Low colonocyte folate is associated with uracil misincorporation and global DNA hypomethylation in human colorectum

Targeting beta-catenin signaling for prevention of colorectal cancer - Nutraceutical, drug, and dietary options

Progressive up-regulation of β-catenin signaling is very common in the transformation of colorectal epithelium to colorectal cancer (CRC). Practical measures for opposing such signaling hence have potential for preventing or slowing such transformation. cAMP/PKA activity in colon epithelium, as stimulated by COX-2-generated prostaglandins and β2-adrenergic signaling, boosts β-catenin activity, whereas cGMP/PKG signaling has the opposite effect. Bacterial generation of short-chain fatty acids (as supported by unrefined high-carbohydrate diets, berberine, and probiotics), dietary calcium, daily aspirin, antioxidants opposing cox-2 induction, and nicotine avoidance, can suppress cAMP production in colonic epithelium, whereas cGMP can be boosted via linaclotides, PDE5 inhibitors such as sildenafil or icariin, and likely high-dose biotin. Selective activation of estrogen receptor-β by soy isoflavones, support of adequate vitamin D receptor activity with UV exposure or supplemental vitamin D, and inhibition of CK2 activity with flavanols such as quercetin, can also oppose β-catenin signaling in colorectal epithelium. Secondary bile acids, the colonic production of which can be diminished by low-fat diets and berberine, can up-regulate β-catenin activity by down-regulating farnesoid X receptor expression. Stimulation of PI3K/Akt via insulin, IGF-I, TLR4, and EGFR receptors boosts β-catenin levels via inhibition of glycogen synthase-3β; plant-based diets can down-regulate insulin and IGF-I levels, exercise training and leanness can keep insulin low, anthocyanins and their key metabolite ferulic acid have potential for opposing TLR4 signaling, and silibinin is a direct antagonist for EGFR. Partially hydrolyzed phytate can oppose growth factor-mediated down-regulation of β-catenin by inhibiting Akt activation. Multifactorial strategies for safely opposing β-catenin signaling can be complemented with measures that diminish colonic mutagenesis and DNA hypomethylation - such as avoidance of heme-rich meat and charred or processed meats, consumption of phase II-inductive foods and nutraceuticals (e.g., Crucifera), and assurance of adequate folate status.

The enzyme-modified comet assay: Past, present and future

The enzyme-modified comet assay was developed in order to detect DNA lesions other than those detected by the standard version (single and double strand breaks and alkali-labile sites). Various lesion-specific enzymes, from the DNA repair machinery of bacteria and humans, have been combined with the comet assay, allowing detection of different oxidized and alkylated bases as well as cyclobutane pyrimidine dimers, mis-incorporated uracil and apurinic/apyrimidinic sites. The enzyme-modified comet assay has been applied in different fields - human biomonitoring, environmental toxicology, and genotoxicity testing (both in vitro and in vivo) - as well as in basic research. Up to now, twelve enzymes have been employed; here we describe the enzymes and give examples of studies in which they have been applied. The bacterial formamidopyrimidine DNA glycosylase (Fpg) and endonuclease III (EndoIII) have been extensively used while others have been used only rarely. Adding further enzymes to the comet assay toolbox could potentially increase the variety of DNA lesions that can be detected. The enzyme-modified comet assay can play a crucial role in the elucidation of the mechanism of action of both direct and indirect genotoxins, thus increasing the value of the assay in the regulatory context.

Association of Folate Metabolites and Mitochondrial Function in Peripheral Blood Cells in Alzheimer's Disease: A Matched Case-Control Study

BACKGROUND

The nutrition state plays an important role in the progress of aging. Folate may play a role in protecting mitochondrial (mt) DNA by reducing oxidative stress.

OBJECTIVE

The primary aim of this study was to examine the association of mitochondrial oxidative damage with risk of Alzheimer's disease (AD), and to explore the possible role of folate metabolites in this association in a matched case-control study.

METHODS

Serum folate metabolites and mitochondrial function in peripheral blood cells were determined in 82 AD cases and 82 healthy controls, individually matched by age, gender, and education.

RESULTS

AD patients had lower serum levels of folate and higher homocysteine (Hcy) concentration. AD patients had a reduced mtDNA copy number, higher mtDNA deletions, and increased 8-OHdG content in mtDNA indicative of reduced mitochondrial function. The highest level of mtDNA copy number would decrease the risk of AD (OR = 0.157, 95% CI: 0.058-0.422) compared to the lowest level, independently of serum folate, and Hcy levels. Serum folate levels correlated with low 8-OHdG content in mtDNA both in AD patients and controls, independently of serum Hcy level. Moreover, serum Hcy levels correlated with low copy number in mtDNA both in AD patients and controls, independently of serum folate levels.

CONCLUSION

In conclusion, mitochondrial function in peripheral blood cells could be associated with risk of AD independent of multiple covariates. AD patients with a folate deficiency or hyperhomocysteinemia had low mitochondrial function in peripheral blood cells. However, further randomized controlled trials are need to determine a causal effect.

Folate, genomic stability and colon cancer: The use of single cell gel electrophoresis in assessing the impact of folate in vitro, in vivo and in human biomonitoring

Intake of folate (vitamin B₉) is strongly inversely linked with human cancer risk, particularly colon cancer. In general, people with the highest dietary intake of folate or with high blood folate levels are at a reduced risk (approx. 25%) of developing colon cancer. Folate acts in normal cellular metabolism to maintain genomic stability through the provision of nucleotides for DNA replication and DNA repair and by regulating DNA methylation and gene expression. Folate deficiency can accelerate carcinogenesis by inducing misincorporation of uracil into DNA, by increasing DNA strand breakage, by inhibiting DNA base excision repair capacity and by inducing DNA hypomethylation and consequently aberrant gene and protein expression. Conversely, increasing folate intake may improve genomic stability. This review describes key applications of single cell gel electrophoresis (the comet assay) in assessing genomic instability (misincorporated uracil, DNA single strand breakage and DNA repair capacity) in response to folate status (deficient or supplemented) in human cells in vitro, in rodent models and in human case-control and intervention studies. It highlights an adaptation of the SCGE comet assay for measuring genome-wide and gene-specific DNA methylation in human cells and colon tissue.

Colorectal polyp risk is linked to an elevated level of homocysteine

Several studies have reported an association between levels of folate, homocysteine, and vitamin B₁₂ and the risk of colorectal polyps. Here, our aim is to examine the possible effect of folate, homocysteine, and vitamin B₁₂ levels on the risk of colorectal polyps by means of meta-analysis based quantitative synthesis. According to our inclusion/exclusion criteria, a total of 13 case–control studies were enrolled. The P-value of the association test, standard mean difference (SMD), and 95% confidence interval (CI) were calculated. Pooled analysis data showed a negative correlation between the risk of colorectal polyps and the levels of serum folate, red blood cell (RBC) folate, or vitamin B₁₂ (all P>0.05). Nevertheless, for homocysteine level, we also observed a statistically significant difference between cases and controls in the overall and subgroup analysis of hospital-based control (HB), population-based control (PB), Chinese, Caucasian, or Asian (all P<0.05, SMD > 0). We found that increased levels of homocysteine may be statistically and significantly related to the risk of colorectal polyps.

Colorectal Cancer and Alcohol Consumption-Populations to Molecules

Colorectal cancer (CRC) is a major cause of morbidity and mortality, being the third most common cancer diagnosed in both men and women in the world. Several environmental and habitual factors have been associated with the CRC risk. Alcohol intake, a common and rising habit of modern society, is one of the major risk factors for development of CRC. Here, we will summarize the evidence linking alcohol with colon carcinogenesis and possible underlying mechanisms. Some epidemiologic studies suggest that even moderate drinking increases the CRC risk. Metabolism of alcohol involves ethanol conversion to its metabolites that could exert carcinogenic effects in the colon. Production of ethanol metabolites can be affected by the colon microbiota, another recently recognized mediating factor to colon carcinogenesis. The generation of acetaldehyde and alcohol's other metabolites leads to activation of cancer promoting cascades, such as DNA-adduct formation, oxidative stress and lipid peroxidation, epigenetic alterations, epithelial barrier dysfunction, and immune modulatory effects. Not only does alcohol induce its toxic effect through carcinogenic metabolites, but alcoholics themselves are predisposed to a poor diet, low in folate and fiber, and circadian disruption, which could further augment alcohol-induced colon carcinogenesis.

Polyamines, folic acid supplementation and cancerogenesis

Clinical practice and experimental studies have shown the necessity of sufficient quantities of folic acid intake for normal embryogenesis and fetal development in the prevention of neural tube defects (NTDs) and neurological malformations. So, women of childbearing age must be sure to have an adequate folate intake periconceptionally, prior to and during pregnancy. Folic acid fortification of all enriched cereal grain product flour has been implemented in many countries. Thus, hundreds of thousands of people have been exposed to an increased intake of folic acid. Folate plays an essential role in the biosynthesis of methionine. Methionine is the principal aminopropyl donor required for polyamine biosynthesis, which is up-regulated in actively growing cells, including cancer cells. Folates are important in RNA and DNA synthesis, DNA stability and integrity. Clinical and epidemiological evidence links folate deficiency to DNA damage and cancer. On the other hand, long-term folate oversupplementation leads to adverse toxic effects, resulting in the appearance of malignancy. Considering the relationship of polyamines and rapidly proliferating tissues (especially cancers), there is a need for better investigation of the relationship between the ingestion of high amounts of folic acid in food supplementation and polyamine metabolism, related to malignant processes in the human body.

Investigation of methylenetetrahydrofolate reductase tagging polymorphisms with colorectal cancer in Chinese Han population

The aim of this case-control study was to assess the relationship between the tagging polymorphisms in methylenetetrahydrofolate reductase (MTHFR) gene and the susceptibility to colorectal cancer (CRC) in a Chinese Han population. A custom-by-design 48-Plex SNPscan Kit was used to determine the genotypes of MTHFR rs3753584 T>C, rs9651118 T>C, rs1801133 G>A, rs4846048 A>G and rs4845882 G>A polymorphisms in 387 CRC patients and 1,536 non-cancer controls. The results revealed that MTHFR rs1801133 G>A polymorphism was associated with a decreased risk of overall CRC. While MTHFR rs4845882 G>A polymorphism conferred an increased risk to overall CRC. In a stratified analysis by CRC region, we found MTHFR rs3753584 T>C and rs9651118 T>C polymorphisms were associated with the increased risk of colon cancer. In addition, a significantly increased risk of rectum cancer associated with MTHFR rs3753584 T>C polymorphism was overt. However, MTHFR rs1801133 G>A polymorphism conferred a decreased risk to colon cancer. In conclusion, findings of the present study reveal that the tagging polymorphisms in MTHFR gene (rs3753584 T>C, rs9651118 T>C and rs4845882 G>A) are associated with the increased risk of CRC. However, MTHFR rs1801133 G>A polymorphism confers a decreased risk to CRC. Additional studies with larger sample size are needed to confirm these findings.

[Research advances in the association between maternal intake of methyl donor nutrients during pregnancy and DNA methylation in offspring]

Maternal nutrition during pregnancy plays a vital role in the health of the offspring. Methyl donor nutrients, including folate, vitamin B₁₂, choline, betaine, and methionine, directly affect DNA methylation and are closely associated with the health of the offspring. As an important part of epigenetics, DNA methylation plays an important role in the maintenance of normal cellular function, gene expression regulation, and embryonic development. Recent studies have shown that maternal nutrition may have a long-lasting effect on the health of the offspring via the changes in genomic DNA and/or methylation level in the promoter region in specific genes. Therefore, this review article focuses on the effect of maternal intake of methyl donor nutrients during pregnancy on DNA methylation, in order to explore the effect of the changed methylation status on the health of the offspring at the molecular level.

Folic Acid Supplementation in Postpolypectomy Patients in a Randomized Controlled Trial Increases Tissue Folate Concentrations and Reduces Aberrant DNA Biomarkers in Colonic Tissues Adjacent to the Former Polyp Site

BACKGROUND

Low folate status is associated with an increased risk of colorectal carcinogenesis. Optimal folate status may be genoprotective by preventing uracil misincorporation into DNA and DNA hypomethylation. Adenomatous polyps have low folate status compared with normal colonic mucosa, and they are surrounded by histologically normal mucosa that also is of low folate status.

OBJECTIVE

In a randomized controlled trial conducted at a single Dublin hospital between April 2002 and March 2004, we assessed the effect of folic acid supplementation on tissue folate, uracil misincorporation into DNA, and global DNA hypomethylation in colonocytes isolated from sites of adenomatous polyps and from histologically normal tissue adjacent and 10-15 cm distal to them.

METHODS

Twenty patients with adenomatous polyps on initial colonoscopy and polypectomy were randomly assigned to receive either 600 μg folic acid/d [n = 12, 38% men, mean age 64.3 y, and body mass index (BMI, in kg/m(2)) 26.6] or placebo (n = 8, 50% men, mean age 68.4 y, and BMI 27.2) for 6 mo, and then repeat the colonoscopy. Blood and colonocyte tissue folate concentrations were measured with the use of a microbiological assay. Uracil misincorporation and global DNA hypomethylation were measured in colonocytes with the use of modified comet assays.

RESULTS

Over time, folic acid supplementation, compared with placebo, increased tissue folate (mean ± SEM) from 15.6 ± 2.62 pg/10(5) cells to 18.1 ± 2.12 pg/10(5) cells (P < 0.001) and decreased the global DNA hypomethylation ratio from 1.7 ± 0.1 to 1.0 ± 0.1 (P < 0.001). The uracil misincorporation ratio decreased by 0.5 ± 0.1 for the site adjacent to the polyp over time (P = 0.05).

CONCLUSION

A response to folic acid supplementation, which increased colonocyte folate and improved folate-related DNA biomarkers of cancer risk, was seen in the participants studied. Exploratory analysis points toward the area formerly adjacent to polyps as possibly driving the response. That these areas persist after polypectomy in the absence of folate supplementation is consistent with a potentially carcinogenic field's causing the appearance of the polyp.

Association of folate and other one-carbon related nutrients with hypermethylation status and expression of RARB, BRCA1, and RASSF1A genes in breast cancer patients

Dietary methyl group donors could influence the hypermethylation status of certain putative genes. The present study explored the possible associations of dietary intake of one-carbon metabolism-related nutrients with promoter hypermethylation status and expression of retinoic acid receptor-beta (RARB), breast cancer-1 (BRCA1), and Ras association domain family-1, isoform A (RASSF1A) genes in Iranian women with breast cancer (BC). The hypermethylation status was investigated in 146 dissected BC tissue samples using methylation-specific PCR. The expression level was evaluated by real-time RT-PCR. Dietary nutrients were estimated using a validated 136-item food frequency questionnaire. Expression levels of the genes were associated with the unmethylated status of related promoters (p < 0.05). The crude dietary folate and adjusted cobalamin intakes were inversely associated with methylated RARB and BRCA1. Low intake of residual folate and cobalamin was correlated with the methylated status of RARB for subjects at <48 years of age, and folate alone was linked to BRCA1 at >48 years of age. High dietary intake of riboflavin and pyridoxine was the only determinant of the methylated promoter of RARB at odds ratios (ORs) of 4.15 (95 % confidence interval (CI) 1.28-13.50) and 2.53 (95 % CI 1.14-3.83) in multivariate models, respectively. One-carbon nutrients most often correlated inversely with the methylation-influenced expression of RARB. Although high folate intake increased the chance of unmethylation-dependent overexpression of BRCA1 3-fold, cobalamin and methionine were inversely linked to methylation-mediated expression. Nutritional epigenomics less actively influenced RASSF1A. These findings provide new insights into and a basic understanding of the selective contributions of individual B vitamins on hypermethylation and methylation-related expression of RARB and BRCA1 in BC.

KEY MESSAGE

Hypermethylation at promoters of RARB, BRCA1, and RASSF1A is associated with reduced transcript levels of the respective gene in primary breast cancer tissue samples. Dietary folate and cobalamin intake is inversely associated with methylated RARB and BRCA1. High dietary intake of riboflavin and pyridoxine is associated with increased methylation in the RARB promoter. There is evidence for the age-dependent effects of nutrient intake on promoter methylation status. Bioavailability to the pool of nutrients might determine selectivity.

Biomarkers of Nutrition for Development-Folate Review

The Biomarkers of Nutrition for Development (BOND) project is designed to provide evidence-based advice to anyone with an interest in the role of nutrition in health. Specifically, the BOND program provides state-of-the-art information and service with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect. To accomplish this objective, expert panels are recruited to evaluate the literature and to draft comprehensive reports on the current state of the art with regard to specific nutrient biology and available biomarkers for assessing nutrients in body tissues at the individual and population level. Phase I of the BOND project includes the evaluation of biomarkers for 6 nutrients: iodine, iron, zinc, folate, vitamin A, and vitamin B-12. This review represents the second in the series of reviews and covers all relevant aspects of folate biology and biomarkers. The article is organized to provide the reader with a full appreciation of folate's history as a public health issue, its biology, and an overview of available biomarkers (serum folate, RBC folate, and plasma homocysteine concentrations) and their interpretation across a range of clinical and population-based uses. The article also includes a list of priority research needs for advancing the area of folate biomarkers related to nutritional health status and development.

Etiologic field effect: reappraisal of the field effect concept in cancer predisposition and progression

The term 'field effect' (also known as field defect, field cancerization, or field carcinogenesis) has been used to describe a field of cellular and molecular alteration, which predisposes to the development of neoplasms within that territory. We explore an expanded, integrative concept, 'etiologic field effect', which asserts that various etiologic factors (the exposome including dietary, lifestyle, environmental, microbial, hormonal, and genetic factors) and their interactions (the interactome) contribute to a tissue microenvironmental milieu that constitutes a 'field of susceptibility' to neoplasia initiation, evolution, and progression. Importantly, etiological fields predate the acquisition of molecular aberrations commonly considered to indicate presence of filed effect. Inspired by molecular pathological epidemiology (MPE) research, which examines the influence of etiologic factors on cellular and molecular alterations during disease course, an etiologically focused approach to field effect can: (1) broaden the horizons of our inquiry into cancer susceptibility and progression at molecular, cellular, and environmental levels, during all stages of tumor evolution; (2) embrace host-environment-tumor interactions (including gene-environment interactions) occurring in the tumor microenvironment; and, (3) help explain intriguing observations, such as shared molecular features between bilateral primary breast carcinomas, and between synchronous colorectal cancers, where similar molecular changes are absent from intervening normal colon. MPE research has identified a number of endogenous and environmental exposures which can influence not only molecular signatures in the genome, epigenome, transcriptome, proteome, metabolome and interactome, but also host immunity and tumor behavior. We anticipate that future technological advances will allow the development of in vivo biosensors capable of detecting and quantifying 'etiologic field effect' as abnormal network pathology patterns of cellular and microenvironmental responses to endogenous and exogenous exposures. Through an 'etiologic field effect' paradigm, and holistic systems pathology (systems biology) approaches to cancer biology, we can improve personalized prevention and treatment strategies for precision medicine.

Folic acid fortification and colorectal cancer risk

The U.S. has been reported as the only country experiencing a decline in incidence rates of colorectal cancer (CRC), despite increasing prevalence of CRC major risk factors, including the Western dietary pattern and obesity. This paper presents a hypothesis that improved folate status in the U.S. is the factor that could most likely explain the seemingly contradictory phenomenon, although a momentary increase in CRC incidence rates was observed in the later 1990s with the initiation of nationwide folic acid fortification. To corroborate this hypothesis, time trends in CRC incidence rates and death rates in the U.S. were plotted by age, race, and gender based on data from the Surveillance, Epidemiology, and End Results (SEER); data were analyzed by simultaneously addressing the following four critical factors: (1) a long induction period between improved folate status and potential protection of CRC; (2) a change in the U.S. Food and Drug Administration regulation in 1973 on the dose of folic acid allowed in supplements; (3) differential impacts of 1973 regulatory change and 1990s mandatory fortification by race; and (4) changes in CRC screening over time in the U.S. Although this type of analysis precludes a definitive conclusion, available evidence suggests that the increase in CRC incidence rates in the later 1990s is unlikely due to folic acid fortification and, assuming a time lag of a decade or longer to see a benefit on CRC, folate appears to be one of the most promising factors that could explain the downward trend of CRC incidence rates in the U.S.

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

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.

Long-term use of multivitamins and risk of colorectal adenoma in women

Background:

Use of multivitamins may reduce the risk of colorectal adenoma, but the duration of use needed is unclear.

Methods:

We prospectively examined years of multivitamin use and risk of colorectal adenoma among 43 641 women who had a first endoscopy between 1991 and 2007 in the Nurses' Health Study II. Use of multivitamins was assessed through biennial questionnaires since 1989.

Results:

We documented 2277 colorectal adenoma cases. Reporting multivitamin use at any time during the study period compared with never reporting its use was associated with a reduced risk of adenoma (multivariable relative risk (RR)=0.86, 95% confidence interval (CI): 0.76–0.97). There was no clear trend with duration of multivitamin use: years of use compared with never use, ⩽4 years (RR=0.84, 95% CI: 0.74–0.96), 5–9 years (RR=0.89, 95% CI: 0.77, 1.02), 10–14 years (RR=0.86, 95% CI: 0.74, 1.01), 15–19 years (RR=0.85, 95% CI: 0.70, 1.02), and 20–26 years (RR=0.80, 95% CI: 0.64, 1.01); (P trend=0.87). The strongest associations (years of use vs never user) were for size of adenoma: large (⩾1 cm) <4 years (RR=0.75, 95% CI: 0.58–0.96) and in alcohol users (⩾1.4 g per day) 20–26 years (RR=0.67, 95% CI: 0.49–0.91).

Conclusion:

Our findings suggest that use of multivitamins is associated with lower risk of colorectal adenoma, even with relatively short duration of use.