Tryptophan: A gut microbiota-derived metabolites regulating inflammation

Recent Advances in Current Uptake Situation, Metabolic and Nutritional Characteristics, Health, and Safety of Dietary Tryptophan

Tryptophan (Trp) is an essential amino acid which is unable to be synthesized in the body. Main sources of Trp are uptake of foods such as oats and bananas. In this review, we describe the status of current dietary consumption, metabolic pathways and nutritional characteristics of Trp, as well as its ingestion and downstream metabolites for maintaining body health and safety. This review also summarizes the recent advances in Trp metabolism, particularly the 5-HT, KYN, and AhR activation pathways, revealing that its endogenous host metabolites are not only differentially affected in the body but also are closely linked to health. More attention should be paid to targeting its specific metabolic pathways and utilizing food molecules and probiotics for manipulating Trp metabolism. However, the complexity of microbiota-host interactions requires further exploration to precisely refine targets for innovating the gut microbiota-targeted diagnostic approaches and informing subsequent studies and targeted treatments of diseases.

MASLD-Related HCC-Update on Pathogenesis and Current Treatment Options

Hepatocellular carcinoma (HCC) is a common complication of chronic liver diseases and remains a relevant cause of cancer-related mortality worldwide. The global prevalence of metabolic dysfunction-associated steatotic liver disease (MASLD) as a risk factor for hepatocarcinogenesis is on the rise. Early detection of HCC has been crucial in improving the survival outcomes of patients with metabolic dysfunction-associated steatohepatitis (MASH), even in the absence of cirrhosis. Understanding how hepatocarcinogenesis develops in MASH is increasingly becoming a current research focus. Additive risk factors such as type 2 diabetes mellitus (T2DM), genetic polymorphisms, and intestinal microbiota may have specific impacts. Pathophysiological and epidemiological associations between MASH and HCC will be discussed in this review. We will additionally review the available tumor therapies concerning their efficacy in MASH-associated HCC treatment.

Postbiotics: An alternative and innovative intervention for the therapy of inflammatory bowel disease

Inflammatory Bowel Disease (IBD) is a persistent gastrointestinal (GI) tract inflammatory disease characterized by downregulated mucosal immune activities and a disrupted microbiota environment in the intestinal lumen. The involvement of bacterium postbiotics as mediators between the immune system and gut microbiome could be critical in determining why host-microbial relationships are disrupted in IBD. Postbiotics including Short-chain fatty acids (SCFAs), Organic acids, Proteins, Vitamins, Bacteriocins, and Tryptophan (Trp) are beneficial bioactive compounds formed via commensal microbiota in the gut environment during the fermentation process that can be used to improve consumer health. The use of metabolites or fragments from microorganisms can be a very attractive treatment and prevention technique in modern medicine. Postbiotics are essential in the immune system's development since they alter the barrier tightness, and the gut ecology and indirectly shape the microbiota's structure. As a result, postbiotics may be beneficial in treating or preventing various diseases, even some for which there is no effective causative medication. Postbiotics may be a promising tool for the treatment of IBD in individuals of all ages, genders, and even geographical locations. Direct distribution of postbiotics may provide a new frontier in microbiome-based therapy for IBD since it allows both the management of host homeostasis and the correction of the negative implications of dysbiosis. Further studies of the biological effects of these metabolites are expected to reveal innovative applications in medicine and beyond. This review attempts to explore the possible postbiotic-based interventions for the treatment of IBD.

Tryptophan alleviates intestinal damage through regulating necroptosis and TLR4/NOD signaling pathways in pigs after lipopolysaccharide challenge

This study aimed to test the hypothesis that necroptosis, toll-like receptor 4 (TLR4)/nucleotide-binding oligomerization domain (NOD) signaling pathway in the jejunum of lipopolysaccharide (LPS)-challenged piglets are involved in the alleviation of intestinal injury and inflammation by tryptophan supplementation. Tryptophan supplementation has improved intestinal morphology. Also, tryptophan has been found to increase the mRNA and protein expression of tight junction proteins and decrease the expression of pro-inflammatory cytokines. Dietary tryptophan decreased the mRNA expression of heat shock protein 70, TLR4, NOD1, NOD2, myeloid differentiation primary response gene 88, interleukin 1 receptor-associated kinase 1, TNF receptor-associated factor 6, receptor-interacting serine/threonine-protein kinase 2-like, nuclear factor-kappaB transcription factor P65 in the jejunum of piglets. Tryptophan alleviated LPS-induced necroptosis and decreased the mRNA expression of mixed lineage kinase domain-like, receptor-interacting serine/threonine kinase 1, receptor-interacting serine/threonine-protein kinase 3-like, Fas (TNFRSF6)-associated via death domain, PGAM family member 5. Collectively, our results suggest that tryptophan supplementation helps in the attenuation of intestinal injury and inflammation by alleviating necroptosis and TLR4/NOD in lipopolysaccharide-challenged pigs.

Effects of Lactobacillus plantarum and Weissella viridescens on the Gut Microbiota and Serum Metabolites of Mice with Antibiotic-Associated Diarrhea

Antibiotic-associated diarrhea (AAD) refers to diarrhea caused by gut microbiota disorders after the use of antibiotics, which seriously threatens the health of humans and animals. Therefore, it is necessary to find an effective therapy to treat AAD. This research aimed to explore the effects of Lactobacillus plantarum H-6 (L. plantarum H-6) and Weissella viridescens J-1 (W. viridescens J-1) on alleviating antibiotic-associated diarrhea induced by lincomycin hydrochloride (LH) in mice. The results show that L. plantarum H-6 could significantly reduce the expression of pro-inflammatory factors such as IL-1β and IL-6 in colon tissue. At the same time, L. plantarum H-6 significantly increased the abundance of Lactobacillus and Akkermansia, decreased the abundance of Bacteroides, and increased the contents of L-tryptophan, LysoPC (20:4 (8Z, 11Z, 14Z, 17Z)), reduced riboflavin, threoninyl-methionine, and N-palmitoyl in serum. However, W. viridescens J-1 had little effect on the treatment of AAD. It can be concluded that L. plantarum H-6 can regulate mice's colonic microbial composition, improve their serum metabolic process, and alleviate antibiotic-associated diarrhea. This research may provide a novel therapeutic option for AAD.

Tumorigenesis in Inflammatory Bowel Disease: Microbiota-Environment Interconnections

Colo-rectal cancer (CRC) is undoubtedly one of the most severe complications of inflammatory bowel diseases (IBD). While sporadic CRC develops from a typical adenoma-carcinoma sequence, IBD-related CRC follows different and less understood pathways and its pathophysiological mechanisms were not completely elucidated. In contrast to chronic inflammation, which is nowadays a well-recognised drive towards neoplastic transformation in IBD, only recently was gut microbiota demonstrated to interfere with both inflammation processes and immune-mediated anticancer surveillance. Moreover, the role of microbiota appears particularly complex and intriguing when also considering its multifaceted interactions with multiple environmental stimuli, notably chronic pathologies such as diabetes and obesity, lifestyle (diet, smoking) and vitamin intake. In this review, we presented a comprehensive overview on current evidence of the influence of gut microbiota on IBD-related CRC, in particular its mutual interconnections with the environment.

A critical review on inflammatory bowel diseases risk factors, dietary nutrients regulation and protective pathways based on gut microbiota during recent 5 years

The treatment of inflammatory bowel diseases (IBDs) has become a worldwide problem. Intestinal flora plays an important role in the development and progression of IBDs. Various risk factors (psychology, living habits, dietary patterns, environment) influence the structure and composition of the gut microbiota and contribute to the susceptibility to IBDs. This review aims to provide a comprehensive overview on risk factors regulating intestinal microenvironment which was contributed to IBDs. Five protective pathways related to intestinal flora were also discussed. We hope to provide systemic and comprehensive insights of IBDs treatment and to offer theoretical guidance for personalized patients with precision nutrition.

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

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

Gut microbial response to host metabolic phenotypes

A large number of studies have proved that biological metabolic phenotypes exist objectively and are gradually recognized by humans. Gut microbes affect the host's metabolic phenotype. They directly or indirectly participate in host metabolism, physiology and immunity through changes in population structure, metabolite differences, signal transduction and gene expression. Obtaining comprehensive information and specific identification factors associated with gut microbiota and host metabolic phenotypes has become the focus of research in the field of gut microbes, and it has become possible to find new and effective ways to prevent or treat host metabolic diseases. In the future, precise treatment of gut microbes will become one of the new therapeutic strategies. This article reviews the content of gut microbes and carbohydrate, amino acid, lipid and nucleic acid metabolic phenotypes, including metabolic intermediates, mechanisms of action, latest research findings and treatment strategies, which will help to understand the relationship between gut microbes and host metabolic phenotypes and the current research status.

Oral supplementation with selected Lactobacillus acidophilus triggers IL-17-dependent innate defense response, activation of innate lymphoid cells type 3 and improves colitis

Live biotherapeutic products constitute an emerging therapeutic approach to prevent or treat inflammatory bowel diseases. Lactobacillus acidophilus is a constituent of the human microbiota with probiotic potential, that is illustrated by improvement of intestinal inflammation and antimicrobial activity against several pathogens. In this study, we evaluated the immunomodulatory properties of the L. acidophilus strain BIO5768 at steady state and upon acute inflammation. Supplementation of naïve mice with BIO5768 heightened the transcript level of some IL-17 target genes encoding for protein with microbicidal activity independently of NOD2 signaling. Of these, the BIO5768-induced expression of Angiogenin-4 was blunted in monocolonized mice that are deficient for the receptor of IL-17 (but not for NOD2). Interestingly, priming of bone marrow derived dendritic cells by BIO5768 enhanced their ability to support the secretion of IL-17 by CD4⁺ T cells. Equally of importance, the production of IL-22 by type 3 innate lymphoid cells is concomitantly heightened in response to BIO5768. When administered alone or in combination with Bifidobacterium animalis spp. lactis BIO5764 and Limosilactobacillus reuteri, BIO5768 was able to alleviate at least partially intestinal inflammation induced by Citrobacter rodentium infection. Furthermore, BIO5768 was also able to improve colitis induced by 2,4,6-trinitrobenzene sulfonic acid (TNBS). In conclusion, we identify a new potential probiotic strain for the management of inflammatory bowel diseases, and provide some insights into its IL-17-dependent and independent mode of action.

Integrated Analysis of the Alterations in Gut Microbiota and Metabolites of Mice Induced After Long-Term Intervention With Different Antibiotics

Objectives

We aimed to study the effect of antibiotic-induced disruption of gut microbiome on host metabolomes and inflammatory responses after long-term use of antibiotics.

Methods

A total of three groups of 3-week-old female C57BL/6 mice (n = 44) were continuously treated with vancomycin (VAN), polymyxin B (PMB), or water, respectively, for up to 28 weeks. Fecal samples collected at different time points were analyzed by bacterial 16S rRNA gene sequencing and untargeted metabolomics by ultraperformance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC Q-TOF MS). Serum cytokines (IFN-γ, IL-2, IL-10, IL-13, IL-17A, and TNF-α) were determined by multiplex immunoassay.

Results

Treatment by VAN or PMB did not affect the average body weight of mice. However, a heavier caecum observed in VAN-treated mice. Compared with PMB-treated and control mice, VAN treatment induced more rapid dysbiosis of gut microbiota and dysmetabolism. Instead of Bacteroides, VAN-treated mice had a compositional shift to Proteobacteria and its species Escherichia coli and Verrucomicrobia and its species Akkermansia muciniphila. The shift was accompanied by decreased richness and diversity in microbiota. PMB-treated mice had an increased Firmicutes, and the diversity was shortly increased and further decreased to the baseline. Decreased levels of short-chain and long-chain fatty acids, bile acids, L-arginine, dopamine, L-tyrosine, and phosphatidylcholine (all p < 0.05) were observed in VAN-treated mice. In contrast, significantly increased levels of amino acids including L-aspartic acid, beta-alanine, 5-hydroxy-L-tryptophan, L-glutamic acid, and lysophosphatidylcholines (all p < 0.05) were found. These changes occurred after 3-week treatment and remained unchanged up to 28 weeks. For PMB-treated mice, metabolites involved in the metabolic pathway of vitamin B6 were decreased, whereas glycocholic acid and chenodeoxycholic acid were increased (all p < 0.05). After 8-week treatment, VAN-treated mice had significantly higher levels of serum IFN-γ, IL-13, and IL-17A, and PMB-treated mice had higher levels of IL-13 and IL-17 compared to control mice. At 28-week treatment, only IL-17A remained high in PMB-treated mice.

Conclusion

This study showed that the antibiotic-induced alterations in gut microbiota contribute to host inflammatory responses through the change in metabolic status, which are likely related to the type, rather than timing of antibiotic used.

Integrated Analysis Reveals the Targets and Mechanisms in Immunosuppressive Effect of Mesalazine on Ulcerative Colitis

Background

Ulcerative colitis (UC) is an inflammatory bowel disease that causes inflammation and ulcers in the digestive tract. Approximately 3 million US adults suffer from this disease. Mesalazine, an anti-inflammatory agent, is commonly used for the treatment of UC. However, some studies have demonstrated side effects of mesalazine, such as acute pancreatitis and hypereosinophilia. Therefore, a better understanding of the anti-inflammatory mechanism of mesalazine in UC could help improve the effectiveness of the drug and reduce its side effects. In this study, we used a dextran sodium sulfate-induced UC mouse model, and applied network pharmacology and omics bioinformatics approaches to uncover the potential pharmaceutical targets and the anti-inflammatory mechanism of mesalazine.

Results

Network pharmacology analysis identified the core targets of mesalazine, biological processes, and cell signaling related to immunity and inflammatory responses mediated by mesalazine. Molecular docking analysis then indicated possible binding motifs on the core targets (including TNF-α, PTGS2, IL-1β, and EGFR). Metabolomics and 16S metagenomic analyses highlighted the correlation between gut microbiota and metabolite changes caused by mesalazine in the UC model.

Conclusions

Collectively, the omics and bioinformatics approaches and the experimental data unveiled the detailed molecular mechanisms of mesalazine in UC treatment, functional regulation of the gut immune system, and reduction of intestinal inflammation. More importantly, the identified core targets could be targeted for the treatment of UC.

Ginsenoside Rg1 Alleviates Acute Ulcerative Colitis by Modulating Gut Microbiota and Microbial Tryptophan Metabolism

Ulcerative colitis (UC) is a chronic and recurrent inflammatory disorder in the gastrointestinal tract. Here, we examined the pharmacological effects of ginsenoside Rg1, a natural compound with low bioavailability, on the acute experimental colitis mice induced by dextran sulfate sodium (DSS) and explored underlying mechanisms. Acute UC was induced in C57BL/6 mice by 2.5% DSS for 7 days, meanwhile, 2 mg/10 g b.w. ginsenoside Rg1 was administrated to treat the mice. Body weight, colon length, colon tissue pathology, and colon tissue inflammatory cytokines were assessed. The composition structure of gut microbiota was profiled using 16s rRNA sequencing. Global metabolomic profiling of the feces was performed, and tryptophan and its metabolites in the serum were detected. The results showed that Rg1 significantly ameliorated DSS-induced colonic injury and colonic inflammation. In addition, Rg1 also partly reversed the imbalance of gut microbiota composition caused by DSS. Rg1 intervention can regulate various metabolic pathways of gut microbiota such as valine, leucine, and isoleucine biosynthesis and vitamin B6 metabolism and the most prominent metabolic alteration was tryptophan metabolism. DSS decreased the levels of tryptophan metabolites in the serum, including indole-3-carboxaldehyde, indole-3-lactic acid, 3-indolepropionic acid, and niacinamide and Rg1 can increase the levels of these metabolites. In conclusion, the study discovered that Rg1 can protect the intestinal barrier and alleviate colon inflammation in UC mice, and the underlying mechanism is closely related to the regulation of gut microbiota composition and microbial tryptophan metabolism.

Role of metabolites derived from gut microbiota in inflammatory bowel disease

Over the past two decades, it is improved gut microbiota plays an important role in the health and disease pathogenesis. Metabolites, small molecules produced as intermediate or end products of microbial metabolism, is considered as one of the major interaction way for gut microbiota with the host. Bacterial metabolisms of dietary substrates, modification of host molecules or bacteria are the major source of metabolites. Signals from microbial metabolites affect immune maturation and homeostasis, host energy metabolism as well as mucosal integrity maintenance. Based on many researches, the composition and function of the microbiota can be changed, which is also seen in the metabolite profiles of patients with inflammatory bowel disease (IBD). Additionally, some specific classes of metabolites also can trigger IBD. In this paper, definition of the key classes of microbial-derived metabolites which are changed in IBD, description of the pathophysiological basis of association and identification of the precision therapeutic modulation in the future are the major contents.

Role of metabolites derived from gut microbiota in inflammatory bowel disease

Over the past two decades, it is improved gut microbiota plays an important role in the health and disease pathogenesis. Metabolites, small molecules produced as intermediate or end products of microbial metabolism, is considered as one of the major interaction way for gut microbiota with the host. Bacterial metabolisms of dietary substrates, modification of host molecules or bacteria are the major source of metabolites. Signals from microbial metabolites affect immune maturation and homeostasis, host energy metabolism as well as mucosal integrity maintenance. Based on many researches, the composition and function of the microbiota can be changed, which is also seen in the metabolite profiles of patients with inflammatory bowel disease (IBD). Additionally, some specific classes of metabolites also can trigger IBD. In this paper, definition of the key classes of microbial-derived metabolites which are changed in IBD, description of the pathophysiological basis of association and identification of the precision therapeutic modulation in the future are the major contents.

Metabolic reprogramming in a slowly developing orthologous model of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited kidney disease and affects 1 in 1,000 individuals. There is accumulating evidence suggesting that there are shared cellular mechanisms responsible for cystogenesis in human and murine PKD and that reprogramming of metabolism is a key disease feature. In this study, we used a targeted metabolomics approach in an orthologous mouse model of PKD (Pkd1RC/RC) to investigate the metabolic modifications a cystic kidney undergoes during disease progression. Using the Kyoto Encyclopedia of Genes and Genomes pathway database, we identified several biologically relevant metabolic pathways that were altered early in this disease (in 3-mo-old Pkd1RC/RC mice), the most highly represented being arginine biosynthesis and metabolism and tryptophan and phenylalanine metabolism. During the next 6 mo of disease progression, multiple uremic solutes accumulated in the kidney of cystic mice, including several established markers of oxidative stress and endothelial dysfunction (allantoin, asymmetric dimethylarginine, homocysteine, malondialdehyde, methionine sulfoxide, and S-adenosylhomocysteine). Levels of kynurenines and polyamines were also augmented in kidneys of Pkd1RC/RC versus wild-type mice, as were the levels of bacteria-produced indoles, whose increase within PKD kidneys suggests microbial dysbiosis. In summary, we confirmed previously published and identified novel metabolic markers and pathways of PKD progression that may prove helpful for diagnosis and monitoring of cystic kidney disease in patients. Furthermore, they provide targets for novel therapeutic approaches that deserve further study and hint toward currently understudied pathomechanisms.NEW & NOTEWORTHY This report delineates the evolution of metabolic changes occurring during autosomal dominant polycystic kidney disease (ADPKD) progression. Using an orthologous model, we performed kidney metabolomics and confirmed dysregulation of metabolic pathways previously found altered in nonorthologous or rapidly-progressive PKD models. Importantly, we identified novel alterations, including augmentation of kynurenines, polyamines, and indoles, suggesting increased inflammation and microbial dysbiosis that provide insights into PKD pathomechanisms and may prove helpful for diagnosing, monitoring, and treating ADPKD.

Tryptophan Ameliorates Barrier Integrity and Alleviates the Inflammatory Response to Enterotoxigenic Escherichia coli K88 Through the CaSR/Rac1/PLC-γ1 Signaling Pathway in Porcine Intestinal Epithelial Cells

Background

Impaired intestinal barrier integrity plays a crucial role in the development of many diseases such as obesity, inflammatory bowel disease, and type 2 diabetes. Thus, protecting the intestinal barrier from pathological disruption is of great significance. Tryptophan can increase gut barrier integrity, enhance intestinal absorption, and decrease intestinal inflammation. However, the mechanism of tryptophan in decreasing intestinal barrier damage and inflammatory response remains largely unknown. The objective of this study was to test the hypothesis that tryptophan can enhance intestinal epithelial barrier integrity and decrease inflammatory response mediated by the calcium-sensing receptor (CaSR)/Ras-related C3 botulinum toxin substrate 1 (Rac1)/phospholipase Cγ1 (PLC-γ1) signaling pathway.

Methods

IPEC-J2 cells were treated with or without enterotoxigenic Escherichia coli (ETEC) K88 in the absence or presence of tryptophan, CaSR inhibitor (NPS-2143), wild-type CaSR overexpression (pcDNA3.1-CaSR-WT), Rac1-siRNA, and PLC-γ1-siRNA.

Results

The results showed that ETEC K88 decreased the protein concentration of occludin, zonula occludens-1 (ZO-1), claudin-1, CaSR, total Rac1, Rho family member 1 of porcine GTP-binding protein (GTP-rac1), phosphorylated phospholipase Cγ1 (p-PLC-γ1), and inositol triphosphate (IP3); suppressed the transepithelial electrical resistance (TEER); and enhanced the permeability of FITC-dextran compared with the control group. Compared with the control group, 0.7 mM tryptophan increased the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; elevated the TEER; and decreased the permeability of FITC-dextran and contents of interleukin-8 (IL-8) and TNF-α. However, 0.7 mM tryptophan+ETEC K88 reversed the effects induced by 0.7 mM tryptophan alone. Rac1-siRNA+tryptophan+ETEC K88 or PLC-γ1-siRNA+tryptophan+ETEC K88 reduced the TEER, increased the permeability of FITC-dextran, and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. NPS2143+tryptophan+ETEC K88 decreased the TEER and the protein concentration of CaSR, total Rac1, GTP-rac1, p-PLC-γ1, ZO-1, claudin-1, occludin, and IP3; increased the permeability of FITC-dextran; and improved the contents of IL-8 and TNF-α compared with tryptophan+ETEC K88. pcDNA3.1-CaSR-WT+Rac1-siRNA+ETEC K88 and pcDNA3.1-CaSR-WT+PLC-γ1-siRNA+ETEC K88 decreased the TEER and enhanced the permeability in porcine intestine epithelial cells compared with pcDNA3.1-CaSR-WT+ETEC K88.

Conclusion

Tryptophan can improve intestinal epithelial barrier integrity and decrease inflammatory response through the CaSR/Rac1/PLC-γ1 signaling pathway.

Cross Talk between Gut Microbiota and Intestinal Mucosal Immunity in the Development of Ulcerative Colitis

Ulcerative colitis (UC), a nonspecific inflammatory disease, is characterized by inflammation and mucosal damage in the colon, and its prevalence in the world is increasing. Nevertheless, the exact pathogenesis of UC is still unclear. Accumulating data have suggested that its pathogenesis is multifactorial, involving genetic predisposition, environmental factors, microbial dysbiosis, and dysregulated immune responses. Generally, UC is aroused by inappropriate immune activation based on the interaction of host and intestinal microbiota. The relationship between microbiota and host immune system in the pathogenesis of UC is complicated. However, increasing evidence indicates that the shift of microbiota composition can substantially influence intestinal immunity. In this review, we primarily focus on the delicate balance between microbiota and gut mucosal immunity during UC progression.

The Intestinal Microbiota: Impacts of Antibiotics Therapy, Colonization Resistance, and Diseases

Trillions of microbes exist in the human body, particularly the gastrointestinal tract, coevolved with the host in a mutually beneficial relationship. The main role of the intestinal microbiome is the fermentation of non-digestible substrates and increased growth of beneficial microbes that produce key antimicrobial metabolites such as short-chain fatty acids, etc., to inhibit the growth of pathogenic microbes besides other functions. Intestinal microbiota can prevent pathogen colonization through the mechanism of colonization resistance. A wide range of resistomes are present in both beneficial and pathogenic microbes. Giving antibiotic exposure to the intestinal microbiome (both beneficial and hostile) can trigger a resistome response, affecting colonization resistance. The following review provides a mechanistic overview of the intestinal microbiome and the impacts of antibiotic therapy on pathogen colonization and diseases. Further, we also discuss the epidemiology of immunocompromised patients who are at high risk for nosocomial infections, colonization and decolonization of multi-drug resistant organisms in the intestine, and the direct and indirect mechanisms that govern colonization resistance to the pathogens.

Gene Polymorphisms of NOD2, IL23R, PTPN2 and ATG16L1 in Patients with Crohn's Disease: On the Way to Personalized Medicine?

Genetic and environmental factors are involved in the pathogenesis of inflammatory bowel diseases (IBD). The study aimed at investigating the potential influence of single nucleotide polymorphisms (SNPs) NOD2 rs2066844, NOD2 rs2066845, NOD2 rs2066847, IL23R rs11209026, PTPN2 rs2542151, PTPN2 rs7234029, and ATG16L1 rs2241880 on the response to immunomodulatory therapies and disease course in Crohn’s disease (CD). This is an uncontrolled retrospective monocentric study including patients from the IBD outpatient clinic of Heidelberg University Hospital. Therapy responses and disease courses were related to genetic findings. 379 patients with CD were included. The presence of at least one PTPN2 rs7234029 risk allele was associated with nonresponse to anti-interleukin-12/23 treatment (89.9% vs. 67.6%, p = 0.005). The NOD2 rs2066844 risk allele was associated with a first-degree family history of colon cancer (12.7% vs. 4.7%, p = 0.02), the ATG16L1 rs2241880 risk allele with ileal CD manifestation (p = 0.027), and the IL23R rs11209026 risk allele with a higher rate of CD-related surgeries per disease year (0.08 vs. 0.02, p = 0.025). The results of this study underline the relevance of genetic influences in CD. The association of the PTPN2 rs7234029 risk allele with nonresponse to anti-interleukin-12/23 treatment in CD patients is a novel finding and requires further investigation.

Microbiota, renal disease and renal transplantation

Aim of this frontier review has been to highlight the role of microbiota in healthy subjects and in patients affected by renal diseases with particular reference to renal transplantation. The microbiota has a relevant role in conditioning the healthy status and the diseases. In particular gut microbiota is essential in the metabolism of food and has a relevant role for its relationship with the immune system. The indigenous microbiota in patients with chronic renal failure is completely different than that of the healthy subjects and pathobionts appear. This abnormality in microbiota composition is called dysbiosis and may cause a rapid deterioration of the renal function both for activating the immune system and producing large quantity of uremic toxins. Similarly, after renal trans-plantation the microbiota changes with the appearance of pathobionts, principally in the first period because of the assumption of immunosuppressive drugs and antibiotics. These changes may deeply interfere with the graft outcome causing acute rejection, renal infections, diarrhea, and renal interstitial fibrosis. In addition, change in the microbiota may modify the metabolism of immuno-suppressive drugs causing in some patients the need of modifying the immunosuppressant dosing. The restoration of the indigenous microbiota after transplantation is important, either to avoiding the complications that impair the normal renal graft, and because recent studies have documented the role of an indigenous microbiota in inducing tolerance towards the graft. The use of prebiotics, probiotics, smart bacteria and diet modification may restore the indigenous microbiota, but these studies are just at their beginning and more data are needed to draw definitive conclusions.

Effects of incremental exercise and dietary tryptophan supplementation on the amino acid metabolism, serotonin status, stool quality, fecal metabolites, and body composition of mid-distance training sled dogs

Exercise improves the health of dogs; however, the extreme exertion experienced by sled dogs may lead to variable metabolic and fecal characteristics. Nutritional interventions, such as dietary tryptophan (Trp), may reduce the prevalence of these exercise-induced disturbances. Sporting diets tend to have high crude protein concentrations in contrast to adult maintenance diets and this results in less Trp relative to other amino acids (AA). Therefore, sporting dogs represent an ideal cohort to assess the effects of supplemental Trp. The objective was to evaluate the effects of supplemental dietary Trp and an incremental training regimen on AA and serotonin status, fecal scores and metabolites, and body composition in client-owned Siberian huskies. Sixteen dogs (nine females and seven males) were used, with a mean age of 4.8 ± 2.5 yr and body weight (BW) of 24.3 ± 4.3 kg. Dogs were blocked for sex, age, and BW and randomly allocated into two groups with eight fed a dry extruded control diet (Ctl) and eight fed Ctl supplemented with Trp to reach a Trp:large-neutral AA (LNAA) ratio of 0.075:1 (treatment, Trt). The exercise regimen was designed to increase in distance each week, but weather played a role in setting the daily distance. Each week BW was recorded and food allotments were adjusted to maintain initial BW. Pre and post-exercise blood samples were taken every 3 wk, dogs then received a meal followed by 1, 2, and 4 h post meal blood collections (serum AA, serotonin). Stool collection and scoring occurred each week and body composition was measured on weeks -1 and 11. Serotonin, AA, fecal metabolite, and body composition data were analyzed using PROC MIXED of SAS with dog as a random effect and week and Trt as fixed effects. Stool score data were analyzed using PROC FREQ to compare stool score and Trt, and PROC CORR was used to analyze associations between fecal score, temperature, humidity, and run distance. Dogs on Trt had greater fasted Trp compared with baseline, greater post-meal Trp and serotonin compared with baseline, greater post-meal Trp compared with fasted, and greater post-meal Trp and serotonin compared with Ctl (P < 0.05). Fecal data indicated that Trp improved stool scores (P < 0.05) yet had no effect on fecal metabolites. An overall increase in lean and decrease in fat mass was found (P < 0.05), but Trt had no effect on body composition. Optimization of the dietary Trp:LNAA ratio may help to improve GI health without compromising performance in actively training sled dogs.

Tryptophan Metabolism, Regulatory T Cells, and Inflammatory Bowel Disease: A Mini Review

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder of the gastrointestinal tract resulting from the homeostasis imbalance of intestinal microenvironment, immune dysfunction, environmental and genetic factors, and so on. This disease is associated with multiple immune cells including regulatory T cells (Tregs). Tregs are a subset of T cells regulating the function of various immune cells to induce immune tolerance and maintain intestinal immune homeostasis. Tregs are correlated with the initiation and progression of IBD; therefore, strategies that affect the differentiation and function of Tregs may be promising for the prevention of IBD-associated pathology. It is worth noting that tryptophan (Trp) metabolism is effective in inducing the differentiation of Tregs through microbiota-mediated degradation and kynurenine pathway (KP), which is important for maintaining the function of Tregs. Interestingly, patients with IBD show Trp metabolism disorder in the pathological process, including changes in the concentrations of Trp and its metabolites and alteration in the activities of related catalytic enzymes. Thus, manipulation of Treg differentiation through Trp metabolism may provide a potential target for prevention of IBD. The purpose of this review is to highlight the relationship between Trp metabolism and Treg differentiation and the role of this interaction in the pathogenesis of IBD.

Evodiamine has therapeutic efficacy in ulcerative colitis by increasing Lactobacillus acidophilus levels and acetate production

Emerging evidence implicates gut microbiota have an important role in ulcerative colitis (UC). Previous study indicated that Evodiamine (EVO) can alleviate colitis through downregulating inflammatory pathways. However, specific relationship between EVO-treated colitis relief and regulation of gut microbiota is still unclear. Here, our goal was to determine the potential role of gut microbiota in the relief of UC by EVO. By using pathology-related indicators, 16S rRNA sequencing and metabolomics profiling, we assessed the pharmacological effect of EVO on dextran sulfate sodium (DSS)-induced colitis rats as well as on the change of gut microbiota and metabolism. Fecal derived from EVO-treated rats was transplanted into colitis rats to verify the effect of EVO on gut microbiota, and 'driver bacteria' was found and validated by 16S rRNA sequencing, metagenome and qRT-PCR. The effect of Lactobacillus acidophilus (L. acidophilus) was investigated by vivo experiment, microbiota analysis, Short-chain fatty acids (SCFAs) quantification and colon transcriptomics. EVO reduced the susceptibility to DSS-induced destruction of epithelial integrity and severe inflammatory response, and regulated the gut microbiota and metabolites. Fecal Microbiota Transplantation (FMT) alleviated DSS-induced colitis, increased the abundance of L. acidophilus and the level of acetate. Furthermore, gavaged with L. acidophilus reduced pro-inflammatory cytokines, promoted the increase of goblet cells and the secretion of antimicrobial peptides, regulated the ratio of Firmicutes/Bacteroidetes and increased the level of acetate. Our results indicated that EVO mitigation of DSS-induced colitis is associated with increased in L. acidophilus and protective acetate production, which may be a promising strategy for treating UC.

The impact of maternal and early life malnutrition on health: a diet-microbe perspective

BACKGROUND

Early-life malnutrition may have long-lasting effects on microbe-host interactions that affect health and disease susceptibility later in life. Diet quality and quantity in conjunction with toxin and pathogen exposure are key contributors to microbe-host physiology and malnutrition. Consequently, it is important to consider both diet- and microbe-induced pathologies as well as their interactions underlying malnutrition.

MAIN BODY

Gastrointestinal immunity and digestive function are vital to maintain a symbiotic relationship between the host and microbiota. Childhood malnutrition can be impacted by numerous factors including gestational malnutrition, early life antibiotic use, psychological stress, food allergy, hygiene, and exposure to other chemicals and pollutants. These factors can contribute to reoccurring environmental enteropathy, a condition characterized by the expansion of commensal pathobionts and environmental pathogens. Reoccurring intestinal dysfunction, particularly during the critical window of development, may be a consequence of diet-microbe interactions and may lead to life-long immune and metabolic programming and increased disease risk. We provide an overview of the some key factors implicated in the progression of malnutrition (protein, fat, carbohydrate, iron, vitamin D, and vitamin B12) and discuss the microbiota during early life that may contribute health risk later in life.

CONCLUSION

Identifying key microbe-host interactions, particularly those associated with diet and malnutrition requires well-controlled dietary studies. Furthering our understanding of diet-microbe-host interactions will help to provide better strategies during gestation and early life to promote health later in life.

From IBS to ME - The dysbiotic march hypothesis

Irritable bowel syndrome (IBS) is often associated with other unexplained complaints like chronic fatigue syndrome (CFS), fibromyalgia and myalgic encephalopathy (ME). The pathogenesis of the relationship is unknown. Intestinal dysbiosis may be a common abnormality, but based on 1100 consecutive IBS patients examined over a nine years period, we hypothesize that the development of the disease, often from IBS to ME, actually manifests a "dysbiotic march". In analogy with "the atopic march" in allergic diseases, we suggest "a dysbiotic march" in IBS; initiated by extensive use of antibiotics during childhood, often before school age. Various abdominal complaints including IBS may develop soon thereafter, while systemic symptom like CFS, fibromyalgia and ME may appear years later.

Unique and specific Proteobacteria diversity in urinary microbiota of tolerant kidney transplanted recipients

Host-microbiota interactions can modulate the immune system both at local and systemic levels, with potential consequences for organ transplantation outcomes. In this study, we hypothesized that differences in the urinary microbiome following kidney transplantation would be associated with posttransplantation status: stable, minimally immunosuppressed, or tolerant. One hundred thirteen urine samples from stable (n = 51), minimally immunosuppressed (n = 19), and spontaneously tolerant (n = 16) patients, paired with age-matched controls (n = 27) were profiled and compared to each other at a taxonomic level with special interest in the immunosuppressive regimen. All comparisons and correlations were adjusted on sex and time posttransplantation. Our results highlighted a unique and specific urinary microbiota associated with spontaneous tolerance characterized by a high diversity and a clear Proteobacteria profile. Finally, we report that this profile is (1) impacted by gender, (2) inversely correlated with immunosuppressive drugs (calcineurin inhibitors and mammalian target of rapamycin inhibitors), and (3) stable in time.

Increased expression of kynurenine aminotransferases mRNA in lymphocytes of patients with inflammatory bowel disease

BACKGROUND

Complex interaction of genetic defects with environmental factors seems to play a substantial role in the pathogenesis of inflammatory bowel disease (IBD). Accumulating data implicate a potential role of disturbed tryptophan metabolism in IBD. Kynurenic acid (KYNA), a derivative of tryptophan (TRP) along the kynurenine (KYN) pathway, displays cytoprotective and immunomodulating properties, whereas 3-OH-KYN is a cytotoxic compound, generating free radicals.

METHODS

The expression of lymphocytic mRNA encoding enzymes synthesizing KYNA (KAT I-III) and serum levels of TRP and its metabolites were evaluated in 55 patients with IBD, during remission or relapse [27 patients with ulcerative colitis (UC) and 28 patients with Crohn's disease (CD)] and in 50 control individuals.

RESULTS

The increased expression of KAT1 and KAT3 mRNA characterized the entire cohorts of patients with UC and CD, as well as relapse-remission subsets. Expression of KAT2 mRNA was enhanced in patients with UC and in patients with CD in remission. In the entire cohorts of UC or CD, TRP levels were lower, whereas KYN, KYNA and 3-OH-KYN were not altered. When analysed in subsets of patients with UC and CD (active phase-remission), KYNA level was significantly lower during remission than relapse, yet not versus control. Functionally, in the whole groups of patients with UC or CD, the TRP/KYN ratio has been lower than control, whereas KYN/KYNA and KYNA/3-OH-KYN ratios were not altered. The ratio KYN/3-OH-KYN increased approximately two-fold among all patients with CD; furthermore, patients with CD with relapse, manifested a significantly higher KYNA/3-OH-KYN ratio than patients in remission.

CONCLUSION

The presented data indicate that IBD is associated with an enhanced expression of genes encoding KYNA biosynthetic enzymes in lymphocytes; however, additional mechanisms appear to influence KYNA levels. Higher metabolic conversion of serum TRP in IBD seems to be followed by the functional shift of KYN pathway towards the arm producing KYNA during exacerbation. We propose that KYNA, possibly via interaction with aryl hydrocarbon receptor or G-protein-coupled orphan receptor 35, may serve as a counter-regulatory mechanism, decreasing cytotoxicity and inflammation in IBD. Further longitudinal studies evaluating the individual dynamics of TRP and KYN pathway in patients with IBD, as well as the nature of precise mechanisms regulating KYNA synthesis, should be helpful in better understanding the processes underlying the observed changes.

Predictive metabolomic profiling of microbial communities using amplicon or metagenomic sequences

Microbial community metabolomics, particularly in the human gut, are beginning to provide a new route to identify functions and ecology disrupted in disease. However, these data can be costly and difficult to obtain at scale, while amplicon or shotgun metagenomic sequencing data are readily available for populations of many thousands. Here, we describe a computational approach to predict potentially unobserved metabolites in new microbial communities, given a model trained on paired metabolomes and metagenomes from the environment of interest. Focusing on two independent human gut microbiome datasets, we demonstrate that our framework successfully recovers community metabolic trends for more than 50% of associated metabolites. Similar accuracy is maintained using amplicon profiles of coral-associated, murine gut, and human vaginal microbiomes. We also provide an expected performance score to guide application of the model in new samples. Our results thus demonstrate that this 'predictive metabolomic' approach can aid in experimental design and provide useful insights into the thousands of community profiles for which only metagenomes are currently available.

Galectin-3 Regulates Indoleamine-2,3-dioxygenase-Dependent Cross-Talk between Colon-Infiltrating Dendritic Cells and T Regulatory Cells and May Represent a Valuable Biomarker for Monitoring the Progression of Ulcerative Colitis

Galectin-3 regulates numerous biological processes in the gut. We investigated molecular mechanisms responsible for the Galectin-3-dependent regulation of colon inflammation and evaluated whether Galectin-3 may be used as biomarker for monitoring the progression of ulcerative colitis (UC). The differences in disease progression between dextran sodium sulphate-treated wild type and Galectin-3-deficient mice were investigated and confirmed in clinical settings, in 65 patients suffering from mild, moderate, and severe colitis. During the induction phase of colitis, Galectin-3 promoted interleukin-1β-induced polarization of colonic macrophages towards inflammatory phenotype. In the recovery phase of colitis, Galectin-3 was required for the immunosuppressive function of regulatory dendritic cells (DCs). Regulatory DCs in Galectin-3:Toll-like receptor-4:Kynurenine-dependent manner promoted the expansion of colon-infiltrated T regulatory cells (Tregs) and suppressed Th1 and Th17 cell-driven colon inflammation. Concentration of Galectin-3 in serum and stool samples of UC patients negatively correlated with clinical, endoscopic, and histological parameters of colitis. The cutoff serum values of Galectin-3 that allowed the discrimination of mild from moderate and moderate from severe colitis were 954 pg/mL and 580 pg/mL, respectively. Fecal levels of Galectin-3 higher than 553.44 pg/mL indicated attenuation of UC. In summing up, Galectin-3 regulates the cross-talk between colon-infiltrating DCs and Tregs and represents a new biomarker for monitoring the progression of UC.

Interactions Between the Gut Microbiota and the Host Innate Immune Response Against Pathogens

The mammalian intestine is colonized by over a trillion microbes that comprise the "gut microbiota," a microbial community which has co-evolved with the host to form a mutually beneficial relationship. Accumulating evidence indicates that the gut microbiota participates in immune system maturation and also plays a central role in host defense against pathogens. Here we review some of the mechanisms employed by the gut microbiota to boost the innate immune response against pathogens present on epithelial mucosal surfaces. Antimicrobial peptide secretion, inflammasome activation and induction of host IL-22, IL-17, and IL-10 production are the most commonly observed strategies employed by the gut microbiota for host anti-pathogen defense. Taken together, the body of evidence suggests that the host gut microbiota can elicit innate immunity against pathogens.

Arabinoxylan Attenuates Type 2 Diabetes by Improvement of Carbohydrate, Lipid, and Amino Acid Metabolism

SCOPE

Type 2 diabetes is a complex metabolic and endocrine disorder worldwide, which causes severe health and economic problems. The aim of this study is to investigate the molecular mechanisms by which arabinoxylan from Plantago asiatica L. attenuates type 2 diabetes from the perspective of urine metabolomics.

METHODS AND RESULTS

High-fat diet and streptozotocin-induced type 2 diabetic rats are treated with arabinoxylan, then the urine samples are collected for untargeted metabolomics analysis by UPLC-Triple-TOF/MS. Diabetes causes significant increases in the levels of acetone, glucose, 2-oxoglutarate, and leucine, and significant decreases in the concentrations of creatine, histidine, lysine, l-tryptophan, hippurate, l-cysteine, kynurenine, and arabitol as compared with normal rats (p < 0.01). And these 12 metabolites (with VIP cut-off value > 1) can be used as biomarkers in type 2 diabetes. A total of 21 urinary metabolites are significantly improved by arabinoxylan administration in diabetic rats, and these metabolites are mainly involved in TCA cycle, and metabolism of lipid and ketone body, taurine and hypotaurine, tryptophan, and branched chain amino acids.

CONCLUSION

Arabinoxylan administration improves carbohydrate, lipid, and amino acid metabolism in type 2 diabetic rats, which provide important insights into the mechanisms underlying type 2 diabetes as well as the effects of arabinoxylan.

Indoleamine 2,3-dioxygenase-dependent expansion of T-regulatory cells maintains mucosal healing in ulcerative colitis

BACKGROUND

Dendritic cell (DC)-derived indolamine 2,3-dioxygenase (IDO) degrades tryptophan to kynurenine, which promotes conversion of inflammatory T cells in immunosuppressive regulatory T cells (Tregs). We analyzed the significance of the IDO:Treg axis for inducing and maintaining mucosal healing in ulcerative colitis (UC).

METHODS

Dextran sodium sulphate (DSS)-induced colitis in BALB/c mice (model for mucosal healing) and C57BL/6 mice (model for persistent disease) was used. Serum, fecal samples and colon-infiltrating immune cells of 65 patients with UC with mucosal healing or persistent colitis were analyzed.

RESULTS

Significantly higher serum levels of kynurenine and downregulated inflammatory cytokines were noticed in DSS-treated BALB/c mice compared with C57BL/6 mice. Increased IDO activity and attenuated capacity for antigen presentation and production of inflammatory cytokines, observed in BALB/c DCs, was followed by a significantly lower number of inflammatory T helper 1 (Th1) and Th17 cells and a notably increased number of Tregs in the colons of DSS-treated BALB/c mice. DCs and Tregs were crucially important for the maintenance of mucosal healing since their depletion aggravated colitis. Mucosal healing, followed by an increase in kynurenine and intestinal Tregs, was re-established when BALB/c DCs were transferred into DC-depleted or Treg-depleted DSS-treated BALB/c mice. This phenomenon was completely abrogated by the IDO inhibitor. Significantly higher serum and fecal levels of kynurenine, accompanied by an increased presence of intestinal Tregs, were noticed in patients with UC with mucosal healing and negatively correlated with disease severity, fecal calprotectin, colon-infiltrating interferon γ and interleukin-17-producing cells, serum and fecal levels of inflammatory cytokines.

CONCLUSION

IDO-dependent expansion of endogenous Tregs should be further explored as a new approach for the induction and maintenance of mucosal healing in patients with UC.

Caspase recruitment domain (CARD) family (CARD9, CARD10, CARD11, CARD14 and CARD15) are increased during active inflammation in patients with inflammatory bowel disease

Background

The CARD family plays an important role in innate immune response by the activation of NF-κB. The aim of this study was to determine the gene expression and to enumerate the protein-expressing cells of some members of the CARD family (CARD9, CARD10, CARD11, CARD14 and CARD15) in patients with IBD and normal controls without colonic inflammation.

Methods

We included 48 UC patients, 10 Crohn’s disease (CD) patients and 18 non-inflamed controls. Gene expression was performed by RT-PCR and protein expression by immunohistochemistry. CARD-expressing cells were assessed by estimating the positively staining cells and reported as the percentage.

Results

The CARD9 and CARD10 gene expression was significantly higher in UC groups compared with CD (P < 0.001). CARD11 had lower gene expression in UC than in CD patients (P < 0.001). CARD14 gene expression was higher in the group with active UC compared to non-inflamed controls (P < 0.001). The low expression of CARD14 gene was associated with a benign clinical course of UC, characterized by initial activity followed by long-term remission longer than 5 years (P = 0.01, OR = 0.07, 95%CI:0.007–0.70). CARD15 gene expression was lower in UC patients versus CD (P = 0.004). CARD9 protein expression was detected in inflammatory infiltrates; CARD14 in parenchymal cells, while CARD15 in inflammatory and parenchymal cells. CARD9−, CARD14− and CARD15 − expressing cells were significantly higher in patients with active UC versus non-inflamed controls (P < 0.05).

Conclusion

The CARD family is involved in the inflammatory process and might be involved in the IBD pathophysiology.

Expression and Metabolomic Profiling in Axial Spondyloarthritis

PURPOSE OF REVIEW

The purpose of this review is to highlight recent evidence with respect to expression and metabolomic profiling in axial spondyloarthritis (axSpA) that included ankylosing spondylitis (AS).

RECENT FINDINGS

AxSpA is not only characterized by the strongest genetic contribution for any complex rheumatic disease but is also influenced by environmental and immunological factors. Large-scale association-based studies have identified over 100 genetic variants contributing to 30% of the genetic risk of ankylosing spondylitis. Recent studies in global expression and metabolomic profiling appear to highlight common themes despite differences in tissues, populations, techniques, and relative paucity of patients in many of these studies. Expression studies support a role for immunomodulation and bone remodeling in the pathogenesis and progression of axSpA/AS, while metabolomic studies implicate the importance of the intestinal microbial metabolism as well as fat and choline metabolic pathways in AS.

Intestinal Microbiota Influences Non-intestinal Related Autoimmune Diseases

The human body is colonized by millions of microorganisms named microbiota that interact with our tissues in a cooperative and non-pathogenic manner. These microorganisms are present in the skin, gut, nasal, oral cavities, and genital tract. In fact, it has been described that the microbiota contributes to balancing the immune system to maintain host homeostasis. The gut is a vital organ where microbiota can influence and determine the function of cells of the immune system and contributes to preserve the wellbeing of the individual. Several articles have emphasized the connection between intestinal autoimmune diseases, such as Crohn's disease with dysbiosis or an imbalance in the microbiota composition in the gut. However, little is known about the role of the microbiota in autoimmune pathologies affecting other tissues than the intestine. This article focuses on what is known about the role that gut microbiota can play in the pathogenesis of non-intestinal autoimmune diseases, such as Grave's diseases, multiple sclerosis, type-1 diabetes, systemic lupus erythematosus, psoriasis, schizophrenia, and autism spectrum disorders. Furthermore, we discuss as to how metabolites derived from bacteria could be used as potential therapies for non-intestinal autoimmune diseases.

Functions and Signaling Pathways of Amino Acids in Intestinal Inflammation

Intestine is always exposed to external environment and intestinal microorganism; thus it is more sensitive to dysfunction and dysbiosis, leading to intestinal inflammation, such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), and diarrhea. An increasing number of studies indicate that dietary amino acids play significant roles in preventing and treating intestinal inflammation. The review aims to summarize the functions and signaling mechanisms of amino acids in intestinal inflammation. Amino acids, including essential amino acids (EAAs), conditionally essential amino acids (CEAAs), and nonessential amino acids (NEAAs), improve the functions of intestinal barrier and expressions of anti-inflammatory cytokines and tight junction proteins but decrease oxidative stress and the apoptosis of enterocytes as well as the expressions of proinflammatory cytokines in the intestinal inflammation. The functions of amino acids are associated with various signaling pathways, including mechanistic target of rapamycin (mTOR), inducible nitric oxide synthase (iNOS), calcium-sensing receptor (CaSR), nuclear factor-kappa-B (NF-κB), mitogen-activated protein kinase (MAPK), nuclear erythroid-related factor 2 (Nrf2), general controlled nonrepressed kinase 2 (GCN2), and angiotensin-converting enzyme 2 (ACE2).

Impact of the Gut Microbiota on Intestinal Immunity Mediated by Tryptophan Metabolism

The gut microbiota influences the health of the host, especially with regard to gut immune homeostasis and the intestinal immune response. In addition to serving as a nutrient enhancer, L-tryptophan (Trp) plays crucial roles in the balance between intestinal immune tolerance and gut microbiota maintenance. Recent discoveries have underscored that changes in the microbiota modulate the host immune system by modulating Trp metabolism. Moreover, Trp, endogenous Trp metabolites (kynurenines, serotonin, and melatonin), and bacterial Trp metabolites (indole, indolic acid, skatole, and tryptamine) have profound effects on gut microbial composition, microbial metabolism, the host's immune system, the host-microbiome interface, and host immune system-intestinal microbiota interactions. The aryl hydrocarbon receptor (AhR) mediates the regulation of intestinal immunity by Trp metabolites (as ligands of AhR), which is beneficial for immune homeostasis. Among Trp metabolites, AhR ligands consist of endogenous metabolites, including kynurenine, kynurenic acid, xanthurenic acid, and cinnabarinic acid, and bacterial metabolites, including indole, indole propionic acid, indole acetic acid, skatole, and tryptamine. Additional factors, such as aging, stress, probiotics, and diseases (spondyloarthritis, irritable bowel syndrome, inflammatory bowel disease, colorectal cancer), which are associated with variability in Trp metabolism, can influence Trp-microbiome-immune system interactions in the gut and also play roles in regulating gut immunity. This review clarifies how the gut microbiota regulates Trp metabolism and identifies the underlying molecular mechanisms of these interactions. Increased mechanistic insight into how the microbiota modulates the intestinal immune system through Trp metabolism may allow for the identification of innovative microbiota-based diagnostics, as well as appropriate nutritional supplementation of Trp to prevent or alleviate intestinal inflammation. Moreover, this review provides new insight regarding the influence of the gut microbiota on Trp metabolism. Additional comprehensive analyses of targeted Trp metabolites (including endogenous and bacterial metabolites) are essential for experimental preciseness, as the influence of the gut microbiota cannot be neglected, and may explain contradictory results in the literature.

Alteration of Gut Microbiota and Inflammatory Cytokine/Chemokine Profiles in 5-Fluorouracil Induced Intestinal Mucositis

Disturbed homeostasis of gut microbiota has been suggested to be closely associated with 5-fluorouracil (5-Fu) induced mucositis. However, current knowledge of the overall profiles of 5-Fu-disturbed gut microbiota is limited, and so far there is no direct convincing evidence proving the causality between 5-Fu-disturbed microbiota and colonic mucositis. In mice, in agreement with previous reports, 5-Fu resulted in severe colonic mucositis indicated by weight loss, diarrhea, bloody stool, shortened colon, and infiltration of inflammatory cells. It significantly changed the profiles of inflammatory cytokines/chemokines in serum and colon. Adhesion molecules such as vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and VE-Cadherin were increased. While tight junction protein occludin was reduced, however, zonula occludens-1 (ZO-1) and junctional adhesion molecule-A (JAM-A) were increased in colonic tissues of 5-Fu treated mice. Meanwhile, inflammation related signaling pathways including NF-κB and mitogen activated protein kinase (MAPKs) in the colon were activated. Further study disclosed that 5-Fu diminished bacterial community richness and diversity, leading to the relative lower abundance of Firmicutes and decreased Firmicutes/Bacteroidetes (F/B) ratio in feces and cecum contents. 5-Fu also reduced the proportion of Proteobacteria, Tenericutes, Cyanobacteria, and Candidate division TM7, but increased that of Verrucomicrobia and Actinobacteria in feces and/or cecum contents. The fecal transplant from healthy mice prevented body weight loss and colon shortening of 5-Fu treated mice. In addition, the fecal transplant from 5-Fu treated mice reduced body weight and colon length of vancomycin-pretreated mice. Taken together, our study demonstrated that gut microbiota was actively involved in the pathological process of 5-Fu induced intestinal mucositis, suggesting potential attenuation of 5-Fu induced intestinal mucositis by manipulating gut microbiota homeostasis.

Secretome of Intestinal Bacilli: A Natural Guard against Pathologies

Current studies of human gut microbiome usually do not consider the special functional role of transient microbiota, although some of its members remain in the host for a long time and produce broad spectrum of biologically active substances. Getting into the gastrointestinal tract (GIT) with food, water and probiotic preparations, two representatives of Bacilli class, genera Bacillus and Lactobacillus, colonize epithelium blurring the boundaries between resident and transient microbiota. Despite their minor proportion in the microbiome composition, these bacteria can significantly affect both the intestinal microbiota and the entire body thanks to a wide range of secreted compounds. Recently, insufficiency and limitations of pure genome-based analysis of gut microbiota became known. Thus, the need for intense functional studies is evident. This review aims to characterize the Bacillus and Lactobacillus in GIT, as well as the functional roles of the components released by these members of microbial intestinal community. Complex of their secreted compounds is referred by us as the "bacillary secretome." The composition of the bacillary secretome, its biological effects in GIT and role in counteraction to infectious diseases and oncological pathologies in human organism is the subject of the review.

Therapeutic Potential of Amino Acids in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD), which includes both ulcerative colitis and Crohn’s disease, is a chronic relapsing inflammation of the gastrointestinal tract, and is difficult to treat. The pathophysiology of IBD is multifactorial and not completely understood, but genetic components, dysregulated immune responses, oxidative stress, and inflammatory mediators are known to be involved. Animal models of IBD can be chemically induced, and are used to study etiology and to evaluate potential treatments of IBD. Currently available IBD treatments can decrease the duration of active disease but because of their adverse effects, the search for novel therapeutic strategies that can restore intestinal homeostasis continues. This review summarizes and discusses what is currently known of the effects of amino acids on the reduction of inflammation, oxidative stress, and cell death in the gut when IBD is present. Recent studies in animal models have identified dietary amino acids that improve IBD, but amino acid supplementation may not be adequate to replace conventional therapy. The animal models used in dietary amino acid research in IBD are described.

Magnolol, a Natural Polyphenol, Attenuates Dextran Sulfate Sodium-Induced Colitis in Mice

Magnolol is a lignan with anti-inflammatory activity identified in Magnolia officinalis. Ulcerative colitis (UC), one of the types of inflammatory bowel disease (IBD), is a disease that causes inflammation and ulcers in the colon. To investigate the effect of magnolol in dextran sulfate sodium (DSS)-induced experimental UC model, male C57 mice were treated with 2% DSS drinking water for 5 consecutive days followed by intragastric administration with magnolol (5, 10 and 15 mg/kg) daily for 7 days. The results showed that magnolol significantly attenuated disease activity index, inhibited colonic shortening, reduced colonic lesions and suppressed myeloperoxidase (MPO) activity. Moreover, colonic pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β) induced by colitis were dramatically decreased by magnolol. To further unveil the metabolic signatures upon magnolol treatment, mass spectrometry-based metabolomic analysis of the small molecular metabolites in mice serum were performed. Compared with controls, abnormality of serum metabolic phenotypes in DSS-treated mice were effectively reversed by different doses of magnolol. In particular, magnolol treatment effectively elevated the serum levels of tryptophan metabolites including kynurenic acid (KA), 5-hydroxyindoleacetic acid, indoleacetic acid (IAA), indolelactic acid and indoxylsulfuric acid, which are potential aryl hydrocarbon receptor (AHR) ligands to impact colitis. These findings suggest that magnolol exerts anti-inflammatory effect on DSS-induced colitis and its underlying mechanisms are associated with the restoring of tryptophan metabolites that inhibit the colonic inflammation.