Reduction in Ki-67 in benign breast tissue of high-risk premenopausal women with the SERM acolbifene

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Background: Selective Estrogen Receptor Modulators (SERMs) are approved for reduction of risk for breast cancer; however, uptake and use is limited. We conducted a pilot study of a 4th generation SERM to determine tolerability and effect on tissue biomarkers in healthy women at high risk for development of breast cancer. Methods: Premenopausal women at elevated risk for breast cancer were screened by random periareolar fine needle aspiration (RPFNA) performed during the follicular phase of the menstrual cycle. Women were eligible if breast epithelial cells exhibited evidence of cytologic hyperplasia with or without atypia, as well as Ki-67 ≥2% by immunocytochemistry. Following 6-8 months of open-label acolbifene (20 mg/d), the RPFNA was repeated. The primary endpoint was modulation of the proportion of cells that expressed Ki-67. Body composition (DEXA), pelvic sonography, mammographic breast density, and serum levels of IGF-1/IGFBP3 and several bioavailable hormones were assessed pre and post intervention. Results: 76 women were screened by RPFNA, with 25 eligible and enrolled in the intervention over a 9 month period. All 25 (7 on oral contraceptives) subjects completed the study, had a second RPFNA, and were evaluable. Median Ki-67 at baseline was 4.6% (range 2.4 – 21.9%) and off study 1.4% (range 0 – 6.6%); median change was a reduction of 3.0% (range -20.2% to +2.8%; decreased in 23, increased in 2) or a relative reduction of 77%. The end-of-study Ki-67 was significantly less than baseline (p<0.001, 2-tailed Wilcoxon test). There were no statistically significant changes in cytomorphology over this short intervention period. There was a marginal effect on breast density (16 decreased; 8 increased; p=0.067). Adverse events were minimal with greatest grade of 3 reported by 2 subjects, grade 2 by 7 subjects, and grade 1 by 11 subjects. No serious adverse event was reported and no subject discontinued the study due to an AE. Conclusions: Based on preliminary evaluation showing favorable modulation of proliferation and minimal adverse events, further investigation of acolbifene, a fourth generation SERM, as a breast cancer chemoprevention agent for premenopausal women appears warranted. Supported by NO1-CN-35135.

The autoimmune regulator prevents premature reproductive senescence in female mice

Loss-of-function mutations in the autoimmune regulator (AIRE) gene are responsible for autoimmune polyglandular syndrome type 1 (APS-1), which commonly manifests as infertility in women. AIRE is a transcriptional regulator that promotes expression of tissue-restricted antigens in the thymus, including antigens specific to the ovary. Thymic expression of ovarian genes under AIRE's control may be critical for preventing ovarian autoimmune disease. Because mice lacking Aire are an important APS-1 model, we examined the reproductive properties of female Aire-deficient (Aire(-/-)) mice. Female Aire(-/-) mice on the BALB/c background were examined for reproductive parameters, including fertility, litter sizes, and ovarian follicular reserves. Although delayed puberty was observed in Aire(-/-) mice, all mice entered puberty and exhibited mating behavior. Only 50% of Aire(-/-) females gave an initial litter, and only 16% were able to produce two litters. Ovarian histopathologic examination revealed that 83% of previously bred females lost all ovarian follicular reserves. Among virgin females, follicular depletion was observed in 25% by 8 wk, and by 20 wk, 50%-60% of mice lost all follicles. This was associated with elevated serum follicle-stimulating hormone level and ovarian infiltration of proliferating CD3+ T lymphocytes. Ovulation rates of 6-wk-old Aire(-/-) mice were reduced by 22%, but this difference was not statistically significant. Finally, transplantation experiments revealed that follicular loss depended on factors extrinsic to the ovary. These results suggest that immune-mediated ovarian follicular depletion is a mechanism of infertility in Aire(-/-) mice. The results have important implications in the pathogenesis of ovarian autoimmune disease in women.

The aryl hydrocarbon receptor agonist 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) alters early embryonic development in a rat IVF exposure model

Aryl hydrocarbon receptor (AHR) ligands, including 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD), accelerate reproductive senescence and one proposed target is the early embryo. To discriminate between direct effects on the oocyte and early embryo and those mediated by complex ovarian interactions with TCDD, IVF was carried out in the presence of TCDD (10, 100 nM) and the aryl hydrocarbon antagonist CH-223191 (1 μM) combined factorially. TCDD-induced Cyp1a1 mRNA expression was absent in 2-cell embryos; however morulae exhibit dose-dependent Cyp1a1 expression. TCDD induced accumulation of sperm in the perivitelline space and displacement of blastomere nuclei. At 100 nM TCDD, aberrations in cytokinesis and nuclear positioning were observed 2-cell embryos and morula and these effects were reversed in the presence of CH-223191. Our data suggest that acute exposure to TCDD has direct effects on early development in the rat that permit discrimination of AHR-mediated and AHR-independent mechanisms through which environmental toxicants impair mammalian reproduction.

Reduction in Ki-67 in benign breast tissue of high-risk women with the lignan secoisolariciresinol diglycoside

Preclinical and correlative studies suggest reduced breast cancer with higher lignan intake or blood levels. We conducted a pilot study of modulation of risk biomarkers for breast cancer in premenopausal women after administration of the plant lignan secoisolariciresinol given as the diglycoside (SDG). Eligibility criteria included regular menstrual cycles, no oral contraceptives, a >3-fold increase in 5-year risk, and baseline Ki-67 of ≥2% in areas of hyperplasia in breast tissue sampled by random periareolar fine-needle aspiration (RPFNA) during the follicular phase of the menstrual cycle. SDG (50 mg/d) was given for 12 months, followed by repeat RPFNA. The primary end point was change in Ki-67. Secondary end points included change in cytomorphology, mammographic breast density, serum bioavailable estradiol and testosterone insulin-like growth factor-I and IGF-binding protein-3, and plasma lignan levels. Forty-five of 49 eligible women completed the study with excellent compliance (median = 96%) and few serious side effects (4% grade 3). Median plasma enterolactone increased ∼9-fold, and total lignans increased 16-fold. Thirty-six (80%) of the 45 evaluable subjects showed a decrease in Ki-67, from a median of 4% (range, 2-16.8%) to 2% (range, 0-15.2%; P < 0.001, Wilcoxon signed rank test). A decrease from baseline in the proportion of women with atypical cytology (P = 0.035) was also observed. Based on favorable risk biomarker modulation and lack of adverse events, we are initiating a randomized trial of SDG versus placebo in premenopausal women.

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin disturbs the establishment and maintenance of cell polarity in preimplantation rat embryos

Maternal exposure to the environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces a variety of defects in compaction-stage embryos, including monopolar spindle formation, errors in chromosome segregation, and fragmentation resulting from aberrant cytokinesis. In this study, we investigated the possibility that a failure in centrosome duplication, separation, or positioning within blastomeres might underlie the observed effects of TCDD on early embryos. The subcellular localization of the centrosomal marker TUBG1 was analyzed in preimplantation embryos collected from female rats exposed to either chronic (50 ng kg(-1) wk(-1) for 3 wk) or acute (50 ng/kg or 1 microg/kg at proestrus) doses of TCDD. In treated embryos, interphase TUBG1 foci were more abundant and cortically displaced when compared to those in controls. At prophase, some blastomeres exhibited a single large perinuclear TUBG1 aggregate, suggesting a failure in centrosome duplication or separation. Furthermore, the presence of monopolar spindles at metaphase was confirmed by the localization of TUBG1 to the single spindle pole. Therefore, the misregulation of centrosome number and localization, as indicated by TUBG1 staining, may contribute to errors in chromosome segregation and cytokinesis in embryos following maternal TCDD exposure.

Temporal and anatomical sensitivities to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin leading to premature acyclicity with age in rats

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that mediates diverse dioxin toxicities. While the acute effects of activation of the AhR pathway by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) have been a focus of past study, the role of this pathway in normal physiology and ageing is unclear. The purpose of this study was to identify the portion of the reproductive axis [ovary vs. hypothalamus and pituitary gland (H-H axis)] and the stages of the reproductive lifespan (foetal and early post-natal life vs. adolescence and adulthood) that are particularly sensitive to the effects of TCDD during female reproductive ageing. Adult pregnant Lewis rat dams were dosed with corn oil vehicle or TCDD (50 ng/kg-week by gavage) on days 14 and 21 of gestation and post-natal days 7 and 14 to provide in utero and lactational (IUL) exposure to pups. Female pups (n = 96) were weaned on post-natal day 21 and dosed with TCDD or vehicle weekly. Half of the pups were used as donors for ovary transplantation while the remainder were recipients. Following ovary transplantation, rats (n = 6-8 per group) received weekly TCDD or vehicle again until sacrifice at 8 months of age. Beginning at vaginal opening, reproductive cycles were monitored by vaginal cytology for 10 days each month. Blood samples were collected at 22.00 h on proestrus to measure concentration of 17beta-oestradiol in serum. Real-time PCR was used to determine differences in Cyp1a1, Cyp19a1, Cyp17a1, LH receptor (LHR), FoxA2 and FoxJ1 genes expression between control and remaining groups. IUL exposure of the H-H axis plus adult exposure of the whole body to TCDD significantly delayed puberty in females rats. Data analysis revealed an accelerated onset of acyclicity by 5 months in all groups involving IUL exposure of the developing ovary to TCDD. 17beta-oestradiol was significantly decreased in animals receiving TCDD during IUL exposure of the H-H axis. CYP1a1 expression was markedly greater in the liver than in ovarian tissue and correlated with ongoing TCDD exposure. Aromatase, 17alpha-hydroxylase and LHR gene expressions were largely unchanged (or occasionally elevated) by TCDD. FoxA2 and FoxJ1 mRNAs were similarly of limited value mechanistically, although FoxJ1 was much higher in TTT females (receiving TCDD as donor, recipient and adult). This study reveals a particular sensitivity of the developing ovary to TCDD leading to early loss of reproductive function with age.

Effects of phytoestrogen daidzein and estradiol on steroidogenesis and expression of estrogen receptors in porcine luteinized granulosa cells from large follicles

The aims of the study were to compare the in vitro effects of daidzein or 17beta-estradiol (E(2)) on: 1) progesterone (P(4)) secretion by luteinized granulosa cells harvested from large porcine follicles, as well as 2) estrogen receptor alpha and beta (ERalpha and ERbeta) mRNA and protein expression in the cells. In addition, the effect of daidzein on E(2) secretion and viability of the granulosa cells was examined. We found that basal and gonadotropin-stimulated P(4) secretion were inhibited in granulosa cells cultured in the presence of daidzein either for 24 or 48 hours. In contrast to daidzein, E(2) reduced P(4) secretion only during 24-hour cell cultures increasing it during longer cultures. Daidzein did not affect E(2) secretion by granulosa cells. The expression of ERalpha and ERbeta mRNA, as well as ERbeta protein, was up-regulated by daidzein but unaffected by E(2). To conclude, the soy estrogen daidzein acts directly on the porcine ovary to decrease progesterone production and to increase expression of ERbeta mRNA and protein. Daidzein actions in porcine luteinized granulosa cells differ from those of estradiol and it may suggest disadvantageous effects of the phytoestrogen on reproductive processes in females.

Effect of chronic exposure to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin in female rats on ovarian gene expression

The aryl hydrocarbon receptor (AHR) mediates the effects of many endocrine disruptors and contributes to the loss of fertility in polluted environments. Female rats exposed chronically to environmentally relevant doses of the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) across their lifespan experience accelerated reproductive senescence preceded by ovarian endocrine disruption. The purpose of this study was to determine the changes in ovarian gene expression that accompany the loss of ovarian function caused by chronic exposure to TCDD. Beginning in utero, female Sprague-Dawley rats received TCDD (1, 5, 50, or 200 ng/kg-week; n=4 per group) or vehicle weekly throughout their lifespan, and were sacrificed on diestrus just prior to loss of reproductive cyclicity at 11 months of age. Microarray analysis was used to determine differences in ovarian gene expression between control and TCDD-treated (200 ng/kg-week) animals. To confirm microarray results, real-time PCR was used to assess changes in gene expression among treatment groups. TCDD treatment decreased (p<0.05) proestrus serum estradiol concentrations with no effect on serum progesterone. In ovaries from rats treated with 200 ng/kg-week TCDD compared to controls, 19 genes of known function were found to be up-regulated, while 31 ovarian genes were found to be down-regulated >or=1.5-fold (p<or=0.05). Gene expression of 17 alpha-hydroxylase decreased following chronic TCDD treatment, suggesting the decrease in estradiol biosynthesis may be a consequence of decreased substrate. Taken together with past studies indicating a lack of effect on hypothalamus or pituitary function, the apparent regulation of key ovarian genes support the hypothesis that chronic TCDD exposure directly affects ovarian function.

Tamoxifen prevents premalignant changes of breast, but not ovarian, cancer in rats at high risk for both diseases

Women at increased risk for breast cancer are at increased risk for ovarian cancer as well, reflecting common risk factors and intertwined etiology of the two diseases. We previously developed a rat model of elevated breast and ovarian cancer risk, allowing evaluation of dual-target cancer prevention strategies. Tamoxifen, a Food and Drug Administration-approved breast cancer chemoprevention drug, has been shown to promote ovarian cysts in premenopausal women; however, the effect of tamoxifen on ovarian cancer risk is still controversial. In the current experiment, Fischer 344 rats (n = 8 per treatment group) received tamoxifen (TAM) or vehicle (control) in factorial combination with combined breast and ovarian carcinogen (17beta-estradiol and 7,12 dimethylbenza[a]anthracene, respectively). Mammary and ovarian morphologies were normal in the control and TAM groups. Carcinogen (CARC) treatment induced mammary dysplasia with elevated cell proliferation and reduced estrogen receptor-alpha expression and promoted preneoplastic changes in the ovary. In the CARC + TAM group, tamoxifen reduced preneoplastic changes and proliferation rate in the mammary gland, but not in the ovary, compared with rats treated with carcinogen alone. Putative stem cell markers (Oct-4 and aldehyde dehydrogenase 1) were also elevated in the mammary tissue by carcinogen and this expansion of the stem cell population was not reversed by tamoxifen. Our study suggests that tamoxifen prevents early progression to mammary cancer but has no effect on ovarian cancer progression in this rat model.

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin disrupts morphogenesis of the rat pre-implantation embryo

Background

Environmental toxicants, whose actions are often mediated through the aryl hydrocarbon receptor (AhR) pathway, pose risks to the health and well-being of exposed species, including humans. Of particular concern are exposures during the earliest stages of development that while failing to abrogate embryogenesis, may have long term effects on newborns or adults. The purpose of this study was to evaluate the effect of maternal exposure to the AhR-specific ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the development of rat pre-implantation embryos with respect to nuclear and cytoskeletal architecture and cell lineage allocation.

Results

We performed a systematic 3 dimensional (3D) confocal microscopy analysis of rat pre-implantation embryos following maternal exposure to environmentally relevant doses of TCDD. Both chronic (50 ng/kg/wk for 3 months) and acute (50 ng/kg and 1 μg/kg at proestrus) maternal TCDD exposure disrupted morphogenesis at the compaction stage (8–16 cell), with defects including monopolar spindle formation, f-actin capping and fragmentation due to aberrant cytokinesis. Additionally, the size, shape and position of nuclei were modified in compaction stage pre-implantation embryos collected from treated animals. Notably, maternal TCDD exposure did not compromise survival to blastocyst, which with the exception of nuclear shape, were morphologically similar to control blastocysts.

Conclusion

We have identified the compaction stage of pre-implantation embryogenesis as critically sensitive to the effects of TCDD, while survival to the blastocyst stage is not compromised. To the best of our knowledge this is the first in vivo study to demonstrate a critical window of pre-implantation mammalian development that is vulnerable to disruption by an AhR ligand at environmentally relevant doses.

Ovarian Endocrine Disruption Underlies Premature Reproductive Senescence Following Environmentally Relevant Chronic Exposure to the Aryl Hydrocarbon Receptor Agonist 2,3,7,8-Tetrachlorodibenzo-p-Dioxin1

The aryl hydrocarbon receptor (AHR) mediates the effects of many endocrine disruptors and contributes to the loss of fertility in polluted environments. While previous work has focused on mechanisms of short-term endocrine disruption and ovotoxicity in response to AHR ligands, we have shown recently that chronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces premature reproductive senescence in female rats without depletion of ovarian follicular reserves. In the current study, premature reproductive senescence was induced using a range of low-dose exposure to TCDD (0, 1, 5, 50, and 200 ng kg(-1) wk(-1)) beginning in utero and continuing until the transition to reproductive senescence. Doses of 50 and 200 ng TCDD kg(-1) wk(-1) delayed the age at vaginal opening and accelerated the loss of normal reproductive cyclicity with age without depletion of follicular reserves. Serum estradiol concentrations were decreased in a dose-dependent fashion (> or = 5 ng kg(-1) wk(-1)) across the estrous cycle in perisenescent rats still displaying normal cyclic vaginal cytology. Serum FSH, LH, and progesterone profiles were unchanged by TCDD. The loss of reproductive cyclicity following chronic exposure to TCDD was not accompanied by decreased responsiveness to GnRH. Ovarian endocrine disruption is the predominant functional change preceding the premature reproductive senescence induced by chronic exposure to low doses of the AHR-specific ligand TCDD.

Reduction in proliferation with six months of letrozole in women on hormone replacement therapy

The objective of this study was to determine if 6 months of the aromatase inhibitor letrozole, administered to postmenopausal women taking a stable dose of hormone replacement remedy, would be safe and would modulate biomarkers of breast cancer risk. The intent was to reduce the proliferation marker Ki-67 while maintaining adequate systemic levels of estradiol so as to avoid perimenopausal symptoms. Postmenopausal women at high risk for development of breast cancer and taking a stable dose of estrogen or estrogen plus progestin were screened by random periareolar fine needle aspiration (RPFNA). To be eligible, the acquired breast epithelial cells had to be characterized as cytologic atypia or borderline atypia with > or =1,000 epithelial cells on the cytomorphology slide; plus > or =500 epithelial cells on a slide processed for Ki-67 immunocytochemistry. Forty-two women were enrolled in the one arm study and received 2.5 mg letrozole per day for 6 months, followed by repeat assessment of biomarkers. Ki-67 was reduced by a median relative value of 66%. There was no significant change in breast cell cytomorphology; ER weighted index score; serum estradiol, testosterone, or IGF-1:IGFBP-3 ratio; mammographic breast density, or frequency or severity of perimenopausal symptoms. Given the dramatic reduction in proliferation, the effect of letrozole on risk and response biomarkers should be explored further in a randomized, placebo-controlled Phase IIB breast cancer chemoprevention trial.

Optimization of estrogen receptor analysis by immunocytochemistry in random periareolar fine-needle aspiration samples of breast tissue processed as thin-layer preparations

Immunostaining of estrogen receptor alpha (ER) in samples of benign breast tissue obtained by random periareolar fine-needle aspiration (RPFNA) is a practical tool for breast cancer chemoprevention trials. The authors report an optimized method of ER immunostaining for use with thin-layer preparations of modified Cytolyt-fixed benign breast tissue acquired by RPFNA. Samples of benign breast tissue and MCF-7 controls processed as thin-layer preparations were tested for the effects of antibody titer, antigen retrieval temperature (90 degrees or 115 degrees C), buffer (20% nuclear decloaker, pH 9.3; 10 mM citrate buffer, pH 6), and blocking solution (0.01% glucose oxidase or 0.3% H2O2) on ER immunostaining. The prevalence of positively stained breast epithelial cells, mean intensity of ER staining, and composite immunostaining score were evaluated for effect of immunostaining protocol. RPFNA samples and MCF-7 cells processed using nuclear decloaker and low-temperature antigen retrieval had more ER-positive cells (P<0.0001) and increased mean staining intensity and weighted staining indices (P<0.05) compared with samples prepared with citrate buffer and high-temperature antigen retrieval. Glucose oxidase increased ER-positive cells in comparison to hydrogen peroxide (P<0.04) when combined with low-temperature antigen retrieval and the use of nuclear decloaker. Staining was negative for all non-immune controls regardless of protocol. The combination of low-temperature antigen retrieval, diluted commercial nuclear decloaker solution, and a glucose oxidase blocking step yielded optimal ER immunostaining for thin-layer preparations of benign breast tissue harvested by RPFNA.

Detection of biomarker gene expression by real-time polymerase chain reaction using amplified ribonucleic acids from formalin-fixed random periareolar fine needle aspirates of human breast tissue

OBJECTIVE

To address the detection of breast cancer biomarker gene expression in formalin-fixed random periareolar fine needle aspiration (RPFNA) samples of benign breast tissue collected during breast cancer prevention trials by quantitative real-time polymerase chain reaction (qPCR).

STUDY DESIGN

Formalin-fixed breast epithelial cells collected by RPFNA and processed as thin layer preparations were isolated by laser capture microdissection (LCM). Ribonucleic acid (RNA) was extracted and amplified using a single round of T7-based linear amplification followed by quality assessment and biomarker assay using TaqMan chemistry.

RESULTS

More than 80% of RPFNA samples yielded RNA of sufficient quantity and quality for measurement of a panel of biomarker genes following a single round of linear amplification. RNA and protein expression for estrogen receptor alpha, as assessed by LCM/qPCR and immunohistochemistry, were correlated. Amplification plots were similar for cDNA standards and cDNA derived from RPFNA samples.

CONCLUSION

Assessment of gene expression using amplified RNA from microdissected formalin-fixed RPFNAs can increase the number of biomarkers used during breast cancer chemoprevention trials.

Expression of enzymes of cyclooxygenase pathway and secretion of prostaglandin E2 and F2α by porcine myometrium during luteolysis and early pregnancy

Past studies of uterine prostaglandin (PGs) and pig reproduction have focused on endometrial rather than myometrial PGs. This study documents the synthesis and secretion of myometrial prostaglandins (PGs) in pigs and the involvement of oxytocin (OT) in these processes. Cyclooxygenase-2 (COX-2) expression was similar in myometrial explants from cyclic and pregnant pigs (days 14-16) and OT (10(-7) M) in vitro significantly increased COX-2 protein regardless of reproductive state. Basal expression of prostaglandin E2 synthase (PGES) was higher during pregnancy than during luteolysis. Conversely, prostaglandin F synthase (PGFS) was highest during luteolysis and lower in myometrium from gravid animals. OT had no influence on the expression of PGES and PGFS. In another tissue culture experiment, myometrial slices produced more PGE2 than PGF2alpha regardless of reproductive state of the female. OT stimulated PGE2 production in myometrium harvested during luteolysis and increased PGF2alpha production in all tissues examined. Progesterone (P4; 10(-5) M) blocked stimulatory effect of OT on myometrial PG release. Myometrial OTr mRNA was higher (P=0.03) during luteolysis than during pregnancy.

IN CONCLUSION

(1) oxytocin increases myometrial COX-2 expression, but does not influence the expression of terminal enzymes of PGs synthesis (PGES and PGFS); (2) porcine myometrium preferentially produces PGs during early pregnancy and secretes more PGE2 than PGF2alpha; (3) myometrial OT and OTr support secretion of PGs from myometrium during luteolysis.

Characterization of a preclinical model of simultaneous breast and ovarian cancer progression

Women at increased risk for breast cancer are often also at increased risk for ovarian cancer, reflecting common risk factors and intertwined etiologies for both diseases. Unlike breast cancer prevention, primary ovarian cancer prevention has been impractical due to the low incidence, lack of risk and response biomarkers and difficulties in sampling ovarian tissue. Challenges in the development of ovarian cancer prevention drugs, however, may be circumvented through the development of breast cancer prevention strategies that simultaneously decrease ovarian cancer. In the present study, three commonly used mammary cancer carcinogen models [7,12-dimethylbenz[alpha]anthracene (DMBA), N-methyl-N-nitrosourea (MNU) and estradiol (E2)] were combined with local ovarian DMBA administration to induce progression to mammary and ovarian cancer concurrently in the rat. Animals were treated for 3 or 6 months, and tissue histology as well as proliferation, hormonal and inflammation biomarkers were assessed. Mammary and ovarian morphologies (measured as descriptive histology and dysplasia scores) were normal in vehicle controls. Mammary hyperplasia was observed in DMBA/DMBA (mammary carcinogen/ovarian carcinogen) and MNU/DMBA-treated rats; however, ovarian preneoplastic changes were seldom observed after these treatments. All E2/DMBA-treated rats had mammary hyperplasia, atypia, ductal carcinoma in situ and/or invasive adenocarcinoma, while 50% also developed preneoplastic changes in the ovary (ovarian epithelial and stromal hyperplasia and inclusion cyst formation). In both the mammary gland and ovary, decreased estrogen receptor alpha expression was detected, and in the mammary gland elevated Ki-67 and cyclooxygenase-2 expressions were observed. This combined breast and ovarian cancer rat model (systemic E2 treatment and local ovarian DMBA) may be useful for future dual target breast and ovarian cancer prevention studies.

The effect of progesterone on oxytocin-stimulated intracellular mobilization of Ca2+ and prostaglandin E2 and F2alpha secretion from porcine myometrial cells

Our past studies have shown that porcine myometrium produce prostaglandins (PG) during luteolysis and early pregnancy and that oxytocin (OT) and its receptor (OTr) support myometrial secretion of prostaglandins E2 and F2alpha (PGE2 and PGF2alpha) during luteolysis. This study investigates the role of intracellular Ca2+ [Ca2+]i as a mediator of OT effects on PG secretion from isolated myometrial cells in the presence or absence of progesterone (P4). Basal [Ca2+]i was similar in myometrial cells from cyclic and pregnant pigs (days 14-16). OT (10(-7)M) increased [Ca2+]i in myometrial cells of cyclic and pregnant pigs, although this effect was delayed in myometrium from pregnant females. After pre-incubation of the myocytes with P4 (10(-5)M) the influence of OT on [Ca2+]i)was delayed during luteolysis and inhibited during pregnancy. Myometrial cells in culture produce more PGE2 than PGF2alpha regardless of reproductive state of the female. OT (10(-7)M) increased PGE2 secretion after 6 and 12 h incubation for the tissue harvested during luteolysis and after 12 h incubation when myometrium from gravid females was used. In the presence of P4 (10(-5)M), the stimulatory effect of OT on PG secretion was diminished.

IN CONCLUSION

(1) porcine myometrial cells in culture secrete PG preferentially during early pregnancy and produce more PGE2 than PGF2alpha, (2) OT controls myometrial PGF2alpha secretion during luteolysis, (3) release of [Ca2+]i is associated with the influence of OT on PG secretion, and (4) the effects of OT on PG secretion and Ca2+ accumulation are delayed by P4 during luteolysis and completely inhibited by P4 during pregnancy.

Effects of Acute and Chronic Exposure to the Aryl Hydrocarbon Receptor Agonist 2,3,7,8-Tetrachlorodibenzo-p-Dioxin on the Transition to Reproductive Senescence in Female Sprague-Dawley Rats1

Activation of the aryl hydrocarbon receptor (AHR) can occur in polluted environments, either from smoking-related toxicants or from endogenous ligands. We tested whether acute or chronic exposure to the AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alters the transition to reproductive senescence in female Sprague-Dawley rats. In experiment 1, rats (n = 6 per experimental group) received a single dose of 0 or 10 mug/kg of TCDD orally (p.o.) on Postnatal Day 29. Vaginal cytology was monitored for 1 wk each month until rats were killed at 1 yr of age. The single prepubertal exposure to TCDD hastened the transition to reproductive senescence in female rats and was associated with delayed puberty, abnormal cyclicity, and premature reproductive senescence. In a second experiment, rats were exposed to TCDD chronically through weekly dosing (0, 50, or 200 ng kg(-1) wk(-1) p.o., n = 7 each dose) beginning in utero. Lifelong exposure to these lower doses of TCDD induced a dose- and time-dependent loss of normal cyclicity and significantly hastened the onset of the transition to reproductive senescence (P < 0.05). This premature transition to reproductive senescence was associated with prolonged estrous cycles and, at the highest dose of TCDD, persistent estrus or diestrus. The number and size of ovarian follicles were not altered by TCDD. Diestrous concentrations of LH in rats exposed chronically to TCDD were similar to those in controls, whereas progesterone tended to be elevated at both doses of the dioxin (P < 0.08). Serum FSH was elevated in the group exposed to 50 ng/kg of TCDD (P < 0.02), whereas estradiol was decreased at both doses of dioxin (P < 0.01). Data thus far support endocrine disruption rather than depletion of follicular reserves as a primary mechanism of the premature transition to reproductive senescence following activation of the AHR pathway by TCDD in female rats.

Potential roles of the aryl hydrocarbon receptor in female reproductive senescence

The transition to reproductive senescence involves changes in neuroendocrine and ovarian functions, and is accelerated by activation of the aryl hydrocarbon pathway by environmental toxicants such as 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD). In this article, studies which provide evidence as to the possible mechanisms by which the aryl hydrocarbon receptor (AhR) acts in this capacity (i.e. disruption of ovarian, hypothalamic or suprachiasmatic nucleus function, or any combination of these) are reviewed, along with the normal physiological changes that occur during the transition to reproductive senescence in female humans and rodents. Based on findings that the AhR is evolutionarily conserved and necessary for normal fertility, we suggest that the AhR has not only a pathological but also a physiological role in the process of aging. Studies of realistic lifelong AhR activation by dioxins on the hypothalamic-pituitary-ovarian axis and its impact on the transition to reproductive senescence in the aging female are a previously neglected area of research that warrants further consideration.

Pharmacokinetics of ovarian steroids in Sprague-Dawley rats after acute exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces abnormalities in steroid-dependent processes such as mammary cell proliferation, gonadotropin release and maintenance of pregnancy. In the current study, the effects of TCDD on the pharmacokinetics of 17beta-estradiol and progesterone were examined. Adult Sprague-Dawley rats were ovariectomized and pretreated with TCDD (15 microg/kg p.o.) or vehicle. A single bolus of 17beta-estradiol (E2, 0.3 micromol/kg i.v.) or progesterone (P4, 6 micromol/kg i.v.) was administered 24 hours after TCDD and blood was collected serially from 0-72 hours post-injection. Intravenous E2 and P4 in DMSO vehicle had elimination half-lives of approximately 10 and 11 hours, respectively. TCDD had no significant effect on the pharmacokinetic parameters of P4. The elimination constant and clearance of E2 were decreased by TCDD while the elimination half-life, volume of distribution and area under the time*concentration curve were not altered significantly. Overall, these results indicate that diminished serum progesterone and estradiol concentrations following exposure to TCDD are due primarily to actions on steroid synthesis and release rather than any alterations in pharmacokinetics.

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) stimulates gonadotropin secretion in the immature female Sprague-Dawley rat through a pentobarbital- and estradiol-sensitive mechanism but does not alter gonadotropin-releasing hormone (GnRH) secretion by immortalized GnRH neurons in vitro

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) induces aberrant release of gonadotropins, FSH, and LH and blocks ovulation during induced ovarian follicular development in rats by an unknown mechanism. In the current study, TCDD (0, 8, or 32 microg/kg orally) was administered to immature female Sprague-Dawley rats, and synchronous follicular development was induced 24 h later with equine chorionic gonadotropin (eCG, 5 IU s.c.). Both doses of TCDD induced a significant premature increase in serum FSH and LH (P < 0.05) at 12 h post-eCG. This premature gonadotropin surge was facilitated by the administration of a long-acting estradiol (estradiol cypionate, 0.01, 0.1, and 0.5 mg/kg s.c.), whereas the progesterone and cortisol receptor antagonist RU486 (0, 1, and 10 mg/kg s.c.) potentiated the premature release of FSH and LH following TCDD as well. Pentobarbital (32 mg/kg i.p.) administered at 6 or 9 h, but not 0 h, post-eCG ablated the ability of TCDD to stimulate the release of FSH and LH in vivo. TCDD had no significant effect on GnRH accumulation in vitro from immortalized GnRH neuronal (GT1-7) cells and failed to alter the cell number. Transfection of these cells with a rat GnRH promoter-reporter construct revealed no significant acute effect of TCDD on GnRH promoter activity. Aryl hydrocarbon receptor mRNA was not detected in the GT1-7 cells by reverse transcription polymerase chain reaction. TCDD appears to stimulate premature gonadotropin release in the gonadotropin-primed immature rat by interacting with an estradiol- and pentobarbital-sensitive neural signal for GnRH release but not by acting upon the GnRH neuron directly.

Endocrine disruption by indole-3-carbinol and tamoxifen: blockage of ovulation

Immature Sprague-Dawley rats received daily doses of indole-3-carbinol (I3C, 0-1.5 g/kg/day), 3,3'-diindolymethane (DIM, 0-400 mg/kg/day), tamoxifen (TAM, 0-0.5 mg/kg/day), or vehicle to determine if their antiestrogenic effects occur by the same mechanism and whether I3C's action is mediated by DIM. Follicular development was induced on day 24 of age by equine chorionic gonadotropin (eCG, 5 IU) 1 day after the initial dose. In a hormone replacement study, human chorionic gonadotropin (hCG, 10 IU sc, 48 h post-eCG) was used to mimic a normal preovulatoy luteinizing hormone (LH) surge following treatment with either I3C or TAM. Blood and ovaries were collected throughout follicular development and the number of ova shed was measured on the morning following expected ovulation (72 h post-eCG). I3C but not TAM reduced body weight gain at higher doses after 4 days of dosing. Ovarian weight gain and ovulation were inhibited by both I3C and TAM in a dose-dependent fashion. During the preovulatory period, both I3C and TAM blocked normal LH and follicle-stimulating hormone (FSH) surges and suppressed serum progesterone (P(4)) profoundly without changing circulating levels of estrogen (E(2)). At the time of expected ovulation, serum E(2) was increased in rats receiving I3C or tamoxifen, whereas serum P(4) was dose-dependently decreased. DIM exerted no significant effects on any of the endpoints studied, even at the highest dose, indicating that the antiestrogenic effects of I3C are not mediated by this metabolite of I3C. hCG successfully restored ovarian weight gain and ovulation in TAM-treated rats. However, hCG only partially reversed the blockage of ovulation by I3C, although ovarian weight gain was restored to normal. In summary, both I3C and TAM block ovulation by altering preovulatory concentrations of LH and FSH, but I3C appears to exert its effect(s) by (a) different mechanism(s) of action. I3C seems to act at both the ovarian and hypothalamic levels by mechanisms similar to those seen in TCDD-treated rats, whereas TAM appears to act only on the hypothalamic-pituitary axis as an anti-estrogen.

Effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on serum inhibin concentrations and inhibin immunostaining during follicular development in female Sprague-Dawley rats

Intact and hypophysectomized immature rats were pretreated with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; 0 or 32 microg/kg p.o.) and sacrificed throughout synchronized follicular development (0, 12, 24, 48, and 72 h after equine chorionic gonadotropin, eCG). TCDD administration to intact rats resulted in a premature elevation of serum FSH and LH by 12 h post-eCG. In intact rats pretreated with TCDD, the intensity of ovarian immunoreactivity for inhibin and the number of ovarian follicles staining for inhibin in midsaggital ovarian sections were decreased at the time of eCG administration (24 h post-TCDD) in comparison to controls. However, this decreased ovarian staining for inhibin was not associated with alterations in serum inhibin concentrations. Serum inhibin was suppressed in TCDD-treated rats when compared to intact controls only at 24 h post-eCG. Hypophysectomized animals exhibited no effect of TCDD on serum inhibin at any timepoint but did have decreased estradiol concentrations during follicular development. In summary, TCDD reduced serum concentrations of inhibin after the premature increases in FSH and LH suggesting that inhibin is not important in the initial elevation of FSH following exposure to TCDD.