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Evaluation of Transcriptomic Responses in Livers of Mice Exposed to the Short-Chain PFAS Compound HFPO-DA

ABSTRACT: HFPO-DA (ammonium 2,3,3,3-tetrafluoro-2-(heptafluoropropoxy)-propanoate; CASRN 62037-80-3; trade name “GenX”) is an alternative to environmentally persistent per- and poly-fluorinated alkyl substances (PFAS). The liver is the primary target of toxicity for HFPO-DA in rodents and previous examination of hepatic transcriptomic responses in mice following oral exposure to HFPO-DA for 90 days showed induction of peroxisome proliferator-activated receptor (PPAR) signaling pathways, predominantly by PPAR alpha, as well as increased gene expression of both peroxisomal and mitochondrial fatty acid metabolism. To further investigate the mechanism of liver toxicity, transcriptomic analysis was conducted on liver tissue from mice orally exposed to 0, 0.1, 0.5 or 5 mg/kg-bw/day HFPO-DA in a reproduction/developmental toxicity study. Hepatic gene expression changes were consistent with the previous 90-day mouse study, demonstrating activation of the PPAR alpha signaling pathway. Peroxisomal and mitochondrial fatty acid beta-oxidation gene sets were enriched at lower HFPO-DA concentrations, and complement cascade, cell cycle and apoptosis related gene sets were enriched at higher HFPO-DA concentrations. These results support the reported histopathological findings in livers of mice from this study and indicate that these effects are mediated through rodent-specific PPAR alpha signaling mechanisms.

ORGANISM(S): Mus musculus

PROVIDER: GSE202302 | GEO | 2022/06/08

REPOSITORIES: GEO

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Project description:Nafion byproduct 2 (NBP2; CAS: 749836-20-2; Product #: 6164-3-3J; Lot: 512400; SynQuest Laboratories Alachua, FL, USA) 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.

Project description:Per- and polyfluoroalkyl substances (PFAS) are chemicals that are relatively resistant to degradation. While such features are desirable in a variety of consumer and industry products, such as firefighting foams and non-stick cookware coating, some PFAS, including perfluorooctanoic acid (PFOA), are toxic and bioaccumulate. Hexafluoropropylene oxide dimer acid (HFPO-DA) is an emerging PFAS developed to replace PFOA and has not been extensively studied. To evaluate the potential toxicity of HFPO-DA with a cost- and time-efficient approach, we exposed C. elegans larvae to 4×10-9–4 g/L HFPO-DA in liquid media and performed assays measuring developmental, behavioral, locomotor, and transcriptional effects at various exposure levels. After 48 hours of 1.5–4 g/L HFPO-DA exposure, acute developmental toxicity was observed as developmental delay; statistically significantly delayed (p < 0.05) progeny production was observed in worms exposed to 2–4 g/L HFPO-DA. After 48 hours of 4×10-9–0.4 g/L exposure, no significant behavioral or locomotor effect was observed relative to the 0 g/L control group. Statistically significant differential gene expression was identified with over 99% confidence via the R-package NOISeq in all fourteen 48-hour 1.25×10¬-5–4 g/L HFPO-DA exposure groups, except for 6.25×10¬-5 g/L. Among 10298 genes analyzed, 2624 differentially expressed genes (DEGs) were identified in the developmentally delayed 4 g/L group only, and 78 genes were differentially expressed in at least one of the thirteen exposure groups testing 1.25×10¬-5–2 g/L HFPO-DA exposures. Genes encoding for detoxification proteins such as cytochrome P450 enzymes and UDP glucuronosyltransferases are upregulated in 0.25–4 g/L acute exposure groups. In the lower exposure concentration groups, statistically significant gene expression changes were also observed, though these DEGs did not share any biological functions, except for six ribosomal protein-coding genes. While our transcriptional data is insufficient for conclusive mechanistic explanation, the statistically significant gene expression differences detected at 1.25×10¬-5 g/L, the lowest concentration tested for transcriptional changes, is concerning and calls for further targeted analyses that focus on low-dose HFPO-DA exposure effects.

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Evaluation of Transcriptomic Responses in Livers of Mice Exposed to the Short-Chain PFAS Compound HFPO-DA

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