Estrogenic action of DDT analogs

Organochlorine Residues and Risk of Breast Cancer

Considerable attention has recently been focused on the possible role of estrogenic compounds as etiologic agents in the development of human breast cancer. This review summarizes data from relevant laboratory and epidemiological studies to assess the hypothesis that exposure to organochlo-rines, and specifically 2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane (DDT), increases breast cancer risk. Organochlorine compounds, including pesticides such as DDT and industrial compounds such as the polychlorinated biphenyls (PCBs), have had a long history of use. In general, these compounds are characterized by their high lipophilicity and environmental persistence. DDT was widely used in agriculture and public health programs from 1943 to 1972, when it was removed from use in the Western world. DDT is still used, however, in many developing nations. The International Agency for Research on Cancer concluded that there was adequate evidence that DDT was carcinogenic in laboratory animals, yet epidemiological evidence has not been compelling. The estrogenic activity of o, p'-DDT has been well characterized; however, the affinity of estrogen receptors for this compound is very weak and reported to be 1/2,000–1/10,000 that of 17β-estradiol. Epidemiologically, some investigators have reported elevated levels of 1,1-dichloro-2,2-bis(p-chloro-phenyl)ethylene, a DDT metabolite, and PCBs in breast adipose tissue and blood serum taken from breast cancer patients when compared with controls, while others have reported the absence of such an association. While the etiology of breast cancer is not fully understood, it is generally recognized that estrogenic compounds may increase the risk of disease. Contemporary human exposure to DDT and other organochlorines is very limited and would likely play an insignificant role when compared with other sources of exposure, such as estrogen replacement therapy and phytoestrogens in food.

Low concentrations of o,p'-DDT inhibit gene expression and prostaglandin synthesis by estrogen receptor-independent mechanism in rat ovarian cells

o,p'-DDT is an infamous xenoestrogen as well as a ubiquitous and persistent pollutant. Biomonitoring studies show that women have been internally exposed to o,p'-DDT at range of 0.3-500 ng/g (8.46×10(-10) M-1.41×10(-6) M) in blood and other tissues. However, very limited studies have investigated the biological effects and mechanism(s) of o,p'-DDT at levels equal to or lower than current exposure levels in human. In this study, using primary cultures of rat ovarian granulosa cells, we determined that very low doses of o,p'-DDT (10(-12)-10(-8) M) suppressed the expression of ovarian genes and production of prostaglandin E2 (PGE2). In vivo experiments consistently demonstrated that o,p'-DDT at 0.5-1 mg/kg inhibited the gene expression and PGE2 levels in rat ovary. The surprising results from the receptor inhibitors studies showed that these inhibitory effects were exerted independently of either classical estrogen receptors (ERs) or G protein-coupled receptor 30 (GPR30). Instead, o,p'-DDT altered gene expression or hormone action via inhibiting the activation of protein kinase A (PKA), rather than protein kinase C (PKC). We further revealed that o,p'-DDT directly interfered with the PKA catalytic subunit. Our novel findings support the hypothesis that exposure to low concentrations of o,p'-DDT alters gene expression and hormone synthesis through signaling mediators beyond receptor binding, and imply that the current exposure levels of o,p'-DDT observed in the population likely poses a health risk to female reproduction.

Optimization of an MCF7-E3 Cell Proliferation Assay and Effects of Environmental Pollutants and Industrial Chemicals

Environmental contaminants might adversely affect human health by acting as endocrine disruptors and thus need to be identified. Our objective was to optimize the MCF7 cell proliferation assay to screen industrial chemicals for potential oestrogenic effects. Growth conditions, performance of the clone E3 and WT-MCF7 cells and five methods to derive proliferation indices were compared. The E3 cells were further characterized by testing the effects of transforming growth factorbeta (TGFbeta), epidermal growth factor (EGF), insulin, testosterone, the anti-oestrogen ICI 164,384 (ICI) and environmental contaminants with known oestrogenic potential. Industrial chemicals with unknown oestrogenic effects were then tested. As expected, induction of proliferation by estradiol-17beta (E2) was greater and less variable using the clone E3. To generate proliferation indices, the alamarBlue assay had a sensitivity comparable to that of [(3)H]thymidine incorporation ((3)H-TI). The E3 cells were not responsive to EGF (0-100 ng/ml) or insulin (0-313 ng/ml) but their proliferation was decreased (P<0.05) by TGFbeta (45 ng/ml) and testosterone (10(-8)m), which might be typical of highly oestrogen-responsive MCF7 cells. ICI (5x10(-7)m) inhibited the proliferative effects of 10(-10)m E2 and that of 10(-6)m 4-tert-octylphenol (Op) but not the proliferative effect of 10(-5)m Op, suggesting displacement of ICI by Op or induction of oestrogen-receptor independent proliferation. N-oxydiethylene-2-benzothiazole sulfenamide (OBTS) altered (3)H-TI in the MCF7 cells, although not in a dose related manner. OBTS did not induce uterotrophic effects in immature female rats, or any response in a human oestrogen chimeric receptor/reporter gene assay, suggesting that its effects were not mediated through the binding of the oestrogen-receptor. Seven other industrial chemicals were tested and had no effects. In conclusion, the MCF7 cell proliferation assay is one screening tool that permits identification of chemicals with oestrogenic potential which thus require further testing.

Activated Estrogens and Antiestrogens: A 30-Year Journey with David Kupfer

David Kupfer had a passion for drug metabolism and used his talents to understand the putative metabolic activation of the insecticides o, p'DDT and methoxychlor to estrogens. His research helped to create a scientific foundation for the current interest in endocrine disruption. With the increasing clinical significance of tamoxifen in the late 1980s, and the proposal to test tamoxifen as a breast cancer chemopreventive in healthy women, David initiated laboratory studies on the mechanisms of tamoxifen metabolism. He was the first to note that tamoxifen is metabolically activated to alkylating species. Tamoxifen and insecticides covalently bind to microsomal proteins. His contribution presaged worldwide studies of the induction of rat liver carcinogenesis by tamoxifen.

Effects of xenoestrogens on the differentiation of behaviorally-relevant neural circuits

It has become increasingly clear that environmental chemicals have the capability of impacting endocrine function. Moreover, these endocrine disrupting chemicals (EDCs) have long term consequences on adult reproductive function, especially if exposure occurs during embryonic development thereby affecting sexual differentiation. Of the EDCs, most of the research has been conducted on the effects of estrogen active compounds. Although androgen active compounds are also present in the environment, much less information is available about their action. However, in the case of xenoestrogens, there is mounting evidence for long-term consequences of early exposure at a range of doses. In this review, we present data relative to two widely used animal models: the mouse and the Japanese quail. These two species long have been used to understand neural, neuroendocrine, and behavioral components of reproduction and are therefore optimal models to understand how these components are altered by precocious exposure to EDCs. In particular we discuss effects of bisphenol A and methoxychlor on the dopaminergic and noradrenergic systems in rodents and the impact of these alterations. In addition, the effects of embryonic exposure to diethylstilbestrol, genistein or ethylene,1,1-dichloro-2,2-bis(p-chlorophenyl) is reviewed relative to behavioral impairment and associated alterations in the sexually dimorphic parvocellular vasotocin system in quail. We point out how sexually dimorphic behaviors are particularly useful to verify adverse developmental consequences produced by chemicals with endocrine disrupting properties, by examining either reproductive or non-reproductive behaviors.

Immunization prevents DDT buildup in mouse tissues

DDT is used for pest control, causing health and environmental hazards in some parts of the world. The goal of this study was to assess whether immunization against a toxic compound could reduce the toxicant uptake of an organism, specifically to develop a DDT immunization that promotes the production of specific antibodies and assess whether it reduces DDT levels in the bodies of mice that are exposed to DDT by intake. BALB/c mice were immunized with DDT-keyhole limpet hemocyanine (DDT-KLH) conjugate (n=10) or unconjugated KLH (n=10), which was used as a control. After the immunization specific DDT antibodies in the mouse serum were determined by ELISA and then the mice were fed chow containing 40 mg/kg of DDT for 45 days. Finally, the concentration of DDT and its metabolites, DDE and DDD, in various tissues was measured by gas chromatography. Specific DDT antibody levels were significantly higher in the DDT immunized group than in the control group. DDT, DDE and DDD levels in adipose tissue, blood, brain and spleen were significantly reduced in the DDT immunized animals relative to control animals. However, DDT and DDD levels were higher in the liver compared to the control group. The findings indicate that the DDT immunization reduces the total uptake of DDT in animal tissues, which is reflected by the lower levels in adipose tissue, blood, brain and spleen. The elevated levels in liver suggest that DDT-antibody complexes in mouse serum are delivered to the liver.

The pesticide methoxychlor decreases myotube formation in cell culture by slowing myoblast proliferation

We studied the effect of the estrogenic pesticide methoxychlor (MXC) on skeletal muscle development using C2C12 cell culture. Myoblast cultures were exposed to various concentrations of MXC at various times during the process of myoblast fusion into myotubes. We observed that MXC exposure decreased myotube formation. In addition, we observed myoblasts with cytoplasmic vacuoles in cultures exposed to MXC. Because cytoplasmic vacuoles can be characteristic of cell death, apoptosis assays and trypan blue exclusion assays were performed. We found no difference in the frequency of apoptosis or in the frequency of cell death for cultures exposed to MXC and untreated cultures. Collectively, these results indicate that MXC exposure decreases myotube formation without causing cell death. In contrast, when cell proliferation was assessed, untreated cultures had a myoblast proliferation rate 50% greater than cultures exposed to MXC. We conclude that MXC decreases myotube formation at least in part by slowing myoblast proliferation. Furthermore, we suggest that direct exposure to MXC could affect skeletal muscle development in animals or humans, in addition to the defects in reproductive development that have previously been reported.

Pesticide exposure and timing of menopause: the Agricultural Health Study

Age at menopause has implications for fertility and risk of hormonally related chronic diseases. Some pesticides disrupt reproductive hormones or are toxic to the ovary, but little is known about the association between pesticide exposure and timing of menopause. Cox proportional hazards modeling was used to examine the association between use of pesticides and age at menopause among 8,038 women living and working on farms in Iowa and North Carolina. Premenopausal women aged 35-55 years were followed from enrollment (1993-1997) to the date of their last menstrual period, or their follow-up interview (1999-2003) if still premenopausal. Women who experienced surgical menopause were censored at the date of surgery. Approximately 62% of the women reported ever mixing or applying pesticides; women who had never used pesticides were the comparison group for all analyses. After control for age, smoking status, and past use of oral contraceptives, the median time to menopause increased by approximately 3 months for women who used pesticides (hazard ratio = 0.87, 95% confidence interval: 0.78, 0.97) and by approximately 5 months for women who used hormonally active pesticides (hazard ratio = 0.77, 95% confidence interval: 0.65, 0.92). Pesticide use may be associated with a later age at menopause.

Persistent organic pollutants in plasma of delivering women from Arkhangelsk

The high levels of persistent organic pollutants have caused concern about human health, especially the health of the foetus and newborn child. This has especially been the case for Greenlandic and Canadian Inuits, where elevated levels of PCB and p,p'-DDE have been reported. In recent studies from arctic Russia the levels of beta-HCH and the DDT-group have been reported to be high, whereas the levels of PCB are low. However, the information from Northern Russia is, so far, incomplete. In this study, 27 delivering women from the city of Arkhangelsk, Russia, participated. They completed a questionnaire before delivery and plasma samples were collected after delivery. The analytical method developed to support this study involved gel permeation chromatography and silica gel purification, in addition to a traditional GC-MS method, and thus include acid labile compounds. The arithmetic mean levels of p,p'-DDE, beta-HCH and p,p'-DDT were 5.42, 3.59 and 1.17 microg/l, respectively. Toxaphene 26 and 50 were the only toxaphenes above the limit of detection, with arithmetic mean levels of 0.05 and 0.09 microg/l, respectively. Among the PCB congeners, PCB 138/163 was the most abundant with an arithmetic mean of 0.53 microg/l. The elevated levels of beta-HCH and p,p'-DDT as well as a low DDE/DDT ratio is a strong indication of fresh and maybe local sources in this area.

The pesticide methoxychlor disrupts the fusion of myoblasts into myotubes in skeletal muscle cell culture

We studied the effect of the estrogenic pesticide methoxychlor (MXC) on skeletal muscle development using C2C12 muscle cell culture. Various concentrations of MXC or beta-estradiol (E) were added to the culture media. MXC (100 microM) disrupted myoblast fusion into myotubes, but 10 microM MXC or 10 microM E had no effect. Correlated with the diminished size of the myotubes, the clustering of acetylcholine receptors (AChRs) was inhibited by 100 microM MXC, but not by 10 microM MXC or 10 microM E. However, since clusters of AChR receptors did form, the postsynaptic clustering mechanism remained intact. Since E did not disrupt myoblast fusion into myotubes or the clustering of AChRs, we conclude that the abnormality induced by MXC is mediated by a mechanism of action that is independent of E. We believe this to be the first demonstration that MXC induces abnormal effects in the process of muscle development in skeletal muscle cell culture.

Effects of prenatal exposure to low doses of diethylstilbestrol, o,p'DDT, and methoxychlor on postnatal growth and neurobehavioral development in male and female mice

We examined effects of a wide range of doses of three man-made estrogenic chemicals during fetal life on neurobehavioral changes during early postnatal life in mice. Pregnant mice were fed a 4-log range of o,p'DDT, methoxychlor (MXC), and the drug diethystilbestrol (DES) from gestation days 11 to 17. Offspring were examined for changes in postnatal growth and the development of neuromuscular reflexes. Fetal exposure to the estrogenic chemicals altered the number of live pups per litter, the sex ratio of the litters, the anogenital distance of male and female offspring at birth (a bioassay for fetal androgen action), and the body weight of offspring at birth and during the first 5 days of postnatal life. In most cases, however, the dose-response relationships were complex (non-monotonic), with effects at the highest dose examined being opposite to effects seen at lower doses. The two markers of neurobehavioral development, righting and cliff avoidance reflexes, were not sensitive indicators of prenatal estrogen exposure. Only maternal exposure to the lowest MXC dose produced an increase in reactivity in righting and cliff avoidance tests in offspring.

Analyses of lindane, vinclozolin, aldrin, p,p'-DDE, o,p'-DDT and p,p'-DDT in human serum using gas chromatography with electron capture detection and tandem mass spectrometry

A sensitive, selective and reliable procedure was developed and validated to determine organochlorinated compounds, which present endocrine-disrupting effects, lindane, vinclozolin, aldrin, p,p'-DDT, o,p'-DDT and p,p'-DDE, in human serum. The analytical methodology combines serum extraction with organic solvents, clean-up of the organic extract using acid treatment with H2SO4, elution of the cleaned-up extract through liquid column chromatography system and analysis of the fraction eluted by gas chromatography (GC) with electron capture detection (ECD) and tandem mass spectrometry (MS-MS) detection mode. Performance characteristics, such as linearity, sensitivity, precision, accuracy or recovery, of both chromatographic methods were studied. The proposed analytical methodology was applied to analyse the target compounds in serum samples from women living in agricultural areas of Almería (Spain). Comparison of the MS-MS and the ECD results was made and the advantage of the MS-MS operation mode to determine endocrine disrupting compounds in complex matrices is also presented.

Parental consumption of contaminated sport fish from Lake Ontario and predicted fecundability

Wildlife studies suggest that consumption of contaminated fish from the Great Lakes may expose humans to polychlorinated biphenyls and persistent chlorinated pesticides. To assess whether time to pregnancy or fecundability is affected, we conducted a telephone survey in 1993 with female members of the New York State Angler Cohort Study who were considering pregnancy between 1991 and 1994 (N = 2,445). Among the 1,234 (50%) women who became pregnant, 895 (73%) had a known time to pregnancy. Upon enrollment into the cohort in 1991, both partners reported duration and frequency of Lake Ontario sport fish consumption. We estimated lifetime exposure to polychlorinated biphenyls from recent consumption and used a discrete-time analog of Cox proportional hazards analysis to estimate conditional fecundability ratios and 95% confidence intervals (CIs) for fish consumption among couples with complete exposure data who discontinued birth control to become pregnant (N = 575). Maternal consumption of fish for 3-6 years was associated with reduced fecundability (fecundability ratio = 0.75; 95% CI = 0.59-0.91), as was more than a monthly fish meal in 1991 (fecundability ratio = 0.73; 95% CI = 0.54-0.98). Our findings suggest that maternal but not paternal consumption of contaminated fish may reduce fecundability among couples attempting pregnancy.

DDT congener effects on secondary sex coloration in the reed frog Hyperolius argus: a partial evaluation of the Hyperolius argus endocrine screen

Organochlorine compounds such as o,p'DDT can mimic estrogen effects. We compared the effects of o,p'DDT and six other DDT congeners to the effects of estradiol by comparing in vivo color changes in the reed frog (Hyperolius argus). Premature female color pattern induction in H. argus is specific to estrogens and the current study suggests that this assay has potential for use in discriminating between xenobiotic estrogens and non-estrogens. Animals were treated at forelimb emergence and maintained in treated solution until final evaluation. Estradiol, o,p.DDT (0.1 microg/ml), o,p'DDE (1 microg/ml) and o,p'DDD (1 microg/ml) prematurely induced adult female coloration patterns in juvenile animals, whereas p,p'DDT, p, p'DDE and p,p'DDD did not.

In utero exposure to antiandrogens alters the responsiveness of the prostate to p,p'-DDE in adult rats and may induce prostatic inflammation

DDE is an environmental pollutant with antiandrogenic properties. Following administration to pregnant rats, DDE was shown to cause feminization in the male offspring at the neonatal stages but did not affect the pubertal growth of accessory sex organs. In this study, we examined the potential of in utero exposure to antiandrogens to alter the responsiveness of the male rats to subsequent DDE challenge. Pregnant Long-Evans rats were dosed by gavage from Gestation Day 14 to 18 at 0, 10 (low dose), or 100 (high dose) mg DDE, or 40 mg flutamide/kg body wt (bw)/day (in utero treatment). At approximately 80 days of age, the male offspring from each of the four in utero treatment groups were divided into two groups. One group received the adult treatment of four daily gavage administrations of DDE at 70 mg/kg bw (adult treatment), while the second group served as the adult treatment control (adult control). The in utero treatment resulted in 18, 31, and 53% reductions of ventral prostate weights at approximately 85 days of age compared to the control for the low- and high-dose DDE and flutamide groups, respectively. These results suggest that the in utero antiandrogen treatments produced a latent effect on prostate growth that became pronounced only in the postpubertal stage. The in utero treatment also altered the responsiveness of the prostate to the adult treatment, indicated by a significant reduction in ventral prostate weight that was seen only in the control group of the in utero treatment but not in the other groups. The in utero treatment was also associated with expression of testosterone-repressed prostatic message-2 in the adult ventral prostate. In addition, a few prostates in the high-dose DDE- and flutamide-treated groups of the in utero treatment were found to have chronic suppurative prostatitis. While other types of hormonal manipulations have been shown to incite similar responses in rat prostate, the possible linkage between in utero antiandrogen treatment and prostatic inflammation needs to be further evaluated.

Plasma steroid concentrations and male phallus size in juvenile alligators from seven Florida lakes

Neonatal and juvenile alligators from contaminated Lake Apopka in central Florida exhibit abnormal plasma sex steroid concentrations as well as morphological abnormalities of the gonad and phallus. This study addresses whether similar abnormalities occur in juvenile alligators inhabiting six other lakes in Florida. For analysis, animals were partitioned into two subsets, animals 40-79 cm total length (1-3 years old) and juveniles 80-130 cm total length (3-7 years old). Plasma testosterone (T) concentrations were lower in small males from lakes Apopka, Griffin, and Jessup than from Lake Woodruff National Wildlife Refuge (NWR). Similar differences were observed in the larger juveniles, with males from lakes Jessup, Apopka, and Okeechobee having lower plasma T concentrations than Lake Woodruff males. Plasma estradiol-17beta (E(2)) concentrations were significantly elevated in larger juvenile males from Lake Apopka compared to Lake Woodruff NWR. When compared to small juvenile females from Lake Woodruff NWR, females from lakes Griffin, Apopka, Orange, and Okeechobee had elevated plasma E(2) concentrations. Phallus size was significantly smaller in males from lakes Griffin and Apopka when compared to males from Lake Woodruff NWR. An association existed between body size and phallus size on all lakes except Lake Apopka and between phallus size and plasma T concentration on all lakes except lakes Apopka and Orange. Multiple regression analysis, with body size and plasma T concentration as independent covariables, explained the majority of the variation in phallus size on all lakes. These data suggest that the differences in sex steroids and phallus size observed in alligators from Lake Apopka are not limited to that lake, nor to one with a history of a major pesticide spill. Further work examining the relationship of sex steroids and phallus size with specific biotic and abiotic factors, such as antiandrogenic or estrogenic contaminants, is needed.

Prenatal exposure to endocrine disrupting chemicals: effects on behavioral development

Numerous chemicals released into the environment by man are able to disrupt the functioning of the endocrine system by binding to hormonal receptors. Exposure to estrogenic endocrine disruptors during critical periods in fetal life can alter the development of reproductive organs, the neuroendocrine system and subsequent behavior. We present a series of studies on the effects of exposure during fetal life to low, environmentally relevant doses of two pesticides, o,p'DDT and methoxychlor, and of low doses of the synthetic estrogen, diethylstilbestrol on subsequent neuro-behavioral development in house mice. The main findings can be summarized as follows: (1) Mice prenatally exposed to methoxychlor showed changes in reflex development. Exposure to a very low dose of methoxychlor appeared to produce an increased reactivity during early postnatal life. (2) Methoxychlor exposed periadolescent mice showed a decreased reaction time exploring both a novel environment and a novel object. (3) The onset of male intrasex aggression appeared to be delayed in males prenatally exposed to low doses of methoxychlor, since exposed males showed low levels of aggressive interactions during early adolescence but not after they reached adulthood. (4) The rate of depositing urine marks in a novel environment was increased in males prenatally exposed to DES, and also to o,p'DDT and methoxychlor. (5) The proportion of both males and females attacking a same-sex conspecific was increased in mice prenatally exposed to low doses of DES and, marginally, to o,p'DDT. This effect appeared to be related to a decreased latency to attack. However, males prenatally exposed to o,p'DDT displayed a decreased intensity of aggression. The possible implications of perturbing the hormonal milieu during fetal development on the modulation of developmental turnpoints and future behavioral responses are discussed.

Transplacental and lactational transfer of p,p'-DDE in Sprague-Dawley rats

p,p'-DDE (hereafter DDE), a persistent metabolite of p,p'-DDT, is a widespread environmental contaminant that can induce antiandrogenic developmental effects in rats. Quantitative measurements of the transfer of DDE from pregnant or lactating dams to the fetus or suckling neonate were performed, and physiologically based pharmacokinetic (PBPK) models for the transplacental and lactational transfer of DDE were developed. Pregnant Sprague-Dawley rats were dosed by gavage in corn oil with either 10 or 100 mg DDE per kg body wt per day from Gestation Day (gd) 14 to 18. DDE was analyzed in several maternal tissues as well as in fetal and neonatal tissues from gd 15 to Postnatal Day (pnd) 21. Fetal DDE concentrations were about threefold lower than corresponding placental concentrations. By adopting a cross-fostering design, the contributions of transplacental and lactational transfer were compared. In the pup liver, where DDE was detectable in the 100 mg/kg groups on pnd 10, the lactationally exposed group had DDE concentrations about 50 times higher than those of the in utero only exposure group; the lactation only exposure groups had DDE tissue dose profiles very similar to those of the in utero plus lactation exposure groups, indicating that the lactational route is far more important than the in utero route quantitatively. The PBPK models postulated initial absorption of DDE into both the blood circulation and lymphatic system with the primary storage sites being maternal and neonatal adipose tissues. Mobilization of DDE from its storage sites is postulated to occur via its association with mobilized fatty acids and lipoproteins. The results provide an overall framework for evaluating the tissue dosimetry of DDE and for understanding how maternal exposure to DDE could affect perinatal sexual development in utero or in the early postnatal period.

Declining male fertility and environmental factors

Male reproductive function has recently attracted increasing attention due to reports on time-related decline in semen quality. Analysis of retrospective data indicates that sperm counts may have declined in some parts of the world, but there seem to be regional differences both in the quality of semen and regarding the secular trend. Whereas data on sperm counts may be somewhat difficult to interpret, there is no doubt that incidence of testicular cancer has increased worldwide. In occupational studies, only a few types of exposures were shown to have an impact on male reproductive function; lifestyle and general environmental factors may play a more important role. Prospective studies on secular and geographic trends in male reproductive function are warranted.

Inhibition of androgen receptor-dependent transcriptional activity by DDT isomers and methoxychlor in HepG2 human hepatoma cells

Recent reports have raised new concerns that chemicals in our environment may disrupt normal reproduction and development through inhibition of androgen receptor function. This heightened concern has also increased our need for methods that allow us to characterize chemical interaction with the androgen receptor. In this report we describe an androgen receptor assay that utilizes the HepG2 human hepatoma cell line transiently transfected with the human androgen receptor and an androgen-responsive reporter. We used this assay to characterize the interaction with the androgen receptor of several steroidal and nonsteroidal chemicals, including isomers of DDT and methoxychlor. Chemicals were tested either in the absence (for determining agonist activity) or presence of 10(-7) M dihydrotestosterone (for determining antagonist activity). Testosterone and dihydrotestosterone were equally potent agonists in this assay. Estradiol and progesterone displayed partial agonist/antagonist activity. Flutamide was a complete agonist, whereas its hydroxylated metabolite, hydroxyflutamide, only partially antagonized and displayed some agonist activity at 10(-6) M and above. o,p'-DDT, o,p'-DDE, o,p'-DDD, p,p'-DDT, p,p'-DDE, and p, p'-DDD all behaved as antagonists at concentrations above 10(-6) M. p,p'-DDE also showed some agonist activity at 10(-5) M. Methoxychlor was only weakly antagonistic while its hydroxylated metabolite, HPTE, was approximately 10-fold more potent. Our results demonstrate that the HepG2 assay is a sensitive and specific method for detecting chemical interaction with the androgen receptor. This reporter gene assay, which we have used to characterize interaction with both the estrogen and androgen receptors, coupled with more extensive in vivo studies, should be useful for determining the role of multiple steroid receptors in the mechanism of action of endocrine active chemicals.

Environmental estrogen stimulation of growth and estrogen receptor function in preneoplastic and cancerous human breast cell lines

BACKGROUND

DDT and polychlorinated biphenyls (PCBs), which are widespread in the ecosystem, can mimic estrogen-mediated cell activities. Thus, they can potentially interfere with many physiologic processes. We compared the effects of organochlorines belonging to the DDT and PCB families, alone and in combination, for their ability to influence the estrogen receptor-mediated activities in preneoplastic breast epithelial cells and breast cancer cells.

METHODS

Multiple assay systems requiring functional estrogen receptor were employed to test estrogen-like activity of organochlorine ligands. Two-sided statistical tests were used to compare the data.

RESULTS

p,p'-DDT, the predominant form of DDT in the environment, is a more potent estrogen than o,p'-DDT (P<.001), although it is less effective than o,p'-DDT in inhibiting the binding of estradiol (natural estrogen) to estrogen receptor. Among the PCBs, Heptachlor is estrogenic (in transient reporter assays; P< or =.001), whereas Aroclor 1221 and Aroclor 1254, both individually and in combination, are only weakly estrogenic.

CONCLUSION

p,p'-DDT is the most effective organochlorine in regulating estrogen receptor-mediated cellular responses. In estrogen receptor-positive breast cancer cells, p,p'-DDT evokes responses by itself and enhances the responses in collaboration with estradiol or o,p'-DDT.

DDE-induced eggshell thinning in birds: effects of p,p'-DDE on the calcium and prostaglandin metabolism of the eggshell gland

1. The focus of this review is the effects and mechanism of action of p,p'-DDE on eggshell formation in birds. Inhibition of prostaglandin synthesis in the eggshell gland mucosa is a probable mechanism for p,p'-DDE-induced eggshell thinning. 2. The duck is sensitive to p,p'-DDE-induced eggshell thinning but the domestic fowl is not, and studies comparing the two species in regard to the calcium and prostaglandin metabolism of the eggshell gland have shown that eggshell thinning induced by p,p'-DDE in ducks is accompanied by reduced activity of prostaglandin synthetase, reduced levels of prostaglandin E2, and reduced uptake of 45Ca by the eggshell gland mucosa. The content of calcium, bicarbonate, chloride, sodium, and potassium are also reduced in the eggshell gland lumen in ducks exhibiting eggshell thinning. None of these effects are seen in the domestic fowl. 3. Inhibition of prostaglandin synthesis is a specific effect of p,p'-DDE. The detrimental effects of p,p'-DDE on the eggshell gland seem to be unique when comparing the compound with structurally related substances, i.e., similar treatment regimens with o,p'-DDE, p,p'-DDT, o,p'-DDT, and p,p'-DDD do not cause eggshell thinning in ducks. Neither do they inhibit prostaglandin synthesis in the eggshell gland mucosa. 4. Administration of other compounds that do inhibit prostaglandin synthesis, e.g., indomethacin, does cause the same effects as those seen with p,p'-DDE, i.e., eggshell thinning and the described effects on the calcium and prostaglandin metabolism of the eggshell gland.

Organochlorine compounds: Risk of non-Hodgkin's lymphoma and breast cancer?

Organochlorines (i.e., synthetic chlorinated hydrocarbon compounds) are widespread, environmental contaminants that are present throughout the United States. Strong epidemiological evidence has linked occupational exposure to a high incidence of non-Hodgkin's lymphoma. Recently, it has been postulated that exposure to organochlorines increases the risk of developing breast cancer. Human data on this issue remain insufficient, but recent results are very consistent. Observations in human populations of the immunotoxic and hormone-mimicking properties of some organochlorines add biological plausibility to the epidemiologic findings. Limitations in our ability to measure organochlorine exposure still preclude a quantitative risk assessment, relative to these cancer endpoints. Public health action with respect to restriction of ongoing production and use of organochlorines, however, appears warranted for purposes of prevention.

Estrogenic pesticides: binding relative to estradiol in MCF-7 cells and effects of exposure during fetal life on subsequent territorial behaviour in male mice

Numerous chemicals released into the environment by man are able to disrupt the functioning of the endocrine system by binding to estrogen receptors in estrogen-responsive cells. The ability of o,p'-dichlorodiphenyl trichloroethane (DDT) and methoxychlor to compete with estradiol for binding to estrogen receptors in MCF-7 cells (relative binding affinity; RBA) was examined in both serum-free medium and 100% serum; this is referred to as a relative binding affinity-serum modified access (RBA-SMA) assay. RBA's ranged from 0.04% for o,p'-DDT (which showed enhanced access to cells in serum relative to serum-free medium) to 0.004% for methoxychlor (which did not show enhanced access in serum). Based on these findings, these pesticides, along with diethylstilbestrol (DES) as a positive control, were fed to pregnant mice from days 11-17 of pregnancy. When the male offspring were examined in adulthood for their rate of urine marking in a novel territory (territorial behaviour), the rate of urine marking increased dramatically with low doses of DES (relative to controls) and then decreased significantly at the highest dose administered prenatally. Relative binding in MCF-7 cells accurately predicted the doses of o,p'-DDT and methoxychlor that produced the same results, providing support for the hypothesis that effects on behaviour were mediated by binding to estrogen receptors in the developing brain.

Nuclear remodeling in response to steroid hormone action

Steroid and similar hormones comprise the broadest class of gene regulatory agents known, spanning vertebrates through the lower animals, and even fungi. Not unexpectedly, therefore, steroid receptors belong to an evolutionarily highly conserved family of proteins. After complexing with their cognate ligands, receptors interact with hormone response elements on target genes and modulate transcription. These actions are multifaceted and only partly understood, and include large-scale changes in the structure and molecular composition of the affected cell nuclei. This chapter examines steroid hormone action and the resultant nuclear remodeling from the following perspectives: (1) Where are the receptors located? (2) Which nuclear domains are most affected? (3) Are there extended or permanent nuclear changes? (4) What is the role of coiled bodies and similar structures in this regard? To address these and related questions, information is drawn from several sources, including vertebrates, insects, and malignant tissues. Entirely new data are presented as well as a review of the literature.

Organochlorine compounds in relation to breast cancer, endometrial cancer, and endometriosis: an assessment of the biological and epidemiological evidence

There is an increasing public and scientific concern that certain chlorinated compounds, recognized as environmental pollutants, may cause estrogen-related neoplastic disease in humans. The main hypothesis has been that certain organochlorines, through their estrogenic actions, might cause breast cancer. From experimental studies, both in vitro and in vivo, there is evidence that certain organochlorine compounds may cause estrogenic effects, whereas others may cause antiestrogenic effects. In limited studies, some of these compounds in high doses have also been shown to increase and reduce the frequency of estrogen-related tumors in animals. The epidemiological findings regarding the association between organochlorines and breast cancer are inconclusive. However, the largest and best designed study has been interpreted as negative with respect to DDT and polychlorinated biphenyls (PCB) in relation to breast cancer. Associations between organochlorine exposure and endometrial cancer or endometriosis have even more limited empirical basis. The hypothesis that human exposure to environmental levels or organochlorines would favor an estrogenic overactivity leading to an increase in estrogen-dependent formation of mammary or endometrial tumors is not supported by the existing in vitro, animal and epidemiological evidence. It can, however, not be conclusively rejected on the basis of available data.

Concentrations and profiles of PCDDs and PCDFs in human mammary carcinoma tissue

PCDD/PCDF concentrations in eight mammary carcinoma tissue samples obtained after surgical excision were similar to those found in two healthy breast glandular tissue samples from autopsy material. These levels agree well with mean concentrations in human adipose tissue from German adults. An analogous consistency was found for the congener profiles of the normalized concentrations, also in comparison with mothers' milk from Germany. In spite of similar congener profiles the concentrations in four axillary adipose tissue samples corresponding to the carcinoma samples were about 40% lower. This discrepancy was not found in one tissue pair from a healthy breast.

Identification of hydroxyl radical-induced lesions in DNA base structure: biomarkers with a putative link to cancer development

Hydroxyl radical-induced DNA base lesions of guanine and adenine were originally found in neoplastic and microscopically normal livers of fish exposed to environmental carcinogens. They were later identified in a mammalian tissue--the cancerous female breast. This evidence suggested that the base lesions are broadly present in the cancerous and microscopically normal tissues of a variety of eukaryotic organisms. The base lesion concentrations in both neoplastic tissues frequently exceeded 1 modified base in 1000 normal bases. By contrast, the base lesion:normal base ratios in healthy tissues were generally 10-100 times less. A greater variety of base lesions was found subsequently in the cancerous lung, brain, and other human tissues, although information relating to their biological significance is largely confined to the originally found purine derivatives. The biochemistry of the base lesions and the relationship of ring-opening (Fapy) derivatives to OH adducts in the DNA of normal and cancerous tissues is discussed with regard to the etiology of cancer and the potential use of the lesions as biomarkers for cancer risk assessment.

The effect of 6-nitro-1,3,8-trichlorodibenzofuran as a partial estrogen in the female rat uterus

Administration of 6-nitro-1,3,8-trichlorodibenzofuran (6-NCDF) caused a dose- and time-dependent increase in uterine wet weight and cytosolic and nuclear estrogen receptor (ER) and progesterone receptor (PR) levels in immature female Sprague-Dawley rats. These estrogenic effects persisted for up to 96 or 144 hr after initial administration of 6-NCDF and could be observed at a dose as low as 2 mumol/kg. In contrast, 6-NCDF (25 mumol/kg) did not increase rat uterine peroxidase activity or epidermal growth factor (EGF) receptor binding activity. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), which exhibits a broad spectrum of antiestrogenic effects in the female rat uterus, inhibited the 17 beta-estradiol-induced increase in uterine wet weights, cytosolic and nuclear ER and PR levels, peroxidase activity, and EGF receptor binding activity. In contrast, 2,3,7,8-TCDD inhibited the uterotropic effects caused by 6-NCDF but did not affect the 6-NCDF-induced uterine ER and PR levels. 6-NCDF is a weak inducer of hepatic microsomal ethoxyresorufin O-deethylase activity and competitively binds to the aryl hydrocarbon (Ah) receptor but not the PR or ER. Thus both 6-NCDF and 2,3,7,8-TCDD, two ligands which bind to the Ah receptor, exhibit both partial estrogenic and antiestrogenic properties and serve as useful models for delineating the complex biochemical interactions between the ER and Ah receptor signal transduction pathways.

Protein secretions in mouse uterus after methoxychlor or estradiol exposure

Four-month-old, ovariectomized mice were treated with 14 daily ip injections of either 10.0 micrograms of 17 beta-estradiol or 1.0 mg technical grade methoxychlor. Uterine luminal proteins were radiolabeled with 35S-methionine and run on 2-dimensional electrophoresis gels. The influence of methoxychlor or estradiol was compared to untreated controls by examining reproductive tract weights, uterine histology, and the patterns of uterine protein secretions. The data indicate that the stimulation of the uterus in ovariectomized, adult mice by methoxychlor is indistinguishable from that caused by estradiol. Both substances alter reproductive tract weights, promote cellular hypertrophy, stimulate uterine development, and induce the secretion of comparable levels of incorporation of methionine into a large number of proteins. The data further indicate that the alterations in gene expression promoted by estradiol in terms of secreted proteins appear to be qualitatively similar to those caused by the pesticide methoxychlor.

The effect of neonatal exposure to DES and o,p'-DDT on pituitary responsiveness to GnRH in adult castrated rats

While exposure of vertebrates to estrogens during early development has been shown to alter adult reproductive behavior, neuroanatomy, and neurophysiology, effects on gonadotropin secretion have not been studied. We conducted the present studies to assess the effects of neonatal exposure to xenobiotic estrogens on luteinizing hormone secretion in castrated adult rats. Rat pups were injected with either corn oil, 1 micrograms diethylstilbestrol (DES), or 0.5 mg o,p'-DDT on postnatal days 1 to 10, and castration was performed on day 21. On day 42 of life, GnRH (50 ng/kg) was administered via right heart catheters, and blood was sampled for LH at 0, 5, 10, 15, and 30 min. Neonatal exposure to DES in both males and females significantly decreased basal and GnRH-induced LH secretion throughout the sampling period in castrated adults. o,p'-DDT significantly suppressed initial LH levels and blunted GnRH-induced release in males at the 5 min interval, while in females it had no effect. These data show that early exposure to environmental estrogens alters adult pituitary response to GnRH. Our results suggest that sexually distinct effects of environmental estrogens occur and can be readily demonstrated in this experimental model.

Progestins and Antiprogestins: A Review of Their Role in Medicine and Bioassays Used in Their Development

The physiological role of ovarian progesterone in reproduction and the medical uses of synthetic progestins and antiprogestins are briefly reviewed. Although a number of progestins are in wide use, the search continues for better analogues that display fewer of the unwanted effects of the present compounds. The one antiprogestin approved for human use to date, RU486, exhibits considerable antiglucocortoid activity

The classical bioassays currently in use for the development of these steroid analogues depend upon in vivo progestin effects. However, progestins induce measurable responses in several cell culture systems that could be used as alternative bioassays. Rabbit uterine stromal cells in primary culture are especially suitable for such use. Addition of progesterone to these cultures stimulates synthesis of a 42 kilodalton (42kD) protein that appears in the medium. The 42kD protein response is specific for a progesterone receptor-mediated event and it can be blocked by known progestins. Using this culture system as a bioassay, one rabbit yields enough cells to measure the effect of 30 test doses in triplicate. Thus, a culture system is described that could substitute for current in vivo bioassays. This culture bioassay would allow large scale screening for potential progestin or antiprogestin activity.

The distribution of calmodulin in the mucosa of the avian oviduct and the effect of p-p'-DDE on some of its metabolic parameters

1. Since calmodulin or some closely related peptide may activate the Ca2(+)-transporting system in the avian eggshell gland, the calmodulin content in different parts of the oviduct mucosa was determined in egg-laying birds killed at 1600 hr. 2. The highest content was noted in the shell gland mucosa both in egg-laying ducks and hens. The calmodulin content was high even in the isthmus part, where the shell formation begins. 3. Treatment of ducks (Indian runner variety) with DDE (40 ppm for 45 days) did not influence the calmodulin content of the shell gland, however. 4. The content of the protein avidin, the formation of which is stimulated by progesterone, was increased significantly in the oviduct. The carbanhydrase activity did not change significantly. 5. The dry weight of the shell gland was reduced by DDE administration in ducks but not in domestic fowls. 6. These and earlier observations indicate that DDE can act as an partial agonist which is able both to stimulate and to inhibit reactions in the shell gland and other parts of the oviduct. 7. In vivo DDE in the dose used probably acted on higher centres, influencing the activity of the shell gland and probably other parts of the oviduct. 8. A regulation centre which influences several sexual functions is the hypothalamic-hypophyseal region, but the endocrine function of the ovary has also been considered.

The effects of DDE, PCB and chlordane on the binding of progesterone to its cytoplasmic receptor in the eggshell gland mucosa of birds and the endometrium of mammalian uterus

1. The specific binding of progesterone to its cytoplasmic receptor in the mucosa of the shell gland from egg-laying ducks, domestic fowls and from the endometrium of the rabbit uterus was compared. The effect of DDE, PCBs and chlordane added in vitro was also studied. 2. The KD value for progesterone with regard to its receptor was about four times lower in the domestic fowl and the rabbit than in the duck. 3. The chlorinated hydrocarbons decreased the binding of progesterone to its receptor. Their potency was higher in the duck than in the domestic fowl. In rabbit uterine mucosa their effects were similar to those observed in the duck. 4. DDE is an inhibitor of calmodulin: other calmodulin inhibitors as calmidazolium and trifluoperazin also reduced the binding of progesterone in similar concentrations. It is suggested that DDE reduced the progesterone binding by inhibiting calmodulin.