Gut microbiota regulates bile acid metabolism by reducing the levels of tauro-beta-muricholic acid, a naturally occurring FXR antagonist

Increased dietary protein stimulates amino acid catabolism via the gut microbiota and secondary bile acid production

Excess amino acids from a protein-rich diet are mainly catabolized in the liver. However, it is still unclear to what extent the gut microbiota may be involved in the mechanisms governing this catabolism. Therefore, the aim of this study was to investigate whether consumption of different dietary protein concentrations induces changes in the taxonomy of the gut microbiota, which may contribute to the regulation of hepatic amino acid catabolism. Consumption of a high-protein diet caused overexpression of HIF-1α in the colon and increase in mitochondrial activity, creating a more anaerobic environment that was associated with changes in the taxonomy of the gut microbiota promoting an increase in the synthesis of secondary bile acids, increased secretion of pancreatic glucagon. This effect was demonstrated in pancreatic islets, where secondary bile acids stimulated the expression of the PC2 enzyme that promotes glucagon formation. The increase in circulating glucagon was associated with an induction of the expression of hepatic amino acid-degrading enzymes, an effect attenuated by antibiotics. Thus, high protein intake in mice and humans induced the increase of different species in the gut microbiota with the capacity to produce secondary bile acids leading to an increase in secondary bile acids and glucagon levels, promoting amino acid catabolism.

Emodin-8-O-β-D-glucopyranoside alleviates cholestasis by maintaining intestinal homeostasis and regulating lipids and bile acids metabolism in mice

Cholestatic liver disease(CLD) is caused by impaired bile flow due to obstruction of the biliary tract, and long-term exposure to bile acids in the liver triggers inflammation, eventually leading to liver toxicity and liver fibrosis. Emodin-8-O-β-D-glucopyranoside(EG) is anthraquinone compound that is widely found in traditional Chinese medicine. It possessed antioxidative and anti-inflammatory activities. However, the effect of EG on cholestatic liver injury(CLI) has not been explored. In this study, Alpha-naphthyl isothiocyanate(ANIT)-induced CLI mice were used to investigate the anti-cholestasis and hepatoprotective effects of EG through serum biochemical index detection, non-targeted metabolomics, lipidomics, and intestinal flora 16S rRNA sequencing. The results suggested that EG restores homeostasis of the gut microbiome while regulating bile acids metabolism and lipid-related metabolic pathways to reduce liver damage in ANIT-induced cholestasis. This study provides a new perspective on the mechanism of EG, and help offer a more natural approach to managing liver damage.

Non-starch polysaccharides and health: gut-target organ axis influencing obesity

Obesity is recognized as a global epidemic that can result in changes in the human body and metabolism. Accumulating evidence indicates that gut microbiota (GM) can affect the development of obesity. The GM not only plays a crucial role in digesting and absorbing nutrients, but also in maintaining the overall health of the host. Dietary supplements such as non-starch polysaccharides are mainly fermented by the GM in the colon. Recent findings suggest that shaping the GM through the prebiotic function of non-starch polysaccharides may be a viable strategy against obesity. In this paper, the effects of non-starch polysaccharides on host health, together with their prebiotic function influencing the GM to control obesity via the gut-target organ axis, are reviewed. Potential perspectives of non-starch polysaccharides exhibiting anti-obesity effects via the gut-target organ axis are proposed for future research.

Graphical abstract

Schisandra chinensis lignans ameliorate hepatic inflammation and steatosis in methionine choline-deficient diet-fed mice by modulating the gut-liver axis

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis is used as a traditional Chinese medicine to treat a variety of diseases. Schisandra chinensis lignans (SCL) are one of the most active components extracted from Schisandrae chinensis fructus, exhibit a broad array of pharmacological properties, especially anti-inflammatory and hepatic lipid-lowering effects, suggesting SCL may have potential anti-nonalcoholic steatohepatitis (NASH) ability. However, the therapeutic efficacy of SCL against NASH and the underlying mechanism remains unclear.

AIM OF THE STUDY

In the current study, we aimed to investigate the anti-NASH action of SCL and explore the underlying mechanism in vitro and in vivo. We also assess the involvement of the gut-liver axis in the anti-NASH effects of SCL.

METHODS

Palmitic acid (PA)-treated HepG2 cells, mouse primary hepatocytes (MPHs) and methionine-choline deficient (MCD) diet-fed mice were selected as NASH models. ORO staining and qRT-PCR were performed to assess hepatic steatosis and inflammatory responses, respectively. Protein expression was detected by Western blotting or immunohistochemistry. The changes of gut microbiota were analyzed using 16S rDNA sequencing in mice. The levels of metabolites in liver and feces were measured by metabolomics.

RESULTS

The results showed that SCL treatment alleviated steatosis and inflammation in palmitic acid (PA)-treated HepG2 cells and mouse primary hepatocytes (MPHs). SCL treatment suppressed the phosphorylation of key components involved in NF-κB signaling and enhanced the expression of fatty acid oxidation (FAO)-related enzymes (e.g. CPT1, HMGCS2, and ACOX1) in PA-treated HepG2 cells. SCL could ameliorate hepatic steatosis and inflammation in NASH mice. SCL also ameliorated intestinal barrier injury and restructured the gut microbiota in NASH mice. SCL also modulated hepatic and colonic bile acid metabolism via FXR signaling.

CONCLUSION

These findings indicate that SCL treatment ameliorates hepatic inflammation and steatosis in NASH, potentially though to the suppression of NF-κB signaling and the promotion of fatty acid β-oxidation. Moreover, SCL could restore gut microbiota-mediated bile acid homeostasis via activation of FXR/FGF15 signaling. Our study presents a pharmacological rationale for using SCL in the management of NASH.

Gut microbes-muscle axis in muscle function and meat quality

The concept of the gut microbes-muscle axis underscores the impact of intestinal microbiota on the muscular system, an area that is increasingly coming to light. However, current interpretations and applications of this concept remain underdeveloped. In this review, we concluded and discussed factors, such as short-chain fatty acids, amino acids, vitamins, bile acids, antibiotics, cytokines, hormones, and extracellular vesicles that mediate gut microbes-muscle crosstalk and influence the gut microbes-muscle axis. Additionally, we examined how the gut microbes-muscle axis affects muscle mass, muscle strength, muscle metabolism, as well as muscle oxidative and immune status. Furthermore, we reviewed the influence of the microbes-muscle axis on muscle fiber type transition, muscle fat deposition, and meat quality. These insights illuminate the potential mechanisms by which the gut microbes-muscle axis operates in humans and animals. Thus, this review provides a theoretical foundation for future research and offers practical guidance for its application in biomedical and livestock industries.

Integrating deep learning and molecular dynamics simulations for FXR antagonist discovery

Farnesoid X receptor (FXR) is a key regulator of bile acid, lipid, and glucose homeostasis, making it a promising target for treating metabolic diseases. FXR antagonists have shown therapeutic potential in cholestasis, metabolic disorders, and certain cancers, while clinically approved FXR antagonists remain unavailable and underrepresented in current treatment strategies. To address this, we developed deep learning models for predicting FXR antagonistic activity (ANTCL) and toxicity (TOXCL). Screening 217,345 compounds from the HMDB database identified eleven human metabolite candidates with significant FXR binding potential. Molecular dynamics simulations and binding free energy calculations revealed five more stable complexes compared to the reference compound Gly-MCA, with HMDB0253354 (Fulvestrant) and HMDB0242367 (ZM 189154) standing out for their binding free energies. Hydrophobic interactions, particularly involving residues MET328, PHE329, and ALA291, contributed to their stability. These results demonstrate the effectiveness of deep learning in FXR antagonist discovery and highlight the potential of HMDB0253354 and HMDB0242367 as promising candidates for metabolic disease treatment.

Activation of gut FXR improves the metabolism of bile acids, intestinal barrier, and microbiota under cholestatic condition caused by GCDCA in mice

Abnormal bile acid (BA) metabolism is involved in liver fibrosis. In a previous study, we discovered that the hydrophobic BA glycochenodeoxycholate (GCDCA) induced liver fibrosis and that GW4064, an agonist of farnesoid X receptor (FXR), alleviated liver fibrosis caused by GCDCA. However, the impacts of GCDCA on liver BAs, gut BAs, the intestinal barrier, and the gut microbiota are unclear, and obtaining this information would provide additional information into the role of GCDCA in the development of liver fibrosis. In the present study, ultra-performance liquid chromatography‒tandem mass spectrometry revealed that mice administered GCDCA by gavage had higher levels of total and primary liver BAs than those in the control group, and a significant reduction in primary liver BAs was observed in the GCDCA + GW4064 group compared with those in the GCDCA group. Compared with those in the control group, the mice administered GCDCA by gavage had greater levels of total and primary BAs in the gut, especially T-alpha-MCA and T-beta-MCA, and no significant differences in the terminal ileum were observed between the GCDCA and GCDCA + GW4064 groups. Immunohistochemistry indicated that GCDCA administration inhibited gut FXR and FGF15 expression, whereas GW4064 activated gut FXR and promoted FGF15 expression. Moreover, immunohistochemistry revealed that GCDCA administration decreased mucin2, claudin-1, occludin, and ZO-1 expression, whereas GW4064 restored their expression. 16S rDNA sequencing revealed that the alpha diversity of the microbiota did not significantly differ among the three groups, but differences in the beta diversity of the microbiota were observed among the three groups. At the phylum level, GCDCA significantly disturbed the gut microbiota, as indicated by reductions in Desulfobacterota, Bacteroidota, and Actinobacteria in the GCDCA group compared with those in the control group. However, significantly increased abundances of Proteobacteria, Cyanobacteria, and Patescibacteria were noted in the GCDCA group compared with the control group. GW4064 administration significantly improved the microbiota structure at the phylum level. The efficacy of GW4064 was also observed at the genus level. Correlation analyses revealed fewer relationships between the gut microbiota and gut BAs, whereas the gut microbiota was more closely related to liver BAs in the GCDCA and GW4064 intervention groups. Together, GCDCA induced cholestasis and disturbed BA metabolism in the gut and liver, as well as the intestinal barrier and structure of the gut microbiota. Activation of gut FXR improved intestinal barrier injury and alleviated BA metabolism dysfunction and dysbacteriosis caused by GCDCA under cholestatic conditions.

IMPORTANCE

Glycochenodeoxycholate (GCDCA) is a hydrophobic bile acid (BA) in humans and is highly increased in the serum and stool of liver fibrosis patients. However, the effects of GCDCA were not comprehensively investigated in the process of liver bile acid metabolism, gut microbiota, and intestinal barrier. It was reported that GCDCA can promote liver fibrosis via the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome pathway in mice, and gut farnesoid X receptor activation alleviated the fibrosis caused by GCDCA in our previous study. Gut microbiota is also responsible for BA metabolism; meanwhile, BA metabolism may also exert an effect on the intestinal barrier. Nowadays, the comprehensive understanding of gut microbiota and intestinal barrier in relation to BA disorder was still insufficient. Current study further investigated the role of GCDCA in BA metabolism, gut microbiota, and intestinal barrier to help understand the effects of GCDCA in liver fibrosis, which may provide intervention methods for liver fibrosis caused by dysregulation of BA metabolism.

Bile acid metabolism in type 2 diabetes mellitus

Type 2 diabetes mellitus is a complex disorder associated with insulin resistance and hyperinsulinaemia that is insufficient to maintain normal glucose metabolism. Changes in insulin signalling and insulin levels are thought to directly explain many of the metabolic abnormalities that occur in diabetes mellitus, such as impaired glucose disposal. However, molecules that are directly affected by abnormal insulin signalling might subsequently go on to cause secondary metabolic effects that contribute to the pathology of type 2 diabetes mellitus. In the past several years, evidence has linked insulin resistance with the concentration, composition and distribution of bile acids. As bile acids are known to regulate glucose metabolism, lipid metabolism and energy balance, these findings suggest that bile acids are potential mediators of metabolic distress in type 2 diabetes mellitus. In this Review, we highlight advances in our understanding of the complex regulation of bile acids during insulin resistance, as well as how bile acids contribute to metabolic control.

Systematic review: The gut microbiota as a link between colorectal cancer and obesity

Microbiome modulation is one of the novel strategies in medicine with the greatest future to improve the health of individuals and reduce the risk of different conditions, including metabolic, immune, inflammatory, and degenerative diseases, as well as cancer. Regarding the latter, many studies have reported the role of the gut microbiome in carcinogenesis, formation and progression of colorectal cancer (CRC), as well as its response to different systemic therapies. Likewise, obesity, one of the most important risk factors for CRC, is also well known for its association with gut dysbiosis. Moreover, obesity and CRC display, apart from microbial dysbiosis, chronic inflammation, which participates in their pathogenesis. Although human and murine studies demonstrate the significant impact of the microbiome in regulating energy metabolism and CRC development, little is understood about the contribution of the microbiome to the development of obesity-associated CRC. Therefore, this systematic review explores the evidence for microbiome changes associated with these conditions and hypothesizes that this may contribute to the pathogenesis of obesity-related CRC. Two databases were searched, and different studies on the relationship among obesity, intestinal microbiota and CRC in clinical and preclinical models were selected. Data extraction was carried out by two reviewers independently, and 101 studies were finally considered. Findings indicate the existence of a risk association between obesity and CRC derived from metabolic, immune, and microbial disorders.

Advances in Fecal Microbiota Transplantation for Gut Dysbiosis-Related Diseases

This article provides an overview of the advancements in the application of fecal microbiota transplantation (FMT) in treating diseases related to intestinal dysbiosis. FMT involves the transfer of healthy donor fecal microbiota into the patient's body, aiming to restore the balance of intestinal microbiota and thereby treat a variety of intestinal diseases such as recurrent Clostridioides difficile infection (rCDI), inflammatory bowel disease (IBD), constipation, short bowel syndrome (SBS), and irritable bowel syndrome (IBS). While FMT has shown high efficacy in the treatment of rCDI, further research is needed for its application in other chronic conditions. This article elaborates on the application of FMT in intestinal diseases and the mechanisms of intestinal dysbiosis, as well as discusses key factors influencing the effectiveness of FMT, including donor selection, recipient characteristics, treatment protocols, and methods for assessing microbiota. Additionally, it emphasizes the key to successful FMT. Future research should focus on optimizing the FMT process to ensure long-term safety and explore the potential application of FMT in a broader range of medical conditions.

Farnesoid X Receptor Regulated Sepsis-Induced Abnormal Bile Acid Metabolism via the Fibroblast Growth Factor 15/Fibroblast Growth Factor Receptor 4 Pathway

OBJECTIVE

The study aims to investigate the mechanism of Farnesoid X receptor (FXR) activation in sepsis-induced abnormal bile acid metabolism and the metabolism status of each bile acid type.

METHODS

The sepsis mouse model was developed via lipopolysaccharide intraperitoneal injection and confirmed via hematoxylin and eosin (H&E) staining. FXR agonist activated the FXR/fibroblast growth factor (FGF)15/FGFR pathway via quantitative real-time polymerase chain reaction and Western blot. Consequently, metabolomics and bioinformatics analysis were conducted to identify the alterations in each kind of bile acid content following FXR agonist/inhibitor intervention.

RESULTS

The H&E staining indicated that FXR activation alleviates the liver injury of the sepsis mouse model. The increased FGF15 and FXFR expression levels and decreased CYP7A1 demonstrated FXR/FGF15/FGFR pathway activation following FXR agonist treatment. Furthermore, total bile acid, interleukin (IL)-6, and tumor necrosis factor-α concentrations were downregulated after FXR activation, whereas IL-10 concentration was upregulated, indicating the alleviated effect of FXR agonist in sepsis. Consequently, metabolomics and bioinformatics analysis determined that T-a-MCA were downregulated in both FXR agonist and inhibitor groups, whereas six bile acid types were altered in the control group.

CONCLUSION

FXR activation was crucial in alleviating sepsis-induced hepatic injury and cholestasis through the FGF15/FGFR signaling pathway, and FXR may act as a potential preventive and intervention target of sepsis.

Inhibition of ATGL alleviates MASH via impaired PPARα signalling that favours hydrophilic bile acid composition in mice

BACKGROUND & AIMS

Adipose triglyceride lipase (ATGL) is an attractive therapeutic target in insulin resistance and metabolic dysfunction-associated steatotic liver disease (MASLD). This study investigated the effects of pharmacological ATGL inhibition on the development of metabolic dysfunction-associated steatohepatitis (MASH) and fibrosis in mice.

METHODS

Streptozotocin-injected male mice were fed a high-fat diet to induce MASH. Mice receiving the ATGL inhibitor atglistatin (ATGLi) were compared to controls using liver histology, lipidomics, metabolomics, 16s rRNA, and RNA sequencing. Human ileal organoids, HepG2 cells, and Caco2 cells treated with the human ATGL inhibitor NG-497, HepG2 ATGL knockdown cells, gel-shift, and luciferase assays were analysed for mechanistic insights. We validated the benefits of ATGLi on steatohepatitis and fibrosis in a low-methionine choline-deficient mouse model.

RESULTS

ATGLi improved serum liver enzymes, hepatic lipid content, and histological liver injury. Mechanistically, ATGLi attenuated PPARα signalling, favouring hydrophilic bile acid (BA) synthesis with increased Cyp7a1, Cyp27a1, Cyp2c70, and reduced Cyp8b1 expression. Additionally, reduced intestinal Cd36 and Abca1, along with increased Abcg5 expression, were consistent with reduced levels of hepatic triacylglycerol species containing polyunsaturated fatty acids, like linoleic acid, as well as reduced cholesterol levels in the liver and plasma. Similar changes in gene expression associated with PPARα signalling and intestinal lipid transport were observed in ileal organoids treated with NG-497. Furthermore, HepG2 ATGL knockdown cells revealed reduced expression of PPARα target genes and upregulation of genes involved in hydrophilic BA synthesis, consistent with reduced PPARα binding and luciferase activity in the presence of the ATGL inhibitors.

CONCLUSIONS

Inhibition of ATGL attenuates PPARα signalling, translating into hydrophilic BA composition, interfering with dietary lipid absorption, and improving metabolic disturbances. Validation with NG-497 opens a new therapeutic perspective for MASLD.

IMPACT AND IMPLICATIONS

Despite the recent approval of drugs novel mechanistic insights and pathophysiology-oriented therapeutic options for MASLD (metabolic dysfunction-associated steatotic liver disease) are still urgently needed. Herein, we show that pharmacological inhibition of ATGL, the key enzyme in lipid hydrolysis, using atglistatin (ATGLi), improves MASH (metabolic dysfunction-associated steatohepatitis), fibrosis, and key features of metabolic dysfunction in mouse models of MASH and liver fibrosis. Mechanistically, we demonstrated that attenuation of PPARα signalling in the liver and gut favours hydrophilic bile acid composition, ultimately interfering with dietary lipid absorption. One of the drawbacks of ATGLi is its lack of efficacy against human ATGL, thus limiting its clinical applicability. Against this backdrop, we could show that ATGL inhibition using the human inhibitor NG-497 in human primary ileum-derived organoids, Caco2 cells, and HepG2 cells translated into therapeutic mechanisms similar to ATGLi. Collectively, these findings reveal a possible new avenue for MASLD treatment.

Gut microbial metabolism in ferroptosis and colorectal cancer

Ferroptosis is programmed cell death induced by iron-driven lipid peroxidation. Numerous studies have shown that ferroptosis is implicated in the progression of colorectal cancer (CRC) and has emerged as a promising strategy to combat therapy-resistant CRC. While the intrinsic antiferroptotic and proferroptotic pathways in CRC cells have been well characterized, extrinsic metabolism pathways regulating ferroptosis in CRC pathogenesis remain less understood. Emerging evidence shows that gut microbial metabolism is tightly correlated with the progression of CRC. This review provides an overview of gut microbial metabolism and discusses how these metabolites derived from intestinal microflora contribute to cancer plasticity through ferroptosis. Targeting gut microbe-mediated ferroptosis is a potential approach for CRC treatment.

Gut Microbiota Regulate Lipid Metabolism via the Bile Acid Pathway: Resistance to Hypoxia in Gansu Zokor (Eospalax cansus)

The Gansu zokor (Eospalax cansus), a subterranean rodent endemic to the Loess Plateau of China, exhibits remarkable adaptability to hypoxic environments. While gut microbiota are known to regulate lipid metabolism through bile acid (BA) pathways, this phenomenon has not been investigated in subterranean rodents exposed to hypoxia. This study employed 16SrRNA sequencing, targeted analysis of BA metabolites in colonic contents, and assessments of BA and lipid metabolites alongside molecular analyses in the liver and ileum under conditions of acute and chronic hypoxia in Gansu zokors. The results revealed that hypoxia altered the composition of gut microbiota and BA pools in Gansu zokors. Hypoxia-induced changes increased the abundance of gut microbiota associated with BA metabolism, thereby modulating lipid metabolism via farnesoid X receptor (FXR) signaling in the distal ileum and liver cells. Under acute hypoxia, FXR upregulated lipid synthesis and suppressed fatty acid β-oxidation by downregulating the carnitine palmitoyl-transferase1A (CPT1A) expression. Conversely, during chronic hypoxia, particularly under long-term exposure, FXR reduced lipid synthesis and enhanced fatty acid β-oxidation by upregulating acyl-CoA oxidase (ACOX1) expression. In both hypoxic conditions, FXR facilitated lipoprotein metabolism. In summary, this study elucidates that gut microbiota-mediated BA metabolic pathways contribute to the Gansu zokor's ability to maintain lipid metabolic homeostasis and adaptation to hypoxia.

Targeting Bile-Acid Metabolism: Nutritional and Microbial Approaches to Alleviate Ulcerative Colitis

Ulcerative colitis (UC) is a chronic inflammatory disease affecting the colorectum, posing a significant global health burden. Recent studies highlight the critical role of gut microbiota and its metabolites, particularly bile acids (BAs), in UC's pathogenesis. The relationship between BAs and gut microbiota is bidirectional: microbiota influence BA composition, while BAs regulate microbiota diversity and activity through receptors like Farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5). Targeting bile-acid metabolism to reshape gut microbiota presents a promising therapeutic strategy for UC. This review examines the classification and synthesis of BAs, their interactions with gut microbiota, and the potential of nutritional and microbial interventions. By focusing on these therapies, we aim to offer innovative approaches for effective UC management.

Loss of FXR or Bile Acid-dependent Inhibition accelerate carcinogenesis of Gastroesophageal Adenocarcinoma

BACKGROUND & AIMS

The incidence of Barrett esophagus (BE) and gastroesophageal adenocarcinoma (GEAC) correlates with obesity and a diet rich in fat. Bile acids (BAs) support fat digestion and undergo microbial metabolism in the gut. The farnesoid X receptor (FXR) is an important modulator of the BA homeostasis. When activated, FXR can inhibit cancer-related processes, and thus, it is an appealing therapeutic target. Here, we assess the effect of diet on the microbiota-BA axis and evaluate the role of FXR in disease progression.

METHODS

L2-IL1B mice (mouse model of BE and GEAC) under different diets, and L2-IL1B-FXR KO-mice were characterized. L2-IL1B-derived organoids were exposed to different BAs and to the FXR agonist obeticholic acid (OCA). The BA profile in serum and stool of healthy controls and patients with BE and GEAC was assessed.

RESULTS

Here we show that a high-fat diet accelerated tumorigenesis in L2-IL1B mice while increasing BA levels and altering the composition of the gut microbiota. Although upregulated in BE, expression of FXR was downregulated in GEAC in mice and humans. In L2-IL1B mice, FXR knockout enhanced the dysplastic phenotype and increased Lgr5 progenitor cell numbers. Treatment of murine BE organoids and L2-IL1B mice with OCA notably ameliorated the phenotype.

CONCLUSION

GEAC carcinogenesis appears to be partially driven via loss or inhibition of FXR on progenitor cells at the gastroesophageal junction. Considering that the resulting aggravation in the phenotype could be reversed with OCA treatment, we suggest that FXR agonists have great potential as a preventive strategy against GEAC progression.

S-Nitrosoglutathione Is Not a Substrate of OATP1B1, but Stimulates Its Expression and Activity

S-nitrosoglutathione (GSNO) is the S-nitrosated derivative of glutathione (GSH). GSNO is an endogenous class of NO donors and a natural NO depot in biological systems. Organic anion transporting polypeptide 1B1 (OATP1B1) is an influx transporter that is expressed in the liver. OATP1B1 plays an important role in the transport of endogenous and exogenous substances. Various pathways for the regulation of OATP1B1 have been described. In the present study, the involvement of OATP1B1 in GSNO transport and the regulation of OATP1B1 by GSNO was examined. For HEK293-OATP1B1, it has been shown that GSNO is not a substrate of OATP1B1, but OATP1B1 can participate in the transport of GSH across the cell membrane. GSNO at concentrations of 1-100 μM and exposure for 3 h do not affect the expression and activity of OATP1B1, but exposure for 24 and 72 h stimulates the expression of the SLCO1B1 gene, OATP1B1, and transporter activity. Up-regulation of OATP1B1 by GSNO is carried out through the NO-cGMP signaling pathway, Nrf2, and LXRa.

Branched-chain amino acids promote hepatic Cyp7a1 expression and bile acid synthesis via suppressing FGF21-ERK pathway

Branched-chain amino acids (BCAAs) including leucine, isoleucine and valine have been linked with metabolic and cardiovascular diseases. BCAAs homeostasis is tightly controlled by their catabolic pathway. BCKA dehydrogenase (BCKD) complex is the rate-limiting step for BCAA catabolism. Mitochondrial phosphatase 2C (PP2Cm) dephosphorylates the BCKD E1alpha subunit and activates BCKD complex. Deficiency of PP2Cm impairs BCAA catabolism, leading to higher plasma BCAA concentrations. Emerging evidence shows that bile acids are key regulators of glucose, lipid and energy metabolism. In this study, we investigated whether a direct link existed between BCAAs and bile acids metabolism. Wild-type mice were fed with normal-BCAA or high-BCAA diet, while PP2Cm deficiency mice were fed with normal chow for 14 weeks. The mice were fasted for 6 h before tissue harvest to exclude metabolic changes due to immediate food intake. We showed that the bile acids in tissues and feces were significantly elevated in wild-type mice fed with high-BCAA diet as well as in PP2Cm deficiency mice fed with normal chow. These mice displayed significantly increased expression of cholesterol 7 alpha-hydroxylase (CYP7A1), the rate-limiting enzyme of bile acid synthesis in liver, and 7α-hydroxy-4-cholesten-3-one (C4), a freely diffusible metabolite downstream of CYP7A1 in plasma. BCAAs induced Cyp7a1 expression in cultured hepatocytes. In mouse liver and cultured hepatocytes, we demonstrated that elevated BCAAs inhibited fibroblast growth factor 21 (FGF21) expression and ERK signaling pathway. Direct inhibition of ERK by U0126 (800 nM) markedly induced Cyp7a1 expression in cultured hepatocytes. Moreover, the induced Cyp7a1 expression and inhibitory effects of BCAAs on ERK signaling pathway were abolished by treatment with recombinant FGF21 protein in mouse liver and cultured hepatocytes. Collectively, this study demonstrates a direct link between BCAAs and bile acid synthesis. BCAAs promotes Cyp7a1 expression and bile acid synthesis in liver via inhibiting FGF21-ERK signaling pathway. BCAAs-regulated bile acid synthesis and homeostasis may contribute to developing novel therapeutic strategies for the treatment of metabolic disorders.

Bile acid diarrhea in patients with chronic diarrhea. Current appraisal and recommendations for clinical practice

Bile Acid Diarrhea (BAD) is a common cause of chronic diarrhea, often accompanied by urgency, occasional fecal incontinence, abdominal pain, and fatigue. A nationwide survey has shown limited awareness of BAD within the Italian medical community, prompting a panel of experts to develop a Position Paper that outlines the most practical and cost-saving diagnostic investigations and treatments for this frequently overlooked condition. The document provides an overview of the epidemiology, pathophysiology, clinical manifestations, and classification of the different types of Bile Acid Diarrhea (BAD). A key focus is the diagnostic approach to identifying and managing the many undiagnosed BAD patients in both primary care and specialized medical settings. Finally, the paper addresses the optimal therapeutic strategies for BAD, including traditional bile acid sequestrants and newer, promising treatments.

Alpha-aminobutyric acid ameliorates diet-induced metabolic dysfunction-associated steatotic liver disease (MASLD) progression in mice via enhancing AMPK/SIRT1 pathway and modulating the gut-liver axis

Alpha-aminobutyric acid (ABA) is a nonproteinogenic amino acid, a metabolite which could be generated from the metabolism of methionine, threonine, serine and glycine or as a gut-microbiome-derived metabolite. Changes in ABA levels have been embroiled in metabolic dysfunction-associated steatotic liver disease (MASLD) intervention studies, but their relation to MASLD pathogenesis remains unclear. Hence, this present study aimed to investigate the effect of oral ABA supplementation on the progression of a high fat/high cholesterol diet (HFD) induced MASLD mice model. ABA was found to remodel the gut microbiome composition and ameliorate MASLD parameters in HFD-fed mice. ABA mitigated HFD-induced gain in liver weight, hepatic steatosis, insulin resistance, serum and hepatic triglyceride levels, and liver cholesterol levels. Modulation of lipid metabolism was observed in the liver, in which expression of proteins and/or genes involved in de novo lipogenesis were suppressed, while those involved in fatty acid oxidation and autophagy were upregulated together with cellular antioxidant capacity, in addition to the enhancement of the AMPK/SIRT1 pathway. ABA reshaped the gut composition by enriching nine bacterial species, including Helicobacter hepaticus, Desulfovibrio sp. G11, Parabacteroides distasonis, and Bacteroides fragilis, while diminishing the abundance of 16 species, which included four Helicobacter species. KEGG pathway analysis of microbial functions found that ABA impeded secondary bile acid biosynthesis - which was reflected in the faecal BA composition analysis. Notably, ABA also inhibited ileal FXR-Fgf15 signaling, allowing for increased hepatic Cyp7a1 expression to eliminate cholesterol buildup in the liver. Overall, our findings indicate that ABA could be used as a promising therapeutic approach for the intervention of MASLD.

Hepatic Lamp2a deficiency promotes inflammation of murine autoimmune cholangitis via affecting bile acid metabolism

Primary biliary cholangitis is characterized by breaking of immune tolerance and disorders of bile acid metabolism. Our previous study found that abnormal expression of Lamp2 was detected in PBC patients. However, the specific role of Lamp2a in disease progression is still unclear. In this study, we showed that hepatic-specific Lamp2a deficiency could aggravate the inflammatory phenotype of murine autoimmune cholangitis. Mechanistically, the loss of Lamp2a in hepatocytes contributed to the abnormal accumulation of Acot8, thus altered the bile acid components, thereby enhancing the lymphocyte activities, and ultimately promoting the inflammatory phenotype of model mice. Moreover, we also found that Acot8 knockdown could alleviate the liver inflammation caused by Lamp2a deficiency. Altogether, our findings explored the effect of Lamp2a deficiency on the murine autoimmune cholangitis by the perspective of bile acid metabolism, and marked the possibility of Acot8 as a new target for the treatment of PBC disease.

Select microbial metabolites in the small intestinal lumen regulate vagal activity via receptor-mediated signaling

The vagus nerve is proposed to enable communication between the gut microbiome and the brain, but activity-based evidence is lacking. We find that mice reared germ-free exhibit decreased vagal tone relative to colonized controls, which is reversed via microbiota restoration. Perfusing antibiotics into the small intestines of conventional mice, but not germ-free mice, acutely decreases vagal activity which is restored upon re-perfusion with intestinal filtrates from conventional, but not germ-free, mice. Microbiome-dependent short-chain fatty acids, bile acids, and 3-indoxyl sulfate indirectly stimulate vagal activity in a receptor-dependent manner. Serial perfusion of each metabolite class activates both shared and distinct neuronal subsets with varied response kinetics. Metabolite-induced and receptor-dependent increases in vagal activity correspond with the activation of brainstem neurons. Results from this study reveal that the gut microbiome regulates select metabolites in the intestinal lumen that differentially activate vagal afferent neurons, thereby enabling the microbial modulation of chemosensory signals for gut-brain communication.

Quantitative analysis of sterol balance in a mouse model of hepatic lipid accumulation induced by cholesterol and cholic acid supplementation

The cholesterol balance and bile acid metabolism in a mouse model of hepatic lipid accumulation induced by a diet supplemented with cholesterol and cholic acid (CA) were quantitatively evaluated. The mice were fed diets supplemented with different levels of cholesterol (0, 3, or 6 g/kg of diet) and CA (0.5 g/kg of diet) for 6 weeks. Cholesterol supplementation doubled the hepatic triglyceride concentration, regardless of the supplementation level, without inflammation or gallstone formation. Both cholesterol supplementations enhanced fecal excretion of muricholic acid. Additionally, the higher cholesterol supplementation led to an increase in fecal cholesterol excretion, accompanied by elevated expression of hepatic cholesterol exporters and a reduction in fecal bile acid excretion. In this mouse study, supplementation with 3 g cholesterol/kg diet and 0.5 g CA/kg diet was sufficient to induce hepatic lipid accumulation.

Triterpenoids from ilicis rotundae cortex ameliorate hyperlipidemia by affecting bile acids-hepatointestinal FXR axis

BACKGROUND

Hyperlipidemia is a lipid metabolism disorder that, in severe cases, can lead to conditions such as hypertension, coronary heart disease, and cirrhosis. Previous studies have identified Ilicis Rotundae Cortex (IRC) crude extract as having the potential to regulate blood lipids. However, whether the triterpenoids therein are the principal agents responsible for hypolipidemic effects and their specific mechanisms of action remain unexplored. This study aimed to investigate the effects of total triterpenoids (TT) extract derived from IRC on hyperlipidemia and to elucidate their potential mechanisms.

METHODS

TT extract was first prepared and characterized to assess their hypolipidemic activity in cell models. A hyperlipidemia mouse model was established by using C57BL/6 J mice fed a high-fat, high-sugar, and high-cholesterol diet for 8 weeks. TT extract was administered as a prophylactic intervention for 4 weeks to evaluate its impact on blood lipid levels, liver lipid metabolism, and liver function. Based on progressive analysis, this study integrated serum non-targeted metabolomics analysis strategy and bile acids-targeted metabolomics analysis strategy. It was combined with modern molecular biology techniques to reveal the mechanism by which TT extract ameliorated the symptoms of hyperlipidemia through a cascade approach.

RESULTS

TT extract treatment significantly reduced lipid levels in hyperlipidemic mice. Notably, TT extract down-regulated bile acid levels, particularly bile acids as FXR antagonists such as T-β-MCA, β-MCA, TUDCA, and UDCA. This effect is likely mediated through alterations in the hepatic FXR-SHP and ileal FXR-FGF15 signaling pathways. TT extract administration led to decreased expression of CYP7A1 and CYP7B1, resulting in reduced bile acid levels in vivo. Additionally, FXR expression was upregulated in both the liver and ileum, potentially activating FGF15 in the ileum, which in turn transmits signals to the liver and modulates SHP and BSEP expression. These changes contribute to the regulation of bile acid synthesis, metabolism, and excretion. In vitro experiments also demonstrated that TT extract influenced the protein expression of FXR and FGF19.

CONCLUSION

Our findings demonstrate that TT extract from IRC has hypolipidemic effects. This study is the first to reveal the mechanism by which TT extract improves hyperlipidemia from the perspective of the hepatic-intestinal axis and bile acid metabolism. Its underlying mechanism is related to activating the intestinal FXR-FGF15/19 signaling pathway, which transmits signals to the liver, thereby affecting the hepatic FXR-SHP signaling pathway. This results in improved bile acid metabolism, ultimately reducing hepatic injury and ileal inflammation to exert hypolipidemic effects.

Bi-Directional Relationship Between Bile Acids (BAs) and Gut Microbiota (GM): UDCA/TUDCA, Probiotics, and Dietary Interventions in Elderly People

The gut microbiota (GM), the set of microorganisms that colonizes our intestinal tract, can undergo many changes, some of which are age related. Several studies have shown the importance of maintaining a healthy GM for a good quality of life. In the elderly, maintaining a good GM may become a real defense against infection by pathogens, such as C. difficile. In addition to the GM, bile acids (BAs) have been shown to provide an additional defense mechanism against the proliferation of pathogenic bacteria and to regulate bacterial colonization of the gut. BAs are molecules produced in the host liver and secreted with the bile into the digestive tract, and they are necessary for the digestion of dietary lipids. In the gut, host-produced BAs are metabolized by commensal bacteria to secondary BAs. In general GM and host organisms interact in many ways. This review examines the relationship between GM, BAs, aging, and possible new approaches such as dietary interventions, administration of ursodesoxycholic acid/tauroursodesoxycholic acid (UDCA/TUDCA), and probiotics to enrich the microbial consortia of the GM in the elderly and achieve a eubiotic state necessary for maintaining good health. The presence of Firmicutes and Actinobacteria together with adequate levels of secondary BAs would provide protection and improve the frailty state in the elderly. In fact, an increase in secondary BAs has been observed in centenarians who have reached old age without serious health issues, which may justify their active role in achieving longevity.

Glycyrrhiza uralensis Fisch. Attenuates Dioscorea bulbifera L.-induced liver injury by regulating the FXR/Nrf2-BAs-related proteins and intestinal microbiota

ETHNOPHARMACOLOGICAL RELEVANCE

Dioscorea bulbifera L. (DBL) was a traditional Chinese medicine commonly used to treat goitre and cancer. Nevertheless, its clinical application may lead to liver injury. Glycyrrhiza uralensis Fisch. (GRR) was primarily utilized in traditional Chinese medicine for its ability to harmonize various medicines and mitigate the toxic effects of poisonous herbs. However, the role of GRR in mitigating the liver toxicity of DBL has not been established after combination.

AIM OF THE STUDY

This study aimed to clarify the protective effect of GRR against DBL-induced liver injury in mice and investigate its mechanisms of action.

MATERIALS AND METHODS

75% ethanol was employed to extract DBL and GRR. The extracted components were characterized using LC-MS. Mice were orally gavaged with extracts from each group for 30 days. After the experiment, the pathological changes in the liver of mice were evaluated. Additionally, biochemical markers associated with liver injury were assessed. The primary mechanisms through which GRR mitigates DBL-induced liver injury and the modulation of the liver-intestinal axis by GRR were explored utilizing untargeted metabolomics, targeted BAs metabolomics and 16S rDNA analyses. Furthermore, Western blot and qPCR assessed the protein and mRNA transcription of the farnesoid X receptor (FXR) and nuclear factor-erythroid 2-related factor 2 (Nrf2) as well as BA-related transporters.

RESULTS

GRR dose-dependently attenuated DBL-induced liver injury in mice. It mitigated hepatic pathological changes and alleviated hepatic inflammation and oxidative stress. GRR improved metabolic disorders induced by DBL in mice at the metabolite level, focusing on the ABC transporter. Moreover, GRR may be attributed to its activation of FXR/Nrf2 expression, reduction of cholesterol 7-alpha hydroxylase (CYP7A1) expression, promotion of bile salt export pump (BSEP), multi-drug resistance protein 2 (MRP2), P-glycoprotein (P-gp) and sodium taurocholate cotransport polypeptide (NTCP) expression, reduction of bile acid (BA) synthesis, promotion of BA efflux and reabsorption, and improvement of BA metabolic disorders. In addition, GRR ameliorated DBL-induced intestinal barrier injury and improved the structural organization of the intestinal flora, restoring the overall composition of the intestinal microbiota.

CONCLUSION

GRR exhibited significant alleviation of DBL-induced liver injury, potentially by modulating FXR/Nrf2-BA-related proteins, reducing hepatic BA accumulation, mitigating liver inflammation and oxidative stress, and regulating intestinal flora.

Advancements in the Pathogenesis, Diagnosis, and Therapeutic Implications of Intestinal Bacteria

Intestinal bacteria form one of the most complex microbial communities in the human body, playing a crucial role in maintaining host health and contributing to the development of various diseases. Here, we provide a comprehensive overview of the composition and function of intestinal bacteria, the factors affecting their homeostasis, and their association and mechanisms with a range of diseases (e.g., inflammatory bowel diseases, colorectal cancer, metabolic diseases). Additionally, their advanced potential in disease diagnosis and treatment is highlighted. Therapies, such as chemotherapy, radiotherapy, and immunotherapy, are significantly impacted by intestinal bacteria, with research indicating that bacteria can enhance chemoimmunotherapy efficiency by affecting T cell recruitment and immune cell infiltration. Fecal microbiota transplantation has emerged as a promising option for treating recurrent Clostridium difficile infections and certain metabolic and neurological disorders. Gut bacteria-related serum metabolites serve as non-invasive indicators for diagnosing CRC, while fecal immunochemical tests offer promising applications in CRC screening. Future research is needed to better understand the causal relationships between intestinal bacteria and diseases, develop more precise diagnostic tools, and evaluate the effectiveness and safety of microbiome-targeted therapies in clinical treatment. This study provides deeper insights into the role of intestinal bacteria in human health and disease, providing a scientific basis for innovative therapeutic strategies that have the potential to transform the landscape of healthcare.

Identification of disease-specific gut microbial markers in vitiligo

There is a potential correlation between vitiligo and gut microbiota, although research in this area is currently limited. The research employed high-throughput sequencing of 16S rRNA to examine the gut microbiome in the stool samples of 49 individuals with vitiligo and 49 without the condition. The study encompassed four comparison groups: (1) DI (disease) group vs. HC (healthy control) group; (2) DI_m group (disease group of minors) vs. HC_m group (healthy control group of minors); (3) DI_a group (adult disease group) vs. HC_a group (adult healthy control group); (4) DI_m group vs. DI_a group. Research findings have indicated the presence of spatial heterogeneity in the gut microbiota composition between individuals with vitiligo and healthy controls. A significant reduction in gut microbiota diversity has been observed in vitiligo patients across both minors and adult groups. However, variations have been noted in the composition of disease-related differential microbial markers among different age groups. Specifically, Bacteroides and Parabacteroides have been identified as specific markers of the intestinal microbiota of vitiligo patients in both minor and adult groups. Correlative analyses have revealed a positive correlation of these two genera with the Vitiligo Area Scoring Index (VASI) and disease duration. It is noteworthy that there are no significant differences in diversity between the DI_m group and the DI_a group, with similarities in microbiota composition and functional characteristics. Nevertheless, correlative analyses suggest a declining trend in Bacteroides and Parabacteroides with increasing age. Individuals with vitiligo exhibit distinct features in their gut microbiome when contrasted with those in the healthy control group. Additionally, the microbial marker genera that show variances between patients and healthy controls vary among different age groups. Disease-specific microbial marker genera (Bacteroides and Parabacteroides) are associated with VASI, duration of the condition, and age. These findings are essential for improving early diagnosis and developing potential treatment strategies for individuals with vitiligo.

Gut colonization of Bacteroides plebeius suppresses colitis-associated colon cancer development

Colon cancer development may be initiated by multiple factors, including chronic inflammation, genetic disposition, and gut dysbiosis. The loss of beneficial bacteria and increased abundance of detrimental microbes exacerbates disease progression. Bacteroides plebeius (B. plebeius) is a human gut microbe, and its colon colonization is enhanced by a seaweed-supplemented diet. We found that mice orally administered with B. plebeius and fed a diet containing 1% seaweed developed a unique gut microbial composition. By linear discriminant analysis effect size analysis, we found that B. plebeius colonization increased the abundance of Blautia coccoides and reduced the abundance of Akkermansia sp. and Dubosiella sp. We also showed that colonization of B. plebeius suppressed the colon tumor development induced by azoxymethane/dextran sulfate sodium in specific-pathogen-free mice, coinciding with a reduced abundance of Muribaculaceae sp., Closteridale sp., and Bilophila sp. Moreover, B. plebeius colonization in gnotobiotic mice resulted in enhanced production of selected metabolites, including propionic, taurocholic, cholic, alpha-, and beta-muricholic, as well as ursodeoxycholic acids. Importantly, some of these metabolites show anti-inflammatory and tumor-suppressive effects. We conclude that B. plebeius is able to restructure the gut microbial community and produce beneficial metabolites, leading to inhibition of colitis-associated colon cancer development.IMPORTANCEThis work delves into the pivotal role of gut microbiota in suppressing the progression of colitis-associated colon cancer. By investigating the impact of Bacteroides plebeius that can be colonized in mouse gut by feeding the animal with seaweed diet, we unveil a novel mechanism through which this beneficial bacterium reshapes the gut microbial community and produces metabolites with anti-inflammatory and tumor-suppressive properties. Such findings underscore the potential of harnessing specific microbes, like B. plebeius shown in this study, to modulate the gut ecosystem and mitigate the risk of colitis-associated colon cancer.

Cross-tissue multi-omics analyses reveal the gut microbiota's absence impacts organ morphology, immune homeostasis, bile acid and lipid metabolism

The gut microbiota influences host immunity and metabolism, and changes in its composition and function have been implicated in several non-communicable diseases. Here, comparing germ-free (GF) and specific pathogen-free (SPF) mice using spatial transcriptomics, single-cell RNA sequencing, and targeted bile acid metabolomics across multiple organs, we systematically assessed how the gut microbiota's absence affected organ morphology, immune homeostasis, bile acid, and lipid metabolism. Through integrated analysis, we detect marked aberration in B, myeloid, and T/natural killer cells, altered mucosal zonation and nutrient uptake, and significant shifts in bile acid profiles in feces, liver, and circulation, with the alternate synthesis pathway predominant in GF mice and pronounced changes in bile acid enterohepatic circulation. Particularly, autophagy-driven lipid droplet breakdown in ileum epithelium and the liver's zinc finger and BTB domain-containing protein (ZBTB20)-Lipoprotein lipase (LPL) (ZBTB20-LPL) axis are key to plasma lipid homeostasis in GF mice. Our results unveil the complexity of microbiota-host interactions in the crosstalk between commensal gut bacteria and the host.

Retinol metabolism signaling participates in microbiota-regulated fat deposition in obese mice

Obesity is a global pandemic threatening public health, excess fat accumulation and overweight are its characteristics. In this study, the interplay between gut microbiota and retinol metabolism in modulating fat accumulation was verified. We observed gut microbiota depletion reduced the body weight and the ratios of white adipose tissues (WATs) to body weight in high-fat diet (HFD) fed-mice. The kyoto encyclopedia of genes and genomes (KEGG) analysis and protein-protein interaction (PPI) network of RNA-seq results indicated that retinol metabolism signaling may be involved in the microbiota-regulated fat deposition. Furthermore, activated retinol metabolism signaling by all-trans retinoic acid (atRA) supplementation reduced body weight and WAT accumulation in obese mice. 16S rRNA gene sequencing of the ileal microbiota suggested that atRA supplementation increased the microbial diversity and induced the growth of beneficial bacteria including Parabacteroides, Bacteroides, Clostridium_XVIII, Bifidobacterium, Enterococcus, Bacillus, Leuconostoc, and Lactobacillus in obese mice. Spearman correlation showed that the microbiota altered by atRA were associated with body and WAT weights. Together, this study reveals the interaction between the gut microbiota and retinol metabolism signaling in regulating adipose accumulation and obesity. It is expected of this finding to provide new insights to prevent and develop therapeutic measures of obesity-related metabolic syndrome.

MetALD: Clinical aspects, pathophysiology and treatment

Metabolic dysfunction-associated steatotic liver disease (MASLD) and alcohol-related liver disease (ALD) are the most prevalent causes of chronic liver disease worldwide. Both conditions have many pathophysiological mechanisms in common, such as altered lipid and bile acid metabolism, and share some similar clinical features. Furthermore, metabolic risk factors and alcohol often co-exist in the same individuals and have recently been shown to act synergistically to markedly increase the risk of liver disease. Given the high prevalence and impact of this interaction, steatotic liver disease due to the combination of metabolic dysfunction and moderate-to-high alcohol intake has been termed MetALD in the new steatotic liver disease nomenclature, attracting the interest of the scientific community. Subsequent studies have investigated the prevalence of MetALD, which ranges from 1.7% to 17% in cohorts of patients with steatotic liver disease, depending on the population setting and study design. A few cohort studies have also assessed the prognosis of this patient population, with preliminary data suggesting that MetALD is associated with an intermediate risk of liver fibrosis, decompensation and mortality among steatotic liver disease subtypes. In this review article, we examine the clinical evidence and the experimental models of MetALD and discuss the clinical implications of the term for early detection and management. We provide insight into the pathophysiological mechanisms of the synergistic effect of alcohol and metabolic risk factors, possible screening strategies, the use of biomarkers and emerging models of care, as well as potential therapeutic interventions with a special focus on medications for MASLD, highlighting the most promising drugs for patients with MetALD.

An Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Deoxycholic Acid and Application to a Pharmacokinetic Study in Human Plasma

Deoxycholic acid (DCA) injection is applied in treating moderate to severe submental bulge or facial fullness caused by excessive submental fat accumulation. Using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) technology, which was swiftly, precisely, and reliably confirmed, DCA was determined in human plasma with low quantification limits of 56 ng/mL. We selected six healthy individual blank human plasma with low concentrations of endogenous DCA and mixed them to prepare standard curve samples. The samples were purified by the protein precipitation technique and then separated using a BEH C18 column (2.1 × 50 mm, 1.7 μm). Using multiple reaction monitoring (MRM) and electrospray ionization (ESI) sources operating in negative mode, the mass was identified and measured. The precursor-to-product ion transitions were observed at m/z 391.2- → 345.2- and m/z 395.2- → 349.2- for DCA and DCA-d4 (isotope internal standard), respectively. This method was thoroughly validated, encompassing assessments of linearity, sensitivity, precision, selectivity, stability, matrix effect, accuracy, carryover, and recovery. In a word, the validation results demonstrated that this method exhibited sensitivity, accuracy, and reproducibility and could effectively be utilized for studying the pharmacokinetic properties of DCA in a randomized, parallel, controlled, Phase I clinical trial.

Long-term effects of Nε-carboxymethyllysine intake on intestinal barrier permeability: Associations with gut microbiota and bile acids

Advanced glycation end products (AGEs) in processed foods are closely linked to intestinal injury. However, the long-term effects of exposure to free Nɛ-carboxymethyl lysine (CML), a prevalent AGE molecule, on intestinal barrier integrity have been rarely evaluated. This study investigated the temporal effects of CML exposure on intestinal barrier permeability in C57BL/6N mice at diet-related doses over 12, 14, and 16 weeks. No significant changes were observed at 12 weeks, but CML exposure significantly increased intestinal permeability at 14 and 16 weeks, accompanied by elevated serum LPS levels, colonic histological damage, and reduced tight junction protein expression at 16 weeks. CML exposure also altered gut microbiota composition and intestinal bile acid (BA) profiles, specifically reducing TDCA, GDCA, and GCDCA levels. Given the important role of colonic BA receptor signaling in maintaining the intestinal barrier integrity, the impact of CML on BA receptor signaling was assessed. CML exposure significantly downregulated BA receptor TGR5-YAP signaling in mice, while no significant effects were observed in vitro, suggesting that the changes observed in TGR5-YAP signaling in vivo may not result from the direct effects of CML. Spearman's correlation analysis revealed strong associations between altered gut microbiota, BA levels, TGR5-YAP signaling, and intestinal barrier injury. This study highlighted the chronic health risks of long-term CML intake and provided new insights into the links between CML-induced intestinal toxicity, gut microbiota, BA profiles, and BA receptor signaling.

Host metabolism balances microbial regulation of bile acid signalling

Metabolites derived from the intestinal microbiota, including bile acids (BA), extensively modulate vertebrate physiology, including development1, metabolism2-4, immune responses5-7 and cognitive function8. However, to what extent host responses balance the physiological effects of microbiota-derived metabolites remains unclear9,10. Here, using untargeted metabolomics of mouse tissues, we identified a family of BA-methylcysteamine (BA-MCY) conjugates that are abundant in the intestine and dependent on vanin 1 (VNN1), a pantetheinase highly expressed in intestinal tissues. This host-dependent MCY conjugation inverts BA function in the hepatobiliary system. Whereas microbiota-derived free BAs function as agonists of the farnesoid X receptor (FXR) and negatively regulate BA production, BA-MCYs act as potent antagonists of FXR and promote expression of BA biosynthesis genes in vivo. Supplementation with stable-isotope-labelled BA-MCY increased BA production in an FXR-dependent manner, and BA-MCY supplementation in a mouse model of hypercholesteraemia decreased lipid accumulation in the liver, consistent with BA-MCYs acting as intestinal FXR antagonists. The levels of BA-MCY were reduced in microbiota-deficient mice and restored by transplantation of human faecal microbiota. Dietary intervention with inulin fibre further increased levels of both free BAs and BA-MCY levels, indicating that BA-MCY production by the host is regulated by levels of microbiota-derived free BAs. We further show that diverse BA-MCYs are also present in human serum. Together, our results indicate that BA-MCY conjugation by the host balances host-dependent and microbiota-dependent metabolic pathways that regulate FXR-dependent physiology.

Desmodium styracifolium (Osb.) Merr. Extracts alleviate cholestatic liver disease by FXR pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Cholestatic liver disease (CLD) is a disease characterized by cholestasis. Farnesoid X receptor (FXR) is a nuclear receptor that maintains homeostasis in bile acid metabolism. Studies have shown that gut microbiota interfered with the FXR pathway. Modulation of FXR to inhibit cholestasis has become a key measure in the treatment of CLD. In traditional folk medicine, Desmodium styracifolium (Osb.) Merr. was used as a primary treatment for gallstones, gonorrhea, jaundice, cholecystitis and other diseases. Modern pharmacological studies had also found that the herb has anti-calculus, anti-inflammatory, antioxidant, diuretic and liver damage. Therefore, we speculated that Desmodium styracifolium (Osb.) Merr. extracts (DME) could alleviate CLD through the FXR pathway and might be associated with the gut microbiota. However, studies of DME alleviating CLD through the FXR pathway have not been reported.

AIM OF STUDY

To study the effect and mechanism of DME in relieving CLD through in vivo and in vitro experiments.

MATERIALS AND METHODS

First, mice were administrated with alpha-naphthyl isothiocyanate (ANIT) to establish a CLD model in vivo. Meanwhile, HepG2 cells were induced by lithocholic acid (LCA) to establish the CLD model in vitro. To evaluate the therapeutic effect of DME on CLD mice, hematoxylin-eosin (HE) staining, and biochemical indicators were performed. The prototype of the blood components in mice serum was detected by ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). 16S rDNA sequencing was used to analyze the gut microbiota. Finally, the protein and mRNA expression of the FXR pathway in mice liver tissues or HepG2 cells were detected by Western blot, qRT-PCR, or immunofluorescence.

RESULTS

Pathological testing and biochemical indexes showed that DME significantly reduced serum ALT, AST, ALP, TBIL, DBIL, TBA and liver TBA levels, and attenuated liver tissue injury, necrosis and jaundice in CLD mice. In addition, MetagenomeSeq analysis of gut microbiota showed that DME significantly up-regulated the abundance of Parvibacter, down-regulated the abundance of Paenalcaligenes, and regulated bile acid homeostasis. In terms of mRNA expression, DME significantly upregulated the mRNA levels of Nr1h4, Abcb11, Cyp7a1 and Slc10a1. Meanwhile, in terms of protein expression, DME significantly up-regulated the protein expression levels of FXR, BSEP, CYP7A1 and NTCP, which regulated bile acid homeostasis. Finally, the molecular docking results showed that the components of DME, such as Lumichrome, Daidzein and Folic acid, all had good binding ability with FXR, and the surface plasmon resonance (SPR) results also showed that both Lumichrome and Daidzein had a relatively high affinity with FXR.

CONCLUSION

DME alleviated CLD through the FXR pathway, and the mechanisms might be associated with the gut microbiota.

Simiao Wan attenuates high-fat diet-induced hyperlipidemia in mice by modulating the gut microbiota-bile acid axis

ETHNOPHARMACOLOGICAL RELEVANCE

Hyperlipidemia is a lipid metabolism disorder and a risk factor for obesity, diabetes, and coronary heart disease. It occurs mostly in the old adults; however, its incidence rate is increasing annually and there is a trend towards younger adults. Current clinical drugs for treating hyperlipidemia have multiple side effects. Therefore, it is necessary to develop safe and effective drugs from natural products to prevent and treat hyperlipidemia. Simiao Wan (SMW) is a classic Chinese medicine prescription first recorded in the Cheng Fang Bian Du of the Qing Dynasty. Studies have shown that SMW has excellent efficacy in metabolic diseases, which can effectively improve hyperlipidemia combined with other metabolic diseases. However, its underlying mechanism in hyperlipidemia treatment is yet to be clarified.

AIM OF THE STUDY

To investigate the hypolipidemic effect of SMW on hyperlipidemic mice and explore whether the gut microbiota-bile acid (BA) axis is the potential mechanism.

MATERIALS AND METHODS

A hyperlipidemic mouse model was established using a high-fat diet (HFD), and the hypolipidemic effect of SMW was detected in vivo. We performed 16S ribosomal RNA sequencing and BA metabolism analysis to explore the hypolipidemic mechanisms of SMW. Western blotting was conducted to detect the expression of proteins involved in the gut microbiota-BA axis to determine the potential lipid-lowering pathway.

RESULTS

Excessive obesity in hyperlipidemic mice was alleviated after 8 weeks of SMW treatment. The total cholesterol and low-density lipoprotein cholesterol levels decreased significantly, whereas high-density lipoprotein cholesterol levels increased. SMW also reduced hepatic lipid and inguinal white adipose tissue accumulation in HFD-induced hyperlipidemic mice. Furthermore, intestinal bile saline hydrolase (BSH) level, associated with BA excretion, decreased. Meanwhile, SMW decreased the abundance of BSH-enriched microbes in hyperlipidemic mice. SMW increased the intestinal conjugated-BAs contents in hyperlipidemic mice, especially tauro-β-muricholic acid and tauro-ursodeoxycholic acid, which are ileac farnesoid X receptor (FXR) antagonists. Inhibited intestinal FXR signaling with SMW was accompanied by a decreased expression of intestinal fibroblast growth factor 15 and the activation of hepatic FXR, which promoted hepatic cholesterol conversion to BA.

CONCLUSION

SMW indirectly attenuated HFD-induced hyperlipidemia in mice by regulating the gut microbiota-BA axis. Our results provide a pharmacological basis for SMW treating hyperlipidemia and suggest a new idea for developing lipid-lowering drugs.

Microbiome interplays in the gut-liver axis: implications for liver cancer pathogenesis and therapeutic insights

Globally, primary liver cancer (PLC) ranks the most fatal malignancy. Most of the patients are in advanced stage of PLC at the very time they are diagnosed with it, accounting much for its poor prognosis. With the advancement of modern medical research and care system, the main etiology of PLC more and more switches from hepatitis viruses such as HAV, HBV, HCV, HEV to other causes like metabolism-associated steatohepatitis (MASH) and metabolic-associated fatty liver disease (MAFLD). As a result, it is of great necessity to find out new ways for treatment and early diagnosis to cope with this problem. Nowadays, as the mechanism of the Gut-Liver Axis in the formation of MAFLD, MASH and PLC has been gradually elucidated. The association between gut microbiome and the formation of PLC is of great significance to take an insight into. In this review, we present the concept of Gut-Liver Axis and its function in the mutual influence between gut microbiota and PLC from several aspects in which we will focus on the structure of gut barrier and the functional influences the gut microbiota have on the immune response and metabolic changes on human liver. Furthermore, we conclude the potential association of gut microbiota constitution with the PLC. Eventually, we hope this review can offer novel instructions for early diagnosis and treatment for liver cancer.

High-fat diet promotes gestational diabetes mellitus through modulating gut microbiota and bile acid metabolism

Introduction

Gestational diabetes mellitus (GDM) is a condition characterized by glucose intolerance during pregnancy, estimated to affect approximately 20% of the whole pregnancies and is increasing in prevalence globally. However, there is still a big gap in knowledge about the association between gut microbiota associated metabolism alterations and GDM development.

Methods

All the participants accomplished the validated internet-based dietary questionnaire for Chinese and serum, fecal samples were collected. HFD, control diet or colesevelam intervention was fed to GDM mice models or Fxr-/- mice models, with or without antibiotics cocktail treatment. Fecal microbiota transplantation were used for further validation. Gut microbiota and metabolites were detected by metagenomic sequencing and high-performance liquid chromatography-mass spectrometry, respectively. Bile acids of serum, fecal samples from human and mice were analysised. Body weight, average feed intake, blood glucose, insulin levels and oral glucose tolerance test was performed among each groups. Expression levels of Fxr, Shp and Fgf15 mRNA and protein were detected by quantitative reverse transcription polymerase chain reaction and western blot, respectively.

Results

Our data indicated that high fat diet (HFD) was linked with higher prevalence of GDM, and HFD was positively associated with poor prognosis in GDM patients. Moreover, compared with normal diet (ND) group, GDM patients from HFD group performed a loss of gut microbiota diversity and enrichment of Alistipes onderdonkii, Lachnospiraceae bacterium 1_7_58FAA, and Clostridium aspaaragiforme while ruduction of Akkermansiaceae, Paraprevotell xylaniphila, and Prevotella copri. Additionally, HFD aggravated GDM in mice and gut microbiota depletion by antibiotics crippled the effect of excess fat intake. BAs profile altered in HFD GDM patients and mice models. Fecal microbiota transplantation (FMT) further confirmed that gut microbiota contributed to bile acids (BAs) metabolic dysfunction during HFD-associated GDM development. Mechanically, HFD-FMT administration activated Fxr, Shp, and Fgf15 activity, disturbed the glucose metabolism and aggravated insulin resistance but not in HFD-FMT Fxr-/- mice and ND-FMT Fxr-/- mice. Furthermore, colesevelam intervention alleviated HFD-associated GDM development, improved BAs metabolism, suppressed Fxr, Shp, and Fgf15 activity only in WT mice but not in the Fxr-/- HFD + Colesevelam group and Fxr-/- HFD group. HFD induced GDM and contributed to poor prognosis in GDM parturients through inducing gut microbial dysbiosis and metabolic alteration, especially appeared in BAs profile. Moreover, Fxr pathway participated in regulating HFD-associated gut microbiota disordered BAs metabolites and aggravating GDM in mice.

Discussion

Modulating gut microbiota and BAs metabolites could be a potential therapeutic strategy in the prevention and treatment of HFD-associated GDM.

Effect of SY009, a novel SGLT1 inhibitor, on the plasma metabolome and bile acids in patients with type 2 diabetes mellitus

Context

As a novel SGLT1 inhibitor, SY-009 has been preliminarily confirmed in a phase Ib clinical study for its ability to reduce postprandial blood glucose in patients with type 2 diabetes mellitus (T2DM). However, the effects of SY-009 on human plasma metabolomics are still unknown.

Objective

This study aimed to explore the effects of SY-009 on plasma metabolomics in patients with T2DM and the potential metabolic regulatory mechanism involved.

Study design

In the phase Ib study, a total of 50 participants with T2DM were enrolled and randomly assigned to the 0.5 mg BID, 1 mg BID, 2 mg BID, 1 mg QD, and 2 mg QD dose groups, with a 4:1 random allocation within each group to receive either the SY-009 capsule or placebo. We conducted untargeted and targeted metabolomics analyses on plasma samples from the phase Ib clinical study.

Results

Untargeted metabolomics revealed that, after SY009 treatment, there were differences in metabolic pathways, including primary bile acid biosynthesis; biosynthesis of unsaturated fatty acid; steroid hormone biosynthesis; purine metabolism; phenylalanine, tyrosine and tryptophan biosynthesis. In particular, the increase in bile acid-related metabolites in the 2 mg BID group was significantly greater than that in the placebo group, and unsaturated fatty acid-related metabolites decreased in both the 2 mg BID group and the placebo group, but there was no significant difference between the two groups. After comprehensive consideration, bile acids were taken as our target for accurate quantification via targeted metabolomics. Compared with those in the placebo group, the levels of several bile acids were significantly greater in the SY-009-treated groups. Moreover, the proportion of free bile acids decreased significantly, the proportion of glycine-conjugated bile acids increased significantly, the proportion of taurine-conjugated bile acids tended to be stable, and PBA/SBA significantly increased after SY-009 administration.

Conclusions

SY-009 caused a series of postprandial plasma metabolite changes in patients with T2DM, especially significant changes in the bile acid profile, which provides a new perspective on the mechanism by which SY-009 lowers blood glucose.

Clinical trial registration

https://www.clinicaltrials.gov, identifier NCT04345107.

Functional regulation of cytotoxic T cells by gut microbial metabolites

Metabolites from gut microbes have a wide range of functions within the host body. One important function of these metabolites is to either positively or negatively control CD8+ cytotoxic T lymphocytes (CTLs), which can kill cancer and virus-infected cells. In healthy conditions, gut microbes produce a mixture of metabolites that promote CTL activity but also suppress excessive inflammatory responses. However, gut microbial dysbiosis occurs in patients with cancer, and this leads to changes in the production of gut microbial metabolites that can suppress CTL activity, promote inflammatory responses, and/or aid cancer growth. Decreased levels of CTL-promoting metabolites such as short-chain fatty acids, indole metabolites and polyamines but increased levels of CTL-suppressing metabolites, such as certain bile acids along with oncogenic metabolites, have been observed in patients with cancer. This review summarizes the altered production of major microbial metabolites in patients with cancer and discusses the impact of these changes on anti-cancer CTL responses.

Beyond digestion: Exploring how the gut microbiota modulates human social behaviors

For a long time, traditional medicine has acknowledged the gut's impact on general health. Contemporary science substantiates this association through investigations of the gut microbiota, the extensive community of microorganisms inhabiting our gastrointestinal system. These microscopic residents considerably improve digestive processes, nutritional absorption, immunological function, and pathogen defense. Nevertheless, a variety of gastrointestinal and extra-intestinal disorders can result from dysbiosis, an imbalance of the microbial composition of the gut microbiota. A groundbreaking discovery is the gut-brain axis, a complex communication network that links the enteric and central nervous system (CNS). This bidirectional communication allows the brain to influence gut activities and vice versa, impacting mental health and mood disorders like anxiety and depression. The gut microbiota can influence this communication by creating neurotransmitters and short-chain fatty acids, among other biochemical processes. These factors may affect our mental state, our ability to regulate our emotions, and the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to explore the complex interrelationships between the brain and the gut microbiota. We also conducted a thorough examination of the existing understanding in the area of how microbiota affects social behaviors, including emotions, stress responses, and cognitive functions. We also explored the potential of interventions that focus on the connection between the gut and the brain, such as using probiotics to treat diseases of the CNS. This research opens up new possibilities for addressing mental health and neurological conditions in an innovative manner.

Effects of Bile Acids on Growth Performance, Hepatopancreatic Antioxidant Capacity, Intestinal Immune-Related Gene Expression, and Gut Microbiota of Penaeus vannamei

This study aimed to examine the impact of varying concentrations of bile acids (BA) added to the feed on several aspects of Penaeus vannamei. The purity of BA was 25.29%, and its main components were 5.74% chenodeoxycholic acid, 6.27% allocholic acid, 3.20% cholic acid, 5.79% hyodeoxycholic acid, and 2.31% hyocholic acid. The experiment was designed with four groups: CT, BA1, BA2, and BA3, where BA were added to the shrimp basal diet at concentrations of 0.0 mg/kg, 0.1 mg/kg, 1.0 mg/kg, and 10.0 mg/kg, respectively. After 60 days of farming P. vannamei (initial body weight: 1.21 ± 0.05 g), the results showed that BA supplementation significantly improved growth performance, and BA2 group was the most significant, which increased the final weight (FBW) by 18.6%, weight gain rate (WGR) by 19.5%, and survival rate (SR) by 5.8% compared with the CT group (p < 0.05). Additionally, the activities of trypsin and lipase in gut tissue were significantly increased (p < 0.05). Furthermore, BA supplementation increased the activity of antioxidant-related enzymes in the hepatopancreas and enhanced the mRNA expression levels of gut-associated immune genes. In addition, the supplementation of 0.1 mg/kg BA significantly altered the gut microbial composition, reducing the proportion of harmful Proteobacteria while enhancing the relative abundance of beneficial microorganisms such as Firmicutes and Bacteroides. In conclusion, 1.0 mg/kg and 10.0 mg/kg BA supplementation significantly improved the growth performance, digestive capacity, and antioxidant capacity of shrimp, among which 1.0 mg/kg supplementation had the most significant effect and improved the intestinal microbial composition of shrimp.

The impact of a humanized bile acid composition on atherosclerosis development in hypercholesterolaemic Cyp2c70 knockout mice

Bile acids (BAs) play important roles in the context of lipid homeostasis and inflammation. Based on extensive preclinical mouse studies, BA signaling pathways have been implicated as therapeutic targets for cardiovascular diseases. However, differences in BA metabolism between mice and humans hamper translation of preclinical outcomes. Recently, we generated Cyp2c70-/- mice with a human-like BA composition lacking mouse/rat specific muricholic acids. We employed this model to assess the consequences of a human-like BA pool on atherosclerosis and heart function in hypercholesterolaemic mice. We overexpressed a PCSK9 gain-of-function (GOF) mutation in the liver of male Cyp2c70-/- and Cyp2c70+/- control mice, and fed these mice a Western-type diet (WD) for 12 weeks. Cyp2c70-/- mice displayed a hydrophobic BA pool rich in chenodeoxycholic acid. Cyp2c70-/- mice showed reduced hepatic total cholesterol and triglycerides (p < 0.05) combined with lower plasma total cholesterol (p < 0.05) and triglycerides (p = 0.05) due to lower VLDL levels. Circulating white blood cells remained largely unaffected in Cyp2c70-/- mice. Interestingly, we found a trend (p = 0.08) towards smaller atherosclerotic lesions in the aortic root of Cyp2c70-/- mice, but no effect on cardiac morphology or function was observed. To conclude, a human-like BA composition ameliorated PCSK9-GOF-induced hypercholesterolaemia in WD-fed mice which translated into a tendency towards smaller atherosclerotic lesions.

Malnutrition and Its Influence on Gut sIgA-Microbiota Dynamics

In the current era, malnutrition is seen as both undernutrition and overweight and obesity; both conditions are caused by nutrient deficiency or excess and improper use or imbalance in the intake of macro and micronutrients. Recent evidence suggests that malnutrition alters the intestinal microbiota, known as dysbiosis. Secretory immunoglobulin A (sIgA) plays an important role in maintaining and increasing beneficial intestinal microbiota populations and protecting against pathogenic species. Depletion of beneficial bacterial populations throughout life is also conditioned by malnutrition. This review aims to synthesize the evidence that establishes an interrelationship between diet, malnutrition, changes in the intestinal flora, and sIgA levels. Targeted nutritional therapies combined with prebiotic, probiotic, and postbiotic administration can restore the immune response in the intestine and the host's homeostasis.

Exploring the molecular mechanisms of tirzepatide in alleviating metabolic dysfunction-associated fatty liver in mice through integration of metabolomics, lipidomics, and proteomics

Clinical studies have suggested that tirzepatide may also possess hepatoprotective effects; however, the molecular mechanisms underlying this association remain unclear. In our study, we performed biochemical analyses of serum and histopathological examinations of liver tissue in mice. To preliminarily explore the molecular mechanisms of tirzepatide on metabolic dysfunction-associated fatty liver disease (MAFLD), liquid chromatography-mass spectrometry (LC-MS) was employed for comprehensive metabolomic, lipidomic, and proteomic analyses in MAFLD mice fed a high-fat diet (HFD). The results demonstrated that tirzepatide significantly reduced serum levels of alanine transaminase (ALT) and aspartate transaminase (AST), as well as hepatic triglycerides (TG) and total cholesterol (TC), indicating its efficacy in treating MAFLD. Further findings revealed that tirzepatide reduced fatty acid uptake by downregulating Cd36 and Fabp2/4, as well as enhance the mitochondrial-lysosomal function by upregulating Lamp1/2. In addition, tirzepatide promoted cholesterol efflux and reduced cholesterol reabsorption by upregulating the expression of Hnf4a, Abcg5, and Abcg8. These results suggest that tirzepatide exerts its therapeutic effects on MAFLD by reducing fatty acid uptake, promoting cholesterol excretion, and enhancing mitochondrial-lysosomal function, providing a theoretical basis for a comprehensive understanding of tirzepatide.

Role of T cell metabolism in brain tumor development: a genetic and metabolic approach

BACKGROUND

Malignant brain tumors are among the most lethal cancers. Recent studies emphasized the crucial involvement of the immune system, especially T cells, in driving tumor progression and influencing patient outcomes. The emerging field of immunometabolism has shown that metabolic pathways play a pivotal role in regulating immune responses within the tumor microenvironment. This study aims to clarify the relationships between specific T cell phenotypes, circulating metabolites, and malignant brain tumors.

METHODS

We utilized a multiple mendelian randomization approach to investigate the associations between T cell phenotypes and malignant brain tumors, as well as the role of plasma metabolites in mediating these interactions. Instrumental variables were selected based on stringent criteria, and multiple mendelian randomization methods were utilized to identify causal pathways and metabolites potentially mediating these effects.

RESULTS

Our analysis identified significant associations between seven distinct T cell phenotypes, including various CD8 + and regulatory T cell subsets, and the presence of malignant brain tumors. We also identified 87 plasma metabolites correlated with these tumors. Notably, metabolites such as octadecanedioylcarnitine (C18-DC) and eicosanedioate (C20-DC) were implicated in modulating the risk of developing malignant brain tumors. Furthermore, metabolites such as 5-dodecenoate (12:1n7) and arachidonate (20:4n6) were found to influence tumor risk, particularly in relation to CD28 - CD8 + T cells.

CONCLUSION

The study identifies key T cell phenotypes and plasma metabolites involved in the pathogenesis of malignant brain tumors, offering potential biomarkers and therapeutic targets for future interventions.

The Gut Microbiota-Related Antihyperglycemic Effect of Metformin

It is critical to sustain the diversity of the microbiota to maintain host homeostasis and health. Growing evidence indicates that changes in gut microbial biodiversity may be associated with the development of several pathologies, including type 2 diabetes mellitus (T2DM). Metformin is still the first-line drug for treatment of T2DM unless there are contra-indications. The drug primarily inhibits hepatic gluconeogenesis and increases the sensitivity of target cells (hepatocytes, adipocytes and myocytes) to insulin; however, increasing evidence suggests that it may also influence the gut. As T2DM patients exhibit gut dysbiosis, the intestinal microbiome has gained interest as a key target for metabolic diseases. Interestingly, changes in the gut microbiome were also observed in T2DM patients treated with metformin compared to those who were not. Therefore, the aim of this review is to present the current state of knowledge regarding the association of the gut microbiome with the antihyperglycemic effect of metformin. Numerous studies indicate that the reduction in glucose concentration observed in T2DM patients treated with metformin is due in part to changes in the biodiversity of the gut microbiota. These changes contribute to improved intestinal barrier integrity, increased production of short-chain fatty acids (SCFAs), regulation of bile acid metabolism, and enhanced glucose absorption. Therefore, in addition to the well-recognized reduction of gluconeogenesis, metformin also appears to exert its glucose-lowering effect by influencing gut microbiome biodiversity. However, we are only beginning to understand how metformin acts on specific microorganisms in the intestine, and further research is needed to understand its role in regulating glucose metabolism, including the impact of this remarkable drug on specific microorganisms in the gut.

An integrated analysis of bile acid metabolism in humans with severe obesity

BACKGROUND AND AIMS

Bile acids (BA) are vital regulators of metabolism. BAs are AQ6 secreted in the small intestine, reabsorbed, and transported back to the liver, where they can modulate metabolic functions. There is a paucity of data regarding the portal BA composition in humans. This study aimed to address this knowledge gap by investigating portal BA composition and the relation with peripheral and fecal BA dynamics in conjunction with the gut microbiome.

APPROACH AND RESULTS

Thirty-three individuals from the BARIA cohort were included. Portal plasma, peripheral plasma, and feces were collected. BA and C4 levels were measured employing mass spectrometry. FGF19 was measured using ELISA. Gut microbiota composition was determined through metagenomics analysis on stool samples. Considerable diversity in the portal BA composition was observed. The majority (n = 26) of individuals had a 9-fold higher portal than peripheral BA concentration. In contrast, 8 individuals showed lower portal BA concentration compared with peripheral and had higher levels of unconjugated and secondary BA in this compartment, suggesting more distal origin. The altered portal BA profile was associated with altered gut microbiota composition. In particular, taxa within Bacteroides were reduced in abundance in the feces of these individuals.

CONCLUSIONS

Characterization of the portal BA composition in relation to peripheral and fecal BA increased insight into the dynamics of BA metabolism in individuals with obesity. Peripheral BA composition was much more diverse due to microbial metabolism. About 24% of the portal samples was surprisingly low in total BA; the underlying mechanism requires further exploration.