Evaluation of Nitrosamide Formation in the Cytochrome P450-Mediated Metabolism of Tobacco-Specific Nitrosamines

被引:24
作者
Carlson, Erik S. [1 ,2 ]
Upadhyaya, Pramod [1 ]
Hecht, Stephen S. [1 ]
机构
[1] Univ Minnesota, Masonic Canc Ctr, 2231 Sixth St SE,2-210 CCRB, Minneapolis, MN 55455 USA
[2] Univ Minnesota, Sch Med, Dept Pharmacol, 321 Church St SE,6-120 Jackson Hall, Minneapolis, MN 55455 USA
关键词
DNA ADDUCT FORMATION; ACTIVATED DOUBLE-BONDS; ALKYL-N-NITROSOAMIDES; F344; RATS; 4-(METHYLNITROSAMINO)-1-(3-PYRIDYL)-1-BUTANONE; CARCINOGENICITY; OXIDATION; ALDEHYDES; NICOTINE; LIVER;
D O I
10.1021/acs.chemrestox.6b00384
中图分类号
R914 [药物化学];
学科分类号
100701 ;
摘要
N'-Nitrosonornicotine (NNN) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) are carcinogenic tobacco-specific nitrosamines believed to play a vital role in the initiation of tobacco-related cancers. For their carcinogenicities to be exhibited, both NNN and NNK must be metabolically activated by cytochrome P450s, specifically P450 2A6 and P450 2A13, respectively. Prior research has focused on alpha-hydroxylation, which leads to the formation of several DNA adducts that have been identified and quantified in vivo. However, some studies indicate that P450s can retain substrates within their active sites and perform processive oxidation. For nitrosamines, this would oxidize the highly unstable alpha-hydroxynitrosamines to potentially more stable nitrosamides, which could also alkylate DNA. Thus, we hypothesized that both NNN and NNK are processively oxidized in vitro to nitrosamides by P450 2A6 and P450 2A13, respectively. To test this hypothesis, we synthesized the NNN- and NNK-derived nitrosamides, determined their half-lives at pH 7.4 and 37 degrees C, and monitored for nitrosamide formation in an in vitro P450 system with product analysis by LC/NSI+-HRMS/MS. Half-lives of the nitrosamides were determined by HPLC-UV and ranged from 7-35 min, which is more than 40 times longer than the corresponding a-hydroxynitrosamines. Incubation of NNN in the P450 2A6 system resulted in the formation of the nitrosamide N'-nitrosonorcotinine (NNC) at low levels. Similarly, the nitrosamide 4-(methylnitrosamino)-1-(3-pyridyl)-1,4-butanedione (CH2-oxo-NNK) was detected in low amounts in the incubation of NNK with the P450 2A13 system. The other possible NNK-derived nitrosamide, 4-(nitrosoformamido)-1-(3-pyridyl)-1-butanone (CH3-oxo-NNK), was not observed in the P450 2A13 reactions. CH2-oxo-NNK readily formed O(6)meGua in reactions with dGuo and calf thymus DNA. These results demonstrate that NNC and CH2-oxo-NNK are novel metabolites of NNN and NNK, respectively. Though low-forming, their increased stability may allow for mutagenic DNA damage in vivo. More broadly, this study provides the first account of a cytochrome P450-mediated conversion of nitrosamines to nitrosamides, which warrants further studies to determine how general this phenomenon is in nitrosamine metabolism.
引用
收藏
页码:2194 / 2205
页数:12
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