Bile acids: natural ligands for an orphan nuclear receptor

Bile acids and their receptors in regulation of gut health and diseases

It is well established that bile acids play important roles in lipid metabolism. In recent decades, bile acids have also been shown to function as signaling molecules via interacting with various receptors. Bile acids circulate continuously through the enterohepatic circulation and go through microbial transformation by gut microbes, and thus bile acids metabolism has profound effects on the liver and intestinal tissues as well as the gut microbiota. Farnesoid X receptor and G protein-coupled bile acid receptor 1 are two pivotal bile acid receptors that highly expressed in the intestinal tissues, and they have emerged as pivotal regulators in bile acids metabolism, innate immunity and inflammatory responses. There is considerable interest in manipulating the metabolism of bile acids and the expression of bile acid receptors as this may be a promising strategy to regulate intestinal health and disease. This review aims to summarize the roles of bile acids and their receptors in regulation of gut health and diseases.

Cystic fibrosis rabbits develop spontaneous hepatobiliary lesions and CF-associated liver disease (CFLD)-like phenotypes

Cystic fibrosis (CF) is an autosomal recessive genetic disease affecting multiple organs. Approximately 30% CF patients develop CF-related liver disease (CFLD), which is the third most common cause of morbidity and mortality of CF. CFLD is progressive, and many of the severe forms eventually need liver transplantation. The mechanistic studies and therapeutic interventions to CFLD are unfortunately very limited. Utilizing the CRISPR/Cas9 technology, we recently generated CF rabbits by introducing mutations to the rabbit CF transmembrane conductance regulator (CFTR) gene. Here we report the liver phenotypes and mechanistic insights into the liver pathogenesis in these animals. CF rabbits develop spontaneous hepatobiliary lesions and abnormal biliary secretion accompanied with altered bile acid profiles. They exhibit nonalcoholic steatohepatitis (NASH)-like phenotypes, characterized by hepatic inflammation, steatosis, and fibrosis, as well as altered lipid profiles and diminished glycogen storage. Mechanistically, our data reveal that multiple stress-induced metabolic regulators involved in hepatic lipid homeostasis were up-regulated in the livers of CF-rabbits, and that endoplasmic reticulum (ER) stress response mediated through IRE1α-XBP1 axis as well as NF-κB- and JNK-mediated inflammatory responses prevail in CF rabbit livers. These findings show that CF rabbits manifest many CFLD-like phenotypes and suggest targeting hepatic ER stress and inflammatory pathways for potential CFLD treatment.

Mucosal and hormonal adaptations after Roux-en-Y gastric bypass

The aim of this study was to perform a comprehensive literature review regarding the relevant hormonal and histologic changes observed after Roux-en-Y gastric bypass (RYGB). We aimed to describe the relevant hormonal (glucagon-like peptides 1 and 2 [GLP-1 and GLP-2], peptide YY [PYY], oxyntomodulin [OXM], bile acids [BA], cholecystokinin [CCK], ghrelin, glucagon, gastric inhibitory polypeptide [GIP], and amylin) profiles, as well as the histologic (mucosal cellular) adaptations happening after patients undergo RYGB. Our review compiles the current evidence and furthers the understanding of the rationale behind the food intake regulatory adaptations occurring after RYGB surgery. We identify gaps in the literature where the potential for future investigations and therapeutics may lie. We performed a comprehensive database search without language restrictions looking for RYGB bariatric surgery outcomes in patients with pre- and postoperative blood work hormonal profiling and/or gut mucosal biopsies. We gathered the relevant study results and describe them in this review. Where human findings were lacking, we included animal model studies. The amalgamation of physiologic, metabolic, and cellular adaptations following RYGB is yet to be fully characterized. This constitutes a fundamental aspiration for enhancing and individualizing obesity therapy.

Anti-infective bile acids bind and inactivate a Salmonella virulence regulator

Bile acids are prominent host and microbiota metabolites that modulate host immunity and microbial pathogenesis. However, the mechanisms by which bile acids suppress microbial virulence are not clear. To identify the direct protein targets of bile acids in bacterial pathogens, we performed activity-guided chemical proteomic studies. In Salmonella enterica serovar Typhimurium, chenodeoxycholic acid (CDCA) most effectively inhibited the expression of virulence genes and invasion of epithelial cells and interacted with many proteins. Notably, we discovered that CDCA can directly bind and inhibit the function of HilD, an important transcriptional regulator of S. Typhimurium virulence and pathogenesis. Our characterization of bile acid-resistant HilD mutants in vitro and in S. Typhimurium infection models suggests that HilD is one of the key protein targets of anti-infective bile acids. This study highlights the utility of chemical proteomics to identify the direct protein targets of microbiota metabolites for mechanistic studies in bacterial pathogens.

Biomimetic Total Synthesis and the Biological Evaluation of Natural Product (-)-Fargesone A as a Novel FXR Agonist

Farnesoid X receptor (FXR), a member of the nuclear receptor superfamily, plays an important role in maintaining or reversing metabolic homeostasis during the development of liver diseases. However, developing FXR modulators to intervene in FXR-related diseases is still an unmet clinical need. Therefore, it is significant to develop novel small-molecule agonists for drug discovery targeting FXR. Through a high-throughput chemical screen and follow-up biological validations, we first identified the natural product Fargesone A (FA) as a potent and selective FXR agonist. The limited, variable supply of FA from natural product isolation, however, has impeded its biological exploration and potential drug development. Accordingly, we have developed a biomimetic and scalable total synthesis of FA in nine steps that provides a solution to the supply of FA. Enabled by chemical synthesis, the in vivo efficacy of FA has been further investigated. The results showed that FA alleviates hepatocyte lipid accumulation and cell death in an FXR-dependent manner. Moreover, treatment of bile duct ligation (BDL)-induced liver disorder with FA ameliorates pathological features in mice. Therefore, our work lays the foundation to develop new small-molecule FXR agonists as a potential therapy for liver diseases.

Regulation of Chromatin Accessibility by the Farnesoid X Receptor Is Essential for Circadian and Bile Acid Homeostasis In Vivo

The Farnesoid X Receptor (FXR) belongs to the nuclear receptor superfamily and is an essential bile acid (BA) receptor that regulates the expression of genes involved in the metabolism of BAs. FXR protects the liver from BA overload, which is a major etiology of hepatocellular carcinoma. Herein, we investigated the changes in gene expression and chromatin accessibility in hepatocytes by performing RNA-seq in combination with the Assay for Transposase-Accessible Chromatin with high-throughput sequencing (ATAC-seq) using a novel FXR knockout mouse model (Fxr^ex5Δ: Nr1h4^ex5Δ/ex5Δ) generated through CRISPR/Cas9. Consistent with previous Fxr knockout models, we found that Fxr^ex5Δ mice develop late-onset HCC associated with increased serum and hepatic BAs. FXR deletion was associated with a dramatic loss of chromatin accessibility, primarily at promoter-associated transcription factor binding sites. Importantly, several genes involved in BA biosynthesis and circadian rhythm were downregulated following loss of FXR, also displayed reduced chromatin accessibility at their promoter regions. Altogether, these findings suggest that FXR helps to maintain a transcriptionally active state by regulating chromatin accessibility through its binding and recruitment of transcription factors and coactivators.

Liver-derived metabolites as signaling molecules in fatty liver disease

Excessive fat accumulation in the liver has become a major health threat worldwide. Unresolved fat deposition in the liver can go undetected until it develops into fatty liver disease, followed by steatohepatitis, fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Lipid deposition in the liver is governed by complex communication, primarily between metabolic organs. This can be mediated by hormones, organokines, and also, as has been more recently discovered, metabolites. Although how metabolites from peripheral organs affect the liver is well documented, the effect of metabolic players released from the liver during the development of fatty liver disease or associated comorbidities needs further attention. Here we focus on interorgan crosstalk based on metabolites released from the liver and how these molecules act as signaling molecules in peripheral tissues. Due to the liver's specific role, we are covering lipid and bile mechanism-derived metabolites. We also discuss the high sucrose intake associated with uric acid release from the liver. Excessive fat deposition in the liver during fatty liver disease development reflects disrupted metabolic processes. As a response, the liver secretes a variety of signaling molecules as well as metabolites which act as a footprint of the metabolic disruption. In the coming years, the reciprocal exchange of metabolites between the liver and other metabolic organs will gain further importance and will help to better understand the development of fatty liver disease and associated diseases.

Immunomodulation by foods and microbes: Unravelling the molecular tango

Metabolic health and immune function are intimately connected via diet and the microbiota. Nearly 90% of all immune cells in the body are associated with the gastrointestinal tract and these immune cells are continuously exposed to a wide range of microbes and microbial-derived compounds, with important systemic ramifications. Microbial dysbiosis has consistently been observed in patients with atopic dermatitis, food allergy and asthma and the molecular mechanisms linking changes in microbial populations with disease risk and disease endotypes are being intensively investigated. The discovery of novel bacterial metabolites that impact immune function is at the forefront of host-microbe research. Co-evolution of microbial communities within their hosts has resulted in intertwined metabolic pathways that affect physiological and pathological processes. However, recent dietary and lifestyle changes are thought to negatively influence interactions between microbes and their host. This review provides an overview of some of the critical metabolite-receptor interactions that have been recently described, which may underpin the immunomodulatory effects of the microbiota, and are of relevance for allergy, asthma and infectious diseases.

NUDT7 regulates total hepatic CoA levels and the composition of the intestinal bile acid pool in male mice fed a Western diet

Nudix hydrolase 7 (NUDT7) is an enzyme that hydrolyzes CoA species, is highly expressed in the liver, and resides in the peroxisomes. Peroxisomes are organelles where the preferential oxidation of dicarboxylic fatty acids occurs and where the hepatic synthesis of the primary bile acids cholic acid and chenodeoxycholic acid is completed. We previously showed that liver-specific overexpression of NUDT7 affects peroxisomal lipid metabolism but does not prevent the increase in total liver CoA levels that occurs during fasting. We generated Nudt7^-/- mice to further characterize the role that peroxisomal (acyl-)CoA degradation plays in the modulation of the size and composition of the acyl-CoA pool and in the regulation of hepatic lipid metabolism. Here, we show that deletion of Nudt7 alters the composition of the hepatic acyl-CoA pool in mice fed a low-fat diet, but only in males fed a Western diet does the lack of NUDT7 activity increase total liver CoA levels. This effect is driven by the male-specific accumulation of medium-chain dicarboxylic acyl-CoAs, which are produced from the β-oxidation of dicarboxylic fatty acids. We also show that, under conditions of elevated synthesis of chenodeoxycholic acid derivatives, Nudt7 deletion promotes the production of tauromuricholic acid, decreasing the hydrophobicity index of the intestinal bile acid pool and increasing fecal cholesterol excretion in male mice. These findings reveal that NUDT7-mediated hydrolysis of acyl-CoA pathway intermediates in liver peroxisomes contributes to the regulation of dicarboxylic fatty acid metabolism and the composition of the bile acid pool.

Recent Advances in the Digestive, Metabolic and Therapeutic Effects of Farnesoid X Receptor and Fibroblast Growth Factor 19: From Cholesterol to Bile Acid Signaling

Bile acids (BA) are amphiphilic molecules synthesized in the liver (primary BA) starting from cholesterol. In the small intestine, BA act as strong detergents for emulsification, solubilization and absorption of dietary fat, cholesterol, and lipid-soluble vitamins. Primary BA escaping the active ileal re-absorption undergo the microbiota-dependent biotransformation to secondary BA in the colon, and passive diffusion into the portal vein towards the liver. BA also act as signaling molecules able to play a systemic role in a variety of metabolic functions, mainly through the activation of nuclear and membrane-associated receptors in the intestine, gallbladder, and liver. BA homeostasis is tightly controlled by a complex interplay with the nuclear receptor farnesoid X receptor (FXR), the enterokine hormone fibroblast growth factor 15 (FGF15) or the human ortholog FGF19 (FGF19). Circulating FGF19 to the FGFR4/β-Klotho receptor causes smooth muscle relaxation and refilling of the gallbladder. In the liver the binding activates the FXR-small heterodimer partner (SHP) pathway. This step suppresses the unnecessary BA synthesis and promotes the continuous enterohepatic circulation of BAs. Besides BA homeostasis, the BA-FXR-FGF19 axis governs several metabolic processes, hepatic protein, and glycogen synthesis, without inducing lipogenesis. These pathways can be disrupted in cholestasis, nonalcoholic fatty liver disease, and hepatocellular carcinoma. Thus, targeting FXR activity can represent a novel therapeutic approach for the prevention and the treatment of liver and metabolic diseases.

EDP-297: A novel, farnesoid X receptor agonist-Results of a phase I study in healthy subjects

EDP-297 is a farnesoid X receptor agonist under development for treating nonalcoholic steatohepatitis. The pharmacokinetic (PK), pharmacodynamic (PD), food effect, and safety were evaluated in a single ascending dose (SAD) and multiple ascending dose (MAD) phase I study. Healthy subjects received single EDP-297 doses of 20-600 μg or once daily doses of 5-90 μg for 14 days. Safety, PKs, and PDs were assessed, including fibroblast growth factor 19 (FGF-19) and 7-α-hydroxy-4-cholesten-3-one (C4). Among 82 subjects, EDP-297 was generally well-tolerated. Pruritus was observed in four subjects in the SAD phase and seven subjects in the MAD phase; four severe cases occurred at 90 μg in the MAD phase, including one that led to drug discontinuation. A grade 2 elevation in alanine aminotransferase occurred with 90 μg. Mean lipid values remained within normal range. Plasma exposures of EDP-297 increased with SADs and MADs, with mean half-life following multiple doses of 9-12.5 h. No food effect was observed. Mean FGF-19 increased and C4 decreased up to 95% and 92%, respectively. EDP-297 was generally well-tolerated up to 60 μg MAD, with linear PKs suitable for once daily oral dosing, target engagement, and no food effect.

AIBP Regulates Metabolism of Ketone and Lipids but Not Mitochondrial Respiration

Accumulating evidence indicates that the APOA1 binding protein (AIBP)-a secreted protein-plays a profound role in lipid metabolism. Interestingly, AIBP also functions as an NAD(P)H-hydrate epimerase to catalyze the interconversion of NAD(P)H hydrate [NAD(P)HX] epimers and is renamed as NAXE. Thus, we call it NAXE hereafter. We investigated its role in NAD(P)H-involved metabolism in murine cardiomyocytes, focusing on the metabolism of hexose, lipids, and amino acids as well as mitochondrial redox function. Unbiased metabolite profiling of cardiac tissue shows that NAXE knockout markedly upregulates the ketone body 3-hydroxybutyric acid (3-HB) and increases or trends increasing lipid-associated metabolites cholesterol, α-linolenic acid and deoxycholic acid. Paralleling greater ketone levels, ChemRICH analysis of the NAXE-regulated metabolites shows reduced abundance of hexose despite similar glucose levels in control and NAXE-deficient blood. NAXE knockout reduces cardiac lactic acid but has no effect on the content of other NAD(P)H-regulated metabolites, including those associated with glucose metabolism, the pentose phosphate pathway, or Krebs cycle flux. Although NAXE is present in mitochondria, it has no apparent effect on mitochondrial oxidative phosphorylation. Instead, we detected more metabolites that can potentially improve cardiac function (3-HB, adenosine, and α-linolenic acid) in the Naxe^-/- heart; these mice also perform better in aerobic exercise. Our data reveal a new role of NAXE in cardiac ketone and lipid metabolism.

Intestinal microbiota in the treatment of metabolically associated fatty liver disease

Metabolically associated fatty liver disease (MAFLD) is a common cause of chronic liver disease, the hepatic manifestation of metabolic syndrome. Despite the increasing incidence of MAFLD, no effective treatment is available. Recent research indicates a link between the intestinal microbiota and liver diseases such as MAFLD. The composition and characteristics of the intestinal microbiota and therapeutic perspectives of MAFLD are reviewed in the current study. An imbalance in the intestinal microbiota increases intestinal permeability and exposure of the liver to adipokines. Furthermore, we focused on reviewing the latest "gut-liver axis" targeted therapy.

Activation of Pancreatic Acinar FXR Protects against Pancreatitis via Osgin1-Mediated Restoration of Efficient Autophagy

Pancreatitis is the leading cause of hospitalization in gastroenterology, and no medications are available for treating this disease in current clinical practice. FXR plays an anti-inflammatory role in diverse inflammatory diseases, while its function in pancreatitis remains unknown. In this study, we initially observed a marked increase of nuclear FXR in pancreatic tissues of human patients with pancreatitis. Deleting the FXR in pancreatic acinar cells (FXRacinarΔ/Δ ) led to more severe pancreatitis in mouse models of caerulein-induced acute and chronic pancreatitis, while the FXR agonist GW4064 significantly attenuated pancreatitis in caerulein or arginine-induced acute pancreatitis and caerulein-induced chronic pancreatitis. FXR deletion impaired the viability and stress responses of pancreatic exocrine organoids (PEOs) in vitro. Utilizing RNA-seq and ChIP-seq of PEOs, we identified Osgin1 as a direct target of FXR in the exocrine pancreas, which was also increasingly expressed in human pancreatitis tissues compared to normal pancreatic tissues. Pancreatic knockdown of Osgin1 by AAV-pan abolished the therapeutic effects of FXR activation on pancreatitis, whereas pancreatic overexpression of Osgin1 effectively alleviated caerulein-induced pancreatitis. Mechanistically, we found that the FXR-OSGIN1 axis stimulated autophagic flux in the pancreatic tissues and cell lines, which was considered as the intrinsic mechanisms through which FXR-OSGIN1 protecting against pancreatitis. Our results highlight the protective role of the FXR-OSGIN1 axis in pancreatitis and provided a new target for the treatment of this disease.

A history of research into the physiology of bile, from Hippocrates to molecular medicine

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Xanthohumol improves cognition in farnesoid X receptor-deficient mice on a high-fat diet

Xanthohumol (XN) improves cognition of wild-type rodents on a high-fat diet (HFD). Bile acids and ceramide levels in the liver and hippocampus might be linked to these effects. XN modulates activity of the nuclear farnesoid X receptor (FXR; also known as NR1H4), the primary receptor for bile acids. To determine the role of FXR in the liver and intestine in mediating the effects of XN on cognitive performance, mice with intestine- and liver-specific FXR ablation (FXRIntestine-/- and FXRLiver-/-, respectively) on an HFD or an HFD containing XN were cognitively tested. XN improved cognitive performance in a genotype- and sex-dependent manner, with improved task learning in females (specifically wild-type), reversal learning in males (specifically wild-type and FXRIntestine-/- mutant) and spatial learning (both sexes). XN increased hippocampal diacylglycerol and sphingomyelin levels in females but decreased them in males. XN increased the ratio of shorter-chain to longer-chain ceramides and hexaceramides. Higher diacylglycerol and lower longer-chain ceramide and hexaceramide levels were linked to improved cognitive performance. Thus, the beneficial sex-dependent cognitive effects of XN are linked to changes in hippocampal diacylglycerol and ceramide levels. This article has an associated First Person interview with the first author of the paper.

Bile Acid and Gut Microbiota in Irritable Bowel Syndrome

Gut microbiota and their metabolites like bile acid (BA) have been investigated as causes of irritable bowel syndrome (IBS) symptoms. Primary BAs are synthesized and conjugated in the liver and released into the duodenum. BA biotransformation by gut microbiota begins in the intestine and results in production of a broad range of secondary BAs. Deconjugation is considered the gateway reaction for further modification and is mediated by bile salt hydrolase, which is widely expressed by the gut microbiota. However, gut bacteria that convert primary BAs to secondary BAs belong to a limited number of species, mainly Clostridiales. Like gut microbiota modify BA profile, BAs can shape gut microbiota via direct and indirect actions. BAs have prosecretory effects and regulates gut motility. BAs can also affect gut sensitivity. Because of the vital role of the gut microbiota and BAs in gut function, their bidirectional relationship may contribute to the pathophysiology of IBS. Individuals with IBS have been reported to have altered microbial profiles and modified BA profiles. A significant increase in fecal primary BA and a corresponding decrease in secondary BA have been observed in IBS with predominant diarrhea. In addition, primary BA was positively correlated with IBS symptoms. In IBS with predominant diarrhea, bacteria with reduced abundance mainly belonged to the genera in Ruminococcaceae and exhibited a negative correlation with primary BAs. Integrating the analysis of the gut microbiota and BAs could better understanding of IBS pathophysiology. The gap in this field needs to be further filled in the future.

Transcription Factor FXR Activates DHRS9 to Inhibit the Cell Oxidative Phosphorylation and Suppress Colon Cancer Progression

BACKGROUND

Colon cancer is a common gastrointestinal malignancy. It has been discovered that Farnesoid X receptor (FXR) plays an imperative regulatory role in multitype cancers in recent years. However, its regulatory mechanism in colon cancer has not been clearly explored. This study intended to explore the molecular regulatory mechanism of FXR and its downstream genes on the malignant progression of colon cancer.

METHODS

The mRNA and protein expression of FXR in colon cancer cells were measured by quantitative real-time polymerase chain reaction and Western blot. The effects of FXR on the biological function of colon cancer cells were measured by Cell Counting Kit-8, colony formation, and transwell assays. The downstream target gene of FXR was predicted by bioinformatics analysis and found to be associated with cellular oxidative phosphorylation. The binding relationship between FXR and its downstream gene dehydrogenase/reductase member 9 (DHRS9) was verified through luciferase reporter assay and chromatin immunoprecipitation assay. The changes of oxidative phosphorylation were detected by Western blot and oxygen consumption rate determination. The effect of FXR/DHRS9 axis on the malignant progression of colon cancer cells was further confirmed by rescue experiments.

RESULTS

FXR was underexpressed in colon cancer tissues and cells, and overexpressing FXR could repress the malignant behaviors of colon cancer cells. Besides, DHRS9 was a downstream gene of FXR, and FXR/DHRS9 inhibited the deterioration of colon cancer through inhibiting oxidative phosphorylation. Moreover, promoting FXR expression in colon cancer cells could partially reverse the biological function changes caused by silencing DHRS9 expression.

CONCLUSION

FXR inhibited the oxidative phosphorylation and inhibited the malignant progression of colon cancer cells via targeting DHRS9.

Chaihu-shugan-san alleviates depression-like behavior in mice exposed to chronic unpredictable stress by altering the gut microbiota and levels of the bile acids hyocholic acid and 7-ketoDCA

Chaihu-Shugan-San (CSS) is a traditional botanical drug formula often prescribed to treat depression in oriental countries, but its pharmacotherapeutic mechanism remains unknown. It was recently reported that CSS alters the composition of intestinal microflora and related metabolites such as bile acids (BAs). Since the intestinal microflora affects physiological functions of the brain through the gut-microbiota-brain axis, herein we investigated whether CSS altered BA levels, gut microflora, and depression-like symptoms in chronic unpredictable mild stress (CUMS) mice, a well-established mouse model of depression. Furthermore, we determined whether BA manipulation and fecal microbiota transplantation altered CSS antidepressant actions. We found that the BA chelator cholestyramine impaired the antidepressant effects of CSS, which was partially rescued by dietary cholic acid. CSS increased the relative abundance of Parabacteroides distasonis in the colon of CUMS mice, and increased serum levels of various BAs including hyocholic acid (HCA) and 7-ketodeoxycholic acid (7-ketoDCA). Furthermore, gut bacteria transplantation from CSS-treated mice into untreated or cholestyramine-treated CUMS mice restored serum levels of HCA and 7-ketoDCA, alleviating depression-like symptoms. In the hippocampus, CSS-treated mice had decreased expression of genes associated with BA transport (Bsep and Fxr) and increased expression of brain-derived neurotrophic factor and its receptor, TrkB. Overall, CSS increases intestinal P. distasonis abundance, leading to elevated levels of secondary BAs in the circulation and altered expression of hippocampal genes implicated in BA transport and neurotrophic signaling. Our data strongly suggest that the gut microbiota-brain axis contributes to the potent antidepressant action of CSS by modulating BA metabolism.

Bile Acids-A Peek Into Their History and Signaling

Bile acids wear many hats, including those of an emulsifier to facilitate nutrient absorption, a cholesterol metabolite, and a signaling molecule in various tissues modulating itching to metabolism and cellular functions. Bile acids are synthesized in the liver but exhibit wide-ranging effects indicating their ability to mediate organ-organ crosstalk. So, how does a steroid metabolite orchestrate such diverse functions? Despite the inherent chemical similarity, the side chain decorations alter the chemistry and biology of the different bile acid species and their preferences to bind downstream receptors distinctly. Identification of new modifications in bile acids is burgeoning, and some of it is associated with the microbiota within the intestine. Here, we provide a brief overview of the history and the various receptors that mediate bile acid signaling in addition to its crosstalk with the gut microbiota.

Non-alcoholic fatty liver disease and cardiovascular pathology: features of patient management on a clinical example

Non-alcoholic fatty liver disease (NAFLD) is recognized as an interdisciplinary problem at the intersection of therapy, gastroenterology and endocrinology. In recent years, there has been a significant increase in interest in NAFLD as an accomplice of cardiovascular disease (CVD) and type 2 diabetes mellitus (DM2). The article discusses the mechanisms of NAFLD in the development and progression of cardiovascular diseases depending on risk factors and comorbidity, including a clinical case. The proven clear association of NAFLD with obesity, DM 2, CVD suggests that these comorbid diseases are interdependent in their natural course. Pathogenetically substantiated management of NAFLD can positively influence the course of comorbid conditions. The role of ursodeoxycholic acid drugs in the treatment of NAFLD and the effect of this therapy on the course of associated diseases and conditions are discussed.

Pentacyclic triterpenes modulate farnesoid X receptor expression in colonic epithelial cells: implications for colonic secretory function

The nuclear bile acid receptor, farnesoid X receptor (FXR), is an important regulator of intestinal and metabolic function. Previous studies suggest that pentacyclic triterpenes (PCTs), a class of plant-derived bioactive phytochemical, can modulate FXR activity and may therefore offer therapeutic benefits. Here, we investigated the effects of a prototypical PCT, hederagenin (HG), on FXR expression, activity, and antisecretory actions in colonic epithelial cells. T₈₄ cells and murine enteroid-derived monolayers were employed to assess HG effects on FXR expression and activity in colonic epithelia. We measured mRNA levels by qRT-PCR and protein by ELISA and immunoblotting. Transepithelial Cl⁻ secretion was assessed as changes in short circuit current in Ussing chambers. We determined HG treatment (5–10 μM) alone did not induce FXR activation but significantly increased expression of the receptor, both in T₈₄ cells and murine enteroid-derived monolayers. This effect was accompanied by enhanced FXR activity, as assessed by FGF-15/19 induction in response to the synthetic, GW4064, or natural FXR agonist, chenodeoxycholic acid. Effects of HG on FXR expression and activity were mimicked by another PCT, oleanolic acid. Furthermore, we found FXR-induced downregulation of cystic fibrosis transmembrane conductance regulator Cl⁻ channels and inhibition of transepithelial Cl⁻ secretion were enhanced in HG-treated cells. These data demonstrate that dietary PCTs have the capacity to modulate FXR expression, activity, and antisecretory actions in colonic epithelial cells. Based on these data, we propose that plants rich in PCTs, or extracts thereof, have excellent potential for development as a new class of “FXR-targeted nutraceuticals”.

Multiple Timescale Dynamic Analysis of Functionally-Impairing Mutations in Human Ileal Bile Acid-Binding Protein

Human ileal bile acid-binding protein (hI-BABP) has a key role in the enterohepatic circulation of bile salts. Its two internal binding sites exhibit positive cooperativity accompanied by a site-selectivity of glycocholate (GCA) and glycochenodeoxycholate (GCDA), the two most abundant bile salts in humans. To improve our understanding of the role of dynamics in ligand binding, we introduced functionally impairing single-residue mutations at two key regions of the protein and subjected the mutants to NMR relaxation analysis and MD simulations. According to our results, mutation in both the vicinity of the C/D (Q51A) and the G/H (Q99A) turns results in a redistribution of motional freedom in apo hI-BABP. Mutation Q51A, deteriorating the site-selectivity of GCA and GCDA, results in the channeling of ms fluctuations into faster motions in the binding pocket hampering the realization of key side chain interactions. Mutation Q99A, abolishing positive binding cooperativity for GCDA, leaves ms motions in the C-terminal half unchanged but by decoupling βD from a dynamic cluster of the N-terminal half displays an increased flexibility in the vicinity of site 1. MD simulations of the variants indicate structural differences in the portal region and mutation-induced changes in dynamics, which depend on the protonation state of histidines. A dynamic coupling between the EFGH portal, the C/D-region, and the helical cap is evidenced highlighting the interplay of structural and dynamic effects in bile salt recognition in hI-BABP.

Perinatal exposure to UDCA prevents neonatal cholestasis in Cyp2c70-/- mice with human-like bile acids

BACKGROUND

Cyp2c70^-/- mice with a human-like bile acid (BA) composition display features of neonatal cholestasis. We assessed whether perinatal ursodeoxycholic acid (UDCA) exposure prevents neonatal cholestasis in Cyp2c70^-/- mice and reduces cholangiopathy development later in life.

METHODS

Cyp2c70^+/- males were crossed with Cyp2c70^+/- females fed either a regular chow diet or a 0.1% UDCA-containing diet during breeding, gestation, and suckling. Cholestasis and liver function parameters were assessed in their Cyp2c70^-/- and wild-type offspring at 3 and 8 weeks of age.

RESULTS

Three-week-old Cyp2c70^-/- pups showed features of neonatal cholestasis, including elevated plasma BAs and transaminases, which were completely prevented in Cyp2c70^-/- pups upon perinatal UDCA exposure. In addition, UDCA administration to the dams corrected altered hepatic gene expression patterns in Cyp2c70^-/- pups, reduced markers of fibrogenesis and inflammation, and prevented cholangiocyte proliferation. Yet, these beneficial effects of perinatal UDCA exposure were not retained into adulthood upon discontinuation of treatment.

CONCLUSION

Perinatal exposure of Cyp2c70^-/- mice to UDCA has beneficial effects on liver function parameters, supporting a direct role of BA hydrophobicity in the development of neonatal cholestasis in these mice. However, prevention of neonatal cholestasis in Cyp2c70^-/- mice has no long-lasting effects on liver pathophysiology.

IMPACT

This is the first study showing that perinatal UDCA exposure prevents features of neonatal cholestasis that are observed in mice with a human-like bile acid composition, i.e., Cyp2c70^-/- mice. Perinatal UDCA exposure of Cyp2c70^-/- pups leads to UDCA enrichment in their circulating bile acid pool and, consequently, to a reduced hydrophobicity of biliary bile acids. Perinatal UDCA exposure of Cyp2c70^-/- pups has no long-lasting effects on the development of cholangiopathy after discontinuation of treatment. The results in this study expand current knowledge regarding acute and long-lasting effects of UDCA treatment in early life.

CEBPB regulates the bile acid receptor FXR to accelerate colon cancer progression by modulating aerobic glycolysis

BACKGROUND

Aerobic glycolysis is a main characteristic of tumors, and inhibited glycolysis impedes the tumor development. Farnesoid X Receptor (FXR) mainly regulates bile acid metabolism. In this research, we mainly investigated whether FXR was involved in the regulation of glycolysis in colon cancer.

METHODS

The differential expression analysis was performed on FXR and Enhancer Binding Protein Beta (CEBPB) data in colon cancer downloaded from The Cancer Genome Atlas (TCGA) database. Western blot and qRT-PCR were used to detect the expression levels of CEBPB and FXR. The upstream gene of FXR was predicted through bioinformatic analysis. ChIP and dual luciferease assays were performed to confirm the targeted relationship between CEBPB and FXR. Gene Set Enrichment Analysis (GSEA) was performed on FXR. Finally, the glycolysis capabilities of cells in each treatment group were detected. CCK-8, colony formation assay and flow cytometry were performed to test proliferation and apoptosis of colon cancer cells.

RESULTS

FXR was lowly expressed at the cell level in colon cancer. In vitro assays verified the antitumor effect of FXR on colon cancer. ChIP and dual luciferase assays verified that transcription factor CEBPB bound with the promotor region of FXR, and negatively regulated the expression of FXR. Cell function assays proved that silenced expression of FXR promoted glycolysis, which promoted the development of colon cancer cells.

CONCLUSION

The study on FXR-regulated glycolysis of colon cancer cells helps us to further understand the molecular mechanism by which FXR regulated the development of colon cancer cells.

Metabolomic and transcriptomic signatures of influenza vaccine response in healthy young and older adults

Seasonal influenza causes mild to severe respiratory infections and significant morbidity, especially in older adults. Transcriptomic analysis in populations across multiple flu seasons has provided insights into the molecular determinants of vaccine response. Still, the metabolic changes that underlie the immune response to influenza vaccination remain poorly characterized. We performed untargeted metabolomics to analyze plasma metabolites in a cohort of younger and older subjects before and after influenza vaccination to identify vaccine-induced molecular signatures. Metabolomic and transcriptomic data were combined to define networks of gene and metabolic signatures indicative of high and low antibody response in these individuals. We observed age-related differences in metabolic baselines and signatures of antibody response to influenza vaccination and the abundance of α-linolenic and linoleic acids, sterol esters, fatty-acylcarnitines, and triacylglycerol metabolism. We identified a metabolomic signature associated with age-dependent vaccine response, finding increased tryptophan and decreased polyunsaturated fatty acids (PUFAs) in young high responders (HRs), while fatty acid synthesis and cholesteryl esters accumulated in older HRs. Integrated metabolomic and transcriptomic analysis shows that depletion of PUFAs, which are building blocks for prostaglandins and other lipid immunomodulators, in young HR subjects at Day 28 is related to a robust immune response to influenza vaccination. Increased glycerophospholipid levels were associated with an inflammatory response in older HRs to flu vaccination. This multi-omics approach uncovered age-related molecular markers associated with influenza vaccine response and provides insight into vaccine-induced metabolic responses that may help guide development of more effective influenza vaccines.

Nuclear Receptor Pathways Mediating the Development of Boar Taint

The nuclear receptors PXR, CAR, and FXR are activated by various ligands and function as transcription factors to control the expression of genes that regulate the synthesis and metabolism of androstenone and skatole. These compounds are produced in entire male pigs and accumulate in the fat to cause the development of a meat quality issue known as boar taint. The extent of this accumulation is influenced by the synthesis and hepatic clearance of androstenone and skatole. For this reason, PXR, CAR, and FXR-mediated signaling pathways have garnered interest as potential targets for specialized treatments designed to reduce the development of boar taint. Recent research has also identified several metabolites produced by gut microbes that act as ligands for these nuclear receptors (e.g., tryptophan metabolites, short-chain fatty acids, bile acids); however, the connection between the gut microbiome and boar taint development is not clear. In this review, we describe the nuclear receptor signaling pathways that regulate the synthesis and metabolism of boar taint compounds and outline the genes involved. We also discuss several microbial-derived metabolites and dietary additives that are known or suspected nuclear receptor ligands and suggest how these compounds could be used to develop novel treatments for boar taint.

Bile acids in immunity: Bidirectional mediators between the host and the microbiota

Host-microbiota interactions are bidirectional. On one hand, ecological pressures exerted by the host shape the composition and function of the microbiota. On the other, resident microbes trigger multiple pathways that influence the immunity of the host. Bile acids participate in both parts of this interplay. As host-derived compounds, they display bacteriostatic properties and affect the survival and growth of the members of the microbial community. As microbiota-modified metabolites, they further influence the microbiota composition and, in parallel, modulate the immunity of the host. Here, we provide a comprehensive overview of the mechanisms behind this unique dialogue and discuss how we can harness bile acids to treat intestinal inflammation.

Automating Predictive Toxicology Using ComptoxAI

ComptoxAI is a new data infrastructure for computational and artificial intelligence research in predictive toxicology. Here, we describe and showcase ComptoxAI's graph-structured knowledge base in the context of three real-world use-cases, demonstrating that it can rapidly answer complex questions about toxicology that are infeasible using previous technologies and data resources. These use-cases each demonstrate a tool for information retrieval from the knowledge base being used to solve a specific task: The "shortest path" module is used to identify mechanistic links between perfluorooctanoic acid (PFOA) exposure and nonalcoholic fatty liver disease; the "expand network" module identifies communities that are linked to dioxin toxicity; and the quantitative structure-activity relationship (QSAR) dataset generator predicts pregnane X receptor agonism in a set of 4,021 pesticide ingredients. The contents of ComptoxAI's source data are rigorously aggregated from a diverse array of public third-party databases, and ComptoxAI is designed as a free, public, and open-source toolkit to enable diverse classes of users including biomedical researchers, public health and regulatory officials, and the general public to predict toxicology of unknowns and modes of action.

Bile Salt Hydrolase-Competent Probiotics in the Management of IBD: Unlocking the "Bile Acid Code"

Bile acid (BA) species and the gut microbiota (GM) contribute to intestinal mucosa homeostasis. BAs shape the GM and, conversely, intestinal bacteria with bile salt hydrolase (BSH) activity modulate the BA pool composition. The mutual interaction between BAs and intestinal microorganisms also influences mucosal barrier integrity, which is important for inflammatory bowel disease (IBD) pathogenesis, prevention and therapy. High levels of secondary BAs are detrimental for the intestinal barrier and increase the intestinal inflammatory response and dysbiosis. Additionally, a lack of BSH-active bacteria plays a role in intestinal inflammation and BA dysmetabolism. Thus, BSH-competent bacteria in probiotic formulations are being actively studied in IBD. At the same time, studies exploring the modulation of the master regulator of BA homeostasis, the Farnesoid X Receptor (FXR), in intestinal inflammation and how this impacts the GM are gaining significant momentum. Overall, the choice of probiotic supplementation should be a peculiar issue of personalized medicine, considering not only the disease but also the specific BA and metabolic signatures of a given patient.

Nonalcoholic Steatohepatitis Drug Development Pipeline: An Update

Nonalcoholic steatohepatitis (NASH) is a burgeoning global health crisis that mirrors the obesity pandemic. This global health crisis has stimulated active research to develop novel NASH pharmacotherapies targeting dysregulated inflammatory, cellular stress, and fibrogenetic processes that include (1) metabolic pathways to improve insulin sensitivity, de novo lipogenesis, and mitochondrial utilization of fatty acids; (2) cellular injury or inflammatory targets that reduce inflammatory cell recruitment and signaling; (3) liver-gut axis targets that influence bile acid enterohepatic circulation and signaling; and (4) antifibrotic targets. In this review, we summarize several of the therapeutic agents that have been studied in phase 2 and 3 randomized trials. In addition to reviewing novel therapeutic drugs targeting nuclear receptor pathways, liver chemokine receptors, liver lipid metabolism, lipotoxicity or cell death, and glucagon-like peptide-1 receptors, we also discuss the rationale behind the use of combination therapy and the lessons learned from unsuccessful or negative clinical trials.

Bile Acid-Drug Interaction via Organic Anion-Transporting Polypeptide 4C1 Is a Potential Mechanism of Altered Pharmacokinetics of Renally Excreted Drugs

Patients with liver diseases not only experience the adverse effects of liver-metabolized drugs, but also the unexpected adverse effects of renally excreted drugs. Bile acids alter the expression of renal drug transporters, however, the direct effects of bile acids on drug transport remain unknown. Renal drug transporter organic anion-transporting polypeptide 4C1 (OATP4C1) was reported to be inhibited by chenodeoxycholic acid. Therefore, we predicted that the inhibition of OATP4C1-mediated transport by bile acids might be a potential mechanism for the altered pharmacokinetics of renally excreted drugs. We screened 45 types of bile acids and calculated the IC50, Ki values, and bile acid−drug interaction (BDI) indices of bile acids whose inhibitory effect on OATP4C1 was >50%. From the screening results, lithocholic acid (LCA), glycine-conjugated lithocholic acid (GLCA), and taurine-conjugated lithocholic acid (TLCA) were newly identified as inhibitors of OATP4C1. Since the BDI index of LCA was 0.278, LCA is likely to inhibit OATP4C1-mediated transport in clinical settings. Our findings suggest that dose adjustment of renally excreted drugs may be required in patients with renal failure as well as in patients with hepatic failure. We believe that our findings provide essential information for drug development and safe drug treatment in clinics.

Versatile Triad Alliance: Bile Acid, Taurine and Microbiota

Taurine is the most abundant free amino acid in the body, and is mainly derived from the diet, but can also be produced endogenously from cysteine. It plays multiple essential roles in the body, including development, energy production, osmoregulation, prevention of oxidative stress, and inflammation. Taurine is also crucial as a molecule used to conjugate bile acids (BAs). In the gastrointestinal tract, BAs deconjugation by enteric bacteria results in high levels of unconjugated BAs and free taurine. Depending on conjugation status and other bacterial modifications, BAs constitute a pool of related but highly diverse molecules, each with different properties concerning solubility and toxicity, capacity to activate or inhibit receptors of BAs, and direct and indirect impact on microbiota and the host, whereas free taurine has a largely protective impact on the host, serves as a source of energy for microbiota, regulates bacterial colonization and defends from pathogens. Several remarkable examples of the interaction between taurine and gut microbiota have recently been described. This review will introduce the necessary background information and lay out the latest discoveries in the interaction of the co-reliant triad of BAs, taurine, and microbiota.

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.

Circulating bile acid concentrations and non-alcoholic fatty liver disease in Guatemala

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is a major liver disease worldwide. Bile acid dysregulation may be a key feature in its pathogenesis and progression.

AIMS

To characterise the relationship between bile acid levels and NAFLD at the population level METHODS: We conducted a cross-sectional study in Guatemala in 2016 to examine the prevalence of NAFLD. Participants (n = 415) completed questionnaires, donated blood samples and had a brief medical exam. NAFLD was determined by calculation of the fatty liver index. The levels of 15 circulating bile acids were determined by LC-MS/MS. Adjusted prevalence odds ratios (POR_adj ) and 95% CI were calculated to examine the relationships between bile acid levels (in tertiles) and NAFLD.

RESULTS

Persons with NAFLD had significantly higher levels of the conjugated primary bile acids glycocholic acid (GCA) (POR_{adj T3 vs T1}  = 1.85), taurocholic acid (TCA) (POR_{adj T3 vs T1}  = 2.45) and taurochenodeoxycholic acid (TCDCA) (POR_{adj T3 vs T1}  = 2.10), as well as significantly higher levels the unconjugated secondary bile acid, deoxycholic acid (DCA) (POR_{adj T3 vs T1}  = 1.78) and its conjugated form, taurodeoxycholic acid (TDCA) (POR_{adj T3 vs T1}  = 1.81).

CONCLUSIONS

The bile acid levels of persons with and without NAFLD differed significantly. Among persons with NAFLD, higher levels of the conjugated forms of CA (i.e. GCA, TCA) and the secondary bile acids that derive from CA (i.e. DCA, TDCA) may indicate there is hepatic overproduction of CA, which may affect the liver via aberrant signalling mediated by the bile acids.

Role of bile acids and their receptors in gastrointestinal and hepatic pathophysiology

Bile acids (BAs) can regulate their own metabolism and transport as well as other key aspects of metabolic homeostasis via dedicated (nuclear and G protein-coupled) receptors. Disrupted BA transport and homeostasis results in the development of cholestatic disorders and contributes to a wide range of liver diseases, including nonalcoholic fatty liver disease and hepatocellular and cholangiocellular carcinoma. Furthermore, impaired BA homeostasis can also affect the intestine, contributing to the pathogenesis of irritable bowel syndrome, inflammatory bowel disease, and colorectal and oesophageal cancer. Here, we provide a summary of the role of BAs and their disrupted homeostasis in the development of gastrointestinal and hepatic disorders and present novel insights on how targeting BA pathways might contribute to novel treatment strategies for these disorders.

Immunomodulatory functions of FXR

The Farnesoid-x-receptor (FXR) is a bile acids sensor activated in humans by primary bile acids. FXR is mostly expressed in liver, intestine and adrenal glands but also by cells of innate immunity, including macrophages, liver resident macrophages, the Kupffer cells, natural killer cells and dendritic cells. In normal physiology and clinical disorders, cells of innate immunity mediate communications between liver, intestine and adipose tissues. In addition to FXR, the G protein coupled receptor (GPBAR1), that is mainly activated by secondary bile acids, whose expression largely overlaps FXR, modulates chemical communications from the intestinal microbiota and the host's immune system, integrating epithelial cells and immune cells in the entero-hepatic system, providing a mechanism for development of a tolerogenic state toward the intestinal microbiota. Disruption of FXR results in generalized inflammation and disrupted bile acids metabolism. While FXR agonism in preclinical models provides counter-regulatory signals that attenuate inflammation-driven immune dysfunction in a variety of liver and intestinal disease models, the clinical relevance of these mechanisms in the setting of FXR-related disorders remain poorly defined.

Bile acids and their receptors: modulators and therapeutic targets in liver inflammation

Bile acids participate in the intestinal emulsion, digestion, and absorption of lipids and fat-soluble vitamins. When present in high concentrations, as in cholestatic liver diseases, bile acids can damage cells and cause inflammation. After the discovery of bile acids receptors about two decades ago, bile acids are considered signaling molecules. Besides regulating bile acid, xenobiotic, and nutrient metabolism, bile acids and their receptors have shown immunomodulatory properties and have been proposed as therapeutic targets for inflammatory diseases of the liver. This review focuses on bile acid-related signaling pathways that affect inflammation in the liver and provides an overview of the preclinical and clinical applications of modulators of these pathways for the treatment of cholestatic and autoimmune liver diseases.

Intestinal FXR Activation via Transgenic Chimera or Chemical Agonism Prevents Colitis-Associated and Genetically-Induced Colon Cancer

Simple Summary

Disruption of Bile Acids (BA) regulation with increased BA concentration and modulation or their detergent pro-inflammatory activity has been linked to colorectal cancer (CRC). Farnesoid X Receptor (FXR) is the master regulator of BA homeostasis; FXR is a nuclear receptor that transcriptionally modulates their synthesis, transport and metabolism. In this study, we demonstrated that intestinal FXR activation prevented both inflammation- and genetically-driven colorectal tumorigenesis by modulating BA pool size and composition. This could open new avenues for the therapeutic management of intestinal inflammation and tumorigenesis.

Abstract

The Farnesoid X Receptor (FXR) is the master regulator of Bile Acids (BA) homeostasis orchestrating their synthesis, transport and metabolism. Disruption of BA regulation has been linked to gut-liver axis diseases such as colorectal cancer (CRC). In this study, firstly we examined the role of constitutive activation of intestinal FXR in CRC; then we pre-clinically investigated the therapeutic potential of a diet enriched with a synthetic FXR agonist in two models of CRC (chemically-induced and genetic models). We demonstrated that mice with intestinal constitutive FXR activation are protected from AOM/DSS-induced CRC with a significant reduction of tumor number compared to controls. Furthermore, we evaluated the role of chemical FXR agonism in a DSS model of colitis in wild type (WT) and FXR^null mice. WT mice administered with the FXR activating diet showed less morphological alterations and decreased inflammatory infiltrates compared to controls. The FXR activating diet also protected WT mice from AOM/DSS-induced CRC by reducing tumors’ number and size. Finally, we proved that the FXR activating diet prevented spontaneous CRC in APC^Min/+ mice via an FXR-dependent modulation of BA homeostasis. Our results demonstrate that intestinal FXR activation prevented both inflammation- and genetically-driven colorectal tumorigenesis by modulating BA pool size and composition. This could open new avenues for the therapeutic management of intestinal inflammation and tumorigenesis.

Lipids from gut microbiota: pursuing a personalized treatment

The discovery of microbiome metabolites has enlivened the field of fecal transplantation for therapeutic purposes. However, the transfer of pathogenic living organisms was recently observed to limit its therapeutic potential by increasing the risk of infection. Lipids produced by gut microbiota enter the circulation and control many phenotypic changes associated with microbiota composition. Fecal lipids significantly impact the regulation of several cell signaling pathways, including inflammation. Focusing on these molecules, we review how bioactive gut microbiota-associated lipids affect cellular functioning and clinical outcome. Here, we interrogate whether the gut microbiota can be considered a cutting-edge biotechnological tool for rapid metabolic engineering of meaningful lipids to offer a novel personalized therapy.

Discovery of BMS-986339, a Pharmacologically Differentiated Farnesoid X Receptor Agonist for the Treatment of Nonalcoholic Steatohepatitis

While several farnesoid X receptor (FXR) agonists under clinical investigation for the treatment of nonalcoholic steatohepatitis (NASH) have shown beneficial effects, adverse effects such as pruritus and elevation of plasma lipids have limited their clinical efficacy and approvability. Herein, we report the discovery and preclinical evaluation of compound 32 (BMS-986339), a nonbile acid FXR agonist with a pharmacologically distinct profile relative to our previously reported agonist BMS-986318. Compound 32 exhibited potent in vitro and in vivo activation of FXR, albeit with a context-dependent profile that resulted in tissue-selective effects in vivo. To our knowledge, this is the first report that demonstrates differential induction of Fgf15 in the liver and ileum by FXR agonists in vivo. Compound 32 demonstrated robust antifibrotic efficacy despite reduced activation of certain genes in the liver, suggesting that the additional pharmacology of BMS-986318 does not further benefit efficacy, possibly presenting an opportunity for reduced adverse effects. Further evaluation in humans is warranted to validate this hypothesis.

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.

A minimal bile salt excretory pump promoter allows bile acid-driven physiological regulation of transgene expression from a gene therapy vector

Background

Bile acid (BA) homeostasis is mainly regulated by bile salt excretory pump (BSEP), a hepatocyte transporter that transfers BAs to the bile. BSEP expression is regulated by BA levels through activation of farnesoid X receptor transcription factor, which binds to the inverted repeat (IR-1) element in the BSEP promoter. Gene therapy of cholestatic diseases could benefit from using vectors carrying endogenous promoters physiologically regulated by BAs, however their large size limits this approach, especially when using adeno-associated viral vector (AAV) vectors.

Results

We evaluated the functionality and BA-mediated regulation of minimal versions of human and mouse BSEP promoters containing IR-1 using AAV vectors expressing luciferase. Unexpectedly, a minimal mouse BSEP promoter (imPr) showed higher BA-mediated expression and inducibility than a minimal human promoter (ihPr) or than full-length BSEP promoters in human hepatic cells. In addition, in mice receiving an AAV8 vector carrying imPr promoter-driven luciferase expression was efficiently regulated by administration of a BA-enriched diet. Interestingly, this vector also expressed significantly higher luciferase levels in Abcb4^−/− mice, which have high levels of BAs, compared to wild type mice, or to mice receiving a vector containing the luciferase gene downstream of the constitutive alpha-1 antitrypsin promoter. In contrast, the AAV vector containing ihPr showed very low luciferase expression with no inducibility. Finally, we optimized imPr by adding three IR-1 repeats at its 5′ end. This new promoter provided higher levels of luciferase than imPr both in vitro and in vivo.

Conclusions

The imPr could represent a useful tool for gene therapy approaches in which physiological BA regulation is desired.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00803-9.