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

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.

Male Reproductive Toxicity of Antifouling Chemicals: Insights into Oxidative Stress-Induced Infertility and Molecular Mechanisms of Zinc Pyrithione (ZPT)

Zinc pyrithione (ZPT), a widely utilized industrial chemical, is recognized for its versatile properties, including antimicrobial, antibacterial, antifungal, and antifouling activities. Despite its widespread use, recent research has shed light on its toxicity, particularly towards the male reproductive system. While investigations into ZPT's impact on male reproduction have been conducted, most of the attention has been directed towards marine organisms. Notably, ZPT has been identified as a catalyst for oxidative stress, contributing to various indicators of male infertility, such as a reduced sperm count, impaired sperm motility, diminished testosterone levels, apoptosis, and degenerative changes in the testicular tissue. Furthermore, discussions surrounding ZPT's effects on DNA and cellular structures have emerged. Despite the abundance of information regarding reproductive toxicity, the molecular mechanisms underlying ZPT's detrimental effects on the male reproductive system remain poorly understood. This review focuses specifically on ZPT, delving into its reported toxicity on male reproduction, while also addressing the broader context by discussing other antifouling chemicals, and emphasizing the need for further exploration into its molecular mechanisms.

A systematic review of the evaluation of endocrine-disrupting chemicals in the Japanese medaka (Oryzias latipes) fish

Japanese medaka (Oryzias latipes) is an acceptable small laboratory fish model for the evaluation and assessment of endocrine-disrupting chemicals (EDCs) found in the environment. In this research, we used this fish as a potential tool for the identification of EDCs that have a significant impact on human health. We conducted an electronic search in PubMed (http://www.ncbi.nlm.nih.gov/pubmed) and Google Scholar (https://scholar.google.com/) using the search terms, Japanese medaka, Oryzias latipes, and endocrine disruptions, and sorted 205 articles consisting of 128 chemicals that showed potential effects on estrogen-androgen-thyroid-steroidogenesis (EATS) pathways of Japanese medaka. From these chemicals, 14 compounds, namely, 17β-estradiol (E2), ethinylestradiol (EE2), tamoxifen (TAM), 11-ketotestosterone (11-KT), 17β-trenbolone (TRB), flutamide (FLU), vinclozolin (VIN), triiodothyronine (T3), perfluorooctanoic acid (PFOA), tetrabromobisphenol A (TBBPA), terephthalic acid (TPA), trifloxystrobin (TRF), ketoconazole (KTC), and prochloraz (PCZ), were selected as references and used for the identification of apical endpoints within the EATS modalities. Among these endpoints, during classification, priorities are given to sex reversal (masculinization of females and feminization of males), gonad histology (testis-ova or ovotestis), secondary sex characteristics (anal fin papillae of males), plasma and liver vitellogenin (VTG) contents in males, swim bladder inflation during larval development, hepatic vitellogenin (vtg) and choriogenin (chg) genes in the liver of males, and several genes, including estrogen-androgen-thyroid receptors in the hypothalamus-pituitary-gonad/thyroid axis (HPG/T). After reviewing 205 articles, we identified 108 (52.68%), 46 (22.43%), 19 (9.26%), 22 (17.18%), and 26 (12.68%) papers that represented studies on estrogen endocrine disruptors (EEDs), androgen endocrine disruptors (AEDs), thyroid endocrine disruptors (TEDs), and/or steroidogenesis modulators (MOS), respectively. Most importantly, among 128 EDCs, 32 (25%), 22 (17.18%), 15 (11.8%), and 14 (10.93%) chemicals were classified as EEDs, AEDs, TEDs, and MOS, respectively. We also identified 43 (33.59%) chemicals as high-priority candidates for tier 2 tests, and 13 chemicals (10.15%) show enough potential to be considered EDCs without any further tier-based studies. Although our literature search was unable to identify the EATS targets of 45 chemicals (35%) studied in 60 (29.26%) of the 205 articles, our approach has sufficient potential to further move the laboratory-based research data on Japanese medaka for applications in regulatory risk assessments in humans.

Influence of Bisphenol A and 17β-Trenbolone Exposure in Oryzias Congeners

Japanese medaka is specified as a model fish in the test guidelines of the Organisation for Economic Co-operation and Development. Recently, populations of Japanese medaka in Japan were divided into two species, the northern Oryzias sakaizumii and the southern O. latipes. Previously, we reported that induction concentrations for sex reversal by exposure to 17α-methyltestosterone differed significantly between these two species, indicating that they respond differently to endocrine-disrupting chemica. In the present study, we examined the effects of exposure to two more endocrine-disrupting chemicals (bisphenol A and 17β-trenbolone) in O. sakaizumii, and compared the results with those previously reported for O. latipes. Exposure to both bisphenol A and 17β-trenbolone induced testis-ova formation or sex reversal in O. sakaizumii. Exposure to 17β-trenbolone also increased expression of gonadal soma-derived factor (gsdf). Least-observed-effect concentrations for gonadal sex differentiation and gsdf expression were lower for O. latipes than for O. sakaizumii after exposure to bisphenol A, and were lower for O. sakaizumii than for O. latipes after exposure to 17β-trenbolone. These results demonstrate that O. sakaizumii and O. latipes respond differently to androgenic and estrogenic endocrine-disrupting chemicals. Environ Toxicol Chem 2023;42:673-678. © 2022 SETAC.

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.

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

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

Tributyltin impaired spermatogenesis and reproductive behavior in male zebrafish

Tributyltin (TBT) was reported to affect sexual behavior and gametogenesis in fish. However, the modes of action involved are largely unclear. In order to elucidate the toxicological mechanisms of TBT in reproduction, zebrafish (Danio rerio) males were exposed to TBT at concentrations of 100 and 500 ng/L for 28 days. After exposure, the sperm count of the treated fish was sharply decreased though the testis weight and gonadosomatic index remained unchanged. Moreover, reduced number of spermatogonia and spermatozoa and increased spermatocytes were observed in TBT-treated fish by histological observation and PCNA-immunostaining. Increased number of apoptotic-positive spermatocytes was also present in TBT-treated fish, indicating an enhanced apoptosis in these cells. Consistent to decreased number of spermatogonia, down-regulated expressions of genes responsible for germ cell proliferation (cyclind1 and pcna) were observed in TBT-treated fish. In contrast, TBT elevated the expressions of genes involved in meiotic entry and maintenance (aldhla2, sycp3 and dmc1) while suppressed the mRNA level of gene responsible for terminus of meiotic entry (cyp26a1), in agreement with arrested meiosis and reduced sperm count. Furthermore, TBT significantly elevated the ratios of bax/bcl-2 and tnfrsf1a/tnfrsf1b in testis, which are markers for intrinsic- and extrinsic-apoptotic pathways, consistent with the enhanced TUNEL positive signals in spermatocytes. Moreover, TBT also significantly affected the parameter of reproductive behaviors in treated fish (reflected by decreased frequency of meeting, visits and time spent in spawning area). Consistently, the expressions of genes responsible for the modulation of reproductive behaviors in brain (such as cyp19a1b, kiss2, gnrh3 and ompb) were significantly down-regulated in treated-fish. Interestingly, disrupted reproductive behaviors of untreated female fish were also observed in the present study. The present study indicated that TBT might affect the reproduction of zebrafish male by disrupting the spermatogenesis and reproductive behavior of the fish.

Zinc chloride influences embryonic development, growth, and Gh/Igf-1 gene expression during the early life stage in zebrafish (Danio rerio)

Although zinc is an essential element for organisms, excess zinc exposure is harmful. We assessed the possible negative influence of zinc (Zn) on the freshwater fish Danio rerio during its early life stage by using Organization for Economic Cooperation and Development test guideline no. 210. Lethality of Zn after hatching occurred in a concentration dependent manner. The LC₅₀ and lowest observed effect concentration of mortality values in the present toxicity assay were 2.31 mg/L (95% confidence limit: 1.81-3.05) and 1.5 mg/L, respectively. These values were close to the reported concentration recorded in aquatic environments. Growth inhibition was observed at 15 and 30 days post-hatching with Zn exposure of 1.5 mg/L. In general, the growth hormone (Gh)/insulin-like growth factor-I (Igf-1) axis is important for growth in fishes, and Zn exposure induced a significant reduction of igf-1 expression at the concentration that caused growth inhibition. These findings suggest that the observed growth inhibition was induced by the suppression of igf-1 expression. In addition, these results suggest that by examining gene expression on the Gh/Igf-1 axis, it may be possible to predict growth suppression by chemical exposure.

Bisphenol A induces a shift in sex differentiation gene expression with testis-ova or sex reversal in Japanese medaka (Oryzias latipes)

Bisphenol A (BPA), a very important raw material in the plastics industry, is an endocrine-disrupting chemical in teleost fish. Although BPA induces testis-ova and sex reversal in teleost fish species, the molecular mechanism remains unclear. We evaluated the effects of BPA (measured concentrations: 45, 92, 326, 1030 and 3406 μg/L) on Japanese medaka (Oryzias latipes) using OECD TG234 (2011, Fish Sexual Development Test, OECD Guidelines for the Testing of Chemicals, Section 2). BPA at 1030 and 3406 μg/L induced testis-ova and sex reversal with female-type secondary sexual characteristics in XY males at 30 and 60 days posthatching (dph). Then we examined the BPA effect on the expression of sex differentiation genes related to the testis-ova and sex reversal in XY medaka. BPA exposure (1030 and 3406 μg/L) suppressed gsdf mRNA expression and increased cyp19a1a mRNA expression in XY individuals at stage 38 and 30 dph, although foxl2 mRNA expression showed no change. Interestingly, the concentration of BPA that suppressed gsdf mRNA expression at the larval stage was consistent with that needed to induce testis-ova and sex reversal. These results suggest that the gsdf gene at the embryonic stage can be used as a useful biomarker for predicting the impact of estrogenic endocrine-disrupting chemicals on sexual differentiation in Japanese medaka.

Molecular analysis of population and De Novo transcriptome sequencing of Thai medaka, Oryzias minutillus (Teleostei: Adrianichthyidae)

Thai medaka (Oryzias minutillus) are alternatively known as Thai rice-fish or dwarf medaka, and they widely inhabit natural freshwater environments in all regions of Thailand. In this study, we aimed to investigate the molecular genetics of the Thai medaka population in Thailand inferred from the mitochondrial control region (D-loop) and the cytochrome c oxidase subunit 1 (coxI) sequences. Furthermore, we examined RNA sequencing (RNA-seq) of adult males and females was performed with next-generation sequencing. Together, the combination of the D-loop and coxI sequences clearly distinguished the Thai medaka populations into 2 groups, such as group 1, which generally included samples from the central, northern, western, and eastern regions of the northeastern region. In this group, the fish populations seem to be a little monophyly in which the first subpopulation comprised the main samples from the northern and central regions. The second subpopulation commonly contained fish from the eastern region and specimens from the southern part of the central region near the Gulf of Thailand. Although these subgroups related to geographical distribution, bootstrap values were low in branch considered significant for both subgroups. Group 2 consisted of almost all samples from the southern population and those from the central and southern part of the northeastern region. Group 2 was found that it was made of samples from the northeastern region and samples from the southern population. A total of 73551 unigenes were identified after gene annotation. Signal transduction was the predominant protein classification among the Thai medaka orthologous groups. A differentially expressed gene (DEG) analysis identified 6 subclusters between both sexes that were composed of 257, 131, 364, 386, 114 and 108 genes. Phototransduction was the most enriched pathway and was highly expressed in males, while viral carcinogenesis, oocyte genesis, and the complement and coagulation cascades were highly expressed in females. Further details of these DEGs are discussed below. These results suggest that Thai medaka may genetically exhibit independent populations in the geographic habitats of Thailand. Moreover, these fish also reveal the genes that are conserved in other organisms and those that may be specific to this species.

On the effectiveness of tributyltin ban: Distribution and changes in butyltin concentrations over a 9-year period in Klaipėda Port, Lithuania

This study provides an insight on a long-term butyltin pressure, spatio-temporal changes and current tributyltin distribution in the Klaipėda Port sediments. Moreover, it examines whether the restrictions on tributyltin use led to a decreased pollution in the area. Changes over a 9-year period in tributyltin and its metabolites concentrations were analyzed in surface sediments from semi-enclosed bays of the Port. Reduction in organotin level was observed after tributyltin ban came into force: tributyltin concentration reached 3000 ng Sn g^-1 d.w. in 2005 whereas 1793 ng Sng^-1 d.w. was found to be the highest tributyltin concentration in 2013. The highest contamination was detected in the zones with ship maintenance activity. As late as in 2013, the latter areas still exhibited fresh tributyltin input while the progress of organotin degradation has been observed for other sampling stations along the Port.

Influences of Salinity and Organic Compounds on Embryo Development in Three Medaka Oryzias Congeners with Habitats Ranging from Freshwater to Marine

To clarify whether Oryzias congeners, including freshwater, brackish water, and marine medaka, would be useful models for evaluating environmental chemical effects in various aquatic ecosystems, we examined the influence of salinity on their embryo development. We also compared the toxicity values of the organotin compounds triphenyltin and tributyltin, which remain pollutants of marine and freshwater ecosystems, between Oryzias latipes (freshwater), Oryzias melastigma (brackish water), and Oryzias javanicus (saltwater). Hatching and survival rates of O. latipes were significantly decreased at a salinity of 34, whereas O. melastigma and O. javanicus were adaptable to various salinities from freshwater to seawater. The lowest observed effect concentrations of organotin compounds for survival and embryo development were the similar in the three species. The similarity of the species' responses to organotin compounds indicated that Oryzias congeners are useful for ecological risk assessment of chemicals in a range of aquatic ecosystems, from freshwater to marine.

Changes in fish sex ratio as a basis for regulating endocrine disruptors

Fish sex ratio (SR) is an endpoint potentially indicating both endocrine activity and adversity, essential elements for identifying Endocrine Disrupting Chemicals (EDCs) as required by the EU regulations. Due to different protocols and methods in the literature studies, SR data vary greatly. This study analyses literature SR data and discusses important considerations for using SR data in the regulatory context for the hazard identification, classification, PBT (persistent, bioaccumulative and toxic) assessment, testing, and risk assessment. A total number of 106 studies were compiled for SR of zebrafish, medaka and fathead minnow exposed to 84 chemicals or mixtures. About 53% of literature studies determined SR by methods different from the standard histology method, leading to uncertainty of quantifying SR and differential sensitivity. SR was determined after depuration in 40 papers, which may lead to chemical-induced SR changes reversible to the control. SR was responsive to chemicals with EAS (estrogen, androgen, steoroidogenesis) activity and also to those with thyroid and progesterone activity. Besides, SR was influenced by non-chemical factors, e.g., inbreeding and temperature, leading to difficulty in data interpretation. The ECHA/EFSA/JRC Guidance suggests that SR and gonad histology data can be used for identifying EDCs. Due to reversibility, influence of confounding factors, and responsiveness to chemicals with endocrine activity other than EAS, this study suggests that SR/gonad histology should be combined with certain mode of action evidence for identifying EDCs. Important considerations for using SR data in the identification, classification, PBT assessment, testing, and risk assessment are discussed.

Triphenyltin exposition induces spermatic parameter alters of Calomys laucha species

The present study aims to evaluate the influence of triphenyltin (TPT) exposure on reproductive physiology on Calomys laucha species, since this species inhabits regions susceptible to exposure to this contaminant. Animals exposed to the highest dose (10.0 mg/kg) presented signs of severe intoxication in only 7 days of exposure, demonstrating a higher sensitivity of this species to triphenyltin. The 10.0 mg TPT/kg dose was analyzed separately for short-term exposure and results suggest that exposure to this dose was severely detrimental to sperm activity. Among the main results obtained in the evaluation of sperm kinetics, a reduction in total motility was observed from the 0.5 mg TPT/kg group, accentuated according to the increase in the doses of TPT. In progressive motility, there was a decrease from the dose of 0.5 mg TPT/kg and maintained the plateau until the dose of 5.0 mg TPT/kg. It was also observed an increase in the distances and velocities average path, rectilinear and curvilinear in doses of 2.5 and 5.0 mg/kg. From the flow cytometry, evaluation a decrease in mitochondrial functionality was observed as the dose increased. Increased membrane fluidity was also observed from the 5.0 mg TPT/kg dose and the acrosome reaction presented higher values at doses of 0.5 and 5.0 mg TPT/kg. We can conclude that TPT causes impairment of the sperm activity, reducing it in individuals exposed in the adult phase.

Ecotoxicological Test Assay Using OECD TG 212 in Marine Java Medaka (Oryzias javanicus) and Freshwater Japanese Medaka (Oryzias latipes)

The lethal effects of chemicals is a serious concern to the protection of ecosystems, and the OECD TG 212 was established to estimate the lethal and sublethal effects on embryo and sac-fry stages of fish. It is still unclear, however, whether this test can effectively estimate the impacts of chemicals using marine fish. Therefore, this study aimed to use a recognized testing method on the marine fish Oryzias javanicus, and to assess differences in response to organotin compounds between a freshwater congener (Oryzias latipes) and O. javanicus. The lowest observed effect concentration (LOEC) of triphenyltin for lethal effect was the same in both species. The LOEC of tributyltin for lethal and sublethal effects were the same in both species. Our results provide the first evidence that O. javanicus and O. latipes are similarly affected by organotin compounds, suggesting that O. javanicus is a good model marine fish for the ecotoxicological assessment of chemicals.