Previous research has shown that a range of nitrosated glycine derivatives react with DNA to form O6-carboxymethylguanine and O6-methylguanine DNA adducts [Harrison et al. (1999) Chem. Res. Toxicol. 12, 106-111). Nitrosated glycine derivatives may be formed in the gastrointestinal tract from the reaction of dietary glycine with nitrosating agents. The aim of this study was to further investigate the role of dietary glycine in the formation of O6-guanine adducts at physiologically relevant concentrations. In vitro studies were performed by reacting 10 microM to 50 mM glycine with nitric oxide in the presence of oxygen. An HPLC assay was developed to measure the resulting nitrosated glycine derivative, diazoacetate anion. The amount of nitrosating agent present in the reaction mixture was determined by colorimetric measurement of nitrite, the hydrolysis product of N2O3. Diazoacetate anion formation depended linearly on glycine concentration. Solutions of nitrosated glycine reacted with 2'-deoxyguanosine and calf thymus DNA to give O6-carboxymethyl-2'-deoxyguanosine and, at high concentrations of glycine and nitric oxide, O6-methyl-2'-deoxyguanosine. At physiological concentrations of glycine and nitric oxide, diazoacetate anion was not detectable. Studies with synthetic diazoacetate anion showed that concentrations < 14 microM did not give detectable O6-carboxyethylguanine in DNA, even when a sensitive immunoslot blot assay was used. However, O6-carboxymethylguanine was detected in human blood DNA samples obtained from three volunteers consuming a standardized high meat diet, using the immunoslot blot assay. O6-Carboxymethylguanine levels ranged from 35 to 80 (detection limit = 15) O6-carboxymethylguanine per 10(8) bases. These studies provide further evidence that nitrosated amino acids may be risk factors for gastrointestinal tract cancers.

Immunoslot blot assays have been used for the analysis of many DNA adducts but problems are frequently encountered in achieving reproducible results. Each step of the assay has been systematically examined and it was found that the major problems are in the DNA fragmentation step and the use of the manifold apparatus. Optimisation was performed upon both the malondialdehyde-deoxyguanosine adduct (M 1 dG) and the O 6 -carboxymethyldeoxyguanosine adduct (O 6 CMdG) to demonstrate the applicability to other DNA adducts.Blood samples from the EPIC study (n = 162) were analysed for M 1 dG adducts and the data showed no correlation with adduct levels in other tissues indicating that the EPIC blood samples were not useful for studying M 1 dG adducts. Blood samples from a processed meat vs vegetarian diet intervention (n = 6) were analysed for O 6 CMdG and many were below the limit of detection. The reduction of background adduct levels in standard DNA was investigated using chemical and whole-genome amplification approaches. The latter gave a sensitivity improvement of 2.6 adducts per 10 7 nucleotides for the analysis of O 6 CMdG.Subsequent reanalysis for O 6 CMdG showed a weakly significant increase in O 6 CMdG on the processed meat diet compared with the vegetarian diet, demonstrating that further studies are warranted.