Indirect mutagenesis by oxidative DNA damage: formation of the pyrimidopurinone adduct of deoxyguanosine by base propenal

Abstract

Oxidation of endogenous macromolecules can generate electrophiles capable of forming mutagenic adducts in DNA. The lipid peroxidation product malondialdehyde, for example, reacts with DNA to form M1G, the mutagenic pyrimidopurinone adduct of deoxyguanosine. In addition to free radical attack of lipids, DNA is also continuously subjected to oxidative damage. Among the products of oxidative DNA damage are base propenals. We hypothesized that these structural analogs of malondialdehyde would react with DNA to form M1G. Consistent with this hypothesis, we detected a dose-dependent increase in M1G in DNA treated with calicheamicin and bleomycin, oxidizing agents known to produce base propenal. The hypothesis was proven when we determined that 9-(3-oxoprop-1-enyl)adenine gives rise to the M1G adduct with greater efficiency than malondialdehyde itself. The reactivity of base propenals to form M1G and their presence in the target DNA suggest that base propenals derived from oxidative DNA damage may contribute to the mutagenic burden of a cell.

Figure 1

Structures of malondialdehyde, its tautomer, adenine propenal, and M₁G and a proposed mechanism for the formation of M₁G from adenine propenal.

Figure 2

Formation of base propenal following radical-mediated 4′-hydrogen atom abstraction (15). (A) The pathway leading to base propenal is oxygen dependent for both calicheamicin and bleomycin, while the oxidized abasic site produced by bleomycin is oxygen independent (33). (B) A model for the formation of M₁G in DNA by reaction of base propenal (cytidine) with a neighboring guanine.

Figure 3

Formation of M₁G in DNA treated with calicheamicin and bleomycin. Calf thymus DNA was treated with the indicated concentrations of these radical-mediated DNA cleavers and M₁G was quantified as described in Materials and Methods. Error bars represent deviation about the mean for duplicate determinations.

Figure 4

Formation of M₁G in DNA treated with adenine propenal. Oligonucleotide DNA was treated with the indicated concentrations of adenine propenal and M₁G was quantified as described in Materials and Methods. Error bars are deviation about the mean for triplicate determinations.