Circulating levels of the anti-oxidant indoleproprionic acid are associated with higher gut microbiome diversity

Influence of Natural Polysaccharides on Intestinal Microbiota in Inflammatory Bowel Diseases: An Overview

The incidence of inflammatory bowel disease (IBD) has increased in recent years. Considering the potential side effects of conventional drugs, safe and efficient treatment methods for IBD are required urgently. Natural polysaccharides (NPs) have attracted considerable attention as potential therapeutic agents for IBD owing to their high efficiency, low toxicity, and wide range of biological activities. Intestinal microbiota and their fermentative products, mainly short-chain fatty acids (SCFAs), are thought to mediate the effect of NPs in IBDs. This review explores the beneficial effects of NPs on IBD, with a special focus on the role of intestinal microbes. Intestinal microbiota exert alleviation effects via various mechanisms, such as increasing the intestinal immunity, anti-inflammatory activities, and intestinal barrier protection via microbiota-dependent and microbiota-independent strategies. The aim of this paper was to document evidence of NP–intestinal microbiota-associated IBD prevention, which would be helpful for guidance in the treatment and management of IBD.

The Mechanism Underlying the Influence of Indole-3-Propionic Acid: A Relevance to Metabolic Disorders

The increasing prevalence of metabolic syndrome has become a serious public health problem. Certain bacteria-derived metabolites play a key role in maintaining human health by regulating the host metabolism. Recent evidence shows that indole-3-propionic acid content can be used to predict the occurrence and development of metabolic diseases. Supplementing indole-3-propionic acid can effectively improve metabolic disorders and is considered a promising metabolite. Therefore, this article systematically reviews the latest research on indole-3-propionic acid and elaborates its source of metabolism and its association with metabolic diseases. Indole-3-propionic acid can improve blood glucose and increase insulin sensitivity, inhibit liver lipid synthesis and inflammatory factors, correct intestinal microbial disorders, maintain the intestinal barrier, and suppress the intestinal immune response. The study of the mechanism of the metabolic benefits of indole-3-propionic acid is expected to be a potential compound for treating metabolic syndrome.

Analysis of the gut microbiota composition of myostatin mutant cattle prepared using CRISPR/Cas9

Myostatin (MSTN) negatively regulates muscle development and positively regulates metabolism through various pathways. Although MSTN function in cattle has been widely studied, the changes in the gut microbiota due to MSTN mutation, which contribute to host health by regulating its metabolism, remain unclear. Here, high-throughput sequencing of the 16S rRNA gene was conducted to analyze the gut microbiota of wild-type (WT) and MSTN mutant (MT) cattle. A total of 925 operational taxonomic units (OTUs) were obtained, which were classified into 11 phyla and 168 genera. Alpha diversity results showed no significant differences between MT and WT cattle. Beta diversity analyses suggested that the microbial composition of WT and MT cattle was different. Three dominant phyla and 21 dominant genera were identified. The most abundant bacterial genus had a significant relationship with the host metabolism. Moreover, various bacteria beneficial for health were found in the intestines of MT cattle. Analysis of the correlation between dominant gut bacteria and serum metabolic factors affected by MSTN mutation indicated that MSTN mutation affected the metabolism mainly by three metabolism-related bacteria, Ruminococcaceae_UCG-013, Clostridium_sensu_stricto_1, and Ruminococcaceae_UCG-010. This study provides further insight into MSTN mutation regulating the host metabolism by gut microbes and provides evidence for the safety of gene-edited animals.

Taxifolin Alleviates DSS-Induced Ulcerative Colitis by Acting on Gut Microbiome to Produce Butyric Acid

Taxifolin is a bioflavonoid which has been used to treat Inflammatory Bowel Disease. However, taxifolin on DSS-induced colitis and gut health is still unclear. Here, we studied the effect of taxifolin on DSS-induced intestinal mucositis in mice. We measured the degree of intestinal mucosal injury and inflammatory response in DSS treated mice with or without taxifolin administration and studied the changes of fecal metabolites and intestinal microflora using 16S rRNA. The mechanism was further explored by fecal microbiota transplantation. The results showed that the weight loss and diarrhea score of the mice treated with taxifolin decreased in DSS-induced mice and longer colon length was displayed after taxifolin supplementation. Meanwhile, the expression of GPR41 and GPR43 in the colon was significantly increased by taxifolin treatment. Moreover, the expression of TNF-α, IL-1β, and IL-6 in colon tissue was inhibited by taxifolin treatment. The fecal metabolism pattern changed significantly after DSS treatment, which was reversed by taxifolin treatment. Importantly, taxifolin significantly increased the levels of butyric acid and isobutyric acid in the feces of DSS-treated mice. In terms of gut flora, taxifolin reversed the changes of Akkermansia, and further decreased uncultured_bacterium_f_Muribaculaceae. Fecal transplantation from taxifolin-treated mice showed a lower diarrhea score, reduced inflammatory response in the colon, and reduced intestinal mucosal damage, which may be related to the increased level of butyric acid in fecal metabolites. In conclusion, this study provides evidence that taxifolin can ameliorate DSS-induced colitis by altering gut microbiota to increase the production of SCFAs.

Using Machine Learning to Identify Metabolomic Signatures of Pediatric Chronic Kidney Disease Etiology

BACKGROUND

Untargeted plasma metabolomic profiling combined with machine learning (ML) may lead to discovery of metabolic profiles that inform our understanding of pediatric CKD causes. We sought to identify metabolomic signatures in pediatric CKD based on diagnosis: FSGS, obstructive uropathy (OU), aplasia/dysplasia/hypoplasia (A/D/H), and reflux nephropathy (RN).

METHODS

Untargeted metabolomic quantification (GC-MS/LC-MS, Metabolon) was performed on plasma from 702 Chronic Kidney Disease in Children study participants (n: FSGS=63, OU=122, A/D/H=109, and RN=86). Lasso regression was used for feature selection, adjusting for clinical covariates. Four methods were then applied to stratify significance: logistic regression, support vector machine, random forest, and extreme gradient boosting. ML training was performed on 80% total cohort subsets and validated on 20% holdout subsets. Important features were selected based on being significant in at least two of the four modeling approaches. We additionally performed pathway enrichment analysis to identify metabolic subpathways associated with CKD cause.

RESULTS

ML models were evaluated on holdout subsets with receiver-operator and precision-recall area-under-the-curve, F1 score, and Matthews correlation coefficient. ML models outperformed no-skill prediction. Metabolomic profiles were identified based on cause. FSGS was associated with the sphingomyelin-ceramide axis. FSGS was also associated with individual plasmalogen metabolites and the subpathway. OU was associated with gut microbiome-derived histidine metabolites.

CONCLUSION

ML models identified metabolomic signatures based on CKD cause. Using ML techniques in conjunction with traditional biostatistics, we demonstrated that sphingomyelin-ceramide and plasmalogen dysmetabolism are associated with FSGS and that gut microbiome-derived histidine metabolites are associated with OU.

Xenobiotic receptors and the regulation of intestinal homeostasis: harnessing the chemical output of the intestinal microbiota

The commensal bacteria that reside in the gastrointestinal tract exist in a symbiotic relationship with the host, driving the development of the immune system and maintaining metabolic and tissue homeostasis in the local environment. The intestinal microbiota has the capacity to generate a wide array of chemical metabolites to which the cells of the intestinal mucosa are exposed. Host cells express xenobiotic receptors, such as the aryl hydrocarbon receptor (AhR) and the pregnane X receptor (PXR), that can sense and respond to chemicals that are generated by nonhost pathways. In this review, we outline the physiological and immunological processes within the intestinal environment that are regulated by microbial metabolites through the activation of the AhR and the PXR, with a focus on ligands generated by the stepwise catabolism of tryptophan.

Flavonoid-Amyloid Fibril Hybrid Hydrogels for Obesity Control via Construction of Gut Microbiota

Innovative precise clinical approaches to protect humans from the alarming global growth of epidemics of chronic diseases, such as metabolic syndrome (MetS), are urgently needed. Here, we introduce protein hydrogels...

Leveraging the Microbiome for Obesity: Moving From Form to Function

Treatment of obesity, an ongoing global epidemic, is challenging, as weight-loss efforts require a multidisciplinary approach addressing both behavioral and biologic needs that are not completely understood. Recent studies of the gut microbiome may provide better insight into the condition, and ultimately serve to advance more effective therapies. Research in this field has shifted from analyzing microbiome compositional differences to investigating functional changes that affect disease pathophysiology and outcome. Bacteria-derived metabolites are a way to bridge compositional changes to functional consequences. Through the production of metabolites, such as short chain fatty acids, tryptophan derivatives and bile acids, and interactions with peripheral and central signaling pathways, the gut microbiome may alter the body's metabolic and behavioral responses to food. Here, we summarize these mechanisms driven by gut-derived metabolites, through which the microbiome is thought to contribute to obesity, as well as review recent investigations of interventions related to these metabolites. Limitations of existing research, primarily due to paucity of causal studies in humans, are also discussed in this review.

Multi-Omic Approaches to Identify Genetic Factors in Metabolic Syndrome

Metabolic syndrome (MetS) is a highly heritable disease and a major public health burden worldwide. MetS diagnosis criteria are met by the simultaneous presence of any three of the following: high triglycerides, low HDL/high LDL cholesterol, insulin resistance, hypertension, and central obesity. These diseases act synergistically in people suffering from MetS and dramatically increase risk of morbidity and mortality due to stroke and cardiovascular disease, as well as certain cancers. Each of these component features is itself a complex disease, as is MetS. As a genetically complex disease, genetic risk factors for MetS are numerous, but not very powerful individually, often requiring specific environmental stressors for the disease to manifest. When taken together, all sequence variants that contribute to MetS disease risk explain only a fraction of the heritable variance, suggesting additional, novel loci have yet to be discovered. In this article, we will give a brief overview on the genetic concepts needed to interpret genome-wide association studies (GWAS) and quantitative trait locus (QTL) data, summarize the state of the field of MetS physiological genomics, and to introduce tools and resources that can be used by the physiologist to integrate genomics into their own research on MetS and any of its component features. There is a wealth of phenotypic and molecular data in animal models and humans that can be leveraged as outlined in this article. Integrating these multi-omic QTL data for complex diseases such as MetS provides a means to unravel the pathways and mechanisms leading to complex disease and promise for novel treatments. © 2022 American Physiological Society. Compr Physiol 12:1-40, 2022.

Enhanced Intestinal Barriers by Puerarin in Combination with Tryptophan

The intestinal barrier is essential for maintaining human intestinal health. The growing number of studies has shown that both puerarin and tryptophan and its metabolites have a beneficial effect on the intestinal barrier. This study aims at the combination of puerarin and tryptophan or its metabolites for improving the intestinal barrier. In our study, 40 female Sprague-Dawley rats were randomly divided into five groups (n = 8) for a 4-week experiment and dextran sodium sulfate was used to induce an intestinal barrier injury in rats. Our results showed that puerarin combined with tryptophan or its metabolites (indole-3-propionic acid, IPA) improved the intestinal barrier by enhancing the mucus layer barrier, which was mainly achieved by increasing the number of goblet cells and promoting the secretion of MUC2. Both TRPM5 and VAMP8 promoted MUC2 secretion in goblet cells through exocytosis, but their mechanisms of action are different. In our study, we found that puerarin and tryptophan showed different effects on TRPM5 and VAMP8, respectively. Puerarin enhances the expression of TRPM5, and tryptophan inhibits the expression of TRPM5; however, puerarin and tryptophan have no significant effect on the expression of VAMP8.

Association between gut microbiota and elevated serum urate in two independent cohorts

OBJECTIVES

Hyperuricemia is a precursor to gout and is often present in other metabolic diseases that are promoted by microbiome dysbiosis; however, no study has examined the association of gut microbiota with hyperuricemia and serum urate in humans.

METHODS

Study participants were derived from a community-based observational study, the Xiangya Osteoarthritis Study (discovery cohort). Hyperuricemia was defined as the presence of serum urate level >357 μmol/L for women and >416 μmol/L for men. Gut microbiota was analyzed using 16S rRNA sequencing from stool samples. We examined the relation of microbiota dysbiosis (i.e., richness, diversity, composition, and relative abundance of microbiota taxa) and predicted functional pathways to prevalent hyperuricemia and serum urate levels. We verified the associations in an independent observational study, the Step Study (validation cohort).

RESULTS

The discovery cohort consisted of 1,392 rural participants (mean age: 61.3 years; women: 57.4%; hyperuricemia: 17.2%). Participants with hyperuricemia had decreased richness and diversity, altered composition of microbiota, and lower relative abundances of genus Coprococcus compared with those with normouricemia. Predicted Kyoto Encyclopedia of Genes and Genomes metabolism pathways belonged to amino acid and nucleotide metabolisms were significantly altered in individuals with hyperuricemia compared with those with normouricemia. Gut microbiota richness, diversity and low relative abundances of genus Coprococcus were also associated with high levels of serum urate. These findings were replicated in the validation cohort with 480 participants.

CONCLUSIONS

Gut microbiota dysbiosis was associated with elevated serum urate levels. Our study raises the possibility that microbiota dysbiosis may modulate serum urate levels.

Electroacupuncture interventions alleviates myocardial ischemia reperfusion injury through regulating gut microbiota in rats

Electroacupuncture (EA) intervention has a remarkable cardioprotection against myocardial ischemia reperfusion injury (MIRI). Recently, it has been suggested that the gut microbiota plays an important role in regulating the progression and prognosis of MIRI. The purpose of this study was to illustrate the relationship between gut microbiota and cardioprotection of EA on MIRI. We conducted a MIRI model by ligating the left anterior descending coronary artery for 30 min followed by reperfusion in male Sprague Dawley rats, which then received 7 days of EA intervention. Echocardiography was employed to evaluate left ventricular function. Fecal samples were collected for microbial analysis by 16S rDNA high-throughput sequencing. Blood samples and myocardium were collected for inflammatory cytokine detection by enzyme linked immunosorbent assay (ELISA) and Western blot. Hematoxylin & eosin (HE) staining and immunofluorescence of ileum tissue were performed for intestinal damage evaluation. After 7 days of EA intervention, the left ventricular function was improved with significantly increased ejection fraction and fractional shortening. Furthermore, we found that EA intervention reversed the changed gut microbiota induced by MIRI, including Clostridiales, RF39, S24-7, Desulfovibrio, and Allobaculum, improved the impaired gut barrier, reduced the production and circulation of lipopolysaccharide (LPS), inhibited the level of interleukin 6 (IL-6) and interleukin 12 (IL-12) in periphery and decreased the expression of Toll like receptor 4 (TLR4) and IL-6 in myocardium. EA intervention could improve the impaired gut mucosal barrier and reduce the production and circulation of LPS after MIRI through regulating gut microbiota, thus inhibiting the circulation and myocardium inflammation and finally exerted the cardioprotective effect.

Indole-3-Propionic Acid, a Gut-Derived Tryptophan Metabolite, Associates with Hepatic Fibrosis

Background and Aims: Gut microbiota-derived metabolites play a vital role in maintenance of human health and progression of disorders, including obesity and type 2 diabetes (T2D). Indole-3-propionic acid (IPA), a gut-derived tryptophan metabolite, has been recently shown to be lower in individuals with obesity and T2D. IPA’s beneficial effect on liver health has been also explored in rodent and cell models. In this study, we investigated the association of IPA with human liver histology and transcriptomics, and the potential of IPA to reduce hepatic stellate cell activation in vitro. Methods: A total of 233 subjects (72% women; age 48.3 ± 9.3 years; BMI 43.1 ± 5.4 kg/m²) undergoing bariatric surgery with detailed liver histology were included. Circulating IPA levels were measured using LC-MS and liver transcriptomics with total RNA-sequencing. LX-2 cells were used to study hepatoprotective effect of IPA in cells activated by TGF-β1. Results: Circulating IPA levels were found to be lower in individuals with liver fibrosis compared to those without fibrosis (p = 0.039 for all participants; p = 0.013 for 153 individuals without T2D). Accordingly, levels of circulating IPA associated with expression of 278 liver transcripts (p < 0.01) that were enriched for the genes regulating hepatic stellate cells (HSCs) activation and hepatic fibrosis signaling. Our results suggest that IPA may have hepatoprotective potential because it is able to reduce cell adhesion, cell migration and mRNA gene expression of classical markers of HSCs activation in LX-2 cells (all p < 0.05). Conclusion: The association of circulating IPA with liver fibrosis and the ability of IPA to reduce activation of LX-2 cells suggests that IPA may have a therapeutic potential. Further molecular studies are needed to investigate the mechanisms how IPA can ameliorate hepatic fibrosis.

Circulating acetylated polyamines correlate with Covid-19 severity in cancer patients

Cancer patients are particularly susceptible to the development of severe Covid-19, prompting us to investigate the serum metabolome of 204 cancer patients enrolled in the ONCOVID trial. We previously described that the immunosuppressive tryptophan/kynurenine metabolite anthranilic acid correlates with poor prognosis in non-cancer patients. In cancer patients, we observed an elevation of anthranilic acid at baseline (without Covid-19 diagnosis) and no further increase with mild or severe Covid-19. We found that, in cancer patients, Covid-19 severity was associated with the depletion of two bacterial metabolites, indole-3-proprionate and 3-phenylproprionate, that both positively correlated with the levels of several inflammatory cytokines. Most importantly, we observed that the levels of acetylated polyamines (in particular N1-acetylspermidine, N1,N8-diacetylspermidine and N1,N12-diacetylspermine), alone or in aggregate, were elevated in severe Covid-19 cancer patients requiring hospitalization as compared to uninfected cancer patients or cancer patients with mild Covid-19. N1-acetylspermidine and N1,N8-diacetylspermidine were also increased in patients exhibiting prolonged viral shedding (>40 days). An abundant literature indicates that such acetylated polyamines increase in the serum from patients with cancer, cardiovascular disease or neurodegeneration, associated with poor prognosis. Our present work supports the contention that acetylated polyamines are associated with severe Covid-19, both in the general population and in patients with malignant disease. Severe Covid-19 is characterized by a specific metabolomic signature suggestive of the overactivation of spermine/spermidine N1-acetyl transferase-1 (SAT1), which catalyzes the first step of polyamine catabolism.

Indoles as essential mediators in the gut-brain axis. Their role in Alzheimer's disease

Sporadic late-onset Alzheimer's disease (AD) is the most frequent cause of dementia associated with aging. Due to the progressive aging of the population, AD is becoming a healthcare burden of unprecedented proportions. Twenty years ago, it was reported that some indole molecules produced by the gut microbiota possess essential biological activities, including neuroprotection and antioxidant properties. Since then, research has cemented additional characteristics of these substances, including anti-inflammatory, immunoregulatory, and amyloid anti-aggregation features. Herein, we summarize the evidence supporting an integrated hypothesis that some of these substances can influence the age of onset and progression of AD and are central to the symbiotic relationship between intestinal microbes and the brain. Studies have shown that some of these substances' activities result from interactions with biologically conserved pathways and with genetic risk factors for AD. By targeting multiple pathologic mechanisms simultaneously, certain indoles may be excellent candidates to ameliorate neurodegeneration. We propose that management of the microbiota to induce a higher production of neuroprotective indoles (e.g., indole propionic acid) will promote brain health during aging. This area of research represents a new therapeutic paradigm that could add functional years of life to individuals who would otherwise develop dementia.

Metabolomics in Bariatric Surgery: Towards Identification of Mechanisms and Biomarkers of Metabolic Outcomes

Bariatric surgery has been widely performed for the treatment of obesity and type 2 diabetes. Efforts have been made to investigate the mechanisms underlying the metabolic effects achieved by bariatric surgery and to identify candidates who will benefit from this surgery. Metabolomics, which includes comprehensive profiling of metabolites in biological samples, has been utilized for various disease entities to discover pathophysiological metabolic pathways and biomarkers predicting disease progression or prognosis. Over the last decade, metabolomic studies on patients undergoing bariatric surgery have identified significant biomarkers related to metabolic effects. This review describes the significance, progress, and challenges for the future of metabolomics in the area of bariatric surgery.

Mediterranean Diet to Prevent the Development of Colon Diseases: A Meta-Analysis of Gut Microbiota Studies

Gut microbiota dysbiosis is a common feature in colorectal cancer (CRC) and inflammatory bowel diseases (IBD). Adoption of the Mediterranean diet (MD) has been proposed as a therapeutic approach for the prevention of multiple diseases, and one of its mechanisms of action is the modulation of the microbiota. We aimed to determine whether MD can be used as a preventive measure against cancer and inflammation-related diseases of the gut, based on its capacity to modulate the local microbiota. A joint meta-analysis of publicly available 16S data derived from subjects following MD or other diets and from patients with CRC, IBD, or other gut-related diseases was conducted. We observed that the microbiota associated with MD was enriched in bacteria that promote an anti-inflammatory environment but low in taxa with pro-inflammatory properties capable of altering intestinal barrier functions. We found an opposite trend in patients with intestinal diseases, including cancer. Some of these differences were maintained even when MD was compared to healthy controls without a defined diet. Our findings highlight the unique effects of MD on the gut microbiota and suggest that integrating MD principles into a person’s lifestyle may serve as a preventive method against cancer and other gut-related diseases.

Metabolomic Markers of Southern Dietary Patterns in the Jackson Heart Study

SCOPE

New biomarkers are needed that are representative of dietary intake.

METHODS AND RESULTS

We assess metabolites associated with Southern dietary patterns in 1401 Jackson Heart Study participants. Three dietary patterns are empirically derived using principal component analysis: meat and fast food, fish and vegetables, and starchy foods. We randomly select two subsets of the study population: two-third sample for discovery (n = 934) and one-third sample for replication (n = 467). Among the 327 metabolites analyzed, 14 are significantly associated with the meat and fast food dietary pattern, four are significantly associated with the fish and vegetables dietary pattern, and none are associated with the starchy foods dietary pattern in the discovery sample. In the replication sample, nine remain associated with the meat and fast food dietary pattern [indole-3-propanoic acid, C24:0 lysophosphatidylcholine (LPC), N-methyl proline, proline betaine, C34:2 phosphatidylethanolamine (PE) plasmalogen, C36:5 PE plasmalogen, C38:5 PE plasmalogen, cotinine, hydroxyproline] and three remain associated with the fish and vegetables dietary pattern [1,7-dimethyluric acid, C22:6 lysophosphatidylethanolamine, docosahexaenoic acid (DHA)].

CONCLUSION

Twelve metabolites are discovered and replicated in association with dietary patterns detected in a Southern U.S. African-American population, which could be useful as biomarkers of Southern dietary patterns.

A comprehensive review for gut microbes: technologies, interventions, metabolites and diseases

Gut microbes have attracted much more attentions in the recent decade since their essential roles in the development of metabolic diseases, cancer and neurological diseases. Considerable evidence indicates that the metabolism of gut microbes exert influences on intestinal homeostasis and human diseases. Here, we first reviewed two mainstream sequencing technologies involving 16s rRNA sequencing and metagenomic sequencing for gut microbes, and data analysis methods assessing alpha and beta diversity. Next, we introduced some observational studies reflecting that many factors, such as lifestyle and intake of diets, drugs, contribute to gut microbes' quantity and diversity. Then, metabolites produced by gut microbes were presented to understand that gut microbes exert on host homeostasis in the intestinal epithelium and immune system. Finally, we focused on the molecular mechanism of gut microbes on the occurrence and development of several common diseases. In-depth knowledge of the relationship among interventions, gut microbes and diseases might provide new insights in to disease prevention and treatment.

The role of short-chain fatty acids in the interplay between gut microbiota and diet in cardio-metabolic health

The gut microbiota plays an important role in cardio-metabolic diseases with diet being among the strongest modulators of gut microbiota composition and function. Resistant dietary carbohydrates are fermented to short-chain fatty acids (SCFAs) by the gut bacteria. Fiber and omega-3 rich diets increase SCFAs production and abundance of SCFA-producing bacteria. Likewise, SCFAs can improve gut barrier integrity, glucose, and lipid metabolism, regulate the immune system, the inflammatory response, and blood pressure. Therefore, targeting the gut microbiota with dietary strategies leading to increased SCFA production may benefit cardio-metabolic health. In this review, we provide an overview of the association between diet, SCFAs produced by the gut microbiota and cardio-metabolic diseases. We first discuss the association between the human gut microbiota and cardio-metabolic diseases, then investigate the role of SCFAs and finally explore the beneficial effects of specific dietary interventions that can improve cardio-metabolic outcomes through boosting the SCFA production.

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.

Serum metabolites reflecting gut microbiome alpha diversity predict type 2 diabetes

Type 2 diabetes (T2D) is associated with reduced gut microbiome diversity, although the cause is unclear. Metabolites generated by gut microbes also appear to be causative factors in T2D. We therefore searched for serum metabolites predictive of gut microbiome diversity in 1018 females from TwinsUK with concurrent metabolomic profiling and microbiome composition. We generated a Microbial Metabolites Diversity (MMD) score of six circulating metabolites that explained over 18% of the variance in microbiome alpha diversity. Moreover, the MMD score was associated with a significantly lower odds of prevalent (OR[95%CI] = 0.22[0.07;0.70], P = .01) and incident T2D (HR[95%CI] = 0.31[0.11,0.90], P = .03). We replicated our results in 1522 individuals from the ARIC study (prevalent T2D: OR[95%CI] = 0.79[0.64,0.96], P = .02, incident T2D: HR[95%CI] = 0.87[0.79,0.95], P = .003). The MMD score mediated 28%[15%,94%] of the total effect of gut microbiome on T2D after adjusting for confounders. Metabolites predicting higher microbiome diversity included 3-phenylpropionate(hydrocinnamate), indolepropionate, cinnamoylglycine and 5-alpha-pregnan-3beta,20 alpha-diol monosulfate(2) of which indolepropionate and phenylpropionate have already been linked to lower incidence of T2D. Metabolites correlating with lower microbial diversity included glutarate and imidazole propionate, of which the latter has been implicated in insulin resistance. Our results suggest that the effect of gut microbiome diversity on T2D is largely mediated by microbial metabolites, which might be modifiable by diet.

Role of Gut Microbiome and Microbial Metabolites in Alleviating Insulin Resistance After Bariatric Surgery

Insulin resistance (IR) is the most common pathophysiological change in patients with type 2 diabetes mellitus (T2DM). Several recent studies have suggested that the gut microbiome and microbial metabolites are involved in the pathogenesis of IR. Bariatric surgery, as an effective treatment for T2DM, can markedly alleviate IR through mechanisms that have not been elucidated. In this review, we summarize the current evidence on the changes in the gut microbiome and microbial metabolites (including lipopolysaccharide, short-chain fatty acids, branched-chain amino acids, aromatic amino acids, bile acids, methylamines, and indole derivatives) after bariatric surgery. Additionally, we discuss the mechanisms that correlate the changes in microbial metabolites with the postoperative alleviation of IR. Furthermore, we discuss the prospect of bariatric surgery as a treatment for T2DM.

Knockout of the non-essential gene SUGCT creates diet-linked, age-related microbiome disbalance with a diabetes-like metabolic syndrome phenotype

SUGCT (C7orf10) is a mitochondrial enzyme that synthesizes glutaryl-CoA from glutarate in tryptophan and lysine catabolism, but it has not been studied in vivo. Although mutations in Sugct lead to Glutaric Aciduria Type 3 disease in humans, patients remain largely asymptomatic despite high levels of glutarate in the urine. To study the disease mechanism, we generated SugctKO mice and uncovered imbalanced lipid and acylcarnitine metabolism in kidney in addition to changes in the gut microbiome. After SugctKO mice were treated with antibiotics, metabolites were comparable to WT, indicating that the microbiome affects metabolism in SugctKO mice. SUGCT loss of function contributes to gut microbiota dysbiosis, leading to age-dependent pathological changes in kidney, liver, and adipose tissue. This is associated with an obesity-related phenotype that is accompanied by lipid accumulation in kidney and liver, as well as "crown-like" structures in adipocytes. Furthermore, we show that the SugctKO kidney pathology is accelerated and exacerbated by a high-lysine diet. Our study highlights the importance of non-essential genes with no readily detectable early phenotype, but with substantial contributions to the development of age-related pathologies, which result from an interplay between genetic background, microbiome, and diet in the health of mammals.

Connecting the Dots Between Inflammatory Bowel Disease and Metabolic Syndrome: A Focus on Gut-Derived Metabolites

The role of the microbiome in health and disease has gained considerable attention and shed light on the etiology of complex diseases like inflammatory bowel disease (IBD) and metabolic syndrome (MetS). Since the microorganisms inhabiting the gut can confer either protective or harmful signals, understanding the functional network between the gut microbes and the host provides a comprehensive picture of health and disease status. In IBD, disruption of the gut barrier enhances microbe infiltration into the submucosae, which enhances the probability that gut-derived metabolites are translocated from the gut to the liver and pancreas. Considering inflammation and the gut microbiome can trigger intestinal barrier dysfunction, risk factors of metabolic diseases such as insulin resistance may have common roots with IBD. In this review, we focus on the overlap between IBD and MetS, and we explore the role of common metabolites in each disease in an attempt to connect a common origin, the gut microbiome and derived metabolites that affect the gut, liver and pancreas.

Lower gut microbiome diversity and higher abundance of proinflammatory genus Collinsella are associated with biopsy-proven nonalcoholic steatohepatitis

There is increasing evidence for the role of gut microbial composition in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Nonalcoholic steatohepatitis (NASH) is the most serious form of NAFLD where inflammation causes liver damage that can progress to cirrhosis. We have characterized the gut microbiome composition in UK patients with biopsy-proven NASH (n = 65) and compared it to that in healthy controls (n = 76). We report a 7% lower Shannon alpha diversity in NASH patients without cirrhosis (n = 40) compared to controls (p = 2.7x 10^-4) and a 14% drop in NASH patients with cirrhosis (n = 25, p = 5.0x 10^-4). Beta diversity (Unweighted UniFrac distance) was also significantly reduced in both NASH (p = 5.6x 10^-25) and NASH-cirrhosis (p = 8.1x 10^-7) groups. The genus most strongly associated with NASH in this study was Collinsella (0.29% abundance in controls, 3.45% in NASH without cirrhosis (False Discovery Rate (FDR) p = .008), and 4.38% in NASH with cirrhosis (FDR p = .02)). This genus, which has been linked previously to obesity and atherosclerosis, was also positively correlated with fasting levels of triglycerides (p = .01) and total cholesterol (p = 1.2x 10^-4) and negatively correlated with high-density lipoprotein cholesterol (p = 2.8x 10^-6) suggesting that some of the pathways present in this microbial genus may influence lipid metabolism in the host. In patients, we also found decreased abundance of some of the Ruminococcaceae which are known to produce high levels of short-chain fatty acids which can lower inflammation. This may thus contribute to pathology associated with NASH.

The Controversial Role of Human Gut Lachnospiraceae

The complex polymicrobial composition of human gut microbiota plays a key role in health and disease. Lachnospiraceae belong to the core of gut microbiota, colonizing the intestinal lumen from birth and increasing, in terms of species richness and their relative abundances during the host's life. Although, members of Lachnospiraceae are among the main producers of short-chain fatty acids, different taxa of Lachnospiraceae are also associated with different intra- and extraintestinal diseases. Their impact on the host physiology is often inconsistent across different studies. Here, we discuss changes in Lachnospiraceae abundances according to health and disease. With the aim of harnessing Lachnospiraceae to promote human health, we also analyze how nutrients from the host diet can influence their growth and how their metabolites can, in turn, influence host physiology.

Hepatotoxicity and the role of the gut-liver axis in rats after oral administration of titanium dioxide nanoparticles

Background

Due to its excellent physicochemical properties and wide applications in consumer goods, titanium dioxide nanoparticles (TiO₂ NPs) have been increasingly exposed to the environment and the public. However, the health effects of oral exposure of TiO₂ NPs are still controversial. This study aimed to illustrate the hepatotoxicity induced by TiO₂ NPs and the underlying mechanisms. Rats were administered with TiO₂ NPs (29 nm) orally at exposure doses of 0, 2, 10, 50 mg/kg daily for 90 days. Changes in the gut microbiota and hepatic metabolomics were analyzed to explore the role of the gut-liver axis in the hepatotoxicity induced by TiO₂ NPs.

Results

TiO₂ NPs caused slight hepatotoxicity, including clear mitochondrial swelling, after subchronic oral exposure at 50 mg/kg. Liver metabolomics analysis showed that 29 metabolites and two metabolic pathways changed significantly in exposed rats. Glutamate, glutamine, and glutathione were the key metabolites leading the generation of energy-related metabolic disorders and imbalance of oxidation/antioxidation. 16S rDNA sequencing analysis showed that the diversity of gut microbiota in rats increased in a dose-dependent manner. The abundance of Lactobacillus_reuteri increased and the abundance of Romboutsia decreased significantly in feces of TiO₂ NPs-exposed rats, leading to changes of metabolic function of gut microbiota. Lipopolysaccharides (LPS) produced by gut microbiota increased significantly, which may be a key factor in the subsequent liver effects.

Conclusions

TiO₂ NPs could induce slight hepatotoxicity at dose of 50 mg/kg after long-term oral exposure. The indirect pathway of the gut-liver axis, linking liver metabolism and gut microbiota, played an important role in the underlying mechanisms.