phytoestrogens and Pituitary-Neoplasms

Phytoestogens are a group of lipophillic plant compounds that can have estrogenic effects in animals; both tumorigenic and anti-tumorigenic effects have been reported. Prolactin-secreting adenomas are the most prevalent form of pituitary tumors in humans and have been linked to estrogen exposures. We examined the proliferative effects of phytoestrogens on a rat pituitary tumor cell line, GH3/B6/F10, originally subcloned from GH3 cells based on its ability to express high levels of the membrane estrogen receptor-alpha.. We measured the proliferative effects of these phytoestrogens using crystal violet staining, the activation of several mitogen-activated protein kinases (MAPKs) and their downstream targets via a quantitative plate immunoassay, and caspase enzymatic activities.. Four phytoestrogens (coumestrol, daidzein, genistein, and trans-resveratrol) were studied over wide concentration ranges. Except trans-resveratrol, all phytoestrogens increased GH3/B6/F10 cell proliferation at some concentration relevant to dietary levels. All four phytoestrogens attenuated the proliferative effects of estradiol when administered simultaneously. All phytoestrogens elicited MAPK and downstream target activations, but with time course patterns that often differed from that of estradiol and each other. Using selective antagonists, we determined that MAPKs play a role in the ability of these phytoestrogens to elicit these responses. In addition, except for trans-resveratrol, a serum removal-induced extrinsic apoptotic pathway was blocked by these phytoestrogens.. Phytoestrogens can block physiological estrogen-induced tumor cell growth in vitro and can also stimulate growth at high dietary concentrations in the absence of endogenous estrogens; these actions are correlated with slightly different signaling response patterns. Consumption of these compounds should be considered in strategies to control endocrine tumor cell growth, such as in the pituitary.

Topics: Animals; Caspases; Cell Line, Tumor; Cell Proliferation; Enzyme Activation; Humans; Mitogen-Activated Protein Kinases; Phosphorylation; Phytoestrogens; Pituitary Neoplasms; Rats; Signal Transduction

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. Consumption of soy and genistein has been associated with a variety of beneficial effects in animals and humans, but concerns have also been raised concerning potential adverse effects of genistein, particularly with regard to reproductive toxicity and the induction or potentiation of carcinogenesis, due primarily to its weak estrogenic activity. Because of these concerns, genistein was selected as one of the compounds to be examined in a protocol utilizing Sprague-Dawley rats to evaluate the effects of multigenerational and long-term exposures to doses of estrogenic agents that produce subtle reproductive tract lesions in developmentally exposed Sprague-Dawley rat pups. Results from the multigenerational reproductive toxicology feed study are reported in this report, and results of the 2-year feed study are reported separately (NTP, 2008a). Data from a preliminary reproductive dose range-finding feed study (NTP, 2007) that utilized exposure concentrations of up to 1,250 ppm genistein were used to select dietary exposure concentrations of 0, 5, 100, and 500 ppm for the current study. These dietary doses resulted in ingested genistein doses of approximately 0, 0.3, 7, or 35 mg genistein/kg body weight per day for males and 0, 0.5, 10, or 51 mg/kg per day for females during the time that the rats were directly consuming dosed feed. The current study was a multigenerational study (F(0) through F(4), with F(5) litters terminated at weaning) focused on reproductive endpoints. Animals were continuously exposed to genistein from the time that the F(0) generation was 6 weeks old through weaning of the F(3) generation, and animals of the F(0) through F(4) generations were sacrificed and necropsied on postnatal day 140 (PND 140). Dosed feed was removed from the F(3) pups at the time of weaning, and this generation and subsequent generations were maintained on control feed for the remainder of the study. For this study, 140 animals of each sex were obtained from the NCTR CD (Sprague-Dawley) rat colony at weaning and placed on a soy- and alfalfa-free diet that was used throughout the study in an attempt to maintain consistently low background exposure to phytoestrogens. Thirty-five animals per sex were assi

Topics: Adenocarcinoma; Adenoma; Animals; Carcinogens; Female; Genistein; Male; Mammary Neoplasms, Animal; Neoplasms, Experimental; Phytoestrogens; Pituitary Neoplasms; Pregnancy; Rats; Rats, Sprague-Dawley; Recovery of Function; Reproduction; Toxicity Tests, Chronic; Withholding Treatment

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. Consumption of soy and genistein has been associated with a variety of beneficial effects in animals and humans, but concerns have also been raised regarding potential adverse effects of genistein, particularly with regard to reproductive toxicity and the induction or potentiation of carcinogenesis, due primarily to its weak estrogenic activity. Because of these concerns, genistein was selected as one of the compounds to be examined using a protocol designed to evaluate the effects of multigenerational and long-term exposures to doses of estrogenic agents that produce subtle reproductive tract lesions in developmentally exposed Sprague-Dawley rat pups. Results from the 2-year study are reported here, and results from the multigenerational reproductive toxicology feed study are reported separately (NTP, 2008a). Data from a preliminary dose range-finding feed study (NTP, 2007) that utilized exposure concentrations up to 1,250 ppm genistein were used to select dietary exposure concentrations of 0, 5, 100, and 500 ppm for the current study. The multigenerational reproductive toxicology study examined F(0) through F(4) generations with F(5) litters terminated at weaning and focused on reproductive endpoints (NTP, 2008a). Animals were exposed from the time that the F(0) generation was 6 weeks old through weaning of the F(3) generation, and animals of the F(0) through F(4) generations were necropsied at 20 weeks of age. The current study was a 2-year dietary study utilizing three exposure arms: continuous exposure from conception through 2 years (designated F(1) continuous, or F(1)C), exposure from conception through 20 weeks followed by control diet to 2 years [designated F(1) truncated at postnatal day (PND) 140, or F(1)T140], and exposure from conception through weaning followed by control diet to 2 years (designated F(3) truncated at PND 21, or F(3)T21). The "F(3)" designation for the F(3)T21 arm indicates that these animals were siblings of the F(3) animals from the multigenerational reproductive toxicology study (NTP, 2008a). The F(1)C and F(1)T140 animals were also siblings but were derived from a separate breeding that was identical to the procedure used to produce the F(1) generation of the mu. Under the conditions of this 2-year feed study with continuous exposure to the test compound from conception through termination (F(1)C), there was no evidence of carcinogenic activity of genistein in male Sprague-Dawley rats exposed to 5, 100, or 500 ppm. There was some evidence of carcinogenic activity of genistein in female Sprague-Dawley rats based on increased incidences of mammary gland adenoma or adenocarcinoma (combined) and pituitary gland neoplasms. The incidence of benign mammary gland fibroadenoma in female rats was significantly decreased in the 500 ppm group. Under the conditions of this 2-year feed study with exposure to the test compound from conception through 20 weeks followed by control feed until termination (F(1)T140), there was no evidence of carcinogenic activity of genistein in male Sprague-Dawley rats exposed to 5, 100, or 500 ppm. There was equivocal evidence of carcinogenic activity of genistein in female Sprague-Dawley rats based on marginally increased incidences of pituitary gland neoplasms. Under the conditions of this 2-year feed study where offspring of three prior generations of animals exposed to the test compound were exposed from conception through weaning (PND 21) followed by control feed until termination (F(3)T21), there was no evidence of carcinogenic activity of genistein in male Sprague-Dawley rats exposed to 5, 100, or 500 ppm. There was equivocal evidence of carcinogenic activity of genistein in female Sprague-Dawley rats based on increased incidences of mammary gland adenoma or adenocarcinoma (combined). Exposure to genistein was also shown to accelerate the onset of aberrant estrous cycles in female Sprague-Dawley rats whether exposures were continuous or truncated at PND 140 or at weaning. The effects of genistein on estrous cycling and the incidences of common hormonally related spontaneous neoplasms of female Sprague-Dawley rats are consistent with an estrogenic mechanism of toxicity.

Topics: Animals; Body Weight; Estrous Cycle; Female; Genistein; Kidney; Litter Size; Longevity; Male; Mammary Glands, Animal; Mammary Neoplasms, Animal; Neoplasms, Experimental; Phytoestrogens; Pituitary Neoplasms; Pregnancy; Prenatal Exposure Delayed Effects; Rats; Rats, Sprague-Dawley; Reproduction; Toxicity Tests, Chronic; Xenobiotics

The modifying effects of three endocrine disrupting chemicals on the promotion phase of estrogen dependent tumor development were investigated with a transplantable rat pituitary cell line, MtT/E-2. The EDCs examined were genistein (Gen), a phytoestrogen, p-nonylphenol (NP), a surfactant and atrazine (Atz), a herbicide. Since potential exposure is through food and drinking water, oral administration was examined in the present study. Gen and NP stimulated in vitro MtT/E-2 growth at concentrations of 10(-8) and 10(-6) M, respectively, while Atz did not show any effects. The estrogenic activity was further confirmed by measuring transcription of an ERE-luciferase reporter transiently transfected in the cells. When MtT/E-2 cells are inoculated into ovariectomized female F344 rats, estrogen dependent tumors develop providing a simple and sensitive model to examine modulation effects of estrogenic compounds in the promotion phase. Ovariectomized F344 rats implanted with MtT/E-2 were fed diet containing NP or Gen at 25 and 250 mg/kg, or Atz at 5, 50 and 500 mg/kg. NP and Atz did not exert any modifying effects on pituitary tumor development, while Gen at 250 mg/kg exhibited a promotion influence. These results indicate that Gen might facilitate the estrogen responsive tumor development if only the promotion phase is concerned, while NP and Atz at doses used in the present study were without effect.

Topics: Animals; Atrazine; Cell Division; Cell Line, Tumor; Diet; Eating; Environmental Pollutants; Estrogens, Non-Steroidal; Female; Genes, Reporter; Genistein; Herbicides; Isoflavones; Luciferases; Neoplasm Transplantation; Organ Size; Phenols; Phytoestrogens; Pituitary Gland; Pituitary Neoplasms; Plant Preparations; Prolactin; Radioimmunoassay; Rats; Rats, Inbred F344; Uterus

There is renewed interest in the medicinal value of natural plant products. One group of plant compounds, the phytoestrogens (PE), has been given considerable attention due to their ability to decrease the incidence of certain estrogen-dependent cancers. In this study, we evaluate the effects of PE on estrogen-dependent pituitary tumor cells by using the immortalized pituitary cell line PR1. Several PE were found to be active in PR1 cells, in that they bound to the estrogen receptor (ER), stimulated growth of PR1 cells, and induced an estrogenic response, prolactin secretion. The PE genistein, coumestrol, and zearalenone bound to the ER present in PR1 cells with an affinity 100-times lower than that of estradiol. However, resveratrol, a plant antitumor agent found in grapes, showed no significant binding to the ER. Zearalenone, coumestrol, and genistein were found to induce prolactin secretion and to stimulate growth, whereas resveratrol showed prolactin secretion but no growth stimulation. The estrogenic effects of PE in PR1 cells were ER dependent, in that addition of the antiestrogen ICI-182,780 inhibited prolactin response. Although resveratrol did not bind to the ER or stimulate growth, it induced prolactin secretion in both a dose- and time-dependent manner. The data presented here demonstrate that PE are active in lactotroph cells of the pituitary.

Topics: Animals; Blotting, Northern; Cell Division; DNA; Dose-Response Relationship, Drug; Estradiol; Estrogen Antagonists; Estrogens; Estrogens, Non-Steroidal; Fulvestrant; Inhibitory Concentration 50; Isoflavones; Phytoestrogens; Pituitary Neoplasms; Plant Preparations; Plants; Prolactin; Rats; Rats, Inbred F344; Receptors, Estrogen; RNA, Messenger; Time Factors; Tumor Cells, Cultured