Methyl-deficient diets, methylated ER genes and breast cancer: an hypothesized association

The association between the 844ins68 polymorphism in the CBS gene and breast cancer

INTRODUCTION

The cystathionine beta synthase (CBS) gene plays an important role in homocysteine metabolism because it catalyzes the first step of the transsulfuration pathway, during which homocysteine is converted to cystathionine. Polymorphisms of CBS have been associated with cancer.

MATERIAL AND METHODS

We examined the role of the 844ins68 polymorphism by comparing the genotypes of 371 healthy Mexican women with the genotypes of 323 Mexican women with breast cancer (BC).

RESULTS

The observed genotype frequencies for controls and BC patients were 1% and 2% for Ins/Ins, 13% and 26% for W/Ins, and 86% and 72% for W/W, respectively. We found that the odds ratio (OR) was 2.2, with a 95% confidence interval (95% CI) of 1.5-3.3, p = 0.0001. The association was also evident when comparing the distribution of the W/Ins-Ins/Ins genotypes in patients in the following categories: 1) menopause and high γ-glutamyltransferase (GGT) levels (OR of 2.17, 95% CI: 1.17-4.26, p = 0.02), 2) chemotherapy response and high lactate dehydrogenase (LDH) levels (OR 2.2, 95% CI: 1.08-4.4, p = 0.027), 3) chemotherapy response and high GGT levels (OR 2.46, 95% CI: 1.2-4.8, p = 0.007), and 4) body mass index (BMI) and III-IV tumor stage (OR 3.2, 95% CI: 1.2-8.3, p = 0.013).

CONCLUSIONS

We conclude that the genotypes W/Ins-Ins/Ins of the 844ins68 polymorphism in the CBS gene contribute significantly to BC susceptibility in the analyzed sample from the Mexican population.

Lack of effects of dietary folate intake on risk of breast cancer: an updated meta-analysis of prospective studies

BACKGROUND

Epidemiological findings are controversial relating to the relationship between dietary folate intake and the risk of breast cancer. We therefore conducted a meta-analysis of prospective cohort studies to clarify this association.

MATERIALS AND METHODS

PUPMED, EMBASE, and MEDLINE databases were searched for all relevant literature published in English from January 1, 1966 to August 2013. Summary relative risk (RR) and 95% confidence intervals (CIs) were calculated using a fixed or random effects model.

RESULTS

Dietary folate intake was not significantly associated with the risk of breast cancer. The combined PR with 95% CI for the highest vs. lowest category dietary intake of folate [fifteen studies; 1,836,566 participants and 24,083 patients with breast cancer] was 0.98 (0.90-1.05). Among subgroup analysis by menstrual status, hormonal status and the consumption of alcohol, methionine and vitamin B12, no significant association was observed for the dietary intake of folate and the risk of breast cancer. Dose-response analysis showed that a 220 μg/day increment in dietary folate intake was not associated with the risk of breast cancer.

CONCLUSIONS

Our findings indicate that dietary folate intake has no significant effect on the risk of breast cancer.

Dietary intake of B vitamins and methionine and breast cancer risk

PURPOSE

We investigated prospectively the relationship between dietary intakes of methionine and B vitamins associated with one-carbon metabolism and breast cancer risk, including modification by age, hormone receptor status and alcohol consumption. Interactions between different B vitamins and methionine were also examined.

METHODS

During follow-up of 20,756 women from the Melbourne Collaborative Cohort Study for an average of 16 years, we ascertained 936 incident breast cancers. Dietary intakes were estimated using a 121-item food frequency questionnaire. Hazard ratios (HR) and 95 % confidence intervals were estimated using Cox regression.

RESULTS

We found weak evidence for an inverse association between breast cancer risk and riboflavin intake (fourth versus first quartile, HR Q4 vs. Q1 = 0.84 (0.69, 1.01); p linear trend = 0.05) and a positive association for vitamin B12 (HR Q4 vs. Q1 = 1.21 (1.00, 1.46); p linear trend = 0.06). We did not find any significant interactions between alcohol consumption and any of the B vitamins or methionine intake (all p interaction > 0.17) or between methionine or folate intake and any other B vitamins (all p interaction > 0.07). No association varied by tumor hormone receptor status (all p homogeneity > 0.14).

CONCLUSIONS

We found weak evidence of an inverse association between breast cancer risk and riboflavin intake and a positive association with vitamin B12.

Dietary intake of folate, B-vitamins and methionine and breast cancer risk among Hispanic and non-Hispanic white women

Background

Low dietary folate intake is associated with several neoplasias, but reports are inconsistent for breast cancer. Additionally, the association of folate with breast cancer estrogen receptor (ER) status is not well established.

Objective

To determine if dietary intakes of folate, B-vitamins (B₂, B₆, B₁₂) and methionine are associated with breast cancer risk and ER status in Hispanic, and non-Hispanic White women in the southwestern US.

Materials and Methods

Primary breast cancer cases (n = 2,325) in the 4-Corners region (Arizona, Colorado, New Mexico and Utah), diagnosed between October 1999 and May 2004, were identified through state cancer registries. Controls (n = 2,525) were frequency-matched by ethnicity and age (±5 years). Dietary intake, physical activity and other exposures were assessed using in-person interviews. Risk was assessed through multivariable and multinomial logistic regression with adjustment for relevant covariates.

Result

While there was no overall association with breast cancer, the highest quartile of folate intake was marginally inversely associated with ER− breast cancer (Odds Ratio (OR) = 0.50, 95%CI 0.25–1.00, p for trend = 0.07). Vitamin B₁₂ intake was inversely associated with breast cancer also (OR = 0.73, 95%CI 0.53–1.00, p for trend = 0.06), particularly for the highest quartile of ER+ breast cancer (OR = 0.67, 95%CI 0.46–0.99, p for trend = 0.06), among NHW women (OR = 0.49, 95%CI 0.29–0.81, p for trend = 0.01) and invasive breast cancer (OR = 0.63; 95%CI: 0.42, 0.93, P_trend = 0.01). Methionine intake was also inversely associated with ER+ breast cancer (OR for 4^th quartile = 0.83, 95%CI 0.66–1.03, p for trend = 0.04), primarily among Hispanic women (OR = 0.71, 95%CI 0.47–1.06, and P for trend = 0.02).

Conclusion

Higher intake of folate is marginally associated with a lower risk for ER− breast cancer, and higher intakes of vitamin B-12 and methionine are marginally associated with a lower risk of ER+ breast cancer.

Dietary intake of vitamin B(6) and risk of breast cancer in Taiwanese women

BACKGROUND

B vitamins, including vitamin B(6), are coenzymes that are important for DNA integrity and stability. Deficiencies in B vitamins may promote tumor carcinogenesis.

METHODS

We examined the association of dietary vitamin B(6) intake with overall breast cancer risk and breast cancers stratified by hormone receptor status. This case-control study included 391 breast cancer cases and 782 control subjects enrolled at the Tri-Service General Hospital in Taipei, Taiwan. Energy-adjusted intake of vitamin B(6) was derived from a food frequency questionnaire. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using logistic regression.

RESULTS

As compared with women in the lowest tertile, the multivariate-adjusted ORs for breast cancer among women in the second and highest tertiles of vitamin B(6) intake were 0.78 (95% CI, 0.64-2.52) and 0.64 (0.26-0.92), respectively. In addition, higher vitamin B(6) intake was associated with a significantly lower risk of developing ER-negative breast tumors.

CONCLUSIONS

Our findings suggest that higher intake of vitamin B(6) is associated with a reduction in breast cancer risk, particularly ER-negative tumors.

Plasma folate concentrations are positively associated with risk of estrogen receptor beta negative breast cancer in a Swedish nested case control study

Folate's role in breast cancer development is controversial. Not only estrogen receptor (ER) alpha status, but also ERbeta status of tumors may have confounded results from previous epidemiological studies. We aimed to examine associations between plasma folate concentration and postmenopausal breast cancer defined by ER status. This nested case-control study, within the Malmö diet and cancer cohort, included 204 incident breast cancer cases with information on ERalpha and ERbeta status determined by immunochemistry on tissue micro-array sections. Plasma folate concentration was analyzed for the cases and 408 controls (matched on age and blood sample date). Odds ratios (OR) for ER-defined breast cancers in tertiles of plasma folate concentration were calculated with unconditional logistic regression. All tests were 2-sided. Women in the third tertile of plasma folate concentration (> 12 nmol/L) had higher incidence of ERbeta- breast cancer than women in the first tertile (OR: 2.67; 95% CI: 1.44-4.92; P-trend = 0.001). We did not observe significant associations between plasma folate concentration and other breast cancer subgroups defined by ER status. We observed a difference between risks for ERbeta + and ERbeta- cancer (P-heterogeneity = 0.003). Our findings, which indicate a positive association between plasma folate and ERbeta- breast cancer, highlight the importance of taking ERbeta status into consideration in studies of folate and breast cancer. The study contributes knowledge concerning folate's multifaceted role in cancer development. If replicated in other populations, the observations may have implications for public health, particularly regarding folic acid fortification.

The silent estrogen receptor--can we make it speak?

One of the most common cancers in women world wide, breast cancer is classically an endocrine-dependent cancer. It has been known for over a century that development, progression and metastasis of breast cancer are strongly influenced by hormonal factors. Indeed about two-thirds of breast cancers express the estrogen receptor α (ERα) protein, a key predictor of prognosis and response to endocrine therapy. These cancers are frequently amenable to therapies that target estrogen signaling pathways, including selective estrogen receptor modulators like tamoxifen, selective estrogen receptor downregulators like fulvestrant; and agents that reduce estrogen ligand like aromatase inhibitors and ovarian suppression through luteinizing hormone-releasing hormone (LHRH) agonists. It is likely that these approaches, especially adjuvant tamoxifen, have contributed to the reduction in breast cancer mortality that has been observed in recent years. However, data from clinical studies have suggested that only about 60% of ERα-positive breast cancers respond to hormonal therapy. Further, those tumors that lack expression of ERα and the estrogen-regulated progesterone receptor (PgR) are unresponsive to hormone therapy. Thus the problem of acquired or de novo endocrine resistance is a substantial one. Recent molecular and biological advances have contributed to our understanding about potential underlying mechanisms. Here we will focus especially on silencing the expression of ERα as one such endocrine-resistance mechanism and how it might be exploited clinically.

Strategies for cancer prevention: the role of diet

Linkages between diet habits and cancer risk have surfaced from a multitude of epidemiological and preclinical studies. Collectively these studies provide rather compelling evidence that dietary components modify the incidence and biological behavior of tumors. While the risk of breast, prostate, colon, lung and liver cancers are frequently associated with dietary patterns, inconsistencies are not uncommon. These inconsistencies likely reflect the multi-factorial and complex nature of cancer and the specificity that individual dietary constituents have in modifying cancer related genetic pathways. The complexity of defining the role of diet is underscored by the numerous and diverse essential and non-essential components that may alter one or more phases of the cancer process. The explosive increase in the recognition of genes and pathways for regulating cell growth and development, and evaluating the response to hormones and other chemicals synthesized by the body, offers exciting opportunities for unraveling the molecular targets by which dietary components influence cancer prevention. It is recognized that all cells have unique ‘signatures’ that are characterized by active and inactive genes and cellular products. It is certainly plausible that bridging knowledge about these unique cellular characteristics with the molecular targets for nutrients can be used to assist in optimizing nutrition and minimizing cancer risk.

Folate Intake and Risk of Breast Cancer Characterized by Hormone Receptor Status

Folate plays an important role in DNA methylation, and aberrant methylation of the estrogen receptor (ER) gene may be related to the loss of ER gene expression in breast tumors. Thus, deficient folate status has been hypothesized to be associated primarily with ER gene-negative breast tumors, but data relating folate intake to breast cancer risk according to ER status are sparse. We conducted a prospective cohort analysis of folate intake among 88,744 women in the Nurses' Health Study who completed a food frequency questionnaire in 1980 and every 2 to 4 years thereafter. During 20 years of follow-up, 2,812 ER+ and 985 ER- invasive breast cancer cases were documented. Higher total folate intake was significantly associated with lower risk of developing ER- but not ER+ breast cancer; the multivariable relative risks (RR) and 95% confidence intervals (95% CI) comparing the highest to the lowest quintile were 0.81 (0.66-0.99) for ER- tumors and 1.00 (0.89-1.14) for ER+ tumors. The inverse association between total folate intake and ER- breast cancer was mainly present among women consuming at least 15 g/d of alcohol (multivariable RR, 0.46; 95% CI,=0.25-0.86; top versus bottom quintile). These findings support the hypothesis that higher folate intake reduces the risk of developing ER- breast cancer. Ensuring adequate folate intake seems particularly important for women at higher risk of breast cancer because of alcohol consumption.

Aging, cancer and nutrition: the DNA methylation connection

Cancer and aging are two coupled developmental processes as reflected by the higher incidence of cancer in the elderly human population group. Genetic mutations accumulate in somatic cells with age, which may explain in part the association of age with cancer. Epigenetic mechanisms are also frequently involved in controlling gene functions during development and tumorigenesis. A common molecular feature associated with both aging and tumorigenesis is global hypomethylation of the genomic DNA. The contributing mechanisms underlying this hypomethylation are not yet well understood. Epigenetic investigation of cancer and aging has recently emerged as a fruitful area of study and has added exciting insights into some of the mysteries surrounding aging and cancer. Recent studies have also shown that dietary factors can modulate DNA methylation and thereby contribute to aging and tumorigenesis. Thus, DNA methylation provides an important common link between aging, cancer and nutrition.

Choline availability modulates human neuroblastoma cell proliferation and alters the methylation of the promoter region of the cyclin-dependent kinase inhibitor 3 gene

Choline is an important methyl donor and a component of membrane phospholipids. In this study, we tested the hypothesis that choline availability can modulate cell proliferation and the methylation of genes that regulate cell cycling. In several other model systems, hypomethylation of cytosine bases that are followed by a guanosine (CpG) sites in the promoter region of a gene is associated with increased gene expression. We found that in choline-deficient IMR-32 neuroblastoma cells, the promoter of the cyclin-dependent kinase inhibitor 3 gene (CDKN3) was hypomethylated. This change was associated with increased expression of CDKN3 and increased levels of its gene product, kinase-associated phosphatase (KAP), which inhibits the G(1)/S transition of the cell cycle by dephosphorylating cyclin-dependent kinases. Choline deficiency also reduced global DNA methylation. The percentage of cells that accumulated bromodeoxyuridine (proportional to cell proliferation) was 1.8 times lower in the choline-deficient cells than in the control cells. Phosphorylated retinoblastoma (p110) levels were 3 times lower in the choline-deficient cells than in control cells. These findings suggest that the mechanism whereby choline deficiency inhibits cell proliferation involves hypomethylation of key genes regulating cell cycling. This may be a mechanism for our previously reported observation that stem cell proliferation in hippocampus neuroepithelium is decreased in choline-deficient rat and mouse fetuses.

Diet, methyl donors and DNA methylation: interactions between dietary folate, methionine and choline

DNA methylation influences the expression of some genes and depends upon the availability of methyl groups from S-adenosylmethionine (SAM). Dietary methyl groups derive from foods that contain methionine, one-carbon units and choline (or the choline metabolite betaine). Humans ingest approximately 50 mmol of methyl groups per day; 60% of them are derived from choline. Transmethylation metabolic pathways closely interconnect choline, methionine, methyltetrahydrofolate (methyl-THF) and vitamins B-6 and B-12. The pathways intersect at the formation of methionine from homocysteine. Perturbing the metabolism of one of these pathways results in compensatory changes in the others. For example, methionine can be formed from homocysteine using methyl groups from methyl-THF, or using methyl groups from betaine that are derived from choline. Similarly, methyl-THF can be formed from one-carbon units derived from serine or from the methyl groups of choline via dimethylglycine, and choline can be synthesized de novo using methyl groups derived from methionine (via SAM). When animals and humans are deprived of choline, they use more methyl-THF to remethylate homocysteine in the liver and increase dietary folate requirements. Conversely, when they are deprived of folate, they use more methyl groups from choline, increasing the dietary requirement for choline. The availability of transgenic and knockout mice has made possible additional studies that demonstrate the interrelationship of these methyl sources. In summary, as we consider dietary requirements and possible effects on DNA methylation, it is important to realize that methionine, methyl-THF and choline can be fungible sources of methyl groups, and the design of our studies should reflect this.

Diet and cancer prevention

Research from several sources provides strong evidence that vegetables, fruits, and whole grains, dietary fibre, certain micronutrients, some fatty acids and physical activity protect against some cancers. In contrast, other factors, such as obesity, alcohol, some fatty acids and food preparation methods may increase risks. Unravelling the multitude of plausible mechanisms for the effects of dietary factors on cancer risk will likely necessitate that nutrition research moves beyond traditional epidemiological and metabolic studies. Nutritional sciences must build on recent advances in molecular biology and genetics to move the discipline from being largely 'observational' to focusing on 'cause and effect'. Such basic research is fundamental to cancer prevention strategies that incorporate effective dietary interventions for target populations.

Creating a new paradigm in nutrition research within the National Cancer Institute

Almost two decades after Doll and Peto (1981) provided evidence that one third of cancer deaths are related to diet, it remains unclear which dietary components may be key in cancer prevention. Although the complexity of the diet can become overwhelming, the National Cancer Institute (NCI) of the National Institutes of Health (NIH) has remained steadfast in its commitment to defining the roles that diet and nutrition have in the development of cancer and has provided increased research and training support to assist in unraveling this interrelationship. Evidence for this sustained commitment is highlighted by a fourfold increase in NCI expenditures for nutrition research and training from 1983 to 1998; this substantial increase reflects a trend that is occurring in some universities and the private sector. More than one third of the nutrition-related NCI research is funded by the Division of Cancer Prevention. Supported investigations cover the gamut from basic mechanisms of action of dietary constituents, methodology development, human metabolic studies, clinical trials of dietary modification and the chemopreventive potential of individual nutrients to population-based studies.