Frandsen H, Grivas S, Turesky R J, Andersson R, Dragsted L O, Larsen J C
Institute of Toxicology, National Food Agency, Søborg, Denmark.
Carcinogenesis. 1994 Nov;15(11):2553-8. doi: 10.1093/carcin/15.11.2553.
The covalent binding of the mutagenic N2-hydroxy metabolite of the food mutagen 2-amino-3,4,8-trimethyl-3H-imidazo[4,5-f]quinoxaline (4,8-DiMeIQx) to 2'-deoxynucleosides and DNA was investigated in vitro and in vivo. N2-Hydroxy-4,8-DiMeIQx reacted to a small extent spontaneously with 2-deoxyguanosine. However, acetylation of N2-hydroxy-4,8-DiMeIQx with acetic anhydride to form the N2-acetoxy derivative prior to reaction with 2-deoxyguanosine resulted in much higher yield of adduct. N2-Acetoxy-4,8-DiMeIQx did not form adducts with 2'-deoxyadenosine, 2'-deoxycytidine or 2'-deoxythymidine. The adduct formed between the N2-OH metabolite of 4,8-DiMeIQx and 2-deoxyguanosine was analysed by mass spectrometry and NMR spectroscopy and the structure of the adduct was shown to be N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx. N2-Acetoxy-4,8-DiMeIQx reacted with calf thymus DNA and formed a covalently bound 4,8-DiMeIQx residue, which could not be removed by repeated precipitations or solvent extractions. The 4,8-DiMeIQx-DNA was hydrolysed enzymatically with nuclease P1/acid phosphatase and HPLC analysis showed that 70% of the bound mutagen was recovered as N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx. An additional minor adduct accounting for approximately 15% of the bound mutagen showed UV spectral characteristics similar to N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx and is probably an undigested oligomer. 32P-Postlabelling analysis of calf thymus DNA modified with 4,8-DiMeIQx in vitro and liver DNA from rats dosed with 50 mg/kg 4,8-DiMeIQx showed a similar adduct pattern. In both samples N2-(2'-deoxyguanosin-8-yl)-4,8-DiMeIQx accounted for 60-70% of the bound mutagen. Thus, these results show that 4,8-DiMeIQx similar to other heterocyclic amines form adducts with C-8 of guanine both in vitro and in vivo via its N2-OH metabolite.
对食品诱变剂2-氨基-3,4,8-三甲基-3H-咪唑并[4,5-f]喹喔啉（4,8-二甲基-IQx）的诱变N2-羟基代谢物与2'-脱氧核苷及DNA的共价结合进行了体内和体外研究。N2-羟基-4,8-二甲基-IQx与2'-脱氧鸟苷有少量自发反应。然而，在与2'-脱氧鸟苷反应之前，用乙酸酐将N2-羟基-4,8-二甲基-IQx乙酰化形成N2-乙酰氧基衍生物，可使加合物的产率大大提高。N2-乙酰氧基-4,8-二甲基-IQx不与2'-脱氧腺苷、2'-脱氧胞苷或2'-脱氧胸苷形成加合物。通过质谱和核磁共振光谱分析了4,8-二甲基-IQx的N2-OH代谢物与2'-脱氧鸟苷之间形成的加合物，结果表明该加合物的结构为N2-(2'-脱氧鸟苷-8-基)-4,8-二甲基-IQx。N2-乙酰氧基-4,8-二甲基-IQx与小牛胸腺DNA反应，形成一个共价结合的4,8-二甲基-IQx残基，该残基不能通过反复沉淀或溶剂萃取去除。用核酸酶P1/酸性磷酸酶对4,8-二甲基-IQx-DNA进行酶解，HPLC分析表明，70%的结合诱变剂以N2-(2'-脱氧鸟苷-8-基)-4,8-二甲基-IQx的形式回收。另一种占结合诱变剂约15%的次要加合物，其紫外光谱特征与N2-(2'-脱氧鸟苷-8-基)-4,8-二甲基-IQx相似，可能是一种未消化的寡聚物。对体外经4,8-二甲基-IQx修饰的小牛胸腺DNA和经50 mg/kg 4,8-二甲基-IQx给药的大鼠肝脏DNA进行32P后标记分析，结果显示加合物模式相似。在两个样品中，N2-(2'-脱氧鸟苷-8-基)-4,8-二甲基-IQx占结合诱变剂的60-70%。因此，这些结果表明，4,8-二甲基-IQx与其他杂环胺类似，在体内和体外均可通过其N2-OH代谢物与鸟嘌呤的C-8形成加合物。
