Carcinogenicity and DNA adduct formation of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and enantiomers of its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in F-344 rats

Abstract

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is metabolized to enantiomers of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), found in the urine of virtually all people exposed to tobacco products. We assessed the carcinogenicity in male F-344 rats of (R)-NNAL (5 ppm in drinking water), (S)-NNAL (5 ppm), NNK (5 ppm) and racemic NNAL (10 ppm) and analyzed DNA adduct formation in lung and pancreas of these rats after 10, 30, 50 and 70 weeks of treatment. All test compounds induced a high incidence of lung tumors, both adenomas and carcinomas. NNK and racemic NNAL were most potent; (R)-NNAL and (S)-NNAL had equivalent activity. Metastasis was observed from primary pulmonary carcinomas to the pancreas, particularly in the racemic NNAL group. DNA adducts analyzed were O (2)-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O (2)-POB-dThd), 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine(7-POB-Gua),O (6)-[4-(3-pyridyl)-4-oxobut-1-yl]deoxyguanosine(O (6)-POB-dGuo),the 4-(3-pyridyl)-4-hydroxybut-1-yl(PHB)adductsO (2)-PHB-dThd and 7-PHB-Gua, O (6)-methylguanine (O (6)-Me-Gua) and 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB)-releasing adducts. Adduct levels significantly decreased with time in the lungs of rats treated with NNK. Pulmonary POB-DNA adducts and O (6)-Me-Gua were similar in rats treated with NNK and (S)-NNAL; both were significantly greater than in the (R)-NNAL rats. In contrast, pulmonary PHB-DNA adduct levels were greatest in the rats treated with (R)-NNAL. Total pulmonary DNA adduct levels were similar in (S)-NNAL and (R)-NNAL rats. Similar trends were observed for DNA adducts in the pancreas, but adduct levels were significantly lower than in the lung. The results of this study clearly demonstrate the potent pulmonary carcinogenicity of both enantiomers of NNAL in rats and provide important new information regarding DNA damage by these compounds in lung and pancreas.

γ-H2AX is a sensitive marker of DNA damage induced by metabolically activated 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

“…a-Hydroxylation occurs at either methylene or the methyl carbon adjacent to the N-nitroso group to generate unstable intermediates. These intermediates decompose to form electrophilic methyl-, pyridyloxobutyl-, and pyridylhydroxybutyldiazonium ions, which can attack DNA molecules, resulting in the formation of methyl-DNA and pyridyloxo(hydroxyl)butyl-DNA adducts (Balbo et al, 2014a;Chiang et al, 2011;Jalas et al, 2005). Inhibition of a-hydroxylation reduces the levels of these DNA adducts and of NNK-dependent tumor induction (Jalas et al, 2003;Staretz et al, 1997).…”

“…Some DNA adducts formed during NNK metabolism contribute to lung tumorigenesis (Balbo et al, 2014a). NNK metabolism mainly occurs via hydroxylation of one of the two a-carbons of the N-nitroso group by CYP2A6 and CYP2A13 (Chiang et al, 2011;Jalas et al, 2005), and leads to the formation of reactive intermediates that can form either DNA adducts (methyl DNA adducts and pyridyloxo(hydroxyl)butyl DNA adducts) or stable metabolites (e.g., 4-hydroxy-1-(3-pyridyl)-1-butanone and 4-oxo-1-(3-pyridyl)-1-butanone).…”

Methyl DNA Phosphate Adduct Formation in Rats Treated Chronically with 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and Enantiomers of Its Metabolite 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol

“…2 NNK is metabolized to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, 2 , Figure 1), which is also a potent lung carcinogen with activity similar to NNK. 1,3,4 Both NNK and NNAL are metabolically activated by α-hydroxylation catalyzed by cytochrome P450s to form a series of intermediates which react with DNA to form adducts. The formation of these DNA adducts can cause miscoding and mutations in growth control genes, 5−7 which is a critical step in carcinogenesis by NNK and NNAL.…”

“…12 The major POB and PHB base adducts and B 1 p(POB)B 2 and B 1 p(PHB)B 2 phosphate adducts have been characterized, and their levels in NNK- and NNAL-treated animals have been quantified in our laboratory. 4,8,10−14 α-Hydroxylation also occurs on the α-methylene carbons of NNK and NNAL, which produces intermediates α-methylenehydroxyNNK ( 4 ) and α-methylenehydroxyNNAL ( 5 ), respectively. Both 4 and 5 decompose to methane diazohydroxide ( 8 ), which reacts with DNA to form methyl DNA base adducts (Figure 1).…”

Smoking induced pancreatitis and pancreatic cancer

“…However the protective effect observed in PEP may occur through nicotine, a major toxic component of tobacco (see section on Nicotine), which activates the nicotinic anti-inflammatory pathway, and can reduce pancreatic inflammation (48,73,109,113). Nicotine can also relax the sphincter of Oddi in experimental models and might reduce sphincter spasm and obstruction which can cause PEP (12).…”