Hepatic FXR: key regulator of whole-body energy metabolism

Intestinal Bacteria Interplay With Bile and Cholesterol Metabolism: Implications on Host Physiology

Bile is a biological fluid synthesized in the liver, mainly constituted by bile acids and cholesterol, which functions as a biological detergent that emulsifies and solubilizes lipids, thereby playing an essential role in fat digestion. Besides, bile acids are important signaling molecules that regulate key functions at intestinal and systemic levels in the human body, affecting glucose and lipid metabolism, and immune homeostasis. Apart from this, due to their amphipathic nature, bile acids are toxic for bacterial cells and, thus, exert a strong selective pressure on the microbial populations inhabiting the human gut, decisively shaping the microbial profiles of our gut microbiota, which has been recognized as a metabolic organ playing a pivotal role in host health. Remarkably, bacteria in our gut also display a range of enzymatic activities capable of acting on bile acids and, to a lesser extent, cholesterol. These activities can have a direct impact on host physiology as they influence the composition of the intestinal and circulating bile acid pool in the host, affecting bile homeostasis. Given that bile acids are important signaling molecules in the human body, changes in the microbiota-residing bile biotransformation ability can significantly impact host physiology and health status. Elucidating ways to fine-tune microbiota-bile acids-host interplay are promising strategies to act on bile and cholesterol-related disorders. This manuscript summarizes the current knowledge on bile and cholesterol metabolism by intestinal bacteria, as well as its influence on host physiology, identifying knowledge gaps and opportunities to guide further advances in the field.

Bile Acid-Activated Receptors: A Review on FXR and Other Nuclear Receptors

Nuclear receptors (NRs) are ligand-dependent transcription factors that are involved in various biological processes including metabolism, reproduction, and development. Upon activation by their ligands, NRs bind to their specific DNA elements, exerting their biological functions by regulating their target gene expression. Bile acids are detergent-like molecules that are synthesized in the liver. They not only function as a facilitator for the digestion of lipids and fat-soluble vitamins but also serve as signaling molecules for several nuclear receptors to regulate diverse biological processes including lipid, glucose, and energy metabolism, detoxification and drug metabolism, liver regeneration, and cancer. The nuclear receptors including farnesoid X receptor (FXR), pregnane X receptor (PXR), constitutive androstane receptor (CAR), vitamin D receptor (VDR), and small heterodimer partner (SHP) constitute an integral part of the bile acid signaling. This chapter reviews the role of the NRs in bile acid homeostasis, highlighting the regulatory functions of the NRs in lipid and glucose metabolism in addition to bile acid metabolism.

Nonsteroidal FXR Ligands: Current Status and Clinical Applications

FXR agonists have demonstrated very promising clinical results in the treatment of liver disorders such as primary biliary cirrhosis (PBC), primary sclerosing cholangitis (PSC), and nonalcoholic steatohepatitis (NASH). NASH, in particular, is one of the last uncharted white territories in the pharma landscape, and there is a huge medical need and a large potential pharmaceutical market for a NASH pharmacotherapy. Clinical efficacy superior to most other treatment options was shown by FXR agonists such as obeticholic acid (OCA) as they improved various metabolic features including liver steatosis as well as liver inflammation and fibrosis. But OCA's clinical success comes with some major liabilities such as pruritus, high-density lipoprotein cholesterol (HDL_c) lowering, low-density lipoprotein cholesterol (LDL_c) increase, and a potential for drug-induced liver toxicity. Some of these effects can be attributed to on-target effects exerted by FXR, but with others it is not clear whether it is FXR- or OCA-related. Therefore a quest for novel, proprietary FXR agonists is ongoing with the aim to increase FXR potency and selectivity over other proteins and to overcome at least some of the OCA-associated clinical side effects through an improved pharmacology. In this chapter we will discuss the historical and ongoing efforts in the identification and development of nonsteroidal, which largely means non-bile acid-type, FXR agonists for clinical use.

Expression of the key metabolic regulators in the white adipose tissue of rats; the role of high-fat diet and aerobic training

Lipid metabolism, especially in the white adipose tissue as an active metabolic organ, is tightly regulated by the key transcription factors, such as the sterol regulatory element binding protein 1c (SREBP-1c) and the Farnesoid X Receptor (FXR). We have studied the expression of these genes in the white adipose tissue to see how a high fat diet (HFD) and two intensities of aerobic training change the lipogenic and lipolytic pathways. 44 male Wistar rats randomly divided into the normal (12% calories from fat) and HFD (56% calories from fat) groups. Each group included control (n=6), moderate trained (n=8, ~65% Vo2max) and high intensity trained (n=8, ~75% Vo2max) rats. After 8 weeks of training, the weight changes, plasma insulin and lipid profile levels and the relative gene expression of SREBP-1c and FXR in the adipose tissue was measured. Data were analysed by 2-way ANOVA (P<0.05). HFD fed rats showed higher levels of insulin and dyslipidemia that was correlated with the higher weight gain. Also, the adipose expression of SREBP-1c was higher in the HFD fed rats that it was strongly correlated with the lower FXR expression. Trained rats independent of the intensity of the training showed lower SREBP-1c and higher FXR expression, but no change was observed in the lipid profile levels. HFD-induced dyslipidemia could occur via SREBP-1c activation in the adipose tissue while the aerobic training activates FXR and inhibits the lipogenic pathways. Despite the activation of lipolytic pathways in the trained rats, it seems that diet has more effect on the lipid profile than the aerobic training.

Trimethylamine N-Oxide: A Link among Diet, Gut Microbiota, Gene Regulation of Liver and Intestine Cholesterol Homeostasis and HDL Function

Recent evidence, including massive gene-expression analysis and a wide-variety of other multi-omics approaches, demonstrates an interplay between gut microbiota and the regulation of plasma lipids. Gut microbial metabolism of choline and l-carnitine results in the formation of trimethylamine (TMA) and concomitant conversion into trimethylamine-N-oxide (TMAO) by liver flavin monooxygenase 3 (FMO3). The plasma level of TMAO is determined by the genetic variation, diet and composition of gut microbiota. Multiple studies have demonstrated an association between TMAO plasma levels and the risk of atherothrombotic cardiovascular disease (CVD). We aimed to review the molecular pathways by which TMAO production and FMO3 exert their proatherogenic effects. TMAO may promote foam cell formation by upregulating macrophage scavenger receptors, deregulating enterohepatic cholesterol and bile acid metabolism and impairing macrophage reverse cholesterol transport (RCT). Furthermore, FMO3 may promote dyslipidemia by regulating multiple genes involved in hepatic lipogenesis and gluconeogenesis. FMO3 also impairs multiple aspects of cholesterol homeostasis, including transintestinal cholesterol export and macrophage-specific RCT. At least part of these FMO3-mediated effects on lipid metabolism and atherogenesis seem to be independent of the TMA/TMAO formation. Overall, these findings have the potential to open a new era for the therapeutic manipulation of the gut microbiota to improve CVD risk.

Characterization of a murine nonalcoholic steatohepatitis model induced by high fat high calorie diet plus fructose and glucose in drinking water

There are varieties of murine models of nonalcoholic steatohepatitis (NASH) with different pathophysiologic characteristics. For preclinical assessment, a standardized model would allow comparisons of various pharmacotherapeutic candidates in efficacy, pharmacokinetics, pharmaco-metabolism, and adverse effects under a same system. The present study aims to characterize murine NASH models by comparing end-points of major abnormalities. NASH was induced by feeding high fructose/glucose in drinking water (HF/G), high-fat/calorie diet (HFCD), and in combination (HFCD-HF/G) in mice for 8 or 16 weeks. HF/G feeding caused a minimal fat accumulation and increase in free fatty acids (FFA). In contrast, HFCD-HF/G feeding resulted in a remarkable increase in body weight, subcutaneous and visceral adipose tissue, macrosteatosis with a nearly seven-fold increase in triglyceride and FFA content, accompanied with marked hepatocellular injury, inflammatory responses, fibrosis, and insulin resistance, and represented as typical NASH in histopathology, metabolic, and adipokine profiles in a progressive manner. Meanwhile, mice fed HFCD displayed significant steatosis, necroptosis, fibrosis, insulin resistance, metabolic, and adipokine profiles, and the extent is less than those fed HFCD-HF/G. Significant MCP-1, CCR-2, and NLRP-1/3 activation were found in mice fed HFCD and HFCD-HF/G for 16 weeks, whereas gene expression of CPT-1 and ACOX-1 was down-regulated in these two groups in comparison to the controls. Nuclear receptors, such as SREBP-1c, FXR, LXR-α, PPAR-α, and PPAR-γ, were strikingly elevated in the HFCD-HF/G group. In conclusion, feeding HFCD-HF/G resulted in a reliable NASH model in mice with remarkable necroptosis, steatosis, fibrosis, and insulin resistance as well as a disordered profile of lipid metabolism and adipokine, and HFCD caused significant NASH features in histopathology and metabolic profiles only at a late stage. Whereas HF/G feeding barely led to minimal fat accumulation, some changes at molecular levels and metabolic disturbance in mice.

Update on FXR Biology: Promising Therapeutic Target?

Farnesoid X receptor (FXR), a metabolic nuclear receptor, plays critical roles in the maintenance of systemic energy homeostasis and the integrity of many organs, including liver and intestine. It regulates bile acid, lipid, and glucose metabolism, and contributes to inter-organ communication, in particular the enterohepatic signaling pathway, through bile acids and fibroblast growth factor-15/19 (FGF-15/19). The metabolic effects of FXR are also involved in gut microbiota. In addition, FXR has various functions in the kidney, adipose tissue, pancreas, cardiovascular system, and tumorigenesis. Consequently, the deregulation of FXR may lead to abnormalities of specific organs and metabolic dysfunction, allowing the protein as an attractive therapeutic target for the management of liver and/or metabolic diseases. Indeed, many FXR agonists have been being developed and are under pre-clinical and clinical investigations. Although obeticholic acid (OCA) is one of the promising candidates, significant safety issues have remained. The effects of FXR modulation might be multifaceted according to tissue specificity, disease type, and/or energy status, suggesting the careful use of FXR agonists. This review summarizes the current knowledge of systemic FXR biology in various organs and the gut–liver axis, particularly regarding the recent advancement in these fields, and also provides pharmacological aspects of FXR modulation for rational therapeutic strategies and novel drug development.

What Has Bariatric Surgery Taught Us About the Role of the Upper Gastrointestinal Tract in the Regulation of Postprandial Glucose Metabolism?

The interaction between the upper gastrointestinal tract and the endocrine system is important in the regulation of metabolism and of weight. The gastrointestinal tract has a heterogeneous cellular content and comprises a variety of cells that elaborate paracrine and endocrine mediators that collectively form the entero-endocrine system. The advent of therapy that utilizes these pathways as well as the association of bariatric surgery with diabetes remission has (re-)kindled interest in the role of the gastrointestinal tract in glucose homeostasis. In this review, we will use the changes wrought by bariatric surgery to provide insights into the various gut-pancreas interactions that maintain weight, regulate satiety, and limit glucose excursions after meal ingestion.

Microengineered cultures containing human hepatic stellate cells and hepatocytes for drug development

In non-alcoholic steatohepatitis (NASH), hepatic stellate cells (HSC) differentiate into myofibroblast-like cells that cause fibrosis, which predisposes patients to cirrhosis and hepatocellular carcinoma. Thus, modeling interactions between activated HSCs and hepatocytes in vitro can aid in the development of anti-NASH/fibrosis therapeutics and lead to a better understanding of disease progression. Species-specific differences in drug metabolism and disease pathways now necessitate the supplementation of animal studies with data acquired using human liver models; however, current models do not adequately model the negative effects of primary human activated HSCs on the phenotype of otherwise well-differentiated primary human hepatocytes (PHHs) as in vivo. Therefore, here we first determined the long-term effects of primary human activated HSCs on PHH phenotype in a micropatterned co-culture (MPCC) platform while using 3T3-J2 murine embryonic fibroblasts as the control cell type since it has been shown previously to stabilize PHH functions for 4-6 weeks. We found that HSCs were not able to stabilize the PHH phenotype to the same magnitude and longevity as the fibroblasts, which subsequently inspired the development of a micropatterned tri-culture (MPTC) platform in which (a) micropatterned PHHs were functionally stabilized using fibroblasts, and (b) the PHH phenotype was modulated by culturing HSCs within the fibroblast monolayer at physiologically-relevant ratios with PHHs. Transwell inserts containing HSCs were placed atop MPCCs containing fibroblasts to confirm the effects of paracrine signaling between PHHs and HSCs. We found that while albumin and urea secretions were relatively similar in MPTCs and MPCCs (suggesting well-differentiated PHHs), increasing HSC numbers within MPTCs downregulated hepatic cytochrome-P450 (2A6, 3A4) and transporter activities, and caused steatosis over 2 weeks. Furthermore, MPTCs secreted higher levels of pro-inflammatory interleukin-6 (IL-6) cytokine and C-reactive protein (CRP) than MPCCs. Treatment of MPCCs with HSC-conditioned culture medium confirmed that HSC secretions mediate the altered phenotype of PHHs observed in MPTCs, partly via IL-6 signaling. Lastly, we found that NADPH oxidase (NOX) inhibition and farnesoid X receptor (FXR) activation using clinically relevant drugs alleviated hepatic dysfunctions in MPTCs. In conclusion, MPTCs recapitulate symptoms of NASH- and early fibrosis-like dysfunctions in PHHs and have utility for drug discovery in this space.

Microbial Factors in Inflammatory Diseases and Cancers

The intestinal microbes form a symbiotic relationship with their human host to harvest energy for themselves and their host and to shape the immune system of their host. However, alteration of this relationship, which is named as a dysbiosis, has been associated with the development of different inflammatory diseases and cancers. It is found that metabolites, cellular components, and virulence factors derived from the gut microbiota interact with the host locally or systemically to modulate the dysbiosis and the development of these diseases. In this book chapter, we discuss the role of these microbial factors in regulating the host signaling pathways, the composition and load of the gut microbiota, the co-metabolism of the host and the microbiota, the host immune system, and physiology. In particular, we highlight how each microbial factor can contribute in the manifestation of many diseases such as cancers, Inflammatory Bowel Diseases, obesity, type-2 diabetes, non-alcoholic fatty liver diseases, nonalcoholic steatohepatitis, and cardiovascular diseases.

Regulation of Ca2+-Sensitive K+ Channels by Cholesterol and Bile Acids via Distinct Channel Subunits and Sites

Cholesterol (CLR) conversion into bile acids (BAs) in the liver constitutes the major pathway for CLR elimination from the body. Moreover, these steroids regulate each other's metabolism. While the roles of CLR and BAs in regulating metabolism and tissue function are well known, research of the last two decades revealed the existence of specific protein receptors for CLR or BAs in tissues with minor contribution to lipid metabolism, raising the possibility that these lipids serve as signaling molecules throughout the body. Among other lipids, CLR and BAs regulate ionic current mediated by the activity of voltage- and Ca²⁺-gated, K⁺ channels of large conductance (BK channels) and, thus, modulate cell physiology and participate in tissue pathophysiology. Initial work attributed modification of BK channel function by CLR or BAs to the capability of these steroids to directly interact with bilayer lipids and thus alter the physicochemical properties of the bilayer with eventual modification of BK channel function. Based on our own work and that of others, we now review evidence that supports direct interactions between CLR or BA and specific BK protein subunits, and the consequence of such interactions on channel activity and organ function, with a particular emphasis on arterial smooth muscle. For each steroid type, we will also briefly discuss several mechanisms that may underlie modification of channel steady-state activity. Finally, we will present novel computational data that provide a chemical basis for differential recognition of CLR vs lithocholic acid by distinct BK channel subunits and recognition sites.

Obeticholic acid, a selective farnesoid X receptor agonist, regulates bile acid homeostasis in sandwich-cultured human hepatocytes

Farnesoid X receptor (FXR) is a master regulator of bile acid homeostasis through transcriptional regulation of genes involved in bile acid synthesis and cellular membrane transport. Impairment of bile acid efflux due to cholangiopathies results in chronic cholestasis leading to abnormal elevation of intrahepatic and systemic bile acid levels. Obeticholic acid (OCA) is a potent and selective FXR agonist that is 100‐fold more potent than the endogenous ligand chenodeoxycholic acid (CDCA). The effects of OCA on genes involved in bile acid homeostasis were investigated using sandwich‐cultured human hepatocytes. Gene expression was determined by measuring mRNA levels. OCA dose‐dependently increased fibroblast growth factor‐19 (FGF‐19) and small heterodimer partner (SHP) which, in turn, suppress mRNA levels of cholesterol 7‐alpha‐hydroxylase (CYP7A1), the rate‐limiting enzyme for de novo synthesis of bile acids. Consistent with CYP7A1 suppression, total bile acid content was decreased by OCA (1 μmol/L) to 42.7 ± 20.5% relative to control. In addition to suppressing de novo bile acids synthesis, OCA significantly increased the mRNA levels of transporters involved in bile acid homeostasis. The bile salt excretory pump (BSEP), a canalicular efflux transporter, increased by 6.4 ± 0.8‐fold, and the basolateral efflux heterodimer transporters, organic solute transporter α (OST_α) and OST_β increased by 6.4 ± 0.2‐fold and 42.9 ± 7.9‐fold, respectively. The upregulation of BSEP and OST_α and OST_β, by OCA reduced the intracellular concentrations of d₈‐TCA, a model bile acid, to 39.6 ± 8.9% relative to control. These data demonstrate that OCA does suppress bile acid synthesis and reduce hepatocellular bile acid levels, supporting the use of OCA to treat bile acid‐induced toxicity observed in cholestatic diseases.

Chemoproteomic Profiling of Bile Acid Interacting Proteins

Bile acids (BAs) are a family of endogenous metabolites synthesized from cholesterol in liver and modified by microbiota in gut. Being amphipathic molecules, the major function of BAs is to help with dietary lipid digestion. In addition, they also act as signaling molecules to regulate lipid and glucose metabolism as well as gut microbiota composition in the host. Remarkably, recent discoveries of the dedicated receptors for BAs such as FXR and TGR5 have uncovered a number of novel actions of BAs as signaling hormones which play significant roles in both physiological and pathological conditions. Disorders in BAs' metabolism are closely related to metabolic syndrome and intestinal and neurodegenerative diseases. Though BA-based therapies have been clinically implemented for decades, the regulatory mechanism of BA is still poorly understood and a comprehensive characterization of BA-interacting proteins in proteome remains elusive. We herein describe a chemoproteomic strategy that uses a number of structurally diverse, clickable, and photoreactive BA-based probes in combination with quantitative mass spectrometry to globally profile BA-interacting proteins in mammalian cells. Over 600 BA-interacting protein targets were identified, including known endogenous receptors and transporters of BA. Analysis of these novel BA-interacting proteins revealed that they are mainly enriched in functional pathways such as endoplasmic reticulum (ER) stress response and lipid metabolism, and are predicted with strong implications with Alzheimer's disease, non-alcoholic fatty liver disease, and diarrhea. Our findings will significantly improve the current understanding of BAs' regulatory roles in human physiology and diseases.

Farnesoid X Receptor Activation Promotes Hepatic Amino Acid Catabolism and Ammonium Clearance in Mice

BACKGROUND & AIMS

The nuclear receptor subfamily 1 group H member 4 (NR1H4 or farnesoid X receptor [FXR]) regulates bile acid synthesis, transport, and catabolism. FXR also regulates postprandial lipid and glucose metabolism. We performed quantitative proteomic analyses of liver tissues from mice to evaluate these functions and investigate whether FXR regulates amino acid metabolism.

METHODS

To study the role of FXR in mouse liver, we used mice with a disruption of Nr1h4 (FXR-knockout mice) and compared them with floxed control mice. Mice were gavaged with the FXR agonist obeticholic acid or vehicle for 11 days. Proteome analyses, as well as targeted metabolomics and chromatin immunoprecipitation, were performed on the livers of these mice. Primary rat hepatocytes were used to validate the role of FXR in amino acid catabolism by gene expression and metabolomics studies. Finally, control mice and mice with liver-specific disruption of Nr1h4 (liver FXR-knockout mice) were re-fed with a high-protein diet after 6 hours fasting and gavaged a ¹⁵NH₄Cl tracer. Gene expression and the metabolome were studied in the livers and plasma from these mice.

RESULTS

In livers of control mice and primary rat hepatocytes, activation of FXR with obeticholic acid increased expression of proteins that regulate amino acid degradation, ureagenesis, and glutamine synthesis. We found FXR to bind to regulatory sites of genes encoding these proteins in control livers. Liver tissues from FXR-knockout mice had reduced expression of urea cycle proteins, and accumulated precursors of ureagenesis, compared with control mice. In liver FXR-knockout mice on a high-protein diet, the plasma concentration of newly formed urea was significantly decreased compared with controls. In addition, liver FXR-knockout mice had reduced hepatic expression of enzymes that regulate ammonium detoxification compared with controls. In contrast, obeticholic acid increased expression of genes encoding enzymes involved in ureagenesis compared with vehicle in C57Bl/6 mice.

CONCLUSIONS

In livers of mice, FXR regulates amino acid catabolism and detoxification of ammonium via ureagenesis and glutamine synthesis. Failure of the urea cycle and hyperammonemia are common in patients with acute and chronic liver diseases; compounds that activate FXR might promote ammonium clearance in these patients.

Obeticholic acid improves adipose morphometry and inflammation and reduces steatosis in dietary but not metabolic obesity in mice

OBJECTIVE

Nonalcoholic steatohepatitis (NASH) is the outcome of interactions between overnutrition, energy metabolism, and adipose function. Obeticholic acid (OCA) improves steatosis in patients but for unknown reasons does not resolve NASH pathology. This study therefore investigated OCA effects in Wt mice, which develop obesity with atherogenic dietary feeding, and appetite-dysregulated, Alms1 mutant foz/foz mice fed the same diet, which develop metabolic obesity and diabetes.

METHODS

OCA (1 mg/kg) was administered orally to female foz/foz mice and Wt littermates from weaning until 28 weeks. Adipose indices, glucose tolerance, and fatty liver pathology were studied. Experiments were repeated with OCA 10 mg/kg.

RESULTS

OCA reduced body weight and hepatic lipids and improved glucose disposal only in Wt mice. OCA limited Wt adipose expansion, altered morphometry in favor of small adipocytes, enhanced expression of genes indicating adipose browning, and reduced crown-like structure number in visceral adipose tissue. foz/foz mice showed more crown-like structures in all compartments; OCA failed to alter adipose morphometry, browning, inflammation, or improve NASH severity, even at 10 mg/kg.

CONCLUSIONS

OCA improved adipose indices, glucose tolerance, and steatosis in a milder metabolic phenotype but failed to improve these factors in morbidly obese diabetic mice. These results help explain OCA's limited efficacy to reverse human NASH.

The bile acid chenodeoxycholic acid directly modulates metabolic pathways in white adipose tissue in vitro: insight into how bile acids decrease obesity

Obesity is a worldwide epidemic, and associated pathologies, including type 2 diabetes and cardiovascular alterations, are increasingly escalating morbidity and mortality. Despite intensive study, no effective simple treatment for these conditions exists. As such, the need for go-to drugs is serious. Bile acids (BAs) present the possibility of reversing these problems, as various in vivo studies and clinical trials have shown significant effects with regard to weight and obesity reduction, insulin sensitivity restoration and cardiovascular improvements. However, the mechanism of action of BA-induced metabolic improvement has yet to be fully established. The currently most accepted model involves non-shivering thermogenesis for energy waste, but this is disputed. As such, we propose to determine whether the BA chenodeoxycholic acid (CDCA) can exert anti-obesogenic effects in vitro, independent of thermogenic brown adipose tissue activation. By exposing differentiated 3 T3-L1 adipocytes to high glucose and CDCA, we demonstrate that this BA has anti-obesity effects in vitro. Nuclear magnetic resonance spectroscopic analysis of metabolic pathways clearly indicates an improvement in metabolic status, as these cells become more oxidative rather than glycolytic, which may be associated with an increase in fatty acid oxidation. Our work demonstrates that CDCA-induced metabolic alterations occur in white and brown adipocytes and are not totally dependent on endocrine/nervous system signaling, as thought until now. Furthermore, future exploration of the mechanisms behind these effects will undoubtedly reveal interesting targets for clinical modulation.

Contextualizing Hepatocyte Functionality of Cryopreserved HepaRG Cell Cultures

Over the last decade HepaRG cells have emerged as a promising alternative to primary human hepatocytes (PHH) and have been featured in over 300 research publications. Most of these reports employed freshly differentiated HepaRG cells that require time-consuming culture (∼28 days) for full differentiation. Recently, a cryopreserved, predifferentiated format of HepaRG cells (termed here "cryo-HepaRG") has emerged as a new model that improves global availability and experimental flexibility; however, it is largely unknown whether HepaRG cells in this format fully retain their hepatic characteristics. Therefore, we systematically investigated the hepatocyte functionality of cryo-HepaRG cultures in context with the range of interindividual variation observed with PHH in both sandwich-culture and suspension formats. These evaluations uncovered a novel adaptation period for the cryo-HepaRG format and demonstrated the impact of extracellular matrix on cryo-HepaRG functionality. Pharmacologically important drug-metabolizing alleles were genotyped in HepaRG cells and poor metabolizer alleles for CYP2D6, CYP2C9, and CYP3A5 were identified and consistent with higher frequency alleles found in individuals of Caucasian decent. We observed liver enzyme inducibility with aryl hydrocarbon receptor, constitutive androstane receptor (CAR), and pregnane X receptor activators comparable to that of sandwich-cultured PHH. Finally, we show for the first time that cryo-HepaRG supports proper CAR cytosolic sequestration and translocation to hepatocyte nuclei in response to phenobarbital treatment. Taken together, these data reveal important considerations for the use of this cell model and demonstrate that cryo-HepaRG are suitable for metabolism and toxicology screening.

Does bariatric surgery improve adipose tissue function?

Bariatric surgery is currently the most effective treatment for obesity. Not only do these types of surgeries produce significant weight loss but also they improve insulin sensitivity and whole body metabolic function. The aim of this review is to explore how altered physiology of adipose tissue may contribute to the potent metabolic effects of some of these procedures. This includes specific effects on various fat depots, the function of individual adipocytes and the interaction between adipose tissue and other key metabolic tissues. Besides a dramatic loss of fat mass, bariatric surgery shifts the distribution of fat from visceral to the subcutaneous compartment favoring metabolic improvement. The sensitivity towards lipolysis controlled by insulin and catecholamines is improved, adipokine secretion is altered and local adipose inflammation as well as systemic inflammatory markers decreases. Some of these changes have been shown to be weight loss independent, and novel hypothesis for these effects includes include changes in bile acid metabolism, gut microbiota and central regulation of metabolism. In conclusion bariatric surgery is capable of improving aspects of adipose tissue function and do so in some cases in ways that are not entirely explained by the potent effect of surgery. © 2016 World Obesity.

Intestinal Crosstalk between Bile Acids and Microbiota and Its Impact on Host Metabolism

The gut microbiota is considered a metabolic "organ" that not only facilitates harvesting of nutrients and energy from the ingested food but also produces numerous metabolites that signal through their cognate receptors to regulate host metabolism. One such class of metabolites, bile acids, is produced in the liver from cholesterol and metabolized in the intestine by the gut microbiota. These bioconversions modulate the signaling properties of bile acids via the nuclear farnesoid X receptor and the G protein-coupled membrane receptor 5, which regulate numerous metabolic pathways in the host. Conversely, bile acids can modulate gut microbial composition both directly and indirectly through activation of innate immune genes in the small intestine. Thus, host metabolism can be affected through microbial modifications of bile acids, which lead to altered signaling via bile acid receptors, but also by altered microbiota composition.

Beneficial effect of farnesoid X receptor activation on metabolism in a diabetic rat model

Farnesoid X receptor (FXR) is an important regulator of glucose and lipid homeostasis. However, the exact role of FXR in diabetes remains to be fully elucidated. The present study examined the effects of chenodeoxycholic acid (CDCA), an agonist of FXR, on metabolism profile in a rat model of type 2 diabetes mellitus (T2DM). Male Wistar rats (8‑week‑old; n=40) were randomized into the following four groups (n=10): Untreated control, CDCA‑treated, T2DM, and CDCA‑treated T2DM. To establish the T2DM model, the rats were fed a high‑fat diet (HFD) for 4 weeks and received a single low‑dose intraperitoneal injection of streptozotocin (30 mg/kg), followed by an additional 4 weeks of HFD feeding. CDCA was administrated (10 mg/kg/d) intraperitoneally for 10 days. Reverse transcription‑quantitative polymerase chain reaction and western blotting assays were performed to determine the RNA and protein expression of FXR, phosphoenolpyruvate carboxykinase, G6Pase, proliferator‑activated receptor‑γ coactivator‑1 and short heterodimer partner in rat liver tissue. The results revealed that FXR activation by CDCA did not reduce body weight, but it lowered the plasma levels of fasting glucose, insulin and triglycerides in the T2DM rats. CDCA administration reversed the downregulation of the mRNA and protein expression of FXR in the T2DM rat liver tissue samples. Furthermore, treatment with CDCA reduced the mRNA and protein expression levels of phosphoenolpyruvate carboxykinase, glucose 6‑phosphatase and peroxisome proliferator‑activated receptor‑γ coactivator‑1 in the liver tissue samples of the T2DM rats. By contrast, CDCA treatment increased the mRNA and protein expression levels of short heterodimer partner in the liver tissue samples of the T2DM rats. In conclusion, FXR agonist treatment induces beneficial effects on metabolism in the rat T2DM model. In conclusion, the present study indicated that the FXR agonist may be useful for the treatment of T2DM and hypertriglyceridemia.

Impact of physiological, pathological and environmental factors on the expression and activity of human cytochrome P450 2D6 and implications in precision medicine

With only 1.3-4.3% in total hepatic CYP content, human CYP2D6 can metabolize more than 160 drugs. It is a highly polymorphic enzyme and subject to marked inhibition by a number of drugs, causing a large interindividual variability in drug clearance and drug response and drug-drug interactions. The expression and activity of CYP2D6 are regulated by a number of physiological, pathological and environmental factors at transcriptional, post-transcriptional, translational and epigenetic levels. DNA hypermethylation and histone modifications can repress the expression of CYP2D6. Hepatocyte nuclear factor-4α binds to a directly repeated element in the promoter of CYP2D6 and thus regulates the expression of CYP2D6. Small heterodimer partner represses hepatocyte nuclear factor-4α-mediated transactivation of CYP2D6. GW4064, a farnesoid X receptor agonist, decreases hepatic CYP2D6 expression and activity while increasing small heterodimer partner expression and its recruitment to the CYP2D6 promoter. The genotypes are key determinants of interindividual variability in CYP2D6 expression and activity. Recent genome-wide association studies have identified a large number of genes that can regulate CYP2D6. Pregnancy induces CYP2D6 via unknown mechanisms. Renal or liver diseases, smoking and alcohol use have minor to moderate effects only on CYP2D6 activity. Unlike CYP1 and 3 and other CYP2 members, CYP2D6 is resistant to typical inducers such as rifampin, phenobarbital and dexamethasone. Post-translational modifications such as phosphorylation of CYP2D6 Ser135 have been observed, but the functional impact is unknown. Further functional and validation studies are needed to clarify the role of nuclear receptors, epigenetic factors and other factors in the regulation of CYP2D6.

The direction of cross affects [corrected] obesity after puberty in male but not female offspring

BACKGROUND

We investigated parent-of-origin and allele-specific expression effects on obesity and hepatic gene expression in reciprocal crosses between the Berlin Fat Mouse Inbred line (BFMI) and C57Bl/6NCrl (B6N).

RESULTS

We found that F1-males with a BFMI mother developed 1.8 times more fat mass on a high fat diet at 10 weeks than F1-males of a BFMI father. The phenotype was detectable from six weeks on and was preserved after cross-fostering. RNA-seq data of liver provided evidence for higher biosynthesis and elongation of fatty acids (p = 0.00635) in obese male offspring of a BFMI mother versus lean offspring of a BFMI father. Furthermore, fatty acid degradation (p = 0.00198) and the peroxisome pathway were impaired (p = 0.00094). The circadian rhythm was affected as well (p = 0.00087). Among the highest up-regulated protein coding genes in obese males were Acot4 (1.82 fold, p = 0.022), Cyp4a10 (1.35 fold, p = 0.026) and Cyp4a14 (1.32 fold, p = 0.012), which hydroxylize fatty acids and which are known to be increased in liver steatosis. Obese males showed lower expression of the genetically imprinted and paternally expressed 3 (Peg3) gene (0.31 fold, p = 0.046) and higher expression of the androgen receptor (Ar) gene (2.38 fold, p = 0.068). Allelic imbalance was found for expression of ATP-binding cassette transporter gene Abca8b. Several of the differentially expressed genes contain estrogen response elements.

CONCLUSIONS

Parent-of-origin effects during gametogenesis and/or fetal development in an obese mother epigenetically modify the transcription of genes that lead to enhanced fatty acid synthesis and impair β-oxidation in the liver of male, but not female F1 offspring. Down-regulation of Peg3 could contribute to trigger this metabolic setting. At puberty, higher amounts of the androgen receptor and altered access to estrogen response elements in affected genes are likely responsible for male specific expression of genes that were epigenetically triggered. A suggestive lack of estrogen binding motifs was found for highly down-regulated genes in adult hepatocytes of obese F1 males (p = 0.074).

Bile acids: emerging role in management of liver diseases

Bile acids are well known for their effects on cholesterol homeostasis and lipid digestion. Since the discovery of bile acid receptors, of which there are farnesoid X receptor (FXR), a nuclear receptor, and the plasma membrane G-protein receptor, as well as Takeda G-protein coupled receptor clone 5, further roles have been elucidated for bile acids including glucose and lipid metabolism as well as inflammation. Additionally, treatment with bile acid receptor agonists has shown a decrease in the amount of atherosclerosis plaque formation and decreased portal vascular resistance and portal hypotension in animal models. Furthermore, rodent models have demonstrated antifibrotic activity using bile acid receptor agonists. Early human data using a FXR agonist, obeticholic acid, have shown promising results with improvement of histological activity and even a reduction of fibrosis. Human studies are ongoing and will provide further information on bile acid receptor agonist therapies. Thus, bile acids and their derivatives have the potential for management of liver diseases and potentially other disease states including diabetes and the metabolic syndrome.

Discovery and SAR study of 3-(tert-butyl)-4-hydroxyphenyl benzoate and benzamide derivatives as novel farnesoid X receptor (FXR) antagonists

3-(tert-Butyl)-4-hydroxyphenyl 2,4-dichlorobenzoate (1) was discovered in our in-house high throughput screening as a moderate FXR antagonist. To improve the potency and the stability of the hit 1, forty derivatives were synthesized and SAR was systematically explored. The results turn out that replacing the 2,4-dichlorophenyl with 2,6-dichloro-4-amidophenyl shows great improvement in potency, replacing the benzoate with benzamide shows improvement in stability and slight declining of potency and 3-(tert-butyl)-4-hydroxyphenyl unit is essential in obtaining the FXR antagonistic activity.

Estrogen and Estrogen Receptor-α-Mediated Transrepression of Bile Salt Export Pump

Among diseases unique to pregnancy, intrahepatic cholestasis of pregnancy is the most prevalent disorder with elevated serum bile acid levels. We have previously shown that estrogen 17β-estradiol (E2) transrepresses bile salt export pump (BSEP) through an interaction between estrogen receptor (ER)-α and farnesoid X receptor (FXR) and transrepression of BSEP by E2/ERα is an etiological contributing factor to intrahepatic cholestasis of pregnancy. Currently the mechanistic insights into such transrepression are not fully understood. In this study, the dynamics of coregulator recruitment to BSEP promoter after FXR activation and E2 treatment were established with quantitative chromatin immunoprecipitation assays. Coactivator peroxisome proliferator-activated receptor-γ coactivator-1 was predominantly recruited to the BSEP promoter upon FXR activation, and its recruitment was decreased by E2 treatment. Meanwhile, recruitment of nuclear receptor corepressor was markedly increased upon E2 treatment. Functional evaluation of ERα and ERβ chimeras revealed that domains AC of ERα are the determinants for ERα-specific transrepression on BSEP. Further studies with various truncated ERα proteins identified the domains in ERα responsible for ligand-dependent and ligand-independent transrepression. Truncated ERα-AD exhibited potent ligand-independent transrepressive activity, whereas ERα-CF was fully capable of transrepressing BSEP ligand dependently in vitro in Huh 7 cells and in vivo in mice. Both ERα-AD and ERα-CF proteins were associated with FXR in the coimmunoprecipitation assays. In conclusion, E2 repressed BSEP expression through diminishing peroxisome proliferator-activated receptor-γ coactivator-1 recruitment with a concurrent increase in nuclear receptor corepressor recruitment to the BSEP promoter. Domains AD and CF in ERα mediated ligand-independent and ligand-dependent transrepression on BSEP, respectively, through interacting with FXR.

Farnesoid x receptor in human metabolism and disease: the interplay between gene polymorphisms, clinical phenotypes and disease susceptibility

INTRODUCTION

Farnesoid x receptor (FXR) belongs to the group of nuclear receptors (NRs), which regulate the expression of various genes by binding to DNA either as a monomer or a heterodimer with retinoid x receptor.

AREAS COVERED

FXR affects several metabolic pathways through its specific target genes, regulating bile acid (BA) synthesis and homeostasis, glucose and lipid metabolism, also exhibiting a crucial role in intestinal bacterial growth and liver regeneration. Additionally, FXR is involved in the pathogenesis of different cholestatic diseases, as well as non-alcoholic fatty liver disease, inflammatory bowel disease (IBD) and primary idiopathic BA malabsorption.

EXPERT OPINION

Analyses of certain FXR polymorphisms revealed associations with clinical phenotypes and susceptibility to various human diseases. FXR single-nucleotide polymorphisms seem to be correlated with differences in glucose homeostasis, gallstone formation, intrahepatic cholestasis of pregnancy, IBD and therapeutic response to hypolipidemic therapy, among studied populations. Unfortunately, little data are still available and more studies remain to be done to determine the contribution of FXR polymorphisms in estimating risk factors and clinical outcomes for several diseases.

Energy metabolism in the liver

The liver is an essential metabolic organ, and its metabolic function is controlled by insulin and other metabolic hormones. Glucose is converted into pyruvate through glycolysis in the cytoplasm, and pyruvate is subsequently oxidized in the mitochondria to generate ATP through the TCA cycle and oxidative phosphorylation. In the fed state, glycolytic products are used to synthesize fatty acids through de novo lipogenesis. Long-chain fatty acids are incorporated into triacylglycerol, phospholipids, and/or cholesterol esters in hepatocytes. These complex lipids are stored in lipid droplets and membrane structures, or secreted into the circulation as very low-density lipoprotein particles. In the fasted state, the liver secretes glucose through both glycogenolysis and gluconeogenesis. During pronged fasting, hepatic gluconeogenesis is the primary source for endogenous glucose production. Fasting also promotes lipolysis in adipose tissue, resulting in release of nonesterified fatty acids which are converted into ketone bodies in hepatic mitochondria though β-oxidation and ketogenesis. Ketone bodies provide a metabolic fuel for extrahepatic tissues. Liver energy metabolism is tightly regulated by neuronal and hormonal signals. The sympathetic system stimulates, whereas the parasympathetic system suppresses, hepatic gluconeogenesis. Insulin stimulates glycolysis and lipogenesis but suppresses gluconeogenesis, and glucagon counteracts insulin action. Numerous transcription factors and coactivators, including CREB, FOXO1, ChREBP, SREBP, PGC-1α, and CRTC2, control the expression of the enzymes which catalyze key steps of metabolic pathways, thus controlling liver energy metabolism. Aberrant energy metabolism in the liver promotes insulin resistance, diabetes, and nonalcoholic fatty liver diseases.

Transcriptional dynamics of bile salt export pump during pregnancy: mechanisms and implications in intrahepatic cholestasis of pregnancy

Bile salt export pump (BSEP) is responsible for biliary secretion of bile acids, a rate-limiting step in the enterohepatic circulation of bile acids and transactivated by nuclear receptor farnesoid X receptor (FXR). Intrahepatic cholestasis of pregnancy (ICP) is the most prevalent disorder among diseases unique to pregnancy and primarily occurs in the third trimester of pregnancy, with a hallmark of elevated serum bile acids. Currently, the transcriptional regulation of BSEP during pregnancy and its underlying mechanisms and involvement in ICP are not fully understood. In this study the dynamics of BSEP transcription in vivo in the same group of pregnant mice before, during, and after gestation were established with an in vivo imaging system (IVIS). BSEP transcription was markedly repressed in the later stages of pregnancy and immediately recovered after parturition, resembling the clinical course of ICP in human. The transcriptional dynamics of BSEP was inversely correlated with serum 17β-estradiol (E2) levels before, during, and after gestation. Further studies showed that E2 repressed BSEP expression in human primary hepatocytes, Huh 7 cells, and in vivo in mice. Such transrepression of BSEP by E2 in vitro and in vivo required estrogen receptor α (ERα). Mechanistic studies with chromatin immunoprecipitation (ChIP), protein coimmunoprecipitation (Co-IP), and bimolecular fluorescence complementation (BiFC) assays demonstrated that ERα directly interacted with FXR in living cells and in vivo in mice.

CONCLUSION

BSEP expression was repressed by E2 in the late stages of pregnancy through a nonclassical E2/ERα transrepressive pathway, directly interacting with FXR. E2-mediated repression of BSEP expression represents an etiological contributing factor to ICP and therapies targeting the ERα/FXR interaction may be developed for prevention and treatment of ICP.

Quantitative profiling of bile acids in blood, adipose tissue, intestine, and gall bladder samples using ultra high performance liquid chromatography-tandem mass spectrometry

An ultra high performance liquid chromatography tandem mass spectrometry method (UHPLC-MS/MS) was developed for the determination of 33 target and 28 unknown bile acids (BAs) in biological samples. Sixty-one BAs could be measured in 20 min using only a small amount of sample and with a simple sample preparation. The method proved to be very sensitive (limit of detection 5-350 pg/mL, lower limit of quantitation 0.1-2.6 ng/mL), linear (R(2) > 0.99) and reproducible (typically CV <15 % in biological matrixes). The method was used to analyze human adipose tissue, plasma, and serum (from same subjects) and mouse serum, gall bladder, small intestine, and colon samples (from same animals). Cholic acid, ursodeoxycholic acid, and chenodeoxycholic acid, deoxycholic acid, and their conjugates (mainly glycine, but also taurine conjugates) were the main metabolites in human samples, and cholic acid, glycine cholic acid, and several taurine conjugates in mouse samples. Using the method, 28 unknown BAs could also be detected. UHPLC-MS/MS spectra, accurate mass, and tissue distribution suggested that nine of the unknown bile acids were taurine conjugates, 13 were glycine conjugates, and six were intact BAs, respectively. To our knowledge, this was the first time BAs were detected in adipose tissue. Results showed that 17 targeted BAs were found at ng/g level in human adipose tissue. Our findings give a novel insight of the endogenous role of BAs in adipose tissue and their role as biomarkers (e.g., in metabolic diseases).

Gastrointestinal metabolic surgery for the treatment of type 2 diabetes mellitus

Medical therapy for type 2 diabetes mellitus is ineffective in the long term due to the progressive nature of the disease, which requires increasing medication doses and polypharmacy. Conversely, bariatric surgery has emerged as a cost-effective strategy for obese diabetic individuals; it has low complication rates and results in durable weight loss, glycemic control and improvements in the quality of life, obesity-related co-morbidity and overall survival. The finding that glucose homeostasis can be achieved with a weight loss-independent mechanism immediately after bariatric surgery, especially gastric bypass, has led to the paradigm of metabolic surgery. However, the primary focus of metabolic surgery is the alteration of the physio-anatomy of the gastrointestinal tract to achieve glycemic control, metabolic control and cardio-metabolic risk reduction. To date, metabolic surgery is still not well defined, as it is used most frequently for less obese patients with poorly controlled diabetes. The mechanism of glycemic control is still incompletely understood. Published research findings on metabolic surgery are promising, but many aspects still need to be defined. This paper examines the proposed mechanism of diabetes remission, the efficacy of different types of metabolic procedures, the durability of glucose control, and the risks and complications associated with this procedure. We propose a tailored approach for the selection of the ideal metabolic procedure for different groups of patients, considering the indications and prognostic factors for diabetes remission.

Molecular pathways in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a clinicopathological change characterized by the accumulation of triglycerides in hepatocytes and has frequently been associated with obesity, type 2 diabetes mellitus, hyperlipidemia, and insulin resistance. It is an increasingly recognized condition that has become the most common liver disorder in developed countries, affecting over one-third of the population and is associated with increased cardiovascular- and liver-related mortality. NAFLD is a spectrum of disorders, beginning as simple steatosis. In about 15% of all NAFLD cases, simple steatosis can evolve into non-alcoholic steatohepatitis, a medley of inflammation, hepatocellular injury, and fibrosis, often resulting in cirrhosis and even hepatocellular cancer. However, the molecular mechanism underlying NAFLD progression is not completely understood. Its pathogenesis has often been interpreted by the “double-hit” hypothesis. The primary insult or the “first hit” includes lipid accumulation in the liver, followed by a “second hit” in which proinflammatory mediators induce inflammation, hepatocellular injury, and fibrosis. Nowadays, a more complex model suggests that fatty acids (FAs) and their metabolites may be the true lipotoxic agents that contribute to NAFLD progression; a multiple parallel hits hypothesis has also been suggested. In NAFLD patients, insulin resistance leads to hepatic steatosis via multiple mechanisms. Despite the excess hepatic accumulation of FAs in NAFLD, it has been described that not only de novo FA synthesis is increased, but FAs are also taken up from the serum. Furthermore, a decrease in mitochondrial FA oxidation and secretion of very-low-density lipoproteins has been reported. This review discusses the molecular mechanisms that underlie the pathophysiological changes of hepatic lipid metabolism that contribute to NAFLD.

Novel diagnostic and prognostic biomarkers in biliary tract cancer

INTRODUCTION

The worldwide incidence of biliary tract carcinoma (BTC, tumours of the bile ducts and gall-bladder) continues to rise, with the only potentially curative treatment remaining surgical resection or transplantation, possible in only a minority of patients. Late presentation and a paucity of effective treatments mandate the development of techniques for early lesion detection.

AREAS COVERED

This article reviews currently available biomarkers for the diagnosis and prognosis of BTC, as well as recently published studies describing novel serum, bile and urinary biomarkers.

EXPERT OPINION

The incorporation of novel analysis techniques, such as digital image analysis and fluorescence in situ hybridization, into existing management algorithms enhances the accuracy of brush cytology taken at the time of therapeutic endoscopy. However, a key goal is the discovery of reliable non-invasive biomarkers with high sensitivity and specificity. Recent advances in gene sequencing and expression, clonal evolution and tumour heterogeneity in other cancers should advance understanding of BTC tumour biology and facilitate biomarker discovery.

Cross-talk between liver and intestine in control of cholesterol and energy homeostasis

A major hurdle for organisms to dispose of cholesterol is the inability to degrade the sterol nucleus which constitutes the central part of the molecule. Synthesis of the sterol nucleus requires a complex, energy costly, metabolic pathway but also generates a diverse array of intermediates serving crucial roles in cellular energy metabolism and signal transduction. This may be the reason why this complex pathway has survived evolutionary pressure. The only way to get rid of substantial amounts of cholesterol is conversion into bile acid or direct excretion of the sterol in the feces. The lack of versatility in disposal mechanisms causes a lack of flexibility to regulate cholesterol homeostasis which may underlie the considerable human pathology linked to cholesterol removal from the body. Export of cholesterol from the body requires an intricate communication between intestine and the liver. The last decade this inter-organ cross talk has been focus of intense research leading to considerable new insight. This novel information on particular the cross-talk between liver and intestine and role of bile acids as signal transducing molecules forms the focus of this review.

Discovery and SAR study of hydroxyacetophenone derivatives as potent, non-steroidal farnesoid X receptor (FXR) antagonists

Compound 1 (IC50=35.2 ± 7.2 μM), a moderate FXR antagonist was discovered via high-throughput screening. Structure-activity relationship studies indicated that the shape and the lipophilicity of the substituents of the aromatic ring affect the activity dramatically, increasing the shape and the lipophilicity of the substituents of the aromatic ring enhances the potency of FXR antagonists. Especially, when the OH at C2 position of the aromatic ring was replaced by the OBn substituent (analog 2b), its activity could be improved to IC50=1.1 ± 0.1μM. Besides, the length of the linker and the tetrazole structure are essential for retaining the activity.

Enhancement of brown fat thermogenesis using chenodeoxycholic acid in mice

OBJECTIVE

Besides their role in lipid absorption, bile acids (BAs) can act as signalling molecules. Cholic acid was shown to counteract obesity and associated metabolic disorders in high-fat-diet (cHF)-fed mice while enhancing energy expenditure through induction of mitochondrial uncoupling protein 1 (UCP1) and activation of non-shivering thermogenesis in brown adipose tissue (BAT). In this study, the effects of another natural BA, chenodeoxycholic acid (CDCA), on dietary obesity, UCP1 in both interscapular BAT and in white adipose tissue (brite cells in WAT), were characterized in dietary-obese mice.

RESEARCH DESIGN

To induce obesity and associated metabolic disorders, male 2-month-old C57BL/6J mice were fed cHF (35% lipid wt wt(-1), mainly corn oil) for 4 months. Mice were then fed either (i) for 8 weeks with cHF or with cHF with two different doses (0.5%, 1%; wt wt(-1)) of CDCA (8-week reversion); or (ii) for 3 weeks with cHF or with cHF with 1% CDCA, or pair-fed (PF) to match calorie intake of the CDCA mice fed ad libitum; mice on standard chow diet were also used (3-week reversion).

RESULTS

In the 8-week reversion, the CDCA intervention resulted in a dose-dependent reduction of obesity, dyslipidaemia and glucose intolerance, which could be largely explained by a transient decrease in food intake. The 3-week reversion revealed mild CDCA-dependent and food intake-independent induction of UCP1-mediated thermogenesis in interscapular BAT, negligible increase of UCP1 in subcutaneous WAT and a shift from carbohydrate to lipid oxidation.

CONCLUSIONS

CDCA could reverse obesity in cHF-fed mice, mainly in response to the reduction in food intake, an effect probably occuring but neglected in previous studies using cholic acid. Nevertheless, CDCA-dependent and food intake-independent induction of UCP1 in BAT (but not in WAT) could contribute to the reduction in adiposity and to the stabilization of the lean phenotype.

Effect of the combinations between pea proteins and soluble fibres on cholesterolaemia and cholesterol metabolism in rats

Many functional foods and dietary supplements have been reported to be beneficial for the management of dyslipidaemia, one of the major risk factors for CVD. Soluble fibres and legume proteins are known to be a safe and practical approach for cholesterol reduction. The present study aimed at investigating the hypocholesterolaemic effect of the combinations of these bioactive vegetable ingredients and their possible effects on the expression of genes regulating cholesterol homeostasis. A total of six groups of twelve rats each were fed, for 28 d, Nath's hypercholesterolaemic diets, differing in protein and fibre sources, being, respectively, casein and cellulose (control), pea proteins and cellulose (pea), casein and oat fibres (oat), casein and apple pectin (pectin), pea proteins and oat fibres (pea+oat) and pea proteins and apple pectin (pea+pectin). Administration of each vegetable-containing diet was associated with lower total cholesterol concentrations compared with the control. The combinations (pea+oat and pea+pectin) were more efficacious than fibres alone in modulating cholesterolaemia ( - 53 and - 54%, respectively, at 28 d; P< 0·005). In rats fed the diets containing oat fibres or apple pectin, alone or in combination with pea proteins, a lower hepatic cholesterol content (P< 0·005) and higher hepatic mRNA concentrations of CYP7A1 and NTCP were found when compared with the control rats (P< 0·05). In summary, the dietary combinations of pea proteins and oat fibres or apple pectin are extremely effective in lowering plasma cholesterol concentrations in rats and affect cellular cholesterol homeostasis by up-regulating genes involved in hepatic cholesterol turnover.

Regulation of triglyceride metabolism by the Farnesoid X receptor

Farnesoid x receptor (FXR) is a ligand-dependent nuclear transcription factor, belonging to the nuclear receptor superfamily. It is activated by bile acids (BAs) and is expressed in the liver, intestine, kidney, and adrenal gland. Upon activation by endogenous ligand (BAs), FXR can regulate triglyceride (TG) metabolism by modulating the activity of related enzymes, lipoprotein and receptors, and maintaining the balance between the contents of TG in the liver and circulation. This review aims to elucidate the regulation of triglyceride metabolism by FXR.

Modulation of farnesoid X receptor results in post-translational modification of poly (ADP-ribose) polymerase 1 in the liver

The farnesoid X receptor (FXR) is a bile acid-activated transcription factor belonging to the nuclear receptor superfamily. FXR deficiency in mice results in cholestasis, metabolic disorders, and tumorigenesis in liver and intestine. FXR is known to contribute to pathogenesis by regulating gene transcription; however, changes in the post-transcriptional modification of proteins associated with FXR modulation have not been determined. In the current study, proteomic analysis of the livers of wild-type (WT) and FXR knockout (FXR-KO) mice treated with a FXR synthetic ligand or vehicle was performed. The results identified five proteins as novel FXR targets. Since FXR deficiency in mice leads to liver tumorigenesis, poly (ADP-ribose) polymerase family, member 1 (Parp1) that is important for DNA repair, was validated in the current study by quantitative real-time PCR, and 1- and 2-dimensional gel electrophoresis/western blot. The results showed that Parp1 mRNA levels were not altered by FXR genetic status or by agonist treatment. However, total Parp1 protein levels were increased in FXR-KO mice as early as 3 month old. Interestingly, total Parp1 protein levels were increased in WT mice in an age-dependent manner (from 3 to 18 months), but not in FXR-KO mice. Finally, activation of FXR in WT mice resulted in reduction of phosporylated Parp1 protein in the liver without affecting total Parp1 protein levels. In conclusion, this study reveals that FXR genetic status and agonist treatment affects basal levels and phosphorylation state of Parp1, respectively. These alterations, in turn, may be associated with the hepatobiliary alterations observed in FXR-KO mice and participate in FXR agonist-induced protection in the liver.

MicroRNAs in biliary diseases

Cholangiopathies are a group of diseases primarily or secondarily affecting bile duct cells, and result in cholangiocyte proliferation, regression, and/or transformation. Their etiopathogenesis may be associated with a broad variety of causes of different nature, which includes genetic, neoplastic, immune-associated, infectious, vascular, and drug-induced alterations, or being idiopathic. miRNAs, small non-coding endogenous RNAs that post-transcriptionally regulate gene expression, have been associated with pathophysiological processes in different organs and cell types, and are postulated as potential targets for diagnosis and therapy. In the current manuscript, knowledge regarding the role of miRNAs in the development and/or progression of cholangiopathies has been reviewed and the most relevant findings in this promising field of hepatology have been highlighted.

The significance of the nuclear farnesoid X receptor (FXR) in β cell function

Bile acids (BAs) are important signaling molecules that are involved in the regulation of their own metabolism, lipid metabolism, energy expenditure and glucose homeostasis. The nuclear farnesoid X receptor (FXR) and the G-protein-coupled TGR-5 are the most prominent BA receptors. FXR is highly expressed in liver and activation of liver FXR profoundly affects glucose homeostasis. Strikingly, the effect of FXR activation on glucose metabolism seems to depend on the nutritional status of the organism, i.e., slimness or obesity. Recently, it became evident that FXR is present in pancreatic β cells and that activation of β cell FXR contributes to the regulation of glucose homeostasis. Interestingly, FXR activation increases glucose-induced insulin secretion by non-genomic effects on stimulus-secretion coupling. The first chapter of this review shortly introduces the role of liver FXR in glucose metabolism, the second part focuses on the impact of FXR in lean and obese animals, and the third chapter highlights the significance of FXR in β cells.

Progress in understanding the role of FXR in promoting liver regeneration

The regenerative capacity of the liver is well known, and it can regenerate itself by a compensatory regrowth in response to partial hepatectomy or injury. Farnesoid X receptor (FXR) is a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. Bile acids are FXR physiological ligands. As a metabolic regulator, FXR plays key roles in regulating metabolism of bile acids, lipids and glucose. Recently, activation of intercellular signal transduction has been shown to play an important role in liver regeneration by binding of bile acids to their receptor FXR. Bile acid/FXR signaling pathway is required for normal liver regeneration. Furthermore, FXR promotes liver repair after injury, and activation of FXR is able to alleviate age-related defective liver regeneration. These novel findings suggest that FXR-mediated bile acid signaling is an important component of normal liver regeneration and highlight the potential use of FXR ligands to promote liver regeneration after segmental liver transplantation or resection of liver tumors. This review summarizes the recent progress in understanding the role of FXR in promoting liver regeneration.

Bile acid profiling in human biological samples: comparison of extraction procedures and application to normal and cholestatic patients

The role of bile acids in cell metabolism, membrane biology and cell signaling is increasingly recognized, thus making necessary a robust and versatile technique to extract, separate and quantify a large concentration range of these numerous molecular species. HPLC-MS/MS analysis provides the highest sensitivity to detect and identify bile acids. However, due to their large chemical diversity, extraction methods are critical and quite difficult to optimize, as shown by a survey of the literature. This paper compares the performances of four bile acid extraction protocols applied to either liquid (serum, urine, bile) or solid (stool) samples. Acetonitrile was found to be the best solvent for deproteinizing liquid samples and NaOH the best one for stool extraction. These optimized extraction procedures allowed us to quantitate as much as 27 distinct bile acids including sulfated species in a unique 30 min HPLC run, including both hydrophilic and hydrophobic species with a high efficiency. Tandem MS provided a non ambiguous identification of each metabolite with a good sensitivity (LOQ below 20 nmol/l except for THDCA and TLCA). After validation, these methods, successfully applied to a group of 39 control patients, detected 14 different species in serum in the range of 30-800 nmol/l, 11 species in urine in the range of 20-200 nmol/l and 25 species in stool in the range of 0.4-2000 nmol/g. The clinical interest of this method has been then validated on cholestatic patients. The proposed protocols seem suitable for profiling bile acids in routine analysis.

The farnesoid X receptor -1G>T polymorphism influences the lipid response to rosuvastatin

The bile acid-activated nuclear receptor farnesoid X receptor (FXR) plays an important role in lipid and glucose metabolism, and in addition, it regulates multiple drug transporters involved in statin disposition. We examined whether a functional single nucleotide polymorphism (SNP) in FXR (-1G>T) influenced the lipid-lowering effect of rosuvastatin. In 385 Chinese patients with hyperlipidemia who had been treated with rosuvastatin 10 mg daily for at least 4 weeks, the association between the FXR -1G>T SNP and lipid response to rosuvastatin was analyzed. The FXR -1G>T SNP was not associated with baseline lipids but was significantly associated with the LDL cholesterol (LDL-C) and total cholesterol response to rosuvastatin. Carriers of the T-variant allele (GT+TT = 68+3) had 4.4% (95% CI: 1.2, 7.5%, P = 0.006) and 2.6% (95% CI: 0.3, 5.0%; P < 0.05) greater reductions in LDL-C and total cholesterol, respectively, compared with those with homozygous wild-type alleles. The association between the FXR polymorphism and the LDL-C response to rosuvastatin remained significant after adjusting for other covariants. This association of the variant allele of the FXR -1G>T polymorphism with a greater LDL-C response to rosuvastatin may suggest that this polymorphism influences the expression of the hepatic efflux transporters involved in biliary excretion of rosuvastatin.

Farnesoid X receptor induces murine scavenger receptor Class B type I via intron binding

Farnesoid X receptor (FXR) is a nuclear receptor and a key regulator of liver cholesterol and triglyceride homeostasis. Scavenger receptor class B type I (SR-BI) is critical for reverse cholesterol transport (RCT) by transporting high-density lipoprotein (HDL) into liver. FXR induces SR-BI, however, the underlying molecular mechanism of this induction is not known. The current study confirmed induction of SR-BI mRNA by activated FXR in mouse livers, a human hepatoma cell line, and primary human hepatocytes. Genome-wide FXR binding analysis in mouse livers identified 4 putative FXR response elements in the form of inverse repeat separated by one nucleotide (IR1) at the first intron and 1 IR1 at the downstream of the mouse Sr-bi gene. ChIP-qPCR analysis revealed FXR binding to only the intronic IR1s, but not the downstream one. Luciferase assays and site-directed mutagenesis further showed that 3 out of 4 IR1s were able to activate gene transcription. A 16-week high-fat diet (HFD) feeding in mice increased hepatic Sr-bi gene expression in a FXR-dependent manner. In addition, FXR bound to the 3 bona fide IR1s in vivo, which was increased following HFD feeding. Serum total and HDL cholesterol levels were increased in FXR knockout mice fed the HFD, compared to wild-type mice. In conclusion, the Sr-bi/SR-BI gene is confirmed as a FXR target gene in both mice and humans, and at least in mice, induction of Sr-bi by FXR is via binding to intronic IR1s. This study suggests that FXR may serve as a promising molecular target for increasing reverse cholesterol transport.