Low dose TBT exposure decreases amphipod immunocompetence and reproductive fitness

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.

Toxic Relationships: Prediction of TBT's Affinity to the Ecdysteroid Receptor of Triops longicaudatus

Tributyltin (TBT) is a biocide introduced in the 1960s in antifouling paints. Despite legislation banning its use, its persistence in the environment still causes significant harm to organisms. Tributyltin is a ligand of retinoid X receptors (RXR) and ecdysteroid receptors (EcRs), which in arthropods act as homologs of RXR. Focusing on Metazoan species, this study used genomic and proteomic information from different sources to compare their three-dimensional structure, phylogenetic distribution, and amino acid sequence alterations. The objective was to identify possible patterns that relate organisms' sensitivity to TBT using the species Triops longicaudatus as the basis for the comparisons. The results showed great conservation of this protein across several species when comparing the interaction amino acids described to RXR (an EcR analog) in Homo sapiens. The three-dimensional comparison of RXR showed little conformational variation between different sequences by maintaining the interaction pocket. As for the Species Sensitivity Distribution (SSD) curve, an HC05 = 0.2649 [0.0789-0.7082] µg/L was obtained with no specific distribution between the different taxa. Protein-ligand docking analysis was then used to confirm the SSD curve ranking of species. Still, the results showed an opposite trend that may be related, for example, to differences in the LC50 values used in the calculations. This study serves as the first step for applying bioinformatics techniques to produce information that can be used as an alternative to animal or cellular experimentation. These techniques could be adapted to various chemicals and proteins, allowing for observations in a shorter timeframe and providing information on a broader spectrum.

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.

Applications of Adductomics in Chemically Induced Adverse Outcomes and Major Emphasis on DNA Adductomics: A Pathbreaking Tool in Biomedical Research

Adductomics novel and emerging discipline in the toxicological research emphasizes on adducts formed by reactive chemical agents with biological molecules in living organisms. Development in analytical methods propelled the application and utility of adductomics in interdisciplinary sciences. This review endeavors to add a new dimension where comprehensive insights into diverse applications of adductomics in addressing some of society's pressing challenges are provided. Also focuses on diverse applications of adductomics include: forecasting risk of chronic diseases triggered by reactive agents and predicting carcinogenesis induced by tobacco smoking; assessing chemical agents' toxicity and supplementing genotoxicity studies; designing personalized medication and precision treatment in cancer chemotherapy; appraising environmental quality or extent of pollution using biological systems; crafting tools and techniques for diagnosis of diseases and detecting food contaminants; furnishing exposure profile of the individual to electrophiles; and assisting regulatory agencies in risk assessment of reactive chemical agents. Characterizing adducts that are present in extremely low concentrations is an exigent task and more over absence of dedicated database to identify adducts is further exacerbating the problem of adduct diagnosis. In addition, there is scope of improvement in sample preparation methods and data processing software and algorithms for accurate assessment of adducts.

Crustaceans, One Health and the changing ocean

Crustaceans permeate every habitat on Earth but are especially impactful in the marine environment. They can be small and extremely abundant like the ubiquitous marine copepods found throughout the world's oceans, or large and highly prized by fishermen like spiny lobsters found in tropical and temperate seas, globally. The latter are among the decapod crustaceans, a group which includes crabs, shrimps, and lobsters - those targeted most commonly by fishery and aquaculture industries. Hence, crustaceans are ecologically important, but they are also directly linked to the economic and nutritional health of human populations. To most effectively manage and conserve crustacean populations in the face of a changing ocean environment, whether they are harvested or not, requires a One Health approach that underscores the linkages between crustacean, human, and environmental health. Here, we give an overview of the need, benefits, and challenges to taking the One Health approach to crustacean health and argue that when viewed through the One Health lens, there is perhaps no other group of marine animals more worthy of that perspective.

Pathological evidence in Plicopurpura pansa associated with the stranding of a bulk carrier ship during Hurricane "Patricia" in the Mexican Central Pacific

Due to the effects of Hurricane Patricia (2015), the bulk freighter "El Llanitos" ran aground in the rocky intertidal zone of Colima, Mexico. We assessed the impact of this ship's stranding on a population of the gastropod Plicopurpura pansa. Toxic elements, hydrocarbons, shell deformities, presence of tumors, imposex, and morphological relationships were analyzed. Two years after the stranding occurred, high cyanide concentrations (0.0363 mg/l) and Ni concentrations above permissible limits (3.35 mg/l) were found in surface seawater. Hydrocarbon concentrations were high in the aft zone of the ship and decreased towards the bow area of the freighter. The P. pansa specimens collected closest to the ship structure presented a high prevalence of tumorations in the structure of the foot and morphological anomalies in the shell structure; imposex was 32% and there was evidence of effects on the growth indicator. The evidence presented here supports the existence of a significant impact from the grounding of the ship on a protected gastropod species associated with the rocky intertidal zone on the coast of Colima. The potential of P. pansa as a bioindicator species of pollution caused by toxic elements and hydrocarbons associated with stranding events in the tropical Pacific is documented.

DNA epigenetic marks are linked to embryo aberrations in amphipods

Linking exposure to environmental stress factors with diseases is crucial for proposing preventive and regulatory actions. Upon exposure to anthropogenic chemicals, covalent modifications on the genome can drive developmental and reproductive disorders in wild populations, with subsequent effects on the population persistence. Hence, screening of chemical modifications on DNA can be used to provide information on the probability of such disorders in populations of concern. Using a high-resolution mass spectrometry methodology, we identified DNA nucleoside adducts in gravid females of the Baltic amphipods Monoporeia affinis, and linked the adduct profiles to the frequency of embryo malformations in the broods. Twenty-three putative nucleoside adducts were detected in the females and their embryos, and eight modifications were structurally identified using high-resolution accurate mass data. To identify which adducts were significantly associated with embryo malformations, partial least squares regression (PLSR) modelling was applied. The PLSR model yielded three adducts as the key predictors: methylation at two different positions of the DNA (5-methyl-2'-deoxycytidine and N6-methyl-2'-deoxyadenosine) representing epigenetic marks, and a structurally unidentified nucleoside adduct. These adducts predicted the elevated frequency of the malformations with a high classification accuracy (84%). To the best of our knowledge, this is the first application of DNA adductomics for identification of contaminant-induced malformations in field-collected animals. The method can be adapted for a broad range of species and evolve as a new omics tool in environmental health assessment.

Coupled Application of Antioxidant Defense Response and Embryo Development in Amphipod Crustaceans in the Assessment of Sediment Toxicity

Survival rate, frequency of malformed embryos, and antioxidant defense system responses in the benthic amphipod Gmelinoides fasciatus from the Baltic Sea were measured to examine the effects of toxic sediments, and to assess the usefulness of these endpoints in sediment toxicity biotesting. A highly contaminated sediment sample from the Baltic Sea was diluted with sediment from a clean site to come up with a series of 5 test sediments with dilutions from 1:32 to 1:1024, and the reference sediment. The 1:32 dilution of the test sediment was analyzed for organotins (2862 µg tin [Sn] kg dry wt ^-1 ), polycyclic aromatic hydrocarbons (6064 µg kg dry wt ^-1 ), and selected trace metals (e.g., copper 352 mg kg dry wt ^-1 ). The survival rate of G. fasciatus (10-d toxicity test) was 100% in the reference and 1:1024 treatments, and began to decline from the 1:256 dilution onward. In a 28-d experiment, various types of morphological malformations were observed in 11 to 80% of the amphipod embryos in the 1:64, 1:128, and 1:256 dilutions, with only <5% in the reference treatment. Also, elevated activities in the antioxidant defense system enzymes glutathione S-transferase and catalase were observed in amphipods exposed to the contaminated sediments compared with the reference treatment, with responses at lower contamination levels compared with the appearance of malformations in the embryos. The results obtained illustrate the effectiveness of the combined application of embryonic malformations and antioxidant defense system biomarkers in amphipods in the assessment of sediment toxicity, and potentially also of sublethal effects of chemical contamination in aquatic ecosystems. Environ Toxicol Chem 2019;38:2020-2031. © 2019 SETAC.

Population screening and transmission experiments indicate paramyxid-microsporidian co-infection in Echinogammarus marinus represents a non-hyperparasitic relationship between specific parasite strains

Phylogenetically distant parasites often infect the same host. Indeed, co-infections can occur at levels greater than expected by chance and are sometimes hyperparasitic. The amphipod Echinogammarus marinus presents high levels of co-infection by two intracellular and vertically transmitted parasites, a paramyxid (Paramarteilia sp. Em) and a microsporidian strain (Dictyocoela duebenum Em). This co-infection may be hyperparasitic and result from an exploitative ‘hitchhiking’ or a symbiotic relationship between the parasites. However, the best-studied amphipod species are often collected from contaminated environments and may be immune-compromised. Immune-challenged animals frequently present co-infections and contaminant-exposed amphipods present significantly higher levels of microsporidian infection. This suggests the co-infections in E. marinus may result from contaminant-associated compromised immunity. Inconsistent with hyperparasitism, we find that artificial infections transmit Paramarteilia without microsporidian. Our population surveys reveal the co-infection relationship is geographically widespread but find only chance co-infection between the Paramarteilia and another species of microsporidian, Dictyocoela berillonum. Furthermore, we identify a haplotype of the Paramarteilia that presents no co-infection, even in populations with otherwise high co-infection levels. Overall, our results do not support the compromised-immunity hypothesis but rather that the co-infection of E. marinus, although non-hyperparasitic, results from a relationship between specific Paramarteilia and Dictyocoela duebenum strains.

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.

Crustacean intersexuality is feminization without demasculinization: implications for environmental toxicology

The dysfunction associated with intersexuality in vertebrates and molluscs is often a serious threat to ecosystems. Although poorly understood, crustacean intersexuality is associated with contamination and includes forms linked to increased sex-ratio distorting parasites at polluted sites. Despite the importance of crustaceans for monitoring vulnerable aquatic habitats, little is known about the molecular basis of this abnormal sexual differentiation and any associated sexual dysfunction. To increase the relevance of crustaceans to environmental toxicologists, we comprehensively analyzed gene expression in amphipods presenting parasite- and nonparasite-associated intersexuality. Our findings reveal existing vertebrate biomarkers of feminization should not be applied to crustaceans, as orthologous genes are not induced in feminized amphipods. Furthermore, in contrast to vertebrates, where feminization and intersexuality is often associated with deleterious demasculinization, we find males maintain masculinity even when unambiguously feminized. This reveals a considerable regulatory separation of the gene pathways responsible for male and female characteristics and demonstrates that evidence of feminization (even if detected with appropriate biomarkers) is not a proxy for demasculinization in crustaceans. This study has also produced a comprehensive spectrum of potential molecular biomarkers that, when combined with our new molecular understanding, will greatly facilitate the use of crustaceans to monitor aquatic habitats.

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.

454 pyrosequencing-based analysis of gene expression profiles in the amphipod Melita plumulosa: transcriptome assembly and toxicant induced changes

Next generation sequencing using Roche's 454 pyrosequencing platform can be used to generate genomic information for non-model organisms, although there are bioinformatic challenges associated with these studies. These challenges are compounded by a lack of a standardized protocol to either assemble data or to evaluate the quality of a de novo transcriptome. This study presents an assembly of the control and toxicant responsive transcriptome of Melita plumulosa, an Australian amphipod commonly used in ecotoxicological studies. RNA was harvested from control amphipods, juvenile amphipods, and from amphipods exposed to either metal or diesel contaminated sediments. This RNA was used as the basis for a 454 based transcriptome sequencing effort. Sequencing generated 1.3 million reads from control, juvenile, metal-exposed and diesel-exposed amphipods. Different read filtering and assembly protocols were evaluated to generate an assembly that (i) had an optimal number of contigs; (ii) had long contigs; (iii) contained a suitable representation of conserved genes; and (iv) had long ortholog alignment lengths relative to the length of each contig. A final assembly, generated using fixed-length trimming based on the sequence quality scores, followed by assembly using the MIRA algorithm, produced the best results. The 26,625 contigs generated via this approach were annotated using Blast2GO, and the differential expression between treatments and control was determined by mapping with BWA followed by DESeq. Although the mapping generated low coverage, many differentially expressed contigs, including some with known developmental or toxicological function, were identified. This study demonstrated that 454 pyrosequencing is an effective means of generating reference transcriptome information for organisms, such as the amphipod M. plumulosa, that have no genomic information available in databases or in closely related sequenced species. It also demonstrated how optimization of read filtering protocols and assembly approaches changes the utility of results obtained from next generation sequencing studies, and establishes criteria to determine the quality of a de novo assembly in species lacking a reference genome. This new transcriptomic knowledge provides the genomic foundation for the creation of microarray and qPCR assays, serving as a reference transcriptome in future RNAseq studies, and allowing both the biology and ecotoxicology of this organism to be better understood. This approach will allow genomics-based methodology to be applied to a wider range of environmentally relevant species.

Ecotoxicological evaluation of tributyltin toxicity to the equilateral venus clam, Gomphina veneriformis (Bivalvia: Veneridae)

Tributyltin (TBT) is the most common pesticide in marine and freshwater environments. To evaluate the potential ecological risk posed by TBT, we measured biological responses such as growth rate, gonad index, sex ratio, the percentage of intersex gonads, filtration rate, and gill abnormalities in the equilateral venus clam (Gomphina veneriformis). Additionally, the biochemical and molecular responses were evaluated in G. veneriformis exposed to various concentrations of TBT. The growth of G. veneriformis was significantly delayed in a dose-dependent manner after exposure to all tested TBT concentrations. After TBT was administered to G. veneriformis, the gonad index decreased and the sex balance was altered. The percentage of intersex gonads also increased significantly in treated females, whereas no intersex gonads were detected in the solvent control group. Additionally, intersex gonads were detected in male G. veneriformis specimens exposed to relatively high TBT concentrations (20 μg L⁻¹). The filtration rate was also reduced in a dose-dependent manner in TBT-exposed G. veneriformis. We also noted abnormal gill morphology in TBT-exposed G. veneriformis. Furthermore, increases in antioxidant enzyme activities were observed in TBT-exposed G. veneriformis clams, regardless of dosage. Vitellogenin gene expression also increased significantly in a dose-dependent manner in G. veneriformis exposed to TBT. These results provide valuable information regarding our understanding of the toxicology of TBT in G. veneriformis. Moreover, the responses of biological and molecular factors could be utilized as information for risk assessments and marine monitoring of TBT toxicity.

Effects of tributyltin exposure in hermit crabs: Clibanarius vittatus as a model

Tributyltin (TBT) contamination affects the reproductive system of many species of invertebrates worldwide. The present study was designed to evaluate the effects of exposure to TBT pollution on the reproduction of the hermit crab Clibanarius vittatus. An orthogonal experiment was designed with two treatments: contamination (with or without TBT in the food) and crab sex (males and females). The animals were reared in the laboratory for nine months, and macroscopic and histological analyses of reproductive organs were carried out after the end of the experiment. Tributyltin was recorded in exposed crabs, but no morphological alterations were detected in the gonads of males, regardless of whether they were exposed to TBT. In contrast, females exposed to TBT displayed disorganization and atrophy of their ovaries, thus directly affecting reproduction in this hermit crab species. This effect observed in female hermit crabs may harm populations located in harbor regions, where TBT concentration is high, even after the worldwide TBT ban.

Microsporidia parasites disrupt the responses to cadmium exposure in a gammarid

Microsporidia parasites are commonly found in amphipods, where they are often asymptomatic, vertically-transmitted and have several effects on host sexuality and behaviour. As amphipods are often used as models in ecotoxicological studies, we investigated the effect of microsporidian infections on energy reserves and defence capacities of Gammarus roeseli under cadmium stress. Only females were infected by two microsporidia parasites: Dictyocoela roeselum or Dictyocoela muelleri. In physiological conditions, microsporidia had no major effect on energy reserves and defence capacities of G. roeseli, while under cadmium exposure, energy reserves and antioxidant defence were weaker in infected females. Moreover, higher malondialdehyde levels detected in infected females revealed that they suffered more cellular damages. Our results suggest that microsporidia may affect gammarid fitness in stressful conditions, when parasitic stress cannot be compensated by the host. Consequently, microsporidia parasites should be a factor necessary to take into account in ecotoxicology studies involving amphipods.