Accounting for an isobaric interference allows correct determination of folate vitamers in serum by isotope dilution-liquid chromatography-tandem MS

Simultaneous quantification of seven B vitamins from wheat grains using UHPLC-MS/MS

B-group vitamins are important micronutrients for maintaining human health; nevertheless, B vitamin deficiency is a globally widespread issue. Thus, it is relevant to accurately assess the B-vitamin content in staple crop products such as wheat grains. Here, we developed a multi-enzyme extraction method allowing accurate quantification of seven B vitamins in wheat using ultra high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Free forms of thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), pyridoxine (B6), biotin (B7) and folates (B9) were determined with recoveries ranging from 81 to 118% and accuracy below 15% bias. The precision was below 20% relative standard deviation and the internal standards adequately compensated for matrix effects. The method was applied to determine the B vitamin stabilities in wheat grains stored at different temperatures and periods. The results provide an important basis in future studies aiming at understanding nutritional availability of B vitamins.

Intake and biomarkers of folate and folic acid as determinants of chemotherapy-induced toxicities in patients with colorectal cancer: a cohort study

BACKGROUND

Capecitabine is an oral chemotherapeutic drug showing antitumor activity through inhibition of thymidylate synthase, an enzyme involved in folate metabolism. There are concerns about the high intake of certain vitamins, and specifically folate, during chemotherapy with capecitabine. Whether folate or folic acid, the synthetic variant of the vitamin, impact treatment toxicity remains unclear.

OBJECTIVE

We studied associations between intake and biomarkers of folate as well as folic acid and toxicities in patients with colorectal cancer (CRC) receiving capecitabine.

METHODS

Within the prospective COLON (Colorectal cancer: Longitudinal, Observational study on Nutritional and lifestyle factors that influence recurrence, survival, and quality of life) cohort, 290 patients with stage II to III CRC receiving capecitabine were identified. Dietary and supplemental intake of folate and folic acid were assessed at diagnosis and during chemotherapy using questionnaires (available for 280 patients). Plasma folate and folic acid levels were determined by liquid chromatography tandem mass spectrometry (LC-MS/MS) and were available for 212 patients. Toxicities were defined as toxicity-related modifications of treatment, including dose reductions, regimen switches, and early discontinuation. Associations of intake and biomarkers of folate and folic acid with toxicities were determined using Cox proportional hazards regression adjusted for age and sex.

RESULTS

In total, 153 (53%) patients experienced toxicities leading to modification of capecitabine treatment. Folate intake and plasma folate levels were not associated with risk of toxicities. However, use of folic acid-containing supplements during treatment (hazard ratio (HR) 1.81 and 95% confidence interval (CI) 1.15-2.85) and presence of folic acid in plasma at diagnosis (HR 2.09, 95% CI: 1.24, 3.52) and during treatment (HR 2.31, 95% CI: 1.29, 4.13) were associated with an increased risk of toxicities.

CONCLUSIONS

This study suggests a potential association between folic acid and capecitabine-induced toxicities, providing a rationale to study diet-drug interactions and raise further awareness of the use of dietary supplements during oncological treatment.

CLINICAL TRIAL DETAILS

This trial was registered at clinicaltrials.gov as NCT03191110.

Supplementation with (6S)-5-methyltetrahydrofolic acid appears as effective as folic acid in maintaining maternal folate status while reducing unmetabolised folic acid in maternal plasma: a randomised trial of pregnant women in Canada

Folic acid supplementation is recommended during pregnancy to support healthy fetal development; (6S)-5-methyltetrahydrofolic acid ((6S)-5-MTHF) is available in some commercial prenatal vitamins as an alternative to folic acid, but its effect on blood folate status during pregnancy is unknown. To address this, we randomised sixty pregnant individuals at 8-21 weeks' gestation to 0·6 mg/d folic acid or (6S)-5-MTHF × 16 weeks. Fasting blood specimens were collected at baseline and after 16 weeks (endline). Erythrocyte and serum folate were quantified via microbiological assay (as globally recommended) and plasma unmetabolised folic acid (UMFA) via LC-MS/MS. Differences in biochemical folate markers between groups were explored using multivariable linear/quantile regression, adjusting for baseline concentrations, dietary folate intake and gestational weeks. At endline (n 54), the mean values and standard deviations (or median, inter-quartile range) of erythrocyte folate, serum folate and plasma UMFA (nmol/l) in those supplemented with (6S)-5-MTHF v. folic acid, respectively, were 1826 (sd 471) and 1998 (sd 421); 70 (sd 13) and 78 (sd 17); 0·5 (0·4, 0·8) and 1·3 (0·9, 2·1). In regression analyses, erythrocyte and serum folate did not differ by treatment group; however, concentrations of plasma UMFA in pregnancy were 0·6 nmol/l higher (95 % CI 0·2, 1·1) in those supplementing with folic acid as compared with (6S)-5-MTHF. In conclusion, supplementation with (6S)-5-MTHF may reduce plasma UMFA by ∼50 % as compared with supplementation with folic acid, the biological relevance of which is unclear. As folate is currently available for purchase in both forms, the impact of circulating maternal UMFA on perinatal outcomes needs to be determined.

Human milk unmetabolized folic acid is increased following supplementation with synthetic folic acid as compared to (6S)-5-methyltetrahydrofolic acid

Folic acid supplementation is recommended perinatally, but may increase unmetabolized folic acid (UMFA) in human milk; this is concerning as it is an inactive form which may be less bioavailable for the infant. "Natural" (6S)-5-methyltetrahydrofolic acid [(6S)-5-MTHF] is available as an alternative to folic acid, and may prevent the accumulation of UMFA in human milk. Pregnant women (n = 60) were enrolled at 8-21 weeks of gestation and randomized to 0.6 mg/day folic acid or (6S)-5-MTHF. At ~ 1-week postpartum, participants provided a human milk specimen. Total human milk folate (nmol/L) and concentrations of UMFA (nmol/L) were quantified via LC-MS/MS. Differences between groups were evaluated using multivariable quantile/linear regression, adjusting for dietary folate, weeks supplementing, and milk collection methods. No significant difference in total milk folate was found; however, the median milk UMFA concentration was 11 nmol/L higher in those receiving folic acid versus (6S)-5-MTHF (95% CI = 6.4-17 nmol/L), with UMFA representing 28% and 2% of total milk folate. In conclusion, the form of supplemental folate had markedly differential effects on the human milk folate profile, with folic acid increasing the mean proportion of milk UMFA by ~ 14-fold. Investigation of whether increased UMFA impacts folate-related metabolism and infant health outcomes is required.

A sensitive, robust and high-throughput isotope dilution LC-MS/MS method for quantifying three folate forms in serum

This study aimed to establish an isotope dilution LC-MS/MS method for the determination of folic acid, 5-formyltetrahydrofolate and 5-methyltetrahydrofolate in human serum. This method was then used to quantify these three folate forms in the healthy adult population and supplement users. A stable 96-well solid-phase extraction system was used to prepare serum samples. The highly sensitive method was established using a Shimadzu LCMS-8060NX. The linearity was good in the range of 0.1-10 nmol/l for folic acid and 5-formyltetrahydrofolate and 1.0-100 nmol/l for 5-methyltetrahydrofolate. The accuracy and precision were good. The method was sensitive, robust and high-throughput and could be used for the routine clinical monitoring of these three folate forms in the Chinese population.

Development of an improved standard reference material for folate vitamers in human serum

The US National Institute of Standards and Technology (NIST) developed a Standard Reference Material® (SRM®) 3949 Folate Vitamers in Frozen Human Serum to replace SRM 1955 Homocysteine and Folate in Human Serum. The presence of increased endogenous levels of folic acid and 5-methyltetrahydrofolate (5mTHF) in SRM 3949, enhanced folate stability via addition of ascorbic acid, and inclusion of values for additional minor folates are improvements over SRM 1955 that should better serve the clinical folate measurement community. The new SRM contains folates at three levels. To produce SRM 3949, pilot sera were collected from 15 individual donors, 5 of whom were given a 400-µg folic acid supplement 1 h prior to blood draw to increase serum levels of 5mTHF and folic acid for the high-level material. To stabilize the folates, 0.5% (mass concentration) ascorbic acid was added as soon as possible after preparation of serum. These pilot sera were screened for five folates plus the pyrazino-s-triazine derivative of 4-α-hydroxy-5-methyltetrahydrofolate (MeFox) at the US Centers for Disease Control and Prevention (CDC) by isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS). Based on these results, a blending protocol was specified to obtain the three desired folate concentrations for SRM 3949. ID-LC-MS/MS analysis at the CDC and NIST was utilized to assign values for folic acid and 5mTHF, as well as several minor folates.

Association Between High Serum Tetrahydrofolate and Low Cognitive Functions in the United States: A Cross-Sectional Study

Background: The relationship between serum folate status and cognitive functions is still controversial. Objective: To evaluate the association between serum tetrahydrofolate and cognitive functions. Methods: A total of 3,132 participants (60–80 years old) from the 2011–2014 NHANES were included in this cross-sectional study. The primary outcome measure was cognitive function assessment, determined by the Consortium to Establish a Registry for Alzheimer’s Disease Word Learning Test (CERAD-WL), CERAD-Delayed Recall Test (CERAD-DR), Animal Fluency Test (AF), Digit Symbol Substitution Test (DSST), and global cognitive score. Generalized linear model (GLM), multivariate logistic regression models, weighted generalized additive models (GAM), and subgroup analyses were performed to evaluate the association between serum tetrahydrofolate and low cognitive functions. Results: In GLM, and the crude model, model 1, model 2 of multivariate logistic regression models, increased serum tetrahydrofolate was associated with reduced cognitive functions via AF, DSST, CERAD-WL, CERAD-DR, and global cognitive score (p <  0.05). In GAM, the inflection points were 1.1, 2.8, and 2.8 nmol/L tetrahydrofolate, determined by a two-piece wise linear regression model of AF, DSST, and global cognitive score, respectively. Also, in GAM, there were no non-linear relationship between serum tetrahydrofolate and low cognitive functions, as determined by CERAD-WL or CERAD-DR. The results of subgroup analyses found that serum tetrahydrofolate levels and reduced cognitive functions as determined by AF had significant interactions for age and body mass index. The association between high serum tetrahydrofolate level and reduced cognitive functions as determined using DSST, CERAD-WL, CERAD-DR, or global cognitive score had no interaction with the associations between cognition and gender, or age, or so on. Conclusion: High serum tetrahydrofolate level is associated with significantly reduced cognitive function.

Bioaccessibility of folate in faba bean, oat, rye and wheat matrices

Cereals and legumes are rich in folate. However, due to the instability of folate, processing and digestion can induce significant folate loss. In this paper, folate bioaccessibility of faba bean, oat, rye and wheat flours and pastes was studied using a static in vitro digestion model. Folate bioaccessibility depended on food matrices, varying from 42% to 67% in flours and from 40% to 123% in pastes. Digestion was associated with the interconversion of formyl folates, as well as the increase of oxidised vitamers and decrease of reduced vitamers. Especially in faba bean, 5-methyltetrahydrofolate showed surprisingly good stability both in digestion and heat treatment, resulting in high bioaccessibility. The physiological concentration of ascorbic acid did not stabilise folate in digestion; however, a higher level helped to maintain reduced vitamers. Heat treatment (10-min paste making) could improve folate bioaccessibility by liberating folate from the food matrices and by altering folate vitamer distribution.

Folate content and retention in wheat grains and wheat-based foods: Effects of storage, processing, and cooking methods

Folates are essential micronutrients for human health. The aim of this study was to evaluate the effects of storage, processing and cooking methods on folate content and identify factors with great influence on folate retention in wheat grains and wheat-based foods. For this, the folate levels of wheat grains after 2-8 months of storage, wheat flours, noodles, fermented dough, steamed bun, and bread were sequentially analyzed. An average of 26% folate loss was observed after eight-month storage in wheat grains. The milling process, with an extraction rate of 70%, led to a severe (71%) folate loss. The folate retention rate in noodles was 78%. Fermentation by yeast production enabled a 1.5-4-fold enhancement of folate levels in steamed bun and bread. Boiling, steaming and baking led to a folate loss of 13%, 16%, and 11%, respectively. These results help to guide industrial/household preparation of wheat-based foods for folate nutrition.

Serum Folate Forms Are Stable during Repeated Analysis in the Presence of Ascorbic Acid and during Frozen Sample Storage

BACKGROUND

Serum folate forms, and particularly tetrahydrofolate, are sensitive to oxidation.

METHODS

Using a repeated measures design, we investigated the stability of folate forms in convenience samples with added ascorbic acid (AA; 5 g/L) analyzed initially and after variable (approximately 1-33 weeks) storage time at -70 °C. We examined the recovery of tetrahydrofolate added at different spiking levels to serum with and without AA (5 g/L). We also assessed the long-term frozen storage stability of folate forms.

RESULTS

Repeat analysis produced consistent results with the initial analysis; the mean relative change (95% CI; Lin's concordance correlation between initial and repeat result; sample size) was 0.08% (-0.24% to 0.39%; r _c = 0.999; n = 301) for 5-methyltetrahydrofolate, 4.23% (2.44%-6.05%; r _c = 0.984; n = 211) for pyrazino-s-triazine derivative of 4α-hydroxy-5-methyltetrahydrofolate (MeFox), -0.22% (-1.90% to 1.49%; r _c = 0.986; n = 214) for folic acid, and 1.49% (-2.71% to 5.88%; r _c = 0.889; n = 81) for tetrahydrofolate. Linear regression testing for a time trend indicated an estimated average percent change of less than ±5% for samples retested after 4 months: 5-methyltetrahydrofolate P _trend = 0.0007, folic acid P _trend < 0.0001, MeFox P _trend = 0.38, and tetrahydrofolate P _trend = 0.0256. The mean ± SD tetrahydrofolate spiking recovery was 96.7% ± 9.4% for serum with added AA, but <50% for serum without added AA. We observed ≤10% loss for most serum folate forms during 4 years of storage at -70 °C.

CONCLUSIONS

Serum containing added AA showed acceptable stability of folate forms during repeat analysis from the same vial within 4 months, complete spiking recovery of tetrahydrofolate during sample processing, and long-term frozen storage stability of folate forms.

Two International Round-Robin Studies Showed Good Comparability of 5-Methyltetrahydrofolate but Poor Comparability of Folic Acid Measured in Serum by Different High-Performance Liquid Chromatography-Tandem Mass Spectrometry Methods

Background: Serum folate methods produce different results. The comparability of HPLC-mass spectrometry (MS)/MS methods is not well documented.Objective: We conducted an international "round-robin" investigation to assess the comparability, precision, and accuracy of serum folate HPLC-MS/MS methods.Methods: The CDC laboratory, 7 laboratories with independently developed methods (group 1), and 6 laboratories with an adapted CDC method (group 2) analyzed folate forms in 6 serum pools and 6 calibrators from the CDC (duplicate analysis over 2 d) and in two 3-level reference materials (duplicate analysis).Results: All laboratories measured 5-methyltetrahydrofolate (5-methylTHF) and folic acid; some measured additional folate forms. The geometric mean (range) concentrations (nanomoles per liter) for 5-methylTHF in the 6 serum pools were 18.3 nmol/L (CDC), 13.8-28.9 nmol/L (group 1), and 16.8-18.6 nmol/L (group 2); for folic acid the concentrations were 3.42 nmol/L (CDC), 1.09-4.74 nmol/L (group 1), and 1.74-2.90 nmol/L (group 2). The median imprecision (CV) for 5-methylTHF was 4.1% (CDC), 4.6-11% (group 1), and 1.7-6.0% (group 2); for folic acid it was 6.9% (CDC), 4.9-20% (group 1), and 3.9-23% (group 2). The mean ± SD (range) recovery of 5-methylTHF spiked into serum was 98% ± 27% (59-138%) for group 1 and 98% ± 10% (82-111%) for group 2; for folic acid it was 93% ± 29% (67-198%) for group 1 and 81% ± 16% (64-102%) for group 2. The mean relative bias for 5-methylTHF compared with the reference material certificate value was 12% (CDC), -24% to 30% (group 1), and -0.6% to 16% (group 2); for folic acid it was 73% (CDC), -47% to 578% (group 1), and -3.3% to 67% (group 2).Conclusions: For 5-methylTHF, group 2 laboratories demonstrated better agreement and precision, less variable spiking recovery, and less bias by using a reference material. Laboratory performance for folic acid was highly variable and needs improvement. Certified reference materials for serum folate forms and total folate are needed to improve method accuracy.

Origins of the difference between food folate analysis results obtained by LC-MS/MS and microbiological assays

To investigate the often reported disagreement in food folate quantitation between the microbiological assay and high-performance liquid chromatography methods, different foods were analyzed both by a microbiological assay and by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. For the LC-MS/MS analysis we emphasize the need for complete deconjugation of polyglutamic folate forms. Moreover, our results revealed no need for an additional enzyme treatment except in the deconjugation step. To check the efficiency of deconjugation without additional sample preparations, the amount of diglutamates was quantified and samples were screened for additional polyglutamates. A thorough investigation of a substance with a polyglutamate chain deconjugated like the folates revealed that it was an oxidation product of 5-methyltetrahydrofolate, a pyrazino-s-triazine called MeFox in previous reports. The latter is not microbiologically active and, therefore, does not contribute to the amount of total folates. But we found it is commonly present in foods, especially in those low in ascorbic acid. The microbiological assay showed different responses to the single vitamers. Therefore, it was necessary to perform calibration with the folate that had the highest portion in the folate distribution. The investigations showed that both methods can provide similar results when they both include a deconjugation step. This is particularly important for LC-MS/MS but probably also for the microbiological assay. Additionally, consideration of the folate distribution was found to be crucial for the accurate calibration of the microbiological assay.

Development of stable isotope dilution assays for the quantitation of intra- and extracellular folate patterns of Bifidobacterium adolescentis

Folate-producing bifidobacteria have been studied extensively but appropriate methods for detailed quantitation of intra- and extracellular pteroylmono- and pteroylpolyglutamate patterns are lacking. Therefore, B. adolescentis DSM 20083^T was cultivated in folate-free medium (FFM) for 24h to develop and validate stable isotope dilution assays (SIDAs) coupled with LC-MS/MS for the determination of 5-formyltetrahydrofolic acid (5-HCO-H₄folate), 10-formylfolic acid (10-HCO-PteGlu), tetrahydrofolic acid (H₄folate), folic acid (PteGlu) and 5-methyltetrahydrofolic acid (5-CH₃-H₄folate) including its di-, tri-, and tetraglutamic vitamers (5-CH₃-H₄PteGlu_2-4). The respective monoglutamylated isotopologues labelled with deuterium were used as internal standards for quantitation. Limits of detection and quantitation (LOD/LOQ) were sufficiently low to quantify 48.2nmol L^-1 5-CH₃-H₄folate (5.7/17nmolL^-1) and 71.0nmolL^-1 5-HCO-H₄folate (10/30nmolL^-1) as major folate vitamers extracellularly and 124nmolL^-1 5-CH₃-H₄folate (3.4/10nmolL^-1), 213nmolL^-1 5-HCO-H₄folate (4.8/14nmolL^-1), and 61.4nmolL^-1 H₄folate (2.3/7.0nmolL^-1) intracellularly after deconjugation. The major portion of native 5-CH₃-H₄folate vitamer was ascribed to its tetraglutamate ( > 95%). Concentrations of mono-, di-, tri-, and pentaglutamylated folates were below LOD or LOQ. Intra-assay precision coefficients of variation (CVs) ranged from 7% (at a concentration of 53.9nmolL^-1 for 5-CH₃-H₄PteGlu₄), 15% (25.5nmolL^-1 5-CH₃-H₄folate) to 18% (78.5nmolL^-1 5-HCO-H₄folate), extracellularly, and from 6% (60.7nmolL^-1 5-CH₃-H₄PteGlu₄), 7% (202nmolL^-1 5-HCO-H₄folate), 10% (67.1nmolL^-1 H₄folate) to 11% (127nmolL^-1 5-CH₃-H₄folate), intracellularly. Inter-assay precision CVs ranged from 2% (54.7nmolL^-1 5-CH₃-H₄PteGlu₄), 3% (71nmolL^-1 5-HCO-H₄folate) to 11% (48.2nmolL^-1 5-CH₃-H₄folate), extracellularly, and from 1% (61.4nmolL^-1 H₄folate), 5% (213nmolL^-1 5-HCO-H₄folate), 6% (63.5nmolL^-1 5-CH₃-H₄PteGlu₄) to 10% (124nmolL^-1 5-CH₃-H₄folate), intracellularly, thus showing excellent reproducibility. Recoveries for all analytes under study ranged between 81 and 113%. These newly developed methods enable reproducible, precise and sensitive quantitation of eight bacterially synthesized folate vitamers in two totally different matrices, including both monoglutamates and polyglutamates. Furthermore, we here present the first assay using solely monoglutamylated [²H₄]-5-CH₃-H₄folate to quantify native polyglutamate patterns of this vitamer in bacteria which might replace time-consuming determination of monoglutamates in the future.

Mass spectrometry imaging of therapeutics from animal models to three-dimensional cell cultures

Mass spectrometry imaging (MSI) is a powerful label-free technique for the investigation of the spatial distribution of molecules at complex surfaces and has been widely used in the pharmaceutical sciences to understand the distribution of different drugs and their metabolites in various biological samples, ranging from cell-based models to tissues. Here, we review the current applications of MSI for drug studies in animal models, followed by a discussion of the novel advances of MSI in three-dimensional (3D) cell cultures for accurate, efficient, and high-throughput analyses to evaluate therapeutics.

Biomarkers of Nutrition for Development-Folate Review

The Biomarkers of Nutrition for Development (BOND) project is designed to provide evidence-based advice to anyone with an interest in the role of nutrition in health. Specifically, the BOND program provides state-of-the-art information and service with regard to selection, use, and interpretation of biomarkers of nutrient exposure, status, function, and effect. To accomplish this objective, expert panels are recruited to evaluate the literature and to draft comprehensive reports on the current state of the art with regard to specific nutrient biology and available biomarkers for assessing nutrients in body tissues at the individual and population level. Phase I of the BOND project includes the evaluation of biomarkers for 6 nutrients: iodine, iron, zinc, folate, vitamin A, and vitamin B-12. This review represents the second in the series of reviews and covers all relevant aspects of folate biology and biomarkers. The article is organized to provide the reader with a full appreciation of folate's history as a public health issue, its biology, and an overview of available biomarkers (serum folate, RBC folate, and plasma homocysteine concentrations) and their interpretation across a range of clinical and population-based uses. The article also includes a list of priority research needs for advancing the area of folate biomarkers related to nutritional health status and development.

Folate status and concentrations of serum folate forms in the US population: National Health and Nutrition Examination Survey 2011-2

Serum and erythrocyte (RBC) total folate are indicators of folate status. No nationally representative population data exist for folate forms. We measured the serum folate forms (5-methyltetrahydrofolate (5-methylTHF), unmetabolised folic acid (UMFA), non-methyl folate (sum of tetrahydrofolate (THF), 5-formyltetrahydrofolate (5-formylTHF), 5,10-methenyltetrahydrofolate (5,10-methenylTHF)) and MeFox (5-methylTHF oxidation product)) by HPLC-MS/MS and RBC total folate by microbiologic assay in US population ≥ 1 year (n approximately 7500) participating in the National Health and Nutrition Examination Survey 2011-2. Data analysis for serum total folate was conducted including and excluding MeFox. Concentrations (geometric mean; detection rate) of 5-methylTHF (37·5 nmol/l; 100 %), UMFA (1·21 nmol/l; 99·9 %), MeFox (1·53 nmol/l; 98·8 %), and THF (1·01 nmol/l; 85·2 %) were mostly detectable. 5-FormylTHF (3·6 %) and 5,10-methenylTHF (4·4 %) were rarely detected. The biggest contributor to serum total folate was 5-methylTHF (86·7 %); UMFA (4·0 %), non-methyl folate (4·7 %) and MeFox (4·5 %) contributed smaller amounts. Age was positively related to MeFox, but showed a U-shaped pattern for other folates. We generally noted sex and race/ethnic biomarker differences and weak (Spearman's r< 0·4) but significant (P< 0·05) correlations with physiological and lifestyle variables. Fasting, kidney function, smoking and alcohol intake showed negative associations. BMI and body surface area showed positive associations with MeFox but negative associations with other folates. All biomarkers showed significantly higher concentrations with recent folic acid-containing dietary supplement use. These first-time population data for serum folate forms generally show similar associations with demographic, physiological and lifestyle variables as serum total folate. Patterns observed for MeFox may suggest altered folate metabolism dependent on biological characteristics.

Unmetabolized folic acid is detected in nearly all serum samples from US children, adolescents, and adults

BACKGROUND

Serum total folate consists mainly of 5-methyltetrahydrofolate (5-methylTHF). Unmetabolized folic acid (UMFA) may occur in persons consuming folic acid-fortified foods or supplements.

OBJECTIVES

We describe serum 5-methylTHF and UMFA concentrations in the US population ≥1 y of age by demographic variables and fasting time, stratified by folic acid-containing dietary supplement use. We also evaluate factors associated with UMFA concentrations >1 nmol/L.

METHODS

Serum samples from the cross-sectional NHANES 2007-2008 were measured for 5-methylTHF (n = 2734) and UMFA (n = 2707) by HPLC-tandem mass spectrometry.

RESULTS

In supplement users compared with nonusers, we found significantly higher geometric mean concentrations of 5-methylTHF (48.4 and 30.7 nmol/L, respectively) and UMFA (1.54 and 0.794 nmol/L, respectively). UMFA concentrations were detectable (>0.3 nmol/L) in >95% of supplement users and nonusers, regardless of demographic or fasting characteristics; concentrations differed significantly by age and fasting time, but not by sex and race-ethnicity, both in supplement users and nonusers. The prevalence of UMFA concentrations >1 nmol/L was 33.2% overall and 21.0% in fasting (≥8 h) adults (≥20 y of age). Using multiple logistic regression analysis, UMFA concentrations >1 nmol/L were associated with being older, non-Hispanic black, nonfasting (<8 h), having smaller body surface area, higher total folic acid intake (diet and supplements), and higher red blood cell folate concentrations. In fasting adults, a decrease in the mean daily alcohol consumption was also associated with increased odds of UMFA concentrations >1 nmol/L.

CONCLUSIONS

UMFA detection was nearly ubiquitous, and concentrations >1 nmol/L were largely but not entirely explained by fasting status and by total folic acid intake from diet and supplements. These new UMFA data in US persons ≥1 y of age provide much-needed information on this vitamer in a fortified population with relatively high use of dietary supplements.

The loss of 5-methyltetrahydrofolate in human serum under suboptimal preanalytical conditions can only partially be recovered by an oxidation product

BACKGROUND

Maintaining folate stability during sample handling is important, yet challenging.

OBJECTIVE

We investigated the effects of suboptimal preanalytical conditions on serum folate stability.

METHODS

By using an HPLC-tandem MS method we measured folates [5-methyltetrahydrofolate (5-methylTHF), folic acid, MeFox (5-methylTHF oxidation product, pyrazino-s-triazine derivative of 4α-hydroxy-5-methylTHF), and other minor folate forms at or below the limit of detection] in human serum exposed to suboptimal conditions.

RESULTS

Whole blood samples (n = 21) stored at 32°C for ≤ 3 d (Expt. 1: delayed processing) showed significant decreases in serum total folate (tFOL; sum of folate forms: 11-32%, 5.5-15.9 nmol/L) and 5-methylTHF (36-62%, 14.5-25.1 nmol/L) and a significant increase in MeFox (346-415%, 7.17-8.63 nmol/L). Serum samples (n = 21) stored at 11°C for 7-14 d (Expt. 2: delayed freezing) also showed significant decreases in tFOL (4.6-10.4%, 2.3-5.1 nmol/L) and 5-methylTHF (8.4-29%, 3.4-11.6 nmol/L) and significant increases in MeFox (88-320%, 1.82-6.62 nmol/L). The molar loss in 5-methylTHF exceeded the gain in MeFox in these 2 experiments. When we exposed 3 serum pools (tFOL: 16.7-58.3 nmol/L) for 24 h to an elevated temperature of 37°C (Expt. 3), the significant decrease in 5-methylTHF (33% on average) was compensated for by an equimolar gain in MeFox. Repeated freeze/thaw cycles (≤ 3 cycles) of serum [closed (Expt. 4) and open (Expt. 5) vials] showed generally stable folates with small (<1 nmol/L) changes. Long-term (≤ 12 mo) exposure of 3 serum pools (tFOL: 17.5-63.7 nmol/L) to a suboptimal (-20°C) freezing temperature (Expt. 6) showed significant decreases in tFOL (5% on average) already after 3 mo. The molar loss in 5-methylTHF exceeded the gain in MeFox. Folic acid generally showed good stability.

CONCLUSIONS

To avoid folate losses, unprocessed whole blood should be protected from elevated temperatures and serum should not be refrigerated for >2 d or for a long term stored at -20°C.

Folate determination in human health: UPLC-MS/MS is the emerging methodology of choice

This Perspective provides a brief description of the essential role that folates play in human health, together with an overview of the various analytical methods that have been used for quantitation of folates in human populations over the past few decades. Essentially, folate methodology has evolved from microbiological assay-based, to binding-based technology and, more recently, to separation-based methodology. Separation-based methods initially used traditional LC in conjunction with various detection techniques, with the most recent methods utilizing UPLC-MS/MS. Current UPLC methods offer exceptional speed, sensitivity and quantitation ability for the monoglutamate folate isoforms. It appears that the only limitation to properly quantifying all folates as polyglutamates, some 40-50 species, is the current lack of corresponding stable-isotope standards. Clearly, UPLC-MS/MS is emerging as the 'method of choice' for the determination of folates, whether in support of basic research, clinical investigations or population studies.

Nutrient intake values for folate during pregnancy and lactation vary widely around the world

Folate is a B-vitamin with particular importance during reproduction due to its role in the synthesis and maintenance of DNA. Folate is well known for its role in preventing neural tube defects (NTDs) during the periconceptional period. There is also an increased need for folate throughout pregnancy to support optimal growth and development of the fetus and blood volume expansion and tissue growth of the mother. During lactation, women are at risk of folate deficiency due to increased demands to accommodate milk folate levels. Nutrient Intake Values (NIVs) for folate have been calculated to take into account additional needs during pregnancy and lactation. However, these values vary widely between countries. For example, the folate requirement that is set to meet the needs of almost all healthy women during pregnancy varies from 300 µg/day in the United Kingdom to 750 µg/day in Mexico. Currently, there is no accepted standardized terminology or framework for establishing NIVs. This article reviews country-specific NIVs for folate during pregnancy and lactation and the basis for setting these reference values.

A high-throughput LC-MS/MS method suitable for population biomonitoring measures five serum folate vitamers and one oxidation product

Small specimen volume and high sample throughput are key features needed for routine methods used for population biomonitoring. We modified our routine eight-probe solid phase extraction (SPE) LC-MS/MS method for the measurement of five folate vitamers [5-methyltetrahydrofolate (5-methylTHF), folic acid (FA), plus three minor forms: THF, 5-formylTHF, 5,10-methenylTHF] and one oxidation product of 5-methylTHF (MeFox) to require less serum volume (150 μL instead of 275 μL) by using 96-well SPE plates with 50 mg instead of 100 mg phenyl sorbent and to provide faster throughput by using a 96-probe SPE system. Total imprecision (10 days, two replicates/day) for three serum quality control pools was 2.8-3.6% for 5-methylTHF (19.5-51.1 nmol/L), 6.6-8.7% for FA (0.72-11.4 nmol/L), and ≤11.4% for the minor folate forms (<1-5 nmol/L). The mean (±SE) recoveries of folates spiked into serum (3 days, four levels, two replicates/level) were: 5-methylTHF, 99.4 ± 3.6%; FA, 100 ± 1.8%; minor folates, 91.7-108%. SPE extraction efficiencies were ≥85%, except for THF (78%). Limits of detection were ≤0.3 nmol/L. The new method correlated well with our routine method [n = 150, r = 0.99 for 5-methylTHF, FA, and total folate (tFOL, sum of folate forms)] and produced slightly higher tFOL (5.6%) and 5-methylTHF (7.3%) concentrations, likely due to the faster 96-probe SPE process (1 vs. 5 h), resulting in improved SPE efficiency and recovery compared to the eight-probe SPE method. With this improved LC-MS/MS method, 96 samples can be processed in ~2 h, and all relevant folate forms can be accurately measured using a small serum volume.