Diabetic embryopathy: a role for the epigenome?

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.

Intrauterine Programming of Diabetes Induced Cardiac Embryopathy

BACKGROUND

Maternal hyperglycemia is a well-recognized risk factor for fetal congenital heart disease. However, the underlying cellular and molecular mechanisms are not well characterized. We hypothesize that maternal hyperglycemia leading to congenital heart are linked to abnormal DNA methylation and mRNA expression at cardiac specific loci.

METHODS

Hyperglycemia was induced in normal 8-week old CD-1 female mice with a one-time intraperitoneal injection of 150 mg/kg of streptozotocin (STZ) 2 weeks prior to mating. Histological analysis of fetal cardiac morphology was evaluated for malformations on embryonic day (E) 16.5 of control pups and pups exposed to maternal hyperglycemia. We used a massively-parallel sequencing-based methylation sensitive restriction based assay to examine genome-wide cytosine methylation levels at >1.65 million loci in neonatal hearts on post-natal (P) day 0. Functional validation was performed with real time quantitative polymerase chain reaction (RT-qPCR).

RESULTS

Cardiac structural defects occurred in 28% of the pups (n=12/45) of hyperglycemic dams versus 7% (n=4/61) of controls. Notable phenotypes were hypoplastic left or right ventricle, double outlet right ventricle, ventricular septal defect, and left ventricular outflow tract obstruction. A 10-fold increase in DNA methylation of gene promoter regions was seen in many cardiac important genes in the experimental versus control P0 neonates and have corresponding decreases in gene expression in 21/32 genes functionally validated.

CONCLUSION

Maternal hyperglycemia alters DNA methylation and mRNA expression of some cardiac genes during heart development. Quantitative, genome-wide assessment of cytosine methylation can be used as a discovery platform to gain insight into the mechanisms of hyperglycemia-induced cardiac anomalies.

Fish consumption in early pregnancy and congenital gastrointestinal tract atresia in the Japan Environment and Children's Study

Current evidence suggests that the aetiology of congenital gastrointestinal (GI) tract atresia is multifactorial, and not based solely on genetic factors. However, there are no established modifiable risk factors for congenital GI tract atresia. We used data from a Japanese nationwide birth cohort study launched in 2011, and examined whether fish consumption in early pregnancy was associated with congenital GI tract atresia. We analysed data of 89 495 women (mean age at delivery=31·2 years) who delivered singleton live births without chromosomal anomalies. Based on the results of the FFQ, we estimated the daily intake of fish and n-3 PUFA consumption in early pregnancy. We defined a composite outcome (oesophageal atresia, duodenal atresia, jejunoileal atresia and/or anorectal malformation) as congenital GI tract atresia. In this population, median fish intake was 31·9 g/d, and seventy-four cases of congenital GI tract atresia were identified. Fish consumption in early pregnancy was inversely associated with the composite outcome (multivariable-adjusted OR for the high v. low consumption category=0·5, 95 % CI 0·3, 1·0). For all the specific types of atresia, decreased OR were observed in the high consumption category, although not statistically significant. Reduced atresia occurrence was observed even beyond the US Food and Drug Administration's recommended consumption of no more than 340 g/week. Also, n-3 PUFA-rich fish and n-3 PUFA consumptions tended to be inversely associated with atresia. Fish consumption in early pregnancy may be a preventive factor for congenital GI tract atresia.

Folates in Plants: Research Advances and Progress in Crop Biofortification

Folates, also known as B9 vitamins, serve as donors and acceptors in one-carbon (C1) transfer reactions. The latter are involved in synthesis of many important biomolecules, such as amino acids, nucleic acids and vitamin B5. Folates also play a central role in the methyl cycle that provides one-carbon groups for methylation reactions. The important functions fulfilled by folates make them essential in all living organisms. Plants, being able to synthesize folates de novo, serve as an excellent dietary source of folates for animals that lack the respective biosynthetic pathway. Unfortunately, the most important staple crops such as rice, potato and maize are rather poor sources of folates. Insufficient folate consumption is known to cause severe developmental disorders in humans. Two approaches are employed to fight folate deficiency: pharmacological supplementation in the form of folate pills and biofortification of staple crops. As the former approach is considered rather costly for the major part of the world population, biofortification of staple crops is viewed as a decent alternative in the struggle against folate deficiency. Therefore, strategies, challenges and recent progress of folate enhancement in plants will be addressed in this review. Apart from the ever-growing need for the enhancement of nutritional quality of crops, the world population faces climate change catastrophes or environmental stresses, such as elevated temperatures, drought, salinity that severely affect growth and productivity of crops. Due to immense diversity of their biochemical functions, folates take part in virtually every aspect of plant physiology. Any disturbance to the plant folate metabolism leads to severe growth inhibition and, as a consequence, to a lower productivity. Whereas today's knowledge of folate biochemistry can be considered very profound, evidence on the physiological roles of folates in plants only starts to emerge. In the current review we will discuss the implication of folates in various aspects of plant physiology and development.

Embryonic defence mechanisms against glucose-dependent oxidative stress require enhanced expression of Alx3 to prevent malformations during diabetic pregnancy

Oxidative stress constitutes a major cause for increased risk of congenital malformations associated to severe hyperglycaemia during pregnancy. Mutations in the gene encoding the transcription factor ALX3 cause congenital craniofacial and neural tube defects. Since oxidative stress and lack of ALX3 favour excessive embryonic apoptosis, we investigated whether ALX3-deficiency further increases the risk of embryonic damage during gestational hyperglycaemia in mice. We found that congenital malformations associated to ALX3-deficiency are enhanced in diabetic pregnancies. Increased expression of genes encoding oxidative stress-scavenging enzymes in embryos from diabetic mothers was blunted in the absence of ALX3, leading to increased oxidative stress. Levels of ALX3 increased in response to glucose, but ALX3 did not activate oxidative stress defence genes directly. Instead, ALX3 stimulated the transcription of Foxo1, a master regulator of oxidative stress-scavenging genes, by binding to a newly identified binding site located in the Foxo1 promoter. Our data identify ALX3 as an important component of the defence mechanisms against the occurrence of developmental malformations during diabetic gestations, stimulating the expression of oxidative stress-scavenging genes in a glucose-dependent manner via Foxo1 activation. Thus, ALX3 deficiency provides a novel molecular mechanism for developmental defects arising from maternal hyperglycaemia.

Maternal diabetes modulates dental epithelial stem cells proliferation and self-renewal in offspring through apurinic/apyrimidinicendonuclease 1-mediated DNA methylation

Maternal gestational diabetes mellitus (GDM) has many adverse effects on the development of offspring. Aberrant DNA methylation is a potential mechanism associated with these effects. However, the effects of GDM on tooth development and the underlying mechanisms have not been thoroughly investigated. In the present study, a GDM rat model was established and incisor labial cervical loop tissue and dental epithelial stem cells (DESCs) were harvested from neonates of diabetic and control dams. GDM significantly suppressed incisor enamel formation and DESCs proliferation and self-renewal in offspring. Gene expression profiles showed that Apex1 was significantly downregulated in the offspring of diabetic dams. In vitro, gain and loss of function analyses showed that APEX1 was critical for DESCs proliferation and self-renewal and Oct4 and Nanog regulation via promoter methylation. In vivo, we confirmed that GDM resulted in significant downregulation of Oct4 and Nanog and hypermethylation of their promoters. Moreover, we found that APEX1 modulated DNA methylation by regulating DNMT1 expression through ERK and JNK signalling. In summary, our data suggest that GDM-induced APEX1 downregulation increased DNMT1 expression, thereby inhibiting Oct4 and Nanog expression, through promoter hypermethylation, resulting in suppression of DESCs proliferation and self-renewal, as well as enamel formation.

Prepregnancy Diabetes and Offspring Risk of Congenital Heart Disease: A Nationwide Cohort Study

BACKGROUND

Maternal diabetes mellitus is associated with an increased risk of offspring congenital heart defects (CHD); however, the causal mechanism is poorly understood. We further investigated this association in a Danish nationwide cohort.

METHODS AND RESULTS

In a national cohort study, we identified 2 025 727 persons born from 1978 to 2011; among them were 7296 (0.36%) persons exposed to maternal pregestational diabetes mellitus. Pregestational diabetes mellitus was identified by using the National Patient Register and individual-level information on all prescriptions filled in Danish pharmacies. Persons with CHD (n=16 325) were assigned to embryologically related cardiac phenotypes. The CHD prevalence in the offspring of mothers with pregestational diabetes mellitus was 318 per 10 000 live births (n=232) in comparison with a baseline risk of 80 per 10 000; the adjusted relative risk for CHD was 4.00 (95% confidence interval, 3.51-4.53). The association was not modified by year of birth, maternal age at diabetes onset, or diabetes duration, and CHD risks associated with type 1 (insulin-dependent) and type 2 (insulin-independent) diabetes mellitus did not differ significantly. Persons born to women with previous acute diabetes complications had a higher CHD risk than those exposed to maternal diabetes mellitus without complications (relative risk, 7.62; 95% confidence interval, 5.23-10.6, and relative risk, 3.49; 95% confidence interval, 2.91-4.13, respectively; P=0.0004). All specific CHD phenotypes were associated with maternal pregestational diabetes mellitus (relative risk range, 2.74-13.8).

CONCLUSIONS

The profoundly increased CHD risk conferred by maternal pregestational diabetes mellitus neither changed over time nor differed by diabetes subtype. The association with acute pregestational diabetes complications was particularly strong, suggesting a role for glucose in the causal pathway.

The status of diabetic embryopathy

Diabetic embryopathy is a theoretical enigma and a clinical challenge. Both type 1 and type 2 diabetic pregnancy carry a significant risk for fetal maldevelopment, and the precise reasons for the diabetes-induced teratogenicity are not clearly identified. The experimental work in this field has revealed a partial, however complex, answer to the teratological question, and we will review some of the latest suggestions.

High glucose-induced oxidative stress represses sirtuin deacetylase expression and increases histone acetylation leading to neural tube defects

Aberrant epigenetic modifications are implicated in maternal diabetes-induced neural tube defects (NTDs). Because cellular stress plays a causal role in diabetic embryopathy, we investigated the possible role of the stress-resistant sirtuin (SIRT) family histone deacetylases. Among the seven sirtuins (SIRT1-7), pre-gestational maternal diabetes in vivo or high glucose in vitro significantly reduced the expression of SIRT 2 and SIRT6 in the embryo or neural stem cells, respectively. The down-regulation of SIRT2 and SIRT6 was reversed by superoxide dismutase 1 (SOD1) over-expression in the in vivo mouse model of diabetic embryopathy and the SOD mimetic, tempol and cell permeable SOD, PEGSOD in neural stem cell cultures. 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), a superoxide generating agent, mimicked high glucose-suppressed SIRT2 and SIRT6 expression. The acetylation of histone 3 at lysine residues 56 (H3K56), H3K14, H3K9, and H3K27, putative substrates of SIRT2 and SIRT6, was increased by maternal diabetes in vivo or high glucose in vitro, and these increases were blocked by SOD1 over-expression or tempol treatment. SIRT2 or SIRT6 over-expression abrogated high glucose-suppressed SIRT2 or SIRT6 expression, and prevented the increase in acetylation of their histone substrates. The potent sirtuin activator (SRT1720) blocked high glucose-increased histone acetylation and NTD formation, whereas the combination of a pharmacological SIRT2 inhibitor and a pan SIRT inhibitor mimicked the effect of high glucose on increased histone acetylation and NTD induction. Thus, diabetes in vivo or high glucose in vitro suppresses SIRT2 and SIRT6 expression through oxidative stress, and sirtuin down-regulation-induced histone acetylation may be involved in diabetes-induced NTDs. The mechanism underlying pre-gestational diabetes-induced neural tube defects (NTDs) is still elusive. Our study unravels a new epigenetic mechanism in which maternal diabetes-induced oxidative stress represses sirtuin deacetylase 2 (SIRT2) and 6 (SIRT6) expression leading to histone acetylation and gene expression. SIRT down-regulation mediates the teratogenicity of diabetes leading to (NTD) formation. The study provides a mechanistic basis for the development of natural antioxidants and SIRT activators as therapeutics for diabetic embryopathy.

Effect of maternal diabetes on the embryo, fetus, and children: congenital anomalies, genetic and epigenetic changes and developmental outcomes

INTRODUCTION

Pregestational and gestational diabetes mellitus (PGDM; GDM) are significant health concerns because they are associated with an increased rate of malformations and maternal health complications.

METHODS

We reviewed the data that help us to understand the effects of diabetes in pregnancy.

RESULTS

Diabetic embryopathy can affect any developing organ system, but cardiovascular and neural tube defects are among the most frequent anomalies. Other complications include preeclampsia, preterm delivery, fetal growth abnormalities, and perinatal mortality. Neurodevelopmental studies on offspring of mothers with diabetes demonstrated increased rate of Gross and Fine motor abnormalities, of Attention Deficit Hyperactivity Disorder, learning difficulties, and possibly also Autism Spectrum Disorder. The mechanisms underlying the effects of maternal hyperglycemia on the developing fetus may involve increased oxidative stress, hypoxia, apoptosis, and epigenetic changes. Evidence for epigenetic changes are the following: not all progeny are affected and not to the same extent; maternal diet may influence pregnancy outcomes; and maternal diabetes alters embryonic transcriptional profiles and increases the variation between transcriptomic profiles as a result of altered gene regulation. Research in animal models has revealed that maternal hyperglycemia is a teratogen, and has helped uncover potential therapeutic targets which, when blocked, can mitigate or ameliorate the negative effects of diabetes on the developing fetus.

CONCLUSIONS

Tight metabolic control, surveillance, and labor management remain the cornerstone of care for pregnant women with diabetes, but advances in the field indicate that new treatments to protect the mother and baby are not far from becoming clinical realities.

A novel association of biventricular cardiac noncompaction and diabetic embryopathy: case report and review of the literature

Diabetic embryopathy refers to a constellation of congenital malformations arising in the setting of poorly controlled maternal diabetes mellitus. Cardiac abnormalities are the most frequently observed findings, with a 5-fold risk over normal pregnancies. Although a diverse spectrum of cardiac defects has been documented, cardiac noncompaction morphology has not been associated with this syndrome. In this report, we describe a novel case of biventricular cardiac noncompaction in a neonate of a diabetic mother. The patient was a late preterm female with right anotia, caudal dysgenesis, multiple cardiac septal and aortic arch defects, and biventricular cardiac noncompaction. Examination of both ventricles demonstrated spongy myocardium with increased myocardial trabeculation greater than 50% left ventricular thickness and greater than 75% right ventricular thickness, with hypoplasia of the bilateral papillary muscles, consistent with noncompaction morphology. Review of the literature highlights the importance of gene expression and epigenomic regulation in cardiac embryogenesis.

Gene expression in teratogenic exposures: a new approach to understanding individual risk

The phenomenon of partial or incomplete penetrance is common to many paradigms of exposure to teratogens, where only some of the exposed individuals exhibit developmental defects. We here argue that the most widely used experimental approaches in reproductive toxicology do not take partial penetrance into account, and are thus likely to miss differences between affected and unaffected individuals that contribute to susceptibility for teratogenesis. We propose that focus on the variation between exposed individuals could help to discover factors that may play a causative role for abnormal developmental processes that occur with incomplete penetrance.

Epigenetics and primary care

Epigenetics, the study of functionally relevant chemical modifications to DNA that do not involve a change in the DNA nucleotide sequence, is at the interface between research and clinical medicine. Research on epigenetic marks, which regulate gene expression independently of the underlying genetic code, has dramatically changed our understanding of the interplay between genes and the environment. This interplay alters human biology and developmental trajectories, and can lead to programmed human disease years after the environmental exposure. In addition, epigenetic marks are potentially heritable. In this article, we discuss the underlying concepts of epigenetics and address its current and potential applicability for primary care providers.

Diabetic embryopathy: a developmental perspective from fertilization to adulthood

Maternal diabetes mellitus is one of the strongest human teratogens. Despite recent advances in the fields of clinical embryology, experimental teratology and preventive medicine, diabetes-related perturbations of the maternofetal unit maintain a considerable impact on the Healthcare System. Classic consequences of prenatal exposure to hyperglycemia encompass (early) spontaneous abortions, perinatal death and malformations. The spectrum of related malformations comprises some recurrent blastogenic monotopic patterns, i.e. holoprosencephaly, caudal dysgenesis and oculoauriculovertebral spectrum, as well as pleiotropic syndromes, i.e. femoral hypoplasia-unusual face syndrome. Despite this, most malformed fetuses display multiple blastogenic defects of the VACTERL type, whose (apparently) casual combination preclude recognizing recurrent patterns, but accurately testifies to their developmental stage at onset. With the application of developmental biology in modern medicine, the effects of diabetes on the unborn patient are expanded to include the predisposition to develop insulin resistance in adulthood. The mechanisms underlying the transgenerational correlation between maternal diabetes and proneness to adult disorders in the offspring remain unclear, and the epigenetic plasticity may represent the missing link. In this scenario, a development-driven summary of the multifaced consequences of maternal diabetes on fertility and child health may add a practical resource to the repertoire of available information on early stages of embryogenesis.

Increased susceptibility of HIF-1α heterozygous-null mice to cardiovascular malformations associated with maternal diabetes

Cardiovascular malformations are the most common manifestation of diabetic embryopathy. The molecular mechanisms underlying the teratogenic effect of maternal diabetes have not been fully elucidated. Using genome-wide expression profiling, we previously demonstrated that exposure to maternal diabetes resulted in dysregulation of the hypoxia-inducible factor 1 (HIF-1) pathway in the developing embryo. We thus considered a possible link between HIF-1-regulated pathways and the development of congenital malformations. HIF-1α heterozygous-null (Hif1a(+/-)) and wild type (Wt) littermate embryos were exposed to the intrauterine environment of a diabetic mother to analyze the frequency and morphology of congenital defects, and assess gene expression changes in Wt and Hif1a(+/-) embryos. We observed a decreased number of embryos per litter and an increased incidence of heart malformations, including atrioventricular septal defects and reduced myocardial mass, in diabetes-exposed Hif1a(+/-) embryos as compared to Wt embryos. We also detected significant differences in the expression of key cardiac transcription factors, including Nkx2.5, Tbx5, and Mef2C, in diabetes-exposed Hif1a(+/-) embryonic hearts compared to Wt littermates. Thus, partial global HIF-1α deficiency alters gene expression in the developing heart and increases susceptibility to congenital defects in a mouse model of diabetic pregnancy.

Variation in ultraviolet radiation and diabetes: evidence of an epigenetic effect that modulates diabetics' lifespan

Background

Published research has shown that month-of-birth variations modulate the incidence of adult human diseases. This article explores diabetes type 2 as one of those diseases. This study uses the death records of approximately 829,000 diabetics (approximately 90% were type-2) born before the year 1945 (and dying between 1979 and 2005) to show that variations in adult lifespan vary with ultraviolet radiation (UVR) at solar cycle peaks (MAX, approximately a three-year period) with less at non-peaks (MIN, approximately an eight-year period). The MAX minus MIN (in years) was our measure of sensitivity (for example, responsiveness) to long-term variations in UVR.

Results

Diabetics were less sensitive than non-diabetics, and ethnic minorities were more sensitive than whites. Diabetic males gained 6.1 years, and females 2.3 years over non-diabetics, with diabetic males gaining an average of 3.8 years over diabetic females. Most variation in lifespan occurred in those conceived around the seasonal equinoxes, suggesting that the human epigenome at conception is especially influenced by rapid variation in UVR. With rapidly decreasing UVR at conception, lifespan decreased in the better-nourished, white, female diabetic population.

Conclusions

Rapidly changing UVR at the equinoxes modulates the expression of an epigenome involving the conservation of energy, a mechanism especially canalized in women. Decreasing UVR at conception and early gestation stimulates energy conservation in persons we consider ‘diabetic’ in today’s environment of caloric surfeit. In the late 19th and early 20th centuries ethnic minorities had poorer nutrition, laborious work, and leaner bodies, and in that environment a calorie-conserving epigenome was a survival advantage. Ethnic minorities with a similar epigenome lived long enough to express diabetes as we define it today and exceeded the lifespan of their non-diabetic contemporaries, while that epigenome in diabetics in the nutritional environment of today is detrimental to lifespan.

Altered pregnancy outcomes in mice following treatment with the hyperglycaemia mimetic, glucosamine, during the periconception period

Exposure of cumulus–oocyte complexes to the hyperglycaemia mimetic, glucosamine, during in vitro maturation impairs embryo development, potentially through upregulation of the hexosamine biosynthesis pathway. This study examined the effects of in vivo periconception glucosamine exposure on reproductive outcomes in young healthy mice, and further assessed the effects in overweight mice fed a high-fat diet. Eight-week-old mice received daily glucosamine injections (20 or 400 mg kg–1) for 3–6 days before and 1 day after mating (periconception). Outcomes were assessed at Day 18 of gestation. Glucosamine treatment reduced litter size independent of dose. A high-fat diet (21% fat) for 11 weeks before and during pregnancy reduced fetal size. No additional effects of periconception glucosamine (20 mg kg–1) on pregnancy outcomes were observed in fat-fed mice. In 16-week-old mice fed the control diet, glucosamine treatment reduced fetal weight and increased congenital abnormalities, but did not alter litter size. As differing effects of glucosamine were observed in 8-week-old and 16-week-old mice, maternal age effects were assessed. Periconception glucosamine at 8 weeks reduced litter size, whereas glucosamine at 16 weeks reduced fetal size. Thus, in vivo periconception glucosamine exposure perturbs reproductive outcomes in mice, with the nature of the outcomes dependent upon maternal age.

Early determinants of type-2 diabetes

The global prevalence of type-2 diabetes (T2D) has more than doubled in the last 30 years and is predicted to continue to rise at an alarming rate. The associated health and financial burdens are considerable. The aetiology of common forms of T2D is multifactorial and involves a complex interplay between genetic, epigenetic and environmental factors. The influential role of the environment, in particular our diet and sedentary lifestyles, in diabetes risk is well established. Of major concern is the increasing prevalence of early onset T2D or pre-diabetic characteristics in children. In recent years, the role of the early life environment in programming diabetes risk has been the focus of numerous human and animal studies. Historical studies highlighted an association between low birthweight, a proxy for suboptimal in utero growth, and diabetes risk in adulthood. Over more recent years it has become apparent that a variety of expositions, including maternal obesity and/or maternal diabetes, can have a significant effect on offspring health outcomes. Further complicating matters, paternal and transgenerational transmission of T2D can occur thus mediating a perpetuating cycle of disease risk between generations. It is imperative for the underlying mechanisms to be elucidated so that interventions can be introduced. In doing so, it may be possible to prevent, delay or reverse a pre-programmed risk for T2D induced by pre- and/or postnatal environmental factors to improve health outcomes and curb premature metabolic decline. This review presents evidence for how the early life environment may programme T2D risk and suggests some mechanisms by which this may occur.

Responses of the embryonic epigenome to maternal diabetes

Maternal diabetes and obesity are independent risk factors for neural tube defects, although it is unclear whether the effects are mediated by common pathogenic mechanisms. In this manuscript, we report a genome-wide survey of histone acetylation in neurulation stage embryos from mouse pregnancies with different metabolic conditions: maternal diabetes, and maternal consumption of a high fat content diet. We find that maternal diabetes, and independently, exposure to high-fat diet, are associated with increases and decreases of H3 and H4 histone acetylation in the embryo. Intriguingly, changes of H3K27 acetylation marks are significantly enriched near genes known to cause neural tube defects in mouse mutants. These data suggest that epigenetic changes in response to diet and metabolic condition may contribute to increased risk for neural tube defects in diabetic and obese pregnancies. Importantly, the responses to high-fat diet and maternal diabetes were distinct, suggesting that perturbed embryonic development under these conditions is mediated by different molecular pathways. This conclusion is supported by morphometric analyses that reveal a trend for maternal diabetes to delay embryonic development in the C57BL/6 strain, while high-fat diet appears to be associated with accelerated development. Taken together, our results link changes in histone acetylation to metabolic conditions during pregnancy, and implicate distinct epigenetic mechanisms in susceptibility to neural tube defects under conditions of maternal diabetes and obesity.

Genetic susceptibility to teratogens: state of the art

There is evidence that the susceptibility to the teratogenic effect of drugs within human populations varies extremely from one individual to another, even after identical exposures. One of the factors that may explain these interindividual differences is the genetic makeup in the pharmacokinetics and pharmacodynamics of the respective drugs. In fact, both maternal and embryonic/fetal genotypes can affect placental transport, absorption, metabolism, distribution and receptor binding of an agent, influencing its teratogenicity. We have reviewed the literature and commented on the reported correlations between genetic factors and drug-induced birth defects. There is still a clear lack of knowledge regarding this issue and the available data are often conflicting. However, the identification of specific polymorphisms associated with predisposition to teratogenesis may allow in the future the development of personalized non-teratogenic therapies for pregnant women.

Genetic and epigenomic footprints of folate

Dietary micronutrient composition has long been recognized as a determining factor for human health. Historically, biochemical research has successfully unraveled how vitamins serve as essential cofactors for enzymatic reactions in the biochemical machinery of the cell. Folate, also known as vitamin B9, follows this paradigm as well. Folate deficiency is linked to adverse health conditions, and dietary supplementation with folate has proven highly beneficial in the prevention of neural tube defects. With its function in single-carbon metabolism, folate levels affect nucleotide synthesis, with implications for cell proliferation, DNA repair, and genomic stability. Furthermore, by providing the single-carbon moiety in the synthesis pathway for S-adenosylmethionine, the main methyl donor in the cell, folate also impacts methylation reactions. It is this capacity that extends the reach of folate functions into the realm of epigenetics and gene regulation. Methylation reactions play a major role for several modalities of the epigenome. The specific methylation status of histones, noncoding RNAs, transcription factors, or DNA represents a significant determinant for the transcriptional output of a cell. Proper folate status is therefore necessary for a broad range of biological functions that go beyond the biochemistry of folate. In this review, we examine evolutionary, genetic, and epigenomic footprints of folate and the implications for human health.

Fetoplacental vascular endothelial dysfunction as an early phenomenon in the programming of human adult diseases in subjects born from gestational diabetes mellitus or obesity in pregnancy

Gestational diabetes mellitus (GDM) and obesity in pregnancy (OP) are pathological conditions associated with placenta vascular dysfunction coursing with metabolic changes at the fetoplacental microvascular and macrovascular endothelium. These alterations are seen as abnormal expression and activity of the cationic amino acid transporters and endothelial nitric oxide synthase isoform, that is, the "endothelial L-arginine/nitric oxide signalling pathway." Several studies suggest that the endogenous nucleoside adenosine along with insulin, and potentially arginases, are factors involved in GDM-, but much less information regards their role in OP-associated placental vascular alterations. There is convincing evidence that GDM and OP prone placental endothelium to an "altered metabolic state" leading to fetal programming evidenced at birth, a phenomenon associated with future development of chronic diseases. In this paper it is suggested that this pathological state could be considered as a metabolic marker that could predict occurrence of diseases in adulthood, such as cardiovascular disease, obesity, diabetes mellitus (including gestational diabetes), and metabolic syndrome.