Genetic polymorphisms and modulation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-DNA adducts in human lymphocytes

2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is the most abundant heterocyclic amine derived from food, possibly involved in human carcinogenesis. We evaluated the formation of PhIP-DNA adducts in lymphocytes from 76 incident colorectal cancer patients likely to be exposed to dietary PhIP. To address the role of the metabolic polymorphisms relevant to PhIP-DNA adduct formation, the patients were genotyped for common polymorphisms in the N-acetyltransferase (NAT1 and NAT2), sulfotransferase (SULT1A1) and glutathione S-transferase (GSTM1 and GSTA1) genes. PhIP released from adducted DNA after hydrolysis was quantitated by liquid chromatography-tandem mass spectrometry. Overall, adducts were 3.24 +/- 3.58/10(8) nucleotides (mean +/- SD); they were not related to sex, smoking habits or age, though levels were not significantly higher in smokers, young subjects and high meat consumers. High vegetable intake significantly reduced PhIP-DNA adducts (Mann-Whitney U, p = 0.044). Individuals with the GSTM1 null genotype showed colon cancer onset at earlier age (58.8 +/- 1.8 vs. 63.5 +/- 1.6 years; Mann-Whitney U, p = 0.047). None of the genetic polymorphisms studied significantly affected PhIP-DNA adducts. However, individuals carrying 2 mutated GSTA1 alleles and younger than the median age had higher adduct levels than homozygous wild-type and heterozygous ones (Kruskal-Wallis p = 0.0008). In conclusion, these preliminary data indicate that PhIP-DNA adducts are formed in people likely to be exposed to this carcinogen through the diet, suggesting this biomarker may be useful to detect human exposure and DNA damage. Overall, the genetic polymorphisms considered had limited effect on PhIP-DNA levels, but young people with lower detoxification capacity may form a subgroup particularly susceptible to dietary carcinogen.