Release of chitobiase as an indicator of potential molting disruption in juvenile Daphnia magna exposed to the ecdysone receptor agonist 20-hydroxyecdysone

Zooplankton-based adverse outcome pathways: A tool for assessing endocrine disrupting compounds in aquatic environments

Endocrine disrupting compounds (EDCs) pose a significant ecological risk, particularly in aquatic ecosystems. EDCs have become a focal point in ecotoxicology, and their identification and regulation have become a priority. Zooplankton have gained global recognition as bioindicators, benefiting from rigorous standardization and regulatory validation processes. This review aims to provide a comprehensive summary of zooplankton-based adverse outcome pathways (AOPs) with a focus on EDCs as toxicants and the utilisation of freshwater zooplankton as bioindicators in ecotoxicological assessments. This review presents case studies in which zooplankton have been used in the development of AOPs, emphasizing the identification of molecular initiating events (MIEs) and key events (KEs) specific to zooplankton exposed to EDCs. Zooplankton-based AOPs may become an important resource for understanding the intricate processes by which EDCs impair the endocrine system. Furthermore, the data sources, experimental approaches, advantages, and challenges associated with zooplankton-based AOPs are discussed. Zooplankton-based AOPs framework can provide vital tools for consolidating toxicological knowledge into a structured toxicity pathway of EDCs, offering a transformative platform for facilitating enhanced risk assessment and chemical regulation.

Exploring BPA alternatives - Environmental levels and toxicity review

Bisphenol A alternatives are manufactured as potentially less harmful substitutes of bisphenol A (BPA) that offer similar functionality. These alternatives are already in the market, entering the environment and thus raising ecological concerns. However, it can be expected that levels of BPA alternatives will dominate in the future, they are limited information on their environmental safety. The EU PARC project highlights BPA alternatives as priority chemicals and consolidates information on BPA alternatives, with a focus on environmental relevance and on the identification of the research gaps. The review highlighted aspects and future perspectives. In brief, an extension of environmental monitoring is crucial, extending it to cover BPA alternatives to track their levels and facilitate the timely implementation of mitigation measures. The biological activity has been studied for BPA alternatives, but in a non-systematic way and prioritized a limited number of chemicals. For several BPA alternatives, the data has already provided substantial evidence regarding their potential harm to the environment. We stress the importance of conducting more comprehensive assessments that go beyond the traditional reproductive studies and focus on overlooked relevant endpoints. Future research should also consider mixture effects, realistic environmental concentrations, and the long-term consequences on biota and ecosystems.

Endocrine disruption in crustaceans: New findings and perspectives

A significant advance has been made, especially during the last two decades, in the knowledge of the effects on crustacean species of pollutants proven to be endocrine disruptors in vertebrates. Such effects have been also interpreted in the light of recent studies on crustacean endocrinology. Year after year, the increased number of reports refer to the effects of endocrine disruptors on several processes hormonally controlled. This review is aimed at summarizing and discussing the effects of several kinds of endocrine disruptors on the hormonal control of reproduction (including gonadal growth, sexual differentiation, and offspring development), molting, and intermediate metabolism of crustaceans. A final discussion about the state of the art, as well as the perspective of this toxicological research line is given.

Knockdown of the ecdysone receptor disrupts development and causes mortality in the melon fly, Zeugodacus cucurbitae

Cucurbits are important economic plants that are attacked by numerous pests, among which the melon fly Zeugodacus cucurbitae is extremely problematic. New sustainable pest control strategies are necessary to replace chemical insecticides that are harmful to the environment, human health and nontarget species. The RNA interference (RNAi) technology is one of the most promising tools due to high efficiency and species specificity. We developed an RNAi strategy targeting the ecdysone receptor (ECR) of Z. cucurbitae, which plays an important role in moulting and reproduction. We identified, described and isolated the ECR gene of Z. cucurbitae and measured its expression pattern across developmental stages and tissues. ZcECR knockdown via dsZcECR ingestion caused a significant larval mortality and abnormal phenotypes in pupae and adults. About 68% of larvae fed with a dsZcECR-treated diet failed to enter the pupal stage and died. In addition, ZcECR knockdown dramatically reduced pupal weight (by 3.24 mg on average) and fecundity (by about 23%). RNAi targeting the ECR gene is therefore a promising method to control Z. cucurbitae, paving the way for the development of novel sustainable and highly specific control strategies.

A molting chemical cue (N-acetylglucosamine-6-phosphate) contributes to cannibalism of Chinese mitten crab Eriocheir sinensis

Under high-density culture, cannibalism occurs frequently during the molting of the Chinese mitten crabs Eriocheir sinensis, resulting in a large reduction in production. We found that the leakage of molting fluid from sexually immature crabs informs conspecifics that they are in a molting process. This hypothesis was verified through metabolomics analyses combined with behavioral experiments. The GlcNAc-6-P was identified as a molting biomarker from the differential metabolites by non-targeted metabolomics. In addition, we found that the concentration of GlcNAc-6-P in the molting fluid was significantly higher than other molting metabolites at different molting stages, reaching 5.84 μmol L-1, indicating that the molting fluid was the source of GlcNAc-6-P. Moreover, the behavioral experiments showed that crabs were actively approached to high concentrations of GlcNAc-6-P (1 μmol L-1), but had no obvious choice tendency at different concentrations of UTP, 20-HE and low concentrations of GlcNAc-6-P (0.1 μmol L-1, 0.01 μmol L-1) compared with the control groups. In conclusion, that E. sinensis by sensing the concentration change of GlcNAc-6-P can locate the source of GlcNAc-6-P release and actively approach the high concentration GlcNAc-6-P area and attack the molting crab, causing cannibalism. Blocking the reception pathway of molting chemical cues in E. sinensis, thereby preventing the perception of signals originating from conspecifics' molting in the vicinity, could lead to a reduction in cannibalistic behavior and an increase in overall production. Additionally, this method presents a prospective solution for addressing cannibalism in other crustacean species where such behavior is prevalent.

Environmental RNA as a Noninvasive Tool for Assessing Toxic Effects in Fish: A Proof-of-concept Study Using Japanese Medaka Exposed to Pyrene

Although environmental RNA (eRNA) is emerging as a noninvasive tool to assess the health status of aquatic macroorganisms, the potential of eRNA in assessing chemical hazards remain largely untested. In this study, we investigated the ability of eRNA to detect changes in gene expression in Japanese medaka fish (Oryzias latipes) in response to sublethal pyrene exposure, as a model toxic chemical. We performed standardized acute toxicity tests and collected eRNA from tank water and RNA from fish tissue after 96 h of exposure. Our results showed that over 1000 genes were detected in eRNA and the sequenced read counts of these genes correlated with those in fish tissue (r = 0.50). Moreover, eRNA detected 86 differentially expressed genes in response to pyrene, some of which were shared by fish RNA, including the suppression of collagen fiber genes. These results suggest that eRNA has the potential to detect changes in gene expression in fish in response to environmental stressors without the need for sacrificing or causing pain to fish. However, we also found that the majority of sequenced reads of eRNA (>99%) were not mapped to the reference medaka genome and they originated from bacteria and fungi, resulting in low sequencing depth. In addition, eRNA, in particular nuclear genes, was highly degraded with a median transcript integrity number (TIN) of <20. These limitations highlight the need for future studies to improve the analytical methods of eRNA application.

Freshwater crustacean exposed to active pharmaceutical ingredients: ecotoxicological effects and mechanisms

Concerns over the ecotoxicological effects of active pharmaceutical ingredients (APIs) on aquatic invertebrates have been raised in the last decade. While numerous studies have reported the toxicity of APIs in invertebrates, no attempt has been made to synthesize and interpret this dataset in terms of different exposure scenarios (acute, chronic, multigenerational), multiple crustacean species, and the toxic mechanisms. In this study, a thorough literature review was performed to summarize the ecotoxicological data of APIs tested on a range of invertebrates. Therapeutic classes including antidepressants, anti-infectives, antineoplastic agents, hormonal contraceptives, immunosuppressants, and neuro-active drugs exhibited higher toxicity to crustaceans than other API groups. The species sensitivity towards APIs exposure is compared in D. magna and other crustacean species. In the case of acute and chronic bioassays, ecotoxicological studies mainly focus on the apical endpoints including growth and reproduction, whereas sex ratio and molting frequency are commonly used for evaluating the substances with endocrine-disrupting properties. The multigenerational and "Omics" studies, primarily transcriptomics and metabolomics, were confined to a few API groups including beta-blocking agents, blood lipid-lowing agents, neuroactive agents, anticancer drugs, and synthetic hormones. We emphasize that in-depth studies on the multigenerational effects and the toxic mechanisms of APIs on the endocrine systems of freshwater crustacean are warranted.

Herbicide prometryn adversely affects the development and reproduction of Tigriopus japonicus by disturbing the ecdysone signal pathway and chitin metabolic pathway

Prometryn, a widely used triazine herbicide in agriculture and aquaculture, has been commonly detected in marine environments, but its effects on the marine copepod are unknown. In this study, marine copepod Tigriopus japonicus was chronically exposed to environmentally relevant concentrations of prometryn to investigate its impacts and potential mechanism of action. The results showed that 0.5, 5, and 50 μg/L prometryn delayed the first spawning time and hatching time, reduced the fecundity, and inhibited the population growth rate. Moreover, exposure to 0.5, 5 and 50 μg/L prometryn decreased food ingestion, the content of C and N elements, nutrient accumulation and body size, but increased the content of 20-hydroxyecdysone (20E). Transcriptome analysis showed that 50 μg/L prometryn down-regulated 1431 genes, which were mainly enriched in lysosome pathway and chitin binding and cuticle construction process. The results of qRT-PCR showed that the expression of key genes involved in juvenile hormone synthesis and chitin metabolic pathways were also inhibited after prometryn exposure. Molecular docking revealed that prometryn could bind to ecdysone receptor (EcR) and UDP-N-acetylglucosamine pyrophosphorylase (UAP), components of the ecdysteroid nuclear receptor complex. Therefore, environmental relevant prometryn delayed the molting and development of T. japonicus by disrupting the ecdysone signal pathway and chitin metabolic pathway through binding to EcR and UAP. This study provides new insights into toxic effects and molecular mechanisms of prometryn on marine copepods.

New Insights into the Mechanism of Action of PirAB from Vibrio Parahaemolyticus

PirAB toxins secreted by Vibrio parahaemolyticus (Vp) harbor the pVA1 virulence plasmid, which causes acute hepatopancreatic necrosis disease (AHPND), an emerging disease in Penaeid shrimp that can cause 70–100% mortality and that has resulted in great economic losses since its first appearance. The cytotoxic effect of PirAB^Vp on the epithelial cells of the shrimp hepatopancreas (Hp) has been extensively documented. New insights into the biological role of the PirB^Vp subunit show that it has lectin-like activity and recognizes mucin-like O-glycosidic structures in the shrimp Hp. The search for toxin receptors can lead to a better understanding of the infection mechanisms of the pathogen and the prevention of the host disease by blocking toxin–receptor interactions using a mimetic antagonist. There is also evidence that Vp AHPND changes the community structure of the microbiota in the surrounding water, resulting in a significant reduction of several bacterial taxa, especially Neptuniibacter spp. Considering these findings, the PirAB^vp toxin could exhibit a dual role of damaging the shrimp Hp while killing the surrounding bacteria.

The Vibrio parahaemolyticus subunit toxin PirBvp recognizes glycoproteins on the epithelium of the Penaeus vannamei hepatopancreas

Vibrio parahaemolyticus toxin PirAB^vp is the major virulence factor exotoxin that contributes to the disruption of the hepatopancreatic epithelium in acute hepatopancreatic necrosis disease in shrimp. The PirB^vp subunit is a lectin that recognizes amino sugars; however, its potential role in recognition of the hepatopancreas has not been identified. In the present work, we identified the cellular receptor for PirB^vp in the shrimp hepatopancreas. A ligand blot assay of hepatopancreas lysate showed that the PirB^vp subunit recognizes two glycoprotein bands of 60 and 70 kDa (Gc60 and Gc70). The hepatopancreas lysate was fractionated by anion-exchange chromatography, and the three main fractions obtained contained the recognized Gc60 and Gc70 protein bands. LC-MS/MS indicated that beta-hexosaminidases subunit beta and mucin-like 5 AC corresponded to the 60 and 70 kDa bands, respectively, which seem to be expressed in the epithelial cells of the hepatopancreas. Endoglycosidase treatment of hepatopancreas lysate with the O-glycosidase from Enterococcus faecalis, inhibits the binding of PirB^vp. Altogether, these results suggest the relevance of the interaction of PirB^vp with the hepatopancreas in the pathogenesis of acute hepatopancreatic necrosis disease in shrimp.

AOP Report: Inhibition of Chitin Synthase 1 Leading to Increased Mortality in Arthropods

Arthropods (including insects, crustaceans, and arachnids) rely on the synthesis of chitin to complete their life cycles (Merzendorfer 2011). The highly conserved chitin synthetic process and the absence of this process in vertebrates make it an exploitable target for pest management and veterinary medicines (Merzendorfer 2013; Junquera et al. 2019). Susceptible, nontarget organisms, such as insects and aquatic invertebrates, exposed to chitin synthesis inhibitors may suffer population declines, which may have a negative impact on ecosystems and associated services. Hence, it is important to properly identify, prioritize, and regulate relevant chemicals posing potential hazards to nontarget arthropods. The need for a more cost-efficient and mechanistic approach in risk assessment has been clearly evident and triggered the development of the adverse outcome pathway (AOP) framework (Ankley et al. 2010). An AOP links a molecular initiating event (MIE) through key events (KEs) to an adverse outcome. The mechanistic understanding of the underlying toxicological processes leading to a regulation-relevant adverse outcome is necessary for the utilization of new approach methodologies (NAMs) and efficient coverage of wider chemical and taxonomic domains. In the last decade, the AOP framework has gained traction and expanded within the (eco)toxicological research community. However, there exists a lack of mature invertebrate AOPs describing molting defect-associated mortality triggered by direct inhibition of relevant enzymes in the chitin biosynthetic pathway (chitin synthesis inhibitors) or interference with associated endocrine systems by environmental chemicals (endocrine disruptors). Arthropods undergo molting to grow and reproduce (Heming 2018). This process is comprised of the synthesis of a new exoskeleton, followed by the exuviation of the old exoskeleton (Reynolds 1987). The arthropod exoskeleton (cuticle) can be divided into 2 layers, the thin and nonchitinous epicuticle, which is the outermost layer of the cuticle, and the underlying chitinous procuticle. A single layer of epithelial cells is responsible for the synthesis and secretion of both cuticular layers (Neville 1975). The cuticle protects arthropods from predators and desiccation, acts as a physical barrier against pathogens, and allows for locomotion by providing support for muscular function (Vincent and Wegst 2004). Because the procuticle mainly consists of chitin microfibrils embedded in a matrix of cuticular proteins supplemented by lipids and minerals in insects (Muthukrishnan et al. 2012) and crustaceans (Cribb et al. 2009; Nagasawa 2012), chitin is a determinant factor for the appropriate composition of the cuticle and successful molting (Cohen 2001). A detailed overview of the endocrine mechanisms regulating chitin synthesis is given in Supplemental Data, Figure S1. The shedding of the old exoskeleton in insects is mediated by a sequence of distinct muscular contractions, the ecdysis motor program (EMP; Ayali 2009; Song et al. 2017a). Like the expression of chitin synthase isoform 1 (CHS-1), the expression of peptide hormones regulating the EMP is also controlled by ecdysteroids (Antoniewski et al. 1993; Gagou et al. 2002; Ayali 2009). Cuticular chitin is polymerized from uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc) by the transmembrane enzyme CHS-1, which is localized in the epithelial plasma membrane in insects (Locke and Huie 1979; Binnington 1985; Merzendorfer and Zimoch 2003; Merzendorfer 2006). Because crustaceans are also dependent on the synthesis of chitin, the underlying mechanisms are believed to be similar, although less is known about different CHS isoforms and their localization (Rocha et al. 2012; Qian et al. 2014; Uddowla et al. 2014; Harðardóttir et al. 2019). Disruption of either chitin synthesis or the upstream endocrine pathways can lead to lethal molting disruption (Arakawa et al. 2008; Merzendorfer et al. 2012; Song et al. 2017a, 2017b). In the case of chitin synthesis inhibition, molting disruption can be referred to as "premature molting." If ecdysis cannot be completed because of decreased chitin synthesis, the organism may not successfully molt. Even if ecdysis can be completed on inhibition of chitin synthesis, the organism may not survive because of the poor integrity of the new cuticle. These effects are observed in arthropods following molting, which fail to survive subsequent molts (Arakawa et al. 2008; Chen et al. 2008) or animals being stuck in their exuviae (Wang et al. 2019) and ultimately dying as a result of insufficient food or oxygen intake (Camp et al. 2014; Song et al. 2017a). The term "premature molting" is used to differentiate from the term "incomplete ecdysis," which describes inhibition of ecdysis on a behavioral level, namely through reduction of the EMP (Song et al. 2017a). The present AOP describes molting-associated mortality through direct inhibition of the enzyme CHS-1. It expands the small but increasing number of invertebrate AOPs that have relevance to arthropods, the largest phylum within the animal kingdom (Bar-On et al. 2018). The development of this AOP will be useful in further research and regulatory initiatives related to assessment of CHS inhibitors and identification of critical knowledge gaps and may suggest new strategies for ecotoxicity testing efforts. Environ Toxicol Chem 2021;40:2112-2120. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A Crab Is Not a Fish: Unique Aspects of the Crustacean Endocrine System and Considerations for Endocrine Toxicology

Crustaceans-and arthropods in general-exhibit many unique aspects to their physiology. These include the requirement to moult (ecdysis) in order to grow and reproduce, the ability to change color, and multiple strategies for sexual differentiation. Accordingly, the endocrine regulation of these processes involves hormones, receptors, and enzymes that differ from those utilized by vertebrates and other non-arthropod invertebrates. As a result, environmental chemicals known to disrupt endocrine processes in vertebrates are often not endocrine disruptors in crustaceans; while, chemicals that disrupt endocrine processes in crustaceans are often not endocrine disruptors in vertebrates. In this review, we present an overview of the evolution of the endocrine system of crustaceans, highlight endocrine endpoints known to be a target of disruption by chemicals, and identify other components of endocrine signaling that may prove to be targets of disruption. This review highlights that crustaceans need to be evaluated for endocrine disruption with consideration of their unique endocrine system and not with consideration of the endocrine system of vertebrates.

Effect of chronic UVR exposure on zooplankton molting and growth

Molting is a crucial physiological process in arthropods development, growth, and adult reproduction, where the chitinolytic enzyme chitobiase (CB) and the apoptosis process (caspase-3 activity) play crucial roles. Both molecular endpoints have been observed to be affected by different toxics that may be present in aquatic environments. However, the role of ultraviolet radiation (UVR) in the molting process remains with poor evidence and the possible effect of the previous exposure on F1 generation is unknown. Here, we conducted laboratory experiments with chronic UVR exposure to test the effect on the molting process of Daphnia commutata. Our results showed a clear negative effect of the UVR that affected the molting process with a reduction in individual growth. This trend was also observed in CB and caspase-3 activities. Our results also suggest that the UV dose received by the mother and eggs has an additive effect with the dose received by the offspring. These results imply that the cumulative impact of small UVR doses (2 h per day, daily dose: 2520 J m^-2 of 340 nm) on mothers and eggs (which cannot be discriminated in our experiments) can have an additive or synergistic effect along with the generations through a potential increase in lethal effect. Finally, the observed desynchronization in the molting process by UVR will affect the fitness of individuals and population dynamics.

Roundup® disrupts chitinolytic enzyme activity and ecdysteroid concentration in Macrobrachium potiuna

The endocrine system of crustaceans regulates the molt cycle with ecdysteroid hormones, mainly the 20-hydroxyecdysone (20-HE). Moreover, the molt process requires the action of chitinolytic enzymes (e.g., chitinase, chitobiase) to break down the old cuticle. However, endocrine disrupting compounds (EDC) are capable of altering their normal functioning. Glyphosate-based herbicides (GBH), such as Roundup®, the most widely used herbicides, are found in freshwater environments and have been considered EDC for many aquatic organisms. Therefore, this study examined the effects of environmentally relevant GBH concentrations (0.0065, 0.065, and 0.28 mg L^-1) on the 20-HE concentration and chitobiase activity in the decapod prawn Macrobrachium potiuna exposed for 14 days. Additionally, lipid peroxidation, a biomarker of membrane lipid degradation, was evaluated in hepatopancreas to assess cellular damage. Results showed that GBH decreased the 20-HE concentration in females at the two highest concentrations tested, while an increase was observed in males exposed to the highest GBH concentration. In addition, GBH also decreased chitobiase activity in males (all concentrations) and females (the two highest concentrations). Finally, GBH caused increased lipid peroxidation in males, indicating cellular damage in the hepatopancreas. In conclusion, this work suggests that GBH is an EDC for crustaceans by disrupting molting, which could lead to altered reproduction and thus population dynamics. Graphical abstract Decrease in the 20-HE concentration and chitobiase activity in muscle of males and females of the freshwater prawn Macrobrachium potiuna exposed to the herbicide Roundup® for 14 days.

In Silico Identification of Chemicals Capable of Binding to the Ecdysone Receptor

The process of molting, known alternatively as ecdysis, is a feature integral in the life cycles of species across the arthropod phylum. Regulation occurs as a function of the interaction of ecdysteroid hormones with the arthropod nuclear ecdysone receptor-a process preceding the triggering of a series of downstream events constituting an endocrine signaling pathway highly conserved throughout environmentally prevalent insect, crustacean, and myriapod organisms. Inappropriate ecdysone receptor binding and activation forms the essential molecular initiating event within possible adverse outcome pathways relating abnormal molting to mortality in arthropods. Definition of the characteristics of chemicals liable to stimulate such activity has the potential to be of great utility in mitigation of hazards posed toward vulnerable species. Thus the aim of the present study was to develop a series of rule-sets, derived from the key structural and physicochemical features associated with identified ecdysone receptor ligands, enabling construction of Konstanz Information Miner (KNIME) workflows permitting the flagging of compounds predisposed to binding at the site. Data describing the activities of 555 distinct chemicals were recovered from a variety of assays across 10 insect species, allowing for formulation of KNIME screens for potential binding activity at the molecular initiating event and adverse outcome level of biological organization. Environ Toxicol Chem 2020;39:1438-1450. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Ecdysteroid and juvenile hormone biosynthesis, receptors and their signaling in the freshwater microcrustacean Daphnia

The two essential insect hormones, ecdysteroids and juvenile hormones, are possessed not only by insects, but also widely by arthropods, and regulate various developmental and physiological processes. In contrast to the abundant information about molecular endocrine mechanisms in insects, the knowledge of non-insect arthropod endocrinology is still limited. In this review, we summarize recent reports about the molecular basis of these two major insect hormones in the freshwater microcrustacean Daphnia, a keystone taxon in limnetic ecology and a bioindicator in environmental studies. Comprehensive comparisons of endocrine signaling pathways between insects and daphnids may shed light on the regulatory mechanisms of various biological phenomena and, moreover, evolutionary processes of arthropod species.