Prenatal perfluoroalkyl substances exposure and neurodevelopment in toddlers: Findings from SMBCS

Adverse outcome pathway for the neurotoxicity of Per- and polyfluoroalkyl substances: A systematic review

Per- and polyfluoroalkyl substances (PFAS) are endocrine disruptors with unambiguous neurotoxic effects. However, due to variability in experimental models, population characteristics, and molecular endpoints, the elucidation of mechanisms underlying PFAS-induced neurotoxicity remains incomplete. In this review, we utilized the adverse outcome pathway (AOP) framework, a comprehensive tool for evaluating toxicity across multiple biological levels (molecular, cellular, tissue and organ, individual, and population), to elucidate the mechanisms of neurotoxicity induced by PFAS. Based on 271 studies, the reactive oxygen species (ROS) generation emerged as the molecular initiating event 1 (MIE1). Subsequent key events (KEs) at the cellular level include oxidative stress, neuroinflammation, apoptosis, altered Ca2+ signal transduction, glutamate and dopamine signaling dyshomeostasis, and reduction of cholinergic and serotonin. These KEs culminate in synaptic dysfunction at organ and tissue levels. Further insights were offered into MIE2 and upstream KEs associated with altered thyroid hormone levels, contributing to synaptic dysfunction and hypomyelination at the organ and tissue levels. The inhibition of Na+/I- symporter (NIS) was identified as the MIE2, initiating a cascade of KEs at the cellular level, including altered thyroid hormone synthesis, thyroid hormone transporters, thyroid hormone metabolism, and binding with thyroid hormone receptors. All KEs ultimately result in adverse outcomes (AOs), including cognition and memory impairment, autism spectrum disorders, attention deficit hyperactivity disorders, and neuromotor development impairment. To our knowledge, this review represents the first comprehensive and systematic AOP analysis delineating the intricate mechanisms responsible for PFAS-induced neurotoxic effects, providing valuable insights for risk assessments and mitigation strategies against PFAS-related health hazards.

Sex-specific associations of per- and polyfluoroalkyl substances with brain-derived neurotrophic factors (BDNF) in cord serum

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) is perceived as an emerging environmental endocrine disruptor, which have been linked to children neurodevelopment. However, the potential mechanisms are not clear. Brain-derived neurotrophic factor (BDNF) is a vital protein in neurodevelopment, and the associations between PFAS exposure and BDNF require exploration.

OBJECTIVE

We aimed to explore the relationships between PFAS exposure and the levels of BDNF in cord serum.

METHODS

A total of 1,189 mother-infant dyads from the Sheyang Mini Birth Cohort Study (SMBCS) were enrolled. The levels of 12 PFAS and BDNF were measured in cord serum. We utilized generalized linear models (GLMs), quantile-based g-computation (QGC) models, and Bayesian Kernel Machine Regression (BKMR) models to explore the relationships between single and mixed PFAS exposure and BDNF concentration. Additionally, the potential sex differences were explored by sex-stratified analysis.

RESULTS

Median concentrations of the included 10 PFAS ranged from 0.04 to 3.97 μg/L. In the single chemical models, four PFAS congeners, namely perfluorononanoic acid (PFNA), perfluorooctane sulfonic acid (PFOS), perfluorodecanoic acid (PFDA), perfluoroundecanoic acid (PFUnDA), were negatively associated with BDNF levels in cord serum among females only (β: -0.116 to -0.062, p < 0.05). In the BKMR models of total mother-infant dyads and female fetuses, the significant negative relationships between PFAS mixtures and BDNF were observed, and PFUnDA was identified as an important contributor (Posterior inclusion probability, PIP = 0.8584 for the total subjects; PIP = 0.8488 for the females). PFOS was another important driver based on the mixture approaches.

CONCLUSIONS

We found that PFNA, PFOS, PFDA, and PFUnDA were associated with decreased BDNF concentration in the females, although the causal inference might be limited. PFAS mixtures were also negatively linked with BDNF levels in the total mother-infant pairs and female fetuses. The adverse effect of PFAS exposure on fetal BDNF levels might be sex-specific.

Effect of per- and polyfluoroalkyl substances on neurodevelopment: Evidence-based risk assessment in the TRAEC strategy context

Although emerging evidence on the association between per- and polyfluoroalkyl substances (PFASs) and neurodevelopment have been investigated, there is no consensus on the effect of maternal PFASs on neurodevelopment in offspring. Here, we assessed the risk of maternal PFASs exposure on the neurodevelopment of offspring using a novel Targeted Risk Assessment of Environmental Chemicals (TRAEC) strategy based on multiple evidence. The evidence from five online databases were analyzed the effect of PFASs on neurodevelopment. The potential neurodevelopment risk of PFASs was evaluated by the TRAEC strategy, which was conducted on a comprehensive scoring system with reliability, correlation, outcome fitness and integrity. The studies from five databases and additional researchers' experiments were included the present study to proceed following risk assessment. Based on the framework with TRAEC strategy, the comprehensive evaluation of health risks was classified as low (absolute value 0-4), medium (absolute value 4-8), high (absolute value 8-10). In the present study, the effect of PFASs exposure on neurodevelopment was a medium-risk level with 5.61 overall risk-score. The population-attributable risk (PAR) was 8.26 % for maternal PFASs exposure. The study identified a low-risk effect of prenatal PFASs exposure on ASD and behavioral disabilities. The chain length, type of PFASs and neurodevelopmental trajectories contributed to the risk of maternal PFASs on the neurodevelopment of offspring. Consistent with results of four criteria-based tools (ToxRTool, SciRAP, OHAT and IRIS), health risk assessment based on the TRAEC strategy demonstrated robustness and reliability in the present study. These results illustrated a medium-risk effect of maternal PFASs exposure on neurodevelopmental disorders of offspring. In addition, the TRAEC strategy provided a scientific and structured method for effect evaluation between prenatal PFASs and neurodevelopmental disorders, promoting the consistency and validation in risk assessment.

Prenatal exposure to per- and polyfluoroalkyl substances and child behavioral problems

BACKGROUND

Prenatal exposure to per- and polyfluoroalkyl substances (PFAS) may adversely affect child behaviors; however, findings of epidemiologic studies are inconsistent. We examined prenatal PFAS exposure in association with child behavioral problems.

METHODS

Participants were 177 mother-child pairs from MARBLES (Markers of Autism Risk in Babies - Learning Early Signs), a cohort with elevated familial likelihood of autism spectrum disorder (ASD). We quantified nine PFAS in maternal serum (1-3 samples per mother) collected from the 1st to 3rd trimesters of pregnancy. Child behavioral problems were assessed at 3 years of age using the Child Behavior Checklist (CBCL), developed to test for various behavioral problems of children. We examined associations of the CBCL scores with individual PFAS concentrations and with their mixture using negative binomial regression and weighted quantile sum regression models.

RESULTS

Higher prenatal perfluorononanoate (PFNA) concentrations were associated with higher scores of externalizing problems [β = 0.16, 95% CI (0.01, 0.32)] and aggressive behavior [β = 0.17 (0.01, 0.32)]. Higher PFNA, perfluorooctane sulfonate (PFOS), and perfluorodecanoate (PFDA) were associated with higher scores of sleep problems [β = 0.34 (0.15, 0.54) for PFNA, β = 0.20 (0.02, 0.37) for PFOS, and β = 0.19 (0.00, 0.37) for PFDA]. No significant associations observed for typically developing children, whereas PFOS, PFNA, and PFDA were associated with several behavioral problems among children diagnosed with ASD or other neurodevelopmental concerns. Exposure to a mixture of PFAS was associated with higher scores of sleep problems and aggressive behavior, mostly contributed by PFNA and PFDA.

CONCLUSIONS

Our study showed that prenatal exposure to some PFAS could increase child behavioral problems at 3 years of age. However, our results should be interpreted with caution because we relied on data from a cohort with increased familial likelihood of ASD and thereby had more behavioral problems.

Prenatal exposure to per- and polyfluoroalkyl substances, fetal thyroid function, and intelligence quotient at 7 years of age: Findings from the Sheyang Mini Birth Cohort Study

BACKGROUND

Prenatal exposure to per- and polyfluoroalkyl substances (PFASs) influences neurodevelopment. Thyroid homeostasis disruption is thought to be a possible underlying mechanism. However, current epidemiological evidence remains inconclusive.

OBJECTIVES

This study aimed to explore the effects of prenatal PFAS exposure on the intelligence quotient (IQ) of school-aged children and assess the potential mediating role of fetal thyroid function.

METHODS

The study included 327 7-year-old children from the Sheyang Mini Birth Cohort Study (SMBCS). Cord serum samples were analyzed for 12 PFAS concentrations and 5 thyroid hormone (TH) levels. IQ was assessed using the Wechsler Intelligence Scale for Children-Chinese Revised (WISC-CR). Generalized linear models (GLM) and Bayesian Kernel Machine Regression (BKMR) were used to evaluate the individual and combined effects of prenatal PFAS exposure on IQ. Additionally, the impact on fetal thyroid function was examined using a GLM, and a mediation analysis was conducted to explore the potential mediating roles of this function.

RESULTS

The molar sum concentration of perfluorinated carboxylic acids (ΣPFCA) in cord serum was significantly negatively associated with the performance IQ (PIQ) of 7-year-old children (β = -6.21, 95 % confidence interval [CI]: -12.21, -0.21), with more pronounced associations observed among girls (β = -9.57, 95 % CI: -18.33, -0.81) than in boys. Negative, albeit non-significant, cumulative effects were noted when considering PFAS mixture exposure. Prenatal exposure to perfluorooctanoic acid, perfluorononanoic acid, and perfluorooctanesulfonic acid was positively associated with the total thyroxine/triiodothyronine ratio. However, no evidence supported the mediating role of thyroid function in the link between PFAS exposure and IQ.

CONCLUSIONS

Increased prenatal exposure to PFASs negatively affected the IQ of school-aged children, whereas fetal thyroid function did not serve as a mediator in this relationship.

Association of prenatal exposure to perfluorinated and polyfluoroalkyl substances with childhood neurodevelopment: A systematic review and meta-analysis

BACKGROUND

Although previous studies have shown an association between prenatal exposure to perfluorinated and polyfluoroalkyl substances (PFAS) and neurodevelopmental disorders in children, the results have been inconsistent. We summarize studies on the association between prenatal PFAS exposure and neurodevelopment in children in order to better understand the relationship.

OBJECTIVE

We conducted a meta-analysis of prenatal PFAS exposure and developmental outcomes associated with intellectual, executive function and behavioral difficulty in children to explore the relationship between prenatal exposure to perfluorinated and polyfluoroalkyl substances (PFAS) and neurodevelopmental disorders in children.

METHODS

We searched for articles published up to August 3, 2023, included and quantified original studies on PFAS and child Intelligence Quotient (IQ), executive function and behavioral difficulty during pregnancy, and systematically summarized articles that could not be quantified.

CONCLUSION

There is evidence of sex-specific relationship between PFAS exposure and children's PIQ. We found that PFOS [β = -1.56, 95% CI = -2.96, - 0.07; exposure = per 1 ln (ng/ml) increase], PFOA [β = -1.87, 95% CI = -3.29, - 0.46; exposure = per 1 ln (ng/ml) increase], PFHxS [β = -2.02, 95% CI = -3.23, - 0.81; exposure = per 1 ln (ng/ml) increase] decreased performance IQ in boys, but PFOS [β = 1.56, 95% CI = 0.06, 3.06; exposure = per 1 ln (ng/ml) increase] increased performance IQ in girls. PFAS are associated with executive function impairments in children, but not related to behavioral difficulty in children.

Early-Life Exposure to Perfluoroalkyl Substances (PFAS) and Child Language and Communication Development: A Systematic Review

Language development starts during the fetal period when the brain is sensitive to endocrine disruptions from environmental contaminants. This systematic review aims to systematically summarize the existing literature on early-life exposure to PFAS and children's language and communication development, which is an indicator of neurocognitive development. A structured literature search was conducted using three databases, PubMed, Scopus, and CINAHL, last updated in April 2023. The population was defined as children and young adults. PFAS exposure was assessed pre- or postnatally. The outcome was defined as a language and communication ability assessed with validated instruments, parental self-reports, or clinical language disorder diagnoses. In total, 15 studies were identified for subsequent analyses. Thirteen were performed in background-exposed populations and two in highly exposed populations. There were some indications of potential adverse effects; however, these were not consistent across child sex, age of assessment, or PFAS exposure levels. No systematic effect of early-life PFAS exposure on language and communication development was found. These inconclusive findings may partly be explained by the use of general test instruments with limited validity as to children's language and communication development. Further studies over a wider exposure range using specific language test instruments are needed.

Association between prenatal exposure to per- and polyfluoroalkyl substances and neurodevelopment in children: Evidence based on birth cohort

BACKGROUND

Although numerous studies have examined the effect of prenatal per- and polyfluoroalkyl substances (PFAS) exposure on neurodevelopment in children, findings have been inconsistent.

OBJECTIVE

To better understand the effects of PFAS exposure during pregnancy on offspring neurodevelopment, we conducted a systematic review of prenatal exposure to different types of PFAS and neurodevelopment in children.

METHODS

A comprehensive search was conducted in the PubMed, Web of Science, and EMBASE electronic databases up to March 2023. Only birth cohort studies that report a specific association between PFAS exposure during pregnancy and neurodevelopment were included in this review.

RESULTS

31 birth cohort studies that met the inclusion criteria were qualitatively integrated. Among these, 14 studies investigated the impact of PFAS exposure during pregnancy on cognition, 13 on neurobehavior, and 4 on both cognition and neurobehavior. Additionally, 4 studies explored the influence of PFAS on children's comprehensive development.

CONCLUSION

Prenatal PFAS exposure was associated with poor neurodevelopment in children, including psychomotor development, externalizing behavior, and comprehensive development. However, conclusive evidence regarding its effects on other neurological outcomes remains limited. In addition, sex-specific effects on social behavior and sleep problems were identified.

Prenatal Exposure to Perfluoroalkyl Substances and Cognitive and Neurobehavioral Development in Children at 6 Years of Age

Epidemiological evidence regarding the effects of prenatal exposure to perfluoroalkyl substances (PFASs) on neurodevelopment in children is inconclusive. In 449 mother-child pairs from the Shanghai-Minhang Birth Cohort Study, we measured the concentrations of 11 PFASs in maternal plasma samples obtained at 12-16 weeks of gestation. We assessed children's neurodevelopment at 6 years of age by the fourth edition of the Chinese Wechsler Intelligence Scale for Children and Child Behavior Checklist for ages 6-18. We evaluated the association between prenatal exposure to PFASs and children's neurodevelopment and the effect modification of maternal dietary factors during pregnancy and the child's sex. We found that prenatal exposure to multiple PFASs was associated with increased scores for attention problems, and the individual effect of perfluorooctanoic acid (PFOA) was statistically significant. However, no statistically significant association between PFASs and cognitive development was observed. Additionally, we found the effect modification of maternal nut intake and child's sex. In conclusion, this study suggests that prenatal exposure to PFASs was associated with more attention problems, and maternal nut intake during pregnancy may alter the potential effect of PFASs. However, these findings were exploratory because of multiple testing and the relatively small sample size.