Environmental obesogens: organotins and endocrine disruption via nuclear receptor signaling

Over the last two decades, the incidence of obesity and associated metabolic syndrome diseases has risen dramatically, becoming a global health crisis. Increased caloric intake and decreased physical activity are believed to represent the root causes of this dramatic rise. However, recent findings highlight the possible involvement of environmental obesogens, xenobiotic chemicals that can disrupt the normal developmental and homeostatic controls over adipogenesis and energy balance. Environmental estrogens, i.e. chemicals with estrogenic potential, have been reported to perturb adipogenic mechanisms using in vitro model systems, but other classes of endocrine-disrupting chemicals are now coming under scrutiny as well. Organotins represent one class of widespread persistent organic pollutants with potent endocrine-disrupting properties in both invertebrates and vertebrates. New data identify tributyltin chloride and triphenyltin chloride as nanomolar agonist ligands for retinoid X receptor (RXR alpha, RXR beta, and RXR gamma) and peroxisome proliferator-activated receptor gamma, nuclear receptors that play pivotal roles in lipid homeostasis and adipogenesis. The environmental obesogen hypothesis predicts that inappropriate receptor activation by organotins will lead directly to adipocyte differentiation and a predisposition to obesity and/or will sensitize exposed individuals to obesity and related metabolic disorders under the influence of the typical high-calorie, high-fat Western diet. The linking of organotin exposure to adipocyte differentiation and obesity opens an important new area of research into potential environmental influences on human health and disease.

Toxicity of dibutyltin, tributyltin and other organotin compounds to humans and to experimental animals

Alkyltin compounds are used as stabilizers and antifouling agents. Food chain accumulation and bioconcentration have been demonstrated in crabs, oysters and salmon exposed to tributyltin oxide. In mammalian species, tributyltin compounds may be metabolized to dibutyltin derivatives and related metabolites. Di- and tributyltins appear to be less potent neurotoxicants than trimethyltins and triethyltins. Dibutyltins and tributyltins produced bile duct damage in rats, mice and hamsters. Tributyltin oxide and dibutyltin and dioctyltin compounds are potent thymolytic and immunotoxic agents in rats. Tributyltin oxide at 5 ppm in the rat diet produced immunotoxicity in a 2-year feeding study, and at 50 ppm increased the incidence of tumors of endocrine origin. In preliminary reports, 5 ppm tributyltin produced no detectable increase in tumor incidence, and 0.5 ppm produced no detectable immunotoxicity in long-term studies. Tributyltin oxide and dibutyltin acetate did not appear to be mutagenic in a large battery of mutagenicity assays but produced base-pair substitutions in one of the bacterial strains tested. Tributyltin oxide produced mutations in Chinese hamster ovary cells, increased the incidence of micronuclei in the erythrocytes of exposed male BALB/c mice, and was highly embryotoxic in vitro. Embryotoxic and teratogenic effects in mice exposed to tributyltin oxide in vivo may have been due either to direct tributyltin oxide action or responses secondary to maternal toxicity. More information is needed to determine the applicability to human risk assessments of the immunotoxicity data derived from rat studies and to establish a definitive tolerable daily intake for tributyltin oxide.

Immunotoxicity in invertebrates: measurement and ecotoxicological relevance

Concern is growing regarding the impact of chemicals suspected of altering the function of the immune system in humans and wildlife. There are numerous examples of links between pollution and increased susceptibility to disease in wildlife species, including immunosuppression in harbour seals feeding on fish from contaminated sites, altered immune function in riverine fish and decreased host resistance in birds exposed to pollutants. Laboratory tests have identified potential immunological hazards posed by a range of anthropogenic chemicals in mammals and higher vertebrates. However, few reports have considered the ecological relevance of pollution-induced immunosuppression in invertebrate phyla, which constitute around 95% of all animal species and occupy key structural and functional roles in ecosystems. In this paper effects of chemicals on immune function in invertebrates are briefly reviewed and biomarkers of immunotoxicity are identified. Examples of new approaches for the measurement of immunological inflammatory reactions and stress in molluscan haemocytes are detailed. The relevance of defining the immune system as a target organ of toxicity in invertebrates is discussed and an integrated approach for the use of immunological biomarkers in environment management is proposed, combining measures of immune function and organismal viability at the biochemical, cellular and population level.

Biological activity of organotin compounds--an overview

As a consequence of the rapid expansion of the uses and applications of the organotin compounds, the concern about their environmental and health effects is increasing. The main subject of this overview is the current understanding of the mammalian toxicity of the organotin compounds. Four different types of target organ toxicity, namely neurotoxicity, hepatoxicity, immunotoxicity, and cutaneous toxicity, are discussed in more detail. The effects of the organotin compounds on the mitochondrial and cellular level are summarized and discussed in relation to the mode of action of these compounds on the central nervous system, the liver and bile duct, the immune system, and the skin.

Immunotoxicity of environmentally relevant concentrations of butyltins on human natural killer cells in vitro

The widespread environmental contamination, bio-accumulation, and toxic effects of butyltins (BTs) in wildlife is well documented, but the role of BTs in debilitating human immune function mediated through natural killer (NK) lymphocytes (a primary immune defense against tumor and virally infected cells) has not been described. In this study, we assessed the effects of in vitro exposure to a range of concentrations (encompassing environmentally relevant concentrations) of MBT, DBT, and TBT on human natural killer lymphocytes obtained from adult male and female donors. TBT inhibited the tumor-killing capacity of NK cells when the NK cells were pretreated in vitro at 200 nM for as little as 1 h. Inhibition of NK cytotoxic function ranged from 40 to greater than 90%. The toxic potential of butyltins followed the order of TBT > DBT > MBT. Conjugation assays revealed that after a 24-h exposure to TBT, there was about a 50% decrease in NK cell binding to tumor cells, indicating alteration of the NK cell receptors for tumor cells. Analysis of whole-blood samples for BTs revealed the presence of detectable concentrations of MBT, DBT, and TBT in all of the donors, indicating possible exposure of NK cells to BTs in the blood. The results of this study provide evidence that butyltin compounds significantly inhibit NK cell function and possible NK cell-mediated immunotoxic potential in humans.

Organotin Compounds: Toxicokinetic Aspects

Organotin compounds have a broad range of applications. While dialkyltin compounds are used primarily as stabilizers for plastics, trisubstituted organotins are mainly used as biocides e.g., as an active ingredient of marine antifouling paints for boats and ships. Since a number of organotin compounds have been demonstrated to be toxic, there is increasing concern that their widespread use may cause adverse effects within environmental and biological systems. Besides carcinogenic and neurotoxic effects, as well as effects on the reproductive system, the most obvious mammalian effects of both various di- and trisubstituted organotins were found on the immune system. Exposure of humans to organotin compounds can take place through consumption of contaminated fish and seafood. In human liver samples, mainly dibutyltin, the metabolite of tributyltin, could be detected indicating that organotin compounds are bioavailable after dietary exposure. The objective of this short review is to present various toxicokinetic aspects of organotin compounds in more detail. While several studies using in vitro systems investigated their metabolism especially by the monooxygenase system, various aspects of absorption, distribution, metabolism, and excretion (ADME) pathways of different organotin compounds were described by data obtained from several studies with laboratory animals. However, most of these studies were not conducted as full ADME studies but dealt only with some of these aspects. Therefore, for definitive conclusions in some cases, additional information is requested. By reviewing and updating the current literature consideration was given preferentially to those organotin compounds which have relevance with respect to human exposure and/or toxicological effects.

A review of pollutants in the sea-surface microlayer (SML): a unique habitat for marine organisms

Boundary layers between different environmental compartments represent critical interfaces for biological, chemical and physical processes. The sea-surface microlayer (uppermost 1-1000 microm layer) forms the boundary layer interface between the atmosphere and ocean. Environmental processes are controlled by the SML, and it is known to play a key role in the global distribution of anthropogenic pollutants. Due to its unique chemical composition, the upper organic film of the SML represents both a sink and a source for a range of pollutants including chlorinated hydrocarbons, organotin compounds, petroleum hydrocarbons, polycyclic aromatic hydrocarbons (PAH) and heavy metals. These pollutants can be enriched in the SML by up to 500 times relative to concentrations occurring in the underlying bulk water column. The SML is also a unique ecosystem, serving as an important habitat for fish eggs and larvae. Concentration ranges and enrichment factors of pollutants in the SML in different areas of the world's oceans have been critically reviewed, together with available toxicity data for marine biota found within the SML. Overall, the SML is highly contaminated in many urban and industrialized areas of the world, resulting in severe ecotoxicological impacts. Such impacts may lead to drastic effects on the marine food web and to fishery recruitment in coastal waters. Studies of the toxicity of fish eggs and larvae exposed to the SML contaminants have shown that the SML in polluted areas leads to significantly higher rates of mortality and abnormality of fish embryos and larvae.

Synthesis, characterization and in vitro antitumor activity of di- and triorganotin derivatives of polyoxa- and biologically relevant carboxylic acids

An overview of the development of anti-tumor organotin derivatives, sometimes as active in vitro as doxorubicin, is presented and discussed. Solubility in water is an important issue, dominating the in vivo testing of compounds with promising in vitro properties. Several water-soluble organotin compounds gave the best in vitro activities. Novel, useful organotin anti-tumor compounds should be designed toward improved water solubility.

Acute and sublethal effects of organotin compounds on aquatic biota: an interpretative literature evaluation

The objectives of this review were to: (1) collect, synthesize, and interpret acute and sublethal organotin toxicity data in both freshwater and estuarine-marine ecosystems; (2) present environmental water column and sediment concentrations of organotin compounds in both freshwater and estuarine-marine systems to facilitate interpretation of toxicity data; and (3) identify deficiencies in available data to recommend areas of future research for assessing ecological effects of organotin compounds in aquatic systems. The following recommendations are suggested: (1) evaluation of the bioavailability of organotin compounds in aquatic systems; (2) assessment of the relationship between physicochemical characteristics of organotin compounds and subsequent toxicity effects on aquatic organisms; (3) determination of organotin effects on food chains; (4) evaluation of the specific mechanisms and modes of toxicity for organotin compounds with aquatic biotia; (5) evaluations of the adaptive responses of aquatic biota to organotins; (6) measurement of organotin concentrations in testing chambers throughout toxicity tests using peer-reviewed analytical techniques (nominal concentrations can provide misleading data); (7) assessment of long-term "low level" exposures of organotin compounds on histological, histochemical, behavioral, and physiological responses of aquatic biota; and (8) toxicity assessment of plasticizer organotin compounds to aquatic biota.

Involvement of the retinoid X receptor in the development of imposex caused by organotins in gastropods

Organotin compounds released from antifouling paints, such as tributyltin (TBT) and triphenyltin (TPT), are potent inducers of imposex (a superimposition of male genital tracts, such as penis and vas deferens, on females) in marine gastropods. Little is known about the induction mechanism of gastropod imposex. Here, we show that organotins bind the human retinoid X receptors (hRXRs) with high affinity and that injection of 9-cis retinoic acid (RA), the natural ligand of hRXRs, into females of the rock shell (Thais clavigera) induces the development of imposex. Cloning of the RXR homologue from T. clavigera revealed that the ligand-binding domain of rock shell RXR was very similar to vertebrate RXR and bound to both 9-cis RA and to organotins. These suggest that RXR plays an important role in inducing the development of imposex, namely, the differentiation and growth of male genital tracts in female gastropods.

Endocrine disrupting chemicals and other substances of concern in food contact materials: an updated review of exposure, effect and risk assessment

Food contact materials (FCM) are an underestimated source of chemical food contaminants and a potentially relevant route of human exposure to endocrine disrupting chemicals (EDCs). Quantifying the exposure of the general population to substances from FCM relies on estimates of food consumption and leaching into food. Recent studies using polycarbonate plastics show that food simulants do not always predict worst-case leaching of bisphenol A, a common FCM substance. Also, exposure of children to FCM substances is not always realistically predicted using the common conventions and thus possibly misjudged. Further, the exposure of the whole population to substances leaching into dry foods is underestimated. Consumers are exposed to low levels of substances from FCM across their entire lives. Effects of these compounds currently are assessed with a focus on mutagenicity and genotoxicity. This approach however neglects integrating recent new toxicological findings, like endocrine disruption, mixture toxicity, and developmental toxicity. According to these new toxicology paradigms women of childbearing age and during pregnancy are a new sensitive population group requiring more attention. Furthermore, in overweight and obese persons a change in the metabolism of xenobiotics is observed, possibly implying that this group of consumers is insufficiently protected by current risk assessment practice. Innovations in FCM risk assessment should therefore include routine testing for EDCs and an assessment of the whole migrate toxicity of a food packaging, taking into account all sensitive population groups. In this article I focus on recent issues of interest concerning either exposure to or effects of FCM-related substances. Further, I review the use of benzophenones and organotins, two groups of known or suspected EDCs, in FCM authorized in the US and EU.

Toxicity of triorganotin compounds: comparative in vivo studies with a series of trialkyltin compounds and triphenyltin chloride in male rats

In 2-week feeding studies, a series of trialkyltin chlorides and triphenyltin chloride were fed to male weanling rats at different dietary concentrations to evaluate their toxic effects, especially on the brains and the lymphoid organs, thymus and spleen. The lower trialkyltin homologs, trimethyltin chloride (TMTC) and triethyltin chloride (TETC), were neurotoxic, causing neuronal degradation and cerebral edema, respectively, at dietary concentrations of 15 ppm. The intermediate homologs, tri-n-propyltin chloride (TPTC) and tri-n-butyltin chloride (TBTC), and the aromatic compound, triphenyltin chloride (TPhTC), caused a dose-related reduction of thymus weight. At a dietary concentration of 150 ppm decreases in thymus weight to 53, 39, and 81% of controls were found following treatment with TPTC, TBTC, and TPhTC, respectively. Microscopically, thymus atrophy was associated with a lymphocyte depletion in the thymic cortex. Only 16% of the total number of nucleated thymocytes could be isolated from rats fed 150 ppm TBTC. These effects were completely reversed within 2 weeks. Slight thymus atrophy was observed after feeding a relatively high dose of 150 mg tri-n-hexyltin chloride (THTC)/kg diet, whereas tri-n-octyltin chloride (TOTC) was ineffective. A dose-related decrease in spleen weight was noticed after 2 weeks feeding of TPTC, TBTC, and TPhTC. Liver weights were increased in rats fed TBTC, THTC, and TPhTC for 2 weeks. Nevertheless, no enlarged livers and normal spleen weights were found upon feeding 100 ppm TPTC or TBTC for 4 weeks, whereas thymus weight was severely decreased. Therefore, atrophy of the thymus was considered to be the predominant effect of the intermediate trialkyltins (TPTC, TBTC). From this study it is concluded that the lower trialkyltins (TMTC, TETC) are essentially neurotoxic, the intermediate trialkytins (TPTC, TBTC) and triphenyltin are primarily immunotoxic, and the higher homologs (THTC, TOTC) are only slightly toxic or not toxic at all.

Case study: bioavailability of tin and tin compounds

This article reviews the literature related to the bioavailability of tin, inorganic tin compounds, and organotin compounds. On the one hand, the toxicity of metallic tin and inorganic tin compounds is low. In aqueous systems, the potential bioavailability of tin seems to depend on the concentration of the truly dissolved ion species. Some studies suggest that tin is an essential trace element for humans. However, organotin compounds have been proven to be of toxicological relevance. Triorganotin compounds are particularly toxic explaining their wide use as biocides (e.g., in antifouling paints or pesticides). Persistence of organotin compounds is governed by moderate to fast aerobic biotic degradation processes, slow anaerobic biotic degradation, slow abiotic degradation by photolysis, and fast, but reversible, adsorption/desorption processes. Organotin compounds are ubiquitously distributed in aquatic organisms. Bioconcentration in organisms and ecotoxicity are dependent on the bioavailable fraction. The bioavailability is highest at neutral and slightly alkaline pH and is reduced in the presence of dissolved organic carbon. The biomagnification of organotin compounds via the food chain is of minor importance compared with the bioconcentration from the water phase.

Tributyltin or triphenyltin inhibits aromatase activity in the human granulosa-like tumor cell line KGN

The superimposition of male sex organs (penis and vas deferens) in a female gastropod, called imposex, is widely attributed to the exposure to tributyltin (TBT) compounds, used world-wide in antifouling paints for ships. It has been hypothesized that the TBT-induced imposex is mediated by an increasing androgen level relative to the estrogen level, namely a decreased conversion of androgens to estrogens (i.e., aromatization). In the present study, we tested this hypothesis by examining the effects of TBT or triphenyltin (TPT) on the aromatase activity in a cultured human granulosa-like tumor cell line, KGN, which was recently established by our group. Treatment with more than 1000 ng/ml TBT compounds was very toxic to the cells and caused immediate cell death within 24 h, while 200 ng/ml was found to cause apoptosis of the cells. Treatment of the KGN cells for more than 48 h with 20 ng/ml TBT or TPT, which is a concentration level reported to cause imposex in marine species, did not affect cell proliferation but significantly suppressed the aromatase activity determined by a [(3)H]H(2)O release assay. Treatment with 20 ng/ml TBT compounds for 7 days also resulted in a reduction of the E2 production from Delta 4-androstenedione stimulated by db-cAMP. The changes in the aromatase activity by TBT compounds were associated with comparable changes in P450arom mRNA assessed by RT-PCR. The luciferase activity of the P450arom promoter II (1 kb) decreased after the addition of 20 ng/ml TBT compounds in transfected KGN cells either in a basic state or in states stimulated by db-cAMP. The Ad4BP-dependent increase in the luciferase activity of P450arom promoter II was also downregulated by such treatments. These results indicate that TBT compounds inhibited the aromatase activity and also decreased the P450arom mRNA level at the transcriptional level in KGN cells. The direct inhibitory effect of TBT compounds on the aromatase activity may therefore partly explain the induction of imposex by these compounds in female species.

Ecotoxicological problems associated with contaminated sites

Contamination sites pose significant environmental hazards for terrestrial and aquatic ecosystems. They are important sources of pollution and may result in ecotoxicological effects. At severely contaminated sites acute effects occur, but the core problem lies in possible long-term chronic effects. Ecotoxicological effects occur at all levels of the biological organization, from the molecular to the ecosystem level. Not only certain organisms may be affected, but the ecosystems as a whole in its function and structure. Contaminants at large contaminated sites often share critical properties such as toxicity, high environmental persistence, often high mobility prone to contamination of groundwater, and high lipophilicity resulting in bioaccumulation in food webs. Contaminants present at polluted sites occur as mixtures; therefore, interactions between individual compounds may be of importance. The bioavailability is a key factor responsible for ecotoxicological effects of contaminants: only the bioavailable fraction induces ecotoxicological effects, as shown for organotin compounds. Organotins belong to the most toxic pollutants known so far for aquatic life. Widespread contamination of harbor sediments occurs globally due to the ongoing use of organotins in antifouling paints on large ships. In lake sediments, tributyl- and triphenyltin are very persistent and bioavailable to biota even after a long time. The bioavailability of organotins is dependent on the pH and the content of organic matter. Organotins accumulate in sediments, but remobilization occurs during disturbance and dredging. A key question in dealing with contaminated sites is whether, and to what extent ecotoxicity occurs. Usually, established OECD tests and whole effluent toxicity tests are performed for an ecotoxicological evaluation and for risk assessment. However, these assays are often expensive, laborious and sometimes not sensitive enough. As a consequence, we have used rapid and inexpensive in vitro systems such as fish cell lines for the evaluation of sediments and landfill leachates, which were contaminated by polycyclic aromatic hydrocarbons (PAHs). The determination of cytotoxicity as a measure for acute toxicity, and the induction of cytochrome P4501A (CYP1A) as a biomarker of exposure and effects were found to be important measures, which can be used for hazard and risk assessment. We have developed a concept for the ecotoxicological evaluation of PAH contamination based on induction equivalents, which can be applied for aquatic and terrestrial ecosystems. One of the key question and present gaps, however, includes the long-term chronic ecotoxicological effects of single compounds and mixtures on soil and aquatic biota at contaminated sites. This should be addressed in the future.

Organotins induce apoptosis by disturbance of [Ca(2+)](i) and mitochondrial activity, causing oxidative stress and activation of caspases in rat thymocytes

Di-n-butyltin dichloride (DBTC) and tri-n-butyltin chloride (TBTC) cause thymus atrophy in rodents. At low doses, antiproliferative modes of action have been shown to be involved, whereas at higher doses apoptosis seems to be the mechanism of thymotoxicity by these chemicals. In vitro, a similar concentration-dependency has been observed. The purpose of the present research was to investigate the mechanisms underlying DNA fragmentation induced by these organotin compounds in freshly isolated rat thymocytes. As previously shown for TBTC, DBTC is also able to significantly increase intracellular Ca(2+) level ([Ca(2+)](i)). The rise in [Ca(2+)](i), already evident 5 min after treatment, was followed by a dose- and time-dependent generation of reactive oxygen species (ROS) at the mitochondrial level. Simultaneously, organotins induced the release of cytochrome c from the mitochondrial membrane into the cytosol. ROS production and the release of cytochrome c were reduced by BAPTA, an intracellular Ca(2+) chelator, or rotenone, an inhibitor of the electron entry from complex I to ubiquinone, indicating the important role of Ca(2+) and mitochondria during these early intracellular events. Furthermore, we demonstrated that rotenone prevents apoptosis induced by 3 microM DBTC or TBTC and, in addition, that both BAPTA and Z-DEVD FMK (mainly a caspase-3 inhibitor) decreased apoptosis by DBTC (already shown for TBTC). Taken together these data show the apoptotic pathway followed by organotin compounds starts with an increase of [Ca(2+)](i), then continues with release of ROS and cytochrome c from mitochondria, activation of caspases, and finally results in DNA fragmentation.

Reproductive inhibition and transgenerational toxicity of triphenyltin on medaka (Oiyzias latipes) at environmentally relevant levels

An increasing number of studies have reported unexpectedly high body burdens of triphenyltin (TPT) in wild fishes around the world. To assess the effects of TPT on fish, we exposed pairs of medaka (Oryzias latipes) to different levels of TPT for 5 weeks, and the reproduction responses and transgenerational effects were studied. The results demonstrated that TPT exposure markedly suppressed the spawning frequency, spawned egg number, egg quality and gonad development, and induced teratogenesis, such as hemorrhaging, eye defects, morphological malformation and conjoined twins, less hatchability, and swim-up failure in the F1 generation, thereby resulting in a significant decrease in the capacity to produce viable offspring (p < 0.01). The residual TPT levels in the exposure fish are in the range of 6.52 +/- 0.56 to 5595 +/- 1016 ng of TPT/g of wet weight, similar to those reported in wild fish around the world, indicating TPT contamination in the real world would have a significant adverse effect on the health of fish population. Down-regulation of vitellogenin (VTG) genes in the female of the TPT exposure groups was recognized as a cause for the decreased fecundity. Expressions of VEGFs and PAX6 associated with vascular or ocular development respectively, were measured in hemorrhaging and eye defects embryos and showed good correlations with response outcomes.

Toxicity and health effects of selected organotin compounds: a review

The toxicity of selected tin compounds is reviewed. Over the years, a variety of uses has been found for organic and inorganic tin compounds, as fungicides, as stablizers in plastics, moluscicides, and miticides; they have also been suggested as insect chemosterilants and for other industrial uses. Many of these products are unpalatable when mixed into diets and have been suggested as rodent repellents. Inhaling tin as dust or fumes may cause a benign pneumoconiosis in exposed workers. The organotin compounds can be divided into alkyltin and aryltin compounds. The trimethyl and triethyltin compounds are well absorbed from the gastrointestinal tract and are the most toxic in this group. Triethyltin particularly produces status spongiosus of the white matter of the central nervous system. Most of the other alkyl and aryl tin compounds are poorly absorbed from the gastrointestinal tract, and are less toxic when given orally than when given parentally. Only one compound, tricyclohexyltin hydroxide, is now registered by the Environmental Protection Agency as a miticide. This product produces skin irritation in rabbits. Studies should be conducted to determine whether it causes contact dermatitis in humans.

Biomarkers inRuditapes decussatus: a potential bioindicator species

The clam Ruditapes decussatus is distributed worldwide and due to its ecological and economical interest has been proposed as a bioindicator in areas where mussels are not available. The accumulation of several anthropogenic compounds in their tissues suggests that they possess mechanisms that allow them to cope with the toxic effects of these contaminants. Besides pollutant uptake, the use of biomarkers is pointed out in this paper since it is a promising approach to monitor the effect of these contaminants in the marine environment. Biomarkers complement the information of the direct chemical characterization of different types of contaminants. Therefore, the aim of this paper is to review the role of several biomarkers: (metallothioneins (MT), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx) (total and selenium-dependent), lipid peroxidation (measured as MDA, one of the final products of lipid peroxidation), glutathione S-transferase (GST) and acetylcholinesterase (AChE), measured in different tissues of the clam R. decussatus, in laboratory conditions and under various environmental stresses, in two ecosystems (Ria Formosa lagoon- Portugal) and Bizerta lagoon (Tunisia) in a perspective of a multibiomarker approach to assess environmental changes. Experiment and field studies are in good agreement since MT levels, especially in the gills, the first target tissue of these contaminants, can be used as biomarker of exposure to Cd. GPx and MDA may also be determined in this respect. AChE activity is inhibited by pesticide and, to a less extent, by metal exposure in the gills and whole soft body of clams. However, the induction of GST isoforms experimentally demonstrated is not observed in the field because only global GST activity was determined. The whole set of results opens new research perspectives for the use of this species to assess the effect of mixtures of pollutants in the aquatic environment.

Dibutyltin and tributyltin compounds induce thymus atrophy in rats due to a selective action on thymic lymphoblasts

Di-n-butyltin dichloride (DBTC) or tri-n-butyltin chloride (TBTC) given in the diets of rats have previously been shown to cause atrophy of the thymus and subsequently suppression of the T-cell-dependent immune responses. To study the mechanism of the immunotoxic effects, the dose-effect relationships and the kinetics of the thymus atrophy caused by DBTC and TBTC were investigated in detail. A single oral dose of DBTC or TBTC to rats induced a dose-related reduction of relative thymus weight, which was maximal 4 days after intubation. The log dose-effect relationships for both compounds were linear and ran parallel over a dose range of 5-60 mg/kg. Dose levels calculated to cause 50% reduction of relative thymus weight were 18 mg DBTC and 29 mg TBTC per kg body wt. A single oral dose of mono-n-butyltin trichloride (MBTC), however, did not cause thymus atrophy at dose levels up to 180 mg/kg. The kinetics of the dibutyltin- and tributyltin-induced thymus atrophy in rats were investigated by measuring thymus weight, total thymic cell count, number of small, intermediate and large cells and the incorporation of DNA, RNA and protein precursors into isolated thymocytes during a period of 9 days after a single oral dose. DBTC and TBTC caused atrophy of the thymus due to a selective reduction in the number of rapidly proliferating lymphoblasts in the first 2 days after dosing. As a consequence the large pool of small lymphocytes declined in the following 2 days. On the fourth day, when atrophy was most pronounced, the frequency of the lymphoblasts increased above the controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Ecotoxicological effects at contaminated sites

Contamination sites pose significant environmental hazards for terrestrial and aquatic ecosystems. They are important sources of pollution and may result in ecotoxicological effects on terrestrial, groundwater and aquatic ecosystems. At severely contaminated sites, acute effects occur, but the core problem lies in long-term chronic effects. Ecotoxicological effects occur at all levels of biological organization, from the molecular to the ecosystem level. Not only certain organisms may be affected, but the ecosystems as a whole, both terrestrial and aquatic, in its function and structure. Contaminants at large contaminated sites often share critical properties such as high acute and/or chronic toxicity, high environmental persistence, often high mobility leading to contamination of groundwater, and high lipophilicity leading to bioaccumulation in food webs. Contaminants present at polluted sites occur as mixtures, therefore interactions between individual compounds are of importance. The bioavailability is a key factor for ecotoxicological effects of contaminants. This is demonstrated by a case study on organotins. Organotins belong to the most toxic pollutants known so far for aquatic life. Widespread contamination of harbor sediments occurs globally due to the ongoing use of organotins in antifouling paints in large ships. In lake sediments, tributyl- and triphenyltin are very persistent and bioavailable to biota even after a long time. Bioavailability of these compounds is dependent on pH and organic matter. Organotins are accumulated in sediments, but remobilization occurs when contaminated sediments are disturbed and dredged. A key question in dealing with contaminated sites is the assessment and evaluation of the toxicity of contaminants to the environment. Usually, established OECD tests and whole effluent toxicity tests are performed for an ecotoxicological evaluation and for hazard assessment. However, these assays are often expensive, laborious and sometimes not sensitive enough. As a consequence, we have used fast and reliable in vitro systems such as fish cell lines for the evaluation of sediments and landfill leachates contaminated by polychlorinated hydrocarbons (PAH). Determination of cytotoxicity as a measure for acute toxicity, and induction of cytochrome P4501A (CYP1A) as a biomarker of exposure and toxicity were found to be important measures, which can be used for hazard and risk assessment. We have developed a concept for the ecotoxicological evaluation of PAH contamination based on induction equivalents, which can be applied for aquatic and terrestrial ecosystems. One of the key question and present gaps, however, includes the long-term chronic ecotoxicological effects on soil and aquatic biota, which are largely unknown.

The ion channel of F-ATP synthase is the target of toxic organotin compounds

ATP is the universal energy currency of living cells, and the majority of it is synthesized by the F1F0 ATP synthase. Inhibitors of this enzyme are therefore potentially detrimental for all life forms. Tributyltin chloride (TBT-Cl) inhibits ATP hydrolysis by the Na(+)-translocating ATP synthase of Ilyobacter tartaricus or the H(+)-translocating counterpart of Escherichia coli with apparent Ki of 200 nM. To target the site of this inhibition, we synthesized a tritium-labeled derivative of TBT-Cl in which one of the butyl groups was replaced by a photoactivatable aryldiazirine residue. Upon illumination, subunit a of the ATP synthase becomes specifically modified, and this labeling is suppressed in the presence of the original inhibitor. In case of the Na+ ATP synthase, labeling is also suppressed in the presence of Na+ ions, suggesting an interference in Na+ or TBT-Cl binding to subunit a. This interference is corroborated by the protection of ATP hydrolysis from TBT-Cl inhibition by 105 mM Na+. TBT-Cl strongly inhibits Na+ exchange by the reconstituted I. tartaricus ATP synthase. Taken together these results indicate that the subunit a ion channel is the target site for ATPase inhibition by toxic organotin compounds. An inhibitor interacting specifically with this site has not been reported previously.

Effects of organotin compounds on pubertal male rats

Tributyltin (TBT) and triphenyltin (TPT) induce effects in male and female reproductive organs of rodents. They also cause tumors in these organs and it is theorized that they result from endocrine disruption. We studied the effects of 40 mg methyltestosterone (MTT), 0.5 or 15 mg TBT and 2, 6 or 12 mg TPT/kg bw on the male sexual development using a modification of the Rodent 20-Day Thyroid/Pubertal Male Assay. Male Wistar rats were treated per gavage for 30 days beginning at 23 days of age. A delay in the completion of preputial separation was observed after administration of MTT and 15 mg/kg TBT. Changes in weights of one or more reproductive organs were observed in all treatment groups. Testosterone concentration was decreased in the MTT, the 15 mg TBT as well as in the 6 and 12 mg TPT groups. A decrease in luteinizing hormone (LH) concentration was observed in the MTT and 15 mg TBT groups while an increase was seen after exposure to 6 mg TPT/kg bw. We conclude that peripubertal exposure to 15 mg TBT and 6 mg TPT/kg bw clearly affected male sexual development.