Kynurenines: Tryptophan's metabolites in exercise, inflammation, and mental health

Implications of altered NAD metabolism in metabolic disorders

Nicotinamide adenine dinucleotide (NAD) is an important coenzyme that participates in various energy metabolism pathways, including glycolysis, β-oxidation, and oxidative phosphorylation. Besides, it is a required cofactor for post-translational modifications such as ADP-ribosylation and deacetylation by poly (ADP-ribose) polymerases (PARPs) and sirtuins, respectively. Thus, NAD regulates energy metabolism, DNA damage repair, gene expression, and stress response through these enzymes. Numerous studies have shown that NAD levels decrease with aging and under disturbed nutrient conditions, such as obesity. Additionally, a decline in NAD levels is closely related to the development of various metabolic disorders, including diabetes and fatty liver disease. In addition, many studies have revealed that administration of NAD precursors, such as nicotinamide mononucleotide (NMN) and nicotinamide riboside (NR), efficiently increase NAD levels in various tissues and prevent such metabolic diseases. These NAD precursors are contained in natural foods, such as cow milk, vegetables, and meats. Therefore, altered NAD metabolism can be a practical target for nutritional intervention. Recently, several human clinical trials using NAD precursors have been conducted to investigate the safety, pharmacokinetics, and efficacy against metabolic disorders such as glucose intolerance. In this review, we summarize current knowledge on the implications of NAD metabolism in metabolic diseases and discuss the outcomes of recent human clinical trials.

Exercise-mediated improvement of depression in patients with gastro-esophageal junction cancer is linked to kynurenine metabolism

Background: Exercise may improve depression in cancer patients, yet the molecular mechanism behind this protection is poorly understood. Here, we aimed to explore the link between exercise and regulation of kynurenine (Kyn) metabolism and inflammation in patients with operable gastro-esophageal junction (GEJ) cancer patients, who improved significantly in depression score with exercise training. Material and Methods: Fifty GEJ cancer patients were allocated to 12 weeks of supervised training twice weekly including interval-based aerobic exercise and resistance training, or standard care. Depression score was evaluated by HADS, and blood samples and muscle biopsies were collected for determination of Kyn metabolism and inflammation across the intervention. Results: Depression scores decreased by -1.3 points in the exercise group (p < 0.01), whereas no changes were observed in the control group. Plasma 3-hydroxykynurenine (HK), a Kyn metabolite giving rise to other neurotoxic metabolites, increased by 48% (p <0.001) in the control group, while exercise training attenuated this accumulation. The production of HK is induced by inflammation, and while we observed no differences in systemic pro-inflammatory cytokines, exercise training ameliorated the treatment-induced intramuscular inflammation. Moreover, exercise has been suggested to convert Kyn to the neuroprotective metabolite, kynurenic acid (KA), but despite marked functional and muscular exercise-mediated adaptations, we did not observe any enhancement of KA production and related enzyme expression in the muscles of GEJ cancer patients. Conclusion: Exercise training reduced symptoms of depression in patients with GEJ cancer, and this effect was associated with an exercise-dependent attenuation of the inflammation-induced conversion of Kyn to neurotoxic metabolites.

PPARα contributes to protection against metabolic and inflammatory derangements associated with acute kidney injury in experimental sepsis

Sepsis-associated acute kidney injury (AKI) is a significant problem in critically ill children and adults resulting in increased morbidity and mortality. Fundamental mechanisms contributing to sepsis-associated AKI are poorly understood. Previous research has demonstrated that peroxisome proliferator-activated receptor α (PPARα) expression is associated with reduced organ system failure in sepsis. Using an experimental model of polymicrobial sepsis, we demonstrate that mice deficient in PPARα have worse kidney function, which is likely related to reduced fatty acid oxidation and increased inflammation. Ultrastructural evaluation with electron microscopy reveals that the proximal convoluted tubule is specifically injured in septic PPARα deficient mice. In this experimental group, serum metabolomic analysis reveals unanticipated metabolic derangements in tryptophan-kynurenine-NAD+ and pantothenate pathways. We also show that a subgroup of children with sepsis whose genome-wide expression profiles are characterized by repression of the PPARα signaling pathway has increased incidence of severe AKI. These findings point toward interesting associations between sepsis-associated AKI and PPARα-driven fatty acid metabolism that merit further investigation.

Ovarian progesterone suppresses depression and anxiety-like behaviors by increasing the Lactobacillus population of gut microbiota in ovariectomized mice

Depression and anxiety, which are severe symptoms during menopause, are caused by ceased ovarian activity and declined serum progesterone levels. Studies have demonstrated that gut microbiota can regulate brain function and change the microbiota composition during the perimenopause period. This study investigated whether progesterone affects depressant and anxious behaviors via gut microbiota. In ovariectomized (OVX) mice, treatment with progesterone improved depressive and anxious behaviors, and gut microbiota composition was significantly changed. In particular, increased Lactobacillus spp. were observed in these mice. Reduction of microbiota by antibiotic treatment abolished the effect of progesterone on depression and anxiety. In addition, administration of Lactobacillus (L.) reuteri that was increased by progesterone also reduced the depressant behavior in OVX mice, and BDNF gene expression was elevated by progesterone treatment and L. reuteri administration in the hippocampus. Moreover, we found that progesterone stimulated the growth of L. reuteri in vitro. In summary, our findings indicate that progesterone reduces depression and anxiety through changes in gut microbiota composition, particularly by increasing the Lactobacillus spp. population.

Orchestration of Tryptophan-Kynurenine Pathway, Acute Decompensation, and Acute-on-Chronic Liver Failure in Cirrhosis

Systemic inflammation (SI) is involved in the pathogenesis of acute decompensation (AD) and acute-on-chronic liver failure (ACLF) in cirrhosis. In other diseases, SI activates tryptophan (Trp) degradation through the kynurenine pathway (KP), giving rise to metabolites that contribute to multiorgan/system damage and immunosuppression. In the current study, we aimed to characterize the KP in patients with cirrhosis, in whom this pathway is poorly known. The serum levels of Trp, key KP metabolites (kynurenine and kynurenic and quinolinic acids), and cytokines (SI markers) were measured at enrollment in 40 healthy subjects, 39 patients with compensated cirrhosis, 342 with AD (no ACLF) and 180 with ACLF, and repeated in 258 patients during the 28-day follow-up. Urine KP metabolites were measured in 50 patients with ACLF. Serum KP activity was normal in compensated cirrhosis, increased in AD and further increased in ACLF, in parallel with SI; it was remarkably higher in ACLF with kidney failure than in ACLF without kidney failure in the absence of differences in urine KP activity and fractional excretion of KP metabolites. The short-term course of AD and ACLF (worsening, improvement, stable) correlated closely with follow-up changes in serum KP activity. Among patients with AD at enrollment, those with the highest baseline KP activity developed ACLF during follow-up. Among patients who had ACLF at enrollment, those with immune suppression and the highest KP activity, both at baseline, developed nosocomial infections during follow-up. Finally, higher baseline KP activity independently predicted mortality in patients with AD and ACLF. Conclusion: Features of KP activation appear in patients with AD, culminate in patients with ACLF, and may be involved in the pathogenesis of ACLF, clinical course, and mortality.

Ultrahigh-Performance Liquid Chromatography Tandem Mass Spectrometry with Electrospray Ionization Quantification of Tryptophan Metabolites and Markers of Gut Health in Serum and Plasma-Application to Clinical and Epidemiology Cohorts

A targeted ultrahigh-performance liquid chromatography tandem mass spectrometry with electrospray ionization (UHPLC-ESI-MS/MS) method has been developed for the quantification of tryptophan and its downstream metabolites from the kynurenine and serotonin pathways. The assay coverage also includes markers of gut health and inflammation, including citrulline and neopterin. The method was designed in 96-well plate format for application in multiday, multiplate clinical and epidemiology population studies. A chromatographic cycle time of 7 min enables the analysis of two 96-well plates in 24 h. To protect chromatographic column lifespan, samples underwent a two-step extraction, using solvent protein precipitation followed by delipidation via solid-phase extraction (SPE). Analytical validation reported accuracy of each analyte <20% for the lowest limit of quantification and <15% for all other quality control (QC) levels. The analytical precision for each analyte was 2.1–12.9%. To test the applicability of the method to multiplate and multiday preparations, a serum pool underwent periodic repeat analysis during a run consisting of 18 plates. The % CV (coefficient of variation) values obtained for each analyte were <15%. Additional biological testing applied the assay to samples collected from healthy control participants and two groups diagnosed with inflammatory bowel disease (IBD) (one group treated with the anti-inflammatory 5-aminosalicylic acid (5-ASA) and one group untreated), with results showing significant differences in the concentrations of picolinic acid, kynurenine, and xanthurenic acid. The short analysis time and 96-well plate format of the assay makes it suitable for high-throughput targeted UHPLC-ESI-MS/MS metabolomic analysis in large-scale clinical and epidemiological population studies.

The gut microbiota promotes the pathogenesis of schizophrenia via multiple pathways

Schizophrenia is a severe mental disorder with unknown etiology. Many mechanisms, including dysregulation of neurotransmitters, immune disturbance, and abnormal neurodevelopment, are proposed for the pathogenesis of schizophrenia. The significance of communication between intestinal flora and the central nervous system through the gut-brain axis is increasingly being recognized. The intestinal microbiota plays an important role in regulating neurotransmission, immune homeostasis, and brain development. We hypothesize that an imbalance in intestinal flora causes immune activation and dysfunction in the gut-brain axis, contributing to schizophrenia. In this review, we examine recent studies that explore the intestinal flora and immune-mediated neurodevelopment of schizophrenia. We conclude that an imbalance in intestinal flora may reduce protectants and increase neurotoxin and inflammatory mediators, causing neuronal and synaptic damage, which induces schizophrenia.

Influence of different rehabilitative aerobic exercise programs on (anti-) inflammatory immune signalling, cognitive and functional capacity in persons with MS - study protocol of a randomized controlled trial

BACKGROUND

Studies have shown positive effects of therapeutic exercise on motor- and cognitive function as well as on psychosocial outcomes in persons with multiple sclerosis (MS). A reduction of inflammatory stress through physical exercise has been suspected as one key mechanism, mediating the positive effects of exercise in the context of MS. The primary objective of this trial is to investigate the acute and chronic effects of different exercise modalities on (anti-)inflammatory immune signalling as well as on cognitive and functional capacity in persons with MS.

METHODS

A two armed single-blind randomized controlled design will investigate 72 persons with relapsing remitting or secondary progressive MS (EDSS 3.0-6.0), during 3 weeks of inpatient rehabilitation. Participants will be randomized into either a high-intensity interval training (HIIT) or a moderate continuous training group; the latter represents the local standard therapy (ST). Both groups will exercise 3x per week. The HIIT group will perform 5 × 1.5-min high-intensive exercise bouts at 95-100% of their maximum heart rate (HRmax) followed by active breaks of unloaded pedalling (60% HRmax) for 2 min. In contrast, the ST group will exercise for 24 min continuously at 65% of HRmax. The proportion of circulating regulatory T-cells will be measured as primary outcome. Secondary outcomes comprise numbers and proportions of further immune cells including Th17-cells, soluble factors ((anti-) inflammatory cytokines, tryptophan metabolites), endurance capacity, cognitive performance, processing skills for activities of daily living, fatigue, depression and healthcare-related quality of life. Outcomes will be assessed before (T0) and after (T3) the 3-week exercise intervention program. Blood samples of T0 will be taken immediately before the first exercise session. Additionally, blood samples for the soluble factors will be collected immediately after (T1) and three hours (T2) after the first exercise session of each group.

DISCUSSION

This study will be the first to investigate both acute and chronic effects of aerobic exercise on immune function and disease associated biomarkers in persons with MS. Combining biological analyses with cognitive and functional capacity assessments may contribute to a better understanding of responses to rehabilitative training, needed to improve exercise recommendations for persons with MS.

TRIAL REGISTRATION

This trial was prospectively registered at ClinicalTrials.gov ( NCT03652519 ; 29 August 2018).

Metabolomic Insights into Human Arboviral Infections: Dengue, Chikungunya, and Zika Viruses

The global burden of arboviral diseases and the limited success in controlling them calls for innovative methods to understand arbovirus infections. Metabolomics has been applied to detect alterations in host physiology during infection. This approach relies on mass spectrometry or nuclear magnetic resonance spectroscopy to evaluate how perturbations in biological systems alter metabolic pathways, allowing for differentiation of closely related conditions. Because viruses heavily depend on host resources and pathways, they present unique challenges for characterizing metabolic changes. Here, we review the literature on metabolomics of arboviruses and focus on the interpretation of identified molecular features. Metabolomics has revealed biomarkers that differentiate disease states and outcomes, and has shown similarities in metabolic alterations caused by different viruses (e.g., lipid metabolism). Researchers investigating such metabolomic alterations aim to better understand host⁻virus dynamics, identify diagnostically useful molecular features, discern perturbed pathways for therapeutics, and guide further biochemical research. This review focuses on lessons derived from metabolomics studies on samples from arbovirus-infected humans.

Amino acids at the intersection of nutrition and insulin sensitivity

A systems network that is coordinated in the sensing and management of nutrient signals is paramount to energy homeostasis, and its dysfunction induces metabolic stress and insulin resistance. Amino acids have recently emerged as a collection of signaling metabolites that underlie the metabolic impacts of different dietary patterns and life styles. This relationship is beginning to be understood from the close coupling of immune and metabolic systems, and serves to enrich our understanding of metabolic diseases, such as type 2 diabetes mellitus. In this review, we provide an overview of several amino acids or their metabolites that link nutrients with insulin sensitivity and discuss how they integrate into organ crosstalk pathways to influence physiological or pathological metabolic states.

Latent toxoplasmosis and psychiatric symptoms - A role of tryptophan metabolism?

Toxoplasma gondii (TOX) is a common parasite which infects approximately one third of the human population. In recent years, it has been suggested that latent toxoplasmosis may be a risk factor for the development of mental disorders, particularly schizophrenia and anxiety. With regards to depression the results have been varied. The main objective of this study was to examine subpopulations from the Danish PRISME and GENDEP populations for TOX IgG antibodies. These consisted of: a group with symptoms of anxiety, a group suffering from burnout syndrome, as well as two different subpopulations with depression of differing severity. The secondary objective of this study was to examine whether tryptophan metabolism was altered in TOX-positive subjects within each subpopulation. Our results show that the anxiety and burnout populations were more likely to be TOX IgG seropositive. Furthermore, we find that the moderate-severe but not mild-moderate depressive subpopulation were associated with TOX seropositivety, suggesting a possible role of symptom severity. Additionally, we found that TOX positive subjects in the anxiety and burnout subpopulations had altered tryptophan metabolism. This relationship did not exist in the mild-moderate depressive subpopulation. These results suggest that TOX seropositivity may be related to anxiety, burnout and potentially to severity of depression. We furthermore show that the psychiatric symptoms could be associated with an altered tryptophan metabolism.

Kynurenine 3-monooxygenase is a critical regulator of renal ischemia-reperfusion injury

Acute kidney injury (AKI) following ischemia–reperfusion injury (IRI) has a high mortality and lacks specific therapies. Here, we report that mice lacking kynurenine 3-monooxygenase (KMO) activity (Kmo^null mice) are protected against AKI after renal IRI. We show that KMO is highly expressed in the kidney and exerts major metabolic control over the biologically active kynurenine metabolites 3-hydroxykynurenine, kynurenic acid, and downstream metabolites. In experimental AKI induced by kidney IRI, Kmo^null mice had preserved renal function, reduced renal tubular cell injury, and fewer infiltrating neutrophils compared with wild-type (Kmo^wt) control mice. Together, these data confirm that flux through KMO contributes to AKI after IRI, and supports the rationale for KMO inhibition as a therapeutic strategy to protect against AKI during critical illness.

Inhibition of a metabolic enzyme linked to inflammation could be a novel treatment approach for sudden kidney failure following a “reperfusion” injury caused by blood flow returning to the organ after a period of insufficient blood supply. Damian Mole and colleagues from the University of Edinburgh, UK, temporarily blocked blood vessels leading to the kidneys of mice to induce organ damage. Mice that lacked a working copy of kynurenine 3-monooxygenase (KMO), a gene that encodes an enzyme involved in metabolizing an essential amino acid linked to immune activation, were protected from injury. These KMO-mutant mice experienced less damage to the kidney’s tubular cells and had fewer pro-inflammatory cells than genetically normal animals. The findings support the idea that blocking KMO and its associated metabolic pathway could help mitigate kidney damage following reperfusion injury in humans.

Serum Omega-6 Fatty Acids and Immunology-Related Gene Expression in Peripheral Blood Mononuclear Cells: A Cross-Sectional Analysis in Healthy Children

SCOPE

Some studies suggest that a high dietary intake of omega-6 fatty acids is pro-inflammatory. However, whether omega-6 fatty acids actually cause pathogenic inflammation in humans is debated. Therefore, the associations between expression of immunology-related genes in peripheral blood mononuclear cells (PBMCs) and serum total omega-6 PUFA status are investigated.

METHODS AND RESULTS

Serum fatty acid profile and expression of 460 immunology-related genes in PBMCs from 58 healthy children (6-13 years) is measured, and examined the expression differences between children with high or low total omega-6 PUFA status (upper vs lower tertile). Taken together, both univariate analyses and integrated omics analyses support that while high omega-6 PUFA level associated with higher expressing of genes related to innate immune responses, it also associated with lower expression of several genes related to adaptive immune responses.

CONCLUSION

Omega-6 PUFA status associated both positively and negatively with expression of specific immunology-related genes in PBMCs in healthy children. The results may suggest a nuanced role for omega-6 fatty acids in the interphase of lipids and inflammation, and warrants further examination in gene-environment studies and randomized controlled trials.

Blood-brain barrier permeability and physical exercise

In this narrative review, a theoretical framework on the crosstalk between physical exercise and blood-brain barrier (BBB) permeability is presented. We discuss the influence of physical activity on the factors affecting BBB permeability such as systemic inflammation, the brain renin-angiotensin and noradrenergic systems, central autonomic function and the kynurenine pathway. The positive role of exercise in multiple sclerosis and Alzheimer’s disease is described. Finally, the potential role of conditioning as well as the effect of exercise on BBB tight junctions is outlined. There is a body of evidence that regular physical exercise diminishes BBB permeability as it reinforces antioxidative capacity, reduces oxidative stress and has anti-inflammatory effects. It improves endothelial function and might increase the density of brain capillaries. Thus, physical training can be emphasised as a component of prevention programs developed for patients to minimise the risk of the onset of neuroinflammatory diseases as well as an augmentation of existing treatment. Unfortunately, despite a sound theoretical background, it remains unclear as to whether exercise training is effective in modulating BBB permeability in several specific diseases. Further research is needed as the impact of exercise is yet to be fully elucidated.

Biochemical Differences in Cerebrospinal Fluid between Secondary Progressive and Relapsing⁻Remitting Multiple Sclerosis

To better understand the pathophysiological differences between secondary progressive multiple sclerosis (SPMS) and relapsing-remitting multiple sclerosis (RRMS), and to identify potential biomarkers of disease progression, we applied high-resolution mass spectrometry (HRMS) to investigate the metabolome of cerebrospinal fluid (CSF). The biochemical differences were determined using partial least squares discriminant analysis (PLS-DA) and connected to biochemical pathways as well as associated to clinical and radiological measures. Tryptophan metabolism was significantly altered, with perturbed levels of kynurenate, 5-hydroxytryptophan, 5-hydroxyindoleacetate, and N-acetylserotonin in SPMS patients compared with RRMS and controls. SPMS patients had altered kynurenine compared with RRMS patients, and altered indole-3-acetate compared with controls. Regarding the pyrimidine metabolism, SPMS patients had altered levels of uridine and deoxyuridine compared with RRMS and controls, and altered thymine and glutamine compared with RRMS patients. Metabolites from the pyrimidine metabolism were significantly associated with disability, disease activity and brain atrophy, making them of particular interest for understanding the disease mechanisms and as markers of disease progression. Overall, these findings are of importance for the characterization of the molecular pathogenesis of SPMS and support the hypothesis that the CSF metabolome may be used to explore changes that occur in the transition between the RRMS and SPMS pathologies.

Stereoselective Assembly of Gigantic Chiral Molybdenum Blue Wheels Using Lanthanide Ions and Amino Acids

The synthesis of chiral polyoxometalates (POMs) is a challenge because of the difficulty to induce the formation of intrinsically chiral metal-oxo frameworks. Herein we report the stereoselective synthesis of a series of gigantic chiral Mo Blue (MB) POM clusters 1-5 that are formed by exploiting the synergy between coordinating lanthanides ions as symmetry breakers to produce MBs with chiral frameworks decorated with amino acids ligands; these promote the selective formation of enantiopure MBs. All the compounds share the same framework archetype, based on {Mo124Ce4}, which forms an intrinsically chiral Δ or Λ configurations, controlled by the configurations of functionalized chiral amino acids. The chirality and stability of 1-5 in solution are confirmed by circular dichroism, 1H NMR, and electrospray ion mobility-mass spectrometry studies. In addition, the framework of the {Mo124Ce4} MB not only behaves as a host able to trap a chiral {Mo8} cluster that is not accessible by traditional synthesis but also promotes the transformation of tryptophan to kynurenine in situ. This work demonstrates the potential and applicability of our synthetic strategy to produce gigantic chiral POM clusters capable of host-guest chemistry and selective synthetic transformations.

Gut Microbiota Regulation of Tryptophan Metabolism in Health and Disease

The gut microbiota is a crucial actor in human physiology. Many of these effects are mediated by metabolites that are either produced by the microbes or derived from the transformation of environmental or host molecules. Among the array of metabolites at the interface between these microorganisms and the host is the essential aromatic amino acid tryptophan (Trp). In the gut, the three major Trp metabolism pathways leading to serotonin (5-hydroxytryptamine), kynurenine (Kyn), and indole derivatives are under the direct or indirect control of the microbiota. In this review, we gather the most recent advances concerning the central role of Trp metabolism in microbiota-host crosstalk in health and disease. Deciphering the complex equilibrium between these pathways will facilitate a better understanding of the pathogenesis of human diseases and open therapeutic opportunities.

Exploratory metabolomics of metabolic syndrome: A status report

Metabolic syndrome (MetS) is as a cluster of cardio-metabolic factors that greatly increase the risk of chronic diseases such as type II diabetes mellitus and atherosclerotic cardiovascular disease. In the United States, obesity, physical inactivity, aging, and genetics (to a minor extent) have arisen as risk factors for developing MetS. Although 35% of American adults suffer from MetS, its pathogenesis largely remains unknown. Worse, there is a lack of screening and optimum therapy for this disease. Researchers have consequently turned towards metabolomics to identify biomarkers to better understand MetS. The purpose of this review is to characterize various metabolites and their potential connections to MetS. Numerous studies have also characterized MetS as a disease of increased inflammation, and therefore this review also explores how metabolites play a role in various inflammatory pathways. Our review explores a broad range of metabolites including biogenic amines, branched chain amino acids, aromatic amines, phosphatidylcholines, as well as a variety of other molecules. We will explore their biochemical pathways and their potential role in serving as biomarkers.

The kynurenine pathway and cognitive performance in community-dwelling older adults. The Hordaland Health Study

INTRODUCTION

Tryptophan, its downstream metabolites in the kynurenine pathway and neopterin have been associated with inflammation and dementia. We aimed to study the associations between plasma levels of these metabolites and cognitive function in community-dwelling, older adults.

METHODS

This cross-sectional study included 2174 participants aged 70-72 years of the community-based Hordaland Health Study. Tryptophan, kynurenine, neopterin and eight downstream kynurenines were measured in plasma. Kendrick Object Learning Test (KOLT), Digit Symbol Test (DST) and the Controlled Oral Word Association Test (COWAT) were all outcomes in standardized Zellner's regression. The Wald test of a composite linear hypothesis of an association with each metabolite was adjusted by the Bonferroni method. Age, body mass index, C-reactive protein, depressive symptoms, diabetes, education, glomerular filtration rate, hypertension, previous myocardial infarction, prior stroke, pyridoxal 5'phosphate, sex and smoking were considered as potential confounders.

RESULTS

Higher levels of the kynurenine-to-tryptophan ratio (KTR) and neopterin were significantly associated with poorer, overall cognitive performance (p < 0.002). Specifically, KTR was negatively associated with KOLT (β -0.08, p = 0.001) and COWAT (β -0.08, p = 0.001), but not with DST (β -0.03, p = 0.160). This pattern was also seen for neopterin (KOLT: β -0.07; p = 0.001; COWAT: β -0.06, p = 0.010; DST: β -0.01, p = 0.800). The associations were not confounded by the examined variables. No significant associations were found between the eight downstream kynurenines and cognition.

CONCLUSION

Higher KTR and neopterin levels, biomarkers of cellular immune activation, were associated with reduced cognitive performance, implying an association between the innate immune system, memory, and language.

Supplementation with compound polysaccharides contributes to the development and metabolic activity of young rat intestinal microbiota

Compound polysaccharides may be used as a functional food to modulate the composition and metabolism of gut microbiota, and to help maintain the health of the intestinal microecosystem.

Targeting regulation of tryptophan metabolism for colorectal cancer therapy: a systematic review

Colorectal cancer (CRC) is one of the most malignant cancers resulting from abnormal metabolism alterations. As one of the essential amino acids, tryptophan has a variety of physiological functions, closely related to regulation of immune system, central nervous system, gastrointestinal nervous system and intestinal microflora. Colorectal cancer, a type of high-grade malignancy disease, stems from a variety of factors and often accompanies inflammatory reactions, dysbacteriosis, and metabolic disorders. Colorectal cancer accompanies inflammation and imbalance of intestinal microbiota and affects tryptophan metabolism. It is known that metabolites, rate-limiting enzymes, and ARH in tryptophan metabolism are associated with the development of CRC. Specifically, IDO1 may be a potential therapeutic target in colorectal cancer treatment. Furthermore, the reduction of tryptophan amount is proportional to the poor quality of life for colorectal cancer patients. This paper aims to discuss the role of tryptophan metabolism in a normal organism and investigate the relationship between this amino acid and colorectal cancer. This study is expected to provide theoretical support for research related to targeted therapy for colorectal cancer. Furthermore, strategies that modify tryptophan metabolism, effectively inhibiting tumor progression, may be more effective for CRC treatment.

Colorectal cancer (CRC) is one of the most malignant cancers resulting from abnormal metabolism alterations.

Antidepressant effects of direct-acting antivirals against hepatitis C virus-Results from a pilot study

BACKGROUND AND AIMS

The new direct-acting antiviral agents (DAA) have revolutionized the treatment of patients with chronic hepatitis C virus (HCV) infection. This study investigates to which extent DAA affect fatigue and mood and, if so, whether this results from changes to tryptophan (TRP) metabolism, as reflected by two critical biosynthetic pathways, serotonin (SRT) generation from TRP and TRP degradation through kynurenines (KYN) via indoleamine 2,3-dioxygenase (IDO).

METHODS

This study assessed 24 patients with chronic HCV infection, before (T1), during (T2: at 4 weeks) and 12 weeks post-treatment with DAA (T3) with respect to viral load, fatigue and depressive symptoms (BDI-II questionnaire), physical activity (actigraph) and plasma serotonin-tryptophan metabolites (LC/MS). The KYN:TRP ratio reflected IDO activity.

RESULTS

All participants achieved sustained virological response (SVR12) with DAA treatment (79% sofosbuvir-based). Fatigue (scores at T1:0.83 ± 0.70, T2:0.48 ± 0.70, T3:0.30 ± 0.50; P = 0.023) and depressive symptoms (scores at T1:9.8 ± 10.2, T2:6.0 ± 7.3, T3:5.0 ± 7.6; P = 0.005) improved significantly on therapy, whereas no changes were noted in five untreated controls. TRP plasma concentrations markedly decreased (T1:306 ± 179 mg/L, T2:283 ± 84 mg/L), whereas 5-HTP levels increased (T1:0.08 ± 0.01 mg/L, T2:0.10 ± 0.06 mg/L). KYN concentrations (T1:2.4 ± 2.0 mg/L, T2:3.7 ± 1.4 mg/L, P = 0.003) increased significantly during treatment, as did IDO activity (T1:0.008 ± 0.006 mg/L, T2:0.014 ± 0.004 mg/L; P < 0.001).

CONCLUSIONS

In this study, DAA exert positive and persistent effects on both fatigue and mood in patients with chronic HCV infection. These extrahepatic benefits are, at least in part, related to the modulation of TRP metabolism. The robust elevation of KYN concentrations challenges the current paradigm of low KYN levels as prerequisite for mental health.

Metabolite and lipoprotein responses and prediction of weight gain during breast cancer treatment

Background

Breast cancer treatment has metabolic side effects, potentially affecting risk of cardiovascular disease (CVD) and recurrence. We aimed to compare alterations in serum metabolites and lipoproteins during treatment between recipients and non-recipients of chemotherapy, and describe metabolite profiles associated with treatment-related weight gain.

Methods

This pilot study includes 60 stage I/II breast cancer patients who underwent surgery and were treated according to national guidelines. Serum sampled pre-surgery and after 6 and 12 months was analysed by MR spectroscopy and mass spectrometry. In all, 170 metabolites and 105 lipoprotein subfractions were quantified.

Results

The metabolite and lipoprotein profiles of chemotherapy recipients and non-recipients changed significantly 6 months after surgery (p < 0.001). Kynurenine, the lipid signal at 1.55–1.60 ppm, ADMA, 2 phosphatidylcholines (PC aa C38:3, PC ae C42:1), alpha-aminoadipic acid, hexoses and sphingolipids were increased in chemotherapy recipients after 6 months. VLDL and small dense LDL increased after 6 months, while HDL decreased, with triglyceride enrichment in HDL and LDL. At baseline, weight gainers had less acylcarnitines, phosphatidylcholines, lyso-phosphatidylcholines and sphingolipids, and showed an inflammatory lipid profile.

Conclusion

Chemotherapy recipients exhibit metabolic changes associated with inflammation, altered immune response and increased risk of CVD. Altered lipid metabolism may predispose for treatment-related weight gain.

The weight of nutrients: kynurenine metabolites in obesity and exercise

Obesity ultimately results from an imbalance between energy intake and expenditure. However, in addition to their bioenergetic value, nutrients and their metabolites can function as important signalling molecules in energy homeostasis. Indeed, macronutrients and their metabolites can be direct regulators of metabolism through their actions on different organs. In turn, target organs can decide to use, store or transform the incoming nutrients depending on their physiological context and in coordination with other cell types. Tryptophan-kynurenine metabolites are an example of a family of compounds that can serve as systemic integrators of energy metabolism by signalling to different cell types. These include adipocytes, immune cells and muscle fibres, in addition to the well-known effects of kynurenine metabolites on the central nervous system. In the context of energy metabolism, several of the effects elicited by kynurenic acid are mediated by the G-protein-coupled receptor, GPR35. As GPR35 is expressed in tissues such as the adipose tissue, immune cells and the gastrointestinal tract, this receptor could be a potential therapeutic target for the treatment of obesity, diabetes and other metabolic diseases. In addition, metabolic disorders often coincide with states of chronic inflammation, which further highlights GPR35 as an integration node in conditions where inflammation skews metabolism. Defining the molecular interplay between different tissues in the regulation of energy homeostasis can help us understand interindividual variability in the response to nutrient intake and develop safe and efficient therapies to fight obesity and metabolic disease.

Plasma metabolomic profiling of a ketamine and placebo crossover trial of major depressive disorder and healthy control subjects

(R,S)-Ketamine produces rapid, robust, and sustained antidepressant effects in major depressive disorder. Specifically, its pharmacological efficacy in treatment refractory depression is considered a major breakthrough in the field. However, the mechanism of action of ketamine's rapid effect remains to be determined. In order to identify pathways that are responsible for ketamine's effect, a targeted metabolomic approach was carried out using a double-blind, placebo-controlled crossover design, with infusion order randomized with medication-free patients with treatment-resistant major depressive disorder (29 subjects) and healthy controls (25 subjects). The metabolomic profile of these subjects was characterized at multiple time points, and a comprehensive analysis was investigated between the following: MDD and healthy controls, treatment and placebo in both groups and the corresponding response to ketamine treatment. Ketamine treatment resulted in a general increase in circulating sphingomyelins, levels which were not correlated with response. Ketamine response resulted in more pronounced effects in the kynurenine pathway and the arginine pathway at 4 h post-infusion, where a larger decrease in circulating kynurenine levels and a larger increase in the bioavailability of arginine were observed in responders to ketamine treatment, suggesting possible mechanisms for response to ketamine treatment.

Rapamycin Treatment Ameliorates Age-Related Accumulation of Toxic Metabolic Intermediates in Brains of the Ts65Dn Mouse Model of Down Syndrome and Aging

Down syndrome (DS), caused by trisomy of chromosome 21, is the most common genetic cause of intellectual disability. Individuals with DS exhibit changes in neurochemistry and neuroanatomy that worsen with age, neurological delay in learning and memory, and predisposition to Alzheimer's disease. The Ts65Dn mouse is the best characterized model of DS and has many features reminiscent of DS, including developmental anomalies and age-related neurodegeneration. The mouse carries a partial triplication of mouse chromosome 16 containing roughly 100 genes syntenic to human chromosome 21 genes. We hypothesized that there would be differences in brain metabolites with trisomy and age, and that long-term treatment with rapamycin, mechanistic target of rapamycin (mTOR) inhibitor and immunosuppressant, would correct these differences. Using HPLC coupled with electrochemical detection, we identified differences in levels of metabolites involved in dopaminergic, serotonergic, and kynurenine pathways in trisomic mice that are exacerbated with age. These include homovanillic acid, norepinephrine, and kynurenine. In addition, we demonstrate that prolonged treatment with rapamycin reduces accumulation of toxic metabolites (such as 6-hydroxymelatonin and 3-hydroxykynurenine) in aged mice.

Autoimmune phenotypes in schizophrenia reveal novel treatment targets

Typical and atypical antipsychotics are the first-line treatments for schizophrenia, but these classes of drugs are not universally effective, and they can have serious side effects that impact compliance. Antipsychotic drugs generally target the dopamine pathways with some variation. As research of schizophrenia pathophysiology has shifted away from a strictly dopamine-centric focus, the development of new pharmacotherapies has waned. A field of inquiry with centuries-old roots is gaining traction in psychiatric research circles and may represent a new frontier for drug discovery in schizophrenia. At the forefront of this investigative effort is the immune system and its many components, pathways and phenotypes, which are now known to actively engage the brain. Studies in schizophrenia reveal an intricate association of environmentally-driven immune activation in concert with a disrupted genetic template. A consistent conduit through this gene-environmental milieu is the gut-brain axis, which when dysregulated can generate pathological autoimmunity. In this review, we present epidemiological and biochemical evidence in support of an autoimmune component in schizophrenia and depict gut processes and a dysbiotic microbiome as a source and perpetuator of autoimmune dysfunction in the brain. Within this framework, we review the role of infectious agents, inflammation, gut dysbioses and autoantibody propagation on CNS pathologies such as neurotransmitter receptor hypofunction and complement pathway-mediated synaptic pruning. We then review the new pharmacotherapeutic horizon and novel agents directed to impact these pathological conditions. At the core of this discourse is the understanding that schizophrenia is etiologically and pathophysiologically heterogeneous and thus its treatment requires individualized attention with disease state variants diagnosed with objective biomarkers.

Role of Kynurenine pathway and its metabolites in mood disorders: A systematic review and meta-analysis of clinical studies

Activation of the kynurenine pathway is one of the described mechanisms by which inflammation can induce depression. It involves multiple pathways including interference with the bioavailability of tryptophan central to the synthesis of the neurotransmitter serotonin. In this systematic review, we examine the relationship between kynurenine metabolites (kynurenine, kynurenic acid, tryptophan, quinolinic acid, the ratio of kynurenine and tryptophan) and mood disorders by conducting a meta-analysis. Fifty-six studies were identified, 21 met inclusion criteria and 14 were deemed suitable (9 investigating unipolar depression and 5 bipolar disorder). We found decreased levels of kynurenine in unipolar major depression vs. healthy controls but studies were significantly heterogeneous in nature. No significant differences were found in tryptophan levels or kynurenine/tryptophan ratios. Kynurenine metabolites are likely to play a role in major depression but an exact etiological role in mood disorder seem complex and requires further research.

Hydrocortisone Affects Fatigue and Physical Functioning Through Metabolism of Tryptophan: A Randomized Controlled Trial

CONTEXT

Hydrocortisone (HC) treatment influences health-related quality of life (HRQOL) in secondary adrenal insufficiency (AI). Glucocorticoids regulate tryptophan metabolism through the kynurenine pathway, which modulates mood and energy homeostasis.

OBJECTIVE

This study investigated whether tryptophan metabolism mediated the effect of HC dose on HRQOL in patients with secondary AI.

DESIGN, SETTING, AND PATIENTS

Forty-seven patients with secondary AI participated in this double-blind randomized controlled cross-over trial in the University Medical Center Groningen.

INTERVENTION

Patients were treated for two 10-week periods with a daily HC dose of 0.2 to 0.3 mg/kg and 0.4 to 0.6 mg/kg body weight, respectively.

MAIN OUTCOME MEASURES

Diary data and questionnaires were used to assess HRQOL. Tryptophan, kynurenine and 3-hydroxykynurenine were measured in serum and dialyzed plasma and the kynurenine-to-tryptophan ratio (Kyn/Trp ratio) ratio was calculated.

RESULTS

A higher dose HC was associated with increased levels of tryptophan (95% CI for mean difference 0.37 to 12.5, P = 0.038), reduced levels of kynurenine (95% CI, -0.49 to -0.10, P = 0.004) and 3-hydroxykynurenine (95% CI, -10.6 to -2.35, P = 0.003), and a reduced Kyn/Trp ratio (95% CI, -0.84 to -0.50, P < 0.001). The Kyn/Trp ratio mediated the effect of a higher dose HC on fatigue (P = 0.041) and physical functioning (P = 0.005).

CONCLUSION

Metabolism of tryptophan through the kynurenine pathway is reduced after a 10-week treatment with a higher dose HC and plays a role in the effect of HC on fatigue and physical functioning in patients with secondary AI.

An Integrated, High-Throughput Strategy for Multiomic Systems Level Analysis

Proteomics, metabolomics, and transcriptomics generate comprehensive data sets, and current biocomputational capabilities allow their efficient integration for systems biology analysis. Published multiomics studies cover methodological advances as well as applications to biological questions. However, few studies have focused on the development of a high-throughput, unified sample preparation approach to complement high-throughput omic analytics. This report details the automation, benchmarking, and application of a strategy for transcriptomic, proteomic, and metabolomic analyses from a common sample. The approach, sample preparation for multi-omics technologies (SPOT), provides equivalent performance to typical individual omic preparation methods but greatly enhances throughput and minimizes the resources required for multiomic experiments. SPOT was applied to a multiomics time course experiment for zinc-treated HL-60 cells. The data reveal Zn effects on NRF2 antioxidant and NFkappaB signaling. High-throughput approaches such as these are critical for the acquisition of temporally resolved, multicondition, large multiomic data sets such as those necessary to assess complex clinical and biological concerns. Ultimately, this type of approach will provide an expanded understanding of challenging scientific questions across many fields.

De novo NAD+ biosynthetic impairment in acute kidney injury in humans

Nicotinamide adenine dinucleotide (NAD+) extends longevity in experimental organisms, raising interest in its impact on human health. De novo NAD+ biosynthesis from tryptophan is evolutionarily conserved yet considered supplanted among higher species by biosynthesis from nicotinamide (Nam). Here we show that a bottleneck enzyme in de novo biosynthesis, quinolinate phosphoribosyltransferase (QPRT), defends renal NAD+ and mediates resistance to acute kidney injury (AKI). Following murine AKI, renal NAD+ fell, quinolinate rose, and QPRT declined. QPRT^+/− mice exhibited higher quinolinate, lower NAD+, and higher AKI susceptibility. Metabolomics proposed elevated urinary quinolinate/tryptophan (uQ:T) as an indicator of reduced QPRT. Elevated uQ:T predicted AKI and other adverse outcomes in critically ill patients. A Phase 1 placebo-controlled study of oral Nam demonstrated dose-related increase in circulating NAD+ metabolites. Nam was well-tolerated and was associated with less AKI. Impaired NAD+ biosynthesis may therefore be a feature of high-risk hospitalizations for which NAD+ augmentation could be beneficial.

Dietary L-Tryptophan Modulates the Structural and Functional Composition of the Intestinal Microbiome in Weaned Piglets

Background: Intestinal microbiota plays an important role in regulating metabolism, physiology, and immune response of the host. L-Tryptophan (Trp) are metabolized by several genera of bacteria. It remains largely unknown whether Trp can regulate the composition and diversity of the intestinal microbiota and contribute to intestinal homeostasis.

Methods: A total of 126 weaning piglets were fed a corn- and soybean meal-based diet supplemented with 0, 0.2, or 0.4% Trp for 4 weeks. The intestinal microbiota was measured by using bacterial 16S rRNA gene-based high-throughput sequencing methods. Metabolites of Trp and short-chain fatty acids (SCFAs) in the hindgut were determined by high-performance liquid chromatography and gas chromatography, respectively. The mRNA levels for aromatic hydrocarbon receptor (AhR), tumor necrotic factor-α (TNF-α), interleukin-8 (IL-8), and protein abundances of tight junction proteins were determined.

Results: Compared with the control group, Trp supplementation enhanced piglet growth performance and markedly altered the intestinal microbial composition as evidenced by enhanced alpha and beta diversity in the microbiome (P < 0.05). The abundances of Prevotella, Roseburia, and Succinivibrio genera were enriched, but those of Clostridium sensu stricto and Clostridium XI, opportunistic pathogens, were decreased with dietary Trp supplementation. Analysis of metabolic pathways indicated enhanced indole alkaloid biosynthesis and Trp metabolism, which was validated by elevated concentrations of 3-indoleacetic acid and indole in the intestinal contents of Trp-supplemented piglets (P < 0.05). These changes in Trp metabolites were correlated with activation of AhR and cytochrome p4501 A1 (CYP1A1) in cecum and colonic tissues, and with a decrease in the intestinal mucosal IL-8 mRNA level. Moreover, the protein abundances for zonula occluden (ZO)-1 and occludin were upregulated by Trp supplementation in colonic tissues.

Conclusion: Dietary Trp supplementation altered intestinal microbial composition and diversity, improved intestinal mucosal barrier function, activated AhR signaling, and downregulated expression of inflammatory cytokines in the large intestine of weaned piglets. These results indicate a crosstalk between dietary Trp and intestine in nutrition, microbial metabolism, and mucosal immunity.

Reversal of indoleamine 2,3-dioxygenase-mediated cancer immune suppression by systemic kynurenine depletion with a therapeutic enzyme

Increased tryptophan (Trp) catabolism in the tumor microenvironment (TME) can mediate immune suppression by upregulation of interferon (IFN)-γ-inducible indoleamine 2,3-dioxygenase (IDO1) and/or ectopic expression of the predominantly liver-restricted enzyme tryptophan 2,3-dioxygenase (TDO). Whether these effects are due to Trp depletion in the TME or mediated by the accumulation of the IDO1 and/or TDO (hereafter referred to as IDO1/TDO) product kynurenine (Kyn) remains controversial. Here we show that administration of a pharmacologically optimized enzyme (PEGylated kynureninase; hereafter referred to as PEG-KYNase) that degrades Kyn into immunologically inert, nontoxic and readily cleared metabolites inhibits tumor growth. Enzyme treatment was associated with a marked increase in the tumor infiltration and proliferation of polyfunctional CD8⁺ lymphocytes. We show that PEG-KYNase administration had substantial therapeutic effects when combined with approved checkpoint inhibitors or with a cancer vaccine for the treatment of large B16-F10 melanoma, 4T1 breast carcinoma or CT26 colon carcinoma tumors. PEG-KYNase mediated prolonged depletion of Kyn in the TME and reversed the modulatory effects of IDO1/TDO upregulation in the TME.

Early Maternal Deprivation Induces Microglial Activation, Alters Glial Fibrillary Acidic Protein Immunoreactivity and Indoleamine 2,3-Dioxygenase during the Development of Offspring Rats

Maternal deprivation (MD) induces behavioral changes and impacts brain circuits that could be associated with the pathophysiology of depression. This study investigated the markers of microglia and astrocyte activation as well as indoleamine 2,3-dioxygenase (IDO) expression in developmental programming after early life MD (on postnatal days (PNDs) 20, 30, 40, and 60). On PND 60, the rats that were subjected to MD displayed depressive-like behavior. On PND 10, it was found that there was a decrease in the level of glial fibrillary acidic protein (GFAP) immunopositive cells, a decrease in the level of IDO expression, and an increase in the level of Iba-1 (microglial marker) in the hippocampus of rats that were subjected to MD. On PND 20, levels of GFAP were also found to have decreased in the hippocampus, and there was an increase in the level of Iba-1 in the hippocampus. AIF-1 (microglial marker) expression was observed in the PFC following MD. On PND 30, the levels of Iba-1 remained elevated. On PND 40, the levels of GFAP were found to have increased in the hippocampus of rats that were subjected to MD. On PND 60, the levels of GFAP and AIF-1 remained elevated following MD. These results suggest that early life stress induces negative developmental programming in rats, as demonstrated by depressive-like behavior in adult life. Moreover, MD increases microglial activation in both early and late developmental phases. The levels of GFAP and IDO decreased in the early stages but were found to be higher in later developmental periods. These findings suggest that MD could differentially affect the expression of the IDO enzyme, astrocytes, and microglial activation depending on the neurodevelopmental period. The onset of an inflammatory state from resident brain cells could be associated with the activation of the kynurenine pathway and the development of depressive behavior in adulthood.

Characterizing amino-acid biosignatures amongst individuals with schizophrenia: a case-control study

Amino acids and derivatives participate in the biosynthesis and downstream effects of numerous neurotransmitters. Variations in specific amino acids have been implicated in the pathophysiology of schizophrenia. Herein, we sought to compare levels of amino acids and derivatives between subjects with schizophrenia and healthy controls (HC). Two hundred and eight subjects with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition criteria (DSM-IV)-defined schizophrenia and 175 age- and sex-matched HC were enrolled. The levels of twenty-five amino acids and seven related derivatives were measured in plasma samples using hydrophilic interaction liquid chromatography (HILIC) liquid chromatography-tandem mass spectrometry (LC-MS). After controlling for age, sex and body mass index (BMI), four amino acids and derivatives (i.e., cysteine, GABA, glutamine and sarcosine) were observed to be higher in the schizophrenia group when compared with HC; seven amino acids and derivatives were lower in the schizophrenia group (i.e., arginine, L-ornithine, threonine, taurine, tryptophan, methylcysteine, and kynurenine). Statistically significant differences in plasma amino-acid profiles between subjects with first-episode vs. recurrent schizophrenia for aspartate and glutamine were also demonstrated using generalized linear models controlling for age, sex, and BMI. The differences in amino acids and derivatives among individuals with schizophrenia when compared to HC may represent underlying pathophysiology, including but not limited to dysfunctional proteinogenic processes, alterations in excitatory and inhibitory neurotransmission, changes in ammonia metabolism and the urea cycle. Taken together, amino-acid profiling may provide a novel stratification approach among individuals with schizophrenia.

Kynurenine pathway metabolism and the neurobiology of treatment-resistant depression: Comparison of multiple ketamine infusions and electroconvulsive therapy

Current first-line antidepressants can take weeks or months to decrease depressive symptoms. Low dose ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, shows potential for a more rapid antidepressant effect, with efficacy also evident in previously treatment-resistant populations. However, a greater understanding of the physiological mechanisms underlying such effects is required. We assessed the potential impact of ketamine infusion on neurobiological drivers of kynurenine pathway metabolism in major depression (HPA axis hyperactivity, inflammation) in patients with treatment-resistant depression compared to gender-matched healthy controls. Furthermore, we assessed these biomarkers before and after electroconvulsive therapy (ECT), which is currently the gold standard for management of treatment-resistant depression. As previously demonstrated, treatment with ketamine and ECT was associated with improved depressive symptoms in patients. At baseline, waking cortisol output was greater in the ECT cohort, kynurenine was greater in the ketamine cohort, and kynurenic acid was lower in patients compared to healthy controls, although inflammatory markers (IL-6, IL-8, IL-10 or IFN-γ) were similar in patients and controls. Furthermore, in patients who responded to ECT, the cortisol awakening response was decreased following treatment. Despite a trend towards reduced kynurenine concentrations in those who responded to ketamine, ketamine was not associated with significant alterations in any of the biomarkers assessed.

Comparative metabolomics of aging in a long-lived bat: Insights into the physiology of extreme longevity

Vespertilionid bats (Mammalia: Order Chiroptera) live 3–10 times longer than other mammals of an equivalent body size. At present, nothing is known of how bat fecal metabolic profiles shift with age in any taxa. This study established the feasibility of using a non-invasive, fecal metabolomics approach to examine age-related differences in the fecal metabolome of young and elderly adult big brown bats (Eptesicus fuscus) as an initial investigation into using metabolomics for age determination. Samples were collected from captive, known-aged big brown bats (Eptesicus fuscus) from 1 to over 14 years of age: these two ages represent age groups separated by approximately 75% of the known natural lifespan of this taxon. Results showed 41 metabolites differentiated young (n = 22) and elderly (n = 6) Eptesicus. Significant differences in metabolites between young and elderly bats were associated with tryptophan metabolism and incomplete protein digestion. Results support further exploration of the physiological mechanisms bats employ to achieve exceptional longevity.

Duodenal L cell density correlates with features of metabolic syndrome and plasma metabolites

BACKGROUND

Enteroendocrine cells are essential for the regulation of glucose metabolism, but it is unknown whether they are associated with clinical features of metabolic syndrome (MetS) and fasting plasma metabolites.

OBJECTIVE

We aimed to identify fasting plasma metabolites that associate with duodenal L cell, K cell and delta cell densities in subjects with MetS with ranging levels of insulin resistance.

RESEARCH DESIGN AND METHODS

In this cross-sectional study, we evaluated L, K and delta cell density in duodenal biopsies from treatment-naïve males with MetS using machine-learning methodology.

RESULTS

We identified specific clinical biomarkers and plasma metabolites associated with L cell and delta cell density. L cell density was associated with increased plasma metabolite levels including symmetrical dimethylarginine, 3-aminoisobutyric acid, kynurenine and glycine. In turn, these L cell-linked fasting plasma metabolites correlated with clinical features of MetS.

CONCLUSIONS

Our results indicate a link between duodenal L cells, plasma metabolites and clinical characteristics of MetS. We conclude that duodenal L cells associate with plasma metabolites that have been implicated in human glucose metabolism homeostasis. Disentangling the causal relation between L cells and these metabolites might help to improve the (small intestinal-driven) pathophysiology behind insulin resistance in human obesity.

Reassignment of the human aldehyde dehydrogenase ALDH8A1 (ALDH12) to the kynurenine pathway in tryptophan catabolism

The kynurenine pathway is the primary route for l-tryptophan degradation in mammals. Intermediates and side products of this pathway are involved in immune response and neurodegenerative diseases. This makes the study of enzymes, especially those from mammalian sources, of the kynurenine pathway worthwhile. Recent studies on a bacterial version of an enzyme of this pathway, 2-aminomuconate semialdehyde (2-AMS) dehydrogenase (AMSDH), have provided a detailed understanding of the catalytic mechanism and identified residues conserved for muconate semialdehyde recognition and activation. Findings from the bacterial enzyme have prompted the reconsideration of the function of a previously identified human aldehyde dehydrogenase, ALDH8A1 (or ALDH12), which was annotated as a retinal dehydrogenase based on its ability to preferentially oxidize 9-cis-retinal over trans-retinal. Here, we provide compelling bioinformatics and experimental evidence that human ALDH8A1 should be reassigned to the missing 2-AMS dehydrogenase of the kynurenine metabolic pathway. For the first time, the product of the semialdehyde oxidation by AMSDH is also revealed by NMR and high-resolution MS. We found that ALDH8A1 catalyzes the NAD⁺-dependent oxidation of 2-AMS with a catalytic efficiency equivalent to that of AMSDH from the bacterium Pseudomonas fluorescens Substitution of active-site residues required for substrate recognition, binding, and isomerization in the bacterial enzyme resulted in human ALDH8A1 variants with 160-fold increased K_m or no detectable activity. In conclusion, this molecular study establishes an additional enzymatic step in an important human pathway for tryptophan catabolism.

Profiling of Amino Acids and Their Derivatives Biogenic Amines Before and After Antipsychotic Treatment in First-Episode Psychosis

Schizophrenia (SCH) is a heterogeneous disorder, deriving from a potential multitude of etiopathogenetic factors. During the past few years there has been an increasing interest in the role of circulating amino acids (AAs) and biogenic amines (BAs) in the pathophysiology of SCH. In the present study, we aimed to provide an insight into the potential role of alterations in levels of AAs and BAs as well as examine their more specific metabolic shifts in relation to early stage of SCH. We measured 21 AAs and 17 BAs in serum samples of patients with first-episode psychosis (FEP) before and after 7-month antipsychotic treatment in comparison to control subjects (CSs). According to multivariate analysis, antipsychotic-naïve FEP patients had significantly higher levels of taurine and spermine, whereas values of proline (Pro), alpha-aminoadipic acid (alpha-AAA), kynurenine (Kyn), valine (Val), tyrosine (Tyr), citrulline (Citr), tryptophan (Trp), and histidine (His) were diminished compared to CSs. Increased levels of taurine and spermine, as well as reduced levels of alpha-AAA and Kyn probably reflect the compromised function of N-methyl-D-aspartate (NMDA) receptors in patients. The decreased levels of Pro (AA modulating the function of glutamate decarboxylase) likely reflect the imbalanced function of gamma-aminobutyric acid (GABA) system in the brain of FEP patients. The alterations in ratio between Tyr and phenylalanine (Phe) can be taken as a sign of compromised function of dopaminergic system. These metabolic shifts were reinstated by 7-month antipsychotic treatment. Serum metabolic profiles can be regarded as important indicators to investigate clinical course of SCH and treatment response.

Impact of a single, short morning bright light exposure on tryptophan pathways and visuo- and sensorimotor performance: a crossover study

Background

Bright light (BL) has been shown to be effective in enhancing both cognitive and physical performances. Alterations in nighttime melatonin levels have also been observed. However, evaluations of light-induced changes in the preceding biochemical processes are absent. Therefore, the impact of a single morning BL exposure on sensorimotor and visuomotor performance, as well as tryptophan (trp) and trp metabolites, was evaluated in this study.

Methods

In a crossover design, 33 healthy volunteers were randomly exposed to 30 min of < 150 lx at eye level (office light, OL) and 5000 lx at eye level (bright light, BL) of 6500 K in the morning hours. Trp, sulfatoxymelatonin (aMT6s), and kynurenine (kyn) courses over the morning hours were analyzed, and changes in sensori- and visuomotor measures were examined.

Results

Motoric performance increased in both setups, independent of light intensity. aMT6s and kyn decreased equally under both lighting conditions. Trp levels decreased from a mean (95% confidence interval) of 82.0 (77.2–86.9) to 66.5 (62.5–70.1) in the OL setup only.

Conclusion

These data suggest that BL in the morning hours has a limited effect on visuo- and sensorimotor performance. Nevertheless, trp degradation pathways in the morning show diverse courses after OL and BL exposure. This suggests that trp courses can potentially be altered by BL exposure.

Gut microbiota, metabolism and psychopathology: A critical review and novel perspectives

Psychiatric disorders are often associated with metabolic comorbidities. However, the mechanisms through which metabolic and psychiatric disorders are connected remain unclear. Pre-clinical studies in rodents indicate that the bidirectional signaling between the intestine and the brain, the so-called microbiome-gut-brain axis, plays an important role in the regulation of both metabolism and behavior. The gut microbiome produces a vast number of metabolites that may be transported into the host and play a part in homeostatic control of metabolism as well as brain function. In addition to short chain fatty acids, many of these metabolites have been identified in recent years. To what extent both microbiota and their products control human metabolism and behavior is a subject of intense investigation. In this review, we will discuss the most recent findings concerning alterations in the gut microbiota as a possible pathophysiological factor for the co-occurrence of metabolic comorbidities in psychiatric disorders.

Stepwise O-Atom Transfer in Heme-Based Tryptophan Dioxygenase: Role of Substrate Ammonium in Epoxide Ring Opening

Heme-based tryptophan dioxygenases are established immunosuppressive metalloproteins with significant biomedical interest. Here, we synthesized two mechanistic probes to specifically test if the α-amino group of the substrate directly participates in a critical step of the O atom transfer during catalysis in human tryptophan 2,3-dioxygenase (TDO). Substitution of the nitrogen atom of the substrate to a carbon (probe 1) or oxygen (probe 2) slowed the catalytic step following the first O atom transfer such that transferring the second O atom becomes less likely to occur, although the dioxygenated products were observed with both probes. A monooxygenated product was also produced from probe 2 in a significant quantity. Analysis of this new product by HPLC coupled UV-vis spectroscopy, high-resolution mass spectrometry, 1H NMR, 13C NMR, HSQC, HMBC, and infrared (IR) spectroscopies concluded that this monooxygenated product is a furoindoline compound derived from an unstable epoxyindole intermediate. These results prove that small molecules can manipulate the stepwise O atom transfer reaction of TDO and provide a showcase for a tunable mechanism by synthetic compounds. The product analysis results corroborate the presence of a substrate-based epoxyindole intermediate during catalysis and provide the first substantial experimental evidence for the involvement of the substrate α-amino group in the epoxide ring-opening step during catalysis. This combined synthetic, biochemical, and biophysical study establishes the catalytic role of the α-amino group of the substrate during the O atom transfer reactions and thus represents a substantial advance to the mechanistic comprehension of the heme-based tryptophan dioxygenases.