Bosentan Alters Endo- and Exogenous Bile Salt Disposition in Sandwich-Cultured Human Hepatocytes.

Bosentan, a well-known cholestatic agent, was not identified as cholestatic at concentrations up to 200 µM based on the drug-induced cholestasis (DIC) index value, determined in a sandwich-cultured human hepatocyte (SCHH)-based DIC assay. To obtain further quantitative insights into the effects of bosentan on cellular bile salt handling by human hepatocytes, the present study determined the effect of 2.5-25 µM bosentan on endogenous bile salt levels and on the disposition of 10 µM chenodeoxycholic acid (CDCA) added to the medium in SCHHs. Bosentan reduced intracellular as well as extracellular concentrations of both endogenous glycochenodeoxycholic acid (GCDCA) and glycocholic acid in a concentration-dependent manner. When exposed to 10 µM CDCA, bosentan caused a shift from canalicular efflux to sinusoidal efflux of GCDCA. CDCA levels were not affected. Our mechanistic model confirmed the inhibitory effect of bosentan on canalicular GCDCA clearance. Moreover, our results in SCHHs also indicated reduced GCDCA formation. We confirmed the direct inhibitory effect of bosentan on CDCA conjugation with glycine in incubations with liver S9 fraction. SIGNIFICANCE STATEMENT: Bosentan was evaluated at therapeutically relevant concentrations (2.5-25 µM) in sandwich-cultured human hepatocytes. It altered bile salt disposition and inhibited canalicular secretion of glycochenodeoxycholic acid (GCDCA). Within 24 hours, bosentan caused a shift from canalicular to sinusoidal efflux of GCDCA. These results also indicated reduced GCDCA formation. This study confirmed a direct effect of bosentan on chenodeoxycholic acid conjugation with glycine in liver S9 fraction.

Safety Assessment of Compounds after In Vitro Metabolic Conversion Using Zebrafish Eleuthero Embryos.

Zebrafish-based platforms have recently emerged as a useful tool for toxicity testing as they combine the advantages of in vitro and in vivo methodologies. Nevertheless, the capacity to metabolically convert xenobiotics by zebrafish eleuthero embryos is supposedly low. To circumvent this concern, a comprehensive methodology was developed wherein test compounds (i.e., parathion, malathion and chloramphenicol) were first exposed in vitro to rat liver microsomes (RLM) for 1 h at 37 °C. After adding methanol, the mixture was ultrasonicated, placed for 2 h at -20 °C, centrifuged and the supernatant evaporated. The pellet was resuspended in water for the quantification of the metabolic conversion and the detection of the presence of metabolites using ultra high performance liquid chromatography-Ultraviolet-Mass (UHPLC-UV-MS). Next, three days post fertilization (dpf) zebrafish eleuthero embryos were exposed to the metabolic mix diluted in Danieau's medium for 48 h at 28 °C, followed by a stereomicroscopic examination of the adverse effects induced, if any. The novelty of our method relies in the possibility to quantify the rate of the in vitro metabolism of the parent compound and to co-incubate three dpf larvae and the diluted metabolic mix for 48 h without inducing major toxic effects. The results for parathion show an improved predictivity of the toxic potential of the compound.

MRP2 Inhibition by HIV Protease Inhibitors in Rat and Human Hepatocytes: A Quantitative Confocal Microscopy Study.

Hepatic drug transporters play a pivotal role in the excretion of drugs from the body, in drug-drug interactions, as well as in drug-induced liver toxicity. Hepatocytes cultured in sandwich configuration are an advantageous model to investigate the interactions of drug candidates with apical efflux transporters in a biorelevant manner. However, the commonly used "offline" assays (i.e., that rely on measuring intracellular accumulated amounts after cell lysis) are time- and resource-consuming, and the data output is often highly variable. In the present study, we used confocal microscopy to investigate the inhibitory effect of all marketed HIV protease inhibitors (10 µM) on the apical efflux transporter multidrug resistance-associated protein 2 (MRP2; ABCC2) by visualizing the biliary accumulation of the fluorescent substrate 5(6)-carboxy-2',7'-dichlorofluorescein (CDF). This method was applied with sandwich-cultured human and rat hepatocytes. Alterations in the biliary excretion index of CDF were calculated on the basis of quantitative analysis of fluorescence intensities in the confocal images. In human hepatocytes, lopinavir followed by tipranavir, saquinavir, atazanavir, and darunavir were the most potent inhibitors of MRP2-mediated efflux of CDF. In rat hepatocytes, tipranavir inhibited Mrp2-mediated CDF efflux most potently, followed by lopinavir and nelfinavir. In conclusion, a comparison of these findings with previously published data generated in offline transporter inhibition assays indicates that this microscopy-based approach enables investigation of the inhibitory effect of drugs on efflux transporters in a very sensitive but nondestructive manner.

Relationship between In Vivo CYP3A4 Activity, CYP3A5 Genotype, and Systemic Tacrolimus Metabolite/Parent Drug Ratio in Renal Transplant Recipients and Healthy Volunteers.

CYP3A5 genotype is a major determinant of tacrolimus clearance, and has been shown to affect systemic tacrolimus metabolite/parent ratios in healthy volunteers, which may have implications for efficacy and toxicity. In a cohort of 50 renal transplant recipients who underwent quantification of CYP3A4 activity using the oral midazolam drug probe, we confirmed that CYP3A5 genotype is the single most important determinant of tacrolimus metabolite/parent ratio [CYP3A5 expressors displayed 2.7- and 2-fold higher relative exposure to 13-desmethyltacrolimus (DMT) and 31-DMT, respectively; P < 0.001]. There was, however, no relationship between CYP3A4 activity and tacrolimus metabolite/parent ratios. Additional analyses in 16 healthy volunteers showed that dual pharmacological inhibition of CYP3A4 and P-glycoprotein using itraconazole resulted in increased tacrolimus metabolite/parent ratios (+65%, +112%, and 25% for 13-, 15-, and 31-DMT, respectively; P < 0.01). This finding was confirmed in a cohort of nine renal transplant recipients who underwent tacrolimus pharmacokinetic assessments before and during CYP3A4 inhibition (58% increase in overall metabolite/tacrolimus ratio; P = 0.017).

Omics-based responses induced by bosentan in human hepatoma HepaRG cell cultures.

Bosentan is well known to induce cholestatic liver toxicity in humans. The present study was set up to characterize the hepatotoxic effects of this drug at the transcriptomic, proteomic, and metabolomic levels. For this purpose, human hepatoma-derived HepaRG cells were exposed to a number of concentrations of bosentan during different periods of time. Bosentan was found to functionally and transcriptionally suppress the bile salt export pump as well as to alter bile acid levels. Pathway analysis of both transcriptomics and proteomics data identified cholestasis as a major toxicological event. Transcriptomics results further showed several gene changes related to the activation of the nuclear farnesoid X receptor. Induction of oxidative stress and inflammation were also observed. Metabolomics analysis indicated changes in the abundance of specific endogenous metabolites related to mitochondrial impairment. The outcome of this study may assist in the further optimization of adverse outcome pathway constructs that mechanistically describe the processes involved in cholestatic liver injury.

Metabolism of the synthetic cannabinoid 5F-PY-PICA by human and rat hepatocytes and identification of biliary analytical targets by directional efflux in sandwich-cultured rat hepatocytes using UHPLC-HR-MS/MS.

Analytical strategies for detecting drugs in biological samples rely on information on metabolism and elimination. 5F-PY-PICA belongs to the group of synthetic cannabinoids that are known to undergo excretion into the bile. The aims of this study were the in vitro identification of metabolites of 5F-PY-PICA and to determine which analytical targets are excreted into the bile and urine. Metabolites identified after incubation of 5F-PY-PICA with pooled human liver microsomes (pHLM), pooled human hepatocytes (pHH), or suspended and sandwich-cultured rat hepatocytes (SCRH). Rat hepatocytes were harvested following a two-step perfusion protocol and the SCRH were prepared between layers of rat-tail collagen. The biliary efflux of 5F-PY-PICA and its metabolites was determined in three-day-cultured SCRH by differential efflux into either standard buffer from intact bile canaliculi or standard buffer without divalent cations, which disrupts the bile canaliculi. The metabolites were identified using liquid chromatography-high resolution mass spectrometry/mass spectrometry (LC-HR-MS/MS). The main metabolites were the COOH-ω-metabolite (M4) in pHH, the defluoro-HO-ω-metabolite (M3) in pHLM, and the COOH-pyrrolidine-metabolite (M6) in rat hepatocytes. Efflux into standard buffer without divalent cations was significantly higher (p<0.050) for 5F-PY-PICA, M4, and the HO-indole-glucuronide-metabolite (M22). M6 did not undergo significant biliary efflux, indicating that basolateral efflux dominates for this metabolite. 5F-PY-PICA, M4, and M22 are proposed as analytical targets for bile analysis in forensic screening protocols, whereas M6 should be one of the main urinary targets for 5F-PY-PICA analysis.

Extra collagen overlay prolongs the differentiated phenotype in sandwich-cultured rat hepatocytes.

INTRODUCTION: Sandwich-cultured rat hepatocytes (SCRH) have become an invaluable in vitro model to study hepatic drug disposition. SCRH are maintained between two layers of extracellular matrix. In this configuration, culture periods of 4days are typically applicable. The aim of the present study was to modify conventional SCRH by applying an additional collagen overlay to prolong the hepatic phenotype in SCRH and thus to extend the applicability of the model. METHODS: The cultures receiving an extra top layer ('SCRH-plus' cultures) were compared with the conventional SCRH by testing the morphology, cell functionality, metabolic capacity and Mrp2-activity. RESULTS: In the SCRH-plus cultures, cell functionality, evaluated by measuring urea production, was increased from day 5 onwards, compared to conventional cultures. Furthermore, these cells retained the appearance of typical hepatocytes, in contrast with conventional sandwich cultures which showed rapid dedifferentiation. SCRH-plus exhibited significantly improved metabolic clearance mediated by cytochrome P450 3A compared to conventional SCRH whereas UDP-glucuronosyltransferase-mediated metabolism was unaffected. Both conventional SCRH and SCRH-plus showed extensive biliary networks at day 4 of culture. However, from day 4 onwards, a decline in biliary excretion index (BEI) was observed in the conventional SCRH, while BEI values in SCRH-plus cultures did not decrease until day 7. DISCUSSION: The application of an extra top layer of collagen on the SCRH prolongs their useful life-span to 7days. Therefore, SCRH-plus cultures will broaden the applications of SCRH in terms of long-term toxicity evaluation and when determining metabolism of low turnover compounds.

On the Role of Illness Duration and Nutrient Restriction in Cholestatic Alterations that Occur During Critical Illness.

BACKGROUND AND AIMS: Elevated markers of cholestasis are common in response to critical illness, and associated with adverse outcome. The role of illness duration and of nutrient restriction on underlying molecular pathways of such cholestatic responses have not been thoroughly investigated. METHODS: In a mouse model of surgery- and sepsis-induced critical illness, molecular pathways of cholestasis were investigated up to 7 days. To assess which changes are explained by illness-induced lack of feeding, nutrient-restricted healthy mice were studied and compared with ad libitum fed healthy mice. Furthermore, serum bile acid (BA) concentrations were quantified in 1,114 human patients with either short or long intensive care unit (ICU) stay, matched for type and severity of illness, up to ICU-day-7. RESULTS: In critically ill mice, either evoked by surgery or sepsis, circulating and hepatic BA-levels progressively increased with time from day-3 onward, preceded by unsuppressed or upregulated CYP7A1 and CYP27A1 protein expression. From 30 h onward, nuclear farnesoid-X-receptor-retinoid-X-receptor staining was significantly suppressed in both critically ill groups, followed from day-3 onward by decreased gene expression of the apical exporter BA-specific export pump and increased expression of basolateral exporters multidrug resistance-associated protein 3 (MRP3) and MRP4. Nutrient restriction in healthy mice only partly mirrored illness-induced alterations in circulating BA and BA-transporters, without changing nuclear receptors or synthesis markers expression. Also in human critically ill patients, serum BA increased with time in long-stay patients only, similarly for patients with or without sepsis. CONCLUSIONS: Circulating BA concentrations rose days after onset of sepsis- and surgery-induced, critical illness, only partially explained by lack of feeding, preceded by suppressed nuclear feedback-sensors and ongoing BA synthesis. Expression of transporters suggested ongoing reversed BA-flow toward the blood.

Drug-induced cholestasis risk assessment in sandwich-cultured human hepatocytes.

Drug-induced cholestasis (DIC) is recognized as one of the prime mechanisms for DILI. Hence, earlier detection of drug candidates with cholestatic signature is crucial. Recently, we introduced an in vitro model for DIC and evaluated its performance with several cholestatic drugs. We presently expand on the validation of this model by 14 training compounds (TCs) of the EU-EFPIA IMI project MIP-DILI. Several batches of human hepatocytes in sandwich-culture were qualified for DIC assessment by verifying the bile acid-dependent increase in sensitivity to the toxic effects of cyclosporin A. The cholestatic potential of the TCs was expressed by determining the drug-induced cholestasis index (DICI). A safety margin (SM) was calculated as the ratio of the lowest TC concentration with a DICI≤0.80 to the Cmax,total. Nefazodone, bosentan, perhexiline and troglitazone were flagged for cholestasis (SM<30). The hepatotoxic (but non-cholestatic) compounds, amiodarone, diclofenac, fialuridine and ximelagatran, and all non-hepatotoxic compounds were cleared as "safe" for DIC. Tolcapone and paracetamol yielded DICI-based SM values equal to or higher than those based on cytotoxicity, thus excluding DIC as a DILI mechanism. This hepatocyte-based in vitro assay provides a unique tool for early and reliable identification of drug candidates with cholestasis risk.

Primary Hepatocytes in Sandwich Culture.

Hepatocytes in sandwich configuration constitute of primary hepatocytes cultured between two layers of extracellular matrix. Sandwich-cultured hepatocytes maintain expression of liver-specific proteins and gradually form intact bile canaliculi with functional biliary excretion of endogenous compounds and xenobiotics. Both freshly isolated and cryopreserved hepatocytes can be used to establish sandwich cultures. Therefore, this preclinical model has become an invaluable in vitro tool to evaluate hepatobiliary drug transport, metabolism, hepatotoxicity, and drug interactions. In this chapter, commonly used procedures to cultivate primary hepatocytes from human and rat in sandwich configuration are described.

Drug-induced cholestasis detection in cryopreserved rat hepatocytes in sandwich culture.

INTRODUCTION: In vitro identification of compounds that cause cholestasis in vivo still remains a problem in pharmaceutical R&D. Currently existing in vitro systems show poor predictivity towards the clinical situation. Recently, our research group developed a model, based on sandwich-cultured (rat) hepatocytes (SC(R)H), to detect compounds causing cholestasis via altered bile acid (BA) homeostasis (Chatterjee et al., 2014). In the present study, we assessed whether this model performs equally well with freshly-isolated and cryopreserved hepatocytes. METHODS: We exposed sandwich cultures from rat hepatocytes before and after cryopreservation to the cholestatic compounds, cyclosporin A (CsA) and troglitazone (Tro), in the presence and in the absence of a BA mixture. At the end of the incubations, the capability of the hepatocytes to produce urea was measured to determine changes in the drug-induced cholestasis index (DICI). RESULTS: The mean (± SEM) urea production was significantly higher in sandwich cultures from freshly-isolated hepatocytes (27.88 (± 0.96) nmol/cm(2)), compared to cultures from cryopreserved hepatocytes (22.86 (± 1.91) nmol urea/cm(2)). However, after normalization for confluence rate (based on light microscopic image analysis), it appeared that the urea production was similar for all the batches of SCRH. The mean (± SEM) DICI values for CsA 10 µM and Tro 75 µM were 0.89 (± 0.03) and 0.93 (± 0.03), respectively. Higher concentrations, CsA (≥ 15 µM) and Tro (≥ 100 µM), elicited a significant decrease in urea production when incubated in the presence of a BA mixture compared to the compound alone. This was the case for all the batches of SCRH, irrespective of cryopreservation history. DISCUSSION: In conclusion, no significant differences were seen when the previously described in vitro cholestasis model was applied in SCRH before or after cryopreservation. This study demonstrates the robustness of the model, which implies that it can be used with SCRH obtained from both freshly-isolated and cryopreserved hepatocytes.