Associations between single nucleotide polymorphisms in folate uptake and metabolizing genes with blood folate, homocysteine, and DNA uracil concentrations
AMERICAN JOURNAL OF CLINICAL NUTRITION
Authors: DeVos, Lauren; Chanson, Aurelie; Liu, Zhenhua; Ciappio, Eric D.; Parnell, Laurence D.; Mason, Joel B.; Tucker, Katherine L.; Crott, Jimmy W.
Abstract
Background: Folate is an essential nutrient that supports nucleotide synthesis and biological methylation reactions. Diminished folate status results in chromosome breakage and is associated with several diseases, including colorectal cancer. Folate status is also inversely related to plasma homocysteine concentrations - a risk factor for cardiovascular disease. Objective: We sought to gain further understanding of the genetic determinants of plasma folate and homocysteine concentrations. Because folate is required for the synthesis of thymidine from uracil, the latter accumulating and being misincorporated into DNA during folate depletion, the DNA uracil content was also measured. Design: Thirteen single nucleotide polymorphisms (SNPs) in genes involved in folate uptake and metabolism, including folate hydrolase (FOLH1), folate polyglutamate synthase (FPGS), gamma-glutamyl hydrolase (GGH), methylene tetrahydrofolate reductase (MTHFR), methionine synthase (MTR), proton- coupled folate transporter (PCFT), and reduced folate carrier (RFC1), were studied in a cohort of 991 individuals. Results: The MTHFR 677TT genotype was associated with increased plasma homocysteine and decreased plasma folate. MTHFR 1298A > C and RFC1 intron 5A > Gpolymorphisms were associated with significantly altered plasma homocysteine concentrations. The FOLH1 1561C > T SNP was associated with altered plasma folate concentrations. The MTHFR 677TT genotype was associated with a approximate to 34% lower DNA uracil content (P = 0.045), whereas the G allele of the GGH - 124T > GSNP was associated with a stepwise increase in DNA uracil content (P = 0.022). Conclusion: Because the accumulation of uracil in DNA induces chromosome breaks, mutagenic lesions, we suggest that, as for MTHFR C677T, the GGH - 124 T > G SNP may modulate the risk of carcinogenesis and therefore warrants further attention.
Micronuclei in Cord Blood Lymphocytes and Associations with Biomarkers of Exposure to Carcinogens and Hormonally Active Factors, Gene Polymorphisms, and Gene Expression: The NewGeneris Cohort
ENVIRONMENTAL HEALTH PERSPECTIVES
Authors: Merlo, Domenico Franco; Agramunt, Silvia; Anna, Livia; Besselink, Harrie; Botsivali, Maria; Brady, Nigel J.; Ceppi, Marcello; Chatzi, Leda; Chen, Bowang; Decordier, Ilse; Farmer, Peter B.; Fleming, Sarah; Fontana, Vincenzo; Foersti, Asta; Fthenou, Eleni; Gallo, Fabio; Georgiadis, Panagiotis; Gmuender, Hans; Godschalk, Roger W.; Granum, Berit; Hardie, Laura J.; Hemminki, Kari; Hochstenbach, Kevin; Knudsen, Lisbeth E.; Kogevinas, Manolis; Kovacs, Katalin; Kyrtopoulos, Soterios A.; Lovik, Martinus; Nielsen, Jeanette K.; Nygaard, Unni Cecilie; Pedersen, Marie; Rydberg, Per; Schoket, Bernadette; Segerback, Dan; Singh, Rajinder; Sunyer, Jordi; Tornqvist, Margareta; van Loveren, Henk; van Schooten, Frederik J.; vande Loock, Kim; von Stedingk, Hans; Wright, John; Kleinjans, Jos C.; Kirsch-Volders, Micheline; van Delft, Joost H. M.
Abstract
Background: Leukemia incidence has increased in recent decades among European children, -suggesting that early-life environmental exposures play an important role in disease development. Objectives: We investigated the hypothesis that childhood susceptibility may increase as a result of in utero exposure to carcinogens and hormonally acting factors. Using cord blood samples from the NewGeneris cohort, we examined associations between a range of biomarkers of carcinogen exposure and hormonally acting factors with micronuclei (MN) frequency as a proxy measure of cancer risk. Associations with gene expression and genotype were also explored. Methods: DNA and protein adducts, gene expression profiles, circulating hormonally acting factors, and GWAS (genome-wide association study) data were investigated in relation to genomic damage measured by MN frequency in lymphocytes from 623 newborns enrolled between 2006 and 2010 across Europe. Results: Malondialdehyde DNA adducts (M(1)dG) were associated with increased MN frequency in binucleated lymphocytes (MNBN), and exposure to androgenic, estrogenic, and dioxin-like compounds was associated with MN frequency in mononucleated lymphocytes (MNMONO), although no monotonic exposure-outcome relationship was observed. Lower frequencies of MNBN were associated with a 1-unit increase expression of PDCD11, LATS2, TRIM13, CD28, SMC1A, IL7R, and NIPBL genes. Gene expression was significantly higher in association with the highest versus lowest category of bulky and M(1)dG-DNA adducts for five and six genes, respectively. Gene expression levels were significantly lower for 11 genes in association with the highest versus lowest category of plasma AR CALUX (R) (chemically activated luciferase expression for androgens) (8 genes), ER alpha CALUX (R) (for estrogens) (2 genes), and DR CALUX (R) (for dioxins). Several SNPs (single-nucleotide polymorphisms) on chromosome 11 near FOLH1 significantly modified associations between androgen activity and MNBN frequency. Polymorphisms in EPHX1/ 2 and CYP2E1 were associated with MNBN. Conclusion: We measured in utero exposure to selected environmental carcinogens and circulating hormonally acting factors and detected associations with MN frequency in newborns circulating T lymphocytes. The results highlight mechanisms that may contribute to carcinogen-induced leukemia and require further research.