Glatt Hansruedi, Pabel Ulrike, Meinl Walter, Frederiksen Hanne, Frandsen Henrik, Muckel Eva
German Institute of Human Nutrition (DIfE) Potsdam-Rehbrücke, Department of Toxicology, Arthur-Scheunert-Allee 114-116, D-14558 Nuthetal, Germany.
Carcinogenesis. 2004 May;25(5):801-7. doi: 10.1093/carcin/bgh077. Epub 2004 Jan 16.
2-Amino-3-methyl-9H-pyrido[2,3-b]indole (MeAalphaC) and some metabolites were investigated for mutagenicity in mammalian cell lines and bacterial strains engineered for the expression of human enzymes. MeAalphaC induced gene mutations (studied at the hprt locus) in Chinese hamster V79-derived cells co-expressing cytochrome (CYP) 1A2 and sulphotransferase (SULT) 1A1 even at a concentration of 30 nM, but was inactive in cells co-expressing CYP1A2 and N-acetyltransferase (NAT) 1 or 2. MeAalphaC, tested in the presence of rat liver post-mitochondrial fraction, showed strongly enhanced mutagenicity in a Salmonella typhimurium strain expressing human SULT1A1 compared with the control (recipient) strain TA1538/1,8-DNP (deficient in endogenous acetyltransferase). Mutagenicity was also enhanced, although to a lesser extent, when NAT2 was expressed in the latter strain. The metabolite, 2-hydroxylamino-3-methyl-9H-pyrido[2,3-b]indole (N-OH-MeAalphaC) was a direct mutagen to strains TA1538 and TA1538/ 1,8-DNP. This mutagenicity was strongly enhanced in corresponding strains expressing SULT1A1. A moderate enhancement was observed when SULT1A2, SULT1B1, SULT1C2 or NAT2 were expressed in strain TA1538. The remaining enzymes studied (SULT1A3, 1C1, 1E1, 2A1, 2B1a, 2B1b, 4A1 and NAT1) did not indicate any activation of N-OH-MeAalphaC. Preliminary mutagenicity experiments in SULT-expressing S.typhimurium strains were conducted with other hydroxylated metabolites of MeAalphaC. The phenols, 6- and 7-hydroxy-MeAalphaC, were inactive under the conditions studied. The benzylic alcohol, 2-amino-3-hydroxymethyl-9H-pyrido[2,3-b]indole, was mutagenic in a strain expressing SULT1A1, but its activity was much weaker than that of N-OH-MeAalphaC. Thus, N-hydroxylation (e.g. mediated by CYP1A2) and sulpho conjugation (primarily mediated by SULT1A1) was the dominating activation pathway of MeAalphaC in model systems engineered for human enzymes. Some other SULT forms as well as NAT2 were also capable of activating N-OH-MeAalphaC, although with much lower efficiency than SULT1A1. Another minor activation pathway involved benzylic hydroxylation followed by sulpho conjugation by SULT1A1.
对2-氨基-3-甲基-9H-吡啶并[2,3-b]吲哚（MeAαC）及其一些代谢产物在表达人酶的哺乳动物细胞系和细菌菌株中的致突变性进行了研究。即使在浓度为30 nM时，MeAαC也能在共表达细胞色素（CYP）1A2和磺基转移酶（SULT）1A1的中国仓鼠V79衍生细胞中诱导基因突变（在hprt基因座处研究），但在共表达CYP1A2和N-乙酰转移酶（NAT）1或2的细胞中无活性。在大鼠肝脏线粒体后组分存在的情况下进行测试时，与对照（受体）菌株TA1538/1,8-DNP（内源性乙酰转移酶缺陷）相比，MeAαC在表达人SULT1A1的鼠伤寒沙门氏菌菌株中显示出强烈增强的致突变性。当在后者菌株中表达NAT2时，致突变性也有所增强，尽管程度较小。代谢产物2-羟基氨基-3-甲基-9H-吡啶并[2,3-b]吲哚（N-OH-MeAαC）对菌株TA1538和TA1538/1,8-DNP是直接诱变剂。在表达SULT1A1的相应菌株中，这种致突变性得到了强烈增强。当在菌株TA1538中表达SULT1A2、SULT1B1、SULT1C2或NAT2时，观察到适度增强。所研究的其余酶（SULT1A3、1C1、1E1、2A1、2B1a、2B1b、4A1和NAT1）未显示N-OH-MeAαC有任何活化作用。用MeAαC的其他羟基化代谢产物在表达SULT的鼠伤寒沙门氏菌菌株中进行了初步致突变性实验。酚类物质6-羟基-MeAαC和7-羟基-MeAαC在所研究的条件下无活性。苄醇2-氨基-3-羟甲基-9H-吡啶并[2,3-b]吲哚在表达SULT1A1的菌株中具有致突变性，但其活性远低于N-OH-MeAαC。因此，N-羟基化（例如由CYP1A2介导）和磺基结合（主要由SULT1A1介导）是在为表达人酶而构建的模型系统中MeAαC的主要活化途径。其他一些SULT形式以及NAT2也能够活化N-OH-MeAαC，尽管效率远低于SULT1A1。另一个次要的活化途径涉及苄基羟基化，随后由SULT1A1进行磺基结合。
