Drug-induced cholestasis

Low-fat, high-carbohydrate parenteral nutrition (PN) may potentially reverse liver disease in long-term PN-dependent infants

INTRODUCTION

Parenteral nutrition-associated cholestasis (PNAC) is a complication of long-term parenteral nutrition (PN). Removal of lipids may reverse PNAC but compromises the energy to ensure infant growth. The purpose of this study was to test whether a low-fat, high-carbohydrate PN regimen, which prevents and reverses PNAC in adults, could do the same in infants. This regimen could potentially avoid the problem of diminished energy input after removing nutritional lipids.

METHODS

Infants developing PNAC over a 2-year period were started on a low-fat PN regimen with calories primarily from carbohydrates. The fat-free PN, containing 314 kJ/ml, was provided 5-6 times a week and fat, including essential fatty acids and fat-soluble vitamins, 1-2 times a week. Enteral feeding was continued according to individual tolerance.

RESULTS

The study included 10 infants with short bowel syndrome (six with intestinal failure due to necrotizing enterocolitis, one with gastroschisis, one with complications due to unrecognized anal atresia and two with midgut volvulus). Median duration of PN with fat before initiating the low-fat regime was 69 days (25-75 % percentile: 41-75 days), and mean s-bilirubin was 139 µmol/l (range 87-323 µmol/l). Median duration with low-fat regimen was 69 days (25-75 % percentile: 18-123 days). Bilirubin reversed to normal (<50 µmol/l) in all infants. Seven children showed catch-up growth. No essential fatty acid deficiency, steatosis or deaths were observed.

CONCLUSIONS

A low-fat, high-carbohydrate PN regimen together with enteral feeding is well tolerated and may be used in reversing liver disease in PN-dependent infants without compromising growth.

Comparison of minipig, dog, monkey and human drug metabolism and disposition

INTRODUCTION

This article gives an overview of the drug metabolism and disposition (ADME) characteristics of the most common non-rodent species used in toxicity testing of drugs (minipigs, dogs, and monkeys) and compares these to human characteristics with regard to enzymes mediating the metabolism of drugs and the transport proteins which contribute to the absorption, distribution and excretion of drugs.

METHODS

Literature on ADME and regulatory guidelines of relevance in drug development of small molecules has been gathered.

RESULTS

Non-human primates (monkeys) are the species that is closest to humans in terms of genetic homology. Dogs have an advantage due to the ready availability of comprehensive background data for toxicological safety assessment and dogs are easy to handle. Pigs have been used less than dogs and monkeys as a model in safety assessment of drug candidates. However, when a drug candidate is metabolised by aldehyde oxidase (AOX1), N-acetyltransferases (NAT1 and NAT2) or cytochrome (CYP2C9-like) enzymes which are not expressed in dogs, but are present in pigs, this species may be a better choice than dogs, provided that adequate exposure can be obtained in pigs. Conversely, pigs might not be the right choice if sulfation, involving 3-phospho-adenosyl-5-phosphosulphate sulphotransferase (PAPS) is an important pathway in the human metabolism of a drug candidate.

DISCUSSION

In general, the species selection should be based on comparison between in vitro studies with human cell-based systems and animal-cell-based systems. Results from pharmacokinetic studies are also important for decision-making by establishing the obtainable exposure level in the species. Access to genetically humanized mouse models and highly sensitive analytical methods (accelerator mass spectrometry) makes it possible to improve the chance of finding all metabolites relevant for humans before clinical trials have been initiated and, if necessary, to include another animal species before long term toxicity studies are initiated. In conclusion, safety testing can be optimized by applying knowledge about species ADME differences and utilising advanced analytical techniques.

Mitigation of Methimazole-Induced Hepatic Injury by Taurine in Mice

Methimazole is the most widely prescribed antithyroid medication in humans. However, hepatotoxicity is a deleterious adverse effect associated with methimazole administration. No specific protective agent has been developed against this complication yet. This study was designed to investigate the role of taurine as a hepatoprotective agent against methimazole-induced liver injury in mice. Different reactive metabolites were proposed to be responsible for methimazole hepatotoxicity. Hence, methimazole-induced liver injury was investigated in intact and/or enzyme-induced animals in the current investigation. Animals were treated with methimazole (200 mg/kg, by gavage), and hepatic injury induced by this drug was investigated in intact and/or enzyme-induced groups. Markers such as lipid peroxidation, hepatic glutathione content, alanine aminotransferase (ALT) and alkaline phosphatase (ALP) in plasma, and histopathological changes in the liver of animals were monitored after drug administration. Methimazole caused liver injury as revealed by increased plasma ALT. Furthermore, a significant amount of lipid peroxidation was detected in the drug-treated animals, and hepatic glutathione reservoirs were depleted. Methimazole-induced hepatotoxicity was more severe in enzyme-induced mice. The above-mentioned alterations in hepatotoxicity markers were endorsed by significant histopathological changes in the liver. Taurine administration (1 g/kg, i.p.) effectively alleviated methimazole-induced liver injury in both intact and/or enzyme-induced animals.

Glycodeoxycholic acid levels as prognostic biomarker in acetaminophen-induced acute liver failure patients

Acetaminophen (APAP)-induced acute liver failure (ALF) remains a major clinical problem. Although a majority of patients recovers after severe liver injury, a subpopulation of patients proceeds to ALF. Bile acids are generated in the liver and accumulate in blood during liver injury, and as such, have been proposed as biomarkers for liver injury and dysfunction. The goal of this study was to determine whether individual bile acid levels could determine outcome in patients with APAP-induced ALF (AALF). Serum bile acid levels were measured in AALF patients using mass spectrometry. Bile acid levels were elevated 5-80-fold above control values in injured patients on day 1 after the overdose and decreased over the course of hospital stay. Interestingly, glycodeoxycholic acid (GDCA) was significantly increased in non-surviving AALF patients compared with survivors. GDCA values obtained at peak alanine aminotransferase (ALT) and from day 1 of admission indicated GDCA could predict survival in these patients by receiver-operating characteristic analysis (AUC = 0.70 for day 1, AUC = 0.68 for peak ALT). Of note, AALF patients also had significantly higher levels of serum bile acids than patients with active cholestatic liver injury. These data suggest measurements of GDCA in this patient cohort modestly predicted outcome and may serve as a prognostic biomarker. Furthermore, accumulation of bile acids in serum or plasma may be a result of liver cell dysfunction and not cholestasis, suggesting elevation of circulating bile acid levels may be a consequence and not a cause of liver injury.

Timosaponin A3 induces hepatotoxicity in rats through inducing oxidative stress and down-regulating bile acid transporters

Aim:

To investigate the mechanisms underlying the hepatotoxicity of timosaponin A3 (TA3), a steroidal saponin from Anemarrhena asphodeloides, in rats.

Methods:

Male SD rats were administered TA3 (100 mg·kg⁻¹·d⁻¹, po) for 14 d, and the blood and bile samples were collected after the final administration. The viability of a sandwich configuration of cultured rat hepatocytes (SCRHs) was assessed using WST-1. Accumulation and biliary excretion index (BEI) of d8-TCA in SCRHs were determined with LC-MS/MS. RT-PCR and Western blot were used to analyze the expression of relevant genes and proteins. ROS and ATP levels, and mitochondrial membrane potential (MMP) were measured. F-actin cytoskeletal integrity was assessed under confocal microscopy.

Results:

TA3 administration in rats significantly elevated the total bile acid in serum, and decreased bile acid (BA) component concentrations in bile. TA3 inhibited the viability of the SCRHs with an IC₅₀ value of 15.21±1.73 μmol/L. Treatment of the SCRHs with TA3 (1–10 μmol/L) for 2 and 24 h dose-dependently decreased the accumulation and BEI of d8-TCA. The TA3 treatment dose-dependently decreased the expression of BA transporters Ntcp, Bsep and Mrp2, and BA biosynthesis related Cyp7a1 in hepatocytes. Furthermore, the TA3 treatment dose-dependently increased ROS generation and HO-1 expression, decreased the ATP level and MMP, and disrupted F-actin in the SCRHs. NAC (5 mmol/L) significantly ameliorated TA3-induced effects in the SCRHs, whereas mangiferin (10–200 μg/mL) almost blocked TA3-induced ROS generation.

Conclusion:

TA3 triggers liver injury through inducing ROS generation and suppressing the expression of BA transporters. Mangiferin, an active component in Anemarrhena, may protect hepatocytes from TA3-induced hepatotoxicity.

Cephalexin induced cholestatic jaundice

Cephalexin is a very commonly prescribed orally administered antibiotic which has many potential side effects. Amongst these cholestatic jaundice has been infrequently reported as an adverse reaction. We present a case of a 57-year-old male who exhibited features of cholestatic jaundice including elevated liver function tests (LFTs) after taking cephalexin and showed improvement on removal of the offending agent. During this time he was symptomatically treated with cholestyramine. Complete resolution of LFTs was seen in four weeks. Cephalexin induced cholestasis is rare and hence requires a high degree of clinical suspicion for prompt diagnosis and treatment.

Atypical causes of cholestasis

Cholestatic liver disease consists of a variety of disorders. Primary sclerosing cholangitis and primary biliary cirrhosis are the most commonly recognized cholestatic liver disease in the adult population, while biliary atresia and Alagille syndrome are commonly recognized in the pediatric population. In infants, the causes are usually congenital or inherited. Even though jaundice is a hallmark of cholestasis, it is not always seen in adult patients with chronic liver disease. Patients can have “silent” progressive cholestatic liver disease for years prior to development of symptoms such as jaundice and pruritus. In this review, we will discuss some of the atypical causes of cholestatic liver disease such as benign recurrent intrahepatic cholestasis, progressive familial intrahepatic cholestasis, Alagille Syndrome, biliary atresia, total parenteral nutrition induced cholestasis and cholestasis secondary to drug induced liver injury.

Withholding parenteral nutrition during critical illness increases plasma bilirubin but lowers the incidence of biliary sludge

Cholestatic liver dysfunction (CLD) and biliary sludge often occur during critical illness and are allegedly aggravated by parenteral nutrition (PN). Delaying initiation of PN beyond day 7 in the intensive care unit (ICU) (late PN) accelerated recovery as compared with early initiation of PN (early PN). However, the impact of nutritional strategy on biliary sludge and CLD has not been fully characterized. This was a preplanned subanalysis of a large randomized controlled trial of early PN versus late PN (n = 4,640). In all patients plasma bilirubin (daily) and liver enzymes (alanine aminotransferase [ALT], aspartate aminotransferase [AST], gamma-glutamyl transpeptidase [GGT], alkaline phosphatase [ALP], twice weekly; n = 3,216) were quantified. In a random predefined subset of patients, plasma bile acids (BAs) were also quantified at baseline and on days 3, 5, and last ICU-day (n = 280). Biliary sludge was ultrasonographically evaluated on ICU-day 5 (n = 776). From day 1 after randomization until the end of the 7-day intervention window, bilirubin was higher in the late PN than in the early PN group (P < 0.001). In the late PN group, as soon as PN was started on day 8 bilirubin fell and the two groups became comparable. Maximum levels of GGT, ALP, and ALT were lower in the late PN group (P < 0.01). Glycine/taurine-conjugated primary BAs increased over time in ICU (P < 0.01), similarly for the two groups. Fewer patients in the late PN than in the early PN group developed biliary sludge on day 5 (37% versus 45%; P = 0.04).

CONCLUSION

Tolerating substantial caloric deficit by withholding PN until day 8 of critical illness increased plasma bilirubin but reduced the occurrence of biliary sludge and lowered GGT, ALP, and ALT. These results suggest that hyperbilirubinemia during critical illness does not necessarily reflect cholestasis and instead may be an adaptive response that is suppressed by early PN.

In silico identification and in vitro validation of potential cholestatic compounds through 3D ligand-based pharmacophore modeling of BSEP inhibitors

Drug-induced cholestasis is a frequently observed side effect of drugs and is often caused by an unexpected interaction with the bile salt export pump (BSEP/ABCB11). BSEP is the key membrane transporter responsible for the transport of bile acids from hepatocytes into bile. Here, we developed a pharmacophore model that describes the molecular features of compounds associated with BSEP inhibitory activity. To generate input and validation data sets, in vitro experiments with membrane vesicles overexpressing human BSEP were used to assess the effect of compounds (50 μM) on BSEP-mediated (3)H-taurocholic acid transport. The model contains two hydrogen bond acceptor/anionic features, two hydrogen bond acceptor vector features, four hydrophobic/aromatic features, and exclusion volumes. The pharmacophore was validated against a set of 59 compounds, including registered drugs. The model recognized 9 out of 12 inhibitors (75%), which could not be identified based on general parameters, such as molecular weight or SlogP, alone. Finally, the model was used to screen a virtual compound database. A number of compounds found via virtual screening were tested and displayed statistically significant BSEP inhibition, ranging from 13 ± 1% to 67 ± 7% of control (P < 0.05). In conclusion, we developed and validated a pharmacophore model that describes molecular features found in BSEP inhibitors. The model may be used as an in silico screening tool to identify potentially harmful drug candidates at an early stage in drug development.

Hepatobiliary transporters in drug-induced cholestasis: a perspective on the current identifying tools

INTRODUCTION

Impaired bile formation leads to the accumulation of cytotoxic bile salts in hepatocytes and, consequently, cholestasis and severe liver disease. Knowledge of the role of hepatobiliary transporters, especially the bile salt export pump (BSEP), in the pathogenesis of cholestasis is continuously increasing.

AREAS COVERED

This review provides an introduction into the role of these transport proteins in bile formation. It addresses the clinical relevance and pathophysiologic consequences of altered functions of these transporters by genetic mutations and drugs. In particular, the current practical aspects of identification and mitigation of drug candidates with liver liabilities employed during drug development, with an emphasis on preclinical screening for BSEP interaction, are discussed.

EXPERT OPINION

Within the potential pathogenetic mechanisms of acquired cholestasis, the inhibition of BSEP by drugs is well established. Interference of a new compound with BSEP transport activity should raise a warning sign to conduct follow-up experiments and to monitor liver function during clinical development. A combination of in vitro screening for transport interaction, in silico predicting models, and consideration of physicochemical and metabolic properties should lead to a more efficient screening of potential liver liability.

Review article: controversies in the management of primary biliary cirrhosis and primary sclerosing cholangitis

BACKGROUND

Despite considerable advances over the last two decades in the molecular understanding of cholestasis and cholestatic liver disease, little improvement has been made in diagnostic tools and therapeutic strategies.

AIMS

To critically review controversial aspects of the scientific basis for common clinical practice in primary biliary cirrhosis (PBC) and primary sclerosing cholangitis (PSC) and to discuss key ongoing challenges to improve patient management.

METHODS

We performed a literature search using PubMed and by examining the reference lists of relevant review articles related to the clinical management of PBC and PSC. Articles were considered on the background of the European Association for the Study of the Liver (EASL) and the American Association for the Study of Liver Diseases (AASLD) practice guidelines and clinical experience of the authors.

RESULTS

Ongoing challenges in PBC mainly pertain to the improvement of medical therapy, particularly for patients with a suboptimal response to ursodeoxycholic acid. In PSC, development of medical therapies and sensitive screening protocols for cholangiocarcinoma represent areas of intense research. To rationally improve patient management, a better understanding of pathogenesis, including complications like pruritis and fatigue, is needed and there is a need to identify biomarker end-points for treatment effect and prognosis. Timing of liver transplantation and determining optimal regimens of immunosuppression post-liver transplantation will also benefit from better appreciation of pre-transplant disease mechanisms.

CONCLUSION

Controversies in the management of PBC and PSC relate to topics where evidence for current practice is weak and further research is needed.

An integrated proteomic and transcriptomic approach to understanding azathioprine- induced hepatotoxicity in rat primary hepatocytes

Azathioprine, an immunosuppressant, has gained a prominent position in the clinic for prevention of graft rejection in organ transplants, as well as dermatological autoimmune diseases. However, according to a number of research reports, hepatotoxicity, as one of the side effects, is a major obstacle in azathioprine therapy. In this study, an integrated toxicoproteomic and toxicotranscriptomic analysis was performed using rat primary hepatocytes, in order to gain insight into the in-depth pathway map related to azathioprine-induced hepatotoxicity. For proteomic and transcriptomic analysis, rat primary hepatocytes were exposed to azathioprine at IC20 concentration for 24 h. In particular, 2D LC-MS/MS and informatics-assisted label-free strategy for proteomic analysis were applied in order to increase the number of identified proteins and to improve the confidence of the quantitation results. Among 119 differentially identified protein species, 69 were upregulated and 50 were downregulated in the azathioprine-treated group. At the mRNA level, results of transcriptomic analysis showed increased transcription of 340 genes and decreased transcription of 63 genes in the azathioprine-treated group. Based on the analysis of transcriptomic and proteomic results using the DAVID program, drug metabolism/oxidative stress enzymes, xenobiotic metabolism by cytochrome P450, fatty acid metabolism, primary bile acid biosynthesis, contraction, inflammation metabolism, and mitogen-activated protein kinase (MAPK) kinase (ERK/JNK/p38 kinase) pathways were affected in azathioprine-treated hepatotoxicity. The effects on genes and proteins related to several important pathways were confirmed by real-time PCR and immunoblot analysis, respectively. This study is the first to report on relevant pathways related to azathioprine-induced hepatotoxicity through performance of integrated transcriptomic and proteomic analyses.

Bile formation and secretion

Bile is a unique and vital aqueous secretion of the liver that is formed by the hepatocyte and modified down stream by absorptive and secretory properties of the bile duct epithelium. Approximately 5% of bile consists of organic and inorganic solutes of considerable complexity. The bile-secretory unit consists of a canalicular network which is formed by the apical membrane of adjacent hepatocytes and sealed by tight junctions. The bile canaliculi (∼1 μm in diameter) conduct the flow of bile countercurrent to the direction of portal blood flow and connect with the canal of Hering and bile ducts which progressively increase in diameter and complexity prior to the entry of bile into the gallbladder, common bile duct, and intestine. Canalicular bile secretion is determined by both bile salt-dependent and independent transport systems which are localized at the apical membrane of the hepatocyte and largely consist of a series of adenosine triphosphate-binding cassette transport proteins that function as export pumps for bile salts and other organic solutes. These transporters create osmotic gradients within the bile canalicular lumen that provide the driving force for movement of fluid into the lumen via aquaporins. Species vary with respect to the relative amounts of bile salt-dependent and independent canalicular flow and cholangiocyte secretion which is highly regulated by hormones, second messengers, and signal transduction pathways. Most determinants of bile secretion are now characterized at the molecular level in animal models and in man. Genetic mutations serve to illuminate many of their functions.

Role of hepatic efflux transporters in regulating systemic and hepatocyte exposure to xenobiotics

Hepatic efflux transporters include numerous well-known and emerging proteins localized to the canalicular or basolateral membrane of the hepatocyte that are responsible for the excretion of drugs into the bile or blood, respectively. Altered function of hepatic efflux transporters due to drug-drug interactions, genetic variation, and/or disease states may lead to changes in xenobiotic exposure in the hepatocyte and/or systemic circulation. This review focuses on transport proteins involved in the hepatocellular efflux of drugs and metabolites, discusses mechanisms of altered transporter function as well as the interplay between multiple transport pathways, and highlights the importance of considering intracellular unbound concentrations of transporter substrates and/or inhibitors. Methods to evaluate hepatic efflux transport and predict the effects of impaired transporter function on systemic and hepatocyte exposure are discussed, and the sandwich-cultured hepatocyte model to evaluate comprehensively the role of hepatic efflux in the hepatobiliary disposition of xenobiotics is characterized.

Hypoxic liver injury and cholestasis in critically ill patients

PURPOSE OF REVIEW

Liver dysfunction frequently complicates the clinical picture of critical illness and leads to increased morbidity and mortality. The purpose of this review is to characterize the most frequent patterns of liver dysfunction at the intensive care unit, cholestasis and hypoxic liver injury (HLI), and to illustrate its clinical impact on outcome in critically ill patients.

RECENT FINDINGS

Liver dysfunction at the intensive care unit can be divided into two main patterns: cholestatic and HLI, also known as ischemic hepatitis or shock liver. Both hepatic dysfunctions occur frequently and early in critical illness. Major issues are the early recognition and subsequent initiation of therapeutic measures.

SUMMARY

Clinical awareness of the liver not only as a victim, but also as a trigger of multiorgan failure is of central clinical importance. Physicians have to identify the underlying factors that contribute to its development to initiate curative measures as early as possible.

Integrative analysis of proteomic and transcriptomic data for identification of pathways related to simvastatin-induced hepatotoxicity

Hepatocytes are used widely as a cell model for investigation of xenobiotic metabolism and the toxic mechanism of drugs. Simvastatin is the first statin drug used extensively in clinical practice for control of elevated cholesterol or hypercholesterolemia. However, it has also been reported to cause adverse effects in liver due to cellular damage. In this study, for proteomic and transcriptomic analysis, rat primary hepatocytes were exposed to simvastatin at IC20 concentration for 24 h. Among a total of 607 differentially expressed proteins, 61 upregulated and 29 downregulated proteins have been identified in the simvastatin-treated group. At the mRNA level, results of transcriptomic analysis revealed 206 upregulated and 41 downregulated genes in the simvastatin-treated group. Based on results of transcriptomic and proteomic analysis, NRF2-mediated oxidative stress response, xenobiotics by metabolism of cytochrome P450, fatty acid metabolism, bile metabolism, and urea cycle and inflammation metabolism pathways were focused using IPA software. Genes (FASN, UGT2B, ALDH1A1, CYP1A2, GSTA2, HAP90, IL-6, IL-1, FABP4, and ABC11) and proteins (FASN, CYP2D1, UG2TB, ALDH1A1, GSTA2, HSP90, FABP4, and ABCB11) related to several important pathways were confirmed by real-time PCR andWestern blot analysis, respectively. This study will provide new insight into the potential toxic pathways induced by simvastatin.

An updated review on drug-induced cholestasis: mechanisms and investigation of physicochemical properties and pharmacokinetic parameters

Drug-induced cholestasis is an important form of acquired liver disease and is associated with significant morbidity and mortality. Bile acids are key signaling molecules, but they can exert toxic responses when they accumulate in hepatocytes. This review focuses on the physiological mechanisms of drug-induced cholestasis associated with altered bile acid homeostasis due to direct (e.g., bile acid transporter inhibition) or indirect (e.g., activation of nuclear receptors, altered function/expression of bile acid transporters) processes. Mechanistic information about the effects of a drug on bile acid homeostasis is important when evaluating the cholestatic potential of a compound, but experimental data often are not available. The relationship between physicochemical properties, pharmacokinetic parameters, and inhibition of the bile salt export pump among 77 cholestatic drugs with different pathophysiological mechanisms of cholestasis (i.e., impaired formation of bile vs. physical obstruction of bile flow) was investigated. The utility of in silico models to obtain mechanistic information about the impact of compounds on bile acid homeostasis to aid in predicting the cholestatic potential of drugs is highlighted.

Drug-induced cholestasis

Cholestasis caused by drugs is an important differential diagnosis in patients presenting with a biochemical cholestatic pattern. The extent of serologic tests and radiological imaging depends on the clinical context. The underlying condition of the patient and detailed information on drug use, results of rechallenge, and the documented hepatotoxicity of the drug are important to establish a diagnosis of drug-induced liver injury (DILI). Most cases of cholestatic DILI are mild, but in rare cases, ductopenia and cholestatic cirrhosis can develop. Approximately 10% of patients with cholestatic jaundice caused by drugs develop liver failure.

Genetic determinants of cholestasis

Cholestasis is an overarching term applied for conditions whereby biliary constituents are found in the circulation because of impairment to bile flow. A variety of processes can lead to cholestasis, be they acute or chronic injuries to hepatocytes, cholangiocytes, or the broader biliary tree itself. Such injuries may be driven by rare but highly informative primary genetic abnormalities, or may be seen in individuals with a prior genetic predisposition when confronted by specific environmental challenges such as drug exposure. This review provides a broad outline of some fundamental primary genetic cholestatic syndromes and an update on varying genetic predisposition underlying several acquired cholestatic processes.

The SLC10 carrier family: transport functions and molecular structure

The SLC10 family represents seven genes containing 1-12 exons that encode proteins in humans with sequence lengths of 348-477 amino acids. Although termed solute carriers (SLCs), only three out of seven (i.e. SLC10A1, SLC10A2, and SLC10A6) show sodium-dependent uptake of organic substrates across the cell membrane. These include the uptake of bile salts, sulfated steroids, sulfated thyroidal hormones, and certain statin drugs by SLC10A1 (Na(+)-taurocholate cotransporting polypeptide (NTCP)), the uptake of bile salts by SLC10A2 (apical sodium-dependent bile acid transporter (ASBT)), and uptake of sulfated steroids and sulfated taurolithocholate by SLC10A6 (sodium-dependent organic anion transporter (SOAT)). The other members of the family are orphan carriers not all localized in the cell membrane. The name "bile acid transporter family" arose because the first two SLC10 members (NTCP and ASBT) are carriers for bile salts that establish their enterohepatic circulation. In recent years, information has been obtained on their 2D and 3D membrane topology, structure-transport relationships, and on the ligand and sodium-binding sites. For SLC10A2, the putative 3D morphology was deduced from the crystal structure of a bacterial SLC10A2 analog, ASBT(NM). This information was used in this chapter to calculate the putative 3D structure of NTCP. This review provides first an introduction to recent knowledge about bile acid synthesis and newly found bile acid hormonal functions, and then describes step-by-step each individual member of the family in terms of expression, localization, substrate pattern, as well as protein topology with emphasis on the three functional SLC10 carrier members.

Membrane vesicle ABC transporter assays for drug safety assessment

The use of plasma membrane vesicles that overexpress the bile salt export pump (BSEP) or multidrug resistance-associated protein 2, 3, or 4 (MRP2-4) with an in vitro vacuum filtration system offers a rapid and reliable means for screening drug candidates for their effects on transporter function in hepatocytes and thus their potential for causing drug-induced liver injury (DILI). Comparison of transporter activity in the presence and absence of ATP allows for determination of a specific assay window for each transporter. This window is used to determine the degree to which each test compound inhibits transporter activity. This assay battery is helpful for prioritizing and rank-ordering compounds within a chemical series with respect to each other and in the context of known inhibitors of transporter activity and/or liver injury. This model can be used to influence the drug development process at an early stage and provide rapid feedback regarding the selection of compounds for advancement to in vivo safety evaluations. A detailed protocol for the high-throughput assessment of ABC transporter function is provided, including specific recommendations for curve-fitting to help ensure consistent results.

Oxidative stress plays a major role in chlorpromazine-induced cholestasis in human HepaRG cells

Drugs induce cholestasis by diverse and still poorly understood mechanisms in humans. Early hepatic effects of chlorpromazine (CPZ), a neuroleptic drug known for years to induce intrahepatic cholestasis, were investigated using the differentiated human hepatoma HepaRG cells. Generation of reactive oxygen species (ROS) was detected as early as 15 minutes after CPZ treatment and was associated with an altered mitochondrial membrane potential and disruption of the pericanalicular distribution of F-actin. Inhibition of [3H]-taurocholic acid efflux was observed after 30 minutes and was mostly prevented by N-acetyl cysteine (NAC) cotreatment, indicating a major role of oxidative stress in CPZ-induced bile acid (BA) accumulation. Moreover, 24-hour treatment with CPZ decreased messenger RNA (mRNA) expression of the two main canalicular bile transporters, bile salt export pump (BSEP) and multidrug resistance protein 3 (MDR3). Additional CPZ effects included inhibition of Na+ -dependent taurocholic cotransporting polypeptide (NTCP) expression and activity, multidrug resistance-associated protein 4 (MRP4) overexpression and CYP8B1 inhibition that are involved in BA uptake, basolateral transport, and BA synthesis, respectively. These latter events likely represent hepatoprotective responses which aim to reduce intrahepatic accumulation of toxic BA. Compared to CPZ effects, overloading of HepaRG cells with high concentrations of cholic and chenodeoxycholic acids induced a delayed oxidative stress and, similarly, after 24 hours it down-regulated BSEP and MDR3 in parallel to a decrease of NTCP and CYP8B1 and an increase of MRP4. By contrast, low BA concentrations up-regulated BSEP and MDR3 in the absence of oxidative stress.

CONCLUSION

These data provide evidence that, among other mechanisms, oxidative stress plays a major role as both a primary causal and an aggravating factor in the early CPZ-induced intrahepatic cholestasis in human hepatocytes.

In vivo visualization and quantification of (Disturbed) Oatp-mediated hepatic uptake and Mrp2-mediated biliary excretion of 99mTc-mebrofenin in mice

Hepatic transport of (99m)Tc-mebrofenin through organic anion transport protein 1a and 1b (Oatp1a/1b) and multidrug resistance protein 2 (Mrp2) was investigated by small-animal SPECT. On the basis of the results, a noninvasive method to visualize and quantify disturbances in hepatic transport is proposed.

METHODS

Friend virus B wild-type mice (untreated, bile duct-ligated, vehicle- or rifampicin-treated) and strain-matched knockout mice unable to express the uptake transporters Oatp1a/1b (Slco1a/1b(-/-)/(-/-)) or the efflux transporter Mrp2 (Abcc2(-/-)) were intravenously injected with (99m)Tc-mebrofenin (n = 3 per group). After dynamic small-animal SPECT and short CT acquisitions, time-activity curves of the liver and of the gallbladder and intestines were obtained and correlated with direct blood samples.

RESULTS

Normal hepatobiliary clearance of (99m)Tc-mebrofenin was severely impaired in the bile duct-ligated animal, as evidenced by elevated hepatic tracer levels. In Slco1a/1b(-/-)/(-/-) mice, a lower area under the curve (AUC) for the liver (P = 0.014) was obtained and no activity was detected in the gallbladder and intestines. Renal rerouting was observed, along with an increase in the blood AUC (P = 0.01). Abcc2(-/-) mice had a higher liver AUC (P = 0.009), a delayed emergence time of (99m)Tc-mebrofenin in the gallbladder (P = 0.009), and a lower AUC for the gallbladder and intestines (P = 0.001). The blood curve was similar to that of wild-type mice. (99m)Tc-mebrofenin disposition was altered after rifampicin treatments. We observed a dose-dependent delayed time point at which tracer maximized in liver, an increased AUC for liver, and a lower AUC for gallbladder and intestines (P = 0.042, 0.034, and 0.001, respectively, highest dose). Emergence in the gallbladder occurred later (P = 0.009, highest dose), and blood AUC was higher (P = 0.006).

CONCLUSION

The current study visualized and quantified hepatic uptake and biliary efflux of (99m)Tc-mebrofenin. Our results demonstrated the possibility of discriminating, on a quantitative level, between lack of functional activity of sinusoidal uptake versus that of biliary efflux transporters.

Evaluation of hepatotoxicity and cholestasis in rats treated with EtOH extract of Fructus Psoraleae

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Psoraleae (FP) has been widely used to heal skin diseases as well as osteoporosis, osteomalacia, and bone fracture. There also exist many clinical reports about FP-induced hepatotoxicity associated with acute cholestatic hepatic injury. However, the FP-induced hepatotoxicity and the underlying mechanisms remain unclear.

AIMS OF THE STUDY

The present study aims to determine the hepatotoxicity of FP in Sprague-Dawley (SD) rats and to investigate the underlying mechanisms.

MATERIALS AND METHODS

Sprague-Dawley rats of both sexes were intragastrically administered with the EtOH extract of FP (EEFP) at doses of 1.875, 1.25 and 0.625 g/kg for 28 day. Body weight, relative liver weight, biochemical analysis, histopathology, the mRNA and protein expression of Cholesterol 7α-hydroxylase (CYP7A1), farnesoid X receptor (FXR), bile-salt export pump (BSEP), multidrug resistance-associated protein 2 (MRP2), multidrug resistance-associated protein 3 (MRP3) were evaluated to study the EEFP-induced hepatotoxicity and its underlying mechanisms.

RESULTS

Many abnormalities were observed in the EEFP-treated groups including suppression of weight gain and food intake, change of some parameters in serum biochemistry, increased weight of liver, and decreased concentration of bile acid in bile. The mRNA and protein expression of CYP7A1, MRP3, MRP2, BSEP increased and the expression of FXR decreased in EEFP-treated female groups; the mRNA and protein of FXR and CYP7A1 decreased and that of the others remained the same in EEFP-treated male groups.

CONCLUSION

In conclusion, we provide evidence for the first time that EEFP can induce sex-related cholestatic hepatotoxicity, and that female rats are more sensitive to EEFP-induced hepatotoxicity, which involves the destruction of the biosynthesis and transportation of bile acid. Further investigation is still needed to uncover the mechanism of the sex-dimorphic EEFP-induced hepatotoxicity.

Optimization of the HepaRG cell model for drug metabolism and toxicity studies

The HepaRG cell line is the first human cell line able to differentiate in vitro into mature hepatocyte-like cells. Our main objective within the framework of the EEC-LIINTOP project was to optimize the use of this cell line for drug metabolism and toxicity studies, especially after repeat treatments. The main results showed that differentiated HepaRG cells: (i) retained their drug metabolism capacity (major CYPs, phase 2 enzymes, transporters and nuclear receptors) and responsiveness to prototypical inducers at relatively stable levels for several weeks at confluence. The levels of several functions, including some CYPs such as CYP3A4, were dependent on the addition of dimethyl sulfoxide in the culture medium; (ii) sustained the different types of chemical-induced hepatotoxicity, including steatosis, phospholipidosis and cholestasis, after acute and/or repeat treatment with reference drugs. In particular, drug-induced vesicular steatosis was demonstrated in vitro for the first time. In conclusion, our results from the LIINTOP project, together with other studies reported concomitantly or more recently in the literature, support the conclusion that the metabolically competent human HepaRG cells represent a surrogate to primary human hepatocytes for investigating drug metabolism parameters and both acute and chronic effects of xenobiotics in human liver.

[N-methyl-11C]cholylsarcosine, a novel bile acid tracer for PET/CT of hepatic excretory function: radiosynthesis and proof-of-concept studies in pigs

Excretion of conjugated bile acids into bile is an essential function of the liver, and impairment of canalicular bile acid secretion leads to cholestatic liver injury. However, hepatic excretory function cannot be quantified in vivo because of the lack of suitable methods. Cholylsarcosine is an analog of the endogenous bile acid conjugate cholylglycine and exhibits characteristics in vivo that led us to hypothesize that the (11)C-labeled form, that is, [N-methyl-(11)C]cholylsarcosine ((11)C-cholylsarcosine), would be a suitable PET tracer for quantification of hepatic excretory function.

METHODS

A method for radiosynthesis of (11)C-cholylsarcosine was developed involving (11)C-methylation of glycine followed by conjugation with cholic acid. Blood-to-liver uptake and liver-to-bile excretion were investigated in vivo by dynamic (11)C-cholylsarcosine PET/CT of 2 anesthetized pigs. In pig 1, a second dynamic (11)C-cholylsarcosine PET/CT examination was preceded by a high dose of the endogenous bile acid conjugate cholyltaurine to investigate possible inhibition of the transhepatocellular transport of (11)C-cholylsarcosine. In pig 2, a second (11)C-cholylsarcosine administration was given to determine the biodistribution of the tracer by means of 5 successive whole-body PET/CT recordings. Possible formation of (11)C-metabolites was investigated by analysis of blood and bile samples from a third pig.

RESULTS

The radiochemical yield was 13% ± 3% (n = 7, decay-corrected) and up to 1.1 GBq of (11)C-cholylsarcosine was produced with a radiochemical purity greater than 99%. PET/CT studies showed rapid blood-to-liver uptake and liver-to-bile excretion of (11)C-cholylsarcosine, with radioactivity concentrations being more than 90 times higher in the bile ducts than in liver tissue. Cholyltaurine inhibited the transhepatocellular transport of (11)C-cholylsarcosine, indicating that the tracer is transported by one or more of the same hepatic transporters as cholyltaurine. (11)C-cholylsarcosine underwent an enterohepatic circulation and reappeared in liver tissue and bile ducts after approximately 70 min. There were no detectable (11)C-metabolites in the plasma or bile samples, indicating that the novel conjugated bile acid (11)C-cholylsarcosine was not metabolized in the liver or in the intestines. The effective absorbed dose of (11)C-cholylsarcosine was 4.4 μSv/MBq.

CONCLUSION

We have synthesized a novel conjugated bile acid analog, (11)C-cholylsarcosine, and PET/CT studies on anesthetized pigs showed that the hepatic handling of tracer uptake from blood and excretion into the bile was comparable to that for the endogenous bile acid cholyltaurine. This tracer may be valuable for future studies of normal and pathologic hepatic excretory functions in humans.

Xenobiotic-induced liver injury and fibrosis

INTRODUCTION

Many different drugs and xenobiotics (chemical compounds foreign to an organism) can injure the bile duct epithelium and cause inflammatory bile duct diseases (cholangiopathies) ranging from transient cholestasis to vanishing bile duct syndrome, sclerosing cholangitis with development of biliary fibrosis and cirrhosis. Animal models of xenobiotic-induced liver injury have provided major mechanistic insights into the molecular mechanisms of xenobiotic-induced cholangiopathies and biliary fibrosis including primary biliary cirrhosis and primary sclerosing cholangitis.

AREAS COVERED

In this review, the authors discuss the basic principles of xenobiotic-induced liver and bile duct injury and biliary fibrosis with emphasis on animal models. A PubMed search was performed using the search terms "xenobiotic," "liver injury," "cholestasis," and "biliary fibrosis." Reference lists of retrieved articles were also searched for relevant literature.

EXPERT OPINION

Xenobiotic-induced cholangiopathies are underestimated and frequently overlooked medical conditions due to their often transient nature. However, biliary disease may progress to vanishing bile duct syndrome, biliary fibrosis, and cirrhosis. Moreover, xenobiotics may prime the liver for subsequent liver disease by other agents and may also contribute to the development of hepatobiliary cancer though interaction with resident stem cells.