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Cui Y, Wang Y. Mass spectrometry-based DNA adductomics. Trends Analyt Chem 2022. [DOI: 10.1016/j.trac.2022.116773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Baldauf KJ, Salazar-González RA, Doll MA, Pierce WM, States JC, Hein DW. Role of Human N-Acetyltransferase 2 Genetic Polymorphism on Aromatic Amine Carcinogen-Induced DNA Damage and Mutagenicity in a Chinese Hamster Ovary Cell Mutation Assay. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2020; 61:235-245. [PMID: 31490564 PMCID: PMC7017392 DOI: 10.1002/em.22331] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2019] [Revised: 08/27/2019] [Accepted: 08/30/2019] [Indexed: 05/10/2023]
Abstract
Carcinogenic aromatic amines such as 4-aminobiphenyl (ABP) and 2-aminofluorene (AF) require metabolic activation to form electrophilic intermediates that mutate DNA leading to carcinogenesis. Bioactivation of these carcinogens includes N-hydroxylation catalyzed by CYP1A2 followed by O-acetylation catalyzed by arylamine N-acetyltransferase 2 (NAT2). To better understand the role of NAT2 genetic polymorphism in ABP- and AF-induced mutagenesis and DNA damage, nucleotide excision repair-deficient (UV5) Chinese hamster ovary (CHO) cells were stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles. ABP and AF both caused significantly (P < 0.001) greater mutagenesis measured at the hypoxanthine phosphoribosyl transferase (hprt) locus in the UV5/CYP1A2/NAT2*4 acetylator cell line compared to the UV5, UV5/CYP1A2, and UV5/CYP1A2/NAT2*5B cell lines. ABP- and AF-induced hprt mutant cDNAs were sequenced and over 80% of the single-base substitutions were at G:C base pairs. DNA damage also was quantified by γH2AX in-cell western assays and by identification and quantification of the two predominant DNA adducts, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) and N-(deoxyguanosin-8-yl)-2-aminofluorene (dG-C8-AF) by liquid chromatography-mass spectrometry. DNA damage and adduct levels were dose-dependent, correlated highly with levels of hprt mutants, and were significantly (P < 0.0001) greater in the UV5/CYP1A2/NAT2*4 rapid acetylator cell line following treatment with ABP or AF as compared to all other cell lines. Our findings provide further clarity on the importance of O-acetylation in CHO mutagenesis assays for aromatic amines. They provide evidence that NAT2 genetic polymorphism modifies aromatic amine-induced DNA damage and mutagenesis that should be considered in human risk assessments following aromatic amine exposures. Environ. Mol. Mutagen. 61:235-245, 2020. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
| | | | | | | | | | - David W. Hein
- Correspondence to: David W. Hein, Kosair Charities CTR-Room 303, 505 South Hancock Street, Louisville, Kentucky 40202.
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Liu S, Wang Y. Mass spectrometry for the assessment of the occurrence and biological consequences of DNA adducts. Chem Soc Rev 2015; 44:7829-54. [PMID: 26204249 PMCID: PMC4787602 DOI: 10.1039/c5cs00316d] [Citation(s) in RCA: 98] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Exogenous and endogenous sources of chemical species can react, directly or after metabolic activation, with DNA to yield DNA adducts. If not repaired, DNA adducts may compromise cellular functions by blocking DNA replication and/or inducing mutations. Unambiguous identification of the structures and accurate measurements of the levels of DNA adducts in cellular and tissue DNA constitute the first and important step towards understanding the biological consequences of these adducts. The advances in mass spectrometry (MS) instrumentation in the past 2-3 decades have rendered MS an important tool for structure elucidation, quantification, and revelation of the biological consequences of DNA adducts. In this review, we summarized the development of MS techniques on these fronts for DNA adduct analysis. We placed our emphasis of discussion on sample preparation, the combination of MS with gas chromatography- or liquid chromatography (LC)-based separation techniques for the quantitative measurement of DNA adducts, and the use of LC-MS along with molecular biology tools for understanding the human health consequences of DNA adducts. The applications of mass spectrometry-based DNA adduct analysis for predicting the therapeutic outcome of anti-cancer agents, for monitoring the human exposure to endogenous and environmental genotoxic agents, and for DNA repair studies were also discussed.
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Affiliation(s)
- Shuo Liu
- Environmental Toxicology Graduate Program, University of California, Riverside, California, USA
| | - Yinsheng Wang
- Environmental Toxicology Graduate Program, University of California, Riverside, California, USA and Department of Chemistry, University of California, Riverside, CA 92521-0403, USA.
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Gavina JMA, Yao C, Feng YL. Recent developments in DNA adduct analysis by mass spectrometry: a tool for exposure biomonitoring and identification of hazard for environmental pollutants. Talanta 2014; 130:475-94. [PMID: 25159438 DOI: 10.1016/j.talanta.2014.06.050] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2014] [Revised: 06/19/2014] [Accepted: 06/22/2014] [Indexed: 02/08/2023]
Abstract
DNA adducts represent an important category of biomarkers for detection and exposure surveillance of potential carcinogenic and genotoxic chemicals in the environment. Sensitive and specific analytical methods are required to detect and differentiate low levels of adducts from native DNA from in vivo exposure. In addition to biomonitoring of environmental pollutants, analytical methods have been developed for structural identification of adducts which provides fundamental information for determining the toxic pathway of hazardous chemicals. In order to achieve the required sensitivity, mass spectrometry has been increasingly utilized to quantify adducts at low levels as well as to obtain structural information. Furthermore, separation techniques such as chromatography and capillary electrophoresis can be coupled to mass spectrometry to increase the selectivity. This review will provide an overview of advances in detection of adducted and modified DNA by mass spectrometry with a focus on the analysis of nucleosides since 2007. Instrument advances, sample and instrument considerations, and recent applications will be summarized in the context of hazard assessment. Finally, advances in biomonitoring applying mass spectrometry will be highlighted. Most importantly, the usefulness of DNA adducts measurement and detection will be comprehensively discussed as a tool for assessment of in vitro and in vivo exposure to environmental pollutants.
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Affiliation(s)
- Jennilee M A Gavina
- Exposure and Biomonitoring Division, Environmental Health Science and Research Bureau, Environmental and Radiation Health Sciences Directorate, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Columbine Driveway, AL: 0800C, Ottawa, Ontario, Canada K1A 0K9
| | - Chunhe Yao
- Exposure and Biomonitoring Division, Environmental Health Science and Research Bureau, Environmental and Radiation Health Sciences Directorate, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Columbine Driveway, AL: 0800C, Ottawa, Ontario, Canada K1A 0K9
| | - Yong-Lai Feng
- Exposure and Biomonitoring Division, Environmental Health Science and Research Bureau, Environmental and Radiation Health Sciences Directorate, Healthy Environments and Consumer Safety Branch, Health Canada, 50 Columbine Driveway, AL: 0800C, Ottawa, Ontario, Canada K1A 0K9.
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Optimized enzymatic hydrolysis of DNA for LC-MS/MS analyses of adducts of 1-methoxy-3-indolylmethyl glucosinolate and methyleugenol. Anal Biochem 2012; 434:4-11. [PMID: 23142629 DOI: 10.1016/j.ab.2012.11.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2012] [Revised: 10/29/2012] [Accepted: 11/01/2012] [Indexed: 01/30/2023]
Abstract
Mass spectrometric analyses of DNA adducts usually require enzymatic digestion of the DNA to nucleosides. The digestive enzymes used in our laboratory included a calf spleen phosphodiesterase, whose marketing was stopped recently. Using DNA adducted with bioactivated methyleugenol and 1-methoxy-3-indolylmethyl glucosinolate-each forming dA and dG adducts-we demonstrate that replacement of calf spleen phosphodiesterase (Merck) with bovine spleen phosphodiesterase (Sigma-Aldrich) leads to unchanged results. Enzyme levels used for DNA digestion are extremely variable in different studies. Therefore, we sequentially varied the level of each of the three enzymes used. All dose (enzyme)-response (adduct level) curves involved a long plateau starting below the enzyme levels employed previously. Thus, we could reduce the amounts of micrococcal nuclease, phosphodiesterase, and alkaline phosphatase for quantitative DNA digestion by factors of 4, 2, and 333, respectively, compared to our previous protocols. Moreover, we observed significant phosphatase activity of both phosphodiesterase preparations used, which may affect the recovery of adducts with methods requiring digestion to 2'-deoxynucleoside-3'-monophosphates (e.g., (32)P-postlabeling). In addition, the phosphodiesterase from Sigma-Aldrich, but not that from Merck, deaminated dA. This was irrelevant for the dA adducts studied, involving bonding at N(6), but might complicate the analysis of other dA adducts.
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Sugamori KS, Brenneman D, Sanchez O, Doll MA, Hein DW, Pierce WM, Grant DM. Reduced 4-aminobiphenyl-induced liver tumorigenicity but not DNA damage in arylamine N-acetyltransferase null mice. Cancer Lett 2011; 318:206-13. [PMID: 22193722 DOI: 10.1016/j.canlet.2011.12.022] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2011] [Revised: 12/08/2011] [Accepted: 12/08/2011] [Indexed: 01/23/2023]
Abstract
The aromatic amine 4-aminobiphenyl (ABP) is a liver procarcinogen in mice, requiring enzymatic bioactivation to exert its tumorigenic effect. To assess the role of arylamine N-acetyltransferase (NAT)-dependent acetylation capacity in the risk for ABP-induced liver tumors, we compared 1-year liver tumor incidence following the postnatal exposure of wild-type and NAT-deficient Nat1/2(-/-) mice to ABP. At an ABP exposure of 1200 nmol, male Nat1/2(-/-) mice had a liver tumor incidence of 36% compared to 69% in wild-type males, and at 600 nmol there was a complete absence of tumors compared to 60% in wild-type mice. Only one female wild-type mouse had a tumor using this exposure protocol. However, levels of N-deoxyguanosin-8-yl-ABP-DNA adducts did not correlate with either the strain or sex differences in tumor incidence. These results suggest that female sex and NAT deficiency reduce risk for ABP-induced liver tumors, but by mechanisms unrelated to differences in DNA-damaging events.
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Affiliation(s)
- Kim S Sugamori
- Department of Pharmacology & Toxicology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada
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Singh R, Arlt VM, Henderson CJ, Phillips DH, Farmer PB, Gamboa da Costa G. Detection and quantitation of N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine adducts in DNA using online column-switching liquid chromatography tandem mass spectrometry. J Chromatogr B Analyt Technol Biomed Life Sci 2010; 878:2155-62. [PMID: 20598652 PMCID: PMC2923026 DOI: 10.1016/j.jchromb.2010.06.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Revised: 06/03/2010] [Accepted: 06/03/2010] [Indexed: 10/19/2022]
Abstract
The heterocyclic aromatic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is formed by the grilled cooking of certain foods such as meats, poultry and fish. PhIP has been shown to induce tumours in the colon, prostate and mammary glands of rats and is regarded as a potential human dietary carcinogen. PhIP is metabolically activated via cytochrome P450 mediated oxidation to an N-hydroxylamino-PhIP intermediate that is subsequently converted to an ester by N-acetyltransferases or sulfotransferases and undergoes heterolytic cleavage to produce a PhIP-nitrenium ion, which reacts with DNA to form the N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP-C8-dG) adduct. Thus far, the detection and quantification of PhIP-DNA adducts has relied to a large extent on (32)P-postlabelling methodologies. In order to expand the array of available techniques for the detection and improved quantification of PhIP-C8-dG adducts in DNA we have developed an online column-switching liquid chromatography (LC)-electrospray ionization (ESI)-tandem mass spectrometry (MS/MS) selected reaction monitoring (SRM) method incorporating an isotopically [(13)C(10)]-labelled PhIP-C8-dG internal standard for the analysis of DNA enzymatically hydrolysed to 2'-deoxynucleosides. A dose-dependent increase was observed for PhIP-C8-dG adducts when salmon testis DNA was reacted with N-acetoxy-PhIP. Analysis of DNA samples isolated from colon tissue of mice treated by oral gavage daily for 5 days with 50 mg/kg body weight of PhIP resulted in the detection of an average level of 14.8+/-3.7 PhIP-C8-dG adducts per 10(6) 2'-deoxynucleosides. The method required 50 microg of hydrolysed animal DNA on column and the limit of detection for PhIP-C8-dG was 2.5 fmol (1.5 PhIP-C8-dG adducts per 10(8) 2'-deoxynucleosides). In summary, the LC-ESI-MS/MS SRM method provides for the rapid automation of the sample clean up and a reduction in matrix components that would otherwise interfere with the mass spectrometric analysis, with sufficient sensitivity and precision to analyse DNA adducts in animals exposed to PhIP.
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Affiliation(s)
- Rajinder Singh
- Cancer Biomarkers and Prevention Group, Biocentre, Department of Cancer Studies and Molecular Medicine, University of Leicester, University Road, Leicester LE1 7RH, UK.
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Bendaly J, Metry KJ, Doll MA, Jiang G, States JC, Smith NB, Neale JR, Holloman JL, Pierce WM, Hein DW. Role of human CYP1A1 and NAT2 in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine-induced mutagenicity and DNA adducts. Xenobiotica 2010; 39:399-406. [PMID: 19301197 DOI: 10.1080/00498250902748953] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is carcinogenic in multiple organs and numerous species. Bioactivation of PhIP is initiated by PhIP N(2)-hydroxylation catalysed by cytochrome P450s. Following N-hydroxylation, O-acetylation catalysed by N-acetyltransferase 2 (NAT2) is considered a further possible activation pathway. Genetic polymorphisms in NAT2 may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles were used to test the effect of CYP1A1 and NAT2 polymorphism on PhIP genotoxicity. Cells transfected with NAT2*4 had significantly higher levels of N-hydroxy-PhIP O-acetyltransferase (p = 0.0150) activity than cells transfected with NAT2*5B. Following PhIP treatment, CHO cell lines transfected with CYP1A1, CYP1A1/NAT2*4 and CYP1A1/NAT2*5B each showed concentration-dependent cytotoxicity and hypoxanthine phosphoribosyl transferase (hprt) mutagenesis not observed in untransfected CHO cells. dG-C8-PhIP was the primary DNA adduct formed and levels were dose dependent in transfected CHO cells in the order: CYP1A1 < CYP1A1 and NAT2*5B < CYP1A1 and NAT2*4, although levels did not differ significantly (p > 0.05) following one-way analysis of variance. These results strongly support activation of PhIP by CYP1A1 with little effect of human NAT2 genetic polymorphism on mutagenesis and DNA damage.
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Affiliation(s)
- J Bendaly
- Department of Pharmacology and Toxicology, James Graham Brown Cancer Center, and Center for Environmental Genomics and Integrative Biology, University of Louisville School of Medicine, Louisville, KY, USA
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Abstract
The ability to conduct validated analyses of biomarkers is critically important in order to establish the sensitivity and selectivity of the biomarker in identifying a particular disease. The use of stable-isotope dilution (SID) methodology in combination with LC–MS/MS provides the highest possible analytical specificity for quantitative determinations. This methodology is now widely used in the discovery and validation of putative exposure and disease biomarkers. This review will describe the application of SID LC–MS methodology for the analysis of small-molecule and protein biomarkers. It will also discuss potential future directions for the use of this methodology for rigorous biomarker analysis.
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Affiliation(s)
- Eugene Ciccimaro
- Thermo Fisher Scientific, 265 Davidson Avenue, Somerset, NJ 08873–4120, USA
| | - Ian A Blair
- Centers of Excellence in Environmental Toxicology and Cancer Pharmacology, Department of Pharmacology, University of Pennsylvania School of Medicine, 421 Curie Blvd, Philadelphia, PA 19104–6160, USA
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Metry KJ, Neale JR, Doll MA, Howarth AL, States JC, McGregor WG, Pierce WM, Hein DW. Effect of rapid human N-acetyltransferase 2 haplotype on DNA damage and mutagenesis induced by 2-amino-3-methylimidazo-[4,5-f]quinoline (IQ) and 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline (MeIQx). Mutat Res 2009; 684:66-73. [PMID: 20004212 DOI: 10.1016/j.mrfmmm.2009.12.001] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Revised: 12/01/2009] [Accepted: 12/02/2009] [Indexed: 01/01/2023]
Abstract
Heterocyclic amines such as 2-amino-3-methylimidazo-[4,5-f]quinoline (IQ) and 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline (MeIQx) are dietary carcinogens generated when meats are cooked well-done. Bioactivation includes N-hydroxylation catalyzed by cytochrome P4501A2 (CYP1A2) followed by O-acetylation catalyzed by N-acetyltransferase 2 (NAT2). Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human CYP1A2 and either NAT2*4 (rapid acetylator) or NAT2*5B (slow acetylator) alleles were treated with IQ or MeIQx to examine the effect of NAT2 genetic polymorphism on IQ- or MeIQx-induced DNA adducts and mutagenesis. MeIQx and IQ both induced decreases in cell survival and significantly (p<0.001) greater number of endogenous hypoxanthine phosphoribosyl transferase (hprt) mutants in the CYP1A2/NAT2*4 than the CYP1A2/NAT2*5B cell line. IQ- and MeIQx-induced hprt mutant cDNAs were sequenced and over 85% of the mutations were single-base substitutions with the remainder exon deletions likely caused by splice-site mutations. For the single-base substitutions, over 85% were at G:C base pairs. Deoxyguanosine (dG)-C8-IQ and dG-C8-MeIQx adducts were significantly (p<0.001) greater in the CYP1A2/NAT2*4 than the CYP1A2/NAT2*5B cell line. DNA adduct levels correlated very highly with hprt mutants for both IQ and MeIQx. These results suggest substantially increased risk for IQ- and MeIQx-induced DNA damage and mutagenesis in rapid NAT2 acetylators.
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Affiliation(s)
- Kristin J Metry
- Department of Pharmacology & Toxicology, James Graham Brown Cancer Center and Center for Environmental Genomics and Integrative Biology, University of Louisville School of Medicine, Louisville, KY 40292, USA
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Bendaly J, Doll MA, Millner LM, Metry KJ, Smith NB, Pierce WM, Hein DW. Differences between human slow N-acetyltransferase 2 alleles in levels of 4-aminobiphenyl-induced DNA adducts and mutations. Mutat Res 2009; 671:13-9. [PMID: 19682468 DOI: 10.1016/j.mrfmmm.2009.08.003] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2009] [Revised: 07/28/2009] [Accepted: 08/04/2009] [Indexed: 12/25/2022]
Abstract
Aromatic amines such as 4-aminobiphenyl (ABP) require biotransformation to exert their carcinogenic effects. Genetic polymorphisms in biotransformation enzymes such as N-acetyltransferase 2 (NAT2) may modify cancer risk following exposure. Nucleotide excision repair-deficient Chinese hamster ovary (CHO) cells stably transfected with human cytochrome P4501A1 (CYP1A1) and a single copy of either NAT2*4 (rapid acetylator), NAT2*5B (common Caucasian slow acetylator), or NAT2*7B (common Asian slow acetylator) alleles (haplotypes) were treated with ABP to test the effect of NAT2 polymorphisms on DNA adduct formation and mutagenesis. ABP N-acetyltransferase catalytic activities were detectable only in cell lines transfected with NAT2 and were highest in cells transfected with NAT2*4, lower in cells transfected with NAT2*7B, and lowest in cells transfected with NAT2*5B. Following ABP treatment, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP) was the primary adduct formed. Cells transfected with both CYP1A1 and NAT2*4 showed the highest concentration-dependent cytotoxicity, hypoxanthine phosphoribosyl transferase (hprt) mutants, and dG-C8-ABP adducts. Cells transfected with CYP1A1 and NAT2*7B showed lower levels of cytotoxicity, hprt mutagenesis, and dG-C8-ABP adducts. Cells transfected with CYP1A1 only or cells transfected with both CYP1A1 and NAT2*5B did not induce cytotoxicity, hprt mutagenesis or dG-C8-ABP adducts. ABP-DNA adduct levels correlated very highly (r>0.96) with ABP-induced hprt mutant levels following each treatment. The results of the present study suggest that investigations of NAT2 genotype or phenotype associations with disease or toxicity could be more precise and reproducible if heterogeneity within the "slow" NAT2 acetylator phenotype is considered and incorporated into the study design.
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Affiliation(s)
- Jean Bendaly
- Department of Pharmacology & Toxicology, University of Louisville School of Medicine, Louisville, KY 40292, United States
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Metry KJ, Neale JR, Bendaly J, Smith NB, Pierce WM, Hein DW. Effect of N-acetyltransferase 2 polymorphism on tumor target tissue DNA adduct levels in rapid and slow acetylator congenic rats administered 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine or 2-amino-3,8-dimethylimidazo-[4,5-f]quinoxaline. Drug Metab Dispos 2009; 37:2123-6. [PMID: 19666988 DOI: 10.1124/dmd.109.029512] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
2-Amino-3,8-dimethylimidazo-[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) are suspected human carcinogens generated in well done meats. After N-hydroxylation, they are O-acetylated by N-acetyltransferase 2 (NAT2) to electrophiles that form DNA adducts. dG-C8-MeIQx and dG-C8-PhIP adducts have been identified in human tissues. In the female rat, administration of PhIP leads to mammary and colon tumors, whereas MeIQx induces liver tumors. Both humans and rats exhibit NAT2 genetic polymorphism yielding rapid and slow acetylator phenotypes. Because O-acetylation is an activation pathway, we hypothesized that MeIQx- and PhIP-induced DNA damage would be greater in tumor target tissues and higher in rapid than slow NAT2 acetylators. Adult female rapid and slow acetylator rats congenic at the Nat2 locus received a single dose of 25 mg/kg MeIQx or 50 mg/kg PhIP by gavage, and tissue DNA was isolated after 24 h. Deoxyribonucleoside adducts were identified and quantified by capillary liquid chromatography-tandem mass spectrometry using isotope dilution methods with deuterated internal standards. Major adducts were those bound to the C8 position of deoxyguanosine. dG-C8-PhIP DNA adducts were highest in colon, lowest in liver and did not significantly differ between rapid and slow acetylator congenic rats in any tissue tested. In contrast, dG-C8-MeIQx adducts were highest in liver and significantly (p < 0.001) higher in rapid acetylator liver than in slow acetylator liver. Our results are consistent with the tumor target specificity of PhIP and MeIQx and with increased susceptibility to MeIQx-induced liver tumors in rapid NAT2 acetylators.
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Affiliation(s)
- Kristin J Metry
- Department of Pharmacology and Toxicology, James Graham Brown Cancer Center and Center for Environmental Genomics and Integrative Biology, University of Louisville School of Medicine, Louisville, Kentucky, USA
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