Sandwich-cultured hepatocytes: an in vitro model to evaluate hepatobiliary transporter-based drug interactions and hepatotoxicity

A perspective on efflux transport proteins in the liver

Detailed knowledge regarding the influence of hepatic transport proteins on drug disposition has advanced at a rapid pace over the past decade. Efflux transport proteins located in the basolateral and apical (canalicular) membranes of hepatocytes play an important role in the hepatic elimination of many endogenous and exogenous compounds, including drugs and metabolites. This review focuses on the role of these efflux transporters in hepatic drug excretion. The impact of these proteins as underlying factors for disease is highlighted, and the importance of hepatic efflux proteins in the efficacy and toxicity of drugs is discussed. In addition, a brief overview of methodology to evaluate the function of hepatic efflux transport proteins is provided. Current challenges in predicting the impact of altered efflux protein function on systemic, intestinal, and hepatocyte exposure to drugs and metabolites are highlighted.

Structural influence of isothiocyanates on expression of cytochrome P450, phase II enzymes, and activation of Nrf2 in primary rat hepatocytes

Primary cultures of rat hepatocytes were used to investigate whether and how eight isothiocynates (ITCs) with different chemical structures (the aromatic benzyl, 4-hydroxybenzyl, phenethyl isothiocyanates and the aliphatic allyl, napin, iberin, raphasatin isothiocyanates and sulforaphane) derived from hydrolyzed glucosinolates, were able to modulate cytochrome P450 (CYP) and antioxidant/detoxifying enzymes and to activate the Nrf2 transcription factor. The aromatic ITCs at 40 μM markedly increased the transcription of CYP1A1 and 1A2 mRNA and increased the associated ethoxyresorufin O-deethylase (EROD) activity after 24 h of treatment. By contrast, the aliphatic ITCs (40 μM) decreased CYP1A1 and 1A2 transcription, together with the corresponding EROD activity. The same treatment also caused a striking and similar transcriptional repression of CYP3A2, and the corresponding benzyloxyquinoline debenzylase activity in response to all the ITCs tested. In the same culture conditions, most of the antioxidant/detoxifying enzymes were significantly up-regulated by 40μM ITCs. In particular, NAD(P)H:quinone oxidoreductase and heme oxygenase-1 were induced, although to different levels, at transcriptional, protein and/or activity levels by all the ITCs. However, glutathione S-transferase activity was not induced by the allyl, benzyl, and 4-hydroxybenzyl ITCs, glutathione reductase activity was not induced by benzyl, and 4-hydroxybenzyl ITCs and catalase activity was not induced by allyl ITC. As for the Nrf2 transcription factor, a partial translocation of its protein from the cytosol to the nucleus was revealed by immunoblotting after 1h of treatment for all the ITCs tested. The ability of ITCs to induce the antioxidant and phase II enzymes did not appear to be affected by their hydrophilicity or other structural factors. Taken together, these results show that these ITCs are effective inducers of ARE/Nrf2-regulated antioxidant/detoxifying genes and have the potential to inhibit, at least in rat liver, the bioactivation of carcinogens dependent on CYP3A2 catalysis.

The HepaRG cell line: a unique in vitro tool for understanding drug metabolism and toxicology in human

INTRODUCTION

HepaRG is a unique cell line showing a great plasticity, which differentiates to both canaliculae-like and hepatocyte-like cells. The long-term stability of key cell functions, for example, the drug-metabolizing cytochrome P450 (CYP) enzyme activities, in culture is especially useful in drug metabolism, disposition and toxicity studies.

AREAS COVERED

This review describes features of the HepaRG cells focusing on drug-metabolizing enzymes and drug transporters, their functionality and regulation. Several applications in drug discovery studies are discussed and the use of HepaRG, as a human relevant predictive in vitro CYP induction model, is described. In addition, promising studies using HepaRG cells for understanding liver toxicity mechanisms by drug compounds are also discussed.

EXPERT OPINION

HepaRG cells exhibit features which make them useful as an in vitro model for drug metabolism, disposition and toxicity studies, and could, for many studies, replace the requirement for primary human hepatocytes. Care should be taken since HepaRG cells are of a specific genotype which is reflected in the expression of drug processing proteins. The finding that HepaRG cells form tight junctions provides the basis for formation of functional canalicular structures and this should be investigated further to aid development of human relevant hepatic in vitro 2D and 3D models.

Models to predict unbound intracellular drug concentrations in the presence of transporters

Knowledge of free drug intracellular concentration is necessary to predict the impacts of drugs on intracellular targets. The goal of this study was to develop models to predict free intracellular drug concentrations in the presence of apical efflux transporters. The apical efflux transporter P-glycoprotein (P-gp), encoded by human gene multidrug resistance 1 (MDR1), was studied. Apparent permeabilities for 10 compounds in Madin-Darby canine kidney (MDCK) and MDR1-MDCK cell monolayers were obtained experimentally. Six of these compounds were evaluated additionally in the presence of the P-gp inhibitor cyclosporine A. A three-compartment model was developed, and passive and apical efflux clearances (CL(d) and CL(ae), respectively) were estimated. Endogenous canine transporters also were delineated. The three-compartment model was unable to simulate experimentally observed lag times and exhibited systematic bias across the simulations. Next, a five-compartment model with explicit membrane compartments was developed. This model resulted in lower systematic errors and simulated the lag time observed experimentally. Apical efflux was modeled out of the cell or out of the membrane. The five-compartment model with apical efflux out of the membrane predicted marked differences in unbound intracellular concentrations between the apical-to-basolateral and the basolateral-to-apical directions. Upon apical drug addition, large decreases in intracellular concentrations were observed with the efflux transporter. No such difference was predicted upon basolateral drug addition. This is consistent with experimental differences in the impact of P-gp on hepatic and brain distribution and supports the hypothesis that apical efflux occurs out of the apical membrane.

Comparisons between in vitro whole cell imaging and in vivo zebrafish-based approaches for identifying potential human hepatotoxicants earlier in pharmaceutical development

Drug-induced liver injury (DILI) is a major cause of attrition during both the early and later stages of the drug development and marketing process. Reducing or eliminating drug-induced severe liver injury, especially those that lead to liver transplants or death, would be tremendously beneficial for patients. Therefore, developing new pharmaceuticals that have the highest margins and attributes of hepatic safety would be a great accomplishment. Given the current low productivity of pharmaceutical companies and the high costs of bringing new medicines to market, any early screening assay(s) to identify and eliminate pharmaceuticals with the potential to cause severe liver injury in humans would be of economic value as well. The present review discusses the background, proof-of-concept, and validation studies associated with high-content screening (HCS) by two major pharmaceutical companies (Pfizer Inc and Jansen Pharmaceutical Companies of Johnson & Johnson) for detecting compounds with the potential to cause human DILI. These HCS assays use fluorescent-based markers of cell injury in either human hepatocytes or HepG2 cells. In collaboration with Evotec, an independent contract lab, these two companies also independently evaluated larval zebrafish as an early-stage in vivo screen for hepatotoxicity in independently conducted, blinded assessments. Details about this model species, the need for bioanalysis, and, specifically, the outcome of the phenotypic-based zebrafish screens are presented. Comparing outcomes in zebrafish against both HCS assays suggests an enhanced detection for hepatotoxicants of most DILI concern when used in combination with each other, based on the U.S. Food and Drug Administration DILI classification list.

Endogenous bile acid disposition in rat and human sandwich-cultured hepatocytes

Sandwich-cultured hepatocytes (SCH) are used commonly to investigate hepatic transport protein-mediated uptake and biliary excretion of substrates. However, little is known about the disposition of endogenous bile acids (BAs) in SCH. In this study, four endogenous conjugated BAs common to rats and humans [taurocholic acid (TCA), glycocholic acid (GCA), taurochenodeoxycholic acid (TCDCA), and glycochenodeoxycholic acid (GCDCA)], as well as two BA species specific to rodents (α- and β-tauromuricholic acid; α/β TMCA), were profiled in primary rat and human SCH. Using B-CLEAR® technology, BAs were measured in cells+bile canaliculi, cells, and medium of SCH by LC-MS/MS. Results indicated that, just as in vivo, taurine-conjugated BA species were predominant in rat SCH, while glycine-conjugated BAs were predominant in human SCH. Total intracellular BAs remained relatively constant over days in culture in rat SCH. Total BAs in control (CTL) cells+bile, cells, and medium were approximately 3.4, 2.9, and 8.3-fold greater in human than in rat. The estimated intracellular concentrations of the measured total BAs were 64.3±5.9 μM in CTL rat and 183±56 μM in CTL human SCH, while medium concentrations of the total BAs measured were 1.16±0.21 μM in CTL rat SCH and 9.61±6.36 μM in CTL human SCH. Treatment of cells for 24h with 10 μM troglitazone (TRO), an inhibitor of the bile salt export pump (BSEP) and the Na⁺-taurocholate cotransporting polypeptide (NTCP), had no significant effect on endogenous BAs measured at the end of the 24-h culture period, potentially due to compensatory mechanisms that maintain BA homeostasis. These data demonstrate that BAs in SCH are similar to in vivo, and that SCH may be a useful in vitro model to study alterations in BA disposition if species differences are taken into account.

Differential modulation of cytochrome P450 activity and the effect of 1-aminobenzotriazole on hepatic transport in sandwich-cultured human hepatocytes

Sandwich-cultured human hepatocytes (SCHH) have been widely used for in vitro assessments of biliary clearance. However, the modulation of metabolism enzymes has not been fully evaluated in this system. The present study was therefore undertaken to determine the activity of cytochrome P450 (P450) 1A2, 2C8, 2C9, 2C19, 2D6, and 3A and to evaluate the impact of 1-aminobenzotriazole (ABT) on hepatic uptake and biliary excretion in SCHH. The SCHH maintained integrity and viability as determined by lactate dehydrogenase release and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium assays conducted over the culture period. Although all assessed P450 activity decreased in day 2 SCHH, the extent of the decrease and the subsequent rebound in activity varied across the different isoforms. Day 5 CYP1A2 activity was approximately 2.5-fold higher than day 1 activity, whereas the CYP3A and CYP2C9 activities were 90 and 60% of the day 1 levels, respectively. In contrast, the initial CYP2C8, CYP2C19, and CYP2D6 activity losses did not rebound over the 5-day culture period. Furthermore, ABT was not found to have an effect, whether directly or indirectly as a P450 inactivator, with respect to the hepatic transport of rosuvastatin, atrovastatin, and midazolam in SCHH. Taken together, these results suggest that the SCHH model is a reliable tool to characterize hepatic uptake and biliary excretion. Due to the differential modulation of P450 activity, SCHH may not be considered a suitable tool for metabolic stability assessments with compounds predominantly cleared by certain P450 enzymes.

Cross-species comparisons of transcriptomic alterations in human and rat primary hepatocytes exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

A toxicogenomics approach was used to qualitatively and quantitatively compare the gene expression changes in human and rat primary hepatocytes exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Hepatocytes from five individual rats and five individual humans were exposed for 24 h to 11 concentrations of TCDD ranging from 0.00001 to 100nM and a vehicle control. Gene expression changes were analyzed using whole-genome microarrays containing 13,002 orthologs. Significant changes in expression of individual orthologs at any concentration (fold change [FC] ± 1.5 and false discovery rate < 0.05) were higher in the rat (1547) compared with human hepatocytes (475). Only 158 differentially expressed orthologs were common between rats and humans. Enrichment analysis was performed on the differentially expressed orthologs in each species with 49 and 34 enriched human and rat pathways, respectively. Only 12 enriched pathways were shared between the two species. The results demonstrate significant cross-species differences in expression at both the gene and pathway level. Benchmark dose analysis of gene expression changes showed an average 18-fold cross-species difference in potency among differentially expressed orthologs with the rat more sensitive than the human. Similar cross-species differences in potency were observed for signaling pathways. Using the maximum FC in gene expression as a measure of efficacy, the human hepatocytes showed on average a 20% lower efficacy among the individual orthologs showing differential expression. The results provide evidence for divergent cross-species gene expression changes in response to TCDD and are consistent with epidemiological and clinical evidence showing humans to be less sensitive to TCDD-induced hepatotoxicity.

A semiphysiologically based pharmacokinetic modeling approach to predict the dose-exposure relationship of an antiparasitic prodrug/active metabolite pair

Dose selection during antiparasitic drug development in animal models and humans traditionally has relied on correlations between plasma concentrations obtained at or below maximally tolerated doses that are efficacious. The objective of this study was to improve the understanding of the relationship between dose and plasma/tissue exposure of the model antiparasitic agent, pafuramidine, using a semiphysiologically based pharmacokinetic (semi-PBPK) modeling approach. Preclinical and clinical data generated during the development of pafuramidine, a prodrug of the active metabolite, furamidine, were used. A whole-body semi-PBPK model for rats was developed based on a whole-liver PBPK model using rat isolated perfused liver data. A whole-body semi-PBPK model for humans was developed on the basis of the whole-body rat model. Scaling factors were calculated using metabolic and transport clearance data generated from rat and human sandwich-cultured hepatocytes. Both whole-body models described pafuramidine and furamidine disposition in plasma and predicted furamidine tissue (liver and kidney) exposure and excretion profiles (biliary and renal). The whole-body models predicted that the intestine contributes significantly (30-40%) to presystemic furamidine formation in both rats and humans. The predicted terminal elimination half-life of furamidine in plasma was 3- to 4-fold longer than that of pafuramidine in rats (170 versus 47 h) and humans (64 versus 19 h). The dose-plasma/tissue exposure relationship for the prodrug/active metabolite pair was determined using the whole-body models. The human model proposed a dose regimen of pafuramidine (40 mg once daily) based on a predefined efficacy-safety index. A similar approach could be used to guide dose-ranging studies in humans for next-in-class compounds.

Absolute quantification and differential expression of drug transporters, cytochrome P450 enzymes, and UDP-glucuronosyltransferases in cultured primary human hepatocytes

The levels of metabolizing enzymes and transporters expressed in hepatocytes are decisive factors for hepatobiliary disposition of most drugs. Induction via nuclear receptor activation can significantly alter those levels, with the coregulation of multiple enzymes and transporters occurring to different extents. Here, we report the use of a targeted liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) method for concurrent quantification of multiple cytochrome P450 (P450), UDP-glucuronosyltransferase (UGT), and transporter proteins in cultured primary human hepatocytes. The effects of culture format (i.e., sandwich culture versus conventional culture) and of dexamethasone (DEX) media concentrations on mRNA, protein, and activity levels were determined for three donors, and protein expression was compared with that in liver. In general, P450 and UGT expression was lower in hepatocyte cultures than that in liver, and CYP2C9 was found to be the most abundant P450 isoform expressed in cultured hepatocytes. The sandwich culture format and 0.1 μM DEX in media retained the protein expression in the hepatocytes closest to the levels found in liver. However, higher in vitro expression was observed for drug transporters, especially for multidrug resistance protein 1 and breast cancer resistance protein. Direct protein quantification was applied successfully to study in vitro induction in sandwich cultured primary hepatocytes in a 24-well format using the prototypical inducers rifampicin, omeprazole, and phenobarbital. We conclude that targeted absolute LC-MS/MS quantification of drug-metabolizing enzymes and transporters can broaden the scope and significantly increase the impact of in vitro drug metabolism studies, such as induction, as an important supplement or future alternative to mRNA and activity data.

Effect of culture time on the basal expression levels of drug transporters in sandwich-cultured primary rat hepatocytes

Sandwich-cultured rat hepatocytes are used in drug discovery for pharmacological and toxicological assessment of drug candidates, yet their utility as a functional model for drug transporters has not been fully characterized. To evaluate the system as an in vitro model for drug transport, expression changes of hepatic transporters relative to whole liver and freshly isolated hepatocytes (day 0) were examined by real-time quantitative reverse transcription-polymerase chain reaction for 4 consecutive days of culture. No significant differences in transporter expression levels were observed between freshly isolated hepatocytes and whole liver. Two distinct mRNA profiles were detected over time showing 1) a more than 5-fold decline in levels of uptake transporters such as Na(+)-taurocholate cotransporting polypeptide (Ntcp), organic anion transporter (Oat) 2, organic anion-transporting polypeptide (Oatp) 1a1, Oatp1a4, and Oatp1b2 and 2) a greater than 5-fold increase of efflux transporters P-glycoprotein (P-gp), breast cancer resistance protein (Bcrp), and multidrug resistance-related proteins (Mrp) 1, 2, 3, and 4. In addition, protein levels and functional activities for selected transporters were also determined. Protein levels for Mrp2, Bcrp, P-gp, Ntcp, and Oatp1a4 corresponded to changes in mRNA. Functional activities of Oatps and Oct1 exhibited a 3- and 4-fold decrease on day 2 and day 4, respectively, relative to that on day 0, whereas a more than 10-fold reduction in Oat2 activity was observed. These results indicate that the cell culture conditions used herein did not provide an optimal environment for expression of all hepatic transporters. Significant time-dependent alterations in basal gene expression patterns of transporters were detected compared with those in liver or freshly isolated hepatocytes. Further work and new strategies are required to improve the validity of this model as an in vitro tool for in vivo drug transport or biliary clearance prediction.

BSEP inhibition: in vitro screens to assess cholestatic potential of drugs

Bile salt export pump (BSEP, ABC11) is a membrane protein that is localized in the cholesterol-rich canalicular membrane of hepatocytes. Its function is to eliminate unconjugated and conjugated bile acids/salts from hepatocyte into the bile. In humans there is no compensatory mechanism for the loss of this transporter. Mutations of BSEP result in a genetic disease, called progressive familial intrahepatic cholestasis type 2 (PFIC2), that is characterized with decreased biliary bile salt secretion, leading to decreased bile flow and accumulation of bile salts inside the hepatocyte, inflicting damage. BSEP inhibitor drugs produce similar bile salt retention that may lead to severe cholestasis and liver damage. Drug-induced liver injury is a relevant clinical issue, in severe cases ending in liver transplantation. Therefore, measurement of BSEP inhibition by candidate drugs has high importance in drug discovery and development. Although several methods are suitable to detect BSEP-drug interactions, due to interspecies differences in bile acid composition, differences in hepatobiliary transporter modulation, they have limitations. This review summarizes appropriate in vitro methods that could be able to predict BSEP-drug candidate interactions in humans before the start of clinical phases.

Bile salt export pump inhibitors are associated with bile acid-dependent drug-induced toxicity in sandwich-cultured hepatocytes

Drug-induced liver injury (DILI) is a major reason for the dropout of candidate compounds from drug testing and the withdrawal of pharmaceuticals from clinical use. Among the various mechanisms of liver injury, the accumulation of bile acids (BAs) within hepatocytes is thought to be a primary mechanism for the development of DILI. Although bile salt export pump (BSEP) dysfunction is considered a susceptibility factor for DILI, little is known about the relationship between drug-induced BSEP dysfunction and BA-dependent hepatotoxicity. Furthermore, few methods are at hand for the systematic and quantitative evaluation of BA-dependent DILI. This study aimed to construct a model of DILI by employing sandwich-cultured hepatocytes (SCHs). SCHs can be used to assess functions of canalicular transporters such as BSEP and the activity of metabolic enzymes. Here, the impact of 26 test compounds (ritonavir, troglitazone, etc.) was investigated on BA-dependent cytotoxicity in SCHs. SCHs were exposed to each compound for 24h with or without BAs (glycochenodeoxycholic acid, deoxycholic acid, etc.). As a result, BA-dependent toxicity was observed for 11 test compounds in SCHs treated in the presence of BAs, while no signs of toxicity were observed for SCHs treated in the absence of BAs. Of the 11 compounds, nine were known BSEP inhibitors. Moreover, for some compounds, an increase in the severity of BA-dependent toxicity was observed in SCHs that were co-treated with 1-aminobenzotriazole, a non-selective inhibitor of cytochrome P450 (CYP450)-mediated drug metabolism. These results indicate that the SCH-based model is likely to prove useful for the evaluation of BA-dependent DILI, including the effects of drug metabolism and BSEP inhibition on liver injury.

The evolution of the OATP hepatic uptake transport protein family in DMPK sciences: from obscure liver transporters to key determinants of hepatobiliary clearance

Over the last two decades the impact on drug pharmacokinetics of the organic anion transporting polypeptides (OATPs: OATP-1B1, 1B3 and 2B1), expressed on the sinusoidal membrane of the hepatocyte, has been increasingly recognized. OATP-mediated uptake into the hepatocyte coupled with subsequent excretion into bile via efflux proteins, such as MRP2, is often referred to as hepatobiliary excretion. OATP transporter proteins can impact some drugs in several ways including pharmacokinetic variability, pharmacodynamic response and drug-drug interactions (DDIs). The impact of transporter mediated hepatic clearance is illustrated with case examples, from the literature and also from the Pfizer portfolio. The currently available in vitro techniques to study the hepatic transporter proteins involved in the hepatobiliary clearance of drugs are reviewed herein along with recent advances in using these in vitro data to predict the human clearance of compounds recognized by hepatic uptake transporters.

Novel in vitro-in vivo extrapolation (IVIVE) method to predict hepatic organ clearance in rat

PURPOSE

Drug elimination in the liver consists of uptake, metabolism, biliary excretion, and sinusoidal efflux from the hepatocytes to the blood. We aimed to establish an accurate prediction method for liver clearance in rats, considering these four elimination processes. In vitro assays were combined to achieve improved predictions.

METHODS

In vitro clearances for uptake, metabolism, biliary excretion and sinusoidal efflux were determined for 13 selected compounds with various physicochemical and pharmacokinetic properties. Suspended hepatocytes, liver microsomes and sandwich-cultured hepatocytes were evaluated as in vitro models. Based on the individual processes, in vivo hepatic clearance was calculated. Subsequently, the predicted clearances were compared with the corresponding in vivo values from literature.

RESULTS

Using this in vitro-in vivo extrapolation method good linear correlation was observed between predicted and reported clearances. Linear regression analysis revealed much improved prediction for the novel method (r(2) = 0.928) as compared to parameter analysis using hepatocyte uptake only (r(2) = 0.600), microsomal metabolism only (r(2) = 0.687) or overall hepatobiliary excretion in sandwich-cultured hepatocytes (r(2) = 0.321).

CONCLUSIONS

In this new attempt to predict hepatic elimination under consideration of multiple clearance processes, in vivo hepatic clearances of 13 compounds in rats were well predicted using an IVIVE analysis method based on in vitro assays.

Culture period-dependent changes in the uptake of transporter substrates in sandwich-cultured rat and human hepatocytes

Sandwich-cultured hepatocytes (SCH) are a useful tool for evaluating hepatobiliary drug transport in vitro. Some studies have investigated the in vitro-in vivo correlations of the biliary clearance of drugs using SCH. In most cases, the biliary clearance observed in vivo correlated well with the predicted clearance, but the predicted absolute values were underestimated when based on in vitro experiments with SCH. We hypothesized that the down-regulated function of uptake transporters is one of the causes of this underestimation. Therefore, the uptake of taurocholate, digoxin, pravastatin, and rosuvastatin was investigated in sandwich-cultured rat hepatocytes (SCRH) cultured for 5, 24, 48, and 96 h, and the predicted hepatic clearance from in vitro uptake clearance (CL(H, vitro)) was calculated with a dispersion model. In SCRH cultured for 96 h, the saturable uptake of taurocholate, digoxin, pravastatin, and rosuvastatin decreased to 7.5, 3.3, 64, and 23%, respectively, of their uptake in hepatocytes cultured for 5 h, and a better prediction of in vivo hepatic clearance (CL(H, vivo)) was achieved when based on CL(H, vitro) of 5-h-cultured hepatocytes. These results suggest that the uptake activity is considerably reduced in cell culture, even in a sandwich-culture format. In a similar study, we also examined taurocholate and rosuvastatin in sandwich-cultured human hepatocytes (SCHH). Unlike in SCRH, the saturable uptake of these compounds did not differ markedly in SCHH cultured for 5 or 96 h. Thus, the uptake activity in SCHH was maintained relatively well compared with that in SCRH.

Mechanisms underlying differences in systemic exposure of structurally similar active metabolites: comparison of two preclinical hepatic models

Selection of in vitro models that accurately characterize metabolite systemic and hepatobiliary exposure remains a challenge in drug development. In the present study, mechanisms underlying differences in systemic exposure of two active metabolites, furamidine and 2,5-bis (5-amidino)-2-pyridyl furan (CPD-0801), were examined using two hepatic models from rats: isolated perfused livers (IPLs) and sandwich-cultured hepatocytes (SCH). Pafuramidine, a prodrug of furamidine, and 2,5-bis [5-(N-methoxyamidino)-2-pyridyl] furan (CPD-0868), a prodrug of CPD-0801, were selected for investigation because CPD-0801 exhibits greater systemic exposure than furamidine, despite remarkable structural similarity between these two active metabolites. In both IPLs and SCH, the extent of conversion of CPD-0868 to CPD-0801 was consistently higher than that of pafuramidine to furamidine over time (at most 2.5-fold); area under the curve (AUC) of CPD-0801 in IPL perfusate and SCH medium was at least 7-fold higher than that of furamidine. Pharmacokinetic modeling revealed that the rate constant for basolateral (liver to blood) net efflux (k(A_net efflux)) of total formed CPD-0801 (bound + unbound) was 6-fold higher than that of furamidine. Hepatic accumulation of both active metabolites was extensive (>95% of total formed); the hepatic unbound fraction (f(u,L)) of CPD-0801 was 5-fold higher than that of furamidine (1.6 versus 0.3%). Incorporation of f(u,L) into the pharmacokinetic model resulted in comparable k(A_net efflux,u) between furamidine and CPD-0801. In conclusion, intrahepatic binding markedly influenced the disposition of these active metabolites. A higher f(u,L) explained, in part, the enhanced perfusate AUC of CPD-0801 compared with furamidine in IPLs. SCH predicted the disposition of prodrug/metabolite in IPLs.

Improved preclinical safety assessment using micro-BAL devices: the potential impact on human discovery and drug attrition

Hepatotoxicity is often unpredictable in the early phase of drug discovery and leads to drug attrition in preclinical and clinical development. Here, we discuss the conventional preclinical liver models that do not mimic in vivo livers. We focus on key components such as new sources of hepatocyte-derived human stem cells, enhanced direct oxygenation, defined biocompatibility nanoscaffolds, organotypical cellular models, dynamic culture, and metabolite status inside and outside the cell for effective configuration for the development of a bioartificial liver (BAL) device to mimic the in vivo liver microenvironment. The potential for development of BAL devices could open up new avenues in: (i) hepatotoxicity assessment for selecting drug candidates during preclinical screening; and (ii) therapeutic approaches for liver cell therapy at the clinical stage.

Genetic variations of bile salt transporters as predisposing factors for drug-induced cholestasis, intrahepatic cholestasis of pregnancy and therapeutic response of viral hepatitis

INTRODUCTION

Drug-induced cholestasis, intrahepatic cholestasis of pregnancy and viral hepatitis are acquired forms of liver disease. Cholestasis is a pathophysiologic state with impaired bile formation and subsequent accumulation of bile salts in hepatocytes. The bile salt export pump (BSEP) (ABCB11) is the key export system for bile salts from hepatocytes.

AREAS COVERED

This article provides an introduction into the physiology of bile formation followed by a summary of the current knowledge on the key bile salt transporters, namely, the sodium-taurocholate co-transporting polypeptide NTCP, the organic anion transporting polypeptides (OATPs), BSEP and the multi-drug resistance protein 3. The pathophysiologic consequences of altered functions of these transporters, with an emphasis on molecular and genetic aspects, are then discussed.

EXPERT OPINION

Knowledge of the role of hepatocellullar transporters, especially BSEP, in acquired cholestasis is continuously increasing. A common variant of BSEP (p.V444A) is now a well-established susceptibility factor for acquired cholestasis and recent evidence suggests that the same variant also influences the therapeutic response and disease progression of viral hepatitis C. Studies in large independent cohorts are now needed to confirm the relevance of p.V444A. Genome-wide association studies should lead to the identification of additional genetic factors underlying cholestatic liver disease.

Influence of seeding density and extracellular matrix on bile Acid transport and mrp4 expression in sandwich-cultured mouse hepatocytes

This study was undertaken to examine the influence of seeding density, extracellular matrix and days in culture on bile acid transport proteins and hepatobiliary disposition of the model bile acid taurocholate. Mouse hepatocytes were cultured in a sandwich configuration on six-well Biocoat plates with an overlay of Matrigel (BC/MG) or gelled-collagen (BC/GC) for 3 or 4 days at seeding densities of 1.0, 1.25, or 1.5 x 10(6) cells/well. The lower seeding densities of 1.0 and 1.25 x 10(6) cells/well resulted in good hepatocyte morphology and bile canalicular network formation, as visualized by 5-(and 6)-carboxy-2',7'-dichlorofluorescein accumulation. In general, taurocholate cellular accumulation tended to increase as a function of seeding density in BC/GC; cellular accumulation was significantly increased in hepatocytes cultured in BC/MG compared to BC/GC at the same seeding density on both days 3 and 4 of culture. In general, in vitro intrinsic biliary clearance of taurocholate was increased at higher seeding densities. Levels of bile acid transport proteins on days 3 and 4 were not markedly influenced by seeding density or extracellular matrix except for multidrug resistance protein 4 (Mrp4), which was inversely related to seeding density. Mrp4 levels decreased approximately 2- to 3-fold between seeding densities of 1.0 x 10(6) and 1.25 x 10(6) cells/well regardless of extracellular matrix; an additional approximately 3- to 5-fold decrease in Mrp4 protein was noted in BC/GC between seeding densities of 1.25 x 10(6) and 1.5 x 10(6) cells/well. Results suggest that seeding density, extracellular matrix and days in culture profoundly influence Mrp4 expression in sandwich-cultured mouse hepatocytes. Primary mouse hepatocytes seeded in a BC/MG configuration at densities of 1.25 x 10(6) cells/well and 1.0 x 10(6), and cultured for 3 days, yielded optimal transport based on the probes studied. This work demonstrates the applicability of the sandwich-cultured model to mouse hepatocytes.