Thermospray liquid chromatography/mass spectrometry studies on mechanisms of nucleic acid alkylation by some deuterated carcinogens.
Alkylation of liver nucleic acids of rats treated with nitrosobis(2-oxopropyl)amine (BOP), nitrosomethyl(2-oxopropyl)amine (NMOP), and (methylazoxy)methane (AOM) was studied by using deuterium-labeled compounds. Six hours after treatment of each rat with 5-10 mg of compound, nucleic acids were isolated from the liver of two rats and hydrolyzed in dilute acid, and the fraction containing 7-methylguanine (7-MeG) was separated by ion-exchange high-pressure liquid chromatography. After purification by repeated chromatography, the sample was analyzed by liquid chromatography in ammonium acetate coupled with thermospray positive ion mass spectrometry. AOM containing a deuterated methyl group proximal to the oxygen-bearing nitrogen gave 7-MeG containing three deuterium atoms (169 amu), whereas AOM having the methyl group distal to oxygen deuterated produced 7-MeG without deuterium (166 amu). This indicates that methylation of nucleic acids is through oxidation of AOM to (methylazoxy)methanol and the corresponding aldehyde. BOP-d4, in which both alpha-methylenes contained deuterium, gave rise to 7-MeG containing two atoms of deuterium (168 amu). NMOP-d5, with deuterium in the N-methyl and in the alpha-methylene, gave rise only to 7-MeG containing three deuterium atoms. The methyl-d3 group must originate from the N-methyl of NMOP, probably through formation of a methyldiazonium ion. This result lends support to a mechanism involving a Baeyer-Villiger oxidation of the ketone, rather than oxidation of the N-methyl and formation of an (oxopropyl)diazonium ion, which could give rise to a methylating agent following cyclization.
Liberato
D J
DJ
Department of Drug Metabolism, Hoffmann-La Roche Inc., Nutley, New Jersey 07110.
Saavedra
J E
JE
Farnsworth
D W
DW
Lijinsky
W
W
D000478:Alkylation; D000818:Animals; D001397:Azoxymethane / Q000737:chemistry / Q000494:pharmacology; D002273:Carcinogens / Q000737:chemistry*; D002853:Chromatography, Liquid; D004247:DNA / Q000737:chemistry* / Q000187:drug effects; D004128:Dimethylnitrosamine / Q000737:chemistry / Q000494:pharmacology; D005260:Female; D006147:Guanine / Q000031:analogs & derivatives / Q000737:chemistry / Q000494:pharmacology; D013058:Mass Spectrometry; D009602:Nitrosamines / Q000737:chemistry / Q000494:pharmacology; D051381:Rats; D011916:Rats, Inbred F344
D002273:Carcinogens; D009602:Nitrosamines; C044502:3-methylguanine; C028133:N-nitrosomethyl-2-oxopropylamine; D006147:Guanine; C013622:nitrosobis(2-oxopropyl)amine; D004247:DNA; D004128:Dimethylnitrosamine; D001397:Azoxymethane