Legacy and emerging per- and polyfluoroalkyl substances suppress the neutrophil respiratory burst

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.

Associations between prenatal exposure to per- and polyfluoroalkyl substances and plasma immune molecules in three-year-old children in China

BACKGROUND

Many studies have reported that prenatal exposure to Per- and Polyfluoroalkyl Substances (PFASs) can disrupt immune function. However, little is known about the effects of PFASs on immune molecules. The study analyzed the association between prenatal exposure to mixed and single PFASs and plasma immune molecules in three-year-old children.

METHODS

Ten PFASs were measured in umbilical cord serum, while peripheral blood samples were collected at age three to measure immune molecules. Associations between exposure to individual and combined PFASs and immune molecules were analyzed using Generalized Linear Models and Weighted Quantile Sum (WQS) regression.

RESULTS

(1) Interleukin-4 (IL-4) increased by 23.85% (95% CI:2.99,48.94) with each doubling of Perfluorooctanoic Acid (PFOA), and Interleukin-6 (IL-6) increased by 39.07% (95%CI:4.06,85.86) with Perfluorotridecanoic Acid (PFTrDA). Elevated PFOA and Perfluorononanoic Acid (PFNA) were correlated with increases of 34.06% (95% CI: 6.41, 70.28) and 24.41% (95% CI: 0.99, 53.27) in Eotaxin-3, respectively. Additionally, the doubling of Perfluorohexane Sulfonic Acid (PFHxS) was associated with a 9.51% decrease in Periostin (95% CI: -17.84, -0.33). (2) The WQS analysis revealed that mixed PFASs were associated with increased IL-6 (β = 0.37, 95%CI:0.04,0.69), mainly driven by PFTrDA, PFNA, and 8:2 Chlorinated Perfluoroethyl Sulfonamide (8:2 Cl-PFESA). Moreover, mixed PFASs were linked to an increase in Eotaxin-3 (β = 0.32, 95% CI: 0.09,0.55), primarily influenced by PFOA, PFTrDA, and Perfluorododecanoic Acid (PFDoDA).

CONCLUSIONS

Prenatal PFASs exposure significantly alters the levels of immune molecules in three-year-old children, highlighting the importance of understanding environmental impacts on early immune development.

Mary L, Truong L, McClure R, Martin JK, Leonard SW, Thunga P, Simonich MT, Waters KM, Field JA, Tanguay RL. Diverse PFAS produce unique transcriptomic changes linked to developmental toxicity in zebrafish

Per- and polyfluoroalkyl substances (PFAS) are a widespread and persistent class of contaminants posing significant environmental and human health concerns. Comprehensive understanding of the modes of action underlying toxicity among structurally diverse PFAS is mostly lacking. To address this need, we recently reported on our application of developing zebrafish to evaluate a large library of PFAS for developmental toxicity. In the present study, we prioritized 15 bioactive PFAS that induced significant morphological effects and performed RNA-sequencing to characterize early transcriptional responses at a single timepoint (48 h post fertilization) after early developmental exposures (8 h post fertilization). Internal concentrations of 5 of the 15 PFAS were measured from pooled whole fish samples across multiple timepoints between 24-120 h post fertilization, and additional temporal transcriptomics at several timepoints (48-96 h post fertilization) were conducted for Nafion byproduct 2. A broad range of differentially expressed gene counts were identified across the PFAS exposures. Most PFAS that elicited robust transcriptomic changes affected biological processes of the brain and nervous system development. While PFAS disrupted unique processes, we also found that similarities in some functional head groups of PFAS were associated with the disruption in expression of similar gene sets. Body burdens after early developmental exposures to select sulfonic acid PFAS, including Nafion byproduct 2, increased from the 24-96 h post fertilization sampling timepoints and were greater than those of sulfonamide PFAS of similar chain lengths. In parallel, the Nafion byproduct 2-induced transcriptional responses increased between 48 and 96 h post fertilization. PFAS characteristics based on toxicity, transcriptomic effects, and modes of action will contribute to further prioritization of PFAS structures for testing and informed hazard assessment.

Prenatal and childhood air pollution exposure, cellular immune biomarkers, and brain connectivity in early adolescents

Introduction

Ambient air pollution is a neurotoxicant with hypothesized immune-related mechanisms. Adolescent brain structural and functional connectivity may be especially vulnerable to ambient pollution due to the refinement of large-scale brain networks during this period, which vary by sex and have important implications for cognitive, behavioral, and emotional functioning. In the current study we explored associations between air pollutants, immune markers, and structural and functional connectivity in early adolescence by leveraging cross-sectional sex-stratified data from the Adolescent Brain Cognitive Development℠ Study®.

Methods

Pollutant concentrations of fine particulate matter, nitrogen dioxide, and ozone were assigned to each child's primary residential address during the prenatal period and childhood (9-10 years-old) using an ensemble-based modeling approach. Data collected at 11-13 years-old included resting-state functional connectivity of the default mode, frontoparietal, and salience networks and limbic regions of interest, intracellular directional and isotropic diffusion of available white matter tracts, and markers of cellular immune activation. Using partial least squares correlation, a multivariate data-driven method that identifies important variables within latent dimensions, we investigated associations between 1) pollutants and structural and functional connectivity, 2) pollutants and immune markers, and 3) immune markers and structural and functional connectivity, in each sex separately.

Results

Air pollution exposure was related to white matter intracellular directional and isotropic diffusion at ages 11-13 years, but the direction of associations varied by sex. There were no associations between pollutants and resting-state functional connectivity at ages 11-13 years. Childhood exposure to nitrogen dioxide was negatively correlated with white blood cell count in males. Immune biomarkers were positively correlated with white matter intracellular directional diffusion in females and both white matter intracellular directional and isotropic diffusion in males. Lastly, there was a reliable negative correlation between lymphocyte-to-monocyte ratio and default mode network resting-state functional connectivity in females, as well as a compromised immune marker profile associated with lower resting-state functional connectivity between the salience network and the left hippocampus in males. In post-hoc exploratory analyses, we found that the PLSC-identified white matter tracts and resting-state networks related to processing speed and cognitive control performance from the NIH Toolbox.

Conclusions

We identified novel links between childhood nitrogen dioxide and cellular immune activation in males, and brain network connectivity and immune markers in both sexes. Future research should explore the potentially mediating role of immune activity in how pollutants affect neurological outcomes as well as the potential consequences of immune-related patterns of brain connectivity in service of improved brain health for all.

Maternal and Neonatal Effects of Maternal Oral Exposure to Perfluoro-2-methoxyacetic Acid (PFMOAA) during Pregnancy and Early Lactation in the Sprague-Dawley Rat

Perfluoro-2-methoxyacetic acid (PFMOAA) is a short-chain perfluoroalkyl ether carboxylic acid that has been detected at high concentrations (∼10 μg/L) in drinking water in eastern North Carolina, USA, and in human serum and breastmilk in China. Despite documented human exposure there are almost no toxicity data available to inform risk assessment of PFMOAA. Here we exposed pregnant Sprague-Dawley rats to a range of PFMOAA doses (10-450 mg/kg/d) via oral gavage from gestation day (GD) 8 to postnatal day (PND) 2 and compared results to those we previously reported for perfluorooctanoic acid (PFOA) and hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX). Newborn pups displayed reduced birthweight (≥30 mg/kg), depleted liver glycogen concentrations (all doses), hypoglycemia (≥125 mg/kg), and numerous significantly altered genes in the liver associated with fatty acid and glucose metabolism similar to gene changes produced by HFPO-DA. Pup survival was significantly reduced at ≥125 mg/kg, and at necropsy on PND2 both maternal and neonatal animals displayed increased liver weights, increased serum aspartate aminotransferase (AST), and reduced serum thyroid hormones at all doses (≥10 mg/kg). Pups also displayed highly elevated serum cholesterol at all doses. PFMOAA concentrations in serum and liver increased with maternal oral dose in both maternal and F1 animals and were similar to those we reported for PFOA but considerably higher than HFPO-DA. We calculated 10% effect levels (ED10 or EC10) and relative potency factors (RPF; PFOA = index chemical) among the three compounds based on maternal oral dose and maternal serum concentration (μM). Reduced pup liver glycogen, increased liver weights and reduced thyroid hormone levels (maternal and pup) were the most sensitive end points modeled. PFMOAA was ∼3-7-fold less potent than PFOA for most end points based on maternal serum RPFs, but slightly more potent for increased maternal and pup liver weights. PFMOAA is a maternal and developmental toxicant in the rat producing a constellation of adverse effects similar to PFOA and HFPO-DA.

PFHxS Exposure and the Risk of Non-Alcoholic Fatty Liver Disease

Perfluorohexanesulfonic acid (PFHxS) is a highly prevalent environmental pollutant, often considered to be less toxic than other poly- and perfluoroalkyl substances (PFASs). Despite its relatively lower environmental impact compared to other PFASs, several studies have suggested that exposure to PFHxS may be associated with disruptions of liver function in humans. Nevertheless, the precise pathomechanisms underlying PFHxS-induced non-alcoholic fatty liver disease (NAFLD) remain relatively unclear. Therefore, this study applied our previously published transcriptome dataset to explore the effects of PFHxS exposure on the susceptibility to NAFLD and to identify potential mechanisms responsible for PFHxS-induced NAFLD through transcriptomic analysis conducted on zebrafish embryos. Results showed that exposure to PFHxS markedly aggravated hepatic symptoms resembling NAFLD and other metabolic syndromes (MetS) in fish. Transcriptomic analysis unveiled 17 genes consistently observed in both NAFLD and insulin resistance (IR), along with an additional 28 genes identified in both the adipocytokine signaling pathway and IR. These shared genes were also found within the NAFLD dataset, suggesting that hepatic IR may play a prominent role in the development of PFHxS-induced NAFLD. In conclusion, our study suggests that environmental exposure to PFHxS could be a potential risk factor for the development of NAFLD, challenging the earlier notion of PFHxS being safer as previously claimed.

Automated, high-throughput quantification of EGFP-expressing neutrophils in zebrafish by machine learning and a highly-parallelized microscope

Normal development of the immune system is essential for overall health and disease resistance. Bony fish, such as the zebrafish (Danio rerio), possess all the major immune cell lineages as mammals and can be employed to model human host response to immune challenge. Zebrafish neutrophils, for example, are present in the transparent larvae as early as 48 hours post fertilization and have been examined in numerous infection and immunotoxicology reports. One significant advantage of the zebrafish model is the ability to affordably generate high numbers of individual larvae that can be arrayed in multi-well plates for high throughput genetic and chemical exposure screens. However, traditional workflows for imaging individual larvae have been limited to low-throughput studies using traditional microscopes and manual analyses. Using a newly developed, parallelized microscope, the Multi-Camera Array Microscope (MCAM™), we have optimized a rapid, high-resolution algorithmic method to count fluorescently labeled cells in zebrafish larvae in vivo. Using transgenic zebrafish larvae, in which neutrophils express EGFP, we captured 18 gigapixels of images across a full 96-well plate, in 75 seconds, and processed the resulting datastream, counting individual fluorescent neutrophils in all individual larvae in 5 minutes. This automation is facilitated by a machine learning segmentation algorithm that defines the most in-focus view of each larva in each well after which pixel intensity thresholding and blob detection are employed to locate and count fluorescent cells. We validated this method by comparing algorithmic neutrophil counts to manual counts in larvae subjected to changes in neutrophil numbers, demonstrating the utility of this approach for high-throughput genetic and chemical screens where a change in neutrophil number is an endpoint metric. Using the MCAM™ we have been able to, within minutes, acquire both enough data to create an automated algorithm and execute a biological experiment with statistical significance. Finally, we present this open-source software package which allows the user to train and evaluate a custom machine learning segmentation model and use it to localize zebrafish and analyze cell counts within the segmented region of interest. This software can be modified as needed for studies involving other zebrafish cell lineages using different transgenic reporter lines and can also be adapted for studies using other amenable model species.

Transcriptome analysis reveals the mechanism of the effect of perfluorocaproic acid exposure on brain injury in Carassius auratus

Perfluorocaproic acid (PFHxA) has received much attention as an emerging pollutant linked to neurological problems in humans and fish. However, the potential mechanism remains unknown. In this study, the pathological damage to tissue sections demonstrated that perfluorocaproic acid caused brain tissue damage, and the increased antioxidant index malondialdehyde (MDA) and decrease in superoxide Dismutase (SOD), acid phosphatase (ACP), alkaline phosphatase (AKP), glutathione peroxidase (GSH-Px), Catalase (CAT), and Lysozyme (LZM) that perfluorocaproic acid activated antioxidant stress and caused brain damage. Transcriptome sequencing discovered 1,532 divergent genes, 931 upregulated, and 601 down-regulated. Furthermore, according to GO enrichment analysis, the differently expressed genes were shown to be involved in biological processes, cellular components, and molecular functions. The MAPK, calcium, and Neuroactive ligand-receptor interaction were considerably enriched in the KEGG enrichment analysis. We then analyzed qRT-PCR and chose ten essential differentially expressed genes for validation. The qRT-PCR results followed the same pattern as the RNA-Seq results. In conclusion, our study shows that perfluorocaproic acid exposure causes oxidative stress in the brain. It establishes a theoretical foundation for future research into genes linked to perfluorocaproic acid toxicity.

Automated, high-throughput quantification of EGFP-expressing neutrophils in zebrafish by machine learning and a highly-parallelized microscope

Normal development of the immune system is essential for overall health and disease resistance. Bony fish, such as the zebrafish (Danio rerio), possess all the major immune cell lineages as mammals and can be employed to model human host response to immune challenge. Zebrafish neutrophils, for example, are present in the transparent larvae as early as 48 hours post fertilization and have been examined in numerous infection and immunotoxicology reports. One significant advantage of the zebrafish model is the ability to affordably generate high numbers of individual larvae that can be arrayed in multi-well plates for high throughput genetic and chemical exposure screens. However, traditional workflows for imaging individual larvae have been limited to low-throughput studies using traditional microscopes and manual analyses. Using a newly developed, parallelized microscope, the Multi-Camera Array Microscope (MCAM™), we have optimized a rapid, high-resolution algorithmic method to count fluorescently labeled cells in zebrafish larvae in vivo. Using transgenic zebrafish larvae, in which neutrophils express EGFP, we captured 18 gigapixels of images across a full 96-well plate, in 75 seconds, and processed the resulting datastream, counting individual fluorescent neutrophils in all individual larvae in 5 minutes. This automation is facilitated by a machine learning segmentation algorithm that defines the most in-focus view of each larva in each well after which pixel intensity thresholding and blob detection are employed to locate and count fluorescent cells. We validated this method by comparing algorithmic neutrophil counts to manual counts in larvae subjected to changes in neutrophil numbers, demonstrating the utility of this approach for high-throughput genetic and chemical screens where a change in neutrophil number is an endpoint metric. Using the MCAM™ we have been able to, within minutes, acquire both enough data to create an automated algorithm and execute a biological experiment with statistical significance. Finally, we present this open-source software package which allows the user to train and evaluate a custom machine learning segmentation model and use it to localize zebrafish and analyze cell counts within the segmented region of interest. This software can be modified as needed for studies involving other zebrafish cell lineages using different transgenic reporter lines and can also be adapted for studies using other amenable model species.

Cross-Species Transcriptomics Analysis Highlights Conserved Molecular Responses to Per- and Polyfluoroalkyl Substances

In recent decades, per- and polyfluoroalkyl substances (PFASs) have garnered widespread public attention due to their persistence in the environment and detrimental effects on the health of living organisms, spurring the generation of several transcriptome-centered investigations to understand the biological basis of their mechanism. In this study, we collected 2144 publicly available samples from seven distinct animal species to examine the molecular responses to PFAS exposure and to determine if there are conserved responses. Our comparative transcriptional analysis revealed that exposure to PFAS is conserved across different tissues, molecules and species. We identified and reported several genes exhibiting consistent and evolutionarily conserved transcriptional response to PFASs, such as ESR1, HADHA and ID1, as well as several pathways including lipid metabolism, immune response and hormone pathways. This study provides the first evidence that distinct PFAS molecules induce comparable transcriptional changes and affect the same metabolic processes across inter-species borders. Our findings have significant implications for understanding the impact of PFAS exposure on living organisms and the environment. We believe that this study offers a novel perspective on the molecular responses to PFAS exposure and provides a foundation for future research into developing strategies for mitigating the detrimental effects of these substances in the ecosystem.

Perfluoroalkyl Substances (PFAS) Affect Inflammation in Lung Cells and Tissues

Adverse lung outcomes from exposure to per-and polyfluoroalkyl substances (PFAS) are known; however, the mechanism of action is poorly understood. To explore this, human bronchial epithelial cells were grown and exposed to varied concentrations of short-chain (perfluorobutanoic acid, perflurobutane sulfonic acid and GenX) or long-chain (PFOA and perfluorooctane sulfonic acid (PFOS)) PFAS, alone or in a mixture to identify cytotoxic concentrations. Non-cytotoxic concentrations of PFAS from this experiment were selected to assess NLRP3 inflammasome activation and priming. We found that PFOA and PFOS alone or in a mixture primed and activated the inflammasome compared with vehicle control. Atomic force microscopy showed that PFOA but not PFOS significantly altered the membrane properties of cells. RNA sequencing was performed on the lungs of mice that had consumed PFOA in drinking water for 14 weeks. Wild type (WT), PPARα knock-out (KO) and humanized PPARα (KI) were exposed to PFOA. We found that multiple inflammation- and immune-related genes were affected. Taken together, our study demonstrated that PFAS exposure could alter lung biology in a significant manner and may contribute to asthma/airway hyper-responsiveness.