Association between mercury in cord serum and sex-specific DNA methylation in cord tissues

Second phase Chiba study of mother and child health (C-MACH): Japanese birth cohort study with multiomics analyses

PURPOSE

Epidemiological studies have reported that environmental factors from fetal period to early childhood can influence the risk of non-communicable diseases in adulthood. This concept has been termed the developmental origins of health and disease (DOHaD). The Chiba study of Mother and Child Health (C-MACH) is a DOHaD concept-based birth cohort study which started in 2014. This study aims to investigate the effects of genetic and environmental factors, particularly fetal and postnatal living environment, on children's health. We also aim to identify candidate biomarkers for their health status. Moreover, the second phase study of C-MACH which was initiated in 2021 aimed at expanding the sample size, especially for gut microbiota and epigenomic analysis; it also aimed at clarifying the impact of the coronavirus disease 2019 (COVID-19) pandemic on children's health.

PARTICIPANTS

This study consists of four hospital-based cohorts. Women who were <13 weeks pregnant and their partners were enrolled in the study. All data and biological samples will be stored in the Chiba University Centre for Preventive Medical Sciences.

FINDINGS TO DATE

A total of 561 women and their partners provided their consent to participate in this study. Of these women, 505 completed the questionnaire during the early gestational period. The mean age of the 505 women at enrolment was 33.0 (SD, 4.5) years. The mean prepregnancy body mass index (BMI) was 21.7 (SD, 3.6) kg/m2, with 74.5% of the women having a BMI of 18.5-24.9 kg/m2. About 5.2% of the women smoked cigarettes during the early stages of pregnancy.

FUTURE PLANS

The primary study outcomes are allergies, obesity, endocrine and metabolic disorders and developmental difficulties in children. Variables related to genome, metabolome, epigenome, gut microbiota and exposome will be evaluated as health-related factors. The relationships between these outcomes and the health-related factors will be analysed.

Urinary metals are associated with obesity in U.S. children and adolescents: A cross-sectional study

Heavy metals are pervasive in the environment, and exposure to these metals may contribute to obesity in children and adolescents. We hypothesized that metal exposures are associated with obesity in children and adolescents. Data were drawn from children and adolescents aged 6 to 19 years from the 2007 to 2018 National Health and Nutrition Examination Survey. We employed weighted multivariate logistic regression and restricted cubic spline to explore the effects of individual metal exposures on obesity, and weighted quantile sum regression, quantile g-computed regression, and Bayesian kernel machine regression to explore the effects of mixed metal exposures on obesity. Subgroup analyses by gender were also performed. All models were adjusted for age, gender, race, poverty to income ratio, and serum cotinine. Among the 3,650 children and adolescents studied, 21.04% had obesity. Logistic regression revealed positive associations between barium (OR = 1.23, 95% CI: 1.07-1.40) and thallium (OR = 1.55, 95% CI: 1.23-2.15) with obesity, while cadmium (OR = 0.74, 95% CI: 0.61-0.89), cobalt (OR = 0.51, 95% CI: 0.41-0.62), and lead (OR = 0.70, 95% CI: 0.57-0.86) were negatively associated with obesity. Restricted cubic spline indicated a nonlinear relationship between lead and thallium and obesity. Quantile g-computed regression demonstrated that mixed metal exposure was negatively associated with obesity (OR = 0.50, 95% CI: 0.42-0.59). Subgroup analyses revealed a gender-specific effect for mercury (P for interaction = 0.03), which was negatively associated with obesity in females (OR = 0.83, 95% CI: 0.69-0.99). In conclusion, metal exposures are associated with obesity in children and adolescents, with gender differences.

Heavy Metals in Umbilical Cord Blood: Effects on Epigenetics and Child Development

Heavy metals like arsenic, mercury, cadmium, and lead are harmful pollutants that can change how our genes are regulated without altering the DNA sequence, specifically through a process called DNA methylation (DNAm) at 5-methylcytosine, an epigenetic mark that we will focus on in this review. These changes in DNAm are most sensitive during pregnancy, a critical time for development when these modifications can affect how traits are expressed. Historically, most research on these environmental effects has focused on adults, but now there is more emphasis on studying the impacts during early development and childhood. The placenta acts as a protective barrier between the mother and the baby, and by examining it, scientists can identify changes in key genes that might affect long-term health. This review looks at how exposure to heavy metals during pregnancy can cause changes in the gene regulation by DNAm in newborns, as seen in their umbilical cord blood. These changes reflect the baby's genetic state during pregnancy and can be influenced by the mother's environment and genetics, as well as the baby's own genetics.

Accumulation of heavy metals in meat and their relationship with water and food intake of aquatic animals in Kermanshah, western Iran

Accumulation of heavy metals in aquatic meat can have a destructive role in food safety and is also closely related to the water and feed consumed by animals. Thus, the aim of this study is to evaluate the heavy metals in three aquatic species and their relationship with water and food. Fresh samples included 65 trout, 40 carp, and 45 shrimp, and their water and food were collected from Kermanshah aquaculture. After the preparation phase, the concentration of heavy metals was determined by using inductively-coupled plasma-mass-spectrometry. Lead in carp, arsenic in shrimp, cadmium, and mercury in trout had the highest concentrations of toxic metals. The lead, arsenic, and mercury concentrations in all three farmed aquatic species were higher than the maximum permissible limits. A significant correlation coefficient was observed between the concentration of these metals in the meat and their consumed water and food (p≤0.001). Of the essential metals, except for selenium in trout, and zinc in all three aquatic species, the concentration of other metals was higher than that of the permissible consumption limit. There was also a significant correlation between the concentration of essential metals and their consumed feed (p<0.001). The target hazard quotient of toxic metals was less than 1, but the target cancer risk for arsenic and mercury was in the range of carcinogenicity. Thereby, it is vital to monitor the quality of aquatic meat and pay special attention to their water and feed sources in this region of Iran, which will consequently guarantee human health.

Sex-specific relationships between prenatal exposure to metal mixtures and birth weight in a Chinese birth cohort

Birth weight is an indicator linking intrauterine environmental exposures to later-life diseases, and intrauterine metal exposure may affect birth weight in a sex-specific manner. We investigated sex-specific associations between prenatal exposure to metal mixtures and birth weight in a Chinese birth cohort. The birth weight of 1296 boys and 1098 girls were recorded, and 10 metals in maternal urine samples collected during pregnancy were measured using inductively coupled plasma mass spectrometry. Bayesian Kernel Machine Regression was used to estimate the association of individual metals or metal mixtures and birth weight for gestational age (BW for GA). The model showed a sex-specific relationship between prenatal exposure to metal mixtures and BW for GA with a significant negative association in girls and a non-significant positive association in boys. Cadmium (Cd) and nickel (Ni) were positively and negatively associated with BW for GA in girls, respectively. Moreover, increasing thallium (Tl) concentration lowered the positive association between Cd and BW for GA and enhanced the negative association between Ni and BW for GA in girls. When exposure to other metals increased, the positive association with Cd diminished, whereas the negative association with Ni or Tl increased. Our findings provide evidence supporting the complex effects of intrauterine exposure to metal mixtures on the birth weight of girls and further highlight the sex heterogeneity in fetal development influenced by intrauterine environmental factors.

Epigenetics of methylmercury

PURPOSE OF REVIEW

Methylmercury (MeHg) is neurotoxic at high levels and particularly affects the developing brain. One proposed mechanism of MeHg neurotoxicity is alteration of the epigenetic programming. In this review, we summarise the experimental and epidemiological literature on MeHg-associated epigenetic changes.

RECENT FINDINGS

Experimental and epidemiological studies have identified changes in DNA methylation following in utero exposure to MeHg, and some of the changes appear to be persistent. A few studies have evaluated associations between MeHg-related changes in DNA methylation and neurodevelopmental outcomes. Experimental studies reveal changes in histone modifications after MeHg exposure, but we lack epidemiological studies supporting such changes in humans. Experimental and epidemiological studies have identified microRNA-related changes associated with MeHg; however, more research is needed to conclude if these changes lead to persistent and toxic effects.

SUMMARY

MeHg appears to interfere with epigenetic processes, potentially leading to persistent changes. However, observed associations of mercury with epigenetic changes are as of yet of unknown relevance to neurodevelopmental outcomes.

Epigenetics as a Biomarker for Early-Life Environmental Exposure

PURPOSE OF REVIEW

There is interest in evaluating the developmental origins of health and disease (DOHaD) which emphasizes the role of prenatal and early-life environments on non-communicable health outcomes throughout the life course. The ability to rigorously assess and identify early-life risk factors for later health outcomes, including those with childhood onset, in large population samples is often limited due to measurement challenges such as impractical costs associated with prospective studies with a long follow-up duration, short half-lives for some environmental toxicants, and lack of biomarkers that capture inter-individual differences in biologic response to external environments.

RECENT FINDINGS

Epigenomic patterns, and DNA methylation in particular, have emerged as a potential objective biomarker to address some of these study design and exposure measurement challenges. In this article, we summarize the literature to date on epigenetic changes associated with specific prenatal and early-life exposure domains as well as exposure mixtures in human observational studies and their biomarker potential. Additionally, we highlight evidence for other types of epigenetic patterns to serve as exposure biomarkers. Evidence strongly supports epigenomic biomarkers of exposure that are detectable across the lifespan and across a range of exposure domains. Current and future areas of research in this field seek to expand these lines of evidence to other environmental exposures, to determine their specificity, and to develop predictive algorithms and methylation scores that can be used to evaluate early-life risk factors for health outcomes across the life span.

Metals Exposures and DNA Methylation: Current Evidence and Future Directions

PURPOSE OF THE REVIEW

Exposure to essential and non-essential metals is widespread. Metals exposure is linked to epigenetic, particularly DNA methylation, differences. The strength of evidence with respect to the metal exposure type, timing, and level, as well as the DNA methylation association magnitude, and reproducibility are not clear. Focusing on the most recent 3 years, we reviewed the human epidemiologic evidence (n = 26 studies) and the toxicologic animal model evidence (n = 18 studies) for associations between metals exposure and DNA methylation.

RECENT FINDINGS

In humans, the greatest number of studies focused on lead exposure, followed by studies examining cadmium and arsenic. Approximately half of studies considered metals exposure during the in utero period and measured DNA methylation with the genome-wide Illumina arrays in newborn blood or placenta. Few studies performed formal replication testing or meta-analyses. Toxicology studies of metals and epigenetics had diversity in model systems (mice, rats, drosophila, tilapia, and zebrafish were represented), high heterogeneity of tissues used for DNA methylation measure (liver, testis, ovary, heart, blood, brain, muscle, lung, kidney, whole embryo), and a variety of technologies used for DNA methylation assessment (global, gene specific, genome-wide). The most common metals tested in toxicologic studies were lead and cadmium. Together, the recent studies reviewed provide the strongest evidence for DNA methylation signatures with prenatal metals exposures. There is also mounting epidemiologic evidence supporting lead, arsenic, and cadmium exposures with DNA methylation signatures in adults. The field of metals and DNA methylation is strengthened by the inclusion of both epidemiology and toxicology approaches, and further advancements can be made by coordinating efforts or integrating analyses across studies. Future advances in understanding the molecular basis of sequence specific epigenetic responses to metals exposures, methods for handling exposure mixtures in a genome-wide analytic framework, and pipelines to facilitate collaborative testing will continue to advance the field.

Methylmercury-induced DNA methylation—From epidemiological observations to experimental evidence

Methylmercury (MeHg) is a developmental neurotoxicant, and one potential mechanism of MeHg toxicity is epigenetic dysregulation. In a recent meta-analysis of epigenome-wide association studies (EWAS), associations between prenatal MeHg exposure and DNA methylation at several genomic sites were identified in blood from newborns and children. While EWASs reveal human-relevant associations, experimental studies are required to validate the relationship between exposure and DNA methylation changes, and to assess if such changes have implications for gene expression. Herein, we studied DNA methylation and gene expression of five of the top genes identified in the EWAS meta-analysis, MED31, MRPL19, GGH, GRK1, and LYSMD3, upon MeHg exposure in human SH-SY5Y cells exposed to 8 or 40 nM of MeHg during differentiation, using bisulfite-pyrosequencing and qPCR, respectively. The concentrations were selected to cover the range of MeHg concentrations in cord blood (2–8.5 μg/L) observed in the cohorts included in the EWAS. Exposure to MeHg increased DNA methylation at MED31, a transcriptional regulator essential for fetal development. The results were in concordance with the epidemiological findings where more MED31 methylation was associated with higher concentrations of MeHg. Additionally, we found a non-significant decrease in DNA methylation at GGH, which corresponds to the direction of change observed in the EWAS, and a significant correlation of GGH methylation with its expression. In conclusion, this study corroborates some of the EWAS findings and puts forward candidate genes involved in MeHg’s effects on the developing brain, thus highlighting the value of experimental validation of epidemiological association studies.

Sex-specific DNA methylation: impact on human health and development

Human evolution has shaped gender differences between males and females. Over the years, scientific studies have proposed that epigenetic modifications significantly influence sex-specific differences. The evolution of sex chromosomes with epigenetics as the driving force may have led to one sex being more adaptable than the other when exposed to various factors over time. Identifying and understanding sex-specific differences, particularly in DNA methylation, will help determine how each gender responds to factors, such as disease susceptibility, environmental exposure, brain development and neurodegeneration. From a medicine and health standpoint, sex-specific methylation studies have shed light on human disease severity, progression, and response to therapeutic intervention. Interesting findings in gender incongruent individuals highlight the role of genetic makeup in influencing DNA methylation differences. Sex-specific DNA methylation studies will empower the biotechnology and pharmaceutical industry with more knowledge to identify biomarkers, design and develop sex bias drugs leading to better treatment in men and women based on their response to different diseases.

Sample management: a primary critical starting point for successful omics studies

Biological samples collected from cohort studies are widely utilized in molecular genetic studies and are typically stored long term for future applications, such as omics analyses. The extent of sample availability is determined by proper sample handling, and it is of primary importance for successful omics studies. However, questions on whether samples in long-term storage are properly available for omics experiments has been raised, because the quality and availability of such samples remain unknown until their actual utilization. In that perspective, several guidelines for proper sample management have been suggested. In addition, several researchers assessed how improper management damages sample using mock sample and suggested a set of requirements for sample handling. In this review, we present several considerations for sample handling eligible for omics studies. Focusing on birth cohorts, we describe the types of samples collected from which omics data were generated. This review ultimately aims to provide proper guidelines for sample handling for successful human omics studies.

Developmental exposure to methylmercury and ADHD, a literature review of epigenetic studies

Attention-deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder that affects the competence of academic performance and social wellness in children and adults. The causes of ADHD are unclear. Both genetic and environmental factors contribute to the development of ADHD. The behavioral impairments in ADHD are associated with epigenetic changes in genes that are important for neurodevelopment. Among environmental causes of ADHD, the neurotoxin methylmercury (MeHg) is associated with an increased risk for ADHD. Developing children are susceptible to neurotoxic effects of prenatal MeHg exposure. Human epidemiology studies have shown that prenatal MeHg exposure could invoke epigenetic changes in genes that are involved in ADHD. In addition, the pathogenesis of ADHD involves dopaminergic system, which is a target of developmental MeHg exposure. MeHg-induced alterations in the dopaminergic system have a profound impact on behavioral functions in adults. As a trace level of MeHg (around nM) can induce long-lasting behavioral alterations, potential mechanisms of MeHg-induced functional changes in the dopaminergic system may involve epigenetic mechanisms. Here, we review the relevant evidence on developmental MeHg exposures and the risk for ADHD. We also point out research gaps in understanding environmental causes of ADHD.

Exposure to Perfluoroalkyl Substances During Pregnancy and Fetal BDNF Level: A Prospective Cohort Study

BACKGROUND

Humans are widely exposed to environmental perfluoroalkyl substances (PFAS), which may affect fetal neurodevelopment. Brain-derived neurotrophic factor (BDNF) is an important factor in neurodevelopment, but its role in PFAS-induced neurotoxicity is unclear. We investigated the association between prenatal PFAS exposure and fetal BDNF level in the umbilical cord blood in a large prospective cohort.

METHODS

A total of 725 pregnant women who participated in the Shanghai Birth Cohort were included. 10 PFAS were measured by high-performance liquid chromatography/tandem mass spectrometry (HPLC/MS-MS) in the plasma samples of early pregnancy. The BDNF level was determined by ELISA. The concentration of total mercury (Hg) in the umbilical cord blood was tested by cold vapor atomic absorption spectrometry (AAS) and included as a main confounder, along with other covariates. Multiple linear regression was used to explore the associations between PFAS concentrations and BDNF level. Quantile-based g-computation was applied to explore the joint and independent effects of PFAS on BDNF level.

RESULTS

The mean BDNF level in the total population was 10797 (±4713) pg/ml. Male fetuses had a higher level than female fetuses (P<0.001). A significant positive association was observed between PFHxS and BDNF level after adjusting for potential confounders [β=1285 (95% CI: 453, 2118, P=0.003)]. No association was observed between other PFAS congeners and BDNF level. Results of the mixed exposure model showed that the joint effects of PFAS mixture were not associated with BDNF [β=447 (95% CI: -83, 978, P=0.10)], while the positive association with PFHxS exposure remained significant after controlling for other PFAS [β=592 (95% CI: 226, 958, P=0.002)]. The above associations were more prominent in male [β=773 (95% CI: 25, 1520, P= 0.04)] than female fetuses [β=105 (95% CI: -791, 1002, P= 0.82)] for the mixed effects.

CONCLUSIONS

Prenatal exposure to PFHxS was associated with an increased BDNF level in the umbilical blood, especially in male fetuses.