and MDD.

Development and validation of a UPLC-MS/MS method for the simultaneous determination of gamma-aminobutyric acid and glutamic acid in human plasma

Gamma-aminobutyric acid (GABA) and its precursor glutamic acid are important neurotransmitters. Both are also present in peripheral tissues and the circulation, where abnormal plasma concentrations have been linked to specific mental disorders. In addition to endogenous synthesis, GABA and glutamic acid can be obtained from dietary sources. An increasing number of studies suggest beneficial cardio-metabolic effects of GABA intake, and therefore GABA is being marketed as a food supplement. The need for further research into their health effects merits accurate and sensitive methods to analyze GABA and glutamic acid in plasma. To this end, an ultra-pressure liquid chromatography coupled to tandem mass spectrometry (UPLC-MS/MS) method was developed and validated for the quantification of GABA and glutamic acid in human plasma. Samples were prepared by a protein precipitation step and subsequent solid phase extraction using acetonitrile. Chromatographic separation was achieved on an Acquity UPLC HSS reversed phase C18 column using gradient elution. Analytes were detected using electrospray ionization and selective reaction monitoring. Standard curve concentrations for GABA ranged from 3.4 to 2500 ng/mL and for glutamic acid from 30.9 ng/mL to 22,500 ng/mL. Within- and between-day accuracy and precision were <10% in quality control samples at low, medium and high concentrations for both GABA and glutamic acid. GABA and glutamic acid were found to be stable in plasma after freeze-thaw cycles and up to 12 months of storage. The validated method was applied to human plasma from 17 volunteers. The observed concentrations ranged between 11.5 and 20.0 ng/ml and 2269 and 7625 ng/ml for respectively GABA and glutamic acid. The reported method is well suited for the measurement of plasma GABA and glutamic acid in pre-clinical or clinical studies.