The association between MTHFR 677C>T genotype and folate status and genomic and gene-specific DNA methylation in the colon of individuals without colorectal neoplasia

Abstract

Background: Decreased genomic and increased gene-specific DNA methylation predispose to colorectal cancer. Dietary folate intake and the methylenetetrahydrofolate reductase polymorphism (MTHFR 677C>T) may influence risk by modifying DNA methylation.

Objective: We investigated the associations between MTHFR 677C>T genotype, folate status, and DNA methylation in the colon.

Design: We conducted a cross-sectional study of 336 men and women (age 19-92 y) in the United Kingdom without colorectal neoplasia. We obtained blood samples for measurement of serum and red blood cell folate, plasma homocysteine, and MTHFR 677C>T genotype and colonic tissue biopsies for measurement of colonic tissue folate and DNA methylation (genomic- and gene-specific, estrogen receptor 1, ESR1; myoblast determination protein 1, MYOD1; insulin-like growth factor II, IGF2; tumor suppressor candidate 33, N33; adenomatous polyposis coli, APC; mut-L homolog 1, MLH1; and O(6)-methylguanine-DNA methyltransferase, MGMT) by liquid chromatography/electrospray ionization mass spectrometry and pyrosequencing, respectively.

Results: Of the 336 subjects recruited, 185 (55%) carried the CC, 119 (35%) the CT, and 32 (10%) the TT alleles. No significant differences in systemic markers of folate status and colonic tissue folate between genotypes were found. The MTHFR TT genotype was not associated with genomic or gene-specific DNA methylation. Biomarkers of folate status were not associated with genomic DNA methylation. Relations between biomarkers of folate status and gene-specific methylation were inconsistent. However, low serum folate was associated with high MGMT methylation (P = 0.001).

Conclusion: MTHFR 677C>T genotype and folate status were generally not associated with DNA methylation in the colon of a folate-replete population without neoplasia.

FIGURE 1.

Genomic DNA methylation by MTHFR 677C>T genotype. Bars represent means and 95% CIs for unadjusted values (CC, n = 185; CT, n = 119; TT, n = 32; P = 0.60). P = 0.60 for comparison between genotypes (ANOVA).

FIGURE 2.

Gene-specific DNA methylation by MTHFR 677C>T genotype. Boxes represent medians and IQRs; whiskers are the expected range and outliers. A: ESR1, N33, MYOD1, and IGF2 methylation. B: APC, MGMT, and MLH1 methylation (CC, n = 185; CT, n = 119; TT, n = 32). Kruskal-Wallis tests were used for comparison between genotypes (ESR1, P = 0.92; N33, P = 0.12; MYOD1, P = 0.24; IGF2, P = 0.77; APC, P = 0.45; MGMT, P = 0.68; MLH1, P = 0.89).

FIGURE 3.

Association between gene-specific methylation in colonic mucosa, biomarkers of folate status, and MTHFR 677C>T genotype. Dots and horizontal lines represent the coefficients and 95% CIs, respectively, obtained from generalized linear models adjusted for age, sex (male or female), ethnicity (white or nonwhite), supplement use (user or nonuser), serum vitamin B-12, and MTHFR 677C>T genotype. The coefficients give the amount of change in the log odds of having high methylation in each gene investigated for each unit increase in the independent variables (with all other variables held constant) serum folate (nmol/L) (A), red blood cell folate (nmol/L) (B), tissue folate (nmol/g tissue) (C), and plasma homocysteine (μmol/L) (D) or the log odds of having high methylation in individuals carrying the MTHFR CT genotype (E) or TT genotype (F) compared with individuals carrying the CC genotype. The vertical dotted line (coefficient of 0) shows the line of no effect. Coefficients >0 indicate an increased odds of having high methylation (positive association), whereas coefficients <0 indicate a decreased odds of having high methylation (negative association), for each unit increase in biomarker concentrations, or for the CT or TT genotype compared with the CC genotype (reference). The threshold for significance with Bonferroni correction for 8 repeated tests is P = 0.006. ¹P = 0.001 (significant after Bonferroni correction); ²P = 0.04; ³P = 0.01; ⁴P = 0.02; ⁵P = 0.02; ⁶P = 0.02.