IDO and TDO as a potential therapeutic target in different types of depression

Intricate mechanism of anxiety disorder, recognizing the potential role of gut microbiota and therapeutic interventions

Anxiety is a widespread psychological disorder affecting both humans and animals. It is a typical stress reaction; however, its longer persistence can cause severe health disorders affecting the day-to-day life activities of individuals. An intriguing facet of the anxiety-related disorder can be addressed better by investigating the role of neurotransmitters in regulating emotions, provoking anxiety, analyzing the cross-talks between neurotransmitters, and, most importantly, identifying the biomarkers of the anxiety. Recent years have witnessed the potential role of the gut microbiota in human health and disorders, including anxiety. Animal models are commonly used to study anxiety disorder as they offer a simpler and more controlled environment than humans. Ultimately, developing new strategies for diagnosing and treating anxiety is of paramount interest to medical scientists. Altogether, this review article shall highlight the intricate mechanisms of anxiety while emphasizing the emerging role of gut microbiota in regulating metabolic pathways through various interaction networks in the host. In addition, the review will foster information about the therapeutic interventions of the anxiety and related disorder.

Maternal dysbiosis produces long-lasting behavioral changes in offspring

Advanced maternal age (AMA) is defined as a pregnancy in a woman older than 35 years of age. AMA increases the risk for both maternal and neonatal complications, including miscarriage and stillbirth. AMA has also been linked to neurodevelopmental and neuropsychiatric disorders in the offspring. Recent studies have found that age-associated compositional shifts in the gut microbiota contribute to altered microbial metabolism and enhanced inflammation in the host. We investigated the specific contribution of the maternal microbiome on pregnancy outcomes and offspring behavior by recolonizing young female mice with aged female microbiome prior to pregnancy. We discovered that pre-pregnancy colonization of young dams with microbiome from aged female donors significantly increased fetal loss. There were significant differences in the composition of the gut microbiome in pups born from dams recolonized with aged female biome that persisted through middle age. Offspring born from dams colonized with aged microbiome also had significant changes in levels of neurotransmitters and metabolites in the blood and the brain. Adult offspring from dams colonized with an aged microbiome displayed persistent depressive- and anxiety-like phenotypes. Collectively, these results demonstrate that age-related changes in the composition of the maternal gut microbiome contribute to chronic alterations in the behavior and physiology of offspring. This work highlights the potential of microbiome-targeted approaches, even prior to birth, may reduce the risk of neuropsychiatric disorders.

Gene expression of kynurenine pathway enzymes in depression and following electroconvulsive therapy

OBJECTIVE

This study aimed to investigate changes in mRNA expression of the kynurenine pathway (KP) enzymes tryptophan 2, 3-dioxygenase (TDO), indoleamine 2, 3-dioxygenase 1 and 2 (IDO1, IDO2), kynurenine aminotransferase 1 and 2 (KAT1, KAT2), kynurenine monooxygenase (KMO) and kynureninase (KYNU) in medicated patients with depression (n = 74) compared to age- and sex-matched healthy controls (n = 55) and in patients with depression after electroconvulsive therapy (ECT). Associations with mood score (24-item Hamilton Depression Rating Scale, HAM-D24), plasma KP metabolites and selected glucocorticoid and inflammatory immune markers known to regulate KP enzyme expression were also explored.

METHODS

HAM-D24 was used to evaluate depression severity. Whole blood mRNA expression was assessed using quantitative real-time polymerase chain reaction.

RESULTS

KAT1, KYNU and IDO2 were significantly reduced in patient samples compared to control samples, though results did not survive statistical adjustment for covariates or multiple comparisons. ECT did not alter KP enzyme mRNA expression. Changes in IDO1 and KMO and change in HAM-D24 score post-ECT were negatively correlated in subgroups of patients with unipolar depression (IDO1 only), psychotic depression and ECT responders and remitters. Further exploratory correlative analyses revealed altered association patterns between KP enzyme expression, KP metabolites, NR3C1 and IL-6 in depressed patients pre- and post-ECT.

CONCLUSION

Further studies are warranted to determine if KP measures have sufficient sensitivity, specificity and predictive value to be integrated into stress and immune associated biomarker panels to aid patient stratification at diagnosis and in predicting treatment response to antidepressant therapy.

Core antibiotic resistance genes mediate gut microbiota to intervene in the treatment of major depressive disorder

INTRODUCTION

The relationship between depression and gut microbiota remains unclear, but an important role of gut microbiota has been verified. The relationship between gut microbiota and antibiotic resistance genes (ARGs) may be a potential new explanatory pathway.

METHODS

We collected samples from 63 depressed patients and 30 healthy controls for metagenomic sequencing. The two groups' microbiota characteristics, functional characteristics, and ARG differences were analyzed.

RESULTS

We obtained 30 differential KEGG orthologs (KOs) and their producers in 5 genera and 7 species by HUMAnN3. We found 6 KOs from Weissella_cibaria and Lactobacillus_plantaru are potentially coring functional mechanism of gut microbiota. Different metabolites including sphingolipids, pyrans, prenol lipids, and isoflavonoids also showed significance between MDD and HC. We detected 48 significantly different ARGs: 5 ARGs up-regulated and 43 ARGs down-regulated in MDD compared to HC. Based on Cox model results, Three ARGs significantly affected drug efficacy (ARG29, ARG105, and ARG111). Eggerthella, Weissella, and Lactobacillus were correlated with different core ARGs, which indicated different mechanisms in affecting MDD.

LIMITATIONS

The present study needs to be replicated in different ethnic groups. At the same time, a larger Chinese cohort study and detailed experimental verification are also the key to further discussion.

CONCLUSION

Our findings suggest that ARGs play a role in the interplay between major depressive disorder and gut microbiota. The role of ARGs should be taken into account when understanding the relationship between depression and gut microbiota.

Tryptophan Metabolism Disorder-Triggered Diseases, Mechanisms, and Therapeutic Strategies: A Scientometric Review

BACKGROUND

Tryptophan is widely present in foods such as peanuts, milk, and bananas, playing a crucial role in maintaining metabolic homeostasis in health and disease. Tryptophan metabolism is involved in the development and progression of immune, nervous, and digestive system diseases. Although some excellent reviews on tryptophan metabolism exist, there has been no systematic scientometric study as of yet.

METHODS

This review provides and summarizes research hotspots and potential future directions by analyzing annual publications, topics, keywords, and highly cited papers sourced from Web of Science spanning 1964 to 2022.

RESULTS

This review provides a scientometric overview of tryptophan metabolism disorder-triggered diseases, mechanisms, and therapeutic strategies.

CONCLUSIONS

The gut microbiota regulates gut permeability, inflammation, and host immunity by directly converting tryptophan to indole and its derivatives. Gut microbial metabolites regulate tryptophan metabolism by activating specific receptors or enzymes. Additionally, the kynurenine (KYN) pathway, activated by indoleamine-2, 3-dioxygenase (IDO) and tryptophan 2, 3-dioxygenase, affects the migration and invasion of glioma cells and the development of COVID-19 and depression. The research and development of IDO inhibitors help to improve the effectiveness of immunotherapy. Tryptophan metabolites as potential markers are used for disease therapy, guiding clinical decision-making. Tryptophan metabolites serve as targets to provide a new promising strategy for neuroprotective/neurotoxic imbalance affecting brain structure and function. In summary, this review provides valuable guidance for the basic research and clinical application of tryptophan metabolism.

Unlocking the potential of the 3-hydroxykynurenine/kynurenic acid ratio: a promising biomarker in adolescent major depressive disorder

Metabolites disruptions in tryptophan (TRP) and kynurenine pathway (KP) are believed to disturb neurotransmitter homeostasis and contribute to depressive symptoms. This study aims to investigate serum levels of KP metabolites in adolescent major depressive disorder (AMDD), and examine their relationship with depression severities. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to analyze serum levels of TRP, kynurenic acid (KYNA), kynurenine (KYN), and 3-hydroxy-kynurenine (3-HK) in 143 AMDD participants and 98 healthy controls (HC). Clinical data, including Children's Depression Inventory (CDI) scores, were collected and analyzed using statistical methods, such as ANOVA, logistic regression, Receiver operating characteristic curve analysis and a significance level of p < 0.05 was used for all analyses. AMDD showed significantly decreased serum levels of KYNA (-25.5%), KYN (-14.2%), TRP (-11.0%) and the KYNA/KYN ratio (-11.9%) compared to HC (p < 0.01). Conversely, significant increases were observed in 3-HK levels (+50.4%), the 3-HK/KYNA ratio (+104.3%) and the 3-HK/KYN ratio (+93.0%) (p < 0.01). Logistic regression analysis identified increased level of 3-HK as a contributing factor to AMDD, while increased level of KYNA acted as a protective factor against AMDD. The 3-HK/KYNA ratio demonstrated an area under the curve (AUC) of 0.952. This study didn't explore AMDD's inflammatory status and its metabolites relationship explicitly. These findings indicate that metabolites of TRP and KP may play a crucial role in the pathogenesis of AMDD, emphasizing the potential of the 3-HK/KYNA ratio as a laboratory biomarker for early detection and diagnosis of AMDD.

Implications of Kynurenine Pathway Metabolism for the Immune System, Hypothalamic-Pituitary-Adrenal Axis, and Neurotransmission in Alcohol Use Disorder

In recent years, there has been a marked increase in interest in the role of the kynurenine pathway (KP) in mechanisms associated with addictive behavior. Numerous reports implicate KP metabolism in influencing the immune system, hypothalamic-pituitary-adrenal (HPA) axis, and neurotransmission, which underlie the behavioral patterns characteristic of addiction. An in-depth analysis of the results of these new studies highlights interesting patterns of relationships, and approaching alcohol use disorder (AUD) from a broader neuroendocrine-immune system perspective may be crucial to better understanding this complex phenomenon. In this review, we provide an up-to-date summary of information indicating the relationship between AUD and the KP, both in terms of changes in the activity of this pathway and modulation of this pathway as a possible pharmacological approach for the treatment of AUD.

Topical Steroid Withdrawal is a Targetable Excess of Mitochondrial NAD

Background

Topical corticosteroids (TCS) are first-line therapies for numerous skin conditions. Topical Steroid Withdrawal (TSW) is a controversial diagnosis advocated by patients with prolonged TCS exposure who report severe systemic reactions upon treatment cessation. However, to date there have been no systematic clinical or mechanistic studies to distinguish TSW from other eczematous disorders.

Methods

A re-analysis of a previous survey with eczematous skin disease was performed to evaluate potential TSW distinguishing symptoms. We subsequently conducted a pilot study of 16 patients fitting the proposed diagnostic criteria. We then performed: tissue metabolomics, transcriptomics, and immunostaining on skin biopsies; serum metabolomics and cytokine assessments; shotgun metagenomics on microbiome skin swabs; genome sequencing; followed by functional, mechanistic studies using human skin cell lines and mice.

Results

Clinically distinct TSW symptoms included burning, flushing, and thermodysregulation. Metabolomics and transcriptomics both implicated elevated NAD+ oxidation stemming from increased expression of mitochondrial complex I and conversion of tryptophan into kynurenine metabolites. These abnormalities were induced by glucocorticoid exposure both in vitro and in a cohort of healthy controls (N=19) exposed to TCS. Targeting complex I via either metformin or the herbal compound berberine improved outcomes in both cell culture and in an open-label case series for patients with TSW.

Conclusion

Taken together, our results suggest that TSW has a distinct dermatopathology. While future studies are needed to validate these results in larger cohorts, this work provides the first mechanistic evaluation into TSW pathology, and offers insights into clinical identification, pharmacogenomic candidates, and directed therapeutic strategies.

Depression-associated gut microbes, metabolites and clinical trials

Depression is one of the most prevalent mental disorders today. Over the past decade, there has been considerable attention given to the field of gut microbiota associated with depression. A substantial body of research indicates a bidirectional communication pathway between gut microbiota and the brain. In this review, we extensively detail the correlation between gut microbiota, including Lactobacillus acidophilus and Bifidobacterium longum, and metabolites such as short-chain fatty acids (SCFAs) and 5-hydroxytryptamine (5-HT) concerning depression. Furthermore, we delve into the potential health benefits of microbiome-targeted therapies, encompassing probiotics, prebiotics, and synbiotics, in alleviating depression. Lastly, we underscore the importance of employing a constraint-based modeling framework in the era of systems medicine to contextualize metabolomic measurements and integrate multi-omics data. This approach can offer valuable insights into the complex metabolic host-microbiota interactions, enabling personalized recommendations for potential biomarkers, novel drugs, and treatments for depression.

Mechanisms for the biological activity of Gastrodia elata Blume and its constituents: A comprehensive review on sedative-hypnotic, and antidepressant properties

BACKGROUND

Insomnia and depressive disorder are two common symptoms with a reciprocal causal relationship in clinical practice, which are usually manifested in comorbid form. Several medications have been widely used in the treatment of insomnia and depression, but most of these drugs show non-negligible side effects. Currently, many treatments are indicated for insomnia and depressive symptom, including Chinese herbal medicine such as Gastrodia elata Blume (G. elata), which has excellent sedative-hypnotic and antidepressant effects in clinical and animal studies.

PURPOSE

To summarize the mechanisms of insomnia and depression and the structure-activity mechanism for G. elata to alleviate these symptoms, particularly by hypothalamic-pituitary-adrenal (HPA) axis and intestinal flora, aiming to discover new approaches for the treatment of insomnia and depression.

METHODS

The following electronic databases were searched from the beginning to November 2023: PubMed, Web of Science, Google Scholar, Wanfang Database, and CNKI. The following keywords of G. elata were used truncated with other relevant topic terms, such as depression, insomnia, antidepressant, sedative-hypnotic, neuroprotection, application, safety, and toxicity.

RESULTS

Natural compounds derived from G. elata could alleviate insomnia and depressive disorder, which is involved in monoamine neurotransmitters, inflammatory response, oxidative stress, and gut microbes, etc. Several clinical trials showed that G. elata-derived natural compounds that treat depression and insomnia have significant and safe therapeutic effects, but further well-designed clinical and toxicological studies are needed.

CONCLUSION

G. elata exerts a critical role in treating depression and insomnia due to its multi-targeting properties and fewer side effects. However, more clinical and toxicological studies should be performed to further explore the sedative-hypnotic and antidepressant mechanisms of G. elata and provide more evidence and recommendations for its clinical application. Our review provides an overview of G. elata treating insomnia with depression for future research direction.

Cortisol as a Target for Treating Mental Disorders: A Promising Avenue for Therapy

Cortisol, commonly known as the "stress hormone," plays a critical role in the body's response to stress. Elevated cortisol levels have been associated with various mental disorders, including anxiety, depression, and post-traumatic stress disorder. Consequently, researchers have explored cortisol modulation as a promising avenue for treating these conditions. However, the availability of research on cortisol as a therapeutic option for mental disorders is limited, and existing studies employ diverse methodologies and outcome measures. This review article aimed to provide insights into different treatment approaches, both pharmacological and non-pharmacological, which can effectively modulate cortisol levels. Pharmacological interventions involve the use of substances, such as somatostatin analogs, dopamine agonists, corticotropin-releasing hormone antagonists, and cortisol synthesis inhibitors. Additionally, non-pharmacological techniques, including cognitivebehavioral therapy, herbs and supplements, transcranial magnetic stimulation, lifestyle changes, and surgery, have been investigated to reduce cortisol levels. The emerging evidence suggests that cortisol modulation could be a promising treatment option for mental disorders. However, more research is needed to fully understand the effectiveness and safety of these therapies.

Identification of paeoniflorin from Paeonia lactiflora pall. As an inhibitor of tryptophan 2,3-dioxygenase and assessment of its pharmacological effects on depressive mice

ETHNOPHARMACOLOGICAL RELEVANCE

The radix of Paeonia lactiflora Pall. (PaeR) is a traditional Chinese medicine (TCM) clinically used for treating depression. Although it has been established that PaeR can protect the liver and alleviate depressive-like behaviors, its bioactive chemicals and antidepressant mechanism remain unclear. Our pilot study showed that PaeR reduced the expression of the L-tryptophan- catabolizing enzyme tryptophan 2,3-dioxygenase (TDO) in the livers of stress-induced depression-like mice.

AIM OF THE STUDY

This study aimed to screen potential TDO inhibitors from PaeR and investigate the potential therapeutic use of TDO inhibition for treating depression.

MATERIALS AND METHODS

Molecular docking, magnetic ligand fishing, and secrete-pair dual luminescence assay were conducted for in vitro ligand discovery and high-throughput screening of TDO inhibitors. Stable TDO overexpression was achieved in HepG2 cell lines to evaluate the TDO inhibitory activities of drugs in vitro by RT-PCR and Western blot analyses of TDO at mRNA and protein levels. In vivo validation of TDO inhibitory potency and evaluation of TDO inhibition as a potential therapeutic strategy for major depressive disorder (MDD) were performed using mice subjected to "3 + 1″ combined stresses for at least 30 days to induce depression-like behaviors. A well-known TDO inhibitor, LM10, was evaluated in parallel.

RESULTS

The PaeR extract significantly ameliorated depressive-like behaviors of stressed mice, attributed to inhibition of TDO expression and tryptophan modulation metabolism. After a comprehensive analysis of molecular docking, ligand fishing, and luciferase assay, paeoniflorin was screened as a TDO inhibitor from the PaeR extract. This compound, structurally different from LM10, potently inhibited human and mouse TDO in cell- and animal-based assays. The effects of TDO inhibitors on MDD symptoms were evaluated in a stress-induced depression-like mouse model. In mice, both inhibitors had beneficial effects on stress-induced depressive-like behavioral despair and unhealthy physical status. Moreover, both inhibitors increased the liver serotonin/tryptophan ratio and decreased the kynurenine/tryptophan ratio after oral administration, demonstrating in vivo inhibition of TDO activity. Our data substantiated the potential of TDO inhibition as a therapeutic strategy to improve behavioral activity and decrease despair symptoms in major depressive disorder.

CONCLUSIONS

This study introduced a hitherto undocumented comprehensive screening strategy to identify TDO inhibitors in PaeR extract. Our findings also highlighted the potential of PaeR as a source of antidepressant constituents and pinpointed the inhibition of TDO as a promising therapeutic approach for managing major depressive disorder.

Nutritional considerations in major depressive disorder: current evidence and functional testing for clinical practice

Depression is a multifaceted condition with diverse underlying causes. Several contributing and inter-related factors such as genetic, nutritional, neurological, physiological, gut-brain-axis, metabolic and psychological stress factors play a role in the pathophysiology of depression. This review aims to highlight the role that nutritional factors play in the aetiology of depression. Secondly, we discuss the biomedical and functional pathology tests which measure these factors, and the current evidence supporting their use. Lastly, we make recommendations on how practitioners can incorporate the latest evidence-based research findings into clinical practice. This review highlights that diet and nutrition greatly affect the pathophysiology of depression. Nutrients influence gene expression, with folate and vitamin B12 playing vital roles in methylation reactions and homocysteine regulation. Nutrients are also involved in the tryptophan/kynurenine pathway and the expression of brain-derived neurotrophic factor (BDNF). Additionally, diet influences the hypothalamic-pituitary-adrenal (HPA) response and the composition and diversity of the gut microbiome, both of which have been implicated in depression. A comprehensive dietary assessment, combined with appropriate evaluation of biochemistry and blood pathology, may help uncover contributing factors to depressive symptoms. By employing such an approach, a more targeted and personalised treatment strategy can be devised, ultimately leading to improved patient outcomes.

Discovery of 2-Aminothiazole-4-carboxylic Acids as Broad-Spectrum Metallo-β-lactamase Inhibitors by Mimicking Carbapenem Hydrolysate Binding

Metallo-β-lactamases (MBLs) are zinc-dependent enzymes capable of hydrolyzing all bicyclic β-lactam antibiotics, posing a great threat to public health. However, there are currently no clinically approved MBL inhibitors. Despite variations in their active sites, MBLs share a common catalytic mechanism with carbapenems, forming similar reaction species and hydrolysates. We here report the development of 2-aminothiazole-4-carboxylic acids (AtCs) as broad-spectrum MBL inhibitors by mimicking the anchor pharmacophore features of carbapenem hydrolysate binding. Several AtCs manifested potent activity against B1, B2, and B3 MBLs. Crystallographic analyses revealed a common binding mode of AtCs with B1, B2, and B3 MBLs, resembling binding observed in the MBL-carbapenem product complexes. AtCs restored Meropenem activity against MBL-producing isolates. In the murine sepsis model, AtCs exhibited favorable synergistic efficacy with Meropenem, along with acceptable pharmacokinetics and safety profiles. This work offers promising lead compounds and a structural basis for the development of potential drug candidates to combat MBL-mediated antimicrobial resistance.

The kynurenine pathway in traumatic brain injuries and concussion

Up to 10 million people per annum experience traumatic brain injury (TBI), 80-90% of which are categorized as mild. A hit to the brain can cause TBI, which can lead to secondary brain injuries within minutes to weeks after the initial injury through unknown mechanisms. However, it is assumed that neurochemical changes due to inflammation, excitotoxicity, reactive oxygen species, etc., that are triggered by TBI are associated with the emergence of secondary brain injuries. The kynurenine pathway (KP) is an important pathway that gets significantly overactivated during inflammation. Some KP metabolites such as QUIN have neurotoxic effects suggesting a possible mechanism through which TBI can cause secondary brain injury. That said, this review scrutinizes the potential association between KP and TBI. A more detailed understanding of the changes in KP metabolites during TBI is essential to prevent the onset or at least attenuate the severity of secondary brain injuries. Moreover, this information is crucial for the development of biomarker/s to probe the severity of TBI and predict the risk of secondary brain injuries. Overall, this review tries to fill the knowledge gap about the role of the KP in TBI and highlights the areas that need to be studied.

Glucocorticoid Hormones as Modulators of the Kynurenine Pathway in Chronic Pain Conditions

The pathogenesis of chronic pain entails a series of complex interactions among the nervous, immune, and endocrine systems. Defined as pain lasting or recurring for more than 3 months, chronic pain is becoming increasingly more prevalent among the US adult population. Pro-inflammatory cytokines from persistent low-grade inflammation not only contribute to the development of chronic pain conditions, but also regulate various aspects of the tryptophan metabolism, especially that of the kynurenine pathway (KP). An elevated level of pro-inflammatory cytokines exerts similar regulatory effects on the hypothalamic-pituitary-adrenal (HPA) axis, an intricate system of neuro-endocrine-immune pathways and a major mechanism of the stress response. As the HPA axis counters inflammation through the secretion of endogenous cortisol, we review the role of cortisol along with that of exogenous glucocorticoids in patients with chronic pain conditions. Considering that different metabolites produced along the KP exhibit neuroprotective, neurotoxic, and pronociceptive properties, we also summarize evidence rendering them as reliable biomarkers in this patient population. While more in vivo studies are needed, we conclude that the interaction between glucocorticoid hormones and the KP poses an attractive venue of diagnostic and therapeutic potential in patients with chronic pain.

Canagliflozin attenuates chronic unpredictable mild stress induced neuroinflammation via modulating AMPK/mTOR autophagic signaling

Although vast progress has been made to understand the pathogenesis of depression, existing antidepressant remedies, with several adverse effects, are not fully adequate. Interestingly, new emerging theories implicating an altered HPA-axis, tryptophan metabolism, neuroinflammation and altered gut integrity were proposed to further identify novel therapeutic targets. Along these lines, canagliflozin (CAN), a novel antidiabetic medication with anti-inflammatory and neuroprotective activity may present an effective treatment for depression; nevertheless, no studies have explored its effect on depressive disorder yet. To this end, this study aimed to investigate the possible antidepressant activity of CAN in CUMS and the mechanisms underlying its action on the gut-brain inflammation axis as well as the alteration in the TRY/KYN pathway in addition to its role in modulating the autophagic signaling cascade. Interestingly, CAN successfully attenuated the CUMS-induced elevations in despair and anhedonic behaviors as well as the elevated serum CORT. Furthermore, it enhanced gut integrity via hampering the CUMS-induced colonic inflammation and amending colonic tight junction proteins. The enhanced gut integrity was further corroborated by a notable anti-inflammatory and neuroprotective activity manifested via the observed mitigation of immune cell activation in addition to IDO hippocampal protein content and promotion of the autophagy cascade. Our findings postulate the possible anti-inflammatory and neuroprotective effects of CAN and the implication of TRY/KYN and AMPK/mTOR signaling pathways in the CUMS-induced MDD. Hence, this study shed light to the promising role of CAN in the augmentation of the current antidepressant treatments.

Anti-Inflammatory Therapy as a Promising Target in Neuropsychiatric Disorders

This chapter analyzes the therapeutic potential of current anti-inflammatory drugs in treating psychiatric diseases from a neuro-immunological perspective. Based on the bidirectional brain-immune system relationship, the rationale is that a dysregulated inflammation contributes to the pathogenesis of psychiatric and neurological disorders, while the immunology function is associated with psychological variables like stress, affective disorders, and psychosis. Under certain social, psychological, and environmental conditions and biological factors, a healthy inflammatory response and the associated "sickness behavior," which are aimed to resolve a physical injury and microbial threat, become harmful to the central nervous system. The features and mechanisms of the inflammatory response are described across the main mental illnesses with a special emphasis on the profile of cytokines and the function of the HPA axis. Next, it is reviewed the potential clinical utility of immunotherapy (cytokine agonists and antagonists), glucocorticoids, unconventional anti-inflammatory agents (statins, minocycline, statins, and polyunsaturated fatty acids (PUFAs)), the nonsteroidal anti-inflammatory drugs (NSAIDs), and particularly celecoxib, a selective cyclooxygenase-2 (Cox-2) inhibitor, as adjuvants of conventional psychiatric medications. The implementation of anti-inflammatory therapies holds great promise in psychiatry. Because the inflammatory background may account for the etiology and/or progression of psychiatric disorders only in a subset of patients, there is a need to elucidate the immune underpinnings of the mental illness progression, relapse, and remission. The identification of immune-related bio-signatures will ideally assist in the stratification of the psychiatric patient to predict the risk of mental disease, the prognosis, and the response to anti-inflammatory therapy.

Antidepressant effects of the traditional Chinese herbal formula Xiao-Yao-San and its bioactive ingredients

BACKGROUND

Depression is one of the most debilitating and severe psychiatric disorders and a serious public health concern. Currently, many treatments are indicated for depression, including traditional Chinese medicinal formulae such as Xiao-Yao-San (XYS), which has effective antidepressant effects in clinical and animal studies.

PURPOSE

To summarize current evidence of XYS in terms of the preclinical and clinical studies and to identify the multi-level, multi-approach, and multi-target potential antidepressant mechanisms of XYS and active components of XYS by a comprehensive search of the related electronic databases.

METHODS

The following electronic databases were searched from the beginning to April 2022: PubMed, MEDLINE, Web of Science, Google Scholar, and China National Knowledge Infrastructure.

RESULTS

This review summarizes the antidepressant mechanisms of XYS and its active ingredients, which are reportedly correlated with monoamine neurotransmitter regulation, synaptic plasticity, and hypothalamic-pituitary-adrenal axis, etc. CONCLUSION: XYS plays a critical role in the treatment of depression by the regulation of several factors, including the monoaminergic systems, hypothalamic-pituitary-adrenal axis, synaptic plasticity, inflammation, brain-derived neurotrophic factor levels, brain-gut axis, and other pathways. However, more clinical and animal studies should be conducted to further investigate the antidepressant function of XYS and provide more evidence and recommendations for its clinical application. Our review provides an overview of XYS and guidance for future research direction.

Tryptophan 2,3-dioxygenase may be a potential prognostic biomarker and immunotherapy target in cancer: A meta-analysis and bioinformatics analysis

Background

Tryptophan 2,3-dioxygenase (TDO2) is one of the emerging immune checkpoints. Meanwhile, TDO2 is also a key enzyme in the tryptophan (Trp)–kynurenine (Kyn) signaling pathway. Many studies have evaluated that TDO2 is highly expressed in various malignant tumor patients and plays a prognostic role. However, the sample size of a single prognostic study was small, and the results were still controversial.

Methods

We used Stata software and referenced the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) statement to conduct a meta-analysis on TDO2 and its clinical features and prognosis. We searched the PubMed, Cochrane Library, and Web of Science databases to find publications concerning TDO2 expression in malignant tumor patients up to June 2021. We used the Newcastle–Ottawa Scale (NOS) to evaluate the bias risk of the included literature. Risk ratios (RRs) and hazard ratios (HRs) were used for clinical outcomes, specifically overall survival (OS) and progression-free survival (PFS). In addition, we used data from The Cancer Genome Atlas (TCGA) to verify our conclusions.

Results

Nine studies including 667 patients with malignant tumors were identified. Our results suggested that overexpression of TDO2 was statistically correlated with poor OS and poor PFS (HR = 2.58, 95% CI = 1.52–4.40, p = 0.0005; HR = 2.38, 95% CI = 0.99–5.73, p = 0.05). In terms of clinicopathological characteristics, the overexpression level of TDO2 was statistically correlated with TNM (tumor–node–metastasis) stage (RR = 0.65, 95% CI = 0.48–0.89, p = 0.002) and regional lymph node metastasis (RR = 0.76, 95% CI = 0.59–0.99, p = 0.04). Subgroup analysis revealed the potential sources of heterogeneity. In addition, bioinformatics studies suggested that the level of TDO2 was high in malignant tumors and higher in cancer tissue than in matched paracarcinoma tissue. Gene enrichment analysis showed that TDO2 was closely related to immune response.

Conclusion

Overall, TDO2 may be a biomarker for the survival and prognosis of patients with malignant tumors and a potential therapeutic target in the future.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=260442, identifier (CRD42021260442)

Research progress on microRNA-1258 in the development of human cancer

microRNAs (miRNAs) are small endogenous RNAs composed of 20-22 nucleotides that do not encode proteins, which regulate the expression of downstream genes by targeting the 3' untranslated region of mRNA. Plentiful research has demonstrated that miRNAs participate in the initiation and development of diverse diseases and malignant tumors. miR-1258 exerts great influence on tumors, including tumor growth, distant metastasis, migration, invasion, chemosensitivity, cell glycolysis, apoptosis, and stemness. Interestingly, miR-1258 is a miRNA with explicit functions and has been investigated to act as a tumor suppressor in studies on various types of tumors. With accumulating research on miR-1258, it has been found to be used as a biomarker in the early diagnosis and prognosis prediction of tumor patients. In this review, we outline the development of miR-1258 research, describe its regulatory network, and discuss its roles in cancer. Additionally, we generalize the potential clinical applications of miR-1258. This review offers emerging perspectives and orientations for further comprehending the function of miR-1258 as a diagnostic and prognostic biomarker and potent therapeutic target in cancer.

A randomized controlled trial of a multicomponent online stress reduction intervention in inflammatory bowel disease

BACKGROUND

Psychological stress negatively impacts inflammatory bowel disease (IBD) outcomes. Patients have prioritized access to online interventions; yet, the data on these have been limited by mixed in-person/online interventions, low adherence, and non-randomized controlled trial (RCT) design.

OBJECTIVES

We assessed the efficacy of and adherence to a 12-week online multicomponent stress reduction intervention in IBD.

DESIGN

This is a RCT.

METHODS

Adult participants on stable IBD medical therapy with elevated stress levels from four centers were randomized to intervention or control groups. Intervention participants received a 12-week online program including a weekly yoga, breathwork and meditation video (target 2-3 times/week), a weekly cognitive behavioral therapy/positive psychology informed video activity, and weekly 10-min check-ins by a study team member. Control participants received weekly motivational messages by email. All patients received standard of care IBD therapy. The primary outcome was Cohen's Perceived Stress Scale (PSS). Secondary outcomes evaluated mental health, resilience, health-related quality of life (HRQoL), symptom indices, acceptability, adherence, and inflammatory biomarkers. Analysis of covariance was used to determine between-group differences.

RESULTS

Of 150 screened patients, 101 were randomized to the intervention (n = 49) and control (n = 52) groups (mean age: 42.5 ± 14.1 years; M:F 1:3, 48% with ulcerative colitis and 52% with Crohn's disease). The between-group PSS improved by 22.4% (95% confidence interval, 10.5-34.3, p < 0.001). Significant improvements were seen in mental health, resilience, and HRQoL measures, with a median satisfaction score of 89/100 at the end of the 12 weeks. In the 44/49 patients who completed the intervention, 91% achieved program adherence targets.

CONCLUSION

This 12-week online intervention improved perceived stress, mental health, and HRQoL, but did not impact IBD symptom indices or inflammatory biomarkers. The program was readily adopted and adhered to by participants with high retention rates. After iterative refinement based on participant feedback, future studies will evaluate the impact of a longer/more intense intervention on disease course.

REGISTRATION

ClinicalTrials.gov Identifier NCT03831750.

PLAIN LANGUAGE SUMMARY

An online stress reduction intervention in inflammatory bowel disease patients improves stress, mental health, and quality of life People with inflammatory bowel disease (IBD) have high levels of stress, anxiety, and depression. Although IBD patients have expressed the need for online mental wellness interventions, the existing data to support these interventions in IBD are limited. In this trial, 101 IBD patients had the chance to participate in a 12-week online stress reduction intervention. In those patients randomly selected to participate in the online intervention, each week they received the following: a 20- to 30-min yoga, breathwork, and meditation video that they were asked to do 2-3 times a week, a 10- to 20-min mental wellness activity they were asked to do once during the week, and a 10-min telephone check-in with a study team member. Participants who were not selected to use the online intervention received a weekly motivational message by email. In all, 90 of the 101 participants (89%) completed the study with the mean age of participants being 43 years and the majority being females (75%). Ninety-one percent of participants who completed the intervention met the program target of doing the yoga, breathwork, and meditation video at least 2 times per week. Significant improvements were seen in perceived stress (by 22.4%), depression (by 29.5%), anxiety (by 23.7%), resilience (by 10.6%), and quality of life (by 8.9%). No changes were seen in IBD severity or in blood markers of inflammation. In conclusion, this study demonstrates evidence that a 12-week online stress reduction intervention had low dropout rates, high adherence and beneficial effects on stress, mental health, and quality of life measures. Continued feedback will be sought from study participants and our IBD patient partners to refine the intervention and assess the impact in future studies of patients with active IBD, as well as the impact of a longer/more intense intervention.

Discovery of 1-(Hetero)aryl-β-carboline Derivatives as IDO1/TDO Dual Inhibitors with Antidepressant Activity

Depression is the leading cause of global burden of disease and disability. Abnormalities in the kynurenine pathway of tryptophan degradation have been closely linked to the pathogenesis of depression. An integrative bioinformatics analysis demonstrated that indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) are potential targets for the development of antidepressants. A series of 1-(hetero)aryl-β-carboline derivatives were designed, synthesized, and evaluated as novel IDO1/TDO dual inhibitors. Among them, compound 28 displayed potent inhibition of both IDO1 (IC₅₀ = 3.53 μM) and TDO (IC₅₀ = 1.15 μM) and had an acceptable safety profile and pharmacokinetic properties. Compound 28 also rescued lipopolysaccharide-induced depressive-like behavior in mice. Further studies revealed that 28 likely had unique antidepressant mechanisms involving suppressing microglial activation, lowering IDO1 expression, and reducing proinflammatory cytokine and kynurenine levels in the mouse brain. Overall, this work provides practical guidance for the development of IDO1/TDO dual inhibitors to treat inflammation-induced depression.

Tryptophan Metabolism in Depression: A Narrative Review with a Focus on Serotonin and Kynurenine Pathways

Depression is a common and serious disorder, characterized by symptoms like anhedonia, lack of energy, sad mood, low appetite, and sleep disturbances. This disease is very complex and not totally elucidated, in which diverse molecular and biological mechanisms are involved, such as neuroinflammation. There is a high need for the development of new therapies and gaining new insights into this disease is urgent. One important player in depression is the amino acid tryptophan. This amino acid can be metabolized in two important pathways in the context of depression: the serotonin and kynurenine pathways. These metabolic pathways of tryptophan are crucial in several processes that are linked with depression. Indeed, the maintenance of the balance of serotonin and kynurenine pathways is critical for the human physiological homeostasis. Thus, this narrative review aims to explore tryptophan metabolism (particularly in the serotonin and kynurenine pathways) in depression, starting with a global overview about these topics and ending with the focus on these pathways in neuroinflammation, stress, microbiota, and brain-derived neurotrophic factor regulation in this disease. Taken together, this information aims to clarify the metabolism of tryptophan in depression, particularly the serotonin and kynurenine pathways.

Proposed Pathway Linking Respiratory Infections with Depression

Depression is one of the most important causes of disability and loss of useful life of people around the world. Acute respiratory infection caused a large number of severe illnesses and deaths of the world and most of these due to viral infections, which is estimated more than 80% of respiratory infections. Detection of viruses by immune pathogen recognition receptors activates the intracellular signaling cascade and eventually cause produces interferons. Inflammatory process begins with secretion of interferons and the expression of interferon-stimulated genes. One of the most important of these genes is indoleamine-pyrrole 2,3-dioxygenase (IDO), which plays a major role in tryptophan catabolism. IDO is an intracellular monomeric enzyme that is also responsible for breaking down and consuming tryptophan in the Kynurenine pathway. Increased inflammation has been linked to decrease tryptophan concentrations and increase kynurenine levels. We tried to explain the role of inflammation by viral respiratory infections in causing depression.

Regulation of the kynurenine/serotonin pathway by berberine and the underlying effect in the hippocampus of the chronic unpredictable mild stress mice

BACKGROUND

Depression is a common mental disorder and is one of the main causes of disability. Berberine (BBR), the major constituent alkaloid originally from the famous Chinese herb Huanglian (Coptis chinensis), has been shown to exert antidepressant-like effects. This study was to investigate the hypothesis that BBR treats depressive-like behavior by shifting the balance of the kynurenine (KYN)/serotonin (5-HT) pathway toward the 5-HT pathway through downregulated indoleamine 2,3-dioxygenase 1 (IDO1), monoamine oxidase A (MAOA) and upregulated dopamine decarboxylase (DDC) in hippocampus.

METHOD

A chronic unpredictable mild stress (CUMS) mice model of depression was established via 21 days unpredictable stimulation. Then the mice were randomly assigned into six groups, namely control, model, fluoxetine [FLU, (10 mg/kg)], BBRL (25 mg/kg), BBRM (50 mg/kg), and BBRH (100 mg/kg) groups. Behavioral assessments were conducted to evaluate the antidepressant effects of BBR. The levels of 5-HT, KYN, tryptophan (TRP), and 5-hydroxyindoleacetic acid (5-HIAA) in hippocampus were estimated using high performance liquid chromatography (HPLC). The mRNA and protein levels of DDC, MAOA and IDO1 in hippocampus were detected by real-time quantitative polymerase chain reaction (qRT-PCR) and western blot (WB), respectively.

RESULT

The results showed that a successful CUMS mice model was established through 21 days of continuous unpredictable stimulation, as indicated by the significant decrease in locomotor activity and increase in immobility time, reduction in body weight and sucrose preference rate etc. Compared with the normal group, the concentrations of KYN/TRP had significantly increased (p^## <0.01) and 5-HT/5-HIAA had decreased (p^#<0.05) at day 21 in the control group, but then improved after drug treatment with FLU and BBR. Compared with the normal group, the mRNA of IDO1 and MAOA were significantly upregulated (p^#<0.05) in the control group, MAOA and IDO1 gene were downregulated by FLU and BBR treatment. Protein expressions of IDO1 and MAOA was significantly increased (p^#<0.05) and DDC downregulated (p^##<0.01). BBR treatment downregulated IDO1 and MAOA, upregulated DDC.

CONCLUSIONS

BBR reversed the abnormalities of the KYN/5-HT pathway in depressed mice and achieved an excellent antidepressant effect. Its direct impact may be observed as changes in biological indicators in mice hippocampus tissue.

Tryptophan 2,3-dioxygenase, a novel therapeutic target for Parkinson's disease

INTRODUCTION

Alterations in the activity of tryptophan 2,3-dioxygenase (TDO) cause imbalances in the levels of serotonin and other neuroactive metabolites which can contribute to motor, psychiatric, gastrointestinal, and other dysfunctions often seen in Parkinson's disease (PD). TDO is a key enzyme of tryptophan metabolism at the entry of the kynurenine pathway (KP) which moderates production of neuroactive compounds primarily outside the central nervous system (CNS). Recent data from experimental models indicate that TDO modulation could have beneficial effects on PD symptoms not targeted by traditional dopamine substitution therapies.

AREAS COVERED

Based on data available in PubMed and ClinicalTrials databases up until 1 August 2021, we summarize current knowledge of KP alterations in relation to PD. We overview effects of TDO inhibition in preclinical models of neurodegeneration and discuss findings of the impact of enzyme inhibition on motor, memory and gastrointestinal dysfunctions, and neuronal cell loss.

EXPERT OPINION

TDO inhibition potentially alleviates motor and non-motor dysfunctions of PD. However, data suggesting harmful effects of long-term TDO inhibition raise concerns. To exploit possibilities of TDO inhibitory treatment, development of further selective TDO inhibitor compounds with good bioavailability features and models adequately replicating PD symptoms of systemic origin should be prioritized.

Changes in kynurenine pathway metabolites after acute psychosocial stress in healthy males: a single-arm pilot study

Chronic stress is associated with an increased conversion of tryptophan (TRP) into kynurenine (KYN). However, only a few studies investigated KYN pathway metabolite concentrations following acute stress in healthy subjects. We hypothesized that TRP/KYN metabolism changes following acute stress, and that KYN pathway metabolites are associated with cortisol and subjective stress responses. In a single-arm pilot study, we explored whether KYN pathway metabolites concentrations were altered after acute stress induced by the Maastricht Acute Stress Test in healthy males (n = 56, mean age: 27 (SD = 4.5) years, BMI: 23 (SD = 1.8) kg/m²). In particular, we examined whether concentrations of TRP decreased, and KYN, kynurenic acid (KYNA), and the ratio of KYN to TRP (KYN:TRP) increased after acute stress. Furthermore, we assessed whether cortisol and subjective stress responses correlated with KYN pathway metabolite measures after stress induction, based on both the area under the curve with respect to the ground (AUCg) as well as the incremental area under the curve (AUCi). Concentrations of TRP, KYN, KYNA, and KYN:TRP were significantly lower after stress induction compared to pre-stress induction (all p < 0.01). AUCi and AUCg reflecting cortisol and subjective stress responses did not correlate with AUCi and AUCg reflecting KYN pathway metabolite responses. These preliminary results indicate that KYN pathway metabolites are lower after acute psychosocial stress induction. Moreover, although chronic stress and subsequent prolonged elevated cortisol concentrations and subjective stress stimulate the conversion of TRP into KYN, acute stress is not associated with such conversion up to 35 minutes after stress induction.

A Potential Interface between the Kynurenine Pathway and Autonomic Imbalance in Schizophrenia

Schizophrenia is a neuropsychiatric disorder characterized by various symptoms including autonomic imbalance. These disturbances involve almost all autonomic functions and might contribute to poor medication compliance, worsened quality of life and increased mortality. Therefore, it has a great importance to find a potential therapeutic solution to improve the autonomic disturbances. The altered level of kynurenines (e.g., kynurenic acid), as tryptophan metabolites, is almost the most consistently found biochemical abnormality in schizophrenia. Kynurenic acid influences different types of receptors, most of them involved in the pathophysiology of schizophrenia. Only few data suggest that kynurenines might have effects on multiple autonomic functions. Publications so far have discussed the implication of kynurenines and the alteration of the autonomic nervous system in schizophrenia independently from each other. Thus, the coupling between them has not yet been addressed in schizophrenia, although their direct common points, potential interfaces indicate the consideration of their interaction. The present review gathers autonomic disturbances, the impaired kynurenine pathway in schizophrenia, and the effects of kynurenine pathway on autonomic functions. In the last part of the review, the potential interaction between the two systems in schizophrenia, and the possible therapeutic options are discussed.

Behavioral and Neurochemical Shifts at the Hippocampus and Frontal Cortex Are Associated to Peripheral Inflammation in Balb/c Mice Infected with Brucella abortus 2308

Brucellosis is a zoonosis affecting 50,000,000 people annually. Most patients progress to a chronic phase of the disease in which neuropsychiatric symptoms upsurge. The biological processes underlying the progression of these symptoms are yet unclear. Peripheral inflammation mounted against Brucella may condition neurochemical shifts and hence unchained neuropsychiatric disorders. Our work aimed at establishing whether neurological, behavioral, and neurochemical disarrays are circumstantially linked to peripheral inflammation uprise secondary to Brucella abortus 2308 infections. We then evaluated, in control and Brucella-infected mice, skeletal muscle strength, movement coordination, and balance and motivation, as well as dopamine, epinephrine, norepinephrine, and serotonin availability in the cerebellum, frontal cortex, and hippocampus. Serum levels of proinflammatory cytokines and corticosterone in vehicle-injected and -infected mice were also estimated. All estimates were gathered at the infection acute and chronic phases. Our results showed that infected mice displayed motor disabilities, muscular weakness, and reduced motivation correlated with neurochemical and peripheral immunological disturbances that tended to decrease after 21 days of infection. The present observations support that disturbed peripheral inflammation and the related neurochemical disruption might lead to mood disorders in infected mice. Future experiments must be aimed at establishing causal links and to explore whether similar concepts might explain neurological and mood disorders in humans affected by brucellosis.

Activation and deactivation steps in the tryptophan breakdown pathway in major depressive disorder: A link to the monocyte inflammatory state of patients

It is unclear how the tryptophan (TRP) breakdown pathway relates to the activated inflammatory state of patients with major depressive disorder (MDD). We determined in two different cohorts of patients with MDD (n = 281) and healthy controls (HCs) (n = 206) collected for the EU-MOODINFLAME project: We then correlated outcomes to each other, and to the clinical characteristics of patients. Both cohorts of patients differed clinically; patients of the Munich cohort (n = 50) were less overweight, less medicated, were less in the current episode and showed a higher HAM-D 17 score as compared with patients of the Muenster cohort (n = 231). An increased expression of ICCGs was found in the circulating monocytes of patients of both cohorts; this was in particular evident in the Munich cohort. In contrast, ISGs monocyte expression levels tended to be reduced (both cohorts). TRP serum levels were linked to the pro-inflammatory (ICCGs) monocyte state of patients; a decrease in TRP serum levels was found in the Munich cohort; TRP levels correlated negatively to patient's HAM-D 17 score. Contrary to what expected, KYN serum levels were not increased in patients (both cohorts); and an increased KYN/TRP ratio was only found in the Munich patients (who showed the lowest TRP serum levels). IDO-1 monocyte expression levels were decreased in patients (both cohorts) and negatively associated to their pro-inflammatory (ICCGs) monocyte state. Thus, a depletion of TRP via an ICCGs-inflammatory IDO activation is not likely in MDD. Downstream from KYN, and regarding compounds influencing glutamate receptors (GR), reduced serum levels of KYNA (NMDA-R antagonist), 3-HK (NMDA-R agonist), and XA (mGlu2/3 agonist) were found in patients of both cohorts; PIC serum levels (NMDA-R antagonist) were increased in patients of both cohorts. Reduced QUIN serum levels (NMDA-R agonist) were found in patients of the Muenster cohort,only. 3-HK levels correlated to the monocyte inflammatory ICCG state of patients. The ultimate effect on brain glutamate receptor triggering of this altered equilibrium between peripheral agonists and antagonists remains to be elucidated.

Kynurenine Pathway of Tryptophan Metabolism in Neuropsychiatric Disorders: Pathophysiologic and Therapeutic Considerations

Under physiological conditions 95% of the ingested essential amino acid tryptophan is metabolized by the kynurenine pathway (KP) to yield the ubiquitous co-enzyme nicotinamide adenine dinucleotide, fulfilling cellular energy require-ments. Importantly, the intermediaries of KP exert crucial effects throughout the body, including the central nervous system. Besides, KP metabolites are implicated in diverse disease processes such as inflammation/immune disorders, endocrine/metabolic conditions, cancers and neuropsychiatric diseases. A burgeoning body of research indicates that the KP plays a pathogenic role in major psychiatric diseases like mood disorders and schizophrenia. Triggered by inflammatory processes, the balance between neurotoxic and neuroprotective branches of the KP is disturbed. In preclinical models these discrepancies result in behaviors reminiscent of depression and psychosis. In clinical samples, recent studies are discovering key kynurenine pathway abnormalities which incriminate it in the pathogenesis of the main psychiatric disorders. Harnessing this knowledge has the potential to find disease biomarkers helpful in identifying and prognosticating neuropsychiatric disorders. Concurrently, earnest research efforts directed towards manipulating the KP hold the promise of discovering novel pharmacological agents that have therapeutic value. In this manuscript, an in-depth appraisal of the extant literature is done to understand the working of KP as this applies to neuropsychiatric disorders. It is concluded that this pathway plays an overarching role in the development of major psychiatric disorders, the KP metabolites have the potential to serve as disease markers and new medications based on KP modulation can bring lasting cures for patients suffering from these intractable conditions.

TDO Promotes Hepatocellular Carcinoma Progression

Purpose

Tryptophan 2,3-dioxygenase (TDO), encoded by the gene TDO2, is an enzyme that catalyses the first and rate-limiting step of tryptophan (Try) degradation in the kynurenine (Kyn) pathway in the liver. Recently, TDO has been demonstrated to be expressed in various human tumours, especially hepatocellular carcinoma (HCC). However, the role of TDO in HCC is still not very clear. Here, we studied the role of TDO in HCC.

Methods

We demonstrated that TDO is overexpressed in human HCC tissues and is significantly correlated with malignant phenotype characteristics, including tumour size, tumour differentiation, vascular invasion, etc. Kaplan–Meier analysis showed a poor overall survival rate in patients with TDO-overexpressing tumours. In addition, the effects of TDO on HCC tumour growth and metastasis were detected both in vivo and in vitro. TDO overexpression facilitated HCC cell growth, invasion and migration.

Conclusion

Our results suggest that TDO positively regulates HCC proliferation and invasion and acts as a new prognostic biomarker of HCC.

Acute and Chronic Mental Stress Both Influence Levels of Neurotransmitter Precursor Amino Acids and Derived Biogenic Amines

Acute and chronic mental stress are both linked to somatic and psychiatric morbidity, however, the neurobiological pathways of these associations are still not fully elucidated. Mental stress is known to be immunomodulatory, which is one of the basic concepts of psychoneuroimmunology. In the present study, neurotransmitter precursor amino acid levels and derived biogenic amines were analyzed prior to and at 0, 30 and 60 min following an acute mental stress test (with/without chronic mental stress) in 53 healthy subjects. Psychometric measurements of mental stress, depression and anxiety were collected. Kynurenine/tryptophan was influenced by the factor acute mental stress (KYN/TRP increase), no influence of the factor chronic mental stress or any interaction was found. Phenylalanine/tyrosine was influenced by the factor acute mental stress (PHE/TYR increase) as well as by chronic mental stress (PHE/TYR decrease). Interactions were not significant. KYN/TRP correlated with state anxiety values, while PHE/TYR correlated negatively with chronic stress parameters. Kynurenic acid was significantly reduced in the acute and quinolinic acid in the chronic mental stress condition. In conclusion, neurotransmitter precursor amino acid levels and derived biogenic amines are influenced by acute and chronic mental stress. Mechanisms beyond direct immunological responses may be relevant for the modulation of neurotransmitter metabolism such as effects on enzyme function through cofactor availability or stress hormones.

PCC0208009, an indirect IDO1 inhibitor, alleviates neuropathic pain and co-morbidities by regulating synaptic plasticity of ACC and amygdala

BACKGROUND AND PURPOSE

Indoleamine 2, 3-dioxygenase 1 (IDO1) has been linked to neuropathic pain and IDO1 inhibitors have been shown to reduce pain in animals. Some studies have indicated that IDO1 expression increased after neuropathic pain in hippocampus and spinal cord, whether these changes existing in anterior cingulate cortex (ACC) and amygdala remains obscure and how IDO1 inhibition leads to analgesia is largely unknown. Here, we evaluated the antinociceptive effect of PCC0208009, an indirect IDO1 inhibitor, on neuropathic pain and examined the related neurobiological mechanisms.

EXPERIMENTAL APPROACH

The effects of PCC0208009 on pain, cognition and anxiogenic behaviors were evaluated in a rat model of neuropathic pain. Motor disorder, sedation and somnolence were also assessed. Biochemical techniques were used to measure IDO1-mediated signaling changes in ACC and amygdala.

KEY RESULTS

In rats receiving spinal nerve ligation (SNL), IDO1 expression level was increased in ACC and amygdala. PCC0208009 attenuated pain-related behaviors in the formalin test and SNL model and increased cognition and anxiogenic behaviors in SNL rats at doses that did not affect locomotor activity and sleeping. PCC0208009 inhibited IDO1 expression in ACC and amygdala by inhibiting the IL-6-JAK2/STAT3-IDO1-GCN2-IL-6 pathway. In addition, PCC0208009 reversed synaptic plasticity at the functional and structural levels by suppressing NMDA2B receptor and CDK5/MAP2 or CDK5/Tau pathway in ACC and amygdala.

CONCLUSION AND IMPLICATIONS

These results support the role of IDO1-mediated molecular mechanisms in neuropathic pain and suggest that the IDO1 inhibitor PCC0208009 demonstrates selective pain suppression and could be a useful pharmacological therapy for neuropathic pain.

Pathoetiology and pathophysiology of borderline personality: Role of prenatal factors, gut microbiome, mu- and kappa-opioid receptors in amygdala-PFC interactions

The pathoetiology and pathophysiology of borderline personality disorder (BPD) have been relatively under-explored. Consequently, no targetted pharmaceutical treatments or preventative interventions are available. The current article reviews the available data on the biological underpinnings of BPD, highlighting a role for early developmental processes, including prenatal stress and maternal dysbiosis, in BPD pathoetiology. Such factors are proposed to drive alterations in the infant's gut microbiome, in turn modulating amygdala development and the amygdala's two-way interactions with other brain regions. Alterations in opioidergic activity, including variations in the ratio of the mu-and kappa-opioid receptors seem a significant aspect of BPD pathophysiology, contributing to its comorbidities with depression, anxiety, impulsivity and addiction. Stress and dysphoria are commonly experienced in people classed with BPD. A growing body of data, across a host of medical conditions, indicate that stress and mood dysregulation may be intimately associated with gut dysbiosis and increased gut permeability, coupled to heightened levels of oxidative stress and immune-inflammatory activity. It urgently requires investigation as to the relevance of such gut changes in the course of BPD symptomatology. Accumulating data indicates that BPD symptom exacerbations may be linked to cyclical variations in estrogen, in turn decreasing serotonin and local melatonin synthesis, and thereby overlapping with the pathophysiology of migraine and endometriosis, which also have a heightened association with BPD. Future research directions and treatment implications are indicated.

Indoleamine-2,3-Dioxygenase Mediates Emotional Deficits by the Kynurenine/Tryptophan Pathway in the Ethanol Addiction/Withdrawal Mouse Model

Objective

Our study was designed to investigate whether the indoleamine-2,3-dioxygenase (IDO)-mediated kynurenine/tryptophan (KYN/TRP) pathway participates in the development of emotional deficits from ethanol addiction/withdrawal mice.

Methods

The expression of proinflammatory factors, including tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6), was tested by enzyme-linked immunosorbent assay (ELISA). The IDO levels in the hippocampus, cerebral cortex, and amygdala were measured by polymerase chain reaction (PCR) and western blot, and the neurotransmitters were tested by high performance liquid chromatography (HPLC). Emotional deficits of mice were evaluated by behavioral tests.

Results

Expression levels of inflammatory factors (TNF-α, IL-1β, and IL-6) were increased in mice after 4 weeks of alcohol exposure. As for indoleamine 2,3-dioxygenase (IDO) expression, only the subtype IDO1 was found to increase at both mRNA level and protein level in all the tested brain regions of ethanol addiction/withdrawal mice. In behavioral tests, mice exposed to alcohol showed gradually declined memory function accompanied by anxiety-like and depressive-like behaviors. Meanwhile, increased expression of KYN, decreased expression of 5-HT, and abnormal expression of 3-HK and KA were found in the hippocampus, cerebral cortex, and amygdala of ethanol addiction/withdrawal mice. Interestingly, the IDO1 inhibitor, 1-methyl-L-tryptophan (1-MT), reversed all above alterations induced by ethanol in mice.

Conclusion

Our results suggested that the TRP/KYN pathway, medicated by IDO1, in the hippocampus, cerebral cortex, and amygdala, plays an important role in the development of emotional deficits caused by ethanol addiction and withdrawal.

Modeling Tryptophan/Indoleamine 2,3-Dioxygenase with Heme Superoxide Mimics: Is Ferryl the Key Intermediate?

Tryptophan oxidation in biology has been recently implicated in a vast array of paramount pathogenic conditions in humans, including multiple sclerosis, rheumatoid arthritis, type-I diabetes, and cancer. This 2,3-dioxygenative cleavage of the indole ring of tryptophan with dioxygen is mediated by two heme enzymes, tryptophan 2,3-dioxygenase (TDO) and indoleamine 2,3-dioxygenase (IDO), during its conversion to N-formylkynurenine in the first and rate-limiting step of kynurenine pathway. Despite the pivotal significance of this enzymatic transformation, a vivid viewpoint of the precise mechanistic events is far from complete. A heme superoxide adduct is thought to be the active oxidant in both TDO and IDO, which, following O-O bond cleavage, presumably generates a key ferryl (Fe^IV=O) reaction intermediate. This study, for the first time in model chemistry, demonstrates the potential of synthetic heme superoxide adducts to mimic the bioinorganic chemistry of indole dioxygenation by TDO and IDO, challenging the widely accepted categorization of these metal adducts as weak oxidants. Herein, an electronically divergent series of ferric heme superoxo oxidants mediates the facile conversion of an array of indole substrates into their corresponding 2,3-dioxygenated products, while shedding light on an unequivocally occurring, putative ferryl intermediate. The oxygenated indole products have been isolated in ∼31% yield, and characterized by LC-MS, ¹H and ¹³C NMR, and FT-IR methodologies, as well as by ¹⁸O_2(g) labeling experiments. Distinctly, the most electron-deficient superoxo adduct is observed to react the fastest, specifically with the most electron-rich indole substrate, underscoring the cruciality of electrophilicity of the heme superoxide moiety in facilitating the initial indole activation step. Comprehensive understanding of such mechanistic subtleties will benefit future attempts in the rational design of salient therapeutic agents, including next generation anticancer drug targets with amplified effectivity.

Curcumin in Depression: Potential Mechanisms of Action and Current Evidence-A Narrative Review

Major depressive disorder (MDD) is one of the most prevalent and debilitating disorders. Current available treatments are somehow limited, so alternative therapeutic approaches targeting different biological pathways are being investigated to improve treatment outcomes. Curcumin is the main active component in the spice turmeric that has been used for centuries in Ayurvedic medicine to treat a variety of conditions, including anxiety and depressive disorders. In the past decades, curcumin has drawn researchers' attention and displays a broad range of properties that seem relevant to depression pathophysiology. In this review, we break down the potential mechanisms of action of curcumin with emphasis on the diverse systems that can be disrupted in MDD. Curcumin has displayed, in a number of studies, a potency in modulating neurotransmitter concentrations, inflammatory pathways, excitotoxicity, neuroplasticity, hypothalamic-pituitary-adrenal disturbances, insulin resistance, oxidative and nitrosative stress, and endocannabinoid system, all of which can be involved in MDD pathophysiology. To date, a handful of clinical trials have been published and suggest a benefit of curcumin in MDD. With evidence that is progressively growing, curcumin appears as a promising alternative option in the management of MDD.

Ultra-performance liquid chromatography-tandem mass spectrometry quantitative profiling of tryptophan metabolites in human plasma and its application to clinical study

A sensitive, rapid and reliable ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to assay tryptophan (TRP) and its nine metabolites, including kynurenine (KYN), kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK), 3-hydroxyanthranilic acid (3-HAA), xanthurenic acid (XA), 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), 3-indolepropionic acid (IPA) and 3-indoleacetic acid (IAA) in human plasma. Tryptophan-d5 (TRP-d5) and carbamazepine (CAR) were applied to the method quantification, where TRP-d5 was the corresponding internal standard (IS) for TRP and KYN, and CAR was the corresponding IS for the other analytes. Plasma samples were processed by deproteinisation with acetonitrile, followed by separation on an Acquity UPLC HSS T3 column by using gradient elution with 0.1% (v/v) formic acid in water and acetonitrile and detection by electrospray ionisation tandem mass spectrometry in positive ion multiple reaction monitoring (MRM) within a total run time of 5 min. The calibration ranges were 3-600 ng/mL for 3-HK, 1.5-300 ng/mL for 5-HT, 25-5000 ng/mL for KYN, 1-200 ng/mL for XA, 100-20,000 ng/mL for TRP, 5-1000 ng/mL for KYNA, 2-400 ng/mL for 3-HAA, 2.5-500 ng/mL for 5-HIAA and 10-2000 ng/mL for IAA and IPA. All intra- and inter-day analytical variations were acceptable. Matrix effect and recovery evaluation proved that matrix effect can be negligible, and sample preparation approach was effective. The newly developed method can simultaneously determine a panel of TRP metabolites and was successfully applied in the clinical study characterising TRP metabolism in healthy volunteers.

Antidepressant effect of venlafaxine in chronic unpredictable stress: Evidence of the involvement of key enzymes responsible for monoamine neurotransmitter synthesis and metabolism

A number of studies have linked abnormalities in the function of the serotonergic and noradrenergic systems to the pathophysiology of depression. It has been reported that selective serotonin reuptake inhibitors promote the expression of tryptophan hydroxylase (TPH), which is involved in the synthesis of serotonin. However, limited evidence of TPH alteration has been found in selective serotonin and noradrenaline reuptake inhibitors (SNRIs), and more key enzymes need to be investigated. The aim of the present study was to determine whether venlafaxine (VLX; a classical SNRI) regulates TPH and other key enzymes responsible for the synthesis and metabolism of monoaminergic transmitters in rats with chronic unpredictable stress (CUS). The present results suggested that CUS‑exposed rats exhibited decreased locomotor activity in the open‑field test and increased immobility time in the forced swim test, as compared with the controls. Pretreatment with VLX (20 mg/kg) significantly increased locomotor activity and reduced immobility time in the CUS‑exposed rats. In addition, VLX (20 mg/kg) treatment prevented the CUS‑induced reduction in tyrosine hydroxylase and TPH expression in the cortex and hippocampus. Furthermore, VLX alleviated the CUS‑induced oxidative stress in the serum, cortex and hippocampus. However, VLX administration did not have an effect on indoleamine‑2,3‑dioxygenase overexpression in the hippocampus. It was therefore concluded that the regulation of abnormalities in the synthesis and metabolism of monoaminergic transmitters may be associated with the antidepressant effects of VLX, suggesting that multimodal pharmacological treatments can efficiently treat depression.

Therapeutic Duration and Extent Affect the Effect of Moxibustion on Depression-Like Behaviour in Rats via Regulating the Brain Tryptophan Transport and Metabolism

Moxibustion has been widely accepted as an alternative therapy for major depressive disease (MDD). However, the efficacy of moxibustion treatment on MDD is highly variable because of its irregular operation. This study was designed to investigate how therapeutic duration and extent influence the anti-depression effect of moxibustion and the underlying mechanism involved. Rats with lipopolysaccharide-induced depression-like behavior were treated by moxibustion treatment. The anti-depression effect was determined by forced swimming test and open field test. Tryptophan (Trp) transport and its metabolism to serotonin (5-HT) and kynurenine (Kyn) were evaluated to explore the anti-depression mechanism. The results showed that moxibustion treatment could alleviate the depression-like behavior in rats. Trp transport and 5-HT generation were significantly increased, and the Trp-Kyn pathway was moderately inhibited by moxibustion. Prolonged therapy could be beneficial to the anti-depression effect by promoting the brain uptake of Trp and shifting the Trp metabolism to 5-HT. An enhanced therapeutic extent could increase 5-HT generation. In conclusion, this study determined that the anti-depression effect of moxibustion involves improved Trp transport and metabolism. The therapeutic duration benefits antidepressant effects, but the complex influence of the therapeutic extent on moxibustion efficacy requires further studies.

Development of an underivatized LC-MS/MS method for quantitation of 14 neurotransmitters in rat hippocampus, plasma and urine: Application to CUMS induced depression rats

Sensitive and comprehensive measurement of systemic metabolites of tryptophan, phenylalanine and glutamate metabolism in biological samples is effective for understanding the pathogenesis of depression and other neurological diseases. Therefore, this study developed an underivatized liquid chromatography tandem mass spectrometry (LC-MS/MS) method for simultaneous monitoring the 3 components of glutamate metabolism in rat hippocampus and 11 components of tryptophan and phenylalanine metabolism in rat hippocampus, plasma and urine, and applied it to investigate their changes in rats induced by chronic unpredictable mild stress (CUMS). The investigated analytes are as follows: tryptophan, serotonin, 5-hydroxyindoleacetic acid, kynurenine, kynurenic acid, xanthurenic acid, 3-hydroxyanthranilic acid, quinolinic acid, phenylalanine, tyrosine, tyramine, glutamate, glutamine and gamma-aminobutyric acid. The method was verified to be sensitive and effective with satisfactory linearity, accuracies in the range of 78.2%-120.4%, and precisions less than 17.8% for all identified analytes. A series of significant changes in CUMS-induced rats can be detected: tryptophan, serotonin and tyrosine levels decreased and quinolinic acid increased in both hippocampus and plasma. In addition, the kynurenine/tryptophan ratios increased in hippocampus and plasma, the kynurenic acid/quinolinic acid ratios of plasma and urine were significantly reduced. These findings demonstrated that the CUMS procedure could lead to the central and peripheral imbalances of tryptophan and phenylalanine metabolism. In conclusion, a LC-MS/MS method for simultaneous measurement of several neurotransmitters in rat hippocampus, plasma and urine was developed and successfully applied to investigation of the central and peripheral changes in CUMS-induced rats. The method would be expected to provide applicability to the study of the mechanisms of depression and other related diseases associated with these neurotransmitters.

Is the HPA Axis as Target for Depression Outdated, or Is There a New Hope?

Major depressive disorder (MDD) is a very common stress-related mental disorder that carries a huge burden for affected patients and the society. It is associated with a high mortality that derives from suicidality and the development of serious medical conditions such as heart diseases, diabetes, and stroke. Although a range of effective antidepressants are available, more than 50% of the patients do not respond to the first treatment they are prescribed and around 30% fail to respond even after several treatment attempts. The heterogeneous condition of MDD, the lack of biomarkers matching patients with the right treatments and the situation that almost all available drugs are only targeting the serotonin, norepinephrine, or dopamine signaling, without regulating other potentially dysregulated systems may explain the insufficient treatment status. The hypothalamic-pituitary-adrenal (HPA) axis is one of these other systems, there is numerous and robust evidence that it is implicated in MDD and other stress-related conditions, but up to date there is no specific drug targeting HPA axis components that is approved and no test that is routinely used in the clinical setting identifying patients for such a specific treatment. Is there still hope after these many years for a breakthrough of agents targeting the HPA axis? This review will cover tests detecting altered HPA axis function and the specific treatment options such as glucocorticoid receptor (GR) antagonists, corticotropin-releasing hormone 1 (CRH₁) receptor antagonists, tryptophan 2,3-dioxygenase (TDO) inhibitors and FK506 binding protein 5 (FKBP5) receptor antagonists.