著者

祖父尼 俊雄 能美 健彦 太田 敏博 林 真

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.61-73, 2005-07-31

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The concept of a "biological threshold" is attracting interest as an evaluation criterion for the mutagenic activity of DNA-targeting mutagens. In this context, the concept is defined as "a concentration of a chemical which does not produce any damage through its inability to perform the necessary biochemical reactions, even though present at the target in finite amount". To clarify whether this criterion is indeed applicable to DNA-targeting mutagens, we re-evaluated the reverse mutation assay data using DNA repair-deficient bacterial strains, such as S. typhimurium strains lacking the O^6-methylguanine DNA methyltransferase genes (ada_<ST> and ogt_<ST>), the nucleotide excision repair gene (uvrB) or the 8-hydroxyguanine DNA glycosylase gene (mutM_<ST>), and E. coli strains lacking the nucleotide excision repair gene (uvrA). Mutagenic responses of 20 test chemicals including alkylating and non-alkylating agents were compared between the repair-deficient and their wild-type strains. All the alkylating agents, such as MNNG, ENNG, EMS, ENU, DMN and DEN, exhibited more sensible mutagenic responses in strains YG7108 (Δada_<ST>, Δogt_<ST>) and YG7113 (same as YG7108 but containing the plasmid pKM101) than in the parental strains TA1535 and TA100 (same as TA1535 but containing the pKM101), respectively. Upon applying MNNG, YG7108 showed about 2-100 fold increase in the number of His^+ revertants above the spontaneous level over the range of 0.00025-0.25μg/plate, whereas TA1535 did not show any significant increase in the number of His^+ revertants over the same dose range. On TA1535, an increasing tendency of the number of revertants was observed at 0.5μg/plate or above. This indicates an approximate 2,000-fold difference at the mutagenic concentration level between the wild-type and the repair-deficient strains. Other alkylating agents also showed significant differences in mutagenic responses between YG7108 and TA1535, or between YG7113 and TA100 respectively, with some variations among test chemicals. On the other hand, non-alkylating agents, such as 4-NQO, AF-2, 2-NF and MX, did not show any differences in the dose-response relationships between YG7113 and TA100. When non-alkylating agents, such as 4-NQO, 2-NF and MX were applied to TA1535 (ΔuvrB), TA1538 (ΔuvrB) and WP2uvrA (ΔuvrA), clearly different mutagenic responses, i.e. about 30- to 60-fold, were observed between the repair-deficient and the parental strains (TA1975, TA1978 and WP2, respectively). 4-NQO showed different mutagenic responses between YG3002 (ΔmutM_<ST>) and TA1975 (about 10-fold), though the application of other oxidative agents such as hydrogen peroxide resulted in less than 10-fold differences. The present results indicate that the wild-type strains having normal repair capacity show no gene mutation induction at the concentrations at which gene mutations are clearly induced in the repair-deficient strains through DNA damage. Thus, the present results suggest the existence of a "biological threshold" below which no mutagenic response is induced by DNA-targeting mutagenic substances.

著者

祖父尼 俊雄 能美 健彦 太田 敏博 林 真

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.27, no.2, pp.61-73, 2005 (Released:2005-12-26)

参考文献数

23

被引用文献数

9 9 1

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The concept of a “biological threshold” is attracting interest as an evaluation criterion for the mutagenic activity of DNA-targeting mutagens. In this context, the concept is defined as “a concentration of a chemical which does not produce any damage through its inability to perform the necessary biochemical reactions, even though present at the target in finite amount”. To clarify whether this criterion is indeed applicable to DNA-targeting mutagens, we re-evaluated the reverse mutation assay data using DNA repair-deficient bacterial strains, such as S. typhimurium strains lacking the O6-methylguanine DNA methyltransferase genes (adaST and ogtST), the nucleotide excision repair gene (uvrB) or the 8-hydroxyguanine DNA glycosylase gene (mutMST), and E. coli strains lacking the nucleotide excision repair gene (uvrA). Mutagenic responses of 20 test chemicals including alkylating and non-alkylating agents were compared between the repair-deficient and their wild-type strains.All the alkylating agents, such as MNNG, ENNG, EMS, ENU, DMN and DEN, exhibited more sensible mutagenic responses in strains YG7108 (ΔadaST, ΔogtST) and YG7113 (same as YG7108 but containing the plasmid pKM101) than in the parental strains TA1535 and TA100 (same as TA1535 but containing the pKM101), respectively. Upon applying MNNG, YG7108 showed about 2-100 fold increase in the number of His+ revertants above the spontaneous level over the range of 0.00025-0.25 μg/plate, whereas TA1535 did not show any significant increase in the number of His+ revertants over the same dose range. On TA1535, an increasing tendency of the number of revertants was observed at 0.5 μg/plate or above. This indicates an approximate 2,000-fold difference at the mutagenic concentration level between the wild-type and the repairdeficient strains. Other alkylating agents also showed significant differences in mutagenic responses between YG7108 and TA1535, or between YG7113 and TA100 respectively, with some variations among test chemicals. On the other hand, non-alkylating agents, such as 4-NQO, AF-2, 2-NF and MX, did not show any differences in the dose-response relationships between YG7113 and TA100. When non-alkylating agents, such as 4-NQO, 2-NF and MX were applied to TA1535 (ΔuvrB), TA1538 (ΔuvrB) and WP2uvrA (ΔuvrA), clearly different mutagenic responses, i.e. about 30- to 60-fold, were observed between the repair-deficient and the parental strains (TA1975, TA1978 and WP2, respectively). 4-NQO showed different mutagenic responses between YG3002 (ΔmutMST) and TA1975 (about 10-fold), though the application of other oxidative agents such as hydrogen peroxide resulted in less than 10-fold differences. The present results indicate that the wild-type strains having normal repair capacity show no gene mutation induction at the concentrations at which gene mutations are clearly induced in the repair-deficient strains through DNA damage. Thus, the present results suggest the existence of a “biological threshold” below which no mutagenic response is induced by DNA-targeting mutagenic substances.

著者

能美 健彦 清水 雅富 グルーズ ピーター

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.2, pp.159-165, 2004 (Released:2005-12-21)

参考文献数

47

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Altered oxidative metabolism is a property of many tumor cells. Oxidation of dNTP pool as well as DNA is a source of genome instability. We report here that two Y-family DNA polymerases of the archaeon Sulfolobus solfataricus strains P1 and P2 incorporate oxidized dNTPs into nascent DNA in an erroneous manner: the polymerases exclusively incorporate 8-hydroxy-dGTP opposite template A, and incorporate 2-hydroxy-dATP opposite G and T. Extension onto the incorporated analogs is only slightly reduced. Human DNA polymerase η, a member of human Y-family DNA polymerases, incorporates the oxidized dNTPs in a similar erroneous manner. These DNA polymerases are shown to bypass a variety of DNA lesions. Thus, our results suggest the Y-family DNA polymerases promote mutagenesis through the erroneous incorporation of the oxidized dNTPs during DNA synthesis in addition to facilitating translesion DNA synthesis.

著者

林 真 長尾 美奈子 祖父尼 俊雄 森田 健 能美 健彦 本間 正充 宇野 芳文 葛西 宏 佐々木 有 太田 敏博 田中 憲穂 中嶋 圓 布柴 達夫

出版者

日本環境変異原学会

雑誌

環境変異原研究 (ISSN:09100865)

巻号頁・発行日

vol.26, no.3, pp.275-283, 2004-12-20

被引用文献数

1

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食品関連物質の遺伝毒性の評価,解釈をするための戦略を構築するため,日本環境変異原学会に臨時委員会を設立し,厚生労働科学研究費補助金食品安全性確保研究事業「既存添加物等における遺伝毒性評価のための戦略構築に関する研究」の研究班と共同し,定例の検討会議を毎月開催し,統一的な考えについて検討を続けている.本戦略を構築するためのモデルとして,コウジ酸を選択し,評価に必要と考えられる試験を実施し,その結果の評価,解釈を国際的議論のもとに標準化可能なものとするため,海外から指導的立場にある研究者をコンサルタントとして招聘し,議論,提言を受けた.本臨時委員会の活動は3年計画で進められており,現在は約1年半が経過したところである.ここでは,本委員会の設置意図を中心に活動の中間報告を行う.