title: Use of LC-MS/MS and stable isotopes to differentiate hydroxymethyl and methyl DNA adducts from formaldehyde and nitrosodimethylamine.
abstract: Formaldehyde is a known human and animal carcinogen that forms DNA adducts, and causes mutations. While there is widespread exposure to formaldehyde in the environment, formaldehyde is also an essential biochemical in all living cells. The presence of both endogenous and exogenous sources of formaldehyde makes it difficult to develop exposure-specific DNA biomarkers. Furthermore, chemicals such as nitrosodimethylamine form one mole of formaldehyde for every mole of methylating agent, raising questions about potential cocarcinogenesis. Formaldehyde-induced hydroxymethyl DNA adducts are not stable and need to be reduced to stable methyl adducts for detection, which adds another layer of complexity to identifying the origins of these adducts. In this study, highly sensitive mass spectrometry methods and isotope labeled compounds were used to differentiate between endogenous and exogenous hydroxymethyl and methyl DNA adducts. We demonstrate that N(2)-hydroxymethyl-dG is the primary DNA adduct formed in cells following formaldehyde exposure. In addition, we show that alkylating agents induce methyl adducts at N(2)-dG and N(6)-dA positions, which are identical to the reduced forms of hydroxymethyl adducts arising from formaldehyde. The use of highly sensitive LC-MS/MS and isotope labeled compounds for exposure solves these challenges and provides mechanistic insights on the formation and role of these DNA adducts.
authors.affiliation: Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
authors.forename: Kun
authors.initials: K
authors.lastname: Lu
authors.forename: Sessaly
authors.initials: S
authors.lastname: Craft
authors.forename: Jun
authors.initials: J
authors.lastname: Nakamura
authors.forename: Benjamin C
authors.initials: BC
authors.lastname: Moeller
authors.forename: James A
authors.initials: JA
authors.lastname: Swenberg
mesh_terms: D002247:Carbon Isotopes; D002273:Carcinogens / Q000633:toxicity*; D002851:Chromatography, High Pressure Liquid; D002853:Chromatography, Liquid; D018736:DNA Adducts / Q000032:analysis*; D019175:DNA Methylation; D003903:Deuterium; D004128:Dimethylnitrosamine / Q000633:toxicity*; D005557:Formaldehyde / Q000633:toxicity*; D006367:HeLa Cells; D006801:Humans; D053719:Tandem Mass Spectrometry
chemical_list: D002247:Carbon Isotopes; D002273:Carcinogens; D018736:DNA Adducts; D005557:Formaldehyde; D003903:Deuterium; D004128:Dimethylnitrosamine