The effects of inducing agents on cytochrome P450 and UDP-glucuronyltransferase activities in human HEPG2 hepatoma cells

Unveiling hepatotoxicity distinction of coumarin-related compounds from glycosides to aglycones in Fructus Psoraleae by integrating UPLC-Q-TOF-MS and high content analysis

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Psoraleae (FP), the dried and ripe fruit of Cullen corylifolium (L.) Medik., is widely used due to its various clinical pharmacological effects, but its hepatotoxicity restricts its clinical application. So far, its hepatotoxic components and their underlying mechanism have not been systematically elucidated.

AIM OF THE STUDY

This study was undertaken to reveal the hepatotoxicity distinction of coumarin-related compounds from glycosides to aglycones in FP and elucidate their potential mechanism.

METHODS

Rats were administrated with the aqueous extract of Fructus Psoraleae (AEFP), in which eight coumarin-related compounds were focused. Subsequently, compounds exposed in rats' livers were detected by UPLC-Q-TOF-MS, and the identified hepatotoxic compounds were evaluated to elaborate their possible mechanism by the aid of high content analysis (HCA).

RESULTS

Eight coumarin-related compounds were identified, among which psoralenoside (PO), isopsoralenoside (IPO), psoralen (P), and isopsoralen (IP) were the principally exposed compounds in rats' livers. Furocoumarinic acid glucoside (FAG), (E)-3-(4-(((2S, 3R, 4S, 5S, 6R)-3,4,5-trihydroxy-6-(hydroxymethyl) tetrahydro-2H-pyran-2-yl) oxy) benzofuran-5-yl) acrylic acid (isofurocoumarinic acid glucoside, IFAG), furocoumarinic acid (FA), and (E)-3-(4-hydroxybenzofuran-5-yl) acrylic acid (isofurocoumarinic acid, IFA) were also detected in low abundance. P, IP, FA, and IFA were identified as the hepatotoxic compounds, while their glycosides were almost non-hepatotoxic. The HCA's results showed that hepatotoxic compounds disrupted the balance in reactive oxygen species (ROS), nuclear area, and mitochondrial membrane potential of HepG2 cells, leading to the occurrence of hepatotoxicity.

CONCLUSIONS

P, IP, FA, and IFA were identified as hepatotoxic compounds, from which P and IP were proposed as the important risk components for hepatotoxicity. The conversion from glycosides to aglycones played an essential role in FP-induced hepatotoxicity.

Prediction of Moxifloxacin Concentrations in Tuberculosis Patient Populations by Physiologically Based Pharmacokinetic Modeling

Moxifloxacin has an important role in the treatment of tuberculosis (TB). Unfortunately, coadministration with the cornerstone TB drug rifampicin results in suboptimal plasma exposure. We aimed to gain insight into the moxifloxacin pharmacokinetics and the interaction with rifampicin. Moreover, we provided a mechanistic framework to understand moxifloxacin pharmacokinetics. We developed a physiologically based pharmacokinetic model in Simcyp version 19, with available and newly generated in vitro and in vivo data, to estimate pharmacokinetic parameters of moxifloxacin alone and when administered with rifampicin. By combining these strategies, we illustrate that the role of P-glycoprotein in moxifloxacin transport is limited and implicate MRP2 as transporter of moxifloxacin-glucuronide followed by rapid hydrolysis in the gut. Simulations of multiple dose area under the plasma concentration-time curve (AUC) of moxifloxacin (400 mg once daily) with and without rifampicin (600 mg once daily) were in accordance with clinically observed data (predicted/observed [P/O] ratio of 0.87 and 0.80, respectively). Importantly, increasing the moxifloxacin dose to 600 mg restored the plasma exposure both in actual patients with TB as well as in our simulations. Furthermore, we extrapolated the single dose model to pediatric populations (P/O AUC ratios, 1.04-1.52) and the multiple dose model to children with TB (P/O AUC ratio, 1.51). In conclusion, our combined approach resulted in new insights into moxifloxacin pharmacokinetics and accurate simulations of moxifloxacin exposure with and without rifampicin. Finally, various knowledge gaps were identified, which may be considered as avenues for further physiologically based pharmacokinetic refinement.

Development of an in vitro screening method of acute cytotoxicity of the pyrrolizidine alkaloid lasiocarpine in human and rodent hepatic cell lines by increasing susceptibility

ETHNOPHARMACOLOGICAL RELEVANCE

Pyrrolizidine alkaloids (PAs) are secondary plant ingredients formed in many plant species to protect against predators. PAs are generally considered acutely hepatotoxic, genotoxic and carcinogenic. Up to now, only few in vitro and in vivo investigations were performed to evaluate their relative toxic potential.

AIM OF THE STUDY

The aim was to develop an in vitro screening method of their cytotoxicity.

MATERIALS AND METHODS

Human and rodent hepatocyte cell lines (HepG2 and H-4-II-E) were used to assess cytotoxicity of the PA lasiocarpine. At concentrations of 25 µM up to even 2400 µM, no toxic effects in neither cell line was observed with standard cell culture media. Therefore, different approaches were investigated to enhance the susceptibility of cells to PA toxicity (using high-glucose or galactose-based media, induction of toxifying cytochromes, inhibition of metabolic carboxylesterases, and inhibition of glutathione-mediated detoxification).

RESULTS

Galactose-based culture medium (11.1 mM) increased cell susceptibility in both cell-lines. Cytochrome P450-induction by rifampicin showed no effect. Inhibition of carboxylesterase-mediated PA detoxification by specific carboxylesterase 2 inhibitor loperamide (2.5 µM) enhanced lasiocarpine toxicity, whereas the unspecific carboxylesterase inhibitor bis(4-nitrophenyl)phosphate (BNPP, 100 µM)) had a weaker effect. Finally, the inhibition of glutathione-mediated detoxification by buthionine sulphoximine (BSO, 100 µM) strongly enhanced lasiocarpine toxicity in H-4-II-E cells in low and medium, but not in high concentrations.

CONCLUSIONS

If no toxicity is observed under standard conditions, susceptibility enhancement by using galactose-based media, loperamide, and BSO may be useful to assess relative acute cytotoxicity of PAs in different cell lines.

Cytotoxicity and genotoxicity of nanosilver in stable GADD45α promoter-driven luciferase reporter HepG2 and A549 cells

OBJECTIVES

The intense commercial application of silver nanoparticles (AgNPs) has been raising concerns about their potential adverse health effects to human. This study aimed to explore the potency of AgNPs to induce GADD45α gene, an important stress sensor, and its relationships with the cytotoxicity and genotoxicity elicited by AgNPs.

METHODS

Two established HepG2 and A549 cell lines containing the GADD45α promoter-driven luciferase reporter were treated with increasing concentrations of AgNPs for 48 hours. After the treatment, transcriptional activation of GADD45α indicated by luciferase activity, cell viability, cell cycle arrest, and levels of genotoxicity were determined. The uptake and intracellular localization of AgNPs, cellular Ag doses as well as Ag⁺ release were also detected.

RESULTS

AgNPs could activate GADD45α gene at the transcriptional level as demonstrated by the dose-dependent increases in luciferase activity in both the reporter cells. The relative luciferase activity was greater than 12× the control level in HepG2-luciferase cells at the highest concentration tested where the cell viability decreased to 17.0% of the control. These results was generally in accordance with the positive responses in cytotoxicity, cell cycle arrest of Sub G1 and G2/M phase, Olive tail moment, micronuclei frequency, and the cellular Ag content.

CONCLUSIONS

The cytotoxicity and genotoxicity of AgNPs seems to occur mainly via particles uptake and the subsequent liberation of ions inside the cells. And furthermore, the GADD45α promoter-driven luciferase reporter cells, especially the HepG2-luciferase cells, could provide a new and valuable tool for predicting nanomaterials genotoxicity in humans.

Antiretroviral treatment in HIV-infected children who require a rifamycin-containing regimen for tuberculosis

INTRODUCTION

In high prevalence settings, tuberculosis and HIV dual infection and co-treatment is frequent. Rifamycins, especially rifampicin, in combination with isoniazid, ethambutol and pyrazinamide are key components of short-course antituberculosis therapy. Areas covered: We reviewed available data, for which articles were identified by a Pubmed search, on rifamycin-antiretroviral interactions in HIV-infected children. Rifamycins have potent inducing effects on phase I and II drug metabolising enzymes and transporters. Antiretroviral medications are often metabolised by the enzymes induced by rifamycins or may suppress specific enzyme activity leading to drug-drug interactions with rifamycins. These may cause significant alterations in their phamacokinetic and pharmacodynamic properties, and sometimes that of the rifamycin. Recommended strategies to adapt to these interactions include avoidance and dose adjustment. Expert opinion: Despite the importance and frequency of tuberculosis as an opportunistic disease in HIV-infected children, current data on the management of co-treated children is based on few studies. We need new strategies to rapidly assess the use of rifamycins, new anti-tuberculosis drugs and antiretroviral drugs together as information on safety and dosing of individual drugs becomes available.

In vitro studies on the toxicity of isoniazid in different cell lines

The aim of the present study was to investigate in vitrothe mechanism of toxicity of isoniazid (-INH), the drug most widely used for treatment of tuberculosis. The human hepatoma line HepG2, the human lymphoblastoid line AHH-1 and the murine lymphoma cells YAC-1 were used as test systems. Active cell death (-apoptosis) and necrosis were detected by different flow cytometric methods: the binding of annexin V to the cell membrane and staining with propidium iodide (PI), the TUNEL assay for detection of DNA fragmentation and the occurrence of a sub G1 peak in cell cycle histograms. Mitochondrial membrane potential was analysed with the fluorescent probe JC-1. In addition to cytotoxicity, effects of INH on cell cycle were studied in HepG2 cells. The data of the present investigations indicate that INH induces cytotoxicity via apoptosis both in hepatoma and lymphoma cells. Twenty-four hours of application of INH in concentrations -26 mM led to a remarkable number of apoptotic cells positive for Annexin V. The induction of apoptosis was accompanied by a break down of the mitochondrial membrane potential and the occurrence of DNA strand breaks. At incubation times from 36 to 48 hours, a sub-G1 peak of late apoptotic cells was detected in cell cycle analysis. Furthermore, cell cycle studies showed a disruption of the cycle at low concentrations of INH which are only mildly cytotoxic. Thus the present study unequivocally demonstrated that INH induces cytotoxicity via apoptosis and can lead to a significant disturbance of the cell cycle in mammalian cells.

Profound reduction in tamoxifen active metabolite endoxifen in a breast cancer patient treated with rifampin prior to initiation of an anti-TNFα biologic for ulcerative colitis: a case report

BACKGROUND

Tamoxifen, a common anti-estrogen breast cancer medication, is a prodrug that undergoes bioactivation via cytochrome P450 enzymes, CYP2D6 and to a lesser degree, CYP3A4 to form the active metabolite endoxifen. With an increasing use of oral anti-cancer drugs, the risk for drug-drug interactions mediated by enzyme inhibitors and inducers may also be expected to increase. Here we report the first case demonstrating a potent drug-drug interaction in a real-world clinical setting between tamoxifen and rifampin in a breast cancer patient being treated concurrently for ulcerative colitis.

CASE PRESENTATION

We describe a patient on adjuvant tamoxifen therapy for breast cancer that was prescribed rifampin for TB prophylaxis prior to initiation of an anti-tumor necrosis factor (TNF)-α agent due to worsening ulcerative colitis. This 39 year old Caucasian woman had been followed by our personalized medicine clinic where CYP2D6 genotyping and therapeutic monitoring of tamoxifen and endoxifen levels had been carried out. The patient, known to be a CYP2D6 intermediate metabolizer, had a previous history of therapeutic endoxifen levels. Upon admission to hospital for a major flare of her ulcerative colitis a clinical decision was made to initiate an anti-TNFα biological agent. Due to concerns regarding latent TB, rifampin as an anti-mycobacterial agent was initiated which the patient was only able tolerate for 10 days. Interestingly, her plasma endoxifen concentration measured 2 weeks after cessation of rifampin was sub-therapeutic at 15.8 nM and well below her previous endoxifen levels which exceeded 40 nM.

CONCLUSION

Rifampin should be avoided in patients on tamoxifen therapy for breast cancer unless continued tamoxifen efficacy can be assured through endoxifen monitoring. Drug-drug interactions can pose a significant risk of sub-therapeutic benefit in tamoxifen patients.

Anti-genotoxicity and anti-mutagenicity of Apis mellifera venom

The search for substances able to inhibit and/or diminish the effects of genotoxic and mutagenic substances has been the target of several investigations performed in recent times. Hymenoptera venoms constitute a considerable source of substances with pharmacological potential. The present study aimed to evaluate the cytotoxic, genotoxic and anti-genotoxic, mutagenic and anti-mutagenic potentials of Apis mellifera venom in HepG2 cells. In this evaluation, the MTT test was applied to determine the most appropriate concentrations for the genotoxicity and mutagenicity tests. It was verified that the concentrations of 0.1, 0.05 and 0.01μg/mL were not cytotoxic, hence these concentrations were used in the experiments. For the evaluation of the genotoxic and mutagenic potential of the bee venom the comet assay and the micronucleus test were applied, respectively. The concentrations mentioned above presented both genotoxic and mutagenic potential for HepG2 cells and it was necessary to test lower concentrations of the venom (10pg/mL, 1pg/mL and 0.1pg/mL) for the anti-genotoxicity and anti-mutagenicity tests, which were performed subjecting the cells to the action of MMS (methyl methanesulfonate) in order to verify the ability of the venom to inhibit or diminish the action of this compound, which has a recognized action on the genetic material. Pre-, post-treatment and simultaneous treatment with and without incubation with the venom were performed. It was observed that the lowest three concentrations tested did not present any anti-genotoxic and anti-mutagenic activity on the cells. The use of bee venom for pharmacological purposes in treatments such as cancer must be done with extreme caution, since it was observed that even at very low concentrations the venom can induce genotoxicity and mutagenicity in human cells, as was verified for the HepG2 cells.

Expression of Cytochromes P-450 2E1, 3A4 and 1A1/1A2 in Growing and Confluent Human HepG2 Hepatoma Cells-Effect of Ethanol

In cultured human hepatoma HepG2 cells, cytochrome (CYP) 1A-associated 7-ethoxyresorufin-O-deethylase (EROD), CYP 3A-associated benzyloxyresorufin O-debenzylase (BROD) and CYP 2E1-associated p-nitrophenol-hydroxylase (PNPH) decreased during time in culture. The enzyme activities in cells at confluence were 35-60% of the activities in cells 24 hours after seeding. Similarly, CYP 3A and CYP 2E1 proteins were present at higher concentrations in growing (G) than in confluent (C) HepG2 cells. CYP 1A1/1A2 protein was not detected, neither in G nor in C HepG2 cells but was strongly induced by 3-methylcholanthrene (3-MC) treatment. Ethanol (EtOH) was shown to increase CYP 2E1 and CYP 3A proteins and CYP 1A1/1A2-, CYP 2E1- and CYP 3A-associated mixed-function oxidase activities (MFOs) in HepG2 cells, as has been previously reported for primary cultures of human hepatocytes. These effects were observed only at the beginning of culture, in growing HepG2 cells, demonstrating the influence of the growth stage of HepG2 cells on their response to EtOH treatment. This is, to our knowledge, the first report on increases in CYP proteins and associated MFOs by EtOH in HepG2 cells. It suggests that growing HepG2 cells provide a useful in vitro model system in which to study the regulation of human CYPs by EtOH.

Development of stable HSPA1A promoter-driven luciferase reporter HepG2 cells for assessing the toxicity of organic pollutants present in air

HSPA1A (HSP70-1) is a highly inducible heat shock gene up-regulated in response to environmental stresses and pollutants. The aim of our study was to evaluate the sensitivity of the stable metabolically competent HepG2 cells containing a human HSPA1A promoter-driven luciferase reporter (HepG2-luciferase cells) for assessing the toxicity of organic pollutants present in air. The HepG2-luciferase cells were validated by heat shock treatment and testing three organic compounds (pyrene, benzo[a]pyrene, and formaldehyde) that are ubiquitous in the air. The maximal level of HSPA1A (HSP70-1) and relative luciferase activity induced by heat shock were over three and nine times the control level, respectively. Pyrene, benzo[a]pyrene, and formaldehyde all induced significantly elevated levels of relative luciferase activity in a dose-dependent manner. Extractable organic matter (EOM) from urban traffic and coke oven emissions in ambient air were tested on the HepG2-luciferase cells. The traffic EOM induced significant increase in relative luciferase activity at concentrations of picogram per liter. The coke oven EOM produced a strong dose-dependent induction of relative luciferase activity up to six times the control value. Significant increases in relative luciferase activity were observed at concentrations that were as low, or lower than the concentrations that the tested organic pollutants decreased cell viability, and increased malondialdehyde concentration, Olive tail moment, and micronuclei frequency. Therefore, we conclude that the HepG2-luciferase cells are a valuable tool for rapid screening of the overall toxicity of organic pollutants present in air.

Hepatocyte nuclear factor-1 alpha is associated with UGT1A1, UGT1A9 and UGT2B7 mRNA expression in human liver

Experimental evidence suggests HNF1alpha regulates UGT expression. This study investigates (1) whether the variability in HNF1alpha expression is associated with the variability in UGT1A1, UGT1A9 and UGT2B7 expression in human livers and (2) the functionality of 12 HNF1alpha variants using mRNA expression as phenotype. Controlling for known UGT variation in cis-acting elements known to affect UGT expression, we demonstrate that a combination of HNF1alpha mRNA levels and UGT genotype predicts variance in UGT expression to a higher extent than UGT genotype alone. None of the HNF1alpha polymorphisms studied, however, seem to have an effect on HNF1alpha, UGT1A1, UGT1A9 and UGT2B7 expression, ruling out their functional role. Our data provide evidence for HNF1alpha being a determinant of UGT1A1, UGT1A9 and UGT2B7 mRNA expression. However, the amount of UGT intergenotype variability explained by HNF1alpha expression appears to be modest, and further studies should investigate the role of multiple transcription factors.

Application of human hepatoma cell line HepG2 and its progress in the detection of genotoxicants

Genotoxicity test is widely used in the detection of various carcinogens and mutagens. HepG2 is derived from human hepatoblastoma, and it retains the activities of drug-metabolizing enzymes. It has been demonstrated that various carcinogens can be detected in genotoxicity test with HepG2 cells at several endpoints, whereas negative results have been obtained with non-carcinogens.

Hepatocyte cell lines: their use, scope and limitations in drug metabolism studies

Gaining knowledge on the metabolism of a drug, the enzymes involved and its inhibition or induction potential is a necessary step in pharmaceutical development of new compounds. Primary human hepatocytes are considered a cellular model of reference, as they express the majority of drug-metabolising enzymes, respond to enzyme inducers and are capable of generating in vitro a metabolic profile similar to what is found in vivo. However, hepatocytes show phenotypic instability and have a restricted accessibility. Different alternatives have been explored in the past recent years to overcome the limitations of primary hepatocytes. These include immortalisation of adult or fetal human hepatic cells by means of transforming tumour virus genes, oncogenes, conditionally immortalised hepatocytes, and cell fusion. New strategies are currently being used to upregulate the expression of drug-metabolising enzymes in cell lines or to derive hepatocytes from progenitor cells. This paper reviews the features of liver-derived cell lines, their suitability for drug metabolism studies as well as the state-of-the-art of the strategies pursued in order to generate metabolically competent hepatic cell lines.

Protective effects of garlic sulfur compounds against DNA damage induced by direct- and indirect-acting genotoxic agents in HepG2 cells

The aim of this study was to assess the antigenotoxic activity of several garlic organosulfur compounds (OSC) in the human hepatoma cell line HepG2, using comet assay. The OSC selected were allicin (DADSO), diallyl sulfide (DAS), diallyl disulfide (DADS), S-allyl cysteine (SAC) and allyl mercaptan (AM). To explore their potential mechanisms of action, two approaches were performed: (i) a pre-treatment protocol which allowed study of the possible modulation of drug metabolism enzymes by OSC before treatment of the cells with the genotoxic agent; (ii) a co-treatment protocol by which the ability of OSC to scavenge direct-acting compounds was assessed. Preliminary studies showed that, over the concentration range tested (5-100 microM), the studied OSC neither affected cell viability nor induced DNA damage by themselves. In the pre-treatment protocol, aflatoxin B1 genotoxicity was significantly reduced by all the OSC tested except AM. DADS was the most efficient OSC in reducing benzo(a)pyrene genotoxicity. SAC and AM significantly decreased DNA breaks in HepG2 cells treated with dimethylnitrosamine. Additionally, all the OSC studied were shown to decrease the genotoxicity of the direct-acting compounds, hydrogen peroxide and methyl methanesulfonate. This study demonstrated that garlic OSC displayed antigenotoxic activity in human metabolically competent cells.

Vinclozolin, a widely used fungizide, enhanced BaP-induced micronucleus formation in human derived hepatoma cells by increasing CYP1A1 expression

Vinclozolin, a widely used fungicide, can be identified as a residue in numerous vegetable and fruit samples. To get insight in its genetic toxicity, we investigated the genotoxic effect of vinclozolin in the human derived hepatoma cell line HepG2 using the micronucleus (MN) assay. Additionally, to evaluate the co- or anti-mutagenic potency of vinclozolin, we treated HepG2 cells with different concentrations of vinclozolin for 24 h. Subsequently, the cells were exposed to benzo[a]pyrene (BaP) for 1h. Exposure of HepG2 cells to 50-400 microM vinclozolin alone did not cause any induction of micronuclei. However, a pronounced co-mutagenic effect was observed. MN frequencies caused by BaP increased by 30.6%, 52.8% and 65.3% after pretreatment of the cell cultures with 50, 100 and 200 microM vinclozolin, respectively. The highest concentration (400 microM) of vinclozolin tested caused cytotoxicity. Therefore, micronuclei were not considered for that concentration. To clarify the mechanism of cogenotoxicity, we assayed cytochrome P450 1A1 (CYP1A1), which plays a pivotal role in activation of BaP. Cells exposed to vinclozolin led to significant increase of CYP1A1 expression in Western blot. The result suggested that induction of CYP1A1 by vinclozolin account for its enhancing effect on genotoxicity caused by BaP.

Phase I Trial of Tipifarnib in Patients With Recurrent Malignant Glioma Taking Enzyme-Inducing Antiepileptic Drugs: A North American Brain Tumor Consortium Study

Purpose

To determine the maximum-tolerated dose (MTD), toxicities, and clinical effect of tipifarnib, a farnesyltransferase (FTase) inhibitor, in patients with recurrent malignant glioma taking enzyme-inducing antiepileptic drugs (EIAEDs). This study compares the pharmacokinetics and pharmacodynamics of tipifarnib at MTD in patients on and off EIAEDs.

Patients and Methods

Recurrent malignant glioma patients were treated with tipifarnib using an interpatient dose-escalation scheme. Pharmacokinetics and pharmacodynamics were assessed.

Results

Twenty-three assessable patients taking EIAEDs received tipifarnib in escalating doses from 300 to 700 mg bid for 21 of 28 days. The dose-limiting toxicity was rash, and the MTD was 600 mg bid. There were significant differences in pharmacokinetic parameters at 300 mg bid between patients on and not on EIAEDs. When patients on EIAEDs and not on EIAEDs were treated at MTD (600 and 300 mg bid, respectively), the area under the plasma concentration–time curve (AUC)0-12 hours was approximately two-fold lower in patients on EIAEDs. Farnesyltransferase inhibition was noted at all tipifarnib dose levels, as measured in peripheral-blood mononuclear cells (PBMC).

Conclusion

Toxicities and pharmacokinetics differ significantly when comparing patients on or off EIAEDs. EIAEDs significantly decreased the maximum concentration, AUC0-12 hours, and predose trough concentrations of tipifarnib. Even in the presence of EIAEDs, the levels of tipifarnib were still sufficient to potently inhibit FTase activity in patient PBMCs. The relevance of these important findings to clinical activity will be determined in ongoing studies with larger numbers of patients.

Modulation of UDP-glucuronosyltransferase 1A1 in primary human hepatocytes by prototypical inducers

The primary objective of this study was to evaluate the modulation of UGT1A1 expression in human hepatocytes using prototypical CYP450 inducers. A bank of 16 human livers was utilized to obtain an estimate of the range of UGT1A1 protein expression and catalytic activity. Concentration-dependent changes in UGT1A1 response were evaluated in hepatocyte cultures after treatment with 3-methylchloranthrene, beta-napthoflavone, rifampicin, or phenobarbital. Pharmacodynamic analyses of UGT1A1 expression were conducted and compared to those of CYP450 after treatment with inducers in 2-3 different hepatocyte preparations. Additionally, expression of UGT1A1 mRNA and protein was evaluated in human hepatocytes treated with 14 different compounds known to activate differentially the human pregnane-X-receptor or constitutive androstane receptor. Pharmacodynamic modeling revealed EC50 values statistically significant between UGT1A1 and CYP2B6 after treatment with PB, but not statistically distinguishable between UGT1A1 and CYP's 1A2 or 3A4 after treatment with 3-methylchloranthrene or rifampicin, respectively. UGT1A1 was most responsive to the pregnane-X-receptor-agonists rifampicin, ritonavir, and clotrimazole at the mRNA level and, to a lesser extent, the constitutive androstane receptor-activators, phenobarbital and phenytoin. Pharmacodynamic analyses support a mechanism of coordinate regulation between UGT1A1 and a number of CYP450 enzymes by multiple nuclear receptors.

Organochlorine insecticides: impacts on human HepG2 cytochrome P4501A, 2B activities and glutathione levels

This study examined the effects of the organochlorine (OC) insecticides chlordane, o,p'-DDT, dieldrin, endosulfan, kepone, methoxychlor, and toxaphene on human HepG2 cytochrome P450 (1A-EROD and 2B-PROD) activities and glutathione (GSH) levels. Cells were exposed for 24 h at high concentrations (1, 5 or 10 mM) and for 48 h at lower concentrations ranging from 0.01 to 1 mM to evaluate dose responses. Our results show that after 48 h all but dieldrin significantly induced both P4501A and 2B. P4502B responses were greater at all exposure concentrations and times. Mixed responses in GSH levels were observed. All OCs except dieldrin and MXC significantly depleted GSH after 24 h. At 48 h, chlordane, endosulfan and toxaphene significantly increased GSH at low levels and decreased GSH at high levels, while kepone and methoxychlor produced significant declines in GSH at all concentrations. These results support findings of OC insecticides inducing CYP1A, 2B in rats, with CYP2B responses more important. GSH levels declined when P4502B activity was significantly elevated and were significantly increased in the absence of significant P450 activity, suggesting that GSH levels influence the catalytic activity of the cytochrome P450s and the cytochrome P450s influence the cell's ability to regulate GSH.

Determination of interleukin-4-responsive region in the human cytochrome P450 2E1 gene promoter

Cytochrome P450 2E1 (CYP2E1) gene expression is known to be induced by interleukin-4 (IL4) and repressed by inflammatory cytokines, such as interleukin-1beta3 (IL1beta3) in human hepatocytes. The mechanisms involved in these transcriptional regulations remain elusive. In order to study these mechanisms, various constructs of the human CYP2E1 promoter were prepared and transfected into the human HepG2 hepatoma cell line. Our findings revealed that an IL4-responsive region of 128bp (-671/-544) was required to mediate induction by IL4. IL1beta caused moderate but significant decrease of the promoter activity, which was abolished when the two cytokines were combined. The IL1beta inhibitory effect is mediated through a regulatory sequence independent of that of IL4. Furthermore, by using specific signaling pathway inhibitors, we demonstrated that IL4 activation required protein kinase C (PKC) activation. In addition, our results suggest that induction by IL4 was not dependent on a single binding site but rather on a complex region which includes putative binding sites for signal transducer and activator of transcription (STAT)6, activator protein (AP)-1, nuclear factor kappa-B (NFkappaB), nuclear factor of activated T cells (NFAT) and CCAAT enhancer binding protein (C/EBP). Electrophoretic mobility shift assays suggest that AP1 and NFAT transcription factors are able to bind to three sites in the IL4-responsive region.

Alginate-encapsulated human hepatoblastoma cells in an extracorporeal perfusion system improve some systemic parameters of liver failure in a xenogeneic model

Previous studies have demonstrated that alginate encapsulation of proliferating hepatocyte-derived cell lines (e.g., HepG2 cells) enhances the expression of differentiated hepatocyte function compared with conventional monolayer culture. Furthermore, such capsules have the advantage of cryopreservability, and can be readily manipulated, e.g., for the charging of extracorporeal devices. We utilize a rabbit model of acute liver failure caused by acetaminophen administration to rabbits pretreated to enhance cytochrome p450 enzyme activity, and demonstrate that encapsulated HepG2 cells, in an extracorporeal chamber, perfused by rabbit plasma separated on-line at a rate of 2-5 mL/min, and perfused over cells at 40-60 mL/min, improve systemic parameters of liver failure (diastolic blood pressure and transjugular venous oxygen saturation). Such encapsulated cells have the potential to be developed for extracorporeal liver support systems for acute liver failure.

Effect of rifampicin on pravastatin pharmacokinetics in healthy subjects

AIMS

Previous work has shown that rifampicin, a potent inducer of several cytochrome P450 (CYP) enzymes and transporters, decreased the plasma concentrations of simvastatin acid by more than 90%. This study was conducted to investigate the effect of rifampicin on the pharmacokinetics of pravastatin.

METHODS

In a randomised, cross-over two-phase study with a washout of 4 weeks, 10 healthy volunteers received a 5-day pretreatment with rifampicin (600 mg daily) or placebo. On day 6, a single 40 mg dose of pravastatin was administered orally. Plasma concentrations of pravastatin were measured up to 12 h by a sensitive LC-MS-MS method.

RESULTS

During the rifampicin phase, the mean total area under the plasma concentration-time curve of pravastatin [AUC(0-infinity )] was 69% (range 24-220%) of the corresponding value during the placebo phase (P < 0.05, 95% confidence interval for the difference -51.9 - -0.4 ng ml-1.h). In five of the 10 subjects the AUC(0-infinity ) of pravastatin during the rifampicin phase was 50% or less of that during the placebo phase. Rifampicin had no significant effect on the peak concentration, elimination half-life or renal clearance of pravastatin.

CONCLUSIONS

Rifampicin caused a statistically significant decrease in the plasma concentration of pravastatin given as a single oral dose to healthy subjects. However, the effect of rifampicin varied greatly between subjects. The mean rifampicin-induced decrease in pravastatin concentration was considerably smaller than that observed previously for simvastatin.

Pharmacokinetic interactions with rifampicin : clinical relevance

The antituberculosis drug rifampicin (rifampin) induces a number of drug-metabolising enzymes, having the greatest effects on the expression of cytochrome P450 (CYP) 3A4 in the liver and in the small intestine. In addition, rifampicin induces some drug transporter proteins, such as intestinal and hepatic P-glycoprotein. Full induction of drug-metabolising enzymes is reached in about 1 week after starting rifampicin treatment and the induction dissipates in roughly 2 weeks after discontinuing rifampicin. Rifampicin has its greatest effects on the pharmacokinetics of orally administered drugs that are metabolised by CYP3A4 and/or are transported by P-glycoprotein. Thus, for example, oral midazolam, triazolam, simvastatin, verapamil and most dihydropyridine calcium channel antagonists are ineffective during rifampicin treatment. The plasma concentrations of several anti-infectives, such as the antimycotics itraconazole and ketoconazole and the HIV protease inhibitors indinavir, nelfinavir and saquinavir, are also greatly reduced by rifampicin. The use of rifampicin with these HIV protease inhibitors is contraindicated to avoid treatment failures. Rifampicin can cause acute transplant rejection in patients treated with immunosuppressive drugs, such as cyclosporin. In addition, rifampicin reduces the plasma concentrations of methadone, leading to symptoms of opioid withdrawal in most patients. Rifampicin also induces CYP2C-mediated metabolism and thus reduces the plasma concentrations of, for example, the CYP2C9 substrate (S)-warfarin and the sulfonylurea antidiabetic drugs. In addition, rifampicin can reduce the plasma concentrations of drugs that are not metabolised (e.g. digoxin) by inducing drug transporters such as P-glycoprotein. Thus, the effects of rifampicin on drug metabolism and transport are broad and of established clinical significance. Potential drug interactions should be considered whenever beginning or discontinuing rifampicin treatment. It is particularly important to remember that the concentrations of many of the other drugs used by the patient will increase when rifampicin is discontinued as the induction starts to wear off.

The effects of benzimidazole anthelmintics on P4501A in rat hepatocytes and HepG2 cells

Benzimidazole anthelmintics including albendazole, fenbendazole, and mebendazole are widely used in veterinary medicine. The effects of these benzimidazoles on cytochrome P4501A were investigated in primary cultures of rat hepatocytes and in the HepG2 cell line. After incubation of rat hepatocytes and HepG2 for 24-, 48-, and 72-h cells with drugs at various concentrations (0.1-50 microM), the enzyme activities associated with P4501A1/2 (7-ethoxyresorufin O-deethylation and 7-methoxyresorufin O-demethylation) were measured. The P4501A1/2 protein levels in both model systems were determined by Western blotting. Although all benzimidazoles provoked a significant increase of P4501A1/2 protein levels and P4501A activities, large differences in the induction response were found which was dependent on drug structure, concentration, and model system used. Based on the results, relationships between induction potency and structure of drug were demonstrated, as well as differences between the in vitro systems used. Therefore, pharmacological and toxicological consequences of cytochrome P4501A induction by benzimidazole drugs should be taken into account in veterinary therapy.

In vitro activation of 7-benzyloxyresorufin O-debenzylation and nifedipine oxidation in human liver microsomes

1. The effects of substrate concentration and enzyme source (human liver microsomes and recombinant cytochrome P450s, CYP) on the activation of 7-benzyloxyresorufin O-debenzylation and nifedipine oxidation were investigated. 2. 7-Benzyloxyresorufin O-debenzylase activity in human liver microsomes was inhibited by a monoclonal antibody against CYP2B6 and a polyclonal antibody against CYP3A2 by 53-69 and 19-44%, respectively, suggesting that CYP2B6 and CYP3A4 mainly catalyse 7-benzyloxyresorufin O-debenzylation in human liver microsomes. 3. 7-Benzyloxyresorufin O-debenzylase activity at 0.2-5 micro M substrate concentrations in human liver microsomes was increased by the addition of alpha-naphthoflavone, quinidine, testosterone and progesterone, and the V(max) of 7-benzyloxyresorufin O-debenzylation increased with increasing alpha-naphthoflavone concentrations, whereas the K(m) remained constant. Additionally, 7-benzyloxyresorufin O-debenzylation by recombinant CYP3A4 was increased by the addition of alpha-naphthoflavone, testosterone and progesterone but not by quinidine, whereas no chemicals tested could activate the O-debenzylation of 7-benzyloxyresorufin by CYP2B6. 4. The K(m) for nifedipine oxidation activity by CYP3A4 decreased by the addition of progesterone, whereas the V(max) remained constant. Quinidine and testosterone increased 7-benzyloxyresorufin O-debenzylase and nifedipine oxidase activities, respectively, in human liver microsomes, whereas activation was not observed in CYP3A4. 5. The results suggest that in vitro activation patterns are substrate dependent and that selection of the enzyme source can influence the activation phenomenon.

The effects of mebendazole on P4501A activity in rat hepatocytes and HepG2 cells. Comparison with tiabendazole and omeprazole

Mebendazole is a benzimidazole anthelmintic widely used in veterinary and human therapy. Among benzimidazole derivatives, several drugs with inducing effect on cytochromes P450 can be found. However, the induction capacity of mebendazole on P450s has not been explored yet. In this study, the effects of mebendazole on P4501A activity was tested in primary cultures of rat hepatocytes and in human hepatoma HepG2 cell line. Two known P4501A inducers with benzimidazole structure, tiabendazole and omeprazole, were also included in the experiments with the aim of studying structure-induction relationships. After 24-, 48- and 72-h incubation of rat hepatocytes and HepG2 cells with drugs in various concentrations (0.1-100 microM), enzyme activity associated with P4501A1/2 (EROD, MROD) was measured. In addition, the P4501A1/2 protein levels in both in-vitro systems were determined by Western-blotting. Mebendazole provoked a significant increase in P4501A1/2 protein expression and P4501A activity in both in-vitro systems. Omeprazole caused a significant dose-dependent increase of P4501A activity only in HepG2 cells. Although tiabendazole treatment led to significant increase of P4501A protein level, no effect on P4501A activity was observed in either system. The results demonstrate that mebendazole possesses the ability to significantly induce P4501A. Thus, pharmacological and toxicological consequences of P4501A induction should be taken into account in human therapy. The structure-induction relationships and differences between in-vitro systems used are discussed.

Effect of intrapatient dosage escalation of irinotecan on its pharmacokinetics in pediatric patients who have high-grade gliomas and receive enzyme-inducing anticonvulsant therapy

The authors set out to determine the effect of intrapatient dose escalation of irinotecan on its disposition in pediatric patients with high-grade glioma who received concomitant enzyme-inducing anticonvulsants (EIAs). During Course 1, a 60-minute intravenous infusion of irinotecan (20 mg/m(2) per day) was administered once daily for 5 days on each of 2 consecutive weeks. The authors measured the concentrations of the lactone forms of irinotecan and its metabolites 7-ethyl-10-hydroxycamptothecin (SN-38), SN-38 glucuronide, and 7-ethyl-10-[4-N-(5-aminopeptanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC) in serial plasma samples collected on Days 1 and 12 of Course 1. For the 6 patients who received EIAs but whose SN-38 areas under the concentration-time curve (AUCs) on Day 1 were below clinically significant levels, irinotecan dosage was increased, and subsequent pharmacokinetic studies were performed. Thirty-five patients were enrolled. The rate of irinotecan clearance was greater for patients who received EIAs than for those who did not (P = 0.0008), whereas systemic exposure to irinotecan (P = 0.02) and SN-38 (P = 0.0001) was lower for those treated with EIAs than for those who were not. Of the 6 patients whose irinotecan dosages were increased, 3 experienced an increase in the SN-38 AUC between Days 1 and 12. For 1 patient, the SN-38 AUC on Day 12 was lower than on Day 1; this result likely was due to an increased dose of EIAs during the same period. Despite irinotecan dose escalation to 60 and 80 mg/m(2), the SN-38 AUCs for 2 patients did not increase to clinically significant levels. The type and grade of toxicity did not differ between the two patient groups. Increasing the dosage of irinotecan increased the SN-38 AUC in some patients who received concomitant EIA therapy.

Induction of human UDP-glucuronosyltransferase UGT1A1 by flavonoids-structural requirements

Recent studies in our laboratory in the human hepatic and intestinal cell lines Hep G2 and Caco-2 have demonstrated induction of UGT1A1 by the flavonoid chrysin (5,7-dihydroxyflavone) using catalytic activity assays and Western and Northern blotting. In the present study, we examined which features of the flavonoid structures were associated with induction of UGT1A1 and whether common drug-metabolizing enzyme inducers also produce this induction. We also determined whether flavonoid treatment affected sulfate conjugation and CYP1A1 activity. We used intact Hep G2 cells for these studies, with chrysin as the model substrate. Both glucuronidation and sulfation were measured. Hep G2 cells were pretreated for 3 days with 25 microM concentrations of 22 flavonoids (n = 4-12). Only four flavonoids demonstrated induction of glucuronidation similar to that of chrysin (i.e., 3-5-fold in the intact cells). These were acacetin, apigenin, luteolin, and diosmetin, all of which, like chrysin, are 5,7-dihydroxyflavones with varying substituents in the B-ring. 5-Hydroxy-7-methoxyflavone and 5-methyl-7-hydroxyflavone produced a modest 1.5 to 2-fold induction, whereas all other flavonoids examined were without effect. None of the flavonoids caused more than a modest change in sulfation activity (60-140% of control). In contrast, all tested 5,7-dihydroxyflavones and -flavonols induced CYP1A1 activity (ethoxyresorufin deethylation). Of seven common drug-metabolizing enzyme inducers only 3-methylcholanthrene and oltipraz showed modest induction of chrysin glucuronidation but not 2,3,7,8-tetrachlorodibenzo-p-dioxin or phenobarbital. Together, these results strongly suggest that the flavonoid induction of UGT1A1 is through a novel nonaryl hydrocarbon receptor-mediated mechanism.

Sedanolide, a natural phthalide from celery seed oil: effect on hydrogen peroxide and tert-butyl hydroperoxide-induced toxicity in HepG2 and CaCo-2 human cell lines

Sedanolide is a natural compound occurring in edible umbelliferous plants. Celery seed oil, a significant source of sedanolide, is used as an herbal remedy to treat inflammatory-associated conditions such as gout and rheumatism. The objective of this study was to assess the potential protective properties of sedanolide against hydrogen peroxide (H(2)O(2))- and tert-butyl hydroperoxide (tBOOH)-induced toxicity in HepG2 and CaCo-2 cells. Viability of HepG2 and CaCo-2 cells was unaffected by a 24-h exposure to sedanolide (7-500 microM), however, when the cells were cultured in sedanolide-free medium for a further two cell cycles (72 h), a decrease in cell viability was observed for HepG2 cells previously exposed to 500 microM of the compound. Cells pretreated with sedanolide (100 microM for 24 h) and exposed to either H(2)O(2) or tBOOH did not exhibit statistically significant difference in viability from controls. A significant increase (p < 0.05) in DNA strand breaks, as measured by the comet assay, was observed in HepG2 but not CaCo-2 cells following a 24-h incubation with 500 microM sedanolide. Sedanolide did not modulate H(2)O(2)- and tBOOH-induced DNA damage. Sedanolide is relatively nontoxic to cells in culture, however, the protection it afforded against H(2)O(2)- and tBOOH-induced toxicity was not statistically significant.

Ethanol-induced apoptosis in hepatoma cells proceeds via intracellular Ca(2+) elevation, activation of TLCK-sensitive proteases, and cytochrome c release

Ethanol is known to induce apoptosis in hepatocytes. However, intracellular signaling events of ethanol-induced death are still only partially understood. We studied such processes in ethanol-induced apoptosis in HepG2 cells as a model system for human liver cells. We determined the incidence of apoptosis by DNA fragmentation and tested the effects of various known inhibitors. Ethanol induces apoptosis in HepG2 cells in a dose- and time-dependent manner as well as in rat primary hepatocytes. This effect was not mediated through the death receptor CD95 and the tumor necrosis factor receptors. It was efficiently inhibited by the caspase inhibitor N-benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone (zVAD-fmk), the Ca(2+) chelator EGTA, and the serine protease inhibitor N-p-tosyl-l-lysine chloromethyl ketone (TLCK). Upon ethanol treatment, the intracellular calcium ion concentration was increased and cytochrome c was released from the mitochondria, and caspases were activated. EGTA and TLCK could inhibit cytochrome c release from the mitochondria. Furthermore, overexpression of Bcl-x(L) saved cells from ethanol-induced apoptosis. These data suggest that ethanol-induced apoptosis in liver cells is initiated by the intracellular Ca(2+) elevation in the cytoplasm and activation of TLCK-sensitive serine proteases. Our data provide new insight into ethanol-induced apoptosis in liver cells and may lead to therapeutic strategies to prevent liver damage.

Musk ketone enhances benzo(a)pyrene induced mutagenicity in human derived Hep G2 cells

Musk ketone is a widely used artificial fragrance which has been identified in human fatty tissue and milk. The mutagenic and comutagenic effects of this compound were studied in micronucleus tests with a human derived hepatoma cell line (Hep G2). Exposure of the cells to MK alone in the range between 5 and 5000 ng/ml did not cause induction of MN. When the cells were treated simultaneously with MK (5-5000 ng/ml) and 0.2 microg/ml benzo(a)pyrene, no synergistic effects were detected; benzo(a)pyrene (B(a)P) itself caused an 1.5-fold increase of MN over the spontaneous background frequency (60 versus 39 MN/1000 binucleated cells). In a third experimental series, the cells were pretreated with MK for 28h and subsequently exposed to 0.2 microg/ml B(a)P. In this case, a pronounced comutagenic effect was observed: The LOAEL for MK was 0.05 microg/ml. With higher doses (0.5, 1.0 and 5.0 microg MK/ml), a significant increase of B(a)P induced MN frequencies was measured, the induction rates being 50, 66, and 88%, respectively. Additional measurements of 7-ethoxyresorufin deethylase indicated that MK induces cytochrome P450 isoenzymes (1A1) which play a key role in the activation of B(a)P. The results of the present study show that MK amplifies the genotoxic effects of B(a)P in human derived cells and indicate that exposure of humans to MK might increase their susceptibility to the health hazards of B(a)P and other polycyclic aromatic hydrocarbons.

Expression and induction of a large set of drug-metabolizing enzymes by the highly differentiated human hepatoma cell line BC2

The BC2 cell line derived from the human hepatocarcinoma, HGB, undergoes a spontaneous sharp differentiation process in culture as it becomes confluent, remains stably differentiated for several weeks, and may return to proliferation thereafter under appropriate density conditions. The relevance of the line as an hepatic model has been evaluated. Cells synthesize a large number of plasma proteins, and rates of glycogen and urea synthesis increase with time of confluency and become sensitive to insulin, reflecting the process of differentiation. Differentiated BC2 cells express the most relevant cytochrome P-450 (CYP) isozyme activities (CYP1A1/2, 2A6, 2B6, 2C9, 2E1, and 3A4) and conjugating enzymes (glutathione S-transferase and UDP-glucuronyltransferase) and also respond to model inducers. Methylcholanthrene induced an increase in CYP1A1/2 enzyme activity (eightfold), phenobarbital induced CYP2B6 activity (1.7-fold), and dexamethasone induced CYP3A4 activity (fivefold). In parallel, expression of the most relevant liver-enriched transcription factors, HNF-4, HNF-1, C/EBP-alpha and C/EBP-beta mRNAs, was significantly increased in differentiated cultures. This increase was largest in HNF-1 and HNF-4, which supports the idea that a redifferentiation process towards the hepatic phenotype takes place. BC2 is an hepatic cell line that is able to express most hepatic functions, especially the drug-biotransformation function, far more efficiently than any previously described human hepatoma cell line.

Glutathione S-transferase and UDP-glucuronyltransferase activity in primary cultures of rainbow trout gill epithelial cells

The objective of this study was to characterize rainbow trout (Oncorhynchus mykiss) gill epithelial cells in primary culture by evaluating their ability to maintain glutathione and glucuronide conjugating enzymes. The activity and inducibility of the phase II enzymes was investigated as a function of culture time. Glutathione S-transferase (GST) and UDP-glucuronyltransferase (UDPGT) enzyme activities were measured in freshly isolated cells and in cells cultured for 7 and 12 days. GST activity, determined with 1-chloro-2,4-dinitrobenzene, decreased gradually to 72% after 7 days and to 38% after 12 days in culture compared with freshly isolated cells. There was no significant difference between UDPGT activities in freshly isolated cells compared with cells cultured up to 12 days although a transient decrease in activity was observed at day 7. In vitro induction of the enzymes was studied using beta-naphtoflavone (BNF) and 3-methylcholanthrene (3-MC) as inducers. GST activity increased 2-fold after exposure to BNF and 1.5-fold after 3-MC exposure for 48 h in 7 days old cultures. No induction was observed in 12 days old cultures. UDPGT activity was not induced either at day 7 or 12.

Effects of model inducers on thyroxine UDP-glucuronosyl-transferase activity in vitro in rat and mouse hepatocyte cultures

Thyroxine (T(4))-UDP-glucuronosyltransferase (UGT) activity was measured directly in cultured male Sprague-Dawley rat and OF-1 mouse hepatocyte monolayers. The activity of T(4)-UGT (pmol/min/g liver) in vitro in hepatocyte cultures was, after 24 hr in culture, equivalent to that previously measured in vivo in rat and mouse liver microsomes (Viollon-Abadie et al., 1999). A progressive decline in T(4)-UGT activity occurred over time in both rat and mouse hepatocyte cultures. Treatment of cultures with various model inducers such as phenobarbital (PB), beta-naphthoflavone (NF) and clofibric acid (CLO) induced a strong increase in T(4)-UGT activity in rat hepatocyte monolayers. In addition, and as expected from available in vivo data, treatment of rat hepatocyte cultures with NF also increased p-nitrophenol (PNP)-UGT activity and treatment with PB or CLO increased bilirubin (Bili)-UGT activity. In contrast, T(4)-UGT activity in mouse hepatocyte monolayers was not affected by the treatments, neither were PNP- and Bili- UGT activities. These in vitro data confirm our previous in vivo observations that these inducers increase rat but not mouse liver T(4)-UGT activities (Viollon-Abadie et al., 1999). The present study thus demonstrates that hepatocyte monolayers are appropriated for the evaluation and inter-species comparison of the effects of xenobiotics on T(4)-UGT activities.

Induction of cytochrome P450 1A1 in human hepatoma HepG2 cells by 6-nitrochrysene

The present study has determined the effects of 6-nitrochrysene (6-NC) on human cytochrome P450-dependent monooxygenases in human hepatoma HepG2 cells. Treatment of HepG2 cells with 6-NC increased the activities of microsomal benzo[a]pyrene hydroxylase, 7-ethoxycoumarin and 7-ethoxyresorufin O-deethylases, cytosolic glutathione S-transferase and N-acetyltransferase, and S9 metabolic activation of 6-NC in the Ames mutagenicity test. Immunoblot and RNA blot analyses revealed that 6-NC induced CYP1A1 protein and mRNA levels in the hepatoma cells. Nuclear transcription assay demonstrated that 6-NC increased the transcription rate of CYP1A1 gene in HepG2 cells. Treatment of human lung carcinoma NCI-H322 cells with 6-NC increased benzo[a]pyrene hydroxylase activity and CYP1A1 protein and mRNA levels. These results demonstrate that 6-NC is an inducer of human CYP1A1 and the induction occurs at a transcriptional level in HepG2 cells. The ability of 6-NC to induce liver and lung CYP1A1 may be an important factor to consider in assessing 6-NC metabolism and toxicity in humans.

Identification of human cytochrome P450 isoforms that contribute to all-trans-retinoic acid 4-hydroxylation

The role of specific human cytochrome P450 (CYP) isoforms in the oxidative metabolism of all-trans-retinoic acid was investigated by studies in human liver microsomes using isoform-specific chemical inhibitors and inhibitory antibodies. Studies using individual isoforms expressed in lymphoblastoid cells and correlation analysis using different microsome preparations were also performed. With expressed isoforms, evidence for a role for CYP2C8, CYP3A4, CYP2C9, and CYP1A1 in 4-hydroxylation was obtained, with the highest catalytic efficiency being observed for CYP2C8. Using inhibition studies and correlation analysis, we also concluded that CYP2C8 was the major all-trans-retinoic acid 4-hydroxylating cytochrome P450 in human liver microsomes, though CYP3A4 and, to a lesser extent CYP2C9, also made a contribution. In addition, we compared the rate of retinoic acid degredation in HepG2 cells when cultured in the absence and presence of 3-methylcholanthrene or all-trans-retinoic acid. Culture in the presence of all-trans-retinoic acid decreased the half-life twofold and resulted in an increased sensitivity of retinoic acid degredation to ketoconazole. Since no induction of either CYP1A1, CYP2C8, CYP2C9, or CYP3A4 was detected using immunoblotting and as mRNA encoding another cytochrome P450 enzyme, CYP26, has been previously demonstrated to be induced by retinoic acid treatment of HepG2 cells and to be highly sensitive to ketoconazole, this enzyme in addition to CYP2C8, CYP2C9 and CYP3A4 likely plays a role in all-trans-retinoic acid oxidation in the liver at high retinoic acid levels.

Comparison of three different in vitro mutation assays used for the investigation of cytochrome P450-mediated mutagenicity of nitro-polycyclic aromatic hydrocarbons

Three different in vitro mutation assays were used to investigate the involvement of cytochrome P450 enzymes in the activation of the nitro-polycyclic aromatic hydrocarbons (nitroPAHs) 1-nitropyrene and 2-nitrofluorene and their reduced metabolites amino-polycyclic aromatic hydrocarbons (aminoPAHs) 1-aminopyrene and 2-aminofluorene. Mutagenicity was investigated at the HPRT locus in Chinese hamster V79 cells with (V79-NH) or without (V79-MZ) endogenous acetyltransferase activity, stably expressing human cytochrome P450 cDNAs; in NIH/3T3 control or stably expressing human CYP1A2 cells, in combination with a shuttle vector containing a reporter gene; and in Salmonella typhimurium TA98, by inhibition of cytochrome P450 enzymes in rat liver S9 mix. Both the HPRT assay and the Ames test did not show any involvement of CYP3A in the activation of 1-nitropyrene to a mutagenic metabolite. In addition, a clear involvement of CYP1A2 in the activation of the nitroPAH 1-nitropyrene was demonstrated in both mutation assays using eukaryotic cells. However, no activation of 1-nitropyrene was seen in the eukaryotic cell lines when expressing only CYP1A2 (V79-MZ1A2) or acetyltransferase (V79-NH, 3T3-LNCX). The reduced metabolite of 1-nitropyrene, 1-aminopyrene, was also shown to be activated to a mutagenic metabolite by CYP1A2, using 3T3-1A2 cells in combination with a shuttle vector, and the Amestest in combination with the specific CYP1A2 inhibitor furafylline. No clear involvement of cytochrome P450 could be demonstrated for activation of 2-nitrofluorene to a mutagenic metabolite, whereas a role for CYP1A2 in the bioactivation of 2-aminofluorene is suggested. In the present study, we have demonstrated the complementary value of the three in vitro mutation assays in the examination of promutagen activation pathways.

Peroxisome proliferators induce apoptosis and decrease DNA synthesis in hepatoma cell lines

We examined the effects of various peroxisome proliferators (PPs) such as the hypolipidaemic agents clofibric acid (CLO), bezafibrate (BEZA), ciprofibrate (CIPRO) and nafenopin (NAFE) and the plasticizer di-(2-ethylhexyl)phthalate (DEHP) on peroxisomal enzyme activities, apoptosis and DNA synthesis in rat FaO and human HepG2 hepatoma cell lines. Both growing and confluent cultures were treated with PPs (250 microM) for 48 or 72 h. In accordance with our previous observations in PP-treated primary hepatocyte cultures of rat and human origin, the various PPs increased peroxisomal enzyme activities in rat FaO cells but not in human HepG2 cells. PPs strongly induced apoptosis in FaO cells. They did not affect TGFbeta-induced apoptosis, with the exception of DEHP and NAFE, respectively blocking and increasing induced apoptosis in confluent cultures. Moreover, PPs produced a minor, but significant, decrease in DNA synthesis in FaO cells. PPs also decreased DNA synthesis in growing HepG2 cells, and CLO, CIPRO and NAFE induced apoptosis in confluent HepG2 cultures. This is in opposition with the effects of PPs on primary hepatocyte cultures, i.e. inhibition of both spontaneous and TGFbeta-induced apoptosis and increases in DNA synthesis in rat hepatocytes, and unchanged mitosis-apoptosis balance in human hepatocytes.

Induction of zidovudine glucuronidation and amination pathways by rifampicin in HIV-infected patients

AIMS

The objective of the study was to determine the effect of multiple doses of rifampicin on the steady-state pharmacokinetics of zidovudine and its 5'-glucuronosyl (GZDV) and 3'-amino (AMT) metabolites.

METHODS

Eight asymptomatic HIV-infected patients (seven male, one female) participated in this three-period longitudinal study. Each patient received zidovudine (200 mg every 8 h) for 14 days (period 1), followed by rifampicin (600 mg every 24 h) with zidovudine for 14 days (period 2), and then zidovudine alone for a further 14 days (period 3). Blood and urine samples were collected over 6 h on the last day of each period for measurements of zidovudine and GZDV by h.p.l.c.-u.v. and AMT by h.p.l.c.-m.s-m.s.

RESULTS

Compared with zidovudine-alone values in period 1, 14 days of coadministration with rifampicin significantly increased zidovudine oral clearance (89%) and formation clearances to GZDV (100%) and AMT (82%). Correspondingly, there were decreases in maximum plasma concentration (43%), AUC (47%) and urine recovery (37%) of zidovudine. GZDV/zidovudine and AMT/zidovudine AUC ratios increased by 99% and 36%, respectively, despite a significant 29% decrease in AMT AUC. After stopping rifampicin for 14 days, values of these pharmacokinetic parameters returned to within 26% of baseline. Over the three periods AMT plasma levels were <18 ng ml-1 (n=6) and <40 ng ml-1 (n=2), and molar AMT/zidovudine AUC ratios ranged from 1.7% to 4.5%.

CONCLUSIONS

Rifampicin induced zidovudine glucuronidation and amination pathways resulting in decreased plasma and urine exposures to zidovudine. AMT plasma exposure decreased because induction was more pronounced for the major GZDV metabolite. The magnitude of the residual inductive effect was minimal at 14 days after stopping rifampicin.

Protection from 1-cyano-3,4-epithiobutane nephrotoxicity by aminooxyacetic acid and effect on xenobiotic-metabolizing enzymes in male Fischer 344 rats

1-Cyano-3,4-epithiobutane (CEB), a naturally occurring nitrile derived from cruciferous plants, causes nephrotoxicity and increased renal glutathione (GSH) concentration in male F-344 rats. This CEB-induced nephrotoxicity is dependent on GSH conjugation and bioactivation. The objectives of the present study were to investigate the effect of CEB on several xenobiotic-metabolizing enzymes and to evaluate the effect of modulators of GSH transport and metabolism on CEB-induced nephrotoxicity and GSH concentration. Animals received 125 mg kg-1 CEB alone or following pretreatment with one of three selective inhibitors of GSH metabolism: acivicin, probenecid or aminooxyacetic acid. There were no significant alterations in epoxide hydrolase (EH), P-450, ethoxyresorufin O-deethylase (EROD) or pentoxyresorufin O-depentylase (PROD) enzyme activity, but renal glutamyl cysteine synthetase (GCS) activity was decreased at 12 and 24 h, as was renal glutathione S-transferase 4 h after CEB administration. Renal ECOD activity was also diminished at 24 h and at 12 and 24 h in liver. Aminooxyacetic acid (AOAA) abrogated the nephrotoxicity, the renal GSH-enhancing effect, and decreased GCS of CEB alone. These findings provide further evidence for the importance of GSH conjugation as a significant pathway in CEB metabolism and the role of a reactive thiol in nephrotoxicity and altered renal GSH.

Comparison of HepG2 feeder cells generated by exposure to gamma-rays, X-rays, UV-C light or mitomycin C for ability to activate 7,12-dimethylbenz[a]anthracene in a cell-mediated Chinese hamster V79/HGPRT mutation assay

The cell-mediated Chinese hamster V79/HGPRT mutagenicity assay is an established in vitro testing method. Although gamma-irradiated human HepG2 hepatoma cells have been used recently for chemical activation, an alternative is now needed due to scheduled retirement of the available gamma-source. X-irradiation, 254 nm UV-C light and mitomycin C were examined as possible HepG2 mitotic inhibitors, and treated cells compared for activation of 7, 12-dimethylbenz[a]anthracene (DMBA). In colony-forming assays, V79 and HepG2 cells differed in sensitivity to DMBA, with V79 survival declining sharply between 1-2.5 microM (LD50=1.75 microM) while HepG2 survival decreased gradually, beginning at 0.01 microM DMBA (LD50=0.045 microM). When HepG2 feeder cells generated by each method were included in V79/HGPRT mutation assays, activation of 1 microM DMBA was found to vary according to the mitotic inhibitor used, with mutation frequencies decreasing in the order 4000 rads gamma-rays>25 microg/ml mitomycin C>4000 rads X-rays>25 J/m2 UV-C light. Only assays containing gamma-irradiated HepG2 cells generated an increase (2-3-fold) in mutation frequency when DMBA exposure was extended from 24 to 48 h. The effect of HepG2 preincubation with either Aroclor 1254 or DMBA on feeder cell activation of DMBA was also assessed using concentrations of Aroclor 1254 (10 microg/ml) or DMBA (1.0 microM) which were found to produce optimum induction of ethoxyresorufin-O-deethylase (EROD) activity (3.1-fold and 2-fold increases, respectively). Compared to results obtained with uninduced HepG2 cells, assays incorporating HepG2 cells activated by either Aroclor 1254 or DMBA produced slightly increased V79/HGPRT mutation frequencies after 24 h of exposure to mutagen; however, a 48 h incubation with mutagen in the presence of HepG2 preincubated with either Aroclor 1254 or DMBA resulted in higher mutation frequencies regardless of the mitotic inhibitor treatment. EROD activity was also induced 1.4-fold following exposure of HepG2 cells to mitomycin C alone. Although gamma-irradiation remains the treatment of choice for producing metabolically active HepG2 feeder cells, comparison of the alternatives tested suggests that mitomycin C would be a convenient and suitable replacement.

cDNA cloning and inducible expression of human multidrug resistance associated protein 3 (MRP3)

Previously, we cloned rat MRP3 as a candidate for an inducible transporter for the biliary excretion of organic anions [Hirohashi et al. (1998) Mol. Pharmacol. 53, 1068-10751. In the present study, we cloned human MRP3 (1527 amino acids) from Caco-2 cells. Human MRP3 is predominantly expressed in liver, small intestine and colon; hepatic expression of MRP3 was observed in humans but not in normal rats. In HepG2 cells, the expression of MRP3 was induced by phenobarbital. These results suggest that MRP3 may act as an inducible transporter in the biliary and intestinal excretion of organic anions.

Use of metabolically competent human hepatoma cells for the detection of mutagens and antimutagens

The human hepatoma line (Hep G2) has retained the activities of various phase I and phase II enzymes which play a crucial role in the activation/detoxification of genotoxic procarcinogens and reflect the metabolism of such compounds in vivo better than experimental models with metabolically incompetent cells and exogenous activation mixtures. In the last years, methodologies have been developed which enable the detection of genotoxic effects in Hep G2 cells. Appropriate endpoints are the induction of 6-TGr mutants, of micronuclei and of comets (single cell gel electrophoresis assay). It has been demonstrated that various classes of environmental carcinogens such as nitrosamines, aflatoxins, aromatic and heterocyclic amines and polycyclic aromatic hydrocarbons can be detected in genotoxicity assays with Hep G2 cells. Furthermore, it has been shown that these assays can distinguish between structurally related carcinogens and non-carcinogens, and positive results have been obtained with rodent carcinogens (such as safrole and hexamethylphosphoramide) which give false negative results in conventional in vitro assays with rat liver homogenates. Hep G2 cells have also been used in antimutagenicity studies and can identify mechanisms not detected in conventional in vitro systems such as induction of detoxifying enzymes, inactivation of endogenously formed DNA-reactive metabolites and intracellular inhibition of activating enzymes.

Quantitative reverse transcriptase/PCR assay for the measurement of induction in cultured hepatocytes

Hepatic enzyme induction is often evoked as the cause for a variety of effects in animal studies, e.g. hepatic hypertrophy and secondary thyroid neoplasms in rodents. In clinical practice, enzyme induction often enhances drug clearance and may result in reduced efficacy. For example, carbamazepine or rifampin treatment induces P450 3A in humans, and as a result, dramatically reduces the efficacy of midazolam or cyclosporine. Due to species differences in substrate specificity and the regulation of various drug-metabolizing enzymes, assessing enzyme induction in human tissues is a desirable goal. Since induction often occurs as a result of increased synthesis of mRNA coding for a particular enzyme, induction may be quantified by measuring specific mRNA levels. We describe an approach to quantifying mRNA levels using reverse transcriptase-polymerase chain reaction (RT-PCR). This approach makes use of either radiolabeled PCR primers or fluorimetric quantification of product and does not require the synthesis of a competitor RNA or DNA molecule. Thus, Cyp2B1/2 mRNA can be shown to be induced 17-fold in the H4IIE rat hepatoma cell line. Likewise, Cyp3A and Cyp2A6 mRNAs can be shown to be induced in primary human hepatocytes cultured on collagen-coated plates and treated with rifampin for 72 h. By contrast, mRNA levels for Cyp1A1 and Cyp2E1 were not increased by rifampin treatment. This report demonstrates the potential of this approach for examining a number of mRNAs from drug-treated cultured cells, as a means of assessing metabolic enzyme induction.

Role of nitroreductases but not cytochromes P450 in the metabolic activation of 1-nitropyrene in the HepG2 human hepatoblastoma cell line

1-Nitropyrene is an environmental contaminant that is mutagenic in many prokaryotic and eukaryotic systems, including the hypoxanthine-guanosine phosphoribosyl transferase (HGPRT) locus in the human hepatoma cell line HepG2. Metabolism and DNA adduct formation of [3H]1-nitropyrene in the HepG2 were quantified to understand the role of nitroreduction and/or cytochrome P450-mediated C-oxidation of 1-nitropyrene in DNA adduct formation and mutagenicity. In uninduced HepG2 cells, 10 microM [3H]1-nitropyrene was metabolized principally by nitroreduction to 1-aminopyrene (516 pmol/24 hr/10(6) cells), and by cytochrome P450-mediated C-oxidation to K-region trans-dihydrodiols (37 pmol/24 hr/10(6) cells), 1-nitropyren-3-ol (51 pmol/24 hr/10(6) cells), and 1-nitropyren-6-ol and 1-nitropyren-8-ol (77 pmol/24 hr/10(6) cells). Pretreatment of the HepG2 cells for 24 hr with 5 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in a complete change in the metabolism of [3H]1-nitropyrene, with 1-nitropyren-6-ol and 1-nitropyren-8-ol formation (449 pmol/24 hr/10(6) cells) being 80-fold greater than 1-aminopyrene formation (6 pmol/24 hr/10(6) cells). This increase in C-oxidation of 1-nitropyrene was consistent with increased levels of cytochrome P450 1A. The only DNA adduct detected using the 32P-postlabeling assay in the HepG2 cells administered 1-nitropyrene was N-(2'-deoxyguanosin-8-yl)-1-aminopyrene (dG-C8-AP). Induction of C-oxidative metabolism through TCDD treatment resulted in a concomitant decrease in dG-C8-AP formation. DNA adducts for oxidized 1-nitropyrene metabolites were not detected in the TCDD-treated HepG2 cells administered 1-nitropyrene, which indicates that cytochrome P450-mediated C-oxidative pathways are detoxification pathways in HepG2 cells.

Activity and inducibility of drug-metabolizing enzymes in immortalized hepatocyte-like cells (mhPKT) derived from a L-PK/Tag1 transgenic mouse

This report describes the establishment and characterization of the mhPKT cell line derived from the liver of a transgenic mouse harboring the simian virus (SV40) large T and small t antigens placed under the control of the 5' regulatory sequence of the rat L-type pyruvate kinase (L-PK) gene. mhPKT cells had a prolonged life span, expressed the SV40-encoded nuclear large T antigen when grown in glucose-enriched medium, and induced tumors when injected subcutaneously into athymic (nu-nu) mice. Growth on petri dishes or filters yielded multiple layers of cuboid cells, with numerous spaces between adjacent cells that were closed by junctional complexes. These bile canaliculi-like structures exhibited numerous microvilli in which villin, an actin-binding brush-border protein, colocalized with actin. These bile canaliculi-like structures appeared to be functional as they accumulated fluorescein. mhPKT cells conserved the expression of the liver-specific transcription factors HNF1, HNF3, HNF4, and DBP together with substantial levels of L-PK and albumin but not alpha-fetoprotein mRNA transcripts. mhPKT cells mainly metabolized testosterone into androstenedione and 6beta-hydroxytestosterone, as in vivo. 3-Methylcholanthrene and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) markedly increased ethoxyresorufin-O-deethylase activity and the related cytochrome P450 (CYP) 1A1/2 protein, whereas alpha-naphtoflavone antagonized the TCDD-elicited induction. Phenobarbital slightly increased the CYP2B-mediated activities of pentoxyresorufin-O-depentylase, 2beta- and 16beta-testosterone hydroxylase. mhPKT cells also had substantial sulfotransferase, UDP-glucuronyltransferase, and glutathione S-transferase activities. This model may serve as a tool for long-term in vitro studies of xenobiotic metabolism, potent CYP inducers, and hepatocyte damage due to drugs and other factors.