Bile salts and cholestasis

Cholestatic pruritus: Emerging mechanisms and therapeutics

Patients suffering from cholestasis often report experiencing a debilitating, unrelenting itch. In contrast to conditions, such as urticaria, in which histamine primarily drives itch (pruritus), cholestatic pruritus is multifactorial and more difficult to treat. Existing therapies are not always effective and have undesirable adverse effect profiles. Here, we conducted a systematic literature review to evaluate conventional treatment strategy, current pathophysiologic understanding, and the role of new therapies in the context of cholestatic pruritus. We discuss novel findings implicating bile acids, lysophosphatidic acid, and bilirubin as potential important mediators of cholestatic itch. New therapies that aim to remove or modulate pruritogens have been supported in observational cohort studies and randomized controlled trials. Although these new therapies show promise, further research is needed to confirm the pathophysiology of cholestatic pruritus so that targeted therapy can be developed.

Mechanism of inhibition of taurolithocholate-induced retrieval of plasma membrane MRP2 by cyclic AMP and tauroursodeoxycholate

Taurolithocholate (TLC) produces cholestasis by inhibiting biliary solute secretion in part by retrieving MRP2 from the plasma membrane (PM). Tauroursodeoxycholate (TUDC) and cAMP reverse TLC‐induced cholestasis by inhibiting TLC‐induced retrieval of MRP2. However, cellular mechanisms for this reversal are incompletely understood. Recently, we reported that TLC decreases PM‐MRP2 by activating PKCε followed by phosphorylation of myristoylated alanine‐rich C kinase substrate (MARCKS). Thus, cAMP and TUDC may reverse TLC‐induced cholestasis by inhibiting the TLC/PKCε/MARCKS phosphorylation pathway. We tested this hypothesis by determining whether TUDC and/or cAMP inhibit TLC‐induced activation of PKCε and phosphorylation of MARCKS. Studies were conducted in HuH‐NTCP cell line and rat hepatocytes. Activation of PKCε was determined from the translocation of PKCε to PM using a biotinylation method. Phosphorylation of MARCKS was determined by immunoblotting with a phospho‐MARCKS antibody. TLC, but not cAMP and TUDC, activated PKCε and increased MARCKS phosphorylation in HuH‐NTCP as well in rat hepatocytes. Treatment with TUDC or cAMP inhibited TLC‐induced activation of PKCε and increases in MARCKS phosphorylation in both cell types. Based on these results, we conclude that the reversal of TLC‐induced cholestasis by cAMP and TUDC involves, at least in part, inhibition of TLC‐mediated activation of the PKCε/MARCKS phosphorylation pathway.

N-(4-[18F]fluorobenzyl)cholylglycine, a novel tracer for PET of enterohepatic circulation of bile acids: Radiosynthesis and proof-of-concept studies in rats

INTRODUCTION

Enterohepatic circulation (EHC) of conjugated bile acids is an important physiological process crucial for regulation of intracellular concentrations of bile acids and their function as detergents and signal carriers. Only few bile acid-derived imaging agents have been synthesized and hitherto none have been evaluated for studies of EHC. We hypothesized that N-(4-[¹⁸F]fluorobenzyl)cholylglycine ([¹⁸F]FBCGly), a novel fluorine-18 labeled derivative of endogenous cholylglycine, would be a suitable tracer for PET of the EHC of conjugated bile acids, and we report here a radiosynthesis of [¹⁸F]FBCGly and a proof-of-concept study by PET/MR in rats.

METHODS

A radiosynthesis of [¹⁸F]FBCGly was developed based on reductive alkylation of glycine with 4-[¹⁸F]fluorobenzaldehyde followed by coupling to cholic acid. [¹⁸F]FBCGly was investigated in vivo by dynamic PET/MR in anesthetized rats; untreated or treated with cholyltaurine or rifampicin. Possible in vivo metabolites of [¹⁸F]FBCGly were investigated by analysis of blood and bile samples, and the stability of [¹⁸F]FBCGly towards enzymatic de-conjugation by Cholylglycine Hydrolase was tested in vitro.

RESULTS

[¹⁸F]FBCGly was produced with a radiochemical purity of 96% ± 1% and a non-decay corrected radiochemical yield of 1.0% ± 0.3% (mean ± SD; n = 12). PET/MR studies showed that i.v.-administrated [¹⁸F]FBCGly underwent EHC within 40-60 min with a rapid transhepatic transport from blood to bile. In untreated rats, the radioactivity concentration of [¹⁸F]FBCGly was approximately 15 times higher in bile than in liver tissue. Cholyltaurine and rifampicin inhibited the biliary secretion of [¹⁸F]FBCGly. No fluorine-18 metabolites of [¹⁸F]FBCGly were observed.

CONCLUSION

We have developed a radiosynthesis of a novel fluorine-18 labeled bile acid derivative, [¹⁸F]FBCGly, and shown by PET/MR that [¹⁸F]FBCGly undergoes continuous EHC in rats without metabolizing. This novel tracer may prove useful in PET studies on the effect of drugs or diseases on the EHC of conjugated bile acids.

N-3 Polyunsaturated Fatty Acids Stimulate Bile Acid Detoxification in Human Cell Models

Cholestasis is characterized by the accumulation of toxic bile acids (BAs) in liver cells. The present study aimed to evaluate the effects of n-3 polyunsaturated fatty acids (n-3 PUFAs), such as docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids, on BA homeostasis and toxicity in human cell models. The effects of EPA and/or DHA on the expression of genes involved in the maintenance of BA homeostasis were analyzed in human hepatoma (HepG2) and colon carcinoma (Caco-2) cells, as well as in primary culture of human intestinal (InEpC) and renal (RPTEC) cells. Extracellular BA species were quantified in culture media using LC-MS/MS. BA-induced toxicity was evaluated using caspase-3 and flow cytometry assays. Gene expression analyses of HepG2 cells reveal that n-3 PUFAs reduce the expression of genes involved in BA synthesis (CYP7A1, CYP27A1) and uptake (NTCP), while activating genes encoding metabolic enzymes (SULT2A1) and excretion transporters (MRP2, MRP3). N-3 PUFAs also generate a less toxic BA pool and prevent the BA-dependent activation of apoptosis in HepG2 cells. Conclusion. The present study reveals that n-3 PUFAs stimulate BA detoxification.

Chenodeoxycholic acid activates NLRP3 inflammasome and contributes to cholestatic liver fibrosis

Accumulation of hydrophobic bile acids in the liver contributes to cholestatic liver injury. Inflammation induced by excessive bile acids is believed to play a crucial role, however, the mechanisms of bile acids triggered inflammatory response remain unclear. Recent studies have highlighted the effect of NLRP3 inflammasome in mediating liver inflammation and fibrosis. In this study, we for the first time showed that chenodeoxycholic acid (CDCA), the major hydrophobic primary bile acid involved in cholestatic liver injury, could dose-dependently induce NLRP3 inflammasome activation and secretion of pro-inflammatory cytokine-IL-1β in macrophages by promoting ROS production and K⁺ efflux. Mechanistically, CDCA triggered ROS formation in part through TGR5/EGFR downstream signaling, including protein kinase B, extracellular regulated protein kinases and c-Jun N-terminal kinase pathways. Meanwhile, CDCA also induced ATP release from macrophages which subsequently causes K⁺ efflux via P2X7 receptor. Furthermore, in vivo inhibition of NLRP3 inflammasome with caspase-1 inhibitor dramatically decreased mature IL-1β level of liver tissue and ameliorated liver fibrosis in bile duct ligation (BDL) mouse model. In conclusion, excessive CDCA may represent an endogenous danger signal to activate NLRP3 inflammasome and initiate liver inflammation during cholestasis. Our finding offers a mechanistic basis to ameliorate cholestatic liver fibrosis by targeting inflammasome activation.

Sildenafil protects against bile duct ligation induced hepatic fibrosis in rats: Potential role for silent information regulator 1 (SIRT1)

Hepatic fibrosis is a potential health problem that may end with life-threatening cirrhosis and primary liver cancer. Recent studies point out to the protective effects of silent information regulator1 (SIRT1), against different models of organs fibrosis. This work aimed to investigate the possible protective effect of sildenafil (SIRT1 activator) against hepatic fibrosis induced by bile duct ligation (BDL). Firstly, three different doses of sildenafil (5, 10, 20mg/kg/day) were investigated; to detect the most protective one against BDL induced liver dysfunction and hepatic fibrosis. The most protective dose is then used; to study its effect on BDL induced SIRT1 downregulation, imbalance of oxidant/antioxidant status, increased inflammatory cytokines and fibrosis. Sildenafil (20mg/kg/day) was the most protective one, it caused upregulation of SIRT1, reduction of hepatic malondialdehyde (MDA) content, increase in expression of nuclear factor erythroid 2-related factor 2 (Nrf2), hemeoxygenease (HO)-1, reduced glutathione (GSH) content and superoxide dismutase (SOD) activity. Hepatic content of tumor necrosis factor-α (TNF-α) and nuclear factor κB (NFκB) expression & content displayed significant reductions with sildenafil treatment, Furthermore, sildenafil caused marked reductions of transforming growth factor (TGF)-β content, expression of plasminogen activator inhibitor-1 (PAI-1), matrix metalloproteinase-9 (MMP-9), tissue inhibitor of metalloproteinase-1 (TIMP-1), α-smooth muscle actin (α-SMA), fibronectin, collagen I (α1) and hydroxyproline content. However, sildenafil protective effects were significantly reduced by co-administration of EX527 (SIRT1 inhibitor). Our work showed, for the first time that, sildenafil has promising protective effects against BDL induced liver dysfunction and hepatic fibrosis. These effects may be, in part, mediated by up regulation of SIRT1.

Quantitative profiling of 19 bile acids in rat plasma, liver, bile and different intestinal section contents to investigate bile acid homeostasis and the application of temporal variation of endogenous bile acids

Bile acid homeostasis is maintained by liver synthesis, bile duct secretion, microbial metabolism and intestinal reabsorption into the blood. When drug insults result in liver damage, the variances of bile acids (BAs) are related to the physiological status of the liver. Here, we established a method to simultaneously quantify 19 BAs in rat plasma, liver, bile and different intestinal section contents (duodenum, jejunum, ileum, cecum and colon) using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) to reveal the pattern of bile acid homeostasis in the enterohepatic circulation of bile acids in physiological situations. Dynamic changes in bile acid composition appeared throughout the enterohepatic circulation of the BAs; taurine- and glycine-conjugated BAs and free BAs had different dynamic homeostasis levels in the circulatory system. cholic acid (CA), beta-muricholic acid (beta-MCA), lithocholic acid (LCA), glycocholic acid (GCA) and taurocholic acid (TCA) greatly fluctuated in the bile acid pool under physiological conditions. Taurine- and glycine-conjugated bile acids constituted more than 90% in the bile and liver, whereas GCA and TCA accounted for more than half of the total bile acids and the secretion of bile mainly via conjugating with taurine. While over 80% of BAs in plasma were unconjugated bile acids, CA and HDCA were the most abundant elements. Unconjugated bile acids constituted more than 90% in the intestine, and CA, beta-MCA and HDCA were the top three bile acids in the duodenum, jejunum and ileum content, but LCA and HDCA were highest in the cecum and colon content. As the main secondary bile acid converted by microflora in the intestine, LCA was enriched in the cecum and DCA mostly in the colon. As endogenous substances, the concentrations of plasma BAs were closely related to time rhythm and diet. In conclusion, analyzing detailed BA profiles in the enterohepatic circulation of bile acids in a single run is possible using LC-MS/MS. Based on the physiological characteristics of the metabolic profiling of 19 BAs in the total bile acid pool and the time rhythm variation of the endogenous bile acids, this study provided a new valuable method and theoretical basis for the clinical research of bile acid homeostasis.

EASL Clinical Practice Guidelines: The diagnosis and management of patients with primary biliary cholangitis

Primary biliary cholangitis (PBC) is a chronic inflammatory autoimmune cholestatic liver disease, which when untreated will culminate in end-stage biliary cirrhosis. Diagnosis is usually based on the presence of serum liver tests indicative of a cholestatic hepatitis in association with circulating antimitochondrial antibodies. Patient presentation and course can be diverse and risk stratification is important to ensure all patients receive a personalised approach to their care. The goals of treatment and management are the prevention of end-stage liver disease, and the amelioration of associated symptoms. Pharmacologic approaches in practice, to reduce the impact of the progressive nature of disease, currently include licensed therapies (ursodeoxycholic acid and obeticholic acid) and off-label therapies (fibric acid derivatives, budesonide). These clinical practice guidelines summarise the evidence for the importance of a structured, life-long and individualised, approach to the care of patients with PBC, providing a framework to help clinicians diagnose and effectively manage patients.

Circulating FGF19 closely correlates with bile acid synthesis and cholestasis in patients with primary biliary cirrhosis

BACKGROUND AND AIM

Bile acid (BA) synthesis in the liver is regulated by Fibroblast Growth Factor 19 (FGF19) secreted from the ileum as an enterohepatic feedback mechanism. Although FGF19 mRNA is absent in normal liver, FGF19 gene expression was reported to increase in response to both extrahepatic and intrahepatic cholestasis. The impact of upregulated FGF19 expression on BA synthesis is unclear and the overall role of circulating FGF19 and BA synthesis under cholestatic conditions needs to be further investigated.

METHODS

BA synthesis was directly quantified by measuring serum concentrations of 7alpha-hydroxycholest-4-en-3-one (C4), along with serum FGF19 and other parameters, in 44 patients with primary biliary cirrhosis (PBC) and 10 healthy subjects.

RESULTS

Serum C4 were substantially lower, while those of FGF19 were higher, in cirrhotic PBC patients, as compared to those of either healthy or non-cirrhotic PBC patients. Analyses of the relationships between circulating FGF19, BA synthesis and cholestasis revealed that circulating FGF19 was strongly correlated with BA synthesis (r = -0.735, p<0.0001) and the severity of cholestasis (r = 0.590, p<0.001). Moreover, BA synthesis was found to be strongly correlated with the degree of cholestasis (r = 0.522, p = 0.0005).

CONCLUSION

These findings demonstrate that the regulation of BA synthesis in response to cholestasis is primarily controlled by circulating FGF19 and that under cholestatic conditions, the FGF19-BA synthesis feedback mechanism remains intact. Administering FGF19, or suitable mimetic, as a pharmacological intervention to increase circulating levels of FGF19 and suppress BA synthesis by inhibiting CYP7A1 gene expression is likely to provide therapeutic benefits for many PBC patients.

Ursodeoxycholic acid and lithocholic acid exert anti-inflammatory actions in the colon

Ward JB, Lajczak NK, Kelly OB, O'Dwyer AM, Giddam AK, Ní Gabhann J, Franco P, Tambuwala MM, Jefferies CA, Keely S, Roda A, Keely SJ. Ursodeoxycholic acid and lithocholic acid exert anti-inflammatory actions in the colon. Am J Physiol Gastrointest Liver Physiol 312: G550-G558, 2017. First published March 30, 2017; doi:10.1152/ajpgi.00256.2016.-Inflammatory bowel diseases (IBD) comprise a group of common and debilitating chronic intestinal disorders for which currently available therapies are often unsatisfactory. The naturally occurring secondary bile acid, ursodeoxycholic acid (UDCA), has well-established anti-inflammatory and cytoprotective actions and may therefore be effective in treating IBD. We aimed to investigate regulation of colonic inflammatory responses by UDCA and to determine the potential impact of bacterial metabolism on its therapeutic actions. The anti-inflammatory efficacy of UDCA, a nonmetabolizable analog, 6α-methyl-UDCA (6-MUDCA), and its primary colonic metabolite lithocholic acid (LCA) was assessed in the murine dextran sodium sulfate (DSS) model of mucosal injury. The effects of bile acids on cytokine (TNF-α, IL-6, Il-1β, and IFN-γ) release from cultured colonic epithelial cells and mouse colonic tissue in vivo were investigated. Luminal bile acids were measured by gas chromatography-mass spectrometry. UDCA attenuated release of proinflammatory cytokines from colonic epithelial cells in vitro and was protective against the development of colonic inflammation in vivo. In contrast, although 6-MUDCA mimicked the effects of UDCA on epithelial cytokine release in vitro, it was ineffective in preventing inflammation in the DSS model. In UDCA-treated mice, LCA became the most common colonic bile acid. Finally, LCA treatment more potently inhibited epithelial cytokine release and protected against DSS-induced mucosal inflammation than did UDCA. These studies identify a new role for the primary metabolite of UDCA, LCA, in preventing colonic inflammation and suggest that microbial metabolism of UDCA is necessary for the full expression of its protective actions.NEW & NOTEWORTHY On the basis of its cytoprotective and anti-inflammatory actions, the secondary bile acid ursodeoxycholic acid (UDCA) has well-established uses in both traditional and Western medicine. We identify a new role for the primary metabolite of UDCA, lithocholic acid, as a potent inhibitor of intestinal inflammatory responses, and we present data to suggest that microbial metabolism of UDCA is necessary for the full expression of its protective effects against colonic inflammation.

Physical Chemistry of Bile: Detailed Pathogenesis of Cholelithiasis

Despite the overwhelming prevalence of cholelithiasis, many health care professionals are not familiar with the basic pathophysiology of gallstone formation. This article provides an overview of the biochemical pathways related to bile, with a focus on the physical chemistry of bile. We describe the important factors in bile synthesis and secretion that affect the composition of bile and consequently its liquid state. Within this biochemical background lies the foundation for understanding the clinical and sonographic manifestation of cholelithiasis, including the pathophysiology of cholesterol crystallization, gallbladder sludge, and gallstones. There is a brief discussion of the clinical manifestations of inflammatory and obstructive cholestasis and the impact on bile metabolism and subsequently on liver function tests. Despite being the key modality in diagnosing cholelithiasis, ultrasound has a limited role in the characterization of stone composition.

Preference of Conjugated Bile Acids over Unconjugated Bile Acids as Substrates for OATP1B1 and OATP1B3

Bile acids, the metabolites of cholesterol, are signaling molecules that play critical role in many physiological functions. They undergo enterohepatic circulation through various transporters expressed in intestine and liver. Human organic anion-transporting polypeptides (OATP) 1B1 and OATP1B3 contribute to hepatic uptake of bile acids such as taurocholic acid. However, the transport properties of individual bile acids are not well understood. Therefore, we selected HEK293 cells overexpressing OATP1B1 and OATP1B3 to evaluate the transport of five major human bile acids (cholic acid, chenodeoxycholic acid, deoxycholic acid, ursodeoxycholic acid, lithocholic acid) together withtheir glycine and taurine conjugates via OATP1B1 and OATP1B3. The bile acids were quantified by liquid chromatography-tandem mass spectrometry. The present study revealed that cholic acid, chenodeoxyxcholic acid, and deoxycholic acid were transported by OATP1B1 and OATP1B3, while ursodeoxycholic acid and lithocholic acid were not significantly transported by OATPs. However, all the conjugated bile acids were taken up rapidly by OATP1B1 and OATP1B3. Kinetic analyses revealed the involvement of saturable OATP1B1- and OATP1B3-mediated transport of bile acids. The apparent Km values for OATP1B1 and OATP1B3 of the conjugated bile acids were similar (0.74-14.7 μM for OATP1B1 and 0.47-15.3 μM for OATP1B3). They exhibited higher affinity than cholic acid (47.1 μM for OATP1B1 and 42.2 μM for OATP1B3). Our results suggest that conjugated bile acids (glycine and taurine) are preferred to unconjugated bile acids as substrates for OATP1B1 and OATP1B3.

Sandwich-Cultured Hepatocytes as a Tool to Study Drug Disposition and Drug-Induced Liver Injury

Sandwich-cultured hepatocytes (SCH) are metabolically competent and have proper localization of basolateral and canalicular transporters with functional bile networks. Therefore, this cellular model is a unique tool that can be used to estimate biliary excretion of compounds. SCH have been used widely to assess hepatobiliary disposition of endogenous and exogenous compounds and metabolites. Mechanistic modeling based on SCH data enables estimation of metabolic and transporter-mediated clearances, which can be used to construct physiologically based pharmacokinetic models for prediction of drug disposition and drug-drug interactions in humans. In addition to pharmacokinetic studies, SCH also have been used to study cytotoxicity and perturbation of biological processes by drugs and hepatically generated metabolites. Human SCH can provide mechanistic insights underlying clinical drug-induced liver injury (DILI). In addition, data generated in SCH can be integrated into systems pharmacology models to predict potential DILI in humans. In this review, applications of SCH in studying hepatobiliary drug disposition and bile acid-mediated DILI are discussed. An example is presented to show how data generated in the SCH model were used to establish a quantitative relationship between intracellular bile acids and cytotoxicity, and how this information was incorporated into a systems pharmacology model for DILI prediction.

Simple steatosis sensitizes cholestatic rats to liver injury and dysregulates bile salt synthesis and transport

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder. It is uncertain if simple steatosis, the initial and prevailing form of NAFLD, sensitizes the liver to cholestasis. Here, we compared the effects of obstructive cholestasis in rats with a normal liver versus rats with simple steatosis induced by a methionine/choline-deficient diet. We found that plasma liver enzymes were higher and hepatic neutrophil influx, inflammation, and fibrosis were more pronounced in animals with combined steatosis and cholestasis compared to cholestasis alone. Circulating bile salt levels were markedly increased and hepatic bile salt composition shifted from hydrophilic tauro-β-muricholate to hydrophobic taurocholate. This shift was cytotoxic for HepG2 hepatoma cells. Gene expression analysis revealed induction of the rate-limiting enzyme in bile salt synthesis, cytochrome P450 7a1 (CYP7A1), and modulation of the hepatic bile salt transport system. In conclusion, simple steatosis sensitizes the liver to cholestatic injury, inflammation, and fibrosis in part due to a cytotoxic shift in bile salt composition. Plasma bile salt levels were elevated, linked to dysregulation of bile salt synthesis and enhanced trafficking of bile salts from the liver to the systemic circulation.

Yinzhihuang attenuates ANIT-induced intrahepatic cholestasis in rats through upregulation of Mrp2 and Bsep expressions

BACKGROUND

The treatment of intrahepatic cholestasis has been limited, and development of an effective drug is needed. Clinical studies have shown that Yinzhihuang (YZH), a traditional Chinese decoction, enhances bilirubin clearance. The goal of this study was to determine the protective effect of YZH on experimental intrahepatic cholestasis in young rats and to explore its underlying molecular mechanisms.

METHODS

Intrahepatic cholestasis in rats was induced by α-naphthylisothiocyanate (ANIT) on days 1 and 8. The rats received YZH, ursodeoxycholic acid (UDCA), or vehicle for 9 d and were killed on either day 3 or day 10. Serum biomarkers, liver histology, and the distribution of protein and mRNA expression of Mrp2 and Bsep were analyzed.

RESULTS

YZH treatment resulted in decreased levels of serum biomarkers except γ-glutamyl transpeptidase, attenuated liver histological injuries, increased protein expressions of Mrp2 and Bsep, and upregulated expressions of Mrp2 and Bsep mRNAs. The effects of YZH on serum biomarkers (aminotransferase, alanine aminotransferase, and direct bilirubin), liver histology, and Mrp2 mRNA expressions were significantly greater and earlier than those of UDCA.

CONCLUSION

Our results suggest that YZH has protective effect against ANIT-induced intrahepatic cholestasis in rats, through upregulation of Mrp2 and Bsep expressions.

Increased risk of colorectal neoplasia in patients with primary sclerosing cholangitis and inflammatory bowel disease: a meta-analysis of 16 observational studies

Ulcerative colitis (UC) patients with concomitant primary sclerosing cholangitis (PSC) carry an increased risk of colorectal neoplasia (dysplasia and cancer), whereas the association between PSC and the development of colorectal neoplasia in Crohn's disease (CD) is controversial. A meta-analysis was carried out to compare the risk of this neoplasia in patients with inflammatory bowel disease (IBD) with and without PSC. A systematic research of MEDLINE, EMBASE and the Cochrane Central Register of Controlled Trials was performed to identify studies that compared the risk of colorectal neoplasia (dysplasia and cancer) in patients with IBD with and without PSC. Quality assessment was performed using the Newcastle-Ottawa Scale. Pooled odds ratio (OR) was calculated using the random-effects model by STATA 12.0. A total of 16 studies (four cohort studies, 12 case-control studies; nine prospective studies and seven retrospective studies) were selected for further study. These studies included 13 379 IBD patients, of whom 1022 also had PSC. Patients with IBD and PSC were at an increased risk of colorectal dysplasia and cancer compared with patients with IBD alone [OR 3.24; 95% confidence interval (CI): 2.14-4.90]. This increased risk was present even when the risk of colorectal cancer alone was analysed (OR 3.41; 95% CI: 2.13-5.48). Data only from patients with UC showed that PSC was associated with an increased risk for the development of colorectal neoplasia and cancer in patients with UC (OR 2.98; 95% CI: 1.54-5.76) (OR 3.01; 95% CI: 1.44-6.29), but there were high heterogeneity among studies (I=76.9 and 62.8%, respectively). Heterogeneity of the studies was affected by the study design (prospective or retrospective). The OR of colorectal neoplasia was 2.32 (95% CI: 0.70-7.70, P=0.133) and that of cancer was 2.91 (95% CI: 0.84-10.16, P=0.388) for patients with CD and concurrent PSC. Patients with IBD and PSC have a markedly higher risk for the development of colorectal neoplasia than patients with IBD, but not PSC. Stratification by IBD type show that the presence of PSC is associated with an increased risk for the development of colorectal neoplasia in patients with UC; however, there is a nonsignificant association in CD patients. When the risk of colorectal cancer alone is analysed, the conclusion does not change.

Classification of Cholestatic and Necrotic Hepatotoxicants Using Transcriptomics on Human Precision-Cut Liver Slices

Human toxicity screening is an important stage in the development of safe drug candidates. Hepatotoxicity is one of the major reasons for the withdrawal of drugs from the market because the liver is the major organ involved in drug metabolism, and it can generate toxic metabolites. There is a need to screen molecules for drug-induced hepatotoxicity in humans at an earlier stage. Transcriptomics is a technique widely used to screen molecules for toxicity and to unravel toxicity mechanisms. To date, the majority of such studies were performed using animals or animal cells, with concomitant difficulty in interpretation due to species differences, or in human hepatoma cell lines or cultured hepatocytes, suffering from the lack of physiological expression of enzymes and transporters and lack of nonparenchymal cells. The aim of this study was to classify known hepatotoxicants on their phenotype of toxicity in humans using gene expression profiles ex vivo in human precision-cut liver slices (PCLS). Hepatotoxicants known to induce either necrosis (n = 5) or cholestasis (n = 5) were used at concentrations inducing low (<30%) and medium (30-50%) cytotoxicity, based on ATP content. Random forest and support vector machine algorithms were used to classify hepatotoxicants using a leave-one-compound-out cross-validation method. Optimized biomarker sets were compared to derive a consensus list of markers. Classification correctly predicted the toxicity phenotype with an accuracy of 70-80%. The classification is slightly better for the low than for the medium cytotoxicity. The consensus list of markers includes endoplasmic reticulum stress genes, such as C2ORF30, DNAJB9, DNAJC12, SRP72, TMED7, and UBA5, and a sodium/bile acid cotransporter (SLC10A7). This study shows that human PCLS are a useful model to predict the phenotype of drug-induced hepatotoxicity. Additional compounds should be included to confirm the consensus list of markers, which could then be used to develop a biomarker PCR-array for hepatotoxicity screening.

Hormesis in Cholestatic Liver Disease; Preconditioning with Low Bile Acid Concentrations Protects against Bile Acid-Induced Toxicity

Introduction

Cholestasis is characterized by accumulation of bile acids and inflammation, causing hepatocellular damage. Still, liver damage markers are highest in acute cholestasis and drop when this condition becomes chronic, indicating that hepatocytes adapt towards the hostile environment. This may be explained by a hormetic response in hepatocytes that limits cell death during cholestasis.

Aim

To investigate the mechanisms that underlie the hormetic response that protect hepatocytes against experimental cholestatic conditions.

Methods

HepG2.rNtcp cells were preconditioned (24 h) with sub-apoptotic concentrations (0.1–50 μM) of various bile acids, the superoxide donor menadione, TNF-α or the Farsenoid X Receptor agonist GW4064, followed by a challenge with the apoptosis-inducing bile acid glycochenodeoxycholic acid (GCDCA; 200 μM for 4 h), menadione (50 μM, 6 h) or cytokine mixture (CM; 6 h). Levels of apoptotic and necrotic cell death, mRNA expression of the bile salt export pump (ABCB11) and bile acid sensors, as well as intracellular GCDCA levels were analyzed.

Results

Preconditioning with the pro-apoptotic bile acids GCDCA, taurocholic acid, or the protective bile acids (tauro)ursodeoxycholic acid reduced GCDCA-induced caspase-3/7 activity in HepG2.rNtcp cells. Bile acid preconditioning did not induce significant levels of necrosis in GCDCA-challenged HepG2.rNtcp cells. In contrast, preconditioning with cholic acid, menadione or TNF-α potentiated GCDCA-induced apoptosis. GCDCA preconditioning specifically reduced GCDCA-induced cell death and not CM- or menadione-induced apoptosis. The hormetic effect of GCDCA preconditioning was concentration- and time-dependent. GCDCA-, CDCA- and GW4064- preconditioning enhanced ABCB11 mRNA levels, but in contrast to the bile acids, GW4064 did not significantly reduce GCDCA-induced caspase-3/7 activity. The GCDCA challenge strongly increased intracellular levels of this bile acid, which was not lowered by GCDCA-preconditioning.

Conclusions

Sub-toxic concentrations of bile acids in the range that occur under normal physiological conditions protect HepG2.rNtcp cells against GCDCA-induced apoptosis, which is independent of FXR-controlled changes in bile acid transport.

In vitro model systems to investigate bile salt export pump (BSEP) activity and drug interactions: A review

The bile salt export pump protein (BSEP), expressed on the canalicular membranes of hepatocytes, is primarily responsible for the biliary excretion of bile salts. The inhibition of BSEP transport activity can lead to an increase in intracellular bile salt levels and liver injury. This review discusses the various in vitro assays currently available for assessing the effect of drugs or other chemical entities to modulate BSEP transport activity. BSEP transporter assays use one of the following platforms: Xenopus laevis oocytes; canalicular membrane vesicles (CMV); BSEP-expressed membrane vesicles; cell lines expressing BSEP; sandwich cultured hepatocytes (SCH); and hepatocytes in suspension. Two of these, BSEP-expressed insect membrane vesicles and sandwich cultured hepatocytes, are the most commonly used assays. BSEP membrane vesicles prepared from transfected insect cells are useful for assessing BSEP inhibition or substrate specificity and exploring mechanisms of BSEP-associated genetic diseases. This model can be applied in a high-throughput format for discovery-drug screening. However, experimental results from use of membrane vesicles may lack physiological relevance and the model does not allow for investigation of in situ metabolism in modulation of BSEP activity. Hepatocyte-based assays that use the SCH format provide results that are generally more physiologically relevant than membrane assays. The SCH model is useful in detailed studies of the biliary excretion of drugs and BSEP inhibition, but due to the complexity of SCH preparation, this model is used primarily for determining biliary clearance and BSEP inhibition in a limited number of compounds. The newly developed hepatocyte in suspension assay avoids many of the complexities of the SCH method. The use of pooled cryopreserved hepatocytes in suspension minimizes genetic variance and individual differences in BSEP activity and also provides the opportunity for higher throughput screening and cross-species comparisons.

Na(+) /H(+) exchanger regulatory factor 1 knockout mice have an attenuated hepatic inflammatory response and are protected from cholestatic liver injury

The intercellular adhesion molecule 1 (ICAM-1) is induced in mouse liver after bile duct ligation (BDL) and plays a key role in neutrophil-mediated liver injury in BDL mice. ICAM-1 has been shown to interact with cytoskeletal ezrin-radixin-moesin (ERM) proteins that also interact with the PDZ protein, Na(+) /H(+) exchanger regulatory factor 1 (NHERF-1/EBP50). In NHERF-1(-/-) mice, ERM proteins are significantly reduced in brush-border membranes from kidney and small intestine. ERM knockdown reduces ICAM-1 expression in response to tumor necrosis factor alpha. Here we show that NHERF-1 assembles ERM proteins, ICAM-1 and F-actin into a macromolecule complex that is increased in mouse liver after BDL. Compared to wild-type (WT) mice, both sham-operated and BDL NHERF-1(-/-) mice have lower levels of activated ERM and ICAM-1 protein in the liver accompanied by significantly reduced hepatic neutrophil accumulation, serum alanine aminotransferase, and attenuated liver injury after BDL. However, total bile acid concentrations in serum and liver of sham and BDL NHERF-1(-/-) mice were not significantly different from WT controls, although hepatic tetrahydroxylated bile acids and Cyp3a11 messenger RNA levels were higher in NHERF-1(-/-) BDL mice.

CONCLUSION

NHERF-1 participates in the inflammatory response that is associated with BDL-induced liver injury. Deletion of NHERF-1 in mice leads to disruption of the formation of ICAM-1/ERM/NHERF-1 complex and reduction of hepatic ERM proteins and ICAM-1, molecules that are up-regulated and are essential for neutrophil-mediated liver injury in cholestasis. Further study of the role of NHERF-1 in the inflammatory response in cholestasis and other forms of liver injury should lead to discovery of new therapeutic targets in hepatic inflammatory diseases.

Fasiglifam (TAK-875) Inhibits Hepatobiliary Transporters: A Possible Factor Contributing to Fasiglifam-Induced Liver Injury

Fasiglifam (TAK-875), a selective G-protein-coupled receptor 40 agonist, was developed for the treatment of type 2 diabetes mellitus; however, its development was terminated in phase III clinical trials because of liver safety concerns. Our preliminary study indicated that intravenous administration of 100 mg/kg of TAK-875 increased the serum total bile acid concentration by 3 to 4 times and total bilirubin levels by 1.5 to 2.6 times in rats. In the present study, we examined the inhibitory effects of TAK-875 on hepatobiliary transporters to explore the mechanisms underlying its hepatotoxicity. TAK-875 decreased the biliary excretion index and the in vitro biliary clearance of d₈-taurocholic acid in sandwich-cultured rat hepatocytes, suggesting that TAK-875 impaired biliary excretion of bile acids, possibly by inhibiting bile salt export pump (Bsep). TAK-875 inhibited the efflux transporter multidrug resistance-associated protein 2 (Mrp2) in rat hepatocytes using 5 (and 6)-carboxy-2',7'-dichlorofluorescein as a substrate. Inhibition of MRP2 was further confirmed by reduced transport of vinblastine in Madin-Darby canine kidney cells overexpressing MRP2 with IC₅₀ values of 2.41 μM. TAK-875 also inhibited the major bile acid uptake transporter Na(+)/taurocholate cotransporting polypeptide (Ntcp), which transports d₈-taurocholic acid into rat hepatocytes, with an IC₅₀ value of 10.9 μM. TAK-875 significantly inhibited atorvastatin uptake in organic anion transporter protein (OATP) 1B1 and OATP1B3 cells with IC₅₀ values of 2.28 and 3.98 μM, respectively. These results indicate that TAK-875 inhibited the efflux transporter MRP2/Mrp2 and uptake transporters Ntcp and OATP/Oatp, which may affect bile acid and bilirubin homeostasis, resulting in hyperbilirubinemia and cholestatic hepatotoxicity.

Hepatic encephalopathy induces site-specific changes in gene expression of GluN1 subunit of NMDA receptor in rat brain

We investigate changes in gene expression of GluN1 subunit of N-Methyl-D-Aspartate (NMDA) receptor in the prefrontal cortex (PFC), hippocampus and striatum in a rat model of hepatic encephalopathy (HE). We used male Wistar rats in which HE was induced after a common bile duct ligation (BDL). The animals were divided into three sets, and each set included three groups of control, sham operated and BDL. In the first set of animals, blood samples collected for biochemical analysis on day 21 of BDL. In the second set, changes in nociception threshold was assessed on day 21 of BDL using a hotplate test. In the third set, whole brain extracted, and the PFC, the hippocampus and the striatum in each rat were immediately dissected. We used a semi-quantitative RT-PCR method for evaluating the GluN1 gene expression. The biochemical analyses showed that plasma levels of ammonia and bilirubin in BDL rats were significantly increased compared to the sham control group on day 21 of BDL (P < 0.01). Nociception threshold was also increased in rats with BDL compared to sham group (P < 0.001). The results revealed that the GluN1 gene expression at mRNA levels in BDL group was decreased by 19 % in the PFC (P < 0.05) but increased by 82 % in the hippocampus (P < 0.01) compared to the sham control group; however, no significant change was observed in the striatum. It can be concluded that HE affects the GluN1 gene expression in rat brain with a site-specific pattern, and the PFC and hippocampus are more sensitive areas than striatum.

Serum Bile Acid Levels in Children With Nonalcoholic Fatty Liver Disease

OBJECTIVE

Because the prevalence of obesity in children is increasing, the frequency of pediatric nonalcoholic fatty liver disease (NAFLD) is growing. A reliable noninvasive biomarker for monitoring progression of liver fibrosis would be useful. In cirrhotic persons serum bile acid (BA) levels are significantly elevated. We hypothesized that BA levels and composition in pediatric NAFLD vary depending on the stage of fibrosis.

METHODS

Children with NAFLD were compared with controls and classified by stages of fibrosis (NAFLD-F0, n = 27; NAFLD-F≥1, n = 65) based on liver-biopsy findings. Fasted metabolic and cholestasis status was assessed by several blood tests. BA profiles were measured by tandem mass spectrometry and compared with healthy controls (n = 105).

RESULTS

Compared with controls, all of the NAFLD patients were overweight and showed significantly elevated glucose, insulin, aspartate transaminase, and alanine transaminase levels. Total serum BAs were lower in nonfibrotic NAFLD children than in a control cohort (1.73 vs 3.6 μmol/L) because low glycine-conjugated BA levels were incompletely compensated by increases in taurine-conjugated or unconjugated BA. In patients with fibrotic NAFLD, BA levels were lower than in controls (2.45 vs 3.6 μmol/L) but higher than in nonfibrotic patients (2.45 vs 1.73 μmol/L), and the BA pattern resembled that of healthy controls. Fibroblast growth factor 19 levels were significantly lower in both NAFLD groups than in controls (P ≤ 0.001) and were positively correlated with ursodeoxycholic acid levels.

CONCLUSIONS

Our data indicate that serum BA levels decrease in early NAFLD and increase during progression to fibrosis. Given that BA levels are increased in cirrhotic adults, we postulate a continuous rise as NAFLD advances. BA may have a value as a noninvasive biomarker in pediatric NAFLD progression.

Protective effect of bicyclol against bile duct ligation-induced hepatic fibrosis in rats

AIM: To evaluate the protective effect of bicyclol against bile duct ligation (BDL)-induced hepatic fibrosis in rats.

METHODS: Sprague-Dawley male rats underwent BDL and sham-operated animals were used as healthy controls. The BDL rats were divided into two groups which received sterilized PBS or bicyclol (100 mg/kg per day) orally for two consecutive weeks. Serum, urine and bile were collected for biochemical determinations. Liver tissues were collected for histological analysis and a whole genome oligonucleotide microarray assay. Reverse transcription-polymerase chain reaction and Western blotting were used to verify the expression of liver fibrosis-related genes.

RESULTS: Treatment with bicyclol significantly reduced liver fibrosis and bile duct proliferation after BDL. The levels of alanine aminotransferase (127.7 ± 72.3 vs 230.4 ± 69.6, P < 0.05) and aspartate aminotransferase (696.8 ± 232.6 vs 1032.6 ± 165.8, P < 0.05) were also decreased by treatment with bicyclol in comparison to PBS. The expression changes of 45 fibrogenic genes and several fibrogenesis-related pathways were reversed by bicyclol in the microarray assay. Bicyclol significantly reduced liver mRNA and/or protein expression levels of collagen 1a1, matrix metalloproteinase 2, tumor necrosis factor, tissue inhibitors of metalloproteinases 2, transforming growth factor-β1 and α-smooth muscle actin.

CONCLUSION: Bicyclol significantly attenuates BDL-induced liver fibrosis by reversing fibrogenic gene expression. These findings suggest that bicyclol might be an effective anti-fibrotic drug for the treatment of cholestatic liver disease.

The Cholangiocyte Glycocalyx Stabilizes the 'Biliary HCO3 Umbrella': An Integrated Line of Defense against Toxic Bile Acids

BACKGROUND

Destruction of cholangiocytes is the hallmark of chronic cholangiopathies such as primary biliary cirrhosis. Under physiologic conditions, cholangiocytes display a striking resistance to the high, millimolar concentrations of toxic bile salts present in bile. We recently showed that a 'biliary HCO3(-) umbrella', i.e. apical cholangiocellular HCO3(-) secretion, prevents cholangiotoxicity of bile acids, and speculated on a role for extracellular membrane-bound glycans in the stabilization of this protective layer. This paper summarizes published and thus far unpublished evidence supporting the role of the glycocalyx in stabilizing the 'biliary HCO3(-) umbrella' and thus preventing cholangiotoxicity of bile acids.

KEY MESSAGES

The apical glycocalyx of a human cholangiocyte cell line and mouse liver sections were visualized by electron microscopy. FACS analysis was used to characterize the surface glycan profile of cultured human cholangiocytes. Using enzymatic digestion with neuraminidase the cholangiocyte glycocalyx was desialylated to test its protective function. Using lectin assays, we demonstrated that the main N-glycans in human and mouse cholangiocytes were sialylated biantennary structures, accompanied by high expression of the H-antigen (α1-2 fucose). Apical neuraminidase treatment induced desialylation without affecting cell viability, but lowered cholangiocellular resistance to bile acid-induced toxicity: both glycochenodeoxycholate and chenodeoxycholate (pKa ≥4), but not taurochenodeoxycholate (pKa <2), displayed cholangiotoxic effects after desialylation. A 24-hour reconstitution period allowed cholangiocytes to recover to a pretreatment bile salt susceptibility pattern.

CONCLUSION

Experimental evidence indicates that an apical cholangiocyte glycocalyx with glycosylated mucins and other glycan-bearing membrane glycoproteins stabilizes the 'biliary HCO3(-) umbrella', thus aiding in the protection of human cholangiocytes against bile acid toxicity.

The anti-fibrotic effects of epigallocatechin-3-gallate in bile duct-ligated cholestatic rats and human hepatic stellate LX-2 cells are mediated by the PI3K/Akt/Smad pathway

AIM

(-)-Epigallocatechin-3-gallate (EGCG) is one of the most abundant polyphenols in green tea with strong antioxidant activity and various therapeutic effects. In this study, we investigated the anti-fibrotic effects of EGCG and underlying mechanisms in bile duct-ligated (BDL) rats and a liver fibrosis model in vitro.

METHODS

BDL rats were treated with EGCG (25 mg·kg(-1)·d(-1), po) for 14 d, and then the serum, bile and liver samples were collected. Liver fibrosis was assessed by serum, urine and bile biochemistry analyses and morphological studies of liver tissues. TGF-β1-stimulated human hepatic stellate LX-2 cells were used as a liver fibrosis model in vitro. The expression of liver fibrogenic genes and signaling proteins in the PI3K/Akt/Smad pathway was examined using Western blotting and/or real-time PCR.

RESULTS

In BDL rats, EGCG treatment significantly ameliorates liver necrosis, inflammation and fibrosis, and suppressed expression of the genes associated with liver inflammation and fibrogenesis, including TNF-α, IL-1β, TGF-β1, MMP-9, α-SMA, and COL1A1. In LX-2 cells, application of EGCG (10, 25 μmol/L) dose-dependently suppressed TGF-β1-stimulated expression of COL1A1, MMP-2, MMP-9, TGF-β1, TIMP1, and α-SMA. Furthermore, EGCG significantly suppressed the phosphorylation of Smad2/3 and Akt in the livers of BDL rats and in TGF-β1-stimulated LX-2 cells. Application of LY294002, a specific inhibitor of PI3K, produced similar effects as EGCG did in TGF-β1-stimulated LX-2 cells, but co-application of EGCG and LY294002 did not produce additive effects.

CONCLUSION

EGCG exerts anti-fibrotic effects in BDL rats and TGF-β1-stimulated LX-2 cells in vitro via inhibiting the PI3K/Akt/Smad pathway.

Species differences in hepatobiliary disposition of taurocholic acid in human and rat sandwich-cultured hepatocytes: implications for drug-induced liver injury

The bile salt export pump (BSEP) plays an important role in bile acid excretion. Impaired BSEP function may result in liver injury. Bile acids also undergo basolateral efflux, but the relative contributions of biliary (CLBile) versus basolateral efflux (CLBL) clearance to hepatocellular bile acid excretion have not been determined. In the present study, taurocholic acid (TCA; a model bile acid) disposition was characterized in human and rat sandwich-cultured hepatocytes (SCH) combined with pharmacokinetic modeling. In human SCH, biliary excretion of TCA predominated (CLBile = 0.14 ± 0.04 ml/min per g liver; CLBL = 0.042 ± 0.019 ml/min per g liver), whereas CLBile and CLBL contributed approximately equally to TCA hepatocellular excretion in rat SCH (CLBile = 0.34 ± 0.07 ml/min per g liver; CLBL = 0.26 ± 0.07 ml/min per g liver). Troglitazone decreased TCA uptake, CLBile, and CLBL; membrane vesicle assays revealed for the first time that the major metabolite, troglitazone sulfate, was a noncompetitive inhibitor of multidrug resistance-associated protein 4, a basolateral bile acid efflux transporter. Simulations revealed that decreased CLBile led to a greater increase in hepatic TCA exposure in human than in rat SCH. A decrease in both excretory pathways (CLBile and CLBL) exponentially increased hepatic TCA in both species, suggesting that 1) drugs that inhibit both pathways may have a greater risk for hepatotoxicity, and 2) impaired function of an alternate excretory pathway may predispose patients to hepatotoxicity when drugs that inhibit one pathway are administered. Simulations confirmed the protective role of uptake inhibition, suggesting that a drug's inhibitory effects on bile acid uptake also should be considered when evaluating hepatotoxic potential. Overall, the current study precisely characterized basolateral efflux of TCA, revealed species differences in hepatocellular TCA efflux pathways, and provided insights about altered hepatic bile acid exposure when multiple transport pathways are impaired.

Species differences in hepatobiliary disposition of taurocholic acid in human and rat sandwich-cultured hepatocytes: implications for drug-induced liver injury

The bile salt export pump (BSEP) plays an important role in bile acid excretion. Impaired BSEP function may result in liver injury. Bile acids also undergo basolateral efflux, but the relative contributions of biliary (CLBile) versus basolateral efflux (CLBL) clearance to hepatocellular bile acid excretion have not been determined. In the present study, taurocholic acid (TCA; a model bile acid) disposition was characterized in human and rat sandwich-cultured hepatocytes (SCH) combined with pharmacokinetic modeling. In human SCH, biliary excretion of TCA predominated (CLBile = 0.14 ± 0.04 ml/min per g liver; CLBL = 0.042 ± 0.019 ml/min per g liver), whereas CLBile and CLBL contributed approximately equally to TCA hepatocellular excretion in rat SCH (CLBile = 0.34 ± 0.07 ml/min per g liver; CLBL = 0.26 ± 0.07 ml/min per g liver). Troglitazone decreased TCA uptake, CLBile, and CLBL; membrane vesicle assays revealed for the first time that the major metabolite, troglitazone sulfate, was a noncompetitive inhibitor of multidrug resistance-associated protein 4, a basolateral bile acid efflux transporter. Simulations revealed that decreased CLBile led to a greater increase in hepatic TCA exposure in human than in rat SCH. A decrease in both excretory pathways (CLBile and CLBL) exponentially increased hepatic TCA in both species, suggesting that 1) drugs that inhibit both pathways may have a greater risk for hepatotoxicity, and 2) impaired function of an alternate excretory pathway may predispose patients to hepatotoxicity when drugs that inhibit one pathway are administered. Simulations confirmed the protective role of uptake inhibition, suggesting that a drug's inhibitory effects on bile acid uptake also should be considered when evaluating hepatotoxic potential. Overall, the current study precisely characterized basolateral efflux of TCA, revealed species differences in hepatocellular TCA efflux pathways, and provided insights about altered hepatic bile acid exposure when multiple transport pathways are impaired.

Hepatoprotective and antifibrotic effects of sodium molybdate in a rat model of bile duct ligation

PROJECT

Cholestasis liver fibrosis has been increasingly recognized as a cause of high morbidity and mortality in humans. The accumulation of toxic bile salts in a bile duct ligation (BDL) animal model plays a pivotal role in the induction of liver fibrosis. Cholestatic liver fibrosis is characterized by excessive collagen production and deposition, which is mediated by reactive oxygen species (ROS). Molybdenum is an essential micronutrient trace element which acts as a cofactor in many detoxification system enzymes. The aim of the present study was to evaluate the antifibrotic effect of sodium molybdate on liver cholestasis induced by bile duct ligation in rats.

PROCEDURE

After BDL, rats were given sodium molybdate (0.05 or 0.1 or 0.2g/kg) or urosodeoxycholic acid (UDCA, 25mg/kg) via intragastric gavage for 45 consecutive days (once per day).

RESULTS

BDL drastically increased the serum levels of aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, total bilirubin and direct bilirubin, whereas it reduced the levels of antioxidant enzymes, superoxide dismutase and catalase in the liver. Treatment of BDL rats with sodium molybdate significantly attenuated these changes. As determined by Masson's trichrome staining, BDL markedly induced the liver fibrosis. These alterations were also significantly attenuated by sodium molybdate administration.

CONCLUSIONS

The results of this study indicate the hepatoprotective and antifibrotic effect of sodium molybdate in the cholestatic liver. Sodium molybdate, by inhibiting the activation of Ito cells, decreases the collagen production in the liver. The antifibrotic effect of sodium molybdate is likely due to the antioxidative and free radical scavenging effects of this trace element.

Resveratrol effectively attenuates α-naphthyl-isothiocyanate-induced acute cholestasis and liver injury through choleretic and anti-inflammatory mechanisms

AIM

α-Naphthylisothiocyanate (ANIT) is a well-characterized cholestatic agent for rats. The aim of this study was to examine whether resveratrol could attenuate ANIT-induced acute cholestasis and liver injury in rats.

METHODS

SD rats were treated with resveratrol (15 or 30 mg/kg, ip) or a positive control drug ursodeoxycholic acid (100 mg/kg, po) for 5 consecutive days followed by a single dose of ANIT (60 mg/kg, po). Bile flow, and serum biochemical markers and bile constituents were measured 48 h after ANIT administration. Hepatic levels of oxidative repair enzymes (glutathione peroxidase, catalase and MnSOD), myeloperoxidase activity, TNF-α, IL-6 and ATP content, as well as the expression of liver transporter genes and proteins were assayed.

RESULTS

ANIT exposure resulted in serious cholestasis and liver injury, as shown by marked neutrophil infiltration in liver, dramatically increased serum levels of ALT, AST, GGT, ALP, TBA, TBIL, IBIL and DBIL, and significantly decreased bile excretion and biliary output of GSH and HCO3(-). ANIT significantly increased TNF-α and IL-6 release and myeloperoxidase activity, decreased mitochondrial biogenesis in liver, but had little effect on hepatic oxidative repair enzymes and ATP content. Furthermore, ANIT significantly decreased the expression of Mrp2, FXR and Cyp7a1, markedly increased Mrp3 expression in liver. Pretreatment with resveratrol attenuated ANIT-induced acute cholestasis and liver injury, and other pathological changes. Pretreatment with ursodeoxycholic acid was less effective.

CONCLUSION

Resveratrol effectively attenuates ANIT-induced acute cholestasis and liver injury in rats, possibly through suppression of neutrophil infiltration, as well as upregulation of expression of hepatic transporters and enzymes, thus decreasing accumulation of bile acids.

Role of protein kinase C isoforms in bile formation and cholestasis

Transhepatic solute transport provides the osmotic driving force for canalicular bile formation. Choleretic and cholestatic agents affect bile formation, in part, by altering plasma membrane localizations of transporters involved in bile formation. These short-term dynamic changes in transporter location are highly regulated posttranslational events requiring various cellular signaling pathways. Interestingly, both choleretic and cholestatic agents activate the same intracellular signaling kinases, such as phosphoinositide-3-kinase (PI3K), protein kinase C (PKC), and mitogen-activated protein kinase (MAPK). An emerging theme is that choleretic and cholestatic effects may be mediated by different isoforms of these kinases. This is most evident for PKC-mediated regulation of plasma membrane localization of Na+-taurocholate cotransporting polypeptide (NTCP) and multidrug resistance-associated protein 2 (MRP2) by conventional PKCα (cPKCα), novel PKCδ (nPKCδ), nPKCε, and atypical PKCζ (aPKCζ). aPKCζ may mediate choleretic effects by inserting NTCP into the plasma membrane, and nPKCε may mediate cholestatic effects by retrieving MRP2 from the plasma membrane. On the other hand, cPKCα and nPKCδ may be involved in choleretic, cholestatic, and anticholestatic effects by inserting, retrieving, and inhibiting retrieval of transporters, respectively. The effects of PKC isoforms may be mediated by phosphorylation of the transporters, actin binding proteins (radixin and myristoylated alanine-rich C kinase substrate), and Rab proteins. Human NTCP plays an important role in the entry of hepatitis B and D viruses into hepatocytes and consequent infection. Thus, PKCs, by regulating NTCP trafficking, may also play an important role in hepatic viral infections.

Systems pharmacology modeling predicts delayed presentation and species differences in bile acid-mediated troglitazone hepatotoxicity

Troglitazone (TGZ) causes delayed, life-threatening drug-induced liver injury in some patients but was not hepatotoxic in rats. This study investigated altered bile acid homeostasis as a mechanism of TGZ hepatotoxicity using a systems pharmacology model incorporating drug/metabolite disposition, bile acid physiology/pathophysiology, hepatocyte life cycle, and liver injury biomarkers. In the simulated human population, TGZ (200-600 mg/day × 6 months) resulted in delayed increases in serum alanine transaminase >3× the upper limit of normal in 0.3-5.1%, with concomitant bilirubin elevations >2× the upper limit of normal in 0.3-3.6%, of the population. By contrast, pioglitazone (15-45 mg/day × 6 months) did not elicit hepatotoxicity, consistent with clinical data. TGZ was not hepatotoxic in the simulated rat population. In summary, mechanistic modeling based only on bile acid effects accurately predicted the incidence, delayed presentation, and species differences in TGZ hepatotoxicity, in addition to predicting the relative liver safety of pioglitazone. Systems pharmacology models integrating physiology and experimental data can evaluate drug-induced liver injury mechanisms and may be useful to predict the hepatotoxic potential of drug candidates.

Hepatocellular exposure of troglitazone metabolites in rat sandwich-cultured hepatocytes lacking Bcrp and Mrp2: interplay between formation and excretion

Inhibition of bile acid transport by troglitazone (TGZ) and its major metabolite, TGZ sulfate (TS), may lead to hepatocellular accumulation of toxic bile acids; TS accumulation and hepatotoxicity may be associated with impaired TS biliary excretion. This study evaluated the impact of impaired transport of breast cancer resistance protein (Bcrp) and multidrug resistance-associated protein 2 (Mrp2) on the hepatobiliary disposition of generated metabolites, TS and TGZ glucuronide (TG). Sandwich-cultured hepatocytes (SCH) from Mrp2-deficient (TR(-)) rats in combination with Bcrp knockdown using RNA interference were employed. The biliary excretion index (BEI) of generated TS was not significantly altered by impaired Bcrp (20.9 to 21.1%) and/or Mrp2 function (24.4% and 17.5% in WT and TR(-) rat SCH, respectively). Thus, loss-of-function of Mrp2 and/or Bcrp do not appear to be risk factors for increased hepatocellular TS accumulation in rats, potentially because of a compensatory transporter(s) that excretes TS into bile. Further investigations revealed that the compensatory TS biliary transporter was not the bile salt export pump (Bsep) or P-glycoprotein (P-gp). Interestingly, TGZ sulfation was significantly decreased in TR(-) compared with WT rat SCH (total recovery: 2.8 versus 5.0% of TGZ dose), resulting in decreased hepatocellular TS accumulation, even though sulfotransferase activity in TR(-) rat hepatocyte S9 fraction was similar. Hepatocellular TG accumulation was significantly increased in TR(-) compared with WT rat SCH due to increased glucuronidation and negligible TG biliary excretion. These data emphasize that the interplay between metabolite formation and excretion determines hepatocellular exposure to generated metabolites such as TS and TG.

INTRACELLULAR SIGNALING BY BILE ACIDS

Bile acids, synthesized from cholesterol, are known to produce beneficial as well as toxic effects in the liver. The beneficial effects include choleresis, immunomodulation, cell survival, while the toxic effects include cholestasis, apoptosis and cellular toxicity. It is believed that bile acids produce many of these effects by activating intracellular signaling pathways. However, it has been a challenge to relate intracellular signaling to specific and at times opposing effects of bile acids. It is becoming evident that bile acids produce different effects by activating different isoforms of phosphoinositide 3-kinase (PI3K), Protein kinase Cs (PKCs), and mitogen activated protein kinases (MAPK). Thus, the apoptotic effect of bile acids may be mediated via PI3K-110γ, while cytoprotection induce by cAMP-GEF pathway involves activation of PI3K-p110α/β isoforms. Atypical PKCζ may mediate beneficial effects and nPKCε may mediate toxic effects, while cPKCα and nPKCδ may be involved in both beneficial and toxic effects of bile acids. The opposing effects of nPKCδ activation may depend on nPKCδ phosphorylation site(s). Activation of ERK1/2 and JNK1/2 pathway appears to mediate beneficial and toxic effects, respectively, of bile acids. Activation of p38α MAPK and p38β MAPK may mediate choleretic and cholestatic effects, respectively, of bile acids. Future studies clarifying the isoform specific effects on bile formation should allow us to define potential therapeutic targets in the treatment of cholestatic disorders.

Models of hepatotoxicity and the underlying cellular, biochemical and immunological mechanism(s): a critical discussion

Liver is a primary organ involved in biotransformation of food and drugs. Hepatic diseases are a major worldwide problem. Hepatic disorders are mainly caused by toxic chemicals (alcohol), xenobiotics (carbon tetrachloride, chlorinated hydrocarbons and gases CO₂ and O₂) anticancer (azathioprine, doxorubicin, cisplatin), immunosuppressant (cyclosporine), analgesic anti-inflammatory (paracetamol, thioacetamide), anti-tubercular (isoniazid, rifampicin) drugs, biologicals (Bacillus-Calmette-Guerin vaccine), radiations (gamma radiations), heavy metals (cadmium, arsenic), mycotoxin (aflatoxin), galactosamine, lipopolysaccharides, etc. Various risk factors for hepatic injury include concomitant hepatic diseases, age, gender, alcoholism, nutrition and genetic polymorphisms of cytochrome P450 enzymes have also been emphasized. The present review enumerates various in vivo animal models and in vitro methods of hepatic injury using diverse toxicants, their probable metabolic pathways, and numerous biochemical changes viz. serum biomarkers enzymes, liver function, oxidative stress associated events like free radicals formation, lipid peroxidation, enzyme antioxidants and participation of cytokines (tumour necrosis factor-α, transforming growth factor-β, tumour necrosis factor-related apoptosis inducing ligand), and other biomolecules (Fas and C-jun N-terminal kinase) are also discussed. The underlying cellular, molecular, immunological, and biochemical mechanism(s) of action responsible for liver damage (toxicity) are also been discussed. This review should be immensely useful for researchers especially for phytochemists, pharmacologists and toxicologists working on hepatotoxicity, hepatotoxic chemicals and drugs, hepatoprotective agents and drug research organizations involved especially in phytopharmaceuticals and other natural products.

Apoptosis and necrosis in the liver

Because of its unique function and anatomical location, the liver is exposed to a multitude of toxins and xenobiotics, including medications and alcohol, as well as to infection by hepatotropic viruses, and therefore, is highly susceptible to tissue injury. Cell death in the liver occurs mainly by apoptosis or necrosis, with apoptosis also being the physiologic route to eliminate damaged or infected cells and to maintain tissue homeostasis. Liver cells, especially hepatocytes and cholangiocytes, are particularly susceptible to death receptor-mediated apoptosis, given the ubiquitous expression of the death receptors in the organ. In a quite unique way, death receptor-induced apoptosis in these cells is mediated by both mitochondrial and lysosomal permeabilization. Signaling between the endoplasmic reticulum and the mitochondria promotes hepatocyte apoptosis in response to excessive free fatty acid generation during the metabolic syndrome. These cell death pathways are partially regulated by microRNAs. Necrosis in the liver is generally associated with acute injury (i.e., ischemia/reperfusion injury) and has been long considered an unregulated process. Recently, a new form of "programmed" necrosis (named necroptosis) has been described: the role of necroptosis in the liver has yet to be explored. However, the minimal expression of a key player in this process in the liver suggests this form of cell death may be uncommon in liver diseases. Because apoptosis is a key feature of so many diseases of the liver, therapeutic modulation of liver cell death holds promise. An updated overview of these concepts is given in this article.

New therapeutic avenues in ulcerative colitis: thinking out of the box

Ulcerative colitis (UC) is a chronic idiopathic inflammatory disease of the gastrointestinal tract that affects the mucosal lining of the colon. Recent epidemiological data show that its incidence and prevalence are increasing in many parts of the world, in parallel with altered lifestyles, improved access to health, improved sanitation and industrialisation rates. Current therapeutic strategies for treating UC have only been moderately successful. Despite major recent advances in inflammatory bowel disease therapeutic resources, a considerable proportion of patients are still refractory to conventional treatment. Less than half of all patients achieve long-term remission, many require colectomy, and the disease still has a major impact on patients' lives. Moreover, recent data point to slightly raised mortality. While these outcomes could be partly improved by optimising current therapeutic strategies, they clearly highlight the need to develop new therapies. Currently, a number of promising and innovative therapeutic approaches are being explored, some of which will hopefully survive to reach the clinic. Until such a time arrives, it is important that a better understanding of the clinical particularities of the disease, an improved knowledge of the host-microbiome negative interactions and of the environmental factors beyond disease development is achieved to obtain the final and desired outcome: to provide better treatment and quality of life for patients with this disabling disease.

Liver protective effect of ursodeoxycholic acid includes regulation of ADAM17 activity

BACKGROUND

Ursodeoxycholic acid (UDCA) is used to treat primary biliary cirrhosis, intrahepatic cholestasis, and other cholestatic conditions. Although much has been learned about the molecular basis of the disease pathophysiology, our understanding of the effects of UDCA remains unclear. Possibly underlying its cytoprotective, anti-apoptotic, anti-oxidative effects, UDCA was reported to regulate the expression of TNFα and other inflammatory cytokines. However, it is not known if this effect involves also modulation of ADAM family of metalloproteinases, which are responsible for release of ectodomains of inflammatory cytokines from the cell surface. We hypothesized that UDCA modulates ADAM17 activity, resulting in amelioration of cholestasis in a murine model of bile duct ligation (BDL).

METHODS

The effect of UDCA on ADAM17 activity was studied using the human liver hepatocellular carcinoma cell line HepG2. Untransfected cells or cells ectopically expressing human ADAM17 were cultured with or without UDCA and further activated using phorbol-12-myristate-13-acetate (PMA). The expression and release of ADAM17 substrates, TNFα, TGFα, and c-Met receptor (or its soluble form, sMet) were evaluated using ELISA and quantitative real-time (qRT) PCR. Immunoblotting analyses were conducted to evaluate expression and activation of ADAM17 as well as the level of ERK1/2 phosphorylation after UDCA treatment. The regulation of tissue inhibitor of metalloproteinases-1 (TIMP-1) by UDCA was studied using zymography and qRT-PCR. A mouse model of acute cholestasis was induced by common BDL technique, during which mice received daily orogastric gavage with either UDCA or vehicle only. Liver injury was quantified using alkaline phosphatase (ALP), relative liver weight, and confirmed by histological analysis. ADAM17 substrates in sera were assessed using a bead multiplex assay.

RESULTS

UDCA decreases amount of shed TNFα, TGFα, and sMet in cell culture media and the phosphorylation of ERK1/2. These effects are mediated by the reduction of ADAM17 activity in PMA stimulated cells although the expression ADAM17 is not affected. UDCA reduced the level of the mature form of ADAM17. Moreover, UDCA regulates the expression of TIMP-1 and gelatinases activity in PMA stimulated cells. A BDL-induced acute cholangitis model was characterized by increased relative liver weight, serum levels of ALP, sMet, and loss of intracellular glycogen. UDCA administration significantly decreased ALP and sMet levels, and reduced relative liver weight. Furthermore, hepatocytes of UDCA-treated animals retained their metabolic activity as evidenced by the amount of glycogen storage.

CONCLUSIONS

The beneficial effect of UDCA appears to be mediated in part by the inhibition of ADAM17 activation and, thus, the release of TNFα, a strong pro-inflammatory factor. The release of other ADAM17 substrates, TGFα and sMet, are also regulated this way, pointing to a general impact on the release of ADAM17 substrates, which are pivotal for liver regeneration and function. In parallel, UDCA upregulates TIMP-1 that in turn inhibits matrix metalloproteinases, which destroy the hepatic ECM in diseased liver. This control of extracellular matrix turnover represents an additional beneficial path of UDCA treatment.

The profile of bile acids and their sulfate metabolites in human urine and serum

The role of sulfation in ameliorating the hepatotoxicity of bile acids (BAs) in humans remains unknown due to the lack of proper analytical methods to quantify individual BAs and their sulfate metabolites in biological tissues and fluids. To this end, a simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to characterize the detailed BA profile in human urine and serum. The limit of quantification was 1ng/mL and baseline separation of all analytes was achieved within in a run time of 32min. The method was validated over the dynamic range of 1-1000ng/mL. The LC-MS/MS method was more accurate, precise, and selective than the commercially available kits for the quantification of sulfated and unsulfated BAs, and the indirect quantification of individual sulfated BAs after solvolysis. The LC-MS/MS method was applied to characterize the BA profile in urine and serum of healthy subjects. Thirty three percent of serum BAs were sulfated, whereas 89% of urinary BAs existed in the sulfate form, indicating the role of sulfation in enhancing the urinary excretion of BAs. The percentage of sulfation of individual BAs increased with the decrease in the number of hydroxyl groups indicating the role of sulfation in the detoxification of the more hydrophobic and toxic BA species. Eighty percent of urinary BAs and 55% of serum BAs were present in the glycine-amidated form, whereas 8% of urinary BAs and 13% of serum BAs existed in the taurine-amidated form.