Differential activation of the human farnesoid X receptor depends on the pattern of expressed isoforms and the bile acid pool composition. Biochem Pharmacol. 2013;86:926-939. [PMID: 23928191 DOI: 10.1016/j.bcp.2013.07.022]

Farnesoid X receptor‑driven metabolic plasticity: Bridging physiological adaptation and malignant transformation in lipid handling (Review)

Metabolic reprogramming represents a hallmark of malignant tumors, manifested through progressive alterations in nutrient utilization patterns during oncogenesis. As fundamental constituents of biological membranes, essential components of signaling pathways, and critical energy substrates, lipids undergo comprehensive metabolic restructuring in neoplastic cells. This lipid remodeling confers enhanced adaptability to sustain uncontrolled proliferation while promoting aggressive migratory phenotypes. Farnesoid X receptor (FXR), a ligand‑activated nuclear receptor responsive to bile acid (BA) derivatives and cholesterol metabolites, orchestrates key aspects of lipid homeostasis. Its regulatory network encompasses cholesterol/BA metabolism, fatty acid (FA) metabolism and plasma lipoprotein trafficking pathways. Emerging evidence positions FXR as a pleiotropic modulator in oncogenesis, with dysregulated expression patterns documented across multiple tumor lineages and premalignant lesions. This mechanistic understanding has propelled FXR‑targeted therapeutics into the forefront of precision oncology development. The present review critically examines the FXR‑lipid axis in lipid‑enriched malignancies, with particular emphasis on its regulatory circuitry governing BA flux and FA turnover.

Alternative splicing: hallmark and therapeutic opportunity in metabolic liver disease

Metabolic dysfunction-associated fatty liver disease (MAFLD) has become the leading cause of chronic liver disease worldwide, with fibrosis recognized as the main prognostic factor and therapeutic target. While early-stage fibrosis is reversible, advanced fibrosis poses a significant clinical challenge due to limited treatment options, highlighting the need for innovative management strategies. Recent studies have shown that alternative pre-mRNA splicing, a critical mechanism regulating gene expression and protein diversity, plays a fundamental role in the pathogenesis of MAFLD and associated fibrosis. Understanding the complex relationship between alternative splicing and fibrosis progression in MAFLD could pave the way for novel therapeutic approaches and improve clinical outcomes. In this review, we describe the intricate mechanisms of alternative splicing in fibrosis associated with MAFLD. Specifically, we explored the pivotal of splicing factors, and RNA-binding proteins, highlighting their critical interactions with metabolic and epigenetic regulators. Furthermore, we provide an overview of the latest advancements in splicing-based therapeutic strategies and biomarker development. Particular emphasis is placed on the potential application of antisense oligonucleotides for rectifying splicing anomalies, thereby laying the foundation for precision medicine approaches in the treatment of MAFLD-associated fibrosis.

β-Sitosterol protects against lithocholic acid-induced hepatotoxicity and cholestasis via farnesoid X receptor-mediated regulation of transporters and enzymes in vitro and in vivo

Cholestasis arises as a clinical syndrome triggered by the accumulation and aggregation of bile acids. Currently, there are only a few treatment options available for cholestasis. Therefore, it is necessary to explore novel therapeutic strategies. β-sitosterol (SIT), the phytosterol most abundantly found in plants, exhibits diverse pharmacological activities. This study examined SIT's protective role against hepatotoxicity and cholestasis induced by lithocholic acid (LCA). LCA was administered twice a day to male C57BL/6 mice for four days to cause hepatotoxicity and cholestasis. Assessment of the improvement in cholestasis following SIT treatment used H&E staining and serum biomarkers. Mice hepatocyte culture, real-time PCR, immunofluorescence staining, and Western blot were utilized to clarify the mechanisms of SIT hepatoprotection. Furthermore, molecular docking and dual-luciferase reporter gene analysis were utilized to show that SIT would activate the farnesoid X receptor (FXR). In vivo, SIT reduced bile acid accumulation by inducing the bile salt export pump (Bsep), multidrug resistance-related protein 2 (Mrp2), and reduced hepatic uptake of bile acids by inhibiting Na+/taurocholate co-transporting polypeptide (Ntcp), and cholesterol 7α-hydroxylase (Cyp7a1) and oxysterol 12α-hydroxylase (Cyp8b1) while in vitro, it restored FXR expression and transcriptional activity. Besides, SIT decreased hepatic inflammation by suppressing the inflammatory genes NF-κB p65 and p-NF-κB p65, TNF-α, IL-6, and IL-1β. However, the hepatoprotective effects of SIT were abolished by the FXR antagonist guggulsterone in vivo and FXR siRNA in vitro, confirming FXR-dependent mechanisms. In conclusion, SIT protects against LCA-induced hepatotoxicity and cholestasis via FXR activation. These findings highlight SIT as a promising therapeutic candidate for cholestasis.

Bile acid and microbiome interactions in the developing child

Interactions between the gut microbiome and bile acids are complex and are linked to outcomes in pediatric liver disease by mechanisms that are incompletely understood. In adults, primary bile acids are synthesized in the liver and secreted into the intestine, where complex communities of gut microbes deconjugate, oxidize, epimerize, and 7α-dehydroxylate bile acids into a diverse array of unconjugated, secondary, allo-, iso-, and oxo-bile acids. In contrast, the infant gut microbiota contains a simple, Bifidobacterium-dominant community that transitions to a more diverse, adult-like community as additional microbes colonize the gut. This microbial succession gradually confers deconjugation, oxidation, epimerization, and 7α-dehydroxylation activities that mature the bile acid pool from a profile dominated by primary bile acids early in life to a more diverse, adult-like bile acid profile in later childhood. Altered bile acid profiles in pediatric cholestatic disorders have the potential to change the developmental trajectory of the microbiome. Conversely, alterations in the gut microbiome may re-shape the bile acid pool and hepatic bile acid metabolism. Understanding the mechanisms underlying these interactions will increase our understanding of liver pathophysiology and will motivate new therapeutic strategies for pediatric hepatic disorders. This review aims to highlight differences between the pediatric and adult intestinal microbiome and bile acid pool, and to discuss interactions between gut microbes and bile acids that are critical in early life and that may impact outcomes in infants and children with cholestatic liver disease, including biliary atresia.

β-sitosterol protects against ANIT-induced hepatotoxicity and cholestasis via FXR activation

Cholestasis, a condition marked by bile acid accumulation in the liver and body systems, leads to liver dysfunction and cirrhosis. Currently, ursodeoxycholic acid (UDCA) and obeticholic acid (OCA) are the only two FDA-approved drugs for Cholestasis. Thus, new therapeutic approaches need to be developed. In this study, we validated the liver-protective properties of β-sitosterol (SIT), a key bioactive element abundant in plants, against hepatic toxicity and cholestasis induced by alpha-naphthylisothiocyanate(ANIT), while elucidating its mechanisms of action both in vivo and in vitro. SIT's FXR activation was confirmed via molecular docking and dual-luciferase assays. In the mechanisms of SIT hepatoprotection, the expression levels of bile salt export pump (Bsep) and multidrug resistance protein2 (Mrp2) which are bile acid efflux transporter, and sulfate transferase 2a1 (Sult2a1) which is a bile acid metabolizing enzyme were all increased by SIT, whereas the expression of uptake transporter sodium taurocholate transporting polypeptide (Ntcp), bile acid synthesis enzyme cholesterol 7α-hydroxylase (Cyp7a1) and oxysterol 12α-hydroxylase (Cyp8b1) was decreased by SIT. In addition, SIT alleviated liver inflammation by suppressing inflammatory factor expression. However, FXR antagonist guggulsterone and FXR siRNA abolished SIT's improvements in liver histology, bile acid transporters, and enzymes. Conclusively, through activating FXR, SIT provides a protective effect against hepatotoxicity and cholestasis. SIT might serve as a new potential therapeutic strategy for the treatment of cholestatic liver diseases.

Gut Microbiome and Bile Acid Interactions: Mechanistic Implications for Cholangiocarcinoma Development, Immune Resistance, and Therapy

Cholangiocarcinoma (CCA) is a rare but highly malignant carcinoma of bile duct epithelial cells with a poor prognosis. The major risk factors of CCA carcinogenesis and progression are cholestatic liver diseases. The key feature of primary sclerosing cholangitis and primary biliary cholangitis is chronic cholestasis. It indicates a slowdown of hepatocyte secretion of biliary lipids and metabolites into bile as well as a slowdown of enterohepatic circulation (bile acid recirculation) of bile acids with dysbiosis of the gut microbiome. This leads to enterohepatic recirculation and an increase of toxic secondary bile acids. Alterations of serum and liver bile acid compositions via the disturbed enterohepatic circulation of bile acids and the disturbance of the gut microbiome then activate a series of hepatic and cancer cell signaling pathways that promote CCA carcinogenesis and progression. This review focuses on the mechanistic roles of bile acids and the gut microbiome in the pathogenesis and progression of CCA. It also evaluates the therapeutic potential of targeting the gut microbiome and bile acid-mediated signaling pathways for the therapy and prophylaxis of CCA.

A Collection of Novel Antitumor Agents That Regulate Lipid Metabolism in the Tumor Microenvironment

Lipid metabolism disorder is the cause of one of the most significant metabolic changes in tumors. In the process of tumor occurrence and development, tumor cells choose a continuous metabolic adaptation to accommodate the changing environment to the maximum extent possible. In a variety of tumors, the uptake, production, and storage of lipids are generally upregulated. Tumor cells take advantage of lipid metabolism to access basic energy, biofilm components, and signal molecules of the tumor microenvironment required for proliferation, survival, invasion, and metastasis. This Perspective briefly uncovers the main metabolic processes and key factors involved in lipid metabolism reprogramming, mainly related to lipid uptake, de novo synthesis and storage of fatty acids, oxidation of fatty acids, cholesterol synthesis, and related regulatory factors. From a medicinal chemistry perspective, agents against related key targets are reviewed, expecting to pave the way for promising antitumor drugs with prospects for application through lipid metabolism reprogramming.

Alternative splicing is an FXRα loss-of-function mechanism and impacts energy metabolism in hepatocarcinoma cells

Farnesoid X receptor α (FXRα, NR1H4) is a bile acid-activated nuclear receptor that regulates the expression of glycolytic and lipogenic target genes by interacting with the 9-cis-retinoic acid receptor α (RXRα, NR2B1). Along with cofactors, the FXRα proteins reported thus far in humans and rodents have been observed to regulate both isoform (α1-4)- and tissue-specific gene expression profiles to integrate energy balance and metabolism. Here, we studied the biological functions of an FXRα naturally occurring spliced exon 5 isoform (FXRαse5) lacking the second zinc-binding module of the DNA-binding domain. We demonstrate spliced exon 5 FXRα expression in all FXRα-expressing human and mouse tissues and cells, and that it is unable to bind to its response element or activate FXRα dependent transcription. In parallel, this spliced variant displays differential interaction capacities with its obligate heterodimer partner retinoid X receptor α that may account for silencing of this permissive dimer for signal transduction. Finally, deletion of exon 5 by gene edition in HepG2 cells leads to FXRα loss-of-function, increased expression of LRH1 metabolic sensor and CD36 fatty acid transporter in conjunction with changes in glucose and triglycerides homeostasis. Together, these findings highlight a novel mechanism by which alternative splicing may regulate FXRα gene function to fine-tune adaptive and/or metabolic responses. This finding deepens our understanding on the role of splicing events in hindering FXRα activity to regulate specific transcriptional programs and their contribution in modifying energy metabolism in normal tissues and metabolic diseases.

Activation of Nrf2 and FXR via Natural Compounds in Liver Inflammatory Disease

Liver inflammation is frequently linked to oxidative stress and dysregulation of bile acid and fatty acid metabolism. This review focuses on the farnesoid X receptor (FXR), a critical regulator of bile acid homeostasis, and its interaction with the nuclear factor erythroid 2-related factor 2 (Nrf2), a key modulator of cellular defense against oxidative stress. The review explores the interplay between FXR and Nrf2 in liver inflammatory diseases, highlighting the potential therapeutic effects of natural FXR agonists. Specifically, compounds such as auraptene, cafestol, curcumin, fargesone A, hesperidin, lycopene, oleanolic acid, resveratrol, rutin, ursolic acid, and withaferin A are reviewed for their ability to modulate both the FXR and Nrf2 pathways. This article discusses their potential to alleviate liver inflammation, oxidative stress, and damage in diseases such as metabolic-associated fatty liver disease (MAFLD), cholestatic liver injury, and viral hepatitis. In addition, we address the molecular mechanisms driving liver inflammation, including oxidative stress, immune responses, and bile acid accumulation, while also summarizing relevant experimental models. This review emphasizes the promising therapeutic potential of targeting both the Nrf2 and FXR pathways using natural compounds, paving the way for future treatments for liver diseases. Finally, the limitations of the clinical application were indicated, and further research directions were proposed.

The role of botanical triterpenoids and steroids in bile acid metabolism, transport, and signaling: Pharmacological and toxicological implications

Bile acids (BAs) are synthesized by the host liver from cholesterol and are delivered to the intestine, where they undergo further metabolism by gut microbes and circulate between the liver and intestines through various transporters. They serve to emulsify dietary lipids and act as signaling molecules, regulating the host's metabolism and immune homeostasis through specific receptors. Therefore, disruptions in BA metabolism, transport, and signaling are closely associated with cholestasis, metabolic disorders, autoimmune diseases, and others. Botanical triterpenoids and steroids share structural similarities with BAs, and they have been found to modulate BA metabolism, transport, and signaling, potentially exerting pharmacological or toxicological effects. Here, we have updated the research progress on BA, with a particular emphasis on new-found microbial BAs. Additionally, the latest advancements in targeting BA metabolism and signaling for disease treatment are highlighted. Subsequently, the roles of botanical triterpenoids in BA metabolism, transport, and signaling are examined, analyzing their potential pharmacological, toxicological, or drug interaction effects through these mechanisms. Finally, a research paradigm is proposed that utilizes the gut microbiota as a link to interpret the role of these important natural products in BA signaling.

Biotransformation of chenodeoxycholic acid by human intestinal fungi and the agonistic effects on FXR

Bile acids play a vital role in modulating host metabolism, with chenodeoxycholic acid (CDCA) standing out as a primary bile acid that naturally activates farnesoid X receptor (FXR). In this study, we investigated the microbial transformations of CDCA by seven human intestinal fungal species. Our findings revealed that hydroxylation and dehydrogenation were the most prevalent metabolic pathways. Incubation of CDCA with Rhizopus microspores (PT2906) afforded eight undescribed compounds (6-13) alongside five known analogs (1-5) which were elucidated by HRESI-MS and NMR data. Notably, compounds 8, 12 and 13 exhibited an inhibitory effect on FXR in contrast to the FXR activation observed with CDCA in vitro assays. This study shone a light on the diverse transformations of CDCA by intestinal fungi, unveiling potential modulators of FXR activity with implications for host metabolism.

Microbial metabolite trimethylamine-N-oxide induces intestinal carcinogenesis through inhibiting farnesoid X receptor signaling

PURPOSE

Microbial dysbiosis is considered as a hallmark of colorectal cancer (CRC). Trimethylamine-N-oxide (TMAO) as a gut microbiota-dependent metabolite has recently been implicated in CRC development. Nevertheless, evidence relating TMAO to intestinal carcinogenesis remains largely unexplored. Herein, we aimed to examine the crucial role of TMAO in CRC progression.

METHODS

Apcmin/+ mice were treated with TMAO or sterile PBS for 14 weeks. Intestinal tissues were isolated to evaluate the effects of TMAO on the malignant transformation of intestinal adenoma. The gut microbiota of mouse feces was detected by 16S rRNA sequencing analysis. HCT-116 cells were used to provide further evidence of TMAO on the progression of CRC.

RESULTS

TMAO administration increased tumor cell and stem cell proliferation, and decreased apoptosis, accompanied by DNA damage and gut barrier impairment. Gut microbiota analysis revealed that TMAO induced changes in the intestinal microbial community structure, manifested as reduced beneficial bacteria. Mechanistically, TMAO bound to farnesoid X receptor (FXR), thereby inhibiting the FXR-fibroblast growth factor 15 (FGF15) axis and activating the Wnt/β-catenin signaling pathway, whereas the FXR agonist GW4064 could blunt TMAO-induced Wnt/β-catenin pathway activation.

CONCLUSION

The microbial metabolite TMAO can enhance intestinal carcinogenesis by inhibiting the FXR-FGF15 pathway.

Zearalenone Decreases Food Intake by Disrupting the Gut-Liver-Hypothalamus Axis Signaling via Bile Acids

Zearalenone (ZEN) is a mycotoxin that is harmful to humans and animals. In this study, female and male rats were exposed to ZEN, and the results showed that ZEN reduced the farnesoid X receptor (FXR) expression levels in the liver and disrupted the enterohepatic circulation of bile acids (BAs). A decrease in food intake induced by ZEN was negatively correlated with an increase in the level of total BAs. BA-targeted metabolomics revealed that ZEN increased glycochenodeoxycholic acid levels and decreased the ratio of conjugated BAs to unconjugated BAs, which further increased the hypothalamic FXR expression levels. Preventing the increase in total BA levels induced by ZEN via Lactobacillus rhamnosus GG intervention restored the appetite. In conclusion, ZEN disrupted the enterohepatic circulation of BAs to decrease the level of food intake. This study reveals a possible mechanism by which ZEN affects food intake and provides a new approach to decrease the toxic effects of ZEN.

Targeting Farnesoid X Receptor in Tumor and the Tumor Microenvironment: Implication for Therapy

The farnesoid-X receptor (FXR), a member of the nuclear hormone receptor superfamily, can be activated by bile acids (BAs). BAs binding to FXR activates BA signaling which is important for maintaining BA homeostasis. FXR is differentially expressed in human organs and exists in immune cells. The dysregulation of FXR is associated with a wide range of diseases including metabolic disorders, inflammatory diseases, immune disorders, and malignant neoplasm. Recent studies have demonstrated that FXR influences tumor cell progression and development through regulating oncogenic and tumor-suppressive pathways, and, moreover, it affects the tumor microenvironment (TME) by modulating TME components. These characteristics provide a new perspective on the FXR-targeted therapeutic strategy in cancer. In this review, we have summarized the recent research data on the functions of FXR in solid tumors and its influence on the TME, and discussed the mechanisms underlying the distinct function of FXR in various types of tumors. Additionally, the impacts on the TME by other BA receptors such as takeda G protein-coupled receptor 5 (TGR5), sphingosine-1-phosphate receptor 2 (S1PR2), and muscarinic receptors (CHRM2 and CHRM3), have been depicted. Finally, the effects of FXR agonists/antagonists in a combination therapy with PD1/PD-L1 immune checkpoint inhibitors and other anti-cancer drugs have been addressed.

The Role of the FGF19 Family in the Pathogenesis of Gestational Diabetes: A Narrative Review

Gestational diabetes mellitus (GDM) is one of the most common pregnancy complications. Understanding the pathogenesis and appropriate diagnosis of GDM enables the implementation of early interventions during pregnancy that reduce the risk of maternal and fetal complications. At the same time, it provides opportunities to prevent diabetes, metabolic syndrome, and cardiovascular diseases in women with GDM and their offspring in the future. Fibroblast growth factors (FGFs) represent a heterogeneous family of signaling proteins which play a vital role in cell proliferation and differentiation, repair of damaged tissues, wound healing, angiogenesis, and mitogenesis and also affect the regulation of carbohydrate, lipid, and hormone metabolism. Abnormalities in the signaling function of FGFs may lead to numerous pathological conditions, including metabolic diseases. The FGF19 subfamily, also known as atypical FGFs, which includes FGF19, FGF21, and FGF23, is essential in regulating metabolic homeostasis and acts as a hormone while entering the systemic circulation. Many studies have pointed to the involvement of the FGF19 subfamily in the pathogenesis of metabolic diseases, including GDM, although the results are inconclusive. FGF19 and FGF21 are thought to be associated with insulin resistance, an essential element in the pathogenesis of GDM. FGF21 may influence placental metabolism and thus contribute to fetal growth and metabolism regulation. The observed relationship between FGF21 and increased birth weight could suggest a potential role for FGF21 in predicting future metabolic abnormalities in children born to women with GDM. In this group of patients, different mechanisms may contribute to an increased risk of cardiovascular diseases in women in later life, and FGF23 appears to be their promising early predictor. This study aims to present a comprehensive review of the FGF19 subfamily, emphasizing its role in GDM and predicting its long-term metabolic consequences for mothers and their offspring.

Pre-RNA splicing in metabolic homeostasis and liver disease

The liver plays a key role in sensing nutritional and hormonal inputs to maintain metabolic homeostasis. Recent studies into pre-mRNA splicing and alternative splicing (AS) and their effects on gene expression have revealed considerable transcriptional complexity in the liver, both in health and disease. While the contribution of these mechanisms to cell and tissue identity is widely accepted, their role in physiological and pathological contexts within tissues is just beginning to be appreciated. In this review, we showcase recent studies on the splicing and AS of key genes in metabolic pathways in the liver, the effect of metabolic signals on the spliceosome, and therapeutic intervention points based on RNA splicing.

Current Therapeutical Approaches Targeting Lipid Metabolism in NAFLD

Nonalcoholic fatty liver disease (NAFLD, including nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH)) is a high-prevalence disorder, affecting about 1 billion people, which can evolve to more severe conditions like cirrhosis or hepatocellular carcinoma. NAFLD is often concomitant with conditions of the metabolic syndrome, such as central obesity and insulin-resistance, but a specific drug able to revert NAFL and prevent its evolution towards NASH is still lacking. With the liver being a key organ in metabolic processes, the potential therapeutic strategies are many, and range from directly targeting the lipid metabolism to the prevention of tissue inflammation. However, side effects have been reported for the drugs tested up to now. In this review, different approaches to the treatment of NAFLD are presented, including newer therapies and ongoing clinical trials. Particular focus is placed on the reverse cholesterol transport system and on the agonists for nuclear factors like PPAR and FXR, but also drugs initially developed for other conditions such as incretins and thyromimetics along with validated natural compounds that have anti-inflammatory potential. This work provides an overview of the different therapeutic strategies currently being tested for NAFLD, other than, or along with, the recommendation of weight loss.

Relevance of Bile Acids in Cholangiocarcinoma Pathogenesis: Critical Revision and Future Directions

Cholangiocarcinoma (CCA), a highly heterogeneous cancer, is the second most common type of primary liver cancer. It is characterized by resistance to therapy and poor prognosis, with a 5-year survival rate lower than 20%. The pathogenesis of CCA is complex and multifactorial, and in recent years, bile acids (BAs) have been implicated in CCA development and prognosis. BAs belong to a category of amphipathic compounds that hold significant importance as signaling molecules and inflammatory agents. They possess the ability to activate transcriptional factors and cellular signaling pathways, thereby governing the regulation of lipid, glucose, and energy metabolism in diverse human disorders. These disorders encompass chronic liver diseases among other conditions. In this review, we provided an update on the current knowledge on the molecular mechanisms involving BAs in cholangiocarcinogenesis. Additionally, we analyzed the role of gut and biliary microbiota in CCA pathogenesis. Future research is required to better understand how to modulate BA activity and, possibly, identify new therapeutic strategies.

Bile acid-mediated signaling in cholestatic liver diseases

Chronic cholestatic liver diseases, such as primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC), are associated with bile stasis and gradually progress to fibrosis, cirrhosis, and liver failure, which requires liver transplantation. Although ursodeoxycholic acid is effective in slowing the disease progression of PBC, it has limited efficacy in PSC patients. It is challenging to develop effective therapeutic agents due to the limited understanding of disease pathogenesis. During the last decade, numerous studies have demonstrated that disruption of bile acid (BA) metabolism and intrahepatic circulation promotes the progression of cholestatic liver diseases. BAs not only play an essential role in nutrition absorption as detergents but also play an important role in regulating hepatic metabolism and modulating immune responses as key signaling molecules. Several excellent papers have recently reviewed the role of BAs in metabolic liver diseases. This review focuses on BA-mediated signaling in cholestatic liver disease.

Supplemental Clostridium butyricum modulates lipid metabolism by reshaping the gut microbiota composition and bile acid profile in IUGR suckling piglets

BACKGROUND

Intrauterine growth restriction (IUGR) can cause lipid disorders in infants and have long-term adverse effects on their growth and development. Clostridium butyricum (C. butyricum), a kind of emerging probiotics, has been reported to effectively attenuate lipid metabolism dysfunctions. Therefore, the objective of this study was to investigate the effects of C. butyricum supplementation on hepatic lipid disorders in IUGR suckling piglets.

METHODS

Sixteen IUGR and eight normal birth weight (NBW) neonatal male piglets were used in this study. From d 3 to d 24, in addition to drinking milk, the eight NBW piglets (NBW-CON group, n = 8) and eight IUGR piglets (IUGR-CON group, n = 8) were given 10 mL sterile saline once a day, while the remaining IUGR piglets (IUGR-CB group, n = 8) were orally administered C. butyricum at a dose of 2 × 10⁸ colony-forming units (CFU)/kg body weight (suspended in 10 mL sterile saline) at the same frequency.

RESULTS

The IUGR-CON piglets exhibited restricted growth, impaired hepatic morphology, disordered lipid metabolism, increased abundance of opportunistic pathogens and altered ileum and liver bile acid (BA) profiles. However, C. butyricum supplementation reshaped the gut microbiota of the IUGR-CB piglets, characterized by a decreased abundance of opportunistic pathogens in the ileum, including Streptococcus and Enterococcus. The decrease in these bile salt hydrolase (BSH)-producing microbes increased the content of conjugated BAs, which could be transported to the liver and function as signaling molecules to activate liver X receptor α (LXRα) and farnesoid X receptor (FXR). This activation effectively accelerated the synthesis and oxidation of fatty acids and down-regulated the total cholesterol level by decreasing the synthesis and promoting the efflux of cholesterol. As a result, the growth performance and morphological structure of the liver improved in the IUGR piglets.

CONCLUSION

These results indicate that C. butyricum supplementation in IUGR suckling piglets could decrease the abundance of BSH-producing microbes (Streptococcus and Enterococcus). This decrease altered the ileum and liver BA profiles and consequently activated the expression of hepatic LXRα and FXR. The activation of these two signaling molecules could effectively normalize the lipid metabolism and improve the growth performance of IUGR suckling piglets.

Metabolomic profiling for the preventive effects of dietary grape pomace against colorectal cancer

Colorectal cancer (CRC) is one of the most common and deadly cancers worldwide. Grape pomace (GP) is a rich source of bioactive compounds with anti-inflammatory, and anticancer effects. We recently found that dietary GP had protective effects against CRC development in the azoxymethane (AOM)/dextran sulfate sodium (DSS) CRC mouse model through suppression of cell proliferation and modulation of DNA methylation. However, the underlying molecular mechanisms associated with changes in metabolites remain unexamined. This study profiled fecal metabolomic changes in a mouse CRC model in response to GP supplementation using gas chromatography-mass spectrometry (GC-MS) based metabolomic analysis. A total of 29 compounds showed significant changes due to GP supplementation, including bile acids, amino acids, fatty acids, phenols/flavonoids, glycerolipids, carbohydrates, organic acids, and others. The major changes in metabolites of feces include increased deoxycholic acid (DCA) and decreased amino acid content. Dietary GP upregulated the expression of farnesoid X receptor (FXR) downstream genes while decreasing fecal urease activity. DNA repair enzyme MutS Homolog 2 (MSH2) was upregulated by GP supplementation. Consistently, γ-H2AX, as a DNA damage marker, decreased in GP supplemented mice. Moreover, MDM2, a protein in the ataxia telangiectasia mutated (ATM) signaling, was decreased by GP supplementation. These data provided valuable metabolic clues for unraveling the protective effects of GP supplementation against CRC development.

Minocycline-induced disruption of the intestinal FXR/FGF15 axis impairs osteogenesis in mice

Antibiotic-induced shifts in the indigenous gut microbiota influence normal skeletal maturation. Current theory implies that gut microbiota actions on bone occur through a direct gut/bone signaling axis. However, our prior work supports that a gut/liver signaling axis contributes to gut microbiota effects on bone. Our purpose was to investigate the effects of minocycline, a systemic antibiotic treatment for adolescent acne, on pubertal/postpubertal skeletal maturation. Sex-matched specific pathogen-free (SPF) and germ-free (GF) C57BL/6T mice were administered a clinically relevant minocycline dose from age 6-12 weeks. Minocycline caused dysbiotic shifts in the gut bacteriome and impaired skeletal maturation in SPF mice but did not alter the skeletal phenotype in GF mice. Minocycline administration in SPF mice disrupted the intestinal farnesoid X receptor/fibroblast growth factor 15 axis, a gut/liver endocrine axis supporting systemic bile acid homeostasis. Minocycline-treated SPF mice had increased serum conjugated bile acids that were farnesoid X receptor (FXR) antagonists, suppressed osteoblast function, decreased bone mass, and impaired bone microarchitecture and fracture resistance. Stimulating osteoblasts with the serum bile acid profile from minocycline-treated SPF mice recapitulated the suppressed osteogenic phenotype found in vivo, which was mediated through attenuated FXR signaling. This work introduces bile acids as a potentially novel mediator of gut/liver signaling actions contributing to gut microbiota effects on bone.

Akkermansia muciniphila protects mice against an emerging tick-borne viral pathogen

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging tick-borne disease caused by a phlebovirus in the Bunyaviridae family. Infection can result in systemic inflammatory response syndrome with a high fatality rate, and there are currently no treatments or vaccines available. The microbiota has been implicated in host susceptibility to systemic viral infection and disease outcomes, but whether the gut microbiota is implicated in severe fever with thrombocytopenia syndrome virus (SFTSV) infection is unknown. Here, we analysed faecal and serum samples from patients with SFTS using 16S ribosomal RNA-sequencing and untargeted metabolomics, respectively. We found that the gut commensal Akkermansia muciniphila increased in relative abundance over the course of infection and was reduced in samples from deceased patients. Using germ-free or oral antibiotic-treated mice, we found that A. muciniphila produces the β-carboline alkaloid harmaline, which protects against SFTSV infection by suppressing NF-κB-mediated systemic inflammation. Harmaline indirectly modulated the virus-induced inflammatory response by specifically enhancing bile acid-CoA: amino acid N-acyltransferase expression in hepatic cells to increase conjugated primary bile acids, glycochenodeoxycholic acid and taurochenodeoxycholic acid. These bile acids induced transmembrane G-protein coupled receptor-5-dependent anti-inflammatory responses. These results indicate the probiotic potential of A. muciniphila in mitigating SFTSV infection.

The Farnesoid X Receptor as a Master Regulator of Hepatotoxicity

The nuclear receptor farnesoid X receptor (FXR, NR1H4) is a bile acid (BA) sensor that links the enterohepatic circuit that regulates BA metabolism and elimination to systemic lipid homeostasis. Furthermore, FXR represents a real guardian of the hepatic function, preserving, in a multifactorial fashion, the integrity and function of hepatocytes from chronic and acute insults. This review summarizes how FXR modulates the expression of pathway-specific as well as polyspecific transporters and enzymes, thereby acting at the interface of BA, lipid and drug metabolism, and influencing the onset and progression of hepatotoxicity of varying etiopathogeneses. Furthermore, this review article provides an overview of the advances and the clinical development of FXR agonists in the treatment of liver diseases.

Recent advances on FXR-targeting therapeutics

The bile acid receptor FXR has emerged as a bona fide drug target for chronic cholestatic and metabolic liver diseases, ahead of all non-alcoholic fatty liver disease (NAFLD). FXR is highly expressed in the liver and intestine and activation at both sites differentially contributes to its desired metabolic effects. Unrestricted FXR activation, however, also comes along with undesired effects such as a pro-atherogenic lipid profile, pruritus and hepatocellular toxicity under certain conditions. Several pre-clinical studies have confirmed the potency of FXR activation for cholestatic and metabolic liver diseases, but overall it remains still open whether selective activation of intestinal FXR is advantageous over pan-FXR activation and whether restricted or modulated FXR activation can limit some of the side effects. Even more, FXR antagonist also bear the potential as intestinal-selective drugs in NAFLD models. In this review we will discuss the molecular prerequisites for FXR activation, pan-FXR activation and intestinal FXR in/activation from a therapeutic point of view, different steroidal and non-steroidal FXR agonists, ways to restrict FXR activation and finally what we have learned from pre-clinical models and clinical trials with different FXR therapeutics.

Renal Farnesoid X Receptor improves high fructose-induced salt-sensitive hypertension in mice by inhibiting DNM3 to promote nitro oxide production

OBJECTIVE

Farnesoid X Receptor (FXR) is highly expressed in renal tubules, activation of which attenuates renal injury by suppressing inflammation and fibrosis. However, whether renal FXR contributes to the regulation of blood pressure (BP) is poorly understood. This study aimed to investigate the anti-hypertensive effect of renal FXR on high-fructose-induced salt-sensitive hypertension and underlying mechanism.

METHODS

Hypertension was induced in male C57BL/6 mice by 20% fructose in drinking water with 4% sodium chloride in diet (HFS) for 8 weeks. The effects of FXR on NO production were estimated in vitro and in vivo.

RESULTS

Compared with control, HFS intake elevated BP, enhanced renal injury and reduced renal NO levels as well as FXR expression in the kidney of mice. In the mouse renal collecting duct cells mIMCD-K2, FXR agonists promoted NO production by enhancing the expression of neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS), whereas this effect was diminished by fxr knockdown. We further found that Dynamin 3 (DNM3), a binding protein with nNOS in the renal medulla, was inhibited by FXR and its deficiency elevated NO production in mIMCD-K2 cells. In HFS-fed mice, renal fxr overexpression significantly attenuated hypertension and renal fibrosis, regulated the expression of DNM3/nNOS/iNOS, and increased renal NO levels.

CONCLUSION

Our results demonstrated that renal FXR prevents HFS-induced hypertension by inhibiting DNM3 to promote NO production. These findings provide insights into the role and potential mechanism of renal FXR for the treatment of hypertension.

Enterohepatic and non-canonical roles of farnesoid X receptor in controlling lipid and glucose metabolism

Farnesoid X receptor (FXR) is a nuclear receptor that transcriptionally regulates bile acid homeostasis along with nutrient metabolism. In addition to the gastrointestinal (GI) tract, FXR expression has been widely noted in kidney, adrenal gland, pancreas, adipose, skeletal muscle, heart, and brain. Except for the liver and gut, the relevance of FXR signaling in metabolism in other tissues remains poorly understood. This review examines the classical and non-canonical tissue-specific roles of FXR in regulating, lipids, and glucose homeostasis under normal and diseased states. FXR activation has been reported to be protective against cholestasis, nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), type 2 diabetes, cardiovascular and kidney diseases. Several ongoing clinical trials are investigating FXR ligands as a therapeutic target for primary biliary cholangitis (PBC) and NASH, which substantiate the significance of FXR signaling in modulating metabolic processes. This review highlights that FXR ligands, albeit an attractive therapeutic target for treating metabolic diseases, tissue-specific modulation of FXR may be the key to overcoming some of the adverse clinical effects.

Liver metabolomics identifies bile acid profile changes at early stages of alcoholic liver disease in mice

Alcohol consumption is a global healthcare problem with enormous social, economic, and clinical consequences. The liver sustains the earliest and the greatest degree of tissue injury due to chronic alcohol consumption and it has been estimated that alcoholic liver disease (ALD) accounts for almost 50% of all deaths from cirrhosis in the world. In this study, we used a modified Lieber-DeCarli (LD) diet to treat mice with alcohol and simulate chronic alcohol drinking. Using an untargeted metabolomics approach, our aim was to identify the various metabolites and pathways that are altered in the early stages of ALD. Histopathology showed minimal changes in the liver after 6 weeks of alcohol consumption. However, untargeted metabolomics analyses identified 304 metabolic features that were either up- or down-regulated in the livers of ethanol-consuming mice. Pathway analysis revealed significant alcohol-induced alterations, the most significant of which was in the FXR/RXR activation pathway. Targeted metabolomics focusing on bile acid biosynthesis showed elevated taurine-conjugated cholic acid compounds in ethanol-consuming mice. In summary, we showed that the changes in the liver metabolome manifest very early in the development of ALD, and when minimal changes in liver histopathology have occurred. Although alterations in biochemical pathways indicate a complex pathology in the very early stages of alcohol consumption, bile acid changes may serve as biomarkers of the early onset of ALD.

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

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

Roles and action mechanisms of bile acid-induced gastric intestinal metaplasia: a review

Gastric intestinal metaplasia (IM) is a precancerous lesion that increases the risk of subsequent gastric cancer (GC) development. Therefore, the mechanism of IM has been the focus of basic and clinical research. Helicobacter pylori (H. pylori) infection has been recognized as the main pathogenesis of gastric IM. However, more and more studies have shown that chronic inflammation of gastric mucosa caused by bile reflux is the key pathogenic factor of gastric IM. Bile reflux activates the expression of IM biomarkers via the bile acid receptor. In addition, microRNAs, exosomes, and epigenetics are also involved in the occurrence and development of bile acid-induced gastric IM. Currently, the relevant research is still very few. The molecular mechanism of the phenotypic transformation of gastrointestinal epithelial cells induced by bile acids has not been fully understood. This article mainly reviews the physiology and pathology of bile acid, mechanism of gastric IM induced by bile acid, bile acid receptors, and so on, in order to provide reference for further research.

Bile acids and salt-sensitive hypertension: a role of the gut-liver axis

Salt-sensitivity of blood pressure (SSBP) affects 50% of the hypertensive and 25% of the normotensive populations. Importantly, SSBP is associated with increased risk for mortality in both populations independent of blood pressure. Despite its deleterious effects, the pathogenesis of SSBP is not fully understood. Emerging evidence suggests a novel role of bile acids in salt-sensitive hypertension and that they may play a crucial role in regulating inflammation and fluid volume homeostasis. Mechanistic evidence implicates alterations in the gut microbiome, the epithelial sodium channel (ENaC), the farnesoid X receptor, and the G protein-coupled bile acid receptor TGR5 in bile acid-mediated effects on cardiovascular function. The mechanistic interplay between excess dietary sodium-induced alterations in the gut microbiome and immune cell activation, bile acid signaling, and whether such interplay may contribute to the etiology of SSBP is still yet to be defined. The main goal of this review is to discuss the potential role of bile acids in the pathogenesis of cardiovascular disease with a focus on salt-sensitive hypertension.

Bile acid metabolism and FXR-mediated effects in human cholestatic liver disorders

Intrahepatic cholestasis is the main feature of a group of liver diseases that are characterized by hepatic and systemic accumulation of bile acids due to impaired excretion of bile, based on inflammation of intrahepatic and extrahepatic bile ducts or dysfunction of hepatobiliary transport proteins. The nuclear bile acid sensor farnesoid X receptor (FXR) is central for the regulation of bile acid turnover, including synthesis, hepatic excretion and intestinal and hepatic uptake. Several drugs targeting FXR have been developed for the treatment of cholestatic liver diseases, and so far one of them has been granted conditional approval. In this review, we will discuss the current knowledge and the clinical and experimental data available on agents affecting FXR and bile acid turnover.

Importance of Conjugation of the Bile Salt on the Mechanism of Lipolysis

We aim to advance the discussion on the significance of the conjugation of bile salts (BS) in our organism. We hypothesize that conjugation influences the rate of lipolysis. Since the rate of lipolysis is a compound parameter, we compare the effect of conjugation on four surface parameters, which contribute to the rate. Since deconjugation is due to gut microbiota, we hypothesize that microbiota may affect the rate of lipolysis. A meta-analysis of literature data of critical micelle concentration, β, aggregation number, and molar solubilization ratio has been performed for the first time. In addition, critical micelle concentration (CMC), interfacial tension, and lipolysis rate measurements were performed. It was found that the unconjugated BS in mixed micelles increases the antagonism between the BS, therefore, increasing the CMC. This correlated with the effect of unconjugated BS on the solubilization capacity of mixed micelles. The collected literature information indicates that the role of the BS and its conjugation in our organism is a key factor influencing the functioning of our organism, where too high levels of unconjugated BS may lead to malabsorption of fat-soluble nutrients. The experimental lipolysis results irrevocably showed that conjugation is a significant factor influencing the rate.

Identification and characterization of novel splice variants of human farnesoid X receptor

Farnesoid X receptor (FXR, NR1H4) is a ligand-activated nuclear receptor, which regulates bile acid, lipid and glucose metabolism. Due to these functions, FXR has been investigated as a potential drug target for the treatment of liver diseases, such as primary biliary cholangitis and non-alcoholic steatohepatitis. Based on the previously described four splice variants, it has been suggested that alternative promoter usage and splicing may have an impact on total FXR activity as a result of encoding functionally diverse variants. Here we aimed for a systematic analysis of human hepatic FXR splice variants. In addition to the previously described FXRα1-4, we identified four novel splice variants (FXRα5-8) in human hepatocytes, which resulted from previously undetected exon skipping events. These newly identified isoforms displayed diminished DNA binding and impaired transactivation activities. Isoform FXRα5, which suppressed the transactivation activity of the functional isoform FXRα2, was further characterized as deficient in heterodimerization, coactivator recruitment and ligand binding. These findings were further supported by molecular dynamics simulations, which offered an explanation for the behavior of this isoform on the molecular level. FXRα5 exhibited low uniform expression levels in nearly all human tissues. Our systematic analysis of FXR splice variants in human hepatocytes resulted in the identification of four novel FXR isoforms, which all proved to be functionally deficient, but one novel variant, FXRα5, also displayed dominant negative activity. The possible associations with and roles of these novel isoforms in human liver diseases require further investigation.

Bile Acids, Their Receptors, and the Gut Microbiota

Bile acids (BAs) are a family of hydroxylated steroids secreted by the liver that aid in the breakdown and absorption of dietary fats. BAs also function as nutrient and inflammatory signaling molecules, acting through cognate receptors, to coordinate host metabolism. Commensal bacteria in the gastrointestinal tract are functional modifiers of the BA pool, affecting composition and abundance. Deconjugation of host BAs creates a molecular network that inextricably links gut microtia with their host. In this review we highlight the roles of BAs in mediating this mutualistic relationship with a focus on those events that impact host physiology and metabolism.

Splice variants of metabolic nuclear receptors: Relevance for metabolic disease and therapeutic targeting

Metabolic nuclear receptors are ligand-activated transcription factors which control a wide range of metabolic processes and signaling pathways in response to nutrients and xenobiotics. Targeting these NRs is at the forefront of our endeavours to generate novel treatment options for diabetes, metabolic syndrome and fatty liver disease. Numerous splice variants have been described for these metabolic receptors. Structural changes, as a result of alternative splicing, lead to functional differences among NR isoforms, resulting in the regulation of different metabolic pathways by these NR splice variants. In this review, we describe known splice variants of FXR, LXRs, PXR, RXR, LRH-1, CAR and PPARs. We discuss their structure and functions, and elaborate on the regulation of splice variant abundance by nutritional signals. We conclude that NR splice variants pose an intriguing new layer of complexity in metabolic signaling, which needs to be taken into account in the development of treatment strategies for metabolic diseases.

Marine Bile Natural Products as Agonists of the TGR5 Receptor

Agonism of the G protein-coupled bile acid receptor "Takeda G-protein receptor 5" (TGR5) aids in attenuating cholesterol accumulation due to atherosclerotic progression. Although mammalian bile compounds can activate TGR5, they are generally weak agonists, and more effective compounds need to be identified. In this study, two marine bile compounds (5β-scymnol and its sulfate) were compared with mammalian bile compounds deoxycholic acid (DCA) and ursodeoxycholic acid (UDCA) using an in vitro model of TGR5 agonism. The response profiles of human embryonic kidney 293 cells (HEK293) transfected to overexpress TGR5 (HEK293-TGR5) and incubated with subcytotoxic concentrations of test compounds were compared to nontransfected HEK293 control cells using the specific calcium-binding fluorophore Fura-2AM to measure intracellular calcium [Ca²⁺]_i release. Scymnol and scymnol sulfate caused a sustained increase in [Ca²⁺]_i within TGR5 cells only, which was abolished by a specific inhibitor for G_αq protein (UBO-QIC). Sustained increases in [Ca²⁺]_i were seen in both cell types with DCA exposure; this was unaffected by UBO-QIC, indicating that TGR5 activation was not involved. Exposure to UDCA did not alter [Ca²⁺]_i, suggesting a lack of TGR5 bioactivity. These findings demonstrated that both scymnol and scymnol sulfate are novel agonists of TGR5 receptors, showing therapeutic potential for treating atherosclerosis.

The identification of farnesoid X receptor modulators as treatment options for nonalcoholic fatty liver disease

INTRODUCTION

The farnesoid-x-receptor (FXR) is a ubiquitously expressed nuclear receptor selectively activated by primary bile acids.

AREA COVERED

FXR is a validated pharmacological target. Herein, the authors review preclinical and clinical data supporting the development of FXR agonists in the treatment of nonalcoholic fatty liver disease.

EXPERT OPINION

Development of systemic FXR agonists to treat the metabolic liver disease has been proven challenging because the side effects associated with these agents including increased levels of cholesterol and LDL-c and reduced HDL-c raising concerns over their long-term cardiovascular safety. Additionally, pruritus has emerged as a common, although poorly explained, dose-related side effect with all FXR ligands, but is especially common with OCA. FXR agonists that are currently undergoing phase 2/3 trials are cilofexor, tropifexor, nidufexor and MET409. Some of these agents are currently being developed as combination therapies with other agents including cenicriviroc, a CCR2/CCR5 inhibitor, or firsocostat an acetyl CoA carboxylase inhibitor. Additional investigations are needed to evaluate the beneficial effects of combination of these agents with statins. It is expected that in the coming years, FXR agonists will be developed as a combination therapy to minimize side effects and increase likelihood of success by targeting different metabolic pathways.

FXR in liver physiology: Multiple faces to regulate liver metabolism

The liver is the central metabolic hub which coordinates nutritional inputs and metabolic outputs. Food intake releases bile acids which can be sensed by the bile acid receptor FXR in the liver and the intestine. Hepatic and intestinal FXR coordinately regulate postprandial nutrient disposal in a network of interacting metabolic nuclear receptors. In this review we summarize and update the "classical roles" of FXR as a central integrator of the feeding state response, which orchestrates the metabolic processing of carbohydrates, lipids, proteins and bile acids. We also discuss more recent and less well studied FXR effects on amino acid, protein metabolism, autophagic turnover and inflammation. In addition, we summarize the recent understanding of how FXR signaling is affected by posttranslational modifications and by different FXR isoforms. These modifications and variations in FXR signaling might be considered when FXR is targeted pharmaceutically in clinical applications.

Heteromeric Solute Carriers: Function, Structure, Pathology and Pharmacology

Solute carriers form one of three major superfamilies of membrane transporters in humans, and include uniporters, exchangers and symporters. Following several decades of molecular characterisation, multiple solute carriers that form obligatory heteromers with unrelated subunits are emerging as a distinctive principle of membrane transporter assembly. Here we comprehensively review experimentally established heteromeric solute carriers: SLC3-SLC7 amino acid exchangers, SLC16 monocarboxylate/H⁺ symporters and basigin/embigin, SLC4A1 (AE1) and glycophorin A exchanger, SLC51 heteromer Ost α-Ost β uniporter, and SLC6 heteromeric symporters. The review covers the history of the heteromer discovery, transporter physiology, structure, disease associations and pharmacology - all with a focus on the heteromeric assembly. The cellular locations, requirements for complex formation, and the functional role of dimerization are extensively detailed, including analysis of the first complete heteromer structures, the SLC7-SLC3 family transporters LAT1-4F2hc, b^0,+AT-rBAT and the SLC6 family heteromer B⁰AT1-ACE2. We present a systematic analysis of the structural and functional aspects of heteromeric solute carriers and conclude with common principles of their functional roles and structural architecture.

Bile acids and their receptors in metabolic disorders

Bile acids are a large family of atypical steroids which exert their functions by binding to a family of ubiquitous cell membrane and nuclear receptors. There are two main bile acid activated receptors, FXR and GPBAR1, that are exclusively activated by bile acids, while other receptors CAR, LXRs, PXR, RORγT, S1PR2and VDR are activated by bile acids in addition to other more selective endogenous ligands. In the intestine, activation of FXR and GPBAR1 promotes the release of FGF15/19 and GLP1 which integrate their signaling with direct effects exerted by theother receptors in target tissues. This network is tuned in a time ordered manner by circadian rhythm and is critical for the regulation of metabolic process including autophagy, fast-to-feed transition, lipid and glucose metabolism, energy balance and immune responses. In the last decade FXR ligands have entered clinical trials but development of systemic FXR agonists has been proven challenging because their side effects including increased levels of cholesterol and Low Density Lipoproteins cholesterol (LDL-c) and reduced High-Density Lipoprotein cholesterol (HDL-c). In addition, pruritus has emerged as a common, dose related, side effect of FXR ligands. Intestinal-restricted FXR and GPBAR1 agonists and dual FXR/GPBAR1 agonists have been developed. Here we review the last decade in bile acids physiology and pharmacology.

The Liver under the Spotlight: Bile Acids and Oxysterols as Pivotal Actors Controlling Metabolism

Among the myriad of molecules produced by the liver, both bile acids and their precursors, the oxysterols are becoming pivotal bioactive lipids which have been underestimated for a long time. Their actions are ranging from regulation of energy homeostasis (i.e., glucose and lipid metabolism) to inflammation and immunity, thereby opening the avenue to new treatments to tackle metabolic disorders associated with obesity (e.g., type 2 diabetes and hepatic steatosis) and inflammatory diseases. Here, we review the biosynthesis of these endocrine factors including their interconnection with the gut microbiota and their impact on host homeostasis as well as their attractive potential for the development of therapeutic strategies for metabolic disorders.

Association of Serum Bile Acids Profile and Pathway Dysregulation With the Risk of Developing Diabetes Among Normoglycemic Chinese Adults: Findings From the 4C Study

OBJECTIVE

Comprehensive assessment of serum bile acids (BAs) aberrations before diabetes onset remains inconclusive. We examined the association of serum BA profile and coregulation with the risk of developing type 2 diabetes mellitus (T2DM) among normoglycemic Chinese adults.

RESEARCH DESIGN AND METHODS

We tested 23 serum BA species in subjects with incident diabetes (n = 1,707) and control subjects (n = 1,707) matched by propensity score (including age, sex, BMI, and fasting glucose) from the China Cardiometabolic Disease and Cancer Cohort (4C) Study, which was composed of 54,807 normoglycemic Chinese adults with a median follow-up of 3.03 years. Multivariable-adjusted odds ratios (ORs) for associations of BAs with T2DM were estimated using conditional logistic regression.

RESULTS

In multivariable-adjusted logistic regression analysis, per SD increment of unconjugated primary and secondary BAs were inversely associated with incident diabetes, with an OR (95% CI) of 0.89 (0.83-0.96) for cholic acid, 0.90 (0.84-0.97) for chenodeoxycholic acid, and 0.90 (0.83-0.96) for deoxycholic acid (P < 0.05 and false discovery rate <0.05). On the other hand, conjugated primary BAs (glycocholic acid, taurocholic acid, glycochenodeoxycholic acid, taurochenodeoxycholic acid, and sulfated glycochenodeoxycholic acid) and secondary BA (tauroursodeoxycholic acid) were positively related with incident diabetes, with ORs ranging from 1.11 to 1.19 (95% CIs ranging between 1.05 and 1.28). In a fully adjusted model additionally adjusted for liver enzymes, HDL cholesterol, diet, 2-h postload glucose, HOMA-insulin resistance, and waist circumference, the risk estimates were similar. Differential correlation network analysis revealed that perturbations in intraclass (i.e., primary and secondary) and interclass (i.e., unconjugated and conjugated) BA coregulation preexisted before diabetes onset.

CONCLUSIONS

These findings reveal novel changes in BAs exist before incident T2DM and support a potential role of BA metabolism in the pathogenesis of diabetes.

Farnesoid X receptor: a potential therapeutic target in multiple organs

Farnesoid X receptor (FXR), a member of the nuclear receptor family, is a common receptor found in the intestine and liver, and helps to maintain systemic metabolic homeostasis through regulating bile acid, glucose, lipid metabolism, and energy homeostatsis. In addition, FXR regulates the functions of various organs, such as liver, intestine, kidney, breast, pancreas, cardiovascular system and brain. FXR also plays a key role in regulation of gut-microbiota through mediating the various signaling pathways. Accordingly, FXR has become an attractive therapeutic target in a variety of diseases. This review combines classical and recent research reports to introduce the basic information about FXR and its important roles in various organs of the body.

Post-Translational Modifications of FXR; Implications for Cholestasis and Obesity-Related Disorders

The Farnesoid X receptor (FXR) is a nuclear receptor which is activated by bile acids. Bile acids function in solubilization of dietary fats and vitamins in the intestine. In addition, bile acids have been increasingly recognized to act as signaling molecules involved in energy metabolism pathways, amongst others via activating FXR. Upon activation by bile acids, FXR controls the expression of many genes involved in bile acid, lipid, glucose and amino acid metabolism. An inability to properly use and store energy substrates may predispose to metabolic disorders, such as obesity, diabetes, cholestasis and non-alcoholic fatty liver disease. These diseases arise through a complex interplay between genetics, environment and nutrition. Due to its function in metabolism, FXR is an attractive treatment target for these disorders. The regulation of FXR expression and activity occurs both at the transcriptional and at the post-transcriptional level. It has been shown that FXR can be phosphorylated, SUMOylated and acetylated, amongst other modifications, and that these modifications have functional consequences for DNA and ligand binding, heterodimerization and subcellular localization of FXR. In addition, these post-translational modifications may selectively increase or decrease transcription of certain target genes. In this review, we provide an overview of the posttranslational modifications of FXR and discuss their potential involvement in cholestatic and metabolic disorders.

Effect of different bile acids on the intestine through enterohepatic circulation based on FXR

Farnesoid X receptor (FXR) is a nuclear receptor for bile acids (BAs) that is widely expressed in the intestine, liver and kidney. FXR has important regulatory impacts on a wide variety of metabolic pathways (such as glucose, lipid, and sterol metabolism) and has been recognized to ameliorate obesity, liver damage, cholestasis and chronic inflammatory diseases. The types of BAs are complex and diverse. BAs link the intestine with the liver through the enterohepatic circulation. BAs derivatives have entered clinical trials for liver disease. In addition to the liver, the intestine is also targeted by BAs. This article reviews the effects of different BAs on the intestinal tract through the enterohepatic circulation from the perspective of FXR, aiming to elucidate the effects of different BAs on the intestinal tract and lay a foundation for new treatment methods.

FXR Isoforms Control Different Metabolic Functions in Liver Cells via Binding to Specific DNA Motifs

BACKGROUND & AIMS

The nuclear receptor subfamily 1 group H member 4 (NR1H4, also called FXR) is a ligand-activated transcription factor that, upon binding of bile acids, regulates the expression of genes involved in bile acid, fat, sugar, and amino acid metabolism. Transcript variants encode the FXR isoforms alpha 1, alpha 2, alpha 3, and alpha 4, which activate different genes that regulate metabolism. Little is known about the mechanisms by which the different isoforms regulate specific genes or how the expression of these genes affects the outcomes of patients given drugs that target FXR.

METHODS

We determined genome-wide binding of FXR isoforms in mouse liver organoids that express individual FXR isoforms using chromatin immunoprecipitation, followed by sequencing analysis and DNA motif discovery. We validated regulatory DNA sequences by mobility shift assays and with luciferase reporters using mouse and human FXR isoforms. We analyzed mouse liver organoids and HepG2 cells that expressed the FXR isoforms using chromatin immunoprecipitation, quantitative polymerase chain reaction, and immunoblot assays. Organoids were analyzed for mitochondrial respiration, lipid droplet content, and triglyceride excretion. We used the FXR ligand obeticholic acid to induce FXR activity in organoids, cell lines, and mice. We collected data on the binding of FXR in mouse liver and the expression levels of FXR isoforms and gene targets in human liver tissue and primary human hepatocytes from the Gene Expression Omnibus.

RESULTS

In mouse liver cells, 89% of sites that bound FXR were bound by only FXRα2 or FXRα4, via direct interactions with the DNA sequence motif ER-2. Via DNA binding, these isoforms regulated metabolic functions in liver cells, including carbon metabolism and lipogenesis. Incubation with obeticholic acid increased mitochondrial pyruvate transport and reduced insulin-induced lipogenesis in organoids that expressed FXRα2 but not FXRα1. In human liver tissues, levels of FXRα2 varied significantly and correlated with expression of genes predicted to be regulated via an ER-2 motif.

CONCLUSIONS

Most metabolic effects regulated by FXR in mouse and human liver cells are regulated by the FXRα2 isoform via specific binding to ER-2 motifs. The expression level of FXRα2 in liver might be used to predict responses of patients to treatment with FXR agonists.

Farnesoid X receptor antagonizes Wnt/β-catenin signaling in colorectal tumorigenesis

Farnesoid X receptor (FXR, encoded by NR1H4), a critical regulator of bile acid homeostasis, is widely implicated in human tumorigenesis. However, the functional role of FXR in colorectal cancer (CRC) and the precise molecular mechanism remain unclear. In this study, we demonstrated that FXR expression was downregulated in colon cancer tissues and decreased expression of FXR predicted a poor prognosis. Knockdown of FXR promoted colon cancer cell growth and invasion in vitro, and facilitated xenograft tumor formation and distant metastasis in vivo, whereas ectopic expression of FXR had the reserved change. Mechanistic studies indicated that FXR exerted its tumor suppressor functions by antagonizing Wnt/β-catenin signaling. Furthermore, we identified an FXR/β-catenin interaction in colon cancer cells. The FXR/β-catenin interaction impaired β-catenin/TCF4 complex formation. In addition, our study suggested a reciprocal relationship between FXR and β-catenin, since loss of β-catenin increased the transcriptional activation of SHP by FXR. Altogether, these data indicated that FXR functions a tumor-suppressor role in CRC by antagonizing Wnt/β-catenin signaling.

Antibiotic Therapy as a Risk Factor of Obesity Development in Children

Настоящий обзор научной литературы посвящен вопросам, связанным с механизмами антибактериально-индуцированного адипогенеза. Антибиотиками, наиболее высоко ассоциированными с развитием ожирения у детей, считают: амоксициллин, цефотаксим, макролиды, тетрациклины, ванкомицин. На основании результатов филогенетических, метагеномных исследований эффектов антибиотиков установлено, что их применение в антенатальном, раннем постнатальном периоде приводит к пролонгированным изменениям как состава, так и функционирования микробиома, которые ассоциированы с повышенным риском последующего увеличения массы тела ребенка. Механизмы непосредственного влияния антибиотиков на адипогенез связаны с их способностью повышать аппетит за счет стимуляции высвобождения орексина и меланин-концентрирующего гормона; увеличивать абсорбцию пищевых ингредиентов; активировать липогенез; индуцировать митохондриальную дисфункцию и тем самым способствовать накоплению жирных кислот. Применение антибиотиков существенно изменяет структуру микробиома кишечника, а именно: развитие ожирения связано с высоким уровнем представительства бактерий филюмов Actinobacteria и Firmicutes в сочетании со снижением численности бактерий Bacteroidetes, Verrucomicrobia и Faecalibacterium prausnitzii. Антибиотик-индуцированные изменения микробиома могут существенно влиять на аппетит, так как уровень грелина, вызывающего аппетит, положительно коррелирует с представительством бактерий Bacteroides и Prevotella, и отрицательно – с численностью бактерий Bifidobacterium, Lactobacillus, Blautia coccoides и Eubacterium rectale. Доказано, что применение некоторых антибиотиков сопровождается не только накоплением висцерального жира, но и приводит к развитию как неалкогольной болезни печени, так и инсулинорезистентности. Рецепторы FXR и TGR5 являются сенсорами изменений микробиоты кишечника, которые участвуют в регуляции метаболических процессов макроорганизма. Развитие ожирения характеризуется наличием низкоуровневого системного воспаления. При развитии ожирения по мере увеличения размеров адипоцитов фенотип макрофагов меняется на провоспалительный фенотип М1. Накопление провоспалительных клеток в висцеральной жировой ткани является важной причиной развития инсулинорезистентности. В настоящее время необходимость применения антибиотиков при лечении инфекционных заболеваний, вызванных бактериальными агентами, не вызывает никаких клинических сомнений. Однако появление научных сведений о метаболических эффектах, возникновение которых ассоциировано с антибиотикотерапией, ставит клинические новые задачи, решение которых, вероятно, лежит в оптимизации режимов применения антибиотиков и выборе сопровождающих лекарственных средств.

This review of scientific literature is devoted to issues related to the mechanisms of antibacterial- induced adipogenesis. The antibiotics most highly associated with the development of obesity in children are the following: amoxicillin, cefotaxime, macrolides, tetracyclines, vancomycin. On the base of the results of phylogenetic, metagenomic studies of the effects of antibiotics, it was found that their use in the antenatal, early postnatal period leads to prolonged changes in both the composition and functioning of the microbiome, which is associated with the increased risk of subsequent increase of body weight of the child. The mechanisms of direct effect of antibiotics on adipogenesis are associated with their ability to increase appetite, by stimulating the release of orexin and melanin-concentrating hormone; increase the absorption of food ingredients; activate lipogenesis; induce mitochondrial dysfunction and thereby contribute to accumulation of fatty acids. The use of antibiotics significantly changes the structure of the intestinal microbiome, namely, the development of obesity is associated with a high representation of phylum bacteria Actinobacteria and Firmicutes in combination with the decrease of the number of bacteria Bacteroidetes, Verrucomicrobia and Faecalibacterium prausnitzii. Antibiotic-induced changes in the microbiome can significantly affect appetite, because the level of ghrelin that causes appetite positively correlates with the presence of bacteria Bacteroides and Prevotella, and negatively with the number of bacteria Bifidobacterium, Lactobacillus, Blautia coccoides and Eubacterium rectale. It was proved that the use of certain antibiotics is accompanied not only by the accumulation of visceral fat, but also leads to the development of both non-alcoholic liver disease and insulin resistance. The FXR and TGR5 receptors are the sensors of changes in the intestinal microbiota, which is involved in the regulation of the metabolic processes of the macroorganism. The development of obesity is characterized by the presence of low-level systemic inflammation. With the development of obesity, as the size of adipocytes increases, the macrophage phenotype changes to the pro- inflammatory M1 phenotype. The accumulation of pro-inflammatory cells in visceral adipose tissue is an important reason for development of insulin resistance. Currently, the need for antibiotics in the treatment of infectious diseases caused by bacterial agents does not raise any clinical doubts. However, the emergence of scientific information about metabolic effects, the occurrence of which is associated with antibiotic therapy, presents new clinical challenges, the solution of which probably lies in optimizing antibiotic regimens and choosing the accompanying drugs.

Impaired bile acid metabolism with defectives of mitochondrial-tRNA taurine modification and bile acid taurine conjugation in the taurine depleted cats

Taurine that conjugates with bile acid (BA) and mitochondrial-tRNA (mt-tRNA) is a conditional essential amino acid in humans, similarly to cats. To better understand the influence of acquired depletion of taurine on BA metabolism, the profiling of BAs and its intermediates, BA metabolism-enzyme expression, and taurine modified mt-tRNAs were evaluated in the taurine deficient diet-supplemented cats. In the taurine depleted cats, taurine-conjugated bile acids in bile and taurine-modified mt-tRNA in liver were significantly decreased, whereas unconjugated BA in serum was markedly increased. Impaired bile acid metabolism in the liver was induced accompanied with the decreases of mitochondrial cholesterol 27-hydroxylase expression and mitochondrial activity. Consequently, total bile acid concentration in bile was significantly decreased by the low activity of mitochondrial bile acid synthesis. These results implied that the insufficient dietary taurine intake causes impaired bile acid metabolism, and in turn, a risk for the various diseases similar to the mitochondrial diseases would be enhanced.