An evaluation of endocrine modulators: implications for human health

Imprinting and Reproductive Health: A Toxicological Perspective

This overview discusses the role of imprinting in the development of an organism, and how exposure to environmental chemicals during fetal development leads to the physiological and biochemical changes that can have adverse lifelong effects on the health of the offspring. There has been a recent upsurge in the use of chemical products in everyday life. These chemicals include industrial byproducts, pesticides, dietary supplements, and pharmaceutical products. They mimic the natural estrogens and bind to estradiol receptors. Consequently, they reduce the number of receptors available for ligand binding. This leads to a faulty signaling in the neuroendocrine system during the critical developmental process of 'imprinting'. Imprinting causes structural and organizational differentiation in male and female reproductive organs, sexual behavior, bone mineral density, and the metabolism of exogenous and endogenous chemical substances. Several studies conducted on animal models and epidemiological studies provide profound evidence that altered imprinting causes various developmental and reproductive abnormalities and other diseases in humans. Altered metabolism can be measured by various endpoints such as the profile of cytochrome P-450 enzymes (CYP450's), xenobiotic metabolite levels, and DNA adducts. The importance of imprinting in the potentiation or attenuation of toxic chemicals is discussed.

Common and unique testosterone and 17 beta-estradiol degradation mechanisms in Comamonas testosteroni JLU460ET by transcriptome analysis

Strain C. testosteroni JLU460ET was isolated for testosterone and 17 beta-estradiol degradation by our group. In this study, strain C. testosteroni JLU460ET was induced by testosterone and 17 beta-estradiol and then subjected to transcriptome analysis. There were 2,047 upregulated genes after 3 h of testosterone induction, 2,040 upregulated genes after 13 h of testosterone induction, 2,078 upregulated genes after 3 h of 17 beta-estradiol induction, and 2,095 upregulated genes after 13 h of 17 beta-estradiol induction. Significantly upregulated genes were mainly involved in steroid and aromatic compound degradation. A 100 kb steroid-degrading gene cluster was found by transcriptome analysis, which included 92 annotated genes and 58 novel genes. Among them, MucB/RseB and Fiu are secretory proteins for sensing substrates in the environment. MFS-1 and TonB are transporters of testosterone and 17 beta-estradiol. Ring-cleavage enzymes and beta-oxidation enzymes are important for degradation. The genes upregulated by both substrates were almost the same, but the degree of induction by testosterone was higher than that by 17 beta-estradiol. Nine upregulated genes were selected for verification by quantitative real-time polymerase chain reaction (qRT-PCR). The qRT-PCR results were consistent with the transcriptome sequencing results. In this study, the common and unique metabolic mechanisms of testosterone and 17 beta-estradiol were compared by transcriptome analysis in C. testosteroni JLU460ET for the first time.

Health risk and source assessment of semi-volatile phenols, p-chloroaniline and plasticizers in plastic packaged (sachet) drinking water

The presence of U.S. EPA priority organic contaminants in drinking water poses a dire health risk on consumers. Packaged drinking water such as plastic sachet drinking water has significantly gained market in both developed and developing countries, especially, its dominance in the Ghanaian market. The treatment process, packaging, and storage of the sachet drinking water contribute to the levels of genotoxic semi-volatile phenols, p-chloroaniline, and plasticizers contamination in the drinking water. The study thus sought to investigate the levels of semi-volatile phenols, p-chloroaniline, and plasticizer contaminants in sachet drinking water on the Ghanaian market and the associated health risk of exposure. The study also investigated the possible sources of the contaminants. A total of thirty (30) different brands of sachet water on the Ghanaian market were studied. The samples were extracted in replicates (n = 3) using Solid Phase Extraction (SPE) cartridges and further analysed with GC-MS (SIM mode). The source apportionment was conducted using absolute principal component analysis coupled with multiple, linear regression (APCA-MLR) and automatic linear regression (APCA-MALR) modelling. The mean total levels for the phenols, p-chloroaniline, and plasticizers were between 210.2 and 18,914.9, 11.2 and 18,871.0, and 21.2 and 69,834.1 ng/L respectively. The cumulative non-cancer risk (hazard quotient) and cancer risk upon exposure were computed to range between 2.1 × 10^-3 and 1.2 and 1.5 × 10^-7 and 1.3 × 10^-4 respectively. About 37% of the samples had elevated cancer risk (>10^-6) which may contribute to the existing incidence, cause for concern. The five sources found for the contaminants were apportioned as "environmental background (major)", "water treatment/disinfectant", "plastic/plasticizers", "storage and preservation", and "residual inter-conversion/degradation sources".

Endocrine-Disrupting Organochlorine Pesticides in Human Breast Milk: Changes during Lactation

The aim of the present study was to assess infant safety associated with the occurrence of endocrine-disrupting organochlorine pesticides (OCP) in breast milk. Moreover, the association between pregnant mothers' dietary habits and these compounds levels in breast milk was investigated. Breast milk was collected at various stages of lactation. The samples were analyzed by the GC-MS method. The OCP concentrations ranged from < limit of detection (LOD) to 6.81 ng/g lipids. The highest OCP concentrations in breast milk occurred primarily within the first month of lactation, and decreased over the lactation period. It was found that the maternal consumption of certain food products-in particular pork, beef, poultry, eggs, and dairy products-could have affected the content of 1,1'-(2,2,2-Trichloroethane-1,1-diyl)bis(4-chlorobenzene), called DDT and its metabolites in the breast milk. The levels of beta-endosulfan were positively correlated with fish and poultry consumption. The redundancy analysis indicated that the diets of the pregnant women had an important impact on pesticide residues in the breast milk. There is a potential possibility of lowering the content of organochlorine compounds in breast milk by adhering to nutritional recommendations, e.g., avoiding the excessive consumption of fish and other raw food materials of unknown origin.

Levels and predictors of persistent organic pollutants in an adult population from four Spanish regions

This research aimed to assess serum concentrations of a group of persistent organic pollutants (POPs) in a sample of adults recruited in four different regions from Spain and to assess socio-demographic, dietary, and lifestyle predictors of the exposure. The study population comprised 312 healthy adults selected from among controls recruited in the MCC-Spain multicase-control study. Study variables were collected using standardized questionnaires, and pollutants were analyzed by means of gas chromatography with electron capture detection. Multivariable analyses were performed to identify predictors of log-transformed pollutant concentrations, using combined backward and forward stepwise multiple linear regression models. Detection rates ranged from 89.1% (hexachlorobenzene, HCB) to 93.6% (Polychlorinated biphenyl-153 [PCB-153]); p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) showed the highest median concentrations (1.04ng/ml), while HCB showed the lowest (0.24ng/ml). In the multivariable models, age was positively associated with HCB, p,p'-DDE, and PCB-180. BMI was associated positively with p,p'-DDE but negatively with PCB-138. Total accumulated time residing in an urban area was positively associated with PCB-153 concentrations. The women showed higher HCB and lower p,p'-DDE concentrations versus the men. Notably, POP exposure in our study population was inversely associated with the breastfeeding received by participants and with the number of pregnancies of their mothers but was not related to the participants' history of breastfeeding their children or parity. Smoking was negatively associated with HCB and PCB-153 concentrations. Consumption of fatty foods, including blue fish, was in general positively associated with POP levels. Although POP environmental levels are declining worldwide, there is a need for the continuous monitoring of human exposure in the general population. The results of the present study confirm previous findings and point to novel predictors of long-term exposure to persistent organic pollutants.

Characterising the individual health risk in infants exposed to organochlorine pesticides via breast milk by applying appropriate margins of safety derived from estimated daily intakes

Milk secretion being an important way of elimination of organochlorine pesticides (OCPs) poses a concern due to potential risk for breastfed infants. This study aims to provide a tool for assessing such risks to infants exposed to OCPs (through accumulation in the mother's body), using calculated individual margins of safety (MoS). Selected OCPs included; p,p'-DDT, p,p'-DDD, p,p'-DDE, β-HCH, γ-HCH and HCB which were analysed in 28 samples of maternal milk. The highest intakes were recorded for p,p'-DDE (at 2.90 μg kg(-1)bw d(-1)) whilst the lowest was for γ-HCH, (at 0.019 μg kg(-1)bwd(-1)). For the risk characterisation purposes MoSs were calculated for the compounds for which toxicological reference values (e.g. ADI, TDI) were adopted. The MoS for average ∑DDT concentrations was found to be relatively low (2.82) somewhat similar to that for HCB at 7.08, and for γ-HCH, the MoS was substantially higher at 263.1. This, however does not take into account the extremely high individual concentrations. Thus, it was decided to calculate estimated daily intake (EDI) values based on OCP levels in individual milk samples. MoS levels of <1 (meaning unacceptable risk) were noted both for HCB in one sample as well as for ∑DDT in 3 samples indicating likely threats to infant's health. The lowest MoS noted for γ-HCH equalled to 60.6, indicating that this compound was not a threat to the health of any of the breastfed infants from the study group.

Screening of endocrine-disrupting phenols, herbicides, steroid estrogens, and estrogenicity in drinking water from the waterworks of 35 Italian cities and from PET-bottled mineral water

We investigated contamination by endocrine-disrupting chemicals in drinking water from 35 major Italian cities and five popular Italian brands of bottled mineral water. The quality of Italian drinking water was assessed by combing chemical analysis with bioassay to quantify specific estrogenic contaminants and to characterize the actual biological effect of the mixture of chemicals present in drinking water including the contribution of not targeted compounds. The selected contaminants were natural and synthetic steroid estrogens, alkylphenols and bisphenol A, linuron, triazine herbicides, and their metabolites. A specific analytical method was developed based on solid phase extraction of 1 L of water and concentration to 100 μL for quantification by electrospray ionization liquid chromatography tandem mass spectrometry, achieving quantification limits of 0.05-0.36 ng/L for herbicides and 0.64-7.70 ng/L for steroids and phenols. No steroid estrogens were detected in any of the samples, while bisphenol A and nonylphenols were detected in the ranges of 0.82-102.00 and 10.30-84.00 ng/L respectively. Herbicides and their degradation products, when present, were found from slightly above the quantification limits up to 49.91 ng/L, mainly from cities in northern Italy. Chemical analyses were complemented by the performance of a bioassay for the determination of the estrogenic activity in the extracts based on the transactivation of estrogen receptor α-transfected reporter HeLa-ERE-Luciferase-Neomycin cell line. Activity was generally low with maximum estrogenicity of 13.6 pg/L estradiol equivalents.

Correlations between meteorological parameters and prostate cancer

Background

There exists a north-south pattern to the distribution of prostate cancer in the U.S., with the north having higher rates than the south. The current hypothesis for the spatial pattern of this disease is low vitamin D levels in individuals living at northerly latitudes; however, this explanation only partially explains the spatial distribution in the incidence of this cancer. Using a U.S. county-level ecological study design, we provide evidence that other meteorological parameters further explain the variation in prostate cancer across the U.S.

Results

In general, the colder the temperature and the drier the climate in a county, the higher the incidence of prostate cancer, even after controlling for shortwave radiation, age, race, snowfall, premature mortality from heart disease, unemployment rate, and pesticide use. Further, in counties with high average annual snowfall (>75 cm/yr) the amount of land used to grow crops (a proxy for pesticide use) was positively correlated with the incidence of prostate cancer.

Conclusion

The trends found in this USA study suggest prostate cancer may be partially correlated with meteorological factors. The patterns observed were consistent with what we would expect given the effects of climate on the deposition, absorption, and degradation of persistent organic pollutants including pesticides. Some of these pollutants are known endocrine disruptors and have been associated with prostate cancer.

Detection of estrogenic activity in municipal wastewater effluent using primary cell cultures from three-spined stickleback and chemical analysis

Environmental estrogens are substances that imitate the effects of endogenous estrogens. Effluents from municipal wastewater treatment plants are known to contain substances with estrogenic activity including steroidal estrogens and xenoestrogens. In the current study, a combination of biological and chemical analysis was applied to determine the estrogenic activity in municipal wastewater effluents in Finland. The male three-spined stickleback (Gasterosteus aculeatus) hepatocyte assay with vitellogenin induction as an endpoint was used for the detection of estrogenic activity in solid phase extracts of wastewater effluents, and 17beta-estradiol (E2) as a positive control. The wastewater extracts and E2 were found to induce vitellogenin production. The extracts were also subjected to chromatographic fractionation and the collected fractions were assayed. The only active fraction was the one in which E2, estrone and ethynylestradiol were eluted. Its activity corresponded to the activity of the original wastewater extract. The LC-MS/MS analyses of the wastewater extracts showed that the concentration of estrone was about 65 ng L(-1), the concentration of E2 was less than 1 ng L(-1), while estriol and 17alpha-ethynylestradiol could not be detected. These findings showed that the activity of the wastewater extracts and the chromatographic fraction was much higher than the activity which could have been expected on the base of the chemical analysis. This strongly indicates that other compounds, possibly acting by additivity or synergism, are playing a major role in the induced vitellogenin production by the hepatocytes.

Evaluation of reproductive safety of beta-sitosterol on the American mink (Neovison vison)

beta-Sitosterol is a weakly estrogenic phytosterol used extensively in functional foods to lower elevated serum cholesterol concentrations due to its inhibitory action on intestinal cholesterol absorption. It caused previously decreased sex steroid concentrations in fish and lowered sperm counts in rats. In the American mink (Neovison vison), litter size increased slightly due to dietary beta-sitosterol supplement. The aim of the present experiment was to conduct a dose-response study on the effects of beta-sitosterol on the reproduction of the American mink. Juvenile male and female mink (n=480) were exposed to 0, 5, 10 or 50 mg of peroral beta-sitosterol kg(-1)d(-1) for 10 months. After 3 months of exposure in November, 15 males per group were sacrificed and general biochemical variables reflecting overall health were determined. The beta-sitosterol-treated male mink had increased absolute and relative masses of intraabdominal fat and higher blood hemoglobin and serum high-density lipoprotein cholesterol concentrations. In spring, the top-rated male mink were mated with multiple females within each study group and reproductive success was assessed. No differences in the reproductive performance of the males (10-11 per group) or females (47-50 per group) could be detected in the exposed groups and the kits of all groups developed in a similar manner. The results suggest that dietary beta-sitosterol presents no significant risk to mammalian fertility.

Differential regulation of thyroid hormone receptor-mediated function by endocrine disruptors

It is well known that endocrine disruptors (EDs) act as anti-estrogenic agents and affect the function of reproductive organ. EDs are also thought to affect thyroid hormone (TH) system which is important for biological functions such as growth, development and metabolism. However, it is still not clear how EDs are able to regulate TH receptor (TR)-mediated functions. In this study, therefore, the modulatory effects of representative EDs such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyl (Aroclor 1254) and bisphenol A (BPA) were examined using TR-expressing GH3 cells (a rat pituitary gland epithelial tumor cell line) activated by triiodothyronine (T3). EDs tested significantly blocked T3 binding to TR in a dose-dependent manner. Biochemical characterization by Scatchard and Lineweaver-Burk plot analyses indicated that TCDD and aroclor 1254 bound to TH receptors in a competitive inhibitory manner, whereas BPA bound to TH receptors in a non-competitive pattern. The different inhibitory mode of action by EDs was also found in regulating TR-mediated production of prolactin (PRL). Aroclor 1254 exposure for 48 h enhanced T3-mediated PRL production, but BPA down-regulated. These results suggest that the EDs (TCDD, Aroclor 1254 and BPA) could differentially bind to TR and distinctly regulate the action of TR function, even though EDs are structurally similar.

Influence of estrogen and xenoestrogens on basolateral uptake of tetraethylammonium by opossum kidney cells in culture

The sex steroid hormone estrogen down-regulates renal organic cation (OC) transport in animals, and it may contribute to sex-related differences in xenobiotic accumulation and excretion. Also, the presence of various endocrine-disrupting chemicals, i.e., environmental chemicals that possess estrogenic activity (e.g., xenoestrogens) may down-regulate various transporters involved in renal accumulation and excretion of xenobiotics. The present study characterizes the mechanism by which long-term (6-day) incubation with physiological concentrations of 17beta-estradiol (E(2)) or the xenoestrogens diethylstilbestrol (DES) and bisphenol A (BPA) regulates the basolateral membrane transport of the OC tetraethylammonium (TEA) in opossum kidney (OK) cell renal cultures. Both 17beta-E(2) and the xenoestrogen DES produced a dose- and time-dependent inhibition of basolateral TEA uptake in OK cell cultures, whereas the weakly estrogenic BPA had no effect on TEA uptake. Treatment for 6 days with either 1 nM 17beta-E(2) or DES reduced TEA uptake by approximately 30 and 40%, respectively. These effects were blocked completely by the estrogen receptor antagonist ICI 182780 (Faslodex, fulvestrant), suggesting that these estrogens regulate OC transport through the estrogen receptor, which was detected (estrogen receptor alpha) in OK cell cultures by reverse transcription-polymerase chain reaction. The J(max) value for TEA uptake in 17beta-E(2)- and DES-treated OK cell cultures was approximately 40 to 50% lower than for ethanol-treated cultures, whereas K(t) was unaffected. This reduction in transport capacity was correlated with a reduction in OC transporter OCT1 protein expression following treatment with both agents.

Screening of endocrine disrupting chemicals with MELN cells, an ER-transactivation assay combined with cytotoxicity assessment

There is growing concern that some chemicals can cause endocrine disrupting effects to wild animals and humans. Therefore a rapid and reliable screening assay to assess the activity of endocrine disrupting chemicals (EDCs) is required. These EDCs can act at multiple sites. Most studied mechanism is direct interaction with the hormone receptors, e.g. estrogen receptor. In this study the luciferase reporter gene assay using transgenic human MELN cells was used. Since cytotoxicity of the chemicals can decrease the luminescent signal in the transactivation assays, a cytotoxicity assay must be implemented. Mostly the neutral red (NR) assay is performed in parallel with the estrogenicity assay. To increase the reliability and cost-efficiency of the test, a method to measure estrogenicity and cytotoxicity in the same cell culture plate instead of in parallel plates was developed and evaluated. Therefore the NR-assay was compared with the CytoTox-ONE homogeneous membrane integrity assay. The latter measures LDH (lactate dehydrogenase) leakage based on a fluorometric method. For all compounds tested, the CytoTox-ONE test showed comparable curves and EC50-values to those obtained by the NR-assay. So the CytoTox-ONE kit, which seemed more sensitive than measurements of LDH-leakage based on a colorimetric method, is recommended to test cytotoxicity to MELN cells, with the advantage to use the same cells for ER-transactivation measurements. The chemicals tested in the optimised MELN assay showed estrogenic potencies comparable to those reported for several other transactivation assays.

Xenoestrogens modulate genotoxic (UVB)-induced cellular responses in estrogen receptors positive human breast cancer cells

Human populations and wildlife are exposed to mixtures of both anthropogenic and natural chemicals. Some of these compounds are known to interact principally with the endocrine function, whereas others act mainly on genomic DNA. Given this evidence, we wanted to address the question of whether concomitant exposure of such chemicals was able to interact at the cellular level. We have previously shown that 17β-Estradiol (E(2)) modulates the DNA repair capacity of cells. In this work, we wanted to examine if other xenoestrogens (i.e. industrial compounds, pesticides or pharmaceuticals) were able to interact with the UVB-induced cellular response as E(2) does. Here, we show that xenoestrogens modulate the capacity of cells to repair their DNA damage according to the type of compounds. For example, the oral contraceptive 17α-Ethinylestradiol down-regulated the repair of UVB-induced DNA damage whereas the UV filter Eusolex 6007 up-regulated this pathway. The notion that xenoestrogens could interact with a genotoxic stress is reinforced by the modulation of the estrogens-dependent luciferase reporter gene expression when cells are UVB-irradiated. Finally, these observations suggested the potential role of xenoestrogens in carcinogenesis by their capacity to modulate cells responses to genotoxic stress.

Analysis of estrogenic activity in coastal surface waters of the Baltic Sea using the yeast estrogen screen

In the present study, the yeast estrogen screen (YES) has been used to assess the estrogenic activity in surface waters of a coastal region in the German Baltic Sea. Solid-phase extraction using the copolymer Oasis HLB followed by a clean-up on silica was carried out on approximately 50-l water samples. From the final 400 microl extract volume, 100 microl aliquots were used for the measurement of estrogenic activity and for chemical analysis, which was performed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). From 29 samples taken during two campaigns (2003 and 2004) at five different stations 27 samples showed an estrogenic response higher than 10%. The response in the YES was expressed as measured estradiol equivalents (EEQs), which were in the range of 0.01 (Darss Peninsula) to 0.82 ng/l (Inner Wismar Bay). Samples from stations located in inner coastal waters showed higher estrogenic activities than those from outer located stations. A comparison of measured estrogenicity (YES) and calculated estrogenicity (chemical analysis) showed significant differences, probably due to the presence of anti-estrogenic compounds and/or the estrogenic activity of unknown, not identified contaminants. The main contributors to the overall estrogenic activity were synthetic and natural hormones.

Toxicity on crustaceans and endocrine disrupting activity on Saccharomyces cerevisiae of eight alkylphenols

In the last few years many concerns have been raised regarding the environmental safety of alkylphenol polyethoxylate surfactants (APnEOs). They are widely used in detergents, paints, herbicides and many other formulated products. It has been estimated that 60% of APnEOs end up in the aquatic environment; they are biodegradable and transformed into alkylphenols, such as nonylphenol and octylphenol that are hydrophobic and tend to accumulate. In the present study, acute and chronic aquatic toxicity and the estrogenic activity of the following eight alkylphenols were assessed: 4-nonylphenol, 4-octylphenol, 4-nonylphenol-10-ethoxylate, 4-tert-octylphenol, POE (1 to 2)-nonylphenol, POE (6)-nonylphenol, POE (3)-tert-octylphenol and POE (9 to 10)-tert-octylphenol. The toxic potential was measured on the crustaceans Daphnia magna and Ceriodaphnia dubia, while the estrogenic activity was determined by using the YES-test with the strain Saccharomyces cerevisiae RMY326. The results showed that the exposure of crustaceans to the eight xenoestrogens investigated caused both acute and chronic effects. The EC50 values found for C. dubia at 48 h were compared to D. magna at 24h and, gave a first indication about the toxic activity of the compounds investigated, that is better expressed in the long-term. In fact, chronic data showed a strong increase in toxicity with EC50 values one or two orders of magnitude lower than the acute values. The results of the YES-test showed that nonylphenol, octylphenol and 4-tert-octylphenol were the most estrogenic and the bioassay was able to detect their estrogenicity at very low concentrations (ng-microg/l).

Assessment of xenoestrogens using three distinct estrogen receptors and the zebrafish brain aromatase gene in a highly responsive glial cell system

The brain cytochrome P450 aromatase (Aro-B) in zebrafish is expressed in radial glial cells and is strongly stimulated by estrogens (E2); thus, it can be used in vivo as a biomarker of xenoestrogen effects on the central nervous system. By quantitative real-time polymerase chain reaction, we first confirmed that the expression of Aro-B gene is robustly stimulated in juvenile zebrafish exposed to several xenoestrogens. To investigate the impact of environmental estrogenic chemicals on distinct estrogen receptor (ER) activity, we developed a glial cell-based assay using Aro-B as the target gene. To this end, the ER-negative glial cell line U251-MG was transfected with the three zebrafish ER subtypes and the Aro-B promoter linked to a luciferase reporter gene. E2 treatment of U251-MG glial cells cotransfected with zebrafish ER-alpha and the Aro-B promoter-luciferase reporter resulted in a 60- to 80-fold stimulation of luciferase activity. The detection limit was <0.05 nM, and the EC50 (median effective concentration) was 1.4 nM. Interestingly, in this glial cell context, maximal induction achieved with the Aro-B reporter was three times greater than that observed with a classical estrogen-response-element reporter gene (ERE-tk-Luc). Dose-response analyses with ethynylestradiol (EE2), estrone (E1), alpha-zeralenol, and genistein showed that estrogenic potency of these agents markedly differed depending on the ER subtype in the assay. Moreover, the combination of these agents showed an additive effect according to the concept of concentration addition. This confirmed that the combined additive effect of the xenoestrogens leads to an enhancement of the estrogenic potency, even when each single agent might be present at low effect concentrations. In conclusion, we demonstrate that our bioassay provides a fast, reliable, sensitive, and efficient test for evaluating estrogenic potency of endocrine disruptors on ER subtypes in a glial context.

Estrogen and bisphenol A disrupt spontaneous [Ca(2+)](i) oscillations in mouse oocytes

The present work aims to study the effects of estrogen or endocrine disrupters (EDs) on the dynamic changes in intracellular Ca(2+) concentration of mouse immature oocytes (IOs) loaded with Ca(2+)-sensitive dye Fura-2 using an image analyzer. The majority of IOs isolated from the ovary exhibited spontaneous Ca(2+) oscillations at regular intervals. Entry of external Ca(2+), probably through gap junctions, contributes to Ca(2+) oscillations since they were reversibly inhibited by removing Ca(2+) from the bathing medium or by the application of a gap-junction inhibitor carbenoxolone (CBX, 30 microM). Both 17beta-estradiol (E2) and E2-BSA, a membrane impermeable estrogen, shortened the duration of Ca(2+) oscillations in a dose-dependent manner (1-1000 nM), and produced an irregular pattern of the oscillations, strongly suggesting that E2 acts on the plasma membrane of the oocyte. For bisphenol A (BPA), one of the estrogen-mimicking EDs, a 10,000-fold higher concentration (100 microM) was necessary to exert similar inhibitory action to that of E2.

Investigation of circulatory and tissue ACE activity during development of lead-induced hypertension

Prolonged exposure to low levels of lead causes systemic hypertension. Several mechanisms have been proposed to explain lead-induced hypertension. Recently, the etiological role of the renin-angiotensin system (RAS) has been investigated in this context. This study assessed the alterations of circulatory and tissue angiotensin converting enzyme (ACE) activity during development of lead induced hypertension. Male rats were divided to two main groups: lead-treated animals which received lead acetate, 100 ppm, in drinking water for 2, 4, 6, and 8 weeks and a control group given distilled water. The ACE activity in serum and tissues was analyzed by HPLC. The blood pressure gradually increased in correlation with lead exposure with time. The study also revealed significant elevation of local and serum ACE activity in the early phase of lead treatment; however, chronic lead exposure suppressed ACE activity in serum and tissues. These results emphasize the etiological role of ACE activity in the early phase of lead-induced hypertension.

An alternative mode of action of endocrine-disrupting chemicals and chemoprevention

Endocrine-disrupting chemicals (EDCs) produce a wide variety of endocrine-disruption effects, including developmental disorders, carcinogenicity, and mutagenicity. Our recent study demonstrated that about 94% of the 48 EDCs classified by Centers for Disease Control and Prevention (CDC) generated free radicals and that this free radical generation induced by EDCs might represent a common toxic mechanism of action of EDCs. The chemoprevention of endocrine-disrupting effects, such as employed in the control of caner by interfering with common toxic mechanisms of action of EDCs, represents a promising approach to this problem. In this context, it is proposed that EDCs may produce endocrine-disrupting effects including carcinogenicity via the generation of free radicals, and thus the effects may be modulated or prevented by scavenging free radicals with antioxidants, such as vitamins, curcumin, isoflavonoids, resveratrol, and plant polysaccharides. Here, an alternative mode of action of EDCs and their possible chemoprevention are proposed.

The public health implications of polychlorinated biphenyls (PCBs) in the environment

Polychlorinated biphenyls (PCBs) were widely used in various industrial applications. Research confirmed that some PCB congeners degrade slowly in the environment and can build up in the food chain. Poisoning episodes in Asia were initially attributed to PCB-contaminated oil, although subsequent analysis suggested that thermal degradation products of PCBs were responsible for the observed toxicity. Commercial production of PCBs in the United States was banned in 1979. Several agencies have categorized PCBs as animal carcinogens; however, studies of workers exposed to high doses of PCBs have not demonstrated an increased cancer risk. Health effects attributable to PCBs include skin and eye irritation. There is no reliable evidence that PCBs in the environment result in either "endocrine disruption" or intellectual deterioration in children exposed in utero. Because PCB exposures from environmental sources do not pose a significant health risk, little benefit to public health can result from continued remediation of PCB sources.

Comparative study of estrogenic potencies of estradiol, tamoxifen, bisphenol-A and resveratrol with two in vitro bioassays

This study was undertaken to compare the sensitivity of two in vitro screening test methods and to determine the accuracy of predicted response to spiked laboratory water samples. A newly developed enzyme-linked receptor assay (ELRA) and a widely used yeast estrogen screen (YES) assay were selected to evaluate the estrogenic responses. Four natural, pharmaceutical, xenobiotic or phytobiotic chemicals: 17beta-estradiol (E2), tamoxifen, bisphenol-A and resveratrol were examined, and 17beta-E2 was used as a positive control. 17beta-E2 can strongly induce estrogenic response in both test systems, however, ELRA was found to be more sensitive to 17beta-E2 with a detection limit of 0.07 microg/l compared to 0.88 microg/l in YES assay. Similar results were obtained for bisphenol-A and resveratrol, and their estrogen potencies relative to E2 (100%) determined by ELRA were at least 5.6 times greater than produced by YES assay. ELRA was unable to distinguish the anti-estrogen tamoxifen and YES assay is also poor at distinguishing. Comparison of response to spiked laboratory water samples show that ELRA can give accurate determination to all four chemicals with recoveries among 70-120%, while YES can only give accurate determination to 17beta-E2 and bisphenol-A with recoveries among 69-112%. The comparative results provide evidence that ELRA is more suitable for rapid screening estrogenic potency of the environmental samples. Combination of ELRA and mammalian cellular assay will constitute an advantageous test to specify agonistic or antagonistic effects.

Toxicological characteristics of endocrine-disrupting chemicals: developmental toxicity, carcinogenicity, and mutagenicity

It is generally accepted that endocrine-disrupting chemicals (EDCs) play a role in a variety of adverse health effects in an intact organism or its progeny as a consequence of changes in the endocrine system. Primary toxic effects of EDCs were reported to be related to infertility, reduction in sperm count, and teratogenicity, but other important toxic effects of EDCs such as carcinogenicity and mutagenicity have also been demonstrated. The aim of the present study was to systematically analyze the toxicological characteristics of EDCs in pesticides, industrial chemicals, and metals. A comprehensive literature survey on the 48 EDCs classified by the Centers for Disease Control and Prevention (CDC) was conducted using a number of databases which included Medline, Toxline, and Toxnet. The survey results revealed that toxicological characteristics of EDCs were shown to produce developmental toxicity (81%), carcinogenicity (79%, when positive in at least one animal species; 48%, when classified based on IARC evaluation), mutagenicity (79%), immunotoxicity (52%), and neurotoxicity (50%). Regarding the hormone-modulating effects of the 48 EDCs, estrogenic effects were the most predominant in pesticides, while effects on thyroid hormone were found for heavy metals. EDCs showing estrogen-modulating effects were closely related to carcinogenicity or mutagenicity with a high degree of sensitivity. Systematic information on the toxicological characteristics of the EDCs will be useful for future research directions on EDCs, the development of new screening methods, legal regulation, and for investigations of their mechanism of action.

Dithioerythritol (DTE) prevents inhibitory effects of triphenyltin (TPT) on the key enzymes of the human sex steroid hormone metabolism

Organotins are known to induce imposex (pseudohermaphroditism) in marine neogastropods and are suggested to act as specific endocrine disruptors, inhibiting the enzyme-mediated conversion of steroid hormones. Therefore, we investigated the in vitro effects of triphenyltin (TPT) on human 5alpha-reductase type 2 (5alpha-Re 2), cytochrome P450 aromatase (P450arom), 17beta-hydroxysteroid dehydrogenase type 3 (17beta-HSD 3), 3beta-HSD type 2 and 17beta-HSD type 1 activity. First, the present study demonstrates that significant amounts of TPT occurred in the blood of eight human volunteers (0.17-0.67 microg organotin cation/l, i.e. 0.49-1.92 nmolcation/l). Second, TPT showed variable inhibitory effects on all the enzymes investigated. The mean IC(50) values were 0.95 microM for 5alpha-Re 2 (mean of n=4 experiments), 1.5 microM for P450arom (n=5), 4.0 microM for 3beta-HSD 2 (n=1), 4.2 microM for 17beta-HSD 3 (n=3) and 10.5 microM for 17beta-HSD 1 (n=3). To exclude the possibility that the impacts of TPT are mediated by oxidizing essential thiol residues of the enzymes, the putative compensatory effects of the reducing agent dithioerythritol (DTE) were investigated. Co-incubation with DTE (n=3) resulted in dose-response prevention of the inhibitory effects of 100 microM deleterious TPT concentrations on 17beta-HSD 3 (EC(50) value of 12.9 mM; mean of n=3 experiments), 3beta-HSD 2 (0.90 mM; n=3), P450 arom (0.91 mM; n=3) and 17beta-HSD 1 (0.21 mM; n=3) activity. With these enzymes, the use of 10mM DTE resulted in an at least 80% antagonistic effect, whereas, the effect of TPT on 5alpha-Re 2 was not compensated. In conclusion, the present study shows that TPT acts as an unspecific, but significant inhibitor of human sex steroid hormone metabolism and suggests that the inhibitory effects are mediated by the interaction of TPT with critical cysteine residues of the enzymes.

Environmental exposure, DNA methylation, and gene regulation: lessons from diethylstilbesterol-induced cancers

DNA methylation is an epigenetic mechanism that regulates chromosomal stability and gene expression. Abnormal DNA methylation patterns have been observed in many types of human tumors, including those of the breast, prostate, colon, thyroid, stomach, uterus, and cervix. We and others have shown that exposure to a wide variety of xenobiotics during critical periods of mammalian development can persistently alter the pattern of DNA methylation, resulting in potentially adverse biological effects such as aberrant gene expression. Thus, this epigenetic mechanism may underlie the observed increased risk in adulthood of several chronic diseases, including cancer, in response to xenobiotic exposures early in life. We present here the lessons learned from studies on the effects of perinatal diethylstilbesterol (DES) exposure on the methylation pattern of the promoters of several estrogen-responsive genes associated with the development of reproductive organs. Perinatal DES exposure, which induces epithelial tumors of the uterus in mice and is associated with several reproductive tract abnormalities and increased vaginal and cervical cancer risk in women, provides a clear example of how estrogenic xenobiotic exposure during a critical period of development can abnormally demethylate DNA sequences during organ development and possibly increase cancer risk later in life. In addition, nutritional factors and stress may also alter DNA methylation during early life and modulate the risk of cancer and other chronic diseases in adulthood. We suggest that DNA methylation status may be influenced by environmental exposures in early life, leading to increased risk of cancer in adulthood.

A sensitive and inexpensive yeast bioassay for the mycotoxin zearalenone and other compounds with estrogenic activity

Zearalenone (ZON) is a nonsteroidal estrogenic mycotoxin produced by plant-pathogenic species of Fusarium. As a consequence of infection with Fusarium culmorum and Fusarium graminearum, ZON can be found in cereals and derived food products. Since ZON is suspected to be a cause of human disease, including premature puberty syndrome, as well as hyperestrogenism in farm animals, several countries have established monitoring programs and guidelines for ZON levels in grain intended for human consumption and animal feed. We developed a low-cost method for monitoring ZON contamination in grain based on a sensitive yeast bioassay. The indicator Saccharomyces cerevisiae strain YZRM7 is unable to grow unless an engineered pyrimidine biosynthetic gene is activated by the expressed human estrogen receptor in the presence of exogenous estrogenic substances. Deletion of the genes encoding ATP-binding cassette (ABC) transporters Pdr5p and Snq2p increases net ZON uptake synergistically. Less than 1 microg of ZON per liter of medium is sufficient to allow growth of the indicator strain. To prevent interference with pyrimidines potentially present in biological samples, we also disrupted the genes FUR1 and URK1, blocking the pyrimidine salvage pathway. The bioassay strain YZRM7 allows qualitative detection and quantification of total estrogenic activity in cereal extracts without requiring further cleanup steps. Its high sensitivity makes this assay suitable for low-cost monitoring of contamination of maize and small grain cereals with estrogenic Fusarium mycotxins.

Biomarkers for male reproductive health hazards: are they available?

This review aims to give an overview of some of the biomarkers that have been used for the monitoring of human exposure to xenobiotics as well as to provide a summary of some of the recent epidemiological studies on male reproductive health of exposure to environmental and occupational toxicants. Possible molecular mechanisms on seminal quality change are also suggested. Studies using various biomarkers have no doubt enabled us to better characterize the effect of environmental pollutants on the male reproductive system. However, the sensitivity and specificity of these biomarkers have not been comprehensively validated. Furthermore, many epidemiological findings are difficult to replicate owing to the inherited methodological problems of male reproductive health investigations, such as the small number of study subjects, low compliance rate, substantial intra-individual variability in semen parameters, measurement techniques and misclassifications based on single assay. Oxidative damage, in particular DNA-damage caused by free radicals, generated either by xenobiotics, or endogenously, is now thought to be a key molecular mechanism associated with semen quality and sperm function. Laboratory studies and epidemiological findings have suggested that the male reproductive system is susceptible to reactive oxygen species (ROS). On the other hand, there is so far no single all-encompassing biomarker of reproductive capacity in men. A panel of biomarkers with specific goals should be considered. Collaborative multidisciplinary studies are also needed to overcome some of the issues mentioned here.

Endocrine disruptors: can biological effects and environmental risks be predicted?

A large number of diverse nonsteroidal chemicals, referred to as xenoestrogens, bind to the estrogen receptor (ER) and evoke biological responses. The activity of most xenoestrogens is weak (from about 1/1000 th to 1/1000000 th that of estradiol). These substances interact with the binding pocket of the ER because they have chemical similarities to estradiol (usually a phenolic A-ring). Reduced activity of xenoestrogens probably results from lack of fit of the remainder of the molecule within the binding pocket. ER binding per se has only limited influence on endocrine disruption. The nature (estrogenic or antiestrogenic) or magnitude of the response is a function of the substance itself, complexities within the various stages of the ER signaling pathway, as well as other factors (such as, plasma binding of xenoestrogens, cross-talk between ER and other signaling pathways, androgen antagonism, and alternate modes of estrogen action). Whereas there is general agreement that high doses of nonsteroidal chemicals can evoke endocrine disruptive effects, there is no consensus that such substances produce low-dose effects or that humans are at risk of endocrine disruption due to exposure to environmentally relevant levels of such chemicals. Furthermore, screening programs to identify hormonally active chemicals (such as the Endocrine Disruptor Screening Program) may be premature in view of the complexity of the mechanisms involved.

Estrogenic effect of leachates and soil extracts from lysimeters spiked with sewage sludge and reference endocrine disrupters

Several experiments were conducted to evaluate the behavior and performance of some potential endocrine disrupters (ECDs). Two in vitro screening assays, one based on MCF7-cell proliferation (E-screen test) and the other on estrogenic receptor activity [enzyme-linked receptor assay (ELRA)], were used for the tests, which were done in lysimeters 80 cm in diameter with depth of 30 cm (shallow) or 90 cm (deep). A sandy soil was used to fill in all lysimeters, which were spiked on the surface with either: (a) a sewage sludge (SS) at a dose equivalent to 20 tons ha-1; (b) a mixture of reference ECDs, comprising 17 alpha- and 17 beta-estradiol (E2), nonylphenol, octylphenol, and bisphenol A at doses 100 times higher than the maximum concentrations respectively found in the applied SS; or (c) a mixture of ECDs and SS. After percolation of the lysimeters with rain and/or artificial water, five leachates were sampled from each lysimeter during a period of 210 days. Immediately after the lysimeter percolation experiments, four and six soil fractions were dissected from, respectively, the 30-cm and 90-cm lysimeters and extracted by water. Both the leachate and soil extract samples were analyzed for their estrogenicity using the assays indicated above. The E-screen assay was highly sensitive only for some leachate and extract samples but gave no response for most leachates and soil extracts. The results of the ELRA assay suggests a significantly higher estrogenicity of leachate samples from shallow lysimeters compared with that of leachates from deep lysimeters. In contrast, the estrogenic effect measured for soil extracts of shallow lysimeters was lower than that measured for soil extracts of deep lysimeters. The results of the E-screen assay suggests the occurrence of a fast mobilization of applied ECDs and a moderate retardation effect of native ECDs contained in applied SS in the sandy soil used in the lysimeters. In lysimeters spiked with a mixture of SS and ECDs, the washing-out effect of ECDs in the first leachate fraction decreased, but the distribution of ECDs in the lysimeters increased. The relatively high estrogenic impact measured for soil water extracts suggests that the ECDs were mostly associated with water-soluble fractions of organic matter and/or water-suspended fractions of the mineral soil matrix. The application of SS to agricultural and forest fields may determine the immobilization of ECDs in soil or their movement to surface and/or groundwater. Therefore, an endocrine risk of exposure exists for the water and soil organisms.

Endocrine disruptors: a new scientific role for clinical pharmacologists? Impact on human health, wildlife, and the environment

It is important for the clinical pharmacologist to understand the potential human health implications of exposure to environmental chemicals that may act as hormonally active agents. It is necessary to have an understanding of how pharmaceutical and personal care products and other chemicals affect the ecosystem of planet Earth and to understand how they may negatively contribute to human disease. Clinical pharmacologists must understand the various definitions of endocrine disruptors and be able to "decipher" these terms for their patients. Understanding the need for the EPA endocrine disruptor screening program and possessing knowledge of the screening assays used to assess endocrine activity potential are two essential components relevant to the topic of endocrine disruptors. Clinical pharmacologists have an opportunity to play an important role in resolving the question of what role endocrine disruptors play in initiating human disease since some scientists argue that the present evidence is not compelling. Clinical pharmacologists can also play an important role in the evaluation of the risk assessment and use of risk management and risk communication tools required to address public health concerns related to actions of endocrine disruptors. It is important that clinical pharmacologists work with veterinary clinical pharmacologists, toxicologists, industrial chemists, regulators, the scientific community, the general public, and environmental groups to understand the impact of endocrine disruptors on human health, wildlife, and the environment with an ultimate goal to minimize and/or alleviate the unwanted, detrimental effects of the endocrine disruptors.

Effects and neuro-toxic mechanisms of 2, 2', 4, 4', 5, 5'-hexachlorobiphenyl and endosulfan in neuronal stem cells

Endocrine disrupters are exogenous compounds thought to mimic the action of estrogen or other hormones and influence endocrine activity in the body (Juberg, 2000). These chemicals have adverse effects not only in the reproductive system but also in the central nervous system during development and throughout life. Polychlorinated biphenyls (PCBs) are a class of environmentally persistent and widespread halogenated hydrocarbons. It has been reported that PCBs are potential neurotoxicants. Endosulfan is an organochlorine insecticide that is extensively used to control pests in vegetables, cotton, and fruits. To determine the effect of 2, 2', 4, 4', 5, 5',-hexachlorobiphenyl(2, 4, 5-HCB) and endosulfan on embryo nervous system, we isolated neural stem cells from rat brain at embryonic day 17. Isolated neural stem cells showed pluripotenty. Stem cells could differentiate into neurons and glia. Neurite formation in endosulfan and 2, 4, 5-HCB treated cells. And it appeared to be decreased as compared with that in untreated cells. In order to know the neuro-toxic mechanisms of 2, 4, 5-HCB and endosulfan in neuronal stem cells, we investigated mitogen-activated protein kinase activity (MAPK) and gap junctional intercellular communication (GJIC). Endosulfan decreased the MAPK activity in dose dependent manner. Endosulfan and 2, 4, 5-HCB inhibited GJIC compared to the untreated cell by scrape loading dye transfer (SL/DT). 2, 4, 5-HCB and endosulfan decreased the expression of connexin 43 in dose dependent manner. These results indicated that 2, 4, 5-HCB and endosulfan may inhibit differentiation and proliferation of neural stem cells and gap junctional intercellular communication which play a crucial role in the maintenance of cellular homeostasis.

Genetic susceptibility and environmental estrogen-like compounds

Environmental chemicals with estrogenic activities have been suggested to be able to interact with the endocrine system. Endogenous estrogen is synthesized in the ovarian theca cells of premenopausal women or in the stromal adipose cells of the breast of postmenopausal women and minor quantities in peripheral tissue. These cells, as well as breast tissue, express all the necessary enzymes for this synthesis, CYP17, CYP11a, CYP19, 17-beta-hydroxysteroid hydrogenase, steroid sulfatase as well as enzymes further hydroxylating estradiol, such as CYP1A1, CYP3A4, CYP1B1, catechol-o-methyltransferase (COMT). Polymorphisms in these enzymes may have a possible role in the link between environmental estrogens and hormone-like substances and the interindividual risk of breast cancer.

Comparison of an array of in vitro assays for the assessment of the estrogenic potential of natural and synthetic estrogens, phytoestrogens and xenoestrogens

Many chemicals in surface waters and sediments have recently been discovered to have estrogenic/antiestrogenic activity. Among these compounds, known as 'endocrine disrupters', are natural and synthetic hormones, phytoestrogenes and a variety of industrial chemicals, such as certain detergents and pesticides. These substances are supposed to affect the development and reproduction in wildlife and humans and may also be involved in the induction of cancer. In order to assess the estrogenic/antiestrogenic potential of pure compounds and complex environmental samples we compared an array of in vitro test systems, (i) two luciferase reporter gene assays using transgenic human MVLN cells (derived from MCF-7 cells) and HGELN cells (derived from HeLa cells); (ii) a competitive binding assay with recombinant human estrogen receptors (ER) alpha and beta; and (iii) a proliferation assay with MCF7-cells (E-Screen). The sensitivity of the assays for 17-beta-estradiol decreased in the order: MVLN-cells=E-Screen>HGELN-cells>binding to ER-alpha>binding to ER-beta. A good correlation was obtained between the estrogenic potencies of 11 compounds (17-beta-estradiol (E(2)), estrone (E(1)), estriol (E(3)), ethinylestradiol (EE(2)), diethylstilbestrol (DES), coumestrol, beta-sitosterol, genistein, 4-nonylphenol, 4-octylphenol, bisphenol A) in the three tissue culture assays. The relative potencies of the compounds obtained by the cell free binding assays were one to two orders of magnitude higher compared with the cell culture assays. The phytoestrogens showed a preference to bind to ER-beta, but only genistein showed a much lower activity in the E-Screen (growth induction in breast cancer cells) compared with the luciferase induction in MVLN and HGELN-cells.

Reduced sperm counts in guppies (Poecilia reticulata) following exposure to low levels of tributyltin and bisphenol A

There is increasing evidence that normal male reproductive function can be disrupted by exposure to pollutants in the environment that can exogenously mimic, antagonize or block sex-hormone function. One possible consequence of exposure to these xenobiotics is disruption to spermatogenesis, but results thus far provide only indirect and inconsistent evidence. In this study we exposed adult male guppies (Poeciliidae: Teleostei) to environmentally relevant levels of the common xenobiotics tributyltin (11.2-22.3 ngl-1) and bisphenol A (274-549 micrograms l-1) in experimental aquaria. After 21 days of exposure, we found significant declines (by 40-75%) in total sperm counts for male fishes exposed to tributyltin and bisphenol A compared with controls. This short-term decline in sperm count is unlikely to be the result of endocrine-mediated alteration of the germ line, and we found no change in testis size or sperm lengths between treatments. However, Sertoli cells, which facilitate the transport of maturing sperm into the testicular deferent duct (where they are stored prior to ejaculation), are directly sensitive to xenobiotic action and it is therefore possible that spermatogenesis was inhibited through in vivo interference with normal Sertoli-cell function.