Formation of formaldehyde adducts in the reactions of DNA and deoxyribonucleosides with alpha-acetates of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), and N-nitrosodimethylamine (NDMA).
The cytochrome P450-mediated alpha-hydroxylation of the carcinogenic nitrosamines N-nitrosodimethylamine (NDMA, 1), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 6a), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL, 6b) produces diazonium ions and formaldehyde. The DNA-binding properties of the diazonium ions have been thoroughly characterized, and there is no doubt that they are critical in cancer induction by these nitrosamines. However, the possibility of additional DNA damage via released formaldehyde has not been reported. In this study, we used acetoxymethylmethylnitrosamine (5), 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanone (10a), and 4-(acetoxymethylnitrosamino)-1-(3-pyridyl)-1-butanol (10b) as stable precursors to the alpha-hydroxymethylnitrosamines that would be formed in the metabolism of NDMA, NNK, and NNAL. These alpha-acetates were incubated with calf thymus DNA in the presence of esterase at pH 7.0 and 37 degrees C. The DNA was isolated and enzymatically hydrolyzed to deoxyribonucleosides, and the hydrolysates were analyzed by liquid chromatography-electrospray ionization-mass spectrometry-selected ion monitoring for formaldehyde DNA adducts. Convincing evidence for the formation of the formaldehyde adducts N6-hydroxymethyl-dAdo (11), N4-hydroxymethyl-dCyd (12), N2-hydroxymethyl-dGuo (13), and the cross-links di-(N6-deoxyadenosyl)methane (14), (N6-deoxyadenosyl- N2-deoxyguanosyl)methane (15), and di-(N2-deoxyguanosyl)methane (16) was obtained in these reactions. These results demonstrate that NDMA, NNK, and NNAL have the potential to be bident carcinogens, damaging DNA through the metabolic formation of both diazonium ions and formaldehyde.
Cheng
Guang
G
University of Minnesota Cancer Center, MMC 806, 420 Delaware Street Southeast, Minneapolis, Minnesota 55455, USA.
Wang
Mingyao
M
Upadhyaya
Pramod
P
Villalta
Peter W
PW
Hecht
Stephen S
SS
D000085:Acetates / Q000737:chemistry*; D002273:Carcinogens / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D003432:Cross-Linking Reagents; D018736:DNA Adducts / Q000737:chemistry*; D003853:Deoxyribonucleosides / Q000737:chemistry*; D004128:Dimethylnitrosamine / Q000737:chemistry*; D005557:Formaldehyde / Q000737:chemistry*; D009602:Nitrosamines / Q000737:chemistry*; D011725:Pyridines / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization
D000085:Acetates; D002273:Carcinogens; D003432:Cross-Linking Reagents; D018736:DNA Adducts; D003853:Deoxyribonucleosides; D009602:Nitrosamines; D011725:Pyridines; D005557:Formaldehyde; C016583:4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone; C099565:4-(methylnitrosamino)-1-(3-pyridyl)-1-butan-1-ol; D004128:Dimethylnitrosamine