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Wang H, Zhang L, Xia Z, Cui JY. Effect of Chronic Cadmium Exposure on Brain and Liver Transporters and Drug-Metabolizing Enzymes in Male and Female Mice Genetically Predisposed to Alzheimer's Disease. Drug Metab Dispos 2022; 50:1414-1428. [PMID: 35878927 PMCID: PMC9513859 DOI: 10.1124/dmd.121.000453] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Accepted: 06/27/2022] [Indexed: 11/22/2022] Open
Abstract
Cadmium (Cd) exposure is associated with increased Alzheimer's disease (AD) risks. The human Apolipoprotein E (ApoE) gene encodes a lipid-transporting protein that is critical for brain functions. Compared with ApoE2 and E3, ApoE4 is associated with increased AD risk. Xenobiotic biotransformation-related genes have been implicated in the pathogenesis of AD. However, little is known about the effects of Cd, ApoE, and sex on drug-processing genes. We investigated the Cd-ApoE interaction on the transcriptomic changes in the brains and livers of ApoE3/ApoE4 transgenic mice. Cd disrupts the transcriptomes of transporter and drug-processing genes in brain and liver in a sex- and ApoE-genotype-specific manner. Proinflammation related genes were enriched in livers of Cd-exposed ApoE4 males, whereas circadian rhythm and lipid metabolism related genes were enriched in livers of Cd-exposed ApoE3 females. In brains, Cd up-regulated the arachidonic acid-metabolizing Cyp2j isoforms only in the brains of ApoE3 mice, whereas the dysregulation of cation transporters was male-specific. In livers, several direct target genes of the major xenobiotic-sensing nuclear receptor pregnane X receptor were uniquely upregulated in Cd-exposed ApoE4 males. There was a female-specific hepatic upregulation of the steroid hormone-metabolizing Cyp2 isoforms and the bile acid synthetic enzyme Cyp7a1 by Cd exposure. The dysregulated liver transporters were mostly involved in intermediary metabolism, with the most significant response observed in ApoE3 females. In conclusion, Cd dysregulated the brain and liver drug-processing genes in a sex- and ApoE-genotype specific manner, and this may serve as a contributing factor for the variance in the susceptibility to Cd neurotoxicity. SIGNIFICANCE STATEMENT: Xenobiotic biotransformation plays an important role in modulating the toxicity of environmental pollutants. The human ApoE4 allele is the strongest genetic risk factor for AD, and cadmium (Cd) is increasingly recognized as an environmental factor of AD. Very little is known regarding the interactions between Cd exposure, sex, and the genes involved in xenobiotic biotransformation in brain and liver. The present study has addressed this critical knowledge gap.
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Affiliation(s)
- Hao Wang
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
| | - Liang Zhang
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
| | - Zhengui Xia
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
| | - Julia Yue Cui
- Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington
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Hernandez‐Jerez AF, Adriaanse P, Aldrich A, Berny P, Coja T, Duquesne S, Focks A, Marinovich M, Millet M, Pelkonen O, Pieper S, Tiktak A, Topping CJ, Widenfalk A, Wilks M, Wolterink G, Gundert‐Remy U, Louisse J, Rudaz S, Testai E, Lostia A, Dorne J, Parra Morte JM. Scientific Opinion of the Scientific Panel on Plant Protection Products and their Residues (PPR Panel) on testing and interpretation of comparative in vitro metabolism studies. EFSA J 2021; 19:e06970. [PMID: 34987623 PMCID: PMC8696562 DOI: 10.2903/j.efsa.2021.6970] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
EFSA asked the Panel on Plant Protection Products and their residues to deliver a Scientific Opinion on testing and interpretation of comparative in vitro metabolism studies for both new active substances and existing ones. The main aim of comparative in vitro metabolism studies of pesticide active substances is to evaluate whether all significant metabolites formed in the human in vitro test system, as a surrogate of the in vivo situation, are also present at comparable level in animal species tested in toxicological studies and, therefore, if their potential toxicity has been appropriately covered by animal studies. The studies may also help to decide which animal model, with regard to a particular compound, is the most relevant for humans. In the experimental strategy, primary hepatocytes in suspension or culture are recommended since hepatocytes are considered the most representative in vitro system for prediction of in vivo metabolites. The experimental design of 3 × 3 × 3 (concentrations, time points, technical replicates, on pooled hepatocytes) will maximise the chance to identify unique (UHM) and disproportionate (DHM) human metabolites. When DHM and UHM are being assessed, test item-related radioactivity recovery and metabolite profile are the most important parameters. Subsequently, structural characterisation of the assigned metabolites is performed with appropriate analytical techniques. In toxicological assessment of metabolites, the uncertainty factor approach is the first alternative to testing option, followed by new approach methodologies (QSAR, read-across, in vitro methods), and only if these fail, in vivo animal toxicity studies may be performed. Knowledge of in vitro metabolites in human and animal hepatocytes would enable toxicological evaluation of all metabolites of concern, and, furthermore, add useful pieces of information for detection and evaluation of metabolites in different matrices (crops, livestock, environment), improve biomonitoring efforts via better toxicokinetic understanding, and ultimately, develop regulatory schemes employing physiologically based or physiology-mimicking in silico and/or in vitro test systems to anticipate the exposure of humans to potentially hazardous substances in plant protection products.
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Sugiyama S, Uno Y, Amano T, Kitazawa T, Teraoka H. Genetic diversity of cytochrome P450 2A with different metabolic activities in domestic cats. J Vet Med Sci 2019; 81:983-985. [PMID: 31118352 PMCID: PMC6656804 DOI: 10.1292/jvms.19-0107] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Knowledge of genetic polymorphisms of cytochrome P450 (CYP), the most important xenobiotic metabolizing enzyme, is very limited in cats. Preliminarily, we investigated genetic polymorphisms
in CYP2A13, one of the major CYP isoforms in the liver and lung. Four synonymous and three non-synonymous polymorphic variants were identified in feline CYP2A13 in domestic cats in Japan,
without an obvious major type. Metabolic parameters, Km and Vmax, of coumarin hydroxylation of CYP2A13 were shown to range within two times for the identified non-synonymous polymorphic
variants by using heterologous coexpression system in Escherichia coli. The results confirmed the polymorphic nature of CYP2A13 as a basis for effective application of
medicines and prevention of adverse reactions in treatment of domestic cats.
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Affiliation(s)
- Souta Sugiyama
- School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan
| | - Yasuhiro Uno
- Shin Nippon Biomedical Laboratories, Ltd., Kainan, Wakayama 642-0017, Japan
| | - Tomoko Amano
- College of Agriculture, Food and Environment Sciences, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan
| | - Takio Kitazawa
- School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan
| | - Hiroki Teraoka
- School of Veterinary Medicine, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, Japan
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Bailey J, Thew M, Balls M. An Analysis of the Use of Animal Models in Predicting Human Toxicology and Drug Safety. Altern Lab Anim 2019; 42:181-99. [DOI: 10.1177/026119291404200306] [Citation(s) in RCA: 72] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Affiliation(s)
- Jarrod Bailey
- British Union for the Abolition of Vivisection (BUAV), London, UK
| | - Michelle Thew
- British Union for the Abolition of Vivisection (BUAV), London, UK
| | - Michael Balls
- c/o Fund for the Replacement of Animals in Medical Experiments (FRAME), Nottingham, UK
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Iswandana R, Irianti MI, Oosterhuis D, Hofker HS, Merema MT, de Jager MH, Mutsaers HAM, Olinga P. Regional Differences in Human Intestinal Drug Metabolism. Drug Metab Dispos 2018; 46:1879-1885. [DOI: 10.1124/dmd.118.083428] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Accepted: 09/27/2018] [Indexed: 01/05/2023] Open
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Deng J, Guo L, Wu B. Circadian Regulation of Hepatic Cytochrome P450 2a5 by Peroxisome Proliferator-Activated Receptor γ. Drug Metab Dispos 2018; 46:1538-1545. [PMID: 30154104 DOI: 10.1124/dmd.118.083071] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Accepted: 08/17/2018] [Indexed: 11/22/2022] Open
Abstract
Human CYP2A6 (Cyp2a5 in mice) plays an important role in metabolism and detoxification of various drugs and chemicals. Here, we investigated a potential role of peroxisome proliferator-activated receptor γ (Ppar-γ) in circadian regulation of the Cyp2a5 enzyme. We first showed that Cyp2a5 mRNA and protein in mouse liver displayed robust circadian oscillations. Consistent with a circadian protein pattern, Cyp2a5-mediated 7-hydroxylation of coumarin was circadian time-dependent. Formation of 7-hydroxycoumarin was more extensive at a dosing time of Zeitgeber time 2 (ZT2) than that at ZT14. Interestingly, the nuclear receptor Ppar-γ was also a circadian gene. Circadian Ppar-γ protein level was strongly correlated with the Cyp2a5 mRNA level (r = 0.989). Furthermore, Ppar-γ activation (by a selective agonist, rosiglitazone) upregulated Cyp2a5 expression in Hepa-1c1c7 cells, whereas Ppar-γ knockdown downregulated Cyp2a5 expression. Also, Ppar-γ knockdown blunted the rhythmicity of Cyp2a5 mRNA in serum-shocked Hepa-1c1c7 cells. In addition, a combination of promoter truncation analysis, mobility shift, and chromatin immunoprecipitation assays revealed that Ppar-γ directly bound to a PPAR response element (i.e., the -1418- to -1396-bp region) within Cyp2a5 promoter and activated the gene transcription. Taken together, Ppar-γ was a transcriptional activator of Cyp2a5, and its rhythmic expression contributed to circadian expression of Cyp2a5.
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Affiliation(s)
- Jiangming Deng
- Research Center for Biopharmaceutics and Pharmacokinetics, College of Pharmacy (J.D., L.G., B.W.) and Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research (J.D., B.W.), Jinan University, Guangzhou, China
| | - Lianxia Guo
- Research Center for Biopharmaceutics and Pharmacokinetics, College of Pharmacy (J.D., L.G., B.W.) and Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research (J.D., B.W.), Jinan University, Guangzhou, China
| | - Baojian Wu
- Research Center for Biopharmaceutics and Pharmacokinetics, College of Pharmacy (J.D., L.G., B.W.) and Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research (J.D., B.W.), Jinan University, Guangzhou, China
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Feng M, Zhang H, Cao B, Liu S, Mao J, Zhang Q. Effects of 8-methoxypsoralen on the metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone in mice. Drug Metab Pharmacokinet 2015. [PMID: 26210672 DOI: 10.1016/j.dmpk.2015.06.001] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
8-Methoxypsoralen (8-MOP) is a well established drug in the treatment of various skin diseases. Pretreatment of mice with 8-MOP before administration of 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) significantly reduced the incidence of NNK-induced tumor. The present study was designed to evaluate the in vivo effects of 8-MOP on the bioactivation of NNK in mice. Decrease in the α-hydroxylation of NNK in mouse blood and tissues was observed as the most pronounced effect of 8-MOP. The catalytic property of cytochrome P450 2A5 (CYP2A5) enzyme in mice was determined by the coumarin 7-hydroxylation reaction, suggesting that 8-MOP produced remarkable inhibition on CYP2A5 in female C57BL/6 mice. These results implied that 8-MOP could prevent NNK-induced mutagenesis and tumorigenesis in mice through the inhibition of NNK α-hydroxylation, which may be achieved through the effect of 8-MOP on the bioactivities of CYP2A5.
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Affiliation(s)
- Mingfei Feng
- Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou 450001, China
| | - Hongtu Zhang
- Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
| | - Baojun Cao
- Tobacco Production Technology Center, Bijie Tobacco Company of Guizhou Province, Bijie 551700, China
| | - Shuaidong Liu
- Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou 450001, China
| | - Jian Mao
- Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou 450001, China.
| | - Qidong Zhang
- Zhengzhou Tobacco Research Institute of CNTC, Zhengzhou 450001, China.
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Hong F, Liu X, Ward S, Xiong H, Cederbaum AI, Lu Y. Absence of cytochrome P450 2A5 enhances alcohol-induced liver injury in mice. Dig Liver Dis 2015; 47:470-7. [PMID: 25804444 PMCID: PMC4442740 DOI: 10.1016/j.dld.2015.02.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Revised: 02/05/2015] [Accepted: 02/26/2015] [Indexed: 12/11/2022]
Abstract
BACKGROUND Ethanol can induce cytochrome P450 2E1, an active generator of reactive oxygen species, and this cytochrome is considered a risk factor for oxidative liver injury. Recently, we found that in addition to P450 2E1 also cytochrome P450 2A5, another isoform of cytochrome P450, can be induced by ethanol, and that ethanol induction of cytochrome P450 2A5 is P450 2E1-dependent. AIMS To investigate the role of cytochrome P450 2A5 in alcohol-induced liver injury. METHODS Cytochrome P450 2A5-knockout mice and wild type mice were fed the Lieber-Decarli ethanol liquid diet to induce liver injury. Controls were fed the Lieber-Decarli control diet. RESULTS After 4 weeks of feeding with Lieber-Decarli diet, ethanol-induced liver injury was enhanced in the knockout mice compared with wild type mice, as indicated by serum transaminases, hepatic fat accumulation (steatosis), and necroinflammation observed in liver sections with Haematoxylin & Eosin staining. Ethanol-induced oxidative stress was also higher in the knockout mice than the wild types. Ethanol feeding induced cytochrome P450 2A5 in wild type mice but not in the knockout mice, while induction of cytochrome P450 2E1 was comparable in the knockout and wild type mice. CONCLUSION These results suggest that cytochrome P450 2A5 protects against ethanol-induced oxidative liver injury.
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Affiliation(s)
- Feng Hong
- Institute of liver diseases, Affiliated Hospital of Jining Medical University, Jining, China
| | - Xiyu Liu
- Department of Hepatobiliary and Pancreatic Surgery, the First Bethune Hospital, Jilin University, Jilin 130021, China
| | - Stephen Ward
- Department of Pathology, Icahn School of Medicine at Mount Sinai, One Gustave L Levy Place, New York, NY 10029
| | - Huabao Xiong
- Division of Immunology, Department of medicine, Icahn School of Medicine at Mount Sinai, One Gustave L Levy Place, New York, NY 10029
| | - Arthur I. Cederbaum
- Department of Pharmacology and Systems Therapeutics, Icahn School of Medicine at Mount Sinai, One Gustave L Levy Place, New York, NY 10029
| | - Yongke Lu
- Department of Structural and Chemical Biology, Icahn School of Medicine at Mount Sinai, One Gustave L Levy Place, New York, NY 10029
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Hazard assessment of nitrosamine and nitramine by-products of amine-based CCS: Alternative approaches. Regul Toxicol Pharmacol 2015; 71:601-23. [DOI: 10.1016/j.yrtph.2014.01.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Revised: 01/10/2014] [Accepted: 08/06/2014] [Indexed: 11/21/2022]
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10
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Okamatsu G, Komatsu T, Kubota A, Onaga T, Uchide T, Endo D, Kirisawa R, Yin G, Inoue H, Kitazawa T, Uno Y, Teraoka H. Identification and functional characterization of novel feline cytochrome P450 2A. Xenobiotica 2014; 45:503-10. [PMID: 25547627 DOI: 10.3109/00498254.2014.998322] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
1. Cytochrome P450s are the major metabolizing enzymes for xenobiotics in humans and other mammals. Although the domestic cat Felis catus, an obligate carnivore, is the most common companion animal, the properties of cytochrome P450 subfamilies are largely unknown. 2. We newly identified the feline CYP2A13, which consists of 494 deduced amino acids, showing the highest identity to CYP2As of dogs, followed by those of pigs, cattle and humans. 3. The feline CYP2A13 transcript and protein were expressed almost exclusively in the liver without particular sex-dependent differences. 4. The feline CYP2A13 protein heterogeneously expressed in Escherichia coli showed metabolic activity similar to those of human and canine CYP2As for coumarin, 7-ethoxycoumarin and nicotine. 5. The results indicate the importance of CYP2A13 in systemic metabolism of xenobiotics in cats.
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Affiliation(s)
- Gaku Okamatsu
- School of Veterinary Medicine, Rakuno Gakuen University , Ebetsu, Hokkaido , Japan
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Buist H, Bausch-Goldbohm R, Devito S, Venhorst J, Stierum R, Kroese E. WITHDRAWN: Hazard assessment of nitrosamine and nitramine by-products of amine-based CCS: An alternative approach. Regul Toxicol Pharmacol 2014; 70:392. [DOI: 10.1016/j.yrtph.2014.01.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Revised: 01/10/2014] [Accepted: 01/12/2014] [Indexed: 11/25/2022]
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Konstandi M, Johnson EO, Lang MA. Consequences of psychophysiological stress on cytochrome P450-catalyzed drug metabolism. Neurosci Biobehav Rev 2014; 45:149-67. [DOI: 10.1016/j.neubiorev.2014.05.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2014] [Revised: 04/17/2014] [Accepted: 05/18/2014] [Indexed: 12/11/2022]
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13
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Konstandi M. Psychophysiological stress: a significant parameter in drug pharmacokinetics. Expert Opin Drug Metab Toxicol 2013; 9:1317-34. [DOI: 10.1517/17425255.2013.816283] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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Sharma A, Dinesh K, Yadav S, Jain SK, Pant MC, Parmar D. Cytochrome P450 2A isoenzymes in freshly prepared blood lymphocytes isolated from rats and validation as a biomarker for clinical studies in humans. Xenobiotica 2012; 43:311-9. [PMID: 22934830 DOI: 10.3109/00498254.2012.717728] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
1. The present study aimed to identify the expression of carcinogen metabolizing cytochrome P4502A (CYP2A) isoenzymes in freshly prepared rat peripheral blood lymphocytes (PBL) isolated from adult rats and investigate similarities in the regulation of lymphocyte CYP2A-isoenzymes with the tissue enzyme. 2. qRT-PCR studies demonstrated significant constitutive mRNA expression of CYP2A-isoenzymes in PBL isolated from male and female rats which further increases significantly after pretreatment with nicotine or 3-methylcholanthrene (MC) indicating responsiveness of CYP2A-isoenzymes in PBL. This increase in the CYP2A expression was associated with an increase in the protein expression and CYP2A3-dependent coumarin hydroxylase (COH) activity in PBL. 3. Clinical studies further demonstrated significant increase in the expression of CYP2A6 and associated enzyme activity in PBL isolated from lung cancer patients. Our data thus provided evidence for similarities in the regulation of carcinogen metabolizing CYP2A-isoenzymes in PBL with the tissue enzymes. Further, responsiveness of blood CYP2A6 in human blood lymphocytes isolated from lung cancer patients has led us to suggest that associating expression profiles of CYP2A6 and other polycyclic aromatic hydrocarbons (PAH)-responsive CYPs in PBL with the genotyping data could lead to the development of a possible screen to monitor and predict environment-induced diseases and toxicity in humans.
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Affiliation(s)
- Amit Sharma
- Developmental Toxicology Division, Indian Institute of Toxicology Research (Council of Scientific and Industrial Research), Lucknow, UP, India
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Ferguson CS, Miksys S, Palmour RM, Tyndale RF. Differential Effects of Nicotine Treatment and Ethanol Self-Administration on CYP2A6, CYP2B6 and Nicotine Pharmacokinetics in African Green Monkeys. J Pharmacol Exp Ther 2012; 343:628-37. [DOI: 10.1124/jpet.112.198564] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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Lu Y, Zhuge J, Wu D, Cederbaum AI. Ethanol induction of CYP2A5: permissive role for CYP2E1. Drug Metab Dispos 2010; 39:330-6. [PMID: 21051534 DOI: 10.1124/dmd.110.035691] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
CYP2A5 metabolizes xenobiotics and activates hepatocarcinogens, and induction occurs in response to hepatic damage and cellular stress. We evaluated whether ethanol can elevate CYP2A5 and whether CYP2E1 plays a role in the ethanol induction of CYP2A5. Wild-type (WT), CYP2E1 knockout (KO), and CYP2E1 knockin (KI) mice were fed ethanol for 3 weeks. Ethanol increased CYP2E1 and CYP2A5 protein and activity in WT mice but not in the KO mice. Induction of CYP2A5 (and CYP2E1) was restored in the KI mice. Ethanol induction of CYP2A5 occurred only after CYP2E1 was first induced. Immunohistochemical staining revealed that CYP2E1 and CYP2A5 colocalize to the same zones in the liver. Ethanol also elevated CYP2A5 mRNA levels in WT and KI mice but not in KO mice. Induction of CYP2A5 by cadmium was partially decreased in KO mice compared with WT or KI mice. Ethanol elevated CYP2A4 mRNA levels in all mice although the extent of induction was lowest in the KO mice. In summary, ethanol elevated mouse hepatic CYP2A5 levels, which may be of toxicological significance because CYP2A5 metabolizes nicotine and other drugs and activates hepatocarcinogens. Induction of CYP2A5 by ethanol is potentiated by the induction of CYP2E1. We speculate that ethanol induction of CYP2E1 followed by increases in reactive oxygen species and activation of Nrf2 are important steps in the mechanism by which ethanol induces CYP2A5. The possibility that induction of CYP2E1 is permissive for the induction of CYP2A5 may reflect a new contribution by CYP2E1 to the actions of ethanol.
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Affiliation(s)
- Yongke Lu
- Department of Medicine, Division of Liver Diseases, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA
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Behera D, Damre A, Varghese A, Addepalli V. In vitro evaluation of hepatic and extra-hepatic metabolism of coumarins using rat subcellular fractions: correlation of in vitro clearance with in vivo data. ACTA ACUST UNITED AC 2010; 23:329-50. [PMID: 19326776 DOI: 10.1515/dmdi.2008.23.3-4.329] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
7-Ethoxycoumarin (7-EC) and 7-hydroxycoumarin (7-HC) were chosen as model compounds to study hepatic and extra-hepatic metabolism in rat tissue subcellular (microsomal and S9) fractions and to scale the observed in vitro clearance to in vivo plasma clearance. 7-EC and 7-HC showed significant metabolic degradation in liver subcellular fractions as compared to subcellular fractions obtained from intestine, kidney, lung and brain. The total in vitro metabolic clearance for 7-EC and 7-HC was determined by adding the individual in vitro organ clearance values obtained in hepatic and extra-hepatic microsomes or S9 fractions. The predicted in vivo clearance for 7-HC was 63.6 and 81.6 ml/min/kg by in vitro scaling from microsomes and S9 fractions, respectively. For 7-EC, the values were 78.5 and 76.8 ml/min/kg, respectively. The predicted clearance was found to be reasonably accurate with slight over- and underprediction. Interestingly, the relative contribution of hepatic and extra-hepatic metabolism to the total clearance of 7-EC and 7-HC was remarkably high, ranging from 62-77% and 22-38%, respectively, of the total metabolic clearance. It is concluded that the model of multi-organ subcellular fractions is a useful in vitro tool for the prediction of in vivo metabolic clearance, as it can provide information about the relative contribution of extra-hepatic and hepatic metabolism to total metabolic clearance.
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Affiliation(s)
- Dayanidhi Behera
- School of Pharmacy and Technology Management, NMIMS University, Mumbai, India
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Schlicht KE, Berg JZ, Murphy SE. Effect of CYP2A13 active site mutation N297A on metabolism of coumarin and tobacco-specific nitrosamines. Drug Metab Dispos 2009; 37:665-71. [PMID: 19074523 PMCID: PMC2680511 DOI: 10.1124/dmd.108.025072] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2008] [Accepted: 12/10/2008] [Indexed: 11/22/2022] Open
Abstract
Cytochrome P450 2A13-catalyzed alpha-hydroxylation is a critical step in the activation of the tobacco carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and (S)-N'-nitrosonornicotine [(S)-NNN]. In the enzyme's active site, a single polar residue, Asn297, can influence substrate binding, orientation, and metabolism. We determined the effects of N297A mutation on enzyme kinetics and specificity for NNK, NNN, and coumarin metabolism. [5-(3)H]-NNK, [5-(3)H]-(S)-NNN, [(14)C]coumarin, and radioflow high-performance liquid chromatography analysis were used to quantify metabolites. Cytochrome P450 (P450) 2A13 N297A catalyzed NNK alpha-hydroxylation, with a 3-fold preference for methylene versus methyl hydroxylation, similar to wild type. Docking studies using the P450 2A13 crystal structure predicted that when the pyridine ring of NNK cannot hydrogen bond to residue 297 it tilts and orients NNK in positions unfavorable for alpha-hydroxylation. The N297A mutation resulted in a 5- and 4-fold decrease in catalytic efficiency of NNK and NNN metabolism, respectively, primarily because of increased K(m) values. The N297A mutation strikingly affected coumarin metabolism. The ratio of coumarin 7-hydroxylation to coumarin 3,4-epoxidation is approximately equal for wild-type enzyme, whereas the ratio was 1:9 for the N297A mutant. Coumarin 3,4-epoxidation was significantly underestimated unless the epoxide was trapped and quantified as its glutathione conjugate. The K(m) value for this reaction was 4-fold greater for the mutant enzyme; the V(max) value increased nearly 40-fold. The observed shift toward coumarin 3,4-epoxidation is consistent with docking studies. In summary, Asn297 in P450 2A13 is important for orienting NNK and coumarin in the active site, changing this residue to Ala results in altered enzyme kinetics for NNK, NNN, and coumarin.
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Affiliation(s)
- Kari E Schlicht
- Department of Biochemistry Molecular Biology and Biophysics and Masonic Cancer Center, University of Minnesota,Minneapolis, Minnesota 55455, USA
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19
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Raunio H, Pokela N, Puhakainen K, Rahnasto M, Mauriala T, Auriola S, Juvonen RO. Nicotine metabolism and urinary elimination in mouse: in vitro and in vivo. Xenobiotica 2008; 38:34-47. [PMID: 18098062 DOI: 10.1080/00498250701708539] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
This study aimed at elucidating the in vivo metabolism of nicotine both with and without inhibitors of nicotine metabolism. Second, the role of mouse CYP2A5 in nicotine oxidation in vitro was studied as such information is needed to assess whether the mouse is a suitable model for studying chemical inhibitors of the human CYP2A6. The oxidation of nicotine to cotinine was measured and the ability of various inhibitors to modify this reaction was determined. Nicotine and various inhibitors were co-administered to CD2F1 mice, and nicotine and urinary levels of nicotine and four metabolites were determined. In mouse liver microsomes anti-CYP2A5 antibody and known chemical inhibitors of the CYP2A5 enzyme blocked cotinine formation by 85-100%, depending on the pre-treatment of the mice. The amount of trans-3-hydroxycotine was five times higher than cotinine N-oxide, and ten times higher than nicotine N-1-oxide and cotinine. Methoxsalen, an irreversible inhibitor of CYP2A5, significantly reduced the metabolic elimination of nicotine in vivo, but the reversible inhibitors had no effect. It is concluded that the metabolism of nicotine in mouse is very similar to that in man and, therefore, that the mouse is a suitable model for testing novel chemical inhibitors of human CYP2A6.
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Affiliation(s)
- H Raunio
- Department of Pharmacology and Toxicology, University of Kuopio, Kuopio, Finland
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20
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Oesch F, Fabian E, Oesch-Bartlomowicz B, Werner C, Landsiedel R. Drug-metabolizing enzymes in the skin of man, rat, and pig. Drug Metab Rev 2007; 39:659-98. [PMID: 18058329 DOI: 10.1080/03602530701690366] [Citation(s) in RCA: 135] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most drug metabolizing enzymes occur in the suprabasal (i.e. differentiating) layers of the epidermis, but the rat CYP1A1 rather in the basal layer and human UDP-glucuronosyltransferase rather in the stratum corneum. The pattern of drug metabolizing enzymes and their localization will impact not only the beneficial as well as detrimental properties of drugs for the skin but also dictate whether a drug reaches the blood flow unchanged or as activated or inactivated metabolite(s).
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Affiliation(s)
- Franz Oesch
- Institute of Toxicology, University of Mainz, Mainz, Germany.
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21
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Lesage MG, Keyler DE, Burroughs D, Pentel PR. Effects of pregnancy on nicotine self-administration and nicotine pharmacokinetics in rats. Psychopharmacology (Berl) 2007; 194:413-21. [PMID: 17619178 DOI: 10.1007/s00213-007-0830-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/18/2006] [Accepted: 05/15/2007] [Indexed: 11/28/2022]
Abstract
RATIONALE Because of the adverse effects of smoking during pregnancy, understanding the factors that influence maternal smoking may help in developing better treatments to help women quit smoking during pregnancy. Animal models could be useful for this purpose. OBJECTIVE The purpose of the present study was to begin the development of an animal model of smoking during pregnancy by initially characterizing nicotine self-administration (NSA) in pregnant rats. Another purpose was to begin to explore the effects of pregnancy on nicotine pharmacokinetics in rats. MATERIALS AND METHODS In experiment 1, female rats self-administering nicotine during 23-h sessions were examined throughout gestation and lactation. In experiment 2, locomotor activity was measured during pregnancy to assess further potential motor effects of pregnancy. Experiments 3 and 4 compared the single-dose pharmacokinetics of nicotine in male, nonpregnant female, and pregnant females in the first and third trimester of pregnancy and the first week of lactation. RESULTS NSA decreased over the course of pregnancy with NSA significantly lower in the third trimester compared to nonpregnant controls. NSA remained suppressed for up to 10 days into lactation. Locomotor behavior was also significantly suppressed during the second and third trimesters and throughout lactation. Nicotine elimination was slower in pregnant females compared to nonpregnant females only in the third trimester. CONCLUSIONS NSA, locomotor behavior, and nicotine elimination in rats are decreased during late pregnancy. The present study is the first to characterize NSA during pregnancy in animals, providing a potential model of maternal smoking in humans.
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Affiliation(s)
- Mark G Lesage
- Minneapolis Medical Research Foundation, 914 South 8th Street, D3-860, Minneapolis, MN 55404, USA.
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22
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Martignoni M, Groothuis GMM, de Kanter R. Species differences between mouse, rat, dog, monkey and human CYP-mediated drug metabolism, inhibition and induction. Expert Opin Drug Metab Toxicol 2007; 2:875-94. [PMID: 17125407 DOI: 10.1517/17425255.2.6.875] [Citation(s) in RCA: 987] [Impact Index Per Article: 58.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Animal models are commonly used in the preclinical development of new drugs to predict the metabolic behaviour of new compounds in humans. It is, however, important to realise that humans differ from animals with regards to isoform composition, expression and catalytic activities of drug-metabolising enzymes. In this review the authors describe similarities and differences in this respect among the different species, including man. This may be helpful for drug researchers to choose the most relevant animal species in which the metabolism of a compound can be studied for extrapolating the results to humans. The authors focus on CYPs, which are the main enzymes involved in numerous oxidative reactions and often play a critical role in the metabolism and pharmacokinetics of xenobiotics. In addition, induction and inhibition of CYPs are compared among species. The authors conclude that CYP2E1 shows no large differences between species, and extrapolation between species appears to hold quite well. In contrast, the species-specific isoforms of CYP1A, -2C, -2D and -3A show appreciable interspecies differences in terms of catalytic activity and some caution should be applied when extrapolating metabolism data from animal models to humans.
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Affiliation(s)
- Marcella Martignoni
- Nerviano Medical Sciences, Preclinical Development, Viale Pasteur 10, Nerviano (MI), Italy.
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23
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Yano JK, Denton TT, Cerny MA, Zhang X, Johnson EF, Cashman JR. Synthetic inhibitors of cytochrome P-450 2A6: inhibitory activity, difference spectra, mechanism of inhibition, and protein cocrystallization. J Med Chem 2007; 49:6987-7001. [PMID: 17125252 DOI: 10.1021/jm060519r] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of 3-heteroaromatic analogues of nicotine were synthesized to delineate structural and mechanistic requirements for selectively inhibiting human cytochrome P450 (CYP) 2A6. Thiophene, substituted thiophene, furan, substituted furan, acetylene, imidazole, substituted imidazole, thiazole, pyrazole, substituted pyrazole, and aliphatic and isoxazol moieties were used to replace the N-methylpyrrolidine ring of nicotine. A number of potent inhibitors were identified, and several exhibited high selectivity for CYP2A6 relative to CYP2E1, -3A4, -2B6, -2C9, -2C19, and -2D6. The majority of these inhibitors elicited type II difference spectra indicating the formation of a coordinate covalent bond to the heme iron. The majority of inhibitors were reversible inhibitors although several mechanism-based inactivators were identified. Most of the inhibitors were also relatively metabolically stable. X-ray crystal structures of CYP2A6 cocrystallized with three furan analogues bearing methanamino side chains indicated that the amine side chain coordinated to the heme iron. The pyridyl moiety was positioned to accept a hydrogen bond from Asn297, and all three inhibitors exhibited orthogonal aromatic-aromatic interactions with protein side chains. For comparison, the cocrystal structure of 4,4'-dipyridyl disulfide was also obtained and showed that the pyridine moiety could assume a different orientation than that observed for the 3-heteroaromatic pyridines examined. For the 3-heteroromatic pyridines, N-methyl and N,N-dimethyl amino groups increased the apparent Ki and distorted helix I of the protein. Substitution of a phenyl ring for the pyridyl ring also increased the apparent Ki, which is likely to reflect the loss of the hydrogen bonding interaction with Asn297. In contrast, inhibitory potency for other P450s was increased, and the selectivity of the phenyl analogues for CYP2A6 was decreased relative to the pyridyl compounds. The results suggest that inhibitors that compliment the active site features of CYP2A6 can exhibit significant selectivity for CYP2A6 relative to other human liver drug-metabolizing P450s.
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Affiliation(s)
- Jason K Yano
- Human BioMolecular Research Institute, 5310 Eastgate Mall, San Diego, California 92121, USA
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24
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Takeuchi H, Saoo K, Matsuda Y, Yokohira M, Yamakawa K, Zeng Y, Miyazaki M, Fujieda M, Kamataki T, Imaida K. Dose dependent inhibitory effects of dietary 8-methoxypsoralen on NNK-induced lung tumorigenesis in female A/J mice. Cancer Lett 2006; 234:232-8. [PMID: 15893417 DOI: 10.1016/j.canlet.2005.03.038] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2004] [Revised: 03/18/2005] [Accepted: 03/25/2005] [Indexed: 11/15/2022]
Abstract
We have reported that pretreatment by stomach tube with 8-methoxypsoralen (methoxsalen; 8-MOP), a potent human CYP2A6 inhibitor, strongly suppresses lung tumorigenesis by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in female A/J mice (Cancer Res. 2003). Here, we examined inhibitory effects with administration in the diet. When the mice were 7 weeks of age, they received dietary supplementation with 8-MOP at concentrations of 1, 10 or 100 ppm for 3 days prior to a single dose of NNK (2mg/0.1 ml saline/mouse, i.p.) or an equal volume of saline (vehicle control). The experiment was terminated 16 weeks after the first 8-MOP treatment and lung proliferative lesions were analyzed. The incidences and multiplicities in the 8-MOP 100 ppm-treated group were significantly reduced as compared with values for the NNK alone group (P<0.001). Multiplicities of NNK-induced lung proliferative lesions were also reduced in a dose dependent manner (Spearman rank correlation coefficient; rho=-0.806, correction P<0.0001). Mouse CYP2A4 and CYP2A5 differ from each other only 11 amino acids, and are closely related to the human CYP2A6. One hour after the last of three daily doses of 8-MOP (0.5, 5 or 50mg/kg body weight in 0.2 ml corn oil, given by stomach tube) or an equal volume of corn oil (vehicle control), given to the mice at 7 weeks of age, isolation of lung and liver RNAs demonstrated no effects on CYP2A4 and CYP2A5 mRNA levels with 8-MOP. In conclusion, the results of this study showed that clear dose response inhibitory effects of 8-MOP on NNK-induced lung tumorigenesis in female A/J mice fed diets containing 8-MOP, due to inhibition of enzyme activity of CYP2A4 and CYP2A5, rather than their gene expression.
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Affiliation(s)
- Hijiri Takeuchi
- Onco-Pathology, Department of Pathology and Host-Defense, Faculty of Medicine, Kagawa University, 1750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793, Japan
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25
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Miyazaki M, Yamazaki H, Takeuchi H, Saoo K, Yokohira M, Masumura KI, Nohmi T, Funae Y, Imaida K, Kamataki T. Mechanisms of chemopreventive effects of 8-methoxypsoralen against 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced mouse lung adenomas. Carcinogenesis 2005; 26:1947-55. [PMID: 15958517 DOI: 10.1093/carcin/bgi156] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Recently we reported that the occurrence of lung adenoma caused by 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) was completely prevented by pretreatment of female A/J mice with 8-methoxypsoralen, a potent inhibitor of cytochrome P450 (P450 or CYP) 2A [Takeuchi et al. (2003) Cancer Res., 63, 7581-7583]. Thus, the aim of this study was to confirm that 8-methoxypsoralen exhibits chemopreventive effects by inhibiting CYP2A in the mouse lung. The involvement of CYP2A in the metabolic activation of NNK in the lung was first evidenced by the fact that the mutagenic activation of NNK by mouse lung microsomes was inhibited by 8-methoxypsoralen, coumarin and antibodies to rat CYP2A1. Supporting this, the mutagenic activation of NNK was efficiently catalyzed by mouse CYP2A4 and CYP2A5 co-expressed with NADPH-P450 reductase in a genetically engineered Salmonella typhimurium YG7108. The expression of mRNA for CYP2A5, but not for CYP2A4 or CYP2A12, in the mouse lung was proven by reverse transcriptase-polymerase chain reaction, probably indicating that CYP2A5 present in the mouse lung was involved in the metabolic activation of NNK. In accordance with these in vitro data, treatment of gpt delta transgenic mice with 8-methoxypsoralen prior to NNK completely inhibited the mutation of the gpt delta gene. The in vivo chemopreventive effects of 8-methoxypsoralen towards NNK-induced adenoma was seen only when the agent was given to female A/J mice prior to, but not posterior to, NNK, lending support to the idea that NNK is activated by CYP2A5 in the mouse lung as an initial step to cause adenoma. The inhibition by 8-methoxypsoralen of NNK-induced adenoma was seen in a dose-dependent manner: the dose to show apparent 50% suppression was calculated to be 1.0 mg/kg. To our surprise, CYP2A protein(s) was expressed in the lesion of NNK-induced lung adenomas, probably suggesting that 8-methoxypsoralen could inhibit the possible occurrence of further mutation of the adenoma cells induced by NNK. Based on these lines of evidence, we propose that 8-methoxypsoralen inhibits the CYP2A5-mediated metabolic activation of NNK in the mouse lung, leading to the prevention of NNK-induced adenoma.
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Affiliation(s)
- Masafumi Miyazaki
- Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo 060-0812, Japan
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26
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Murphy SE, Raulinaitis V, Brown KM. Nicotine 5'-oxidation and methyl oxidation by P450 2A enzymes. Drug Metab Dispos 2005; 33:1166-73. [PMID: 15860657 DOI: 10.1124/dmd.105.004549] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In smokers, the primary pathway of nicotine metabolism is P450 2A6-catalyzed 5'-oxidation. The nicotine Delta(5'(1'))-iminium ion product of this reaction is further metabolized to cotinine by aldehyde oxidase. Previous investigators have reported kinetic parameters for cotinine formation using human liver cytosol as a source of aldehyde oxidase. Using [5-(3)H]nicotine and radioflow high-performance liquid chromatography analysis, we determined kinetic parameters for nicotine 5'-oxidation by P450 2A6 and the closely related human extrahepatic P450 2A13 as well as the rodent P450s 2A3, 2A4, and 2A5. The formation of both cotinine and nicotine Delta(5'(1'))-iminium ion was monitored. The K(m) and V(max) values for P450 2A6 were 144 +/- 15 muM and 1.30 +/- 0.05 pmol/min/pmol, respectively. Previously reported K(m) values for cotinine formation by P450 2A6 in the presence of cytosol were much lower, ranging from 11 to 45 muM. P450 2A13 was a somewhat better catalyst of nicotine Delta(5'(1'))-iminium formation, with 2-fold lower K(m) and 2-fold higher V(max) values than P450 2A6. The rat P450 2A3 and the mouse P450 2A5, which are 85 and 84% identical to P450 2A6, were much more efficient catalysts of nicotine 5'-oxidation. P450 2A4 was not an efficient catalyst of nicotine metabolism. Whereas 5'-oxidation was the major pathway of nicotine metabolism for all five P450 2A enzymes, these enzymes also catalyzed methyl oxidation. Nornicotine, the product of this reaction was detected as 5 to 15% of the total nicotine metabolites. Nornicotine is the amine precursor to the esophageal carcinogen N'-nitrosonornicotine. Therefore, methyl oxidation of nicotine by P450 2A6 or P450 2A13 followed by nitrosation of nornicotine are possible endogenous pathways of N'-nitrosonornicotine formation.
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Affiliation(s)
- Sharon E Murphy
- The Cancer Center, University of Minnesota, Mayo Mail Code 806, 420 Delaware St. SE, Minneapolis, MN 55455, USA.
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27
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Jalas JR, Hecht SS, Murphy SE. Cytochrome P450 enzymes as catalysts of metabolism of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, a tobacco specific carcinogen. Chem Res Toxicol 2005; 18:95-110. [PMID: 15720112 DOI: 10.1021/tx049847p] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- John R Jalas
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA
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28
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Ling G, Hauer CR, Gronostajski RM, Pentecost BT, Ding X. Transcriptional regulation of rat CYP2A3 by nuclear factor 1: identification of a novel NFI-A isoform, and evidence for tissue-selective interaction of NFI with the CYP2A3 promoter in vivo. J Biol Chem 2004; 279:27888-95. [PMID: 15123731 DOI: 10.1074/jbc.m403705200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rat CYP2A3 and its mouse and human orthologs are expressed preferentially in the olfactory mucosa. We found previously that an element in the proximal promoter region of CYP2A3 (the nasal predominant transcriptional activating (NPTA) element), which is similar to a nuclear factor 1 (NFI)-binding site, is critical for transcriptional activation of CYP2A3 in vitro. We proposed that this element might be important for tissue-selective CYP2A3 expression. The goals of the present study were to characterize NPTA-binding proteins and to obtain more definitive evidence for the role of NFI in the transcriptional activation of CYP2A3. The NPTA-binding proteins were isolated by DNA-affinity purification from rat olfactory mucosa. Mass spectral analysis indicated that isoforms corresponding to all four NFI genes were present in the purified NPTA-binding fraction. Further analysis of NPTA-binding proteins led to the identification of a novel NFI-A isoform, NFI-A-short, which was derived from alternative splicing of the NFI-A transcript. Transient transfection assay showed that NFI-A2, an NFI isoform previously identified in the olfactory mucosa, transactivated the CYP2A3 promoter, whereas NFI-A-short, which lacks the transactivation domain, counteracted the activation. Chromatin immunoprecipitation assays indicated that NFI proteins are associated with the CYP2A3 promoter in vivo, in rat olfactory mucosa, but essentially not in the liver where the CYP2A3 promoter is hypermethylated and CYP2A3 is not expressed. These data strongly support a role for NFI transcription factors in the transcriptional activation of CYP2A3.
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Affiliation(s)
- Guoyu Ling
- New York State Department of Health, and School of Public Health, Wadsworth Center, State University of New York, Empire State Plaza, Albany, NY 12201, USA
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29
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Cauffiez C, Lo-Guidice JM, Quaranta S, Allorge D, Chevalier D, Cenée S, Hamdan R, Lhermitte M, Lafitte JJ, Libersa C, Colombel JF, Stücker I, Broly F. Genetic polymorphism of the human cytochrome CYP2A13 in a French population: implication in lung cancer susceptibility. Biochem Biophys Res Commun 2004; 317:662-9. [PMID: 15063809 DOI: 10.1016/j.bbrc.2004.03.092] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2004] [Indexed: 10/26/2022]
Abstract
The human cytochrome CYP2A13, which is mainly expressed in the respiratory tract, has been shown to be highly efficient in vitro in the metabolism of tobacco-smoke carcinogens and procarcinogens such as 4-methylnitroso-1-(3-pyridyl)-1-butanone (NNK). In order to investigate the extent of CYP2A13 genetic polymorphism in a French Caucasian population of 102 individuals, a screening for sequence variations in the 5'-untranslated and protein encoding regions of its gene was performed using a polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) strategy. Six polymorphisms in the coding region were identified, including two rare missense mutations (C474G or Asp158Glu, G967T or Val323Leu) and one nonsense mutation (Arg101Stop). This deleterious mutation, the most frequent (5%) in our population, presumably encodes a severely truncated protein. The influence of the nonsense mutation in lung cancer susceptibility was examined by PCR-SSCP using peripheral blood DNA from 204 cases of lung cancer and 201 controls. The CYP2A13*7 allele, which harbours the C301T mutation, was present in 2.0% of controls and 3.4% of cases. However, multivariate analysis showed an elevated risk for small cell lung cancer in subjects heterozygous for the null allele (odds ratio OR=9.9; 95% confidence interval CI=1.9-52.2). This increased risk was not linked to other histological types of lung cancer.
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Affiliation(s)
- Christelle Cauffiez
- Equipe d'accueil 2679, Faculté de Médecine de Lille, Pôle Recherche, Lille, France.
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30
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Asikainen A, Tarhanen J, Poso A, Pasanen M, Alhava E, Juvonen RO. Predictive value of comparative molecular field analysis modelling of naphthalene inhibition of human CYP2A6 and mouse CYP2A5 enzymes. Toxicol In Vitro 2003; 17:449-55. [PMID: 12849728 DOI: 10.1016/s0887-2333(03)00065-1] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The objects of this study were first to compare how well the recently constructed structure-inhibition activity relationship models of mouse CYP2A5 and human CYP2A6 predict the interaction of naphthalene in liver microsomes and secondly to study if these CYP enzymes actually oxidize naphthalene. The CoMFA model of CYP2A5 predicted the IC(50) value of naphthalene to be 42 microM (18-115 microM 95% CL) whereas in the in vitro experiment the result was 74 microM (65-83 microM) with the corresponding values for CYP2A6 being 41 microM (18-112 microM) and 25 microM (21-30 microM), respectively. Naphthalene appeared to be a competitive inhibitor both for mouse and human liver microsomal coumarin 7-hydroxylase, which is the specific probe activity for CYP2A5 and CYP2A6. The K(i)-value for the mouse enzyme was between 12-26 microM and for the human enzyme 1.2-5.6 microM. A 1-h in vitro incubation of naphthalene with human and pyrazole treated mouse liver microsomes produced more 1-naphthol than 2-naphthol. Antibody against the purified CYP2A5 inhibited 50-60% of the formation of 1-naphthol and 30-40% of the formation of 2-naphthol. These results indicate that in silico CoMFA models predict relatively well the interaction of naphthalene with CYP2A5 and CYP2A6 and that these CYPs actually oxidize naphthalene in vitro. CoMFA CYP2A5 and CYP2A6 models are thus useful as a technique for elucidating the interaction and potency of untested chemicals with these CYPs.
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Affiliation(s)
- Arja Asikainen
- Department of Environmental Sciences, University of Kuopio, Box 1627, 70211, Kuopio, Finland
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31
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Jalas JR, McIntee EJ, Kenney PMJ, Upadhyaya P, Peterson LA, Hecht SS. Stereospecific deuterium substitution attenuates the tumorigenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). Chem Res Toxicol 2003; 16:794-806. [PMID: 12807363 DOI: 10.1021/tx034022l] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Stereochemical determinants of the tumorigenicity and metabolism of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) were investigated using the stereospecifically deuterated isotopomers (4R)-[4-(2)H(1)]NNK and (4S)-[4-(2)H(1)]NNK. Upon ip administration to groups of 20 female A/J mice, NNK and (4S)-[4-(2)H(1)]NNK exhibited similar lung tumorigenicity at three different doses, whereas (4R)-[4-(2)H(1)]NNK was 2-fold less tumorigenic at all three doses. In a parallel experiment, levels of O(6)-methylguanine and 7-methylguanine were 2-fold lower in lung DNA of mice treated with (4R)-[4-(2)H(1)]NNK than in mice treated with NNK or (4S)-[4-(2)H(1)]NNK. To corroborate these in vivo data, the in vitro metabolism of these compounds was investigated using A/J mouse lung microsomes and Spodoptera frugiperda (Sf9)-expressed mouse cytochrome p450s 2A4 and 2A5. Kinetic isotope effects on the apparent V(max) ((D)V) for the product of NNK 4-hydroxylation, OPB, were 2.7 +/- 0.2 and 2.8 +/- 0.4 when (4R)- and (4S)-[4-(2)H(1)]NNK were incubated with mouse lung microsomes, respectively. The (D)V values for OPB formation were 3.2 +/- 0.2 and 2.2 +/- 0.2 when (4R)-[4-(2)H(1)]NNK was the substrate for p2A4 and 2A5, respectively, whereas they were 1.3 +/- 0.1 and 1.1 +/- 0.1 when (4S)-[4-(2)H(1)]NNK was the substrate for these respective enzymes. Analysis of an OPB derivative (10) for deuterium content by LC/MS confirmed the results from the kinetic assays and indicated that p450s 2A4 and 2A5 preferentially abstract the pro-R 4-hydrogen of NNK. The results obtained using Sf9-expressed p450s provide a rationale for the differences observed in the lung tumor and DNA adduct experiments, namely, that the attenuated tumorigenicity of (4R)-[4-(2)H(1)]NNK relative to (4S)-[4-(2)H(1)]NNK is due to prochiral selectivity during p450-catalyzed metabolic activation.
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Affiliation(s)
- John R Jalas
- Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA
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32
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Teng XW, Cutler DJ, Davies NM. Kinetics of metabolism and degradation of mometasone furoate in rat biological fluids and tissues. J Pharm Pharmacol 2003; 55:617-30. [PMID: 12831504 DOI: 10.1211/002235703765344522] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/31/2022]
Abstract
Mometasone furoate (MF) is a potent glucocorticoid developed for the treatment of glucocorticoid-responsive inflammatory disorders. The in-vitro and ex-vivo kinetics of the degradation and metabolism of MF were studied in selected biological fluids of rat and subcellular fractions of different rat tissues. In-vitro, MF was found to degrade slowly into four products in serum and urine, and metabolized rapidly and extensively in rat liver, minimally in extrahepatic tissues, including intestine, stomach, lung and kidney. Further investigation found that the microsomal fraction was the major intracellular site of MF 6 beta-hydroxylation in rat liver. Using chemical inhibitors, CYP3A was found to be the major enzyme involved in the in-vitro MF 6 beta-hydroxylation in rat liver microsomes. Enzyme kinetic studies in rat liver microsomes showed that the overall metabolic process of MF followed biphasic Michaelis-Menten kinetics, while 6 beta-hydroxylation obeyed monophasic Michaelis-Menten kinetics. The kinetic parameters derived from the kinetic models along with the enzyme inhibition studies suggest that MF is mainly metabolized via 6 beta-hydroxylation mediated by CYP3A primarily, and also biotransformed via other pathway(s) catalysed by other enzymes in rat liver in-vitro.
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Affiliation(s)
- X W Teng
- Department of Pharmaceutical Sciences, College of Pharmacy and Center for Integrated Biotechnology, Washington State University, Pullman, Washington 99164, USA
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33
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Lewis DFV, Lake BG, Dickins M, Goldfarb PS. Homology modelling of CYP2A6 based on the CYP2C5 crystallographic template: enzyme-substrate interactions and QSARs for binding affinity and inhibition. Toxicol In Vitro 2003; 17:179-90. [PMID: 12650672 DOI: 10.1016/s0887-2333(02)00132-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The results of homology modelling of the human P450 enzyme CYP2A6, based on the CYP2C5 crystallographic template structure are reported. A substantial number of selective substrates of the CYP2A6 enzyme fit the putative active site in a manner that is consistent with their known metabolites. Moreover, the evidence from site-directed mutagenesis experiments is in accordance with the current model, particularly in relation to complementary amino acid contacts within the haem environment. The binding of substrates is rationalized in terms of QSAR analyses and from a consideration of the contributory factors affecting the binding affinity. The latter approach appears to represent a highly correlated (R=0.99) method for estimating the relative strength of enzyme-substrate binding within CYP2A6-selective compounds, albeit within a fairly limited dataset of substrates.
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Affiliation(s)
- D F V Lewis
- School of Biomedical, Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK.
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34
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Lewis DFV. Essential requirements for substrate binding affinity and selectivity toward human CYP2 family enzymes. Arch Biochem Biophys 2003; 409:32-44. [PMID: 12464242 DOI: 10.1016/s0003-9861(02)00349-1] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
A detailed analysis of substrate selectivity within the cytochrome P450 2 (CYP2) family is reported. From a consideration of specific interactions between drug substrates for human CYP2 family enzymes and the putative active sites of CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, and CYP2E1, it is likely that the number and disposition of hydrogen bond donor/acceptors and aromatic rings within the various P450 substrate molecules determines their enzyme selectivity and binding affinity, together with directing their preferred routes of metabolism by the CYP2 enzymes concerned. Although many aliphatic residues are present in most P450 active sites, it would appear that their main contribution centers around hydrophobic interactions and desolvation processes accompanying substrate binding. Molecular modeling studies based on the recent CYP2C5 crystal structure appear to show close agreement with site-directed mutagenesis experiments and with information on substrate metabolism and selectivity within the CYP2 family.
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Affiliation(s)
- David F V Lewis
- Molecular Toxicology Group, School of Biomedical and Life Sciences, University of Surrey, Guildford, UK.
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35
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Abstract
1. We investigated the total metabolism of coumarin by baculovirus (BV)-expressed CYP2A13 and compared it with metabolism by BV-expressed CYP2A6. The major coumarin metabolite formed by CYP2A13 was 7-hydroxycoumarin, which accounted for 43% of the total metabolism. The product of 3,4-epoxidation, o-hydroxyphenylacetaldehyde (o-HPA), accounted for 30% of the total metabolites. 2. The K(m) and V(max) for CYP2A13-mediated coumarin 7-hydroxylation were 0.48+/-0.07 micro m and 0.15+/-0.006 nmol min(-1) nmol(-1) CYP, respectively. The V(max) of coumarin 7-hydroxylation by CYP2A13 was about 16-fold lower than that of CYP2A6, whereas the K(m) was 10-fold lower. 3. In the mouse, there were two orthologues for CYP2A6: CYP2A4 and CYP2A5, which differed by only 11 amino acids. However, CYP2A5 is an efficient coumarin 7-hydroxylase, where as CYP2A4 is not. We report here that BV-expressed CYP2A4 metabolizes coumarin by 3,4-epoxidation. Two products of the 3,4-epoxidation pathway, o-HPA and o-hydroxyphenylacetic acid (o-HPAA), were detected by radioflow HPLC. 4. The K(m) and V(max) for the coumarin 3,4-epoxidation by CYP2A4 were 8.7+/-3.6 micro m and 0.20+/-0.04 nmol min(-1) nmol(-1) CYP, respectively. Coumarin 7-hydroxylation by CYP2A5 was more than 200 times more efficient than 3,4 epoxidation by CYP2A4.
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Affiliation(s)
- L B von Weymarn
- Department of Biochemistry, Molecular Biology & Biophysics, University of Minnesota Cancer Center, Mayo Mail Code 806, 420 Delaware Street SE., Minneapolis, MN 55455, USA
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36
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Abstract
Human cytochrome P450 2A6 (CYP2A6) has been shown to have large interindividual and interethnic variability in levels of expression and activity. This is thought to be largely due to genetic polymorphisms. In recent years, 13 genetic variants (CYP2A6*1-*11 and the gene duplication, *1 x 2) of CYP2A6 have been identified and a number of these have been shown to result in altered CYP2A6 enzyme activity. For example, there are alleles which result in variants that are in inactive (e.g. due to a gene deletion), have decreased activity (e.g. altered enzyme structure or transcriptional activity) or have increased activity (e.g. due to gene duplications). The resulting interindividual variation in metabolic activity may affect the metabolism of CYP2A6 substrates including nicotine, cotinine (the major metabolite of nicotine), several tobacco-specific procarcinogens, coumarin and many toxins. The frequencies of the CYP2A6 alleles vary considerably among different ethnic populations, which may partially explain the interethnic variability found in CYP2A6-related metabolic activity (e.g. nicotine metabolism), behaviors (i.e. smoking) and disease (i.e. lung cancer). Investigations of the genetic variation of CYP2A6 and its resulting effects on metabolism and health consequences are still fairly early; this review summarizes what is presently known about CYP2A6, its genetic variants and their clinical consequences.
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Affiliation(s)
- Chun Xu
- Centre for Addiction and Mental Health, University of Toronto, Toronto M5S 1A8, Canada
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37
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Seubert JM, Webb CD, Bend JR. Acute sodium arsenite treatment induces Cyp2a5 but not Cyp1a1 in the C57Bl/6 mouse in a tissue (kidney) selective manner. J Biochem Mol Toxicol 2002; 16:96-106. [PMID: 11979426 DOI: 10.1002/jbt.10023] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Modulation of hepatic and extrahepatic detoxication enzymes Cyp1a1, Cyp2a5, glutathione S-transferse Ya (GSTYa) and NAD(P)H:quinone oxidoreductase (QOR) dependent catalytic activity and mRNA levels were investigated at 1, 2, or 4 days in liver, lung, or kidney of male, adult CD57 Bl/6 mice treated sc with a single dose (85 micromol/kg) of sodium arsenite (As3+). Maximum decreases of total hepatic cytochrome P450 (CYP) monooxygenase content and catalytic activities, occurring at 24 h, corresponded with maximum increases of heme oxygenase (HO-1) in all tissues, as well as maximum plasma total bilirubin. Extrahepatic increases in CYP were observed only in non-AHR dependent isozymes in the kidney, where both Cyp2a5 mRNA and catalytic activity increased maximally 24 h after treatment. In contrast, no significant changes in Cyp2b1/2-dependent PROD or mRNA activity and decreases in Cyp1a1-dependent-EROD activity were noted 1, 2, or 4 days after treatment. Increases in QOR catalytic activities were observed in all tissues examined with increased mRNA in kidney. On the other hand, GSTYa catalytic activity and mRNA increases were only detected in kidney. This study demonstrates the differential modulation of CYP, QOR, and GST-Ya, important drug metabolizing enzymes after acute As3+ administration. The induction of Cyp2a5, QOR, and GSTYa catalytic activity and gene expression occurred primarily in kidney during or shortly after conditions of oxidant stress.
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Affiliation(s)
- John M Seubert
- Department of Pharmacology and Toxicology, University of Western Ontario, London, Ontario, Canada N6A 5C1
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Su T, Zhang QY, Zhang J, Swiatek P, Ding X. Expression of the rat CYP2A3 gene in transgenic mice. Drug Metab Dispos 2002; 30:548-52. [PMID: 11950786 DOI: 10.1124/dmd.30.5.548] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Rat CYP2A3 and mouse CYP2A5 are predominantly expressed in the olfactory mucosa. CYP2A3 is also expressed in the lung at a low level, whereas CYP2A5 is expressed in several additional tissues. To better understand the transcriptional regulation of the CYP2A genes, transgenic mice were generated with a full-length CYP2A3 gene fragment containing 3.4 kilobases of the 5'-flanking region. CYP2A3 mRNA was detected in the brain and olfactory bulb in four transgenic mouse lines, in the olfactory mucosa in three lines, and in kidney, liver, lung, and small intestine in two lines. Thus, the expression of the CYP2A3 transgene mimicked the tissue distribution pattern of mouse CYP2A5 rather than that of rat CYP2A3. Furthermore, the levels of CYP2A3 mRNA were very low in all lines examined, suggesting that more distal regulatory regions may be involved in the abundant expression of the CYP2A genes in the olfactory mucosa.
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Affiliation(s)
- Ting Su
- Wadsworth Center, New York State Department of Health and School of Public Health, State University of New York at Albany, Albany, New York 12201-0509, USA
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Nakamura K, Martin MV, Guengerich FP. Random mutagenesis of human cytochrome p450 2A6 and screening with indole oxidation products. Arch Biochem Biophys 2001; 395:25-31. [PMID: 11673862 DOI: 10.1006/abbi.2001.2569] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cytochrome P450 (P450) 2A6 mutants from randomized libraries generated in the substrate recognition sequence (SRS) regions were screened in Escherichia coli on the basis of indole metabolism. SRS 3 and 4 libraries yielded colonies that produced indigo at least as well as wild-type (WT) P450 2A6, and some colonies were consistently more blue upon replating. One mutant, F209T, showed indole 3-hydroxylation <WT but had a k(cat) for coumarin 7-hydroxylation 13-fold >WT. The double mutant L240C/N297Q consistently produced very blue colonies. Five mutants yielded mixtures of pigments from indole different than WT, as judged by visible spectra and HPLC of products. When bacteria expressing the mutants were grown in the presence of each of 26 substituted indoles, a variety of patterns of formation of different dyes was seen with several of the mutants. This approach has potential value in understanding P450 2A6 function and generating new dyestuffs and other products.
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Affiliation(s)
- K Nakamura
- Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, TN 37232-0146, USA
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40
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Hoffman SM, Nelson DR, Keeney DS. Organization, structure and evolution of the CYP2 gene cluster on human chromosome 19. PHARMACOGENETICS 2001; 11:687-98. [PMID: 11692077 DOI: 10.1097/00008571-200111000-00007] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
The cytochrome P450 superfamily of mixed-function oxygenases has been extensively studied due to its many critical metabolic roles, and also because it is a fascinating example of gene family evolution. The cluster of genes on human chromosome 19 from the CYP2A, 2B, and 2F subfamilies has been previously described as having a complex organization and many pseudogenes. We describe the discovery of genes from three more CYP2 subfamilies inside the cluster, and assemble a complete map of the region. We comprehensively review the organization, structure, and expression of genes from all six subfamilies. A general hypothesis for the evolution of this complex gene cluster is also presented.
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Affiliation(s)
- S M Hoffman
- Department of Zoology, Miami University, Oxford, OH 45056, USA.
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41
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Hanna IH, Kim MS, Guengerich FP. Heterologous expression of cytochrome P450 2D6 mutants, electron transfer, and catalysis of bufuralol hydroxylation: the role of aspartate 301 in structural integrity. Arch Biochem Biophys 2001; 393:255-61. [PMID: 11556812 DOI: 10.1006/abbi.2001.2510] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cytochrome P450 (P450) 2D6 is a polymorphic human enzyme involved in the oxidation of >50 drugs, most of which contain a basic nitrogen. In confirmation of previous work by others, substitutions at Asp301 decreased rates of substrate oxidation by P450 2D6. An anionic residue (Asp, Glu) at this position was found to be important in proper protein folding and heme incorporation, and positively charged residues were particularly disruptive in bacterial and also in baculovirus expression systems. Truncation of 20 N-terminal amino acids had no significant effect on catalytic activity except to attenuate P450 2D6 interaction with membranes and NADPH-P450 reductase. The truncation of the N-terminus increased the level of bacterial expression of wild-type P450 2D6 (Asp301) but markedly reduced expression of all codon 301 mutants, including Glu301. Reduction of ferric P450 2D6 by NADPH-P450 reductase was enhanced in the presence of the prototypic substrate bufuralol. Bacterial flavodoxin, an NADPH-P450 reductase homolog, binds tightly to P450 2D6 but is inefficient in electron transfer to the heme. These results collectively indicate that the acidic residue at position 301 in P450 2D6 has a structural role in addition to any in substrate binding and that the N-terminus of P450 2D6 is relatively unimportant to catalytic activity beyond a role in facilitating binding to NADPH-P450 reductase.
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Affiliation(s)
- I H Hanna
- Department of Biochemistry and Center in Molecular Toxicology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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42
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Elfarra AA, Krause RJ, Kemper RA. Cellular and molecular basis for species, sex and tissue differences in 1,3-butadiene metabolism. Chem Biol Interact 2001; 135-136:239-48. [PMID: 11397394 DOI: 10.1016/s0009-2797(01)00193-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Species differences in 1,3-butadiene (BD) bioactivation and detoxication have been implicated in the greater sensitivity of mice to the carcinogenic effects of BD compared to rats, but the molecular basis for species differences in BD metabolism is not well understood. Previous and recent work conducted in this laboratory has examined the relative rates of BD oxidation to epoxybutene (EB) in male and female B6C3F1 mouse tissues, characterized the major cytochrome P450 enzymes involved in BD bioactivation in these tissues, and determined the potential utility of the freshly isolated hepatocyte model to investigate species differences in metabolism of BD and related compounds. Collectively, the results suggest a role for P450s 2E1, 2A5, and 4B1 in sex and tissue differences in BD bioactivation in the mouse. When coordinated metabolism of EB was investigated in male B6C3F1 mouse and Sprague-Dawley rat hepatocytes, the hepatocytes from both species were found to catalyze EB oxidation to meso- and (+/-)-diepoxybutane (DEB), EB hydrolysis to 3-butene-1,2-diol (BDD), and EB conjugation to form GSH conjugates (GSEB). The metabolite area under the curve (AUC) exhibited dependence on the EB concentration used. However, the EB activation/detoxication ratios with the mouse hepatocytes were much higher than the ratios obtained with the rat hepatocytes. These results illustrate the potential utility of the hepatocyte model for estimating flux through competing metabolic pathways and predicting in-vivo metabolism of EB. Collectively, the results may allow a better understanding of the molecular and kinetic basis of species differences in BD metabolism and may lead to a more accurate assessment of human risk.
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Affiliation(s)
- A A Elfarra
- Department of Comparative Biosciences, University of Wisconsin School of Veterinary Medicine, 2015 Linden Drive West, Madison, WI 53706-1102, USA.
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43
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Poso A, Gynther J, Juvonen R. A comparative molecular field analysis of cytochrome P450 2A5 and 2A6 inhibitors. J Comput Aided Mol Des 2001; 15:195-202. [PMID: 11289074 DOI: 10.1023/a:1008102217770] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Structure-activity relationships of 23 P450 2A5 and 2A6 inhibitors were analysed using the CoMFA and GOLPE/GRID with smart region definition (SRD). The predictive power of the resulting models was validated using five compounds not belonging to the model set. All models have high internal and external predictive power and resulting 3D-QSAR models are supporting each other. Both Sybyl and GOLPE highlight properties near lactone moiety to be important for 2A5 and 2A6 inhibition. Another important feature for pIC50 was the size of the substituent in the 7-positon of coumarin. The models suggest that the 2A5 binding site is larger that that of 2A6 due to larger steric regions in the CoMFA coefficient maps and corresponding GOLPE maps. In addition, the maps reveal that 2A6 disfavours negative charge near the lactone moiety of coumarin.
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Affiliation(s)
- A Poso
- Department of Pharmaceutical Chemistry, University of Kuopio, Finland
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44
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Abstract
Members of the nuclear-receptor superfamily mediate crucial physiological functions by regulating the synthesis of their target genes. Nuclear receptors are usually activated by ligand binding. Cytochrome P450 (CYP) isoforms often catalyse both formation and degradation of these ligands. CYPs also metabolize many exogenous compounds, some of which may act as activators of nuclear receptors and disruptors of endocrine and cellular homoeostasis. This review summarizes recent findings that indicate that major classes of CYP genes are selectively regulated by certain ligand-activated nuclear receptors, thus creating tightly controlled networks.
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45
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Bogaards JJ, Bertrand M, Jackson P, Oudshoorn MJ, Weaver RJ, van Bladeren PJ, Walther B. Determining the best animal model for human cytochrome P450 activities: a comparison of mouse, rat, rabbit, dog, micropig, monkey and man. Xenobiotica 2000; 30:1131-52. [PMID: 11307970 DOI: 10.1080/00498250010021684] [Citation(s) in RCA: 281] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
1. In the present study, nine cytochrome P450 enzyme activities in seven species were characterized to allow a practical means of comparing this important metabolic step between various test animals and man. 2. Enzyme activities and kinetic parameters were first determined towards marker substrates for human cytochrome P450 enzymes. Inhibition profiles were then determined with both antibodies directed against various cytochrome P450 enzymes and with chemical inhibitors. 3. Both the enzyme kinetic parameters/enzyme activities, and the inhibition profiles obtained for the animal species were compared with those obtained for human liver microsomes in order to postulate the animal species most similar to man with regard to each individual cytochrome P450 enzyme activity. 4. It was found that, as expected, none of the tested species was similar to man for all the measured P450 enzyme activities, but that in each species only some of the P450 enzyme activities could be considered as similar to man. 5. When it is known which human cytochrome P450 enzymes are involved in the metabolism of a compound, the comparative data presented here can be used for selecting the most suitable species for in vitro and in it no experiments.
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Affiliation(s)
- J J Bogaards
- Department of Kinetics and Metabolism, AJ Zeist, The Netherlands.
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46
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Felicia ND, Rekha GK, Murphy SE. Characterization of Cytochrome P450 2A4 and 2A5-Catalyzed 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) Metabolism. Arch Biochem Biophys 2000; 384:418-24. [PMID: 11368333 DOI: 10.1006/abbi.2000.2128] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is a potent lung carcinogen in the A/J mouse, and is believed to be a causative agent for human lung cancer. NNK requires metabolic activation by alpha-hydroxylation to exert its carcinogenic potential. The human P450, 2A6 is a catalyst of this reaction. There are two closely related enzymes in the mouse, P450 2A4 and 2A5, which differ from each other by only 11 amino acids. In the present study these two mouse P450s were expressed in Spodoptera frugiperda (Sf9) cells using recombinant baculovirus. The catalysis of NNK metabolism by Sf9 microsomal fractions containing either P450 2A4 or 2A5 was determined. Both enzymes catalyzed the alpha-hydroxylation of NNK but with strikingly different efficiencies and specificities. P450 2A5 preferentially catalyzed NNK methyl hydroxylation, while P450 2A4 preferentially catalyzed methylene hydroxylation. The KM and Vmax for the former were 1.5 microM and 4.0 nmol/min/nmol P450, respectively, and for the latter 3.9 mM and 190 nmol/min/nmol P450. The mouse coumarin 7-hydroxylase, P450 2A5 is a significantly better catalyst of NNK alpha-hydroxylation than is the closely related human enzyme, P450 2A6.
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Affiliation(s)
- N D Felicia
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Cancer Center, Minneapolis 55455, USA
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47
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Hecht SS, Hochalter JB, Villalta PW, Murphy SE. 2'-Hydroxylation of nicotine by cytochrome P450 2A6 and human liver microsomes: formation of a lung carcinogen precursor. Proc Natl Acad Sci U S A 2000; 97:12493-7. [PMID: 11050152 PMCID: PMC18791 DOI: 10.1073/pnas.220207697] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Smokers or people undergoing nicotine replacement therapy excrete approximately 10% of the nicotine dose as 4-oxo-4-(3-pyridyl)butanoic acid (keto acid) and 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid). Previously, these acids were thought to arise by secondary metabolism of the major nicotine metabolite cotinine, but our data did not support this mechanism. Therefore, we hypothesized that nicotine is metabolized by 2'-hydroxylation, which would ultimately yield keto acid and hydroxy acid as urinary metabolites. This pathway had not been established previously in mammalian systems and is potentially significant because the product of nicotine 2'-hydroxylation, 4-(methylamino)-1-(3-pyridyl)-1-butanone (aminoketone), can be converted to the potent tobacco-specific lung carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. Incubation of nicotine with cytochrome P450 2A6 and cofactors did indeed produce aminoketone, which was identified as its N-benzoyl derivative by GC-MS. The rate was 11% of that of cotinine production. Incubation of human liver microsomes with nicotine gave keto acid by using aminoketone as an intermediate; keto acid was not formed from cotinine. In 10 human liver samples, rates of formation of keto acid were 5.7% of those of cotinine and production of these metabolites correlated. These results provide definitive evidence for mammalian 2'-hydroxylation of nicotine and elucidate a pathway by which endogenous formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone could occur in humans.
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Affiliation(s)
- S S Hecht
- University of Minnesota Cancer Center, Minneapolis, MN 55455, USA.
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48
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Abstract
Members of the nuclear-receptor superfamily mediate crucial physiological functions by regulating the synthesis of their target genes. Nuclear receptors are usually activated by ligand binding. Cytochrome P450 (CYP) isoforms often catalyse both formation and degradation of these ligands. CYPs also metabolize many exogenous compounds, some of which may act as activators of nuclear receptors and disruptors of endocrine and cellular homoeostasis. This review summarizes recent findings that indicate that major classes of CYP genes are selectively regulated by certain ligand-activated nuclear receptors, thus creating tightly controlled networks.
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Affiliation(s)
- P Honkakoski
- Department of Pharmaceutics, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland.
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49
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von Weymarn LB, Felicia ND, Ding X, Murphy SE. N-Nitrosobenzylmethylamine hydroxylation and coumarin 7-hydroxylation: catalysis by rat esophageal microsomes and cytochrome P450 2A3 and 2A6 enzymes. Chem Res Toxicol 1999; 12:1254-61. [PMID: 10604876 DOI: 10.1021/tx990128y] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
N-Nitrosobenzylmethylamine (NBzMA) is a potent and selective esophageal carcinogen in the rat and may be a causative agent for human esophageal cancer. This nitrosamine, like most, must be metabolically activated to exert its carcinogenic potential. NBzMA may be metabolized by P450-catalyzed methyl or methylene hydroxylation; the latter is believed to be the activation pathway. The sensitivity of the esophagus to NBzMA-induced tumorigenesis is believed to be due, at least in part, to the presence of efficient P450 catalysts in this tissue. However, while it was reported almost 20 years ago that the rat esophagus catalyzes the methylene hydroxylation of NBzMA, the P450 that catalyzes this reaction has yet to be identified. We report here that human P450 2A6 and the closely related extrahepatic rat enzyme P450 2A3 both efficiently catalyze NBzMA methylene hydroxylation, characterized as benzaldehyde formation. The catalytic efficiency of P450 2A3 in this reaction was 3-fold greater than that of P450 2A6, 7.6 (K(m) = 0.63 +/- 0.18 microM and the V(max) = 4.8 nmol min(-)(1) nmol of P450(-)(1)) versus 2.3 (K(m) = 6.7 +/- 2.9 microM and the V(max) = 15.7 nmol min(-)(1) nmol of P450(-)(1)), respectively. Both enzymes catalyzed methylene hydroxylation at least 4-fold more efficiently than methyl hydroxylation. In addition, P450 2A6, but not P450 2A3, catalyzed benzyl ring hydroxylation, generating N-(p-hydroxybenzyl)methylamine. The identity of this metabolite was confirmed by synthesis of a standard and LC/MS and LC/MS/MS analysis. P450 2A6 is an efficient coumarin 7-hydroxylase, and we report here that P450 2A3 is an equally good catalyst of this reaction (K(m) = 1. 7 +/- 0.41 microM and V(max) = 1.7 +/- 0.08 nmol min(-)(1) nmol of P450(-)(1)). Rat esophageal microsomes (REM), like P450 2A3, were efficient catalysts of NBzMA methylene hydroxylation. However, in contrast to P450 2A3, the major product of this reaction was the product of benzaldehyde oxidation, benzoic acid. Antibody to the closely related mouse P450, 2A5, did not inhibit REM-catalyzed NBzMA metabolism, and most importantly, REM did not catalyze the 7-hydroxylation of coumarin. Therefore, P450 2A3 does not appear to be the P450 in the rat esophagus responsible for catalyzing the methylene hydroxylation of NBzMA.
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Affiliation(s)
- L B von Weymarn
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Cancer Center, Minneapolis, Minnesota 55455, USA
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Kurose K, Isozaki E, Tohkin M, Fukuhara M. Cloning and expression analysis of a new member of the cytochrome P450, CYP2A15 from the Chinese hamster, encoding testosterone 7alpha-hydroxylase. Arch Biochem Biophys 1999; 371:270-6. [PMID: 10545214 DOI: 10.1006/abbi.1999.1457] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We cloned a new cytochrome P450 cDNA encoding testosterone 7alpha-hydroxylase in the Chinese hamster, designated CYP2A15 which shares significant amino acid sequence homology with members of the CYP2A subfamily. The CYP2A15 cDNA was isolated by screening a liver cDNA library and the sequence contains an open reading frame of 1482 nucleotides encoding a polypeptide of 493 amino acids with a calculated molecular mass of 56,295 Da. This is flanked by a 5'-untranslated region of 2 bp and a 3' untranslated region of 191 bp including the poly(A) tail. We determined the catalytic activity of CYP2A15 using microsomes obtained by transient expression of its cDNA in transfected COS-7 cells. The heterologously expressed CYP2A15 was found to hydroxylate testosterone at position 7alpha in a reconstituted system. RT-PCR experiments revealed that the mRNA of CYP2A15 was expressed in liver, but not detected in kidney, lung, or small intestine. The expression of CYP2A15 mRNA was slightly induced by treatment with either rifampicin or 3-methylcholanthrene.
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Affiliation(s)
- K Kurose
- Department of Pharmaceutical Sciences, National Institute of Public Health, 4-6-1 Shirokanedai, Minato-ku, Tokyo, 108-8638, Japan.
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