A previous observation that an N-nitroso-N-carboxymethyl derivative reacts with
DNA to give both O6-carboxymethyl-2'-deoxyguanosine (O6-CMdGuo) and O6-methyl-2'-deoxyguanosine (O6-MedGuo) [Shuker, D. E. G., and Margison, G. P. (1997)
Cancer Res. 57, 366-369] has been confirmed using a range of nitrosated
glycine derivatives [N-acetyl-N'-nitroso-N'-
prolylglycine (APNG),
azaserine (AS), and
potassium diazoacetate (KDA)]. In addition, mesyloxyacetic
acid (MAA) was also found to give both O6-adducts in
DNA. O6-CMdGuo and O6-MedGuo were assessed in enzymatic hydrolysates of treated
calf thymus DNA using a combined immunoaffinity/HPLC/fluorescence procedure. The ratio of O6-CMdGuo to O6-MedGuo varied somewhat between the different compounds with APNG giving the most methylation (O6-CM:O6-Me ratio of 10) and AS the least (39), with KDA and MAA giving intermediate amounts (16 and 18, respectively). The formation of O6-MedGuo by the four compounds probably arises through decarboxylation at various stages in the decomposition pathways, but the exact mechanisms remain to be clarified. The formation of O6-MedGuo from reactions of nitrosated
glycine derivatives with
DNA in vitro may explain the frequent detection of this adduct in human gastrointestinal
DNA, as nitrosation of dietary
glycine may occur. O6-CMdGuo is likely to be a useful
biomarker of this pathway in vivo and has been detected in human tissues.