GenX analogs exposure induced greater hepatotoxicity than GenX mainly via activation of PPARα pathway while caused hepatomegaly in the absence of PPARα in female mice.

Despite their use as substitutes for perfluorooctanoic acid, the potential toxicities of hexafluoropropylene oxide dimer acid (HFPO-DA, commercial name: GenX) and its analogs (PFDMOHxA, PFDMO2HpA, and PFDMO2OA) remain poorly understood. To assess the hepatotoxicity of these chemicals on females, each chemical was orally administered to female C57BL/6 mice at the dosage of 0.5 mg/kg/d for 28 d. The contribution of peroxisome proliferator-activated receptors (PPARα and γ) and other nuclear receptors involving in these toxic effects of GenX and its analogs were identified by employing two PPAR knockout mice (PPARα-/- and PPARγΔHep) in this study. Results showed that the hepatotoxicity of these chemicals increased in the order of GenX < PFDMOHxA < PFDMO2HpA < PFDMO2OA. The increases of relative liver weight and liver injury markers were significantly much lower in PPARα-/- mice than in PPARα+/+ mice after GenX analog exposure, while no significant differences were observed between PPARγΔHep and its corresponding wildtype groups (PPARγF/F mice), indicating that GenX analog induce hepatotoxicity mainly via PPARα instead of PPARγ. The PPARα-dependent complement pathways were inhibited in PFDMO2HpA and PFDMO2OA exposed PPARα+/+ mice, which might be responsible for the observed liver inflammation. In PPARα-/- mice, hepatomegaly and increased liver lipid content were observed in PFDMO2HpA and PFDMO2OA treated groups. The activated pregnane X receptor (PXR) and constitutive activated receptor (CAR) pathways in the liver of PPARα-/- mice, which were highlighted by bioinformatics analysis, provided a reasonable explanation for hepatomegaly in the absence of PPARα. Our results indicate that GenX analogs could induce more serious hepatotoxicity than GenX whether there is a PPARα receptor or not. These chemicals, especially PFDMO2HpA and PFDMO2OA, may not be appropriate PFOA alternatives.

Bile acid metabolism disorder mediates hepatotoxicity of Nafion by-product 2 and perfluorooctane sulfonate in male PPARα-KO mice.

Perfluorooctane sulfonate (PFOS) and Nafion by-product 2 (H-PFMO2OSA) induce hepatotoxicity in male mice via activation of the peroxisome proliferator-activated receptor α (PPARα) pathway; however, accumulating evidence suggests that PPARα-independent pathways also play a vital role in hepatotoxicity after exposure to per- and polyfluoroalkyl substances (PFASs). Thus, to assess the hepatotoxicity of PFOS and H-PFMO2OSA more comprehensively, adult male wild-type (WT) and PPARα knockout (PPARα-KO) mice were exposed to PFOS and H-PFMO2OSA (1 or 5 mg/kg/d) for 28 d via oral gavage. Results showed that although elevations in alanine transaminase (ALT) and aspartate aminotransferase (AST) were alleviated in PPARα-KO mice, liver injury, including liver enlargement and necrosis, was still observed after PFOS and H-PFMO2OSA exposure. Liver transcriptome analysis identified fewer differentially expressed genes (DEGs) in the PPARα-KO mice than in the WT mice, but more DEGs associated with the bile acid secretion pathway after PFOS and H-PFMO2OSA treatment. Total bile acid content in the liver was increased in the 1 and 5 mg/kg/d PFOS-exposed and 5 mg/kg/d H-PFMO2OSA-exposed PPARα-KO mice. Furthermore, in PPARα-KO mice, proteins showing changes in transcription and translation levels after PFOS and H-PFMO2OSA exposure were involved in the synthesis, transportation, reabsorption, and excretion of bile acids. Thus, exposure to PFOS and H-PFMO2OSA in male PPARα-KO mice may disturb bile acid metabolism, which is not under the control of PPARα.