Folate Levels and Polymorphisms in the Genes MTHFR, MTR, and TS in Colorectal Cancer

Abstract

Aim: The aim of the study was to explore and describe the effect of polymorphisms in folate-associated genes regarding the levels of different folate forms and their distribution in tumors and mucosa in patients with colorectal cancer.

Materials and methods: Tumor and mucosa tissues from 53 patients with colorectal cancer were analyzed. The concentrations of tetrahydrofolate (THF), 5-methylTHF, and 5,10-methyleneTHF were measured by liquid chromatography-mass spectrometry. Genotyping of polymorphisms in the folate-associated genes methylenetetrahydrofolate reductase (MTHFR, C677T), methionine synthase (MTR, A2756G), and thymidylate synthase (TS, 5'-TSER 28 bp tandem repeat and 3'-TSUTR 6 bp deletion/insertion), were done by real-time polymerase chain reaction. Folate levels and distributions were determined in the total patient cohort and after subgrouping by genotypes.

Results: The total folate level, as well as the THF and 5,10-methyleneTHF levels, were significantly higher in the tumor compared with mucosa tissue (P = 0.030, 0.031, and 0.015, respectively). The individual variation in folate levels in both tumor and mucosa were larger than the variation found when the patients were subgrouped by the gene polymorphisms. No significant differences in the mean concentration of any folate in the mucosa or tumor tissue were found in relation to the analyzed polymorphisms. The percentage level of 5,10-methyleneTHF in tumors was highest in patients with the MTHFR 677 CC genotype, and lowest in patients with the TT genotype (P = 0.033). A significantly lower percentage level of the 5,10-methyleneTHF level was found in tumors of patients with the 5'-TSER 3R/3R genotype (P = 0.0031).

Conclusion: A significant difference was found between the percentage level of 5,10-methyleneTHF in tumor tissues in relation to the MTHFR C677T and 5'-TSER 28 bp repeat polymorphisms. However, no differences were found in the actual tissue folate levels, or in their distribution, in relation to the polymorphisms in the MTHFR, MTR, or TS genes. These findings could be of importance for further research in the field by explaining some of the difficulties of obtaining reproducible and uniform results when using a few selected polymorphisms as predictive markers.

Keywords: colorectal cancer; folate levels; gene polymorphisms.

Figure 1

A simplified overview of folate metabolism showing the enzyme steps catalyzed by MTHFR, MTR, and TS. Notes: Within the cells, folate polyglutamates are converted to 5,10-methyleneTHF, which is required as a methyl donor in the synthesis of dTMP from dUMP. The reaction requires the catalytic activity of the enzyme TS. In addition, 5,10-MethyleneTHF is also the precursor of metabolically active 5-methyl- THF, utilized in the remethylation of the amino acid HCy to methionine. This reaction is catalyzed by MTR. Endogenous methionine is then catabolized to produce the universal methyl donor SAM. The conversion of 5,10-methylene-THF to 5-methyl-THF is dependent on the enzyme MTHFR. Abbreviations: SAM, S-adenosylmethionine; SAH, S-adenosylhomocysteine; HCy, homocysteine; DHF, dihydrofolate; dUMP, deoxyuridine monophosphate; dTMP, deoxythymidine monophosphate.