Beyond estrogenicity: a comparative assessment of bisphenol A and its alternatives in in vitro assays questions safety of replacements

Bisphenol A (BPA) is a well-known endocrine disruptor linked to numerous adverse health outcomes and was, therefore, banned in food-contact materials in the European Union. Numerous alternatives are now in commerce, but their health hazards are often inadequately addressed. This study compared BPA and 26 alternatives in six in vitro bioassays for cytotoxicity, endocrine disruption, xenobiotic metabolism, adaptive stress responses, mitochondrial toxicity, and neurotoxicity. We developed a cumulative specificity ratio score that integrates the degree of specific activation and overall toxicological activity across a test battery, enabling direct comparison of BPA with its alternatives. Several alternatives with close structural resemblance showed similar or stronger activation of the estrogen receptor α (ERα) than BPA. The lack of estrogenicity for several BPA alternatives, e.g., 4-(4-phenylmethoxyphenyl)sulfonylphenol (BPS-MPE), was accompanied by a shift toward peroxisome proliferator-activated receptor γ (PPARγ) activation, a receptor that is not relevant for BPA itself. Some alternatives additionally inhibited mitochondrial functions and caused neurotoxicity. Simulated phase I metabolism reduced the cytotoxicity of all alternatives except for methyl bis(4-hydroxyphenyl)acetate (Bz) and 4-[[4-(allyloxy)phenyl]sulfonyl]phenol (BPS-MAE), while estrogenic activity remained unchanged or decreased. This study demonstrates the utility of bioassays for rapid hazard assessment and comparative evaluation, suggesting that many BPA alternatives are regrettable substitutes, although 2,2,4,4-tetramethyl-1,3-cyclobutanediol (TMCD) is a potentially more benign alternative.