Identification of DNA adducts of acetaldehyde

Acetaldehyde is a mutagen and carcinogen which occurs widely in the human e nvironment, sometimes in considerable amounts, but little is known about it s reactions with DNA. In this study, we identified three new types of stabl e acetaldehyde DNA adducts, including an interstrand cross-link. These were formed in addition to the previously characterized N-2-ethylidenedeoxyguan osine. Acetaldehyde was allowed to react with calf thymus DNA or deoxyguano sine. The DNA was isolated and hydrolyzed enzymatically; in some cases, the DNA was first treated with NaBH3CN. Reaction mixtures were analyzed by HPL C, and adducts were isolated and characterized by UV, H-1 NMR, and MS. The major adduct was N-2-ethylidenedeoxyguanosine (1), which was identified as N-2-ethyldeoxyguanosine (7) after treatment of the DNA with NaBH3CN. The ne w acetaldehyde adducts were 3-(2-deoxyribos-1-yl)-5,6, 7,8-tetrahydro-8-hyd roxy-6-methylpyrimido [1,2-a]purine-10(3H)one (9), 3-(2-deoxyribos-1-yl)-5, 6,7,8-tetrahydro-8-(N-2-deoxyguanosy)- 6-methylpyrimido[1,2-a]purine-10(3H) one (12), and N-2-(2,6-dimethyl-1,3-dioxan-4-yl)deoxyguanosine (11). Adduct 9 has been previously identified in reactions of crotonaldehyde with DNA. However, the distribution of diastereomers was different in the acetaldehyd e and crotonaldehyde reactions, indicating that the formation of 9 from ace taldehyde does not proceed through crotonaldehyde. Adduct 12 is an interstr and cross-link. Although previous evidence indicates the formation of cross -links in DNA reacted with acetaldehyde, this is the first reported structu ral characterization of such an adduct. This adduct is also found in croton aldehyde-deoxyguanosine reactions, but in a diastereomeric ratio different than that observed here. A common intermediate, N2-(4-oxobut-2-yl)deoxyguan osine (6), is proposed to be involved in formation of adducts 9 and 12. Add uct 11 is produced ultimately from 3-hydroxybutanal, the major aldol conden sation product of acetaldehyde. Levels of adducts 9, 11, and 12 were less t han 10% of those of N2-ethylidenedeoxyguanosine (1) in reactions of acetald ehyde with DNA. As nucleosides, adducts 9, 11, and 12 were stable, whereas N2-ethylidenedeoxyguanosine (1) had a half-life of 5 min. These new stable adducts of acetaldehyde may be involved in determination of its mutagenic a nd carcinogenic properties.