RESUMO
Choline contributes to the biogenesis of methyl groups, neurotransmitters, and cell membranes. Our genome-wide association study (GWAS) of circulating choline in 2228 college students found that alleles in SLC25A48 (rs6596270) influence choline concentrations in men (p = 9.6 × 10-8), but not women. Previously, the subcellular location and function of SLC25A48 were unknown. Using super-resolution immunofluorescence microscopy, we localized SLC25A48 to the inner mitochondrial membrane. Our results suggest that SLC25A48 transports choline across the inner mitochondrial membrane.
RESUMO
(1) Background: Antifolate methotrexate (MTX) is the most common disease-modifying antirheumatic drug (DMARD) for treating human rheumatoid arthritis (RA). The mitochondrial-produced formate is essential for folate-mediated one carbon (1C) metabolism. The impacts of MTX on formate homeostasis in unknown, and rigorously controlled kinetic studies can greatly help in this regard. (2) Methods: Combining animal model (8-week old female C57BL/6JNarl mice, n = 18), cell models, stable isotopic tracer studies with gas chromatography/mass spectrometry (GC/MS) platforms, we systematically investigated how MTX interferes with the partitioning of mitochondrial and cytosolic formate metabolism. (3) Results: MTX significantly reduced de novo deoxythymidylate (dTMP) and methionine biosyntheses from mitochondrial-derived formate in cells, mouse liver, and bone marrow, supporting our postulation that MTX depletes mitochondrial 1C supply. Furthermore, MTX inhibited formate generation from mitochondria glycine cleavage system (GCS) both in vitro and in vivo. Folinate selectively rescued 1C metabolic pathways in a tissue-, cellular compartment-, and pathway-specific manner: folinate effectively reversed the inhibition of mitochondrial formate-dependent 1C metabolism in mouse bone marrow (dTMP, methionine, and GCS) and cells (dTMP and GCS) but not methionine synthesis in liver/liver-derived cells. Folinate failed to fully recover hepatic mitochondrial-formate utilization for methionine synthesis, suggesting that the efficacy of clinical folinate rescue in MTX therapy on hepatic methionine metabolism is poor. (4) Conclusion: Conducting studies in mouse and cell models, we demonstrate novel findings that MTX specifically depletes mitochondrial 1C supply that can be ameliorated by folinate supplementation except for hepatic transmethylation. These results imply that clinical use of low-dose MTX may particularly impede 1C metabolism via depletion of mitochondrial formate. The MTX induced systematic and tissue-specific formate depletion needs to be addressed more carefully, and the efficacy of folinate with respect to protecting against such depletion deserves to be evaluated in medical practice.
Assuntos
Antirreumáticos/uso terapêutico , Artrite Reumatoide/tratamento farmacológico , Formiatos/metabolismo , Leucovorina/uso terapêutico , Metotrexato/uso terapêutico , Complexo Vitamínico B/uso terapêutico , Animais , Antirreumáticos/farmacologia , Artrite Reumatoide/metabolismo , Suplementos Nutricionais , Feminino , Humanos , Leucovorina/farmacologia , Redes e Vias Metabólicas/efeitos dos fármacos , Metotrexato/farmacologia , Camundongos Endogâmicos C57BL , Mitocôndrias/efeitos dos fármacos , Mitocôndrias/metabolismo , Complexo Vitamínico B/farmacologiaRESUMO
Vitamin B12 deficiency is common in older individuals. Circulating vitamin B12 concentration can be used to diagnose deficiency, but this test has substantial false positive and false negative rates. We conducted genome-wide association studies (GWAS) in which we resolved total serum vitamin B12 into the fractions bound to transcobalamin and haptocorrin: two carrier proteins with very different biological properties. We replicated reported associations between total circulating vitamin B12 concentrations and a common null variant in FUT2. This allele determines the secretor phenotype in which blood group antigens are found in non-blood body fluids. Vitamin B12 bound to haptocorrin (holoHC) remained highly associated with FUT2 rs601338 (p.Trp154Ter). Transcobalamin bound vitamin B12 (holoTC) was not influenced by this variant. HoloTC is the bioactive the form of the vitamin and is taken up by all tissues. In contrast, holoHC is only taken up by the liver. Using holoHC from individuals with known FUT2 genotypes, we demonstrated that FUT2 rs601338 genotype influences the glycosylation of haptocorrin. We then developed an experimental model demonstrating that holoHC is transported into cultured hepatic cells (HepG2) via the asialoglycoprotein receptor (ASGR). Our data challenge current published hypotheses on the influence of genetic variation on this clinically important measure and are consistent with a model in which FUT2 rs601338 influences holoHC by altering haptocorrin glycosylation, whereas B12 bound to non-glycosylated transcobalamin (i.e. holoTC) is not affected. Our findings explain some of the observed disparity between use of total B12 or holoTC as first-line clinical tests of vitamin B12 status.
Assuntos
Fucosiltransferases/genética , Fucosiltransferases/metabolismo , Transcobalaminas/genética , Adulto , Idoso , Transporte Biológico , Feminino , Variação Genética , Estudo de Associação Genômica Ampla/métodos , Genótipo , Glicosilação , Células Hep G2/metabolismo , Humanos , Irlanda , Masculino , Pessoa de Meia-Idade , Polimorfismo de Nucleotídeo Único/genética , Transcobalaminas/metabolismo , Vitamina B 12/análise , Vitamina B 12/sangue , Vitamina B 12/metabolismo , Deficiência de Vitamina B 12/metabolismo , Galactosídeo 2-alfa-L-FucosiltransferaseRESUMO
Methylmalonic acid (MMA) is a by-product of propionic acid metabolism through the vitamin B12 (cobalamin)-dependent enzyme methylmalonyl CoA mutase. Elevated MMA concentrations are a hallmark of several inborn errors of metabolism and indicators of cobalamin deficiency in older persons. In a genome-wide analysis of 2,210 healthy young Irish adults (median age 22 years) we identified a strong association of plasma MMA with SNPs in 3-hydroxyisobutyryl-CoA hydrolase (HIBCH, p = 8.42 × 10(-89)) and acyl-CoA synthetase family member 3 (ACSF3, p = 3.48 × 10(-19)). These loci accounted for 12% of the variance in MMA concentration. The most strongly associated SNP (HIBCH rs291466; c:2T>C) causes a missense change of the initiator methionine codon (minor-allele frequency = 0.43) to threonine. Surprisingly, the resulting variant, p.Met1?, is associated with increased expression of HIBCH mRNA and encoded protein. These homozygotes had, on average, 46% higher MMA concentrations than methionine-encoding homozygotes in young adults with generally low MMA concentrations (0.17 [0.14-0.21] µmol/L; median [25(th)-75(th) quartile]). The association between MMA levels and HIBCH rs291466 was highly significant in a replication cohort of 1,481 older individuals (median age 79 years) with elevated plasma MMA concentrations (0.34 [0.24-0.51] µmol/L; p = 4.0 × 10(-26)). In a longitudinal study of 185 pregnant women and their newborns, the association of this SNP remained significant across the gestational trimesters and in newborns. HIBCH is unique to valine catabolism. Studies evaluating flux through the valine catabolic pathway in humans should account for these variants. Furthermore, this SNP could help resolve equivocal clinical tests where plasma MMA values have been used to diagnose cobalamin deficiency.
Assuntos
Anormalidades Múltiplas/genética , Erros Inatos do Metabolismo dos Aminoácidos/genética , Ácido Metilmalônico/sangue , Polimorfismo Genético/genética , Tioléster Hidrolases/deficiência , Vitamina B 12/sangue , Anormalidades Múltiplas/sangue , Adolescente , Adulto , Idoso , Erros Inatos do Metabolismo dos Aminoácidos/sangue , Estudos de Casos e Controles , Feminino , Homozigoto , Humanos , Recém-Nascido , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Gravidez , Tioléster Hidrolases/sangue , Tioléster Hidrolases/genética , População Branca , Adulto JovemRESUMO
Objective: Currently, no guidelines are established for pharmacogenomic testing involving folate metabolic genes in long-term disease-modifying antirheumatic drugs' (DMARD) therapies. We carefully investigated how common genetic variations in methylenetetrahydrofolate reductase (MTHFR) influence cellular metabolic kinetics in response to methotrexate (MTX). Designs: Two distinct cell models: HepG2 with stabilized MTHFR inhibition using shRNA delivered by a Lentiviral vector; and Epstein-Barr virus transformed human lymphoblasts expressing MTHFR polymorphic allele 677C and 677T were used. Disease activity and DMARD use were compared between MTHFR-677CC, CT and TT rheumatoid arthritis (RA) patients in a cross-sectional study (n=120). Results: Compared with MTHFR-CC, MTHFR-TT carriers had lower mean weakly MTX dose (9.8 ± 3.3 compared with 12.1 ± 3.5, P<0.05). More MTHFR-TT carriers (8/11, 73%) reported MTX-related side effects compared with MTHFR-677CC (32/57, 56%) and MTHFR-677CT (30/51, 59%). No genotypic difference was found in other DMARDs. At the same dose of MTX, lymphoblasts were more sensitive in cell survival, protein and thymidine syntheses whereas HepG2 models were more susceptible to the inhibition of S-adenosylmethionine (adoMet) synthesis. MTHFR-C677T altered protein turnover and folate mediated 1-carbon metabolic fluxes in lymphoblasts with and without MTX. MTHFR function significantly affected transmethylation fluxes and adoMet homeostasis but not nucleotide biosyntheses in MTX-treated HepG2 cell-lines. Conclusion: Combining cell models, kinetic studies, and genetic tests in humans, the present study gives insight on how MTHFR effects hepatic transmethylation homeostasis during MTX therapy. We provide platforms that help predict the genetic impact on antifolate drugs, and further delineate tissue-specific target pathway in DMARD therapies. We suggest that genetic factors should be taken into account in clinical practice.
Assuntos
Antirreumáticos/uso terapêutico , Artrite Reumatoide/tratamento farmacológico , Fígado/efeitos dos fármacos , Linfócitos/efeitos dos fármacos , Metotrexato/uso terapêutico , Metilenotetra-Hidrofolato Redutase (NADPH2)/genética , Variantes Farmacogenômicos , S-Adenosilmetionina/metabolismo , Adulto , Idoso , Antirreumáticos/metabolismo , Artrite Reumatoide/enzimologia , Artrite Reumatoide/genética , Linhagem Celular Transformada , Feminino , Células Hep G2 , Heterozigoto , Homozigoto , Humanos , Cinética , Fígado/enzimologia , Linfócitos/enzimologia , Masculino , Metotrexato/metabolismo , Metilenotetra-Hidrofolato Redutase (NADPH2)/metabolismo , Pessoa de Meia-Idade , Fenótipo , Estudos ProspectivosRESUMO
BACKGROUND: Changes in tryptophan metabolism through the vitamin B-6-dependent kynurenine pathway have been linked to activation of the immune system. OBJECTIVE: We hypothesized that blood concentrations of tryptophan and its catabolites were associated with biomarkers relevant to inflammatory processes in healthy noninflamed subjects. METHODS: Healthy young adults (n = 737) aged 18-28 y without any known diseases or clinical evidence of inflammation provided blood samples for analysis of serum tryptophan/kynurenine metabolites, neopterin, C-reactive protein (CRP), and plasma pyridoxal 5'-phosphate (PLP) with LC-tandem mass spectrometry methodologies. A panel of cytokines was measured in serum by using high-sensitivity ELISA assays. Anthropometric and lifestyle data were collected by questionnaire. Multiple linear regression analysis to determine the effect of measured serum cytokine concentrations as predictors of tryptophan metabolites was performed on inverse normal-rank transformations of the data, adjusted for sex, body mass index, smoking, alcohol intake, and contraceptive use in women. RESULTS: Median serum CRP and neopterin concentrations were well below established clinical cutoffs for inflammation. We observed significant positive associations between serum interleukin-10 (IL-10) and serum kynurenine (P = 0.0002), the kynurenine-to-tryptophan ratio (KTR) (P = 0.003), 3-hydroxykynurenine (P = 0.01), and 3-hydroxyanthranilic acid (P = 0.04). Serum neopterin was positively associated with kynurenine, the KTR (both P < 0.0001), and anthranilic acid (P = 0.004), and was negatively associated with serum tryptophan (P = 0.01) and PLP (P < 0.0001). Serum tumor necrosis factor α was also negatively associated with tryptophan (P < 0.001). CONCLUSIONS: In healthy young adults with no apparent inflammatory conditions, serum tryptophan metabolites are significantly associated with key immune system biomarkers. The observed association between IL-10 and kynurenine is unexpected and suggests that kynurenine-linked mechanisms promoting negative regulation of inflammatory responses are associated with normal immune homeostasis.
Assuntos
Biomarcadores/sangue , Interleucina-10/sangue , Neopterina/sangue , Triptofano/sangue , Ácido 3-Hidroxiantranílico/metabolismo , Adolescente , Adulto , Índice de Massa Corporal , Proteína C-Reativa/metabolismo , Estudos Transversais , Feminino , Humanos , Inflamação/sangue , Cinurenina/análogos & derivados , Cinurenina/sangue , Modelos Lineares , Masculino , Fosfato de Piridoxal/sangue , Inquéritos e Questionários , Triptofano/metabolismo , Vitamina B 6/sangue , Adulto Jovem , ortoaminobenzoatos/sangueAssuntos
Estudos de Associação Genética , Predisposição Genética para Doença , Defeitos do Tubo Neural/genética , Tetra-Hidrofolato Desidrogenase/genética , Estudos de Coortes , Etnicidade/genética , Feminino , Humanos , Irlanda/epidemiologia , Masculino , Defeitos do Tubo Neural/epidemiologia , Defeitos do Tubo Neural/patologia , Polimorfismo de Nucleotídeo Único/genética , Reino Unido/epidemiologiaRESUMO
BACKGROUND: Dihydrofolate reductase (DHFR) is essential for the conversion of folic acid to active folate needed for one-carbon metabolism. Common genetic variation within DHFR is restricted to the noncoding regions, and previous studies have focused on a 19 bp deletion/insertion polymorphism (rs70991108) within intron 1. Reports of an association between this polymorphism and blood folate biomarker concentrations are conflicting. OBJECTIVE: In this study, we evaluated whether the DHFR 19 bp deletion/insertion polymorphism affects circulating folate biomarkers in, to our knowledge, the largest cohort to address this question to date. METHODS: Healthy young Irish individuals (n = 2507) between 19 and 36 y of age were recruited between February 2003 and February 2004. Folic acid intake from supplements and fortified foods was assessed with the use of a customized food intake questionnaire. Concentrations of serum folate and vitamin B-12, red blood cell (RBC) folate, and plasma total homocysteine (tHcy) were measured. Data were analyzed with the use of linear regression models. RESULTS: Folic acid intake was positively associated with serum (P < 0.0001) and RBC (P = 0.0005) folate concentration and was inversely associated with plasma tHcy (P = 0.001) as expected. The DHFR 19 bp polymorphism was not significantly associated with either serum (P = 0.82) or RBC (P = 0.21) folate, or plasma tHcy (P = 0.20), even in those within the highest quintile of folic acid intake (>326 µg folic acid/d; P = 0.96). A nonsignificant trend toward lower RBC folate by genotype (P = 0.09) was observed in the lowest folic acid intake quintile (0-51 µg/d). CONCLUSION: In this cohort of healthy young individuals, the DHFR 19 bp deletion allele did not significantly affect circulating folate status, irrespective of folic acid intake. Our data rule out a strong functional effect from this polymorphism on blood folate concentrations.
Assuntos
Suplementos Nutricionais , Deficiência de Ácido Fólico/genética , Ácido Fólico/administração & dosagem , Alimentos Fortificados , Estado Nutricional , Polimorfismo Genético , Tetra-Hidrofolato Desidrogenase/genética , Adulto , Biomarcadores/sangue , Estudos de Coortes , Dieta/efeitos adversos , Feminino , Ácido Fólico/sangue , Ácido Fólico/uso terapêutico , Deficiência de Ácido Fólico/etiologia , Deficiência de Ácido Fólico/metabolismo , Deficiência de Ácido Fólico/prevenção & controle , Estudos de Associação Genética , Homocisteína/sangue , Humanos , Íntrons , Irlanda , Masculino , Tetra-Hidrofolato Desidrogenase/metabolismo , Vitamina B 12/sangue , Adulto JovemRESUMO
BACKGROUND: Vitamin B-6 interconversion enzymes are important for supplying pyridoxal 5'-phosphate (PLP), the co-enzyme form, to tissues. Variants in the genes for these enzymes [tissue nonspecific alkaline phosphatase (ALPL), pyridoxamine 5'-phosphate oxidase, pyridoxal kinase, and pyridoxal phosphatase] could affect enzyme function and vitamin B-6 status. OBJECTIVES: We tested whether single-nucleotide polymorphisms (SNPs) in these genes influence vitamin B-6 status markers [plasma PLP, pyridoxal (PL), and 4-pyridoxic acid (PA)], and explored potential functional effects of the SNPs. METHODS: Study subjects were young, healthy adults from Ireland (n = 2345). We measured plasma PLP, PL, and PA with liquid chromatography-tandem mass spectrometry and genotyped 66 tag SNPs in the 4 genes. We tested for associations with single SNPs in candidate genes and also performed genome-wide association study (GWAS) and gene-based analyses. RESULTS: Seventeen SNPs in ALPL were associated with altered plasma PLP in candidate gene analyses (P < 1.89 × 10(-4)). In the GWAS, 5 additional ALPL SNPs were associated with altered plasma PLP (P < 5.0 × 10(-8)). Gene-based analyses that used the functional linear model ß-spline (P = 4.04 × 10(-15)) and Fourier spline (P = 5.87 × 10(-15)) methods also showed associations between ALPL and altered plasma PLP. No SNPs in other genes were associated with plasma PLP. The association of the minor CC genotype of 1 ALPL SNP, rs1256341, with reduced ALPL expression in the HapMap Northern European ancestry population is consistent with the positive association between the CC genotype and plasma PLP in our study (P = 0.008). No SNP was associated with altered plasma PL or PA. CONCLUSIONS: In healthy adults, common variants in ALPL influence plasma PLP concentration, the most frequently used biomarker for vitamin B-6 status. Whether these associations are indicative of functional changes in vitamin B-6 status requires more investigation.
Assuntos
Fosfatase Alcalina/genética , Polimorfismo de Nucleotídeo Único , Fosfato de Piridoxal/sangue , Adolescente , Adulto , Fosfatase Alcalina/sangue , Aspartato Aminotransferases/sangue , Biomarcadores/sangue , Cromatografia Líquida , Feminino , Estudo de Associação Genômica Ampla , Voluntários Saudáveis , Humanos , Irlanda , Modelos Lineares , Masculino , Piridoxal/sangue , Ácido Piridóxico/sangue , Espectrometria de Massas em Tandem , Vitamina B 6/sangue , Adulto JovemRESUMO
BACKGROUND: Abnormalities of tryptophan (Trp) metabolism through the kynurenine (Kyn) pathway have been reported in various diseases; however, nutritional and lifestyle factors that affect this pathway in healthy individuals are not well documented. OBJECTIVE: Our aim was to examine the effect of vitamin B-6 status and lifestyle factors including the use of vitamin B-6 supplements, alcohol, smoking, and oral contraceptives on Trp and its Kyn metabolites in a cohort of 2436 healthy young adults aged 18-28 y. METHODS: Anthropometric and lifestyle data were collected by questionnaire. Participants provided blood samples for analysis of Trp, Kyn, anthranilic acid, kynurenic acid (KA), 3-hydroxykynurenine (HK), 3-hydroxyanthranilic acid (HAA), and xanthurenic acid (XA). Vitamin B-6 species were also measured. RESULTS: Serum Trp metabolites were 10-15% higher among men (n = 993) compared with women (n = 1443; P < 0.0001), except for HK and XA. In all participants, serum Trp was positively associated with plasma pyridoxal 5'-phosphate (PLP; r = 0.28, P < 0.0001), reaching a plateau at PLP concentrations of â¼83 nmol/L. HK was inversely associated with PLP (r = -0.14, P < 0.01). Users of vitamin B-6 supplements (n = 671) had 6% lower concentrations of HK than nonusers (n = 1765; P = 0.0006). Oral contraceptive users (n = 385) had lower concentrations of KA (20.7%) but higher XA (24.1%) and HAA (9.0%) than did nonusers (n = 1058; P < 0.0001). After adjustment for gender and other lifestyle variables, XA concentrations were 16% higher in heavy drinkers (n = 713) than in never or occasional drinkers (n = 975; P = 0.0007). Concentrations of 2 other essential amino acids, methionine and arginine, also were positively associated with serum Trp (r = 0.65 and 0.33, respectively; P < 0.0001). CONCLUSIONS: In this population of healthy young adults, gender has the largest influence on serum Kyn metabolite concentrations. The significant covariance of Trp with unrelated amino acids suggests that protein intake may be an important consideration in evaluating Kyn metabolism.
Assuntos
Suplementos Nutricionais , Estilo de Vida , Fatores Sexuais , Triptofano/sangue , Vitamina B 6/administração & dosagem , Vitamina B 6/sangue , Ácido 3-Hidroxiantranílico/metabolismo , Adolescente , Adulto , Arginina/sangue , Biomarcadores/sangue , Feminino , Voluntários Saudáveis , Humanos , Ácido Cinurênico/sangue , Cinurenina/análogos & derivados , Cinurenina/sangue , Masculino , Metionina/sangue , Fosfato de Piridoxal/sangue , Inquéritos e Questionários , Xanturenatos/sangue , Adulto Jovem , ortoaminobenzoatos/sangueRESUMO
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.
Assuntos
Biomarcadores/sangue , Ácido Fólico/sangue , Suplementos Nutricionais , Ácido Fólico/administração & dosagem , Humanos , Iodo/sangue , Ferro/sangue , Avaliação Nutricional , Estado Nutricional , Recomendações Nutricionais , Vitamina A/sangue , Vitamina B 12/sangue , Zinco/sangueRESUMO
BACKGROUND: Neural tube defects (NTDs), which are among the most common congenital malformations, are influenced by environmental and genetic factors. Low maternal folate is the strongest known contributing factor, making variants in genes in the folate metabolic pathway attractive candidates for NTD risk. Multiple studies have identified nominally significant allelic associations with NTDs. We tested whether associations detected in a large Irish cohort could be replicated in an independent population. METHODS: Replication tests of 24 nominally significant NTD associations were performed in racially/ethnically matched populations. Family-based tests of fifteen nominally significant single nucleotide polymorphisms (SNPs) were repeated in a cohort of NTD trios (530 cases and their parents) from the United Kingdom, and case-control tests of nine nominally significant SNPs were repeated in a cohort (190 cases, 941 controls) from New York State (NYS). Secondary hypotheses involved evaluating the latter set of nine SNPs for NTD association using alternate case-control models and NTD groupings in white, African American and Hispanic cohorts from NYS. RESULTS: Of the 24 SNPs tested for replication, ADA rs452159 and MTR rs10925260 were significantly associated with isolated NTDs. Of the secondary tests performed, ARID1A rs11247593 was associated with NTDs in whites, and ALDH1A2 rs7169289 was associated with isolated NTDs in African Americans. CONCLUSIONS: We report a number of associations between SNP genotypes and neural tube defects. These associations were nominally significant before correction for multiple hypothesis testing. These corrections are highly conservative for association studies of untested hypotheses, and may be too conservative for replication studies. We therefore believe the true effect of these four nominally significant SNPs on NTD risk will be more definitively determined by further study in other populations, and eventual meta-analysis.
Assuntos
5-Metiltetra-Hidrofolato-Homocisteína S-Metiltransferase/genética , Adenosina Desaminase/genética , Defeitos do Tubo Neural/etnologia , Defeitos do Tubo Neural/genética , Proteínas Nucleares/genética , Retinal Desidrogenase/genética , Fatores de Transcrição/genética , Negro ou Afro-Americano/genética , Família Aldeído Desidrogenase 1 , Povo Asiático/genética , Proteínas de Ligação a DNA , Estudos de Associação Genética , Predisposição Genética para Doença , Humanos , New York/etnologia , Polimorfismo de Nucleotídeo Único , Reino Unido/etnologia , População Branca/genéticaRESUMO
BACKGROUND: Folic acid supplements can protect against neural tube defects (NTDs). Low folate and low vitamin B12 status may be maternal risk factors for having an NTD affected pregnancy. However, not all NTDs are preventable by having an adequate folate/ B12 status and other potentially modifiable factors may be involved. Folate and vitamin B12 status have important links to iron metabolism. Animal studies support an association between poor iron status and NTDs, but human data are scarce. We examined the relevance of low iron status in a nested NTD case-control study of women within a pregnant population-based cohort. METHODS: Pregnant women were recruited between 1986 and 1990, when vitamin or iron supplementation in early pregnancy was rare. Blood samples, taken at an average of 14 weeks gestation, were used to measure ferritin and hemoglobin in 64 women during an NTD affected pregnancy and 207 women with unaffected pregnancies. RESULTS: No significant differences in maternal ferritin or hemoglobin concentrations were observed between NTD affected and nonaffected pregnancies (case median ferritin 16.9 µg/L and hemoglobin 12.4 g/dl versus 15.4 µg/L and 12.3g/dl in controls). As reported previously, red cell folate and vitamin B12 concentrations were significantly lower in cases. Furthermore, there was no significant association of iron status with type of NTD lesion (anencephaly or spina bifida). CONCLUSION: We conclude that low maternal iron status during early pregnancy is not an independent risk factor for NTDs. Adding iron to folic acid for periconceptional use may improve iron status but is not likely to prevent NTDs.
Assuntos
Anencefalia/sangue , Ferritinas/sangue , Hemoglobinas/metabolismo , Ferro/sangue , Disrafismo Espinal/sangue , Adulto , Anencefalia/diagnóstico , Anencefalia/patologia , Estudos de Casos e Controles , Feminino , Humanos , Recém-Nascido , Ferro/metabolismo , Fatores de Risco , Disrafismo Espinal/diagnóstico , Disrafismo Espinal/patologiaRESUMO
The de novo thymidylate biosynthetic pathway in mammalian cells translocates to the nucleus for DNA replication and repair and consists of the enzymes serine hydroxymethyltransferase 1 and 2α (SHMT1 and SHMT2α), thymidylate synthase, and dihydrofolate reductase. In this study, we demonstrate that this pathway forms a multienzyme complex that is associated with the nuclear lamina. SHMT1 or SHMT2α is required for co-localization of dihydrofolate reductase, SHMT, and thymidylate synthase to the nuclear lamina, indicating that SHMT serves as scaffold protein that is essential for complex formation. The metabolic complex is enriched at sites of DNA replication initiation and associated with proliferating cell nuclear antigen and other components of the DNA replication machinery. These data provide a mechanism for previous studies demonstrating that SHMT expression is rate-limiting for de novo thymidylate synthesis and indicate that de novo thymidylate biosynthesis occurs at replication forks.
Assuntos
Replicação do DNA/fisiologia , DNA/biossíntese , Glicina Hidroximetiltransferase/metabolismo , Complexos Multienzimáticos/metabolismo , Lâmina Nuclear/enzimologia , Timidina Monofosfato/biossíntese , DNA/genética , Reparo do DNA/fisiologia , Glicina Hidroximetiltransferase/genética , Células HeLa , Humanos , Complexos Multienzimáticos/genética , Lâmina Nuclear/metabolismo , Tetra-Hidrofolato Desidrogenase/genética , Tetra-Hidrofolato Desidrogenase/metabolismo , Timidina Monofosfato/genéticaRESUMO
BACKGROUND: Neural tube defects (NTDs) are common birth defects (~1 in 1000 pregnancies in the US and Europe) that have complex origins, including environmental and genetic factors. A low level of maternal folate is one well-established risk factor, with maternal periconceptional folic acid supplementation reducing the occurrence of NTD pregnancies by 50-70%. Gene variants in the folate metabolic pathway (e.g., MTHFR rs1801133 (677 C > T) and MTHFD1 rs2236225 (R653Q)) have been found to increase NTD risk. We hypothesized that variants in additional folate/B12 pathway genes contribute to NTD risk. METHODS: A tagSNP approach was used to screen common variation in 82 candidate genes selected from the folate/B12 pathway and NTD mouse models. We initially genotyped polymorphisms in 320 Irish triads (NTD cases and their parents), including 301 cases and 341 Irish controls to perform case-control and family based association tests. Significantly associated polymorphisms were genotyped in a secondary set of 250 families that included 229 cases and 658 controls. The combined results for 1441 SNPs were used in a joint analysis to test for case and maternal effects. RESULTS: Nearly 70 SNPs in 30 genes were found to be associated with NTDs at the p < 0.01 level. The ten strongest association signals (p-value range: 0.0003-0.0023) were found in nine genes (MFTC, CDKN2A, ADA, PEMT, CUBN, GART, DNMT3A, MTHFD1 and T (Brachyury)) and included the known NTD risk factor MTHFD1 R653Q (rs2236225). The single strongest signal was observed in a new candidate, MFTC rs17803441 (OR = 1.61 [1.23-2.08], p = 0.0003 for the minor allele). Though nominally significant, these associations did not remain significant after correction for multiple hypothesis testing. CONCLUSIONS: To our knowledge, with respect to sample size and scope of evaluation of candidate polymorphisms, this is the largest NTD genetic association study reported to date. The scale of the study and the stringency of correction are likely to have contributed to real associations failing to survive correction. We have produced a ranked list of variants with the strongest association signals. Variants in the highest rank of associations are likely to include true associations and should be high priority candidates for further study of NTD risk.
Assuntos
Variação Genética , Defeitos do Tubo Neural/genética , Animais , Estudos de Casos e Controles , Modelos Animais de Doenças , Feminino , Ácido Fólico/genética , Ácido Fólico/metabolismo , Frequência do Gene , Estudos de Associação Genética , Predisposição Genética para Doença , Humanos , Irlanda , Camundongos , Polimorfismo de Nucleotídeo Único , Fatores de Risco , Vitamina B 12/genética , Vitamina B 12/metabolismoRESUMO
Individual studies of the genetics of neural tube defects (NTDs) contain results on a small number of genes in each report. To identify genetic risk factors for NTDs, we evaluated potentially functional single nucleotide polymorphisms (SNPs) that are biologically plausible risk factors for NTDs but that have never been investigated for an association with NTDs, examined SNPs that previously showed no association with NTDs in published studies, and tried to confirm previously reported associations in folate-related and non-folate-related genes. We investigated 64 SNPs in 34 genes for association with spina bifida in up to 558 case families (520 cases, 507 mothers, 457 fathers) and 994 controls in Ireland. Case-control and mother-control comparisons of genotype frequencies, tests of transmission disequilibrium, and log-linear regression models were used to calculate effect estimates. Spina bifida was associated with over-transmission of the LEPR (leptin receptor) rs1805134 minor C allele [genotype relative risk (GRR): 1.5; 95% confidence interval (CI): 1.0-2.1; P = 0.0264] and the COMT (catechol-O-methyltransferase) rs737865 major T allele (GRR: 1.4; 95% CI: 1.1-2.0; P = 0.0206). After correcting for multiple comparisons, these individual test P-values exceeded 0.05. Consistent with previous reports, spina bifida was associated with MTHFR 677C>T, T (Brachyury) rs3127334, LEPR K109R, and PDGFRA promoter haplotype combinations. The associations between LEPR SNPs and spina bifida suggest a possible mechanism for the finding that obesity is a NTD risk factor. The association between a variant in COMT and spina bifida implicates methylation and epigenetics in NTDs.
Assuntos
Predisposição Genética para Doença/genética , Polimorfismo de Nucleotídeo Único/genética , Disrafismo Espinal/genética , Catecol O-Metiltransferase/genética , Pai , Feminino , Genótipo , Humanos , Irlanda , Modelos Lineares , Desequilíbrio de Ligação , Masculino , Mães , Receptor alfa de Fator de Crescimento Derivado de Plaquetas/genética , Receptores para Leptina/genética , Fatores de RiscoRESUMO
Folate, an essential nutrient found naturally in foods in a reduced form, is present in dietary supplements and fortified foods in an oxidized synthetic form (folic acid). There is widespread agreement that maintaining adequate folate status is critical to prevent diseases due to folate inadequacy (e.g., anemia, birth defects, and cancer). However, there are concerns of potential adverse effects of excess folic acid intake and/or elevated folate status, with the original concern focused on exacerbation of clinical effects of vitamin B-12 deficiency and its role in neurocognitive health. More recently, animal and observational studies have suggested potential adverse effects on cancer risk, birth outcomes, and other diseases. Observations indicating adverse effects from excess folic acid intake, elevated folate status, and unmetabolized folic acid (UMFA) remain inconclusive; the data do not provide the evidence needed to affect public health recommendations. Moreover, strong biological and mechanistic premises connecting elevated folic acid intake, UMFA, and/or high folate status to adverse health outcomes are lacking. However, the body of evidence on potential adverse health outcomes indicates the need for comprehensive research to clarify these issues and bridge knowledge gaps. Three key research questions encompass the additional research needed to establish whether high folic acid or total folate intake contributes to disease risk. 1) Does UMFA affect biological pathways leading to adverse health effects? 2) Does elevated folate status resulting from any form of folate intake affect vitamin B-12 function and its roles in sustaining health? 3) Does elevated folate intake, regardless of form, affect biological pathways leading to adverse health effects other than those linked to vitamin B-12 function? This article summarizes the proceedings of an August 2019 NIH expert workshop focused on addressing these research areas.
Assuntos
Ácido Fólico/administração & dosagem , Adolescente , Adulto , Criança , Pré-Escolar , Suplementos Nutricionais , Relação Dose-Resposta a Droga , Humanos , Pessoa de Meia-Idade , Estados UnidosRESUMO
Low-folate status and genetic polymorphisms in folate metabolism have been linked to several cancers. Possible biological mechanisms for this association include effects on purine and thymidine synthesis, DNA methylation, or homocysteine concentrations. The influence of genetic variation in folate metabolism on these putative mechanisms or biomarkers of cancer risk has been largely unexplored. We used a mathematical model that simulates folate metabolism biochemistry to predict (a) the effects of polymorphisms with defined effects on enzyme function (MTHFR and TS) and (b) the effects of potential, as-of-yet-unidentified polymorphisms in a comprehensive set of folate-metabolizing enzymes on biomarkers and mechanisms related to cancer risk. The model suggests that there is substantial robustness in the pathway. Our predictions were consistent with measured effects of known polymorphisms in MTHFR and TS on biomarkers. Polymorphisms that alter enzyme function of FTD, FTS, and MTCH are expected to affect purine synthesis, FTS more so under a low-folate status. In addition, MTCH polymorphisms are predicted to influence thymidine synthesis. Polymorphisms in methyltransferases should affect both methylation rates and thymidylate synthesis. Combinations of polymorphisms in MTHFR, TS, and SHMT are expected to affect nucleotide synthesis in a nonlinear fashion. These investigations provide information on effects of genetic polymorphisms on biomarkers, including those that cannot be measured well, and highlight robustness and sensitivity in this complex biological system with regard to genetic variability. Although the proportional changes in biomarkers of risk with individual polymorphisms are frequently small, they may be quite relevant if present over an individual's lifetime.
Assuntos
Biomarcadores Tumorais/metabolismo , DNA de Neoplasias/genética , Ácido Fólico/genética , Ácido Fólico/metabolismo , Modelos Teóricos , Neoplasias/metabolismo , Polimorfismo Genético , Biomarcadores Tumorais/genética , Metilação de DNA , Ácido Fólico/análogos & derivados , Genótipo , Humanos , Neoplasias/genética , Reprodutibilidade dos TestesRESUMO
This paper provides a general review on folate and vitamin B12 nutrition and metabolism and the metabolic interrelationship between these vitamins. The effects of some common polymorphisms in folate and vitamin B12 genes and the influence of vitamin B6 and riboflavin status on folate and vitamin B12 metabolism are also discussed.