Kynurenine pathway of tryptophan metabolism in pathophysiology and therapy of major depressive disorder

Metabolomics signatures of serotonin reuptake inhibitor (escitalopram), serotonin norepinephrine reuptake inhibitor (duloxetine) and cognitive-behavioral therapy on key neurotransmitter pathways in major depressive disorder

Metabolomics provides powerful tools that can inform about heterogeneity in disease and response to treatments. In this exploratory study, we employed an electrochemistry-based targeted metabolomics platform to assess the metabolic effects of three randomly-assigned treatments: escitalopram, duloxetine, and Cognitive-Behavioral Therapy (CBT) in 163 treatment-naïve outpatients with major depressive disorder. Serum samples from baseline and 12 weeks post-treatment were analyzed using targeted liquid chromatography-electrochemistry for metabolites related to tryptophan, tyrosine metabolism and related pathways. Changes in metabolite concentrations related to each treatment arm were identified and compared to define metabolic signatures of exposure. In addition, association between metabolites and depressive symptom severity (assessed with the 17-item Hamilton Rating Scale for Depression [HRSD17]) and anxiety symptom severity (assessed with the 14-item Hamilton Rating Scale for Anxiety [HRSA14]) were evaluated, both at baseline and after 12 weeks of treatment. Significant reductions in serum serotonin level and increases in tryptophan-derived indoles that are gut bacterially derived were observed with escitalopram and duloxetine arms but not in CBT arm. These include indole-3-propionic acid (I3PA), indole-3-lactic acid (I3LA) and Indoxyl sulfate (IS), a uremic toxin. Purine-related metabolites were decreased across all arms. Different metabolites correlated with improved symptoms in the different treatment arms revealing potentially different mechanisms between response to antidepressant medications and to CBT.

Genome-wide interaction association analysis identifies interactive effects of childhood maltreatment and kynurenine pathway on depression

Childhood maltreatment stands out as a pivotal risk factor for depression, with gene-by-environment interaction serving as a crucial mechanism. Here we perform genome-wide interaction analyzes of childhood maltreatment in the UK Biobank, integrating methylation evidence through colocalization analysis and identifying associated brain structure abnormalities from childhood to adulthood. A genome-wide significant genomic region interacting with childhood maltreatment is identified at 8p11.21 (IDO2 rs7846217, P = 2.02e-08), implicating the tryptophan-kynurenine pathway. Colocalization analysis reveals that IDO2 rs11777027, rs2340953 and rs28631334 are associated with depression in individuals exposed to childhood maltreatment and colocalize with methylation signals in both blood and brain for IDO2. These interactions affect cortical thickness of the left supramarginal gyrus in children (P = 9.72e-04) and adults (P = 1.34e-04), as well as cortical volume in the right angular gyrus in children (P = 1.02e-04). Furthermore, the interactions significantly predict new-onset depression at a 2-year follow-up in children. Stunted increase in cortical thickness of the left middle-anterior cingulate gyrus and sulcus significantly mediates the interaction between childhood maltreatment and IDO2 on childhood depression. These interactions also moderate antidepressant treatment efficacy at 4-6 weeks.

Sex-Specific Alterations of the Kynurenine Pathway in Association With Risk for and Remission of Depression in Adolescence

BACKGROUND

The imbalance between neurotoxic and neuroprotective metabolites of the kynurenine pathway has been implicated in the pathophysiology of major depressive disorder (MDD) in adulthood but has not been fully investigated among adolescents. In this study, we tested the association of kynurenine pathway metabolites with risk for and remission of adolescent depression and whether abnormalities in the kynurenine pathway are sex specific.

METHODS

Kynurenine pathway metabolites were measured in plasma at baseline in the IDEA-RiSCo (Identifying Depression Early in Adolescence Risk-Stratified Cohort), a longitudinal study of adolescents (15.6 ± 0.8 years; 50% female) stratified into 3 groups (each n = 50): 1) at low risk for developing depression, 2) at high risk for developing depression, or 3) with MDD. Adolescents with MDD at baseline were followed up after 3 years (n = 41) to assess remission or persistence of MDD.

RESULTS

Cross-sectional analyses at baseline showed that adolescents at high risk for depression and adolescents with MDD had lower kynurenic acid concentrations and kynurenic acid/quinolinic acid ratio than low-risk adolescents. These differences were not present in males but appeared to be driven by females. Proinflammatory cytokines positively correlated with neurotoxic metabolites, specifically in the high-risk and MDD groups. Female individuals with persistent MDD at the 3-year follow-up showed lower baseline kynurenine and higher 3-hydroxykynurenine/kynurenine ratio than those who experienced remission at 3-year follow-up.

CONCLUSIONS

The findings suggest a sex-specific kynurenine pathway alteration in adolescent depression. Female adolescents at higher risk for or with depression showed a reduction in neuroprotective metabolites. An increased diversion of kynurenine toward production of neurotoxic metabolites predicted persistent depression in female adolescents with MDD.

Isobicyclogermacrenal ameliorates hippocampal ferroptosis involvement in neurochemical disruptions and neuroinflammation induced by sleep deprivation in rats

BACKGROUND

Sleep deprivation (SLD) is a widespread condition that disrupts physiological functions and may increase mortality risk. Valeriana officinalis, a traditional medicinal herb known for its sedative and hypnotic properties, contains isobicyclogermacrenal (IG), a newly isolated active compound. However, research on the therapeutic potential of IG for treating SLD remains limited.

METHODS

In this study, IG was extracted and characterized from Valeriana officinalis, and an SLD model was established in rats using p-chlorophenylalanine (PCPA). Behavioral tests and pathological studies were conducted to assess the effects of IG on SLD, and transcriptomic and metabolomic analyses were utilized to investigate its underlying mechanisms.

RESULTS

IG administration significantly improved the cognitive performance of SLD rats in behavioral tests and ameliorated histological injuries in the hippocampus and cerebral cortex. IG treatment increased the levels of brain-derived neurotrophic factor (BDNF) and neurotransmitters such as serotonin (5-HT) in SLD rats. Additionally, IG directly targets TFRC, thereby improving iron metabolism in the hippocampus. Comprehensive transcriptomic and metabolomic analyses revealed that the improvements from IG stemmed from the mitigation of abnormalities in iron metabolism, cholesterol metabolism, and glutathione metabolism, leading to reduced oxidative stress, ferroptosis, and neuroinflammation in the hippocampus caused by SLD.

CONCLUSIONS

Collectively, these findings suggest that IG has the potential to ameliorate neurological damage and cognitive impairment caused by SLD, offering a novel strategy for protection against the adverse effects of SLD.

Depression, stress, and tryptophan metabolism through the kynurenine pathway: treatment strategies from the perspective of Chinese herbal medicine

The pathogenesis of depression is complex, involving abnormalities in tryptophan (TRP) metabolism through the kynurenine pathway (KP). Moreover, depression is closely related to the hypothalamic-pituitary-adrenal (HPA) axis, the gut-brain axis, neuroinflammation, and stress. These factors collectively influence the multidimensional pathological mechanisms of depression. TRP, a fundamental amino acid, serves as a precursor for neuroactive metabolites vital to physiological functions. Central to TRP metabolism is the KP, and the imbalance between neurotoxic and neuroprotective metabolites is closely related to the onset and progression of depression. Therefore, maintaining the balance of KP metabolites is important. In this review, we have investigated the role of the KP in depression and explored the complexity of KP dysregulation and its therapeutic importance. Here, we highlight how a deeper understanding of the KP and its regulation can pave the way for new treatment strategies. Specifically, we have summarized the latest advances in elucidating the key mechanisms of rate-limiting enzyme inhibitors, providing insights into their potential therapeutic efficacy. In addition, we have explored the emerging field of Chinese herbal medicine, discussing its potential to regulate KP metabolites and alleviate depressive symptoms, thereby expanding the treatment options for depression. Our findings emphasize the multifaceted nature of depression and the necessity of interdisciplinary research to fully utilize KP regulation and Chinese herbal medicine as strategies to advance the treatment of depression.

Level of selected exponents of the kynurenine pathway in patients diagnosed with depression and selected cancers

Altered immune system activity is one of the common pathomechanisms of depressive disorders and cancer. The aim of this study is to evaluate level of selected elements of the kynurenine pathway in groups of depressed and oncological patients. The study included 156 individuals, aged 19-65 years (M = 43.46, SD = 13.99), divided into three groups, namely depressive disorders (DD), oncology patients (OG), and a comparison group of healthy subjects (CG). A sociodemographic questionnaire and the Hamilton Depression Rating Scale (HDRS) were used in the study to assess the intensity of depressive symptoms. Level of TDO2, L-KYN, HK, AA and QA was significantly higher in patients from OG and DD groups than in the comparison group. TDO2 level in the OG group was positively correlated with the severity of depressive symptoms. When the OG and DD groups were analyzed together, level of TDO2, 3-HKYN, AA, QA correlated positively with the severity of depressive symptoms. Thus, kynurenine pathway might play an integral role in the pathogenesis of depression.

Pathogenesis and therapeutic strategies for cancer-related depression

Depression is a common co-morbidity among cancer cases, which has a detrimental influence on cancer treatment and prognosis. Recent advancements in the neurobiology of depression and cancer pathophysiology have revealed several shared biobehavioral mechanisms and introduced new therapeutic strategies. In this review, we summarize the biological mechanisms driving cancer-related depression, including psychosocial factors, immuno-inflammatory processes, chronic stress, dysbiosis of gut microbiota, and medically-induced factors. Interventions used for cancer-related depression may include psychosocial therapies, pharmacological therapies, immunotherapies, psychobiological medications, and dietary strategies. This review could inspire the elucidation of possible co-occurring mechanisms and complex interactions between cancer and depression, provide an opportunity to propose faster and more effective therapies for cancer-related depression, and well as new strategies for cancer in the future.

The Complex World of Kynurenic Acid: Reflections on Biological Issues and Therapeutic Strategy

It has been unequivocally established that kynurenic acid has a number of actions in a variety of cells and tissues, raising, in principle, the possibility of targeting its generation, metabolism or sites of action to manipulate those effects to a beneficial therapeutic end. However, many basic aspects of the biology of kynurenic acid remain unclear, potentially leading to some confusion and misinterpretations of data. They include questions of the source, generation, targets, enzyme expression, endogenous concentrations and sites of action. This essay is intended to raise and discuss many of these aspects as a source of reference for more balanced discussion. Those issues are followed by examples of situations in which modulating and correcting kynurenic acid production or activity could bring significant therapeutic benefit, including neurological and psychiatric conditions, inflammatory diseases and cell protection. More information is required to obtain a clear overall view of the pharmacological environment relevant to kynurenic acid, especially with respect to the active concentrations of kynurenine metabolites in vivo and changed levels in disease. The data and ideas presented here should permit a greater confidence in appreciating the sites of action and interaction of kynurenic acid under different local conditions and pathologies, enhancing our understanding of kynurenic acid itself and the many clinical conditions in which manipulating its pharmacology could be of clinical value.

Research fronts and researchers of World Journal of Psychiatry in 2023: A visualization and analysis of mapping knowledge domains

BACKGROUND

In the rapidly evolving landscape of psychiatric research, 2023 marked another year of significant progress globally, with the World Journal of Psychiatry (WJP) experiencing notable expansion and influence.

AIM

To conduct a comprehensive visualization and analysis of the articles published in the WJP throughout 2023. By delving into these publications, the aim is to determine the valuable insights that can illuminate pathways for future research endeavors in the field of psychiatry.

METHODS

A selection process led to the inclusion of 107 papers from the WJP published in 2023, forming the dataset for the analysis. Employing advanced visualization techniques, this study mapped the knowledge domains represented in these papers.

RESULTS

The findings revealed a prevalent focus on key topics such as depression, mental health, anxiety, schizophrenia, and the impact of coronavirus disease 2019. Additionally, through keyword clustering, it became evident that these papers were predominantly focused on exploring mental health disorders, depression, anxiety, schizophrenia, and related factors. Noteworthy contributions hailed authors in regions such as China, the United Kingdom, United States, and Turkey. Particularly, the paper garnered the highest number of citations, while the American Psychiatric Association was the most cited reference.

CONCLUSION

It is recommended that the WJP continue in its efforts to enhance the quality of papers published in the field of psychiatry. Additionally, there is a pressing need to delve into the potential applications of digital interventions and artificial intelligence within the discipline.

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.

Metabolomics Signatures of serotonin reuptake inhibitor (Escitalopram), serotonin norepinephrine reuptake inhibitor (Duloxetine) and Cognitive Behavior Therapy on Key Neurotransmitter Pathways in Major Depressive Disorder

Metabolomics provides powerful tools that can inform about heterogeneity in disease and response to treatments. In this study, we employed an electrochemistry-based targeted metabolomics platform to assess the metabolic effects of three randomly-assigned treatments: escitalopram, duloxetine, and Cognitive Behavior Therapy (CBT) in 163 treatment-naïve outpatients with major depressive disorder. Serum samples from baseline and 12 weeks post-treatment were analyzed using targeted liquid chromatography-electrochemistry for metabolites related to tryptophan, tyrosine metabolism and related pathways. Changes in metabolite concentrations related to each treatment arm were identified and compared to define metabolic signatures of exposure. In addition, association between metabolites and depressive symptom severity (assessed with the 17-item Hamilton Rating Scale for Depression [HRSD17]) and anxiety symptom severity (assessed with the 14-item Hamilton Rating Scale for Anxiety [HRSA14]) were evaluated, both at baseline and after 12 weeks of treatment. Significant reductions in serum serotonin level and increases in tryptophan-derived indoles that are gut bacterially derived were observed with escitalopram and duloxetine arms but not in CBT arm. These include indole-3-propionic acid (I3PA), indole-3-lactic acid (I3LA) and Indoxyl sulfate (IS), a uremic toxin. Purine-related metabolites were decreased across all arms. Different metabolites correlated with improved symptoms in the different treatment arms revealing potentially different mechanisms between response to antidepressant medications and to CBT.

Amelioration of Neurochemical Alteration and Memory and Depressive Behavior in Sepsis by Allopurinol, a Tryptophan 2,3-Dioxygenase Inhibitor

BACKGROUND

In response to inflammation and other stressors, tryptophan is catalyzed by Tryptophan 2,3-Dioxygenase (TDO), which leads to activation of the kynurenine pathway. Sepsis is a serious condition in which the body responds improperly to an infection, and the brain is the inflammation target in this condition.

OBJECTIVE

This study aimed to determine if the induction of TDO contributes to the permeability of the Blood-Brain Barrier (BBB), mortality, neuroinflammation, oxidative stress, and mitochondrial dysfunction, besides long-term behavioral alterations in a preclinical model of sepsis.

METHODS

Male Wistar rats with two months of age were submitted to the sepsis model using Cecal Ligation and Perforation (CLP). The rats received allopurinol (Allo, 20 mg/kg, gavage), a TDO inhibitor, or a vehicle once a day for seven days.

RESULTS

Sepsis induction increased BBB permeability, IL-6 level, neutrophil infiltrate, nitric oxide formation, and oxidative stress, resulting in energy impairment in 24h after CLP and Allo administration restored these parameters. Regarding memory, Allo restored short-term memory impairment and decreased depressive behavior. However, no change in survival rate was verified.

CONCLUSION

In summary, TDO inhibition effectively prevented depressive behavior and memory impairment 10 days after CLP by reducing acute BBB permeability, neuroinflammation, oxidative stress, and mitochondrial alteration.

Optimizing Treatment for Major Depressive Disorder in Adolescents: The Impact of Intradermal Acupuncture - A Randomized Controlled Trial Protocol

Background

Major depressive disorder (MDD) exhibits a pronounced occurrence among adolescents, aligning closely with the lifetime prevalence rate of 16.6% observed in adults. It is difficult to treat and prone to recurrence. Acupuncture has shown potential in enhancing treatment effectiveness. Nonetheless, there is a lack of research on the use of intradermal acupuncture (IA) in treating adolescent MDD.

Methods

This study is a double-blind, randomized controlled trial. A cohort of 120 participants will be assigned randomly to three distinct groups, namely a Selective Serotonin Reuptake Inhibitors (SSRIs)-only group, a sham intradermal acupuncture combined with SSRIs (SIA) group, and an active intradermal acupuncture combined with SSRIs (AIA) group. Hamilton Depression Rating Scale will serve as the primary outcome, while Patient Health Questionnaire-9, Self-Rating Depression Scale, Pittsburgh Sleep Quality Index, and Short Form 36 Questionnaire will serve as secondary outcomes in assessing the amelioration of depressive symptoms in patients. These data will be analyzed using SPSS26.0 software.

Results

We will assess the efficacy and safety of IA for MDD using commonly employed clinical psychiatric scales.

Conclusion

The efficacy of IA in treating adolescent MDD may be demonstrated in this study, suggesting its potential for optimizing MDD treatment schemes.

Trial Registration

ClinicalTrials.gov Identifier: NCT05832619 (April 27, 2023).

Liver tryptophan 2,3-dioxygenase: a determinant of anxiety-like behaviour - studies with chronic nicotine administration in rats

Deletion of the tryptophan 2,3-dioxygenase ( TDO2 ) gene induces an anxiolytic-like behaviour in mice and TDO inhibition by allopurinol elicits an antidepressant-like effect in rats exposed to restraint stress. Chronic nicotine administration inhibits TDO activity, enhances brain serotonin synthesis and exerts anxiolytic- and antidepressant-like effects in rodent models. There is a strong association between anxiety, depression and tobacco use, which is stronger in women than in men. The present study aimed to examine the relationship between behavioural measures of anxiety and depression with liver TDO activity, brain tryptophan concentration and serotonin synthesis in rats treated chronically with nicotine. Behavioural measures included the elevated plus maze (EPM), open field (OFT) and forced swim (FST) tests. Biochemical measures included TDO activity, serum corticosterone and brain Trp, 5-HT and 5-HIAA concentrations. Anxiolytic-like and antidepressant-like effects of chronic nicotine were confirmed in association with TDO inhibition and elevation of brain Trp and 5-HT. Sex differences in behaviour were independent of the biochemical changes. At baseline, female rats performed better than males in OFT and FST. Nicotine was less anxiolytic in females in the open arm test. Nicotine treatment did not elicit different responses between sexes in the FST. Our findings support the notion that liver TDO activity exhibits a strong association with behavioural measures of anxiety and depression in experimental models, but provide little evidence for sex differences in behavioural response to nicotine. The TDO-anxiety link may be underpinned by kynurenine metabolites as well as serotonin.