An integrated meta-analysis of peripheral blood metabolites and biological functions in major depressive disorder

Microbiota alterations leading to amino acid deficiency contribute to depression in children and adolescents

BACKGROUND

Major depressive disorder (MDD) in children and adolescents is a growing global public health concern. Metabolic alterations in the microbiota-gut-brain (MGB) axis have been implicated in MDD pathophysiology, but their specific role in pediatric populations remains unclear.

RESULTS

We conducted a multi-omics study on 256 MDD patients and 307 healthy controls in children and adolescents, integrating plasma metabolomics, fecal metagenomics, and resting-state functional magnetic resonance imaging (rs-fMRI) of the brain. KEGG enrichment analysis of 360 differential expressed metabolites (DEMs) indicated significant plasma amino acid (AA) metabolism deficiencies (p-value < 0.0001). We identified 58 MDD-enriched and 46 MDD-depleted strains, as well as 6 altered modules in amino acid metabolism in fecal metagenomics. Procrustes analysis revealed the association between the altered gut microbiome and circulating AA metabolism (p-value = 0.001, M2 = 0.932). Causal analyses suggested that plasma AAs might mediate the impact of altered gut microbiota on depressive and anxious symptoms. Additionally, rs-fMRI revealed that connectivity deficits in the frontal lobe are associated with depression and 22 DEMs in AA metabolism. Furthermore, transplantation of fecal microbiota from MDD patients to adolescent rats induced depressive-like behaviors and 14 amino acids deficiency in the prefrontal cortex (PFC). Moreover, the dietary lysine restriction increased depression susceptibility in adolescent rats by reducing the expression of excitatory amino acid transporters in the PFC.

CONCLUSIONS

Our findings highlight that gut microbiota alterations contribute to AAs deficiency, particularly lysine, which plays a crucial role in MDD pathogenesis in children and adolescents. Targeting AA metabolism may offer novel therapeutic strategies for pediatric depression. Video Abstract.

Alterations of serum metabolic profile in major depressive disorder: A case-control study in the Chinese population

BACKGROUND

Major depressive disorder (MDD) is characterized by persistent depressed mood and cognitive symptoms. This study aimed to discover biomarkers for MDD, explore its pathological mechanisms, and examine the associations of the identified biomarkers with clinical and psychological variables.

AIM

To discover candidate biomarkers for MDD identification and provide insight into the pathological mechanism of MDD.

METHODS

The current study adopted a single-center cross-sectional case-control design. Serum samples were obtained from 100 individuals diagnosed with MDD and 97 healthy controls (HCs) aged between 18 to 60 years. Metabolomics was performed on an Ultimate 3000 UHPLC system coupled with Q-Exactive MS (Thermo Scientific). The online software Metaboanalyst 6.0 was used to process and analyze the acquired raw data of peak intensities from the instrument.

RESULTS

The study included 100 MDD patients and 97 HCs. Metabolomic profiling identified 35 significantly different metabolites (e.g., cortisol, sebacic acid, and L-glutamic acid). Receiver operating characteristic curve analysis highlighted 8-HETE, 10-HDoHE, cortisol, 12-HHTrE, and 10-hydroxydecanoic acid as top diagnostic biomarkers for MDD. Significant correlations were found between metabolites (e.g., some lipids, steroids, and amino acids) and clinical and psychological variables.

CONCLUSION

Our study reported metabolites (some lipids, steroids, amino acids, carnitines, and alkaloids) responsible for discriminating MDD patients and HCs. This metabolite profile may enable the development of a laboratory-based diagnostic test for MDD. The mechanisms underlying the association between psychological or clinical variables and differential metabolites deserve further exploration.

B vitamins as adjunct therapies for depressive disorder

The rising prevalence of depressive disorder worldwide requires better interventional avenues. B vitamins are gaining increasing interest as potential therapeutic approaches in this context given current evidence for a bidirectional association between B vitamin deficiency and depressive disorder. We discuss how B vitamins and B vitamin-associated probiotic supplementation may represent an effective adjunctive treatment for depression, and highlight the key metabolic mechanisms involved. We also provide a perspective on the future of this field and advocate for further high-quality clinical trials to assess the benefits of B vitamins in this context and optimize their clinical implementation.

Serum lipid and plasma fatty acid profiles in PTSD patients and healthy individuals: Associations with symptoms, cognitive function, and inflammatory markers

Increasing evidence suggests that posttraumatic stress disorder (PTSD), a serious mental health condition, is associated with physical health problems. Lipid-related molecules are crucial for central nervous system functions associated with PTSD symptoms; however, case-control studies exploring the relationship between PTSD and lipid-related molecules are scarce. We examined 68 civilian PTSD patients and 97 healthy controls, evaluating PTSD symptoms, childhood maltreatment history, suicidality, and cognitive functions. Cholesterol, triglycerides, and inflammation-related marker levels were analyzed in serum, while fatty acid levels were measured in plasma. Compared to controls, patients exhibited significantly lower high-density lipoprotein cholesterol and n-6 linoleic acid levels, alongside higher saturated palmitic acid levels and the triene-to-tetraene (T/T) ratio. PTSD symptoms, particularly hyperarousal, were significantly positively correlated with n-6 γ-linolenic, n-6 dihomo-γ-linolenic, and n-9 mead acid levels, and the T/T ratio. Cognitive functions were significantly positively correlated with n-3 docosahexaenoic acid and total n-3 fatty acid levels, and negatively correlated with saturated lauric, palmitic, and total saturated fatty acid levels. Suicidality was significantly positively correlated with dihomo-γ-linolenic acid, mead acid levels, and the T/T ratio, and negatively correlated with polyunsaturated fatty acid (PUFA) levels. Inflammation-related marker levels were significantly correlated with higher palmitic, n-9 oleic, and total n-9 fatty acid levels, and lower linoleic acid and PUFA levels. Latent profile analysis (LPA) revealed distinct subgroups associated with unique fatty acid profiles. These lipid-related alterations may improve the understanding of PTSD pathophysiology. Distinct fatty acid profiles identified by LPA may help subtype PTSD patients and guide nutrition-based personalized treatment strategies.

Environmental Enrichment Exposure Alleviates Geriatric Depressive-Like Symptoms through Regulating Neurogenesis and Neuroinflammation

Environmental enrichment (EE) is a significant approach to influencing brain function by altering the environment and changing living conditions and has been shown to modulate mood-related diseases, including depression. Among the elderly, depression is particularly prevalent and is often linked to social isolation. However, the specific role of EE in social isolation-related geriatric depression remains imprecise. This study was intended to explore the status of EE exposure in geriatric depression and to uncover its underlying mechanisms. We utilized 19-month-old male C57BL/6J mice, which are equivalent to humans aged 50-60 years, and induced depression through social isolation. After 2 weeks of social isolation, mice were identified as depressive by using the sugar preference test and then classified into either standard or enrichment environment groups for 4 weeks. Subsequently, conventional indices associated with depression, including neurogenesis, neurotrophic factors, and neuroinflammation, were measured. Results display that EE alleviated the depressive-like symptoms in elderly mice and enriched their social activities. Concurrently, EE regulated levels of certain neurotransmitters in the hippocampus, including the systems of glutamate, tyrosine, and histamine. Moreover, the ability of neurogenesis also increased in the hippocampus of EE mice. At the neuroinflammation level, the activation of Natural Killer (NK) cells and ARG1+ microglia is considered a major contributor to mediating the effects of EE-regulated geriatric depression. Collectively, these results underline the importance of EE in the treatment of geriatric depression and partially elucidate its underlying mechanism, offering valuable suggestions for treating social isolation--related depression via environmental modulation.

Lipidomics and genomics in mental health: insights into major depressive disorder, bipolar disorder, schizophrenia, and obsessive-compulsive disorder

INTRODUCTION

This systematic review explores the hypothesis that various lipid categories and lipid metabolism-related genomic variations link to mental disorders, seeking potential clinically useful markers.

METHODS

We searched PubMed, Scopus, and PsycInfo databases until October 12th, 2024, using terms related to lipidomics, lipid-related genomics, and different mental disorders, i.e., Major Depressive Disorder (MDD), Bipolar Disorder (BD), Schizophrenia (SCZ), and Obsessive-Compulsive Disorder (OCD). Eligible studies were assessed. Extracted data included author, year, methodology, outcomes, genes, and lipids linked to disorders. Bias and evidence certainty were evaluated. The systematic review adhered to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines and a registered protocol (PROSPERO: CRD42023438862).

RESULTS

A total of 27 studies were included. SCZ showed alterations in 77 lipids, including triglycerides (TG), ceramides, and phosphatidylcholine, while MDD and BD exhibited 97 and 47 altered lipids, respectively, with overlap among disorders. Shared genes, such as ABCA13, DGKZ, and FADS, and pathways involving inflammation, lipid metabolism, and mitochondrial function were identified. OCD was associated with sphingolipid signaling and peroxisomal metabolism.

DISCUSSION

Lipid signatures in MDD, BD, and SCZ shed light on underlying processes. Further research is needed to validate biomarkers and refine their clinical applications in precision psychiatry.

Sex-specific differences in peripheral blood metabolites and biological functions in major depressive disorder: A systematic review and meta-analysis

To explore the sex-specific peripheral blood metabolites and biological functions altered in patients with major depressive disorder (MDD). A search was conducted on PubMed, Cochrane, Embase, Web of Science, and other databases published up to 11/2023. To maximize the search, we also reviewed systematic reviews and meta-analyses on the same topic. We included studies that conducted metabolic characterizations during current depressive episodes or after antidepressant treatments, with all data stratified by sex. Fifty-eight studies involving 83 cohorts with 5285 MDD participants were included in this meta-analysis. Random effects meta-analysis was conducted for data from ≥3 cohorts. We identified 5 sex-specific metabolites from 22 candidate peripheral blood metabolites. In males with MDD, we observed lower levels of estradiol and progesterone, alongside higher levels of androstenedione, dihydrotestosterone, and uric acid compared with female MDD patients. In addition, steroid hormone biosynthesis has been identified as a potentially sex-specific pathway. Our findings highlight significant evidence for targeting sex hormones as a broad understanding of MDD, providing potentially objective diagnostic and therapeutic insights.

A Longitudinal Study of the Association of Blood Unsaturated Fatty Acids With Posttraumatic Stress Disorder (PTSD)

AIM

This study aimed to investigate the association between blood fatty acid fractions and posttraumatic stress disorder (PTSD) judgment in individuals who have experienced physical trauma.

METHODS

Patients admitted to the emergency department for trauma, excluding those with brain damage or serious psychiatric disorders, were enrolled. Blood samples were collected on admission, and PTSD symptoms were assessed using a questionnaire 1 and 3 months after the injury. Multiple regression analysis was used to evaluate the association between fatty acids and Posttraumatic Diagnostic Scale severity scores, adjusting for age, sex, the Childhood Trauma Questionnaire (CTQ), and the use of psychotropic medications.

RESULTS

A significant association was observed between certain fatty acids and PTSD judgment. Mann-Whitney U test results revealed that arachidonic acid was associated with PTSD judgment at 1 month and palmitic acid, stearic acid, oleic acid, linoleic acid, linolenic acid, eicosenoic acid, and eicosadiene acid with PTSD judgment at 3 months. Multiple regression analysis revealed that stearic acid, linoleic acid, arachidic acid, docosatetraenoic acid, lignoceric acid, docosahexaenoic acid, and total omega-6 fatty acids (ω6) were associated with PTSD judgment after 1 month after trauma. In contrast, only linoleic acid and total ω6 were associated with PTSD judgment 3 months after trauma.

CONCLUSIONS

This study is the first to enroll patients with general physical trauma and examine the relationship between fatty acids and PTSD. The findings suggest a potential relationship between blood fatty acid fractions and the development of PTSD symptoms in individuals who have experienced physical trauma. However, further research is needed to confirm and expand on these findings.

Lower creatinine levels are associated with an increased risk of depression: evidence from the China Health and Retirement Longitudinal Study

Introduction

Previous studies have found that depressive patients tend to have low levels of creatinine; however, the extent to which creatinine levels are associated with depression has been poorly investigated. Therefore, this study aimed to explore the relationship between creatinine levels and depression.

Methods

The participants and follow-up data from the China Health and Retirement Longitudinal Study (CHARLS), as well as metabolomics data from the Metabolite Network of Depression Database (MENDA), were collected. The 10-item Center for Epidemiologic Studies Depression Scale (CESD-10) was used to assess the severity of depression. Spearman correlation analysis, spline regression, and binary logistic regression models were employed to explore the relationship between creatinine levels and depression.

Results

A total of 7,826 participants and 3,886 follow-up participants were included in the CHARLS 2011 and 2015 surveys. Of these, 37.9% (2,966/7,826) and 34.6% (13,44/3,886) of participants experienced depression in CHARLS 2011 and 2015, respectively. The creatinine level was negatively correlated with the total CESD-10 score and dimensions scores, showing an inverse dose-response relationship between creatinine levels and depression. Compared with participants with high creatinine levels, those with middle creatinine levels were associated with a higher risk of depression (OR = 1.22, 95% CI = 1.08-1.38), while participants with low creatinine levels had the highest risk of depression (OR = 1.30, 95% CI = 1.13-1.49) in the fully adjusted model. Similar results were observed in the follow-up data, and the MENDA metabolomics data validated the negative correlation between creatinine levels and the severity of depression.

Conclusion

Lower levels of creatinine were closely associated with a higher risk of depression, and it could serve as a potential marker for identifying individuals at high risk of depression.

Characterizing metabolomic and proteomic changes in depression: a systematic analysis

Despite the widespread use of metabolomics and proteomics to explore the molecular landscape of depression, there is a lack of consensus regarding dysregulated molecules with replicable evidence. Thus, this study aimed to identify robust metabolomic and proteomic features in depression by integrating evidence from large-scale studies. In this study, a knowledge base-mining approach was adopted to compile a list of dysregulated molecules derived from metabolomic and proteomic studies. A vote-counting approach was performed to identify consistently altered molecules in the blood and urine samples of patients with depression. A total of 2398 molecular entries were selected, comprising 857 unique metabolites and 468 unique proteins from 143 metabolomic and 23 proteomic studies in depression. The results of vote-counting analyses revealed that 11 metabolites in blood and 5 metabolites in urine exhibited consistent disturbances across studies. Circulating levels of glutamic acid and phosphatidylcholine (32:0) were elevated in depressive patients, whereas the levels of tryptophan, kynurenic acid, kynurenine, acetylcarnitine, serotonin, creatinine, inosine, phenylalanine, and valine were lower. Urinary levels of isobutyric acid, alanine, and nicotinic acid were higher, whereas the levels of N-methylnicotinamide and tyrosine were lower. Moreover, analysis of the proteomic dataset identified only one circulating protein, ceruloplasmin, that was consistently dysregulated. Convergence comparison prioritized tryptophan as the top-ranked circulating metabolite, followed by kynurenic acid, acetylcarnitine, creatinine, serotonin, and valine. Collectively, robust evidence of metabolomic changes was observed in patients with depression, pointing to a role as potential biomarkers. Further investigation of consensus proteomic features for depression is necessitated.

Gut Microbiome, Diet and Depression: Literature Review of Microbiological, Nutritional and Neuroscientific Aspects

PURPOSE OF REVIEW

This review explores the intricate relationships among the gut microbiota, dietary patterns, and mental health, focusing specifically on depression. It synthesizes insights from microbiological, nutritional, and neuroscientific perspectives to understand how the gut-brain axis influences mood and cognitive function.

RECENT FINDINGS

Recent studies underscore the central role of gut microbiota in modulating neurological and psychological health via the gut-brain axis. Key findings highlight the importance of dietary components, including probiotics, prebiotics, and psychobiotics, in restoring microbial balance and enhancing mood regulation. Different dietary patterns exhibit a profound impact on gut microbiota composition, suggesting their potential as complementary strategies for mental health support. Furthermore, mechanisms like tryptophan metabolism, the HPA axis, and microbial metabolites such as SCFAs are implicated in linking diet and microbiota to depression. Clinical trials show promising effects of probiotics in alleviating depressive symptoms. This review illuminates the potential of diet-based interventions targeting the gut microbiota to mitigate depression and improve mental health. While the interplay between microbial diversity, diet, and brain function offers promising therapeutic avenues, further clinical research is needed to validate these findings and establish robust, individualized treatment strategies.

Role of the gut microbiome in psychological symptoms associated with inflammatory bowel diseases

The brain-gut axis constitutes the basis for the bidirectional communication between the central nervous system and the gastrointestinal tract driven by neural, hormonal, metabolic, immunological, and microbial signals. Alterations in the gut microbiome composition as observed in inflammatory bowel diseases can modulate brain function and emerging empirical evidence has indicated that interactions among the brain-gut microbiome-axis seem to play a significant role in the pathogenesis of both inflammatory bowel diseases and psychiatric disorders and their comorbidity. Yet, the immunological and molecular mechanisms underlying the co-occurrence of inflammatory bowel diseases and psychological symptoms are still poorly understood. The aim of this narrative review is to highlight contemporary empirical findings supporting a pivotal role of the gut microbiome in the pathophysiology of highly prevalent neuropsychiatric symptoms in inflammatory bowel diseases such as fatigue, depression, and anxiety. Finally, we focus on microbiome modulation as potential treatment option for comorbid neuropsychiatric symptoms in immune-mediated diseases and especially in inflammatory bowel diseases. High-quality clinical trials are required to clarify how microbiome modulation through dietary interventions or probiotic, prebiotic or synbiotic treatment can be used clinically to improve mental health and thus quality of life of patients with inflammatory bowel diseases.

Neurological mechanism-based analysis of the role and characteristics of physical activity in the improvement of depressive symptoms

Depression is a common mental disorder characterized by a high prevalence and significant adverse effects, making the searching for effective interventions an urgent priority. In recent years, physical activity (PA) has increasingly been recognized as a standard adjunctive treatment for mental disorders owing to its low cost, easy application, and high efficiency. Epidemiological data shows positive preventive and therapeutic effects of PA on mental illnesses such as depression. This article systematically describes the prophylactic and therapeutic effects of PA on depression and its biological basis. A comprehensive literature analysis reveals that PA significantly improves depressive symptoms by upregulating the expression of "exerkines" such as irisin, adiponectin, and BDNF to positively impacting neuropsychiatric conditions. In particular, lactate could also play a critical role in the ameliorating effects of PA on depression due to the findings about protein lactylation as a novel protein post-transcriptional modification. The literature also suggests that in terms of brain structure, PA may improve hippocampal volume, basal ganglia (neostriatum, caudate-crustal nucleus) and PFC density in patients with MDD. In summary, this study elucidates the multifaceted positive effects of PA on depression and its potential biological mechanisms with a particular emphasis on the roles of various exerkines. Future research may further investigate the effects of different types, intensities, and durations of PA on depression, as well as how to better integrate PA interventions into existing treatment strategies to achieve optimal outcomes in mental health interventions.

Horticultural activity in soil inoculated with Streptomyces rimosus improved depressive mood with altered electroencephalogram and serum metabolism in adults

This study investigated the psychophysiological and metabolomic changes during horticultural activities involving the inhalation of volatile organic compounds (VOCs) in individuals experiencing depressive mood based on the presence or absence of the soil microbe Streptomyces rimosus, which emits VOCs. Thirty participants met the specific depression and anxiety criteria and engaged in horticultural activities using soil inoculated with S. rimosus (experimental group) or medium (control group). Electroencephalogram (EEG) was used to analyze the resulting psychophysiological response, and blood samples were collected after each activity. Significant increases were observed in the FZ channel of the central frontal lobe for relative theta, relative alpha, relative slow alpha, ratio of sensorimotor rhythm mid beta to theta, and ratio of alpha to high beta, whereas significant decreases were noted for relative beta, relative high beta, and relative gamma and spectral edge frequency 50% and 90%. GC-TOF-MS analysis identified 44 altered serum metabolites, showing an increasing trend in succinate, glycolate, glycerate, acetate, palmitate, myristate, laurate, caprynate, and octanoate, which are related to the citrate cycle, glyoxylate and dicarboxylate metabolism, and fatty acid biosynthesis. In conclusion, this study suggests that inhalation of VOCs during horticultural activities can help alleviate depression and depressive moods.

Biosignals in the Gut-Brain Axis Transmission: Function and Detection

The gut-brain axis (GBA) is an important information pathway connecting the brain, the central nervous system (CNS), and the gastrointestinal (GI) tract. On the one hand, gut microbiota can influence the function brain through GBA; on the other hand, the brain can also change the structural composition of gut microbiota via GBA. It contains a myriad of biosignals, such as monoamines, inflammatory cytokines, and macro-biomolecules, as the information carriers. Highly selective, sensitive, and reliable sensing techniques are essential to resolve the specific function of individual biosignals. This review summarizes the widely reported biosignals related to GBA and their functions, and organizes the latest sensing tools to provide feasible characterization ideas for GBA-related work. In addition, these low-cost, fast-responding sensors can also be used for early identification and diagnosis of GBA-related diseases (e.g., depression). Finally, the problems and deficiencies in this field are pointed out to provide a reference for the orientation of researchers in the sensing field.

Treatment response of venlafaxine induced alterations of gut microbiota and metabolites in a mouse model of depression

Antidepressants remain the first-line treatment for depression. However, the factors influencing medication response are still unclear. Accumulating evidence implicates an association between alterations in gut microbiota and antidepressant response. Therefore, the aim of this study is to investigate the role of the gut microbiota-brain axis in the treatment response of venlafaxine. After chronic social defeat stress and venlafaxine treatment, mice were divided into responders and non-responders groups. We compared the composition of gut microbiota using 16 S ribosomal RNA sequencing. Meanwhile, we quantified metabolomic alterations in serum and hippocampus, as well as hippocampal neurotransmitter levels using liquid chromatography-mass spectrometry. We found that the abundances of 29 amplicon sequence variants (ASVs) were significantly altered between the responders and non-responders groups. These ASVs belonged to 8 different families, particularly Muribaculaceae. Additionally, we identified 38 and 39 differential metabolites in serum and hippocampus between the responders and non-responders groups, respectively. Lipid, amino acid, and purine metabolisms were enriched in both serum and hippocampus. In hippocampus, the concentrations of tryptophan, phenylalanine, gamma-aminobutyric acid, glutamic acid, and glutamine were increased, while the level of succinic acid was decreased in the responders group, compared with the non-responders group. Our findings suggest that the gut microbiota may play a role in the antidepressant effect of venlafaxine by modulating metabolic processes in the central and peripheral tissues. This provides a novel microbial and metabolic framework for understanding the impact of the gut microbiota-brain axis on antidepressant response.

Metabolomics in atrial fibrillation - A review and meta-analysis of blood, tissue and animal models

BACKGROUND

Atrial fibrillation (AF) is a highly prevalent cardiac arrhythmia associated with severe cardiovascular complications. AF presents a growing global challenge, however, current treatment strategies for AF do not address the underlying pathophysiology. To advance diagnosis and treatment of AF, a deeper understanding of AF root causes is needed. Metabolomics is a fast approach to identify, quantify and analyze metabolites in a given sample, such as human serum or atrial tissue. In the past two decades, metabolomics have enabled research on metabolite biomarkers to predict AF, metabolic features of AF, and testing metabolic mechanisms of AF in animal models. Due to the field's rapid evolution, the methods of AF metabolomics studies have not always been optimal. Metabolomics research has lacked standardization and requires expertise to face methodological challenges.

PURPOSE OF THE REVIEW

We summarize and meta-analyze metabolomics research on AF in human plasma and serum, atrial tissue, and animal models. We present the current progress on metabolic biomarkers candidates, metabolic features of clinical AF, and the translation of metabolomics findings from animal to human. We additionally discuss strengths and weaknesses of the metabolomics method and highlight opportunities for future AF metabolomics research.

Identification of Potential Biomarkers for Major Depressive Disorder: Based on Integrated Bioinformatics and Clinical Validation

Major depressive disorder (MDD) is a severe mental illness characterized by a lack of objective biomarkers. Mounting evidence suggests there are extensive transcriptional molecular changes in the prefrontal cortex (PFC) of individuals with MDD. However, it remains unclear whether there are specific genes that are consistently altered and possess diagnostic power. In this study, we conducted a systematic search of PFC datasets of MDD patients from the Gene Expression Omnibus database. We calculated the differential expression of genes (DEGs) and identified robust DEGs using the RRA and MetaDE methods. Furthermore, we validated the consistently altered genes and assessed their diagnostic power through enzyme-linked immunosorbent assay experiments in our clinical blood cohort. Additionally, we evaluated the diagnostic power of hub DEGs in independent public blood datasets. We obtained eight PFC datasets, comprising 158 MDD patients and 263 healthy controls, and identified a total of 1468 unique DEGs. Through integrated analysis, we identified 290 robustly altered DEGs. Among these, seven hub DEGs (SLC1A3, PON2, AQP1, EFEMP1, GJA1, CENPD, HSD11B1) were significantly down-regulated at the protein level in our clinical blood cohort. Moreover, these hub DEGs exhibited a negative correlation with the Hamilton Depression Scale score (P < 0.05). Furthermore, these hub DEGs formed a panel with promising diagnostic power in three independent public blood datasets (average AUCs of 0.85) and our clinical blood cohort (AUC of 0.92). The biomarker panel composed of these genes demonstrated promising diagnostic efficacy for MDD and serves as a useful tool for its diagnosis.

Hypoxanthine Produces Rapid Antidepressant Effects by Suppressing Inflammation in Serum and Hippocampus

The occurrence and development of depression are closely related to disorders of the brain and peripheral substances. Abnormal metabolites in the blood affect the signal regulation function of the nerve center, which is one of the key factors for depression episodes. This study was focused on metabolites in serum and the mechanism of its antidepressant in the hippocampus. In the present study, serum metabolites in patients with depression were screened by metabolomic techniques. Various depressive mouse models and behavioral tests were used to assess its antidepressant effects. The expressions of inflammatory signaling were detected by using Western blot, ELISA, and immunofluorescence. We found that the metabolite hypoxanthine in the serum of patients with depression was significantly reduced, and the same result was also found in two mouse models of depression such as chronic unpredictable mild stress (CUMS) and social defeat stress (SD). By administering different doses of hypoxanthine (5, 10, 15 mg/kg), we found that only 15 mg/kg was able to significantly reduce the latency and increase food consumption in the novelty suppressed-feeding test (NSF), which was also able to reverse the depressive phenotypes of mice in the CUMS model after a single administration at 2 h later. Hypoxanthine obviously reduced the expressions of inflammation in serum and downregulated the expressions of MAPK and NLRP3-related pathways in the hippocampus in CUMS mice. Moreover, hypoxanthine also suppressed the activations of glial cells including GFAP and IBA-1 in hippocampal CA1, CA3, and dentate gyrus (DG). To sum up, hypoxanthine exerted antidepressant effect relying on the inhibition of peripheral and hippocampal inflammations by regulating MAPK, NLRP3-related pathways, and glial cells. This was the first time that we have found a disordered metabolite in patients with depression and further systematically demonstrated its efficacy and potential mechanism of antidepressants, providing new ideas for antidepressant drug development.

A personalised nutrition intervention for adolescent depression: a mixed-methods feasibility pilot study

Randomised controlled trials have demonstrated the benefit of diet modification to improve diet quality in the treatment of adult major depressive disorder (MDD). However, research examining nutritional interventions for adolescents with MDD is sparse. This pilot study examined the feasibility of a personalised nutrition intervention for adolescents with MDD. Ten adolescents with MDD and their parents recruited from a tertiary care setting participated in an 8-week, single-arm mixed-methods study. Feasibility was assessed using five criteria (demand, acceptability, implementation, adaptation and limited efficacy testing) alongside qualitative interviews. The intervention involved four bi-weekly virtual nutrition counselling sessions with a stepped approach to dietary change, menu planning, grocery delivery and educational eHealth messages. Study participants sought positive changes in diet, health and lifestyle for adolescents and family-wide benefits. Recruitment challenges included concerns about managing mood fluctuations, anticipated dietary restrictions and the potential time and effort required for diet adherence. Feedback based on interviews emphasised moderate to high acceptability, satisfaction with menu planning and counselling and recognition of the benefits of trying new foods and sustaining positive dietary changes beyond the study. Improvements in depression symptoms (Cohen's d = 0·36, 95 % CI (-0·24, 3·36)), parent food modeling (Cohen's d = 0·24, 95 % CI (-0·43, 1·16) and the family food environment (Cohen's d = 0·61, 95 % CI (-0·04, 2·61)) were observed. This nutrition intervention was feasible for adolescents with MDD and was acceptable to both parents and depressed adolescents. These preliminary data suggest that further examination of the intervention and its potential benefits on depression symptoms and family food dynamics are warranted.

Identification of molecular targets of Hypericum perforatum in blood for major depressive disorder: a machine-learning pharmacological study

BACKGROUND

Major depressive disorder (MDD) is one of the most common psychiatric disorders worldwide. Hypericum perforatum (HP) is a traditional herb that has been shown to have antidepressant effects, but its mechanism is unclear. This study aims to identify the molecular targets of HP for the treatment of MDD.

METHODS

We performed differential analysis and weighted gene co-expression network analysis (WGCNA) with blood mRNA expression cohort of MDD and healthy control to identify DEGs and significant module genes (gene list 1). Three databases, CTD, DisGeNET, and GeneCards, were used to retrieve MDD-related gene intersections to obtain MDD-predicted targets (gene list 2). The validated targets were retrieved from the TCMSP database (gene list 3). Based on these three gene lists, 13 key pathways were identified. The PPI network was constructed by extracting the intersection of genes and HP-validated targets on all key pathways. Key therapeutic targets were obtained using MCODE and machine learning (LASSO, SVM-RFE). Clinical diagnostic assessments (Nomogram, Correlation, Intergroup expression), and gene set enrichment analysis (GSEA) were performed for the key targets. In addition, immune cell analysis was performed on the blood mRNA expression cohort of MDD to explore the association between the key targets and immune cells. Finally, molecular docking prediction was performed for the targets of HP active ingredients on MDD.

RESULTS

Differential expression analysis and WGCNA module analysis yielded 933 potential targets for MDD. Three disease databases were intersected with 982 MDD-predicted targets. The TCMSP retrieved 275 valid targets for HP. Separate enrichment analysis intersected 13 key pathways. Five key targets (AKT1, MAPK1, MYC, EGF, HSP90AA1) were finally screened based on all enriched genes and HP valid targets. Combined with the signaling pathway and immune cell analysis suggested the effect of peripheral immunity on MDD and the important role of neutrophils in immune inflammation. Finally, the binding of HP active ingredients (quercetin, kaempferol, and luteolin) and all 5 key targets were predicted based on molecular docking.

CONCLUSIONS

The active constituents of Hypericum perforatum can act on MDD and key targets and pathways of this action were identified.

Association between gut microbiota and postpartum depression: A bidirectional Mendelian randomization study

BACKGROUNDS

Empirical investigations have shown an association between gut microbiota and postpartum depression (PPD); nevertheless, the precise cause-and-effect relationship between these two variables remains ambiguous. This research aimed to examine the possible reciprocal causal relationship between the gut microbiota and PPD.

METHODS

In this work, we used Mendelian randomization (MR) to analyze the relationship between the gut microbiota (n = 18,340) and PPD (n = 67,205). We obtained the relevant SNPs from publicly accessible genome-wide association studies (GWAS). The SNP estimations were combined by the inverse-variance weighted (IVW) method, including sensitivity analyses such as weighted median, MR Egger, and MR Pleiotropy Residual Sum and Outlier (PRESSO).

RESULTS

We have identified strong correlations between six bacterial characteristics and the likelihood of developing PPD. Our research revealed that the genus Ruminococcaceae UCG010, the family Veillonellaceae, and the class Clostridia had a beneficial effect on preventing PPD. The class Alphaproteobacteria, genus Slackia, and order NB1n were found to have a significant negative impact on PPD. The sensitivity studies conducted on these bacterial features consistently confirmed these finding.

LIMITATIONS

It is crucial to acknowledge that our study was conducted just within a European society, which may restrict its applicability to other groups.

CONCLUSIONS

The findings from our MR investigation indicate a potential causal relationship between certain kinds of gut bacteria and PPD. Additional investigation is required to elucidate the influence of gut microbiota on the advancement of PPD.

Distinguishing bipolar depression, bipolar mania, and major depressive disorder by gut microbial characteristics

BACKGROUND

Gut microbial disturbance has been widely confirmed in mood disorders. However, little is known about whether gut microbial characteristics can distinguish major depressive disorder (MDD), bipolar depression (BP-D), and bipolar mania (BP-M).

METHODS

This was a prospective case-control study. The composition of gut microbiota was profiled using 16S ribosomal RNA (rRNA) gene sequencing of fecal samples and compared between healthy controls (HC; n = 46), MDD (n = 51), BP-D (n = 44), and patients with BP-M (n = 45).

RESULTS

Gut microbial compositions were remarkably changed in the patients with MDD, BP-D, and BP-M. Compared to HC, distinct gut microbiome signatures were found in MDD, BP-D, and BP-M, and some gut microbial changes were overlapping between the three mood disorders. Furthermore, we identified a signature of 7 operational taxonomic units (OUT; Prevotellaceae-related OUT22, Prevotellaceae-related OUT31, Prevotellaceae-related OTU770, Ruminococcaceae-related OUT70, Bacteroidaceae-related OTU1536, Propionibacteriaceae-related OTU97, Acidaminococcaceae-related OTU34) that can distinguish patients with MDD from those with BP-D, BP-M, or HC, with area under the curve (AUC) values ranging from 0.910 to 0.996.

CONCLUSION

Our results provide the clinical rationale for the discriminative diagnosis of MDD, BP-D, and BP-M by characteristic gut microbial features.

Long-term Treatment with a 5-Alpha-Reductase Inhibitor Alleviates Depression-like Behavior in Obese Male Rats

Several studies have reported side effects of finasteride (FIN), such as anxiety/depression in young men. Obesity is also positively associated with anxiety/depression symptoms; however, the impacts of long-term FIN treatment and FIN withdrawal in young obese individuals are still elusive. The present study aimed to investigate the effect of long-term treatment and its withdrawal on anxiety/depression and brain pathologies in lean and obese adult male rats. Forty-eight male Wistar rats were equally divided into two groups and fed either a normal or high-fat diet. At age 13 weeks, rats in each dietary group were divided into three subgroups: 1) the control group receiving drinking water, 2) the long-term treatment group receiving FIN orally at 5 mg/kg/day for 6 weeks, and 3) the withdrawal group receiving FIN orally at 5 mg/kg/day for 2 weeks followed by a 4-week withdrawal period. Anxiety/depression-like behaviors, biochemical analysis, brain inflammation, oxidative stress, neuroactive steroids, brain metabolites, and microglial complexity were tested. The result showed that lean rats treated with long-term FIN and its withdrawal exhibited metabolic disturbances, depressive-like behavior, and both groups showed increased neurotoxic metabolites and reduced microglial complexity. Obesity itself led to metabolic disturbances and brain pathologies, including increased inflammation, oxidative stress, and quinolinic acid, as well as reduced microglial complexity, resulting in increased anxiety- and depression-like behaviors. Interestingly, the long-term FIN treatment group in obese rats showed attenuation of depressive-like behaviors, brain inflammation, and oxidative stress, along with increased brain antioxidants, suggesting the possible benefits of FIN in obese conditions.

Intestinal Barrier, Immunity and Microbiome: Partners in the Depression Crime

Depression is a highly prevalent disorder and a leading cause of disability worldwide. It has a major impact on the affected individual and on society as a whole. Regrettably, current available treatments for this condition are insufficient in many patients. In recent years, the gut microbiome has emerged as a promising alternative target for treating and preventing depressive disorders. However, the microbes that form this ecosystem do not act alone but are part of a complicated network connecting the gut and the brain that influences our mood. Host cells that are in intimate contact with gut microbes, such as the epithelial cells forming the gut barrier and the immune cells in their vicinity, play a key role in the process. These cells continuously shape immune responses to maintain healthy communication between gut microbes and the host. In this article, we review how the interplay among epithelial cells, the immune system, and gut microbes mediates gut-brain communication to influence mood. We also discuss how advances in our knowledge of the mechanisms underlying the gut-brain axis could contribute to addressing depression. SIGNIFICANCE STATEMENT: This review does not aim to systematically describe intestinal microbes that might be beneficial or detrimental for depression. We have adopted a novel point of view by focusing on potential mechanisms underlying the crosstalk between gut microbes and their intestinal environment to control mood. These pathways could be targeted by well defined and individually tailored dietary interventions, microbes, or microbial metabolites to ameliorate depression and decrease its important social and economic impact.

Persistent PTSD symptoms are associated with plasma metabolic alterations relevant to long-term health: A metabolome-wide investigation in women

Background

Posttraumatic stress disorder (PTSD) is characterized by severe distress and associated with cardiometabolic diseases. Studies in military and clinical populations suggest dysregulated metabolomic processes may be a key mechanism. Prior work identified and validated a metabolite-based distress score (MDS) linked with depression and anxiety and subsequent cardiometabolic diseases. Here, we assessed whether PTSD shares metabolic alterations with depression and anxiety and also if additional metabolites are related to PTSD.

Methods

We leveraged plasma metabolomics data from three subsamples nested within the Nurses' Health Study II, including 2835 women with 2950 blood samples collected across three timepoints (1996-2014) and 339 known metabolites consistently assayed by mass spectrometrybased techniques. Trauma and PTSD exposures were assessed in 2008 and characterized as follows: lifetime trauma without PTSD, lifetime PTSD in remission, and persistent PTSD symptoms. Associations between the exposures and the MDS or individual metabolites were estimated within each subsample adjusting for potential confounders and combined in random-effects meta-analyses.

Results

Persistent PTSD symptoms were associated with higher levels of the previously developed MDS for depression and anxiety. Out of 339 metabolites, we identified nine metabolites (primarily elevated glycerophospholipids) associated with persistent symptoms (false discovery rate<0.05). No metabolite associations were found with the other PTSD-related exposures.

Conclusions

As the first large-scale, population-based metabolomics analysis of PTSD, our study highlighted shared and distinct metabolic differences linked to PTSD versus depression or anxiety. We identified novel metabolite markers associated with PTSD symptom persistence, suggesting further connections with metabolic dysregulation that may have downstream consequences for health.

The relationship of peripheral blood cell inflammatory biomarkers and psychological stress in unmedicated major depressive disorder

BACKGROUND

Recent research has explored the linkage between major depressive disorder (MDD) and inflammation, especially via altered peripheral blood immune markers. However, the relationship between several novel leukocyte-derived ratios (LDR) and psychological stress in MDD remains uncertain. This study aimed to explore the relationship between LDR, clinical characteristics, recent life events, and childhood maltreatment in MDD patients.

METHODS

A cross-sectional case-control study was conducted involving 59 healthy controls (HC) and 50 unmedicated MDD patients. Subjects underwent psychological assessments and peripheral blood measurements. LDR assessed in this study included neutrophil-to-lymphocyte ratio (NLR), derived NLR (dNLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), white blood cell-to-mean platelet volume ratio (WMR), systemic immune inflammation index (SII), multiplication of neutrophil and monocyte counts (MNM), and systemic inflammation response index (SIRI).

RESULTS

MDD patients displayed significant alterations in WMR, PLR, and MNM compared to HC, as well as correlations between several LDR and various clinical features (duration of untreated psychosis and dNLR, the nine-item Patient Health Questionnaire and PLR, the 7-item Generalized Anxiety Disorder Questionnaire and SIRI (NLR and dNLR). There was a significant difference in the comparison of WMR in first-episode patients than in recurrent patients. Analyses further revealed an association between Life Event Scale total scores and NLR (dNLR). No correlation was found between Childhood Trauma Questionnaire total (or subscale) scores and LDR. Additionally, WMR and dNLR presented potential predictive value for distinguishing between MDD and HC.

CONCLUSION

The study concludes that MDD and some clinical features are associated with alterations in some peripheral blood LDR. These findings emphasize the potential role of peripheral blood LDR in the pathogenesis and clinical heterogeneity of MDD.

Serum Metabolites as Potential Markers and Predictors of Depression-like Behavior and Effective Fluoxetine Treatment in Chronically Socially Isolated Rats

Metabolic perturbation has been associated with depression. An untargeted metabolomics approach using liquid chromatography-high resolution mass spectrometry was employed to detect and measure the rat serum metabolic changes following chronic social isolation (CSIS), an animal model of depression, and effective antidepressant fluoxetine (Flx) treatment. Univariate and multivariate statistics were used for metabolic data analysis and differentially expressed metabolites (DEMs) determination. Potential markers and predictive metabolites of CSIS-induced depressive-like behavior and Flx efficacy in CSIS were evaluated by the receiver operating characteristic (ROC) curve, and machine learning (ML) algorithms, such as support vector machine with linear kernel (SVM-LK) and random forest (RF). Upregulated choline following CSIS may represent a potential marker of depressive-like behavior. Succinate, stachydrine, guanidinoacetate, kynurenic acid, and 7-methylguanine were revealed as potential markers of effective Flx treatment in CSIS rats. RF yielded better accuracy than SVM-LK (98.50% vs. 85.70%, respectively) in predicting Flx efficacy in CSIS vs. CSIS, however, it performed almost identically in classifying CSIS vs. control (75.83% and 75%, respectively). Obtained DEMs combined with ROC curve and ML algorithms provide a research strategy for assessing potential markers or predictive metabolites for the designation or classification of stress-induced depressive phenotype and mode of drug action.

The role of gut microbiota and blood metabolites in postpartum depression: a Mendelian randomization analysis

Background

Postpartum depression (PPD) is a common complication of pregnancy that imposes a heavy health and economic burden on individuals, families and society. The etiology of PPD is complex and incompletely defined, and recent studies have identified an important role for gut microbiota (GM) and their metabolites in neurological disorders. However, fewer studies on GM and PPD are available and have not yielded uniform results.

Methods

Instrumental variables for GM and blood metabolites were obtained from the MiBioGen consortium and metabolomics GWAS server. Single nucleotide polymorphisms (SNPs) associated with PPD phenotypes were obtained from the FinnGen consortium. Inverse variance weighted (IVW), weighted median, weighted mode, and MR-Egger methods were used to assess causal effects. Inverse MR analysis and sensitivity analysis were also utilized to improve the stability of the results.

Results

In this study, 5 intestinal species and 24 blood metabolites causally associated with PPD were identified using MR analysis. In addition, MR analysis showed that Prevotellaceae and Bifidobacteria may reduce the risk of PPD by elevating Xanthine and 1-arachidonoylglycerophosphoinositol (LysoPI) levels.

Conclusions

This study identified GM and blood metabolites causally associated with PPD. The results of this study may provide a theoretical basis for the discovery of PPD-related biomarkers and the treatment of the disease by regulating the gut microenvironment.

MDDOmics: multi-omics resource of major depressive disorder

Major depressive disorder (MDD) is a pressing global health issue. Its pathogenesis remains elusive, but numerous studies have revealed its intricate associations with various biological factors. Consequently, there is an urgent need for a comprehensive multi-omics resource to help researchers in conducting multi-omics data analysis for MDD. To address this issue, we constructed the MDDOmics database (Major Depressive Disorder Omics, (https://www.csuligroup.com/MDDOmics/), which integrates an extensive collection of published multi-omics data related to MDD. The database contains 41 222 entries of MDD research results and several original datasets, including Single Nucleotide Polymorphisms, genes, non-coding RNAs, DNA methylations, metabolites and proteins, and offers various interfaces for searching and visualization. We also provide extensive downstream analyses of the collected MDD data, including differential analysis, enrichment analysis and disease-gene prediction. Moreover, the database also incorporates multi-omics data for bipolar disorder, schizophrenia and anxiety disorder, due to the challenge in differentiating MDD from similar psychiatric disorders. In conclusion, by leveraging the rich content and online interfaces from MDDOmics, researchers can conduct more comprehensive analyses of MDD and its similar disorders from various perspectives, thereby gaining a deeper understanding of potential MDD biomarkers and intricate disease pathogenesis. Database URL: https://www.csuligroup.com/MDDOmics/.

Gut microbial GABAergic signaling improves stress-associated innate immunity to respiratory viral infection

INTRODUCTION

Epidemiological evidences reveal that populations with psychological stress have an increased likelihood of respiratory viral infection involving influenza A virus (IAV) and SARS-CoV-2.

OBJECTIVES

This study aims to explore the potential correlation between psychological stress and increased susceptibility to respiratory viral infections and how this may contribute to a more severe disease progression.

METHODS

A chronic restraint stress (CRS) mouse model was used to infect IAV and estimate lung inflammation. Alveolar macrophages (AMs) were observed in the numbers, function and metabolic-epigenetic properties. To confirm the central importance of the gut microbiome in stress-exacerbated viral pneumonia, mice were conducted through microbiome depletion and gut microbiome transplantation.

RESULTS

Stress exposure induced a decline in Lactobacillaceae abundance and hence γ-aminobutyric acid (GABA) level in mice. Microbial-derived GABA was released in the peripheral and sensed by AMs via GABAAR, leading to enhanced mitochondrial metabolism and α-ketoglutarate (αKG) generation. The metabolic intermediator in turn served as the cofactor for the epigenetic regulator Tet2 to catalyze DNA hydroxymethylation and promoted the PPARγ-centered gene program underpinning survival, self-renewing, and immunoregulation of AMs. Thus, we uncover an unappreciated GABA/Tet2/PPARγ regulatory circuitry initiated by the gut microbiome to instruct distant immune cells through a metabolic-epigenetic program. Accordingly, reconstitution with GABA-producing probiotics, adoptive transferring of GABA-conditioned AMs, or resumption of pulmonary αKG level remarkably improved AMs homeostasis and alleviated severe pneumonia in stressed mice.

CONCLUSION

Together, our study identifies microbiome-derived tonic signaling tuned by psychological stress to imprint resident immune cells and defensive response in the lungs. Further studies are warranted to translate these findings, basically from murine models, into the individuals with psychiatric stress during respiratory viral infection.

ProMENDA: an updated resource for proteomic and metabolomic characterization in depression

Depression is a prevalent mental disorder with a complex biological mechanism. Following the rapid development of systems biology technology, a growing number of studies have applied proteomics and metabolomics to explore the molecular profiles of depression. However, a standardized resource facilitating the identification and annotation of the available knowledge from these scattered studies associated with depression is currently lacking. This study presents ProMENDA, an upgraded resource that provides a platform for manual annotation of candidate proteins and metabolites linked to depression. Following the establishment of the protein dataset and the update of the metabolite dataset, the ProMENDA database was developed as a major extension of its initial release. A multi-faceted annotation scheme was employed to provide comprehensive knowledge of the molecules and studies. A new web interface was also developed to improve the user experience. The ProMENDA database now contains 43,366 molecular entries, comprising 20,847 protein entries and 22,519 metabolite entries, which were manually curated from 1370 human, rat, mouse, and non-human primate studies. This represents a significant increase (more than 7-fold) in molecular entries compared to the initial release. To demonstrate the usage of ProMENDA, a case study identifying consistently reported proteins and metabolites in the brains of animal models of depression was presented. Overall, ProMENDA is a comprehensive resource that offers a panoramic view of proteomic and metabolomic knowledge in depression. ProMENDA is freely available at https://menda.cqmu.edu.cn .

The microbiota-gut-brain axis: A crucial immunomodulatory pathway for Bifidobacterium animalis subsp. lactis' resilience against LPS treatment in neonatal rats

An imbalanced gut microflora may contribute to immune disorders in neonates due to an immature gut barrier. Bacterial toxins, particularly, can trigger the immune system, potentially resulting in uncontrolled gut and systemic inflammation. Previous research has revealed that Bifidobacterium animalis subsp. lactis (B. lactis) could protect against early-life pathogen infections by enhancing the gut barrier. However, the effects of B. lactis on a compromised immune system remain uncertain. Hence, this study concentrated on the immunomodulatory effects and mechanisms of B. lactis in neonatal rats intraperitoneally injected with lipopolysaccharide (LPS), a bacterial toxin and inflammatory mediator. First, B. lactis significantly alleviated the adverse effects induced by LPS on the growth, development, and body temperature of neonatal rats. Second, B. lactis significantly reduced the immune responses and damage induced by LPS, affecting both systemic and local immune responses in the peripheral blood, gut, and brain. Notably, B. lactis exhibited extra potent neuroprotective and neurorepair effects. Our research found that pre-treatment with B. lactis shaped the diverse gut microecology by altering both microbial populations and metabolic biomolecules, closely linked to immunomodulation. Overall, this study elucidated the multifaceted roles of B. lactis in neonatal hosts against pathogenic infection and immune disorder, revealing the existence of the microbiota-gut-brain axis.

Longitudinal associations of plasma kynurenines and ratios with anxiety and depression scores in colorectal cancer survivors up to 12 months post-treatment

INTRODUCTION

Colorectal cancer (CRC) survivors often experience neuropsychological symptoms, including anxiety and depression. Mounting evidence suggests a role for the kynurenine pathway in these symptoms due to potential neuroprotective and neurotoxic roles of involved metabolites. However, evidence remains inconclusive and insufficient in cancer survivors. Thus, we aimed to explore longitudinal associations of plasma tryptophan, kynurenines, and their established ratios with anxiety and depression in CRC survivors up to 12 months post-treatment.

METHODS

In 249 stage I-III CRC survivors, blood samples were collected at 6 weeks, 6 months, and 12 months post-treatment to analyze plasma concentrations of tryptophan and kynurenines using liquid-chromatography tandem-mass spectrometry (LC/MS-MS). At the same timepoints, anxiety and depression were assessed using the Hospital Anxiety and Depression Scale (HADS). Confounder-adjusted linear mixed models were used to analyze longitudinal associations. Sensitivity analyses with false discovery rate (FDR) correction were conducted to adjust for multiple testing.

RESULTS

Higher plasma tryptophan concentrations were associated with lower depression scores (β as change in depression score per 1 SD increase in the ln-transformed kynurenine concentration: -0.31; 95%CI: -0.56,-0.05), and higher plasma 3-hydroxyanthranilic acid concentrations with lower anxiety scores (-0.26; -0.52,-0.01). A higher 3-hydroxykynurenine ratio (HKr; the ratio of 3-hydroxykynurenine to the sum of kynurenic acid, xanthurenic acid, anthranilic acid, and 3-hydroxyanthranilic acid) was associated with higher depression scores (0.34; 0.04,0.63) and higher total anxiety and depression scores (0.53; 0.02,1.04). Overall associations appeared to be mainly driven by inter-individual associations, which were statistically significant for tryptophan with depression (-0.60; -1.12,-0.09), xanthurenic acid with total anxiety and depression (-1.04; -1.99,-0.10), anxiety (-0.51; -1.01,-0.01), and depression (-0.56; -1.08,-0.05), and kynurenic-acid-to-quinolinic-acid ratio with depression (-0.47; -0.93,-0.01). In sensitivity analyses, associations did not remain statistically significant after FDR adjustment.

CONCLUSION

We observed that plasma concentrations of tryptophan, 3-hydroxyanthranilic acid, xanthurenic acid, 3-hydroxykynurenine ratio, and kynurenic-acid-to-quinolinic-acid ratio tended to be longitudinally associated with anxiety and depression in CRC survivors up to 12 months post-treatment. Future studies are warranted to further elucidate the association of plasma kynurenines with anxiety and depression.

A microfluidic-based gut-on-a-chip model containing the gut microbiota of patients with depression reveals physiological characteristics similar to depression

The diverse commensal microbiome of the human intestine has been considered to play a central role in depression. However, no host-microbiota co-culture system has been developed for depression, which hinders the controlled study of the interaction between depression and gut microbiota. We designed and manufactured a microfluidic-based gut-on-a-chip model containing the gut microbiota of patients with depression (depression-on-gut-chip, DoGC), which enables the extended co-culture of viable aerobic human intestinal epithelial cells and anaerobic gut microbiota, and allows the direct study of interactions between human gut microbiota and depression. We introduced representative gut microbiota from individuals with depression into our constructed DoGC model, successfully recapitulating the gut microbiota structure of depressed patients. This further led to the manifestation of physiological characteristics resembling depression, such as reduced gut barrier function, chronic low-grade inflammatory responses and decreased neurotransmitter 5-HT levels. Metabolome analysis of substances in the DoGC revealed a significant increase in lipopolysaccharides and tyrosine, while hyodeoxycholic acid, L-proline and L-threonine were significantly reduced, indicating the occurrence of depression. The proposed DoGC can serve as an effective platform for studying the gut microbiota of patients with depression, providing important cues for their roles in the pathology of this condition and acting as a powerful tool for personalized medicine.

Effects of chronic unpredictable mild stress on gut microbiota and fecal amino acid and short-chain fatty acid pathways in mice

Depression is a serious disease that has a significant impact on social functioning. However, the exact causes of depression are still not fully understood. Therefore, it is necessary to explore new pathways leading to depression. In this study, we used 16 S rDNA to examine changes in gut microbiota and predict related pathways in depression-like mice. Additionally, we employed liquid chromatography-mass spectrometry (LC-MS) to identify changes in amino acids and gas chromatography-mass spectrometry (GC-MS) to identify changes in short-chain fatty acids (SCFAs) in fecal samples. We conducted Pearson/Spearman correlation analysis to investigate the associations between changes in amino acids/SCFAs and behavioral outcomes. The 16 S rDNA sequencing revealed significant alterations in gut microbiota at the phylum and genus levels in mice subjected to chronic unpredictable mild stress (CUMS). The relative abundances of Bacteroidetes, Proteobacteria, Bacteroides, and Alloprevotella were increased, while Firmicutes, Verrucomicrobia, Actinobacteria, Lactobacillus, Akkermansia, Lachnospirillum, and Enterobacter were decreased in the CUMS mice. We used PICRUSt software to annotate the kyoto encyclopedia of genes and genomes (KEGG) pathway function related to depression-like behavior in mice. Our analysis identified sixty functional pathways associated with the gut microbiota of mice exhibiting depression-like behavior. In the amino acid concentration analysis, we observed decreased levels of hydroxyproline and tryptophan, and increased levels of alanine in CUMS mice. In the SCFAs concentration assay, we found decreased levels of butyric acid and valeric acid, and increased levels of acetic acid in CUMS mice. Some of these changes were significantly correlated with depressive-like behaviors. Our study contributes to the understanding of the mechanism of the gut-brain axis in the occurrence and development of depression.

Identifying plasma metabolic characteristics of major depressive disorder, bipolar disorder, and schizophrenia in adolescents

Major depressive disorder (MDD), bipolar disorder (BD), and schizophrenia (SCZ) are classified as major mental disorders and together account for the second-highest global disease burden, and half of these patients experience symptom onset in adolescence. Several studies have reported both similar and unique features regarding the risk factors and clinical symptoms of these three disorders. However, it is still unclear whether these disorders have similar or unique metabolic characteristics in adolescents. We conducted a metabolomics analysis of plasma samples from adolescent healthy controls (HCs) and patients with MDD, BD, and SCZ. We identified differentially expressed metabolites between patients and HCs. Based on the differentially expressed metabolites, correlation analysis, metabolic pathway analysis, and potential diagnostic biomarker identification were conducted for disorders and HCs. Our results showed significant changes in plasma metabolism between patients with these mental disorders and HCs; the most distinct changes were observed in SCZ patients. Moreover, the metabolic differences in BD patients shared features with those in both MDD and SCZ, although the BD metabolic profile was closer to that of MDD than to SCZ. Additionally, we identified the metabolites responsible for the similar and unique metabolic characteristics in multiple metabolic pathways. The similar significant differences among the three disorders were found in fatty acid, steroid-hormone, purine, nicotinate, glutamate, tryptophan, arginine, and proline metabolism. Interestingly, we found unique characteristics of significantly altered glycolysis, glycerophospholipid, and sphingolipid metabolism in SCZ; lysine, cysteine, and methionine metabolism in MDD and BD; and phenylalanine, tyrosine, and aspartate metabolism in SCZ and BD. Finally, we identified five panels of potential diagnostic biomarkers for MDD-HC, BD-HC, SCZ-HC, MDD-SCZ, and BD-SCZ comparisons. Our findings suggest that metabolic characteristics in plasma vary across psychiatric disorders and that critical metabolites provide new clues regarding molecular mechanisms in these three psychiatric disorders.

Metabolomics on depression: A comparison of clinical and animal research

BACKGROUND

Depression is a major cause of suicide and mortality worldwide. This study aims to conduct a systematic review to identify metabolic biomarkers and pathways for major depressive disorder (MDD), a prevalent subtype of clinical depression.

METHODS

We searched for metabolomics studies on depression published between January 2000 and January 2023 in the PubMed and Web of Science databases. The reported metabolic biomarkers were systematically evaluated and compared. Pathway analysis was implemented using MetaboAnalyst 5.0.

RESULTS

We included 26 clinical studies on MDD and 78 metabolomics studies on depressive-like animal models. A total of 55 and 77 high-frequency metabolites were reported consistently in two-thirds of clinical and murine studies, respectively. In the comparison between murine and clinical studies, we identified 9 consistently changed metabolites (tryptophan, tyrosine, phenylalanine, methionine, fumarate, valine, deoxycholic acid, pyruvate, kynurenic acid) in the blood, 1 consistently altered metabolite (indoxyl sulfate) in the urine and 14 disturbed metabolic pathways in both types of studies. These metabolic dysregulations and pathways are mainly implicated in enhanced inflammation, impaired neuroprotection, reduced energy metabolism, increased oxidative stress damage and disturbed apoptosis, laying solid molecular foundations for MDD.

LIMITATIONS

Due to unavailability of original data like effect-size results in many metabolomics studies, a meta-analysis cannot be conducted, and confounding factors cannot be fully ruled out.

CONCLUSIONS

This systematic review delineated metabolic biomarkers and pathways related to depression in the murine and clinical samples, providing opportunities for early diagnosis of MDD and the development of novel diagnostic targets.

Pre-mating nitenpyram exposure in male mice leads to depression-like behavior in offspring by affecting tryptophan metabolism in gut microbiota

Several studies have confirmed that the health status of the paternal affects the health of the offspring, however, it remains unknown whether paternal exposure to pesticides affect the offspring health. Here, we used untargeted metabolomics and 16S rRNA sequencing technology, combined with tail suspension test and RT-qPCR to explore the effects of paternal exposure to nitenpyram on the neurotoxicity of offspring. Our results found that the paternal exposure to nitenpyram led to the offspring's depressive-like behaviors, accompanied by the reduction of tryptophan content and the disorder of microbial abundance in the gut of the offspring. Further, we determined the expression of tryptophan metabolism-related genes tryptophanase (tnaA) and tryptophan hydroxylase 1 (TpH1) in gut bacteria and colonic tissues. We found that tryptophan is metabolized to indoles rather than being absorbed into colonocytes, which coursed the reduce of tryptophan availability after nitenpyram exposure. In conclusion, our study deepens our understanding of the intergenerational toxic effects of pesticides.

Metabolites and depressive symptoms: Network- and longitudinal analyses from the Finnish Depression and Metabolic Syndrome in Adults (FDMSA) Study

BACKGROUND

Depression is associated with metabolic abnormalities linked to metabolic syndrome and tissue inflammation, but the interplay between metabolic markers and their association with subsequent depression is unknown. Therefore, we aimed to describe the network of metabolites and their prospective association with depressive symptoms.

METHODS

The Finnish Depression and Metabolic Syndrome in Adults (FDMSA) cohort, originally a prospective case-control study, comprised a group with Beck Depression Inventory (BDI)-I scores ≥10 at baseline, and controls (n = 319, BDI-I < 10); mean (sd) follow-up time: 7.4 (0.7) years. Serum metabolic biomarkers were determined by proton nuclear magnetic resonance (NMR), and depressive symptoms sum-score by using the BDI-I. We examined the prospective associations between metabolites at baseline and BDI score at follow-up utilizing multivariate linear regression, parsimonious predictions models and network analysis.

RESULTS

Some metabolites tended to be either negatively (e.g. histidine) or positively associated (e.g. glycoprotein acetylation, creatinine and triglycerides in very large high density lipoproteins [XL-HDL-TG]) with depressive symptoms. None of the associations were significant after correction for multiple testing. The network analysis suggested high correlation among the metabolites, but that none of the metabolites directly influenced subsequent depressive symptoms.

LIMITATIONS

Although the sample size may be considered satisfactory in a prospective context, we cannot exclude the possibility that our study was underpowered.

CONCLUSIONS

Our results suggest that the investigated metabolic biomarkers are not a driving force in the development of depressive symptoms. These findings should be confirmed in studies with larger samples and studies that account for the heterogeneity of depressive disorders.

Sex- and suicide-specific alterations in the kynurenine pathway in the anterior cingulate cortex in major depression

Major depressive disorder (MDD) is a serious psychiatric disorder that in extreme cases can lead to suicide. Evidence suggests that alterations in the kynurenine pathway (KP) contribute to the pathology of MDD. Activation of the KP leads to the formation of neuroactive metabolites, including kynurenic acid (KYNA) and quinolinic acid (QUIN). To test for changes in the KP, postmortem anterior cingulate cortex (ACC) was obtained from the National Institute of Health NeuroBioBank. Gene expression of KP enzymes and relevant neuroinflammatory markers were investigated via RT-qPCR (Fluidigm) and KP metabolites were measured using liquid chromatography-mass spectrometry in tissue from individuals with MDD (n = 44) and matched nonpsychiatric controls (n = 36). We report increased IL6 and IL1B mRNA in MDD. Subgroup analysis found that female MDD subjects had significantly decreased KYNA and a trend decrease in the KYNA/QUIN ratio compared to female controls. In addition, MDD subjects that died by suicide had significantly decreased KYNA in comparison to controls and MDD subjects that did not die by suicide, while subjects that did not die by suicide had increased KYAT2 mRNA, which we hypothesise may protect against a decrease in KYNA. Overall, we found sex- and suicide-specific alterations in the KP in the ACC in MDD. This is the first molecular evidence in the brain of subgroup specific changes in the KP in MDD, which not only suggests that treatments aimed at upregulation of the KYNA arm in the brain may be favourable for female MDD sufferers but also might assist managing suicidal behaviour.

The Kynurenine Pathway in Attention-Deficit/Hyperactivity Disorder: A Systematic Review and Meta-Analysis of Blood Concentrations of Tryptophan and Its Catabolites

Preliminary evidence shows that the kynurenine pathway (KP) may be altered in attention-deficit/hyperactivity disorder (ADHD). We thus conducted a systematic review and meta-analysis exploring the peripheral blood concentrations of tryptophan catabolites (TRYCATs) in people with ADHD. We searched the main electronic databases up to 7th December 2023. Standardised mean differences (SMDs) with 95% confidence intervals (95%CIs) were used to compare TRYCAT concentrations between participants with ADHD and healthy controls (HCs). We included eight studies. Random-effects meta-analyses found higher kynurenine (SMD = 0.56; 95%CI: 0.04 to 1.08; p = 0.033; I2 = 90.3%) and lower kynurenic acid (SMD = -0.33; 95%CI: -0.49 to -0.17; p < 0.001; I2 = 0%) concentrations in people with ADHD compared to HCs. Additional analyses on drug-free children with ADHD showed higher tryptophan (SMD = 0.31; 95%CI: 0.11 to 0.50; p = 0.002; I2 = 0%) and kynurenine (SMD = 0.74; 95%CI: 0.30 to 1.17; p < 0.001; I2 = 76.5%), as well as lower kynurenic acid (SMD = -0.37; 95%CI: -0.59 to -0.15; p < 0.001; I2 = 0%) blood levels, as compared to HCs. Despite some limitations, our work provides preliminary evidence on KP alterations in ADHD that may suggest decreased neuroprotection. Further research is needed to clarify the role of the KP in ADHD.

The contribution of polyamine pathway to determinations of diagnosis for treatment-resistant depression: A metabolomic analysis

OBJECTIVES

Approximately one-third of major depressive disorder (MDD) patients do not respond to standard antidepressants and develop treatment-resistant depression (TRD). We aimed to reveal metabolic differences and discover promising potential biomarkers in TRD.

METHODS

Our study recruited 108 participants including healthy controls (n = 40) and patients with TRD (n = 35) and first-episode drug-naive MDD (DN-MDD) (n = 33). Plasma samples were presented to ultra performance liquid chromatography-tandem mass spectrometry. Then, a machine-learning algorithm was conducted to facilitate the selection of potential biomarkers.

RESULTS

TRD appeared to be a distinct metabolic disorder from DN-MDD and healthy controls (HCs). Compared to HCs, 199 and 176 differentially expressed metabolites were identified in TRD and DN-MDD, respectively. Of all the metabolites that were identified, spermine, spermidine, and carnosine were considered the most promising biomarkers for diagnosing TRD and DN-MDD patients, with the resulting area under the ROC curve of 0.99, 0.99, and 0.93, respectively. Metabolic pathway analysis yielded compelling evidence of marked changes or imbalances in both polyamine metabolism and energy metabolism, which could potentially represent the primary altered pathways associated with MDD. Additionally, L-glutamine, Beta-alanine, and spermine were correlated with HAMD score.

CONCLUSIONS

A more disordered metabolism structure is found in TRD than in DN-MDD and HCs. Future investigations should prioritize the comprehensive analysis of potential roles played by these differential metabolites and disturbances in polyamine pathways in the pathophysiology of TRD and depression.

Metabolomic profiles of 38 acylcarnitines in major depressive episodes before and after treatment

BACKGROUND

Major depression is associated with changes in plasma L-carnitine and acetyl-L-carnitine. But its association with acylcarnitines remains unclear. The aim of this study was to assess metabolomic profiles of 38 acylcarnitines in patients with major depression before and after treatment compared to healthy controls (HCs).

METHODS

Metabolomic profiles of 38 plasma short-, medium-, and long-chain acylcarnitines were performed by liquid chromatography-mass spectrometry in 893 HCs from the VARIETE cohort and 460 depressed patients from the METADAP cohort before and after 6 months of antidepressant treatment.

RESULTS

As compared to HCs, depressed patients had lower levels of medium- and long-chain acylcarnitines. After 6 months of treatment, increased levels of medium- and long-chain acyl-carnitines were observed that no longer differed from those of controls. Accordingly, several medium- and long-chain acylcarnitines were negatively correlated with depression severity.

CONCLUSIONS

These medium- and long-chain acylcarnitine dysregulations argue for mitochondrial dysfunction through fatty acid β-oxidation impairment during major depression.

Plasma metabolomics reveals the intervention mechanism of different types of exercise on chronic unpredictable mild stress-induced depression rat model

OBJECTIVE

To study the effects of different types of exercise on the plasma metabolomics of chronic unpredictable mild stress (CUMS)-induced depressed rats based on 1H-NMR metabolomics techniques, and to explore the potential mechanisms of exercise for the treatment of depression. Rats were randomly divided into blank control group (C), CUMS control group (D), pre-exercise with CUMS group (P), CUMS with aerobic exercise group, CUMS with resistance exercise group (R), and CUMS with aerobic + resistance exercise group (E). The corresponding protocol intervention was applied to each group of rats. Body weight, sucrose preference and open field tests were performed weekly during the experiment to evaluate the extent of depression in rats. Plasma samples from each group of rats were collected at the end of the experiment, and then the plasma was analyzed by 1H-NMR metabolomics combined with multivariate statistical analysis methods to identify differential metabolites and perform metabolic pathway analysis. (1) Compared with the group D, the body weight, sucrose preference rate, and the number of crossings and standings in the different types of exercise groups were significantly improved (p < 0.05 or p < 0.01). (2) Compared to group C, a total of 15 differential metabolites associated with depression were screened in the plasma of rats in group D, involving 6 metabolic pathways. Group P can regulate the levels of 6 metabolites: valine, lactate, inositol, glucose, phosphocreatine, acetoacetic acid. Group A can regulate the levels of 6 metabolites: N-acetylglycoprotein, leucine, lactate, low density lipoprotein, glucose and acetoacetic acid. Group R can regulate the levels of 6 metabolites: choline, lactate, inositol, glucose, phosphocreatine and acetoacetic acid. Group E can regulate the levels of 5 metabolites: choline, citric acid, glucose, acetone and acetoacetic acid. The different types of exercise groups can improve the depressive symptoms in CUMS rats, and there are common metabolites and metabolic pathways for their mechanism of effects. This study provides a powerful analytical tool to study the mechanism of the antidepressant effect of exercise, and provides an important method and basis for the early diagnosis, prevention and treatment of depression.

Thyroid function, renal function, and depression: an association study

Objective

To investigate the correlations between thyroid function, renal function, and depression.

Methods

Clinical data of 67 patients with Major depressive disorder (MDD) and 36 healthy control subjects between 2018 and 2021 were collected to compare thyroid and renal function. Thyroid and renal functions of depressed patients were then correlated with the Hamilton Depression Rating Scale (HAMD) and the Hamilton Anxiety Rating Scale (HAMA).Spearman correlation analysis was used to find the correlation between renal function, thyroid function, and depression. A logistic regression was performed to find significant predictors of depression.

Results

Triiodothyronine protamine (T3), thyroxine (T4), free triiodothyronine protamine (FT3), uric acid, sodium, and anion gap were lower in the MDD group than in the control group (p < 0.05). Correlation analysis of thyroid function, renal function, and factor terms of HAMD in the MDD group suggested that diurnal variation, hopelessness, and depression level were positively correlated with thyrotropin (TSH) (p < 0.05). Cognitive disturbance, retardation, and depression level were negatively correlated with creatinine (p < 0.05). Diurnal variation was negatively correlated with sodium ion (p < 0.01); hopelessness and depression level were positively correlated with chloride ion (p < 0.05); diurnal variation, retardation, and depression level were negatively correlated with anion gap (p < 0.05). Diurnal variation (p < 0.01) and retardation (p < 0.05) were negatively correlated with osmolality. Cognitive disturbance and depression level were positively correlated with estimated glomerular filtration rate (eGFR) (p < 0.05). In the MDD group, correlation analysis of thyroid function, renal function, and HAMA factor terms suggested that the total HAMA score and anxiety level were positively correlated with chloride ion (p < 0.05); psychic anxiety, total HAMA score, and anxiety level were negatively correlated with anion gap (p < 0.05). Furthermore, a low level of anion gap was an independent risk factor for depression and anxiety levels (p < 0.05).

Conclusion

Low thyroid function and reduced waste metabolized by the kidneys in patients with MDD suggest a low intake and low metabolism in depressed patients. In addition, subtle fluctuations in the anion gap in depressed patients were strongly correlated with the degree of depression and anxiety.

A review on linking stress, depression, and insulin resistance via low-grade chronic inflammation

Stress is a disturbance in homeostasis caused by psychological, physiological, or environmental factors. Prolonged reactions to chronic stress can be detrimental, resulting in various metabolic abnormalities, referred to as metabolic syndrome (MS). There is a reciprocal increased risk between MS and major depressive disorder. Recent studies established an association between inflammation and insulin signaling in type 2 diabetes mellitus with depression. In the present review, we discuss chronic low-grade inflammation, pathways of insulin resistance, and brain glucose metabolism in the context of neuroinflammation and depression. Specific attention is given to psychotropic drugs such as bupropion, mirtazapine, and nefazodone, anti-inflammatory drugs like Celecoxib (COX-2 inhibitor), Etanercept, adalimumab, IL-4Ra antagonist, Anti-IL- 17A antibody (Ixekizumab) and lifestyle modifications including exercise, dietary changes, and sleep hygiene. These therapeutic solutions offer potential in treating depression by targeting metabolic conditions like insulin resistance and inflammatory pathways. The article further explains the significance of a nutrition and antioxidants-rich diet, emphasizing the role of omega-3 fatty acids, vitamin D, zinc, and polyphenols, to improve immunity and activate anti-inflammatory signaling pathways.

Major depressive disorder as a neuro-immune disorder: Origin, mechanisms, and therapeutic opportunities

Notwithstanding advances in understanding the pathophysiology of major depressive disorder (MDD), no single mechanism can explain all facets of this disorder. An expanding body of evidence indicates a putative role for the inflammatory response. Several meta-analyses showed an increase in systemic peripheral inflammatory markers in individuals with MDD. Numerous conditions and circumstances in the modern world may promote chronic systemic inflammation through mechanisms, including alterations in the gut microbiota. Peripheral cytokines may reach the brain and contribute to neuroinflammation through cellular, humoral, and neural pathways. On the other hand, antidepressant drugs may decrease peripheral levels of inflammatory markers. Anti-inflammatory drugs and nutritional strategies that reduce inflammation also could improve depressive symptoms. The present study provides a critical review of recent advances in the role of inflammation in the pathophysiology of MDD. Furthermore, this review discusses the role of glial cells and the main drivers of changes associated with neuroinflammation. Finally, we highlight possible novel neurotherapeutic targets for MDD that could exert antidepressant effects by modulating inflammation.

Metabolome subtyping reveals multi-omics characteristics and biological heterogeneity in major psychiatric disorders

Growing evidence suggests that major psychiatric disorders (MPDs) share common etiologies and pathological processes. However, the diagnosis is currently based on descriptive symptoms, which ignores the underlying pathogenesis and hinders the development of clinical treatments. This highlights the urgency of characterizing molecular biomarkers and establishing objective diagnoses of MPDs. Here, we collected untargeted metabolomics, proteomics and DNA methylation data of 327 patients with MPDs, 131 individuals with genetic high risk and 146 healthy controls to explore the multi-omics characteristics of MPDs. First, differential metabolites (DMs) were identified and we classified MPD patients into 3 subtypes based on DMs. The subtypes showed distinct metabolomics, proteomics and DNA methylation signatures. Specifically, one subtype showed dysregulation of complement and coagulation proteins, while the DNA methylation showed abnormalities in chemical synapses and autophagy. Integrative analysis in metabolic pathways identified the important roles of the citrate cycle, sphingolipid metabolism and amino acid metabolism. Finally, we constructed prediction models based on the metabolites and proteomics that successfully captured the risks of MPD patients. Our study established molecular subtypes of MPDs and elucidated their biological heterogeneity through a multi-omics investigation. These results facilitate the understanding of pathological mechanisms and promote the diagnosis and prevention of MPDs.

APOE Polymorphism Is Associated with Changes in the Kynurenine Pathway

BACKGROUND

APOE polymorphism and the Kynurenine pathway (KP) are associated with many disorders, but little is known about associations between APOE polymorphism and the KP. This study explored the associations between the KP and APOE polymorphism in disorders associated with APOE polymorphism and changes in the KP.

METHODS

Subjects with morbid obesity before and after bariatric surgery (numbers 139 and 95, respectively), depression (number 49), and unspecified neurological symptoms (number 39) were included. The following grouping of the APOE genotypes was used: E2 = ɛ2ɛ2 + ɛ2ɛ3, E3 = ɛ3ɛ3 + ɛ2ɛ4, and E4 = ɛ3ɛ4 + ɛ4ɛ4. The KP metabolites Tryptophan, Kynurenine, Kynurenic acid, Quinolinic acid, and Xanthurenic acid were quantified in serum.

RESULTS

The main findings were a significant positive association between E3 and Quinolinic acid (difference between E3 and E2E4: 12.0 (3.5; 18.6) ng/mL); p = 0.005), and a negative association between E4 and Kynurenine (difference between E4 and E2E3: -31.3 (-54.2; -3.2) ng/mL; p = 0.008). Quinolinic acid has been ascribed neurotoxic and inflammatory effects, and Kynurenine is a marker of inflammation.

CONCLUSIONS

The findings indicate that APOE polymorphism might cause changes in the KP that contribute to the disease. Inflammation could be the link between APOE and the KP.