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Zhang H, Li H, Yu H. Analysis of the role of rs2031920 and rs3813867 polymorphisms within the cytochrome P450 2E1 gene in the risk of squamous cell carcinoma. Cancer Cell Int 2018; 18:67. [PMID: 29743817 PMCID: PMC5930765 DOI: 10.1186/s12935-018-0561-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 04/19/2018] [Indexed: 11/12/2022] Open
Abstract
Background To explore the genetic effect of rs2031920 and rs3813867 polymorphisms within the cytochrome P450 2E1 (CYP2E1) gene on the risk of squamous cell carcinoma (SCC), a meta-analysis was performed. Methods The eligible case–control studies were obtained by database searching and screening, and the specific statistical analysis was performed with STATA 12.0 software. Results After the process of database searching and screening, a total of 32 case–control studies with 7435 cases and 10,466 controls were ultimately included in our meta-analysis. With regard to the rs2031920 C/T polymorphism, in comparison to controls, a reduced risk in cases of esophageal squamous cell carcinoma (ESCC) was detected for the models of allele T vs. allele C [P = 0.025, odds ratio (OR) = 0.67], carrier T vs. carrier C (P = 0.014, OR = 0.70), TT vs. CC (P = 0.029, OR = 0.65), CT vs. CC (P = 0.040, OR = 0.56), CT + TT vs. CC (P = 0.035, OR = 0.58). Similarly, a decreased SCC risk was observed for the rs3813867 G/C polymorphism in the allele, carrier, homozygote, dominant, and recessive models of overall SCC meta-analysis and “ESCC” subgroup analysis (all P < 0.05, OR < 1) and in all genetic models of “Asian” and “population-based control (PB)” subgroup analysis (all P < 0.05, OR < 1). Additionally, for the rs2031920/rs3813867 haplotype, a decreased SCC risk was also detected in the overall SCC meta-analysis under the allele, carrier, homozygote and dominant model (all P < 0.05, OR < 1) and the subgroup analysis of “PB” under the allele, carrier, and dominant models (all P < 0.05, OR < 1). Conclusions Our meta-analysis supports the “T” allele carrier of the CYP2E1 rs2031920 C/T polymorphism and “C” allele carrier of the rs3813867 G/C polymorphism as protective factors for ESCC patients, especially in Asian populations.
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Affiliation(s)
- Hai Zhang
- Department of Otorhinolaryngology Head and Neck Surgery, Tianjin Huanhu Hospital, No 6, Ji Zhao Road, Jinnan District, Tianjin, 300060 People's Republic of China
| | - Haiyan Li
- Department of Otorhinolaryngology Head and Neck Surgery, Tianjin Huanhu Hospital, No 6, Ji Zhao Road, Jinnan District, Tianjin, 300060 People's Republic of China
| | - Huanxin Yu
- Department of Otorhinolaryngology Head and Neck Surgery, Tianjin Huanhu Hospital, No 6, Ji Zhao Road, Jinnan District, Tianjin, 300060 People's Republic of China
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Peng Q, Chen H, Huo JR. Alcohol consumption and corresponding factors: A novel perspective on the risk factors of esophageal cancer. Oncol Lett 2016; 11:3231-3239. [PMID: 27123096 DOI: 10.3892/ol.2016.4401] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Accepted: 02/25/2016] [Indexed: 12/17/2022] Open
Abstract
Esophageal cancer is the eighth most common type of cancer in the world, and the sixth most common cause of mortality from cancer. Alcohol consumption is the major risk factor for esophageal cancer, due to the worldwide prevalence and high carcinogenicity of the ethanol metabolite. In epidemiological studies, the efficiency of alcohol intake to enhance the risk of esophageal cancer is altered by daily ethanol consumption, type of alcoholic beverages ingested, time since quitting drinking, age of drinking initiation, differences in population and subtypes of esophageal cancer. Corresponding factors, including gene polymorphisms, tobacco smoking, oral microorganisms and folate deficiency, reveal a synergistic effect in concurrent alcohol users that may lead to an increased risk of developing esophageal cancer. Consequently, esophageal cancer prevention involves multiple aspects, including quitting drinking and smoking, maintaining an adequate oral health and ingesting adequate quantities of folate, particularly in genetically high-risk populations.
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Affiliation(s)
- Qiao Peng
- Department of Gastroenterology, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, P.R. China
| | - Hui Chen
- Department of Gastroenterology, People's Hospital of Taizhou, Taizhou, Jiangsu 225300, P.R. China
| | - Ji-Rong Huo
- Department of Gastroenterology, The Second Xiangya Hospital of Central South University, Changsha, Hunan 410011, P.R. China
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Gulati S, Yadav A, Kumar N, Kumar G, Aggarwal N, Gupta R. Frequency distribution of high risk alleles of CYP2C19, CYP2E1, CYP3A4 genes in Haryana population. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2014; 37:1186-1193. [PMID: 24814262 DOI: 10.1016/j.etap.2014.03.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2013] [Revised: 03/12/2014] [Accepted: 03/16/2014] [Indexed: 06/03/2023]
Abstract
The genotype of an individual can significantly influence the disposition of a chemical, and determine their susceptibility to its toxicity. Many enzymes involved in either activation or detoxification of chemical carcinogen metabolism are polymorphically expressed, with the alleles presenting different enzymatic activities and some of them having been associated with susceptibility to cancer. Cytochrome P450 (P450 or CYP) constitutes the most important phase I enzyme group responsible for the metabolism of endogenous and exogenous (xenobiotics) substances. The present study was aimed to analyze the frequencies of commonly known polymorphisms of human xenobiotic metabolizing genes (XMG) in the Haryana State population of North India. The study was conducted in 308 healthy Haryana volunteers. DNA was extracted from leucocytes and the genetic polymorphisms in CYP2C19*2, CYP2C19*3, CYP2E1*5B and CYP3A4*1B were determined by digesting the PCR Product with restriction enzymes BamHI, SmaI, PstI and PstI respectively. The genotype frequencies of CYP2C19*2, CYP2C19*3, CYP2E1*5B, and CYP3A4*1B were found to be 22.0%, 0.0%, 2.11% and 2.0% respectively. The North Indian population which is known to be Caucasoid Aryans is ethnically different from South Indians known as Caucasoid Dravidians but no significant difference in genetic polymorphism was found.
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Affiliation(s)
- Sachin Gulati
- Department of Biotechnology, Kurukshetra University, Kurukshetra (Haryana) 136119, India.
| | - Anita Yadav
- Department of Biotechnology, Kurukshetra University, Kurukshetra (Haryana) 136119, India.
| | - Neeraj Kumar
- Department of Biotechnology, Kurukshetra University, Kurukshetra (Haryana) 136119, India.
| | - Gaurav Kumar
- Department of Biochemistry, Kurukshetra University, Kurukshetra (Haryana) 136119, India.
| | - Neeraj Aggarwal
- Department of Microbiology, Kurukshetra University, Kurukshetra (Haryana) 136119, India.
| | - Ranjan Gupta
- Department of Biochemistry, Kurukshetra University, Kurukshetra (Haryana) 136119, India.
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Population pharmacokinetics of dimethylacetamide in children during standard and once-daily IV busulfan administration. Cancer Chemother Pharmacol 2013; 72:1149-55. [PMID: 24036908 DOI: 10.1007/s00280-013-2284-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2013] [Accepted: 08/28/2013] [Indexed: 10/26/2022]
Abstract
PURPOSE N,N-dimethylacetamide (DMA) is administered to children during high-dose chemotherapy as a solubilizer with the intravenous formulation of busulfan (Busilvex®). DMA has shown liver toxicity in rats. However, little is known regarding its pharmacokinetics (PK) in humans. The aim of this analysis was to compare the PK of DMA after a once-daily dose of Busilvex® with the standard scheme consisting of 3-4 administrations per day in children. METHODS Out of 42 children, aged 0.1-18.9 years, receiving Busilvex®, 18 children received the first dose as a loading dose, giving a double dose of 1.4-2.0 mg/kg over a 4 h infusion followed by 15 doses of 0.7-1.0 mg/kg as 2 h infusions every 6 h. The other 24 children received Busilvex® as 3 h infusions once-daily for 4 consecutive days with a targeted busulfan AUC of 4,263 μM*min. Using NONMEM™ plasma, concentration-time data were analyzed. Assuming an increase in clearance overtime as found in our previous investigation, separate time factors for the two different dosing schedules included in the dataset were tested. RESULTS A one-compartment model with clearance increasing over time described the DMA kinetics sufficiently. Peak plasma concentrations of DMA, up to 3.09 mmoL/L (median 0.75 mmoL/L) for the current licensed dose regimen and up to 8.77 mmoL/L (median 3 mmoL/L) for the once-daily application, were observed. The examined increase in clearance was found to be 58 mL/h/kg and 6.1 mL/h/kg per day for the current licensed and the once-daily dose regimen, respectively. CONCLUSION N,N-dimethylacetamide as solvent of lipophilic drugs such as busulfan has a linear PK in children of all ages using a dose split into one or four administrations per day. The rapid clearance with different dosing in patients of different body weights indicates that it is safe to use DMA in children in both a once and four times daily regimen.
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Catanzaro I, Naselli F, Saverini M, Giacalone A, Montalto G, Caradonna F. Cytochrome P450 2E1 variable number tandem repeat polymorphisms and health risks: a genotype-phenotype study in cancers associated with drinking and/or smoking. Mol Med Rep 2012; 6:416-20. [PMID: 22614694 DOI: 10.3892/mmr.2012.914] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 04/25/2012] [Indexed: 11/06/2022] Open
Abstract
Cytochrome P450 2E1 (CYP2E1) is one of the main enzymes involved in the oxidation of ethanol and in the transformation of a number of potentially dangerous compounds. It has various polymorphic sites, one of which is a variable number tandem repeat (VNTR) polymorphism previously described in the 5'-flanking region. The aim of this study was to investigate the genotype-phenotype association between CYP2E1 VNTR polymorphisms and risky health habits in healthy subjects and to analyze the associations between these polymorphisms with drinking- and/or smoking-related cancers. We analyzed 166 healthy subjects by genotyping for the CYP2E1 VNTR polymorphism associated with drinking and/or smoking habits by the more sensitive restriction fragment length polymorphism-polymerase chain reaction (RFLP-PCR) method, using the NlaIV restriction enzyme. Sixty cases of pancreatic adenocarcinoma (PA) and 66 with hepatocellular carcinoma (HCC), were also genotyped. Statistical analysis was carried out to investigate the genotype-phenotype associations and to compare certain genotypes and cancer. We found 7 genotypes both in the healthy subjects and patients. The A1/A1 genotype was observed to be mainly associated with non-drinkers and -smokers (87.5 and 75.0%, respectively); moreover it was never found in the PA or HCC patients. Conversely, a weak association between A2/A3 with smokers (45.8%) and A4/A4 with drinkers (53.9%) was detected. In addition, the A4/A4 genotype was found to be significantly associated to PA [odds ratio (OR)=3.25; 95% confidence interval (CI) 1.21-7.50]. Our data demonstrate that certain CYP2E1 VNTR genotypes are associated with drinking and/or smoking habits; consequently, they may contribute either to the decreased or increased risk of developing drinking- and/or smoking-related cancers. In particular, we hypothesize that the A1/A1 VNTR genotype may have a protective role against drinking- and/or smoking-related cancers, and that A4/A4 may be a high-risk genotype during the early stages of cancer.
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Affiliation(s)
- Irene Catanzaro
- Department of Molecular and Biomolecular Sciences and Technologies (STEMBIO), Section of Cellular Biology, University of Palermo, I-90128 Palermo, Italy
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Li Q, Csanády GA, Kessler W, Klein D, Pankratz H, Pütz C, Richter N, Filser JG. Kinetics of ethylene and ethylene oxide in subcellular fractions of lungs and livers of male B6C3F1 mice and male fischer 344 rats and of human livers. Toxicol Sci 2011; 123:384-98. [PMID: 21785163 PMCID: PMC3179684 DOI: 10.1093/toxsci/kfr194] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Accepted: 07/13/2011] [Indexed: 12/01/2022] Open
Abstract
Ethylene (ET) is metabolized in mammals to the carcinogenic ethylene oxide (EO). Although both gases are of high industrial relevance, only limited data exist on the toxicokinetics of ET in mice and of EO in humans. Metabolism of ET is related to cytochrome P450-dependent mono-oxygenase (CYP) and of EO to epoxide hydrolase (EH) and glutathione S-transferase (GST). Kinetics of ET metabolism to EO and of elimination of EO were investigated in headspace vessels containing incubations of subcellular fractions of mouse, rat, or human liver or of mouse or rat lung. CYP-associated metabolism of ET and GST-related metabolism of EO were found in microsomes and cytosol, respectively, of each species. EH-related metabolism of EO was not detectable in hepatic microsomes of rats and mice but obeyed saturation kinetics in hepatic microsomes of humans. In ET-exposed liver microsomes, metabolism of ET to EO followed Michaelis-Menten-like kinetics. Mean values of V(max) [nmol/(min·mg protein)] and of the apparent Michaelis constant (K(m) [mmol/l ET in microsomal suspension]) were 0.567 and 0.0093 (mouse), 0.401 and 0.031 (rat), and 0.219 and 0.013 (human). In lung microsomes, V(max) values were 0.073 (mouse) and 0.055 (rat). During ET exposure, the rate of EO production decreased rapidly. By modeling a suicide inhibition mechanism, rate constants for CYP-mediated catalysis and CYP inactivation were estimated. In liver cytosol, mean GST activities to EO expressed as V(max)/K(m) [μl/(min·mg protein)] were 27.90 (mouse), 5.30 (rat), and 1.14 (human). The parameters are most relevant for reducing uncertainties in the risk assessment of ET and EO.
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Affiliation(s)
- Qiang Li
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
- Institut für Toxikologie und Umwelthygiene, Technische Universität München, D-80802 München, Germany
| | - György András Csanády
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
- Institut für Toxikologie und Umwelthygiene, Technische Universität München, D-80802 München, Germany
| | - Winfried Kessler
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
| | - Dominik Klein
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
- Institut für Toxikologie und Umwelthygiene, Technische Universität München, D-80802 München, Germany
| | - Helmut Pankratz
- Institut für Rechtsmedizin, Ludwig-Maximilians-Universität München, D-80336 München, Germany
| | - Christian Pütz
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
| | - Nadine Richter
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
- Institut für Toxikologie und Umwelthygiene, Technische Universität München, D-80802 München, Germany
| | - Johannes Georg Filser
- Institute of Toxicology, German Research Center for Environmental Health, Helmholtz Zentrum München, D-85764 Neuherberg, Germany
- Institut für Toxikologie und Umwelthygiene, Technische Universität München, D-80802 München, Germany
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Pohl HR, Scinicariello F. The impact of CYP2E1 genetic variability on risk assessment of VOC mixtures. Regul Toxicol Pharmacol 2011; 59:364-74. [PMID: 21295098 DOI: 10.1016/j.yrtph.2011.01.013] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2010] [Revised: 01/26/2011] [Accepted: 01/28/2011] [Indexed: 01/14/2023]
Abstract
Humans are simultaneously exposed to multiple chemicals in the environment. Many of the chemicals use the same enzymes in their metabolic pathways. Competitive inhibition may occur as one of the possible interactions between the xenobiotics in human body. For example, many volatile organic compounds (VOCs) are metabolized using P450 enzymes, specifically CYP2E1. Inheritable gene alterations may result in changes of function of the enzymes in different human subpopulations. Variations in quantity and/or quality of particular isoenzymes may cause differences in the metabolism of VOCs. These variations may cause higher sensitivity in certain populations. Using examples of three different mixtures, this review paper outlines the variances in CYP2E1 isoenzymes, effect of exposure to such mixtures on sensitive populations, and approaches to mixtures risk assessment.
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Affiliation(s)
- Hana R Pohl
- Agency for Toxic Substances and Disease Registry, US Department of Health and Human Services, Atlanta, GA 30333, USA.
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8
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Knudsen TB, Houck KA, Sipes NS, Singh AV, Judson RS, Martin MT, Weissman A, Kleinstreuer NC, Mortensen HM, Reif DM, Rabinowitz JR, Setzer RW, Richard AM, Dix DJ, Kavlock RJ. Activity profiles of 309 ToxCast™ chemicals evaluated across 292 biochemical targets. Toxicology 2011; 282:1-15. [PMID: 21251949 DOI: 10.1016/j.tox.2010.12.010] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Revised: 12/10/2010] [Accepted: 12/21/2010] [Indexed: 12/01/2022]
Abstract
Understanding the potential health risks posed by environmental chemicals is a significant challenge elevated by the large number of diverse chemicals with generally uncharacterized exposures, mechanisms, and toxicities. The present study is a performance evaluation and critical analysis of assay results for an array of 292 high-throughput cell-free assays aimed at preliminary toxicity evaluation of 320 environmental chemicals in EPA's ToxCast™ project (Phase I). The chemicals (309 unique, 11 replicates) were mainly precursors or the active agent of commercial pesticides, for which a wealth of in vivo toxicity data is available. Biochemical HTS (high-throughput screening) profiled cell and tissue extracts using semi-automated biochemical and pharmacological methodologies to evaluate a subset of G-protein coupled receptors (GPCRs), CYP450 enzymes (CYPs), kinases, phosphatases, proteases, HDACs, nuclear receptors, ion channels, and transporters. The primary screen tested all chemicals at a relatively high concentration 25 μM concentration (or 10 μM for CYP assays), and a secondary screen re-tested 9132 chemical-assay pairs in 8-point concentration series from 0.023 to 50 μM (or 0.009-20 μM for CYPs). Mapping relationships across 93,440 chemical-assay pairs based on half-maximal activity concentration (AC50) revealed both known and novel targets in signaling and metabolic pathways. The primary dataset, summary data and details on quality control checks are available for download at http://www.epa.gov/ncct/toxcast/.
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Affiliation(s)
- Thomas B Knudsen
- National Center for Computational Toxicology (B205-01), Office of Research & Development, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
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Kirman CR, Albertini RJ, Sweeney LM, Gargas ML. 1,3-Butadiene: I. Review of metabolism and the implications to human health risk assessment. Crit Rev Toxicol 2010; 40 Suppl 1:1-11. [PMID: 20868266 DOI: 10.3109/10408444.2010.507181] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
1,3-Butadiene (BD) is a multisite carcinogen in laboratory rodents following lifetime exposure, with mice demonstrating greater sensitivity than rats. In epidemiology studies of men in the styrene-butadiene rubber industry, leukemia mortality is associated with butadiene exposure, and this association is most pronounced for high-intensity BD exposures. Metabolism is an important determinant of BD carcinogenicity. BD is metabolized to several electrophilic intermediates, including epoxybutene (EB), diepoxybutane (DEB), and epoxybutane diol (EBD), which differ considerably in their genotoxic potency (DEB >> EB > EBD). Important species differences exist with respect to the formation of reactive metabolites and their subsequent detoxification, which underlie observed species differences in sensitivity to the carcinogenic effects of BD. The modes of action for human leukemia and for the observed solid tumors in rodents are both likely related to the genotoxic potencies for one or more of these metabolites. A number of factors related to metabolism can also contribute to nonlinearity in the dose-response relationship, including enzyme induction and inhibition, depletion of tissue glutathione, and saturation of oxidative metabolism. A quantitative risk assessment of BD needs to reflect these species differences and sources of nonlinearity if it is to reflect the current understanding of the disposition of BD.
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10
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Zeng T, Xie KQ. The Differential Modulation on Cytochrome P450 Enzymes by Garlic Components. FOOD REVIEWS INTERNATIONAL 2010. [DOI: 10.1080/87559129.2010.496023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Filser JG, Bhowmik S, Faller TH, Hutzler C, Kessler W, Midpanon S, Pütz C, Schuster A, Semder B, Veereshwarayya V, Csanády GA. Quantitative Investigation on the Metabolism of 1,3-Butadiene and of Its Oxidized Metabolites in Once-through Perfused Livers of Mice and Rats. Toxicol Sci 2009; 114:25-37. [DOI: 10.1093/toxsci/kfp297] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Abstract
Cytochrome P450 (CYP450) enzymes are predominantly involved in the Phase I metabolism of xenobiotics. Metabolic inhibition and induction can give rise to clinically important drug-drug interactions. Metabolic stability is a prerequisite for sustaining the therapeutically relevant concentrations, and very often drug candidates are sacrificed due to poor metabolic profiles. Computational tools such as quantitative structure-activity relationships are widely used to study different metabolic end points successfully to accelerate the drug discovery process. There are a lot of computational studies on clinically important CYPs already reported in recent years. But other clinically significant families are to yet be explored computationally. Powerfulness of quantitative structure-activity relationship will drive computational chemists to develop new potent and selective inhibitors of different classes of CYPs for the treatment of different diseases with least drug-drug interactions. Furthermore, there is a need to enhance the accuracy, interpretability and confidence in the computational models in accelerating the drug discovery pathways.
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Affiliation(s)
- Kunal Roy
- Jadavpur University, Division of Medicinal and Pharmaceutical Chemistry, Department of Pharmaceutical Technology, Drug Theoretics and Cheminformatics Lab, Kolkata 700 032, India.
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The formation and biological significance of N7-guanine adducts. Mutat Res 2009; 678:76-94. [PMID: 19465146 DOI: 10.1016/j.mrgentox.2009.05.006] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2009] [Accepted: 05/13/2009] [Indexed: 11/24/2022]
Abstract
DNA alkylation or adduct formation occurs at nucleophilic sites in DNA, mainly the N7-position of guanine. Ever since identification of the first N7-guanine adduct, several hundred studies on DNA adducts have been reported. Major issues addressed include the relationships between N7-guanine adducts and exposure, mutagenesis, and other biological endpoints. It became quickly apparent that N7-guanine adducts are frequently formed, but may have minimal biological relevance, since they are chemically unstable and do not participate in Watson Crick base pairing. However, N7-guanine adducts have been shown to be excellent biomarkers for internal exposure to direct acting and metabolically activated carcinogens. Questions arise, however, regarding the biological significance of N7-guanine adducts that are readily formed, do not persist, and are not likely to be mutagenic. Thus, we set out to review the current literature to evaluate their formation and the mechanistic evidence for the involvement of N7-guanine adducts in mutagenesis or other biological processes. It was concluded that there is insufficient evidence that N7-guanine adducts can be used beyond confirmation of exposure to the target tissue and demonstration of the molecular dose. There is little to no evidence that N7-guanine adducts or their depurination product, apurinic sites, are the cause of mutations in cells and tissues, since increases in AP sites have not been shown unless toxicity is extant. However, more research is needed to define the extent of chemical depurination versus removal by DNA repair proteins. Interestingly, N7-guanine adducts are clearly present as endogenous background adducts and the endogenous background amounts appear to increase with age. Furthermore, the N7-guanine adducts have been shown to convert to ring opened lesions (FAPy), which are much more persistent and have higher mutagenic potency. Studies in humans are limited in sample size and differences between controls and study groups are small. Future investigations should involve human studies with larger numbers of individuals and analysis should include the corresponding ring opened FAPy derivatives.
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Miller GP. Advances in the interpretation and prediction of CYP2E1 metabolism from a biochemical perspective. Expert Opin Drug Metab Toxicol 2008; 4:1053-64. [PMID: 18680440 DOI: 10.1517/17425255.4.8.1053] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
BACKGROUND Cytochrome P450 2E1 (CYP2E1) plays a central role in the metabolism and metabolic activation of a large number of small, mostly xenobiotic compounds. These qualities distinguish CYP2E1 from traditional enzymes and pose significant challenges to understanding the role and consequences of CYP2E1-mediated metabolism. OBJECTIVE This review discusses recent advances in kinetic profiling, quantitative structure-activity relationships and structural studies that have furthered the development of tools to interpret and predict CYP2E1 metabolism. METHODS Analysis of kinetic profiles by specific mechanisms produces important parameters describing specificity, stoichiometry and metabolism of molecules. Quantitative structure-activity relationships reveal a more specific basis for molecular recognition by CYP2E1. The corresponding protein structures imparting these interactions are the focus of chemical modifications, site-directed mutagenesis and homology modeling studies. RESULTS Compilation of kinetic profiling for CYP2E1 substrates established the selectivity for small substrates, whose characteristics could be generalized in parameters for hydrophobicity and steric properties as determined by quantitative structure-activity relationships. The possibility of an effector site for monocyclic compounds added an interesting variable to these modeling efforts. Various structural studies identified important residues contributing to binding and catalysis as well as the volume and location of the active site relative to the heme moiety. Pressure and carbon monoxide-binding experiments also demonstrated the inherent conformational flexibility of CYP2E1 that may contribute to rate-limiting steps during catalytic turnover. CONCLUSION Although combinations of these approaches have reinforced important observations, more work is needed to verify findings and seek broader impacts for various interpretative and predictive tools.
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Affiliation(s)
- Grover P Miller
- University of Arkansas for Medical Sciences, Department of Biochemistry and Molecular Biology, 4301 W. Markham Street, Slot 516, Little Rock, AR 72205, USA.
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Fratev F, Benfenati E. A combination of 3D-QSAR, docking, local-binding energy (LBE) and GRID study of the species differences in the carcinogenicity of benzene derivatives chemicals. J Mol Graph Model 2008; 27:147-60. [PMID: 18495507 DOI: 10.1016/j.jmgm.2008.04.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Revised: 03/27/2008] [Accepted: 04/02/2008] [Indexed: 11/16/2022]
Abstract
A combination of 3D-QSAR, docking, local-binding energy (LBE) and GRID methods was applied as a tool to study and predict the mechanism of action of 100 carcinogenic benzene derivatives. Two 3D-QSAR models were obtained: (i) model of mouse carcinogenicity on the basis of 100 chemicals (model 1) and (ii) model of the differences in mouse and rat carcinogenicity on the basis of 73 compounds (model 2). 3D-QSAR regression maps indicated the important differences in species carcinogenicity, and the molecular positions associated with them. In order to evaluate the role of P450 metabolic process in carcinogenicity, the following approaches were used. The 3D models of CYP2E1 for mouse and rat were built up. A docking study was applied and the important ligand-protein residues interactions and oxidation positions of the molecules were identified. A new approach for quantitative assessment of metabolism pathways was developed, which enabled us to describe the species differences in CYP2E1 metabolism, and how it can be related to differences in the carcinogenic potential for a subset of compounds. The binding energies of the important substituents (local-binding energy-LBE) were calculated, in order to quantitatively demonstrate the contribution of the substituents in metabolic processes. Furthermore, a computational procedure was used for determining energetically favourable binding sites (GRID examination) of the enzymes. The GRID procedure allowed the identification of some important differences, related to species metabolism in CYP2E1. Comparing GRID, 3D-QSAR maps and LBE results, a similarity was identified, indicating a relationship between P450 metabolic processes and the differences in the carcinogenicity.
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Affiliation(s)
- Filip Fratev
- Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.
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16
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Jamakhandi AP, Kuzmic P, Sanders DE, Miller GP. Global analysis of protein-protein interactions reveals multiple CYP2E1-reductase complexes. Biochemistry 2007; 46:10192-201. [PMID: 17685587 PMCID: PMC2592557 DOI: 10.1021/bi7003476] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Although a single binary functional complex between cytochrome P450 (P450 or CYP for a specific isoform) and cytochrome P450 reductase (CPR) has been generally accepted in the literature, this simple model failed to explain the experimentally observed catalytic activity of recombinant CYP2E1 in dependence on the total concentration of the added CPR-K56Q mutant. Our rejection of the simplest 1:1 binding model was based on two independent lines of experimental evidence. First, under the assumption of the 1:1 binding model, separate analyses of titration curves obtained while varying either P450 or CPR concentrations individually produced contradictory results. Second, an asymmetric Job plot suggested the existence of higher order molecular complexes. To identify the most probable complexation mechanism, we generated a comprehensive data set where the concentrations of both P450 and P450 were varied simultaneously, rather than one at a time. The resulting two-dimensional data were globally fit to 32 candidate mechanistic models, involving the formation of binary, ternary, and quaternary P450.CPR complexes, in the absence or presence or P450 and CPR homodimers. Of the 32 candidate models (mechanisms), two models were approximately equally successful in explaining our experimental data. The first plausible model involves the binary complex P450.CPR, the quaternary complex (P450)2.(CPR)2, and the homodimer (P450)2. The second plausible model additionally involves a weakly bound ternary complex (P450)2.CPR. Importantly, only the binary complex P450.CPR seems catalytically active in either of the two most probable mechanisms.
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Affiliation(s)
- Arvind P. Jamakhandi
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | | | - Daniel E. Sanders
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
| | - Grover P. Miller
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
- Corresponding author: Grover Paul Miller, Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, 4301 W. Markham St. Slot 516, Little Rock, AR 72205, USA; Telephone: 501.526.6486; Fax: 501.686.8169;
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17
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Hempel G, Oechtering D, Lanvers-Kaminsky C, Klingebiel T, Vormoor J, Gruhn B, Boos J. Cytotoxicity of Dimethylacetamide and Pharmacokinetics in Children Receiving Intravenous Busulfan. J Clin Oncol 2007; 25:1772-8. [PMID: 17470868 DOI: 10.1200/jco.2006.08.8807] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
PurposeTo assess the cytotoxicity and the exposure of N,N-dimethylacetamide (DMA) in children during high-dose therapy with an intravenous (IV) formulation of busulfan containing the potentially hepatotoxic and neurotoxic DMA as a solvent.Patients and MethodsEighteen children aged 0.9 to 17.3 years (median age, 4.0 years) received IV busulfan in 15 doses of 0.7 to 1.0 mg/kg busulfan containing overall DMA amounts of between 5 mmol (437 mg) and 70.5 mmol (6,142 mg) per dose. Plasma concentrations of DMA and busulfan were quantified and analyzed using nonlinear mixed-effects modeling. Four different leukemic cell lines were incubated with DMA, and cytotoxicity was assessed in comparison with busulfan as well as in a combination reflecting the ratio in the formulation.ResultsMaximal plasma concentrations of DMA up to 3.09 mmol/L were observed. No accumulation of the solvent occurred. Instead, the trough levels decreased over the 4 treatment days. The population pharmacokinetic analysis revealed a clearance of 86.9 mL h−1kg−1± 27% that increased to 298 mL h−1kg−1on the fourth day and a volume of distribution of 469 mL kg ± 22% (population mean ± interindividual variability). DMA volume of distribution correlated with the volume of distribution of busulfan. The cytotoxicity of DMA in vitro was 3 orders of magnitude lower than that of busulfan. No synergism was observed.ConclusionThe lack of accumulation of DMA confirms that there is no safety concern related to the DMA content in this IV busulfan formulation. The contribution of DMA to the antileukemic effect of the formulation seems to be limited.
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Affiliation(s)
- Georg Hempel
- Klinik und Poliklinik für Kinder und Jugendmedizin, Pädiatrische Hämatologie/Onkologie, Münster, Germany.
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18
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Davenport DM, Wargovich MJ. Modulation of cytochrome P450 enzymes by organosulfur compounds from garlic. Food Chem Toxicol 2005; 43:1753-62. [PMID: 16000231 DOI: 10.1016/j.fct.2005.05.018] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2004] [Revised: 05/17/2005] [Accepted: 05/24/2005] [Indexed: 11/26/2022]
Abstract
Organosulfur compounds (OSCs) derived from garlic have been studied for the ability to inhibit experimental cancer in various animal models, primarily through modification of carcinogen detoxification enzymes, such as cytochrome P450 (CYP) enzymes. OSCs vary in structural and physical properties, and a detailed analysis of these properties has not been performed with respect to their ability of inhibit chemically-induced colon cancer development. Gastric intubation of rats with a single dose of 200 mg/kg diallyl sulfide (DAS), diallyl disulfide (DADS), and allyl methyl sulfide (AMS) decreased hepatic CYP2E1 protein by 45%, 25% and 47%, respectively, and this inhibition was sustained after 1, 4 and 8 weeks of treatment by these compounds. Dipropyl sulfide (DPS), dipropyl disulfide (DPDS), propyl methyl sulfide (PMS) and S-allylcysteine (SAC) did not inhibit hepatic CYP2E1 protein expression, nor did any of the OSCs affect CYP2E1 mRNA levels. A single dose of 200 mg/kg DAS and AMS increased hepatic CYP1A2 protein (but not mRNA) by 282% and 70%, and DAS increased CYP1A1 protein levels by 684%. Daily treatment for 1, 4 and 8 weeks with 200 mg/kg DAS and AMS resulted in time-dependent increases in hepatic CYP1A1 and CYP1A2 protein levels to a maximum of 600% and 50% for DAS, and 1600% and 240% for AMS after 8 weeks. Dosing with 200 mg/kg of each of the OSCs used in this study increased hepatic CYP3A2 protein levels at all time points. Dosing for 8 weeks with 200 mg/kg DAS, but not AMS or lower doses of DAS, induced bile duct obstruction and focal areas of necrosis. These results indicate that OSCs present in garlic, including DAS and AMS, may be beneficial in inhibiting chemically-induced colon cancer, but that longer dosing with higher concentrations of DAS may elicit minor hepatic toxicity.
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Affiliation(s)
- Destiny M Davenport
- Department of Pathology and Microbiology, University of South Carolina, School of Medicine and South Carolina Cancer Center, Columbia, SC 29208, USA.
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19
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Jimenez-Lopez JM, Cederbaum AI. CYP2E1-dependent oxidative stress and toxicity: role in ethanol-induced liver injury. Expert Opin Drug Metab Toxicol 2005; 1:671-85. [PMID: 16863432 DOI: 10.1517/17425255.1.4.671] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Ethanol-induced oxidative stress plays a major role in the mechanisms by which ethanol causes liver injury. Many pathways contribute to how ethanol induces a state of oxidative stress. One central pathway appears to be the induction, by ethanol, of the CYP2E1 form of cytochrome P450 enzymes. CYP2E1 is of interest because it metabolises and activates many toxicological substrates, including ethanol, to more reactive products. Levels of CYP2E1 are elevated under a variety of physiological and pathophysiological conditions. CYP2E1 is an effective generator of reactive oxygen species. This review summarises some of the biochemical and toxicological properties of CYP2E1, and briefly describes the use of HepG2 cell lines in assessing the actions of CYP2E1. Future directions, which may help to better understand the actions of CYP2E1 and its role in alcoholic liver injury, are suggested.
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Affiliation(s)
- Jose M Jimenez-Lopez
- Mount Sinai School of Medicine, Department of Pharmacology and Biological Chemistry, New York, NY 10029, USA
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20
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de Graaf C, Vermeulen NPE, Feenstra KA. Cytochrome P450 in Silico: An Integrative Modeling Approach. J Med Chem 2005; 48:2725-55. [PMID: 15828810 DOI: 10.1021/jm040180d] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Chris de Graaf
- Leiden/Amsterdam Center for Drug Research, Division of Molecular Toxicology, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands
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21
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Baranová J, Anzenbacherová E, Anzenbacher P, Soucek P. MINIPIG CYTOCHROME P450 2E1: COMPARISON WITH HUMAN ENZYME. Drug Metab Dispos 2005; 33:862-5. [PMID: 15778271 DOI: 10.1124/dmd.104.003392] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Cytochrome P450 2E1 was isolated from minipig liver microsomes. The protein has been cloned and the respective cDNA sequenced (GenBank Accession Number AY581116). Minipig CYP2E1 is two residues shorter than its human ortholog. The only difference between pig and minipig sequence is the presence of aspartic acid residue in position 346 contrary to valine in the pig enzyme. Minipig CYP2E1 was shown to be able to convert two prototypical substrates of human CYP2E1, chlorzoxazone and p-nitrophenol, to the respective metabolites. The experiments performed with both the liver microsomal fraction and reconstituted systems with human or minipig CYP2E1 confirmed the similarity of both enzymes. Inhibition with diethyldithiocarbamate gave comparable Ki values for minipig as well as for the human CYP2E1. The results indicate that the systems containing minipig CYP2E1 may be used to model the respective CYP2E1-catalyzed reactions of drug metabolism in humans.
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Affiliation(s)
- Jana Baranová
- Institute of Pharmacology, Faculty of Medicine, Palacky University, Hnevotinska 3, CZ-775 15 Olomouc, Czech Republic
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22
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Reisfeld B, Yang RSH. A reaction network model for CYP2E1-mediated metabolism of toxicant mixtures. ENVIRONMENTAL TOXICOLOGY AND PHARMACOLOGY 2004; 18:173-179. [PMID: 21782746 DOI: 10.1016/j.etap.2004.02.012] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2003] [Accepted: 02/26/2004] [Indexed: 05/31/2023]
Abstract
In this paper, we describe a modeling approach to predict the interlinked pathways and kinetics resulting from CYP2E1-mediated metabolism of both pure species and chemical mixtures. This approach is based on the concept of chemical reaction networks, an idea that has formed the basis for simulation tools that have shown good predictive capabilities in the petroleum industry, but also an idea that has heretofore seen minimal application in the biomedical research arena. Although the initial target for developing this reaction network approach was cytochrome P450 2E1 (CYP2E1) and its over 200 substrates, this technology has been used for other families of CYP enzymes and their substrates in our laboratory. Utilizing this approach, we have produced a modular 'predictive metabolomics' simulation framework comprising interdependent software components that perform such tasks as testing of substrate binding feasibility, performing virtual chemistry, formulating reaction-rate equations, computing reaction kinetics and predicting time-dependent species concentrations. As an illustrative example, we outline the application of this framework to the prediction of the reaction networks resulting from the Phase I metabolism of two compounds of important toxicological interest. The potential of this modeling technology is immense in providing a computer simulation platform for complex-chemical mixtures and complex-biological systems. It is possible that this technology will play an important role in formulating a 'Virtual Human'.
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Affiliation(s)
- Brad Reisfeld
- Quantitative and Computational Toxicology Group, Center for Environmental Toxicology and Technology, Department of Environmental and Radiological Health Sciences, Colorado State University, 3195 Rampart Road, Foothills Campus, Fort Collins, CO 80523-1690, USA
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23
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Lewis DFV, Lake BG, Bird MG, Loizou GD, Dickins M, Goldfarb PS. Homology modelling of human CYP2E1 based on the CYP2C5 crystal structure: investigation of enzyme-substrate and enzyme-inhibitor interactions. Toxicol In Vitro 2003; 17:93-105. [PMID: 12537967 DOI: 10.1016/s0887-2333(02)00098-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The construction of a homology model of human cytochrome P450 2E1 (CYP2E1) is reported, based on the CYP2C5 crystallographic template. A relatively high degree of primary sequence homology (identity=59%), as expected for proteins of the same CYP family, ensured a straightforward generation of the 3-dimensional model due to relatively few deletions and insertions of amino acid residues with respect to the CYP2C5 crystal structure. Probing the CYP2E1 model with typical substrates of the enzyme showed a good agreement with experimental information in the form of positions of metabolism for substrates, and with site-directed mutagenesis data on certain residues. Furthermore, quantitative relationships between substrate binding affinity and various structural parameters associated with the substrate molecules facilitated the formulation of a procedure for estimating relative binding energy and, consequently, K(m) or K(D) values towards the CYP2E1 enzyme. This method has been based on a consideration of the active site interactions between substrates and key amino acid residues lining the haem pocket, together with compound lipophilicity data from partition coefficients.
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Affiliation(s)
- D F V Lewis
- School of Biomedical and Life Sciences, University of Surrey, Guildford, Surrey GU2 7XH, UK.
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24
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Lewis DFV. Modelling human cytochromes P450 involved in drug metabolism from the CYP2C5 crystallographic template. J Inorg Biochem 2002; 91:502-14. [PMID: 12237218 DOI: 10.1016/s0162-0134(02)00429-4] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
A historical background to homology modelling of human P450s involved in drug metabolism is outlined, showing that the progress in crystallographic studies of bacterial forms of enzyme and, latterly, determination of a mammalian P450 crystal structure, has enabled the production of increasingly satisfactory models of human P450 enzymes. The methodology for the generation of P450 models by homology with crystallographic template structures is summarized, and recent results of CYP2C5-constructed models of P450s are described. These indicate that selective substrates are able to fit within the putative active sites of each enzyme, where key contacts with complementary amino acid residues are largely consistent with the results of site-directed mutagenesis experiments and metabolic studies. Consequently, the CYP2C5 crystal structure can be regarded at the current paradigm for homology modelling of the drug metabolizing P450s, especially those from the CYP2 family.
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Affiliation(s)
- David F V Lewis
- School of Biomedical and Life Sciences, University of Surrey, Guildford, UK.
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25
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Lewi DFV, Bird MG, Jacobs MN. Human carcinogens: an evaluation study via the COMPACT and HazardExpert procedures. Hum Exp Toxicol 2002; 21:115-22. [PMID: 12102536 DOI: 10.1191/0960327102ht233oa] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The results of computer-optimized molecular parametric analysis of chemical toxicity (COMPACT) and HazardExpert evaluations on 14 established human carcinogens are reported. The concordances between COMPACT and carcinogenicity (71%) and between HazardExpert and carcinogenicity (57%) are significantly improved when taken in combination, where all 14 carcinogens are correctly identified by the two systems used in conjunction. However, if a negative energy of the highest occupied molecular orbital (E(HOMO)) value is regarded as evidence of electrophilic reactivity likely to give rise to mutagenicity and carcinogenicity, then 13/14 (93%) of the carcinogens are correctly identified by combination with the COMPACT procedure alone. It is possible, therefore, to establish likely carcinogenicity arising from either P450 mediation (CYP1 and CYP2E) or compound electrophilicity via the employment of a straightforward approach to molecular and electronic structure calculation, a process that can be performed in a relatively short time frame (i.e., less than 1 hour per chemical) and at a low cost.
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Affiliation(s)
- D F V Lewi
- Molecular Toxicology Group, School of Biomedical and Life Sciences, University of Surrey, Guildford, UK.
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26
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Lewis DF. On the recognition of mammalian microsomal cytochrome P450 substrates and their characteristics: towards the prediction of human p450 substrate specificity and metabolism. Biochem Pharmacol 2000; 60:293-306. [PMID: 10856424 DOI: 10.1016/s0006-2952(00)00335-x] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
The characteristics of mammalian microsomal P450 xenobiotic substrates are described, particularly with reference to the major P450 isoforms associated with drug metabolism in humans. It is further reported that a relatively small number of molecular, electronic, and physico-chemical properties are required to discriminate between chemicals that exhibit specificity for human P450 isoforms: CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4. Molecular templates of superimposed substrates are shown to be complementary with the putative active sites of the relevant enzymes, thus enabling a possible prediction of P450 specificity from structure. Factors contributing to metabolic clearance and binding affinity are also discussed, and methods for their calculation are described.
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Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, Guildford, GU2 5XH, Surrey, UK.
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27
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Lewis DF, Dickins M, Eddershaw PJ, Tarbit MH, Goldfarb PS. Cytochrome P450 substrate specificities, substrate structural templates and enzyme active site geometries. DRUG METABOLISM AND DRUG INTERACTIONS 2000; 15:1-49. [PMID: 10707112 DOI: 10.1515/dmdi.1999.15.1.1] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The structural characteristics of human cytochrome P450 substrates are outlined in the light of extensive studies on P450 substrate specificity. Templates of superimposed substrates for individual P450 isozymes are shown to fit the corresponding enzyme active sites, where contacts with specific amino acid residues appear to be involved in the interaction with each structural template. Procedures leading to the evaluation of likely P450 specificity, binding affinity and rate of metabolism are described in the context of key examples in which molecular modelling appears to rationalize experimentally observed findings.
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Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, Guildford, UK
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28
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De Rienzo F, Fanelli F, Menziani MC, De Benedetti PG. Theoretical investigation of substrate specificity for cytochromes P450 IA2, P450 IID6 and P450 IIIA4. J Comput Aided Mol Des 2000; 14:93-116. [PMID: 10702928 DOI: 10.1023/a:1008187802746] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Three-dimensional models of the cytochromes P450 IA2, P450 IID6 and P450 IIIA4 were built by means of comparative modeling using the X-ray crystallographic structures of P450 CAM, P450 BM-3, P450 TERP and P450 ERYF as templates. The three cytochromes were analyzed both in their intrinsic structural features and in their interaction properties with fifty specific and non-specific substrates. Substrate/enzyme complexes were obtained by means of both automated rigid and flexible body docking. The comparative analysis of the three cytochromes and the selected substrates, in their free and bound forms, allowed for the building of semi-quantitative models of substrate specificity based on both molecular and intermolecular interaction descriptors. The results of this study provide new insights into the molecular determinants of substrate specificity for the three different eukaryotic P450 isozymes and constitute a useful tool for predicting the specificity of new compounds.
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Affiliation(s)
- F De Rienzo
- Dipartimento di Chimica, Università di Modena e Reggio Emilia, Italy
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29
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Lewis DF. Homology modelling of human cytochromes P450 involved in xenobiotic metabolism and rationalization of substrate selectivity. EXPERIMENTAL AND TOXICOLOGIC PATHOLOGY : OFFICIAL JOURNAL OF THE GESELLSCHAFT FUR TOXIKOLOGISCHE PATHOLOGIE 1999; 51:369-74. [PMID: 10445400 DOI: 10.1016/s0940-2993(99)80024-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
Molecular modelling of human cytochrome P450 (CYP) isoforms is described, based on amino acid sequence homology with a unique bacterial P450 (CYP102) of known crystal structure. It is found that for the human hepatic P450s involved in the metabolism of xenobiotics, ie. CYPIA2, CYP 1A6, CYP2B6, CYP2C9, CYP2C 19, CYP2D6, CYP2E1 and CYP3A4, there is a satisfactory agreement between specific substrate characteristics and topographical features of the putative active sites, including complementarity with key amino acid residues in the P450 haem environments. A combination of homology model interactions with substrates and certain molecular properties of the compounds themselves provides a methodology for the evaluation of potential P450 selectivity in new chemical entities (NCEs).
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Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, UK.
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Lewis DF, Ioannides C, Parke DV. An improved and updated version of the compact procedure for the evaluation of P450-mediated chemical activation. Drug Metab Rev 1998; 30:709-37. [PMID: 9844807 DOI: 10.3109/03602539808996328] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, Guildford, UK
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31
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Lewis DF, Eddershaw PJ, Dickins M, Tarbit MH, Goldfarb PS. Structural determinants of cytochrome P450 substrate specificity, binding affinity and catalytic rate. Chem Biol Interact 1998; 115:175-99. [PMID: 9851289 DOI: 10.1016/s0009-2797(98)00068-4] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
The structural characteristics of cytochrome P450 substrates are summarised, showing that molecular descriptors can discriminate between chemicals of differing P450 isozyme specificity. Procedures for the estimation of P450 substrate binding interaction energies and rates of metabolism are described, providing specific examples in both individual compounds binding to P450s, including those of known crystal structure, and within series of structurally related chemicals. It is demonstrated that binding energy components are primarily hydrophobic/desolvation and electrostatic/hydrogen-bonded in nature, whereas electronic factors are of importance in determining variations in reaction rates. It is thus shown that the prediction of P450 substrate binding affinities and catalytic rates may be feasible, provided that sufficient structural information is available for the relevant enzyme-substrate complex.
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Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, Guildford, UK.
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Lewis DF, Ioannides C, Parke DV. A combined COMPACT and HazardExpert study of 40 chemicals for which information on mutagenicity and carcinogenicity is known, including the results of human epidemiological studies. Hum Exp Toxicol 1998; 17:577-86. [PMID: 9821022 DOI: 10.1177/096032719801701009] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The COMPACT approach for defining structural criteria for substrates and inducers of cytochrome P450 (CYP) enzymes which mediate the formation of reactive intermediates is discussed in the context of prediction of potential carcinogenicity. This is broadened to encompass structural studies on mammalian P450s, including those relevant to genetic polymorphism in man. The use of the COMPACT system, in parallel with the structure alert program HazardExpert (now incorporated into the Pallas system), for evaluating human carcinogenicity data is reported, as an example of the possible employment of a battery of short-term test procedures for safety evaluation. In particular, the importance of using the log P value (as a measure of compound lipophilicity) to assess the likelihood of a potentially toxic compound reaching the site of activation, is emphasized by the finding that most procarcinogens requiring metabolic activation by P450s are lipophilic in nature.
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Affiliation(s)
- D F Lewis
- Molecular Toxicology Group, School of Biological Sciences, University of Surrey, Guildford, UK
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Lewis DF, Watson E, Lake BG. Evolution of the cytochrome P450 superfamily: sequence alignments and pharmacogenetics. Mutat Res 1998; 410:245-70. [PMID: 9630657 DOI: 10.1016/s1383-5742(97)00040-9] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The evolution of the cytochrome P450 (CYP) superfamily is described, with particular reference to major events in the development of biological forms during geological time. It is noted that the currently accepted timescale for the elaboration of the P450 phylogenetic tree exhibits close parallels with the evolution of terrestrial biota. Indeed, the present human P450 complement of xenobiotic-metabolizing enzymes may have originated from coevolutionary 'warfare' between plants and animals during the Devonian period about 400 million years ago. A number of key correspondences between the evolution of P450 system and the course of biological development over time, point to a mechanistic molecular biology of evolution which is consistent with a steady increase in atmospheric oxygenation beginning over 2000 million years ago, whereas dietary changes during more recent geological time may provide one possible explanation for certain species differences in metabolism. Alignment between P450 protein sequences within the same family or subfamily, together with across-family comparisons, aid the rationalization of drug metabolism specificities for different P450 isoforms, and can assist in an understanding of genetic polymorphisms in P450-mediated oxidations at the molecular level. Moreover, the variation in P450 regulatory mechanisms and inducibilities between different mammalian species are likely to have important implications for current procedures of chemical safety evaluation, which rely on pure genetic strains of laboratory bred rodents for the testing of compounds destined for human exposure.
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Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, Guildford, Surrey, GU2 5XH, UK
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Nieusma JL, Claffey DJ, Koop DR, Chen W, Peter RM, Nelson SD, Ruth JA, Ross D. Oxidation of 1,3-butadiene to (R)- and (S)-butadiene monoxide by purified recombinant cytochrome P450 2E1 from rabbit, rat and human. Toxicol Lett 1998; 95:123-9. [PMID: 9635416 DOI: 10.1016/s0378-4274(98)00026-5] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
1,3-Butadiene (BD) is a gas used widely in the rubber and plastics industry as an intermediate in production processes and has been detected in automobile exhaust and cigarette smoke. BD requires metabolic activation to exert toxicity and has been shown to be carcinogenic in rodents. IARC has classified BD as a group 2A (probably carcinogenic to humans) carcinogen. The initial oxidation of BD to butadiene monoxide (BMO) occurs primarily via cytochrome P450 2E1 and two stereoisomers of BMO (R and S) can be formed. (R) and (S)-BMO are metabolized differently and demonstrate markedly different toxicities in isolated rat hepatocytes. This work examined the generation of (R) and (S)-BMO from BD by cytochrome P450 2E1 from rabbit, rat and human. BMO level was measured by GC-MS analysis and enantiomeric composition was determined by GC-FID. The greatest rate of formation of BMO from BD was obtained with rabbit cytochrome P4502E1 followed by human and then by rat. Enantiomeric distribution of R and S-BMO produced by the three species demonstrated no significant differences.
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Affiliation(s)
- J L Nieusma
- Department of Pharmaceutical Sciences, School of Pharmacy, University of Colorado Health Sciences Center, Denver 80262, USA
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Anderson D, Hughes JA, Edwards AJ, Brinkworth MH. A comparison of male-mediated effects in rats and mice exposed to 1,3-butadiene. Mutat Res 1998; 397:77-84. [PMID: 9463554 DOI: 10.1016/s0027-5107(97)00197-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
There is current concern that exposure of men to certain agents such as radiation and smoking can adversely affect their offspring in terms of cancer outcome. Studies in laboratory animals after radiation have supported such an association, and other studies after male exposure to radiation and various chemicals have also resulted in congenital malformations. The present study was undertaken to examine congenital malformations in offspring from males exposed to 1,3-butadiene over a lower dose range than that in an earlier mouse study and to determine if there was a species difference in sensitivity between rats and mice. An earlier extended dominant lethal study of male CD-1 mice exposed by inhalation to 12.5 ppm and 1250 ppm of 1,3-butadiene for 6 h/day, 5 days/wk, for 10 weeks produced an increase in F1 abnormalities and late deaths at 12.5 ppm and in early deaths at 1250 ppm. The present study examined the same reproductive effects after exposure of male CD-1 mice for 6 h/day, 5 days/wk, for 4 weeks to 12.5, 65 and 130 ppm of 1,3-butadiene. There was no increase in early deaths at 12.5 ppm as in the earlier study but there were statistically significant increases in early deaths at 65 and 130 ppm study and these were not dose-related. There was a non-significant increase in F1 gross abnormalities at 130 ppm and no increase in late deaths. The present study also examined male Sprague-Dawley rats after exposure to 65,400 and 1250 ppm for 6 h/day, 5 days/wk, for 10 weeks. There were no effects on early deaths, late deaths, or congenital malformations in the rat study. There was a reduction in implants at 65 ppm but this was not considered to be biologically/genetically significant as there was no corresponding increase in early deaths and the response was not dose-related. The differences observed between the rat and mouse studies would confirm the greater sensitivity to 1,3-butadiene of the mouse by comparison with the rat as reported by other workers for other parameters.
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Affiliation(s)
- D Anderson
- BIBRA International, Carshalton, Surrey, UK.
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Lewis DF, Ioannides C, Parke DV. Further evaluation of COMPACT, the molecular orbital approach for the prospective safety evaluation of chemicals. Mutat Res 1998; 412:41-54. [PMID: 9508363 DOI: 10.1016/s1383-5718(97)00145-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The molecular dimensions and electronic structures of the first group of 100 US NCI/NTP miscellaneous chemicals, evaluated for potential carcinogenicity by computer-optimized molecular parametric analysis for chemical toxicity (COMPACT) have been re-determined. Using improved criteria for cytochrome P450 (CYP) substrate specificity, re-defined for CYP1 as having a COMPACT radius [square root of (deltaE - 9.5)2 + (a/d(2) - 7.8)2] of < 6.5, and for CYP2E as having a collision diameter of 6.5 angstroms or less and deltaE < 15.5, the likely substrates of CYP1 and CYP2E, which are regarded as potential carcinogens, have been identified. In addition, log P values have been taken into account; those chemicals with log P < 0 are non-lipophilic substrates unlikely to reach the activating cytochrome enzymes, and have been regarded as non-carcinogens. The second group of 100 US NCI/NTP chemicals have also now been categorized by COMPACT into CYP1 and CYP2E substrates, and their potential carcinogenicities evaluated. Of the 203 chemicals in the 2 groups, those positive in the rodent two-species life-span carcinogenicity study (rodent assay) were 53%, those positive in the Ames test (mutagenicity) were 48%, and those positive in the COMPACT programme (carcinogenicity, mutagenicity, cytotoxicity) were 54%. Concordance between the COMPACT prediction of carcinogenicity/cytotoxicity and rodent two species life-span carcinogenicity data for the 203 chemicals is 69%, and correlation of COMPACT with Ames test data is 61%. The sensitivity of COMPACT for predicting rodent carcinogenicity is 72%, whereas the sensitivity of the Ames test for predicting carcinogenicity for the 203 chemicals was only 57%. The degree (severity) of rodent carcinogenicity also showed correlation with the COMPACT predictive evaluations of the chemicals.
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Affiliation(s)
- D F Lewis
- School of Biological Sciences, University of Surrey, Guildford, UK
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