Examples Of Endocrine Disruption Research Articles

EFFETTI DEGLI INTERFERENTI ENDOCRINI SULLE COMUNITÀ DI INVERTEBRATI MARINI

Organic pollutants with disrupting activity on the endocrine system are known as endocrine disrupting compounds (ECDs) and are broadly diffuse on the Planet. By different pathways, they reach the marine environment that is the ultimate collector of these substances. Several researches pointed out acute and chronic effects of these pollutants on the reproduction and development of fish and marine mammals. Fewer studies have been dedicated to explore the effects of ECDs on marine invertebrates though these represent most of marine biodiversity. Researches are hampered by limited knowledge of endocrinology and physiology of several animal groups, which has been studied only for few phyla such as mollusks, annelids and arthropods. The clearest example of endocrine disruption by a chemical compound in marine environment is the pseudo-hermaphroditism caused in females of prosobranch mollusks by the exposure to tributyltin, an antifouling agent used in the paints for ships. This molecule has an adverse effect also on crustaceans in which it inhibits the signaling pathway of the molting hormone. Several studies evidenced that lot of marine invertebrate species are sensible to the action of estrogenic compounds (xeno-estrogens) such as Bisphenol A and Nonylphenol that are used in the manufacturing of the plastic materials. Nevertheless, molecular mechanisms responsible for the observed effects are still uncertain. In my laboratory, we demonstrated that tunicates, that do not have estrogen receptors, are sensible to the action of xeno-estrogens that act by binding to a different group of receptors, the Estrogen Related Receptors. Since these receptors are present also in mammals, our studies could help to clarify pathogenic mechanisms shared with humans.

Endocrine Disruption in Invertebrates: A Survey of Research Progress.

Manmade chemicals can interfere with endocrine processes and have permeated many ecosystems. Arguably, the most devastating example of endocrine disruption occurred in gastropod molluscs which led to the banning of tributyltin. The invertebrates consist of ∼95% of all known animals and possess endocrine systems that can significantly differ from that of vertebrates. An expert group in the late 1990s highlighted considerable paucity in our knowledge of these endocrine systems and the limited ability to ascertain risks of endocrine-disrupting chemicals (EDCs) to invertebrates. Twenty years later, we surveyed experts in this field on the current state of the science. Respondents agreed that endocrine disruption is still a significant issue and noted that there was key evidence that EDCs were impacting invertebrates groups. Respondents noted a variety of impediments to advancing the science, including inadequate funding, insufficient knowledge to develop appropriate assays, and generally low support for invertebrate studies. Several scientists highlighted that resources were being misdirected with studies that address impacts of vertebrate EDCs or using biomarkers specific to vertebrate endocrine disruption. Sadly, many of the recommendations proposed by respondents matched those made over two decades ago. Accordingly, the field has not advanced as much as one might have expected.

Populations Collapses in Marine Invertebrates Due to Endocrine Disruption: A Cause for Concern?

In the beginning of the twenty first century, the International Program on Chemical Safety published a document entitled Global Assessment of the State-Of-The-Science of Endocrine Disruptors. The work indicated only weak evidence of endocrine-related effects in human populations, and in wild animal populations. This document was revised in 2012 (State of the Science of Endocrine Disrupting Chemicals−2012) (1). The new document and the extensive scientific evidence it provided showed clearly that ED effects could be a risk to human and wildlife health. These works, however, were focused in human health and related animal models, mainly vertebrates and particularly mammals. It can be argued that invertebrates and many other taxa are important parts of all ecosystems, and, in many instances, have been shown to be also vulnerable to endocrine disruption. Thus, this work is aimed to show some observations on important marine invertebrate taxa, from an ecological point of view. The most important example of endocrine disruption in marine wild populations is the imposex response of marine gastropods, known for more than 40 years, and worldwide used to evaluate marine antifouling pollution. Among the mollusks, other important natural resources are bivalve species, used as human food sources and cephalopods, free-living, highly specialized mollusks, and also human food sources. Effects derived from endocrine disruptors in these species indicate that consumption could bring these compounds to human populations in an almost direct way, sometimes without any form of cooking or preparation. While discussing these questions, this work is also aimed to stimulate research on endocrine disruption among the invertebrate taxa that inhabited our oceans, and on which these effects are poorly known today.

Differences in retinoid levels and metabolism among gastropod lineages: Imposex-susceptible gastropods lack the ability to store retinoids in the form of retinyl esters

The presence of a complex retinoid system was long believed to be a chordate/vertebrate novelty. However, recent findings indicate otherwise since the gastropod mollusk Osilinus lineatus was found to have the capacity to store retinoids in the form of retinyl esters (REs), a key feature to maintain a homeostatic control of retinoid levels. Here, we investigated whether such a complex retinoid system is widely distributed among gastropod lineages. Additionally, since one of the most spectacular examples of endocrine disruption in the wild, the masculinization of female gastropods (imposex) by the retinoid X receptor (RXR) agonist, tributyltin (TBT), has been linked with perturbed retinoid signaling, we also investigated if retinoid storage mechanisms in the form of retinyl esters were present in imposex-susceptible gastropods. Initially, we determined the presence of both polar (active retinoic acid isomers) and nonpolar retinoids (retinol, REs) in selected gastropod species: the limpet Patella depressa and the imposex-susceptible whelks Nucella lapillus and Nassarius reticulatus. Although all species presented active retinoid forms, N. lapillus and N. reticulatus were shown to lack nonpolar retinoids. The absence of REs, which are the common retinoid storage form found in vertebrates and in O. lineatus suggest that those species are unable to use them to maintain a homeostatic control of their retinoid levels. In order to further clarify the retinoid metabolic pathways in imposex-susceptible gastropods, a retinoid exposure study was carried out with N. lapillus. The results demonstrate that although N. lapillus is able to metabolize several retinoid precursors, it lacks the capacity to store retinoids as REs. Whether the lack of retinoid storage mechanisms in the form of REs in imposex-susceptible gastropods plays an important role in the susceptibility to RXR agonists warrants additional studies.

Differences in sensitivity but not selectivity of xenoestrogen binding to alligator versus human estrogen receptor alpha

Reproductive abnormalities in alligators exposed to contaminants in Lake Apopka, Florida, USA represent a clear example of endocrine disruption in wildlife. Several of these contaminants that are not able to bind to mammalian estrogen receptors (such as atrazine and cyanazine) have previously been reported to bind to the alligator estrogen receptor from oviductal tissue. Binding of known Lake Apopka contaminants to full length estrogen receptors alpha from human (hERalpha) and alligator (aERalpha) was assessed in a side-by-side comparison within the same assay system. Baculovirus-expressed recombinant hERalpha and aERalpha were used in a competitive binding assay. Atrazine and cyanazine were not able to bind to either receptor. p,p'-Dicofol was able to bind to aERalpha with a concentration inhibiting 50% of binding (IC50) of 4 microM, while only partially displacing 17beta-estradiol (E2) from hERalpha and yielding a projected IC50 of 45 microM. Chemicals that only partially displaced E2 from either receptor, including some dichlorodiphenyltrichloroethane (DDT) metabolites and trans-nonachlor, appeared to have higher affinity for aERalpha than hERalpha. p,p'-Dicofol-mediated transcriptional activation through aERalpha and hERalpha was assessed to further explore the preferential binding of p,p'-dicofol to aERalpha over hERalpha. p,p'-Dicofol was able to stimulate transcriptional activation in a similar manner with both receptors. However, the in vitro results obtained with p,p'-dicofol were not reflected in an in vivo mammalian model, where Kelthane (mixed o,p'- and p,p'-dicofol isomers) did not elicit estrogenic effects. In conclusion, although there was no evidence of exclusively species-specific estrogen receptor binders, some xenoestrogens, especially p,p'-dicofol, had a higher affinity for aERalpha than for hERalpha.

Imposex induction is mediated through the Retinoid X Receptor signalling pathway in the neogastropod Nucella lapillus

The imposex phenomenon in female prosobranch gastropods provides one of the best documented examples of endocrine disruption in wildlife. While many field studies have demonstrated the negative impact of tributyltin (TBT) upon female gastropods, the mechanism(s) underlying imposex development has not yet been fully clarified. Over the years several hypotheses have been raised to determine the biochemical and molecular determinants of this process. Nevertheless, the interplay between the different suggested pathways (neuroendocrine, steroid and retinoid) is still unknown. Hence, through a combination of exposure experiments, we show that the 9- cis-retinoic acid (9cisRA), the proposed natural ligand of the retinoic X receptor (RXR), induces imposex in females of Nucella lapillus to the same degree as tributyltin, when administered at similar concentrations (1 μg/g body weight). Methoprene acid, a selective ligand for RXR, also induces imposex, albeit to a lower degree than that of the positive control. In contrast, testosterone significantly induced imposex, but had no effect on female penis induction, while the neuropeptide APGWamide had no effect on imposex development. These results clearly demonstrate that imposex induction in N. lapillus is mediated through the modulation of the RXR signalling pathways. In addition to the effects reported in female dogwhelks, both TBT and RA significantly increased male penis length, thus suggesting that TBT may also impact male secondary sex organs through the RXR signalling pathways. As a step for future studies, we have cloned the orthologue of N. lapillus RXR and provide experimental evidence that it binds 9cisRA. Finally, the basal expression level of RXR in several tissues of N. lapillus was determined through real-time PCR, thus showing that RXR is ubiquitously expressed in mollusc tissues, with the highest expression levels being recorded in female and male gonads. The mechanistic impacts of the overall findings to the imposex process are discussed.

Endocrine disruption in aquatic pulmonate molluscs: few evidences, many challenges

As compared to other groups of aquatic gastropods, documented examples of endocrine disruption in pulmonates are rather limited. This is quite surprising because the endocrine control of physiological functions has been extensively studied in these animals. In the model-species Lymnaea stagnalis, the neurohormonal regulation of reproduction has been thoroughly investigated, and the primary structure of several peptides and receptors involved in endocrine processes has been established. However, the use of this knowledge has been fairly limited in the context of ecotoxicology, to investigate the effects of endocrine-disrupting chemicals. The present review summarizes the main and more recent findings on the neuroendocrine control of reproduction in aquatic pulmonate snails (Basommatophora). It then comprehensively describes selected in vivo laboratory and semi-field studies which provide evidence for possible endocrine disrupting effects of estrogenic and androgenic test compounds [e.g., ethynylestradiol, methyltestosterone (MT)], and of environmental contaminants [e.g., cadmium (Cd), tributyltin (TBT), and nonylphenol (NP), pesticides]. Finally, challenging perspectives for future research are discussed.

How parasitism and pollution affect the physiological homeostasis of aquatic hosts

Parasitism poses a serious threat to hosts under certain circumstances, while the well-being of organisms is also negatively affected by environmental pollution. Little information is available on the simultaneous effects of parasites and pollutants on the physiological homeostasis of organisms. The present paper demonstrates that parasites: (i) may influence the metabolism of pollutants in infected hosts, (ii) interact with pollution in synergistic or antagonistic ways, and (iii) may induce physiological reactions in hosts which were thought to be pollutant-induced. Experimental studies on the uptake and accumulation of metals by fish reveal that fish infected with acanthocephalans have lower metal levels than uninfected hosts; e.g. Pomphorhynchus laevis reduces lead levels in fish bile, thereby diminishing or impeding the hepatic intestinal cycling of lead, which may reduce the quantity of metals available for fish. Alterations in pollutant uptake and accumulation in different intermediate and final hosts due to parasites are thus very important in the field of ecotoxicology. In addition to such alterations, there is a close interaction between the effects of pollutants and parasites which seems to be mediated at least partly by the endocrine system, which itself is closely related to the immune system in fish. Laboratory studies on eels experimentally infected with the swimbladder nematode Anguillicola crassus reveal that toxic chemicals such as polychlorinated biphenyls produce immunosuppressive effects which facilitate parasite infection. Similarly, an increase in serum cortisol concentration in eels due to chemical exposure and infection is correlated with decreasing levels of anti-A. crassus antibodies. Furthermore, parasites are able to elicit physiological changes which are attributed to chemicals with endocrine disrupting activity, e.g. the cestode Ligula intestinalis is known to suppress gonad development in roach. The most thoroughly documented examples of endocrine disruption in wild fish are in roach, and it is conceivable that this disruption is not only due to chemical activity but also to parasites such as L. intestinalis or species of the phylum Microspora.

Endocrine Disrupters in the Aquatic Environment: An Overview

Although a relatively new area of environmental research, the field of endocrine disruption has grown very rapidly, and currently many hundreds, perhaps even a few thousand, papers are published annually on the many different aspects covered by the field. As far as endocrine disruption in wildlife is concerned, most attention has been focused on aquatic organisms, for two reasons. Firstly, the aquatic environment receives most of the pollutants intentionally released into the environment, through effluents from wastewater treatment plants, and secondly because many of the best documented examples of endocrine disruption in wildlife are of partially or completely aquatic species. These two reasons are probably not unconnected, of course. Hence, aquatic organisms can receive continuous exposure to endocrine-disrupting chemicals throughout their lives, albeit usually to low concentrations of these chemicals. Analysis of effluents has identified many of the endocrine-disrupting chemicals present, and shown that these are both natural and man-made, and vary greatly in potency. Most attention has been directed to identifying the main estrogenic chemicals, because many of the effects reported in wildlife appear to be a consequence of ‘feminization’ of males. However, chemical analysis of effluents has also demonstrated that chemicals with other types of endocrine activity are present, such as androgens, anti-androgens, progestagens, etc. The effects (if any, of course) of such chemicals on aquatic organisms are unknown, and largely uninvestigated, presently. Much of the biological research has centred on the effects of estrogenic chemicals, especially to fish. These effects, such as elevated vitellogenin concentrations and intersexuality, have to date been studied almost exclusively at the level of the individual, and hence whether endocrine-disrupting chemicals cause population-level consequences is largely unknown (the undeniable effects of TBT on molluscs, leading to local extinctions, being the exception). It is my opinion that rather too much of the recent research has not advanced our understanding of endocrine disruption a great deal, and we are probably not much further forward now than we were five years or so ago. It is surely time to tackle some of the outstanding, unresolved issues, such as the impact of endocrine disruption at the population level, and the issue of how organisms respond when exposed to complex mixtures of endocrine active chemicals. Such research will not be easy, and will require multidisciplinary teams, including people with expertise in areas not yet involved in the field of endocrine disruption, such as mathematical modellers. However, until such research is done, it will not be possible to decide how important an issue endocrine disruption is to wildlife, and how that importance compares to the other factors adversely affecting wildlife, such as habitat loss, climate change, and the introduction of exotic species and novel diseases.

Gender benders at the beach: Endocrine disruption in marine and estuarine organisms

Several consensus definitions of the term endocrine disruptor have appeared recently, but all definitions include the important, though frequently implicit, stipulation that the animal is not distressed or in obvious discomfort. Instead, a superficially healthy animal is experiencing alterations in hormone synthesis, transport, receptor interaction, metabolism, excretion, or feedback regulation. In addition, hormone disruption may occur during sex differentiation, and its effects may not be manifested until after sexual maturation. Many cases of chemically induced reproductive impairment have been reported for both freshwater and marine species. However, reproductive impairment may not necessarily result from hormone disruption and should be considered suggestive, but not conclusive, evidence of endocrine disruption. A suite of in vivo and in vitro assays will more adequately assess whether a compound is truly endocrine disrupting. This review will cover basic endocrinology of marine and estuarine invertebrates and vertebrates, methods for detecting endocrine disruption, and examples of endocrine disruption in various species.

Ecological Significance of Endocrine Disruption in Marine Invertebrates

Anthropogenic chemicals which can disrupt the hormonal (endocrine) systems of wildlife species are currently a major cause for concern. Reproductive hormone-receptor systems appear to be especially vulnerable. In the past few years, numerous effects of endocrine disrupting chemicals on wildlife have emerged including changes in the sex of riverine fish, reproductive failure in birds and abnormalities in the reproductive organs of alligators and polar bears. Much less is known regarding endocrine disruption in marine invertebrates, the key structural and functional components of marine ecosystems. In this paper, potential effects of different classes of endocrine disrupting chemicals are reviewed. The endocrinology of several major invertebrate groups is briefly examined to identify which phyla are most likely to be at risk. Gaps in our knowledge concerning the availability and uptake of endocrine disruptors are identified. For example, the relative importance of different routes of chemical uptake (from seawater vs food) is considered. Feeding strategies (herbivores, carnivores, deposit feeders, suspension feeders) in relation to uptake of endocrine disruptors are also discussed. Examples of endocrine disruption in marine invertebrates in situ are provided, including imposex in gastropod molluscs exposed to organotin compounds and intersex in crustaceans exposed to sewage discharges. Laboratory data are presented concerning the effects of endocrine disruptors on the growth and reproductive output of the deposit feeding amphipod Corophium volutator and the polychaete worm Dinophilus gyrociliatus. Recent findings are reported which demonstrate reductions in settlement following exposure of barnacle larvae to the xeno-estrogen, 4 nonyl phenol. The potential use of cyprid major protein as a biomarker of oestrogenicity is explored. The ecological significance of endocrine disruption in marine invertebrates is discussed. With regard to environmental management action, an evidence-based approach is advocated. A protocol for collecting evidence of ecologically significant endocrine disruption is outlined.

Establishing an In Vitro method for detecting estrogen-mimicking chemicals in environmental samples

The presence of a complex retinoid system was long believed to be a chordate/vertebrate novelty. However, recent findings indicate otherwise since the gastropod mollusk Osilinus lineatus was found to have the capacity to store retinoids in the form of retinyl esters (REs), a key feature to maintain a homeostatic control of retinoid levels. Here, we investigated whether such a complex retinoid system is widely distributed among gastropod lineages. Additionally, since one of the most spectacular examples of endocrine disruption in the wild, the masculinization of female gastropods (imposex) by the retinoid X receptor (RXR) agonist, tributyltin (TBT), has been linked with perturbed retinoid signaling, we also investigated if retinoid storage mechanisms in the form of retinyl esters were present in imposex-susceptible gastropods. Initially, we determined the presence of both polar (active retinoic acid isomers) and nonpolar retinoids (retinol, REs) in selected gastropod species: the limpet Patella depressa and the imposex-susceptible whelks Nucella lapillus and Nassarius reticulatus. Although all species presented active retinoid forms, N. lapillus and N. reticulatus were shown to lack nonpolar retinoids. The absence of REs, which are the common retinoid storage form found in vertebrates and in O. lineatus suggest that those species are unable to use them to maintain a homeostatic control of their retinoid levels. In order to further clarify the retinoid metabolic pathways in imposex-susceptible gastropods, a retinoid exposure study was carried out with N. lapillus. The results demonstrate that although N. lapillus is able to metabolize several retinoid precursors, it lacks the capacity to store retinoids as REs. Whether the lack of retinoid storage mechanisms in the form of REs in imposex-susceptible gastropods plays an important role in the susceptibility to RXR agonists warrants additional studies.

Reproductive effects from oestrogen activity in polluted water.

A new area of ecotoxicology, now usually called endocrine disruption, has arisen in the last few years. However, despite the present topicality of this issue, some of the best documented examples of endocrine disruption were reported a decade or more ago (see, for example, Fry, 1995). The issue is concerned with the effects of chemicals that mimic endogenous hormones on the physiology of exposed wildlife and humans. As many of these xenohormones mimic steroid hormones, especially oestrogens and androgens, most of the reported effects have involved effects on the reproductive system of exposed organisms. Many of these reported effects on wildlife have concerned aquatic, rather than terrestrial, organisms (even the well-documented effects on birds are primarily concerned with water birds, which feed predominantly on fish); the reproductive abnormalities seen in alligators living in some lakes in Florida (Guillette et al, 1994), and the oestrogenic effects on fish reported in British rivers (this example is discussed in detail below) provide good examples of the type of effects observed in aquatic organisms. This predominance of effects on aquatic organisms could reflect an unconscious bias of the interests of research scientists (are there more wildlife biologists interested in aquatic, rather than terrestrial, animals?), but is perhaps more likely a consequence of the fact that the aquatic environment is the ultimate “sink” for the intentional or unintentional disposal of much waste. Thus, this brief review is focused exclusively on the aquatic environment, and particularly on the effects on fish. However, I have attempted to emphasize the general nature of the phenomena illustrated by studies on endocrine disruption in fish, because they apply to most, if not all, examples of endocrine disruption in all wildlife.

Critical appraisal of the evidence for tributyltin‐mediated endocrine disruption in mollusks

AbstractThis article reviews the field and laboratory evidence for endocrine disruption in gastropod mollusks caused by tributyltin (TBT). Abundant and undisputed field data link TBT with an irreversible sexual abnormality of female neogastropod snails known as “imposex.” This phenomenon is a masculinization process involving the development of male sex organs, notably a penis and a vas deferens; in certain species the imposition of a vas deferens disrupts oviducal structure and function, preventing normal breeding activity and causing population disappearance. In some species, oogenesis is supplanted by spermatogenesis. A related condition referred to as “intersex” has been reported in littorinid mesogastropods, and these too become unable to lay eggs. Field evidence clearly associates these syndromes with the use of TBT as an antifoulant, chiefly on boat hulls, and dose‐related effects can be replicated in laboratory exposures to environmentally relevant concentrations of TBT compounds. It has now been established that imposex and intersex are forms of endocrine disruption caused by elevated testosterone titers that masculinize TBT‐exposed females. The precise mechanism by which increased levels of testosterone are produced has not been fully described, but the weight of evidence suggests that TBT acts as a competitive inhibitor of cytochrome P450‐mediated aromatase. Some recent data suggest that TBT may also inhibit the formation of sulfur conjugates of testosterone and its active metabolites, thus interfering with its excretion. In summary, TBT‐induced masculinization in gastropods, imposex and intersex, is the clearest example of endocrine disruption described in invertebrates to date that is unequivocally linked to a specific environmental pollutant.