Analysis of the malondialdehyde‐2′‐deoxyguanosine adduct in rat liver DNA by gas chromatography/electron capture negative chemical ionization mass spectrometry

Malondialdehyde (MDA), a product of lipid peroxidation, causes mutations in bacterial and mammalian cells and cancer in rats. MDA reacts with deoxynucleosides in vitro and the monomeric adduct of MDA with deoxyguanosine (M 1 G‐dR) is the major adduct formed. We have developed a sensitive analytical method to characterize and quantify M 1 G‐dR from biological matrices using gas chromatogrphy/electron capture negative chemical ionization mass spectrometry (GC/ECNCI MS). Reduction of M 1 G‐dR with sodium borohydride produced a dihydro derivative (H 2 ‐M 1 G‐dR). This more stable analog had improved high‐performance liquid chromatographic characteristics which facilitated its isolation from biological fluids. H 2 ‐M 1 G‐dR was converted to a mono‐pentafluorobenzyl derivative with simultaneous depurination; it was then converted to the corresponding t ‐butyldimethylsilyl derivative and analyzed by GC/ECNCI MS. ( 2 H 2 )H 2 ‐M 1 G was used as internal standard. Quantitative analysis was carried out using selected ion monitoring of m/z 302 and m/z 304 where the limit of detection was 10 pg (30 fmol) injected on‐column. The level of M 1 G‐dR in normal rat liver was 5.2 ± 0.2 modified bases per 10 7 bases ( n = 6 rats).