XRCC1 and XRCC3 polymorphisms and their role as effect modifiers of unsaturated fatty acids and antioxidant intake on colorectal adenomas risk.

Whereas animal and in vitro studies support a role of unsaturated fatty acids in colon carcinogenesis, the epidemiologic evidence is inconclusive. Using a large sigmoidoscopy-based case-control study (753 cases and 799 controls) in Los Angeles County, we investigated possible associations between single-nucleotide polymorphisms in the XRCC1 (codons 194 Arg/Trp and codon 399 Arg/Gln) and XRCC3 (codon 241 Thr/Met) genes and colorectal adenoma risk and their possible role as modifiers of the effect of monounsaturated fatty acid, the ratio of omega-6/omega-3 polyunsaturated fatty acids, and antioxidant intake. We found no evidence of associations between the XRCC1 codon 194 Arg/Trp or Trp/Trp genotypes and the XRCC3 codon 241 Thr/Met or Met/Met genotypes. Subjects with the XRCC1 Gln/Gln genotype were inversely associated with adenoma risk (odds ratio, 0.6; 95% confidence interval, 0.4-0.9; P = 0.01) when compared with subjects with Arg/Arg and Arg/Gln genotypes combined. We found no evidence of gene-dietary fat interactions for the XRCC3 codon 241 polymorphism. However, our data suggest an XRCC1-unsaturated fat interaction. High monounsaturated fatty acid intake was associated with adenoma risk only among subjects with the XRCC1 codon 194 Arg/Arg and codon 399 Gln/Gln combined genotypes (P for interaction = 0.018). High omega-6/omega-3 polyunsaturated fatty acid ratios were associated with adenoma risk among subjects with the XRCC1 codon 194 Arg/Arg and codon 399 Gln/Gln or the codon 194 Arg/Trp or Trp/Trp and codon 399 Arg/Arg or Arg/Gln combined genotypes (P for interaction = 0.026). These interactions were not modified by antioxidant intake. However, low antioxidant intake was associated with an inverse association only among subjects with the XRCC1 codon 194 Arg/Trp or Trp/Trp and codon 399 Arg/Arg or Arg/Gln combined genotypes (P for interaction = 0.022), which was independent of unsaturated fat intake. Our data suggest that the XRCC1 codon 194 and codon 399 single nucleotide polymorphisms may modify the effect of unsaturated fatty acid and antioxidant intake and that this XRCC1 effect modification may explain, in part, previously reported inconsistencies on the role of unsaturated fatty acids and adenoma risk.