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

The potential for Treg-enhancing therapies in tissue, in particular skeletal muscle, regeneration

Foxp3+CD4+ regulatory T cells (Tregs) are famous for their role in maintaining immunological tolerance. With their distinct transcriptomes, growth-factor dependencies and T-cell receptor (TCR) repertoires, Tregs in nonlymphoid tissues, termed "tissue-Tregs," also perform a variety of functions to help assure tissue homeostasis. For example, they are important for tissue repair and regeneration after various types of injury, both acute and chronic. They exert this influence by controlling both the inflammatory tenor and the dynamics of the parenchymal progenitor-cell pool in injured tissues, thereby promoting efficient repair and limiting fibrosis. Thus, tissue-Tregs are seemingly attractive targets for immunotherapy in the context of tissue regeneration, offering several advantages over existing therapies. Using skeletal muscle as a model system, we discuss the existing literature on Tregs' role in tissue regeneration in acute and chronic injuries, and various approaches for their therapeutic modulation in such contexts, including exercise as a natural Treg modulator.

Physical exercise modulates the microglial complement pathway in mice to relieve cortical circuitry deficits induced by mutant human TDP-43

The aggregation of TAR DNA binding protein 43 kDa (TDP-43) is related to different neurodegenerative diseases, which leads to microglial activation and neuronal loss. The molecular mechanism driving neuronal death by reactive microglia, however, has not been completely resolved. In this study, we generated a mouse model by overexpressing mutant human TDP-43 (M337V) in the primary motor cortex, leading to prominent motor-learning deficits. In vivo 2-photon imaging shows an active approach of microglia toward parvalbumin interneurons, resulting in disrupted cortical excitatory-inhibitory balance. Proteomics studies suggest that activation of the complement pathway induces microglial activity. To develop an early interventional strategy, treadmill exercise successfully prevents the deterioration of motor dysfunction under enhanced adipocytic release of clusterin to block the complement pathway. These results demonstrate a previously unrecognized pathway by which TDP-43 induces cortical deficits and provide additional insights for the mechanistic explanation of exercise training in disease intervention.

1H NMR Metabolomics and Lipidomics To Monitor Positive Responses in Children with Autism Spectrum Disorder Following a Guided Parental Intervention: A Pilot Study

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition that is characterized by patients displaying at least two out of the classical symptoms, such as impaired social communication, impaired interactions, and restricted repetitive behavior. Early parent-mediated interventions, such as video modeling for parental training, were demonstrated to be a successful low-cost way to deliver care for children with ASD. Nuclear magnetic resonance (NMR)-based metabolomics/lipidomics has been successfully employed in several mental disorder studies. Metabolomics and lipidomics of 37 ASD patients (children, aged 3-8 years), who were divided into two groups, one control group with no parental-training intervention (N = 18) and the other in which the parents were trained by a video modeling intervention (ASD parental training, N = 19), were analyzed by proton NMR spectroscopy. Patients in the ASD parental-training group sera were seen to have increased glucose, myo-inositol, malonate, proline, phenylalanine, and gangliosides in their blood serum, while cholesterol, choline, and lipids were decreased, compared to the control group, who received no parental-training. Taken together, we demonstrated here significant changes in serum metabolites and lipids in ASD children, previously demonstrated to show clinical positive effects following a parental training intervention based on video modeling, delivered over 22 weeks. We demonstrate the value of applying metabolomics and lipidomics to identify potential biomarkers for clinical interventions follow-up in ASD.

Uncovering the specificity and predictability of tryptophan metabolism in lactic acid bacteria with genomics and metabolomics

Tryptophan is metabolized by microorganisms into various indole derivatives that have been proven to alleviate diseases and promote human health. Lactic acid bacteria (LAB) are a broad microbial concept, some of which have been developed as probiotics. However, the capacity of most LAB to metabolize tryptophan is unknown. In this study, the aim is to reveal the rule of tryptophan metabolism in LAB by multi-omics. The findings showed that LAB were rich in genes for tryptophan catabolism and that multiple genes were shared among LAB species. Although the number of their homologous sequences was different, they could still form the same metabolic enzyme system. The metabolomic analysis revealed that LAB were capable of producing a variety of metabolites. Strains belonging to the same species can produce the same metabolites and have similar yields. A few strains showed strain-specificity in the production of indole-3-lactic acid (ILA), indole-3-acetic acid, and 3-indolealdehyde (IAld). In the genotype-phenotype association analysis, the metabolites of LAB were found to be highly consistent with the outcomes of gene prediction, particularly ILA, indole-3-propionic acid, and indole-3-pyruvic acid. The overall prediction accuracy was more than 87% on average, which indicated the predictability of tryptophan metabolites of LAB. Additionally, genes influenced the concentration of metabolites. The levels of ILA and IAld were significantly correlated with the numbers of aromatic amino acid aminotransferase and amidase, respectively. The unique indolelactate dehydrogenase in Ligilactobacillus salivarius was the primary factor contributing to its large production of ILA. In summary, we demonstrated the gene distribution and production level of tryptophan metabolism in LAB and explored the correlation between genes and phenotypes. The predictability and specificity of the tryptophan metabolites in LAB were proven. These results provide a novel genomic method for the discovery of LAB with tryptophan metabolism potential and offer experimental data for probiotics that produce specific tryptophan metabolites.

Therapeutic potential of targeting kynurenine pathway in neurodegenerative diseases

Kynurenine pathway (KP), the primary pathway of L-tryptophan (Trp) metabolism in mammals, contains several neuroactive metabolites such as kynurenic acid (KA) and quinolinic acid (QA). Its imbalance involved in aging and neurodegenerative diseases (NDs) has attracted much interest in therapeutically targeting KP enzymes and KP metabolite-associated receptors, especially kynurenine monooxygenase (KMO). Currently, many agents have been discovered with significant improvement in animal models but only one aryl hydrocarbon receptor (AHR) agonist 30 (laquinimod) has entered clinical trials for treating Huntington's disease (HD). In this review, we describe neuroactive KP metabolites, discuss the dysregulation of KP in aging and NDs and summarize the development of KP regulators in preclinical and clinical studies, offering an outlook of targeting KP for NDs treatment in future.

Angiotensin-converting enzyme 2-at the heart of the COVID-19 pandemic

ACE2 is the indispensable entry receptor for SARS-CoV and SARS-CoV-2. Because of the COVID-19 pandemic, it has become one of the most therapeutically targeted human molecules in biomedicine. ACE2 serves two fundamental physiological roles: as an enzyme, it alters peptide cascade balance; as a chaperone, it controls intestinal amino acid uptake. ACE2's tissue distribution, affected by co-morbidities and sex, explains the broad tropism of coronaviruses and the clinical manifestations of SARS and COVID-19. ACE2-based therapeutics provide a universal strategy to prevent and treat SARS-CoV-2 infections, applicable to all SARS-CoV-2 variants and other emerging zoonotic coronaviruses exploiting ACE2 as their cellular receptor.

Effect of metabolism on the immune microenvironment of breast cancer

Breast cancer (BC) is a highly prevalent primary malignancy worldwide with poor prognosis. Despite the development of aggressive interventions, mortality due to BC remains high. BC cells reprogram nutrient metabolism to adapt to the energy acquisition and progression of the tumor. The metabolic changes in cancer cells are closely related to the abnormal function and effect of immune cells and immune factors, including chemokines, cytokines, and other related effector molecules in the tumor microenvironment (TME), leading to tumor immune escape, whereby the complex crosstalk between immune cells and cancer cells has been considered the key mechanism regulating cancer progression. In this review, we summarized the latest findings on metabolism-related processes in the immune microenvironment during BC progression. Our findings showing the impact of metabolism on the immune microenvironment may suggest new strategies for regulating the immune microenvironment and attenuating BC through metabolic interventions.

Potential plasma biomarker panels identification for the diagnosis of first-episode schizophrenia and monitoring antipsychotic monotherapy with the use of metabolomics analyses

Schizophrenia (SCZ) is a severe mental disorder. Using liquid chromatography mass spectrometry, we performed comprehensive metabolomics analyses of plasma samples from healthy controls (HC) and first episode SCZ patients before and after an acute period of medication. Ten lipid metabolites and 27 soluble small molecules were identified as potential biomarkers associated with the diagnosis and treatment of SCZ. These metabolites were significantly reduced in SCZ, and lipids and sulfate were significantly increased after treatment. Of the metabolites identified, four showed significant correlations with the Positive and Negative Syndrome Scale total scores. A biomarker panel composed of alpha-dimorphecolic, Phosphatidylcholine (PC) (16:0/18:1(11Z)), 1-methylnicotinamide, Phosphatidylethanolamine (PE) (20:2(11Z,14Z)/18:2(9Z,12Z)), sulfate, and L-tryptophan was selected to distinguish SCZ from HC; this provided the maximum classification performance with an AUC of 0.972. A biomarker panel including C16 sphinganine, gamma-linolenic acid, linoleic acid, PC(16:0/18:1(11Z)), PE(20:2(11Z,14Z)/18:2(9Z,12Z)), and sulfate, was selected for discrimination between SCZ before and after medication, and produced the optimal classification performance with an AUC of 0.905. Disturbances in lipid metabolism, sulfation modification, tryptophan metabolism, anti-inflammatory and antioxidant systems, and unsaturated fatty acids metabolism, were identified in SCZ. Our findings could facilitate the development of objective diagnostic or drug treatment monitoring tools for schizophrenia.

Alpha-Asarone modulates kynurenine disposal in muscle and mediates resilience to stress-induced depression via PGC-1α induction

INTRODUCTION

Kynurenine (KYN) accumulation in periphery induces brain injury, responsible for depression. α-Asarone is a simple phenylpropanoids that exerts beneficial effects on central nervous system. However, the effect of α-asarone on periphery is unexplored.

AIMS

Here, we investigated its protective role against depression from the aspect of KYN metabolism in skeletal muscle.

METHODS

The antidepressant effects of α-asarone were evaluated in chronic mild stress (CMS) and muscle-specific PGC-1α-deficient mice. The effects of KYN metabolism were determined in mice and C2C12 myoblasts.

RESULTS

α-Asarone exerted antidepressant effects in CMS and KYN-challenged mice via modulating KYN metabolism. In myoblasts, α-asarone regulated PGC-1α induction via cAMP/CREB signaling and upregulated KYN aminotransferases (KATs) to increase KYN clearance in a manner dependent on PGC-1α. KAT function is coupled with malate-aspartate shuttle (MAS), while α-asarone combated oxidative stress to protect MAS and mitochondrial integrity by raising the NAD⁺ /NADH ratio, ensuring effective KYN disposal. In support, the antidepressant effect of α-asarone was diminished by muscle-specific PGC-1α deficient mice subjected to KYN challenge.

CONCLUSION

KATs coupled with MAS to clear KYN in muscle. α-Asarone increased PGC-1α induction and promoted KYN disposal in muscle, suggesting that protection of mitochondria is a way for pharmacological intervention to depression.

HIV and comorbidities - the importance of gut inflammation and the kynurenine pathway

PURPOSE OF REVIEW

The purpose of this article is to review alterations in microbiota composition, diversity, and functional features in the context of chronic inflammation and comorbidities associated with HIV infection.

RECENT FINDINGS

The gut microbiome is an important mediator of host immunity, and disruption of gut homeostasis can contribute to both systemic inflammation and immune activation. Ageing and HIV share features of intestinal damage, microbial translocation and alterations in bacterial composition that contribute to a proinflammatory state and development of age-related comorbidities. One such inflammatory pathway reviewed is the nicotinamide adenine dinucleotide (NAD+) producing kynurenine pathway (KP). Kynurenine metabolites regulate many biological processes including host-microbiome communication, immunity and oxidative stress and the KP in turn is influenced by the microbiome environment. Age-associated decline in NAD+ is implicated as a driving factor in many age-associated diseases, including those seen in people with HIV (PWH). Recent studies have shown that KP can influence metabolic changes in PWH, including increased abdominal adiposity and cardiovascular disease. Furthermore, KP activity increases with age in the general population, but it is elevated in PWH at all ages compared to age-matched controls. Host or microbiome-mediated targeting of this pathway has merits to increase healthy longevity and has potential therapeutic applications in PWH.

SUMMARY

As a growing proportion of PWH age, many face increased risks of developing age-related comorbidities. Chronic inflammation, a pillar of geroscience, the science of ageing and of age-related disease, is influenced by the gut microbiome and its metabolites. Combined, these contribute to a systemic inflammatory signature. Advances in geroscience-based approaches and therapeutics offer a novel paradigm for addressing age-related diseases and chronic inflammation in HIV infection. Whether targeted inhibition of KP activity alleviates pathological conditions or promotes successful ageing in PWH remains to be determined.

Higher dietary intake of aromatic amino acids was associated with lower risk of cardiovascular disease mortality in adult participants in NHANES III

Little is known about the associations between dietary aromatic amino acids (AAAs) intake and mortality from all causes and cardiovascular disease (CVD). Accordingly, we evaluated these associations in the adult population of the United States using data from the Third National Health and Nutrition Examination Survey. This was a cohort study. Dietary intake of AAAs (tyrosine, phenylalanine, and tryptophan) was determined from the total nutrient intake document. We hypothesized that higher dietary AAA intake would lower all-cause and CVD mortality in adults in the United States. First, we categorized participants into quintiles based on their dietary intakes of total AAAs, tyrosine, phenylalanine, and tryptophan. Then, we established 4 Cox proportional-hazards models (models 1-4) and calculated hazard ratios and 95% confidence intervals to estimate the associations between dietary intakes of total AAAs, tyrosine, phenylalanine, and tryptophan and all-cause and CVD mortality. Mortality status was primarily obtained from files linked to the National Death Index records up to December 31, 2015. After multivariate adjustment, the hazard ratios (95% confidence intervals) of CVD mortality in the highest quintiles of dietary total AAAs, tyrosine, phenylalanine, and tryptophan intake (reference: the lowest quintiles) were 0.66 (0.52-0.84), 0.65 (0.51-0.83), 0.66 (0.52-0.85) and 0.64 (0.50-0.82), respectively. In a nationally representative cohort, higher dietary intakes of total AAA and the 3 individual AAAs were independently associated with a lower risk of CVD mortality, and these associations were stronger in non-Hispanic White people than in other people.

Recent advances on the molecular mechanisms of exercise-induced improvements of cognitive dysfunction

Physical exercise is of great significance for maintaining human health. Exercise can provide varying degrees of benefits to cognitive function at all stages of life cycle. Currently, with the aging of the world's population and increase of life expectancy, cognitive dysfunction has gradually become a disease of high incidence, which is accompanied by neurodegenerative diseases in elderly individuals. Patients often exhibit memory loss, aphasia and weakening of orientation once diagnosed, and are unable to have a normal life. Cognitive dysfunction largely affects the physical and mental health, reduces the quality of life, and causes a great economic burden to the society. At present, most of the interventions are aimed to maintain the current cognitive level and delay deterioration of cognition. In contrast, exercise as a nonpharmacological therapy has great advantages in its nontoxicity, low cost and universal application. The molecular mechanisms underlying the effect of exercise on cognition are complex, and studies have been extensively centered on neural plasticity, the direct target of exercise in the brain. In addition, mitochondrial stability and energy metabolism are essential for brain status. Meanwhile, the organ-brain axis responds to exercise and induces release of cytokines related to cognition. In this review, we summarize the latest evidence on the molecular mechanisms underlying the effects of exercise on cognition, and point out directions for future research.

The Effect of the Stress Induced by Hydrogen Peroxide and Corticosterone on Tryptophan Metabolism, Using Human Neuroblastoma Cell Line (SH-SY5Y)

L-tryptophan (L-Trp) is an important amino acid in several physiological mechanisms, being metabolized into two important pathways: the kynurenine and the serotonin (5-HT) pathways. It is important in processes such as mood and stress response, the 5-HT pathway begins with the conversion of L-Trp to 5-hydroxytryptophan (5-HTP), that is metabolized into 5-HT, converted to melatonin or to 5-hydroxyindoleacetic acid (5-HIAA). Disturbances in this pathway are reported to be connected with oxidative stress and glucocorticoid-induced stress, are important to explore. Thus, our study aimed to understand the role of hydrogen peroxide (H₂O₂) and corticosterone (CORT)-induced stress on the serotonergic pathway of L-Trp metabolism, and on SH-SY5Y cells, focusing on the study of L-Trp, 5-HTP, 5-HT, and 5-HIAA in combination with H₂O₂ or CORT. We evaluated the effect of these combinations on cellular viability, morphology, and on the extracellular levels of the metabolites. The data obtained highlighted the different ways that stress induction led to different extracellular medium concentration of the studied metabolites. These distinct chemical transformations did not lead to differences in cell morphology/viability. Additionally, serotonin may be the most sensitive metabolite to the exposure to the different stress inducers, being more promissory to study conditions associated with cellular stress.

Dietary tryptophan deficiency promotes gut RORγt+ Treg cells at the expense of Gata3+ Treg cells and alters commensal microbiota metabolism

Micronutrient deficiency is a major cause of disease throughout the world. Yet, how perturbations influence the immune-microbiome interface remains poorly understood. Here, we report that loss of dietary tryptophan (Trp) reshapes intestinal microbial communities, including the depletion of probiotic L. reuteri, drives transcriptional changes to immune response genes in the intestinal ileum, and reshapes the regulatory T cell (Treg) compartment. Dietary Trp deficiency promotes expansion of RORγt⁺ Treg cells and the loss of Gata3⁺ Tregs in a microbiota-dependent manner. In the absence of dietary Trp, provision of the AhR ligand indole-3-carbinol is sufficient to restore the Treg compartment. Together, these data show that dietary Trp deficiency perturbs the interaction between the host and its bacterial symbionts to regulate Treg homeostasis via the deprivation of bacterially derived Trp metabolites. Our findings highlight an essential role for immune-microbiome crosstalk as a key homeostatic regulator during nutrient deficiency.

Metabolic Features of Increased Gut Permeability, Inflammation, and Altered Energy Metabolism Distinguish Agricultural Workers at Risk for Mesoamerican Nephropathy

Mesoamerican nephropathy (MeN) is a form of chronic kidney disease found predominantly in young men in Mesoamerica. Strenuous agricultural labor is a consistent risk factor for MeN, but the pathophysiologic mechanism leading to disease is poorly understood. We compared the urine metabolome among men in Nicaragua engaged in sugarcane harvest and seed cutting (n = 117), a group at high risk for MeN, against three referents: Nicaraguans working less strenuous jobs at the same sugarcane plantations (n = 78); Nicaraguans performing non-agricultural work (n = 102); and agricultural workers in Spain (n = 78). Using proton nuclear magnetic resonance, we identified 136 metabolites among participants. Our non-hypothesis-based approach identified distinguishing urine metabolic features in the high-risk group, revealing increased levels of hippurate and other gut-derived metabolites and decreased metabolites related to central energy metabolism when compared to referent groups. Our complementary hypothesis-based approach, focused on nicotinamide adenine dinucleotide (NAD+) related metabolites, and revealed a higher kynurenate/tryptophan ratio in the high-risk group (p = 0.001), consistent with a heightened inflammatory state. Workers in high-risk occupations are distinguishable by urinary metabolic features that suggest increased gut permeability, inflammation, and altered energy metabolism. Further study is needed to explore the pathophysiologic implications of these findings.

Kynurenine pathway metabolites modulated the comorbidity of IBD and depressive symptoms through the immune response

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis, is defined as chronic inflammation in the gastrointestinal tract. Notably, more than 20% of people with IBD experience depressive symptoms. Understanding the immunological mechanism of chronic intestinal inflammation on cognitive behavior has become a key research focus. Previous studies have shown that a dysregulated immune response contributes to chronic inflammation and depressive symptoms. The tolerant phenotype exhibited by immune cells regulates the course of chronic inflammation in distinct ways. In addition, neuroglia, such as microglia and astrocytes specific to the brain, are also influenced by deregulated inflammation to mediate the development of depressive symptoms. The kynurenine pathway (KP), a significant tryptophan metabolic pathway, transforms tryptophan into a series of KP metabolites that modulate chronic inflammation and depressive symptoms. In particular, indoleamine 2,3-dioxygenase 1 (IDO1), a rate-limiting enzyme in the KP, is activated by chronic inflammation and leads to the production of kynurenine. In addition, disruption of the brain-gut axis induced by IBD allows kynurenine to cross the blood-brain barrier (BBB) and form a series of neuroactive kynurenine metabolites in glial cells. Among them, quinolinic acid continuously accumulates in the brain, indicating depression. Thus, KP metabolites are critical for driving the comorbidity of IBD and depressive symptoms. In this review, the pathological mechanism of KP metabolite-mediated chronic intestinal inflammation and depressive symptoms by regulating the immune response is summarized according to the latest reports.

A machine-learning algorithm integrating baseline serum proteomic signatures predicts exercise responsiveness in overweight males with prediabetes

The molecular transducers conferring the benefits of chronic exercise in diabetes prevention remain to be comprehensively investigated. Herein, serum proteomic profiling of 688 inflammatory and metabolic biomarkers in 36 medication-naive overweight and obese men with prediabetes reveals hundreds of exercise-responsive proteins modulated by 12-week high-intensity interval exercise training, including regulators of metabolism, cardiovascular system, inflammation, and apoptosis. Strong associations are found between proteins involved in gastro-intestinal mucosal immunity and metabolic outcomes. Exercise-induced changes in trefoil factor 2 (TFF2) are associated with changes in insulin resistance and fasting insulin, whereas baseline levels of the pancreatic secretory granule membrane major glycoprotein GP2 are related to changes in fasting glucose and glucose tolerance. A hybrid set of 23 proteins including TFF2 are differentially altered in exercise responders and non-responders. Furthermore, a machine-learning algorithm integrating baseline proteomic signatures accurately predicts individualized metabolic responsiveness to exercise training.

The "Superoncogene" Myc at the Crossroad between Metabolism and Gene Expression in Glioblastoma Multiforme

The concept of the Myc (c-myc, n-myc, l-myc) oncogene as a canonical, DNA-bound transcription factor has consistently changed over the past few years. Indeed, Myc controls gene expression programs at multiple levels: directly binding chromatin and recruiting transcriptional coregulators; modulating the activity of RNA polymerases (RNAPs); and drawing chromatin topology. Therefore, it is evident that Myc deregulation in cancer is a dramatic event. Glioblastoma multiforme (GBM) is the most lethal, still incurable, brain cancer in adults, and it is characterized in most cases by Myc deregulation. Metabolic rewiring typically occurs in cancer cells, and GBM undergoes profound metabolic changes to supply increased energy demand. In nontransformed cells, Myc tightly controls metabolic pathways to maintain cellular homeostasis. Consistently, in Myc-overexpressing cancer cells, including GBM cells, these highly controlled metabolic routes are affected by enhanced Myc activity and show substantial alterations. On the other hand, deregulated cancer metabolism impacts Myc expression and function, placing Myc at the intersection between metabolic pathway activation and gene expression. In this review paper, we summarize the available information on GBM metabolism with a specific focus on the control of the Myc oncogene that, in turn, rules the activation of metabolic signals, ensuring GBM growth.

A Vegetarian Diet Significantly Changes Plasma Kynurenine Concentrations

Tryptophan is an essential amino acid and a precursor of a number of physiologically important metabolites, including serotonin, melatonin, tryptamine, and kynurenines. We assessed tryptophan, kynurenines, and vitamin B2 and B6, as well as biomarkers of liver function and inflammation, in a group of 158 female omnivores and vegetarians aged 18-40 years. The majority of women were omnivores, and 22% were vegetarians. Vegetarians had 25% lower serum ALT, significantly higher pyridoxal concentrations, and significantly lower plasma concentrations of most kynurenines, varying from 8% lower concentrations of median plasma kynurenine to 42% lower concentrations of plasma xanthurenic acid, compared to omnivores. No significant differences were observed in vitamin B2 status or in inflammation markers, C-reactive protein and neopterin between the groups. Vegetarians had lower levels of several plasma kynurenines compared to omnivores. The reason for this is unknown; however, lower ALT concentrations, suggesting a better liver status, and a more favourable vitamin B6 status might be contributing factors.

The prevalence and the effect of interferon -γ in the comorbidity of rheumatoid arthritis and depression

BACKGROUND

Depression is the most common comorbidities associated with rheumatoid arthritis (RA). We aimed to explore the mechanism of association between RA and depression.

METHODS

120 subjects were enrolled and depression was diagnosed and assessed using DSM-5 and 24-item version of Hamilton Depression Scale. Pain intensity and joint function in patients with RA were assessed using the visual analog scale (VAS) and health assessment questionnaire (HAQ). Serum levels of interferon-gamma (IFN-γ), indoleamine 2,3-dioxygenase (IDO), kynurenine (KYN), tryptophan (TRP), and quinolinic acid (QUIN)were detected. In animal experiments, K/BxN mice with RA-like phenotype was used and depressive behavior was observed. The protein expression level of N-methyl -D- aspartate receptor 2B (NR2B) in the hippocampus was detected.

RESULTS

In this study, 36.67 % of patients with RA also had depression. The working status, month family income, tender joint count, the VAS and HAQ score were the main factors influencing the depression in RA patients. HAQ score was found to be an independent risk factor for depression in RA. Serum IDO, IFN-γ, KYN were increased and TRP contents were decreased in RA group. K/BxN mice with RA-like phenotype showed depressive behavior. However, injection of IFN-γ neutralizing antibody could inhibit kynurenine pathway and reverse the depressive behavior in mice. The levels of QUIN in the neurotoxic metabolic pathway were increased and N-methyl -D- aspartate receptors (NMDAR) were activated, which may be the mechanism behind the onset of depression.

CONCLUSIONS

From clinical and preclinical aspects, the occurrence of depression in RA was explored and the related mechanism was revealed.

UPLC-Q-Exactive-based rats serum metabolomics for characterization of traditional Chinese medicine Natures and Flavors

ETHNOPHARMACOLOGY RELEVANT: "Four Natures and five "Flavors" comes from the high generalization of medicine pharmacological rules from clinical practice by ancients. "Flavor" and "Natures"are both descriptions of the effect properties of traditional Chinese medicine. At present, researchers have realized that the "Flavors" (Pungent, Sour, Sweet, Bitter and Salty) are related to the different pharmacological effects of treatment. The "Natures" (Warm, Hot, Cold and Cool) are closely related to energy and substance metabolism and contribute to the effect of the "Flavors". Since "Four Natures and five Flavors" are the rules derived from clinical practice, how to describe and characterize "Natures" and "Flavors" scientifically is still a problem that needs to be solved.

AIM OF THE STUDY

the aim is to objectively further understand the scientific connotations of properties ("Flavors"and "Natures") from the perspective of metabolomics and characterize them by metabolites.

MATERIALS AND METHOD

"Pungent-Neutral", "Sweet-Neutral and "Bitter-Neutral" TCMs were selected to characterize the "Flavors" (Pungent, Sweet and Bitter). "Pungent-Warm" and "Bitter-Cold" were selected to characterize the "Natures" (Warm and Cold). The rat serum metabolomics was performed on UHPLC-Q-Exactive. Metabolites were identified through the metabolites databases and related literature.

RESULTS

The "Flavors" and "Natures" metabolites were identified, respectively, including four "Pungent", four "Sweet" and thirteen "Bitter" characterized metabolites and thirteen "Cold" and sixteen "Warm"related metabolites.

CONCLUSIONS

The "Natures" characterized metabolites show the "Natures" are closely related to lipid and energy metabolism. The "Warm" may promote lipid metabolism to produce ATP to generate energy through bile acid metabolism and purine metabolism. The "Cold" may inhibit lipid metabolism to generate ATP to decrease energy through the way of tryptophan metabolism and purine metabolism. The "Flavors" characteristic metabolites can provide a theoretical basis for the rules of the "Flavors". These metabolites can also be used to characterize TCM's "Natures" and "Flavors" in the development of traditional Chinese medicine resources and quality control.

A Systematic Role of Metabolomics, Metabolic Pathways, and Chemical Metabolism in Lung Cancer

Lung cancer (LC) is considered as one of the leading causes of cancer-associated mortalities. Cancer cells' reprogrammed metabolism results in changes in metabolite concentrations, which can be utilized to identify a distinct metabolic pattern or fingerprint for cancer detection or diagnosis. By detecting different metabolic variations in the expression levels of LC patients, this will help and enhance early diagnosis methods as well as new treatment strategies. The majority of patients are identified at advanced stages after undergoing a number of surgical procedures or diagnostic testing, including the invasive procedures. This could be overcome by understanding the mechanism and function of differently regulated metabolites. Significant variations in the metabolites present in the different samples can be analyzed and used as early biomarkers. They could also be used to analyze the specific progression and type as well as stages of cancer type making it easier for the treatment process. The main aim of this review article is to focus on rewired metabolic pathways and the associated metabolite alterations that can be used as diagnostic and therapeutic targets in lung cancer diagnosis as well as treatment strategies.

Dysregulation of tryptophan metabolism and distortion of cell signaling after oral exposure to ethanol and Kynurenic acid

Kynurenic acid (KYNA), an unavoidable tryptophan metabolite during fermentation is naturally blended with alcohol in all alcoholic beverages. Thus, alcohol drinking inevitably results in co-intake of KYNA. Effects of alcohol or KYNA on human health have been widely studied. However, the combined effects of both remain unknown. Here we report that alcohol and KYNA have a synergistic impact of on global gene expression, especially the gene sets related to tryptophan metabolism and cell signaling. Adult mice were exposed to alcohol (ethanol) and/or KYNA daily for a week. Transcriptomes of the brain, kidney and liver were profiled via bulk RNA sequencing. Results indicate that while KYNA alone largely promotes, and alcohol alone mostly inhibits gene expression, alcohol and KYNA co-administration has a stronger inhibition of global gene expression. Tryptophan metabolism is severely skewed towards kynurenine pathway by decreasing tryptophan hydroxylase 2 and increasing tryptophan dioxygenase. Quantification of tryptophan metabolic enzymes corroborates the transcriptional changes of these enzymes. Furthermore, the co-administration greatly enhances the GnRH signaling pathway. This research provides critical data to better understand the effects of alcohol and KYNA in mix on human health.

Human Chorionic Gonadotropin-Stimulated Interleukin-4-Induced-1 (IL4I1) Promotes Human Decidualization via Aryl Hydrocarbon Receptor

Decidualization is necessary for the successful establishment of early pregnancy in rodents and humans. Disturbed decidualization results in recurrent implantation failure, recurrent spontaneous abortion, and preeclampsia. Tryptophan (Trp), one of the essential amino acids in humans, has a positive effect on mammalian pregnancy. Interleukin 4-induced gene 1 (IL4I1) is a recently identified enzyme that can metabolize L-Trp to activate aryl hydrocarbon receptor (AHR). Although IDO1-catalyzed kynurenine (Kyn) from Trp has been shown to enhance human in vitro decidualization via activating AHR, whether IL4I1-catalyzed metabolites of Trp are involved in human decidualization is still unknown. In our study, human chorionic gonadotropin stimulates IL4I1 expression and secretion from human endometrial epithelial cells through ornithine decarboxylase-induced putrescine production. Either IL4I1-catalyzed indole-3-pyruvic acid (I3P) or its metabolite indole-3-aldehyde (I3A) from Trp is able to induce human in vitro decidualization by activating AHR. As a target gene of AHR, Epiregulin induced by I3P and I3A promotes human in vitro decidualization. Our study indicates that IL4I1-catalyzed metabolites from Trp can enhance human in vitro decidualization through AHR-Epiregulin pathway.

Targeting immune-onco-metabolism for precision cancer therapy

Immune cells play a key role in host defence against infection and cancer. Unlike infection, cancer is a multidimensional disease where cancer cells require continuous activation of certain pathways to sustain their growth and survival. The tumour milieu plays an important role in defining the metabolic reprogramming to support this growth and evasion from the immune system. Cancer and stromal cells modulate each other's metabolism during cancer progression or regression. The mechanism related to change in the metabolism and its role in the crosstalk between tumour and immune cells is still an area of immense importance. Current treatment modalities can be immensely complemented and benefited by targeting the immuno-oncology metabolism, that can improve patient prognosis. This emerging aspect of immune-oncology metabolism is reviewed here, discussing therapeutic possibilities within various metabolic pathways and their effect on immune and cancer cell metabolism.

Linking nervous and immune systems in psychiatric illness: A meta-analysis of the kynurenine pathway

Tryptophan is an essential amino acid absorbed by the gut depending on a homoeostatic microbiome. Up to 95% of unbound tryptophan is converted into tryptophan catabolites (TRYCATs) through the kynurenine system. Recent studies identified conflicting associations between altered levels of TRYCATs and genetic polymorphisms in major depressive disorder (MDD), schizophrenia (SCZ), and bipolar disorder (BD). This meta-analysis aimed to understand how tryptophan catabolic pathways are altered in MDD, SCZ, and BD. When compared to healthy controls, participants with MDD had moderately lower levels of tryptophan associated with a moderate increase of kynurenine/tryptophan ratios and no differences in kynurenine. While significant differences were found in SCZ for any of the TRYCATs, studies on kynurenic acid found opposing directions of effect sizes depending on the sample source. Unique changes in levels of TRYCATs were also observed in BD. Dynamic changes in levels of cytokines and other immune/inflammatory elements modulate the transcription and activity of kynurenine system enzymes, which lastly seems to be impacting glutamatergic neurotransmission via N-methyl-D-aspartate and α-7 nicotine receptors.

Gut microbiota-derived metabolites and their importance in neurological disorders

Microbial-derived metabolites are the intermediate or end products of bacterial digestion. They are one of the most important molecules for the gut to connect with the brain. Depending on the levels of specific metabolites produced in the host, it can exert beneficial or detrimental effects on the brain and have been linked to several neurodegenerative and neuropsychiatric disorders. However, the underlying mechanisms remain largely unexplored. Insight into these mechanisms could reveal new pathways or targets, resulting in novel treatment approaches targeting neurodegenerative diseases. We have reviewed selected metabolites, including short-chain fatty acids, aromatic amino acids, trimethylamine-N-oxide,  urolithin A, anthocyanins, equols, imidazole, and propionate to highlight their mechanism of action, underlying role in maintaining intestinal homeostasis and regulating neuro-immunoendocrine function. Further discussed on  how altered metabolite levels can influence the gut-brain axis could lead to new prevention strategies or novel treatment approaches to neural disorders.

Indoleamine 2,3 dioxygenase 1 immobilization on magnetic nanoparticles for screening inhibitors from coffee

In this study, a ligand fishing method was developed to screen potential indoleamine 2,3-dioxygenase 1 (IDO1) inhibitors from coffee extracts by immobilization of IDO1 enzyme on amino-modified magnetic nanoparticles combined with UHPLC-Q-TOF-MS/MS analysis. Parameters including enzyme concentration, immobilization time, the pH of glutaraldehyde and the amount of magnetic nanoparticles were optimized. The results indicated that immobilized IDO1 could be reused 5 times and was stable during storage for 7 days. Several IDO1 ligands were captured by incubating immobilized IDO1 with coffee extract, of which 10 showed an obvious difference comparing to non-conjugated bare nanoparticles. In vitro inhibitory activity was further performed by CE analysis, in which ferulic acid and chlorogenic acid had better IDO1 inhibitory activity, with IC₅₀ value of 113.7 μM and 307.5 μM. These results demonstrate that this method provides an effective platform for identifying and screening IDO1 inhibitors from natural products.

Citrulline and kynurenine to tryptophan ratio: potential EED (environmental enteric dysfunction) biomarkers in acute watery diarrhea among children in Bangladesh

Two emerging biomarkers of environmental enteric dysfunction (EED) include plasma citrulline (CIT), and the kynurenine (KYN): tryptophan (TRP)/ (KT) ratio. We sought to investigate the plasma concentration of CIT and KT ratio among the children having dehydrating diarrhea and examine associations between concentrations of CIT and KT ratio with concurrent factors. For this analysis, we used cross-sectional data from a total of 102, 6-36 months old male children who suffered from non-cholera acute watery diarrhea and had some dehydration admitted to an urban diarrheal hospital, in Bangladesh. CIT, TRP, and KYN concentrations were determined at enrollment from plasma samples using ELIZA. At enrollment, the mean plasma CIT concentration was 864.48 ± 388.55 µmol/L. The mean plasma kynurenine, tryptophan concentrations, and the KT ratio (× 1000) were 6.93 ± 3.08 µmol/L, 33.44 ± 16.39 µmol/L, and 12.12 ± 18.10, respectively. With increasing child age, KYN concentration decreased (coefficient: - 0.26; 95%CI: - 0.49, - 0.04; p = 0.021); with increasing lymphocyte count, CIT concentration decreased (coef.: - 0.01; 95% CI: - 0.02,0.001, p = 0.004); the wasted child had decreased KT ratio (coef.: - 0.6; 95% CI: - 1.18, - 0.02; p = 0.042) after adjusting for potential covariates. The CIT concentration was associated with blood neutrophils (coef.: 0.02; 95% CI: 0.01, 0.03; p < 0.001), lymphocytes (coef.: - 0.02; 95% CI: - 0.03, - 0.02; p < 0.001) and monocyte (coef.: 0.06; 95% CI: 0.01, 0.11; p = 0.021); KYN concentration was negatively associated with basophil (coef.: - 0.62; 95% CI: - 1.23, - 0.01; p = 0.048) after adjusting for age. In addition, total stool output (gm) increased (coef.: 793.84; 95% CI: 187.16, 1400.52; p = 0.011) and also increased duration of hospital stay (hour) (coef.: 22.89; 95% CI: 10.24, 35.54; p = 0.001) with increasing CIT concentration. The morphological changes associated with EED may increase the risk of enteric infection and diarrheal disease among children. Further research is critically needed to better understand the complex mechanisms by which EED biomarkers may impact susceptibility to dehydrating diarrhea in children.

Temperature-dependent metabolite orchestration to acute submaximal exercise indicates cardiorespiratory fitness in humans

AIMS

Cardiorespiratory fitness (CRF), an important biomarker of human health, is impaired in cold environment compared to thermoneutral condition. The study aimed to investigate the role of metabolome response to acute exercise in regulation of CRF at different ambient temperatures.

MAIN METHODS

A total of 27 young adults were recruited, and each subject underwent a cardiopulmonary exercise test (CPET) and a constant load submaximal exercise at both room temperature (25 °C) and cold temperature (0 °C). The serum samples were collected before and immediately after constant load exercise.

KEY FINDINGS

Acute cold exposure decreased CRF by 41 %, accompanied by a metabolic shift to anaerobic respiration. It also decreased VO₂ and increased respiratory quotient during constant load exercise. Metabolome profiling revealed that acute exercise reprogrammed serum metabolome in an ambient temperature-dependent manner. Specifically, exercise increased a cluster of fatty acids during cold exposure, possibly due to impaired fatty acid oxidation. The correlations between metabolite responses to acute exercise and exercise parameters were analyzed using partial least squares regression and machine learning, revealing that metabolite responses to acute exercise were highly correlated with exercise parameters and predictive of CRF. Among the contributors, tryptophan and its metabolites stood out as important ones.

SIGNIFICANCE

These results suggested that the metabolite responses to acute submaximal exercise unmasks the exercise performance at different ambient temperatures, highlighting the role of metabolite orchestration in the physiological regulation of CRF.

Psychiatric disorders, personality and neuropsychological alterations in Erdheim-Chester disease

Although neurological manifestations and changes in brain volumes have been described in Erdheim-Chester disease (ECD), it remains unknown whether ECD may be associated with psychiatric symptoms and cognitive dysfunctions. We assessed the presence of psychiatric disorders, changes in temperaments and characters, and neuropsychological performances in 32 ECD patients (mean age = 59) younger than 70, not treated with interferon alpha during the last 6 months, and without other serious illnesses. ECD patients exhibited high level of past depressive disorder (80%) and anxiety disorder, especially agoraphobia (29%). They revealed personality changes, especially with high agreeableness (t = 3.18, p < 0.005) and high conscientiousness (t = 3.81, p < 0.001). Neuropsychological assessments showed impairments in attention (GZ: t = 16.12, p < 0.0001, KL: t = 37.01, p < 0.0001) and episodic memory performances (STIR: t = - 3.01, p = 0.006, LTFR: t = - 2.87, p = 0.008, LTIR: t = - 3.63, p = 0.001). Executive functions, such as flexibility, inhibitory control, were unimpaired. Although it remains to be clarified whether these psychiatric symptoms and cognitive impairments may impact the daily functioning and the quality of life, the present study highlights the need to consider cognitive and emotional states in ECD management.

Microbiota of the gastrointestinal tract: Friend or foe?

The gut microbiota is currently considered an external organ of the human body that provides important mechanisms of metabolic regulation and protection. The gut microbiota encodes over 3 million genes, which is approximately 150 times more than the total number of genes present in the human genome. Changes in the qualitative and quantitative composition of the microbiome lead to disruption in the synthesis of key bacterial metabolites, changes in intestinal barrier function, and inflammation and can cause the development of a wide variety of diseases, such as diabetes, obesity, gastrointestinal disorders, cardiovascular issues, neurological disorders and oncological concerns. In this review, I consider issues related to the role of the microbiome in the regulation of intestinal barrier function, its influence on physiological and pathological processes occurring in the body, and potential new therapeutic strategies aimed at restoring the gut microbiome. Herewith, it is important to understand that the gut microbiota and human body should be considered as a single biological system, where change of one element will inevitably affect its other components. Thus, the study of the impact of the intestinal microbiota on health should be considered only taking into account numerous factors, the role of which has not yet been fully elucidated.

Molecular pathways of major depressive disorder converge on the synapse

Major depressive disorder (MDD) is a psychiatric disease of still poorly understood molecular etiology. Extensive studies at different molecular levels point to a high complexity of numerous interrelated pathways as the underpinnings of depression. Major systems under consideration include monoamines, stress, neurotrophins and neurogenesis, excitatory and inhibitory neurotransmission, mitochondrial dysfunction, (epi)genetics, inflammation, the opioid system, myelination, and the gut-brain axis, among others. This review aims at illustrating how these multiple signaling pathways and systems may interact to provide a more comprehensive view of MDD's neurobiology. In particular, considering the pattern of synaptic activity as the closest physical representation of mood, emotion, and conscience we can conceptualize, each pathway or molecular system will be scrutinized for links to synaptic neurotransmission. Models of the neurobiology of MDD will be discussed as well as future actions to improve the understanding of the disease and treatment options.

Untargeted metabolomic profiling of sepsis-induced cardiac dysfunction

OBJECTIVE

Sepsis is a life-threatening condition secondary to infection that evolves into a dysregulated host response and is associated with acute organ dysfunction. Sepsis-induced cardiac dysfunction is one of the most complex organ failures to characterize. This study performed comprehensive metabolomic profiling that distinguished between septic patients with and without cardiac dysfunction.

METHOD

Plasma samples collected from 80 septic patients were analysed by untargeted liquid chromatography-mass spectrometry (LC-MS) metabolomics. Principal component analysis (PCA), partial least squares discrimination analysis (PLS-DA), and orthogonal partial least square discriminant analysis (OPLS-DA) were applied to analyse the metabolic model between septic patients with and without cardiac dysfunction. The screening criteria for potential candidate metabolites were as follows: variable importance in the projection (VIP) >1, P < 0.05, and fold change (FC) > 1.5 or < 0.7. Pathway enrichment analysis further revealed associated metabolic pathways. In addition, we constructed a subgroup metabolic analysis between the survivors and non-survivors according to 28-day mortality in the cardiac dysfunction group.

RESULTS

Two metabolite markers, kynurenic acid and gluconolactone, could distinguish the cardiac dysfunction group from the normal cardiac function group. Two metabolites, kynurenic acid and galactitol, could distinguish survivors and non-survivors in the subgroup analysis. Kynurenic acid is a common differential metabolite that could be used as a candidate for both diagnosis and prognosis for septic patients with cardiac dysfunction. The main associated pathways were amino acid metabolism, glucose metabolism and bile acid metabolism.

CONCLUSION

Metabolomic technology could be a promising approach for identifying diagnostic and prognostic biomarkers of sepsis-induced cardiac dysfunction.

Research progress on short-term prognosis of acute-on-chronic liver failure

INTRODUCTION

Acute-on-chronic liver failure (ACLF) is a clinical syndrome characterized as a severe condition with rapid progression, poor therapeutic response and poor prognosis. Early and timely evaluation of the prognosis is helpful for providing appropriate clinical intervention and prolonging patient survival.

AREAS COVERED

Currently, there are no specific dynamic and comprehensive approaches to assess the prognosis of patients with ACLF. This article reviews the progress in evaluating the short-term prognosis of ACLF to provide future directions for more dynamic prospective large-scale multicenter studies and a basis for individualized and precise treatment for ACLF patients. We searched PubMed and Web of Science with the term 'acute on chronic liver failure' and 'prognosis.' There was no date or language restriction, and our final search was on 26 October 2022.

EXPERT OPINION

ACLF is a dynamic process, and the best prognostic marker is the clinical evolution of organ failure over time. New prognostic markers are developing not only in the fields of genetics and histology but also toward diversification combined with imaging. Determining which patients will benefit from continued advanced life support is a formidable challenge, and accurate short-term prognostic assessments of ACLF are a good approach to addressing this issue.

Simultaneous determination of serum tryptophan metabolites in an older Chinese population

Tryptophan (TRP) and its metabolites exhibit significant biological effects and are strongly associated with age-related disease and mortality. However, reports on quantitatively analyzing these metabolites in older individuals are not available. We used ultra-high-performance liquid chromatography-tandem mass spectrometry to optimize and validate a method for isotope dilution analysis of TRP metabolites in older individuals. The targeted analytes are TRP, serotonin or 5-hydroxytryptamine, kynurenine, kynurenic acid, xanthurenic acid, indole-3-acetic acid, indole-3-propionic acid, and tryptamine. The serum sample was purified using solid-phase extraction and was separated on a Waters HSS T3 column (100 mm × 2.1 mm, 1.8 μm). The analytes were detected in the multiple reaction monitoring mode under positive ionization. TRP was confirmed and measured after being diluted 100 times. This method exhibited satisfactory linearity (r > 0.99). The intrabatch and interbatch accuracies (85.7-114%) and precisions (<15%) were acceptable. The standard-normalized matrix effects ranged from 51.6 to 145%. This method was successfully applied to a cohort of 1021 older Chinese individuals, and this study may enable further understanding of the metabolic phenotypes associated with TRP in other populations.

Akkermansia muciniphila inhibits nonalcoholic steatohepatitis by orchestrating TLR2-activated γδT17 cell and macrophage polarization

Current evidence indicates that the next-generation probiotic Akkermansia muciniphila (A. muciniphila) has therapeutic potential for nonalcoholic fatty liver disease (NAFLD), especially its inflammatory stage known as nonalcoholic steatohepatitis (NASH). However, the mechanisms of A. muciniphila in NASH prevention remain unknown. Here, A. muciniphila supplementation prevented hepatic inflammation in high-fat diet-induced NASH mice, characterized by reduced hepatic proinflammatory macrophages (M1) and γδT and γδT17 cells. Consistently, hepatic M1 and γδT cells were enriched in biopsy-proven NASH patients and high-fat/high-carbohydrate diet-induced NASH mice. Antibiotics reduced hepatic M1, γδT and γδT17 cells in NASH mice. Furthermore, A. muciniphila inhibited intestinal barrier disruption and accordingly downregulated hepatic Toll-like receptor 2 (TLR2) expression in NASH mice. The activation of TLR2 by lipoteichoic acid enriched hepatic γδT17 cells (not M1) in normal diet-fed mice and neutralized the γδT cell-lowering and liver inflammation-protecting effects of A. muciniphila in NASH mice. Additionally, activated γδT cells could promote macrophage polarization via IL-17. Our study first supported that A. muciniphila prevented NASH by modulating TLR2-activated γδT17 cells and further macrophage polarization, facilitating clinical therapeutic applications.

Tryptophan intake, not always the more the better

Objectives

To investigate the effects of excessive tryptophan intake on the body and the effects of tryptophan metabolism-related aryl hydrocarbon receptor (AhR) pathway in healthy rats and chronic kidney disease rats, to study the adverse effects of excess tryptophan.

Design

In Part I Experiment, the healthy rats were fed with diet containing 0.6, 1.2 and 1.8% tryptophan for 12 weeks. After the intervention, the blood and kidney tissues were collected. Serum creatinine and blood urea nitrogen were detected. Hematoxylin-eosin (H&E) staining was used to observe renal pathological changes. Enzyme-linked immunosorbent assay was used to detect serum kynurenic acid and AhR levels. The kidney levels of AhR, CyP1A1 and CyP1B1 were detected by western-blot. In Part II Experiment, the chronic kidney disease (CKD) model was induced by intra-gastric gavage with adenine for 4 weeks. Then the CKD rats were given tryptophan at a dose of 100 mg/kg or 500 mg/kg for eight weeks. Rat survival curve, renal function, renal tissue pathology and serum AhR were detected. Tryptophan-targeted ultra-high-performance liquid chromatography coupled with multiple reaction monitoring mass spectrometry (UHPLC-MRM-MS) was employed to quantitatively access the tryptophan-targeted metabolites in two parts experiments.

Results

In part I experiment, high tryptophan diet can increase the level of blood urea nitrogen (BUN) in healthy rats and induce focal renal tubulointerstitial injury. Tryptophan-targeted analyzes showed that high tryptophan diet feeding can significantly increase the concentration of kynurenine and indole metabolites. The serum AhR level and kidney AhR, CyP1A1 and CyP1B1 were also significantly increased in high tryptophan diet rats. In part II experiment, high tryptophan intervention induced a significant increase in mortality, serum creatinine, urea nitrogen levels, and renal pathological damage in CKD rats. The levels of tryptophan-targeted metabolites, kynurenine, xanthurenate, picolinic acid, 5-hydroxyindole-3-acetic acid, indole-3-lactic acid, indoleacetate and indoxyl sulfate, showed an upward trend in the high-dose tryptophan group (Ade + Trp-H) compared with the adenine group. The serum AhR of Ade + Trp-H rats was significantly higher than those of adenine rats.

Conclusion

Moderate tryptophan intake may be beneficial, but excessive tryptophan can lead to accumulation of kynurenine and indole metabolites, activate AhR pathway and induce kidney injury.

PTSD, Immune System, and Inflammation

Posttraumatic stress disorder (PTSD) is a severe trauma and stress-related disorder associated with different somatic comorbidities, especially cardiovascular and metabolic disorders, and with chronic low-grade inflammation. Altered balance of the hypothalamic-pituitary-adrenal (HPA) axis, cytokines and chemokines, C-reactive protein, oxidative stress markers, kynurenine pathways, and gut microbiota might be involved in the alterations of certain brain regions regulating fear conditioning and memory processes, that are all altered in PTSD. In addition to the HPA axis, the gut microbiota maintains the balance and interaction of the immune, CNS, and endocrine pathways forming the gut-brain axis. Disbalance in the HPA axis, gut-brain axis, oxidative stress pathways and kynurenine pathways, altered immune signaling and disrupted homeostasis, as well as the association of the PTSD with the inflammation and disrupted cognition support the search for novel strategies for treatment of PTSD. Besides potential anti-inflammatory treatment, dietary interventions or the use of beneficial bacteria, such as probiotics, can potentially improve the composition and the function of the bacterial community in the gut. Therefore, bacterial supplements and controlled dietary changes, with exercise, might have beneficial effects on the psychological and cognitive functions in patients with PTSD. These new treatments should be aimed to attenuate inflammatory processes and consequently to reduce PTSD symptoms but also to improve cognition and reduce cardio-metabolic disorders associated so frequently with PTSD.

Serum metabolomics using ultra-high performance liquid chromatography-Q-Exactive tandem mass spectrometry reveals the mechanism of action of exercise training on chronic obstructive pulmonary disease rats

Exercise training is the cornerstone component of pulmonary rehabilitation, which results in symptom-reducing, psychosocial, and health economic benefits for chronic obstructive pulmonary disease (COPD) patients. However, the potential mechanisms of its action are poorly understood. This study conducted serum metabolomics using ultra-high performance liquid chromatography-Q-Exactive tandem mass spectrometry to determine the metabolic changes in COPD rats, and the effects of exercise training on improvement in COPD were further investigated. Twelve differential metabolites-which are primarily related to tryptophan metabolism, sphingolipid metabolism, glycerophospholipid metabolism, riboflavin metabolism, pantothenate and CoA biosynthesis, and lysine degradation-were identified in relation to COPD. After the intervention of exercise training, the levels of most metabolites were restored, and the changes in five metabolites were statistically significant, which suggested that exercise training provided effective protection against COPD and might play its role by rebalancing disordered metabolism pathways. This work enhanced our comprehension of the protective mechanism of exercise training on COPD.

Inflammation and Epigenetic Aging Are Largely Independent Markers of Biological Aging and Mortality

Limited evidence exists on the link between inflammation and epigenetic aging. We aimed to (a) assess the cross-sectional and prospective associations of 22 inflammation-related plasma markers and a signature of inflammaging with epigenetic aging and (b) determine whether epigenetic aging and inflammaging are independently associated with mortality. Blood samples from 940 participants in the Melbourne Collaborative Cohort Study collected at baseline (1990-1994) and follow-up (2003-2007) were assayed for DNA methylation and 22 inflammation-related markers, including well-established markers (eg, interleukins and C-reactive protein) and metabolites of the tryptophan-kynurenine pathway. Four measures of epigenetic aging (PhenoAge, GrimAge, DunedinPoAm, and Zhang) and a signature of inflammaging were considered, adjusted for age, and transformed to Z scores. Associations were assessed using linear regression, and mortality hazard ratios (HR) and 95% confidence intervals (95% CI) were estimated using Cox regression. Cross-sectionally, most inflammation-related markers were associated with epigenetic aging measures, although with generally modest effect sizes (regression coefficients per SD ≤ 0.26) and explaining altogether between 1% and 11% of their variation. Prospectively, baseline inflammation-related markers were not, or only weakly, associated with epigenetic aging after 11 years of follow-up. Epigenetic aging and inflammaging were strongly and independently associated with mortality, for example, inflammaging: HR = 1.41, 95% CI = 1.27-1.56, p = 2 × 10-10, which was only slightly attenuated after adjustment for 4 epigenetic aging measures: HR = 1.35, 95% CI = 1.22-1.51, p = 7 × 10-9). Although cross-sectionally associated with epigenetic aging, inflammation-related markers accounted for a modest proportion of its variation. Inflammaging and epigenetic aging are essentially nonoverlapping markers of biological aging and may be used jointly to predict mortality.

Toward Elucidating the Human Gut Microbiota-Brain Axis: Molecules, Biochemistry, and Implications for Health and Diseases

In recent years, a substantial amount of data have supported an active role of gut microbiota in mediating mammalian brain function and health. Mining gut microbiota and their metabolites for neuroprotection is enticing but requires that the fundamental biochemical details underlying such microbiota-brain crosstalk be deciphered. While a neuronal gut-brain axis (through the vagus nerve) is not disputable, accumulating studies also point to a humoral route (via blood/lymphatic circulation) by which innumerable microbial molecular cues translocate from local gut epithelia to circulation with potentials to further cross the blood-brain barrier and reach the brain. In this Perspective, we review a realm of gut microbial molecules to evaluate their fate, function, and neuroactivities in vivo as mediated by microbiota. We turn to seminal studies of neurophysiology and neurologic disease models for the elucidation of biochemical pathways that link microbiota to gut-brain signaling. In addition, we discuss opportunities and challenges for advancing the microbiota-brain axis field while calling for high-throughput discovery of microbial molecules and studies for resolving the interspecies, interorgan, and interclass interaction among these neuroactive microbial molecules.

Modulation of adipose tissue metabolism by microbial-derived metabolites

Obesity and its complications, including type 2 diabetes, cardiovascular disease, and certain cancers, have posed a significant burden on health and healthcare systems over the years due to their high prevalence and incidence. Gut microbial derivatives are necessary for the regulation of energy metabolism and host immunity, as well as for maintaining homeostasis of the intestinal environment. Gut flora metabolites may be a link between gut microbes and diseases, such as obesity, and help understand why alterations in the microbiota can influence the pathophysiology of human disease. This is supported by emerging evidence that microbial-derived metabolites, such as short-chain fatty acids, bile acids, tryptophan, trimethylamine-N-oxide, and lipopolysaccharides, can be beneficial or detrimental to the host by affecting organs outside the gut, including adipose tissue. Adipose tissue is the largest lipid storage organ in the body and an essential endocrine organ that plays an indispensable role in the regulation of lipid storage, metabolism, and energy balance. Adipose tissue metabolism includes adipocyte metabolism (lipogenesis and lipolysis), thermogenesis, and adipose tissue metabolic maladaptation. Adipose tissue dysfunction causes the development of metabolic diseases, such as obesity. Here, we review the current understanding of how these microbial metabolites are produced and discuss both established mechanisms and the most recent effects of microbial products on host adipose tissue metabolism. We aimed to identify novel therapeutic targets or strategies for the prevention and treatment of obesity and its complications.

Moxibustion alleviates depression-like behavior in rats with Crohn's disease by inhibiting the kynurenine pathway metabolism in the gut-brain axis

Background

Moxibustion is a potential therapy for inflammatory bowel disease-related depression, but its specific mechanism of action is unclear. This study aimed to investigate the molecular mechanism by which moxibustion alleviates depressive behavior in rats with Crohn's disease (CD).

Methods

The CD rat model was established with 2,4,6-trinitrobenzenesulfonic acid. Treatment with moxibustion was applied to Tianshu (ST25, bilateral), Qihai (CV6), and Baihui (GV20) acupoints, and the effect of moxibustion was compared with that of the combination of moxibustion plus indoleamine-2,3-dioxygenase 1 (IDO1) inhibitor, 1-methyltryptophan (1-MT). The effects of moxibustion and moxibustion plus 1-MT combination on colonic inflammation and depressive behavior (assessed by forced swimming test, sucrose preference test, and open field test) were investigated. The changes in IDO1, TNF-α, and IL-1β in rat colon and hippocampus were assessed by Western blot (WB). Gas chromatography-mass spectrometry, immunofluorescence staining, and WB were applied to detect kynurenine pathway (KP) metabolites, hippocampal neuronal activity, and microglia activation, respectively.

Results

Both moxibustion and moxibustion plus 1-MT combination significantly alleviated intestinal inflammation and depressive behavior, downregulated the levels of IDO1 in the colon and hippocampus, and inhibited inflammation-inducing factors IL-1β and TNF-α, as well as the kynurenine/tryptophan (KYN/TRP) ratio of KP metabolites, and upregulated the kynurenic acid (KYNA)/KYN ratio and the KYNA/quinolinic acid (QUIN) ratio in the hippocampus in rats with CD; Hippocampal ionized calcium-binding adaptor molecule-1 (Iba-1), c-fos protein expression, activated microglia, and neuronal activation was also significantly reduced by moxibustion and moxibustion plus 1-MT. The addition of 1-MT did not significantly increase the therapeutic effect of moxibustion.

Conclusion

Moxibustion can improve depressive behavior in rats with CD, which may be related to its regulation of KP metabolism in the gut-brain axis and inhibition of hippocampal microglia activation and neuronal activation.

Longitudinal Associations of Adherence to the Dietary World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) and Dutch Healthy Diet (DHD) Recommendations with Plasma Kynurenines in Colorectal Cancer Survivors after Treatment

The tryptophan-kynurenine pathway has been linked to cancer aetiology and survivorship, and diet potentially affects metabolites of this pathway, but evidence to date is scarce. Among 247 stage I-III CRC survivors, repeated measurements were performed at 6 weeks, 6 months, and 1 year post-treatment. Adherence to the World Cancer Research Fund/ American Institute for Cancer Research (WCRF) and Dutch Healthy Diet (DHD) recommendations was operationalized using seven-day dietary records. Plasma kynurenines of nine metabolites were analysed. Longitudinal associations of adherence to these dietary patterns and plasma kynurenines were analysed using confounder-adjusted linear mixed-models. In general, higher adherence to the dietary WCRF/AICR and DHD recommendations was associated with lower concentrations of kynurenines with pro-oxidative, pro-inflammatory, and neurotoxic properties (3-hydroxykynurenine (HK) and quinolinic acid (QA)), and higher concentrations of kynurenines with anti-oxidative, anti-inflammatory, and neuroprotective properties (kynurenic acid (KA) and picolinic acid (Pic)), but associations were weak and not statistically significant. Statistically significant positive associations between individual recommendations and kynurenines were observed for: nuts with kynurenic-acid-to-quinolinic-acid ratio (KA/QA); alcohol with KA/QA, KA, and xanthurenic acid (XA); red meat with XA; and cheese with XA. Statistically significant inverse associations were observed for: nuts with kynurenine-to-tryptophan ratio (KTR) and hydroxykynurenine ratio; alcohol with KTR; red meat with 3-hydroxyanthranilic-to-3-hydroxykynurenine ratio; ultra-processed foods with XA and KA/QA; and sweetened beverages with KA/QA. Our findings suggest that CRC survivors might benefit from adhering to the dietary WCRF and DHD recommendations in the first year after treatment, as higher adherence to these dietary patterns is generally, but weakly associated with more favourable concentrations of kynurenines and their ratios. These results need to be validated in other studies.

Amino acid metabolism in skeletal cells

Amino acid metabolism regulates essential cellular functions, not only by fueling protein synthesis, but also by supporting the biogenesis of nucleotides, redox factors and lipids. Amino acids are also involved in tricarboxylic acid cycle anaplerosis, epigenetic modifications, next to synthesis of neurotransmitters and hormones. As such, amino acids contribute to a broad range of cellular processes such as proliferation, matrix synthesis and intercellular communication, which are all critical for skeletal cell functioning. Here we summarize recent work elucidating how amino acid metabolism supports and regulates skeletal cell function during bone growth and homeostasis, as well as during skeletal disease. The most extensively studied amino acid is glutamine, and osteoblasts and chondrocytes rely heavily on this non-essential amino acid during for their functioning and differentiation. Regulated by lineage-specific transcription factors such as SOX9 and osteoanabolic agents such as parathyroid hormone or WNT, glutamine metabolism has a wide range of metabolic roles, as it fuels anabolic processes by producing nucleotides and non-essential amino acids, maintains redox balance by generating the antioxidant glutathione and regulates cell-specific gene expression via epigenetic mechanisms. We also describe how other amino acids affect skeletal cell functions, although further work is needed to fully understand their effect. The increasing number of studies using stable isotope labelling in several skeletal cell types at various stages of differentiation, together with conditional inactivation of amino acid transporters or enzymes in mouse models, will allow us to obtain a more complete picture of amino acid metabolism in skeletal cells.

Metabolomics of blood reveals age-dependent pathways in Parkinson’s Disease

Background

Parkinson’s Disease (PD) is the second most frequent degenerative disorder, the risk of which increases with age. A preclinical PD diagnostic test does not exist. We identify PD blood metabolites and metabolic pathways significantly correlated with age to develop personalized age-dependent PD blood biomarkers.

Results

We found 33 metabolites producing a receiver operating characteristic (ROC) area under the curve (AUC) value of 97%. PCA revealed that they belong to three pathways with distinct age-dependent behavior: glycine, threonine and serine metabolism correlates with age only in PD patients; unsaturated fatty acids biosynthesis correlates with age only in a healthy control group; and, finally, tryptophan metabolism characterizes PD but does not correlate with age.

Conclusions

The targeted analysis of the blood metabolome proposed in this paper allowed to find specific age-related metabolites and metabolic pathways. The model offers a promising set of blood biomarkers for a personalized age-dependent approach to the early PD diagnosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00831-5.

A kynurenine pathway enzyme aminocarboxymuconate-semialdehyde decarboxylase may be involved in treatment-resistant depression, and baseline inflammation status of patients predicts treatment response: a pilot study

The kynurenine pathway (KP) and inflammation are substantial in depression pathogenesis. Although there is a crosstalk between the KP, inflammation, and neurotrophic factors, few studies examine these topics together. Novel medications may be developed by clarifying dysregulations related to inflammation, KP, and neurotrophic factors in treatment-resistant depression (TRD). We aimed to evaluate the serum levels of KP metabolites, proinflammatory biomarkers, and brain-derived neurotrophic factor (BDNF) in healthy controls (HC) and the patients with TRD whose followed up with three different treatments. Moreover, the effect of electroconvulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS) on biomarkers was investigated. Study groups comprised a total of 30 unipolar TRD patients consisting of three separate patient groups (ECT = 8, rTMS = 10, pharmacotherapy = 12), and 9 HC. The decision to administer only pharmacotherapy or ECT/rTMS besides pharmacotherapy was given independently of this research by psychiatrists. Blood samples and symptom scores were obtained three times for patients. At baseline, quinolinic acid (QUIN) was higher in the patients with TRD compared to HC, whereas picolinic acid (PIC), PIC/QUIN, and PIC/3-hydroxykynurenine were lower. Baseline interleukin-6 (IL-6), and high-sensitivity C-reactive protein (hsCRP) were higher in nonresponders and non-remitters. ECT had an acute effect on cytokines. In the rTMS group, tumor necrosis factor-α (TNF-α) decreased in time. PIC, QUIN, and aminocarboxymuconate-semialdehyde decarboxylase (ACMSD) enzyme may play a role in TRD pathogenesis, and have diagnostic potential. rTMS and ECT have modulatory effects on low-grade inflammation seen in TRD. Baseline inflammation severity is predictive in terms of response and remission in depression.

Serum Kynurenic Acid and Kynurenine Are Negatively Associated with the Risk of Adult Moyamoya Disease

Background and aim. Kynurenine (KYN) and kynurenic acid (KYNA) are key intermediate metabolites associated with inflammation and immune responses in the kynurenine pathway. It remains unknown whether KYN or KYNA is associated with the risk of adult moyamoya disease (MMD). The aim of this study was to prospectively investigate the association between serum KYN or KYNA and the risk of adult MMD. Methods. The study was conducted from July 2020 to December 2021. We measured serum KYN and KYNA levels for 360 adult MMD patients (259 cases of ischemic MMD, 101 cases of hemorrhagic MMD) and 89 age-sex-matched healthy controls. Clinical and laboratory characteristics were collected from the medical record. Results. After multivariate adjustment, decreased serum KYNA (OR, 0.085; 95% CI, 0.035−0.206; p = 0.000) or KYN (OR, 0.430; 95% CI, 0.225−0.820; p = 0.010) levels were associated with increased risk of MMD when upper and lower tertiles were compared. In addition, a higher trend of hemorrhagic MMD was found in MMD patients in KYNA tertile 1 compared with those in tertile 2 to 3 (OR, 0.584; 95% CI, 0.345−0.987; p = 0.044). Addition of serum KYNA (net reclassification improvement: 73.24%, p = 0.000; integrated discrimination improvement: 9.60%, p = 0.000) or KYN (integrated discrimination improvement: 1.70%, p = 0.037) to conventional risk factors significantly improved the risk prediction of MMD. In the exploratory analysis, we observed an interaction between KYN and age (≥40 versus <40 years) or homocysteine levels (≥13.0 versus <13.0 μmol/L) on the risk of MMD. Conclusions. Decreased serum KYNA or KYN levels were associated with an increased risk of adult MMD, suggesting that serum KYNA or KYN may be a valuable predictive biomarker for adult MMD.

Changes in Tryptophan-Kynurenine Metabolism in Patients with Depression Undergoing ECT-A Systematic Review

The kynurenine pathway of tryptophan (Trp) metabolism generates multiple biologically active metabolites (kynurenines) that have been implicated in neuropsychiatric disorders. It has been suggested that modulation of kynurenine metabolism could be involved in the therapeutic effect of electroconvulsive therapy (ECT). We performed a systematic review with aims of summarizing changes in Trp and/or kynurenines after ECT and assessing methodological issues. The inclusion criterium was measures of Trp and/or kynurenines before and after ECT. Animal studies and studies using Trp administration or Trp depletion were excluded. Embase, MEDLINE, PsycInfo and PubMed were searched, most recently in July 2022. Outcomes were levels of Trp, kynurenines and ratios before and after ECT. Data on factors affecting Trp metabolism and ECT were collected for interpretation and discussion of the reported changes. We included 17 studies with repeated measures for a total of 386 patients and 27 controls. Synthesis using vote counting based on the direction of effect found no evidence of effect of ECT on any outcome variable. There were considerable variations in design, patient characteristics and reported items. We suggest that future studies should include larger samples, assess important covariates and determine between- and within-subject variability. PROSPERO (CRD42020187003).