Involution is not modified by exposure to benzophenone-3 during pregnancy and mammary gland differentiation

Mammary involution involves extensive tissue remodeling, and its disruption can impair lactation or increase susceptibility to tumor development. Benzophenone-3 (BP3), a UV filter with estrogenic and pro-apoptotic activity, may interfere with this process. Our aim was to evaluate the effects of BP3 on mammary gland involution using in vivo and in vitro models. In the in vivo experiment, pregnant C57BL/6 mice were dermally exposed to vehicle (sesame oil) or BP3 (5 or 50 mg/kg/day) from pregnancy day 8.5-18.5. Pups were weaned on lactation day 10 (L10), and mammary glands were collected at L10, and 48 (I48) and 96 h (I96) post-weaning. In the in vitro experiment, HC11 mammary epithelial cells were treated with vehicle or BP3 (0.001, 1, or 1000 nM) for 72 h, differentiated with lactogenic hormones for another 72 h, and analyzed for apoptosis and gene expression at 0, 24, and 48 h post-hormone withdrawal. 3T3-L1 preadipocytes were also differentiated and exposed to BP3 to assess adipogenesis. BP3 exposure did not affect alveolar area, apoptosis, or expression of apoptosis-related genes (Stat3, Bax, Igfbp5, Bcl2) in vivo or in HC11 cells. Stromal remodeling was unchanged, with no significant differences in collagen or adipocyte area in vivo or in lipid accumulation in 3T3-L1 cells. Additionally, expression of genes involved in adipocyte differentiation and remodeling (perilipin 1, perilipin 2, Pparγ, fatty acid synthase, and metalloproteinase 3) was unaltered. In conclusion, under the conditions and doses evaluated, BP3 exposure during pregnancy or during mammary epithelial cell differentiation does not alter mammary involution.