Effect of tributyltin, benzo(a)pyrene and their mixture exposure on the sex hormone levels in gonads of cuvier (Sebastiscus marmoratus)

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

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

DISCUSSION

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

Study of DNA methylation of hsd17β, er and reproductive endocrine disrupting effects in female Chlamys farreri under benzo[a]pyrene stress

Benzo[a]pyrene (B[a]P) is one kind of persistent organic pollutants (POPs) in the marine environment which has multiple toxic effects. However, epigenetic studies correlated with reproductive endocrine disruption in invertebrates have not been explored. In our study, Chlamys farreri in the mature stage were exposed to B[a]P (0, 0.4, 2 and 10 μg/L) for 5 and 10 d to explore the effects on reproductive endocrine and DNA methylation. The results proved that B[a]P stress significantly restrained the growth of mature oocytes, reduced the content of sex hormones, and affected the expression of genes related to ovarian development. Histological observation showed that the ovarian microstructure was damaged. The detection of SAM/SAH, dnmts, GNMT in the ovary showed that the level of global DNA methylation fluctuated. Significant hypermethylation of the hsd17β promoter region in the ovary was associated with a significant downregulation of its gene expression. In summary, our results suggested that exposure to B[a]P might affect DNA methylation to regulate key reproductive genes, interfere with the synthesis of sex hormones, and inhibit ovarian development. These findings provide a basis for a better understanding of how epigenetic mechanisms are involved in the response of marine invertebrates to POPs stress, opening up new avenues for incorporating environmental epigenetic approaches into marine invertebrate management and conservation plans.

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.

Toxicity of organotin compounds and the ecological risk of organic tin with co-existing contaminants in aquatic organisms

Although organotin (OT) use is restricted worldwide, with the development of industry and agriculture, a large amount of OT is still discharged into aquatic environments. These OTs may interact with other pollutants that cause adverse biological effects (through bioaccumulation and/or toxicity), resulting in combined toxicity. Most research on OTs have focused on the exposure of a single analyte. Information on the toxicity of OTs and coexisting pollutants is quite limited, but is developing rapidly. This is the first review paper evaluating the current state of knowledge on the combined effects of OTs with co-pollutants. This paper reviews 1) the degradation of organotin; and 2) the combined toxicity of OTs and emerging pollutants (EP), heavy metals, and organic pollutants. Future research needs are discussed to better understand the risks associated with co-exposure to OT pollutants.

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

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

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

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

Plasma biomarkers in juvenile marine fish provide evidence for endocrine modulation potential of organotin compounds

Organotin compounds, such as tributyltin (TBT) and triphenyltin (TPT), have been widely used to control marine fouling. Here, we show that organotin stimulation reduces the hormone levels in the plasma of two economically important aquaculture fish. Blood plasma samples were collected from juvenile red seabream and black rockfish exposed to environmentally realistic concentrations of TBT and TPT for 14 days. The levels of two plasma biomarkers, namely the yolk protein precursor vitellogenin (VTG) and the sex steroid 17β-estradiol (E2), were measured to determine the endocrine disrupting potential of the organotin compounds. Both organotin compounds were dose-dependently accumulated in the blood of two fish. Exposure to waterborne TBT and TBT significantly decreased the plasma VTG levels in both the juvenile fish in a dose-dependent manner. In contrast, the treatment with E2, a well-known VTG inducer, significantly increased the plasma VTG levels in both the fish. In addition, the mRNA levels of vtg were also downregulated in the liver tissues of both the fish at 100 and/or 1000 ng L^-1 of TBT or TPT exposure. The plasma E2 titers were significantly suppressed at 100 and/or 1000 ng L^-1 of TBT or TPT exposure for 14 days compared to their titer in the control. Since estrogen directly regulates vtg gene expression and VTG synthesis, our results reveal the endocrine disrupting potential of organotin compounds, and subsequently the endocrine modulation at early stage of fish can trigger further fluctuations in sexual differentiation, maturation, sex ration or egg production. In addition, the results demonstrate their effects on non-target organisms, particularly on animals reared in aquaculture and fisheries.

Ultrastructural changes during spermatogenesis, biochemical and hormonal evidences of testicular toxicity caused by TBT in freshwater prawn Macrobrachium rosenbergii (De Man, 1879)

The present investigation documents the impact of tributyltin (TBT) on the ultrastructural variation of spermatogenesis in freshwater prawn Macrobrachium rosenbergii. The environmentally realistic concentration of TBT can cause damages to the endocrine and reproductive physiology of crustaceans. In this context, three concentrations viz. 10, 100, and 1000 ng/L were selected and exposed to prawns for 90 days. The TBT exposed prawn exhibited decrease the reproductive activity as evidenced by sperm count and sperm length compared to control. Histopathological results revealed the retarded testicular development, abnormal structure of seminiferous tubule, decrease in the concentration of spermatozoa, diminution of seminiferous tubule membrane, abundance of spermatocytes and vacuolation in testis of treated prawns. Ultrastructural study also confirmed the impairment of spermatogenesis in treated prawns. Furthermore, radioimmunoassay (RIA) clearly documented the reduction of testosterone level in TBT exposed groups. Thus, TBT substantially reduced the level of male sex hormone as well as biochemical constituents which ultimately led to impairment of spermatogenesis in the freshwater male prawn M. rosenbergii.

Influence of short term exposure of TBT on the male reproductive activity in freshwater prawn Macrobrachium rosenbergii (De Man)

In the present study, the effect of tributyltin (TBT) on the histopathological and hormonal changes during spermatogenesis in freshwater prawn Macrobrachium rosenbergii was documented. Three experimental concentrations such as 10, 100 and 1,000 ng/L were selected and exposed to prawns for 45 days. After TBT exposure, the reproductive activities like sperm count and sperm length were decreased when compared with control. Further, abnormal structure of the seminiferous tubule, decrease in spermatozoa concentration, diminution of the seminiferous tubule membrane and the abundance of spermatocytes in the testis were noticed in treated prawns. Interestingly, radioimmunoassay clearly revealed the reduction of testosterone level in TBT exposed groups. Thus, TBT has considerably reduced the level of testosterone and caused the impairment of spermatogenesis in the freshwater male prawn M. rosenbergii.

Imposex development in Nucella lapillus--evidence for the involvement of retinoid X receptor and androgen signalling pathways in vivo

Imposex in female gastropods is a widely documented masculinisation phenomenon in response to tributyltin (TBT) exposure. Although it is generally accepted that imposex is a case of endocrine disruption the underlying mechanisms are controversially discussed with aromatase inhibition and retinoid X receptor (RXR) signalling pathways as two conflicting hypotheses. Hence, we performed injection experiments with the marine dogwhelk Nucella lapillus. As expected TBT induced imposex in all test specimens while the natural RXR ligand 9 cis-retinoic acid did not cause significant effects. Additionally, TBT effects were suppressed if the organotin compound was simultaneously injected with an androgen receptor inhibitor (cyproterone acetate) but not if co-administered with the synthetic RXR antagonist HX531. In contrast, the injection of the RXR agonist HX630 resulted in imposex development in nearly 100% females. Therefore, the results provide evidence for the involvement of the RXR and the androgen signalling pathway. Further investigations are necessary to resolve the biochemical mechanism of imposex development.

Tributyltin exposure causes brain damage in Sebastiscus marmoratus

Tributyltin (TBT) is a ubiquitous marine environmental contaminant characterized primarily by its reproductive toxicity. However, the neurotoxic effect of TBT has not been extensively described, especially in fishes which have a high number of species in the marine environment. This study was conducted to investigate the neurotoxic effects of TBT at environmental levels (1, 10, and 100ngl(-1)) on female Sebastiscus marmoratus. The results showed that TBT exposure induced apoptosis in brain cells of three regions including the pallial areas of the telencephalon, the granular layer of the optic tectum, and the cerebellum. In addition, the increase of reactive oxygen species and nitric oxide levels, and the decrease of Na+/K+-ATPase activity were found in the brain. The results strongly indicated neurotoxicity of TBT to fishes. According to the regions in which apoptosis was found in the brain, TBT exposure might influence the schooling, sensory and motorial functions of fishes.

Effect of tributyltin on the development of ovary in female cuvier (Sebastiscus marmoratus)

Organotin compounds, such as tributyltin (TBT) used as an antifouling biocide, can induce masculinization in female mollusks. However, few studies addressing the effect of TBT in fish have been reported. This study was conducted to investigate effects of TBT at environmental levels (1, 10, 100ng/L) on the development of ovary in female cuvier. TBT exposure elevated testosterone levels, increased the ratio of testosterone to 17beta-estradiol and decreased 17beta-estradiol levels in ovaries after 50 days compared to the control. Three stages of follicles (primary growth stage, yolk vesicle stage, vitellogenic stage) were observed in the ovaries of cuvier at the control and 1ng/L TBT group. The ovaries at the 10ng/L TBT group were characterized by the lack of vitellogenic stage follicles and instead had higher proportions of primary growth stage follicles. 100ng/L TBT resulted in follicles that were entirely at the earliest (primary growth stage) stages of development. There was a significant increase in apoptotic ovarian follicular cells judged by TUNEL-positive cell at the 10ng/L TBT group. The TUNEL-positive follicles were observed at the 100ng/L TBT group. The result in the present study showed that TBT at environmentally realistic concentrations can inhibit the ovarian development in fish. Besides the changes of sex hormone induced by TBT, apoptosis appears to be one mechanism affecting ovarian development.

Endocrine disruption in prosobranch molluscs: evidence and ecological relevance

Prosobranch snails represent almost 50% of all recent molluscs, are ubiquitously distributed, play important roles in various ecosystems and exhibit a variety of reproductive modes and life-cycle-strategies. Many of them attain life spans of several years, which in combination with their limited ability to metabolize organic chemicals, may contribute to the fact that prosobranchs constitute one of the most endangered taxonomic groups in aquatic ecosystems. Although it is not yet known to what extent endocrine disrupting chemicals (EDCs) contribute to this situation, the case of tributyltin (TBT) and its population-level impact on prosobranchs demonstrates the general susceptibility of these invertebrates. The existing evidence for comparable population-level effects in prosobranch snails by other androgens, antiandrogens, and estrogens is critically reviewed. The example of TBT demonstrates the difficulty to prove an endocrine mode of action for a given chemical. Although it is generally accepted that TBT causes imposex and intersex in prosobranch snails as a result of endocrine disruption, the detailed biochemical mechanism is still a matter of debate. The strengths and weaknesses of the five competing hypotheses are discussed, together with previously unpublished data. Finally, the ecological relevance of EDC effects on the population and community level and the application of prosobranchs for the assessment of EDCs are addressed.