[Structural modification of environment by microorganisms: formation of Liesegang rings around Dictyostelium discoideum population]

The results of the experimental study of the environment modification--the emergence of Liesegang rings around a Dictyostelium discoideum population are presented. The formation of Liesegang rings induced by D. discoideum cells is observed on addition of glucose into the semi-solid nutrient medium (agar concentration 0.5-1.5%). We show that the emergence of Liesegang rings is attended with a redistribution of folic acid in the nutrient substrate. A pH decrease in the course of D. discoideum cultivation is shown to be a factor inducing the redistribution of folic acid. The mechanisms of structural modification of the D. discoideum environment are discussed.

Amniotic fluid B12, calcium, and lead levels associated with neural tube defects

The group mean differences and relationships between folate, B12, calcium, lead, and methionine levels in amniotic fluid from 29 non-NTD and 11 NTD pregnancies (15-20 weeks' gestation age) were determined. The study population was predominantly Hispanic in both groups (48% in non-NTD and 36% in NTD group) with an average maternal age of 29 years in the non-NTD group and 24 years in the NTD group; and, an average gestation age of 18.5 weeks in the non-NTD and 17.5 weeks in the NTD group. The folate, B12, lead, calcium, and methionine levels of the two groups were compared by Student's t-test and by Pearson's correlation. The NTD levels were lower for calcium (p< or =0.0001), B12 (p< or =0.001), and methionine (P< or =0.001); but, the lead level was higher (p< or =0.0001). A negative correlation was observed between lead and both B12 (p< or =0.007) and methionine (p< or =0.02).

Analysis of some folate monoglutamates by high-performance liquid chromatography-mass spectrometry. I

The use of high-performance liquid chromatography for the determination of folates is well documented. The methods used are based on reversed-phase chromatography with UV and/or fluorescence detection. In many instances it is difficult to reach the required detection limits and many of the methods lack specificity. High-performance liquid chromatography-mass spectrometry (LC-MS) has become a well established analytical tool in modern laboratories. It can offer superior specificity and often lower detection limits than conventional LC detection methods and thus is ideally suited to the analysis of folates. A system capable of separating the four main folates [folic acid (pteroylglutamic acid, PGA)], 5-methyltetrahydrofolic acid, terahydrofolic acid and 5- and/or 10-formyltetrahydrofolic acid [folinic acid (CHOTHF)] using LC-MS with negative ion electrospray has been developed. After optimisation, a system using a 12.5 cm x 3 mm, 3 microm Hypersil ODS column and a mobile phase of 2.5 mM acetic acid-acetonitrile (88:12, v/v) was developed which was capable of separating the four folates in under 10 min without the use of a gradient system. Extraction of the folates is by heat treatment and sample clean-up is by solid-phase extraction (C18). On column limits of confirmation are 0.6 ng for PGA and CHOTHF.

Determination of folate vitamers in food and in Italian reference diet by high-performance liquid chromatography

A trienzyme treatment (conjugase, alpha-amylase, protease) followed by affinity chromatography and reversed-phase HPLC with UV and fluorescence detection was performed for the quantification of folate vitamers in legumes (chickpea and beans), processed meats (salami Milano and Parma ham) and in an Italian reference diet. This method allowed a good separation of six folate vitamers: 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, folic acid, 10-formylfolic acid, 10-formyldihydrofolate and tetrahydrofolate within 30 min. Recovery, reproducibility and limits of detection of the method are reported. HPLC results were 24-52% lower than the microbiological assay findings.

Folate-homocysteine interrelations: potential new markers of folate status

We report a transient drop in plasma Hcy and Cys following a single oral dose of PteGlu. The thiol change was concomitant with both the peak plasma 5CH3H4PteGlu1 level (by HPLC) and the maximum plasma Lactobacillus casei activity which reflects absorption of unmodified PteGlu. The significant reciprocal association of Hcy with radioassay RBC folate (r = -0.28, 99% CI -0.48, -0.05, P = 0.0016), serum folate (r = -0.37, 99% CI -0.56, -16, P = 0.0001), and vitamin B12 (r = -0.42, 99% CI -0.59, -21, P = 0.0001) is shown and reflects the long-term nutritional effect of B vitamins on this important, potentially atherogenic thiol. These are now well-established associations. We extend the potential for investigation of folate metabolism in health and disease by evaluating a range of new folate indices which are based on erythrocyte coenzymes. These have been looked at independently and in association with established parameters. Erythrocyte methylfolates (mono- to hexaglutamate-5CH3H4PteGlu1-6), formylfolates (tri- to pentaglutamate-5CHOH4PteGlu3-5),formiminotetrahydrofolate (formiminoH4PteGlu1), unsubstituted tetrahydrofolate (H4PteGlu1), andpara-aminobenzoylglutamate (P-ABG) have been measured by HPLC with fluorescence detection. A positive linear association exists between (i) H4PteGlu1 and radioassay RBC folate (r = 0.50, 99% CI 0. 07, 0.77, P = 0.0036), and (ii) H4PteGlu1 and tetraglutamates of both formyl- and methylfolate (r = 0.52, 99% CI 0.10, 0.78, P = 0. 0022, and r = 0.56, 99% CI 0.15, 0.80, P = 0.0009, respectively). Since, in addition, a reciprocal linear association exists between Hcy and tetraglutamyl formylfolate (r = -0.41, 99% CI -0.73, 0.05, P = 0.0206), erythrocyte tetraglutamates may be a good reflection of the bodies' active coenzyme pools. Pentaglutamyl formylfolate, the longest oligo-gamma-glutamyl chain form of this coenzyme may be a good indicator of folate depletion. The abundance of this coenzyme both increases with increasing Hcy (r = 0.55, 99% CI 0.13, 0.80, P = 0.0014) and increases as H4PteGlu1, the principle folate congener, decreases (r = -0.59, 99% CI -0.82, -0.20, P = 0.0004). Furthermore, the apparent equilibrium between substrate (5CH3H4PteGlu1) and product (H4PteGlu1) of methionine synthase is significantly associated with the abundance of 5CHOH4PteGlu5 (r = -0.53, 99% CI -0. 79, -0.11, P = 0.0018). This suggests that low methionine synthase activity for whatever reason (metabolic or dietary) may lead to an increase in the relative abundance of 5CHOH4PteGlu5. Like 5CHOH4PteGlu5, evidence is given that 5CH3H4PteGlu6, the longest oligo-gamma-glutamyl chain form of this particular coenzyme pool, may also be a good indicator of folate depletion. This is shown by a change in the relative proportion of erythrocyte methylfolate polyglutamates following supplementation with 400 microg/day PteGlu. Short-chain polyglutamates of methylfolate (5CH3H4PteGlu1--> 5CH3H4PteGlu4) increase in proportion to the total methylfolate pool, while long-chain polyglutamates of methylfolate (5CH3H4PteGlu5 and particularly 5CH3H4PteGlu6) decrease in their relative abundance.

Maternal folate status during extended lactation and the effect of supplemental folic acid

BACKGROUND

Folate requirements during lactation are not well established.

OBJECTIVE

We assessed the effects of dietary and supplemental folate intakes during extended lactation.

DESIGN

Lactating women (n = 42) were enrolled in a double-blind, randomized, longitudinal supplementation trial and received either 0 or 1 mg folic acid/d. At 3 and 6 mo postpartum, maternal folate status was assessed by measuring erythrocyte, plasma, milk, and dietary folate concentrations; plasma homocysteine; and hematologic indexes. Infant anthropometric measures of growth, milk intake, and folate intake were also assessed.

RESULTS

In supplemented women, values at 6 mo for erythrocyte and milk folate concentrations and for plasma homocysteine were not significantly different from those at 3 mo. In supplemented women compared with unsupplemented women at 6 mo, values for erythrocyte folate (840 compared with 667 nmol/L; P < 0.05), hemoglobin (140 compared with 134 g/L; P < 0.02), and hematocrit (0.41 compared with 0.39; P < 0.02) were higher and values for reticulocytes were lower. In unsupplemented women, milk folate declined from 224 to 187 nmol/L (99 to 82 ng/mL), whereas plasma homocysteine increased from 6.7 to 7.4 micromol/L. Dietary folate intake was not significantly different between groups (380+/-19 microg/d) and at 6 mo was correlated with plasma homocysteine in unsupplemented women (r = -0.53, P < 0.01) and with plasma folate in supplemented women (r = 0.49, P < 0.02).

CONCLUSIONS

A dietary folate intake of approximately 380 microg/d may not be sufficient to prevent mobilization of maternal folate stores during lactation.

Amniotic fluid B12 and folate levels associated with neural tube defects

Amniotic fluid levels of B12 and folate in neural tube defect (NTD) affected pregnancies were compared with the weekly group mean +/-SD changes in amniotic fluid B12 and folate levels of 10 unaffected pregnancies each week between 15 and 20 weeks' gestation age. Comparison was by analysis of variance (ANOVA) and Pearson's correlation to B12 and folate levels and to the NTD samples of corresponding gestation age. Amniotic fluid B12 and folate decreased 67 and 62%, respectively, between 15 and 20 weeks' gestation in the unaffected pregnancies, associated with an increase in amniotic fluid volume. The mean +/-SD B12 and folate of the NTD affected pregnancies (308+/-156 pg/mL and 3.1+/-1.6 ng/mL) were below the mean +/-SD B12 and folate of the total population of unaffected pregnancies (453+/-155 pg/mL and 3.9+/-1.2 ng/mL). The correlation between gestation age and amniotic fluid B12 was -0.9914 (p< or =.0001) and -0.9599 (p< or =.002) for amniotic fluid folate. The B12 levels of the affected pregnancies were below the range of unaffected pregnancies in four of the nine affected pregnancies, and folate levels in two of the nine affected pregnancies.

A validated liquid chromatographic method for determining folates in vegetables, milk powder, liver, and flour

A liquid chromatographic (LC) method was elaborated for determining folates in foods. Folates were extracted by homogenizing in buffer and heat treatment. A portion was incubated with an enzyme preparation containing conjugase, amylase, and protease. After purification by affinity chromatography, folate monoglutamates were determined by reversed-phase LC with fluorescence and diode array detection. Gradient elution with phosphate buffer and acetonitrile was used to separate vitamers. The most abundant folate forms naturally present in foods were detected, including tetrahydrofolic acid, 5-methyltetrahydrofolic acid, and 5-formyltetrahydrofolic acid. 10-Formylfolic acid could be detected by applying a second fluorescence detector. Folic acid, used for fortification, might also be quantitated with this system. The difference between folate concentrations in sample extracts, with and without treatment of conjugase, is a measure of the quantity of polyglutamates in the food matrixes. An additional treatment with conjugase, amylase, and protease reflects the amount of matrix-bound folates. The LC system gave a linear response over the range 0-100 ng/mL. Detection limit for these compounds were 7 pg/mL for tetrahydrofolic acid and 5-methyltetrahydrofolic acid and 59 pg/mL for 10-formylfolic acid (signal-to-noise ratio > or = 3) when 100 microL was injected. Detection limits for 5-formyltetrahydrofolic acid and folic acid were 1 ng/mL. Repeatability relative standard deviation values for separate folates in 3 candidate Certified Reference Materials (CRMs)--mixed vegetables (CRM 485), pig liver (CRM 487), and whole-meal flour (CRM 121)--and a Certified Reference Material milk powder (CRM 421) varied from 3.3 to 21.0% for the concentration range 1.8-1440 micrograms/100 g. Recoveries ranged from 73 to 109%. Use of amylase and protease was advantageous. Use of a commercially available folate-binding protein for cleanup saved time and money and was effective. Results for 5-methyltetrahydrofolic acid were in good agreement with results obtained with other LC methods. Results for total folates were lower than results obtained with microbiological methods.

Liquid chromatographic method for determining added folic acid in fortified cereal products

Reversed-phase ion-pair high-performance liquid chromatography (HPLC) was coupled with detection by UV absorption (280 nm) for separation and quantitation of added folic acid (FA) in fortified cereal based foods. A simple and rapid liquid-solid extraction method, combined with enzymatic digestion, to recover FA from the sample matrices is also presented. The quantitation of added FA was achieved in products including corn (maize), wheat-, rice- and oat-based cereal breakfast foods fortified at 25% and 100% of the reference daily intake (RDI). The retention time for FA was ca. 15 min, and the detection limit was 2 ng/20 microliters injection for standard FA. When FA was added to unfortified samples of wheat flour at concentrations of 3.08 or 20.0 micrograms/g, recoveries were 93% and 96%, respectively. Comparison of HPLC results with those of a standard microbiological assay has shown quite good agreement (r = 0.998). A solid-phase extraction clean-up procedure has also been developed for use with samples fortified with low levels of FA, where interferences may otherwise hinder quantitation.

A continuous spectrophotometric assay for thymidine and deoxycytidine kinases

We have developed a continuous spectrophotometric assay for thymidine and deoxycytidine kinase activities by coupling nucleoside 5'-monophosphate formation to a methylation reaction which generates a product absorbing at 340 nm. With thymidine kinase, we used the alternate substrate deoxyuridine and coupled the reaction to thymidylate synthase. For deoxycytidine kinase, we coupled the reaction to a thymidylate synthase mutant which converts the product 2'-deoxycytidine-5'-monophosphate (dCMP) to m5dCMP. In both cases, the methylation reactions are accompanied by conversion of 5,10-methylene-5,6,7,8-tedrahydrofolate to 7,8-dihydrofolate and can be continuously monitored by the increase of absorbance at 340 nm. The assay should be particularly useful for kinetic studies, and for the purification of these enzymes from various sources.

Properties of food folates determined by stability and susceptibility to intestinal pteroylpolyglutamate hydrolase action

The intestinal absorption of folate occurs at the monoglutamyl level, and an important measure of food folate bioavailability is how much folate from the food reaches the intestinal sites in forms that can readily be absorbed. In the absence of protecting agents, e.g., vitamin C and reduced thiols, many labile folates may be lost during cooking and during residence in the acid-peptic milieu of the stomach. On the other hand, the presence of polyglutamyl folate necessitates the action of intestinal hydrolases, which could be affected by food constituents. In this study, we developed an in vitro assay for the determination of an index of food folate availability. The index of folate availability in this study was defined as that proportion of folate that has been identified as monoglutamyl derivatives after tests for stability and susceptibility to an enzymatic hydrolysis. The index of folate availability varied widely among foods. The highest index was for egg yolk (72.2%), followed by cow's livers (55.7%), orange juice (21. 3%), cabbage (6.0%), lima beans (4.5%) and lettuce (2.9%). Yeast folate had the lowest index (0.3%). The availability indices generated by this study correlate with the indices of the bioavailability of the corresponding food folate observed in earlier studies, R2 = 0.529 (P = 0.068). Additional information is required on the bioavailability of other food products to test the usefulness of this in vitro approach for assessing food folate availability.

Hypomethylation in cervical tissue: is there a correlation with folate status?

We have shown previously that DNA hypomethylation is significantly associated with grade of cervical intraepithelial neoplasia (CIN; Y.I. Kim et al., Cancer, 74: 893-899, 1994). The objective of this study was to further describe this relationship and to investigate the role of folate in the observed association of DNA hypomethylation and CIN. Eighty-three patients with abnormal PAP smear results were referred to the Cervical Dysplasia Clinic at the University of Arizona for colposcopic examination and biopsy. Patients completed a short questionnaire and provided a nonfasting serum sample. DNA hypomethylation was assessed by incubating DNA extracted from biopsy samples with [3H]methyl-S-adenosylmethionine and Sss 1 methylase. Cervical tissue and serum folate concentrations were assessed using a microbiological assay. All folate levels were log transformed prior to statistical analysis. The histological distribution of the samples was: 7 adjacent normal, 30 CIN I, 18 CIN II, 13 CIN III, and 11 carcinoma in situ (CIS). The mean age of participants was 29.8 +/- 9.6 years. DNA hypomethylation was significantly different between select histological levels. Both cervical tissue folate and serum folate levels were significantly correlated to methylation level (P = 0.0211 and P = 0.0569, respectively). Smoking, hormonal contraceptive use, parity, and human papillomavirus infection were not associated with DNA hypomethylation or folate status. The current use of vitamins was significantly associated with serum folate level but not with methylation or cervical folate levels. These data extend our earlier findings that DNA hypomethylation is an early event in cervical carcinogenesis. To conclude that the folate level is significantly related to DNA hypomethylation, further investigation of DNA hypomethylation of specific genes is required.

Investigation of serine hydroxymethyltransferase in methanogens

The cofactor specificity of serine hydroxymethyltransferase (SHMT) activities was tested in extracts of several methanogens using tetrahydromethanopterin (H4MPt) from Methanobacterium thermoautotrophicum Marburg, tetrahydrosarcinapterin (H4SPt) from Methanosarcina barkeri, and tetrahydrofolate (H4folate) as the potential C1 carrier. In Methanosphaera stadtmanae and Methanococcus thermolithotrophicus, the activities were H4MPt dependent. In Methanospirillum hungatei GP1, Methanosaeta concilii, Methanolobus tindarius, and Methanosarcina barkeri Fusaro, the activities were strictly H4folate dependent. H4SPt was reactive with the SHMT of Methanosphaera stadtmanae but not with that of Methanosarcina barkeri. In both Methanosarcina barkeri and Methanospirillum hungatei, pyridoxal phosphate stimulated SHMT activity. The apparent K(m) values for H4folate and L-serine were 0.086 and 0.29 mM in Methanosarcina barkeri and 0.065 and 0.31 mM in Methanospirillum hungatei, respectively.

Neural-tube defects are associated with low concentrations of cobalamin (vitamin B12) in amniotic fluid

While folate supplementation reduces the risk of recurrent neural-tube defects (NTD), both folate and cobalamin deficiencies may be independent risk-factors for neural-tube defects. Folate-dependence and impaired remethylation of homocysteine are implicated as mechanisms for NTD. There are few references reported for folate, cobalamin, homocysteine and methionine in the fetal compartment. This case-controlled pilot study of amniotic fluid (AF) samples derived from 16 NTD pregnancies and 64 age-matched controls quantities total homocysteine (tHcy), total cysteine (tCys), folate, cobalamin (B12), and methionine. Only decreased AF B12 concentrations were found (150 pg/ml versus 540 pg/ml, P < 0.02). Since cobalamin, folate and homocysteine participate in the remethylation of homocysteine, via methyl transfer from 5-methyltetrahydrofolate to B12, to methionine, we compared ratios of these methionine synthase (EC 2.1.1.13)-related intermediates. The ratio of B12/folate for NTD versus controls was 48 (34-90) versus 126 (123-182), P < 0.001. The ratio of methionine/(folate x tHcy) was 1.4 (1.2-2.2) versus 2.7 (2.4-3.3), P < 0.001. We conclude that AF from pregnancies with NTD have lower B12 concentrations, and that ratios of product to substrate(s) of homocysteine remethylation suggest impaired methionine synthase in the fetal compartment through the early second trimester.

Trienzyme treatment for food folate analysis: optimal pH and incubation time for alpha-amylase and protease treatment

Recent reports have indicated that trienzyme treatment before folate determination is essential to obtain the proper folate content in foods. Trienzyme treatment is performed by using alpha-amylase and protease for folate extraction from carbohydrate and protein matrices, and folate conjugase for the hydrolysis of polyglutamyl folates. We evaluated the conditions of pH and incubation time for the treatment with alpha-amylase and protease. Four food items, including fresh beef, white bread, cow's milk, and fresh spinach, were selected for this investigation. We found that optimal pHs for alpha-amylase treatment of beef and cow's milk were 7.0 and 5.0, respectively, whereas those for white bread and spinach were not distinctive at pHs from 2.0 to 7.0. The optimal incubation time for alpha-amylase was 4 h for fresh beef and cow's milk, whereas no distinctive optimal incubation period was found for white bread and fresh spinach. Our data indicate that the conditions for enzyme treatments vary depending on food items. Trienzyme treatment resulted in an increase of more than 50% in the mean folate content over folate conjugase treatment alone. It is necessary to treat food samples with not only traditional folate conjugase, but also with alpha-amylase and protease before folate determination to obtain the actual folate content.

A high-affinity folate binding protein in fluid of benign cysts of human liver and mammary gland

The presence of a folate binding protein in fluid of benign cysts of human liver and mammary gland was demonstrated. Radioligand binding was of a high-affinity type (K approximately 10(10) M -1). The gel filtration profile of cystic fluid contained two peaks of radiolabelled folate, a large one of 25 kDa and a small one of 100 kDa. The concentration of radioligand bound protein in samples of cystic fluid ranged from nil to 6 nM. In most cases the protein immunoreacted with antibodies against human milk folate binding protein. The data suggest that fluid of human liver and mammary gland cysts contains a folate binding protein which appears to be homologous to human milk folate binding protein.

Reduced red-cell folate in mania

Forty-five hospitalised patients with DSM-III-R diagnosis of mania, were found to have a mean red-cell folate level of 193 nmol/l, as compared to 896 nmol/l in the control group (P < 0.00001). Assessment of serum folate in both groups showed no significant differences in the levels. Furthermore the manic patients and the controls were matched by the socio-economic status. This indicated that the reduced red-cell folate in mania is associated with the illness and not due to reduced absorption or dietary deficiency of folate. Considering previous studies that showed reduced red-cell folate in depression, our findings suggest that reduced red-cell folate occurred in both phases of bipolar disorders.

Phenytoin-induced depletion of folate in rats originates in liver and involves a mechanism that does not discriminate folate form

The anticonvulsant phenytoin causes a decrease in plasma concentrations of folate in epileptic patients. The mechanism underlying this depletion is unknown. To study this mechanism, phenytoin was administered to rats by addition to the diet (3 g phenytoin/kg diet) for up to 8 wk. At selected times during phenytoin administration (0, 3, 7, 10, 14, 28, 42 and 56 d), the composition of the folate pools of intestinal mucosa, liver, bile and brain was determined. The 0-d administration served as the control group. The controls were fed the same diet without phenytoin for the eight weeks of the experiment. Phenytoin administration had minimal effect on either the folate concentration or the composition of the folate pool in intestinal mucosa. Phenytoin administration did, however, cause a depletion of total hepatic folate to about 50% of control, causing the pentaglutamate derivatives of each of the pteridine derivatives to decline rapidly, with the formyl and dihydro derivatives of the pteridine moiety falling more rapidly than the methyl and methylene + tetrahydro derivatives. The monoglutamate of the methylene + unsubstituted tetrahydro derivative increased significantly with time of phenytoin treatment. The mono- and di-glutamate derivatives of the methyltetrahydrofolate increased transiently and significantly in the bile, and the polyglutamate chain length increased significantly in the brain with time of phenytoin treatment. We conclude that phenytoin inhibits the formation of polyglutamyl folates in rat liver.

High performance liquid chromatographic determination of folic acid and its photodegradation products in the presence of riboflavin

A high performance liquid chromatographic procedure was developed to determine folic acid and its photodegradation products, p-aminobenzoic acid, pterine-6-carboxylic acid, p-aminobenzoyl-L-glutamic acid, and pteroic acid in the presence of riboflavin. The method involves reversed phase, paired-ion chromatography on mu-BondaPak C18 column using a UV detector (254 nm), and isocratic solvent system (at ambient temperature) comprising 0.017 M monobasic potassium phosphate, tetrabutyl ammonium hydroxide solution (20%, aqueous) and methanol (870:15:250, v/v). The range of quantitation for the individual compounds was found to be: p-aminobenzoic acid, 0.01 - 1.25 x 10(-5) M; pterine-6-carboxylic acid, 0.01-2.0 x 10(-5) M; p-aminobenzoyl-L-glutamic acid, 0.02-2.0 x 10(-5) M; pteroic acid, 0.02-2.5 x 10(-5) M; folic acid, 1.0-5.0 x 10(-5) M; riboflavin, 1.0-5.0 x 10(-5) M. Linear regression analysis of the data demonstrates adequate performance of the method in terms of accuracy and precision (R. S. D. 3%). The method is specific, rapid and convenient and has been applied to photodegradation studies of folic acid in the presence and absence of riboflavin.

Folate depletion induced by methotrexate affects methionine synthase activity and its susceptibility to inactivation by nitrous oxide

We compared the effects of methotrexate (MTX) and nitrous oxide on the methionine (Met) synthase system in two variants of a human glioma cell line. The cells were protected from cytotoxic effect of MTX by adding thymidine and hypoxanthine to the cell culture medium. MTX (0-1 microM) was associated with a dose- and time-dependent reduction in 5-methyltetrahydrofolate (5-methyl-THF) in both cell lines. Already after 3 hr of exposure, 5-methyl-THF was reduced by 50% and after additional 48 hr, the level was undetectable. In addition to reduction in folate level, homocysteine (Hcy) remethylation in intact cells was markedly inhibited as judged by an increased export of Hcy from the cells, and Met synthase activity in cell extracts and level of cellular methylcobalamin (CH3Cbl) declined. MTX reduced Hcy remethylation and CH3Cbl level more efficiently than nitrous oxide. In both cell variants, the inactivation of Met synthase by nitrous oxide was almost completely prevented in cells pre-exposed to MTX. This indicates that there is no catalytic turnover in cells exposed to MTX, and emphasizes the importance of the sequence of administration for synergistic effect of this drug combination. In conclusion, our data show that MTX through depletion of 5-methyl-THF reduces both the Met synthase activity and the cellular CH3Cbl level. Moreover, the effect of MTX on the Hcy remethylation is more pronounced than the inhibition caused by nitrous oxide. These observations should be taken into account in studies on MTX pharmacodynamics.

Folate and 10-formyltetrahydrofolate dehydrogenase (FDH) expression in the central nervous system of the mature rat

10-Formyltetrahydrofolate dehydrogenase (10-FTHFDH) is a folate-binding protein that is important in folate metabolism. In addition, 10-FTHFDH catalyzes the rate-limiting step in hepatic folate-dependent formate oxidation. We measured folate concentrations and examined cellular 10-FTHFDH expression in regions of the adult rat central nervous system (CNS), to study components of CNS oxidative formate metabolism. Folate was detected in every CNS region studied; the concentrations ranged from 3 to 14% of that detected in the liver. Immunohistochemical expression of 10-FTHFDH was identified in many CNS structures. 10-FTHFDH was mostly expressed by glia, especially astrocytes and ventricular ependyma. Neuronal expression was weak but evident in the cerebral cortex, basal ganglia, cerebellum, and spinal cord. Thus, CNS tissue has the chief components of folate-dependent formate oxidation and the chief site of this oxidation appears to be glia.

Effect of folic acid supplementation on folate status and formate oxidation rate in mink (Mustela vision)

We investigated the folate-dependent toxicity of formate to mink to better understand the use of formic acid in fur animal feeds. Folic acid supplementation (0, 1, 5, 10, and 20 mg/kg of DM) in the feed of weanling mink for 4 wk resulted in hepatic tetrahydrofolate (H4folate) concentrations of 3.94, 8.51, 9.15, 10.4, and 15.0 nmol/g, respectively (SE 1.03). Oxidation tests in metabolic chambers, preceeding a single injection of sodium [14C]formate (500 mg/kg BW), showed that the nonsupplemented mink oxidized formate into CO2 at a rate 37% less than that of the supplemented mink. The oxidation rate increased with supplementation level and was maximal, 54.2 mEq.kg1.h1 (SE 3.0), at 10 mg of folate/kg; at the highest level of supplementation (20 mg/kg), CO2 production tended to be lower. Concentration of hepatic 14C increased with the hepatic H4folate, and its accumulation continued after the highest point of oxidation. These observations indicate that mink oxidize formate readily but at a slightly lower rate than do rats. However, if extra folate is not supplemented in the feed during the period of early intensive growth, hepatic H4folate level may decline to the levels found in humans and monkeys, which are susceptible to formate accumulation. Average daily weight gain improved with each increase in supplementation of folic acid; however, only the differences between the nonsupplemented diet and the two highest levels of the vitamin reached statistical significance (P < .05).

Unmetabolized folic acid in serum: acute studies in subjects consuming fortified food and supplements

Periconceptual consumption of folic acid has been shown to decrease the incidence of neural tube defects. The strategy of universal fortification of staple foodstuffs with folic acid presents the possibility of life-long exposure to unmetabolized folic acid. Chief among the risks of exposure to folic acid in the circulation is that of masking the diagnosis of cobalamin deficiency in pernicious anemia and the progression of neurologic disease. Other effects are unknown. For instance, the effect of in vivo chronic exposure of adult and fetal cells to the synthetic form of the vitamin has never been investigated at the population level. This study examined the acute appearance of unmetabolized folic acid in serum in response to the consumption of some fortified foodstuffs by young and elderly volunteers. Subjects on a 5-d regimen of fortified ready-to-eat-cereal and bread in addition to their normal diet had a threshold intake of 266 micrograms folic acid per meal at which unaltered folic acid appeared in the serum. Subjects given folic acid in either isotonic saline, milk, or white bread also had a threshold > 200 micrograms. From patterns of food consumption in the United States, the implementation of flour fortification at 1.4 mg/kg is unlikely to lead to folic acid appearance in serum, assuming that consumption is spread throughout the day. Increasing this level of fortification, however, as has been advocated by some agencies, may result in the repeated appearance of folic acid in serum over many years, particularly in consumers in nontargeted populations of large amounts of fortified foods. The "safe level of intake" of 1 mg folate/d set by the US Food and Drug Administration may cause a serum folic acid effect. Furthermore, a repeated serum folic acid response is likely to be found in many women complying with the advice to take 400 micrograms folic acid/d to prevent the occurrence of neural tube defects.