Farnesoid X Receptor Agonists and Other Bile Acid Signaling Strategies for Treatment of Liver Disease

Angelica dahurica extract and its effective component bergapten alleviated hepatic fibrosis by activating FXR signaling pathway

Angelica dahurica (A. dahurica) has a wide range of pharmacological effects, including analgesic, anti-inflammatory and hepatoprotective effects. In this study, we investigated the effect of A. dahurica extract (AD) and its effective component bergapten (BG) on hepatic fibrosis and potential mechanisms. Hepatic fibrosis was induced by intraperitoneal injection with carbon tetrachloride (CCl4) for 1 week, and mice were administrated with AD or BG by gavage for 1 week before CCl4 injection. Hepatic stellate cells (HSCs) were stimulated by transforming growth factor-β (TGF-β) and cultured with AD, BG, GW4064 (FXR agonist) or Guggulsterone (FXR inhibitor). In CCl4-induced mice, AD significantly decreased serum aminotransferase, reduced excess accumulation of extracellular matrix (ECM), inhibited caspase-1 and IL-1β, and increased FXR expressions. In activated HSCs, AD suppressed the expressions of α-SMA, collagen I, and TIMP-1/MMP-13 ratio and inflammatory factors, functioning as FXR agonist. In CCl4-induced mice, BG significantly improved serum transaminase and histopathological changes, reduced ECM excessive deposition, inflammatory response, and activated FXR expression. BG increased FXR expression and inhibited α-SMA and IL-1β expressions in activated HSCs, functioning as GW4064. FXR deficiency significantly attenuated the decreasing effect of BG on α-SMA and IL-1β expressions in LX-2 cells. In conclusion, AD could regulate hepatic fibrosis by regulating ECM excessive deposition and inflammation. Activating FXR signaling by BG might be the potential mechanism of AD against hepatic fibrosis.

Inhibiting Wnt Signaling Reduces Cholestatic Injury by Disrupting the Inflammatory Axis

BACKGROUND & AIMS

β-Catenin, the effector molecule of the Wnt signaling pathway, has been shown to play a crucial role in bile acid homeostasis through direct inhibition of farnesoid X receptor (FXR), which has pleiotropic effects on bile acid homeostasis. We hypothesize that simultaneous suppression of β-catenin signaling and activation of FXR in a mouse model of cholestasis will reduce injury and biliary fibrosis through inhibition of bile acid synthesis.

METHODS

To induce cholestasis, we performed bile duct ligation (BDL) on wild-type male mice. Eight hours after surgery, mice received FXR agonists obeticholic acid, tropifexor, or GW-4064 or Wnt inhibitor Wnt-C59. Severity of cholestatic liver disease and expression of target genes were evaluated after either 5 days or 12 days of treatment.

RESULTS

We found that although the FXR agonists worsened BDL-induced injury and necrosis after 5 days, Wnt-C59 did not. After 12 days of BDL, Wnt-C59 treatment, but not GW-4064 treatment, reduced both the number of infarcts and the number of inflammatory cells in liver. RNA sequencing analysis of whole livers revealed a notable suppression of nuclear factor kappa B signaling when Wnt signaling is inhibited. We then analyzed transcriptomic data to identify a cholangiocyte-specific signature in our model and demonstrated that Wnt-C59-treated livers were enriched for genes expressed in quiescent cholangiocytes, whereas genes expressed in activated cholangiocytes were enriched in BDL alone. A similar decrease in biliary injury and inflammation occurred in Mdr2 KO mice treated with Wnt-C59.

CONCLUSIONS

Inhibiting Wnt signaling suppresses cholangiocyte activation and disrupts the nuclear factor kappa B-dependent inflammatory axis, reducing cholestatic-induced injury.

Current and investigational drugs in early clinical development for portal hypertension

Introduction

The development of portal hypertension leads to a majority of complications associated with chronic liver disease. Therefore, adequate treatment of portal hypertension is crucial in the management of such patients. Current treatment options are limited and consist mainly of medications that decrease the hyperdynamic circulation, such as non-selective beta blockers, and treatment of hypervolemia with diuretics. Despite these options, mortality rates have not improved over the last two decades. Newer, more effective treatment options are necessary to help improve survival and quality of life in these patients.

Areas covered

Multiple preclinical models and clinical studies have demonstrated potential efficacy of a variety of new treatment modalities. We introduce treatment options including the use of vasodilation promotors, vasoconstriction inhibitors, anticoagulants, antiangiogenics, and anti-inflammatory drugs. We examine the most recent studies for treatment options within these drug classes and offer insights as to which show the most promise in this field.

Methodology

Published studies that identified novel medical treatment options of portal hypertension were searched using PubMed (https://pubmed.ncbi.nlm.nih.gov/). Clinical trials listed in Clinicaltrials.gov were also searched with a focus on more recent and ongoing studies, including those with completed recruitment. Searching with key terms including "portal hypertension" as well as individually searching specific treatment medications that were listed in other publications was carried out. Finally, current societal guidelines and recent review articles relevant to the management of portal hypertension were evaluated, and listed references of interest were included.

Conclusion

Many ongoing early phase studies demonstrate promising results and may shape the field of portal hypertension management in future. As concrete results become available, larger RCTs will be required before making definitive conclusions regarding safety and efficacy and whether or not they can be incorporated into routine clinical practice. Statins, anticoagulants, and PDE inhibitors have been among the most studied and appear to be most promising.

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.

The Crosstalk Between Liver Sinusoidal Endothelial Cells and Hepatic Microenvironment in NASH Related Liver Fibrosis

Chronic liver injury can be caused by many factors, including virus infection, alcohol intake, cholestasis and abnormal fat accumulation. Nonalcoholic steatohepatitis (NASH) has become the main cause of liver fibrosis worldwide. Recently, more and more evidences show that hepatic microenvironment is involved in the pathophysiological process of liver fibrosis induced by NASH. Hepatic microenvironment consists of various types of cells and intercellular crosstalk among different cells in the liver sinusoids. Liver sinusoidal endothelial cells (LSECs), as the gatekeeper of liver microenvironment, play an irreplaceable role in the homeostasis and alterations of liver microenvironment. Many recent studies have reported that during the progression of NASH to liver fibrosis, LSECs are involved in various stages mediated by a series of mechanisms. Therefore, here we review the key role of crosstalk between LSECs and hepatic microenvironment in the progression of NASH to liver fibrosis (steatosis, inflammation, and fibrosis), as well as promising therapeutic strategies targeting LSECs.

FXR: structures, biology, and drug development for NASH and fibrosis diseases

The nuclear receptor farnesoid-X-receptor (FXR) plays an essential role in bile acid, glucose, and lipid homeostasis. In the last two decades, several diseases, such as obesity, type 2 diabetes, nonalcoholic fatty liver disease, cholestasis, and chronic inflammatory diseases of the liver and intestine, have been revealed to be associated with alterations in FXR functions. FXR has become a promising therapeutic drug target, particularly for enterohepatic diseases. Despite the large number of FXR modulators reported, only obeticholic acid (OCA) has been approved for primary biliary cholangitis (PBC) therapy as FXR modulator. In this review, we summarize the structure and function of FXR, the development of FXR modulators, and the structure-activity relationships of FXR modulators. Based on the structural analysis, we discuss potential strategies for developing future therapeutic FXR modulators to overcome current limitations, providing new perspectives for enterohepatic and metabolic diseases treatment.

Intercellular crosstalk of liver sinusoidal endothelial cells in liver fibrosis, cirrhosis and hepatocellular carcinoma

Intercellular crosstalk among various liver cells plays an important role in liver fibrosis, cirrhosis, and hepatocellular carcinoma (HCC). Capillarization of liver sinusoidal endothelial cells (LSECs) precedes fibrosis and accumulating evidence suggests that the crosstalk between LSECs and other liver cells is critical in the development and progression of liver fibrosis. LSECs dysfunction, a key event in the progression from fibrosis to cirrhosis, and subsequently obstruction of hepatic sinuses and increased intrahepatic vascular resistance (IHVR) contribute to development of portal hypertension (PHT) and cirrhosis. More importantly, immunosuppressive tumor microenvironment (TME), which is closely related to the crosstalk between LSECs and immune liver cells like CD8+ T cells, promotes advances tumorigenesis, especially HCC. However, the connections within the crosstalk between LSECs and other liver cells during the progression from liver fibrosis to cirrhosis to HCC have yet to be discussed. In this review, we first summarize the current knowledge of how different crosstalk between LSECs and other liver cells, including hepatocytes, hepatic stellate cells (HSCs), macrophoges, immune cells in liver and extra cellular matrix (ECM) contribute to the physiological function and the progrssion from liver fibrosis to cirrhosis, or even to HCC. Then we examine current treatment strategies for LSECs crosstalk in liver fibrosis, cirrhosis and HCC.

Targeting Gut–Liver Axis for Treatment of Liver Fibrosis and Portal Hypertension

Antifibrotic therapies for the treatment of liver fibrosis represent an unconquered area of drug development. The significant involvement of the gut microbiota as a driving force in a multitude of liver disease, be it pathogenesis or fibrotic progression, suggest that targeting the gut–liver axis, relevant signaling pathways, and/or manipulation of the gut’s commensal microbial composition and its metabolites may offer opportunities for biomarker discovery, novel therapies and personalized medicine development. Here, we review potential links between bacterial translocation and deficits of host-microbiome compartmentalization and liver fibrosis that occur in settings of advanced chronic liver disease. We discuss established and emerging therapeutic strategies, translated from our current knowledge of the gut–liver axis, targeted at restoring intestinal eubiosis, ameliorating hepatic fibrosis and rising portal hypertension that characterize and define the course of decompensated cirrhosis.

Lipid Droplet-Associated Factors, PNPLA3, TM6SF2, and HSD17B Proteins in Hepatopancreatobiliary Cancer

Simple Summary

Aberrant lipid synthesis and reprogrammed lipid metabolism are both associated with the development and progression of pancreatic and liver cancer. Most cells store fatty acids in the form of triacylglycerols in lipid droplets. Lipid droplets are intracellular organelles that not only store neutral lipids, but also play roles as molecular messengers and signaling factors. Some cancer cells accumulate massive amount of lipid droplets. Lipid droplets and lipid droplet-associated factors are further implicated to mediate proliferation, invasion, metastasis, as well as chemotherapy resistance in several types of cancer. This review dissected recent findings on the role of several lipid droplet-associated factors, patatin-like phospholipase domain-containing 3 (PNPLA3), Transmembrane 6 superfamily member 2 (TM6SF2), and 17β-hydroxysteroid dehydrogenase (HSD17B) 11 and 13 as well as their genetic variations in hepatopancreatobiliary diseases, especially cancer.

Abstract

Pancreatic and liver cancer are leading causes of cancer deaths, and by 2030, they are projected to become the second and the third deadliest cancer respectively. Cancer metabolism, especially lipid metabolism, plays an important role in progression and metastasis of many types of cancer, including pancreatic and liver cancer. Lipid droplets are intracellular organelles that store neutral lipids, but also act as molecular messengers, and signaling factors. It is becoming increasingly evident that alterations in the regulation of lipid droplets and their associated factors influence the risk of developing not only metabolic disease but also fibrosis and cancer. In the current review article, we summarized recent findings concerning the roles of lipid droplet-associated factors, patatin-like phospholipase domain-containing 3, Transmembrane 6 superfamily member 2, and 17β-hydroxysteroid dehydrogenase 11 and 13 as well as genetic variants in pancreatic and hepatic diseases. A better understanding of cancer type- and cell type-specific roles of lipid droplet-associated factors is important for establishing new therapeutic options in the future.

Isotschimgine alleviates nonalcoholic steatohepatitis and fibrosis via FXR agonism in mice

Farnesoid X receptor (FXR) agonist obeticholic acid (OCA) has emerged as a potential therapy for nonalcoholic fatty liver disease (NAFLD). However, the side effects of OCA may limit its application in clinics. We identified previously that isotschimgine (ITG) is a non-steroidal FXR selective agonist and has potent therapeutic effects on NAFLD in mice. Here, we aimed to evaluate the therapeutic effects of ITG on nonalcoholic steatohepatitis (NASH) and fibrosis in mice. We used methionine and choline deficient (MCD) diet-induced NASH mice, bile duct ligation (BDL), and carbon tetrachloride (CCl₄ )-treated hepatic fibrosis mice to investigate the effects of ITG on NASH, fibrosis, and cholestatic liver injury. Our results showed that ITG improved steatosis and inflammation in the liver of MCD diet-fed mice, as well as alleviated fibrosis and inflammation in the liver of CCl₄ -treated mice. Furthermore, ITG attenuated serum bile acid levels, and reduced vacuolization, inflammatory infiltration, hepatic parenchymal necrosis, and collagen accumulation in the liver of BDL mice. Mechanistically, ITG increased the expression of FXR target genes. These data suggest that ITG is an FXR agonist and may be developed as a novel therapy for NASH, hepatic fibrosis, or primary biliary cholangitis.

3β-Isoobeticholic acid efficiently activates the farnesoid X receptor (FXR) due to its epimerization to 3α-epimer by hepatic metabolism

Bile acids (BAs) are important signaling molecules acting via the farnesoid X nuclear receptor (FXR) and the membrane G protein-coupled bile acid receptor 1 (GPBAR1). Besides deconjugation of BAs, the oxidoreductive enzymes of colonic bacteria and hepatocytes enable the conversion of BAs into their epimers or dehydrogenated forms. Obeticholic acid (OCA) is the first-in-class BA-derived FXR agonist approved for the treatment of primary biliary cholangitis. Herein, a library of OCA derivatives, including 7-keto, 6-ethylidene derivatives and 3β-epimers, was synthetized and investigated in terms of interactions with FXR and GPBAR1 in transaction assays and evaluated for FXR target genes expression in human hepatocytes and C57BL/6 mice. The derivatives were further subjected to cell-free analysis employing in silico molecular docking and a TR-FRET assay. The conversion of the 3βhydroxy epimer and its pharmacokinetics in mice were studied using LC-MS. We found that only the 3β-hydroxy epimer of OCA (3β-isoOCA) possesses significant activity to FXR in hepatic cells and mice. However, in a cell-free assay, 3β-isoOCA had about 9-times lower affinity to FXR than did OCA. We observed that 3β-isoOCA readily epimerizes to OCA in hepatocytes and murine liver. This conversion was significantly inhibited by the hydroxy-Δ⁵-steroid dehydrogenase inhibitor trilostane. In addition, we found that 3,7-dehydroobeticholic acid is a potent GPBAR1 agonist. We conclude that 3β-isoOCA significantly activates FXR due to its epimerization to the more active OCA by hepatic metabolism. Other modifications as well as epimerization on the C3/C7 positions and the introduction of 6-ethylidene in the CDCA scaffold abrogate FXR agonism and alleviate GPBAR1 activation.

NAFLD as a driver of chronic kidney disease

Non-alcoholic fatty liver disease (NAFLD) and chronic kidney disease (CKD) are worldwide public health problems, affecting up to 25-30% (NAFLD), and up to 10-15% (CKD) of the general population. Recently, it has also been established that there is a strong association between NAFLD and CKD, regardless of the presence of potential confounding diseases such as obesity, hypertension and type 2 diabetes. Since NAFLD and CKD are both common diseases that often occur alongside other metabolic conditions, such as type 2 diabetes or metabolic syndrome, elucidating the relative impact of NAFLD on the risk of incident CKD presents a substantial challenge for investigators working in this research field. A growing body of epidemiological evidence suggests that NAFLD is an independent risk factor for CKD and recent evidence also suggests that associated factors such as metabolic syndrome, dysbiosis, unhealthy diets, platelet activation and processes associated with ageing could also contribute mechanisms linking NAFLD and CKD. This narrative review provides an overview of the literature on: a) the evidence for an association and causal link between NAFLD and CKD and b) the underlying mechanisms by which NAFLD (and factors strongly linked with NAFLD) may increase the risk of developing CKD.

A human-like bile acid pool induced by deletion of hepatic Cyp2c70 modulates effects of FXR activation in mice

Bile acids (BAs) facilitate intestinal absorption of lipid-soluble nutrients and modulate various metabolic pathways through the farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5. These receptors are targets for therapy in cholestatic and metabolic diseases. However, dissimilarities in BA metabolism between humans and mice complicate translation of preclinical data. Cytochrome P450 family 2 subfamily c polypeptide 70 (CYP2C70) was recently proposed to catalyze the formation of rodent-specific muricholic acids (MCAs). With CRISPR/Cas9-mediated somatic genome editing, we generated an acute hepatic Cyp2c70 knockout mouse model (Cyp2c70^ako) to clarify the role of CYP2C70 in BA metabolism in vivo and evaluate whether its activity modulates effects of pharmacologic FXR activation on cholesterol homeostasis. In Cyp2c70^ako mice, chenodeoxycholic acid (CDCA) increased at the expense of βMCA, resulting in a more hydrophobic human-like BA pool. Tracer studies demonstrated that, in vivo, CYP2C70 catalyzes the formation of βMCA primarily by sequential 6β-hydroxylation and C7-epimerization of CDCA, generating αMCA as an intermediate metabolite. Physiologically, the humanized BA composition in Cyp2c70^ako mice blunted the stimulation of fecal cholesterol disposal in response to FXR activation compared with WT mice, predominantly due to reduced stimulation of transintestinal cholesterol excretion. Thus, deletion of hepatic Cyp2c70 in adult mice translates into a human-like BA pool composition and impacts the response to pharmacologic FXR activation. This Cyp2c70^ako mouse model may be a useful tool for future studies of BA signaling and metabolism that informs human disease development and treatment.

Iron overload reduces synthesis and elimination of bile acids in rat liver

Excessive iron accumulation in the liver, which accompanies certain genetic or metabolic diseases, impairs bile acids (BA) synthesis, but the influence of iron on the complex process of BA homeostasis is unknown. Thus, we evaluated the effect of iron overload (IO) on BA turnover in rats. Compared with control rats, IO (8 intraperitoneal doses of 100 mg/kg every other day) significantly decreased bile flow as a consequence of decreased biliary BA secretion. This decrease was associated with reduced expression of Cyp7a1, the rate limiting enzyme in the conversion of cholesterol to BA, and decreased expression of Bsep, the transporter responsible for BA efflux into bile. However, IO did not change net BA content in faeces in response to increased intestinal conversion of BA into hyodeoxycholic acid. In addition, IO increased plasma cholesterol concentrations, which corresponded with reduced Cyp7a1 expression and increased expression of Hmgcr, the rate-limiting enzyme in de novo cholesterol synthesis. In summary, this study describes the mechanisms impairing synthesis, biliary secretion and intestinal processing of BA during IO. Altered elimination pathways for BA and cholesterol may interfere with the pathophysiology of liver damage accompanying liver diseases with excessive iron deposition.

Metabolism of obeticholic acid in brown bullhead (Ameiurus nebulosus)

Analysis of brown bullhead (Ameiurus nebulosus) bile by ultra performance liquid chromatography high-resolution mass spectrometry (UPLC/HRMS) revealed a series of bile acids similar to those found in humans. Accordingly, we chose this fish as a model organism to examine the metabolism of obeticholic acid, a bile acid used to treat a number of human liver diseases and the one that has the potential to occur as an environmental contaminant. The taurine and glycine conjugates of obeticholic acid and keto-obeticholic acid were identified, as well as the D-cysteinolic acid conjugate of obeticholic acid, likely a metabolite specific to fish. In addition, metabolites of obeticholic acid (sulphate and glucuronide) and several hydroxy-obeticholic acid derivatives were found, representing typical pathways of primary and secondary steroid metabolism. Brown bullhead exposed to obeticholic acid at a dose of 100 mg/kg gave no overt signs of distress or toxicity.

Activated NF-κB/Nrf2 and Wnt/β-catenin pathways are associated with lipid metabolism in CKD patients with microalbuminuria and macroalbuminuria

Early diagnosis of CKD patients at risk for microalbuminuria or macroalbuminuria could facilitate clinical outcomes and long-term survival. Considering the few and limited efficacy of current biomarkers in early detection, we aim to discover plasma lipids that effectively predict the development of CKD paitents with microalbuminuria or macroalbuminuria. A total of 380 healthy controls and 1156 patients with CKD stages 3 to 5 were stratified by urine albumin-creatinine ratio as microalbuminuria (30-300 mg/g) and macroalbuminuria (>300 mg/g). Fasting plasma samples were determined by UPLC-HDMS based on lipidomics. Quantitative real-time polymerase chain reaction, Western blot and immunohistochemical analyses were used to validate the lipid metabolism-associated pathways. Pathway analysis demonstrated that these lipids were closely associated with PPARγ, inflammatory mediator regulation of TRP channels and RAS signaling, which were intimately involved in activated NF-κB and Nrf2 pathways. We further carried out pathway validation and demonstrated that NF-κB pathway was activated in patients with macroalbuminuria compared with CKD patients with microalbuminuria, while Nrf2-associated protein expression was downregulated, which was accompanied by the up-regulation of Wnt/β-catenin signaling pathway. Four lipids including DTA, 5,8-TDA, GGD3 and DHA that showed great potential in the discrimination of CKD patients with microalbuminuria and healthy controls were selected by logistic regression analysis. Additionally, six lipid species including CDCA, glucosylceramide, GGD2, TTA, DHA and EDA that contributed to the discrimination of CKD patients with microalbuminuria and macroalbuminuria were selected by logistic LASSO regression Gangliosides were first identified and might be promising therapeutic targets for CKD patients with the different degree of albuminuria. Collectively, this study first demonstrates the association of plasma inflammation, oxidative stress, Wnt/β-catenin and lipid metabolism in CKD patients with microalbuminuria and macroalbuminuria.

Potential mechanisms linking gut microbiota and portal hypertension

Gut microbiota is the largest collection of commensal micro-organisms in the human body, engaged in reciprocal cellular and molecular interactions with the liver. This mutually beneficial relationship may break down and result in dysbiosis, associated with disease phenotypes. Altered composition and function of gut microbiota has been implicated in the pathobiology of nonalcoholic fatty liver disease (NAFLD), a prevalent condition linked to obesity, insulin resistance and endothelial dysfunction. NAFLD may progress to cirrhosis and portal hypertension, which is the result of increased intrahepatic vascular resistance and altered splanchnic circulation. Gut microbiota may contribute to rising portal pressure from the earliest stages of NAFLD, although the significance of these changes remains unclear. NAFLD has been linked to lower microbial diversity and weakened intestinal barrier, exposing the host to bacterial components and stimulating pathways of immune defence and inflammation. Moreover, disrupted host-microbial metabolic interplay alters bile acid signalling and the release of vasoregulatory gasotransmitters. These perturbations become prominent in cirrhosis, increasing the risk of clinically significant portal hypertension and leading to bacterial translocation, sepsis and acute-on-chronic liver failure. Better understanding of the gut-liver axis and identification of novel microbial molecular targets may yield specific strategies in the prevention and management of portal hypertension.

FXR and TGR5 Agonists Ameliorate Liver Injury, Steatosis, and Inflammation After Binge or Prolonged Alcohol Feeding in Mice

Bile acids (BAs) activate various dedicated receptors, including the farnesoid X receptor (FXR) and the Takeda G protein‐coupled receptor 5 (TGR5). The FXR agonist obeticholic acid (OCA) is licensed for the treatment of primary biliary cholangitis and has shown promising results in NASH patients, whereas TGR5 agonists target inflammation and metabolism. We hypothesized that FXR and/or TGR5 agonists may be therapeutic in early alcoholic liver disease (ALD) in mice, in which hepatic inflammation plays a major role. OCA, INT‐777, and INT‐767 are BA derivatives with selective agonist properties for FXR, TGR5, or both, respectively. These compounds were tested in two mouse models (3‐day binge model and prolonged Lieber DeCarli diet for 12 days) of early ALD. Serum alanine aminotransferase and liver histology were used to assess liver injury, Oil Red O staining of liver sections to assess steatosis, and real‐time polymerase chain reaction to assess changes in gene expression. In the ethanol binge model, treatment with OCA and INT‐777 decreased hepatic macrovesicular steatosis and protected from ethanol‐induced liver injury. After prolonged ethanol administration, mice treated with OCA, INT‐767, or INT‐777 showed decreased hepatic steatosis, associated with reduced liver fatty acid synthase protein expression, and protection from liver injury. Treatment with BA receptor agonists in both models of ethanol administration modulated lipogenic gene expression, and decreased liver interleukin‐1β mRNA expression associated with increased ubiquitination of NLRP3 inflammasome through cyclic adenosine monophosphate–induced activation of protein kinase A. Conclusion: OCA, INT‐767, or INT‐777 administration is effective in reducing acute and chronic ethanol‐induced steatosis and inflammation in mice, with varying degrees of efficacy depending on the duration of ethanol administration, indicating that both FXR and TGR5 activation can protect from liver injury in ALD models.

β-Defensin 1 Is Prominent in the Liver and Induced During Cholestasis by Bilirubin and Bile Acids via Farnesoid X Receptor and Constitutive Androstane Receptor

Background & aims

Knowledge about innate antimicrobial defense of the liver is limited. We investigated hepatic expression and regulation of antimicrobial peptides with focus on the human beta defensin-1 (hBD-1).

Methods

Radial diffusion assay was used to analyze antimicrobial activity of liver tissue. Different defensins including hBD-1 and its activator thioredoxin-1 (TXN) were analyzed in healthy and cholestatic liver samples by qPCR and immunostaining. Regulation of hBD-1 expression was studied in vitro and in vivo using bile duct-ligated mice. Regulation of hBD-1 via bilirubin and bile acids (BAs) was studied using siRNA.

Results

We found strong antimicrobial activity of liver tissue against Escherichia coli. As a potential mediator of this antimicrobial activity we detected high expression of hBD-1 and TXN in hepatocytes, whereas other defensins were minimally expressed. Using a specific antibody for the reduced, antimicrobially active form of hBD-1 we found hBD-1 in co-localization with TXN within hepatocytes. hBD-1 was upregulated in cholestasis in a graded fashion. In cholestatic mice hepatic AMP expression (Defb-1 and Hamp) was enhanced. Bilirubin and BAs were able to induce hBD-1 in hepatic cell cultures in vitro. Treatment with siRNA and/or agonists demonstrated that the farnesoid X receptor (FXR) mediates basal expression of hBD-1, whereas both constitutive androstane receptor (CAR) and FXR seem to be responsible for the induction of hBD-1 by bilirubin.

Conclusion

hBD-1 is prominently expressed in hepatocytes. It is induced during cholestasis through bilirubin and BAs, mediated by CAR and especially FXR. Reduction by TXN activates hBD-1 to a potential key player in innate antimicrobial defense of the liver.

Obstructive jaundice induced kidney damage is mediated by down-regulation of bile acid receptors FXR and TGR5

AIM

To investigate the changes in the expression of bile acid receptors FXR and TGR5 in obstructive jaundice (OJ) induced renal injury.

METHODS

Twelve male Sprague-Dawley rats were randomly divided into two groups to undergo either sham operation (CON) or bile duct ligation (BDL). The animals were operated by surgical ligation of the common bile duct to establish an OJ model. Two weeks post operation, serum samples were collected to assess renal associated biochemical markers including alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bile acid (TBA), total bilirubin (TBIL), direct bilirubin (DBIL), serum urea nitrogen (BUN), creatinine (Cr), and uric acid (UA). In addition, the urine of the rats was collected for urine chemistry analysis. Transcription and translation of FXR and TGR5 genes were detected by qRT-PCR and Western blot, respectively. Tissue sections of the kidneys were stained with hematoxylin and eosin (HE) and examined for microscopically pathological changes.

RESULTS

Compared with the CON group, the protein and mRNA expression of FXR and TGR5 was significantly decreased in the kidneys of the BDL rats. HE staining revealed that the kidneys of the BDL rats had decreased glomerular density and the local epithelial cells of the tubules shed. Also, the small tube lacuna was expanded, accompanied with the presence of a large number of unstructured substances.

CONCLUSION

This in vivo study demonstrated significant down-regulation of the bile acid receptors FXR and TGR5 in the kidneys of OJ rats, suggesting their role in kidney damage.

Nuclear receptors and liver disease: Summary of the 2017 basic research symposium

The nuclear receptor superfamily contains important transcriptional regulators that play pleiotropic roles in cell differentiation, development, proliferation, and metabolic processes to govern liver physiology and pathology. Many nuclear receptors are ligand-activated transcription factors that regulate the expression of their target genes by modulating transcriptional activities and epigenetic changes. Additionally, the protein complex associated with nuclear receptors consists of a multitude of coregulators, corepressors, and noncoding RNAs. Therefore, acquiring new information on nuclear receptors may provide invaluable insight into novel therapies and shed light on new interventions to reduce the burden and incidence of liver diseases. (Hepatology Communications 2018;2:765-777).

Xenobiotic Nuclear Receptor Signaling Determines Molecular Pathogenesis of Progressive Familial Intrahepatic Cholestasis

Progressive familial intrahepatic cholestasis (PFIC) is a genetically heterogeneous disorder of bile flow disruption due to abnormal canalicular transport or impaired bile acid (BA) metabolism, causing excess BA accumulation and liver failure. We previously reported an intrahepatic cholestasis mouse model based on loss of function of both farnesoid X receptor (FXR; NR1H4) and a small heterodimer partner (SHP; NR0B2) [double knockout (DKO)], which has strong similarities to human PFIC5. We compared the pathogenesis of DKO livers with that of another intrahepatic cholestasis model, Bsep-/-, which represents human PFIC2. Both models exhibit severe hepatomegaly and hepatic BA accumulation, but DKO showed greater circulating BA and liver injury, and Bsep-/- had milder phenotypes. Molecular profiling of BAs uncovered specific enrichment of cholic acid (CA)-derived BAs in DKO livers but chenodeoxycholate-derived BAs in Bsep-/- livers. Transcriptomic and proteomic analysis revealed specific activation of CA synthesis and alternative basolateral BA transport in DKO but increased chenodeoxycholic acid synthesis and canalicular transport in Bsep-/-. The constitutive androstane receptor (CAR)/pregnane X receptor (PXR)-CYP2B/CYP2C axis is activated in DKO livers but not in other cholestasis models. Loss of this axis in Fxr:Shp:Car:Pxr quadruple knockouts blocked Cyp2b/Cyp2c gene induction, impaired bilirubin conjugation/elimination, and increased liver injury. Differential CYP2B expression in DKO and Bsep-/- was recapitulated in human PFIC5 and PFIC2 livers. In conclusion, loss of FXR/SHP results in distinct molecular pathogenesis and CAR/PXR activation, which promotes Cyp2b/Cyp2c gene transcription and bilirubin clearance. CAR/PXR activation was not observed in Bsep-/- mice or PFIC2 patients. These findings provide a deeper understanding of the heterogeneity of intrahepatic cholestasis.

Origins of Portal Hypertension in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) advanced to cirrhosis is often complicated by clinically significant portal hypertension, which is primarily caused by increased intrahepatic vascular resistance. Liver fibrosis has been identified as a critical determinant of this process. However, there is evidence that portal venous pressure may begin to rise in the earliest stages of NAFLD when fibrosis is far less advanced or absent. The biological and clinical significance of these early changes in sinusoidal homeostasis remains unclear. Experimental and human observations indicate that sinusoidal space restriction due to hepatocellular lipid accumulation and ballooning may impair sinusoidal flow and generate shear stress, increasingly disrupting sinusoidal microcirculation. Sinusoidal endothelial cells, hepatic stellate cells, and Kupffer cells are key partners of hepatocytes affected by NAFLD in promoting endothelial dysfunction through enhanced contractility, capillarization, adhesion and entrapment of blood cells, extracellular matrix deposition, and neovascularization. These biomechanical and rheological changes are aggravated by a dysfunctional gut-liver axis and splanchnic vasoregulation, culminating in fibrosis and clinically significant portal hypertension. We may speculate that increased portal venous pressure is an essential element of the pathogenesis across the entire spectrum of NAFLD. Improved methods of noninvasive portal venous pressure monitoring will hopefully give new insights into the pathobiology of NAFLD and help efforts to identify patients at increased risk for adverse outcomes. In addition, novel drug candidates targeting reversible components of aberrant sinusoidal circulation may prevent progression in NAFLD.

Protective effects of yangonin from an edible botanical Kava against lithocholic acid-induced cholestasis and hepatotoxicity

Accumulation of toxic bile acids in liver could cause cholestasis and liver injury. The purpose of the current study is to evaluate the hepatoprotective effect of yangonin, a product isolated from an edible botanical Kava against lithocholic acid (LCA)-induced cholestasis, and further to elucidate the involvement of farnesoid X receptor (FXR) in the anticholestatic effect using in vivo and in vitro experiments. The cholestatic liver injury model was established by intraperitoneal injections of LCA in C57BL/6 mice. Serum biomarkers and H&E staining were used to identify the amelioration of cholestasis after yangonin treatment. Mice hepatocytes culture, gene silencing experiment, real-time PCR and Western blot assay were used to elucidate the mechanisms underlying yangonin hepatoprotection. The results indicated that yangonin promoted bile acid efflux and reduced hepatic uptake via an induction in FXR-target genes Bsep, Mrp2 expression and an inhibition in Ntcp, all of which are responsible for bile acid transport. Furthermore, yangonin reduced bile acid synthesis through repressing FXR-target genes Cyp7a1 and Cyp8b1, and increased bile acid metabolism through an induction in gene expression of Sult2a1, which are involved in bile acid synthesis and metabolism. In addition, yangonin suppressed liver inflammation through repressing inflammation-related gene NF-κB, TNF-α and IL-1β. In vitro evidences showed that the changes in transporters and enzymes induced by yangonin were abrogated when FXR was silenced. In conclusions, yangonin produces protective effect against LCA-induced hepatotoxity and cholestasis due to FXR-mediated regulation. Yangonin may be an effective approach for the prevention against cholestatic liver diseases.

Biliary bile acids in hepatobiliary injury - What is the link?

The main trigger for liver injury in acquired cholestatic liver disease remains unclear. However, the accumulation of bile acids (BAs) undoubtedly plays a role. Recent progress in deciphering the pathomechanisms of inborn cholestatic liver diseases, decoding mechanisms of BA-induced cell death, and generating modern BA-derived drugs has improved the understanding of the regulation of BA synthesis and transport. Now is the appropriate time to reassess current knowledge about the specific role of BAs in hepatobiliary injury.

Clinical significance of farnesoid X receptor expression in thyroid neoplasia

Aim: To evaluate the clinical significance of farnesoid X receptor (FXR) in thyroid neoplasia. Patients & methods: FXR expression was assessed immunohistochemically on 88 thyroid neoplastic tissues (benign = 44, malignant = 44). Results: Enhanced FXR was more frequently observed in papillary carcinomas compared with hyperplastic nodules (p = 0.0489). In malignant lesions, elevated FXR was associated with capsular (p = 0.0004) and vascular invasion (p = 0.0056) and increased follicular cells’ proliferative rate (p < 0.0001). Elevated FXR expression was also associated with larger tumor size (p = 0.0086), presence of lymph node metastases (p = 0.0239) and lymphatic invasion (p = 0.0086) and increased recurrence rate risk (p = 0.0239). Conclusion: FXR may be associated with tumor aggressiveness that affects patients’ survival in thyroid neoplasia.

Novel treatment options for portal hypertension

Portal hypertension is most frequently associated with cirrhosis and is a major driver for associated complications, such as variceal bleeding, ascites or hepatic encephalopathy. As such, clinically significant portal hypertension forms the prelude to decompensation and impacts significantly on the prognosis of patients with liver cirrhosis. At present, non-selective β-blockers, vasopressin analogues and somatostatin analogues are the mainstay of treatment but these strategies are far from satisfactory and only target splanchnic hyperemia. In contrast, safe and reliable strategies to reduce the increased intrahepatic resistance in cirrhotic patients still represent a pending issue. In recent years, several preclinical and clinical trials have focused on this latter component and other therapeutic avenues. In this review, we highlight novel data in this context and address potentially interesting therapeutic options for the future.

New therapeutic concepts in bile acid transport and signaling for management of cholestasis

The identification of the key regulators of bile acid (BA) synthesis and transport within the enterohepatic circulation has revealed potential targets for pharmacological therapies of cholestatic liver diseases. Novel drug targets include the bile BA receptors, farnesoid X receptor and TGR5, the BA-induced gut hormones, fibroblast growth factor 19 and glucagon-like peptide 1, and the BA transport systems, apical sodium-dependent bile acid transporter and Na⁺ -taurocholate cotransporting polypeptide, within the enterohepatic circulation. Moreover, BA derivatives undergoing cholehepatic shunting may allow improved targeting to the bile ducts. This review focuses on the pathophysiological basis, mechanisms of action, and clinical development of novel pharmacological strategies targeting BA transport and signaling in cholestatic liver diseases. (Hepatology 2017;65:1393-1404).