The 2018 EFSA/ECHA guidance for identifying endocrine-disrupting (ED) properties in biocidal and plant protection products (BP/PPPs) requires linking mechanistic data with in vivo adverse effects, focusing on EATS modalities (estrogen, androgen, thyroid, and steroidogenesis). Non-EATS modalities, such as retinoid signaling, also play critical roles in ED effects. This project explored chemical effects on retinoid signaling by targeting a key enzyme in retinoic acid biosynthesis (RALDH) and the retinoic acid receptor (RAR) as well as inhibition of CYP19 (aromatase) as part of the steroidogenesis pathway.
We tested 21 BP/PPP active substances and selected pharmaceuticals using RAR activity, RALDH inhibition, and CYP19 inhibition assays. Several chemicals increased RARα activity, whereas none antagonized the activity of the receptor. Ten test chemicals inhibited aromatase activity with azoles causing most marked effects. RALDH inhibition was observed for dimethomorph and fenitrothion, while triphenyltin and tributyltin chloride displayed non-monotonic concentration-response patterns. In vitro results were largely consistent with US Tox21 data, supporting model robustness. QSAR models for RAR inhibition were developed and validated using available experimental data from ~10,000 compounds. Finally, Adverse Outcome Pathway (AOP) relevant for perturbed retinoid signaling were developed, focusing on reproductive effects.
These methods, if combined, can enhance the ability to screen for non-EATS-mediated ED effects and provide mechanistic insights into reproductive toxicity, supplementing EFSA/ECHA guidelines. While in vitro and in silico methods alone are insufficient to confirm ED properties, they improve chemical prioritization, reduce reliance on animal testing, and advance the development of integrated testing strategies emphasizing multiple mechanisms of action.
ToAD - Improved Tools to Assess whether biocides and plant protection products have endocrine Disrupting properties
Pesticide Research no. 229