Mixture Of Endocrine Disruptors Research Articles

Mixtures of endocrine disruptors: How similar must mechanisms be for concentration addition to apply?

Must molecular mechanisms be the same for concentration addition to predict the effect of a mixture or is it sufficient for compounds to affect similar pathways or common outcomes? Does concentration addition provide a closer approximation to observations than alternative models such as independent action? Suppose effects are mediated by hormone A through receptor R, synthesis of A is reduced by compound B, and that C is a competitive antagonist to A. Both B and C reduce levels of the receptor–ligand complex AR but via different specific mechanisms. Are combinations of B and C concentration additive? We used simple pharmacodynamic models, deriving mathematical models using equilibrium binding and mass balance. Assume A binds the receptor at one site of R with effects proportional to the concentration of AR. Let C act as a competitive antagonist via the Gaddum equation. Let B affect synthesis of A via a function g(B). We derive a model describing the joint response surface of B and C, and a function describing its isoboles. Under concentration addition, the isoboles must be negatively sloped straight lines. We show that linearity of the isoboles depends crucially on g(B). The mixture is concentration additive if g″(B), the second derivative of g(B) with respect to B, is always zero. Responses are greater than concentration additive if g″(B) is always positive and less than concentration additive if g″(B) is always negative. We describe functions g(B) that lead to all three cases as well as one that is greater than concentration additive in some regions and less than concentration additive in others. At least in this simple model, concentration addition cannot be assumed: mixtures of competitive antagonists and compounds that alter hormone synthesis can lead to results that are concentration additive, greater than concentration additive or less than concentration additive. Nevertheless, concentration addition appears to provide a closer approximation to the pharmacodynamic model examined here than independent action. Care needs to be taken in extrapolating to other situations, but analysis of simple pharmacodynamic models appears to be a useful strategy.

Abnormal peripubertal development of the rat mammary gland following exposure in utero and during lactation to a mixture of genistein and the food contaminant vinclozolin

The impact of early exposure to endocrine disruptor mixtures on mammary gland development is poorly known. Here, we identify the effects of a conception to weaning exposure of rats to the phytoestrogen genistein (G) and/or the antiandrogen vinclozolin (V) at 1 mg/kg-d, alone or in association. Using several approaches, we found that G- and GV-exposed rats displayed significantly greater epithelial branching and proliferation, wider terminal end buds than controls at PND35, as well as ductal hyperplasia and periductal fibrosis. Focal branching defects were present in V-exposed rats. An increased ER and AR expression was observed in G- and GV- as compared to V-exposed rats at PND35. Surprisingly, a significant number of GV- and to a lesser extent, V-exposed animals displayed abnormal hyperplasic alveolar structures at PND50. Thus, gestational and lactational exposure to low doses of genistein plus vinclozolin may seriously affect peripubertal development of the rat mammary gland.

Further analysis of behavioral and endocrine consequences of chronic exposure of male Wistar rats to subtoxic doses of endocrine disruptor chlorobenzenes

Many chemicals utilized by humans are present as environmental pollutants and may influence homeostasis from neurological, immunological, endocrinological and/or behavioral aspects. Such agents, acting alone or in ambient mixtures, may be biologically active even at extremely low doses, and it may be postulated that stable, bioaccumulative, reactive endorine disruptors may affect central and/or peripheral secretion of arginine–vasopressin (AVP) and oxytocin (OXT) and thereby related physiological and behavioral functions, potentially leading to disorders in exposed subjects. The primary aim of this study was to demonstrate effects of chronic exposure to a low dose of an orally administered chlorobenzene mixture on anxiety-related and aggressive behavior mediated largely by AVP and OXT. Chlorobenzenes were applied to model ambient mixtures of endocrine disruptors. Adult, male Wistar rats were exposed daily to 0.1μg/kg of 1,2,4-trichlorobenzene and hexachlorobenzene via a stomach tube for 30, 60 or 90days, after which anxiety-related and aggressive behavioral elements were examined in open-field, elevated plus maze and resident–intruder tests. The plasma levels of AVP, OXT and adrenocorticotrophic hormone at the endpoints were measured by radioimmunoassay or immunochemiluminescence assay. The levels of basal and serotonin- or norepinephrine-stimulated AVP and OXT secretion in pituicyte cultures prepared from the posterior lobe of the pituitaries were also measured. The hormone levels proved to be increased to extents depending on the duration of exposure to the chlorobenzenes. Several anxiety-related and aggressive behavioral elements were also enhanced following chlorobenzene exposure, while certain explorative and locomotive elements of the animals were decreased. As both physiological and behavioral elements were modulated by chronic, subtoxic doses of chlorobenzenes, it is concluded that doses of such environmental pollutants low enough to fall outside the range of legal regulation may pose potential risks of anxiogenic and/or aggressive consequences in exposed subjects, including humans.

The application of reporter gene assays for the detection of endocrine disruptors in sport supplements

The increasing availability and use of sports supplements is of concern as highlighted by a number of studies reporting endocrine disruptor contamination in such products. The health food supplement market, including sport supplements, is growing across the Developed World. Therefore, the need to ensure the quality and safety of sport supplements for the consumer is essential. The development and validation of two reporter gene assays coupled with solid phase sample preparation enabling the detection of estrogenic and androgenic constituents in sport supplements is reported. Both assays were shown to be of high sensitivity with the estrogen and androgen reporter gene assays having an EC 50 of 0.01 ng mL −1 and 0.16 ng mL −1 respectively. The developed assays were applied in a survey of 63 sport supplements samples obtained across the Island of Ireland with an additional seven reference samples previously investigated using LC–MS/MS. Androgen and estrogen bio-activity was found in 71% of the investigated samples. Bio-activity profiling was further broken down into agonists, partial agonists and antagonists. Supplements (13) with the strongest estrogenic bio-activity were chosen for further investigation. LC–MS/MS analysis of these samples determined the presence of phytoestrogens in seven of them. Supplements (38) with androgen bio-activity were also selected for further investigation. Androgen agonist bio-activity was detected in 12 supplements, antagonistic bio-activity was detected in 16 and partial antagonistic bio-activity was detected in 10. A further group of supplements (7) did not present androgenic bio-activity when tested alone but enhanced the androgenic agonist bio-activity of dihydrotestosterone when combined. The developed assays offer advantages in detection of known, unknown and low-level mixtures of endocrine disruptors over existing analytical screening techniques. For the detection and identification of constituent hormonally active compounds the combination of biological and physio-chemical techniques is optimal.

Biological assessments of a mixture of endocrine disruptors at environmentally relevant concentrations in water following UV/H2O2 oxidation

Numerous studies have investigated degradation of individual endocrine disrupting compounds (EDCs) in lab or natural waters. However, natural variations in water matrices and mixtures of EDCs in the environment may confound analysis of the treatment efficiency. Because chemical based analytical methods cannot represent the combined or synergistic activities between water quality parameters and/or the EDC mixtures at environmentally relevant concentrations (microg L(-1)-ng L(-1)), bioanalytical assessments of residual estrogenic activity in treated water were used to evaluate the performance of the UV based advanced oxidation process for estrogenic contaminants in water. Four EDCs including estradiol (E(2)), ethinyl estradiol (EE(2)), bisphenol-A (BPA) and nonylphenol (NP) were spiked individually or as a mixture at mug L(-1)-ng L(-1) in laboratory or natural river water. The removal rates of estrogenic activity were quantitatively evaluated by in vitro yeast estrogen screen (YES) and in vivo Vitellogenin (VTG) assays with Japanese medaka fish (Oryzias latipes). UV in combination with 10 ppm H(2)O(2) as an oxidation process was capable of decreasing in vitro and in vivo estrogenic activity, however, in vivo estrogenic activity of the EDC mixture in natural water was not completely removed at UV fluence up to 2000 mJ cm(-2). The removal rates of in vitro estrogenic activity of the EDC mixtures were lower than those observed for single compounds, and slower in natural waters, likely due to lower steady-state concentrations of hydroxyl radicals (*OH) in the presence of *OH scavengers from the water matrix and EDC mixture.

Environmental Engineering and Endocrine Disrupting Chemicals

Endocrine disruptors are a class of chemicals of growing interest to the environmental community. The U.S. Environmental Protection Agency’s ~EPA! Risk Assessment Forum defined an endocrine disrupting chemical ~EDC! as ‘‘an exogenous agent that interferes with the synthesis, secretion, transport, binding, action, or elimination of natural hormones in the body that are responsible for the maintenance of homeostasis, reproduction, development, and/or behavior’’ ~EPA 1997!. Most of us are more familiar with chemicals of concern that have a specific health outcome such as lung cancer. However, EDCs are a class of chemicals defined by their mode of action and can result in a variety of health outcomes. For example, an EDC can initiate a health-related outcome in humans or wildlife by binding to and stimulating estrogen or androgen receptors. Gaining a thorough understanding of the endocrine-related effects of chemicals on humans and wildlife is the goal of domestic and international research that will continue far into the future. The Global Endocrine Disruptor Research Inventory ~EPA 2001a! indicates over 600 human and wildlife health effects studies currently underway. The Food Quality Protection Act requires the U.S. EPA to build a screening and testing program to identify those industrial chemicals that cause endocrine-related effects to human and wildlife health ~see http://www.epa.gov/scipoly/ oscpendo/index.htm!. To obtain results for existing industrial chemicals will likely take most of this decade. However, the literature already points to some chemicals as likely endocrine disruptors including certain phthalate esters, particular biodegradation products of octylphenol and nonylphenol polyethoxylate surfactants, several specific PCBs, some chlorinated dioxins, DDT and DDE, bisphenol A, tributyltin, the pesticides methoxychlor and endosulfan, and exogenous steroid hormones, among others. Studies are also underway, worldwide, to characterize the levels of suspected endocrine disruptors to which humans and wildlife are exposed ~EPA 2001a!. Once adequate effects and exposure information are collected, the risk of individual or mixtures of endocrine disruptors can be assessed. Some political bodies have begun to implement risk management strategies for EDCs. For example, the European Union and some individual European nations have banned or are phasing out the use of some endocrine disruptor-related chemicals such as nonylphenol polyethoxylate surfactants and certain phthalate esters. Decisions on how and when to begin actively managing or reducing unacceptable risks posed by EDCs must be determined by stakeholder organizations. Whether or not to apply risk management tools to an EDC-related environmental problem depends on currently available risk information, available management technologies, their economic impact, and social and political factors. Some level of uncertainty is always associated with risk management decision making. The earlier risk management tools are applied to reduce exposure to a chemical of concern, the greater the level of uncertainty. However, early application of risk management tools can reduce exposure of humans and wildlife while additional and more detailed information is acquired. As more information about the chemical of concern is obtained ~e.g., levels in the environment, effects on human and ecosystem health, specific sources, etc.!, risk management decisions are made with less uncertainty. Our role as research and development environmental engineers is to provide engineering information to stakeholders so that decisions on the application of risk management tools or processes can be made with minimal uncertainty. The input we can provide regarding EDCs includes the following: ~1! identification of currently available tools that can be adapted to lower exposure of humans and wildlife to EDCs; and ~2! development of new approaches to reduce exposure if adequate tools are not readily available. Environmental engineering research on managing exposure to EDCs has begun in the last several years. This initial work is an international effort addressing, among others, the following questions: