Environmental Epigenetic Changes, as Risk Factors for the Development of Diseases in Children: A Systematic Review

Association of prenatal multiple metal exposures with child neurodevelopment at 3 years of age: A prospective birth cohort study

Prenatal exposures to toxic metals and trace elements have been linked to childhood neurodevelopment. However, existing evidence remains inconclusive, and further research is needed to investigate the mixture effects of multiple metal exposures on childhood neurodevelopment. We aimed to examine the associations between prenatal exposure to specific metals and metal mixtures and neurodevelopment in children. In this prospective cohort study, we used the multivariable linear regressions and the robust modified Poisson regressions to explore the associations of prenatal exposure to 25 specific metals with neurodevelopment among children at 3 years of age in 854 mother-child pairs from the Jiangsu Birth Cohort (JBC) Study. The Bayesian kernel machine regression (BKMR) was employed to assess the joint effects of multiple metals on neurodevelopment. Prenatal manganese (Mn) exposure was negatively associated with the risk of non-optimal cognition development of children, while vanadium (V), copper (Cu), zinc (Zn), antimony (Sb), cerium (Ce) and uranium (U) exposures were positively associated with the risk of non-optimal gross motor development. BKMR identified an interaction effect between Sb and Ce on non-optimal gross motor development. Additionally, an element risk score (ERS), representing the mixture effect of multiple metal exposures including V, Cu, Zn, Sb, Ce and U was constructed based on weights from a Poisson regression model. Children with ERS in the highest tertile had higher probability of non-optimal gross motor development (RR = 2.37, 95 % CI: 1.15, 4.86) versus those at the lowest tertile. Notably, Sb [conditional-posterior inclusion probabilities (cPIP) = 0.511] and U (cPIP = 0.386) mainly contributed to the increased risk of non-optimal gross motor development. The findings highlight the importance of paying attention to the joint effects of multiple metals on children's neurodevelopment. The ERS score may serve as an indicator of comprehensive metal exposure risk for children's neurodevelopment.

Multi-omic integration reveals alterations in nasal mucosal biology that mediate air pollutant effects on allergic rhinitis

BACKGROUND

Allergic rhinitis is a common inflammatory condition of the nasal mucosa that imposes a considerable health burden. Air pollution has been observed to increase the risk of developing allergic rhinitis. We addressed the hypotheses that early life exposure to air toxics is associated with developing allergic rhinitis, and that these effects are mediated by DNA methylation and gene expression in the nasal mucosa.

METHODS

In a case-control cohort of 505 participants, we geocoded participants' early life exposure to air toxics using data from the US Environmental Protection Agency, assessed physician diagnosis of allergic rhinitis by questionnaire, and collected nasal brushings for whole-genome DNA methylation and transcriptome profiling. We then performed a series of analyses including differential expression, Mendelian randomization, and causal mediation analyses to characterize relationships between early life air toxics, nasal DNA methylation, nasal gene expression, and allergic rhinitis.

RESULTS

Among the 505 participants, 275 had allergic rhinitis. The mean age of the participants was 16.4 years (standard deviation = 9.5 years). Early life exposure to air toxics such as acrylic acid, phosphine, antimony compounds, and benzyl chloride was associated with developing allergic rhinitis. These air toxics exerted their effects by altering the nasal DNA methylation and nasal gene expression levels of genes involved in respiratory ciliary function, mast cell activation, pro-inflammatory TGF-β1 signaling, and the regulation of myeloid immune cell function.

CONCLUSIONS

Our results expand the range of air pollutants implicated in allergic rhinitis and shed light on their underlying biological mechanisms in nasal mucosa.

Persistent gene expression and DNA methylation alterations linked to carcinogenic effects of dichloroacetic acid

Background

Mechanistic understanding of transient exposures that lead to adverse health outcomes will enhance our ability to recognize biological signatures of disease. Here, we measured the transcriptomic and epigenomic alterations due to exposure to the metabolic reprogramming agent, dichloroacetic acid (DCA). Previously, we showed that exposure to DCA increased liver tumor incidence in B6C3F1 mice after continuous or early life exposures significantly over background level.

Methods

Using archived formalin-fixed liver samples, we utilized modern methodologies to measure gene expression and DNA methylation levels to link to previously generated phenotypic measures. Gene expression was measured by targeted RNA sequencing (TempO-seq 1500+ toxicity panel: 2754 total genes) in liver samples collected from 10-, 32-, 57-, and 78-week old mice exposed to deionized water (controls), 3.5 g/L DCA continuously in drinking water ("Direct" group), or DCA for 10-, 32-, or 57-weeks followed by deionized water until sample collection ("Stop" groups). Genome-scaled alterations in DNA methylation were measured by Reduced Representation Bisulfite Sequencing (RRBS) in 78-week liver samples for control, Direct, 10-week Stop DCA exposed mice.

Results

Transcriptomic changes were most robust with concurrent or adjacent timepoints after exposure was withdrawn. We observed a similar pattern with DNA methylation alterations where we noted attenuated differentially methylated regions (DMRs) in the 10-week Stop DCA exposure groups compared to the Direct group at 78-weeks. Gene pathway analysis indicated cellular effects linked to increased oxidative metabolism, a primary mechanism of action for DCA, closer to exposure windows especially early in life. Conversely, many gene signatures and pathways reversed patterns later in life and reflected more pro-tumorigenic patterns for both current and prior DCA exposures. DNA methylation patterns correlated to early gene pathway perturbations, such as cellular signaling, regulation and metabolism, suggesting persistence in the epigenome and possible regulatory effects.

Conclusion

Liver metabolic reprogramming effects of DCA interacted with normal age mechanisms, increasing tumor burden with both continuous and prior DCA exposure in the male B6C3F1 rodent model.

Epigenetics as a target to mitigate excess stroke risk in people of African ancestry: A scoping review

BACKGROUND

Globally, individuals of African ancestry have a relatively greater stroke preponderance compared to other racial/ethnic groups. The higher prevalence of traditional stroke risk factors in this population, however, only partially explains this longstanding disparity. Epigenetic signatures are transgenerational and could be a plausible therapeutic target to further bend the stroke disparities curve for people of African ancestry. There is, however, limited data on epigenetics and stroke risk in this population.

PURPOSE

To examine existing evidence and knowledge gaps on the potential contribution of epigenetics to excess stroke risk in people of African ancestry and avenues for mitigation.

MATERIALS AND METHODS

We conducted a scoping review of studies published between January 2003 and July 2023, on epigenetics and stroke risk. We then summarized our findings, highlighting the results for people of African ancestry.

RESULTS

Of 104 studies, there were only 6 studies that specifically looked at epigenetic mechanisms and stroke risk in people of African ancestry. Results of these studies show how patterns of DNA methylation and non-coding RNA interact with lifestyle choices, xenobiotics, and FVIII levels to raise stroke risk in people of African ancestry. However, no studies evaluated epigenetic patterns as actionable targets for the influence of psychosocial stressors or social context and excess stroke risk in this population (versus others). Also, no studies interrogated the role of established or novel therapeutic agents with the potential to reprogram DNA by adding or removing epigenetic markers in people of African ancestry.

CONCLUSION

Epigenetics potentially offers a promising target for modifying the effects of lifestyle, environmental exposures, and other factors that differentially affect people of African ancestry and place them at relatively greater stroke risk compared to other populations. Studies that precisely assess the pathways by which epigenetic mechanisms modulate population-specific disparities in the risk of stroke are needed.

Prenatal exposure to triclosan assessed in multiple urine samples and placental DNA methylation

A previous study reported positive associations of maternal urinary concentrations of triclosan, a synthetic phenol with widespread exposure in the general population, with placental DNA methylation of male fetuses. Given the high number of comparisons performed in -omic research, further studies were needed to validate and extend on these findings. Using a cohort of male and female fetuses with repeated maternal urine samples to assess exposure, we studied the associations between triclosan and placental DNA methylation. We assessed triclosan concentrations in two pools of 21 urine samples collected among 395 women from the SEPAGES cohort. We used Infinium Methylation EPIC arrays to measure DNA methylation in placental biopsies collected at delivery. We performed a candidate study restricted to a set of candidate CpGs (n = 500) identified in a previous work as well as an exploratory epigenome-wide association study to investigate the associations between triclosan and differentially methylated probes and regions. Analyses were conducted on the whole population and stratified by child's sex. Mediation analysis was performed to test whether heterogeneity of placental tissue may mediate the observed associations. In the candidate approach, we confirmed 18 triclosan-associated genes when both sexes were considered. After stratification for child's sex, triclosan was associated with 72 genes in females and three in males. Most of the associations were positive and several CpGs mapped to imprinted genes: FBRSL1, KCNQ1, RHOBTB3, and SMOC1. A mediation effect by placental tissue heterogeneity was identified for most of the observed associations. In the exploratory analysis, we identified a few isolated associations in the sex-stratified analysis. In line with a previous study on male placentas, our approach revealed several positive associations between triclosan exposure and placental DNA methylation. Several identified loci mapped to imprinted genes.

Differential methylation of microRNA encoding genes may contribute to high myopia

Introduction: High myopia (HM), an eye disorder with a refractive error ≤-6.0 diopters, has multifactorial etiology with environmental and genetic factors involved. Recent studies confirm the impact of alterations in DNA methylation and microRNAs (miRNAs) on myopia. Here, we studied the combined aspects evaluating to the role of methylation of miRNA encoding genes in HM. Materials and Methods: From the genome-wide DNA methylation data of 18 Polish children with HM and 18 matched controls, we retrieved differentially methylated CG dinucleotides localized in miRNA encoding genes. Putative target genes of the highest-ranked miRNAs were obtained from the miRDB and included in overrepresentation analyses in the ConsensusPathDB. Expression of target genes was assessed using the RNA sequencing data of retinal ARPE-19 cell line. Results: We identified differential methylation of CG dinucleotides in promoter regions of MIR3621, MIR34C, MIR423 (increased methylation level), and MIR1178, MIRLET7A2, MIR885, MIR548I3, MIR6854, MIR675, MIRLET7C, MIR99A (decreased methylation level) genes. Several targets of these miRNAs, e.g. GNAS, TRAM1, CTNNB1, EIF4B, TENM3 and RUNX were previously associated with myopia/HM/refractive error in Europeans in genome-wide association studies. Overrepresentation analyses of miRNAs' targets revealed enrichment in pathways/processes related to eye structure/function, such as axon guidance, transcription, focal adhesion, and signaling pathways of TGF-β, insulin, MAPK and EGF-EGFR. Conclusion: Differential methylation of indicated miRNA encoding genes might influence their expression and contribute to HM pathogenesis via disrupted regulation of transcription of miRNAs' target genes. Methylation of genes encoding miRNAs may be a new direction in research on both the mechanisms determining HM and non-invasive indicators in diagnostics.

Perspectives for the application of neurogenetic research in programming Neurorehabilitation

Certain genetic variants underlie the proper functioning of the nervous system. They affect the nervous system in all aspects - molecular, systemic, cognitive, computational and sensorimotor. The greatest changes in the nervous system take place in the process of its maturation in the period of psychomotor development, as well as during neurorehabilitation, the task of which is to rebuild damaged neuronal pathways, e.g. by facilitating movement or training cognitive functions. Certain genetic polymorphisms affect the effectiveness of the processes of reconstruction or restoration of neural structures, which is clearly reflected in the effects of neurorehabilitation. This review presents the perspectives for the application of neurogenetic research in programming neurorehabilitation by determining the relationship of as many as 16 different genetic polymorphisms with specific functions of importance in rehabilitation. Thanks to this broad view, it may be possible to predict the effectiveness of rehabilitation on the basis of genetic testing, which would significantly contribute to the development of personalized medicine and to the optimal management of medical services in healthcare systems.

Gene-environment interactions in Alzheimer disease: the emerging role of epigenetics

With the exception of a few monogenic forms, Alzheimer disease (AD) has a complex aetiology that is likely to involve multiple susceptibility genes and environmental factors. The role of environmental factors is difficult to determine and, until a few years ago, the molecular mechanisms underlying gene-environment (G × E) interactions in AD were largely unknown. Here, we review evidence that has emerged over the past two decades to explain how environmental factors, such as diet, lifestyle, alcohol, smoking and pollutants, might interact with the human genome. In particular, we discuss how various environmental AD risk factors can induce epigenetic modifications of key AD-related genes and pathways and consider how epigenetic mechanisms could contribute to the effects of oxidative stress on AD onset. Studies on early-life exposures are helping to uncover critical time windows of sensitivity to epigenetic influences from environmental factors, thereby laying the foundations for future primary preventative approaches. We conclude that epigenetic modifications need to be considered when assessing G × E interactions in AD.

Decreased Levels of DNA Methylation in the PCDHA Gene Cluster as a Risk Factor for Early-Onset High Myopia in Young Children

Purpose

High myopia (HM), an eye disorder with at least –6.0 diopters refractive error, has a complex etiology with environmental, genetic, and likely epigenetic factors involved. To complement the DNA methylation assessment in children with HM, we analyzed genes that had significantly lower DNA methylation levels.

Methods

The DNA methylation pattern was studied based on the genome-wide methylation data of 18 Polish children with HM paired with 18 controls. Genes overlapping CG dinucleotides with decreased methylation level in HM cases were assessed by enrichment analyses. From those, genes with CG dinucleotides in promoter regions were further evaluated based on exome sequencing (ES) data of 16 patients with HM from unrelated Polish families, Sanger sequencing data of the studied children, and the RNA sequencing data of human retinal ARPE-19 cells.

Results

The CG dinucleotide with the most decreased methylation level in cases was identified in a promoter region of PCDHA10 that overlaps intronic regions of PCDHA1–9 of the PCDHA gene cluster in myopia 5q31 locus. Also, two single nucleotide variants, rs200661444, detected in our ES, and rs246073, previously found as associated with a refractive error in a genome-wide association study, were revealed within this gene cluster. Additionally, genes previously linked to ocular phenotypes, myopia-related traits, or loci, including ADAM20, ZFAND6, ETS1, ABHD13, SBSPON, SORBS2, LMOD3, ATXN1, and FARP2, were found to have decreased methylation.

Conclusions

Alterations in the methylation pattern of specific CG dinucleotides may be associated with early-onset HM, so this could be used to develop noninvasive biomarkers of HM in children and adolescents.

Associations between plasma levels of brominated flame retardants and methylation of DNA from peripheral blood: A cross-sectional study in a cohort of French women

BACKGROUND

Brominated flame retardants (BFRs) are organic compounds that are widespread in the environment. Because of their persistence, they are able to bioaccumulate with major impacts on human health. It has been hypothesized that the effect of BFRs on human health is mediated by alterations of DNA methylation.

OBJECTIVE

The aim of this study was to examine the association between methylation of DNA extracted from peripheral blood and circulating levels of BFRs measured in plasma.

METHODS

We conducted a methylation wide association study on 336 blood samples from a study within the E3N (Etude Epidémiologique auprès de femmes de l'Education Nationale) cohort, a long-term longitudinal cohort of French women. DNA methylation at more than 850 000 cytosine-guanine dinucleotide (CpG) sites was measured with the Illumina Infinium HumanMethylation - EPIC BeadChip. Circulating levels of seven BFRs (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154 and PBB-153) were measured by gas chromatography coupled to high-resolution mass spectrometry in plasma samples. The association between DNA methylation and BFRs plasma levels was assessed through linear mixed-effects models followed by gene-set enrichment analyses (GSEA).

RESULTS

We identified 253 CpG sites whose methylation levels were significantly associated with exposure to BFRs after Bonferroni correction. For 50 of these CpGs the p-values were less than 2.2x10^-9 with the strongest association being between BDE-154 and cg23619365 (4.32x10^-13). GSEA of CpG sites associated with exposure to BFRs identified significant enrichment of genes involved in hypoxia, glycolysis and adipogenesis.

CONCLUSIONS

Exposure to BFRs appears to be related to numerous alterations in DNA methylation. These findings, if replicated in independent studies, provide insights into the biological and health effects of BFRs.

DNA methylation: a potential mediator between air pollution and metabolic syndrome

Given the global increase in air pollution and its crucial role in human health, as well as the steep rise in prevalence of metabolic syndrome (MetS), a better understanding of the underlying mechanisms by which environmental pollution may influence MetS is imperative. Exposure to air pollution is known to impact DNA methylation, which in turn may affect human health. This paper comprehensively reviews the evidence for the hypothesis that the effect of air pollution on the MetS is mediated by DNA methylation in blood. First, we present a summary of the impact of air pollution on metabolic dysregulation, including the components of MetS, i.e., disorders in blood glucose, lipid profile, blood pressure, and obesity. Then, we provide evidence on the relation between air pollution and endothelial dysfunction as one possible mechanism underlying the relation between air pollution and MetS. Subsequently, we review the evidence that air pollution (PM, ozone, NO₂ and PAHs) influences DNA methylation. Finally, we summarize association studies between DNA methylation and MetS. Integration of current evidence supports our hypothesis that methylation may partly mediate the effect of air pollution on MetS.

Prenatal exposure to PM10 and changes in DNA methylation and telomere length in cord blood

BACKGROUND

Air pollution exposure in pregnancy can cause molecular level alterations that might influence later disease susceptibility.

OBJECTIVES

We investigated DNA methylation (DNAm) and telomere length (TL) in the cord blood in relation to gestational PM₁₀ exposure and explored potential gestational windows of susceptibility.

METHODS

Cord blood epigenome-wide DNAm (N = 384) and TL (N = 500) were measured in children of the Italian birth cohort Piccolipiù, using the Infinium Methylation EPIC BeadChip and qPCR, respectively. PM₁₀ daily exposure levels, based on maternal residential address, were estimated for different gestational periods using models based on satellite data. Epigenome-wide analysis to identify differentially methylated probes (DMPs) and regions (DMRs) was conducted, followed by a pathway analysis and replication analysis in an second Piccolipiù dataset. Distributed lag models (DLMs) using weekly exposures were used to study the association of PM₁₀ exposure across pregnancy with telomere length, as well as with the DMPs that showed robust associations.

RESULTS

Gestational PM₁₀ exposure was associated with the DNA methylation of more than 250 unique DMPs, most of them identified in early gestation, and 1 DMR. Out of 151 DMPs available in the replication dataset, ten DMPs showed robust associations: eight were associated with exposure during early gestation and 2 with exposure during the whole pregnancy. These exposure windows were supported by the DLM analysis. The PM₁₀ exposure between 15th and 20th gestational week seem to be associated with shorter telomeres at birth, while exposure between 24th and 29th was associated with longer telomeres.

DISCUSSION

The early pregnancy period is a potential critical window during which PM₁₀ exposure can influence cord blood DNA methylation. The results from the TL analysis were consistent with previous findings and merit further exploration in future studies. The study underlines the importance of considering gestational windows outside of the predefined trimesters that may not always overlap with biologically relevant windows of exposure.

Global DNA Methylation in Cord Blood as a Biomarker for Prenatal Lead and Antimony Exposures

DNA methylation is an epigenetic mechanism for gene expression modulation and can be used as a predictor of future disease risks. A prospective birth cohort study was performed to clarify the effects of neurotoxicants on child development, namely, the Tohoku Study of Child Development, in Japan. This study aimed to evaluate the association of prenatal exposure to five toxic metals—arsenic, cadmium, mercury, lead (Pb), antimony (Sb), and polychlorinated biphenyls (PCBs, N = 166)—with global DNA methylation in umbilical cord blood DNA. DNA methylation markers, 5-methyl-2′-deoxycytidine (mC) and 5-hydroxymethyl-2′-deoxycytidine (hmC), were determined using liquid chromatography-tandem mass spectrometry. The mC content in cord blood DNA was positively correlated with Pb and Sb levels (r = 0.435 and 0.288, respectively) but not with cord blood PCBs. We also observed significant positive correlations among Pb levels, maternal age, and hmC content (r = 0.155 and 0.243, respectively). The multiple regression analysis among the potential predictors demonstrated consistent positive associations between Pb and Sb levels and mC and hmC content. Our results suggest that global DNA methylation is a promising biomarker for prenatal exposure to Pb and Sb.

DNA Methylation Levels of the TBX5 Gene Promoter Are Associated with Congenital Septal Defects in Mexican Paediatric Patients

The TBX5 gene regulates morphological changes during heart development, and it has been associated with epigenetic abnormalities observed in congenital heart defects (CHD). The aim of this research was to evaluate the association between DNA methylation levels of the TBX5 gene promoter and congenital septal defects. DNA methylation levels of six CpG sites in the TBX5 gene promoter were evaluated using pyrosequencing analysis in 35 patients with congenital septal defects and 48 controls. Average methylation levels were higher in individuals with congenital septal defects than in the controls (p < 0.004). In five CpG sites, we also found higher methylation levels in patients than in the controls (p < 0.05). High methylation levels were associated with congenital septal defects (OR = 3.91; 95% CI = 1.02–14.8; p = 0.045). The analysis of Receiver Operating Characteristic (ROC) showed that the methylation levels of the TBX5 gene could be used as a risk marker for congenital septal defects (AUC = 0.68, 95% CI = 0.56–0.80; p = 0.004). Finally, an analysis of environmental factors indicated that maternal infections increased the risk (OR = 2.90; 95% CI = 1.01–8.33; p = 0.048) of congenital septal defects. Our data suggest that a high DNA methylation of the TBX5 gene could be associated with congenital septal defects.

Pregnancy exposure to synthetic phenols and placental DNA methylation - An epigenome-wide association study in male infants from the EDEN cohort

In utero exposure to environmental chemicals, such as synthetic phenols, may alter DNA methylation in different tissues, including placenta - a critical organ for fetal development. We studied associations between prenatal urinary biomarker concentrations of synthetic phenols and placental DNA methylation. Our study involved 202 mother-son pairs from the French EDEN cohort. Nine phenols were measured in spot urine samples collected between 22 and 29 gestational weeks. We performed DNA methylation analysis of the fetal side of placental tissues using the IlluminaHM450 BeadChips. We evaluated methylation changes of individual CpGs in an adjusted epigenome-wide association study (EWAS) and identified differentially methylated regions (DMRs). We performed mediation analysis to test whether placental tissue heterogeneity mediated the association between urinary phenol concentrations and DNA methylation. We identified 46 significant DMRs (≥5 CpGs) associated with triclosan (37 DMRs), 2,4-dichlorophenol (3), benzophenone-3 (3), methyl- (2) and propylparaben (1). All but 2 DMRs were positively associated with phenol concentrations. Out of the 46 identified DMRs, 7 (6 for triclosan) encompassed imprinted genes (APC, FOXG1, GNAS, GNASAS, MIR886, PEG10, SGCE), which represented a significant enrichment. Other identified DMRs encompassed genes encoding proteins responsible for cell signaling, transmembrane transport, cell adhesion, inflammatory, apoptotic and immunological response, genes encoding transcription factors, histones, tumor suppressors, genes involved in tumorigenesis and several cancer risk biomarkers. Mediation analysis suggested that placental cell heterogeneity may partly explain these associations. This is the first study describing the genome-wide modifications of placental DNA methylation associated with pregnancy exposure to synthetic phenols or their precursors. Our results suggest that cell heterogeneity might mediate the effects of triclosan exposure on placental DNA methylation. Additionally, the enrichment of imprinted genes within the DMRs suggests mechanisms by which certain exposures, mainly to triclosan, could affect fetal development.

Associations between infant sex and DNA methylation across umbilical cord blood, artery, and placenta samples

DNA methylation (DNAm) is vulnerable to dysregulation by environmental exposures during epigenetic reprogramming that occurs in embryogenesis. Sexual dimorphism in environmentally induced DNAm dysregulation has been identified and therefore it is important to understand sex-specific DNAm patterns. DNAm at several autosomal sites has been consistently associated with sex in cord blood and placental foetal tissues. However, there is limited research comparing sex-specific DNAm across tissues, particularly differentially methylated regions (DMRs). This study leverages DNAm data measured using the Illumina HumanMethylation450 BeadChip in cord blood (N = 179), placenta (N = 229), and umbilical artery samples (N = 229) in the PRogramming of Intergenerational Stress Mechanisms (PRISM) cohort to identify autosomal DMRs and differentially methylated positions (DMPs). A replication analyses was conducted in an independent cohort (GEO Accession GSE129841). We identified 183, 257, and 419 DMRs and 2119, 2281, and 3405 DMPs (p_Bonferroni < 0.05) in cord blood, placenta, and artery samples, respectively. Thirty-nine DMRs overlapped in all three tissues, overlapping with genes involved in spermatogenesis (NKAPL, PIWIL2 and AURKC) and X-inactivation (LRIF1). In replication analysis, 85% of DMRs overlapped with those identified in PRISM. Overall, DMRs and DMPs had higher methylation levels among females in cord blood and artery samples, but higher methylation levels among males in placenta samples. Further research is necessary to understand biological mechanisms that contribute to differences in sex-specific DNAm signatures across tissues, as well as to determine if sexual dimorphism in the epigenome impacts response to environmental stressors.

Gestational blood levels of toxic metal and essential element mixtures and associations with global DNA methylation in pregnant women and their infants

BACKGROUND

Pregnant women and their fetuses are exposed to multiple toxic metals that together with variations in essential element levels may alter epigenetic regulation, such as DNA methylation.

OBJECTIVES

The aim of the study was to investigate the associations between gestational levels of toxic metals and essential elements and mixtures thereof, with global DNA methylation levels in pregnant women and their newborn children.

METHODS

Using 631 mother-child pairs from a prospective birth cohort (The Norwegian Mother, Father and Child Cohort Study), we measured maternal blood concentration (gestation week ~18) of five toxic metals and seven essential elements. We investigated associations as individual exposures and two-way interactions, using elastic net regression, and total mixture, using quantile g-computation, with blood levels of 5-methylcytocine (5mC) and 5-hydroxymethylcytosine (5hmC) in mothers during pregnancy and their newborn children (cord blood). Multiple testing was adjusted for using the Benjamini and Hochberg false discovery rate (FDR) approach.

RESULTS

The most sensitive marker of DNA methylation appeared to be 5mC levels. In pregnant mothers, elastic net regression indicated associations between 5mC and selenium and lead (non-linear), while in newborns results indicated relationships between maternal selenium, cobalt (non-linear) and mercury and 5mC, as well as copper (non-linear) and 5hmC levels. Several possible two-way interactions were identified (e.g. arsenic and mercury, and selenium and maternal smoking in newborns). None of these findings met the FDR threshold for multiple testing. No net effect was observed in the joint (mixture) exposure-approach using quantile g-computation.

CONCLUSION

We identified few associations between gestational levels of several toxic metals and essential elements and global DNA methylation in pregnant mothers and their newborn children. As DNA methylation dysregulation might be a key mechanism in disease development and thus of high importance for public health, our results should be considered as important candidates to investigate in future studies.

Metal and essential element concentrations during pregnancy and associations with autism spectrum disorder and attention-deficit/hyperactivity disorder in children

BACKGROUND

Prenatal exposure to toxic metals or variations in maternal levels of essential elements during pregnancy may be a risk factor for neurodevelopmental disorders such as attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) in offspring.

OBJECTIVES

We investigated whether maternal levels of toxic metals and essential elements measured in mid-pregnancy, individually and as mixtures, were associated with childhood diagnosis of ADHD or ASD.

METHODS

This study is based on the Norwegian Mother, Father and Child Cohort Study and included 705 ADHD cases, 397 ASD cases and 1034 controls. Cases were identified through linkage with the Norwegian Patient Registry. Maternal concentrations of 11 metals/elements were measured in blood at week 17 of gestation; cadmium; cesium; cobalt; copper; lead; magnesium; manganese; selenium; zinc; total arsenic; and total mercury. Multivariable adjusted logistic regression models were used to examine associations between quartile levels of individual metals/elements and outcomes. We also investigated non-linear associations using restricted cubic spline models. The joint effects of the metal/element mixture on ASD and ADHD diagnoses were estimated using a quantile-based g-computation approach.

RESULTS

For ASD, we identified positive associations (increased risks) in the second quartile of arsenic [OR = 1.77 (CI: 1.26, 2.49)] and the fourth quartiles of cadmium and manganese [OR = 1.57 (CI: 1.07 2.31); OR = 1.84 (CI: 1.30, 2.59)], respectively. In addition, there were negative associations between cesium, copper, mercury, and zinc and ASD. For ADHD, we found increased risk in the fourth quartiles of cadmium and magnesium [OR = 1.59 (CI: 1.15, 2.18); [OR = 1.42 (CI: 1.06, 1.91)]. There were also some negative associations, among others with mercury. In addition, we identified non-linear associations between ASD and arsenic, mercury, magnesium, and lead, and between ADHD and arsenic, copper, manganese, and mercury. There were no significant findings in the mixture approach analyses.

CONCLUSION

Results from the present study show several associations between levels of metals and elements during gestation and ASD and ADHD in children. The most notable ones involved arsenic, cadmium, copper, mercury, manganese, magnesium, and lead. Our results suggest that even population levels of these compounds may have negative impacts on neurodevelopment. As we observed mainly similarities among the metals' and elements' impact on ASD and ADHD, it could be that the two disorders share some neurochemical and neurodevelopmental pathways. The results warrant further investigation and replication, as well as studies of combined effects of metals/elements and mechanistic underpinnings.

Low‑Level Environmental Heavy Metals are Associated with Obesity Among Postmenopausal Women in a Southern State

Both arsenic and cadmium are reported to be toxic to humans. The use of saliva as a biomarker of low-level exposures to these elements has not been adequately explored, and the putative relationship between exposure and obesity is unclear. This cross-sectional study aims to investigate the relationship between salivary arsenic and cadmium concentrations and their association with obesity. Arsenic and cadmium concentrations were analyzed in human saliva samples by Inductively Coupled Plasma-Mass Spectrometry on 270 randomly selected women who participated in the Arkansas Rural Community Health Study. Multivariable logistic regression was performed to evaluate the association between heavy metal concentrations and obesity. Stratified logistic regression was performed based on menopausal status. Generalized linear models were used to evaluate weight gain velocity. Significant positive associations were observed in postmenopausal women for both arsenic (OR = 4.43, 95% CI 1.91-10.28) and cadmium (OR = 2.72, 95% CI 1.23-5.99) concentrations, as well as significant trends among tertiles (p < 0.01 and p = 0.01, respectively). No relationship with obesity was evident among premenopausal women for either metal. A dose-response relationship was observed between increasing weight gain velocity and increasing metal concentrations. At concentrations well below governmental and industrial standards for acute toxicity, significant associations between obesity and concentration of these heavy metals are evident. The rate at which individuals gain weight is affected by metal concentrations and may play a role in the rapid increase in weight in postmenopausal women. These results might explain, in part, the missing variability in the increasing obesity pandemic in certain population exposed to these environmental toxicants.

N6-Methyladenine in Eukaryotic DNA: Tissue Distribution, Early Embryo Development, and Neuronal Toxicity

DNA methylation is one of the most important epigenetic modifications and is closely related with several biological processes such as regulation of gene transcription and the development of non-malignant diseases. The prevailing dogma states that DNA methylation in eukaryotes occurs essentially through 5-methylcytosine (5mC) but recently adenine methylation was also found to be present in eukaryotes. In mouse embryonic stem cells, 6-methyladenine (6mA) was associated with the repression and silencing of genes, particularly in the X-chromosome, known to play an important role in cell fate determination. Here, we have demonstrated that 6mA is a ubiquitous eukaryotic epigenetic modification that is put in place during epigenetically sensitive periods such as embryogenesis and fetal development. In somatic cells there are clear tissue specificity in 6mA levels, with the highest 6mA levels being observed in the brain. In zebrafish, during the first 120 h of embryo development, from a single pluripotent cell to an almost fully formed individual, 6mA levels steadily increase. An identical pattern was observed over embryonic days 7–21 in the mouse. Furthermore, exposure to a neurotoxic environmental pollutant during the same early life period may led to a decrease in the levels of this modification in female rats. The identification of the periods during which 6mA epigenetic marks are put in place increases our understanding of this mammalian epigenetic modification, and raises the possibility that it may be associated with developmental processes.

Epigenetic Alterations of Maternal Tobacco Smoking during Pregnancy: A Narrative Review

In utero exposure to maternal tobacco smoking is the leading cause of birth complications in addition to being associated with later impairment in child’s development. Epigenetic alterations, such as DNA methylation (DNAm), miRNAs expression, and histone modifications, belong to possible underlying mechanisms linking maternal tobacco smoking during pregnancy and adverse birth outcomes and later child’s development. The aims of this review were to provide an update on (1) the main results of epidemiological studies on the impact of in utero exposure to maternal tobacco smoking on epigenetic mechanisms, and (2) the technical issues and methods used in such studies. In contrast with miRNA and histone modifications, DNAm has been the most extensively studied epigenetic mechanism with regard to in utero exposure to maternal tobacco smoking. Most studies relied on cord blood and children’s blood, but placenta is increasingly recognized as a powerful tool, especially for markers of pregnancy exposures. Some recent studies suggest reversibility in DNAm in certain genomic regions as well as memory of smoking exposure in DNAm in other regions, upon smoking cessation before or during pregnancy. Furthermore, reversibility could be more pronounced in miRNA expression compared to DNAm. Increasing evidence based on longitudinal data shows that maternal smoking-associated DNAm changes persist during childhood. In this review, we also discuss some issues related to cell heterogeneity as well as downstream statistical analyses used to relate maternal tobacco smoking during pregnancy and epigenetics. The epigenetic effects of maternal smoking during pregnancy have been among the most widely investigated in the epigenetic epidemiology field. However, there are still huge gaps to fill in, including on the impact on miRNA expression and histone modifications to get a better view of the whole epigenetic machinery. The consistency of maternal tobacco smoking effects across epigenetic marks and across tissues will also provide crucial information for future studies. Advancement in bioinformatic and biostatistics approaches is key to develop a comprehensive analysis of these biological systems.

Impact of dietary mercury intake during pregnancy on the health of neonates and children: a systematic review

CONTEXT

Growing evidence suggests that prenatal exposure to methyl mercury through the maternal diet could have great influence on the neurological and physical development of neonates and young children.

OBJECTIVE

The aim of this review was to evaluate the clinical repercussions of maternal exposure to methyl mercury during pregnancy on the health of fetuses, neonates, and children up to 8 years of age.

DATA SOURCES

The Web of Science, PubMed, CINAHL, Scopus, and Dialnet Plus databases were searched for articles published in English or Spanish from 1990 to 2020.

STUDY SELECTION

Original articles published in English or Spanish from 1990 to 2020 were eligible for inclusion. All study designs were eligible. Animal studies were excluded. Two authors independently screened studies for inclusion. From the 971 records initially identified, 19 studies were included in the systematic review.

DATA EXTRACTION

PRISMA guidelines were followed. Outcomes extracted included maternal dietary exposure to methyl mercury during pregnancy, possible health repercussions in offspring up to 8 years of age, and quantitative measurement of mercury in a biological sample. All studies met the requirements established for assessing both study quality and risk of bias.

RESULTS

Prenatal exposure to mercury was consistently associated with lower birth weight, but only one study reported a negative association with length at birth. Higher mercury levels were also related to lower scores in various neuropsychological and developmental tests.

CONCLUSION

The literature shows clear evidence of the adverse effects of maternal methyl mercury exposure on anthropometric variables and cognitive or physical development in children. It is noteworthy, however, that mercury toxicity may sometimes be mitigated by other essential nutrients in the maternal diet, such as polyunsaturated fatty acids.

The relationship of childhood trauma and DNA methylation of NMDA receptor genes in first-episode schizophrenia

Aim: We investigated GRIN1, GRIN2A, GRIN2B and LINE-1 DNA methylation in first-episode schizophrenia patients, their nonaffected siblings and age- and sex-matched controls testing for associations between DNA methylation and exposition to childhood trauma. Materials & methods: The Childhood Trauma Questionnaire evaluated the history of childhood trauma. Genomic DNA was bisulfite converted and pyrosequencing was employed to quantify DNA methylation. Results: GRIN2A, GRIN2B and LINE-1 DNA methylation was not associated with childhood trauma in patients, siblings and controls. Siblings with childhood trauma had hypermethylation at CpG1 of GRIN1 compared with siblings without trauma. Conclusion: Childhood trauma may influence GRIN1 methylation in subjects with liability to psychosis, but not in frank schizophrenia or controls.

Deoxyribonucleic acid (DNA) methylation in children exposed to air pollution: a possible mechanism underlying respiratory health effects development

Air pollution is a substantial environmental threat to children and acts as acute and chronic disease risk factors alike. Several studies have previously evaluated epigenetic modifications concerning its exposure across various life stages. However, findings on epigenetic modifications as the consequences of air pollution during childhood are rather minimal. This review evaluated highly relevant studies in the field to analyze the existing literature regarding exposure to air pollution, with a focus on epigenetic alterations during childhood and their connections with respiratory health effects. The search was conducted using readily available electronic databases (PubMed and ScienceDirect) to screen for children's studies on epigenetic mechanisms following either pre- or post-natal exposure to air pollutants. Studies relevant enough and matched the predetermined criteria were chosen to be reviewed. Non-English articles and studies that did not report both air monitoring and epigenetic outcomes in the same article were excluded. The review found that epigenetic changes have been linked with exposure to air pollutants during early life with evidence and reports of how they may deregulate the epigenome balance, thus inducing disease progression in the future. Epigenetic studies evolve as a promising new approach in deciphering the underlying impacts of air pollution on deoxyribonucleic acid (DNA) due to links established between some of these epigenetic mechanisms and illnesses.

The anti-lipidemic drug simvastatin modifies epigenetic biomarkers in the amphipod Gammarus locusta

The adverse effects of certain environmental chemicals have been recently associated with the modulation of the epigenome. Although changes in the epigenetic signature have yet to be integrated into hazard and risk assessment, they are interesting candidates to link environmental exposures and altered phenotypes, since these changes may be passed across multiple non-exposed generations. Here, we addressed the effects of simvastatin (SIM), one of the most prescribed pharmaceuticals in the world, on epigenetic regulation using the amphipod Gammarus locusta as a proxy, to support its integration into hazard and environmental risk assessment. SIM is a known modulator of the epigenome in mammalian cell lines and has been reported to impact G. locusta ecological endpoints at environmentally relevant levels. G. locusta juveniles were exposed to three SIM environmentally relevant concentrations (0.32, 1.6 and 8 µg L^-1) for 15 days. Gene transcription levels of selected epigenetic regulators, i.e., dnmt1, dmap1, usp7, kat5 and uhrf1 were assessed, along with the quantification of DNA methylation levels and evaluation of key ecological endpoints: survival and growth. Exposure to 0.32 and 8 µg L^-1 SIM induced significant downregulation of DNA methyltransferase 1 (dnmt1), concomitant with global DNA hypomethylation and growth impacts. Overall, this work is the first to validate the basal expression of key epigenetic regulators in a keystone marine crustacean, supporting the integration of epigenetic biomarkers into hazard assessment frameworks.

It Takes Time to Unravel the Ecology of War in Gaza, Palestine: Long-Term Changes in Maternal, Newborn and Toddlers' Heavy Metal Loads, and Infant and Toddler Developmental Milestones in the Aftermath of the 2014 Military Attacks

Toxicant, teratogen and carcinogen metal war remnants negatively affect human health. The current study analyzes, first, the persistence of heavy metal contamination in newborn hair in four cohorts across time in Gaza Palestine; second, the change in mothers’ and infants’ heavy metal contamination from birth to toddlerhood; and third, the impact of heavy metal contamination on infants’ and toddlers’ growth and development. The hair of newborns was analyzed for twelve heavy metals by Inductively Coupled Plasma Mass Spectrometry (ICP/MS) in cohorts recruited at delivery in 2011, 2015, 2016, and 2018–2019. In the 2015 cohort, mothers’ hair samples were taken at delivery, and toddlers and mothers hair were also analyzed 18 months later. Growth levels of infants at six months and toddlers at 18 months were assessed according to World Health Organization (WHO) standards according to a mother report and pediatric check-up, respectively. 1. The level of metal contamination in utero was persistently high across 8 years, 2011, 2015, 2016, 2019, following three major military attacks (2009, 2012, 2014). 2. The 2015 cohort babies exposed in utero to attacks in 2014 at six months showed association of high load at birth in mother of arsenic and in newborn of barium with underweight, of barium and molybdenum in newborn with stunting. 3. Eighteen months after birth, toddlers had a higher level of metals in hairs than when they were born, while, in their mothers, such levels were similar to those at delivery, confirming persistence in the environment of war remnants. Underweight and stunting, both in infants and toddlers, were higher than reported for previous years, as well as being progressive within the cohort. Severe environmental factors, metal contamination and food insecurity put Gaza’s infant health at risk.

Healthy live births from transfer of low-mosaicism embryos after preimplantation genetic testing for aneuploidy

PURPOSE

This study evaluated the potential viability of embryos with low mosaicism level (< 50%) by comparing the clinical outcomes of single mosaic versus euploid blastocyst transfer. In addition, the live birth outcomes for various types of mosaicism with respect to abnormalities in chromosome structure and content were analyzed.

METHODS

This study included patients who underwent in vitro fertilization with preimplantation genetic testing for aneuploidy (PGT-A). The PGT-A cycles performed through next-generation sequencing with single euploid or mosaic embryo transfers were included. We collected 299 frozen single embryo transfer cycles-216 single euploid and 83 mosaic-between July 2016 and July 2018. This study analyzed clinical outcomes, including fetal karyotyping by using amniocentesis, gestational age at delivery, and live birth weight after single mosaic embryo transfer.

RESULTS

The average birth weight of infants in the euploid and mosaic blastocyst transfer groups was 3146.2 and 2997.7 g, respectively. The karyotyping results of prenatal diagnosis in all pregnant women were normal. Our study indicated that mosaic embryos can develop into euploid healthy infants with various levels or types of mosaicism. No significant difference was observed between infants from euploid and mosaic blastocyst transfers.

CONCLUSION

If patients have no euploid embryos, mosaic embryos can be transferred as they have potential for implantation and development into euploid healthy infants. This study is invaluable for counseling clinical results after single mosaic embryo transfers.

Long Term Risks to Neonatal Health from Exposure to War-9 Years Long Survey of Reproductive Health and Contamination by Weapon-Delivered Heavy Metals in Gaza, Palestine

Introduction: High levels of environmental contaminants with long term effects and teratogenic and carcinogenic potential, such as heavy metals, were introduced by weaponry in war areas in the last decades. Poorer reproductive health and increases in non-communicable diseases were reported after wars and are the suspected long term effects of contamination by stable war remnants. Although potentially affecting millions of people, this is still an understudied issue of public health. Background: Gaza, Palestine since 2006 has been an object of repeated severe military attacks that left heavy metals remnants in the environment, in wound tissues and that were assumed by the population. Retrospective studies showed a progressive increase in birth defects since the 2006 attacks. In 2011 we started surveillance at birth alongside analysis of the heavy metals load carried by pregnant women and their babies. Methods: We used protocols for birth registration which also document the extent of exposures to attacks, war remnants and to other environmental risks that allow comparison of 3 data sets-2011, 2016 and 2018-2019 (4000-6000 women in each set). By ICP/MS analysis we determined the content of 23 metals in mothers' hair. Appropriate statistical analysis was performed. Results: Comparison of data in birth registers showed a major increase in the prevalence in birth defects and preterm babies between 2011 and 2016, respectively from 1.1 to 1.8% and from 1.1 to 7.9%, values remaining stable in 2019. Negative outcomes at birth in 2016 up to 2019 were associated with exposure of the mothers to the attacks in 2014 and/or to hot spots of heavy metals contamination. Metal loads since the attacks in 2014 were consistently high until 2018-2019 for barium, arsenic, cobalt, cadmium, chrome, vanadium and uranium, pointing to these metals as potential inducers for the increased prevalence of negative health outcomes at birth since 2016. Conclusions: Bodily accumulation of metals following exposure whilst residing in attacked buildings predispose women to negative birth outcomes. We do not know if the metals act in synergy. Trial for mitigation of the documented negative effects of high metal load on reproductive health, and ensuing perinatal deaths, could now be done in Gaza, based on this documentary record. High load of heavy metals may explain recent increases in non-communicable diseases and cancers at all ages in Gaza. Modern war's legacy of diseases and deaths extends in time to populations and demands monitoring.

Prospects for incorporation of epigenetic biomarkers in human health and environmental risk assessment of chemicals

Epigenetic mechanisms have gained relevance in human health and environmental studies, due to their pivotal role in disease, gene × environment interactions and adaptation to environmental change and/or contamination. Epigenetic mechanisms are highly responsive to external stimuli and a wide range of chemicals has been shown to determine specific epigenetic patterns in several organisms. Furthermore, the mitotic/meiotic inheritance of such epigenetic marks as well as the resulting changes in gene expression and cell/organismal phenotypes has now been demonstrated. Therefore, epigenetic signatures are interesting candidates for linking environmental exposures to disease as well as informing on past exposures to stressors. Accordingly, epigenetic biomarkers could be useful tools in both prospective and retrospective risk assessment but epigenetic endpoints are currently not yet incorporated into risk assessments. Achieving a better understanding on this apparent impasse, as well as identifying routes to promote the application of epigenetic biomarkers within environmental risk assessment frameworks are the objectives of this review. We first compile evidence from human health studies supporting the use of epigenetic exposure-associated changes as reliable biomarkers of exposure. Then, specifically focusing on environmental science, we examine the potential and challenges of developing epigenetic biomarkers for environmental fields, and discuss useful organisms and appropriate sequencing techniques to foster their development in this context. Finally, we discuss the practical incorporation of epigenetic biomarkers in the environmental risk assessment of chemicals, highlighting critical data gaps and making key recommendations for future research within a regulatory context.

Bisphenol a Exposure, DNA Methylation, and Asthma in Children

Epidemiological studies have reported the relationship between bisphenol A (BPA) exposure and increased prevalence of asthma, but the mechanisms remain unclear. Here, we investigated whether BPA exposure and DNA methylation related to asthma in children. We collected urinary and blood samples from 228 children (Childhood Environment and Allergic Diseases Study cohort) aged 3 years. Thirty-three candidate genes potentially interacting with BPA exposure were selected from a toxicogenomics database. DNA methylation was measured in 22 blood samples with top-high and bottom-low exposures of BPA. Candidate genes with differential methylation levels were validated by qPCR and promoter associated CpG islands have been investigated. Correlations between the methylation percentage and BPA exposure and asthma were analyzed. According to our findings, MAPK1 showed differential methylation and was further investigated in 228 children. Adjusting for confounders, urinary BPA glucuronide (BPAG) level inversely correlated with MAPK1 promoter methylation (β = -0.539, p = 0.010). For the logistic regression analysis, MAPK1 methylation status was dichotomized into higher methylated and lower methylated groups with cut off continuous variable of median of promoter methylation percentage (50%) while performing the analysis. MAPK1 methylation was lower in children with asthma than in children without asthma (mean ± SD; 69.82 ± 5.88% vs. 79.82 ± 5.56%) (p = 0.001). Mediation analysis suggested that MAPK1 methylation acts as a mediation variable between BPA exposure and asthma. The mechanism of BPA exposure on childhood asthma might, therefore, be through the alteration of MAPK1 methylation. The mechanism of BPA exposure on childhood asthma might, therefore, be through the alteration of MAPK1 methylation.

Stress During Pregnancy and Epigenetic Modifications to Offspring DNA: A Systematic Review of Associations and Implications for Preterm Birth

Offspring born preterm (ie, before 37 weeks of gestation) are more likely to die or experience long-standing illness than full-term offspring. Maternal genetic variants (ie, heritable, stable variations in the genetic code) and epigenetic modifications (ie, chemical modifications to the genetic code that can affect which genes are turned on or off) in response to stress have been implicated in preterm birth. Fetal genetic variants have been linked to preterm birth though the role of offspring epigenetics in preterm birth remains understudied. This systematic review synthesizes the literature examining associations among stress during pregnancy and epigenetic modifications to offspring DNA, with 25 reports identified. Ten reports examined DNA methylation (ie, addition/removal of methyl groups to/from DNA) across the epigenome. The remainder examined DNA methylation near genes of interest, primarily genes linked to hypothalamic-pituitary-adrenal axis function (NR3C1, FKBP51), growth/immune function (IGF2), and socioemotional regulation (SLC6A4, OXTR). The majority of reports noted associations among stress and offspring DNA methylation, primarily when perceived stress, anxiety, or depression served as the predictor. Findings suggest that differences in offspring epigenetic patterns may play a role in stress-associated preterm birth and serve as targets for novel interventions.

Epigenetics and human reproduction: the primary prevention of the noncommunicable diseases

Epigenetic regulation of gene expression plays a key role in affecting human health and diseases with particular regard to human reproduction. The major concern in this field is represented by the epigenetic modifications in the embryo and the increased risk of long-life disorders induced by the use of assisted reproduction techniques, able to affect the epigenetic assessment in the first steps of embryo development. In this review, we analyze the correlation between epigenetic modifications and human reproduction, suggesting that the reversibility of the epigenetic processes could represent a novel resource for the treatment of the couple's infertility and that parental lifestyle in periconceptional period could be considered as an important issue of primary prevention.