Equipotent bisphenol S and bisphenol F with widely differing modes of action exhibit additive effects in immunotoxicity: insights based on intrinsic immunity, apoptosis and regeneration, and oxidative stress.

Bisphenol S (BPS) and Bisphenol F (BPF), as alternatives to bisphenol A (BPA), are recognized for their endocrine-disrupting properties, but their combined immune toxicity mechanisms remain poorly understood. This study systematically evaluates the individual and joint immune toxicity effects of BPS and BPF through ADMET predictions, transgenic zebrafish models, and molecular docking analyses. The results indicate that equal effect concentration BPS and BPF act through distinct immune pathways: BPS primarily targets macrophages to mediate immune responses, while BPF significantly stimulates neutrophil proliferation and induces a stronger inflammatory response through chemokine signaling. Molecular docking studies show that BPF binds more stably to pro-apoptotic protein Mapk8 and oxidative stress-related protein Hsp90aa1, leading to significantly higher levels of apoptosis and reactive oxygen species (ROS) compared to BPS. The similarity of modes of action (MOA)between BPS and BPF based on relevant immune indicators calculated and experimentally is about 0.3; this quantitative result also proves that modes of action differ widely. Nonetheless, most of the indicators showed superimposed effects in the combined experiments, and it is noteworthy that the oxidative stress indicators (SOD, MDA) showed synergistic effects, suggesting that BPS and BPF, which have very different modes of action, are able to be risk assessed using an additive model with respect to immunity, but may exhibit synergistic risks with respect to oxidative stress. This research demonstrates that BPS and BPF induce immune toxicity via different molecular targets and pathways and highlights the need to account for their synergistic effects in risk assessments. These findings provide important insights into the immune toxicity mechanisms of BPA substitutes and the potential risks of combined exposures.