Investigation of the Interaction between Human Serum Albumin and Branched Short-Chain Perfluoroalkyl Compounds

Critical new insights into the interactions of hexafluoropropylene oxide-dimer acid (GenX or HFPO-DA) with albumin at molecular and cellular levels

A key characteristic to be elucidated, to address the harmful health risks of environmental perfluorinated alkyl substances (PFAS), is their binding modes to serum albumin, the most abundant protein in blood. Hexafluoropropylene oxide-dimer acid (GenX or HFPO-DA) is a new industrial replacement for the widespread linear long-chain PFAS. However, the detailed interaction of new-generation short-chain PFAS with albumin is still lacking. Herein, the binding characteristics of bovine serum albumin (BSA) to GenX were explored at the molecular and cellular levels. It was found that this branched short-chain GenX could bind to BSA with affinity lower than that of legacy linear long-chain perfluorooctanoic acid (PFOA). Site marker competitive study and molecular docking simulation revealed that GenX interacted with subdomain IIIA to form BSA-GenX complex. Consistent with its weaker affinity to albumin protein, the cytotoxicity of branched short-chain GenX was less susceptible to BSA binding compared with that of the linear long-chain PFOA. In contrast to the significant effects of strong BSA-PFOA interaction, the weak affinity of BSA-GenX binding did not influence the structure of protein and the cytotoxicity of GenX. The detailed characterization and direct comparisons of serum albumin interaction with new generation short-chain GenX will provide a better understanding for the toxicological properties of this new alternative.

Deriving Membrane-Water and Protein-Water Partition Coefficients from In Vitro Experiments for Per- and Polyfluoroalkyl Substances (PFAS)

The phospholipid membrane-water partition coefficients (KMW) and equilibrium binding affinities for human serum albumin (HSA) of 60 structurally diverse perfluoroalkyl and polyfluoroalkyl substances (PFAS) were evaluated through laboratory measurements and modeling to enhance our understanding of PFAS distribution in organisms. Per- and polyfluoroalkyl carboxylic acids exhibited a 0.36 ± 0.01 log-unit increase in KMW as the fluorinated carbon chain length increased from C4 to C16, while per- and polyfluoroalkyl sulfonates showed a 0.37 ± 0.02 log-unit increase. The highest HSA affinity range was observed between C6 and C10, with the following structural subclass order: per- and polyfluoroalkyl sulfonates ≈ ether sulfonic acids > polyfluoroalkyl carboxylic acids > fluorotelomer unsaturated carboxylic acids > phosphate diesters ≈ per- and polyfluoroether carboxylic acids. A comparison between association rate constants (KA) and HSA-PFAS molecular docking predictions with AutoDock Vina indicated that modeling could effectively predict the affinity of PFAS to HSA, especially for PFAS carbon chain lengths from C4 to C10. Based on in vitro results, exposure-dependent PFAS partitioning in organisms was modeled by comparing distribution coefficients between PFAS in phospholipid membranes and HSA at different PFAS concentrations and demonstrated that at lower concentrations, PFAS had higher partitioning in HSA, while with increasing concentration, the proportion of binding relative to the aqueous phase shifted toward the phospholipid membrane. Few studies have compared the bioaccumulation of PFAS in phospholipid membranes and HSA. This research reports that protein-water distribution coefficients are higher than membrane-water partitioning coefficients at lower PFAS concentrations, which may have implications for interpreting exposure data and toxicity experiments.

An in vitro and machine learning framework for quantifying serum albumin binding of per- and polyfluoroalkyl substances

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of anthropogenic chemicals; many are persistent, bioaccumulative, and mobile in the environment. Worldwide, PFAS bioaccumulation causes serious adverse health impacts, yet the physiochemical determinants of bioaccumulation and toxicity for most PFAS are not well understood, largely due to experimental data deficiencies. As most PFAS are proteinophilic, protein binding is a critical parameter for predicting PFAS bioaccumulation and toxicity. Among these proteins, human serum albumin (HSA) is the predominant blood transport protein for many PFAS. We previously demonstrated the utility of an in vitro differential scanning fluorimetry assay for determining relative HSA binding affinities for 24 PFAS. Here, we report HSA affinities for 65 structurally diverse PFAS from 20 chemical classes. We leverage these experimental data, and chemical/molecular descriptors of PFAS, to build 7 machine learning classifier algorithms and 9 regression algorithms, and evaluate their performance to identify the best predictive binding models. Evaluation of model accuracy revealed that the top-performing classifier model, logistic regression, had an AUROC (area under the receiver operating characteristic curve) statistic of 0.936. The top-performing regression model, support vector regression, had an R2 of 0.854. These top-performing models were then used to predict HSA-PFAS binding for chemicals in the EPAPFASINV list of 430 PFAS. These developed in vitro and in silico methodologies represent a high-throughput framework for predicting protein-PFAS binding based on empirical data, and generate directly comparable binding data of potential use in predictive modeling of PFAS bioaccumulation and other toxicokinetic endpoints.

Protocol for evaluating protein-polyfluoroalkyl substances in vitro using differential scanning fluorimetry

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous synthetic chemicals that threaten public health, and serum albumin binding of PFAS represents one major variable influencing PFAS toxicokinetics. In this protocol, we describe a differential scanning fluorimetry (DSF) assay suitable for the rapid determination of the relative binding affinities of serum albumin proteins to different PFAS. Herein, we address common experimental challenges related to PFAS solubility constraints, the high background fluorescence of DSF with serum albumins, and the limitations of using DSF-derived dissociation constants (KD) to quantify PFAS-albumin interactions. For complete details on the use and execution of this protocol, please refer to Jackson et al.1.

Albumin-based strategies to effectively prolong the circulation half-life of small immunomodulatory payloads in cancer therapy

Small immunomodulatory payloads (IMMs) such as peptide vaccines and cytokines have the capability to activate and boost the immune response against cancer. However, their clinical use has often been hindered by their poor stability and short circulating half-lives. To enhance the pharmacokinetic properties of small IMMs and promote their trafficking and accumulation in lymphatic and tumor tissues, a large variety of strategies have been developed. One of the most successful relies on the use of serum albumin (SA), the most abundant protein in the circulatory and lymphatic system. Here, we report a comparative analysis of the different covalent and noncovalent SA-based strategies applied so far to improve the efficacy of small IMMs in cancer therapy.

An in-depth examination of Per- and Polyfluoroalkyl (PFAS) effects on transporters, with emphasis on the ABC superfamily: A critical review

Per- and polyfluoroalkyl (PFAS) substances are a type of chemical compound unique for their multiple carbon-fluorine bonds, imbuing them with strength and environmental permanence. While legacy substances have been phased out due to human health risks, short-chain and alternative PFAS remain omnipresent. However, a detailed explanation for the pathways through which PFAS interact on a cellular and molecular level is still largely unknown, and the human health effects remain mechanistically unexplained. Of particular interest when focusing on this topic are the interactions between these exogenous chemicals and plasma and membrane proteins. Such proteins include serum albumin which can transport PFAS throughout the body, solute carrier proteins (SLC) and ATP binding cassette (ABC) transporters which are able to move PFAS into and out of cells, and proteins and nuclear receptors which interact with PFAS intracellularly. ABC transporters as a family have little available human data despite being responsible for the export of endogenous substances and drugs throughout the body. The multifactorial regulation of these crucial transporters is affected directly and indirectly by PFAS. Changes, which can include alterations to membrane transport activity and differences in protein expression, vary greatly depending on the specific PFAS and protein of interest. Together, the myriad of changes caused by understudied PFAS exposure to a class of understudied proteins crucial to cellular function and drug treatments has not been fully explored regarding human health and presents room for further exploration. This critical work aims to provide a novel framework of existing human data on PFAS and ABC transporters, allowing for future advancement and investigation into human transporter activity, mechanisms of regulation, and interactions with emerging contaminants.

In silico prediction of the interaction of legacy and novel per- and poly-fluoroalkyl substances (PFAS) with selected human transporters and of their possible accumulation in the human body

Per- and poly-fluorinated compounds constitute a wide group of fluorocarbon chemicals with widespread industrial applications, ranging from non-stick coating in cookware to water surfactants, from fire-fighting foams to water-repellent coatings on textiles. Presently, over 12,000 PFAS are known worldwide. In recent years, extensive research has focused on investigating the biological effects of these molecules on various organisms, including humans. Here, we conducted in silico simulations to examine the potential binding of a representative selection of PFAS to various human proteins known to be involved in chemical transportation and accumulation processes. Specifically, we targeted human serum albumin (HSA), transthyretin (TTR), thyroxine binding protein (TBG), fatty acid binding proteins (FABPs), organic anion transporters (OATs), aiming to assess the potential for bioaccumulation. Molecular docking simulations were employed for this purpose, supplemented by molecular dynamics (MD) simulations to account for protein flexibility, when necessary. Our findings indicate that so-called "legacy PFAS" such as PFOA or PFOS exhibit a higher propensity for interaction with the analysed human protein targets compared to newly formulated PFAS, characterised by higher branching and hydrophilicity, and possibly a higher accumulation in the human body.

Biochemical and haematological effects of serum PFOA, ADV and cC6O4 in workers of a chemical company producing fluoropolymers, Italy, 2013-2022

INTRODUCTION

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are widely used in the manufacture of fluoropolymers. We evaluated biochemical and haematological effects of three PFAS, serum perfluorooctanoic acid (PFOA), ADV, and cC6O4 in workers of a fluoropolymer company.

METHODS

Using data (2013-2022), we fitted random intercept regression models adjusted for several covariates and reciprocal adjustment between the three PFAS.

RESULTS

We analysed data of 814 workers (698 men, 116 women), 607 from the chemical plant, 207 from the research centre, for a total of 4912 blood samples (2065 with all three PFAS measured). Median levels of PFOA and ADV were 21.3 and 120 μg/L. Most (65.5%) cC6O4 measurements were below the limits of quantification (which varied over time from 5 to 0.1 μg/L). For PFOA, we observed positive associations with total cholesterol (+1.1% increase per ln(PFOA) increase) and apolipoprotein B (+1.4%) and negative associations with alkaline phosphatase (-1.5%); suggestive associations were also found with RBC (-0.4%), IgA (-1.5%), IgM (-1.4%). ADV was positively associated with total and LDL cholesterol (+1.0% and +1.6% per ln(ADV) increase), apolipoprotein B (+1.0%), GGT (+2.1%), IgM (+1.4%), and WBC (+1.5%) and negatively associated with direct bilirubin (-2.3%) and alpha-2-globulins (-0.7%); suggestive associations were found for indirect bilirubin (-2.0%), oestradiol (-2.1%), ad CRP (+6.0%). For samples with detectable cC6O4 levels we observed higher values of ALP (+2.3%), proteins (+0.5%), IgG (+0.7%) and platelets (+1.6%) and suggestively increased total bilirubin (+3.9%), RBC (+0.6%), and oestradiol (+5.8%). Some associations (total cholesterol, apolipoprotein B, WBC, total bilirubin, and alkaline phosphatase showed reverse time trends in parallel with the strong decrease of serum PFOA and ADV over the study period.

DISCUSSION

We found associations of serum PFOA and ADV with lipid metabolism, liver function, and immunoglobulins. The reverse time trends of some endpoints in parallel with decrease of serum PFOA and ADV reinforce causal interpretation of results. cC6O4 showed a different pattern of associations.

The pollutant perfluorohexane sulfonate (PFHxS) reduces serum thyroxine but does not alter thyroid action in the postnatal rat brain

Known as "forever chemicals", per- and polyfluoroalkyl substances (PFAS) are synthetic compounds used in consumer goods but pose significant public health concerns, including disruption of the thyroid system. As thyroid hormones (THs) are required for normal brain development, PFAS may also be developmental neurotoxicants. However, this is not well understood. Here we examine the endocrine and neurodevelopmental consequences of perfluorohexane sulfonate (PFHxS) exposure in pregnant, lactating, and developing rats, and compare its effects to an anti-thyroid pharmaceutical (propylthiouracil, PTU) that induces thyroid-mediated developmental neurotoxicity. We show that PFHxS dramatically reduces maternal serum thyroxine (T4), nearly equivalently to PTU (-55 and -51%, respectively). However, only PTU increases thyroid stimulating hormone. The lactational transfer of PFHxS is significant and reduces pup serum T4 across the postnatal period. Surprisingly, brain THs are only minimally decreased by PFHxS, whereas PTU drastically diminishes them. Evaluation of brain TH action by phenotyping, RNA-Sequencing, and quantification of radial glia cell morphology supports that PTU interrupts TH signaling while PFHxS has limited to no effect. These data show that PFHxS induces abnormal serum TH profiles; however, there were no indications of hypothyroidism in the postnatal brain. We suggest the stark differences between the neurodevelopmental effects of PFHxS and a typical antithyroid agent may be due to its interaction with TH distributing proteins like transthyretin.

Impact of perfluorooctanoic acid (PFOA) and perfluorobutanoic acid (PFBA) on oxidative stress and metabolic biomarkers in human neuronal cells (SH-SY5Y)

Perfluorinated alkyl substances (PFAS) are pervasive environmental contaminants that have attracted considerable attention due to their widespread utilization, resilient characteristics, adverse health implications, and regulatory scrutiny. Despite documented toxicity in living organisms, the precise molecular mechanisms governing the induced adverse effects remain unclear. This study aims to elucidate mechanisms of toxic action by collecting empirical data sets along oxidative stress and metabolic disruption pathways. We investigated the impact of long-chain PFAS (perfluorooctanoic acid (PFOA)) and its short-chain analog (perfluorobutanoic acid (PFBA)) on human neuronal cells (SH-SY5Y). The functionalities of enzymes associated with oxidative stress (catalase and glutathione reductase) and cellular metabolism (lactate dehydrogenase and pyruvate dehydrogenase) were also characterized. Our results reveal that a 24-hour exposure to PFOA and PFBA generated significant levels of reactive oxygen species. Correspondingly, there was a notable decline in catalase and glutathione reductase activities, with PFBA demonstrating a more pronounced effect. High concentrations of PFOA and PFBA reduced metabolic activity. Lactate dehydrogenase activity was only impacted by a high concentration of PFBA, while pyruvate dehydrogenase activity was decreased with PFBA exposure and increased with PFOA exposure. The findings from this study contribute to the knowledge of PFAS and cell interactions and reveal the potential underlying mechanisms of PFAS-induced toxicity.

Per- and poly-fluoroalkyl substances (PFAS) effects on lung health: a perspective on the current literature and future recommendations

Per- and poly-fluoroalkyl substances (PFAS) are a broad class of synthetic compounds widely used in commercial applications. The persistent nature of PFAS in the environment has earned them the epithet "forever chemicals." Concerns arise from widespread exposure to PFAS from occupational, household, and environmental sources. This widespread use of PFAS is particularly concerning, as emerging epidemiological evidence highlights their adverse effects on lung health. Such adverse impacts include impaired fetal lung development, reduced immune function in children, and potential links to lung cancer. Both in vivo and in vitro studies illuminate potential mechanisms underlying such adverse health outcomes subsequent to PFAS inhalation exposure, which may include immunomodulation, oxidative stress, and disruptions to epithelial barriers. However, evidence-based information focusing on the mechanisms of PFAS-mediated lung injury is lacking. Additionally, the discrepancies between data collected from animal and epidemiological studies highlight the need for improved approaches to better understand the toxicity results of PFAS exposure. To address these gaps, we recommend leveraging route-to-route extrapolation for risk assessment, prioritizing research on understudied PFAS, and adopting physiologically relevant, high-throughput approaches. These strategies are aimed at enhancing our understanding of PFAS inhalation effects, aiding in more informed risk management decisions. In this review, we summarize the current literature on PFAS exposure, emphasizing its adverse effects on lung health, particularly through inhalation. We then discuss the current knowledge on mechanisms underlying tissue- and cellular-level adverse outcomes caused by PFAS.

An Atomic and Molecular Insight into How PFOA Reduces α-Helicity, Compromises Substrate Binding, and Creates Binding Pockets in a Model Globular Protein

Per- and polyfluoroalkyl substances (PFAS) pose significant health risks due to their widespread presence in various environmental and biological matrices. However, the molecular-level mechanisms underlying the interactions between PFAS and biological constituents, including proteins, carbohydrates, lipids, and DNA, remain poorly understood. Here, we investigate the interactions between a legacy PFAS, viz. perfluorooctanoic acid (PFOA), and the milk protein β-lactoglobulin (BLG) obtained using a combination of experimental and computational techniques. Circular dichroism studies reveal that PFOA perturbs the secondary structure of BLG, by driving a dose-dependent loss of α-helicity and alterations in its β-sheet content. Furthermore, exposure of the protein to PFOA attenuates the on-rate constant for the binding of the hydrophobic probe 8-anilino-1-naphthalene sulfonic acid (ANS), suggesting potential functional impairment of BLG by PFOA. Steered molecular dynamics and umbrella sampling calculations reveal that PFOA binding leads to the formation of an energetically favorable novel binding pocket within the protein, when residues 129-142 are steered to unfold from their initial α-helical structure, wherein a host of intermolecular interactions between PFOA and BLG's residues serve to insert the PFOA into the region between the unfolded helix and beta-sheets. Together, the data provide a novel understanding of the atomic and molecular mechanism(s) by which PFAS modulates structure and function in a globular protein, leading to a beginning of our understanding of altered biological outcomes.

Quantitative cross-species comparison of serum albumin binding of per- and polyfluoroalkyl substances from five structural classes

Per- and polyfluoroalkyl substances (PFAS) are a class of over 8000 chemicals, many of which are persistent, bioaccumulative, and toxic to humans, livestock, and wildlife. Serum protein binding affinity is instrumental in understanding PFAS toxicity, yet experimental binding data is limited to only a few PFAS congeners. Previously, we demonstrated the usefulness of a high-throughput, in vitro differential scanning fluorimetry assay for determination of relative binding affinities of human serum albumin for 24 PFAS congeners from 6 chemical classes. In the current study, we used this assay to comparatively examine differences in human, bovine, porcine, and rat serum albumin binding of 8 structurally informative PFAS congeners from 5 chemical classes. With the exception of the fluorotelomer alcohol 1H, 1H, 2H, 2H-perfluorooctanol (6:2 FTOH), each PFAS congener bound by human serum albumin was also bound by bovine, porcine, and rat serum albumin. The critical role of the charged functional headgroup in albumin binding was supported by the inability of albumin of each species tested to bind 6:2 FTOH. Significant interspecies differences in serum albumin binding affinities were identified for each of the bound PFAS congeners. Relative to human albumin, perfluoroalkyl carboxylic and sulfonic acids were bound with greater affinity by porcine and rat serum albumin, and the perfluoroalkyl ether acid congener bound with lower affinity to porcine and bovine serum albumin. These comparative affinity data for PFAS binding by serum albumin from human, experimental model, and livestock species reduce critical interspecies uncertainty and improve accuracy of predictive bioaccumulation and toxicity assessments for PFAS.

Crystal structure of human serum albumin in complex with megabody reveals unique human and murine cross-reactive binding site

The pharmacokinetic properties of small biotherapeutics can be enhanced via conjugation to cross-reactive albumin-binding ligands in a process that improves their safety and accelerates testing through multiple pre-clinical animal models. In this context, the small and stable heavy-chain-only nanobody NbAlb1, capable of binding both human and murine albumin, has recently been successfully applied to improve the stability and prolong the in vivo plasma residence time of multiple small therapeutic candidates. Despite its clinical efficacy, the mechanism of cross-reactivity of NbAlb1 between human and murine serum albumins has not yet been investigated. To unveil the molecular basis of such an interaction, we solved the crystal structure of human serum albumin (hSA) in complex with NbAlb1. The structure was obtained by harnessing the unique features of a megabody chimeric protein, comprising NbAlb1 grafted onto a modified version of the circularly permutated and bacterial-derived protein HopQ. This structure showed that NbAlb1 contacts a yet unexplored binding site located in the peripheral region of domain II that is conserved in both human and mouse serum albumin proteins. Furthermore, we show that the binding of NbAlb1 to both serum albumin proteins is retained even at acidic pH levels, thus explaining its extended in vivo half-life. The elucidation of the molecular basis of NbAlb1 cross-reactivity to human and murine albumins might guide the design of novel nanobodies with broader reactivity toward a larger panel of serum albumins, thus facilitating the pre-clinical and clinical phases in humans.

Binding of Per- and Polyfluoroalkyl Substances (PFAS) to Serum Proteins: Implications for Toxicokinetics in Humans

Per- and polyfluoroalkyl substances (PFAS) are a diverse class of highly persistent anthropogenic chemicals that are detectable in the serum of most humans. PFAS exposure has been associated with many adverse effects on human health including immunotoxicity, increased risk of certain cancers, and metabolic disruption. PFAS binding to the most abundant blood serum proteins (human serum albumin [HSA] and globulins) is thought to affect transport to active sites, toxicity, and elimination half-lives. However, few studies have investigated the competitive binding of PFAS to these proteins in human serum. Here, we use C18 solid-phase microextraction fibers to measure HSA-water and globulin-water distribution coefficients (DHSA/w, Dglob/w) for PFAS with carbon chains containing 4 to 13 perfluorinated carbons (ηpfc = 4-13) and several functional head-groups. PFAS with ηpfc < 7 were highly bound to HSA relative to globulins, whereas PFAS with ηpfc ≥ 7 showed a greater propensity for binding to globulins. Experimentally measured DHSA/w and Dglob/w and concentrations of serum proteins successfully predicted the variability in PFAS binding in human serum. We estimated that the unbound fraction of serum PFAS varied by up to a factor of 2.5 among individuals participating in the 2017-2018 U.S. National Health and Nutrition Examination Survey. These results suggest that serum HSA and globulins are important covariates for epidemiological studies aimed at understanding the effects of PFAS exposure.

In vitro binding analysis of legacy-linear and new generation-cyclic perfluoro-alkyl substances on sex hormone binding globulin and albumin, suggests low impact on serum hormone kinetics of testosterone

In humans, serum testosterone (T) is largely bound to the sex hormone binding globulin (SHBG) and human serum albumin (hSA), resulting in a 2-3 % of unbound or "free" active quote (FT). Endocrine-disrupting chemicals, including perfluoro-alkyl substances (PFAS), are recognized to interfere with the hormonal axes, but the possible impact on the FT quote has not been addressed so far. Here we investigated the possible competition of two acknowledged PFAS molecules on T binding to SHBG and hSA. In particular, perfluoro-octanoic acid (PFOA) and acetic acid, 2,2-difluoro-2-((2,2,4,5-tetrafluoro-5(trifluoromethoxy)-1,3-dioxolan-4-yl)oxy)-ammonium salt (1:1) (C6O4) were used as, respectively, legacy-linear and new-generation-cyclic PFASs. Human recombinant SHBG 30-234 domain (SHBG30-234), produced in HEK293-F cells, and delipidated recombinant hSA were used as in vitro protein models. Isothermal Titration Calorimetry (ITC) and tryptophan fluorescence quencing (TFQ) were used to evaluate the binding modes of T and PFAS to SHBG30-234 and hSA. ITC revealed the binding of T to SHBG30-234 with a Kd of 44 ± 2 nM whilst both PFOA and C6O4 showed no binding activity. Results were confirmed by TFQ, since only T modified the fluorescence profile of SHBG30-234. In hSA, TFQ confirmed the binding of T on FA6 site of the protein. A similar binding mode was observed for PFOA but not for C6O4, as further verified by displacement experiments with T. Although both PFASs were previously shown to bind hSA, only PFOA is predicted to possibly compete with T for the binding to hSA. However, on the base of the binding stoichiometry and affinity of PFOA for hSA, this appears unlikely at the blood concentrations of the chemical documented to date.

Quantitative Cross-Species Comparison of Serum Albumin Binding of Per- and Polyfluoroalkyl Substances from Five Structural Classes

Per- and polyfluoroalkyl substances (PFAS) are a class of over 8,000 chemicals that are persistent, bioaccumulative, and toxic to humans, livestock, and wildlife. Serum protein binding affinity is instrumental in understanding PFAS toxicity, yet experimental binding data is limited to only a few PFAS congeners. Previously, we demonstrated the usefulness of a high-throughput, in vitro differential scanning fluorimetry assay for determination of relative binding affinities of human serum albumin for 24 PFAS congeners from 6 chemical classes. In the current study, we used this differential scanning fluorimetry assay to comparatively examine differences in human, bovine, porcine, and rat serum albumin binding of 8 structurally informative PFAS congeners from 5 chemical classes. With the exception of the fluorotelomer alcohol 1H,1H,2H,2H-perfluorooctanol (6:2 FTOH), each PFAS congener bound by human serum albumin was also bound by bovine, porcine, and rat serum albumin. The critical role of the charged functional headgroup in albumin binding was supported by the inability of serum albumin of each species tested to bind 6:2 FTOH. Significant interspecies differences in serum albumin binding affinities were identified for each of the bound PFAS congeners. Relative to human albumin, perfluoroalkyl carboxylic and sulfonic acids were bound with greater affinity by porcine and rat serum albumin, and perfluoroalkyl ether congeners bound with lower affinity to porcine and bovine serum albumin. These comparative affinity data for PFAS binding by serum albumin from human, experimental model and livestock species reduce critical interspecies uncertainty and improve accuracy of predictive toxicity assessments for PFAS.

Mechanistic Investigations of Thermal Decomposition of Perfluoroalkyl Ether Carboxylic Acids and Short-Chain Perfluoroalkyl Carboxylic Acids

In this study, we investigated the thermal decomposition mechanisms of perfluoroalkyl ether carboxylic acids (PFECAs) and short-chain perfluoroalkyl carboxylic acids (PFCAs) that have been manufactured as replacements for phased-out per- and polyfluoroalkyl substances (PFAS). C-C, C-F, C-O, O-H, and C═C bond dissociation energies were calculated at the M06-2X/Def2-TZVP level of theory. The α-C and carboxyl-C bond dissociation energy of PFECAs declines with increasing chain length and the attachment of an electron-withdrawing trifluoromethyl (-CF3) group to the α-C. Experimental and computational results show that the thermal transformation of hexafluoropropylene oxide dimer acid to trifluoroacetic acid (TFA) occurs due to the preferential cleavage of the C-O ether bond close to the carboxyl group. This pathway produces precursors of perfluoropropionic acid (PFPeA) and TFA and is supplemented by a minor pathway (CF3CF2CF2OCFCF3COOH → CF3CF2CF2· + ·OCFCF3COOH) through which perfluorobutanoic acid (PFBA) is formed. The weakest C-C bond in PFPeA and PFBA is the one connecting the α-C and the β-C. The results support (1) the C-C scission in the perfluorinated backbone as an effective PFCA thermal decomposition mechanism and (2) the thermal recombination of radicals through which intermediates are formed. Additionally, we detected a few novel thermal decomposition products of studied PFAS.

Short-chain per- and polyfluoralkyl substances (PFAS) effects on oxidative stress biomarkers in human liver, kidney, muscle, and microglia cell lines

Long-chain per- and polyfluoralkyl substances (PFAS) are ubiquitous contaminants implicated in the induction of intracellular reactive oxygen species (ROS), compromising antioxidant defense mechanisms in vitro and in vivo. While a handful of studies have assessed oxidative stress effects by PFAS, few specifically address short-chain PFAS. We conducted an evaluation of oxidative stress biomarkers in vitro following exposures to low (1 nM) and high (1 μM) concentrations of five short-chain PFAS compounds: perfluorobutanesulfonic acid (PFBS), perfluorohexanoic acid (PFHxA), [undecafluoro-2-methyl-3-oxahexanoic acid (HFPO-DA)], 6:2 fluorotelomer alcohol (6:2 FTOH) and perfluorohexanesulfonic acid (PFHxS). We conducted experiments in human kidney (HEK293-hTLR2), liver (HepaRG), microglia (HMC-3), and muscle (RMS-13) cell lines. Fluorescence microscopy measurements in HepaRG cells indicated ROS generation in cells exposed to PFBS and PFHxA for 24 h. Antioxidant enzyme activities were determined following 24 h short-chain PFAS exposures in HepaRG, HEK293-hTLR2, HMC-3, and RMS-13. Notably, exposure to PFBS for 24 h increased the activity of GPX in all four cell types at 1 μM and 1 nM in HepaRG and RMS-13 cells. Every short-chain PFAS evaluated, except for PFHxS, increased the activity of at least one antioxidant enzyme. To our knowledge, this is the first study of its kind to explore antioxidant defense alterations to microglia and muscle cell lines by PFAS. The findings of this study hold great potential to contribute to the limited understanding of short-chain PFAS mechanisms of toxicity and provide data necessary to inform the human health risk assessment process.

Haem-Mediated Albumin Biosensing: Towards Voltammetric Detection of PFOA

The haem group is a promising redox probe for the design of albumin-based voltammetric sensors. Among the endogenous ligands carried by human serum albumin (hSA), haem is characterised by a reversible redox behaviour and its binding kinetics strongly depend on hSA's conformation, which, in turn, depends on the presence of other ligands. In this work, the potential applicability of haem, especially hemin, as a redox probe was first tested in a proof-of-concept study using perfluorooctanoic acid (PFOA) as model analyte. PFOA is known to bind hSA by occupying Sudlow's I site (FA7) which is spatially related to the haem-binding site (FA1). The latter undergoes a conformational change, which is expected to affect hemin's binding kinetics. To verify this hypothesis, hemin:albumin complexes in the presence/absence of PFOA were first screened by UV-Vis spectroscopy. Once the complex formation was verified, haem was further characterised via electrochemical methods to estimate its electron transfer kinetics. The hemin:albumin:PFOA system was studied in solution, with the aim of describing the multiple equilibria at stake and designing an electrochemical assay for PFOA monitoring. This latter could be integrated with protein-based bioremediation approaches for the treatment of per- and polyfluoroalkyl substances polluted waters. Overall, our preliminary results show how hemin can be applied as a redox probe in albumin-based voltammetric sensing strategies.

PFASs in Soil: How They Threaten Human Health through Multiple Pathways and Whether They Are Receiving Adequate Concern

Per- and polyfluoroalkyl substances (PFASs) have been mass-produced and widely applied in consumer and industrial products, resulting in their widespread presence in the environment. Features such as environmental persistence, bioaccumulation, and high toxicity even at low doses have made PFASs an increasing concern. This brief review focuses on soil PFASs, especially the effect of soil PFASs on other environmental media and their potential threats to human health through daily diet. Specifically, soil PFASs contamination caused by different pathways was first investigated. Soil pollution from application of aqueous film-forming foams (AFFFs) is generally more severe than that from fluorochemical manufacturing plants, followed by biosolid land use, landfill, and irrigation. Factors, such as carbon chain length of PFASs, wastewater treatment technology, geographical conditions, and regional development level, are related to soil PFASs' pollution. Then, the migration, bioaccumulation, and toxicity characteristics of soil PFASs were analyzed. Short-chain PFASs have higher solubility, mobility, and bioavailability, while long-chain PFASs have higher bioaccumulation potential and are more toxic to organisms. Factors such as soil texture, solution chemistry conditions, enzymes, and fertilization conditions also influence the environmental behavior of PFASs. The risk of human exposure to PFASs through agricultural and animal products is difficult to control and varies depending on living region, age, eating habits, lifestyle, ethnicity, etc. Soil PFASs threaten drinking water safety, affect soil function, and enter food webs, threatening human health. Knowledge gaps and perspectives in these research fields are also included in current work to assist future research to effectively investigate and understand the environmental risks of soil PFASs, thereby reducing human exposure.