Conjugation is essential for the anticholestatic effect of NorUrsodeoxycholic acid in taurolithocholic acid-induced cholestasis in rat liver

24-Norursodeoxycholic acid ameliorates experimental alcohol-related liver disease and activates hepatic PPARγ

Background & Aims

Alcohol-related liver disease (ALD) is a global healthcare challenge with limited treatment options. 24-Norursodeoxycholic acid (NorUDCA) is a synthetic bile acid with anti-inflammatory properties in experimental and human cholestatic liver diseases. In the present study, we explored the efficacy of norUDCA in experimental ALD.

Methods

NorUDCA was tested in a preventive and therapeutic setting in an experimental ALD model (Lieber-DeCarli diet enriched with ethanol). Liver disease was phenotypically evaluated using histology and biochemical methods, and anti-inflammatory properties and peroxisome proliferator-activated receptor gamma activation by norUDCA were evaluated in cellular model systems.

Results

NorUDCA administration ameliorated ethanol-induced liver injury, reduced hepatocyte death, and reduced the expression of hepatic pro-inflammatory cytokines including tumour necrosis factor (Tnf), Il-1β, Il-6, and Il-10. NorUDCA shifted hepatic macrophages towards an anti-inflammatory M2 phenotype. Further, norUDCA administration altered the composition of the intestinal microbiota, specifically increasing the abundance of Roseburia, Enterobacteriaceae, and Clostridum spp. In a therapeutic model, norUDCA also ameliorated ethanol-induced liver injury. Moreover, norUDCA suppressed lipopolysaccharide-induced IL-6 expression in human peripheral blood mononuclear cells and evoked peroxisome proliferator-activated receptor gamma activation.

Conclusions

NorUDCA ameliorated experimental ALD, protected against hepatic inflammation, and affected gut microbial commensalism. NorUDCA could serve as a novel therapeutic agent in the future management of patients with ALD.

Impact and implications

Alcohol-related liver disease is a global healthcare concern with limited treatment options. 24-Norursodeoxycholic acid (NorUDCA) is a modified bile acid, which was proven to be effective in human cholestatic liver diseases. In the present study, we found a protective effect of norUDCA in experimental alcoholic liver disease. For patients with ALD, norUDCA could be a potential new treatment option.

Taurolithocholic acid but not tauroursodeoxycholic acid rescues phagocytosis activity of bone marrow-derived macrophages under inflammatory stress

Spinal cord injury (SCI) causes cell death and consequently the breakdown of axons and myelin. The accumulation of myelin debris at the lesion site induces inflammation and blocks axonal regeneration. Hematogenous macrophages contribute to the removal of myelin debris. In this study, we asked how the inflammatory state of macrophages affects their ability to phagocytose myelin. Bone marrow‐derived macrophages (BMDM) and Raw264.7 cells were stimulated with lipopolysaccharides (LPS) or interferon gamma (IFNγ), which induce inflammatory stress, and the endocytosis of myelin was examined. We found that activation of the TLR4‐NFκB pathway reduced myelin uptake by BMDM, while IFNγ‐Jak/STAT1 signaling did not. Since bile acids regulate lipid metabolism and in some cases reduce inflammation, our second objective was to investigate whether myelin clearance could be improved with taurolithocholic acid (TLCA), tauroursodeoxycholic acid or hyodeoxycholic acid. In BMDM only TLCA rescued myelin phagocytosis, when this activity was suppressed by LPS. Inhibition of protein kinase A blocked the effect of TLCA, while an agonist of the farnesoid X receptor did not rescue phagocytosis, implicating TGR5‐PKA signaling in the effect of TLCA. To shed light on the mechanism, we measured whether TLCA affected the expression of CD36, triggering receptor on myeloid cells‐2 (TREM2), and Gas6, which are known to be involved in phagocytosis and affected by inflammatory stimuli. Concomitant with an increase in expression of tumour necrosis factor alpha, LPS reduced expression of TREM2 and Gas6 in BMDM, and TLCA significantly diminished this downregulation. These findings suggest that activation of bile acid receptors may be used to improve myelin clearance in neuropathologies.

Association of Gut Microbiota and Metabolites With Disease Progression in Children With Biliary Atresia

Background and Aims

Biliary atresia is the most common cause of liver disease and liver transplantation in children. The accumulation of bile acids in hepatocytes and the stimulation of the intestinal microbiome can aggravate the disease progression. This study investigated changes in the composition of the gut microbiota and its metabolites in biliary atresia and the possible effects of these changes on disease progression.

Methods

Stool samples of biliary atresia at different disease stages and matched control individuals were collected (early stage: 16 patients, 16 controls; later stage: 16 patients, 10 controls). Metagenomic sequencing was performed to evaluate the gut microbiota structure. Untargeted metabolomics was performed to detect and analyze the metabolites and bile acid composition.

Results

A disturbed gut microbiota structure occurred in the early and later stages of biliary atresia. Klebsiella, Streptococcus, Veillonella, and Enterococcus have always been dominant. The abundance of V. atypica displayed significant changes between the early and later stages of biliary atresia. Combined with clinical indicators, Spearman’s analysis showed that Klebsiella and Veillonella atypica strongly correlated with liver enzymes. Enterococcus faecium had an enormously positive relationship with lithocholic acid derivatives. Metabolites involved in tryptophan metabolism were changed in the patients with biliary atresia, which had a significant association with stool V. atypica and blood total bilirubin (p < 0.05).

Conclusions

The liver damage of biliary atresia was directly or indirectly exacerbated by the interaction of enriched Klebsiella (K. pneumoniae), Veillonella (V. atypica), and Enterococcus (E. faecium) with dysmetabolism of tryptophan and bile acid.

Hypothyroidism Increases Cholesterol Gallstone Prevalence in Mice by Elevated Hydrophobicity of Primary Bile Acids

Background: Thyroid hormone (TH) deficiency has been associated with increased cholesterol gallstone prevalence. Hypothyroidism impacts hepatic lipid homeostasis, biliary secretion, gallbladder motility, and gallstone (LITH) gene expression, all potential factors contributing to cholesterol gallstone disease (CGD). However, how TH deficiency may lead to gallstone formation is still poorly understood. Therefore, we performed molecular studies in a CGD mouse model under lithogenic conditions and modulation of TH status. Methods: Male, three-month-old C57BL/6 mice were randomly divided into a control (euthyroid) group, a hypothyroid (hypo) group, a gallstone (litho) group, and a gallstone+hypothyroid (litho+hypo) group and were treated for 2, 4, and 6 weeks (n = 8/treatment period). Gallstone prevalence, biliary composition and cholesterol crystals, hepatic expression of genes participating in cholesterol, bile acid (BA), and phosphatidylcholine synthesis (Hmgcr, Cyp7a1, Pcyt1a), and canalicular transport (Abcg5, Bsep, Abcb4) were investigated. Results: Increased cholesterol gallstone prevalence was observed in hypothyroid mice under lithogenic diet after 4 and 6 weeks of treatment (4 weeks: 25% vs. 0%; 6 weeks: 75% vs. 37.5%). Interestingly, neither the composition of the three main biliary components, cholesterol, BAs, and phosphatidylcholine, nor the hepatic expression of genes involved in synthesis and transport could explain the differences in cholesterol gallstone formation in the mice. However, TH deficiency resulted in significantly increased hydrophobicity of primary BAs in bile. Furthermore, downregulation of hepatic sulfonation enzymes Papss2 and Sult2a8 as well as diminished biliary BA sulfate concentrations in mice were observed under hypothyroid conditions all contributing to a lithogenic biliary milieu as evidenced by microscopic cholesterol crystals and macroscopic gallstone formation. Conclusions: We describe a novel pathogenic link between TH deficiency and CGD and suggest that the increased hydrophobic character of biliary BAs due to the diminished expression of hepatic detoxification enzymes promotes cholesterol crystal precipitation and enhances cholesterol gallstone formation in the bile of hypothyroid mice.

Evidence for functional selectivity in TUDC- and norUDCA-induced signal transduction via α5β1 integrin towards choleresis

Functional selectivity is the ligand-specific activation of certain signal transduction pathways at a receptor and has been described for G protein-coupled receptors. However, it has not yet been described for ligands interacting with integrins without αI domain. Here, we show by molecular dynamics simulations that four side chain-modified derivatives of tauroursodeoxycholic acid (TUDC), an agonist of α₅β₁ integrin, differentially shift the conformational equilibrium of α₅β₁ integrin towards the active state, in line with the extent of β₁ integrin activation from immunostaining. Unlike TUDC, 24-nor-ursodeoxycholic acid (norUDCA)-induced β₁ integrin activation triggered only transient activation of extracellular signal-regulated kinases and p38 mitogen-activated protein kinase and, consequently, only transient insertion of the bile acid transporter Bsep into the canalicular membrane, and did not involve activation of epidermal growth factor receptor. These results provide evidence that TUDC and norUDCA exert a functional selectivity at α₅β₁ integrin and may provide a rationale for differential therapeutic use of UDCA and norUDCA.

Alterations of the bile microbiome in primary sclerosing cholangitis

BACKGROUND

Patients with primary sclerosing cholangitis (PSC) display an altered colonic microbiome compared with healthy controls. However, little is known on the bile duct microbiome and its interplay with bile acid metabolism in PSC.

METHODS

Patients with PSC (n=43) and controls without sclerosing cholangitis (n=22) requiring endoscopic retrograde cholangiography were included prospectively. Leading indications in controls were sporadic choledocholithiasis and papillary adenoma. A total of 260 biospecimens were collected from the oral cavity, duodenal fluid and mucosa and ductal bile. Microbiomes of the upper alimentary tract and ductal bile were profiled by sequencing the 16S-rRNA-encoding gene (V1-V2). Bile fluid bile acid composition was measured by high-performance liquid chromatography mass spectrometry and validated in an external cohort (n=20).

RESULTS

The bile fluid harboured a diverse microbiome that was distinct from the oral cavity, the duodenal fluid and duodenal mucosa communities. The upper alimentary tract microbiome differed between PSC patients and controls. However, the strongest differences between PSC patients and controls were observed in the ductal bile fluid, including reduced biodiversity (Shannon entropy, p=0.0127) and increase of pathogen Enterococcus faecalis (FDR=4.18×10^-5) in PSC. Enterococcus abundance in ductal bile was strongly correlated with concentration of the noxious secondary bile acid taurolithocholic acid (r=0.60, p=0.0021).

CONCLUSION

PSC is characterised by an altered microbiome of the upper alimentary tract and bile ducts. Biliary dysbiosis is linked with increased concentrations of the proinflammatory and potentially cancerogenic agent taurolithocholic acid.

Inflammation: Cause or consequence of chronic cholestatic liver injury

Cholestasis is a result of obstruction of the biliary tracts. It is a common cause of liver pathology after exposure to toxic xenobiotics and during numerous other liver diseases. Accumulation of bile acids in the liver is thought to be a major driver of liver injury during cholestasis and can lead to eventual liver fibrosis and cirrhosis. As such, current therapy in the field of chronic liver diseases with prominent cholestasis relies heavily on increasing choleresis to limit accumulation of bile acids. Many of these same diseases also present with autoimmunity before the onset of cholestasis though, indicating the inflammation may be an initiating component of the pathology. Moreover, cytotoxic inflammatory mediators accumulate during cholestasis and can propagate liver injury. Anti-inflammatory biologics and small molecules have largely failed clinical trials in these diseases though and as such, targeting inflammation as a means to address cholestatic liver injury remains debatable. The purpose of this review is to understand the different roles that inflammation can play during cholestatic liver injury and attempt to define how new therapeutic targets that limit or control inflammation may be beneficial for patients with chronic cholestatic liver disease.

Metabolomics of Aurantio-Obtusin-Induced Hepatotoxicity in Rats for Discovery of Potential Biomarkers

Aurantio-obtusin is an anthraquinone derived from Cassia obtusifolia (cassiae semen). It is also used as a tool and a detection index for the identification of cassiae semen, as stipulated by the Chinese Pharmacopoeia. Anthraquinones, the main components in cassiae semen, have been reported to show hepatotoxicity. This study investigates the hepatotoxicity of aurantio-obtusin in male Sprague–Dawley rats. We randomly divided the animals into a blank control group and treated three test groups with different doses of aurantio-obtusin: Low dose (4 mg/kg), medium dose (40 mg/kg), and high dose (200 mg/kg). Each group was treated with aurantio-obtusin for 28 days, whereas the control group was administered an equal volume of 0.5% carboxymethyl cellulose sodium salt (CMC-Na) aqueous solution. Subsequently, we conducted biochemical, hematological, and pathological investigations and determined the weight of different organs. We used serum metabolomics to identify possible biomarkers related to hepatotoxicity. The low-dose group showed no significant liver injury, whereas the medium- and high-dose groups manifested obvious liver injury. Compared with the control group, the test groups showed an increase in alanine transaminase, aspartate transaminase, and alkaline phosphatase levels. The liver organ coefficient also significantly increased. Additionally, we found significant changes in the hematological indices. Metabolomics analysis showed that aurantio-obtusin induced 28 endogenous markers related to liver injury. Our data indicate that aurantio-obtusin induces hepatotoxicity in rat liver in a dose-dependent manner and is mediated by pathways involving bile acids, fatty acids, amino acids, and energy metabolism. In particular, changes in bile acid content during treatment with therapeutic agents containing aurantio-obtusin deserve increased attention.

Bile salts regulate CYP7A1 expression and elicit a fibrotic response and abnormal lipid production in 3D liver microtissues

Disrupted regulation and accumulation of bile salts (BS) in the liver can contribute towards progressive liver damage and fibrosis. Here, we investigated the role of BS in the progression of cholestatic injury and liver fibrosis using 3D scaffold-free multicellular human liver microtissues (MTs) comprising the cell lines HepaRG, THP-1 and hTERT-HSCs. This in vitro model has been shown to recapitulate cellular events leading to fibrosis including hepatocellular injury, inflammation and activation of HSCs, ultimately leading to increased deposition of extracellular matrix (ECM). In order to better differentiate the contribution of individual cells during cholestasis, the effects of BS were evaluated either on each of the three cell types individually or on the multicellular MTs. Our data corroborate the toxic effects of BS on HepaRG cells and indicate that BS exposure elicited a slight increase in cytokines without causing stellate cell activation. Contrarily, using the MTs, we could demonstrate that low concentrations of BS led to cellular damage and triggered a fibrotic response. This indicates that cellular interplay is required to achieve BS-triggered activation of HSC. Moreover, BS were capable of down-regulating CYP7A1 expression in MTs and elicited abnormal lipid production (accumulation) concordant with clinical cases where chronic cholestasis results in hypercholesterolemia.

Fine-Tuning of Sirtuin 1 Expression Is Essential to Protect the Liver From Cholestatic Liver Disease

Cholestasis comprises aetiologically heterogeneous conditions characterized by accumulation of bile acids in the liver that actively contribute to liver damage. Sirtuin 1 (SIRT1) regulates liver regeneration and bile acid metabolism by modulating farnesoid X receptor (FXR); we here investigate its role in cholestatic liver disease. We determined SIRT1 expression in livers from patients with cholestatic disease, in two experimental models of cholestasis, as well as in human and murine liver cells in response to bile acid loading. SIRT1-overexpressing (SIRT^oe ) and hepatocyte-specific SIRT1-KO (knockout) mice (SIRT^hep-/- ) were subjected to bile duct ligation (BDL) and were fed with a 0.1% DDC (3,5-diethoxycarbonyl-1,4-dihydrocollidine) diet to determine the biological relevance of SIRT1 during cholestasis. The effect of NorUDCA (24-norursodeoxycholic acid) was tested in BDL/SIRT^oe mice. We found that SIRT1 was highly expressed in livers from cholestatic patients, mice after BDL, and Mdr2 knockout mice (Mdr2^-/- ) animals. The detrimental effects of SIRT1 during cholestasis were validated in vivo and in vitro. SIRT^oe mice showed exacerbated parenchymal injury whereas SIRT^hep-/- mice evidenced a moderate improvement after BDL and 0.1% DDC feeding. Likewise, hepatocytes isolated from SIRT^oe mice showed increased apoptosis in response to bile acids, whereas a significant reduction was observed in SIRT^hep-/- hepatocytes. Importantly, the decrease, but not complete inhibition, of SIRT1 exerted by norUDCA treatment correlated with pronounced improvement in liver parenchyma in BDL/SIRT^oe mice. Interestingly, both SIRT1 overexpression and hepatocyte-specific SIRT1 depletion correlated with inhibition of FXR, whereas modulation of SIRT1 by NorUDCA associated with restored FXR signaling. Conclusion: SIRT1 expression is increased during human and murine cholestasis. Fine-tuning expression of SIRT1 is essential to protect the liver from cholestatic liver damage.

NorUDCA promotes degradation of α1-antitrypsin mutant Z protein by inducing autophagy through AMPK/ULK1 pathway

Alpha-1 Antitrypsin (α1AT) Deficiency is a genetic disease in which accumulation of α1AT mutant Z (α1ATZ) protein in the ER of hepatocytes causes chronic liver injury, liver fibrosis, and hepatocellular carcinoma. No effective medical therapy is currently available for the disease. We previously found that norUDCA improves the α1AT deficiency associated liver disease by promoting autophagic degradation of α1ATZ protein in liver in a mouse model of the disease. The current study unravels the novel underlying cellular mechanism by which norUDCA modulates autophagy. HTOZ cells, modified from HeLa Tet-Off cells by transfection with the resulting pTRE1-ATZ plasmid and expressing mutant Z proteins, were studied in these experiments. The role of norUDCA in inducing autophagy, autophagy-mediated degradation of α1ATZ and the role of AMPK in norUDCA-induced autophagy were examined in the current report. NorUDCA promoted disposal of α1ATZ via autophagy-mediated degradation of α1ATZ in HTOZ cells. Activation of AMPK was required for norUDCA-induced autophagy and α1ATZ degradation. Moreover, mTOR/ULK1 was involved in norUDCA-induced AMPK activation and autophagy in HTOZ cells. Our results provide novel mechanistic insights into the therapeutic action of norUDCA in promoting the clearance of α1ATZ in vitro and suggest a novel therapeutic approach for the treatment of α1ATZ deficiency disease and its associated liver diseases.

Bile acid regulation: A novel therapeutic strategy in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is characterized by excessive fat deposition in the liver in the absence of significant alcohol consumption. Dysregulated bile acid (BA) metabolism is an important indicator in the pathology of NAFLD, which could progress into more severe forms of liver injury. Lipid metabolism, immune environment and intestinal bacteria are all affected by dysregulated BA metabolism directly, but the mechanisms remain unclear. Several drug candidates that target BA metabolism, either used alone or in combination with other agents, are currently under development for treatment of NAFLD. Here, we summarize the relationship of dysregulated BA metabolism and NAFLD, discuss the effects and mechanisms of dysregulated BAs-induced lipid metabolism disorder. Challenges in developing novel treatments are also discussed.

High prevalence of cholestasis, with increased conjugated bile acids in inflammatory bowel diseases patients

AIM

To investigate the prevalence and causes of cholestasis in patients with inflammatory bowel diseases in the Swiss Inflammatory Bowel Diseases Cohort.

METHODS

A retrospective cohort study was performed of all the patients in the Swiss Inflammatory bowel disease Cohort. Total bile acid was measured for all patients and cholestasis was defined as a concentration > 8 μmol/L. The characteristics of patients with or without cholestasis were compared. Bile acid profiles were then determined for 80 patients with high total bile acid and 80 matched patients with low total bile acid. Bile acid profiles were compared for smokers vs nonsmokers, ileal vs colonic disease, and inflammatory vs non inflammatory diseases.

RESULTS

Ninety-six patients had more than 8 μmol/L total bile acid, giving a prevalence of 7.15%. Patients with an obvious cause of cholestasis, such as primary sclerosing cholangitis, were then excluded, leaving 1190 participants with total bile acid < 8 μmol/L and 80 with total bile acid > 8 μmol/L. In multivariate analysis, calcium supplementation was significantly associated with cholestasis (odds ratio, 2.36, 95%CI: 1.00-5.21, P = 0.040) whereas current smoking significantly reduced the risk of cholestasis (odds ratio, 0.42, 95%CI: 0.17-0.91, P = 0.041). Levels of all conjugated bile acids were higher in the cholestasis group than in the control group. When we compared patients with ileal vs colonic disease, the former had higher levels of primary, secondary, and tertiary bile acids whereas patients with colonic disease had higher levels of conjugated bile acids.

CONCLUSION

Prevalence of cholestasis is high. Smoking appears to reduce cholestasis. Conjugated bile acids are higher in cholestasis and in colonic disease whereas unconjugated in ileal disease.

Management of cholestatic disease in 2017

Primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) are the most frequent chronic cholestatic liver diseases and serve as model diseases to discuss the management of cholestasis in 2017 in the lecture that is summarized in this report. PBC and PSC are characterized by inflammation and fibrosis of small intrahepatic (PBC) or larger intra- and/or extrahepatic (PSC) bile ducts. Bile duct damage leads to cholestasis and can progress to liver fibrosis and even cirrhosis. Various genetic, environmental and endogenous factors may contribute to the development of chronic cholestatic liver diseases, but the exact pathogenesis of PBC and PSC has not been clarified. Ursodeoxycholic acid (UDCA) is the standard treatment of PBC and is used also for other cholestatic conditions including PSC, and it exerts anticholestatic effects at adequate doses. Novel anticholestatic therapeutic options for patients not adequately responding to UDCA are under development or have, like obeticholic acid, already been proven to have efficacy when combined with UDCA in the treatment of PBC. The future role of immunomodulating/immunosuppressive drug regimens must be critically reviewed.

Autophagy induced by exogenous bile acids is therapeutic in a model of α-1-AT deficiency liver disease

The bile acid nor-ursodeoxycholic acid (norUDCA) has many biological actions, including antiapoptotic effects. Homozygous PIZZ α-1-antitrypsin (A1AT)-deficient humans are known to be at risk for liver disease, cirrhosis, and liver cancer as a result of the accumulation of the toxic, A1AT mutant Z protein within hepatocytes. This accumulation triggers cell death in the hepatocytes with the largest mutant Z-protein burdens, followed by compensatory proliferation. Proteolysis pathways within the hepatocyte, including autophagy, act to reduce the intracellular burden of A1AT Z protein. We hypothesized that norUDCA would reduce liver cell death and injury in A1AT deficiency. We treated groups of PiZ transgenic mice and wild-type mice with norUDCA or vehicle, orally, and examined the effects on the liver. The PiZ mouse is the best model of A1AT liver injury and recapitulates many features of the human liver disease. Mice treated with norUDCA demonstrated reduced hepatocellular death by compensatory hepatocellular proliferation as determined by bromodeoxyuridine incorporation (3.8% control, 0.88% treated, P < 0.04). Ki-67 staining as a marker for hepatocellular senescence and death was also reduced (P < 0.02). Reduced apoptotic signaling was associated with norUDCA, including reduced cleavage of caspases-3, -7, and -8 (all P < 0.05). We determined that norUDCA was associated with a >70% reduction in intrahepatic mutant Z protein (P < 0.01). A 32% increase in hepatic autophagy associated with norUDCA was the likely mechanism. norUDCA administration is associated with increased autophagy, reduced A1AT protein accumulation, and reduced liver injury in a model of A1AT deficiency.

Critical Factors in the Assessment of Cholestatic Liver Injury In Vitro

Cholestasis is a common pathological component of numerous liver diseases. The initiating event during cholestatic liver injury is widely believed to be the accumulation of bile acids in hepatocytes and the hepatic parenchyma. As bile acids are considered the primary toxic compounds in the injury, numerous in vitro models of bile acid-induced injury and bile acid-induced changes in gene expression have been developed to attempt to better define cholestasis at a cellular level. This chapter focuses on the establishment of a system for determining the effects of cholestatic concentrations of bile acids on hepatocytes using primary hepatocytes or hepatoma cell lines. Moreover, this chapter addresses significant differences in the response of different species to bile acid exposure and novel information on the relevance of treating hepatocytes with concentrations of specific bile acids.

Therapeutic targets for cholestatic liver injury

INTRODUCTION

Cholestasis is a reduction in bile flow that occurs during numerous pathologies. Blockage of the biliary tracts results in hepatic accumulation of bile acids or their conjugate bile salts. The molecular mechanisms behind liver injury associated with cholestasis are extensively studied, but not well understood. Multiple models of obstructive cholestasis result in a significant inflammatory infiltrate at the sites of necrosis that characterize the injury.

AREAS COVERED

This review will focus on direct bile acid toxicity during cholestasis, bile acid signaling processes and on the development and continuation of inflammation during cholestasis, with a focus on novel proposed molecular mediators of neutrophil recruitment. While significant progress has been made on these molecular mechanisms, a continued focus on how cholestasis and the innate immune system interact is necessary to discover targetable therapeutics that might protect the liver while leaving global immunity intact.

EXPERT OPINION

While bile acid toxicity likely occurs in humans and other mammals when toxic bile acids accumulate, persistent inflammation is likely responsible for continued liver injury during obstructive cholestasis. Targeting molecular mediators of inflammation may help prevent liver injury during acute cholestasis both in murine models and human patients.

Potential of nor-Ursodeoxycholic Acid in Cholestatic and Metabolic Disorders

24-nor-ursodeoxycholic acid (norUDCA) is a side-chain shortened derivate of ursodeoxycholic acid (UDCA). Since norUDCA is only ineffectively conjugated with glycine or taurine, it has specific physicochemical and therapeutic properties distinct from UDCA. Nonamidated norUDCA undergoes cholehepatic shunting enabling 'ductular targeting' and inducing a bicarbonate-rich hypercholeresis, with cholangioprotective effects. At the same time it has direct anti-inflammatory, antilipotoxic, anti fibrotic, and antiproliferative properties targeting various liver cell populations. norUDCA appears to be one of the most promising novel treatment approaches targeting the liver and the bile duct system at multifactorial and multicellular levels. This review article is a summary of a lecture given at the XXIII International Bile Acid Meeting (Falk Symposium 194) on 'Bile Acids as Signal Integrators and Metabolic Modulators' held in Freiburg, October 8-9, 2014, and summarizes the recent progress with norUDCA as a novel therapeutic approach in cholestatic and metabolic (liver) disorders.

Sensitization to autoimmune hepatitis in group VIA calcium-independent phospholipase A2-null mice led to duodenal villous atrophy with apoptosis, goblet cell hyperplasia and leaked bile acids

Chronic bowel disease can co-exist with severe autoimmune hepatitis (AIH) in an absence of primary sclerosing cholangitis. Genetic background may contribute to this overlap syndrome. We previously have shown that the deficiency of iPLA2β causes an accumulation of hepatocyte apoptosis, and renders susceptibility for acute liver injury. We here tested whether AIH induction in iPLA2β-null mice could result in intestinal injury, and whether bile acid metabolism was altered. Control wild-type (WT) and female iPLA2β-null (iPLA2β(-/-)) mice were intravenously injected with 10mg/kg concanavalinA (ConA) or saline for 24h. ConA treatment of iPLA2β(-/-) mice caused massive liver injury with increased liver enzymes, fibrosis, and necrosis. While not affecting WT mice, ConA treatment of iPLA2β(-/-) mice caused severe duodenal villous atrophy concomitant with increased apoptosis, cell proliferation, globlet cell hyperplasia, and endotoxin leakage into portal vein indicating a disruption of intestinal barrier. With the greater extent than in WT mice, ConA treatment of iPLA2β(-/-) mice increased jejunal expression of innate response cytokines CD14, TNF-α, IL-6, and SOCS3 as well as chemokines CCL2 and the CCL3 receptor CCR5. iPLA2β deficiency in response to ConA-induced AIH caused a significant decrease in hepatic and biliary bile acids, and this was associated with suppression of hepatic Cyp7A1, Ntcp and ABCB11/Bsep and upregulation of intestinal FXR/FGF15 mRNA expression. The suppression of hepatic Ntcp expression together with the loss of intestinal barrier could account for the observed bile acid leakage into peripheral blood. Thus, enteropathy may result from acute AIH in a susceptible host such as iPLA2β deficiency.

New paradigms in the treatment of hepatic cholestasis: from UDCA to FXR, PXR and beyond

Cholestasis is an impairment of bile formation/flow at the level of the hepatocyte and/or cholangiocyte. The first, and for the moment, most established medical treatment is the natural bile acid (BA) ursodeoxycholic acid (UDCA). This secretagogue improves, e.g. in intrahepatic cholestasis of pregnancy or early stage primary biliary cirrhosis, impaired hepatocellular and cholangiocellular bile formation mainly by complex post-transcriptional mechanisms. The limited efficacy of UDCA in various cholestatic conditions urges for development of novel therapeutic approaches. These include nuclear and membrane receptor agonists and BA derivatives. The nuclear receptors farnesoid X receptor (FXR), retinoid X receptor (RXR), peroxisome proliferator-activated receptor α (PPARα), and pregnane X receptor (PXR) are transcriptional modifiers of bile formation and at present are under investigation as promising targets for therapeutic interventions in cholestatic disorders. The membrane receptors fibroblast growth factor receptor 4 (FGFR4) and apical sodium BA transporter (ASBT) deserve attention as additional therapeutic targets, as does the potential therapeutic agent norUDCA, a 23-C homologue of UDCA. Here, we provide an overview on established and future promising therapeutic agents and their potential molecular mechanisms and sites of action in cholestatic diseases.

Novel therapeutic targets in primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is a chronic immune-mediated liver disease characterized by progressive cholestasis, biliary fibrosis and eventually cirrhosis. It results in characteristic symptoms with marked effects on life quality. The advent of large patient cohorts has challenged the view of PBC as a benign condition treated effectively by the single licensed therapy-ursodeoxycholic acid (UDCA). UDCA nonresponse or under-response has a major bearing on outcome, substantially increasing the likelihood that liver transplantation will be required or that patients will die of the disease. In patients with high-risk, treatment-unresponsive or highly symptomatic disease the need for new treatment approaches is clear. Evolution in our understanding of disease mechanisms is rapidly leading to the advent of new and re-purposed therapeutic agents targeting key processes. Notable opportunities are offered by targeting what could be considered as the 'upstream' immune response, 'midstream' biliary injury and 'downstream' fibrotic processes. Combination therapy targeting several pathways or the development of novel agents addressing multiple components of the disease pathway might be required. Ultimately, PBC therapeutics will require a stratified approach to be adopted in practice. This Review provides a current perspective on potential approaches to PBC treatment, and highlights the challenges faced in evaluating and implementing those treatments.

New generation lipid emulsions prevent PNALD in chronic parenterally fed preterm pigs

Total parenteral nutrition (TPN) is associated with the development of parenteral nutrition-associated liver disease (PNALD) in infants. Fish oil-based lipid emulsions can reverse PNALD, yet it is unknown if they can prevent PNALD. We studied preterm pigs administered TPN for 14 days with either 100% soybean oil (IL), 100% fish oil (OV), or a mixture of soybean oil, medium chain triglycerides (MCTs), olive oil, and fish oil (SL); a group was fed formula enterally (ENT). In TPN-fed pigs, serum direct bilirubin, gamma glutamyl transferase (GGT), and plasma bile acids increased after the 14 day treatment but were highest in IL pigs. All TPN pigs had suppressed hepatic expression of farnesoid X receptor (FXR), cholesterol 7-hydroxylase (CYP7A1), and plasma 7α-hydroxy-4-cholesten-3-one (C4) concentrations, yet hepatic CYP7A1 protein abundance was increased only in the IL versus ENT group. Organic solute transporter alpha (OSTα) gene expression was the highest in the IL group and paralleled plasma bile acid levels. In cultured hepatocytes, bile acid-induced bile salt export pump (BSEP) expression was inhibited by phytosterol treatment. We show that TPN-fed pigs given soybean oil developed cholestasis and steatosis that was prevented with both OV and SL emulsions. Due to the presence of phytosterols in the SL emulsion, the differences in cholestasis and liver injury among lipid emulsion groups in vivo were weakly correlated with plasma and hepatic phytosterol content.

Primary sclerosing cholangitis

Primary sclerosing cholangitis is the classic hepatobiliary manifestation of inflammatory bowel disease and is generally chronic and progressive. Patients frequently present with asymptomatic, anicteric cholestasis, but many develop progressive biliary strictures with time, leading to recurrent cholangitis, biliary cirrhosis, and end-stage liver disease. Medical treatment does not slow the progression of disease, and many patients need liver transplantation, after which recurrent disease is a risk. The increased incidence of hepatobiliary cancer, which is not related to the underlying severity of biliary fibrosis, is of particular concern. Risk of colorectal cancer is also increased in patients with coexistent inflammatory bowel disease. Mechanistic insights have arisen from studies of secondary sclerosing cholangitis, in which a similar clinical profile is associated with a specific cause, and genomic studies have elucidated potential disease-initiating pathways in the primary form. The close association between inflammatory bowel disease and primary sclerosing cholangitis underscores the need to further understand the role of environmental factors in generation of lymphocytes that are postulated to be retargeted, deleteriously, to the biliary tree. Treatment of primary sclerosing cholangitis is confined to supportive measures, but advances in pathobiology suggest that new stratified approaches will soon be available.

Bile canalicular abnormalities in the early phase of a mouse model of sclerosing cholangitis

BACKGROUND

The bile canaliculus is the smallest and first biliary channel and is formed by two or three adjacent hepatocytes. Previous studies of chronic cholangiopathies such as primary sclerosing cholangitis have focused on the bile ductules. However, little is known about the pathological alterations in bile canaliculi in the early phase of cholangiopathies.

AIM

To characterize the bile canalicular morphology in the early phase of sclerosing cholangitis we used 3,5-diethoxycarbonyl-1,4-dihydrocollidine-induced mouse model of sclerosing cholangitis.

METHODS

Mice were fed a diet with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (0.1%). Serum biochemical, histological, immunohistochemical, and electron microscopic analyses were performed 1, 2, 4, and 7 days after feeding.

RESULTS

All experimental groups showed significantly increased serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels. From day 1, bile canalicular abnormalities such as dilatation and meandering and loss of microvilli were observed. After bile canalicular abnormalities had appeared, substantial infiltration of inflammatory cells was observed amongst the necrotic cells and periductal region. After these inflammatory changes, cholangiocytes proliferated in the portal area and formed ductular reactions. Finally, periductal fibrosis appeared.

CONCLUSION

This study provides novel evidence of the occurrence of bile canalicular abnormalities during the early phase of sclerosing cholangitis.

Ursodeoxycholic acid and bile-acid mimetics as therapeutic agents for cholestatic liver diseases: an overview of their mechanisms of action

Chronic cholestasis and liver inflammation are the two main pathophysiological components of the two major classes of disease - primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) - leading to bile duct destruction and ultimately to cirrhosis and liver failure. Ursodeoxycholic acid (UDCA), initially introduced as a therapeutic approach to counteract the cholestatic components to PBC and PSC, was subsequently shown to exhibit unexpected anti-inflammatory and immunomodulatoty properties. The use of farnesoid X receptor (FXR) and TGR5 agonists in various animal models have confirmed early observations indicating that bile acids are not only toxicants and inflammagens, but also repressors of innate and adaptive immunity. Obeticholic acid is a bile-acid mimetic, with no toxic or inflammagen behavior, that strongly activates FXR to combat the toxic effects of high concentrations of bile acid. Because UDCA is not an FXR agonist, its combination with obeticholic acid could be a promising tool for the treatment of PBC and PSC. In this overview, the biological properties of UDCA, NorUDCA and FXR agonists are highlighted, as well as their overlapping mechanisms of action in inflammatory biliary disorders.

Molecular targets for the treatment of fibrosing cholangiopathies

Emerging pathophysiologic insights are leading to novel approaches to treating fibrosing cholangiopathies. The current treatment, using ursodeoxycholic acid (UDCA), may slow the progression of some chronic cholangiopathies but cannot heal them. Apart from immunosuppressive interventions aimed at minimizing immune-mediated damage, the use of specific modifiers of hepatobiliary secretory and cytoprotective mechanisms may eventually give rise to a new class of disease-modifying anti-cholangiofibrotic drugs.

The biliary HCO(3)(-) umbrella: experimental evidence revisited

PURPOSE OF REVIEW

To critically review most recent experimental evidence for the protective action of biliary HCO(3)(-) secretion against bile acid-induced bile duct damage and development of fibrosing cholangiopathy in humans and experimental animals.

RECENT FINDINGS

Studies in human cholangiocytes in vitro indicate that a biliary HCO(3)(-) umbrella protects against bile acid-induced cholangiocyte damage and apoptosis in humans. The Cl(-)/HCO(3)(-) exchanger, AE2, and an intact biliary glycocalyx appear crucial for its stability. Related studies with experimental animal models in vivo have to be interpreted with caution as humans and mice differ not only with regard to bile salt pool, but also their expression patterns of transport proteins and signalling molecules.

SUMMARY

Adequate biliary HCO(3)(-) secretion may protect against bile salt-induced cholangiopathies. Future therapeutic strategies in biliary diseases will aim at stabilizing the biliary HCO(3)(-) umbrella.

Ursodeoxycholic acid is conjugated with taurine to promote secretin-stimulated biliary hydrocholeresis in the normal rat

Background & Aims

Secretin induces bicarbonate-rich hydrocholeresis in healthy individuals, but not in untreated patients with primary biliary cirrhosis (PBC). Ursodeoxycholic acid (UDCA) – the first choice treatment for PBC – restores the secretin response. Compared with humans, secretin has poor effect in experimental normal-rat models with biliary drainage, although it may elicit hydrocholeresis when the bile-acid pool is maintained. In view of the benefits of UDCA in PBC, we used normal-rat models to unravel the acute contribution of UDCA (and/or taurine-conjugated TUDCA) for eliciting the biliary secretin response.

Methods

Intravascular and/or intrabiliary administration of agonists and inhibitors was performed in normal rats with biliary monitoring. Secretin/bile-acid interplay was analyzed in 3D cultured rat cholangiocytes that formed expansive cystic structures with intralumenal hydroionic secretion.

Results

In vivo, secretin stimulates hydrocholeresis upon UDCA/TUDCA infusion, but does not modify the intrinsic hypercholeretic effect of dehydrocholic acid (DHCA). The former effect is dependent on microtubule polymerization, and involves PKCα, PI3K and MEK pathways, as shown by colchicine (i.p.) and retrograde biliary inhibitors. In vitro, while secretin alone accelerates the spontaneous expansion of 3D-cystic structures, this effect is enhanced in the presence of TUDCA, but not UDCA or DHCA. Experiments with inhibitors and Ca²⁺-chelator confirmed that the synergistic effect of secretin plus TUDCA involves microtubules, intracellular Ca²⁺, PKCα, PI3K, PKA and MEK pathways. Gene silencing also demonstrated the involvement of the bicarbonate extruder Ae2.

Conclusions

UDCA is conjugated in order to promote secretin-stimulated hydrocholeresis in rats through Ae2, microtubules, intracellular Ca²⁺, PKCα, PI3K, PKA, and MEK.

Management of primary sclerosing cholangitis

Primary sclerosing cholangitis (PSC) is a rare cholestatic liver disease with major morbidity and mortality. Therapeutic management is difficult, due to lack of conclusive data and individual disease progression. High-dose UDCA was used for years as a pharmacotherapeutic agent to prevent disease progression, based on a positive trend in pilot studies, but has recently been proven to have a negative effect in advanced disease. Immunosuppressants might be useful in patients with overlap syndromes. Dominant bile duct stenoses should be treated endoscopically, and cholangiocellular carcinoma (CCC) still remains a therapeutic challenge in PSC patients. Early diagnosis of CCC must be improved and new strategies such as neoadjuvant radiochemotherapy with subsequent liver transplantation in selected patients are further options to be considered.