A State-of-the-Science Review of Interactions of Per- and Polyfluoroalkyl Substances (PFAS) with Renal Transporters in Health and Disease: Implications for Population Variability in PFAS Toxicokinetics

Single-cell RNA sequencing reveals tissue-specific transcriptomic changes induced by perfluorooctanesulfonic acid (PFOS) in larval zebrafish (Danio rerio)

Perfluorooctanesulfonic acid (PFOS) elicits adverse effects on numerous organs and developmental processes but the mechanisms underlying these effects are not well understood. Here, we use single-cell RNA-sequencing to assess tissue-specific transcriptomic changes in zebrafish (Danio rerio) larvae exposed to 16 µM PFOS or dimethylsulfoxide (0.01 %) from 3-72 h post fertilization (hpf). Data analysis was multi-pronged and included pseudo-bulk, untargeted clustering, informed pathway queries, and a cluster curated for hepatocyte biomarkers (fabp10a, and apoa2). Overall, 8.63 % (2390/27698) genes were significantly differentially expressed. Results from untargeted analysis revealed 22 distinct clusters that were manually annotated to specific tissues using a weight-of-evidence approach. The clusters with the highest number of significant differentially expressed genes (DEGs) were digestive organs, muscle, and otolith. Additionally, we assessed the distribution of pathway-specific genes known to be involved in PFOS toxicity: the PPAR pathway, β-oxidation of fatty acids, the Nfe2l2 pathway, and epigenetic modifications by DNA methylation, across clusters and identified the blood-related tissue to be the most sensitive. The curated hepatocyte cluster showed 220 significant DEGs and was enriched for the Notch signaling pathway. These findings provide insights into both established and novel sensitive target tissues and molecular mechanisms of developmental toxicity of PFOS.

Perfluorooctanoic acid serum concentrations and half-lives in a community exposed to contaminated drinking water in New York State

BACKGROUND

Investigations during 2014-2016 in two communities in New York State showed perfluorooctanoic acid (PFOA) in a public system serving 3800 residents (Hoosick Falls) averaging 534 ppt and in a smaller system serving 200 residents (Petersburgh) averaging 92.5 ppt. Bottled water (2015-2016) was provided until filtration brought PFOA levels to non-detectable (2016-2017).

OBJECTIVE

The New York State Department of Health (NYSDOH) sought to address community questions about exposures and evaluate reductions in serum concentrations.

METHODS

NYSDOH tested serum PFOA in 2016 just after drinking water exposure mitigation and again in 2018. Descriptive statistics for serum PFOA by sex, age, length of residence, and water consumption were evaluated using multiple regression, and half-lives were estimated.

RESULTS

Using the serum PFOA GM and median for tests occurring within 3 months of exposure mitigation (N = 1121) (47.5, 54.2) produced serum to water ratios of 89.0 and 101.6. A total of 1573 Hoosick Falls public water consumers (337

IMPACT

This biomonitoring project assisted communities with PFOA-contaminated drinking water by providing comparative exposure information and tracking body burden reductions to confirm exposures were minimized. These data are also critical for filling gaps in knowledge about PFOA modes of action and for the conduct of studies that can identify exposure concentrations associated with health risks. The detailed PFOA serum findings described here are being used to construct and validate pharmacokinetic models that will estimate exposures over the lifespan. These findings provide a foundation for PFOA exposure assessment that will benefit the national Multi-Site PFAS Health Study and future studies as well.

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Key Words

• Biomonitoring
• Drinking water contamination
• Half-life
• Perfluorooctane sulfonate (PFOS)
• Perfluorooctanoic acid (PFOA)

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Affiliation(s)

Elizabeth L Lewis-Michl New York State Department of Health, Bureau of Environmental & Occupational Epidemiology, Division of Environmental Health Assessment, Albany, NY, USA.
Steven P Forand New York State Department of Health, Bureau of Environmental & Occupational Epidemiology, Division of Environmental Health Assessment, Albany, NY, USA
Wan-Hsiang Hsu New York State Department of Health, Bureau of Environmental & Occupational Epidemiology, Division of Environmental Health Assessment, Albany, NY, USA
Sanghamitra S Savadatti New York State Department of Health, Bureau of Environmental & Occupational Epidemiology, Division of Environmental Health Assessment, Albany, NY, USA University at Albany, Department of Epidemiology & Biostatistics, Rensselaer, NY, USA
Ming Liu New York State Department of Health, Bureau of Environmental & Occupational Epidemiology, Division of Environmental Health Assessment, Albany, NY, USA
June Moore New York State Department of Health, Bureau of Environmental & Occupational Epidemiology, Division of Environmental Health Assessment, Albany, NY, USA
Qian Wu New York State Department of Health, Wadsworth Center, Division of Environmental Health Science, Albany, NY, USA
Elizabeth J Mullin New York State Department of Health, Wadsworth Center, Division of Environmental Health Science, Albany, NY, USA
Kenneth M Aldous New York State Department of Health, Wadsworth Center, Division of Environmental Health Science, Albany, NY, USA

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Molecular Mechanisms of Perfluoroalkyl Substances Integration into Phospholipid Membranes

Understanding the molecular interactions of per- and polyfluoroalkyl substances (PFAS) with phospholipids is crucial for elucidating their pathological mechanisms and developing PFAS remediation strategies. In this study, we employ atomistic molecular dynamics simulations to examine PFAS insertion into phospholipid bilayers, including anionic perfluorooctanesulfonic acid (PFOS), perfluorobutanoic acid (PFBA), perfluorooctanoic acid (PFOA), and perfluorododecanoic acid (PFDoA), as well as neutral polytetrafluoroethylene (PTFE). Our study shows that PFAS insertion into lipid bilayers is driven by the free energy gradient between bulk water and the lipid membrane. Positively charged trimethylammonium groups of phospholipids attract negatively charged PFAS, overcoming the surface hydration barrier. Hydrophobic interactions between PFAS fluoroalkyl tails and lipid chains generate a significant driving force for PFAS reorientation and insertion. The increase in electrostatic potential across the lipid surface aids anionic PFAS insertion, but their dehydration hinders further movement. PFAS insertion enhances membrane ordering and decreases lipid fluidity, potentially affecting cellular functions by modifying membrane rigidity. The extended chain length of PFAS facilitates its interactions with the lipid membrane, resulting in a more pronounced influence on altering its structural and dynamic properties.

Estimation of species- and sex-specific PFAS pharmacokinetics in mice, rats, and non-human primates using a Bayesian hierarchical methodology

The carbon chain length, degree of fluorination, and functional group of per- and polyfluoroalkyl substances (PFAS) influences the bioaccumulation and half-lives of these substances in humans and laboratory animals. Pharmacokinetic (PK) studies using laboratory animals characterize the absorption, distribution, metabolism, and excretion (ADME) of a PFAS and can provide the underlying data for inter-species extrapolation to inform human pharmacokinetics. However, variations in ADME arise due to differences in protein binding and renal and hepatobiliary clearance mechanisms. In particular, sex- and species-specific differences in active transporter abundance and PFAS binding affinity challenge body weight-based extrapolation assumptions from animal models to human PK parameters. Because these protein-dependent changes in ADME do not always scale with species body weight, classic allometric scaling assumptions can fail to account for species-specific transporter-mediated clearance. In addition, study-dependent differences in pharmacokinetic modeling approaches and parameterization techniques can result in large differences among the PK parameters reported in the literature. To better quantify PFAS pharmacokinetics and characterize the underlying uncertainty, we implemented a Bayesian inference hierarchical model to estimate PFAS PK parameters for multiple species (mice, rats, and non-human primates) using numerous single-dose animal studies. Through an alternative parameterization of the one- and two-compartment models, this method improved parameter identifiability and allowed for the use of prior information on PFAS absorption rate, clearance, and volume of distribution. Using reported time-course concentration data, we estimated sex-specific clearance, volume of distribution, and half-life across mice, rats, and non-human primates using a consistent modeling methodology for eight PFAS: PFHxA, PFHxS, PFNA, PFDA, PFBS, PFBA, PFOA, and PFOS. The resulting comparison to available human data demonstrated that standard volume of distribution body-mass scaling (BW1) for PFAS generally agrees with reported human values while standard assumptions for allometric scaling of clearance (BW3/4) are not appropriate for most of the PFAS investigated in this study. In addition, we demonstrated that there may be considerable differences in clearance for PFAS in some species when comparing across different sexes and routes of exposure.

High-throughput screening of protein interactions with per- and polyfluoroalkyl substances (PFAS) used in photolithography

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals used extensively across industries, including semiconductor manufacturing. Semiconductors are ubiquitous, and there is increasing global demand for semiconductors, e.g., for advanced technologies and the automotive industry. Despite their extensive use, the toxicity and bioaccumulation potential of PFAS used in photolithography, a critical process in semiconductor manufacturing, remain poorly understood. Moreover, most lack experimental data and standards for testing. Here, we identified 96 photolithography-relevant PFAS and developed a computational framework to evaluate their potential hazards through protein binding. By integrating molecular dynamics (MD) and docking, we predicted the binding affinities and positions of PFAS to five proteins-liver fatty acid binding protein (LFABP), serum albumin (SA), peroxisome proliferator-activated receptors α and γ (PPARα and PPARγ), and transthyretin (TTR). These proteins were chosen as their binding with PFAS has been linked to PFAS bioaccumulation and to hepatic, reproductive, developmental, and endocrine disruption. Comparisons with empirical data demonstrated our approach balances simulation speed and robustness, better estimating absolute and relative binding affinities than docking alone. PFAS-protein binding affinities were generally positively associated with fluorinated chain length and the presence of aromatic rings, but limited by the protein binding pocket dimensions. Notably, we identified 22 PFAS with stronger predicted binding than perfluorooctane sulfonic acid (PFOS), a known hazardous PFAS, to at least one target protein, suggesting the potential for toxicological concern. By enabling proactive evaluation of PFAS that are unavailable for experimental testing, this work contributes to safeguarding environmental and human health amidst rising semiconductor demands.

Paternal and Maternal Exposures to Per- and Polyfluoroalkyl Substances and Child Behavioral Difficulties: A Parental Comparison Study

Per- and polyfluoroalkyl substances (PFAS) are widespread environmental pollutants with documented developmental toxicity. Prior research of prenatal PFAS exposure and offspring neurodevelopment did not consider the possible influence from paternal exposure. Using the INUENDO cohort, we studied 334 father-mother-singleton triads enrolled from antenatal clinics in Greenland, Poland, and Ukraine. We measured five PFAS in parental serum samples collected around the 31 weeks of gestation. We assessed child behavioral difficulties at ages 5-9 years by the parent-rated Strength and Difficulties Questionnaire using country- and sex-specific cut-offs (≥90th percentile). We performed analyses stratified by child's sex, coadjusting for maternal or paternal PFAS and other confounders and estimating PFAS mixture effects using quantile g-computation. In male children, multiple maternal PFAS, modeled as individual chemicals or a mixture, were associated with externalizing difficulties. Maternal perfluorononanoic acid (PFNA) was associated with internalizing difficulties in female children. In contrast, paternal exposure to individual PFAS or PFAS mixture was not associated with behavioral difficulties in children of either sex. In summary, maternal prenatal exposure to PFAS, but not paternal PFAS, was associated with mid-childhood behavioral difficulties in a sex-specific manner. Comparing the parent-specific PFAS associations strengthened evidence against confounding shared in the family.

Association between exposure to per- and polyfluoroalkyl substances and kidney function: a population study

Background

The relationship between per- and polyfluoroalkyl substances (PFAS) and kidney function markers remains uncertain.

Methods

We used PFAS detection data from 5,947 adults in NHANES 2005-2012. We employed multivariable linear regression models to examine associations between PFAS and estimated glomerular filtration rate (eGFR), urine creatinine (UCR), urine albumin (UAL), and urine albumin/creatinine ratio (UACR). To capture non-linear trends, restricted cubic splines were applied. The WQS (weighted quantile sum) and Q-gcomp (quantile g computation) models were used for the mixture analysis. Subgroup analyses were conducted to explore potential interactions.

Results

Perfluorooctanoic acid (PFOA), perfluorooctane sulfonic acid (PFOS), perfluorohexane sulfonic acid (PFHxS), 2-(N-methyl-perfluorooctane sulfonamido) acetic acid (N-MEFOSAA), and perfluorononanoic acid (PFNA) were negatively related to eGFR (β = -2.04, 95% CI = -2.85, -1.23; β = -0.97, 95% CI = -1.78, -0.16; β = -1.50, 95% CI = -2.24, -0.76; β = -0.49, 95% CI = -1.25, 0.27; β = -0.68, 95% CI = -1.46, 0.10). PFOA and PFOS were positive associated with UCR (β = 10.61, 95% CI = -1.89, 23.11; β = 12.98, 95% CI = 0.56, 25.41). PFOA, PFOS, PFHxS, PFNA, and PFUA were negatively related to UAL (β = -0.53, 95% CI = -0.73, -0.32; β = -0.39, 95% CI = -0.59, -0.18; β = -0.59, 95% CI = -0.78, -0.40; β = -0.42, 95% CI = -0.65, -0.19; β = -0.04, 95% CI = -0.22, 0.14). PFDA, PFOA, PFOS, PFHxS, and PFNA are significantly inversely associated with UACR (β = -0.01, 95% CI = -0.16, 0.14; β = -0.52, 95% CI = -0.69, -0.35; β = -0.50, 95% CI = -0.67, -0.33; β = -0.49, 95% CI = -0.64, -0.33; β = -0.27, 95% CI = -0.44, -0.10). Nonlinear relationships were found between PFAS and all kidney function indicators. Mixed PFAS exposure showed a negative association with eGFR, UAL and UACR, while showed a positive relationship with UCR. Interactions between PFASs and most subgroups were observed.

Conclusion

Our study revealed significant associations between PFAS exposure and various kidney function indicators. These findings provide an epidemiological perspective on how PFAS may lead to kidney dysfunction.

Per- and poly-fluoroalkyl substances (PFAS) in circulation in a Canadian population: their association with serum-liver enzyme biomarkers and piloting a novel method to reduce serum-PFAS

Extensive use of per- and polyfluoroalkyl substances (PFAS) has resulted in their ubiquitous presence in human blood. PFAS exposures have been associated with multiple adverse human health effects. Biomonitoring studies have focused on long-chain PFASs, but these are being replaced by short-chain PFASs or with alternate PFAS chemistries (or replacement chemistries such as GenX), resulting in changes in human exposures with time. Here, we take advantage of serum samples collected as part of a clinical trial testing the efficacy of a dietary fiber intervention to reduce serum cholesterol to investigate exposure to PFASs in Canadian participants. Serum samples were collected from 72 participants (adult males with elevated cholesterol) in 2019-2020 at baseline and after 4 weeks of the intervention and were analyzed for 17 PFASs. The highest geometric mean serum concentrations of PFAS measured at baseline corresponded to PFOSA (7.1 ng/ml), PFOS (4.2, ng/ml), PFOA (1.8 ng/ml) and PFHxS (1.3 ng/ml). Four long-chain PFASs (PFOA, PFOS, PFOSA and PFHxS) and two short-chain PFASs (PFBA, PFHxA) were detected in 100% of participants. GenX was detected in 71% of participants. Analyses of associations between serum-PFAS concentrations and biomarkers of adverse health outcomes showed the PFBA, PFHxA, PFDA and PFOSA were associated with higher serum gamma-glutamyl transferase concentrations but not with measures of serum-total or low-density lipoprotein cholesterol. Comparison of PFAS concentrations at baseline and after a 4-week follow-up showed that the total PFAS detected decreased in both the control and cholesterol intervention groups. However, the suite of long-chain PFASs of concern identified by the United States National Academies of Sciences, Engineering, and Medicine, significantly decreased only in the cholesterol intervention group. This observation suggests that a sustained dietary fiber intervention may reduce long-chain PFAS body burden, but future intervention studies need to control for PFAS exposure sources and extend the dietary supplement intake beyond 4 weeks. Overall, the results show that exposures to short-chain and replacement chemistry PFASs are common in this Canadian population.

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 twelve 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 eleven genetically diverse wild strains. Body length was quantified after 48 hr of developmental exposure of L1 arrest-synchronized larvae to estimate effective concentration values (EC50). PFAS toxicity ranged by three orders of magnitude. Long-chain PFAS had greater toxicity than short-chain and fluorosulfonamides were more toxic than carboxylic and sulfonic acids. Genetic variation resulted in variation in susceptibility among twelve 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.

An oat fiber intervention for reducing PFAS body burden: A pilot study in male C57Bl/6 J mice

Perfluoroalkyl substances (PFAS) are a major public health concern, in part because several PFAS have elimination half-lives on the order of years and are associated with adverse health outcomes. While PFAS can be transported into bile, their efficient reuptake by intestinal transporter proteins results in minimal fecal elimination. Here, we tested the hypothesis that consumption of oat β-glucan, a dietary supplement known to disrupt the enterohepatic recirculation of bile acids, will reduce PFAS body burdens. Male C57Bl/6 J mice were fed diets based on the "What we eat in America" analysis that were supplemented with inulin or oat β-glucan and exposed via drinking water to a seven PFAS mixture (PFHpA, PFOA, PFNA, Nafion Byproduct-2, PFHxS and PFOS) for 6 weeks. One cohort of mice was euthanized at the end of the exposure, and one cohort continued on the experimental diets for 4 more weeks without additional PFAS exposure. The β-glucan fed mice drank significantly more water than the inulin fed mice, resulting in a significantly higher dose of PFAS. Relative to overall exposure, we observed lower serum concentration trends (p < 0.1) in β-glucan fed mice for PFHpA, PFOA and PFOS. Additionally, β-glucan fed mice had lower adipose:body weight ratios and liver and jejunum triglyceride concentrations. Hepatic mRNA expression of Cyp4a10, Cyp2b10 and Cyp3a11 were elevated in PFAS exposed mice, with only the expression of Cyp3a11 decreasing following depuration. This pilot study generates support for the hypothesis that oat β-glucan supplementation can reduce PFAS body burdens and stimulate healthful effects on lipid homeostasis.

Per- and Polyfluoroalkyl Substances and Female Health Concern: Gender-based Accumulation Differences, Adverse Outcomes, and Mechanisms

The deleterious health implications of perfluoroalkyl and polyfluoroalkyl substances (PFAS) are widely recognized. Females, in contrast to males, exhibit unique pathways for PFAS exposure and excretion, leading to complex health outcomes. The health status of females is largely influenced by hormone-related processes. PFAS have been reported to be associated with various aspects of female health, including reproductive system disorders and pregnancy-related diseases. In this article, we provide insights into the correlations between PFAS and female-prevalent diseases. Current epidemiological and toxicological evidence has demonstrated that the adverse effects of PFAS on the health of the female reproductive system are primarily attributed to the disruption of the hypothalamic-pituitary-gonadal (HPG) axis and hormonal homeostasis. However, these findings do not sufficiently elucidate the intricate associations between PFAS and specific diseases. Furthermore, autoimmune disorders, another category that is more prevalent in women compared to men, require additional investigation. Immune biomarkers pertinent to autoimmune disorders have been observed to be influenced by PFAS exposure, although epidemiological evidence is insufficient to substantiate these relations. Further thorough exploration encompassing epidemiological and toxicological studies is essential to elucidating the inherent influence of PFAS on human pathologies. Additionally, comprehensive investigations into female health issues beyond their reproductive functions is essential.

Hexafluoropropylene Oxide Trimer Acid Is an Unsafe Substitute to Perfluorooctanoic Acid Due to Its Remarkable Liver Accumulation in Mice Disclosed by Comprehensive Toxicokinetic Models

Hexafluoropropylene oxide trimer acid (HFPO-TA, C2F5(CF2OCF(CF3))2COOH) is widely used as an alternative to perfluorooctanoic acid (PFOA), but whether it is a safe alternative requires further evaluation. In this study, male mice were exposed to three dosages (0.56, 2.8, and 14 mg/kg) of HFPO-TA via single oral gavage or intravenous injection for 28 days. HFPO-TA was rapidly absorbed into the blood and tissues within 15 min postexposure, with a volume of distribution approximately 3 times higher than PFOA, indicating a greater propensity for tissue distribution. Notably, HFPO-TA was distinctly more accumulated in liver compared to plasma and other tissues and very poorly excreted, with only 2.23% in urine and 7.26% in feces on the 21st day after oral exposure. A physiologically based toxicokinetic model, extrapolated to long-term low-dose exposure, revealed a lower bile clearance rate (8-fold) and higher liver partition coefficient (7-fold) than PFOA, and a higher hepatic first-pass effect of HFPO-TA (5-fold) than PFOA, contributing to its remarkable liver accumulation (5-fold). Molecular docking analysis reveals strong binding affinity of HFPO-TA with typical enterohepatic circulation transport proteins due to its strong hydrophobicity, flexible chain structure, and formation of additional hydrogen bonds, favoring HFPO-TA accumulation in the liver. The results suggest that HFPO-TA may not be a safe substitute for legacy PFAS, and further human exposure risk assessments are warranted.

Bioaccumulation potentials of per-and polyfluoroalkyl substances (PFAS) in recreational fisheries: Occurrence, health risk assessment and oxidative stress biomarkers in coastal Biscayne Bay

Per-and polyfluoroalkyl substances (PFAS) are a group of synthetic, highly fluorinated, and emerging chemicals that are reported to be used for both industrial and domestic applications. Several PFAS have demonstrated persistent, bioaccumulative and toxic tendencies in marine organisms. Therefore, this research aims to characterize and quantify these compounds in both recreational fisheries and surface water samples, including estimating their bioaccumulation potentials. In addition, we assessed the potential contribution of biomonitoring tools such as oxidative stressors and morphological index on fish and ecological health. Finally, human health risk assessment was performed based on available toxicological data on limited PFAS. All PFAS were detected in at least one sample except for N-EtFOSAA in lobster which was below the method detection limit. ƩPFAS body burden ranged from 0.15 to 3.40 ng/g wet weight (ww) in blackfin tuna samples and 0.37-5.15 ng/g ww in lobster samples, respectively. Wilcoxon rank paired test (α = 0.05) shows that there is statistical significance (ρ < 0.05) of ƩPFAS between species. Bioaccumulation factors (BAF) suggest an increasing trend in PFAS classes (PFCAs < PFSAs < FTSs), with higher BAFs observed in tuna compared to lobster. Long-chain PFESAs and FASAA were reported at higher concentrations in lobster compared to Blackfin tuna due to their bioavailability through sediment-sorption interactions. Although Fulton's condition factor (FCF) indicates healthy fish conditions, oxidative stress biomarkers suggest that tuna and lobster might be under stress, which can weaken their immune system against exposure to emerging contaminants such as PFAS. Hazard risk (HR) suggests a low risk to human health based on the consumption of the studied species; however, the risk of contaminant exposure may be higher than estimated. This study is aimed at improving food safety by providing better understanding of how PFAS infiltrate into human diet and incorporating data on influence of contaminant exposure and environmental stressors on marine health.

Kidney function mediates the association of per- and poly-fluoroalkyl substances (PFAS) and heavy metals with hepatic fibrosis risk

Heavy metals and per- and polyfluoroalkyl substances (PFAS) are significantly associated with the risk of hepatic fibrosis. However, the potential mediating effect of kidney function in the relationship between heavy metals, PFAS, and hepatic fibrosis risk remains unexplored. This research gap limits the development of hepatic fibrosis prevention and treatment strategies. To address this, this study conducts a cross-sectional analysis based on data from 10,870 participants in NHANES 2005-2018 to explore the relationship between heavy metals, PFAS, and the risk of hepatic fibrosis, as well as the mediating effect of kidney function. Participants with a Fibrosis-4 index <1.45 are defined as not having hepatic fibrosis in this study. Results from generalized linear regression models and weighted quantile sum regression models indicate that both individual and combined exposures to heavy metals and PFAS are positively associated with the risk of hepatic fibrosis. Nonlinear exposure-response functions suggest that there may be a threshold for the relationship between heavy metals (except mercury) and PFAS with the risk of hepatic fibrosis. Furthermore, heavy metals and PFAS increase the risk of kidney function impairment. After stratification by kidney function stage, the relationship between heavy metals (except lead) and proteinuria is not significant, while PFAS show a significant negative association with proteinuria. The decline in kidney function has a significant mediating effect in the relationship between heavy metals and PFAS and the risk of hepatic fibrosis, with mediation effect proportions all above 20%. The findings suggest that individual or combined exposure to heavy metals and PFAS does not increase the risk of hepatic fibrosis until a certain threshold is reached, and the mediating role of declining kidney function is very important. These results highlight the need to consider kidney function in the context of hepatic fibrosis risk assessment and management.

Neurotoxicity of per- and polyfluoroalkyl substances: Evidence and future directions

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals widely used in various products, including food packaging, textiles, and firefighting foam, owing to their unique properties such as amphiphilicity and strong CF bonds. Despite their widespread use, concerns have arisen due to their resistance to degradation and propensity for bioaccumulation in both environmental and human systems. Emerging evidence suggests a potential link between PFAS exposure and neurotoxic effects, spanning cognitive deficits, neurodevelopmental disorders, and neurodegenerative diseases. This review comprehensively synthesizes current knowledge on PFAS neurotoxicity, drawing insights from epidemiological studies, animal experiments, and mechanistic investigations. PFAS, known for their lipophilic nature, tend to accumulate in lipid-rich tissues, including the brain, breaching biological barriers such as the blood-brain barrier (BBB). The accumulation of PFAS within the central nervous system (CNS) has been implicated in a spectrum of neurological maladies. Neurotoxicity induced by PFAS manifests through a multitude of direct and indirect mechanisms. A growing body of research associated PFAS exposure with BBB disruption, calcium dysregulation, neurotransmitter alterations, neuroinflammation, oxidative stress, and mitochondrial dysfunction, all contributing to neuronal impairment. Despite notable strides in research, significant lacunae persist, necessitating further exploration to elucidate the full spectrum of PFAS-mediated neurotoxicity. Prospective research endeavors should prioritize developing biomarkers, delineating sensitive exposure windows, and exploring mitigation strategies aimed at safeguarding neurological integrity within populations vulnerable to PFAS exposure.

Kidney function mediates the effects of four per-and polyfluoroalkyl substances (PFAS) on atherosclerotic cardiovascular disease

BACKGROUND

PFAS pose a significant threat to cardiovascular health and increase the risk of atherosclerotic cardiovascular disease (ASCVD). However, there is limited research evidence regarding the mechanisms by which PFAS affect the risk of ASCVD and the exposure-risk (E-R) relationship. The effect of kidney function in the relationship between PFAS and ASCVD risk has not been adequately validated.

OBJECTIVE

This study aims to explore the mechanisms by which four PFAS (Perfluorooctanoic acid (PFOA), Perfluorooctanesulfonic acid (PFOS), Perfluorohexanesulfonic acid (PFHS), and Perfluorononanoic acid (PFNA)) affect the risk of ASCVD and to verify and discuss the mediating effect of kidney function in this impact.

METHODS

This study utilizes data from 14,607 participants in the NHANES 2005-2018 to conduct a cross-sectional study. Initially, Generalized Linear Model (GLM) and Restricted Cubic Splines models are used to assess the impact of four PFAS on ASCVD risk and the E-R relationship. Subsequently, the Weighted Quantile Sum regression (WQS) model is used to evaluate the relationship between mixed four PFAS exposure and ASCVD risk. Finally, Directed Acyclic Graphs (DAG) and causal mediation models are used to confirm and analyze whether the decline in kidney function mediates the impact of four PFAS on ASCVD risk.

RESULTS

The results from GLM and WQS models indicate that both singular and mixed four PFAS exposures are associated with an increased risk of ASCVD. The E-R curves between four PFAS singular and mixed exposures and ASCVD risk are all characterized by nonlinearity. The results from DAG and causal mediation models clearly indicate that the decline in kidney function plays a significant mediating role in the relationship between four PFAS and ASCVD risk.

CONCLUSION

Exposure levels of four PFAS do not significantly increase the risk of ASCVD unless they reach a certain threshold, and the decline in kidney function exerts a significant mediating effect in the relationship between four PFAS exposure and ASCVD risk.

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.

Associations between co-exposure to per- and polyfluoroalkyl substances and metabolic diseases: The mediating roles of inflammation and oxidative stress

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) pose potential risks to human health. In real-world settings, humans are exposed to various PFAS through numerous pathways.

OBJECTIVES

This study evaluated the associations between co-exposure to PFAS and obesity and its comorbidities, along with the mediating roles of inflammation and oxidative stress.

METHODS

We analyzed 11,090 participants from National Health and Nutrition Examination Survey (NHANES), 2003-2018. Linear regression, logistic regression, and generalized additive models were used to assess the individual effects of PFAS exposure on obesity and its comorbidities. The environmental risk score (ERS) was calculated using the adaptive elastic-net model to assess the co-exposure effects. Linear and logistic regression models explored the associations between ERS and obesity and its comorbidities. Mediation analyses explored the roles of inflammatory (neutrophils, lymphocytes, and alkaline phosphatase) and oxidative stress (gamma-glutamyl transferase, total bilirubin, and uric acid) markers in the associations between ERS and obesity and its comorbidities.

RESULTS

For each unit increase in ERS, the odds of obesity and type 2 diabetes mellitus (T2DM) increased 3.60-fold (95 % CI: 2.03, 6.38) and 1.91-fold (95 % CI: 1.28, 2.86), respectively. For each unit increase in ERS, BMI increased by 2.36 (95 % CI: 1.24, 3.48) kg/m2, waist circumference increased by 6.47 (95 % CI: 3.56, 9.37) cm, and waist-to-height ratio increased by 0.04 (95 % CI: 0.02, 0.06). Lymphocytes, alkaline phosphatase, and total bilirubin were significantly associated with both ERS and obesity, with mediation proportions of 4.17 %, 3.62 %, and 7.37 %, respectively. Lymphocytes, alkaline phosphatase, total bilirubin, and uric acid were significantly associated with both ERS and T2DM, with the mediation proportions of 8.90 %, 8.74 %, 29.73 %, and 38.19 %, respectively.

CONCLUSIONS

Co-exposure to PFAS was associated with obesity and T2DM, and these associations may be mediated by inflammation and oxidative stress. Further mechanistic and prospective studies are required to verify these associations.

Clinical, histological, molecular, and toxicokinetic renal outcomes of per-/polyfluoroalkyl substances (PFAS) exposure: Systematic review and meta-analysis

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals present in the environment that can negatively affect health. Kidney is the major target organ of PFAS exposure, yet the renal impact of PFAS is not completely understood. Here we review the effects of PFAS exposure on kidney health to identify gaps in our understanding and mark potential avenues for future research.

METHODS

PubMed and SCOPUS databases were searched for studies that examined the association between PFAS exposure and kidney-related outcomes. We included all epidemiological, animal, and cell studies and categorized outcomes into four categories: clinical, histological, molecular and toxicokinetic.

RESULTS

We identified 169 studies, including 51 on clinical outcomes, 28 on histological changes, 42 on molecular mechanisms, and 68 on toxicokinetics. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) exposure were associated with kidney dysfunction, chronic kidney diseases, and increased risk of kidney cancer. Various histological changes were reported, especially in tubular epithelial cells, and the etiology of PFAS-induced kidney injury included various molecular mechanisms. Although PFOA and PFOS are not considered genotoxic, they exhibit several characteristics of carcinogens. Toxicokinetics of PFOA and PFOS differed significantly between species, with renal elimination influenced by various factors such as sex, age, and structure of the compound.

CONCLUSION

Evidence suggests that PFAS, especially PFOA and PFOS, negatively affects kidney health, though gaps in our understanding of such effects call for further research.

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.

Kinetics of 15 per- and polyfluoroalkyl substances (PFAS) after single oral application as a mixture - A pilot investigation in a male volunteer

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous environmental contaminants with half-lives in humans in the range of years in case of the long-chain compounds, leading to accumulation and measurable levels in plasma. In contrast, short-chain and "alternative" PFAS have lower levels or are not detectable in humans with background exposure. This may be due to lower exposure, but also due to much shorter half-lives compared to long-chain compounds. To get better data on kinetics, a healthy volunteer orally ingested a mixture of fifteen predominantly 13C-labeled PFAS ("MPFAS") in a pilot investigation (MPFBA, MPFPeA, MPFHxA, MPFHpA, MPFOA, MPFNA, MPFDA, MPFUdA, MPFDoA, PFBS, MPFHxS, MPFOS, DONA, HFPO-DA, 6:2FTS). After application, concentrations were measured over 450 days in plasma, urine and feces, using UHPLC-MS/MS analysis after extraction. The compounds were absorbed quickly and almost completely. Data analysis revealed volumes of distribution between 110 and 177 mL/kg bw for most compounds, but higher values for MPFDA, MPFUdA and MPFDoA (maximum of 354 mL/kg bw). Half-lives were found to vary extremely, from 0.5 days (MPFPeA) and 1.5 days (MPFHxA) to 51 days (PFBS) and 152 days (MPFHpA) in case of the short-chain and "alternative" compounds. For the long-chain compounds, half-lives in the range of several years were confirmed for MPFOA, MPFNA, MPFHxS and MPFOS, but with even higher chain-lengths of the carboxylic acids, the half-lives were found to decrease, with the shortest half-life for MPFDoA (295 days). Elimination from the body was completely explained by the urinary losses in case of the short-chain and "alternative" PFAS, and in part by the fecal losses in case of the long-chain PFCA. Overall, elimination kinetics seem to be determined by several different renal and gastrointestinal factors (fraction unbound in plasma, binding affinity to organic anion transporters causing netto secretion or reabsorption, fecal loss with mechanisms to be clarified).

Fluorotelomer betaines and sulfonic acid in aerobic wetland soil: Stability, biotransformation, and bacterial community response

The microbial degradation of 6:2 fluorotelomer sulfonic acid (6:2 FTSA), fluorotelomer sulfonamide alkylbetaine (6:2 FTAB), and fluorotelomer betaines (5:3 and 5:1:2 FTB) in aerobic wetland soil was investigated during a 100-day incubation. The half-lives of 6:2 FTSA in the treatments with diethylene glycol butyl ether as the sole carbon source (NA treatment) and with additional supplementation of sodium acetate (ED treatment) were determined to be 26.2 and 16.7 days, respectively. By day 100, ∼20 mol% of 6:2 FTAB was degraded in the NA and ED treatments. The potential transformation products of 6:2 FTSA and 6:2 FTAB were identified using liquid/gas chromatography-high resolution mass spectrometry, and their biotransformation pathways were proposed. In contrast, 5:3 and 5:1:2 FTB exhibited high persistence under two carbon source conditions. There was no intense alteration in the diversity of soil bacterial communities under the stress of fluorotelomer compounds at the level of ∼150 μg/L. The supplementation of sodium acetate led to an enrichment of bacterial species within the genera Hydrogenophaga (phylum Proteobacteria) and Rhodococcus (phylum Actinobacteria), promoting the biodegradation of 6:2 FTSA and 6:2 FTAB and the formation of transformation products. Species from the genus Rhodococcus were potentially crucial functional microorganisms involved in the degradation of 6:2 FTSA.

Evaluation of 14 PFAS for permeability and organic anion transporter interactions: Implications for renal clearance in humans

Per- and polyfluoroalkyl substances (PFAS) encompass a diverse group of synthetic fluorinated chemicals known to elicit adverse health effects in animals and humans. However, only a few studies investigated the mechanisms underlying clearance of PFAS. Herein, the relevance of human renal transporters and permeability to clearance and bioaccumulation for 14 PFAS containing three to eleven perfluorinated carbon atoms (ηpfc = 3-11) and several functional head-groups was investigated. Apparent permeabilities and interactions with human transporters were measured using in vitro cell-based assays, including the MDCK-LE cell line, and HEK293 stable transfected cell lines expressing organic anion transporter (OAT) 1-4 and organic cation transporter (OCT) 2. The results generated align with the Extended Clearance Classification System (ECCS), affirming that permeability, molecular weight, and ionization serve as robust predictors of clearance and renal transporter engagement. Notably, PFAS with low permeability (ECCS 3A and 3B) exhibited substantial substrate activity for OAT1 and OAT3, indicative of active renal secretion. Furthermore, we highlight the potential contribution of OAT4-mediated reabsorption to the renal clearance of PFAS with short ηpfc, such as perfluorohexane sulfonate (PFHxS). Our data advance our mechanistic understanding of renal clearance of PFAS in humans, provide useful input parameters for toxicokinetic models, and have broad implications for toxicological evaluation and regulatory considerations.

Associations of Serum Per- and Polyfluoroalkyl Substances with Hyperuricemia in Adults: A Nationwide Cross-Sectional Study

There has been widespread concern about the health hazards of per- and polyfluoroalkyl substances (PFAS), which may be the risk factor for hyperuricemia with evidence still insufficient in the general population in China. Here, we conducted a nationwide study involving 9,580 adults aged 18 years or older from 2017 to 2018, measured serum concentrations of uric acid and PFAS (PFOA, PFOS, 6:2 Cl-PFESA, PFNA, PFHxS) in participants, to assess the associations of individual PFAS with hyperuricemia, and estimated a joint effect of PFAS mixtures. We found positive associations of higher serum PFAS with elevated odds of hyperuricemia in Chinese adults, with the greatest contribution from PFOA (69.37%). The nonmonotonic dose-response (NMDR) relationships were observed for 6:2 Cl-PFESA and PFHxS with hyperuricemia. Participants with less marine fish consumption, overweight, and obesity may be the sensitive groups to the effects of PFAS on hyperuricemia. We highlight the potential health hazards of legacy long-chain PFAS (PFOA) once again because of the higher weights of joint effects. This study also provides more evidence about the NMDR relationships in PFAS with hyperuricemia and emphasizes a theoretical basis for public health planning to reduce the health hazards of PFAS in sensitive groups.

Kidney function decline mediates the adverse effects of per- and poly-fluoroalkyl substances (PFAS) on uric acid levels and hyperuricemia risk

Previous studies indicated per- and poly-fluoroalkyl substances (PFAS) were related to uric acid and hyperuricemia risk, but evidence for the exposure-response (E-R) curves and combined effect of PFAS mixture is limited. Moreover, the potential mediation effect of kidney function was not assessed. Hence, we conducted a national cross-sectional study involving 13,979 US adults in NHANES 2003-2018 to examine the associations of serum PFAS with uric acid and hyperuricemia risk, and the mediation effects of kidney function. Generalized linear models and E-R curves showed positive associations of individual PFAS with uric acid and hyperuricemia risk, and nearly linear E-R curves indicated no safe threshold for PFAS. Weighted quantile sum regression found positive associations of PFAS mixture with uric acid and hyperuricemia risk, and PFOA was the dominant contributor to the adverse effect of PFAS on uric acid and hyperuricemia risk. Causal mediation analysis indicated significant mediation effects of kidney function decline in the associations of PFAS with uric acid and hyperuricemia risk, with the mediated proportion ranging from 19 % to 57 %. Our findings suggested that PFAS, especially PFOA, may cause increased uric acid and hyperuricemia risk increase even at low levels, and kidney function decline plays a crucial mediation effect.

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.

Increased Perfluorooctanesulfonate (PFOS) Toxicity and Accumulation Is Associated with Perturbed Prostaglandin Metabolism and Increased Organic Anion Transport Protein (OATP) Expression

Perfluorooctanesulfonate (PFOS) is a widespread environmental pollutant with a long half-life and clearly negative outcomes on metabolic diseases such as fatty liver disease and diabetes. Male and female Cyp2b-null and humanized CYP2B6-transgenic (hCYP2B6-Tg) mice were treated with 0, 1, or 10 mg/kg/day PFOS for 21 days, and surprisingly it was found that PFOS was retained at greater concentrations in the serum and liver of hCYP2B6-Tg mice than those of Cyp2b-null mice, with greater differences in the females. Thus, Cyp2b-null and hCYP2B6-Tg mice provide new models for investigating individual mechanisms for PFOS bioaccumulation and toxicity. Overt toxicity was greater in hCYP2B6-Tg mice (especially females) as measured by mortality; however, steatosis occurred more readily in Cyp2b-null mice despite the lower PFOS liver concentrations. Targeted lipidomics and transcriptomics from PFOS-treated Cyp2b-null and hCYP2B6-Tg mouse livers were performed and compared to PFOS retention and serum markers of toxicity using PCA. Several oxylipins, including prostaglandins, thromboxanes, and docosahexaenoic acid metabolites, are associated or inversely associated with PFOS toxicity. Both lipidomics and transcriptomics indicate PFOS toxicity is associated with PPAR activity in all models. GO terms associated with reduced steatosis were sexually dimorphic with lipid metabolism and transport increased in females and circadian rhythm associated genes increased in males. However, we cannot rule out that steatosis was initially protective from PFOS toxicity. Moreover, several transporters are associated with increased retention, probably due to increased uptake. The strongest associations are the organic anion transport proteins (Oatp1a4-6) genes and a long-chain fatty acid transport protein (fatp1), enriched in female hCYP2B6-Tg mice. PFOS uptake was also reduced in cultured murine hepatocytes by OATP inhibitors. The role of OATP1A6 and FATP1 in PFOS transport has not been tested. In summary, Cyp2b-null and hCYP2B6-Tg mice provided unique models for estimating the importance of novel mechanisms in PFOS retention and toxicity.