Analysis of Pyridyloxobutyl and Pyridylhydroxybutyl DNA Adducts in Extrahepatic Tissues of F344 Rats Treated Chronically with 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone and Enantiomers of 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanol

Abstract

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and its metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) are potent pulmonary carcinogens in rats. NNK and NNAL require metabolic activation to express their carcinogenicity. Cytochrome P450-catalyzed α-hydroxylation at the methyl position of NNK or NNAL generates reactive intermediates, which alkylate DNA to form pyridyloxobutyl (POB)-DNA adducts or pyridylhydroxybutyl (PHB)-DNA adducts. NNK is metabolized to NNAL in a reversible and stereoselective manner, and the tissue-specific retention of (S)-NNAL is believed to be important to the carcinogenicity of NNK. In the present study, we investigated the formation of POB- and PHB-DNA adducts in extra-hepatic tissues of F344 rats treated chronically with NNK, (R)- and (S)-NNAL (10 ppm in the drinking water, 1–20 weeks). POB- and PHB-DNA adducts were quantified in nasal olfactory mucosa, nasal respiratory mucosa, oral mucosa, and pancreas of treated rats. Adduct formation in the nasal respiratory mucosa exceeded that in the other tissues. O2-[4-(3-pyridyl)-4-oxobut-1-yl]thymidine (O2-POB-dThd) or O2-[4-(3-pyridyl)-4-hydroxybut-1-yl]thymidine (O2-PHB-dThd) was the major adduct, followed by 7-[4-(3-pyridyl)-4-oxobut-1-yl]guanine (7-POB-Gua) or 7-[4-(3-pyridyl)-4-hydroxybut-1-yl]guanine (7-PHB-Gua). There was a remarkable similarity in adduct formation between the NNK and (S)-NNAL groups, both of which were distinctively different from that in the (R)-NNAL group. For example, in the nasal olfactory mucosa, POB-DNA adduct levels in the NNK and (S)-NNAL groups were not significantly different from each other, while (R)-NNAL treatment generated 6 – 33 times lower of POB-DNA adducts than did NNK treatment. In contrast, (R)-NNAL treatment produced significantly higher levels of PHB-DNA adducts than did NNK or (S)-NNAL treatment. Similar trends were observed in the nasal respiratory mucosa, oral mucosa and pancreas. These results suggest extensive retention of (S)-NNAL in various tissues of NNK-treated rats, and support a mechanism in which the preferential metabolism of NNK to (S)-NNAL, followed by sequestration of (S)-NNAL in the target tissues and reoxidation to NNK, is important to NNK tumorigenesis.

Tobacco-related carcinogenesis in head and neck cancer

“…This allows (S)-NNN to produce more (POB)-DNA adducts than (R)-NNN [40]. NNK, NNAL, and 1-HOP also form DNA adducts in their pathway towards carcinogenesis [31,45]. …”

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

“…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).…”

Biotransformation and bioactivation reactions – 2015 literature highlights

“…NNAL is the metabolite of the most potent and one of the most abundant tobacco specific carcinogenic nitrosamines, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). NNAL exists in two enantiomeric forms which are both tumorigenic while their glucuronidated forms are not (Upadhyaya et al, 1999), with the S enantiomer being more carcinogenic in rats and mice than the R-enantiomer (Lao et al, 2007;Upadhyaya et al, 1999;Zhang et al, 2009). Due to this differential carcinogenic potential of the NNAL enantiomers, it is of interest to know which UGT enzymes target the specific NNAL enantiomers for glucuronidation.…”