Is folic acid supplementation to food benefit or risk for human health?

Gordana Bjelakovic; Ivana Stojanovic; Tatjana Jevtovic-Stoimenov; Ljiljana Bjelakovic; Borisav Kamenov; Dusica Pavlovic; Gordana Kocic; Dusan Sokolovic; Jelena Basic; Goran B. Bjelakovic

doi:10.1515/pterid-2013-0024

Article Open Access

Is folic acid supplementation to food benefit or risk for human health?

Gordana Bjelakovic , Ivana Stojanovic , Tatjana Jevtovic-Stoimenov , Ljiljana Bjelakovic , Borisav Kamenov , Dusica Pavlovic , Gordana Kocic , Dusan Sokolovic , Jelena Basic and Goran B. Bjelakovic

Published/Copyright: October 5, 2013

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From the journal Pteridines Volume 24 Issue 3-4

Abstract

The need for sufficient quantities of folic acid for normal embryogenesis and fetal development is well known. Women of childbearing age must be sure to have an adequate intake of folic acid periconceptionally prior to and during pregnancy. Folate plays an essential role in the biosynthesis of RNA and DNA, phospholipid and neurostransmitters synthesis, using S-adenosylmethionine (SAM) as the primary methyl group donor. In some countries, the knowledge that folic acid is preventable for the reduction of the risk for neural tube defects (NTD) and in lowering the high amount of homocysteine (Hcy) led to the recommendation that all women capable of becoming pregnant should consume 400 µg of folic acid daily. Later, in 1998, folic acid fortification of all enriched cereal grain product flour was implemented in some countries. In addition to careful monitoring of adverse effects, the studies are warranted in order to determine the potentially positive and deleterious effects of folic acid fortification and supplementation on the human health or human diseases. To further understand the metabolic action of folates we asked ourselves the question: Is the intake of a sufficient amount of this vitamin a benefit or risk for human health?

Keywords: deficiency; folates; food fortification; human health; polyamines

Introduction

Folic acid (FA), folacin (Vitamin B₉) or pteroylglutamic acid is a water-soluble vitamin. FA gets its name from the Latin word folium meaning ‘leaf’, since it is found in many leafy plants. The best folate sources in the diet are leafy green vegetables, as well as animal liver and kidney. Mammalian cells are devoid of the enzymatic capacity for folate biosynthesis and thus are absolutely dependent on folate uptake from exogenous dietary sources. Thus, the intestine plays a central role in regulating body folate homeostasis; similarly, the kidneys play a pivotal role in regulating body folate homeostasis by reabsorbing the filtered vitamin, thus preventing its loss in urine [1–4]. The primary deposits of folate are liver and kidney [5, 6].

The term folates refer to the various tetrahydrofolate derivatives naturally found in food, whereas FA refers to the oxidized synthetic compound used in dietary supplements and fortified food.

According to its structure, FA belongs to conjugated pteridines, consisting of a pteridine ring, paraaminobenzoic acid and glutamic acid. It appears in monoglutamate or polyglutamate forms. Only the monoglutamate form may be absorbed in intestinal wall [5, 6].

It is well established that adequate folate intake from the consumption of folate-rich foods is essential for health [2, 3]. The FA coenzymes are specifically concerned with biochemical reactions involving the transfer and utilization of the single carbon (C₁) moiety, such as methyl-, methylene-, methenyl-, formyl or formimino-groups to various substrates in a variety of enzymatic reactions that are intimately related to the synthesis of DNA, RNA, proteins and phospholipids (lecithin and sphingomyelin) and for the metabolism of several amino acids, including methionine, histidine, serine, glycine, and for some neurotransmitter synthesis (acetylcholine, epinephrine, melatonin) (Figure 1) [2, 3, 5, 6].

Figure 1

Folate has many functions in the body [3 – modified]. Copyright [2013, Medical faculty].

Within cells (principally liver cells), FA is reduced to dihydrofolate (DHF or H₂-folate) and then to tetrahydrofolate (THF or H₄-5, 6, 7, 8- tetrahydrofolic acid), by the action of folate and dihydrofolate reductase (DHFR), respectively [4]. THF is the form of folate that can enter the main folate metabolic cycle [2, 3, 5–7].

By regulating cellular S-adenosylmethionine (SAM or AdoMet), folates affect the important reactions in intermediary metabolism. SAM acts as a methyl donor for the dozens of different methyltransferases present in all cells. AdoMet is also used for polyamine spermidine (Spd) and spermine (Sp) biosynthesis (Figure 2) [8–10] .

Figure 2

Folate and polyamines biosynthesis.

SAM is generated from methionine and ATP by MAT. dcSAM, decarbocylated SAM; MAT, methionine adenosyl transferase; MTases, methyltransferases; SAH, S-adenosylhomocysteine; SAM, S-adenosyl methionine; SAMDC, S-adenosyl methionine decarboxylase [8]. Copyright [2013, Medical faculty, Nis].

Dietary folate has a major impact on homocysteine (Hcy) levels, which may exert direct neurotoxic and pro-oxidative actions [11–13] with an inverse relationship between plasma folate and Hcy concentrations [14].

DNA methylation, catalyzed by DNA methyltransferases, is an important epigenetic determinant in gene expression, in the maintenance of DNA integrity and stability, in chromosomal modifications, and in the development of mutations, which can regulate tissue-specific expression of certain genes which is particularly important during embryogenesis [15–18]. The inheritance of information based on gene expression levels is known as epigenetics, as opposed to genetics, which refers to information transmitted on the basis of gene sequence [19–21]. DNA methyltransferases transfer methyl groups from SAM to cytosine and this regulates gene transcription. In humans, DNA methylation predominantly involves the covalent addition of a methyl group (CH₃) to the 59 position of cytosine that precedes a guanosine in the DNA sequence (the CpG dinucleotide). This is referred to as an epigenetic modification because it does not change the coding sequence of the DNA [22, 23].

Folate is one of many compounds of fruits and vegetables that could be acting as a cytoprotective agent. It has antioxidant properties, scavenging several reactive oxygen species in vitro and inhibiting lipid peroxidation. FA may decrease oxidative stress in human diseases, significantly lowering the levels of free radicals in liver, brain, and kidney, and increasing the content of SH-groups, the functional groups in glutathione (GSH), the important antioxidant [24–30].

The increased GSH production, due to the block of Hcy remethylation to methionine and potentiation of transulfuration pathway, influences epigenetic processes, including DNA and histone methylation by limiting the availability of SAM, the cofactor utilized during epigenetic control of gene expression by DNA and histone methyltransferases [21, 27, 29].

In our recent investigations in mothers receiving folate supplementation, the significant malondialdehyde (MDA) amount decrease was observed in colostrum and mature human milk [30]. Our results are in agreement with the literature data suggesting that pharmacological doses of folate supplementation lowers plasma Hcy and serum MDA levels, probably by increasing glutathione [24, 30].

FA is able to induce angiogenesis and vasculogenesis [24, 26, 31], in part via a nitric oxide (NO)-dependent mechanism [31].

The random acylation of amino groups in wild-type pancreatic ribonuclease (RNase A) with FA is shown to decrease its catalytic activity dramatically, presumably because of the alteration to a key active-site residue, Lys41 [32, 33]. The recent literature data represent that conjugation to FA is known to enhance the uptake of molecules by human cells that overproduce folate receptors.

Metabolic manifestations of folate deficiency

FA deficiency is considered to be one of the most common nutritional deficiencies. A deficiency of FA may be caused by: deficient food supply, increased needs in pregnant women and nursing mothers, defects in utilization (in alcoholics or individuals with liver disease), malabsorption folate losses in hemodialysis and cancer patients. Also, the reasons for folate deficiency may be impaired functions of the enzymes or cofactors needed for the generation of active FA. In the case of folate deficiency, all of the reactions in one-carbon metabolism will be compromised to varying degrees. Folate deficiency results in the reduction of purine and pyrimidine biosynthesis and, consequently, RNA and DNA biosynthesis and cell division; reduction in the biosynthesis of phospholipids (lecithin and sphingomyelin) and neurotransmitter synthesis by using SAM as the primary methyl group donor. Metabolism of several amino acids (including methionine, gliding, serine, and histidine) and initiation of protein synthesis in the mitochondria are disturbed in the state via folate-dependent deficiency reactions [8, 9, 12, 13]. The fact that folates have the principal places in the regulation of cellular SAM, leads to impairments of methyltransferase reactions in response to a folate deficiency [17, 18]. Folate depletion alters DNA methylation; causing DNA instability and chromosome damage [34–37].

Another abnormality of folates depletion leads to hyperhomocyst (e) inemia. However, homocysteinemia with homocystinuria is a rare inborn error of metabolism, resulting from deficiency of enzyme cistationin-β-synthase, which participates in transulfuration pathway of Hcy [38–41].

Mechanisms of DNA instability in folate deficiency

DNA methylation is one of the most intensively studied epigenetic modifications in mammals. In normal cells, the methylation of DNA assures the proper regulation of gene expression and stable gene silencing. DNA methylation is associated with histone modifications and the interplay of these epigenetic modifications is crucial to regulate the functioning of the genome by changing chromatin architecture [42–46].

DNA hypomethylation

Folate deficiency affects DNA stability principally by two ways: DNA hypomethylation and uracil misincorporation [15–20, 45]. DNA-methylation produces 5-methylcytosine, a modified base that is found mostly at CpG sites in the genome. 5-methylcytosine regulates gene transcription and interferes with the binding of transcription factors or other DNA-binding proteins to block transcription. Alterations in promoter regions and repetitive DNA sequences are associated also with the regulation of non-coding RNAs expression, such as microRNAs that may play role in tumor suppression [46–48].

The extent of methylation of specific genes varies from tissue to tissue and changes during development. Genome sequence analysis reveals that a large fraction of all genes is AdoMet dependent methyltransferases. Undermethylation favors gene expression, whereas increased methylation is associated with gene silencing [44–49].

Uracil misincorporation

The second pathway, uracil misincorporation into DNA, is the other way through which folate may alter DNA synthesis and stability. Normally (at physiological condition), folate, as 5′10-ethylene THF, donates a methyl group to uracil, converting it to thymine, which is used for DNA synthesis and repair. However, if folate is limiting, uracil misincorporation into DNA may occur leading to mutagenesis [15–20]. There is good evidence suggesting that excessive misincorporation of uracil into DNA not only leads to point mutations, but also results in single- and double-strand DNA breaks, chromosome breakage and micronucleus (MN) formation [43–46, 50, 51].

The sensitivity of human thymidylate synthesis to a folate deficiency was reported by Blount et al. [44] who observed the increased misincorporation of uracil into lymphocyte DNA, accompanied by an increased frequency of cellular micronuclei, a measure of DNA and chromosome damage [44]. Uracil misincorporation was markedly reduced by folate supplementation in folate-deficient subjects, which restored thymidylate synthesis [44, 47, 51]. As the cell attempts to repair itself, it breaks the DNA molecule to excise the uracil. If folate is continually limited, imbalances in deoxynucleotide triphosphates in the precursor pool occur. Uracil is misincorporated and repaired in what is termed ‘a catastrophic repair cycle’, which may lead to double-strand breaks, chromosomal damage and cancer [1–3]. Also, DNA hypomethylation potentially induces proto-oncogene expression, leading to cancer [43, 46, 47, 51].

Also, there is evidence that hypomethylation increases the susceptibility of DNA to nuclease attack, which can result in DNA strand breaks, thus disrupting DNA integrity. Hypomethylation and DNA strand breaks, resulting from folate deficiency, enhance the incorporation of tumorigenic viruses, such as human papilloma virus into human DNA [43, 46, 48].

Hyperhomocysteinemia in folate deficiency

Folates have the principal places in regulating cellular SAM [8–11, 52, 53]. The metabolic effect of folate deficiency is an elevation of blood Hcy, natural intermediate in the metabolism of SAM. The byproduct in the methylations, S-adenosylhomocysteine (SHcy), is located at a branch-point of metabolic pathways: either it is irreversibly degraded via the transsulphuration pathway to cysteine, a precursor of the synthesis of GSH, or it is recycled back to methionine via Hcy in the methyl cycle (Figure 1), also called the homocysteine-methionine cycle [38, 53, 54]. The homocysteine-methionine cycle is found in all tissues [39, 40]. The transsulfuration pathway of Hcy involves B₆-dependent enzymes, cystathionine-β-synthase and γ-cystathionase in cysteine and glutathione synthesis. Vitamin B₆ deficiency inhibits Hcy catabolism [55, 56].

The elevated plasma Hcy has been associated with significantly increased risk for cardiovascular, liver, kidney and neurological diseases. Hcy is an independent risk factor for pregnancy complications, birth defects, Down syndrome, cognitive impairment in the elderly, psychiatric disorders, neurodegenerative diseases and they may affect the development of some types of cancer [56–58].

Folate reduces levels of Hcy in the blood, and supports the physiologic functions of many body systems [58, 59]. Hyperhomocysteinemic individuals are characterized by raised plasma levels of asymmetric dimethylarginine (ADMA), a novel risk factor for teratogenesis. FA treatment reduces elevated plasma levels of ADMA in hyperhomocysteinemic subjects [60–62].

Another aspect of nutritional influences of folate-dependent action on one-carbon metabolism is pro-oxidative action with an inverse relationship between plasma folate and Hcy concentrations related to GSH synthesis, scavenging several reactive oxygen species in vitro and inhibiting lipid peroxidation. In folate deficiency, antioxidant properties are decreased. All of theses events are present due to decreased cysteine SH-groups content, the functional groups in GSH [63, 64].

Several studies suggest that Hcy may promote endothelial dysfunction [65–68]. Endothelium-dependent vasodilation possibly involves NO-related mechanisms [68]. A characteristic feature in patients with an inborn error of amino acid Hcy, homocysteinemia (homocystinuria), is premature vascular disease. About 50% of patients with homocysteinemia have thromboembolic events. High plasma Hcy levels are the risk factors for deep-vein thrombosis in the general population. The subjects with untreated homocystinuria are at greatly increased risk of atherothrombotic events. A characteristic feature in patients with homocysteinemia is premature vascular disease; about 50% of patients have thromboembolic events [65–68].

Elevated plasma total homocysteine (tHcy) and low folate levels are associated with reduced bone mass density (BMD) in women, but not in men. These findings suggest that tHcy may be a potential modifiable risk factor for osteoporosis in women. Hcy may play a role in the pathogenesis of osteoporotic fractures. In 2001, Khan et al. [69] showed in in vitro experiments that Hcy impairs cartilage calcification. THcy seems to be a predictor for hip fracture among elderly men and women [69–71].

Interactions between folates and vitamin B₁₂ (cobalamin)

FA works in concert with vitamin B₁₂ in one-carbon metabolism through methionine and folates cycles. FA has a long history of use in conjunction with vitamin B₁₂ for the treatment of macrocytic anemia. Recent research documents the critical nature of two nutrients, vitamin B₁₂ and folate, in brain health and the maintenance of cognitive function, including memory [72–76]. Both vitamin B₁₂ and folate deficiencies can cause peripheral neuropathy, memory loss, depression, personality changes, as well as psychosis. If not treated, mental and neurological changes can become permanent [77–79].

The principal mechanism whereby folate and cobalamin metabolism influences physiological function in human body is through the action of methionine synthase (MS) in methylation cycle [79–83] (Figure 1). MS activity is important for maintaining adequate levels of methionine and for preventing accumulation of Hcy. The mammalian forms of MS require cobalamin as a prosthetic factor in the form methylcobalamin (MeCbl) (Figure 1) [79–83]. The co-dependence of MS on folate and vitamin B₁₂ provides a biochemical explanation why a single deficiency of either vitamin leads to the similar abnormalities [54, 84, 85]. Folates participation in the prevention the impairment of DNA synthesis is compromised when vitamin B₁₂ concentration is low because MS activity is reduced [86].

Since MS is the only enzyme in mammalian cells that uses 5-methyltetrahydrofolate (5-CH₃THF), its deficient activity also results in the trapping of cellular folate as 5-CH₃THF, which becomes unavailable for other folate-dependent reactions involved in purine and pyrimidine biosynthesis, neurotransmitter and other single carbon transfer reactions [79, 86]. The polyamines spermine and spermidine are feedback regulators of MS both in vivo and in vitro [87].

Folates and polyamines

The naturally occurring polyamines (spermine, spermidine and putrescine), are found ubiquitously in mammalian systems.

Polyamines are involved in many different biological processes, such as regulation of gene expression and cell growth and differentiation, regulation of transcription, proliferation of both normal and transformed cells, ion channel regulation, and protein phosphorylation [88–102].

The principal precursor of spermidine and spermine is methionine (Figures 1 and 2). Folate has profound function for polyamine biosynthesis, altogether with vitamin B₁₂ and vitamin B₆, participating in methionine metabolism [90–93, 103].

In the cells, polyamines, as polycations, interact electrostatically with negatively charged moieties, such as DNA, RNA, phospholipids, mucopolysacharides and proteins. Binding to DNA, polyamines play a significant role in stabilizing DNA, especially chromatin structure, during the cell cycle [89, 94–97].

In normal cells, polyamine levels are controlled by biosynthetic and catabolic enzymes (Figure 3) [99–102]. The biosynthetic enzymes are L-ornithine decarboxylase (ODC), S-adenosylmethionine decarboxylase (AdoMetDC), as well as aminopropyl transferase – spermidine- (Spd synthase) and spermine synthase (Sp synthase). SAMDC or AdoMetDC is responsible for decarboxylation of SAM [104]. Spd- and Sp synthase use decarboxylated SAM (dcSAM) as an aminopropyl donor, but are specific in respect to their acceptors, putrescine and spermidine, respectively [99–102]. The byproduct formed during the transfer of aminopropyl group to putrescine or spermidine is 5′-methylthioadenosine (5′-MTA). This nucleoside is rapidly converted back to methionine through the methylthioadenosine cycle, also called the methionine salvage pathway [8–11, 103, 105]. Both of decarboxylases, ODC and AdoMetDC, use active form of vitamin B_6, pyridoxal phosphate-B₆P.

The catabolic pathway of spermine and spermidine is a two-step process involving, in the first reaction, spermidine/spermine N′-acetyltransferase (SSAT), and in the second reaction, polyamine oxidase (PAO) (Figure 3) [106–108]. Acetylated polyamines are generally the preferred substrates of polyamine oxidase (APAO), a flavin containing amine oxidase, a peroxisomal enzyme present in all vertebrate tissues [109]. PAO may also use non-acetylated spermine and spermidine [110, 111].

Figure 3

Role of folate through SAM in polyamine metabolism.

AdoMetDC, S-adenosylmethionine decarboxylase; APAO, acetylpolyamine oxidase: MAT, methionine adenosyltransferase; MTA, methylthioadenosine; ODC, L-ornithine decarboxylase; SAM, S-adenosyl methionine; SMO, spermine oxidase [106 – modified].

Polyamine biosynthesis is up-regulated in actively growing cells, including cancer cells [112–117]. Therefore, polyamine concentration, as well as gene expression and activity of enzymes involved in polyamine biosynthesis, especially ornithine decarboxylase (ODC), are higher in cancer tissues than in normal surrounding tissues. Recent investigations revealed that increased polyamine availability enhances the capability of cancer cells to invade and metastasize to new tissues [118]. Polyamine depletion has been shown to inhibit cell proliferation and migration, whereas over-accumulation of polyamines induces apoptosis and cell transformation [111].

The polyamine-biosynthetic pathway represents an inviting target for the agents, inhibiting carcinogenesis and tumor growth [113].

The administration of FA to hepatectomized animals (30%) resulted in diminution of PAO activity in regenerating rat liver tissue after hepatectomy [119]. The supplementation of experimental animals with vitamin B₁₂ alone or together with FA increased Spd and Sp levels in rat liver. At the same time, the supplementation of experimental animals with vitamin B₁₂ together with FA caused the decreasing of PAO activity. Our experimental results indicated the importance of FA and cobalamin in polyamine metabolism [120].

The spermidine N′-acetyltransferase was induced in the kidney after treatment with FA [121, 122]. 5-FU, the thymidylate synthase (TS) inhibitor, affected polyamine metabolism in colon carcinoma cells through the induction of the key catabolic enzyme SSAT [121, 122].

Folates and cancerogeneses

Many studies have shown that a diet high in folate (from fruits and leafy green vegetables) is associated with lower risks of many types of cancer [1–3, 123]. Some study point out that FA might prevent some cancers and might promote other neoplasias [123–125]. It has been hypothesized that early exposure to FA might prevent tumors through the provision of enough methyl groups to maintain proper methylation patterns and repair of DNA. In contrast, after the development of tumors, higher intake of FA might promote growth of existing tumors [126]. The timing of folate administration during cancer progression can modify outcomes. Folate administration prior to the existence of preneoplastic lesions can prevent tumor development, whereas provision of folate once early lesions are established appears to increase tumorigenesis [125, 126]. However, the presence of unmetabolized FA in blood is associated with decreased natural killer cytotoxicity. Since natural killer cells play a role in tumor cell destruction, this would suggest another way in which excess FA might promote existing premalignant and malignant lesions [126].

There are currently insufficient data to justify such an assessment and current evidence do not show an association between high FA intake and cancer risk, but neither do they confidently exclude [126, 127].

Folic acid antagonists – antifolates

In neoplastic cells, where DNA replication and cell division occur at an accelerated rate, the interruption of folate metabolism causes ineffective DNA synthesis, resulting in inhibition of tumor growth. Indeed, this has been the basis for cancer chemotherapy, using antifolate agents methotrexate (MTX) and 5-FU [123]. The antifolate agents are one group of antimetabolites and structural analogues of normal biochemical compounds. As competitive inhibitors, they compete with the naturally substrate for the active site of an enzyme and block the formation of undesirable metabolic products in the body [128]. Antifolates exert their action by disturbing the nucleic acid metabolism of cancer cells, including its synthesis, methylation and stability [129, 130].

Enzyme DHFR catalyzes tetrahydrofolate regeneration by the reduction of dihydrofolate, using NADPH as a cofactor. DHFR inhibition causes disruption of purine and thymidylate biosynthesis and DNA replication, leading to cell death. Therefore, DHFR has been an attractive target for chemotherapy of many diseases, including cancer [131–134].

The FA antagonists, MTX and aminopterin, close structural analogs of FA, as antitumor agents have found clinical application in the treatment of malignant diseases, especially in the treatment of leukemia in childhood [135]. These antifolates are extremely potent competitive inhibitors of DHFR and TS and, because of that, inhibit the synthesis of RNA and DNA [135].

MTX, a classical antifolate, is one of the most widely used and studied anti-cancer agents [128], including acute lymphoblastic leukemia, lymphoma, osteosarcoma, breast cancer, and head and neck cancer [128]. MTX is a potent and selective inhibitor of DFHR, which results in inhibition of DNA synthesis [132], due to thymidine starvation. Also, MTX is an indirect inhibitor of enzyme MS [132]. It might also induce depletion of intracellular-reduced folate coenzymes, reducing their transport through the folate receptor (FRα) and/or competing with folates for the reduced folate carrier (RFC) [136]. DHFR binds MTX about 100 times better than dihydrofolate. The development of drug resistance to MTX appears in the prolonged chemotherapy. Tumor cells that acquired MTX resistance have been found to have an increased number of DNA gene copies, encoding enzyme DHFR. The amplified DHFR genes in MTX-resistance cells produce a markedly increased number of DHFR copies, exceeding the amount of MTX, which can be delivered to cell, and thereby allow tumor cell DNA synthesis and tumor regrowth occurs [136].

The application of MTX disturbs the metabolism of polyamines in rapidly growing tissues. Inhibition of PAO, induced by MTX, in regenerating rat liver tissue, is probably the consequence of the inhibition of nucleic acids and protein synthesis [137, 138]. More than 90% of MTX, a classical antifolate, is cleared by the kidneys. So, MTX can be safely administered to patients with normal renal function. MTX-induced renal dysfunction leads to delayed drug elimination [132–134].

The enzyme, TS is considered an important target for the development of new anticancer agents. MTX and 5-FU were amongst the earliest anti-cancer drugs developed and both partly act through inhibition of TS [133, 134]. Among novel antifolates is pemetrexed which primarily targets TS as well as pralatrexate which blocks DHFR, and displays enhanced transport and cellular retention properties [135, 138].

Many human cancer cells lines and primary tumors have an absolute need for methionine. Disruption of the cell folate cycle by new generation antifolate drugs exert their action disturbing the nucleic acid metabolism of cancer cells, including its synthesis, methylation and stability. Melanoma cells are highly dependent on methionine and have the high activity of the methionine cycle, which permits the methylation of specific genes and activation of different survival pathways. Blockage of the methionine cycle by the new antifolate, [3-O-(3, 4, 5- trimethoxybenzoyl)-(-)-epicatechin, TMECG], tea catechin, is an effective therapy for melanoma [139, 140].

The specific activity of TMECG on melanoma methionine cycle was confirmed, not only in melanoma cells in culture, but it was also effective in an animal model, where it inhibited growth and metastasis of preformed tumors. This compound was successfully synthesized from the commercially available catechin. TMECG binds efficiently to human DHFR and down-regulates folate cycle gene expression in melanoma cells. Disruption of the folate cycle by TMECG is a plausible explanation for its observed biological effects and suggests that, like other antifolate compounds, TMECG could be of clinical value in cancer therapy [140].

Clinical manifestation of folates deficiency

The impaired folate-dependent intracellular metabolism can lead to several key pathologies, including megaloblastic anemia, homocysteinemia, cardiovascular disease, embryonic defects, in particular neural tube defects (NTDs), congenital heart defects, and possibly, cancer [59].

Megaloblastic anemia

Folates are vitamins essential to the development of the hematopoesis [1–5]. Consequently, the reduction of erythrocytes maturation developed in folate deficiency, causes the appearance of megaloblastic anemia [135, 138, 141].

Megaloblastic anemia is macrocytic anemia due to folate and cobalamin (vitamin B₁₂) deficiency [142]. Megaloblasts are large, abnormal, nucleated cells that are precursors of erythrocytes; in a folate deficiency, they accumulate and are found in the bone marrow (Figure 4). These cells arise as a result of a failure of the red cell precursors to divide normally due to impaired DNA synthesis during the process of hematopoesis and the production of erythrocytes. There are also decreased numbers of white cells and platelets [142, 143]. FA supplementation prevents this type of anemia.

Figure 4

Peripheral bloods smear from a patient with megaloblastic anemia.

Notice that the RBCs are large (macrocytic anemia) and oval shaped, and the poly is hypersegmented serious organ failure can occur in individuals with megaloblastosis [135].

Neural tube defects (NTDs)

Experimental studies, epidemiological data and clinical trials showed the necessity of sufficient quantities of FA (at the time of conception and early pregnancy) for normal embryogenesis and fetal development for the prevention of neural tube defects and other neurological malformations [59, 144]. Alterations in DNA methylation result in changes of gene expression and can have important consequences for embryogenesis [14, 15, 145, 146]. Folate metabolism must adapt during pregnancy to multiple fetal and maternal physiologic influences that change throughout gestation. Increasing folate intake, leading to increased concentrations of folate coenzymes in tissues, may overcome an unidentified metabolic defect in the production of proteins and/or DNA or regulation of gene expression at the time of neural tube development and closure [135, 146, 147]. The literature data have established that low or inadequate folate status may contribute to congenital malformations (spina bifida and anencephaly), important factors of fetal and infant mortality [148].

FA prevents neural tube defects in newborns, so women of childbearing age must be sure to have an adequate intake prior to and during pregnancy. All women of child-bearing age should consume 0.4 mg per day of FA. Also, women, wanting to become pregnant, must take supplements daily before and until the 12th week of pregnancy. The research has shown that a daily supplement of recommended dose reduces the chance of NTDs [147–149].

Metabolic effects of folate on physiological functions of cardiovascular system, liver and kidney

Folates and cardiovascular system

Folate deficiency is an independent risk factor for atherosclerotic vascular disease in the coronary, cerebral, and peripheral vessels and for arterial and venous thromboembolism [150]. Plasma concentrations of folate were positively associated with the risk of myocardial infarction. FA ability to lower Hcy suggests it might have a positive influence on cardiovascular disease [38, 54, 58, 151, 152]. Also, the potential mechanisms by which FA reduces the risk of cardiovascular diseases include antioxidant actions, or direct interactions with endothelial NO synthase [152]. Folates interact with the endothelial enzyme NO synthase (eNOS) and exert effects on the cofactor bioavailability and, thus, on peroxynitrite formation. Hyperhomocysteinemic individuals are characterized by raised plasma levels of ADMA, an endogenous NO synthase inhibitor, a novel marker of risk for endothelial dysfunction in a variety of cardiovascular diseases [60–62, 153].

Studies are now in progress to establish whether supplementation with FA will reduce cardiovascular risk [38]. ‘Homocysteine Theory’ stated that Hcy, is toxic for the vascular wall. In the years to follow, it became clear from both retrospective and prospective studies that also mildly elevated total Hcy levels are independently associated with an increased risk for vascular diseases [59, 65, 67, 151–153].

The place of folates in liver metabolism

Liver tissue serves as storage for FA. Folates play essential functions in hepatocytes metabolism [9, 53]. The liver has the central role of methionine metabolism. Under normal conditions, up to 85% of all methylation reactions and as much as 48% of methionine metabolism occur in the liver, which indicates the crucial importance of this organ in the regulation of blood methionine [154].

Folates, by regulating cellular SAM, are a control switch that regulates essential hepatic functions such as regeneration, differentiation, and the sensitivity of this organ to injury. In folate deficiency, all forms of folate are reduced within cells, impairing the growth and maturation of hepatocytes. In normal liver, the majority of SAM is used in methylation reactions, since the SAM decarboxylation pathway, followed by aminopropylation (the pathway needed for spermidine and spermine biosynthesis) requires <10% of the available SAM. In hepatocytes, SAM levels are related to hepatocytes function. Patients with liver cirrhosis have decreased hepatic GSH levels [155, 156]. Intracellular ROS (superoxide, hydrogen peroxide, the hydroxyl radical and the peroxynitrite), due to their high metabolic activity, are generated continuously in cells during folates depletion. SAMs protective actions in the liver include increased GSH levels and antioxidative properties of folates [155–158].

Lower synthesis of AdoMet, due to folate deficiency, might contribute to hepatocyte dedifferentiation with consequent increases in regeneration and malignant transformation. Reduced tissue AdoMet may facilitate the synthesis and release of tumor necrosis factor and other cytokines [9, 53, 154–160].

Folates and kidneys

The kidneys play a pivotal role in regulating body folate homeostasis by reabsorbing the filtered vitamin, thus preventing its losses in the urine [161]. Administration of pharmacological amounts of FA to rats results in renal cell injury and subsequent hypertrophy and hyperplasia [162]. FA induces dose-dependent nephrotoxicity in mice and rats, with the rapid appearance of FA crystals within renal tubules and subsequent acute tubular necrosis, followed by epithelial regeneration [163].

In rats, single intravenous doses of FA induce damage to renal tubular epithelium, deposition of FA in tubular lumen, increase in wet kidney weight, oliguria and interstitial connective tissue proliferation [164, 165]. There is a predictable relationship between the dosage of FA and the abnormalities of morphologic features and function in kidney injury [164]. FA-induced nephropathy is associated with increased Angiopoietin-1 (Ang-1) protein expression in renal epithelia and arteries. Ang-1 overexpression in vivo produces large, numerous, highly branched vessels [165].

In patients with renal failure, hyperhomocysteinemia is a common feature. Hcy has been implicated as a pathogenetic factor in the development of arterial disease in a number of in vitro and experimental animal studies that have demonstrated an association between hyperhomocysteinemia and endothelial cell damage [166]. The proposed underlying pathophysiological mechanisms for this phenomenon include reduced renal elimination of Hcy and impaired non-renal disposal, possibly because of inhibition of crucial enzymes in the methionine-homocysteine metabolism by the uremic milieu [167]. Hyperhomocysteinemia is a common finding in dialysis-dependent end-stage renal disease patients [168].

Folates, brain and the peripheral nervous system

Folates are essential to the development of the nervous system, playing important roles regulating neurogenesis. Folates are present in relatively high concentrations within the brain. Cerebrospinal fluid level is about three times of that in the blood. FA is poorly transported to the brain and rapidly cleared from the central nervous system [73–77, 81, 169, 170].

The incidence of FA deficiency is high in patients with various psychiatric disorders, including depression, dementia and schizophrenia [171, 172]. In epileptics on anticonvulsants, folate deficiency often occurs because anticonvulsants inhibit folate absorption. In these patients folate deficiency is often associated with psychiatric symptoms. These findings underscore the importance of folate metabolism in neuronal homeostasis [170]. Folate is involved in the synthesis of acetylcholine, norepinephrine, melatonin, histamine, through SAM methylation pathways. Folate deficiency has a greater effect on choline and acetylcholine metabolism in the peripheral nervous system than in the brain and this effect escalates with age [173].

Folate deficiency could have diverse effects on the neurochemistry of schizophrenia, as folate functions as a single carbon donor in the synthesis of glycine from serine (Figure 5) [171–179].

Figure 5

Folate functions as a single carbon donor in the synthesis of glycine from serine in folate cycle.

B6, pyridoxal‘5-phosphate; B12, cobalamin; BHMT, betaine homocysteine methyltransferase; CBS, cystathione βsynthase; MTHFR, 5, 10-methylene-THF reductase; N5-methyl-THF, N5-methyltetrafolate; SAM, S-adenosylmethionine; THF, tetrahydrofolate [179 – modified].

FA functions primarily as a methyl-group donor required for many methylation reactions. Reduction in the methylation cycle has multiple effects on nerve cells, since the interruption of the methylation cycle causes neuropathy.

Disturbance of the methylation cycle can also happen in vitamin B₁₂ deficiency due to reduced activity MS, the vitamin B₁₂-dependent enzyme. In this deficiency, blockage of the methylation cycle causes the folate cofactors in the cell to become trapped as 5-methyltetrahydrofolate; this process produces a pseudo folate deficiency in such cells, preventing cell division and giving rise to an anemia identical to that seen in folate deficiency [63, 73, 75, 77, 171, 172, 174, 175]. There is a risk that if FA is given to people who have undiagnosed deficiency of vitamin B₁₂ because it may lead to neurological damage. Vitamin B₁₂ deficiency produces both an anemia identical to that of folate deficiency, but also causes irreversible damage to the central and peripheral nervous systems [175, 176].

The neurotoxin effects of high blood levels of Hcy may also play a role in the neurological and psychiatric disturbances that are associated with folate and vitamin B₁₂ deficiency [180–182]. High blood levels of Hcy is an independent risk factor for central and peripheral nervous system diseases, including stroke, several neurodegenerative conditions, Alzheimer‘s disease and Parkinson‘s disease, as well as to cognitive decline and schizophrenia [73–78, 175, 176–179].

Folate deprivation, which leads to homocysteinemia, decreased the reduced form of GSH, indicating a depletion of oxidative buffering capacity, the reason for neurodegeneration [23–26, 63, 64, 181, 182].

Many children on the autism-spectrum are manifesting symptoms due to deficiencies in folate in the brain. This is important because folate is critical for the proper brain function and the deficiencies have been associated with learning, language, and cognitive imbalances, as well as propensity for seizures. Imbalances in methylation lead to cognitive problems, attention, focusing, language and social interaction issues. Both folate supplements and methyl-B₁₂ therapy work hand in hand to improve brain function in autism [181, 182].

Folates and reproductive functions

There is increasing evidence that nutritional factors are important in reproduction and thus in spermatogenesis, as well [183–185]. Folates are necessary for normal fertility in men and women, as it is important during cell division and growth periods, such as infancy and pregnancy. In males, folate is necessary for spermatogenesis [20, 185]. Low folate in seminal plasma is associated with increased sperm DNA damage [183–185]. Given those epigenetic signals, such as DNA methylation and histone modifications are crucial for the proper functioning of the genome. Phenotypic differences in sperm production (quantitative as well as qualitative traits) at both inter- and intra-individual levels may also be due to an epigenetic variation. The authors reported significant variations for six genes at both intra- and inter-individual levels, concluding that epigenetic variations may contribute to the variable semen phenotype. There are indications that both FA and cobalamin supplementation may increase fertility [50, 72, 76, 186–188].

Folates have the principal places in affection of gene expression by regulating cellular SAM. Within the folate pathway, methylenetetrahydrofolate reductase (MTHFR) reduces 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate (5-CH₃THF), a methyl donor for remethylation of Hcy to methionine, the precursor of SAM (Figure 5). In adult male mice, MTHFR levels are highest in the testis. These findings, in conjunction with recent clinical evidence, suggest an important role of MTHFR in spermatogenesis [189, 190].

Severe MTHFR deficiency in male mice results in abnormal spermatogenesis and infertility. Deprivation of folates disturbs the Hcy pathway, involved in human subfertility [186–188].

In the recent years, there is an increased interest in the role of antioxidant properties of folates and other antioxidants – α-tocopherol (vitamin E), ascorbic acid (vitamin C) and the retinoid (vitamin A), as modulators of fertility outcome. Oxidative stress is associated with sperm quality and infertility. Abnormalities in the male genome characterized by damaged sperm DNA may be indicative of male subfertility regardless of normal routine semen parameters. Folate has antioxidant properties, scavenging several reactive oxygen species and inhibiting lipid peroxidation by increasing the content of SH-groups, the functional groups in glutathione [188, 191].

Folate deficiency states produce an elevated Hcy concentration and impair the remethylation cycle of Hcy, disturbing the biosynthesis of phospholipids, proteins, DNA and RNA. These processes are essential in spermatogenesis. Wang and Fenech [189] have established that total normal sperm count increases after combined zinc sulfate and FA treatment in both subfertile and fertile men [191, 192]. Low folate concentration in seminal plasma is associated with more sperm DNA damage in fertile men and is detrimental for sperm DNA stability. DNA methylation is important for proper spermatogenesis and male fertility. There are indications that both FA and cobalamin supplementation may increase fertility [186–188].

Deleterious effects of folate supplementation and food fortification on human health

Folate is critical for nucleotide synthesis and methylation reactions and has been associated with a number of health benefits [1–3, 123–127, 193–195]. In doses typically administered for therapeutic purposes, FA is considered non-toxic. There is an accumulation of many good data about the positive effects ranging from the established reduction of neural tube defects, cardiovascular disease and, possibly, dementia, Alzheimer disease and certain types of cancer. It seems to be a ‘wonder drug’ that is not only inexpensive, but also safe for use as a chemopreventive agent [123–127, 195–197]. FA and folates may act as effective antioxidants in vivo. Their activities may become important in view of nutritional supplementation and fortification of food with FA [23, 198].

When fortification is introduced, several hundred thousand people were exposed to an increased intake of FA [148, 149]. The intake of FA from fortified food (100–200 µg/d) together with the use of nutritional supplements, multivitamin preparation, lead to body state of folate oversupplementation. This practice of chronic intake of high doses of FA may lead to the adverse toxic effects of FA [198–200]. Today there is a little knowledge about the potential safety and physiologic consequences of chronic intake of such high doses of FA. At the present, a few reports, however, have raised questions about the safety and physiologic consequences of chronic intake of such high doses of FA [19–21, 123–127, 198–201].

One of the major risks associated with excessive intake of FA is the development of cancer [28, 34, 198]. However, recent human studies have suggested that overdoses of FA (people supplementation and food fortification) may promote the progression of already existing, undiagnosed, preneoplastic and neoplastic lesions [133, 134, 136–138]. However, clinical investigation suggests a decreased colorectal cancer risk in subjects with low folate status [137, 138]. It was concluded that there currently were insufficient data to support the concerns that FA fortification promoted cancer. This possibility of a detrimental component to the role of folate in carcinogenesis could have implications in the ongoing debate in food science, concerning mandatory folate fortification of foods [193–199].

Consumption of FA in excess of 400 μg per day among older adults resulted in significantly faster rate of cognitive decline than supplement non-users. The studies suggest that high FA intake could cause serious cognitive consequences in the elderly as vitamin B₁₂ deficiency [85, 200, 201].

Conclusion

Periconception maternal intake of FA reduces the risk of neural tube defects and, possibly, other birth defects. Therefore, FA supplementation periconceptionally has been recommended to women since the early 1990s. In several countries food fortification with FA has been implemented in order to increase the average serum folate concentration. Until now, most attention has been paid to the beneficial effects of folate and the detrimental effects of tHcy. Fortification of cereal grain flour products with FA, and oversupplementation, may disturb the physiological function of many organs like the brain, cardiovascular system, liver, kidney and for human reproduction as well. Excessive intake of FA is the reason for the development of cancers. In line with this, there is an ongoing discussion about possible adverse effects of excessive folate. The food safety agencies in a number of countries, considering mandatory FA fortification, have reconsidered both beneficial and adverse effects of FAs.

Folate plays a central role in the reaction of methylation and regulation of concentration of SAM. This activity is compromised in folate deficiency. As a result, polyamine, spermidine and spermine biosynthesis is deprived. In the opposed direction, in a situation of high amount of FA, biosynthesis of polyamines increases which may explain the mutagenic activity in oversupplementation of FA. There is a need for better investigations of the relationships between the high presence of FA in human tissues and the amounts of polyamines related to malignant processes in human body.

Also, antifolates (FA antagonists) are widely used in therapy of malignant diseases. Interruption of folate metabolism causes ineffective DNA synthesis, resulting in inhibition of tumor growth.

On the basis of our knowledge about metabolic functions of folate, it may be concluded that FA supplementation is unwonted, except for recommended doses for women periconceptionally and during pregnancy, as well as the recommended doses for some diseases. Also, in health, it is the best to supply these needs by fresh vegetables and fruit dietary intake.

Future directions

Today, it is very important to evaluate the beneficial effects of different levels of FA administration on the human health or in human diseases. Having in mind the importance of folates in the control of intermediary metabolism and the significance for normal human physiology, we suggest that, for maintaining homeostasis in metabolic reactions, the cells need an adequate amount of this vitamin. If there is deprivation or oversupplementation of FA in the regulatory network, defects appear. However, a large knowledge gap remains in understanding its mechanisms and why abnormally very high folate levels may be detrimental for physiological function of many organs like the brain, liver, and kidney and for human reproduction and the cardiovascular system as well.

For future studies, considering the relation of polyamines and rapidly proliferating tissues (especially cancers), there is a need for better investigations of the relationships between high presence of FA and polyamine metabolism related to malignant processes in the human body. There are many questions in folate biochemistry which remain to be resolved.

Corresponding author: Gordana Bjelakovic, Institute of Biochemistry, Faculty of Medicine, University of Nis, Boulevard dr Zorana Djindjica 81, 18000 Nis, Serbia, E-mail: bjelakovic@junis.ni.ac.rs

References

1. Steinberg ES. Mechanisms of folate homeostasis. Am J Physiol 1984;246:G319–24.10.1152/ajpgi.1984.246.4.G319Search in Google Scholar PubMed

2. Wagner C. Biochemical role of folate in cellular metabolism. In: Folate in health and disease. Bailey LB, editor. Marcel Dekker: New York, NY, USA, 1995:23–42.Search in Google Scholar

3. Troen AM, Lutgens E, Smith DE, Rosenberg IH, Selhub J.The atherogenic effect of excess methionine intake. PNAS 2003;100:15089–94.10.1073/pnas.2436385100Search in Google Scholar PubMed PubMed Central

4. Ashokkumar B, Mohammed ZM, Vaziri ND, Said HM. Effect of folate oversupplementation on folate uptake by human intestinal and renal epithelial cells. Am J Clin Nutr 2007;86:159–66. Erratum in: Am J Clin Nutr 2007;91:159.Search in Google Scholar

5. Lehninger A, Nelson D, Cox M. Principles of biochemistry. Worth Publishers: New York, 1993.Search in Google Scholar

6. King WM. Vitamins and minerals. In: King’s the medical biochemistry page. King WM, editor, 2013.Search in Google Scholar

7. Anderson DD, Woeller CF, Chiang EP, Shane B, Stover PJ. Serine hydroxymethyltransferase anchors de novo thymidylate synthesis pathway to nuclear lamina for DNA synthesis. J Biol Chem 2012;287:7051–62.10.1074/jbc.M111.333120Search in Google Scholar PubMed PubMed Central

8. Loenen WA. S-Adenosylmethionine: jack of all trades and master of everything? Biochem Soc Trans 2006;34:330–3.10.1042/BST0340330Search in Google Scholar

9. Mato JM, Corrales FJ, Lu SC, Avila MA. S-Adenosylmethionine: a control switch that regulates liver function. FASEB J 2002;16: 15–26.10.1096/fj.01-0401revSearch in Google Scholar PubMed

10. Bistulfi G, Diegelman P, Foster BA, Kramer DL, Porter CW, Smiraglia DJ. Polyamine biosynthesis impacts cellular folate requirements necessary to maintain S-adenosylmethionine and nucleotide pools. FASEB J 2009;23:2888–97.10.1096/fj.09-130708Search in Google Scholar PubMed PubMed Central

11. Grillo MA, Colombatto S. S-adenosylmethionine and its products. Amino Acids 2008;34:187–93.10.1007/s00726-007-0500-9Search in Google Scholar PubMed

12. Finkelstein JD. Homocysteine: a history in progress. Nutr Rev 2000;58:193–204.10.1111/j.1753-4887.2000.tb01862.xSearch in Google Scholar PubMed

13. Williams KT, Schalinske KL. New insights into the regulation of methyl group and homocysteine metabolism. J Nutr 2007;137:311–4.10.1093/jn/137.2.311Search in Google Scholar PubMed

14. Duthie SJ. Folic acid and DNA stability. Br Med Bull 1999;55: 578–92.10.1258/0007142991902646Search in Google Scholar PubMed

15. Ly A, Hoyt L, Crowell J, Kim YI. Folate and DNA methylation. Antioxid Redox Signal 2012;17:302–26.10.1089/ars.2012.4554Search in Google Scholar

16. Niculescu MD, Zeisel SH. Diet, methyl donors and DNA methylation: interactions between dietary folate, methionine and choline. J Nutr 2002;132:2333S–5S.10.1093/jn/132.8.2333SSearch in Google Scholar

17. Duthie SJ, Narayanan S, Brand GM, Pirie L, Grant G. Impact of folate deficiency on DNA stability. J Nutr 2002;132:2444S–9S.10.1093/jn/132.8.2444SSearch in Google Scholar

18. Pogribny IP, Tryndyak VP, Muskhelishvili L, Rusyn I, Ross SA. Methyl deficiency, alterations in global histone modifications, and carcinogenesis. J Nutr 2007;137:216S–22S.10.1093/jn/137.1.216SSearch in Google Scholar

19. Bistulfi G, Vandette E, Matsui S, Smiraglia DJ. Mild folate deficiency induces genetic and epigenetic instability and phenotype changes in prostate cancer cells. BMC Biol 2010; 8:1–12.10.1186/1741-7007-8-6Search in Google Scholar

20. Hong J, Khurana GK. Genetic and epigenetic influence on the response to environmental particulate matter. J Allergy Clin Immunol 2012;129:33–41.10.1016/j.jaci.2011.11.008Search in Google Scholar

21. Kim Y-I. Role of folate in colon cancer development and progression. J Nutr 2003;133:3731S–9S.10.1093/jn/133.11.3731SSearch in Google Scholar

22. Davis CD, Uthus EO. DNA methylation, cancer susceptibility, and nutrient interactions. Exp Biol Med 2004;229: 988–95.10.1177/153537020422901002Search in Google Scholar

23. Joshi R, Adhikari S, Patro BS, Chattopadhyay S, Mukherjee T. Free radical scavenging behavior of folic acid: evidence for possible antioxidant activity. Free Radic Biol Med 2001;30:1390–9.10.1016/S0891-5849(01)00543-3Search in Google Scholar

24. Gliszczynska-Swiglo A. Folates as antioxidants. Food Chem 2007;101:1480–3.10.1016/j.foodchem.2006.04.022Search in Google Scholar

25. Aghamohammadi V, Gargari BP, Aliasgharzadeh A. Effect of folic acid supplementation on homocysteine, serum total antioxidant capacity and malondialdehyde in patients with type 2 diabetes mellitus. J Am Coll Nutr 2011;30:210–5.10.1080/07315724.2011.10719962Search in Google Scholar

26. Hitchler MJ, Domann FE. An epigenetic perspective on the free radical theory of development. Free Radic Biol Med 2007;43:1023–36.10.1016/j.freeradbiomed.2007.06.027Search in Google Scholar

27. El-Demerdash FM, Yousef MI, Elaswad FA. Biochemical study on the protective role of folic acid in rabbits treated with chromium (VI). J Environ Sci Health Part B 2006;41:731–42.10.1080/03601230600704282Search in Google Scholar

28. Kim YI. Nutritional epigenetics: impact of folate deficiency on DNA methylation and colon cancer susceptibility. J Nutr 2005;135:2703–9.10.1093/jn/135.11.2703Search in Google Scholar

29. Bjelakovic LJ, Kocic G, Stojanovic I, Jevtovic-Stoimenov T, Najman S, Sokolovic D, et al. Folic acid effect on arginase activity in human colostrum and mature milk. Pteridines 2012;23:33–8.10.1515/pteridines.2012.23.1.33Search in Google Scholar

30. Sasaki K, Duan J, Murohara T, Ikeda H, Shintani S, Shimada T, et al. Rescue of hypercholesterolemia-related impairment of angiogenesis by oral folate supplementation. J Am Coll Cardiol 2003;42:364–72.10.1016/S0735-1097(03)00629-6Search in Google Scholar

31. Smith BD, Higgin JJ, Raines RT. Site-specific folate conjugation to a cytotoxic protein. Bioorg Med Chem Lett 2011;21: 5029–32.10.1016/j.bmcl.2011.04.081Search in Google Scholar

32. Gaur D, Swaminathan S, Batra JK. Interaction of human pancreatic ribonuclease with human ribonuclease inhibitor. Generation of inhibitor-resistant cytotoxic variants. J Biol Chem 2001;276:24978–84.10.1074/jbc.M102440200Search in Google Scholar

33. Blount BC, Ames BN. DNA damage in folate deficiency. Baillieres Clin Haematol 1995;8:461–78.10.1016/S0950-3536(05)80216-1Search in Google Scholar

34. Kim YI, Pogribny IP, Basnakian AG, Miller JW, Selhub J, James SJ, et al. Folate deficiency in rats induces DNA strand breaks and hypomethylation within the p53 tumor suppressor gene. Am J Clin Nutr 1997;65:46–52.10.1093/ajcn/65.1.46Search in Google Scholar PubMed

35. Kulis M, Esteller M. DNA methylation and cancer. Adv Genet 2010;70:27–56.10.1016/B978-0-12-380866-0.60002-2Search in Google Scholar

36. Milner JA, McDonald SS, Anderson DE, Greenwald P. Molecular targets for nutrients involved with cancer prevention. Nutr Cancer 2001;41:1–16.10.1207/S15327914NC41-1&2_1Search in Google Scholar

37. Meleady RA, Mulcahy DA, Graham IM. Genes, greens, and homocysteine. Hear 1996;76:103–4.10.1136/hrt.76.2.103Search in Google Scholar

38. Refsum H, Smith AD, Ueland PM, Nexo E, Clarke R, McPartlin J, et al. Facts and recommendations about total homocysteine determinations: an expert opinion. Clin Chem 2004;50:3–32.10.1373/clinchem.2003.021634Search in Google Scholar

39. Finkelstein JD. Inborn errors of sulfur-containing amino acid metabolism. J Nutr 2006;136:1750S–4S.10.1093/jn/136.6.1750SSearch in Google Scholar

40. Barić I. Inherited disorders in the conversion of methionine to homocysteine. J Inherit Metab Dis 2009;32:459–71.10.1007/s10545-009-1146-4Search in Google Scholar

41. Martin C, Zhang Y. The diverse functions of histone lysine methylation. Nature Rev Mol Cell Biol 2005;6:838–49.10.1038/nrm1761Search in Google Scholar

42. Lachner M, Jenuwein T. The many faces of histone lysine methylation. Curr Opin Cell Biol 2002;14:286–98.10.1016/S0955-0674(02)00335-6Search in Google Scholar

43. Friso S, Udali S, Guarini P, Pellegrini C, Pattini P, Moruzzi S, et al. Global DNA hypomethylation in peripheral blood mononuclear cells as a biomarker of cancer risk. Cancer Epidemiol Biomarkers Prev 2013;22:348–55.10.1158/1055-9965.EPI-12-0859Search in Google Scholar PubMed PubMed Central

44. Blount BC, Mack MM, Wehr CM, MacGregor JT, Hiatt RA, Wang G, et al. Folate deficiency causes uracil misincorporation into human DNA and chromosome breakage: implications for cancer and neuronal damage. Proc Natl Acad Sci USA 1997;94: 3290–5.10.1073/pnas.94.7.3290Search in Google Scholar PubMed PubMed Central

45. Iskandar J, Nelson A, Resnick D, Skene JH, Gao P, Johnson C, et al. Folic acid supplementation enhances repair of the adult central nervous system. Ann Neurol 2004;56:221–7.10.1002/ana.20174Search in Google Scholar

46. Kim Y-I. Folate and DNA methylation: a mechanistic link between folate deficiency and colorectal cancer? Cancer Epidemiol Biomarkers Prev 2004;13:511–9.10.1158/1055-9965.511.13.4Search in Google Scholar

47. Pogribny IP, James SJ, Beland FA. Molecular alterations in hepatocarcinogenesis induced by dietary methyl deficiency. Mol Nutr Food Res 2012;56:116–25.10.1002/mnfr.201100524Search in Google Scholar

48. Hu N, Strobl-Mazzulla P, Sauka-Spengler T, Bronner ME. DNA methyltransferase 3A as a molecular switch mediating the neural tube-to-neural crest fate transition. Genes Dev 2012;26:2380–5.10.1101/gad.198747.112Search in Google Scholar

49. Blom HJ. Folic acid, methylation and neural tube closure in humans. Birth Defects Res A Clin Mol Teratol 2009;85:295–302.10.1002/bdra.20581Search in Google Scholar

50. Fenech M. The role of folic acid and vitamin B12 in genomic stability of human cells. Mutat Res 2001;475:57–67.10.1016/S0027-5107(01)00079-3Search in Google Scholar

51. Su JL. Diet, epigenetics, and cancer. Cancer Epigenetics Methods Mol Biol 2012;863:377–93.10.1007/978-1-61779-612-8_24Search in Google Scholar PubMed

52. Finkelstein JD. Methionine metabolism in liver diseases. Am J Clin Nutr 2003;77:1094–5.10.1093/ajcn/77.5.1094Search in Google Scholar PubMed

53. Finkelstein JD. Metabolic regulatory properties of S-adenosylmethionine and S-adenosylhomocysteine. Clin Chem Lab Med 2007;45:1694–9.10.1515/CCLM.2007.341Search in Google Scholar PubMed

54. Jacques PF, Selhub J, Bostom AG, Wilson PW, Rosenberg IH. The effect of folic acid fortification on plasma folate and total homocysteine concentrations. N Engl J Med 1999;340:1449–54.10.1056/NEJM199905133401901Search in Google Scholar PubMed

55. Selhub J, Miller JW. The pathogenesis of homocysteinemia: interruption of the coordinate regulation by S-adenosylmethionine of the remethylation and transsulfuration of homocysteine. Am J Clin Nutr 1992;55:131–8.10.1093/ajcn/55.1.131Search in Google Scholar PubMed

56. Prudova A, Bauman Z, Braun A, Vitvitsky V, Lu SC, Banerjee R. S-adenosylmethionine stabilizes cystathionine beta-synthase and modulates redox capacity. Proc Natl Acad Sci USA 2006;103:6489–94.10.1073/pnas.0509531103Search in Google Scholar

57. Bostom AG, Selhub J, Jacques PF, Rosenberg IH. Power shortage: clinical trials testing the “homocysteine hypothesis” against a background of folic acid-fortified cereal grain flour. Ann Intern Med 2001;135:133–7.10.7326/0003-4819-135-2-200107170-00014Search in Google Scholar

58. Van Guelpen B, Hultdin J, Johansson I, Witthöft C, Weinehall L, Eliasson M, et al. Plasma folate and total homocysteine levels are associated with the risk of myocardial infarction, independently of each other and of renal function. J Intern Med 2009;266:182–95.10.1111/j.1365-2796.2009.02077.xSearch in Google Scholar

59. Blom HJ, Smulders Y. Overview of homocysteine and folate metabolism. With special references to cardiovascular disease and neural tube defects. J Inherit Metab Dis 2011;34:75–81.10.1007/s10545-010-9177-4Search in Google Scholar

60. Holven KB, Haugstad TS, Holm T, Aukrust P, Ose L, Nenseter MS. Folic acid treatment reduces elevated plasma levels of asymmetric dimethylarginine in hyperhomocysteinaemic subjects. Br J Nutr 2003;89:359–63.10.1079/BJN2002779Search in Google Scholar

61. Vinod A, Broadhead M, Malaki M, Whitley G, Leiper J, MacAllister R, et al. Asymmetric dimethylarginine causes hypertension and cardiac dysfunction in humans and is actively metabolized by dimethylarginine dimethylaminohydrolase. Arterioscler Thromb Vasc Biol 2003;23:1455–9.10.1161/01.ATV.0000081742.92006.59Search in Google Scholar

62. Böger RH, Bode-Böger SM, Szub A, Tsao PS, Chan JR, Tangphao O, et al. Asymmetric dimethylarginine (ADMA): a novel risk factor for endothelial dysfunction. Its role in hypercholesterolemia. Circulation 1998;98:1842–7.10.1161/01.CIR.98.18.1842Search in Google Scholar

63. Ho PI, Ashline D, Dhitavat S, Ortiz D, Collins SC, Shea TB, et al. Folate deprivation induces neurodegeneration: roles of oxidative stress and increased homocysteine. Neurobiol Dis 2003;14:32–42.10.1016/S0969-9961(03)00070-6Search in Google Scholar

64. Stanger O, Wonisch W. Enzymatic and non-enzymatic antioxidative effects of folic acid and its reduced derivates. Water soluble vitamins. Subcellular Biochem 2012;56:131–61.10.1007/978-94-007-2199-9_8Search in Google Scholar PubMed

65. Ueland PM, Refsum H. Plasma homocysteine, a risk factor for vascular disease: plasma levels in health, disease, and drug therapy. J Lab Clin Med 1989;114:473–501.Search in Google Scholar

66. Heijer DM, Koster T, Blom HJ, Gerard MJ, Bos MD, Ernest B, et al. Hyperhomocysteinemia as a risk factor for deep-vein thrombosis. N Engl J Med 1996;334:759–62.10.1056/NEJM199603213341203Search in Google Scholar PubMed

67. Nygård O, Nordrehaug JE, Refsum H, Ueland PM, Farstad M, Vollset SE. Plasma homocysteine levels and mortality in patients with coronary artery disease. N Engl J Med 1997;337:230–6.10.1056/NEJM199707243370403Search in Google Scholar

68. Blom HJ. Hyperhomocysteinemia as a risk factor for deep-vein thrombosis. N Engl J Med 1996;334:759–62.10.1056/NEJM199603213341203Search in Google Scholar

69. Khan M, Yamauchi M, Srisawasdi S, Stiner D, Doty S, Paschalis EP, et al. Homocysteine decreases chondrocyte-mediated matrix mineralization in differentiating chick limb-bud mesenchymal cell micro-mass cultures. Bone 2001;28:387–98.10.1016/S8756-3282(01)00409-4Search in Google Scholar

70. Gjesdal CG, Vollset SE, Ueland PM, Refsum H, Drevon CA, Gjessing HK, et al. Plasma total homocysteine level and bone mineral density: the hordaland homocysteine study. Arch Intern Med 2006;166:88–94.10.1001/archinte.166.1.88Search in Google Scholar PubMed

71. Gjesdal CG, Vollset SE, Ueland PM, Refsum H, Meyer HE, Tell GS. Plasma homocysteine, folate, and vitamin B12 and the risk of hip fracture: the Hordaland homocysteine study. J Bone Miner Res 2007;22:747–56.10.1359/jbmr.070210Search in Google Scholar PubMed

72. Shin YS, Beuhring KU, Stokstad EL. The relationships between vitamin B12 and folic acid and the effect of methionine on folate metabolism. Mol Cell Biochem 1975;9:97–108.10.1007/BF01732201Search in Google Scholar PubMed

73. Weir DG, Scott JM. Brain function in the elderly: role of vitamin B12 and folate. Br Med Bull 1999;55:669–82.10.1258/0007142991902547Search in Google Scholar PubMed

74. Scott JM. Folate and vitamin B12. Proc Nutr Soc 1999;58:441–8.10.1017/S0029665199000580Search in Google Scholar PubMed

75. Bottiglieri T. Folate, vitamin B12, and neuropsychiatric disorders. Nutr Rev 1996;54:382–90.10.1111/j.1753-4887.1996.tb03851.xSearch in Google Scholar PubMed

76. Rosenberg IH. Effects of folate and vitamin B12 on cognitive function in adults and the elderly. Food Nutr Bull 2008;29: S132–42.10.1177/15648265080292S118Search in Google Scholar PubMed

77. Reynolds E. Benefits and risks of folic acid to the nervous system. J Neurol Neurosurg Psychiatry 2002;72:567–71.10.1136/jnnp.72.5.567Search in Google Scholar PubMed PubMed Central

78. Fenech M. Folate (vitamin B9) and vitamin B12 and their function in the maintenance of nuclear and mitochondrial genome integrity. Mutat Res 2012;733:21–33.10.1016/j.mrfmmm.2011.11.003Search in Google Scholar PubMed

79. Watkins D, Ru M, Hwang HY, Kim CD, Murray A, Philip NS. Hyperhomocysteinemia due to methionine synthase deficiency, cblG: structure of the MTR gene, genotype diversity, and recognition of a common mutation, P1173L. Am J Hum Genet 2002;71:143–53.10.1086/341354Search in Google Scholar PubMed PubMed Central

80. Carmel R, Green R, Rosenblatt DS, Watkins D. Update on cobalamin, folate, and homocysteine. American Society of Hematology ASH Education Book 2003;1:62–81.10.1182/asheducation-2003.1.62Search in Google Scholar PubMed

81. Malouf M, Grimley EJ, Areosa SA. Folic acid with or without vitamin B12 for cognition and dementia. Cochrane Database Syst Rev 2003;4:CD004514.10.1002/14651858.CD004514Search in Google Scholar PubMed

82. Guéant JL, Caillerez-Fofou M, Battaglia-Hsu S, Alberto JM, Freund JN, Dulluc I, et al. Molecular and cellular effects of vitamin B12 in brain, myocardium and liver through its role as co-factor of methionine synthase. Biochimie 2013;95:1033–40.10.1016/j.biochi.2013.01.020Search in Google Scholar PubMed

83. Bottiglieri T. Homocysteine and folate metabolism in depression. Prog Neuropsychopharmacol Biol Psychiatry 2005;29:1103–12.10.1016/j.pnpbp.2005.06.021Search in Google Scholar PubMed

84. Kräutler B. Biochemistry of B12-cofactors in human metabolism. Water Soluble Vitamins. Subcell Biochem 2012;56:323–46.10.1007/978-94-007-2199-9_17Search in Google Scholar PubMed

85. Tangney CC. Is there a link between vitamin B₁₂ deficiency and cognitive decline in the elderly? Aging Health 2012;8:441–3.10.2217/ahe.12.50Search in Google Scholar

86. Molloy AM, Scott JM. Folates and prevention of disease. Public Health Nutr 2001;4:601–9.10.1079/PHN2001144Search in Google Scholar PubMed

87. Kenyon SH, Nicolaou A, Ast T, Gibbons WA. Stimulation in vitro of vitamin B12-dependent methionine synthase by polyamines. Biochem J 1996;316:661–5.10.1042/bj3160661Search in Google Scholar PubMed PubMed Central

88. Cohen SS. A guide to polyamines. Oxford University Press: New York, USA, 1998.Search in Google Scholar

89. Heby O. Role of polyamines in the control of cell proliferation and differentiation. Differentiation 1981;19:1–20.10.1111/j.1432-0436.1981.tb01123.xSearch in Google Scholar PubMed

90. Tabor CW, Tabor H. Polyamines. Annu Rev Biochem 1984;53:749–90.10.1146/annurev.bi.53.070184.003533Search in Google Scholar PubMed

91. Morgan DM. Polyamines. An overview. Mol Biotechnol 1999;11:229–50.Search in Google Scholar

92. Thomas T, Thomas TJ. Polyamines in cell growth and cell death: molecular mechanisms and therapeutic applications. Cell Mol Life Sci 2001;58:244–58.10.1007/PL00000852Search in Google Scholar PubMed

93. Pegg AE, McCann PP. Polyamine metabolism and function. Am J Physiol 1982;243:C212–21.10.1152/ajpcell.1982.243.5.C212Search in Google Scholar PubMed

94. Igarashi K, Kashiwagi K. Polyamines: mysterious modulators of cellular functions. Biochem Biophys Res Commun 2000;271:559–64.10.1006/bbrc.2000.2601Search in Google Scholar PubMed

95. D’Agostino L, Di Luccia A. Polyamines interact with DNA as molecular aggregates. Eur J Biochem 2002;269:4317–25.10.1046/j.1432-1033.2002.03128.xSearch in Google Scholar PubMed

96. Iacomino G, Picariello G, D‘Agostino L. DNA and nuclear aggregates of polyamines. Biochim Biophys Acta – Mol Cell Res 2012;1823:1745–55.10.1016/j.bbamcr.2012.05.033Search in Google Scholar PubMed

97. Janne J, Alhonen L, Pietila M, Keinanen TA. Genetic approaches to the cellular functions of polyamines in mammals. Eur J Biochem 2004;271:877–94.10.1111/j.1432-1033.2004.04009.xSearch in Google Scholar PubMed

98. Bachrach U. Naturally occurring polyamines: interaction with macromolecules. Curr Protein Pept Sci 2005;6:559–66.10.2174/138920305774933240Search in Google Scholar PubMed

99. Wallace HM, Fraser AV, Hughes A. A perspective of polyamine metabolism. Biochem J 2003;376:1–14.10.1042/bj20031327Search in Google Scholar

100. Persson L. Polyamine homoeostasis. Essays Biochem 2009;46:11–24.10.1042/bse0460002Search in Google Scholar

101. Raina A, Janne J. Physiology of the natural polyamines putrescine, spermidine and spermine. Med Biol 1975;53:121–47.Search in Google Scholar

102. Pegg EA. Recent advances in the biochemistry of polyamines in eukaryotes. Biochem J 1986;234:249–62.10.1042/bj2340249Search in Google Scholar

103. Krebs AH, Hems R, Tyler B. The regulation of folate and methionine metabolism. Biochem J 1976;158:341–53.10.1042/bj1580341Search in Google Scholar

104. Yerlikaya A. Polyamines and S-adenosylmethionine decarboxylase. Turk J Biochem 2004;29:208–14.Search in Google Scholar

105. Albers E. Metabolic Characteristics and importance of the universal methionine salvage pathway recycling methionine from 5′methylthioadenosine. IUBMB Life 2009;61:1132–42.10.1002/iub.278Search in Google Scholar

106. Pegg AE. Spermidine/spermine-N1-acetyltransferase: a key metabolic regulator. Am J Physiol Endocrinol Metab 2008;294:E995–1010.10.1152/ajpendo.90217.2008Search in Google Scholar

107. Matsui I, Pegg AE. Induction of spermidine N1-acetyltransferase in rat kidney by treatment with folic acid. FEBS Lett 1982;139:205–8.10.1016/0014-5793(82)80852-1Search in Google Scholar

108. Casero RA, Pegg AE. Spermidine/spermine N¹-acetyltransferase: the turning point in polyamine metabolism. FASEB J 1993;7:653–61.10.1096/fasebj.7.8.8500690Search in Google Scholar

109. Holtta E. Oxidation of spermidine and spermine in rat liver: purification and properties of polyamine oxidase. Biochemistry 1977;16:91–100.10.1021/bi00620a015Search in Google Scholar PubMed

110. Vujcic S, Liang P, Diegelman P, Kramer DL, Porter CW. Genomic identification and biochemical characterization of the mammalian polyamine oxidase involved in polyamine back-conversion. Biochem J 2003;370:19–28.10.1042/bj20021779Search in Google Scholar PubMed PubMed Central

111. Seiler N, Raul F. Polyamines and apoptosis. J Cell Mol Med 2005;9:623–42.10.1111/j.1582-4934.2005.tb00493.xSearch in Google Scholar

112. Russell HD. The roles of the polyamines, putrescine, spermidine and spermine in normal and malignant tissues. Life Sci 1973;13:1635–47.10.1016/0024-3205(73)90111-2Search in Google Scholar

113. Pegg AE. Polyamine metabolism and its importance in neoplastic growth and as a target for chemotherapy. Cancer Res 1988;48:759–64.Search in Google Scholar

114. Tabib A, Bachrach U. Role of polyamines in mediating malignant transformation and oncogene expression. Inter J Biochem Cell Biol 1999;31:1289–95.10.1016/S1357-2725(99)00098-9Search in Google Scholar

115. Moinard C, Cynober L, de Bandt J–P. Polyamines: metabolism and implications in human diseases. Clin Nutr 2005;24: 184–97.10.1016/j.clnu.2004.11.001Search in Google Scholar PubMed

116. Gerner EW, Meyskens FL. Polyamines and cancer: old molecules, new understanding. Nat Rev Cancer 2004;4: 781–92.10.1038/nrc1454Search in Google Scholar PubMed

117. Criss WE. A review of polyamines and cancer. Turk J Med Sci 2003;33:195–205.Search in Google Scholar

118. Soda K. The mechanisms by which polyamines accelerate tumor spread. J Exp Clin Cancer Res 2011;30:2–9.10.1186/1756-9966-30-95Search in Google Scholar PubMed PubMed Central

119. Bjelakovic G, Kocic G, Pavlovic D, Nikolic J, Stojanovic I, Bjelakovic GB, et al. Effects of folic acid on polyamine concentrations and polyamine oxidase activity in regenerating rat liver. Pteridines 2003;14:109–13.Search in Google Scholar

120. Bjelakovic G, Pavlovic D, Jevtovic T, Stojanovic I, Sokolovic D, Bjelakovic GB, et al. Vitamin B12 and folic acid effects on polyamine metabolism in rat liver. Pteridines 2006;17:90–4.10.1515/pteridines.2006.17.3.90Search in Google Scholar

121. Casero RA, Pegg AE. Polyamine catabolism and disease. Biochem J 2009;421:323–38.10.1042/BJ20090598Search in Google Scholar PubMed PubMed Central

122. Marverti G, Ligabue A, Guerrieri D, Paglietti G, Piras S, Costi MP, et al. Spermidine/spermine N1-acetyltranferase modulation by novel folate cycle inhibitors in cisplatin-sensitive and -resistant human ovarian cancer cell lines. Gynecol Oncol 2010;117:202–10.10.1016/j.ygyno.2009.11.030Search in Google Scholar PubMed

123. Kim Y-I. Folic acid supplementation and cancer risk point. Cancer Epidemiol Biomarkers Prev 2008;17:2220–5.10.1158/1055-9965.EPI-07-2557Search in Google Scholar PubMed

124. Ulrich CM, Potter JD. Folate supplementation: too much of a good thing? Cancer Epidemiol Biomarkers Prev 2006;15:189–93.10.1158/1055-9965.EPI-152COSearch in Google Scholar

125. Ulrich CM, Potter JD. Folate and cancer – timing is everything. J Am Med Assoc 2007;297:2408–9.10.1001/jama.297.21.2408Search in Google Scholar

126. Crider KS, Bailey LB, Berry RJ. Folic acid food fortification – its history, effect, concerns, and future directions. Nutrients 2011;3:370–84.10.3390/nu3030370Search in Google Scholar

127. Kim Y-I. Folate: a magic bullet or a double edged sword for colorectal cancer prevention? Gut 2006;55:1387–89.10.1136/gut.2006.095463Search in Google Scholar

128. Bjelaković G, Stojanović I, Bjelaković GB, Pavlović D, Kocić G, Daković-Milić A. Competitive inhibitors of enzymes and their therapeutic application. Facta Universitatis. Ser Med Biol 2002;9:201–6.Search in Google Scholar

129. Canal P, Chatelut E, Guichard S. Practical treatment guide for dose individualisation in cancer chemotherapy. Drugs 1998;56:1019–38.10.2165/00003495-199856060-00006Search in Google Scholar

130. Salmon SE. Principles of cancer therapy. In: Wyngaarden/Smith/Bennett. Cecil textbook of medicine. 19th ed. Philadelphia: W. B. Saunders, 1992:1049–67.Search in Google Scholar

131. Abali EE, Skacel NE, Celikkaya H, Hsieh YC. Regulation of human dihydrofolate reductase activity and expression. Vitam Horm 2008;79:267–92.10.1016/S0083-6729(08)00409-3Search in Google Scholar

132. Widemann BC, Adamson PC. Understanding and managing methotrexate nephrotoxicity. Oncologist 2006;11:694–703.10.1634/theoncologist.11-6-694Search in Google Scholar

133. Bertino JR. Cancer research: from folate antagonism to molecular targets. Best Pract Res Clin Haemat 2009;l22: 577–82.10.1016/j.beha.2009.09.004Search in Google Scholar

134. Gonen N, Assaraf YG. Antifolates in cancer therapy: structure, activity and mechanisms of drug resistance. Drug Resist Update 2012;15:183–210.10.1016/j.drup.2012.07.002Search in Google Scholar

135. Ifergan I, Assaraf YG. Molecular mechanisms of adaptation to folate deficiency. Vitam Horm 2008;79:99–143.10.1016/S0083-6729(08)00404-4Search in Google Scholar

136. Sanchez del-Campo L, Montenegro MF, Saez-Ayala M, Piedad Fernández-Pérez M, Cabezas-Herrera J, Neptuno Rodriguez-Lopez J. Cellular and molecular mechanisms of methotrexate resistance in melanoma. InTech 2013;14:391–409.Search in Google Scholar

137. Bjelaković G, Pavlović D, Marčetić-Voinović J, Bjelaković G, Kocić G, Nikolić J, et al. Effect of methotrexate on polyamine oxidase activity in regenerating rat liver tissue. Facta Universitatis, Ser Med Biol 1995;2:10–3.Search in Google Scholar

138. Bjelakovic G, Jevtovic T, Stojanovic I, Bjelakovic B, Ilic M. Biochemical study of hematological diseases in childhood. Jugoslov Med Biohem 2003;22:141–4.10.2298/JMH0302141BSearch in Google Scholar

139. Sánchez-del-Campo L, Otón F, Tárraga A, Cabezas-Herrera J, Chazarra S, Rodríguez-López JN. Synthesis and biological activity of a 3,4,5-trimethoxybenzoyl ester analogue of epicatechin-3-gallate. J Med Chem 2008;51:2018–26.10.1021/jm701346hSearch in Google Scholar PubMed

140. Neptuno Rodriguez-Lopez J, Sanchez-del-Campo L, Magali Saez-Ayala C, Montenegro MF, Cabezas-Herrera J. Novel antifolates as prodrugs for the treatment of melanoma. Research on Melanoma. InTech 2011;6:101–24.Search in Google Scholar

141. Stabler SP. Vitamin B₁₂ deficiency. N Engl J Med 2013;368: 149–60.10.1056/NEJMcp1113996Search in Google Scholar PubMed

142. Beck WS. Diagnosis of megaloblastic anemia. Ann Rev Med 1991;42:311–22.10.1146/annurev.me.42.020191.001523Search in Google Scholar PubMed

143. Wickramasinghe SN. Diagnosis of megaloblastic anaemias. Blood Rev 2006;20:299–318.10.1016/j.blre.2006.02.002Search in Google Scholar PubMed

144. Blencowe H, Cousens S, Modell B, Lawn J. Folic acid to reduce neonatal mortality from neural tube disorders. Int J Epidemiol 2010;39(Suppl 1):110–21.10.1093/ije/dyq028Search in Google Scholar PubMed PubMed Central

145. van Mil H, Oosterban AM, Steegers-Theunissen RP. Teratogenicity and underlying mechanisms of homocysteine in animal models: a review. Reprod Toxicol 2010;30:520–31.10.1016/j.reprotox.2010.07.002Search in Google Scholar PubMed

146. O’Neill C. Endogenous folic acid is essential for normal development of preimplantation embryos. Human Reprod 1998;13:1312–6.10.1093/humrep/13.5.1312Search in Google Scholar PubMed

147. Daly S, Mills JL, Molloy AM, Conley M, McPartlin J, Lee YJ, et al. Low-dose folic acid lowers plasma homocysteine levels in women of child-bearing age. Q J Med 2002;95:733–40.10.1093/qjmed/95.11.733Search in Google Scholar PubMed

148. Botto LD, Moore CA, Khoury MJ, Erickson JD. Neural-tube defects. N Engl J Med 1999;341:1509–19.10.1056/NEJM199911113412006Search in Google Scholar PubMed

149. De Wals P, Tairou F, Van Allen MI, Uh S-H, Lowry RB, Sibbald B, et al. Reduction in neural-tube defects after folic acid fortification in Canada. N Engl J Med 2007;357:135–42.10.1056/NEJMoa067103Search in Google Scholar PubMed

150. Verhaar MC, Stroes E, Rabelink TJ. Folates and cardiovascular disease. Arterioscl Thromb Vasc Biol 2002;22:6–13.10.1161/hq0102.102190Search in Google Scholar PubMed

151. Lonn E, Yusuf S, Arnold MJ, Sheridan P, Pogue J, Micks M, et al. Homocysteine lowering with folic acid and B vitamins in vascular disease. N Engl J Med 2006;354:1567–77. (A correction in N Engl J Med 2006;355:746).10.1056/NEJMoa060900Search in Google Scholar PubMed

152. Vertioef P, Stampfer MJ, Buring JE, Gaziano JM, Allen RH, Stabler SP, et al. Homocysteine metabolism and risk of myocardial infarction: relation with vitamins B₁₂, B₉, and folate. Am J Epidemiol 1996;143:845–59.10.1093/oxfordjournals.aje.a008828Search in Google Scholar PubMed

153. Wang Z, Wilson Tang WH, Cho L, Brennan DM, Hazen SL. Targeted metabolomic evaluation of arginine methylation and cardiovascular risks: potential mechanisms beyond nitric oxide synthase inhibition. Arterioscler Thromb Vasc Biol 2009;29:1383–91.10.1161/ATVBAHA.109.185645Search in Google Scholar PubMed PubMed Central

154. Mato JM, Lu SC. Role of S-adenosyl-L-methionine in liver health and injury. Hepatology 2007;45:1306–12.10.1002/hep.21650Search in Google Scholar PubMed

155. Jaeschke H. Reactive oxygen and mechanisms of inflammatory liver injury: present concepts. J Gastroenterol Hepatol 2011;26(Suppl 1):L173–9.10.1111/j.1440-1746.2010.06592.xSearch in Google Scholar PubMed

156. Lee TD, Sadda MR, Mendler MH, Bottiglieri T, Kanel G, Mato JM, et al. Abnormal hepatic methionine and glutathione metabolism in patients with alcoholic hepatitis. Alcohol Clin Exp Res 2004;28:173–81.10.1097/01.ALC.0000108654.77178.03Search in Google Scholar PubMed

157. Anstee QM, Day CP. S-adenosylmethionine (SAMe) therapy in liver disease: a review of current evidence and clinical utility. J Hepatol 2012;57:1097–109.10.1016/j.jhep.2012.04.041Search in Google Scholar PubMed

158. Bailey LB, Gregory JF. Folate metabolism and requirements. J Nut 1999;129:779–82.10.1093/jn/129.4.779Search in Google Scholar PubMed

159. Marsillach J, Ferré N, Camps J, Riu F, Rull A, Joven J. Moderately high folic acid supplementation exacerbates experimentally induced liver fibrosis in rats. Exp Biol Med 2008;233:38–47.10.3181/0703-RM-59Search in Google Scholar

160. Duce AM, Ortiz P, Cabrero C, Mato JM. S-adenosyl-L-methionine synthetase and phospholipid methyltransferase are inhibited in human cirrhosis. Hepatology 1988;8:65–8.10.1002/hep.1840080113Search in Google Scholar

161. Fink M, Henry M, Tange JD. Experimental folic acid nephropathy. Pathology 1987;9:143–9.10.3109/00313028709077125Search in Google Scholar

162. Kavlock RJ, Rehnberg BF, Rogers EH. Amphotericin B and folic acid-induced nephropathies in developing rats. Toxicol Appl Pharmacol 1985;1:407–15.10.1016/0041-008X(85)90412-0Search in Google Scholar

163. Mullin EM, Bonar RA, Paulson DF. Acute tubular necrosis: an experimental model detailing the biochemical events accompanying renal injury and recovery. Invest Urol 1976;13:289–94.Search in Google Scholar

164. Klingler EL, Evan AP, Anderson RE. Folic acid-induced renal injury and repair. Correlation of structural and functional abnormalities. Arch Pathol Lab Med 1980; 104:87–93.Search in Google Scholar

165. Long DA, Woolf AS, Suda T, Yuan HT. Increased renal Angiopoietin-1 expression in folic acid-induced nephrotoxicity in mice. J Am Soc Nephrol 2001;12:2721–31.10.1681/ASN.V12122721Search in Google Scholar

166. van Guldener C, Robinson K. Homocysteine and renal disease. Semin Thromb Hemost 2000;26:313–24.10.1055/s-2000-8407Search in Google Scholar

167. Chauveau P, Chadefaux B, Coudé M, Aupetit J, Hannedouche T, Kamoun P, et al. Hyperhomocysteinemia, a risk factor for atherosclerosis in chronic uremic patients. Kidney Int 1993;(Suppl 41):S72–7.Search in Google Scholar

168. Bostom AG, Culleton BF. Hyperhomocysteinemia in chronic renal disease. JASN 1999;10:891–900.10.1681/ASN.V104891Search in Google Scholar

169. Young SN, Ghadirian AM. Folic acid and psychopathology. Prog Neuropsychopharmacol Biol Psychiatry 1989; 13:841–63.10.1016/0278-5846(89)90037-7Search in Google Scholar

170. Mattson MP, Shea TB. Folate and homocysteine metabolism in neural plasticity and neurodegenerative disorders. Trends Neurosci 2003;26:137–46.10.1016/S0166-2236(03)00032-8Search in Google Scholar

171. Goff DC, Bottiglieri T, Arning E, Shih V, Freudenreich O, Evins AE, et al. Folate, homocysteine, and negative symptoms in schizophrenia. Am J Psychiatry 2004;161:1705–8.10.1176/appi.ajp.161.9.1705Search in Google Scholar PubMed

172. Applebaum J, Shimon H, Sela BA, Belmaker RH, Levine J. Homocysteine levels in newly admitted schizophrenic patients. J Psychiatr Res 2004;38:413–6.10.1016/j.jpsychires.2004.01.003Search in Google Scholar PubMed

173. Crivello NA, Blusztajn JK, Joseph JA, Shukitt-Hale B, Smith DE. Short-term nutritional folate deficiency in rats has a greater effect on choline and acetylcholine metabolism in the peripheral nervous system than in the brain, and this effect escalates with age. Nutr Res 2010;30:722–30.10.1016/j.nutres.2010.09.008Search in Google Scholar PubMed PubMed Central

174. O’Donnell C, Stephens T. The significance of homocysteine levels in schizophrenia. Am J Psychiatry 2005;162: 1387–8.10.1176/ajp.162.7.1387-aSearch in Google Scholar

175. Tanaka T, Scheet P, Giusti B, Bandinelli S, Grazia Piras M, Usala G, et al. Genome-wide association study of vitamin B6, vitamin B12, folate, and homocysteine blood concentrations. Am J Hum Gen 2009;84:477–82.10.1016/j.ajhg.2009.02.011Search in Google Scholar PubMed PubMed Central

176. Shane B, Stokstad EL. Vitamin B12-folate interrelationships. Ann Rev Nutr 1985;5:115–41.10.1146/annurev.nu.05.070185.000555Search in Google Scholar PubMed

177. D‘Anci KE, Rosenberg IH. Folate and brain function in the elderly. Curr Opin Clin Nutr Metab Care 2004;7:659–64.10.1097/00075197-200411000-00011Search in Google Scholar PubMed

178. Levine J, Sela BA, Osher Y, Belmaker RH. High homocystein serum levels in young male schizophrenia and bipolar patients and in an animal model. Prog Neuropsychopharmacol Biol Psychiatry 2005;29:1181–91.10.1016/j.pnpbp.2005.06.029Search in Google Scholar PubMed

179. Krebs MO, Bellon A, Mainguy G, Jay TM Frieling H. One-carbon metabolism and schizophrenia: current challenges and future directions. Trends Mol Med 2009;15:562–70.10.1016/j.molmed.2009.10.001Search in Google Scholar PubMed

180. Kronenberg G, Harms C, Sobol RW, Cardozo-Pelaez F, Linhart H, Winter B. Folate deficiency induces neurodegeneration and brain dysfunction in mice lacking uracil DNA glycosylase. J Neurosci (Neurobiol Dis) 2008;28:7219–230.10.1523/JNEUROSCI.0940-08.2008Search in Google Scholar PubMed PubMed Central

181. Frustaci A, Neri M, Cesario A, Adams JB, Domenici E, Dalla Bernardina B, et al. Oxidative stress-related biomarkers in autism: systematic review and meta-analyses. Free Radic Biol Med 2012;52:2128–41.10.1016/j.freeradbiomed.2012.03.011Search in Google Scholar PubMed

182. Berry RJ, Crider KS, Yeargin-Allsopp M. Periconceptional folic acid and risk of autism spectrum disorders. J Am Med Assoc 2013;309:611–3.10.1001/jama.2013.198Search in Google Scholar PubMed PubMed Central

183. Esteves SC, Agarwal A. Novel concepts in male infertility. Internat Braz J Urol 2011;37:5–15.10.1590/S1677-55382011000100002Search in Google Scholar

184. Tamura T, Picciano MF. Folate and human reproduction. Am J Clin Nutr 2006;83:993–1016.10.1093/ajcn/83.5.993Search in Google Scholar PubMed

185. Zeisel SH. Importance of methyl donors during reproduction. Am J Clin Nutr 2009;89:673S–7S.10.3945/ajcn.2008.26811DSearch in Google Scholar PubMed PubMed Central

186. Boxmeer JC, Brouns RM, Lindemans J, Steegers EA, Martini E, Macklon NS, et al. Preconception folic acid treatment affects the microenvironment of the maturing oocyte in human. Fertil Steril 2008;89:1766–70.10.1016/j.fertnstert.2007.06.036Search in Google Scholar PubMed

187. Boxmeer JC. The homocysteine pathway in human subfertility. Doctoral Disertation. Department of Obstetrics and Gynaecology, Division of Reproductive Medicine, Erasmus MC, University Medical Centre, Rotterdam, The Netherlands, 2009.Search in Google Scholar

188. Boxmeer JC, Smit M, Utomo E, Romijn JC, Eijkemans MJ, Lindemans J, et al. Low folate in seminal plasma is associated with increased sperm DNA damage. Fertil Steril 2009;92:548–56.10.1016/j.fertnstert.2008.06.010Search in Google Scholar PubMed

189. Wang X, Fenech M. A comparison of folic acid and 5-methyltetrahydrofolate for prevention of DNA damage and cell death in human lymphocytes in vitro. Mutagenesis 2003;18:81–6.10.1093/mutage/18.1.81Search in Google Scholar PubMed

190. Kelly TL, Neaga OR, Schwahn BC, Rozen R, Trasler JM. Infertility in 5,10-methylenetetrahydrofolate reductase (MTHFR)-deficient male mice is partially alleviated by lifetime dietary betaine supplementation. Biol Reprod 2005;72:667–77.10.1095/biolreprod.104.035238Search in Google Scholar PubMed

191. Steegers-Theunissen RP. The importance of folate, zinc and antioxidants in the pathogenesis and prevention of subfertility. Hum Reprod Update 2007;13:163–74.10.1093/humupd/dml054Search in Google Scholar PubMed

192. Minor A, Chow V, Ma S. Aberrant DNA methylation at imprinted genes in testicular sperm retrieved from men with obstructive azoospermia and undergoing vasectomy reversal. Reproduction 2011;141:749–57.10.1530/REP-11-0008Search in Google Scholar PubMed

193. Campbell NR. How safe are folic acid supplements? Arch Intern Med 1996;156:1638–44.10.1001/archinte.156.15.1638Search in Google Scholar

194. Mills JL. Fortification of foods with folic acid – How much is enough? N Engl J Med 2000;342:1442–5.10.1056/NEJM200005113421911Search in Google Scholar PubMed

195. Lawrence JM, Chiu V, Petitti DB. Fortification of foods with folic acid. N Engl J Med 2000;343:970–2.10.1056/NEJM200009283431314Search in Google Scholar PubMed

196. KimY-I. Folic acid fortification and supplementation – good for some but not so good for others. Nutrition Rev 2007;65: 504–11.10.1301/nr.2007.nov.504-511Search in Google Scholar

197. Smith AD, Kim Y-I, Refsum H. Is folic acid good for everyone? Am J Clin Nutr 2008;87:517–33.10.1093/ajcn/87.3.517Search in Google Scholar PubMed

198. Figueiredo JC, Grau MV, Haile RW, Sandler RS, Summers RW, Bresalier RS, et al. Folic acid and risk of prostate cancer: results from a randomized clinical trial. J Natl Cancer Inst 2009;101:432–5.10.1093/jnci/djp019Search in Google Scholar PubMed PubMed Central

199. Balasubramaniem A, Zainab MM, Nosratola DV, Hamid MS. Effect of folate oversupplementation on folate uptake by human intestinal and renal epithelial cells. Am J Clin Nutr 2007;86:159–66.10.1093/ajcn/86.1.159Search in Google Scholar PubMed

200. Agarwal R. Vitamin B₁₂ deficiency and cognitive impairment in elderly population. Indian J Med Res 2011;134:410–2.Search in Google Scholar

201. McNulty H, Scott JM. Intake and status of folate and related B-vitamins: considerations and challenges in achieving optimal status. Br J Nutr 2008;99:S48–54.10.1017/S0007114508006855Search in Google Scholar PubMed

Received: 2013-6-22

Accepted: 2013-7-22

Published Online: 2013-10-05

Published in Print: 2013-12-01

This article is distributed under the terms of the Creative Commons Attribution Non-Commercial License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Articles in the same Issue

https://doi.org/10.1515/pterid-2013-0024

Keywords for this article

deficiency; folates; food fortification; human health; polyamines

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BY-NC-ND 3.0

Is folic acid supplementation to food benefit or risk for human health?

Article

Abstract

Introduction

Metabolic manifestations of folate deficiency

Mechanisms of DNA instability in folate deficiency

DNA hypomethylation

Uracil misincorporation

Hyperhomocysteinemia in folate deficiency

Interactions between folates and vitamin B12 (cobalamin)

Folates and polyamines

Folates and cancerogeneses

Folic acid antagonists – antifolates

Clinical manifestation of folates deficiency

Megaloblastic anemia

Neural tube defects (NTDs)

Metabolic effects of folate on physiological functions of cardiovascular system, liver and kidney

Folates and cardiovascular system

The place of folates in liver metabolism

Folates and kidneys

Folates, brain and the peripheral nervous system

Folates and reproductive functions

Deleterious effects of folate supplementation and food fortification on human health

Conclusion

Future directions

References

Articles in the same Issue

Articles in the same Issue

Articles in the same Issue

Interactions between folates and vitamin B₁₂ (cobalamin)