Associations between smoking, GST genotypes and N7-methylguanine levels in DNA extracted from bronchial lavage cells.
N7-Methylguanine (N7-MeG) DNA adducts are markers of human exposure to methylating agents including tobacco-specific nitrosamines (TSNAs). Repair of this adduct is poor, so levels in lung tissue should reflect variation in both intensity of exposure and in metabolism. N7-MeG adducts in lung DNA from bronchial lavage samples were measured to determine whether levels were higher in smokers than non-smokers, and if levels were modified by genetic variation in carcinogen-metabolising enzymes. Adducts were detected in 38 out of 44 DNA samples by 32P post-labelling of the N7-methyldeoxyguanosine-3'-monophosphate (N7-MedGp) isolated from DNA digests by two-stage HPLC. N7-MeG adduct levels were higher in smokers than in never smokers ((9.99 +/-20.3)x10(-7) versus (0.58+/-0.50)x10(-7) N7-MedGp/deoxyguanosine-3'-monophosphate (dGp); P=0.02) and intermediate in ex-smokers ((5.59+/-15.6)x10(-7) N7-MedGp/dGp). Adduct levels tended to be higher in individuals with GSTM1 null, GSTT1 null or GSTP1 ile/ile genotypes. When genotypes were combined, N7-MedGp levels among GSTM1 null/GSTT1 null individuals (n=6) were higher than among those having at least one wild-type allele of these two genes ((26.1+/-38.0)x10(-7) versus (2.73+/-4.07)x10(-7) N7-MedGp/dGp), although the results were not statistically significant (P=0.13). Adduct levels were highest in individuals with three unfavourable genotypes (GSTM1 null/GSTT1 null and GSTP1 ile/ile) compared with others ((74.5+/-13.1)x10(-7) versus (2.64+/-3.89)x10(-7) N7-MedGp/dGp, P=0.02). N7-MeG adduct levels in DNA isolated from lung tissue thus reflect exposure to cigarette smoke, and genetic variation in carcinogen-metabolising enzymes may modify these levels.
Lewis
Sarah J
SJ
Department of Epidemiology and Public Health, University College London, 1-19 Torrington Place, London WC1E 6BT, UK. s.lewis@public-health.ucl.ac.uk
Cherry
Nicola M
NM
Niven
Robert McL
RM
Barber
Phillip V
PV
Povey
Andrew C
AC
D000328:Adult; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology*; D002851:Chromatography, High Pressure Liquid; D018736:DNA Adducts / Q000378:metabolism*; D003848:Deoxyguanine Nucleotides; D014644:Genetic Variation; D005838:Genotype; D005982:Glutathione Transferase / Q000235:genetics*; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism*; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology; D010761:Phosphorus Radioisotopes; D012907:Smoking / Q000378:metabolism*
D018736:DNA Adducts; D003848:Deoxyguanine Nucleotides; D010761:Phosphorus Radioisotopes; C060943:7-methyl-2'-deoxyguanosine 3'-monophosphate; D006147:Guanine; C008450:7-methylguanine; D005982:Glutathione Transferase