Primary rat hepatocytes as in vitro system for gene expression studies: comparison of sandwich, Matrigel and 2D cultures

Recent studies have presented evidence that in vivo obtained gene expression data can be used for carcinogen classification, for instance to differentiate between genotoxic and non-genotoxic carcinogens. However, although primary rat hepatocytes represent a well-established in vitro system for drug metabolism and enzyme induction, they have not yet been systematically optimized for toxicogenomic studies. The latter may be confounded by the fact that cultured hepatocytes show strong spontaneous alterations in gene expression patterns. Therefore, we addressed the following questions: (1) which culture system is optimal, comparing sandwich, Matrigel and 2D cultures, (2) how critical is the impact of culture period on substance-induced alterations in gene expression and (3) do these substance-induced alterations in cultured hepatocytes occur already at in vivo relevant concentrations? For this purpose we analyzed the expression of four genes, namely Abat, Gsk3β, Myd116 and Sult1a1 that recently have been reported to be influenced by the antihistamine and non-genotoxic carcinogen methapyrilene (MPy). The most reproducible effects of MPy were observed in sandwich cultures. Induction factors of Gsk3β and Myd116 at 100 μM MPy were 2 and 4 (medians), respectively, whereas expression of Abat and Sult1a1 were inhibited by factors of 7 and 5, respectively. Similar results were observed in hepatocytes maintained for 24 h or 3 weeks in sandwich culture with respect to the influence of MPy on the expression of Abat, Gsk3β, Myd116 and Sult1a1. To determine whether MPy influences gene expression at in vivo relevant concentrations, 3.5 mg/kg MPy were administered to male Wistar rats intraperitoneally, resulting in plasma concentrations ranging between 1.72 and 0.32 μM 5 and 80 min after injection. Inhibition of Abat and Sult1a1 expression in vitro already occurred at in vivo relevant concentrations of 0.39 μM MPy. Induction of Myd116 was observed at 6.25 μM which is higher but in the same order of magnitude as in vivo relevant concentrations. In conclusion, the presented data strongly suggest that sandwich cultures are most adequate for detection of MPy-induced gene expression alterations and the effect of MPy was detected at in vivo relevant concentrations.     

Type of endothelial cells affects HepaRG cell acetaminophen metabolism in both 2D and 3D porous scaffold cultures

Recent advances in developing in vitro tissue models show that function of hepatocytes is altered in when cultured in 3D configuration and co‐culturing with various non‐parenchymal cells. However, tissue source for such non‐parenchymal cells on viability and metabolic products of hepatocytes have not been explored. In this study, we evaluated the effect of 2D and 3D cultures either with HepaRG cells alone or in combination with liver sinusoidal endothelial cells (LSECs) and human umbilical vein ECs (HUVECs). For 3D cultures, we used chitosan‐gelatin porous structures formed by freeze‐drying. We cultured cells for 8 days before challenging with 1 mm acetaminophen (APAP) and assessed APAP, APAP‐sulfate and APAP‐glucuronide for 24 hours at 6‐hour time intervals using high‐performance liquid chromatography. We used multiple methods (phase contrast, confocal and scanning electron microscopy and histology via hematoxylin and eosin staining) to ensure cell distribution. We also measured total protein content and albumin secretion and viability. HUVEC 3D co‐cultures showed the lowest HepaRG cell viability, while both 2D and 3D LSEC co‐cultures had highest HepaRG cell viability. In addition, 3D cultures had significantly higher EC viability relative to 2D cultures. Further, HUVEC co‐cultures showed reduced total protein content and albumin expression as early as day 4. However, urea production on a total protein content basis did not change. In addition, LSEC 3D co‐cultures had the highest APAP conversion with reduced APAP‐sulfate and APAP‐glucuronide formation. CYP3A4 was higher in co‐culture with HUVEC for 2D and 3D cultures. In conclusion, HepaRG cells with EC co‐cultures demonstrated sensitivity to the EC line used.     

Rifampicin exacerbates isoniazid-induced toxicity in human but not in rat hepatocytes in tissue-like cultures

BACKGROUND AND PURPOSE: Rifampicin has been extensively reported to exacerbate the hepatotoxicity of isoniazid in patients with tuberculosis. However, this was controversially claimed by previous reports using rat models. This study evaluated the effect of rifampicin on isoniazid-induced hepatocyte toxicity by using human and rat hepatocytes in tissue-like culture.EXPERIMENTAL APPROACH: Hepatocytes in tissue-like gel entrapment were used to examine isoniazid toxicity, as shown by cell viability, intracellular glutathione content and albumin secretion. For demonstration of the differential effects of rifampicin on human and rat hepatocytes, induction by rifampicin of cytochrome P450 (CYP) 2E1, a major enzyme associated with isoniazid hepatotoxicity, was detected by 4-nitrocatechol formation and RT-PCR analysis.KEY RESULTS: Rifampicin (12 microM) enhanced isoniazid-induced toxicity in human hepatocytes but not in rat hepatocytes. Enhanced CYP 2E1 enzymic activity and mRNA expression were similarly detected in human hepatocytes but not in rat hepatocytes. Both rat and human hepatocytes in gel entrapment were more sensitive to isoniazid treatment compared with the corresponding hepatocytes in a monolayer culture.CONCLUSIONS AND IMPLICATIONS: The difference in induction of CYP 2E1 by rifampicin between rat and human hepatocytes accounted for the difference in exacerbation of isoniazid hepatocyte toxicity by rifampicin, with more significant toxicity in gel entrapment than in monolayer cultures. Thus, human hepatocytes in tissue-like cultures (gel entrapment) could be an effective model for hepatotoxicity research in vitro, closer to the in vivo situation.     

Prediction of cytochrome 450 mediated drug-drug interactions by three-dimensional cultured hepatocytes

Cytochrome P450 (CYP) inhibition and induction are the key mechanisms in drug-drug interactions which should be avoided in clinic for the uncertain influence on the efficacy and safety of drug co-administration. The CYPmediated drug-drug interactions urgently need to be predicted by in vitro models before animal and clinical trials, while the primary hepatocytes may represent the most appropriate experimental system by now. However, traditional twodimensional (2D) culture of hepatocyte monolayer, regardless of the good facilitation and repeatability, rapidly loses its CYP-inducibility during short-term culture due to the deviated microenvironments from in vivo. Also, 2D culture did not reproduce the CYP-inhibition mediated hepatotoxicity in drug co-administration. Recently, three-dimensional (3D) cultured hepatocytes have been recognized as the promising models for predicting in vivo drug-drug interactions. The 3D cultures such as sandwich and gel entrapped hepatocytes showed the comparable response to CYP inhibitors and inducers as in vivo and well reflected the inhibitor/inducer mediated hepatotoxicity. In this regard, this review, for the first time, compares the effect of 2D and 3D hepatocyte cultures on reflecting CYP-mediated drug-drug interactions in vivo. And the advantage of 3D cultured hepatocytes on predicting in vivo CYP-induction/inhibition will be particularly discussed.     

A comprehensive evaluation of metabolic activity and intrinsic clearance in suspensions and monolayer cultures of cryopreserved primary human hepatocytes

Primary human hepatocytes are widely used for metabolic stability evaluations. However, there are limited data directly comparing phase I and phase II drug‐metabolizing enzymes in fresh and cryopreserved hepatocytes prepared from the same human donor liver. We evaluated the metabolic competency of human hepatocytes prepared from seven donor tissues before and after cryopreservation. Temporal‐dependent enzyme activity in suspension and matched adherent cultures of primary human hepatocytes was also assessed. Cryopreservation of hepatocytes resulted in statistically significant increases in activities of CYP1A2, CYP2B6, CYP2C9, CYP2D6, and CYP3A but not CYP2C8, CYP2C19, FMO, UGT, and SULT, relative to fresh hepatocytes. In suspension cultures of hepatocytes, enzyme stabilities were as follows: UGT相似文献   

Biotransformation of trichloroethylene in collagen gel sandwich cultures of rat hepatocytes

The collagen gel sandwich culture of hepatocytes has been proposed as one of the most suitable culture models available for biotransformation studies of xenobiotics. It is a complex model which imitates the cascade of enzymatic events of in vivo biotransformation and allows investigation of biological endpoints under realistic conditions. The biotransformation of trichloroethylene (TRI) has been studied in this model using rat hepatocytes. Headspace gas chromatographic measurements revealed that hepatocytes, cultured for 4 days in this in vitro system, metabolised TRI into the major oxidative metabolites trichloroacetic acid (TCA) and trichloroethanol (TCE). Cultured hepatocytes were exposed either to TRI, or to TCA and TCE. Endpoints studied were albumin secretion and the cytochrome P450 (CYP)-dependent enzymatic activities ethoxyresorufin O-deethylase (EROD), pentoxyresorufin O-depentylase (PROD) and N-nitrosodimethylamine demethylase (NDMA). The results show that both the parent compound and its metabolites exert specific effects on different CYP-dependent mono-oxygenase activities, as seen in vivo. It is suggested that collagen gel sandwich cultures represent a useful in vitro model for the investigation of metabolism-linked toxicity studies.     

Molecular,cellular, and tissue impact of depleted uranium on xenobiotic-metabolizing enzymes

Enzymes that metabolize xenobiotics (XME) are well recognized in experimental models as representative indicators of organ detoxification functions and of exposure to toxicants. As several in vivo studies have shown, uranium can alter XME in the rat liver or kidneys after either acute or chronic exposure. To determine how length or level of exposure affects these changes in XME, we continued our investigation of chronic rat exposure to depleted uranium (DU, uranyl nitrate). The first study examined the effect of duration (1–18 months) of chronic exposure to DU, the second evaluated dose dependence, from a level close to that found in the environment near mining sites (0.2 mg/L) to a supra-environmental dose (120 mg/L, 10 times the highest level naturally found in the environment), and the third was an in vitro assessment of whether DU exposure directly affects XME and, in particular, CYP3A. The experimental in vivo models used here demonstrated that CYP3A is the enzyme modified to the greatest extent: high gene expression changed after 6 and 9 months. The most substantial effects were observed in the liver of rats after 9 months of exposure to 120 mg/L of DU: CYP3A gene and protein expression and enzyme activity all decreased by more than 40 %. Nonetheless, no direct effect of DU by itself was observed after in vitro exposure of rat microsomal preparations, HepG2 cells, or human primary hepatocytes. Overall, these results probably indicate the occurrence of regulatory or adaptive mechanisms that could explain the indirect effect observed in vivo after chronic exposure.     

The use of human hepatocyte cultures to study the induction of cytochrome P-450.

We have previously reported that paclitaxel (Taxol) is a potent inducer of cytochrome P-450 (CYP) 3A protein and CYP3A mRNA in human hepatocyte cultures. Here we report that Taxol increased CYP3A-dependent testosterone 6beta-hydroxylation in intact hepatocytes. This effect was concentration-dependent, with maximal increase in enzyme activity being observed at 10 microM Taxol. Treatment of hepatocyte cultures with concentrations of Taxol higher than 10 microM caused a dose-dependent decrease in testosterone 6beta-hydroxylase activity, amount of CYP3A protein, and total protein synthesis. The maximal CYP3A activity detected after treatment with Taxol or rifampicin was similar in six separate human hepatocyte cultures, suggesting that the cultures have achieved a limit of maximally inducible CYP3A. The fold increase in enzyme activity, however, was different and was inversely related to the level of expression in untreated hepatocytes, with the greatest increases being observed in the hepatocytes that expressed the lowest basal level of CYP3A. Pretreatment of hepatocytes with triacetyloleandomycin resulted in a 90% inhibition of testosterone 6beta-hydroxylase activity. Our results demonstrate the use of human hepatocyte cultures to investigate the induction of cytochrome P-450 by xenobiotics in intact cells and stress the importance of large dose-response studies as well as the need to assess toxicity in these investigations. The response to inducers of CYP3A activity were very consistent among different hepatocyte donors. Absolute values of testosterone 6beta-hydroxylase activity did not vary more than 2- and 5-fold in induced and untreated hepatocytes, respectively.     

Ginkgolide A contributes to the potentiation of acetaminophen toxicity by Ginkgo biloba extract in primary cultures of rat hepatocytes

The present cell culture study investigated the effect of Ginkgo biloba extract pretreatment on acetaminophen toxicity and assessed the role of ginkgolide A and cytochrome P450 3A (CYP3A) in hepatocytes isolated from adult male Long-Evans rats provided ad libitum with a standard diet. Acetaminophen (7.5-25 mM for 24 h) conferred hepatocyte toxicity, as determined by the lactate dehydrogenase (LDH) assay. G. biloba extract alone increased LDH leakage in hepatocytes at concentrations > or =75 mug/ml and > or =750 mug/ml after a 72 h and 24 h treatment period, respectively. G. biloba extract (25 or 50 mug/ml once every 24 h for 72 h) potentiated LDH leakage by acetaminophen (10 mM for 24 h; added at 48 h after initiation of extract pretreatment). The effect was confirmed by a decrease in [(14)C]-leucine incorporation. At the level present in a modulating concentration (50 mug/ml) of the extract, ginkgolide A (0.55 mug/ml), which increased CYP3A23 mRNA levels and CYP3A-mediated enzyme activity, accounted for part but not all of the potentiating effect of the extract on acetaminophen toxicity. This occurred as a result of CYP3A induction by ginkgolide A because triacetyloleandomycin (TAO), a specific inhibitor of CYP3A catalytic activity, completely blocked the effect of ginkgolide A. Ginkgolide B, ginkgolide C, ginkgolide J, quercetin, kaempferol, isorhamnetin, and isorhamnetin-3-O-rutinoside did not alter the extent of LDH leakage by acetaminophen. In summary, G. biloba pretreatment potentiated acetaminophen toxicity in cultured rat hepatocytes and ginkgolide A contributed to this novel effect of the extract by inducing CYP3A.     

3D organotypic HepaRG cultures as in vitro model for acute and repeated dose toxicity studies

Predictive in vitro models alternative to in vivo animal will have a significant impact in toxicology. Conventional 2D models do not reflect the complexity of a 3D organ resulting in discrepancies between experimental in vitro and in vivo data. Using 3D HepaRG organotypic cultures we tested four drugs (aflatoxin B1, amiodarone, valproic acid and chlorpromazine) for toxic effects and compared the results with 2D HepaRG and HepG2 cultures. We show that 3D HepaRG cultures are more sensitive than the other tested cultures to aflatoxin B1 which is only toxic upon metabolic activation in the liver. We observed that CYP3A4 activity is higher in the 3D HepaRG cultures compared to the 2D HepaRG cultures. Furthermore, we investigated repeated dose toxicity of chlorpromazine and assessed its effects on glucose and lactate metabolism. Sub-toxic concentrations of chlorpromazine induced significant metabolic changes in both 2D and 3D HepaRG cultures upon acute and repeated dose (3 doses) exposure. In summary, our data support the hypothesis that 3D cell culture models better mimic the in vivo tissue and improve cellular functionality. The 3D HepaRG organotypic cultures represent a high throughput system for drug toxicity screening. This system is therefore a promising tool in preclinical testing of human relevance which can allow reducing and/or replacing animal testing for drug adverse effects.     

Time-course activities of Oct1, Mrp3, and cytochrome P450s in cultures of cryopreserved rat hepatocytes

The organic cation transporter 1 (Oct1) has been shown to be one of the most abundant uptake transporters responsible for the uptake of xenobiotics from the sinusoidal blood across the basolateral membrane of hepatocytes. On the same membrane the multidrug resistance-associated protein 3 (Mrp3) mediates the efflux of xenobiotics or their metabolites from the hepatocytes to the blood allowing their systemic exposure. In the present study we investigated the expression and activity of Oct1 and Mrp3 in suspensions and in monolayer- and sandwich cultures, and activities of CYP2B1/2, 2D1, and 3A1 in monolayer- and sandwich cultures of cryopreserved rat hepatocytes. Oct1-mediated active uptake of 10 μM [(3)H]-1-methyl-4-phenylpyridinium (MPP+) into hepatocytes was assessed in the presence of quinidine (1 mM). The results showed the presence of active uptake of MPP+ in suspended hepatocytes (~91 pmol/min/mg protein). In hepatocytes in cultures (monolayer and sandwich) a time-dependent decrease in MPP+ uptake was observed from day 0 to 4, from 80 to 90 pmol/min/mg protein at day 0 to ca. 17 pmol/min/mg protein at day 4. Mrp3 activity in suspensions and in monolayer- and sandwich cultures were investigated by measuring the efflux of [(3)H]-taurocholate from hepatocytes in the presence of the Mrp3 inhibitor taurolithocholate-3-sulfate (TLC-S) (500μM). Cells in suspensions showed efflux of taurocholate by an active transport mechanism indicating Mrp3 activity. Experiments in monolayer- and sandwich cultures also showed Mrp3 activity at day 0 and 1 in culture whereas experiments performed at day 2-4 showed no difference in efflux of taurocholate in the presence or absence of TLC-S, suggesting an absence of Mrp3 activity. The time-dependent decrease in Oct1 activity from day 0 to day 4 in cultures was confirmed by qPCR data also showing a time-dependent decrease in mRNA expression, whereas qPCR data did not support the observed time-dependent decrease in Mrp3 activity in cultures. Time-course activities of CYP2B1/2, 2D1, and 3A1 were also investigated by using bupropion, bufuralol, and midazolam as respective substrates. Activities of CYP2D1 and 3A1 were reduced by ~75% and ~80%, respectively, from day 0 to day 4 in cultures, whereas activity of CYP2B1/2 was reduced by ~50% from day 0 to day 4.     

Re-evaluation of tacrine hepatotoxicity using gel entrapped hepatocytes

Controversial results about the involvement of CYP 1A2 and oxidative stress in tacrine-induced hepatotoxicity have been described by the different research groups. We suggested that different expression levels of CYP 1A2 in cell lines and primary hepatocytes in vitro may be the cause of the controversial results above. Therefore, this paper re-evaluated the toxicity of tacrine by using gel entrapment culture of rat hepatocytes. The toxic effect of tacrine on hepatocytes was assayed by the reduction of methyl thiazolyl tetrazolium (MTT) and intracellular glutathione (GSH), as well as by albumin synthesis. It was found that the detectable hepatotoxic dose of tacrine is much lower in hepatocytes entrapped in gel than in those in monolayer cultures. The fact that fluvoxamine, a potent cytochrome P450 (CYP) 1A2 inhibitor, reduced tacrine toxicity and the expression of the CYP 1A2 gene was maintained in gel entrapped hepatocytes, but not in hepatocyte monolayers, could illustrate a close association between CYP 1A2 expression levels and tacrine toxicity. Glycyrrhetinic acid (GA), a free radical scavenger, protected gel entrapped hepatocytes from tacrine toxicity, but was ineffective in hepatocyte monolayers. Hence, gel entrapped hepatocytes could reflect higher tacrine hepatotoxicity in vivo than hepatocyte monolayers.     

HepG2 cells simultaneously expressing five P450 enzymes for the screening of hepatotoxicity: identification of bioactivable drugs and the potential mechanism of toxicity involved

Use of the HepG2 cell line to assess hepatotoxicity induced by bioactivable compounds is hampered by their low cytochrome P450 expression. To overcome this limitation, we have used adenoviral transfection to develop upgraded HepG2 cells (ADV-HepG2) expressing the major P450 enzymes involved in drug metabolism (CYP1A2, CYP2D6, CYP2C9, CYP2C19, and CYP3A4) at levels comparable to those of human hepatocytes. The potential utility of this new cell model for the in vitro screening of bioactivable drugs was assessed using a high-content screening assay that we recently developed to simultaneously measure multiple parameters indicative of cell injury. To this end, ADV-HepG2 and HepG2 cells, cultured in 96-well plates, were exposed for 24 h to a wide range of concentrations of 12 bioactivable and 3 non-bioactivable compounds. The cell viability and parameters associated with nuclear morphology, mitochondrial function, intracellular calcium concentration, and oxidative stress indicative of prelethal cytotoxicity and representative of different mechanisms of toxicity were evaluated. Bioactivable compounds showed lower IC₅₀ values in ADV-HepG2 cells than in HepG2 cells. Moreover, significant differences in the other parameters analyzed were observed between both cell models, while similar effects were observed for non-bioactivable compounds (negative controls). The changes in cell parameters detected in our assay for a given compound are in good agreement with the previously reported toxicity mechanism. Overall, our results indicate that this assay may be a suitable new in vitro approach for early screening of compounds to identify bioactivable hepatotoxins and the mechanism(s) involved in their toxicity.     

Evaluation of dextromethorphan metabolism using hepatocytes from CYP2D6 poor and extensive metabolizers

It is important to estimate the defective metabolism caused by genetic polymorphism of drug metabolizing enzymes before the clinical stage. We evaluated the utility of cryopreserved human hepatocytes of CYP2D6 poor metabolizer (PM) for the estimation of the metabolism in PM using dextromethorphan (DEX) as the probe drug for CYP2D6 substrate. The results of low formations of dextrorphan (DXO) and 3-hydroxymorphinan (3-HM) in CYP2D6 PM hepatocytes incubated with dextromethorphan reflected the clinical data. Formation of 3-methoxymorphinan (3-MEM) normalized by CYP3A4/5 activity in the PM hepatocytes reached about 2.8-fold higher than that in CYP2D6 extensive metabolizer (EM) hepatocytes, which clearly showed the compensatory metabolic pathway of O-demethylation catalyzed by CYP2D6 as seen in clinical study. On the contrary, in the condition of the EM hepatocytes with CYP2D6 inhibitors, the enhancement of 3-MEM formation was not observed. In phase II reaction, the glucuronide formation rate of DXO in the PM hepatocytes was lower than that in the EM hepatocytes, which was consistent with clinical data of DXO-glucuronide (DXO-glu) concentration. These results would suggest that CYP2D6 PM hepatocytes could be a good in vitro tool for estimating CYP2D6 PM pharmacokinetics.     

A cocktail of metabolic probes demonstrates the relevance of primary human hepatocyte cultures in a microfluidic biochip for pharmaceutical drug screening

In this paper, we compare the biotransformation capacities of cryopreserved primary human hepatocytes cultivated in a liver microfluidic biochip and in plates. The hepatocytes were exposed to the CIME cocktail (Carte d'Identité MEtabolique), a mixture of seven probes (acetaminophen, amodiaquine, caffeine, dextromethorphan, midazolam, omeprazole and tolbutamide) for key enzymes involved in the xenobiotic metabolism and pharmacokinetics. The purpose of the cocktail was to give an overview of the metabolic profile of the hepatocytes due to concomitant exposure and a simultaneous mass spectrometric detection method of the metabolites. The results showed a greater activity for CYP1A2, CYP2C9, CYP2C19 CYP2D6, CYP3A and UGT1A1 after 4 h of incubation in the microfluidic biochip when compared to the plate cultures. Furthermore, the metabolic ratio time-course measured at 1 h, 3 h and 4 h indicated that the enzymatic activity increased when the hepatocytes were cultivated in the microfluidic biochip, in contrast with their response in the plate cultures. These results illustrated the functional relevance of liver culture in the PDMS microfluidic biochip. The original method based on a microfluidic culture coupled with CIME cocktail analysis allowed the maintenance and the evaluation of the metabolic performances of the primary human hepatocytes through a new rapid assay. This metabolic analysis can thus become the reference situation when parallel studies of drug metabolism and toxicities are planned with functional hepatocytes in biochips.     

In vivo and in vitro induction of cytochrome P450 enzymes in beagle dogs.

The aim of this study was to determine the in vitro and in vivo effects of several prototypical inducers, namely beta-naphthoflavone, 3-methylcholanthrene, phenobarbital, isoniazid, rifampin, and clofibric acid, on the expression of cytochrome P450 (P450) enzymes in beagle dogs. For the in vitro induction study, primary cultures of dog hepatocytes were treated with enzyme inducers for 3 days, after which microsomes were prepared and analyzed for P450 activities. For the in vivo induction study, male and female beagle dogs were treated with enzyme inducers for 4 days (with the exception of phenobarbital, which was given for 14 days), after which the livers were removed and microsomal P450 activities were determined ex vivo. Treatment of male beagle dog hepatocyte cultures (n = 3) with beta-naphthoflavone or 3-methlychloranthrene resulted in up to a 75-fold increase in microsomal 7-ethoxyresorufin O-dealkylase (CYP1A1/2) activity, whereas in vivo treatment of male and female beagle dogs with beta-naphthoflavone followed by ex vivo analysis resulted in up to a 24-fold increase. Phenobarbital caused a 13-fold increase in 7-benzyloxyresorufin O-dealkylase (CYP2B11) activity in vitro and up to a 9.9-fold increase in vivo. Isoniazid had little or no effect on 4-nitrophenol hydroxylase activity in vitro. Rifampin caused a 13-fold induction of testosterone 6beta-hydroxylase (CYP3A12) activity in vitro and up to a 4.5-fold increase in vivo. Treatment of dogs in vivo or dog hepatocytes in vitro with clofibric acid appeared to have no effect on CYP4A activity as determined by the 12-hydroxylation of lauric acid. In general, the absolute rates (picomoles per minute per milligram of microsomal protein) of P450 reactions catalyzed by microsomes from cultured hepatocytes (i.e., in vitro rates) were considerably lower than those catalyzed by microsomes from dog liver (i.e., ex vivo rates). These results suggest that beagle dogs have CYP1A, CYP2B, CYP2E, and CYP3A enzymes and that the induction profile resembles the profile observed in humans more than in rats.     

Multi-cell type human liver microtissues for hepatotoxicity testing

Current 2-dimensional hepatic model systems often fail to predict chemically induced hepatotoxicity due to the loss of a hepatocyte-specific phenotype in culture. For more predictive in vitro models, hepatocytes have to be maintained in a 3-dimensional environment that allows for polarization and cell–cell contacts. Preferably, the model will reflect an in vivo-like multi-cell type environment necessary for liver-like responses. Here, we report the characterization of a multi-cell type microtissue model, generated from primary human hepatocytes and liver-derived non-parenchymal cells. Liver microtissues were stable and functional for 5 weeks in culture enabling, for example, long-term toxicity testing of acetaminophen and diclofenac. In addition, Kupffer cells were responsive to inflammatory stimuli such as LPS demonstrating the possibility to detect inflammation-mediated toxicity as exemplified by the drug trovafloxacin. Herewith, we present a novel 3D liver model for routine testing in 96-well format capable of reducing the risk of unwanted toxic effects in the clinic.     

Different in vitro and in vivo tools for elucidating the human metabolism of alpha‐cathinone‐derived drugs of abuse

In vitro and in vivo experiments are widely used for studying the metabolism of new psychoactive substances (NPS). The availability of such data is required for toxicological risk assessments and development of urine screening approaches. This study investigated the in vitro metabolism of the 5 pyrrolidinophenone‐derived NPS alpha‐pyrrolidinobutyrophenone (alpha‐PBP), alpha‐pyrrolidinopentiothiophenone (alpha‐PVT), alpha‐pyrrolidinohexanophenone (alpha‐PHP), alpha‐pyrrolidinoenanthophenone (alpha‐PEP, PV8), and alpha‐pyrrolidinooctanophenone (alpha‐POP, PV9). First, they were incubated with pooled human liver microsomes (pHLM) or pooled human liver S9 fraction (pS9) for identification of the main phase I and II metabolites. All substances formed hydroxy metabolites and lactams. Longer alkyl chains resulted in keto group and carboxylic acid formation. Comparing these results with published data obtained using pHLM, primary human hepatocytes (PHH), and authentic human urine samples, PHH provided the most extensive metabolism. Second, enzyme kinetic studies showed that the initial metabolic steps were formed by cytochrome P450 isoforms (CYP) CYP1A2, CYP2B6, CYP2C9, CYP2C19, CYP2D6, and CYP3A4 resulting in pyrrolidine, thiophene or alkyl hydroxy metabolites depending on the length of the alkyl chain. The kinetic parameters indicated an increasing affinity of the CYP enzymes with increase of the length of the alkyl chain. These parameters were then used to calculate the contribution of a single CYP enzyme to the in vivo hepatic clearance. CYP2C19 and CYP2D6 were mainly involved in the case of alpha‐PBP and CYP1A2, CYP2C9 and CYP2C19 in the case of alpha‐PVT, alpha‐PHP, alpha‐PEP, and alpha‐POP.     

Assessment of induction of cytochrome P450 by NO-1886 (ibrolipim), a lipoprotein lipase-promoting agent, in primary cultures of human hepatocytes and in female rat liver

The mRNA levels of human cytochrome P450 (CYP)2Cs and CYP3As in primary cultures of freshly isolated human hepatocytes were assessed after exposure to NO-1886 and rifampicin, a typical inducer of CYP3As. mRNA levels were analyzed by real-time RT-PCR using an ABI PRISM 7700 Sequence Detector system. Exposure to NO-1886 for 24 hr at a concentration of less than 10 microM showed only a tendency to reduce or increase the expression levels of CYP2C8, CYP2C9, CYP2C19, CYP3A4, or CYP3A5 mRNA. A higher concentration (50 microM) of NO-1886 induced an increase in CYP2C8 mRNA and a decrease in CYP2C19 mRNA, and these changes continued after additional culture for 24 hr in fresh medium without NO-1886. The expression level of CYP3A4 mRNA after exposure to NO-1886 for 24 hr at 50 microM was about twice that in controls. Following additional culture for 24 hr in fresh medium without NO-1886, the expression of CYP3A4 mRNA was comparable to that in controls. On the other hand, the expression levels of CYP2C9 and CYP3A5 mRNA showed small and variable changes in each donor even at a high concentration (50 microM) of NO-1886. Furthermore, the pharmacokinetics of NO-1886 during repeated oral administration for 14 days was studied in female rats. The pharmacokinetic parameters of NO-1886 were nearly the same on days 1, 7, and 14 of repeated administration. The hepatic microsomal content of CYP isoforms was not affected by repeated administration for 7 days at a dose of 1 to 30 mg/kg in female rats, although the total CYP content was increased at a dose of 30 mg/kg. The expression levels of CYP1A2, CYP2B2, CYP2C12, and CYP2E1 mRNA in primary cultures of rat hepatocytes were not affected by exposure to NO-1886 at 2, 10, or 50 microM. The expression levels of CYP3A1 mRNA in primary cultures of rat hepatocytes were not affected by exposure to NO-1886 at 2 or 10 microM, but were increased, with large individual variation, by exposure at 50 microM. The mRNA expression levels in rat hepatocytes exposed to concentrations comparable to free plasma levels did not change significantly, which was consistent with the equivalence in the in vivo plasma concentrations observed on days 1 and 14 of repeated administration. These results suggest that repeated administration of NO-1886 at clinical doses does not significantly affect the expression levels of CYP isoforms in human liver, although the mRNA levels of the CYP isoforms involved in the metabolism of NO-1886 were increased by exposure to higher concentrations of NO-1886 in human hepatocytes in vitro.