Estrogen receptor: A potential linker of estrogenic and dopaminergic pathways in zebrafish larvae following deltamethrin exposure

Lipidomics Atlas Tracks Alterations Associated with Deltamethrin-Induced Developmental Neurotoxicity in Embryonic Zebrafish

Deltamethrin (DM) is a widely used pyrethroid pesticide associated with childhood neurodevelopmental disorders. However, the specific impact of DM exposure during distinct early life stages remains unclear. Here, zebrafish embryos were exposed to DM at different stages: before (10-16 hpf), at the onset of (16-24 hpf), at the peak of (24-36 hpf) hypothalamic neurogenesis, and continuously from 10 to 120 hpf (subchronic exposure), using different dosages (1, 100, and 250 nM). Exposure to middle/high-dose DM at 24-36 and 10-120 hpf significantly reduced zebrafish locomotor activities and increased apoptotic cells in the spinal cord. As a pivotal factor in central nervous system disorder progression, altered lipid metabolism was investigated using nontargeted lipidomic analysis. DM exposure at 10-16 and 24-36 hpf led to the most significant lipidome reprogramming. Despite exhibiting a dose-dependent trend, even low-dose DM changed the lipidome. Cer 40:2;2 and PG 44:12 showed potential in identifying DM exposure effects. Significant changes in sphingolipid, cardiolipin, phosphatidylglycerol, and glycerolipid pathways were linked to DM-induced developmental neurotoxicity, indicating impaired membrane function, mitochondrial damage, and disrupted energy metabolism. Our study sheds new light on assessing early neurodevelopmental disturbances and identifying intervention targets, emphasizing sensitivity to DM during the critical early phase of neurodevelopment.

Hybridization in the Anthropocene - how pollution and climate change disrupt mate selection in freshwater fish

Chemical pollutants and/or climate change have the potential to break down reproductive barriers between species and facilitate hybridization. Hybrid zones may arise in response to environmental gradients and secondary contact between formerly allopatric populations, or due to the introduction of non-native species. In freshwater ecosystems, field observations indicate that changes in water quality and chemistry, due to pollution and climate change, are correlated with an increased frequency of hybridization. Physical and chemical disturbances of water quality can alter the sensory environment, thereby affecting chemical and visual communication among fish. Moreover, multiple chemical compounds (e.g. pharmaceuticals, metals, pesticides, and industrial contaminants) may impair fish physiology, potentially affecting phenotypic traits relevant for mate selection (e.g. pheromone production, courtship, and coloration). Although warming waters have led to documented range shifts, and chemical pollution is ubiquitous in freshwater ecosystems, few studies have tested hypotheses about how these stressors may facilitate hybridization and what this means for biodiversity and species conservation. Through a systematic literature review across disciplines (i.e. ecotoxicology and evolutionary biology), we evaluate the biological interactions, toxic mechanisms, and roles of physical and chemical environmental stressors (i.e. chemical pollution and climate change) in disrupting mate preferences and inducing interspecific hybridization in freshwater fish. Our study indicates that climate change-driven changes in water quality and chemical pollution may impact visual and chemical communication crucial for mate choice and thus could facilitate hybridization among fishes in freshwater ecosystems. To inform future studies and conservation management, we emphasize the importance of further research to identify the chemical and physical stressors affecting mate choice, understand the mechanisms behind these interactions, determine the concentrations at which they occur, and assess their impact on individuals, populations, species, and biological diversity in the Anthropocene.

Long-term impact of embryonic exposure to ethinylestradiol and clotrimazole on behavior and neuroplasticity in zebrafish (Danio rerio)

Estrogen receptors (ER) are widely expressed in the brain of many species and experimental results highlighted the role of estradiol in neuronal plasticity and behavior. Consequently, the brain is therefore a prime target for endocrine disrupting chemicals (EDCs) interacting with estrogen signaling. Very little is known about the late effects of early disruption of estrogen signaling by EDCs. We focused on: ethinylestradiol (EE2; ER agonist) and clotrimazole (inhibitor of key steroidogenesis enzymes, including aromatases). Zebrafish eleutheroembryos were exposed (0-5 days) and then raised normally until adulthood. Several behavioral tests were performed in adults, then cell proliferation and dopaminergic neurons were quantified in several brain regions using immunostaining. Overall, a developmental exposure to EDCs stimulates cell proliferation in the dorsal telencephalon. At environmentally-relevant concentrations, male fish exposed to EE2 exhibited increased activity levels and decreased social behavior, posing a potential risk to population balance and health.

A transcriptomics-based analysis of mechanisms involved in the neurobehavioral effects of 6PPD-quinone on early life stages of zebrafish

As an emerging pollutant frequently detected in aquatic ecosystems, the toxicity of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-quinone) on fish has been confirmed, but insight into the mechanisms underlying those adverse effects is still limited. Thus, we exposed zebrafish embryos to 6PPD-quinone at 0, 0.25, 2.5, and 25 μg/L until 120 h post-fertilization (hpf), and investigated the variations in their development, behavior, monoamine neurotransmitter levels, and transcriptional profile. Exposure to 6PPD-quinone notably elevated the heart rate of zebrafish at 48 hpf (at 2.5 and 25 μg/L) and 72 hpf (at 0.25, 2.5, and 25 μg/L). In the dark-light transition test, the locomotor activity of zebrafish larvae exposed to 6PPD-quinone significantly increased, especially in the dark periods. Exposure to 6PPD-quinone also altered the dopamine level and its turnover in zebrafish, which exhibited significant correlations to their locomotor activity. RNA sequencing identified 394 differentially expressed genes (DEGs), most of which have the molecular function of binding and catalytic activity. Five DEGs were predicted as the key driver genes in the protein-protein interaction networks associated with circadian rhythm (i.e., npas2), protein processing in endoplasmic reticulum (i.e., hsp90b1 and pdia4), and estrogen signaling pathway (i.e., hsp90aa1.1 and hsp90aa1.2). Our findings provide more insights into mechanisms underlying the toxicity of 6PPD-quinone to teleosts and highlight the necessity to assess its potential risks to aquatic ecosystems.

Deltamethrin increased susceptibility to Aeromonas hydrophila in crucian carp through compromising gill barrier

Pyrethroids serve as a significant method for managing and preventing parasitic diseases in fish. Among these, deltamethrin (DEL) is used extensively in aquatic environments. Our previous work has been confirmed that DEL exposure can induce oxidative stress and immunosuppression on the gill mucosal barrier of crucian carp (Carassius auratus). However, it is not clear whether DEL affects the susceptibility of farmed fish to bacterial infection. In this study, fish was pre-exposed to different DEL concentration (0, 0.3 and 0.6 μg L-1) and then challenged by immersion with Aeromonas hydrophila (1.0 × 10^8 CFU mL-1). After immersion challenge, fish pre-exposed to DEL developed prominent lipopolysaccharides level in gill and serum and had a significantly lower survival rate compared to the control group. In DEL pre-exposure fish after immersion, the gill apoptosis levels were significantly higher and disrupted the tight junction barrier by downregulating the zo1 and claudin12. Furthermore, fish pre-exposed to DEL exhibited increased activities of superoxide dismutase (SOD), total antioxidant capacity (T-AOC), and malonaldehyde (MDA) levels in the early stage after immersion but experiencing decreased activities of glutathione peroxidase (GPx) and lysozyme (LZM) in the later stage after immersion. And this process was regulated by the NRF2 pathway. Additionally, fish pre-exposed to DEL after immersion had significantly lower mRNA levels of immune-related genes tlr4, myd88, tnfα, and il-1β. Overall, these findings indicate that DEL damaged the gill barrier, weakened the immune response, raised LPS levels, and heightened vulnerability to A. hydrophila infection in crucian carp, resulting in mortality. Thus, this work will help social groups and aquaculture workers to understand the potential risk of DEL exposure for bacterial secondary infection in cultured fish.

Contribution of Immune Responses to the Cardiotoxicity and Hepatotoxicity of Deltamethrin in Early Life Stage Zebrafish (Danio rerio)

Deltamethrin (DM) is a widely used insecticide that has demonstrated developmental toxicity in the early life stages of fish. To better characterize the underlying mechanisms, embryos from Tg(cmlc2:RFP), Tg(apo14:GFP), and Tg(mpx:GFP) transgenic strains of zebrafish were exposed to nominal DM concentrations of 0.1, 1, 10, 25, and 50 μg/L until 120 h post-fertilization (hpf). Heart size increased 56.7%, and liver size was reduced by 17.1% in zebrafish exposed to 22.7 and 24.2 μg/L DM, respectively. RNA sequencing and bioinformatic analyses predicted that key biological processes affected by DM exposure were related to inflammatory responses. Expression of IL-1 protein was increased by 69.0% in the 24.4 μg/L DM treatment, and aggregation of neutrophils in cardiac and hepatic histologic sections was also observed. Coexposure to resatorvid, an anti-inflammatory agent, mitigated inflammatory responses and cardiac toxicity induced by DM and also restored liver biomass. Our data indicated a complex proinflammatory mechanism underlying DM-induced cardiotoxicity and hepatotoxicity which may be important for key events of adverse outcomes and associated risks of DM to early life stages of fish.

Effect of chronic deltamethrin exposure on brain transcriptome and metabolome of juvenile crucian carp

Deltamethrin (Del), a widely administered pyrethroid insecticide, has been established as a common contaminant of the freshwater environment and detected in many freshwater ecosystems. In this study, we investigated the changes in brain transcriptome and metabolome of crucian carp after exposure to 0.6 μg/L Del for 28 days. Elevated MDA levels and inhibition of SOD activity indicate damage to the antioxidant system. Moreover, a total of 70 differential metabolites (DMs) were identified using the liquid chromatography-mass spectrometry, including 32 upregulated and 38 downregulated DMs in the Del-exposed group. The DMs associated with chronic Del exposure were enriched in steroid hormone biosynthesis, fatty acid metabolism, and glycerophospholipid metabolism for prostaglandin G2, 5-oxoeicosatetraenoic acid, progesterone, androsterone, etiocholanolone, and hydrocortisone. Transcriptomics analysis revealed that chronic Del exposure caused lipid metabolism disorder, endocrine disruption, and proinflammatory immune response by upregulating the pla2g4, cox2, log5, ptgis, lcn, and cbr expression. Importantly, the integrative analysis of transcriptomics and metabolomics indicated that the arachidonic acid metabolism pathway and steroid hormone biosynthesis were decisive processes in the brain tissue of crucian carp after Del exposure. Furthermore, Del exposure perturbed the tight junction, HIF-1 signaling pathway, and thyroid hormone signaling pathway. Overall, transcriptome and metabolome data of our study offer a new insight to assess the risk of chronic Del exposure in fish brains.

A comparative study on endocrine disrupting effects of leachates from virgin and aged plastics under simulated media in marine medaka larvae (Oryzias melastigma)

Marine plastic pollution has garnered substantial attention, but the potential endocrine disrupting effects of plastic leachates in marine organisms remain unclear. In this study, the larvae of marine medaka (Oryzias melastigma) were exposed to the leachates from virgin and aged plastics soaked in simulated seawater and fish digest for 3 days. The concentrations of vitellogenin (VTG), estradiol (E2), and 11-ketotestosterone (11-KT), as well as the transcripts of endocrine-related genes were measured in the larvae. The results revealed that endogenous E2 was more sensitive to plastic leachates than VTG and 11-KT, which was significantly affected by 26.7 % of all plastic leachates. Among all genes, estrogen receptor α was impacted mostly, being up-regulated by 53.3 % of leachates from aged plastics. The comparative results demonstrated that the leachates from plastics with different statuses caused a greater difference than those from plastics in different simulated media, and the leachates from aged plastics resulted in higher endocrine disrupting effects than those from virgin plastics. In addition, seven leached additives (plasticizers and flame retardants) could explain 25.6 % of the hormonal effects using redundancy analysis, indicating that other additives in the plastic leachates can also play important roles in regulating the endocrine system of O. melastigma larvae.

New evidence for neurobehavioral toxicity of deltamethrin at environmentally relevant levels in zebrafish

Deltamethrin, a widely used type II pyrethroid insecticide, was reported with neurotoxicity to aquatic organisms, such as fish. However, the effects and potential mechanisms on the central nervous system remain largely unknown, especially under environmental concentrations. Therefore, we exposed adult female zebrafish to environmentally relevant levels of deltamethrin (30, 100, and 333 ng/L) for 21 days to assess neurobehavioral changes related to the central nervous system and explore the modes of action. Behavioral assays revealed significant increases in the swimming speeds, residence time near other fish and the shoaling cohesion in exposed fish. Transcriptomic results enriched the disrupted neural functions involving the glutamatergic and dopaminergic synapses in the brain. The qRT-PCR confirmed the upregulation of the factors for promoting the glutamate release. The measurement of neurotransmitters showed significantly increased content of the excitatory neurotransmitter glutamate in the brain. Taken together, deltamethrin exposure increased the glutamate level and promoted the release of such an excitatory neurotransmitter between the glutamatergic synapses in the brain, which eventually led to hyperactivity of social behaviors in adult zebrafish.

Vitamin C Mitigates Oxidative Stress and Behavioral Impairments Induced by Deltamethrin and Lead Toxicity in Zebrafish

Environmental contamination from toxic metals and pesticides is an issue of great concern due to their harmful effects to human health and the ecosystems. In this framework, we assessed the adverse effects when aquatic organisms are exposed to toxicants such as deltamethrin (DM) and lead (Pb), alone or in combination, using zebrafish as a model. Moreover, we likewise evaluated the possible protective effect of vitamin C (VC) supplementation against the combined acute toxic effects of the two toxicants. Juvenile zebrafish were exposed to DM (2 μg L^-1) and Pb (60 μg L^-1) alone and in combination with VC (100 μg L^-1) and responses were assessed by quantifying acetylcholinesterase (AChE) activity, lipid peroxidation (MDA), some antioxidant enzyme activities (SOD and GPx), three-dimension locomotion responses and changes of elements concentrations in the zebrafish body. Our results show that VC has mitigative effects against behavioral and biochemical alterations induced by a mixture of contaminants, demonstrating that it can be used as an effective antioxidant. Moreover, the observations in the study demonstrate zebrafish as a promising in vivo model for assessing the neuroprotective actions of bioactive compounds.