Agonistic and potentiating effects of perfluoroalkyl substances (PFAS) on the Atlantic cod (Gadus morhua) peroxisome proliferator-activated receptors (Ppars)

Per- and polyfluoroalkyl substances alter innate immune function: evidence and data gaps

Per- and polyfluoroalkyl substances (PFASs) are a large class of compounds used in a variety of processes and consumer products. Their unique chemical properties make them ubiquitous and persistent environmental contaminants while also making them economically viable and socially convenient. To date, several reviews have been published to synthesize information regarding the immunotoxic effects of PFASs on the adaptive immune system. However, these reviews often do not include data on the impact of these compounds on innate immunity. Here, current literature is reviewed to identify and incorporate data regarding the effects of PFASs on innate immunity in humans, experimental models, and wildlife. Known mechanisms by which PFASs modulate innate immune function are also reviewed, including disruption of cell signaling, metabolism, and tissue-level effects. For PFASs where innate immune data are available, results are equivocal, raising additional questions about common mechanisms or pathways of toxicity, but highlighting that the innate immune system within several species can be perturbed by exposure to PFASs. Recommendations are provided for future research to inform hazard identification, risk assessment, and risk management practices for PFASs to protect the immune systems of exposed organisms as well as environmental health.

Unveiling the Molecular Effects of Replacement and Legacy PFASs: Transcriptomic Analysis of Zebrafish Embryos Reveals Surprising Similarities and Potencies

The prevalence of per- and poly fluoroalkyl substances (PFASs) in the environment has prompted restrictions on legacy PFASs due to their recognized toxic effects. Consequently, alternative "replacement" PFASs have been introduced and are prevalent in environmental matrices. Few studies have investigated the molecular effects of both legacy and replacement PFASs under short-term exposures. This study aimed to address this by utilizing transcriptomic sequencing to compare the molecular impacts of exposure to concentrations 0.001-5 mg/L of the legacy PFOS and two of its replacements, PFECHS and FBSA. Using zebrafish embryos, the research assessed apical effects (mortality, morphology, and growth), identified differentially expressed genes (DEGs) and enriched pathways, and determined transcriptomic points of departure (tPoDs) for each compound. Results indicated that PFOS exhibited the highest relative potency, followed by PFECHS and then FBSA. While similarities were observed among the ranked DEGs across all compounds, over-representation analysis revealed slight differences. Notably, PFOS demonstrated the lowest tPoD identified to date. These findings raise concerns regarding the safety of emerging replacement PFASs and challenge assumptions about PFAS toxicity solely resulting from their accumulative potential. As replacement PFASs proliferate in the environment, this study underscores the need for heightened scrutiny of their effects and questions current regulatory thresholds.

Neurotoxicity and intestinal microbiota dysbiosis induced by per- and polyfluoroalkyl substances in crucian carp (Carassius auratus)

Per- and polyfluoroalkyl substances (PFAS) have been called "forever chemicals" due to their inherent chemical stability. Their potential toxic effects on aquatic animals and health risk assessments have not been fully elucidated. In this study, we investigated the toxic effects of PFASs at environmentally relevant concentrations (200 ng/L) on crucian carp (Carassius auratus). The results showed that PFAS reduced the comfort behaviour of crucian carp and was associated with reduced levels of acetylcholinesterase and dopamine in the brain. PFAS exposure also decreased the activities of total superoxide dismutase, catalase and glutathione peroxidase, while increasing the levels of malondialdehyde. PFAS caused over-expression of the pro-inflammatory cytokines TNF-α, IFN-γ and stress-related genes Caspase-3, HSP-70 in the fish brain. Pathological staining showed that PFAS caused multifocal demyelination and perineural vacuolization in brain, intestinal tissue also showed reduced villus length and focal damage. PFASs altered the composition of the gut microbiota of crucian carp, significantly increasing the abundance of potentially pathogenic bacteria and the potential pathogenicity of the microbiota. It is suggested that PFASs may cause varying degrees of tissue damage by destabilising the gut microbiota. These results provide insights for assessing the toxicity of PFAS contaminants at aquatic environmental concentrations.

Effects of perfluoroalkyl sulfonic acids on developmental, physiological, and immunological measures in northern leopard frog tadpoles

The chronic toxicity of short chain perfluoroalkyl sulfonic acids (PFSAs), such as perfluorobutanesulfonic acid (PFBS) and perfluorohexanesulfonic acid (PFHxS), are relatively understudied despite the increasing detection of these compounds in the environment. We investigated the chronic toxicity and bioconcentration of PFBS and PFHxS using northern leopard frog (Rana [Lithobates] pipiens) tadpoles. We exposed Gosner stage (GS) 25 tadpoles to either PFBS or PFHxS at nominal concentrations of 0.1, 1, 10, 100, and 1000 μg/L until metamorphosis (GS42). We then assessed tadpole growth, development, stress, and immune metrics, and measured fatty acid (FA) composition and PFSA concentrations in liver and whole-body tissues. Tadpole growth and development measures were relatively unaffected by PFSA exposure. However, tadpoles exposed to 1000 μg/L PFBS or PFHxS had significantly increased hepatosomatic indexes (HSI) relative to controls. Further, tadpoles from the 1000 μg/L PFHxS treatment had altered FA profiles relative to controls, with increased total FAs, saturated FAs, monounsaturated FAs, and omega-6 polyunsaturated FAs. In addition, tadpoles from the 1000 μg/L PFHxS treatment had a higher probability of waterborne corticosterone detection. These results suggest that PFBS and PFHxS influence the hepatic health of tadpoles, and that PFHxS may alter lipid metabolism in tadpoles. We also observed a higher probability of tadpoles being phenotypically female after exposure to an environmentally relevant concentration (0.1 μg/L) of PFHxS, suggesting that PFHxS may exert endocrine disrupting effects on tadpoles during early development. The measured bioconcentration factors (BCFs) for both compounds were ≤10 L kg-1 wet weight, suggesting low bioconcentration potential for PFBS and PFHxS in tadpoles. Many of the significant effects observed in this study occurred at concentrations several orders of magnitude above those measured in the environment; however, our work shows effects of PFSAs exposure on amphibians and provides essential information for ecological risk assessments of these compounds.

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

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

Perfluorohexanesulfonic Acid (PFHxS) Impairs Lipid Homeostasis in Zebrafish Larvae through Activation of PPARα

Perfluorohexanesulfonic acid (PFHxS), an emerging short-chain per- and polyfluoroalkyl substance, has been frequently detected in aquatic environments. Adverse outcome pathway studies have shown that perfluorinated compounds impair lipid homeostasis through peroxisome proliferator activated receptors (PPARs). However, many of these studies were performed at high concentrations and may thus be a result of overt toxicity. To better characterize the molecular and key events of PFHxS to biota, early life-stage zebrafish (Danio rerio) were exposed to concentrations detected in the environment (0.01, 0.1, 1, and 10 μg/L). Lipidomic and transcriptomic evaluations were integrated to predict potential molecular targets. PFHxS significantly impaired lipid homeostasis by the dysregulation of glycerophospholipids, fatty acyls, glycerolipids, sphingolipids, prenol lipids, and sterol lipids. Informatic analyses of the lipidome and transcriptome indicated alterations of the PPAR signaling pathway, with downstream changes to retinol, linoleic acid, and glycerophospholipid metabolism. To assess the role of PPARs, potential binding of PFHxS to PPARs was predicted and animals were coexposed to a PPAR antagonist (GW6471). Molecular simulation indicated PFHxS had a 27.1% better binding affinity than oleic acid, an endogenous agonist of PPARα. Antagonist coexposures rescued impaired glycerophosphocholine concentrations altered by PFHxS. These data indicate PPARα activation may be an important molecular initiating event for PFHxS.

A novel molecular pathway of lipid accumulation in human hepatocytes caused by PFOA and PFOS

Exposed to ubiquitously perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) has been associated with non-alcoholic fatty liver disease (NAFLD), yet the underlying molecular mechanism remains elusive. The extrapolation of empirical studies correlating per- and polyfluoroalkyl substance (PFAS) exposure with NAFLD occurrence to real-life exposure was hindered by the limited availability of mechanistic data at environmentally relevant concentrations. Herein, a novel pathway mediating hepatocyte lipid accumulation by PFOA and PFOS at human-relevant dose (<10 μM) was identified by integrating CRISPR-Cas9 genome screening, concentration-dependent transcriptional assay in HepG2 cell and epidemiological data mining. 1) At genetic level, nudt7 showed the highest enriched potency among 569 NAFLD-related genes, and the transcription of nudt7 was significantly downregulated by PFOA and PFOS exposure (<7 μM). 2) At molecular pathway, upon exposure to ≤10-4 μM PFOA and PFOS, the downregulation of nudt7 transcriptional expression triggered the reduction of Ace-CoA hydrolase activity. 3) At cellular level, increased lipids were measured in HepG2 cells with PFOA and PFOS (<2 μM). Overall, we identified a novel mechanism mediated by transcriptional downregulation of nudt7 gene in hepatocellular lipid increase treated with PFOA and PFOS, which could potentially explain the NAFLD occurrence associated with exposure to PFASs in humans.

Interaction of Bisphenol A and Its Analogs with Estrogen and Androgen Receptor from Atlantic Cod (Gadus morhua)

The widespread use of bisphenol A (BPA) in polycarbonate plastics and epoxy resins has made it a prevalent environmental pollutant in aquatic ecosystems. BPA poses a significant threat to marine and freshwater wildlife due to its documented endocrine-disrupting effects on various species. Manufacturers are increasingly turning to other bisphenol compounds as supposedly safer alternatives. In this study, we employed in vitro reporter gene assays and ex vivo precision-cut liver slices from Atlantic cod (Gadus morhua) to investigate whether BPA and 11 BPA analogs exhibit estrogenic, antiestrogenic, androgenic, or antiandrogenic effects by influencing estrogen or androgen receptor signaling pathways. Most bisphenols, including BPA, displayed estrogenic properties by activating the Atlantic cod estrogen receptor alpha (gmEra). BPB, BPE, and BPF exhibited efficacy similar to or higher than that of BPA, with BPB and BPAF being more potent agonists. Additionally, some bisphenols, like BPG, induced estrogenic effects in ex vivo liver slices despite not activating gmEra in vitro, suggesting structural modifications by hepatic biotransformation enzymes. While only BPC2 and BPAF activated the Atlantic cod androgen receptor alpha (gmAra), several bisphenols exhibited antiandrogenic effects by inhibiting gmAra activity. This study underscores the endocrine-disrupting impact of bisphenols on aquatic organisms, emphasizing that substitutes for BPA may pose equal or greater risks to both the environment and human health.

Mixtures of legacy and replacement perfluorosulphonic acids (PFSAs) demonstrate ratio-, concentration- and endpoint-dependent synergistic interactions in vitro

The extensive use of poly- and per-fluoroalkyl substances (PFASs) has les to their widespread presence in the environment, raising concerns about potential toxicity. While certain PFASs of concern have been phased-out or banned, new PFASs continue to be produced. Two such substances are perfluoroethylcyclohexane sulphonate (PFECHS) and perfluorobutane sulphamide (FBSA), replacements of perfluoroctanesulphonic acid (PFOS) that have recently been detected in multiple environmental media around the globe. Despite PFASs generally occurring in the environment as mixtures, few data are available outlining the effects of PFAS mixtures. Therefore, this research investigated the interaction potential of binary and ternary mixtures of emerging and legacy PFASs. The immortalized rainbow trout gill cell line (RTgill-W1) was chosen as the experimental model to investigate two apical endpoints: cytotoxicity and phospholipidosis. RTgill-W1 cells were exposed for 24 h to each compound to obtain endpoint-specific effect concentrations (LCx; ECx). These values were then applied to formulate mixture predictions following the Loewes Additivity and Steel and Peckham methods. Based on cytotoxicity, relative potencies of individual compounds were: PFOS > PFECHS > FSBA. PFOS and PFECHS had nearly identical effects on phospholipidosis, while FSBA did not have any effects. Most mixtures had a synergistic effect on cytotoxicity, but the effect was both dose- and ratio-dependent. PFOS and PFECHS were additive at lower concentrations (LC10) and synergistic at higher concentrations (LC50; 3:1, 1:1, and 1:3). PFECHS and FSBA mixtures were synergistic at all doses and ratios (3:1, 1:1, 1:3), while FBSA and PFOS were mainly synergistic at higher concentrations and at ratios favouring PFOS (1:1, 1:3). Tertiary combinations were mainly synergistic. For phospholipidosis, mixtures were strictly additive. These results are strongly suggestive of synergism between emerging PFAS replacements and highlight that independent apical mechanisms of different PFASs could combine to induce unexpected toxicity. Considering that emerging replacements are continuing to increase in concentration in the environment, such mixture scenarios are also likely to continue to increase in probability.

Role of niche and micro-habitat preferences in per- and polyfluoroalkyl substances occurrence in the gills of tropical lake fish species

The present study has investigated per- and poly-fluoroalkyl substances (PFAS) in the gill tissues of various fish species inhabiting different trophic levels within Eleyele Lake, a tropical freshwater lake in Nigeria. The mean concentrations of PFAS congeners were determined, and their trends and patterns were analyzed across different trophic species. The results revealed variations in congener abundance and species-specific patterns that was influenced by habitat and niche preferences. Multivariate associations using canonical-correlation analysis (CCA) revealed distinct trends in the relationships between gill concentrations of specific PFAS congeners and different trophic groups. The strongest congener relationships were observed in the pelagic omnivore (Oreochromic niloticus: ON) with positive associations for 4:2 FTS, 9CL-PF3ONS, PFTDA, MeFOSA and PFHxS. The differences in congener profiles for the two herbivorous fish (Sarotherodon melanotheron (SM) and Coptodon galilaeus (CG)) reflect possible divergence in microhabitat and niche preferences. Furthermore, the congener overlaps between the herbivore (CG), and benthic omnivore (Clarias gariepinus: ClG) indicate a possible niche and microhabitat overlap. Our study provides valuable insights into the congener dynamics of PFAS at Eleyele Lake. However, the dissimilarity and overlapping PFAS congener profile in fish gills reflects the interplay of species niche preference and microhabitat associations. The present study highlights the need for further research to assess ecological risks and develop effective PFAS management strategies.

Metabolic, neurotoxic and immunotoxic effects of PFAAs and their mixtures on the proteome of the head kidney and plasma from rainbow trout (Oncorhynchus mykiss)

PFAAs (Perfluoroalkyl acids) are a class of bioaccumulative, persistent and ubiquitous environmental contaminants which primarily occupy the hydrosphere and its sediments. Currently, a paucity of toxicological information exists for short chain PFAAs and complex mixtures. In order to address these knowledge gaps, we performed a 3-week, aqueous exposure of rainbow trout to 3 different concentrations of a PFAA mixture (50, 100 and 500 ng/L) modeled after the composition determined in Lake Ontario. We conducted an additional set of exposures to individual PFAAs (25 nM each of PFOS (12,500 ng/L), PFOA (10,300 ng/L), PFBS (7500 ng/L) or PFBA (5300 ng/L) to evaluate differences in biological response across PFAA congeners. Untargeted proteomics and phosphorylated metabolomics were conducted on the blood plasma and head kidney tissue to evaluate biological response. Plasma proteomic responses to the mixtures revealed several unexpected outcomes including Similar proteomic profiles and biological processes as the PFOS exposure regime while being orders of magnitude lower in concentration and an atypical dose response in terms of the number of significantly altered proteins (FDR < 0.1). Biological pathway analysis revealed the low mixture, medium mixture and PFOS to significantly alter (FDR < 0.05) a number of processes including those involved in lipid metabolism, oxidative stress and the nervous system. We implicate plasma increases in PPARD and PPARG as being directly related to these biological processes as they are known to be important regulators in all 3 processes. In contrast to the blood plasma, the high mixture and PFOA exposure regimes caused the greatest change to the head kidney proteome, altering many proteins being involved in lipid metabolism, oxidative stress and inflammation. Our findings support the pleiotropic effect PFAAs have on aquatic organisms at environmentally relevant doses including those on PPAR signaling, metabolic dysregulation, immunotoxicity and neurotoxicity.

The Peroxisome Proliferator-Activated Receptors of Ray-Finned Fish: Unique Structures, Elusive Functions

The Actinopterygian and specifically the Teleostean peroxisome proliferator-activated receptors (PPARs) present an impressive variability and complexity in their structures, both at the gene and protein levels. These structural differences may also reflect functional divergence from their mammalian homologs, or even between fish species. This review, taking advantage of the data generated from the whole-genome sequencing of several fish species, highlights the differences in the primary structure of the receptors, while discussing results from the literature pertaining to the functions of fish PPARs and their activation by natural and synthetic compounds.

Effects of okadaic acid, azaspiracid-1, yessotoxin and their binary mixtures on human intestinal Caco-2 cells

Phycotoxins are responsible for foodborne intoxications. Symptoms depend on the ingested toxins but mostly imply gastro-intestinal and neurological disorders. Importantly, humans are exposed to combinations of several phycotoxins, resulting in possible mixture effects. Most previous studies, however, have been focused on single toxin effects. Thus, the aim of this study was to examine the effects of binary mixtures of three main phycotoxins, okadaic acid (OA), azaspiracid-1 (AZA1) and yessotoxin (YTX), on human intestinal Caco-2 cells. The focus was placed on cell viability studies and inflammation responses using a multi-parametric approach to assess cell population (nuclei staining), cell metabolism/viability (reductase activity and lysosomal integrity), and release of inflammation markers (e.g., interleukins). Mixture effects were evaluated using the concentration addition (CA) and independent action (IA) models. Our assays show that none of the toxins had an impact on the cell population in the tested concentration range. Only OA modulated reductase activity, while all three toxins had strong effects on lysosomal integrity. Furthermore, all toxins triggered the release of interleukin 8 (IL-8), with OA being most potent. Mixture effect analysis showed additivity in most cases. However, supra-additivity was observed in regards to IL-6 and IL-8 release for combinations implying high concentrations of OA. This study extends the knowledge on mixture effects of phycotoxins in human cells.

Association between prenatal exposure to per- and polyfluoroalkyl substances and infant anthropometry: A prospective cohort study

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic organic chemicals with potential endocrine-disrupting effects, and have been found to impair the physical growth of offspring in both experimental and epidemiological studies. We aimed to investigate the effects of prenatal PFAS exposure on repeated measurements of multiple anthropometric indicators in infants.

METHOD

PFAS were measured in serum samples collected from pregnant women at 12-16 gestational weeks. We calculated z-scores for the weight-for-age (WAZ), weight-for-length (WLZ), head circumference-for-age (HCZ), arm circumference-for-age (ACZ), triceps skinfold-for-age (TSZ), and subscapular skinfold-for-age (SSZ) at birth, 6 months, and 12 months of age according to the child growth standards of the World Health Organization (WHO) for anthropometric indicators. A total of 964 mother-infant pairs were included. A multivariate linear regression was performed to examine the associations between prenatal PFAS concentrations and anthropometric indicators at each time point. A generalized estimating equation (GEE) model was used to examine the longitudinal effects of PFAS exposure on repeated measurements of anthropometric indicators. Ultimately, a Bayesian kernel machine regression (BKMR) model was used to assess the joint effects of the PFAS mixture on anthropometric indicators.

RESULTS

In GEE models, perfluorododecanoic acid (PFDoA) in the high tertile group was associated with increased WAZ/WLZ, with β values (95% confidence intervals (CI)) of 0.12 (0.00, 0.23) and 0.18 (0.03, 0.32), respectively. Perfluorononanoic acid (PFNA) was associated with increased ACZ in the middle and high tertile groups. The BKMR models also presented the associations of the PFAS mixture with increased WAZ/WLZ throughout infancy, with more profound effects in females. Meanwhile, a pattern of inverse associations was observed between the perfluorooctanoic acid (PFOA) concentrations in the high tertile group and decreased WAZ, WLZ, and HCZ in males. In addition, the associations between PFAS and increased TSZ/SSZ at birth were identified by both linear regression and BKMR models.

CONCLUSION

Prenatal PFAS exposure (PFNA and PFDoA) was associated with increased infant anthropometry, especially in female infants, while prenatal PFOA exposure was associated with decreased weight, and head and arm circumference in male infants. The findings indicate that prenatal PFAS exposure may impair the growth trajectory of offspring.

Impact of perfluoroalkyl substances (PFAS) and PFAS mixtures on lipid metabolism in differentiated HepaRG cells as a model for human hepatocytes

Per- and polyfluoroalkyl substances (PFAS) are environmental contaminants with various adverse health effects in humans including disruption of lipid metabolism. Aim of the present study was to elucidate the molecular mechanisms of PFAS-mediated effects on lipid metabolism in human cells. Here, we examined the impact of a number of PFAS (PFOS, PFOA, PFNA, PFDA, PFHxA, PFBA, PFHxS, PFBS, HFPO-DA, and PMPP) and of some exposure-relevant PFAS mixtures being composed of PFOS, PFOA, PFNA and PFHxS on lipid metabolism in human HepaRG cells, an in vitro model for human hepatocytes. At near cytotoxic concentrations, the selected PFAS and PFAS mixtures induced triglyceride accumulation in HepaRG cells and consistently affected the expression of marker genes for steatosis, as well as PPARα target genes and genes related to lipid and cholesterol metabolism, pointing to common molecular mechanisms of PFAS in disrupting cellular lipid and cholesterol homeostasis. PPARα activation was examined by a transactivation assay in HEK293T cells, and synergistic effects were observed for the selected PFAS mixtures at sum concentrations higher than 25 µM, whereas additivity was observed at sum concentrations lower than 25 µM. Of note, any effect observed in the in vitro assays occurred at PFAS concentrations that were at least four to five magnitudes above real-life internal exposure levels of the general population.

Mixture Effects of Per- and Polyfluoroalkyl Substances on Embryonic and Larval Sheepshead Minnows (Cyprinodon variegatus)

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous and persistent environmental contaminants originating from many everyday products. Perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are two PFAS that are commonly found at high concentrations in aquatic environments. Both chemicals have previously been shown to be toxic to fish, as well as having complex and largely uncharacterized mixture effects. However, limited information is available on marine and estuarine species. In this study, embryonic and larval sheepshead minnows (Cyprinodon variegatus) were exposed to several PFAS mixtures to assess lethal and sublethal effects. PFOS alone was acutely toxic to larvae, with a 96 h LC50 of 1.97 mg/L (1.64-2.16). PFOS + PFOA resulted in a larval LC50 of 3.10 (2.62-3.79) mg/L, suggesting an antagonistic effect. These observations were supported by significant reductions in malondialdehyde (105% ± 3.25) and increases in reduced glutathione concentrations (43.8% ± 1.78) in PFOS + PFOA exposures compared to PFOS-only treatments, indicating reduced oxidative stress. While PFOA reduced PFOS-induced mortality (97.0% ± 3.03), perfluorohexanoic acid (PFHxA) and perfluorobutanoic acid (PFBA) did not. PFOS alone did not affect expression of peroxisome proliferator-activated receptor alpha (pparα) but significantly upregulated apolipoprotein A4 (apoa4) (112.4% ± 17.8), a downstream product of pparα, while none of the other individually tested PFAS affected apoa4 expression. These findings suggest that there are antagonistic interactions between PFOA and PFOS that may reduce mixture toxicity in larval sheepshead minnows through reduced oxidative stress. Elucidating mechanisms of toxicity and interactions between PFAS will aid environmental regulation and management of these ubiquitous pollutants.

Binding of Per- and Polyfluoroalkyl Substances (PFAS) to the PPARγ/RXRα-DNA Complex

Nuclear receptors are the fundamental building blocks of gene expression regulation and the focus of many drug targets. While binding to DNA, nuclear receptors act as transcription factors, governing a multitude of functions in the human body. Peroxisome proliferator-activator receptor γ (PPARγ) and the retinoid X receptor α (RXRα) form heterodimers with unique properties and have a primordial role in insulin sensitization. This PPARγ/RXRα heterodimer has been shown to be impacted by per- and polyfluoroalkyl substances (PFAS) and linked to a variety of significant health conditions in humans. Herein, a selection of the most common PFAS (legacy and emerging) was studied utilizing molecular dynamics simulations for PPARγ/RXRα. The local and global structural effects of PFAS binding on the known ligand binding pockets of PPARγ and RXRα as well as the DNA binding domain (DBD) of RXRα were inspected. The binding free energies were predicted computationally and were compared between the different binding pockets. In addition, two electronic structure approaches were utilized to model the interaction of PFAS within the DNA binding domain, density functional theory (DFT) and domain-based pair natural orbital coupled cluster with perturbative triples (DLPNO-CCSD(T)) approaches, with implicit solvation. Residue decomposition and hydrogen-bonding analysis were also performed, detailing the role of prominent residues in molecular recognition. The role of l-carnitine is explored as a potential in vivo remediation strategy for PFAS interaction with the PPARγ/RXRα heterodimer. In this work, it was found that PFAS can bind and act as agonists for all of the investigated pockets. For the first time in the literature, PFAS are postulated to bind to the DNA binding domain in a nonspecific manner. In addition, for the PPARγ ligand binding domain, l-carnitine shows promise in replacing smaller PFAS from the pocket.

Insight into the binding model of per- and polyfluoroalkyl substances to proteins and membranes

Legacy per- and polyfluoroalkyl substances (PFASs) have elicited much concern because of their ubiquitous distribution in the environment and the potential hazards they pose to wildlife and human health. Although an increasing number of effective PFAS alternatives are available in the market, these alternatives bring new challenges. This paper comprehensively reviews how PFASs bind to transport proteins (e.g., serum albumin, liver fatty acid transport proteins and organic acid transporters), nuclear receptors (e.g., peroxisome proliferator activated receptors, thyroid hormone receptors and reproductive hormone receptors) and membranes (e.g., cell membrane and mitochondrial membrane). Briefly, the hydrophobic fluorinated carbon chains of PFASs occupy the binding cavities of the target proteins, and the acid groups of PFASs form hydrogen bonds with amino acid residues. Various structural features of PFAS alternatives such as chlorine atom substitution, oxygen atom insertion and a branched structure, introduce variations in their chain length and hydrophobicity, which potentially change the affinity of PFAS alternatives for endogenous proteins. The toxic effects and mechanisms of action of legacy PFASs can be demonstrated and compared with their alternatives using binding models. In future studies, in vitro experiments and in silico quantitative structure-activity relationship modeling should be better integrated to allow more reliable toxicity predictions for both legacy and alternative PFASs.

Disclosing the bioaccumulation and biomagnification behaviors of emerging per/polyfluoroalkyl substances in aquatic food web based on field investigation and model simulation

Emerging poly/perfluoroalkyl substances (PFASs) have been widely detected in the environment, but their bioaccumulation and biomagnification behaviors are not well understood. We collected surface water, sediment, and various aquatic organisms from Lake Taihu, China. Several emerging PFASs, such as fluorotelomer sulfonates (FTSs), hexafluoropropylene oxides (HFPOs), and chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs) were frequently detected in water and sediment samples. The concentrations of HFPO trimer acid (HFPO-TA), 4,8-dioxa-3 H-per-fluorononanoate, and FTSs were remarkably higher than those reported previously, indicating that their application is increasing in Taihu Basin. These emerging PFASs displayed higher sediment/water partitioning coefficients (log K_oc) than the corresponding perfluoroalkyl acids (PFAAs) with the same perfluorinated carbon chain length. HFPOs and Cl-PFESAs were more labile to deposit in fish livers than perfluorooctanoic and perfluorooctane sulfonic acids, respectively. Both field investigations and model simulations indicated that HFPO-TA and Cl-PFESAs, as well as the hydrogen-substituted analogs of 6:2 Cl-PFESA (6:2 H-PFESA), were biomagnified along the aquatic food chain. The bioaccumulation model simulation revealed that the accumulation of these emerging PFASs in fish was mainly through dietary intake, whereas gill respiration and fecal excretion facilitated their elimination. Metabolic transformation might also contribute to their elimination relative to the legacy ones.

West African e-waste-soil assessed with a battery of cell-based bioassays

Soil samples randomly taken from major e-waste sites in West Africa (Nigeria, Benin and Ghana) were examined for an extensive range of organic contaminants. Cytotoxicity measurements and assessment of activation of xeno-sensing receptors from fish (Atlantic cod) were employed as a battery of in vitro biological assays to explore the quality and toxicity profile of West African e-waste soil. The concentrations of the measured contaminants of emerging concerns (CECs) and persistent organic pollutants (POPs) in the e-waste soil differs significantly from the reference soil with chemical profiles typically dominated by legacy polybrominated diphenyl ethers (PBDEs) (405.8 μgkg^-1) and emerging organophosphate ester flame retardant tris (1-chloro-2-propyl) phosphate (TCPP) (404 μgkg^-1), in addition to the short chain perfluorobutane sulfonate (PFBS) (275.3 μgkg^-1) and perfluorobutanoate (PFBA) (16 μgkg^-1). The study revealed that perfluorooctanoic acid (PFOA) occurred only in e-waste soil from Ghana and ranged from 2.6 to 5.0 μgkg^-1. Overall, non-polar e-waste soil-derived extracts had a stronger effect on COS-7 cell viability than the polar extracts and elutriates. The highest receptor activation was observed with single polar and non-polar extracts from the Nigeria and Benin sites, indicating hotspots with Er-, PPARa- and Ahr-agonist activities. Thus, the results obtained with our battery of in vitro biological assays underscored these e-waste sites as remarkably polluted spots with complex toxicity profiles of great concern for human and environmental health.

Integrative omics-analysis of lipid metabolism regulation by peroxisome proliferator-activated receptor a and b agonists in male Atlantic cod

Lipid metabolism is essential in maintaining energy homeostasis in multicellular organisms. In vertebrates, the peroxisome proliferator-activated receptors (PPARs, NR1C) regulate the expression of many genes involved in these processes. Atlantic cod (Gadus morhua) is an important fish species in the North Atlantic ecosystem and in human nutrition, with a highly fatty liver. Here we study the involvement of Atlantic cod Ppar a and b subtypes in systemic regulation of lipid metabolism using two model agonists after in vivo exposure. WY-14,643, a specific PPARA ligand in mammals, activated cod Ppara1 and Ppara2 in vitro. In vivo, WY-14,643 caused a shift in lipid transport both at transcriptional and translational level in cod. However, WY-14,643 induced fewer genes in the fatty acid beta-oxidation pathway compared to that observed in rodents. Although GW501516 serves as a specific PPARB/D ligand in mammals, this compound activated cod Ppara1 and Ppara2 as well as Pparb in vitro. In vivo, it further induced transcription of Ppar target genes and caused changes in lipid composition of liver and plasma. The integrative approach provide a foundation for understanding how Ppars are engaged in regulating lipid metabolism in Atlantic cod physiology. We have shown that WY-14,643 and GW501516 activate Atlantic cod Ppara and Pparb, affect genes in lipid metabolism pathways, and induce changes in the lipid composition in plasma and liver microsomal membranes. Particularly, the combined transcriptomic, proteomics and lipidomics analyses revealed that effects of WY-14,643 on lipid metabolism are similar to what is known in mammalian studies, suggesting conservation of Ppara functions in mediating lipid metabolic processes in fish. The alterations in the lipid profiles observed after Ppar agonist exposure suggest that other chemicals with similar Ppar receptor affinities may cause disturbances in the lipid regulation of fish. Model organism: Atlantic cod (Gadus morhua). LSID: urn:lsid:zoobank.org:act:389BE401-2718-4CF2-BBAE-2E13A97A5E7B. COL Identifier: 6K72F.