Different developmental insecticide exposure windows trigger distinct locomotor phenotypes in the early life stages of zebrafish

Biochemical and Behavioral Responses in the Killer Shrimp Dikerogammarus villosus Following Acute Exposure to Thiacloprid and Calypso®

Neonicotinoids are insecticides that are used globally and can persist in soil and surface water, posing a threat to ecosystems. In this study, we exposed the invasive freshwater amphipod Dikerogammarus villosus to environmentally relevant and relatively high concentrations of thiacloprid, a widely used agricultural neonicotinoid active ingredient and its commercial form Calypso® for two days. The acute effects were investigated at the behavioral (immobility time) and biochemical [glutathione S-transferase (GST) and acetylcholine esterase (AChE) activity] levels. Calypso® concentrations of 10 µg/l and 100 µg/l a significantly increased the immobility time, while thiacloprid exerted such an effect only at 100 µg/l. The GST enzyme activity did not change in the thiacloprid-treated groups; however, the 10 µg/l and 100 µg/l Calypso® concentrations significantly increased the GST activity. All Calypso® concentrations significantly decreased AChE activity until the highest Calypso® concentration was reached, and an interesting outcome was the 'U-shaped dynamics' of AChE activity. In contrast, thiacloprid had no significant blocking effect on AChE activity at any of the concentrations tested. Neonicotinoid insecticides are neurotoxins that selectively target nicotinic acetylcholine receptors in the insect central nervous system. However, their widespread use has a growing impact on nontarget animals. This study confirms the risk of neonicotinoids to aquatic invertebrates by providing evidence that neonicotinoids can also affect both behavioral and biochemical processes in D. villosus.

Developmental toxicity of formulated insecticide mixture containing imidacloprid and beta-cyfluthrin in fish: Insights using zebrafish

Insecticides are critical in controlling pests and disease vectors. However, there is still a lack of ecotoxicological studies using commercial formulations of insecticides containing active ingredients. The study aimed to evaluate the developmental toxicity of a commercial insecticide mixture (imidacloprid [IMI] + beta-cyfluthrin [β-CYF]). Mortality, hatching rate, spontaneous contraction, heartbeat, morphological changes, reactive oxygen species (ROS), skeletal development, and locomotor behavior of zebrafish were analyzed. Embryos were exposed to imidacloprid (IMI) and β-cyfluthrin (β-CYF) in the following ratios: 0.001 mg IMI·L-1 + 0.000125 mg β-CYF·L-1 (C1); 0.01 mg IMI·L-1 + 0.00125 mg β-CYF·L-1 (C2); 0.1 mg IMI·L-1 + 0.0125 mg β-CYF·L-1 (C3); 1.0 mg IMI·L-1 + 0.125 mg β-CYF·L-1 (C4); 10.0 mg IMI·L-1 + 1.25 mg β-CYF·L-1 (C5) for 144 h. The results showed a mortality of 50 % of organisms in the C5 concentration. Embryos exposed to C1 and C3 showed tachycardia and hatched early compared to the negative control, indicating cardiotoxic and embryotoxic effects. The two highest concentrations tested (C4 and C5) induced evident morphological changes (yolk sac and pericardial edema, and spine alterations), and skeletal toxicity (absence of cartilage and bone formation), along with decreased larval swimming behavior. Also, the formulated insecticide (C1) increased ROS levels in zebrafish larvae. Results showed that the formulated insecticide containing IMI and β-CYF induces several toxic effects on developing zebrafish, indicating its environmental risk to aquatic organisms.

Benfuracarb impairs zebrafish swim bladder development via the JNK2 pathway mediated inhibition of autophagy

Benfuracarb is widely utilized for crop protection due to its effective pest control properties; however, little information is available regarding its adverse effects and possible molecular mechanisms in fish development. In the present study, benfuracarb exposure caused defects in the development and inflation of the swim bladder, as well as in the lipid metabolism of zebrafish larvae. Compared with the control, key genes involved in swim bladder development, lipid metabolism, surfactant proteins and autophagy were altered in response to benfuracarb exposure. Furthermore, potential targets of benfuracarb were identified using network toxicology and molecular docking, with c-Jun N-terminal kinase 2 (JNK2 encoded by mapk9) predicted as a critical target. Moreover, the JNK family activator anisomycin was observed to mitigate the inhibitory effects of benfuracarb on zebrafish swim bladder inflation, as well as on the expression of autophagy-related genes, suggesting that benfuracarb may inhibit swim bladder development and inflation by downregulating the JNK2 signaling pathway. Overall, this study suggests that the swim bladder might serve as a potential target organ for benfuracarb toxicity in zebrafish, providing valuable insights for assessing the environmental risks of benfuracarb.

Zebrafish as a model to study PERK function in developmental diseases: implications for Wolcott-Rallison syndrome

Developmental diseases are challenging to investigate due to their clinical heterogeneity and relatively low prevalence. The Wolcott-Rallison Syndrome (WRS) is a rare developmental disease characterized by skeletal dysplasia and permanent neonatal diabetes due to loss-of-function mutations in the endoplasmic reticulum stress kinase PERK (EIF2AK3). The lack of efficient and less invasive therapies for WRS highlights the need for new animal models that replicate the complex pathological phenotypes, while preserving scalability for drug screening. Zebrafish exhibits high fecundity and rapid development that facilitate efficient and scalable in vivo drug testing. Here, we aimed to assess the potential of zebrafish to study PERK function and its pharmacological modulation, and as model organism of developmental diseases such as the WRS. Using bioinformatic analyses, we showed high similarity between human and zebrafish PERK. We used the pharmacological PERK inhibitor GSK2606414, which was bioactive in zebrafish, to modulate PERK function. Using transgenic zebrafish expressing fluorescent pancreatic markers and a fluorescent glucose probe, we observed that PERK inhibition decreased β cell mass and disrupted glucose homeostasis. By combining behavioural and functional assays, we show that PERK-inhibited zebrafish present marked skeletal defects and defective growth, as well as neuromuscular and cardiac deficiencies, which are clinically relevant in WRS patients, while sparing parameters like otolith area and eye/body ratio which are not associated with WRS. These results show that zebrafish holds potential to study PERK function and its pharmacological modulation in developmental disorders like WRS, assisting research on their pathophysiology and experimental treatments.

Sensitivity Variations in Developmental Toxicity of Imidacloprid to Zebrafish Embryos at Different Neurodevelopmental Stages

Neonicotinoids are ubiquitous in global surface waters and pose a significant risk to aquatic organisms. However, information is lacking on the variations in sensitivity of organisms at different developmental stages to the neurotoxic neonicotinoids. We established a spectrum of toxicity to zebrafish embryos at four neurodevelopmental stages (1, 3, 6, and 8 h post fertilization [hpf]) and dechorionated embryos at 6 hpf based on external and internal exposure to imidacloprid as a representative neonicotinoid. Embryos at the gastrula stage (6 and 8 hpf) were more sensitive to imidacloprid than embryos at earlier developmental stages. Dechorionated embryos were more sensitive to imidacloprid than embryos with a chorion, suggesting that the chorion offers protection against pollutants. Nine sublethal effects were induced by imidacloprid exposure, among which uninflated swim bladder (USB) was the most sensitive. Water depth and air availability in the exposure chambers were critical factors influencing the occurrence of USB in zebrafish larvae. Internal residues of metabolites accounted for <10% of imidacloprid, indicating that imidacloprid was metabolized in a limited fashion in the embryos. In addition, acute toxicity of the main metabolite 5-hydroxy-imidacloprid was significantly lower than that of imidacloprid, indicating that the observed toxicity in embryos exposed to imidacloprid was mainly induced by the parent compound. Our research offers a fresh perspective on choosing the initial exposure time in zebrafish embryo toxicity tests, particularly for neurotoxicants. Environ Toxicol Chem 2024;43:2398-2408. © 2024 SETAC.

Rutin hydrate relieves neuroinflammation in zebrafish models: Involvement of NF-κB pathway as a central network

Neuroinflammation is prevalent in multiple brain diseases and may also lead to dementia, cognitive impairment, and impaired spatial memory function associated with neurodegenerative diseases. A neuroprotective and antioxidant flavonoid, rutin hydrate (RH), was evaluated for the anti-neuroinflammatory activity mediated by copper sulfate (CuSO4) solution and lipopolysaccharide (LPS) in zebrafish. The results showed that 100 mg/L RH significantly reduced the ratio of neutrophil mobility in caudal hematopoietic tissue (CHT) region caused by CuSO4 and the number of neutrophils co-localized with facial peripheral nerves. In the LPS model, RH co-injection significantly diminished neutrophil and macrophage migration. Therefore, RH exhibited a significant rescue effect on both models. In addition, RH treatment remarkably reduced the effects of neuroinflammation on the locomotor ability, expression levels of genes associated with behavioral disorders, and acetylcholinesterase (AChE) activity. Furthermore, network pharmacology techniques were employed to investigate the potential mechanisms, and the associated genes and enzyme activities were validated in order to elucidate the underlying mechanisms. Network pharmacological analysis and zebrafish model indicated that RH regulated the expressions of NF-κB pathway-related targets (Toll-like receptor 9 (tlr9), nuclear factor kappa B subunit 1 (nfkb1), RELA proto-oncogene (RelA), nitric oxide synthase 2a, inducible (nos2a), tumour necrosis factor alpha-like (tnfα), interleukin 6 (il6), interleukin 1β (il1β), chemokine 8 (cxcl8), and macrophage migration inhibitory factor (mif)) as well as six key factors (arachidonic acid 4 alpha-lipoxygenase (alox4a), arachidonate 5-lipoxygenase a (alox5), prion protein a (prnpa), integrin, beta 2 (itgb2), catalase (CAT), and alkaline phosphatase (ALP) enzymes). Through this study, a thorough understanding of the mechanism underlying the therapeutic effects of RH in neuroinflammation has been achieved, thereby establishing a solid foundation for further research on the potential therapeutic applications of RH in neuroinflammatory disorders.