title: In vitro metabolism of N'-Nitrosonornicotine catalyzed by cytochrome P450 2A13 and its inhibition by nicotine, N'-Nitrosoanatabine and N'-Nitrosoanabasine.
abstract: N'-Nitrosonornicotine (NNN) is considered to be one of the most carcinogenic compounds of the four conventionally measured tobacco-specific N-nitrosamines (TSNAs). In order to evaluate the significance of metabolic activation for the carcinogenic potential of NNN, its catalysis by different phase I enzymes and its interaction with nicotine and nicotine-derived TSNAs need to be investigated. Using an in vitro model system, NNN was found to interact with various cytochrome P450 enzymes, predominantly CYP2A13. Mass-spectrometric analysis confirmed the presence of various predicted NNN metabolites, including 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and 4-hydroxy-4-(3-pyridyl)-butyric acid (hydroxy acid) but little amount of 4-oxo-4-(3-pyridyl) butanal (OPB), which was somewhat different from in vitro NNK metabolism. Addition of nicotine, N'-Nitrosoanatabine (NAT), N'-Nitrosoanabasine (NAB) resulted in a competitive inhibition for NNN metabolism. The inhibition constant Ki value was calculated as 0.98 μM (nicotine), 1.37 μM (NAT), 0.71 μM (NAB) for HPB formation, 1.35 μM (nicotine), 1.35 μM (NAT), 1.01 μM (NAB) for hydroxy acid formation and 8.40 μM (nicotine), 3.40 μM (NAT), 3.04 μM (NAB) for OPB formation, respectively. These results implied that CYP2A13 is the most efficient enzyme to metabolize NNN in vitro and structurally similar tobacco constitutes including nicotine, NAT and NAB influence the metabolic activation of NNN, which may further interfere in its carcinogenicity.
authors: Shanghai Tobacco Group Corporation of CNTC, 99 Wansheng South Street, Tongzhou District, Beijing 101121, China.
authors: Xingyu
authors: X
authors: Liu
authors: Shanghai Tobacco Group Corporation of CNTC, 99 Wansheng South Street, Tongzhou District, Beijing 101121, China.
authors: Jie
authors: J
authors: Zhang
authors: Dalian Institute of Chemical Physics, University of Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, Liaoning, China.
authors: Limeng
authors: L
authors: Wang
authors: Jiangxi Provincial Maternal and Child Health Hospital, 318 Bayi Road, Nanchang 330006, Jiangxi, China.
authors: Bicheng
authors: B
authors: Yang
authors: Shanghai Tobacco Group Corporation of CNTC, 99 Wansheng South Street, Tongzhou District, Beijing 101121, China.
authors: Chen
authors: C
authors: Zhang
authors: Shanghai Tobacco Group Corporation of CNTC, 99 Wansheng South Street, Tongzhou District, Beijing 101121, China. Electronic address: correspondingbj@sina.com.
authors: Wei
authors: W
authors: Liu
authors: Shanghai Tobacco Group Corporation of CNTC, 99 Wansheng South Street, Tongzhou District, Beijing 101121, China.
authors: Jun
authors: J
authors: Zhou
mesh_terms: D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D055162:Biocatalysis / Q000187:drug effects; D002074:Butanones / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D053858:Metabolic Networks and Pathways / Q000187:drug effects; D055442:Metabolome / Q000187:drug effects; D009538:Nicotine / Q000494:pharmacology*; D009602:Nitrosamines / Q000037:antagonists & inhibitors* / Q000378:metabolism* / Q000494:pharmacology*; D011725:Pyridines / Q000378:metabolism
chemical_list: D002074:Butanones; D009602:Nitrosamines; D011725:Pyridines; C010257:N'-nitrosoanabasine; D009538:Nicotine; C032978:N'-nitrosoanatabine; D001189:Aryl Hydrocarbon Hydroxylases; C414206:CYP2A13 protein, human; C008655:N'-nitrosonornicotine; C482281:4-hydroxy-1-(3-pyridyl)-1-butanone
keywords: Cytochrome P450; Inhibition; Metabolism; NNN