Formation of malonaldehyde-acetaldehyde conjugate adducts in calf thymus DNA

It has previously been shown that malonaldehyde forms conjugates with acetaldehyde and that these conjugates react with nucleobases forming so-called conjugate adducts. In the current study, it is shown that conjugate adducts are also formed in calf thymus DNA when incubated simultaneously with malonaldehyde and acetaldehyde. The adducts were identified in the DNA hydrolysates by their positive ion electrospray MS/MS spectra and by coelution with the 2'-deoxynucleoside standards and, in the case of adducts exhibiting fluorescent properties, also by LC using a fluorescence detector. In the hydrolysates of double-stranded DNA (ds DNA), two deoxyguanosine and two deoxyadenosine conjugate adducts were detected, and in single-stranded DNA (ss DNA) also, the deoxycytidine conjugate adduct was observed. The guanine base was the major target for the malonaldehyde-acetaldehyde conjugates, and 2'-deoxyguanosine adducts were produced in ds DNA at levels of 100-500 adducts/10(5) nucleotides (0.7-3 nmol/mg DNA). The 2'-deoxyadenosine adducts and the 2'-deoxycytidine adduct were generated in higher amounts when the incubation was performed at pH 6.0 than at pH 7.4, while the opposite formation profile was noted for the 2'-deoxyguanosine adducts, especially in the ss DNA reaction. This observation is exactly in accordance with our previously reported pH-dependent reactivity of the individual nucleosides with malonaldehyde-acetaldehyde conjugates. The findings of this work show that the genotoxic effects observed for malonaldehyde and acetaldehyde could be in part due to the formation of the conjugate adducts.