Administration of ammonium salts of perfluorooctanoate (PFOA) to rats results in peroxisome proliferation and benign liver tumors, events associated with activation of the nuclear receptor (NR) peroxisome proliferator-activated receptor-α (PPARα). Due to its fatty acid structure, PFOA may activate other NRs, such as PPARβ, PPARγ, liver X receptor (LXR), or retinoid X receptor (RXR). In this study, the activation of human, mouse, and rat PPARα, PPARβ, PPARγ, LXRβ, and RXRα by PFOA (including its linear and branched isomers) and perfluorooctane sulfonate (PFOS) was investigated and compared to several structural classes of natural fatty acids and appropriate positive control ligands. An NR ligand-binding domain/Gal4 DNA-binding domain chimeric reporter system was used. Human, mouse, and rat PPARα were activated by PFOA isomers and PFOS. PPARβ was less sensitive to the agents tested, with only PFOA affecting the mouse receptor. PFOA and PFOS also activated human, mouse, and rat PPARγ, although the maximum induction of PPARγ was much less than that seen with rosiglitazone, suggesting that PFOA and PFOS are partial agonists of this receptor. Neither LXRβ nor the common heterodimerization partner RXRα was activated by PFOA in any species examined. Taken together, these data show that of the NRs studied, PPARα is the most likely target of PFOA and PFOS, although PPARγ is also activated to some extent. Compared to naturally occurring long-chain fatty acids, e.g. linoleic and α-linolenic acids, these perfluorinated fatty acid analogs were more selective and less potent in their activation of the NRs.
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