Polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, intakes of folate and related B vitamins and colorectal cancer: a case-control study in a population with relatively low folate intake

Genome-wide interaction analysis of folate for colorectal cancer risk

BACKGROUND

Epidemiological and experimental evidence suggests that higher folate intake is associated with decreased colorectal cancer (CRC) risk; however, the mechanisms underlying this relationship are not fully understood. Genetic variation that may have a direct or indirect impact on folate metabolism can provide insights into folate's role in CRC.

OBJECTIVES

Our aim was to perform a genome-wide interaction analysis to identify genetic variants that may modify the association of folate on CRC risk.

METHODS

We applied traditional case-control logistic regression, joint 3-degree of freedom, and a 2-step weighted hypothesis approach to test the interactions of common variants (allele frequency >1%) across the genome and dietary folate, folic acid supplement use, and total folate in relation to risk of CRC in 30,550 cases and 42,336 controls from 51 studies from 3 genetic consortia (CCFR, CORECT, GECCO).

RESULTS

Inverse associations of dietary, total folate, and folic acid supplement with CRC were found (odds ratio [OR]: 0.93; 95% confidence interval [CI]: 0.90, 0.96; and 0.91; 95% CI: 0.89, 0.94 per quartile higher intake, and 0.82 (95% CI: 0.78, 0.88) for users compared with nonusers, respectively). Interactions (P-interaction < 5×10-8) of folic acid supplement and variants in the 3p25.2 locus (in the region of Synapsin II [SYN2]/tissue inhibitor of metalloproteinase 4 [TIMP4]) were found using traditional interaction analysis, with variant rs150924902 (located upstream to SYN2) showing the strongest interaction. In stratified analyses by rs150924902 genotypes, folate supplementation was associated with decreased CRC risk among those carrying the TT genotype (OR: 0.82; 95% CI: 0.79, 0.86) but increased CRC risk among those carrying the TA genotype (OR: 1.63; 95% CI: 1.29, 2.05), suggesting a qualitative interaction (P-interaction = 1.4×10-8). No interactions were observed for dietary and total folate.

CONCLUSIONS

Variation in 3p25.2 locus may modify the association of folate supplement with CRC risk. Experimental studies and studies incorporating other relevant omics data are warranted to validate this finding.

High serum riboflavin is associated with the risk of sporadic colorectal cancer

BACKGROUND

Experimental results indicate that riboflavin is involved in tumorigenesis. Data regarding the relationship between riboflavin and colorectal cancer (CRC) are limited, and findings vary between observational studies.

DESIGN

This was a case-control retrospective study.

OBJECTIVE

This study aimed to evaluate the associations between serum riboflavin level and sporadic CRC risk.

METHODS

In total, 389 participants were enrolled in this study - including 83 CRC patients without family history and 306 healthy controls - between January 2020 and March 2021 at the Department of Colorectal Surgery and Endoscope Center at Xinhua Hospital, Shanghai Jiao Tong University School of Medicine. Age, sex, body mass index, history of polyps, disease conditions (e.g., diabetes), medications, and eight other vitamins were used as confounding factors. Adjusted smoothing spline plots, subgroup analysis, and multivariate logistic regression analysis were conducted to estimate the relative risk between serum riboflavin levels and sporadic CRC risk. After fully adjusting for the confounding factors, an increased risk of colorectal cancer was suggested for individuals with higher levels of serum riboflavin (OR = 1.08 (1.01, 1.15), p = 0.03) in a dose-response relationship.

CONCLUSIONS

Our results support the hypothesis that higher levels of riboflavin may play a role in facilitating colorectal carcinogenesis. The finding of high levels of circulating riboflavin in patients with CRC warrants further investigation.

Influence of methyl donor nutrients as epigenetic regulators in colorectal cancer: A systematic review of observational studies

BACKGROUND

Dietary methyl donors might influence DNA methylation during carcinogenesis of colorectal cancer (CRC). However, whether the influence of methyl donor intake is modified by polymorphisms in such epigenetic regulators is still unclear.

AIM

To improve the current understanding of the molecular basis of CRC.

METHODS

A literature search in the Medline database, Reference Citation Analysis (https://www.referencecitationanalysis.com/), and manual reference screening were performed to identify observational studies published from inception to May 2022.

RESULTS

A total of fourteen case-control studies and five cohort studies were identified. These studies included information on dietary methyl donors, dietary components that potentially modulate the bioavailability of methyl groups, genetic variants of methyl metabolizing enzymes, and/or markers of CpG island methylator phenotype and/or microsatellite instability, and their possible interactions on CRC risk.

CONCLUSION

Several studies have suggested interactions between methylenetetrahydrofolate reductase polymorphisms, methyl donor nutrients (such as folate) and alcohol on CRC risk. Moreover, vitamin B₆, niacin, and alcohol may affect CRC risk through not only genetic but also epigenetic regulation. Identification of specific mechanisms in these interactions associated with CRC may assist in developing targeted prevention strategies for individuals at the highest risk of developing CRC.

Personalized Nutrition-Genes, Diet, and Related Interactive Parameters as Predictors of Cancer in Multiethnic Colorectal Cancer Families

To personalize nutrition, the purpose of this study was to examine five key genes in the folate metabolism pathway, and dietary parameters and related interactive parameters as predictors of colorectal cancer (CRC) by measuring the healthy eating index (HEI) in multiethnic families. The five genes included methylenetetrahydrofolate reductase (MTHFR) 677 and 1298, methionine synthase (MTR) 2756, methionine synthase reductase (MTRR 66), and dihydrofolate reductase (DHFR) 19bp, and they were used to compute a total gene mutation score. We included 53 families, 53 CRC patients and 53 paired family friend members of diverse population groups in Southern California. We measured multidimensional data using the ensemble bootstrap forest method to identify variables of importance within domains of genetic, demographic, and dietary parameters to achieve dimension reduction. We then constructed predictive generalized regression (GR) modeling with a supervised machine learning validation procedure with the target variable (cancer status) being specified to validate the results to allow enhanced prediction and reproducibility. The results showed that the CRC group had increased total gene mutation scores compared to the family members (p < 0.05). Using the Akaike’s information criterion and Leave-One-Out cross validation GR methods, the HEI was interactive with thiamine (vitamin B1), which is a new finding for the literature. The natural food sources for thiamine include whole grains, legumes, and some meats and fish which HEI scoring included as part of healthy portions (versus limiting portions on salt, saturated fat and empty calories). Additional predictors included age, as well as gender and the interaction of MTHFR 677 with overweight status (measured by body mass index) in predicting CRC, with the cancer group having more men and overweight cases. The HEI score was significant when split at the median score of 77 into greater or less scores, confirmed through the machine-learning recursive tree method and predictive modeling, although an HEI score of greater than 80 is the US national standard set value for a good diet. The HEI and healthy eating are modifiable factors for healthy living in relation to dietary parameters and cancer prevention, and they can be used for personalized nutrition in the precision-based healthcare era.

Predictors of the Healthy Eating Index and Glycemic Index in Multi-Ethnic Colorectal Cancer Families

For personalized nutrition in preparation for precision healthcare, we examined the predictors of healthy eating, using the healthy eating index (HEI) and glycemic index (GI), in family-based multi-ethnic colorectal cancer (CRC) families. A total of 106 participants, 53 CRC cases and 53 family members from multi-ethnic families participated in the study. Machine learning validation procedures, including the ensemble method and generalized regression prediction, Elastic Net with Akaike’s Information Criterion with correction and Leave-One-Out cross validation methods, were applied to validate the results for enhanced prediction and reproducibility. Models were compared based on HEI scales for the scores of 77 versus 80 as the status of healthy eating, predicted from individual dietary parameters and health outcomes. Gender and CRC status were interactive as additional predictors of HEI based on the HEI score of 77. Predictors of HEI 80 as the criterion score of a good diet included five significant dietary parameters (with intake amount): whole fruit (1 cup), milk or milk alternative such as soy drinks (6 oz), whole grain (1 oz), saturated fat (15 g), and oil and nuts (1 oz). Compared to the GI models, HEI models presented more accurate and fitted models. Milk or a milk alternative such as soy drink (6 oz) is the common significant parameter across HEI and GI predictive models. These results point to the importance of healthy eating, with the appropriate amount of healthy foods, as modifiable factors for cancer prevention.

Vitamin B2 intake reduces the risk for colorectal cancer: a dose-response analysis

PURPOSE

Several epidemiological studies have assessed the ability of vitamin B₂ to prevent colorectal cancer (CRC), but the results are controversial results. We conducted a dose-response meta-analysis to investigate the association between vitamin B₂ and CRC risk.

METHODS

We searched the PubMed and EMBASE database until January 3, 2018 to identify relevant studies. The pooled relative risks (RRs) with the corresponding 95% confidence intervals (CIs) were calculated using a random-effects model or fixed-effects model. The dose-response relationship was assessed by restricted cubic splines.

RESULTS

A total of 14 studies reporting vitamin B₂ intake and two studies reporting blood vitamin B₂ concentration, comprising 14,934 cases and 1593 cases, respectively, were included in the meta-analysis. Vitamin B₂ intake was inversely associated with CRC risk (RR = 0.87; 95% CI 0.81-0.93). Similar results were found for total vitamin B₂ intake from diet and supplements (RR = 0.86; 95% CI 0.78-0.94) and dietary vitamin B₂ intake (RR = 0.89, 95% CI 0.82-0.98) in subgroup analyses. The dose-response model indicated a non-linear trend, and CRC risk was reduced by 10% when vitamin B₂ intake increased to 5 mg/day. In addition, high blood concentrations of vitamin B₂ could also reduce the CRC risk (RR = 0.74; 95% CI 0.59-0.92).

CONCLUSIONS

This dose-response analysis indicates that vitamin B₂ intake is inversely associated with CRC risk. The inverse association may also exist between blood vitamin B₂ concentration and CRC risk. These results suggest the importance of vitamin B₂ intake in the prevention of CRC.

Methylenetetrahydrofolate reductase C677T polymorphism and colorectal cancer susceptibility: a meta-analysis

The association between methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and colorectal cancer (CRC) susceptibility has been researched in numerous studies. However, the results of these studies were controversial. Therefore, the objective of this meta-analysis was to offer a more convincible conclusion about such association with more included studies. Eligible studies published till May 1, 2017 were searched from PubMed, Embase, Web of Science, and CNKI database about such association. Pooled odds ratios (ORs) together with 95% confidence intervals (CIs) were calculated to evaluate such association. And the Begg's funnel plot and Egger's test were applied to assess the publication bias. This meta-analysis contained 37049 cases and 52444 controls from 87 publications with 91 eligible case-control studies. Because of lack of data for a particular genotype in several studies, all the included studies were analysed barely in the dominant model. Originally, there was no association between MTHFR C677T polymorphism and CRC susceptibility (OR =0.99, 95% CI =0.94-1.05). After excluding 13 studies according to their heterogeneity and publication bias, rs1801133 polymorphism was found to reduce the risks of CRC significantly (OR =0.96, 95% CI =0.94-0.99). In the subgroup analysis of ethnicity, there was a significant association in Asians (OR =0.94, 95% CI =0.89-1.00). Furthermore, when stratified by the source of controls and genotyping methods, the positive results were observed in population-based control group (OR =0.97, 95% CI =0.93-1.00) and PCR-restriction fragment length polymorphism (PCR-RFLP) method (OR =0.95, 95% CI =0.91-0.99. The results of the meta-analysis suggested that MTHFR C677T polymorphism was associated with CRC susceptibility, especially in Asian population.

Dietary Reference Values for riboflavin

Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) derives dietary reference values (DRVs) for riboflavin. The Panel considers that the inflection point in the urinary riboflavin excretion curve in relation to riboflavin intake reflects body saturation and can be used as a biomarker of adequate riboflavin status. The Panel also considers that erythrocyte glutathione reductase activation coefficient is a useful biomarker, but has limitations. For adults, the Panel considers that average requirements (ARs) and population reference intakes (PRIs) can be determined from the weighted mean of riboflavin intake associated with the inflection point in the urinary riboflavin excretion curve reported in four intervention studies. PRIs are derived for adults and children assuming a coefficient of variation of 10%, in the absence of information on the variability in the requirement and to account for the potential effect of physical activity and the methylenetetrahydrofolate reductase 677TT genotype. For adults, the AR and PRI are set at 1.3 and 1.6 mg/day. For infants aged 7–11 months, an adequate intake of 0.4 mg/day is set by upward extrapolation from the riboflavin intake of exclusively breastfed infants aged 0–6 months. For children, ARs are derived by downward extrapolation from the adult AR, applying allometric scaling and growth factors and considering differences in reference body weight. For children of both sexes aged 1–17 years, ARs range between 0.5 and 1.4 mg/day, and PRIs between 0.6 and 1.6 mg/day. For pregnant or lactating women, additional requirements are considered, to account for fetal uptake and riboflavin accretion in the placenta during pregnancy or the losses through breast milk, and PRIs of 1.9 and 2.0 mg/day, respectively, are derived.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.EN-1268/full

Vitamin B2 intake and colorectal cancer risk; results from the Nurses' Health Study and the Health Professionals Follow-Up Study cohort

Vitamin B2 serves as a cofactor to enhance one-carbon metabolism, maintain mucous membranes, and has been implicated in lowering colorectal cancer (CRC) risk. However, few prospective studies have examined the association between vitamin B2 intake and CRC. In this study, we estimated the associations between vitamin B2 intake and CRC risk using the Nurses' Health Study (NHS) and the Health Professionals Follow-Up Study (HPFS) cohorts. Vitamin B2 intake was measured by a validated food frequency questionnaire every 4 years. Among 100,033 women in the NHS and 44,007 men in the HPFS we documented a total of 3,037 incident CRC cases (2,093 women and 944 men) during 24-26 years of follow-up until 2010. Intakes of total (from food and supplements), dietary (from food only), and supplemental vitamin B2 were inversely related to CRC risk in age-adjusted analysis in NHS. However, the association was attenuated and no longer statistically significant in multivariate analysis (p-trend ≥0.08). The pooled multivariate relative risks (95% confidence interval) comparing individuals in the extreme quintiles of intakes were 0.93 (0.81-1.06) for total vitamin B2, 0.89 (0.61-1.28) for dietary vitamin B2 and 0.94 (0.81-1.08) for supplemental vitamin B2. These associations of total vitamin B2 intake were similar for risk of CRC with varying lag-time periods (0-4, 4-8, 8-12 or 12-16 years), for risk of CRC subtypes by tumor location, and across strata of intake of folate or alcohol. Our prospective data do not support a beneficial role of vitamin B2 intake in lowering incidence of CRC.

A dose-response meta-analysis reveals an association between vitamin B12 and colorectal cancer risk

OBJECTIVE

The current meta-analysis evaluated the association between vitamin B12 intake and blood vitamin B12 level and colorectal cancer (CRC) risk.

DESIGN

The PubMed and EMBASE databases were searched. A dose-response analysis was performed with generalized least squares regression, with the relative risk (RR) and 95 % CI as effect values.

SETTING

The meta-analysis included seventeen studies.

SUBJECTS

A total of 10 601 patients.

RESULTS

The non-linear dose-response relationship between total vitamin B12 intake and CRC risk was insignificant (P=0·690), but the relationship between dietary vitamin B12 intake and CRC risk was significant (P<0·001). Every 4·5 μg/d increment in total and dietary vitamin B12 intake was inversely associated with CRC risk (total intake: RR=0·963; 95 % CI 0·928, 0·999; dietary intake: RR=0·914; 95 % CI 0·856, 0·977). The inverse association between vitamin B12 intake and CRC risk was also significant when vitamin B12 intake was over a dosage threshold, enhancing the non-linear relationship. The non-linear dose-response relationship between blood vitamin B12 level and CRC risk was insignificant (P=0·219). There was an insignificant association between every 150 pmol/l increment in blood vitamin B12 level and CRC risk (RR=1·023; 95 % CI 0·881, 1·187).

CONCLUSIONS

Our meta-analysis indicates that evidence supports the use of vitamin B12 for cancer prevention, especially among populations with high-dose vitamin B12 intake, and that the association between CRC risk and total vitamin B12 intake is stronger than between CRC risk and dietary vitamin B12 intake only.

Nutrients, foods, and colorectal cancer prevention

Diet has an important role in the development of colorectal cancer. In the past few decades, findings from extensive epidemiologic and experimental investigations have linked consumption of several foods and nutrients to the risk of colorectal neoplasia. Calcium, fiber, milk, and whole grains have been associated with a lower risk of colorectal cancer, and red meat and processed meat have been associated with an increased risk. There is substantial evidence for the potential chemopreventive effects of vitamin D, folate, fruits, and vegetables. Nutrients and foods also may interact, as a dietary pattern, to influence colorectal cancer risk. Diet likely influences colorectal carcinogenesis through several interacting mechanisms. These include the direct effects on immune responsiveness and inflammation, and the indirect effects of overnutrition and obesity-risk factors for colorectal cancer. Emerging evidence also implicates the gut microbiota as an important effector in the relationship between diet and cancer. Dietary modification therefore has the promise of reducing colorectal cancer incidence.

Folate-related nutrients, genetic polymorphisms, and colorectal cancer risk: the fukuoka colorectal cancer study

One-carbon metabolism plays an important role in colorectal carcinogenesis. Meta-analyses have suggested protective associations of folate and vitamin B6 intakes with colorectal cancer primarily based on studies in Caucasians, and genetic polymorphisms pertaining to the folate metabolism have been a matter of interest. Less investigated are the roles of methionine synthase (MTR) and thymidylate synthetase (TS) polymorphisms in colorectal carcinogenesis. In a study of 816 cases and 815 community controls in Japan, we investigated associations of dietary intakes of folate, methionine, vitamin B2, vitamin B6, and vitamin B12 with colorectal cancer risk. The associations with MTR 2756A>G, MTRR 66A>G, and TSER repeat polymorphism were examined in 685 cases and 778 controls. Methionine and vitamin B12 intakes were inversely associated with colorectal cancer risk, but the associations were totally confounded by dietary calcium and n-3 fatty acids. The other nutrients showed no association with the risk even without adjustment for calcium and n-3 fatty acids. The TSER 2R allele was dose-dependently associated with an increased risk. The MTR and MTRR polymorphisms were unrelated to colorectal cancer risk. There was no measurable gene-gene or gene-nutrient interaction, but increased risk associated with the TSER 2R allele seemed to be confined to individuals with high folate status. This study does not support protective associations for folate and vitamin B6. The TSER 2R allele may confer an increased risk of colorectal cancer. The role of the TSER polymorphism in colorectal carcinogenesis may differ by ethnicity.

Vitamins B6 and cancer

Epidemiologic and laboratory animal studies have suggested that the availability of vitamin B6 modulates cancer risk. The means by which B6 mediates this effect is not known with any surety but it has been reported that high dietary vitamin B6 attenuates and low dietary vitamin B6 increases the risk of cancer. In fact vitamin B6 is widely distributed in foods and overt deficiency of this vitamin is not common. Nevertheless, marginal or secondary vitamin B6 deficiency, which might have an adverse effect on carcinogenesis, is rather common especially among old adults and alcoholics. This chapter addressed currently available information regarding the relationship between vitamin B6 and cancer.

Association of methylenetetrahydrofolate reductase C677T and A1298C polymorphisms with colorectal cancer risk: A meta-analysis

Colorectal cancer (CRC) is one of the most common types of cancer worldwide and a leading cause of cancer-related mortality. This meta-analysis was conducted to determine the effect of methylenetetrahydrofolate reductase (MTHFR) mutants on the risk of CRC. A literature search was conducted on PubMed, Medline and the China National Knowledge Infrastructure (CNKI) databases. Eligible studies were collected based on rigorous criteria of inclusion. The pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated by the fixed- or random-effects model. After all the studies were pooled, the OR of CRC for individuals carrying the MTHFR 677TT genotype, compared to the CC genotype, was 0.89 (95% CI: 0.82-0.97). When analyzed by ethnicity, Asians with the MTHFR 1298CC genotype exhibited a decreased risk of CRC (OR=0.69; 95% CI: 0.54-0.89). In a mixed population, a significantly reduced risk of CRC was observed among carriers of the 677TT (OR=0.86; 95% CI: 0.76-0.96) and the 1298CC (OR=0.82; 95% CI: 0.69-0.98) genotypes, compared to the wild-type homozygous genotype. In the subgroup of colon cancer, the OR of 677TT vs. CC+CT was 0.83 (95% CI: 0.72-0.96) and the OR of 1298CC vs. AA+AC was 0.81 (95% CI: 0.69-0.96). In the rectal cancer subgroup, the OR of 677TT vs. CC+CT was 0.86 (95% CI: 0.77-0.97). Therefore, this meta-analysis suggested that the MTHFR 677T and 1298C alleles were associated with a low risk of CRC.

The 677C>T (rs1801133) polymorphism in the MTHFR gene contributes to colorectal cancer risk: a meta-analysis based on 71 research studies

Background

The 677C>T polymorphism of methylenetetrahydrofolate reductase (MTHFR) gene is considered to have a significant effect on colorectal cancer susceptibility, but the results are inconsistent. In order to investigate the association between the MTHFR 677C>T polymorphism and the risk of colorectal cancer, a meta-analysis was held based on 71 published studies.

Methods

Eligible studies were identified through searching the MEDLINE, EMBASE, PubMed, Web of Science, Chinese Biomedical Literature database (CBM) and CNKI database. Odds ratios (OR) and 95% confidence intervals (CIs) were used to assess the association. The statistical heterogeneity across studies was examined with x²-based Q-test. Begg's and Egger's test were also carried out to evaluate publication bias. Sensitive and subgroup analysis were also held in this meta-analysis.

Results

Overall, 71 publications including 31,572 cases and 44,066 controls were identified. The MTHFR 677 C>T variant genotypes are significantly associated with increased risk of colorectal cancer. In the stratified analysis by ethnicity, significantly increased risks were also found among Caucasians for CC vs TT (OR = 1.076; 95%CI =  1.008–1.150; I² = 52.3%), CT vs TT (OR = 1.102; 95%CI = 1.032–1.177; I² = 51.4%) and dominant model (OR = 1.086; 95%CI = 1.021–1.156; I² = 53.6%). Asians for CC vs TT (OR  = 1.226; 95%CI  = 1.116–1.346; I²  = 55.3%), CT vs TT (OR  = 1.180; 95%CI  = 1.079–1.291; I²  = 36.2%), recessive (OR  = 1.069; 95%CI  = 1.003-1.140; I²  = 30.9%) and dominant model (OR  = 1.198; 95%CI  = 1.101-1.303; I²  = 52.4%), and Mixed populations for CT vs TT (OR  = 1.142; 95%CI  = 1.005-1.296; I²  = 0.0%). However, no associations were found in Africans for all genetic models.

Conclusion

This meta-analysis suggests that the MTHFR 677C>T polymorphism increases the risk for developing colorectal cancer, while there is no association among Africans found in subgroup analysis by ethnicity.

Effects of vitamin B6 metabolism on oncogenesis, tumor progression and therapeutic responses

Pyridoxal-5'-phosphate (PLP), the bioactive form of vitamin B6, reportedly functions as a prosthetic group for >4% of classified enzymatic activities of the cell. It is therefore not surprising that alterations of vitamin B6 metabolism have been associated with multiple human diseases. As a striking example, mutations in the gene coding for antiquitin, an evolutionary old aldehyde dehydrogenase, result in pyridoxine-dependent seizures, owing to the accumulation of a metabolic intermediate that inactivates PLP. In addition, PLP is required for the catabolism of homocysteine by transsulfuration. Hence, reduced circulating levels of B6 vitamers (including PLP as well as its major precursor pyridoxine) are frequently paralleled by hyperhomocysteinemia, a condition that has been associated with an increased risk for multiple cardiovascular diseases. During the past 30 years, an intense wave of clinical investigation has attempted to dissect the putative links between vitamin B6 and cancer. Thus, high circulating levels of vitamin B6, as such or as they reflected reduced amounts of circulating homocysteine, have been associated with improved disease outcome in patients bearing a wide range of hematological and solid neoplasms. More recently, the proficiency of vitamin B6 metabolism has been shown to modulate the adaptive response of tumor cells to a plethora of physical and chemical stress conditions. Moreover, elevated levels of pyridoxal kinase (PDXK), the enzyme that converts pyridoxine and other vitamin B6 precursors into PLP, have been shown to constitute a good, therapy-independent prognostic marker in patients affected by non-small cell lung carcinoma (NSCLC). Here, we will discuss the clinical relevance of vitamin B6 metabolism as a prognostic factor in cancer patients.

Systemic folate status, rectal mucosal folate concentration and dietary intake in patients at differential risk of bowel cancer (The FAB2 Study)

BACKGROUND/OBJECTIVES

Folate has been strongly implicated in the aetiology of colorectal cancer. However, the relationship between dietary folate intake, rectal mucosal folate status and colorectal cancer risk is uncertain. The study aimed to estimate nutrient intakes and measure systemic folate status and rectal mucosal folate concentration in people at differential risk of developing colorectal cancer.

METHODS

Two hundred and twenty-eight individuals were recruited from gastroenterology clinics and subdivided into three patient groups: untreated colorectal cancer (n = 43), adenomatous polyps (n = 90) or normal bowel (n = 95). Biopsies from macroscopically normal rectal mucosa and blood were collected and used for the measurement of rectal mucosal 5-methyltetrahydrofolate (5-MeTHF) and systemic markers of folate status, respectively. Nutrient intake was estimated using a validated food frequency questionnaire.

RESULTS

Dietary intake variables, plasma 5-MeTHF and red cell folate and plasma homocysteine concentrations were similar in all three subject groups and 95% CI fell within normal range for each variable. Rectal mucosal 5-MeTHF concentration was higher in the normal mucosa of adenomatous polyp patients than in normal subjects (P = 0.055). Rectal mucosal 5-MeTHF was associated significantly with plasma folate (P < 0.001, r = 0.294), red cell folate (P = 0.014, r = 0.305), plasma homocysteine (P = 0.017, r = -0.163) and dietary folate intake (P = 0.036, r = 0.152).

CONCLUSIONS

This study demonstrates adequate folate status of patients attending gastroenterology clinics for the investigation of bowel symptoms, with no significant difference in dietary intakes or systemic folate status indices according to diagnosis. Rectal mucosal 5-MeTHF concentrations were elevated in adenomatous polyp patients, but failed to reach significance. Further studies are required to determine the biological significance of this observation.

Folate Intake, MTHFR Polymorphisms, and the Risk of Colorectal Cancer: A Systematic Review and Meta-Analysis

Background. The objective was to determine whether relationships exist between the methylene-tetrahydrofolate reductase (MTHFR) polymorphisms and risk of colorectal cancer (CRC) and examine whether the risk is modified by level of folate intake. Methods. MEDLINE, Embase, and SCOPUS were searched to May 2012 using the terms "folic acid," "folate," "colorectal cancer," "methylenetetrahydrofolate reductase," "MTHFR." Observational studies were included which (1) assessed the risk of CRC for each polymorphism and/or (2) had defined levels of folate intake for each polymorphism and assessed the risk of CRC. Results. From 910 references, 67 studies met our criteria; hand searching yielded 10 studies. The summary risk estimate comparing the 677CT versus CC genotype was 1.02 (95% CI 0.95-1.10) and for 677TT versus CC was 0.88 (95% CI 0.80-0.96) both with heterogeneity. The summary risk estimates for A1298C polymorphisms suggested no reduced risk. The summary risk estimate for high versus low total folate for the 677CC genotype was 0.70 (95% CI 0.56-0.89) and the 677TT genotype 0.63 (95% CI 0.41-0.97). Conclusion. These results suggest that the 677TT genotype is associated with a reduced risk of developing CRC, under conditions of high total folate intake, and this associated risk remains reduced for both MTHFR 677 CC and TT genotypes.

MTHFR C677T polymorphism contributes to colorectal cancer susceptibility: evidence from 61 case-control studies

Methylenetetrahydrofolate reductase (MTHFR) is believed to be involved in folate metabolism which plays a critical role in carcinogenesis. To date, many case-control studies have investigated the association between MTHFR C677T polymorphism and colorectal cancer risk. However, the results were inconsistent. In order to derive a more precise estimation of the association, we conducted this meta-analysis. This meta-analysis recruited 61 published studies which were selected by a search of PubMed up to 31st September 2011, including 16,111 colorectal cancer cases and 23,192 controls. We used crude odds ratios (ORs) with 95 % confidence intervals (CIs) to assess the association between MTHFR C677T polymorphism and colorectal cancer susceptibility. Our results showed that MTHFR C667T polymorphism contributed to the decreased colorectal cancer risk in overall population (for TT vs. CC: OR = 0.89, 95 % CI = 0.82-0.97; for TT vs. CT/CC: OR = 0.88, 95 % CI = 0.83-0.92). In subgroup analysis by ethnicity, the results also indicated a correlation between the T allele of MTHFR C667T and the colorectal cancer risk in Asian population (for TT vs. CC: OR = 0.82, 95 % CI = 0.69-0.97; for TT vs. CT/CC: OR = 0.81, 95 % CI = 0.74-0.90). Additionally, the correlation was also observed in male subgroup in sub-analysis by gender (for TT vs. CC: OR = 0.82, 95 % CI = 0.71-0.93; for TT vs. CT/CC: OR = 0.81, 95 % CI = 0.71-0.92). In summary, our meta-analysis strongly indicated the MTHFR C667T polymorphism was associated with a reduced risk of CRC.

The polymorphisms in methylenetetrahydrofolate reductase, methionine synthase, methionine synthase reductase, and the risk of colorectal cancer

Polymorphisms in genes involved in folate metabolism may modulate the risk of colorectal cancer (CRC), but data from published studies are conflicting. The current meta-analysis was performed to address a more accurate estimation. A total of 41 (17,552 cases and 26,238 controls), 24(8,263 cases and 12,033 controls), 12(3,758 cases and 5,646 controls), and 13 (5,511 cases and 7,265 controls) studies were finally included for the association between methylenetetrahydrofolate reductase (MTHFR) C677T and A1289C, methione synthase reductase (MTRR) A66G, methionine synthase (MTR) A2756G polymorphisms and the risk of CRC, respectively. The data showed that the MTHFR 677T allele was significantly associated with reduced risk of CRC (OR = 0.93, 95%CI 0.90-0.96), while the MTRR 66G allele was significantly associated with increased risk of CRC (OR = 1.11, 95%CI 1.01-1.18). Sub-group analysis by ethnicity revealed that MTHFR C677T polymorphism was significantly associated with reduced risk of CRC in Asians (OR = 0.80, 95%CI 0.72-0.89) and Caucasians (OR = 0.84, 95%CI 0.76-0.93) in recessive genetic model, while the MTRR 66GG genotype was found to significantly increase the risk of CRC in Caucasians (GG vs. AA: OR = 1.18, 95%CI 1.03-1.36). No significant association was found between MTHFR A1298C and MTR A2756G polymorphisms and the risk of CRC. Cumulative meta-analysis showed no particular time trend existed in the summary estimate. Probability of publication bias was low across all comparisons illustrated by the funnel plots and Egger's test. Collectively, this meta-analysis suggested that MTHFR 677T allele might provide protection against CRC in worldwide populations, while MTRR 66G allele might increase the risk of CRC in Caucasians. Since potential confounders could not be ruled out completely, further studies were needed to confirm these results.

Effect of butyrate on aromatase cytochrome P450 levels in HT29, DLD-1 and LoVo colon cancer cells

Epidemiological studies suggest that colonic production of butyrate and estrogen may be involved in human susceptibility to colorectal cancer (CRC). Estrone (E1) can be produced by the aromatase pathway during the conversion of androstenedione (A) to E1. Therefore, we studied the effect of sodium butyrate (NaBu) on the CYP19A1 transcript and protein levels and on the conversion of A to E1 in HT29, DLD-1 and LoVo CRC cells. We found that NaBu significantly downregulated CYP19A1 transcript and protein levels, a phenomenon that was associated with reduced conversion of A to E1 in HT29, DLD-1 and LoVo cells. Our studies demonstrated that, although butyrate exhibited a protective role in CRC development, this compound may reduce aromatase activity and the production of E1 in colon cancer cells.

Effect modification by population dietary folate on the association between MTHFR genotype, homocysteine, and stroke risk: a meta-analysis of genetic studies and randomised trials

BACKGROUND

The MTHFR 677C→T polymorphism has been associated with raised homocysteine concentration and increased risk of stroke. A previous overview showed that the effects were greatest in regions with low dietary folate consumption, but differentiation between the effect of folate and small-study bias was difficult. A meta-analysis of randomised trials of homocysteine-lowering interventions showed no reduction in coronary heart disease events or stroke, but the trials were generally set in populations with high folate consumption. We aimed to reduce the effect of small-study bias and investigate whether folate status modifies the association between MTHFR 677C→T and stroke in a genetic analysis and meta-analysis of randomised controlled trials.

METHODS

We established a collaboration of genetic studies consisting of 237 datasets including 59,995 individuals with data for homocysteine and 20,885 stroke events. We compared the genetic findings with a meta-analysis of 13 randomised trials of homocysteine-lowering treatments and stroke risk (45,549 individuals, 2314 stroke events, 269 transient ischaemic attacks).

FINDINGS

The effect of the MTHFR 677C→T variant on homocysteine concentration was larger in low folate regions (Asia; difference between individuals with TT versus CC genotype, 3·12 μmol/L, 95% CI 2·23 to 4·01) than in areas with folate fortification (America, Australia, and New Zealand, high; 0·13 μmol/L, -0·85 to 1·11). The odds ratio (OR) for stroke was also higher in Asia (1·68, 95% CI 1·44 to 1·97) than in America, Australia, and New Zealand, high (1·03, 0·84 to 1·25). Most randomised trials took place in regions with high or increasing population folate concentrations. The summary relative risk (RR) of stroke in trials of homocysteine-lowering interventions (0·94, 95% CI 0·85 to 1·04) was similar to that predicted for the same extent of homocysteine reduction in large genetic studies in populations with similar folate status (predicted RR 1·00, 95% CI 0·90 to 1·11). Although the predicted effect of homocysteine reduction from large genetic studies in low folate regions (Asia) was larger (RR 0·78, 95% CI 0·68 to 0·90), no trial has evaluated the effect of lowering of homocysteine on stroke risk exclusively in a low folate region.

INTERPRETATION

In regions with increasing levels or established policies of population folate supplementation, evidence from genetic studies and randomised trials is concordant in suggesting an absence of benefit from lowering of homocysteine for prevention of stroke. Further large-scale genetic studies of the association between MTHFR 677C→T and stroke in low folate settings are needed to distinguish effect modification by folate from small-study bias. If future randomised trials of homocysteine-lowering interventions for stroke prevention are undertaken, they should take place in regions with low folate consumption.

FUNDING

Full funding sources listed at end of paper (see Acknowledgments).

Butyrate induces expression of 17β-hydroxysteroid dehydrogenase type 1 in HT29 and SW707 colorectal cancer cells

Epidemiological studies have revealed that butyrate and 17β-estradiol (E2) may decrease the incidence of colorectal cancer (CRC). In peripheral tissue, E2 can be produced locally by 17β-hydroxysteroid dehydrogenase 1 (HSD17B1) estrone (E1) reduction. Using quantitative real-time polymerase chain reaction and western blotting analysis, we found that sodium butyrate significantly upregulates HSD17B1 long and short transcripts and protein levels in HT29 and SW707 CRC cells. Chromatin immunoprecipitation analysis showed that upregulation of these transcript levels correlated with an increase in binding of Polymerase II to proximal and distal promoters of HSD17B1. Moreover, we observed that upregulation of HSD17B1 protein levels was associated with increased conversion of E1 to E2 in HT29 and SW707 CRC cells. Since sodium butyrate increases the conversion of E1 to E2, our findings may support the validity of butyrate in the prophylaxis of CRC incidence.

Folate intake and the risk of colorectal cancer: a systematic review and meta-analysis

INTRODUCTION

Folic acid fortification and supplementation to prevent neural tube defects has led to concerns regarding increased risk of colorectal cancer. The results of existing studies have been inconclusive. The purpose was to examine the relationship between level of folate intake and the incidence of colorectal cancer.

METHODS

A systematic review and meta analysis were conducted. MEDLINE, Embase, and SCOPUS were searched from inception to October 2009 with the following search terms "folic acid," "folate", "colorectal cancer," "colon neoplasms," rectal neoplasms." Observational studies in adult populations were included that defined levels of folate intake and incidence of colorectal cancer.

RESULT

Out of 6427 references, 27 studies met our inclusion criteria. The summary risk estimate for case control studies comparing high versus low total folate intake was 0.85 (CI 95% 0.74-0.99) with no significant heterogeneity among studies. Similarly, for cohort studies, the resulting summary risk estimate for high versus low dietary folate intake was 0.92 (CI 95% 0.81-1.05) with no significant heterogeneity. However, defining what represents a higher intake of folic acid is difficult as there is variability in the upper limit of folic acid intake used in the studies.

DISCUSSION

These results suggest that higher folate intake levels offer a reduction in one of the perceived risks associated with developing colorectal cancer. These data can serve to help reassure women planning a pregnancy to increase folic intake during the preconception period to levels sufficient to prevent neural tube defects.

A candidate gene study of folate-associated one carbon metabolism genes and colorectal cancer risk

BACKGROUND

Folate-associated one-carbon metabolism (FOCM) may play an important role in colorectal carcinogenesis. Variation in FOCM genes may explain some of the underlying risk of colorectal cancer.

METHODS

This study utilized data from 1,805 population-based colorectal cancer cases and 2,878 matched sibling controls from the Colon Cancer Family Registry. We used a comprehensive haplotype tagging single nucleotide polymorphism (tagSNP) approach to select 395 tagSNPs in 15 genes involved in folate and vitamin B(12) metabolism. Genotyping was done using the Illumina GoldenGate or Sequenom platforms. Risk factor and dietary data were collected using self-completed questionnaires. Microsatellite instability (MSI) status was determined using standard techniques, and tumor subsite was obtained from pathology reports. The association between SNPs and colorectal cancer was assessed using conditional logistic regression with sibships as the matching factor and assuming a log additive or codominant model.

RESULTS

In the log additive model, two linked (r(2) = 0.99) tagSNPs in the DHFR gene (rs1677693 and rs1643659) were associated with a significant decrease in colorectal cancer risk after correction for multiple testing (odds ratio, 0.87; 95% confidence interval, 0.71-0.94; P = 0.029; and odds ratio, 0.87; 95% confidence interval, 0.71-0.95; P = 0.034 for rs1677693 and rs1643659, respectively). These two linked (r(2) = 0.99) tagSNPs and one tagSNP in the MTR gene (rs4659744) were significantly associated with reduced colorectal cancer risk only among individuals not using multivitamin supplements.

CONCLUSIONS

Overall, we found only moderate evidence that genetic variation in 15 folate pathway genes may affect colorectal cancer risk except in non-multivitamin users.

IMPACT

This study suggests that multivitamin supplement use may modify the association between folate pathway genes and colorectal cancer risk in a post-folic-acid-supplemented population.

Plasma vitamins B2, B6, and B12, and related genetic variants as predictors of colorectal cancer risk

BACKGROUND

B-vitamins are essential for one-carbon metabolism and have been linked to colorectal cancer. Although associations with folate have frequently been studied, studies on other plasma vitamins B2, B6, and B12 and colorectal cancer are scarce or inconclusive.

METHODS

We carried out a nested case-control study within the European Prospective Investigation into Cancer and Nutrition, including 1,365 incident colorectal cancer cases and 2,319 controls matched for study center, age, and sex. We measured the sum of B2 species riboflavin and flavin mononucleotide, and the sum of B6 species pyridoxal 5'-phosphate, pyridoxal, and 4-pyridoxic acid as indicators for vitamin B2 and B6 status, as well as vitamin B12 in plasma samples collected at baseline. In addition, we determined eight polymorphisms related to one-carbon metabolism. Relative risks for colorectal cancer were estimated using conditional logistic regression, adjusted for smoking, education, physical activity, body mass index, alcohol consumption, and intakes of fiber and red and processed meat.

RESULTS

The relative risks comparing highest to lowest quintile were 0.71 [95% confidence interval (95% CI), 0.56-0.91; P(trend) = 0.02] for vitamin B2, 0.68 (95% CI, 0.53-0.87; P(trend) <0.001) for vitamin B6, and 1.02 (95% CI, 0.80-1.29; P(trend) = 0.19) for vitamin B12. The associations for vitamin B6 were stronger in males who consumed ≥30 g alcohol/day. The polymorphisms were not associated with colorectal cancer.

CONCLUSIONS

Higher plasma concentrations of vitamins B2 and B6 are associated with a lower colorectal cancer risk.

IMPACT

This European population-based study is the first to indicate that vitamin B2 is inversely associated with colorectal cancer, and is in agreement with previously suggested inverse associations of vitamin B6 with colorectal cancer.

Risk factors for colon cancer in Northeastern Thailand: interaction of MTHFR codon 677 and 1298 genotypes with environmental factors

BACKGROUND

Polymorphisms in methylenetetrahydrofolate reductase (MTHFR), such as MTHFR C677T and A1298C, are associated with several cancers. This study aimed to evaluate the effects of MTHFR polymorphisms on colon cancer risk and possible interactions with environmental factors in a population from northeastern Thailand.

METHODS

This hospital-based case-control study was conducted during 2002-2006; 130 colon cancer cases and 130 age- and sex-matched controls were enrolled. Information was collected and blood samples were obtained for assay of MTHFR C677T and A1298C polymorphisms by polymerase chain reaction with restriction fragment length polymorphism techniques. Associations between variables of interest and colon cancer were assessed using conditional logistic regression.

RESULTS

Increased risk of colon cancer was associated with alcohol consumption and bowel habits. Alcohol drinkers who consumed < or = 0.50 or >0.50 units of alcohol per day had elevated risks (OR(adj) = 3.5; 95% CI: 1.19-10.25 and OR(adj) = 1.71; 95% CI: 0.74-3.96, respectively). The risk was also higher in subjects with frequent constipation (11.69; 2.18-62.79) and occasional constipation (3.43; 1.72-6.82). An interaction was observed between the MTHFR C677T polymorphism and freshwater fish consumption on colon cancer risk (P value for interaction = 0.031). Interactions were observed between the MTHFR A1298C polymorphism and bowel habits, family history of cancer, alcohol consumption, and beef consumption on colon cancer risk (P-value for interaction = 0.0005, 0.007, 0.067, 0.003, respectively).

CONCLUSIONS

In a Thai population, colon cancer risk was associated with alcohol and beef consumption, bowel habits, and family history of cancer. Interactions between MTHFR polymorphisms and environmental factors were also observed.

Germline polymorphisms in the one-carbon metabolism pathway and DNA methylation in colorectal cancer

Dietary intake of one-carbon nutrients (methyl donors) and germline variants in the one-carbon metabolism genes may influence global DNA methylation level and methylation in promoter CpG islands. In this study, we evaluated the relationship between single nucleotide polymorphisms (SNPs) in the one-carbon metabolism pathway and DNA methylation status in colorectal cancer. Utilizing 182 colorectal cancers cases in two prospective cohort studies, we determined the CpG island methylator phenotype (CIMP) status on eight CIMP-specific promoters and measured LINE-1 methylation level that correlates well with genome-wide DNA methylation level. We genotyped 23 nonsynonymous SNPs in the one-carbon metabolism genes using buffy coat DNA. Most of the 23 SNPs in the one-carbon metabolism pathway were not significantly associated with CIMP-high status (> or = 6/8 methylated promoters). However, the MTHFR 429 Ala/Ala variant (rs1801131) and the TCN2 259 Arg/Arg variant (rs1801198) were associated with CIMP-high status (MTHFR 429 multivariate odds ratio (MV OR) = 7.56; 95% confidence interval (CI), 1.32-43.3; p trend = 0.10; TCN2 259 Arg/Arg variant MV OR = 3.82; 95% CI, 1.02-14.4; p trend = 0.06). The one-carbon metabolism genotypes were not significantly associated with LINE-1 methylation, although there were modest differences in mean LINE-1 methylation levels between certain genotypes. Collectively, these exploratory data provide suggestive evidence for the association of MTHFR 429 Ala/ Ala and TCN2 259 Arg/Arg and CIMP status in colorectal cancer.

Genetic variability in the MTHFR gene and colorectal cancer risk using the colorectal cancer family registry

BACKGROUND

The MTHFR C677T TT genotype is associated with a 15% to 18% reduction in colorectal cancer risk, but it is not clear if other variants of the gene are associated with colorectal cancer risk.

METHODS

We used a tagSNP approach to comprehensively evaluate associations between variation in the MTHFR gene and colorectal cancer risk using a large family-based case-control study of 1,750 population-based and 245 clinic-based families from the Colon Cancer Family Registry. We assessed 22 TagSNPs, selected based on pairwise r(2) >95%, using the Haploview Tagger and genotyped the TagSNPs on the Illumina GoldenGate or Sequenom platforms. The association between single nucleotide polymorphisms and colorectal cancer was assessed using log-additive, codominant, and recessive models.

RESULTS

From studying the population-based families, the C677T (rs1801133) and A1298C (rs1801131) polymorphisms were associated with a decreased colorectal cancer risk overall [odds ratio (OR), 0.81; 95% confidence interval (95% CI), 0.63-1.04; and OR, 0.82; 95% CI, 0.64-1.07, respectively]. The 677 TT genotype was associated with a decreased risk of microsatellite-stable/microsatellite-low tumors (OR, 0.69; 95% CI, 0.49-0.97) and an increased risk of microsatellite-high tumors (OR, 2.22; 95% CI, 0.91-5.43; P(interaction) = 0.01), as well as an increased risk of proximal cancers and a decreased risk of distal and rectal cancers (P(interaction) = 0.02). No other single nucleotide polymorphism was associated with risk overall or within subgroups.

CONCLUSION

The 677 TT and 1298 CC genotypes may each be associated with a decrease in colorectal cancer risk. We observed little evidence of additional genetic variability in the MTHFR gene relevant to colorectal cancer risk.

Association of polymorphisms MTHFR C677T and A1298C with risk of colorectal cancer, genetic and epigenetic characteristic of tumors, and response to chemotherapy

BACKGROUND AND AIMS

The enzyme MTHFR plays an important role in folate metabolism, and folate is implicated in carcinogenesis due to its role in DNA methylation, repair, and synthesis. We analyze the relationship of MTHFR C677T and A1298C polymorphisms with biological, clinicopathological, genetic and epigenetic features of tumors, and the patient outcome after treatment with 5-FU-based chemotherapy to determine the contribution of MTHFR genotypes in the risk of colorectal cancer (CRC) and in the response to therapy.

METHODS

Genomic DNA of 143 Spanish sporadic CRC and 103 controls was analyzed by polymerase chain reaction/restriction fragment length polymorphism and sequencing.

RESULTS

The C677T polymorphism has protective effect on CRC showing TT genotype an odds ratios of 0.06 (95% confidence interval (CI): 0.10-0.32) and the CT of 0.51 (95% CI: 0.3-0.87). MTHFR A1298C polymorphism is not associated with CRC risk. Patients with 1298CC and AC genotypes exhibit worse survival than those with the wild genotype (log rank, p = 0.001), whereas C677T genotypes do not affect patient survival (log rank, p = 0.92). MTHFR 677T allele carriers responded better to 5-FU-based chemotherapy than patients with the wild CC genotype (log rank, p = 0.05). The variant C allele of A1298C affects negatively the response to 5-FU-based chemotherapy (log rank, p = 0.009).

CONCLUSIONS

The variant allele of the C677T has a protective effect on CRC development, whereas the variant allele of the A1298C does not produce any effect on disease risk. Both MTHFR polymorphisms are relevant and independent factors of patient outcome after 5FU-based treatment of CRC, and MTHFR genotyping may be of predictive benefit in selecting treatment regimens.

Meta- and pooled analyses of the methylenetetrahydrofolate reductase (MTHFR) C677T polymorphism and colorectal cancer: a HuGE-GSEC review

Worldwide, over 1 million cases of colorectal cancer (CRC) were reported in 2002, with a 50% mortality rate, making CRC the second most common cancer in adults. Certain racial/ethnic populations continue to experience a disproportionate burden of CRC. A common polymorphism in the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene has been associated with a lower risk of CRC. The authors performed both a meta-analysis (29 studies; 11,936 cases, 18,714 controls) and a pooled analysis (14 studies; 5,068 cases, 7,876 controls) of the C677T MTHFR polymorphism and CRC, with stratification by racial/ethnic population and behavioral risk factors. There were few studies on different racial/ethnic populations. The overall meta-analysis odds ratio for CRC for persons with the TT genotype was 0.83 (95% confidence interval (CI): 0.77, 0.90). An inverse association was observed in whites (odds ratio = 0.83, 95% CI: 0.74, 0.94) and Asians (odds ratio = 0.80, 95% CI: 0.67, 0.96) but not in Latinos or blacks. Similar results were observed for Asians, Latinos, and blacks in the pooled analysis. The inverse association between the MTHFR 677TT polymorphism and CRC was not significantly modified by smoking status or body mass index; however, it was present in regular alcohol users only. The MTHFR 677TT polymorphism seems to be associated with a reduced risk of CRC, but this may not hold true for all populations.

Increased breast cancer risk at high plasma folate concentrations among women with the MTHFR 677T allele

BACKGROUND

Folate is involved in DNA synthesis and methylation and may thereby influence carcinogenesis.

OBJECTIVES

We examined plasma folate (P-folate) concentration in relation to genotypes of the folate-metabolizing enzyme methylenetetrahydrofolate reductase [MTHFR 677C-->T (rs1801133) and 1298A-->C (rs1801131)]. We also explored whether P-folate was associated with risk of postmenopausal breast cancer overall and in subgroups with genetic variants of the MTHFR single nucleotide polymorphisms (SNPs).

DESIGN

This nested case-control study included 313 cases (age 55-73 y at baseline) with invasive breast cancer and 626 control subjects, matched on age and blood-sample date, from the population-based Malmö Diet and Cancer cohort. P-folate and MTHFR genotypes were determined for 310 cases and 611 controls. P-folate according to genotype was calculated by using analysis of variance. Odds ratios were obtained by using logistic regression. All tests were 2-sided.

RESULTS

The variant 677T allele was associated with lower P-folate. In women with the 677T allele, a high P-folate concentration was associated with increased breast cancer risk (P for trend across P-folate tertiles = 0.03). Interaction was seen between the 677C-->T SNP and P-folate (P = 0.002). A positive association, which was seen between P-folate and breast cancer risk in 1298AA women (P = 0.01), was probably due to linkage between the 2 SNPs. Overall, and in women with other genotypes, no significant associations were observed.

CONCLUSIONS

Our results suggest an association of high P-folate concentration with increased risk of postmenopausal breast cancer in carriers of the 677T allele. The findings underline the importance of genetic variation of MTHFR in the complex relation between folate and cancer.

Genetic variants of methyl metabolizing enzymes and epigenetic regulators: associations with promoter CpG island hypermethylation in colorectal cancer

Aberrant DNA methylation affects carcinogenesis of colorectal cancer. Folate metabolizing enzymes may influence the bioavailability of methyl groups, whereas DNA and histone methyltransferases are involved in epigenetic regulation of gene expression. We studied associations of genetic variants of folate metabolizing enzymes (MTHFR, MTR, and MTRR), DNA methyltransferase DNMT3b, and histone methyltransferases (EHMT1, EHMT2, and PRDM2), with colorectal cancers, with or without the CpG island methylator phenotype (CIMP), MLH1 hypermethylation, or microsatellite instability. Incidence rate ratios were calculated in case-cohort analyses, with common homozygotes as reference, among 659 cases and 1,736 subcohort members of the Netherlands Cohort Study on diet and cancer (n = 120,852). Men with the MTHFR 677TT genotype were at decreased colorectal cancer risk (incidence rate ratio, 0.49; P = 0.01), but the T allele was associated with increased risk in women (incidence rate ratio, 1.39; P = 0.02). The MTR 2756GG genotype was associated with increased colorectal cancer risk (incidence rate ratio, 1.58; P = 0.04), and inverse associations were observed among women carrying DNMT3b C-->T (rs406193; incidence rate ratio, 0.72; P = 0.04) or EHMT2 G-->A (rs535586; incidence rate ratio, 0.76; P = 0.05) polymorphisms. Although significantly correlated (P < 0.001), only 41.5% and 33.3% of CIMP tumors harbored MLH1 hypermethylation or microsatellite instability, respectively. We observed inverse associations between MTR A2756G and CIMP among men (incidence rate ratio, 0.58; P = 0.04), and between MTRR A66G and MLH1 hypermethylation among women (incidence rate ratio, 0.55; P = 0.02). In conclusion, MTHFR, MTR, DNMT3b, and EHMT2 polymorphisms are associated with colorectal cancer, and rare variants of MTR and MTRR may reduce promoter hypermethylation. The incomplete overlap between CIMP, MLH1 hypermethylation, and microsatellite instability indicates that these related "methylation phenotypes" may not be similar and should be investigated separately.

The MTHFR C677T and DeltaDNMT3B C-149T polymorphisms confer different risks for right- and left-sided colorectal cancer

Etiological risk factors for proximal (right-sided) colon cancers may be different to those of distal colon and rectal (left-sided) cancers if these tumors develop along distinct pathways. The CpG Island Methylator Phenotype (CIMP+) occurs in approximately 15% of colorectal cancers (CRC) and predominantly in the proximal colon. CIMP+ tumors have frequent methylation of gene promoter regions and increased tissue folate levels. The aim here was to determine whether polymorphisms in 2 genes involved in cellular methyl group metabolism were associated with different risks for right- and left-sided CRC. This population-based case-control study involved 859 incident cases of CRC and 973 sex and age-matched controls. Information on dietary folate and alcohol intake was obtained from food frequency questionnaires and information on the anatomical site of tumors from pathology reports. DNA was collected using FTA cards and genotyping performed for the MTHFR C677T and DeltaDNMT3B C-149T polymorphisms. The MTHFR 677 T allele was associated with increased risk for proximal colon cancer (adjusted odds ratio, AOR = 1.29) but decreased risk for distal cancers (AOR = 0.87). The increased risk for proximal cancers was especially pronounced in older individuals (AOR = 1.49) and those with a low folate diet (AOR = 1.67) or high alcohol consumption (AOR = 1.90). The DeltaDNMT3B-149 TT genotype was protective against proximal colon cancers (AOR = 0.65), but showed no association with the risk of distal colon and rectal cancers (AOR = 1.02). Epidemiological studies on dietary and genetic risk factors for CRC should take into account these may confer different risks for right- and left-sided tumors.

Folate intake and the risk of colorectal cancer in a Korean population

BACKGROUND

Folate, a water-soluble B vitamin and one of the major micronutrients in vegetables, is known as an essential factor for the de novo biosynthesis of purines and thymidylate, and it plays an important role in DNA synthesis and replication. Thus, folate deficiency results in ineffective DNA synthesis, and has been shown to induce the initiation and progression of colorectal cancer (CRC). Recently, the incidence of CRC in Korea has increased markedly in both men and women; this trend may be related to the adoption of a more 'westernized' lifestyle, including dietary habits.

OBJECTIVE

A hospital-based case-control study was conducted to examine the relationship between folate intake and the risk of CRC within a Korean population.

METHODS

A total of 596 cases and 509 controls, aged 30-79 years, were recruited from two university hospitals. Site- and sex-specific odds ratios (ORs) were estimated using logistic regression models.

RESULTS

Cases were more frequently found to have a family history of CRC among first-degree relatives, to consume more alcohol, to be more likely current smokers and less likely to participate in vigorous physical activity than the controls. In the overall data for men and women combined, multivariate ORs (95% confidence interval (CI), P for trend) comparing the highest vs the lowest quartile of dietary folate intake were: 0.47 (0.32-0.69, <0.001) for CRC, 0.42 (0.26-0.69, <0.001) for colon cancer and 0.48 (0.28-0.81, 0.007) for rectal cancer. An inverse association was also found in women with dietary folate intake: 0.36 (0.20-0.64, <0.001) for CRC, 0.34 (0.16-0.70, 0.001) for colon cancer and 0.30 (0.12-0.74, 0.026) for rectal cancer, but not in men. In addition, the total folate intake of women was strongly associated with a reduced risk of rectal cancer (OR, 0.38; 95% CI, 0.17-0.88; P for trend=0.04).

CONCLUSION

We found a statistically significant relationship between higher dietary folate intake and reduced risk of CRC, colon cancer and rectal cancer in women. A significant association is indicated between higher total folate intake and reduced risk of rectal cancer in women.

Folate and colorectal cancer prevention

Anti-folate chemotherapy agents such as methotrexate and fluorouracil reduce proliferation of neoplastic cells by inhibiting DNA synthesis. Paradoxically epidemiological data suggests an inverse relationship between dietary folate intake and incidence of colorectal cancer (CRC). On the basis of this and other putative health benefits around 35% of the North American population take folic acid supplements, in addition to natural food folates and fortified flour and cereal grains. Recently, randomised controlled trials investigating folic acid as a secondary preventative agent in colorectal neoplasia have shed further light on the relationship between folate and colorectal carcinogenesis, corroborating data from animal models indicating opposing effects dependent on the timing of exposure in relation to the development of neoplastic foci. A ‘dual-modulator’ role for folate in colorectal carcinogenesis has been proposed in which moderate dietary increases initiated before the establishment of neoplastic foci have a protective influence, whereas excessive intake or increased intake once early lesions are established increases tumorigenesis. Functional polymorphic variants in genes encoding key enzymes in the folate metabolic pathway add a further layer of complexity to the relationship between folate and CRC risk. Here, we review the evidence concerning the efficacy and safety of folate as a potential CRC chemopreventive agent.