Adverse effects on female development and reproduction in CD-1 mice following neonatal exposure to the phytoestrogen genistein at environmentally relevant doses

Neonatal exposure to the phytoestrogen genistein alters mammary gland growth and developmental programming of hormone receptor levels

Developmental effects of genistein (Gen) on the mammary gland were investigated using outbred female CD-1 mice treated neonatally on d 1-5 by sc injections at doses of 0.5, 5, or 50 mg/kg.d. Examination of mammary gland whole mounts (no. 4) before puberty (4 wk) revealed no morphological differences in development after Gen treatment. However, mice treated with Gen-50 had stunted development characterized by less branching at 5 wk and decreased numbers of terminal end buds at 5 and 6 wk. Conversely, at 6 wk, Gen-0.5-treated mice exhibited advanced development with increased ductal elongation compared with controls. Measurements of hormone receptor levels showed increased levels of progesterone receptor protein and estrogen receptor-beta mRNA in Gen-0.5-treated mice compared with controls; ERalpha expression was decreased after all doses of Gen treatment. Lactation ability, measured by pup weight gain and survival, was not affected after neonatal Gen-0.5 and Gen-5. Mice treated with Gen-50 did not deliver live pups; therefore, lactation ability could not be determined. Evaluation of mammary glands in aged mice (9 months) showed no differences between Gen-0.5-treated mice and controls but mice treated with Gen-5 and Gen-50 exhibited altered morphology including reduced lobular alveolar development, dilated ducts, and focal areas of "beaded" ducts lined with hyperplastic ductal epithelium. In summary, neonatal Gen exposure altered mammary gland growth and development as well as hormone receptor levels at all doses examined; higher doses of Gen led to permanent long-lasting morphological changes.

Experimental adenomyosis

Adenomyosis has been reported in a number of different animal species, whereas endometriosis appears limited to humans and non-human primates. This suggests a different aetiology of the two conditions. Adenomyosis develops spontaneously in certain strains of laboratory mice. Its incidence in mice can be markedly enhanced by systemic exposure to various hormonal agents, including prolactin, progesterone, synthetic progestins, certain oestrogenic agents, as well as tamoxifen and toremifene. The precise hormonal changes necessary remain unclear, although the evidence suggests that adenomyosis in this model is not due to a simple oestrogenic effect. Study of the pathological and molecular alterations in this model indicates that disturbances to the uterine stroma, blood vessels and myometrium are also important factors in the development of adenomyosis.

Female sexual maturation and reproduction after prepubertal exposure to estrogens and endocrine disrupting chemicals: a review of rodent and human data

Natural hormones and some synthetic chemicals spread into our surrounding environment share the capacity to interact with hormone action and metabolism. Exposure to such compounds can cause a variety of developmental and reproductive detrimental abnormalities in wildlife species and, potentially, in human. Many experimental and epidemiological data have reported that exposure of the developing fetus or neonate to environmentally relevant concentrations of some among these endocrine disrupters induces morphological, biochemical and/or physiological disorders in brain and reproductive organs, by interfering with the hormone actions. The impact of such exposures on the hypothalamic-pituitary-gonadal axis and subsequent sexual maturation is the subject of the present review. We will highlight epidemiological human studies and the effects of early exposure during gestational, perinatal or postnatal life in female rodents.

Genistein and other soya isoflavones are potent ligands for transthyretin in serum and cerebrospinal fluid

Consumption of soya-based nutrients is increasing in modern society because of their potentially protective effects against chronic diseases. Soya products are also heavily advertised as alternative drugs for relief from symptoms of the menopause and for hormone replacement therapy. However, because of their oestrogenic activity, negative effects of isoflavones have been postulated. Therefore, we analysed influences of soya isoflavones, major soya constituents with endocrine activity, on thyroxine (T4) binding to its distribution proteins. Serum binding of (125)I-labelled L-T4 was analysed in the absence or presence of increasing concentrations of soya isoflavones using non-denaturing PAGE for analysis. Complete displacement of [(125)I]T4 binding to transthyretin (TTR) was observed in human serum incubated with genistein at concentrations >10 microM; interference started at >0.1 microM. Glycitein showed decreased and daidzein the lowest displacement potency. [(125)I]T4 was displaced to albumin in rat and to T4-binding globulin in human serum. Soya isoflavones also obstruct [(125)I]T4 binding to TTR in human cerebrospinal fluid (CSF). The inhibitory effect was confirmed in direct binding assays using purified TTR with 50% inhibitory concentration values of 0.07 microM for genistein, 0.2 microM for glycitein and 1.8 microM for daidzein. The present study underlined a potent competition of soya isoflavones for T4 binding to TTR in serum and CSF. Isoflavones might alter free thyroid hormone concentrations resulting in altered tissue availability and metabolism. As a consequence of this interference, one could expect a disturbance in the feedback regulation of hormonal networks, including the pituitary-thyroid-periphery axis during development and in adult organisms.

Infant feeding with soy formula milk: effects on puberty progression, reproductive function and testicular cell numbers in marmoset monkeys in adulthood

BACKGROUND

This marmoset study addresses concerns about feeding human male infants with soy formula milk (SFM).

METHODS

From age 4 to 5 days, seven male co-twin sets were fed standard formula milk (SMA) or SFM for 5-6 weeks; blood samples were subsequently collected at 10-week intervals. Testes from co-twins killed at 120-138 weeks were fixed for cell counts.

RESULTS

SFM- and SMA-fed twins showed normal weight gain; puberty started and progressed normally, based on blood testosterone measurements. Body weight, organ weights (prostate, seminal vesicles, pituitary, thymus and spleen) and penis length were comparable in co-twins. All SMA- and 6/7 SFM-fed males were fertile. Unexpectedly, testis weight (P = 0.041), Sertoli (P = 0.025) and Leydig cell (P = 0.026) numbers per testis were consistently increased in SFM-fed co-twins; the increase in Leydig cell numbers was most marked in males with consistently low-normal testosterone levels. Seminiferous epithelium volume per tubule showed a less consistent, non-significant increase in SFM-fed males; raised germ cell numbers per testis, probably due to increased Sertoli cells, conceivably resulted in larger testes. Average lumen size, although greater in SFM-fed group, was inconsistent between co-twins and the difference was not significant.

CONCLUSIONS

Infant feeding with SFM has no gross adverse reproductive effects in male marmosets, though it alters testis size and cell composition, and there is consistent, if indirect, evidence for possible 'compensated Leydig cell failure'. Similar and perhaps larger changes likely occur in adult men who were fed SFM as infants.

Neonatal Genistein Treatment Alters Ovarian Differentiation in the Mouse: Inhibition of Oocyte Nest Breakdown and Increased Oocyte Survival1

Early in ovarian differentiation, female mouse germ cells develop in clusters called oocyte nests or germline cysts. After birth, mouse germ cell nests break down into individual oocytes that are surrounded by somatic pregranulosa cells to form primordial follicles. Previously, we have shown that mice treated neonatally with genistein, the primary soy phytoestrogen, have multi-oocyte follicles (MOFs), an effect apparently mediated by estrogen receptor 2 (ESR2, more commonly known as ERbeta). To determine if genistein treatment leads to MOFs by inhibiting breakdown of oocyte nests, mice were treated neonatally with genistein (50 mg/kg per day) on Days 1-5, and the differentiation of the ovary was compared with untreated controls. Mice treated with genistein had fewer single oocytes and a higher percentage of oocytes not enclosed in follicles. Oocytes from genistein-treated mice exhibited intercellular bridges at 4 days of age, long after disappearing in controls by 2 days of age. There was also an increase in the number of oocytes that survived during the nest breakdown period and fewer oocytes undergoing apoptosis on Neonatal Day 3 in genistein-treated mice as determined by poly (ADP-ribose) polymerase (PARP1) and deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end-labeling (TUNEL). These data taken together suggest that genistein exposure during development alters ovarian differentiation by inhibiting oocyte nest breakdown and attenuating oocyte cell death.

Large effects from small exposures. II. The importance of positive controls in low-dose research on bisphenol A

Over six-billion pounds per year of the monomer bisphenol A (BPA) are used to manufacture polycarbonate plastic products, resins lining cans, dental sealants, and polyvinyl chloride plastic products. There are 109 published studies as of July 2005 that report significant effects of low doses of BPA in experimental animals, with many adverse effects occurring at blood levels in animals within and below average blood levels in humans; 40 studies report effects below the current reference dose of 50 microg/kg/day that is still assumed to be safe by the US-FDA and US-EPA in complete disregard of the published findings. The extensive list of significant findings from government-funded studies is compared to the 11 published studies that were funded by the chemical industry, 100% of which conclude that BPA causes no significant effects. We discuss the importance of appropriate controls in toxicological research and that positive controls are required to determine whether conclusions from experiments that report no significant effects are valid or false.

Lactational transfer of the soy isoflavone, genistein, in Sprague-Dawley rats consuming dietary genistein

Exposures of Sprague-Dawley rats to the soy isoflavone, genistein, throughout the entire lifespan have produced a number of effects on reproductive tissues, immune function, neuroendocrine function and behavior. Our previous studies investigated pharmacokinetics and disposition of genistein during adult and fetal periods and this study describes the internal exposures of post-natal day 10 (PND10) rat pups due to lactational transfer of genistein. Conjugated and aglycone forms of genistein were measured by using LC/MS/MS in serum (PND10) and milk (PND7) from lactating dams consuming a genistein-fortified soy-free diet, and in serum from their pups at a time when milk was the only food source (PND10). This study shows that limited lactational transfer of genistein to rat pups occurs and that internal exposures to the active aglycone form of genistein are generally lower than those measured previously in the fetal period. These results suggest that developmental effects attributable to genistein exposure in our chronic and multi-generation studies are more likely to result from fetal exposures because of the higher levels of the active estrogenic aglycone form of genistein in utero, although the possibility of neonatal responses cannot be excluded.