Prenatal exposure to perfluorooctane sulfonate alternatives and associations with neonatal thyroid stimulating hormone concentration: A birth cohort study

Maternal per- and polyfluoroalkyl substance concentrations and placental DNA methylation of thyroid hormone-related genes

Studies suggested that per- and polyfluoroalkyl substances (PFAS) may have adverse effects on fetus by altering placental DNA methylation. In the study, we explored associations of maternal PFAS concentrations with placental DNA methylation of thyroid hormone (TH)-related genes and the potential mediating role of DNA methylation levels in PFAS-fetal TH associations. We measured PFAS concentrations in maternal plasma in early pregnancy and levels of total triiodothyronine (TT3), total thyroxine (TT4), free triiodothyronine (FT3), free thyroxine (FT4), and thyroid stimulating hormone (TSH) in cord plasma. We assessed DNA methylation in 345 placental samples for five TH-related genes, i.e., iodothyronine deiodinase 3 (DIO3), solute carrier family 16 member 2 (SLC16A2), solute carrier organic anion transporter family member 1C1 (SLCO1C1), thyrotropin-releasing hormone (TRH), and transthyretin (TTR). We found the associations of PFDA with increased SLC16A2 methylation, PFOA with decreased SLCO1C1 methylation, PFOS with increased TRH methylation, and PFDoA with decreased TRH methylation, and these associations showed sex-specific patterns. Mediation analyses suggested placental SLCO1C1 and SLC16A2 methylation as potential mediators in the associations of PFOA with FT3 and PFUdA with TT4, respectively. These findings provided evidence for associations between prenatal PFAS exposure and epigenetic changes in placental TH-related genes.

Associations between in utero exposure of per- and polyfluoroalkyl substances (PFAS) mixture and anthropometry measures at birth

In utero exposure to per- and polyfluoroalkyl substances (PFAS), which are recognized developmental toxicants, potentially leads to decreased anthropometric measures in infants at birth. We analyzed 16 PFAS in 350 cord serum samples from Jinan, China, using ultra-high-performance liquid chromatography integrated with Orbitrap mass spectrometry. Birth length, birth weight, and head circumference were extracted from medical records and converted into z-scores (BL-z, BW-z and HC-z, respectively). Multivariable linear regression (MLR) models were employed to investigate the associations between individual PFAS and these birth anthropometric z-scores. To assess the cumulative effects of PFAS, quantile g-computation (QGC) and Bayesian kernel machine regression (BKMR) models were employed. Additionally, stratified analyses were performed to derive sex-specific estimates of the associations. MLR analysis revealed significant associations between specific PFAS and reduced birth anthropometric measures varying by infant sex. For example, log2-transformed concentration of cord serum perfluorooctanoic acid (PFOA) was associated with reduced BL-z (β = -0.12 (-0.18, -0.06), p < 0.001) and BW-z (β = -0.20 (-0.31, -0.10), p < 0.001) in all infants. Perfluoroheptanesulfonic acid (PFHpS) was inversely associated with BL-z (β = -0.07 (-0.13, -0.02), p = 0.03) and HC-z (β = -0.06 (-0.11, -0.02), p = 0.01) exclusively in males. BKMR and QGC models suggested general negative dose-response pattern between exposure to PFAS mixtures and BL-z, BW-z, and HC-z in males. Conversely, these associations were not evident in females. The key PFAS identified as contributors to the joint effects, along with the directions of their estimated impacts as determined by the mixture methods, showed marginal consistency with the results obtained from the MLR models. Our study underscored that in utero exposure to certain PFAS was associated with reduced anthropometric measures at birth. Male infants were more susceptible to PFAS exposure, particularly to combined PFAS mixture effects.

Impacts of Gestational F-53B Exposure on Fetal Neurodevelopment: Insights from Placental and Thyroid Hormone Disruption

It has been evidenced that chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs) have strong potential cross the placental barrier, but their adverse effects on offspring remain unclear. In this study, pregnant mice received daily intraperitoneal injections of chlorinated polyfluorinated ether sulfonate (Cl-PFESA; commercially known as F-53B, primarily comprising 6:2 Cl-PFESA and 8:2 Cl-PFESA) at dosages of 40 and 200 μg/kg from gestational days 6 to 17. Following gestational exposure, distinct accumulation of 6:2 and 8:2 Cl-PFESAs was observed in both the placenta and fetal brain, confirming their penetration across the placental and fetal blood-brain barriers. Maternal exposure to F-53B disrupted the placental 11β-hydroxysteroid dehydrogenase type 2 (hsd11b2) barrier, characterized by hypermethylation of its promoter, decreased blood sinusoids in labyrinth layer, and downregulation of the nutrient transport genes, thereby severely impairing the placenta's protective and nutrient transfer functions. Concomitantly, significant fetal intrauterine growth restriction indicated by decreased fetal weight and crown-rump length was observed. Additionally, changes in thyroid hormones, along with transcriptional and DNA methylation alterations in the promoter regions of transthyretin (ttr) and deiodinase 3 (dio3) genes, were noted in the placenta. These epigenetic changes might affect the maternal-fetal transport of thyroid hormones, possibly leading to disrupted thyroid function in the F1 generation. With the decreased nutrient transport capacity of the placenta, T4 levels in the fetus are significantly reduced, resulting in significant fetal neurodevelopmental abnormalities, reduced nerve cell proliferation (Ki67), and damage to synaptic plasticity. This study reveals unveil the hidden dangers of F-53B, highlighting its neurotoxic effects on fetal development through the disruption of thyroid hormone transport across the placenta.

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.

Development of a Physiologically Based Pharmacokinetic (PBPK) Model for F-53B in Pregnant Mice and Its Extrapolation to Humans

Chlorinated polyfluorinated ether sulfonic acid (F-53B), a commonly utilized alternative for perfluorooctane sulfonate, was detected in pregnant women and cord blood recently. However, the lack of detailed toxicokinetic information poses a significant challenge in assessing the human risk assessment for F-53B exposure. Our study aimed to develop a physiologically based pharmacokinetic (PBPK) model for pregnant mice, based on toxicokinetic experiments, and extrapolating it to humans. Pregnant mice were administered 80 μg/kg F-53B orally and intravenously on gestational day 13. F-53B concentrations in biological samples were analyzed via ultraperformance liquid chromatography-mass spectrometry. Results showed the highest F-53B accumulation in the brain, followed by the placenta, amniotic fluid, and liver in fetal mice. These toxicokinetic data were applied to F-53B PBPK model development and evaluation, and Monte Carlo simulations were used to characterize the variability and uncertainty in the human population. Most of the predictive values were within a 2-fold range of experimental data (>72%) and had a coefficient of determination (R2) greater than 0.68. The developed mouse model was then extrapolated to the human and evaluated with human biomonitoring data. Our study provides an important step toward improving the understanding of toxicokinetics of F-53B and enhancing the quantitative risk assessments in sensitive populations, particularly in pregnant women and fetuses.

Per- and Polyfluoroalkyl Substances (PFAS) Affect Female Reproductive Health: Epidemiological Evidence and Underlying Mechanisms

PFAS (per- and polyfluoroalkyl substances) have been extensively used across numerous industries and consumer goods. Due to their high persistence and mobility, they are ubiquitous in the environment. Exposure to PFAS occurs in people via multiple pathways such as dermal contact, water supply, air inhalation, and dietary intake. Even if some PFAS are being phased out because of their persistent presence in the environment and harmful impacts on human health, mixes of replacement and legacy PFAS will continue to pollute the ecosystem. Numerous toxicological investigations have revealed harmful effects of PFAS exposure on female reproductive health, e.g., polycystic ovaries syndrome, premature ovarian failure, endometriosis, reproductive system tumors, pregnancy complications, and adverse pregnancy outcomes. Despite extensive epidemiological studies on the reproductive toxicity of PFAS, research findings remain inconsistent, and the underlying mechanisms are not well understood. In this review, we give an in-depth description of the sources and pathways of PFAS, and then review the reproductive toxicity of PFAS and its possible mechanisms.

Changing the structure of PFOA and PFOS: a chemical industry strategy or a solution to avoid thyroid-disrupting effects?

BACKGROUND

The family of perfluoroalkyl and polyfluoroalkyl substances (PFAS) raised concern for their proven bioaccumulation and persistence in the environment and animals as well as for their hazardous health effects. As a result, new congeners of PFAS have rapidly replaced the so-called "old long-chain PFAS" (mainly PFOA and PFOS), currently out-of-law and banned by most countries. These compounds derive from the original structure of "old long-chain PFAS", by cutting or making little conformational changes to their structure, thus obtaining new molecules with similar industrial applications. The new congeners were designed to obtain "safer" compounds. Indeed, old-long-chain PFAS were reported to exert thyroid disruptive effects in vitro, and in vivo in animals and humans. However, shreds of evidence accumulated so far indicate that the "restyling" of the old PFAS leads to the production of compounds, not only functionally similar to the previous ones but also potentially not free of adverse health effects and bioaccumulation. Studies aimed at characterizing the effects of new-PFAS congeners on thyroid function indicate that some of these new-PFAS congeners showed similar effects.

PURPOSE

The present review is aimed at providing an overview of recent data regarding the effects of novel PFAS alternatives on thyroid function.

RESULTS AND CONCLUSIONS

An extensive review of current legislation and of the shreds of evidence obtained from in vitro and in vivo studies evaluating the effects of the exposure to novel PFOA and PFOS alternatives, as well as of PFAS mixture on thyroid function will be provided.

Firefighting, per- and polyfluoroalkyl substances, and DNA methylation of genes associated with prostate cancer risk

Prostate cancer is the leading incident cancer among men in the United States. Firefighters are diagnosed with this disease at a rate 1.21 times higher than the average population. This increased risk may result from occupational exposures to many toxicants, including per- and polyfluoroalkyl substances (PFAS). This study assessed the association between firefighting as an occupation in general or PFAS serum levels, with DNA methylation. Only genomic regions previously linked to prostate cancer risk were selected for analysis: GSTP1, Alu repetitive elements, and the 8q24 chromosomal region. There were 444 male firefighters included in this study, with some analyses being conducted on fewer participants due to missingness. Statistical models were used to test associations between exposures and DNA methylation at CpG sites in the selected genomic regions. Exposure variables included proxies of cumulative firefighting exposures (incumbent versus academy status and years of firefighting experience) and biomarkers of PFAS exposures (serum concentrations of 9 PFAS). Proxies of cumulative exposures were associated with DNA methylation at 15 CpG sites and one region located within FAM83A (q-value <0.1). SbPFOA was associated with 19 CpG sites (q < 0.1), but due to low detection rates, this PFAS was modeled as detected versus not detected in serum. Overall, there is evidence that firefighting experience is associated with differential DNA methylation in prostate cancer risk loci, but this study did not find evidence that these differences are due to PFAS exposures specifically.

6:2 Chlorinated Polyfluoroalkyl Ether Sulfonates Exert Stronger Thyroid Homeostasis Disruptive Effects in Newborns than Perfluorooctanesulfonate: Evidence Based on Bayesian Benchmark Dose Values from a Population Study

Growing toxicologic evidence suggests that emerging perfluoroalkyl substances (PFASs), like chlorinated polyfluoroalkyl ether sulfonate (Cl-PFESA), may be as toxic or more toxic than perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA). However, further investigations are needed in terms of the human health risk assessment. This study examined the effects of emerging and legacy PFAS exposure on newborn thyroid homeostasis and compared the thyroid disruption caused by 6:2 Cl-PFESA and PFOS using a benchmark dose approach. The health effects of mixture and individual exposure were estimated using the partial least-squares (PLS) model and linear regression, respectively. A Bayesian benchmark dose (BMD) analysis determined the BMD value for adverse effect comparison between 6:2 Cl-PFESA and PFOS. The median (interquartile range) concentrations of 6:2 Cl-PFESA (0.573 [0.351-0.872] ng/mL), PFOS (0.674 [0.462-1.007] ng/mL), and PFOA (1.457 [1.034, 2.405] ng/mL) were found to be similar. The PLS model ranked the PFAS variables' importance in projection (VIP) scores as follows: 6:2 Cl-PFESA > PFOS > PFOA. Linear regression showed that 6:2 Cl-PFESA had a positive association with free triiodothyronine (FT3, P = 0.006) and triiodothyronine (T3, P = 0.014), while PFOS had a marginally significant positive association with FT3 alone (P = 0.042). The BMD analysis indicated that the estimated BMD10 for 6:2 Cl-PFESA (1.01 ng/mL) was lower than that for PFOS (1.66 ng/mL) in relation to a 10% increase in FT3. These findings suggest that 6:2 Cl-PFESA, an alternative to PFOS, has a more pronounced impact on newborns' thyroid homeostasis compared to PFOS and other legacy PFASs.