title: Quantification of Azaserine-Induced Carboxymethylated and Methylated DNA Lesions in Cells by Nanoflow Liquid Chromatography-Nanoelectrospray Ionization Tandem Mass Spectrometry Coupled with the Stable Isotope-Dilution Method.
abstract: Humans are exposed to N-nitroso compounds through environmental exposure and endogenous metabolism. Some N-nitroso compounds can be metabolically activated to yield diazoacetate, which is known to induce DNA carboxymethylation. DNA lesion measurement remains one of the core tasks in toxicology and in evaluating human health risks associated with carcinogen exposure. In this study, we developed a highly sensitive nanoflow liquid chromatography-nanoelectrospray ionization-multistage tandem mass spectrometry (nLC-nESI-MS(3)) method for the simultaneous quantification of O(6)-carboxymethyl-2'-deoxyguanosine (O(6)-CMdG), O(6)-methyl-2'-deoxyguanosine (O(6)-MedG), and N(6)-carboxymethyl-2'-deoxyadenosine (N(6)-CMdA). We were able to measure the levels of these three lesions with the use of low-microgram quantities of DNA from cultured human skin fibroblasts and human colorectal carcinoma cells treated with azaserine, a DNA carboxymethylating agent. Our results revealed that the levels of O(6)-CMdG and O(6)-MedG increased when the dose of azaserine was increased from 0 to 450 μM. We, however, did not observe an apparent dose-dependent induction of N(6)-CMdA, suggesting the presence of repair mechanism(s) for the rapid clearance of this lesion in cells. This is the first report about the application of nLC-nESI-MS(3) technique for the simultaneous quantification of O(6)-CMdG, O(6)-MedG, and N(6)-CMdA. The method reported here will be useful for future investigations about the repair of the carboxymethylated DNA lesions and about the implications of these lesions in carcinogenesis.
authors.affiliation: Environmental Toxicology Graduate Program, and ‡Department of Chemistry, University of California , Riverside, California 92521, United States.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yu
authors.affiliation: Environmental Toxicology Graduate Program, and ‡Department of Chemistry, University of California , Riverside, California 92521, United States.
authors.forename: Jianshuang
authors.initials: J
authors.lastname: Wang
authors.affiliation: Environmental Toxicology Graduate Program, and ‡Department of Chemistry, University of California , Riverside, California 92521, United States.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Wang
authors.affiliation: Environmental Toxicology Graduate Program, and ‡Department of Chemistry, University of California , Riverside, California 92521, United States.
authors.forename: Yinsheng
authors.initials: Y
authors.lastname: Wang
mesh_terms: D001377:Azaserine / Q000032:analysis* / Q000494:pharmacology; D002478:Cells, Cultured; D002853:Chromatography, Liquid; D004249:DNA Damage; D019175:DNA Methylation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007201:Indicator Dilution Techniques; D008745:Methylation / Q000187:drug effects; D015394:Molecular Structure; D036103:Nanotechnology; D021241:Spectrometry, Mass, Electrospray Ionization; D013329:Structure-Activity Relationship; D053719:Tandem Mass Spectrometry
chemical_list: D001377:Azaserine