FXR agonist obeticholic acid reduces hepatic inflammation and fibrosis in a rat model of toxic cirrhosis. Sci Rep. 2016;6:33453. [PMID: 27634375 PMCID: PMC5025787 DOI: 10.1038/srep33453]

A Review of Liver Fibrosis and Emerging Therapies

With the increasing burden of liver cirrhosis, the most advanced stage of hepatic fibrosis, there is a need to better understand the pathological processes and mechanisms to target specific treatments to reverse or cease fibrosis progression. Antiviral therapy for hepatitis B and C has effectively treated underlying causes of chronic liver disease and has induced fibrosis reversal in some; however, this has not been targeted for the majority of aetiologies for cirrhosis including alcohol or nonalcoholic steatohepatitis. Fibrosis, characterised by the accumulation of extracellular matrix proteins, is caused by chronic injury from toxic, infectious, or metabolic causes. The primary event of fibrogenesis is increased matrix production and scar formation mediated by the hepatic stellate cell, which is the principal cell type involved. Experimental models using rodent and human cell lines of liver injury have assisted in better understanding of fibrogenesis, especially in recognising the role of procoagulant factors. This has led to interventional studies using anticoagulants in animal models with reversal of fibrosis as the primary endpoint. Though these trials have been encouraging, no antifibrotic therapies are currently licenced for human use. This literature review discusses current knowledge in the pathophysiology of hepatic fibrosis, including characteristics of the extracellular matrix, signalling pathways, and hepatic stellate cells. Current types of experimental models used to induce fibrosis, as well as up-to-date anticoagulant therapies and agents targeting the hepatic stellate cell that have been trialled in animal and human studies with antifibrotic properties, are also reviewed.

BRD4 inhibition and FXR activation, individually beneficial in cholestasis, are antagonistic in combination

Activation of farnesoid X receptor (FXR) by obeticholic acid (OCA) reduces hepatic inflammation and fibrosis in patients with primary biliary cholangitis (PBC), a life-threatening cholestatic liver failure. Inhibition of bromodomain-containing protein 4 (BRD4) also has antiinflammatory, antifibrotic effects in mice. We determined the role of BRD4 in FXR function in bile acid (BA) regulation and examined whether the known beneficial effects of OCA are enhanced by inhibiting BRD4 in cholestatic mice. Liver-specific downregulation of BRD4 disrupted BA homeostasis in mice, and FXR-mediated regulation of BA-related genes, including small heterodimer partner and cholesterol 7 alpha-hydroxylase, was BRD4 dependent. In cholestatic mice, JQ1 or OCA treatment ameliorated hepatotoxicity, inflammation, and fibrosis, but surprisingly, was antagonistic in combination. Mechanistically, OCA increased binding of FXR, and the corepressor silencing mediator of retinoid and thyroid hormone receptor (SMRT) decreased NF-κB binding at inflammatory genes and repressed the genes in a BRD4-dependent manner. In patients with PBC, hepatic expression of FXR and BRD4 was significantly reduced. In conclusion, BRD4 is a potentially novel cofactor of FXR for maintaining BA homeostasis and hepatoprotection. Although BRD4 promotes hepatic inflammation and fibrosis in cholestasis, paradoxically, BRD4 is required for the antiinflammatory, antifibrotic actions of OCA-activated FXR. Cotreatment with OCA and JQ1, individually beneficial, may be antagonistic in treatment of liver disease patients with inflammation and fibrosis complications.

The Status of Bile Acids and Farnesoid X Receptor in Brain and Liver of Rats with Thioacetamide-Induced Acute Liver Failure

Acute liver failure (ALF) leads to neurological symptoms defined as hepatic encephalopathy (HE). Although accumulation of ammonia and neuroinflammation are generally accepted as main contributors to HE pathomechanism, a buildup of bile acids (BA) in the blood is a frequent component of liver injury in HE patients. Recent studies have identified the nuclear farnesoid X receptor (FXR) acting via small heterodimer partner (SHP) as a mediator of BA-induced effects in the brain of ALF animals. The present study investigated the status of the BA–FXR axis in the brain and the liver, including selective changes in pertinent genes in thioacetamide (TAA)-induced ALF in Sprague–Dawley rats. FXR was found in rat neurons, confirming earlier reports for mouse and human brain. BA accumulated in blood but not in the brain tissue. Expression of mRNAs coding for Fxr and Shp was reduced in the hippocampus and of Fxr mRNA also in the cerebellum. Changes in Fxr mRNA levels were not followed by changes in FXR protein. The results leave open the possibility that mobilization of the BA–FXR axis in the brain may not be necessarily pathognomonic to HE but may depend upon ALF-related confounding factors.

Pharmacological management of portal hypertension and its complications in children: lessons from adults and opportunities for the future

INTRODUCTION

Portal hypertension (PHT) and its complications in children are thought to be distinct from adult PHT in several areas, including the underlying bio-physiology of a child in which PHT develops, but also because of the pediatric-specific etiologies that drive disease progression. And yet pharmacologic approaches to PHT in children are mainly based on adult data, modified for pediatric practice. This reality has been driven by a lack of data specific to children.

AREAS COVERED

The authors discuss current therapeutic approaches to PHT in children, including management of acute gastrointestinal variceal bleed, pharmacotherapy in prophylaxis, and established and emerging therapies to combat systemic co-morbidities that result from PHT. The few areas where pediatric-specific data exist are highlighted and the many gaps in knowledge that remain unresolved are underscored.

EXPERT OPINION

Despite decades of experience, optimal management of pediatric PHT remains undefined. In large part, this can be directly linked to a lack of basic understanding related to the unique pathophysiology and natural history that defines PHT in children. As a result, meaningful research into the utility and effectiveness of pharmacotherapy in children with PHT remains in its infancy. Large, multi-center, prospective studies will be needed to begin to establish an infrastructure on which a pediatric-specific research agenda can be built.

Microbiota-Associated Therapy for Non-Alcoholic Steatohepatitis-Induced Liver Cancer: A Review

Even though advancement in medicine has contributed to the control of many diseases to date, cancer therapy continues to pose several challenges. Hepatocellular carcinoma (HCC) etiology is multifactorial. Recently, non-alcoholic fatty liver disease (NAFLD) has been considered as an important risk factor of HCC. NAFLD can be divided into non-alcoholic simple fatty liver (NAFL) and non-alcoholic steatohepatitis (NASH) based on histopathological features. Recently, studies have indicated that the gut microbiota is associated with NAFLD and HCC. Therefore, in this review, we have discussed the effects of gut microbiota-related mechanisms, including dysbiosis and gut barrier function, and gut microbiota-derived metabolites on NAFLD and HCC pathogenesis and the potential therapeutic strategies for NAFLD and HCC. With a better understanding of the gut microbiota composition and function, new and improved diagnostic, prognostic, and therapeutic strategies for common liver diseases can be developed.

Inflammation Drives MicroRNAs to Limit Hepatocyte Bile Acid Transport in Murine Biliary Atresia

BACKGROUND

Biliary atresia (BA) is an inflammatory pediatric cholangiopathy with only surgical means for treatment. Many contributors to bile acid synthesis and transport have previously been reported to be downregulated in patients with BA; yet, the driving factors of the abnormal bile acid synthesis and transport in regard to BA have not been previously studied.

MATERIALS AND METHODS

Wild type or Ig-α^-/- mice were injected with salt solution (control) or rotavirus on day of life 0, and analyses were performed on day of life 14. The mRNA levels of bile acid transporters/nuclear receptors and liver microRNAs (miRNAs) were compared between groups. A mouse hepatocyte cell line was used to examine the effects of innate cytokines on miRNA levels and bile acid transporter/nuclear receptor expression and miRNAs on bile acid transporter/nuclear receptor expression.

RESULTS

BA mice had significantly increased mRNA expression of innate cytokines and miRNAs known to bind bile acid transporters/nuclear receptors (miRNAs -22-5p, -34a-5p, and -222-3p) and decreased mRNA expression of bile acid transporters and nuclear receptors. In vitro, TNF-α and IL-1β decreased BSEP and CYP7A1 while increasing miRNA-34a-5p and miRNA 222-3p. LXR, SHP, CYP7A1, NTCP, and MRP2 were decreased by miRNA-34a-5p, whereas miRNA-222-3p decreased NTCP and MRP4. TNF-α and IL-1β increased expression of miRNAs 34a-5p and 222-3p and these miRNAs then decrease expression of multiple bile acid transporters and nuclear receptors.

CONCLUSIONS

Loss of bile acid transporters increases hepatotoxicity via bile acid retention. Therapeutic agents that increase bile acid transport or nuclear receptor functioning should be investigated in BA.

Animal models for liver disease - A practical approach for translational research

Animal models are crucial for improving our understanding of human pathogenesis, enabling researchers to identify therapeutic targets and test novel drugs. In the current review, we provide a comprehensive summary of the most widely used experimental models of chronic liver disease, starting from early stages of fatty liver disease (non-alcoholic and alcoholic) to steatohepatitis, advanced cirrhosis and end-stage primary liver cancer. We focus on aspects such as reproducibility and practicality, discussing the advantages and weaknesses of available models for researchers who are planning to perform animal studies in the near future. Additionally, we summarise current and prospective models based on human tissue bioengineering.

Activation of Farnesoid X Receptor by Schaftoside Ameliorates Acetaminophen-Induced Hepatotoxicity by Modulating Oxidative Stress and Inflammation

Aims: Acetaminophen (APAP) overdose leads to acute liver injury by inducing hepatic mitochondrial oxidative stress and inflammation. However, the molecular mechanisms involved are still unclear. Farnesoid X receptor (FXR) serves as a therapeutic target for the treatment of liver disorders, whose activation has been proved to protect APAP-induced hepatotoxicity. In this study, we examined whether FXR activation by schaftoside (SS), a naturally occurring flavonoid from Desmodium styracifolium, could protect mice against APAP-induced hepatotoxicity via regulation of oxidative stress and inflammation. Results: We first found that SS exhibited potent protective effects against APAP-induced hepatotoxicity in mice. The study reveals that SS is a potential agonist of FXR, which protects mice from hepatotoxicity mostly via regulation of oxidative stress and inflammation. Mechanistically, the hepatoprotective SS is associated with the induction of the genes of phase II detoxifying enzymes (e.g., UGT1A1, GSTα1), phase III drug efflux transporters (e.g., bile salt export pump, organic solvent transporter protein β), and glutathione metabolism-related enzymes (e.g., glutamate-cysteine ligase modifier subunit [Gclm], glutamate-cysteine ligase catalytic subunit [Gclc]). More importantly, SS-mediated FXR activation could fine-tune the pro- and anti-inflammatory eicosanoids generation via altering eicosanoids metabolic pathway, thereby resulting in decrease of hepatic inflammation. In contrast, FXR deficiency can abrogate the above effects. Innovation and Conclusion: Our results provided the direct evidence that FXR activation by SS could attenuate APAP-induced hepatotoxicity via inhibition of nuclear factor kappa-B signaling and fine-tuning the generation of proinflammatory mediators' eicosanoids. Our findings indicate that strategies to activate FXR signaling in hepatocytes may provide a promising therapeutic approach to alleviate liver injury induced by APAP overdose.

The liver fibrosis niche: Novel insights into the interplay between fibrosis-composing mesenchymal cells, immune cells, endothelial cells, and extracellular matrix

Liver fibrosis is a hepatic wound-healing response caused by chronic liver diseases that include viral hepatitis, alcoholic liver disease, non-alcoholic steatohepatitis, and cholestatic liver disease. Liver fibrosis eventually progresses to cirrhosis that is histologically characterized by an abnormal liver architecture that includes distortion of liver parenchyma, formation of regenerative nodules, and a massive accumulation of extracellular matrix (ECM). Despite intensive investigations into the underlying mechanisms of liver fibrosis, developments of anti-fibrotic therapies for liver fibrosis are still unsatisfactory. Recent novel experimental approaches, such as single-cell RNA sequencing and proteomics, have revealed the heterogeneity of ECM-producing cells (mesenchymal cells) and ECM-regulating cells (immune cells and endothelial cells). These approaches have accelerated the identification of fibrosis-specific subpopulations among these cell types. The ECM also consists of heterogenous components. Their production, degradation, deposition, and remodeling are dynamically regulated in liver fibrosis, further affecting the functions of cells responsible for fibrosis. These cellular and ECM elements cooperatively form a unique microenvironment: a fibrotic niche. Understanding the complex interplay between these elements could lead to a better understanding of underlying fibrosis mechanisms and to the development of effective therapies.

Bile Acid Sequestrant, Sevelamer Ameliorates Hepatic Fibrosis with Reduced Overload of Endogenous Lipopolysaccharide in Experimental Nonalcoholic Steatohepatitis

Despite the use of various pharmacotherapeutic strategies, fibrosis due to nonalcoholic steatohepatitis (NASH) remains an unsatisfied clinical issue. We investigated the effect of sevelamer, a hydrophilic bile acid sequestrant, on hepatic fibrosis in a murine NASH model. Male C57BL/6J mice were fed a choline-deficient, L-amino acid-defined, high-fat (CDHF) diet for 12 weeks with or without orally administered sevelamer hydrochloride (2% per diet weight). Histological and biochemical analyses revealed that sevelamer prevented hepatic steatosis, macrophage infiltration, and pericellular fibrosis in CDHF-fed mice. Sevelamer reduced the portal levels of total bile acid and inhibited both hepatic and intestinal farnesoid X receptor activation. Gut microbiome analysis demonstrated that sevelamer improved a lower α-diversity and prevented decreases in Lactobacillaceae and Clostridiaceae as well as increases in Desulfovibrionaceae and Enterobacteriaceae in the CDHF-fed mice. Additionally, sevelamer bound to lipopolysaccharide (LPS) in the intestinal lumen and promoted its fecal excretion. Consequently, the sevelamer treatment restored the tight intestinal junction proteins and reduced the portal LPS levels, leading to the suppression of hepatic toll-like receptor 4 signaling pathway. Furthermore, sevelamer inhibited the LPS-mediated induction of fibrogenic activity in human hepatic stellate cells in vitro. Collectively, sevelamer inhibited the development of murine steatohepatitis by reducing hepatic LPS overload.

Discovery, Structural Refinement and Therapeutic Potential of Farnesoid X Receptor Activators

Farnesoid X receptor acts as bile acid sensing transcription factor and has been identified as valuable molecular drug target to treat severe liver disorders, such as non-alcoholic steatohepatitis (NASH). Preclinical and clinical data indicate anti-fibrotic effects obtained with FXR activation that also appear promising for other fibrotic diseases beyond NASH. Strong efforts in FXR ligand discovery have yielded potent steroidal and non-steroidal FXR activators, some of which have been studied in clinical trials. While the structure–activity relationship of some FXR agonist frameworks have been studied extensively, the structural diversity of potent FXR activator chemotypes is still limited to a handful of well-studied compound classes. Together with safety concerns related to full therapeutic activation of FXR, this indicates the need for novel innovative FXR ligands with selective modulatory properties. This chapter evaluates FXR's value as drug target with emphasis on fibrotic diseases, analyses FXR ligand recognition and requirements and focuses on the discovery and structural refinement of leading FXR activator chemotypes.

Farnesoid X Receptor Activation Protects Liver From Ischemia/Reperfusion Injury by Up-Regulating Small Heterodimer Partner in Kupffer Cells

Farnesoid X receptor (FXR) is the nuclear receptor of bile acids and is involved in innate immune regulation. FXR agonists have been shown to protect multiple organs from inflammatory tissue injuries. Because liver expresses high levels of FXR, we explored the potential therapeutic benefits and underlying mechanisms of pharmacologic FXR activation in a murine model of partial liver warm ischemia. Pretreatment of mice with FXR agonist 3-(2,6-dichlorophenyl)-4-(3'-carboxy-2-chlorostilben-4-yl)oxymethyl-5-isopropylisoxazole (GW4064) attenuated liver ischemia/reperfusion injuries (IRIs) in wild-type but not FXR knockout mice. Posttreatment with GW4064 facilitated liver recovery from IRI. Mechanistically, Kupffer cells (KCs) expressed much higher levels of FXR than bone marrow-derived macrophages (BMMs). Pretreatment of KCs but not BMMs with GW4064 resulted in lower tumor necrosis factor α but higher interleukin-10 expressions following toll-like receptor stimulation. FXR-targeted gene small heterodimer partner (SHP) was critical for the regulation of KC response by GW4064. In vivo, the depletion of KCs but not cluster of differentiation (CD) 11b⁺ cells or knockdown of SHP diminished the immune regulatory effect of GW4064 in liver IRI. Thus, FXR activation protects liver from IRI by up-regulating SHP in KCs to inhibit the liver proinflammatory response.

Nidufexor (LMB763), a Novel FXR Modulator for the Treatment of Nonalcoholic Steatohepatitis

Farnesoid X receptor (FXR) agonists are emerging as important potential therapeutics for the treatment of nonalcoholic steatohepatitis (NASH) patients, as they exert positive effects on multiple aspects of the disease. FXR agonists reduce lipid accumulation in the liver, hepatocellular inflammation, hepatic injury, and fibrosis. While there are currently no approved therapies for NASH, the bile acid-derived FXR agonist obeticholic acid (OCA; 6-ethyl chenodeoxycholic acid) has shown promise in clinical studies. Previously, we described the discovery of tropifexor (LJN452), the most potent non-bile acid FXR agonist currently in clinical investigation. Here, we report the discovery of a novel chemical series of non-bile acid FXR agonists based on a tricyclic dihydrochromenopyrazole core from which emerged nidufexor (LMB763), a compound with partial FXR agonistic activity in vitro and FXR-dependent gene modulation in vivo. Nidufexor has advanced to Phase 2 human clinical trials in patients with NASH and diabetic nephropathy.

SUMOylation inhibitors synergize with FXR agonists in combating liver fibrosis

Farnesoid X receptor (FXR) is a promising target for nonalcoholic steatohepatitis (NASH) and fibrosis. Although various FXR agonists have shown anti-fibrotic effects in diverse preclinical animal models, the response rate and efficacies in clinical trials were not optimum. Here we report that prophylactic but not therapeutic administration of obeticholic acid (OCA) prevents hepatic stellate cell (HSC) activation and fibrogenesis. Activated HSCs show limited response to OCA and other FXR agonists due to enhanced FXR SUMOylation. SUMOylation inhibitors rescue FXR signaling and thereby increasing the efficacy of OCA against HSC activation and fibrosis. FXR upregulates Perilipin-1, a direct target gene of FXR, to stabilize lipid droplets and thereby prevent HSC activation. Therapeutic coadministration of OCA and SUMOylation inhibitors drastically impedes liver fibrosis induced by CCl₄, bile duct ligation, and more importantly NASH. In conclusion, we propose a promising therapeutic approach by combining SUMOylation inhibitors and FXR agonists for liver fibrosis.

FXR agonists have been investigated for the treatment of non-alcoholic steatohepatitis and liver fibrosis but the clinical efficacy is not optimal. Here the authors show that enhanced FXR SUMOylation in activated hepatic stellate cells reduces FXR signaling and that this can be rescued by SUMOylation inhibitors.

Pegbelfermin (BMS-986036): an investigational PEGylated fibroblast growth factor 21 analogue for the treatment of nonalcoholic steatohepatitis

Introduction: Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide and is strongly associated with obesity and insulin resistance. NAFLD refers to a spectrum of disorders ranging from asymptomatic hepatic steatosis (nonalcoholic fatty liver, NAFL) to nonalcoholic steatohepatitis (NASH), which increases the risk of developing more severe forms of liver disease such as progressive fibrosis, cirrhosis, and liver cancer. Currently, there are no food and drug administration (FDA) approved drugs to treat NASH. Pegbelfermin (BMS-986036) is a PEGylated fibroblast growth factor 21 (FGF21) analogue that is under investigation for the treatment of NASH.Areas covered: We reviewed the (pre)clinical pegbelfermin studies and compared these with other studies that assessed FGF21 and FGF21 analogues in the treatment of NASH.Expert opinion: With no FDA approved treatments available for NASH, there is an urgent need for novel therapies. Pegbelfermin is a systemic treatment with pleiotropic effects on various tissues. Short-term adverse effects are limited, but more research is required to study potential long-term safety issues. In a phase 2a trial, pegbelfermin has shown promising improvements in several NASH related outcomes. However, clinical trials demonstrating long-term benefits on hard outcomes such as liver histology, cirrhosis development, or survival are required for further validation.

THE EFFECT OF COMPOUND DM509 ON KIDNEY FIBROSIS IN THE CONDITIONS OF THE EXPERIMENTAL MODEL

Renal fibrosis is a critical event in the progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD). Unfortunately, there are few options to target renal fibrosis in order to develop novel anti-fibrotic agents that could prevent CKD progression to ESRD. We evaluated the efficacy of a novel dual-acting molecule, DM509, in preventing renal fibrosis using the unilateral ureteral obstruction (UUO) renal fibrosis mouse model. DM509 acts simultaneously as a farnesoid X receptor agonist (FXRA) and a soluble epoxide hydrolase inhibitor (sEHi). In this study, groups of 8-12 weeks old C57BL/6J male mice went through either UUO or sham surgery (n=6/group). Mice were pre-treated with DM509 (10mg/kg/d) or vehicle administered in drinking water one day prior to the UUO surgery. Sham, vehicle and DM509 treatments continued until day 10 and blood and kidney tissue were collected for biochemical, histological, and gene expression analysis at the end of the treatment protocol. The UUO group exhibited kidney dysfunction with elevated blood urea nitrogen (BUN) compared to the sham group (63±7 vs. 34±6 mg/dL). DM509 treatment prevented renal dysfunction as evident from 36% lower BUN level in the DM509 treated UUO mice compared to UUO mice treated with vehicle. Vehicle treated UUO mice demonstrated renal fibrosis with elevated kidney hydroxyproline content (213±11 vs. 49±9 μg/mg protein) and kidney collagen positive area (13±2% vs. 1.1±0.1%) compared to the sham group. We found that DM509 treatment prevented renal fibrosis and DM509 treated mice had 34-66% lower levels of kidney hydroxyproline and collagen positive renal area compared to vehicle-treated UUO mice. In conclusion, our data provide evidence that the novel dual-acting FXRA and a sEHi, DM509, prevented renal dysfunction and renal fibrosis in UUO mouse model.

The Role of Chemokine Receptors in Renal Fibrosis

Renal fibrosis is the final pathological process common to any ongoing, chronic kidney injury or maladaptive repair. Renal fibrosis is considered to be closely related to various cell types, such as fibroblasts, myofibroblasts, T cells, and other inflammatory cells. Multiple types of cells regulate renal fibrosis through the recruitment, proliferation, and activation of fibroblasts, and the production of the extracellular matrix. Cell trafficking is orchestrated by a family of small proteins called chemokines. Chemokines are cytokines with chemotactic properties, which are classified into 4 groups: CXCL, CCL, CX3CL, and XCL. Similarly, chemokine receptors are G protein-coupled seven-transmembrane receptors classified into 4 groups: XCR, CCR, CXCR, and CX3CR. Chemokine receptors are also implicated in the infiltration, differentiation, and survival of functional cells, triggering inflammation that leads to fibrosis development. In this review, we summarize the different chemokine receptors involved in the processes of fibrosis in different cell types. Further studies are required to identify the molecular mechanisms of chemokine signaling that contribute to renal fibrosis.

Farnesoid X receptor and bile acids regulate vitamin A storage

The nuclear receptor Farnesoid X Receptor (FXR) is activated by bile acids and controls multiple metabolic processes, including bile acid, lipid, carbohydrate, amino acid and energy metabolism. Vitamin A is needed for proper metabolic and immune control and requires bile acids for efficient intestinal absorption and storage in the liver. Here, we analyzed whether FXR regulates vitamin A metabolism. Compared to control animals, FXR-null mice showed strongly reduced (>90%) hepatic levels of retinol and retinyl palmitate and a significant reduction in lecithin retinol acyltransferase (LRAT), the enzyme responsible for hepatic vitamin A storage. Hepatic reintroduction of FXR in FXR-null mice induced vitamin A storage in the liver. Hepatic vitamin A levels were normal in intestine-specific FXR-null mice. Obeticholic acid (OCA, 3 weeks) treatment rapidly reduced (>60%) hepatic retinyl palmitate levels in mice, concurrent with strongly increased retinol levels (>5-fold). Similar, but milder effects were observed in cholic acid (12 weeks)-treated mice. OCA did not change hepatic LRAT protein levels, but strongly reduced all enzymes involved in hepatic retinyl ester hydrolysis, involving mostly post-transcriptional mechanisms. In conclusion, vitamin A metabolism in the mouse liver heavily depends on the FXR and FXR-targeted therapies may be prone to cause vitamin A-related pathologies.

Pharmacologic Management of Portal Hypertension

Terlipressin, somatostatin, or octreotide are recommended as pharmacologic treatment of acute variceal hemorrhage. Nonselective β-blockers decrease the risk of variceal hemorrhage and hepatic decompensation, particularly in those 30% to 40% of patients with good hemodynamic response. Carvedilol, statins, and anticoagulants are promising agents in the management of portal hypertension. Recent advances in the pharmacologic treatment of portal hypertension have mainly focused on modifying an increased intrahepatic resistance through nitric oxide and/or modulation of vasoactive substances. Several novel pharmacologic agents for portal hypertension are being evaluated in humans.

Gut-liver axis signaling in portal hypertension

Portal hypertension (PHT) in advanced chronic liver disease (ACLD) results from increased intrahepatic resistance caused by pathologic changes of liver tissue composition (structural component) and intrahepatic vasoconstriction (functional component). PHT is an important driver of hepatic decompensation such as development of ascites or variceal bleeding. Dysbiosis and an impaired intestinal barrier in ACLD facilitate translocation of bacteria and pathogen-associated molecular patterns (PAMPs) that promote disease progression via immune system activation with subsequent induction of proinflammatory and profibrogenic pathways. Congestive portal venous blood flow represents a critical pathophysiological mechanism linking PHT to increased intestinal permeability: The intestinal barrier function is affected by impaired microcirculation, neoangiogenesis, and abnormal vascular and mucosal permeability. The close bidirectional relationship between the gut and the liver has been termed “gut-liver axis”. Treatment strategies targeting the gut-liver axis by modulation of microbiota composition and function, intestinal barrier integrity, as well as amelioration of liver fibrosis and PHT are supposed to exert beneficial effects. The activation of the farnesoid X receptor in the liver and the gut was associated with beneficial effects in animal experiments, however, further studies regarding efficacy and safety of pharmacological FXR modulation in patients with ACLD are needed. In this review, we summarize the clinical impact of PHT on the course of liver disease, discuss the underlying pathophysiological link of PHT to gut-liver axis signaling, and provide insight into molecular mechanisms that may represent novel therapeutic targets.

Combined effect of a farnesoid X receptor agonist and dipeptidyl peptidase-4 inhibitor on hepatic fibrosis

AIM

Non-alcoholic steatohepatitis (NASH) has a broad clinicopathological spectrum (inflammation to severe fibrosis). The farnesoid X receptor agonist obeticholic acid (OCA) ameliorates the histological features of NASH; satisfactory antifibrotic effects have not yet been reported. Here, we investigated the combined effects of OCA + a dipeptidyl peptidase-4 inhibitor (sitagliptin) on hepatic fibrogenesis in a rat model of NASH.

METHODS

Fifty Fischer 344 rats were fed a choline-deficient L-amino-acid-defined (CDAA) diet for 12 weeks. The in vitro and in vivo effects of OCA + sitagliptin were assessed along with hepatic fibrogenesis, lipopolysaccharide-Toll-like receptor 4 (TLR4) regulatory cascade and intestinal barrier function. Direct inhibitory effects of OCA + sitagliptin on activated hepatic stellate cells (Ac-HSCs) were assessed in vitro.

RESULTS

Treatment with OCA + sitagliptin potentially inhibited hepatic fibrogenesis along with Ac-HSC proliferation and hepatic transforming growth factor (TGF)-β1, α1(I)-procollagen, and tissue inhibitor of metalloproteinase-1 (TIMP-1) mRNA expression and hydroxyproline levels. Obeticholic acid inhibited hepatic TLR4 expression and increased hepatic matrix metalloproteinase-2 expression. Obeticholic acid decreased intestinal permeability by ameliorating CDAA diet-induced zonula occludens-1 disruption, whereas sitagliptin directly inhibited Ac-HSC proliferation. The in vitro suppressive effects of OCA + sitagliptin on TGF-β1 and α1(I)-procollagen mRNA expression and p38 phosphorylation in Ac-HSCs were almost consistent. Sitagliptin directly inhibited the regulation of Ac-HSC.

CONCLUSIONS

Treatment with OCA + sitagliptin synergistically affected hepatic fibrogenesis by counteracting endotoxemia induced by intestinal barrier dysfunction and suppressing Ac-HSC proliferation. Thus, OCA + sitagliptin could be a promising therapeutic strategy for NASH.

Targeting metabolic dysregulation for fibrosis therapy

Fibrosis is the abnormal deposition of extracellular matrix, which can lead to organ dysfunction, morbidity, and death. The disease burden caused by fibrosis is substantial, and there are currently no therapies that can prevent or reverse fibrosis. Metabolic alterations are increasingly recognized as an important pathogenic process that underlies fibrosis across many organ types. As a result, metabolically targeted therapies could become important strategies for fibrosis reduction. Indeed, some of the pathways targeted by antifibrotic drugs in development - such as the activation of transforming growth factor-β and the deposition of extracellular matrix - have metabolic implications. This Review summarizes the evidence to date and describes novel opportunities for the discovery and development of drugs for metabolic reprogramming, their associated challenges, and their utility in reducing fibrosis. Fibrotic therapies are potentially relevant to numerous common diseases such as cirrhosis, non-alcoholic steatohepatitis, chronic renal disease, heart failure, diabetes, idiopathic pulmonary fibrosis, and scleroderma.

Pharmacologic Modulation of Bile Acid-FXR-FGF15/FGF19 Pathway for the Treatment of Nonalcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is within the spectrum of nonalcoholic fatty liver disease (NAFLD) and can progress to fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). The prevalence of NASH is rising and has become a large burden to the medical system worldwide. Unfortunately, despite its high prevalence and severe health consequences, there is currently no therapeutic agent approved to treat NASH. Therefore, the development of efficacious therapies is of utmost urgency and importance. Many molecular targets are currently under investigation for their ability to halt NASH progression. One of the most promising and well-studied targets is the bile acid (BA)-activated nuclear receptor, farnesoid X receptor (FXR). In this chapter, the characteristics, etiology, and prevalence of NASH will be discussed. A brief introduction to FXR regulation of BA homeostasis will be described. However, for more details regarding FXR in BA homeostasis, please refer to previous chapters. In this chapter, the mechanisms by which tissue and cell type-specific FXR regulates NASH development will be discussed in detail. Several FXR agonists have reached later phase clinical trials for treatment of NASH. The progress of these compounds and summary of released data will be provided. Lastly, this chapter will address safety liabilities specific to the development of FXR agonists.

REGENERATE: Design of a pivotal, randomised, phase 3 study evaluating the safety and efficacy of obeticholic acid in patients with fibrosis due to nonalcoholic steatohepatitis

BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a chronic, progressive, and severe form of nonalcoholic fatty liver disease. In FLINT, obeticholic acid (OCA) treatment improved multiple histological NASH features. The design and endpoints of REGENERATE, an ongoing phase 3 study, further evaluate OCA treatment in patients with fibrosis due to NASH.

AIMS

The Month 18 interim analysis assesses the effect of OCA on liver histology, defined as improvement of fibrosis by ≥1 stage with no worsening of NASH or resolution of NASH with no worsening of fibrosis. The end-of-study analyses evaluate the effect of OCA on mortality, liver-related clinical outcomes, and long-term safety.

METHODS

REGENERATE is a pivotal, long-term study of ~2400 patients with NASH, including ~2100 patients with stage 2 or 3 liver fibrosis. Additionally, ~300 patients with stage 1 fibrosis and ≥1 accompanying comorbidity are included to gather information on the safety of OCA and liver disease progression. Patients are randomised 1:1:1 to receive placebo or OCA (10 or 25 mg). A liver biopsy evaluation occurs at screening, Months 18 and 48, and end of study. The duration of the study is dependent upon accrual of a predetermined number of clinical outcome events.

CONCLUSIONS

REGENERATE is designed in conjunction with regulatory authorities to support regulatory approvals in NASH. This robust phase 3 study assesses the effect of OCA on liver histology as a surrogate for transplant-free survival and liver-related outcomes, including progression to cirrhosis and mortality, and will ultimately assess clinical benefit through specific evaluation of these outcomes.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov with the identifier NCT02548351.

Hepatoprotection of yangonin against hepatic fibrosis in mice via farnesoid X receptor activation

Hepatic fibrosis is a reversible would-healing response following chronic liver injury of different aetiologies and represents a major worldwide health problem. Up to date, there is no satisfactory drugs treated for liver fibrosis. The present study was to investigate hepatoprotection of yangonin against liver fibrosis induced by thioacetamide (TAA) in mice and further to clarify the involvement of farnesoid X receptor (FXR) in vivo and in vitro. Yangonin treatment remarkably ameliorated TAA-induced liver injury by reducing relative liver weight, as well as serum ALT and AST activities. Moreover, yangonin alleviated TAA-induced accumulation of bile acids through increasing the expression of bile acid efflux transporters such as Bsep and Mrp2, and reducing hepatic uptake transporter Ntcp expression, all of these are FXR-target genes. The liver sections stained by H&E indicated that the histopathological change induced by TAA was improved by yangonin. Masson and Sirius red staining indicated the obvious anti-fibrotic effect of yangonin. The mechanism of anti-fibrotic effect of yangonin was that yangonin reduced collagen content by regulating the genes involved in hepatic fibrosis including COL1-α1 and TIMP-1. Besides, yangonin inhibited hepatic stellate cell activation by reducing TGF-β1 and α-SMA expression. In addition, yangonin protected against TAA-induced hepatic inflammation via its inhibition of NF-κB and TNF-α. These hepatoprotective effects of yangonin were abrogated by guggulsterone which is a FXR antagonist. In vitro experiment further demonstrated dose-dependent activation of FXR by yangonin using dual-luciferase reporter assay. In summary, yangonin produces hepatoprotection against TAA-induced liver fibrosis via FXR activation.

FXR agonist GW4064 improves liver and intestinal pathology and alters bile acid metabolism in rats undergoing small intestinal resection

Mortality associated with liver disease has been observed in patients with short bowel syndrome (SBS); however, its mechanism remains unclear, but bile acid (BA) dysmetabolism has been proposed as a possible cause. The farnesoid X receptor (FXR) is the key regulator of BA synthesis. Here, we showed that, in a rat model of short bowel resection associated with liver disease (SBR-ALD), the BA composition of hepatic tissues reflected a larger proportion of primary and secondary unconjugated BAs, whereas that of the colon contents and serum showed an increased ratio of secondary unconjugated BAs. Both hepatic and intestinal regulation of BA synthesis was characterized by a blunted hepatic FXR activation response. The mRNA expression levels of cholesterol 7a-hydroxylase (CYP7A1), sterol 12a-hydroxylase (CYP8B1), and sterol 27 hydroxylase (CYP27A1), the key enzymes in BA synthesis, were upregulated. After intervention with the FXR agonist GW4064, both the liver histology and serum transaminase activity were improved, which demonstrated the attenuation of SBR-ALD. The BA compositions of hepatic tissue, the colon contents, and serum recovered and were closer to those of the sham group. The expression levels of hepatic FXR increased, and its target genes were activated. Consistent with this, the expression levels of CYP7A1, CYP8B1, and CYP27A1 were downregulated. Ileum tissue FXR and its target genes were slightly elevated. This study showed that the FXR agonist GW4064 could correct BA dysmetabolism to alleviate hepatotoxicity in SBR animals. GW4064 intervention resulted in a decrease in fecal bile excretion and elevated plasma/hepatic conjugated BA levels. GW4064 increased the reabsorption of conjugated BAs by inducing apical sodium-dependent bile salt transporter expression in the ileum. Concomitantly, FXR activation in the presence of GW4064 decreased BA production by repressing the expression of key synthetases, including CYP7A1, CYP8B1, and CYP27A1. These findings provide a clinical research direction for the prevention of liver disease in patients with SBS.NEW & NOTEWORTHY This study assessed the impact of treatment with GW4064, a farnesoid X receptor agonist, on the development of short bowel resection (SBR) associated with liver disease in a rat model of SBR. GW4064 was able to correct bile acid dysmetabolism and alleviate hepatotoxicity in SBR animals.

Chronic activation of FXR-induced liver growth with tissue-specific targeting Cyclin D1

The nuclear receptor (FXR) plays essential roles in maintaining bile acid and lipid homeostasis by regulating diverse target genes. And its agonists were promising agents for treating various liver diseases. Nevertheless, the potential side effect of chronic FXR activation by specific agonists is not fully understood. In this study, we investigated the mechanism of FXR agonist WAY-362450 induced liver enlargement during treating liver diseases. We demonstrated that chronic ingestion of WAY-362450 induced liver hypertrophy instead of hyperplasia in mouse. Global transcriptional pattern was also examined in mouse livers after treatment with WAY-362450 by RNA-seq assay. Through GO and KEGG enrichment analyses, we demonstrated that the expression of Cyclin D1 (Ccnd1) among the cell cycle-regulating genes was notably increased in WAY-362450-treated mouse liver. Activation of FXR-induced Ccnd1 expression in hepatocyte in a time-dependent manner in vivo and in vitro. Through bioinformatics analysis and ChIP assay, we identified FXR as a direct transcriptional activator of Ccnd1 through binding to a potential enhancer, which was specifically active in livers. We also found active histone acetylation was essential for Ccnd1 induction by FXR. Thus, our study indicated that activation of FXR-induced harmless liver hypertrophy with spatiotemporal modulation of Ccnd1. With a better understanding of the mechanism of tissue-specific gene regulation by FXR, it is beneficial for development and appropriate application of its specific agonist in preventing hepatic diseases.

The farnesoid X receptor agonist EDP-305 reduces interstitial renal fibrosis in a mouse model of unilateral ureteral obstruction

Farnesoid X receptor (FXR) is a nuclear receptor that has emerged as a key regulator in the maintenance of hepatic steatosis, inflammation, and fibrosis. However, the role of FXR in renal fibrosis remains to be established. Here, we investigate the effects of the FXR agonist EDP-305 in a mouse model of tubulointerstitial fibrosis via unilateral ureteral obstruction (UUO). Male C57Bl/6 mice received a UUO on their left kidney. On postoperative d 4, mice received daily treatment by oral gavage with either vehicle control (0.5% methylcellulose) or 10 or 30 mg/kg EDP-305. All animals were euthanized on postoperative d 12. EDP-305 dose-dependently decreased macrophage infiltration as measured by the F4/80 staining area and proinflammatory cytokine gene expression. EDP-305 also dose-dependently reduced interstitial fibrosis as assessed by morphometric quantification of the collagen proportional area and kidney hydroxyproline levels. Finally, yes-associated protein (YAP) activation, a major driver of fibrosis, increased after UUO injury and was diminished by EDP-305 treatment. Consistently, EDP-305 decreased TGF-β1-induced YAP nuclear localization in human kidney 2 cells by increasing inhibitory YAP phosphorylation. YAP inhibition may be a novel antifibrotic mechanism of FXR agonism, and EDP-305 could be used to treat renal fibrosis.-Li, S., Ghoshal, S., Sojoodi, M., Arora, G., Masia, R., Erstad, D. J., Ferriera, D. S., Li, Y., Wang, G., Lanuti, M., Caravan, P., Or, Y. S., Jiang, L.-J., Tanabe, K. K., Fuchs, B. C. The farnesoid X receptor agonist EDP-305 reduces interstitial renal fibrosis in a mouse model of unilateral ureteral obstruction.

Tropifexor-Mediated Abrogation of Steatohepatitis and Fibrosis Is Associated With the Antioxidative Gene Expression Profile in Rodents

Farnesoid X receptor (FXR) agonism is emerging as an important potential therapeutic mechanism of action for multiple chronic liver diseases. The bile acid‐derived FXR agonist obeticholic acid (OCA) has shown promise in a phase 2 study in patients with nonalcoholic steatohepatitis (NASH). Here, we report efficacy of the novel nonbile acid FXR agonist tropifexor (LJN452) in two distinct preclinical models of NASH. The efficacy of tropifexor at <1 mg/kg doses was superior to that of OCA at 25 mg/kg in the liver in both NASH models. In a chemical and dietary model of NASH (Stelic animal model [STAM]), tropifexor reversed established fibrosis and reduced the nonalcoholic fatty liver disease activity score and hepatic triglycerides. In an insulin‐resistant obese NASH model (amylin liver NASH model [AMLN]), tropifexor markedly reduced steatohepatitis, fibrosis, and profibrogenic gene expression. Transcriptome analysis of livers from AMLN mice revealed 461 differentially expressed genes following tropifexor treatment that included a combination of signatures associated with reduction of oxidative stress, fibrogenesis, and inflammation. Conclusion: Based on preclinical validation in animal models, tropifexor is a promising investigational therapy that is currently under phase 2 development for NASH.

Combined obeticholic acid and apoptosis inhibitor treatment alleviates liver fibrosis

Obeticholic acid (OCA), the first FXR-targeting drug, has been claimed effective in the therapy of liver fibrosis. However, recent clinical trials indicated that OCA might not be effective against liver fibrosis, possibly due to the lower dosage to reduce the incidence of the side-effect of pruritus. Here we propose a combinatory therapeutic strategy of OCA and apoptosis inhibitor for combating against liver fibrosis. CCl4-injured mice, d-galactosamine/LPS (GalN/LPS)-treated mice and cycloheximide/TNFα (CHX/TNFα)-treated HepG2 cells were employed to assess the effects of OCA, or together with IDN-6556, an apoptosis inhibitor. OCA treatment significantly inhibited hepatic stellate cell (HSC) activation/proliferation and prevented fibrosis. Elevated bile acid (BA) levels and hepatocyte apoptosis triggered the activation and proliferation of HSCs. OCA treatment reduced BA levels but could not inhibit hepatocellular apoptosis. An enhanced anti-fibrotic effect was observed when OCA was co-administrated with IDN-6556. Our study demonstrated that OCA inhibits HSCs activation/proliferation partially by regulating BA homeostasis and thereby inhibiting activation of HSCs. The findings in this study suggest that combined use of apoptosis inhibitor and OCA at lower dosage represents a novel therapeutic strategy for liver fibrosis.

Bile acid receptor agonists in primary biliary cholangitis: Regulation of the cholangiocyte secretome and downstream T cell differentiation

Primary biliary cholangitis (PBC) is a chronic autoimmune liver disease. Approximately 30% of patients do not respond to therapy with ursodeoxycholic acid (UDCA). Previous studies have implicated increased senescence of cholangiocytes in patients who do not respond to UDCA. This may increase the release of cytokines which drive pathogenic T cell polarization. As FXR agonists are beneficial in treating UDCA non-responsive patients, the current study was designed to model the interactions between cholangiocytes and CD4+ T cells to investigate potential immunomodulatory mechanisms of bile acid receptor agonists. Human cholangiocytes were co-cultured with CD4+ T cells to model the biliary stress response. Senescent cholangiocytes were able to polarize T cells toward a Th17 phenotype and suppressed expression of FoxP3 (P = 0.0043). Whilst FXR and TGR5 receptor agonists were unable directly to alter cholangiocyte cytokine expression, FGF19 was capable of significantly reducing IL-6 release (P = 0.044). Bile acid receptor expression was assessed in PBC patients with well-characterized responsiveness to UDCA therapy. A reduction in FXR staining was observed in both cholangiocytes and hepatocytes in PBC patients without adequate response to UDCA. Increased IL-6 expression by senescent cholangiocytes represents a potential mechanism by which biliary damage in PBC could contribute to excessive inflammation.

Hepatic microcirculation and mechanisms of portal hypertension

The liver microcirculatory milieu, mainly composed of liver sinusoidal endothelial cells (LSECs), hepatic stellate cells (HSCs) and hepatic macrophages, has an essential role in liver homeostasis, including in preserving hepatocyte function, regulating the vascular tone and controlling inflammation. Liver microcirculatory dysfunction is one of the key mechanisms that promotes the progression of chronic liver disease (also termed cirrhosis) and the development of its major clinical complication, portal hypertension. In the present Review, we describe the current knowledge of liver microcirculatory dysfunction in cirrhotic portal hypertension and appraise the preclinical models used to study the liver circulation. We also provide a comprehensive summary of the promising therapeutic options to target the liver microvasculature in cirrhosis.

The links between the gut microbiome and non-alcoholic fatty liver disease (NAFLD)

NAFLD is currently the main cause of chronic liver disease in developed countries, and the number of NAFLD patients is growing worldwide. NAFLD often has similar symptoms to other metabolic disorders, including type 2 diabetes and obesity. Recently, the role of the gut microbiota in the pathophysiology of many diseases has been revealed. Regarding NAFLD, experiments using gut microbiota transplants to germ-free animal models showed that fatty liver disease development is determined by gut bacteria. Moreover, the perturbation of the composition of the gut microbiota has been observed in patients suffering from NAFLD. Numerous mechanisms relating the gut microbiome to NAFLD have been proposed, including the dysbiosis-induced dysregulation of gut endothelial barrier function that allows for the translocation of bacterial components and leads to hepatic inflammation. In addition, the various metabolites produced by the gut microbiota may impact the liver and thus modulate NAFLD susceptibility. Therefore, the manipulation of the gut microbiome by probiotics, prebiotics or synbiotics was shown to improve liver phenotype in NAFLD patients as well as in rodent models. Hence, further knowledge about the interactions among dysbiosis, environmental factors, and diet and their impacts on the gut-liver axis can improve the treatment of this life-threatening liver disease and its related disorders.

Targeting Myeloid-Derived Cells: New Frontiers in the Treatment of Non-alcoholic and Alcoholic Liver Disease

Non-alcoholic fatty liver disease (NAFLD) and Alcoholic Liver Disease (ALD) are major causes of liver-related morbidity and mortality and constitute important causes of liver transplantation. The spectrum of the liver disease is wide and includes isolated steatosis, steatohepatitis, and cirrhosis. The treatment of NAFLD and ALD remains, however, an unmet need, and therefore it is a public health priority to develop effective treatments for these diseases. Alcoholic and non-alcoholic liver disease share common complex pathogenetic pathways that involve different organs and systems beyond the liver, including the gut, the adipose tissue, and the immune system, which cross-talk to generate damage. Myeloid-derived cells have been widely studied in the setting of NAFLD and ALD and are implicated at different levels in the onset and progression of this disease. Among these cells, monocytes and macrophages have been found to be involved in the induction of inflammation and in the progression to fibrosis, both in animal models and clinical studies and they have become interesting potential targets for the treatment of both NAFLD and ALD. The different mechanisms by which these cells can be targeted include modulation of Kupffer cell activation, monocyte recruitment in the liver and macrophage polarization and differentiation. Evidence from preclinical studies and clinical trials (some of them already in phase II and III) have shown encouraging results in ameliorating steatohepatitis, fibrosis, and the metabolic profile, individuating promising candidates for the pharmacological treatment of these diseases. The currently available results of myeloid-derived cells targeted treatments in NAFLD and ALD are covered in this review.

Obeticholic Acid: An Update of Its Pharmacological Activities in Liver Disorders

Obeticholic acid (OCA), 6α-ethyl-3α,7α-dihydroxy-5-cholan-24-oic acid, is a semisynthetic derivative of the chenodeoxycholic acid (CDCA, 3α,7α-dihydroxy-5-cholan-24-oic acid), a relatively hydrophobic primary bile acid synthesized in the liver from cholesterol. OCA, also known as 6-ethyl-CDCA or INT-747, was originally described by investigators at the Perugia University in 2002 as a selective ligand for the bile acid sensor, farnesoid-X-receptor (FXR). In addition to FXR and similarly to CDCA, OCA also activates GPBAR1/TGR5, a cell membrane G protein-coupled receptor for secondary bile acids. In 2016, based on the results of phase II studies showing efficacy in reducing the plasma levels of alkaline phosphatase, a surrogate biomarker for disease progression in primary biliary cholangitis (PBC), OCA has gained approval as a second-line treatment for PBC patients nonresponsive to UDCA. The use of OCA in PBC patients associates with several side effects, the most common of which is pruritus, whose incidence is dose-dependent and is extremely high when this agent is used as a monotherapy. Additionally, the use of OCA associates with the increased risk for the development of liver failure in cirrhotic PBC patients. Currently, OCA is investigated for its potential in the treatment of nonalcoholic steatohepatitis (NASH). Phase II and III trials have shown that OCA might attenuate the severity of liver fibrosis in patients with NASH, but it has no efficacy in reversing the steatotic component of the disease, while reduces the circulating levels of HDL-C and increases LDL-C. In summary, OCA has been the first-in-class of FXR ligands advanced to a clinical stage and is now entering its third decade of life, highlighting the potential benefits and risk linked to FXR-targeted therapies.

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.

Potential of Intestine-Selective FXR Modulation for Treatment of Metabolic Disease

Farnesoid X receptor controls bile acid metabolism, both in the liver and intestine. This potent nuclear receptor not only maintains homeostasis of its own ligands, i.e., bile acids, but also regulates glucose and lipid metabolism as well as the immune system. These findings have led to substantial interest for FXR as a therapeutic target and to the recent approval of an FXR agonist for treating primary biliary cholangitis as well as ongoing clinical trials for other liver diseases. Given that FXR biology is complex, including moderate expression in tissues outside of the enterohepatic circulation, temporal expression of isoforms, posttranscriptional modifications, and the existence of several other bile acid-responsive receptors such as TGR5, clinical application of FXR modulators warrants thorough understanding of its actions. Recent findings have demonstrated remarkable physiological effects of targeting FXR specifically in the intestine (iFXR), thereby avoiding systemic release of modulators. These include local effects such as improvement of intestinal barrier function and intestinal cholesterol turnover, as well as systemic effects such as improvements in glucose homeostasis, insulin sensitivity, and nonalcoholic fatty liver disease (NAFLD). Intriguingly, metabolic improvements have been observed with both an iFXR agonist that leads to production of enteric Fgf15 and increased energy expenditure in adipose tissues and antagonists by reducing systemic ceramide levels and hepatic glucose production. Here we review the recent findings on the role of intestinal FXR and its targeting in metabolic disease.

Obeticholic Acid Modulates Serum Metabolites and Gene Signatures Characteristic of Human NASH and Attenuates Inflammation and Fibrosis Progression in Ldlr-/-.Leiden Mice

Concerns have been raised about whether preclinical models sufficiently mimic molecular disease processes observed in nonalcoholic steatohepatitis (NASH) patients, bringing into question their translational value in studies of therapeutic interventions in the process of NASH/fibrosis. We investigated the representation of molecular disease patterns characteristic for human NASH in high-fat diet (HFD)-fed Ldlr-/-.Leiden mice and studied the effects of obeticholic acid (OCA) on these disease profiles. Multiplatform serum metabolomic profiles and genome-wide liver transcriptome from HFD-fed Ldlr-/-.Leiden mice were compared with those of NASH patients. Mice were profiled at the stage of mild (24 weeks HFD) and severe (34 weeks HFD) fibrosis, and after OCA intervention (24-34 weeks; 10 mg/kg/day). Effects of OCA were analyzed histologically, biochemically, by immunohistochemistry, using deuterated water technology (de novo collagen formation), and by its effect on the human-based transcriptomics and metabolomics signatures. The transcriptomics and metabolomics profile of Ldlr-/-.Leiden mice largely reflected the molecular signature of NASH patients. OCA modulated the expression of these molecular profiles and quenched specific proinflammatory-profibrotic pathways. OCA attenuated specific facets of cellular inflammation in liver (F4/80-positive cells) and reduced crown-like structures in adipose tissue. OCA reduced de novo collagen formation and attenuated further progression of liver fibrosis, but did not reduce fibrosis below the level before intervention. Conclusion: HFD-fed Ldlr-/-.Leiden mice recapitulate molecular transcriptomic and metabolomic profiles of NASH patients, and these signatures are modulated by OCA. Intervention with OCA in developing fibrosis reduces collagen deposition and de novo synthesis but does not resolve already manifest fibrosis in the period studied. These data show that human molecular signatures can be used to evaluate the translational character of preclinical models for NASH.

Obeticholic acid alleviate lipopolysaccharide-induced acute lung injury via its anti-inflammatory effects in mice

Acute lung injury (ALI) is a common disease that may result in acute respiratory failure and death. However, there are still no effective treatments for ALI. Several studies have shown that farnesoid X receptor (FXR) has an anti-inflammatory effect. We investigated the effects of obeticholic acid (OCA), an agonist of FXR, on Lipopolysaccharide (LPS)-induced ALI in mice. Sixty male mice were randomly divided into six groups, and orally administered with or without OCA once daily for 3 consecutive days before LPS (1.0 mg/kg). Animals were sacrificed at 0 h, 2 h or 6 h after LPS. As expected, OCA enhanced pulmonary FXR activity. OCA prevented LPS-induced ALI. Additional experiment showed that OCA alleviated LPS-induced up-regulation of pulmonary pro-inflammatory and chemokine genes. Moreover, OCA also repressed LPS-induced the release of TNF-α and KC in serum and bronchoalveolar lavage fluid. In contrast, OCA further up-regulated LPS-induced the expression of Il-10, an anti-inflammatory cytokine. Further study showed that OCA inhibited LPS-evoked NF-κB signaling in the lungs. OCA attenuated LPS-induced ERK1/2, JNK, p38 and Akt phosphorylation in the lungs. Overall, these results suggest that OCA prevent LPS-induced ALI may be through enhancing pulmonary FXR activity and then blockading several inflammatory signaling pathways.

Adapted Immune Responses of Myeloid-Derived Cells in Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is considered to be one of the most frequent chronic liver diseases worldwide and is associated with an increased risk of developing liver cirrhosis and hepatocellular carcinoma. Hepatic macrophages, mainly comprising monocyte derived macrophages and tissue resident Kupffer cells, are characterized by a high diversity and plasticity and act as key regulators during NAFLD progression, in conjunction with other infiltrating myeloid cells like neutrophils or dendritic cells. The activation and polarization of myeloid immune cells is influenced by dietary components, inflammatory signals like danger-associated molecular patterns (DAMPs) or cytokines as well as gut-derived inflammatory factors such as pathogen-associated molecular patterns (PAMPs). The functionality of myeloid leukocytes in the liver is directly linked to their inflammatory polarization, which is shaped by local and systemic inflammatory mediators such as cytokines, chemokines, PAMPs, and DAMPs. These environmental signals provoke intracellular adaptations in myeloid cells, including inflammasome and transcription factor activation, inflammatory signaling pathways, or switches in cellular metabolism. Dietary changes and obesity also promote a dysbalance in intestinal microbiota, which can facilitate intestinal permeability and bacterial translocation. The aim of this review is to highlight recent findings on the activating pathways of innate immune cells during the progression of NAFLD, dissecting local hepatic and systemic signals, dietary and metabolic factors as well as pathways of the gut-liver axis. Understanding the mechanism by which plasticity of myeloid-derived leukocytes is related to metabolic changes and NAFLD progression may provide options for new therapeutic approaches.

Andrographolide derivative as STAT3 inhibitor that protects acute liver damage in mice

Sustained activation of the Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway contributed to the progression of cancer and liver diseases. STAT3 signaling inhibitor has been extensively investigated for pharmacological use. We synthesized a series of andrographolide derivatives, and characterized their activity against STAT3 signaling pathway both in vitro and in the CCl₄-induced acute liver damage mice model. Among these derivatives, compound 24 effectively inhibited phosphorylation and dimerization of STAT3 but not its DNA binding activity. Compound 24 significantly ameliorated carbon tetrachloride-induced acute liver damage in vivo without changing mice body weight. Treatment with 24 attenuated hepatic pathologic damage and promoted hepatic proliferation and activation of STAT3. Compound 24 inhibited elevated expression of α-smooth muscle actin and serum pro-inflammatory cytokines downstream of STAT3 but not those factors that are regulated by NF-κB or SMADs. In summary, our results suggest that compound 24 may serve as a potential therapeutic agent for the treatment of hepatic damage or a liver protection agent via regulating STAT3 activation.

Cholestatic liver diseases: new targets, new therapies

Cholestatic liver diseases result from gradual destruction of bile ducts, accumulation of bile acids and self-perpetuation of the inflammatory process leading to damage to cholangiocytes and hepatocytes. If left untreated, cholestasis will lead to fibrosis, biliary cirrhosis, and ultimately end-stage liver disease. Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are the two most common chronic cholestatic liver diseases affecting adults, and their etiologies remain puzzling. While treatment with ursodeoxycholic acid (UDCA) has significantly improved outcomes and prolonged transplant-free survival for patients with PBC, treatment options for UDCA nonresponders remain limited. Furthermore, there is no available medical therapy for PSC. With recent advances in molecular biochemistry specifically related to bile acid regulation and understanding of immunologic pathways, novel pharmacologic treatments have emerged. In this review, we discuss the standard of care and emphasize the various emerging treatments for PBC and PSC.

C-type natriuretic peptide (CNP) in endothelial cells attenuates hepatic fibrosis and inflammation in non-alcoholic steatohepatitis

AIMS

Our previous study revealed that mice transgenic for endothelial-cell-specific overexpression of CNP (E-CNP Tg mice) are protected against the increased fat weight, inflammation, and insulin resistance associated with high-fat diet (HFD)-induced obesity. In addition, E-CNP overexpression prevented abnormal lipid profiles and metabolism and blocked inflammation in the livers of HFD-fed mice. Because obesity, dyslipidemia, and insulin resistance increase the risk of various liver diseases, including non-alcoholic steatohepatitis (NASH), we here studied the role of E-CNP overexpression in the livers of mice in which NASH was induced through feeding of either HFD or a choline-deficient defined l‑amino-acid diet (CDAA).

MAIN METHODS

Wild-type (Wt) and E-CNP Tg mice were fed either a standard diet or HFD for 25 weeks or CDAA for 10 weeks. We then assessed hepatic and serum biochemistry; measured blood glucose during glucose tolerance test (GTT) and insulin tolerance test (ITT); evaluated hepatic fibrosis and inflammation; and performed hepatic histology and gene expression analysis.

KEY FINDINGS

Serum triglycerides, total cholesterol, non-esterified fatty acids, asparagine transaminase, glucose tolerance, and insulin resistance were ameliorated by CNP overexpression in endothelial cells of HFD-fed E-CNP Tg mice. In addition, hepatic fibrosis and inflammation were decreased in HFD-fed E-CNP Tg mice compared with HFD-fed Wt mice. CDAA-fed E-CNP Tg mice showed improved glycemic control, but liver parameters, fibrosis, and inflammation were remained elevated and equivalent to those in CDAA-fed Wt mice.

SIGNIFICANCE

The overexpression of CNP in endothelial cells has anti-fibrotic and anti-inflammatory effects in liver during HFD-induced NASH in mice.