Citation:

Matteo, G., K. Leingartner, A. Rowan-Carroll, M. Meier, A. Williams, M. Beal, M. Gagne, R. Farmahin, S. Wickramasuriya, A. Reardon, T. Barton-Maclaren, Jon Corton, C. Yauk, AND E. Atlas. In vitro transcriptomic analyses reveal pathway perturbations, estrogenic activities, and potencies of data-poor BPA alternative chemicals. TOXICOLOGICAL SCIENCES. Society of Toxicology, RESTON, VA, 191(2):266-275, (2023). https://doi.org/10.1093/toxsci/kfac127

Impact/Purpose:

Bisphenol A (BPA) is an endocrine disruptor that interacts with nuclear hormone receptors, as well as altering non-hormonal pathways, to exert its effects (Cimmino et al. 2020). Exposure to BPA is associated with multi-organ toxicity and negative health outcomes including metabolic and endocrine dysfunction, reproductive and developmental disorders, and hormone-related cancer (Ma et al. 2019). Canada was the first country to take regulatory action to limit exposure to BPA in 2008, followed by the USA, the EU, and others (Rogers 2021). As pressures to phase out BPA increase, manufacturers are relying more on BPA alternative chemicals. BPA alternative chemicals are detected in the environment, consumer products, and in humans (Chen et al. 2016). Many of these chemicals are structurally similar to BPA but differ in their adjoining atom and aryl substituents. A systematic review has highlighted the ability of bisphenol S (BPS), a sulfone-based bisphenol, and bisphenol F (4,4’-BPF), a BPA analogue missing the geminal methyl groups, to act as endocrine disruptors at similar concentrations to BPA (Rochester and Bolden 2015). Some substitutes are less structurally related to BPA, like Pergafast201® and BTUM; these are nonphenolic sulphonyl urea-based alterative chemicals used primarily in thermal paper (Björnsdotter et al. 2017). Several of these alternative chemicals are also associated with endocrine disruption, reproductive toxicity, and carcinogenicity (den Braver-Sewradj et al. 2020). Thus, there is a clear need to identify potential hazards and determine relative potencies of BPA alternative chemicals. An important approach to screening BPA alternatives is to specifically compare potencies based on interactions with the estrogen receptor (ER). For example, Kitamura and colleagues tested the effects of several BPA alternatives using MCF-7 cells transfected with an estrogen response element (ERE) luciferase reporter (Kitamura et al. 2005). Bisphenol AF (BPAF) and bisphenol B (BPB) stimulated estrogenic activity at lower concentrations than BPA, whereas BPS and 4,4’-BPF required higher concentrations. Mesnage et al 2017 found that BPAF, a hexafluoro bisphenol, was the most potent BPA alternative in stimulating an ERE-mediated luciferase reporter gene relative to BPB, bisphenol Z (BPZ), BPA, 4,4’-BPF, bisphenol AP (BPAP), and BPS (Mesnage et al. 2017). The same study also conducted whole genome transcriptomic analysis with MCF-7 cells and observed that these BPA alternatives perturbed Gene Ontology (GO) gene sets associated with cell cycle, steroid hormone response, and breast cancer. Nuclear receptor activation can also be assessed through the analysis of transcriptomic biomarkers. Toward this, a 46 transcriptomic biomarker associated with ERα was developed and validated in the ERα-positive MCF-7 cells (Ryan et al. 2016). This biomarker predicts compounds that activate ERα through statistical comparisons of gene expression profiles of the 46 biomarker genes, with a pattern of 32 up-regulated and 14 down-regulated genes following ER activation. This approach can be used to identify the potential for the chemicals to interact with ERα and produce a composite BMC score for the biomarker to compare potencies for this specific molecular initiating event. 

Description:

Since initial regulatory action in 2010 in Canada, bisphenol A (BPA) has been progressively replaced by structurally related alternative chemicals. Unfortunately, many of these chemicals are data-poor, limiting toxicological risk assessment. We used high-throughput transcriptomics to evaluate potential hazards and compare potencies of BPA and 15 BPA alternative chemicals in cultured breast cancer cells. MCF-7 cells were exposed to BPA and 15 alternative chemicals (0.0005 – 100 µM) for 48 hrs. TempO-Seq (BioSpyder Inc.) was used to examine global transcriptomic changes and estrogen receptor alpha (ERα)-associated transcriptional changes. Benchmark concentration (BMC) analysis was conducted to identify two global transcriptomic points of departure (tPODs): (a) the lowest pathway median gene BMC and (b) the 25th lowest rank-ordered gene BMC. ERα activation was evaluated using a published transcriptomic biomarker and an ERα-specific tPOD was derived. Genes fitting BMC models were subjected to upstream regulator and canonical pathway analysis in Ingenuity Pathway Analysis. Biomarker analysis identified BPA and eight alternative chemicals as ERα active. Global and ERα tPODs produced highly similar potency rankings with bisphenol AF (BPAF) as the most potent chemical tested, followed by BPA and bisphenol C (BPC). Further, BPA and transcriptionally active alternative chemicals enriched similar gene sets associated with increased cell division and cancer-related processes. These data provide support for future read-across applications of transcriptomic profiling for risk assessment of data-poor chemicals and suggest that several BPA alternative chemicals may cause hazards at similar concentrations to BPA.

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