Conjugated Bile Acids Research Articles

Dynamics of Blood Taurine Concentration and its Correlation with Nutritional and Physiological Status during the Fattening Period of Japanese Black Cattle.

Taurine, biosynthesized from methionine or cysteine in the liver, plays a crucial regulatory role in bile acid conjugation, antioxidant effects, and glucose and cholesterol metabolism. This may influence the metabolic changes associated with fat accumulation in beef cattle. However, the physiological role of taurine in this species has not been fully elucidated. In this study, we explored the physiological role of taurine in Japanese Black steers (Bos taurus) in different phases during the fattening period. To examine the correlation among plasma taurine concentrations, various physiological parameters, and genes related to taurine synthesis in the liver, we used biopsied liver tissues, blood samples, and rumen fluids collected from 21 steers at three different stages, i.e., early (T1; 13 months of age), middle (T2; 20 months of age), and late (T3; 28 months of age) phases. Additionally, to investigate the regulatory mechanisms underlying the expression profile of taurine synthesis genes, primary bovine hepatocytes obtained from 4-week-old Holstein calves were treated with palmitate, oleate, acetate, propionate, or β-hydroxybutyrate (BHBA). Plasma taurine and cholesterol concentrations significantly (P < 0.001) increased in the T2 phase, which is potentially attributable to increased energy intake and assimilation induced by increased intake of concentrated feed. Cysteine sulfinic acid decarboxylase (CSAD) expression significantly increased (P < 0.01) in T2 than in other phases. The expression levels of cysteine dioxygenase type 1 (CDO1) and cholesterol 7 alpha-hydroxylase (CYP7A1) were significantly higher (P < 0.001) in T2 than in T3; moreover, the CDO1/glutamate-cysteine ligase catalytic subunit (GCLC) ratio was higher (P < 0.05) in T2 than in T1. Plasma taurine concentrations were positively correlated with plasma methionine (r = 0.51; P < 0.05) and total cholesterol (r = 0.56; P < 0.05) concentrations at T2. Relative CDO1 mRNA expression was upregulated in cultured bovine hepatocytes treated with oleate and propionate, whereas it was downregulated upon acetate treatment. These findings indicate that the increase in plasma taurine concentrations in the T2 phase is associated with changes in lipid and methionine metabolism in Japanese Black steers.

Whole Genome Sequencing Analysis of Model Organisms Elucidates the Association Between Environmental Factors and Human Cancer Development

Determining a novel etiology and mechanism of human cancer requires extraction of characteristic mutational signatures derived from chemical substances. This study explored the mutational signatures of N-nitroso bile acid conjugates using Salmonella strains. Exposing S. typhimurium TA1535 to N-nitroso-glycine/taurine bile acid conjugates induced a predominance of C:G to T:A transitions. Two mutational signatures, B1 and B2, were extracted. Signature B1 is associated with N-nitroso-glycine bile acid conjugates, while Signature B2 is linked to N-nitroso-taurine bile acid conjugates. Signature B1 revealed a strong transcribed strand bias with GCC and GCT contexts, and the mutation pattern of N-nitroso-glycine bile acid conjugates in YG7108, which lacks O6-methylguanine DNA methyltransferases, matched that of the wild-type strain TA1535, suggesting that O6-methyl-deoxyguanosine contributes to mutations in the relevant regions. COSMIC database-based similarity analysis revealed that Signature B1 closely resembled SBS42, which is associated with occupational cholangiocarcinoma caused by overexposure to 1,2-dichlolopropane (1,2-DCP) and/or dichloromethane (DCM). Moreover, the inflammatory response pathway was induced by 1,2-DCP exposure in a human cholangiocyte cell line, and iNOS expression was positive in occupational cholangiocarcinomas. These results suggest that 1,2-DCP triggers an inflammatory response in biliary epithelial cells by upregulating iNOS and N-nitroso-glycine bile acid conjugate production, resulting in cholangiocarcinoma via DNA adduct formation.

Metagenomic, metabolomic, and lipidomic shifts associated with fecal microbiota transplantation for recurrent Clostridioides difficile infection.

Recurrent C. difficile infection (rCDI) is an urgent public health threat, for which the last resort and lifesaving treatment is a fecal microbiota transplant (FMT). However, the exact mechanisms that mediate a successful FMT are not well-understood. Here, we use longitudinal stool samples collected from patients undergoing FMT to evaluate intra-individual changes in the microbiome, metabolome, and lipidome after successful FMTs relative to their baselines pre-FMT. We show changes in the abundance of many lipids, specifically a decrease in acylcarnitines post-FMT, and a shift from conjugated bile acids pre-FMT to deconjugated secondary bile acids post-FMT. These changes correlate with a decrease in Enterobacteriaceae, which encode carnitine metabolism genes, and an increase in Lachnospiraceae, which encode bile acid altering genes such as bile salt hydrolases (BSHs) and the bile acid-inducible (bai) operon, post-FMT. We also show changes in gut microbe-encoded amino acid biosynthesis genes, of which Enterobacteriaceae was the primary contributor to amino acids C. difficile is auxotrophic for. Liquid chromatography, ion mobility spectrometry, and mass spectrometry (LC-IMS-MS) revealed a shift from microbial conjugation of primary bile acids pre-FMT to secondary bile acids post-FMT. Here, we define the structural and functional changes associated with a successful FMT and generate hypotheses that require further experimental validation. This information is meant to help guide the development of new microbiota-focused therapeutics to treat rCDI.IMPORTANCERecurrent C. difficile infection is an urgent public health threat, for which the last resort and lifesaving treatment is a fecal microbiota transplant. However, the exact mechanisms that mediate a successful FMT are not well-understood. Here, we show changes in the abundance of many lipids, specifically acylcarnitines and bile acids, in response to FMT. These changes correlate with Enterobacteriaceae pre-FMT, which encodes carnitine metabolism genes, and Lachnospiraceae post-FMT, which encodes bile salt hydrolases and baiA genes. There was also a shift from microbial conjugation of primary bile acids pre-FMT to secondary bile acids post-FMT. Here, we define the structural and functional changes associated with a successful FMT, which we hope will help aid in the development of new microbiota-focused therapeutics to treat rCDI.

8236 Hepatocyte Vitamin D Receptor (VDR) Regulates Liver Regeneration

Abstract Disclosure: J.E. Gunton: None. Harendran Elangovan [1], Rebecca A. Stokes [1], Jeremy Keane [1], Sarinder Chahal [1], Caroline Samer [1], Miguel Agoncillo [1], Josephine Yu [1], Jennifer Chen [1], Michael Downes 2, Ronald M. Evans 2, Christopher Liddle [1],2, Jenny E. Gunton [1] [1]Centre for Diabetes, Obesity and Endocrinology, The Westmead Institute for Medical Research, University of Sydney, Westmead, NSW, Australia 2 Salk Institute for Biological Studies, La Jolla, CA. USA Background: Vitamin D signals through the vitamin D receptor (VDR) to induce its end-organ effects. Hepatic stellate cells control development of liver fibrosis in response to stressors and vitamin D signaling decreases fibrogenesis. VDR expression in hepatocytes, however, is low in healthy liver, and the role of VDR in hepatocyte proliferation is unclear. Methods: In these studies, hepatocyte-VDR null mice (hVDR) were used to assess the role of VDR and vitamin D signaling in hepatic regeneration. Mice underwent 2/3 partial hepatectomy and liver regeneration and function were studied. Results: hVDR mice had impaired liver regeneration with impaired hepatocyte proliferation. This was associated with significant differential changes in bile salts. Notably, mice lacking hepatocyte VDR had significant increases in expression of conjugated bile acids after partial hepatectomy, consistent with failure to normalize hepatic function by the 14-day time point tested. CDCA (chenodeoxycholate) is an FXR ligand, which was increased after surgery in controls but not in hVDR mice. FXR signaling is important for hepatocyte proliferation. Real-time PCR of hVDR and control livers showed significant changes in expression of cell cycle genes including cyclins D1 and E1 and cyclin-dependent kinase 2. Gene expression profiling of hepatocytes treated with vitamin D or control showed regulation of groups of genes involved in liver proliferation, hepatitis, liver hyperplasia / hyperproliferation and liver necrosis / cell death. Conclusions: Together these studies demonstrate an important functional role for VDR in hepatocytes during liver regeneration. Combined with the known profibrotic effects of impaired VDR signaling in stellate cells, these studies provide a mechanism whereby vitamin D deficiency would both reduce hepatocyte proliferation and permit fibrosis, leading to significant liver compromise. Presentation: 6/2/2024

α-Linolenic acid from Mori Folltfm found as Choloylglycine hydrolase inhibitor by the developed fluorescent probe to alleviate type 2 diabetes

Choloylglycine hydrolase (CH), also known as bile salt hydrolase, is expressed by intestinal microbiota and plays a key role in the hydrolysis of conjugated bile acids, influencing the composition and levels of various bile acids. In this study, a conjugate (CA-ACDI) of cholic acid and a semi-cyanine derivative was developed as an enzyme-activated fluorescent probe for detecting CH activity, showing potential applications in this area. By the high-throughput screening of CH activity using CA-ACDI, Mori Folium was identified as a significant CH inhibitor from a collection of 95 traditional herbal medicines. Further analysis using various chromatographic techniques and spectroscopic data identified α-linolenic acid as the key bioactive component in Mori Folium responsible for inhibiting CH activity. Importantly, α-Linolenic acid, as a natural CH inhibitor, was shown to significantly regulate glucose metabolism in a type 2 diabetes mellitus (T2DM) mouse model via the FXR signaling pathway. This work not only developed a novel fluorescent probe for CH detection but also discovered potential CH inhibitors that may help alleviate type 2 diabetes.

Polysaccharide NAP-3 Synergistically Enhances the Efficiency of Metformin in Type 2 Diabetes via Bile Acid/GLP-1 Axis through Gut Microbiota Remodeling.

The polysaccharides of edible mushrooms are excellent phytochemicals for adjuvant treatment of metabolic diseases, but the potential mechanisms of synergistic effects are unclear. In this work, we discovered that NAP-3 enhanced the efficiency of metformin in lipid and glucose metabolism in type 2 diabetic (T2D) mice in a gut microbiome-dependent way. NAP-3 remodeled the intestinal microbial, resulting in the decreased activity of bile salt hydrolases and upregulation of CYP27A1 and CYP7B1 functions in the alternative pathway of bile acid synthesis, which leads to accumulation of the conjugated bile acids in ileum, specifically TβMCA and TUDCA. The accumulated conjugated bile acids either blocked or stimulated the nuclear receptors Farnesoid-X-receptor and TGR5, inducing the release of GLP-1 and ultimately enhanced glucose metabolism in mice. Collectively, our research indicated that edible mushroom polysaccharide NAP-3 may serve as a promising adjunctive oral therapeutic agent for T2D.

Synthesis, Hemolytic Activity, and In Silico Studies of New Bile Acid Dimers Connected with a 1,2,3-Triazole Ring.

The synthesis of bile acid conjugates plays a significant role in pharmacology and organic chemistry. These complex compounds are widely studied due to their potential therapeutic applications (e.g., drug carriers or antibacterial agents) and their impact on interactions with biological target systems. It is important to determine the biological activity of the obtained conjugates with potential pharmacological applications. The research aimed to synthesize acyl conjugates of bile acids, determine the influence of acyl groups on potential antibacterial activity and evaluate the impact of conjugation on hemolytic activity. New acetyl bile acid acetyl dimers were synthesized using the "Click Chemistry" reaction, aiming to investigate their hemolytic and antibacterial activity. The structures of all compounds were confirmed through spectral analysis techniques, including 1H and 13C nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FT-IR), and electrospray ionization-mass spectrometry (ESI-MS). The PM5 semiempirical method was also used to estimate the heat of formation of individual conjugates, and the prediction of activity spectra for substances (PASS) technique was used to determine the pharmacokinetic potential of compounds. Docking studies indicate that obtained conjugates have the potential ability to inhibit the biosynthesis of Lipid II and block DNA gyrase. These compounds can therefore be treated as potential candidates for antibacterial compounds. Research findings suggest that conjugating bile acids and their derivatives through 1,2,3-triazole ring, results in final products with reduced hemolytic activity.

Saikosaponin D improves non-alcoholic fatty liver disease via gut microbiota-bile acid metabolism pathway

Non-alcoholic fatty liver disease (NAFLD) is the main cause of chronic liver disease worldwide. Bupleurum is widely used in the treatment of non-alcoholic fatty liver, and saikosaponin D (SSD) is one of the main active components of Bupleurum. The purpose of this study was to investigate the efficacy of SSD in the treatment of NAFLD and to explore the mechanism of SSD in the improvement of NAFLD based on “gut-liver axis”. Our results showed that SSD dose-dependently alleviated high fat diet-induced weight gain in mice, improved insulin sensitivity, and also reduced liver lipid accumulation and injury-related biomarkers aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Further exploration found that SSD inhibited the mRNA expression levels of farnesoid X receptor (Fxr), small heterodimer partner (Shp), recombinant fibroblast growth factor 15 (Fgf15) and apical sodium dependent bile acid transporter (Asbt) in the intestine, suggesting that SSD improved liver lipid metabolism by inhibiting intestinal FXR signaling. SSD can significantly reduce the gut microbiota associated with bile salt hydrolase (BSH) expression, such as Clostridium. Decreased BSH expression reduced the ratio of unconjugated to conjugated bile acids, thereby inhibiting the intestinal FXR. These data demonstrated that SSD ameliorated NAFLD potentially through the gut microbiota-bile acid-intestinal FXR pathway and suggested that SSD is a promising therapeutic agent for the treatment of NAFLD.

Abstract P166: Genetic Ablation of the Bile Acid Receptor- Takeda G-protein Coupled Receptor 5 (TGR5) Promotes Weight Gain but Lowers Hypertension

Introduction: TGR5 belongs to G-protein coupled receptor family, that mediates bile acid signaling. Activation of TGR5 by bile acids triggers intestinal glucagon-like peptide-1 secretion, whereby pharmacological activation of TGR5 constitutes a promising incretin-based strategy for the treatment of metabolic disorders. Hypertension is one of the hallmark features of metabolic disorders. We previously reported that hypertension is associated with lower conjugated bile acids, which are ligands for TGR5. Therefore, we hypothesized that lack of activation of TGR5-mediated bile acid signaling promotes not only body weight gain, but also hypertension. Methods: CRISPR/Cas9 technology was used to generate Tgr5 -/- rats from hypertensive Dahl Salt-sensitive (S) rats. Twenty-four-hour blood pressure (BP) readings of 8-weeks-old control female Tgr5 +/+ S rats and age-matched female Tgr5 -/- S rats (n=7/group) were monitored by radiotelemetry for 4 weeks. Body weight, food intake, and water intake were recorded every week. At the end of the study, vascular function was examined using wire myography of dorsal and mesenteric resistance arteries, cardiac function was assessed by echocardiography, and microbiota profiling was conducted via fecal 16S rRNA gene sequencing using Miseq. Results: In support of our hypothesis, despite no difference in food and water intake, at 4 weeks, the body weights of Tgr5 -/- S rats were significantly higher compared to Tgr5 +/+ S rats (236.3gm vs. 225.4gm; p&lt;0.01). Surprisingly, in contrast to our hypothesis, at 4 weeks, Tgr5 -/- S rats had significantly lower systolic BP (151.8mmHg vs. 156.9mmHg, p&lt;0.0001), diastolic BP (107.9mmHg vs. 115.5mmHg, p&lt;0.0001), and mean arterial BP (128.8mmHg vs. 134.9mmHg, p&lt;0.0001) compared to Tgr5 +/+ S rats. However, no significant differences were observed either in vascular reactivity or cardiac function between the groups. Interestingly, fecal microbiota analysis revealed that Tgr5 -/- S rats presented with significant remodeling of gut microbiota with lower α-diversity (observed features; p=0.05), b-diversity (Bray-Curtis; p&lt;0.05, Jaccard; p&lt;0.01), and higher relative abundance of the BP-lowering genera Akkermansia . Conclusion: Our study revealed that deletion of TGR5 resulted in weight gain but lowered BP. It implies that activation of TGR5 may be a risk factor for raising BP. The mechanism by which TGR5 regulates BP seem independent of changes in vascular or cardiac function but is likely mediated by gut microbiota.

Abstract Mo041: Bile Acid Dysregulation in Response to Right Heart Failure and Hepatic Congestion

Introduction: Right heart failure (RHF), the result of impaired RV contractility and/or severe right-sided valvulopathies, is a clinical syndrome that commonly results in chronically elevated central venous pressures and hepatic congestion. Hepatic dysfunction in patients with heart failure portends a poor prognosis. In part, this may be due to the liver’s pivotal role in bile acid synthesis and processing. In addition to the classic role of a digestive surfactant, bile acids serve as important and dynamic signaling molecule. The present study characterizes a unique bile acid profile found in patients with RHF. Research Question: We hypothesize that RHF and hepatic congestion results in a dysregulation of bile acids. These untoward changes in bile acids concentrations may provide both important prognostic value and novel mechanistic pathways in congestive liver disease. Aims: 1) To characterize systemic and hepatic vein bile acid concentrations in patients with right heart failure. 2) To phenotype a mouse model of hepatic congestion and understand the mechanistic effects of specific bile acids on liver biology Methods: We enrolled a total of 60 patients who were referred for right heart catheterization (RHC). Patient demographics, echocardiograms, and routine laboratory tests were captured at enrollment. Blood was sampled from the IVC and hepatic vein during RHC. Bile acids were quantified from serum using liquid chromatography-tandem mass spectrometry. To model hepatic congestion, mice underwent ligation of the IVC. Blood and tissue samples were harvested and underwent mass spectrometry evaluation for the bile acid composition and immunohistochemistry was performed to characterize the immune landscape, respectively. Results: We captured a total of 12 control samples from patients with normal filling pressures, 25 patients with left heart failure (LHF), and 23 patients with RF. Patients with RHF had poorer survival outcomes compared to control or LHF. Patients with RHF had significant increases in specific conjugated bile acids when compared to control or LHF (Figure 1). Conclusions: In this study, we identified several conjugated bile acids that are uniquely elevated in patients with RHF compared to LHF and control. Additionally, patients with RHF had poorer survival. Collectively, these data suggest bile acids may serve as important biomarkers and signaling molecules in the pathogenesis of cardiogenic liver disease.

An insoluble cellulose nanofiber with robust expansion capacity protects against obesity

An imbalance between energy intake and energy expenditure predisposes obesity and its related metabolic diseases. Soluble dietary fiber has been shown to improve metabolic homeostasis mainly via microbiota reshaping. However, the application and metabolic effects of insoluble fiber are less understood. Herein, we employed nanotechnology to design citric acid-crosslinked carboxymethyl cellulose nanofibers (CL-CNF) with a robust capacity of expansion upon swelling. Supplementation with CL-CNF reduced food intake and delayed digestion rate in mice by occupying stomach. Besides, CL-CNF treatment mitigated diet-induced obesity and insulin resistance in mice with enhanced energy expenditure, as well as ameliorated inflammation in adipose tissue, intestine and liver and reduced hepatic steatosis, without any discernible signs of toxicity. Additionally, CL-CNF supplementation resulted in enrichment of probiotics such as Bifidobacterium and decreased in the relative abundances of deleterious microbiota expressing bile salt hydrolase, which led to increased levels of conjugated bile acids and inhibited intestinal FXR signaling to stimulate the release of GLP-1. Taken together, our findings demonstrate that CL-CNF administration protects mice from diet-induced obesity and metabolic dysfunction by reducing food intake, enhancing energy expenditure and remodeling gut microbiota, making it a potential therapeutic strategy against metabolic diseases.

Bile Acid-conjugate as a Promising Anticancer Agent: Recent Progress.

Bile acids have outstanding chemistry due to their amphiphilic nature and have received a lot of interest in the last few decades in the fields of biomedicine, pharmacology, and supramolecular applications. Bile acids are highly sought after by scientists looking for diverse and effective biological activity due to their chirality, rigidity, and hydroxyl group. The hydroxyl group makes it simple to alter the structure in a way that improves bioactivity and bioavailability. Bile acid-bioactive molecule conjugates are compounds in which a bile acid is linked to a bioactive molecule by a linker in order to increase the bioactivity of the bioactive molecule against the target cancer cells. This method has been used to improve the therapeutic efficacy of cytotoxic drugs while reducing their adverse side effects. These new bile acid conjugates are gaining attention because they overcome bioavailability and stability issues. The design, synthesis, and anticancer effectiveness of various bile acid conjugates are discussed together with recent advances in understanding in this review.

Gut microbiota, dietary taurine, and fiber shift taurine homeostasis in adipose tissue of calorie-restricted mice to impact fat loss

Previously, we demonstrated that caloric restriction (CR) stimulates the synthesis, conjugation, secretion, and deconjugation of taurine and bile acids in the intestine, as well as their reuptake. Given taurine's potent antiobesogenic properties, this study aimed to assess whether the CR-induced shift in taurine homeostasis contributes to adipose tissue loss. To verify that, male C57Bl/6 mice were subjected to 20% CR or ad libitum feeding, with variations in cage bedding and gut microbiota conditions. Additional groups received taurine supplementation or were fed a low-taurine diet (LTD). The results showed that in CR animals, taurine derived from the intestine was preferentially trafficked to epididymal white adipose tissue (eWAT) over other tested organs. Besides increased levels of taurine transporter TauT, gene expression of Cysteine dioxygenase (Cdo) involved in taurine synthesis was upregulated in CR eWAT. Taurine concentration in adipocytes was inversely correlated with fat pad weight of CR mice. Different types of cage bedding did not impact eWAT taurine levels; however, the lack of bedding and consumption of a diet high in soluble fiber did. Depleting gut microbiota with antibiotics or inhibiting bile salt hydrolase (BSH) activity reduced WAT taurine concentration in CR mice. Taurine supplementation increased taurine levels in WAT and brown adipose tissue (BAT), promoting fat loss in CR animals. LTD consumption blunted WAT loss in CR animals, with negligible impact on BAT. This study provides multiple insights into taurine's role in CR-triggered fat loss and describes a novel communication path between the liver, gut, microbiota, and WAT, with taurine acting as a messenger.

Metabolomic and sphingolipidomic profiling of human hepatoma cells exposed to widely used pharmaceuticals

Pharmaceutical compounds have become one of the main contaminants of emerging concern (CECs) due to their high usage and increased release into the environment. This study aims to assess the effects caused by three widely consumed hepatotoxic pharmaceutical compounds: an antibiotic (amoxicillin), an antiepileptic (carbamazepine), and an antidepressant (trazodone), on human health when indirectly exposed to toxicologically relevant concentrations (30, 15, and 7.5 μM for amoxicillin and carbamazepine, and 4, 2, and 1 μM for trazodone). A combination of semi-targeted metabolomic and targeted sphingolipid analyses was chosen to unravel the metabolic alterations in human hepatic cells exposed to these CECs at three concentrations for 24 h. HepG2 hepatoma cells were encapsulated in sodium alginate spheroids to improve the physiological relevance of this in vitro approach. Statistical analysis was used to identify the most affected metabolites and sphingolipids for each drug exposure. The results revealed small but significant changes in response to carbamazepine and trazodone exposures, affecting sphingolipid, glycerophospholipid precursors, and amino acid metabolism. Under both drug treatments, a decrease in various ceramide species (related to cell signaling) was observed, along with reduced taurine levels (related to the biosynthesis of bile acid conjugates) and carnitine levels (suggesting an impact on energy production). These and other drug-specific changes indicate that cellular functions in liver cells might be altered under low doses of these CECs, potentially affecting the health of other organs.

How bile acids and the microbiota interact to shape host immunity.

Bile acids are increasingly appearing in the spotlight owing to their novel impacts on various host processes. Similarly, there is growing attention on members of the microbiota that are responsible for bile acid modifications. With recent advances in technology enabling the discovery and continued identification of microbially conjugated bile acids, the chemical complexity of the bile acid landscape in the body is increasing at a rapid pace. In this Review, we summarize our current understanding of how bile acids and the gut microbiota interact to modulate immune responses during homeostasis and disease, with a particular focus on the gut.

Epithelial Na + Channel Activation after Bile Duct Ligation with Mineralocorticoid Receptor Blockade.

Sodium and fluid retention in liver disease are classically thought to result from reduced effective circulating volume and stimulation of the renin-angiotensin-aldosterone system (RAAS). However, evidence of fluid retention in patients without RAAS activation suggests the involvement of additional mechanisms. In vitro, bile acids activate the epithelial Na+ channel (ENaC) found in the aldosterone-sensitive distal nephron. If this occurs in vivo, ENaC may become activated in liver disease even with antagonism of aldosterone signaling. To test this, we performed bile duct ligation to induce liver disease and increase circulating bile acids in mice given spironolactone to antagonize aldosterone signaling. We analyzed effects on blood, urine and body composition. We also determined the effects of taurocholic acid, a primary conjugated bile acid elevated in liver disease, on ion fluxes in microperfused rabbit collecting ducts. Bile duct ligation increased benzamil-sensitive natriuresis compared to sham, indicating ENaC activation. These effects were not explained by effects on ENaC expression, cleavage, or localization. Bile duct ligated mice also gained significantly more fluid than sham-operated animals. Blocking ENaC reversed fluid gains in bile duct ligated mice but had no effect in shams. In dissected collecting ducts from rabbits, which express ENaC, taurocholic acid stimulated net Na+ absorption. Our results provide experimental evidence for a novel aldosterone-independent mechanism for sodium and fluid retention in liver disease.

Taurine-conjugated bile acids and their link to hepatic S1PR2 play a significant role in hepatitis C-related liver disease.

Bile acids mediate gut-liver cross-talk through bile acid receptors. Serum, hepatic, and microbial bile acid metabolism was evaluated in HCV-compensated chronic liver disease. Patients underwent liver biopsy; portal and peripheral blood were obtained before (HCVi), and 6 months after sustained virologic response (SVR), splenic blood was obtained only after SVR. The fecal microbiome and liver transcriptome were evaluated using RNA-Seq. Twenty-four bile acids were measured in serum, summed as free, taurine-conjugated bile acids (Tau-BAs), and glycine-conjugated bile acids. Compared to SVR, HCVi showed elevated conjugated bile acids, predominantly Tau-BA, compounded in HCVi cirrhosis. In the liver, transcription of bile acids uptake, synthesis, and conjugation was decreased with increased hepatic spillover into systemic circulation in HCVi. There was no difference in the transcription of microbial bile acid metabolizing genes in HCVi. Despite an overall decrease, Tau-BA remained elevated in SVR cirrhosis, mainly in splenic circulation. Only conjugated bile acids, predominantly Tau-BA, correlated with serum proinflammatory markers and hepatic proinflammatory pathways, including NLRP3 and NFKB. Among hepatic bile acid receptors, disease-associated conjugated bile acids showed the strongest association with hepatic spingosine-1-phosphate receptor 2 (S1PR2). Enhanced expression of hepatic S1PR2 in HCVi and HCVi-cirrhosis and strong associations of S1PR2 with Tau-BAs suggest pathological relevance of Tau-BA-hepatic S1PR2 signaling in chronic liver disease. These findings have therapeutic implications in chronic liver diseases.

Dietary iron intake has long-term effects on the fecal metabolome and microbiome.

Iron is essential for life, but its imbalances can lead to severe health implications. Iron deficiency is the most common nutrient disorder worldwide, and iron dysregulation in early life has been found to cause long-lasting behavioral, cognitive, and neural effects. However, little is known about the effects of dietary iron on gut microbiome function and metabolism. In this study, we sought to investigate the impact of dietary iron on the fecal metabolome and microbiome by using mice fed with three diets with different iron content: an iron deficient, an iron sufficient (standard), and an iron overload diet for 7 weeks. Additionally, we sought to understand whether any observed changes would persist past the 7-week period of diet intervention. To assess this, all feeding groups were switched to a standard diet, and this feeding continued for an additional 7 weeks. Analysis of the fecal metabolome revealed that iron overload and deficiency significantly alter levels of peptides, nucleic acids, and lipids, including di- and tri-peptides containing branched-chain amino acids, inosine and guanosine, and several microbial conjugated bile acids. The observed changes in the fecal metabolome persist long after the switch back to a standard diet, with the cecal gut microbiota composition and function of each group distinct after the 7-week standard diet wash-out. Our results highlight the enduring metabolic consequences of nutritional imbalances, mediated by both the host and gut microbiome, which persist after returning to the original standard diets.

Vitamin D Receptor Regulates Liver Regeneration After Partial Hepatectomy in Male Mice.

Vitamin D signals through the vitamin D receptor (VDR) to induce its end-organ effects. Hepatic stellate cells control development of liver fibrosis in response to stressors and vitamin D signaling decreases fibrogenesis. VDR expression in hepatocytes is low in healthy liver, and the role of VDR in hepatocyte proliferation is unclear. Hepatocyte-VDR null mice (hVDR) were used to assess the role of VDR and vitamin D signaling in hepatic regeneration. hVDR mice have impaired liver regeneration and impaired hepatocyte proliferation associated with significant differential changes in bile salts. Notably, mice lacking hepatocyte VDR had significant increases in expression of conjugated bile acids after partial hepatectomy, consistent with failure to normalize hepatic function by the 14-day time point tested. Real-time PCR of hVDR and control livers showed significant changes in expression of cell-cycle genes including cyclins D1 and E1 and cyclin-dependent kinase 2. Gene expression profiling of hepatocytes treated with vitamin D or control showed regulation of groups of genes involved in liver proliferation, hepatitis, liver hyperplasia/hyperproliferation, and liver necrosis/cell death. Together, these studies demonstrate an important functional role for VDR in hepatocytes during liver regeneration. Combined with the known profibrotic effects of impaired VDR signaling in stellate cells, the studies provide a mechanism whereby vitamin D deficiency would both reduce hepatocyte proliferation and permit fibrosis, leading to significant liver compromise.

Sex-specific effects of gut microbiome on shaping bile acid metabolism.

Gut microbiome is a group of microorganisms that plays important roles in contributing to health and diseases. These bacterial compositions have been demonstrated to impact bile acids (BAs) profiles, either by directly metabolizing primary BAs to secondary BAs or indirect ways through host metabolism by influencing BAs synthesis, transportation and conjugation in liver. It has been observed sexually dimorphic gut microbiome and bile acids composition, with variations in expression levels of bile acid metabolizing genes in the liver. However, associations between sex-specific differences in gut microbiome and BAs profiles are not well understood. This study aimed to investigate whether gut microbiome could influence BAs profiles in host in a sexspecific manner. We transplanted cecum feces of male and female C57BL/6 mice to male mice and measured BAs concentrations in feces, serum and liver samples 7 days after fecal transplantation. We found different BAs profiles between mice with male and female gut microbiome, including altering levels and proportions of secondary BAs. We also observed varied expression levels of genes related to bile acid metabolism in the liver and distal ileum. Our results highlight sex-specific effects of gut microbiome on shaping bile acid metabolism through gut bacteria and regulation of host genes.