7-methylguanine and Urinary-Bladder-Neoplasms

A major carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is present in cigarette smoke and its metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), is used as an exposure biomarker for environmental tobacco smoke (ETS). This metabolite (NNAL) can be either detoxified into glucuronidated NNAL (NNAL-Gluc) or activated into an unstable reactive metabolite that methylates DNA along with formation of 4-hydroxy-4-(3-pyridyl)-butyric acid [hydroxy acid (HA)]. Therefore, the carcinogenic risk associated with ETS exposure is greatly modulated by individual variations in metabolic activation and detoxification capabilities. In this study, we defined the urinary HA/total NNAL [HA/total NNAL] ratio as the activation index and NNAL-Gluc/free NNAL [(total NNAL-free NNAL)/free NNAL] ratio as the detoxification index of NNK. The major methylated DNA adduct N(7)-methylguanine (N(7)-MeG), considered as the carcinogenic biomarker for cigarette smoking, was excreted in urine. The objective of this study was to investigate the effects of these metabolic indexes of NNK on N(7)-MeG urinary excretion in a population of urothelial carcinoma patients. Urinary levels of total NNAL (free NNAL plus NNAL-Gluc), free NNAL, HA, and N(7)-MeG were positively correlated with smoking. Furthermore, activation index and detoxification index correlated positively and negatively with N(7)-MeG levels, respectively. Our results suggest that these metabolic indices may represent the phenotype of individual metabolism capability and modulate the carcinogenic risk of ETS exposure.

Topics: Adult; Aged; Aged, 80 and over; Biomarkers; Carcinogens; Female; Guanine; Humans; Male; Middle Aged; Nitrosamines; Pyridines; Smoking; Surveys and Questionnaires; Urinary Bladder Neoplasms

Schistosoma haematobium-infected patients are more likely to develop bladder cancer and be more exposed to carcinogenic N-nitroso compounds than uninfected patients. As N7-methylguanine is a marker of exposure to methylating agents of this type, we have measured N7-methyldeoxyguanosine 3'-monophosphate (N7-MedGp) by (32)P postlabeling. DNA was isolated from 42 paired normal and tumor tissue of Egyptians with bladder cancer. N7-MedGp was detected in DNA from 93% of the tumors and 74% of the normal bladder tissue samples. Adduct levels were highly variable and ranged from 0.04 to 6.4 and from 0.02 to 0.72 micromol/mol deoxyguanosine 3'-monophosphate (dGp) in tumor and normal DNA, respectively. N7-MedGp levels in normal and tumor DNA were highly correlated with one another (P = 0.007). The mean difference (95% confidence interval) in adduct levels between tumor and normal DNA was 0.21 (0.13-0.32) micromol/mol dGp and this was statistically significant (P < 0.001). The adduct ratio (tumor DNA/normal DNA) varied between 0.2 and 136 (median, 4.6). N7-MedGp levels were not associated with gender, age, or the presence of schistosomiasis. However, lower N7-MedGp levels were found in normal DNA from individuals lacking the GSTM1 gene (P = 0.03) but not the GSTT1 gene or in subjects with the Ile105Val GSTP1 polymorphism. These results show that exposure to methylating agents is widespread and suggest that such exposure may play a role both in tumor initiation and progression.

Topics: Bacterial Infections; DNA Adducts; DNA Methylation; Egypt; Epithelium; Female; Guanine; Humans; Male; Middle Aged; Schistosomiasis haematobia; Urinary Bladder; Urinary Bladder Neoplasms