Improved microbiological assay for folic acid based on microtiter plating with Streptococcus faecalis

We have developed an improved method, using 96-well microtiter plates, for the microbiological assay of folic acid. With this method, the tedium of conventional microbiological analysis is substantially decreased. Culture volumes have been reduced 33-fold, and pipetting procedures have been simplified. Assay time has been reduced to 14 h, and sensitivity has increased 10-fold (0.1 ng/mL). Analytical recoveries range from 98 to 104%. Intra-assay and interassay variabilities are less than 11%. The assay does not require extensive manipulation of inoculum. Day-to-day variability has been minimized by using saline aliquots of the bacterial suspension stored at 4 degrees C. The procedure is accurate, selective, and useful for direct measurement of folic acid in multivitamin formulations.

Postpartum folic acid supplementation of adolescents: impact on maternal folate and zinc status and milk composition

The objectives of the present study were to assess the impact of lactation on the folate status of adolescents and determine the effect of ingestion of a low-dose postpartum (PP) folic acid supplement on maternal folate and zinc status and milk composition. Pregnant adolescents (aged 14-19 y; n = 71) were recruited; those who initiated breast-feeding on delivery were randomly assigned to a folic acid supplement lactating (SL; 300 micrograms/d, n = 14) group or to a placebo lactating (PL; n = 15) group. Subjects who initiated formula feeding were given a placebo (FF; n = 18). Dietary intakes (two 24-h recalls) were recorded and blood and milk samples were collected at 4, 8, and 12 wk PP. Of the adolescents, 71%, 48%, 67%, and 60% had folate, iron, vitamin B-12, and zinc intakes, respectively, below their predicted requirements. Despite this, most blood indexes were within normal ranges, probably reflecting the subjects' use of supplements during pregnancy. Red blood cell (r = -0.49, P < 0.05) and plasma (r = -0.42, P = 0.08) folate concentrations were negatively correlated with milk zinc concentrations. Mean red blood cell folate content declined between 4 and 12 wk PP among PL (31%) and FF (34%) subjects (P < 0.05) but not among SL subjects. Hence, 300 micrograms folic acid/d was sufficient to prevent a decline in blood folate values of these adolescents PP.

Micellar-enhanced synchronous-derivative fluorescence determination of derivatized folic acid in pharmaceutical preparations

A sensitive and inexpensive micellar-enhanced synchronous-derivative spectrofluorimetric method is described for the determination of folic acid in pharmaceutical preparations. The method is based upon derivatization of the vitamin with fluorescamine in acid solution and enhancement of the fluorescence with a surfactant. Linear fluorimetric analytical curves were obtained for folic acid concentrations of 0.05-6 micrograms ml-1 (detection limit 0.012 micrograms ml-1); the RSD for 1 micrograms ml-1 of folic acid was 2.82%. The method has been applied to the determination of folic acid synthetic mixtures and pharmaceutical preparations.

Folic acid content in thermostabilized and freeze-dried space shuttle foods

This study was designed to determine whether freeze-dried and thermostabilized foods on a space shuttle contain adequate folate and to investigate any effects of freeze-drying on folacin. Frozen vegetables were analyzed after three states of processing: thawed; cooked; and rehydrated. Thermostabilized items were analyzed as supplied with no further processing. Measurable folate decreased in some freeze-dried vegetables and increased in others. Folacin content of thermostabilized food items was comparable with published values. We concluded that although the folacin content of some freeze-dried foods was low, adequate folate is available from the shuttle menu to meet RDA guidelines.

Simultaneous measurement of one-carbon and polyglutamate derivatives of folic acid in rat liver using enzymatic interconversions of folates followed by ternary complex formation with thymidylate synthetase and 5-fluorodeoxyuridylic acid: standardization of the method

A sensitive assay is needed for the measurement of individual folate derivatives in samples that contain low concentrations of folate. The ternary complex method for the determination of folylpolyglutamates has been combined with procedures for interconverting folate derivatives to provide a method capable of measuring 28 different folate derivatives in biological samples. The method takes advantage of the properties of the ternary complex formed with thymidylate synthetase, fluorodeoxyuridylic acid and 5,10-methylenetetrahydrofolic acid. In the presence of excess purified thymidylate synthetase and excess [3H]fluorodeoxyuridylic acid, limiting concentrations of folates were converted to 5,10-methylenetetrahydrofolate using purified folate interconverting enzymes. This process separated folate derivatives into four groups: Tetrahydrofolate + 5,10-methylenetetrahydrofolate; dihydrofolate; 5,10-methenyl-, 5-formyl-, and 10-formyltetrahydrofolates and 5-methyltetrahydrofolate. Within groups specificity was good, showing little overlap between folates. Sensitivities to 100 fmol of folate were achievable and to 1 pmol were standard. Recoveries were linear for each of the groups in this system to 50 pmol of folate. Ternary complexes containing different polyglutamates were separated by isoelectric focusing, visualized by fluorography and measured by densitometry. The densitometry was linear with folate concentration in the range 20-200 fmol for each of the polyglutamates. Primary and secondary coefficients of variation were determined. This method provides the sensitivity to measure individual folates in the femtomole range and the flexibility to determine the concentrations of 28 separate pools of folate derivatives, differentiating between derivatives of the pteridine moiety and glutamate chain length simultaneously.

Neural tube defects and elevated homocysteine levels in amniotic fluid

OBJECTIVE

Our purpose was to study maternal blood and amniotic fluid concentrations of homocysteine and relevant vitamins in relation to neural tube defects.

STUDY DESIGN

Concentrations of total homocysteine, folate, and vitamins B12 and B6 were measured in maternal blood and amniotic fluid of 27 women carrying a fetus with a neural tube defect and 31 control women carrying a healthy fetus.

RESULTS

The mean total homocysteine concentration in amniotic fluid of the study group was significantly higher than that of the control group. The mean concentrations of total homocysteine in blood and the vitamins folate, B12, and B6 in, respectively, blood and amniotic fluid were not significantly different between the groups. The mean concentrations of homocysteine and vitamin B6 were significantly lower in amniotic fluid than in blood in both groups, whereas vitamin B12 in amniotic fluid was higher than in blood.

CONCLUSION

These results support the hypothesis that at least the cause of a subset of neural tube defects could reside in a primary or secondary maternal or fetal derangement of homocysteine metabolism.

[Intake of folic acid in the total daily diet--effect of food preparation on its folic acid content]

The folic acid content of total daily diet was determined by means of high-performance liquid chromatography (HPLC). The contents of tetrahydrofolic acid (THF), 5-methyl-THF and 5-formyl-THF were differentiated. The mean of the folic acid content of the total daily diet samples determined analytically was 205 +/- 60 micrograms and the mean of the individual ingredients of the samples was 401 +/- 78 micrograms, which implies that about 50% of folic acid is destroyed by common household food preparation methods. If the contents of pteroylglutamic acid (PteGlu) and 10-formyl-PteGlu (which cannot be determined analytically) are added, it can be assumed that the folic acid content with only be reduced by about 40%. THF and 5-methyl-THF proved to be less stable than 5-formyl-THF. The monoglutamate portion of the total folat content was higher in the total diet samples than in the individual foodstuffs as a consequence of the action of the enzyme "deconjugase" which is released when the matrix of food-stuffs is destroyed.

[Folic acid and pregnancy. Société française de pdiatrie--Comité de nutrition]

Epidemiological studies have shown a relationship between maternal folic acid status and the incidence of neural tube defects, prematurity, abortions. Based on the actual data, the Committee of Nutrition recommends that all women at age of procreation should be encouraged to regularly eat fresh fruits and vegetables in order to increase their reserve of folic acid, and that pregnant and lactating women should be supplemented with a daily dose of 200 micrograms of folic acid. In addition, the Committee is in favour of a folacin enrichment of some food which would allow to cover the needs of pregnant and lactating women. Those women who gave birth to a child with neural tube defects must be informed of the high risk of recurrence and be encouraged to take a treatment of 4 mg/day of folic acid, ideally starting one month before the beginning of pregnancy and to be maintained during the first 3 months.

Separation of vitamin B complex and folic acid using TLC plates impregnated with some transition metal ions

The separation of Vitamin B complex and folic acid was achieved on silica gel layers impregnated with Mn++, Fe++, Co++, Ni++, Cu++, Cd++, Zn++, or Mg++ (0.1%, 0.2%, 0.3%, 0.4% of each ion). Three new solvent systems n-propanol: n-butanol:water:ammonia (7:5:1:2, by vol), n-propanol:n-butanol:water:ammonia (7:5:1:1.5, by vol), n-propanol:n-butanol:water:ammonia (7:5:0.75:2, by vol) were developed. The spots of vitamins were located by exposing the chromatoplate to iodine vapours.

[Dietary folates--a timely review. Stability, physiological significance, bioavailability, analytical determination methods, effect of food handling]

Because of the unequal and, in some instances, low stability of different folate vitamers against extreme conditions the analytical determination of folate and the estimation of folate losses in food processing and preparation cause considerable difficulties. HPLC allows determination of the native folate derivative patterns. As the bioavailability of folates is influenced by a variety of factors and different methods were employed for assessing bioavailability there is a considerable inconsistency in the results of these studies. Folates labeled with radioactive or stable isotopes provide new approaches to metabolic and bioavailability studies.

Concentrations of folates in ruminal content of steers: responses to a dietary supplement of folic acid in relation with the nature of the diet

In an attempt to evaluate the ruminal effects of dietary supplements of folic acid, eight steers (352 +/- 27 kg BW) fitted with a ruminal cannula were randomly assigned to a replicated 4 x 4 Latin square design. The treatments were 70% rolled barley + 30% timothy hay (HC), HC + 2 mg of folic acid per kilogram of BW (HC + FA), 30% rolled barley + 70% timothy hay (HF), and HF + 2 mg of folic acid per kilogram of BW (HF + FA). After 5 wk of adaptation to the dietary treatments, ruminal contents were sampled over three consecutive days, at 1, 2, 4, 8, 12, and 23 h after feed distribution. Concentrations of folates in solid and liquid ruminal fractions were increased by the dietary supplement of folic acid (P = .0001) and by the ingestion of concentrate compared with hay-based diets (P < .05). Preprandial concentrations of serum folates were not affected by the nature of the diet when steers received no folic acid but the increase of serum folates induced by the dietary supplement of folic acid was more important in steers fed concentrates than in those fed hay-based diets (diet x supplement of folic acid interaction P = .002). Microbial protein (P = .004) and microbial mass (P = .002) in ruminal fluid were increased with concentrate-based diets compared with hay-based diets; folic acid did not have any effect on these variables (P > .05). In conclusion, concentrations of folates in ruminal contents were affected by dietary supplements of folic acid and by the nature of the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Thymidylate synthase activity, folates, and glutathione system in head and neck carcinoma and adjacent tissues

BACKGROUND

Head and neck squamous cell carcinomas (HNSCC) present variable aggressiveness and chemosensitivity. Because the glutathione (GSH) system and thymidylate synthase (TS) are involved in the resistance to the main drugs used in HNSCC (cisplatin and 5-FU), we studied these systems in tumors and normal mucosae.

METHODS

Tumor samples and normal adjacent mucosae were collected from 37 untreated HNSCC patients. GSH and glutathione S-transferase (GST) activity were assayed by spectrophotometry, whereas TS activity and folates were determined by radioassays.

RESULTS

Mean GSH levels were higher in tumors (15.2 +/- 8.2 nmol/mg protein) than in mucosae (8.3 +/- 4.1 nmol/mg protein) (p = 0.005, paired t test). GST activity was also higher in tumors (394 +/- 194 nmol/min/mg protein) than in mucosae (261 +/- 132 nmol/min/mg protein) (p = 0.0003). TS activity was markedly higher in tumors (9.2 +/- 21.5 pmol/min/mg protein) compared to that of mucosae (0.9 +/- 1.2 pmol/min/mg protein) (p = 0.0001). Folate levels in tumors and mucosae were similar (1.2 +/- 1.1 and 0.8 +/- 0.9 pmol/mg protein, respectively; p = 0.1, NS). In relation to clinical stage and tumor size, a statistical difference was found in GSH and GST values between tumors and mucosae for stage IV and T3/T4. The increase in tumor TS compared to that of mucosae was significant for all clinical stages, tumor sizes, and nodal involvement.

CONCLUSIONS

These data enhance our understanding of the enzymatic systems involved in cisplatin and 5-fluorouracil (5-FU) resistance in HNSCC and normal mucosae and may help to elucidate tumor behavior and interpatient differences in drug sensitivity.

Animal model for the study of methanol toxicity: comparison of folate-reduced rat responses with published monkey data

We attempted to develop a rodent model that exhibits characteristics of human methanol toxicities such as acidosis and visual dysfunction, which are correlated with an accumulation of formate, a toxic metabolite of methanol. Initially three groups of Long-Evans rats with different levels of liver folate were prepared and examined for formate accumulation after methanol administration (3.5 g/kg). The folate-reduced (FR) rats prepared by feeding a folate-deficient diet with 1% succinylsulfathiazole yielded blood formate levels equivalent to those found in methanol-intoxicated humans and developed signs of the visual system toxicity (a manuscript on the latter aspect is in preparation). Responses of FR rats to a variety of methanol exposure scenarios were then investigated, and the results were compared with those reported in the literature for monkeys. Formate accumulation and/or lethality were used as toxic parameters for this comparative evaluation. In FR rats dosed orally with 3 g/kg, the blood formate concentration was 9.2 mmol/L at 24 h postadministration and increased to 15.6 mmol/L at 48 h. The same dose given to monkeys yielded a plateau of 7.4 mmol/L at 12 h after methanol administration, and stayed at this level for an additional 12 h. The area under the concentration vs. time curve for blood formate in FR rats was 2.5-fold greater than that in monkeys when 2.0 g/kg methanol was administered. After a 6-h exposure to 1200 ppm and 2000 ppm methanol, the blood formate concentrations in FR rats were increased by 370% and 636% above the endogenous level, respectively. However, blood formate did not accumulate above the endogenous level when monkeys were exposed to methanol up to 2000 ppm for 6 h. Under acute inhalation exposure conditions, FR rats exposed to 3000 ppm methanol, 20 h/d, could not survive more than 4 d. On the other hand, monkeys exposed to 3000 ppm, 21 h/d, out-lived 20 d. Moreover, monkeys survived for more than 4 d even after an exposure to 10,000 ppm. Thus, these results indicate that FR rats are more sensitive to methanol challenges than monkeys, and suggest that the FR rat could be a congruous animal model for evaluating the health effects of methanol in humans.

Methotrexate content in squamous cell carcinoma of the head and neck after low-dose methotrexate

Eleven patients with squamous carcinoma of the head and neck who were scheduled for surgical resection or endoscopic biopsy of tumor received 15 mg/m2 of methotrexate (MTX). Samples of tumor, normal mucosa, and plasma were obtained at surgery or endoscopy, 18-24 hours after the last MTX dose. Tissue content and plasma concentration of MTX and folate were measured using sequential radioligand-binding assays. Median MTX content was 50.0 pmol/g wet weight in tumor, 19.0 in normal mucosa, and < 0.5 nM (pmol/ml) in plasma. Since dihydrofolate reductase (DHFR) content of human tumors has previously been shown to be less than 5 pmol enzyme/g wet weight, tumor MTX content exceeded expected DHFR content in all but one patient. These data support the concept that low doses of MTX saturate tumor DHFR and that, in this regard, dose escalation may have limited value.

Folic acid age correlation established on folates determinations in cell homogenates

From the available data, there has resulted that folic acid quantity in homogenate, coming from various organs, collected from young animals is much larger than for the other age categories. These results may be correlated with intense cell proliferation and development processes that take place in the young tissues as compared to rather low values established from grown-ups and old ranges. When comparing the folates quantity found in homogenate resulting from various organs we may ascertain that, if the folates are related to grams of tissue under the test, they are more in spleen than in kidneys, liver and brains respectively. If the folates are reported to tissue protein milligrams it may be ascertained that a larger quantity of folates is found in the brains than in the other studied organs that may be due to big dilution of the proteins in the brains.

[Determination of the folic acid content of grain, cereal products, baked goods and legumes using high-performance liquid chromatography (HPLC)]

The folic acid content of grain, cereal products (including beer), bakery products and legumes was determined by means of high-performance liquid chromatography (HPLC). Free folate (monoglutamate forms) and total folate (monoglutamate + polyglutamate forms) were differentiated. Of the grain analysed, rye, with a mean value of 143 micrograms/100 g, contained more total folate than wheat (mean = 91 micrograms/100 g). The total folate content of bakery products ranged from 14 micrograms/100 g (whole grain rye bread) to 88 micrograms/100 g (crispbread). Beer had a very low total folate content (mean = 3 micrograms/100 ml). The mean of the free folate portion was 76.5% in grain and cereal products and 65.6% in bakery products. Of the legumes analysed, beans (mean = 128 micrograms/100 g) had the highest content of total folate, followed by lentils (103 micrograms/100 g) and peas (57 micrograms/100 g). The mean value of the free folate portion in legumes (73.1%) was comparable with the values of grain, cereal products and bakery products. In addition to tetrahydrofolic acid (THF), 5-methyl-THF and 5-formyl-THF, pteroylglutamic acid (PteGlu) and 10-formyl-PteGlu were determined in all products (except beer). Their proportion (PteGlu + 10-formyl-PteGlu) of the total folate content ranged from 23.5% to 44.4%.

Study on the presence of homocysteine in ovarian follicular fluid

OBJECTIVE

To study the presence of homocysteine, methionine and the vitamins folate, B12, and B6 in human ovarian follicular fluid (FF).

DESIGN

Measurement of homocysteine, methionine, folate, and vitamins B12 and B6 in ovarian FF and blood.

SETTING

Academic Department of Obstetrics and Gynecology at St. Radboud Hospital, Nijmegen, The Netherlands.

PARTICIPANTS

Fourteen healthy women undergoing an IVF program.

RESULTS

Detectable amounts of homocysteine and methionine were found in FF. Homocysteine concentrations were similar to those in serum. Methionine concentrations proved to be slightly but significantly lower than in corresponding serum samples. Concentrations of vitamins B12 and B6 were significantly lower in FF than in serum, whereas folate concentrations were not significantly different. A statistically significant correlation between corresponding serum and FF concentrations of homocysteine, folate, and vitamin B12 could be established.

CONCLUSIONS

These data support the hypothesis that the ovum might be exposed to high homocysteine or low methionine concentrations, or both, and a lack of vitamins, which might be important in fertilization and early embryogenesis.

Folate metabolism and deposition in eggs by laying hens

White Leghorn hens were fed purified folate-deficient diets or commercial corn- and soybean meal-based diets supplemented with different amounts of folic acid. The folate contents of egg yolk and blood plasma from these hens were estimated with an isotope-dilution, radioligand-binding assay. Folates in egg yolk were concentrated approximately 43-fold relative to the blood plasma from which they were derived. Yolk and plasma folate concentrations became saturated with increasing dietary folate. Hens fed a commercial, folate-sufficient diet (0.72 mg folate/kg) produced eggs with slightly less than half of the maximal folate content. Based on tritium deposition in egg yolk and egg white, the biological half-life of [3H]folic acid injected intraperitoneally into two folate-sufficient hens was approximately 15 days, while it was > or = 40 days in two hens fed a purified folate-deficient diet (0.07 mg folate/kg) that also reduced egg production. Radioactivity in egg yolk was concentrated more than 100-fold relative to egg white in both cases. The [3H]folates remaining in the hens at the end of the experiment were substantially more concentrated in liver than in kidney, heart, or skeletal muscle. The specific radioactivity of folates in the liver of folate-deficient hens after 78 days was almost 10 times greater than in folate-sufficient hens after 39 days. Laying hens have highly efficient conservation and delivery systems for folates.

Influence of sous vide processing, steaming and boiling on vitamin retention and sensory quality in broccoli florets

In this study the effect of sous vide processing, steaming and traditional boiling of broccoli florets on retention of ascorbic acid, vitamin B6 and folacin was investigated. Freshly prepared samples were also sensorily evaluated. In all heat treatments ascorbic acid was found to have the highest retention, and was therefore judged not to be suitable as an indicator for vitamin retention in general. When the three types of heat treatment were compared, boiling showed lowest retention of all the vitamins examined (45-64% in 5 min), whereas sous-vide processing gave the highest retentions (97-100% in 5 min). Retentions during steaming were a little lower (83-100% in 5 min). Sensory evaluation showed that sous-vide cooked and steamed broccoli florets generally had higher acceptability than boiled.

Pancreatic one-carbon metabolism in early folate deficiency in rats

An amino acid-defined, folate-deficient diet was used to investigate the regulation of pancreatic glycine N-methyltransferase in vivo. This enzyme modulates the ratio of S-adenosylmethionine to S-adenosylhomocysteine and is inhibited by bound folate in vitro. Rats were fed either a folate-deficient diet, a folate-supplemented diet (pair-fed to the deficient group), or a folate supplemented diet ad libitum and measurements were made after 2, 3, and 4 wk. Folate concentrations were greatly reduced in the folate-deficient pancreas after only 2 wk and pancreatic glycine N-methyltransferase activity was elevated but the amount of immunologically measured enzyme protein was the same. The ratio of S-adenosylmethionine to S-adenosylhomocysteine was rapidly reduced in the deficient pancreas. This ratio was also reduced with age in the ad libitum control rats. The pancreas of deficient rats had more immature secretory granules and the ducts were devoid of secreted material.

[The determination of the folic acid content of foods of animal origin using high performance liquid chromatography (HPLC)]

The folic acid content of food of animal origin was determined by means of high-performance liquid chromatography (HPLC). Free folate (monoglutamate forms) and total folate (monoglutamate + polyglutamate forms) were differentiated. Liver (bovine 963, hog 136 micrograms/100 g) and kidney (bovine 410, hog 93 micrograms/100 g) contained the highest content of total folate, followed by egg (67 micrograms/100 g), soft cheese (44-62 micrograms/100 g), milk and other dairy products (3-28 micrograms/100 g). Chicken, fish, beef and pork contained only a low content of total folate (1-12 micrograms/100 g). The free folate portion ranged from 14.7 to 100% (mean 69.2%). The main folate derivatives tetrahydrofolic acid (THF), 5-methyl-THF and 5-formyl-THF showed the following distribution. In milk and milk products the mean was 70% for 5-formyl-THF, 20% for 5-methyl-THF and 10% for THF; in the other products the three derivatives were distributed about equally but the range of variation was high.

Decreased vitamin B12 and folate levels in cerebrospinal fluid and serum of multiple sclerosis patients after high-dose intravenous methylprednisolone

Twenty-one patients (15 women, 6 men) with definite multiple sclerosis (MS) were treated with 1000 mg intravenous methylprednisolone-succinate (MP) daily for 10 days. Before MP treatment there was a negative correlation (r = 0.59, P = 0.0084) between serum vitamin B12 and progression rate, defined as the ratio of the score on Kurtzke's Expanded Disability Status Scale and disease duration. A significant decrease was demonstrated in the cerebrospinal fluid (CSF) and serum levels of folate and in the CSF level of vitamin B12 after MP treatment. The decrease in serum B12 was not statistically significant. After MP treatment all median levels of vitamin B12 and folate were below the reference medians. We hypothesize that low or reduced vitamin B12/folate levels found in MS patients may be related to previous corticosteroid treatments. Otherwise a more causal relationship between low vitamin B12/folate and MS cannot be excluded. Further studies may be required to clarify the vitamin B12 and folate metabolism in patients with MS.