A gut bacterial pathway metabolizes aromatic amino acids into nine circulating metabolites

Interplay between gut microbiota and antimicrobial peptides

The gut microbiota is comprised of a diverse array of microorganisms that interact with immune system and exert crucial roles for the health. Changes in the gut microbiota composition and functionality are associated with multiple diseases. As such, mobilizing a rapid and appropriate antimicrobial response depending on the nature of each stimulus is crucial for maintaining the balance between homeostasis and inflammation in the gut. Major players in this scenario are antimicrobial peptides (AMP), which belong to an ancient defense system found in all organisms and participate in a preservative co-evolution with a complex microbiome. Particularly increasing interactions between AMP and microbiota have been found in the gut. Here, we focus on the mechanisms by which AMP help to maintain a balanced microbiota and advancing our understanding of the circumstances of such balanced interactions between gut microbiota and host AMP. This review aims to provide a comprehensive overview on the interplay of diverse antimicrobial responses with enteric pathogens and the gut microbiota, which should have therapeutic implications for different intestinal disorders.

Elucidation of Gut Microbiota-Associated Lipids Using LC-MS/MS and 16S rRNA Sequence Analyses

Host-microbiota interactions create a unique metabolic milieu that modulates intestinal environments. Integration of 16S ribosomal RNA (rRNA) sequences and mass spectrometry (MS)-based lipidomics has a great potential to reveal the relationship between bacterial composition and the complex metabolic network in the gut. In this study, we conducted untargeted lipidomics followed by a feature-based molecular MS/MS spectral networking to characterize gut bacteria-dependent lipid subclasses in mice. An estimated 24.8% of lipid molecules in feces were microbiota-dependent, as judged by > 10-fold decrease in antibiotic-treated mice. Among these, there was a series of unique and microbiota-related lipid structures, including acyl alpha-hydroxyl fatty acid (AAHFA) that was newly identified in this study. Based on the integrated analysis of 985 lipid profiles and 16S rRNA sequence data providing 2,494 operational taxonomic units, we could successfully predict the bacterial species responsible for the biosynthesis of these unique lipids, including AAHFA.

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Feature-based molecular networking was explored in untargeted lipidomics analysis

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Of all lipids, 24.8% of fecal lipids were decreased >10-fold in antibiotics-treated mice

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Acyl alpha-hydroxy fatty acid (AAHFA) was identified as microbiota-specific lipid

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With 16S rRNA data, we revealed the relevance of microbiome and lipidome in mice

Mutual Interplay of Host Immune System and Gut Microbiota in the Immunopathology of Atherosclerosis

Inflammation is the key for the initiation and progression of atherosclerosis. Accumulating evidence has revealed that an altered gut microbiome (dysbiosis) triggers both local and systemic inflammation to cause chronic inflammatory diseases, including atherosclerosis. There have been some microbiome-relevant pro-inflammatory mechanisms proposed to link the relationships between dysbiosis and atherosclerosis such as gut permeability disruption, trigger of innate immunity from lipopolysaccharide (LPS), and generation of proatherogenic metabolites, such as trimethylamine N-oxide (TMAO). Meanwhile, immune responses, such as inflammasome activation and cytokine production, could reshape both composition and function of the microbiota. In fact, the immune system delicately modulates the interplay between microbiota and atherogenesis. Recent clinical trials have suggested the potential of immunomodulation as a treatment strategy of atherosclerosis. Here in this review, we present current knowledge regarding to the roles of microbiota in contributing atherosclerotic pathogenesis and highlight translational perspectives by discussing the mutual interplay between microbiota and immune system on atherogenesis.

Metabolites of microbiota response to tryptophan and intestinal mucosal immunity: A therapeutic target to control intestinal inflammation

In a complex, diverse intestinal environment, commensal microbiota metabolizes excessive dietary tryptophan to produce more bioactive metabolites connecting with kinds of diverse process, such as host physiological defense, homeostasis, excessive immune activation and the progression and outcome of different diseases, such as inflammatory bowel disease, irritable bowel syndrome and others. Although commensal microbiota includes bacteria, fungi, and protozoa and all that, they often have the similar metabolites in tryptophan metabolism process via same or different pathways. These metabolites can work as signal to activate the innate immunity of intestinal mucosa and induce the rapid inflammation response. They are critical in reconstruction of lumen homeostasis as well. This review aims to seek the potential function and mechanism of microbiota-derived tryptophan metabolites as targets to regulate and shape intestinal immune function, which mainly focused on two aspects. First, analyze the character of tryptophan metabolism in bacteria, fungi, and protozoa, and assess the functions of their metabolites (including indole and eight other derivatives, serotonin (5-HT) and d-tryptophan) on regulating the integrity of intestinal epithelium and the immunity of the intestinal mucosa. Second, focus on the mediator and pathway for their recognition, transfer and crosstalk between microbiota-derived tryptophan metabolites and intestinal mucosal immunity. Disruption of intestinal homeostasis has been described in different intestinal inflammatory diseases, available data suggest the remarkable potential of tryptophan-derived aryl hydrocarbon receptor agonists, indole derivatives on lumen equilibrium. These metabolites as preventive and therapeutic interventions have potential to promote proinflammatory or anti-inflammatory responses of the gut.

The aryl hydrocarbon receptor as a mediator of host-microbiota interplay

Increasing evidence suggests a significant role for microbiota dependent metabolites and co-metabolites, acting as aryl hydrocarbon receptor (AHR) ligands, to facilitate bidirectional communication between the host and the microbiota and thus modulate physiology. Such communication is particularly evident within the gastrointestinal tract. Through binding to or activating the AHR, these metabolites play fundamental roles in various physiological processes and likely contribute to the maintenance of intestinal homeostasis. In recent years, tryptophan metabolites were screened to identify physiologically relevant AHR ligands or activators. The discovery of specific microbiota-derived indole-based metabolites as AHR ligands may provide insight concerning how these metabolites affect interactions between gut microbiota and host intestinal homeostasis and how this relates to chronic GI disease and overall health. A greater understanding of the mechanisms that modulate the production of such metabolites and associated AHR activity may be utilized to effectively treat inflammatory diseases and promote human health. Here, we review microbiota-derived AHR ligands generated from tryptophan that modulate host-gut microbiota interactions and discuss possible intervention strategies for potential therapies in the future.

A Universal Gut-Microbiome-Derived Signature Predicts Cirrhosis

Dysregulation of the gut microbiome has been implicated in the progression of non-alcoholic fatty liver disease (NAFLD) to advanced fibrosis and cirrhosis. To determine the diagnostic capacity of this association, we compared stool microbiomes across 163 well-characterized participants encompassing non-NAFLD controls, NAFLD-cirrhosis patients, and their first-degree relatives. Interrogation of shotgun metagenomic and untargeted metabolomic profiles by using the random forest machine learning algorithm and differential abundance analysis identified discrete metagenomic and metabolomic signatures that were similarly effective in detecting cirrhosis (diagnostic accuracy 0.91, area under curve [AUC]). Combining the metagenomic signature with age and serum albumin levels accurately distinguished cirrhosis in etiologically and genetically distinct cohorts from geographically separated regions. Additional inclusion of serum aspartate aminotransferase levels, which are increased in cirrhosis patients, enabled discrimination of cirrhosis from earlier stages of fibrosis. These findings demonstrate that a core set of gut microbiome species might offer universal utility as a non-invasive diagnostic test for cirrhosis.

Dietary resistant starch preserved through mild extrusion of grain alters fecal microbiome metabolism of dietary macronutrients while increasing immunoglobulin A in the cat

Dietary digestion-resistant starch (RS) provides health benefits to the host via gut microbiome-mediated metabolism. The degree to which cats manifest beneficial changes in response to RS intake was examined. Healthy cats (N = 36) were fed identically formulated foods processed under high (n = 17) or low (n = 19) shear extrusion conditions (low and high RS levels [LRS and HRS], respectively). Fecal samples collected after 3 and 6 weeks' feeding were assayed for stool firmness score, short-chain fatty acids, ammonia, and changes to the global metabolome and microbiome; fecal immunoglobulin A (IgA) was analyzed at week 6. Few differences were seen in proximate analyses of the foods; stool firmness scores did not differ. In cats consuming HRS food, concentrations of fecal butyrate and the straight chain:branched chain fatty acid ratio were significantly greater in feces at both weeks 3 and 6, while fecal ammonia was reduced at week 6 relative to feces from LRS-fed cats. Fecal IgA concentrations were significantly higher at week 6 with HRS food. RS consumption altered 47% of the fecal metabolome; RS-derived sugars and metabolites associated with greater gut health, including indoles and polyamines, increased in the cats consuming HRS food relative to those fed the LS food, while endocannabinoid N-acylethanolamines decreased. Consumption of HRS food increased concentrations of the ketone body 3-hydroxybutyrate in feces and elevated concentrations of reduced members of NADH-coupled redox congeners and NADH precursors. At the microbiome genus-level, 21% of operational taxonomic units were significantly different between food types; many involved taxa with known saccharolytic or proteolytic proclivities. Microbiome taxa richness and Shannon and Simpson alpha diversity were significantly higher in the HRS group at both weeks. These data show that feline consumption of grain-derived RS produces potentially beneficial shifts in microbiota-mediated metabolism and increases IgA production.

Effects of gut microbial-based treatments on gut microbiota, behavioral symptoms, and gastrointestinal symptoms in children with autism spectrum disorder: A systematic review

Many studies have identified some abnormalities in gastrointestinal (GI) physiology (e.g., increased intestinal permeability, overall microbiota alterations, and gut infection) in children with autism spectrum disorder (ASD). Furthermore, changes in the intestinal flora may be related to GI and ASD symptom severity. Thus, we decided to systematically review the effects of gut microbial-based interventions on gut microbiota, behavioral symptoms, and GI symptoms in children with ASD. We reviewed current evidence from the Cochrane Library, EBSCO PsycARTICLES, PubMed, Web of Science, and Scope databases up to July 12, 2020. Experimental studies that used gut microbial-based treatments among children with ASD were included. Independent data extraction and quality assessment of studies were conducted according to the PRISMA statement. Finally, we identified 16 articles and found that some interventions (i.e., prebiotic, probiotic, vitamin A supplementation, antibiotics, and fecal microbiota transplantation) could alter the gut microbiota and improve behavioral symptoms and GI symptoms among ASD patients. Our findings highlight that the gut microbiota could be a novel target for ASD patients in the future. However, we only provided suggestive but not conclusive evidence regarding the efficacy of interventions on GI and behavioral symptoms among ASD patients. Additional rigorous trials are needed to evaluate the effects of gut microbial-based treatments and explore potential mechanisms.

Pomegranate Metabolites Impact Tryptophan Metabolism in Humans and Mice

BACKGROUND

We showed that pomegranate juice (PomJ) can help to maintain memory in adults aged >50 y. The mechanism for this effect is unknown, but might involve Trp and its metabolites, which are important in brain function.

OBJECTIVES

We aimed to test the hypothesis that PomJ and its metabolites ellagic acid (EA) and urolithin A (UA) affect Trp metabolism.

METHODS

Stool and plasma from a cohort [11 PomJ, 9 placebo drink (PL)] of subjects enrolled in our double-blind, placebo-controlled trial (NCT02093130) were collected at baseline and after 1 y of PomJ or PL consumption. In a mouse study, cecum and serum were collected from DBA/2J mice receiving 8 wk of dietary 0.1% EA or UA supplementation. Trp metabolites and intestinal microbiota were analyzed by LC-MS and 16S rRNA gene sequencing, respectively.

RESULTS

In the human study, the change in the plasma Trp metabolite indole propionate (IPA) over 1 y was significantly different between PomJ and PL groups (P = 0.03). In serum of experimental mice, we observed a 230% increase of IPA by EA but not UA, a 54% increase of indole sulfate by UA but not EA, and 43% and 34% decreases of kynurenine (KYN) by EA and UA, respectively. In cecum, there was a 32% decrease of Trp by UA but not EA, and an 86% decrease of KYN by EA but not UA (P < 0.05). The abundance of 2 genera, Shigella and Catenibacterium, was reduced by PomJ in humans as well as by UA in mice, and their abundance was negatively associated with blood IPA in humans and mice (P < 0.05).

CONCLUSIONS

These results suggest a novel mechanism involving the regulation of host and microbial Trp metabolism that might contribute to the health benefits of ellagitannins and EA-enriched food, such as PomJ.

Effects of dietary components on intestinal permeability in health and disease

Altered intestinal permeability plays a role in many pathological conditions. Intestinal permeability is a component of the intestinal barrier. This barrier is a dynamic interface between the body and the food and pathogens that enter the gastrointestinal tract. Therefore, dietary components can directly affect this interface, and many metabolites produced by the host enzymes or the gut microbiota can act as signaling molecules or exert direct effects on this barrier. Our aim was to examine the effects of diet components on the intestinal barrier in health and disease states. Herein, we conducted an in-depth PubMed search based on specific key words (diet, permeability, barrier, health, disease, and disorder), as well as cross references from those articles. The normal intestinal barrier consists of multiple components in the lumen, epithelial cell layer and the lamina propria. Diverse methods are available to measure intestinal permeability. We focus predominantly on human in vivo studies, and the literature is reviewed to identify dietary factors that decrease (e.g., emulsifiers, surfactants, and alcohol) or increase (e.g., fiber, short-chain fatty acids, glutamine, and vitamin D) barrier integrity. Effects of these dietary items in disease states, such as metabolic syndrome, liver disease, or colitis are documented as examples of barrier dysfunction in the multifactorial diseases. Effects of diet on intestinal barrier function are associated with precise mechanisms in some instances; further research of those mechanisms has potential to clarify the role of dietary interventions in treating diverse pathologic states.

Gut Microbial Metabolites of Aromatic Amino Acids as Signals in Host-Microbe Interplay

Gut microbial metabolism is intimately coupled with host health and disease. Aromatic amino acid (AAA) catabolism by the gut microbiome yields numerous metabolites that may regulate immune, metabolic, and neuronal responses at local and distant sites. Such a chemical dialog between host cells and the gut microbiome is shaped by environmental cues, and may become dysregulated in gastrointestinal and systems diseases. Increasing knowledge of the bacterial pathway and signaling basis may shed additional light on metabolic host-microbiome crosstalk that remains untapped for drug discovery. Here, we update our understanding of microbial AAA metabolism and its impacts on host physiology and disease. We also consider open questions related to therapeutically mining these signaling metabolites and how recent concepts and tools may drive this area forward.

Indole Propionic Acid, an Unusual Antibiotic Produced by the Gut Microbiota, With Anti-inflammatory and Antioxidant Properties

Most antibiotics are produced by soil microbes and typically interfere with macromolecular synthesis processes as their antibacterial mechanism of action. These natural products are often large and suffer from poor chemical tractability. Here, we discuss discovery, mechanism of action, and the therapeutic potentials of an unusual antibiotic, indole propionic acid (IPA). IPA is produced by the human gut microbiota. The molecule is small, chemically tractable, and targets amino acid biosynthesis. IPA is active against a broad spectrum of mycobacteria, including drug resistant Mycobacterium tuberculosis and non-tuberculous mycobacteria (NTM). Interestingly, the microbiota-produced metabolite is detectable in the serum of healthy individuals, tuberculosis (TB) patients, and several animal models. Thus, the microbiota in our gut may influence susceptibility to mycobacterial diseases. If a gut-lung microbiome axis can be demonstrated, IPA may have potential as a biomarker of disease progression, and development of microbiota-based therapies could be explored. In addition to its antimycobacterial activity, the molecule displays anti-inflammatory and antioxidant properties. This raises the possibility that IPA has therapeutic potential as both antibiotic and add-on host-directed drug for the treatment of TB in patient populations where disease morbidity and mortality is driven by excessive inflammation and tissue damage, such as TB-associated immune reconstitution inflammatory syndrome, TB-meningitis, and TB-diabetes.

Gut bacterial deamination of residual levodopa medication for Parkinson's disease

Background

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Gastrointestinal tract dysfunction is one of the non-motor features, where constipation is reported as the most common gastrointestinal symptom. Aromatic bacterial metabolites are attracting considerable attention due to their impact on gut homeostasis and host’s physiology. In particular, Clostridium sporogenes is a key contributor to the production of these bioactive metabolites in the human gut.

Results

Here, we show that C. sporogenes deaminates levodopa, the main treatment in Parkinson’s disease, and identify the aromatic aminotransferase responsible for the initiation of the deamination pathway. The deaminated metabolite from levodopa, 3-(3,4-dihydroxyphenyl)propionic acid, elicits an inhibitory effect on ileal motility in an ex vivo model. We detected 3-(3,4-dihydroxyphenyl)propionic acid in fecal samples of Parkinson’s disease patients on levodopa medication and found that this metabolite is actively produced by the gut microbiota in those stool samples.

Conclusions

Levodopa is deaminated by the gut bacterium C. sporogenes producing a metabolite that inhibits ileal motility ex vivo. Overall, this study underpins the importance of the metabolic pathways of the gut microbiome involved in drug metabolism not only to preserve drug effectiveness, but also to avoid potential side effects of bacterial breakdown products of the unabsorbed residue of medication.

Taming the Sentinels: Microbiome-Derived Metabolites and Polarization of T Cells

A global increase in the prevalence of metabolic syndromes and digestive tract disorders, like food allergy or inflammatory bowel disease (IBD), has become a severe problem in the modern world. Recent decades have brought a growing body of evidence that links the gut microbiome’s complexity with host physiology. Hence, understanding the mechanistic aspects underlying the synergy between the host and its associated gut microbiome are among the most crucial questions. The functionally diversified adaptive immune system plays a central role in maintaining gut and systemic immune homeostasis. The character of the reciprocal interactions between immune components and host-dwelling microbes or microbial consortia determines the outcome of the organisms’ coexistence within the holobiont structure. It has become apparent that metabolic by-products of the microbiome constitute crucial multimodal transmitters within the host–microbiome interactome and, as such, contribute to immune homeostasis by fine-tuning of the adaptive arm of immune system. In this review, we will present recent insights and discoveries regarding the broad landscape of microbiome-derived metabolites, highlighting the role of these small compounds in the context of the balance between pro- and anti-inflammatory mechanisms orchestrated by the host T cell compartment.

Bifidobacterium alters the gut microbiota and modulates the functional metabolism of T regulatory cells in the context of immune checkpoint blockade

Many millions of people take probiotics over the counter, but very little is known about what they do and whether they really work. Here we show that in mice, introducing Bifidobacterium, one of the most commonly used probiotics, not only colonizes the gut, but also alters the entire microbiotic landscape. We previously found that this treatment rescues mice from an otherwise fatal inflammatory syndrome brought on by anti–CTLA-4 antibody, a checkpoint inhibitor that often causes autoimmunity in humans undergoing cancer treatment. Here we show that this is effect is due, at least in part, to the effect of this probiotic treatment on regulatory CD4⁺ cells, whose metabolic and immune suppressive functions are altered. These CD4⁺ regulatory T cells are known to be a key mechanism in the control of autoreactivity in the immune system in both mice and humans. Thus, we found a direct connection between probiotic treatment and one of the known principal mechanisms for controlling excess immune responses.

Immune checkpoint-blocking antibodies that attenuate immune tolerance have been used to effectively treat cancer, but they can also trigger severe immune-related adverse events. Previously, we found that Bifidobacterium could mitigate intestinal immunopathology in the context of CTLA-4 blockade in mice. Here we examined the mechanism underlying this process. We found that Bifidobacterium altered the composition of the gut microbiota systematically in a regulatory T cell (Treg)-dependent manner. Moreover, this altered commensal community enhanced both the mitochondrial fitness and the IL-10–mediated suppressive functions of intestinal Tregs, contributing to the amelioration of colitis during immune checkpoint blockade.

Bioaminergic Responses in an In Vitro System Studying Human Gut Microbiota-Kiwifruit Interactions

Whole kiwifruit ('Hayward' and 'Zesy002') were examined for their bioaminergic potential after being subjected to in vitro gastrointestinal digestion and colonic fermentation. Controls included the prebiotic inulin and water, a carbohydrate-free vehicle. The dopamine precursor l-dihydroxyphenylalanine (L-DOPA) and the serotonin precursor 5-hydroxytryptophan were increased in the kiwifruit gastrointestinal digesta ('Hayward' > 'Zesy002') in comparison to the water digesta. Fermentation of the digesta with human fecal bacteria for 18 h modulated the concentrations of bioamine metabolites. The most notable were the significant increases in L-DOPA ('Zesy002' > 'Hayward') and γ-aminobutyric acid (GABA) ('Hayward' > 'Zesy002'). Kiwifruit increased Bifidobacterium spp. and Veillonellaceae (correlating with L-DOPA increase), and Lachnospira spp. (correlating with GABA). The digesta and fermenta were incubated with Caco-2 cells for 3 h followed by gene expression analysis. Effects were seen on genes related to serotonin synthesis/re-uptake/conversion to melatonin, gut tight junction, inflammation and circadian rhythm with different digesta and fermenta from the four treatments. These indicate potential effects of the substrates and the microbially generated organic acid and bioamine metabolites on intestinal functions that have physiological relevance. Further studies are required to confirm the potential bioaminergic effects of gut microbiota-kiwifruit interactions.

The intestinal microbial metabolite desaminotyrosine is an anti-inflammatory molecule that modulates local and systemic immune homeostasis

It is considered that intestinal barrier dysfunction and systemic endotoxemia drive obesity and its related complications. However, what causes barrier dysfunction remains to be elucidated. Here, we showed that the gut microbiota from high-fat diet (HFD)-fed mice had impaired ability to degrade dietary flavonoids, and in correspondence, the microbial-derived flavonoid metabolite desaminotyrosine (DAT) was reduced. Supplementation of DAT in the drinking water was able to counter the HFD-induced body fat mass accumulation and body weight increment. This is correlated with the role of DAT in maintaining mucosal immune homeostasis to protect barrier integrity. DAT could attenuate dextran sodium sulfate (DSS)-induced mucosal inflammation in a type I interferon signal-dependent manner. Furthermore, intraperitoneal injection of DAT-protected mice from bacterial endotoxin-induced septic shock. Together, we identified DAT as a gut microbiota-derived anti-inflammatory metabolite that functions to modulate local and systemic immune homeostasis. Our data support the notion of dysbiosis being an important driving force of mucosal barrier dysfunction and systemic metabolic complications.

Upconversion optogenetic micro-nanosystem optically controls the secretion of light-responsive bacteria for systemic immunity regulation

Chemical molecules specifically secreted into the blood and targeted tissues by intestinal microbiota can effectively affect the associated functions of the intestine especially immunity, representing a new strategy for immune-related diseases. However, proper ways of regulating the secretion metabolism of specific strains still remain to be established. In this article, an upconversion optogenetic micro-nanosystem was constructed to effectively regulate the specific secretion of engineered bacteria. The system included two major modules: (i) Modification of secretory light-responsive engineered bacteria. (ii) Optical sensing mediated by upconversion optogenetic micro-nanosystem. This system could regulate the efficient secretion of immune factors by engineered bacteria through optical manipulation. Inflammatory bowel disease and subcutaneously transplanted tumors were selected to verify the effectiveness of the system. Our results showed that the endogenous factor TGF-β1 could be controllably secreted to suppress the intestinal inflammatory response. Additionally, regulatory secretion of IFN-γ was promoted to slow the progression of B16F10 tumor.

What was First, Obesity or Inflammatory Bowel Disease? What Does the Gut Microbiota Have to Do with It?

A sedentary lifestyle and inadequate nutrition often leads to disturbances in intestinal homeostasis, which may predispose people to excess body weight and metabolic syndrome. Obesity is frequently observed in patients with inflammatory bowel diseases (IBD), similar to the general population. Obesity may exert a negative effect on the course of IBD as well as reduce the response to treatment. Moreover, it may also be an additional risk factor for vein thromboembolism during the flare. In both obesity and IBD, it is of great importance to implement proper dietary ingredients that exert desirable effect on gut microbiota. The key to reducing body mass index (BMI) and alleviating the course of IBD is preserving healthy intestinal microflora.

Endogenous Metabolic Modulators: Emerging Therapeutic Potential of Amino Acids

Multifactorial disease pathophysiology is complex and incompletely addressed by existing targeted pharmacotherapies. Amino acids (AAs) and related metabolites and precursors are a class of endogenous metabolic modulators (EMMs) that have diverse biological functions and, thus, have been explored for decades as potential multifactorial disease treatments. Here, we review the literature on this class of EMMs in disease treatment, with a focus on the emerging clinical studies on AAs and related metabolites and precursors as single- and combination-agents targeted to a single biology. These clinical research insights, in addition to increasing understanding of disease metabolic profiles and combinatorial therapeutic design principles, highlight an opportunity to develop EMM compositions with AAs and related metabolites and precursors to target multifactorial disease biology. EMM compositions are uniquely designed to enable a comprehensive approach, with potential to simultaneously and safely target pathways underlying multifactorial diseases and to regulate biological processes that promote overall health.

Analysis of the intestinal microbiota in COVID-19 patients and its correlation with the inflammatory factor IL-18

The ongoing global pandemic of COVID-19 disease, which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), mainly infect lung epithelial cells, and spread mainly through respiratory droplets. However, recent studies showed potential intestinal infection of SARS-CoV-2, implicated the possibility that the intestinal infection of SARS-CoV-2 may correlate with the dysbiosis of gut microbiota, as well as the severity of COVID-19 symptoms. Here, we investigated the alteration of the gut microbiota in COVID-19 patients, as well as analyzed the correlation between the altered microbes and the levels of intestinal inflammatory cytokine IL-18, which was reported to be elevated in the serum of in COVID-19 patients. Comparing with healthy controls or seasonal flu patients, the gut microbiota showed significantly reduced diversity, with increased opportunistic pathogens in COVID-19 patients. Also, IL-18 level was higher in the fecal samples of COVID-19 patients than in those of either healthy controls or seasonal flu patients. Moreover, the IL-18 levels were even higher in the fecal supernatants obtained from COVID-19 patients that tested positive for SARS-CoV-2 RNA than those that tested negative in fecal samples. These results indicate that changes in gut microbiota composition might contribute to SARS-CoV-2-induced production of inflammatory cytokines in the intestine and potentially also to the onset of a cytokine storm.

Gut microbiome and cardiovascular disease

PURPOSE OF REVIEW

This review aims to highlight the association between gut microbiome and cardiovascular disease (CVD) with emphasis on the possible molecular mechanisms by which how gut microbiome contributes to CVD.

RECENT FINDINGS

Increasingly, the roles of gut microbiome in cardiovascular health and disease have gained much attention. Most of the investigations focus on how the gut dysbiosis contributes to CVD risk factors and which gut microbial-derived metabolites mediate such effects.

SUMMARY

In this review, we discuss the molecular mechanisms of gut microbiome contributing to CVD, which include gut microbes translocalization to aortic artery because of gut barrier defect to initiate inflammation and microbial-derived metabolites inducing inflammation-signaling pathway and renal insufficiency. Specifically, we categorize beneficial and deleterious microbial-derived metabolites in cardiovascular health. We also summarize recent findings in the gut microbiome modulation of drug efficacy in treatment of CVD and the microbiome mechanisms by which how physical exercise ameliorates cardiovascular health. Gut microbiome has become an essential component of cardiovascular research and a crucial consideration factor in cardiovascular health and disease.

Gut microbial metabolites as multi-kingdom intermediates

The gut microbiota contributes to host physiology through the production of a myriad of metabolites. These metabolites exert their effects within the host as signalling molecules and substrates for metabolic reactions. Although the study of host-microbiota interactions remains challenging due to the high degree of crosstalk both within and between kingdoms, metabolite-focused research has identified multiple actionable microbial targets that are relevant for host health. Metabolites, as the functional output of combined host and microorganism interactions, provide a snapshot in time of an extraordinarily complex multi-organism system. Although substantial work remains towards understanding host-microbiota interactions and the underlying mechanisms, we review the current state of knowledge for each of the major classes of microbial metabolites with emphasis on clinical and translational research implications. We provide an overview of methodologies available for measurement of microbial metabolites, and in addition to discussion of key challenges, we provide a potential framework for integration of discovery-based metabolite studies with mechanistic work. Finally, we highlight examples in the literature where this approach has led to substantial progress in understanding host-microbiota interactions.

Nutritional Therapy to Modulate Tryptophan Metabolism and Aryl Hydrocarbon-Receptor Signaling Activation in Human Diseases

The aryl hydrocarbon receptor (AhR) is a nuclear protein which, upon association with certain endogenous and exogenous ligands, translocates into the nucleus, binds DNA and regulates gene expression. Tryptophan (Trp) metabolites are one of the most important endogenous AhR ligands. The intestinal microbiota is a critical player in human intestinal homeostasis. Many of its effects are mediated by an assembly of metabolites, including Trp metabolites. In the intestine, Trp is metabolized by three main routes, leading to kynurenine, serotonin, and indole derivative synthesis under the direct or indirect involvement of the microbiota. Disturbance in Trp metabolism and/or AhR activation is strongly associated with multiple gastrointestinal, neurological and metabolic disorders, suggesting Trp metabolites/AhR signaling modulation as an interesting therapeutic perspective. In this review, we describe the most recent advances concerning Trp metabolism and AhR signaling in human health and disease, with a focus on nutrition as a potential therapy to modulate Trp metabolites acting on AhR. A better understanding of the complex balance between these pathways in human health and disease will yield therapeutic opportunities.

Hypoglycemic and Hypolipidemic Mechanism of Tea Polysaccharides on Type 2 Diabetic Rats via Gut Microbiota and Metabolism Alteration

Diabetes mellitus is a serious threat to human health. Tea is cultivated around the world, and its polysaccharide components are reported to be an effective approach for managing type 2 diabetes with fewer adverse effects than medication. To examine the therapeutic effect of tea polysaccharides on diabetes, a type 2 diabetic rat model was generated. We showed that tea polysaccharides remarkably decreased fasting blood glucose and the levels of total cholesterol, total triglyceride, low-density lipoprotein cholesterol, and free fatty acid of type 2 diabetic rats. 16S rRNA sequencing and metabolomics were used to investigate the variation of gut microbiota and the metabolites profiles of diabetic rats after intervention of tea polysaccharides. We found that tea polysaccharides maintained the diversity of gut microbiota and restored the relative abundance of some bacterial genera (Lachnospira, Victivallis, Roseburia, and Fluviicola) which was reduced by diabetes. According to metabolomics analysis, we found that amino acid and other related metabolites was influenced by tea polysaccharides intervention. Correlation analysis among metabolites, gut microbiota, and parameters of hypoglycemic indicated that tea polysaccharides had hypoglycemic and hypolipidemic effect on type 2 diabetes via the modulation of gut microbiota and the improvement of host metabolism.

Fecal microbiota transplantation alters the susceptibility of obese rats to type 2 diabetes mellitus

Obesity is one of the susceptibility factors for type 2 diabetes (T2DM), both of which could accelerate the aging of the body and bring many hazards. A causal relationship is present between intestinal microbiota and body metabolism, but how the microbiota play a role in the progression of obesity to T2DM has not been elucidated. In this study, we transplanted healthy or obese-T2DM intestinal microbiota to ZDF and LZ rats, and used 16S rRNA and targeted metabonomics to evaluate the directional effect of the microbiota on the susceptibility of obese rats to T2DM. The glycolipid metabolism phenotype could be changed bidirectionally in obese rats instead of in lean ones. One possible mechanism is that the microbiota and metabolites alter the structure of the intestinal tract, and improve insulin and leptin resistance through JAK2 / IRS / Akt pathway. It is worth noting that 7 genera, such as Lactobacillus, Clostridium and Roche, can regulate 15 metabolites, such as 3-indolpropionic acid, acetic acid and docosahexaenoic acid, and have a significant improvement on glycolipid metabolism phenotype. Attention to intestinal homeostasis may be the key to controlling obesity and preventing T2DM.

Possible links between gut-microbiota and attention-deficit/hyperactivity disorders in children and adolescents

An association between gut-microbiota and several neuropsychiatric conditions including autism, depression, anxiety, schizophrenia, and attention-deficit/hyperactivity disorder (ADHD) has been observed. Despite being the most prevalent neurodevelopmental disorders in children and adolescents worldwide, the etiology and curative approaches to treatment of ADHD remain unclear. There is a probability that gut-microbiota may contribute to ADHD via bidirectional communication between the gut and brain, a system known as the "gut-brain axis". Although a mechanistic link in the gut-brain axis in ADHD has been proposed, there is still a lack of information about the correlation of the microbiome profile with the mechanisms involved. The objective of this review was to summarize the diversity of the gut-microbiota and taxonomic profiles in children and adolescents with ADHD. In this review, we have provided an overview of the association between ADHD and gut-microbiota. The evidence pertinent to potentially distinctive gut-microbiota in children and adolescents with ADHD is also discussed and compared to that of their non-ADHD peers. Finally, the implications and future directions for investigation into the gut microbiome in ADHD patients are proposed.

The importance of genetic research on the dominant species of human intestinal indigenous microbiota

Comparisons of the changes in the gut microbiota and transcriptomes as a result of changes in diet have demonstrated that the regulation of the gene functions of intestinal bacteria is fundamental for the regulation of the intestinal environment. However, the functions of only about half of the genes can be predicted using nucleotide sequences obtained from the metagenomic data of the human gut microbiota. Therefore, the regulation of gut bacterial gene functions is hindered. To resolve this issue, the functions of the genes of intestinal bacteria must be identified. In our previous study, a high-throughput cultivation system was established for the dominant species of indigenous human intestinal microbiota. Using this system, we analyzed the synthesis and transport of polyamines by intestinal bacteria. Comparison of the results with those obtained by in silico analysis indicated the existence of novel polyamine synthetic enzymes and transport proteins. Next, strains with gene deletions and complementation for the polyamine synthetic system of the genus Bacteroides were analyzed. Furthermore, we co-cultured genetically engineered Escherichia coli and Enterococcus faecalis strains to demonstrate the presence of a polyamine synthetic pathway spanning multiple bacterial species. Here, we outline the trends of research using genetically engineered intestinal bacteria and the ripple effects of studies in which intestinal bacteria have been analyzed genetically. Moreover, because studies on intestinal bacteria at the gene level are indispensable for improving our understanding of their regulation, the importance of this research will continue to increase in the future.

Impacts of Amino Acids on the Intestinal Defensive System

The intestine interacts with a diverse community of antigens and bacteria. To keep its homeostasis, the gut has evolved with a complex defense system, including intestinal microbiota, epithelial layer and lamina propria. Various factors (e.g., nutrients) affect the intestinal defensive system and progression of intestinal diseases. This review highlights the current understanding about the role of amino acids (AAs) in protecting the intestine from harm. Amino acids (e.g., arginine, glutamine and tryptophan) are essential for the function of intestinal microbiota, epithelial cells, tight junction, goblet cells, Paneth cells and immune cells (e.g., macrophages, B cells and T cells). Through the modulation of the intestinal defensive system, AAs maintain the integrity and function of the intestinal mucosa and inhibit the progression of various intestinal diseases (e.g., intestinal infection and intestinal colitis). Thus, adequate intake of functional AAs is crucial for intestinal and whole-body health in humans and other animals.

Amino Acids in Intestinal Physiology and Health

Dietary protein digestion is an efficient process resulting in the absorption of amino acids by epithelial cells, mainly in the jejunum. Some amino acids are extensively metabolized in enterocytes supporting their high energy demand and/or production of bioactive metabolites such as glutathione or nitric oxide. In contrast, other amino acids are mainly used as building blocks for the intense protein synthesis associated with the rapid epithelium renewal and mucin production. Several amino acids have been shown to support the intestinal barrier function and the intestinal endocrine function. In addition, amino acids are metabolized by the gut microbiota that use them for their own protein synthesis and in catabolic pathways releasing in the intestinal lumen numerous metabolites such as ammonia, hydrogen sulfide, branched-chain amino acids, polyamines, phenolic and indolic compounds. Some of them (e.g. hydrogen sulfide) disrupts epithelial energy metabolism and may participate in mucosal inflammation when present in excess, while others (e.g. indole derivatives) prevent gut barrier dysfunction or regulate enteroendocrine functions. Lastly, some recent data suggest that dietary amino acids might regulate the composition of the gut microbiota, but the relevance for the intestinal health remains to be determined. In summary, amino acid utilization by epithelial cells or by intestinal bacteria appears to play a pivotal regulator role for intestinal homeostasis. Thus, adequate dietary supply of amino acids represents a key determinant of gut health and functions.

Probiotics, Prebiotics, Synbiotics, Postbiotics, and Obesity: Current Evidence, Controversies, and Perspectives

PURPOSE OF REVIEW

In this review, we summarize current evidence on gut microbiome and obesity; we discuss the role of probiotics, prebiotics, synbiotics, and postbiotics in obesity prevention and management; and we highlight and analyze main limitations, challenges, and controversies of their use.

RECENT FINDINGS

Overall, the majority of animal studies and meta-analyses of human studies examining the use of probiotics and synbiotics in obesity has shown their beneficial effects on weight reduction and other metabolic parameters via their involvement in gut microbiota modulation. Bifidobacterium and Lactobacillus strains are still the most widely used probiotics in functional foods and dietary supplements, but next generation probiotics, such as Faecalibacterium prausnitzii, Akkermansia muciniphila, or Clostridia strains, have demonstrated promising results. On the contrary, meta-analyses of human studies on the use of prebiotics in obesity have yielded contradictory results. In animal studies, postbiotics, mainly short-chain fatty acids, may increase energy expenditure through induction of thermogenesis in brown adipose tissue as well as browning of the white adipose tissue. The main limitations of studies on biotics in obesity include the paucity of human studies; heterogeneity among the studied subgroups regarding age, gender, and lifestyle; and use of different agents with potential therapeutic effects in different formulations, doses, ratio and different pharmacodynamics/pharmacokinetics. In terms of safety, the supplementation with prebiotics, probiotics, and synbiotics has not been associated with serious adverse effects among immune-competent individuals, with the exception of the use of probiotics and synbiotics in immunocompromised patients. Further large-scale Randomized Controlled Trials (RCTs) in humans are required to evaluate the beneficial properties of probiotics, prebiotics, synbiotics, and postbiotics; their ideal dose; the duration of supplementation; and the durability of their beneficial effects as well as their safety profile in the prevention and management of obesity.

Metabolic cross-feeding in imbalanced diets allows gut microbes to improve reproduction and alter host behaviour

The impact of commensal bacteria on the host arises from complex microbial-diet-host interactions. Mapping metabolic interactions in gut microbial communities is therefore key to understand how the microbiome influences the host. Here we use an interdisciplinary approach including isotope-resolved metabolomics to show that in Drosophila melanogaster, Acetobacter pomorum (Ap) and Lactobacillus plantarum (Lp) a syntrophic relationship is established to overcome detrimental host diets and identify Ap as the bacterium altering the host's feeding decisions. Specifically, we show that Ap uses the lactate produced by Lp to supply amino acids that are essential to Lp, allowing it to grow in imbalanced diets. Lactate is also necessary and sufficient for Ap to alter the fly's protein appetite. Our data show that gut bacterial communities use metabolic interactions to become resilient to detrimental host diets. These interactions also ensure the constant flow of metabolites used by the microbiome to alter reproduction and host behaviour.

Delayed Motor Milestones Achievement in Infancy Associates with Perturbations of Amino Acids and Lipid Metabolic Pathways

The relationship between developmental milestone achievement in infancy and later cognitive function and mental health is well established, but underlying biochemical mechanisms are poorly described. Our study aims to discover pathways connected to motor milestone achievement during infancy by using untargeted plasma metabolomic profiles from 571 six-month-old children in connection with age of motor milestones achievement (Denver Developmental Index) in the Copenhagen Prospective Studies on Asthma in Childhood 2010 (COPSAC2010) mother-child cohort. We used univariate regression models and multivariate modelling (Partial Least Squares Discriminant Analysis: PLS-DA) to examine the associations and the VDAART (Vitamin D Antenatal Asthma Reduction Trial) cohort for validation. The univariate analyses showed 62 metabolites associated with gross-motor milestone achievement (p < 0.05) as well as the PLS-DA significantly differentiated between slow and fast milestone achievers (AUC = 0.87, p = 0.01). Higher levels of tyramine-O-sulfate in the tyrosine pathway were found in the late achievers in COPSAC (p = 0.0002) and in VDAART (p = 0.02). Furthermore, we observed that slow achievers were characterized by higher levels of fatty acids and products of fatty acids metabolism including acyl carnitines. Finally, we also observed changes in the lysine, histidine, glutamate, creatine and tryptophan pathways. Observing these metabolic changes in relation to gross-motor milestones in the first year of life, may be of importance for later cognitive function and mental health.

Metabolomic Profiling Reveals Distinct and Mutual Effects of Diet and Inflammation in Shaping Systemic Metabolism in Ldlr-/- Mice

Changes in modern dietary habits such as consumption of Western-type diets affect physiology on several levels, including metabolism and inflammation. It is currently unclear whether changes in systemic metabolism due to dietary interventions are long-lasting and affect acute inflammatory processes. Here, we investigated how high-fat diet (HFD) feeding altered systemic metabolism and the metabolomic response to inflammatory stimuli. We conducted metabolomic profiling of sera collected from Ldlr^−/− mice on either regular chow diet (CD) or HFD, and after an additional low-dose lipopolysaccharide (LPS) challenge. HFD feeding, as well as LPS treatment, elicited pronounced metabolic changes. HFD qualitatively altered the systemic metabolic response to LPS; particularly, serum concentrations of fatty acids and their metabolites varied between LPS-challenged mice on HFD or CD, respectively. To investigate whether systemic metabolic changes were sustained long-term, mice fed HFD were shifted back to CD after four weeks (HFD > CD). When shifted back to CD, serum metabolites returned to baseline levels, and so did the response to LPS. Our results imply that systemic metabolism rapidly adapts to dietary changes. The profound systemic metabolic rewiring observed in response to diet might affect immune cell reprogramming and inflammatory responses.

IL4I1 Is a Metabolic Immune Checkpoint that Activates the AHR and Promotes Tumor Progression

Aryl hydrocarbon receptor (AHR) activation by tryptophan (Trp) catabolites enhances tumor malignancy and suppresses anti-tumor immunity. The context specificity of AHR target genes has so far impeded systematic investigation of AHR activity and its upstream enzymes across human cancers. A pan-tissue AHR signature, derived by natural language processing, revealed that across 32 tumor entities, interleukin-4-induced-1 (IL4I1) associates more frequently with AHR activity than IDO1 or TDO2, hitherto recognized as the main Trp-catabolic enzymes. IL4I1 activates the AHR through the generation of indole metabolites and kynurenic acid. It associates with reduced survival in glioma patients, promotes cancer cell motility, and suppresses adaptive immunity, thereby enhancing the progression of chronic lymphocytic leukemia (CLL) in mice. Immune checkpoint blockade (ICB) induces IDO1 and IL4I1. As IDO1 inhibitors do not block IL4I1, IL4I1 may explain the failure of clinical studies combining ICB with IDO1 inhibition. Taken together, IL4I1 blockade opens new avenues for cancer therapy.

Dietary and Microbial Determinants in Food Allergy

The steep rise in food allergy (FA) has evoked environmental factors involved in disease pathogenesis, including the gut microbiota, diet, and their metabolites. Early introduction of solid foods synchronizes with the "weaning reaction," a time during which the microbiota imprints durable oral tolerance. Recent work has shown that children with FA manifest an early onset dysbiosis with the loss of Clostridiales species, which promotes the differentiation of ROR-γt+ regulatory T cells to suppress FA. This process can be reversed in pre-clinical mouse models by targeted bacteriotherapy. Here, we review the dominant tolerance mechanisms enforced by the microbiota to suppress FA and discuss therapeutic intervention strategies that act to recapitulate the early life window of opportunity in stemming the FA epidemic.

A Cardiovascular Disease-Linked Gut Microbial Metabolite Acts via Adrenergic Receptors

Using untargeted metabolomics (n = 1,162 subjects), the plasma metabolite (m/z = 265.1188) phenylacetylglutamine (PAGln) was discovered and then shown in an independent cohort (n = 4,000 subjects) to be associated with cardiovascular disease (CVD) and incident major adverse cardiovascular events (myocardial infarction, stroke, or death). A gut microbiota-derived metabolite, PAGln, was shown to enhance platelet activation-related phenotypes and thrombosis potential in whole blood, isolated platelets, and animal models of arterial injury. Functional and genetic engineering studies with human commensals, coupled with microbial colonization of germ-free mice, showed the microbial porA gene facilitates dietary phenylalanine conversion into phenylacetic acid, with subsequent host generation of PAGln and phenylacetylglycine (PAGly) fostering platelet responsiveness and thrombosis potential. Both gain- and loss-of-function studies employing genetic and pharmacological tools reveal PAGln mediates cellular events through G-protein coupled receptors, including α2A, α2B, and β2-adrenergic receptors. PAGln thus represents a new CVD-promoting gut microbiota-dependent metabolite that signals via adrenergic receptors.

Gut microbiota regulates neuropathic pain: potential mechanisms and therapeutic strategy

Neuropathic pain (NP) is a sustained and nonreversible condition characterized by long-term devastating physical and psychological damage. Therefore, it is urgent to identify an effective treatment for NP. Unfortunately, the precise pathogenesis of NP has not been elucidated. Currently, the microbiota-gut-brain axis has drawn increasing attention, and the emerging role of gut microbiota is investigated in numerous diseases including NP. Gut microbiota is considered as a pivotal regulator in immune, neural, endocrine, and metabolic signaling pathways, which participates in forming a complex network to affect the development of NP directly or indirectly. In this review, we conclude the current understanding of preclinical and clinical findings regarding the role of gut microbiota in NP and provide a novel therapeutic method for pain relief by medication and dietary interventions.

The Human Microbial Metabolism of Quercetin in Different Formulations: An In Vitro Evaluation

Quercetin is one of the main dietary flavonols, but its beneficial properties in disease prevention may be limited due to its scarce bioavailability. For this purpose, delivery systems have been designed to enhance both stability and bioavailability of bioactive compounds. This study aimed at investigating the human microbial metabolism of quercetin derived from unformulated and phytosome-formulated quercetin through an in vitro model. Both ingredients were firstly characterized for their profile in native (poly)phenols, and then fermented with human fecal microbiota for 24 h. Quantification of microbial metabolites was performed by ultra-high performance liquid chromatography coupled to mass spectrometry (uHPLC-MSn) analyses. Native quercetin, the main compound in both products, appeared less prone to microbial degradation in the phytosome-formulated version compared to the unformulated one during fecal incubation. Quercetin of both products was bioaccessible to colonic microbiota, resulting in the production of phenylpropanoic acid, phenylacetic acid and benzoic acid derivatives. The extent of the microbial metabolism of quercetin was higher in the unformulated ingredient, in a time-dependent manner. This study opened new perspectives to investigate the role of delivery systems on influencing the microbial metabolism of flavonols in the colonic environment, a pivotal step in the presumed bioactivity associated to their intake.

The Role of Astrocytes in CNS Inflammation

Astrocytes are the most abundant cell type in the central nervous system (CNS), performing complex functions in health and disease. It is now clear that multiple astrocyte subsets or activation states (plastic phenotypes driven by intrinsic and extrinsic cues) can be identified, associated to specific genomic programs and functions. The characterization of these subsets and the mechanisms that control them may provide unique insights into the pathogenesis of neurologic diseases, and identify potential targets for therapeutic intervention. In this article, we provide an overview of the role of astrocytes in CNS inflammation, highlighting recent discoveries on astrocyte subsets and the mechanisms that control them.

Pyridoxal 5'-Phosphate-Dependent Enzymes at the Crossroads of Host-Microbe Tryptophan Metabolism

The chemical processes taking place in humans intersects the myriad of metabolic pathways occurring in commensal microorganisms that colonize the body to generate a complex biochemical network that regulates multiple aspects of human life. The role of tryptophan (Trp) metabolism at the intersection between the host and microbes is increasingly being recognized, and multiple pathways of Trp utilization in either direction have been identified with the production of a wide range of bioactive products. It comes that a dysregulation of Trp metabolism in either the host or the microbes may unbalance the production of metabolites with potential pathological consequences. The ability to redirect the Trp flux to restore a homeostatic production of Trp metabolites may represent a valid therapeutic strategy for a variety of pathological conditions, but identifying metabolic checkpoints that could be exploited to manipulate the Trp metabolic network is still an unmet need. In this review, we put forward the hypothesis that pyridoxal 5′-phosphate (PLP)-dependent enzymes, which regulate multiple pathways of Trp metabolism in both the host and in microbes, might represent critical nodes and that modulating the levels of vitamin B6, from which PLP is derived, might represent a metabolic checkpoint to re-orienteer Trp flux for therapeutic purposes.

Dietary Components, Microbial Metabolites and Human Health: Reading between the Lines

Trillions of bacteria reside in the human gut and they metabolize dietary substances to obtain nutrients and energy while producing metabolites. Therefore, different dietary components could affect human health in various ways through microbial metabolism. Many such metabolites have been shown to affect human physiological activities, including short-chain fatty acids metabolized from carbohydrates; indole, kynurenic acid and para-cresol, metabolized from amino acids; conjugated linoleic acid and linoleic acid, metabolized from lipids. Here, we review the features of these metabolites and summarize the possible molecular mechanisms of their metabolisms by gut microbiota. We discuss the potential roles of these metabolites in health and diseases, and the interactions between host metabolism and the gut microbiota. We also show some of the major dietary patterns around the world and hope this review can provide insights into our eating habits and improve consumers' health conditions.

Altered gut microbiota associated with symptom severity in schizophrenia

BACKGROUND

The gut microbiome and microbiome-gut-brain (MGB) axis have been receiving increasing attention for their role in the regulation of mental behavior and possible biological basis of psychiatric disorders. With the advance of next-generation sequencing technology, characterization of the gut microbiota in schizophrenia (SZ) patients can provide rich clues for the diagnosis and prevention of SZ.

METHODS

In this study, we compared the differences in the fecal microbiota between 82 SZ patients and 80 demographically matched normal controls (NCs) by 16S rRNA sequencing and analyzed the correlations between altered gut microbiota and symptom severity.

RESULTS

The alpha diversity showed no significant differences between the NC and SZ groups, but the beta diversity revealed significant community-level separation in microbiome composition between the two groups (pseudo-F =3.337, p < 0.001, uncorrected). At the phylum level, relatively more Actinobacteria and less Firmicutes (p < 0.05, FDR corrected) were found in the SZ group. At the genus level, the relative abundances of Collinsella, Lactobacillus, Succinivibrio, Mogibacterium, Corynebacterium, undefined Ruminococcus and undefined Eubacterium were significantly increased, whereas the abundances of Adlercreutzia, Anaerostipes, Ruminococcus and Faecalibacterium were decreased in the SZ group compared to the NC group (p < 0.05, FDR corrected). We performed PICRUSt analysis and found that several metabolic pathways differed significantly between the two groups, including the Polyketide sugar unit biosynthesis, Valine, Leucine and Isoleucine biosynthesis, Pantothenate and CoA biosynthesis, C5-Branched dibasic acid metabolism, Phenylpropanoid biosynthesis, Ascorbate and aldarate metabolism, Nucleotide metabolism and Propanoate metabolism pathways (p < 0.05, FDR corrected). Among the SZ group, the abundance of Succinivibrio was positively correlated with the total Positive and Negative Syndrome Scale (PANSS) scores (r = 0.24, p < 0.05, uncorrected) as well as the general PANSS scores (r = 0.22, p < 0.05, uncorrected); Corynebacterium was negatively related to the negative scores of PANSS (r = 0.22, p < 0.05, uncorrected).

CONCLUSIONS

Our findings provided evidence of altered gut microbial composition in SZ group. In addition, we found that Succinvibrio and Corynebacterium were associated with the severity of symptoms for the first time, which may provide some new biomarkers for the diagnosis of SZ.

Beef cattle that respond differently to fescue toxicosis have distinct gastrointestinal tract microbiota

Tall fescue (Lolium arundinaceum) is a widely used forage grass which shares a symbiosis with the endophytic fungus Epichloë coenophiala. The endophyte produces an alkaloid toxin that provides herbivory, heat and drought resistance to the grass, but can cause fescue toxicosis in grazing livestock. Fescue toxicosis can lead to reduced weight gain and milk yields resulting in significant losses to the livestock industry. The objective of this study was to identify bacterial and fungal communities associated with fescue toxicosis tolerance. In this trial, 149 Angus cows across two farms were continuously exposed to toxic, endophyte-infected, fescue for a total of 13 weeks. Of those 149 cows, 40 were classified into either high (HT) or low (LT) tolerance groups according to their growth performance (weight gain). 20 HT and 20 LT cattle balanced by farm were selected for amplicon sequencing to compare the fecal microbiota of the two tolerance groups. This study reveals significantly (q<0.05) different bacterial and fungal microbiota between HT and LT cattle, and indicates that fungal phylotypes may be important for an animal’s response to fescue toxicosis: We found that fungal phylotypes affiliating to the Neocallimastigaceae, which are known to be important fiber-degrading fungi, were consistently more abundant in the HT cattle. Whereas fungal phylotypes related to the genus Thelebolus were more abundant in the LT cattle. This study also found more pronounced shifts in the microbiota in animals receiving higher amounts of the toxin. We identified fungal phylotypes which were consistently more abundant either in HT or LT cattle and may thus be associated with the respective animal’s response to fescue toxicosis. Our results thus suggest that some fungal phylotypes might be involved in mitigating fescue toxicosis.

Determination of Tryptophan Metabolites in Serum and Cerebrospinal Fluid Samples Using Microextraction by Packed Sorbent, Silylation and GC-MS Detection

Indole-containing acids-tryptophan metabolites-found in serum and cerebrospinal fluid (CSF) samples of patients with diseases of the central nervous system (CNS) were determined with the use of microextraction by packed sorbent (MEPS) followed by silylation and gas chromatography-mass spectrometry (GC-MS) analysis. MEPS with the following silylation led to the reproducible formation of derivatives with an unsubstituted hydrogen ion in the indole ring, the chromatographic peaks of which are symmetric and can be used for GC-MS analysis without additional derivatization. The recoveries of analytes at the limit of quantitation (LOQ) levels were 40-80% for pooled CSF and 40-60% for serum. The limit of detection (LOD) and LOQ values were 0.2-0.4 and 0.4-0.5 µM, respectively, for both CSF and serum. The precision (the reproducibility, RSD) value of less than 20% and the accuracy (the relative error, RE) value of less than ±20% at the LOQ concentrations meet the Food and Drug Administration (FDA) recommendations. Linear correlations for all analytes were determined over a potentially clinically significant range of concentrations (0.4-10 µM for serum, R2 ≥ 0.9942, and 0.4-7 µM for CSF, R2 ≥ 0.9949). Moreover, MEPS significantly reduced the matrix effect of serum compared to liquid-liquid extraction (LLE), which was revealed in the example of reducing the amount of cholesterol and its relative compounds.

Caution in studying and interpreting the lupus metabolome

Several metabolomics studies have shed substantial light on the pathophysiological pathways underlying multiple diseases including systemic lupus erythematosus (SLE). This review takes stock of our current understanding of this field. We compare, collate, and investigate the metabolites in SLE patients and healthy volunteers, as gleaned from published metabolomics studies on SLE. In the surveyed primary reports, serum or plasma samples from SLE patients and healthy controls were assayed using mass spectrometry or nuclear magnetic resonance spectroscopy, and metabolites differentiating SLE from controls were identified. Collectively, the circulating metabolome in SLE is characterized by reduced energy substrates from glycolysis, Krebs cycle, fatty acid β oxidation, and glucogenic and ketogenic amino acid metabolism; enhanced activity of the urea cycle; decreased long-chain fatty acids; increased medium-chain and free fatty acids; and augmented peroxidation and inflammation. However, these findings should be interpreted with caution because several of the same metabolic pathways are also significantly influenced by the medications commonly used in SLE patients, common co-morbidities, and other factors including smoking and diet. In particular, whereas the metabolic alterations relating to inflammation, oxidative stress, lipid peroxidation, and glutathione generation do not appear to be steroid-dependent, the other metabolic changes may in part be influenced by steroids. To conclude, metabolomics studies of SLE and other rheumatic diseases ought to factor in the potential contributions of confounders such as medications, co-morbidities, smoking, and diet.

Bacteria-immune cells dialog and the homeostasis of the systems

The dialog between microbes and immune cells is critical for the establishment and maintenance of immune homeostasis. Bacterial-derived metabolites or structural components initiate immune signaling pathways and transcriptional factors, inducing a broad range of specificities and functional repertoires of the immune cells. Conversely, the immune system regulates the composition and function of bacterial communities. Elements of the adaptive immunity, including maternal antibodies and mucosal antibody responses, play crucial roles in protecting the hosts from pathogens in addition to promoting colonization of symbiotic bacteria at mucosal surfaces. The complex interactions set from an early stage in life between the microbiota and adaptive immunity, impact other major physiological systems. In this review, we summarize recent advances in our understanding of how gut bacteria regulate systemic homeostasis by highlighting the finely orchestrated interactions between gut bacteria, immune responses and the nervous system.

Gut microbiota metabolites as integral mediators in cardiovascular diseases (Review)

Cardiovascular diseases (CVDs), such as atherosclerosis, hypertension, myocardial infarction and diabetic heart disease, are associated with high morbidity and mortality rates worldwide, and may also induce multiple organ failure in their later stages, greatly reducing the long-term survival of the patients. There are several causes of CVDs, but after nearly a decade of investigation, researchers have found that CVDs are usually accompanied by an imbalance of gut microbiota and a decreased abundance of flora. More importantly, the metabolites produced by intestinal flora, such as trimethylamine and trimethylamine N-oxide, bile acids, short-chain fatty acids and aromatic amino acids, exert different effects on the occurrence and development of CVDs, as observed in the relevant pathways in the cells, which may either promote or protect against CVD occurrence. It is known that changes in the intestinal flora following antibiotic administration, diet supplementation with probiotics, or exercise, can interfere with the composition of the intestinal flora and may represent an effective approach to preventing or treating CVDs. The focus of this review was the analysis of gut microbiota metabolites to elucidate their effects on CVDs and to identify the most cost-effective and beneficial methods for treating CVDs with minimal side effects.