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.