Genetic variation of folate-mediated one-carbon transfer pathway predicts susceptibility to choline deficiency in humans

Choline and polyunsaturated fatty acids in preterm infants' maternal milk

BACKGROUND

Choline, docosahexaenoic acid (DHA), and arachidonic acid (ARA) are essential to fetal development, particularly of the brain. These components are actively enriched in the fetus. Deprivation from placental supply may therefore result in impaired accretion in preterm infants.

OBJECTIVE

To determine choline, choline metabolites, DHA, and ARA in human breast milk (BM) of preterm infants compared to BM of term born infants.

DESIGN

We collected expressed BM samples from 34 mothers (N = 353; postnatal day 6-85), who had delivered 35 preterm infants undergoing neonatal intensive care (postmenstrual age 30 weeks, range 25.4-32.0), and from mothers after term delivery (N = 9; postnatal day 6-118). Target metabolites were analyzed using tandem mass spectrometry and gas chromatography and reported as medians and 25th/75th percentiles.

RESULTS

In BM, choline was mainly present in the form of phosphocholine and glycerophosphocholine, followed by free choline, phosphatidylcholine, sphingomyelin, and lyso-phosphatidylcholine. In preterm infants' BM total choline ranged from 61 to 360 mg/L (median: 158 mg/L) and was decreased compared to term infants' BM (range 142-343 mg/L; median: 258 mg/L; p < 0.01). ARA and DHA comprised 0.81 (range: 0.46-1.60) and 0.43 (0.15-2.42) % of total preterm BM lipids, whereas term BM values were 0.68 (0.52-0.88) and 0.35 (0.18-0.75) %, respectively. Concentrations of all target parameters decreased after birth, and frequently 150 ml/kg/d BM did not meet the estimated fetal accretion rates.

CONCLUSIONS

Following preterm delivery, BM choline concentrations are lower, whereas ARA and DHA levels are comparable versus term delivery. Based on these findings we suggest a combined supplementation of preterm infants' BM with choline, ARA and DHA combined to improve the nutritional status of preterm infants.

STUDY REGISTRATION

This study was registered at www.clinicaltrials.gov. Identifier: NCT01773902.

The Pediatric Methionine Requirement Should Incorporate Remethylation Potential and Transmethylation Demands

The metabolic demand for methionine is great in neonates. Indeed, methionine is the only indispensable sulfur amino acid and is required not only for protein synthesis and growth but is also partitioned to a greater extent to transsulfuration for cysteine and taurine synthesis and to >50 transmethylation reactions that serve to methylate DNA and synthesize metabolites, including creatine and phosphatidylcholine. Therefore, the pediatric methionine requirement must accommodate the demands of rapid protein turnover as well as vast nonprotein demands. Because cysteine spares the methionine requirement, it is likely that the dietary provision of transmethylation products can also feasibly spare methionine. However, understanding the requirement of methionine is further complicated because demethylated methionine can be remethylated by the dietary methyl donors folate and betaine (derived from choline). Intakes of dietary methyl donors are highly variable, which is of particular concern for newborns. It has been demonstrated that many populations have enhanced requirements for these nutrients, and nutrient fortification may exacerbate this phenomenon by selecting phenotypes that increase methyl requirements. Moreover, higher transmethylation rates can limit methyl supply and affect other transmethylation reactions as well as protein synthesis. Therefore, careful investigations are needed to determine how remethylation and transmethylation contribute to the methionine requirement. The purpose of this review is to support our hypothesis that dietary methyl donors and consumers can drive methionine availability for protein synthesis and transmethylation reactions. We argue that nutritional strategies in neonates need to ensure that methionine is available to meet requirements for growth as well as for transmethylation products.

Choline metabolites: gene by diet interactions

PURPOSE OF REVIEW

The review highlights recent advances in our understanding of the interactions between genetic polymorphisms in genes that metabolize choline and the dietary requirements of choline and how these interactions relate to human health and disease.

RECENT FINDINGS

The importance of choline as an essential nutrient has been well established, but our appreciation of the interaction between our underlying genetic architecture and dietary choline requirements is only beginning. It has been shown in both human and animal studies that choline deficiencies contribute to diseases such as nonalcoholic fatty liver disease and various neurodegenerative diseases. An adequate supply of dietary choline is important for optimum development, highlighted by the increased maternal requirements during fetal development and in breast-fed infants. We discuss recent studies investigating variants in PEMT and MTHFR1 that are associated with a variety of birth defects. In addition to genetic interactions, we discuss several recent studies that uncover changes in fetal global methylation patterns in response to maternal dietary choline intake that result in changes in gene expression in the offspring. In contrast to the developmental role of adequate choline, there is now an appreciation of the role choline has in cardiovascular disease through the gut microbiota-mediated metabolite trimethylamine N-oxide. This pathway highlights some of our understanding of how the microbiome affects nutrient processing and bioavailability. Finally, to better characterize the genetic architecture regulating choline requirements, we discuss recent results focused on identifying polymorphisms that regulate choline and its derivative products.

SUMMARY

Here we discuss recent studies that have advanced our understanding of how specific alleles in key choline metabolism genes are related to dietary choline requirements and human disease.

Plasma 1-carbon metabolites and academic achievement in 15-yr-old adolescents

Academic achievement in adolescents is correlated with 1-carbon metabolism (1-CM), as folate intake is positively related and total plasma homocysteine (tHcy) negatively related to academic success. Because another 1-CM nutrient, choline is essential for fetal neurocognitive development, we hypothesized that choline and betaine could also be positively related to academic achievement in adolescents. In a sample of 15-yr-old children (n= 324), we measured plasma concentrations of homocysteine, choline, and betaine and genotyped them for 2 polymorphisms with effects on 1-CM, methylenetetrahydrofolate reductase (MTHFR) 677C>T, rs1801133, and phosphatidylethanolamineN-methyltransferase (PEMT), rs12325817 (G>C). The sum of school grades in 17 major subjects was used as an outcome measure for academic achievement. Lifestyle and family socioeconomic status (SES) data were obtained from questionnaires. Plasma choline was significantly and positively associated with academic achievement independent of SES factors (paternal education and income, maternal education and income, smoking, school) and of folate intake (P= 0.009,R(2)= 0.285). With the addition of thePEMTrs12325817 polymorphism, the association value was only marginally changed. Plasma betaine concentration, tHcy, and theMTHFR677C>T polymorphism did not affect academic achievement in any tested model involving choline. Dietary intake of choline is marginal in many adolescents and may be a public health concern.-Nilsson, T. K., Hurtig-Wennlöf, A., Sjöström, M., Herrmann, W., Obeid, R., Owen, J. R., Zeisel, S. Plasma 1-carbon metabolites and academic achievement in 15-yr-old adolescents.

Choline, Its Potential Role in Nonalcoholic Fatty Liver Disease, and the Case for Human and Bacterial Genes

Our understanding of the impact of poor hepatic choline/phosphatidylcholine availability in promoting the steatosis characteristic of human nonalcoholic fatty liver disease (NAFLD) has recently advanced and possibly relates to phosphatidylcholine/phosphatidylethanolamine concentrations in various, membranes as well as cholesterol dysregulation. A role for choline/phosphatidylcholine availability in the progression of NAFLD to liver injury and serious hepatic consequences in some individuals requires further elucidation. There are many reasons for poor choline/phosphatidylcholine availability in the liver, including low intake, estrogen status, and genetic polymorphisms affecting, in particular, the pathway for hepatic de novo phosphatidylcholine synthesis. In addition to free choline, phosphatidylcholine has been identified as a substrate for trimethylamine production by certain intestinal bacteria, thereby reducing host choline bioavailability and providing an additional link to the increased risk of cardiovascular disease faced by those with NAFLD. Thus human choline requirements are highly individualized and biomarkers of choline status derived from metabolomics studies are required to predict those at risk of NAFLD induced by choline deficiency and to provide a basis for human intervention trials.

Maternal Choline Status, but Not Fetal Genotype, Influences Cord Plasma Choline Metabolite Concentrations

BACKGROUND

Choline deficiency during pregnancy can lead to adverse birth outcomes, including impaired neurodevelopment and birth defects. Genetic variants of choline and one-carbon metabolism may also influence birth outcomes by altering plasma choline concentrations. The effects of maternal ad libitum choline intake during pregnancy and fetal genetic variants on maternal and cord concentrations of choline and its metabolites are unknown.

OBJECTIVES

This prospective study sought to assess the effect of 1) maternal dietary choline intake on maternal and cord plasma concentrations of choline and its metabolites, and 2) fetal genetic polymorphisms on cord plasma concentrations.

METHODS

The dietary choline intake of 368 pregnant Canadian women was assessed in early (0-16 wk) and late (23-37 wk) pregnancy with the use of a food frequency questionnaire. Plasma concentrations of free choline and its metabolites were measured in maternal samples at recruitment and delivery, and in the cord blood. Ten fetal genetic variants in choline and one-carbon metabolism were assessed for their association with cord plasma concentrations of free choline and its metabolites.

RESULTS

Mean maternal plasma free choline, dimethylglycine, and trimethylamine N-oxide (TMAO) concentrations increased during pregnancy by 49%, 17%, and 13%, respectively (P < 0.005), whereas betaine concentrations decreased by 21% (P < 0.005). Cord plasma concentrations of free choline, betaine, dimethylglycine, and TMAO were 3.2, 2.0, 1.3, and 0.88 times corresponding maternal concentrations at delivery, respectively (all P < 0.005). Maternal plasma concentrations of betaine, dimethylglycine, and TMAO (r(2) = 0.19-0.51; P < 0.0001) at delivery were moderately strong, whereas maternal concentrations of free choline were not significant (r(2) = 0.12; P = 0.06), predictors of cord plasma concentrations of these metabolites. Neither maternal dietary intake nor fetal genetic variants predicted maternal or cord plasma concentrations of choline and its metabolites.

CONCLUSION

These data collectively indicate that maternal choline status, but not fetal genotype, influences cord plasma concentrations of choline metabolites. This trial was registered at clinicaltrials.gov as NCT02244684.

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.

Evidence for negative selection of gene variants that increase dependence on dietary choline in a Gambian cohort

Choline is an essential nutrient, and the amount needed in the diet is modulated by several factors. Given geographical differences in dietary choline intake and disparate frequencies of single-nucleotide polymorphisms (SNPs) in choline metabolism genes between ethnic groups, we tested the hypothesis that 3 SNPs that increase dependence on dietary choline would be under negative selection pressure in settings where choline intake is low: choline dehydrogenase (CHDH) rs12676, methylenetetrahydrofolate reductase 1 (MTHFD1) rs2236225, and phosphatidylethanolamine-N-methyltransferase (PEMT) rs12325817. Evidence of negative selection was assessed in 2 populations: one in The Gambia, West Africa, where there is historic evidence of a choline-poor diet, and the other in the United States, with a comparatively choline-rich diet. We used 2 independent methods, and confirmation of our hypothesis was sought via a comparison with SNP data from the Maasai, an East African population with a genetic background similar to that of Gambians but with a traditional diet that is higher in choline. Our results show that frequencies of SNPs known to increase dependence on dietary choline are significantly reduced in the low-choline setting of The Gambia. Our findings suggest that adequate intake levels of choline may have to be reevaluated in different ethnic groups and highlight a possible approach for identifying novel functional SNPs under the influence of dietary selective pressure.—Silver, M. J., Corbin, K. D., Hellenthal, G., da Costa, K.-A., Dominguez-Salas, P., Moore, S. E., Owen, J., Prentice, A. M., Hennig, B. J., Zeisel, S. H. Evidence for negative selection of gene variants that increase dependence on dietary choline in a Gambian cohort.

Choline Alleviates Parenteral Nutrition-Associated Duodenal Motility Disorder in Infant Rats

BACKGROUND

Parenteral nutrition (PN) has been found to influence duodenal motility in animals. Choline is an essential nutrient, and its deficiency is related to PN-associated organ diseases. Therefore, this study was aimed to investigate the role of choline supplementation in an infant rat model of PN-associated duodenal motility disorder.

MATERIALS AND METHODS

Three-week-old Sprague-Dawley male rats were fed chow and water (controls), PN solution (PN), or PN plus intravenous choline (600 mg/kg) (PN + choline). Rats underwent jugular vein cannulation for infusion of PN solution or 0.9% saline (controls) for 7 days. Duodenal oxidative stress status, concentrations of plasma choline, phosphocholine, and betaine and serum tumor necrosis factor (TNF)-α were assayed. The messenger RNA (mRNA) and protein expression of c-Kit proto-oncogene protein (c-Kit) and membrane-bound stem cell factor (mSCF) together with the electrophysiological features of slow waves in the duodenum were also evaluated.

RESULTS

Rats on PN showed increased reactive oxygen species; decreased total antioxidant capacity in the duodenum; reduced plasma choline, phosphocholine, and betaine; and enhanced serum TNF-α concentrations, which were reversed by choline intervention. In addition, PN reduced mRNA and protein expression of mSCF and c-Kit, which were inversed under choline administration. Moreover, choline attenuated depolarized resting membrane potential and declined the frequency and amplitude of slow waves in duodenal smooth muscles of infant rats induced by PN, respectively.

CONCLUSION

The addition of choline to PN may alleviate the progression of duodenal motor disorder through protecting smooth muscle cells from injury, promoting mSCF/c-Kit signaling, and attenuating impairment of interstitial cells of Cajal in the duodenum during PN feeding.

Genetic epidemiology and insights into interactive genetic and environmental effects in autism spectrum disorders

Understanding the pathogenesis of neurodevelopmental disorders has proven to be challenging. Using autism spectrum disorder (ASD) as a paradigmatic neurodevelopmental disorder, this article reviews the existing literature on the etiological substrates of ASD and explores how genetic epidemiology approaches including gene-environment interactions (G×E) can play a role in identifying factors associated with ASD etiology. New genetic and bioinformatics strategies have yielded important clues to ASD genetic substrates. The next steps for understanding ASD pathogenesis require significant effort to focus on how genes and environment interact with one another in typical development and its perturbations. Along with larger sample sizes, future study designs should include sample ascertainment that is epidemiologic and population-based to capture the entire ASD spectrum with both categorical and dimensional phenotypic characterization; environmental measurements with accuracy, validity, and biomarkers; statistical methods to address population stratification, multiple comparisons, and G×E of rare variants; animal models to test hypotheses; and new methods to broaden the capacity to search for G×E, including genome-wide and environment-wide association studies, precise estimation of heritability using dense genetic markers, and consideration of G×E both as the disease cause and a disease course modifier. Although examination of G×E appears to be a daunting task, tremendous recent progress in gene discovery has opened new horizons for advancing our understanding of the role of G×E in the pathogenesis of ASD and ultimately identifying the causes, treatments, and even preventive measures for ASD and other neurodevelopmental disorders.

Geographical and ethnic distribution of single nucleotide polymorphisms within genes of the folate/homocysteine pathway metabolism

High levels of plasma homocysteine are associated with an increased risk of many health conditions influenced by both environmental and genetic factors. The objective of this study was to provide the geographical distribution of folate pathway genetic polymorphisms in Mexico and the comparison with the reported frequencies in different continental populations. This study included the analysis of the genotypic frequencies of eight polymorphisms in genes of the folate/homocysteine metabolic pathway in 1,350 Mestizo and Amerindian subjects from different regions in Mexico and 836 individuals from European, African and Asian populations of the 1,000 Genomes Project. In Mexican Mestizo and Amerindian populations, the MTHFR C677T risk genotype (TT) was highly prevalent (frequency: 25 and 57 %, respectively). In Mestizos, the frequency showed clear regional variation related to ancestry; the Guerrero subpopulation with the highest Amerindian contribution had the highest TT frequency (33 %). The MTHFD1 G1958A AA risk genotype was also enriched in Mexican Mestizos and Amerindians (frequency: 34 and 58 %, respectively), whereas in African and Asian ancestry populations the frequency for AA was low (~4 %). All together risk genotypes showed regional differences, and Sonora had significantly different genetic frequencies compared with the other regions (P value <0.05). Our study illustrates differential geographical distribution of the risk variants in the folate/homocysteine metabolic pathway relative to ethnic background. This work supports that certain areas of the world have increased needs for folic acid and vitamin B supplementation, and this information needs to be considered in public health guidelines and eventually policies.

The effects of choline on hepatic lipid metabolism, mitochondrial function and antioxidative status in human hepatic C3A cells exposed to excessive energy substrates

Choline plays a lipotropic role in lipid metabolism as an essential nutrient. In this study, we investigated the effects of choline (5, 35 and 70 μM) on DNA methylation modifications, mRNA expression of the critical genes and their enzyme activities involved in hepatic lipid metabolism, mitochondrial membrane potential (Δψm) and glutathione peroxidase (GSH-Px) in C3A cells exposed to excessive energy substrates (lactate, 10 mM; octanoate, 2 mM and pyruvate, 1 mM; lactate, octanoate and pyruvate-supplemented medium (LOP)). Thirty five micromole or 70 μM choline alone, instead of a low dose (5 μM), reduced hepatocellular triglyceride (TG) accumulation, protected Δψm from decrement and increased GSH-Px activity in C3A cells. The increment of TG accumulation, reactive oxygen species (ROS) production and Δψm disruption were observed under LOP treatment in C3A cells after 72 h of culture, which were counteracted by concomitant treatment of choline (35 μM or 70 μM) partially via reversing the methylation status of the peroxisomal proliferator-activated receptor alpha (PPARα) gene promoter, upregulating PPARα, carnitine palmitoyl transferase-I (CPT-I) and downregulating fatty acid synthase (FAS) gene expression, as well as decreasing FAS activity and increasing CPT-I and GSH-Px activities. These findings provided a novel insight into the lipotropic role of choline as a vital methyl-donor in the intervention of chronic metabolic diseases.

Maternal choline supplementation: a nutritional approach for improving offspring health?

The modulatory role of choline on the fetal epigenome and the impact of in utero choline supply on fetal programming and health are of great interest. Studies in animals and/or humans suggest that maternal choline supplementation during pregnancy benefits important physiologic systems such as offspring cognitive function, response to stress, and cerebral inhibition. Because alterations in offspring phenotype frequently coincide with epigenetic modifications and changes in gene expression, maternal choline supplementation may be a nutritional strategy to improve lifelong health of the child. Future studies are warranted to elucidate further the effect of choline on the fetal epigenome and to determine the level of maternal choline intake required for optimal offspring physiologic function.

One-carbon metabolism in neurodevelopmental disorders: using broad-based nutraceutics to treat cognitive deficits in complex spectrum disorders

Folate and choline, two nutrients involved in the one-carbon metabolic cycle, are intimately involved in regulating DNA integrity, synthesis, biogenic amine synthesis, and methylation. In this review, we discuss evidence that folate and choline play an important role in normal cognitive development, and that altered levels of these nutrients during periods of high neuronal proliferation and synaptogenesis can result in diminished cognitive function. We also discuss the use of these nutrients as therapeutic agents in a spectrum of developmental disorders in which intellectual disability is a prominent feature, such as in Fragile-X, Rett syndrome, Down syndrome, and Autism spectrum disorders. A survey of recent literature suggests that nutritional supplements have mild, but generally consistent, effects on improving cognition. Intervening with supplements earlier rather than later during development is more effective in improving cognitive outcomes. Given the mild improvements seen after treatments using nutrients alone, and the importance of the genetic profile of parents and offspring, we suggest that using nutraceutics early in development and in combination with other therapeutics are likely to have positive impacts on cognitive outcomes in a broad spectrum of complex neurodevelopmental disorders.

A nutrient combination that can affect synapse formation

Brain neurons form synapses throughout the life span. This process is initiated by neuronal depolarization, however the numbers of synapses thus formed depend on brain levels of three key nutrients-uridine, the omega-3 fatty acid DHA, and choline. Given together, these nutrients accelerate formation of synaptic membrane, the major component of synapses. In infants, when synaptogenesis is maximal, relatively large amounts of all three nutrients are provided in bioavailable forms (e.g., uridine in the UMP of mothers' milk and infant formulas). However, in adults the uridine in foods, mostly present at RNA, is not bioavailable, and no food has ever been compelling demonstrated to elevate plasma uridine levels. Moreover, the quantities of DHA and choline in regular foods can be insufficient for raising their blood levels enough to promote optimal synaptogenesis. In Alzheimer's disease (AD) the need for extra quantities of the three nutrients is enhanced, both because their basal plasma levels may be subnormal (reflecting impaired hepatic synthesis), and because especially high brain levels are needed for correcting the disease-related deficiencies in synaptic membrane and synapses.

Identification of new genetic polymorphisms that alter the dietary requirement for choline and vary in their distribution across ethnic and racial groups

Effect alleles (alleles with a polymorphism that is associated with the effect being measured) in a small number of single-nucleotide polymorphisms (SNPs) are known to influence the dietary requirement for choline. In this study, we examined a much larger number of SNPs (n=200) in 10 genes related to choline metabolism for associations with development of organ dysfunction (liver or muscle) when 79 humans were fed a low-choline diet. We confirmed that effect alleles in SNPs such as the C allele of PEMT rs12325817 increase the risk of developing organ dysfunction in women when they consume a diet low in choline, and we identified novel effect alleles, such as the C allele of CHKA SNP rs7928739, that alter dietary choline requirements. When fed a low-choline diet, some people presented with muscle damage rather than liver damage; several effect alleles in SLC44A1 (rs7873937, G allele; rs2771040, G; rs6479313, G; rs16924529, A; and rs3199966, C) and one in CHKB (rs1557502, A) were more common in these individuals. This suggests that pathways related to choline metabolism are more important for normal muscle function than previously thought. In European, Mexican, and Asian Americans, and in individuals of African descent, we examined the prevalence of the effect alleles in SNPs that alter choline requirement and found that they are differentially distributed among people of different ethnic and racial backgrounds. Overall, our study has identified novel genetic variants that modulate choline requirements and suggests that the dietary requirement for choline may be different across racial and ethnic groups.-Da Costa, K.-A., Corbin, K. D., Niculescu, M. D., Galanko, J. A., Zeisel, S. H. Identification of new genetic polymorphisms that alter the dietary requirement for choline and vary in their distribution across ethnic and racial groups.

Metabolic crosstalk between choline/1-carbon metabolism and energy homeostasis

There are multiple identified mechanisms involved in energy metabolism, insulin resistance and adiposity, but there are here-to-fore unsuspected metabolic factors that also influence these processes. Studies in animal models suggest important links between choline/1-carbon metabolism and energy homeostasis. Rodents fed choline deficient diets become hypermetabolic. Mice with deletions in one of several different genes of choline metabolism have phenotypes that include increased metabolic rate, decreased body fat/lean mass ratio, increased insulin sensitivity, decreased ATP production by mitochondria, or decreased weight gain on a high fat diet. In addition, farmers have recognized that the addition of a metabolite of choline (betaine) to cattle and swine feed reduces body fat/lean mass ratio. Choline dietary intake in humans varies over a > three-fold range, and genetic variation exists that modifies individual requirements for this nutrient. Although there are some epidemiologic studies in humans suggesting a link between choline/1-carbon metabolism and energy metabolism, there have been no controlled studies in humans that were specifically designed to examine this relationship.

A novel mouse model for genetic variation in 10-formyltetrahydrofolate synthetase exhibits disturbed purine synthesis with impacts on pregnancy and embryonic development

Genetic variants in one-carbon folate metabolism have been identified as risk factors for disease because they may impair the production or use of one-carbon folates required for nucleotide synthesis and methylation. p.R653Q (1958G>A) is a single-nucleotide polymorphism (SNP) in the 10-formyltetrahydrofolate (formylTHF) synthetase domain of the trifunctional enzyme MTHFD1; this domain produces the formylTHF which is required for the de novo synthesis of purines. Approximately 20% of Caucasians are homozygous for the Q allele. MTHFD1 p.R653Q has been proposed as a risk factor for neural tube defects (NTDs), congenital heart defects (CHDs) and pregnancy losses. We have generated a novel mouse model in which the MTHFD1 synthetase activity is inactivated without affecting protein expression or the other activities of this enzyme. Complete loss of synthetase activity (Mthfd1S(-/-)) is incompatible with life; embryos die shortly after 10.5 days gestation, and are developmentally delayed or abnormal. The proportion of 10-formylTHF in the plasma and liver of Mthfd1S(+/-) mice is reduced (P < 0.05), and de novo purine synthesis is impaired in Mthfd1S(+/-) mouse embryonic fibroblasts (MEFs, P < 0.005). Female Mthfd1S(+/-) mice had decreased neutrophil counts (P < 0.05) during pregnancy and increased incidence of developmental defects in embryos (P = 0.052). These findings suggest that synthetase deficiency may lead to pregnancy complications through decreased purine synthesis and reduced cellular proliferation. Additional investigation of the impact of synthetase polymorphisms on human pregnancy is warranted.

Dietary and genetic manipulations of folate metabolism differentially affect neocortical functions in mice

Converging evidence suggests that folate-mediated one-carbon metabolism may modulate cognitive functioning throughout the lifespan, but few studies have directly tested this hypothesis. This study examined the separate and combined effects of dietary and genetic manipulations of folate metabolism on neocortical functions in mice, modeling a common genetic variant in the MTHFD1 gene in humans. Mutant (Mthfd1(gt/+)) and wildtype (WT) male mice were assigned to a folate sufficient or deficient diet at weaning and continued on these diets throughout testing on a series of visual attention tasks adapted from the 5-choice serial reaction time task. WT mice on a deficient diet exhibited impulsive responding immediately following a change in task parameters that increased demands on attention and impulse control, and on trials following an error. This pattern of findings indicates a heightened affective response to stress and/or an inability to regulate negative emotions. In contrast, Mthfd1(gt/+) mice (regardless of diet) exhibited attentional dysfunction and a blunted affective response to committing an error. The Mthfd1(gt/+) mice also showed significantly decreased expression levels for genes encoding choline dehydrogenase and the alpha 7 nicotinic cholinergic receptor. The effects of the MTHFD1 mutation were less pronounced when combined with a deficient diet, suggesting a compensatory mechanism to the combined genetic and dietary perturbation of folate metabolism. These data demonstrate that common alterations in folate metabolism can produce functionally distinct cognitive and affective changes, and highlight the importance of considering genotype when making dietary folate recommendations.

Choline's role in maintaining liver function: new evidence for epigenetic mechanisms

PURPOSE OF REVIEW

Humans eating diets low in choline develop fatty liver and liver damage. Rodents fed choline-methionine-deficient diets not only develop fatty liver, but also progress to develop fibrosis and hepatocarcinoma. This review focuses on the role of choline in liver function, with special emphasis on the epigenetic mechanisms of action.

RECENT FINDINGS

Dietary intake of methyl donors like choline influences the methylation of DNA and histones, thereby altering the epigenetic regulation of gene expression. The liver is the major organ within which methylation reactions occur, and many of the hepatic genes involved in pathways for the development of fatty liver, hepatic fibrosis, and hepatocarcinomas are epigenetically regulated.

SUMMARY

Dietary intake of choline varies over a three-fold range and many humans have genetic polymorphisms that increase their demand for choline. Choline is an important methyl donor needed for the generation of S-adenosylmethionine. Dietary choline intake is an important modifier of epigenetic marks on DNA and histones, and thereby modulates the gene expression in many of the pathways involved in liver function and dysfunction.

Nutrition in pregnancy: the argument for including a source of choline

Women, during pregnancy and lactation, should eat foods that contain adequate amounts of choline. A mother delivers large amounts of choline across the placenta to the fetus, and after birth she delivers large amounts of choline in milk to the infant; this greatly increases the demand on the choline stores of the mother. Adequate intake of dietary choline may be important for optimal fetal outcome (birth defects, brain development) and for maternal liver and placental function. Diets in many low income countries and in approximately one-fourth of women in high income countries, like the United States, may be too low in choline content. Prenatal vitamin supplements do not contain an adequate source of choline. For women who do not eat foods containing milk, meat, eggs, or other choline-rich foods, a diet supplement should be considered.

Choline intake influences phosphatidylcholine DHA enrichment in nonpregnant women but not in pregnant women in the third trimester

BACKGROUND

Phosphatidylcholine (PC) produced via the S-adenosylmethionine-dependent phosphatidylethanolamine (PE) N-methyltransferase (PEMT) pathway is enriched with docosahexaenoic acid (DHA). DHA plays a critical role in fetal development and is linked to health endpoints in adulthood. It is unknown whether choline, which can serve as a source of S-adenosylmethionine methyl groups, influences PC-DHA or the PC:PE ratio in pregnant and nonpregnant women.

OBJECTIVE

This study tested whether choline intake affects indicators of choline-related lipid metabolism, including erythrocyte and plasma PC-DHA and PC:PE ratios, in pregnant women in the third trimester and nonpregnant women.

DESIGN

Pregnant (n = 26) and nonpregnant (n = 21) women consumed 480 or 930 mg choline/d and a daily DHA supplement for 12 wk. Blood was collected at baseline and at the midpoint and end of the study. PC-DHA was analyzed as the proportion of total PC fatty acids.

RESULTS

Pregnant women had greater (P = 0.002) PC-DHA concentrations than did nonpregnant women at baseline. The proportion of erythrocyte and plasma PC-DHA increased (P ≤ 0.002) in pregnant and nonpregnant women regardless of choline intake. However, in nonpregnant women, consumption of 930 mg choline/d led to greater (P < 0.001) erythrocyte PC-DHA and a more rapid increase (P < 0.001) in plasma PC-DHA. Lower (P = 0.001-0.024) erythrocyte and plasma PC:PE in pregnant women was not modified by choline intake.

CONCLUSIONS

A higher choline intake may increase PEMT activity, resulting in greater PC-DHA enrichment of the PC molecule in nonpregnant women. Increased production of PC-DHA during pregnancy indicates elevated PEMT activity and a higher demand for methyl donors. This trial was registered at clinicaltrials.gov as NCT01127022.

Strain-dependent dysregulation of one-carbon metabolism in male mice is associated with choline- and folate-deficient diet-induced liver injury

Dysregulation of one-carbon metabolism-related metabolic processes is a major contributor to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). It is well established that genetic and gender-specific variations in one-carbon metabolism contribute to the vulnerability to NAFLD in humans. To examine the role of one-carbon metabolism dysregulation in the pathogenesis and individual susceptibility to NAFLD, we used a "population-based" mouse model where male mice from 7 inbred were fed a choline- and folate-deficient (CFD) diet for 12 wk. Strain-dependent down-regulation of several key one-carbon metabolism genes, including methionine adenosyltransferase 1α (Mat1a), cystathionine-β-synthase (Cbs), methylenetetrahydrofolate reductase (Mthfr), adenosyl-homocysteinase (Ahcy), and methylenetetrahydrofolate dehydrogenase 1 (Mthfd1), was observed. These changes were strongly associated with interstrain variability in liver injury (steatosis, necrosis, inflammation, and activation of fibrogenesis) and hyperhomocysteinemia. Mechanistically, the decreased expression of Mat1a, Ahcy, and Mthfd1 was linked to a reduced level and promoter binding of transcription factor CCAAT/enhancer binding protein β (CEBPβ), which directly regulates their transcription. The strain specificity of diet-induced dysregulation of one-carbon metabolism suggests that interstrain variation in the regulation of one-carbon metabolism may contribute to the differential vulnerability to NFLD and that correcting the imbalance may be considered as preventive and treatment strategies for NAFLD.

Genetic signatures in choline and 1-carbon metabolism are associated with the severity of hepatic steatosis

Choline metabolism is important for very low-density lipoprotein secretion, making this nutritional pathway an important contributor to hepatic lipid balance. The purpose of this study was to assess whether the cumulative effects of multiple single nucleotide polymorphisms (SNPs) across genes of choline/1-carbon metabolism and functionally related pathways increase susceptibility to developing hepatic steatosis. In biopsy-characterized cases of nonalcoholic fatty liver disease and controls, we assessed 260 SNPs across 21 genes in choline/1-carbon metabolism. When SNPs were examined individually, using logistic regression, we only identified a single SNP (PNPLA3 rs738409) that was significantly associated with severity of hepatic steatosis after adjusting for confounders and multiple comparisons (P=0.02). However, when groupings of SNPs in similar metabolic pathways were defined using unsupervised hierarchical clustering, we identified groups of subjects with shared SNP signatures that were significantly correlated with steatosis burden (P=0.0002). The lowest and highest steatosis clusters could also be differentiated by ethnicity. However, unique SNP patterns defined steatosis burden irrespective of ethnicity. Our results suggest that analysis of SNP patterns in genes of choline/1-carbon metabolism may be useful for prediction of severity of steatosis in specific subsets of people, and the metabolic inefficiencies caused by these SNPs should be examined further.

Reduced MTHFD1 activity in male mice perturbs folate- and choline-dependent one-carbon metabolism as well as transsulfuration

Impaired utilization of folate is caused by insufficient dietary intake and/or genetic variation and has been shown to prompt changes in related pathways, including choline and methionine metabolism. These pathways have been shown to be sensitive to variation within the Mthfd1 gene, which codes for a folate-metabolizing enzyme responsible for generating 1-carbon (1-C)-substituted folate derivatives. The Mthfd1(gt/+) mouse serves as a potential model of human Mthfd1 loss-of-function genetic variants that impair MTHFD1 function. This study investigated the effects of the Mthfd1(gt/+) genotype and folate intake on markers of choline, folate, methionine, and transsulfuration metabolism. Male Mthfd1(gt/+) and Mthfd1(+/+) mice were randomly assigned at weaning (3 wk of age) to either a control (2 mg/kg folic acid) or folate-deficient (0 mg/kg folic acid) diet for 5 wk. Mice were killed at 8 wk of age following 12 h of food deprivation; blood and liver samples were analyzed for choline, methionine, and transsulfuration biomarkers. Independent of folate intake, mice with the Mthfd1(gt/+) genotype had higher hepatic concentrations of choline (P = 0.005), betaine (P = 0.013), and dimethylglycine (P = 0.004) and lower hepatic concentrations of glycerophosphocholine (P = 0.002) relative to Mthfd1(+/+) mice. Mthfd1(gt/+) mice also had higher plasma concentrations of homocysteine (P = 0.0016) and cysteine (P < 0.001) as well as lower plasma concentrations of methionine (P = 0.0003) and cystathionine (P = 0.011). The metabolic alterations observed in Mthfd1(gt/+) mice indicate perturbed choline and folate-dependent 1-C metabolism and support the future use of Mthfd1(gt/+) mice as a tool to investigate the impact of impaired 1-C metabolism on disease outcomes.

Plasma choline metabolites associate with metabolic stress among young overweight men in a genotype-specific manner

OBJECTIVES

We aimed to test the hypotheses that (i) plasma choline metabolites differ between normal (body mass index (BMI)<25 kg m(-2)) and overweight (BMI 25 kg m(-2)) men, and (ii) an elevated BMI alters associations between plasma choline metabolites and indicators of metabolic stress.

DESIGN

This was a cross-sectional study. A one-time fasting blood sample was obtained for measurements of the choline metabolites and metabolic stress indicators (that is, serum alanine aminotransferase (ALT), glucose, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides and homocysteine), and for genotype determination.

SUBJECTS

The analysis was conducted with 237 Mexican American men with a median age of 22 years.

RESULTS

Compared with men with a normal BMI (n=98), those with an elevated BMI (n=139) had 6% lower (P=0.049) plasma betaine and an 11% lower (P=0.002) plasma betaine to choline ratio. Among men with an elevated BMI, plasma betaine and the plasma betaine to choline ratio positively associated (P0.044) with a favorable serum cholesterol profile, and inversely associated (P=0.001) with serum ALT, a marker of liver dysfunction. The phosphatidylethanolamine N-methyltransferase (PEMT) 5465GA (rs7946) genotype interacted (P0.007) with the plasma betaine to choline ratio to modulate indicators of metabolic stress with stronger inverse associations observed among overweight men with the PEMT 5465GG genotype.

CONCLUSIONS

Plasma choline metabolites predict metabolic stress among overweight men often in a genotype-specific manner. The diminished betaine among overweight men coupled with the inverse association between betaine and metabolic stress suggest that betaine supplementation may be effective in mitigating some of the metabolic insults arising from lipid overload.

Highlights of the 2012 Research Workshop: Using nutrigenomics and metabolomics in clinical nutrition research

The American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.) Research Workshop, "Using Nutrigenomics and Metabolomics in Clinical Nutrition Research," was held on January 21, 2012, in Orlando, Florida. The conference brought together experts in human nutrition who use nutrigenomic and metabolomic methods to better understand metabolic individuality and nutrition effects on health. We are beginning to understand how genetic variation and epigenetic events alter requirements for and responses to foods in our diet (the field of nutrigenetics/nutrigenomics and epigenetics). At the same time, methods for profiling almost all of the products of metabolism in plasma, urine, and tissues (metabolomics) are being refined. The relationships between diet and nutrigenomic-metabolomic profiles, as well as between these profiles and health, are being elucidated, and this will dramatically alter clinical practice in nutrition.

Why randomized controlled trials of calcium and vitamin D sometimes fail

The importance of nutrients for promotion of health and prevention of disease has long been recognized. Nonetheless, scientists are still trying to delineate the optimal intakes of various nutrients and their potential benefits for different populations. To that end, evidence-based medicine (EBM) has been applied to the study of nutrition. EBM methods basically call for the use of randomized controlled trials (RCTs) to establish causal connection between the intervention and any particular endpoint. This paper focuses on problems that arise in the use of RCTS to establish a causal link between nutrients and various clinical endpoints. While many RCTS of calcium and vitamin D have been positive, many others have been null. In this paper, we discuss the reasons why effective nutrient agents may be found to be ineffective in particular studies, giving examples of such null results, and focusing on the nearly universal failure to consider biological criteria in designing RCTs. Our purpose is (1) to inform future study design so as to ensure that relevant biological facts are considered and (2) to aid in the interpretation of the abundant, but often inconsistent literature on this topic.

Choline deprivation: an overview of the major hepatic metabolic response pathways

Choline (Ch) is an important nutrient that is involved in many physiological functions. Deprivation of Ch (CD) may lead to hepatocellular modifications and/or even hepatic tumorigenesis and it can be a frequent problem in clinical settings; it can accompany various common pathological (alcoholism and malnutrition) or physiological states (pregnancy and lactation). The aim of this review is to provide an up-to-date overview of the major metabolic pathways involved in the hepatic response toward the experimentally or clinically induced CD, and to shed more light on the implicated (and probably interrelated) mechanisms responsible for the observed hepatocellular modifications and/or carcinogenesis.

Early second trimester maternal plasma choline and betaine are related to measures of early cognitive development in term infants

BACKGROUND

The importance of maternal dietary choline for fetal neural development and later cognitive function has been well-documented in experimental studies. Although choline is an essential dietary nutrient for humans, evidence that low maternal choline in pregnancy impacts neurodevelopment in human infants is lacking. We determined potential associations between maternal plasma free choline and its metabolites betaine and dimethylglycine in pregnancy and infant neurodevelopment at 18 months of age.

METHODOLOGY

This was a prospective study of healthy pregnant women and their full-term, single birth infants. Maternal blood was collected at 16 and 36 weeks of gestation and infant neurodevelopment was assessed at 18 months of age for 154 mother-infant pairs. Maternal plasma choline, betaine, dimethylglycine, methionine, homocysteine, cysteine, total B12, holotranscobalamin and folate were quantified. Infant neurodevelopment was evaluated using the Bayley Scales of Infant Development-III. Multivariate regression, adjusting for covariates that impact development, was used to determine the associations between maternal plasma choline, betaine and dimethylglycine and infant neurodevelopment.

RESULTS

The maternal plasma free choline at 16 and 36 weeks gestation was median (interquartile range) 6.70 (5.78-8.03) and 9.40 (8.10-11.3) µmol/L, respectively. Estimated choline intakes were (mean ± SD) 383 ± 98.6 mg/day, and lower than the recommended 450 mg/day. Betaine intakes were 142 ± 70.2 mg/day. Significant positive associations were found between infant cognitive test scores and maternal plasma free choline (B=6.054, SE=2.283, p=0.009) and betaine (B=7.350, SE=1.933, p=0.0002) at 16 weeks of gestation. Maternal folate, total B12, or holotranscobalamin were not related to infant development.

CONCLUSION

We show that choline status in the first half of pregnancy is associated with cognitive development among healthy term gestation infants. More work is needed on the potential limitation of choline or betaine in the diets of pregnant women.

Choline nutrition programs brain development via DNA and histone methylation

Choline is an essential nutrient for humans. Metabolically choline is used for the synthesis of membrane phospholipids (e.g. phosphatidylcholine), as a precursor of the neurotransmitter acetylcholine, and, following oxidation to betaine, choline functions as a methyl group donor in a pathway that produces S-adenosylmethionine. As a methyl donor choline influences DNA and histone methylation--two central epigenomic processes that regulate gene expression. Because the fetus and neonate have high demands for choline, its dietary intake during pregnancy and lactation is particularly important for normal development of the offspring. Studies in rodents have shown that high choline intake during gestation improves cognitive function in adulthood and prevents memory decline associated with old age. These behavioral changes are accompanied by electrophysiological, neuroanatomical, and neurochemical changes and by altered patterns of expression of multiple cortical and hippocampal genes including those encoding key proteins that contribute to the biochemical mechanisms of learning and memory. These actions of choline are observed long after the exposure to the nutrient ended (months) and correlate with fetal hepatic and cerebral cortical choline-evoked changes in global- and gene-specific DNA cytosine methylation and with dramatic changes of the methylation pattern of lysine residues 4, 9 and 27 of histone H3. Moreover, gestational choline modulates the expression of DNA (Dnmt1, Dnmt3a) and histone (G9a/Ehmt2/Kmt1c, Suv39h1/Kmt1a) methyltransferases. In addition to the central role of DNA and histone methylation in brain development, these processes are highly dynamic in adult brain, modulate the expression of genes critical for synaptic plasticity, and are involved in mechanisms of learning and memory. A recent study documented that in a cohort of normal elderly people, verbal and visual memory function correlated positively with the amount of dietary choline consumption. It will be important to determine if these actions of choline on human cognition are mediated by epigenomic mechanisms or by its influence on acetylcholine or phospholipid synthesis.

Diet-gene interactions underlie metabolic individuality and influence brain development: implications for clinical practice derived from studies on choline metabolism

One of the underlying mechanisms for metabolic individuality is genetic variation. Single nucleotide polymorphisms (SNPs) in genes of metabolic pathways can create metabolic inefficiencies that alter the dietary requirement for, and responses to, nutrients. These SNPs can be detected using genetic profiling and the metabolic inefficiencies they cause can be detected using metabolomic profiling. Studies on the human dietary requirement for choline illustrate how useful these new approaches can be, as this requirement is influenced by SNPs in genes of choline and folate metabolism. In adults, these SNPs determine whether people develop fatty liver, liver damage and muscle damage when eating diets low in choline. Because choline is very important for fetal development, these SNPs may identify women who need to eat more choline during pregnancy. Some of the actions of choline are mediated by epigenetic mechanisms that permit 'retuning' of metabolic pathways during early life.

Interaction and exposure modification: are we asking the right questions?

Most diseases arise not purely through genetic abnormalities nor purely through environmental causes, but as "complex" conditions brought about by the combined effects of genetic susceptibility factors, nongenetic experiences and exposures, and bad luck. Finding simple models capable of both characterizing such joint effects and providing new insight into pathogenesis remains an ongoing challenge in etiologic epidemiology. Additive null models can capture certain pure forms of independent etiologic effects in studies of rare conditions and can be useful for predicting possible effects of interventions. The concept of exposure modification is here proposed as useful, particularly in thinking about biologic interactions between exposures and genetic variants. Openness to parsimonious joint models and the insights they can provide is key to advancing our understanding of etiology.

Choline intake in a large cohort of patients with nonalcoholic fatty liver disease

BACKGROUND

There is significant histologic and biochemical overlap between nonalcoholic fatty liver disease (NAFLD) and steatohepatitis associated with choline deficiency.

OBJECTIVE

We sought to determine whether subjects with biopsy-proven NAFLD and evidence of an inadequate intake of choline had more severe histologic features.

DESIGN

We performed a cross-sectional analysis of 664 subjects enrolled in the multicenter, prospective Nonalcoholic Steatohepatitis Clinical Research Network (NASH CRN) with baseline data on diet composition (from a recall-based food-frequency questionnaire) within 6 mo of a liver biopsy. Food questionnaires were analyzed with proprietary software to estimate daily intakes of choline. Liver biopsies were centrally read, and consensus was scored with the NASH CRN-developed scoring system. Because choline needs vary by age, sex, and menopausal status, participants were segregated into corresponding categories (children 9-13 y old, males ≥14 y old, premenopausal women ≥19 y old, and postmenopausal women) on the basis of the Institute of Medicine's definition of adequate intake (AI) for choline. Deficient intake was defined as <50% AI.

RESULTS

Postmenopausal women with deficient choline intake had worse fibrosis (P = 0.002) once factors associated with NAFLD (age, race-ethnicity, obesity, elevated triglycerides, diabetes, alcohol use, and steroid use) were considered in multiple ordinal logistic regression models. Choline intake was not identified as a contributor to disease severity in children, men, or premenopausal women.

CONCLUSION

Decreased choline intake is significantly associated with increased fibrosis in postmenopausal women with NAFLD. The Pioglitazone vs Vitamin E vs Placebo for Treatment of Non-Diabetic Patients With Nonalcoholic Steatohepatitis trial was registered at clinicaltrials.gov as NCT00063622, and the Treatment of Nonalcoholic Fatty Liver Disease in Children trial was registered at clinicaltrials.gov as NCT00063635.

Choline metabolism provides novel insights into nonalcoholic fatty liver disease and its progression

PURPOSE OF REVIEW

Choline is an essential nutrient and the liver is a central organ responsible for choline metabolism. Hepatosteatosis and liver cell death occur when humans are deprived of choline. In the last few years, there have been significant advances in our understanding of the mechanisms that influence choline requirements in humans and in our understanding of choline's effects on liver function. These advances are useful in elucidating why nonalcoholic fatty liver disease (NAFLD) occurs and progresses sometimes to hepatocarcinogenesis.

RECENT FINDINGS

Humans eating low-choline diets develop fatty liver and liver damage. This dietary requirement for choline is modulated by estrogen and by single-nucleotide polymorphisms in specific genes of choline and folate metabolism. The spectrum of choline's effects on liver range from steatosis to development of hepatocarcinomas, and several mechanisms for these effects have been identified. They include abnormal phospholipid synthesis, defects in lipoprotein secretion, oxidative damage caused by mitochondrial dysfunction, and endoplasmic reticulum stress. Furthermore, the hepatic steatosis phenotype can be characterized more fully via metabolomic signatures and is influenced by the gut microbiome. Importantly, the intricate connection between liver function, one-carbon metabolism, and energy metabolism is just beginning to be elucidated.

SUMMARY

Choline influences liver function, and the dietary requirement for this nutrient varies depending on an individual's genotype and estrogen status. Understanding these individual differences is important for gastroenterologists seeking to understand why some individuals develop NAFLD and others do not, and why some patients tolerate total parenteral nutrition and others develop liver dysfunction.

The nutrigenetics and nutrigenomics of the dietary requirement for choline

Advances in nutrigenetics and nutrigenomics have been instrumental in demonstrating that nutrient requirements vary among individuals. This is exemplified by studies of the nutrient choline, in which gender, single-nucleotide polymorphisms, estrogen status, and gut microbiome composition have been shown to influence its optimal intake level. Choline is an essential nutrient with a wide range of biological functions, and current studies are aimed at refining our understanding of its requirements and, importantly, on defining the molecular mechanisms that mediate its effects in instances of suboptimal dietary intake. This chapter introduces the reader to challenges in developing individual nutrition recommendations, the biological function of choline, current and future research paradigms to fully understand the consequences of inadequate choline nutrition, and some forward thinking about the potential for individualized nutrition recommendations to become a tangible application for improved health.

Dietary choline deficiency causes DNA strand breaks and alters epigenetic marks on DNA and histones

Dietary choline is an important modulator of gene expression (via epigenetic marks) and of DNA integrity. Choline was discovered to be an essential nutrient for some humans approximately one decade ago. This requirement is diminished in young women because estrogen drives endogenous synthesis of phosphatidylcholine, from which choline can be derived. Almost half of women have a single nucleotide polymorphism that abrogates estrogen-induction of endogenous synthesis, and these women require dietary choline just as do men. In the US, dietary intake of choline is marginal. Choline deficiency in people is associated with liver and muscle dysfunction and damage, with apoptosis, and with increased DNA strand breaks. Several mechanisms explain these modifications to DNA. Choline deficiency increases leakage of reactive oxygen species from mitochondria consequent to altered mitochondrial membrane composition and enhanced fatty acid oxidation. Choline deficiency impairs folate metabolism, resulting in decreased thymidylate synthesis and increased uracil misincorporation into DNA, with strand breaks resulting during error-prone repair attempts. Choline deficiency alters DNA methylation, which alters gene expression for critical genes involved in DNA mismatch repair, resulting in increased mutation rates. Any dietary deficiency which increases mutation rates should be associated with increased risk of cancers, and this is the case for choline deficiency. In rodent models, diets low in choline and methyl-groups result in spontaneous hepatocarcinomas. In human epidemiological studies, there are interesting data that suggest that this also may be the case for humans, especially those with SNPs that increase the dietary requirement for choline.

The supply of choline is important for fetal progenitor cells

Fetal progenitor cells proliferate, migrate, differentiate and undergo apoptosis at specific times during fetal development. Choline is needed by these cells for membrane synthesis and for methylation. There is growing evidence that this nutrient also modulates epigenetic regulation of gene expression in both neuronal and endothelial progenitor cells, thereby modifying brain development. It is likely that these mechanisms explain why, in rodent models, maternal dietary intake of choline influences both angiogenesis and neurogenesis in fetal hippocampus, and results in life-long changes in memory function. This also may explain why women eating diets low in choline have a greater risk of having a baby with a birth defect. Choline is mainly found in foods that contain fat and cholesterol, and intake of such foods has diminished in response dietary advice from nutritionists and physicians. Forty years ago, diets commonly contained choline-rich foods but now women in the USA tend to eat diets low in choline content. Premenopausal women normally may require less choline in their diet than do men and postmenopausal women, because estrogen induces the gene for the enzyme catalyzing endogenous biosynthesis of the choline-containing phospholipid phosphatidylcholine. However, many women have a single nucleotide polymorphism (SNP) that blocks the induction of endogenous biosynthesis, thereby making them require more dietary choline. When these women eat diets low in choline, the supply of this nutrient to the fetus is likely to be inadequate, and may perturb progenitor cell proliferation, migration, differentiation and apoptosis.

Docosahexaenoic acid in plasma phosphatidylcholine may be a potential marker for in vivo phosphatidylethanolamine N-methyltransferase activity in humans

BACKGROUND

Choline is an essential nutrient for humans, and part of this requirement is met by endogenous synthesis catalyzed by hepatic phosphatidylethanolamine N-methyltransferase (PEMT). PEMT activity is difficult to estimate in humans because it requires a liver biopsy. Previously, we showed that mice that lack functional PEMT have dramatically reduced concentrations of docosahexaenoic acid (DHA; 22:6n-3) in plasma and of liver phosphatidylcholine (PtdCho)-a phospholipid formed by PEMT.

OBJECTIVE

The objective was to evaluate plasma PtdCho-DHA concentrations as a noninvasive marker of liver PEMT activity in humans.

DESIGN

Plasma PtdCho-DHA concentrations were measured in 72 humans before and after they consumed a low-choline diet, and correlations were analyzed in relation to estrogen status, PEMT polymorphism rs12325817, the ratio of plasma S-adenosylmethionine (AdoMet) to S-adenosylhomocysteine (AdoHcy), and dietary choline intake; all of these factors are associated with changes in liver PEMT activity. PtdCho-DHA and PEMT activity were also measured in human liver specimens.

RESULTS

At baseline, the portion of PtdCho species containing DHA (pmol PtdCho-DHA/nmol PtdCho) was higher in premenopausal women than in men and postmenopausal women (P < 0.01). This ratio was lower in premenopausal women with the rs12325817 polymorphism in the PEMT gene (P < 0.05), and PtdCho-DHA concentration and PEMT activity were lower in human liver samples from women who were homozygous for PEMT rs12325817 (P < 0.05). The ratio of DHA-PtdCho to PtdCho in plasma was directly correlated with the ratio of AdoMet to AdoHcy (P = 0.0001). The portion of PtdCho species containing DHA in plasma was altered in subjects who consumed a low-choline diet.

CONCLUSION

PtdCho-DHA may be useful as a surrogate marker for in vivo hepatic PEMT activity in humans. This trial was registered at clinicaltrials.gov as NCT00065546.

Altered folate availability modifies the molecular environment of the human colorectum: implications for colorectal carcinogenesis

Low folate status increases colorectal cancer risk. Paradoxically, overly abundant folate supplementation, which is not uncommon in the United States, may increase risk. The mechanisms of these effects are unknown. We conducted two translational studies to define molecular pathways in the human colon altered either by folate supplementation or by dietary folate depletion (followed by repletion). In the first study, 10 healthy, at-risk volunteers (with documented stable/normal folate intake) received supplemental folic acid (1 mg/d) for 8 weeks. In the second study, 10 similar subjects were admitted to a hospital as inpatients for 12 weeks to study folate depletion induced by a low folate diet. A repletion regimen of folic acid (1 mg/d) was provided for the last 4 of these weeks. Both studies included an 8-week run-in period to ensure stabilized folate levels prior to intervention. We obtained 12 rectosigmoid biopsies (from 4 quadrants of normal-appearing mucosa 10-15 cm from the anal verge) at baseline and at measured intervals in both studies for assessing the primary endpoints: genome-wide gene expression, genomic DNA methylation, promoter methylation (depletion/repletion study only), and p53 DNA strand breaks. Serum and rectosigmoid folate concentrations accurately tracked all changes in folate delivery (P < 0.05). In the first study, gene array analysis revealed that supplementation upregulated multiple inflammation- and immune-related pathways in addition to altering several 1-carbon-related enzymes (P < 0.001). In the second study, folate depletion downregulated genes involved in immune response, inflammation, the cell cycle, and mitochondrial/energy pathways; repletion reversed most of these changes. However, changes in gene expression after repletion in the second study (involving immune response and inflammation) did not reach the levels seen after supplementation in the first study. Neither genomic nor promoter-specific DNA methylation changed during the course of the depletion/repletion protocol, and genomic methylation did not change with supplementation in the first study. p53 DNA strand breaks increased with depletion after 12 weeks. In sum, depletion downregulates, whereas repletion or supplementation upregulates pathways related to inflammation and immune response. These findings provide novel support to the concept that excessive folate supplementation might promote colorectal carcinogenesis by enhancing proinflammatory and immune response pathways. These results indicate that modest changes in folate delivery create substantial changes in the molecular milieu of the human colon.

Nutritional genomics: defining the dietary requirement and effects of choline

As it becomes evident that single nucleotide polymorphisms (SNPs) in humans can create metabolic inefficiencies, it is reasonable to ask if such SNPs influence dietary requirements. Epidemiologic studies that examine SNPs relative to risks for diseases are common, but there are few examples of clinically sized nutrition studies that examine how SNPs influence metabolism. Studies on how SNPs influence the dietary requirement for choline provide a model for how we might begin examining the effects of SNPs on nutritional phenotypes using clinically sized studies (clinical nutrigenomics). Most men and postmenopausal women develop liver or muscle dysfunction when deprived of dietary choline. More than one-half of premenopausal women may be resistant to choline deficiency-induced organ dysfunction, because estrogen induces the gene [phosphatidylethanolamine-N-methyltransferase (PEMT)] that catalyzes endogenous synthesis of phosphatidylcholine, which can subsequently yield choline. Those premenopausal women that do require a dietary source of choline have a SNP in PEMT, making them unresponsive to estrogen induction of PEMT. It is important to recognize differences in dietary requirements for choline in women, because during pregnancy, maternal dietary choline modulates fetal brain development in rodent models. Because choline metabolism and folate metabolism intersect at the methylation of homocysteine, manipulations that limit folate availability also increase the use of choline as a methyl donor. People with a SNPs in MTHFD1 (a gene of folate metabolism that controls the use of folate as a methyl donor) are more likely to develop organ dysfunction when deprived of choline; their dietary requirement is increased because of increased need for choline as a methyl donor.