Folate Depletion Research Articles

Accumulation of mitochondrial DNA deletions is age, tissue and folate-dependent in rats

Folate is essential for the synthesis, repair and methylation of DNA. Folate depletion causes nuclear genetic and epigenetic aberrations in cell culture, rodents and humans. We hypothesized that folate depletion may also damage mitochondrial (Mt) DNA and induce large-scale deletions due to DNA breakage. MtDNA deletions and mutations accumulate during aging and tumorogenesis and may play causative roles in these processes. Weanling and adult (12 months) Sprague Dawley rats consumed folate deplete, replete and supplemented diets (0, 2 and 8 mg/kg folate, respectively) for 20 weeks. The presence of random and common (4.8 kb) MtDNA deletions was measured in colonic mucosa and liver. Six Mt genomes (<16 kb) harboring random deletions were detected in the liver (3.5–7.0 kb) and three in the colon (3.8–8 kb). Older rats had significantly more random hepatic MtDNA deletions than young rats (64 and 3.2% of samples, respectively, P < 0.0001), while age had no effect on these deletions in the colon (3.1 and 7.7% in young and old, respectively). Folate intake had no effect on the frequency of random deletions in either tissue. There was no discrete effect of aging on the common 4.8 kb deletion in the liver or colon. However, in the liver of old rats, increasing amounts of dietary folate reduced the deletion frequency, with replete and supplemented rats having 2.2- and 3.2-fold less deletions than the depleted rats. Our results confirm that random MtDNA deletions accumulate with age in a tissue-specific fashion. Furthermore, in contrast to previous work, we report that the common 4.8 kb deletion was not modulated by age, but is reduced by folate supplementation in the liver of rats.

Vitamin B12 and Folate Depletion

In cross-sectional studies, low levels of folate and vitamin B12 have been associated with poor cognition and dementia. Results are quite controversial and a debate continues in the literature. Still not completely understood are the differential roles of folate and vitamin B12 in memory acquisition and cognitive development. More intriguing and not fully understood is the rule that treating a vitamin B12-deficient patient with folate may exacerbate the neurological consequences of either deficiency. Starting from these quite confusing perspectives, the aim of this study was to define a possible role of vitamin B12 and folate in cognitive disruption. Data were collected among a cohort of people, admitted to the Neurology Clinic of the University of Trieste, in a period between November 1,2000, and November 1, 2002. We examine potential risk factors, concomitant drug-therapies, and cognitive global performance and correlate these parameters with folate and vitamin B 12 serum levels.We discuss the results with an overview of the literature.

Methylenetetrahydrofolate reductase C677T and A1298C polymorphisms and colorectal cancer: The Fukuoka Colorectal Cancer Study

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme regulating folate metabolism, which affects DNA synthesis and methylation. This study investigated the relation of MTHFR C677T and A1298C polymorphisms to colorectal cancer in a case-control study in Fukuoka, Japan. The subjects comprised 685 incident cases of histologically confirmed colorectal adenocarcinomas and 778 community controls selected randomly in the study area. The genotype was determined by the PCR-RFLP method using genomic DNA extracted from buffy coat. Alcohol use was ascertained by in-person interview. Statistical adjustment was made for gender, age class, area, and alcohol use. The MTHFR 677TT genotype was associated with a statistically significant decrease in the risk with an adjusted odds ratio of 0.69 (95% confidence interval 0.51-0.93) compared with the 677CC and 677CT combined, and the decrease was most evident in individuals with no alcohol consumption. While the A1298C polymorphism showed no measurable association with the overall risk of colorectal cancer, the 1298CC genotype was associated with a statistically significant increase in the risk when alcohol consumption was high, and was also associated with an approximately 2-fold increase in the risk of each of proximal and distal colon cancer. The findings add to evidence that individuals with the MTHFR 677TT genotype have a decreased risk of colorectal cancer in the absence of folate depletion, suggesting a protective role of folate by ensuring a sufficient thymidylate pool for DNA synthesis. Because very few individuals had the 1298CC genotype, the findings regarding the A1298C polymorphism need careful interpretation and confirmation in larger studies.

Methylenetetrahydrofolate reductase 677C→T polymorphism affects DNA methylation in response to controlled folate intake in young women

DNA methylation is critical for normal genomic structure and function and is dependent on adequate folate status. A polymorphism (677C→T) in a key folate enzyme, methylenetetrahydrofolate reductase (MTHFR), may impair DNA methylation when folate intake is inadequate and may increase the risk of reproductive abnormalities. The present study was designed to evaluate the effect of the MTHFR 677C→T polymorphism on changes in global DNA methylation in young women consuming a low folate diet followed by repletion with the current Recommended Dietary Allowance (RDA). Women (age 20–30 years) with the TT (variant; n = 19) or CC ( n = 22) genotype for the MTHFR 677C→T polymorphism participated in a folate depletion-repletion study (7 weeks, 115 μg DFE/day; 7 weeks, 400 μg DFE/day). DNA methylation was measured at baseline, week 7, and week 14 using a [ 3H]methyl acceptance assay and a novel liquid chromatography tandem mass spectrometry assay of the DNA bases methylcytosine and cytosine. [ 3H]Methyl group acceptance tended to increase ( P = 0.08) during depletion in all subjects, indicative of a decrease in global DNA methylation. During repletion, the raw change and the percent change in the methylcytosine/total cytosine ratio increased ( P = 0.03 and P = 0.04, respectively) only in the subjects with the TT genotype. Moderate folate depletion in young women may cause a decrease in overall DNA methylation. The response to folate repletion suggests that following folate depletion women with the MTHFR 677 TT genotype have a greater increase in DNA methylation with folate repletion than women with the CC genotype.

Ethnicity and Race Influence the Folate Status Response to Controlled Folate Intakes in Young Women

Population-based studies report differences in folate status indicators among Mexican American (MA), African American (AA) and Caucasian (CA) women. It is unclear, however, whether these differences are due to variations in dietary folate intake. The present study was designed to investigate the influence of ethnicity/race on folate status parameters in MA, AA, and CA women (18-45 y; n = 14 in each group) under conditions of strictly controlled folate intake. In addition, the adequacy of the 1998 folate U.S. recommended dietary allowance (RDA), 400 micro g/d as dietary folate equivalents (DFE), for non-Caucasian women was assessed. Subjects (n = 42) with the methylenetetrahydrofolate reductase 677 CC genotype consumed a low-folate diet (135 micro g DFE/d) for 7 wk followed by repletion with 400 (7 MA, 7 AA, 7 CA) or 800 micro g DFE/d (7 MA, 7 AA, 7 CA) for 7 wk. AA women had lower (P </= 0.05) blood folate concentrations and excreted less (P </= 0.05) urinary folate throughout folate depletion and repletion with 400 and/or 800 micro g DFE/d compared with MA and/or CA women. MA women had lower (P </= 0.05) plasma total homocysteine (tHcy) throughout folate depletion and during repletion with 400 micro g DFE/d relative to the other ethnic/racial groups. Repletion with the 1998 folate U.S. RDA led to normal blood folate and plasma tHcy for all 3 ethnic/racial groups. Collectively, these data demonstrate that ethnicity/race is an important determinant of folate status under conditions of strictly controlled dietary folate intake and support the adequacy of the 1998 folate U.S. RDA for the 3 largest ethnic/racial groups in the United States.

Sulfasalazine is a potent inhibitor of the reduced folate carrier: implications for combination therapies with methotrexate in rheumatoid arthritis.

To investigate whether interactions of sulfasalazine (SSZ) with reduced folate carrier (RFC), the dominant cell membrane transporter for natural folates and methotrexate (MTX), may limit the efficacy of combination therapy with MTX and SSZ in patients with rheumatoid arthritis. Human RFC-(over)expressing CEM cells of T cell origin were used to analyze the effect of SSZ on the RFC-mediated cellular uptake of radiolabeled MTX and the natural folate leucovorin. Moreover, both cells with and those without acquired resistance to SSZ were used to assess the antiproliferative effects of MTX in combination with SSZ. Transport kinetic analyses revealed that SSZ was a potent noncompetitive inhibitor of RFC-mediated cellular uptake of MTX and leucovorin, with mean +/- SD K(i) (50% inhibitory concentration) values of 36 +/- 6 microM and 74 +/- 7 microM, respectively. Consistent with the inhibitory interaction of SSZ with RFC, a marked loss of MTX efficacy was observed when MTX was coadministered with SSZ: up to 3.5-fold for CEM cells in the presence of 0.25 mM of SSZ, and >400-fold for SSZ-resistant cells in the presence of 2.5 mM of SSZ. Importantly, along with diminished efficacy of MTX, evidence for cellular folate depletion was obtained by the demonstration of an SSZ dose-dependent decrease in leucovorin accumulation. At clinically relevant plasma concentrations, interactions of SSZ with RFC provide a biochemical rationale for 2 important clinical observations: 1) the onset of (sub)clinical folate deficiency during SSZ treatment, and 2) the lack of additivity/synergism of the combination of SSZ and MTX when these disease-modifying antirheumatic drugs are administered simultaneously. Thus, when considering use of these drugs in combination therapies, the present results provide a rationale both for the use of folate supplementation and for spacing administration of these drugs over time.

Hyperhomocysteinemia, Oxidative Stress, and Cerebral Vascular Dysfunction

An elevated circulating concentration of the sulfur-containing amino acid homocysteine, hyperhomocysteinemia, produces complex changes within the blood vessel wall. In the peripheral circulation, these changes include oxidative stress, proinflammatory effects such as expression of tumor necrosis factor-α and inducible nitric oxide (NO) synthase (iNOS), and endothelial dysfunction.1–6 Hyperhomocysteinemia-induced oxidative stress may occur as a result of decreased expression and/or activity of key antioxidant enzymes as well as increased enzymatic generation of superoxide anion (the precursor for multiple reactive oxygen and reactive nitrogen species).2,4 Do hyperhomocysteinemia-induced changes occur in the cerebral circulation and why are they potentially important? Hyperhomocysteinemia is a an emerging risk factor for carotid artery disease (atherosclerosis) and stroke and is associated with Alzheimer’s disease and vascular dementia.7–11 It was not until relatively recently, however, that experimental studies began to define the impact of hyperhomocysteinemia on cerebral vascular biology and the molecular mechanisms that account for these changes. This work has been facilitated by the development of mouse models with genetic alterations in different components of the homocysteine metabolic pathway (see below). Early work in the cerebral microcirculation observed that acute local administration of a very high concentration of homocysteine (1 mmol/L) in the presence of exogenous Cu2+ produced superoxide-mediated reductions in resting cerebral blood flow (CBF) as well as attenuation of endothelium-dependent and NO-mediated responses.12 Our group was among the first to show that mild chronic hyperhomocysteinemia produces endothelial dysfunction in the carotid artery.1,13 Moderate hyperhomocysteinemia, induced by acute methionine loading, …

Folate, colorectal carcinogenesis, and DNA methylation: lessons from animal studies.

Folate, a water-soluble B vitamin and cofactor in one-carbon transfer, is an important nutritional factor that may modulate the development of colorectal cancer (CRC). Epidemiologic and clinical studies indicate that dietary folate intake and blood folate levels are inversely associated with CRC risk. Collectively, these studies suggest an approximately 40% reduction in the risk of CRC in individuals with the highest dietary folate intake compared with those with the lowest intake. Animal studies using chemical and genetically predisposed rodent models have provided considerable support for a causal relationship between folate depletion and colorectal carcinogenesis as well as a dose-dependent protective effect of folate supplementation. However, animal studies also have shown that the dose and timing of folate intervention are critical in providing safe and effective chemoprevention; exceptionally high supplemental folate levels and folate intervention after microscopic neoplastic foci are established in the colorectal mucosa promote, rather than suppress, colorectal carcinogenesis. These animal studies, in conjunction with clinical observations, suggest that folate possesses dual modulatory effects on carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect, whereas folate supplementation has a promoting effect on the progression of established neoplasms. In contrast, folate deficiency in normal epithelial tissues appears to predispose them to neoplastic transformation, and modest levels of folate supplementation suppress the development of tumors in normal tissues. Notwithstanding the limitations associated with animal models, these studies suggest that the optimal timing and dose of folate intervention must be established for safe and effective chemoprevention in humans. Folate is an important factor in DNA synthesis, stability, and integrity, the repair aberrations of which have been implicated in colorectal carcinogenesis. Folate may also modulate DNA methylation, which is an important epigenetic determinant in gene expression (an inverse relationship), in the maintenance of DNA integrity and stability, in chromosomal modifications, and in the development of mutations. A mechanistic understanding of how folate status modulates colorectal carcinogenesis further strengthens the case for a causal relationship and provides insight into a possible chemopreventive role of folate.

Folic Acid Role in Mutagenesis, Carcinogenesis, Prevention and Treatment of Cancer

ABSTRACTIn 1987 we have published a hypothesis for the role of folic acid in the cancer prevention. Many research data, concerning the involvement of folate in the aetiology of cancer, accumulated since 1987 till now, support our hypothesis. Nowadays, the important role of folic acid in the normal cell metabolism, especially in the DNA synthesis and gene expression, and the role of folate deficiency in the development of some pathological processes, including cancer, are considered to be proved. In the present article we show the suppressive effect of folic and tetrahydrofolic acid on the DNA alkylation with a spin-labeled (containing nitroxyl radical) hydrazine mustard antitumor agent, by the electron spin resonance (ESR) method in vitro. We follow briefly the normal biological functions of folic acid and the established molecular effects of folate deficiency. Basing on our and other authors studies, including quantum biochemical ones, on the folic acid and other low molecular weight nucleophilic compounds in the cell we connect the folate depletion with the strong nucleophilic properties of hydrogenated folates, especially tetrahydrofolate, that determinate it as one of the first targets of the electrophilic attack of agents with carcinogenic potential, including the reactive oxygen species. We consider that an unified theory for mutagenesis, carcinogenesis, cancer prevention and therapy putting the folate and tetrahydrofolate in the center of the events, has been created.

Association between short birth intervals and schizophrenia in the offspring

Pregnancy burdens maternal folate reserves. Postpartum restoration to normal folate values may take up to 1 year. Maternal folate deficiency during early pregnancy has been hypothesized as a cause of schizophrenia in the offspring. We investigated whether the risk of schizophrenia is increased in persons conceived shortly after another birth. A population-based cohort was established of 1.43 million persons born in Denmark between 1950 and 1983, yielding 17.6 million person-years of follow-up. Schizophrenia in cohort members (5095 cases) and their siblings and parents was identified by linkage with the Danish Psychiatric Case Register. Relative risks of schizophrenia were estimated by use of log-linear Poisson regression. As compared to intervals of 45 months and longer, the schizophrenia risk ratio was 1.14 (95% confidence interval [CI], 0.97 to 1.35) for interbirth intervals of up to 15 months, 1.32 (95% CI, 1.12 to 1.56) for intervals of 15 to 17 months, 1.38 (95% CI, 1.18 to 1.61), for intervals of 18 to 20 months and 1.13 (95% CI, 1.00 to 1.29) for intervals of 21 to 26 months. Relative risks did not essentially change after adjustment for age, sex, calendar year of diagnosis, maternal and paternal age, history of mental illness in a parent or sibling, sibship size, place of birth, and distance to younger sibling. These results show an association between short birth intervals and schizophrenia in the offspring. Although maternal folate depletion may play a role in this association, we cannot rule out other explanations such as maternal stress during pregnancy and childhood infections.

Role of Folate in Colon Cancer Development and Progression

Folate, a water-soluble B vitamin and important cofactor in 1-carbon transfer, is an important nutritional factor that may modulate the development of colorectal cancer. Epidemiologic and clinical studies indicate that dietary folate intake and blood folate levels are inversely associated with colorectal cancer risk. Collectively, these studies suggest an approximately 40% reduction in the risk of colorectal cancer in individuals with the highest dietary folate intake compared with those with the lowest intake. Animal studies using chemical and genetically predisposed rodent models have provided considerable support for a causal relationship between folate depletion and colorectal carcinogenesis as well as a dose-dependent protective effect of folate supplementation. However, animal studies have also shown that the dose and timing of folate intervention are critical in providing safe and effective chemoprevention; exceptionally high supplemental folate levels and folate intervention after microscopic neoplastic foci are established in the colorectal mucosa promote rather than suppress colorectal carcinogenesis. These animal studies in conjunction with clinical observations suggest that folate possesses the dual modulatory effects on carcinogenesis depending on the timing and dose of folate intervention. Folate deficiency has an inhibitory effect whereas folate supplementation has a promoting effect on progression of established neoplasms. In contrast, folate deficiency in normal epithelial tissues appears to predispose them to neoplastic transformation, and modest levels of folate supplementation suppress the development of tumors in normal tissues. Notwithstanding the limitations associated with animal models, these animal studies suggest that the optimal timing and dose of folate intervention need to be established for safe and effective chemoprevention in humans.

Effects of dietary folate and aging on gene expression in the colonic mucosa of rats: implications for carcinogenesis.

Folate depletion and aging are risk factors for colorectal cancer. We investigated the effects of folate status and aging on gene expression in the rat colon. Young (weanling) and older (12 month) rats were fed folic acid depleted (0 mg/kg) and supplemented (8 mg/kg) diets for 20 weeks. Gene expression was measured in colonic mucosal scrapings (n = 3 per group) using oligonucleotide arrays (Affymetrix U34A). Folate depletion induced the up-regulation of immune-related genes, urokinase and inducible nitric oxide synthase and the down-regulation of adhesion molecules (protocadherin-4, nidogen and integrin alphaV) and vascular endothelial growth factor in young rats. The abbreviated response to depletion in old rats (62 changes versus 136 in the young) included up-regulation of caspase-2 and deleted in colon cancer. Gene expression changes due to aging were more abundant in folate depleted than supplemented rats (38 versus 119 genes, respectively). In folate-deficient rats, aging induced the down-regulation of immune-related genes, urokinase, p53, insulin-like growth factor binding protein-3 and vav-1 oncogene. In folate supplemented rats, aging induced the down-regulation of vascular endothelial growth factor and caspase-2. Lower expression of adhesion molecules and higher expression of urokinase with folate depletion in young rats may indicate that cell detachment and migration, cancer-related processes, may be modulated by folate status. An age-related decline in p53 and IGF-BP3 expression was only observed in folate depleted animals, indicating that folate supplementation may reduce the risk for age-associated cancers by suppressing deleterious changes in the expression of certain genes.

Reduced folate transport to the CNS in female Rett patients.

Previous CSF studies in Rett syndrome suggest reduced turnover of the biogenic monoamines serotonin and dopamine. Because diminished turnover may result from CNS folate depletion, the authors studied transport of folate across the blood-brain barrier. In four patients with Rett syndrome, the authors measured CSF values of 5-methyltetrahydrofolate (5MTHF), biogenic monoamine end-metabolites, and pterins together with serum and red blood cell folate. In CSF, the overall folate binding capacity by the two soluble folate-binding proteins FBP1 and FBP2 (sFBP) was measured using a radioligand binding method for H3-labeled folate. A specific immunoreactive test (ELISA) detected sFBP1, which normally contributes to 30 to 35% of the total folate binding capacity. Genetic analysis included DNA sequencing of the MECP2, FBP1, and FBP2 genes. Empirical treatment with oral folinic acid was evaluated. Two patients without and two with mutations of the MECP2 gene had normal values for red blood cell folate, serum folate, homocysteine, and methionine. In CSF, all patients had low values for 5MTHF, neopterin, and the serotonin end-metabolite 5-hydroxyindoleacetic acid (5-HIAA). Genetic analysis of FBP1 and FBP2 genes had normal results. Compared to controls, patients with Rett syndrome had normal immunoreactive sFBP1 in CSF, whereas the total folate binding capacity was disproportionately lowered. Empirical treatment with oral folinic acid normalized 5-MHTF and 5-HIAA levels in CSF, and led to partial clinical improvement. Irrespective of the MECP2 genotype, 5MTHF transfer to the CNS is reduced in Rett syndrome. Folinic acid supplementation restores 5MTHF levels and serotoninergic turnover. The lowered folate binding capacity of FBP is not explained by a defect of the FBP1 or FBP2 gene, but most likely occurs as a secondary phenomenon in Rett syndrome.

Plasma homocysteine and glycine are sensitive indices of folate status in a rodent model of folate depletion and repletion.

The objectives of the current studies included the characterization of the temporal changes in indices of folate status and amino acid concentrations during both folate depletion and repletion phases. In trial 1, a 6 week folate depletion protocol was employed, using 60 weanling rats assigned to receive an amino acid-defined diet with or without 1 mg/kg folic acid. A 4 week folate depletion period was judged to be optimal on the basis of the development of nadirs in both plasma and hepatic folate stores and elevated (>6-fold relative to folate-adequate controls) concentrations of plasma homocysteine and glycine. In trial 2, 54 weanling rats, previously maintained on a folate-devoid diet for 4 weeks, were assigned to receive 0.25 mg/kg folate as either crystalline folic acid or folate from a folate-enriched egg yolk powder. Both forms of folate supported similar rates of gain, increases in plasma and hepatic folate stores, and reductions in plasma glycine concentrations, whereas the folate in egg yolk powder lowered plasma homocysteine concentrations further than the crystalline folic acid (P < 0.05). These data support the use of both plasma glycine and homocysteine as sensitive response criteria for folate status in a rat bioassay of folate depletion and repletion and establish appropriate temporal end-points for such studies.

Leukoencephalopathy and Cortical Laminar Necrosis Associated with Intrathecal Methotrexate and Cranial Irradiation

Leukoencephalopathy and Cortical Laminar Necrosis Associated with Intrathecal Methotrexate and Cranial Irradiation

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.

Gene expression profiles of folate deficient colon cancer cells

Folate is a B vitamin that inversely modulates colorectal carcinogenesis. Folate status is also an important determinant in chemotherapeutic response. Mediating the transfer of onecarbon moieties is the sole biochemical function known for folate, and in this role folate plays a critical role in DNA synthesis, repair and methylation This study determined the gene expression profiles induced by tolate deficiency in 2 human colon adenocarcinoma cell lines, HCT116 and Caco2. Cells were grown in either standard (2.3 ~tM Mate) or folate deficient (0 ~M) RPMI medium for 20 days. Folate-deficient HCTll6 and Caco2 cells showed sigmficantly reduced growth rates and had sigmficantly decreased (by 80-90%) intracellular folate concentrations compared with corresponding folate-sufficient ceils (P<O.001 ). The deoxyuridine suppression test confirmed functionally significant intracellular folate depletion in folate-deficlent cells (P<0.01). Total RNA from folate-deficient and sufficient ceils of each cell line was hybridized onto 2 commercially available human cancer pathway (a panel of key genes involved in 6 biological pathways frequently altered during transformation and tumongenesis) and apoptosis (a panel of key genes involved in apoptosis) cDNA arrays and differentially expressed genes were identified RT-PCR analysis was used to confirm the results of cDNA array. A total of 13 and 22 cancer pathway genes were differential expressed in folate-defictent HCT116 and Caco2 cells, respectively, compared with corresponding folate-sufficient cells; 4 genes were differentially expressed in both folatedeficient ceils Most notably affected changes were upregulated ATM and downregulated MDM2 in folate-deficient Caco2 cells, upregulated p21 in folate-deficient HCT 116 cells and upregulated b-catenin and VEGF in both folate-deficient ceils. A total of 5 and 12 apoptosis genes were difterentially expressed in folate-deficient HCT 116 and Caco2 cells, respectively, compared with corresponding folate-sufficient cells; 1 gene was differentially expressed in both fofate-deficient cells. Most significantly altered changes were downregulated MDM2 and BAX in folate-deficient Caco2 cells and upregulated B1RC3 in both folate-deficient HCT116 and Caco2 cells. These data suggest that folate deficiency affects the expression of key genes that are related to cell cycle control, DNA damage and repair, apoptosis, signal transduction and angiogenesis in colon cancer cells in a cell-specific manner.

Moderate hyperhomocysteinaemia and immune activation in Parkinson's disease.

Moderate hyperhomocysteinaemia has been linked to an increased risk for cardiovascular diseases. Increased homocysteine concentrations may follow folate depletion due to insufficient dietary intake of the vitamin, but there is also some indication that immune activation could play a role. In this preliminary study, homocysteine, folate, and vitamin B(12) concentrations were measured in 19 patients with Parkinson's disease, 61-90 years of age, and compared to a healthy control group of similar age and to neopterin concentrations as an indicator of immune activation. A subgroup of patients presented with increased homocysteine and low folate concentrations. Homocysteine levels correlated inversely with vitamins folate and B(12) and positively with neopterin concentrations. Disturbed homocysteine metabolism in Parkinson's disease may be associated with vitamin deficiency and with immune system activation which may underlie folate depletion.

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.

Involvement of DNA mismatch repair in folate deficiency-induced apoptosis☆

Folate is a critical factor for DNA metabolism and its deficiency is associated with a number of human diseases and cancers. Although it has been shown that folate deficiency induces genomic instability and apoptotic cell death, the underlying mechanism is largely unknown. Given the role of mismatch repair in maintaining genomic integrity, mismatch repair was tested for its involvement in folate deficiency-induced genomic instability and cell death. Cells proficient in mismatch repair were highly sensitive to folate deficiency compared with cells defective in either hMutSα or hMutLα. Since wild-type cells but not mutant cells underwent apoptosis upon extensive folate depletion, the apoptotic response is dependent on a functional mismatch repair system. Our data also indicate that p53 is required for the folate depletion-induced apoptosis. In vitro biochemical studies demonstrated that hMutSα specifically recognized DNA damage induced by folate deficiency, suggesting a direct participation of mismatch repair proteins in mediating the apoptotic response. We conclude that while the mismatch repair-dependent apoptosis is necessary to protect damaged cells from tumorigenesis, it may damage a whole tissue or organ, as seen in patients with megaloblastic anemia, during extensive folate deficiency.