2'-deoxycytidine in free nucleosides and double-stranded DNA as the major target of lipid peroxidation products

Lipid peroxidation generates a variety of reactive products that covalently modify DNA, yielding several types of adducts with nucleobases. In the present study, we characterized the modification of nucleobases during peroxidation of linoleate and found that 2'-deoxycytidine (dC) could be a major target of the modification by lipid peroxidation reactions. Upon incubation with oxidized linoleate, dC and 2'-deoxyguanosine (dG) were significantly modified among four 2'-deoxynucleosides. The major product in dG/linoleate was identical to the 2-oxo-heptyl-substituted 1,N(2)-etheno-dG that had been previously identified as a 4-oxo-2-nonenal (ONE)-dG adduct. On the basis of spectroscopic and chemical characterization, we identified the major product in dC/linoleate as the 2-oxo-heptyl-substituted 3,N(4)-etheno-dC. The same adduct was also produced upon reaction of dC with ONE, suggesting that ONE might represent the major reactive species that modifies DNA during lipid peroxidation. Indeed, this proposition was supported by the observation that ONE was far more reactive with dC and dG than other genotoxic aldehydes, such as 4-hydroxy-2-nonenal. More strikingly, we found that, in contrast to the similar reactivity of ONE toward free nucleobases (dC and dG), ONE preferentially reacted with dC residues in double-stranded DNA. These results suggest that ONE and other 4-oxo-2-alkenals may possess by far the strongest electrophilic potential vs. dC and that the formation of 4-oxo-2-alkenal-adducted dC may thus serve as one mechanism for oxidative damage to DNA in vivo.