Hazard assessment through hybrid in vitro / in silico approach: The case of zearalenone

Abstract

SummaryWithin the framework of reduction, refinement and replacement of animal experiments, new approaches for identification and characterization of chemical hazards have been developed. Grouping and read-across has been promoted as a most promising alternative approach. It uses existing toxicological information on a group of chemicals to make predictions on the toxicity of uncharacterized ones. In the present work, the feasibility of applying in vitro and in silico techniques to group chemicals for read-across was studied using the food mycotoxin zearalenone (ZEN) and metabolites as a case study. ZEN and its reduced metabolites are known to act through activation of the estrogen receptor α (ERα). The ranking of their estrogenic potencies appeared highly conserved across test systems including binding, in vitro and in vivo assays. This data suggests that activation of ERα may play a role in the molecular initiating event (MIE) and be predictive of adverse effects, and it provides the rationale to model receptor-binding for hazard identification. The investigation of receptor-ligand interactions through docking simulation proved to accurately rank estrogenic potencies of ZEN and reduced metabolites, showing the suitability of the model to address estrogenic potency for this group of compounds. Therefore, the model was further applied to biologically uncharacterized, commercially unavailable, oxidized ZEN metabolites (6α-, 6β-, 8α-, 8β-, 13-and 15-OH-ZEN). Except for 15-OH-ZEN, the data indicate that in general, the oxidized metabolites would be considered of lower estrogenic concern than ZEN and reduced metabolites.

Hazard identification of cis/trans -zearalenone through the looking-glass

“…All protein structures and ligands were processed by using the software Sybyl version 8.1 (www.tripos.com), as previously reported (Ehrlich et al, 2015).…”

“…More in details, HINT score provides the evaluation of thermodynamic benefits of protein-ligand complex formation, and therefore low/negative scores indicate the lack of appreciable protein-ligand interactions (Kellogg and Abraham, 2000;Cozzini et al, 2002;Fornabaio et al, 2003Fornabaio et al, , 2004. Software setting and rescoring procedures reported by Ehrlich (Ehrlich et al, 2015) were used. With the only exception, in docking parameters only H524 was set as flexible in order to reduce computing time for docking simulation on ERa-LBD.…”

“…The human and livestock exposure to ZEN through the diet poses health concern due to the onset of several sexual disorders and alterations in the development of sexual apparatus (Massart and Saggese, 2010;Schoevers et al, 2012). The direct binding and activation of the estrogen receptors (ERs), which are ligand-induced transcriptional factors, have been recognized as the molecular initiating event triggering the xenoestrogenic response (Ehrlich et al, 2015). Due to the estrogenic activity for mammals, major efforts are spent to develop strategies for mitigating ZEN contamination levels in food, feed and raw materials.…”

“…We have already shown that an in silico approach based on docking simulations and rescoring procedure can be used to assess the xenoestrogenic activity of trans-ZEN and metabolites by estimating the interaction with the alpha isoform of the estrogen receptor ligand binding domain (ERa-LBD) (Ehrlich et al, 2015;Cozzini and Dellafiora, 2012). In order to widely estimate the effect of human metabolism on the activity of cis-ZEN, several computed metabolites and the phase-I human metabolites resolved so far (i.e.…”

Mycotoxins and Nuclear Receptors: A Still Underexplored Issue

“…This approach was further exploited to predict and rank ZEN metabolites towards ER for hazard characterization [43,44]. The investigation of receptor-ligand interactions through docking simulation proved to accurately rank estrogenic potencies of ZEN and its metabolites, showing the suitability of the model to address estrogenic potency for this group of compounds [43,44].…”