Increased maternal non-oxidative energy metabolism mediates association between prenatal di-(2-ethylhexyl) phthalate (DEHP) exposure and offspring autism spectrum disorder symptoms in early life: A birth cohort study

Effect of prenatal phthalate exposure on fetal development and maternal/neonatal health consequences: A systematic review

The ubiquitous presence of phthalate compounds in cosmetics, personal care products and plastics commonly used in toys, food packaging or household products, results in human exposure with adverse effects on reproductive health and fetal development. Following the PRISMA methodology, this systematic review analyzes the effect of prenatal phthalate exposure on major pregnancy complications, such as gestational diabetes, pregnancy-induced hypertension, fetal growth restriction and preterm birth, and its role in fetal neurodevelopment. This review includes >100 articles published in the last 10 years, showing an association between maternal exposure to phthalates and the risk of developing pregnancy complications. Phthalates are negatively associated with motor skills and memory, and also increase the risk of delayed language acquisition, autism spectrum disorder traits, and behavioral deficits, such as attention deficit hyperactivity disorder in children prenatally exposed to phthalates. Di (2-ethylhexyl) phthalate and its metabolites (mono(2-ethylhexyl) phthalate, mono(3-carboxypropyl) phthalate, mono(2-ethyl-5-hydroxyhexyl) phthalate, mono(2-ethyl-5-oxohexyl) phthalate) are the main compounds associated with the above-mentioned pregnancy complications and fetal neurodevelopmental disorders. In addition, this review discusses the molecular mechanisms responsible for various pregnancy complications and neurodevelopmental disorders, and the critical window of exposure, in order to clarify these aspects. Globally, the most common molecular mechanisms involved in the effects of phthalates are endocrine disruption, oxidative stress induction, intrauterine inflammation, and DNA methylation disorders. In general, the critical window of exposure varies depending on the pathophysiology of the complication being studied, although the first trimester is considered an important period because some of the most vulnerable processes (embryogenesis and placentation) begin early in pregnancy. Future research should aim to understand the specific mechanism of the disruptive effect of each component and to establish the toxic dose of phthalates, as well as to elucidate the most critical period of pregnancy for exposure and the long-term consequences for human health.

2-Ethylhexyl Diphenyl Phosphate Induces Autism Spectrum Disorder-Like Behaviors in Offspring Mice by Disrupting Postsynaptic Development

As organophosphorus flame retardants (OPFRs) are constantly detected in human samples, the neurotoxicity of OPFRs is of concern. In this study, pregnant ICR mice were exposed to 2-ethylhexyl diphenyl phosphate (EHDPP) in drinking water from gestation to lactation to investigate its effects on autism spectrum disorder-like (ASD-like) behaviors in offspring. Serum EHDPP concentrations in dams in the 0.4, 2, and 10 mg/kg groups were 0.282 ± 0.051, 0.713 ± 0.115, and 0.974 ± 0.048 ng/mL, respectively, within the concentration range in humans. At the highest dose, EHDPP exposure induced ASD-like behaviors in both female and male offspring. Significant reductions in mature dendritic spines and structural damage to the postsynaptic density zone were noted in all but the lowest exposure groups, indicating postsynaptic membrane impairment. Mechanistically, EHDPP significantly downregulated disc large MAGUK scaffold protein 4 expression by inhibiting protein kinase B and type 1 insulin-like growth factor receptor phosphorylation. In the heterologous synapse formation assay in vivo, EHDPP significantly reduced the levels of postsynaptic density protein 95 expression in neurons at 1 μM. Overall, the study utilized in vitro and in vivo experiments to confirm that EHDPP damaged postsynaptic membrane formation and might increase the incidence of ASD in offspring.

Concerted monoamine oxidase activity following exposure to di-2-ethylhexyl phthalate is associated with aggressive neurobehavioral response and neurodegeneration in zebrafish brain

Di-2-ethylhexyl phthalate (DEHP) is the most commonly preferred synthetic organic chemical in plastics and its products for making them ductile, flexible and durable. As DEHP is not chemically bound to the macromolecular polymer of plastics, it can be easily leached out to accumulate in food and environment. Our recent report advocated that exposure to DEHP significantly transformed the innate bottom-dwelling and scototaxis behaviour of zebrafish. Our present study aimed to understand the possible role of DEHP exposure pertaining towards the development of aggressive behaviour and its association with amplified monoamine oxidase activity and neurodegeneration in the zebrafish brain. As heightened monoamine oxidase (MAO) is linked with genesis of aggressive behaviour, our observation also coincides with DEHP-persuaded aggressive neurobehavioral transformation in zebrafish. Our preliminary findings also showed that DEHP epitomized as a prime factor in transforming native explorative behaviour and genesis of aggressive behaviour through oxidative stress induction and changes in the neuromorphology in the periventricular grey zone (PGZ) of the zebrafish brain. With the finding demarcating towards heightened chromatin condensation in the PGZ of zebrafish brain, our further observation by immunohistochemistry showed a profound augmentation in apoptotic cell death marker cleaved caspase 3 (CC3) expression following exposure to DEHP. Our further observation by immunoblotting study also demarcated a temporal augmentation in CC3 and tyrosine hydroxylase expression in the zebrafish brain. Therefore, the gross findings of the present study delineate the idea that chronic exposure to DEHP is associated with MAO-instigated aggressive neurobehavioral transformation and neurodegeneration in the zebrafish brain.

Phthalate exposure during pregnancy and its association with thyroid hormones: A prospective cohort study

Phthalate esters (PAEs) possess endocrine-disrupting properties. Studies in humans have indicated that in utero phthalate exposure affects maternal thyroid hormones, which are essential for fetal growth and development. However, these studies also reported inconsistent results on the relationship between phthalates and thyroid hormones. This prospective cohort study aimed to assess phthalate exposure across the three trimesters of pregnancy and its association with thyroid hormone levels. From 2019 to 2022, we recruited 672 pregnant women, and two urine samples and one blood sample were collected from each participant during the pregnancy. We examined the urine samples from 663, 335, and 294 women in the first, second, and third trimester, respectively, for the following seven phthalate metabolites: monoethyl phthalate (MEP) from diethyl phthalate (DEP); mono-n-butyl phthalate (MnBP) and mono-iso-butyl phthalate (MiBP) from dibutyl phthalate (DBP); monobenzyl phthalate (MBzP) from butyl benzyl phthalate; and three di(2-ethylhexyl) phthalate (DEHP) metabolites, mono-(2-ethyl-5-hydroxyhexyl) phthalate (MEHHP), mono-(2-ethyl-5-oxohexyl) phthalate (MEOHP), and mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP). Additionally, we examined the levels of free thyroxine (FT4), thyroid-stimulating hormone (TSH), and total triiodothyronine (TT3) in the serum samples of the following participants: 596, 627, and 576 in the first trimester; 292, 293, and 282 in the second trimester; and 250, 250, and 248 in the third trimester, respectively. Other than MBzP, which was detected in 25%-33% of the samples, other metabolites were detectable in >86% of urine samples, indicating widespread exposure to DEP, DBP, and DEHP. The detected phthalate exposure levels in our cohort were significantly higher than those reported in other countries. Metabolite levels varied across the trimesters, implying changes in exposure and metabolism throughout pregnancy. The observed variability in urinary concentrations of phthalate metabolites, which ranged from poor to moderate, underscores the importance of taking multiple measurements during pregnancy for precise exposure assessment. Using a linear mixed model, we analyzed the effects of repeated phthalate exposure on thyroid hormone levels while adjusting for potential confounders. We observed significant linear trends in FT4, TSH, and, to a lesser extent, TT3 across quartiles of specific phthalate metabolites. Comparing the highest to the lowest quartiles, we found a significant increase in FT4 levels, ranging from 2 to 3.7%, associated with MEP; MECPP; MEHHP; and the sum of seven metabolites (∑7PAE), three DEHP metabolites (∑3DEHP), two DBP metabolites (∑DBP), and both low molecular weight (∑LMW) and high molecular weight metabolites. Increased TSH levels (5%-16%) were observed for all phthalate metabolites (except MEHHP) and their molar sums, including ∑7PAE. For TT3, a significant increase was observed with MEP (2.2%) and a decrease was observed with ∑DBP (-2.7%). A higher TSH/FT4 ratio was observed with the highest quartiles (third or fourth) of several phthalate metabolites: MEP (8.8%), MiBP (8.7%), MnBP (22.2%), ∑7PAE (15.3%), ∑DBP (16.4%), and ∑LMW (18.6%). These hormonal alterations, most notably in the second and third trimesters, suggest that phthalate exposure may impact fetal growth and development by affecting maternal thyroid function.

Disrupted prenatal metabolism may explain the etiology of suboptimal neurodevelopment: a focus on phthalates and micronutrients and their relationship to autism spectrum disorder

Pregnancy is a time of high metabolic coordination, as maternal metabolism adapts to support the growing fetus. Many of these changes are coordinated by the placenta, a critical fetal endocrine organ and the site of maternal-fetal crosstalk. Dysregulation in maternal and placental metabolism during pregnancy has been linked to adverse outcomes, including altered neurodevelopment. Autism spectrum disorder (ASD) is a neurodevelopmental disorder linked to metabolic alterations in both children and their mothers. Prenatal environmental exposures have been linked to risk of ASD through dysregulated maternal, placental, and fetal metabolism. In this review, we focus on recent studies investigating the associations between prenatal metabolism in the maternal-placental-fetal unit and the impact of prenatal environmental exposures to phthalates and micronutrients on ASD risk. By identifying the mechanisms through which phthalates and other ubiquitous endocrine disrupting chemicals influence development, and how nutritional interventions can impact those mechanisms, we can identify promising ways to prevent suboptimal neurodevelopment.

Biomarkers of mitochondrial dysfunction in autism spectrum disorder: A systematic review and meta-analysis

Autism spectrum disorder (ASD) is a neurodevelopmental disorder affecting 1 in 36 children and is associated with physiological abnormalities, most notably mitochondrial dysfunction, at least in a subset of individuals. This systematic review and meta-analysis discovered 204 relevant articles which evaluated biomarkers of mitochondrial dysfunction in ASD individuals. Significant elevations (all p < 0.01) in the prevalence of lactate (17%), pyruvate (41%), alanine (15%) and creatine kinase (9%) were found in ASD. Individuals with ASD had significant differences (all p < 0.01) with moderate to large effect sizes (Cohen's d' ≥ 0.6) compared to controls in mean pyruvate, lactate-to-pyruvate ratio, ATP, and creatine kinase. Some studies found abnormal TCA cycle metabolites associated with ASD. Thirteen controlled studies reported mitochondrial DNA (mtDNA) deletions or variations in the ASD group in blood, peripheral blood mononuclear cells, lymphocytes, leucocytes, granulocytes, and brain. Meta-analyses discovered significant differences (p < 0.01) in copy number of mtDNA overall and in ND1, ND4 and CytB genes. Four studies linked specific mtDNA haplogroups to ASD. A series of studies found a subgroup of ASD with elevated mitochondrial respiration which was associated with increased sensitivity of the mitochondria to physiological stressors and neurodevelopmental regression. Lactate, pyruvate, lactate-to-pyruvate ratio, carnitine, and acyl-carnitines were associated with clinical features such as delays in language, social interaction, cognition, motor skills, and with repetitive behaviors and gastrointestinal symptoms, although not all studies found an association. Lactate, carnitine, acyl-carnitines, ATP, CoQ10, as well as mtDNA variants, heteroplasmy, haplogroups and copy number were associated with ASD severity. Variability was found across biomarker studies primarily due to differences in collection and processing techniques as well as the intrinsic heterogeneity of the ASD population. Several studies reported alterations in mitochondrial metabolism in mothers of children with ASD and in neonates who develop ASD. Treatments targeting mitochondria, particularly carnitine and ubiquinol, appear beneficial in ASD. The link between mitochondrial dysfunction in ASD and common physiological abnormalities in individuals with ASD including gastrointestinal disorders, oxidative stress, and immune dysfunction is outlined. Several subtypes of mitochondrial dysfunction in ASD are discussed, including one related to neurodevelopmental regression, another related to alterations in microbiome metabolites, and another related to elevations in acyl-carnitines. Mechanisms linking abnormal mitochondrial function with alterations in prenatal brain development and postnatal brain function are outlined. Given the multisystem complexity of some individuals with ASD, this review presents evidence for the mitochondria being central to ASD by contributing to abnormalities in brain development, cognition, and comorbidities such as immune and gastrointestinal dysfunction as well as neurodevelopmental regression. A diagnostic approach to identify mitochondrial dysfunction in ASD is outlined. From this evidence, it is clear that many individuals with ASD have alterations in mitochondrial function which may need to be addressed in order to achieve optimal clinical outcomes. The fact that alterations in mitochondrial metabolism may be found during pregnancy and early in the life of individuals who eventually develop ASD provides promise for early life predictive biomarkers of ASD. Further studies may improve the understanding of the role of the mitochondria in ASD by better defining subgroups and understanding the molecular mechanisms driving some of the unique changes found in mitochondrial function in those with ASD.

An in-situ versatile screening method for identifying SVOC sources in indoor environments

Indoor semivolatile organic compounds (SVOCs) pose a substantial threat to human health. However, identifying the sources of these emissions has been challenging owing to the scarcity of convenient and practical on-site methodologies. Herein, a novel method for source screening was proposed using aluminum silicate sampling strips to adsorb SVOCs from the surface air of indoor materials. The adsorbed SVOC levels indicate the emission intensity of these materials into indoor environments. Additionally, compact sampling strips can be readily fixed to any vertical surface using a static sticker, facilitating the characterization of various materials in practical settings. Laboratory-simulated experiments demonstrated the capability of the proposed method to differentiate between source and non-source materials within a 10-cm distance in the same space. In practical scenarios, the primary emission sources identified via this method exhibited a consistent correlation with the contents of the corresponding materials obtained from the traditional solvent-extraction method. As the adsorbed SVOCs were directly transferred to a GC-MS through thermal desorption instead of the solvent-extraction procedure, the proposed method demonstrated several-fold improvements in analytical sensitivity and efficiency. Using this versatile screening technique, some emerging and important SVOC species were identified within specific indoor materials. Eliminating these sources has been demonstrated as an effective approach to mitigate SVOC pollution. Overall, the proposed method offers a powerful tool for managing indoor pollutants and safeguarding human health.

The associations between pre-conception urinary phthalate concentrations, the serum metabolome, and live birth among women undergoing assisted reproduction

BACKGROUND

Phthalates are ubiquitous endocrine disruptors. Past studies have shown an association between higher preconception urinary concentrations of phthalate metabolites and lower fertility in women; however, the biological mechanisms remain unclear. Our exploratory study aimed to understand the metabolites and pathways associated with maternal preconception phthalate exposure and examine if any may underline the association between phthalate exposure and live birth using untargeted metabolomics.

METHODS

Participants (n = 183) were part of the Environment and Reproductive Health (EARTH) study, a prospective cohort that followed women undergoing in vitro fertilization (IVF) at the Massachusetts General Hospital Fertility Center (2005-2016). On the same day, women provided a serum sample during controlled ovarian stimulation, which was analyzed for metabolomics using liquid chromatography coupled with high-resolution mass spectrometry and two chromatography columns, and a urine sample, which was analyzed for 11 phthalate metabolites using targeted approaches. We used multivariable generalized linear models to identified metabolic features associated with urinary phthalate metabolite concentrations and live birth, followed by enriched pathway analysis. We then used a meet-in-the-middle approach to identify overlapping pathways and features.

RESULTS

Metabolic pathway enrichment analysis revealed 43 pathways in the C18 negative and 32 pathways in the HILIC positive columns that were significantly associated (p < 0.05) with at least one of the 11 urinary phthalate metabolites or molar sum of di-2-ethylhexyl phthalate metabolites. Lipid, amino acid, and carbohydrate metabolism were the most common pathways associated with phthalate exposure. Five pathways, tryptophan metabolism, tyrosine metabolism, biopterin metabolism, carnitine shuttle, and vitamin B6 metabolism, were also identified as being associated with at least one phthalate metabolite and live birth following IVF.

CONCLUSION

Our study provides further insight into the metabolites and metabolomics pathways, including amino acid, lipid, and vitamin metabolism that may underlie the observed associations between phthalate exposures and lower fertility in women.

Patterns of infant fecal metabolite concentrations and social behavioral development in toddlers

BACKGROUND

Gut-derived metabolites, products of microbial and host co-metabolism, may inform mechanisms underlying children's neurodevelopment. We investigated whether infant fecal metabolites were related to toddler social behavior.

METHODS

Stool samples collected from 6-week-olds (n = 86) and 1-year-olds (n = 209) in the New Hampshire Birth Cohort Study (NHBCS) were analyzed using nuclear magnetic resonance spectroscopy metabolomics. Autism-related behavior in 3-year-olds was assessed by caregivers using the Social Responsiveness Scale (SRS-2). To assess the association between metabolites and SRS-2 scores, we used a traditional single-metabolite approach, quantitative metabolite set enrichment (QEA), and self-organizing maps (SOMs).

RESULTS

Using a single-metabolite approach and QEA, no individual fecal metabolite or metabolite set at either age was associated with SRS-2 scores. Using the SOM method, fecal metabolites of six-week-olds organized into four profiles, which were unrelated to SRS-2 scores. In 1-year-olds, one of twelve fecal metabolite profiles was associated with fewer autism-related behaviors, with SRS-2 scores 3.4 (95%CI: -7, 0.2) points lower than the referent group. This profile had higher concentrations of lactate and lower concentrations of short chain fatty acids than the reference.

CONCLUSIONS

We uncovered metabolic profiles in infant stool associated with subsequent social behavior, highlighting one potential mechanism by which gut bacteria may influence neurobehavior.

IMPACT

Differences in host and microbial metabolism may explain variability in neurobehavioral phenotypes, but prior studies do not have consistent results. We applied three statistical techniques to explore fecal metabolite differences related to social behavior, including self-organizing maps (SOMs), a novel machine learning algorithm. A 1-year-old fecal metabolite pattern characterized by high lactate and low short-chain fatty acid concentrations, identified using SOMs, was associated with social behavior less indicative of autism spectrum disorder. Our findings suggest that social behavior may be related to metabolite profiles and that future studies may uncover novel findings by applying the SOM algorithm.

Cord blood lipid correlation network profiles are associated with subsequent attention-deficit/hyperactivity disorder and autism spectrum disorder symptoms at 2 years: a prospective birth cohort study

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) are neurodevelopmental conditions with early life origins. Alterations in blood lipids have been linked to ADHD and ASD; however, prospective early life data are limited. This study examined (i) associations between the cord blood lipidome and ADHD/ASD symptoms at 2 years of age, (ii) associations between prenatal and perinatal predictors of ADHD/ASD symptoms and cord blood lipidome, and (iii) mediation by the cord blood lipidome.

METHODS

From the Barwon Infant Study cohort (1074 mother-child pairs, 52.3% male children), child circulating lipid levels at birth were analysed using ultra-high-performance liquid chromatography-tandem mass spectrometry. These were clustered into lipid network modules via Weighted Gene Correlation Network Analysis. Associations between lipid modules and ADHD/ASD symptoms at 2 years, assessed with the Child Behavior Checklist, were explored via linear regression analyses. Mediation analysis identified indirect effects of prenatal and perinatal risk factors on ADHD/ASD symptoms through lipid modules.

FINDINGS

The acylcarnitine lipid module is associated with both ADHD and ASD symptoms at 2 years of age. Risk factors of these outcomes such as low income, Apgar score, and maternal inflammation were partly mediated by higher birth acylcarnitine levels. Other cord blood lipid profiles were also associated with ADHD and ASD symptoms.

INTERPRETATION

This study highlights that elevated cord blood birth acylcarnitine levels, either directly or as a possible marker of disrupted cell energy metabolism, are on the causal pathway of prenatal and perinatal risk factors for ADHD and ASD symptoms in early life.

FUNDING

The foundational work and infrastructure for the BIS was sponsored by the Murdoch Children's Research Institute, Deakin University, and Barwon Health. Subsequent funding was secured from the Minderoo Foundation, the European Union's Horizon 2020 research and innovation programme (ENDpoiNTs: No 825759), National Health and Medical Research Council of Australia (NHMRC) and Agency for Science, Technology and Research Singapore [APP1149047], The William and Vera Ellen Houston Memorial Trust Fund (via HOMER Hack), The Shepherd Foundation, The Jack Brockhoff Foundation, the Scobie & Claire McKinnon Trust, the Shane O'Brien Memorial Asthma Foundation, the Our Women Our Children's Fund Raising Committee Barwon Health, the Rotary Club of Geelong, the Ilhan Food Allergy Foundation, Geelong Medical and Hospital Benefits Association, Vanguard Investments Australia Ltd, the Percy Baxter Charitable Trust, and Perpetual Trustees.