Affinity of PFAS with Baikal PPARα seals revealed by in vitro and in silico approaches

A team of researchers from the Ehime University revealed the affinity affinities of perfluoroalkyl substances (PFAS) with the Baikal peroxisome proliferator activated receptor α (PPARα) using in vitro and in silico approaches. The discovery was published Jan. 16 in the highly regarded journal Environmental Science, Environmental Science and Technology.

PFAS, such as perfluoroalkyl carboxylates (PFCA) and perfluoroalkyl sulfonates (PFSA), are synthetic organic chemicals, which have been detected globally in the environment, humans and wildlife. Because of their persistence in the environment, their bioaccumulation potential and their toxic properties, one PFAS, perfluorooctane sulfonic acid (PFOS), is regulated internationally by the Stockholm Convention on Organic Pollutants. Persistent (POP). Moreover, no other PFSA regulations have been implemented worldwide.

The Baikal seal (Pusa sibirica), a species of freshwater mammal, is one of the main predators of Lake Baikal, Russia. It is exposed to various POPs such as dioxins, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and organochlorine pesticides. In addition, our research group previously determined levels of accumulation of various PFAS in wild Baikal seal tissues, particularly high for PFOS, perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA). However, the toxic effects and risks of PFAS in animals, particularly in non-modeled wildlife, are not fully understood.

In this paper, we evaluated the binding affinities of PFAS with different carbon chain lengths (C4-C11) at the in vitro synthesized Baikal joint, PPARα. Similar experiments were also performed for human PPARα and the results were compared to those of Baikal seal PPARα to investigate interspecific differences in the role of PPARα in PFAS toxicity. PPARα is a member of the ligand-activated nuclear receptor superfamily. This receptor protein participates in the regulation of lipid metabolism in the liver and is therefore involved in liver tumors. Previous studies have investigated the ability of PFAS to activate mouse, rat and human PPARα in in vitro reporter gene badays, suggesting disruption of the PPARα signaling pathway by PFAS. However, it has not been investigated whether PFAS may interact with PPARa seals actually contaminated with PFAS.

A competitive in vitro binding baday showed that six PFCAs and two APFS bound to the Baikal seal PPARa synthesized in vitro in a dose-dependent manner. PFOS, PFDA, PFNA and perfluoroundecanoic acid (PFUnDA) showed higher binding affinities with PPARa from the Baikal seal compared with other PFAS. In addition, PPARα in silico homology modeling predicted the existence of two ligand binding pockets in PPARα of the Baikal seal and the LBD of human PPARÎ ±. Structure-activity relationship badyzes suggest that PPARα PFAS binding capabilities may be dependent on LBP binding cavity volume, hydrogen bonding interactions, perfluorinated carbon number, and PFAS hydrophobicity. An interspecific comparison of in vitro binding affinities revealed that PPARα of the Baikal seal had a higher preference for PFAS with long carbon chains than that of human PPARα. In silico mooring simulations suggested that the 1st LBP of the Baikal PPARÎ ± seal had higher affinities than that of human PPARα; however, the second LBP of Baikal seals PPARα had lower affinities than human PPARα. The interaction energies of the PFAS with the Baikal seal PPARα (first and second LBP) determined using in silico coupling simulations showed a significant negative correlation with their binding affinities determined at the same time. Assay of PPARα binding badays in vitro. These results suggest that in silico docking simulation could be a useful tool for the screening of potential PPARα ligands for the seal. To our knowledge, this is the first evidence to show interspecific differences in binding. PFASs to PPARa and their structure-activity relationships. These results prompt us to integrate these in vitro and in silico approaches into the badessment of PFAS risk in seal species.