Analytical recovery of folate and its degradation products in human serum stored at -25 degrees C for up to 29 years

Aging-accumulated methylmalonic acid serum levels at breast cancer diagnosis are not associated with distant metastases

PURPOSE

Recent evidence suggests that age-accumulated methylmalonic acid (MMA) promotes breast cancer progression in mice. This study aims to investigate the association between baseline serum MMA concentrations in patients with breast cancer and the development of subsequent distant metastases.

METHODS

We included 32 patients with early Luminal B-like breast cancer (LumB, median age 62.4y) and 52 patients with early triple-negative breast cancer (TNBC, median age 50.5y) who developed distant metastases within 5 years. They were matched to an equal number of early breast cancer patients (median age 62.2y for LumB and 50.5y for TNBC) who did not develop distant metastases with at least 5 years of follow-up.

RESULTS

Baseline serum MMA levels at breast cancer diagnosis showed a positive correlation with age (P < 0.001) and a negative correlation with renal function and vitamin B12 (all P < 0.02), but no statistical association was found with BMI or tumor stage (P > 0.6). Between matched pairs, no significant difference was observed in MMA levels, after adjusting for kidney function and age (P = 0.19). Additionally, in a mouse model, a significant decline in MMA levels was observed in the tumor-bearing group compared to the group without tumors before and after tumor establishment or at identical times for the control group (P = 0.03).

CONCLUSION

Baseline serum MMA levels in patients with breast cancer are not correlated with secondary distant metastasis. Evidence in the mouse model suggests that the presence of a tumor perturbates MMA levels.

Associations between folic acid supplement use and folate status biomarkers in the first and third trimesters of pregnancy in the Maternal-Infant Research on Environmental Chemicals (MIREC) Pregnancy Cohort Study

BACKGROUND

Achieving optimal folate status during early gestation reduces the risk of neural tube defects (NTDs). While inadequate folate intake remains a concern, it is becoming increasingly common for individuals to consume higher than recommended doses of folic acid (FA) with minimal additional benefit.

OBJECTIVE

Here, we sought to investigate the determinants, including FA supplement dose and use, of plasma total and individual folate vitamer concentrations in the first and third trimesters of pregnancy.

METHODS

Using data from the Maternal-Infant Research on Environmental Chemicals (MIREC) Study, a cohort exposed to mandatory FA fortification, we measured plasma total folate and individual folate vitamer [5-methyltetrahydrofolate (5-methylTHF), unmetabolized FA (UMFA), and non-methyl folates (sum of THF, 5-formylTHF, 5,10-methenyl-THF)] concentrations in the first and third trimesters (n = 1,893). Using linear mixed models, we estimated associations between plasma folate concentrations, total daily supplemental FA intake, plasma vitamin B-12 concentrations, and multiple demographic, maternal, and reproductive factors.

RESULTS

Almost 95% of MIREC study participants met or exceeded the recommended daily supplemental FA intake from supplements (≥400 μg/d), with approximately 25% consuming more than the Tolerable Upper Intake Level (>1000 μg/d). Over 99% of MIREC participants had a plasma total folate status indicative of maximal NTD risk reduction (25.5 nmol/L) regardless of FA supplement dose. UMFA was detected in almost all participants, with higher concentrations associated with higher FA doses. Determinants of adequate FA supplement intake and folate status associated with reduced NTD risk included indicators of higher socioeconomic position, higher maternal age, nulliparity, and lower prepregnancy BMI.

CONCLUSIONS

In the context of mandatory FA fortification, our data indicate that higher-than-recommended FA doses are unwarranted, with the exception of individuals at higher risk for NTDs. Ideally, prenatal supplements would contain 400 rather than 1000 µg FA, thereby enabling the consumption of optimal and safe FA doses.

Characterizing the extent human milk folate is buffered against maternal malnutrition and infection in drought‐stricken northern Kenya

Objectives

Folate is an essential nutrient fundamental to human growth and development. Human milk maintains high folate content across the maternal folate status range, suggesting buffering of milk folate with prioritized delivery to milk at the expense of maternal depletion. We investigated whether and how the extent of this buffering may diminish under prolonged nutritional and/or disease stress, while taking into consideration infants' varying vulnerability to malnutrition‐related morbidity/mortality.

Methods

A cross‐sectional study analyzed milk specimens from northern Kenyan mothers (n  = 203), surveyed during a historic drought and ensuing food shortage. Multiple regression models for folate receptor‐α (FOLR1) in milk were constructed. Predictors included maternal underweight (BMI < 18.5), iron‐deficiency anemia (hemoglobin <12 g/dl and dried‐blood‐spot transferrin receptor >5 mg/L), folate deficiency (hyperhomocysteinemia, homocysteine >12 or 14 μmol/L), inflammation (serum C‐reactive protein >5 mg/L), infant age and sex, and mother‐infant interactions.

Results

In adjusted models, milk FOLR1 was unassociated with maternal underweight, iron‐deficiency anemia and inflammation. FOLR1 was positively associated with maternal folate deficiency, and inversely associated with infant age. There was interaction between infant age and maternal underweight, and between infant sex and maternal folate deficiency, predicting complex changes in FOLR1.

Conclusions

Our results suggest that mothers buffer milk folate against their own nutritional stress even during a prolonged drought; however, the extent of this buffering may vary with infant age, and, among folate‐deficient mothers, with infant sex. Future research is needed to better understand this variability in maternal buffering of milk folate and how it relates to folate status in nursing infants.

Human mothers might have the capacity to buffer milk nutrient content against undue fluctuations under nutritional or disease stress. In the case of the micronutrient folate, this buffering is most apparent for younger infants.

Circulating unmetabolized folic acid and 5-methyltetrahydrofolate and risk of breast cancer: a nested case-control study

BACKGROUND/OBJECTIVES

Folates found in natural foods are thought to protect against cancer. However, folic acid (FA), a synthetic form of folate used in supplements and fortified foods, may increase breast cancer risk if present in unmetabolized form (UMFA) in the circulation. This study examined the associations of serum UMFA and 5-methyltetrahydrofolate (5-mTHF), the predominant form of circulating folate, with breast cancer risk.

SUBJECTS/METHODS

We conducted a nested case-control study in a prospective cohort. In total, 553 cases of invasive breast cancer, diagnosed before mandatory FA fortification of grain in the US in 1998, were individually-matched to 1059 controls. Serum UMFA and 5-mTHF were measured using liquid chromatography-tandem mass spectrometry in stored serum samples, and 5-mTHF was corrected for storage degradation.

RESULTS

Serum UMFA was not associated with breast cancer risk: the percentage of women with detectable levels of UMFA was similar in cases and controls (18% and 20%, respectively; p = 0.46). Two tag-SNPs in the promoter region of the FA-metabolizing gene were also not associated with risk. There was a marginally significant inverse association of 5-mTHF_corrected with breast cancer risk (odds ratio for the highest vs. lowest quintile = 0.69, 95% CI = 0.49 to 0.97; p_trend = 0.08).

CONCLUSIONS

Circulating UMFA was not associated with breast cancer risk. These results apply to countries without mandatory FA food fortification. Studies are needed in countries with mandatory fortification, where levels of UMFA are much higher than in our study.

Towards Harmonized Biobanking for Biomonitoring: A Comparison of Human Biomonitoring-Related and Clinical Biorepositories

Human biomonitoring (HBM) depends on high-quality human samples to identify status and trends in exposure and ensure comparability of results. In this context, much effort has been put into the development of standardized processes and quality assurance for sampling and chemical analysis, while effects of sample storage and shipment on sample quality have been less thoroughly addressed. To characterize the currently applied storage and shipment procedures within the consortium of the European Human Biomonitoring Initiative (HBM4EU), which aims at harmonization of HBM in Europe, a requirement analysis based on data from an online survey was conducted. In addition, the online survey was addressed to professionals in clinical biobanking represented by members of the European, Middle Eastern and African Society for Biopreservation and Biobanking (ESBB) to identify the current state-of-the-art in terms of sample storage and shipment. Results of this survey conducted in these two networks were compared to detect processes with potential for optimization and harmonization. In general, many similarities exist in sample storage and shipment procedures applied by ESBB members and HBM4EU partners and many requirements for ensuring sample quality are already met also by HBM4EU partners. Nevertheless, a need for improvement was identified for individual steps in sample storage, shipment, and related data management with potential impact on sample and data quality for HBM purposes. Based on these findings, recommendations for crucial first steps to further strengthen sample quality, and thus foster advancement in HBM on a pan-European level are given.

Maternal blood folate status during early pregnancy and occurrence of autism spectrum disorder in offspring: a study of 62 serum biomarkers

BACKGROUND

Autism spectrum disorder (ASD) evolves from an interplay between genetic and environmental factors during prenatal development. Since identifying maternal biomarkers associated with ASD risk in offspring during early pregnancy might result in new strategies for intervention, we investigated maternal metabolic biomarkers in relation to occurrence of ASD in offspring using both univariate logistic regression and multivariate network analysis.

METHODS

Serum samples from 100 women with an offspring diagnosed with ASD and 100 matched control women with typically developing offspring were collected at week 14 of pregnancy. Concentrations of 62 metabolic biomarkers were determined, including amino acids, vitamins (A, B, D, E, and K), and biomarkers related to folate (vitamin B₉) metabolism, lifestyle factors, as well as C-reactive protein (CRP), the kynurenine-tryptophan ratio (KTR), and neopterin as markers of inflammation and immune activation.

RESULTS

We found weak evidence for a positive association between higher maternal serum concentrations of folate and increased occurrence of ASD (OR per 1 SD increase: 1.70, 95% CI 1.22-2.37, FDR adjusted P = 0.07). Multivariate network analysis confirmed expected internal biochemical relations between the biomarkers. Neither inflammation markers nor vitamin D₃ levels, all hypothesized to be involved in ASD etiology, displayed associations with ASD occurrence in the offspring.

CONCLUSIONS

Our findings suggest that high maternal serum folate status during early pregnancy may be associated with the occurrence of ASD in offspring. No inference about physiological mechanisms behind this observation can be made at the present time because blood folate levels may have complex relations with nutritional intake, the cellular folate status and status of other B-vitamins. Therefore, further investigations, which may clarify the potential role and mechanisms of maternal blood folate status in ASD risk and the interplay with other potential risk factors, in larger materials are warranted.

Stability of Folate and Vitamin B12 in Human Serum after Long-Term Storage: A Follow-Up after 13 Years

In epidemiological and nutrition research, it is very important to evaluate the stability of biomarkers as function of both storage time and temperature. In this study, the stability of folate and vitamin B₁₂ in human serum samples has been tested after long-term storage at −80°C up to 13 years. Serum samples of 16 individuals were used in this study. The concentration of folate and vitamin B₁₂ has been determined at t=0 and at 1, 8, and 13 years after storage at −80°C. The folate concentrations in serum samples remained stable at −80°C. The concentration of vitamin B₁₂ was decreasing during the time of the study to about 50%. The correlation of the folate and also of the vitamin B₁₂ concentrations in the stored samples compared with the starting values was still good. Therefore, although the concentration of vitamin B₁₂ decreased upon storage, reliable comparative analyses can still be performed.

Folate, homocysteine and the ovarian cycle among healthy regularly menstruating women

STUDY QUESTION

How are concentrations of plasma homocysteine and serum folate associated with reproductive hormones and anovulation in regularly menstruating women?

SUMMARY ANSWER

Higher homocysteine was associated with sporadic anovulation and hormonal changes that may be indicative of impaired ovulatory function, but higher serum folate was associated only with higher luteal phase progesterone.

WHAT IS KNOWN ALREADY

Higher folate levels as well as some variants in genes relevant to one-carbon metabolism, are associated with improved reproductive outcomes and responses to fertility treatment, but only a few small studies have explored the relationship between markers of one-carbon metabolism and menstrual cycle characteristics.

STUDY DESIGN, SIZE, DURATION

The BioCycle Study (2005-2007) is a prospective, longitudinal cohort of 259 regularly menstruating women not using hormonal contraceptives or dietary supplements who were followed for up to two menstrual cycles.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Serum folate and reproductive hormones were measured up to eight times per cycle and plasma homocysteine up to three times. Linear mixed models were used to estimate associations between serum folate or plasma homocysteine and log-transformed reproductive hormone levels while accounting for multiple observations and cycles per woman. Generalized estimating equations were used to examine risk of sporadic anovulation. All models were adjusted for age, race, body mass index, cigarette and alcohol use, and energy and fiber intake.

MAIN RESULTS AND THE ROLE OF CHANCE

Higher plasma homocysteine concentrations were associated with lower total estradiol across the cycle (adjusted percent change per unit increase in homocysteine [aPC] -2.3%, 95% CI: -4.2, -0.03), higher follicle stimulating hormone around the time of expected ovulation (aPC 2.4%, 95% CI: 0.2, 4.7) and lower luteal phase progesterone (aPC -6.5%, 95% CI: -11.1, -1.8). Higher serum folate concentrations were associated with higher luteal phase progesterone (aPC per unit increase in folate 1.0%, 95% CI: 0.4, 1.6). Higher homocysteine concentrations at expected ovulation were associated with a 33% increased risk of sporadic anovulation. We observed no risk associated with decreased folate concentrations, but a higher ratio of folate to homocysteine at ovulation was associated with a 10% decreased risk of anovulation.

LIMITATIONS, REASONS FOR CAUTION

Our results are generalizable to healthy women with adequate serum folate levels. The independent influence of homocysteine should be confirmed in larger cohorts and among women with folate deficiency or increased risks of anovulation.

WIDER IMPLICATIONS OF THE FINDINGS

If these findings are confirmed, it is possible that lowering homocysteine with B-vitamins through diet or supplementation could improve ovulatory function in some women.

Study FUNDING/COMPETING INTEREST(S)

This work was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health (Contract numbers: HHSN275200403394C, HHSN275201100002I and Task one HHSN27500001). None of the authors has any conflicts of interest to disclose.

Circulating Folate and Vitamin B12 and Risk of Prostate Cancer: A Collaborative Analysis of Individual Participant Data from Six Cohorts Including 6875 Cases and 8104 Controls

BACKGROUND

Folate and vitamin B12 are essential for maintaining DNA integrity and may influence prostate cancer (PCa) risk, but the association with clinically relevant, advanced stage, and high-grade disease is unclear.

OBJECTIVE

To investigate the associations between circulating folate and vitamin B12 concentrations and risk of PCa overall and by disease stage and grade.

DESIGN, SETTING, AND PARTICIPANTS

A study was performed with a nested case-control design based on individual participant data from six cohort studies including 6875 cases and 8104 controls; blood collection from 1981 to 2008, and an average follow-up of 8.9 yr (standard deviation 7.3). Odds ratios (ORs) of incident PCa by study-specific fifths of circulating folate and vitamin B12 were calculated using multivariable adjusted conditional logistic regression.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Incident PCa and subtype by stage and grade.

RESULTS AND LIMITATIONS

Higher folate and vitamin B12 concentrations were associated with a small increase in risk of PCa (ORs for the top vs bottom fifths were 1.13 [95% confidence interval (CI), 1.02-1.26], ptrend=0.018, for folate and 1.12 [95% CI, 1.01-1.25], ptrend=0.017, for vitamin B12), with no evidence of heterogeneity between studies. The association with folate varied by tumour grade (pheterogeneity<0.001); higher folate concentration was associated with an elevated risk of high-grade disease (OR for the top vs bottom fifth: 2.30 [95% CI, 1.28-4.12]; ptrend=0.001), with no association for low-grade disease. There was no evidence of heterogeneity in the association of folate with risk by stage or of vitamin B12 with risk by stage or grade of disease (pheterogeneity>0.05). Use of single blood-sample measurements of folate and B12 concentrations is a limitation.

CONCLUSIONS

The association between higher folate concentration and risk of high-grade disease, not evident for low-grade disease, suggests a possible role for folate in the progression of clinically relevant PCa and warrants further investigation.

PATIENT SUMMARY

Folate, a vitamin obtained from foods and supplements, is important for maintaining cell health. In this study, however, men with higher blood folate levels were at greater risk of high-grade (more aggressive) prostate cancer compared with men with lower folate levels. Further research is needed to investigate the possible role of folate in the progression of this disease.

Plasma folate, vitamin B-6, and vitamin B-12 and breast cancer risk in BRCA1- and BRCA2-mutation carriers: a prospective study

BACKGROUND

B vitamins [vitamins B-6, B-9 (folate), and B-12] play important roles in nucleotide biosynthesis and biological methylation reactions, aberrancies of which have all been implicated in carcinogenesis. In the general population, evidence has suggested that high circulating folate and folic acid (synthetic form of folate) supplement use may increase breast cancer risk, but the role of folate in BRCA-associated breast cancer is not clear.

OBJECTIVE

We prospectively evaluated the relation between plasma folate, pyridoxal 5'-phosphate (PLP; the biologically active form of vitamin B-6), and vitamin B-12 and breast cancer risk in women with a BRCA1/2 mutation.

DESIGN

Baseline blood samples and biennial follow-up questionnaires were available for 164 BRCA1/2-mutation carriers with no previous history of cancer other than nonmelanoma skin cancer. Plasma folate, PLP, and vitamin B-12 concentrations were categorized dichotomously as high compared with low based on the upper 25% and the lower 75% of distribution, respectively. Cox proportional hazards were used to estimate the HR and 95% CI for the association between plasma biomarkers of each B vitamin and incident breast cancer.

RESULTS

Over a mean follow-up of 6.3 y, 20 incident primary invasive breast cancers were observed. Women with high plasma folate concentrations (>24.4 ng/mL) were associated with significantly increased breast cancer risk (HR: 3.20; 95% CI: 1.03, 9.92; P = 0.04, P-trend across quintiles = 0.07) compared with that of women with low plasma folate concentrations (≤24.4 ng/mL). Plasma PLP and vitamin B-12 concentrations were not associated with breast cancer risk.

CONCLUSIONS

Our data suggest that elevated plasma folate concentrations may be associated with increased risk of breast cancer in women with a BRCA1/2 mutation. Additional studies with a larger sample size and longer follow-up periods are warranted to clarify the relation between folate status and breast cancer risk in high-risk women.

Preanalytical Variables Affecting the Integrity of Human Biospecimens in Biobanking

BACKGROUND

Most errors in a clinical chemistry laboratory are due to preanalytical errors. Preanalytical variability of biospecimens can have significant effects on downstream analyses, and controlling such variables is therefore fundamental for the future use of biospecimens in personalized medicine for diagnostic or prognostic purposes.

CONTENT

The focus of this review is to examine the preanalytical variables that affect human biospecimen integrity in biobanking, with a special focus on blood, saliva, and urine. Cost efficiency is discussed in relation to these issues.

SUMMARY

The quality of a study will depend on the integrity of the biospecimens. Preanalytical preparations should be planned with consideration of the effect on downstream analyses. Currently such preanalytical variables are not routinely documented in the biospecimen research literature. Future studies using biobanked biospecimens should describe in detail the preanalytical handling of biospecimens and analyze and interpret the results with regard to the effects of these variables.

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.

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.

Cobalamin and folate status in 6 to 35 months old children presenting with acute diarrhea in Bhaktapur, Nepal

BACKGROUND

Cobalamin and folate are essential micronutrients and are important in DNA and RNA synthesis, cell proliferation, growth, hematopoiesis, and cognitive function. However, data on cobalamin and folate status are lacking particularly from young children residing in low and middle income countries.

OBJECTIVE

To measure cobalamin and folate status and identifies their predictors among 6 to 35 months old children presenting with acute diarrhea.

DESIGN

This was a cross-sectional study in 823 children presenting with acute diarrhea. We measured plasma cobalamin, folate, methylmalonic acid and total homocysteine who sought treatment for acute diarrhea between June 1998 and August 2000.

RESULTS

The mean (SD) plasma concentrations of cobalamin, folate, total homocysteine and methylmalonic acid were 206 (124) pmol/L, 55 (32) nmol/L, 11.4 (5.6) µmol/L and 0.79 (1.2) µmol/L, respectively. The prevalence of low plasma cobalamin (<150 pmol/L) was 41% but less than 2% (15) children had low folate concentration (<10 nmol/L). Plasma homocysteine and methylmalonic acid concentrations were negatively associated with cobalamin concentration but not associated with folate status. The prevalence of cobalamin deficiency was higher in breastfed than non-breastfed children (44% vs 24%; p = <0.001). The prevalence of hyperhomocysteinemia (>10 µmol/L) and elevated methylmalonic acid (>0.28 µmol/L) were 73% and 52%, respectively. In the regression analyses, the plasma cobalamin concentration was positively associated with age, and introduction of animal or formula milk.

CONCLUSIONS

Our study indicated that poor cobalamin status was common particularly among breastfed children. Folate deficiency was virtually none existent. Possible consequences of cobalamin deficiency in young children need to be explored.

Interactions between plasma concentrations of folate and markers of vitamin B(12) status with cognitive performance in elderly people not exposed to folic acid fortification: the Hordaland Health Study

A combination of high folate with low vitamin B12 plasma status has been associated with cognitive impairment in a population exposed to mandatory folic acid fortification. The objective of the present study was to examine the interactions between plasma concentrations of folate and vitamin B12 markers in relation to cognitive performance in Norwegian elderly who were unexposed to mandatory or voluntary folic acid fortification. Cognitive performance was assessed by six cognitive tests in 2203 individuals aged 72-74 years. A combined score was calculated using principal component analysis. The associations of folate concentrations, vitamin B12 markers (total vitamin B12, holotranscobalamin (holoTC) and methylmalonic acid (MMA)) and their interactions in relation to cognitive performance were evaluated by quantile regression and least-squares regression, adjusted for sex, education, apo-ɛ4 genotype, history of CVD/hypertension and creatinine. Cross-sectional analyses revealed an interaction (P= 0·009) between plasma concentrations of folate and vitamin B12 in relation to cognitive performance. Plasma vitamin B12 concentrations in the lowest quartile ( < 274 pmol/l) combined with plasma folate concentrations in the highest quartile (>18·5 nmol/l) were associated with a reduced risk of cognitive impairment compared with plasma concentrations in the middle quartiles of both vitamins (OR 0·22, 95 % CI 0·05, 0·92). The interaction between folate and holoTC or MMA in relation to cognitive performance was not significant. In conclusion, this large study population unexposed to mandatory folic acid fortification showed that plasma folate, but not plasma vitamin B12, was associated with cognitive performance. Among the elderly participants with vitamin B12 concentrations in the lower range, the association between plasma folate and cognitive performance was strongest.

Quantifying the dose-response relationship between circulating folate concentrations and colorectal cancer in cohort studies: a meta-analysis based on a flexible meta-regression model

Most epidemiologic studies on folate intake suggest that folate may be protective against colorectal cancer, but the results on circulating (plasma or serum) folate are mostly inconclusive. We conducted a meta-analysis of case-control studies nested within prospective studies on circulating folate and colorectal cancer risk by using flexible meta-regression models to test the linear and nonlinear dose-response relationships. A total of 8 publications (10 cohorts, representing 3,477 cases and 7,039 controls) were included in the meta-analysis. The linear and nonlinear models corresponded to relative risks of 0.96 (95% confidence interval (CI): 0.91, 1.02) and 0.99 (95% CI: 0.96, 1.02), respectively, per 10 nmol/L of circulating folate in contrast to the reference value. The pooled relative risks when comparing the highest with the lowest category were 0.80 (95% CI: 0.61, 0.99) for radioimmunoassay and 1.03 (95% CI: 0.83, 1.22) for microbiological assay. Overall, our analyses suggest a null association between circulating folate and colorectal cancer risk. The stronger association for the radioimmunoassay-based studies could reflect differences in cohorts and study designs rather than assay performance. Further investigations need to integrate more accurate measurements and flexible modeling to explore the effects of folate in the presence of genetic, lifestyle, dietary, and hormone-related factors.

Serum folate and vitamin B12 concentrations in relation to prostate cancer risk--a Norwegian population-based nested case-control study of 3000 cases and 3000 controls within the JANUS cohort

BACKGROUND

Although individual studies have been inconsistent, meta-analyses of epidemiological data suggest that high folate and vitamin B12 levels may be associated with increased prostate cancer risk.

METHODS

Within JANUS, a prospective cohort in Norway (n = 317 000) with baseline serum samples, we conducted a nested case-control study among 3000 prostate cancer cases and 3000 controls, matched on age and time at serum sampling, and county of residence. Using conditional logistic regression, odds ratios (OR) and 95% confidence intervals (CI) for prostate cancer risk were estimated according to quintiles of serum folate, vitamin B12, methylmalonic acid (MMA), total homocysteine (tHcy) and methionine, and according to MTHFR 677C→T genotypes. To correct for degradation during sample storage, folate concentration was measured as p-aminobenzoylglutamate (pABG) equivalents following oxidation and acid hydrolysis.

RESULTS

We observed a weak positive association between folate concentration and prostate cancer risk [OR highest vs lowest quintile = 1.15 (0.97-1.37), P-trend = 0.04], which was more pronounced among individuals ≥ 50 years at inclusion [OR 1.40 (1.07-1.84), P-trend = 0.02]. tHcy showed an inverse trend with risk [OR 0.92 (0.77-1.10), P-trend = 0.03]. Vitamin B12, MMA and methionine concentrations were not associated with prostate cancer risk. Compared with the MTHFR 677CC genotype, the CT and TT variants, both of which were related to lower folate concentrations, were associated with reduced prostate cancer risk [OR 0.82 (0.72-0.94) and OR 0.78 (0.64-0.94), respectively].

CONCLUSION

This large-scale population-based study suggests that high serum folate concentration may be associated with modestly increased prostate cancer risk. We did not observe an association between vitamin B12 status and prostate cancer risk.

Sarcosine and other metabolites along the choline oxidation pathway in relation to prostate cancer--a large nested case-control study within the JANUS cohort in Norway

Methyl group donors and intermediates of one-carbon metabolism affect DNA synthesis and DNA methylation, and may thereby affect prostate carcinogenesis. Choline, the precursor of betaine, and the one-carbon metabolite sarcosine have been associated with increased prostate cancer risk. Within JANUS, a prospective cohort in Norway (n = 317,000) with baseline serum samples, we conducted a nested case-control study among 3,000 prostate cancer cases and 3,000 controls. Using conditional logistic regression, odds ratios (ORs) and 95% confidence intervals (CIs) for prostate cancer risk were estimated according to quintiles of circulating betaine, dimethylglycine (DMG), sarcosine, glycine and serine. High sarcosine and glycine concentrations were associated with reduced prostate cancer risk of borderline significance (sarcosine: highest vs. lowest quintile OR = 0.86, CI = 0.72-1.01, p(trend) = 0.03; glycine: OR = 0.83, CI = 0.70-1.00, p(trend) = 0.07). Serum betaine, DMG and serine were not associated with prostate cancer risk. However, individuals with a high glycine/serine ratio were at decreased prostate cancer risk (OR = 0.74, CI = 0.69-0.85, p(trend) < 0.001). This population-based study suggested that men with high serum sarcosine or glycine concentrations have modestly reduced prostate cancer risk. Ratios of metabolites reflecting one-carbon balance may be associated with prostate cancer risk, as demonstrated for the glycine/serine ratio, and should be explored in future studies.

In situ spectroscopic quantification of protein-ice interactions

FTIR and confocal Raman microspectroscopy were used to measure interactions between albumin and ice in situ during quasi-equilibrium freezing in dimethyl sulfoxide (DMSO) solutions. At temperatures of -4 and -6 °C, albumin was found to be preferentially excluded from the ice phase during near-equilibrium freezing. This behavior reversed at lower temperatures. Instead, DMSO was preferentially excluded from the ice phase, resulting in an albumin concentration in the freeze-concentrated liquid phase that was lower than predicted. It is hypothesized that this was caused by the albumin in the freeze-concentrated liquid getting adsorbed onto the ice surface or becoming entrapped in the ice phase. It was observed that, under certain freezing protocols, as much as 20% of the albumin in solutions with starting concentrations of 32-53 mg/mL may be adsorbed onto the ice interface or entrapped in the ice phase.

Folate catabolites in spot urine as non-invasive biomarkers of folate status during habitual intake and folic acid supplementation

BACKGROUND

Folate status, as reflected by red blood cell (RCF) and plasma folates (PF), is related to health and disease risk. Folate degradation products para-aminobenzoylglutamate (pABG) and para-acetamidobenzoylglutamate (apABG) in 24 hour urine have recently been shown to correlate with blood folate.

AIM

Since blood sampling and collection of 24 hour urine are cumbersome, we investigated whether the determination of urinary folate catabolites in fasted spot urine is a suitable non-invasive biomarker for folate status in subjects before and during folic acid supplementation.

STUDY DESIGN AND METHODS

Immediate effects of oral folic acid bolus intake on urinary folate catabolites were assessed in a short-term pre-study. In the main study we included 53 healthy men. Of these, 29 were selected for a 12 week folic acid supplementation (400 µg). Blood, 24 hour and spot urine were collected at baseline and after 6 and 12 weeks and PF, RCF, urinary apABG and pABG were determined.

RESULTS

Intake of a 400 µg folic acid bolus resulted in immediate increase of urinary catabolites. In the main study pABG and apABG concentrations in spot urine correlated well with their excretion in 24 hour urine. In healthy men consuming habitual diet, pABG showed closer correlation with PF (rs = 0.676) and RCF (rs = 0.649) than apABG (rs = 0.264, ns and 0.543). Supplementation led to significantly increased folate in plasma and red cells as well as elevated urinary folate catabolites, while only pABG correlated significantly with PF (rs = 0.574) after 12 weeks.

CONCLUSION

Quantification of folate catabolites in fasted spot urine seems suitable as a non-invasive alternative to blood or 24 hour urine analysis for evaluation of folate status in populations consuming habitual diet. In non-steady-state conditions (folic acid supplementation) correlations between folate marker (RCF, PF, urinary catabolites) decrease due to differing kinetics.

Isothermal vitrification methodology development for non-cryogenic storage of archival human sera

Biorepositories worldwide collect human serum samples and store them for future research. Currently, hundreds of biorepositories across the world store human serum samples in refrigerators, freezers, or liquid nitrogen without following any specific cryopreservation protocol. This method of storage is both expensive and potentially detrimental to the biospecimens. To decrease both cost of storage and the freeze/thaw stresses, we explored the feasibility of storing archival human serum samples at non-cryogenic temperatures using isothermal vitrification. When biospecimens are vitrified, biochemical reactions can be stopped, the specimen ceases to degrade, and macromolecules can be stabilized without requiring cryogenic storage. In this study, 0.2, 0.4, or 0.8M trehalose; 0, 0.005 or 0.01M dextran; and 0 or 10% (v/v) glycerol was added to human serum samples. The samples were either dried diffusively as sessile droplets or desiccated under vacuum after they are adsorbed onto glass microfiber filters. The glass transition temperatures (Tg) of the desiccated samples were measured by temperature-ramp Fourier Transform Infrared (FTIR) spectroscopy. Sera samples vitrified at 4±2°C when 0.8M trehalose and 0.01M dextran were added and the samples were vacuum dried for two hours. Western immunoblotting showed that vitrified serum proteins were minimally degraded when stored for up to one month at 4°C. About 80% of all proteins were recovered after storage at 4°C on glass microfiber filters, and recovery did not decrease with storage time. These results demonstrated the feasibility of long-term storage of vitrified serum at hypothermic (and non-cryogenic) temperatures.

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

Mild and prolonged oxidative degradation of 5-methyltetrahydrofolate (5-methylTHF) leads to the biologically inactive pyrazino-s-triazine derivative of 4α-hydroxy-5-methylTHF (MeFox). MeFox and the biologically active 5-formyltetrahydrofolate (5-formylTHF) are isobaric compounds that behave similarly during chromatographic and mass separation, making coelution and misidentification likely. Our published routine liquid chromatography-tandem MS (LC-MS/MS) method did not discern between 5-formylTHF and MeFox, measuring the sum of these compounds at a mass to charge ratio (m/z) of 474→327 as 5-formylTHF. We modified this method to separate MeFox and 5-formylTHF by either chromatography or unique mass transitions and then applied the 2 methods to serum specimens to determine typical concentrations of these compounds. The 2 unique transitions (m/z: 5-formylTHF, 474→299; MeFox, 474→284) showed good sensitivity [limit of detection (nmol/L): 5-formylTHF, 0.21; MeFox, 0.34], selectivity (no interfering peaks), spiking recovery (mean ± SD: 5-formylTHF, 103 ± 3.4%; MeFox, 94 ± 10%), and low imprecision (CV: 5-formylTHF, 3.9% at 2.4 nmol/L; MeFox, 5.1% at 2.9 nmol/L). The mass separation method detected 5-formylTHF in the same specimens as the chromatographic separation method. Analysis of several thousand serum specimens showed that the majority (∼85%) contained MeFox at <3 nmol/L but no detectable 5-formylTHF concentrations, some (∼14%) contained 5-formylTHF at <0.5 nmol/L, and a few specimens contained 5-formylTHF at >1 nmol/L and MeFox at >10 nmol/L. In summary, serum can contain 5-formylTHF high enough to contribute to total folate and contains MeFox that will bias total folate if not appropriately separated. Including measurements of MeFox and 5-formylTHF along with the other folate vitamers will enhance assessments of the association between biologically active folate and health effects.

Kinetic modeling of storage effects on biomarkers related to B vitamin status and one-carbon metabolism

BACKGROUND

Biomarkers and metabolites related to B vitamin function and one-carbon metabolism have been studied as predictors of chronic diseases in studies based on samples stored in biobanks. For most biomarkers, stability data are lacking or fragmentary.

METHODS

Degradation and accumulation kinetics of 32 biomarkers were determined at 23 °C in serum and plasma (EDTA, heparin, and citrate) collected from 16 individuals and stored for up to 8 days. In frozen serum (-25 °C), stability was studied cross-sectionally in 650 archival samples stored for up to 29 years. Concentration vs time curves were fitted to monoexponential, biexponential, linear, and nonlinear models.

RESULTS

For many biomarkers, stability was highest in EDTA plasma. Storage effects were similar at room temperature and at -25 °C; notable exceptions were methionine, which could be recovered as methionine sulfoxide, and cystathionine, which decreased in frozen samples. Cobalamin, betaine, dimethylglycine, sarcosine, total homocysteine, total cysteine, tryptophan, asymetric and symmetric dimethyl argenine, creatinine, and methylmalonic acid were essentially stable under all conditions. Most B vitamins (folate and vitamins B2 and B6) were unstable; choline increased markedly, and some amino acids also increased, particularly in serum. The kynurenines showed variable stability. For many biomarkers, degradation (folate and flavin mononucleotide) or accumulation (pyridoxal, riboflavin, choline, amino acids) kinetics at room temperature were non-first order.

CONCLUSIONS

Data on stability and deterioration kinetics for individual biomarkers are required to optimize procedures for handling serum and plasma, and for addressing preanalytical bias in epidemiological and clinical studies.

Comparisons of plasma/serum micronutrients between Okinawan and Oregonian elders: a pilot study

Certain micronutrients are protective against cognitive decline. We examined whether there is any uniform pattern of circulating micronutrients cross-culturally that are associated with successful cognitive aging. For the U.S. sample, we used the stored serum/plasma of 115 participants, collected in Oregon, USA. The Okinawa sample consisted of 49 participants selected using similar inclusion criteria as the Oregon sample, from the Keys to Optimal Cognitive Aging Project. All participants were aged 85 years and older without cognitive impairment. We found that the Okinawan elders used fewer vitamin supplements but had similar levels of vitamin B(12) and α-tocopherol, lower folate and γ-tocopherol, compared with Oregonian elders. That is, we did not find a uniform pattern of circulating micronutrients, suggesting that micronutrients other than those examined here or other lifestyle factors than nutrition could play an important role in achieving successful cognitive aging.