Evaluation of the role of polymorphisms within the xenobiotic metabolizing enzymes and acrylamide metabolism as risk factors for Differentiated Thyroid Carcinoma

Differentiated thyroid carcinoma (DTC) results from complex interactions between genetic and environmental factors. Known etiological factors include exposure to ionizing radiations, previous thyroid diseases, and hormone factors. It has been speculated that dietary acrylamide (AA) formed in diverse foods following the Maillard's reaction could be a contributing factor for DTC in humans. Upon absorption, AA is biotransformed mainly by cytochrome P450 2E1 (CYP2E1) to glycidamide (GA). Considering that polymorphisms within CYP2E1 were found associated with endogenous levels of AA-Hb and GA-Hb adducts in humans, we raised the hypothesis that specific CYP2E1 genotypes could be associated with the risk of DTC. Analysis of four haplotype tagging SNPs (ht- SNPs) within the locus in a discovery case-control study (N=350/350) indicated an association between rs2480258 and DTC risk. This ht-SNP resides within a linkage disequilibrium block spanning intron VIII and the 3'-untranslated region. Extended analysis in a large replication set (2429 controls and 767 cases) confirmed the association, with odds ratios for CT and TT genotypes of 1.24 (95 % confidence interval (CI) 1.03-1.48) and 1.56 (95 % CI, 1.06-2.30), respectively. Functionally, the minor allele was associated with low levels of CYP2E1 mRNA and protein expression as well as lower enzymatic activity in a series of 149 human liver samples. This association suggested that the risk of DTC could, at least in part, be ascribed to AA. We performed an in vivo study to assess the association of AA, GA and their ratio with SNPs of genes encoding for the metabolizing enzymes CYP2E1, EPHX1, GSTM1, GSTT1 and GSTP1 in 60 DTC patients and 60 healthy controls. The ratio of GA-Hb/AA-Hb was found associated in a statistically significant way with rs2480258 and the null genotype of GSTM1. The GSTM1 null genotype was also associated with high GA-Hb levels. The multiple regression analysis showed that the joint effect of CYP2E1 and GSTs was significantly associated with the ratio of GA-Hb/AA-Hb levels. Thus, present results not only confirmed previous findings on the role of GSTs in the AA metabolism but reinforced the notion that rs2480258 is a marker of the functional activity of CYP2E1. Since we didn't find any correlation between DTC and AA we therefore extended the human study by performing a screening of 19 other compounds, both identified and unidentified, observed as Hb adducts to N-terminal valine. The adductomics screening of the 19 compounds revealed that the levels of Methyl vinyl ketone and Ethyl vinyl ketone were significantly higher in controls and the levels of 575 m/z and 561_23 m/z were significantly higher in cases. Furthermore, a significant association was also found between the two unknown compounds and Acrylic acid with CYP2E1. Further studies are needed to completely understand the correlation between the different compounds, health status and SNPs.