Fetal Alcohol Exposure Alters Mammary Epithelial Cell Subpopulations and Promotes Tumorigenesis.

BACKGROUND: Fetal alcohol exposure (FAE) increases the risk of mammary tumorigenesis in adult offspring; however, the underlying mechanism remains unknown. This study tested the hypothesis that FAE shifts the mammary epithelial cell (MEC) composition toward one that promotes tumorigenesis. METHODS: Pregnant Friend Virus B NIH Jackson dams bred to MMTV-Wnt1 male mice were given ad libitum access to 5% alcohol in 0.2% saccharin solution from GD9-10 and 10% alcohol in 0.2% saccharin from GD11-GD19 or 0.2% saccharin solution from GD9-GD19. Thoracic and inguinal mammary glands from wild-type (WT) and transgenic (Tg) female offspring were harvested at 5 and 10 weeks of age and dissociated to yield a single cell suspension enriched for MECs for flow cytometry, mammosphere assay, and gene analysis. A subset of Tg offspring was followed for tumor formation. RESULTS: WT glands of FAE animals exhibited a decreased basal cell population and increased luminal: basal ratio at 10 weeks of age. qRT-PCR analysis of total MECs found that Hey1 mRNA expression was increased in the WT FAE group at 10 weeks of age. In Tg glands, FAE increased the luminal progenitor cell population at 5 weeks of age but did not alter MEC composition at 10 weeks of age. Tertiary mammosphere-forming efficiency was greater in the WT glands of FAE animals at 10 weeks of age. Tumor latency was decreased in the FAE group. Flow cytometry analysis indicated that FAE females developed tumors with an increased basal cell population. CONCLUSIONS: These data indicate that FAE can shift MEC subpopulations, increasing the proportion of cells that are potentially vulnerable to transformation and affecting cancer risk.

Peroral Estradiol Is Sufficient to Induce Carcinogen-Induced Mammary Tumorigenesis in Ovariectomized Rats without Progesterone.

A role for estrogens in breast cancer is widely accepted, however, recent evidence highlights that timing and exposure levels are important in determining whether they elicit harmful versus beneficial effects. The rat chemical carcinogen model has been widely used to study the effects of estrogens but conclusions on the levels that lead to tumor development and an absolute requirement for progesterone (P4) are lacking. A newer method of hormone administration mixes hormones with nut butter for peroral consumption allowing for a less stressful method of long-term administration with lower spikes in serum estradiol (E2) levels. The present study was designed to determine if estrogens alone at a physiological dose can drive carcinogen-induced tumors in ovariectomized (OVX) rats or if P4 is also required using this method of hormone administration. Short-term studies were conducted to determine the dose of estrogen (E) that would lead to increased uterine weight following OVX. Subsequently, rats were OVX on postnatal day (PND) 40 then treated daily with E (600 µg/kg/day), P4 (15 mg/kg/day), or the combination. On PND 50, all rats were injected with nitrosomethylurea to induce mammary tumors. Uterine weights, body weights, and serum E2 levels were measured to demonstrate the efficacy of the method for increasing E2 levels during long-term treatment. After 26 weeks, tumor incidence was similar in Sham, E, and E + P4 animals indicating that E was sufficient to induce tumorigenesis when hormone levels were normalized by this method. This study demonstrates peroral administration can be used in long-term studies to elucidate relationships between different types and levels of steroid hormones.