Modification of urinary N7-methylguanine excretion in smokers by glutathione-S-transferase M1 polymorphism

Tobacco smoke contains many carcinogens which can lead to DNA methylation. Glutathione-S-transferases (GSTs) are detoxifying enzymes, and the effects of the genes GSTM1, GSTT1, and GSTP1 on cigarette smoke-induced methylated adducts have not been elucidated. Therefore, we investigated the association of the GSTM1, GSTT1, and GSTP1 genes and N7-methylguanine (N7-MeG) adducts in smokers. Urinary N7-MeG concentrations were measured by using liquid chromatography–tandem mass spectrometry in 112 smokers and 89 non-smokers, and GSTM1, GSTT1, and GSTP1 genotypes were identified by polymerase chain reaction. Smokers had higher N7-MeG concentrations than did non-smokers (3238 ± 305 ng/mg creatinine [standard error] vs. 2386 ± 153 ng/mg creatinine; P = 0.01). Higher N7-MeG concentrations were observed with the GSTM1 null genotype than with the GSTM1 non-null genotype (3230 ± 292 ng/mg creatinine vs. 2336 ± 153 ng/mg creatinine; P = 0.007), particularly in smokers (3775 ± 483 ng/mg creatinine vs. 2468 ± 228 ng/mg creatinine; P = 0.02). However, the GSTT1 and GSTP1 genotypes were not associated with urinary N7-MeG concentrations. Therefore, the susceptible GSTM1 genotype may modulate the concentrations of N7-MeG adducts in the DNA of smokers.