Continued efforts to phase out bisphenol A (BPA) from consumer products have been met with the challenges of finding safer alternatives.
This study aimed to determine whether early-life exposure to BPA and its related analogues, bisphenol AF (BPAF) and bisphenol S (BPS), could affect female pubertal mammary gland development and long-term mammary health in mice.
Timed pregnant CD-1 mice were exposed to vehicle, BPA (0.5, 5, 50mg/kg), BPAF (0.05, 0.5, 5mg/kg), or BPS (0.05, 0.5, 5mg/kg) via oral gavage between gestation days 10–17. Mammary glands were collected from resulting female offspring at postnatal day (PND) 20, 28, 35, and 56, and at 3, 8, and 14 months for whole mount, histopathological evaluation, and quantitative real-time polymerase chain reaction (qPCR); serum steroid concentrations were also measured at these time points.
In the bisphenol-exposed mice, accelerated mammary gland development was evident during early puberty and persisted into adulthood. By late adulthood, mammary glands from bisphenol-exposed female offspring exhibited adverse morphology in comparison with controls; most prominent were undifferentiated duct ends, significantly more lobuloalveolar hyperplasia and perivascular inflammation, and various tumors, including adenocarcinomas. Effects were especially prominent in the BPAF 5mg/kg and BPS 0.5mg/kg groups. Serum steroid concentrations and mammary mRNA levels of Esr1, Pgr, Ar, and Gper1 were similar to controls.
These data demonstrate that prenatal exposure of mice to BPAF or BPS induced precocious development of the mammary gland, and that siblings were significantly more susceptible to spontaneous preneoplastic epithelial lesions and inflammation, with an incidence greater than that observed in vehicle- and BPA-exposed animals.
Our findings suggest that exposure to BPAF and BPS by consumers such as women of child-bearing age or infants and children should be restricted. The fetal mammary gland is a sensitive target organ for these chemicals. BPAF and BPS prenatally exposed female mice developed proliferative epithelial lesions by midlife, concomitant with a significant inflammatory response that may predispose them to tumor formation later in life. In fact, animals in the high-dose BPS group developed adenocarcinomas prior to one year of life and those diagnoses triggered a necropsy at 14 months of age in the remaining animals. Most neoplasia incidents in this study (7/8) occurred in the BPS-exposed animals. The extended presence of TEBs into adulthood (confirmed by histopathology), the significant prepubertal spikes in serum estradiol, and the altered immune responses (e.g., increased perivascular inflammation) may have been important modifiers of the persistent adverse effects observed later in life. To our knowledge, this study is the first report of BPAF- and BPS-induced adverse developmental effects in the mammary gland, and these findings warrant further studies to determine relevance of these findings for human breast cancer susceptibility. Featured image credit PNAS.