Microcosm study reveals the microbial and environmental effects on tributyltin degradation in an estuarine sediment

Tributyltin (TBT) is one of the most harmful contaminants ever released into the aquatic environment. Despite being banned, it is still present at many locations throughout the world. Its degradation in sediment mainly occurs through microbial biodegradation, a process that remains unclear. This study therefore aimed at better understanding TBT biodegradation in estuarine sediment and the microbial community associated with it. Microcosm experiments were set up, embracing a range of environmental control parameters. Major community shifts were recorded, mainly attributed to the change in oxygen status. The highest percentage of degradation (36,8%) occurred at 4 °C in anaerobic conditions. These results are encouraging for the in-situ bioremediation of TBT contaminated muddy sediment in temperate ports worldwide. However, with TBT able to persist in the coastal environment for decades when undisturbed in anoxic sediment, further research is needed to fully understand the mechanisms that triggered this biodegradation observed in the microcosms.

Binding profiles of human and mouse complement component 8γ to trisubstituted organometallic compounds

Complement component 8gamma (C8γ), a member of the lipocalin protein family, is suggested to act as a carrier protein for various chemicals. Although C8γ has been identified in both humans and rodents for some time, our understanding of the species differences in its chemical binding properties remains limited. In the present study, with the aim to elucidate the potential role of C8γ as a carrier protein in both humans and mice, we conducted a radioligand binding assay to examine the chemical binding properties of human C8γ (hC8γ) and mouse C8γ (mC8γ). Scatchard analysis revealed that [14C]TPT bound to hC8γ with an equilibrium dissociation constant (Kd) of 64.2 ± 32.4 nM, comparable to that of [14C]TPT to mC8γ. Competitive ligand-binding assays demonstrated binding of TPT and TBT to hC8γ, while diphenyltin, dibutyltin, monophenyltin, monobutyltin, and tetrabutyltin did not exhibit binding. These results suggest that for effective binding to C8γ, chemicals must possess substituents of appropriate bulkiness. Further analyses with other group 14 compounds with triphenyl substituents revealed that a central metal atom, rather than a central non-metal or semi-metal atom, is crucial for specific binding to both hC8γ and mC8γ. Overall our findings imply that C8γ may play a role in the physiological or toxicological actions of group 14 metal compounds with tributyl or triphenyl substituents by binding to these chemicals in both humans and mice.

Maternal exposure to tributyltin alters the breast milk, hormonal profile, and thyroid morphology of dams and induces sex-specific changes in neonate rat offspring

Tributyltin (TBT) is the chemical substance commonly used worldwide to prevent biofouling of vessels. Due to its ability to bioaccumulate and biomagnify, even after being banned, significant concentrations of TBT can be detected in sediment, affecting marine and human life. Although studies have shown that direct exposure to TBT alters physiological parameters in mammals, the relationship between exposure to TBT during pregnancy and lactation, considered critical windows for metabolic programming, has not been fully elucidated. Our hypothesis is that offspring whose mothers were exposed to TBT during critical stages of development may exhibit dysfunctions in endocrine-metabolic parameters. We used pregnant Wistar rats that were divided into groups and received the following treatments from gestational day 7 until the end of lactation by intragastric gavage: vehicle (ethanol 0.01%; Control), low TBT dose (100 ng/kg of body weight (bw)/day; TBT100ng) and high TBT dose (1000 ng/kg bw/day; TBT1000ng). Dams and offspring at birth and weaning (21 days old) were studied. Maternal exposure to TBT promoted dose-dependent changes in dams. The findings for adiposity, milk composition and lipid profile were more pronounced in TBT100 ng dam; however, thyroid morphology was altered in TBT1000 ng dam. Female offspring were differentially affected by the dose of exposure. At birth, females in the TBT100ng group had low body weight, lower naso-anal length (NAL), and higher plasma T4, and at weaning, females in the TBT100ng group had lower insulin and leptin levels. Females in the TBT1000ng group had lower NAL at birth and lower leptinemia and weight of white adipose tissue at weaning. Male offspring from TBT groups showed high T3 at birth, without biometric alterations at birth or weaning. Despite these findings, both sexes exhibited dose-dependent morphological changes in the thyroid gland. Thus, maternal exposure to TBT constitutes an important route of contamination for both dams and offspring.

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.

Tributyltin-induced oxidative stress causes developmental damage in the cardiovascular system of zebrafish (Danio rerio)

Tributyltin (TBT) can be used as an antifouling agent with anticorrosive, antiseptic and antifungal properties and is widely used in wood preservation and ship painting. However, it has recently been found that TBT can be harmful to aquatic organisms. In this study, to gain insight into the effects of TBT with respect to the development of the cardiovascular system in zebrafish embryos, zebrafish embryos were exposed to different concentrations of TBT solutions (0.2 μg/L, 1 μg/L, and 2 μg/L) at 2 h post-fertilization (hpf) TBT exposure resulted in decreased hatchability and heart rate, deformed features such as pericardial edema, yolk sac edema, and spinal curvature in zebrafish embryos, and impaired heart development. Expression of cardiac development-related genes (vmhc, myh6, nkx2.5, tbx5a, gata4, tbx2b, nppa) is dysregulated. Transgenic zebrafish Tg (fli1: EGFP) were used to explore the effects of TBT exposure on vascular development. It was found that TBT exposure could lead to impaired development of intersegmental vessels (ISVs), common cardinal vein (CCV), subintestinal vessels (SIVs) and cerebrovascular. The expression of vascular endothelial growth factor (VEGF) signaling pathway-related genes (flt1, flt4, kdr, vegfa) was downregulated. Biochemical indices showed that ROS and MDA levels were significantly elevated and that SOD and CAT activities were significantly reduced. The expression of key genes for prostacyclin synthesis (pla2, ptgs2a, ptgs2b, ptgis, ptgs1) is abnormal. Therefore, it is possible that oxidative stress induced by TBT exposure leads to the blockage of arachidonic acid (AA) production in zebrafish embryos, which affects prostacyclin synthesis and consequently the normal development of the heart and blood vessels in zebrafish embryos.

Tributyltin causes generational neurodevelopmental toxicity and the protective effect of folic acid in zebrafish

Tributyltin (TBT), a common organotin environmental pollutant, may pose a threat to human development during critical early-life periods. We aimed to assess the neurodevelopmental intergenerational toxicity of early-life exposure to TBT and the protective effect of DNA methyl donor folic acid (FA). Specifically, after early-life exposure (1-21 days post-fertilization, dpf) to TBT (0, 1, 10 and 100 ng/L), zebrafish (Danio rerio) were cultured in clean medium until sexual maturity. The exposed females were mated with unexposed males to produce embryos (F1). The F1 generation were cultured (4-120 hours post-fertilization, hpf) with and without 1 mmol/L FA. The neurotoxic effects of early-life TBT exposure for zebrafish and their offspring (F1) were significantly enhanced anxiety and reduced aggression, decreased gene expression of DNA methyltransferase in the brain and increased serotonin levels in the body. Moreover, the intergenerational neurodevelopmental toxicity, as manifested in the F1 generation, was attenuated by FA supplementation. In summary, early-life TBT exposure led to intergenerational neurodevelopmental deficits in zebrafish, and DNA methyl donors had a protective effect on F1 neurodevelopment, which can inform the prevention and treatment of intergenerational neurotoxicity due to organotin pollutants.

Whole-Transcriptome Analysis Reveals the RNA Profiles in Mouse Bone Marrow Mesenchymal Stem Cells or Zebrafish Embryos After Exposure to Environmental Level of Tributyltin

To understand the underlying molecular mechanisms, mouse bone marrow mesenchymal stem cells (BMSCs) and zebrafish embryos were exposed to the control group and Tributyltin (TBT) group (10 ng/L, environmental concentration) for 48 h, respectively. The expression profiles of RNAs were investigated using whole-transcriptome analysis in mouse BMSCs or zebrafish embryos after TBT exposure. For mouse BMSCs, the results showed 2,449 differentially expressed (DE) mRNAs, 59 DE miRNAs, 317 DE lncRNAs, and 15 circRNAs. Similarly, for zebrafish embryos, the results showed 1,511 DE mRNAs, 4 DE miRNAs, 272 DE lncRNAs, and 28 circRNAs. According to KEGG pathway analysis showed that DE RNAs were mainly associated with immune responses, signaling, and cellular interactions. Competing endogenous RNA (ceRNA) network analysis revealed that the regulatory network of miRNA-circRNA constructed in zebrafish embryos was more complex compared to that of mouse BMSCs.

Emerging marine environmental pollution and ecosystem disturbance in ship hull cleaning for biofouling removal

Numerous marine sessile organisms adhere to ship hulls and increase the sailing resistance. Antibiofouling paints are employed to maintain the ship performance. However, the chemicals employed for antifouling purposes are becoming increasingly diverse, lacking clear toxicological information. Particularly, the imperfect antibiofouling efficacies of these chemicals necessitate periodic hull cleaning to dislodge attached marine organisms. This hull cleaning process inadvertently releases a plethora of hazardous substances, including antibiofouling chemicals, heavy metals, and cleaning agents, alongside exotic microorganisms. This results in profound marine pollution and ecosystem disruption. Specifically, these exotic microorganisms pose a novel ecological threat in coastal waters. However, despite the gravity of ship hull cleaning-related issues, comprehensive investigations have been lacking, and international regulatory measures are gaining attention recently. Aiming to provide solutions to the emerging challenges associated with hull cleaning, this review endeavors to comprehensively address the biofouling organisms and their mechanisms, potential antifouling paint hazards, and effective hull cleaning methodologies.

Factors affecting the accumulation of organotins by wild fish: A case study in the Three Gorges Reservoir, China

Organotin compounds (OTs) accumulate in fish easily, however, research on their influencing factors is still limited. This study collected 25 species of fish with different diets, habitats, and age from the Three Gorges Reservoir (TGR), the largest deep-water river channel-type reservoir in China, and analyzed the accumulation characteristics of OTs in these fish. The results showed that tributyltin (TBT) and triphenyltin (TPhT) were the dominant OTs in fish from the TGR. The correlation between OTs concentration and age, body length, and body weight varied with fish species. The concentrations of TBT and TPhT in carnivorous fish (mean, 25.78 and 11.69 ng Sn/g dw, respectively) were higher than those in other diet fish (P<0.01), but there was no significant difference in fish at different habitat water layers (P>0.05). In addition, the degradation rates of TBT and TPhT in different fish species were all below 50%. In summary, the accumulation of TBT and TPhT in fish is mainly influenced by diet, and both TBT and TPhT were difficult to degrade in fish. These results reveal the pollution characteristics of OTs in fish from the TGR, and can improve our understanding of the factors influencing TBT and TPhT accumulation in freshwater fish.

The possible ameliorative role of Lycopene on Tributyltin induced thyroid damage in adult male albino rats (histological, immunohistochemical and biochemical study)

Tributyltin is used in industrial applications. This current research aimed to study the effect of Tributyltin on the thyroid gland structure and function of adult male albino rats and the protective effect of Lycopene. Twenty-one male adult albino rats were classified into three groups: Control, treated that received Tributyltin, and protective that received Lycopene with Tributyltin. At the end of the experiment, blood samples were collected and T4, T3, and (TSH) were measured. Tissue superoxide dismutase (SOD) and malondialdehyde (MDA) were estimated. Thyroid gland specimens were processed for histological and immunohistochemical examination. Then morphometric and statistical analyses were done. The treated group showed affection in thyroid function and histological structure as vacuolated colloid and cytoplasm and dark nuclei. Ultrastructurally, follicular cells showed irregular shrunken nuclei, atrophied apical microvilli, vacuoles, multiple lysosomal granules, mitochondria with destructed cristae, and extensively dilated rough endoplasmic reticulum. There was increase in Caspase-3 immunoexpression and decrease in Beclin-1 immunoexpression. The thyroid structure and biochemical markers improved after Lycopene administration. The thyroid gland damage caused by Tributyltin is ameliorated by Lycopene.

Lipid accumulation and gene expression changes induced by tributyltin exposure in primary hepatocytes of lined seahorse (Hippocampus erectus)

Tributyltin (TBT), an antifouling biocide frequently detected in aquatic systems, is generally considered to be an environmental obesogen. However, alterations in lipid metabolism in aquatic animals that are exposed to TBT are scarcely known. This study examined the effects of in vitro exposure to TBT on hepatic lipid homeostasis in the lined seahorse (Hippocampus erectus). Primary seahorse hepatocyte cultures were established for the first time. TBT exposure (100 and 500 nM for 24 h) significantly promoted lipid accumulation in seahorse hepatocytes and drastically reduced the number of active intracellular lysosomes. Furthermore, exposure to TBT significantly upregulated the gene expression of lipogenic enzymes and transcription factors but downregulated that of genes involved in the catabolism of lipid droplets in seahorse hepatocytes. These results indicate that TBT disrupts hepatic lipid homeostasis by simultaneously promoting lipid synthesis and inhibiting lipid droplet breakdown in seahorses. The present study extends our understanding of the utilization of primary hepatocytes from marine animals for toxicological research, and the molecular evidence of the effects of TBT on hepatic lipid homeostasis in teleost fishes.

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.

Subacute and low dose of tributyltin exposure leads to brown adipose abnormalities in male rats

Tributyltin (TBT) is an obesogenic endocrine disrupting chemical (EDC) linked with several metabolic complications. Brown adipose tissue (BAT) is the principal site for thermogenesis, making it a potential target for obesity management and metabolic disease. However, few studies have evaluated TBT effect on BAT function. In this investigation, we assessed whether subacute (15 days) and low dose of TBT exposure (100 ng/kg/day) results in abnormal BAT morphophysiology in adult male rats. Body temperature, BAT morphology, inflammation, oxidative stress, collagen deposition and BAT metabolic gene expression markers were assessed in room temperature (Room, ∼24 ºC) and after cold tolerance test (Cold, ∼4 ºC) conditions. A reduction in body temperature was observed in both Room and Cold conditions in TBT rats, suggesting abnormal BAT thermogenic function. Changes in BAT morphology were observed in TBT rats, with an increase in BAT lipid accumulation, an increase in BAT unilocular adipocyte number and a decrease in BAT multilocular adipocyte number in Room condition. All these parameters were opposite in Cold condition TBT rats, leading to a borderline increase in BAT UCP1 protein expression. An increase in BAT mast cell number was observed in TBT rats in Room condition. An increase in ED1 protein expression (macrophage marker) was observed in TBT rats in Cold condition. Oxidative stress and collagen deposition increased in both Room and Cold conditions in TBT rats. TBT exposure caused a borderline increase in BAT COL1A1 protein expression in Cold condition. Further, strong negative correlations were observed between body temperature and BAT lipid accumulation, and BAT lipid accumulation and multilocular adipocyte number. Thus, these data suggest that TBT exposure impaired BAT morphophysiology through impacts on lipid accumulation, inflammation, fibrosis and oxidative stress in male rats.

A ubiquitous endocrine disruptor tributyltin induces muscle wasting and retards muscle regeneration

BACKGROUND

Organotin pollutant tributyltin (TBT) is an environmental endocrine disrupting chemical and is a known obesogen and diabetogen. TBT can be detected in human following consumption of contaminated seafood or water. The decrease in muscle strength and quality has been shown to be associated with type 2 diabetes in older adults. However, the adverse effects of TBT on the muscle mass and function still remain unclear. Here, we investigated the effects and molecule mechanisms of low-dose TBT on skeletal muscle regeneration and atrophy/wasting using the cultured skeletal muscle cell and adult mouse models.

METHODS

The mouse myoblasts (C2C12) and differentiated myotubes were used to assess the in vitro effects of low-dose tributyltin (0.01-0.5 μM). The in vivo effects of TBT at the doses of 5 and 25 μg/kg/day (n = 6/group), which were five times lower than the established no observed adverse effect level (NOAEL) and equal to NOAEL, respectively, by oral administration for 4 weeks on muscle wasting and muscle regeneration were evaluated in a mouse model with or without glycerol-induced muscle injury/regeneration.

RESULTS

TBT reduced myogenic differentiation in myoblasts (myotube with 6-10 nuclei: 53.9 and 35.8% control for 0.05 and 0.1 μM, respectively, n = 4, P < 0.05). TBT also decreased myotube diameter, upregulated protein expression levels of muscle-specific ubiquitin ligases (Atrogin-1 and MuRF1), myostatin, phosphorylated AMPKα, and phosphorylated NFκB-p65, and downregulated protein expression levels of phosphorylated AKT and phosphorylated FoxO1 in myotubes (0.2 and 0.5 μM, n = 6, P < 0.05). Exposure of TBT in mice elevated body weight, decreased muscle mass, and induced muscular dysfunction (5 and 25 μg/kg, P > 0.05 and P < 0.05, respectively, n = 6). TBT inhibited soleus muscle regeneration in mice with glycerol-induced muscle injury (5 and 25 μg/kg, P > 0.05 and P < 0.05, respectively, n = 6). TBT upregulated protein expression levels of Atrogin-1, MuRF1, myostatin, and phosphorylated AMPKα and downregulated protein expression level of phosphorylated FoxO1 in the mouse soleus muscles (5 and 25 μg/kg, P > 0.05 and P < 0.05, respectively, n = 6).

CONCLUSIONS

This study demonstrates for the first time that low-dose TBT significantly inhibits myogenic differentiation and triggers myotube atrophy in a cell model and significantly decreases muscle regeneration and muscle mass and function in a mouse model. These findings suggest that low-dose TBT exposure may be an environmental risk factor for muscle regeneration inhibition, atrophy/wasting, and disease-related myopathy.

Low-dose tributyltin triggers human chondrocyte senescence and mouse articular cartilage aging

Tributyltin (TBT) is known as an endocrine-disrupting chemical. This study investigated the effects and possible mechanisms of TBT exposure on inducing human articular chondrocyte senescence in vitro at the human-relevant concentrations of 0.01-0.5 μM and mouse articular cartilage aging in vivo at the doses of 5 and 25 μg/kg/day, which were 5 times lower than the established no observed adverse effect level (NOAEL) and equal to NOAEL, respectively. TBT significantly increased the senescence-associated β-galactosidase activity and the protein expression levels of senescence markers p16, p53, and p21 in chondrocytes. TBT induced the protein phosphorylation of both p38 and JNK mitogen-activated protein kinases in which the JNK signaling was a main pathway to be involved in TBT-induced chondrocyte senescence. The phosphorylation of both ataxia-telangiectasia mutated (ATM) and histone protein H2AX (termed γH2AX) was also significantly increased in TBT-treated chondrocytes. ATM inhibitor significantly inhibited the protein expression levels of γH2AX, phosphorylated p38, phosphorylated JNK, p16, p53, and p21. TBT significantly stimulated the mRNA expression of senescence-associated secretory phenotype (SASP)-related factors, including IL-1β, TGF-β, TNF-α, ICAM-1, CCL2, and MMP13, and the protein expression of GATA4 and phosphorylated NF-κB-p65 in chondrocytes. Furthermore, TBT by oral gavage for 4 weeks in mice significantly enhanced the articular cartilage aging and abrasion. The protein expression of phosphorylated p38, phosphorylated JNK, GATA4, and phosphorylated NF-κB-p65, and the mRNA expression of SASP-related factors were enhanced in the mouse cartilages. These results suggest that TBT exposure can trigger human chondrocyte senescence in vitro and accelerating mouse articular cartilage aging in vivo.

Organotin and organochlorine toxicants activate key translational regulatory proteins in human immune cells

Environmental contaminant exposures occur due to the widespread use of synthetic chemicals. Tributyltin (TBT), dibutyltin (DBT), and pentachlorophenol (PCP) are each used in a variety of applications, including antifouling paints and stabilizers in certain plastics. Each of these compounds has been found in human blood, as well as other tissues, and they have been shown to stimulate pro-inflammatory cytokine production in human immune cells, Inflammatory cytokines mediate response to injury or infection. However, if their levels are increased in the absence of an appropriate stimulus, chronic inflammation can occur. Chronic inflammation is associated with a number of pathologies including cancer. Stimulation of pro-inflammatory cytokine production by these toxicants is dependent on activation of ERK 1/2 and/or p38 MAPK pathways. MAPK pathways have the capacity to regulate translation by increasing phosphorylation of key translation regulatory proteins. There have been no previous studies examining the effects of TBT, DBT, or PCP on translation. The current study shows that ribosomal protein S6 (S6), eukaryotic initiation factor 4B (eIF4B), and eIF4E are phosphorylated (activated) and/or their total levels are elevated in response to each of these compounds at concentrations found in human blood. Activation/increased levels of translational proteins occurred at concentrations of the compounds that have been shown to elevate pro-inflammatory cytokine production, but where there is no increase in mRNA for those proteins was seen. Compound-stimulated increases in translation appear to be part of the mechanism by which they elevate protein production in immune cells.

Tributyltin activates the Keap1-Nrf2 pathway via a macroautophagy-independent reduction in Keap1

Tributyltin (TBT) is an environmental chemical, which was used as an antifouling agent for ships. Although its use has been banned, it is still persistently present in ocean sediments. Although TBT reportedly causes various toxicity in mammals, few studies on the mechanisms of biological response against TBT toxicity exist. The well-established Keap1-Nrf2 pathway is activated as a cytoprotective mechanism under stressful conditions. The relationship between TBT and the Keap1-Nrf2 pathway remains unclear. In the present study, we evaluated the effect of TBT on the Keap1-Nrf2 pathway. TBT reduced Keap1 protein expression in Neuro2a cells, a mouse neuroblastoma cell line, after 6 hr without altering mRNA expression levels. TBT also promoted the nuclear translocation of Nrf2, a transcription factor for antioxidant proteins, after 12 hr and augmented the expression of heme oxygenase 1, a downstream protein of Nrf2. Furthermore, TBT decreased Keap1 levels in mouse embryonic fibroblast (MEF) cells, with the knockout of Atg5, which is essential for macroautophagy, as well as in wild-type MEF cells. These results suggest that TBT activates the Keap1-Nrf2 pathway via the reduction in the Keap1 protein level in a macroautophagy-independent manner. The Keap1-Nrf2 pathway is activated by conformational changes in Keap1 induced by reactive oxygen species or electrophiles. Furthermore, any unutilized Keap1 protein is degraded by macroautophagy. Understanding the novel mechanism governing the macroautophagy-independent reduction in Keap1 by TBT may provide insights into the unresolved biological response mechanism against TBT toxicity and the activation mechanism of the Keap1-Nrf2 pathway.

The study on contamination of bottom sediments from the Odra River estuary (SW Baltic Sea) by tributyltin using environmetric methods

We present the first comprehensive study on the occurrence of tributyltin (TBT) in the Odra River estuary (SW Baltic Sea) that encompasses both densely populated and urbanized agglomeration Szczecin city, and sparsely populated biosphere reserves "Natura 2000". Relationship between TBT and physicochemical parameters of bottom sediments such as granulometry total organic carbon (TOC), total nitrogen (TN), acid volatile sulfide (AVS), As, and metals: Ba, Cd, Co, Cr, Cu, Fe, Hg, Ni, Mn, Mo, Pb, Sn, and Zn was investigated in 120 samples collected in 2017 and 2018. The highest TBT concentrations were over 3000 ng g^-1 (dry weight). They were observed in samples collected in the vicinity of the ship maintenance zones of the Szczecin city. Despite the EU ban on its use since 2003, TBT is still present in the environment. Environmetrics analyses such as correlation, cluster, and principal component analysis of obtained results revealed that the main source of sediments contamination by TBT, metalloids, and metals is likely related to the maritime industry: shipyards, ship maintenance as well as ports and marines. TBT is still present in the bottom sediments because of its emission to the environment with dust and paint chips formed during sandblasting cleaning of ship surfaces. The pollutant is further transported with water current to remote localization in the Szczecin Lagoon. Slow water exchange between the Szczecin Lagoon and the Baltic Sea favors accumulation of pollutants in the lagoon sediments. Therefore, it is necessary to implement environmentally friendly methods into ship maintenance and management of the materials from dredged waterways, harbors, and marinas.

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.

Effects of tributyltin (TBT) on the intermediate metabolism of the crab Callinectes sapidus

This study investigated if the exposure to tributyltin (TBT), a chemical used worldwide in boat antifouling paints, could result in metabolic disturbances in the blue crab Callinectes sapidus. After the exposure to TBT 100 or 1000 ng.L^-1 for 48 and 96 h, hemolymph and tissues were collected to determine the concentration of metabolites and lipid peroxidation. The levels of glucose, lactate, cholesterol, and triglycerides in the hemolymph were not affected by TBT exposure. Hemolymph protein and heart glycogen increased in the crabs exposed to TBT 1000 for 96 h. Anterior gills protein and lipoperoxidation decreased after 96 h in all groups. These results suggest that C. sapidus can maintain energy homeostasis when challenged by the TBT exposure for 48 h and that metabolic alterations initiate after 96 h.

Effects of the antifouling agent tributyltin on the sinking behavior, photosynthetic rate and biochemical composition of the marine planktonic diatom Thalassiosira pseudonana

This study investigated the changes in the sinking rates and physiochemical characteristics of the planktonic marine diatom, Thalassiosira pseudonana, caused by 72 h exposure to antifouling agent tributyltin (TBT) at 1.0 µg L^-1 (72-h 10% effective concentration for growth rate, EC10), and 1.7 µg L^-1 (EC50). After 72 h of exposure, the sinking rates of T. pseudonana cells were changed from 0.13-0.08 m day^-1 in the control, 0.08-0.05 m day^-1 in the EC10 treatment, and 0.04-0.006 m day^-1 in the EC50 treatment. The results revealed that the sinking rate of T. pseudonana decreased significantly compared with the control at 48 h in the EC10 treatment group and at 24, 48, and 72 h in the EC50 treatment group. The photosynthetic performance index on an absorption basis and the maximum quantum yields of photosystem II also decreased significantly (P < 0.05) in the TBT treatments compared with the control. There was a significant (P < 0.05) positive correlation between sinking rates and cellular protein contents (ng cell^-1). Changes in the biochemical and physiochemical composition of the cells suggest that interference with photosynthetic processes by TBT may have reduced their specific gravity and thereby caused a decrease in the sinking rates of T. pseudonana. The results of this investigation suggest the importance of considering the effects of pollutants on the sinking behaviors of diatoms when evaluating the adverse effects of pollutants on marine primary production.

iChip increases the success of cultivation of TBT-resistant and TBT-degrading bacteria from estuarine sediment

Standard methods of microbial cultivation only enable the isolation of a fraction of the total environmental bacteria. Numerous techniques have been developed to increase the success of isolation and cultivation in the laboratory, some of which derive from diffusion chambers. In a diffusion chamber, environmental bacteria in agar medium are put back in the environment to grow as close to their natural conditions as possible, only separated from the environment by semi-permeable membranes. In this study, the iChip, a device that possesses hundreds of mini diffusion chambers, was used to isolate tributyltin (TBT) resistant and degrading bacteria. IChip was shown to be efficient at increasing the number of cultivable bacteria compared to standard methods. TBT-resistant strains belonging to Oceanisphaera sp., Pseudomonas sp., Bacillus sp. and Shewanella sp. were identified from Liverpool Dock sediment. Among the isolates in the present study, only members of Pseudomonas sp. were able to use TBT as a sole carbon source. It is the first time that members of the genus Oceanisphaera have been shown to be TBT-resistant. Although iChip has been used in the search for molecules of biomedical interest here we demonstrate its promising application in bioremediation.

Environmentally relevant dose of the endocrine disruptor tributyltin disturbs redox balance in female thyroid gland

Tributyltin (TBT) is an endocrine disruptor used as a biocide in nautical paints. Even though many TBT effects in marine species are known, data in mammals are scarce, especially regarding the thyroid gland. The present study aimed to evaluate the effect of a subchronic exposure to TBT on thyroid oxidative stress of female Wistar rats. Rats received vehicle (control group), 200 or 1000 ng TBT/kg body weight/day for 40 days. After euthanasia, one part of the thyroids were collected in order to assess iodide uptake; activity and/or mRNA expression of thyroperoxidase (TPO) and dual oxidases (DUOXs); activity and/or mRNA expression of catalase, glutathione peroxidase, superoxide dismutase and NADPH oxidase 4 (CAT, GPx, SOD and NOX4); 4-hydroxynonenal (4-HNE) expression and total thiol groups levels; and mRNA expression of estrogen receptors alpha and beta (ERα and ERβ). The remaining part of the thyroid was processed for morphological analysis of estrogen receptor alpha (ERα) and for collagen deposition. Iodide uptake was not changed with treatments. TPO activity and expression were increased in the TBT1000 group (259.81% and 95.17%). The activity, but not mRNA, of CAT (17.36% TBT200; 27.10% TBT1000) and GPx (29.24% TBT200; 28.97% TBT1000) were decreased by TBT. SOD and NADPH oxidase activity, as well as thiol group and 4-HNE levels remained unchanged. Interstitial collagen deposition increased in the TBT200 group (39.54%). The mRNA expression of ERα increased in TBT-treated rats (44.87% TBT200; 36.43% TBT1000), while protein expression was increased but not reaching significance (TBT1000, p = 0.056) by TBT. Therefore, our results show that TBT increases TPO expression and reduces antioxidant enzyme activities in the thyroid gland leading to oxidative stress. Some of these effects could be mediated by the ERα pathway.

Contribution to the determination of tributyltin in water by stir bar sorptive extraction‒thermal desorption‒gas chromatography‒tandem mass spectrometry

An environmentally friendly method was developed to determine tributyltin (TBT) in water at the levels required by the European Union Water Framework Directive (EU WFD) using stir bar sorptive extraction (SBSE) in combination with thermal desorption‒gas chromatography‒triple quadrupole tandem mass spectrometry. The main focus of the method development was on addressing some aspects of reducing blank values (minimizing the use of chemicals, glassware cleaning, pretreatment of sorptive stir bars) and optimizing the SBSE procedure variables (sample volume, polarity of sample solution, extraction time). The performance of the method was studied in terms of linearity, matrix effect, method limits and accuracy (precision and trueness) using MilliQ, tap and surface water. TBT quantification limit for the studied matrices ranged from 0.049 to 0.055 ng L^‒1 and repeatability (RSD%, n = 10) and recovery at the environmental quality standard (EQS) concentration of 0.2 ng L^‒1 were in the range of 6‒18% and 88‒107%, respectively, indicating good performance of the method. The matrix effect of river water (‒78%) and artificial seawater (‒83%) compared to MilliQ water showed the necessity to use a matrix-matched calibration when analysing TBT in surface water samples. The developed sample preparation was further evaluated for greenness using the recently introduced AGREEprep assessment, which revealed a much greener performance of the proposed method over the compared CEN/TS 16692 method. The method meets the requirements of the EU WFD and is suitable for monitoring, evaluation and classification of the chemical status of surface waters.

Subacute and low-dose tributyltin exposure disturbs the mammalian hypothalamus-pituitary-thyroid axis in a sex-dependent manner

Tributyltin (TBT) is an endocrine disruptor chemical (EDC) capable of altering the proper function of the hypothalamus-pituitary thyroid (HPT) axis. This study aimed to evaluate the subacute effects of TBT on the HPT axis of male and female rats. A dose of 100 ng/kg/day TBT was used in both sexes over a 15-day period, and the morphophysiology and gene expression of the HPT axis were assessed. TBT exposure increased the body weight in both sexes, while food efficiency increased - only in male rats. It was also possible to note alterations in the thyroid, with the presence of a stratified epithelium, cystic degeneration, and increased interstitial collagen deposition. A reduction in T3 and T4 levels was only observed in TBT male rats. A reduction in TSH levels was observed in TBT female rats. Evaluating mRNA expression, we observed a decrease in hepatic D1 and TRH mRNA levels in TBT female rats. An increase in D2 mRNA expression in the hypothalamus was observed in TBT male rats. Additionally, no significant changes in TRH or hepatic D1 mRNA expression in TBT male rats or in hypothalamic D1 and D2 mRNA expression in TBT female rats were observed. Thus, we can conclude that TBT has different toxicological effects on male and female rats by altering thyroid gland morphophysiology, leading to abnormal HPT axis function, and even at subacute and low doses, it may be involved in complex endocrine and metabolic disorders.

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.

Evaluation of the effects produced by subacute tributyltin administration on vascular reactivity of male wistar rats

Tributyltin chloride (TBT) is an organotin compound widely used in several high biocides for agroindustrial applications, such as fungicides, and marine antifouling paints leading to endocrine disrupting actions, such as imposex development in mollusks. In female rats, TBT has been shown to promote ovarian dysfunction, reduction of estrogen protective effect in the vascular morphophysiology, at least in part by oxidative stress consequences. Estrogen causes coronary endothelium-dependent and independent vasodilation. However, the TBT effects on cardiovascular system of male rats are not fully understood. The aim of this study was to evaluate the effects of subacute TBT exposure in aorta vascular reactivity from male wistar rats. Rats were randomly divided into three groups: control (C), TBT 500 ng/kg/day and TBT 1000 ng/kg/day. TBT was administered daily for 30 days by oral gavage. We found that TBT exposure enhanced testosterone serum levels and it was also observed obesogenic properties. TBT exposure evoked an increase in endothelium-dependent and independent phenylephrine-induced contraction, associated to an inhibition in eNOS activity. On the other hand, it was observed an enhancement of iNOS and NF-kB protein expression. We also observed an increase in oxidative stress parameters, such as superoxide dismutase (SOD) and catalase expression, and also an increase in malondialdehyde production. Finally, TBT exposure produced aortic intima-media thickness. Taken together, these data suggest a potential cardiovascular toxicological effect after subacute TBT exposure in male rats.

Tributyltin inhibits autophagy by decreasing lysosomal acidity in SH-SY5Y cells

Tributyltin (TBT) is an environmental pollutant that remains in marine sediments and is toxic to mammals. For example, TBT elicits neurotoxic and immunosuppressive effects on rats. However, it is not entirely understood how TBT causes toxicity. Autophagy plays a pivotal role in protein quality control and eliminates aggregated proteins and damaged organelles. We previously reported that TBT dephosphorylates mammalian target of rapamycin (mTOR), which may be involved in enhancement of autophagosome synthesis, in primary cultures of cortical neurons. Autophagosomes can accumulate due to enhancement of autophagosome synthesis or inhibition of autophagic degradation, and we did not clarify whether TBT alters autophagic flux. Here, we investigated the mechanism by which TBT causes accumulation of autophagosomes in SH-SY5Y cells. TBT inhibited autophagy without affecting autophagosome-lysosome fusion before it caused cell death. TBT dramatically decreased the acidity of lysosomes without affecting lysosomal membrane integrity. TBT decreased the mature protein level of cathepsin B, and this may be related to the decrease in lysosomal acidity. These results suggest that TBT inhibits autophagic degradation by decreasing lysosomal acidity. Autophagy impairment may be involved in the mechanism underlying neuronal death and/or T-cell-dependent thymus atrophy induced by TBT.

Effects of chronic exposure to environmental levels of tributyltin on the lined seahorse (Hippocampus erectus) liver: Analysis of bioaccumulation, antioxidant defense, and immune gene expression

Tributyltin (TBT), an organotin compound frequently detected in the coastal environments, poses a threat to aquatic organisms. The lined seahorse (Hippocampus erectus) is a vulnerable species found in nearshore water habitats. The mechanisms by which this fish responds to TBT exposure are not yet fully understood. Histological, biochemical, and transcriptional analyses were conducted, and the results showed that 60 days of exposure to 50 and 500 ng/L TBT caused significant tin accumulation and liver damage to seahorses. Antioxidant defenses and immune responses to TBT exposure in the livers of seahorses were further investigated. The enzymatic activity of superoxide dismutase and malondialdehyde content increased, while catalase activity decreased. Transcriptomic analysis revealed that a series of genes involved in the antioxidant defense system were highly induced to protect the hepatic cells from oxidative damage. TBT exposure also resulted in the induction of genes associated with immune and inflammatory processes, representing a stress response to combat the adverse environmental conditions in the exposed seahorses. Furthermore, seahorses showed an increased health risk, according to the elevation of the expression of genes with tumor-promoting effects, when exposed to TBT. These findings contribute to our understanding of the adverse effects of TBT exposure on seahorses, and their potential defense mechanisms.

Transgenerational metabolomic fingerprints in mice ancestrally exposed to the obesogen TBT

BACKGROUND

Endocrine disrupting chemicals (EDCs) contribute to the etiology of metabolic disorders such as obesity, insulin resistance and hepatic dysfunction. Concern is growing about the consequences of perinatal EDC exposure on disease predisposition later in life. Metabolomics are promising approaches for studying long-term consequences of early life EDC exposure. These approaches allow for the identification and characterization of biomarkers of direct or ancestral exposures that could be diagnostic for individual susceptibility to disease and help to understand mechanisms through which EDCs act.

OBJECTIVES

We sought to identify metabolomic fingerprints in mice ancestrally exposed to the model obesogen tributyltin (TBT), to assess whether metabolomics could discriminate potential trans-generational susceptibility to obesity and recognize metabolic pathways modulated by ancestral TBT exposure.

METHODS

We used non-targeted ¹H NMR metabolomic analyses of plasma and liver samples collected from male and female mice ancestrally exposed to TBT in two independent transgenerational experiments in which F3 and F4 males became obese when challenged with increased dietary fat.

RESULTS

Metabolomics confirmed transgenerational obesogenic effects of environmentally relevant doses of TBT in F3 and F4 males, in two independent studies. Although females never became obese, their specific metabolomic fingerprint evidenced distinct transgenerational effects of TBT in female mice consistent with impaired capacity for liver biotransformation.

DISCUSSION

This study is the first application of metabolomics to unveil the transgenerational effects of EDC exposure. Very early, significant changes in the plasma metabolome were observed in animals ancestrally exposed to TBT. These changes preceded the onset of obesogenic effects elicited by increased dietary fat in the TBT groups, and which ultimately resulted in significant changes in the liver metabolome. Development of metabolomic fingerprints could facilitate the identification of individuals carrying the signature of ancestral obesogen exposure that might increase their susceptibility to other risk factor such as increased dietary fat.

Tributyltin and the female hypothalamic-pituitary-gonadal disruption

The hypothalamic-pituitary-gonadal (HPG) axis is the principal modulator of reproductive function. Proper control of this system relies on several hormonal pathways, which make the female reproductive components susceptible to disruption by endocrine-disrupting chemicals such as tributyltin (TBT). Here, we review the relevant research on the associations between TBT exposure and dysfunction of the female HPG axis components. Specifically, TBT reduced hypothalamic gonadotropin-releasing hormone (GnRH) expression and gonadotropin release, and impaired ovarian folliculogenesis, steroidogenesis, and ovulation, at least in part, by causing abnormal sensitivity to steroid feedback mechanisms and deleterious ovarian effects. This review covers studies using environmentally relevant doses of TBT in vitro (1 ng-20 ng/mL) and in vivo (10 ng-20 mg/Kg) in mammals. The review also includes discussion of important gaps in the literature and suggests new avenue of research to evaluate the possible mechanisms underlying TBT-induced toxicity in the HPG axis. Overall, the evidence indicates that TBT exposure is associated with toxicity to the components of the female reproductive axis. Further studies are needed to better elucidate the mechanisms through which TBT impairs the ability of the HPG axis to control reproduction.

Tributyltin protects against ovariectomy-induced trabecular bone loss in C57BL/6J mice with an attenuated effect in high fat fed mice

Risk factors for poor bone quality include estrogen loss at menopause, a high fat diet and exposures to drugs/chemicals that activate peroxisome proliferator activated receptor gamma (PPARγ). We previously reported that the PPARγ and retinoid X receptor dual ligand, tributyltin (TBT), repressed periosteal bone formation but enhanced trabecular bone formation in vivo. Here, we examined the interaction of diet, ovariectomy (OVX) and TBT exposure on bone structure. C57BL/6J mice underwent either sham surgery or OVX at 10 weeks of age. At 12 weeks of age, they were placed on a low (10% kcal) or high (45% kcal) fat, sucrose-matched diet and treated with vehicle or TBT (1 or 5 mg/kg) for 14 weeks. OVX increased body weight gain in mice on either diet. TBT enhanced body weight gain in intact mice fed a high fat diet, but decreased weight gain in OVX mice. Elemental tin concentrations increased dose-dependently in bone. TBT had marginal effects on cortical and trabecular bone in intact mice fed either diet. OVX caused a reduction in cortical and trabecular bone, regardless of diet. In high fat fed OVX mice, TBT further reduced cortical thickness, bone area and total area. Interestingly, TBT protected against OVX-induced trabecular bone loss in low fat fed mice. The protective effect of TBT was nullified by the high fat. These results show that TBT protects against trabecular bone loss, even in the presence of a strongly resorptive environment, at an even lower level of exposure than we showed repressed homeostatic resorption.

Effects of tributyltin on retinoid X receptor gene expression and global DNA methylation during intracapsular development of the gastropod Tritia mutabilis (Linnaeus, 1758)

The tributyltin (TBT)-mediated induction of imposex in marine snails is considered a common mechanism of endocrine disruption through the retinoid X receptor (RXR)-dependent pathway. However, there is evidence that regulation of RXR also relates to metabolic processes, differentiation, apoptosis, and embryonic development, playing a key role in molluscan neuronal differentiation and organogenesis. In this regard, very little is known about the gastropod Tritia mutabilis especially in relation to the effects of TBT exposure during intracapsular embryonic development. In this study, we have investigated the RXR expression fold changes of T. mutabilis encapsulated embryos exposed to different concentrations (10^-10 to 10^-12 M) of TBT up to 10 days of treatment. We demonstrate that RXR is sequentially expressed during development and that exposure to the lowest and highest TBT doses induces time-dependent changes in RXR gene transcription. We also show that TBT treatment is associated with global DNA demethylation and reduced DNA-methyltransferase I (DNMT1) expression and activity levels. Overall, our data indicate that RXR has important functions during the early stages of T. mutabilis embryo development and is involved in mediating the potential epigenetic alterations induced by TBT exposure.

Effects of microplastics (MPs) and tributyltin (TBT) alone and in combination on bile acids and gut microbiota crosstalk in mice

Microplastics (MPs) and tributyltin (TBT) are both potential environmental pollutants that enter organisms through the food chain and affect bodily functions. However, the effects and mechanisms of MPs and TBT exposure (especially the co-exposure of both pollutants) on mammals remain unclear. In this study, Ф5μm MPs (5MP) was administered alone or in combination with TBT to investigate the health risk of oral exposure in mice. All three treatments induced inflammation in the liver, altered gut microbiota composition and disturbed fecal bile acids profiles. In addition to decreasing triglyceride (TG) and increasing aspartate aminotransferase (AST) and macrophage-expressed gene 1 (Mpeg1), 5MP induced hepatic cholestasis by stimulating the expression of the cholesterol hydroxylase enzymes CYP8B1 and CYP27A1, and inhibiting multidrug resistance-associated protein 2 and 3 (MRP2, MRP3), and bile-salt export pump (BSEP) to prevent bile acids for entering the blood and bile. Correspondingly, 5MP treatment decreased 7-ketolithocholic acid (7-ketoLCA) and taurocholic acid (TCA), which were positively correlated with decreased Bacteroides and Marvinbryantia and negatively correlated with increased Bifidobacterium. In addition, TBT increased interferon γ (IFNγ) and Mpeg1 levels to induce inflammation, accompanied by decreased 7-ketoLCA, tauro-alpha-muricholic acid (T-alpha-MCA) and alpha-muricholic acid (alpha-MCA) levels, which were negatively related to Coriobacteriaceae_UCG-002 and Bifidobacterium. Co-exposure to 5MP and TBT also decreased TG and induced bile acids accumulation in the liver due to inhibited BSEP, which might be attributed to the co-regulation of decreased T-alpha-MCA and Harryflintia. In conclusion, the administration of 5MP and TBT alone and in combination could cause gut microbiome dysbiosis and subsequently alter bile acids profiles, while the combined exposure of 5MP and TBT weakened the toxic effects of 5MP and TBT alone.

Retinoids promote penis development in sequentially hermaphroditic snails

Sexual systems are surprisingly diverse, considering the ubiquity of sexual reproduction. Sequential hermaphroditism, the ability of an individual to change sex, has emerged multiple times independently across the animal kingdom. In molluscs, repeated shifts between ancestrally separate sexes and hermaphroditism are generally found at the level of family and above, suggesting recruitment of deeply conserved mechanisms. Despite this, molecular mechanisms of sexual development are poorly known. In molluscs with separate sexes, endocrine disrupting toxins bind the retinoid X receptor (RXR), activating ectopic male development in females, suggesting the retinoid pathway as a candidate controlling sexual transitions in sequential hermaphrodites. We therefore tested the role of retinoic acid signaling in sequentially hermaphroditic Crepidula snails, which develop first into males, then change sex, maturing into females. We show that retinoid agonists induce precocious penis growth in juveniles and superimposition of male development in females. Combining RXR antagonists with retinoid agonists significantly reduces penis length in induced juveniles, while similar treatments using retinoic acid receptor (RAR) antagonists increase penis length. Transcripts of both receptors are expressed in the induced penis. Our findings therefore show that retinoid signaling can initiate molluscan male genital development, and regulate penis length. Further, we show that retinoids induce ectopic male development in multiple Crepidula species. Species-specific influence of conspecific induction of sexual transitions correlates with responsiveness to retinoids. We propose that retinoid signaling plays a conserved role in molluscan male development, and that shifts in the timing of retinoid signaling may have been important for the origins of sequential hermaphroditism within molluscs.

Metal load and oxidative stress driven by organotin compounds on rainbow trout

Tributyltin-based (TBT) antifouling paints, widely used for the treatment of flooded surfaces, have been banned in 2008 for their high environmental persistence and bioaccumulation in aquatic organisms. Although it is still present in aquatic ecosystems, oxidative stress driven by TBT has been still poorly investigated in fish. The aim of the study was to examine the time-course stress responses in liver of rainbow trout that received a single intraperitoneal injection of tributyltin chloride (TBTC) or tributyltin ethoxide (TBTE), both at a dose of 0.05 and 0.5 mg/kg. Levels of metallothioneins, total glutathione, malondialdehyde, superoxide dismutase, catalase, glutathione peroxidase and glutathione S-transferase were evaluated at 3 and 6 days post-injection. Tin load was measured in the muscle of the same fish. Differences were observed in the time-course accumulation of tin with a clear dose-response relationship. Although individual oxidative stress biomarkers varied, the biomarker profile indicated different stress mechanisms caused by both TBTC and TBTE. The weak induction of metal-trapping metallothioneins and the changes of oxidative stress biomarkers suggested a stress-pressure in both TBT-treated trout, advising for an ecotoxicological risk for freshwater ecosystems.

Tributyltin perturbs femoral cortical architecture and polar moment of inertia in rat

Background

Tributyltin, a well-known endocrine disruptor, is widely used in agriculture and industry. Previous studies have shown that tributyltin could cause deleterious effects on bone health by impairing the adipo-osteogenic balance in bone marrow.

Methods

To investigate further the effects of tributyltin on bone, weaned male SD rats were treated with tributyltin (0.5, 5 or 50 μg·kg^− 1) or corn oil by gavage once every 3 days for 60 days in this study. Then, we analyzed the effects of tributyltin on geometry, the polar moment of inertia, mineral content, relative abundances of mRNA from representative genes related to adipogenesis and osteogenesis, serum calcium ion and inorganic phosphate levels.

Results

Micro-computed tomography analysis revealed that treatment with 50 μg·kg^− 1 tributyltin caused an obvious decrease in femoral cortical cross sectional area, marrow area, periosteal circumference and derived polar moment of inertia in rats. However, other test results showed that exposure to tributyltin resulted in no significant changes in the expression of genes detected, femoral cancellous architecture, ash content, as well as serum calcium ion and inorganic phosphate levels.

Conclusions

Exposure to a low dose of tributyltin from the prepubertal to adult stage produced adverse effects on skeletal architecture and strength.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04298-2.

Legacy and emerging antifouling biocide residues in a tropical estuarine system (Espirito Santo state, SE, Brazil)

The contamination by antifouling biocide residues (booster biocides - diuron, Irgarol, chlorothalonil, dichlofluanid and DCOIT; butyltin compounds-BTs (TBT, DBT and MBT); and antifouling paint particles-APPs) was appraised in sediments of Vitoria Estuarine System (VES). Even at its historical lower (ΣBTs ≤113 ng Sn g^-1 dry wt), the current environmental levels of BTs in areas with a predominance of boatyards still pose a risk to the local biota and human population. DCOIT, among booster biocides, was the most frequently detected, especially in boatyards (≤40 ng g^-1 dry wt) and Vitoria Port (64 ng g^-1 dry wt), while APPs were also detected mainly in sediments of boatyards (≤5,969 μg g^-1 dry wt). Since levels of diuron and DCOIT in APPs were as high as 1,670,000 and 899,000 ng g^-1 dry wt, respectively, they are acting as secondary sources of these antifouling biocides. Therefore, VES is threatened by antifouling biocide residues due to the multiple diffuse sources of contamination, showing the need for more efforts on public policies (including temporal trend monitoring studies).

Neurotoxicity and physiological stress in brain of zebrafish chronically exposed to tributyltin

Tributyltin (TBT), an organotin compound, is hazardous in aquatic ecosystems. However, the mechanisms underlying TBT-induced central nervous system (CNS) toxicity remain to be determined especially in freshwater aquatic vertebrates. The aim of present study was to investigate the effects of chronic exposure to TBT on brain functions in a freshwater teleost the adult wild-type zebrafish (Danio rerio). Fish were exposed to sublethal concentrations of TBT (10, 100 or 300 ng/L) for 6 weeks. The influence of long-term TBT exposure was assessed in the brain of zebrafish with antioxidant related indices including malondialdehyde (MDA) levels and total antioxidant capacity, neurological parameters such as activities of acetylcholinesterase, and monoamine oxidase as well as levels of nitric oxide, dopamine, 5-hydroxytryptamine. In addition indices related to sensitivity of toxic insult such as cytochrome P450 1 regulation and heat shock protein 70 were determined. The regulation of related genes involved in endoplasmic reticulum stress (ERS), apoptosis and Nrf2 pathway were measured. Adverse physiological and biochemical responses were significantly enhanced in a concentration-dependent manner reflecting neurotoxicity attributed to TBT exposure. Our findings provide further insight into TBT-induced toxicity in wild-type zebrafish. and enhance our understanding of the molecular mechanisms underlying TBT-initiated CNS effects.

Effects of the tributyltin on the blood parameters, immune responses and thyroid hormone system in zebrafish

Tributyltin (TBT) is a widely used organotin compound around the world and was frequently detected in surface waters, which would pose risk to aquatic organisms. However, the mechanisms of TBT-induced toxicity is not full clear. The present study investigated the effects of the tributyltin (TBT) on the blood parameters, immune responses and thyroid hormone system in zebrafish. Fish were exposed to sublethal concentrations of TBT (10 ng/L, 100 ng/L and 300 ng/L) for 6 weeks. The effects of long-term exposure to TBT on blood parameters (NH3, ammonia; GLU, glucose; TP, total proteins; CK, creatine kinase; ALT, alanine aminotransferase; AST, aspartate aminotransferase), immune responses (Lys, lysozyme; IgM, immunoglobulin M) and some indexes related thyroid hormone system (T3, 3,5,3'-triiodothyronine; T4, thyroxine) were measured in zebrafish, as well as the expression of genes related to immune responses and thyroid hormone system. Based on the results, the physiological-biochemical responses was significantly enhanced with an increase in TBT concentration, reflected by the abnormal blood indices, dysregulation of endocrine system and immunotoxicity in zebrafish under TBT stress. The present study greatly extends our understanding of adverse effects of TBT on aquatic organisms.

Quantification of tributyltin in seawater using triple isotope dilution gas chromatography-inductively coupled plasma mass spectrometry achieving high accuracy and complying with European Water Framework Directive limits

A triple isotope dilution GC-ICPMS method for the determination of tributyltin (TBT) was developed and validated to meet the European Water Framework Directive (WFD) requirements. The validation procedure involved the evaluation of trueness, precision (repeatability, intermediate precision), limit of detection (LOD) and limit of quantification (LOQ), stability, measurement uncertainty and traceability studies. The method is one of the most sensitive methods published to date with good accuracy, 103% average recovery in the range with %RSDs of 2.8-6.7%. A LOD value of 0.015 ng L^-1 for the TBT cation was achieved with a sample volume of 12 mL seawater. TBT was derivatized using 20 µL sodium tetraethylborate solution (0.05% NaBEt₄) to make volatile for GC-ICPMS. Measurement uncertainty was in the range of 4.8-13% which was achieved through dissolution of tributyltinchloride (TBTCl) in 1-propanol, a low-volatility solvent combined with the use of a triple isotope dilution (ID) calibration technique. Isotope dilution calibration was performed by adding ¹¹⁷Sn isotopically enriched TBT to the seawater samples. The stability test results showed that TBT concentration was stable for three months in seawater samples after passing through a 0.2 µm filter and stored in amber glass bottles at 4°C. The response surface methodology (RSM) approach was successfully implemented to provide optimal conditions for large volume injection (LVI) to obtain the maximum analytical signal. The key variables selected in the experimental design were evaporation time, evaporation temperature, carrier flow, and injection speed. This method was applied to seawater samples collected from the Bay of Izmit, Kocaeli, Turkey, where TBT pollution has not been measured yet.

Tributyltin Induces the Tissue-Specific Stresses in Zebrafish, a Study in Various Tissues of Muscle, Gill and Intestine

Because the mechanism of tissue-specific toxicity of tributyltin (TBT) in aquatic organisms has not been explained clearly, the aim of this study is to investigate the effect of chronic exposure to TBT on muscle-related energy metabolism, gill-related ATPase enzymatic system and intestine-related digestive enzymes activities in zebrafish. Male zebrafish were exposed to sub-lethal concentrations of TBT (10, 100 and 300 ng/L) for 6 weeks. Multiple biomarkers were measured (such as glucose, lactate, hexokinase, pyruvate kinase, lactate dehydrogenase, ATP content, ATPases, trypsin, lipase and amylase), which reflected more serious physiological stress with increasing TBT concentrations during the experimental period. Through principal component analysis (PCA) and integrated biomarker response (IBR) analysis, the toxic effect of TBT in zebrafish was in a concentration-dependent manner. Shortly, the results of this study can provide new evidence for a comprehensive understanding of the toxic effects of TBT.

A functional benchmark dose analysis

Exposure to the antifouling tributyltin (TBT) has been related to imposex in mollusks and to obesogenicity, adipogenesis and masculinization in fish. To understand the underlying molecular mechanisms, we evaluated dose-response effects of TBT (1.7-56 nM) in zebrafish eleutheroembryos transcriptome exposed from 2 to 5 days post-fertilization. RNA-sequencing analysis identified 3238 differentially expressed transcripts in eleutheroembryos exposed to TBT. Benchmark dose analyses (BMD) showed that the point of departure (PoD) for transcriptomic effects (9.28 nM) was similar to the metabolomic PoD (11.5 nM) and about one order of magnitude lower than the morphometric PoD (67.9 nM) or the median lethal concentration (LC₅₀: 93.6 nM). Functional analysis of BMD transcriptomic data identified steroid metabolism and cholesterol and vitamin D₃ biosynthesis as the most sensitive pathways to TBT (<50% PoD). Conversely, transcripts related to general stress and DNA damage became affected only at doses above the PoD. Therefore, our results indicate that transcriptomes can act as early molecular indicators of pollutant exposure, and illustrates their usefulness for the mechanistic identification of the initial toxic events. As the estimated molecular PoDs are close to environmental levels, we concluded that TBT may represent a substantial risk in some natural environments.

Gut microbiome alterations induced by tributyltin exposure are associated with increased body weight, impaired glucose and insulin homeostasis and endocrine disruption in mice

Tributyltin (TBT), an organotin compound once widely used in agriculture and industry, has been reported to induce obesity and endocrine disruption. Gut microbiota has a strong connection with the host's physiology. Nevertheless, the influences of TBT exposure on gut microbiota and whether TBT-influenced gut microbiota is related to TBT-induced toxicity remain unclear. To fill these gaps, ICR (CD-1) mice were respectively exposed to TBT at NOEL (L-TBT) and tenfold NOEL (H-TBT) daily by gavage for 8 weeks in the current study. The results showed that TBT exposure significantly increased body weight as well as epididymal fat, and led to adipocyte hypertrophy, dyslipidemia and impaired glucose and insulin homeostasis in mice. Additionally, TBT exposure significantly decreased the levels of T4, T3 and testosterone in serum. Also of note, TBT exposure changed gut microbiota composition mainly by decreasing Bacteroidetes and increasing Firmicutes proportions. To confirm the role of gut microbiota in TBT-induced overweight and hormonal disorders, fecal microbiota transplantation was performed and the mice receiving gut microbiota from H-TBT mice had similar phenotypes with their donor mice including significant body weight and epididymal fat gain, glucose and insulin dysbiosis and hormonal disorders. These results suggested that gut microbiome altered by TBT exposure was involved in the TBT-induced increased body weight, impaired glucose and insulin homeostasis and endocrine disruption in mice, providing significant evidence and a novel perspective for better understanding the mechanism by which TBT induces toxicity.

Tributyltin enhanced anxiety of adult male zebrafish through elevating cortisol level and disruption in serotonin, dopamine and gamma-aminobutyric acid neurotransmitter pathways

Tributyltin (TBT), a widely and persistently distributed organontin, has been well documented to disrupt reproduction and behaviors in animals due to its anti-aromatase activity. TBT has been also reported to enhance anxiety in several fish species, whereas the mechanism underlying remains largely unknown. To investigate the disruption of TBT on fish anxiety and the mechanisms possibly involved, adult male zebrafish (Danio rerio) were treated with TBT (100 and 500 ng/L) for 28 days and anxiety behavior was further investigated using a novel tank dive test. Result showed that TBT treatment significantly enhanced the total time of the fish spent in the lower half, delayed the onset time to the higher half of the tank and increased the total duration of freezing of the fish, indicating an enhanced anxiety in TBT-treated fish. Accordingly, TBT sharply elevated the cortisol levels in plasma in a concentration-dependent manner, suggesting that the elevated cortisol level might be involved in the enhanced anxiety. Although the expression of crha was significantly increased and crhbp was significantly decreased in the brain of TBT-treated fish which is consistent to the elevated cortisol level, the expressions of actha and acthb were sharply down-regulated. In contrast, the expressions of genes responsible for the synthesis and action of serotonin (5-HT) (pet1, thp2 and htr1aa), dopamine (DA) (th1, slc6a3, drd2a and drd2b) and gamma-aminobutyric acid (GABA) (gad2 and gabrg2) were all significantly inhibited. The down-regulation of these pivotal genes acting in 5-HT, DA and GABA neurotransmitter systems in response to TBT corresponded well with the TBT-enhanced anxiety in fish. It was thus strongly suggested that these neurotransmitters might be also involved in TBT-enhanced anxiety in adult male zebrafish. The present study extended our understanding of the neurotoxicity of TBT on the anxiety control and behavioral modulation in fish.

Survey of imposex in Nucella lapillus as an indicator of tributyltin pollution in Northern Irish coastal waters, 2004 to 2017

Tributyltin (TBT) was a commonly used biocide in anti-fouling paints for marine vessels, however, it had negative impacts on non-target species, including causing imposex in dogwhelks (Nucella lapillus). Since the 1980s, legislation has been introduced to curtail its usage, culminating in a ban by the International Maritime Organisation (IMO) in 2008. In 2004 a national imposex monitoring network was established in Northern Ireland to determine the level and extent of TBT pollution. The level of imposex in N. lapillus was assessed according to the degree of male sexual development in the female using three measures: percentage of imposex-affected females (%I), the relative penis size index (RPSI), and the vas deferens sequence index (VDSI). All sites showed improvement since the initial survey with a reduction in imposex and an improvement in ecological quality under the classification of the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR).

Detoxification roles of tributyltin-binding protein type 2 in Japanese medaka (Oryzias latipes) exposed to tributyltin

Tributyltin-binding protein type 2 (TBT-bp2), a homolog of α1-acid glycoprotein, may contribute to both accumulation and detoxification of TBT in fish. In this study, we conducted acute TBT exposure tests using both wide-type (WT) and TBT-bp2^-/- (KO) strains of medaka and compared their responses in survival time and accumulation of TBT. Deficiency of TBT-bp2 significantly accelerated the time to death of medaka and decreased the LC₅₀ of TBT, indicating that the KO-strain is more sensitive to TBT. No significant difference in the intrinsic TBT concentration in surviving fish was observed between the two strains. However, the intrinsic TBT concentration in dead KO-strain was significantly lower than that in WT-strain. These findings provide direct evidence, supporting the hypothesis that TBT-bp2 plays a critical role in the detoxification of TBT in fish.

A quarter century of recovery of the whelk Thais orbita from tributyltin pollution off Perth, Western Australia

Imposex is a condition in which females of dioecious marine snails develop rudimentary male characteristics. It is caused by tributyltin (TBT) used as an antifoulant in vessel paints since the late 1960s. Following the 2008 international ban on TBT, a decreasing rate of imposex has been observed worldwide. In Western Australia, imposex surveys of the whelk Thais orbita up to 2011 in the Perth metropolitan area suggested a decreasing trend but a significant recovery has not been confirmed. Collection of T. orbita from 11 sites in 2019 demonstrated a virtually complete recovery from imposex. Although it is generally accepted that male snails are not affected by TBT, the historical data set allowed confirmation that the male penis is of similar size in T. orbita collected at heavily affected sites and at relatively unaffected sites. Similarly, imposexed female snails had similar shell lengths to female snails at non-impacted sites.

Short term chronic toxicity of tributyltin on the testes of adult albino rats and the possible protective role of omega-3

The declining rate of male fertility is a growing concern. Tributyltin (TBT) is a well-known endocrine disruptor (ED), that induces imposex in female gastropods and is widely used in various industrial applications. The aim of this study was to evaluate the toxic effects of TBT on the testes of adult albino rats and the possible role of omega-3. Forty two adult male albino rats were divided into five groups; control group (Group I) and four experimental groups: omega-3 treated group, TBT treated group, TBT & omega-3 treated group and follow up group. At the end of the study, the rats were subjected to biochemical, histological, immunohistochemical staining for Ki-67 and seminal examinations. Our results clarfied that TBT induced a significant decrease in testosterone, FSH, LH and serum glutathione peroxidase levels and a significant increase in the serum Malondialdehyde as compared to the control group. Tributyltin induced disorganization and shrinkage of seminiferous tubules, apoptosis, cellular damage and marked reduction in the germinal epithelium. A significant decrease in the cell proliferation and arrested spermatogenesis were also detected. Seminal analysis of TBT group showed a significant affection of all parameters as compared to other groups. Omega-3 ameliorated all of these hazardous effects. Follow up group still showed toxic effects. In conclusion, TBT has a toxic effect on the testis. Increased testicular oxidative stress, cellular damage and arrest of spermatogenesis with attenuation in antioxidant defenses are all contributing factors. Omega-3 can protect against TBT induced reproductive toxicity.

Establishment of a Japanese medaka (Oryzias latipes) transgenic line expressing Takifugu rubripes pufferfish saxitoxin and tetrodotoxin binding protein 1, and evaluation of tributyltin toxicity via in ovo nanoinjection

Pufferfish saxitoxin and tetrodotoxin binding proteins (PSTBPs) play an important role in the toxification of certain species of pufferfish. Recombinant Takifugu rubripes PSTBP1 (rTrub.PSTBP1) is reported to bind to tributyltin, and so it has been suggested that rTrub.PSTBP1 may reduce the toxicity of tributyltin. However, the role of PSTBP1 in vivo remains to be elucidated. Here, we established a transgenic medaka line showing whole-body Renilla reniformis green fluorescent protein and Trub.PSTBP1 expression, as confirmed by real-time polymerase chain reaction and mRNA-Seq analysis. mRNA-Seq analysis also showed that cytochrome P450 superfamily genes and the gene encoding ATP-binding cassette sub-family G member 2 were highly expressed in the transgenic medaka. Using embryos of the transgenic medaka line, we conducted an in ovo nanoinjection test to examine the effect of Trub.PSTBP1 in vivo, and obtained data suggesting that Trub.PSTBP1 expression may have reduced the toxicity of tributyltin in our transgenic medaka line. Our findings will be useful for future functional analyses of Trub.PSTBP1.