Host: The Japanese Society of Toxicology
Name : The 51st Annual Meeting of the Japanese Society of Toxicology
Date : July 03, 2024 - July 05, 2024
[Introduction] PXR has attracted attention as a target for the toxic effects of chemicals due to its low ligand specificity and activated with a wide range of chemicals. Recently, we found four phenolic antioxidants (PAs) have potent agonist activity against human PXR (hPXR) compared to rat PXR (rPXR). Here, we performed in vitro and in silico analyses to study in detail the responsiveness of hPXR to PAs and the factors responsible for species difference.
[Methods] The hPXR agonist activity of the four PAs was evaluated using reporter assay in human HepG2 cells. In addition, the expression of PXR target genes in response to PAs in human LS180 cells was analyzed using RT-PCR. Then, docking analysis was performed to calculate the binding affinity and mode of binding of PAs to the hPXR LBD. Lastly, the PA responsiveness of the rPXR mutant converted to the human form was assessed by reporter analysis.
【Results & Discussion】 In reporter and mRNA expression analyses, all four PAs showed potent hPXR agonist activity, two of which were more potent at lower concentrations than the known agonist RIF. The known antagonist SPA70 strongly inhibited their effect. Subsequent docking analysis predicted that two polar amino acid residues within the LBD contributed to the interaction with PAs. Lastly, replacement of amino acids in the rPXR with the corresponding human residues reduced constitutive and maximal activity but increased the fold activation by PAs. In conclusion, our study provides details of the interaction of PAs with PXRs, which may be useful for the safety assessment of PAs.
