DNA adducts induced by lipids and lipid peroxidation products: possible relationships to I-compounds

A methanol-extractable lipid fraction of oats has been found previously to induce three specific I-compounds (age-dependent covalent DNA modifications) in female rat liver DNA, as detected by the 32P-postlabeling assay. The current report used an in vitro system to explore the possible mechanisms involved in the formation of these DNA derivatives. Ground oats or commercial oatmeal were extracted with methanol, and the extracts were incubated with rat lung DNA in vitro. DNA was recovered and analyzed by the nuclease P1-enhanced version of the 32P-postlabeling assay. A number of adducts were induced by the in vitro reaction but none of them was identical by chromatographic analysis to oats-specific I-compounds detected in vivo. Addition of rat liver microsomes and cofactors (NADPH or cumene hydroperoxide) to the in vitro reaction also failed to induce any of the oats-specific I-compounds. Pretreatment of oat lipids with soybean lipoxidase and oxygen enhanced formation of most adducts formed in vitro in a dose- and time-dependent manner. Several of these adducts were related to peroxide derivatives of linoleic acid. Chromatographic evidence suggests that one of the major adducts is derived from 4-hydroxynonenal, a reactive intermediate lipid peroxidation product. This adduct was detectable in liver and kidney DNA of untreated rats and its level increased with age. These results were in line with previous in vivo results, suggesting that the oats-specific I-compounds are presumably formed via an indirect mechanism rather than by direct binding of oats components to DNA.