title: Dietary variables associated with DNA N7-methylguanine levels and O6-alkylguanine DNA-alkyltransferase activity in human colorectal mucosa.
abstract: Components of human diets may influence the incidence of colorectal adenomas, by modifying exposure or susceptibility to DNA-damaging alkylating agents. To examine this hypothesis, a food frequency questionnaire was used to assess the diet of patients recruited for a case-referent study where biopsies of normal colorectal mucosa were collected during colonoscopy and subsequently analysed for DNA N7-methylguanine (N7-MeG) levels, as an indicator of exposure, and activity of the DNA repair protein O6-alkylguanine DNA-alkyltransferase (MGMT), as an indicator of potential susceptibility. Cases with histologically proven colorectal adenomas (n = 38) were compared with referents (n = 35) free of gastrointestinal neoplasia. The case group consumed significantly more red meat (4.5 versus 3.4 servings/week, P < 0.05), processed meats, (4.7 versus 3.2 servings/week, P < 0.05) and % food energy as fat (34.9 versus 30.7%, P < 0.001). N7-MeG [mean: 95% confidence interval (CI)] levels were significantly lower in the group that consumed the highest proportion of dietary fibre/1000 kcal in comparison with the group with the lowest intake (0.61; 0.35-0.86 versus 1.88; 0.88-2.64 micromol/mol dG, P < 0.05). N7-MeG levels were also inversely associated with folate consumption (P < 0.05). MGMT activity (mean; 95% CI) was significantly higher in the group with the lowest consumption of vegetables than in the group with the greatest vegetable consumption (7.02; 5.70-8.33 versus 4.93; 3.95-5.91 fmol/microg DNA, P < 0.05). Our results are consistent with the hypothesis that dietary factors may modify exposure or susceptibility, respectively, to DNA damage by alkylating agents.
authors.affiliation: Occupational and Environmental Health Research Group, School of Translational Medicine, University of Manchester, Manchester M13 9PL, UK.
authors.forename: H A
authors.initials: HA
authors.lastname: Billson
authors.forename: K L
authors.initials: KL
authors.lastname: Harrison
authors.forename: N P
authors.initials: NP
authors.lastname: Lees
authors.forename: C N
authors.initials: CN
authors.lastname: Hall
authors.forename: G P
authors.initials: GP
authors.lastname: Margison
authors.forename: A C
authors.initials: AC
authors.lastname: Povey
mesh_terms: D000236:Adenoma / Q000378:metabolism* / Q000473:pathology; D000368:Aged; D016022:Case-Control Studies; D015331:Cohort Studies; D003111:Colonic Polyps / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D003113:Colonoscopy; D015179:Colorectal Neoplasms / Q000378:metabolism* / Q000473:pathology; D004247:DNA / Q000378:metabolism*; D015254:DNA Modification Methylases / Q000378:metabolism*; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004032:Diet; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000378:metabolism* / Q000473:pathology; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D025521:Tumor Suppressor Proteins; D006147:Guanine; C008450:7-methylguanine; D004247:DNA; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D045643:DNA Repair Enzymes