Latent, sex-specific metabolic health effects in CD-1 mouse offspring exposed to PFOA or HFPO-DA (GenX) during gestation

Comparative study on gene expression profiles in the liver of male neonatal mice prenatally exposed to PFOA and its alternative HFPO-DA

Hexafluoropropylene oxide dimer acid (HFPO-DA), which belongs to the class of perfluoroalkyl ether carboxylic acid (PFECA), is a new alternative to perfluorooctanoic acid (PFOA). However, whether HFPO-DA is a safer alternative to PFOA in neonates remains unclear. In this study, we evaluated neonatal hepatic toxicity on postnatal days 9-10 by orally exposing pregnant CD-1 mice to 0.3 or 3.0 mg/kg/day (low or high doses) of HFPO-DA or PFOA from gestation days 15-17. The results showed that exposure of pregnant mice to HFPO-DA and PFOA induced similar phenotypic effects, including significant decreases in neonatal body weight (BW) and significant increases in liver weight relative to BW in the high-dose. Notably, HFPO-DA exposure significantly decreased in neonatal BW in the low-dose group, whereas PFOA did not. Comprehensive gene expression analysis revealed significant alterations in 408 and 1402 differentially expressed genes (DEGs) in the liver of neonates from the low- and high-dose HFPO-DA groups, respectively, while PFOA significantly altered 0 and 292 DEGs in the corresponding groups. Gene set enrichment analysis indicated that the DEGs induced by HFPO-DA and PFOA were enriched in pathway related to "PPAR signaling", "fatty acid metabolism", and "biological oxidations". In addition, transactivation assays revealed that mouse (m)PPARα and mPPARγ activity of HFPO-DA exceeds that of PFOA and molecular docking simulations analysis predicted that the binding conformation differ between PFOA and HFPO-DA. Overall, our findings demonstrate that HFPO-DA consistently affected neonatal phenotypes, liver gene expression and the molecular initiating events involving PPARα/γ, at lower concentrations than PFOA.

Exposure to environmentally relevant levels of GenX affects placental and offspring development in mice

Hexafluoropropylene Oxide Dimer Acid (GenX or HFPO-DA), a fluorochemical used in industrial applications such as non-stick coatings and water-repellent textiles, has emerged as a replacement for perfluorooctanoic acid (PFOA). Its widespread use has led to detection in air, soil, and drinking water, raising concerns about potential health impacts. This study investigates the effects of exposure to environmentally relevant levels of GenX on placental and offspring development in mice. Female mice were exposed to GenX for short-term (11 days) or subchronic (100 days) durations. Both short-term and subchronic exposure resulted in alterations in body weight gain, placental weight, and placental efficiency. Dams exposed subchronically also exhibit altered fetal weight and impaired placental structure. In the labyrinth layer of placenta, subchronic exposure to GenX caused disordered vasculature, characterized by enlarged vessel lumens, discontinuous signals of maternal (MCT1) and fetal (MCT4) vascular networks, and impaired mitochondria in fetal sinus endothelial cells. The placental mRNA profile revealed imbalanced expression of factors essential for proper angiogenesis, with increased levels of Vegfa and Angpt1, and decreased levels of Tie2. Additionally, male pups of the subchronically exposed dams exhibited higher birth weight, increased weight gain and reduced anogenital distance (AGD), while premature puberty onset was observed in female pups. This study provides the first evidence that subchronic exposure to environmentally relevant levels of GenX affects placental angiogenesis, potentially contributing to altered development in offspring. These findings offer new insights into the health impacts of GenX on reproductive development and raise concerns about its safety as a PFOA alternative.

Comparative Proteomics Highlights that GenX Exposure Leads to Metabolic Defects and Inflammation in Astrocytes

Exposure to PFAS such as GenX (HFPO dimer acid) has become increasingly common due to the replacement of older generation PFAS in manufacturing processes. While neurodegenerative and developmental effects of legacy PFAS exposure have been studied in depth, there is a limited understanding specific to the effects of GenX exposure. To investigate the effects of GenX exposure, we exposed Drosophila melanogaster to GenX and assessed the motor behavior and performed quantitative proteomics of fly brains to identify molecular changes in the brain. Additionally, metabolic network-based analysis using the iDrosophila1 model unveiled a potential link between GenX exposure and neurodegeneration. Since legacy PFAS exposure has been linked to Parkinson's disease (PD), we compared the proteome data sets between GenX-exposed flies and a fly model of PD expressing human α-synuclein. Considering the proteomic data- and network-based analyses that revealed GenX may be regulating GABA-associated pathways and the immune system, we next explored the effects of GenX on astrocytes, as astrocytes in the brain can regulate GABA. An array of assays demonstrated GenX exposure may lead to mitochondrial dysfunction and neuroinflammatory response in astrocytes, possibly linking non-cell autonomous neurodegeneration to the motor deficits associated with GenX exposure.

Gene expression patterns associated with PFOA exposure in Czech young men and women

Perfluorooctanoic acid (PFOA), a member of per- and polyfluoroalkyl substances (PFASs), has been widely used in manufacturing for decades. Currently, PFOA is strictly regulated, but due to its high stability and persistence, it is detected in both environmental as well as in human matrices. To elucidate mechanisms of PFOA toxicity in humans, we determined the genome-wide transcriptomic changes of peripheral blood mononuclear cells (PBMC) responding to PFOA exposure in a sex-stratified analysis. This work employed samples from 145 female and 143 male participants of the CELSPAC: YA study to characterize PFOA-associated transcripts in a broader context using computational analysis. PFOA-associated gene expression differed significantly between men and women, as only 2 % of mapped genes were expressed in both sexes. Disease-specific enrichment analysis revealed cancer and immune-related disease terms as those most enriched in male and female populations. Patterns of enriched terms within the gene set enrichment analysis indicated three main targets of PFOA toxicity: i) lipid metabolism for women; ii) cell cycle regulation for men; and iii) immune system response for both sexes. In summary, our genome-wide transcriptomics analysis described sex-specific differences in PFOA-associated gene expression and provided evidence about biological pathways underlying PFOA toxicity in humans.

Multi-omics reveal disturbance of glucose homeostasis in pregnant rats exposed to short-chain perfluorobutanesulfonic acid

Perfluorobutanesulfonic acid (PFBS), a short-chain alternative to perfluorooctanesulfonic acid (PFOS), is widely used in various products and is increasingly present in environmental media and human bodies. Recent epidemiological findings have raised concerns about its potential adverse health effects, although the specific toxic mechanism remains unclear. This study aimed to investigate the metabolic toxicity of gestational PFBS exposure in maternal rats. Pregnant Sprague Dawley (SD) rats were randomly assigned to three groups and administered either 3% starch gel (control), 5, or 50 mg/kg bw·d PFBS. Oral glucose tolerance tests (OGTT) and lipid profiles were measured, and integrated omics analysis (transcriptomics and non-targeted metabolomics) was employed to identify changes in genes and metabolites and their relationships with metabolic phenotypes. The results revealed that rats exposed to 50 mg/kg bw·d PFBS exhibited a significant decrease in 1-h glucose levels and the area under the curve (AUC) of OGTT compared with the starch group. Transcriptomics analysis indicated significant alterations in gene expression related to cytochrome P450 exogenous metabolism, glutathione metabolism, bile acid secretion, tumor pathways, and retinol metabolism. Differentially expressed metabolites (DEMs) were enriched in pathways such as pyruvate metabolism, the glucagon signaling pathway, central carbon metabolism in cancer, and the citric acid cycle. Co-enrichment analysis and pairwise correlation analysis among genes, metabolites, and outcomes identified several differentially expressed genes (DEGs), including Gstm1, Kit, Adcy1, Gck, Ppp1r3c, Ppp1r3d, and DEMs such as fumaric acid, L-lactic acid, 4-hydroxynonenal, and acetylvalerenolic acid. These DEGs and DEMs may play a role in the modulation of glucolipid metabolic pathways. In conclusion, our results suggest that gestational exposure to PFBS may induce molecular perturbations in glucose homeostasis. These findings provide insights into the potential mechanisms contributing to the heightened risk of abnormal glucose tolerance associated with PFBS exposure.

Persistent metabolic toxicities following developmental exposure to hexafluoropropylene oxide trimer acid (HFPO-TA): Roles of peroxisome proliferator activated receptor gamma

BACKGROUND

Hexafluoropropylene oxide trimer acid (HFPO-TA), a perfluorooctanoic acid (PFOA) substitute, exhibited strong affinity and capability to activate peroxisome proliferator activated receptor gamma (PPARγ), a lipid metabolism regulator, suggesting potential to induce metabolic toxicities.

METHODS

Fertile chicken eggs were exposed to 0, 0.5, 1 or 2 mg/kg (egg weight) HFPO-TA and incubated until hatch. Serum from 0- and 3- month-old chickens were subjected to liquid chromatography ultra-high resolution mass spectrometry for HFPO-TA concentration, while liver, pancreas and adipose tissue samples were collected for histopathological assessments. In ovo PPARγ reporter and silencing system were established with lentivirus microinjection. qRT-PCR and immunohistochemistry were utilized to evaluate the expression levels of PPARγ downstream genes.

RESULTS

In 3-month-old animals developmentally exposed to HFPO-TA, adipose tissue hyperplasia, hepatic steatosis, pancreas islet hypertrophy and elevated serum free fatty acid / insulin levels were observed. Results of reporter assay and qRT-PCR indicated HFPO-TA-mediated PPARγ transactivation in chicken embryo. Silencing of PPARγ alleviated HFPO-TA-induced changes, while PPARγ agonist rosiglitazone mimicked HFPO-TA-induced effects. qRT-PCR and immunohistochemistry revealed that FASN and GPD1 were upregulated following developmental exposure to HFPO-TA in 3-month-old animals.

CONCLUSIONS

Developmental exposure to HFPO-TA induced persistent metabolic toxicities in chickens, in which PPARγ played a central role.

Structure-specific variation in per- and polyfluoroalkyl substances toxicity among genetically diverse Caenorhabditis elegans strains

Background

There are >14,500 structurally diverse per- and polyfluoroalkyl substances (PFAS). Despite knowledge that these "forever chemicals" are in 99% of humans, mechanisms of toxicity and adverse health effects are incompletely known. Furthermore, the contribution of genetic variation to PFAS susceptibility and health consequences is unknown.

Objectives

We determined the toxicity of a structurally distinct set of PFAS in twelve genetically diverse strains of the genetic model system Caenorhabditis elegans.

Methods

Dose-response curves for four perfluoroalkyl carboxylic acids (PFNA, PFOA, PFPeA, and PFBA), two perfluoroalkyl sulfonic acids (PFOS and PFBS), two perfluoroalkyl sulfonamides (PFOSA and PFBSA), two fluoroether carboxylic acids (GenX and PFMOAA), one fluoroether sulfonic acid (PFEESA), and two fluorotelomers (6:2 FCA and 6:2 FTS) were determined in the C. elegans laboratory reference strain, N2, and eleven genetically diverse wild strains. Body length was quantified by image analysis at each dose after 48 hr of developmental exposure of L1 arrest-synchronized larvae to estimate effective concentration values (EC50).

Results

There was a significant range in toxicity among PFAS: PFOSA > PFBSA ≈ PFOS ≈ PFNA > PFOA > GenX ≈ PFEESA > PFBS ≈ PFPeA ≈ PFBA. Long-chain PFAS had greater toxicity than short-chain, and fluorosulfonamides were more toxic than carboxylic and sulfonic acids. Genetic variation explained variation in susceptibility to PFBSA, PFOS, PFBA, PFOA, GenX, PFEESA, PFPeA, and PFBA. There was significant variation in toxicity among C. elegans strains due to chain length, functional group, and between legacy and emerging PFAS.

Conclusion

C. elegans respond to legacy and emerging PFAS of diverse structures, and this depends on specific structures and genetic variation. Harnessing the natural genetic diversity of C. elegans and the structural complexity of PFAS is a powerful New Approach Methodology (NAM) to investigate structure-activity relationships and mechanisms of toxicity which may inform regulation of other PFAS to improve human and environmental health.

Inulin alleviates perfluorooctanoic acid-induced intestinal injury in mice by modulating the PI3K/AKT/mTOR signaling pathway

Perfluorooctanoic acid (PFOA) is a widely used industrial compound that has been found to induce intestinal toxicity. However, the underlying mechanisms have not been fully clarified and effective interventions are rarely developed. Inulin, a prebiotic, has been used as a supplement in human daily life as well as in gastrointestinal diseases and metabolic disorders. In this study, male mice were exposed to PFOA with or without inulin supplementation to investigate the enterotoxicity and potential intervention effects of inulin. Mice were administered PFOA at 1 mg/kg/day, PFOA with inulin at 5 g/kg/day, or Milli-Q water for 12 weeks. Histopathological analysis showed that PFOA caused colon shortening, goblet cell reduction, and inflammatory cell infiltration. The expression of the tight junction proteins ZO-1, occludin and claudin5 significantly decreased, indicating impaired barrier function. According to the RNA-sequencing analysis, PFOA exposure resulted in 917 differentially expressed genes, involving 39 significant pathways, such as TNF signaling and cell cycle pathways. In addition, the protein expression of TNF-α, IRG-47, cyclinB1, and cyclinB2 increased, while Gadd45γ, Lzip, and Jam2 decreased, suggesting the involvement of the TNF signaling pathway, cell cycle, and cell adhesion molecules in PFOA-associated intestinal injury. Inulin intervention alleviated PFOA-induced enterotoxicity by activating the PI3K/AKT/mTOR signaling pathway and increasing the protein expression of Wnt1, β-catenin, PI3K, Akt3, and p62, while suppressing MAP LC3β, TNF-α, and CyclinE expression. These findings suggested that PFOA-induced intestinal injury, including inflammation and tight junction disruption, was mitigated by inulin through modifying the PI3K/AKT/mTOR signaling pathways. Our study provides valuable insights into the enterotoxic effects of PFOA and highlights the potential therapeutic role of inulin.

Gestational GenX and PFOA exposures induce hepatotoxicity, metabolic pathway, and microbiome shifts in weanling mice

Ammonium perfluoro (2-methyl-3-oxahexanoate) (GenX), a replacement for perfluorooctanoic acid (PFOA), has been detected in multiple environmental media and biological samples worldwide. Accumulated evidence implies that GenX exposure might exert adverse health effects, although the underlying mechanisms have not been fully revealed. In this study, pregnant BALB/c mice were exposed to GenX (2 mg/kg/day), PFOA (1 mg/kg/day), or Milli-Q water by gavage from the first day of gestation (GD0) until GD21. Necropsy and tissue collection were conducted in pups at 4 weeks of age. PFOA and GenX induced similar histopathological changes in both the liver and the intestinal mucosa, accompanied by higher serum levels of alanine and aspartate aminotransferase. Moreover, the capacity of hepatic glycogen storage and intestinal mucus secretion were significantly decreased, suggesting dysfunction of liver metabolism and the intestinal mucosal barrier. A total of 637 and 352 differentially expressed genes (DEGs) were identified in the liver tissues of GenX and PFOA group, respectively. Most of the enriched pathways from the DEGs by KEGG enrichment analysis were metabolism-associated. Moreover, overexpression of CYP4A14, Sult2a1, Cpt1b, Acaa1b, Igfbp1, Irs-2 and decreased expression of Gys2 were observed in livers of GenX exposed pups, supporting the hypothesis that there was metabolic disruption. Furthermore, DNA damage and cell cycle arrest proteins (Gadd45β, p21, Ppard) were significantly increased, while cell proliferation-related proteins (Cyclin E, Myc, EGFR) were decreased by gestational GenX exposure in the pups' liver. In addition, imbalance of gut microbiota and dysfunction of the intestinal mucosa barrier might contribute to hepatotoxicity at least in part. Taken together, our results suggested that gestational GenX exposure triggered metabolic disorder, which might be responsible for the hepatotoxicity in the pups in addition to dysfunction of the intestinal mucosa barrier. This study enriches the mechanisms of GenX-induced developmental hepatotoxicity by associating metabolic disorder with intestinal homeostasis.

Hepatic and ovarian effects of perfluorooctanoic acid exposure differ in lean and obese adult female mice

Obesity and overweight cause poor oocyte quality, miscarriage, infertility, polycystic ovarian syndrome, and offspring birth defects and affects 40% and 20% of US women and girls, respectively. Perfluorooctanoic acid (PFOA), a per- and poly-fluoroalkyl substance (PFAS), is environmentally persistent and has negative female reproductive effects including endocrine disruption, oxidative stress, altered menstrual cyclicity, and decreased fertility in humans and animal models. PFAS exposure is associated with non-alcoholic fatty liver disease which affects ∼24-26% of the US population. This study investigated the hypothesis that PFOA exposure impacts hepatic and ovarian chemical biotransformation and alters the serum metabolome. At 7 weeks of age, female lean, wild type (KK.Cg-a/a) or obese (KK.Cg-Ay/J) mice received saline (C) or PFOA (2.5 mg/Kg) per os for 15 d. Hepatic weight was increased by PFOA exposure in both lean and obese mice (P < 0.05) and obesity also increased liver weight (P < 0.05) compared to lean mice. The serum metabolome was also altered (P < 0.05) by PFOA exposure and differed between lean and obese mice. Exposure to PFOA altered (P < 0.05) the abundance of ovarian proteins with roles in xenobiotic biotransformation (lean - 6; obese - 17), metabolism of fatty acids (lean - 3; obese - 9), cholesterol (lean - 8; obese - 11), amino acids (lean - 18; obese - 19), glucose (lean - 7; obese - 10), apoptosis (lean - 18; obese - 13), and oxidative stress (lean - 3; obese - 2). Use of qRT-PCR determined that exposure to PFOA increased (P < 0.05) hepatic Ces1 and Chst1 in lean but Ephx1 and Gstm3 in obese mice. Also, obesity basally increased (P < 0.05) Nat2, Gpi and Hsd17b2 mRNA levels. These data identify molecular changes resultant from PFOA exposure that may cause liver injury and ovotoxicity in females. In addition, differences in toxicity induced by PFOA exposure occurs in lean and obese mice.

RISING STARS: Sex differences in toxicant-associated fatty liver disease

Based on biological sex, the consequential health outcomes from exposures to environmental chemicals or toxicants can differ in disease pathophysiology, progression, and severity. Due to basal differences in cellular and molecular processes resulting from sexual dimorphism of organs including the liver and additional factors influencing 'gene-environment' interactions, males and females can exhibit different responses to toxicant exposures. Associations between environmental/occupational chemical exposures and fatty liver disease (FLD) have been well-acknowledged in human epidemiologic studies and their causal relationships demonstrated in experimental models. However, studies related to sex differences in liver toxicology are still limited to draw any inferences on sex-dependent chemical toxicity. The purpose of this review is to highlight the present state of knowledge on the existence of sex differences in toxicant-associated FLD (TAFLD), discuss potential underlying mechanisms driving these differences, implications of said differences on disease susceptibility, and emerging concepts. Chemicals of interest include various categories of pollutants that have been investigated in TAFLD, namely persistent organic pollutants, volatile organic compounds, and metals. Insight into research areas requiring further development is also discussed, with the objective of narrowing the knowledge gap on sex differences in environmental liver diseases. Major conclusions from this review exercise are that biological sex influences TAFLD risks, in part due to (i) toxicant disruption of growth hormone and estrogen receptor signaling, (ii) basal sex differences in energy mobilization and storage, and (iii) differences in chemical metabolism and subsequent body burden. Finally, further sex-dependent toxicological assessments are warranted for the development of sex-specific intervention strategies.

Pre-differentiation GenX exposure induced neurotoxicity in human dopaminergic-like neurons

GenX, also known as hexafluoropropylene oxide dimer acid (HFPO) was introduced as a safer alternative to perfluorooctanoic acid (PFOA) in 2009. After nearly two decades of applications there are increasing safety concerns about GenX due to its association with various organ damages. Few studies, however, have systematically assessed the molecular neurotoxicity of low-dose GenX exposure. Here, we evaluated the effects of pre-differentiation exposure of GenX on dopaminergic (DA) -like neurons using SH-SY5Y cell line; and assessed changes in epigenome, mitochondrion, and neuronal characteristics. Low dose GenX exposure at 0.4 and 4 μg/L prior to differentiation induces persistent changes in nuclear morphology and chromatin arrangements, manifested specifically in the facultative repressive marker H3K27me3. We also observed impaired neuronal network, increased calcium activity along with alterations in Tyrosine hydroxylase (TH) and α-Synuclein after prior exposure to GenX. Collectively, our results identified neurotoxicity of low-dose GenX exposure in human DA-like neurons following a developmental exposure scheme. The observed changes in neuronal characteristics suggest GenX as a potential neurotoxin and risk factor for Parkinson's disease.

Per- and Polyfluoroalkyl Substances and Breastfeeding as a Vulnerable Function: A Systematic Review of Epidemiological Studies

Milk formation in the breast during breastfeeding is a complex hormonally regulated process, potentially sensitive to the effects of endocrine-disrupting chemical exposures. The environmental chemicals, per- and polyfluoroalkyl substances (PFAS) are known endocrine disruptors. PFAS exposure have been associated with insufficient mammary gland development in mice and reduced breastfeeding duration in humans. The aim of this review was to gather the epidemiological evidence on the association between PFAS exposure and breastfeeding duration. Using PubMed and Embase, we performed a systematic literature search (on 23 January 2023) to identify epidemiological studies examining the association between maternal PFAS exposure and breastfeeding duration. Animal studies, reviews, and non-English studies were excluded. The risk of bias was assessed using the risk of bias in non-randomized studies of exposures tool. Estimates describing the association between PFAS exposure and the duration of breastfeeding were identified, and the data were synthesized separately for each type of PFAS and for the duration of exclusive and total breastfeeding. Six studies with between 336 and 2374 participants each were identified. PFAS exposure was assessed in serum samples (five studies) or based on residential address (one study). Five out of six studies found shorter total duration of breastfeeding with higher PFAS exposure. The most consistent associations were seen for perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and perfluorononanoic acid (PFNA). The finding of a potential causal association between PFAS exposure and breastfeeding duration is in agreement with findings from experimental studies.

Gestational exposure to perfluoroalkyl substances is associated with placental DNA methylation and birth size

DNA methylation is one potential mechanism for the effects of gestational exposure to perfluoroalkyl substances (PFASs) on fetal growth. We investigated 180 pregnant women who participated in a cohort study conducted in Tangshan City, Northern China, and determined the concentrations of 11 PFASs and the methylation of two genes related to fetal growth [insulin-like growth factor 2 (IGF2) and nuclear receptor subfamily 3 group C member 1 (NR3C1)] and one surrogate marker for global methylation [long interspersed nuclear element-1 (LINE-1)] in placenta tissue. Multiple linear regression analysis was performed to examine the associations of log transformed PFASs with the DNA methylation and birth size. Weighted quantile sum regression was used to determine the mixture effect of PFASs. After adjusting for potential confounders, perfluorooctane sulfonate (PFOS) was negatively associated with the overall methylation of LINE-1. PFASs mixture was negatively associated with the methylation of all CpG loci of LINE-1 and overall methylation of NR3C1. Perfluorootanoic acid (PFOA), perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and the PFASs mixture showed negative associations with head circumference. After stratified by newborns' sex, PFOA, PFNA and the PFASs mixture was negatively associated with overall methylation of LINE-1 only in the male subgroup and the methylation of all CpG loci of LINE-1 was negatively associated with ponderal index only in the female subgroup. The interaction of newborns' sex with PFOS and PFOA on overall methylation of IGF2 was statistically significant and so was the interaction of sex with PFOS on overall methylation of LINE-1. These findings suggested that intrauterine exposure to PFASs affected placental DNA methylation and reduced fetal growth, which might be modified by sex.

Assessment of Mouse Liver Histopathology Following Exposure to HFPO-DA With Emphasis on Understanding Mechanisms of Hepatocellular Death

Ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate (HFPO-DA) is a short chain member of per- and polyfluoroalkyl substances (PFAS). To better understand the relevance of histopathological effects seen in livers of mice exposed to HFPO-DA for human health risk assessment, histopathological effects were summarized from hematoxylin and eosin (H&E)-stained sections in several repeat-dose toxicity studies in mice. Findings across studies revealed histopathological changes consistent with peroxisomal proliferation, whereas two reports of steatosis could not be confirmed in the published figures. In addition, mechanisms of hepatocellular death were assessed in H&E sections as well as with the apoptotic marker cleaved caspase-3 (CCasp3) in newly cut sections from archived liver blocks from select studies. A comparison of serially CCasp3 immunolabeled and H&E-stained sections revealed that mechanisms of hepatocellular death cannot be clearly discerned in H&E-stained liver sections alone as several examples of putatively necrotic cells were positive for CCasp3. Published whole genome transcriptomic data were also reevaluated for enrichment of various forms of hepatocellular death in response to HFPO-DA, which revealed enrichment of apoptosis and autophagy, but not ferroptosis, pyroptosis, or necroptosis. These morphological and molecular findings are consistent with transcriptomic evidence for peroxisome proliferator-activated receptor alpha (PPARα) signaling in HFPO-DA exposed mice.

Transcriptional pathways linked to fetal and maternal hepatic dysfunction caused by gestational exposure to perfluorooctanoic acid (PFOA) or hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX) in CD-1 mice

Per- and polyfluoroalkyl substances (PFAS) comprise a diverse class of chemicals used in industrial processes, consumer products, and fire-fighting foams which have become environmental pollutants of concern due to their persistence, ubiquity, and associations with adverse human health outcomes, including in pregnant persons and their offspring. Multiple PFAS are associated with adverse liver outcomes in adult humans and toxicological models, but effects on the developing liver are not fully described. Here we performed transcriptomic analyses in the mouse to investigate the molecular mechanisms of hepatic toxicity in the dam and its fetus after exposure to two different PFAS, perfluorooctanoic acid (PFOA) and its replacement, hexafluoropropylene oxide-dimer acid (HFPO-DA, known as GenX). Pregnant CD-1 mice were exposed via oral gavage from embryonic day (E) 1.5-17.5 to PFOA (0, 1, or 5 mg/kg-d) or GenX (0, 2, or 10 mg/kg-d). Maternal and fetal liver RNA was isolated (N = 5 per dose/group) and the transcriptome analyzed by Affymetrix Array. Differentially expressed genes (DEG) and differentially enriched pathways (DEP) were obtained. DEG patterns were similar in maternal liver for 5 mg/kg PFOA, 2 mg/kg GenX, and 10 mg/kg GenX (R2: 0.46-0.66). DEG patterns were similar across all 4 dose groups in fetal liver (R2: 0.59-0.81). There were more DEGs in fetal liver compared to maternal liver at the low doses for both PFOA (fetal = 69, maternal = 8) and GenX (fetal = 154, maternal = 93). Upregulated DEPs identified across all groups included Fatty Acid Metabolism, Peroxisome, Oxidative Phosphorylation, Adipogenesis, and Bile Acid Metabolism. Transcriptome-phenotype correlation analyses demonstrated > 1000 maternal liver DEGs were significantly correlated with maternal relative liver weight (R2 >0.92). These findings show shared biological pathways of liver toxicity for PFOA and GenX in maternal and fetal livers in CD-1 mice. The limited overlap in specific DEGs between the dam and fetus suggests the developing liver responds differently than the adult liver to these chemical stressors. This work helps define mechanisms of hepatic toxicity of two structurally unique PFAS and may help predict latent consequences of developmental exposure.

Cumulative maternal and neonatal effects of combined exposure to a mixture of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) during pregnancy in the Sprague-Dawley rat

Globally, biomonitoring data demonstrate virtually all humans carry residues of multiple per- and polyfluoroalkyl substances (PFAS). Despite pervasive co-exposure, limited mixtures-based in vivo PFAS toxicity research has been conducted. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are commonly detected PFAS in human and environmental samples and both produce adverse effects in laboratory animal studies, including maternal and offspring effects when orally administered during pregnancy and lactation. To evaluate the effects of combined exposure to PFOA and PFOS, we orally exposed pregnant Sprague-Dawley rats from gestation day 8 (GD8) to postnatal day 2 (PND2) to PFOA (10-250 mg/kg/d) or PFOS (0.1-5 mg/kg/d) individually to characterize effects and dose response curve parameters, followed by a variable-ratio mixture experiment with a constant dose of PFOS (2 mg/kg/d) mixed with increasing doses of PFOA (3-80 mg/kg/d). The mixture study design was intended to: 1) shift the PFOA dose response curves for endpoints shared with PFOS, 2) allow comparison of dose addition (DA) and response addition (RA) model predictions, 3) conduct relative potency factor (RPF) analysis for multiple endpoints, and 4) avoid overt maternal toxicity. Maternal serum and liver concentrations of PFOA and PFOS were consistent between the individual chemical and mixture experiments. Combined exposure with PFOS significantly shifted the PFOA dose response curves towards effects at lower doses compared to PFOA-only exposure for multiple endpoints and these effects were well predicted by dose addition. For endpoints amenable to mixture model analyses, DA produced equivalent or better estimates of observed data than RA. All endpoints evaluated were accurately predicted by RPF and DA approaches except for maternal gestational weight gain, which produced less-than-additive results in the mixture. Data support the hypothesis of cumulative effects on shared endpoints from PFOA and PFOS co-exposure and dose additive approaches for predictive estimates of mixture effects.

Neurotransmission Targets of Per- and Polyfluoroalkyl Substance Neurotoxicity: Mechanisms and Potential Implications for Adverse Neurological Outcomes

Per- and polyfluoroalkyl substances (PFAS) are a group of persistent environmental pollutants that are ubiquitously found in the environment and virtually in all living organisms, including humans. PFAS cross the blood-brain barrier and accumulate in the brain. Thus, PFAS are a likely risk for neurotoxicity. Studies that measured PFAS levels in the brains of humans, polar bears, and rats have demonstrated that some areas of the brain accumulate greater amounts of PFAS. Moreover, in humans, there is evidence that PFAS exposure is associated with attention-deficit/hyperactivity disorder (ADHD) in children and an increased cause of death from Parkinson's disease and Alzheimer's disease in elderly populations. Given possible links to neurological disease, critical analyses of possible mechanisms of neurotoxic action are necessary to advance the field. This paper critically reviews studies that investigated potential mechanistic causes for neurotoxicity including (1) a change in neurotransmitter levels, (2) dysfunction of synaptic calcium homeostasis, and (3) alteration of synaptic and neuronal protein expression and function. We found growing evidence that PFAS exposure causes neurotoxicity through the disruption of neurotransmission, particularly the dopamine and glutamate systems, which are implicated in age-related psychiatric illnesses and neurodegenerative diseases. Evaluated research has shown there are highly reproduced increased glutamate levels in the hippocampus and catecholamine levels in the hypothalamus and decreased dopamine in the whole brain after PFAS exposure. There are significant gaps in the literature relative to the assessment of the nigrostriatal system (striatum and ventral midbrain) among other regions associated with PFAS-associated neurologic dysfunction observed in humans. In conclusion, evidence suggests that PFAS may be neurotoxic and associated with chronic and age-related psychiatric illnesses and neurodegenerative diseases. Thus, it is imperative that future mechanistic studies assess the impact of PFAS and PFAS mixtures on the mechanism of neurotransmission and the consequential functional effects.

Internal Relative Potency Factors for the Risk Assessment of Mixtures of Per- and Polyfluoroalkyl Substances (PFAS) in Human Biomonitoring

BACKGROUND

In human biomonitoring, blood is often used as a matrix to measure exposure to per- and polyfluoroalkyl substances (PFAS). Because the toxicokinetics of a substance (determining the steady-state blood concentration) may affect the toxic potency, the difference in toxicokinetics among PFAS has to be accounted for when blood concentrations are used in mixture risk assessment.

OBJECTIVES

This research focuses on deriving relative potency factors (RPFs) at the blood serum level. These RPFs can be applied to PFAS concentrations in human blood, thereby facilitating mixture risk assessment with primary input from human biomonitoring studies.

METHODS

Toxicokinetic models are generated for 10 PFAS to estimate the internal exposure in the male rat at the blood serum level over time. By applying dose-response modeling, these internal exposures are used to derive quantitative internal RPFs based on liver effects.

RESULTS

Internal RPFs were successfully obtained for nine PFAS. Perfluorobutanoic acid (PFBA), perfluorohexanoic acid (PFHxA), perfluorononanoic acid (PFNA), perfluorododecanoic acid (PFDoDA), perfluorooctane sulfonic acid (PFOS), and hexafluoropropylene oxide-dimer acid (HFPO-DA, or GenX) were found to be more potent than perfluorooctanoic acid (PFOA) at the blood serum level in terms of relative liver weight increase, whereas perfluorobutane sulfonic acid (PFBS) and perfluorohexane sulfonic acid (PFHxS) were found to be less potent. The practical implementation of these internal RPFs is illustrated using the National Health and Nutrition Examination Survey (NHANES) biomonitoring data of 2017-2018.

DISCUSSION

It is recommended to assess the health risk resulting from exposure to PFAS as combined, aggregate exposure to the extent feasible. https://doi.org/10.1289/EHP10009.

Per- and perfluoroalkyl substances alternatives, mixtures and liver function in adults: A community-based population study in China

Experimental evidence has shown that per- and polyfluoroalkyl substances (PFAS) alternatives and mixtures may exert hepatotoxic effects in animals. However, epidemiological evidence is limited. This research aimed to explore associations of PFAS and the alternatives with liver function in a general adult population. The study participants consisted of 1,303 adults from a community-based cross-sectional investigation in Guangzhou, China, from November 2018 to August 2019. We selected 13 PFAS with detection rates > 85% in serum samples and focused on perfluorooctane-sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and their alternatives [6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA), 8:2 Cl-PFESA, and perfluorohexanoic acid (PFHxA)] as predictors of outcome. Six liver function biomarkers (ALB, ALT, AST, GGT, ALP, and DBIL) were chosen as outcomes. We applied regression models with restricted cubic spline function to explore correlations between single PFAS and liver function and inspected the combined effect of PFAS mixtures on liver by applying Bayesian kernel machine regression (BKMR). We discovered positive associations among PFAS and liver function biomarkers except for ALP. For example, compared with the 25th percentile of PFAS concentration, the level of ALT increased by 12.36% (95% CI: 7.91%, 16.98%) for ln-6:2 Cl-PFESA, 5.59% (95% CI: 2.35%, 8.92%) for ln-8:2 Cl-PFESA, 3.56% (95% CI: -0.39%, 7.68%) for ln-PFHxA, 13.91% (95% CI: 8.93%, 19.13%) for ln-PFOA, and 14.25% (95% CI: 9.91%, 18.77%) for ln-PFOS at their 75th percentile. In addition, higher exposed serum PFAS was found to be correlated with greater odds of abnormal liver function. Analysis from BKMR models also showed an adverse association between PFAS mixtures and liver function. The combined effect of the PFAS mixture appeared to be non-interactive, in which PFOS was the main contributor to the overall effect. Our findings provide evidence of associations between PFAS alternatives, PFAS mixtures, and liver function in the general adult population.

A Critical Review and Meta-Analysis of Impacts of Per- and Polyfluorinated Substances on the Brain and Behavior

Per- and polyfluoroalkyl substances (PFAS) are a class of structurally diverse synthetic organic chemicals that are chemically stable, resistant to degradation, and persistent in terrestrial and aquatic environments. Widespread use of PFAS in industrial processing and manufacturing over the last 70 years has led to global contamination of built and natural environments. The brain is a lipid rich and highly vascularized organ composed of long-lived neurons and glial cells that are especially vulnerable to the impacts of persistent and lipophilic toxicants. Generally, PFAS partition to protein-rich tissues of the body, primarily the liver and blood, but are also detected in the brains of humans, wildlife, and laboratory animals. Here we review factors impacting the absorption, distribution, and accumulation of PFAS in the brain, and currently available evidence for neurotoxic impacts defined by disruption of neurochemical, neurophysiological, and behavioral endpoints. Emphasis is placed on the neurotoxic potential of exposures during critical periods of development and in sensitive populations, and factors that may exacerbate neurotoxicity of PFAS. While limitations and inconsistencies across studies exist, the available body of evidence suggests that the neurobehavioral impacts of long-chain PFAS exposures during development are more pronounced than impacts resulting from exposure during adulthood. There is a paucity of experimental studies evaluating neurobehavioral and molecular mechanisms of short-chain PFAS, and even greater data gaps in the analysis of neurotoxicity for PFAS outside of the perfluoroalkyl acids. Whereas most experimental studies were focused on acute and subchronic impacts resulting from high dose exposures to a single PFAS congener, more realistic exposures for humans and wildlife are mixtures exposures that are relatively chronic and low dose in nature. Our evaluation of the available human epidemiological, experimental, and wildlife data also indicates heightened accumulation of perfluoroalkyl acids in the brain after environmental exposure, in comparison to the experimental studies. These findings highlight the need for additional experimental analysis of neurodevelopmental impacts of environmentally relevant concentrations and complex mixtures of PFAS.

Protracted Impairment of Maternal Metabolic Health in Mouse Dams Following Pregnancy Exposure to a Mixture of Low Dose Endocrine-Disrupting Chemicals, a Pilot Study

Pregnancy, a period of increased metabolic demands coordinated by fluctuating steroid hormones, is an understudied critical window of disease susceptibility for later-life maternal metabolic health. Epidemiological studies have identified associations between exposures to various endocrine-disrupting chemicals (EDCs) with an increased risk for metabolic syndrome, obesity, and diabetes. Whether such adverse outcomes would be heightened by concurrent exposures to multiple EDCs during pregnancy, consistent with the reality that human exposures are to EDC mixtures, was examined in the current pilot study. Mouse dams were orally exposed to relatively low doses of four EDCs: (atrazine (10 mg/kg), bisphenol-A (50 µg/kg), perfluorooctanoic acid (0.1 mg/kg), 2,3,7,8-tetrachlorodibenzo-p-dioxin (0.036 µg/kg)), or the combination (MIX), from gestational day 7 until birth or for an equivalent 12 days in non-pregnant females. Glucose intolerance, serum lipids, weight, and visceral adiposity were assessed six months later. MIX-exposed dams exhibited hyperglycemia with a persistent elevation in blood glucose two hours after glucose administration in a glucose tolerance test, whereas no such effects were observed in MIX-exposed non-pregnant females. Correspondingly, MIX dams showed elevated serum low-density lipoprotein (LDL). There were no statistically significant differences in weight or visceral adipose; MIX dams showed an average visceral adipose volume to body volume ratio of 0.09, while the vehicle dams had an average ratio of 0.07. Collectively, these findings provide biological plausibility for the epidemiological associations observed between EDC exposures during pregnancy and subsequent maternal metabolic dyshomeostasis, and proof of concept data that highlight the importance of considering complex EDC mixtures based of off common health outcomes, e.g., for increased risk for later-life maternal metabolic effects following pregnancy.