Cross-talk between one-carbon metabolism and xenobiotic metabolism: implications on oxidative DNA damage and susceptibility to breast cancer.

The aim of this case-control study is to explore the role of aberrations in xenobiotic metabolism in inducing oxidative DNA damage and altering the susceptibility to breast cancer. Cytochrome P4501A1 (CYP1A1) m1 (OR: 1.41, 95% CI 1.08-1.84), CYP1A1 m4 (OR: 5.13, 95% CI 2.68-9.81), Catecholamine-O-methyl transferase (COMT) H108L (OR: 1.49, 95% CI 1.16-1.92), and glutathione S-transferase (GST) T1 null (OR: 1.68, 95% CI 1.09-2.59) variants showed association with breast cancer risk. Reduced folate carrier 1 (RFC1) 80A/CYP1A1 m1/CYP1A1 m4 and RFC1 80A/thymidylate synthase (TYMS) 5'-UTR 2R/methionine synthase (MTR) 2756G/COMT 108L genetic combinations were found to inflate breast cancer risk under the conditions of low dietary folate (345 ± 110 vs. 379 ± 139 μg/day) and low plasma folate (6.81 ± 1.25 vs. 7.09 ± 1.26 ng/ml) by increasing plasma 8-oxo-2'-deoxyguanosine (8-oxodG). This increase in 8-oxodG is attributed to low methionine (49.38 ± 23.74 vs. 53.90 ± 23.85 μmol/l); low glutathione (378 ± 242 vs. 501 ± 126 μmol/l) and GSTT1 null variant; and hypermethylation of CpG island of extracellular-superoxide dismutase (EC-SOD) (92.78 ± 11.49 vs. 80.45 ± 9.86%), which impair O-methylation of catechol estrogens to methoxy estrogens, conjugation of glutathione to semiquinones/quinones and free radical scavenging respectively. Our results suggest cross-talk between one-carbon metabolism and xenobiotic metabolism influencing oxidative DNA damage and susceptibility to breast cancer.