Physiological Role of Bile Acids Modified by the Gut Microbiome

Effects of probiotics supplementation on glycemic profile in adults with type 2 diabetes mellitus: A grade-assessed systematic review and dose-response meta-analysis of randomized controlled trials

BACKGROUND

Disturbed glycemia and the resulting type 2 diabetes (T2D) are significant health concerns. Various approaches have been examined to improve glycemic control in patients with T2D. Modification of gut microbiome via administering probiotics has been extensively studied. The present study aims to sum up the existing literature which investigated the effect of probiotics on glycemic indices in individuals with T2D in the format of randomized controlled trials (RCTs).

METHODS

Online medical databases (PubMed, Scopus, and Web of Science) were searched from inception to January 2024. Eligible studies were included using pre-defined inclusion and exclusion criteria. Outcome variables included fasting blood sugar (FBS), insulin, hemoglobin A1c (HbA1c), and homeostatic model of insulin resistance (HOMA-IR). Weighted mean differences (WMDs) were estimated. Subgroup and dose-response analyses were conducted. P-values <0.05 were considered as statistically significant.

RESULTS

Out of 5636 records retrieved by the initial search, thirty-two RCTs were included in the final analyses. Supplementation with probiotics was observed to significantly improve indices of glycemic control; including FBS (WMD: -13.27 mg/dl; 95 % CI: -18.31, -8.22), HbA1c (WMD: -0.44 %; 95 % CI: -0.59, -0.28), insulin (WMD: -1.33 μIU/ml; 95 % CI: -2.57, -0.08), and HOMA-IR (WMD: -0.95; 95 % CI: -1.71, -0.18). Dose-response analysis revealed that increased duration of intervention results in a larger reduction only in FBS.

CONCLUSION

Supplementation with probiotics seems to improve indices of glycemic control. Nonetheless, taken into account the notable heterogeneity (with regard to dosage, duration, and the species/strains used) between the included studies and low quality of evidence, caution must be considered, especially when long-term clinical implications are intended.

Development of a rapid and robust hydrop interaction liquid chromatography tandem mass spectrometry method for the detection of 13 endogenous amino acids as well as trimethylamine oxide in serum and tissues of the mice

This work aimed to establish an HILIC-MS/MS method to simultaneously determine the levels of 13 endogenous amino acids and trimethylamine oxide in the biological samples from the mice. Electrospray ion source was used for the analysis of mass spectrometry. The 20 min separation was applied in a Dikma Inspire Hilic column (2.1 × 100.0 mm, 3 μM). Positive ion mode under an MRM model gave a satisfying response value. The limits of quantitation were evaluated by accuracy from -12.59% to 7.89% and precision from 1.77% to 14.00% as well as acceptable interday and intraday precision, matrix effect, recovery, and stability. Later, the assay was successfully used to measure the concentrations of the determinands in the biological samples. Individual and tissue distribution differences for these metabolites were observable. The amino acids had a consistent highest content in the spleens, while the lowest levels were found in the livers. Alanine was the most abundant amino acid in the serum, and taurine kept the highest content in all of the tissues. Trimethylamine oxide remained low level, especially in the liver samples.

The role of intestinal microbiota and metabolites in intestinal inflammation

With the imbalance of intestinal microbiota, the body will then face an inflammatory response, which has serious implications for human health. Bodily allergies, injury or pathogens infections can trigger or promote inflammation and alter the intestinal environment. Meanwhile, excessive changes in the intestinal environment cause the imbalance of microbial homeostasis, which leads to the proliferation and colonization of opportunistic pathogens, invasion of the body's immune system, and the intensification of inflammation. Some natural compounds and gut microbiota and metabolites can reduce inflammation; however, the details of how they interact with the gut immune system and reduce the gut inflammatory response still need to be fully understood. The review focuses on inflammation and intestinal microbiota imbalance caused by pathogens. The body reacts differently to different types of pathogenic bacteria, and the ingestion of pathogens leads to inflamed gastrointestinal tract disorders or intestinal inflammation. In this paper, unraveling the interactions between the inflammation, pathogenic bacteria, and intestinal microbiota based on inflammation caused by several common pathogens. Finally, we summarize the effects of intestinal metabolites and natural anti-inflammatory substances on inflammation to provide help for related research of intestinal inflammation caused by pathogenic bacteria.

Effects of Phenolic Acids Produced from Food-Derived Flavonoids and Amino Acids by the Gut Microbiota on Health and Disease

The gut microbiota metabolizes flavonoids, amino acids, dietary fiber, and other components of foods to produce a variety of gut microbiota-derived metabolites. Flavonoids are the largest group of polyphenols, and approximately 7000 flavonoids have been identified. A variety of phenolic acids are produced from flavonoids and amino acids through metabolic processes by the gut microbiota. Furthermore, these phenolic acids are easily absorbed. Phenolic acids generally represent phenolic compounds with one carboxylic acid group. Gut microbiota-derived phenolic acids have antiviral effects against several viruses, such as SARS-CoV-2 and influenza. Furthermore, phenolic acids influence the immune system by inhibiting the secretion of proinflammatory cytokines, such as interleukin-1β and tumor necrosis factor-α. In the nervous systems, phenolic acids may have protective effects against neurodegenerative diseases, such as Alzheimer's and Parkinson's diseases. Moreover, phenolic acids can improve levels of blood glucose, cholesterols, and triglycerides. Phenolic acids also improve cardiovascular functions, such as blood pressure and atherosclerotic lesions. This review focuses on the current knowledge of the effects of phenolic acids produced from food-derived flavonoids and amino acids by the gut microbiota on health and disease.

Lactobacillus Kefir M20 Adaptation to Bile Salts: A Novel Pathway for Cholesterol Reduction

(1) Background: This study investigated the impact of in vitro adaptations to acid and bile stress on the cholesterol-lowering activity of the probiotic Lactobacillus kefir M20. (2) Methods: Lactobacillus kefir M20 was extracted from fermented dairy products in Xinjiang, China, and isolated using MRS medium. The lactic acid bacteria were cultured for stress resistance to acid and bile salts and then gavaged into mice for animal experiments. (3) Results: The adaptation to bile stress treatment resulted in a notable enhancement of the cholesterol-lowering capacity of Lactobacillus kefir M20, with reductions of 16.5% and 33.1% in total and non-HDL cholesterol, respectively, compared to the untreated strain. Furthermore, the daily fecal total bile acid excretion was 9.2, 5.4 and 5.0 times higher in the M20-BSA group compared to the HC, M20 and M20-ASA groups, respectively. (4) Conclusions: This study suggests that targeted probiotics have the potential for application in the next generation of functional foods and probiotic formulations aimed at combating hypercholesterolemia.

Mechanisms by which microbiome-derived metabolites exert their impacts on neurodegeneration

Recent developments in microbiome research suggest that the gut microbiome may remotely modulate central and peripheral neuronal processes, ranging from early brain development to age-related changes. Dysbiotic microbiome configurations have been increasingly associated with neurological disorders, such as neurodegeneration, but causal understanding of these associations remains limited. Most mechanisms explaining how the microbiome may induce such remote neuronal effects involve microbially modulated metabolites that influx into the 'sterile' host. Some metabolites are able to cross the blood-brain barrier (BBB) to reach the central nervous system, where they can impact a variety of cells and processes. Alternatively, metabolites may directly signal to peripheral nerves to act as neurotransmitters or exert modulatory functions, or impact immune responses, which, in turn, modulate neuronal function and associated disease propensity. Herein, we review the current knowledge highlighting microbiome-modulated metabolite impacts on neuronal disease, while discussing unknowns, controversies and prospects impacting this rapidly evolving research field.

Vitamin A carotenoids, but not retinoids, mediate the impact of a healthy diet on gut microbial diversity

BACKGROUND

Vitamin A is essential for physiological processes like vision and immunity. Vitamin A's effect on gut microbiome composition, which affects absorption and metabolism of other vitamins, is still unknown. Here we examined the relationship between gut metagenome composition and six vitamin A-related metabolites (two retinoid: -retinol, 4 oxoretinoic acid (oxoRA) and four carotenoid metabolites, including beta-cryptoxanthin and three carotene diols).

METHODS

We included 1053 individuals from the TwinsUK cohort with vitamin A-related metabolites measured in serum and faeces, diet history, and gut microbiome composition assessed by shotgun metagenome sequencing. Results were replicated in 327 women from the ZOE PREDICT-1 study.

RESULTS

Five vitamin A-related serum metabolites were positively correlated with microbiome alpha diversity (r = 0.15 to r = 0.20, p < 4 × 10-6). Carotenoid compounds were positively correlated with the short-chain fatty-acid-producing bacteria Faecalibacterium prausnitzii and Coprococcus eutactus. Retinol was not associated with any microbial species. We found that gut microbiome composition could predict circulating levels of carotenoids and oxoretinoic acid with AUCs ranging from 0.66 to 0.74 using random forest models, but not retinol (AUC = 0.52). The healthy eating index (HEI) was strongly associated with gut microbiome diversity and with all carotenoid compounds, but not retinoids. We investigated the mediating role of carotenoid compounds on the effect of a healthy diet (HEI) on gut microbiome diversity, finding that carotenoids significantly mediated between 18 and 25% of the effect of HEI on gut microbiome alpha diversity.

CONCLUSIONS

Our results show strong links between circulating carotene compounds and gut microbiome composition and potential links to a healthy diet pattern.

Effects of pectin methyl-esterification on intestinal microbiota and its immunomodulatory properties in naive mice

Pectins are dietary fibers that are attributed with several beneficial immunomodulatory effects. Depending on the degree of esterification (DE), pectins can be classified as high methoxyl pectin (HMP) or low methoxyl pectin (LMP). The aim of this study was to investigate the effects of pectin methyl-esterification on intestinal microbiota and its immunomodulatory properties in naive mice. Supplementation of the diet with LMP or HMP induced changes in the composition of the intestinal microbiota in mice toward Bacteroides, which was mainly promoted by HMP. Metabolome analysis of stool samples from pectin-fed mice showed a different effect of the two types of pectin on the levels of short-chain fatty acids and bile acids, which was consistent with highly efficient in vivo fermentation of LMP. Analysis of serum antibody levels showed a significant increase in IgG and IgA levels by both pectins, while FACS analysis revealed a decrease of infiltrating inflammatory cells in the intestinal lamina propria by HMP. Our study revealed that the structural properties of the investigated pectins determine fermentability, effects on microbial composition, metabolite production, and modulation of immune responses. Consumption of HMP preferentially altered the gut microbiota and suppressed pro-inflammatory immune responses, suggesting a beneficial role in inflammatory diseases.

The footprint of gut microbiota in gallbladder cancer: a mechanistic review

Gallbladder cancer (GBC) is the most common malignant tumor of the biliary system with the worst prognosis. Even after radical surgery, the majority of patients with GBC have difficulty achieving a clinical cure. The risk of tumor recurrence remains more than 65%, and the overall 5-year survival rate is less than 5%. The gut microbiota refers to a variety of microorganisms living in the human intestine, including bacteria, viruses and fungi, which profoundly affect the host state of general health, disease and even cancer. Over the past few decades, substantial evidence has supported that gut microbiota plays a critical role in promoting the progression of GBC. In this review, we summarize the functions, molecular mechanisms and recent advances of the intestinal microbiota in GBC. We focus on the driving role of bacteria in pivotal pathways, such as virulence factors, metabolites derived from intestinal bacteria, chronic inflammatory responses and ecological niche remodeling. Additionally, we emphasize the high level of correlation between viruses and fungi, especially EBV and Candida spp., with GBC. In general, this review not only provides a solid theoretical basis for the close relationship between gut microbiota and GBC but also highlights more potential research directions for further research in the future.

Neuroactive metabolites and bile acids are altered in extremely premature infants with brain injury

The gut microbiome is associated with pathological neurophysiological evolvement in extremely premature infants suffering from brain injury. The exact underlying mechanism and its associated metabolic signatures in infants are not fully understood. To decipher metabolite profiles linked to neonatal brain injury, we investigate the fecal and plasma metabolome of samples obtained from a cohort of 51 extremely premature infants at several time points, using liquid chromatography (LC)-high-resolution mass spectrometry (MS)-based untargeted metabolomics and LC-MS/MS-based targeted analysis for investigating bile acids and amidated bile acid conjugates. The data are integrated with 16S rRNA gene amplicon gut microbiome profiles as well as patient cytokine, growth factor, and T cell profiles. We find an early onset of differentiation in neuroactive metabolites between infants with and without brain injury. We detect several bacterially derived bile acid amino acid conjugates in plasma and feces. These results provide insights into the early-life metabolome of extremely premature infants.

The role of microbial metabolites in endocrine tumorigenesis: From the mechanistic insights to potential therapeutic biomarkers

Microbial metabolites have been indicated to communicate with the host's endocrine system, regulating hormone production, immune-endocrine communications, and interactions along the gut-brain axis, eventually affecting the occurrence of endocrine cancer. Furthermore, microbiota metabolites such as short-chain fatty acids (SCFAs) have been found to affect the tumor microenvironment and boost immunity against tumors. SCFAs, including butyrate and acetate, have been demonstrated to exert anti-proliferative and anti-protective activity on pancreatic cancer cells. The employing of microbial metabolic products in conjunction with radiation and chemotherapy has shown promising outcomes in terms of reducing treatment side effects and boosting effectiveness. Certain metabolites, such as valerate and butyrate, have been made known to improve the efficiency of CAR T-cell treatment, whilst others, such as indole-derived tryptophan metabolites, have been shown to inhibit tumor immunity. This review explores the intricate interplay between microbial metabolites and endocrine tumorigenesis, spanning mechanistic insights to the discovery of potential therapeutic biomarkers.

Characterization and Bile Acid Binding Capacity of Dietary Fiber Obtained from Three Different Amaranth Products

Amaranth is a dicotyledonous plant, now considered a health-promoting food. It has been rediscovered by the worldwide food industry, which is increasingly becoming aware of the many uses and benefits provided by amaranth in various food preparations. Amaranth dietary fibers, soluble and insoluble fractions, obtained from flour, protein isolate, and beverage were physicochemically characterized and their potential bile acid binding capacity was evaluated. Primary bile acids binding to fiber might contribute to a hypocholesterolemic effect, while the binding of secondary bile acids could minimize the cytotoxic effect that these metabolites exert on the colon. Amaranth fiber fractions were capable of sequestering cholate, taurocholate, deoxycholate, and bovine bile, with a percentage depending not only on the origin and the type of amaranth fiber evaluated but also on the bile acid studied. Flour fiber and the protein isolate insoluble fractions were the most efficient for binding bile and bile acids with uptake values between 29 and 100% relative to cholestyramine. Moreover, deoxycholate, a hydrophobic secondary bile acid, was the most captured by all the fractions, reaching 100% uptake with total and insoluble fibers of the three amaranth products. These results would suggest that the main effect through which amaranth fiber binds bile acids corresponds to an adsorptive effect mediated by hydrophobic interactions.

Game of microbes: the battle within - gut microbiota and multiple sclerosis

Multiple sclerosis (MS) is a chronic and progressive autoimmune disease of the central nervous system (CNS), with both genetic and environmental factors contributing to the pathobiology of the disease. While human leukocyte antigen (HLA) genes have emerged as the strongest genetic factor, consensus on environmental risk factors are lacking. Recently, trillions of microbes residing in our gut (microbiome) have emerged as a potential environmental factor linked with the pathobiology of MS as PwMS show gut microbial dysbiosis (altered gut microbiome). Thus, there has been a strong emphasis on understanding the factors (host and environmental) regulating the composition of the gut microbiota and the mechanism(s) through which gut microbes contribute to MS disease, especially through immune system modulation. A better understanding of these interactions will help harness the enormous potential of the gut microbiota as a therapeutic approach to treating MS.

Non-alcoholic fatty liver disease and gut microbial dysbiosis- underlying mechanisms and gut microbiota mediated treatment strategies

Non-alcoholic fatty liver disease (NAFLD) is by far the most prevalent form of liver disease worldwide. It's also the leading cause of liver-related hospitalizations and deaths. Furthermore, there is a link between obesity and NAFLD risk. A projected 25% of the world's population grieves from NAFLD, making it the most common chronic liver disorder. Several factors, such as obesity, oxidative stress, and insulin resistance, typically accompany NAFLD. Weight loss, lipid-lowering agents, thiazolidinediones, and metformin help prominently control NAFLD. Interestingly, pre-clinical studies demonstrate gut microbiota's potential causal role in NAFLD. Increased intestinal permeability and unhindered transport of microbial metabolites into the liver are the major disruptions due to gut microbiome dysbiosis, contributing to the development of NAFLD by dysregulating the gut-liver axis. Hence, altering the pathogenic bacterial population using probiotics, prebiotics, synbiotics, and fecal microbiota transplantation (FMT) could benefit patients with NAFLD. Therefore, it is crucial to acknowledge the importance of microbiota-mediated therapeutic approaches for NAFLD and comprehend the underlying mechanisms that establish a connection between NAFLD and gut microbiota. This review provides a comprehensive overview of the affiliation between dysbiosis of gut microbiota and the progress of NAFLD, as well as the potential benefits of prebiotic, probiotic, synbiotic supplementation, and FMT in obese individuals with NAFLD.

The Role of Gut Microbiota-Derived Lithocholic Acid, Deoxycholic Acid and Their Derivatives on the Function and Differentiation of Immune Cells

A wide variety and large number of bacterial species live in the gut, forming the gut microbiota. Gut microbiota not only coexist harmoniously with their hosts, but they also induce significant effects on each other. The composition of the gut microbiota can be changed due to environmental factors such as diet and antibiotic intake. In contrast, alterations in the composition of the gut microbiota have been reported in a variety of diseases, including intestinal, allergic, and autoimmune diseases and cancer. The gut microbiota metabolize exogenous dietary components ingested from outside the body to produce short-chain fatty acids (SCFAs) and amino acid metabolites. Unlike SCFAs and amino acid metabolites, the source of bile acids (BAs) produced by the gut microbiota is endogenous BAs from the liver. The gut microbiota metabolize BAs to generate secondary bile acids, such as lithocholic acid (LCA), deoxycholic acid (DCA), and their derivatives, which have recently been shown to play important roles in immune cells. This review focuses on current knowledge of the role of LCA, DCA, and their derivatives on immune cells.

Gut microbiota of the small intestine as an antimicrobial barrier against foodborne pathogens: Impact of diet on the survival of S. Typhimurium and L. monocytogenes during in vitro digestion

The human gastrointestinal tract employs an assortment of chemical, enzymatic and immune barriers to impede pathogen colonization. An essential component of these barriers is the gut microbiota, which infers protection against ingested pathogens through its colonization resistance mechanisms. Specifically, the gut microbiota of the distal small intestine (ileum) renders a crucial line of defense, given that this location is regarded as an important interaction site. This study aimed to evaluate the impact of the ileal microbiota on the survival of the foodborne pathogens Salmonella enterica serotype Typhimurium and Listeria monocytogenes, utilizing an in vitro digestion model system. Moreover, the effect of diet on the gut microbiota colonization resistance mechanisms was assessed, by comparing a healthy (high fiber/low sugar) and a western diet (low fiber/high sugar). For S. Typhimurium, the results revealed that the digestion of a healthy diet led to a similar inactivation compared to the western diet, with the values of total log reduction being 0.83 and 0.82 log(CFU), respectively; yet the lack of readily accessible nutrients in the healthy diet combined with the acidic shock during gastric digestion caused the induction of stress tolerance to the pathogen. This resulted in increased pathogen survival in the presence of gut microbiota, with S. Typhimurium proliferating during the ileal phase with a maximum specific growth rate of 0.16 1/h. On the contrary, for L. monocytogenes, the healthy diet was associated with a greater inactivation than the western diet (total log reduction values: 3.08 and 1.30 log(CFU), respectively), which appeared strongly influenced by the encounter of the pathogen with the gut microbiota. Regarding the latter, the species Escherichia coli and Bacteroides thetaiotaomicron appeared to be the most prevalent in most cases. Finally, it was also demonstrated that the ileal microbiota colonization resistance mechanisms largely relied on competitive responses. The obtained knowledge of this research can contribute to the development and/or complementation of defensive strategies against pathogen infection, while also underlining the value of in vitro approaches.

Integration of semi-empirical MS/MS library with characteristic features for the annotation of novel amino acid-conjugated bile acids

Recently, amino acids other than glycine and taurine were found to be conjugated with bile acids by the gut microbiome in mouse and human. As potential diagnostic markers for inflammatory bowel disease and farnesoid X receptor agonists, their physiological effects and mechanisms, however, remain to be elucidated. A tool for the rapid and comprehensive annotation of such new metabolites is required. Thus, we developed a semi-empirical MS/MS library for bile acids conjugated with 18 common amino acids, including alanine, arginine, asparagine, aspartate, glutamine, glutamate, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine, and valine. To investigate their fragmentation rules, these amino acids were chemically conjugated with lithocholic acid, deoxycholic acid, and cholic acid, and their accurate-mass MS/MS spectra were acquired. The common fragmentation patterns from the amino acid moieties were combined with 10 general bile acid skeletons to generate a semi-empirical MS/MS library of 180 structures. Software named BAFinder 2.0 was developed to combine the semi-empirical library in negative mode and the characteristic fragments in positive mode for automatic unknown identification. As a proof of concept, this workflow was applied to the LC-MS/MS analysis of the feces of human, beagle dogs, and rats. In total, 171 common amino acid-conjugated bile acids were annotated and 105 of them were confirmed with the retention times of synthesized compounds. To explore other potential bile acid conjugates, user-defined small molecules were in-silico conjugated with bile acids and searched in the fecal dataset. Four novel bile acid conjugates were discovered, including D-Ala-D-Ala, Lys(iso)-Gly, L-2-aminobutyric acid, and ornithine.

Metabolic Clues to Bile Acid Patterns and Prolonged Survival in Patients with Metastatic Soft-Tissue Sarcoma Treated with Trabectedin

Metastatic soft-tissue sarcomas (mSTS) encompass a highly heterogeneous group of rare tumours characterized by different clinical behaviours and outcomes. Currently, prognostic factors for mSTS are very limited, posing significant challenges in predicting patient survival. Within a cohort of 39 mSTS patients undergoing trabectedin treatment, it was remarkable to find one patient who underwent 73 cycles of trabectedin achieving an unforeseen clinical outcome. To identify contributing factors to her exceptional long-term survival, we have explored circulation metabolomics and biohumoral biomarkers to uncover a potential distinct host biochemical phenotype. The long-term survival patient compared with the other mSTS patients exhibited a distinctive metabolic profile characterized by remarkably higher levels of ursodeoxycholic acid (UDCA) derivatives and vitamin D and lower levels of lithocholic acid (LCA) derivatives, as well as reduced levels of inflammatory C-Reactive Protein 4 (C-RP4) biomarker. Despite its exploratory nature, this study reveals a potential association between specific bile acid metabolic profiles and mSTS patients' prognosis. Enhanced clinical understanding of the interplay between bile acid metabolism and disease progression could pave the way for new targeted therapeutic interventions which may improve the overall survival of mSTS patients.

Immunological mechanisms of inflammatory diseases caused by gut microbiota dysbiosis: A review

The gut microbiota is indispensable for maintaining host health by enhancing the host's digestive capacity, safeguarding the intestinal epithelial barrier, and preventing pathogen invasion. Additionally, the gut microbiota exhibits a bidirectional interaction with the host immune system and promotes the immune system of the host to mature. Dysbiosis of the gut microbiota, primarily caused by factors such as host genetic susceptibility, age, BMI, diet, and drug abuse, is a significant contributor to inflammatory diseases. However, the mechanisms underlying inflammatory diseases resulting from gut microbiota dysbiosis lack systematic categorization. In this study, we summarize the normal physiological functions of symbiotic microbiota in a healthy state and demonstrate that when dysbiosis occurs due to various external factors, the normal physiological functions of the gut microbiota are lost, leading to pathological damage to the intestinal lining, metabolic disorders, and intestinal barrier damage. This, in turn, triggers immune system disorders and eventually causes inflammatory diseases in various systems. These discoveries provide fresh perspectives on how to diagnose and treat inflammatory diseases. However, the unrecognized variables that might affect the link between inflammatory illnesses and gut microbiota, need further studies and extensive basic and clinical research will still be required to investigate this relationship in the future.

Regulation of PD-L1 Expression by Nuclear Receptors

The suppression of excessive immune responses is necessary to prevent injury to the body, but it also allows cancer cells to escape immune responses and proliferate. Programmed cell death 1 (PD-1) is a co-inhibitory molecule that is present on T cells and is the receptor for programmed cell death ligand 1 (PD-L1). The binding of PD-1 to PD-L1 leads to the inhibition of the T cell receptor signaling cascade. PD-L1 has been found to be expressed in many types of cancers, such as lung, ovarian, and breast cancer, as well as glioblastoma. Furthermore, PD-L1 mRNA is widely expressed in normal peripheral tissues including the heart, skeletal muscle, placenta, lungs, thymus, spleen, kidney, and liver. The expression of PD-L1 is upregulated by proinflammatory cytokines and growth factors via a number of transcription factors. In addition, various nuclear receptors, such as androgen receptor, estrogen receptor, peroxisome-proliferator-activated receptor γ, and retinoic-acid-related orphan receptor γ, also regulate the expression of PD-L1. This review will focus on the current knowledge of the regulation of PD-L1 expression by nuclear receptors.

Intestinal Production of Alpha-Glucosidase Inhibitor by Bacillus coagulans Spores

This study examines the possibility of directly producing and utilizing useful substances in the intestines of animals using anaerobic bacteria that can grow in the intestines of animals. A facultative anaerobe producing a large amount of α-glucosidase inhibitor was isolated from hay and identified and named Bacillus coagulans CC. The main compound of α-glucosidase inhibitor produced by Bacillus coagulans CC was identified as 1-deoxynojirimycin. α-glucosidase inhibitor activity was confirmed in the intestinal contents and feces of mice orally administered with spores of this strain, and it was confirmed that this strain could efficiently reach the intestines, proliferate, and produce α-glucosidase inhibitors. As a result of administering Bacillus coagulans CC to mice at 10⁹ cells per 1 kg body weight of spores for 8 weeks, the high-carbohydrate diet and the high-fat diet showed a 5% lower weight gain compared to the non-administrated group. At this point, in the spore-administered group, a decrease was observed in both the visceral and subcutaneous fat layers of the abdomen and thorax in both high-carbohydrate and high-fat diet groups compared to the non-administered group on computed tomography. The results of this study show that α-glucosidase inhibitors produced in the intestine by specific strains can work efficiently.

Gut microbiota derived bile acid metabolites maintain the homeostasis of gut and systemic immunity

Bile acids (BAs) as cholesterol-derived molecules play an essential role in some physiological processes such as nutrient absorption, glucose homeostasis and regulation of energy expenditure. They are synthesized in the liver as primary BAs such as cholic acid (CA), chenodeoxycholic acid (CDCA) and conjugated forms. A variety of secondary BAs such as deoxycholic acid (DCA) and lithocholic acid (LCA) and their derivatives is synthesized in the intestine through the involvement of various microorganisms. In addition to essential physiological functions, BAs and their metabolites are also involved in the differentiation and functions of innate and adaptive immune cells such as macrophages (Macs), dendritic cells (DCs), myeloid derived suppressive cells (MDSCs), regulatory T cells (Treg), Breg cells, T helper (Th)17 cells, CD4 Th1 and Th2 cells, CD8 cells, B cells and NKT cells. Dysregulation of the BAs and their metabolites also affects development of some diseases such as inflammatory bowel diseases. We here summarize recent advances in how BAs and their metabolites maintain gut and systemic homeostasis, including the metabolism of the BAs and their derivatives, the role of BAs and their metabolites in the differentiation and function of immune cells, and the effects of BAs and their metabolites on immune-associated disorders.

Intrahepatic cholestasis of pregnancy worsening perinatal depressive tendency: A follow-up study from the second trimester to the sixth week postpartum

The total bile acid (TBA) is usually used to diagnose intrahepatic cholestasis of pregnancy (ICP) as a common clinical index. Recently many research reports on the microbiota-gut-brain axis (MGB axis) suggest that bile acids have an influence on human mental illnesses such as anxiety and depression, linked closely to intestinal microbial population. However, there is still a lack of clinical data to support intrinsic relationships about human cases. In this study, we conducted a follow-up study of 25 ICP and 98 healthy pregnant women to investigate the influence of ICP disease on perinatal depression. To further explore the effect of TBA concentration, we reviewed data of another 41 ICP women then added their cross-sectional data. The results showed that ICP disease increased mental scale scores but a conventional efficient treatment by using ursodeoxycholic acid (UDCA) could not decrease scores, suggesting intrahepatic cholestasis might make some key bile acids not to be processed by gut microbiota. UDCA could not replace the function of gut microbiota for easing depression and the change of bile acid composition in intestines worsened perinatal depressive tendency through the MGB axis.

An Insight into the Arising Role of MicroRNAs in Hepatocellular Carcinoma: Future Diagnostic and Therapeutic Approaches

Hepatocellular carcinoma (HCC) constitutes a frequent highly malignant form of primary liver cancer and is the third cause of death attributable to malignancy. Despite the improvement in the therapeutic strategies with the exploration of novel pharmacological agents, the survival rate for HCC is still low. Shedding light on the multiplex genetic and epigenetic background of HCC, such as on the emerging role of microRNAs, is considered quite promising for the diagnosis and the prediction of this malignancy, as well as for combatting drug resistance. MicroRNAs (miRNAs) constitute small noncoding RNA sequences, which play a key role in the regulation of several signaling and metabolic pathways, as well as of pivotal cellular functions such as autophagy, apoptosis, and cell proliferation. It is also demonstrated that miRNAs are significantly implicated in carcinogenesis, either acting as tumor suppressors or oncomiRs, while aberrations in their expression levels are closely associated with tumor growth and progression, as well as with local invasion and metastatic dissemination. The arising role of miRNAs in HCC is in the spotlight of the current scientific research, aiming at the development of novel therapeutic perspectives. In this review, we will shed light on the emerging role of miRNAs in HCC.

Metabolomic Study of Aging in fa/fa Rats: Multiplatform Urine and Serum Analysis

Zucker fatty (fa/fa) rats represent a well-established and widely used model of genetic obesity. Because previous metabolomic studies have only been published for young fa/fa rats up to 20 weeks of age, which can be considered early maturity in male fa/fa rats, the aim of our work was to extend the metabolomic characterization to significantly older animals. Therefore, the urinary profiles of obese fa/fa rats and their lean controls were monitored using untargeted NMR metabolomics between 12 and 40 weeks of age. At the end of the experiment, the rats were also characterized by NMR and LC-MS serum analysis, which was supplemented by a targeted LC-MS analysis of serum bile acids and neurotransmitters. The urine analysis showed that most of the characteristic differences detected in young obese fa/fa rats persisted throughout the experiment, primarily through a decrease in microbial co-metabolite levels, the upregulation of the citrate cycle, and changes in nicotinamide metabolism compared with the age-related controls. The serum of 40-week-old obese rats showed a reduction in several bile acid conjugates and an increase in serotonin. Our study demonstrated that the fa/fa model of genetic obesity is stable up to 40 weeks of age and is therefore suitable for long-term experiments.

Role of Microbiota-Modified Bile Acids in the Regulation of Intracellular Organelles and Neurodegenerative Diseases

Bile acids (BAs) are amphiphilic steroidal molecules generated from cholesterol in the liver and facilitate the digestion and absorption of fat-soluble substances in the gut. Some BAs in the intestine are modified by the gut microbiota. Because BAs are modified in a variety of ways by different types of bacteria present in the gut microbiota, changes in the gut microbiota can affect the metabolism of BAs in the host. Although most BAs absorbed from the gut are transferred to the liver, some are transferred to the systemic circulation. Furthermore, BAs have also been detected in the brain and are thought to migrate into the brain through the systemic circulation. Although BAs are known to affect a variety of physiological functions by acting as ligands for various nuclear and cell-surface receptors, BAs have also been found to act on mitochondria and autophagy in the cell. This review focuses on the BAs modified by the gut microbiota and their roles in intracellular organelles and neurodegenerative diseases.

Bile salt hydrolase of Lactiplantibacillus plantarum plays important roles in amelioration of DSS-induced colitis

Bile salt hydrolases are thought to be the gatekeepers of bile acid metabolism. To study the role of BSH in colitis, we investigated the ameliorative effects of different BSH-knockout strains of Lactiplantibacillus plantarum AR113. The results showed that L. plantarum Δbsh 1 and Δbsh 3 treatments did not improve body weight and alleviate the hyperactivated myeloperoxidase activity to the DSS group. However, the findings for L. plantarum AR113, L. plantarum Δbsh 2 and Δbsh 4 treatments were completely opposite. The double and triple bsh knockout strains further confirmed that BSH 1 and BSH 3 are critical for the ameliorative effects of L. plantarum AR113. In addition, L. plantarum Δbsh 1 and Δbsh 3 did not significantly inhibit the increase in pro-inflammatory cytokines or the decrease in an anti-inflammatory cytokine. These results suggest that BSH 1 and BSH 3 in L. plantarum play important roles in alleviating enteritis symptoms.

Novel insights into bile acid detoxification via CYP, UGT and SULT enzymes

Bile acid (BA) homeostasis is a complex and precisely regulated process to prevent impaired BA flow and the development of cholestasis. Several reactions, namely hydroxylation, glucuronidation and sulfation are involved in BA detoxification. In the present study, we employed a comprehensive approach to identify the key enzymes involved in BA metabolism using human recombinant enzymes, human liver microsomes (HLM) and human liver cytosol (HLC). We showed that CYP3A4 was a crucial step for the metabolism of several BAs and their taurine and glycine conjugated forms and quantitatively described their metabolites. Glucuronidation and sulfation were also identified as important drivers of the BA detoxification process in humans. Moreover, lithocholic acid (LCA), the most hydrophobic BA with the highest toxicity potential, was a substrate for all investigated processes, demonstrating the importance of hepatic metabolism for its clearance. Collectively, this study identified CYP3A4, UGT1A3, UGT2B7 and SULT2A1 as the major contributing (metabolic) processes in the BA detoxification network. Inhibition of these enzymes by drug candidates is therefore considered as a critical mechanism in the manifestation of drug-induced cholestasis in humans and should be addressed during the pre-clinical development.

Swainsonine Induces Liver Inflammation in Mice via Disturbance of Gut Microbiota and Bile Acid Metabolism

Swainsonine induced liver inflammation in livestock; however, the underlying mechanisms, especially the role of bile acids (BAs), in the pathogenesis remained elusive. Here, our results showed that swainsonine induced hepatic inflammation via changing BA metabolism and gut microbiota in mice. Swainsonine significantly upregulated the levels of deoxycholic acid (DCA) and taurine-β-muricholic acid (T-β-MCA) in the serum and liver of mice due to the markedly increased genus Clostridium and the decreased genus Lactobacillus in the gut. As antagonists of the farnesoid X receptor (FXR), elevated DCA and T-β-MCA inhibited hepatic Fxr gene expression and thus suppressed FXR-SHP signaling and activated hepatic Cyp7a1 gene expression, which induced a significant upregulation of the total BA level in serum, contributing to liver inflammation. These findings offer new insights into the underlying mechanisms in which swainsonine induced liver inflammation in mice via the gut-liver axis and suggest that gut microbiota and its metabolite BAs may be underlying triggering factors.

OAT, OATP, and MRP Drug Transporters and the Remote Sensing and Signaling Theory

The coordinated movement of organic anions (e.g., drugs, metabolites, signaling molecules, nutrients, antioxidants, gut microbiome products) between tissues and body fluids depends, in large part, on organic anion transporters (OATs) [solute carrier 22 (SLC22)], organic anion transporting polypeptides (OATPs) [solute carrier organic (SLCO)], and multidrug resistance proteins (MRPs) [ATP-binding cassette, subfamily C (ABCC)]. Depending on the range of substrates, transporters in these families can be considered multispecific, oligospecific, or (relatively) monospecific. Systems biology analyses of these transporters in the context of expression patterns reveal they are hubs in networks involved in interorgan and interorganismal communication. The remote sensing and signaling theory explains how the coordinated functions of drug transporters, drug-metabolizing enzymes, and regulatory proteins play a role in optimizing systemic and local levels of important endogenous small molecules. We focus on the role of OATs, OATPs, and MRPs in endogenous metabolism and how their substrates (e.g., bile acids, short chain fatty acids, urate, uremic toxins) mediate interorgan and interorganismal communication and help maintain and restore homeostasis in healthy and disease states.

Alteration of gastric microbiota and transcriptome in a rat with gastric intestinal metaplasia induced by deoxycholic acid

Objective

Bile reflux plays a key role in the development of gastric intestinal metaplasia (GIM), an independent risk factor of gastric cancer. Here, we aimed to explore the biological mechanism of GIM induced by bile reflux in a rat model.

Methods

Rats were treated with 2% sodium salicylate and allowed to freely drink 20 mmol/L sodium deoxycholate for 12 weeks, and GIM was confirmed by histopathological analysis. Gastric microbiota was profiled according to the 16S rDNA V3-V4 region, gastric transcriptome was sequenced, and serum bile acids (BAs) were analyzed by targeted metabolomics. Spearman's correlation analysis was used in constructing the network among gastric microbiota, serum BAs, and gene profiles. Real-time polymerase chain reaction (RT-PCR) measured the expression levels of nine genes in the gastric transcriptome.

Results

In the stomach, deoxycholic acid (DCA) decreased the microbial diversity but promoted the abundances of several bacterial genera, such as Limosilactobacillus, Burkholderia-Caballeronia-Paraburkholderia, and Rikenellaceae RC9 gut group. Gastric transcriptome showed that the genes enriched in gastric acid secretion were significantly downregulated, whereas the genes enriched in fat digestion and absorption were obviously upregulated in GIM rats. The GIM rats had four promoted serum BAs, namely cholic acid (CA), DCA, taurocholic acid, and taurodeoxycholic acid. Further correlation analysis showed that the Rikenellaceae RC9 gut group was significantly positively correlated with DCA and RGD1311575 (capping protein-inhibiting regulator of actin dynamics), and RGD1311575 was positively correlated with Fabp1 (fatty acid-binding protein, liver), a key gene involved in fat digestion and absorption. Finally, the upregulated expression of Dgat1 (diacylglycerol acyltransferase 1) and Fabp1 related to fat digestion and absorption was identified by RT-PCR and IHC.

Conclusion

DCA-induced GIM enhanced gastric fat digestion and absorption function and impaired gastric acid secretion function. The DCA-Rikenellaceae RC9 gut group-RGD1311575/Fabp1 axis might play a key role in the mechanism of bile reflux-related GIM.

Dietary carbon loaded with nano-ZnO alters the gut microbiota community to mediate bile acid metabolism and potentiate intestinal immune function in fattening beef cattle

BACKGROUND

To our knowledge, carbon loaded with nano-ZnO (NZnOC) represents a new nutritional additive for the animal husbandry industry. However, the mechanism by which NZnOC mediates beef cattle growth and intestinal health is not fully understood. This study aimed to investigate the effects of carbon loaded with nano-ZnO (NZnOC) supplementation on growth performance, gut microbiota, bile acid (BAs) metabolism and intestinal immunity in fattening cattle. Twenty cattle (16 ± 0.95 months) were randomly assigned to two dietary groups: CON (control, without feed additive) and NZnOC (diet supplemented with 80 mg NZnOC/kg diet dry matter basic) for 60 d. The colon digesta microbiota composition and BAs concentration were determined by microbiota metagenomics and gas chromatography methods, respectively.

RESULTS

The results showed that the NZnOC-supplemented cattle had greater final weight, average daily gain and gain-to-feed ratio than those in the CON group. Cattle fed the NZnOC diet had a higher relative abundance of the secondary BAs synthesizing phyla Firmicutes, Tenericutes and Actinobacteria than those fed the CON diet. Dietary supplementation with NZnOC increased the relative abundance of the secondary BAs synthesis microbiota genera Clostridium, Ruminococcus, Eubacterium, and Brevibacillus in colon digesta. Cattle fed the NZnOC diet had increased activities of 3α-hydroxysteroid dehydrogenase (EC: 1.1.1.52) and bile acid-CoA ligase BaiB (EC: 6.2.1.7) in the colon digesta compared with those fed the CON diet. The primary BAs taurocholic acid, taurochenodeoxycholic acid and taurodeoxycholate acid were significantly decreased by dietary NZnOC supplementation, while the secondary BAs deoxycholic acid, taurolithocholic acid, beta-muricholic acid, 12-ketolithocholic acid and ursodeoxycholic acid were significantly increased. Dietary supplementation with NZnOC increased the mRNA abundance of G protein-coupled bile acid receptor 1, protein kinase cAMP-activated catalytic subunit alpha, cyclic-AMP response element binding protein 1 and interleukin (IL)-10 in the colon mucosa of cattle, while the mRNA abundance of tumor necrosis factor and IL-1β were significantly decreased.

CONCLUSIONS

In summary, dietary supplementation with NZnOC can facilitate the growth performance and intestinal immune function of cattle by improving BAs metabolism. NZnOC can be supplemented in the diet as a safe regulator of gut microbiota and as a feed additive in the ruminants industry.

Gut-Liver Axis and Non-Alcoholic Fatty Liver Disease: A Vicious Circle of Dysfunctions Orchestrated by the Gut Microbiome

Non-alcoholic fatty liver disease (NAFLD) is a prevalent, multifactorial, and poorly understood liver disease with an increasing incidence worldwide. NAFLD is typically asymptomatic and coupled with other symptoms of metabolic syndrome. The prevalence of NAFLD is rising in tandem with the prevalence of obesity. In the Western hemisphere, NAFLD is one of the most prevalent causes of liver disease and liver transplantation. Recent research suggests that gut microbiome dysbiosis may play a significant role in the pathogenesis of NAFLD by dysregulating the gut-liver axis. The so-called "gut-liver axis" refers to the communication and feedback loop between the digestive system and the liver. Several pathological mechanisms characterized the alteration of the gut-liver axis, such as the impairment of the gut barrier and the increase of the intestinal permeability which result in endotoxemia and inflammation, and changes in bile acid profiles and metabolite levels produced by the gut microbiome. This review will explore the role of gut-liver axis disruption, mediated by gut microbiome dysbiosis, on NAFLD development.

Bifidobacterial carbohydrate/nucleoside metabolism enhances oxidative phosphorylation in white adipose tissue to protect against diet-induced obesity

BACKGROUND

Comparisons of the gut microbiome of lean and obese humans have revealed that obesity is associated with the gut microbiome plus changes in numerous environmental factors, including high-fat diet (HFD). Here, we report that two species of Bifidobacterium are crucial to controlling metabolic parameters in the Korean population.

RESULTS

Based on gut microbial analysis from 99 Korean individuals, we observed the abundance of Bifidobacterium longum and Bifidobacterium bifidum was markedly reduced in individuals with increased visceral adipose tissue (VAT), body mass index (BMI), blood triglyceride (TG), and fatty liver. Bacterial transcriptomic analysis revealed that carbohydrate/nucleoside metabolic processes of Bifidobacterium longum and Bifidobacterium bifidum were associated with protecting against diet-induced obesity. Oral treatment of specific commercial Bifidobacterium longum and Bifidobacterium bifidum enhanced bile acid signaling contributing to potentiate oxidative phosphorylation (OXPHOS) in adipose tissues, leading to reduction of body weight gain and improvement in hepatic steatosis and glucose homeostasis. Bifidobacterium longum or Bifidobacterium bifidum manipulated intestinal sterol biosynthetic processes to protect against diet-induced obesity in germ-free mice.

CONCLUSIONS

Our findings support the notion that treatment of carbohydrate/nucleoside metabolic processes-enriched Bifidobacterium longum and Bifidobacterium bifidum would be a novel therapeutic strategy for reprograming the host metabolic homeostasis to protect against metabolic syndromes, including diet-induced obesity. Video Abstract.

The role of the gut microbiota in health and cardiovascular diseases

The gut microbiota is critical to human health, such as digesting nutrients, forming the intestinal epithelial barrier, regulating immune function, producing vitamins and hormones, and producing metabolites to interact with the host. Meanwhile, increasing evidence indicates that the gut microbiota has a strong correlation with the occurrence, progression and treatment of cardiovascular diseases (CVDs). In patients with CVDs and corresponding risk factors, the composition and ratio of gut microbiota have significant differences compared with their healthy counterparts. Therefore, gut microbiota dysbiosis, gut microbiota-generated metabolites, and the related signaling pathway may serve as explanations for some of the mechanisms about the occurrence and development of CVDs. Several studies have also demonstrated that many traditional and latest therapeutic treatments of CVDs are associated with the gut microbiota and its generated metabolites and related signaling pathways. Given that information, we summarized the latest advances in the current research regarding the effect of gut microbiota on health, the main cardiovascular risk factors, and CVDs, highlighted the roles and mechanisms of several metabolites, and introduced corresponding promising treatments for CVDs regarding the gut microbiota. Therefore, this review mainly focuses on exploring the role of gut microbiota related metabolites and their therapeutic potential in CVDs, which may eventually provide better solutions in the development of therapeutic treatment as well as the prevention of CVDs.

Replacing saturated fatty acids with polyunsaturated fatty acids increases the abundance of Lachnospiraceae and is associated with reduced total cholesterol levels-a randomized controlled trial in healthy individuals

Background

Improving dietary fat quality strongly affects serum cholesterol levels and hence the risk of cardiovascular diseases (CVDs). Recent studies have identified dietary fat as a potential modulator of the gut microbiota, a central regulator of host metabolism including lipid metabolism. We have previously shown a significant reduction in total cholesterol levels after replacing saturated fatty acids (SFAs) with polyunsaturated fatty acids (PUFAs). The aim of the present study was to investigate the effect of dietary fat quality on gut microbiota, short-chain fatty acids (SCFAs), and bile acids in healthy individuals. In addition, to investigate how changes in gut microbiota correlate with blood lipids, bile acids, and fatty acids.

Methods

Seventeen participants completed a randomized, controlled dietary crossover study. The participants received products with SFAs (control) or PUFAs in random order for three days. Fecal samples for gut microbiota analyses and fasting blood samples (lipids, fatty acids, and bile acids) were measured before and after the three-day intervention.

Results

Of a panel of 40 bacteria, Lachnospiraceae and Bifidobacterium spp. were significantly increased after intervention with PUFAs compared with SFAs. Interestingly, changes in Lachnospiraceae, as well as Phascolarlactobacterium sp. and Eubacterium hallii, was also found to be negatively correlated with changes in total cholesterol levels after replacing the intake of SFAs with PUFAs for three days. No significant differences in SCFAs or bile acids were found after the intervention.

Conclusion

Replacing SFAs with PUFAs increased the abundance of the gut microbiota family of Lachnospiraceae and Bifidobacterium spp. Furthermore, the reduction in total cholesterol after improving dietary fat quality correlated with changes in the gut microbiota family Lachnospiraceae. Future studies are needed to reveal whether Lachnospiraceae may be targeted to reduce total cholesterol levels.

Trial registration

The study was registered at Clinical Trials (https://clinicaltrials.gov/, registration identification number: NCT03658681).

Microbiota mitochondria disorders as hubs for early age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive neurodegenerative disease affecting the central area (macula lutea) of the retina. Research on the pathogenic mechanism of AMD showed complex cellular contribution governed by such risk factors as aging, genetic predisposition, diet, and lifestyle. Recent studies suggested that microbiota is a transducer and a modifier of risk factors for neurodegenerative diseases, and mitochondria may be one of the intracellular targets of microbial signaling molecules. This review explores studies supporting a new concept on the contribution of microbiota-mitochondria disorders to AMD. We discuss metabolic, vascular, immune, and neuronal mechanism in AMD as well as key alterations of photoreceptor cells, retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris endothelial, immune, and neuronal cells. Special attention was paid to alterations of mitochondria contact sites (MCSs), an organelle network of mitochondria, endoplasmic reticulum, lipid droplets (LDs), and peroxisomes being documented based on our own electron microscopic findings from surgically removed human eyes. Morphometry of Bruch's membrane lipids and proteoglycans has also been performed in early AMD and aged controls. Microbial metabolites (short-chain fatty acids, polyphenols, and secondary bile acids) and microbial compounds (lipopolysaccharide, peptidoglycan, and bacterial DNA)-now called postbiotics-in addition to local effects on resident microbiota and mucous membrane, regulate systemic metabolic, vascular, immune, and neuronal mechanisms in normal conditions and in various common diseases. We also discuss their antioxidant, anti-inflammatory, and metabolic effects as well as experimental and clinical observations on regulating the main processes of photoreceptor renewal, mitophagy, and autophagy in early AMD. These findings support an emerging concept that microbiota-mitochondria disorders may be a crucial pathogenic mechanism of early AMD; and similarly, to other age-related neurodegenerative diseases, new treatment approaches should be targeted at these disorders.

Molecular Basis of Bile Acid-FXR-FGF15/19 Signaling Axis

Bile acids (BAs) are a group of amphiphilic molecules consisting of a rigid steroid core attached to a hydroxyl group with a varying number, position, and orientation, and a hydrophilic side chain. While BAs act as detergents to solubilize lipophilic nutrients in the small intestine during digestion and absorption, they also act as hormones. Farnesoid X receptor (FXR) is a nuclear receptor that forms a heterodimer with retinoid X receptor α (RXRα), is activated by BAs in the enterohepatic circulation reabsorbed via transporters in the ileum and the colon, and plays a critical role in regulating gene expression involved in cholesterol, BA, and lipid metabolism in the liver. The FXR/RXRα heterodimer also exists in the distal ileum and regulates production of fibroblast growth factor (FGF) 15/FGF19, a hormone traveling via the enterohepatic circulation that activates hepatic FGF receptor 4 (FGFR4)-β-klotho receptor complex and regulates gene expression involved in cholesterol, BA, and lipid metabolism, as well as those regulating cell proliferation. Agonists for FXR and analogs for FGF15/19 are currently recognized as a promising therapeutic target for metabolic syndrome and cholestatic diseases.

Bifidobacterium breve and Bifidobacterium longum Attenuate Choline-Induced Plasma Trimethylamine N-Oxide Production by Modulating Gut Microbiota in Mice

Atherosclerosis is the main cause of myocardial infarction and stroke, and the morbidity and mortality rates of cardiovascular disease are among the highest of any disease worldwide. Excessive plasma trimethylamine-N-oxide (TMAO), an intestinal metabolite, promotes the development of atherosclerosis. Therefore, effective measures for reducing plasma TMAO production can contribute to preventing atherosclerosis. Probiotics are living microorganisms that are beneficial to the human body, and some of them can attenuate plasma TMAO production. To explore the effects of probiotic supplementation on plasma TMAO in choline-fed mice, we intragastrically administered eight strains of Bifidobacterium breve and eight strains of Bifidobacterium longum to mice for 6 weeks. B. breve Bb4 and B. longum BL1 and BL7 significantly reduced plasma TMAO and plasma and cecal trimethylamine concentrations. However, hepatic flavin monooxygenase (FMO) activity, flavin-containing monooxygenase 3 (FMO3), farnesoid X receptor (FXR) protein expression and TMAO fractional excretion were not significantly affected by Bifidobacterium supplementation. The treatment of Bifidobacterium strains modulated the abundances of several genera such as Ruminococcaceae UCG-009, Ruminococcaceae UCG-010, which belong to the Firmicutes that has been reported with cut gene clusters, which may be related to the reduction in intestinal TMA and plasma TMAO. Additionally, a reduction in Ruminococcaceae indicates a reduction in circulating glucose and lipids, which may be another pathway by which Bifidobacterium strains reduce the risk of atherosclerosis. The effect of Bifidobacterium strains on Bacteroides also suggests a relationship between the abundance of this genus and TMA concentrations in the gut. Therefore, the mechanism underlying these changes might be gut microbiota regulation. These Bifidobacterium strains may have therapeutic potential for alleviating TMAO-related diseases.