Dietary methoxychlor exposure modulates splenic natural killer cell activity, antibody-forming cell response and phenotypic marker expression in F0 and F1 generations of Sprague Dawley rats

Methoxychlor, a chlorinated hydrocarbon pesticide, is a persistent environmental contaminant that has been identified in human reproductive tissues. Methoxychlor has been shown to be estrogenic in both in vivo and in vitro studies. As an endocrine disrupter, it may have the potential to adversely affect endocrine, reproductive, and immune systems in animals. The present study evaluated methoxychlor's immunotoxic potential in F0 (dams) and F1 generations of Sprague Dawley rats exposed to an isoflavone-free diet containing methoxychlor at concentrations of 10, 100, and 1000 ppm. In dams, exposure to methoxychlor from gestation day 7 to postpartum day 51 (65 days total exposure) produced a significant increase in the NK activity (1000 ppm) and the percentages of T cells (1000 ppm), helper T cells (1000 ppm) and macrophages (100 and 1000 ppm). In contrast, a decrease in the numbers of splenocytes and B cells was observed at the 100 and 1000 ppm concentrations. In F1 males, exposure to methoxychlor gestationally, lactationally and through feed from postnatal day 22-64 (78 days total exposure) produced an increase in the spleen IgM antibody-forming cell response to sheep red blood cells (100 and 1000 ppm) and the activity of NK cells (1000 ppm). However, there was a decrease in the terminal body weight (1000 ppm), spleen weight (1000 ppm), thymus weight (100 and 1000 ppm), and the numbers of splenocytes (1000 ppm), B cells (100 and 1000 ppm), cytotoxic T cells (1000 ppm) and NK cells (100 and 1000 ppm). In F1 females, exposure to methoxychlor produced a decrease in the terminal body weight (1000 ppm) and the percentages of cytotoxic T cells (10, 100 and 1000 ppm). These results demonstrate that developmental and adult dietary exposure to methoxychlor modulates immune responses in Sprague Dawley rats. Immunological changes were more pronounced in the F1 generation male rats that were exposed during gestation and postpartum, when compared to the F0 and F1 generation females. Increases in antibody-forming cell response and NK cell activity, and altered spleen cell subpopulation numbers were observed in the F1 generation male rats, without similar changes to the F1 generation females.

Developmental exposure to diethylstilbestrol (DES) alters uterine response to estrogens in prepubescent mice: low versus high dose effects

Outbred CD-1 mice received subcutaneous injections on neonatal days 1-5 with DES (0.0001-1000 microg/kg per day), a model xenoestrogen. At 17 days of age, uterine wet weight increase in response to estrogen was altered in neonatally DES-treated mice compared to controls. The response varied depending on the neonatal DES dose; a low dose (0.01 microg/kg) caused an enhanced uterine response but higher neonatal doses dampened the response. Western blots and immunolocalization of estrogen receptor alpha (ERalpha) showed high ER levels at DES 0.01 microg/kg, but decreased levels at higher doses compared to controls. Genes responding through ER-mediated pathways (c-fos, proliferating cell nuclear antigen (PCNA), and lactoferrin (LF)) mirrored altered wet weight responses, i.e., enhancement at low doses and dampening at higher doses. A similar dose-response curve was seen in 4 months old ovariectomized DES-treated mice suggesting the altered response was long-term. These data suggest xenoestrogen exposure during critical developmental windows alters hormone programming so that the uterus responds abnormally to estrogen later in life, and that the response differs following high versus low doses of neonatal exposure.

Increased volume of the calbindin D28k-labeled sexually dimorphic hypothalamus in genistein and nonylphenol-treated male rats

The adult rat brain develops through an interplay of neuronal proliferation and programmed cell death. Steroid hormones and growth factors may alter the balance between these competing processes. "Endocrine disrupters" (EDs) may also alter brain development, by mimicry or modulation of endogenous hormone systems. Under control conditions, the sexually dimorphic nucleus (SDN) of the medial preoptic hypothalamus becomes larger in adult males than females, but its final volume may also reflect the hormonal conditions prevailing during development. Two EDs that have recently been studied in protocols involving lifespan exposures are the phytoestrogen genistein and the weakly estrogenic compound para-nonylphenol, which is used in the production of many surfactants and plastics. Experimental dietary exposure of adult female rats to genistein or p-nonylphenol began 28 days prior to their mating at concentrations of 5 ppm, 100 ppm, and 500 ppm for genistein or 25 ppm, 200 ppm, and 750 ppm for p-nonylphenol. Exposure of the offspring continued throughout gestation and lactation, as well as in their chow after weaning, until they were sacrificed at 140 days of age for immunohistochemical labeling of the calbindin D28k-labeled subdivision of the SDN: the CALB-SDN. Both genistein and nonylphenol were found to increase the volume of the CALB-SDN in male rats (p's < 0.01), but not in female rats.

Lessons learned from perinatal exposure to diethylstilbestrol

The synthetic estrogen diethylstilbestrol (DES) is well documented to be a perinatal carcinogen in both humans and experimental animals. Exposure to DES during critical periods of differentiation permanently alters the programming of estrogen target tissues resulting in benign and malignant abnormalities in the reproductive tract later in life. Using the perinatal DES-exposed rodent model, cellular and molecular mechanisms have been identified that play a role in these carcinogenic effects. Although DES is a potent estrogenic chemical, effects of low doses of the compound are being used to predict health risks of weaker environmental estrogens. Therefore, it is of particular interest that developmental exposure to very low doses of DES has been found to adversely affect fertility and to increase tumor incidence in murine reproductive tract tissues. These adverse effects are seen at environmentally relevant estrogen dose levels. New studies from our lab verify that DES effects are not unique; when numerous environmental chemicals with weak estrogenic activity are tested in the experimental neonatal mouse model, developmental exposure results in an increased incidence of benign and malignant tumors including uterine leiomyomas and adenocarcinomas that are similar to those shown following DES exposure. Finally, growing evidence in experimental animals suggests that some adverse effects can be passed on to subsequent generations, although the mechanisms involved in these trans-generational events remain unknown. Although the complete spectrum of risks to DES-exposed humans are uncertain at this time, the scientific community continues to learn more about cellular and molecular mechanisms by which perinatal carcinogenesis occurs. These advances in knowledge of both genetic and epigenetic mechanisms will be significant in ultimately predicting risks to other environmental estrogens and understanding more about the role of estrogens in normal and abnormal development.

Nonylphenol alters the activity of splenic NK cells and the numbers of leukocyte subpopulations in Sprague–Dawley rats: a two-generation feeding study

Nonylphenol (NP) has been identified at low levels in surface waters throughout North America. This industrial chemical is primarily used for the production of certain non-ionic surfactants, and has been reported to have weak estrogen-like activity. As estrogen has immunoregulatory properties and is crucial for normal fetal development, it was hypothesized that adult and developmental exposures to NP had the potential to adversely affect the immune system. Furthermore, developmental exposure to NP might also produce differential immunomodulation in F(1) male and female rats. Thus, a two-generation feeding study was conducted to evaluate the potential for NP to modulate certain immune parameters. Pregnant female Sprague-Dawley rats were exposed to NP (0, 25, 500, and 2000 ppm) in their feed for 65 days, beginning 7 days into gestation. The F(1) generation male and female offspring were exposed in utero at the respective treatment levels, commencing the 7th day of gestation, and continuing through to 64 days of age. Changes in splenic antibody-forming cell response, natural killer cell activity, and leukocyte numbers were used to evaluate NP immunotoxicity. The results from the present study indicate that dietary exposure to NP can increase splenic natural killer (NK) cell activity and splenocyte subpopulation numbers in the F(1) generation rats, without similar changes to the F(0) generation. The immunological changes that were observed in the F(1) generation also appeared to be gender-specific.

A Natural Antioxidant Mixture from Spinach Does Not Have Estrogenic or Antiestrogenic Activity in Immature CD-1 Mice

The use of natural antioxidants and flavonoids in nutritional and pharmaceutical applications is increasing. Because some phytochemicals such as genistein, found in soy products, have estrogenic activity, we investigated the estrogenic potential of a natural antioxidant mixture (NAO) isolated from spinach leaves, using an in vivo uterotrophic bioassay and an in vitro transcriptional activation assay for the estrogen receptor (ER). Outbred female CD-1 mice (17 d old) were given subcutaneous injections of 17beta-estradiol or genistein [500 and 500,000 microg /(kg x d), respectively] as positive controls or NAO [1000 to 1,000,000 microg/(kg x d)] for 3 d. Uterine wet weight/body weight ratios were determined. Both 17beta-estradiol and genistein significantly increased uterine wet weight ratios compared with untreated controls, but NAO did not. Histological examination of the uterus showed that 17beta-estradiol and genistein increased epithelial cell height, number and gland development, but NAO did not. Estrogenic activity of NAO was investigated in vitro using the ER transcriptional activation assay. BG1Luc4E2 cells expressing ER were stably transfected with a luciferase reporter gene responsive to estrogens. 17beta-estradiol dose dependently increased luciferase activity; NAO had no effect. When NAO was tested for antiestrogenic activity, it did not lessen the effects of 17beta-estradiol. These data suggest that NAO does not have estrogenic or antiestrogenic activity. Thus, an antioxidant mixture has been identified that does not have potentially adverse estrogenic activity.

Determination using liquid-chromatography-electrospray tandem mass spectroscopy of ethinylestradiol serum pharmacokinetics in adult Sprague-Dawley rats

The pharmacokinetics of ethinylestradiol (EE2), a potent synthetic estrogen, was investigated in male and female Sprague-Dawley rats as part of a series of endocrine-active compounds, including genistein and nonylphenol. A method based on solid-phase extraction and LC with negative ion electrospray tandem mass spectrometric detection was developed and validated. The limit of detection in untreated rat serum was below 0.01 ng/ml (0.03 nM), the limit of quantification was 0.03 ng/ml (0.10 nM), the intra- and inter-day precision was 2-9%, and the intra- and inter-day accuracy was 89-94%. This method was used to determine the serum pharmacokinetics of EE2 in rats following oral gavage administration of 1 mg/kg body weight. EE2 was present in serum primarily in the unconjugated form at concentrations below 0.5 ng/ml. The maximal serum concentration was proportional to dose over the range of 0.04-0.5 mg/kg body weight and pharmacokinetic parameters were determined using model-independent analysis. Significant sex differences were observed for elimination half-times and volumes of distribution, but not for total serum clearance or maximal concentrations. The pharmacokinetic analysis of EE2 will be useful for comparing the toxicological effects of EE2 to those of other environmental estrogens in related rodent endocrine disruptor studies.

Dietary ethinyl estradiol exposure during development causes increased voluntary sodium intake and mild maternal and offspring toxicity in rats

Exogenous estrogen exposure during development often results in behavioral masculinization and/or defeminization of genetic females. Genetic males may be defeminized, hypermasculinized or even demasculinized after similar treatment. Here, pregnant Sprague-Dawley rats consumed phytoestrogen-free diets containing 0, 1, 5 or 200 ppb EE(2) beginning on gestational day (GD) 7. Offspring were weaned to the same maternal diet and maintained gonadally intact. There were mild effects on body weight and food consumption in dams of the 200 ppb group and their offspring weighed less at birth than those of the control group; however, gross assessments of nursing behavior were normal in all dietary groups. Postweaning, offspring of the 200 ppb group weighed less and consumed less food than controls. There were no EE(2)-related effects on open-field activity (tested at postnatal days (PND) 22-24, 43-45 and 64-66), play behavior (tested at PND 35), running wheel activity (PND 63-77) or intake of a 0.3% saccharin-flavored solution (PND 69-71). Intake of a 3.0% sodium chloride-flavored solution on PND 73-75 was increased in both male and female offspring of the 200 ppb group relative to same-sex controls, an effect that is reportedly estrogen mediated. Sodium chloride-flavored solution intake is a sexually dimorphic behavior for which female rats consume more than males. Here, while EE(2) exposure had few effects on the conventional tests of sexually dimorphic behaviors, exposure to 200 ppb in the diet appeared to feminize genetic males and hyperfeminize genetic females with regard to sodium intake.

Neonatal exposure to genistein induces estrogen receptor (ER)alpha expression and multioocyte follicles in the maturing mouse ovary: evidence for ERbeta-mediated and nonestrogenic actions

Outbred CD-1 mice were treated neonatally on Days 1-5 with the phytoestrogen, genistein (1, 10, or 100 micro g per pup per day), and ovaries were collected on Days 5, 12, and 19. Ribonuclease protection assay analysis of ovarian mRNA showed that estrogen receptor beta (ERbeta) predominated over ERalpha in controls and increased with age. Genistein treatment did not alter ERbeta expression, however, ERalpha expression was higher on Days 5 and 12. ERbeta was immunolocalized in granulosa cells, whereas ERalpha was immunolocalized in interstitial and thecal cells. Genistein treatment caused a dramatic increase in ERalpha in granulosa cells. Genistein-treated ERbeta knockout mice showed a similar induction of ERalpha, which is seen in CD-1 mice, suggesting that ERbeta does not mediate this effect. Similar ERalpha induction in granulosa cells was seen in CD-1 mice treated with lavendustin A, a tyrosine kinase inhibitor that has no known estrogenic actions, which suggests that this property of genistein may be responsible. As a functional analysis, genistein-treated mice were superovulated and the number of oocytes was counted. A statistically significant increase in the number of ovulated oocytes was observed with the lowest dose, whereas a decrease was observed with the two higher doses. This increase in ovulatory capacity with the low dose coincided with higher ERalpha expression. Histological evaluations on Day 19 revealed a dose-related increase in multioocyte follicles (MOFs) in genistein-treated mice. Tyrosine kinase inhibition was apparently not responsible for MOFs because they were not present in mice that had been treated with lavendustin; however, ERbeta must play a role, because mice lacking ERbeta showed no MOFs. These data taken together demonstrate alterations in the ovary following neonatal exposure to genistein. Given that human infants are exposed to high levels of genistein in soy-based foods, this study indicates that the effects of such exposure on the developing reproductive tract warrant further investigation.

Pharmacokinetic analysis in serum of genistein administered subcutaneously to neonatal mice

Genistein, the principal soy isoflavone, was previously shown to induce uterine adenocarcinomas by 18 months of age in female CD-1 mice following administration by subcutaneous injections on postnatal days 1-5. A serum pharmacokinetic analysis of genistein in male and female mice treated identically showed that: maximal concentrations of total (conjugated+aglycone) genistein in females (6.8+/-1.4 microM) and males (3.8+/-1.1 microM, mean+/-SD) were comparable to those previously reported from dietary exposures in adult rats or in human infants consuming soy formulas; the average fraction present as active aglycone (31%) was similar to those in fetal and neonatal rats from placental and lactational exposures; and elimination half-times were longer than those in rats (three- to seven-fold) and adult humans (two- to three-fold). These results are consistent with a diminished capacity for enzymatic conjugation of genistein, based on the ontogeny, as an important determinant of estrogenicity in neonatal mice.

Characterization of uterine leiomyomas in CD-1 mice following developmental exposure to diethylstilbestrol (DES)

Experimental animal and clinical studies have well established the association of prenatal exposure to diethylstilbestrol (DES) and the subsequent development of reproductive tract abnormalities, including poor reproductive outcome and neoplasia. Overwhelmingly, the focus has been on DES-induced epithelial lesions, particularly vaginal adenosis and adenocarcinoma; however, uterine smooth muscle cells are also recognized as cellular targets of DES. This descriptive report characterizes uterine leiomyomas that occur in outbred CD-1 mice following exposure to DES prenatally on days 9 to 16 of gestation or on neonatal days 1 to 5. These DES-induced uterine leiomyomas have typical histomorphologic, and some immunohistochemical characteristics of spontaneously occurring uterine smooth muscle tumors of B6C3F1 mice previously described in our laboratory, and they are also similar to uterine leiomyomas (fibroids) commonly observed in premenopausal women.

Assessing estrogenic activity of phytochemicals using transcriptional activation and immature mouse uterotrophic responses

The estrogenic responses of several phytoestrogens including genistein, daidzein, coumestrol, alpha-zearalanol, zearalenone, naringenin, taxifolin and biochanin A were compared over a wide dose range using an in vitro assay that measures transcriptional activation of the estrogen receptor (ER) and an in vivo immature mouse uterotrophic assay consisting of measuring uterine wet weight increase plus sensitive morphological and biochemical endpoints in the uterus. The transcriptional activation assay showed activation of the ER by all compounds tested except taxifolin with varying magnitudes of response as compared to estradiol or diethylstilbestrol. Results from the uterotropic bioassay showed that genistein, coumestrol, zearalanol, and zearalenone caused an increase in uterine wet weight, while naringenin, taxifolin, daidzein and biochanin A failed to do so over the dose range tested. However, sensitive morphological and biochemical parameters such as uterine epithelial cell height increase, uterine gland number increase, and induction of the estrogen-responsive protein lactoferrin demonstrated that all compounds tested in this study gave some measure of estrogenicity although a wide range of estrogenic responses across compounds was shown. Use of multiple in vitro and in vivo estrogenic endpoints as described in this paper will be useful in developing estrogenic profiles for individual compounds and ultimately mixtures of compounds. Furthermore, having an estrogenic "fingerprint" for each phytochemical is an essential first step in determining potential adverse effects of exposure to phytoestrogens.

Genistein modulates splenic natural killer cell activity, antibody-forming cell response, and phenotypic marker expression in F(0) and F(1) generations of Sprague-Dawley rats

The potential effects of the phytoestrogen genistein (GEN) on the immune system were evaluated in both F(0) (dams) and F(1) generations of Sprague-Dawley rats exposed to a soy-free diet containing low (L: 25 ppm), middle (M: 250 ppm), and high (H: 1250 ppm) levels of GEN. In dams, exposure to GEN from Gestation Day 7 to Postpartum Day 51 (totally 65 days) produced a significant increase in NK cell activity (M and H), while a decrease in the percentage of helper T cells (H). In F(1) males, exposure to GEN gestationally, lactationally, and through feed from Postnatal Days 22 to 64 (total 78 days) produced an increase in the relative weights (% body) of spleen (L and H) and thymus (L). Furthermore, exposure to GEN increased the number of splenic B cells (H), T cells (L, M, and H), and T-cell subsets (L, M, and H). Although GEN decreased the percentages of splenic NK cells (L, M, and H), no effect on the activity of NK cells was observed. In F(1) females, exposure to GEN produced a decrease in terminal body weight (H), with an increase in the relative weight of spleen (L, M, and H). Exposure to GEN also increased the number of splenic B cells (L), macrophages (L and M), T cells (H), helper T cells (L and H), and cytotoxic T cells (M and H). Additionally, exposure to GEN increased the percentages of T cells (M and H), helper T cells (H), and cytotoxic T cells (M and H). Moreover, the spleen IgM antibody-forming cell response to sheep red blood cells was enhanced (H), although the percentages of B cells were decreased (M and H). No effect on the activity of NK cells was observed; however, the percentages of splenic NK cells were decreased by GEN (L and H). In conclusion, these results demonstrate that exposure to GEN can modulate the immune responses in Sprague-Dawley rats. Furthermore, the sexual dimorphic effects of GEN in F(1) male and female rats suggest that there may be interactions between GEN and the responses modulated by sex hormones.

Multigenerational exposure to dietary nonylphenol has no severe effects on spatial learning in female rats

Nonylphenol is a common intermediate in the production of many consumer compounds and reportedly acts as an estrogen mimic. Because estrogen affects the spatial learning and memory in rats, the effects of nonylphenol exposure on the performance of female rats in the Morris water maze were investigated. Here, Sprague-Dawley rats (F0) consumed soy-free diets containing 0, 25, 200 or 750 ppm nonylphenol (0, 2, 16 or 60 mg/kg per day) beginning on postnatal day (PND) 42 and continuing for two generations (F1 and F2) with breeding occurring within treatments. Females to be behaviorally tested (n = 7-8 per treatment per generation) were ovariectomized at adulthood and assessed for spatial learning and memory between PND 125-150 (young adult age). Each rat was tested for four consecutive days (three trials per day) in the Morris water maze with the platform in a fixed location. One week later, each subject was primed with estrogen and progesterone and assessed on a single day (three trials). The F1 rats continued on the same diets until PND 380-395 (middle aged) when they were re-tested as above (four consecutive days followed 1 week later with hormonal priming and a single test day). Latency to find the platform, path length and swim speed were averaged over the three trials per day and analyzed using repeated measures analyses of variance. There were no consistent effects of dietary nonylphenol exposure and no interactions of nonylphenol exposure on any measure of performance in either generation at the young age nor at the middle age in the F1 generation. When tested at the young adult age, however, hormone priming resulted in latencies and path lengths that were significantly shorter than in those exhibited during the unprimed test days, and there was no such effect when tested at middle age. Middle aged rats exhibited better performance than the same animals tested at a young age, likely as a result of familiarity and practice with the test paradigm. These data suggest that multigenerational dietary nonylphenol exposure does not cause gross alterations in Morris water maze performance in young adult or middle aged ovariectomized female rats.

Effect of nonylphenol on serum testosterone levels and testicular steroidogenic enzyme activity in neonatal, pubertal, and adult rats

Previous dose range-finding studies with nonylphenol (NP) administered to rats in a soy- and alfalfa-free diet showed apparent feminization of several endpoints in male rats at doses of 25 ppm and above. One possible mechanism contributing to these effects is a reduction of testosterone at critical developmental periods. The present study was conducted as an adjunct to a multigeneration study and was designed to examine the effect of NP on testosterone production. Male rats in the F1 and F2 generations were exposed through their dams or directly to various dietary doses of NP (0, 25, 200 and 750 ppm) throughout gestation and until sacrifice at either postnatal day 2 (PND2), PND50, or PND140. Male pups in the F3 generation were examined only on PND2. At PND2, serum testosterone levels were significantly decreased in all groups exposed to NP in the F1 generation, but not in the F2 or F3 generations. The activity of 17alpha-hydroxylase/C17, 20 lyase (P450c17) in PND2 testicular homogenates was not affected by NP treatment. In F1 and F2 PND50 and PND140 rats, NP treatment did not affect serum testosterone levels. The absolute dorsolateral prostate weight was increased in the 200 and 750 ppm dose groups only in the F1 PND50 rats, however, no significant effects were observed in other male reproductive organs. NP treatment did not affect P450c17 activity in microsomes prepared from testes of F1 PND50 or PND140 rats. However, P450c17 activity was significantly decreased in testicular microsomes of F(2) PND50 (200 and 750 ppm dose groups) and PND140 (25, 200, and 750 ppm dose groups) rats. A decrease in testicular beta-nicotinamide adenine dinucleotide phosphate (NADPH) P450 reductase was also observed in all PND50 and PND140 NP-exposed rats of the F1 and F2 generations. The ability of NP to directly inhibit P450c17 activity in vitro at concentrations of 1-100 microM was also demonstrated. These results indicate that NP can inhibit the activity of enzymes involved in testosterone synthesis, but suggest minimal effects on testosterone or testosterone-dependent endpoints via this mechanism.

Mass spectrometric determination of p-nonylphenol metabolism and disposition following oral administration to Sprague-Dawley rats

Isomers of 4-nonylphenol (NP), which are important industrial compounds and environmental breakdown products from widely used surfactants, have estrogenic activity in vitro and in vivo that has prompted interest in its potential for modulation of endocrine function in humans and wildlife. Mass spectrometry was used to quantify NP and metabolites in serum and endocrine-responsive tissues from dietary exposure in Sprague-Dawley rats. Tissue accumulation of NP aglycone was observed despite the predominance of glucuronidation in blood. Serum toxicokinetics of total NP, measured following gavage administration, showed rapid absorption and elimination (average half-times 0.8 and 3.5 h, respectively). NP was similarly administered by gavage to pregnant dams and total and aglycone NP were measured in dam serum and fetuses to show placental transfer into serum and brain. These data provide a basis for future correlations of biologic effects observed following dietary exposure in rats with those predicted from environmental exposures to humans.

Effects of lifelong dietary exposure to genistein or nonylphenol on amphetamine-stimulated striatal dopamine release in male and female rats

Estrogen modulates baseline and amphetamine-stimulated dopamine (DA) release in the adult female rat striatum. The isoflavone found in soybeans, genistein, is a phytoestrogen and may have comparable effects on striatal DA levels. Similarly, the industrial intermediate and potential endocrine disrupter, para-nonylphenol, has estrogen-like effects. Here, Sprague-Dawley rats were continuously exposed to phytoestrogen-free diets containing 0, 100, or 500 ppm genistein (Experiment 1) or 0 or 200, or 750 ppm nonylphenol (Experiment 2) beginning at conception and continuing throughout. To eliminate estrous cycle influences on DA levels, females were ovariectomized at adulthood. As adults, striatal levels of DA and its metabolites [3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA)] were measured in unanesthetized male and female rats via cerebral microdialysis before and for 200 min after an intraperitoneal injection of 2 mg/kg D-amphetamine. Although baseline 5-hydroxyindoleacetic acid (5-HIAA) levels indicated an isolated effect in genistein-treated females, there were no meaningful differences among treatment groups in baseline levels of DA, DOPAC, or HVA. However, dietary exposure to 500 ppm genistein significantly potentiated amphetamine-stimulated DA release in males and a similar trend was apparent, but not statistically significant, in females. Dietary exposure to 200 or 750 ppm nonylphenol had no significant effects in males or females. These results suggest that dietary genistein exposure may act similarly to estradiol in augmenting amphetamine-stimulated DA release.

Promoter CpG methylation of Hox-a10 and Hox-a11 in mouse uterus not altered upon neonatal diethylstilbestrol exposure

Mouse abdominal B-like Hoxa genes are expressed and functionally required in the developing reproductive tracts. Mice lacking either Hoxa-10 or Hoxa-11, two of the AbdB Hoxa genes, exhibit abnormal uterine development similar to that induced by in utero diethylstilbestrol (DES) exposure. Indeed, uterine Hoxa-10 and Hoxa-11 expression is potently repressed by perinatal DES exposure, providing a potential molecular mechanism for DES-induced reproductive tract malformations. We have shown previously that DES can permanently alter uterine lactoferrin gene expression through modulation of the lactoferrin promoter methylation pattern. Here we ask whether a similar mechanism also functions to deregulate uterine Hoxa-10 or Hoxa-11 expression during neonatal DES exposure. We mapped the Hoxa-10 promoter by cloning a 1.485 kb DNA fragment 5' of the Hoxa-10 exon1a. A 5' rapid amplification of cDNA ends (RACE) experiment revealed a transcription start site for the a10-1 transcript. Functional analysis of the proximal 200-bp sequences demonstrated significant promoter activity, confirming the location of the Hoxa-10 promoter. Moreover, methylation assays performed on eight CpGs in Hoxa-10 and 19 CpGs in Hoxa-11 proximal promoters demonstrated that all these CpGs were highly unmethylated in both control and DES-dosed mice from postnatal day 5 to day 30. Significant methylation around Hoxa-10 and Hoxa-11 promoters was only observed in DES-induced uterine carcinomas in 18-mo-old mice. Our results suggest that DES-induced downregulations of Hoxa-10 or Hoxa-11 gene expression are not associated with methylation changes in their proximal promoters and that gene imprinting by developmental DES exposure may be a gene-specific phenomenon.

Effects of dietary genistein exposure during development on male and female CD (Sprague-Dawley) rats

Genistein is a naturally occurring isoflavone that interacts with estrogen receptors and multiple other molecular targets. Human exposure to genistein is predominantly through consumption of soy products, including soy-based infant formula and dietary supplements. A dose range-finding study was conducted as a prelude to a multigeneration bioassay to assess potential toxicities associated with genistein consumption. Genistein was administered in a soy- and alfalfa-free diet at 0, 5, 25, 100, 250, 625, or 1250 ppm to pregnant dams starting on Gestation day 7 and continuing throughout pregnancy. Dietary exposure of the dams continued through lactation, and pups were maintained on the same dosed feed as their mother after weaning until sacrifice at Postnatal day 50. Body weight and feed consumption of the treated dams prior to parturition showed a decreasing trend with a significant reduction at the highest dose. Litter birth weight was depressed in the 1250 ppm dose group, and pups of both sexes in that dose group had significantly decreased body weights relative to controls at the time of sacrifice. The most pronounced organ weight effects in the pups were decreased ventral prostate weight in males at the 1250 ppm dose and a trend toward higher pituitary gland to body weight ratios in both sexes. Histopathologic examination of female pups revealed ductal/alveolar hyperplasia of the mammary glands at 250 to 1250 ppm. Ductal/alveolar hyperplasia and hypertrophy also occurred in males, with significant effects seen at 25 ppm and above. Abnormal cellular maturation in the vagina was observed at 625 and 1250 ppm, and abnormal ovarian antral follicles were observed at 1250 ppm. In males, aberrant or delayed spermatogenesis in the seminiferous tubules relative to controls was observed at 1250 ppm. There was a deficit of sperm in the epididymis at 625 and 1250 ppm relative to controls, although testicular spermatid head counts and epididymal spermatozoa counts did not show significant differences from controls at these doses. Both sexes showed an increase in the incidence and/or severity of renal tubal mineralization at doses of 250 ppm and above. Dietary genistein thus produced effects in multiple estrogen-sensitive tissues in males and females that are generally consistent with its estrogenic activity. These effects occurred within exposure ranges achievable in humans.

The immature mouse is a suitable model for detection of estrogenicity in the uterotropic bioassay

The traditional rodent uterotropic response assay has been incorporated into the U.S. Environmental Protection Agency's screening and testing program for environmental endocrine-disrupting chemicals (EDCs). While much effort continues to focus on determining protocol variables, few studies compare uterotropic responses in rats, a species commonly used in toxicologic testing, with other rodent species. In this study, we compared uterine responses in immature outbred CD-1 mice and Sprague-Dawley rats. After three daily subcutaneous injections with 17beta-estradiol (0.1-500 microg/kg/day), immature mice and rats demonstrated a similar dose-response increase in absolute uterine wet weight and uterine weight:body weight ratio. Further, morphologic and biochemical parameters of estrogenicity, including uterine epithelial cell height and number, gland number, and induction of estrogen-responsive proteins lactoferrin and complement C3, mirror wet weight increases. We conclude that mice are as well suited as rats for the uterotropic bioassay. Because of the advantages of using mice, including lower costs, less space required, and smaller amounts of compound needed for tests, mice should be given appropriate consideration in testing paradigms for EDCs.

Polycystic kidney disease induced in F(1) Sprague-Dawley rats fed para-nonylphenol in a soy-free, casein-containing diet

para-Nonylphenol (NP; CAS #84852-15-3), an alkylphenol with a 9-carbon olefin side chain, is widely used in the manufacture of nonionic surfactants, lubricant additives, polymer stabilizers, and antioxidants. Due to its wide commercial use and putative endocrine activity in humans and wildlife, the NTP elected to assess its effects on reproduction in multigenerational studies. To avoid known estrogenic activity of phytoestrogens in soy and alfalfa, a soy- and alfalfa-free, casein-containing diet was used in a range-finding study to determine the doses of NP to be tested further. NP was administered to Sprague-Dawley rats in the diet at 0, 5, 25, 200, 500, 1000, or 2000 ppm to F(0) dams beginning on gestation-day 7. The F(1) pups were weaned at postnatal day (PND) 21, and their exposure via diet was continued at the same dose level as their respective dams. Pup weights from birth through weaning were not significantly different from controls in any dose group, but the average weight of both sexes was significantly less compared to controls, beginning with the PND 28 weighing. The F(1) rats were sacrificed on PND 50 (n = 15, 3 pups of each sex from 5 litters for all dose groups). Terminal body weights of males and females in the 2000-ppm dose group were 74% and 85% of controls, respectively. Severe polycystic kidney disease (PKD) was present in 100% of the 2000 ppm-exposed male and female rats. At 1000 ppm, 67% of males and 53% of females had mild to moderate PKD versus none of either sex in the control and lower-dose groups. The no-adverse-effect level (NOAEL) for PKD was determined to be 500 ppm. Previous studies with comparable duration and route of exposure, but using soy-containing diets, reported either no or only mild PKD at 2000 ppm NP. We conclude that the renal toxicity of NP is highly dependent on the diet on which the animals are maintained. The potential interaction of diet and test compounds on nonreproductive as well as reproductive endpoints should be considered when contemplating the use of special diets formulated to minimize exogenous "hormone" content for the study of the effects of putative endocrine disruptive chemicals.

Uterine adenocarcinoma in mice treated neonatally with genistein

The developing fetus is uniquely sensitive to perturbation with estrogenic chemicals. The carcinogenic effect of prenatal exposure to diethylstilbestrol (DES) is the classic example. Because phytoestrogen use in nutritional and pharmaceutical applications for infants and children is increasing, we investigated the carcinogenic potential of genistein, a naturally occurring plant estrogen in soy, in an experimental animal model previously reported to result in a high incidence of uterine adenocarcinoma after neonatal DES exposure. Outbred female CD-1 mice were treated on days 1-5 with equivalent estrogenic doses of DES (0.001 mg/kg/day) or genistein (50 mg/kg/day). At 18 months, the incidence of uterine adenocarcinoma was 35% for genistein and 31% for DES. These data suggest that genistein is carcinogenic if exposure occurs during critical periods of differentiation. Thus, the use of soy-based infant formulas in the absence of medical necessity and the marketing of soy products designed to appeal to children should be closely examined.

Cell response endpoints enhance sensitivity of the immature mouse uterotropic assay

Outbred immature CD-1 mice were subcutaneously (s.c.) injected once on postnatal day 17 or on postnatal days 17, 18, and 19 with 17beta-estradiol, diethylstilbestrol, tamoxifen, 4-hydroxytamoxifen, methoxychlor, the methoxychlor metabolite HPTE, nonylphenol, o,p'-DDT, endosulfan, or kepone over a wide dose range (0.1 to 1,000,000 microg/kg). On the day following the last injection, uterine weight/body weight ratios were determined and uterine tissues processed for histologic examination. All compounds except endosulfan and kepone increased uterine wet weight compared to vehicle controls; however, the dose response curve and magnitude of response varied depending on the compound. Choosing the maximum wet weight dose for each compound, uterine tissue was evaluated for epithelial cell height, epithelial and stromal cell proliferation, endometrial gland number, and induction of estrogen-inducible proteins lactoferrin and complement C3. All compounds elicited estrogen-responsive changes in these endpoints that were individually more sensitive than uterine weight alone. We conclude that these endpoints enhance the sensitivity of the uterotropic bioassay.

From malformations to molecular mechanisms in the male: three decades of research on endocrine disrupters

For three decades, we have known that estrogens alter the development of the mammalian reproductive system in predictable ways. In mice exposed prenatally to diethylstilbestrol (DES) or other estrogens, the male offspring exhibit structural malformations including cryptorchidism, epididymal cysts and retained Mullerian ducts. The estrogen-associated alterations in the genital tract phenotype can be usefully considered as a model called Developmental Estrogenization Syndrome. While estrogen treatment during critical periods of morphogenesis of the male reproductive system has been associated with these changes, the mechanisms at the molecular level are still being discovered. Parallel findings on the hormones involved in Mullerian duct regression and testicular descent have helped guide research on the mechanisms of developmental estrogenization of the male. Cellular localization of molecular signals associated with key steps in genital tract development, use of mice with gene disruption, and knowledge of the mechanisms underlying persistent changes in gene expression are beginning to provide a blue print for both the physiological role and pathological effects of estrogens in reproductive tract development. Since many of the same biological principles underlie genital tract morphogenesis in mammals, one may expect some of the same changes in males of other species exposed to estrogen during the appropriate developmental periods.