Assessment of the Mode of Action Underlying the Effects of GenX in Mouse Liver and Implications for Assessing Human Health Risks

A research synthesis of humans, animals, and environmental compartments exposed to PFAS: A systematic evidence map and bibliometric analysis of secondary literature

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are a class of widely used anthropogenic chemicals. Concerns regarding their persistence and potential adverse effects have led to multiple secondary research publications. Here, we aim to assess the resulting evidence base in the systematic secondary literature by examining research gaps, evaluating the quality of reviews, and exploring interdisciplinary connections.

METHODS

This study employed a systematic evidence-mapping approach to assess the secondary literature on the biological, environmental, and medical aspects of exposure to 35 fluorinated compounds. The inclusion criteria encompassed systematic reviews published in peer-reviewed journals, pre-prints, and theses. Comprehensive searches across electronic databases and grey literature identified relevant reviews. Data extraction and synthesis involved mapping literature content and narrative descriptions. We employed a modified version of the AMSTAR2 checklist to evaluate the methodological rigour of the reviews. A bibliometric data analysis uncovered patterns and trends in the academic literature. A research protocol for this study was previously pre-registered (osf.io/2tpn8) and published (Vendl et al., Environment International 158 (2022) 106973). The database is freely accessible through the interactive and user-friendly web application of this systematic evidence map at https://hi-this-is-lorenzo.shinyapps.io/PFAS_SEM_Shiny_App/.

RESULTS

Our map includes a total of 175 systematic reviews. Over the years, there has been a steady increase in the annual number of publications, with a notable surge in 2021. Most reviews focused on human exposure, whereas environmental and animal-related reviews were fewer and often lacked a rigorous systematic approach to literature search and screening. Review outcomes were predominantly associated with human health, particularly with reproductive and children's developmental health. Animal reviews primarily focused on studies conducted in controlled laboratory settings, and wildlife reviews were characterised by an over-representation of birds and fish species. Recent reviews increasingly incorporated quantitative synthesis methodologies. The methodological strengths of the reviews included detailed descriptions of study selection processes and disclosure of potential conflicts of interest. However, weaknesses were observed in the critical lack of detail in reporting methods. A bibliometric analysis revealed that the most productive authors collaborate within their own country, leading to limited and clustered international collaborations.

CONCLUSIONS

In this overview of the available systematic secondary literature, we map literature content, assess reviews' methodological quality, highlight data gaps, and draw research network clusters. We aim to facilitate literature reviews, guide future research initiatives, and enhance opportunities for cross-country collaboration. Furthermore, we discuss how this systematic evidence map and its publicly available database benefit scientists, regulatory agencies, and other stakeholders by providing access to current systematic secondary literature on PFAS exposure.

Comparison of transcriptomic profiles between HFPO-DA and prototypical PPARα, PPARγ, and cytotoxic agents in wild-type and PPARα knockout mouse hepatocytes

Recent in vitro transcriptomic analyses for the short-chain polyfluoroalkyl substance, HFPO-DA (ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate), support conclusions from in vivo data that HFPO-DA-mediated liver effects in mice are part of the early key events of the peroxisome proliferator-activated receptor alpha (PPARα) activator-induced rodent hepatocarcinogenesis mode of action (MOA). Transcriptomic responses in HFPO-DA-treated rodent hepatocytes have high concordance with those treated with a PPARα agonist and lack concordance with those treated with PPARγ agonists or cytotoxic agents. To elucidate whether HFPO-DA-mediated transcriptomic responses in mouse liver are PPARα-dependent, additional transcriptomic analyses were conducted on samples from primary PPARα knockout (KO) and wild-type (WT) mouse hepatocytes exposed for 12, 24, or 72 h with various concentrations of HFPO-DA, or well-established agonists of PPARα (GW7647) and PPARγ (rosiglitazone), or cytotoxic agents (acetaminophen or d-galactosamine). Pathway and predicted upstream regulator-level responses were highly concordant between HFPO-DA and GW7647 in WT hepatocytes. A similar pattern was observed in PPARα KO hepatocytes, albeit with a distinct temporal and concentration-dependent delay potentially mediated by compensatory responses. This delay was not observed in PPARα KO hepatocytes exposed to rosiglitazone, acetaminophen, d-galactosamine. The similarity in transcriptomic signaling between HFPO-DA and GW7647 in both the presence and absence of PPARα in vitro indicates these compounds share a common MOA.

Comparison of transcriptomic profiles between HFPO-DA and prototypical PPARα, PPARγ, and cytotoxic agents in mouse, rat, and pooled human hepatocytes

Like many per- or polyfluorinated alkyl substances (PFAS), toxicity studies with HFPO-DA (ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate), a short-chain PFAS used in the manufacture of some types of fluorinated polymers, indicate that the liver is the primary target of toxicity in rodents following oral exposure. Although the current weight of evidence supports the PPARα mode of action (MOA) for liver effects in HFPO-DA-exposed mice, alternate MOAs have also been hypothesized including PPARγ or cytotoxicity. To further evaluate the MOA for HFPO-DA in rodent liver, transcriptomic analyses were conducted on samples from primary mouse, rat, and pooled human hepatocytes treated for 12, 24, or 72 h with various concentrations of HFPO-DA, or agonists of PPARα (GW7647), PPARγ (rosiglitazone), or cytotoxic agents (ie, acetaminophen or d-galactosamine). Concordance analyses of enriched pathways across chemicals within each species demonstrated the greatest concordance between HFPO-DA and PPARα agonist GW7647-treated hepatocytes compared with the other chemicals evaluated. These findings were supported by benchmark concentration modeling and predicted upstream regulator results. In addition, transcriptomic analyses across species demonstrated a greater transcriptomic response in rodent hepatocytes treated with HFPO-DA or agonists of PPARα or PPARγ, indicating rodent hepatocytes are more sensitive to HFPO-DA or PPARα/γ agonist treatment. These results are consistent with previously published transcriptomic analyses and further support that liver effects in HFPO-DA-exposed rodents are mediated through rodent-specific PPARα signaling mechanisms as part of the MOA for PPARα activator-induced rodent hepatocarcinogenesis. Thus, effects observed in mouse liver are not appropriate endpoints for toxicity value development for HFPO-DA in human health risk assessment.

Identifying novel mechanisms of per- and polyfluoroalkyl substance-induced hepatotoxicity using FRG humanized mice

Per- and polyfluoroalkyl substances (PFAS) such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) and perfluoro-2-methyl-3-oxahexanoic acid (GenX), the new replacement PFAS, are major environmental contaminants. In rodents, these PFAS induce several adverse effects on the liver, including increased proliferation, hepatomegaly, steatosis, hypercholesterolemia, nonalcoholic fatty liver disease and liver cancers. Activation of peroxisome proliferator receptor alpha by PFAS is considered the primary mechanism of action in rodent hepatocyte-induced proliferation. However, the human relevance of this mechanism is uncertain. We investigated human-relevant mechanisms of PFAS-induced adverse hepatic effects using FRG liver-chimeric humanized mice with livers repopulated with functional human hepatocytes. Male FRG humanized mice were treated with 0.067 mg/L of PFOA, 0.145 mg/L of PFOS, or 1 mg/L of GenX in drinking water for 28 days. PFOS caused a significant decrease in total serum cholesterol and LDL/VLDL, whereas GenX caused a significant elevation in LDL/VLDL with no change in total cholesterol and HDL. All three PFAS induced significant hepatocyte proliferation. RNA-sequencing with alignment to the human genome showed a total of 240, 162, and 619 differentially expressed genes after PFOA, PFOS, and GenX exposure, respectively. Upstream regulator analysis revealed that all three PFAS induced activation of p53 and inhibition of androgen receptor and NR1D1, a transcriptional repressor important in circadian rhythm. Further biochemical studies confirmed NR1D1 inhibition and in silico modeling indicated potential interaction of all three PFAS with the DNA-binding domain of NR1D1. In conclusion, our studies using FRG humanized mice have revealed new human-relevant molecular mechanisms of PFAS including their previously unknown effect on circadian rhythm.

GenX caused liver injury and potential hepatocellular carcinoma of mice via drinking water even at environmental concentration

Hexafluoropropylene oxide dimer acid (GenX) is an alternative to perfluorooctanoic acid (PFOA), whose environmental concentration is close to its maximum allowable value established by the US Environmental Protection Agency, so its effects on human health are of great concern. The liver is one of the most crucial target organ for GenX, but whether GenX exposure induces liver cancer still unclear. In this research project, male C57 mice were disposed to GenX in drinking water at environmental concentrations (0.1 and 10 μg/L) and higher concentrations (1 and 100 mg/L) for 14 weeks to explore its effects on liver injury and potential carcinogenicity in mice. GenX was found to cause a dose-dependent increase in the serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), total cholesterol (TC), and triglyceride (TG). As the content of GenX in drinking water increased, so did the concentrations of Glypican-3 (GPC-3) and detachment gamma-carboxyprothrombin (DCP), indicators of early hepatocellular cancer. GenX destroyed the boundaries and arrangements of hepatocytes, in which monocyte infiltration, balloon-like transformation, and obvious lipid vacuoles were observed between cells. Following exposure to GenX, Masson sections revealed a significant quantity of collagen deposition in the liver. Alpha-feto protein (AFP), vascular endothelial growth factor (VEGF), Ki67, matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) gene expression increased in a dose-dependent manner in the treatment group relative to the control group. In general, drinking water GenX exposure induced liver function impairment, elevated blood lipid level, caused liver pathological structure damage and liver fibrosis lesions, changed the liver inflammatory microenvironment, and increased the concentration of liver-related tumor indicator even in the environmental concentration, suggesting GenX is a potential carcinogen.

GenX analogs exposure induced greater hepatotoxicity than GenX mainly via activation of PPARα pathway while caused hepatomegaly in the absence of PPARα in female mice

Despite their use as substitutes for perfluorooctanoic acid, the potential toxicities of hexafluoropropylene oxide dimer acid (HFPO-DA, commercial name: GenX) and its analogs (PFDMOHxA, PFDMO2HpA, and PFDMO2OA) remain poorly understood. To assess the hepatotoxicity of these chemicals on females, each chemical was orally administered to female C57BL/6 mice at the dosage of 0.5 mg/kg/d for 28 d. The contribution of peroxisome proliferator-activated receptors (PPARα and γ) and other nuclear receptors involving in these toxic effects of GenX and its analogs were identified by employing two PPAR knockout mice (PPARα-/- and PPARγΔHep) in this study. Results showed that the hepatotoxicity of these chemicals increased in the order of GenX < PFDMOHxA < PFDMO2HpA < PFDMO2OA. The increases of relative liver weight and liver injury markers were significantly much lower in PPARα-/- mice than in PPARα+/+ mice after GenX analog exposure, while no significant differences were observed between PPARγΔHep and its corresponding wildtype groups (PPARγF/F mice), indicating that GenX analog induce hepatotoxicity mainly via PPARα instead of PPARγ. The PPARα-dependent complement pathways were inhibited in PFDMO2HpA and PFDMO2OA exposed PPARα+/+ mice, which might be responsible for the observed liver inflammation. In PPARα-/- mice, hepatomegaly and increased liver lipid content were observed in PFDMO2HpA and PFDMO2OA treated groups. The activated pregnane X receptor (PXR) and constitutive activated receptor (CAR) pathways in the liver of PPARα-/- mice, which were highlighted by bioinformatics analysis, provided a reasonable explanation for hepatomegaly in the absence of PPARα. Our results indicate that GenX analogs could induce more serious hepatotoxicity than GenX whether there is a PPARα receptor or not. These chemicals, especially PFDMO2HpA and PFDMO2OA, may not be appropriate PFOA alternatives.

Screening Peptide-Binding Partners for GenX via Phage Display

Per- and poly-fluoroalkyl substances (PFAS), such as GenX, are a class of highly stable synthetic compounds that have recently become the focus of environmental remediation endeavors due to their toxicity. While considerable strides have been made in PFAS remediation, the diversity of these compounds, and the costs associated with approaches such as ion exchange resins and advanced oxidation technologies, remain challenging for widespread application. In addition, little is known about the potential binding and impacts of GenX on human proteins. To address these issues, we applied phage display and screened short peptides that bind specifically to GenX, with the ultimate goal of identifying human proteins that bind with GenX. In this study we identified the amino acids that contribute to the binding and measured the binding affinities of the two discovered peptides with NMR. A human protein, ankyrin-repeat-domain-containing protein 36B, with matching sequences of one of the peptides, was identified, and the binding positions were predicted by docking and molecular dynamics simulation. This study created a platform to screen peptides that bind with toxic chemical compounds, which ultimately helped us identify biologically relevant molecules that could be inhibited by the GenX, and also provided information that will contribute to future bioengineered GenX-binding device design.

Hepatic Transcriptome Comparative In Silico Analysis Reveals Similar Pathways and Targets Altered by Legacy and Alternative Per- and Polyfluoroalkyl Substances in Mice

Per- and poly-fluoroalkyl substances (PFAS) are a large class of fluorinated carbon chains that include legacy PFAS, such as perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorohexane sulfonate (PFHxS). These compounds induce adverse health effects, including hepatotoxicity. Potential alternatives to the legacy PFAS (HFPO-DA (GenX), HFPO4, HFPO-TA, F-53B, 6:2 FTSA, and 6:2 FTCA), as well as a byproduct of PFAS manufacturing (Nafion BP2), are increasingly being found in the environment. The potential hazards of these new alternatives are less well known. To better understand the diversity of molecular targets of the PFAS, we performed a comparative toxicogenomics analysis of the gene expression changes in the livers of mice exposed to these PFAS, and compared these to five activators of PPARα, a common target of many PFAS. Using hierarchical clustering, pathway analysis, and predictive biomarkers, we found that most of the alternative PFAS modulate molecular targets that overlap with legacy PFAS. Only three of the 11 PFAS tested did not appreciably activate PPARα (Nafion BP2, 6:2 FTSA, and 6:2 FTCA). Predictive biomarkers showed that most PFAS (PFHxS, PFOA, PFOS, PFNA, HFPO-TA, F-53B, HFPO4, Nafion BP2) activated CAR. PFNA, PFHxS, PFOA, PFOS, HFPO4, HFPO-TA, F-53B, Nafion BP2, and 6:2 FTSA suppressed STAT5b, activated NRF2, and activated SREBP. There was no apparent relationship between the length of the carbon chain, type of head group, or number of ether linkages and the transcriptomic changes. This work highlights the similarities in molecular targets between the legacy and alternative PFAS.

Perfluoroalkyl and polyfluoroalkyl substances and hypertensive disorders of pregnancy: A systematic review and meta-analysis

Hypertensive disorders of pregnancy (HDP), including gestational hypertension (GH) and preeclampsia (PE), cause significant morbidity and mortality among pregnant women. Several environmental toxins, particularly those that affect the normal function of the placenta and the endothelium, are emerging as potential risk factors for HDP. Among them, per- and polyfluoroalkyl substances (PFAS), widely used in a variety of commercial products, have been related to a variety of adverse health effects including HDP. This study was conducted by searching three databases for observational studies reporting associations between PFAS and HDP, all of which were published before December 2022. We used random-effects meta-analysis to calculate pooled risk estimates, and assessing each combination of exposure and outcome for quality and level of evidence. In total, 15 studies were included in the systematic review and meta-analysis. The results from meta-analyses showed that risk of PE was increased with exposure to PFOA (perfluorooctanoic acid) (RR = 1.39, 95% CI = 1.05, 1.85; N = 6 studies; exposure = 1 ln-unit increment; low certainty), PFOS (perfluorooctane sulfonate) (RR = 1.51, 95% CI = 1.23, 1.86; N = 6 studies; exposure = 1 ln-unit increment; moderate certainty), and PFHxS (perfluorohexane sulfonate) (RR = 1.39, 95% CI = 1.10, 1.76; N = 6 studies; exposure = 1 ln-unit increment; low certainty). PFOS was also associated with an increased risk of HDP (RR = 1.39, 95% CI = 1.10, 1.76; exposure = 1 ln-unit increment; low certainty). Exposure to legacy PFAS (PFOA, PFOS, PFHxS) is associated with an increased risk of PE, and PFOS is further associated with HDP. In view of the limitations of meta-analysis and quality of evidence, these findings should be interpreted with caution. Further research is required that assesses exposure to multiple PFAS in diverse and well-powered cohorts.

Pathological epigenetic events and reversibility review: the intersection between hallmarks of aging and developmental origin of health and disease

We discuss pathological epigenetic events that are reversible (PEERs). A recent study by Poganik and colleagues showed that severe stress in mice and humans transiently elevates biological age of several tissues, and this transient age increase is reversible when the stress is removed. These studies suggest new strategies for reversing normal aging. However, it is important to note that developmental origin of health and disease studies have shown that developmental exposure to toxic chemicals such as lead causes permanent changes in neuron shape, connectivity and cellular hyperplasia of organs such as the heart and liver. In this review, the PEER hypothesis speculates that the hallmarks of aging and the hallmarks of developmental origin of health and disease intersect at PEERs.

Exposure to PFOA and its novel analogs disrupts lipid metabolism in zebrafish

Perfluorooctanoic acid (PFOA), a typical perfluoroalkyl group compound, has received worldwide attention due to its significant environmental toxicity. Following regulatory bans on the production and emission of PFOA, concerns have been raised about the potential health risks and the safety of novel perfluoroalkyl analogues. HFPO-DA (trade name Gen-X) and HFPO-TA are two perfluoroalkyl analogues known to be bioaccumulative, whose level of toxicity and whether they are safe alternatives to PFOA remain unclear. In the following study, the physiological and metabolic effects of exposure to PFOA and its novel analogues were explored in zebrafish using 1/3 LC₅₀ (PFOA 100 μM, Gen-X 200 μM, HFPO-TA 30 μM). At the same LC₅₀ toxicological effect, exposure to PFOA and HFPO-TA resulted in abnormal phenotypes such as spinal curvature, pericardial edema and aberrant body length, while Gen-X was little changed. Metabolically, PFOA, HFPO-TA and Gen-X all significantly increased total cholesterol in exposed zebrafish with PFOA and HFPO-TA also increasing total triglyceride levels. Transcriptome analysis showed that the number of differentially expressed genes in PFOA, Gen-X, and HFPO-TA treated conditions compared to control groups were 527, 572, and 3, 933, respectively. KEGG and GO analysis of differentially expressed genes revealed pathways and functions related to lipid metabolism as well as significant activation of the peroxisome proliferators-activated receptor (PPARs) pathway. Furthermore, RT-qPCR analysis identified significant dysregulation in the downstream target genes of PPARα, which is responsible for lipid oxidative catabolism, and the SREBP pathway, which is responsible for lipid synthesis. In conclusion, both perfluoroalkyl analogues HFPO-TA and Gen-X exhibit significant physiological and metabolic toxicity to aquatic organisms and their environmental accumulation should be closely regulated.

Perfluorooctanoic acid (PFOA) and hexafluoropropylene oxide-dimer acid (GenX): Hepatic stress and bile acid metabolism with different pathways

Per- and polyfluoroalkyl substances (PFASs) and perfluoroalkyl ether carboxylic acids (PFECAs) are organic chemicals that are widely used in the manufacture of a wide range of human-made products. Many monitoring findings revealed the presence of PFASs and PFECAs in numerous environmental sources, including water, soil, and air, which drew more attention to both chemicals. Because of their unknown toxicity, the discovery of PFASs and PFECAs in a variety of environmental sources was viewed as a cause for concern. In the present study, male mice were given orally one of the typical PFASs, perfluorooctanoic acid (PFOA), and one of the representative PFECAs, hexafluoropropylene oxide-dimer acid (HFPO-DA). The liver index showing hepatomegaly rose significantly after 90 d of exposure to PFOA and HFPO-DA, respectively. While sharing similar suppressor genes, both chemicals demonstrated unique hepatotoxic mechanisms. In different ways, these two substances altered the expression of hepatic stress-sensing genes as well as the regulation of nuclear receptors. Not only are bile acid metabolism-related genes in the liver altered, but cholesterol metabolism-related genes as well. These results indicate that PFOA and HFPO-DA both cause hepatotoxicity and bile acid metabolism impairment with distinct mechanisms.

Probing the Interactions of Perfluorocarboxylic Acids of Various Chain Lengths with Human Serum Albumin: Calorimetric and Spectroscopic Investigations

Despite an exponential increase in PFAS research over the past two decades, the mechanisms behind how PFAS cause adverse health effects are still poorly understood. Protein interactions are considered a significant driver of bioaccumulation and subsequent toxicity from re-exposure; however, most of the available literature is limited to legacy PFAS. We utilized microcalorimetric and spectroscopic methods to systematically investigate the binding between human serum albumin (HSA) and perfluorocarboxylic acids (PFCAs) of varying chain lengths and their nonfluorinated fatty acid (FA) counterparts. The results reveal the optimal chain length for significant PFCA-HSA binding and some fundamental interactions, i.e., the polar carboxylic head of PFCA is countered by ionizable amino acids such as arginine, and the fluorocarbon tails stabilized by hydrophobic residues like leucine and valine. Additionally, fluorine's unique polarizability contributes to PFCA's stronger binding affinities relative to the corresponding fatty acids. Based on these observations, we posit that PFCAs likely bind to HSA in a "cavity-filling" manner, provided they have an appropriate size and shape to accommodate the electrostatic interactions. The results reported herein widen the pool of structural information to explain PFAS bioaccumulation patterns and toxicity and support the development of more accurate computational modeling of protein-PFAS interactions. TOC graphic created with Biorender.com.

Perfluoroethylcyclohexane sulphonate, an emerging perfluoroalkyl substance, disrupts mitochondrial membranes and the expression of key molecular targets in vitro

Perfluoroethylcyclohexane sulphonate (PFECHS) is an emerging, replacement perfluoroalkyl substance (PFAS) with little information available on the toxic effects or potencies with which to characterize its potential impacts on aquatic environments. This study aimed to characterize effects of PFECHS using in vitro systems, including rainbow trout liver cells (RTL-W1 cell line) and lymphocytes separated from whole blood. It was determined that exposure to PFECHS caused minor acute toxic effects for most endpoints and that little PFECHS was concentrated into cells with a mean in vitro bioconcentration factor of 81 ± 25 L/kg. However, PFECHS was observed to affect the mitochondrial membrane and key molecular receptors, such as the peroxisome proliferator receptor, cytochrome p450-dependent monooxygenases, and receptors involved in oxidative stress. Also, glutathione-S-transferase was significantly down-regulated at a near environmentally relevant exposure concentration of 400 ng/L. These results are the first to report bioconcentration of PFECHS, as well as its effects on the peroxisome proliferator and glutathione-S-transferase receptors, suggesting that even with little bioconcentration, PFECHS has potential to cause adverse effects.

A review of cardiovascular effects and underlying mechanisms of legacy and emerging per- and polyfluoroalkyl substances (PFAS)

Cardiovascular disease (CVD) poses the leading threats to human health and life, and their occurrence and severity are associated with exposure to environmental pollutants. Per- and polyfluoroalkyl substances (PFAS), a group of widely used industrial chemicals, are characterized by persistence, long-distance migration, bioaccumulation, and toxicity. Some PFAS, particularly perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and perfluorohexanesulfonic acid (PFHxS), have been banned, leaving only legacy exposure to the environment and human body, while a number of novel PFAS alternatives have emerged and raised concerns, such as polyfluoroalkyl ether sulfonic and carboxylic acid (PFESA and PFECA) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS). Overall, this review systematically elucidated the adverse cardiovascular (CV) effects of legacy and emerging PFAS, emphasized the dose/concentration-dependent, time-dependent, carbon chain length-dependent, sex-specific, and coexposure effects, and discussed the underlying mechanisms and possible prevention and treatment. Extensive epidemiological and laboratory evidence suggests that accumulated serum levels of legacy PFAS possibly contribute to an increased risk of CVD and its subclinical course, such as cardiac toxicity, vascular disorder, hypertension, and dyslipidemia. The underlying biological mechanisms may include oxidative stress, signaling pathway disturbance, lipid metabolism disturbance, and so on. Various emerging alternatives to PFAS also play increasingly prominent toxic roles in CV outcomes that are milder, similar to, or more severe than legacy PFAS. Future research is recommended to conduct more in-depth CV toxicity assessments of legacy and emerging PFAS and explore more effective surveillance, prevention, and treatment strategies, accordingly.

Assessment of the mode of action underlying development of liver lesions in mice following oral exposure to HFPO-DA and relevance to humans

HFPO-DA (ammonium, 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)propanoate) is a short-chain polyfluorinated alkyl substance (PFAS) used in the manufacture of some types of fluorinated polymers. Like many PFAS, toxicity studies with HFPO-DA indicate the liver is the primary target of toxicity in rodents following oral exposure. Due to the structural diversity of PFAS, the mode of action (MOA) can differ between PFAS for the same target tissue. There is significant evidence for involvement of peroxisome proliferator-activated receptor alpha (PPARα) activation based on molecular and histopathological responses in the liver following HFPO-DA exposure, but other MOAs have also been hypothesized based on limited evidence. The MOA underlying the liver effects in mice exposed to HFPO-DA was assessed in the context of the Key Events (KEs) outlined in the MOA framework for PPARα activator-induced rodent hepatocarcinogenesis. The first 3 KEs (ie, PPARα activation, alteration of cell growth pathways, and perturbation of cell growth/survival) are supported by several lines of evidence from both in vitro and in vivo data available for HFPO-DA. In contrast, alternate MOAs, including cytotoxicity, PPARγ and mitochondrial dysfunction are generally not supported by the scientific literature. HFPO-DA-mediated liver effects in mice are not expected in humans as only KE 1, PPARα activation, is shared across species. PPARα-mediated gene expression in humans produces only a subset (ie, lipid modulating effects) of the responses observed in rodents. As such, the adverse effects observed in rodent livers should not be used as the basis of toxicity values for HFPO-DA for purposes of human health risk assessment.

Sources, occurrence and toxic effects of emerging per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) cause potential threats to biota and are persistent and never-ending substances in the environment. Regulations and ban on legacy PFAS by various global organizations and national level regulatory agencies had shifted the fluorochemical production to emerging PFAS and fluorinated alternatives. Emerging PFAS are mobile and more persistent in aquatic systems, posing potential greater threats to human and environmental health. Emerging PFAS have been found in aquatic animals, rivers, food products, aqueous film-forming foams, sediments, and a variety of other ecological media. This review summarizes the physicochemical properties, sources, occurrence in biota and the environment, and toxicity of the emerging PFAS. Fluorinated and non-fluorinated alternatives for several industrial applications and consumer goods as the replacement of historical PFAS are also discussed in the review. Fluorochemical production plants and wastewater treatment plants are the main sources of emerging PFAS to various environmental matrices. Information and research are scarcely available on the sources, existence, transport, fate, and toxic effects of emerging PFAS to date.

Identifying Human Specific Adverse Outcome Pathways of Per- and Polyfluoroalkyl Substances Using Liver-Chimeric Humanized Mice

Background

Per- and polyfluoroalkyl substances (PFAS) are persistent organic pollutants with myriad adverse effects. While perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) are the most common contaminants, levels of replacement PFAS, such as perfluoro-2-methyl-3-oxahexanoic acid (GenX), are increasing. In rodents, PFOA, PFOS, and GenX have several adverse effects on the liver, including nonalcoholic fatty liver disease.

Objective

We aimed to determine human-relevant mechanisms of PFAS induced adverse hepatic effects using FRG liver-chimeric humanized mice with livers repopulated with functional human hepatocytes.

Methods

Male humanized mice were treated with 0.067 mg/L of PFOA, 0.145 mg/L of PFOS, or 1 mg/L of GenX in drinking water for 28 days. Liver and serum were collected for pathology and clinical chemistry, respectively. RNA-sequencing coupled with pathway analysis was used to determine molecular mechanisms.

Results

PFOS caused a significant decrease in total serum cholesterol and LDL/VLDL, whereas GenX caused a significant elevation in LDL/VLDL with no change in total cholesterol and HDL. PFOA had no significant changes in serum LDL/VLDL and total cholesterol. All three PFAS induced significant hepatocyte proliferation. RNA-sequencing with alignment to the human genome showed a total of 240, 162, and 619 differentially expressed genes after PFOA, PFOS, and GenX exposure, respectively. Upstream regulator analysis revealed inhibition of NR1D1, a transcriptional repressor important in circadian rhythm, as the major common molecular change in all PFAS treatments. PFAS treated mice had significant nuclear localization of NR1D1. In silico modeling showed PFOA, PFOS, and GenX potentially interact with the DNA-binding domain of NR1D1.

Discussion

These data implicate PFAS in circadian rhythm disruption via inhibition of NR1D1. These studies show that FRG humanized mice are a useful tool for studying the adverse outcome pathways of environmental pollutants on human hepatocytes in situ.

Impacts of PFOAC8, GenXC6, and their mixtures on zebrafish developmental toxicity and gene expression provide insight about tumor-related disease

Concerns about per- and polyfluoroalkyl substances (PFASs) have grown in importance in the fields of ecotoxicology and public health. This study aims to compare the potential effects of long-chain (carbon atoms ≥ 7) and short-chain derivatives and their mixtures' exposure according to PFASs-exposed (1, 2, 5, 10, and 20 mg/L) zebrafish's (Danio rerio) toxic effects and their differential gene expression. Here, PFOA_C8, GenX_C6, and their mixtures (v/v, 1:1) could reduce embryo hatchability and increase teratogenicity and mortality. The toxicity of PFOA_C8 was higher than that of GenX_C6, and the toxicity of their mixtures was irregular. Their exposure (2 mg/L) caused zebrafish ventricular edema, malformation of the spine, blood accumulation, or developmental delay. In addition, all of them had significant differences in gene expression. PFOA_C8 exposure causes overall genetic changes, and the pathways of this transformation were autophagy and apoptosis. More importantly, in order to protect cells from PFOA_C8, GenX_C6, and their mixtures' influences, zebrafish inhibited the expression of ATPase and Ca²⁺ transport gene (atp1b2b), mitochondrial function-related regulatory genes (mt-co2, mt-co3, and mt-cyb), and tumor or carcinogenic cell proliferation genes (laptm4b and ctsbb). Overall, PFOA_C8, GenX_C6, and their mixtures' exposures will affect the gene expression effects of zebrafish embryos, indicating that PFASs may pose a potential threat to aquatic biological safety. These results showed that the relevant genes in zebrafish that were inhibited by PFASs exposure were related to tumorigenesis. Therefore, the effect of PFASs on zebrafish can be further used to study the pathogenesis of tumors.

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.

Exposure to low-dose perfluorooctanoic acid promotes hepatic steatosis and disrupts the hepatic transcriptome in mice

OBJECTIVE

Perfluoroalkyl substances (PFAS) are man-made chemicals with demonstrated endocrine-disrupting properties. Exposure to perfluorooctanoic acid (PFOA) has been linked to disturbed metabolism via the liver, although the exact mechanism is not clear. Moreover, information on the metabolic effects of the new PFAS alternative GenX is limited. We examined whether exposure to low-dose PFOA and GenX induces metabolic disturbances in mice, including NAFLD, dyslipidemia, and glucose tolerance, and studied the involvement of PPARα.

METHODS

Male C57BL/6J wildtype and PPARα^-/- mice were given 0.05 or 0.3 mg/kg body weight/day PFOA, or 0.3 mg/kg body weight/day GenX while being fed a high-fat diet for 20 weeks. Glucose and insulin tolerance tests were performed after 18 and 19 weeks. Plasma metabolite levels were measured next to a detailed assessment of the liver phenotype, including lipid content and RNA sequencing.

RESULTS

Exposure to high-dose PFOA decreased body weight and increased liver weight in wildtype and PPARα^-/- mice. High-dose but not low-dose PFOA reduced plasma triglycerides and cholesterol, which for triglycerides was dependent on PPARα. PFOA and GenX increased hepatic triglycerides in a PPARα-dependent manner. RNA sequencing showed that the effects of GenX on hepatic gene expression were entirely dependent on PPARα, while the effects of PFOA were mostly dependent on PPARα. In the absence of PPARα, the involvement of PXR and CAR became more prominent.

CONCLUSION

Overall, we show that long-term and low-dose exposure to PFOA and GenX disrupts hepatic lipid metabolism in mice. Whereas the effects of PFOA are mediated by multiple nuclear receptors, the effects of GenX are entirely mediated by PPARα. Our data underscore the potential of PFAS to disrupt metabolism by altering signaling pathways in the liver.

GenX induces fibroinflammatory gene expression in primary human hepatocytes

The toxicity induced by the persistent organic pollutants per- and polyfluoroalkyl substances (PFAS) is dependent on the length of their polyfluorinated tail. Long-chain PFASs have significantly longer half-lives and profound toxic effects compared to their short-chain counterparts. Recently, production of a short-chain PFAS substitute called ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoate, also known as GenX, has significantly increased. However, the adverse health effects of GenX are not completely known. In this study, we investigated the dose-dependent effects of GenX on primary human hepatocytes (PHH). Freshly isolated PHH were treated with either 0.1, 10, or 100 μM of GenX for 48 and 96 h; then, global transcriptomic changes were determined using Human Clariom™ D arrays. GenX-induced transcriptional changes were similar at 0.1 and 10 μM doses but were significantly different at the 100 μM dose. Genes involved in lipid, monocarboxylic acid, and ketone metabolism were significantly altered following exposure of PHH at all doses. However, at the 100 μM dose, GenX caused changes in genes involved in cell proliferation, inflammation and fibrosis. A correlation analysis of concentration and differential gene expression revealed that 576 genes positively (R > 0.99) and 375 genes negatively (R < -0.99) correlated with GenX concentration. The upstream regulator analysis indicated HIF1α was inhibited at the lower doses but were activated at the higher dose. Additionally, VEGF, PPARα, STAT3, and SMAD4 signaling was induced at the 100 µM dose. These data indicate that at lower doses GenX can interfere with metabolic pathways and at higher doses can induce fibroinflammatory changes in human hepatocytes.

Association of emerging and legacy per- and polyfluoroalkyl substances with unexplained recurrent spontaneous abortion

Emerging per- and polyfluoroalkyl substances (PFAS) alternatives are increasingly used in daily life. Although legacy PFAS have been associated with miscarriage in previous studies, it remains unknown whether exposure to emerging and legacy PFAS has any impact on the risk of unexplained recurrent spontaneous abortion (URSA). We conducted a case-control study with 464 URSA cases who had at least 2 unexplained miscarriages and 440 normal controls who had at least one normal livebirth. Concentrations of 21 PFAS in plasma, including three emerging PFAS alternatives, eight linear and branched PFAS isomers, four short-chain PFAS, and six legacy PFAS, were measured by ultra-performance liquid chromatography coupled with a tandem mass spectrometry (UPLC-MS/MS). Multiple logistic regression was applied to evaluate the relationship between PFAS and URSA risk. Perfluorooctanoic acid (PFOA, median: 6.18 ng/mL), perfluorooctane sulfonate (PFOS, median: 4.10 ng/mL), and 6:2 chlorinated perfluoroalkyl ether sulfonic acid (6:2 Cl-PFESA, median: 2.27 ng/mL) were the predominant PFAS in the controls. Exposure to 6:2 Cl-PFESA [adjusted odds ratio (aOR) = 1.18 (95% CI: 1.00, 1.39)] and hexafluoropropylene oxide dimer acid (HFPO-DA) [aOR = 1.35 (95% CI: 1.15, 1.59)] were significantly associated with increased risks of URSA. Women with older age (>30 years old) had a stronger association between PFAS and URSA. Our results suggest that emerging PFAS alternatives may be an important risk factor for URSA.

Evaluation of Transcriptomic Responses in Livers of Mice Exposed to the Short-Chain PFAS Compound HFPO-DA

HFPO-DA (ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate; CASRN 62037-80-3) is a component of the GenX technology platform used as a polymerization aid in the manufacture of some types of fluoropolymers. The liver is the primary target of toxicity for HFPO-DA in rodents and previous examination of hepatic transcriptomic responses in mice following oral exposure to HFPO-DA for 90 days showed induction of peroxisome proliferator-activated receptor signaling pathways, predominantly by PPARα, as well as increased gene expression of both peroxisomal and mitochondrial fatty acid metabolism. To further investigate the mechanism of liver toxicity, transcriptomic analysis was conducted on liver tissue from mice orally exposed to 0, 0.1, 0.5 or 5 mg/kg-bw/day HFPO-DA in a reproduction/developmental toxicity study. Hepatic gene expression changes demonstrated activation of the PPARα signaling pathway. Peroxisomal and mitochondrial fatty acid β-oxidation gene sets were enriched at lower HFPO-DA concentrations, and complement cascade, cell cycle and apoptosis related gene sets were enriched at higher HFPO-DA concentrations. These results support the reported histopathological findings in livers of mice from this study and indicate that the effects of HFPO-DA are mediated through rodent-specific PPARα signaling mechanisms regardless of reproductive status in mice.

Toward a Mechanistic Understanding of Poly- and Perfluoroalkylated Substances and Cancer

Simple Summary

Poly- and perfluoroalkylated substances (PFAS) are industrial chemicals found in many household products that persist in the environment. While several excellent review articles exist on the potential harmful effects of PFAS, there are few focused on cancer. This concise and streamlined mini-review focuses on summarizing molecular mechanisms related to the potential cancer-promoting properties of PFAS. This review organizes and interprets the vast primary PFAS cancer biology literature and provides a coherent, unified, and digestible model of the molecular mechanisms that potentially explains PFAS cancer promotion.

Abstract

Poly- and perfluoroalkylated substances (PFAS) are chemicals that persist and bioaccumulate in the environment and are found in nearly all human populations through several routes of exposure. Human occupational and community exposure to PFAS has been associated with several cancers, including cancers of the kidney, testis, prostate, and liver. While evidence suggests that PFAS are not directly mutagenic, many diverse mechanisms of carcinogenicity have been proposed. In this mini-review, we organize these mechanisms into three major proposed pathways of PFAS action—metabolism, endocrine disruption, and epigenetic perturbation—and discuss how these distinct but interdependent pathways may explain many of the proposed pro-carcinogenic effects of the PFAS class of environmental contaminants. Notably, each of the pathways is predicted to be highly sensitive to the dose and window of exposure which may, in part, explain the variable epidemiologic and experimental evidence linking PFAS and cancer. We highlight testicular and prostate cancer as models to validate this concept.

Next generation per- and poly-fluoroalkyl substances: Status and trends, aquatic toxicity, and risk assessment

Widespread application of poly- and per-fluoroalkyl substances (PFAS) has resulted in some substances being ubiquitous in environmental matrices. That and their resistance to degradation have allowed them to accumulate in wildlife and humans with potential for toxic effects. While specific substances of concern have been phased-out or banned, other PFAS that are emerging as alternative substances are still produced and are being released into the environment. This review focuses on describing three emerging, replacement PFAS: perfluoroethylcyclohexane sulphonate (PFECHS), 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFAES), and hexafluoropropylene oxide dimer acid (HFPO-DA). By summarizing their physicochemical properties, environmental fate and transport, and toxic potencies in comparison to other PFAS compounds, this review offers insight into the viabilities of these chemicals as replacement substances. Using the chemical scoring and ranking assessment model, the relative hazards, uncertainties, and data gaps for each chemical were quantified and related to perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) based on their chemical and uncertainty scores. The substances were ranked PFOS > 6:2 Cl-PFAES > PFOA > HFPO-DA > PFECHS according to their potential toxicity and PFECHS > HFPO-DA > 6:2 Cl-PFAES > PFOS > PFOA according to their need for future research. Since future uses of PFAS remain uncertain in the face of governmental regulations and production bans, replacement PFAS will continue to emerge on the world market and in the environment, raising concerns about their general lack of information on mechanisms and toxic potencies.

GenX in water: Interactions and self-assembly

2,3,3,3-tetrafluoro-2-(heptafluoropropoxy) propanoate, a.k.a. "GenX", is a surfactant introduced as a safer alternative to replace perfluorooctanoate (PFOA) in the manufacturing of fluorinated polymers, however, GenX is shown to cause adverse health effects similar to, or even worse than, those of the legacy PFOA. With an overarching goal to understand the behavior of GenX molecules in aqueous media, we report here on GenX micelle formation and structure in aqueous solutions, on the basis of results obtained from a combination of experimental techniques such as surface tension, fluorescence, viscosity, and small-angle neutron scattering (SANS), and molecular dynamics (MD) simulations. To our best knowledge, this is the first report on GenX micelles. The critical micelle concentration (CMC) of GenX ammonium salt in water is 175 mM. GenX forms small micelles with association number 6-8 and 10 Å radius. GenX molecules prefer to align along the micelle surface, and the ether oxygen of GenX has very little interaction with and exposure to water. Information on the surfactant and interfacial properties of GenX is crucial, since such properties are manifestations of interactions between GenX molecules and between GenX and water molecules and, in turn, the amphiphilic character of GenX dictates its fate and transport in the aqueous environment, its interactions with various biomolecules, and its binding to adsorbent materials.

Exposure to per- and Polyfluoroalkyl Substances and Markers of Liver Injury: A Systematic Review and Meta-Analysis

BACKGROUND

Experimental evidence indicates that exposure to certain pollutants is associated with liver damage. Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic chemicals widely used in industry and consumer products and bioaccumulate in food webs and human tissues, such as the liver.

OBJECTIVE

The objective of this study was to conduct a systematic review of the literature and meta-analysis evaluating PFAS exposure and evidence of liver injury from rodent and epidemiological studies.

METHODS

PubMed and Embase were searched for all studies from earliest available indexing year through 1 December 2021 using keywords corresponding to PFAS exposure and liver injury. For data synthesis, results were limited to studies in humans and rodents assessing the following indicators of liver injury: serum alanine aminotransferase (ALT), nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, or steatosis. For human studies, at least three observational studies per PFAS were used to conduct a weighted z-score meta-analysis to determine the direction and significance of associations. For rodent studies, data were synthesized to qualitatively summarize the direction and significance of effect.

RESULTS

Our search yielded 85 rodent studies and 24 epidemiological studies, primarily of people from the United States. Studies focused primarily on legacy PFAS: perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorononanoic acid (PFNA), and perfluorohexanesulfonic acid. Meta-analyses of human studies revealed that higher ALT levels were associated with exposure to PFOA (z-score= 6.20, p<0.001), PFOS (z-score= 3.55, p<0.001), and PFNA (z-score= 2.27, p=0.023). PFOA exposure was also associated with higher aspartate aminotransferase and gamma-glutamyl transferase levels in humans. In rodents, PFAS exposures consistently resulted in higher ALT levels and steatosis.

CONCLUSION

There is consistent evidence for PFAS hepatotoxicity from rodent studies, supported by associations of PFAS and markers of liver function in observational human studies. This review identifies a need for additional research evaluating next-generation PFAS, mixtures, and early life exposures. https://doi.org/10.1289/EHP10092.

Elucidation of specific binding sites and extraction of toxic Gen X from HSA employing cyclodextrin

The presence of per and poly-fluoroalkyl substances (PFAS), commonly referred to as forever chemicals, in aquatic systems is a serious global health problem. While the remediation of PFAS from aqueous media has been extensively investigated, their interactions with and removal from biological systems have received far less attention. We report herein structural alterations to human serum albumin (HSA) upon addition of perfluoro(2-methyl-3-oxahexanoic) acid (Gen X) monitored by changes to the fluorescence and circular dichroism (CD) spectra of HSA. The equilibrium association constant for Gen X binding to HSA is 7( ± 1) × 10³ M^-1 determined from changes in HSA fluorescence emission data during titration. Site-specific HSA binding fluorophores, 8-anilinonaphthalene-1-sulfonic acid (1,8-ANS), warfarin and dansyl-L-proline were used to investigate the specific binding sites of Gen X on HSA. A competitive displacement study yields association constants for Gen X to HSA at the 1,8-ANS, warfarin, and dansyl-L-proline binding sites to be 6.25 ( ± 0.5) × 10⁴ M^-1, 1.1 × 10⁶ M^-1, and 2.5( ± 0.2) × 10⁹ M^-1 respectively. Addition of β-cyclodextrin (β-CD) and heptakis(6-deoxy-6-amino)-β-cyclodextrin heptahydrochloride to the HSA:Gen X complex leads to the effective extraction of Gen X from the complex with the return of HSA in its native form. Gen X also leads to displacement of site-specific binding fluorophores bound to HSA, while subsequent addition of β-CD extracts Gen X from HSA with the return of the characteristic fluorescence of the HSA bound site-specific agent. These results illustrate the strong and specific binding sites of Gen X on HSA and demonstrate the principles for the potential application of β-CD for the remediation of PFAS from biological systems.

Exposure to GenX and its novel analogs disrupts fatty acid metabolism in male mice

Perfluoroalkyl ether carboxylic acids (PFECAs), including hexafluoropropylene oxide dimer acid (HFPO-DA, GenX), have been widely used as alternatives to perfluorooctanoic acid (PFOA) and subsequently detected in various environmental matrices. Despite this, public information regarding their hepatotoxicity remains limited. Here, to compare the hepatotoxicity of PFECAs and identify better alternatives for GenX, adult male mice were exposed to different concentrations (0.4, 2, and 10 mg/kg/d) of PFOA, GenX, and its analogs (PFMO2HpA and PFMO3NA) for 28 d. Results demonstrated increased hepatomegaly and disturbed fatty acid metabolism with increasing treatment doses. After dimensionality reduction analysis, significant differences were observed in the relative liver weights and liver and serum biochemical parameters among the four clusters. Furthermore, when chemical concentrations in the liver were similar, no differences in the indicators of liver injury associated with fatty acid metabolism were observed among groups in the same clusters. Our results suggest that dimensionality reduction analysis is a useful strategy for analyzing samples exposed to multiple compounds at different doses. Furthermore, PFECAs exhibit similar hepatotoxicities at the same cumulative hepatic concentration in mice with constant body weight, while PFMO2HpA exhibits lower hepatotoxicity compared to GenX at the same dose.

Exposure to hexafluoropropylene oxide dimer acid (HFPO-DA) disturbs the gut barrier function and gut microbiota in mice

Hexafluoropropylene oxide dimer acid (HFPO-DA) is the substitute for perfluoro octanoic acid (PFOA), and recently it has been detected in environmental water samples worldwide and has multiple toxicities. However, whether it will affect the intestines and gut microbiota remains unclear. In this study, in order to evaluate the gut toxicity of HFPO-DA in mammals, male mice were orally exposed to 0, 2, 20, 200 μg/L HFPO-DA, respectively, for 6 weeks. Our results showed that HFPO-DA exposure caused colonic inflammation which was coupled with increased TNF-α levels in serum and increased mRNA expression levels of TNF-α, p65, TLR4, MCP-1 of the colon in mice after exposure to 200 μg/L HFPO-DA. We also found that HFPO-DA exposure induced the decreased mRNA expression levels and protein levels of MUC2 and ZO-1, which means the dysfunction of gut barrier in the colon. In the ileum, we found that HFPO-DA exposure induced the increased mRNA expression levels of various inflammatory factors, but no obvious changes was found to barrier function. Additionally, HFPO-DA exposure caused the imbalance of cecal gut microbiota and changes of cecal microbiota diversity. Taken together, all these results indicate the potential gut toxicity of HFPO-DA and is perceived as a major problem of health risk that affects the inflammation, gut barrier dysfunction, and gut microbiota disturbance in mammals.

Hexafluoropropylene oxide dimer acid (GenX) exposure induces apoptosis in HepG2 cells

Hexafluoropropylene oxide dimer acid, also known as GenX, is a poly- and perfluoroalkyl substance (PFAS). PFASs are nonvolatile synthetic substances that can be readily disseminated into the environment during processing and use, making them easy to implement in the soil, drinking water, and air. Compared to other PFASs, GenX has a comparatively short carbon chain length and is expected to have a lower tendency to accumulate in humans; therefore, GenX has recently been used as a substitute to other PFASs. However, the mechanisms underlying GenX action and intoxication in humans remains unclear. In this study, the apoptotic capacity of GenX in human liver cells was investigated. When representative human-derived liver cells (HepG2 cells) were treated with GenX for 12 h, cell viability was reduced, and apoptosis was greatly increased. In addition, GenX increased the generation of intracellular reactive oxygen species (ROS), indicating the induction of oxidative stress in a dose-dependent manner. GenX treatment increased the expression of major apoptosis-related genes relative to the untreated control group. This research indicates that GenX causes apoptosis through ROS mediation in HepG2 cells, which may expand our knowledge of the molecular and toxicological mechanisms of GenX.

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Hexafluoropropylene oxide dimer acid (GenX) can be harmful to the liver.

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Through the mediation of ROS, GenX causes apoptosis in HepG2 cells.

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GenX activates Bax, caspase 3/9, CHOP, and p53 via the apoptosis.

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The intrinsic pathway links GenX mode of action to apoptosis-related stimuli.

The new PFAS C6O4 and its effects on marine invertebrates: First evidence of transcriptional and microbiota changes in the Manila clam Ruditapes philippinarum

There is growing concern for the wide use ofperfluorooctanoic acid (PFOA) because of its toxic effects on the environment and on human health. A new compound - the so called C6O4 (perfluoro ([5-methoxy-1,3-dioxolan-4-yl]oxy) acetic acid) - was recently introduced as one of the alternative to traditional PFOA, however this was done without any scientific evidence of the effects of C6O4 when dispersed into the environment. Recently, the Regional Agency for the Protection of the Environment of Veneto (Italy) detected high levels of C6O4 in groundwater and in the Po river, increasing the alarm for the potential effects of this chemical into the natural environment. The present study investigates for the first time the effects of C6O4 on the Manila clam Ruditapes philippinarum exposed to environmental realistic concentrations of C6O4 (0.1 µg/L and 1 µg/L) for 7 and 21 days. Furthermore, in order to better understand if C6O4 is a valid and less hazardous alternative to its substitute, microbial and transcriptomic alterations were also investigated in clams exposed to 1 µg/L ofPFOA. Results indicate that C6O4 may cause significant perturbations to the digestive gland microbiota, likely determining the impairment of host physiological homeostasis. Despite chemical analyses suggest a 5 times lower accumulation potential of C604 as compared to PFOA in clam soft tissues, transcriptional analyses reveal several alterations of gene expression profile. A large part of the altered pathways, including immune response, apoptosis regulation, nervous system development, lipid metabolism and cell membrane is the same in C6O4 and PFOA exposed clams. In addition, clams exposed to C6O4 showed dose-dependent responses as well as possible narcotic or neurotoxic effects and reduced activation of genes involved in xenobiotic metabolism. Overall, the present study suggests that the potential risks for marine organism following environmental contamination are not reduced by replacing PFOA with C6O4. In addition, the detection of both C6O4 and PFOA into tissues of clams inhabiting the Lagoon of Venice - where there are no point sources of either compounds - recommends a similar capacity to spread throughout the environment. These results prompt the urgent need to re-evaluate the use of C6O4 as it may represent not only an environmental hazard but also a potential risk for human health.

Legacy and Emerging Per- and Polyfluoroalkyl Substances: Analytical Techniques, Environmental Fate, and Health Effects

Due to their unique chemical properties, per- and polyfluoroalkyl substances (PFAS) have been used extensively as industrial surfactants and processing aids. While several types of PFAS have been voluntarily phased out by their manufacturers, these chemicals continue to be of ecological and public health concern due to their persistence in the environment and their presence in living organisms. Moreover, while the compounds referred to as “legacy” PFAS remain in the environment, alternative compounds have emerged as replacements for their legacy predecessors and are now detected in numerous matrices. In this review, we discuss the historical uses of PFAS, recent advances in analytical techniques for analysis of these compounds, and the fate of PFAS in the environment. In addition, we evaluate current biomonitoring studies of human exposure to legacy and emerging PFAS and examine the associations of PFAS exposure with human health impacts, including cancer- and non-cancer-related outcomes. Special focus is given to short-chain perfluoroalkyl acids (PFAAs) and ether-substituted, polyfluoroalkyl alternatives including hexafluoropropylene oxide dimer acid (HFPO-DA; tradename GenX), 4,8-dioxa-3H-perfluorononanoic acid (DONA), and 6:2 chlorinated polyfluoroethersulfonic acid (6:2 Cl-PFESA; tradename F-53B).

Diet as an Exposure Source and Mediator of Per- and Polyfluoroalkyl Substance (PFAS) Toxicity

Per- and polyfluoroalkyl substances (PFAS) are ubiquitously found in the environment due to their widespread commercial use and high chemical stability. Humans are exposed primarily through ingestion of contaminated water and food and epidemiological studies over the last several decades have shown that PFAS levels are associated with adverse chronic health effects, including cardiometabolic disorders such as hyperlipidemia and non-alcoholic fatty liver disease. Perhaps the most well-established effects, as demonstrated in animal studies and human epidemiological studies, are the metabolic alterations PFAS exposure can lead to, especially on lipid homeostasis and signaling. This altered lipid metabolism has often been linked to conditions such as dyslipidemia, leading to fatty liver disease and steatosis. Western diets enriched in high fat and high cholesterol containing foods may be an important human exposure route of PFAS and may also act as an important modulator of associated toxicities. In fact, the chemical structure of PFAS resemble fatty acids and may activate some of the same signaling cascades critical for endogenous metabolism. In this review we aim to outline known dietary exposure sources of PFAS, describe the detrimental metabolic health effects associated with PFAS exposure, and focus on studies examining emerging interaction of dietary effects with PFAS exposure that further alter the dysregulated metabolic state.

Association of perfluoroalkyl substances with gestational hypertension and preeclampsia in the MIREC study

BACKGROUND

Perfluoroalkyl substances (PFAS) have been linked with a number of developmental, reproductive, hepatic, and cardiovascular health outcomes. However, the evidence for an association between PFAS and hypertensive disorders of pregnancy (including gestational hypertension and preeclampsia) is equivocal and warrants further investigation.

OBJECTIVES

To examine the relationship between background levels of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorohexane sulfonate (PFHxS) and the development of gestational hypertension or preeclampsia in a Canadian pregnancy cohort. We also explored the potential for effect modification according to fetal sex.

METHODS

Maternal plasma samples were collected in the first trimester from participants in the MIREC study and were analyzed for PFOA, PFOS, and PFHxS. Blood pressure was measured during each trimester. Gestational hypertension and preeclampsia were defined using the Society of Obstetricians and Gynaecologists of Canada guidelines. Logistic regression models were used to derive adjusted odds ratios (OR) and 95% confidence intervals (CI) for associations between PFAS concentrations (per doubling of concentration as well as according to tertiles) and gestational hypertension or preeclampsia. Linear mixed models were used to examine the association between PFAS concentrations and changes in blood pressure throughout pregnancy.

RESULTS

Data from 1739 participants were analyzed. 90% of women were normotensive throughout pregnancy, 7% developed gestational hypertension without preeclampsia, and 3% developed preeclampsia. In the full analyses, neither PFOA nor PFOS were associated with gestational hypertension or preeclampsia. However, each doubling of PFHxS plasma concentration was associated with higher odds of developing preeclampsia (OR = 1.32; 95% CI: 1.03, 1.70). In addition, participants in the highest PFHxS tertile (1.4-40.0 μg/L) had higher odds of developing preeclampsia relative to those in the lowest tertile (OR = 3.06; 95% CI: 1.27, 7.39). In stratified analyses, this effect was only apparent among women carrying a female fetus (OR = 4.90; 95% CI: 1.02, 22.3). However, among women carrying a male fetus, both PFOS and PFHxS were associated with gestational hypertension, but not preeclampsia. Higher plasma concentrations of all three PFAS were associated with increases in diastolic blood pressure throughout pregnancy, and PFOA and PFHxS were also associated with systolic blood pressure. Discrepant findings were similarly revealed in analyses stratified by fetal sex.

CONCLUSIONS

Higher levels of PFHxS were associated with the development of preeclampsia, but not gestational hypertension. Neither PFOA nor PFOS were associated with either outcome. However, we show, for the first time, that fetal sex may modify these associations, a finding which warrants replication and further study.

Toxicity of Balb-c mice exposed to recently identified 1,1,2,2-tetrafluoro-2-[1,1,1,2,3,3-hexafluoro-3-(1,1,2,2-tetrafluoroethoxy)propan-2-yl]oxyethane-1-sulfonic acid (PFESA-BP2)

1,1,2,2-tetrafluoro-2-[1,1,1,2,3,3-hexafluoro-3-(1,1,2,2-tetrafluoroethoxy)propan-2-yl]oxyethane-1-sulfonic acid (PFESA-BP2) was first detected in 2012 in the Cape Fear River downstream of an industrial manufacturing facility. It was later detected in the finished drinking water of municipalities using the Cape Fear River for their water supply. No toxicology data exist for this contaminant despite known human exposure. To address this data gap, mice were dosed with PFESA-BP2 at 0, 0.04, 0.4, 3, and 6 mg/kg-day for 7 days by oral gavage. As an investigative study, the final dose groups evolved from an original dose of 3 mg/kg which produced liver enlargement and elevated liver enzymes. The dose range was extended to explore a no effect level. PFESA-BP2 was detected in the sera and liver of all treated mice. Treatment with PFESA-BP2 significantly increased the size of the liver for all mice at 3 and 6 mg/kg-day. At the 6 mg/kg-day dose, the liver more than doubled in size compared to the control group. Male mice treated with 3 and 6 mg/kg-day and females treated with 6 mg/kg-day demonstrated significantly elevated serum markers of liver injury including alanine aminotransferase (ALT), glutamate dehydrogenase (GLDH), and liver/body weight percent. The percent of PFESA-BP2 in serum relative to the amount administered was similar in male and female mice, ranged from 9 to 13 %, and was not related to dose. The percent accumulation in the liver of the mice varied by sex (higher in males), ranged from 30 to 65 %, and correlated positively with increasing dose level.