Elizabeth Cho

Prepubertal exposure to zearalenone or genistein reduces mammary tumorigenesis.

SummaryPrepubertal exposure to a pharmacological dose (500 mg kg–1) of the phyto-oestrogen genistein can reduce the incidence and multiplicity of carcinogen-induced mammary tumours in rats. However, such an exposure also disrupts the function of the hypothalamic–pituitary–gonadal axis, making it unsuitable for breast cancer prevention. We studied whether prepubertal exposure to genistein at a total body dose broadly comparable to the level typical of Oriental countries, approximately 1 mg kg–1 body weight, affects mammary tumorigenesis. We also studied whether prepubertal exposure to zearalenone, a major source for phyto-oestrogens in the USA, influences breast cancer risk. Prepubertal rats were treated between postnatal days 7 and 20, with 20 μg (~ 1 mg kg–1 body weight) of either genistein or zearalenone. Zearalenone exposure significantly reduced both the incidence and multiplicity of mammary tumours induced by 7,12-dimethylbenz(a)anthracene (DMBA). Genistein exposure significantly reduced tumour multiplicity, but not tumour incidence, when compared with vehicle-treated animals. Furthermore, 60% of the tumours in the genistein group were not malignant, while all the tumours analysed for histopathology in the vehicle and zearalenone groups were adenocarcinomas. A higher number of differentiated alveolar buds, and lower number of terminal ducts, were present in the DMBA-treated mammary glands of the phyto-oestrogen exposed rats. The concentration of oestrogen receptor (ER) binding sites after the DMBA treatment was low in the mammary glands of all groups but a significantly higher proportion of the glands in the zearalenone exposed rats were ER-positive (i.e. ER levels ≥ 5 fmol mg–1 protein) than the glands of the vehicle controls. Our data suggest that a prepubertal exposure to a low dose of either zearalenone or genistein may protect the mammary gland from carcinogen-induced malignant transformation, possibly by increasing differentiation of the mammary epithelial tree.

Alterations in mammary gland development following neonatal exposure to estradiol, transforming growth factor α, and estrogen receptor antagonist ICI 182,780

High fetal/early postnatal levels of estrogen increase breast cancer risk, but the mechanisms remain unknown. Growth factors, such as transforming growth factor α (TGFα), may participate as secondary modifiers in this process. We characterized a modulatory role of early postnatal exposure to 17β‐estradiol (E2) on the developing mammary gland morphology by treating intact female CD‐1 mice with physiological doses of E2 (2–4 μg), human recombinant TGFα (4 μg), or an estrogen receptor (ER) antagonist ICI 182,780 (20 μg) during postnatal days 1–3. Early postnatal exposure of E2 stimulated mammary ductal growth by days 25 and 35, but by day 50 this was inhibited. The level of differentiation from terminal end buds (TEBs) to the lobulo‐alveolar units (LAUs) also was reduced by day 50. The number of TEBs was increased throughout most of the development in the female mice exposed to E2 during early life. An exposure to TGFα or ICI 182,780 between postnatal days 1 and 3 stimulated ductal growth, formation of TEBs, and the differentiation of mammary epithelial structures. ICI 182,80 treatment also caused hyperplastic lobular‐like structures in 54‐day‐old females. Thus, neonatal exposure to TGFα and ICI 182,780 induced both similar (increase in TEBs) and different (increase/decrease in lobulo‐alveolar differentiation) developmental changes in the mouse mammary gland, when compared with an exposure to E2. A unique feature of the postnatal E2 treatment was that it inhibited ductal migration by days 50–54. Our data suggest than an exposure to E2 on postnatal days 1–3, possibly combined with secondary epigenetic alterations, leads to various changes within the developing mammary tree. These changes may be potential prerequisites for mammary tumorigenesis. J. Cell. Physiol. 170:279–289, 1997.

High-fat diet induces aggressive behavior in male mice and rats

The present study investigated whether dietary fat increases aggressive behavior in male mice and rats. High fat consumption may elevate circulating estrogen levels and estrogens, in turn, are associated with various non-reproductive behaviors, such as male aggression. The animals were assigned to two groups including those consuming a diet high in polyunsaturated fats (43% calories from fat) and those consuming a low-fat diet (16% calories from fat). Each male animal was housed with two females for three weeks. The male mice and rats were then confronted with an intruder kept on a medium-fat feed. The latency to first aggressive encounter was significantly shorter among the male animals kept on a high-fat diet than those males kept on a low-fat diet. Furthermore, the time spent exhibiting aggression was longer in the high-fat groups. Serum levels of estradiol (E2) were elevated by 2-fold in the male animals consuming a high-fat diet, when compared with the male animals kept on a low-fat diet. These findings suggest that dietary fat can increase aggressive behavior in male mice and rats, possibly by elevating circulating E2 levels.

Estrogens, phytoestrogens, and breast cancer.

Estrogens have been widely implicated in the genesis and progression of breast cancer. Over 200 years ago, the Italian physician Ramazzini observed an increased incidence of breast cancer among nuns. Almost 100 years ago the Scottish physician Beatson described the beneficial effects of ovariectomy on the progress of breast cancer in premenopausal women.1 Nevertheless, the precise role(s) of estrogens and estrogenic stimuli in breast cancer remains unknown. Indeed, it is difficult to provide a universal definition of either an estrogen or an estrogenic response.

Serum estradiol levels and ethanol-induced aggression

The biological mechanisms behind ethanol-induced aggression are not known. Because gonadal hormones are linked both to aggression and ethanol, the present study examined relationships among the levels of serum estradiol (E2), testosterone (T), and aggressive behavior in ethanol-treated male mice. We found that among group-housed male mice, serum E2 levels were significantly elevated 30 min after a single injection of 0.6 g/kg ethanol. Serum T levels showed a nonsignificant decrease by ethanol. The E2/T ratio, an index of aromatization of T to E2, was significantly higher in the ethanol-treated animals when compared with the vehicle-treated animals. We also determined aggressive behavior in the resident-intruder test among isolated male mice at baseline (after a vehicle), and after an injection of 0.6 g/kg ethanol. The mice were grouped accordingly to those that increased, decreased, or remained nonaggressive in response to ethanol administration. We found that at baseline, neither serum T or E2 levels, nor E2/T ratio differed significantly between the increased or reduced aggressor mice. In contrast to the increase in serum E2 levels seen in the nonaggressive mice, ethanol significantly reduced circulating E2 levels, but did not affect aromatization of E2 from T in the mice that became aggressive following an ethanol injection. These data suggest that mice who exhibit a paradoxical decrease in serum E2 levels by ethanol may be particularly prone to ethanol-induced aggression.

Early Life Affects the Risk of Developing Breast Cancer

It has been suggested that early life, and maternal estrogen levels in particular, may play a critical role in breast cancer risk.l” This hypothesis is supported by the observations that gonadal hormones and estrogen-regulated growth factors regulate the differentiation of the mammary g la r~d .~ ,~ There is also some evidence that high fetal estrogen levels increase the number of mammary epithelial cells: accelerate differentiation of the nipple, and cause extensive proliferation of the surrounding mesenchyma.6 An increased number of epithelial and/or stromal cells offers more targets for carcinogens and a greater probability for genetidepigenetic events that affect the susceptibility of the gland to subsequent neoplastic transformation? Many factors influence maternal estrogen levels; however, diet may have a major influence during normal pregnancy. Epidemiological studies provide indirect evidence that a maternal high-fat diet and excessive weight gain that are associated with high serum estrogen level^^^^ may increase breast cancer risk and shorten survival among daughters.”” Furthermore, food manufacturing and dietary habits underwent radical changes at the time when the mothers of those women suffering from breast cancer today were pregnant. Thus, it is critical to determine whether maternal diet is associated with breast cancer risk among daughters.

Early Postnatal Treatment With Transforming Growth Factor α Does Not Alter Nonreproductive Behavior

Estrogen acting during the critical developmental period has been postulated to defeminize and possibly masculinize male sexual behavior. Transforming growth factor alpha (TGF alpha) also may be involved, because this growth factor, at least partly, mediates the mitotic effects of estrogen on target tissues. Male transgenic mice overexpressing TGF alpha have elevated serum estradiol (E2) levels and they exhibit feminization of many nonreproductive actions, suggesting that either TGF alpha and/or E2, or both, participate in the control of some nonreproductive behavior. Male and female CD-1 mice were treated with 4 microg of recombinant human TGF alpha or 2-4 microg E2 during the first 3 days of life. Although early TGF alpha treatment accelerates physical development and influences the growth of the uterus and mammary gland, it failed to have any effect on behavior, either in male or female mice. Early E2 treatment significantly lengthened immobility time in the swim test and reduced voluntary alcohol intake among the male mice. No changes in locomotor activity or aggressive behavior were noted. The expression of TGF alpha mRNA in the brainstem of adult male mice was not altered following neonatal TGF alpha or E2 treatment. However, neonatal exposure to TGF alpha caused a moderate elevation in TGF alpha mRNA expression in the female brainstem. Our results indicate that in male, but not in female mice, an excess of E2 during early life affects some nonreproductive behavior. Furthermore, early treatment with recombinant human TGF alpha does not alter nonreproductive behavior in mice.