l,A^-Ethenodeoxyguanosine as a Potential Marker for DNA Adduci Formation by fra/is-4-Hydroxy-2-nonenal!

The reaction of rraiu-4-hydroxy-2-nonenaL,a major a,/}-unsaturated aldehyde released during lipid peroxidation, with deoxyguanosine under physiological conditions was investigated in order to assess its DNA damaging potential. This aldehyde was dissolved in tetrahydrofuran (THF) prior to addition to the reaction mixture. The results showed that structurally different adducts were formed in these reactions depending on the THF used. Using THF unprotected from light, reactions yielded adducts 1 to 6. Adduci 1 was characterizedas l^-ethenodeoxyguanosine (5,9-dihydro-9-oxo-3-/3-D-deoxyribofuranosyIimidazo|l,2-a|purine)by its tIV, proton nuclear magnetic resonance, and mass spectrum and by comparison to the correspondingguanosine and guanine adducts reported in the literature. The IV spectrum of adduct 4 was indicative of a substituted 1jV-etheno derivative. Adducts 2,3,5, and 6 were essentially identical in UV spectra and appeared to be ^-substituted deoxyguano sine diastereomers. At room temperature adducts 2, 3, 5, and 6 were converted quantitatively to a single productat pH 10.5. This productwas shown to be identical to l .A^-uthenodcoxyguanosine (adduct 1). Analo gous conversions to l./V'-cthenoguaninc were also observed for the cor responding guanine adducts. Using THF that had been protected from the light, however, the reactions of fraiu-4-hydroxy-2-nonenal with deox yguanosinegave three majoradducts, 7,8, and9. These adducts possessed UV spectra similar to that of l^V2-propanodeoxyguanosineand were not converted to 1,/V-ethenodeoxygtianosine upon base treatment. Evidence obtained suggests that adducts 1 to 6 were formed from the reaction of deoxyguanosine with the epoxide of rraru-4-hydroxy-2-nonenalgenerated in the presence of hydroperoxide in the light unprotected THF, whereas adducts 7 to 9 were formed by direct Michael addition. Adducts 1 to 6 were formed presumably as a result of nucleophilic addition of the exoamino of deoxyguanosine to the aldehydic group of the epoxide of trans4-hydroxy-2-nonenal. Base treatment of these adducts facilitated subse quent cyclization and eliminations and finally gave l,/V--ethcnodeoxyj¡uanosine. These results demonstrated that troiu-4-hydroxy-2-nonenal read ily forms adducts with deoxyguanosine either by direct Michael addition or via its epoxide formation. The facile conversion of some of these adducts to a single adduct suggests that l^-ethenodeoxy guanosine may provide a simple and useful marker for assessing potential DNA damage by fnuu-4-hydroxy-2-nonenal and related alkenals associated with lipid peroxidation.