Pregnane X Receptor Activation Attenuates Inflammation-Associated Intestinal Epithelial Barrier Dysfunction by Inhibiting Cytokine-Induced Myosin Light-Chain Kinase Expression and c-Jun N-Terminal Kinase 1/2 Activation

Microbial tryptophan catabolism as an actionable target via diet-microbiome interactions

In recent years, the role of microbial tryptophan (Trp) catabolism in host-microbiota crosstalk has become a major area of scientific interest. Microbiota-derived Trp catabolites positively contribute to intestinal and systemic homeostasis by acting as ligands of aryl hydrocarbon receptor and pregnane X receptor, and as signaling molecules in microbial communities. Accumulating evidence suggests that microbial Trp catabolism could be therapeutic targets in treating human diseases. A number of bacteria and metabolic pathways have been identified to be responsible for the conversion of Trp in the intestine. Interestingly, many Trp-degrading bacteria can benefit from the supplementation of specific dietary fibers and polyphenols, which in turn increase the microbial production of beneficial Trp catabolites. Thus, this review aims to highlight the emerging role of diets and food components, i.e., food matrix, fiber, and polyphenol, in modulating the microbial catabolism of Trp and discuss the opportunities for potential therapeutic interventions via specifically designed diets targeting the Trp-microbiome axis.

Tauroursodeoxycholic Acid Reverses Dextran Sulfate Sodium-Induced Colitis in Mice via Modulation of Intestinal Barrier Dysfunction and Microbiome Dysregulation

Ulcerative colitis (UC) is an immune-mediated inflammatory disease that can lead to persistent damage and even cancer without any intervention. Conventional treatments can alleviate UC symptoms but are costly and cause various side effects. Tauroursodeoxycholic acid (TUDCA), a secondary bile acid derivative, possesses anti-inflammatory and cytoprotective properties for various diseases, but its potential therapeutic benefits in UC have not been fully explored. Mice were subjected to colitis induction using 3% dextran sulfate sodium (DSS). The therapeutic effect of TUDCA was evaluated by body weight loss, disease activity index (DAI), colon length, and spleen weight ratio. Tissue pathology was assessed using H&E staining, while the levels of pro-inflammatory and anti-inflammatory cytokines in colonic tissue were quantified via ELISA. Tight junction proteins were detected by immunoblotting and intestinal permeability was assessed using fluorescein isothiocyanate (FITC)-dextran. Moreover, the gut microbiota was profiled using high-throughput sequencing of the 16S rDNA gene. TUDCA alleviated the colitis in mice, involving reduced DAI, attenuated colon and spleen enlargement, ameliorated histopathological lesions, and normalized levels of pro-inflammatory and anti-inflammatory cytokines. Furthermore, TUDCA treatment inhibited the downregulation of intestinal barrier proteins, including zonula occludens-1 and occludin, thus reducing intestinal permeability. The analysis of gut microbiota suggested that TUDCA modulated the dysbiosis in mice with colitis, especially for the remarkable rise in Akkermansia TUDCA exerted a therapeutic efficacy in DSS-induced colitis by reducing intestinal inflammation, protecting intestinal barrier integrity, and restoring gut microbiota balance. SIGNIFICANCE STATEMENT: This study demonstrates the potential therapeutic benefits of Tauroursodeoxycholic acid (TUDCA) in ulcerative colitis. TUDCA effectively alleviated colitis symptoms in mice, including reducing inflammation, restoring intestinal barrier integrity and the dysbiosis of gut microbiota. This work highlights the promising role of TUDCA as a potentially alternative treatment, offering new insights into managing this debilitating condition.

The effects of whole grain cereals on tryptophan metabolism and intestinal barrier function: underlying factors of health impact

This review aims to investigate the relationship between the health impact of whole grains mediated via the interaction with intestinal microbiota and intestinal barrier function with special interest on tryptophan metabolism, focusing on the role of the intestinal microbiota and their impact on barrier function. Consuming various types of whole grains can lead to the growth of different microbiota species, which in turn leads to the production of diverse metabolites, including those derived from tryptophan metabolism, although the impact of whole grains on intestinal microbiota composition results remains inconclusive and vary among different studies. Whole grains can exert an influence on tryptophan metabolism through interactions with the intestinal microbiota, and the presence of fibre in whole grains plays a notable role in establishing this connection. The impact of whole grains on intestinal barrier function is closely related to their effects on the composition and activity of intestinal microbiota, and SCFA and tryptophan metabolites serve as potential links connecting whole grains, intestinal microbiota and the intestinal barrier function. Tryptophan metabolites affect various aspects of the intestinal barrier, such as immune balance, mucus and microbial barrier, tight junction complexes and the differentiation and proliferation of epithelial cells. Despite the encouraging discoveries in this area of research, the evidence regarding the effects of whole grain consumption on intestine-related activity remains limited. Hence, we can conclude that we are just starting to understand the actual complexity of the intestinal factors mediating in part the health impacts of whole grain cereals.

Gut microbiota in pathophysiology, diagnosis, and therapeutics of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a multifactorial disease, which is thought to be an interplay between genetic, environment, microbiota, and immune-mediated factors. Dysbiosis in the gut microbial composition, caused by antibiotics and diet, is closely related to the initiation and progression of IBD. Differences in gut microbiota composition between IBD patients and healthy individuals have been found, with reduced biodiversity of commensal microbes and colonization of opportunistic microbes in IBD patients. Gut microbiota can, therefore, potentially be used for diagnosing and prognosticating IBD, and predicting its treatment response. Currently, there are no curative therapies for IBD. Microbiota-based interventions, including probiotics, prebiotics, synbiotics, and fecal microbiota transplantation, have been recognized as promising therapeutic strategies. Clinical studies and studies done in animal models have provided sufficient evidence that microbiota-based interventions may improve inflammation, the remission rate, and microscopic aspects of IBD. Further studies are required to better understand the mechanisms of action of such interventions. This will help in enhancing their effectiveness and developing personalized therapies. The present review summarizes the relationship between gut microbiota and IBD immunopathogenesis. It also discusses the use of gut microbiota as a noninvasive biomarker and potential therapeutic option.

Potential role of bile acids in the pathogenesis of necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is one of the most common acute gastrointestinal diseases in preterm infants. Recent studies have found that NEC is not only caused by changes in the intestinal environment but also by the failure of multiple systems and organs, including the liver. The accumulation of bile acids (BAs) in the ileum and the disorder of ileal BA transporters are related to the ileum injury of NEC. Inflammatory factors such as tumor necrosis factor (TNF)-α and interleukin (IL)-18 secreted by NEC also play an important role in regulating intrahepatic BA transporters. As an important link connecting the liver and intestinal circulation, the bile acid metabolic pathway plays an important role in the regulation of intestinal microbiota, cell proliferation, and barrier protection. In this review, we focus on how bile acids explore the dynamic changes of bile acid metabolism in necrotizing enterocolitis and the potential therapeutic value of targeting the bile acid signaling pathways.

The role of the indoles in microbiota-gut-brain axis and potential therapeutic targets: A focus on human neurological and neuropsychiatric diseases

At present, a large number of relevant studies have suggested that the changes in gut microbiota are related to the course of nervous system diseases, and the microbiota-gut-brain axis is necessary for the proper functioning of the nervous system. Indole and its derivatives, as the products of the gut microbiota metabolism of tryptophan, can be used as ligands to regulate inflammation and autoimmune response in vivo. In recent years, some studies have found that the levels of indole and its derivatives differ significantly between patients with central nervous system diseases and healthy individuals, suggesting that they may be important mediators for the involvement of the microbiota-gut-brain axis in the disease course. Tryptophan metabolites produced by gut microbiota are involved in multiple physiological reactions, take indole for example, it participates in the process of inflammation and anti-inflammatory effects through various cellular physiological activities mediated by aromatic hydrocarbon receptors (AHR), which can influence a variety of neurological and neuropsychiatric diseases. This review mainly explores and summarizes the relationship between indoles and human neurological and neuropsychiatric disorders, including ischemic stroke, Alzheimer's disease, Parkinson's disease, multiple sclerosis, cognitive impairment, depression and anxiety, and puts forward that the level of indoles can be regulated through various direct or indirect ways to improve the prognosis of central nervous system diseases and reverse the dysfunction of the microbiota-gut-brain axis. This article is part of the Special Issue on "Microbiome & the Brain: Mechanisms & Maladies".

Aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) play both distinct and common roles in the regulation of colon homeostasis and intestinal carcinogenesis

Both aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) belong among key regulators of xenobiotic metabolism in the intestinal tissue. AhR in particular is activated by a wide range of environmental and dietary carcinogens. The data accumulated over the last two decades suggest that both of these transcriptional regulators play a much wider role in the maintenance of gut homeostasis, and that both transcription factors may affect processes linked with intestinal tumorigenesis. Intestinal epithelium is continuously exposed to a wide range of AhR, PXR and dual AhR/PXR ligands formed by intestinal microbiota or originating from diet. Current evidence suggests that specific ligands of both AhR and PXR can protect intestinal epithelium against inflammation and assist in the maintenance of epithelial barrier integrity. AhR, and to a lesser extent also PXR, have been shown to play a protective role against inflammation-induced colon cancer, or, in mouse models employing overactivation of Wnt/β-catenin signaling. In contrast, other evidence suggests that both receptors may contribute to modulation of transformed colon cell behavior, with a potential to promote cancer progression and/or chemoresistance. The review focuses on both overlapping and separate roles of the two receptors in these processes, and on possible implications of their activity within the context of intestinal tissue.

Demystifying the impact of prenatal tobacco exposure on the placental immune microenvironment: Avoiding the tragedy of mending the fold after death

Prenatal tobacco exposure (PTE) correlates significantly with a surge in adverse pregnancy outcomes, yet its pathological mechanisms remain partially unexplored. This study aims to meticulously examine the repercussions of PTE on placental immune landscapes, employing a coordinated research methodology encompassing bioinformatics, machine learning and animal studies. Concurrently, it aims to screen biomarkers and potential compounds that could sensitively indicate and mitigate placental immune disorders. In the course of this research, two gene expression omnibus (GEO) microarrays, namely GSE27272 and GSE7434, were included. Gene set enrichment analysis (GSEA) and immune enrichment investigations on differentially expressed genes (DEGs) indicated that PTE might perturb numerous innate or adaptive immune-related biological processes. A cohort of 52 immune-associated DEGs was acquired by cross-referencing the DEGs with gene sets derived from the ImmPort database. A protein-protein interaction (PPI) network was subsequently established, from which 10 hub genes were extracted using the maximal clique centrality (MCC) algorithm (JUN, NPY, SST, FLT4, FGF13, HBEGF, NR0B2, AREG, NR1I2, SEMA5B). Moreover, we substantiated the elevated affinity of tobacco reproductive toxicants, specifically nicotine and nitrosamine, with hub genes through molecular docking (JUN, FGF13 and NR1I2). This suggested that these genes could potentially serve as crucial loci for tobacco's influence on the placental immune microenvironment. To further elucidate the immune microenvironment landscape, consistent clustering analysis was conducted, yielding three subtypes, where the abundance of follicular helper T cells (p < 0.05) in subtype A, M2 macrophages (p < 0.01), neutrophils (p < 0.05) in subtype B and CD8+ T cells (p < 0.05), resting NK cells (p < 0.05), M2 macrophages (p < 0.05) in subtype C were significantly different from the control group. Additionally, three pivotal modules, designated as red, blue and green, were identified, each bearing a close association with differentially infiltrated immunocytes, as discerned by the weighted gene co-expression network analysis (WGCNA). Functional enrichment analysis was subsequently conducted on these modules. To further probe into the mechanisms by which immune-associated DEGs are implicated in intercellular communication, 20 genes serving as ligands or receptors and connected to differentially infiltrating immunocytes were isolated. Employing a variety of machine learning techniques, including one-way logistic regression, LASSO regression, random forest and artificial neural networks, we screened 11 signature genes from the intersection of immune-associated DEGs and secretory protein-encoding genes derived from the Human Protein Atlas. Notably, CCL18 and IFNA4 emerged as prospective peripheral blood markers capable of identifying PTE-induced immune disorders. These markers demonstrated impressive predictive power, as indicated by the area under the curve (AUC) of 0.713 (0.548-0.857) and 0.780 (0.618-0.914), respectively. Furthermore, we predicted 34 potential compounds, including cyclosporine, oestrogen and so on, which may engage with hub genes and attenuate immune disorders instigated by PTE. The diagnostic performance of these biomarkers, alongside the interventional effect of cyclosporine, was further corroborated in animal studies via ELISA, Western blot and immunofluorescence assays. In summary, this study identifies a disturbance in the placental immune landscape, a secondary effect of PTE, which may underlie multiple pregnancy complications. Importantly, our research contributes to the noninvasive and timely detection of PTE-induced placental immune disorders, while also offering innovative therapeutic strategies for their treatment.

IPA and its precursors differently modulate the proliferation, differentiation, and integrity of intestinal epithelial cells

BACKGROUND/OBJECTIVES

Indole-3-propionic acid (IPA) is a tryptophan-derived microbial metabolite that has been associated with protective effects against inflammatory and metabolic diseases. However, there is a lack of knowledge regarding the effects of IPA under physiological conditions and at the intestinal level.

MATERIALS/METHODS

Human intestinal epithelial Caco-2 cells were treated for 2, 24, and/or 72 h with IPA or its precursors - indole, tryptophan, and propionate - at 1, 10, 100, 250, or 500 μM to assess cell viability, integrity, differentiation, and proliferation.

RESULTS

IPA induced cell proliferation and this effect was associated with a higher expression of extracellular signal-regulated kinase 2 (ERK2) and a lower expression of c-Jun. Although indole and propionate also induced cell proliferation, this involved ERK2 and c-Jun independent mechanisms. On the other hand, both tryptophan and propionate increased cell integrity and reduced the expression of claudin-1, whereas propionate decreased cell differentiation.

CONCLUSIONS

In conclusion, these findings suggested that IPA and its precursors distinctly contribute to the proliferation, differentiation, and barrier function properties of human intestinal epithelial cells. Moreover, the pro-proliferative effect of IPA in intestinal epithelial cells was not explained by its precursors and is rather related to its whole chemical structure. Maintaining IPA at physiological levels, e.g., through IPA-producing commensal bacteria, may be important to preserve the integrity of the intestinal barrier and play an integral role in maintaining metabolic homeostasis.

Terpenes: Modulating anti-inflammatory signaling in inflammatory bowel disease

Inflammatory Bowel Disease (IBD) are autoimmune diseases characterized by chronic intestinal inflammation. Considered a western disease, IBD incidence in newly developed countries is skyrocketing. Accordingly, global prevalence is steadily increasing. There are two major IBD phenotypes, ulcerative colitis (UC) and Crohn's disease (CD). UC manifests as uninterrupted inflammation localized in the colon and rectum. Meanwhile, CD presents as interrupted inflammation that can occur throughout the digestive tract. As a result, therapeutics have focused on anti-inflammatory approaches for its treatment. Unfortunately, only 50% of patients benefit from current Food and Drug Administration approved treatments, and all are associated with serious adverse effects. Thus, there is a need for safer and novel therapeutics to increase the efficacy in this population. One aspect that is critical in understanding IBD is how food and phytochemicals therein may be associated with modifying the pathogenesis of IBD. A variety of retrospective and prospective studies, and clinical trials have shown benefits of plant-rich diets on the prevention and symptomatic improvement of IBD. The Mediterranean diet is rich in vegetables, fruits, legumes, and herbs; and characterized by the abundance of anti-inflammatory phytochemicals. An understudied phytochemical class enriched in this diet is terpenes; isoprene-based molecules are widely available in Mediterranean herbs and citrus fruits. Various terpenes have been evaluated in different IBD models. However, some present contradictory or inconclusive results. Therefore, in this review we evaluated preclinical studies of terpenes modulating basic inflammatory signaling related to IBD.

Metabolite interactions between host and microbiota during health and disease: Which feeds the other?

Metabolites produced by the host and microbiota play a crucial role in how human bodies develop and remain healthy. Most of these metabolites are produced by microbiota and hosts in the digestive tract. Metabolites in the gut have important roles in energy metabolism, cellular communication, and host immunity, among other physiological activities. Although numerous host metabolites, such as free fatty acids, amino acids, and vitamins, are found in the intestine, metabolites generated by gut microbiota are equally vital for intestinal homeostasis. Furthermore, microbiota in the gut is the sole source of some metabolites, including short-chain fatty acids (SCFAs). Metabolites produced by microbiota, such as neurotransmitters and hormones, may modulate and significantly affect host metabolism. The gut microbiota is becoming recognized as a second endocrine system. A variety of chronic inflammatory disorders have been linked to aberrant host-microbiota interplays, but the precise mechanisms underpinning these disturbances and how they might lead to diseases remain to be fully elucidated. Microbiome-modulated metabolites are promising targets for new drug discovery due to their endocrine function in various complex disorders. In humans, metabolotherapy for the prevention or treatment of various disorders will be possible if we better understand the metabolic preferences of bacteria and the host in specific tissues and organs. Better disease treatments may be possible with the help of novel complementary therapies that target host or bacterial metabolism. The metabolites, their physiological consequences, and functional mechanisms of the host-microbiota interplays will be highlighted, summarized, and discussed in this overview.

The Pregnane X Receptor and Indole-3-Propionic Acid Shape the Intestinal Mesenchyme to Restrain Inflammation and Fibrosis

BACKGROUND & AIMS

Fibrosis is a common complication of inflammatory bowel diseases (IBDs). The pregnane X receptor (PXR) (encoded by NR1I2) suppresses intestinal inflammation and has been shown to influence liver fibrosis. In the intestine, PXR signaling is influenced by microbiota-derived indole-3-propionic acid (IPA). Here, we sought to assess the role of the PXR in regulating intestinal inflammation and fibrosis.

METHODS

Intestinal inflammation was induced using dextran sulfate sodium (DSS). Fibrosis was assessed in wild-type (WT), Nr1i2^-/-, epithelial-specific Nr1i2^-/-, and fibroblast-specific Nr1i2^-/- mice. Immune cell influx was quantified by flow cytometry and cytokines by Luminex. Myofibroblasts isolated from WT and Nr1i2^-/- mice were stimulated with cytomix or lipopolysaccharide, and mediator production was assessed by quantitative polymerase chain reaction and Luminex.

RESULTS

After recovery from DSS-induced colitis, WT mice exhibited fibrosis, a response that was exacerbated in Nr1i2^-/- mice. This was correlated with greater neutrophil infiltration and innate cytokine production. Deletion of the PXR in fibroblasts, but not the epithelium, recapitulated this phenotype. Inflammation and fibrosis were reduced by IPA administration, whereas depletion of the microbiota exaggerated intestinal fibrosis. Nr1i2-deficient myofibroblasts were hyperresponsive to stimulation, producing increased levels of inflammatory mediators compared with WT cells. In biopsies from patients with active Crohn's disease (CD) and ulcerative colitis (UC), expression of NR1I2 was reduced, correlating with increased expression of fibrotic and innate immune genes. Finally, both CD and UC patients exhibited reduced levels of fecal IPA.

CONCLUSIONS

These data highlight a role for IPA and its interactions with the PXR in regulating the mesenchyme and the development of inflammation and fibrosis, suggesting microbiota metabolites may be a vital determinant in the progression of fibrotic complications in IBD.

Skatole: A thin red line between its benefits and toxicity

Skatole (3-methylindole) is a heterocyclic compound naturally found in the feces of vertebrates and is produced by certain flowers. Skatole has been used in specific products of the perfume industry or as a flavor additive in ice cream. Additionally, skatole is formed by tryptophan pyrolysis of tobacco and has been demonstrated to be a mutagen. Skatole-induced pulmonotoxicity was reliably described in ruminants and rodents, but no studies have been conducted in humans. Initially, we provide basic knowledge and a historical overview of skatole. Then, skatole bacterial formation in the intestine is described, and the importance of the microbiome during this process is evaluated. Increased skatole concentrations could serve as a marker for intestinal disease development. Therefore, the human molecular targets of skatole that may have significant effects on various processes in the human body are described. Ultimately, we suggest a link between skatole intestinal formation in humans and skatole-induced pulmonotoxicity, which should be explored further in the future.

Rifaximin and lubiprostone mitigate liver fibrosis development by repairing gut barrier function in diet-induced rat steatohepatitis

BACKGROUND

Although gut-derived lipopolysaccharide (LPS) affects the progression of non-alcoholic steatohepatitis (NASH) pathogenesis, few studies have focused on this relationship to develop treatments for NASH.

AIMS

To explore the effects of combination with rifaximin and lubiprostone on NASH liver fibrosis through the modulation of gut barrier function.

METHODS

To induce steatohepatitis, F344 rats were fed a choline-deficient l-amino acid-defined (CDAA) diet for 12 weeks and received oral administration of rifaximin and/or lubiprostone. Histological, molecular, and fecal microbial analyses were performed. Barrier function in Caco-2 cells were assessed by in vitro assays.

RESULTS

Combination rifaximin/lubiprostone treatment significantly suppressed macrophage expansion, proinflammatory responses, and liver fibrosis in CDAA-fed rats by blocking hepatic translocation of LPS and activation of toll-like receptor 4 signaling. Rifaximin and lubiprostone improved intestinal permeability via restoring tight junction proteins (TJPs) with the intestinal activation of pregnane X receptor and chloride channel-2, respectively. Moreover, this combination increased the abundance of Bacteroides, Lactobacillus, and Faecalibacterium as well as decreased that of Veillonella resulting in an increase of fecal short-chain fatty acids and a decrease of intestinal sialidase activity. Both agents also directly suppressed the LPS-induced barrier dysfunction and depletion of TJPs in Caco-2 cells.

CONCLUSION

The combination of rifaximin and lubiprostone may provide a novel strategy for treating NASH-related fibrosis.

PXR as the tipping point between innate immune response, microbial infections, and drug metabolism

Pregnane X receptor (PXR) is a xenosensor that acts as a transcription factor in the cell nucleus to protect cells from toxic insults. In response to exposure to several chemical agents, PXR induces the expression of enzymes and drug transporters that biotransform xenobiotic and endobiotic and eliminate metabolites. Recently, PXR has been shown to have immunomodulatory effects that involve cross-communication with molecular pathways in innate immunity cells. Conversely, several inflammatory factors regulate PXR signaling. This review examines the crosstalk between PXR and nuclear factor kappa B (NFkB), Toll-like receptors (TLRs), and inflammasome components. Discussions of the consequences of these interactions on immune responses to infections caused by viruses, bacteria, fungi, and parasites are included together with a review of the effects of microorganisms on PXR-associated drug metabolism. This paper aims to encourage researchers to pursue studies that will better elucidate the relationship between PXR and the immune system and thus inform treatment development.

Role of Bile Acids and Nuclear Receptors in Acupuncture in Improving Crohn's Disease

Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the transcription of target genes. Bile acids (BAs) can be used as effector molecules to regulate physiological processes in the gut, and NRs are important receptors for bile acid signaling. Relevant studies have shown that NRs are closely related to the occurrence of Crohn's disease (CD). Although the mechanism of NRs in CD has not been clarified completely, growing evidence shows that NRs play an important role in regulating intestinal immunity, mucosal barrier, and intestinal flora. NRs can participate in the progress of CD by mediating inflammation, immunity, and autophagy. As the important parts of traditional Chinese medicine (TCM) therapy, acupuncture and moxibustion in the treatment of CD curative mechanism can get a lot of research support. At the same time, acupuncture and moxibustion can regulate the changes of related NRs. Therefore, to explore whether acupuncture can regulate BA circulation and NRs expression and then participate in the disease progression of CD, a new theoretical basis for acupuncture treatment of CD is provided.

Bile acid-gut microbiota crosstalk in irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder of gut-brain interaction with an increasing prevalence, and its precise aetiology remains unclear. Gut microbiota dysbiosis has been found to be associated with IBS pathogenesis. In addition, a high incidence of bile acid diarrhoea and disturbed bile acid metabolism has been observed in IBS patients. The abundant microorganisms inhabited in human gut have essential functions in bile acid biotransformation, and can immensely affect the size and constitution of bile acid pool. Meanwhile, the alterations of bile acid profile can inversely interfere with the gut microbiota. This review discussed the role of intricate correlations between bile acids and gut microbiota in IBS pathogenesis and delineated the possible molecular mechanisms, mainly the signalling induced by farnesoid X receptor and transmembrane G protein-coupled receptor 5. Besides, some biomarkers for identifying bile acid diarrhoea in IBS population were listed, assisting the diagnosis and classification of IBS. Moreover, it also assessed some therapeutic strategies for IBS that regulate the bile acid-gut microbiota axis, such as dietary modulation, probiotics/prebiotics, faecal microbiota transplantation, and antibiotics. Collectively, this article illustrated the relationship between bile acids and gut microbiota in IBS pathophysiology and might offer some novel therapeutic options for IBS.

Gut microbiota and inflammatory bowel disease

Gut microbiota refers to the complex aggregation of microbes in gut, including bacteria, archaea, fungi, and viruses, and they exert marked influence on the host's health. Perturbations in the gut microbiota have been closely linked to initiation and progression of IBD, which has become a disease with accelerating incidence worldwide, but it remains to be thoroughly investigated how microbial involvement might contribute to IBD. In this review, we discuss the current research findings concerning alterations in the gut microbiota, trans-kingdom interaction between the members of the gut microbiota, their interactions with the immune system of host, their potential role in the IBD pathogenesis, and the relationship between gut microbiota and IBD. We hope to provide a better understanding of the causes of IBD and shed light on the development of microbiome-based therapeutic approaches, which might be a promising strategy to alleviate, manage, and eventually cure IBD. This article is categorized under: Infectious Diseases > Genetics/Genomics/Epigenetics Infectious Diseases > Molecular and Cellular Physiology.

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

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

Implication of Intestinal Barrier Dysfunction in Gut Dysbiosis and Diseases

The intestinal mucosal barrier, also referred to as intestinal barrier, is widely recognized as a critical player in gut homeostasis maintenance as it ensures the complex crosstalk between gut microbes (both commensals and pathogens) and the host immune system. Highly specialized epithelial cells constantly cope with several protective and harmful agents to maintain the multiple physiological functions of the barrier as well as its integrity. However, both genetic defects and environmental factors can break such equilibrium, thus promoting gut dysbiosis, dysregulated immune-inflammatory responses, and even the development of chronic pathological conditions. Here, we review and discuss the molecular and cellular pathways underlying intestinal barrier structural and functional homeostasis, focusing on potential alterations that may undermine this fine balance.

Dual therapy with zinc acetate and rifaximin prevents from ethanol-induced liver fibrosis by maintaining intestinal barrier integrity

BACKGROUND

Hepatic overload of gut-derived lipopolysaccharide dictates the progression of alcoholic liver disease (ALD) by inducing oxidative stress and activating Kupffer cells and hepatic stellate cells through toll-like receptor 4 signaling. Therefore, targeting the maintenance of intestinal barrier integrity has attracted attention for the treatment of ALD. Zinc acetate and rifaximin, which is a nonabsorbable antibiotic, had been clinically used for patients with cirrhosis, particularly those with hepatic encephalopathy, and had been known to improve intestinal barrier dysfunction. However, only few studies focused on their efficacies in preventing the ALD-related fibrosis development.

AIM

To investigate the effects of a combined zinc acetate with rifaximin on liver fibrosis in a mouse ALD model.

METHODS

To induce ALD-related liver fibrosis, female C57BL/6J mice were fed a 2.5% (v/v) ethanol-containing Lieber-DeCarli liquid diet and received intraperitoneal carbon tetrachloride (CCl₄) injection twice weekly (1 mL/kg) for 8 wk. Zinc acetate (100 mg/L) and/or rifaximin (100 mg/L) were orally administered during experimental period. Hepatic steatosis, inflammation and fibrosis as well as intestinal barrier function were evaluated by histological and molecular analyses. Moreover, the direct effects of both agents on Caco-2 barrier function were assessed by in vitro assays.

RESULTS

In the ethanol plus CCl₄-treated mice, combination of zinc acetate and rifaximin attenuated oxidative lipid peroxidation with downregulation of Nox2 and Nox4. This combination significantly inhibited the Kupffer cells expansion and the proinflammatory response with blunted hepatic exposure of lipopolysaccharide and the toll-like receptor 4/nuclear factor kB pathway. Consequently, liver fibrosis and hepatic stellate cells activation were efficiently suppressed with downregulation of Mmp-2, -9, -13, and Timp1. Both agents improved the atrophic changes and permeability in the ileum, with restoration of tight junction proteins (TJPs) by decreasing the expressions of tumor necrosis factor α and myosin light chain kinase. In the in vitro assay, both agents directly reinforced ethanol or lipopolysaccharide-stimulated paracellular permeability and upregulated TJPs in Caco-2 cells.

CONCLUSION

Dual therapy with zinc acetate and rifaximin may serve as a strategy to prevent ALD-related fibrosis by maintaining intestinal barrier integrity.

The Correlation Between MYO9B Gene Polymorphism and Inflammatory Bowel Disease in the Guangxi Zhuang Population

Objective

To analyze the correlation between site rs962917 of the MYO9B gene and inflammatory bowel disease (IBD) in the Guangxi Zhuang nationality population.

Methods

The intestinal mucosa tissue of 153 IBD subjects (Han and Zhuang patients only) in the Guangxi Zhuang autonomous region comprised the case group, and the intestinal mucosa tissue of 155 healthy subjects (Han and Zhuang patients only) in the same region represented the control group. Deoxyribonucleic acid was extracted from the intestinal mucosa tissue of each experimental group, and the MYO9B gene-target fragment containing the single nucleotide polymorphism (SNP) site rs962917 was designed. Finally, polymerase chain reaction products were obtained by amplification, analyzed, and compared using the sequencing results.

Results

The results indicated that the genotype frequency of the MYO9B SNP site rs962917 between Crohn’s disease (CD) and control groups of Zhuang and Han participants differed significantly (P < 0.05). Furthermore, the genotype frequency of MYO9B site rs962917 differed significantly between the Zhuang and Han population groups (P < 0.05).

Conclusion

Site rs962917 of the MYO9B gene is related to CD susceptibility and incidence among the Guangxi Zhuang population.

The Interface between Cell Signaling Pathways and Pregnane X Receptor

Highly expressed in the enterohepatic system, pregnane X receptor (PXR, NR1I2) is a well-characterized nuclear receptor (NR) that regulates the expression of genes in the liver and intestines that encode key drug metabolizing enzymes and drug transporter proteins in mammals. The net effect of PXR activation is to increase metabolism and clear drugs and xenobiotics from the body, producing a protective effect and mediating clinically significant drug interaction in patients on combination therapy. The complete understanding of PXR biology is thus important for the development of safe and effective therapeutic strategies. Furthermore, PXR activation is now known to specifically transrepress the inflammatory- and nutrient-signaling pathways of gene expression, thereby providing a mechanism for linking these signaling pathways together with enzymatic drug biotransformation pathways in the liver and intestines. Recent research efforts highlight numerous post-translational modifications (PTMs) which significantly influence the biological function of PXR. However, this thrust of research is still in its infancy. In the context of gene-environment interactions, we present a review of the recent literature that implicates PXR PTMs in regulating its clinically relevant biology. We also provide a discussion of how these PTMs likely interface with each other to respond to extracellular cues to appropriately modify PXR activity.

Imidacloprid increases intestinal permeability by disrupting tight junctions

The neonicotinoid pesticide, imidacloprid (IMI), is frequently detected in the environment and in foods. It is absorbed and metabolized by the intestine; however, its effects on intestinal barrier integrity are not well studied. We investigated whether IMI disrupts the permeability of the intestinal epithelial barrier via in vivo tests on male Wistar rats, in vitro assays using the human intestinal epithelial cell line, Caco-2, and in silico analyses. A repeated oral dose 90-day toxicity study was performed (0.06 mg/kg body weight/day). IMI exposure significantly increased intestinal permeability, which led to significantly elevated serum levels of endotoxin and inflammatory biomarkers (tumor necrosis factor-alpha and interleukin-1 beta) without any variation in body weight. Decreased transepithelial electrical resistance with increased permeability was also observed in 100 nM and 100 μM IMI-treated Caco-2 cell monolayers. Amounts of tight junction proteins in IMI-treated colon tissues and between IMI-treated Caco-2 cells were significantly lower than those of controls. Increased levels of myosin light chain phosphorylation, myosin light chain kinase (MLCK), and p65 subunit of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB p65) phosphorylation were found in IMI-exposed cells compared with control cells. Furthermore, the barrier loss caused by IMI was rescued by the MLCK inhibitor, ML-7, and cycloheximide. Pregnane X receptor (PXR, NR1I2) was inhibited by low-dose IMI treatment. In silico analysis indicated potent binding sites between PXR and IMI. Together, these data illustrate that IMI induces intestinal epithelial barrier disruption and produces an inflammatory response, involving the down-regulation of tight junctions and disturbance of the PXR-NF-κB p65-MLCK signaling pathway. The intestinal barrier disruption caused by IMI deserves attention in assessing the safety of this neonicotinoid pesticide.

Gut microbiota alterations and health status in aging adults: From correlation to causation

The deterioration of tissue structure and decline in physiological function during aging are accompanied by alterations to the gut microbiota. The elderly has higher risks of various diseases and chronic diseases. However, inter-individual differences are more apparent in elderly than younger, and a proportion of individuals have a delayed onset or even avoid developing chronic diseases. This difference in health status is influenced by both heredity and Lifestyle and environmental factors. During the process of aging, the gut microbiota is also affected by the external environment, and provides a buffer to external challenge, and thus the gut microbiota reflects an individual's personal experience. Moreover, the immune system undergoes a series of changes with age, which are related to chronic inflammation in the elderly. The formation, maturation and senescence of the intestinal immune system is closely related to the gut microbiota. Additionally, changes in the gut microbiota of elderly individuals may modulate the immune system, which may in turn affect health status. Herein, we summarize the correlations between the gut microbiota with individual health status in the elderly and explore the related mechanisms, which may provide a basis to maintain or enhance the health of the elderly though interventions targeting the gut microbiota.

Aging, hormones and receptors

Ageing is accompanied by deterioration in physical condition and a number of physiological processes and thus a higher risk of a range of diseases and disorders. In particular, we focused on the changes associated with aging, especially the role of small molecules, their role in physiological and pathophysiological processes and potential treatment options. Our previously published results and data from other authors lead to the conclusion that these unwanted changes are mainly linked to the hypothalamic-pituitary-adrenal axis can be slowed down, stopped, or in some cases even reversed by an appropriate treatment, but especially by a life-management adjustment.

Targeting Dietary and Microbial Tryptophan-Indole Metabolism as Therapeutic Approaches to Colon Cancer

Tryptophan metabolism, via the kynurenine (Kyn) pathway, and microbial transformation of tryptophan to indolic compounds are fundamental for host health; both of which are altered in colon carcinogenesis. Alterations in tryptophan metabolism begin early in colon carcinogenesis as an adaptive mechanism for the tumor to escape immune surveillance and metastasize. The microbial community is a key part of the tumor microenvironment and influences cancer initiation, promotion and treatment response. A growing awareness of the impact of the microbiome on tryptophan (Trp) metabolism in the context of carcinogenesis has prompted this review. We first compare the different metabolic pathways of Trp under normal cellular physiology to colon carcinogenesis, in both the host cells and the microbiome. Second, we review how the microbiome, specifically indoles, influence host tryptophan pathways under normal and oncogenic metabolism. We conclude by proposing several dietary, microbial and drug therapeutic modalities that can be utilized in combination to abrogate tumorigenesis.

Ketogenic Diets Induced Glucose Intolerance and Lipid Accumulation in Mice with Alterations in Gut Microbiota and Metabolites

The ketogenic diet (KD), which can induce changes in gut microbiota, has shown benefits for epilepsy and several neurodegenerative diseases. However, the effects of a KD on glucose and lipid metabolism remain inconclusive. Using two formulas of ketogenic diets (KDR with 89.5% fat and KDH with 91.3% fat), which are commonly used in mouse trials, we found that KDR but not KDH induced insulin resistance and damaged glucose homeostasis, while KDH induced more fat accumulation in mice. Further study showed that KD impacted glucose metabolism, which was related to the sources of fat, while both the sources and proportions of fat affected lipid metabolism. And the KD widely used in human studies still induced insulin resistance and fat accumulation in mice. Moreover, KDs changed the gut microbiota and metabolites in mice, and the sources and proportions of fat in the diets respectively changed the abundance of specific bacteria and metabolites which were correlated with parameters related to glucose intolerance and lipid accumulation. Overall, our study demonstrated that the metabolic disorders induced by KDs are closely related to the source and proportion of fat in the diet, which may be associated with the changes of the gut microbiota and metabolites.IMPORTANCE The ketogenic diet with extremely high fat and very low carbohydrate levels is very popular in society today. Although it has beneficial effects on epilepsy and neurodegenerative diseases, how ketogenic diets impact host glucose and lipid metabolism and gut microbiota still needs further investigation. Here, we surveyed the effects of two ketogenic diets which are commonly used in mouse trials on metabolic phenotypes, gut microbiota, and metabolites in mice. We found that both ketogenic diets impaired glucose and lipid metabolism in mice, and this may be due to the sources and proportions of fat in the diets. This work highlights the potential risk of glucose and lipid metabolism disorders and the importance of evaluating the sources and proportions of fat in the diets, when using ketogenic diets for weight loss and the treatment of diseases.

Polychlorinated biphenyls altered gut microbiome in CAR and PXR knockout mice exhibiting toxicant-associated steatohepatitis

Polychlorinated biphenyls (PCBs) are persistent organic pollutants associated with non-alcoholic fatty liver disease (NAFLD). Previously, we demonstrated that the PCB mixture, Aroclor1260, exacerbated NAFLD, reflective of toxicant-associated steatohepatitis, in diet-induced obese mice, in part through pregnane-xenobiotic receptor (PXR) and constitutive androstane receptor (CAR) activation. Recent studies have also reported PCB-induced changes in the gut microbiome that consequently impact NAFLD. Therefore, the objective of this study is to examine PCB effects on the gut-liver axis and characterize the role of CAR and PXR in microbiome alterations. C57Bl/6 (wildtype, WT), CAR and PXR knockout mice were fed a high fat diet and exposed to Aroclor1260 (20 mg/kg, oral gavage, 12 weeks). Metagenomics analysis of cecal samples revealed that CAR and/or PXR ablation increased bacterial alpha diversity regardless of exposure status. CAR and PXR ablation also increased bacterial composition (beta diversity) versus WT; Aroclor1260 altered beta diversity only in WT and CAR knockouts. Distinct changes in bacterial abundance at different taxonomic levels were observed between WT and knockout groups; however Aroclor1260 had modest effects on bacterial abundance within each genotype. Notably, both knockout groups displayed increased Actinobacteria and Verrucomicrobia abundance. In spite of improved bacterial diversity, the knockout groups however failed to show protection from PCB-induced hepato- and intestinal- toxicity including decreased mRNA levels of ileal permeability markers (occludin, claudin3). In summary, CAR and PXR ablation significantly altered gut microbiome in diet-induced obesity while Aroclor1260 compromised intestinal integrity in knockout mice, implicating interactions between PCBs and CAR, PXR on the gut-liver axis.

Bioinformatis analysis reveals possible molecular mechanism of PXR on regulating ulcerative colitis

Inflammatory bowel disease (IBD) is a chronic, recurrent inflammatory disease of the gastrointestinal (GI) tract. Ulcerative colitis (UC) is a type of IBD. Pregnane X Receptor (PXR) is a member of the nuclear receptor superfamily. In order to deepen understanding and exploration of the molecular mechanism of regulation roles of PXR on UC, biological informatics analysis was performed. First, 878 overlapping differentially expressed genes (DEGs) between UC and normal samples were obtained from the Gene Expression Omnibus (GEO) database (GSE59071 and GSE38713) by using the "limma" R language package. Then WGCNA analysis was performed by 878 DEGs to obtain co-expression modules that were positively and negatively correlated with clinical traits. GSEA analysis of PXR results obtained the signal pathways enriched in the PXR high and low expression group and the active genes of each signal pathway. Then the association of PXR with genes that are both active in high expression group and negatively related to diseases (gene set 1), or both active in low expression group and negatively related to diseases (gene set 2) was analyzed by String database. Finally, carboxylesterase 2 (CES2), ATP binding cassette subfamily G member 2 (ABCG2), phosphoenolpyruvate carboxykinase (PCK1), PPARG coactivator 1 alpha (PPARGC1A), cytochrome P450 family 2 subfamily B member 6 (CYP2B6) from gene set 1 and C-X-C motif chemokine ligand 8 (CXCL8) from gene set 2 were screened out. After the above analysis and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) verification, we speculated that PXR may exert a protective role on UC by promoting CES2, ABCG2, PCK1, PPARGC1A, CYP2B6 expression and inhibiting CXCL8 expression in their corresponding signal pathway in intestinal tissue.

Probiotics mixture reinforces barrier function to ameliorate necrotizing enterocolitis by regulating PXR-JNK pathway

Background

Intestinal dysbiosis is believed to be one of the factors inducing neonatal necrotizing enterocolitis (NEC). Probiotics have been employed to treat NEC in a number of animal experiments and clinical trials, and some significant benefits of utilizing probiotics for the prevention or alleviation of NEC have been confirmed. However, the mechanism underlying the efficacy of probiotics in treating NEC has not been elucidated.

Results

Impairment of the intestinal barrier, which was characterized by the decreased expression of tight junction components, was observed in the pathogenesis of NEC. The probiotic mixture alleviated this intestinal damage by enhancing the function of the barrier. Meanwhile, the probiotics remodeled the composition of the intestinal microbiota in NEC mice. Furthermore, increased expression of the pregnane X receptor (PXR) was observed after treatment with the probiotic mixture, and PXR overexpression in Caco-2 cells protected the barrier from lipopolysaccharide (LPS) damage. Further research showed that PXR could inhibit the phosphorylation of c-Jun N-terminal kinase (JNK) and could increase the expression of tight junction components.

Conclusions

Our study confirmed that probiotics could ameliorate intestinal lesions by enhancing the function of the mucosal barrier. Specifically, probiotics may target PXR, which may subsequently enhance the expression of tight junction components by inhibiting the phosphorylation of JNK and enhance the function of the barrier.

Transcriptional programmes underlying cellular identity and microbial responsiveness in the intestinal epithelium

The intestinal epithelium serves the unique and critical function of harvesting dietary nutrients, while simultaneously acting as a cellular barrier separating tissues from the luminal environment and gut microbial ecosystem. Two salient features of the intestinal epithelium enable it to perform these complex functions. First, cells within the intestinal epithelium achieve a wide range of specialized identities, including different cell types and distinct anterior-posterior patterning along the intestine. Second, intestinal epithelial cells are sensitive and responsive to the dynamic milieu of dietary nutrients, xenobiotics and microorganisms encountered in the intestinal luminal environment. These diverse identities and responsiveness of intestinal epithelial cells are achieved in part through the differential transcription of genes encoded in their shared genome. Here, we review insights from mice and other vertebrate models into the transcriptional regulatory mechanisms underlying intestinal epithelial identity and microbial responsiveness, including DNA methylation, chromatin accessibility, histone modifications and transcription factors. These studies are revealing that most transcription factors involved in intestinal epithelial identity also respond to changes in the microbiota, raising both opportunities and challenges to discern the underlying integrative transcriptional regulatory networks.

Associations between Pregnane X Receptor and Breast Cancer Growth and Progression

Pregnane X receptor (PXR, NR1I2) is a member of the ligand-activated nuclear receptor superfamily. This receptor is promiscuous in its activation profile and is responsive to a broad array of both endobiotic and xenobiotic ligands. PXR is involved in pivotal cellular detoxification processes to include the regulation of genes that encode key drug-metabolizing cytochrome-P450 enzymes, oxidative stress response, as well as enzymes that drive steroid and bile acid metabolism. While PXR clearly has important regulatory roles in the liver and gastrointestinal tract, this nuclear receptor also has biological functions in breast tissue. In this review, we highlight current knowledge of PXR’s role in mammary tumor carcinogenesis. The elevated level of PXR expression in cancerous breast tissue suggests a likely interface between aberrant cell division and xeno-protection in cancer cells. Moreover, PXR itself exerts positive effect on the cell cycle, thereby predisposing tumor cells to unchecked proliferation. Activation of PXR also plays a key role in regulating apoptosis, as well as in acquired resistance to chemotherapeutic agents. The repressive role of PXR in regulating inflammatory mediators along with the existence of genetic polymorphisms within the sequence of the PXR gene may predispose individuals to developing breast cancer. Further investigations into the role that PXR plays in driving tumorigenesis are needed.

Microbial Metabolites and Intestinal Stem Cells Tune Intestinal Homeostasis

Microorganisms that colonize the gastrointestinal tract, collectively known as the gut microbiota, are known to produce small molecules and metabolites that significantly contribute to host intestinal development, functions, and homeostasis. Emerging insights from microbiome research reveal that gut microbiota-derived signals and molecules influence another key player maintaining intestinal homeostasis-the intestinal stem cell niche, which regulates epithelial self-renewal. In this review, the literature on gut microbiota-host crosstalk is surveyed, highlighting the effects of gut microbial metabolites on intestinal stem cells. The production of various classes of metabolites, their actions on intestinal stem cells are discussed and, finally, how the production and function of metabolites are modulated by aging and dietary intake is commented upon.

The xenobiotic sensing pregnane X receptor regulates tissue damage and inflammation triggered by C difficile toxins

Clostridioides difficile (formerly Clostridium difficile; C difficile), the leading cause of nosocomial antibiotic‐associated colitis and diarrhea in the industrialized world, triggers colonic disease through the release two toxins, toxin A (TcdA) and toxin B (TcdB), glucosyltransferases that modulate monomeric G‐protein function and alter cytoskeletal function. The initial degree of the host immune response to C difficile and its pathogenic toxins is a common indicator of disease severity and infection recurrence. Thus, targeting the intestinal inflammatory response during infection could significantly decrease disease morbidity and mortality. In the current study, we sought to interrogate the influence of the pregnane X receptor (PXR), a modulator of xenobiotic and detoxification responses, which can sense and respond to microbial metabolites and modulates inflammatory activity, during exposure to TcdA and TcdB. Following intrarectal exposure to TcdA/B, PXR‐deficient mice (Nr1i2^−/−) exhibited reduced survival, an effect that was associated with increased levels of innate immune cell influx. This exacerbated response was associated with a twofold increase in the expression of Tlr4. Furthermore, while broad‐spectrum antibiotic treatment (to deplete the intestinal microbiota) did not alter the responses in Nr1i2^−/− mice, blocking TLR4 signaling significantly reduced TcdA/B‐induced disease severity and immune responses in these mice. Lastly, to assess the therapeutic potential of targeting the PXR, we activated the PXR with pregnenolone 16α‐carbonitrile (PCN) in wild‐type mice, which greatly reduced the severity of TcdA/B‐induced damage and intestinal inflammation. Taken together, these data suggest that the PXR plays a role in the host's response to TcdA/B and may provide a novel target to dampen the inflammatory tissue damage in C difficile infections.

Pregnane X receptor activation by its natural ligand Ginkgolide-A improves tight junction proteins expression and attenuates bacterial translocation in cirrhosis

BACKGROUND AND AIMS

Pregnane X receptor (PXR) is a ligand-activated transcription factor and nuclear receptor expressed ubiquitously along gut-liver-axis. Inflammatory bowel disorders have been reported to implicate PXR in maintaining tight junction (TJ) integrity and countering inflammation. However, the hepatoprotective role of PXR activation in soothing bacterial translocation in liver cirrhosis has not been explored. Ginkgolide A (GA), a terpene trilactone from Ginkgo Biloba extract, is a natural ligand of rodent and human PXR. This study aims to investigate the effect of GA in activating PXR and improving associated tight junction integrity and reducing bacterial translocation in gut-liver axis of CCl₄ induced cirrhosis model.

METHODS

Swiss albino mice were administered with CCl₄ (0.5 ml/kg body weight, i.p) in corn oil for 12 weeks at an interval of two times a week. Following ascites induction, mice were randomized & administered 100 mg/kg body weight of GA through oral gavage for 2 weeks. At termination, blood, gut and liver tissues were collected for biochemical and molecular studies.

RESULTS

When compared to naïve mice, protein expression of hepatic and small intestinal PXR, CYP3A, ZO-1 and occludin were found to be significantly (p < 0.01) decreased in CCl₄ induced cirrhotic mice. Treatment with GA to cirrhotic mice significantly (p < 0.05) induced the expression of both hepatic and small intestinal PXR, CYP3A, ZO-1 and Occludin. Furthermore, increased (p < 0.01) hepatic and small intestinal NFκB was observed in CCl₄ induced cirrhotic mice that was significantly (p < 0.05) lowered following GA treatment. Over expression of TLR4/MyD88/NFκB axis and its downstream pro-inflammatory mediators TNF-α, IL6 and IFN-γ were observed in CCl₄ induced mice, and these indices were abrogated significantly after GA treatment. Furthermore, significantly increased plasma levels of bacterial translocation markers LBP and procalcitonin were found in CCl₄ mice, which were reduced significantly (p < 0.05 & p < 0.0001) after GA treatment.

CONCLUSION

In conclusion, our data supports the hypothesis that, GA treatment to CCl₄ induced cirrhotic mice, activated hepatic and small intestinal PXR and diminished inflammation, thereby improving tight junction integrity and attenuating bacterial translocation.

Activation of Adrenal Steroidogenesis and an Improvement of Mood Balance in Postmenopausal Females after Spa Treatment Based on Physical Activity

Spa treatment can effectively reestablish mood balance in patients with psychiatric disorders. In light of the adrenal gland’s role as a crossroad of psychosomatic medicine, this study evaluated changes in 88 circulating steroids and their relationships with a consolidation of somatic, psychosomatic and psychiatric components from a modified N-5 neurotic questionnaire in 46 postmenopausal 50+ women with anxiety-depressive complaints. The patients underwent a standardized one-month intervention therapy with physical activity and an optimized daily regimen in a spa in the Czech Republic. All participants were on medication with selective serotonin reuptake inhibitors. An increase of adrenal steroidogenesis after intervention indicated a reinstatement of the hypothalamic-pituitary-adrenal axis. The increases of many of these steroids were likely beneficial to patients, including immunoprotective adrenal androgens and their metabolites, neuroactive steroids that stimulate mental activity but protect from excitotoxicity, steroids that suppress pain perception and fear, steroids that consolidate insulin secretion, and steroids that improve xenobiotic clearance. The positive associations between the initial values of neurotic symptoms and their declines after the intervention, as well as between initial adrenal activity and the decline of neurotic symptoms, indicate that neurotic impairment may be alleviated by such therapy provided that the initial adrenal activity is not seriously disrupted.

Pregnane X Receptor Activation Triggers Rapid ATP Release in Primed Macrophages That Mediates NLRP3 Inflammasome Activation

The pregnane X receptor (PXR) is a ligand-activated nuclear receptor that acts as a xenobiotic sensor, responding to compounds of foreign origin, including pharmaceutical compounds, environmental contaminants, and natural products, to induce transcriptional events that regulate drug detoxification and efflux pathways. As such, the PXR is thought to play a key role in protecting the host from xenobiotic exposure. More recently, the PXR has been reported to regulate the expression of innate immune receptors in the intestine and modulate inflammasome activation in the vasculature. In the current study, we report that activation of the PXR in primed macrophages triggers caspase-1 activation and interleukin-1β release. Mechanistically, we show that this response is nucleotide-binding oligomerization domain, leucine-rich repeat, and pyrin domain-containing 3-dependent and is driven by the rapid efflux of ATP and P2X purinoceptor 7 activation following PXR stimulation, an event that involves pannexin-1 gating, and is sensitive to inhibition of Src-family kinases. Our findings identify a mechanism whereby the PXR drives innate immune signaling, providing a potential link between xenobiotic exposure and the induction of innate inflammatory responses.

Clinical applications of small molecule inhibitors of Pregnane X receptor

The canonical effect of Pregnane X Receptor (PXR, NR1I2) agonism includes enhanced hepatic uptake and a concomitant increase in the first-pass metabolism and efflux of drugs in mammalian liver and intestine. In patients undergoing combination therapy, PXR-mediated gene regulation represents the molecular basis of numerous food-drug, herb-drug, and drug-drug interactions. Moreover, PXR activation promotes chemotherapeutic resistance in certain malignancies. Additional research efforts suggest that sustained PXR activation exacerbates the development of fatty liver disease. Additional metabolic effects of PXR activation in liver are the inhibition of fatty acid oxidation and gluconeogenesis. The identification of non-toxic and selective PXR antagonists is therefore of current research interest. Inhibition of PXR should decrease adverse effects, improve therapeutic effectiveness, and advance clinical outcomes in patients with cancer, fatty liver, and diabetes. This review identifies small molecule PXR antagonists described to date, discusses possible molecular mechanisms of inhibition, and seeks to describe the likely biomedical consequences of the inhibition of this nuclear receptor superfamily member.

Constitutive androstane receptor and pregnane X receptor cooperatively ameliorate DSS-induced colitis

BACKGROUND

Nuclear receptor pregnane X receptor (PXR) was shown to be protective in case of dextran sulfate sodium (DSS)-induced colitis. Constitutive androstane receptor (CAR) belongs to the same nuclear receptor subfamily with PXR. The roles of both receptors in DSS-induced colitis were evaluated.

METHODS

Wild-type, Car-null, Pxr-null, and Car/Pxr-null mice were treated with a CAR/PXR agonist or vehicle and administered 2.5% DSS in the drinking water. The typical clinical symptoms, histological scoring, proinflammatory cytokine, and apoptosis were analyzed.

RESULTS

Mice treated with the PXR agonist pregnenolone-16α-carbonitrile (PCN) were protected from DSS-induced colitis, as in a previous study. Mice treated with the CAR agonist, 4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) were also protected from DSS-induced colitis. Interestingly, the protective effects of PCN in the Car-null mice and those of TCPOBOP in the Pxr-null mice both decreased. PCN or TCPOBOP pretreatment significantly decreased the macrophage and monocyte infiltration in DSS-induced colitis. PXR and CAR agonists reduced the mRNA expression of several proinflammatory cytokines in a PXR- and CAR-dependent manner, respectively. CAR inhibited apoptosis by inducing Gadd45b. PXR inhibited TNF-α and IL-1b and CAR induced Gadd45b in in vitro cell analyses.

CONCLUSIONS

We showed that CAR and PXR cooperatively ameliorate DSS-induced colitis. PXR and CAR protected against DSS-induced colitis by inhibiting proinflammatory cytokines and apoptosis, respectively.

Nuclear Receptors in the Pathogenesis and Management of Inflammatory Bowel Disease

Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the transcription of target genes. Previous epidemiological and genetic studies have documented the association of NRs with the risk of inflammatory bowel disease (IBD). Although the mechanisms of action of NRs in IBD have not been fully established, accumulating evidence has demonstrated that NRs play complicated roles in regulating intestinal immunity, mucosal barriers, and intestinal flora. As one of the first-line medications for the treatment of IBD, 5-aminosalicylic acid (5-ASA) activates peroxisome proliferator-activated receptor gamma (PPARγ) to attenuate colitis. The protective roles of rifaximin and rifampicin partly depend on promoting pregnane X receptor (PXR) expression. The aims of this review are to discuss the roles of several important NRs, such as PPARγ, PXR, vitamin D receptor (VDR), farnesoid X receptor (FXR), and RAR-related orphan receptor gammat (RORγt), in the pathogenesis of IBD and management strategies based on targeting these receptors.

Activating the pregnane X receptor by imperatorin attenuates dextran sulphate sodium-induced colitis in mice

BACKGROUND AND PURPOSE

Activation of the human pregnane X receptor (PXR; NR1I2) has potential therapeutic uses for inflammatory bowel disease (IBD). Imperatorin (IMP), a naturally occurring coumarin, is the main bioactive ingredient of Angelica dahurica Radix, which is regularly used to treat the common cold and intestinal disorders. However, there are no data on the protective effects of IMP against IBD.

EXPERIMENTAL APPROACH

The effects of IMP on PXR-modulated cytochrome P450 3A4 (CYP3A4) expression were assessed using a PXR transactivation assay, a mammalian two-hybrid assay, a competitive ligand-binding assay, analysis of CYP3A4 mRNA and protein expression levels and measurement of CYP3A4 activity using a cell-based reporter gene assay and in vitro model. The inhibitory effects of IMP on NF-κB activity were evaluated by a reporter assay and NF-κB p65 nuclear translocation. The anti-IBD effects of IMP were investigated in a dextran sulphate sodium (DSS)-induced colitis mouse model. Colon inflammatory cytokines were assessed by elisa.

KEY RESULTS

IMP activated CYP3A4 promoter activity, recruited steroid receptor coactivator 1 to the ligand-binding domain of PXR and increased the expression and activity of CYP3A4. PXR knockdown substantially reduced IMP-induced increase in CYP3A4 expression. Furthermore, IMP-mediated PXR activation suppressed the nuclear translocation of NF-κB and down-regulated LPS-induced expression of pro-inflammatory genes. Nevertheless, PXR knockdown partially reduced the IMP-mediated inhibition of NF-κB. IMP ameliorated DSS-induced colitis by PXR/NF-κB signalling.

CONCLUSIONS AND IMPLICATIONS

IMP acts as a PXR agonist to attenuate DSS-induced colitis by suppression of the NF-κB-mediated pro-inflammatory response in a PXR/NF-κB-dependent manner.

Microbial tryptophan catabolites in health and disease

Accumulating evidence implicates metabolites produced by gut microbes as crucial mediators of diet-induced host-microbial cross-talk. Here, we review emerging data suggesting that microbial tryptophan catabolites resulting from proteolysis are influencing host health. These metabolites are suggested to activate the immune system through binding to the aryl hydrocarbon receptor (AHR), enhance the intestinal epithelial barrier, stimulate gastrointestinal motility, as well as secretion of gut hormones, exert anti-inflammatory, anti-oxidative or toxic effects in systemic circulation, and putatively modulate gut microbial composition. Tryptophan catabolites thus affect various physiological processes and may contribute to intestinal and systemic homeostasis in health and disease.

Enteric Microbiota⁻Gut⁻Brain Axis from the Perspective of Nuclear Receptors

Nuclear receptors (NRs) play a key role in regulating virtually all body functions, thus maintaining a healthy operating body with all its complex systems. Recently, gut microbiota emerged as major factor contributing to the health of the whole organism. Enteric bacteria have multiple ways to influence their host and several of them involve communication with the brain. Mounting evidence of cooperation between gut flora and NRs is already available. However, the full potential of the microbiota interconnection with NRs remains to be uncovered. Herewith, we present the current state of knowledge on the multifaceted roles of NRs in the enteric microbiota–gut–brain axis.

Pharmacokinetic drug evaluation of rifaximin for treatment of diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Rifaximin is a poorly absorbable antibiotic with a broad-spectrum activity against both Gram-negative and -positive bacteria. It is active in the small intestine due to its high bile solubility, whereas in the aqueous environment of the colon, it shows limited efficacy against highly susceptible bacteria. These unique pharmacokinetic properties limit its systemic effects and can correct gut microflora imbalances. Thus, rifaximin has become a major therapeutic agent in several gastrointestinal diseases in which an imbalance in gut microflora may play a role, including diarrhea predominant irritable bowel syndrome (IBS-D). Area covered: This is an up-to-date review focusing on the efficacy of rifaximin in the treatment of IBS-D in both adult and pediatric populations. We will review the pharmacokinetic properties of rifaximin, including its absorption in health and disease, mechanisms of action, and interactions with other drugs. Expert opinion: Given its safety profile and its negligible absorption, rifaximin is a suitable treatment for IBS-D, in both adults and children. The possibility of modulating gut microbiota composition without side effects has made this drug an appealing therapeutic agent in highly prevalent gastrointestinal diseases. However, to date, monitoring for the development of resistant bacterial strains during long-term rifaximin use is still lacking.

The "Gut Feeling": Breaking Down the Role of Gut Microbiome in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system with unknown etiology. Recently, the gut microbiota has emerged as a potential factor in the development of MS, with a number of studies having shown that patients with MS exhibit gut dysbiosis. The gut microbiota helps the host remain healthy by regulating various functions, including food metabolism, energy homeostasis, maintenance of the intestinal barrier, inhibition of colonization by pathogenic organisms, and shaping of both mucosal and systemic immune responses. Alteration of the gut microbiota, and subsequent changes in its metabolic network that perturb this homeostasis, may lead to intestinal and systemic disorders such as MS. Here we discuss the findings of recent MS microbiome studies and potential mechanisms through which gut microbiota can predispose to, or protect against, MS. These findings highlight the need of an improved understanding of the interactions between the microbiota and host for developing therapies based on gut commensals with which to treat MS.

Role of pregnane X-receptor in regulating bacterial translocation in chronic liver diseases

Bacterial translocation (BT) has been impeccably implicated as a driving factor in the pathogenesis of a spectrum of chronic liver diseases (CLD). Scientific evidence accumulated over the last four decades has implied that the disease pathologies in CLD and BT are connected as a loop in the gut-liver axis and exacerbate each other. Pregnane X receptor (PXR) is a ligand-activated transcription factor and nuclear receptor that is expressed ubiquitously along the gut-liver-axis. PXR has been intricately associated with the regulation of various mechanisms attributed in causing BT. The importance of PXR as the mechanistic linker molecule in the gut-liver axis and its role in regulating bacterial interactions with the host in CLD has not been explored. PubMed was used to perform an extensive literature search using the keywords PXR and bacterial translocation, PXR and chronic liver disease including cirrhosis. In an adequate expression state, PXR acts as a sensor for bile acid dysregulation and bacterial derived metabolites, and in response shapes the immune profile beneficial to the host. Activation of PXR could be therapeutic in CLD as it counter-regulates endotoxin mediated inflammation and maintains the integrity of intestinal epithelium. This review mainly focuses PXR function and its regulation in BT in the context of chronic liver diseases.