Utilization of glycosaminoglycans by the human gut microbiota: participating bacteria and their enzymatic machineries

Degradation and fermentation of hyaluronic acid by Bacteroides spp. from the human gut microbiota

Bacteroides spp. are prominent members of the human gut microbiota that play critical roles in the metabolism of complex carbohydrates from the daily diet. Hyaluronic acid (HA) is a multifunctional polysaccharide which has been extensively used in the food and biomedical industry. However, how HA is degraded and fermented by Bacteroides spp. has not been fully characterized. Here, we comprehensively investigated the detailed degradation profiles and fermentation characteristics of four different HAs with discrete molecular weight (Mw) by fourteen distinctive Bacteroides spp. from the human gut microbiota. Our results indicated that high-Mw HAs were more degradable and fermentable than low-Mw HAs. Interestingly, B. salyersiae showed the best degrading capability for both high-Mw and low-Mw HAs, making it a keystone species for HA degradation among Bacteroides spp.. Specifically, HA degradation by B. salyersiae produced significant amounts of unsaturated tetrasaccharide (udp4). Co-culture experiments indicated that the produced udp4 could be further fermented and utilized by non-proficient HA-degraders, suggesting a possible cross-feeding interaction in the utilization of HA within the Bacteroides spp.. Altogether, our study provides novel insights into the metabolism of HA by the human gut microbiota, which has considerable implications for the development of new HA-based nutraceuticals and medicines.

Enzyme-mediated green synthesis of glycosaminoglycans and catalytic process intensification

Glycosaminoglycans (GAGs) are a family of structurally complex heteropolysaccharides that play pivotal roles in biological functions, including the regulation of cell proliferation, enzyme inhibition, and activation of growth factor receptors. Therefore, the synthesis of GAGs is a hot research topic in drug development. The enzymatic synthesis of GAGs has received widespread attention due to their eco-friendly nature, high regioselectivity, and stereoselectivity. The enhancement of the enzymatic synthesis process is the key to its industrial applications. In this review, we overviewed the construction of more efficient in vitro biomimetic synthesis systems of glycosaminoglycans and presented the different strategies to improve enzyme catalysis, including the combination of chemical and enzymatic methods, solid-phase synthesis, and protein engineering to solve the problems of enzyme stability, separation and purification of the product, preparation of structurally defined sugar chains, etc., and discussed the challenges and opportunities in large-scale green synthesis of GAGs.

Bioactive carbohydrate polymers from marine sources as potent nutraceuticals in modulating obesity: a review

The majority of bioactive polysaccharides are present in some marine creatures. These polysaccharides are considered as promising anti-obesity agents, their anti-obesity properties involve a number of mechanisms, including suppression of lipid metabolism and absorption, impact on satiety, and prevention of adipocyte differentiation. Obesity is linked to type 2 diabetes, cardiovascular disease, and other metabolic syndromes. In this review various bioactive polysaccharides like chitin, chitosan, fucosylated chondroitin sulphate, chitooligosaccharides and glycosaminoglycans have been discussed for their anti-obesity effects through various pathways. Critical evaluation of observational studies and intervention trials on obesity, lipid hypertrophy, dyslipidemia, and type 2 diabetes was done with a primary focus on specific marine fauna polysaccharide as a source of seafood that is consumed all over the world. It has been observed that consumption of individual seafood constituents was effective in reducing obesity. Thus, marine derived novel bioactive polysaccharides have potential applications in food and pharmaceutical industries.

Lipid metabolism regulation by dietary polysaccharides with different structural properties

Lipid metabolism plays an important role in energy homeostasis maintenance in response to stress. Nowadays, hyperlipidemia-related chronic diseases such as obesity, diabetes, atherosclerosis, and fatty liver pose significant health challenges. Dietary polysaccharides (DPs) have gained attention for their effective lipid-lowering properties. This review examines the multifaceted mechanisms that DPs employ to lower lipid levels in subjects with hyperlipidemia. DPs could directly inhibit lipid intake and absorption, promote lipid excretion, and regulate key enzymes involved in lipid metabolism pathways, including triglyceride and cholesterol anabolism and catabolism, fatty acid oxidation, and bile acid synthesis. Additionally, DPs indirectly improve lipid homeostasis by modulating gut microbiota composition and alleviating oxidative stress. Moreover, the lipid-lowering mechanisms of particular structural DPs (including β-glucan, pectin, glucomannan, inulin, arabinoxylan, and fucoidan) are summarized. The relationship between the structure and lipid-lowering activity of DPs is also discussed based on current researches. Finally, potential breakthroughs and future directions in the development of DPs in lipid-lowering activity are discussed. The paper could provide a reference for further exploring the mechanism of DPs for lipid regulations and utilizing DPs as lipid-lowering dietary ingredients.

Metabolism mechanism of glycosaminoglycans by the gut microbiota: Bacteroides and lactic acid bacteria: A review

Glycosaminoglycans (GAGs), as a class of biopolymers, play pivotal roles in various biological metabolisms such as cell signaling, tissue development, cell apoptosis, immune modulation, and growth factor activity. They are mainly present in the colon in free forms, which are essential for maintaining the host's health by regulating the colonization and proliferation of gut microbiota. Therefore, it is important to explain the specific members of the gut microbiota for GAGs' degradation and their enzymatic machinery in vivo. This review provides an outline of GAGs-utilizing entities in the Bacteroides, highlighting their polysaccharide utilization loci (PULs) and the enzymatic machinery involved in chondroitin sulfate (CS) and heparin (Hep)/heparan sulfate (HS). While there are some variations in GAGs' degradation among different genera, we analyze the reputed GAGs' utilization clusters in lactic acid bacteria (LAB), based on recent studies on GAGs' degradation. The enzymatic machinery involved in Hep/HS and CS metabolism within LAB is also discussed. Thus, to elucidate the precise mechanisms utilizing GAGs by diverse gut microbiota will augment our understanding of their effects on human health and contribute to potential therapeutic strategies for diseases.

Effect of in ovo feeding of xylobiose and xylotriose on plasma immunoglobulin, cecal metabolites production, microbial ecology, and metabolic pathways in broiler chickens

BACKGROUND

Dietary supplementation of xylooligosaccharides (XOS) has been found to influence gut health by manipulating cecal microbiota and producing microbe-origin metabolites. But no study investigated and compared the effect of in ovo feeding of xylobiose (XOS2) and xylotriose (XOS3) in chickens. This study investigated the effect of in ovo feeding of these XOS compounds on post-hatch gut health parameters in chickens. A total of 144 fertilized chicken eggs were divided into three groups: a) non-injected control (CON), b) XOS2, and c) XOS3. On the 17th embryonic day, the eggs of the XOS2 and XOS3 groups were injected with 3 mg of XOS2 and XOS3 diluted in 0.5 mL of 0.85% normal saline through the amniotic sac. After hatching, the chicks were raised for 21 d. Blood was collected on d 14 to measure plasma immunoglobulin. Cecal digesta were collected for measuring short-chain fatty acids (SCFA) on d 14 and 21, and for microbial ecology and microbial metabolic pathway analyses on d 7 and 21.

RESULTS

The results were considered significantly different at P < 0.05. ELISA quantified plasma IgA and IgG on d 14 chickens, revealing no differences among the treatments. Gas chromatography results showed no significant differences in the concentrations of cecal SCFAs on d 14 but significant differences on d 21. However, the SCFA concentrations were lower in the XOS3 than in the CON group on d 21. The cecal metagenomics data showed that the abundance of the family Clostridiaceae significantly decreased on d 7, and the abundance of the family Oscillospiraceae increased on d 21 in the XOS2 compared to the CON. There was a reduction in the relative abundance of genus Clostridium sensu stricto 1 in the XOS2 compared to the CON on d 7 and the genus Ruminococcus torques in both XOS2 and XOS3 groups compared to the CON on d 21. The XOS2 and XOS3 groups reduced the genes for chondroitin sulfate degradation I and L-histidine degradation I pathways, which contribute to improved gut health, respectively, in the microbiome on d 7. In contrast, on d 21, the XOS2 and XOS3 groups enriched the thiamin salvage II, L-isoleucine biosynthesis IV, and O-antigen building blocks biosynthesis (E. coli) pathways, which are indicative of improved gut health. Unlike the XOS3 and CON, the microbiome enriched the pathways associated with energy enhancement, including flavin biosynthesis I, sucrose degradation III, and Calvin-Benson-Bassham cycle pathways, in the XOS2 group on d 21.

CONCLUSION

In ovo XOS2 and XOS3 feeding promoted beneficial bacterial growth and reduced harmful bacteria at the family and genus levels. The metagenomic-based microbial metabolic pathway profiling predicted a favorable change in the availability of cecal metabolites in the XOS2 and XOS3 groups. The modulation of microbiota and metabolic pathways suggests that in ovo XOS2 and XOS3 feeding improved gut health during the post-hatch period of broilers.

Glycosaminoglycan dermatan sulfate supplementation decreases diet-induced obesity and metabolic dysfunction in mice

Glycosaminoglycans are complex carbohydrates used as nutraceuticals for diverse applications. We studied the potential of the glycosaminoglycan dermatan sulfate (DS) to counteract the development of diet-induced obesity (DIO) using obesity-prone mice fed a high-fat diet (HFD) as a model. Oral DS supplementation protected the animals against HFD-induced increases in whole-body adiposity, visceral fat mass, adipocyte size, blood glucose levels, insulin resistance, and pro-inflammatory lipids levels in brown adipose tissue (BAT) and the liver, where it largely counteracted the HFD-induced changes in the nonpolar metabolome. Protection against DIO in the DS-supplemented mice occurred despite higher energy intake and appeared to be associated with increased energy expenditure, higher uncoupling protein 1 expression in BAT, decreased BAT "whitening," and an enhanced channeling of fuel substrates toward skeletal muscle. This work is the first preclinical study to examine the anti-obesity activity of DS tested individually in vivo. The results support possible uses of DS as an active component in functional foods/supplements to manage obesity and associated metabolic diseases.

Categorization of the effects of E. coli LF82 and mutants lacking the chuT and shuU genes on survival, the transcriptome, and metabolome in germ-free honeybee

The precise etiology of inflammatory bowel diseases (IBDs) remains elusive. The Escherichia coli strain LF82 (LF82) is known to be associated with IBD, and we hypothesized that this association may be related to the chuT and shuU genes. Here we constructed a germ-free (GF) honeybee model to investigate the effects of LF82 chuT and shuU genes on the honeybee intestine and their mechanisms. The chuT and shuU gene deletion strains LF82∆chuT and LF82∆shuU were generated by CRISPR-Cas9. These strains, together with nonpathogenic E. coli MG1655 (MG1655) and wildtype LF82, were allowed to colonize the guts of GF honeybees to establish single bacterial colonization models. Intestinal permeability was assessed following the administration of a sterile Brilliant Blue (FCF) solution. Comprehensive transcriptomic and metabolomic analyses of intestinal samples indicated that MG1655 had few disadvantageous effects on honeybees. Conversely, colonization with LF82 and its gene-deletion mutants provoked pronounced activation of genes associated with innate immune pathways, stimulated defensive responses, and induced expression of genes associated with inflammation, oxidative stress, and glycosaminoglycan degradation. Crucially, the LF82∆chuT and LF82∆shuU strains perturbed host heme and iron regulation, as well as tryptophan metabolism. These findings suggest that the deletion of chuT and shuU genes in E. coli LF82 may alleviate intestinal inflammation by partially modulating tryptophan catabolism. Our study proposes that targeting iron uptake mechanisms could be a potential strategy to mitigate the virulence of IBD-associated bacteria.

Impact of dietary carbohydrate, fat or protein restriction on the human gut microbiome: a systematic review

Restriction of dietary carbohydrates, fat and/or protein is often used to reduce body weight and/or treat (metabolic) diseases. Since diet is a key modulator of the human gut microbiome, which plays an important role in health and disease, this review aims to provide an overview of current knowledge of the effects of macronutrient-restricted diets on gut microbial composition and metabolites. A structured search strategy was performed in several databases. After screening for inclusion and exclusion criteria, thirty-six articles could be included. Data are included in the results only when supported by at least three independent studies to enhance the reliability of our conclusions. Low-carbohydrate (<30 energy%) diets tended to induce a decrease in the relative abundance of several health-promoting bacteria, including Bifidobacterium, as well as a reduction in short-chain fatty acid (SCFA) levels in faeces. In contrast, low-fat diets (<30 energy%) increased alpha diversity, faecal SCFA levels and abundance of some beneficial bacteria, including Faecalibacterium prausnitzii. There were insufficient data to draw conclusions concerning the effects of low-protein (<10 energy%) diets on gut microbiota. Although the data of included studies unveil possible benefits of low-fat and potential drawbacks of low-carbohydrate diets for human gut microbiota, the diversity in study designs made it difficult to draw firm conclusions. Using a more uniform methodology in design, sample processing and sharing raw sequence data could foster our understanding of the effects of macronutrient restriction on gut microbiota composition and metabolic dynamics relevant to health. This systematic review was registered at https://www.crd.york.ac.uk/prospero as CRD42020156929.

In vitro digestion and fecal fermentation of basidiospore-derived exopolysaccharides from Naematelia aurantialba

Mushroom polysaccharides exhibit numerous health-enhancing attributes that are intricately linked to the breakdown, assimilation, and exploitation of polysaccharides within the organism. Naematelia aurantialba polysaccharides (NAPS-A), highly prized polysaccharides derived from mushrooms, remain shrouded in uncertainty regarding their characteristics pertaining to gastrointestinal digestion and gut microbial fermentation. The study aimed to understand the digestion and fecal fermentation patterns of NAPS-A. After simulated digestion, NAPS-A's physicochemical properties remained unchanged. However, during in vitro fecal fermentation, indigestible NAPS-A underwent significant changes in various properties, such as reducing sugar, chemical composition, constituent monosaccharides, Molecular weight, apparent viscosity, FT-IR spectra, and microscopic morphology. Notably, NAPS-A was effectively utilized by the gut microbiota, with unchanged properties after digestion but altered after fermentation. It influenced gut microbe composition by increasing beneficial bacteria (Lactobacillus, Faecalibacterium, and Roseburia), lowering pH, and producing short-chain fatty acids. NAPS-A fermentation enriches carbohydrate, fatty acid, and amino acid metabolic pathways through PICRUSt prediction analysis. Overall, these findings emphasize NAPS-A's role in regulating gut bacteria and their metabolic functions, despite its challenging digestibility.

Bacteroides salyersiae is a potent chondroitin sulfate-degrading species in the human gut microbiota

Chondroitin sulfate (CS) has widely been used as a symptomatic slow-acting drug or a dietary supplement for the treatment and prevention of osteoarthritis. However, CS could not be absorbed after oral intake due to its polyanionic nature and large molecular weight. Gut microbiota has recently been proposed to play a pivotal role in the metabolism of drugs and nutrients. Nonetheless, how CS is degraded by the human gut microbiota has not been fully characterized. In the present study, we demonstrated that each human gut microbiota was characterized with a unique capability for CS degradation. Degradation and fermentation of CS by the human gut microbiota produced significant amounts of unsaturated CS oligosaccharides (CSOSs) and short-chain fatty acids. To uncover which microbes were responsible for CS degradation, we isolated a total of 586 bacterial strains with a potential CS-degrading capability from 23 human fecal samples. Bacteroides salyersiae was a potent species for CS degradation in the human gut microbiota and produced the highest amount of CSOSs as compared to other well-recognized CS-degraders, including Bacteroides finegoldii, Bacteroides thetaiotaomicron, Bacteroides xylanisolvens, and Bacteroides ovatus. Genomic analysis suggested that B. salyersiae was armed with multiple carbohydrate-active enzymes that could potentially degrade CS into CSOSs. By using a spent medium assay, we further demonstrated that the unsaturated tetrasaccharide (udp4) produced by the primary degrader B. salyersiae could serve as a "public goods" molecule for the growth of Bacteroides stercoris, a secondary CS-degrader that was proficient at fermenting CSOSs but not CS. Taken together, our study provides insights into the metabolism of CS by the human gut microbiota, which has promising implications for the development of medical and nutritional therapies for osteoarthritis. Video Abstract.

Effects of microplastics and phenanthrene on gut microbiome and metabolome alterations in the marine medaka Oryzias melastigma

Plastic pollution of the oceans is increasing, and toxic interactions between microplastics (MPs) and organic pollutants have become a major environmental concern. However, the combined effects of organic pollutants and MPs on microbiomes and metabolomes have not been studied extensively. In the present study, to evaluate whether MPs and phenanthrene (Phe) act synergistically in the guts of marine medaka (Oryzias melastigma), we performed toxicity assessments, 16 S rRNA gene sequencing, and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses. Our investigations revealed increased toxicity induced by Phe, as well as disturbances in gut microbiota (known as dysbiosis) when MPs were present. Furthermore, combined exposure to Phe and MPs resulted in greater alterations to microbiota composition and metabolite profiles. Notably, MP exposure was distinctly associated with the abundance of Shewanella and Spongiibacteraceae, while Phe exposure was associated with the abundance of Marimicrobium. Among key microbiota, Marimicrobium and Roseibacillus were significantly correlated with metabolites responsible for coenzyme A and glycerophospholipid metabolism in medaka. These results suggest that interactions between Phe and MPs may have significant effects on the gut microbiota and metabolism of aquatic organisms and underscore the importance of acknowledging the interplay between MPs and contaminants in aquatic environments.

Modulation of gut microbiota ecosystem by a glucan-rich snail mucin heteropolysaccharide attenuates loperamide-induced constipation

The present study aimed to investigate the effect of oral administration of snail-derived mucin extract (SM) on ameliorating constipation symptoms of loperamide-induced constipated rats (n = 6). The analytical results indicated that SM mainly contains a glucan-rich snail mucin heteropolysaccharide with high molecular weights (108.5-267.9 kDa), comprising primarily of glucose (64.9 %) and galactose (22.4 %) with some deoxyhexoses (5.0 %) and hexosamines (4.9 %). Daily SM administration at doses of 10-40 mg/kg/day to the loperamide-induced constipated rats significantly (p < 0.05) ameliorated the deterioration in fecal parameters, such as numbers and weight of feces, fecal water contents, and gastrointestinal transit ratio. The histomorphometric results showed that the loperamide-induced decreases in the thickness of mucosal and muscularis mucosae layers as well as the distribution of mucin and c-KIT-positive areas were significantly (p < 0.05) improved via SM consumption at all doses tested. SM administration at all doses significantly increased the expression of genes encoding tryptophan hydroxylases (TPH1 and TPH2; p < 0.05), tight junction molecules (OCLN, CLDN1, and TJP1; p < 0.05), and mucin (MUC2 and MUC4; p < 0.05), but significantly decreased the aquaporin-encoding genes (AQP3 and AQP8; p < 0.05). Gut microbial community analysis indicated that SM administration could modulate loperamide-induced dysbiosis by increasing the phyla Actinobacteria (11.72-12.64 % at 10-40 mg/kg doses; p < 0.05) and Firmicutes (79.33 % and 74.24 % at 20 and 40 mg/kg doses; p < 0.05) and decreasing the phyla Bacteroidetes (5.98-12.47 % at 10-40 mg/kg doses; p < 0.05) and Verrucomicrobia (2.21 % and 2.78 % at 20 and 40 mg/kg doses; p < 0.05), suggesting that SM administration is effective in ameliorating constipation by controlling gut microbial communities. These findings can be utilized as fundamental data for developing novel functional materials using SM to prevent or treat constipation.

Four functional profiles for fibre and mucin metabolism in the human gut microbiome

BACKGROUND

With the emergence of metagenomic data, multiple links between the gut microbiome and the host health have been shown. Deciphering these complex interactions require evolved analysis methods focusing on the microbial ecosystem functions. Despite the fact that host or diet-derived fibres are the most abundant nutrients available in the gut, the presence of distinct functional traits regarding fibre and mucin hydrolysis, fermentation and hydrogenotrophic processes has never been investigated.

RESULTS

After manually selecting 91 KEGG orthologies and 33 glycoside hydrolases further aggregated in 101 functional descriptors representative of fibre and mucin degradation pathways in the gut microbiome, we used nonnegative matrix factorization to mine metagenomic datasets. Four distinct metabolic profiles were further identified on a training set of 1153 samples, thoroughly validated on a large database of 2571 unseen samples from 5 external metagenomic cohorts and confirmed with metatranscriptomic data. Profiles 1 and 2 are the main contributors to the fibre-degradation-related metagenome: they present contrasted involvement in fibre degradation and sugar metabolism and are differentially linked to dysbiosis, metabolic disease and inflammation. Profile 1 takes over Profile 2 in healthy samples, and unbalance of these profiles characterize dysbiotic samples. Furthermore, high fibre diet favours a healthy balance between profiles 1 and profile 2. Profile 3 takes over profile 2 during Crohn's disease, inducing functional reorientations towards unusual metabolism such as fucose and H2S degradation or propionate, acetone and butanediol production. Profile 4 gathers under-represented functions, like methanogenesis. Two taxonomic makes up of the profiles were investigated, using either the covariation of 203 prevalent genomes or metagenomic species, both providing consistent results in line with their functional characteristics. This taxonomic characterization showed that profiles 1 and 2 were respectively mainly composed of bacteria from the phyla Bacteroidetes and Firmicutes while profile 3 is representative of Proteobacteria and profile 4 of methanogens.

CONCLUSIONS

Integrating anaerobic microbiology knowledge with statistical learning can narrow down the metagenomic analysis to investigate functional profiles. Applying this approach to fibre degradation in the gut ended with 4 distinct functional profiles that can be easily monitored as markers of diet, dysbiosis, inflammation and disease. Video Abstract.

Zearalenone-14-glucoside specifically promotes dysplasia of Gut-Associated Lymphoid Tissue: A natural product for constructing intestinal nodular lymphatic hyperplasia model

INTRODUCTION

Zearalenone-14-glucoside (Z14G) is a modified mycotoxin that widely contaminates food across the world. Our preliminary experiment showed that Z14G degrades to zearalenone (ZEN) in the intestine exerting toxicity. Notably, oral administration of Z14G in rats induces intestinal nodular lymphatic hyperplasia.

OBJECTIVES

To investigate the mechanism of Z14G intestinal toxicity and how it differs from ZEN toxicity. We conducted a precise toxicology study on the intestine of rats exposed to Z14G and ZEN using multi-omics technology.

METHODS

Rats were exposed to ZEN (5 mg/kg), Z14G-L (5 mg/kg), Z14G-H (10 mg/kg), and pseudo germ free (PGF)-Z14G-H (10 mg/kg) for 14 days. Histopathological studies were performed on intestines from each group and compared. Metagenomic, metabolomic, and proteomic analyses were performed on rat feces, serum, and intestines, respectively.

RESULTS

Histopathological studies showed that Z14G exposure resulted in dysplasia of gut-associated lymphoid tissue (GALT) compared to ZEN exposure. The elimination of gut microbes in the PGF-Z14G-H group alleviated or eliminated Z14G-induced intestinal toxicity and GALT dysplasia. Metagenomic analysis revealed that Z14G exposure significantly promoted the proliferation of Bifidobacterium and Bacteroides compared to ZEN. Metabolomic analysis showed that Z14G exposure significantly reduced bile acid, while proteomic analysis found that Z14G exposure significantly reduced the expression of C-type lectins compared to ZEN.

CONCLUSIONS

Our experimental results and previous research suggest that Z14G is hydrolyzed to ZEN by Bifidobacterium and Bacteroides promoting their co-trophic proliferation. This leads to inactivation of lectins by hyperproliferative Bacteroides when ZEN caused intestinal involvement, resulting in abnormal lymphocyte homing and ultimately GALT dysplasia. It is noteworthy that Z14G is a promising model drug to establish rat models of intestinal nodular lymphatic hyperplasia (INLH), which is of great significance for studying the pathogenesis, drug screening and clinical application of INLH.

Relationship among Chinese herb polysaccharide (CHP), gut microbiota, and chronic diarrhea and impact of CHP on chronic diarrhea

Chronic diarrhea, including diarrhea-predominant irritable bowel syndrome (IBS-D), osmotic diarrhea, bile acid diarrhea, and antibiotic-associated diarrhea, is a common problem which is highly associated with disorders of the gut microbiota composition such as small intestinal bacterial overgrowth (SIBO) and so on. A growing number of studies have supported the view that Chinese herbal formula alleviates the symptoms of diarrhea by modulating the fecal microbiota. Chinese herbal polysaccharides (CHPs) are natural polymers composed of monosaccharides that are widely found in Chinese herbs and function as important active ingredients. Commensal gut microbiota has an extensive capacity to utilize CHPs and play a vital role in degrading polysaccharides into short-chain fatty acids (SCFAs). Many CHPs, as prebiotics, have an antidiarrheal role to promote the growth of beneficial bacteria and inhibit the colonization of pathogenic bacteria. This review systematically summarizes the relationship among gut microbiota, chronic diarrhea, and CHPs as well as recent progress on the impacts of CHPs on the gut microbiota and recent advances on the possible role of CHPs in chronic diarrhea.

Biglycan regulated colorectal cancer progress by modulating enteric neuron-derived IL-10 and abundance of Bacteroides thetaiotaomicron

Biglycan (BGN) is a proteoglycan with branch chains and highly expressed in enteric neurons in the tumor tissue of colorectal cancer (CRC), which is negatively associated with survival rates in patients with CRC. However, how the proteoglycan promotes the progress of CRC through interacting with bacteria and regulating the immune response of enteric neurons remains largely unknown. In the present study, we found that biglycan deficiency changed tumor distribution in a colitis-associated colon cancer model. Furthermore, we revealed that BGN deficiency inhibits tumor growth in an allograft tumor model and the migration of cancer cell by upregulating interleukin-10 expression in enteric neurons. Significantly, we demonstrated that biglycan deficiency enriched the abundance of Bacteroides thetaiotaomicron through competing with it for chondroitin sulfate to inhibit CRC progress. Our work provided new insights into the interaction between host proteoglycan and gut microbiota as well as the role of enteric neurons in the tumor microenvironment.

Gut microbiota bridges the iron homeostasis and host health

The gut microbiota acts as a symbiotic microecosystem that plays an indispensable role in the regulation of a number of metabolic processes in the host by secreting secondary metabolites and impacting the physiology and pathophysiology of numerous organs and tissues through the circulatory system. This relationship, referred to as the "gut-X axis", is associated with the development and progression of disorders, including obesity, fatty liver and Parkinson's disease. Given its importance, the gut flora is a vital research area for the understanding and development of the novel therapeutic approaches for multiple disorders. Iron is a common but necessary element required by both mammals and bacteria. As a result, iron metabolism is closely intertwined with the gut microbiota. The host's iron homeostasis affects the composition of the gut microbiota and the interaction between host and gut microbiota through various mechanisms such as nutrient homeostasis, intestinal peaceability, gut immunity, and oxidative stress. Therefore, understanding the relationship between gut microbes and host iron metabolism is not only of enormous significance to host health but also may offer preventative and therapeutic approaches for a number of disorders that impact both parties. In this review, we delve into the connection between the dysregulation of iron metabolism and dysbiosis of gut microbiota, and how it contributes to the onset and progression of metabolic and chronic diseases.

Mucin glycans and their degradation by gut microbiota

The human intestinal tract is inhabited by a tremendous number of microorganisms, which are collectively termed "the gut microbiota". The intestinal epithelium is covered with a dense layer of mucus that prevents penetration of the gut microbiota into underlying tissues of the host. Recent studies have shown that the maturation and function of the mucus layer are strongly influenced by the gut microbiota, and alteration in the structure and function of the gut microbiota is implicated in several diseases. Because the intestinal mucus layer is at a crucial interface between microbes and their host, its breakdown leads to gut bacterial invasion that can eventually cause inflammation and infection. The mucus is composed of mucin, which is rich in glycans, and the various structures of the complex carbohydrates of mucins can select for distinct mucosa-associated bacteria that are able to bind mucin glycans, and sometimes degrade them as a nutrient source. Mucin glycans are diverse molecules, and thus mucin glycan degradation is a complex process that requires a broad range of glycan-degrading enzymes. Because of the increased recognition of the role of mucus-associated microbes in human health, how commensal bacteria degrade and use host mucin glycans has become of increased interest. This review provides an overview of the relationships between the mucin glycan of the host and gut commensal bacteria, with a focus on mucin degradation.

In vitro fermentation of glycosaminoglycans from mackerel fish waste and its role in modulating the antioxidant status and gut microbiota of high fat diet-fed C57BL/6 mice

Bioactive polysaccharides such as glycosaminoglycans (GAGs) exhibit potential health benefits for several health complications including obesity. The gut microbiota plays a key role in regulating host metabolism, nutrition and immunity. The present work assessed the potential of extracted GAGs (e-GAGs) in maintaining the gut microbiota and ameliorating the effects of high fat diet in in vitro and in vivo models. The in vitro fermentability of e-GAGs extracted from mackerel fish waste was analyzed with Lactobacillus plantarum (LP) and Bifidobacterium bifidum (BB); e-GAGs at 0.5 and 1% proved their prebiotic nature up to 48 h. The pH value decreased from 6.23 to 3.32, the cell density increased from 1.70 to 2.32, the viable cell count increased from 8 to 12 log CFU mL^-1, and short chain fatty acid (SCFA) production was ≈33, 31 and 36% for LP and ≈37, 29 and 34% for BB in terms of acetic acid, propionic acid and butyric acid, respectively. In vivo studies on high fat diet (HFD)-fed C57BL/6 mice with e-GAGs (380 and 760 mg kg^-1 diet) showed ameliorated gut microbiome and tissue/plasma antioxidant enzyme activities, and also the e-GAG-fed group showed significantly (P < 0.05) decreased lipid peroxidation. Cecal microbial analysis showed the health-promoting effects of e-GAGs in reducing (P < 0.05) the obesity ratio of Firmicutes to Bacteroidetes (F/B) within the range (5.32 and 5.26) compared with HFD (6.23). Hence, e-GAGs can be a potential molecule for the treatment of obesity by restoring the redox status under oxidative stress and ameliorating the gut microbes that produce SCFAs which are known to have health beneficial effects.

Sulfated and non-sulfated chondroitin affect the composition and metabolism of human colonic microbiota simulated in an in vitro fermentation system

Chondroitin sulfate (CS) is a family of glycosaminoglycans and have a wide range of applications in dietary supplements and pharmaceutical drugs. In this study, we evaluated the effects of several types of CS, differing in their sulfated positions, on the human colonic microbiota and their metabolites. CS (CSA, CSC, and CSE) and non-sulfated chondroitin (CH) were added into an in vitro human colonic microbiota model with fecal samples from 10 healthy individuals. CS addition showed a tendency to increase the relative abundance of Bacteroides, Eubacterium, and Faecalibacterium, and CSC and CSE addition significantly increased the total number of eubacteria in the culture of the Kobe University Human Intestinal Microbiota Model. CSE addition also resulted in a significant increase in short-chain fatty acid (SCFA) levels. Furthermore, addition with CSC and CSE increased the levels of a wide range of metabolites including lysine, ornithine, and Ile-Pro-Pro, which could have beneficial effects on the host. However, significant increases in the total number of eubacteria, relative abundance of Bacteroides, and SCFA levels were also observed after addition with CH, and the trends in the effects of CH addition on metabolite concentrations were identical to those of CSC and CSE addition. These results provide novel insight into the contribution of the colonic microbiota to the beneficial effects of dietary CS.

Fungal β-glucan-facilitated cross-feeding activities between Bacteroides and Bifidobacterium species

The human gut microbiota (HGM) is comprised of a very complex network of microorganisms, which interact with the host thereby impacting on host health and well-being. β-glucan has been established as a dietary polysaccharide supporting growth of particular gut-associated bacteria, including members of the genera Bacteroides and Bifidobacterium, the latter considered to represent beneficial or probiotic bacteria. However, the exact mechanism underpinning β-glucan metabolism by gut commensals is not fully understood. We show that mycoprotein represents an excellent source for β-glucan, which is consumed by certain Bacteroides species as primary degraders, such as Bacteroides cellulosilyticus WH2. The latter bacterium employs two extracellular, endo-acting enzymes, belonging to glycoside hydrolase families 30 and 157, to degrade mycoprotein-derived β-glucan, thereby releasing oligosaccharides into the growth medium. These released oligosaccharides can in turn be utilized by other gut microbes, such as Bifidobacterium and Lactiplantibacillus, which thus act as secondary degraders. We used a cross-feeding approach to track how both species are able to grow in co-culture.

Enzymatic preparation of chondroitin sulfate oligosaccharides and its alleviating effect on ovariectomy-induced osteoporosis in rats

Postmenopausal osteoporosis is the most common type of osteoporosis. Chondroitin sulfate (CS) has been successfully employed as food supplement against osteoarthritis, while the therapeutic potential on postmenopausal osteoporosis is little explored. In this study, CS oligosaccharides (CSOs) were enzymatically prepared through the lysis of CS by a chondroitinase from Microbacterium sp. Strain. The alleviating effects of CS, CSOs and Caltrate D (a clinically used supplement) on ovariectomy (OVX) - induced rat's osteoporosis were comparatively investigated. Our data showed that the prepared CSOs was basically unsaturated CS disaccharide mixture of ∆Di4S (53.1%), ∆Di6S (27.7%) and ∆Di0S (17.7%). 12 weeks' intragastric administration of Caltrate D (250 mg/kg/d), CS or CSOs (500 mg/kg/d, 250 mg/kg/d, 125 mg/kg/d) could obviously regulate the disorder of serum indices, recover the mechanical strength and mineral content of bone, improve the cortical bones' density and the number and length of trabecular bones in OVX rats. Both CS and CSOs in 500 mg/kg/d and 250 mg/kg/d could restore more efficiently the serum indices, bone fracture deflection and femur Ca than Caltrate D. As compared with CS at the same dosage, CSOs exhibited a more significant alleviating effect. These findings suggested that there was great potential of CSOs as daily interventions for delaying the progression of postmenopausal osteoporosis.

In vitro fermentation of heparin by the human gut microbiota: Changes in the microbiota community and metabolic functions

Levels of its utilization suggest that the host glycosaminoglycan heparin is an important carbohydrate in the human gut microbiota. However, the interaction between heparin and the gut microbiota is not well understood. In this study, an in vitro fermentation system combined with microbiome and metabolome technologies was used to study the interaction between heparin and the gut microbiota. Interestingly, we found that heparin can be used by the gut microbiota, which produce large amounts of short chain fatty acids leading to a decrease in pH. In addition, the addition of heparin increased the relative abundance of Bacteroides and Bifidobacterium and decreased the relative abundance of Escherichia-Shigella. Correlation analysis of the microbiome and metabolome revealed that the catabolism of heparin was accompanied by the biosynthesis of bile acids and tryptophan metabolism. Overall, this study provides new evidence on the role of heparin as a stable carbon source for the gut microbiota and forms a strong basis for the use of heparin to condition the gut microbiota.

Urinary Glycosaminoglycans Are Associated with Recurrent UTI and Urobiome Ecology in Postmenopausal Women

Glycosaminoglycans (GAGs) are linear, negatively charged polysaccharides composed of repeating disaccharide units of uronic acid and amino sugars. The luminal surface of the bladder epithelium is coated with a GAG layer. These urothelial GAGs are thought to provide a protective barrier and serve as a potential interaction site with the urinary microbiome (urobiome). Previous studies have profiled urinary GAG composition in mixed cohorts, but the urinary GAG composition in postmenopausal women remains undefined. To investigate the relationship between GAGs and recurrent urinary tract infection (rUTI), we profiled urinary GAGs in a controlled cohort of postmenopausal women. We found that chondroitin sulfate (CS) is the major urinary GAG in postmenopausal women and that urinary CS was elevated in women with active rUTI. We also associated urinary GAGs with urobiome composition and identified bacterial species that significantly associated with urinary GAG concentration. Corynebacterium amycolatum, Porphyromonas somerae, and Staphylococcus pasteuri were positively associated with heparin sulfate or hyaluronic acid, and bacterial species associated with vaginal dysbiosis were negatively correlated with urinary CS. Altogether, this work defines changes in urinary GAG composition associated with rUTI and identifies new associations between urinary GAGs and the urobiome that may play a role in rUTI pathobiology.

Urinary Glycosaminoglycans are Associated with Recurrent UTI and Urobiome Ecology in Postmenopausal Women

Glycosaminoglycans (GAGs) are linear, negatively charged polysaccharides composed of repeating disaccharide units of uronic acid and amino sugars. The luminal surface of the bladder epithelium is coated with a GAG layer. These urothelial GAGs are thought to provide a protective barrier and serve as a potential interaction site with the urinary microbiome (urobiome). Previous studies have profiled urinary GAG composition in mixed cohorts, but the urinary GAG composition in postmenopausal women remains undefined. To investigate the relationship between GAGs and recurrent UTI (rUTI), we profiled urinary GAGs in a controlled cohort of postmenopausal women. We found that chondroitin sulfate (CS) is the major urinary GAG in postmenopausal women and that urinary CS was elevated in women with active rUTI. We also associated urinary GAGs with urobiome composition and identified bacterial species that significantly associated with urinary GAG concentration. Corynebacterium amycolatum, Porphyromonas somerae , and Staphylococcus pasteuri were positively associated with heparin sulfate or hyaluronic acid and bacterial species associated with vaginal dysbiosis were negatively correlated to urinary CS. Altogether, this work defines changes in urinary GAG composition associated with rUTI and identifies new associations between urinary GAGs and the urobiome that may play a role in rUTI pathobiology.

Hungatella hathewayi, an Efficient Glycosaminoglycan-Degrading Firmicutes from Human Gut and Its Chondroitin ABC Exolyase with High Activity and Broad Substrate Specificity

An increased understanding of GAG metabolism by intestinal bacteria is critical in identifying the driving factors for the composition, modulation, and homeostasis of the human gut microbiota. In addition, GAG-depolymerizing polysaccharide lyases are highly desired enzymes for the production of GAG oligosaccharides and as therapeutics.

Xylan Prebiotics and the Gut Microbiome Promote Health and Wellbeing: Potential Novel Roles for Pentosan Polysulfate

This narrative review highlights the complexities of the gut microbiome and health-promoting properties of prebiotic xylans metabolized by the gut microbiome. In animal husbandry, prebiotic xylans aid in the maintenance of a healthy gut microbiome. This prevents the colonization of the gut by pathogenic organisms obviating the need for dietary antibiotic supplementation, a practice which has been used to maintain animal productivity but which has led to the emergence of antibiotic resistant bacteria that are passed up the food chain to humans. Seaweed xylan-based animal foodstuffs have been developed to eliminate ruminant green-house gas emissions by gut methanogens in ruminant animals, contributing to atmospheric pollution. Biotransformation of pentosan polysulfate by the gut microbiome converts this semi-synthetic sulfated disease-modifying anti-osteoarthritic heparinoid drug to a prebiotic metabolite that promotes gut health, further extending the therapeutic profile and utility of this therapeutic molecule. Xylans are prominent dietary cereal components of the human diet which travel through the gastrointestinal tract as non-digested dietary fibre since the human genome does not contain xylanolytic enzymes. The gut microbiota however digest xylans as a food source. Xylo-oligosaccharides generated in this digestive process have prebiotic health-promoting properties. Engineered commensal probiotic bacteria also have been developed which have been engineered to produce growth factors and other bioactive factors. A xylan protein induction system controls the secretion of these compounds by the commensal bacteria which can promote gut health or, if these prebiotic compounds are transported by the vagal nervous system, may also regulate the health of linked organ systems via the gut–brain, gut–lung and gut–stomach axes. Dietary xylans are thus emerging therapeutic compounds warranting further study in novel disease prevention protocols.