Homocysteine inhibits cardiac neural crest cell formation and morphogenesis in vivo

The Association of Folic Acid, Iron Nutrition during Pregnancy and Congenital Heart Disease in Northwestern China: A Matched Case-Control Study

Background: The purpose of this study was to investigate the relationship between folic acid and iron nutrition during pregnancy and congenital heart disease (CHD) in the offspring. Methods: Conditional logistic regression models and nonlinear mixed-effects models were used to analyze the effects of folic acid and iron nutrition during pregnancy on CHD in offspring. Results: After adjusting for confounders, folic acid or iron supplementation during pregnancy reduced the risk for fetal CHD (OR = 0.60 (0.45, 0.82) or 0.36 (0.27, 0.48)). Similarly, dietary iron intake during pregnancy (≥29 mg/d) was associated with a reduced risk of fetal CHD (OR = 0.64 (0.46, 0.88)). Additionally, compared with women who only supplemented folic acid (OR = 0.59 (0.41, 0.84)) or iron (OR = 0.32 (0.16, 0.60)), women who supplemented both folic acid and iron had lower risk for newborns with CHD (OR = 0.22 (0.15, 0.34)). Similarly, compared with women who only supplemented folic acid (OR = 0.59 (0.41, 0.84)) or higher dietary iron intake (≥29 mg/d) (OR = 0.60 (0.33, 1.09)), women who supplemented both folic acid and higher dietary iron intake (≥29 mg/d) had lower risk for the newborn with CHD (OR = 0.41 (0.28, 0.62)). The combined effects were significant in the multiplication model (OR = 0.35 (0.26, 0.48) or 0.66 (0.50, 0.85)) but not in the additive model. Conclusions: Our study found that folic acid and iron nutrition during pregnancy were associated with a reduced risk of CHD in the offspring and confirmed a statistically significant multiplicative interaction between folic acid and iron nutrition on the reduced risk of CHD in offspring.

Maternal sociodemographic characteristics, early pregnancy behaviours, and livebirth outcomes as congenital heart defects risk factors - Northern Ireland 2010-2014

BACKGROUND

Congenital Heart Defects (CHD) is the most commonly occurring congenital anomaly in Europe and a major paediatric health care concern. Investigations are needed to enable identification of CHD risk factors as studies have given conflicting results. This study aim was to identify maternal sociodemographic characteristics, behaviours, and birth outcomes as risk factors for CHD. This was a population based, data linkage cohort study using anonymised data from Northern Ireland (NI) covering the period 2010-2014. The study cohort composed of 94,067 live births with an outcome of 1162 cases of CHD using the International Statistical Classification of Diseases and Related Health Problems (ICD)-10 codes and based on the European Surveillance of Congenital Anomalies (EUROCAT) grouping system for CHD. CHD cases were obtained from the HeartSuite database (HSD) at the Royal Belfast Hospital for Sick Children (RBHSC), maternal data were extracted from the Northern Ireland Maternity System (NIMATS), and medication data were extracted from the Enhanced Prescribing Database (EPD). STATA version 14 was used for the statistical analysis in this study, Odds Ratio (OR), 95% Confident intervals (CI), P value, and logistic regression were used in the analysis. Ethical approval was granted from the National Health Service (NHS) Research Ethics Committee.

RESULT

In this study, a number of potential risk factors were assessed for statistically significant association with CHD, however only certain risk factors demonstrated a statistically significant association with CHD which included: gestational age at first booking (AOR = 1.21; 95% CI = 1.04-1.41; P < 0.05), family history of CHD or congenital abnormalities and syndromes (AOR = 4.14; 95% CI = 2.47-6.96; P < 0.05), woman's smoking in pregnancy (AOR = 1.22; 95% CI = 1.04-1.43; P < 0.05), preterm birth (AOR = 3.01; 95% CI = 2.44-3.01; P < 0.05), multiple births (AOR = 1.89; 95% CI = 1.58-2.60; P < 0.05), history of abortion (AOR = 1.12; 95% CI = 1.03-1.28; P < 0.05), small for gestational age (SGA) (AOR = 1.44; 95% CI = 1.22-1.78; P < 0.05), and low birth weight (LBW) (AOR = 3.10; 95% CI = 2.22-3.55; P < 0.05). Prescriptions and redemptions of antidiabetic (AOR = 2.68; 95% CI = 1.85-3.98; P < 0.05), antiepileptic (AOR = 1.77; 95% CI = 1.10-2.81; P < 0.05), and dihydrofolate reductase inhibitors (DHFRI) (AOR = 2.13; 95% CI = 1.17-5.85; P < 0.05) in early pregnancy also showed evidence of statistically significant association with CHD.

CONCLUSION

The results of this study suggested that there are certain maternal sociodemographic characteristics, behaviours and birth outcomes that are statistically significantly associated with higher risk of CHD. Appropriate prevention policy to target groups with higher risk for CHD may help to reduce CHD prevalence. These results are important for policy makers, obstetricians, cardiologists, paediatricians, midwives and the public.

Maternal B-vitamin intake and B-vitamin supplementation during pregnancy in relation to neonatal congenital heart defects: a case-control study with propensity score matching

BACKGROUND/OBJECTIVES

The effect of dietary folate intake or folic acid (FA) supplementation during pregnancy on neonatal congenital heart defects (CHDs) remains inconclusive. There are limited data about non-folate-B-vitamin intake and the risk of CHDs. Furthermore, few studies have investigated dietary B-vitamin intake and B-vitamin supplement use simultaneously in relation to the risk of CHDs. This study aimed to explore the associations between maternal folate, vitamin B₆, and vitamin B₁₂ intake (dietary intake, total intake from diet and supplements); B-vitamin supplement use during pregnancy; and the risk of CHDs using the propensity score matching (PSM) method.

METHODS

We conducted a case-control study and included 760 cases and 1600 controls in Shaanxi Province, China. Diet, supplement use and other information were collected through a questionnaire interview. By using the 1:2 ratio PSM method, 396 cases were matched with 792 controls. Conditional logistic regression was used to investigate the associations between maternal B-vitamin intake and supplement use during pregnancy and CHDs.

RESULTS

Higher maternal dietary and total intake of folate and vitamin B₁₂ were associated with reduced risk of CHDs, and the tests for linear trend were significant. Compared with non-users, maternal FA + VB₆ + VB₁₂ containing supplement use during pregnancy (OR 0.61, 95%CI 0.40-0.94), FA supplement use during pregnancy (OR 0.70, 95%CI 0.50-0.98) and in the first trimester (OR 0.62, 95%CI 0.46-0.85) were associated with a lower risk of CHDs.

CONCLUSIONS

The findings of this study suggest that a higher intake of folate and vitamin B₁₂ during pregnancy reduces the risk of CHDs.

Analysis of MTR and MTRR Gene Polymorphisms in Chinese Patients With Ventricular Septal Defect

Background:

Congenital heart defects (CHDs) are the most common birth defects and ventricular septal defects (VSDs) are one of the most common types of CHDs. Genes involved in homocysteine/folate metabolism may play important roles in CHDs. Methionine synthase and methionine synthase reductase (MTRR) are key regulatory enzymes involved in the metabolic pathway of homocysteine.

Methods:

We investigated whether a polymorphism (A2756G) of the methionine synthase and 2 polymorphisms (A66G and C524T) of the MTRR gene are associated with VSDs. A total of 183 children with VSDs and 201 healthy children were studied.

Results:

The polymorphisms were detected by polymerase chain reaction amplification and sequencing of the amplified product. Significant differences in the distributions of the A66G and C524T alleles were observed between VSD cases and controls, and a slightly increased risk of VSDs was associated with either of the 66AG, 524CT, and 524TT genotypes [odds ratios (OR)=1.796, 1.909, and 2.088, respectively]. The genotype frequency of 66AG in VSDs patients was significantly different from those of controls (ORs=3.147). In addition, the combined 66AG/524CT and 66GG/524TT in VSDs had ORs 2.937 and 5.344, respectively.

Conclusions:

MTRR A66G and C524T polymorphisms are associated with increased risk of VSDs.

Homocysteine-induced changes in cell proliferation and differentiation in the chick embryo spinal cord: implications for mechanisms of neural tube defects (NTD)

Maternal hyperhomocysteinemia during pregnancy is associated with increased risk of NTD in the offspring. Our study investigated the effects of homocysteine (Hcy) on proliferation and neuronal differentiation of the spinal cord cells in a chick embryo model. Embryos were treated with 20μmol D-L Hcy/50μL saline solution at embryonic day 2 (E2) and analyzed at embryonic days 4 (E4) and 6 (E6). Control embryos received exclusively 50μL saline solution. We performed immunolocalization and flow cytometry analyses using antibodies anti-phosphohistone H3 (pH3), anti-proliferating cell nuclear antigen (PCNA), anti-β-tubulin III and anti-p53. Our results revealed that Hcy interferes in the proliferation of the neural cells, and that this effect is age-dependent and differed between Hcy-treated embryos with and without NTD. Also, Hcy induced a decrease of neuronal differentiation in the spinal cord at both embryonic ages. These findings contribute to clarifying the cellular bases of NTD genesis, under experimental hiperhomocysteinemia.

Effects of Folic Acid and Homocysteine on the Morphogenesis of Mouse Cephalic Neural Crest Cells In Vitro

Folate deficiency and hyperhomocysteinemia have long been associated with developmental anomalies, particularly neural tube defects and neurocristopathies-a group of diverse disorders that result from defective growth, differentiation, and migration of neural crest (NC) cells. However, the exact mechanisms by which homocysteine (Hcys) and/or folate deficiencies disrupt NC development are still poorly understood in mammals. In this work, we employed a well-defined culture system to investigate the effects of Hcys and folic acid (FA) supplementation on the morphogenetic processes of murine NC cells in vitro. We demonstrated that Hcys increases outgrowth and proliferation of cephalic NC cells and impairs their differentiation into smooth muscle cells. In addition, we showed that FA alone does not directly affect the developmental dynamics of the cephalic NC cells but is able to prevent the Hcys-induced effects. Our results, therefore, suggest that elevated Hcys levels per se cause dysmorphogenesis of the cephalic NC and might contribute to neurocristopathies in mammalian embryos.

Maternal folic acid supplementation and the risk of congenital heart defects in offspring: a meta-analysis of epidemiological observational studies

Epidemiological studies have reported conflicting results regarding the association between maternal folic acid supplementation and the risk of congenital heart defects (CHDs). However, a meta-analysis of the association between maternal folic acid supplementation and CHDs in offspring has not been conducted. We searched the MEDLINE and EMBASE databases for articles cataloged between their inceptions and October 10, 2014 and identified relevant published studies that assessed the association between maternal folate supplementation and the risk of CHDs. Study-specific relative risk estimates were pooled using random-effects or fixed-effects models. Out of the 1,606 articles found in our initial literature searches, a total of 1 randomized controlled trial, 1 cohort study, and 16 case-control studies were included in our final meta-analysis. The overall results of this meta-analysis provide evidence that maternal folate supplementation is associated with a significantly decreased risk of CHDs (RR = 0.72, 95% CI: 0.63–0.82). Statistically significant heterogeneity was detected (Q = 82.48, P < 0.001, I² = 79.4%). We conducted stratified and meta-regression analyses to identify the origin of the heterogeneity among the studies, and a Galbraith plot was generated to graphically assess the sources of heterogeneity. This meta-analysis provides a robust estimate of the positive association between maternal folate supplementation and a decreased risk of CHDs.

Homocysteine causes disruptions in spinal cord morphology and changes the expression of Pax 1/9 and Sox 9 gene products in the axial mesenchyme

BACKGROUND

Neural tube defects (NTD) involve disruptions in the axial mesenchyme, and are related to an imbalance between folic acid (FA) and homocysteine (Hcy). This study evaluated the effects of FA/Hcy imbalance on cell proliferation and expression of the Pax 1/9 and Sox 9 gene products in the axial mesenchyme of chickens.

METHODS

Embryos were incubated (38°C) and pretreated at 24 h and treated at 46 h of incubation. The experimental groups were: FA-pretreated with saline and treated with 0.5 μg FA/saline; Hcy-pretreated with 50 μl saline and treated with 20 μmol D,L-Hcy/50 μl saline; FA+Hcy-pretreated with 0.5 μg FA/50 μl saline and treated with 20 μmol D,L-Hcy/50 μl saline; and the control embryos were pretreated and treated with saline. Embryos were analyzed at E4 and E6. Immunohistochemistry was performed to identify proliferating cells and the expression of the gene products of Pax 1/9 and Sox 9. Total RNA of the E4 embryos was extracted and a RT-qPCR assay was performed to quantify Pax 1/9 mRNA expression.

RESULTS

Hcy treatment caused spinal NTD and abnormalities in axial mesenchyme development, affecting the distribution of sclerotomal cells and chondrification. Hcy also reduced cell proliferation and changed the expression of Pax 1/9 and Sox 9 in the mesenchyme.

CONCLUSIONS

Our data clarified the relationship between spinal NTD genesis and disruptions of Pax 1/9 and Sox 9 gene products in the axial mesenchyme caused by the FA/Hcy imbalance.

A66G and C524T polymorphisms of the methionine synthase reductase gene are associated with congenital heart defects in the Chinese Han population

Congenital heart defects (CHDs) are the most common birth defects; genes involved in homocysteine/folate metabolism may play important roles in CHDs. Methionine synthase reductase (MTRR) is one of the key regulatory enzymes involved in the metabolic pathway of homocysteine. We investigated whether two polymorphisms (A66G and C524T) of the MTRR gene are associated with CHDs. A total of 599 children with CHDs and 672 healthy children were included; the polymorphisms were detected by PCR and RFLP analysis. Significant differences in the distributions of A66G and C524T alleles were observed between CHD cases and controls, and slightly increased risks of CHD were associated with 66GG and 524CT genotypes (odds ratios = 1.545 and 1.419, respectively). The genotype frequencies of 524CT in the VSD subgroup, 66GG and 524CT in the PDA subgroup were significantly different from those of controls. In addition, the combined 66AA/524CT, 66AG/524CT and 66GG/524CT in CHDs had odds ratios = 1.589, 1.422 and 1.934, respectively. Increased risks were also observed in 66AA/524CT and 66GG/524CT for ASD, 66AG/524CT for VSD, as well as 66GG/524CT for PDA. In conclusion, MTRR A66G and C524T polymorphisms are associated with increased risk of CHDs.

Maternal intake of folic acid and neural crest stem cells

Maternal folic acid (FA) intake has beneficial effects in preventing neural tube defects and may also play a role in the prevention of adult onset diseases such as Alzheimer's disease, dementia, neuropsychiatric disorders, cardiovascular diseases, and cerebral ischemia. This review will focus on the effects of maternal FA intake on neural crest stem cell proliferation and differentiation. Although FA is generally considered beneficial, it has the potential of promoting cell proliferation at the expense of differentiation. In some situations, this may lead to miscarriage or postnatal developmental abnormalities. Therefore, a blind approach such as "FA for everyone" is not necessarily the best course of action. Ultimately, the best approach for FA supplementation, and potentially other nutritional supplements, will include customized patient genomic profiles for determining dose and duration.

The N-methyl-d-aspartate receptor in heart development: a gene knockdown model using siRNA

Antagonists of the N-methyl-d-aspartate receptor (NMDAR) may disrupt the development of the cardiac neural crest (CNC) and contribute to conotruncal heart defects. To test this interaction, a loss-of-function model was generated using small interfering RNAs (siRNA) directed against the critical NR1-subunit of this receptor in avian embryos. The coding sequence of the chicken NR1 gene and predicted protein sequences were characterized and found to be homologous with other vertebrate species. Analysis of its spatiotemporal expression demonstrated its expression within the neural tube at pre-migratory CNC sites. siRNA targeted to the NR1-mRNA in pre-migratory CNC lead to a significant decrease in NR1 protein expression. However, embryo survival and heart development were not adversely affected. These results indicate that the CNC may function normally in the absence of functional NMDAR, and that NMDAR antagonists may have a complex impact upon the CNC that transcends impairment of a single receptor type.

Homocysteine enhances cardiac neural crest cell attachment in vitro by increasing intracellular calcium levels

Elevated homocysteine (Hcys) increases the risk of neurocristopathies. Previous studies show Hcys inhibits neural crest (NC) cell migration in vivo. However, the mechanisms responsible for this effect are unknown. Here, we evaluated the effect of Hcys on NC cell attachment in vitro and determined if any of the effects were due to altered Ca2+ signaling. We found Hcys enhanced NC cell attachment in a dose and substrate-dependent manner. Ionomycin mimicked the effect of Hcys while BAPTA-AM and 2-APB blocked the effect of Hcys on NC attachment. In contrast, inhibitors of plasma membrane Ca2+ channels had no effect on NC attachment. Hcys also increased the emission of the intracellular Ca2+-sensitive probe, Fluo-4. These results show Hcys alters NC attachment by triggering an increase in intracellular Ca2+ possibly by generating inositol triphosphate. Hence, the teratogenic effect ascribed to Hcys may be due to perturbation of intracellular Ca2+ signaling.

Folate-mediated one-carbon metabolism and neural tube defects: balancing genome synthesis and gene expression

Neural tube defects (NTDs) refer to a cluster of neurodevelopmental conditions associated with failure of neural tube closure during embryonic development. Worldwide prevalence of NTDs ranges from approximately 0.5 to 60 per 10,000 births, with regional and population-specific variation in prevalence. Numerous environmental and genetic influences contribute to NTD etiology; accumulating evidence from population-based studies has demonstrated that folate status is a significant determinant of NTD risk. Folate-mediated one-carbon metabolism (OCM) is essential for de novo nucleotide biosynthesis, methionine biosynthesis, and cellular methylation reactions. Periconceptional maternal supplementation with folic acid can prevent occurrence of NTDs in the general population by up to 70%; currently several countries fortify their food supply with folic acid for the prevention of NTDs. Despite the unambiguous impact of folate status on NTD risk, the mechanism by which folic acid protects against NTDs remains unknown. Identification of the mechanism by which folate status affects neural tube closure will assist in developing more efficacious and better targeted preventative measures. In this review, we summarize current research on the relationship between folate status and NTDs, with an emphasis on linking genetic variation, folate nutriture, and specific metabolic and/or genomic pathways that intersect to determine NTD outcomes.

Microarray analysis of homocysteine-responsive genes in cardiac neural crest cells in vitro

The amino acid homocysteine increases in the serum when there is insufficient folic acid or vitamin B(12), or with certain mutations in enzymes important in methionine metabolism. Elevated homocysteine is related to increased risk for cardiovascular and other diseases in adults and elevated maternal homocysteine increases the risk for certain congenital defects, especially those that result from abnormal development of the neural crest and neural tube. Experiments with the avian embryo model have shown that elevated homocysteine perturbs neural crest/neural tube migration in vitro and in vivo. Whereas there have been numerous studies of homocysteine-induced changes in gene expression in adult cells, there is no previous report of a homocysteine-responsive transcriptome in the embryonic neural crest. We treated neural crest cells in vitro with exogenous homocysteine in a protocol that induces significant changes in neural crest cell migration. We used microarray analysis and expression profiling to identify 65 transcripts of genes of known function that were altered by homocysteine. The largest set of effected genes (19) included those with a role in cell migration and adhesion. Other major groups were genes involved in metabolism (13); DNA/RNA interaction (11); cell proliferation/apoptosis (10); and transporter/receptor (6). Although the genes identified in this experiment were consistent with prior observations of the effect of homocysteine upon neural crest cell function, none had been identified previously as response to homocysteine in adult cells.

Homocysteine Concentrations and Molecular Analysis in Patients with Congenital Heart Defects

BACKGROUND

Congenital heart defects are the result of incomplete heart development and, like many diseases, have been associated with high homocysteine concentration.

METHODS

We evaluated homocysteine, folic acid and vitamin B(12) concentrations, and the mutations 677C>T and 1298A>C in MTHFR, 844ins68 in CBS and 2756A>G in MTR genes in 58 patients with congenital heart defects, 38 control subjects, and mothers of 49 patients and 26 controls.

RESULTS

Control and patients presented normal range concentrations for homocysteine (7.66 +/- 3.16 microM and 6.95 +/- 3.12 microM, respectively), folic acid (8.31 +/- 3.00 ng/mL and 11.84 +/- 10.74 ng/mL) and vitamin B(12,) (613.56 +/- 307.57 pg/mL and 623.37 +/- 303.12 pg/mL), which did not differ among groups. For the mothers studied, homocysteine and vitamin B(12) concentrations also did not differ between groups. However, folic acid concentrations of mothers showed significant difference, the highest values being in the group of patients. No difference was found in allele frequencies among all groups studied.

CONCLUSIONS

In the studied groups, high homocysteine seems not to be correlated with congenital heart defects, as well as folic acid and vitamin B(12). The mutations studied, in isolation, were not related to congenital heart defects, but high concentration of maternal homocysteine is associated with the presence of three or four mutated alleles.

Failure of homocysteine to induce neural tube defects in a mouse model

BACKGROUND

Folate deficiencies have been associated with many adverse congenital abnormalities. It is not clear, however, whether these defects are due to a folate deficiency or to an increase in homocysteine. Homocysteine has been shown to be teratogenic in the chicken-embryo model and it has been suggested that homocysteine-induced defects are mediated by inhibiting the N-methyl-D-aspartate (NMDA) receptor on neural crest cells. The majority of the teratology studies have been carried out using the chicken embryo model. In an effort to develop a murine model of homocysteine-induced neural tube defects, several inbred mouse strains were treated with homocysteine or the NMDA inhibitor MK801 and the fetuses examined for any induced-NTD.

METHODS

Several in-bred mouse strains were administered homocysteine once on gestational day (GD) E8.5 or once daily on GD 6.5-10.5. Additionally, because homocysteine was been reported to mediate its effects through the NMDA receptor, the effect of MK801, an antagonist of this receptor, was also investigated.

RESULTS

Regardless of the mouse treatment time, homocysteine failed to induce neural tube defects in our in-bred mouse strains. Homocysteine also failed to increase the number of neural tube defects in the splotch strain, regardless of the genotype.

CONCLUSIONS

Irrespective of the mouse strain or treatment, homocysteine failed to induce neural tube defects in our mouse models, which is in contrast to what has been reported in the chicken embryo models.

Sulfur amino acid metabolism in pregnancy: the impact of methionine in the maternal diet

Animal studies show that the balance of methionine relative to other amino acids in the maternal diet is critical, as fetal growth is not only retarded by diets that are deficient but also by those containing excess. Diets with an inappropriate balance of methionine can adversely affect both short-term reproductive function and the long-term physiology of the offspring. The catabolism of unused methionine increases the demand for glycine and may cause a deficiency. High levels of methionine may also perturb intracellular S-adenosyl methionine pools and have an effect on the methylation of DNA and proteins. Excess methionine in the diet may also indirectly influence fetal development through the production of homocysteine or by the perturbation of endocrine functions. The metabolic interactions among dietary methionine, folic acid, and choline mean that other diet components can also change the methionine requirement.

The expression of the NR1-subunit of the NMDA receptor during mouse and early chicken development

It has been suggested that homocysteine-induced defects are mediated by the inhibition of the N-methyl-d-aspartate (NMDA) receptor on neural crest cells. However, the majority of this work has been performed using the chicken embryo model. In an effort to better understand the molecular events involved a murine model of homocysteine-induced defects was sought. However, it has been previously shown that homocysteine failed to induce congenital defects in several strains of mouse. Therefore, in an effort to better understand the difference in the susceptibility between these two species we investigated the ontogeny of the NMDA receptor in the mouse and chicken. To determine the expression of the NMDA receptor we performed Western blot analysis using an antibody to the NR1-subunit of the NMDA receptor in both the chicken and mouse embryos. Further, we used RT-PCR to determine the temporal expression of this subunit in the murine embryos from gestational day 8.5 to 18.5 to confirm our Western blot analysis. Results from these studies demonstrated that the expression of the NMDA receptor was expressed during the early stages of development in the chick embryo but neither the transcript nor the protein was detected in mouse embryos until later in development. These results demonstrate that during the stages of neurulation and/or early heart development the expression of the NR1-subunit of the NMDA receptor was not detected. The expression of this gene increased and was detectable by gestational days 14.5-15.5 and continued to increase in its expression until term. Therefore, these experiments suggest that homocysteine-induced defects may be mediated via the NMDA receptor.

Maternal MTHFR 677C>T is a risk factor for congenital heart defects: effect modification by periconceptional folate supplementation

AIMS

Periconceptional folate supplementation prevents neural tube defects and possibly congenital heart defects (CHD) as well. The search for candidate genes involved in the folate metabolism includes the methylenetetrahydrofolate reductase (MTHFR) 677C > T polymorphism. We studied the association between MTHFR 677C > T variants and CHD risk. The interaction with periconceptional folate supplementation was also investigated.

METHODS AND RESULTS

A case-control study and a family-based transmission disequilibrium test (TDT) were conducted to explore this association. In 133 triads, the TDT revealed no association of the fetal 677T allele with the development of a heart defect. In 158 mothers with a CHD-affected child, the maternal MTHFR 677CT and TT genotypes in combination with no use of periconceptional folate supplements were associated with, respectively, a three-fold (OR 3.3 95% CI 1.46-7.32) and six-fold (OR 6.3 95% CI 2.32-17.27) increased risk for conotruncal heart defects in offspring. In a case-only study, the interaction between periconceptional folate supplementation and maternal MTHFR genotype was significant (P = 0.012).

CONCLUSION

The maternal MTHFR 677C > T variants are a risk factor for CHD in offspring, confined to conotruncal heart defects. A gene-environment interaction between maternal MTFHR 677CT and TT genotypes with periconceptional folate supplementation was observed. These findings provide a mechanism of the protective role of folate and support the thesis that periconceptional folate supplementation might prevent CHD.

Cardiac neural crest

Neural crest cells (NCCs) contribute to many organs and tissues during embryonic development. Amongst these, the cardiovascular system represents a fascinating example. In this review, recent advances in our understanding of the developmental biology and molecular genetics regulating cardiac NCC maturation will be summarized. While the existence of a significant neural crest (NC) contribution to the developing heart has been appreciated for more than 20 years, only in the last few years have molecular pathways regulating this process been elucidated and the significant contribution of these mechanisms to the etiology of congenital heart disease in man become apparent. Emerging data suggest that ongoing studies will reveal complex inductive interactions between cardiac NC and a series of other cell types contributing to the developing cardiovascular system.

Maternal methylenetetrahydrofolate reductase deficiency and low dietary folate lead to adverse reproductive outcomes and congenital heart defects in mice

BACKGROUND

Genetic or nutritional disturbances in folate metabolism may affect embryonic development because of the critical role of folate in nucleotide synthesis and methylation reactions. The possible role of a mild deficiency in methylenetetrahydrofolate reductase (MTHFR) and low dietary folate in pregnancy outcomes and heart morphogenesis requires further investigation.

OBJECTIVE

We investigated the effect of mild MTHFR deficiency, low dietary folate, or both on resorption rates, on length and weight, and on the incidence of heart malformations in murine embryos.

DESIGN

Female Mthfr +/+ and +/- mice were fed a control diet (CD) or a folic acid-deficient diet (FADD) before mating with male Mthfr +/- mice. On gestational day 14.5, implantation and resorption sites were recorded and viable embryos were examined for gross malformations, growth delay, and congenital heart defects.

RESULTS

Plasma homocysteine in Mthfr +/- dams and in FADD-treated dams was significantly higher than that in Mthfr +/+ dams and CD-treated dams, respectively. A significantly higher rate of resorption and greater developmental delay were observed in hyperhomocysteinemic mice than in CD-treated +/+ dams. Heart defects were identified in 4 of 11, 5 of 10, and 4 of 10 litters from CD-treated +/-, FADD-treated +/+, and FADD-treated +/- dams, respectively, but not in any of those from CD-treated +/+ dams (0/11 litters).

CONCLUSION

Our findings suggest that mild MTHFR deficiency, low dietary folate, or both in the dams increase the incidence of fetal loss, intrauterine growth retardation, and heart defects. These data support the benefit of folic acid supplementation in pregnant women, particularly in those with MTHFR deficiency.

Developmental consequences of abnormal folate transport during murine heart morphogenesis

BACKGROUND

Folic acid is essential for the synthesis of nucleotides and methyl transfer reactions. Folic acid-binding protein one (Folbp1) is the primary mediator of folic acid transport into murine cells. Folbp1 knockout mouse embryos die in utero with multiple malformations, including severe congenital heart defects (CHDs). Although maternal folate supplementation is believed to prevent human conotruncal heart defects, its precise role during cardiac morphogenesis remains unclear. In this study, we examined the role of folic acid on the phenotypic expression of heart defects in Folbp1 mice, mindful of the importance of neural crest cells to the formation of the conotruncus.

METHODS

To determine if the Folbp1 gene participates in the commitment and differentiation of the cardiomyocytes, relative levels of dead and proliferating precursor cells in the heart were examined by flow cytometry, Western blot, and immunohistostaining.

RESULTS

Our studies revealed that impaired folic acid transport results in extensive apoptosis-mediated cell death, which concentrated in the interventricular septum and truncus arteriosus, thus being anatomically restricted to the two regions of congenital heart defects. Together with a reduced proliferative capacity of the cardiomyocytes, the limited size of the available precursor cell pool may contribute to the observed cardiac defects. Notably, there is a substantial reduction in Pax-3 expression in the region of the presumptive migrating cardiac neural crest, suggesting that this cell population may be the most severely affected by the massive cell death.

CONCLUSIONS

Our findings demonstrate for the first time a prominent role of the Folbp1 gene in mediating susceptibility to heart defects.

The High Atherosclerotic Risk Among Epileptics: the Atheroprotective Role of Multivitamins

Neurologists have little concern about the high atherosclerotic risk among epileptics. Recent evidences mount that chronic epilepsy and prolonged use of antiepileptic drugs (AEDs) are associated with multiple risk factors that are critically implicated in pathobiology and dysfunction of the vessel wall through complex molecular mechanisms that promote atherogenesis. This review is concerned with three metabolic alterations, which are attributed as major risk factors for atherosclerosis among epileptics: altered metabolism of a) homocysteine (Hcy), b) lipids and lipoproteins, and c) uric acid. Most conventional AEDs reduce folic acid levels, thereby raising Hcy levels. Hyperhomosysteinemia is recently believed to induce endothelial dysfunction and promote atherosclerosis through complex oxidative and excitatory neurotoxic molecular mechanisms. However, Hcy itself is a convulsing substance with increased seizure recurrence and intractability to antiepileptic medications. AEDs can disturb lipid metabolism with resultant hypercholestrolemia and dyslipidemia, common recognized risks for atherosclerosis. Altered uric acid metabolism is common among epileptics. Uric acid has been implicated in endothelial cell damage and decreased endothelial nitric oxide bioavailability. In the presence of atherosclerotic milieu, uric acid interacts with other substrate toxicities and increased reactive oxygen species, accelerating atherosclerosis. The above information forms the rationale for future routine screening and correction of such metabolic alterations in epileptics. A convincing argument now develops that routine polyvitamin supplementation (folic acid, vitamin B12, vitamin B6, vitamin C, vitamin E, and beta-carotene) becomes increasingly important for women and men receiving AEDs at all ages. The atheroprotective effect of multivitamins is through their antioxidant and anti-inflammatory effects together with their lipid and Hcy lowering effects.

Similar rhythms of seasonal conceptions in neural tube defects and schizophrenia: A hypothesis of oxidant stress and the photoperiod

BACKGROUND

Numerous studies have found that people with schizophrenia tend to be born most often in late winter and least often in late summer. The same rhythm appears in the birth of children with neural tube defects (NTDs). In the northern hemisphere, both disorders thus show a conception peak in May-June and a trough around November-December. The senior author found the same May-June conception peak among left-handed American baseball players and the opposite effect (a November-December peak) among extreme right-handed players. A similar rhythm appeared with respect to characteristics related to artistic as opposed to scientific modes of thought.

DISCUSSION

Schizophrenia has been proposed to involve a deficit in the establishment of lateral asymmetry, as does left-handedness. The artist-scientist dichotomy is also believed to involve cerebral dominance. Thus, the similarity of seasonal variation in month of conception between NTDs, schizophrenia, left-handedness, and artistic intuition suggests that these four conditions may share some factor affecting the cellular processes involved in both neural tube closure and asymmetry development during the early-fourth week, neural-fold stages of embryogenesis. We propose that maternal oxidant stress, which can rise with exposure to intense solar radiation, may interfere with both neural tube closure and asymmetry development. The June and December extremes of sunlight would thus explain the peak times of the seasonal fluctuations. Moreover, regardless of mechanisms, the parallel between the two conception rhythms suggests that the same periconceptional folate regimens found effective in preventing NTDs may also lower the risk of schizophrenia. This paper reviews some of the clinical and experimental evidence supporting this hypothesis.