Role of CYP2A13 in the bioactivation and lung tumorigenicity of the tobacco-specific lung procarcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone: In vivo studies using a CYP2A13-humanized mouse model

Vandana Megaraj, Xin Zhou, Fang Xie, Zhihua Liu, Weizhu Yang, Xinxin Ding

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), which is abundant in tobacco smoke, is a potent lung procarcinogen. The present study was aimed to prove that transgenic expression of human cytochrome P450 2A13 (CYP2A13), known to be selectively expressed in the respiratory tract and be the most efficient enzyme for NNK bioactivation in vitro, will enhance NNK bioactivation and NNK-induced tumorigenesis in the mouse lung. Kinetic parameters of NNK bioactivation in vitro and incidence of NNK-induced lung tumors in vivo were determined for wild-type, Cyp2a5-null and CYP2A13-humanized (CYP2A13-transgenic/Cyp2a5-null) mice. As expected, in both liver and lung microsomes, the loss of CYP2A5 resulted in significant increases in Michaelis constant (Km) values for the formation of 4-oxo-4-(3-pyridyl)-butanal, representing the reactive intermediate that can lead to the formation of O6-methylguanine (O6-mG) DNA adducts; however, the gain of CYP2A13 at a fraction of the level of mouse lung CYP2A5 led to recovery of the activity in the lung, but not in the liver. The levels of O6-mG, the DNA adduct highly correlated with lung tumorigenesis, were significantly higher in the lungs of CYP2A13-humanized mice than in Cyp2a5-null mice. Moreover, incidences of lung tumorigenesis were significantly greater in CYP2A13-humanized mice than in Cyp2a5-null mice, and the magnitude of the differences in incidence was greater at low (30 mg/kg) than at high (200 mg/ kg) NNK doses. These results indicate that CYP2A13 is a low Km enzyme in catalyzing NNK bioactivation in vivo and support the notion that genetic polymorphisms of CYP2A13 can influence the risks of tobacco-induced lung tumorigenesis in humans.

Original languageEnglish (US)
Pages (from-to)137
Number of pages1
JournalCarcinogenesis
Volume35
Issue number1
DOIs
StatePublished - Jan 1 2014
Externally publishedYes

ASJC Scopus subject areas

  • Cancer Research

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