Regional Differences in Human Intestinal Drug Metabolism.

The intestines are key for the absorption of nutrients and water as well as drug metabolism, and it is well known that there are clear differences in the expression profile of drug metabolism enzymes along the intestinal tract. Yet only a few studies have thoroughly investigated regional differences in human intestinal drug metabolism. In this study, we evaluated phase I and phase II metabolism in matched human ileum and colon precision-cut intestinal slices (PCIS). To this end, human PCIS were incubated for 3 hours with testosterone and 7-hydroxycoumarin (7-HC) to examine phase I and phase II metabolism, respectively. Metabolite formation was assessed by high-performance liquid chromatography analysis. Our results demonstrated that androstenedione, 6ß-hydroxytestosterone, 2ß-hydroxytestosterone, and 7-HC sulfate were predominantly formed in the ileum, while 15α-hydroxytestosterone and 7-HC glucuronide were mainly produced in the colon. Moreover, we also observed sex differences in phase II metabolite formation, which appeared to be higher in men compared with women. Taken together, we demonstrated that phase I metabolism predominantly occurs in ileum PCIS, while phase II metabolism mostly takes place in colon PCIS. Moreover, we revealed that human PCIS can be used to study both regional and sex differences in intestinal metabolism.

Differentiation of human-induced pluripotent stem cell under flow conditions to mature hepatocytes for liver tissue engineering.

Hepatic differentiation of human-induced pluripotent stem cells (hiPSCs) under flow conditions in a 3D scaffold is expected to be a major step forward for construction of bioartificial livers. The aims of this study were to induce hepatic differentiation of hiPSCs under perfusion conditions and to perform functional comparisons with fresh human precision-cut liver slices (hPCLS), an excellent benchmark for the human liver in vivo. The majority of the mRNA expression of CYP isoenzymes and transporters and the tested CYP activities, Phase II metabolism, and albumin, urea, and bile acid synthesis in the hiPSC-derived cells reached values that overlap those of hPCLS, which indicates a higher degree of hepatic differentiation than observed until now. Differentiation under flow compared with static conditions had a strong inducing effect on Phase II metabolism and suppressed AFP expression but resulted in slightly lower activity of some of the Phase I metabolism enzymes. Gene expression data indicate that hiPSCs differentiated into both hepatic and biliary directions. In conclusion, the hiPSC differentiated under flow conditions towards hepatocytes express a wide spectrum of liver functions at levels comparable with hPCLS indicating excellent future perspectives for the development of a bioartificial liver system for toxicity testing or as liver support device for patients.

Maintenance of drug metabolism and transport functions in human precision-cut liver slices during prolonged incubation for 5 days.

Human precision-cut liver slices (hPCLS) are a valuable ex vivo model that can be used in acute toxicity studies. However, a rapid decline in metabolic enzyme activity limits their use in studies that require a prolonged xenobiotic exposure. The aim of the study was to extend the viability and function of hPCLS to 5 days of incubation. hPCLS were incubated in two media developed for long-term culture of hepatocytes, RegeneMed®, and Cellartis®, and in the standard medium WME. Maintenance of phase I and II metabolism was studied both on gene expression as well as functional level using a mixture of CYP isoform-specific substrates. Albumin synthesis, morphological integrity, and glycogen storage was assessed, and gene expression was studied by transcriptomic analysis using microarrays with a focus on genes involved in drug metabolism, transport and toxicity. The data show that hPCLS retain their viability and functionality during 5 days of incubation in Cellartis® medium. Albumin synthesis as well as the activity and gene expression of phase I and II metabolic enzymes did not decline during 120-h incubation in Cellartis® medium, with CYP2C9 activity as the only exception. Glycogen storage and morphological integrity were maintained. Moreover, gene expression changes in hPCLS during incubation were limited and mostly related to cytoskeleton remodeling, fibrosis, and moderate oxidative stress. The expression of genes involved in drug transport, which is an important factor in determining the intracellular xenobiotic exposure, was also unchanged. Therefore, we conclude that hPCLS cultured in Cellartis® medium are a valuable human ex vivo model for toxicological and pharmacological studies that require prolonged xenobiotic exposure.

Viability, function and morphological integrity of precision-cut liver slices during prolonged incubation: Effects of culture medium.

Precision-cut liver slices (PCLS) are an ex vivo model for metabolism and toxicity studies. However, data on the maintenance of the morphological integrity of the various cell types in the slices during prolonged incubation are lacking. Therefore, our aims were to characterize morphological and functional changes in rat PCLS during five days of incubation in a rich medium, RegeneMed®, and a standard medium, Williams' Medium E. Although cells of all types in the slices remain viable, profound changes in morphology were observed, which were more prominent in RegeneMed®. Slices underwent notable fibrosis, bile duct proliferation and fat deposition. Slice thickness increased, resulting in necrotic areas, while slice diameter decreased, possibly indicating cell migration. An increased proliferation of parenchymal and non-parenchymal cells (NPCs) was observed. Glycogen, albumin and Cyp3a1 were maintained albeit to a different level in two media. In conclusion, both hepatocytes and NPCs remain viable and functional, enabling five-day toxicity studies. Tissue remodeling and formation of a new capsule-like cell lining around the slices are evident after 3­4 days. The differences in effects between media emphasize the importance of media selection and of the recognition of morphological changes in PCLS, when interpreting results from toxicological or pharmacological studies.

Human precision-cut liver slices as an ex vivo model to study idiosyncratic drug-induced liver injury.

Idiosyncratic drug-induced liver injury (IDILI) is a major problem during drug development and has caused drug withdrawal and black-box warnings. Because of the low concordance of the hepatotoxicity of drugs in animals and humans, robust screening methods using human tissue are needed to predict IDILI in humans. According to the inflammatory stress hypothesis, the effects of inflammation interact with the effects of a drug or its reactive metabolite, precipitating toxic reactions in the liver. As a follow-up to our recently published mouse precision-cut liver slices model, an ex vivo model involving human precision-cut liver slices (hPCLS), co-incubated for 24 h with IDILI-related drugs and lipopolysaccharide (LPS), was developed to study IDILI mechanisms related to inflammatory stress in humans and to detect potential biomarkers. LPS exacerbated the effects of ketoconazole and clozapine toxicity but not those of their non-IDILI-related comparators, voriconazole and olanzapine. However, the IDILI-related drugs diclofenac, carbamazepine, and troglitazone did not show synergistic toxicity with LPS after incubation for 24 h. Co-incubation of ketoconazole and clozapine with LPS decreased the levels of glutathione in hPCLS, but this was not seen for the other drugs. All drugs affected LPS-induced cytokine release, but interestingly, only ketoconazole and clozapine increased the level of LPS-induced TNF release. Decreased levels of glutathione and cysteine conjugates of clozapine were detected in IDILI-responding livers following cotreatment with LPS. In conclusion, we identified ketoconazole and clozapine as drugs that exhibited synergistic toxicity with LPS, while glutathione and TNF were found to be potential biomarkers for IDILI-inducing drugs mediated by inflammatory stress. hPCLS appear to be suitable for further unraveling the mechanisms of inflammatory stress-associated IDILI.

Mouse precision-cut liver slices as an ex vivo model to study idiosyncratic drug-induced liver injury.

Idiosyncratic drug-induced liver injury (IDILI) has been the top reason for withdrawing drugs from the market or for black box warnings. IDILI may arise from the interaction of a drug's reactive metabolite with a mild inflammation that renders the liver more sensitive to injury resulting in increased toxicity (inflammatory stress hypothesis). Aiming to develop a robust ex vivo screening method to study inflammatory stress-related IDILI mechanisms and to find biomarkers that can detect or predict IDILI, mouse precision-cut liver slices (mPCLS) were coincubated for 24 h with IDILI-related drugs and lipopolysaccharide. Lipopolysaccharide exacerbated ketoconazole (15 µM) and clozapine (45 µM) toxicity but not their non-IDILI-related comparators, voriconazole (1500 µM) and olanzapine (45 µM). However, the other IDILI-related drugs tested [diclofenac (200 µM), carbamazepine (400 µM), and troglitazone (30 µM)] did not cause synergistic toxicity with lipopolysaccharide after 24 h of incubation. Lipopolysaccharide further decreased the reduced glutathione levels caused by ketoconazole or clozapine in mPCLS after 24 h of incubation, which was not the case for the other drugs. Lipopolysaccharide significantly increased nitric oxide (NO), cytokine, and chemokine release into the mPCLS media, while the treatment with the drugs alone did not cause any substantial change. All seven drugs drastically reduced lipopolysaccharide-induced NO production. Interestingly, only ketoconazole and clozapine increased the lipopolysaccharide-induced granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) release. Pilot experiments showed that diclofenac and troglitazone, but not carbamazepine, demonstrated synergistic toxicity with lipopolysaccharide after a longer incubation of 48 h in mPCLS. In conclusion, we have developed an ex vivo model to detect inflammatory stress-related liver toxicity and identified ketoconazole, clozapine, troglitazone, and diclofenac as drugs that showed synergistic toxicity with lipopolysaccharide. Reduced glutathione, G-CSF, and GM-CSF were identified to be potential biomarkers for IDILI-inducing drugs mediated by inflammatory stress, and mPCLS appear to be a promising screening tool to further unravel the mechanism of IDILI.

Comparison of biocompatibility and adsorption properties of different plastics for advanced microfluidic cell and tissue culture models.

Microfluidic technology is providing new routes toward advanced cell and tissue culture models to better understand human biology and disease. Many advanced devices have been made from poly(dimethylsiloxane) (PDMS) to enable experiments, for example, to study drug metabolism by use of precision-cut liver slices, that are not possible with conventional systems. However, PDMS, a silicone rubber material, is very hydrophobic and tends to exhibit significant adsorption and absorption of hydrophobic drugs and their metabolites. Although glass could be used as an alternative, thermoplastics are better from a cost and fabrication perspective. Thermoplastic polymers (plastics) allow easy surface treatment and are generally transparent and biocompatible. This study focuses on the fabrication of biocompatible microfluidic devices with low adsorption properties from the thermoplastics poly(methyl methacrylate) (PMMA), polystyrene (PS), polycarbonate (PC), and cyclic olefin copolymer (COC) as alternatives for PDMS devices. Thermoplastic surfaces were oxidized using UV-generated ozone or oxygen plasma to reduce adsorption of hydrophobic compounds. Surface hydrophilicity was assessed over 4 weeks by measuring the contact angle of water on the surface. The adsorption of 7-ethoxycoumarin, testosterone, and their metabolites was also determined after UV-ozone treatment. Biocompatibility was assessed by culturing human hepatoma (HepG2) cells on treated surfaces. Comparison of the adsorption properties and biocompatibility of devices in different plastics revealed that only UV-ozone-treated PC and COC devices satisfied both criteria. This paper lays an important foundation that will help researchers make informed decisions with respect to the materials they select for microfluidic cell-based culture experiments.

Microfluidics enables small-scale tissue-based drug metabolism studies with scarce human tissue.

Early information on the metabolism and toxicity properties of new drug candidates is crucial for selecting the right candidates for further development. Preclinical trials rely on cell-based in vitro tests and animal studies to characterize the in vivo behavior of drug candidates, although neither are ideal predictors of drug behavior in humans. Improving in vitro systems for preclinical studies both from a technological and biological model standpoint thus remains a major challenge. This article describes how microfluidics can be exploited to come closer to this goal in combination with precision-cut liver slices (PCLS) as an improved organomimetic system. Recently, we developed a novel microfluidic-based system incorporating a microchamber for slice perifusion to perform drug metabolism studies with mammalian PCLS under continuous flow. In the present study, the viability and metabolism of human PCLS were assessed by the measurement of the leakage of liver-specific enzymes and metabolism of four different substrates: lidocaine, 7-hydroxycoumarin, 7-ethoxycoumarin, and testosterone. All experiments were verified with well plates, an excellent benchmark for these experiments. Clearly, however, human tissue is not readily available, and it is worth considering how to perform a maximum number of informative experiments with small amounts of material. In one approach, the microfluidic system was coupled to an HPLC system to allow on-line monitoring and immediate detection of unstable metabolites, something that is generally not possible with conventional well-plate systems. This novel microfluidic system also enables the in vitro measurement of interorgan interactions by connecting microchambers containing different organ slices in series for sequential perfusion. This versatile experimental system has the potential to yield more information about the metabolic profiles of new drug candidates in human and animal tissues in an early stage of development compared with well plates alone.

Hydrogel embedding of precision-cut liver slices in a microfluidic device improves drug metabolic activity.

A microfluidic-based biochip made of poly-(dimethylsiloxane) was recently reported for the first time by us for the incubation of precision-cut liver slices (PCLS). In this system, PCLS are continuously exposed to flow, to keep the incubation environment stable over time. Slice behavior in the biochip was compared with that of slices incubated in well plates, and verified for 24 h. The goal of the present study was to extend this incubation time. The viability and metabolic activity of precision-cut rat liver slices cultured in our novel microflow system was examined for 72 h. Slices were incubated for 1, 24, 48, and 72 h, and tested for viability (enzyme leakage (lactate dehydrogenase)) and metabolic activity (7-hydroxycoumarin (phase II) and 7-ethoxycoumarin (phase I and II)). Results show that liver slices retained a higher viability in the biochip when embedded in a hydrogel (Matrigel) over 72 h. This embedding prevented the slices from attaching to the upper polycarbonate surface in the microchamber, which occurred during prolonged (>24 h) incubation in the absence of hydrogel. Phase II metabolism was completely retained in hydrogel-embedded slices when medium supplemented with dexamethasone, insulin, and calf serum was used. However, phase I metabolism was significantly decreased with respect to the initial values in gel-embedded slices with medium supplements. Slices were still able to produce phase I metabolites after 72 h, but at only about ∼10% of the initial value. The same decrease in metabolic rate was observed in slices incubated in well plates, indicating that this decrease is due to the slices and medium rather than the incubation system. In conclusion, the biochip model was significantly improved by embedding slices in Matrigel and using proper medium supplements. This is important for in vitro testing of drug metabolism, drug-drug interactions, and (chronic) toxicity.

On-line HPLC analysis system for metabolism and inhibition studies in precision-cut liver slices.

A novel approach for on-line monitoring of drug metabolism in continuously perifused, precision-cut liver slices (PCLS) in a microfluidic system has been developed using high-performance liquid chromatography with UV detection (HPLC-UV). In this approach, PCLS are incubated in a microfluidic device made of poly(dimethylsiloxane) (PDMS) by continuous, single-pass perifusion with fresh medium. Two syringe pumps are incorporated into the system to infuse substrates or inhibitors at varying concentrations into the perfusion medium just before the chip entrance. The medium containing the metabolites produced by the PCLS is directed toward an injection loop. Once filled, the content of this injection loop is automatically injected onto an HPLC for analysis. The on-line analysis of metabolites was tested by using the substrate, 7-hydroxycoumarin (7-HC). Rapid switching between substrate and solvent control was possible, and a direct metabolic response of the liver slice to perifusion with substrate was detected. Very stable phase II metabolism over a period of 24 h was observed. The inhibitory effect of phloxine B on the formation of 7-hydroxycoumarin glucuronide (phase II product of 7-HC) was also investigated. Phloxine B was injected into the incubation medium in increasing concentrations varying from 0 to 200 µM. The results showed a concentration-dependent inhibition of 7-HC glucuronide formation and allowed the calculation of an IC50 value (concentration in which 50% of the enzyme is inhibited) of ∼85 µM using one single liver slice. On-line detection was also shown to be advantageous for the detection of unstable metabolites. This was demonstrated by determination of the metabolites of the drug diclofenac. The reactive metabolite, acyl glucuronide, was detected at relatively high concentrations which remained very constant over a period of 4 h. In contrast, only low and decreasing amounts of diclofenac acyl glucuronide could be measured in the conventional well-plate incubation system. The advantages of this novel on-line analysis system for PCLS include the capability to obtain direct information about tissue function, assess the concentration dependence of drug-drug interactions in one single slice, and detect unstable metabolites. The system also enables fast analysis without the need to store samples, thus eliminating the associated freeze-thaw problems, and allows the simultaneous analysis of multiple metabolites.

A microfluidic approach for in vitro assessment of interorgan interactions in drug metabolism using intestinal and liver slices.

Over the past two decades, it has become increasingly clear that the intestine, in addition to the liver, plays an important role in the metabolism of xenobiotics. Previously, we developed a microfluidic-based in vitro system for the perifusion of precision-cut liver slices for metabolism studies. In the present study, the applicability of this system for the perifusion of precision-cut intestinal slices, and for the sequential perifusion of intestinal and liver slices, all from rat, was tested to mimic the in vivo first pass situation. Intestinal and liver slices, exposed to the substrates 7-ethoxycoumarin (7-EC), 7-hydroxycoumarin (7-HC) and lidocaine (Li), exhibited similar metabolic rates in the biochip and in the well plates for periods of at least 3 h. The metabolic rate remained the same when two slices were placed in adjacent microchambers and perifused sequentially. In addition, the system has been adapted to sequentially perifuse intestinal and liver tissue slices in a two-compartment co-culture perfusion system with a continuous flow of medium. It becomes possible to direct metabolites or other excreted compounds formed by an intestinal slice in the first compartment to the second compartment containing a liver slice. The intestine does not influence liver metabolism for these substrates. The interplay between these two organs was demonstrated by exposing the slices to the primary bile acid, chenodeoxycholic acid (CDCA). CDCA induced the expression of fibroblast growth factor 15 (FGF15) in the intestinal slice, which resulted in a stronger down-regulation of the enzyme, cytochrome P450 7A1 (CYP7A1), in the liver slice in the second compartment than when the liver slice was exposed to CDCA in a single-microchamber biochip. We thus demonstrate in this paper that intestinal slices, in addition to liver slices, remain functional in the biochip under flow conditions, and that the two-microchamber biochip has great potential for the study of interorgan effects. This is the first example of the incorporation of both liver and intestinal slices in a microfluidic device. Use of this microfluidic system will improve our insight into interorgan interactions and elucidate as yet unknown mechanisms involved in toxicity, gene regulation and drug-drug interactions.

Preparation and incubation of precision-cut liver and intestinal slices for application in drug metabolism and toxicity studies.

Precision-cut tissue slices (PCTS) are viable ex vivo explants of tissue with a reproducible, well defined thickness. They represent a mini-model of the organ under study and contain all cells of the tissue in their natural environment, leaving intercellular and cell-matrix interactions intact, and are therefore highly appropriate for studying multicellular processes. PCTS are mainly used to study the metabolism and toxicity of xenobiotics, but they are suitable for many other purposes. Here we describe the protocols to prepare and incubate rat and human liver and intestinal slices. Slices are prepared from fresh liver by making a cylindrical core using a drill with a hollow bit, from which slices are cut with a specially designed tissue slicer. Intestinal tissue is embedded in cylinders of agarose before slicing. Slices remain viable for 24 h (intestine) and up to 96 h (liver) when incubated in 6- or 12-well plates under 95% O(2)/5% CO(2) atmosphere.

Microfluidic biochip for the perifusion of precision-cut rat liver slices for metabolism and toxicology studies.

Early detection of kinetic, metabolic, and toxicity (ADME-Tox) profiles for new drug candidates is of crucial importance during drug development. This article describes a novel in vitro system for the incubation of precision-cut liver slices (PCLS) under flow conditions, based on a poly(dimethylsiloxane) (PDMS) device containing 25-microL microchambers for integration of the slices. The microdevice is coupled to a perifusion system, which enables a constant delivery of nutrients and oxygen and a continuous removal of waste products. Both a highly controlled incubation environment and high metabolite detection sensitivity could be achieved using microfluidics. Liver slices were viable for at least 24 h in the microdevice. The compound, 7-ethoxycoumarin (7-EC), was chosen to test metabolism, since its metabolism includes both phase I and phase II metabolism and when tested in the conventional well plate system, correlates well with the in vivo situation (De Kanter et al. 2004. Xenobiotica 34(3): 229-241.). The metabolic rate of 7-EC was found to be 214 +/- 5 pmol/min/mg protein in the microdevice, comparable to well plates, and was constant over time for at least 3 h. This perifusion system better mimics the in vivo situation, and has the potential to significantly contribute to drug metabolism and toxicology studies of novel chemical entities.

The influence of brain death on liver function.

BACKGROUND: In this study, we investigated the influence of brain death on inflammatory response and the effects of brain death on liver function both directly after explantation and after reoxygenation. METHODS: The influence of brain death on liver function was studied in rats using a brain death model and the liver slice model to mimic reoxygenation. Liver function was assessed by measuring the ATP content and the ATP-driven urea synthesis. The activation of non-parenchymal cells was studied by measuring mRNA levels of IL-10, cytokine production (IL-10 and IL-1 beta) and inducible nitric oxide synthases (iNOS) upregulation (mRNA) and protein level. RESULTS: Brain death had no direct influence on the ATP content of the liver. However, it led to induction of several cytokines because of activation of non-parenchymal cells, which led to upregulation of iNOS and to nitric oxide metabolites production. It is known that cytokine production may influence the drug metabolism capacity; however, no influence of brain death on drug metabolism was observed. An explanation may be the relatively short experimental period. CONCLUSIONS: Kupffer cells seem to be activated during the onset of brain death induction; however, they become quiescent when liver slices of brain dead rats were reoxygenated during incubation. Other non-parenchymal cells, possibly the endothelial cells, remain activated during incubation and reoxygenation in slices from brain death donors but not in slices from control livers. Future experiments in our rat liver transplantation model need to elucidate the implications of these findings.

Precision-cut liver slices as a new model to study toxicity-induced hepatic stellate cell activation in a physiologic milieu.

Hepatic stellate cell (HSC) activation is a key event in the natural process of wound healing as well as in fibrosis development in liver. Current in vitro models for HSC activation contribute significantly to the understanding of HSC biology and fibrogenesis but still fall far short of recapitulating in vivo intercellular functional and anatomic relationships. In addition, when cultured on uncoated plastic, HSC spontaneously activate, which makes HSC activation difficult to regulate or analyze. We have examined whether the use of precision-cut liver slices might overcome these limitations. Liver slices (8 mm diameter, 250 microm thickness) were generated from normal rat liver and incubated for 3 or 16 h with increasing doses of carbon tetrachloride (CCl4). Rat liver slices remained viable during incubation, as shown by minimal enzyme leakage. Expression of markers for HSC activation and the onset of fibrogenesis in the liver slices was studied using real-time PCR and Western blotting. In unstimulated liver slices, mRNA and protein levels of desmin, heat shock protein 47, and alpha B-crystallin remained constant, indicating quiescence of HSC, whereas Krüppel-like factor 6 expression was increased. In contrast, incubation with CCl4 led to a time- and dose-dependent increase in mRNA expression of all markers and an increased alpha B-crystallin protein expression. In conclusion, we have developed a technique to induce activation of quiescent HSC in rat liver slices. This model permits the study of toxicity-induced HSC activation within a physiological milieu, not only in animal but ultimately also in human tissue, and could contribute to the reduction of animal experiments.

Organ slice viability extended for pathway characterization: an in vitro model to investigate fibrosis.

Liver slice viability is extended to 96 h for rat, expanding the use of this in vitro model for studying mechanisms of injury and repair, including pathways of fibrosis. The contributing factors to increased organ slice survival consist of the use of a preservation solution for liver perfusion and slice preparation, obtaining rats that are within the weight range of 250-325 g, placing a cellulose filter atop the titanium mesh roller-insert to support the slice, and maintaining the slices in an optimized culture medium which is replaced daily. The liver slices remain metabolically active, synthesizing adenosine triphosphate (ATP), glutathione, and glycogen, and exhibit preserved organelle integrity and slice morphology. Slice preparation results in 2-cut surfaces which likely triggers a repair and regenerative response. The fibrogenic pathways are evident by the activation of stellate cells, the proliferation of myofibroblast-like cells, and an increased collagen deposition by 48 h. Markers indicative of activated stellate cells, alpha-smooth muscle actin, collagen 1a1, desmin, and HSP47 are substantiated by real time-PCR. Increased staining of alpha-smooth muscle actin initially around the vessels and by 72-96 h in the tissue is accompanied by increased collagen staining. Microarray gene expression revealed extracellular matrix changes with the up-regulation of cytoskeleton, filaments, collagens, and actin genes; and the down-regulation of genes linked with lipid metabolism. The improvements in extending liver slice survival, in conjunction with its three-dimensional multi-cellular complexity, increases the application of this in vitro model for investigating pathways of injury and repair, and fibrosis.

LPS-induced downregulation of MRP2 and BSEP in human liver is due to a posttranscriptional process.

Endotoxin-induced cholestasis in rodents is caused by hepatic downregulation of transporters, including the basolateral Na+-dependent taurocholate transporter (ntcp) and the canalicular bile salt export pump (bsep) and multidrug resistance-associated protein 2 (mrp2). Details about the regulation of the human transporter proteins during this process are lacking. We used precision-cut human and rat liver slices to study the regulation of transporter expression during LPS-induced cholestasis. We investigated the effect of LPS on nitrate/nitrite and cytokine production in relation to the expression of inducible nitric oxide synthase, NTCP, BSEP, and MRP2 both at the level of mRNA with RT-PCR and protein using immunofluorescence microscopy. In liver slices from both species, LPS-induced expression of inducible nitric oxide synthase was detected within 1-3 h and remained increased over 24 h. In rat liver slices, this was accompanied by a significant decrease of rat ntcp and mrp2 mRNA levels, whereas bsep levels were not affected. These results are in line with previous in vivo studies and validate our liver slice technique. In LPS-treated human liver slices, NTCP mRNA was downregulated and showed an inverse correlation with the amounts of TNF-alpha and Il-1beta produced. In contrast, MRP2 and BSEP mRNA levels were not affected under these conditions. However, after 24-h LPS challenge, both proteins were virtually absent in human liver slices, whereas marker proteins remained detectable. In conclusion, we show that posttranscriptional mechanisms play a more prominent role in LPS-induced regulation of human MRP2 and BSEP compared with the rat transporter proteins.