Prediction of the endocrine-disrupting ability of 49 per- and polyfluoroalkyl substances: In silico and epidemiological evidence

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

Per- and polyfluoroalkyl substances (PFAS) are in 99% of humans and are associated with a range of adverse health outcomes. It is impossible to test the >14,500 structurally diverse "forever chemicals" for safety, therefore improved assays to quantify structure-activity relationships are needed. Here, we determined the toxicity of a structurally distinct set of PFAS in 12 genetically diverse strains of the genetic model system Caenorhabditis elegans. Dose-response curves for perfluoroalkyl carboxylic acids (PFNA, PFOA, PFPeA, and PFBA), perfluoroalkyl sulfonic acids (PFOS and PFBS), perfluoroalkyl sulfonamides (PFOSA and PFBSA), fluoroether carboxylic acids (GenX and PFMOAA), fluoroether sulfonic acid (PFEESA), and fluorotelomers (6:2 FTCA and 6:2 FTS) were determined in the C. elegans laboratory reference strain, N2, and 11 genetically diverse wild strains. Body length was quantified after 48 h of developmental exposure of L1 arrest-synchronized larvae to estimate effective concentration values (EC50). PFAS toxicity ranged by 3 orders of magnitude. Long-chain PFAS had greater toxicity than short-chain. Fluorosulfonamides were more toxic than carboxylic and sulfonic acids. Genetic variation resulted in variation in susceptibility among 12 strains to almost all chemicals. Different C. elegans strains varied in susceptibility to different PFAS, which suggests distinct molecular responses to specific structural attributes. Harnessing the natural genetic diversity of C. elegans and the structural complexity of PFAS is a powerful approach that can be used to investigate mechanisms of toxicity which may identify potentially susceptible individuals or populations and predict toxicity of untested PFAS to inform regulatory policies and improve human and environmental health.

The impact of endocrine disrupting chemicals on adrenal corticosteroids - A systematic review of epidemiological studies

BACKGROUND

The role of endocrine disrupting chemicals (EDCs) in the development of metabolic syndrome has gained increasing recognition in recent years. The underlying mechanisms are largely unresolved. Disruption of corticosteroid action and hypothalamic-pituitary-adrenal (HPA) axis are considered possible mechanisms.

OBJECTIVE

To summarise epidemiological studies investigating an association between EDC concentration and altered levels of corticosteroids and the adrenocorticotropic hormone (ACTH).

METHODS

Following the PRISMA guidelines, we searched PubMed and the Cochrane Library for epidemiological studies published from database inception until April 1st, 2024. Various groups of EDCs were evaluated with the prerequisite of direct measurement of the chemical, a metabolite, or biomarker.

RESULTS

We identified 2094 articles. After removing duplicates and screening, 27 studies were included. Studies focused predominantly on glucocorticoids (n = 26) compared to mineralocorticoids (n = 5) and ACTH (n = 2). The most studied EDCs were pesticides (n = 9) and phthalates (n = 8). Significant associations between the concentrations of specific EDCs and hormone levels were found in all but three studies. Only one study described an association between EDCs, and hormone concentration and metabolic features.

CONCLUSION

There is clear evidence for the impact of specific EDCs on plasma corticosteroid concentrations in different age groups worldwide, however, results varied according to EDC class, study population and study methodology. Further research combining EDC and hormone concentrations, and clinical features, complemented by experimental investigations to study cell mechanisms, is needed to gain holistic knowledge of EDCs' influence on glucocorticoid- and mineralocorticoid-related disorders.

Per- and polyfluoroalkyl substances as persistent pollutants with metabolic and endocrine-disrupting impacts

The widespread use of per- and polyfluoroalkyl substances (PFASs), and their resistance to degradation, renders human exposure to them inevitable. PFAS exposure disturbs endocrine function, potentially affecting cognitive development in newborns through thyroid dysfunction during pregnancy. Recent studies reveal varying male and female reproductive toxicity across PFAS classes, with alternative analogs affecting sperm parameters and legacy PFASs correlating with conditions like endometriosis. Metabolically, PFASs exposure is linked to metabolic disorders, including obesity, type 2 diabetes mellitus (T2DM), dyslipidemia, and liver toxicity, particularly in early childhood. This review focuses on the endocrine-disrupting impact of PFASs, particularly on fertility, thyroid, and metabolic functions. We highlight the complexity of the PFAS issue, given the large number of molecules and their extremely diverse mixed effects.

PFAS (per- and polyfluorinated alkyl substances) as EDCs (endocrine-disrupting chemicals) - Identification of compounds with high potential to bind to selected terpenoids NHRs (nuclear hormone receptors)

The objective of the subsequent study was to examine the probability of PFAS (per- and polyfluorinated alkyl substances) binding to various NHRs (nuclear hormone receptors) and to identify their structural features that contribute most to the binding score (BS). We evaluated the BS for PFAS in relation to 7 selected NHRs - 4 with additional antagonist forms (Retinoid X receptor alpha - RXRα, Liver X receptor alpha - LXRα, Liver X receptor beta - LXRβ, Estrogen receptor alpha - ERα, Estrogen receptor alpha antagonist - anti-ERα, Estrogen receptor beta - ERβ, Estrogen receptor beta antagonist - anti-ERβ, Glucocorticoid receptor - GR, Glucocorticoid receptor antagonist - anti-GR, Androgen receptor - AR, Androgen receptor antagonist - anti-AR). We based our study on the results of molecular docking, which we used to develop MLR-QSAR (Multiple Linear Regression - Quantitative Structure-Activity Relationship) models. The models we developed allowed us to predict the BS for an extensive set of PFAS compounds from the NORMAN database (more than 4000) - virtual screening. The probability of PFAS binding to selected receptors was determined by structural features such as particle size, branching, and fluorine content. These variables were also identified in the literature reports of experimental studies as the most important for this group of compounds. The research focused on receptors from the terpenoid group. The RXRα, LXRα and β, GR, and anti-GR receptors were shown to be the group less likely to be affected by PFAS. Sex hormones such as AR, anti-AR, ERα and ERβ with their antagonist forms are the most affected.

Per- and polyfluoroalkyl substances (PFAS) and cancer: Detection methodologies, epidemiological insights, potential carcinogenic mechanisms, and future perspectives

Per- and polyfluoroalkyl substances (PFAS), known as "forever chemicals," are synthetic chemicals which have been used since the 1940s. Given their remarkable thermostability and chemical stability, PFAS have been widely utilized in commercial products, including textiles, surfactants, food packages, nonstick coatings, and fire-fighting foams. Thus, PFAS are widely distributed worldwide and have been detected in human urine, blood, breast milk, tissues and other substances. Growing concerns over the risks of PFAS, including their toxicity and carcinogenicity, have attracted people's attention. Recent reviews have predominantly emphasized advancements in the detection, adsorption, and degradation of PFAS through their chemical structures and toxic properties; however, further examination of the literature is needed to determine the link between PFAS exposure and cancer risk. Here, we introduced different PFAS detection methods based on sensors and liquid chromatography-mass spectrometry (LC-MS). Then, we discussed epidemiological investigations on PFAS levels and cancer risks in recent years, as well as the mechanisms underlying the carcinogenesis. Finally, we proposed the "4C principles" for ongoing exploration and refinement in this field. This review highlights PFAS-cancer associations to fill knowledge gaps and provide evidence-based strategies for future research.

Dioxins vs. PFAS: Science and Policy Challenges

BACKGROUND

Dioxin-like chemicals are a group of ubiquitous environmental toxicants that received intense attention in the last two decades of the 20th century. Through extensive mechanistic research and validation, the global community has agreed upon a regulatory strategy for these chemicals that centers on their common additive activation of a single receptor. Applying these regulations has led to decreased exposure in most populations studied. As dioxin-like chemicals moved out of the limelight, research and media attention has turned to other concerning contaminants, including per- and polyfluoroalkyl substances (PFAS). During the 20th century, PFAS were also being quietly emitted into the environment, but only in the last 20 years have we realized the serious threat they pose to health. There is active debate about how to appropriately classify and regulate the thousands of known PFAS and finding a solution for these "forever chemicals" is of the utmost urgency.

OBJECTIVES

Here, we compare important features of dioxin-like chemicals and PFAS, including the history, mechanism of action, and effective upstream regulatory strategies, with the objective of gleaning insight from the past to improve strategies for addressing PFAS.

DISCUSSION

The differences between these two chemical classes means that regulatory strategies for dioxin-like chemicals will not be appropriate for PFAS. PFAS exert toxicity by both receptor-based and nonreceptor-based mechanisms, which complicates mixtures evaluation and stymies efforts to develop inexpensive assays that accurately capture toxicity. Furthermore, dioxin-like chemicals were unwanted byproducts, but PFAS are useful and valuable, which has led to intense resistance against efforts to restrict their production. Nonetheless, useful lessons can be drawn from dioxin-like chemicals and applied to PFAS, including eliminating nonessential production of new PFAS and proactive investment in environmental remediation to address their extraordinarily long environmental persistence. https://doi.org/10.1289/EHP14449.

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

Background

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

Objectives

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

Methods

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

Results

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

Conclusion

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

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.

Priority list of potential endocrine-disrupting chemicals in food chemical contaminants: a docking study and in vitro/epidemiological evidence integration

Diet is an important exposure route of endocrine-disrupting chemicals (EDCs), but many unfiltered potential EDCs remain in food. The in silico prediction of EDCs is a popular method for preliminary screening. Potential EDCs in food were screened using Endocrine Disruptome, an open-source platform for inverse docking, to predict the binding probabilities of 587 food chemical contaminants with 18 human nuclear hormone receptor (NHR) conformations. In total, 25 contaminants were bound to multiple NHRs such as oestrogen receptor α/β and androgen receptor. These 25 compounds mainly include pesticides and per- and polyfluoroalkyl substances (PFASs). The prediction results were validated with the in vitro data. The structural features and the crucial amino acid residues of the four NHRs were also validated based on previous literature. The findings indicate that the screening has good prediction efficiency. In addition, the epidemic evidence about endocrine interference of PFASs in food on children was further validated through this screening. This study provides preliminary screening results for EDCs in food and a priority list for in vitro and in vivo research.

Hepatotoxicity assessment investigations on PFASs targeting L-FABP using binding affinity data and machine learning-based QSAR model

Per- and polyfluoroalkyl substances (PFASs) are persistent organic pollutants that have been detected in various environmental media and human serum, but their safety assessment remains challenging. PFASs may accumulate in liver tissues and cause hepatotoxicity by binding to liver fatty acid binding protein (L-FABP). Therefore, evaluating the binding affinity of PFASs to L-FABP is crucial in assessing the potential hepatotoxic effects. In this study, two binding sites of L-FABP were evaluated, results suggested that the outer site possessed high affinity to polyfluoroalkyl sulfates and the inner site preferred perfluoroalkyl sulfonamides, overall, the inner site of L-FABP was more sensitive to PFASs. The binding affinity data of PFASs to L-FABP were used as training set to develop a machine learning model-based quantitative structure-activity relationship (QSAR) for efficient prediction of potentially hazardous PFASs. Further Bayesian Kernel Machine Regression (BKMR) model disclosed flexibility as the determinant molecular property on PFASs-induced hepatotoxicity. It can influence affinity of PFASs to target protein through affecting binding conformations directly (individual effect) as well as integrating with other molecular properties (joint effect). Our present work provided more understanding on hepatotoxicity of PFASs, which could be significative in hepatotoxicity gradation, administration guidance, and safer alternatives development of PFASs.

Prediction of the Endocrine disruption profile of fluorinated biphenyls and analogues: An in silico study

Fluorinated biphenyls and their analogues (FBAs) are considered new persistent organic pollutants, but their endocrine-disrupting effects are still unknown. To fill this gap, the binding probability of 44 FBAs to different nuclear hormone receptors (NHRs) was predicted using Endocrine Disruptome. And molecular similarity and network toxicology analysis were used to strengthen the docking screening. The docking results showed that FBAs could have high binding potential for various NHRs, such as estrogen receptors β antagonism (ERβ an), liver X receptors α (LXRα), estrogen receptors α (ERα), and liver X receptors β (LXRβ). The similarity analysis found that the degree of overlap of the NHR repertoire was related to the Tanimoto coefficient of FBAs. Network toxicology verified a part of docking screening results and identified endocrine-disrupting pathways worthy of attention. This study found out potential endocrine-disrupting FBAs and their vulnerable, and developed a workflow that would leverage in silico approaches including molecular docking, similarity, and network toxicology for risk prioritization of potential endocrine-disrupting compounds.

How the Structure of Per- and Polyfluoroalkyl Substances (PFAS) Influences Their Binding Potency to the Peroxisome Proliferator-Activated and Thyroid Hormone Receptors-An In Silico Screening Study

In this study, we investigated PFAS (per- and polyfluoroalkyl substances) binding potencies to nuclear hormone receptors (NHRs): peroxisome proliferator-activated receptors (PPARs) α, β, and γ and thyroid hormone receptors (TRs) α and β. We have simulated the docking scores of 43 perfluoroalkyl compounds and based on these data developed QSAR (Quantitative Structure-Activity Relationship) models for predicting the binding probability to five receptors. In the next step, we implemented the developed QSAR models for the screening approach of a large group of compounds (4464) from the NORMAN Database. The in silico analyses indicated that the probability of PFAS binding to the receptors depends on the chain length, the number of fluorine atoms, and the number of branches in the molecule. According to the findings, the considered PFAS group bind to the PPARα, β, and γ only with low or moderate probability, while in the case of TR α and β it is similar except that those chemicals with longer chains show a moderately high probability of binding.

In utero exposure to a mixture of the perfluoroalkyl-isopropyl pesticide pyrifluquinazon with dibutyl phthalate cumulatively disrupts male rat reproductive development via different mechanisms of action

Administration of individual chemicals and mixtures during sexual differentiation that disrupt the androgen signaling pathway can induce reproductive abnormalities in male rats. In the current study, we co-administered the heptafluoroisopropyl pesticide pyrifluquinazon (PFQ), and dibutyl phthalate (DBP) to pregnant rats during sexual differentiation of the reproductive tract. Both chemicals have been shown to disrupt reproductive tract differentiation in a dose-related manner reducing male anogenital distance (AGD), permanently reducing androgen-dependent tissue weights and sperm counts, and inducing reproductive malformations in male offspring, albeit by different mechanisms of action that converge downstream in the androgen signaling pathway on a common key event. Rats were orally dosed from gestation days 14-18 with dilutions of PFQ and DBP at 0, 12.5, 25, 50, 75 and 100% of the top dose (100 mg/kg PFQ and 750 mg/kg DBP). The mixture ratio was selected such that each chemical would contribute equally to multiple effects on the male offspring reproductive tract and the dose range was designed to determine if the mixture produced additive effects predicted by dose addition or response addition models, or whether significant interactions occurred. Observed data were compared to dose and response addition model predictions. As hypothesized, the mixture reduced F1 male AGD, reproductive organ weights and sperm counts and induced hypospadias with dose addition consistently providing a better prediction of the observed effects than response addition. These results support our hypothesis that chemicals that disrupt the androgen signaling pathway induce dose-additive male reproductive abnormalities regardless of the specific mechanism of action.