The potential endocrine disruption mechanism of anthelmintic drug niclosamide by activating estrogen receptors and estrogen-related receptors

Niclosamide (NIC), a helminthic drug used widely for controlling schistosomiasis, can reportedly disrupt the endocrine system. However, its underlying mechanisms are still unclear. In this study, we revealed the potential endocrine disruption mechanism of NIC by activating estrogen receptors (ERs) and estrogen-related receptors (ERRs). The binding potency of NIC with ER alpha, ER beta and ERR alpha were determined by fluorescence competitive binding assays, which shows an IC50 (the concentration of NIC needed to displace 50 % of the probe from the receptor) of 90 +/- 4.1, 10 +/- 1.7 nM and 0.59 +/- 0.07 nM respectively. The IC50 for ERR. is the lowest one among the three detected receptors, which is three orders of magnitude lower than the known agonist GSK4716. The transcriptional activities of NIC on ERs and ERRs were detected by MVLN cells (stably transfected with ERs reporter gene) and HeLa cells (transiently transfected with ERRs reporter gene)-based luciferase reporter gene assay. The lowest observable effective concentration (LOEC) ranked as follows: ERR gamma (0.5 nM) < ERR alpha (10 nM) < ERs (100 nM). The maximum observed induction rate for ERR gamma (294 %) was higher than that for ERRa (191 %). The maximum observed induction rate of NIC for ERs was 30 % relative to 17 beta-estradiol. In addition, we simulated the interactions of NIC with ERs and ERRs by molecular docking. NIC could dock into the ligand binding pockets of ERs and ERRs and form hydrogen bonds with different amino acids. The binding energy ranked as follows: ERR gamma (-8.90 kcal/mol) < ER beta (-7.57 kcal/mol) < ERR alpha (-7.15 kcal/mol) < ER alpha (-6.53 kcal/mol), which implied that NIC bound to ERR gamma with higher binding affinity than the other receptors. Overall, we clarify that ERR gamma might be the dominant target for NIC in cells rather than ERR alpha and ERs. We reveal potential novel mechanisms for the endocrine disruption effects of NIC by activating both ERRs and ERs at environmentally-related nanomolar levels.