Putative Epimutagens in Maternal Peripheral and Cord Blood Samples Identified Using Human Induced Pluripotent Stem Cells

Observational methods for human studies of transgenerational effects

There are substantial challenges in studying human transgenerational epigenetic outcomes resulting from environmental conditions. The task requires specialized methods and tools that incorporate specific knowledge of multigenerational relationship combinations of probands and their ancestors, phenotype data for individuals, environmental information of ancestors and their descendants, which can span historical to present datasets, and informative environmental data that chronologically aligns with ancestors and descendants over space and time. As a result, there are few epidemiologic studies of potential transgenerational effects in human populations, thus limiting the knowledge of ancestral environmental conditions and the potential impacts we face with modern human health outcomes. In an effort to overcome some of the challenges in studying human transgenerational effects, we present two transgenerational study designs: transgenerational space-time cluster detection and transgenerational case-control study design. Like other epidemiological methods, these methods determine whether there are statistical associations between phenotypic outcomes (e.g., adverse health outcomes) among probands and the shared environments and environmental factors facing their ancestors. When the ancestor is a paternal grandparent, a statistically significant association provides some evidence that a transgenerational inheritable factor may be involved. Such results may generate useful hypotheses that can be explored using epigenomic data to establish conclusive evidence of transgenerational heritable effects. Both methods are proband-centric: They are designed around the phenotype of interest in the proband generation for case selection and family pedigree creation. In the examples provided, we incorporate at least three generations of paternal lineage in both methods to observe a potential transgenerational effect.

Selenium-associated DNA methylation modifications in placenta and neurobehavioral development of newborns: An epigenome-wide study of two U.S. birth cohorts

BACKGROUND/AIM

Selenium (Se) levels in pregnancy have been linked to neurobehavioral development of the offspring. DNA methylation is a potential mechanism underlying the impacts of environmental exposures on fetal development; however, very few studies have been done elucidating the role of DNA methylation linking prenatal Se and child neurobehavior. We aimed to investigate the associations between placental Se concentration and epigenome-wide DNA methylation in two U.S. cohorts, and to assess the association between Se-related DNA methylation modifications and newborns' neurobehavior.

METHODS

We measured placental Se concentrations in 343 newborns enrolled in the New Hampshire Birth Cohort Study and in 141 newborns in the Rhode Island Child Health Study. Genome-wide placental DNA methylation was measured by HumanMethylation450 BeadChip, and newborn neurobehavioral development was assessed by the NICU Network Neurobehavioral Scales (NNNS). We meta-analyzed the associations between placental Se concentration and DNA methylation in each cohort, adjusting for covariates. We also fit multiple linear regression and ordinal logistic regression for methylation and newborn NNNS summary scores.

RESULTS

We identified five Se-related differentially methylated CpG sites. Among them was cg09674502 (GFI1), where selenium concentration was positively associated with methylation (β-coefficient = 1.11, FDR-adjusted p-value = 0.045), and where we observed that a one percent methylation level increase was associated with a 15% reduced odds of higher muscle tone in the arms, legs and trunk of newborns, (OR [95% Confidence Interval, CI] = 0.85 [0.77, 0.95]). We also observed for each interquartile range (IQR) increase in selenium concentration in the placenta, there was 1.76 times greater odds of higher hypotonicity (OR [95% CI] = 1.76 [1.12, 2.82]).

CONCLUSIONS

Placental selenium concentration was inversely associated with muscle tone of newborns, and hypermethylation of GFI1 could be a potential mechanism underlying this association.

Evidence of exposure to chemicals and heavy metals during pregnancy in Japanese women

Purpose

Prenatal exposure to environmental chemicals is a growing concern, because such exposures have been shown to be associated with various diseases. The levels of chemicals and heavy metals in maternal blood, cord blood, maternal urine and amniotic fluid in Japanese pregnant women were investigated.

Methods

A total of 145 women, including 14 fetal growth restriction cases, were included in the present study. The levels of phthalates (di[2‐ethylhexyl]phthalate and mono[2‐ethylhexyl]phthalate), perfluorinated compounds (perfluorooctane sulfonate, perfluorohexanoic acid, perfluorooctanoic acid, and perfluorononanoic acid), pesticides (dimethylphosphate, dimethylthiophosphate, diethylphosphate, diethylthiophosphate, 3‐phenoxybenzoic acid, and octachlorodipropyl ether), bisphenol A, nicotine (nicotine, nornicotine, cotinine, norcotinine, and trans‐3’‐hydroxycotinine), polybrominated diphenyl ethers, and heavy metals were measured. The relationship between fetal growth and the levels of chemicals and heavy metals were investigated.

Results

Phthalates, perfluorinated compounds, pesticides, polybrominated diphenyl ethers, and heavy metals were detected in high frequency, whereas nicotine and bisphenol A were almost negative. Phthalates, perfluorinated compounds, and several heavy metals were transferred to the fetus. High perfluorononanoic acid levels in the maternal blood and cord blood, and low perfluorooctanoic acid level in the cord blood were significantly and negatively associated with fetal growth.

Conclusions

The present study showed that pregnant women in Japan and their fetuses are exposed to a variety of chemicals and heavy metals.