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The CD-1 mouse mammary gland is sexually dimorphic, with males lacking nipples. Recent studies have revealed that the underlying epithelium in the male mammary gland is sensitive to estrogenic environmental chemicals. In ongoing investigations, we observed asymmetric morphology in the left and right male mouse mammary glands. Here, we quantified these asymmetries in the embryonic, prepubertal, pubertal and adult male mammary gland. We found that the right gland was typically larger with more branching points compared to the left gland. We next evaluated the response of the left and right glands to 17α-ethinyl estradiol (EE2) after perinatal or peripubertal exposures. We found that the right gland was more responsive to EE2 than the left at both periods of exposure. These results reveal novel aspects of male mammary gland biology and suggest that future studies should control for laterality in the evaluation of hazards associated with exposures to estrogenic chemicals.

Background Technological advancements make lives safer and more convenient. Unfortunately, many of these advances come with costs to susceptible individuals and public health, the environment, and other species and ecosystems. Synthetic chemicals in consumer products represent a quintessential example of the complexity of both the benefits and burdens of modern living. How we navigate this complexity is a matter of a society’s values and corresponding principles. Objectives We aimed to develop a series of ethical principles to guide decision-making within the landscape of environmental health, and then apply these principles to a specific environmental chemical, oxybenzone. Oxybenzone is a widely used ultraviolet (UV) filter added to personal care products and other consumer goods to prevent UV damage, but potentially poses harm to humans, wildlife, and ecosystems. It provides an excellent example of a chemical that is widely used for the alleged purpose of protecting human health and product safety, but with costs to human health and the environment that are often ignored by stakeholders. Discussion We propose six ethical principles to guide environmental health decision-making: principles of sustainability, beneficence, non-maleficence, justice, community, and precautionary substitution. We apply these principles to the case of oxybenzone to demonstrate the complex but imperative decision-making required if we are to address the limits of the biosphere’s regenerative rates. We conclude that both ethical and practical considerations should be included in decisions about the commercial, pervasive application of synthetic compounds and that the current flawed practice of cost-benefit analysis be recognized for what it is: a technocratic approach to support corporate interests.

The mammary gland is a hormone sensitive organ that is susceptible to endocrine disrupting chemicals (EDCs) during the vulnerable periods of parous reorganization (i.e. pregnancy, lactation, and involution). Pregnancy is believed to have long-term protective effects against breast cancer development, however, it is unknown if EDCs can alter this effect. We examined the long-term effects of propylparaben, a common preservative used in personal care products and foods, with estrogenic properties, on the parous mouse mammary gland. Pregnant BALB/c mice were treated with 0, 20, 100, or 10,000 µg/kg/day propylparaben throughout pregnancy and lactation. Unexposed nulliparous females were also evaluated. Five weeks post-involution, mammary glands were collected and assessed for changes in histomorphology, hormone receptor expression, immune cell number, and gene expression. For several parameters of mammary gland morphology, propylparaben reduced the effects of parity. Propylparaben also increased proliferation, but not stem cell number, and induced modest alterations to expression of ERα-mediated genes. Finally, propylparaben altered the effect of parity on the number of several immune cell types in the mammary gland. These results suggest that propylparaben, at levels relevant to human exposure, can interfere with the effects of parity on the mouse mammary gland and induce long-term alterations to mammary gland structure. Future studies should address if propylparaben exposures negate the protective effects of pregnancy on mammary cancer development.

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