Does zearalenone have estrogen-like activity and add to BPA’s endocrine effects?

Zearalenone (ZEN) is a non-steroidal mycoestrogen that functions as a potent endocrine disruptor. Emerging evidence highlights its capacity to mimic natural hormones and interact cumulatively with other environmental estrogens, such as bisphenol A (BPA).

Receptor binding and activation mechanisms

• Direct ER Binding: ZEN competitively binds estrogen receptors, displaying nanomolar affinities with half-maximal inhibitory concentration ($\text{IC}_{50}$) values of approximately 240 nM for $\text{ER}\alpha$ and 166 nM for $\text{ER}\beta$ (representing 7–11% of the relative binding affinity of $17\beta$-estradiol).
• Metabolic Activation: ZEN undergoes hepatic reduction to form $\alpha$-zearalenol ($\alpha$-ZEL), a highly active metabolite that binds estrogen receptors with even greater potency, approaching near-estradiol affinity.
• Downstream Signaling: Upon binding, ZEN and its metabolites drive genomic transcription by binding to estrogen response elements (EREs) on DNA. ZEN acts as a full agonist on $\text{ER}\alpha$ to stimulate cell proliferation, and as a mixed agonist-antagonist on $\text{ER}\beta$.

Additive effects with bisphenol A

• Concentration-Additive Estrogenicity: Direct in vitro research in human endometrial (Ishikawa) cells demonstrates that binary mixtures of ZEN and BPA produce concentration-additive estrogenic effects.
• Shared Receptor Pathways: Co-exposure activates $\text{ER}$-mediated endpoints, such as alkaline phosphatase activity, following a dose-addition model rather than synergistic or antagonistic pathways.
• Cumulative Tissue Risks: Simultaneous exposure increases the overall occupancy of estrogen receptors, jointly promoting proliferative gene expression profiles in estrogen-sensitive tissues and heightening reproductive or tumorigenic risks.

Bottom line

• Zearalenone exerts strong estrogenic activity by binding and activating estrogen receptors—a process potentiated by its highly active metabolite $\alpha$-zearalenol—and acts in a concentration-additive manner with bisphenol A to significantly elevate the cumulative estrogenic burden in human tissues.