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Men S, Wang H. Phenobarbital in Nuclear Receptor Activation: An Update. Drug Metab Dispos 2023; 51:210-218. [PMID: 36351837 PMCID: PMC9900862 DOI: 10.1124/dmd.122.000859] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 11/11/2022] Open
Abstract
Phenobarbital (PB) is a commonly prescribed anti-epileptic drug that can also benefit newborns from hyperbilirubinemia. Being the first drug demonstrating hepatic induction of cytochrome P450 (CYP), PB has since been broadly used as a model compound to study xenobiotic-induced drug metabolism and clearance. Mechanistically, PB-mediated CYP induction is linked to a number of nuclear receptors, such as the constitutive androstane receptor (CAR), pregnane X receptor (PXR), and estrogen receptor α, with CAR being the predominant regulator. Unlike prototypical agonistic ligands, PB-mediated activation of CAR does not involve direct binding with the receptor. Instead, dephosphorylation of threonine 38 in the DNA-binding domain of CAR was delineated as a key signaling event underlying PB-mediated indirect activation of CAR. Further studies revealed that such phosphorylation sites appear to be highly conserved among most human nuclear receptors. Interestingly, while PB is a pan-CAR activator in both animals and humans, PB activates human but not mouse PXR. The species-specific role of PB in gene regulation is a key determinant of its implication in xenobiotic metabolism, drug-drug interactions, energy homeostasis, and cell proliferation. In this review, we summarize the recent progress in our understanding of PB-provoked transactivation of nuclear receptors with a focus on CAR and PXR. SIGNIFICANCE STATEMENT: Extensive studies using PB as a research tool have significantly advanced our understanding of the molecular basis underlying nuclear receptor-mediated drug metabolism, drug-drug interactions, energy homeostasis, and cell proliferation. In particular, CAR has been established as a cell signaling-regulated nuclear receptor in addition to ligand-dependent functionality. This mini-review highlights the mechanisms by which PB transactivates CAR and PXR.
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Affiliation(s)
- Shuaiqian Men
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (S.M., H.W.)
| | - Hongbing Wang
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (S.M., H.W.)
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Li L, Welch MA, Li Z, Mackowiak B, Heyward S, Swaan PW, Wang H. Mechanistic Insights of Phenobarbital-Mediated Activation of Human but Not Mouse Pregnane X Receptor. Mol Pharmacol 2019; 96:345-354. [PMID: 31436536 PMCID: PMC6701513 DOI: 10.1124/mol.119.116616] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Accepted: 07/07/2019] [Indexed: 12/12/2022] Open
Abstract
Phenobarbital (PB), a broadly used antiseizure drug, was the first to be characterized as an inducer of cytochrome P450 by activation of the constitutive androstane receptor (CAR). Although PB is recognized as a conserved CAR activator among species via a well-documented indirect activation mechanism, conflicting results have been reported regarding PB regulation of the pregnane X receptor (PXR), a sister receptor of CAR, and the underlying mechanisms remain elusive. Here, we show that in a human CAR (hCAR)-knockout (KO) HepaRG cell line, PB significantly induces the expression of CYP2B6 and CYP3A4, two shared target genes of hCAR and human PXR (hPXR). In human primary hepatocytes and hCAR-KO HepaRG cells, PB-induced expression of CYP3A4 was markedly repressed by genetic knockdown or pharmacological inhibition of hPXR. Mechanistically, PB concentration dependently activates hPXR but not its mouse counterpart in cell-based luciferase assays. Mammalian two-hybrid assays demonstrated that PB selectively increases the functional interaction between the steroid receptor coactivator-1 and hPXR but not mouse PXR. Moreover, surface plasmon resonance binding affinity assay showed that PB directly binds to the ligand binding domain of hPXR (KD = 1.42 × 10-05). Structure-activity analysis further revealed that the amino acid tryptophan-299 within the ligand binding pocket of hPXR plays a key role in the agonistic binding of PB and mutation of tryptophan-299 disrupts PB activation of hPXR. Collectively, these data reveal that PB, a selective mouse CAR activator, activates both hCAR and hPXR, and provide novel mechanistic insights for PB-mediated activation of hPXR.
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Affiliation(s)
- Linhao Li
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
| | - Matthew A Welch
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
| | - Zhihui Li
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
| | - Bryan Mackowiak
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
| | - Scott Heyward
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
| | - Peter W Swaan
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
| | - Hongbing Wang
- Department of Pharmaceutical Sciences, University of Maryland School of Pharmacy, Baltimore, Maryland (L.L., M.A.W., Z.L., B.M., P.W.S., H.W.); and BioIVT, Halethorpe, Maryland (S.H.)
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Krais AM, Speksnijder EN, Melis JPM, Indra R, Moserova M, Godschalk RW, van Schooten FJ, Seidel A, Kopka K, Schmeiser HH, Stiborova M, Phillips DH, Luijten M, Arlt VM. The impact of p53 on DNA damage and metabolic activation of the environmental carcinogen benzo[a]pyrene: effects in Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice. Arch Toxicol 2016; 90:839-51. [PMID: 25995008 PMCID: PMC4785204 DOI: 10.1007/s00204-015-1531-8] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Accepted: 05/05/2015] [Indexed: 12/22/2022]
Abstract
The tumour suppressor p53 is one of the most important cancer genes. Previous findings have shown that p53 expression can influence DNA adduct formation of the environmental carcinogen benzo[a]pyrene (BaP) in human cells, indicating a role for p53 in the cytochrome P450 (CYP) 1A1-mediated biotransformation of BaP in vitro. We investigated the potential role of p53 in xenobiotic metabolism in vivo by treating Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice with BaP. BaP-DNA adduct levels, as measured by (32)P-postlabelling analysis, were significantly higher in liver and kidney of Trp53(-/-) mice than of Trp53(+/+) mice. Complementarily, significantly higher amounts of BaP metabolites were also formed ex vivo in hepatic microsomes from BaP-pretreated Trp53(-/-) mice. Bypass of the need for metabolic activation by treating mice with BaP-7,8-dihydrodiol-9,10-epoxide resulted in similar adduct levels in liver and kidney in all mouse lines, confirming that the influence of p53 is on the biotransformation of the parent compound. Higher BaP-DNA adduct levels in the livers of Trp53(-/-) mice correlated with higher CYP1A protein levels and increased CYP1A enzyme activity in these animals. Our study demonstrates a role for p53 in the metabolism of BaP in vivo, confirming previous in vitro results on a novel role for p53 in CYP1A1-mediated BaP metabolism. However, our results also suggest that the mechanisms involved in the altered expression and activity of the CYP1A1 enzyme by p53 in vitro and in vivo are different.
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Affiliation(s)
- Annette M Krais
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment & Health, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London, SE1 9NH, UK
| | - Ewoud N Speksnijder
- Center for Health Protection, National Institute for Public Health and the Environment (RIVM), 3721 MA, Bilthoven, The Netherlands
- Department of Human Genetics, Leiden University Medical Center, 2300 RC, Leiden, The Netherlands
| | - Joost P M Melis
- Center for Health Protection, National Institute for Public Health and the Environment (RIVM), 3721 MA, Bilthoven, The Netherlands
- Department of Human Genetics, Leiden University Medical Center, 2300 RC, Leiden, The Netherlands
| | - Radek Indra
- Department of Biochemistry, Faculty of Science, Charles University, 12840, Prague 2, Czech Republic
| | - Michaela Moserova
- Department of Biochemistry, Faculty of Science, Charles University, 12840, Prague 2, Czech Republic
| | - Roger W Godschalk
- Department of Toxicology, School for Nutrition, Toxicology and Metabolism (NUTRIM), Maastricht University Medical Centre, 6200 MD, Maastricht, The Netherlands
| | - Frederik-J van Schooten
- Department of Toxicology, School for Nutrition, Toxicology and Metabolism (NUTRIM), Maastricht University Medical Centre, 6200 MD, Maastricht, The Netherlands
| | - Albrecht Seidel
- Biochemical Institute for Environmental Carcinogens, Prof. Dr. Gernot Grimmer-Foundation, 22927, Grosshansdorf, Germany
| | - Klaus Kopka
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
| | - Heinz H Schmeiser
- Division of Radiopharmaceutical Chemistry, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120, Heidelberg, Germany
| | - Marie Stiborova
- Department of Biochemistry, Faculty of Science, Charles University, 12840, Prague 2, Czech Republic
| | - David H Phillips
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment & Health, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London, SE1 9NH, UK
| | - Mirjam Luijten
- Center for Health Protection, National Institute for Public Health and the Environment (RIVM), 3721 MA, Bilthoven, The Netherlands
- Department of Human Genetics, Leiden University Medical Center, 2300 RC, Leiden, The Netherlands
| | - Volker M Arlt
- Analytical and Environmental Sciences Division, MRC-PHE Centre for Environment & Health, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London, SE1 9NH, UK.
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Liu M, Chen S, Yueh MF, Wang G, Hao H, Tukey RH. Reduction of p53 by knockdown of the UGT1 locus in colon epithelial cells causes an increase in tumorigenesis. Cell Mol Gastroenterol Hepatol 2015; 2:63-76.e5. [PMID: 26807433 PMCID: PMC4721636 DOI: 10.1016/j.jcmgh.2015.08.008] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
BACKGROUND & AIMS The UDP-glucuronosyltransferases (UGTs) are part of the cells machinery that protects the tissues from a toxicant insult by environmental and host cell metabolites. We have investigated the mechanism behind tumor growth and UGT repression. METHODS We initially silenced the Ugt1 locus in human colon cell lines and investigated markers and responses linked to p53 activation. To examine the role of the Ugt1 locus in p53-directed apoptosis and tumorigenesis, experiments were conducted to induce acute colon inflammation and chemical induced colon cancer in mice where we have selectively deleted the Ugt1 locus in the intestinal epithelial cells (Ugt1ΔIEC mice). RESULTS Knockdown of the UGT1A proteins by RNAi in human colon cancer cells and knockout of the Ugt1 locus in intestinal crypt stem cells reduces phosphorylated p53 activation and compromises the ability of p53 to control apoptosis. Targeted deletion of intestinal Ugt1 expression in Ugt1ΔIEC mice represses colon inflammation-induced p53 production and pro-apoptotic protein activation. When we induced colon cancer, the size and number of the tumors were significantly greater in the Ugt1ΔIEC mice when compared to wild type mice. Furthermore, analysis of endoplasmic reticulum (ER) stress-related markers indicated that lack of UGT1A expression causes higher ER stress in intestinal epithelial cells and tissue, which may account for the lower expression of p53. CONCLUSIONS Our results demonstrate that UGT1A expression is required to maintain and sustain p53 activation in stress-induced colon epithelial cells and has a significant impact on p53-mediated apoptosis and tumor suppression, thus protecting the colon tissue from neoplastic transformation.
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Affiliation(s)
- Miao Liu
- Laboratory of Environmental Toxicology, Department of Chemistry & Biochemistry and Pharmacology, University of California at San Diego, La Jolla, California,State Key Laboratory of Natural Medicines, Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing, People’s Republic of China
| | - Shujuan Chen
- Laboratory of Environmental Toxicology, Department of Chemistry & Biochemistry and Pharmacology, University of California at San Diego, La Jolla, California
| | - Mei-Fei Yueh
- Laboratory of Environmental Toxicology, Department of Chemistry & Biochemistry and Pharmacology, University of California at San Diego, La Jolla, California
| | - Guangji Wang
- State Key Laboratory of Natural Medicines, Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing, People’s Republic of China
| | - Haiping Hao
- State Key Laboratory of Natural Medicines, Key Laboratory of Drug Metabolism and Pharmacokinetics, China Pharmaceutical University, Nanjing, People’s Republic of China,Haiping Hao, PhD, China Pharmaceutical University, Tongjiaxiang 24, Nanjing 21009, China.China Pharmaceutical University, Tongjiaxiang 24Nanjing 21009China
| | - Robert H. Tukey
- Laboratory of Environmental Toxicology, Department of Chemistry & Biochemistry and Pharmacology, University of California at San Diego, La Jolla, California,Correspondence Address correspondence to: Robert H. Tukey, PhD, University of California–San Diego, 9500 Gilman Drive, Leichtag Biomedical Research Building, Room 211, La Jolla, California 92093-0722.University of California–San Diego9500 Gilman DriveLeichtag Biomedical Research BuildingRoom 211La JollaCalifornia 92093-0722
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van Kesteren PCE, Zwart PE, Pennings JLA, Gottschalk WHR, Kleinjans JCS, van Delft JH, van Steeg H, Luijten M. Deregulation of cancer-related pathways in primary hepatocytes derived from DNA repair-deficient Xpa-/-p53+/- mice upon exposure to benzo[a]pyrene. Toxicol Sci 2011; 123:123-32. [PMID: 21715664 DOI: 10.1093/toxsci/kfr169] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The current method to predict carcinogenicity of chemicals or drugs is the chronic 2-year rodent bioassay, which has disadvantages in duration, animal use, and specificity. An attractive alternative is the DNA repair-deficient Xpa(-/-)p53(+/-) mouse model that is sensitive to both genotoxic and nongenotoxic carcinogens. A next step in alternative carcinogenicity testing is the development of reliable in vitro systems. We investigated the use of primary hepatocytes, isolated from wild-type (WT) and Xpa(-/-)p53(+/-) mice, in combination with transcriptome analyses for their usefulness to predict carcinogenic features of compounds. As a proof of principle, we studied the response of hepatocytes to the genotoxic carcinogen benzo[a]pyrene (B[a]P). Upon treatment, both WT and Xpa(-/-)p53(+/-) hepatocytes appeared to be metabolically active. However, Xpa(-/-)p53(+/-) hepatocytes were more sensitive than WT hepatocytes to B[a]P treatment in terms of cell survival. In B[a]P-treated WT hepatocytes, DNA repair and cell cycle control genes were transcriptionally activated. Xpa(-/-)p53(+/-) hepatocytes were more responsive to B[a]P exposure, resulting in the downregulation of cancer-related pathways. Deregulation of mitogen-activated protein kinase signaling seems to play an essential role in this and might be the underlying reason for the increased susceptibility of Xpa(-/-)p53(+/-) mice toward carcinogens. Our conclusion is that primary hepatocytes combined with transcriptomics are promising to identify the carcinogenic features of chemicals. Furthermore, these cells seem suitable to gain further insight into the molecular mechanisms of the increased sensitivity of Xpa(-/-)p53(+/-) mice toward both genotoxic and nongenotoxic carcinogens.
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Affiliation(s)
- Petra C E van Kesteren
- Laboratory for Health Protection Research, National Institute for Public Health and the Environment, 3720 BA Bilthoven, The Netherlands
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Maronpot RR, Yoshizawa K, Nyska A, Harada T, Flake G, Mueller G, Singh B, Ward JM. Hepatic Enzyme Induction. Toxicol Pathol 2010; 38:776-95. [DOI: 10.1177/0192623310373778] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Hepatic enzyme induction is generally an adaptive response associated with increases in liver weight, induction of gene expression, and morphological changes in hepatocytes. The additive growth and functional demands that initiated the response to hepatic enzyme induction cover a wide range of stimuli including pregnancy and lactation, hormonal fluctuations, dietary constituents, infections associated with acute-phase proteins, as well as responses to exposure to xenobiotics. Common xenobiotic enzyme inducers trigger pathways involving the constitutive androstane receptor (CAR), the peroxisome proliferator-activated receptor (PPAR), the aryl hydrocarbon receptor (AhR), and the pregnane-X-receptor (PXR). Liver enlargement in response to hepatic enzyme induction is typically associated with hepatocellular hypertrophy and often, transient hepatocyte hyperplasia. The hypertrophy may show a lobular distribution, with the pattern of lobular zonation and severity reflecting species, strain, and sex differences in addition to effects from specific xenobiotics. Toxicity and hepatocarcinogenicity may occur when liver responses exceed adaptive changes or induced enzymes generate toxic metabolites. These undesirable consequences are influenced by the type and dose of xenobiotic and show considerable species differences in susceptibility and severity that need to be understood for assessing the potential effects on human health from similar exposures to specific xenobiotics.
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Affiliation(s)
| | | | | | | | - Gordon Flake
- National Institute for Environmental Health Sciences, Research Triangle Park, North Carolina, USA
| | | | - Bhanu Singh
- DuPont Haskell Global Centers for Health and Environmental Science, Newark, Delaware, USA
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Rhomberg LR, Baetcke K, Blancato J, Bus J, Cohen S, Conolly R, Dixit R, Doe J, Ekelman K, Fenner-Crisp P, Harvey P, Hattis D, Jacobs A, Jacobson-Kram D, Lewandowski T, Liteplo R, Pelkonen O, Rice J, Somers D, Turturro A, West W, Olin S. Issues in the Design and Interpretation of Chronic Toxicity and Carcinogenicity Studies in Rodents: Approaches to Dose Selection. Crit Rev Toxicol 2008; 37:729-837. [DOI: 10.1080/10408440701524949] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Argikar UA, Iwuchukwu OF, Nagar S. Update on tools for evaluation of uridine diphosphoglucuronosyltransferase polymorphisms. Expert Opin Drug Metab Toxicol 2008; 4:879-94. [DOI: 10.1517/17425255.4.7.879] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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Elsby R, Kitteringham NR, Goldring CE, Lovatt CA, Chamberlain M, Henderson CJ, Wolf CR, Park BK. Increased constitutive c-Jun N-terminal kinase signaling in mice lacking glutathione S-transferase Pi. J Biol Chem 2003; 278:22243-9. [PMID: 12646564 DOI: 10.1074/jbc.m301211200] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Glutathione S-transferase Pi (GSTP) detoxifies electrophiles by catalyzing their conjugation with reduced glutathione. A second function of this protein in cell defense has recently been proposed that is related to its ability to interact with c-Jun N-terminal kinase (JNK). The present study aimed to determine whether this interaction results in increased constitutive JNK activity in the absence of GSTP in GstP1/P2(-/-) mice and whether such a phenomenon leads to the up-regulation of genes that are relevant to cell defense. We found a significant increase in constitutive JNK activity in the liver and lung of GstP1/P2-/- compared with GstP1/P2(+/+) mice. The greatest increase in constitutive JNK activity was observed in null liver and was accompanied by a significant increase in activator protein-1 DNA binding activity (8-fold) and in the mRNA levels for the antioxidant protein heme oxygenase-1 compared with wild type. Furthermore UDP-glucuronosyltransferase 1A6 mRNA levels were significantly higher in the livers of GstP1/P2(-/-) compared with GstP1/P2(+/+) mice, which correlated to a 2-fold increase in constitutive activity both in vitro and in vivo. There was no difference in the gene expression of other UDP-glucuronosyltransferase isoforms, manganese superoxide dismutase, microsomal epoxide hydrolase, or GSTA1 between GstP1/P2(-/-) and GstP1/P2(+/+) mice. Additionally there was no phenotypic difference in the induction of heme oxygenase-1 mRNA after acetaminophen administration. This study not only demonstrates the role of GSTP as a direct inhibitor of JNK in vivo but also its role in regulating the constitutive expression of specific downstream molecular targets of the JNK signaling pathway.
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Affiliation(s)
- Robert Elsby
- Department of Pharmacology and Therapeutics, University of Liverpool, Liverpool L69 3GE, United Kingdom
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Torti VR, Cobb AJ, Wong VA, Butterworth BE. Induction of micronuclei in wild-type and p53(+/-) transgenic mice by inhaled bromodichloromethane. Mutat Res 2002; 520:171-8. [PMID: 12297157 DOI: 10.1016/s1383-5718(02)00200-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Bromodichloromethane (BDCM) is commonly present in trace amounts in drinking water as a disinfection by-product. BDCM has been shown to be carcinogenic in mice and rats when given by gavage at relatively high doses. Genotoxic activity as well as induced regenerative cell proliferation may contribute to the carcinogenic potential of BDCM. The purpose of the current studies was to evaluate the ability of BDCM to induce micronuclei (MN) in bone marrow and blood of wild-type and p53(+/-) mice on the C57BL/6 and FVB/N genetic backgrounds using the inhalation route of exposure. Toxicity studies were being conducted in this laboratory with inhaled BDCM to select doses for longer-term cancer bioassays using wild-type and p53(+/-) transgenic mice on different genetic backgrounds. Bone marrow samples from these experiments were evaluated for the induction of MN after 1 and 3 weeks of exposure. Accumulation of MN in the peripheral blood was also evaluated at the 13-week time point of a cancer study with the p53(+/-) mice. For the 1-week time point, male C57BL/6 wild-type and p53(+/-) mice and FVB/N wild-type and p53(+/-) mice were exposed daily for 6h per day for 7 consecutive days to atmospheric BDCM concentrations of 0, 1, 10, 30, 100, or 150 ppm. In a second experiment, mice were exposed daily for 6h per day for 3 weeks to atmospheric BDCM concentrations of 0, 0.5, 1, 3, 10, or 30 ppm. Resulting levels of polychromatic erythrocytes (PCE) containing MN were assessed in the bone marrow. For all of the 1- and 3-week exposure groups, the only statistically significant increase in the percentage of bone marrow PCE cells containing MN was in the 1-week 100 ppm BDCM exposure group in the FVB/N wild-type mice (control 0.26% versus exposed 1.16%). C57BL/6 p53(+/-) mice and FVB/N p53(+/-) mice were exposed daily for 6 h per day for 13 weeks to atmospheric BDCM concentrations of 0, 0.5, 3, 10, or 15 ppm. MN were quantified in samples of peripheral blood. Statistically significant increases in the percentage of peripheral blood NCE cells containing MN were seen at the highest BDCM exposure group of 15 ppm in both the C57BL/6 p53(+/-) strain (control 0.36% versus exposed 0.67%) and the FVB/N p53(+/-) strain (control 0.36% versus exposed 0.86%). These data indicate weak induction of MN by BDCM, but only at high atmospheric concentrations relative to normal environmental exposures and with extended periods of exposure. Although comparisons are difficult because responses were negative or marginal, the p53 genotype or the genetic background did not appear to substantially alter susceptibility to the genotoxic effects of BDCM.
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Affiliation(s)
- Vincent R Torti
- CIIT Centers for Health Research, Research Triangle Park, NC, USA
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