Perfluorooctanoic acid (PFOA) affects distinct molecular signalling pathways in human primary hepatocytes

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.

Exploring the molecular mechanisms by which per- and polyfluoroalkyl substances induce polycystic ovary syndrome through in silico toxicogenomic data mining

The pathogeny of polycystic ovary syndrome (PCOS) is intricate, with endocrine disruptors (EDCs) being acknowledged as significant environmental factors. Research has shown a link between exposure to per- and polyfluoroalkyl substances (PFAS) and the development and progression of PCOS, although the precise mechanism is not fully understood. This study utilized toxicogenomics and comparative toxicogenomics databases to analyze data and investigate how PFAS mixtures may contribute to the development of PCOS. The results indicated that 74 genes are associated with both PFAS exposure and PCOS progression. Enrichment analysis suggested that cell cycle regulation and steroid hormone synthesis may be crucial pathways through which PFAS mixtures participate in the development of PCOS, involving important genes such as CCNB1 and SRD5A1. Furthermore, the study identified transcription factors (TFs) and miRNAs that may be involved in the onset and progression of PCOS, constructing regulatory networks encompassing TFs-mRNA interactions and miRNA-mRNA relationships to elucidate their regulatory roles in gene expression. By utilizing data mining techniques based on toxicogenomic databases, this study provides relatively comprehensive insights into the association between exposure factors and diseases compared to traditional toxicology studies. These findings offer new perspectives for further in vivo or in vitro investigations and contribute to understanding the pathogenesis of PCOS, thereby providing valuable references for identifying clinical treatment targets.

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.

Perfluorooctanoic acid inhibits androgen biosynthesis in rat immature Leydig cells

Perfluorooctanoic acid (PFOA) is a commonly used short-chain synthetic perfluoroalkyl agent. Immature Leydig cells (ILCs) are localized in the testis and responsible for androgen biosynthesis and metabolism. Although PFOA shows toxicity in the reproductive system, it is not clear if it disrupts the function of ILCs. In the present study, primary ILCs were isolated from 35-day-old rats and exposed to a range of PFOA concentrations (0, 0.01, 0.1, or 1 μM). It was determined that 0.1 or 1 μM PFOA reduced total androgen biosynthesis in ILCs. Specifically, 22R-hydroxycholesterol (22R), and pregnenolone (P5) mediated androgen biosynthesis were reduced by 0.1 μM PFOA. PFOA also selectively downregulated mRNA and protein expressions of steroidogenic enzymes including LHCGR, CYP11A1, 3β-HSD1, and NR5A1 at 0.01, 0.1, or 1 μM. Further analysis revealed that 0.1 μM PFOA inhibited CYP11A1 and 3β-HSD1 enzyme activities. However, PFOA did not significantly affect androgen metabolism and turnover under any of the conditions tested. And PFOA gavaging to 35-day-old rats at 5 or 10 mg/kg for 7 or 14 days also reduced serum androgen levels secreted by ILCs. Moreover, PFOA gavaging also downregulated the mRNA and protein expression levels of LHCGR, CYP11A1, 3β-HSD1, and NR5A1 in vivo. Taken together, these findings suggest that PFOA inhibits androgen biosynthesis in ILCs by selectively targeting key enzymes in the synthesis pathway.

HNF4A as a potential target of PFOA and PFOS leading to hepatic steatosis: Integrated molecular docking, molecular dynamic and transcriptomic analyses

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are indeed among the most well known and extensively studied Per- and polyfluoroalkyl substances (PFASs), and increasing evidence confirm their effects on human health, especially liver steatosis. Nonetheless, the molecular mechanisms of their initiation of hepatic steatosis is still elusive. Therefore, potential targets of PFOA/PFOS must be explored to ameliorate its adverse consequences. This research aims to investigate the molecular mechanisms of PFOA and PFOS-induced liver steatosis, with emphasis on identifying a potential target that links these PFASs to liver steatosis. The potential target that causes PFOA and PFOS-induced liver steatosis have been explored and determined based on molecular docking, molecular dynamics (MD) simulation, and transcriptomics analysis. In silico results show that PFOA/PFOS can form a stable binding conformation with HNF4A, and PFOA/PFOS may interact with HNF4A to affect the downstream conduction mechanism. Transcriptome data from PFOA/PFOS-induced human stem cell spheres showed that HNF4A was inhibited, suggesting that PFOA/PFOS may constrain its function. PFOS mainly down-regulated genes related to cholesterol synthesis while PFOA mainly up-regulated genes related to fatty acid β-oxidation. This study explored the toxicological mechanism of liver steatosis caused by PFOA/PFOS. These compounds might inhibit and down-regulate HNF4A, which is the molecular initiation events (MIE) that induces liver steatosis.

Rapid enzymatic activity model (REAM) to decipher the toxic action of per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) have been identified as emerging contaminants and human exposure to these substances is a rising public health concern. We have developed a rapid enzymatic activity model (REAM), which can serve as a cell-free screening tool that elucidates possible mechanisms of toxic action inexpensively and quickly for these and other environmentally relevant chemicals.

Deficiency of spns1 exacerbates per- and polyfluoroalkyl substances mediated hepatic toxicity and steatosis in zebrafish (Danio rerio)

Per- and polyfluoroalkyl substances (PFAS) are man-made long-lasting chemical compounds that are found in everyday household items. Today they occur in the environment as a major group of pollutants. These compounds are broadly used in commercial product preparation such as, for food packaging, nonstick coatings, and firefighting foam. In humans, PFAS can cause immune disorders, impaired fetal development, abnormal skeletal tissue development, osteoarthritis, thyroid dysfunctions, cholesterol changes, affect insulin regulation and lipid metabolism, and are also involved in the development of fatty liver disease. In the current study, we investigated the effect of low, but physiologically relevant, concentrations of perfluorooctanoic acid (PFOA), heptafluorobutyric acid (HFBA), and perfluorotetradecanoic acid (PFTA) on gene expression markers of an inflammatory response (tnfa, il-1b, il-6, rplp0, edem1, and dnajc3a), unfolded protein response (UPR) (bip, atf4a, atf6, xbp1, and ddit3), senescence (p21, pai1, smp30, mdm2, and baxa), lipogenesis (scd1, acc, srebp1, pparγ, and fasn) and autophagy (p62, atg3, atg7, rab7, lc3b, and becn1) in AB wild-type (+/+), spns1-wt sibling (+/+), (+/-) and spns1 homozygous mutant (-/-) zebrafish embryos. Exposure to PFOA and HFBA (50 and 100 nM) specifically modulated inflammatory, UPR, senescence, lipogenic, and autophagy signaling in spns1-wt (+/+), (+/-), and spns1-mutant (-/-) zebrafish embryos. Furthermore, PFOA, but not HFBA, upregulated lipogenic-related gene expression and enhanced hepatic steatosis in spns1-wt (+/+), (+/-) zebrafish embryos. Combined exposure to PFOA, HFBA, and PFTA differentially expressed inflammatory, senescence, lipogenic, and autophagy-associated gene expression in spns1-mutant (-/-) zebrafish embryos compared with spns1-wt (+/+), (+/-) and AB-wt (+/+) zebrafish embryos. In addition, chronic exposure (∼2 months) to PFOA (120-600 nM) upregulated the expression of hepatic lipogenic and steatosis biomarkers in AB-wt (+/+) zebrafish. Collectively, our data suggest that acute/chronic physiologically relevant concentrations of PFOA upregulate inflammatory, UPR, senescence, and lipogenic signaling in spns1-wt (+/+), (+/-) and spns1-mutant (-/-) zebrafish embryos as well as in two-month-old AB-wt zebrafish, by targeting autophagy and hence induces toxicity that could promote nonalcoholic fatty liver disease.

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.

Exposure to serum perfluoroalkyl substances and biomarkers of liver function: The Korean national environmental health survey 2015-2017

BACKGROUND

Exposure to perfluoroalkyl substances (PFAS) may increase the risk of liver disease by disrupting cholesterol and lipid synthesis/metabolism, leading to higher liver-enzyme concentrations. However, most studies assessing association between PFAS and liver enzymes focused on individual PFAS. Moreover, PFAS concentrations differ based on sex and obesity status, and it remains unclear whether these factors affect associations with liver function. Therefore, we examined the association between exposure to both individual and combined PFAS and liver-function biomarkers and assessed sex and obesity as effect modifiers in Korean adults.

METHODS

We measured serum concentrations of the five most abundant PFAS (PFOA, PFOS, PFHxS, PFDA, PFNA) and three liver enzymes (alanine transaminase [ALT], aspartate aminotransferase [AST], γ-glutamyl transferase [GGT]) in 1404 adults from the Korean National Environmental Health Survey Cycle 3, 2015-2017. We used linear regression to evaluate associations between individual PFAS and liver-function biomarkers, assessing sex and obesity as possible effect modifiers, and performed Bayesian kernel machine regression and quantile g-computation to evaluate the overall effect of PFAS mixture on biomarkers of liver function.

RESULTS

Among 1404 Korean adults, all five PFAS were detected. Geometric mean concentration was highest for PFOS (16.11 μg/L), followed by PFOA (5.83 μg/L), PFHxS (2.21 μg/L), PFNA (2.03 μg/L), and PFDA (1.06 μg/L). In multivariable linear regression, all PFAS were positively associated with ALT, AST, and GGT; 2-fold increase in each PFAS was associated with 3.4-8.6% higher ALT, 2.4-4.6% higher AST, and 4.6-11.1% higher GGT (all p < 0.05). Positive associations for PFOA, PFDA, and PFNA with AST were stronger in men, and positive associations for PFOS with ALT and GGT were stronger in women. Compared to obese participants, nonobese participants had higher average percent changes in each enzyme, particularly GGT, when individual PFAS concentration doubled. Additionally, increased exposure to PFAS mixtures was associated with higher ALT, AST, and GGT. In quantile g-computations, simultaneous quartile increase in all PFAS was significantly associated with 6.9% (95%CI: 3.7, 10.2) higher ALT, 4.5% (95%CI: 2.4, 6.6) higher AST, and 8.3% (95%CI: 3.7, 13.1) higher GGT levels, on average.

CONCLUSIONS

Exposure to individual and combined PFAS is associated with higher liver enzymes in Korean adults, providing additional evidence for the association between PFAS exposure and risk of liver disease.

The effects of perfluoroalkyl and polyfluoroalkyl substances on female fertility: A systematic review and meta-analysis

OBJECTIVE

The reproductive toxicity of perfluoroalkyl and polyfluoroalkyl substances (PFAS) has been verified in both animal and in vitro experiments, however, the association between PFAS and female fertility remains contradictory in population studies. Therefore, in this systematic review and meta-analysis, we evaluated the effects of PFAS on female fertility based on population evidence.

METHODS

Electronic searches of the Web of Science, PubMed, The Cochrane Library, and Embase databases were conducted (from inception to March 2022) to collect observational studies related to PFAS and female fertility. Two evaluators independently screened the literature, extracted information and evaluated the risk of bias for the included studies, meta-analysis was performed using R software.

RESULTS

A total of 5468 records were searched and 13 articles fully met the inclusion criteria. Meta-analysis showed that perfluorooctanoic acid (PFOA) exposure was negatively associated with the female fecundability odds ratio (FOR = 0.88, 95% confidence interval (Cl) [0.78; 0.98]) and positively associated with the odds ratio for infertility (OR = 1.33, 95%Cl [1.03; 1.73]). Perfluorooctane sulfonate (PFOS) exposure was negatively associated with the fecundability odds ratio (FOR = 0.94, 95% CI [0.90; 0.98]). Pooled effect values for perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), and perfluorohexane sulfonate (PFHxS) exposure did not find sufficient evidence for an association with female fertility.

CONCLUSION

Based on the evidence provided by the current study, increased levels of PFAS exposure are associated with reduced fertility in women, this was characterized by a reduction in fecundability odds ratio and an increase in odds ratio for infertility. This finding could partially explain the decline in female fertility and provide insight into risk assessment when manufacturing products containing PFAS.

Per- and polyfluoroalkyl substances activate UPR pathway, induce steatosis and fibrosis in liver cells

Per- and polyfluoroalkyl substances (PFAS), which include perfluorooctanoic acid (PFOA), heptafluorobutyric acid (HFBA), and perfluorotetradecanoic acid (PFTA), are commonly occurring organic pollutants. Exposure to PFAS affects the immune system, thyroid and kidney function, lipid metabolism, and insulin signaling and is also involved in the development of fatty liver disease and cancer. The molecular mechanisms by which PFAS cause fatty liver disease are not understood in detail. In the current study, we investigated the effect of low physiologically relevant concentrations of PFOA, HFBA, and PFTA on cell survival, steatosis, and fibrogenic signaling in liver cell models. Exposure of PFOA and HFBA (10 to 1000 nM) specifically promoted cell survival in HepaRG and HepG2 cells. PFAS increased the expression of TNFα and IL6 inflammatory markers, increased endogenous reactive oxygen species (ROS) production, and activated unfolded protein response (UPR). Furthermore, PFAS enhanced cell steatosis and fibrosis in HepaRG and HepG2 cells which were accompanied by upregulation of steatosis (SCD1, ACC, SRBP1, and FASN), and fibrosis (TIMP2, p21, TGFβ) biomarkers expression, respectively. RNA-seq data suggested that chronic exposures to PFOA modulated the expression of fatty acid/lipid metabolic genes that are involved in the development of NFALD and fatty liver disease. Collectively our data suggest that acute/chronic physiologically relevant concentrations of PFAS enhance liver cell steatosis and fibrosis by the activation of the UPR pathway and by modulation of NFALD-related gene expression.

Association between exposure to perfluoroalkyl substances and uric acid in Chinese adults

BACKGROUND

A growing body of evidence suggests the deleterious effects of perfluoroalkyl substances (PFASs) on kidney, but little is known on the association between PFASs joint exposure and uric acid.

METHODS

Serum PFASs concentrations were measured in 661 participants recruited from Tianjin, China using liquid chromatography/mass spectrometry. The associations of single PFASs exposure with uric acid levels and hyperuricemia were assessed using multivariable linear and logistic regression models, respectively. Restricted cubic spline models were established to investigate the dose-response relationships between PFASs concentrations and uric acid levels. Bayesian Kernel Machine Regression (BKMR) model with a hierarchical variable selection was performed to assess the joint effect of PFASs on uric acid.

RESULTS

Potassium perfluoro-1-octanesulfonate (PFOS) and perfluoro-n-octanoic acid (PFOA) were the dominated contributors with median concentrations of 16.80 ng/ml and 9.42 ng/ml, respectively. Increased PFOA concentration (per log₂-unit) was associated with elevated uric acid level (β = 0.088, 95% CI: 0.033-0.143) and higher risk of hyperuricemia (OR = 1.134, 95% CI: 1.006-1.289). Conversely, the estimated change of uric acid associated with log₂-unit increment in perfluoro-n-decanoic acid (PFDA) was -0.081 mg/dL (95% CI: -0.154, -0.009). A significant linear dose-response pattern was found between log₂-transformed PFOA concentration and uric acid level. BKMR analyses indicated a non-significant overall effect of PFASs mixture on uric acid.

CONCLUSIONS

Significant associations between PFOA and PFDA and uric acid, and between PFOA and hyperuricemia were found in the single-pollutant models, but the joint effect of PFASs mixture on uric acid was not observed in the BKMR model, which provided new insights in regulation policies and risk assessment of PFASs.

Perfluorooctane sulfonic acid (PFOS) exposures interfere with behaviors and transcription of genes on nervous and muscle system in zebrafish embryos

Perfluorooctane sulfonic acid (PFOS) has been widely detected in environment and organisms. PFOS has been identified as the driving agent for the behavioral changes of zebrafish larvae, while the underlying molecular mechanism remains unclear. In this study, zebrafish embryos/larvae were exposed to 0, 0.04, 0.1, 0.4 and 1 μM PFOS for 166 h. The locomotor behaviors and the mRNA transcription of genes in neuromuscular system were detected. Exposure to PFOS did not affect the hatching/death rates and body length, but increased the heart beat rates and frequency of spontaneous tail coiling. Locomotor behavior in zebrafish larvae of 0.4 and 1 μM PFOS groups were increased in the light condition. Additionally, the levels of acetylcholine (Ach) in 0.4 μM PFOS group and dopamine (DA) in 0.1, 0.4 and 1 μM PFOS groups were found to be significantly increased. The expression of genes related to the synthesis and decomposition of ACh，the synthesis and receptor of DA, and fosab was increased in the different PFOS treatment groups, while the expression of all the other genes of the neuromuscular system were significantly reduced. The findings of this investigation demonstrated that PFOS exposure may alter the locomotor behavior of zebrafish through disrupting the expressions of genes in neuromuscular system. The disturbed process of neurotransmitter transmission and muscle contraction caused by PFOS may be the dominant mechanism of hyperactivity in zebrafish.

Reduced Birth Weight and Exposure to Per- and Polyfluoroalkyl Substances: A Review of Possible Underlying Mechanisms Using the AOP-HelpFinder

Prenatal exposure to per- and polyfluorinated substances (PFAS) may impair fetal growth. Our knowledge of the underlying mechanisms is incomplete. We used the Adverse Outcome Pathway (AOP)-helpFinder tool to search PubMed for studies published until March 2021 that examined PFAS exposure in relation to birth weight, oxidative stress, hormones/hormone receptors, or growth signaling pathways. Of these 1880 articles, 106 experimental studies remained after abstract screening. One clear finding is that PFAS are associated with oxidative stress in in vivo animal studies and in vitro studies. It appears that PFAS-induced reactive-oxygen species (ROS) generation triggers increased peroxisome proliferator-activated receptor (PPAR)γ expression and activation of growth signaling pathways, leading to hyperdifferentiation of pre-adipocytes. Fewer proliferating pre-adipocytes result in lower adipose tissue weight and in this way may reduce birth weight. PFAS may also impair fetal growth through endocrine effects. Estrogenic effects have been noted in in vivo and in vitro studies. Overall, data suggest thyroid-damaging effects of PFAS affecting thyroid hormones, thyroid hormone gene expression, and histology that are associated in animal studies with decreased body and organ weight. The effects of PFAS on the complex relationships between oxidative stress, endocrine system function, adipogenesis, and fetal growth should be further explored.

Identification of molecular initiating events and key events leading to endocrine disrupting effects of PFOA: Integrated molecular dynamic, transcriptomic, and proteomic analyses

Perfluorooctanoic acid (PFOA) can rapidly activate signaling pathways independent of nuclear hormone receptors through membrane receptor regulation, which leads to endocrine disrupting effects. In the present work, the molecular initiating event (MIE) and the key events (KEs) which cause the endocrine disrupting effects of PFOA have been explored and determined based on molecular dynamics simulation (MD), fluorescence analysis, transcriptomics, and proteomics. MD modeling and fluorescence analysis proved that, on binding to the G protein-coupled estrogen receptor-1 (GPER), PFOA could induce a conformational change in the receptor, turning it into an active state. The results also indicated that the binding to GPER was the MIE that led to the adverse outcome (AO) of PFOA. In addition, the downstream signal transduction pathways of GPER, as regulated by PFOA, were further investigated through genomics and proteomics to identify the KEs leading to thr endocrine disrupting effects. Two pathways (Endocrine resistance, ERP and Estrogen signaling pathway, ESP) containing GPER were regulated by different concentration of PFOA and identified as the KEs. The knowledge of MIE, KEs, and AO of PFOA is necessary to understand the links between PFOA and the possible pathways that lead to its negative effects.

Comparison of sub-lethal metabolic perturbations of select legacy and novel perfluorinated alkyl substances (PFAS) in Daphnia magna

Per- and polyfluoroalkyl substances (PFAS) are a class of pollutants of concern due to their ubiquitous presence, persistence, and toxicity in aquatic environments. Legacy PFAS pollutants such as perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) have been more widely studied in aquatic environments. However, replacement PFAS, such as ammonium perfluoro (2-methyl-3-oxahexanoate; GenX) are increasingly being detected with little known information surrounding their toxicity. Here, Daphnia magna, a model organism for freshwater ecotoxicology was used to compare the acute sub-lethal toxicity of PFOS, PFOA, GenX, and PFAS mixtures. Using liquid chromatography with tandem mass spectrometry (LC-MS/MS), the targeted polar metabolic profile extracted from single Daphnia was quantified to investigate perturbations in the exposure groups versus the unexposed organisms. Multivariate statistical analyses demonstrated significant non-monotonic separation in PFOA, GenX, and PFAS mixture exposures. Sub-lethal exposure to concentrations of PFOS did not lead to significant separation in multivariate analyses. Univariate statistics and pathway analyses were used to elucidate the mode of action of PFAS exposure. Exposure to all individual PFAS led to significant perturbations in many amino acids including cysteine, histidine, tryptophan, glycine, and serine. These perturbations are consistent with biochemical pathway disruptions in the pantothenate and Coenzyme A (CoA) biosynthesis, thiamine metabolism, histidine metabolism, and aminoacyl-tRNA biosynthesis pathways. Overall, the collected metabolomic data is consistent with disruptions in energy metabolism and protein synthesis as the primary mode of action of sub-lethal PFAS exposure. Secondary modes of action among individual pollutant exposures demonstrated that the structural properties (carboxylic acid vs. sulfonic acid group) may play a role in the metabolic perturbations observed. Sub-lethal exposure to PFAS mixtures highlighted a mixed response when compared to the individual pollutants (PFOS, PFOA, and GenX). Overall, this study emphasizes the niche capability of environmental metabolomics to differentiate secondary modes of action from metabolic perturbations in both single pollutant and pollutant mixtures within the same chemical class.

Characterization of Potential Adverse Outcome Pathways Related to Metabolic Outcomes and Exposure to Per- and Polyfluoroalkyl Substances Using Artificial Intelligence

Human exposure to per- and polyfluoroalkyl substances (PFAS) has been associated with numerous adverse health effects, depending on various factors such as the conditions of exposure (dose/concentration, duration, route of exposure, etc.) and characteristics associated with the exposed target (e.g., age, sex, ethnicity, health status, and genetic predisposition). The biological mechanisms by which PFAS might affect systems are largely unknown. To support the risk assessment process, AOP-helpFinder, a new artificial intelligence tool, was used to rapidly and systematically explore all available published information in the PubMed database. The aim was to identify existing associations between PFAS and metabolic health outcomes that may be relevant to support building adverse outcome pathways (AOPs). The collected information was manually organized to investigate linkages between PFAS exposures and metabolic health outcomes, including dyslipidemia, hypertension, insulin resistance, and obesity. Links between PFAS exposure and events from the existing metabolic-related AOPs were also retrieved. In conclusion, by analyzing dispersed information from the literature, we could identify some associations between PFAS exposure and components of existing AOPs. Additionally, we identified some linkages between PFAS exposure and metabolic outcomes for which only sparse information is available or which are not yet present in the AOP-wiki database that could be addressed in future research.

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.

Profiling biotoxicities of hexafluoropropylene oxide trimer acid with human embryonic stem cell-based assays

Hexafluoropropylene oxide trimer acid (HFPO-TA), an emerging replacement of perfluorooctanoic acid (PFOA), has recently been reported to be a potential environmental contaminant. Due to the similar structure to PFOA, HFPO-TA may cause comparable adverse effects on human health. Therefore, evaluating the toxic profiles of HFPO-TA has become an urgent task. In this study, we investigated the cytotoxicity and hepatoxicity of HFPO-TA using human embryonic stem cell (hESC)-based assays. Results showed that HFPO-TA reduced hESCs' viability in a dose dependent manner, and the calculated IC50 for 24, 48 and 72 hr were 222.8, 167.4, and 80.6 μmol/L, respectively. Significant intracellular ROS accumulation and mitochondrion membrane potential reduction were detected with HFPO-TA exposure, and increased apoptotic/necrotic cells were also observed in high dose of HFPO-TA treated group. Moreover, HFPO-TA at noncytotoxic concentrations also significantly impaired the functions of induced hepatocytes by diminishing cell glycogen storage ability and deregulating specific functional genes. Transcriptome sequencing analysis identified a set of hepatic associated biological processes responding to HFPO-TA exposure. PPAR was the most significantly enriched pathway. Genes including FGA, FGB, FGG, AHSG, HRG, ITIH2, ALB were characterized as hub genes by cytoHubba plug-in. These data indicated that HFPO-TA is a potential hepatotoxicant, and may not be a safe replacement for PFOA.

Select Per- and Polyfluoroalkyl Substances (PFAS) Induce Resistance to Carboplatin in Ovarian Cancer Cell Lines

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous environmental contaminants associated with adverse reproductive outcomes including reproductive cancers in women. PFAS can alter normal ovarian function, but the effects of PFAS on ovarian cancer progression and therapy response remain understudied. Ovarian cancer is the most lethal gynecologic malignancy, and a major barrier to effective treatment is resistance to platinum-based chemotherapy. Platinum resistance may arise from exposure to external stimuli such as environmental contaminants. This study evaluated PFAS and PFAS mixture exposures to two human ovarian cancer cell lines to evaluate the ability of PFAS exposure to affect survival fraction following treatment with carboplatin. This is the first study to demonstrate that, at sub-cytotoxic concentrations, select PFAS and PFAS mixtures increased survival fraction in ovarian cancer cells following carboplatin treatment, indicative of platinum resistance. A concomitant increase in mitochondrial membrane potential, measured by the JC-1 fluorescent probe, was observed in PFAS-exposed and PFAS + carboplatin-treated cells, suggesting a potential role for altered mitochondrial function that requires further investigation.

Maternal Sodium p-Perfluorous Nonenoxybenzene Sulfonate Exposure Disturbed Lipid Metabolism and Induced an Imbalance in Tyrosine Metabolism in the F1 Generation of Mice

The toxicity of perfluorinated compounds (PFCs) to mammals has recently received increasing attention. However, the effects of maternal sodium p-perfluorous nonenoxybenzene sulfonate (OBS) exposure during pregnancy and lactation on the liver function of dams (F0) and offspring (F1) mice are still unknown. The results demonstrated that maternal OBS treatment could not only induce lipid metabolism dysfunction but also disrupt amino acid metabolism in the liver of F0 and F1 generations. OBS had marked accumulation in the liver, and the serum and liver triglyceride (TG) levels increased in the F0 and F1 generations after maternal OBS exposure. Moreover, maternal OBS exposure changed the transcriptional levels of genes related to lipid metabolism (fatty acid (FA) synthesis, TG synthesis, and transport) and induced changes in the amino acid level in dams and 20-day-old mice offspring (F1-20 d). Additionally, the regulation of lipid metabolism by OBS was mainly dependent on the activation of peroxisome proliferator-activated receptor γ (PPARγ) and cluster of differentiation 36 (CD36). Interestingly, OBS could also disturb tyrosine (TYR) metabolism by increasing the TYR level and downregulating fumarate acetoacetate hydrolase (FAH). Together, these results indicated that the liver can be perceived as the major target tissue of OBS, which strongly affected metabolic function and ultimately led to an imbalance in the metabolism of lipids and TYR. In summary, maternal OBS exposure during pregnancy and lactation has toxic effects on the hepatic metabolism of dams and offspring, indicating that the toxic effects could obviously cross generations of mice, and we should pay more attention to understanding the health risk to both dams and offspring.

Perfluorooctanoic acid promotes proliferation of the human granulosa cell line HGrC1 and alters expression of cell cycle genes and Hippo pathway effector YAP1

Perfluorooctanoic acid (PFOA) is a common environmental contaminant that belongs to a group of manmade fluorinated chemicals called per- and polyfluoroalkyl substances (PFAS). Due to the pervasive nature of PFOA, the environmental health risks of PFOA contamination and exposure on reproductive health have increasing concern. In the present study, we exposed HGrC1 cells, an immortalized human granulosa cell line, to environmentally relevant (1-10 μM) concentrations of PFOA. Results indicated that HGrC1 cells treated with PFOA had increased proliferation and migration relative to vehicle treated controls. No differences in cell apoptosis were observed with 1-10 μM PFOA. Gene expression analysis revealed increases in mRNA transcripts for cell cycle regulators CCND1, CCNA2, and CCNB1. Upregulation of YAP1 protein and downstream target CTGF protein was also observed, suggesting that the Hippo pathway is involved in the proliferation and migratory effects of PFOA on HGrC1 cells. Further, the YAP1 inhibitor Verteporfin prevented the stimulatory effects of PFOA on HGrC1 cells. Together, these findings support a role for the Hippo pathway effector YAP1 in response to PFOA exposure in human granulosa cells.

Predicting the effects of per- and polyfluoroalkyl substance mixtures on peroxisome proliferator-activated receptor alpha activity in vitro

Human exposure to per- and polyfluoroalkyl substances (PFAS) is ubiquitous, with mixtures of PFAS detected in drinking water, food, household dust, and other exposure sources. Animal toxicity studies and human epidemiology indicate that PFAS may act through shared mechanisms including activation of peroxisome proliferator activated receptor α (PPARα). However, the effect of PFAS mixtures on human relevant molecular initiating events remains an important data gap in the PFAS literature. Here, we tested the ability of modeling approaches to predict the effect of diverse PPARα ligands on receptor activity using Cos7 cells transiently transfected with a full length human PPARα (hPPARα) expression construct and a peroxisome proliferator response element-driven luciferase reporter. Cells were treated for 24 h with two full hPPARα agonists (pemafibrate and GW7647), a full and a partial hPPARα agonist (pemafibrate and mono(2-ethylhexyl) phthalate), or a full hPPARα agonist and a competitive antagonist (pemafibrate and GW6471). Receptor activity was modeled with three additive approaches: effect summation, relative potency factors (RPF), and generalized concentration addition (GCA). While RPF and GCA accurately predicted activity for mixtures of full hPPARα agonists, only GCA predicted activity for full and partial hPPARα agonists and a full agonist and antagonist. We then generated concentration response curves for seven PFAS, which were well-fit with three-parameter Hill functions. The four perfluorinated carboxylic acids (PFCA) tended to act as full hPPARα agonists while the three perfluorinated sulfonic acids (PFSA) tended to act as partial agonists that varied in efficacy between 28-67 % of the full agonist, positive control level. GCA and RPF performed equally well at predicting the effects of mixtures with three PFCAs, but only GCA predicted experimental activity with mixtures of PFSAs and a mixture of PFCAs and PFSAs at ratios found in the general population. We conclude that of the three approaches, GCA most accurately models the effect of PFAS mixtures on hPPARα activity in vitro. Understanding the differences in efficacy with which PFAS activate hPPARα is essential for accurately predicting the effects of PFAS mixtures. As PFAS can activate multiple nuclear receptors, future analyses should examine mixtures effects in intact cells where multiple molecular initiating events contribute to proximate effects and functional changes.

Predicting the effects of per- and polyfluoroalkyl substance mixtures on peroxisome proliferator-activated receptor alpha activity in vitro

Human exposure to per- and polyfluoroalkyl substances (PFAS) is ubiquitous, with mixtures of PFAS detected in drinking water, food, household dust, and other exposure sources. Animal toxicity studies and human epidemiology indicate that PFAS may act through shared mechanisms including activation of peroxisome proliferator activated receptor α (PPARα). However, the effect of PFAS mixtures on human relevant molecular initiating events remains an important data gap in the PFAS literature. Here, we tested the ability of modeling approaches to predict the effect of diverse PPARα ligands on receptor activity using Cos7 cells transiently transfected with a full length human PPARα (hPPARα) expression construct and a peroxisome proliferator response element-driven luciferase reporter. Cells were treated for 24 h with two full hPPARα agonists (pemafibrate and GW7647), a full and a partial hPPARα agonist (pemafibrate and mono(2-ethylhexyl) phthalate), or a full hPPARα agonist and a competitive antagonist (pemafibrate and GW6471). Receptor activity was modeled with three additive approaches: effect summation, relative potency factors (RPF), and generalized concentration addition (GCA). While RPF and GCA accurately predicted activity for mixtures of full hPPARα agonists, only GCA predicted activity for full and partial hPPARα agonists and a full agonist and antagonist. We then generated concentration response curves for seven PFAS, which were well-fit with three-parameter Hill functions. The four perfluorinated carboxylic acids (PFCA) tended to act as full hPPARα agonists while the three perfluorinated sulfonic acids (PFSA) tended to act as partial agonists that varied in efficacy between 28-67 % of the full agonist, positive control level. GCA and RPF performed equally well at predicting the effects of mixtures with three PFCAs, but only GCA predicted experimental activity with mixtures of PFSAs and a mixture of PFCAs and PFSAs at ratios found in the general population. We conclude that of the three approaches, GCA most accurately models the effect of PFAS mixtures on hPPARα activity in vitro. Understanding the differences in efficacy with which PFAS activate hPPARα is essential for accurately predicting the effects of PFAS mixtures. As PFAS can activate multiple nuclear receptors, future analyses should examine mixtures effects in intact cells where multiple molecular initiating events contribute to proximate effects and functional changes.

PFOA regulate adenosine receptors and downstream concentration-response cAMP-PKA pathway revealed by integrated omics and molecular dynamics analyses

As an important pollutant, perfluorooctane acid (PFOA) has been widely concerned and reported by thousands of times, while less is known about the concentration-response pathway of PFOA. The aim of the present work was to reveal the concentration-response mechanism of PFOA in human cells. Omics results showed that calcium-related pathways play key roles in PFOA injury mechanisms. The results of GO and KEGG analyses showed that the cAMP signaling pathway was presented as the top one in all of the regulatory patterns and concentrations groups of PFOA. In the cAMP signaling pathway, the adenosine A₁ receptor (ADORA1) recognized the low concentration of PFOA and induced pathway "G_i-cAMP-PKA" to decrease the concentration of cAMP. This indicated that the low concentration of PFOA may promote breast hyperplasia and inhibit lactation. While adenosine A_2A receptor (ADORA2A) recognized the high concentration of PFOA and induced pathway "G_S-AC-cAMP-RKA" to increase the concentration of cAMP, induce cell damage and may lead to the deterioration of breast cancer. The results of molecular dynamics simulation showed that PFOA could bind to ADORA1 and ADORA2A, thus cause subsequent signal transduction. Furthermore, considering the strong binding ability of PFOA with ADORA1, PFOA tends to bind to ADORA1 at a low concentration. On the other side, PFOA at high concentration will continue to bind to another receptor protein, ADORA2A, and activate subsequent signaling pathways. Combined analyses of transcriptomic and proteomic revealed that different concentrations of PFOA regulate cellular calcium-related pathways. The cAMP pathway showed a concentration-response effect of PFOA. After treatment with different concentrations of PFOA, ADORA1 and ADORA2A were activated respectively, showing opposite cellular effects, leading to kinds of breast lesions. In the nervous system, PFOA might induce a variety of nervous system diseases. The present work was an exploration on the toxicological mechanism of PFOA, providing important information on the health impacts of PFOA in humans.

Association between gestational PFAS exposure and Children's adiposity in a diverse population

Perfluoroalkyl substances (PFAS) are widely distributed suspected obesogens that cross the placenta. However, few data are available to assess potential fetal effects of PFAS exposure on children's adiposity in diverse populations. To address the data gap, we estimated associations between gestational PFAS concentrations and childhood adiposity in a diverse mother-child cohort. We considered 6 PFAS in first trimester blood plasma, measured using ultra-high-performance liquid chromatography with tandem mass spectrometry, collected from non-smoking women with low-risk singleton pregnancies (n = 803). Body mass index (BMI), waist circumference (WC), fat mass, fat-free mass, and % body fat were ascertained in 4-8 year old children as measures of adiposity. We estimated associations of individual gestational PFAS with children's adiposity and overweight/obesity, adjusted for confounders. There were more non-Hispanic Black (31.7 %) and Hispanic (42.6 %) children with overweight/obesity, than non-Hispanic white (18.2 %) and Asian/Pacific Islander (16.4 %) children (p < 0.0001). Perfluorooctane sulfonate (PFOS; 5.3 ng/mL) and perfluorooctanoic acid (2.0 ng/mL) had the highest median concentrations in maternal blood. Among women without obesity (n = 667), greater perfluoroundecanoic acid (PFUnDA) was associated with their children having higher WC z-score (β = 0.08, 95%CI: 0.01, 0.14; p = 0.02), fat mass (β = 0.55 kg, 95%CI: 0.21, 0.90; p = 0.002), and % body fat (β = 0.01 %; 95%CI: 0.003, 0.01; p = 0.004), although the association of PFUnDA with fat mass attenuated at the highest concentrations. Among women without obesity, the associations of PFAS and their children's adiposity varied significantly by self-reported race-ethnicity, although the direction of the associations was inconsistent. In contrast, among the children of women with obesity, greater, PFOS, perfluorononanoic acid, and perfluorodecanoic acid concentrations were associated with less adiposity (n = 136). Our results suggest that specific PFAS may be developmental obesogens, and that maternal race-ethnicity may be an important modifier of the associations among women without obesity.

Prenatal exposure to poly-/per-fluoroalkyl substances is associated with alteration of lipid profiles in cord-blood

INTRODUCTION

Poly-/per-fluoroalkyl substances (PFAS) are widespread environmental pollutants that may induce metabolic perturbations in humans, including particularly alterations in lipid profiles. Prenatal exposure to PFAS can cause lasting effects on offspring metabolic health, however, the underlying mechanisms are still unknown.

OBJECTIVES

The goal of the study was to investigate the impact of prenatal PFAS exposure on the lipid profiles in cord blood.

METHODS

Herein, we combined determination of bile acids (BAs) and molecular lipids by liquid chromatography with ultra-high-resolution mass spectrometry, and separately quantified cord blood concentrations of sixteen PFAS in a cohort of Chinese infants (104 subjects) in a cross-sectional study. We then evaluated associations between PFAS concentration and lipidome using partial correlation network analysis, debiased sparse partial correlation, linear regression analysis and correlation analysis.

RESULTS

PFAS levels showed significant associations with the lipid profiles; specifically, PFAS exposure was positively correlated with triacylgycerols (TG) and several bile acids. Importantly, exposure to perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorononanoic acid (PFNA) and perfluorohexane sulfonic acid (PFHxS) were associated with increased levels of TGs with saturated fatty acids while multiple classes of phospholipids were decreased. In addition, several free fatty acids showed significant positive correlations with PFOS.

CONCLUSIONS

Our results indicated that prenatal exposure to PFAS mediated metabolic changes, which may explain the associations reported between PFAS exposure and metabolic health later in life.

Epigenetic toxicity and cytotoxicity of perfluorooctanoic acid and its effects on gene expression in embryonic mouse hypothalamus cells

Even though the endocrine-disrupting potential of perfluorooctanoic acid (PFOA) is well known, the mechanisms underlying its cellular and epigenetic toxicity at the critical stage of hypothalamic development are poorly understood. This is why we studied its effects on the embryonic mouse hypothalamic cell line N46 (mHypoE-N46) with a hope to shed more light on the mechanisms through which PFOA causes embryonic hypothalamic cell damage. To do that, we studied cell viability, global DNA methylation, and gene expression in cells exposed to PFOA. As the PFOA dose increased, cell viability decreased, while global DNA methylation increased. PFOA also significantly altered the expression of genes related to the apoptosis and cell cycle, neurotrophic genes, and the Tet, Dnmt, and Mecp2 genes. Our findings suggest that exposure to PFOA affects cell survival through the reprogramming of embryonic hypothalamic DNA methylation patterns and altering cell homeostasis genes. DNA methylation and changes in the Mecp2 gene expression induced by PFOA also imply wider ramifications, as they alter genes of other major mechanisms of the embryonic hypothalamus. Our study may therefore serve as a good starting point for further research into the mechanisms of PFOA effect of hypothalamic development.

Perfluorooctanoic acid induces liver and serum dyslipidemia in humanized PPARα mice fed an American diet

Per- and polyfluoroalkyl substances (PFAS) are pervasive in the environment resulting in nearly universal detection in people. Human serum PFAS concentrations are strongly associated with increased serum low-density lipoprotein cholesterol (LDL-C), and growing evidence suggests an association with serum triacylglycerides (TG). Here, we tested the hypothesis that perfluorooctanoic acid (PFOA) dysregulates liver and serum triacylglycerides in human peroxisome proliferator activated receptor α (hPPARα)-expressing mice fed an American diet. Mice were exposed to PFOA (3.5 mg/L) in drinking water for 6 weeks resulting in a serum concentration of 48 ± 9 μg/ml. In male and female hPPARα mice, PFOA increased total liver TG and TG substituted with saturated and monounsaturated fatty acids. Lack of expression of PPARα alone also increased total liver TG, and PFOA treatment had little effect on liver TG in PPARα null mice. In hPPARα mice, PFOA neither significantly increased nor decreased serum TG; however, there was a modest increase in TG associated with very low-density cholesterol particles in both sexes. Intriguingly, in female PPARα null mice, PFOA significantly increased serum TG, with a similar trend in males. PFOA also modified fatty acid and TG homeostasis-related gene expression in liver, in a hPPARα-dependent manner, but not in adipose. The results of our study and others reveal the importance of context (serum concentration and genotype) in determining the effect of PFOA on lipid homeostasis.

Perfluorooctanoic acid inhibits the maturation rate of mouse oocytes cultured in vitro by triggering mitochondrial and DNA damage

BACKGROUND

Perfluorooctanoic acid (PFOA) is widely used in the manufacture of household and industrial products. It has certain toxicity and leaves many residues in the environment. Numerous studies have shown that PFOA exhibits endocrine disrupting properties and immunotoxicity and induces developmental defects. However, there is very little information regarding its toxicity on oocytes.

METHODS

We cultured denuded oocytes in maturation medium supplemented with 0, 300, or 500 PFOA during IVM and evaluated the maturation of oocytes from the aspects of ROS(DCFH-DA), mitochondria(MitoOrange and JC-1), DNA damage(P-H2AX), and cytoskeleton(β-tubulin).

RESULTS

Compared with the control group, the PFOA treatment group exhibited significantly reduced proportion of oocytes matutation. Furthermore, the DCFH-DA test showed that PFOA significantly increased reactive oxygen species (ROS) levels. PFOA disrupted mitochondrial distribution and decreased mitochondrial function as assessed using MitoOrange and JC-1. In addition, PFOA-treated oocytes exhibited a significantly higher percentage of P-H2AX, defective β-tubulin, abnormal chromosome alignment, lower expression of the anti-apoptotic gene Bcl-2, and higher expression of the apoptotic genes caspase3 and Bax.

CONCLUSION

In summary, PFOA could negatively and directly affect oocyte maturation in vitro and cause oxidative stress, mitochondrial function disruption, DNA damage, cytoskeleton damage, and apoptosis.

Systemic PFOS and PFOA exposure and disturbed lipid homeostasis in humans: what do we know and what not?

Associations between per- and polyfluoroalkyl substances (PFASs) and increased blood lipids have been repeatedly observed in humans, but a causal relation has been debated. Rodent studies show reverse effects, i.e. decreased blood cholesterol and triglycerides, occurring however at PFAS serum levels at least 100-fold higher than those in humans. This paper aims to present the main issues regarding the modulation of lipid homeostasis by the two most common PFASs, PFOS and PFOA, with emphasis on the underlying mechanisms relevant for humans. Overall, the apparent contrast between human and animal data may be an artifact of dose, with different molecular pathways coming into play upon exposure to PFASs at very low versus high levels. Altogether, the interpretation of existing rodent data on PFOS/PFOA-induced lipid perturbations with respect to the human situation is complex. From a mechanistic perspective, research on human liver cells shows that PFOS/PFOA activate the PPARα pathway, whereas studies on the involvement of other nuclear receptors, like PXR, are less conclusive. Other data indicate that suppression of the nuclear receptor HNF4α signaling pathway, as well as perturbations of bile acid metabolism and transport might be important cellular events that require further investigation. Future studies with human-relevant test systems would help to obtain more insight into the mechanistic pathways pertinent for humans. These studies shall be designed with a careful consideration of appropriate dosing and toxicokinetics, so as to enable biologically plausible quantitative extrapolations. Such research will increase the understanding of possible perturbed lipid homeostasis related to PFOS/ PFOA exposure and the potential implications for human health.

Per- and Polyfluoroalkyl Substance Toxicity and Human Health Review: Current State of Knowledge and Strategies for Informing Future Research

Reports of environmental and human health impacts of per- and polyfluoroalkyl substances (PFAS) have greatly increased in the peer-reviewed literature. The goals of the present review are to assess the state of the science regarding toxicological effects of PFAS and to develop strategies for advancing knowledge on the health effects of this large family of chemicals. Currently, much of the toxicity data available for PFAS are for a handful of chemicals, primarily legacy PFAS such as perfluorooctanoic acid and perfluorooctane sulfonate. Epidemiological studies have revealed associations between exposure to specific PFAS and a variety of health effects, including altered immune and thyroid function, liver disease, lipid and insulin dysregulation, kidney disease, adverse reproductive and developmental outcomes, and cancer. Concordance with experimental animal data exists for many of these effects. However, information on modes of action and adverse outcome pathways must be expanded, and profound differences in PFAS toxicokinetic properties must be considered in understanding differences in responses between the sexes and among species and life stages. With many health effects noted for a relatively few example compounds and hundreds of other PFAS in commerce lacking toxicity data, more contemporary and high-throughput approaches such as read-across, molecular dynamics, and protein modeling are proposed to accelerate the development of toxicity information on emerging and legacy PFAS, individually and as mixtures. In addition, an appropriate degree of precaution, given what is already known from the PFAS examples noted, may be needed to protect human health. Environ Toxicol Chem 2021;40:606-630. © 2020 SETAC.

Endocrine Disruptor Potential of Short- and Long-Chain Perfluoroalkyl Substances (PFASs)-A Synthesis of Current Knowledge with Proposal of Molecular Mechanism

Endocrine disruptors are a group of chemical compounds that, even in low concentrations, cause a hormonal imbalance in the body, contributing to the development of various harmful health disorders. Many industry compounds, due to their important commercial value and numerous applications, are produced on a global scale, while the mechanism of their endocrine action has not been fully understood. In recent years, per- and polyfluoroalkyl substances (PFASs) have gained the interest of major international health organizations, and thus more and more studies have been aimed to explain the toxicity of these compounds. PFASs were firstly synthesized in the 1950s and broadly used in the industry in the production of firefighting agents, cosmetics and herbicides. The numerous industrial applications of PFASs, combined with the exceptionally long half-life of these substances in the human body and extreme environmental persistence, result in a common and chronic exposure of the general population to their action. Available data have suggested that human exposure to PFASs can occur during different stages of development and may cause short- or/and long-term health effects. This paper synthetizes the current literature reports on the presence, bioaccumulation and, particularly, endocrine toxicity of selected long- and short-chain PFASs, with a special emphasis on the mechanisms underlying their endocrine actions.

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.

Metabolic Signatures of the Exposome-Quantifying the Impact of Exposure to Environmental Chemicals on Human Health

Human health and well-being are intricately linked to environmental quality. Environmental exposures can have lifelong consequences. In particular, exposures during the vulnerable fetal or early development period can affect structure, physiology and metabolism, causing potential adverse, often permanent, health effects at any point in life. External exposures, such as the “chemical exposome” (exposures to environmental chemicals), affect the host’s metabolism and immune system, which, in turn, mediate the risk of various diseases. Linking such exposures to adverse outcomes, via intermediate phenotypes such as the metabolome, is one of the central themes of exposome research. Much progress has been made in this line of research, including addressing some key challenges such as analytical coverage of the exposome and metabolome, as well as the integration of heterogeneous, multi-omics data. There is strong evidence that chemical exposures have a marked impact on the metabolome, associating with specific disease risks. Herein, we review recent progress in the field of exposome research as related to human health as well as selected metabolic and autoimmune diseases, with specific emphasis on the impacts of chemical exposures on the host metabolome.

Prenatal Exposure to Perfluoroalkyl Substances Associated With Increased Susceptibility to Liver Injury in Children

BACKGROUND AND AIMS

Per- and polyfluoroalkyl substances (PFAS) are widespread and persistent pollutants that have been shown to have hepatotoxic effects in animal models. However, human evidence is scarce. We evaluated how prenatal exposure to PFAS associates with established serum biomarkers of liver injury and alterations in serum metabolome in children.

APPROACH AND RESULTS

We used data from 1,105 mothers and their children (median age, 8.2 years; interquartile range, 6.6-9.1) from the European Human Early-Life Exposome cohort (consisting of six existing population-based birth cohorts in France, Greece, Lithuania, Norway, Spain, and the United Kingdom). We measured concentrations of perfluorooctane sulfonate, perfluorooctanoate, perfluorononanoate, perfluorohexane sulfonate, and perfluoroundecanoate in maternal blood. We assessed concentrations of alanine aminotransferase, aspartate aminotransferase, and gamma-glutamyltransferase in child serum. Using Bayesian kernel machine regression, we found that higher exposure to PFAS during pregnancy was associated with higher liver enzyme levels in children. We also measured child serum metabolomics through a targeted assay and found significant perturbations in amino acid and glycerophospholipid metabolism associated with prenatal PFAS. A latent variable analysis identified a profile of children at high risk of liver injury (odds ratio, 1.56; 95% confidence interval, 1.21-1.92) that was characterized by high prenatal exposure to PFAS and increased serum levels of branched-chain amino acids (valine, leucine, and isoleucine), aromatic amino acids (tryptophan and phenylalanine), and glycerophospholipids (phosphatidylcholine [PC] aa C36:1 and Lyso-PC a C18:1).

CONCLUSIONS

Developmental exposure to PFAS can contribute to pediatric liver injury.

Perfluoroalkyl acids, hyperuricemia and gout in adults: Analyses of NHANES 2009-2014

BACKGROUND

Previous studies have reported a positive association of perfluoralkyl acids (PFAAs), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), with hyperuricemia. The objective of the study is to investigate whether there is an association between concurrent serum levels of several PFAAs and gout, serum uric acid (SUA) or hyperuricemia in the U.S. adult population as represented by the National Health and Nutrition Examination Survey (NHANES) 2009-2014 sample (n = 4917). The PFAAs investigated include PFOA, perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluorohexane sulfonic acid (PFHxS) and PFOS.

METHODS

This cross-sectional study used multivariate logistic regressions to analyze the association of single PFAAs with hyperuricemia and self-reported gout; the association with SUA was analyzed by multivariate linear regression. Analyses were adjusted for race/ethnicity, age, sex, education, alcohol consumption, smoking, serum cotinine, BMI, diabetes, hypertension, chronic kidney disease, and SUA (for gout only).

RESULTS

Higher quartile values of serum PFOA and PFHxS were associated with increased odds of self-reported gout. There was a positive association of SUA with increased levels of PFOA, PFNA, PFOS, PFHxS and PFDA. Higher quartile values of PFOA, PFNA, and PFHxS were associated with higher odds of hyperuricemia.

CONCLUSIONS

In this population-based cross-sectional analysis, we found an association between selected PFAAs and self-reported gout. We also confirmed previous reports of an association between several PFAAs and hyperuricemia. Our study suggests that exposure to PFAAs may be a risk factor for hyperuricemia and gout.

Perfluorooctanoic acid activates multiple nuclear receptor pathways and skews expression of genes regulating cholesterol homeostasis in liver of humanized PPARα mice fed an American diet

Humans are exposed to per- and polyfluoroalkyl substances (PFAS) in their drinking water, food, air, dust, and by direct use of consumer products. Increased concentrations of serum total cholesterol and low density lipoprotein cholesterol are among the endpoints best supported by epidemiology. The objectives of this study were to generate a new model for examining PFAS-induced dyslipidemia and to conduct molecular studies to better define mechanism(s) of action. We tested the hypothesis that perfluorooctanoic acid (PFOA) exposure at a human-relevant level dysregulates expression of genes controlling cholesterol homeostasis in livers of mice expressing human PPARα (hPPARα). Female and male hPPARα and PPARα null mice were fed a diet based on the "What we eat in America" analysis and exposed to PFOA in drinking water (8 μM) for 6 weeks. This resulted in a serum PFOA concentration of 48 μg/ml. PFOA increased liver mass, which was associated with histologically-evident lipid accumulation. Pooled analyses of serum lipoprotein cholesterol suggest that PFOA increased serum cholesterol, particularly in male mice. PFOA induced PPARα and constitutive androstane receptor target gene expression in liver. Expression of genes in four pathways regulating cholesterol homeostasis were also measured. PFOA decreased expression of Hmgcr in a PPARα-dependent manner. PFOA decreased expression of Ldlr and Cyp7a1 in a PPARα-independent manner. Apob expression was not changed. Sex differences were evident. This novel study design (hPPARα mice, American diet, long term exposure) generated new insight on the effects of PFOA on cholesterol regulation in the liver and the role of hPPARα.

Early-life exposure to perfluorinated alkyl substances modulates lipid metabolism in progression to celiac disease

Celiac disease (CD) is a systemic immune-mediated disorder with increased frequency in the developed countries over the last decades implicating the potential causal role of various environmental triggers in addition to gluten. Herein, we apply determination of perfluorinated alkyl substances (PFAS) and combine the results with the determination of bile acids (BAs) and molecular lipids, with the aim to elucidate the impact of prenatal exposure on risk of progression to CD in a prospective series of children prior the first exposure to gluten (at birth and at 3 months of age). Here we analyzed PFAS, BAs and lipidomic profiles in 66 plasma samples at birth and at 3 months of age in the Type 1 Diabetes Prediction and Prevention (DIPP) study (n = 17 progressors to CD, n = 16 healthy controls, HCs). Plasma PFAS levels showed a significant inverse association with the age of CD diagnosis in infants who later progressed to the disease. Associations between BAs and triacylglycerols (TGs) showed different patterns already at birth in CD progressors, indicative of different absorption of lipids in these infants. In conclusion, PFAS exposure may modulate lipid and BA metabolism, and the impact is different in the infants who develop CD later in life, in comparison to HCs. The results indicate more efficient uptake of PFAS in such infants. Higher PFAS exposure during prenatal and early life may accelerate the progression to CD in the genetically predisposed children.

Simultaneous determination of perfluoroalkyl substances and bile acids in human serum using ultra-high-performance liquid chromatography-tandem mass spectrometry

There is evidence of a positive association between per- and polyfluoroalkyl substances (PFASs) and cholesterol levels in human plasma, which may be due to common reabsorption of PFASs and bile acids (BAs) in the gut. Here we report development and validation of a method that allows simultaneous, quantitative determination of PFASs and BAs in plasma, using 150 μL or 20 μL of sample. The method involves protein precipitation using 96-well plates. The instrumental analysis was performed with ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS), using reverse-phase chromatography, with the ion source operated in negative electrospray mode. The mass spectrometry analysis was carried out using multiple reaction monitoring mode. The method proved to be sensitive, robust, and with sufficient linear range to allow reliable determination of both PFASs and BAs. The method detection limits were between 0.01 and 0.06 ng mL-1 for PFASs and between 0.002 and 0.152 ng mL-1 for BAs, with the exception of glycochenodeoxycholic acid (0.56 ng mL-1). The PFAS measured showed excellent agreement with certified plasma PFAS concentrations in NIST SRM 1957 reference serum. The method was tested on serum samples from 20 healthy individuals. In this proof-of-concept study, we identified significant associations between plasma PFAS and BA levels, which suggests that PFAS may alter the synthesis and/or uptake of BAs. Graphical Abstract.

Dose Effects of Ammonium Perfluorooctanoate on Lipoprotein Metabolism in APOE*3-Leiden.CETP Mice

Epidemiological studies have reported positive associations between serum perfluorooctanoic acid (PFOA) and total and non-high-density lipoprotein cholesterol (non-HDL-C) although the magnitude of effect of PFOA on cholesterol lacks consistency. The objectives of this study were to evaluate the effect of PFOA on plasma cholesterol and triglyceride metabolism at various plasma PFOA concentrations relevant to humans, and to elucidate the mechanisms using APOE*3-Leiden.CETP mice, a model with a human-like lipoprotein metabolism. APOE*3-Leiden.CETP mice were fed a Western-type diet with PFOA (10, 300, 30 000 ng/g/d) for 4-6 weeks. PFOA exposure did not alter plasma lipids in the 10 and 300 ng/g/d dietary PFOA dose groups. At 30 000 ng/g/d, PFOA decreased plasma triglycerides (TG), total cholesterol (TC), and non-HDL-C, whereas HDL-C was increased. The plasma lipid alterations could be explained by decreased very low-density lipoprotein (VLDL) production and increased VLDL clearance by the liver through increased lipoprotein lipase activity. The concomitant increase in HDL-C was mediated by decreased cholesteryl ester transfer activity and changes in gene expression of proteins involved in HDL metabolism. Hepatic gene expression and pathway analysis confirmed the changes in lipoprotein metabolism that were mediated for a major part through activation of the peroxisome proliferator-activated receptor (PPAR)α. Our data confirmed the findings from a phase 1 clinical trial in humans that demonstrated high serum or plasma PFOA levels resulted in lower cholesterol levels. The study findings do not show an increase in cholesterol at environmental or occupational levels of PFOA exposure, thereby indicating these findings are associative rather than causal.

Binding specificities of estrogen receptor with perfluorinated compounds: A cross species comparison

BACKGROUND

Perfluorinated compounds (PFCs) were reported to result in the endocrine disruption by activating the estrogen receptor (ER) and inducing ER-mediated transcriptions.

OBJECTIVE

The aim of the present work was to perform cross-species comparisons on the characteristics of eight PFCs binding to humans ERα and to rats ERα.

METHODS

In the present work, in vivo tests, including serum estradiol level assay and immunohistochemical staining, fluorescence assay and molecular models were applied.

RESULTS

Based on the in vivo experiments, the exposure of PFOA and PFOS to female rats was proved to increase the ERα expression in the terus, suggesting that PFCs may act as estrogenic compounds to activate ERα in vivo. The further fluorescence assay presented that these eight PFCs have stronger binding abilities to human ERα than to rat ERα. In addition, the differences in binding specificities between human ERα and rat ERα were identified in the process of molecular dynamics modeling with the term of helix position and the ability of coregulator recruitment. It can be found that more and stronger charge clamps could form between PFCs with human ERα than with rat ERα. Also, the eight PFCs presented lower binding energies in human ERα systems, which proved that eight PFCs presented much stronger binding abilities with human ERα.

DISCUSSION

In all, it can be concluded that PFCs might be more sensitive to human ERα than to that of rats, which also suggested the greater susceptibility to adverse effects on humans. The present work was a beginning assessment of a cross-species comparison, providing important information on health impacts of PFCs in humans.

Sex differences in the association between perfluoroalkyl acids and liver function in US adolescents: Analyses of NHANES 2013-2016

Perfluoroalkyl acids (PFAAs) are persistent in the environment, highly bio-accumulative in the body, and likely hepatotoxic in humans. There is evidence of sex-specific physiological responses to PFAA exposure. However, epidemiological studies seldom stratify the analyses by sex. Given the high prevalence of liver disease in general population adolescents, this study was designed to determine whether or not there is association between exposure to PFAAs and biomarkers of liver function in adolescent participants of the 2013-2016 National Health and Nutrition Examination Survey, and whether or not such association is sex-specific. Multivariate linear regressions were performed to examine the association between single PFAAs [perfluorooctane sulfonic acid (PFOS); linear form of perfluorooctanoic acid (PFOA); perfluorohexane sulfonic acid (PFHxS); perfluorononanoic acid (PFNA)], and biomarkers of liver function - gamma glutamyltransferase (GGT), aspartate aminotransferase (AST), alanine aminotransferase (ALT), and total bilirubin. Multivariate logistic regressions were performed to estimate adjusted odd ratios (aOR) of elevated ALT, AST and GGT. The study results show that, in females, there was a positive association of the highest PFOA quartile with increased ALT, AST and GGT, and the highest PFNA quartile with increased ALT and AST. Conversely, in male adolescents there was an association of the highest linear PFOA quartile with decreased ALT, and the highest PFNA quartile with ALT and AST. Females had higher odds of clinically-defined elevated ALT with increased PFOA (aOR = 1.79; 95% CI: 1.05, 3.04) or PFNA (aOR = 2.28; 95% CI: 1.08, 2.28), whereas males had decreased odds of clinically-defined elevated ALT with increased n-PFOA (aOR = 0.43; 95% CI: 0.20, 0.93) or PFNA (aOR = 0.5; 95% CI: 0.28, 0.89). In conclusion, there were sex differences in the association between serum PFAA levels and biomarkers of liver function. These results may provide support for analyzing sex-based adverse effects of PFAAs.

Per- and polyfluoroalkyl substances and blood lipid levels in pre-diabetic adults-longitudinal analysis of the diabetes prevention program outcomes study

Exposure to per- and polyfluoroalkyl substances (PFASs) may interfere with lipid regulation. However, most previous studies were cross-sectional with the risk of reverse causation, suggesting a need for long-term prospective studies. We examined the relationship of baseline plasma PFAS concentrations with repeated measures of blood lipids. We included 888 prediabetic adults from the Diabetes Prevention Program (DPP) and DPP Outcomes Study, who had measurements of 6 plasma PFAS concentrations at baseline (1996-1999) and repeated measures of blood lipids over 15 years of follow-up, and were initially randomized to placebo or a lifestyle intervention. We used linear regression to examine cross-sectional associations of PFAS concentrations and lipid levels at baseline, and evaluated prospective risks of hypercholesterolemia and hypertriglyceridemia using Cox proportional hazard models, and tested for effect modification by study arm. Participants (65.9% female, 57.0% White, 65.9% aged 40-59 years) had comparable PFAS concentrations [e.g., median (IQR) perfluorooctanoic acid (PFOA) 4.9 ng/mL (3.2)] with the general U.S. population in 1999-2000. We observed higher total cholesterol at baseline per doubling of PFOA (β: 6.1 mg/dL, 95% CI: 3.1, 9.04), perfluorohexane sulfonic acid (PFHxS, β: 2.2 mg/dL, 95% CI: 0.2, 4.3), and perfluorononanoic acid (PFNA, β: 2.9 mg/dL, 95% CI: 0.7, 5.0). Prospectively, baseline concentrations of several PFASs, including PFOA, PFOS, PFHxS and PFNA, predicted higher risks of incident hypercholesterolemia and hypertriglyceridemia, but only in the placebo group and not the lifestyle intervention group. For example, participants in the placebo group with PFOA concentration > median (4.9 ng/mL) were almost twice as likely (HR: 1.90, 95% CI: 1.25, 2.88) to develop hypertriglyceridemia compared to those ≤median. Findings suggest adverse effects of some PFASs on lipid profiles in prediabetic adults. However, the detrimental effect was attenuated with a lifestyle intervention.

Effects of perfluorooctanoic acid on stem Leydig cell functions in the rat

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic (PFOS) are two perfluorinated chemical products widely existing in the environment. Evidence suggested that PFOA might relate to male reproductive dysfunction in rats and humans. PFOA exposure inhibited the function of Leydig cells. However, it is still unknown whether PFOA affects stem Leydig cells (SLCs). In the present study, we examined the effects of a short-term exposure to PFOA on Leydig cell regeneration and also explored the possible mechanism involved. Thirty-six adult Sprague-Dawley rats were randomly divided into three groups and intraperitoneally injected with a single dose of 75 mg/kg ethane dimethyl sulfonate (EDS) to eliminate all Leydig cells. From post-EDS day 7, the 3 group rats received 0, 25 or 50 mg/kg/day PFOA (n = 12 per group) for 9 consecutive days. Exposure to PFOA significantly decreased serum testosterone levels by day 21 and day 56 post-EDS treatment. Also, the expression levels of Leydig cell specific genes (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Hsd11b1 and Cyp17a1) and their protein levels were all down-regulated. PFOA exposure may also affect proliferation of SLCs or their progeny since the numbers of PCNA-positive Leydig cells were reduced by post-EDS day 21. These in vivo observations were also confirmed by in vitro studies where the effects of PFOA were tested by culture of seminiferous tubules. In summary, PFOA exposure inhibits the development of Leydig cells, possibly by affecting both the proliferation and differentiation of SLCs or their progeny.

Maternal exposure to perfluorooctanoic acid (PFOA) causes liver toxicity through PPAR-α pathway and lowered histone acetylation in female offspring mice

The study was conducted to investigate the liver toxicity in female offspring mice induced by maternal exposure to perfluorooctanoic acid (PFOA). Fifty pregnant Kunming mice were randomly divided into 5 groups with 10 of each, which were treated with 0.2 mL PFOA solution dissolved with deionized water at 0, 1, 2.5, 5, and 10 mg/kg BW, respectively, from the pregnancy day (PND) 0 to day 17. Female offspring mice were sacrificed to collect serum and liver at postpartum day 21. The results showed that PFOA significantly reduced the body weight at weaning and the survival rate of the female offspring mice (P < 0.01) increased the liver index of the pups (P < 0.01). Meanwhile, PFOA also caused hepatic bleeding, local necrosis, and enlargement of hepatocytes and vacuolization. The levels of serum AST, ALT, SOD, and CAT in PFOA treatment group were upregulated significantly (P < 0.01). The expressions of Acot1, Acox1, and Acsl1 genes were increased significantly (P < 0.01). The expression of PPAR-α gene was decreased significantly (P < 0.01). There was no significant difference in the expression of Cpt1a gene among the 5 groups. HAT activity was reduced significantly and HDAC activity was increased significantly. The expression of anti-acetyl-histone H3 and acetyl-histone H4 was reduced significantly. Thus, our findings indicate that exposure to PFOA during pregnancy affects the growth and development of the pups and causes liver damage, disrupting the secretion of enzymes involved in fatty acid oxidation induced by PPAR-α, leading to liver oxidative stress and a decrease in the degree of histone acetylation. Elevated HDAC may aggravate downstream fatty acid metabolism disorders through PPAR-α.

Hepatic carboxylesterases are differentially regulated in PPARα-null mice treated with perfluorooctanoic acid

Hepatic carboxylesterases (Ces) catalyze the metabolism of drugs, environmental toxicants, and endogenous lipids and are known to be regulated by multiple nuclear receptors. Perfluorooctanoic acid (PFOA) is a synthetic fluorochemical that has been associated with dyslipidemia in exposed populations. In liver, PFOA can activate nuclear receptors such as PPARα, and alter the metabolism and excretion of chemicals. Here, we sought to test the ability of PFOA to modulate Ces expression and activity in the presence and absence of the PPARα receptor. For this purpose, male C57BL/6 NCrl mice were administered PFOA (1 or 3 mg/kg, po, 7 days) and livers collected for assessment of Ces expression and activity. PFOA increased Ces1 and 2 protein and activity. Notably, PFOA increased Ces1d, 1e, 1f, 1 g, 2c, and 2e mRNAs between 1.5- and 2.5-fold, while it decreased Ces1c and 2b. Activation of PPARα by PFOA was confirmed by up-regulation of Cyp4a14 mRNA. In a separate study of PFOA-treated wild-type (WT) and PPARα-null mice, induction of Ces 1e and 1f mRNA and in turn, Ces1 protein, was PPARα-dependent. Interestingly, in PPARα-null mice, Ces1c, 1d, 1 g, 2a, 2b, and 2e mRNAs and Ces2 protein were up-regulated by PFOA which contributed to sustained up-regulation of Ces activity, although to a lower extent than observed in WT mice. Activation of the CAR and PXR receptors likely accounted for up-regulation of select Ces1 and 2 subtypes in PPARα-null mice. In conclusion, the environmental contaminant PFOA modulates the expression and function of hepatic Ces enzymes, in part through PPARα.

Environmental perfluoroalkyl acid exposures are associated with liver disease characterized by apoptosis and altered serum adipocytokines

Exposures to perfluoroalkyl substances (PFAS) including perfluoroalkyl acids (PFAAs) are associated with increased liver enzymes in cohort studies including the C8 Health Study. In animal models, PFAAs disrupt hepatic lipid metabolism and induce apoptosis to cause nonalcoholic fatty liver disease (NAFLD). PFAAs are immunotoxic and inhibit pro-inflammatory cytokine release from stimulated leukocytes in vitro. This cross-sectional study tests the hypothesis that environmental PFAAs are associated with increased hepatocyte apoptosis and decreased pro-inflammatory cytokines in serum. Biomarkers previously associated with PFAS exposures and/or NAFLD were evaluated as secondary endpoints. Two hundred adult C8 Health Study participants were included. Measured serum biomarkers included: perfluorohexane sulfonate (PFHxS); perfluorooctanoic acid (PFOA); perfluorooctane sulfonate (PFOS); perfluorononanoic acid (PFNA); cytokeratin 18 M30 (CK18 M30, hepatocyte apoptosis); adipocytokines; insulin; and cleaved complement 3 (C3a). Confounder-adjusted linear regression models determined associations between PFAS and disease biomarkers with cut-offs determined by classification and regression tree analysis. CK18 M30 was positively associated with PFHxS (β = 0.889, p = 0.042); PFOA (β = 2.1, p = 0.005); and PFNA (β = 0.567, p = 0.03). Tumor necrosis factor α (TNFα) was inversely associated with PFHxS (β = -0.799, p = 0.001); PFOA (β = - 1.242, p = 0.001); and PFOS (β = -0.704, p < 0.001). Interleukin 8 was inversely associated with PFOS and PFNA. PFAAs were also associated with sexually dimorphic adipocytokine and C3a responses. Overall, PFAA exposures were associated with the novel combination of increased biomarkers of hepatocyte apoptosis and decreased serum TNFα. These data support previous findings from cohorts and experimental systems that PFAAs may cause liver injury while downregulated some aspects of the immune response. Further studies of PFAAs in NAFLD are warranted and should evaluate sex differences.

Roles of gender and obesity in defining correlations between perfluoroalkyl substances and lipid/lipoproteins

Data from National Health and Nutrition Examination Survey (NHANES) for 2005-2014 for those aged ≥20 years fasting for ≥8 h (N = 3629) were analyzed to evaluate the role that gender and obesity play in defining correlations between selected perfluoroalkyl substances (PFAS) and total cholesterol (TC), low density lipoprotein cholesterol (LDL), high density lipoprotein cholesterol (HDL), and triglycerides. PFAS considered for analyses were: perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), perfluorodecanoic acid (PFDA), perfluorononanoic acid (PFNA), perfluorohexane sulfonate (PFHxS), perfluoroundecanoic acid (PFUnDA), and 2-(N-methyl-perfluorooctane sulfonamido) acetic acid (Me-FOSAA). Gender and obesity stratified regression models were fitted to estimate associations between PFAS and lipid/lipoproteins with adjustments made for confounders. For obese males, but not for nonobese males, positive associations were found between TC and LDL with PFOA (β = 0.0519, p = 0.01 for TC and β = 0.0822, p = 0.03 for LDL), and PFNA (β = 0.0328, p = 0.03 for TC and β = 0.0679, p = 0.04 for LDL). For obese females, adjusted concentrations of TC increased with increase in the concentrations of PFDA (β = 0.0247, p = 0.048), PFNA (β = 0.0286, p = 0.04), and Me-PFOSAA (β = 0.0274, p = 0.02), and there was a positive association of LDL with PFOS (β = 0.0375, p = 0.04), PFDA (β = 0.0397, p = 0.047), and PFNA (β = 0.0593, p = 0.02). The findings, concerning the relationship of longer chain PFAS to serum lipids, suggest greater susceptibility to elevated TC and LDL cholesterol in the obese participants, with some differences between men and women. The key contributing modifiable risk for nonalcoholic steatosis is obesity, and, the development of nonalcoholic steatosis is recognized to be sexually dimorphic. The epidemiologic observation of a susceptible obese subgroup in our data is consistent with toxicology literature findings of disrupted cholesterol metabolism via induced steatosis following PFAS exposure. Gender differences affect serum concentration of PFAS during the reproductive years, and our data add a secondary question concerning whether they also affect the interaction between PFAS exposure and lipid handling in males and females.