Tributyltin exposure causes lipotoxicity responses in the ovaries of rockfish, Sebastiscus marmoratus

Delineating lipidomic landscapes in human and mouse ovaries: Spatial signatures and chemically-induced alterations via MALDI mass spectrometry imaging: Spatial ovarian lipidomics

This study addresses the critical gap in understanding the ovarian lipidome's abundance, distribution, and vulnerability to environmental disruptors, a largely unexplored field. Leveraging the capabilities of matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI), we embarked on a novel exploration of the ovarian lipidome in both mouse and human healthy tissues. Our findings revealed that the obesogenic chemical tributyltin (TBT), at environmentally relevant exposures, exerts a profound and region-specific impact on the mouse ovarian lipidome. TBT exposure predominantly affects lipid species in antral follicles and oocytes, suggesting a targeted disruption of lipid homeostasis in these biologically relevant regions. Our comprehensive approach, integrating advanced lipidomic techniques and bioinformatic analyses, documented the disruptive effects of TBT, an environmental chemical, on the ovarian lipid landscape. Similar to mice, our research also unveiled distinct spatial lipidomic signatures corresponding to specific ovarian compartments in a healthy human ovary that may also be vulnerable to disruption by chemical exposures. Findings from this study not only underscore the vulnerability of the ovarian lipidome to environmental factors but also lay the groundwork for unraveling the molecular pathways underlying ovarian toxicity mediated through lipid dysregulation.

Long-term tributyltin exposure alters behavior, oocyte maturation, and histomorphology of the ovary due to oxidative stress in adult zebrafish

Tributyltin (TBT), an organotin endocrine-disrupting substance, is recognized as one of the important toxic environmental pollutants. The present study was carried out to investigate the toxic effects of TBT on behavior and the ovary of adult zebrafish with a focus on oxidative stress markers and oocyte maturation. Adult zebrafish were exposed to three different concentrations (125, 250, and 500 ng/L of water) of TBT for 28 days. TBT exposure produced a concentration-dependent negative effect on the body weight and behavior (anxiety-like symptoms) of adult zebrafish. Alterations in the activity of superoxide dismutase (SOD) and catalase (CAT), the total antioxidant capacity of ovarian tissue by the highest exposure level of TBT resulted in lipid peroxidation as indicated by increased malondialdehyde (MDA) level. The numbers of early-vitellogenic oocytes were significantly increased in zebrafish exposed to TBT as low as 125 ng/L. However, the numbers and size of fully-grown (mature) oocytes were significantly reduced in the highest exposure group only. Correlation between the MDA level and pre-vitellogenic oocytes in the 500 ng/L group indicated that lipid peroxidation prevented the maturation of pre-vitellogenic oocytes. TBT exposure produced significant histological changes in the ovary as evidenced by disturbed maturation of oocytes. In conclusion, TBT adversely affected the maturation of oocytes in zebrafish ovary through oxidative stress-mediated mechanisms.

Evaluation of Lipids and Lipid-Related Transcripts in Human and Ovine Theca Cells and an in Vitro Mouse Model Exposed to the Obesogen Chemical Tributyltin

BACKGROUND

Exposure to obesogenic chemicals has been reported to result in enhanced adipogenesis, higher adipose tissue accumulation, and reduced ovarian hormonal synthesis and follicular function. We have reported that organotins [tributyltin (TBT) and triphenyltin (TPT)] dysregulate cholesterol trafficking in ovarian theca cells, but, whether organotins also exert lipogenic effects on ovarian cells remains unexplored.

OBJECTIVE

We investigated if environmentally relevant exposures to organotins [TBT, TPT, or dibutyltin (DBT)] induce lipid dysregulation in ovarian theca cells and the role of the liver X receptor (LXR) in this effect. We also tested the effect of TBT on oocyte maturation and neutral lipid accumulation, and lipid-related transcript expression in cumulus cells and preimplantation embryos.

METHODS

Primary theca cell cultures derived from human and ovine ovaries were exposed to TBT, TPT, or DBT (1, 10, or 50   ng / ml ). The effect of these chemical exposures on neutral lipid accumulation, lipid abundance and composition, lipid homeostasis-related gene expression, and cytokine secretion was evaluated using liquid chromatography-mass spectrometry (LC-MS), inhibitor-based methods, cytokine secretion, and lipid ontology analyses. We also exposed murine cumulus-oocyte complexes to TBT and evaluated oocyte maturation, embryo development, and lipid homeostasis-related mRNA expression in cumulus cells and blastocysts.

RESULTS

Exposure to TBT resulted in higher intracellular neutral lipids in human and ovine primary theca cells. In ovine theca cells, this effect was dose-dependent, independent of cell stage, and partially mediated by LXR. DBT and TPT resulted in higher intracellular neutral lipids but to a lesser extent in comparison with TBT. More than 140 lipids and 9 cytokines were dysregulated in TBT-exposed human theca cells. Expression of genes involved in lipogenesis and fatty acid synthesis were higher in theca cells, as well as in cumulus cells and blastocysts exposed to TBT. However, TBT did not impact the rates of oocyte maturation or blastocyst development.

DISCUSSION

TBT induced dyslipidemia in primary human and ovine theca cells, which may be responsible for some of the TBT-induced fertility dysregulations reported in rodent models of TBT exposure. https://doi.org/10.1289/EHP13955.

Embryonic exposure to environmentally relevant levels of tributyltin affects embryonic tributyltin bioaccumulation and the physiological responses of juveniles in cuttlefish (Sepia pharaonis)

Tributyltin (TBT) is a typical organic pollutant that persists in aquatic sediments due to its wide usage as an antifouling fungicide during the past few decades. Despite increased awareness of the serious negative consequences of TBT on aquatic species, studies on the effects of TBT exposure on cephalopod embryonic development and juvenile physiological performance are scarce. To investigate the lasting effects of TBT toxicity on Sepia pharaonis from embryo to hatchling, embryos (gastrula stage, 3-5 h post fertilization) were exposed to four levels of TBT until hatching: 0 (control), 30 (environmental level), 60, and 120 ng/L. Subsequently, juvenile growth performance endpoints and behavioral alterations were assessed over 15 days post-hatching. Egg hatchability was significantly reduced and embryonic development (i.e., premature hatching) was accelerated in response to 30 ng/L TBT exposure. Meanwhile, TBT-induced alterations in embryonic morphology primarily included yolk-sac lysis, embryonic malformations, and uneven pigment distributions. During the pre-middle stage of embryonic development, the eggshell serves as an effective barrier to safeguard the embryo from exposure to 30-60 ng/L TBT, according to patterns of TBT accumulation and distribution in the egg compartment. However, even environmental relevant levels of TBT (30 ng/L) exposure during embryonic development had a negative impact on juvenile behavior and growth, including slowing growth, shortening eating times, causing more irregular movements, and increasing inking times. These findings indicate that after TBT exposure, negative long-lasting effects on S. pharaonis development from embryo to hatchling persist, suggesting that long-lasting toxic effects endure from S. pharaonis embryos to hatchlings.

Toxicity of tributyltin to the European flat oyster Ostrea edulis: Metabolomic responses indicate impacts to energy metabolism, biochemical composition and reproductive maturation

Tri-Butyl Tin (TBT) remains as a legacy pollutant in the benthic environments. Although the toxic impacts and endocrine disruption caused by TBT to gastropod molluscs have been established, the changes in energy reserves allocated to maintenance, growth, reproduction and survival of European oysters Ostrea edulis, a target species of concerted benthic habitat restoration projects, have not been explored. This study was designed to evaluate the effect of TBT chloride (TBTCl) on potential ions and relevant metabolomic pathways and its association with changes in physiological, biochemical and reproductive parameters in O. edulis exposed to environmental relevant concentrations of TBTCl. Oysters were exposed to TBTCl 20 ng/L (n = 30), 200 ng/L (n = 30) and 2000 ng/L (n = 30) for nine weeks. At the end of the exposure, gametogenic stage, sex, energy reserve content and metabolomic profiling analysis were conducted to elucidate the metabolic alterations that occur in individuals exposed to those compounds. Metabolite analysis showed significant changes in the digestive gland biochemistry in oysters exposed to TBTCl, decreasing tissue ATP concentrations through a combination of the disruption of the TCA cycle and other important molecular pathways involved in homeostasis, mitochondrial metabolism and antioxidant response. TBTCl exposure increased mortality and caused changes in the gametogenesis with cycle arrest in stages G0 and G1. Sex determination was affected by TBTCl exposure, increasing the proportion of oysters identified as males in O. edulis treated at 20ng/l TBTCl, and with an increased proportion of inactive stages in oysters treated with 2000 ng/l TBTCl. The presence and persistence of environmental pollutants, such as TBT, could represent an additional threat to the declining O. edulis populations and related taxa around the world, by increasing mortality, changing reproductive maturation, and disrupting metabolism. Our findings identify the need to consider additional factors (e.g. legacy pollution) when identifying coastal locations for shellfish restoration.

Tributyltin exposure disrupted the locomotor activity rhythms in adult zebrafish (Danio rerio) and the mechanism involved

The fish circadian rhythm system might be an emerging target of tributyltin (TBT), however, the mechanism by which TBT interferes with the circadian rhythm is poorly understood. Therefore, in the present study, zebrafish were used to assess the effects of TBT at environmental concentrations (1 and 10 ng/L) on locomotor activity rhythm. Furthermore, we focused on the visual system to explore the potential mechanism involved. After 90 d of exposure, TBT disturbed the locomotor activity rhythms in zebrafish, which manifested as: (1) low activities and lethargy during the arousing period; (2) inability to fall asleep quickly and peacefully during the period of latency to sleep; and (3) no regular "waves" of locomotor activities during the active period. After TBT exposure, the histological structure of the eyes significantly changed, the boundary between layers became blurred, and the melanin concentrations significantly decreased. Using KEGG and GSEA pathway analyses, the differentially expressed genes in the eyes screened by transcriptomics were significantly enriched in the tyrosine metabolism pathway and retinol metabolism pathway. Furthermore, a decrease in melanin and disruption of retinoic acid were found after TBT exposure, which would affect the reception of phototransduction, and then interfere with the circadian rhythm in fish. The disruption of the circadian rhythm of fish by aquatic pollutants would decrease their ecological adaptability, which should be considered in future research.

Harbours as unique environmental sites of multiple anthropogenic stressors on fish hormonal systems

Fish development and acclimation to environmental conditions are strongly mediated by the hormonal endocrine system. In environments contaminated by anthropogenic stressors, hormonal pathway alterations can be detrimental for growth, survival, fitness, and at a larger scale for population maintenance. In the context of increasingly contaminated marine environments worldwide, numerous laboratory studies have confirmed the effect of one or a combination of pollutants on fish hormonal systems. However, this has not been confirmed in situ. In this review, we explore the body of knowledge related to the influence of anthropogenic stressors disrupting fish endocrine systems, recent advances (focusing on thyroid hormones and stress hormones such as cortisol), and potential research perspectives. Through this review, we highlight how harbours can be used as "in situ laboratories" given the variety of anthropogenic stressors (such as plastic, chemical, sound, light pollution, and invasive species) that can be simultaneously investigated in harbours over long periods of time.

The ecotoxicology of marine tributyltin (TBT) hotspots: A review

Tributyltin (TBT) was widely used as a highly efficient biocide in antifouling paints for ship and boat hulls. Eventually, TBT containing paints became globally banned when TBT was found to cause widespread contamination and non-target adverse effects in sensitive species, with induced pseudohermaphroditism in female neogastropods (imposex) being the best-known example. In this review, we address the history and the status of knowledge regarding TBT pollution and marine TBT hotspots, with a special emphasis on the Norwegian coastline. The review also presents a brief update on knowledge of TBT toxicity in various marine species and humans, highlighting the current understanding of toxicity mechanisms relevant for causing endocrine disruption in marine species. Despite observations of reduced TBT sediment concentrations in many marine sediments over the recent decades, contaminant hotspots are still prevalent worldwide. Consequently, efforts to monitor TBT levels and assessment of potential effects in sentinel species being potentially susceptible to TBT in these locations are still highly warranted.

Solid-state 1H NMR-based metabolomics assessment of tributylin effects in zebrafish bone

Tributyltin (TBT), an endocrine disruptor is used globally in agribusiness and industries as biocides, heat stabilizers, and in chemical catalysis. It is known for its deleterious effects on bone by negatively impacting the functions of osteoblasts, osteoclasts and mesenchymal stem cells. However, the impact of TBT on the metabolomics profile in bone is not yet studied. Here, we demonstrate alterations in chemical metabolomics profiles measured by solid state ¹H nuclear magnetic resonance (¹H NMR) spectroscopy in zebrafish bone following tributyltin (TBT) treatment. TBT of 0, 100, 200, 300, 400 and 500 μg/L were exposed to zebrafish. From this, zebrafish bone has subjected for further metabolomics profiling. Samples were measured via one-dimensional (1D) solvent -suppressed and T₂- filtered methods with in vivo zebrafish metabolites. A dose dependent alteration in the metabolomics profile was observed and results indicated a disturbed aminoacid metabolism, TCA cycle, and glycolysis. We found a significant alteration in the levels of glutamate, glutamine, glutathione, trimethylamine N-oxide (TMAO), and other metabolites. This investigation hints us the deleterious effects of TBT on zebrafish bone enabling a comprehensive understanding of metabolomics profile and is expected to play a crucial role in understanding the deleterious effects of various endocrine disruptor on bone.

Effects of tributyltin on gonad and brood pouch development of male pregnant lined seahorse (Hippocampus erectus) at environmentally relevant concentrations

The male pregnancy of seahorses is unique, but their reproductive response to environmental disturbances has not yet been clarified. Tributyltin (TBT) is known to have an endocrine disrupting effect on the reproductive system of coastal marine organisms. This study evaluated the potential effects of exposure to environmentally relevant concentrations of TBT on the development of gonads and brood pouch of the lined seahorse (Hippocampus erectus). Physiological, histological, and transcriptional analyses were conducted, and results showed that high levels of TBT bioaccumulation occurred in male and female seahorses. TBT led to ovarian follicular atresia and apoptosis with the elevation of androgen levels, accompanied by the induction of genes associated with lysosomes and autophagosomes. Comparative transcriptional analyses revealed the likely inhibition of spermatogenesis via the suppression of cyclic AMP and androgen synthesis. Notably, the transcriptional profiles showed that TBT potentially affects the immune system, angiogenesis, and embryo nourishment of the brood pouch, which indicates that it has negative effects on the male reproductive system of seahorses. In summary, this study reveals that environmental levels of TBT potentially affect the reproductive efficiency of seahorses, and may ultimately lead to a reduction in their populations in coastal environments.

Developing and applying a classification system for ranking the biological effects of endocrine disrupting chemicals on male rockfish Sebastiscus marmoratus in the Maowei Sea, China

Endocrine disrupting compounds (EDCs) in marine environments has become a major environmental concern. Nonetheless, the biological effects of EDCs on organisms in coastal environments remain poorly characterized. In this study, biomonitoring of EDCs in male fish Sebastiscus marmoratus was carried out in the Maowei Sea, China. The results showed that the concentration of 4-nonylphenol (4-NP) was below the detection limit, the concentrations of 4-tert-octylphenol (4-t-OP) and bisphenol A (BPA) in seawater were moderate compared with those in other global regions, and the possible sources are the municipal wastewater discharge. Nested ANOVA analyses suggest significant differences of the brain aromatase activities and plasma vitellogenin (VTG) expression between the port area and the oyster farming area. A new fish expert system (FES) was developed for evaluating the biological effects of EDCs on fish. Our findings show that the FES is a potential tool to evaluate the biological effects of marine pollutants.

Mechanisms involved in tributyltin-enhanced aggressive behaviors and fear responses in male zebrafish

Tributyltin (TBT), an aromatase inhibitor, has been found to disrupt gametogenesis and reproductive behavior in several fish species. However, whether TBT is capable of affecting other behaviors such as aggressive behavior and fear response in fish and the underlying mode(s) of action remain unclear. To study aggressive behavior, adult zebrafish (Danio rerio) males were continuously exposed to two nominal concentrations of TBT (TBT-low, 100 ng/L and TBT-high, 500 ng/L) for 28 days. To study the fear response, the fish were divided into four groups (Blank and Control, 0 ng/L TBT; TBT-low, 100 ng/L; and TBT-high, 500 ng/L). The fish were then treated with DW (Blank) or with alarm substance (AS) (Control, TBT-low and TBT-high). After exposure, the aggressive behavior of the fish was tested using the mirror test (mirror-biting frequency, approaches to the mirror and duration in approach zone).and fighting test (fish-biting frequency) The mirror-biting frequency, approaches to the mirror, duration in approach zone and fish-biting frequency of the TBT-exposed fish increased significantly compared to those of the control fish, indicating enhanced aggressive behavior. The fear response parameters tested using the novel tank dive test (onset time to the higher half, total duration in the lower half and the frequency of turning) of the TBT-exposed fish were also significantly increased after AS administration, suggesting an enhanced fear response. Further investigation revealed that TBT treatment elevated the plasma level of 11-ketotestosterone (11-KT) and decreased the plasma level of estradiol (E2) in a concentration-dependent manner. Moreover, TBT up-regulated the mRNA levels of ar, c-fos and bdnf1, and suppressed the expression of btg-2 in fish. In addition, exposure to AS increased the plasma level of cortisol and down-regulated the mRNA expression levels of genes involved in 5-HT synthesis (such as tph1b and pet1) in both control and TBT-treated fish. AS significantly suppressed the mRNA level of tph1b, tph2, pet1 and npy in the TBT-high group compared to the control fish. The present study demonstrates that TBT enhances aggressive behavior and fear responses in male zebrafish probably through altering plasma levels of 11-KT, E2 and cortisol and altering the expression of genes involved in the regulation of aggressive behavior (ar, c-fos, bdnf1 and btg-2) and fear responses (tph1b, tph2, pet1 and npy). The present study greatly extends our understanding of the behavioral toxicity of TBT to fish.

Overcoming environmental problems of biocides: Synthetic bile acid derivatives as a sustainable alternative

Marine biofouling represents a global economic and ecological challenge. Some marine organisms produce bioactive metabolites, such as steroids, that inhibit the settlement and growth of fouling organisms. The aim of this work was to explore bile acids as a new scaffold with antifouling (AF) activity by using chemical synthesis to produce a series of bile acid derivatives with optimized AF performance and understand their structure-activity relationships. Seven bile acid derivatives were successfully synthesized in moderate to high yields, and their structures were elucidated through spectroscopic methods. Their AF activities were tested against both macro- and microfouling communities. The most potent bile acid against the settlement of Mytilus galloprovincialis larvae was the methyl ester derivative of cholic acid (10), which showed an EC₅₀ of 3.7 μM and an LC₅₀/EC₅₀ > 50 (LC₅₀ > 200 μM) in AF effectiveness vs toxicity studies. Two derivatives of deoxycholic acid (5 and 7) potently inhibited the growth of biofilm-forming marine bacteria with EC₅₀ values < 10 μM, and five bile acids (1, 5, and 7-9) potently inhibited the growth of diatoms, showing EC₅₀ values between 3 and 10 μM. Promising AF profiles were achieved with some of the synthesized bile acids by combining antimacrofouling and antimicrofouling activities. Initial studies on the incorporation of one of these promising bile acid derivatives in polymeric coatings, such as a marine paint, demonstrated the ability of these compounds to generate coatings with antimacrofouling activity.

Antimicrobial activity and mechanisms of multiple antimicrobial peptides isolated from rockfish Sebastiscus marmoratus

Pathogenic disease is a major factor affecting the aquaculture of the rockfish Sebastiscus marmoratus, an important commercial species inhabiting the nearshore waters of the Western Pacific Ocean. Antimicrobial peptides (AMPs), as critical components of innate immunity, have been considered as promising antibiotic substitutes. The aims of this study were 1) to identify major AMPs in the rockfish, 2) to assess their antimicrobial activity and 3) to evaluate their potential therapeutic application. Six AMPs were identified, Hepcidin 1, liver-expressed antimicrobial peptide 2 (LEAP-2), Piscidin, Moronecidin, NK-lysin and β-defensin through analysis of the liver transcriptome of S. marmoratus. The transcriptional expression profiles of these AMPs were investigated by real-time quantitative PCR (RT-qPCR). These AMPs showed tissue-specific distribution patterns, and S. marmoratus displays a time-, dose- and tissue-dependent expression of AMPs in response to lipopolysaccharide (LPS) challenge. While the synthetic peptides of LEAP-2 and Moronecidin exerted broad-spectrum antimicrobial activity against important aquatic pathogens in vitro by directly disrupting microbial membrane, and no cytotoxicity against murine hepatic cells was observed at the effective concentrations from 5 μM to 40 μM. The existence of multiple AMPs and their distinct tissue distribution patterns and inducible expression patterns suggests a sophisticated, highly redundant, and multilevel network of antimicrobial defensive mechanisms of S. marmoratus. Therefore, S. marmoratus-derived AMPs appear to be potential therapeutic applications against pathogen infections in aquaculture.

Triphenyltin exposure affects mating behaviors and attractiveness to females during mating in male guppies (Poecilia reticulata)

The impacts of triphenyltin (TPT) on ecological health have been of great concern due to their widespread use and ubiquity in aquatic ecosystems. However, little is known about the effects of TPT on the reproductive behaviors of fishes. Therefore, the present study was conducted to investigate the effects of TPT at environmentally relevant concentrations (0, 1 and 10 ng Sn/L) on the mating behaviors and the attractiveness to females during mating in male guppies (Poecilia reticulata). The results showed that TPT exposure disturbed the mating behaviors; the TPT-exposed male fish performed more sneaking attempts, but no changes in sigmoid courtship were displayed. The increases in sneaking attempts might be related to increases in testosterone levels induced by TPT exposure. In the context of a competing male, the TPT-exposed males were less attractive to females during mating. The decreases in attractiveness might be related to decreases in carotenoid-based coloration, shown as decreases in caudal fin redness values and skin carotenoid contents. In addition, TPT-induced total antioxidant capacities, the activities of superoxide dismutase and catalase, and the contents of malondialdehyde in liver and intestinal tissues indicated increases in oxidative stress. Both oxidative stress and coloration are linked to carotenoids. Thus, we speculated that the TPT-exposed males might use carotenoids to cope with increases in oxidative stress at the expense of carotenoid-based coloration. The disruption of mating behaviors and the decrease in attractiveness to females in male fish could result in reproductive failure. The present study underscores the importance of using behavioral tests as a sensitive tool in assessing the impact of pollutants present in aquatic environments.

Evolutionary Exploitation of Vertebrate Peroxisome Proliferator-Activated Receptor γ by Organotins

Globally persistent man-made chemicals display ever-growing ecosystemic consequences, a hallmark of the Anthropocene epoch. In this context, the assessment of how lineage-specific gene repertoires influence organism sensitivity toward endocrine disruptors is a central question in toxicology. A striking example highlights the role of a group of compounds known as obesogens. In mammals, most examples involve the modulation of the nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ). To address the structural and biological determinants of PPARγ exploitation by a model obesogen, tributyltin (TBT), in chordates, we employed comparative genomics, transactivation and ligand binding assays, homology modeling, and site-directed-mutagenesis. We show that the emergence of multiple PPARs (α, β and γ) in vertebrate ancestry coincides with the acquisition of TBT agonist affinity, as can be deduced from the conserved transactivation and binding affinity of the chondrichthyan and mammalian PPARγ. The amphioxus single-copy PPAR is irresponsive to TBT; as well as the investigated teleosts, this is a probable consequence of a specific mutational remodeling of the ligand binding pocket. Our findings endorse the modulatory ability of man-made chemicals and suggest an evolutionarily diverse setting, with impacts for environmental risk assessment.

Insight into the endocrine disrupting effect and cell response to butyltin compounds in H295R cell: Evaluated with proteomics and bioinformatics analysis

The widespread use of organotin compounds (OTs) as biocides in antifouling paints and agricultural applications poses a serious threat to the ecosystem and humans. Butyltin compounds (BTs), especially tributyltin (TBT), are considered to be endocrine disrupting chemicals in marine organisms. The underlying mechanism of disrupting effects on mammals, however, has not been sufficiently investigated. To determine the effect and action of these biocides, the present study evaluated the effects of BTs on human adrenocortical carcinoma cells (H295R) with a focus on endocrine disrupting effect. Two-dimensional electrophoresis (2-DE) and subsequent mass finger printing were used to identify proteins expression profiles from the cells after exposure to 0.1μM BTs for 48h. In total, 89 protein spots showed altered expression in at least two treatment groups and 69 of these proteins were subsequently identified. Bioinformatic analysis of the proteins indicated that BTs involved in the regulation of hormone homeostasis, lipid metabolism, cell death, and energy production. IPA analysis revealed LXR/RXR (liver X receptor/retinoid X receptor) activation, FXR/RXR (farnesoid X receptor/retinoid X receptor) activation and fatty acid metabolism were the top three categories on which BTs acted and these systems play vital roles in sterol, glucose and lipid metabolism. The expression of LXR and FXR mRNA in H295R cells was stimulated by TBT, confirming the ability of TBT to activate this nuclear receptor. In summary, the differentially expressed proteins discovered in this study may participate in the toxic actions of BTs, and nuclear receptor activation and lipid metabolism may play important roles in such actions of BTs.

Effects of tributyltin on early life-stage, reproduction, and gonadal sex differentiation in Japanese medaka (Oryzias latipes)

Tributyltin, an organotin compound, was used worldwide as an antifouling agent in aquatic environments and there has been much concern about the toxicological and ecotoxicological properties of organotin compounds. Even though it has been prohibited worldwide, tributyltin is still detected at low concentrations in aquatic environments. Here we investigated the effects of tributyltin on the early life-stage, reproduction, and gonadal sex differentiation in Japanese medaka (Oryzias latipes). In adults, exposure to tributyltin at 3.82 μg/L suppressed fecundity and fertility and increased mortality. At 10.48 μg/L all medaka died by the sixth day of exposure. Exposure to tributyltin during early life-stages induced no significant differences in mortality or embryonic development, but growth was suppressed in groups exposed to 0.13 and 0.68 μg/L. Furthermore, there was no abnormal gonadal development in Japanese medaka exposed to tributyltin. These results provide evidence of the negative effects of tributyltin on reproduction in a teleost fish. Tributyltin did not affect gonadal sex differentiation in Japanese medaka, but fecundity and fertility were suppressed, although it is not clear whether this suppression resulted from the endocrine-disrupting action of tributyltin or its toxicity.

Tributyltin impaired reproductive success in female zebrafish through disrupting oogenesis, reproductive behaviors and serotonin synthesis

Tributyltin (TBT), an organotin acting as aromatase (Cyp19a1) inhibitor, has been found to disrupt gametogenesis and reproductive behaviors in several fish species. However, few studies addressing the mechanisms underlying the impaired gametogenesis and reproduction have been reported. In this study, female adults of zebrafish (Danio rerio) were continuously exposed to two nominal concentrations of TBT (100 and 500 ng/L, actual concentrations: 90.8 ± 1.3 ng/L and 470.3 ± 2.7 ng/L, respectively) for 28 days. After exposures, TBT decreased the total egg number, reduced the hatchability and elevated the mortality of the larvae. Decreased gonadosomatic index (GSI) and altered percentages of follicles in different developmental stages (increased early-stage follicles and reduced mid/late-stage follicles) were also observed in the ovary of TBT-treated fish. TBT also lowered the plasma level of 17β-estradiol and suppressed the expressions of cyp19a1a in the ovary. In treated fish, up-regulated expressions of aldhla2, sycp3 and dmc1 were present in the ovary, indicating an enhanced level of meiosis. The mRNA level of vtg1 was dramatically suppressed in the liver of TBT-treated fish, suggesting an insufficient synthesis of Vtg protein, consistent with the decreased percentage of mid/late-stage follicles in the ovaries. Moreover, TBT significantly suppressed the reproductive behaviors of the female fish (duration of both sexes simultaneously in spawning area, the frequency of meeting and the visit in spawning area) and down-regulated the mRNA levels of genes involved in the regulation of reproductive behaviors (cyp19a1b, gnrh-3 and kiss 2) in the brain. In addition, TBT significantly suppressed the expressions of serotonin-related genes, such as tph2 (encoding serotonin synthase), pet1 (marker of serotonin neuron) and kiss 1 (the modulator of serotonin synthesis), suggesting that TBT might disrupt the non-reproductive behaviors of zebrafish. The present study demonstrated that TBT may impair the reproductive success of zebrafish females probably through disrupting oogenesis, disturbing reproductive behaviors and altering serotonin synthesis. The present study greatly extends our understanding on the reproductive toxicity of TBT on fish.

Organotin Exposure and Vertebrate Reproduction: A Review

Organotin (OTs) compounds are organometallic compounds that are widely used in industry, such as in the manufacture of plastics, pesticides, paints, and others. OTs are released into the environment by anthropogenic actions, leading to contact with aquatic and terrestrial organisms that occur in animal feeding. Although OTs are degraded environmentally, reports have shown the effects of this contamination over the years because it can affect organisms of different trophic levels. OTs act as endocrine-disrupting chemicals (EDCs), which can lead to several abnormalities in organisms. In male animals, OTs decrease the weights of the testis and epididymis and reduce the spermatid count, among other dysfunctions. In female animals, OTs alter the weights of the ovaries and uteri and induce damage to the ovaries. In addition, OTs prevent fetal implantation and reduce mammalian pregnancy rates. OTs cross the placental barrier and accumulate in the placental and fetal tissues. Exposure to OTs in utero leads to the accumulation of lipid droplets in the Sertoli cells and gonocytes of male offspring in addition to inducing early puberty in females. In both genders, this damage is associated with the imbalance of sex hormones and the modulation of the hypothalamic-pituitary-gonadal axis. Here, we report that OTs act as reproductive disruptors in vertebrate studies; among the compounds are tetrabutyltin, tributyltin chloride, tributyltin acetate, triphenyltin chloride, triphenyltin hydroxide, dibutyltin chloride, dibutyltin dichloride, diphenyltin dichloride, monobutyltin, and azocyclotin.

Tributyltin: Advancing the Science on Assessing Endocrine Disruption with an Unconventional Endocrine-Disrupting Compound

Tributyltin (TBT) has been recognized as an endocrine disrupting chemical (EDC) for several decades. However, only in the last decade, was its primary endocrine mechanism of action (MeOA) elucidated-interactions with the nuclear retinoid-X receptor (RXR), peroxisome proliferator-activated receptor γ (PPARγ), and their heterodimers. This molecular initiating event (MIE) alters a range of reproductive, developmental, and metabolic pathways at the organism level. It is noteworthy that a variety of MeOAs have been proposed over the years for the observed endocrine-type effects of TBT; however, convincing data for the MIE was provided only recently and now several researchers have confirmed and refined the information on this MeOA. One of the most important lessons learned from years of research on TBT concerns apparent species sensitivity. Several aspects such as the rates of uptake and elimination, chemical potency, and metabolic capacity are all important for identifying the most sensitive species for a given chemical, including EDCs. For TBT, much of this was discovered by trial and error, hence important relationships and important sensitive taxa were not identified until several decades after its introduction to the environment. As recognized for many years, TBT-induced responses are known to occur at very low concentrations for molluscs, a fact that has more recently also been observed in fish species. This review explores the MeOA and effects of TBT in different species (aquatic molluscs and other invertebrates, fish, amphibians, birds, and mammals) according to the OECD Conceptual Framework for Endocrine Disruptor Testing and Assessment (CFEDTA). The information gathered on biological effects that are relevant for populations of aquatic animals was used to construct Species Sensitivity Distributions (SSDs) based on No Observed Effect Concentrations (NOECs) and Lowest Observed Effect Concentrations (LOECs). Fish appear at the lower end of these distributions, showing that they are as sensitive as molluscs, and for some species, even more sensitive. Concentrations in the range of 1 ng/L for water exposure (10 ng/g for whole-body burden) have been shown to elicit endocrine-type responses, whereas mortality occurs at water concentrations ten times higher. Current screening and assessment methodologies as compiled in the OECD CFEDTA are able to identify TBT as a potent endocrine disruptor with a high environmental risk for the original use pattern. If those approaches had been available when TBT was introduced to the market, it is likely that its use would have been regulated sooner, thus avoiding the detrimental effects on marine gastropod populations and communities as documented over several decades.

Morphological and transcriptomic effects of endocrine modulators on the gonadal differentiation of chicken embryos: The case of tributyltin (TBT)

Morphological malformations induced by tributyltin (TBT) exposure during embryonic development have already been characterized in various taxonomic groups, but, nonetheless, the molecular processes underlying these changes remain obscure. The present study provides the first genome-wide screening for differentially expressed genes that are linked to morphological alterations of gonadal tissue from chicken embryos after exposure to TBT. We applied a single injection of TBT (between 0.5 and 30 pg as Sn/g egg) into incubated fertile eggs to simulate maternal transfer of the endocrine disruptive compound. Methyltestosterone (MT) served as a positive control (30 pg/g egg). After 19 days of incubation, structural features of the gonads as well as genome-wide gene expression profiles were assessed simultaneously. TBT induced significant morphological and histological malformations of gonadal tissue from female embryos that show a virilization of the ovaries. This phenotypical virilization was mirrored by altered expression profiles of sex-dependent genes. Among these are several transcription and growth factors (e.g. FGF12, CTCF, NFIB), whose altered expression might serve as a set of markers for early identification of endocrine active chemicals that affect embryonic development by transcriptome profiling without the need of elaborate histological analyses.

Effects of triphenyltin on reproduction in Japanese medaka (Oryzias latipes) across two generations

Triphenyltin (TPT) is an organotin compound used in marine anti-fouling coatings to prevent the attachment and growth of marine organisms, and it has negative effects on aquatic organisms. TPT is still detected at low concentrations, although its use has been prohibited at least in the European Community and is restricted in Japan as well. Studies using Japanese medaka (Oryzias latipes) indicate that TPT has the potential to inhibit reproduction. Although TPT is detected in many aquatic ecosystems, the multi-generational impact of TPT remains unknown. We investigated the two-generational effects of TPT on Japanese medaka and examined the relationships of several such effects between the F0 and F1 generations. Suppression of fecundity was observed in both generations, and fertility and growth were inhibited in the F1 generation. Moreover, delayed hatching and lower hatchability were observed in F1 embryos. Importantly, the value of the lowest observed effect concentration (LOEC) for these influences in F1 was lower than that in F0: that is, the LOEC values of fecundity and mortality were 3.2μg/L in the F0 generation and 1.0μg/L in the F1 generation. Fertility was not affected by TPT in F0, whereas it was significantly suppressed in the 1.0μg/L-exposure group of the F1 generation. Our results provide the first evidence of the effects of TPT on reproduction in a teleost fish across two generations, highlighting the concern that TPT could affect reproduction and mortality at decreasing concentrations in temporally overlapping generations.

Imposex in Stramonita haemastoma from coastal sites of Cartagena, Colombia

Abstract Imposex is the development of male sexual characteristics caused by the toxic effects of some chemicals that acts as an endocrinal disruptor. Antifouling paints contain these chemicals. Cartagena lacks studies to indicate the extent of imposex in its coastal waters. The aim of this study was to determine the prevalence of imposex in the gastropod Stramonita haemastoma in Cartagena, Colombia. Specimens were collected during 2013 from locations of high and low influence of port activity. Morphometric measurements and the frequency of the occurrence of imposex were registered. The comparison among morphometric variables showed statistically significant differences between the two sites studied. Furthermore, the females of the S. haemastoma species presented an imposex frequency of 93.1% in Birds’ Island, Cartagena Bay, compared to 31.8% in La Bocana. The relative penis size index or RPLI (10.145 and 3.231) and vas deferens sequence index or VDSI (2.83 and 1.16), showed possible contamination by organotin compounds in both places.

Obesogens in the aquatic environment: an evolutionary and toxicological perspective

The rise of obesity in humans is a major health concern of our times, affecting an increasing proportion of the population worldwide. It is now evident that this phenomenon is not only associated with the lack of exercise and a balanced diet, but also due to environmental factors, such as exposure to environmental chemicals that interfere with lipid homeostasis. These chemicals, also known as obesogens, are present in a wide range of products of our daily life, such as cosmetics, paints, plastics, food cans and pesticide-treated food, among others. A growing body of evidences indicates that their action is not limited to mammals. Obesogens also end up in the aquatic environment, potentially affecting its ecosystems. In fact, reports show that some environmental chemicals are able to alter lipid homeostasis, impacting weight, lipid profile, signaling pathways and/or protein activity, of several taxa of aquatic animals. Such perturbations may give rise to physiological disorders and disease. Although largely unexplored from a comparative perspective, the key molecular components implicated in lipid homeostasis have likely appeared early in animal evolution. Therefore, it is not surprising that the obesogen effects are found in other animal groups beyond mammals. Collectively, data indicates that suspected obesogens impact lipid metabolism across phyla that have diverged over 600 million years ago. Thus, a consistent link between environmental chemical exposure and the obesity epidemic has emerged. This review aims to summarize the available information on the effects of putative obesogens in aquatic organisms, considering the similarities and differences of lipid homeostasis pathways among metazoans, thus contributing to a better understanding of the etiology of obesity in human populations. Finally, we identify the knowledge gaps in this field and we set future research priorities.

RNA-sequencing and pathway analysis reveal alteration of hepatic steroid biosynthesis and retinol metabolism by tributyltin exposure in male rare minnow (Gobiocypris rarus)

Tributyltin (TBT) is widely spread in aquatic ecosystems. Although adverse effects of TBT on reproduction and lipogenesis are observed in fishes, the underlying mechanisms, especially in livers, are still scarce and inconclusive. Thus, RNA-sequencing runs were performed on the hepatic libraries of adult male rare minnow (Gobiocypris rarus) after TBT exposure for 60d. After differentially expressed genes were identified, enrichment analysis and validation by quantitative real-time PCR were conducted. The results showed that TBT up-regulated the profile of hepatic genes in the steroid biosynthesis pathway and down-regulated the profile of hepatic genes in the retinol metabolism pathway. In the hepatic steroid biosynthesis pathway, TBT might induce biosynthesis of cholesterol, which could affect the bioavailability of steroid hormones. More important, 3beta-hydroxysteroid 3-dehydrogenase, a key enzyme in the biosynthesis of all active steroid hormones, was up-regulated by TBT exposure. In the hepatic retinol metabolism pathway, TBT impaired retinoic acid homeostasis which plays essential roles in both reproduction and lipogenesis. The results of two pathways offered new mechanisms underlying the toxicology of TBT and represented a starting point from which detailed mechanistic links should be explored.

Disrupting effects of azocyclotin to the hypothalamo-pituitary-gonadal axis and reproduction of Xenopus laevis

Over the past few decades, the hazards associated with the extensive use of organictin compounds have become an issue of extreme concern, while at present the effects of these substances on amphibians remain poorly understood. In the present study, we chose azocyclotin, one of common use acaricides in China. We focused on sexual development and steroidogenesis disrupting effects of azocyclotin in the Xenopus laevis. Tadpoles were exposed to azocyclotin (0.05 and 0.5μg/L) for long-term (4 months) study. Results showed that exposure to azocyclotin caused developmental toxicity, including decreased survival, body weight, body length, gonadosomatic index, hepatosomatic index and female phenotype. At the same time, statistical increase in mean age at completion of metamorphosis was observed in azocyclotin treatments in comparison with control group. Furthermore, hormone concentrations, and steroidogenesis genes expression of adult frog were further evaluated in 28 days exposure. Results demonstrated that the key regulating hormones, e.g. testosterone and pregnenolone, were significantly upregulated. The expression levels of selected steroidogenic genes were also significantly altered. Our study demonstrated that azocyclotin could delay the metamorphosis and disrupt the gonadal differentiation of X. laevis. Steroidogenesis and the expression of genes involved in the hypothalamus-pituitary-gonadal-liver axis in frogs were disrupted after azocyclotin exposure. Azocyclotin showed both androgenic and antiestrogenic activity for X. laevis. Those findings emphasized the influence of azocyclotin on non-target species in the context of ecotoxicological risk assessment.

Levels of TBT and other selected organotin compounds in duplicate diet samples

Organotin compounds (OTs) are ubiquitous contaminants with a broad range of applications ranging from biocides and pesticides to catalysts for the production of polyurethane foams and silicones. The deleterious effects of some OTs (particularly tributyltin - TBT) upon wildlife and experimental animals are well documented and include endocrine disruption, immunotoxicity, neurotoxicity, genotoxicity and metabolic dysfunction in which obesity is included. However, virtually no data on the current human exposure levels is available. In order to bridge this gap, we quantified for the first time the levels of OTs in duplicate diet samples from members of the University of Aveiro in Portugal. OTs were detected in 32% of the 28 diet samples analyzed, at relatively low levels. TBT and monobutyltin were detected only in two samples and dibutyltin was detectable in three samples. Dioctyltin was quantified in four samples and monooctyltin in three samples. Phenyltins were below the detection limit in all the diet samples analyzed. Overall, for the vast majority of the samples (89%), the estimated daily intakes (EDI) of organotins through food were much lower than the established tolerable daily intakes (TDI). Hence, for the majority of the participants the risk associated with food ingestion is low.

Effects of azocyclotin on gene transcription and steroid metabolome of hypothalamic-pituitary-gonad axis, and their consequences on reproduction in zebrafish (Danio rerio)

The widely used organotins have the potential to disrupt the endocrine system, but little is known of underlying mechanisms of azocyclotin toxicity in fish. The objective of the present study was to investigate the impact of azocyclotin on reproduction in zebrafish. Adult zebrafish were exposed to 0.09 and 0.45μg/L azocyclotin for 21days, and effects on steroid hormones and mRNA expression of the genes belonging to the hypothalamic-pituitary-gonad (HPG) axis were investigated. Mass spectrometry methodology was developed to profile steroids within the metabolome of the gonads. They were disrupted as a result of azocyclotin exposure. Alterations in the expression of key genes associated with reproductive endocrine pathways in the pituitary (lhβ), gonad (cyp19a1a, cyp17a1 and 17β-hsd3), and liver (vtg1, vtg2, cyp1a1, comt, ugt1a and gstp1) were correlated with significant reductions in estrogen in both sexes and increased testosterone in females. Azocyclotin-induced down-regulation of cyp19a1a in males suggested a reduction in the rate of estrogen biosynthesis, while up-regulation of hepatic cyp1a1 and comt in both sexes suggested an increase in estrogen biotransformation and clearance. Azocyclotin also induced change in the expression of 17β-hsd3, suggesting increased bioavailability of 11-ketotestosterone (11-KT) in the blood. Furthermore, the down-regulation of lhβ expression in the brains of azocyclotin-exposed fish was associated with inhibition of oocyte maturation in females and retarded spermatogenesis in males. As a histological finding, retarded development of the ovaries was found to be an important cause for decreased fecundity, with down-regulation of vtg suspected to be a likely underlying mechanism. Additionally, relatively high concentrations of azocyclotin in the gonads may have directly caused toxicity, thereby impairing gametogenesis and reproduction. Embryonic or larval abnormalities occurred in the F1 generation along with accumulated burdens of azocyclotin in F1 eggs, following parental exposure. Overall, our results indicate that exposure to azocyclotin can impair reproduction in fish, and induce toxicity related abnormalities in non-exposed offspring.

Tributyltin promoted hepatic steatosis in zebrafish (Danio rerio) and the molecular pathogenesis involved

Endocrine disruptor effects of tributyltin (TBT) are well established in fish. However, the adverse effects on lipid metabolism are less well understood. Since the liver is the predominant site of de novo synthesis of lipids, the present study uses zebrafish (Danio rerio) to examine lipid accumulation in the livers and hepatic gene expression associated with lipid metabolism pathways. After exposure for 90 days, we found that the livers in fish exposed to TBT were yellowish in appearance and with accumulation of lipid droplet, which is consistent with the specific pathological features of steatosis. Molecular analysis revealed that TBT induced hepatic steatosis by increasing the gene expression associated with lipid transport, lipid storage, lipiogenic enzymes and lipiogenic factors in the livers. Moreover, TBT enhanced hepatic caspase-3 activity and up-regulated genes related to apoptosis and cell-death, which indicated steatotic livers of fish exposed to TBT and the subsequent liver damage were likely due to accelerated hepatocyte apoptosis or cell stress. In short, TBT can produce multiple and complex alterations in transcriptional activity of lipid metabolism and cell damage, which provides potential molecular evidence of TBT on hepatic steatosis.

The Mammalian "Obesogen" Tributyltin Targets Hepatic Triglyceride Accumulation and the Transcriptional Regulation of Lipid Metabolism in the Liver and Brain of Zebrafish

Recent findings indicate that different Endocrine Disrupting Chemicals (EDCs) interfere with lipid metabolic pathways in mammals and promote fat accumulation, a previously unknown site of action for these compounds. The antifoulant and environmental pollutant tributyltin (TBT), which causes imposex in gastropod snails, induces an “obesogenic” phenotype in mammals, through the activation of the nuclear receptors retinoid X receptor (RXR) and peroxisome proliferator-activated receptor gamma (PPARγ). In teleosts, the effects of TBT on the lipid metabolism are poorly understood, particularly following exposure to low, environmental concentrations. In this context, the present work shows that exposure of zebrafish to 10 and 50 ng/L of TBT (as Sn) from pre-hatch to 9 months of age alters the body weight, condition factor, hepatosomatic index and hepatic triglycerides in a gender and dose related manner. Furthermore, TBT modulated the transcription of key lipid regulating factors and enzymes involved in adipogenesis, lipogenesis, glucocorticoid metabolism, growth and development in the brain and liver of exposed fish, revealing sexual dimorphic effects in the latter. Overall, the present study shows that the model mammalian obesogen TBT interferes with triglyceride accumulation and the transcriptional regulation of lipid metabolism in zebrafish and indentifies the brain lipogenic transcription profile of fish as a new target of this compound.

Disruptions in aromatase expression in the brain, reproductive behavior, and secondary sexual characteristics in male guppies (Poecilia reticulata) induced by tributyltin

Although bioaccumulation of tributyltin (TBT) in fish has been confirmed, information on possible effects of TBT on reproductive system of fish is still relatively scarce, particularly at environmentally relevant levels. To evaluate the adverse effects and intrinsic toxicological properties of TBT in male fish, we studied aromatase gene expression in the brain, sex steroid contents, primary and secondary sexual characteristics, and reproductive behavior in male guppies (Poecilia reticulata) exposed to tributyltin chloride at the nominal concentrations of 5, 50, and 500 ng/L for 28 days in a semi-static exposure system. Radioimmunoassay demonstrated that treatment with 50 ng/L TBT caused an increase in systemic levels of testosterone of male guppies. Gonopodial index, which showed a positive correlation with testosterone levels, was elevated in the 5 ng/L and 50 ng/L TBT treated groups. Real-time PCR revealed that TBT exposure had inhibiting effects on expression of two isoforms of guppy aromatase in the brain, and these changes at the molecular levels were associated with a disturbance of reproductive behavior of the individuals, as measured by decreases in frequencies of posturing, sigmoid display, and chase activities when males were paired with females. This study provides the first evidence that TBT can cause abnormalities of secondary sexual characteristics in teleosts and that suppression of reproductive behavior in teleosts by TBT is due to its endocrine-disrupting action as an aromatase inhibitor targeting the nervous system.

Modulation of the DNA repair system and ATR-p53 mediated apoptosis is relevant for tributyltin-induced genotoxic effects in human hepatoma G2 cells

The toxic effects of tributyltin (TBT) have been extensively documented in several types of cells, but the molecular mechanisms related to the genotoxic effects of TBT have still not been fully elucidated. Our study showed that exposure of human hepatoma G2 cells to 1-4 μmol/L TBT for 3 hr caused severe DNA damage in a concentration-dependent manner. Moreover, the expression levels of key DNA damage sensor genes such as the replication factor C, proliferating cell nuclear antigen and poly (ADP-ribose) polymerase-1 were inhabited in a concentration-dependent manner. We further demonstrated that TBT induced cell apoptosis via the p53-mediated pathway, which was most likely activated by the ataxia telangiectasia mutated and rad-3 related (ATR) protein kinase. The results also showed that cytochrome c, caspase-3, caspase-8, caspase-9, and the B-cell lymphoma 2 were involved in this process. Taken together, we demonstrated for the first time that the inhibition of the DNA repair system might be more responsible for TBT-induced genotoxic effects in cells. Then the generated DNA damage induced by TBT initiated ATR-p53-mediated apoptosis.

The obesogen tributyltin

The obesogen hypothesis postulates the role of environmental chemical pollutants that disrupt homeostatic controls and adaptive mechanisms to promote adipose-dependent weight gain leading to obesity and metabolic syndrome complications. One of the most direct molecular mechanisms for coupling environmental chemical exposures to perturbed physiology invokes pollutants mimicking endogenous endocrine hormones or bioactive dietary signaling metabolites that serve as nuclear receptor ligands. The organotin pollutant tributyltin can exert toxicity through multiple mechanisms but most recently has been shown to bind, activate, and mediate RXR-PPARγ transcriptional regulation central to lipid metabolism and adipocyte biology. Data in support of long-term obesogenic effects on whole body adipose tissue are also reported. Organotins represent an important model test system for evaluating the impact and epidemiological significance of chemical insults as contributing factors for obesity and human metabolic health.