Endocrine activity assessment approaches: From mechanistic bioassays to adverse pathway outcomes

Pristopi za ocenjevanje endokrine aktivnosti: od mehanističnih bioloških testov do poti neželenih izidov

Abstract

Purpose: To provide an integrated overview of current approaches for detecting and characterizing endo­crine activity in chemicals by em­phasizing the relationship between mechanistic in vitro assays, in vivo models, and regulatory frameworks.

Methods: Recent developments in high-throughput screening (HTS) platforms, validated Organisation for Economic Co-operation and De­velopment (OECD) test guidelines, and effect-based bioassays were crit­ically compared. The review covers representative assays for estrogen­ic, androgenic, thyroid, and ste­roidogenic pathways and evaluates the complementarity within adverse outcome pathway (AOP) frame­works. Attention was given to data integration, bioavailability consid­erations, and regulatory adoption under the European Union Regis­tration, Evaluation, Authorization, and Restriction of Chemicals (REACH) and the US En­vironmental Protection Agency (EPA) Endocrine Dis­ruptor Screening Program.

Results: Mechanistic assays, such as YES, E-Screen, HeLa-9903, and H295R, provide rapid, sensitive, and cost-effective screening for receptor-mediated and ste­roidogenic effects. In contrast, in vivo systems, including vitellogenin induction, Daphnia reproduction, amphib­ian metamorphosis, and zebrafish assays, yield organ­ism-level confirmation. Integrating both tiers within AOP and quantitative in vitro-to-in vivo extrapolation (QIVIVE) frameworks increases predictive reliability. Despite advances in standardization, challenges remain concerning metabolic competence, inter-laboratory variability, and harmonized effect thresholds.

Conclusion: Endocrine testing science is transitioning toward mechanistically anchored, animal-reduced strat­egies that combine HTS, computational modeling, and effect-based monitoring. Harmonized validation cri­teria and performance standards will further enhance regulatory acceptance and facilitate the efficient identi­fication of substances with endocrine activity across both human health and environmental contexts.