Prenatal urinary polycyclic aromatic hydrocarbon metabolites, global DNA methylation in cord blood, and birth outcomes: A cohort study in China

Gestational exposure to environmental chemicals and epigenetic alterations in the placenta and cord blood mononuclear cells

Background

Exposure to environmental chemicals such as phthalates, phenols, and polycyclic aromatic hydrocarbons (PAHs) during pregnancy can increase the risk of adverse newborn outcomes. We explored the associations between maternal exposure to select environmental chemicals and DNA methylation in cord blood mononuclear cells (CBMC) and placental tissue (maternal and fetal sides) to identify potential mechanisms underlying these associations.

Method

This study included 75 pregnant individuals who planned to give birth at the University of Cincinnati Hospital between 2014 and 2017. Maternal urine samples during the delivery visit were collected and analyzed for 37 biomarkers of phenols (12), phthalates (13), phthalate replacements (4), and PAHs (8). Cord blood and placenta tissue (maternal and fetal sides) were also collected to measure the DNA methylation intensities using the Infinium HumanMethylation450K BeadChip. We used linear regression, adjusting for potential confounders, to assess CpG-specific methylation changes in CBMC (n = 54) and placenta [fetal (n = 67) and maternal (n = 68) sides] associated with gestational chemical exposures (29 of 37 biomarkers measured in this study). To account for multiple testing, we used a false discovery rate q-values < 0.05 and presented results by limiting results with a genomic inflation factor of 1±0.5. Additionally, gene set enrichment analysis was conducted using the Kyoto Encyclopedia of Genes and Genomics pathways.

Results

Among the 29 chemical biomarkers assessed for differential methylation, maternal concentrations of PAH metabolites (1-hydroxynaphthalene, 2-hydroxyfluorene, 4-hydroxyphenanthrene, 1-hydroxypyrene), monocarboxyisononyl phthalate, mono-3-carboxypropyl phthalate, and bisphenol A were associated with altered methylation in placenta (maternal or fetal side). Among exposure biomarkers associated with epigenetic changes, 1-hydroxynaphthalene, and mono-3-carboxypropyl phthalate were consistently associated with differential CpG methylation in the placenta. Gene enrichment analysis indicated that maternal 1-hydroxynaphthalene was associated with lipid metabolism and cellular processes of the placenta. Additionally, mono-3-carboxypropyl phthalate was associated with organismal systems and genetic information processing of the placenta.

Conclusion

Among the 29 chemical biomarkers assessed during delivery, 1-hydroxynaphthalene and mono-3-carboxypropyl phthalate were associated with DNA methylation in the placenta.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43682-024-00027-7.

Associations of co-exposure to polycyclic aromatic hydrocarbons and lead (Pb) with IGF1 methylation in peripheral blood of preschool children from an e-waste recycling area

BACKGROUND

Childhood exposure to polycyclic aromatic hydrocarbons (PAHs) or lead (Pb) is associated with epigenetic modifications. However, the effects of their co-exposures on IGF1 (Insulin-like growth factor 1) methylation and the potential role in child physical growth are unclear.

METHODS

From our previous children study (N = 238, ages of 3-6), 75 children with higher total concentrations of urinary ten hydroxyl PAH metabolites (∑10OH-PAHs) from an e-waste recycling area, Guiyu, and 75 with lower ∑10OH-PAHs from Haojiang (reference area) were included. Pb and IGF1 P2 promoter methylation in peripheral blood were also measured. Multivariable linear regression analyses were performed to estimate individual associations, overall effects and interactions of co-exposure to OH-PAHs and Pb on IGF1 methylation were further explored using Bayesian kernel machine regression.

RESULTS

Methylation of IGF1 (CG-232) was lower (38.00 vs. 39.74 %, P < 0.001), but of CG-207 and CG-137 were higher (59.94 vs. 58.41 %; 57.60 vs. 56.28 %, both P < 0.05) in exposed children than the reference. The elevated urinary 2-OHPhe was associated with reduced methylation of CG-232 (B = -0.051, 95 % CI: -0.096, -0.005, P < 0.05), whereas blood Pb was positively associated with methylation of CG-108 (B = 0.106, 95 %CI: 0.013, 0.199, P < 0.05), even after full adjustment. Methylations of CG-224 and 218 significantly decreased when all OH-PAHs and Pb mixtures were set at 35th - 40th and 45th - 55th percentile compared to when all fixed at 50th percentile. There were bivariate interactions of co-exposure to the mixtures on methylations of CG-232, 224, 218, and 108. Methylations correlated with height, weight, were observed in the exposed children.

CONCLUSIONS

Childhood co-exposure to high PAHs and Pb from the e-waste may be associated with IGF1 promoter methylation alterations in peripheral blood. This, in turn, may interrupt the physical growth of preschool children.

Seasonal variation in urinary PAH metabolite levels and associations with neonatal birth outcomes

Previous studies have demonstrated that exposure to polycyclic aromatic hydrocarbons (PAHs) can affect maternal and infant health. However, the conclusions regarding the effects of seasonal PAH exposure on maternal and infant health have been inconsistent. To further elucidate this issue, this study included data from 2282 mother-infant pairs in the Zuni birth cohort. The objective was to investigate the association between maternal late-pregnancy urinary PAH metabolite concentrations and neonatal birth outcomes during the heating and non-heating seasons. The results demonstrated that PAH exposure in Zunyi was primarily dominated by 2-OHNAP and 1-OHNAP and that the concentrations of PAH metabolites were significantly higher during the heating season. Furthermore, PAH metabolite exposure was found to affect neonatal birth weight, birth length, and parity index with seasonal differences. Further dose-effect analyses revealed nonlinear relationships and seasonal differences between PAH metabolites and neonatal birth weight, birth length, and parity index. Bayesian kernel mechanism regression modeling demonstrated that the inverted U-shaped relationship between PAH metabolites and neonatal birth weight and parity index was exclusive to the heating season. Consequently, it can be posited that maternal exposure to PAH metabolites during late pregnancy exerts a detrimental influence on neonatal growth and development, which is further compounded by the use of heating fuels. This highlights the necessity to either control or alter the use of heating fuels during pregnancy.

Prenatal exposure to polycyclic aromatic hydrocarbons and growth parameters

BACKGROUND AND OBJECTIVES

It has long been known that airborne polycyclic aromatic hydrocarbons (PAHs) can negatively affect pregnancy and birth outcomes, such as birth weight, fetal development, and placental growth factors. However, similar studies yield divergent results. Our goal was to estimate the amount of monohydroxylated PAH (OH-PAH) metabolites in the urine of pregnant women/mothers and their newborns in relation to birth outcomes, such as placenta weight, Apgar 5', and the growth parameters of children up to the age of two.

METHODS

Two cohorts of children born in 2013 and 2014 during the summer and winter seasons in the Czech Republic in the cities Karviná (N = 144) and České Budějovice (N = 198), which differ significantly in the level of air pollution, were studied. PAH exposure was assessed by the concentration of benzo[a]pyrene (B[a]P) in the air and the concentration of 11 OH-PAH metabolites in the urine of newborns and mothers. Growth parameters and birth outcomes were obtained from medical questionnaires after birth and from pediatric questionnaires during the following 24 months of the child's life.

RESULTS

Concentrations of B[a]P were significantly higher in Karviná (p < 0.001). OH-PAH metabolites were significantly higher in the mothers' as well as in the newborns' urine in Karviná and during the winter season. Neonatal length was shorter in newborns in Karviná (p < 0.001), but this difference evened out during the next 3 to 24 months. Compared to České Budějovice, newborns in Karviná showed significantly lower weight gain between birth and three months after delivery. The OH-PAH metabolites in mothers' or newborns' urine did not affect birth weight. The presence of seven OH-PAH (top 25% of values of concentrations higher than the median) metabolites in the newborns' urine is associated with decreased length of newborn. Nine OH-PAH metabolites decreased placenta weight, which was the most significant, while seven OH-PAH metabolites decreased Apgar 5'.

CONCLUSION

We have shown a possible connection between higher concentration of OH-PAH metabolites in newborns' urine and decreased length, head circumference, placenta weight, and Apgar 5', but not birth weight.

Prenatal exposures to phthalates and bisphenols in relation to oxidative stress: single pollutant and mixtures analyses

Prenatal exposures to phthalates and bisphenols have been shown to be linked with adverse birth outcomes. Oxidative stress (OS) is considered a potential mechanism. The objective of this study was to explore the individual and mixtures of prenatal exposures to phthalates and bisphenols in associations with OS biomarkers. We measured eight phthalate metabolites and three bisphenols in the urine samples from 105 pregnant women in Wuhan, China. Urinary 8-hydroxydeoxyguanosine (8-OHdG), 8-isoprostaglandin F2α (8-isoPGF2α), and 4-hydroxy-2-nonenal-mercapturic acid (HNE-MA) were determined as OS biomarkers. The OS biomarkers in associations with the individual chemicals were estimated by linear regression models and restricted cubic spline (RCS) models, and their associations with the chemical mixtures were explored by quantile g-computation (qg-comp) models. In single-pollutant analyses, five phthalate metabolites including monomethyl phthalate (MMP), monoethyl phthalate (MEP), mono-(2-ethylhexyl) phthalate (MEHP), (2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), and mono (2-ethyl-5-oxohexyl) phthalate (MEOHP) were positively associated with urinary 8-OHdG levels (all FDR-adjusted P = 0.06). These associations were further confirmed by the RCS models and were linear (P for overall association ≤ 0.05 and P for non-linear association > 0.05). In mixture analyses, qg-comp models showed that a one-quartile increase in the chemical mixtures of phthalate metabolites and bisphenols was positively associated with urinary levels of 8-OHdG and 8-isoPGF2α, and bisphenol A (BPA) and bisphenol F (BPF) were the most contributing chemicals, respectively. Prenatal exposures to individual phthalates and mixtures of phthalates and bisphenols were associated with higher OS levels.

Dietary Polycyclic Aromatic Hydrocarbon (PAH) Consumption and Risk of Adverse Birth Outcomes: A Systematic Review and Meta-Analysis

BACKGROUND

There is suggestive epidemiological evidence that maternal dietary polycyclic aromatic hydrocarbons (PAH) may increase the risk of adverse birth outcomes. We sought to summarize the available evidence on the effect of dietary PAH exposure on birth outcomes.

METHODS

PubMed and Scopus databases were systematically searched from inception up to November 2022. Studies were included if they were original articles, were conducted in a human population, assessed dietary PAH consumption, and investigated the relationship between dietary PAH consumption and any adverse birth outcomes. Risk of bias in the included studies was assessed qualitatively and quantitatively. A random effects model was used to compute summary effect estimates in the meta-analysis.

RESULTS

Six observational studies (five prospective cohort studies, and one prevalence case-control study) were included. The included studies assessed dietary PAH exposure using dietary questionnaires. Information on the outcomes of interest was obtained from medical records. Three of the included studies were rated as good quality with the remaining three studies rated as fair quality. One study was considered as having low risk of bias for selection, information and confounding bias. Dietary PAH consumption was associated with 5.65 g [95% confidence interval (CI): - 16.36 , 5.06] and 0.04 cm   (95% CI: - 0.08 , 0.01) reductions in birth weight and birth length, respectively, and an increase in head circumference [effect size  ( ES ) = 0.001 ; 95% CI: - 0.003 , 0.005]. The CI of all the summary effect estimates, however, included the null value. In the sensitivity analysis that included only studies that assessed dietary PAH exposure as the primary exposure of interest, dietary PAH consumption was associated with much higher reductions in birth weight (ES = - 14.61 ; 95% CI: - 21.07 , - 8.15 ) and birth length (ES = - 0.06 ; 95% CI: - 0.1 , - 0.03 ). High statistical heterogeneity was observed in the birth weight and birth length analysis and in the head circumference sensitivity analysis.

DISCUSSION

The body of epidemiological evidence suggests that maternal dietary PAH exposure is associated with reduced fetal growth, measured as birth weight and length. There was considerable heterogeneity in the measurement of PAH exposure among the included studies. Also, nonstandardized and validated dietary questionnaires were employed by a majority of the included studies with potential exposure misclassification. These issues are likely to impact the summary effect estimates computed and underscores the need for high-quality epidemiological studies with improved exposure assessment and adequate confounding control to strengthen the evidence base. https://doi.org/10.1289/EHP12922.

"Cocktail" of environmental chemicals and early reproductive outcomes of IVF: The insight from paternal and maternal exposure

BACKGROUND

Humans are exposed to various chemicals, including organophosphate esters (OPEs), phthalates (PAEs), and phenols. The effects on early reproductive outcomes of in vitro fertilization (IVF) remain unclear.

METHODS

We recruited 192 women and 157 men who underwent IVF treatment. A total of forty-nine urinary chemicals were detected, including six OPEs, fifteen PAEs, six parabens, two chlorophenols, nine bisphenols, five benzophenones, and six synthetic phenolic antioxidants. We examined the individual and joint effects of parental chemical exposure on early reproductive outcomes.

RESULTS

We found that certain chemicals were associated with early reproductive outcomes in Poisson regression models. For example, urinary diphenyl phosphate was negatively associated with high-quality embryos in both female (β: -0.12, 95%CI: -0.17, -0.07) and male partners (β: -0.09, 95%CI: -0.15, -0.03). A negative association was found between mixed chemicals and high-quality embryos in Bayesian kernel machine regression, weighted quantile sum regression (β: -0.34, 95%CI: -0.60, -0.07), and quantile-based g-computation model (β: -0.69, 95%CI: -1.34, -0.05) among female partners. Paternal mixture exposure was not associated with early reproductive outcomes.

CONCLUSIONS

Our results indicated that increased exposure to environmental chemicals was associated with adverse early reproductive outcomes of IVF, especially female partners.

Single and Joint Associations of Polycyclic Aromatic Hydrocarbon Exposure with Liver Function during Early Pregnancy

The individual and combined associations of polycyclic aromatic hydrocarbons (PAHs) metabolites on liver function during pregnancy are still lacking. We aimed to explore the connection between urinary PAH metabolites and liver function in early pregnant women in southwest China based on the Zunyi birth cohort. Ten urinary PAH metabolites and five liver function parameters during early pregnancy were measured. The associations of single PAHs with parameters of liver function were assessed using multiple linear regression. A Bayesian kernel machine regression (BKMR) model was used to evaluate the joint associations of the PAH mixture with outcomes. We found that each 1% increment of urinary 2-hydroxyphenanthrene (2-OH-PHE) was associated with 3.36% (95% CI: 0.40%, 6.40%) higher alanine aminotransferase (ALT) and 2.22% (95% CI: 0.80%, 3.67%) higher aspartate aminotransferase (AST). Each 1% increment in 1-hydroxy-phenanthrene (1-OH-PHE) was significantly associated with 7.04% (95% CI: 1.61%, 12.75%) increased total bile acid (TBA). Additionally, there was a significant positive linear trend between 2-OH-PHE and AST and 1-OH-PHE and TBA. BKMR also showed a significant positive association of PAH mixture with AST. Our results indicate that PAH metabolites were associated with increased parameters of liver function among early pregnant women. Early pregnant women should pay more attention to the adverse relationships between PAHs and liver function parameters to prevent environment-related adverse perinatal outcomes.

Development and validation of an HPLC-MS/MS method for the simultaneous analysis of volatile organic compound metabolites, hydroxylated polycyclic aromatic hydrocarbons, and 8-hydroxy-2'-deoxyguanosine in human urine

Humans are widely and concurrently exposed to volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs). However, few studies have reported the internal co-exposure levels of these chemicals in occupational and general populations. Specifically, the associations revealed between the urinary levels of metabolites of VOCs (mVOCs), hydroxylated PAHs (OH-PAHs), and oxidative stress biomarkers for humans remain limited. In this study, a method based on solid-phase extraction (SPE) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) was developed for the simultaneous analysis of 22 mVOCs, 12 OH-PAHs, and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in human urine samples. The method was validated with all target analyte accuracies and precisions in the range of 76 %-120 % and 1 %-14 % at three levels of spiked urine samples, respectively. The limit of detection (LOD) and limit of quantification (LOQ) of the target analytes were 0.01-0.34 ng/mL and 0.01-7.57 ng/mL, respectively. And the method was applied to measure urinary levels of target analytes from 38 petrochemical workers in Guangzhou, South China. Except for 3-hydroxy-benzo[a]pyrene, all target analytes were detected in the urine samples. The average levels were 0.05-12.6 ng/mL for individual OH-PAHs, 0.20-73620 ng/mL for individual mVOCs, and 1.00 ng/mL for 8-OHdG. Additionally, 3-hydroxy-phenanthrene, 1-hydroxy-pyrene, 6-hydroxy-chrysene, N-acetyl-S-(trichlorovinyl)-L-cysteine, 2-methylhippuric acid, thiodiacetic acid, trans, trans-Muconic acid, and N-acetyl-S-(3,4-dihydroxybutyl)-L-cysteine had statistically significant positive effects on 8-OHdG levels, while 1-hydroxy-naphthalene, 1,2-dihydroxybenzene, and hippuric acid showed a negative effect on 8-OHdG, indicating these metabolites could lead to synergistic or antagonistic oxidative DNA damage. This study provides a robust analytical method that permits a comprehensive assessment of co-exposure to PAHs and VOCs and their potential adverse health effects.

Interactions between Benzo(a)pyrene exposure and genetic polymorphisms of AhR signaling pathway on missed abortion

Benzo(a)pyrene (BaP) is an environmental pollutant widely exposed to human beings. While the relationship between BaP and missed abortion is few understood. To explore the association between missed abortion and BaP, genetic polymorphisms of AhR pathway, we recruited 112 cases women with missed abortion and 137 controls women with normal pregnancy from Shanxi, China. The BPDE-DNA adducts level in the case group was higher than that in the control group (P < 0.001). The subjects were categorized according to the tertiles of BPDE-DNA adduct concentrations: T1 ( Collapse

Key Words

• AhR signaling pathway
• BaP
• genetic polymorphisms
• missed abortion

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MESH Headings

• Pregnancy
• Humans
• Female
• DNA Adducts
• Benzo(a)pyrene/toxicity
• 7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide/metabolism
• Abortion, Missed
• Signal Transduction
• Polymorphism, Genetic

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Affiliation(s)

Sha Liu Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China
Mei Han Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China
Jiayu Zhang Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China
Jingru Ji Department of Obstetrics, The First Affiliated Hospital, Shanxi Medical University, Taiyuan, Shanxi, China
Yanfei Wu Department of Obstetrics, The First Affiliated Hospital, Shanxi Medical University, Taiyuan, Shanxi, China Department of Chinese Medicine, The First Affiliated Hospital, Shanxi Medical University, Taiyuan, Shanxi, China
Junni Wei Department of Epidemiology, School of Public Health, Shanxi Medical University, Taiyuan, Shanxi, China

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Developing a profile of urinary PAH metabolites among Chinese populations in the 2010s

Polycyclic aromatic hydrocarbons (PAHs) pose significant health risks. However, no nationwide cohort has been established to consistently record biomonitoring data on PAH exposure in the Chinese population. Biomonitoring data from 56 published studies were combined in this study to develop a profile of urinary PAH metabolites among Chinese population in the 2010s. The stacked column charts described the composition profiles of hydroxylated PAHs (OH-PAHs) in general, special, and occupational populations. Hydroxynaphthalene (OH-Nap) and hydroxyfluorene (OH-Flu) accounted for more than half of the urinary OH-PAH in general and special populations. The urine of the occupational populations contained a significant amount of hydroxyphenanthrene (OH-Phe) and 1-hydroxypyrene (1-OHPyr). Furthermore, this study analyzed the distribution profiles of non-occupationally exposed populations, such as spatial distribution, age distribution, and trends over time. The population of the Southern region had higher urinary OH-PAH concentrations than the population of the Northern region. Adults (45-55 years old) had the highest level of internal PAH exposure. Between 2010 and 2018, the overall trend of urinary OH-PAHs in Chinese general populations decreased. The cumulative distribution function (CDF) revealed that 1-OHNap and 1-OHPyr were better at distinguishing internal PAH exposure among different populations. The sum of OH-Flu and OH-Phe in urine can be used to assess the impact of indoor and outdoor environments on human exposure to PAHs. Our findings suggest that more emphasis should be placed on collecting biomonitoring data for adults of all ages (particularly in the Northern region) and vulnerable populations. In conclusion, this study advocates for the establishment of a nationwide cohort study of Chinese populations as soon as possible in the future to evaluate the Chinese population's exposure to environmental contaminants.

PAH-induced metabolic changes related to inflammation in childhood asthma

Epidemiological studies have shown that PAHs may exert adverse effects on childhood asthma. However, the underlying molecular mechanism remains to be fully elucidated. This study aimed to investigate this process in view of metabolic pathways, especially one-carbon metabolism and tryptophan metabolism. Fifty asthmatic children and 50 control subjects were recruited for this study. Serum IgE and IL-17A levels were detected by ELISA. Serum PAH concentrations were measured by GC-MS. One-carbon-related metabolites and tryptophan metabolites were determined by UPLC-Orbitrap-MS. DNA methylation was analyzed by bisulfite sequencing PCR. ChIP assays were used to examine H3K4me3 enrichment on IL-17A gene. Multivariable linear regression was performed to evaluate the association between PAHs and childhood asthma mediated by intermediators. HE staining in lung tissue, IgE and IL-17A in BALF, metabolic profiles in urine, and Ahr, Il-17a, and Cyp1a1 gene expression were determined in PAH-exposed mice. Serum Fla level was associated with childhood asthma (OR = 1.380, 95% CI: 1.063-1.792), and had a great effect on one-carbon metabolites, especially SAH, SAM, and Ser, which exerted significant mediation effects on the relationship between the Fla concentration and asthma. Moreover, we did find significant mediation effects between serum Fla and asthma by LINE-1 DNA methylation and H3K4me3 levels in the IL-17A promoter region. The differential Trp metabolites, such as Trp, tryptamine, IA, IAA, indole, IAld, and IAAld, indicated that asthmatic children had increased indole-AhR pathway. Mediation analysis failed to show a mediator effect of Trp metabolites in the association between PAHs and childhood asthma. An animal study confirmed that PAH exposure increased methylation levels, and altered Trp metabolite-AhR-IL-17A axis, which may be influenced by gender. PAHs disturbed one-carbon metabolism to influence the methyl group refilling DNA methylation and histone methylation, and disturbed tryptophan metabolism to regulate Th17-cell differentiation, which may elevate serum IL-17A concentration in asthmatic children.

Associations between repeated measurements of urinary polycyclic aromatic hydrocarbon metabolites and thyroid hormones among reproductive-aged men

BACKGROUND

Polycyclic aromatic hydrocarbons (PAHs) have been shown to disrupt thyroid function in toxicological studies, but epidemiological evidence is inconsistent. Furthermore, little is known on potential effects of mixtures of PAHs.

OBJECTIVE

This study aimed to examine the associations of exposure to PAHs as individual chemicals and mixtures with thyroid hormones.

METHODS

We included 378 men from a Reproductive Medicine Center in Wuhan, China. Ten monohydroxylated PAH (OH-PAH) metabolites in repeated urine specimens collected at two-time points and three thyroid hormones [thyroid-stimulating hormone (TSH), free thyroxine (FT4), and free triiodothyronine (FT3)] in one serum sample were measured. Multivariable linear regression models were applied to assess the associations between individual OH-PAH metabolites and thyroid hormones, and the associations with mixtures of OH-PAH metabolites were assessed by Bayesian kernel machine regression (BKMR) models.

RESULTS

Multivariable linear regression models showed inverse associations between urinary 1-OHNa and TSH, between urinary 1-OHPh and 9-OHPh and FT3, as well as between urinary 2-OHPh, 3-OHPh, 9-OHPh and ∑OHPh and FT4, regardless of these individual OH-PAH metabolites modeled as continuous or tertile variables (e.g., -21.57 % in TSH; 95 % CI: -35.33 %, -4.88 % for the third vs first tertiles of 1-OHNa; p for trend = 0.014). BKMR models showed negative overall effects of all urinary OH-PAH metabolite mixtures on TSH, FT3, and FT4, and 1-OHNa, 9-OHPh, and 2-OHPh as the most important contributors, respectively, with linear inverse exposure-response associations when holding other OH-PAH metabolites at their median concentrations.

CONCLUSION

Urinary OH-PAH metabolites as individual chemicals and mixtures were adversely associated with thyroid hormones among reproductive-aged men.

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.

Ambient air pollution during pregnancy and DNA methylation in umbilical cord blood, with potential mediation of associations with infant adiposity: The Healthy Start study

BACKGROUND

Prenatal exposure to ambient air pollution has been associated with adverse offspring health outcomes. Childhood health effects of prenatal exposures may be mediated through changes to DNA methylation detectable at birth.

METHODS

Among 429 non-smoking women in a cohort study of mother-infant pairs in Colorado, USA, we estimated associations between prenatal exposure to ambient fine particulate matter (PM2.5) and ozone (O3), and epigenome-wide DNA methylation of umbilical cord blood cells at delivery (2010-2014). We calculated average PM2.5 and O3 in each trimester of pregnancy and the full pregnancy using inverse-distance-weighted interpolation. We fit linear regression models adjusted for potential confounders and cell proportions to estimate associations between air pollutants and methylation at each of 432,943 CpGs. Differentially methylated regions (DMRs) were identified using comb-p. Previously in this cohort, we reported positive associations between 3rd trimester O3 exposure and infant adiposity at 5 months of age. Here, we quantified the potential for mediation of that association by changes in DNA methylation in cord blood.

RESULTS

We identified several DMRs for each pollutant and period of pregnancy. The greatest number of significant DMRs were associated with third trimester PM2.5 (21 DMRs). No single CpGs were associated with air pollutants at a false discovery rate <0.05. We found that up to 8% of the effect of 3rd trimester O3 on 5-month adiposity may be mediated by locus-specific methylation changes, but mediation estimates were not statistically significant.

CONCLUSIONS

Differentially methylated regions in cord blood were identified in association with maternal exposure to PM2.5 and O3. Genes annotated to the significant sites played roles in cardiometabolic disease, immune function and inflammation, and neurologic disorders. We found limited evidence of mediation by DNA methylation of associations between third trimester O3 exposure and 5-month infant adiposity.

Association between mitochondrial DNA methylation and internal exposure to polycyclic aromatic hydrocarbons (PAHs), nitrated-PAHs (NPAHs) and oxygenated-PAHs (OPAHs) in young adults from Tianjin, China

Polycyclic aromatic hydrocarbons (PAHs), nitrated-PAHs (NPAHs) and oxygenated-PAHs (OPAHs) are environmental pollutants with adverse effects on human health. The correlation between the concentrations of PAHs, NPAHs and OPAHs in human plasma and the methylation level of mitochondrial DNA (mtDNA) was investigated using data from 110 plasma samples collected in Tianjin, China. The median concentrations of PAHs, NPAHs and OPAHs were 16.0 (IQR: 14.4-20.7) ng/mL, 82.2 (IQR: 63.1-97.6) ng/mL and 49.6 (IQR: 28.6-53.8) ng/mL, and the mean proportions were 13.4%, 56.5% and 30.1%, respectively. Bisulfite-PCR pyrosequencing was used to measure the methylation level of MT-CO1 and tRNA-Leu. The methylation levels of two mitochondrial genes (MT-CO1, tRNA-Leu) including four CpG sites (MT-CO1-P1, MT-CO1-P2, tRNA-Leu-P1 and tRNA-Leu-P2) were 0.67% ± 1.38%, 13.54% ± 2.59%, 7.23% ± 5.35% and 1.64% ± 2.94%, respectively. To the best of our knowledge, this is the first time that significant correlations were found between PAHs and their derivatives exposure and mtDNA methylation levels.

The effect of maternal polycyclic aromatic hydrocarbons exposure and methylation levels of CHDs-candidate genes on the risk of congenital heart diseases

OBJECTIVE

To evaluate the impact of maternal exposure to polycyclic aromatic hydrocarbons (PAHs) and methylation levels of CHDs-candidate genes on the risk of congenital heart diseases (CHDs), and the effect of PAHs exposure on DNA methylation states.

METHODS

A case-control study involving 60 mother -fetus pairs was performed by measuring 1-OHPG concentration in maternal urine and methylation levels of 20 CHDs-candidate genes in cord bloods. Logistic regression models were applied to determine the effect of maternal PAHs exposure and fetal methylation levels on the risk of CHDs. Spearman correlation was performed to correlate PAHs exposure and methylation levels.

RESULTS

Maternal higher PAHs exposure was associated with the risk of CHDs (aOR = 3.245, 95% CI: 1.060, 9.937) or some subtypes. The methylation levels of 23 amplicons within 11 genes exhibited significant differences between CHDs and controls. Higher methylation of NKX2-5_M1 was associated with decreased risk of CHDs (aOR=0.182, 95% CI:0.034, 0.983). No significant correlations were found between 1-OHPG concentration and methylation levels of NKX2-5_M1.

CONCLUSIONS

Maternal PAHs exposure was linked with CHDs. Higher methylation of the upstream sequence of NKX2-5 promoter decreased the risk of CHDs. There was no correlation between maternal PAHs exposure and the methylation level of NKX2-5. This article is protected by copyright. All rights reserved.

Household use of crop residues and fuelwood for cooking and newborn birth size in rural Bangladesh

OBJECTIVES

We aimed to investigate the association between type of cooking biomass fuels (crop residues vs fuelwood) and newborn birth outcomes in Bangladeshi children.

METHODS

In this birth cohort study, pregnant women who were 18 years or older with ultrasound confirmed singleton pregnancy of ≤16 weeks of gestation were enrolled from two Bangladesh clinics between January 2008 and June 2011. Exposure to cooking biomass fuels during pregnancy was assessed by an administered questionnaire. The newborn size metrics were measured at the time of delivery. We used multiple linear regression and logistic regression to assess the associations between the type of cooking biomass fuels and birth outcomes after adjusting for covariates.

RESULTS

A total of 1137 participants were using biomass fuels, including crop residues (30.3%) and fuelwood (69.7%), respectively, for cooking. After adjusting for covariates, the use of crop residues for cooking was associated with a 0.13 SD decrease in birth length (95% CI 0.25 to -0.01), a 0.14 SD decrease in head circumference (95% CI -0.27 to -0.02), and increased risk of low birth weight (LBW, OR 1.52, 95% CI 1.07 to 2.15) compared with the use of fuelwood.

CONCLUSION

The use of crop residues for cooking was associated with reduced birth size and increased risk for LBW in Bangladeshi children, implying that the use of crop residues during pregnancy may have a detrimental effect on fetal growth.

The exposure levels and health risk assessment of antibiotics in urine and its association with platelet mitochondrial DNA methylation in adults from Tianjin, China: A preliminary study

There has been extensive research on antibiotics exposure in adults by biomonitoring, but the biological mechanisms and potential risks to human health remain limited. In this study, 102 adults aged 26-44 years in Tianjin were studied and 23 common antibiotics in urine were analyzed by Liquid chromatography-mass spectrometry (LC-MS). All antibiotics were detected in urine, with an overall detection frequency of 40.4% (the detection frequencies of phenothiazines, quinolones, sulfonamides, tetracyclines, and chloramphenicol were 77%, 54%, 24%, 28%, and 49%, respectively.). Ofloxacin and enrofloxacin had the highest detection frequencies (85% and 81%), with median concentrations of 0.26 (IQR: 0.05-1.36) and 0.09 (IQR: 0.03-0.14) ng/mL, respectively. Based on health risk assessment, the predicted estimated daily exposures (EDEs) ranged from 0 μg/kg/day to 13.98 μg/kg/day. The hazard quotient (HQ) values of all the antibiotics except ofloxacin and ciprofloxacin were bellow one, which are considered safe. For all blood samples, the mitochondrial DNA (mtDNA) methylation levels in the MT-ATP6 (ranging between 3.86% and 34.18%) were slightly higher than MT-ATP8 and MT-ND5 (ranging between 0.57% and 9.32%, 1.08% and 19.62%, respectively). Furthermore, mtDNA methylation from MT-ATP6, MT-ATP8 and MT-ND5 were measured by bisulfite-PCR pyrosequencing. The association (P < 0.05) was found between mtDNA methylation level (MT-ATP8 and MT-ND5) and individual antibiotics including chlorpromazine, ciprofloxacin, enrofloxacin, norfloxacin, pefloxacin, sulfaquinoxaline, sulfachloropyridazine, chloramphenicol, and thiamphenicol, indicating that persistent exposure to low-dose multiple antibiotics may affect the mtDNA methylation level and in turn pose health risks.

Prenatal exposure to polycyclic aromatic hydrocarbons could increase the risk of low birth weight by affecting the DNA methylation states in a Chinese cohort

Polycyclic aromatic hydrocarbons (PAHs), as a kind of endocrine disruptors, can enter the fetus body cross the placental barrier from prenatal PAHs exposure to cause adverse birth outcomes. However, it is controversial association between prenatal PAHs exposure and low birth weight (LBW) of their infants. So the present study aimed to estimate the effects of prenatal PAHs exposure during the pregnancy on the risk of LBW in a Chinese cohort through modifying the DNA methylation states. A longitudinal prospective study with 407 pregnant women was established from May to October 2019. The prenatal PAHs exposure during the pregnancy was assessed using the internal dose such as the PAHs metabolites and PAH-DNA adducts in the umbilical cord blood. The methylation levels of genomic DNA and growth-related genes (IGF1 and IGF2) were assessed, while the expressions of these genes were both determined by RT-PCR and Elisa methods. The growth outcomes and relevant Z-scores were recorded at birth. The correlations between the DNA methylation status and concentrations of PAHs, expression levels of growth-related genes and body weight/WAZ were investigated as the measures. According to the PAH-DNA adducts, the subjects were divided into two groups: PAHs-exposed group (PAH-DNA adducts>0, n = 55) and non-exposed group (PAH-DNA adducts = 0, n = 352). Compared with the non-exposed group, it displayed marked decreased birth weight, and increased concentrations of PAHs and DNA methylation levels of the global genomic, IGF1 and IGF2 with their lower expressions in the PAHs-exposed group. These hypermethylation (global genomic, CpG14 and CpG15 of IGF1, and CpG14 of IGF2) were positively correlated with the contents of PAHs in the umbilical cord blood, and negatively correlated with the growth outcomes and their expressions. Totally, prenatal PAHs exposures may contribute to an increased risk of LBW of their infants by modulating the DNA methylation states of genomic DNA and growth-related genes (IGF1 and IGF2) in the umbilical cord blood, which could provide the prenatal prevention of PAHs exposure from possible environmental media except from the occupation and tobacco usage to ensure the health of their infants.

Exposure to polycyclic aromatic hydrocarbons, DNA methylation and heart rate variability among non-current smokers

Polycyclic aromatic hydrocarbons (PAHs) exposure is associated with heart rate variability (HRV) reduction, a widely used marker of cardiovascular autonomic dysfunction. The role of DNA methylation in the relationship between PAHs exposure and decreased HRV is largely unknown. This study aims to explore epigenome-wide DNA methylation changes associated with PAHs exposure and further evaluate their associations with HRV alternations among non-current smokers. We measured 10 mono-hydroxylated PAHs (OH-PAHs) in urine and DNA methylation levels in blood leukocytes among participants from three panels of Chinese non-current smokers (152 in WHZH, 99 in SY, and 53 in COW). We conducted linear regression analyses between DNA methylation and OH-PAHs metabolites with adjustment for age, gender, body mass index, drinking, blood cell counts, and surrogate variables in each panel separately, and combined the results by using inverse-variance weighted fixed-effect meta-analysis to obtain estimates of effect size. The median value of total OH-PAHs ranged from 0.92 × 10^-2 in SY panel (62.6% men) to 13.82 × 10^-2 μmol/mmol creatinine in COW panel (43.4% men). The results showed that methylation levels of cg18223625 (COL20A1) and cg07805771 (SLC16A1) were significantly or marginally significantly associated with urinary 2-hydroxynaphthalene [β(SE) = 0.431(0.074) and 0.354(0.068), FDR = 0.016 and 0.056, respectively], while methylation level of cg09235308 (PLEC1) was positively associated with urinary total OH-PAHs [β(SE) = 0.478(0.079), FDR = 0.004]. Hypermethylations of cg18223625, cg07805771, and cg09235308 were inversely associated with HRV indices among the WHZH and COW non-current smokers. However, we did not observe significant epigenome-wide associations for the other 9 urinary OH-PAHs. These findings provide new evidence that PAHs exposure is linked to differential DNA methylation, which may help better understand the influences of PAHs exposure on HRV alternations.

Urinary metabolites of polycyclic aromatic hydrocarbons after short-term fine particulate matter exposure: A randomized crossover trial of air filtration

Research on the relationship between short-term exposure to fine particulate matter (PM_2.5) and urinary metabolites of polycyclic aromatic hydrocarbons (PAHs) is sparse in the nonoccupationally exposed populations. A quasi-experimental observation of haze events nested within a randomized crossover trial of alternative 1-week real or sham indoor air filtration was conducted to evaluate the associations of urinary monohydroxy-PAHs (OH-PAHs) with short-term exposure to PM_2.5 and PM_2.5-bound PAHs. The study was conducted among 57 healthy college students in Beijing, China. PM_2.5-bound PAHs and urinary OH-PAHs were quantified using gas chromatography coupled with a triple-quadrupole tandem mass spectrometer. Linear mixed-effect models were applied to evaluate the association of urinary OH-PAHs with time-weighted personal PM_2.5 and PM_2.5-bound PAHs, controlling for potentially confounding variables. The results demonstrated that air filtration could markedly reduce external exposure to PM_2.5 and PM_2.5-bound parent, nitrated, and oxygenated PAHs. In the intervention trial, the urinary concentrations of 2-hydroxyfluorene (2-OH-FLU) and 9-hydroxyphenanthrene (9-OH-PHE) were elevated significantly by 16.5% (95% CI, 2.1%, 33.1%) and 37.9% (95% CI, 8.4%, 75.4%), respectively, in association with a doubling increase in personal PM_2.5 exposure. Urinary 9-OH-PHE was also significantly positively associated with the increase in the sum of PM_2.5-bound parent PAHs. Furthermore, the levels of urinary OH-PAHs such as 2-OH-FLU and 9-OH-PHE in the haze events were elevated by 31.1% (95% CI, 8.7%, 53.4%) and 73.5% (95% CI, 16.0%, 131.0%), respectively, in association with a doubling increase in personal PM_2.5 exposure. The findings indicated that urinary 2-OH-FLU and 9-OH-PHE could serve as potential internal exposure biomarkers for assessing short-term PM_2.5 exposure in nonoccupational populations.

DNA methylation as a mediator of associations between the environment and chronic diseases: A scoping review on application of mediation analysis

DNA methylation (DNAm) is one of the most studied epigenetic modifications. DNAm has emerged as a key biological mechanism and biomarkers to test associations between environmental exposure and outcomes in epidemiological studies. Although previous studies have focused on associations between DNAm and either exposure/outcomes, it is useful to test for mediation of the association between exposure and outcome by DNAm. The purpose of this scoping review is to introduce the methodological essence of statistical mediation analysis and to examine emerging epidemiological research applying mediation analyses. We conducted this scoping review for published peer-reviewed journals on this topic using online databases (PubMed, Scopus, Cochrane, and CINAHL) ending in December 2020. We extracted a total of 219 articles by initial screening. After reviewing titles, abstracts, and full texts, a total of 69 articles were eligible for this review. The breakdown of studies assigned to each category was 13 for smoking (18.8%), 8 for dietary intake and famine (11.6%), 6 for other lifestyle factors (8.7%), 8 for clinical endpoints (11.6%), 22 for environmental chemical exposures (31.9%), 2 for socioeconomic status (SES) (2.9%), and 10 for genetic factors and race (14.5%). In this review, we provide an exposure-wide summary for the mediation analysis using DNAm levels. However, we found heterogenous methods and interpretations in mediation analysis with typical issues such as different cell compositions and tissue-specificity. Further accumulation of evidence with diverse exposures, populations and with rigorous methodology will be expected to provide further insight in the role of DNAm in disease susceptibility.

Maternal exposure to phenanthrene during gestation disturbs glucose homeostasis in adult mouse offspring

Epidemiological studies have indicated that polycyclic aromatic hydrocarbons were related to diabetes and insulin resistance. However, studies in mammals on the development of diabetes caused by polycyclic aromatic hydrocarbons are lacking. Pregnant mice were orally exposed to phenanthrene (0, 60 and 600 μg kg^-1 body weight) once every 3 days during gestation. In adult mouse offspring, in-utero phenanthrene exposure caused glucose intolerance and decreased insulin levels in females, while caused elevated fasting blood glucose and insulin levels in males. Serum resistin and interleukin-6 levels were elevated in offspring of both sexes. Serum adiponectin levels were decreased in females but increased in males. The insulin receptor signals were upregulated in the liver and downregulated in the skeletal muscle of F1 females, while they were inhibited in both tissues of F1 males. The visceral fat weight and body weight of the treated mice were not increased, suggesting that phenanthrene is not an obesogen, which is supported by the nonsignificant alteration in pparγ transcription in visceral adipose tissue. The transcription of retn in visceral adipose tissue was upregulated in both sexes, and that of adipoq was downregulated in females but upregulated in males, which were matched with the promoter methylation levels of these genes. The results indicated that phenanthrene exposure during gestation could disturb adipocytokine levels via epigenetic modification in adult offspring, and further influence glucose metabolism. These results might be helpful for understanding nonobesogenic pollutant-induced insulin resistance and preventing against diabetes without obesity.

Hypermethylation of WNT3A gene and non-syndromic cleft lip and/or palate in association with in utero exposure to lead: A mediation analysis

OBJECTIVES

We aim to investigate association between WNT3A methylation and risk of non-syndromic cleft lip and/or palate (NSCL/P), and examine mediating effect of WNT3A methylation on the association of NSCL/P and lead (Pb) exposure in fetuses.

METHODS

DNA methylation of WNT3A in umbilical cord blood was determined among 59 NSCL/P cases and 118 non-malformed controls. Mediation analysis was performed to evaluate the potential mediating effect of WNT3A methylation on association between concentrations of Pb in umbilical cord and risk for NSCL/P. Additionally, an animal experiment in which cleft palates were induced by lead acetate was conducted.

RESULTS

The overall average methylation level of WNT3A was significant higher in NSCL/P cases as compared to controls. The risk for NSCL/P was increased by 1.90-fold with hypermethylation of WNT3A. Significant correlation was observed between concentrations of Pb in umbilical cord and methylation level of WNT3A. The hypermethylation of WNT3A had a mediating effect by 9.32% of total effect of Pb on NSCL/P risk. Gender-specific association between WNT3A methylation and NSCL/P was observed in male fetuses, and the percentage of the mediating effect increased to 14.28%. Animal experiment of mice showed that maternal oral exposure to lead acetate may result in cleft palate in offspring.

CONCLUSION

Hypermethylation of WNT3A was associated with the risk for NSCL/P and may be partly explain the association between exposure to Pb and risk for NSCL/P. The teratogenic and fetotoxic effects of Pb were found in mice.

Polycyclic aromatic hydrocarbon exposure results in altered CRH, reproductive, and thyroid hormone concentrations during human pregnancy

Polycyclic aromatic hydrocarbons (PAHs) are byproducts of incomplete combustion reactions and are ubiquitous in the environment, leading to widespread human exposure via inhalation and ingestion pathways. PAHs have been implicated as endocrine disrupting compounds in previous animal and in vitro studies, but human studies are currently lacking. Pregnant women and their developing fetuses are particularly susceptible populations to environmental contaminants, in part because alterations in hormone physiology during gestation can have adverse consequences on the health of the pregnancy. We utilized data on 659 pregnant women from the PROTECT longitudinal birth cohort in Puerto Rico to assess associations between repeated measures of 8 urinary hydroxylated PAH (OH-PAH) metabolites and 9 serum hormones during gestation. Urine samples were collected at 3 study visits (median gestational ages of 18, 22, and 26 weeks at each visit, respectively) and serum samples were collected at the first and third study visits. Linear mixed effects models were used to ascertain longitudinal associations between OH-PAHs and hormones, and sensitivity analyses were employed to assess potential nonlinearity and differences in associations on the basis of fetal sex and timing of biomarker measurement. Among the multiple positive associations we observed between OH-PAHs and CRH, estriol, progesterone, T3, and the ratio of T3 to T4, and inverse associations with testosterone, the most notable are a 24.3% increase (95% CI: 13.0, 36.7) in CRH with an interquartile range (IQR) increase in 1-hydroxyphenanthrene and a 17.2% decrease (95% CI: 8.13, 25.4) in testosterone with an IQR increase in 1-hydroxynapthalene. Many associations observed were dependent on fetal sex, and some relationships showed evidence of nonlinearity. These findings demonstrate the importance of studying PAH exposures during pregnancy and highlight the potential complexity of their impacts on the physiology of human pregnancy.

Prenatal Multivitamin Use and MTHFR Genotype Are Associated with Newborn Cord Blood DNA Methylation

Background: Fetal development involves cellular differentiation and epigenetic changes—complex processes that are sensitive to environmental factors. Maternal nutrient levels during pregnancy affect development, and methylene tetrahydrofolate reductase (MTHFR) is important for processing the nutrient folate. Hypothesis: We hypothesize that supplement intake before pregnancy and maternal genotype are associated with DNA methylation in newborns. Methods: In the pregnancy cohort, Early Autism Risk Longitudinal Investigation (EARLI), health history, and genotype information was obtained (n = 249 families). Cord blood DNA methylation (n = 130) was measured using the Illumina HumanMethylation450k array and global DNA methylation levels were computed over 455,698 sites. Supplement use preconception and during pregnancy were surveyed at visits during pregnancy. We evaluated associations between maternal preconception supplement intake and global DNA methylation or DNA methylation density distributions of newborn cord blood, stratified by the presence of a variant maternal MTHFR C677T allele. Results: Maternal preconceptional multivitamin intake was associated with cord blood methylation, dependent on maternal MTHFR genotype (interaction term p = 0.013). For mothers without the MTHFR variant allele, multivitamin intake was associated with 0.96% (95% CI: 0.09, 1.83) higher global cord blood methylation (p = 0.04) and was also associated with the cumulative density distribution of methylation (p = 0.03). For mothers with at least one variant allele, multivitamin intake had a null −0.06% (95% CI: −0.45, 0.33) association with global cord blood DNA methylation, and was not associated with the cumulative density distribution (p = 0.37). Conclusions: We observed that cord blood DNA methylation was associated with maternal supplement exposure preconception and maternal genotype. Genetic context should be considered when assessing DNA methylation effects of modifiable risk factors around the time of pregnancy.

Early-life exposure to widespread environmental toxicants and maternal-fetal health risk: A focus on metabolomic biomarkers

Prenatal exposure to widespread environmental toxicants is detrimental to maternal health and fetal development. The effects of environmental toxicants on maternal and fetal metabolic profile changes have not yet been summarized. This systematic review aims to summarize the current studies exploring the association between prenatal exposure to environmental toxicants and metabolic profile alterations in mother and fetus. We searched the MEDLINE (PubMed) electronic database for relevant literature conducted up to September 18, 2019 with some key terms. From the initial 155 articles, 15 articles met the inclusion and exclusion criteria, and consist of highly heterogeneous research methods. Seven studies assessed the effects of multiple environmental pollutants (metals, organic pollutants, nicotine, air pollutants) on the maternal urine and blood metabolomic profile; five studies evaluated the effects of arsenic, polychlorinated biphenyls (PCBs), nicotine, and ambient fine particulate matter (PM_2.5) on the cord blood metabolomic profile; and one study assessed the effects of smoking exposure on the amniotic fluid metabolomic profile. The alteration of metabolic pathways in these studies mainly involve energy metabolism, hormone metabolism, oxidative stress and inflammation. No population study investigated the association between environmental toxicants and placental metabolomics. This systematic review provides evidence that prenatal exposure to a variety of environmental pollutants can affect maternal and fetal metabolomic characteristics. Integration of environmental toxicant exposure and metabolomics data in maternal-fetal samples is helpful to understand the interaction between toxicants and metabolites, so as to reveal the pathogenesis of fetal disease or diseases of fetal origin.

The associations between prenatal exposure to polycyclic aromatic hydrocarbon metabolites, umbilical cord blood mitochondrial DNA copy number, and children's neurobehavioral development

Exposure to polycyclic aromatic hydrocarbons (PAHs) during pregnancy is a risk factor for adverse neurobehavioral development outcomes. Mitochondrial DNA are sensitive to environmental toxicants due to the limited ability of repairing. The change of mitochondrial DNA copy number (mtDNAcn) might be a biologically mechanism linking PAH exposure and children's neurobehavioral impairment. Our aims are to explore whether PAH metabolites in maternal urine were associated with children's neurobehavioral development at 2 years old and umbilical cord blood mtDNAcn, and whether mtDNAcn was a mediator of PAH-related neurobehavioral development. We included 158 non-smoking pregnant women from Taiyuan City, Shanxi Province. Maternal urinary eleven PAH metabolites were detected by high performance liquid chromatography with tandem mass spectrometry (HPLC-MS/MS). MtDNAcn in cord blood was detected by real time quantitative polymerase chain reaction (RT-PCR). Children's neurodevelopment was measured by Gesell Developmental Schedules (GDS) when children were two years age. Generalized linear models and restricted cubic spline models were applied to assess the relationships between PAH metabolites in maternal urine and GDS scores and mtDNAcn. A mediation analysis was also conducted. Generalized linear models showed the relationships of sum of PAH metabolites (Σ-OHPAHs) in maternal urine with decreased motor score, and Σ-OHPAHs with increased mtDNAcn (p for trend < 0.05). Urinary levels of Ln (Σ-OHPAHs) increased one unit was related to a 2.08 decreased in motor scores, and Ln (Σ-OHPAHs) increased one unit was related to 0.15 increased in mtDNAcn. Mediation analysis did not find mtDNAcn can be a mediator between PAH metabolites and neurobehavioral development. Our results suggest that prenatal exposure to PAH decreased children's neurobehavioral development scores and increased mtDNAcn. And reducing exposure to PAH during pregnancy will benefit to improving neurobehavioral development in children. In our present cohort study, sum of PAH metabolites in urine of pregnant women were related with motor score and were positively associated with umbilical cord blood mtDNA copy number.

Traffic-related metrics and adverse birth outcomes: A systematic review and meta-analysis

Given the inconsistency of epidemiologic evidence for associations between maternal exposures to traffic-related metrics and adverse birth outcomes, this manuscript aims to provide clarity on this topic. Pooled meta-estimates were calculated using random-effects analyses. Subgroup analyses were conducted by study area, study design, and Newcastle-Ottawa quality score (NOS). Funnel plots and Egger's test were conducted to evaluate the publication bias, and Fail-safe Numbers (Fail-safe N) were measured to evaluate the robustness of models. From the initial 740 studies (last search, July 11, 2019), 26 studies were included in our analysis. The pooled odds ratio for the change in small for gestational age associated with per 500 m decrease in the distance to roads was 1.016 (95% CI: 1.004, 1.029). Subgroup analyses revealed significant positive associations between term low birth weight and traffic density in higher-quality literatures with higher NOS [1.060 (95% CI: 1.002, 1.121)], cohort studies [1.020 (95% CI: 1.006, 1.033)], and studies in North America [1.018 (95% CI: 1.005, 1.131)]. The buffer of traffic density made no difference in the effect size. Traffic density seemed to be a better indicator of traffic pollution than the distance to roads.

Reduction of mitochondrial DNA copy number in peripheral blood is related to polycyclic aromatic hydrocarbons exposure in coke oven workers: Bayesian kernel machine regression

Although association between polycyclic aromatic hydrocarbons (PAHs) exposure and mitochondrial DNA copy number (mtDNAcn) was researched by traditional linear model extensively, most of these studies analyzed independent effect of each PAHs metabolite and adjust for the confounding other metabolites concomitantly, without considering others interactions. As a complex organic pollutant, a reasonable statistical method is needed to study toxic effects of PAHs. Therefore, we aimed to conduct a novel statistical approach, Bayesian Kernel Machine Regression (BKMR), to explore the effect of PAHs exposure on mtDNAcn among coke oven workers. In this cross-sectional study, the concentrations urinary of PAHs metabolites were measured using high performance liquid chromatography mass spectrometry (HPLC-MS). The mtDNAcn was measured using real-time quantitative polymerase chain reaction (RT-PCR) in peripheral blood of 696 Chinese coke oven workers. The relationship of urinary of PAHs metabolites and mtDNAcn were evaluated by BKMR model. And the results showed a significant negative effect of PAHs metabolites on mtDNAcn when PAHs metabolites concentrations were all above 35th percentile compared to the median and the statistically significant negative single-exposure effect of 2-OHNAP and 2-OHPHE on mtDNAcn when all of the other PAHs are fixed at a particular threshold (25th, 50th, 75th percentile). The changes in log 2-OHNAP and 2-OHPHE from the 25th to the 75th percentile when other PAHs metabolites were at the 50th percentile were associated with change in mtDNAcn of -0.082 (-0.021, -0.124) and -0.048 (-0.021, -0.090) respectively. And evidence of a linear effect of urinary 2-OHNAP and 2-OHPHE were found. Finally, our findings suggested that PAHs cumulative exposures and particularly single-exposure of 2-OHNAP and 2-OHPHE might compromise mitochondrial function by decreasing mtDNAcn in Chinese coke oven workers.

Reductions in urinary metabolites of exposure to household air pollution in pregnant, rural Guatemalan women provided liquefied petroleum gas stoves

BACKGROUND

Household air pollution from solid fuels is a leading risk factor for morbidity and mortality worldwide. Pregnant women's exposure to polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs), two components of solid-fuel smoke, is associated with adverse birth outcomes. Even with improved solid-fuel stoves, exposure to PAHs and VOCs remains high. Therefore, cleaner cooking fuels need to be prioritized.

OBJECTIVE

We aimed to quantify exposure reduction to PAHs and VOCs among pregnant women in rural Guatemala with a liquefied petroleum gas (LPG) stove intervention.

MATERIALS AND METHODS

Urine from pregnant women (N = 50) was collected twice: at <20 weeks gestation, when women cooked exclusively with wood, and 6-8 weeks after receiving an LPG stove. Metabolites of four PAHs and eight VOCs were analyzed. Concurrent with urine collection, personal 48-h PM2.5 exposure was measured.

RESULTS

Women cooking exclusively with wood were exposed to high levels of particulate matter (PM2.5), which was reduced by 57% with the LPG stove. Urinary concentrations of total PAH metabolites (-37%), PMA (benzene metabolite; -49%), and CNEMA (acrylonitrile metabolite; -51%) were reduced. However, recent use of a wood-fired sauna bath led to large increases in excretion of urinary toxicant metabolites (+66-135%).

CONCLUSIONS

This is the first study to report PAH and VOC reductions from an LPG stove intervention introduced during pregnancy. However, other sources of air pollution minimized the gains seen from using an LPG stove. Thus, all sources of air pollution must be addressed in concert to reduce exposures to levels that protect health.

Effects of environmental and lifestyle exposures on urinary levels of polycyclic aromatic hydrocarbon metabolites: A cross-sectional study of urban adults in China

Urinary polycyclic aromatic hydrocarbon (PAH) metabolites, biomarkers of internal PAH exposure, are commonly used to explore the effects of PAH on human health. However, the correlation between environmental PAH exposure and the species or levels of urinary PAH metabolites remains unclear. We collected detailed information on PAH exposure sources, including cigarette smoking, cooking, traffic and diet habits via structured questionnaires, and determined 12 urinary monohydroxylated PAH metabolites (OH-PAHs) among 4092 participants from the Wuhan-Zhuhai cohort. Linear mixed models and generalized linear models were conducted to explore the associations of urinary metabolite levels with single or multiple PAH exposure sources. We also calculated the standardized regression coefficients to further compare the contributions of different sources to urinary OH-PAH levels. Our results showed that increasing levels of urinary 1-, 2-hydroxynaphthalene (1-, 2- OHNa) and 2-hydroxyfluorene (2-OHFlu) were significantly correlated with tobacco smoking (all P < 0.01). The concentrations of 1-, 2- OHNa and 9-hydroxyfluorene (9-OHFlu) were positively correlated with dietary intake (all P < 0.05). Individuals who spent a long time in traffic showed elevated levels of 9-OHFlu and 1-hydroxyphenanthrene (1-OHPh) compared with individuals who spent a short time in traffic (all P < 0.05). Self-cooking was associated only with elevated 1-hydroxypyrene (1-OHP) levels. Moreover, good kitchen ventilation resulted in significantly decreased urinary low-molecular-weight OH-PAH levels. These findings suggested that cigarette smoking, self-cooking, high dietary PAH intake and a long time spent in traffic were associated with increased levels of specific urinary PAH metabolites, and good kitchen ventilation effectively reduced the exposure to low-molecular-weight PAHs in self-cooking participants.

Global DNA methylation changes in rock pigeon (Columba livia) as a sentinel species due to polycyclic aromatic hydrocarbons exposure in Tehran (Iran) as a megacity

Global DNA methylation, as an epigenetic modifications, can be a promising genomic marker for monitoring the contaminants and predicting their adverse health effects. The study aims to assess the effects of 16 PAH concentration on the altered DNA methylation levels in the kidney and liver of rock pigeon (Columba livia), as a sentinel species, from Tehran megacity as well as 40 days benzo(a)pyrene in vitro exposure: (0.1, 2.5, 5, 7.5, and 10 mg kg^-1 bw). Data indicated that the total LMW-PAH (low molecular weight PAHs) group (120.22, 121.34, 103.69, and 128.79 ng g^-1 dw in liver, kidney, skin, and muscle, respectively) in the Tehran samples have higher levels than the other PAHs groups. In addition, the DNA methylation level had negative relation with the total amount of PAHs in liver and kidney. A comparatively higher global DNA hypomethylation (by 8.65% in liver and 3.76% in kidney) was observed in birds exposed to B(a)P. Our results lead us to suggest that DNA hypomethylation in liver and kidney associated with the B(a)P may be useful biomarker discovery (more than the amount of PAH concentration in different tissues of C. livia) in urban areas. In conclusion, based on the overall results assessed, DNA methylation changes in pigeon may show a new target pathway for evaluation of environmental health.

CYP1A1 methylation mediates the effect of smoking and occupational polycyclic aromatic hydrocarbons co-exposure on oxidative DNA damage among Chinese coke-oven workers

BACKGROUND

Multiple factors, including co-exposure between lifestyle and environmental risks, are important in susceptibility to oxidative DNA damage. However, the underlying mechanism is not fully understood. This study was undertaken to evaluate whether Cytochrome P4501A1 (CYP1A1) methylation can mediate the co-exposure effect between smoking and occupational polycyclic aromatic hydrocarbons (PAH) in development of oxidative DNA damage.

METHODS

We explored the associations between smoking and occupational PAH co-exposure effect, CYP1A1 methylation and oxidative DNA damage among 500 workers from a coke-oven plant in China. Urine biomarkers of PAH exposure (1-hydroxypyrene, 1-OHP; 2-hydroxynaphthalene, 2-NAP; 2-hydroxyfluorene, 2-FLU; and 9-hydroxyphenanthren, 9-PHE) and a marker of oxidative DNA damage (8-hydroxy- 2'- deoxyguanosine, 8-OHdG) were measured by high performance liquid chromatography. CYP1A1 methylation was measured by pyrosequencing. Finally, mediation analysis was performed to investigate whether CYP1A1 methylation mediated smoking and occupational PAH co-exposure effect on oxidative DNA damage.

RESULTS

We observed significant associations of smoking and 1-OHP co-exposure with CYP1A1 hypomethylation (OR: 1.87, 95% CI: 1.01-3.47) and high 8-OHdG (OR: 2.13, 95% CI: 1.14-3.97). There was a significant relationship between CYP1A1 hypomethylation and high 8-OHdG (1st vs. 3rd tertile = 1.58, 95% CI: 1.01-2.47, P for trend = 0.046). In addition, mediation analysis suggested CYP1A1 hypomethylation could explain 13.6% of effect of high 8-OHdG related to smoking and 1-OHP co-exposure.

CONCLUSIONS

Our findings suggested that the co-exposure effect of smoking and occupational PAH could increase the risk of oxidative DNA damage by a mechanism partly involving CYP1A1 hypomethylation.

Prenatal polycyclic aromatic hydrocarbons metabolites, cord blood telomere length, and neonatal neurobehavioral development

BACKGROUND

Prenatal exposure to polycyclic aromatic hydrocarbon (PAH) is a potential risk factor for child neurobehavioral development. Telomere length (TL) has important implications for health over the life course.

OBJECTIVE

In this study, we aimed to investigate whether prenatal urinary PAH metabolites were associated with adverse neonatal neurobehavioral development and altered cord blood TL and to explore whether the change of TL was a predictor of neonatal neurobehavioral development.

METHOD

We enrolled 283 nonsmoking pregnant women in Taiyuan city. Eleven PAH metabolites were measured in maternal urine samples. TL in cord blood was measured by real time quantitative polymerase chain reaction. Neonatal behavioral neurological assessment (NBNA) tests were conducted when the infants were three days old. Multiple linear regression models were used to analyze the associations of maternal urinary PAH metabolites with NBNA scores and cord blood TL, and restricted cubic spline models were further used to examine the shapes of dose-response relationships. A mediation analysis was also conducted.

RESULT

We observed dose-response associations of maternal urinary 2-hydroxyfluorene (2-OHFlu) and 2-hydroxyphenanthrene (2-OH Phe) with decreased active tone scores, sum of NBNA scores, and cord blood TL (P for trend<0.05). Each 1 unit increase in urinary levels of Ln (2-OH Flu) or Ln (2-OH Phe) was associated with a 0.092 or 0.135 decrease in the active tone scores and a 0.174 or 0.199 decrease in the sum of NBNA scores. Mediation analysis showed TL could explained 21.74% of the effect of sum of NBNA scores change related to prenatal exposure to 2-OH Phe (P for mediator = 0.047).

CONCLUSION

Our data indicates maternal urinary specific PAH metabolites are inversely associated with neonatal neurobehavioral development and cord blood TL. TL mediates the associations of 2-OH Phe with neonatal neurobehavioral development and partly explains the effect of 2-OH Phe on neonatal neurobehavioral development.

Casp8 hypomethylation and neural tube defects in association with polycyclic aromatic hydrocarbon exposure

Background

Epidemiological studies have found that prenatal exposure to polycyclic aromatic hydrocarbons (PAHs) is associated with increased risk for neural tube defects (NTDs). Aberrant DNA methylation, excessive apoptosis, and oxidative stress have been implied as the mechanism underlying the association between PAH exposure and NTDs, respectively. However, the role of DNA methylation aberration of apoptotic initiator CASP8 (caspase-8, apoptosis-related cysteine peptidase) in the formation of NTDs in association with PAH exposure is not known. By combining a case–control study and mouse model, we aimed to explore the full spectrum of the links from PAH exposure, oxidative stress, CASP8 methylation change, caspase-8 activation, apoptosis, to NTD formation.

Results

Hypomethylation of CASP8 promoter was noticed in the microarray profiled by Infinium HumanMethylation450 BeadChip using neural tissues from 10 terminated NTD fetuses and 8 terminated non-malformed fetuses (14 CpG sites, with β difference ranging between 8.8 and 26.3%), and was validated in a larger case–control sample performed with neural tissues from 80 NTD cases and 32 non-malformed fetuses, using the Sequenom MassARRAY system (7 CpG sites). Hypomethylation of CASP8 was a risk factor for NTDs (aOR = 1.11; 95% CI, 1.05–1.17) based on the logistic regression model. According to Pearson’s correlation, methylation levels of CASP8 were inversely correlated with PAH concentrations in maternal serum and with oxidative stress markers in fetal neural tissues (p < 0.05). In the animal study, increased NTD rates (13.5% frequency), Casp8 hypomethylation, caspase-8 upregulation, increased caspase-8 cleavage, and excessive apoptosis were found in mouse embryos cultured with benz(a)pyrene (BaP) in vitro. Antioxidant N-acetyl-L-cysteine (NAC) and BaP co-treatment attenuated the changes found in BaP treatment group.

Conclusions

Hypomethylation of Casp8 promoter is associated with the formation of NTDs, and Casp8 hypomethylation may be induced by oxidative stress that resulted from exposure to PAHs.

Electronic supplementary material

The online version of this article (10.1186/s13148-019-0673-6) contains supplementary material, which is available to authorized users.

Occurrence, composition profiles and risk assessment of polycyclic aromatic hydrocarbons in municipal sewage sludge in China

A nationwide survey, including 75 sludge samples and 18 wastewater samples taken from different wastewater treatment plants (WWTPs) from 23 cities, was carried out to investigate the occurrence and composition profiles of polycyclic aromatic hydrocarbons (PAHs) in China. In total, the concentrations of ∑₁₆PAHs in sludge ranged from 565 to 280,000 ng/g (mean: 9340 ng/g) which was at a moderate level in the world. The composition profiles of PAHs were characterized by 3- and 4-ring PAHs in textile dyeing sludge and 4- and 5-ring PAHs in domestic sludge. Significant variations in regional distribution of PAHs were observed. Both the principal components analysis and diagnostic ratios revealed that vehicle exhaust, coal and natural gas combustion were the main sources of PAHs in China. The estimated concentrations of PAHs were 3820 ng/L and 1120 ng/L in influents and effluents of the WWTPs, respectively. The high toxic equivalent quantity (TEQ) values of PAHs are ascribed to the high PAH levels. Risk quotient values (RQs) in sludge indicated that there was low potential risk to soil ecosystem after sludge had been applied one year except for indeno [1,2,3-cd]pyrene (IcdP) detected in Huaibei, Anhui province.

Maternal urinary metabolites of PAHs and its association with adverse birth outcomes in an intensive e-waste recycling area

Polycyclic aromatic hydrocarbons (PAHs) are well-known carcinogenic and endocrine disrupting chemicals that have been concerned over the past few decades. We aimed to determine the hydroxylated PAH (OHPAH) metabolite concentrations in maternal urine collected from the e-waste-contaminated area of Guiyu and the reference area of Haojiang, China, and to evaluate their health effects on birth outcomes. The median ƩOHPAH concentration was 6.87 μg/g creatinine from Guiyu, and 3.90 μg/g creatinine from Haojiang. 2-OHNap and 1-OHPyr were the predominant metabolites. Residence in Guiyu and recycling in houses were associated with elevated 2-OHNap and 1-OHPyr. Standardized mean difference revealed that compared to low PAH metabolite levels in the first quartile, high PAH metabolite levels in the fourth quartile especially for 1-OHPyr, ƩOHPAHs and sometimes hydroxylphenanthrene compounds, presented a reduced size in birth outcomes (overall SMD: -0.09; 95% CI: -0.15, -0.03), including head circumference, BMI and Apgar 1 score, and increased size in height. After adjusting for confounders in regression models, an interquartile increase in ΣOHPAHs was associated with a decrease of 234.56 g in weight (95% CI: -452.00, -17.13), 1.72 cm in head circumference (95% CI: -2.96, -0.48), 1.06 kg/m² in BMI (95% CI: -1.82, -0.31) and 0.42 in Apgar 1 score (95% CI: -0.66, -0.18), respectively. These findings suggest high exposure to PAHs during pregnancy in e-waste areas, posing a potential threat to neonatal development, which likely can be attributed to direct e-waste recycling activities. Ongoing studies should be continued to monitor human exposure and health, in particular for vulnerable individuals in e-waste-polluted areas.

Maternal urinary 2-hydroxynaphthalene and birth outcomes in Taiyuan, China

BACKGROUND

Naphthalene is the simplest polycyclic aromatic hydrocarbon (PAH). It is easily emitted into the atmosphere, posing a significant risk to human health. However, limited studies have described the impact of naphthalene exposure on birth outcomes. In this study, we investigated the association between the maternal urinary metabolites of naphthalene, 2-hydroxynaphthalene (2-OH NAP), and birth outcomes.

METHOD

In the present study, four urinary PAH metabolites were measured in 263 pregnant women during late pregnancy. Multiple linear regression analysis was used to analyze the relationship between the concentrations of 2-OH NAP and birth outcomes, and restricted cubic spline models were further used to examine the shapes of the dose-response association.

RESULT

General linear models showed that prenatal urinary 2-OH NAP was associated with lower birth weight (BW) (- 4.38% for the high vs. low exposure group of 2-OH NAP; p for trend = 0.049) and higher cephalization index (CI) (4.30% for the high vs. low exposure group of 2-OH NAP; p for trend = 0.038). These associations were linear and significant when 2-OH NAP was modeled as a continuous variable in restricted cubic spline models (P _linear = 0.0293 for 2-OH NAP and BW; P _linear = 0.0326 for 2-OH NAP and CI). Multiple linear regression data indicated that each 1 ln-unit increase in 2-OH NAP was significantly associated with a 2.09 g/cm increase in the CI. The associations among 2-OH NAP, BW, and CI were also observed in a subset of participants residing close to arterial traffic.

CONCLUSION

Our data indicated that prenatal exposure to naphthalene had an adverse effect on fetal birth outcomes, especially the brain development index. Reduced exposure to naphthalene may improve newborn health outcomes. In Taiyuan, naphthalene may result from traffic pollution.

Exposure to Polycyclic Aromatic Hydrocarbons Leads to Non-monotonic Modulation of DNA and RNA (hydroxy)methylation in a Rat Model

Besides genetic modifications, rapidly growing evidence has linked environmental pollutants with epigenetic variations. To date, only a few studies have been performed on DNA methylation changes of polycyclic aromatic hydrocarbons (PAH), which showed contradictory results. These discrepancies might be partially explained by differences in used agents. Generally in in vitro studies, a single compound is used, while in humans environmental studies, multi-residue exposure is investigated. The present study aimed to study epigenetic alterations induced by multi-residue exposure to PAH. Female Long Evans rats were exposed to a mixture of 16 US-EPA priority PAH, 3 times per week over a 90-day period. The livers were used to assess the (hydroxy)methylation status of genomic DNA/RNA, together with reduced and oxidized forms of glutathione. The results of this study demonstrate that a multi-residue exposure to PAH affects glutathione status, DNA (hydroxy)methylation, and RNA (hydroxy)methylation, together with DNA PAH-adducts formation. In addition, a non-monotonic response relationship was demonstrated between PAH concentration, the levels of glutathione and DNA (hydroxy)methylation levels at environmental relevant doses. This hormetic response gives a novel insight concerning the toxicity of environmental pollutants such as PAH and the biological response that may be different depending on the level of exposure.