Folate and carcinogenesis: an integrated scheme

Predictors of oral mucositis in patients receiving hematopoietic cell transplants for chronic myelogenous leukemia

PURPOSE

Oral mucositis is a nearly universal and often severe complication following hematopoietic cell transplantation (HCT). The objective of this study was to evaluate factors predicting oral mucositis severity among 133 patients undergoing allogeneic HCT for chronic myelogenous leukemia.

PATIENTS AND METHODS

All patients were transplanted between 1992 and 1999, were >or= 18 years of age, received either cyclophosphamide/total-body irradiation (TBI) or busulfan/cyclophosphamide conditioning regimens, and received four doses of methotrexate for graft-versus-host disease prophylaxis post-transplant. Oral mucositis was measured by a trained examiner every 2 to 3 days using the Oral Mucositis Index (OMI). Multiple linear regression analysis was used to identify predictors of mean OMI during days 6 to 12, 1 to 18, and the maximum OMI score between days 1 to 18.

RESULTS

TBI containing conditioning regimens, body mass index >or= 25, and methylenetetrahydrofolate reductase 677 TT genotype were found to be predictive of higher mean OMI scores (P <.05). Pretransplant multivitamin supplement use was associated with lower mean OMI scores compared to those who did not use supplements. Smoking status, race, pretransplant treatment with interferon-alfa or hydroxyurea, and patient/donor ABO compatibility were not associated with mean OMI scores.

CONCLUSION

Patients who are scheduled to receive conditioning regimens containing TBI, have a pretransplant body mass index >or= 25, or carry the methylenetetrahydrofolate reductase 677 TT genotype should be considered at greater risk of developing oral mucositis following HCT. Future studies should investigate whether multivitamin supplementation before HCT could reduce mucositis severity.

Methionine synthase D919G polymorphism, folate metabolism, and colorectal adenoma risk

Methionine synthase [5-methyltetrahydrofolate-homocysteine S-methyltransferase (MTR)] is involved in folate-mediated one-carbon metabolism, a pathway known to play a role in colorectal carcinogenesis. We investigated whether the MTR D919G polymorphism was associated with risk of colorectal adenoma in a colonoscopy-based study of 513 cases and 609 controls from Minneapolis, MN. Adenoma risk appeared nonsignificantly increased among women with DG or GG genotype [adjusted odds ratio (OR) versus DD, 1.4; 95% confidence interval (CI), 0.9-2.1] but not men (OR, 1.0; 95% CI, 0.7-1.5). An interaction with methionine intake was observed among women, such that low versus high intake was associated with a 2.3-fold increased risk only among those with DG or GG genotype (95% CI, 1.1-4.9; P for interaction = 0.05). Similarly, risk associated with alcohol intake was not elevated among women with the DD genotype; however, consumption of >7 g of alcohol/day versus none was associated with an increased risk among women with DG or GG genotype (adjusted OR, 2.5; 95% CI, 1.4-4.4; P for interaction = 0.03). An interaction between MTR D919G and the thymidylate synthase (TS or TYMS) 3'-untranslated region polymorphism 1494del6 was also observed among women (P for interaction = 0.007). No evidence of interaction with intake of folate, vitamin B(12), or vitamin B(6) or with genotype at MTHFR C677T or the TS enhancer region 28-bp repeat polymorphism was seen. These findings add to what is known about the complexities of genetic variations in one-carbon-metabolizing enzymes in relation to colorectal carcinogenesis.

Diet, nutrition and the prevention of cancer

OBJECTIVE

To assess the epidemiological evidence on diet and cancer and make public health recommendations.

DESIGN

Review of published studies, concentrating on recent systematic reviews, meta-analyses and large prospective studies.

CONCLUSIONS AND RECOMMENDATIONS

Overweight/obesity increases the risk for cancers of the oesophagus (adenocarcinoma), colorectum, breast (postmenopausal), endometrium and kidney; body weight should be maintained in the body mass index range of 18.5-25 kg/m(2), and weight gain in adulthood avoided. Alcohol causes cancers of the oral cavity, pharynx, oesophagus and liver, and a small increase in the risk for breast cancer; if consumed, alcohol intake should not exceed 2 units/d. Aflatoxin in foods causes liver cancer, although its importance in the absence of hepatitis virus infections is not clear; exposure to aflatoxin in foods should be minimised. Chinese-style salted fish increases the risk for nasopharyngeal cancer, particularly if eaten during childhood, and should be eaten only in moderation. Fruits and vegetables probably reduce the risk for cancers of the oral cavity, oesophagus, stomach and colorectum, and diets should include at least 400 g/d of total fruits and vegetables. Preserved meat and red meat probably increase the risk for colorectal cancer; if eaten, consumption of these foods should be moderate. Salt preserved foods and high salt intake probably increase the risk for stomach cancer; overall consumption of salt preserved foods and salt should be moderate. Very hot drinks and foods probably increase the risk for cancers of the oral cavity, pharynx and oesophagus; drinks and foods should not be consumed when they are scalding hot. Physical activity, the main determinant of energy expenditure, reduces the risk for colorectal cancer and probably reduces the risk for breast cancer; regular physical activity should be taken.

Folate and colorectal neoplasia: relation between plasma and dietary markers of folate and adenoma recurrence

BACKGROUND

The results of epidemiologic studies indicate that higher intakes or blood concentrations of folate are associated with a lower risk of colorectal neoplasia; however, only one study assessed the role of homocysteine.

OBJECTIVE

We assessed the relation between biochemical and dietary markers of folate status and colorectal adenoma recurrence.

DESIGN

Analyses were conducted in 1014 men and women aged 40-80 y who had undergone removal of all colorectal polyps. Diet and supplement use were ascertained through a food-frequency questionnaire administered at study entry. Blood collected at baseline was used to measure plasma folate and homocysteine concentrations. Unconditional logistic regression was used to assess the odds of recurrence associated with the intakes of folate, methionine, and vitamins B-6 and B-12 and with plasma folate and homocysteine.

RESULTS

Relative to subjects in the highest quartile of plasma homocysteine, those in the lowest quartile had an odds ratio (OR) of adenoma recurrence of 0.69 (95% CI: 0.47, 1.02; P for trend = 0.02) after adjustment for confounding factors. Lower odds of recurrence were shown for higher plasma folate (OR: 0.66; 95% CI: 0.46, 0.97) and higher total intakes (dietary plus supplemental) of folate (OR: 0.61; 0.42, 0.89) and vitamin B-6 (OR: 0.65; 0.45, 0.94). Slightly weaker and nonsignificant associations were shown for dietary folate, methionine, and total vitamin B-12.

CONCLUSIONS

A lower recurrence of colorectal adenomas was shown in subjects with higher intakes and plasma concentrations of folate. Additional markers involved in folate metabolism, including lower homocysteine and higher vitamin B-6 intake, were also associated with lower odds of recurrence.

Dietary Folate Intake and Incidence of Ovarian Cancer: The Swedish Mammography Cohort

BACKGROUND

Mounting evidence suggests that a low intake of the water-soluble B vitamin folate is associated with breast and colorectal carcinogenesis, especially among alcohol drinkers. However, epidemiologic data specifically linking folate intake to ovarian cancer risk are limited.

METHODS

We examined the association between dietary folate intake (i.e., folate from food sources) and the incidence of total epithelial ovarian cancer and its subtypes by analyzing data from the Swedish Mammography Cohort, a population-based prospective cohort of 61 084 women, aged 38-76 years, who, at baseline (i.e., from 1987 to 1990), were cancer-free and had completed a food-frequency questionnaire. Through June 30, 2003, 266 incident cases of invasive epithelial ovarian cancer were diagnosed. We used Cox proportional hazards models to estimate multivariable relative risks (RRs) of ovarian cancer with 95% confidence intervals (CIs). All statistical tests were two-sided.

RESULTS

Overall, dietary folate intake was weakly inversely associated with total epithelial ovarian cancer risk (RR for highest versus lowest quartile of intake = 0.67, 95% CI = 0.43 to 1.04; P(trend) =.08). Among women who consumed more than 20 g of alcohol (approximately two drinks) per week, there was a strong inverse association between dietary folate intake and total epithelial ovarian cancer risk (RR for highest versus lowest quartile of intake = 0.26, 95% CI = 0.11 to 0.60; P(trend) =.001), but among women who consumed 20 g or less of alcohol per week, there was no such association (RR for highest versus lowest quartile of intake = 1.00, 95% CI = 0.59 to 1.70; P(trend) =.80). The absolute risk of epithelial ovarian cancer for the lowest three quartiles versus the highest quartile of folate intake was 8 per 100 000 person-years (95% CI = 0 to 16 per 100 000 person-years) overall and 26 per 100 000 person-years (95% CI = 10 to 42 per 100 000 person-years) among those who consumed more than 20 g of alcohol per week. The association between dietary folate intake and cancer risk did not vary substantially among subtypes of epithelial ovarian cancer.

CONCLUSION

A high dietary folate intake may play a role in reducing the risk of ovarian cancer, especially among women who consume alcohol.

The short-term bioavailabilities of [6S]-5-methyltetrahydrofolate and folic acid are equivalent in men

The natural folate derivative, 5-methyltetrahydrofolate ([6S]-5-MTHF), could be an option for supplementation and fortification but its bioavailability remains unclear. This study compared the bioavailability of [6S]-5-MTHF with that of folic acid (FA) by measuring plasma folate responses after a single ingestion of equivalent doses of the two folate forms. In a double-blind, crossover study, 13 men (presaturated with FA) received in random order each of the following treatments administered orally at 1-wk intervals: 1) placebo capsule; 2) 500 micro g FA capsule; and 3) 500 micro g [6S]-5-MTHF capsule. Plasma total folate concentrations were measured before and up to 10 h after each treatment (n = 10 samples per treatment). Plasma folate concentrations increased significantly (compared with baseline) from 0.5 to 5 h after both folate treatments. The maximum plasma folate response did not differ between the two treatments (mean +/- SEM, 33.4 +/- 3.9 vs. 31.8 +/- 3.9 nmol/L, P = 0.7, for FA and [6S]-5-MTHF, respectively) and typically occurred in individuals between 0.5 and 3 h postprandially. The area under the plasma folate response curve was significantly greater after both folate treatments compared with placebo, and the response did not differ between the treatments. These results indicate that the short-term bioavailabilities of [6S]-5-MTHF and FA are equivalent. Supplementation with the natural folate derivative could have all the beneficial effects associated with FA, but without the potential disadvantage of masking the anemia of vitamin B-12 deficiency.

Women with polymorphisms of methylenetetrahydrofolate reductase (MTHFR) and methionine synthase (MS) are less likely to have cervical intraepithelial neoplasia (CIN) 2 or 3

The role of nutrient-related genetic susceptibility factors for pre-cancerous lesions is gaining attention. We conducted a study to examine associations between polymorphisms in folate pathway coenzymes (methylenetetrahydrofolate reductase [MTHFR] and methionine synthase [MS]) and cervical intraepithelial neoplasia (CIN) 2 or 3 in a population exposed to folic acid by the food fortification program in the United States. Status of MTHFR and MS and circulating concentrations of folate, vitamins B12, A, E, C and total carotene were ascertained in 170 Caucasian and 266 African-American women positive for high-risk human papilloma virus (HR-HPV). Polymorphism status was determined using polymerase chain reaction assays. Micronutrient concentrations were measured using radiobinding assays, high performance liquid chromatography or spectrophotometry. Presence/absence of CIN 2 or 3 was determined on the basis of histology results and the association with risk factors was examined using multivariable analyses. Eighty women had CIN 2 or 3 lesions and they were compared to 356 women who had CIN 1, ASCUS or normal cytology. We found that women polymorphic for MTHFR were less likely to have CIN 2 or 3 (odds ratio [OR] = 0.43, 95% confidence interval [CI] = 0.23-0.79). No associations were seen with MS polymorphism alone (OR = 0.72, 95% CI = 0.43-1.21); however, women polymorphic for both MTHFR and MS were less likely to have CIN 2 or 3 (OR = 0.21, 95% CI = 0.08-0.62). We conclude that these polymorphisms in the folate metabolic pathway were associated with a lower likelihood of CIN 2 or 3 in a population exposed to adequate amounts of folate from exposure to food fortification with folic acid.

Folate, methyl-related nutrients, alcohol, and the MTHFR 677C-->T polymorphism affect cancer risk: intake recommendations

Colorectal cancer and adenoma risk are inversely associated with higher total folate intake. Significant modifiers of cancer risk also include other methyl-related nutrients and alcohol. Adequate folate intake is particularly important for women at higher risk for breast cancer because of moderate alcohol consumption. The methylenetetrahydrofolate reductase (MTHFR) 677C-->T polymorphism is associated with a reduced risk of some forms of cancer. The protective effect of this folate-related polymorphism is dependent on adequate folate status. Cancer risk may be increased in individuals with the homozygous genotype for the MTHFR 677C-->T polymorphism who have low status of methyl-related nutrients including folate. Intake recommendations to potentially reduce cancer risk include substitution of low folate foods with folate-dense fruits and vegetables and in countries where there is no mandatory folic acid fortification, increased consumption of folic acid from available fortified foods or supplements. Adequate dietary intake of vitamin B-6 and methionine can be achieved by consumption of low fat, concentrated food sources of these nutrients. The recommended intake for vitamin B-12 for individuals >/==" BORDER="0">51 y should be provided predominately in crystalline form (e.g., fortified ready-to-eat cereal, supplements). If alcohol is consumed, consumption should be restricted to <15 g/d or <1 drink/d. The negative effects of low intakes of the methyl-related nutrients with high intakes of alcohol are additive, therefore changes in overall dietary patterns to ensure the consumption of a protective high methyl diet are recommended.

High-folate diets and breast cancer survival in a prospective cohort study

Recent evidence suggests that adequate dietary folate may attenuate the risk of breast cancer associated with intake of alcohol. However, patients with breast cancer have been commonly treated with antifolate chemotherapies. The present analysis was performed to test the hypothesis that high folate intake may diminish the effectiveness of chemotherapy and, therefore, adversely influence survival. Women at risk of postmenopausal breast cancer (n = 37,105) participated in the Iowa Women's Health Study. Total folate intake (diet + supplements) was estimated from a food frequency questionnaire administered at baseline in 1986 and categorized into tertiles. From all incident breast cancer cases ascertained in the cohort, we selected those with a diagnosis between 1986 and 1994, chemotherapy as first course of treatment, and adequate diet assessment. Mortality was determined through the State Health Registry of Iowa and the National Death Index. Cox regression was used to estimate survival while adjusting for important covariates. Through 14 yr of follow-up, 80 deaths occurred among the 177 breast cancer cases treated with chemotherapy. Among these patients, high folate intake was not associated with worse survival. After adjustment for age, extent of disease, total calories, alcohol, and estrogen receptor status, women with total folate intake in the highest tertile had a mortality risk ratio of 0.88 (95% confidence interval = 0.44-1.76) compared with cases in the lowest tertile of folate. These findings, although preliminary, afford some reassurance that folate supplementation is unlikely to have a significant adverse effect on survival after chemotherapy for breast cancer.

Determination of folate vitamers in human serum by stable-isotope-dilution tandem mass spectrometry and comparison with radioassay and microbiologic assay

BACKGROUND

Current clinical methods for folate give different results and cannot measure the various forms of folate. We developed an isotope-dilution tandem mass spectrometric method coupled to liquid chromatography (LC/MS/MS) as a candidate reference method for 5-methyltetrahydrofolic acid (5MeTHF), 5-formyltetrahydrofolic acid (5FoTHF), and folic acid (FA) in human serum.

METHODS

We quantitatively isolated folates from 275 microL of serum with a phenyl solid-phase extraction cartridge, then detected and quantified them in stabilized serum extracts by positive-ion electrospray ionization LC/MS/MS. We used an isocratic mobile phase of acetic acid in organic solvent on a C(8) analytical column. (13)C-labeled folates were used as internal standards.

RESULTS

Limits of detection in serum were 0.13 (5MeTHF), 0.05 (5FoTHF), and 0.07 (FA) nmol/L. Within- and between-run imprecision (CV) was <7% for 5MeTHF and <10% for 5FoTHF at concentrations >0.5 nmol/L, and <10% for FA at concentrations >2.0 nmol/L. Total folate (TFOL) concentrations determined by competitive protein binding radioassay were approximately 9% lower than results obtained with LC/MS/MS. The microbiologic assay gave approximately 15% higher TFOL results with FA calibrator and no difference with 5MeTHF calibrator. The mean (SD) [range] TFOL in 42 sera was 35.5 (17.8) [6.5-75.6] nmol/L. Thirty-two samples with TFOL <50 nmol/L had, on average, 93.3% 5MeTHF, 2.3% FA, and 4.4% 5FoTHF. Ten samples with TFOL >50 nmol/L had, on average, 81.7% 5MeTHF, 15.7% FA, and 2.5% 5FoTHF.

CONCLUSIONS

This stable-isotope-dilution LC/MS/MS method can quantify 5MeTHF, 5FoTHF, and FA in serum. Currently used clinical assays agree with this candidate reference method.

Heterozygote deficiency in thymidylate synthase enhancer region polymorphism genotype distribution in Hungarian colorectal cancer patients

Thymidylate synthase (TS) gene polymorphisms are important as prognostic factors in cancer chemotherapy, but recent results describe that the TS enhancer region (TSER) polymorphic genotypes may also modulate risk for malignancies. Two functionally important and ethnically diverse polymorphisms are present on the TS transcript, TSER, a repeat polymorphism (2 or 3 repeats; 2R, 3R) affecting TS expression, and a 6 bp ins/del polymorphism on the 3' UTR (position TS1494, del6 or ins6), which may influence mRNA stability. Hungarian population has one of the highest colorectal cancer (CRC) mortality rates in Europe, and several elevated dietary risk factors affect a large part of the population. In our study (99 primary CRC cases), population analysis of the patient group genotype frequencies revealed a departure from the Hardy-Weinberg equilibrium and significant heterozygote deficiency (p < 0.05) at the TSER locus. Despite the strong linkage between the 2 polymorphic loci, case TS1494del genotype frequencies were normally distributed, as well as the genotype frequencies of the healthy control population (n = 102), at both loci. Case-control comparison demonstrated a lower relative risk of TSER heterozygotes (OR = 0.47; CI = 0.27-0.83; p = 0.008) and a possible higher prevalence of the 3R3R&ins6/del6 in the CRC group. The observation that heterozygotes are those less susceptible for CRC in the Hungarian population may support the possibility of 2 different pathways in which TS may play a role in colorectal carcinogenesis, probably nutrient (or folate)-dependently. The lack of similar genotype effect seen with TS1494del polymorphism and the increased presence of one genotype combination (3R3R&ins6/del6) in the patient group suggest a possible TS haplotype effect influencing CRC risk.

Folate deficiency and ionizing radiation cause DNA breaks in primary human lymphocytes: a comparison

DNA double-strand breaks, the most serious DNA lesion caused by ionizing radiation, are also caused by several vitamin or mineral deficiencies, such as for folate. Primary human lymphocytes were either irradiated or cultured at different levels of folate deficiency to assess cell proliferation, apoptosis, cell cycle, DNA breaks, and changes in gene expression. Both radiation and folate deficiency decreased cell proliferation and induced DNA breaks, apoptosis, and cell cycle arrest. Levels of folate deficiency commonly found resulted in effects similar to those caused by 1 Gy of radiation, a relatively high dose. Though both radiation and folate deficiency caused DNA breaks, they affected the expression of different genes. Radiation activated excision and DNA double-strand break repair genes and repressed mitochondrially encoded genes. Folate deficiency activated base and nucleotide excision repair genes and repressed folate-related genes. No DNA double-strand break repair gene was activated by folate deficiency. These findings suggest that a diet poor in folate may pose a risk of DNA damage comparable to that of a relatively high dose of radiation. Our results also suggest that research on biological effects of low-dose radiation should take into account the nutritional status of the subjects, because folate deficiency could confound the effects of low-dose radiation.

Suppression of the protein tyrosine phosphatase receptor type O gene (PTPRO) by methylation in hepatocellular carcinomas

A diet lacking folic acid and choline and low in methionine (folate/methyl deficient diet, FMD diet) fed to rats is known to produce preneoplastic nodules (PNNs) after 36 weeks and hepatocellular carcinomas (tumors) after 54 weeks. FMD diet-induced tumors exhibit global hypomethylation and regional hypermethylation. Restriction landmark genome scanning analysis with methylation-sensitive enzyme NotI (RLGS-M) of genomic DNA isolated from control livers, PNNs and tumor tissues was performed to identify the genes that are differentially methylated or amplified during multistage hepatocarcinogenesis. Out of the 1250 genes analysed, 2 to 5 genes were methylated in the PNNs, whereas 5 to 45 genes were partially or completely methylated in the tumors. This analysis also showed amplification of 3 to 12 genes in the primary tumors. As a first step towards identifying the genes methylated in the PNNs and primary hepatomas, we generated a rat NotI-EcoRV genomic library in the pBluescriptKS vector. Here, we describe identification of one methylated and downregulated gene as the rat protein tyrosine phosphatase receptor type O (PTPRO) and one amplified gene as rat C-MYC. Methylation of PTPRO at the NotI site located immediate upstream of the trancription start site in the PNNs and tumors, and amplification of C-MYC gene in the tumors were confirmed by Southern blot analyses. Bisulfite genomic sequencing of the CpG island encompassing exon 1 of the PTPRO gene revealed dense methylation in the PNNs and tumors, whereas it was methylation free in the livers of animals on normal diet. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed significant decrease in the expression of PTPRO in the tumors and in a transplanted rat hepatoma. The expression of PTPRO mRNA in the transplanted hepatoma after demethylation with 5-azacytidine, a potent inhibitor of DNA methyltransferases, further confirmed the role of methylation in PTPRO gene expression. These results demonstrate alteration in methylation profile and expression of specific genes during tumor progression in the livers of rats in response to folate/methyl deficiency, and further implicate the potential role of PTPRO as a novel growth regulatory gene at least in the hepatocellular carcinomas.

Acute absorption of folic acid from a fortified low-fat spread

OBJECTIVE

To explore the feasibility of low-fat spreads as vehicles for folic acid (FA) fortification by determining the acute absorption of FA from a fortified spread.

DESIGN

Double blind, crossover study to test each of the following treatments administered at 1-weekly intervals: (A) 20 g low-fat (40%) spread fortified with 200 microg FA and a placebo tablet; (B) 20 g low-fat placebo spread and a 200 microg FA tablet; (C) 20 g low-fat placebo spread and a placebo tablet.

SUBJECTS

A total of 13 male volunteers, aged 31.8+/-13.2 y.

MAIN OUTCOME MEASURES

Plasma total folate concentrations, measured before and up to 10 h after each treatment (n=10 samples per treatment).

RESULTS

Plasma folate concentrations were significantly increased compared with baseline values 1 h after administration of the FA tablet, and 1.5 h after the FA spread, and remained significantly higher than the baseline values for up to 7 h after both treatments. The maximum plasma folate response (R(max)), corrected for baseline values and 'placebo response', was established between 1 and 3 h postprandially in response to both FA spread and FA tablet, and no significant difference in R(max) was found between the two treatments (13.4 vs 14.4 nmol/l, P=0.9). The acute absorption of FA from fortified spread relative to that from the tablet, calculated on the basis of area under the plasma folate response curve, was 67% (P=0.04).

CONCLUSION

The absorption of FA from fortified low-fat spread, although lower than from a tablet, is effective. These results suggest that low-fat spreads, typically associated with fat-soluble vitamin fortification, may also be considered feasible as vehicles for FA fortification.

S-Adenosylhomocysteine Enhances Hydrogen Peroxide-Induced DNA Damage by Inhibition of DNA Repair in Two Cell Lines

It has been proposed that hyperhomocysteinemia may exert its pathogenic effects largely through metabolic accumulation of S-adenosylhomocysteine (SAH), a strong noncompetitive inhibitor of most methyltransferases. Here, we investigated the effects of SAH on H(2)O(2)-induced cellular DNA damage in comparison with the effects of homocysteine (Hcy) in a mouse endothelial cell line and a human intestinal cell line. Cells were preincubated for 2 h with H(2)O(2) (20 microM) followed by incubation with SAH or Hcy for 3 h. DNA strand breakage was determined using comet assay and DNA repair capacity determined using the same assay over time at 1, 2, and 3 h during SAH incubation. In both types of cells, SAH at 0.25-2 microM strongly and dose dependently enhanced H(2)O(2)-dependent DNA damage and inhibited DNA repair, whereas Hcy had a much weaker effect. SAH markedly increased uracil misincorporation, and this effect was also much stronger than that of Hcy. Taken together, our results show that SAH potentiates H(2)O(2)-induced DNA damage in cell cultures through impaired DNA repair capability and suggest that such effects are related to uracil misincorporation. Although the in vivo relevance of our findings is unclear, the biological significance of SAH-mediated detrimental effect, secondary to elevated intracellular Hcy, is an interesting area awaiting further exploration.

Uptake of 5-methyltetrahydrofolate into PC-3 human prostate cancer cells is carrier-mediated

Uptake of 5-methyltetrahydrofolate into the PC-3 human prostate cancer cells was linear for the first 60 min. There was no difference in the initial rate of uptake in cells incubated in folate-free medium for 24 or 48 hr compared to control cells grown in folate-containing medium. The initial rate of 5-methyltetrahydrofolate uptake showed little dependence on extracellular pH and it was independent of extracellular sodium ions. Transport of 5-methyltetrahydrofolate into PC-3 cells was saturable - K(m) = 0.74 micro M and V(max) = 7.78 nmol/10(9)cells/min and these kinetic constants were not different in cells incubated for 24 hr in folate-free medium (K(m) = 0.80 +/- 0.22, V(max) = 8.52 +/- 0.50; P = 0.09, N = 3). Uptake of 5-methyltetrahydrofolate was inhibited by structural analogs with the K(i) values being 0.50, 1.79, and 31.8 micro M for 5-formyltetrahydrofolate, methotrexate, and folic acid, respectively. Uptake of 5-methyltetrahydrofolate was inhibited by the energy poisons, sodium cyanide, sodium arsenate, p-chloromercuriphenylsulfonate, and sodium azide. Uptake was inhibited by increasing concentrations of sulfate and phosphate ions, suggesting that 5-methyltetrahydrofolate may be transported by an anion-exchange mechanism. These results show that 5-methyltetrahydrofolate is transported into PC-3 prostate cancer cells by a carrier-mediated process.

Chemoprevention of colon cancer by calcium, vitamin D and folate: molecular mechanisms

Recent findings have indicated that dietary calcium, vitamin D and folate can modulate and inhibit colon carcinogenesis. Supporting evidence has been obtained from a wide variety of preclinical experimental studies, epidemiological findings and a few human clinical trials. Important molecular events and cellular actions of these micronutrients that contribute to their tumour-modulating effects are discussed. They include a complex series of signalling events that affect the structural and functional organization of colon cells.

Folate, vitamin B12, and homocysteine status. findings of no relation between human papillomavirus persistence and cervical dysplasia

OBJECTIVES

Human papillomavirus (HPV) infections are the cause of most, if not all, cervical cancers. Women consistently positive for oncogenic type HPV infections have a greater risk of developing cervical dysplasia compared with women transiently infected. HPV infection alone appears to be insufficient to produce disease, suggesting that other cofactors may be needed. Folate, vitamin B12, and homocysteine, through their role in DNA methylation, may be involved in cervical neoplasia.

METHODS

This study examined the associations between HPV persistence and circulating folate, vitamin B12, and homocysteine levels among 91 low-income Hispanic women. Further, the relation of these nutrients to cervical pathology was evaluated. HPV status was determined at two visits approximately 3 mo apart.

RESULTS

Adjusted mean circulating concentrations of folate, vitamin B12, and homocysteine were not statistically different between women with two positive HPV tests, one positive test, or two negative HPV tests. No association was observed between tertiles of folate, vitamin B12, or homocysteine and HPV persistence risk. Further, adjusted mean levels of these nutrients were not statistically different between cytologic grades.

CONCLUSIONS

Results from this small study did not support a role for folate, vitamin B12, or homocysteine in HPV persistence or cervical dysplasia.

Folic acid supplements and fortification affect the risk for neural tube defects, vascular disease and cancer: evolving science

Folic acid supplements reduce the risk of neural tube defects and may be associated with reduced risk for vascular disease and cancer. Research data from both observational and controlled intervention studies provide strong support for the existing public health policies related to folic acid and neural tube defects. However, educational efforts to promote daily intake of folic acid supplements by women of reproductive age have not, in most cases, resulted in increased supplement use. In contrast, food fortification appears to be associated with a reduction in neural tube defects in the United States and Canada but is not practiced universally. The potential for folic acid supplements to reduce the incidence and severity of vascular disease and cancer is the focus of major research efforts including ongoing intervention studies.

News and views on folate and elderly persons

Elderly persons are especially exposed to folate deficiency, where normal/subnormal folate levels do not exclude tissue deficiency. Accompanying diseases, medication, and lifestyle factors may contribute to/cause deficiency. Symptoms of deficiency can be hematological, neurological, or neuropsychiatric, but it is likely that there are also cardiovascular manifestations as well as associations with malignancies. The physician should make an individualized investigation to establish the probable cause. Among the available determinants of the folate/cobalamin state, plasma homocysteine (Hcy) is a swift and sensitive marker and has the strongest connection to cognitive function. The association is generally stronger between Hcy levels and symptoms than between vitamin-related levels and symptoms. The duration as well as the severity of symptoms are of importance in terms of the improvement of neurological and neuropsychiatric symptoms when substitution is performed. The issue of general folate fortification of flour is complex, and there are as many pros and cons as there are countries in which it is considered to be launched. It is important to bear in mind that in our modern society, deficiency of folate/cobalamin--overt or latent--mainly is a problem of the elderly and a challenge to the doctor.

Biochemical and molecular aberrations in the rat colon due to folate depletion are age-specific

Elder adulthood and diminished folate status are each associated with an enhanced risk of colorectal carcinogenesis. We therefore examined whether these two factors are mechanistically related. Weanling male Sprague-Dawley rats (n = 44) and 1-y-old rats (n = 44) were each divided into three groups and fed diets containing 0, 4.5 or 18 micro mol folic acid/kg (deplete, replete and supplemented groups, respectively). Rats were killed at 0, 8 and 20 wk. The folate concentrations, the distribution of the different coenzymatic forms of folate, uracil incorporation into DNA and genomic DNA methylation were measured in the colonic mucosa. Folate-deplete and folate-replete elder rats had 30-45% lower colonic folate concentrations than young rats. Furthermore, 5-methyltetrahydrofolate was uniformly depleted in colons of the elder, folate-deplete rats, whereas this depletion occurred in only a minority of the younger rats. By the end of the experiment, the folate-deplete and folate-replete elder rats had approximately 50% more uracil incorporated into their colonic DNA than the corresponding young groups (P < 0.05). In elder rats, this uracil misincorporation was incremental across the three diet groups (P-test for trend < 0.05), whereas no excess uracil incorporation was observed in young rats. Neither age nor dietary folate affected genomic DNA methylation in the colon. In conclusion, the colon of elder rats is more susceptible to biochemical and molecular consequences of folate depletion than that of young rats. However, folate supplementation is as effective at sustaining adequate colonic folate status in elder rats as it is in the young.

Biomarkers of nutrient exposure and status in one-carbon (methyl) metabolism

One-carbon metabolism is a network of interrelated biochemical reactions that involve the transfer of one-carbon groups from one compound to another. The coenzymes necessary for several of these reactions include the B-vitamins, folate, vitamin B-12, vitamin B-6 and riboflavin (vitamin B-2), whereas important intermediary compounds in this schema include methionine and choline. There has been renewed interest in one-carbon metabolism during the past several years, engendered by recent insights that indicate that modest dietary inadequacies of the abovementioned nutrients, of a degree insufficient to cause classical deficiency syndromes, can still contribute to important diseases such as neural tube defects, cardiovascular disease and cancer. Traditional means of assessing nutrient exposure with food frequency questionnaires, and nutrient status with plasma and urine vitamin assays, has some genuine validity and utility. Assessing the concentration of appropriate intermediary compounds, such as plasma homocysteine for folate and methylmalonic acid for vitamin B-12, provides further insights because they appear to add a degree of sensitivity that does not exist with the more traditional assays. There may also be value in developing measures that integrate the status of all these nutrients and express it as a functional "methylation capacity" of the individual. Plasma or tissue concentrations of S-adenosylmethionine and S-adenosylhomocysteine, and genomic DNA methylation are two potential candidates in this regard although much work is yet to be done to define the nature of these relationships.

Transport of 5-formyltetrahydrofolate into primary cultured cerebellar granule cells

Transport of 5-formyltetrahydrofolate (5-FTHF) into primary cultured cerebellar granule cells (CGC) was studied. Uptake of 5-FTHF into CGC was saturable with K(m)=2.86 microM and V(max)=40.8 pmol/mg protein/45 min in pH 7.4 medium. Uptake of 5-FTHF in the astrocytes has a similar style in the time curve. Uptake of 5-FTHF is characterized by countertransport because adding unlabeled 5-FTHF in the medium resulted in the efflux of labeled 5-FTHF. Uptake of 5-FTHF was inhibited by the structural analogs 5-methyltetrahydrofolate, methotrexate and folic acid (K(i)=6.64, 7.69, and 19.38 microM, respectively). Uptake was significantly decreased by high concentrations of sodium azide and sodium arsenate but not by sodium cyanide. Uptake was also inhibited by p-chloromercuriphenylsulfonate and by the anions probenecid and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. Acute exposure of the cells to ethanol (100 mM) did not affect the uptake. It is concluded that CGC have a carrier-mediated system for the uptake of 5-FTHF and other folates.

Relation of plasma folate and methylenetetrahydrofolate reductase C677T polymorphism to colorectal adenomas

BACKGROUND

Folate intake may be related to decreased risk of colorectal cancer and adenomas. Methylenetetrahydrofolate reductase (MTHFR) is a key regulatory enzyme in folate metabolism. We examined the relation between plasma folate status and colorectal adenomas with reference to effect modification by the genetic polymorphism (C677T) of MTHFR.

METHODS

Study subjects were middle-aged Japanese men: 177 cases of colorectal adenomas and 192 controls with normal total colonoscopy. Statistical adjustment was made for hospital, rank in the Self Defense Forces, alcohol use, smoking, and body mass index.

RESULTS

Plasma folate levels were slightly lower in adenoma cases than in controls. Adjusted odds ratio (OR) for high (>5.50 ng/ml) versus low plasma folate levels was 0.72 (95% CI: 0.46-1.14). As compared with subjects with the CC or CT genotype having low plasma folate levels, those with the TT genotype showed a decreased risk of colorectal adenomas when they had high levels of plasma folate (adjusted OR = 0.58, 95% CI: 0.21-1.61), and an increased risk when they had low folate levels (adjusted OR = 2.13, 95% CI: 0.82-5.54). There was no clear relation between plasma folate and colorectal adenomas among those with the CC or CT genotype.

CONCLUSIONS

The findings suggest an interaction between folate and the MTHFR genotype on colorectal adenomas.

Folate: a key to optimizing health and reducing disease risk in the elderly

Inadequate folate status is associated with an increased risk for chronic diseases that may have a negative impact on the health of the aging population. Folate, a water-soluble vitamin, includes naturally occurring food folate and synthetic folic acid in supplements and fortified foods. Inadequate folate status may result in hyperhomocysteinemia, a significant risk factor for atherosclerotic vascular disease, changes in DNA that may result in pro-carcinogenic effects and increased risk for cognitive dysfunction. Folate status may be negatively influenced by inadequate intake, genetic polymorphisms and interactions with various drugs. In the US, folic acid is now added to enriched grain products and continues to be included in the majority of ready-to-eat breakfast cereals. Recent data indicate that the folate status in the US population has improved significantly, presumably due to the effects of fortification. Folic acid (not food folate) intake in excess of the Tolerable Upper Intake Level may mask the diagnosis of a vitamin B(12) deficiency, which is more prevalent in the elderly than younger individuals. When folic acid supplements are recommended, a multivitamin that includes vitamin B(12) should also be advised. To safely and effectively increase folate intake in the elderly, naturally occurring folate-rich food sources should be promoted. Folate-rich foods include orange juice, dark green leafy vegetables, asparagus, strawberries and legumes. These foods are also excellent sources of other health-promoting nutrients associated with chronic disease risk reduction.

Transport of 5-formyltetrahydrofolate into primary cultured rat astrocytes

Transport of 5-formyltetrahydrofolate (5-FTHF) into primary cultured rat astrocytes was studied. Uptake of 5-FTHF into astrocytes was linear in the first 60 min and is saturable with K(m)=3.3 microM and V(max)=27.5 pmol/mg protein/45 min in pH 7.4 medium. Uptake of 5-FTHF displayed the characteristics of countertransport. Uptake of 5-FTHF was inhibited by the structural analogs 5-methyltetrahydrofolate, methtrexate, and folic acid (K(i)=3.8, 2.7, and 18.4 microM, respectively). Uptake was significantly decreased by sodium azide but was increased by high concentration of sodium cyanide and low concentration of sodium arsenate. Uptake was also inhibited by p-chloromercuriphenylsulfonate and by the anions probenecid and 4,4(')-diisothiocyanostilbene-2,2(')-disulfonic acid. Acute exposure of the cells to ethanol (100mM) inhibited the uptake for 90 min of the experimental duration. It is concluded that astrocytes have a system for the uptake of 5-FTHF and folate analogs which is carrier mediated, this system is sensitive to energy inhibitors and alcohol exposure.

Spatial and temporal expression of folate-binding protein 1 (Fbp1) is closely associated with anterior neural tube closure in mice

Periconceptional folate supplementation is widely believed to have significant preventive effects on the production of neural tube defects. Folate-binding protein 1 (FBP1) is one of the membrane proteins that mediate cellular uptake of folate. Although recent studies suggest that Fbp1 is essential for neural tube closure, the pattern of Fbp1 expression in embryonic tissues has not been examined in detail. To elucidate how Fbp1 contributes to neural tube closure, we examined the spatial and temporal expression patterns of Fbp1 in the developing neural folds and tube of mouse embryos by in situ hybridization. Fbp1 showed a distinct expression pattern in the neural folds, which preceded initiation of neural tube closure at the cervical region and the prosencephalic/mesencephalic boundary. Fbp1 expression was mainly localized to the most dorsal regions of the neural folds where fusion was to occur. With proceeding of neural fold fusion, Fbp1 expression extended to the adjacent unfused neural folds. In the rhombencephalon, robust expression of Fbp1 was observed in rhombomere2 (r2) and r6, suggesting its roles in development of neural crest cells. Fbp1 also showed intense expression in the yolk sac, indicating that FBP1 may mediate transferring maternal folate to embryos during neurulation. These findings indicate close association between Fbp1 and anterior neural tube closure.

Effect of food fortification on folic acid intake in the United States

BACKGROUND

The addition of folic acid to all enriched cereal-grain foods, mandated by the Food and Drug Administration (FDA), was initiated in January 1998. Although this program was designed such that typical folate intakes would be increased by approximately 100 micro g/d and that the risk of intakes > 1000 micro g/d (the FDA's safe upper limit of daily intake) would be minimal, its actual effect on folate intake has yet to be determined.

OBJECTIVE

The objective was to estimate the effect of folic acid fortification on the amount of folate consumed by persons in the United States.

DESIGN

Linear regression analysis of data from published studies was used to determine the relation between a chronic folic acid dose and the resulting increase in steady state concentrations of folate in plasma or serum. Using this regression equation and reverse prediction, we quantified the increase in folic acid intake from fortification required to achieve the increase in plasma or serum folate observed in published studies.

RESULTS

The increase in circulating folate concentration was linearly related to folic acid intake over the range of 100-1000 micro g/d (r = 0.984, P < 0.0001). Predicted increases in folic acid intake from fortified food ranged from 215 to 240 micro g/d.

CONCLUSIONS

Typical intakes of folic acid from fortified foods are more than twice the level originally predicted. The effect of this much higher level of fortification must be carefully assessed, especially before calls for higher levels of fortification are considered.

Chemoprevention of colorectal cancer: problems, progress, and prospects

Chemoprevention holds great promise as a complement to traditional CRC screening and treatment. Effective chemopreventive agents might improve patient outcomes by reducing the number of missed lesions, the morbidity associated with their identification and treatment, and their malignant potential. In addition, chemoprevention may reduce neoplastic potential simultaneously in several organs and improve clinical outcomes for persons at risk for cancers at multiple sites (e.g., colorectal and extracolonic cancers in HNPCC cohorts). Complex molecular circuits underlie the disease mosaic that is associated with aging. Several of these diseases share common mechanisms against which preventive interventions appear to be effective, such as NSAIDs for colorectal neoplasia and neurodegenerative disease, and statins for cardiovascular disease and colorectal neoplasia. Understanding these mechanisms and effects could raise prevention science to an entirely new level. The number of trials that are investigating chemopreventives against CR neoplasia is relatively small; if these agents live up to a fraction of their promise, the public health impact may be great (see Table 6).

The effect of different cooking methods on folate retention in various foods that are amongst the major contributors to folate intake in the UK diet

Folate intake is strongly influenced by various methods of cooking that can degrade the natural forms of the vitamin in foods. The aim of the present study was to determine the effect of different cooking methods on folate retention in various foods that contribute to folate intake in the UK diet. Typical purchasing and cooking practices of representative food folate sources were determined from a questionnaire survey of local shoppers (n 100). Total folate was determined by microbiological assay (Lactobacillus casei NCIMB 10463) following thermal extraction and tri-enzyme (alpha-amylase, protease and conjugase) treatment in raw foods and after typical methods of cooking. Boiling for typical time periods resulted in only 49 % retention of folate in spinach (191.8 and 94.4 microg/100 g for raw and boiled spinach respectively; P<0.005), and only 44 % in broccoli (177.1 and 77.0 microg/100 g for raw and boiled broccoli respectively, P<0.0001). Steaming of spinach or broccoli, in contrast, resulted in no significant decrease in folate content, even for the maximum steaming periods of 4.5 min (spinach) and 15.0 min (broccoli). Prolonged grilling of beef for the maximum period of 16.0 min did not result in a significant decrease in folate content (54.3 and 51.5 microg/100 g for raw and grilled beef respectively). Compared with raw values, boiling of whole potatoes (skin and flesh) for 60.0 min did not result in a significant change in folate content (125.1 and 102.8 microg/100 g for raw and boiled potato respectively), nor was there any effect on folate retention whether or not skin was retained during boiling. These current results show that the retention of folate in various foods is highly dependent both on the food in question and the method of cooking. Thus, public health efforts to increase folate intake in order to improve folate status should incorporate practical advice on cooking.

In vivo kinetics of folate metabolism

Investigation of the in vivo kinetics of folate metabolism provides information that contributes to a better understanding of the manner in which this vitamin is processed in vivo. Kinetic studies can yield insight into the requirements for folate, especially with respect to factors that may lead to increased requirements. This review considers the strengths and weaknesses of various approaches to the study of folate kinetics and resulting data, followed by a summary and interpretation of existing data.

The human reduced folate carrier gene is regulated by the AP2 and sp1 transcription factor families and a functional 61-base pair polymorphism

Recently, our laboratory reported an intricate regulation of the human reduced folate carrier (hRFC) gene, involving multiple promoters and noncoding exons. We localized promoter activity to a 452-bp GC-rich region upstream of noncoding exon A, including a 47-bp basal promoter with a CRE/AP-1-like consensus element that bound the bZip family of DNA-binding proteins (e.g. CREB-1 and c-Jun). We now report that three nearly identical tandem repeats (49-61 bp) in the hRFC-A upstream region are involved in regulating promoter activity. By in vitro binding assays, multiple transcription factors (e.g. AP2 and Sp1/Sp3) bound this region. When AP2 was cotransfected with the hRFC-A reporter construct into HT1080 cells, promoter activity increased 3-fold. In Drosophila SL2 cells, Sp1 transactivated promoter A and showed synergism with CREB-1. However, c-Jun was antagonistic to the effects of Sp1. A sequence variant in the hRFC-A repeated region was identified, involving an exact duplication of a 61-bp sequence. This variant had an allelic frequency of 78% in 72 genomic DNAs and resulted in a 63% increase in promoter activity. These results identify important regions in the hRFC-A promoter and critical roles for AP2 and Sp1, in combination with the bZip transcription factors. Moreover, they document a functionally novel polymorphism that increases promoter activity and may contribute to interpatient variations in hRFC expression and effects on tissue folate homeostasis and antitumor response to antifolates.

The human reduced folate carrier gene is ubiquitously and differentially expressed in normal human tissues: identification of seven non-coding exons and characterization of a novel promoter

Our previous study identified two alternate non-coding upstream exons (A and B) in the human reduced folate carrier (hRFC) gene, each controlled by a separate promoter. Each minimal promoter was regulated by unique cis -elements and transcription factors, including stimulating protein (Sp) 1 and Sp3 and the basic leucine zipper family of proteins, suggesting opportunities for cell- and tissue-specific regulation. Studies were performed to explore the expression patterns of hRFC in human tissues and cell lines. Levels of hRFC transcripts were measured on a multi-tissue mRNA array from 76 human tissues and tumour cell lines and on a multi-tissue Northern blot of representative tissues, each probed with full-length hRFC cDNA. hRFC transcripts were ubiquitously expressed, with the highest level in placenta and the lowest level in skeletal muscle. By rapid amplification of cDNA 5'-ends assay from nine tissues and two cell lines, hRFC transcripts containing both A and B 5'-untranslated regions (UTRs) were identified. However, five additional 5'-UTRs (designated A1, A2, C, D and E) were detected, mapping over 35 kb upstream from the hRFC translation start site. The 5'-UTRs were characterized by multiple transcription start sites and/or alternative splice forms. At least 18 unique hRFC transcripts were detected. A novel promoter was localized to a 453 bp fragment, including 442 upstream of exon C and 11 bp of exon C. A 346 bp repressor flanked the 3'-end of this promoter. Our results suggest an intricate regulation of hRFC gene expression involving multiple promoters and non-coding exons. Moreover, they provide a transcriptional framework for understanding the role of hRFC in the pathophysiology of folate deficiency and antifolate drug selectivity.

Functional foods and health: a US perspective

Linkages between diet habits and the quality of life continue to surface on numerous fronts. Collectively these epidemiological, pre-clinical and clinical studies provide rather compelling evidence that numerous essential and non-essential dietary components are capable of influencing growth, development and performance and disease prevention. Scientific discoveries and widespread interest in the potential medicinal benefits of foods and food components have fostered a variety of content, health and structure-function claims. Unfortunately, defining the ideal diet is complicated by the numerous and diverse components that may influence biological processes. Inconsistencies in the literature may reflect the multi-factorial nature of these processes and the specificity that individual dietary constituents have in modifying genetic and epigenetic events. New and emerging genomic and proteonomic approaches and technologies offer exciting opportunities for identifying molecular targets for dietary components and thus determining mechanisms by which they influence the quality of life. All cells have unique 'signatures' that are characterized by active and inactive genes and cellular products. It is plausible that bridging knowledge about unique cellular characteristics with molecular targets for nutrients can be used to develop strategies to optimize nutrition and minimize disease risk.

Epidemiology and prevention of colorectal cancer

CRC, the second-leading cause of cancer death in the United States, is a highly preventable disease. Ironically, available and effective screening technologies are not consistently applied, even as new ones are developed. This discordance between preventive opportunity and practice conveys a sobering message regarding nontechnologic issues that must be addressed if the promise of CRC prevention is to be realized. Our response to this message will determine the public health impact of cancer prevention. In the 1980s, cancer chemoprevention was regarded as scientific speculation. Within the last decade, however, cancer has been recognized as a late, nonobligate stage of carcinogenesis, a chronic process that provides time and targets for preventive intervention. Further advances are emerging out of rigorous clinical testing, which remains the limiting factor in transforming ingenious concepts into useful tools for the prevention of CRC. The challenges and rewards of participation in chemoprevention research--both as patients and health care providers-have never been greater.

Folate intake and food sources in Japanese female dietitians

OBJECTIVE

To assess intake of folate/folic acid and food sources in Japanese female dietitians.

SUBJECTS AND METHODS

We evaluated folate consumption based on four season 7 consecutive day weighed diet records (WDRs) provided by 80 Japanese female dietitians and compared the results with data from a national survey. We then selected informative foods for folate intake on the basis of 2,240 WDRs according to contribution and multiple regression analyses.

RESULTS

Daily folate consumption (mean±SD) among Japanese dietitians was 413±158 μg from raw foods and 343±128 μg from cooked foods. Average residual rate after cooking was 84±8%. Folate intake in summer was lower than that in other seasons by analysis of variance. According to contribution and multiple regression analyses, the major contributors were vegetables, fruit and green tea.

CONCLUSIONS

Daily folate intake among Japanese female dietitians was far greater than the 200 μg recommended daily allowance for the Japanese. Irrespective of selection methods and raw/cooked foods, major folate sources were found to be green tea along with vegetables and fruit.

Moderate folate deficiency influences polyamine synthesis in rats

Spermidine, spermine and putrescine are polyamines, essential growth factors in mammalian cells. Decarboxylated S-adenosylmethionine (SAM) is an essential precursor in the formation of both spermidine and spermine. SAM is formed from methionine through the addition of adenosine. Because 5-methyltetrahydrofolate donates a methyl group to homocysteine to produce methionine, folate deficiency may decrease polyamine synthesis. Weanling male Sprague-Dawley rats were fed an amino acid-defined diet with 2 mg folic acid/kg diet (control) or no added folic acid (test). Blood, liver, brain, jejunum, ileum and colon samples were collected at the end of 5 wk. Compared with controls, rats fed the test diet had a 72% reduction in plasma folate (123.6 +/- 13.1 vs. 34.6 +/- 2.2 nmol/L, P < 0.001) and a 42% reduction in RBC folate (2834.4 +/- 218.3 vs. 1651.8 +/- 75.9 nmol/L, P < 0.001). Hepatic spermidine and spermine in folate-depleted rats were 58 (P < 0.001) and 67% (P < 0.01) higher, respectively, than in controls. Plasma putrescine was 27% higher (P < 0.05) than in controls. The polyamine concentrations of the jejunum, ileum, colon and brain did not differ. This study suggests that mild folate deficiency influences polyamine synthesis, but contrary to our hypothesis, hepatic spermidine and spermine were increased, as was circulating putrescine. This may have occurred for a number of reasons including increased enzyme activity or overcompensation by the betaine-homocysteine transmethylation pathway in the liver. Further study is necessary to clarify interactions between folate and polyamine metabolism and to determine whether polyamines are involved in the damaging effects of folate deficiency.

Relationship of folate to colorectal and cervical cancer: review and recommendations for practitioners

Evidence suggests that folate may play a role in cancer prevention. A plausible mechanism for prevention lies in the integral role that folate plays in deoxyribonucleic acid (DNA) synthesis and methylation. DNA methylation most likely regulates gene expression. Abnormal methylation, specifically hypomethylation, has been associated with tumorigenesis. The availability of methyl groups needed for adequate DNA methylation may be negatively influenced by low folate status, alcohol intake, or genetic polymorphisms that affect folate metabolism. Observational studies evaluating the association between folate and risk for colorectal and cervical cancers or precancerous conditions have produced conflicting results, and clinical trial data are needed to confirm a cause-and-effect relationship. However, several studies show interesting associations between cancer risk and factors that influence methyl group availability. Although data relating folate to cancer risk remain equivocal, when coupled with the other potential health benefits associated with folate, evidence supports recommending that people consume folate-rich foods such as fruits and vegetables. People consuming alcohol on a daily basis may especially benefit from additional folate in their diets.

Nutritional and genetic inefficiencies in one-carbon metabolism and cervical cancer risk

Folate deficiency has long been postulated to play a role in the etiology of cervical cancer, the third most frequent cancer among women worldwide. In a large, multiethnic community-based case-control study of invasive cervical cancer in five U.S. areas, we assessed accepted and postulated risk factors with an in-home interview and successfully obtained blood samples, at least 6 mo after completion of cancer treatment, from 51 and 68%, respectively, of interviewed cases and controls. Cases with advanced disease (6%) and/or receiving chemotherapy (4%) were excluded, leaving 183 cases and 540 controls. Serum and red blood cell folate were measured with both microbiologic and radiobinding assays. For all four folate measures, risk was moderately, but nonsignificantly, elevated for women in the lowest quartile, compared to the highest [fully adjusted relative risks (RR), including serologic human papillomavirus (HPV)-16 status = 1.2-1.6]. However, for women in the upper three homocysteine quartiles (>6.31 micro mol/L), risk of invasive cervical cancer was substantially and significantly elevated (fully adjusted RR, including serologic HPV-16 status = 2.4-3.2; P for trend = 0.01). This strong relationship suggests that circulating homocysteine may be 1) an especially accurate indicator of inadequate folate, 2) an integratory measure of insufficient folate in tissues or 3) a biomarker of disruption of one-carbon metabolism. The contribution of common polymorphisms in one-carbon pathway genes, as well as inadequate vitamin B-6, vitamin B-12 and/or riboflavin, to elevated homocysteine, inefficient one-carbon metabolism and increased cervical cancer risk merits further exploration.

Folate status: effects on pathways of colorectal carcinogenesis

Many epidemiologic, animal and human studies suggest that folate status modulates carcinogenesis. Although these observations have been made in a number of tissues, the data are clearly most compelling for the colorectum. The mechanism(s) by which this modulation is mediated remains ill defined. Alterations in either genome-wide or gene-specific DNA methylation and/or alterations in DNA stability, resulting from DNA strand breaks or uracil misincorporation, are leading candidates in this regard. Folate has a central role in biological methylation and nucleotide synthesis, and therefore it is not surprising that folate depletion has been observed to alter DNA methylation and diminish DNA stability. The hypothesis that these two pathways are the means by which folate modulates cancer risk is also supported by the epidemiological observation that a common polymorphism in the methylenetetrahydrofolate reductase (MTHFR; EC 1.5.1.20) gene differentially affects the relative risk of colon cancer depending on folate status, because MTHFR catalyzes the reaction that determines whether cellular folate is diverted into biological methylation or nucleotide synthesis. This phenomenon suggests that it is an imbalance between biological methylation and nucleotide synthesis that is responsible for folate-related carcinogenesis. The control of cell proliferation, which also is related to DNA methylation, is another candidate mechanism by which folate status modulates carcinogenesis. In cell culture studies, folate supplementation has been observed to suppress excessive cell proliferation. Understanding the mechanisms by which folate status modulates carcinogenesis is important for advancing insight into cancer biology and for facilitating those efforts to translate research in folate and carcinogenesis into effective and safe public health initiatives.

Gene-nutrient interactions and DNA methylation

Many micronutrients and vitamins are critical for DNA synthesis/repair and maintenance of DNA methylation patterns. Folate has been most extensively investigated in this regard because of its unique function as methyl donor for nucleotide synthesis and biological methylation. Cell culture and animal and human studies showed that deficiency of folate induces disruption of DNA as well as alterations in DNA methylation status. Animal models of methyl deficiency demonstrated an even stronger cause-and-effect relationship than did studies using a folate-deficient diet alone. Such observations imply that the adverse effects of inadequate folate status on DNA metabolism are mostly due to the impairment of methyl supply. Recently, an interaction was observed between folate status and a common mutation in the gene encoding for methylenetetrahydrofolate reductase, an essential enzyme in one-carbon metabolism, in determining genomic DNA methylation. This finding suggests that the interaction between a nutritional status with a genetic polymorphism can modulate gene expression through DNA methylation, especially when such polymorphism limits the methyl supply. DNA methylation, both genome-wide and gene-specific, is of particular interest for the study of cancer, aging and other conditions related to cell-cycle regulation and tissue-specific differentiation, because it affects gene expression without permanent alterations in DNA sequence such as mutations or allele deletions. Understanding the patterns of DNA methylation through the interaction with nutrients is fundamental, not only to provide pathophysiological explanations for the development of certain diseases, but also to improve the knowledge of possible prevention strategies by modifying a nutritional status in at-risk populations.

Bringing individuality to public health recommendations

The data generated from the human genome project offers unprecedented opportunities to elucidate the etiology of chronic diseases and developmental anomalies that arise from deleterious genome-diet interactions. Folate metabolism is an attractive system to explore such relationships. Folate is necessary for the synthesis of purine and thymidine deoxyribonucleotides and S-adenosylmethionine, a cofactor required for DNA methylation. Impaired folate metabolism results from primary folate deficiency, alcohol, gastrointestinal disorders that result in malabsorption, single nucleotide polymorphisms, increased folate catabolism and secondary nutrient deficiencies in vitamin B-6, vitamin B-12 and iron arising from a variety of pathologies. Any of these conditions singly or in combination influence DNA synthesis, DNA integrity, allelic-specific gene expression, chromatin structure and DNA mutation rates. Biochemical manifestations of impaired folate metabolism include increased uracil uptake into DNA, altered DNA methylation status and elevated homocysteine and S-adenosylhomocysteine in serum and tissues. These biochemical changes are associated with risk for cancer, cardiovascular disease, neural tube defects and some neuropathies and anemia, although direct causative mechanisms have not been established in all cases. Interactions between folate and the genome are reciprocal; polymorphisms in key genes influence folate nutritional requirements, indicating that dietary folate adequacy likely exerts selective pressure and thereby influences genetic variation. Other studies indicate that exposure to excess folate, perhaps at levels that occur at the upper end of the intake distribution curve, may have unintended consequences in promoting embryo viability. Therefore individualizing folic acid dietary recommendations necessitates a detailed understanding of all genetic and physiological variables that influence the interaction of folate with the genome and their relationship to the disease process.