Studies on the induction of rat hepatic CYP1A, CYP2B, CYP3A and CYP4A subfamily form mRNAs in vivo and in vitro using precision-cut rat liver slices

A high-throughput cell-based gaussia luciferase reporter assay for measurement of CYP1A1, CYP2B6, and CYP3A4 induction

The induction of cytochrome P450s can result in reduced drug efficacy and lead to potential drug-drug interactions. The xenoreceptors-aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), and pregnane X receptor (PXR)-play key roles in CYP induction by xenobiotics. In order to be able to rapidly screen for the induction of three enzymes (CYP1A1, CYP2B6, and CYP3A4), we generated a stable AhR-responsive HepG2 cell line, a stable CAR-responsive HepG2 cell line, and a stable PXR-responsive HepG2 cell line.To validate these stable xenoreceptor-responsive HepG2 cell lines, we evaluated the induction of the different Gaussia reporter activities, as well as the mRNA and protein expression levels of endogenous CYPs in response to different inducers.The induction of luciferase activity in the stable xenoreceptor-responsive HepG2 cell lines by specific inducers occurred in a concentration dependent manner. There was a positive correlation between the induction of luciferase activities and the induction endogenous CYP mRNA expression levels. These xenoreceptor-responsive HepG2 cell lines were further validated with known CYP1A1, CYP2B6, and CYP3A4 inducers.These stable xenoreceptor-responsive HepG2 cell lines may be used in preclinical research for the rapid and sensitive detection of AhR, CAR, and PXR ligands that induce CYP450 isoforms.

Pesticide tolerance induced by a generalized stress response in wood frogs (Rana sylvatica)

Increasing evidence suggests that phenotypic plasticity can play a critical role in ecotoxicology. More specifically, induced pesticide tolerance, in which populations exposed to a contaminant show increased tolerance to the contaminants later, has been documented in multiple taxa. However, the physiological mechanisms of induced tolerance remain unclear. We hypothesized that induced pesticide tolerance is the result of a generalized stress response based on previous studies showing that both natural stressors and anthropogenic stressors can induce tolerance to pesticides. We tested this hypothesis by first exposing larval wood frogs (Rana sylvatica) to either an anthropogenic stressor (sublethal carbaryl concentration), a natural stressor (cues from a caged predator), or a simulated stressor via exogenous exposure to the stress hormone corticosterone (125 nM). We also included treatments that inhibited corticosterone synthesis with the compound metyrapone (MTP). We then exposed the larvae to a lethal carbaryl treatment to assess time to death. We found that prior exposure to 125 nM of exogenous CORT and predator cues induced tolerance to a lethal concentration of carbaryl through a slight delay in time to death. Pre-exposure to sublethal carbaryl, as well as MTP alone or in combination with predator cues, did not induce tolerance to the lethal carbaryl concentration relative to the ethanol vehicle control treatment. Our study provides evidence that pesticide tolerance can be induced by a generalized stress response both in the presence and absence (exogenous CORT) of specific cues and highlights the importance of considering physiological ecology and environmental context in ecotoxicology.

Piperonyl butoxide: Mode of action analysis for mouse liver tumour formation and human relevance

In a 79 week bioassay the pesticide synergist piperonyl butoxide (PBO) was shown to significantly increase the incidence of hepatocellular adenoma (but not hepatocellular carcinoma) in male CD-1 mice at dietary levels of 100 and 300 mg/kg/day PBO and in female mice at a dietary level of 300 mg/kg/day. As PBO is not a genotoxic agent, a series of investigative studies were undertaken to elucidate the mode of action (MOA) for PBO-induced mouse liver tumour formation. Male CD-1 mice were fed diets to provide intakes of 0 (control), 30, 100 and 300 mg/kg/day PBO and for purposes of comparison 500 ppm sodium phenobarbital (NaPB), a known constitutive androstane receptor (CAR) activator, for 7 and 14 days. Treatment with 100 and 300 mg/kg/day PBO and 500 ppm NaPB increased relative liver weight which was associated with hepatocyte hypertrophy, with hepatocyte replicative DNA synthesis (RDS) being increased after 7 days treatment. The treatment of CD-1 mice with 30-300 mg/kg/day PBO for 14 days resulted in significant dose-dependent increases in hepatic microsomal cytochrome P450 (CYP) content and 7-pentoxyresorufin O-depentylase (PROD) activity and in hepatic Cyp2b10 mRNA levels. In contrast, PBO produced a biphasic effect on markers of activation of the peroxisome proliferator-activated receptor alpha (PPARα), with small increases in microsomal lauric acid 12-hydroxylase activity and hepatic Cyp4a10 mRNA levels being observed in mice given 100 mg/kg/day with PBO, with either no increase or a significant inhibition being observed in mice given 300 mg/kg/day PBO. The hepatic effects of PBO in male CD-1 mice were generally similar to those produced by NaPB and were reversible after the cessation of treatment for 28 days. Studies were also performed in male C57BL/6J (wild type) mice and in hepatic CAR and pregnane X receptor (PXR) knockout mice (CAR KO/PXR KO mice), where in the CAR KO/PXR KO mice PBO had little effect on markers of CAR activation, but produced some increases in markers of PPARα activation. The treatment of male CD-1 mouse hepatocytes for 4 days with 5-50 μM PBO, 10-1000 μM NaPB and 25 ng/mL epidermal growth factor (EGF) resulted in significant increases in hepatocyte RDS. While treatment of hepatocytes from one male and one female human donor with 5-500 μM PBO and 10-1000 μM NaPB for 4 days had no effect on hepatocyte RDS, treatment with EGF resulted in significant increases in RDS in both human hepatocyte preparations. In summary, PBO is predominantly a hepatic CAR activator at carcinogenic dose levels in CD-1 mice, with activation of hepatic CAR resulting in a suppression of the effect of PBO on hepatic PPARα. A robust MOA for PBO-induced mouse liver tumour formation has been established, this MOA being similar to that previously identified for NaPB and some other rodent liver CAR activators. Based on the lack of effect of PBO on RDS in human hepatocytes, it is considered that the MOA for PBO-induced mouse liver tumour formation is qualitatively not plausible for humans.

Sedaxane-Use of Nuclear Receptor Transactivation Assays, Toxicogenomics, and Toxicokinetics as Part of a Mode of Action Framework for Rodent Liver Tumors

Experimental data demonstrate a mode of action (MOA) for liver tumors in male rats and mice treated with sedaxane that starts with activation of CAR, followed by altered expression of CAR-responsive genes, increased cell proliferation, and eventually clonal expansion of preneoplastic cells, leading to the development of altered foci and tumors. This MOA is nonrelevant to human risk assessments. Methods and results in the MOA work for sedaxane illustrate promising directions that future MOA studies may be able to employ, in the spirit of "Tox21" and reduction of in vivo animal use: (1) currently available in vitro CAR and PXR reporter assays demonstrated that sedaxane is a direct CAR activator in mice and rats, and a weak PXR activator in rats; (2) mouse liver microarray results compared with a published CAR biomarker signature (based on 83 genes) showed a clear, statistical match, and a lack of correlation to similar biomarker signatures for AhR, PPARα, and STAT5B; (3) Ki67 immunohistochemistry and zonal image analysis showed significant increases in this marker of cell proliferation in mouse liver, without the need to dose a DNA labeling agent; and (4) toxicokinetic analysis of Cmax levels of sedaxane in blood showed a marked species difference between mice and rats that helps to explain differences in sensitivity to sedaxane. Incorporating these tools into the study plan for a new agrochemical or drug during development offers a promising alternative to the traditional need to conduct later, specialized MOA studies after the results of chronic bioassays are known.

CYP3A4 inducer and inhibitor strongly affect the pharmacokinetics of triptolide and its derivative in rats

Triptolide is the most active ingredient of Tripterygium wilfordii Hook F, which is used to treat rheumatoid arthritis. (5R)-5-Hydroxytriptolide is a hydroxylation derivative of triptolide with a reduced toxicity. To investigate the metabolic enzymes of the two compounds and the drug-drug interactions with enzyme inducers or inhibitors, a series of in vitro and in vivo experiments were conducted. In vitro studies using recombinant human cytochrome P450 enzyme demonstrated that cytochrome P450 3A4 (CYP3A4) was predominant in the metabolism of triptolide and (5R)-5-hydroxytriptolide, accounting for 94.2% and 64.2% of the metabolism, respectively. Pharmacokinetics studies were conducted in male SD rats following administration of triptolide or (5R)-5-hydroxytriptolide (0.4 mg/kg, po). The plasma exposure to triptolide and (5R)-5-hydroxytriptolide in the rats was significantly increased when co-administered with the CYP3a inhibitor ritonavir (30 mg/kg, po) with the values of AUC_0-∞ (area under the plasma concentration-time curve from time zero extrapolated to infinity) being increased by 6.84 and 1.83 times, respectively. When pretreated with the CYP3a inducer dexamethasone (50 mg·kg^-1·d^-1, for 3 d), the AUC_0-∞ values of triptolide and (5R)-5-hydroxytriptolide were decreased by 85.4% and 91.4%, respectively. These results suggest that both triptolide and (5R)-5-hydroxytriptolide are sensitive substrates of CYP3a. Because of their narrow therapeutic windows, clinical drug-drug interaction studies should be carried out to ensure their clinical medication safety and efficacy.

Characterization of rat or human hepatocytes cultured in microphysiological systems (MPS) to identify hepatotoxicity

The liver is the main site for drug and xenobiotics metabolism, including inactivation or bioactivation. In order to improve the predictability of drug safety and efficacy in clinical development, and to facilitate the evaluation of the potential human health effects from exposure to environmental contaminants, there is a critical need to accurately model human organ systems such as the liver in vitro. We are developing a microphysiological system (MPS) based on a new commercial microfluidic platform (Nortis, Inc.) that can utilize primary liver cells from multiple species (e.g., rat and human). Compared to conventional monolayer cell culture, which typically survives for 5-7days or less, primary rat or human hepatocytes in an MPS exhibited higher viability and improved hepatic functions, such as albumin production, expression of hepatocyte marker HNF4α and canaliculi structure, for up to 14days. Additionally, induction of Cytochrome P450 (CYP) 1A and 3A4 in cryopreserved human hepatocytes was observed in the MPS. The acute cytotoxicity of the potent hepatotoxic and hepatocarcinogen, aflatoxin B₁, was evaluated in human hepatocytes cultured in an MPS, demonstrating the utility of this model for acute hepatotoxicity assessment. These results indicate that MPS-cultured hepatocytes provide a promising approach for evaluating chemical toxicity in vitro.

Pancreatic progenitor-derived hepatocytes are viable and functional in a 3D high density bioreactor culture system

The rat pancreatic progenitor cell line B-13 is of interest for research on drug metabolism and toxicity since the cells trans-differentiate into functional hepatocyte-like cells (B-13/H) when treated with glucocorticoids. In this study we investigated the trans-differentiation and liver-specific functions of B-13/H cells in a three-dimensional (3D) multi-compartment bioreactor, which has already been successfully used for primary liver cell culture. Undifferentiated B-13 cells were inoculated into the bioreactor system and exposed to dexamethasone to promote hepatic trans-differentiation (B-13/HT). In a second approach, pre-differentiated B-13 cells were cultured in bioreactors for 15 days to evaluate the maintenance of liver-typical functions (B-13/HP). During trans-differentiation of B-13 cells into hepatocyte-like cells in the 3D bioreactor system (approach B-13/HT), an increase in glucose metabolism and in liver-specific functions (urea and albumin synthesis; cytochrome P450 [CYP] enzyme activity) was observed, whereas amylase - characteristic for exocrine pancreas and undifferentiated B-13 cells - decreased over time. In bioreactors with pre-differentiated cells (approach B-13/HP), the above liver-specific functions were maintained over the whole culture period. Results were confirmed by gene expression and protein analysis showing increased expression of carbamoyl-phosphate synthase 1 (CPS-1), albumin, CYP2E1, CYP2C11 and CYP3A1 with simultaneous loss of amylase. Immunohistochemical studies showed the formation of 3D structures with expression of liver-specific markers, including albumin, cytokeratin (CK) 18, CCAAT/enhancer-binding protein beta (CEBP-β), CYP2E1 and multidrug resistance protein 2 (MRP2). In conclusion, successful culture and trans-differentiation of B-13 cells in the 3D bioreactor was demonstrated. The requirement for only one hormone and simple culture conditions to generate liver-like cells makes this cell type useful for in vitro research using 3D high-density culture systems.

Gene expression and immunochemical localization of major cytochrome P450 drug-metabolizing enzymes in bovine nasal olfactory and respiratory mucosa

Despite tremendous advancement in the characterization of nasal enzyme expression, knowledge of the role of the nasal mucosa in the metabolism of xenobiotics is still inadequate, primarily due to the limited availability of in vitro models for nasal metabolism screening studies. An extensive knowledge of the oxidative and conjugative metabolizing capacity of the cattle (Bos taurus) olfactory and respiratory mucosa can aid in efficient use of these tissues for pre-clinical investigations of the biotransformation and toxicity of therapeutic agents following nasal administration or inhalation. Cows are also exposed to a variety of airborne pollutants and pesticides during their lifetime, the metabolism of which can have profound toxicological and ecological consequences. The aim of the present study was to characterize cytochrome P450 (CYP) enzyme expression in the bovine nasal mucosa. Amplification of the specific genes through RT-PCR confirmed expression of several CYP enzymes in bovine hepatic and nasal tissues. The results demonstrate that bovine nasal olfactory and respiratory mucosal and liver tissues express similar populations, families, and distributions of CYP enzymes, as has been previously reported with other species, including humans. Bovine ex vivo tissues can serve as a readily available reference tissue to elucidate preclinical toxico-kinetic effects resulting from exposure to substances in the environment or following drug administration.

Dopamine D2-Receptor Antagonists Down-Regulate CYP1A1/2 and CYP1B1 in the Rat Liver

Dopaminergic systems regulate the release of several hormones including growth hormone (GH), thyroid hormones, insulin, glucocorticoids and prolactin (PRL) that play significant roles in the regulation of various Cytochrome P450 (CYP) enzymes. The present study investigated the role of dopamine D₂-receptor-linked pathways in the regulation of CYP1A1, CYP1A2 and CYP1B1 that belong to a battery of genes controlled by the Aryl Hydrocarbon Receptor (AhR) and play a crucial role in the metabolism and toxicity of numerous environmental toxicants. Inhibition of dopamine D₂-receptors with sulpiride (SULP) significantly repressed the constitutive and benzo[a]pyrene (B[a]P)-induced CYP1A1, CYP1A2 and CYP1B expression in the rat liver. The expression of AhR, heat shock protein 90 (HSP90) and AhR nuclear translocator (ARNT) was suppressed by SULP in B[a]P-treated livers, whereas the AhRR expression was increased by the drug suggesting that the SULP-mediated repression of the CYP1 inducibility is due to inactivation of the AhR regulatory system. At signal transduction level, the D₂-mediated down-regulation of constitutive CYP1A1/2 and CYP1B1 expression appears to be mediated by activation of the insulin/PI3K/AKT pathway. PRL-linked pathways exerting a negative control on various CYPs, and inactivation of the glucocorticoid-linked pathways that positively control the AhR-regulated CYP1 genes, may also participate in the SULP-mediated repression of both, the constitutive and induced CYP1 expression. The present findings indicate that drugs acting as D₂-dopamine receptor antagonists can modify several hormone systems that regulate the expression of CYP1A1, CYP1A2 and CYP1B1, and may affect the toxicity and carcinogenicity outcome of numerous toxicants and pre-carcinogenic substances. Therefore, these drugs could be considered as a part of the strategy to reduce the risk of exposure to environmental pollutants and pre-carcinogens.

Regulation of Liver Enriched Transcription Factors in Rat Hepatocytes Cultures on Collagen and EHS Sarcoma Matrices

Liver-enriched transcription factors (LETF) play a crucial role in the control of liver-specific gene expression and for hepatocytes to retain their molecular and cellular functions complex interactions with extra cellular matrix (ECM) are required However, during cell isolation ECM interactions are disrupted and for hepatocytes to regain metabolic competency cells are cultured on ECM substrata. The regulation of LETFs in hepatocytes cultured on different ECM has not been studied in detail. We therefore compared two common sources of ECM and evaluated cellular morphology and hepatocyte differentiation by investigating DNA binding activity of LETFs at gene specific promoters and marker genes of hepatic metabolism. Furthermore, we studied testosterone metabolism and albumin synthesis to assess the metabolic competence of cell cultures. Despite significant difference in morphological appearance and except for HNF1β (p<0.001) most LETFs and several of their target genes did not differ in transcript expression after Bonferroni adjustment when cultured on collagen or Matrigel. Nonetheless, Western blotting revealed HNF1β, HNF3α, HNF3γ, HNF4α, HNF6 and the smaller subunits of C/EBPα and C/EBPβ to be more abundant on Matrigel cultured cells. Likewise, DNA binding activity of HNF3α, HNF3β, HNF4α, HNF6 and gene expression of hepatic lineage markers were increased on Matrigel cultured hepatocytes. To further investigate hepatic gene regulation, the effects of Aroclor 1254 treatment, e.g. a potent inducer of xenobiotic defense were studied in vivo and in vitro. The gene expression of C/EBP-α increased in rat liver and hepatocytes cultured on collagen and this treatment induced DNA binding activity of HNF4α, C/EBPα and C/EBPβ and gene expression of CYP1A1 and CYP1A2 in vivo and in vitro. Taken collectively, two sources of ECM greatly affected hepatocyte morphology, activity of liver enriched transcription factors, hepatic gene expression and metabolic competency that should be considered when used in cell biology studies and drug toxicity testing.

Cell type-specific expression and localization of cytochrome P450 isoforms in tridimensional aggregating rat brain cell cultures

Within the Predict-IV FP7 project a strategy for measurement of in vitro biokinetics was developed, requiring the characterization of the cellular model used, especially regarding biotransformation, which frequently depends on cytochrome P450 (CYP) activity. The extrahepatic in situ CYP-mediated metabolism is especially relevant in target organ toxicity. In this study, the constitutive mRNA levels and protein localization of different CYP isoforms were investigated in 3D aggregating brain cell cultures. CYP1A1, CYP2B1/B2, CYP2D2/4, CYP2E1 and CYP3A were expressed; CYP1A1 and 2B1 represented almost 80% of the total mRNA content. Double-immunolabeling revealed their presence in astrocytes, in neurons, and to a minor extent in oligodendrocytes, confirming the cell-specific localization of CYPs in the brain. These results together with the recently reported formation of an amiodarone metabolite following repeated exposure suggest that this cell culture system possesses some metabolic potential, most likely contributing to its high performance in neurotoxicological studies and support the use of this model in studying brain neurotoxicity involving mechanisms of toxication/detoxication.

ω-Hydroxylation of phylloquinone by CYP4F2 is not increased by α-tocopherol

SCOPE

The objective of this study was to investigate the initial catabolic step of vitamin E and K metabolism, the ω-hydroxylation by human cytochrome P450 4F2 (CYP4F2).

METHODS AND RESULTS

Tocopherol (T) metabolism was compared using rat liver slices incubated with deuterated (d₆)-RRR-α-T (d₆-α-T), racemic 2S-α-T (2S, 4'RS, 8'RS α-T, 2S-α-T), or d₂-γ-T (d₂-γ-T). Following comparable uptake of each T by liver slices, twice as much 13'-OH-T was produced from 2S-α-T or d₂-γ-T (39 ± 15 or 42 ± 5 pmol/g liver, respectively) as from d₆-α-T (17 ± 2, p < 0.01). Kinetic studies were conducted using insect microsomes expressing human CYP4F2 incubated with d₄-phylloquinone (d₄-PK), d₆-RRR-α-T, d₃-SRR-α-T, or d₂-γ-T. CYP4F2 demonstrated similar apparent maximal velocities (Vmax) when either of the α-Ts were used as substrates, which were less than the apparent d₄-PK Vmax (p < 0.0002), while the CYP4F2 catalytic efficiency toward d₄-PK (15.8 Vmax/Km) was five times greater than for α-Ts. Vitamin K had no effect on vitamin E catabolism, while vitamin E slightly decreased the d₄-PK Vmax.

CONCLUSION

CYP4F2 discriminates between Ts and PK in vitro, but α-T does not apparently increase PK ω-hydroxylation by this mechanism.

Metabolism of 2,2',3,3',6,6'-hexachlorobiphenyl (PCB 136) atropisomers in tissue slices from phenobarbital or dexamethasone-induced rats is sex-dependent

1. Chiral polychlorinated biphenyls (PCBs) such as PCB 136 enantioselectively sensitize the ryanodine receptor (RyR). In light of recent evidence that PCBs cause developmental neurotoxicity via RyR-dependent mechanisms, this suggests that enantioselective PCB metabolism may influence the developmental neurotoxicity of chiral PCBs. However, enantioselective disposition of PCBs has not been fully characterized. 2. The effect of sex and cytochrome P450 (P450) enzyme induction on the enantioselective metabolism of PCB 136 was studied using liver tissue slices prepared from naïve control (CTL), phenobarbital (PB; CYP2B inducer) or dexamethasone (DEX; CYP3A inducer) pretreated adult Sprague-Dawley rats. PCB 136 metabolism was also examined in hippocampal slices derived from untreated rat pups. 3. In liver tissue slices, hydroxylated PCB (OH-PCB) profiles depended on sex and inducer pretreatment, and OH-PCB levels followed the rank orders male > female and PB > DEX > CTL. In contrast, the enantiomeric enrichment of PCB 136 and its metabolites was independent of sex and inducer pretreatment. Only small amounts of PCB 136 partitioned into hippocampal tissue slices and no OH-PCB metabolites were detected. 4. Our results suggest that enantioselective metabolism, sex and induction status of P450 enzymes in the liver may modulate the neurotoxic outcomes of developmental exposure to chiral PCBs.

Time-dependent changes in hepatic and intestinal induction of cytochrome P450 3A after administration of dexamethasone to rats

We investigated the effects of the dose of and the number of times an inducer was administered and the duration of induction of hepatic and intestinal cytochrome P450 3A (CYP3A) in rats using dexamethasone 21-phosphate (DEX-P) and midazolam (MDZ) as an inducer and a substrate to CYP3A, respectively. The number of times DEX-P was administered was not a significant factor in the induction of either hepatic or intestinal CYP3A; however, administration of DEX-P multiple times markedly decreased the bioavailability of DEX-P by self-induction of CYP3A. CYP3A induction in the liver increased depending on the dose of DEX-P, whereas that in intestine showed a mild increase, but the induction level was almost constant regardless of the dose of DEX-P. Administration of a single dose of DEX-P showed a temporal increase in CYP3A activity in both tissues and the induction ratios reached maximum values at 12 h after DEX-P administration. On the other hand, a mild increase of CYP3A activity, which lasted for at least 48 h, was observed in both tissues after administration of multiple doses. Some physiological compounds such as cytokines might be involved in decreasing the CYP3A activity to maintain homeostasis of the body.

Stress is a critical player in CYP3A, CYP2C, and CYP2D regulation: role of adrenergic receptor signaling pathways

Stress is a critical player in the regulation of the major cytochrome P-450s (CYPs) that metabolize the majority of the prescribed drugs. Early in life, maternal deprivation (MD) stress and repeated restraint stress (RS) modified CYP expression in a stress-specific manner. In particular, the expression of CYP3A1 and CYP2C11 was increased in the liver of MD rats, whereas RS had no significant effect. In contrast, hepatic CYP2D1/2 activity was increased by RS, whereas MD did not affect it. The primary effectors of the stress system, glucocorticoids and epinephrine, highly induced CYP3A1/2. Epinephrine also induced the expression of CYP2C11 and CYP2D1/2. Further investigation indicated that AR-agonists may modify CYP regulation. In vitro experiments using primary hepatocyte cultures treated with the AR-agonists phenylephrine, dexmedetomidine, and isoprenaline indicated an AR-induced upregulating effect on the above-mentioned CYPs mediated by the cAMP/protein kinase A and c-Jun NH₂-terminal kinase signaling pathways. Interestingly though, in vivo pharmacological manipulations of ARs using the same AR-agonists led to a suppressed hepatic CYP expression profile, indicating that the effect of the complex network of central and peripheral AR-linked pathways overrides that of the hepatic ARs. The AR-mediated alterations in CYP3A1/2, CYP2C11, and CYP2D1/2 expressions are potentially connected with those observed in the activation of signal transducer and activator of transcription 5b. In conclusion, stress and AR-agonists may modify the expression of the major CYP genes involved in the metabolism of drugs used in a wide range of diseases, thus affecting drug efficacy and toxicity.

Human and rat primary hepatocyte CYP1A1 and 1A2 induction with 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,7,8-tetrachlorodibenzofuran, and 2,3,4,7,8-pentachlorodibenzofuran

The concentration dose response for aryl hydrocarbon receptor (AHR)-mediated CYP1A1 and CYP1A2 messenger RNA (mRNA) induction and enzyme activity was determined in primary cultures of rat and human hepatocytes for 2,3,7,8-tetrachlorodibenzo-p-dioxin, 2,3,4,7,8-pentachlorodibenzofuran, and 2,3,7,8-tetrachlorodibenzofuran. Eleven different congener concentrations from 0.00001 to 100 nM were used, thus spanning seven orders of magnitude. The Hill model was used to obtain values of EC(x) and maximal response from the individual data sets. No-observed effect concentration values were derived using several statistical methods including Dunnett's test, the Welch-Aspin test, and step-down bilinear regression. Thresholds were estimated using baseline projection methods and a "hockey stick" fitting method. Human hepatocytes were less responsive and less sensitive with respect to CYP1A1 activity and mRNA induction than rats. On the other hand, the human CYP1A2 response was more robust than the response in rats but generally less sensitive. These data allow an evaluation of relative species sensitivities for developing interspecies toxicodynamic adjustment factors, for assessing AHR activation thresholds, and for evaluating relative congener potencies. Overall, these data support the position that humans are less sensitive than rats to these AHR-dependent end points and support the use of a data-derived adjustment factor of 1.0 or less for extrapolating between rats and humans.

Liverbeads: a practical and relevant in vitro model for gene induction investigations

Cryopreserved rat hepatocytes entrapped within an alginate matrix, commercially available as Liverbeads, were evaluated for their relevance as a screening tool for gene induction in vitro, using quantitative real-time reverse transcriptase-polymerase chain reaction. They were treated with the reference compounds beta-naphthoflavone (BNF), phenobarbital (PB), pregnenolone 16alpha-carbonitrile (PCN), and clofibric acid (CLO) and analyzed for mRNA levels of Cyp1a1, Cyp2b1, Cyp3a1, Cyp4a1, Ugt1a6, and Ugt2b1. In addition, for PB and PCN, the results were compared with those obtained in rat liver in vivo. For each inducer, the gene induction profiles obtained with the Liverbeads in vitro model were time- and dose-dependent. The in vitro gene expression profiles confirmed the corresponding known P450 and UGT induction by each reference compound. In particular, the most strongly induced genes were Cyp1a1 by BNF, Cyp2b1 by PB, Cyp3a1 and Ugt2b1 by PCN, and Cyp4a1 and Cyp2b1 by CLO. Other genes investigated were also induced by the reference compounds, but the expression levels were lower, and increases were seen only after prolonged treatment. In particular, Ugt1a6 and Cyp2b1 were increased by BNF, Cyp1a1, Cyp3a1, and Ugt2b1 by PB, and Cyp3a1 and Ugt2b1 by CLO. All of these results correlated well with published in vitro data and our in vivo data. In conclusion, our results suggest that Liverbeads is a relevant and useful in vitro screening tool for determining gene induction profiles of new molecules. In addition, because Liverbeads from different species are available, this tool offers the possibility to conduct interspecies comparisons.

Effect of prototypical inducers on ligand activated nuclear receptor regulated drug disposition genes in rodent hepatic and intestinal cells

AIM

The aim of this study was to investigate the impact on expression of mRNA and protein by paradigm inducers/activators of nuclear receptors and their target genes in rat hepatic and intestinal cells. Furthermore, assess marked inter laboratory conflicting reports regarding species and tissue differences in expression to gain further insight and rationalise previously observed species differences between rodent and human based systems.

METHODS

Quantitative real time-polymerase chain reaction (QRT-PCR) and immunoblots were used to assess messenger RNA (mRNA) and protein expression for CYP2B2, CYP3A1, CYP3A2, CYP3A9, ABCB1a, ABCB1b, ABCC1, ABCC2, pregnane X receptor (PXR), farnesoid X receptor (FXR) and constituitive androstane receptor (CAR) in rat hepatoma cell line H411E, intestinal cells, Iec-6, and rat primary hepatocytes, in response to exposure for 18 h with prototypical inducers.

RESULTS

Dexamethasone (DEX) and pregnenolone 16alpha carbonitrile (PCN) significantly induced PXR, CYP3A9, ABCB1a and ABCB1b. However, when co-incubated, DEX appeared to restrict PCN-dependent induction. Chenodeoxycholic acid (CDCA) was the only ligand to induce FXR in all three cell types. Despite previously reported species differences between PCN and rifampicin (RIF), both compounds exhibited a similar profile of induction.

CONCLUSION

Data presented herein may explain some of the discrepancies previously reported with respect to species differences from different laboratories and have important implications for study design.

Time-dependent induction of rat hepatic CYP1A1 and CYP1A2 expression after single-dose administration of the anti-angiogenic agent TSU-68

The anti-angiogenic agent TSU-68 is known to rapidly induce cytochrome P450 activity responsible for its own hydroxylation in rats. In this study, we identified CYP1A1 and CYP1A2 as the TSU-68-induced P450 and temporally characterized the rapid induction of these isoforms. Protein and mRNA levels of CYP1A1 and CYP1A2 along with CYP1A activities were examined in rat liver after a single oral administration of 500 mg/kg TSU-68. CYP1A-mediated ethoxyresorufin O-deethylation and TSU-68 hydroxylation activities reached the maximum at 12 hr. The activities were maintained up to 24 hr and then slowly decreased down to control levels. Protein levels of both CYP1A1 and CYP1A2 were also rapidly induced with temporal profiles similar to the profile of CYP1A activity. In contrast, unlike CYP1A2 mRNA levels, which peaked at 12 hr and almost returned to control levels by 48 hr, CYP1A1 mRNA levels peaked as early as 3 hr and returned to control levels by 24 hr. Thus, CYP1A1 showed more rapid elevation and turnover of its mRNA than CYP1A2. In conclusion, TSU-68 administered to rats rapidly induced mRNA and protein of CYP1A1 and CYP1A2 as well as CYP1A activity. Furthermore, the data showed a difference in the time-dependent induction between CYP1A1 and CYP1A2 mRNAs.

3-aminobenzanthrone, a human metabolite of the carcinogenic environmental pollutant 3-nitrobenzanthrone, induces biotransformation enzymes in rat kidney and lung

3-aminobenzanthrone (3-ABA) is the metabolite of the carcinogenic air pollutant 3-nitrobenzanthrone (3-NBA). 3-ABA was investigated for its ability to induce cytochrome P450 1A1 (CYP1A1) and NAD(P)H:quinone oxidoreductase (NQO1) in kidney and lung of rats, and for the influence of such induction on DNA adduct formation by 3-ABA and 3-NBA. NQO1 is the enzyme that reduces 3-NBA to N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) and CYP1A enzymes oxidize 3-ABA to the same intermediate. When activated by cytosolic and and/or microsomal fractions isolated from rat lung, the target organ for 3-NBA carcinogenicity, and kidney, both compounds generated the same DNA-adduct pattern, consisting of five adducts. When pulmonary cytosols isolated from rats that had been treated i.p. with 40 mg/kg bw of 3-ABA were incubated with 3-NBA, DNA adduct formation was up to 1.7-fold higher than in incubations with cytosols from control animals. This increase corresponded to an increase in protein level and enzymatic activity of NQO1. In contrast, no induction of NQO1 expression by 3-ABA treatment was found in the kidney. Incubations of 3-ABA with renal and pulmonary microsomes of 3-ABA-treated rats led to an increase of up to a 4.5-fold in DNA-adduct formation relative to controls. The stimulation of DNA-adduct formation correlated with a higher protein expression and activity of CYP1A1 induced by 3-ABA. These results show that by inducing lung and kidney CYP1A1 and NQO1, 3-ABA increases its own enzymatic activation as well as that of the environmental pollutant, 3-NBA, thereby enhancing the genotoxic and carcinogenic potential of both compounds.

Metabolic and structural viability of precision-cut rat lung slices in culture

1. The principal objective was to evaluate the functional and structural integrity of precision-cut rat lung slices in culture over 72 h. 2. Lung slices metabolized 7-ethoxycoumarin in a time-dependent fashion, the major metabolites being the sulphate and glucuronide of 7-hydroxycoumarin with very low levels of the free compound. Prior treatment of rats with beta-naphthoflavone elevated markedly the rate of metabolism. The optimum slice thickness, as exemplified by the metabolism of 7-ethoxycoumarin, was about 600 microm. 3. Lung slices retained metabolic viability towards 7-ethoxycoumarin for 8 h, but after this point a marked decline in metabolic activity was noted. However, very low levels of activity were still evident following a 72 h incubation. 4. Morphological examination of lung slices revealed nuclear degeneration and loss of tissue architecture following 24h incubation. When cellular integrity was assessed using lactate dehydrogenase, a time-dependent leakage was evident with maximum loss occurring within 24h; longer incubations did not result in further leakage. 5. It is concluded that precision-cut rat lung slices, of 600 microm thickness, can be maintained metabolically viable in culture for some 8 h.

Use of immunofluorescence technique in cultured fibroblasts from Mediterranean cetaceans as new "in vitro" tool to investigate effects of environmental contaminants

The aim of the present study was to propose the immunofluorescence technique in cultured fibroblasts from Mediterranean cetaceans as a new "in vitro" tool to explore the susceptibility of these marine mammals to different xenobiotic compounds. The cell lines were cultured from integument biopsies of free-ranging and stranded cetaceans (dead within 12h). Using the indirect immunofluorescence assay, we detected endogenous proteins induced by different contaminants. Here we present the method used for qualitative and quantitative evaluation of cytochromes P450 (CYP1A1 and CYP2B) induced by some POPs (DDTs and PCBs) and emerging contaminants (PBDEs) in fibroblast cell cultures of striped dolphin (Stenella coeruleoalba) and bottlenose dolphin (Tursiops truncatus). Immunofluorescence was quantified with a specially designed Olympus macro, DetectIntZ. A major result was the possibility of using this "in vitro" assay to quantify induction of endogenous proteins.

Biological models for phytochemical research: from cell to human organism

Nutrigenomics represents a shift of nutrition research from epidemiology and physiology to molecular biology and genetics. Nutrigenomics seeks to understand nutrition influences on homeostasis, the mechanism of genetic predispositions for diseases, to identify the genes influencing risk of diet related diseases. This review presents somein vitromodels applicable in nutrigenomic studies, and discuses the use of animal models, their advantages and limitations and relevance for human situation.In vitroandin vivomodels are suitable for performance of DNA microarrays, proteomic and transcriptomic analyses.In vitromodels (intracellular organelles and suborganellar compartments, cell cultures, or tissue samples/cultures) give insight in metabolic pathways and responses to test stimuli on cellular and molecular levels. Animal models allow evaluation of the biological significance of the effects recordedin vitroand testing of the hypothesis on how a specific factor affects specific species under specific circumstances. Therefore, the evaluation of the data in relation to human organism should be done carefully, considering the species differences. The use ofin vitroandin vivomodels is likely to continue as the effects of nutrition on health and disease cannot be fully explained without understanding of nutrients action at nuclear level and their role in the intra- and intercellular signal transduction. Through advances in cell and molecular biology (including genomic and proteomic), the use of these models should become more predictively accurate. However, this predictive value relies on an underpinning knowledge of the advantages and limitations of the model in nutrigenomic research as in other fields of biomedical research.

Transcriptome analysis provides new insights into liver changes induced in the rat upon dietary administration of the food additives butylated hydroxytoluene, curcumin, propyl gallate and thiabendazole

Transcriptomics was performed to gain insight into mechanisms of food additives butylated hydroxytoluene (BHT), curcumin (CC), propyl gallate (PG), and thiabendazole (TB), additives for which interactions in the liver can not be excluded. Additives were administered in diets for 28 days to Sprague-Dawley rats and cDNA microarray experiments were performed on hepatic RNA. BHT induced changes in the expression of 10 genes, including phase I (CYP2B1/2; CYP3A9; CYP2C6) and phase II metabolism (GST mu2). The CYP2B1/2 and GST expression findings were confirmed by real time RT-PCR, western blotting, and increased GST activity towards DCNB. CC altered the expression of 12 genes. Three out of these were related to peroxisomes (phytanoyl-CoA dioxygenase, enoyl-CoA hydratase; CYP4A3). Increased cyanide insensitive palmitoyl-CoA oxidation was observed, suggesting that CC is a weak peroxisome proliferator. TB changed the expression of 12 genes, including CYP1A2. In line, CYP1A2 protein expression was increased. The expression level of five genes, associated with p53 was found to change upon TB treatment, including p53 itself, GADD45alpha, DN-7, protein kinase C beta and serum albumin. These array experiments led to the novel finding that TB is capable of inducing p53 at the protein level, at least at the highest dose levels employed above the current NOAEL. The expression of eight genes changed upon PG administration. This study shows the value of gene expression profiling in food toxicology in terms of generating novel hypotheses on the mechanisms of action of food additives in relation to pathology.

Comparison of the induction profile for drug disposition proteins by typical nuclear receptor activators in human hepatic and intestinal cells

BACKGROUND AND PURPOSE

Certain nuclear receptors (NRs) such as the constitutive androstane receptor (CAR), pregnane X receptor (PXR) and farnesoid X receptor (FXR) mediate induction of some cytochrome P450 enzymes and ABC transporters but conflicting reports exist. The purpose of this study was to assess the reasons for these discrepancies and use a standardized approach to compare activators of NRs.

EXPERIMENTAL APPROACH

Dexamethasone, pregnenolone 16alpha-carbonitrile, rifampicin, phenobarbital and chenodeoxycholic acid were incubated with HepG2, Caco-2 and cryopreserved human hepatocytes prior to analysis of mRNA and protein for CYP2B6, CYP3A4, CYP3A5, ABCB1, ABCC1, ABCC2, PXR, CAR and FXR.

KEY RESULTS

Dexamethasone significantly up-regulated PXR, CYP3A4 and ABCB1 expression in HepG2 and Caco-2 cells. As a result, including dexamethasone as a media supplement masked the induction of these genes by pregnenolone 16alpha-carbonitrile, which may explain discrepancies between previous reports. In the absence of dexamethasone, significant activator-dependent induction was observed in all cell types. Significant correlations were observed between the fold increase in mRNA and in protein, which were, for most instances, logarithmic. Changes in mRNA expression were greater in cell lines than primary cells but for most transcripts correlations were observed between fold increases in HepG2 and hepatocytes.

CONCLUSIONS AND IMPLICATIONS

Clearly, no in vitro system can imitate the physiology of a hepatocyte or intestinal cell within an intact organ in vivo, but these data explain some of the discrepancies reported between laboratories and have important implications for study design.

o,p'-DDT elicits PXR/CAR-, not ER-, mediated responses in the immature ovariectomized rat liver

Technical-grade dichlorodiphenyltrichloroethane (DDT) is an agricultural pesticide and malarial vector control agent that has been designated a potential human hepatocarcinogen. The o,p'-enantiomer exhibits estrogenic activity that has been associated with the carcinogenicity of DDT. The temporal and dose-dependent hepatic estrogenicity of o,p'-DDT was investigated using complementary DNA microarrays in immature ovariectomized Sprague-Dawley rats with complementary histopathology and tissue-level analysis. Animals were gavaged with 300 mg/kg o,p'-DDT either once or once daily for 3 consecutive days. Liver samples were examined 2, 4, 8, 12, 18, or 24 h after a single dose or following three daily doses. For dose-response studies, a single dose of 3, 10, 30, 100, or 300 mg/kg body weight o,p'-DTT was administered for 3 consecutive days. Genes associated with drug metabolism (Cyp2b2 and Cyp3a2), the nuclear receptors constitutive androstane receptor (CAR) and pregnane X receptor (PXR), cell proliferation (Ccnd1, Ccnb1, Ccnb2, and Stmn1), and oxidative stress (Gclm and Hmox1) were significantly induced. Cyp2b2 exhibited dose-dependent regulation and was significantly induced across all time points, while cell proliferation- and oxidative stress-related genes exhibited transient induction. The induction of Cyp2b2 and Cyp3a2 mRNA levels suggest PXR/CAR activation, consistent with expression of genes associated with oxidative stress. Few genes known to be estrogen receptor (ER) regulated were differentially expressed when compared to the hepatic gene expression profile elicited by ethynyl estradiol in immature ovariectomized C57BL/6 mice using the same study design and analysis methods. These data indicate that o,p'-DDT elicits PXR/CAR-, not ER-, mediated gene expression in the rat liver. Based on the species-specific differences in CAR regulation, the extrapolation of rodent DDT hepatocarcinogenicity to humans warrants further investigation.

Induction of cytochrome P450 enzymes in rat liver by two conazoles, myclobutanil and triadimefon

This study was undertaken to examine the inductive effects of two triazole antifungal agents, myclobutanil and triadimefon, on the expression of hepatic cytochrome P450 (CYP) genes and on the activities of CYP enzymes in male Sprague Dawley rats. Rats were dosed with the conazoles at three dose levels by gavage for 14 days: myclobutanil (150, 75, and 10mgkg(-1) body weight day(-1); triadimefon (115, 50, and 10 mg kg(-1) body weight day-'), which included their maximum tolerated dose levels (MTD). Both myclobutanil and triadimefon significantly induced pentoxyresorufin O-depentylase activities at their MTD levels: myclobutanil, 8.1-fold at 150mgkg(-1) body weight day- ; and triadimefon, 18.5-fold at 115mgkg(-1) body weight day-'. Benzyloxyresorufin O-debenzylase activities were similarly increased: myclobutanil, 13.3-fold; triadimefon, 27.7-fold. Quantitative real-time reverse-transcription polymerase chain reaction assays were used to characterize the mRNA expression of specific CYP genes induced by these two conazoles. Myclobutanil and triadimefon treatment at their MTD levels significantly increased rat hepatic mRNA expression of CYP2B1 (14.3- and 54.6-fold), CYP3A23/3A1 (2.2- and 7.3-fold), and CYP3A2 (1.5- and 1.7-fold). Western immunoblots of rat hepatic microsomal proteins identified significantly increased levels of CYP isoforms after myclobutanil or triadimefon treatment at their MTD levels: CYP2BI/2 (4.8- and 5.3-fold), and CYP3A1 (2.2- and 2.9-fold). Triadimefon also increased CYP3A2 immunoreactive protein levels 1.8-fold. These results indicate that triadimefon and myclobutanil, like other triazole-containing conazoles, induced CYP2B and CYP3A families of cytochromes in rat liver.

Evaluation of the precision-cut liver and lung slice systems for the study of induction of CYP1, epoxide hydrolase and glutathione S-transferase activities

The principal objective was to ascertain whether precision-cut tissue slices can be used to evaluate the potential of chemicals to induce CYP1, epoxide hydrolase and glutathione S-transferase activities, all being important enzymes involved in the metabolism of polycyclic aromatic hydrocarbons. Precision-cut rat liver and lung slices were incubated with a range of benzo[a]pyrene concentrations for various time periods. A rise in the O-deethylation of ethoxyresorufin was seen in both liver and lung slices exposed to benzo[a]pyrene, which was accompanied by increased CYP1A apoprotein levels. Pulmonary CYP1B1 apoprotein levels and hepatic mRNA levels were similarly enhanced. Elevated epoxide hydrolase and glutathione S-transferase activities were also observed in liver slices following incubation for 24h; similarly, a rise in apoprotein levels of both enzymes was evident, peak levels occurring at the same time point. When mRNA levels were monitored, a rise in the levels of both enzymes was seen as early as 4h after incubation, but maximum levels were attained at 24 h. In lung slices, induction of epoxide hydrolase by benzo[a]pyrene was observed after a 24-h incubation, and at a concentration of 1 microM; a rise in apoprotein levels was seen at this time point. Glutathione S-transferase activity was not inducible in lung slices by benzo[a]pyrene but a modest increase was observed in hepatic slices. Collectively, these studies confirmed CYP1A induction in rat liver slices and established that CYP1B1 expression, and epoxide hydrolase and glutathione S-transferase activities are inducible in precision-cut tissue slices.

Peroxisome proliferator-activated receptor alpha-independent effects of peroxisome proliferators on cysteinyl leukotriene production in mast cells

The effects of peroxisome proliferators, the ligands of a nuclear receptor peroxisome proliferator-activated receptor (PPAR) alpha, on cysteinyl leukotriene production were investigated in rodent mast cells. Peroxisome proliferators Wy-14,643 (30 microM) and fenofibrate (100 microM) significantly inhibited the cysteinyl leukotriene production that was induced by antigen (Ag) treatment after overnight sensitization to Ag specific immunoglobulin E (IgE) in a rat basophilic leukemia (RBL)-2H3 mast cell line. Similar inhibition by these drugs was observed in IgE and Ag-treated mouse bone marrow-derived mast cells, A23187-treated RBL-2H3 and A23187-treated mouse peritoneal macrophages. Wy-14,643 (30 microM) and fenofibrate (100 microM) did not affect the release of radioactivity from RBL-2H3 pre-incubated with [(3)H]-arachidonic acid, which is considered an index of phospholipase A(2) activity. Wy-14,643 (30 microM) and fenofibrate (100 microM) did not directly inhibit 5-lipoxygenase activity. Troglitazone was found to directly inhibit the activity of 5-lipoxygenase. The PPARalpha mRNA level was at less than the limit of detection for the realtime polymerase chain reaction both in RBL-2H3 and bone marrow-derived mast cells. Wy-14,643 (30 microM) and fenofibrate (100 microM) did not induce acyl-CoA oxidase mRNA in RBL-2H3, which was reported to be induced by peroxisome proliferators via PPARalpha in hepatocytes. Wy-14,643 (30 microM) and fenofibrate (100 microM) inhibited the cysteinyl leukotriene production in bone marrow-derived mast cells from PPARalpha-null mice. It was concluded that the inhibitory effects of these peroxisome proliferators on cysteinyl leukotriene production are independent of PPARalpha in mast cells.

Induction of CYP2B and CYP2E1 in precision-cut rat liver slices cultured in defined medium

Many drugs and endogenous substances undergo biotransformation by cytochrome P450s (CYPs), and some drugs are also capable of modulating the expression of various CYPs. Knowledge of the potential of a drug to modulate CYPs is useful to help predict potential drug interactions. This study utilized precision-cut rat liver slices in dynamic organ culture to assess the effects of various media on the viability of rat liver slices and the expression of CYP2B and CYP2E1 when the slices are exposed to phenobarbital and isoniazid, which are drugs capable of inducing these respective CYPs. Liver slices were maintained in serum supplemented Waymouths medium and two different serum-free media, Hepatozyme (Life Technologies) and a new defined medium, which is named BPM. While Hepatozyme is considered a suitable medium to support primary hepatocyte cultures, this product did not maintain viable liver slices, even for 24 h. The serum containing and new defined media maintained viable liver slices for up to 96 h in culture. Phenobarbital (0.5 mM) and isoniazid (0.1 or 0.6 mM) did not affect viability in this model. In the absence of phenobarbital or isoniazid, liver slices maintained for 96 h in the new BPM medium maintained the respective levels of CYP2B and 2E1 protein at 1.8 and 1.9-fold higher than in slices maintained in the serum-containing medium. Phenobarbital exposure (0.5 mM) for 96 h induced CYP2B protein 5.2-fold in the BPM medium and 2.5-fold in the serum-containing medium. Isoniazid exposure (0.1 and 0.5 mM) for 96 h induced CYP2E1 protein 1.9 and 2.1-fold (respectively) in the BPM medium and 2.1 and 2.0-fold in the serum-containing medium. The respective CYP enzymatic activities were also increased by these drugs in a similar manner. Thus, the new defined BPM medium provides suitable conditions for maintaining CYP2B and 2E1 in liver slices and supports the investigation of drug-induced modulation of these enzymes.

Thioacetamide induced liver damage in zebrafish embryo as a disease model for steatohepatitis

Steatohepatitis has recently been increasing as a cofactor influencing the progression of fibrosis, cirrhosis, adenoma and carcinoma in liver; however, the mechanisms by which it contributes to liver injury remain uncertain. We induced steatohepatitis in zebrafish embryos using thioacetamide (TAA). TUNEL assay revealed significant increasing of apoptosis in liver after 5 days post fertilization and the increasing of apoptosis was observed to be associated with the up-regulation of apoptotic genes such as, bad, bax, P-38a, caspase-3 and 8, and JNK-1. Histological sections by oil red O stain showed the accumulation of fatty droplets which causes the pushing of the nucleus towards one side. Up-regulation of steatosis markers such as, ACC, adiponectin, PTL, CEBP- alpha and beta, SREBP-1 was also observed. Furthermore, the elevation of glutathione peroxidase in TAA treated embryos indicated that TAA induces lipid peroxidation which leads to causes liver damage. Zebrafish has already been considered as a good human disease model and in this context; TAA-treated zebrafish may serve as a good animal model to study the molecular pathogenesis of steatohepatitis. Moreover, non-availability of specific drugs to prevent steatohepatitis, this animal model may serve as a powerful preclinical platform to study the therapeutic strategies and for evaluating chemoprevention strategies for this disease.

Stability of cytochromes P450 and phase II conjugation systems in precision-cut rat lung slices cultured up to 72h

The objective of the present study was to evaluate the stability of cytochrome P450 enzymes and of the conjugation enzyme systems epoxide hydrolase, glucuronosyl transferase, sulphotransferase and glutathione S-transferase in precision-cut rat lung slices incubated in RPMI media for different time periods up to 72 h. Moreover, the effect of culturing of lung slices on total glutathione levels and glutathione reductase was also investigated. Monitoring of cytochrome P450 activity was achieved using established diagnostic probes, but when activity in the lung was low the maintenance of the various enzymes in culture was determined immunologically using Western blotting. The dealkylation of pentoxyresorufin declined markedly during the first 4h of incubation but in the case of ethoxyresorufin loss of activity was more gradual and less severe. Western blot analysis revealed that the rate of decrease in cytochrome P450 apoprotein levels was isoform-specific with CYP2E1 being the most stable and CYP3A the least stable. Generally, phase II activities, especially cytosolic sulphotransferase, were relatively more stable throughout the incubation period compared with cytochromes P450. Finally, glutathione reductase activity and total glutathione levels were maintained throughout the 72 h incubation. The present studies indicate that xenobiotic-metabolising enzymes in precision-cut rat lung slices decline in culture, but the rate of loss differs and depends on the nature of the enzyme.

Fluconazole-induced hepatic cytochrome P450 gene expression and enzymatic activities in rats and mice

This study was undertaken to examine the effects of the triazole antifungal agent fluconazole on the expression of hepatic cytochrome P450 (Cyp) genes and the activities of Cyp enzymes in male Sprague-Dawley rats and male CD-1 mice. Alkoxyresorufin O-dealkylation (AROD) methods were used as measures of Cyp enzyme activities. Western analyses identified specific Cyp isoforms. Quantitative real-time reverse-transcription polymerase chain reaction (quantitative real time-RT-PCR) assays were used to quantitate the mRNA expression of specific Cyp genes induced by this conazole. Rats and mice were administered fluconazole 2, 25, or 50 mg/kg bw/d by gavage daily for 14 days. In rats, fluconazole treatment (50 mg/kg bw/d) significantly induced pentoxyresorufin O-dealkylation (PROD), benzyloxyresorufin O-dealkylation (BROD), and ethoxyresorufin O-dealkylation (EROD) hepatic microsomal activities. Fluconazole treatment significantly increased rat hepatic mRNA expression of CYP2B1 and CYP3A23/3A1 with dose-related responses. The highest dose of fluconazole gave a 128-fold induction of CYP2B1 and a 4.6-fold induction of CYP3A23/3A1 mRNA. CYP3A2 mRNA levels were also overexpressed 5.6-7.2-fold depending on dose. Western immunoblots of rat hepatic microsomal proteins identified Cyp isoforms: CYP1A1, CYP1A2, CYP2B1/2, CYP3A23/3A1, and Cyp3A2 with increased levels of CYP2B1/2 and CYP3A23/3A1 proteins. In mice, fluconazole induced BROD, PROD, EROD, and methoxyresorufin O-dealkylation hepatic microsomal activities after treatment with 25 and 50 mg/kg bw/d. Fluconazole increased mouse hepatic mRNA expression of Cyp2b10 (1.9-fold) and Cyp3a11 (2.6-fold) in the 50 mg/kg bw/d treatment group. In summary, these results indicated that fluconazole, a triazole-containing conazole, clearly induced CYP2B and CYP3A families of isoforms in rat liver and Cyp2b and Cyp3a families of isoforms in mouse liver.

Cytochrome P450 gene induction in rats ex vivo assessed by quantitative real-time reverse transcriptase-polymerase chain reaction (TaqMan)

Drug-induced changes in expression of cytochrome P450 (P450) genes are a significant issue in the preclinical development of pharmaceuticals. For example, preclinically, P450 induction can affect safety studies by reducing the systemic exposure of a compound undergoing toxicological evaluation, thus limiting the exposure that can be safely investigated in patients. Therefore, the induction potential of candidate drugs has been studied as part of the drug development process, typically using protein and/or catalytic end points. However, measuring changes in the levels of mRNA using TaqMan technology offers the opportunity to investigate this issue with the advantages of better dynamic range and specific enzyme identification. Here, we describe the TaqMan application to study ex vivo the P450 gene induction in the rat. Initially, livers from rats dosed with the prototypic P450 inducers beta-napthoflavone (BNF), phenobarbital (PB), dexamethasone (DEX), and clofibric acid (CLO) were analyzed for mRNA levels of CYP1A1, 1A2, 2B1, 2B2, 2E1, 3A2, 3A23, and 4A1 and compared with control animals. The maximum fold induction of mRNA varied: 2500-fold for CYP1A1 with BNF, 680-fold for CYP2B1 with PB, 59-fold for CYP3A23 with DEX, and 16-fold for CYP4A1 with CLO. This method was then applied to estimate the inductive potential of putative drug candidates undergoing rodent toxicological evaluation. We present a summary of these data that demonstrates the sensitivity and specificity of the TaqMan assay to distinguish between inducers and noninducers and that offers a highly specific alternative to the quantification of drug effects on P450 expression using immunodetection and substrate metabolism.