Microbial Metabolite Regulation of Epithelial Cell-Cell Interactions and Barrier Function

Comprehensive analysis of key host gene-microbe networks in the cecum tissues of the obese rabbits induced by a high-fat diet

The Cecum is a key site for cellulose digestion in nutrient metabolism of intestine, but its mechanisms of microbial and gene interactions has not been fully elucidated during pathogenesis of obesity. Therefore, the cecum tissues of the New Zealand rabbits and their contents between the high-fat diet-induced group (Ob) and control group (Co) were collected and analyzed using multi-omics. The metagenomic analysis indicated that the relative abundances of Corallococcus_sp._CAG:1435 and Flavobacteriales bacterium species were significantly lower, while those of Akkermansia glycaniphila, Clostridium_sp._CAG:793, Mycoplasma_sp._CAG:776, Mycoplasma_sp._CAG:472, Clostridium_sp._CAG:609, Akkermansia_sp._KLE1605, Clostridium_sp._CAG:508, and Firmicutes_bacterium_CAG:460 species were significantly higher in the Ob as compared to those in Co. Transcriptomic sequencing results showed that the differentially upregulated genes were mainly enriched in pathways, including calcium signaling pathway, PI3K-Akt signaling pathway, and Wnt signaling pathway, while the differentially downregulated genes were mainly enriched in pathways of NF-kappaB signaling pathway and T cell receptor signaling pathway. The comparative analysis of metabolites showed that the glycine, serine, and threonine metabolism and cysteine and methionine metabolism were the important metabolic pathways between the two groups. The combined analysis showed that CAMK1, IGFBP6, and IGFBP4 genes were highly correlated with Clostridium_sp._CAG:793, and Akkermansia_glycaniphila species. Thus, the preliminary study elucidated the microbial and gene interactions in cecum of obese rabbit and provided a basis for further studies in intestinal intervention for human obesity.

Gastrointestinal mucositis: a sign of a (systemic) inflammatory response

PURPOSE OF REVIEW

Gastrointestinal mucositis (GIM) is a significant complication of cancer therapy. Whilst inflammation is a central feature of GIM, studies attempting to mitigate mucosal damage via this mechanism are scarce. This review describes the relation between GIM, local and systemic inflammation, and the microbiome and its metabolites, and explores recent research on therapeutics that target this relationship.

RECENT FINDINGS

Recent literature underscores the pivotal role of inflammation in GIM, elucidating its bidirectional relation with disturbance of the gut microbiota composition and intestinal permeability. These events cause a heightened risk of bloodstream infections and lead to systemic inflammation. While studies investigating risk prediction models or therapeutics targeting GIM-related inflammation remain scarce, results have shown promise in finding biomarkers and alleviating GIM and its accompanying clinical symptoms.

SUMMARY

The findings underscore the important role of inflammation and the microbiome in GIM. Understanding the inflammatory pathways driving GIM is crucial for developing effective treatments. Further research is needed using genomics, epigenomics, and microbiomics to explore better risk prediction models or therapeutic strategies aimed at mitigating GIM-related inflammation.

Xylanase Supplement Enhances the Growth Performance of Broiler by Modulating Serum Metabolism, Intestinal Health, Short-Chain Fatty Acid Composition, and Microbiota

This study aimed to investigate the effects of different levels of xylanase supplementation in a wheat-based diet on growth performance, short-chain fatty acids, intestinal health, microbial composition, and serum metabolism. A total of 1200 male chicks were randomly assigned to four wheat-based diet treatments: Group C (adding 0 mg/kg of xylanase), Group L (adding 50 mg/kg of xylanase), Group M (adding 100 mg/kg of xylanase), and Group H (adding 150 mg/kg of xylanase). The experiment lasted for 56 days. The results indicated that Group H broilers experienced a decreased feed-to-gain ratio throughout the study period. Additionally, dietary supplementation with xylanase led to an increase in the physical barrier, as indicated by increased VH and VH/CD in the gut (p < 0.05). Furthermore, levels of D-lactic acid and endotoxin were reduced. Xylanase supplementation also increased the abundance of Muc-2, ZO-1, and Occludin (p < 0.05). Moreover, xylanase supplementation enhanced the activity of sucrase and maltase in the duodenum (p < 0.05), which may be attributable to the upregulation of the abundance of SI and MGA (p < 0.05). Furthermore, xylanase addition promoted propionic acid produced by specific bacteria, such as Phascolarctobacterium, and influenced the microbial composition to some extent, promoting intestinal health. Additionally, 150 mg/kg of xylanase supplementation increased the amino acid, peptide, and carbohydrate content and upregulated the metabolism of amino acids related to histidine, cysteine, methionine, and other pathways (p < 0.05). These findings suggest adequate xylanase supplementation can enhance nutritional digestibility and absorption, improve growth performance, stimulate endogenous enzyme activity, optimize intestinal morphology and barrier function, and positively influence acid-producing bacteria and amino acid metabolic pathways.

Microbial Metabolite Trimethylamine N-Oxide Promotes Campylobacter jejuni Infection by Escalating Intestinal Inflammation, Epithelial Damage, and Barrier Disruption

The interactions between Campylobacter jejuni , a critical foodborne cause of gastroenteritis, and the intestinal microbiota during infection are not completely understood. The crosstalk between C. jejuni and its host is impacted by the gut microbiota through mechanisms of competitive exclusion, microbial metabolites, or immune response. To investigate the role of gut microbiota on C. jejuni pathogenesis, we examined campylobacteriosis in the IL10KO mouse model, which was characterized by an increase in the relative abundance of intestinal proteobacteria, E. coli , and inflammatory cytokines during C. jejuni infection. We also found a significantly increased abundance of microbial metabolite Trimethylamine N-Oxide (TMAO) in the colonic lumens of IL10KO mice. We further investigated the effects of TMAO on C. jejuni pathogenesis. We determined that C. jejuni senses TMAO as a chemoattractant and the administration of TMAO promotes C. jejuni invasion into Caco-2 monolayers. TMAO also increased the transmigration of C. jejuni across polarized monolayers of Caco-2 cells, decreased TEER, and increased C. jejuni -mediated intestinal barrier damage. Interestingly, TMAO treatment and presence during C. jejuni infection of Caco-2 cells synergistically caused an increased inflammatory cytokine expression, specifically IL-1β and IL-8. These results establish that C. jejuni utilizes microbial metabolite TMAO for increased virulence during infection.

Crosstalk between hypoxia-inducible factor-1α and short-chain fatty acids in inflammatory bowel disease: key clues toward unraveling the mystery

The human intestinal tract constitutes a complex ecosystem, made up of countless gut microbiota, metabolites, and immune cells, with hypoxia being a fundamental environmental characteristic of this ecology. Under normal physiological conditions, a delicate balance exists among these complex "residents", with disruptions potentially leading to inflammatory bowel disease (IBD). The core pathology of IBD features a disrupted intestinal epithelial barrier, alongside evident immune and microecological disturbances. Central to these interconnected networks is hypoxia-inducible factor-1α (HIF-1α), which is a key regulator in gut cells for adapting to hypoxic conditions and maintaining gut homeostasis. Short-chain fatty acids (SCFAs), as pivotal gut metabolites, serve as vital mediators between the host and microbiota, and significantly influence intestinal ecosystem. Recent years have seen a surge in research on the roles and therapeutic potential of HIF-1α and SCFAs in IBD independently, yet reviews on HIF-1α-mediated SCFAs regulation of IBD under hypoxic conditions are scarce. This article summarizes evidence of the interplay and regulatory relationship between SCFAs and HIF-1α in IBD, pivotal for elucidating the disease's pathogenesis and offering promising therapeutic strategies.

Volatilome: Smells like microbial spirit

In recent years, the study of volatile compounds has sparked interest due to their implications in signaling and the enormous variety of bioactive properties attributed to them. Despite the absence of analysis methods standardization, there are a multitude of tools and databases that allow the identification and quantification of volatile compounds. These compounds are chemically heterogeneous and their diverse properties are exploited by various fields such as cosmetics, the food industry, agriculture and medicine, some of which will be discussed here. In virtue of volatile compounds being ubiquitous and fast chemical messengers, these molecules mediate a large number of interspecific and intraspecific interactions, which are key at an ecological level to maintaining the balance and correct functioning of ecosystems. This review briefly summarized the role of volatile compounds in inter- and intra-specific relationships as well as industrial applications associated with the use of these compounds that is emerging as a promising field of study.

Adenosine in Intestinal Epithelial Barrier Function

At the intestinal front, several lines of defense are in place to resist infection and injury, the mucus layer, gut microbiome and strong epithelial junctions, to name a few. Their collaboration creates a resilient barrier. In intestinal disorders, such as inflammatory bowel disease (IBD), barrier function is compromised, which results in rampant inflammation and tissue injury. In response to the destruction, the intestinal epithelium releases adenosine, a small but powerful nucleoside that functions as an alarm signal. Amidst the chaos of inflammation, adenosine aims to restore order. Within the scope of its effects is the ability to regulate intestinal epithelial barrier integrity. This review aims to define the contributions of adenosine to mucus production, microbiome-dependent barrier protection, tight junction dynamics, chloride secretion and acid-base balance to reinforce its importance in the intestinal epithelial barrier.

Tryptophan Metabolites And Their Predicted Microbial Sources In Fecal Samples From Healthy Individuals

Gut microbiota produce tryptophan metabolites (TMs) important to homeostasis. However, measuring TM levels in stool and determining their microbial sources can be difficult. Here, we measured TMs from the indole pathway in fecal samples from 21 healthy adults with the goal to: 1) determine fecal TM concentrations in healthy individuals; 2) link TM levels to bacterial abundance using 16S and whole genome shotgun (WGS) sequencing data; and 3) predict likely bacterial sources of TM production. Within our samples, we identified 151 genera (16S) and 592 bacterial species (WGS). Eight TMs were found in ≥17 fecal samples, including four in all persons. To our knowledge, we are the first to report fecal levels for indole-3-lactate, indole-3-propionate, and 3-indoleacrylate levels in healthy persons. Overall, indole, indole-3-acetate (IAA), and skatole accounted for 86% of the eight TMs measured. Significant correlations were found between seven TMs and 29 bacterial species.  Predicted multiple TM sources support the notion of a complex network of TM production and regulation. Further, the data suggest key roles for Collinsella aerofaciens and IAA, a metabolite reported to maintain intestinal homeostasis through enhanced barrier integrity and anti-inflammatory/antioxidant activities. These findings extend our understanding of TMs and their relationship to the microbial species that act as effectors and/or regulators in the healthy intestine and may lead to novel strategies designed to manipulate tryptophan metabolism to prevent disease and/or restore health to the dysbiotic gut.

Mimicry of microbially-derived butyrate reveals templates for potent intestinal epithelial HIF stabilizers

Microbiota-derived short-chain fatty acids, including butyrate (BA), have multiple beneficial health effects. In the colon, BA concentrations range from 10 to 20 mM and up to 95% is utilized as energy by the mucosa. BA plays a key role in epithelial-barrier regulation and anti-inflammation, and regulates cell growth and differentiation, at least in part, due to its direct influence on stabilization of the transcription factor hypoxia-inducible factor (HIF). It remains unclear whether BA is the optimal metabolite for such a response. In this study, we explored metabolite mimicry as an attractive strategy for the biological response to HIF. We discovered that 4-mercapto butyrate (MBA) stabilizes HIF more potently and has a longer biological half-life than BA in intestinal epithelial cells (IECs). We validated the MBA-mediated HIF transcriptional activity through the induction of classic HIF gene targets in IECs and enhanced epithelial barrier formation in vitro. In-vivo studies with MBA revealed systemic HIF stabilization in mice, which was more potent than its parent BA metabolite. Mechanistically, we found that MBA enhances oxygen consumption and that the sulfhydryl group is essential for HIF stabilization, but exclusively as a four-carbon SCFA. These findings reveal a combined biochemical mechanism for HIF stabilization and provide a foundation for the discovery of potent metabolite-like scaffolds.

Effect of Cichorium glandulosum on intestinal microbiota and bile acid metabolism in db/db mice

This study aims to investigate the effects of Chorum glandulosum Boiss. et Huet (CG) on the intestinal microbiota and serum bile acid (BA) in db/db mice. A total of 12 db/db mice were randomly divided into model (MOD), high-dose CG (CGH), and control (CON) groups. The CON and MOD groups received distilled water by gavage for 8 weeks. Whereas, the CGH group received an alcohol extract of CG at a dose of 200 mg/kg/day. Results showed that CG can reduce blood lipid levels. It change the composition of the intestinal microbiota, and increase the relative abundances of Muribaculaceae, Prevotellaceae, Bifidobacterium_pseudolongum, Bacteroidaceae in db/db mice as well. LC-MS metabolomics results showed that CG adjusted the serum BA levels. The results reduced the levels of primary BAs, such as cholic acid (CA) and chenodeoxycholic acid (CDCA). The results decreased the primary BA/secondary BA (PSA/SBA) ratio in db/db mice. Correlation analysis showed that the abundances of Bifidobacterium_pseudolongum and Bacteroidaceae were positively correlated with acetic acid level and negatively correlated with ursocholic acid (UCA), α-muricholic acid (αMCA), triglyceride (TG), and total cholesterol levels (TC), indicating an interaction between the intestinal microbiota and serum BAs. CG may play a positive role in the interaction between the intestinal microbiota and BAs in lipid metabolism.

Small Intestinal Permeability and Metabolomic Profiles in Feces and Plasma Associate With Clinical Response in Patients With Active Psoriatic Arthritis Participating in a Fecal Microbiota Transplantation Trial: Exploratory Findings From the FLORA Trial

OBJECTIVE

We investigated intestinal permeability and fecal, plasma, and urine metabolomic profiles in methotrexate-treated active psoriatic arthritis (PsA) and how this related to clinical response following one sham or fecal microbiota transplantation (FMT).

METHODS

This exploratory study is based on the FLORA trial cohort, in which 31 patients with moderate-to-high peripheral PsA disease activity, despite at least 3 months of methotrexate-treatment, were included in a 26-week, double-blind, 1:1 randomized, sham-controlled trial. Participants were randomly allocated to receive either one healthy donor FMT (n = 15) or sham (n = 16) via gastroscopy. The primary trial end point was the proportion of treatment failures through 26 weeks. We performed a lactulose-to-mannitol ratio (LMR) test at baseline (n = 31) and at week 26 (n = 26) to assess small intestinal permeability. Metabolomic profiles in fecal, plasma, and urine samples collected at baseline, weeks 4, 12, and 26 were measured using 1 H Nuclear Magnetic Resonance.

RESULTS

Trial failures (n = 7) had significantly higher LMR compared with responders (n = 19) at week 26 (0.027 [0.017-0.33]) vs. 0.012 [0-0.064], P = 0.013), indicating increased intestinal permeability. Multivariate analysis revealed a significant model for responders (n = 19) versus failures (n = 12) at all time points based on their fecal (P < 0.0001) and plasma (P = 0.005) metabolomic profiles, whereas urine metabolomic profiles did not differ between groups (P = 1). Fecal N-acetyl glycoprotein GlycA correlated with Health Assessment Questionnaire Disability Index (coefficient = 0.50; P = 0.03) and fecal propionate correlated with American College of Rheumatology 20 response at week 26 (coefficient = 27, P = 0.02).

CONCLUSION

Intestinal permeability and fecal and plasma metabolomic profiles of patients with PsA were associated with the primary clinical trial end point, failure versus responder.

Potential Ability of Probiotics in the Prevention and Treatment of Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer in the world, and its incidence rate and mortality are on the rise in many countries. In recent years, with the improvement of economic conditions, people's living habits have changed, including lack of physical activity, poor diet patterns and circadian rhythm disorder. These risk factors can change the colon environment and the composition of intestinal microbiota. This state is called intestinal imbalance, which increases the risk of cancer. Probiotics, a class of microorganisms that help maintain gut microbial homeostasis and alleviate dysbiosis, may help prevent inflammation and colorectal cancer. These probiotics inhibit or ameliorate the effects of dysbiosis through the production of short-chain fatty acids (SCFAs), modulation of immunity, maintenance of the intestinal epithelial barrier, pro-apoptotic mechanisms, and other mechanisms. This review aims to explain the interaction between probiotics, the gut microenvironment and the gut microbiota, and summarize reports on the possibility of probiotics in the prevention and treatment of colorectal cancer.

The Role of Mucoadhesion and Mucopenetration in the Immune Response Induced by Polymer-Based Mucosal Adjuvants

Mucus is a viscoelastic gel that acts as a protective barrier for epithelial surfaces. The mucosal vehicles and adjuvants need to pass through the mucus layer to make drugs and vaccine delivery by mucosal routes possible. The mucoadhesion of polymer particle adjuvants significantly increases the contact time between vaccine formulations and the mucosa; then, the particles can penetrate the mucus layer and epithelium to reach mucosa-associated lymphoid tissues. This review presents the key findings that have aided in understanding mucoadhesion and mucopenetration while exploring the influence of physicochemical characteristics on mucus-polymer interactions. We describe polymer-based particles designed with mucoadhesive or mucopenetrating properties and discuss the impact of mucoadhesive polymers on local and systemic immune responses after mucosal immunization. In future research, more attention paid to the design and development of mucosal adjuvants could lead to more effective vaccines.

Real-time measurement of the trans-epithelial electrical resistance in an organ-on-a-chip during cell proliferation

The trans-epithelial electrical resistance (TEER) is widely used to quantitatively evaluate cellular barrier function at the organ level in vitro. The measurement of the TEER in organ-on-chips (organ chips) plays a significant role in medical and pharmacological research. However, due to the limitation of the electrical equivalent model for organ chips, the existing TEER measurements usually neglect the changes of the TEER during cell proliferation, resulting in the low accuracy of the measurements. Here, we proposed a new whole-region model of the TEER and developed a real-time TEER measurement system that contains an organ chip with a plate electrode. A whole region circuit model considering the impedance of the non-cell covered region was also established, which enables TEER measurements to be independent of the changes in the cell covered region. The impedance of the non-cell covered region is here attributed to the resistance of the porous membrane. By combining the real-time measurement system and the whole region model, subtle changes in cellular activity during the proliferation stage were measured continuously every 6 minutes and a more sensitive TEER response was obtained. Furthermore, the TEER measurement accuracy was also verified by the real-time measurement of the TEER with stimulation using the permeability enhancer ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA). The obtained results indicated that the new proposed whole region model and the real-time measurement system have higher accuracy and greater sensitivity than the traditional model.

Multiple pathways promote microtubule stabilization in senescent intestinal epithelial cells

Intestinal epithelial cells are critical for gastrointestinal homeostasis. However, their function declines during aging. The aging-related loss of organ performance is largely driven by the increase in senescent cells. To date, the hallmarks and molecular mechanisms related to cellular senescence are not fully understood. Microtubules control epithelial functions, and we identified microtubule stabilization as a phenotypic marker of senescent intestinal epithelial cells. The senescence inducer determined the pathway to microtubule stabilization. Specifically, enhanced microtubule stability was associated with α-tubulin hyperacetylation or increased abundance of the microtubule-binding protein tau. We show further that overexpression of MAPT, which encodes tau, augmented microtubule stability in intestinal epithelial cells. Notably, pharmacological microtubule stabilization was sufficient to induce cellular senescence. Taken together, this study provides new insights into the molecular mechanisms that control epithelial cell homeostasis. Our results support the concept that microtubule stability serves as a critical cue to trigger intestinal epithelial cell senescence.

Systems to model the personalized aspects of microbiome health and gut dysbiosis

The human gut microbiome is a complex and dynamic microbial entity that interacts with the environment and other parts of the body including the brain, heart, liver, and immune system. These multisystem interactions are highly conserved from invertebrates to humans, however the complexity and diversity of human microbiota compositions often yield a context that is unique to each individual. Yet commonalities remain across species, where a healthy gut microbiome will be rich in symbiotic commensal biota while an unhealthy gut microbiota will be experiencing abnormal blooms of pathobiont bacteria. In this review we discuss how omics technologies can be applied in a personalized approach to understand the microbial crosstalk and microbial-host interactions that affect the delicate balance between eubiosis and dysbiosis in an individual gut microbiome. We further highlight the strengths of model organisms in identifying and characterizing these conserved synergistic and/or pathogenic host-microbe interactions. And finally, we touch upon the growing area of personalized therapeutic interventions targeting gut microbiome.

A gut-centric view of aging: Do intestinal epithelial cells contribute to age-associated microbiota changes, inflammaging, and immunosenescence?

Intestinal epithelial cells (IECs) serve as both a physical and an antimicrobial barrier against the microbiota, as well as a conduit for signaling between the microbiota and systemic host immunity. As individuals age, the balance between these systems undergoes a myriad of changes due to age-associated changes to the microbiota, IECs themselves, immunosenescence, and inflammaging. In this review, we discuss emerging data related to age-associated loss of intestinal barrier integrity and posit that IEC dysfunction may play a central role in propagating age-associated alterations in microbiota composition and immune homeostasis.