Exposure to hexafluoropropylene oxide dimer acid (HFPO-DA) disturbs the gut barrier function and gut microbiota in mice

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.

Impacts of PFOS, PFOA and their alternatives on the gut, intestinal barriers and gut-organ axis

With the restricted use of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), a number of alternatives to PFOS and PFOA have attracted great interest. Most of the alternatives are still characterized by persistence, bioaccumulation, and a variety of toxicity. Due to the production and use of these substances, they can be detected in the atmosphere, soil and water body. They affect human health through several exposure pathways and especially enter the gut by drinking water and eating food, which results in gut toxicity. In this review, we summarized the effects of PFOS, PFOA and 9 alternatives on pathological changes in the gut, the disruption of physical, chemical, biological and immune barriers of the intestine, and the gut-organ axis. This review provides a valuable understanding of the gut toxicity of PFOS, PFOA and their alternatives as well as the human health risks of emerging contaminants.

Prenatal exposure to hexafluoropropylene oxide trimer acid (HFPO-TA) disrupts the maternal gut microbiome and fecal metabolome homeostasis

Initially considered a "safe" substitute for perfluorooctanoic acid (PFOA), hexafluoropropylene oxide trimer acid (HFPO-TA) has been extensively used in the production of fluoropolymers for several years, leading to its environmental ubiquity and subsequent discovery of its significant bio-accumulative properties and toxicological effects. However, the specific impact of HFPO-TA on females, particularly those who are pregnant, remains unclear. In the present study, pregnant mice were exposed to 0.63 mg/kg/day HFPO-TA from gestational day (GD) 2 to GD 18. We then determined the potential effects of exposure on gut microbiota and fecal metabolites at GD 12 (mid-pregnancy) and GD 18 (late pregnancy). Our results revealed that, in addition to liver damage, HFPO-TA exposure during the specified window altered the structure and function of cecal gut microbiota. Notably, these changes showed the opposite trends at GD 12 and GD 18. Specifically, at GD 12, HFPO-TA exposure primarily resulted in the down-regulation of relative abundances within genera from the Bacteroidetes and Proteobacteria phyla, as well as associated Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. With extended exposure time, the down-regulated genera within Proteobacteria became significantly up-regulated, accompanied by corresponding up-regulation of human disease- and inflammation-associated pathways, suggesting that HFPO-TA exposure can induce intestinal inflammation and elevate the risk of infection during late pregnancy. Pearson correlation analysis revealed that disturbances in the gut microbiota were accompanied by abnormal fecal metabolite. Additionally, alterations in hormones related to the steroid hormone biosynthesis pathway at both sacrifice time indicated that HFPO-TA exposure might change the steroid hormone level of pregnant mice, but need further study. In conclusion, this study provides new insights into the mechanisms underlying HFPO-TA-induced adverse effects and increases awareness of potential persistent health risks to pregnant females.

Gestational GenX and PFOA exposures induce hepatotoxicity, metabolic pathway, and microbiome shifts in weanling mice

Ammonium perfluoro (2-methyl-3-oxahexanoate) (GenX), a replacement for perfluorooctanoic acid (PFOA), has been detected in multiple environmental media and biological samples worldwide. Accumulated evidence implies that GenX exposure might exert adverse health effects, although the underlying mechanisms have not been fully revealed. In this study, pregnant BALB/c mice were exposed to GenX (2 mg/kg/day), PFOA (1 mg/kg/day), or Milli-Q water by gavage from the first day of gestation (GD0) until GD21. Necropsy and tissue collection were conducted in pups at 4 weeks of age. PFOA and GenX induced similar histopathological changes in both the liver and the intestinal mucosa, accompanied by higher serum levels of alanine and aspartate aminotransferase. Moreover, the capacity of hepatic glycogen storage and intestinal mucus secretion were significantly decreased, suggesting dysfunction of liver metabolism and the intestinal mucosal barrier. A total of 637 and 352 differentially expressed genes (DEGs) were identified in the liver tissues of GenX and PFOA group, respectively. Most of the enriched pathways from the DEGs by KEGG enrichment analysis were metabolism-associated. Moreover, overexpression of CYP4A14, Sult2a1, Cpt1b, Acaa1b, Igfbp1, Irs-2 and decreased expression of Gys2 were observed in livers of GenX exposed pups, supporting the hypothesis that there was metabolic disruption. Furthermore, DNA damage and cell cycle arrest proteins (Gadd45β, p21, Ppard) were significantly increased, while cell proliferation-related proteins (Cyclin E, Myc, EGFR) were decreased by gestational GenX exposure in the pups' liver. In addition, imbalance of gut microbiota and dysfunction of the intestinal mucosa barrier might contribute to hepatotoxicity at least in part. Taken together, our results suggested that gestational GenX exposure triggered metabolic disorder, which might be responsible for the hepatotoxicity in the pups in addition to dysfunction of the intestinal mucosa barrier. This study enriches the mechanisms of GenX-induced developmental hepatotoxicity by associating metabolic disorder with intestinal homeostasis.

Association of adverse fetal outcomes with placental inflammation after oral gestational exposure to hexafluoropropylene oxide dimer acid (GenX) in Sprague-Dawley rats

Hexafluoropropylene oxide dimer acid (HFPO-DA), known as "GenX" for its trade name, is gradually taking the place of Perfluorooctanoic acid (PFOA). However, there is a poor understanding of the developmental effects of GenX. This study aims to explore whether GenX produces adverse effects on offspring development in Sprague-Dawley (SD) rats and the underlying mechanisms. Pregnant rats were orally administered with GenX (0, 1, 10 and 100 mg/kg/day) from gestational 0.5-19.5 days. Experimental data showed that the exposure to GenX resulted in increased rats' gestational weight gain, whereas both body weight and body length of their fetuses born naturally were significantly reduced. This could contribute to the developmental delays of fetal body weight, body length and tail length from postnatal 1-21 days. Histopathological evaluation of placenta indicated that GenX exposure led to neutrophil infiltration in decidual zone and congestion in labyrinth zone. Moreover, placental proteomics showed changes at the expression levels of the inflammation-related proteins in the Rap1 signaling pathway. In conclusion, gestational exposure to GenX induced fetal intrauterine and extrauterine development retardation in SD rats. Placental inflammation may play a key role in this process through the Rap1 signaling pathway.

Inflammation and cardiometabolic diseases induced by persistent organic pollutants and nutritional interventions: Effects of multi-organ interactions

The development and outcome of inflammatory diseases are associated with genetic and lifestyle factors, which include chemical and nonchemical stressors. Persistent organic pollutants (POPs) are major groups of chemical stressors. For example, dioxin-like polychlorinated biphenyls (PCBs), per- and polyfluoroalkyl substances (PFASs), and polybrominated diphenyl ethers (PBDEs) are closely associated with the incidence of inflammatory diseases. The pathology of environmental chemical-mediated inflammatory diseases is complex and may involve disturbances in multiple organs, including the gut, liver, brain, vascular tissues, and immune systems. Recent studies suggested that diet-derived nutrients (e.g., phytochemicals, vitamins, unsaturated fatty acids, dietary fibers) could modulate environmental insults and affect disease development, progression, and outcome. In this article, mechanisms of environmental pollutant-induced inflammation and cardiometabolic diseases are reviewed, focusing on multi-organ interplays and highlighting recent advances in nutritional strategies to improve the outcome of cardiometabolic diseases associated with environmental exposures. In addition, advanced system biology approaches are discussed, which present unique opportunities to unveil the complex interactions among multiple organs and to fuel the development of precision intervention strategies in exposed individuals.

Toxicities of Legacy and Current-Use PFAS in an Anuran: Do Larval Exposures Influence Responses to a Terrestrial Pathogen Challenge?

Legacy polyfluoroalkyl substances (PFAS) [perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA)] are being replaced by various other fluorinated compounds, such as hexafluoropropylene oxide dimer acid (GenX). These alternatives are thought to be less bioaccumulative and, therefore, less toxic than legacy PFAS. Contaminant exposures occur concurrently with exposure to natural stressors, including the fungal pathogen Batrachocytrium dendrobatidis (Bd). Despite evidence that other pollutants can increase the adverse effects of Bd on anurans, no studies have examined the interactive effects of Bd and PFAS. This study tested the growth and developmental effects of PFOS, PFOA, and GenX on gray treefrog (Hyla versicolor) tadpoles, followed by a Bd challenge after metamorphosis. Despite PFAS exposure only occurring during the larval stage, carry-over effects on growth were observed post metamorphosis. Further, PFAS interacted with Bd exposure to influence growth; Bd-exposed animals had significantly shorter SVL [snout-vent length (mm)] with significantly increased body condition, among other time-dependent effects. Our data suggest that larval exposure to PFAS can continue to impact growth in the juvenile stage after exposure has ended. Contrary to predictions, GenX affected terrestrial performance more consistently than its legacy congener, PFOA. Given the role of Bd in amphibian declines, further investigation of interactions of PFAS with Bd and other environmentally relevant pathogens is warranted.

New insights into the degradation mechanism and risk assessment of HFPO-DA by advanced oxidation processes based on activated persulfate in aqueous solutions

Hexafluoropropylene oxide dimer acid (HFPO-DA) is widely used as a substitute for perfluorooctanoic acid (PFOA). HFPO-DA exhibits high water solubility and low adsorption potential, conferring significant fluidity in aquatic environments. Given that the toxicity of HFPO-DA is similar to PFOA, it is necessary to control its content in aquatic environments. Electrochemical and thermally-activated persulfates have been successfully used to degrade HFPO-DA, but UV-activated persulfates cannot degrade the compound. Given that research on degradation mechanisms is still incomplete and lacks kinetic research, the mechanism and kinetic calculations of oxidative degradation were studied in detail using DFT calculations. And the toxicity of HFPO-DA degradation intermediates and products was evaluated to reveal the feasibility of using advanced oxidation process (AOP) technology based on persulfate to degrade HFPO-DA in wastewater. The results showed that the committed step of HFPO-DA degradation was initiated by the electron transfer reaction of SO4•- radicals. This reaction is not spontaneous at room temperature and requires sufficient electrical or thermal energy to be absorbed from the external environment. The perfluoroalcohol produced during this reaction can subsequently undergo four possible reactions: H atom abstraction from alcohol groups by an OH radical; H atom abstraction by SO4•-; direct HF removal; and HF removal with water as the catalyst. The final degradation products of HFPO-DA mainly include CO2, CF3CF2COOH, CF3COOH, FCOOH and HF, which has been identified through previous experimental analysis. Ecotoxicity assessment indicates that degradation does not produce highly toxic intermediates, and that the final products are non-toxic, supporting the feasibility of persulfate-based AOP technologies.

Toxicity comparison of perfluorooctanoic acid (PFOA), hexafluoropropylene oxide dimer acid (HFPO-DA), and hexafluoropropylene oxide trimer acid (HFPO-TA) in zebrafish gut

Hexafluoropropylene oxide dimer acid (HFPO-DA) and hexafluoropropylene oxide trimer acid (HFPO-TA) are considered as alternatives to perfluorooctanoic acid (PFOA). In this study, zebrafish were exposed to different concentrations of PFOA, HFPO-DA, and HFPO-TA (5 μg/L and 500 μg/L), and the toxic effects on oxidative damage, inflammation, and cell apoptosis in the gut were compared. Additionally, changes in gut metabolome profiles and microbial community structure were analyzed. The results revealed that exposures to HFPO-DA and HFPO-TA led to lower levels of oxidative damage compared to PFOA exposure. However, all three treatments had comparable effects on inflammation and apoptosis. The main biological pathways affected by all three exposures were lipid metabolism, nucleotide metabolism, amino acid metabolism, and environmental information processing. The effects on metabolome profiles were much higher for HFPO-DA and HFPO-TA compared to PFOA at a concentration of 5 μg/L. At a concentration of 500 μg/L, HFPO-DA and HFPO-TA showed similar effects to PFOA. This study also examined the Pearson correlations between gut microbiota and the toxic effects mentioned above. The abundance of specific apoptosis-related genera differed among the three target chemicals, suggesting they may act differently in inducing apoptosis. The correlations between HFPO-DA and HFPO-TA were mostly similar, which helps explain the similar effects observed in their respective treatment groups on metabolic profiles. Overall, this study indicates that HFPO-DA and HFPO-TA may not be safe alternatives to PFOA and provides valuable insights into their toxic effects and risk assessment in water environments.

PFAS soil concentrations surrounding a hazardous waste incinerator in East Liverpool, Ohio, an environmental justice community

Per- and polyfluoroalkyl substances (PFAS) are a class of synthetic compounds widely used in industrial and consumer products. While PFAS provide product durability, these chemicals are ubiquitous, persistent, bioaccumulative, and toxic. These characteristics make the ultimate disposal of PFAS a challenge. One current disposal method is incineration; however, little research has been conducted on the safety and effectiveness of PFAS incineration. The characteristics of communities with hazardous waste incinerators that have received PFAS shipments indicate that more individuals with lower incomes and individuals with less education than the US average are at higher risk of exposure, which presents important environmental justice and health equity concerns of PFAS incineration. Situated in eastern Ohio, East Liverpool is an Appalachian community that is home to a large hazardous-waste incinerator, operated by Heritage WTI, that began accepting PFAS in 2019. Residents are concerned that the disposal lacks the research necessary to assure safety for the residents. Due to both community interest and data gaps regarding PFAS incineration, our research team conducted a pilot study to examine the distribution and concentration of PFAS in soil samples surrounding the incinerator. All 35 soil samples had measurable amounts of PFAS including perfluorobutanesulfonic acid (PFBS), perfluorooctanesulfonic acid (PFOS), perfluorooctanoic acid (PFOA), and hexafluoropropylene oxide dimer acid (HFPO-DA)/GenX. PFOS was measured in the majority of soil samples (97%) with a range of 50-8,300 ng/kg. PFOA was measured in 94% of soil samples with a range of 51 ng/kg to 1300 ng/kg. HFPO-DA/GenX was measurable in 12 soil samples with concentrations of ranging from 150 ng/kg to 1500 ng/kg. Further research on PFAS disposal will advance knowledge and action related to regulatory requirements and exposure prevention, ultimately improving individual and community protections and health equity.

Perfluorobutanesulfonate exposure induces metabolic disturbances in different regions of mouse gut

Perfluorobutanesulfonate (PFBS), an alternative to perfluorooctanesulfonate (PFOS), has raised many health concerns. However, PFBS toxicity in the mammalian gut remains unclear. C57BL/6 mice were exposed to 10 μg/L and 500 μg/L PFBS or 500 μg/L PFOS in their water supply for 28 days. PFBS toxicity in the ileum and colon was explored and compared to that of PFOS. Biochemical analysis showed that tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) levels increased in the ileum exposed to 10 μg/L PFBS, whereas no significant changes were observed in those levels in the colon. Catalase (CAT) activity, malondialdehyde (MDA), TNF-α, and IL-1β levels increased and glutathione (GSH) levels decreased in the ileum of the 500 μg/L-PFBS group, whereas only MDA levels increased in the colon of the 500 μg/L-PFBS group. The results showed that more severe damage occurred in the ileum than in the colon after PFBS exposure, and these align with the 500 μg/L-PFOS group exposure as well. Furthermore, metabolomic analysis revealed glutathione metabolism as a vital factor in inducing PFBS and PFOS toxicities in the ileum. Steroid hormone and amino acid metabolisms were other important factors involved in PFBS and PFOS toxicities, respectively. In the colon, GSH, pyrimidine, and glucose (especially galactose) metabolism was the main contributor to PFBS toxicity, and sulfur amino acid metabolism was the main pathway for PFOS toxicity. This study provides more evidence of the health hazards due to low-dose PFBS exposure in the mammalian gut.

Emerging polyfluorinated compound Nafion by-product 2 disturbs intestinal homeostasis in zebrafish (Danio rerio)

Nafion by-product 2 (Nafion BP2), an emerging fluorinated sulfonic acid commonly used in polymer electrolyte membrane technologies, has been detected in various environmental and human matrices. To date, however, few studies have explored its toxicity. In this study, zebrafish embryos were exposed to Nafion BP2 at concentrations of 20, 40, 60, 80, 100, 120, 140, and 160 mg/L from fertilization to 120 post-fertilization (hpf), and multiple developmental parameters (survival rate, hatching rate, and malformation rate) were then determined. Results showed that Nafion BP2 exposure led to a significant decrease in survival and hatching rates and an increase in malformations. The half maximal effective concentration (EC₅₀) of Nafion BP2 for malformation at 120 hpf was 55 mg/L, which is higher than the globally important contaminant perfluorooctane sulfonate (PFOS, 6 mg/L). Furthermore, exposure to Nafion BP2 resulted in additional types of malformations compared to PFOS exposure. Pathologically, Nafion BP2 caused abnormal early foregut development, with exfoliation of intestinal mucosa, damage to lamina propria, and aberrant proliferation of lamina propria cells. Nitric oxide content also decreased markedly. In addition, embryos showed an inflammatory response following Nafion BP2 exposure, with significantly increased levels of pro-inflammatory factors C4 and IL-6. Acidic mucin in the hindgut increased more than two-fold. 16 S rRNA sequencing revealed a marked increase in the pathogen Pseudomonas otitidis. Furthermore, pathways involved in intestinal protein digestion and absorption, inflammatory response, and immune response were significantly altered. Our findings suggest that the intestine is a crucial toxicity target of Nafion BP2 in zebrafish, thus highlighting the need to evaluate its health risks.

Per- and polyfluoroalkyl substances exposure and its influence on the intestinal barrier: An overview on the advances

Per- and polyfluoroalkyl substances (PFAS) are a class of artificially synthetic organic compounds that are hardly degraded in the natural environment. PFAS have been widely used for many decades, and the persistence and potential toxicity of PFAS are an emerging concern in the world. PFAS exposed via diet can be readily absorbed by the intestine and enter the circulatory system or accumulate directly at intestinal sites, which could interact with the intestine and cause the destruction of intestinal barrier. This review summarizes current relationships between PFAS exposure and intestinal barrier damage with a focus on more recent toxicological studies. Exposure to PFAS could cause inflammation in the gut, destruction of the gut epithelium and tight junction structure, reduction of the mucus layer, and induction of the toxicity of immune cells. PFAS accumulation could also induce microbial disorders and metabolic products changes. In addition, there are limited studies currently, and most available studies converge on the health risk of PFAS exposure for human intestinal disease. Therefore, more efforts are deserved to further understand potential associations between PFAS exposure and intestinal dysfunction and enable better assessment of exposomic toxicology and health risks for humans in the future.

Impact of a hexafluoropropylene oxide trimer acid (HFPO-TA) exposure on impairing the gut microbiota in mice

Hexafluoropropylene oxide trimer acid (HFPO-TA) has been used as an alternative of perfluorooctanoic acid (PFOA) in the fluoropolymer industry for several years. HFPO-TA is reported to have high capability of bioaccumulation, widespread environmental distribution, and multiple toxicities. However, its potential toxicity on the intestines and gut microbiota remains unknown. In the present study, male mice were orally exposed to 200 μg/L HFPO-TA for 6 weeks, and after total genomic DNA extraction, 16S rRNA amplicon pyrosequencing was performed. Our results demonstrated that HFPO-TA exposure resulted in the imbalance of cecal microbiota and alterations of cecal microbiota diversity. At the phylum level, the relative abundances of Proteobacteria, Deferribacteres, and Tenericutes increased in mice after exposure to HFPO-TA, while the relative abundances of Verrucomicrobia, Cyanobacteria, and TM7 decreased. At the genus level, the relative abundances of Ver Akkermansia, Pre Prevotella, Lac Coprococcus, Por_Parabacteroides, and Lac Dorea decreased in HFPO-TA exposed mice. Meanwhile, the increased relative abundances of Def_Mucispirillum, Des_Desulfovibrio and Odo Odoribacter were observed in HFPO-TA exposed mice. Additionally, KEGG metabolic pathway analysis revealed that HFPO-TA exposure changed the unsaturated fatty acid synthesis, fatty acid metabolism, glyoxylic acid and dicarboxylic acid metabolism, galactose metabolism pathway and other metabolic pathways. Collectively, all these findings indicate the potential gut toxicity of HFPO-TA and is perceived as a risk of health on gut microbiota. Future investigations should be warranted.

Crocin-I Protects Against High-Fat Diet-Induced Obesity via Modulation of Gut Microbiota and Intestinal Inflammation in Mice

Crocin-I can regulate physiological changes in the human body by altering inflammation and microbial composition. Gut microbiota are also involved in modulating the pathophysiology of obesity. However, crocin-I’s effect on obesity and the mechanism underlying its effects on gut microbiota and inflammation remain poorly understood. Here, high-fat diet (HFD) -induced obese mice were administrated crocin-I (20 mg/kg/day) for 10 weeks using an oral gavage (HFD-C20 group). HFD-C20, HFD, and Normal chow (NC) groups were compared. The fat content, colon tissue inflammatory cytokine levels, gut microbiota, and short-chain fatty acids (SCFAs) levels were measured. We show that crocin-I reduced body weight and liver weight and improved glucose resistance in HFD-induced mice, and reduced the lipid accumulation in the liver. Strikingly, crocin-I alleviated intestinal microbial disorders and decreased the F/B ratio and the abundance of Proteobacteria in HFD-induced obese mice. Crocin-I also rescued the decrease in the levels of SCFAs and repaired altered intestinal barrier functioning and intestinal inflammation in HFD-induced obese mice. These findings indicate that crocin-I may inhibit obesity by modulating the composition of gut microbiota and intestinal inflammation.

Next generation per- and poly-fluoroalkyl substances: Status and trends, aquatic toxicity, and risk assessment

Widespread application of poly- and per-fluoroalkyl substances (PFAS) has resulted in some substances being ubiquitous in environmental matrices. That and their resistance to degradation have allowed them to accumulate in wildlife and humans with potential for toxic effects. While specific substances of concern have been phased-out or banned, other PFAS that are emerging as alternative substances are still produced and are being released into the environment. This review focuses on describing three emerging, replacement PFAS: perfluoroethylcyclohexane sulphonate (PFECHS), 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFAES), and hexafluoropropylene oxide dimer acid (HFPO-DA). By summarizing their physicochemical properties, environmental fate and transport, and toxic potencies in comparison to other PFAS compounds, this review offers insight into the viabilities of these chemicals as replacement substances. Using the chemical scoring and ranking assessment model, the relative hazards, uncertainties, and data gaps for each chemical were quantified and related to perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) based on their chemical and uncertainty scores. The substances were ranked PFOS > 6:2 Cl-PFAES > PFOA > HFPO-DA > PFECHS according to their potential toxicity and PFECHS > HFPO-DA > 6:2 Cl-PFAES > PFOS > PFOA according to their need for future research. Since future uses of PFAS remain uncertain in the face of governmental regulations and production bans, replacement PFAS will continue to emerge on the world market and in the environment, raising concerns about their general lack of information on mechanisms and toxic potencies.

Gestational exposure to GenX induces hepatic alterations by the gut-liver axis in maternal mice: A similar mechanism as PFOA

GenX is an alternative to perfluorooctanoic acid (PFOA) and was included in the accession list of Substances of Very High Concern in 2019. Gestational GenX exposure induces maternal hepatotoxicity in animals. However, the mechanisms of GenX toxicity have not been explored. In the present study, pregnant Balb/c mice were administered with PFOA (1 mg/kg BW/day), GenX (2 mg/kg BW/day), or Milli-Q water by gavage during gestation. Similar hepatic pathological changes, including enlargement of hepatocytes, cytoplasm loss, nucleus migration, inflammatory cell infiltration, and reduction of glycogen storage, were observed in PFOA and GenX groups. Increased expression levels of indicators of the TLR4 pathway indicated activation of inflammation in the liver of maternal mice after exposure to PFOA or GenX, consistent with the pathological changes. Overexpression of cleaved PARP-1, cleaved caspase 3, Bax and decreased Bcl-2 proteins indicated activation of apoptosis, whereas overexpression of ULK-1, p62, beclin-1, LC3-II proteins and downregulation of p-mTOR implied that PFOA and GenX exposure initiated autophagy. Decreased secretion of mucus, reduced expression levels of tight junction proteins, and higher serum levels of lipopolysaccharide indicated disruption of the intestinal barrier. Translocation of lipopolysaccharide may be recognized by TLR4, thus triggering inflammatory pathway in the maternal liver. In summary, gestational exposure to PFOA or GenX induced maternal hepatic alterations through the gut-liver axis.

Developmental toxicity of Nafion byproduct 2 (NBP2) in the Sprague-Dawley rat with comparisons to hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX) and perfluorooctane sulfonate (PFOS)

Nafion byproduct 2 (NBP2) is a polyfluoroalkyl ether sulfonic acid that was recently detected in surface water, drinking water, and human serum samples from monitoring studies in North Carolina, USA. We orally exposed pregnant Sprague-Dawley rats to NBP2 from gestation day (GD) 14-18 (0.1-30 mg/kg/d), GD17-21, and GD8 to postnatal day (PND) 2 (0.3-30 mg/kg/d) to characterize maternal, fetal, and postnatal effects. GD14-18 exposures were also conducted with perfluorooctane sulfonate (PFOS) for comparison to NBP2, as well as data previously published for hexafluoropropylene oxide-dimer acid (HFPO-DA or GenX). NBP2 produced stillbirth (30 mg/kg), reduced pup survival shortly after birth (10 mg/kg), and reduced pup body weight (10 mg/kg). Histopathological evaluation identified reduced glycogen stores in newborn pup livers and hepatocyte hypertrophy in maternal livers at ≥ 10 mg/kg. Exposure to NBP2 from GD14-18 reduced maternal serum total T₃ and cholesterol concentrations (30 mg/kg). Maternal, fetal, and neonatal liver gene expression was investigated using RT-qPCR pathway arrays, while maternal and fetal livers were also analyzed using TempO-Seq transcriptomic profiling. Overall, there was limited alteration of genes in maternal or F1 livers from NBP2 exposure with significant changes mostly occurring in the top dose group (30 mg/kg) associated with lipid and carbohydrate metabolism. Metabolomic profiling indicated elevated maternal bile acids for NBP2, but not HFPO-DA or PFOS, while all three reduced 3-indolepropionic acid. Maternal and fetal serum and liver NBP2 concentrations were similar to PFOS, but ∼10-30-fold greater than HFPO-DA concentrations at a given maternal oral dose. NBP2 is a developmental toxicant in the rat, producing neonatal mortality, reduced pup body weight, reduced pup liver glycogen, reduced maternal thyroid hormones, and altered maternal and offspring lipid and carbohydrate metabolism similar to other studied PFAS, with oral toxicity for pup loss that is slightly less potent than PFOS but more potent than HFPO-DA.