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Zhang S, Coffing SL, Gunther WC, Homiski ML, Spellman RA, Van P, Schuler M. Assessing the genotoxicity of N-nitrosodiethylamine with three in vivo endpoints in male Big Blue® transgenic and wild-type C57BL/6N mice. ENVIRONMENTAL AND MOLECULAR MUTAGENESIS 2024. [PMID: 39012003 DOI: 10.1002/em.22615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Revised: 06/11/2024] [Accepted: 06/14/2024] [Indexed: 07/17/2024]
Abstract
The detection of N-nitrosamines in drug products has raised global regulatory interest in recent years due to the carcinogenic potential of some nitrosamines in animals and a need to identify a testing strategy has emerged. Ideally, methods used would allow for the use of quantitative analysis of dose-response data from in vivo genotoxicity assays to determine a compound-specific acceptable intake for novel nitrosamines without sufficient carcinogenicity data. In a previous study we compared the dose-response relationships of N-nitrosodiethylamine (NDEA) in three in vivo genotoxicity endpoints in rats. Here we report a comparison of NDEA's genotoxicity profile in mice. Big Blue® mice were administered NDEA at doses of 0.001, 0.01, 0.1, 1 and 3 mg/kg/day by oral gavage for 28 days followed by 3 days of expression. Statistically significant increases in the NDEA induced mutations were detected by both the transgenic rodent mutation assay (TGR) using the cII endpoint and by duplex sequencing in the liver but not bone marrow of mice. In addition, administration of NDEA for two consecutive days in male C57BL/6N mice caused elevated DNA damage levels in the liver as measured by % tail DNA in comet assay. The benchmark dose (BMD) analysis shows a BMDL50 of 0.03, 0.04 and 0.72 mg/kg/day for TGR, duplex sequencing and comet endpoints, respectively. Overall, this study demonstrated a similar genotoxicity profile of NDEA between mice and rats and provides a reference that can be used to compare the potential potency of other novel nitrosamines for the induction of gene mutations.
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Affiliation(s)
- Shaofei Zhang
- Pfizer Research, Development, and Medical, Groton, Connecticut, USA
| | | | | | | | | | - Phu Van
- TwinStrand Biosciences, Inc., Seattle, Washington, USA
| | - Maik Schuler
- Pfizer Research, Development, and Medical, Groton, Connecticut, USA
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Jatsenko T, Sidorenko J, Saumaa S, Kivisaar M. DNA Polymerases ImuC and DinB Are Involved in DNA Alkylation Damage Tolerance in Pseudomonas aeruginosa and Pseudomonas putida. PLoS One 2017; 12:e0170719. [PMID: 28118378 PMCID: PMC5261740 DOI: 10.1371/journal.pone.0170719] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 01/09/2017] [Indexed: 12/12/2022] Open
Abstract
Translesion DNA synthesis (TLS), facilitated by low-fidelity polymerases, is an important DNA damage tolerance mechanism. Here, we investigated the role and biological function of TLS polymerase ImuC (former DnaE2), generally present in bacteria lacking DNA polymerase V, and TLS polymerase DinB in response to DNA alkylation damage in Pseudomonas aeruginosa and P. putida. We found that TLS DNA polymerases ImuC and DinB ensured a protective role against N- and O-methylation induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in both P. aeruginosa and P. putida. DinB also appeared to be important for the survival of P. aeruginosa and rapidly growing P. putida cells in the presence of methyl methanesulfonate (MMS). The role of ImuC in protection against MMS-induced damage was uncovered under DinB-deficient conditions. Apart from this, both ImuC and DinB were critical for the survival of bacteria with impaired base excision repair (BER) functions upon alkylation damage, lacking DNA glycosylases AlkA and/or Tag. Here, the increased sensitivity of imuCdinB double deficient strains in comparison to single mutants suggested that the specificity of alkylated DNA lesion bypass of DinB and ImuC might also be different. Moreover, our results demonstrated that mutagenesis induced by MMS in pseudomonads was largely ImuC-dependent. Unexpectedly, we discovered that the growth temperature of bacteria affected the efficiency of DinB and ImuC in ensuring cell survival upon alkylation damage. Taken together, the results of our study disclosed the involvement of ImuC in DNA alkylation damage tolerance, especially at low temperatures, and its possible contribution to the adaptation of pseudomonads upon DNA alkylation damage via increased mutagenesis.
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Affiliation(s)
- Tatjana Jatsenko
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
- * E-mail: (MK); (TJ)
| | - Julia Sidorenko
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Signe Saumaa
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
| | - Maia Kivisaar
- Department of Genetics, Institute of Molecular and Cell Biology, University of Tartu, Tartu, Estonia
- * E-mail: (MK); (TJ)
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Geigle SN, Wyss LA, Sturla SJ, Gillingham DG. Copper carbenes alkylate guanine chemoselectively through a substrate directed reaction. Chem Sci 2017; 8:499-506. [PMID: 28451197 PMCID: PMC5341205 DOI: 10.1039/c6sc03502g] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Accepted: 09/02/2016] [Indexed: 12/19/2022] Open
Abstract
Cu(i) carbenes derived from α-diazocarbonyl compounds lead to selective alkylation of the O6 position in guanine (O6-G) in mono- and oligonucleotides. Only purine-type lactam oxygens are targeted - other types of amides or lactams are poorly reactive under conditions that give smooth alkylation of guanine. Mechanistic studies point to N7G as a directing group that controls selectivity. Given the importance of O6-G adducts in biology and biotechnology we expect that Cu(i)-catalyzed O6-G alkylation will be a broadly used synthetic tool. While the propensity for transition metals to increase redox damage is well-appreciated, our results suggest that transition metals might also increase the vulnerability of nucleic acids to alkylation damage.
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Affiliation(s)
- Stefanie N Geigle
- Department of Chemistry , University of Basel , St. Johanns-Ring 19 , CH-4056 , Basel , Switzerland .
| | - Laura A Wyss
- Department of Health Sciences and Technology , ETH Zurich , Schmelzbergstrasse 9 , CH-8092 Zurich , Switzerland
| | - Shana J Sturla
- Department of Health Sciences and Technology , ETH Zurich , Schmelzbergstrasse 9 , CH-8092 Zurich , Switzerland
| | - Dennis G Gillingham
- Department of Chemistry , University of Basel , St. Johanns-Ring 19 , CH-4056 , Basel , Switzerland .
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Fang Q, Kanugula S, Pegg AE. Function of domains of human O6-alkylguanine-DNA alkyltransferase. Biochemistry 2006; 44:15396-405. [PMID: 16285744 DOI: 10.1021/bi051460d] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
O6-Alkylguanine-DNA alkyltransferase (AGT) is an important DNA repair protein that protects from alkylating agents by converting O6-alkylguanine to guanine forming S-methylcysteine in the AGT protein. The crystal structure of human AGT shows clearly the presence of two domains. The N-terminal domain contains a bound zinc atom, and zinc binding confers a mechanistic enhancement to repair activity, but this domain has no known function. The C-terminal domain contains all residues so far implicated in alkyl transfer including the cysteine acceptor site (Cys145), the O6-alkylguanine binding pocket, and a DNA binding domain. We have expressed and purified the two domains of human AGT separately. The C-terminal domain was totally inactive in vitro, but good activity forming S-alkylcysteine at Cys145 was obtained after recombination with the N-terminal domain via a freeze-thawing procedure. This suggests that the N-terminal domain plays a critical structural role in maintaining an active configuration of the C-terminal domain. However, this C-terminal domain alone had activity in protecting against the cytotoxic and mutagenic activity of the methylating agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) when expressed in Escherichia coli cells lacking endogenous AGT, suggesting that other proteins can fulfill this function. Remarkably, the free N-terminal domain of hAGT was able to repair O6-alkylguanine in vitro via alkyl transfer provided that zinc ions were present. The N-terminal domain was also able to produce moderate protection from MNNG when expressed in E. coli. This cryptic Zn2+-dependent DNA repair activity may be relevant to the evolution and function of AGTs.
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Affiliation(s)
- Qingming Fang
- Department of Cellular and Molecular Physiology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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Cheng B, Wang SY. Expression of DNA repair genes hMTH1 and hOGG1 and repair of oxidative damage of DNA in hepatocellular carcinoma. Shijie Huaren Xiaohua Zazhi 2003; 11:272-275. [DOI: 10.11569/wcjd.v11.i3.272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
AIM: To study the regulatory effect of expression of hMTH1 and hOGG1 genes on the oxidative DNA-adduct 8-OHdG levels in hepatocellular carcinoma (HCC) and non-tumourous liver tissue in order to elucidate the role of the DNA repair enzymes in hepatocarcinogenesis.
METHODS: A reverse transcription (RT)/real-time-polymerase chain reaction (PCR) assay was used to semi-quantify mRNA of hMTH1 and hOGG1 in HCC and non-tumourous liver tissue from 23 patients with HCC. 8-OHdG levels were determined by HPLC/ECD.
RESULTS: The median of 8-OHdG levels in non-tumourousliver tissue was significantly (133 vs 56 nmol/g DNA, P < 0.01) higher than that in HCC tissue. This was correlated with the severity of inflammation in non-tumourous liver tissues. The expression of hMTH1 was significantly (0.476 vs 0.256, P < 0.05) higher in HCC tissue than that in non-tumourous liver tissue. No difference of expression of hOGG1 between non-tumourous liver and HCC tissue was seen. A significant correlation was detected between the expression of hMTH1 and hOGG1 (r = 0.81, P < 0.01).
CONCLUSION: Elevated 8-OHdG levels in non-tumourousliver are likely due to the increased generation of reactive oxygen intermediates by infiltrating inflammatory cells. The expression of DNA repair enzymes hOGG1 and hMTH1 may involve cooperatively in the repair oxidative DNA adduct 8-OHdG and have a potential role in hepatocarcinogenesis.
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Liu L, Pegg AE, Williams KM, Guengerich FP. Paradoxical enhancement of the toxicity of 1,2-dibromoethane by O6-alkylguanine-DNA alkyltransferase. J Biol Chem 2002; 277:37920-8. [PMID: 12151404 DOI: 10.1074/jbc.m205548200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The presence of the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT) paradoxically increases the mutagenicity and cytotoxicity of 1,2-dibromoethane (DBE) in Escherichia coli. This enhancement of genotoxicity did not occur when the inactive C145A mutant of human AGT (hAGT) was used. Also, hAGT did not enhance the genotoxicity of S-(2-haloethyl)glutathiones that mimic the reactive product of the reaction of DBE with glutathione, which is catalyzed by glutathione S-transferase. These experiments support a mechanism by which hAGT activates DBE. Studies in vitro showed a direct reaction between purified recombinant hAGT and DBE resulting in a loss of AGT repair activity and a formation of an hAGT-DBE conjugate at Cys(145). A 2-hydroxyethyl adduct was found by mass spectrometry to be present in the Gly(136)-Arg(147) peptide from tryptic digests of AGT reacted with DBE. Incubation of AGT with DBE and oligodeoxyribonucleotides led to the formation of covalent AGT-oligonucleotide complexes. These results indicate that DBE reacts at the active site of AGT to generate an S-(2-bromoethyl) intermediate, which forms a highly reactive half-mustard at Cys(145). In the presence of DNA, the DNA-binding function of AGT facilitates formation of DNA adducts. In the absence of DNA, the intermediate undergoes hydrolytic decomposition to form AGT-Cys(145)-SCH(2)CH(2)OH.
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Affiliation(s)
- Liping Liu
- Department of Cellular and Molecular Physiology, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033, USA
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Abstract
The predominant pathway for the repair of O(6)-methylguanine in DNA is via the activity of an alkyltransferase protein that transfers the methyl group to a cysteine acceptor site on the protein itself. This review article describes recent studies on this alkyltransferase. The protein repairs not only methyl groups but also 2-chloroethyl-, benzyl- and pyridyloxobutyl-adducts. It acts on double-stranded DNA by flipping the O(6)-guanine adduct out of the DNA helix and into a binding pocket. The free base, O(6)-benzylguanine, is able to bind in this pocket and react with the cysteine, rendering it an effective inactivator of mammalian alkyltransferases. The alkylated form of the protein is rapidly degraded by the ubiquitin/proteasomal system. Some tumor cells do not express alkyltransferase despite having an intact gene. Methylation of key sites in CpG-rich islands in the promoter region are involved in this silencing and a change in the nuclear localization of an enhancer binding protein may also contribute. The alkyltransferase promoter contains Sp1, GRE and AP-1 sites and is slightly inducible by glucocorticoids and protein kinase C activators. There is a complex relationship between p53 and alkyltransferase expression with p53 mediating a rise in alkyltransferase in response to ionizing radiation but having no clear effect on basal levels. DNA adducts at the O(6)-position of guanine are a major factor in the carcinogenic, mutagenic, apoptopic and clastogenic actions of methylating agents and chloroethylating agents. Studies with transgenic mice in which alkyltransferase levels are increased or decreased confirm the importance of this repair pathway in protecting against carcinogenesis. Alkyltransferase activity in tumors protects them from therapeutic agents such as temozolomide and BCNU. This resistance is abolished by O(6)-benzylguanine and this drug is currently in clinical trials to enhance cancer chemotherapy by these agents. Studies are in progress to reduce the toxicity of such therapy towards the bone marrow by gene therapy to express alkyltransferases with mutations imparting resistance to O(6)-benzylguanine at high levels in marrow stem cells. Several polymorphisms in the human alkyltransferase gene have been identified but the significance of these in terms of alkyltransferase action is currently unknown.
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Affiliation(s)
- A E Pegg
- Departments of Cellular and Molecular Physiology and Pharmacology, Milton S. Hershey Medical Center, Pennsylvania State University College of Medicine, P.O. Box 850, 500 University Drive, Hershey, PA, USA.
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