Tributyltin exposure results in craniofacial cartilage defects in rockfish (Sebastiscus marmoratus) embryos

Decrypting the skeletal toxicity of vertebrates caused by environmental pollutants from an evolutionary perspective: From fish to mammals

The rapid development of modern society has led to an increasing severity in the generation of new pollutants and the significant emission of old pollutants, exerting considerable pressure on the ecological environment and posing a serious threat to both biological survival and human health. The skeletal system, as a vital supportive structure and functional unit in organisms, is pivotal in maintaining body shape, safeguarding internal organs, storing minerals, and facilitating blood cell production. Although previous studies have uncovered the toxic effects of pollutants on vertebrate skeletal systems, there is a lack of comprehensive literature reviews in this field. Hence, this paper systematically summarizes the toxic effects and mechanisms of environmental pollutants on the skeletons of vertebrates based on the evolutionary context from fish to mammals. Our findings reveal that current research mainly focuses on fish and mammals, and the identified impact mechanisms mainly involve the regulation of bone signaling pathways, oxidative stress response, endocrine system disorders, and immune system dysfunction. This study aims to provide a comprehensive and systematic understanding of research on skeletal toxicity, while also promoting further research and development in related fields.

Molecular mechanisms of environmental pollutant-induced cartilage damage: from developmental disorders to osteoarthritis

The objective of the present study was to review the molecular mechanisms of the adverse effects of environmental pollutants on chondrocytes and extracellular matrix (ECM). Existing data demonstrate that both heavy metals, including cadmium (Cd), lead (Pb), and arsenic (As), as well as organic pollutants, including polychlorinated dioxins and furans (PCDD/Fs) and polychlorinated biphenyls (PCB), bisphenol A, phthalates, polycyclic aromatic hydrocarbons (PAH), pesticides, and certain other organic pollutants that target cartilage ontogeny and functioning. Overall, environmental pollutants reduce chondrocyte viability through the induction apoptosis, senescence, and inflammatory response, resulting in cell death and impaired ECM production. The effects of organic pollutants on chondrocyte development and viability were shown to be mediated by binding to the aryl hydrocarbon receptor (AhR) signaling and modulation of non-coding RNA expression. Adverse effects of pollutant exposures were observed in articular and growth plate chondrocytes. These mechanisms also damage chondrocyte precursors and subsequently hinder cartilage development. In addition, pollutant exposure was shown to impair chondrogenesis by inhibiting the expression of Sox9 and other regulators. Along with altered Runx2 signaling, these effects also contribute to impaired chondrocyte hypertrophy and chondrocyte-to-osteoblast trans-differentiation, resulting in altered endochondral ossification. Several organic pollutants including PCDD/Fs, PCBs and PAHs, were shown to induce transgenerational adverse effects on cartilage development and the resulting skeletal deformities. Despite of epidemiological evidence linking human environmental pollutant exposure to osteoarthritis or other cartilage pathologies, the data on the molecular mechanisms of adverse effects of environmental pollutant exposure on cartilage tissue were obtained from studies in laboratory rodents, fish, or cell cultures and should be carefully extrapolated to humans, although they clearly demonstrate that cartilage should be considered a putative target for environmental pollutant toxicity.

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.

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.

Toxicity of tributyltin chloride on haarder (Liza haematocheila) after its acute exposure: Bioaccumulation, antioxidant defense, histological, and transcriptional analyses

Liza haematocheila is exposed to various chemical contaminants from anthropogenic sources, including tributyltin chloride (TBTC). Yet the toxicity mechanism of TBTC on haarder remains unclear. The haarder was exposed to different doses (0, 10%, 20%, and 50% of LC₅₀-96 h) of TBTC. In this study, the results revealed its high bioaccumulation in the livers and significant alteration for development. The activities of antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase decreased after 96-h exposure to TBTC, this accompanied by an increased malondialdehyde level. TBTC exposure caused the intense production of reactive oxygen species, a reduction in total blood cell count in serum, and apoptosis-related alterations in livers, indicating that enhanced oxidative stress occurred in the process of TBTC exposure. Histological results revealed angiorrhexis and infiltration of inflammatory cells, vacuolar degeneration of hepatocytes in the livers, and swelling, fusion, and disintegration of gill organs. Interestingly, the obtained transcriptional profiles indicated that high doses of TBTC caused energy disorder, apoptosis, and adipogenesis restriction mediated by cytokines and adipokines in Jak-STAT and adipocytokine signaling pathways. In summary, acute exposure to high doses of TBTC could impair the antioxidant system and pathways related to energy, apoptosis and adipogenesis, eventually posing a serious challenge to the fitness of haarder individuals and its fish populations as marine resources.

Effects of low-concentration glyphosate and aminomethyl phosphonic acid on zebrafish embryo development

Glyphosate (GLY) is the most widely used broad-spectrum, non-selective herbicide in the world, whose main degradation product is aminomethyl phosphonic acid (AMPA). Because of long-term and large-scale use, residual GLY and AMPA in the environment pose great environmental and human health threats. The purpose of this study is to evaluate the effects and mechanism of residual low-concentrations of GLY and AMPA in the environment on the development of zebrafish embryos. Zebrafish embryos were exposed to 0, 1, 10, 100, and 700 ng·mL-1 GLY and AMPA for 72 h (from 2 to 74 h post-fertilization). With increasing exposure dose, heart rates of both embryos and larvae showed a rising trend and obvious arrhythmia appeared. Defects in cardiac development and function of zebrafish juveniles may be related to altered transcription levels of cardiac development genes (TBX5, NKX2.5, BMP4) and apoptosis genes (Bcl-2, Bax). In addition, pericardial edema and bone deformation of zebrafish embryos may be caused by inhibition of Na+/K+-ATPase and Ca2+-ATPase after exposure to GLY and AMPA. The present results demonstrated that at typical environmental residual concentrations of GLY and AMPA had similar developmental toxicity in zebrafish embryos.

The fish early-life stage sublethal toxicity syndrome - A high-dose baseline toxicity response

A large number of toxicity studies report abnormalities in early life-stage (ELS) fish that are described here as a sublethal toxicity syndrome (TxSn_FELS) and generally include a reduced heart rate, edemas (yolk sac and cardiac), and a variety of morphological abnormalities. The TxSn_FELS is very common and not diagnostic for any chemical or class of chemicals. This sublethal toxicity syndrome is mostly observed at high exposure concentrations and appears to be a baseline, non-specific toxicity response; however, it can also occur at low doses by specific action. Toxicity metrics for this syndrome generally occur at concentrations just below those causing mortality and have been reported for a large number of diverse chemicals. Predictions based on tissue concentrations or quantitative-structure activity relationship (QSAR) models support the designation of baseline toxicity for many of the tested chemicals, which is confirmed by observed values. Given the sheer number of disparate chemicals causing the TxSn_FELS and correlation with QSAR derived partitioning; the only logical conclusion for these high-dose responses is baseline toxicity by nonspecific action and not a lock and key type receptor response. It is important to recognize that many chemicals can act both as baseline toxicants and specific acting toxicants likely via receptor interaction and it is not possible to predict those threshold doses from baseline toxicity. We should search out these specific low-dose responses for ecological risk assessment and not rely on high-concentration toxicity responses to guide environmental protection. The goal for toxicity assessment should not be to characterize toxic responses at baseline toxicity concentrations, but to evaluate chemicals for their most toxic potential. Additional aspects of this review evaluated the fish ELS teratogenic responses in relation to mammalian oral LD50s and explored potential key events responsible for baseline toxicity.

Spinal malformations in a naturally isolated Neotropical fish population

Fish populations that reside in completely isolated freshwater ecosystems are rare worldwide. The Vila Velha State Park (VVSP), located in southern Brazil, is recognized for its arenitic formations called sinkholes (furnas), which are completely isolated. Fish populations within, such as those of Psalidodon aff. fasciatus, often develop vertebral malformations due to this isolation from other conspecifics and other species. In this study, we analyzed geometric morphology in digital radiographs to identify congenital deformations of Psalidodon aff. fasciatus in Furna 2 of VVSP. We found many fish with spinal deformities, including wide variation in the number of caudal vertebrae and corporal deformations related to a flattened body and spinal curvature. Females were more affected than males. We also demonstrated that these deformations reflect inbreeding and an absence of gene flow in the population. In conclusion, isolated populations such as fish species in furnas are potential models for evo-devo research.

Oral Exposure to Tributyltin Induced Behavioral Abnormality and Oxidative Stress in the Eyes and Brains of Juvenile Japanese Medaka (Oryzias latipes)

The widely used compound tributyltin (TBT), which can be continuously detected in aquatic species and seafood, may induce diverse adverse effects on aquatic organisms. However, little is known regarding the mechanistic links between behavioral abnormality and oxidative stress in different fish tissues in response to oral TBT exposure. Herein, juvenile Japanese medaka (Oryzias latipes) were orally exposed to TBT at 1 and 10 ng/g-bw/d for four weeks. After exposure, the locomotor activity and social interaction of juvenile medaka were found to be significantly reduced in the 10 ng/g-bw/d TBT-exposed group. Furthermore, the antioxidant biomarkers in different tissues of juvenile medaka showed different levels of sensitivity to TBT exposure. The eye superoxide dismutase (SOD) activities markedly increased in both groups exposed to 1 and 10 ng/g-bw/d TBT, while the eye and brain malondialdehyde (MDA) levels increased in the higher dose group. Furthermore, the eye and brain ATPase activities markedly declined in the 1 ng/g-bw/d TBT-exposed group. A correlation analysis revealed that the decreased locomotor activity and social interaction in medaka were associated with the eye antioxidant enzyme (i.e., SOD and catalase (CAT)) activity and brain oxidative damage level. Thus, our findings suggested that there might be some mechanistic links between the behavioral abnormality induced by TBT exposure and oxidative stress in the eyes and brains of medaka. Thus, our findings indicate that the impacts of oral exposure to TBT should be considered to better assess its risk to the aquatic ecosystem and human health.

Effects of the Hedgehog Signaling Inhibitor Itraconazole on Developing Rat Ovaries

Early ovary development is considered to be largely hormone independent; yet, there are associations between fetal exposure to endocrine disrupting chemicals and reproductive disorders in women. This can potentially be explained by perturbations to establishment of ovarian endocrine function rather than interference with an already established hormone system. In this study we explore if Hedgehog (HH) signaling, a central pathway for correct ovary development, can be disrupted by exposure to HH-disrupting chemicals, using the antifungal itraconazole as model compound. In the mouse Leydig cell line TM3, used as a proxy for ovarian theca cells, itraconazole exposure had a suppressing effect on genes downstream of HH signaling, such as Gli1. Exposing explanted rat ovaries (gestational day 22 or postnatal day 3) to 30 µM itraconazole for 72 h induced significant suppression of genes in the HH signaling pathway with altered Ihh, Gli1, Ptch1, and Smo expression similar to those previously observed in Ihh/Dhh knock-out mice. Exposing rat dams to 50 mg/kg bw/day in the perinatal period did not induce observable changes in the offspring's ovaries. Overall, our results suggest that HH signal disruptors may affect ovary development with potential long-term consequences for female reproductive health. However, potent HH inhibitors would likely cause severe teratogenic effects at doses lower than those causing ovarian dysgenesis, so the concern with respect to reproductive disorder is for the presence of HH disruptors at low concentration in combination with other ovary or endocrine disrupting compounds.

Hedgehog signal disruption, gonadal dysgenesis and reproductive disorders: Is there a link to endocrine disrupting chemicals?

Developmental exposure to chemicals that can disrupt sex hormone signaling may cause a broad spectrum of reproductive disorders. This is because reproductive development is tightly regulated by steroid sex hormones. Consequently, non-animal screening methods currently used to test chemicals for potential endocrine disrupting activities typically include steroidogenesis and nuclear receptor assays. In many cases there is a correlation between in vitro and in vivo data examining endocrine disruption, for example between blocked androgen receptor activity and feminized male genitals. However, there are many examples where there is poor, or no, correlation between in vitro data and in vivo effect outcomes in rodent studies, for various reasons. One possible, and less studied, reason for discordance between in vitro and in vivo data is that the mechanisms causing the in vivo effects are not covered by those typically tested for in vitro. This knowledge gap must be addressed if we are to elaborate robust testing strategies that do not rely on animal experimentation. In this review, we highlight the Hedgehog (HH) signaling pathway as a target for environmental chemicals and its potential implications for reproductive disorders originating from early life exposure. A central proposition is that, by disrupting HH signal transduction during critical stages of mammalian development, the endocrine cells of the testes or ovaries fail to develop normally, which ultimately will lead to disrupted sex hormone synthesis and sexual development in both sexes. If this is the case, then such mechanism must also be included in future test strategies aimed at eliminating chemicals that may cause reproductive disorders in humans.

Tributyltin disrupts fin development in Fundulus heteroclitus from both PCB-sensitive and resistant populations: Investigations of potential interactions between AHR and PPARγ

Tributyltin (TBT) and dioxin-like polychlorinated biphenyls (PCBs) are environmental contaminants that are highly toxic to fish and co-occur in New Bedford Harbor (NBH), an estuarine Superfund site located in Massachusetts, USA. Atlantic killifish (Fundulus heteroclitus) that reside in NBH (and other highly contaminated sites along the east coast of the United States) have developed resistance to activation of the aryl hydrocarbon receptor (AHR) pathway and the toxicity of dioxin-like chemicals, such as 3,3',4,4',5-pentachlorobiphenyl, PCB126. In many biological systems, TBT disregulates adipose and bone development via the PPARγ-RXR pathway; AHR activation also disrupts adipose and bone homeostasis, potentially through molecular crosstalk between AHR and PPARγ. However, little is known about how co-exposure and the interaction of these pathways modulate the toxicological effects of these contaminants. Here, we tested the hypotheses that TBT would induce teratogenesis in killifish via activation of PPARγ and that PCB126 co-exposure would suppress PPARγ pathway activation in PCB-sensitive killifish from a reference site (Scorton Creek, SC, PCB-sensitive) but not in PCB-tolerant NBH killifish. Killifish embryos from both populations exposed to TBT (50 and 100 nM) displayed caudal fin deformities. TBT did not change the expression of pparg or its target genes related to adipogenesis (fabp11a and fabp1b) in either population. However, expression of osx/sp7, an osteoblast marker gene, and col2a1b, a chondroblast marker gene, was significantly suppressed by TBT only in SC killifish. An RXR-specific agonist, but not a PPARγ-specific agonist, induced caudal fin deformities like those observed in TBT-treated embryos. PCB126 did not induce caudal fin deformities and did not exacerbate TBT-induced fin deformities. Further, PCB126 increased expression of pparg in SC embryos and not NBH embryos, but did not change the expression of fabp1b. Taken together, these results suggest that in killifish embryos the PPARγ pathway is regulated in part by AHR, but is minimally active at least in this early life stage. In killifish, RXR activation, rather than PPARγ activation, appears to be the mechanism by which TBT induces caudal fin teratogenicity, which is not modulated by AHR responsiveness.

Fenbuconazole exposure impacts the development of zebrafish embryos

Fenbuconazole (FBZ), a triazole-containing fungicide, is widely used in agriculture and horticulture. In the present study, the development and cardiac functioning were observed and determined in zebrafish embryos exposed to FBZ at 5, 50 and 500 ng/L nominal concentrations for 72 h. The results showed that 500 ng/L FBZ significantly increased pericardial edema rate, spine curvature rate, disturbed cardiac function, and led a shortened lower jaw. The transcription of genes such as tbx5, nkx2.5, tnnt2, gata4, bmp2b, myl7 was altered, which might be responsible for the cardiac developmental and functioning defects in the larvae. The deformation in bone development might be related with the impaired transcription levels of shh and bmp2b. The transcription of cyp26a1 (encoding retinoic acid metabolism enzyme) was significantly up-regulated in the 500 ng/L group, which might be a reason causing the teratogenic effect of FBZ. These results suggest that FBZ could have toxic effects on embryonic development, which should be considered in the risk evaluation of FBZ application.

The developmental effects of low-level procymidone towards zebrafish embryos and involved mechanism

Procymidone (PCM), a dicarboximide fungicide, is widely used in agriculture to control plant diseases. In the present study, zebrafish embryos were exposed to PCM at 0, 10, 100 and 1000 ng/L for 72 h, the development and cardiac functioning of larvae were observed and determined. The results showed that hatching rate was significantly decreased in the 1000 ng/L treatment, and pericardial edema rate and spine curvature rate were significantly increased in the 100 and 1000 ng/L groups. The PCM-treated larvae exhibited an increased heart rate as well as arrhythmia, and shortened low jaw. The transcription levels of cardiac development-related genes tbx5, nkx2.5, tnnt2, gata4, myh6, myl7, cdh2, ryr2 were altered, which might be responsible for the cardiac developmental and functioning defects in the larvae. The deformation in bone development might be related with the impaired transcription levels of ihh, shh, bmp2b, bmp4, gh, igf1, sox9, gli2. The activities of Na⁺/K⁺-ATPase and Ca²⁺-ATPase were significantly inhibited by 100 ng/L and 1000 ng/L PCM exposure, which might be a cause for the occurrence of pericardial edema and skeletal deformation. The results of this study will be helpful in evaluating the potential threat of PCM to fish population in the aquatic environment.

Frontiers in endocrine disruption: Impacts of organotin on the hypothalamus-pituitary-thyroid axis

Endocrine disruptors (EDs), chemical substances widely used in industry and ubiquitously distributed in the environment, are able to interfere with the synthesis, release, transport, metabolism, receptor binding, action, or elimination of endogenous hormones. EDs affect homeostasis mainly by acting on nuclear and nonnuclear steroid receptors but also on serotonin, dopamine, norepinephrine and orphan receptors in addition to thyroid hormone receptors. Tributyltin (TBT), an ED widely used as a pesticide and biocide in antifouling paints, has well-documented actions that include inhibiting aromatase and affecting the nuclear receptors PPARγ and RXR. TBT exposure in humans and experimental models has been shown to mainly affect reproductive function and adipocyte differentiation. Since thyroid hormones play a fundamental role in regulating the basal metabolic rate and energy homeostasis, it is crucial to clarify the effects of TBT on the hypothalamus-pituitary-thyroid axis. Therefore, we review herein the main effects of TBT on important metabolic pathways, with emphasis on disruption of the thyroid axis that could contribute to the development of endocrine and metabolic disorders, such as insulin resistance and obesity.

Tributyltin induces premature hatching and reduces locomotor activity in zebrafish (Danio rerio) embryos/larvae at environmentally relevant levels

Tributyltin (TBT) is an organotin compound that is the active ingredient of many biocides and antifouling agents. In addition to its well established role as an endocrine disruptor, TBT is also associated with adverse effects on the nervous system and behavior. In this study, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations of TBT (0.01, 0.1, 1 nM) to determine how low levels affected development and behavior. Fish exposed to 1 nM TBT hatched earlier when compared to controls. Following a 96-h exposure, total swimming distance, velocity, and activity of zebrafish larvae were reduced compared to controls. To identify putative mechanisms for these altered endpoints, we assessed embryo bioenergetics and gene expression. We reasoned that the accelerated hatch time could be related to ATP production and energy, thus embryos were exposed to TBT for 24 and 48-h exposure prior to hatch. There were no differences among groups for endpoints related to bioenergetics (i.e. basal, ATP-dependent, and maximal respiration). To address mechanisms related to changes in behavioral activity, we measured transcripts associated with muscle function (myf6, myoD, and myoG) and dopamine signaling (th, dat, dopamine receptors) as dopamine regulates behavior. No transcript was altered in expression by TBT in larvae, suggesting that other mechanisms exist that may explain changes in higher level endpoints. These results suggest that endpoints related to the whole animal (i.e. timing of hatch and locomotor behavior) are more sensitive to environmentally-relevant concentrations of TBT compared to the molecular and metabolic endpoints examined here.

Retinoic acid in developmental toxicology: Teratogen, morphogen and biomarker

This review explores the usefulness retinoic acid (RA) related physiological factors as possible biomarkers of embryotoxicity. RA is involved in the morphogenesis of the early embryo as well as in the development and maturation of a wide variety of organ anlagen. The region-specific homeostasis of RA in the embryo is in many ways the driving force determining developmental cell proliferation versus differentiation. As a consequence, RA concentrations are carefully controlled in time and space in the developing embryo. RA deficiency and overdosing both result in characteristic patterns of malformations that may involve many different organ systems. The central role of RA in embryo development provides us with a set of sensitive biomarkers that may be employed in developmental toxicity testing. This includes the synthesizing and metabolizing enzymes of RA, but also a myriad of related morphogenetic factors and their genes, of which the expression may be affected by changes in RA balance. Several examples of embryotoxicants interfering with the homeostasis of RA and related parameters have been described. A preliminary adverse outcome pathway framework for RA mediated malformations has been published. Expansion of this framework and its application in developmental toxicity testing may allow the detection of a large variety of embryotoxicants with diverse modes of action. RA homeostasis therefore provides a promising set of molecular tools that may be employed in the advancement of mode of action driven animal-free developmental toxicity testing.

Effect of tributyltin on antioxidant ability and immune responses of zebrafish (Danio rerio)

Tributyltin (TBT) is a toxic compound released into aquatic ecosystems through antifouling paints. This study was designed to examine the effects of TBT on antioxidant ability and immune responses of zebrafish (Danio rerio). Three hundred sixty healthy zebrafish were randomly grouped into four groups and exposed to different doses of TBT (0, 1, 10 and 100ngL^-1). At the end of 8 weeks, the fish were sampled, and antioxidant capability, immune parameters and immune-related genes were assessed. The results showed that with an increase in TBT dose, the concentration of malonaldehyde in the liver was significantly increased (p<0.05), whereas the activities of total superoxide dismutase, catalase and glutathione peroxidase were significantly decreased (p<0.05) compared to the control. The activity and expression of lysozyme and the content of immunoglobulin M were significantly decreased compared to those of the fish exposed to 0ngL^-1 TBT (p<0.05). However, the expression of the HSP70, HSP90, tumor necrosis factor-α(TNF-α), interleukins (IL-1β, IL-6), and nuclear factor-kappa B p65 (NF-κ B p65) genes were all enhanced with an increase in TBT dose. The results indicated that TBT induced oxidative stress and had immunotoxic effects on zebrafish.

Chronic effects of tributyltin on multiple biomarkers responses in juvenile common carp, Cyprinus carpio

In this study, the chronic toxic effects of tributyltin (TBT), an antifouling paints commonly present in surface and ground water, on morphological indices, reactive oxygen species (ROS) generation, and ATPase activity and heat shock protein (Hsp) 70 protein in tissues (liver, gill, and white muscle) of common carp were investigated. Fish were exposed at sublethal concentrations of TBT (75 ng/L, 0.75 μg/L, and 7.5 μg/L) for 60 days. When compared with the control, there was significant lower condition factor in fish exposed at the higher concentration of TBT. ROS levels in three tissues increased significantly at higher TBT concentrations (0.75 and 7.5 μg/L). The hepatic antioxidant enzymes (total antioxidative capacity and superoxide dismutase) activities were induced at higher concentrations (0.75 μg/L) of TBT. When compared with the hepatic antioxidant enzymes activities in fish exposed to 0.75 μg/L of TBT, there was a decreasing trend in those exposed to TBT with a concentration of 7.5 μg/L. However, all the antioxidant enzymes activities were significantly inhibited in gill and muscle of fish exposed to higher TBT concentrations (0.75 and 7.5 μg/L). Moreover, there was significant lower Na-K-ATPase in three tissues after long-term exposure to higher concentration of TBT, but a significant higher Hsp70 protein levels was observed. In short, environmental concentrations of TBT could not induce obvious impacts on fish, but long-term exposure to higher concentrations of TBT could affect seriously the health status of fish. © 2015 Wiley Periodicals, Inc. Environ Toxicol 31: 937-944, 2016.

Physiological and molecular responses in brain of juvenile common carp (Cyprinus carpio) following exposure to tributyltin

Tributyltin (TBT), as antifouling paints, is widely present in aquatic environment, but little is known regarding the toxicity of TBT on fish brain. In this study, the effects of exposure to TBT on the antioxidant defense system, Na(+) -K(+) -ATPase activity, neurological enzymes activity and Hsp 70 protein level in brain of juvenile common carp (Cyprinus carpio) were studied. Fish were exposed to sublethal concentrations of TBT (5, 10 and 20 μg/L) for 7 days. Based on the results, with increasing concentrations of TBT, oxidative stress was apparent as reflected by the significant higher levels of oxidative indices, as well as the significant inhibition of all antioxidant enzymes activities. Besides, the activities of Acetylcholinesterase (AChE), Monoamine oxidases (MAO) and Na(+) -K(+) -ATPase were significantly inhibited after exposure to TBT with higher concentrations. In addition, the levels of Hsp 70 protein were evaluated under TBT stress with dose-depended manner. These results suggest that selected physiological responses in fish brain could be used as potential biomarkers for monitoring residual organotin compounds present in aquatic environment.

Exposure to low dose benzo[a]pyrene during early life stages causes symptoms similar to cardiac hypertrophy in adult zebrafish

Growing evidence indicates that polycyclic aromatic hydrocarbons (PAHs) can lead to cardiac hypertrophy and recent research indicates that exposure to low dose crude oil during early embryonic development may lead to impacts on heart health at later life stages. The aim of this study was to evaluate whether exposure during early life stages to low dose benzo[a]pyrene (BaP), as a high-ring PAH, would lead to cardiac hypertrophy at later life stages. Zebrafish were exposed to low dose BaP until 96 hpf, then transferred to clean water and maintained for a year before histological and molecular biological analysis. Our results showed that exposure to low level BaP during early life stages increased heart weight to body weight ratios and deposited collagen in the heart of adult zebrafish. ANP, BNP and c-Myc were also induced in the heart of adult zebrafish by BaP. These results proved that low level BaP exposure during early life stages caused symptoms similar to cardiac hypertrophy in adult zebrafish. Our results displayed an elevated expression of CdC42, RhoA, p-ERK1, 2 and Rac1. Therefore, the mechanism of the cardiac hypertrophy caused by BaP exposure during early life stages may be through inducing the expression of CdC42, RhoA and Rac1, together with activating ERK1, 2.

Phenanthrene causes ocular developmental toxicity in zebrafish embryos and the possible mechanisms involved

Recent studies show that polycyclic aromatic hydrocarbons (PAHs) may be a candidate cause of developmental defects of the retina, but the mechanism is still unclear. We evaluated the mechanism(s) underlying PAH-induced retinal development defects due to exposure to environmental concentrations of Phenanthrene (Phe) in zebrafish. We found that exposure to environmental concentrations of Phe caused obvious morphological changes, developmental retardation, apoptosis, and reduction of cell proliferation in the retina. Our results indicated that Phe could cause visual system developmental defects. Phe exposure up-regulated aryl hydrocarbon receptor (AhR) and microphthalmia-associated transcription factor (Mtif) expression, and down-regulated zinc finger E-box binding homeobox 1 (Zeb1) and paired box 6 (Pax6). Moreover, we demonstrated that AhR was a repressor of Zeb1. We propose that Phe's ocular toxicity is mediated by up-regulating AhR, which then down-regulates Zeb1, in turn inducing Mitf expression while inhibiting Pax6 expression.