Animal models to study bile acid metabolism

Exploring bile acid transporters as key players in cancer development and treatment: Evidence from preclinical and clinical studies

Bile acid transporters (BATs) are integral membrane proteins belonging to various families, such as solute carriers, organic anion transporters, and ATP-binding cassette families. These transporters play a crucial role in bile acid transportation within the portal and systemic circulations, with expression observed in tissues, including the liver, kidney, and small intestine. Bile acids serve as signaling molecules facilitating the absorption and reabsorption of fats and lipids. Dysregulation of bile acid concentration has been implicated in tumorigenesis, yet the role of BATs in this process remains underexplored. Emerging evidence suggests that BATs may modulate various stages of cancer progression, including initiation, development, proliferation, metastasis, and tumor microenvironment regulation. Targeting BATs using siRNAs, miRNAs, and small compound inhibitors in preclinical models and their polymorphisms are well-studied for transporters like BSEP, MDR1, MRP2, OATP1A2, etc., and have shed light on their involvement in tumorigenesis, particularly in cancers such as those affecting the liver and gastrointestinal tract. While BATs' role in diseases like Alagille syndrome, biliary atresia, and cirrhosis have been extensively studied, their implications in cancer warrant further investigation. This review highlights the expression and function of BATs in cancer development and emphasizes the potential of targeting these transporters as a novel therapeutic strategy for various malignancies.

Hepatic bile acid accretion correlates with cholestatic liver injury and therapeutic response in Cyp2c70 knockout mice with a humanized bile acid composition

Cyp2c70 knockout (KO) mice lack the liver enzyme responsible for synthesis of 6-hydroxylated muricholate bile acid species and possess a more hydrophobic human-like bile acid composition. Cyp2c70 KO mice develop cholestatic liver injury that can be prevented by the administration of an ileal bile acid transporter (IBAT) inhibitor. In this study, we investigated the potential of an ileal bile acid transporter (IBAT) inhibitor (SC-435) and steroidal farnesoid X receptor (FXR) agonist (cilofexor) to modulate established hepatobiliary injury and the consequent relationship of intrahepatic bile acid content and hydrophobicity to the cholestatic liver injury phenotype. Oral administration of SC-435, cilofexor, or combined treatment for 2 wk markedly reduced serum markers of liver injury and improved histological and gene expression markers of fibrosis, liver inflammation, and ductular reaction in male and female Cyp2c70 KO mice, with the greatest benefit in the combination treatment group. The IBAT inhibitor and FXR agonist significantly reduced intrahepatic bile acid content but not hepatic bile acid pool hydrophobicity, and markers of liver injury were strongly correlated with intrahepatic total bile acid and taurochenodeoxycholic acid accretion. Biomarkers of liver injury increased linearly with similar hepatic thresholds for pathological accretion of hydrophobic bile acids in male and female Cyp2c70 KO mice. These findings further support targeting intrahepatic bile acid retention as a component of treatments for cholestatic liver disease.NEW & NOTEWORTHY Bile acids are implicated as a common contributor to the pathogenesis and progression of cholestatic liver disease. Using a mouse model with a humanized bile acid composition, we demonstrated that mono and combination therapy using an IBAT inhibitor and FXR nonsteroidal agonist were effective at reducing hepatic bile acid accretion and reversing liver injury, without reducing hepatic bile acid hydrophobicity. The findings support the concept of a therapeutically tractable threshold for bile acid-induced liver injury.

The bile acid chenodeoxycholic acid associates with reduced stroke in humans and mice

Bile acids are liver-derived signaling molecules that can be found in the brain, but their role there remains largely unknown. We found increased brain chenodeoxycholic acid (CDCA) in mice with absent 12α-hydroxylase (Cyp8b1), a bile acid synthesis enzyme. In these Cyp8b1-/-, and in Wt mice administered CDCA, stroke infarct area was reduced. Elevated glutamate-induced excitotoxicity mediated by aberrant N-methyl-D-aspartate receptor (NMDAR) overactivation contributes to neuronal death in ischemic stroke. We found reduced glutamate-induced excitotoxicity in neurons from Cyp8b1-/- and CDCA-treated Wt mice. CDCA decreased NMDAR-mediated excitatory post-synaptic currents by reducing over-activation of NMDAR subunit GluN2B in Wt brains. Synaptic NMDAR activity was also decreased in Cyp8b1-/- brains. Expression and synaptic distribution of GluN2B were unaltered in Cyp8b1-/- mice, suggesting CDCA may directly antagonize GluN2B-containing NMDARs. Supporting our findings, in a case-control cohort of acute ischemic stroke patients, we found lower circulatory CDCA. Together, our data suggest that CDCA, acting in the liver-brain axis, decreases GluN2B-containing NMDAR overactivation, contributing to neuroprotection in stroke.

Kinetics of imidazole propionate from orally delivered histidine in mice and humans

Imidazole Propionate (ImP), a gut-derived metabolite from histidine, affects insulin signaling in mice and is elevated in type 2 diabetes (T2D). However, the source of histidine and the role of the gut microbiota remain unclear. We conducted an intervention study in mice and humans, comparing ImP kinetics in mice on a high-fat diet with varying histidine levels and antibiotics, and assessed ImP levels in healthy and T2D subjects with histidine supplementation. Results show that dietary histidine is metabolized to ImP, with antibiotic-induced gut microbiota suppression reducing ImP levels in mice. In contrast, oral histidine supplementation resulted in increases in circulating ImP levels in humans, whereas antibiotic treatment increased ImP levels, which was associated with a bloom of several bacterial genera that have been associated with ImP production, such as Lactobacilli. Our findings highlight the gut microbiota's crucial role in regulating ImP and the complexity of translating mouse models to humans.

Elevated plasma bile acids coincide with cardiac stress and inflammation in young Cyp2c70-/- mice

BACKGROUND

High plasma bile acids (BAs), for instance due to intrahepatic cholestasis of pregnancy or neonatal cholestasis, are associated with cardiac abnormalities. Here, we exploited the variability in plasma BA levels in Cyp2c70-/- mice with a human-like BA composition to investigate the acute effects of elevated circulating BAs on the heart.

METHODS

RNA sequencing was performed on hearts of 3-week-old Cyp2c70-/- mice lacking mouse-specific BA species that show features of neonatal cholestasis. Cardiac transcriptomes were compared between wild-type pups, Cyp2c70-/- pups with low or high plasma BAs, and Cyp2c70-/- pups from dams that were perinatally treated with ursodeoxycholic acid (UDCA).

RESULTS

We identified 1355 genes that were differentially expressed in hearts of Cyp2c70-/- mice with high versus low plasma BAs with enrichment of inflammatory processes. Strikingly, expression of 1053 (78%) of those genes was normalized in hearts of pups of UDCA-treated dams. Moreover, 645 cardiac genes strongly correlated to plasma BAs, of which 172 genes were associated with cardiovascular disease.

CONCLUSIONS

Elevated plasma BAs alter gene expression profiles of hearts of mice with a human-like BA profile, revealing cardiac stress and inflammation. Our findings support the notion that high plasma BAs induce cardiac complications in early life.

IMPACT

Cyp2c70-/- mice with a human-like bile acid composition show features of neonatal cholestasis but the extrahepatic consequences hereof have so far hardly been addressed Elevated plasma bile acids in Cyp2c70-/- pups coincide with cardiac stress and inflammation Perinatal treatment with UDCA prevents dysregulated cardiac gene expression patterns in Cyp2c70-/- pups.

Triclosan exposure causes abnormal bile acid metabolism through IL-1β-NF-κB-Fxr signaling pathway

Triclosan (TCS) is an eminent antibacterial agent. However, extensive usage causes potential health risks like hepatotoxicity, intestinal damage, kidney injury, etc. Existing studies suggested that TCS would disrupt bile acid (BA) enterohepatic circulation, but its toxic mechanism remains unclear. Hence, the current study established an 8-week TCS exposure model to explore its potential toxic mechanism. The results discovered 8 weeks consecutive administration of TCS induced distinct programmed cell death, inflammatory cell activation and recruitment, and excessive BA accumulation in liver. Furthermore, the expression of BA synthesis and transport associated genes were significantly dysregulated upon TCS treatment. Additional mechanism exploration revealed that Fxr inhibition induced by TCS would be the leading cause for unusual BA biosynthesis and transport. Subsequent Fxr up-stream investigation uncovered TCS exposure caused pyroptosis and its associated IL-1β would be the reason for Fxr reduction mediated by NF-κB. NF-κB blocking by dimethylaminoparthenolide ameliorated TCS induced BA disorder which confirmed the contribution of NF-κB in Fxr repression. To sum up, our findings conclud TCS-caused BA disorder is attributed to Fxr inhibition, which is regulated by the IL-1β-NF-κB signaling pathway. Hence, we suggest Fxr would be a potential target for abnormal BA stimulated by TCS and its analogs.

Gut microbial metabolites: Shaping future diagnosis and treatment against gastrointestinal cancer

Gastrointestinal cancer is a worldwide health challenge due to its dramatically increasing prevalence and as a leading cause of cancer-related mortality. Increasing evidence has illustrated the vital role of gut microbes-derived metabolites in gastrointestinal cancer progression and treatment. Microbial metabolites are produced by the gut microbiota that utilizes both extrinsic dietary components and intrinsic host-generated compounds. Meanwhile, certain categories of metabolites such as short-chain fatty acids, bile acids, tryptophan, and indole derivatives, are linked to gastrointestinal malignancy. In this review, the major classes of microbial metabolites and their impacts on various gastrointestinal cancers including colorectal cancer, gastric cancer, and hepatocellular carcinoma, have been introduced. The application of microbial metabolites as predictive biomarkers for early diagnosis and prognosis of gastrointestinal cancer has also been explored. In addition, therapeutic potential of strategies that target microbial metabolites against gastrointestinal cancer is further evaluated.

Quantifying Forms and Functions of Enterohepatic Bile Acid Pools in Mice

BACKGROUNDS & AIMS

Bile acids (BAs) are core gastrointestinal metabolites with dual functions in lipid absorption and cell signaling. BAs circulate between the liver and distal small intestine (i.e., ileum), yet the dynamics through which complex BA pools are absorbed in the ileum and interact with host intestinal cells in vivo remain poorly understood. Because ileal absorption is rate-limiting in determining which BAs in the intestinal lumen gain access to host intestinal cells and receptors, and at what concentrations, we hypothesized that defining the rates and routes of ileal BA absorption in vivo would yield novel insights into the physiological forms and functions of mouse enterohepatic BA pools.

METHODS

Using ex vivo mass spectrometry, we quantified 88 BA species and metabolites in the intestinal lumen and superior mesenteric vein of individual wild-type mice, and cage-mates lacking the ileal BA transporter, Asbt/Slc10a2.

RESULTS

Using these data, we calculated that the pool of BAs circulating through ileal tissue (i.e., the ileal BA pool) in fasting C57BL/6J female mice is ∼0.3 μmol/g. Asbt-mediated transport accounted for ∼80% of this pool and amplified size. Passive permeability explained the remaining ∼20% and generated diversity. Compared with wild-type mice, the ileal BA pool in Asbt-deficient mice was ∼5-fold smaller, enriched in secondary BA species and metabolites normally found in the colon, and elicited unique transcriptional responses on addition to exvivo-cultured ileal explants.

CONCLUSIONS

This study defines quantitative traits of the mouse enterohepatic BA pool and reveals how aberrant BA metabolism can impinge directly on host intestinal physiology.

Strain-dependent induction of primary bile acid 7-dehydroxylation by cholic acid

BACKGROUND

Bile acids (BAs) are steroid-derived molecules with important roles in digestion, the maintenance of host metabolism, and immunomodulation. Primary BAs are synthesized by the host, while secondary BAs are produced by the gut microbiome through transformation of the former. The regulation of microbial production of secondary BAs is not well understood, particularly the production of 7-dehydroxylated BAs, which are the most potent agonists for host BA receptors. The 7-dehydroxylation of cholic acid (CA) is well established and is linked to the expression of a bile acid-inducible (bai) operon responsible for this process. However, little to no 7-dehydroxylation has been reported for other host-derived BAs (e.g., chenodeoxycholic acid, CDCA or ursodeoxycholic acid, UDCA).

RESULTS

Here, we demonstrate that the 7-dehydroxylation of CDCA and UDCA by the human isolate Clostridium scindens is induced when CA is present, suggesting that CA-dependent transcriptional regulation is required for substantial 7-dehydroxylation of these primary BAs. This is supported by the finding that UDCA alone does not promote expression of bai genes. CDCA upregulates expression of the bai genes but the expression is greater when CA is present. In contrast, the murine isolate Extibacter muris exhibits a distinct response; CA did not induce significant 7-dehydroxylation of primary BAs, whereas BA 7-dehydroxylation was promoted upon addition of germ-free mouse cecal content in vitro. However, E. muris was found to 7-dehydroxylate in vivo.

CONCLUSIONS

The distinct expression responses amongst strains indicate that bai genes are regulated differently. CA promoted bai operon gene expression and the 7-dehydroxylating activity in C. scindens strains. Conversely, the in vitro activity of E. muris was promoted only after the addition of cecal content and the isolate did not alter bai gene expression in response to CA. The accessory gene baiJ was only upregulated in the C. scindens ATCC 35704 strain, implying mechanistic differences amongst isolates. Interestingly, the human-derived C. scindens strains were also capable of 7-dehydroxylating murine bile acids (muricholic acids) to a limited extent. This study shows novel 7-dehydroxylation activity in vitro resulting from the presence of CA and suggests distinct bai gene expression across bacterial species.

Bile acid profiles and mRNA abundance of bile acid-related genes in adipose tissue of dairy cows with high versus normal body condition

Besides their lipid-digestive role, bile acids (BA) influence overall energy homeostasis, such as glucose and lipid metabolism. We hypothesized that BA along with their receptors, regulatory enzymes, and transporters are present in subcutaneous adipose tissue (scAT). In addition, we hypothesized that their mRNA abundance varies with the body condition of dairy cows around calving. Therefore, we analyzed BA in serum and scAT as well as the mRNA abundance of BA-related enzymes, transporters, and receptors in scAT during the transition period in cows with different body conditions around calving. In a previously established animal model, 38 German Holstein cows were divided into either a high (HBCS; n = 19) or normal BCS (NBCS; n = 19) group based on their BCS and back-fat thickness (BFT). Cows were fed different diets to achieve the targeted differences in BCS and BFT (NBCS: BCS <3.5, BFT <1.2 cm; HBCS: BCS >3.75, BFT >1.4 cm) until dry-off at 7 wk antepartum. During the dry period and subsequent lactation, both groups were fed the same diets according to their energy demands. Using a targeted metabolomics approach via liquid chromatography-electrospray ionization-MS /MS, BA were analyzed in serum and scAT at wk -7, 1, 3, and 12 relative to parturition. In serum, 15 BA were observed: cholic acid (CA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), taurocholic acid (TCA), glycochenodeoxycholic acid (GCDCA), taurochenodeoxycholic acid, deoxycholic acid (DCA), lithocholic acid, glycodeoxycholic acid (GDCA), glycolithocholic acid, taurodeoxycholic acid, taurolithocholic acid, β-muricholic acid, tauromuricholic acid (sum of α and β), and glycoursodeoxycholic acid, whereas in scAT 7 BA were detected: CA, GCA, TCA, GCDCA, taurochenodeoxycholic acid, GDCA, and taurodeoxycholic acid. In serum and scAT samples, the primary BA CA and its conjugate GCA were predominantly detected. Increasing serum concentrations of CA, CDCA, TCA, GCA, GCDCA, DCA, and β-muricholic acid with the onset of lactation might be related to the increasing DMI after parturition. Furthermore, serum concentrations of CA, CDCA, GCA, DCA, GCDCA, TCA, lithocholic acid, and GDCA were lower in HBCS cows compared with NBCS cows, concomitant with increased lipolysis in HBCS cows. The correlation between CA in serum and scAT may point to the transport of CA across cell membranes. Overall, the findings of the present study suggest a potential role of BA in lipid metabolism depending on the body condition of periparturient dairy cows.

BiliQML: a supervised machine-learning model to quantify biliary forms from digitized whole slide liver histopathological images

The progress of research focused on cholangiocytes and the biliary tree during development and following injury is hindered by limited available quantitative methodologies. Current techniques include two-dimensional standard histological cell-counting approaches, which are rapidly performed, error prone, and lack architectural context or three-dimensional analysis of the biliary tree in opacified livers, which introduce technical issues along with minimal quantitation. The present study aims to fill these quantitative gaps with a supervised machine-learning model (BiliQML) able to quantify biliary forms in the liver of anti-keratin 19 antibody-stained whole slide images. Training utilized 5,019 researcher-labeled biliary forms, which following feature selection, and algorithm optimization, generated an F score of 0.87. Application of BiliQML on seven separate cholangiopathy models [genetic (Afp-CRE;Pkd1l1null/Fl, Alb-CRE;Rbp-jkfl/fl, and Albumin-CRE;ROSANICD), surgical (bile duct ligation), toxicological (3,5-diethoxycarbonyl-1,4-dihydrocollidine), and therapeutic (Cyp2c70-/- with ileal bile acid transporter inhibition)] allowed for a means to validate the capabilities and utility of this platform. The results from BiliQML quantification revealed biological and pathological differences across these seven diverse models, indicating a highly sensitive, robust, and scalable methodology for the quantification of distinct biliary forms. BiliQML is the first comprehensive machine-learning platform for biliary form analysis, adding much-needed morphologic context to standard immunofluorescence-based histology, and provides clinical and basic science researchers with a novel tool for the characterization of cholangiopathies.NEW & NOTEWORTHY BiliQML is the first comprehensive machine-learning platform for biliary form analysis in whole slide histopathological images. This platform provides clinical and basic science researchers with a novel tool for the improved quantification and characterization of biliary tract disorders.

Effect of Bile Acids Supplementation in Fatty Liver Hemorrhagic Syndrome, Production Performance, Physiological and Quality Characteristics of Laying Hen Eggs

This study aimed to investigate the effects of bile acids (BAs) supplementation on fatty liver hemorrhagic syndrome (FLHS), production performance, and physiological and quality characteristics of laying hen eggs. Sixty Sanhuang laying hens, aged 28 weeks, were randomly allocated to six dietary treatments over a 4-week period, including the control (CON) group (feeding basal diet), the high-fat diet (HFD)-treated group (basal diet containing 10% soybean oil), and HFD supplemented with 0.01% and 0.02% of chenodeoxycholic acid (CDCA) or hyodeoxycholic acid (HDCA) groups. Production performance, egg quality, liver morphology, serum biochemical indexes, antioxidant capacity, proinflammatory cytokines, and intestinal microbiota were evaluated. The average body weight in 0.01% CDCA was larger than in the HFD group (p < 0.05). Eggshell Thickness in the CON group was greater than in the HFD, 0.01% CDCA, and HDCA groups (p < 0.05). Albumen height in the 0.02% HDCA group was higher than the HFD group (p < 0.05). Eggshell weight in the HFD group was less than the CON group (p < 0.05). Haugh unit (HU) in the HDCA group was larger than the HFD group (p < 0.05). Albumen weight in the 0.02% HDCA group was greater than the CON and HFD groups (p < 0.05). In the HFD group, the levels of triglyceride (TG), total cholesterol (TC), and low-density lipo-protein cholesterol (LDL-C) were surpassing the other groups (p < 0.05). The levels of catalase (CAT) and total superoxide dismutase (T-SOD) in the HFD group was smaller than the other groups (p < 0.05). The level of malondialdehyde (MDA) in the HFD group was higher than in the other groups (p < 0.05). Tumor necrosis factor-α (TNF-α) levels were larger in the HFD group than in the other groups (p < 0.05). The 16S rRNA sequencing analysis indicated significant variations in the relative abundance of specific bacterial populations among the different treatment groups. The treatment and CON groups exhibited a higher presence of bacteria that inhibit host energy absorption or promote intestinal health such as Firmicutes, Bacteroidetes, and Ruminococcus, whereas the HFD group showed an increased prevalence of potentially pathogenic or deleterious bacteria, such as Desulfovibrio spp. In conclusion, the supplementation of BAs in poultry feed has been demonstrated to effectively mitigate the detrimental effects of FLHS in laying hens. This intervention regulates lipid metabolism, bolsters antioxidant defenses, reduces inflammation, and modulates the gut microbiota, offering a novel perspective on the application of BAs in the poultry industry.

Role of Arthrospira Platensis in Preventing and Treating High-Fat Diet-Induced Hypercholesterolemia in Adult Rats

Hyperlipidaemia is a recognised risk factor for cardiovascular disease. In this study, the antihyperlipidaemic properties of spirulina (Arthrospira platensis, strain S2 from Serbia) were tested in adult Wistar rats before and after induction of hypercholesterolaemia by a high-fat diet (HFD) to compare the preventive with the curative effect. Total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), alanine transaminase (ALT) and aspartate transaminase (AST) levels were measured in the blood samples. The chemical composition (lipids, proteins and cholesterol) and the content of bile acids in the faeces of the animals were also analysed. Feeding rats with an atherogenic diet for 10 weeks led to the successful development of hyperlipidaemia, as serum TC and LDL-C levels as well as lipids, cholesterol and bile acids in the animals' faeces were significantly increased. Pre- and post-treatment with spirulina led to a reduction in serum LDL, TC and ALT levels. Administration of spirulina resulted in both a significant increase in primary bile acids excretion and a decrease in bile acids metabolism, with pre-treatment being more effective than post-treatment in some cases. These results suggest that increased excretion of bile acids as well as an effect on the gut microbiota may be the mechanism responsible for the anti-hyperlipidaemic activity of the tested spirulina strain.

Recreating metabolic interactions of the tumour microenvironment

Tumours are heterogeneous tissues containing diverse populations of cells and an abundant extracellular matrix (ECM). This tumour microenvironment prompts cancer cells to adapt their metabolism to survive and grow. Besides epigenetic factors, the metabolism of cancer cells is shaped by crosstalk with stromal cells and extracellular components. To date, most experimental models neglect the complexity of the tumour microenvironment and its relevance in regulating the dynamics of the metabolism in cancer. We discuss emerging strategies to model cellular and extracellular aspects of cancer metabolism. We highlight cancer models based on bioengineering, animal, and mathematical approaches to recreate cell-cell and cell-matrix interactions and patient-specific metabolism. Combining these approaches will improve our understanding of cancer metabolism and support the development of metabolism-targeting therapies.

Comparative profiling of serum, urine, and feces bile acids in humans, rats, and mice

Bile acids (BAs) play important pathophysiological roles in both humans and mammalian animals. Laboratory rats and mice are widely used animal models for assessing pharmacological effects and their underlying molecular mechanisms. However, substantial physiological differences exist in BA composition between humans and murine rodents. Here, we comprehensively compare BA profiles, including primary and secondary BAs, along with their amino acid conjugates, and sulfated metabolites in serum, urine, and feces between humans and two murine rodents. We further analyze the capabilities in gut microbial transform BAs among three species and compare sex-dependent variations within each species. As a result, BAs undergo amidation predominately with glycine in humans and taurine in mice but are primarily unamidated in rats. BA sulfation is a unique characteristic in humans, whereas rats and mice primarily perform multiple hydroxylations during BA synthesis and metabolism. For gut microbial transformed BA capabilities, humans are comparable to those of rats, stronger than those of mice in deconjugation and 7α-dehydroxylation, while humans are weak than those of rats or mice in oxidation and epimerization. Such differences enhance our understanding of the divergent experimental outcomes observed in humans and murine rodents, necessitating caution when translating findings from these rodent species to humans.

Membrane-bound chemoreception of bitter bile acids and peptides is mediated by the same subset of bitter taste receptors

The vertebrate sense of taste allows rapid assessment of the nutritional quality and potential presence of harmful substances prior to ingestion. Among the five basic taste qualities, salty, sour, sweet, umami, and bitter, bitterness is associated with the presence of putative toxic substances and elicits rejection behaviors in a wide range of animals including humans. However, not all bitter substances are harmful, some are thought to be health-beneficial and nutritious. Among those compound classes that elicit a bitter taste although being non-toxic and partly even essential for humans are bitter peptides and L-amino acids. Using functional heterologous expression assays, we observed that the 5 dominant human bitter taste receptors responsive to bitter peptides and amino acids are activated by bile acids, which are notorious for their extreme bitterness. We further demonstrate that the cross-reactivity of bitter taste receptors for these two different compound classes is evolutionary conserved and can be traced back to the amphibian lineage. Moreover, we show that the cross-detection by some receptors relies on "structural mimicry" between the very bitter peptide L-Trp-Trp-Trp and bile acids, whereas other receptors exhibit a phylogenetic conservation of this trait. As some bile acid-sensitive bitter taste receptor genes fulfill dual-roles in gustatory and non-gustatory systems, we suggest that the phylogenetic conservation of the rather surprising cross-detection of the two substance classes could rely on a gene-sharing-like mechanism in which the non-gustatory function accounts for the bitter taste response to amino acids and peptides.

Another renaissance for bile acid gastrointestinal microbiology

The field of bile acid microbiology in the gastrointestinal tract is going through a current rebirth after a peak of activity in the late 1970s and early 1980s. This renewed activity is a result of many factors, including the discovery near the turn of the century that bile acids are potent signalling molecules and technological advances in next-generation sequencing, computation, culturomics, gnotobiology, and metabolomics. We describe the current state of the field with particular emphasis on questions that have remained unanswered for many decades in both bile acid synthesis by the host and metabolism by the gut microbiota. Current knowledge of established enzymatic pathways, including bile salt hydrolase, hydroxysteroid dehydrogenases involved in the oxidation and epimerization of bile acid hydroxy groups, the Hylemon-Bjӧrkhem pathway of bile acid C7-dehydroxylation, and the formation of secondary allo-bile acids, is described. We cover aspects of bile acid conjugation and esterification as well as evidence for bile acid C3-dehydroxylation and C12-dehydroxylation that are less well understood but potentially critical for our understanding of bile acid metabolism in the human gut. The physiological consequences of bile acid metabolism for human health, important caveats and cautionary notes on experimental design and interpretation of data reflecting bile acid metabolism are also explored.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Effect of Bile on Hemodynamics and Blood Micro-Rheological Parameters in Experimental Models of Bilhemia

As a rare complication of liver injury and certain interventions, bile can enter the bloodstream depending on the pressure gradient, resulting in bilhemia. Its micro-rheological and hemodynamic effects are still unclear. We aimed to study these parameters in experimental bilhemia models. Under general anesthesia, via laparotomy, bile was obtained by gallbladder puncture from pigs and by choledochal duct cannulation from rats. In vitro, 1 µL and 5 µL of bile were mixed with 500 µL of anticoagulated autologous blood. The systemic effect was also assessed (i.v. bile, 200 µL/bwkg). Hemodynamic and hematological parameters were monitored, and red blood cell (RBC) deformability and aggregation were determined. RBC deformability significantly decreased with the increasing bile concentration in vitro (1 µL: p = 0.033; 5 µL: p < 0.001) in both species. The RBC aggregation index values were concomitantly worsened (1 µL: p < 0.001; 5 µL: p < 0.001). The mean arterial pressure and heart rate decreased by 15.2 ± 6.9% and 4.6 ± 2.1% in rats (in 10.6 ± 2.6 s) and by 32.1 ± 14% and 25.2 ± 11.63% in pigs (in 48.3 ± 18.9 s). Restoration of the values was observed in 45 ± 9.5 s (rats) and 130 ± 20 s (pigs). Bilhemia directly affected the hemodynamic parameters and caused micro-rheological deterioration. The magnitude and dynamics of the changes were different for the two species.

Low-dose biliatresone treatment of pregnant mice causes subclinical biliary disease in their offspring: Evidence for a spectrum of neonatal injury

Biliary atresia is a neonatal disease characterized by damage, inflammation, and fibrosis of the liver and bile ducts and by abnormal bile metabolism. It likely results from a prenatal environmental exposure that spares the mother and affects the fetus. Our aim was to develop a model of fetal injury by exposing pregnant mice to low-dose biliatresone, a plant toxin implicated in biliary atresia in livestock, and then to determine whether there was a hepatobiliary phenotype in their pups. Pregnant mice were treated orally with 15 mg/kg/d biliatresone for 2 days. Histology of the liver and bile ducts, serum bile acids, and liver immune cells of pups from treated mothers were analyzed at P5 and P21. Pups had no evidence of histological liver or bile duct injury or fibrosis at either timepoint. In addition, growth was normal. However, serum levels of glycocholic acid were elevated at P5, suggesting altered bile metabolism, and the serum bile acid profile became increasingly abnormal through P21, with enhanced glycine conjugation of bile acids. There was also immune cell activation observed in the liver at P21. These results suggest that prenatal exposure to low doses of an environmental toxin can cause subclinical disease including liver inflammation and aberrant bile metabolism even in the absence of histological changes. This finding suggests a wide potential spectrum of disease after fetal biliary injury.

Allocholic acid protects against α-naphthylisothiocyanate-induced cholestasis in mice by ameliorating disordered bile acid homeostasis

Cholestasis is a pathological condition characterized by disruptions in bile flow, leading to the accumulation of bile acids (BAs) in hepatocytes. Allocholic acid (ACA), a unique fetal BA known for its potent choleretic effects, reappears during liver regeneration and carcinogenesis. In this research, we investigated the protective effects and underlying mechanisms of ACA against mice with cholestasis brought on by α-naphthylisothiocyanate (ANIT). To achieve this, we combined network pharmacology, targeted BA metabolomics, and molecular biology approaches. The results demonstrated that ACA treatment effectively reduced levels of serum AST, ALP, and DBIL, and ameliorated the pathological injury caused by cholestasis. Network pharmacology analysis suggested that ACA primarily regulated BA and salt transport, along with the signaling pathway associated with bile secretion, to improve cholestasis. Subsequently, we examined changes in BA metabolism using UPLC-MS/MS. The findings indicated that ACA pretreatment induced alterations in the size, distribution, and composition of the liver BA pool. Specifically, it reduced the excessive accumulation of BAs, especially cholic acid (CA), taurocholic acid (TCA), and β-muricholic acid (β-MCA), facilitating the restoration of BA homeostasis. Furthermore, ACA pretreatment significantly downregulated the expression of hepatic BA synthase Cyp8b1, while enhancing the expression of hepatic efflux transporter Mrp4, as well as the renal efflux transporters Mdr1 and Mrp2. These changes collectively contributed to improved BA efflux from the liver and enhanced renal elimination of BAs. In conclusion, ACA demonstrated its potential to ameliorate ANIT-induced liver damage by inhibiting BA synthesis and promoting both BA efflux and renal elimination pathways, thus, restoring BA homeostasis.

Dietary chenodeoxycholic acid attenuates high-fat diet-induced growth retardation, lipid accumulation and bile acid metabolism disorder in the liver of yellow catfish Pelteobagrus fulvidraco

This experiment was conducted to investigate whether dietary chenodeoxycholic acid (CDCA) could attenuate high-fat (HF) diet-induced growth retardation, lipid accumulation and bile acid (BA) metabolism disorder in the liver of yellow catfish Pelteobagrus fulvidraco. Yellow catfish (initial weight: 4·40 (sem 0·08) g) were fed four diets: the control (105·8 g/kg lipid), HF diet (HF group, 159·6 g/kg lipid), the control supplemented with 0·9 g/kg CDCA (CDCA group) and HF diet supplemented with 0·9 g/kg CDCA (HF + CDCA group). CDCA supplemented in the HF diet significantly improved growth performance and feed utilisation of yellow catfish (P < 0·05). CDCA alleviated HF-induced increment of hepatic lipid and cholesterol contents by down-regulating the expressions of lipogenesis-related genes and proteins and up-regulating the expressions of lipololysis-related genes and proteins. Compared with the control group, CDCA group significantly reduced cholesterol level (P < 0·05). CDCA significantly inhibited BA biosynthesis and changed BA profile by activating farnesoid X receptor (P < 0·05). The contents of CDCA, taurochenodeoxycholic acid and glycochenodeoxycholic acid were significantly increased with the supplementation of CDCA (P < 0·05). HF-induced elevation of cholic acid content was significantly attenuated by the supplementation of CDCA (P < 0·05). Supplementation of CDCA in the control and HF groups could improve the liver antioxidant capacity. This study proved that CDCA could improve growth retardation, lipid accumulation and BA metabolism disorder induced by HF diet, which provided new insight into understanding the physiological functions of BA in fish.

Exploring Bile-Acid Changes and Microflora Profiles in Chicken Fatty Liver Disease Model

Excessive liver fat causes non-alcoholic fatty liver disease (NAFLD) in laying hens, reducing egg production. Addressing NAFLD via bile-acid metabolism is gaining attention. We induced NAFLD in 7-week-old ISA female chickens with a high-cholesterol, low-choline diet (CLC) for 6 weeks. LC/MS was used to analyze serum and cecal bile acids, while cecal digesta DNA underwent 16S rRNA sequencing. The distribution of bile acid varied in healthy (CON) and CLC-fed chickens. CLC increased secondary bile acids (TLCA, TUDCA, THDCA, TDCA) in serum and primary bile acids (CDCA, TCDCA, isoDCA) in serum, as well as glycochenodeoxycholic acid (GCDCA) in cecal contents. CLC upregulated bile-acid synthesis enzymes (CYP7A1, CYP8B1) in the liver. Bile-acid receptor gene expression (HNF4A, FXR, LXR) was similar between groups. Microbiota abundance was richer in CON (alpha-diversity), with distinct separation (beta-diversity) between CON and CLC. The Firmicutes/Bacteroidetes ratio slightly decreased in CLC. Taxonomic analysis revealed higher Bacteroides, Alistipes, Megamonas in CLC but lower Barnesiella. CLC had more Mucispirillum, Eubacterium_coprostanoligenes_group, Shuttleworthia, and Olsenella, while CON had more Enterococcus, Ruminococcaceae_UCG_014, and Faecalibacterium. This study unveils bile-acid and microflora changes in a chicken NAFLD model, enhancing our understanding of fatty liver disease metabolism and aiding targeted interventions.

Intestinal dual-specificity phosphatase 6 regulates the cold-induced gut microbiota remodeling to promote white adipose browning

Gut microbiota rearrangement induced by cold temperature is crucial for browning in murine white adipose tissue. This study provides evidence that DUSP6, a host factor, plays a critical role in regulating cold-induced gut microbiota rearrangement. When exposed to cold, the downregulation of intestinal DUSP6 increased the capacity of gut microbiota to produce ursodeoxycholic acid (UDCA). The DUSP6-UDCA axis is essential for driving Lachnospiraceae expansion in the cold microbiota. In mice experiencing cold-room temperature (CR) transitions, prolonged DUSP6 inhibition via the DUSP6 inhibitor (E/Z)-BCI maintained increased cecal UDCA levels and cold-like microbiota networks. By analyzing DUSP6-regulated microbiota dynamics in cold-exposed mice, we identified Marvinbryantia as a genus whose abundance increased in response to cold exposure. When inoculated with human-origin Marvinbryantia formatexigens, germ-free recipient mice exhibited significantly enhanced browning phenotypes in white adipose tissue. Moreover, M. formatexigens secreted the methylated amino acid Nε-methyl-L-lysine, an enriched cecal metabolite in Dusp6 knockout mice that reduces adiposity and ameliorates nonalcoholic steatohepatitis in mice. Our work revealed that host-microbiota coadaptation to cold environments is essential for regulating the browning-promoting gut microbiome.

Finasteride delays atherosclerosis progression in mice and is associated with a reduction in plasma cholesterol in men

Finasteride is commonly prescribed to treat benign prostate hyperplasia and male-pattern baldness in cis men and, more recently, trans individuals. However, the effect of finasteride on cardiovascular disease remains elusive. We evaluated the role of finasteride on atherosclerosis using low-density lipoprotein (LDL) receptor-deficient (Ldlr-/-) mice. Next, we examined the relevance to humans by analyzing the data deposited between 2009 and 2016 in the National Health and Nutrition Examination Survey. We show that finasteride reduces total plasma cholesterol and delays the development of atherosclerosis in Ldlr-/- mice. Finasteride reduced monocytosis, monocyte recruitment to the lesion, macrophage lesion content, and necrotic core area, the latter of which is an indicator of plaque vulnerability in humans. RNA sequencing analysis revealed a downregulation of inflammatory pathways and an upregulation of bile acid metabolism, oxidative phosphorylation, and cholesterol pathways in the liver of mice taking finasteride. Men reporting the use of finasteride showed lower plasma levels of cholesterol and LDL-cholesterol than those not taking the drug. Our data unveil finasteride as a potential treatment to delay cardiovascular disease in people by improving the plasma lipid profile.

Barley consumption under a high-fat diet suppresses lipogenic genes through altered intestinal bile acid composition

We evaluated whether barley flour consumption in a high-fat environment affects lipid metabolism through signals mediated by bile acids. Four-week-old mice were fed a high-fat diet supplemented with cellulose (HC) or β-glucan-rich barley flour (HB) for 12 weeks. Bile acid composition in the intestinal tract and feces was measured by GC/MS. Gene expression levels involved in bile acid metabolism in the liver and intestinal tract were determined by RT-PCR. Similar parameters were measured in mice treated with antibiotics (antibiotics-cellulose [AC] and antibiotics-barley [AB]) to reduce the activity of intestinal bacteria. The Results showed that the HB group had lower liver blood cholesterol and triglyceride levels than the HC group. The HB group showed a significant decrease in primary bile acids in the gastrointestinal tract compared to the HC group. On the other hand, the concentration of secondary bile acids relatively increased in the cecum and feces. In the liver, Fxr activation suppressed gene expression levels in synthesizing bile acids and lipids. Furthermore, in the gastrointestinal tract, Tgr5 was activated by increased secondary bile acids. Correspondingly, AMP levels were increased in the HB group compared to the HC group, AMPK was phosphorylated in the liver, and gene expression involved in lipid synthesis was downregulated. A comparison of the AC and AB groups treated with antibiotics did not confirm these effects of barley intake. In summary, our results suggest that the prevention of lipid accumulation by barley consumption involves signaling through changes in bile acid composition in the intestinal tract.

Bile Acids and Farnesoid X Receptor in Renal Pathophysiology

BACKGROUND

Bile acids (BAs) act not only as lipids and lipid-soluble vitamin detergents but also function as signaling molecules, participating in diverse physiological processes. The identification of BA receptors in organs beyond the enterohepatic system, such as the farnesoid X receptor (FXR), has initiated inquiries into their organ-specific functions. Among these organs, the kidney prominently expresses FXR.

SUMMARY

This review provides a comprehensive overview of various BA species identified in kidneys and delves into the roles of renal apical and basolateral BA transporters. Furthermore, we explore changes in BAs and their potential implications for various renal diseases, particularly chronic kidney disease. Lastly, we center our discussion on FXR, a key BA receptor in the kidney and a potential therapeutic target for renal diseases, providing current insights into the protective mechanisms associated with FXR agonist treatments.

KEY MESSAGES

Despite the relatively low concentrations of BAs in the kidney, their presence is noteworthy, with rodents and humans exhibiting distinct renal BA compositions. Renal BA transporters efficiently facilitate either reabsorption into systemic circulation or excretion into the urine. However, adaptive changes in BA transporters are evident during cholestasis. Various renal diseases are accompanied by alterations in BA concentrations and FXR expression. Consequently, the activation of FXR in the kidney could be a promising target for mitigating kidney damage.

Dietary nobiletin regulated cefuroxime- and levofloxacin-associated "gut microbiota-metabolism" imbalance and intestinal barrier dysfunction in mice

Nobiletin (NOB) exhibits significant biological activities and may be a potential dietary treatment for antibiotic-associated gut dysbiosis. In this study, mice were gavaged with 0.2 mL day-1 of 12.5 g L-1 cefuroxime (LFX) and 10 g L-1 levofloxacin (LVX) for a duration of 10 days, accompanied by 0.05% NOB to investigate the regulatory effect and potential mechanisms of NOB on antibiotic-induced intestinal microbiota disorder and intestinal barrier dysfunction. Our results indicated that dietary NOB improved the pathology of intestinal epithelial cells and the intestinal permeability by upregulating the expression of intestinal tight junction proteins (TJs) and the number of goblet cells. Furthermore, dietary NOB reduced the levels of serum lipopolysaccharide (LPS) and pro-inflammatory factors (TNF-α and IL-1β), thereby facilitating the restoration of the intestinal mucosal barrier. Additionally, dietary NOB increased the abundance of beneficial bacteria f_Lachnospiraceae and regulated the metabolic disorders of short-chain fatty acids (SCFAs) and bile acids (BAs). Notably, NOB supplementation resulted in elevated levels of butyric acid and lithocholic acid (LCA), which contributed to the repair of the intestinal mucosal barrier function and the maintenance of intestinal homeostasis. Collectively, our results propose a healthy dietary strategy for the prevention or mitigation of antibiotic-associated gut dysbiosis by dietary NOB.

Biodistribution Analysis of Peptide-Coated Magnetic Iron Nanoparticles: A Simple and Quantitative Method

Biodistribution tracks compounds or molecules of interest in vivo to understand a compound's anticipated efficacy and safety. Nanoparticles deliver nucleic acid and drug payloads and enhance tumor permeability due to multiple properties such as high surface area to volume ratio, surface functionalization, and modifications. Studying the in vivo biodistribution of nanoparticles documents the effectiveness and safety of nanoparticles and facilitates a more application-driven approach for nanoparticle development that allows for more successful translation into clinical use. In this study, we present a relatively simple method to determine the biodistribution of magnetic iron nanoparticles in mice. In vitro, cells take up branched amphiphilic peptide-coated magnetic nanobeads (BAPc-MNBs) like their counterparts, i.e., branched amphiphilic peptide capsules (BAPCs) with a hollow water-filled core. Both BAPc-MNBs and BAPCs have widespread applications as a nanodelivery system. We evaluated the BAPc-MNBs tissue distribution in wild-type mice injected intravenously (i.v.), intraperitoneally (i.p.), or orally gavaged to understand the biological interactions and to further the development of branched amphiphilic peptide-based nanoparticles. The magnetic nanoparticles allowed collection of the BAPc-MNBs from multiple organs by magnetic bead sorting, followed by a high-throughput screening for iron content. When injected i.v., nanoparticles were distributed widely to various organs before elimination from the system via the intestines in feces. The spleen accumulated the highest amount of BAPc-MNBs in mice administered NPs via i.v. and i.p. but not via oral gavage. Taken together, these data demonstrate that the magnetic sorting not only allowed quantification of the BAPc-MNBs but also identified the distribution of BAPc-MNBs after distinct administration methods.

Gut-Liver Axis as a Therapeutic Target for Drug-Induced Liver Injury

Drug-induced liver injury (DILI) is a liver disease that remains difficult to predict and diagnose, and the underlying mechanisms are yet to be fully clarified. The gut-liver axis refers to the reciprocal interactions between the gut and the liver, and its homeostasis plays a prominent role in maintaining liver health. It has been recently reported that patients and animals with DILI have a disrupted gut-liver axis, involving altered gut microbiota composition, increased intestinal permeability and lipopolysaccharide translocation, decreased short-chain fatty acids production, and impaired bile acid metabolism homeostasis. The present review will summarize the evidence from both clinical and preclinical studies about the role of the gut-liver axis in the pathogenesis of DILI. Moreover, we will focus attention on the potential therapeutic strategies for DILI based on improving gut-liver axis function, including herbs and phytochemicals, probiotics, fecal microbial transplantation, postbiotics, bile acids, and Farnesoid X receptor agonists.

Distinct bile acid alterations in response to a single administration of PFOA and PFDA in mice

Per- and polyfluoroalkyl substances (PFASs), a group of synthetic chemicals that were once widely used for industrial purposes and in consumer products, are widely found in the environment and in human blood due to their extraordinary resistance to degradation. Once inside the body, PFASs can activate nuclear receptors such as PPARα and CAR. The present study aimed to investigate the impact of perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA) on liver structure and functions, as well as bile acid homeostasis in mice. A single administration of 0.1 mmole/kg of PFDA, not PFOA, elevated serum ALT and bilirubin levels and caused cholestasis in WT mice. PFDA increased total and various bile acid species in serum but decreased them in the liver. Furthermore, in mouse livers, PFDA, not PFOA, down-regulated mRNA expression of uptake transporters (Ntcp, Oatp1a1, 1a4, 1b2, and 2b1) but induced efflux transporters (Bcrp, Mdr2, and Mrp2-4). In addition, PFDA, not PFOA, decreased Cyp7a1, 7b1, 8b1, and 27a1 mRNA expression in mouse livers with concomitant hepatic accumulation of cholesterol. In contrast, in PPARα-null mice, PFDA did not increase serum ALT, bilirubin, or total bile acids, but produced prominent hepatosteatosis; and the observed PFDA-induced expression changes of transporters and Cyps in WT mice were largely attenuated or abolished. In CAR-null mice, the observed PFDA-induced bile acid alterations in WT mice were mostly sustained. These results indicate that, at the dose employed, PFDA has more negative effects than PFOA on liver function. PPARα appears to play a major role in mediating most of PFDA-induced effects, which were absent or attenuated in PPARα-null mice. Lack of PPARα, however, exacerbated hepatic steatosis. Our findings indicate separated roles of PPARα in mediating the adaptive responses to PFDA: protective against hepatosteatosis but exacerbating cholestasis.

Therapeutic applications of gut microbes in cardiometabolic diseases: current state and perspectives

Cardiometabolic disease (CMD) encompasses a range of diseases such as hypertension, atherosclerosis, heart failure, obesity, and type 2 diabetes. Recent findings about CMD's interaction with gut microbiota have broadened our understanding of how diet and nutrition drive microbes to influence CMD. However, the translation of basic research into the clinic has not been smooth, and dietary nutrition and probiotic supplementation have yet to show significant evidence of the therapeutic benefits of CMD. In addition, the published reviews do not suggest the core microbiota or metabolite classes that influence CMD, and systematically elucidate the causal relationship between host disease phenotypes-microbiome. The aim of this review is to highlight the complex interaction of the gut microbiota and their metabolites with CMD progression and to further centralize and conceptualize the mechanisms of action between microbial and host disease phenotypes. We also discuss the potential of targeting modulations of gut microbes and metabolites as new targets for prevention and treatment of CMD, including the use of emerging technologies such as fecal microbiota transplantation and nanomedicine. KEY POINTS: • To highlight the complex interaction of the gut microbiota and their metabolites with CMD progression and to further centralize and conceptualize the mechanisms of action between microbial and host disease phenotypes. • We also discuss the potential of targeting modulations of gut microbes and metabolites as new targets for prevention and treatment of CMD, including the use of emerging technologies such as FMT and nanomedicine. • Our study provides insight into identification-specific microbiomes and metabolites involved in CMD, and microbial-host changes and physiological factors as disease phenotypes develop, which will help to map the microbiome individually and capture pathogenic mechanisms as a whole.

Clostridium scindens exacerbates experimental necrotizing enterocolitis via upregulation of the apical sodium-dependent bile acid transporter

Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in premature infants. Evidence indicates that bile acid homeostasis is disrupted during NEC: ileal bile acid levels are elevated in animals with experimental NEC, as is expression of the apical sodium-dependent bile acid transporter (Asbt). In addition, bile acids, which are synthesized in the liver, are extensively modified by the gut microbiome, including via the conversion of primary bile acids to more cytotoxic secondary forms. We hypothesized that the addition of bile acid-modifying bacteria would increase susceptibility to NEC in a neonatal rat model of the disease. The secondary bile acid-producing species Clostridium scindens exacerbated both incidence and severity of NEC. C. scindens upregulated the bile acid transporter Asbt and increased levels of intraenterocyte bile acids. Treatment with C. scindens also altered bile acid profiles and increased hydrophobicity of the ileal intracellular bile acid pool. The ability of C. scindens to enhance NEC requires bile acids, as pharmacological sequestration of ileal bile acids protects animals from developing disease. These findings indicate that bile acid-modifying bacteria can contribute to NEC pathology and provide additional evidence for the role of bile acids in the pathophysiology of experimental NEC.NEW & NOTEWORTHY Necrotizing enterocolitis (NEC), a life-threatening gastrointestinal emergency in premature infants, is characterized by dysregulation of bile acid homeostasis. We demonstrate that administering the secondary bile acid-producing bacterium Clostridium scindens enhances NEC in a neonatal rat model of the disease. C. scindens-enhanced NEC is dependent on bile acids and driven by upregulation of the ileal bile acid transporter Asbt. This is the first report of bile acid-modifying bacteria exacerbating experimental NEC pathology.

Vancomycin relieves tacrolimus-induced hyperglycemia by eliminating gut bacterial beta-glucuronidase enzyme activity

Up to 40% of transplant recipients treated long-term with tacrolimus (TAC) develop post-transplant diabetes mellitus (PTDM). TAC is an important risk factor for PTDM, but is also essential for immunosuppression after transplantation. Long-term TAC treatment alters the gut microbiome, but the mechanisms of TAC-induced gut microbiota in the pathogenesis of PTDM are poorly characterized. Here, we showed that vancomycin, an inhibitor of bacterial beta-glucuronidase (GUS), prevents TAC-induced glucose disorder and insulin resistance in mice. Metagenomics shows that GUS-producing bacteria are predominant and flourish in the TAC-induced hyperglycemia mouse model, with upregulation of intestinal GUS activity. Targeted metabolomics analysis revealed that in the presence of high GUS activity, the hydrolysis of bile acid (BAs)-glucuronic conjugates is increased and most BAs are overproduced in the serum and liver, which, in turn, activates the ileal farnesoid X receptor (FXR) and suppresses GLP-1 secretion by L-cells. The GUS inhibitor vancomycin significantly eliminated GUS-producing bacteria and inhibited bacterial GUS activity and BAs levels, thereby enhancing L-cell GLP-1 secretion and preventing hyperglycemia. Our results propose a novel clinical strategy for inhibiting the bacterial GUS enzyme to prevent hyperglycemia without requiring withdrawal of TAC treatment. This strategy exerted its effect through the ileal bile acid-FXR-GLP-1 pathway.

Physical exercise plays a role in rebalancing the bile acids of enterohepatic axis in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is considered as one of the most common diseases of lipid metabolism disorders, which is closely related to bile acids disorders and gut microbiota disorders. Bile acids are synthesized from cholesterol in the liver, and processed by gut microbiota in intestinal tract, and participate in metabolic regulation through the enterohepatic circulation. Bile acids not only promote the consumption and absorption of intestinal fat but also play an important role in biological metabolic signaling network, affecting fat metabolism and glucose metabolism. Studies have demonstrated that exercise plays an important role in regulating the composition and function of bile acid pool in enterohepatic axis, which maintains the homeostasis of the enterohepatic circulation and the health of the host gut microbiota. Exercise has been recommended by several health guidelines as the first-line intervention for patients with NAFLD. Can exercise alter bile acids through the microbiota in the enterohepatic axis? If so, regulating bile acids through exercise may be a promising treatment strategy for NAFLD. However, the specific mechanisms underlying this potential connection are largely unknown. Therefore, in this review, we tried to review the relationship among NAFLD, physical exercise, bile acids, and gut microbiota through the existing data and literature, highlighting the role of physical exercise in rebalancing bile acid and microbial dysbiosis.

Microalgae-derived sterols do not reduce the bioavailability of oral vitamin D3 in mice

Microalgae have drawn increasing attention as sustainable food sources, also because of their lipid-lowering phytosterols. As phytosterols are also discussed critically regarding their effect on the availability of fat-soluble vitamins, this study aimed to investigate microalgae-derived phytosterols and their effect on vitamin D status. GC-MS analysis showed large variations in the phytosterol profiles of microalgal species. The most frequent sterols were β-sitosterol and stigmasterol. To investigate their effects on vitamin D status, 40 mice were randomized to four groups and fed a vitamin D3-adequate (25 μg/kg) Western-style diet with 0% phytosterols (control) or 1% ergosterol (a fungal sterol not typical for microalgae), β-sitosterol or stigmasterol for four weeks. Contrary to the hypothesis that phytosterols adversely affect vitamin D uptake, mice fed β-sitosterol had significantly higher concentrations of vitamin D3 in plasma (3.15-fold, p<0.01), liver (3.15-fold, p<0.05), and skin (4.12-fold, p<0.005) than the control group. Small increases in vitamin D3 in plasma and skin were also observed in mice fed stigmasterol. In contrast, vitamin D3 levels in the ergosterol and control groups did not differ. The increased tissue levels of vitamin D3 in mice fed β-sitosterol and stigmasterol were not attributable to the observed reduction in liver triglycerides in these groups. The data rather suggest that changes in bile acid profiles were responsible for the beneficial effect of microalgae sterols on the bioavailability of vitamin D3. In conclusion, consumption of microalgae might not adversely affect vitamin D status.

Evidence for the contribution of the gut microbiome to obesity and its reversal

Obesity has become a worldwide pandemic affecting more than 650 million people and is associated with a high burden of morbidity. Alongside traditional risk factors for obesity, the gut microbiome has been identified as a potential factor in weight regulation. Although rodent studies suggest a link between the gut microbiome and body weight, human evidence for causality remains scarce. In this Review, we postulate that existing evidence remains to establish a contribution of the gut microbiome to the development of obesity in humans but that modified probiotic strains and supraphysiological dosages of microbial metabolites may be beneficial in combatting obesity.

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

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

Circulating neutrophil anti-pathogen dysfunction in cirrhosis

Neutrophils are the largest population of leucocytes and are among the first cells of the innate immune system to fight against intruding pathogens. In patients with cirrhosis, neutrophils exhibit altered functionality, including changes in phagocytic ability, bacterial killing, chemotaxis, degranulation, reactive oxygen species production and NET (neutrophil extracellular trap) formation. This results in their inability to mount an adequate antibacterial response and protect the individual from infection. Prognosis and survival in patients with cirrhosis are greatly influenced by the development of infectious complications. Multidrug-resistant bacterial infections in patients with cirrhosis are currently a growing problem worldwide; therefore, alternative methods for the prevention and treatment of bacterial infections in cirrhosis are urgently needed. The prevention and treatment of neutrophil dysfunction could be a potential way to protect patients from bacterial infections. However, the reasons for changes in neutrophil function in cirrhosis are still not completely understood, which limits the development of efficient therapeutic strategies. Both cellular and serum factors have been proposed to contribute to the functional impairment of neutrophils. Herein, we review the current knowledge on features and proposed causes of neutrophil dysfunction in cirrhosis, with a focus on current knowledge gaps and limitations, as well as opportunities for future investigations in this field.

The gut-liver axis and gut microbiota in health and liver disease

The trillions of microorganisms in the human intestine are important regulators of health, and disruptions in the gut microbial communities can cause disease. The gut, liver and immune system have a symbiotic relationship with these microorganisms. Environmental factors, such as high-fat diets and alcohol consumption, can disrupt and alter microbial communities. This dysbiosis can lead to dysfunction of the intestinal barrier, translocation of microbial components to the liver and development or progression of liver disease. Changes in metabolites produced by gut microorganisms can also contribute to liver disease. In this Review, we discuss the importance of the gut microbiota in maintenance of health and the alterations in microbial mediators that contribute to liver disease. We present strategies for modulation of the intestinal microbiota and/or their metabolites as potential treatments for liver disease.

A physiologically based model of bile acid metabolism in mice

Bile acid (BA) metabolism is a complex system that includes a wide variety of primary and secondary, as well as conjugated and unconjugated BAs that undergo continuous enterohepatic circulation (EHC). Alterations in both composition and dynamics of BAs have been associated with various diseases. However, a mechanistic understanding of the relationship between altered BA metabolism and related diseases is lacking. Computational modeling may support functional analyses of the physiological processes involved in the EHC of BAs along the gut-liver axis. In this study, we developed a physiologically based model of murine BA metabolism describing synthesis, hepatic and microbial transformations, systemic distribution, excretion, and EHC of BAs at the whole-body level. For model development, BA metabolism of specific pathogen-free (SPF) mice was characterized in vivo by measuring BA levels and composition in various organs, expression of transporters along the gut, and cecal microbiota composition. We found significantly different BA levels between male and female mice that could only be explained by adjusted expression of the hepatic enzymes and transporters in the model. Of note, this finding was in agreement with experimental observations. The model for SPF mice could also describe equivalent experimental data in germ-free mice by specifically switching off microbial activity in the intestine. The here presented model can therefore facilitate and guide functional analyses of BA metabolism in mice, e.g., the effect of pathophysiological alterations on BA metabolism and translation of results from mouse studies to a clinically relevant context through cross-species extrapolation.

Biodistribution Analysis of Peptide-Coated Magnetic Iron Nanoparticles: A Simple and Quantitative Method

Biodistribution is the tracking of compounds or molecules of interest in the subject which is integral to understanding their anticipated efficacy and safety. Nanoparticles are highly desirable delivery systems which have the ability to deliver higher nucleic acid and drug payloads and they have enhanced tumor permeability due to their unique properties such as high surface area to volume ratio. Studying the biodistribution of nanoparticles is crucial to understand their effectiveness and safety in vivo, facilitate a more application driven approach for nanoparticle development which will lead to their successful translation into clinical use. In this study, we present a relatively simple method to determine the biodistribution of magnetic iron nanoparticles in mice. Branched Amphiphilic Peptide coated Magnetic Nanobeads BAPc-MNBs like their counterpart i.e., Branched Amphiphilic Peptide capsules (BAPCs) with a hollow water-filled core, are readily taken up by cells in vitro and have widespread application as a nanodelivery systems. We evaluated the BAPc-MNBs tissue distribution in wildtype mice injected intravenously (i.v.), intraperitoneally (i.p.) or orally gavaged to understand the biological interactions of the peptide nanoparticles and to further the development of branched amphiphilic peptides-based nanoparticles. BAPc-MNBs were distributed widely to various organs when injected i.v. and were eliminated from the system via the intestines in feces. The spleen was found to accumulate the highest amount of BAPc-MNBs in mice administered the NPs i.v. and i.p. while they were not absorbed into the system via oral gavage. This study not only presents a relatively simple quantification method to determine in vivo biodistribution of magnetic iron nanoparticles that can be widely applied but also demonstrates the potential of Branched Amphiphilic Peptides in the form of BAPCs or BAPc-MNBs as a delivery system.

Hepatic Bile Acid Transporters and Drug-induced Hepatotoxicity

Drug-induced liver injury (DILI) remains a major concern in drug development from a patient safety perspective because it is the leading cause of acute liver failure. One mechanism of DILI is altered bile acid homeostasis and involves several hepatic bile acid transporters. Functional impairment of some hepatic bile acid transporters by drugs, disease, or genetic mutations may lead to toxic accumulation of bile acids within hepatocytes and increase DILI susceptibility. This review focuses on the role of hepatic bile acid transporters in DILI. Model systems, primarily in vitro and modeling tools, such as DILIsym, used in assessing transporter-mediated DILI are discussed. Due to species differences in bile acid homeostasis and drug-transporter interactions, key aspects and challenges associated with the use of preclinical animal models for DILI assessment are emphasized. Learnings are highlighted from three case studies of hepatotoxic drugs: troglitazone, tolvaptan, and tyrosine kinase inhibitors (dasatinib, pazopanib, and sorafenib). The development of advanced in vitro models and novel biomarkers that can reliably predict DILI is critical and remains an important focus of ongoing investigations to minimize patient risk for liver-related adverse reactions associated with medication use.

Analysis of the Bile Acid Composition in a Fibroblast Growth Factor 19-Expressing Liver-Humanized Mouse Model and Its Use for CYP3A4-Mediated Drug-Drug Interaction Studies

Numerous biomedical applications have been described for liver-humanized mouse models, such as in drug metabolism or drug-drug interaction (DDI) studies. However, the strong enlargement of the bile acid (BA) pool due to lack of recognition of murine intestine-derived fibroblast growth factor-15 by human hepatocytes and a resulting upregulation in the rate-controlling enzyme for BA synthesis, cytochrome P450 (CYP) 7A1, may pose a challenge in interpreting the results obtained from such mice. To address this challenge, the human fibroblast growth factor-19 (FGF19) gene was inserted into the Fah-/- , Rag2-/- , Il2rg-/- NOD (FRGN) mouse model, allowing repopulation with human hepatocytes capable of responding to FGF19. While a decrease in CYP7A1 expression in human hepatocytes from humanized FRGN19 mice (huFRGN19) and a concomitant reduction in BA production was previously shown, a detailed analysis of the BA pool in these animals has not been elucidated. Furthermore, there are sparse data on the use of this model to assess potential clinical DDI. In the present work, the change in BA composition in huFRGN19 compared with huFRGN control animals was systematically evaluated, and the ability of the model to recapitulate a clinically described CYP3A4-mediated DDI was assessed. In addition to a massive reduction in the total amount of BA, FGF19 expression in huFRGN19 mice resulted in significant changes in the profile of various primary, secondary, and sulfated BAs in serum and feces. Moreover, as observed clinically, administration of the pregnane X receptor agonist rifampicin reduced the oral exposure of the CYP3A4 substrate triazolam. SIGNIFICANCE STATEMENT: Transgenic expression of FGF19 normalizes the unphysiologically high level of bile acids in a chimeric liver-humanized mouse model and leads to massive changes in bile acid composition. These adaptations could overcome one of the potential impediments in the use of these mouse models for drug-drug interaction studies.

Hepatotoxicity of AKR1C3 Inhibitor BAY1128688: Findings from an Early Terminated Phase IIa Trial for the Treatment of Endometriosis

INTRODUCTION

BAY1128688 is a selective inhibitor of aldo-keto reductase family 1 member C3 (AKR1C3), an enzyme implicated in the pathology of endometriosis and other disorders. In vivo animal studies suggested a potential therapeutic application of BAY1128688 in treating endometriosis. Early clinical studies in healthy volunteers supported the start of phase IIa.

OBJECTIVE

This manuscript reports the results of a clinical trial (AKRENDO1) assessing the effects of BAY1128688 in adult premenopausal women with endometriosis-related pain symptoms over a 12-week treatment period.

METHODS

Participants in this placebo-controlled, multicenter phase IIa clinical trial (NCT03373422) were randomized into one of five BAY1128688 treatment groups: 3 mg once daily (OD), 10 mg OD, 30 mg OD, 30 mg twice daily (BID), 60 mg BID; or a placebo group. The efficacy, safety, and tolerability of BAY1128688 were investigated.

RESULTS

Dose-/exposure-dependent hepatotoxicity was observed following BAY1128688 treatment, characterized by elevations in serum alanine transferase (ALT) occurring at around 12 weeks of treatment and prompting premature trial termination. The reduced number of valid trial completers precludes conclusions regarding treatment efficacy. The pharmacokinetics and pharmacodynamics of BAY1128688 among participants with endometriosis were comparable with those previously found in healthy volunteers and were not predictive of the subsequent ALT elevations observed.

CONCLUSIONS

The hepatotoxicity of BAY1128688 observed in AKRENDO1 was not predicted by animal studies nor by studies in healthy volunteers. However, in vitro interactions of BAY1128688 with bile salt transporters indicated a potential risk factor for hepatotoxicity at higher doses. This highlights the importance of in vitro mechanistic and transporter interaction studies in the assessment of hepatoxicity risk and suggests further mechanistic understanding is required.

CLINICAL TRIAL REGISTRATION

NCT03373422 (date registered: November 23, 2017).

Targeting gut microbiota and immune crosstalk: potential mechanisms of natural products in the treatment of atherosclerosis

Atherosclerosis (AS) is a chronic inflammatory reaction that primarily affects large and medium-sized arteries. It is a major cause of cardiovascular disease and peripheral arterial occlusive disease. The pathogenesis of AS involves specific structural and functional alterations in various populations of vascular cells at different stages of the disease. The immune response is involved throughout the entire developmental stage of AS, and targeting immune cells presents a promising avenue for its treatment. Over the past 2 decades, studies have shown that gut microbiota (GM) and its metabolites, such as trimethylamine-N-oxide, have a significant impact on the progression of AS. Interestingly, it has also been reported that there are complex mechanisms of action between GM and their metabolites, immune responses, and natural products that can have an impact on AS. GM and its metabolites regulate the functional expression of immune cells and have potential impacts on AS. Natural products have a wide range of health properties, and researchers are increasingly focusing on their role in AS. Now, there is compelling evidence that natural products provide an alternative approach to improving immune function in the AS microenvironment by modulating the GM. Natural product metabolites such as resveratrol, berberine, curcumin, and quercetin may improve the intestinal microenvironment by modulating the relative abundance of GM, which in turn influences the accumulation of GM metabolites. Natural products can delay the progression of AS by regulating the metabolism of GM, inhibiting the migration of monocytes and macrophages, promoting the polarization of the M2 phenotype of macrophages, down-regulating the level of inflammatory factors, regulating the balance of Treg/Th17, and inhibiting the formation of foam cells. Based on the above, we describe recent advances in the use of natural products that target GM and immune cells crosstalk to treat AS, which may bring some insights to guide the treatment of AS.

Altered bile acid metabolism in skin tissues in response to ionizing radiation: deoxycholic acid (DCA) as a novel treatment for radiogenic skin injury

OBJECTIVE

Radiogenic skin injury (RSI) is a common complication during cancer radiotherapy or accidental exposure to radiation. The aim of this study is to investigate the metabolism of bile acids (BAs) and their derivatives during RSI.

METHODS

Rat skin tissues were irradiated by an X-ray linear accelerator. The quantification of BAs and their derivatives were performed by liquid chromatography-mass spectrometry (LC-MS)-based quantitative analysis. Key enzymes in BA biosynthesis were analyzed from single-cell RNA sequencing (scRNA-Seq) data of RSI in the human patient and animal models. The in vivo radioprotective effect of deoxycholic acid (DCA) was detected in irradiated SD rats.

RESULTS

Twelve BA metabolites showed significant differences during the progression of RSI. Among them, the levels of cholic acid (CA), DCA, muricholic acid (MCA), chenodeoxycholic acid (CDCA), glycocholic acid (GCA), glycohyodeoxycholic acid (GHCA), 12-ketolithocholic acid (12-ketoLCA) and ursodeoxycholic acid (UDCA) were significantly elevated in irradiated skin, whereas lithocholic acid (LCA), tauro-β-muricholic acid (Tβ-MCA) and taurocholic acid (TCA) were significantly decreased. Additionally, the results of scRNA-Seq indicated that genes involved in 7a-hydroxylation process, the first step in BA synthesis, showed pronounced alterations in skin fibroblasts or keratinocytes. The alternative pathway of BA synthesis is more actively altered than the classical pathway after ionizing radiation. In the model of rat radiogenic skin damage, DCA promoted wound healing and attenuated epidermal hyperplasia.

CONCLUSIONS

Ionizing radiation modulates the metabolism of BAs. DCA is a prospective therapeutic agent for the treatment of RSI.

FXR Friend-ChIPs in the Enterohepatic System

Chronic liver diseases encompass a wide spectrum of hepatic maladies that often result in cholestasis or altered bile acid secretion and regulation. Incidence and cost of care for many chronic liver diseases are rising in the United States with few Food and Drug Administration-approved drugs available for patient treatment. Farnesoid X receptor (FXR) is the master regulator of bile acid homeostasis with an important role in lipid and glucose metabolism and inflammation. FXR has served as an attractive target for management of cholestasis and fibrosis; however, global FXR agonism results in adverse effects in liver disease patients, severely affecting quality of life. In this review, we highlight seminal studies and recent updates on the FXR proteome and identify gaps in knowledge that are essential for tissue-specific FXR modulation. In conclusion, one of the greatest unmet needs in the field is understanding the underlying mechanism of intestinal versus hepatic FXR function.

Blood metabolomics reveals the therapeutic effect of Pueraria polysaccharide on calf diarrhea

BACKGROUND

Neonatal calf diarrhea (NCD) is typically treated with antibiotics, while long-term application of antibiotics induces drug resistance and antibiotic residues, ultimately decreasing feed efficiency. Pueraria polysaccharide (PPL) is a versatile antimicrobial, immunomodulatory, and antioxidative compound. This study aimed to compare the therapeutic efficacy of different doses of PPL (0.2, 0.4, 0.8 g/kg body weight (BW)) and explore the effect of plasma metabolites in diarrheal calves by the best dose of PPL.

RESULTS

PPL could effectively improve the daily weight gain, fecal score, and dehydration score, and the dosage of 0.4 g/kg BW could reach curative efficacy against calf diarrhea (with effective rates 100.00%). Metabolomic analysis suggested that diarrhea mainly affect the levels of taurocholate, DL-lactate, LysoPCs, and intestinal flora-related metabolites, trimethylamine N-oxide; however, PPL improved liver function and intestinal barrier integrity by modulating the levels of DL-lactate, LysoPC (18:0/0:0) and bilirubin, which eventually attenuated neonatal calf diarrhea. It also suggested that the therapeutic effect of PPL is related to those differential metabolites in diarrheal calves.

CONCLUSIONS

The results showed that 0.4 g/kg BW PPL could restore the clinical score of diarrhea calves by improving the blood indexes, biochemical indexes, and blood metabolites. And it is a potential medicine for the treatment of calf diarrhea.

The Potential of Bile Acids as Biomarkers for Metabolic Disorders

Bile acids (BAs) are well known to facilitate the absorption of dietary fat and fat-soluble molecules. These unique steroids also function by binding to the ubiquitous cell membranes and nuclear receptors. As chemical signals in gut-liver axis, the presence of metabolic disorders such as nonalcoholic fatty liver disease (NAFLD), type 2 diabetes mellitus (T2DM), and even tumors have been reported to be closely related to abnormal levels of BAs in the blood and fecal metabolites of patients. Thus, the gut microbiota interacting with BAs and altering BA metabolism are critical in the pathogenesis of numerous chronic diseases. This review intends to summarize the mechanistic links between metabolic disorders and BAs in gut-liver axis, and such stage-specific BA perturbation patterns may provide clues for developing new auxiliary diagnostic means.