Determination of narcotic potency using a neurobehavioral assay with larval zebrafish

Developmental neurotoxicity of anesthetic etomidate in zebrafish larvae: Alterations in motor function, neurotransmitter signaling, and lipid metabolism

Etomidate (ETO), a widely used anesthetic, has emerged as a concerning environmental contaminant due to its increasing misuse and demonstrated neurotoxicity in aquatic organisms. This study employed an integrated multi-omics strategy to investigate the developmental neurotoxic effects of ETO in zebrafish (Danio rerio). ETO exposure induced dose-dependent toxicity in zebrafish embryos, characterized by decreased hatching rates (10-20 %), elevated mortality (up to 30 %), and morphological abnormalities such as scoliosis and pericardial edema. Behavioral assays revealed marked locomotor suppression (40-65 % reduction) and disrupted circadian rhythmicity. Neurochemical profiling indicated a 2.1-fold increase in dopamine levels, accompanied by significant reductions in GABAergic (38 %) and serotonergic (42 %) signaling, consistent with transcriptomic downregulation of related pathway genes. Metabolomic analysis revealed dysregulated lipid metabolism, including a 3.2-fold increase in eicosapentaenoic acid (EPA), and perturbations in phenylalanine metabolism. Transgenic zebrafish models (Tg(hb9:eGFP), Tg(coro1a:DsRed), Tg(elavl3:GCaMP6f)) further demonstrated motor neuron damage, inflammatory cell infiltration in the brain, and disrupted Ca2 + dynamics, indicating blood-brain barrier disruption and neuroinflammation responses. Molecular docking analysis confirmed ETO's binding affinity for GABA-A receptors, aligning with observed neurotransmitter imbalances. These findings elucidate ETO's neurotoxic mechanisms, involving neurotransmitter imbalance, metabolic disruption, and neuroinflammatory. The results underscore the dual threat of ETO as both an emerging aquatic pollutant and a developmental neurotoxicant, highlighting the urgent need for stricter environmental monitoring and a reevaluation of its safety profile, particularly during critical developmental windows.

Neurotoxicity and aggressive behavior induced by anesthetic etomidate exposure in zebrafish: Insights from multi-omics and machine learning

Etomidate (ETO), widely employed as a surgical anesthetic and more recently recognized as a drug of abuse, has been frequently detected in aquatic environment. However, the toxicity assessment of ETO is insufficient. Adult zebrafish were used to investigate toxicological effects of ETO. Four weeks ETO exposure could induced abnormal behaviors, including reduced anxiety, memory impairment, and heightened aggression. The increased aggression was quantitatively characterized using machine learning, which revealed significantly elevated instantaneous velocity and drastic changes in angular velocity. ETO was predominantly accumulated in the zebrafish brain, where it binds to GABA-A receptors, leading to a significant increase in GABA content. Furthermore, fluorescent staining of reactive oxygen species (ROS) in the brain revealed that ETO exposure significantly increased the oxidative stress level. This oxidative stress resulted in mitochondrial swelling, rupture, and damage to myelinated nerve fibers, ultimately causing cerebral injury in zebrafish. Multi-omics analysis further elucidated that ETO exposure down-regulated the MAPK signaling pathway, hyperactivated motor proteins, and induced metabolic disorders of lipids and amino acids. In summary, this study demonstrates that ETO induces neurotoxicity and behavioral alterations in zebrafish. These findings provide a critical insight into the mechanisms underlying ETO's neurotoxic effects and contribute to a more comprehensive understanding of its environmental and health risks.

Etomidate as an anesthetic in Colossoma macropomum: Behavioral and electrophysiological data complement each other as a tool to assess anesthetic safety

The use of anesthetic agents in the management of fish in fish farming or ornamental fish breeding aims to minimize stress and promote animal welfare. Therefore, this study aims to investigate behavioral, electrocardiographic, and ventilatory characteristics of tambaquis exposed to anesthetic baths with etomidate. The study was conducted with juvenile tambaquis (27.38 ± 3.5g) n = 99, at etomidate concentrations of 2-4 mg.L -1, analyzing induction and anesthetic recovery behavior (experiment I), electrocardiogram (experiment II), and opercular movement (experiment III). Fish exposed to high concentrations of etomidate reached the stage of general anesthesia faster, however, the recovery time was longer, characterizing a dose-dependent relationship. Cardiorespiratory analyzes demonstrated a reduction in heart rate (69.19%) and respiratory rate (40.70%) depending on the concentration of etomidate used during anesthetic induction. During the recovery period, there was cardiorespiratory reversibility to normality. Therefore, etomidate proved to be safe as an anesthetic agent for this species at concentrations of 2 to 3 mg.L -1 for short-term anesthesia, but at higher doses the animals showed slow reversibility of anesthesia in a gradual manner and without excitability. The hemodynamic effect due to the rapid decrease in heart rate includes a negative factor of using higher concentrations of etomidate for Colossome macropomum anesthesia.

Observed and predicted embryotoxic and teratogenic effects of organic and inorganic environmental pollutants and their mixtures in zebrafish (Danio rerio)

Risk assessment of chemicals is still primarily focusing on single compound evaluation, even if environmental contamination consists of a mixture of pollutants. The concentration addition (CA) and independent action (IA) models have been developed to predict mixture toxicity. Both models assume no interaction between the components, resulting in an additive mixture effect. In the present study, the embryo toxicity test (OECD TG no. 236) with zebrafish embryos (Danio rerio) was performed to investigate whether the toxicity caused by binary, ternary, and quaternary mixtures of organic (Benzo[a]pyrene, perfluorooctanesulfonate, and 3,3´,4,4´,5-pentachlorobiphenyl 126) and inorganic (arsenate) pollutants can be predicted by CA and IA. The acute toxicity and sub-lethal alterations such as lack of blood circulation were investigated. The models estimated the mixture toxicity well and most of the mixtures were additive. However, the binary mixture of PFOS and PCB126 caused a synergistic effect, with almost a ten-fold difference between the observed and predicted LC₅₀-value. For most of the mixtures, the CA model was better in predicting the mixture toxicity than the IA model, which was not expected due to the chemicals' different modes of action. In addition, some of the mixtures caused sub-lethal effects not observed in the single compound toxicity tests. The mixture of PFOS and BaP caused a division of the yolk and imbalance was caused by the combination of PFOS and As and the ternary mixture of PFOS, As, and BaP. Interestingly, PFOS was part of all three mixtures causing the mixture specific sub-lethal effects. In conclusion, the present study shows that CA and IA are mostly resulting in good estimations of the risks that mixtures with few components are posing. However, for a more reliable assessment and a better understanding of mixture toxicity, further investigations are required to study the underlying mechanisms.

Early detection of cyanide, organophosphate and rodenticide pollution based on locomotor activity of zebrafish larvae

Cyanide, organophosphate and rodenticides are highly toxic substances widely used in agriculture and industry. These toxicants are neuro- and organotoxic to mammals at low concentrations, thus early detection of these chemicals in the aqueous environment is of utmost importance. Here, we employed the behavioral toxicity test with wildtype zebrafish larvae to determine sublethal concentrations of the above mentioned common environmental pollutants. After optimizing the test with cyanide, nine rodenticides and an organophosphate were successfully tested. The compounds dose-dependently initially (0-60-min exposure) stimulated locomotor activity of larvae but induced toxicity and reduced swimming during 60-120-min exposure. IC₅₀ values calculated based on swimming distance after 2-h exposure, were between 0.1 and 10 mg/L for both first-generation and second-generation anticoagulant rodenticides. Three behavioral characteristics, including total distance travelled, sinuosity and burst count, were quantitatively analyzed and compared by hierarchical clustering of the effects measured by each three parameters. The toxicity results for all three behavioral endpoints were consistent, suggesting that the directly measured parameter of cumulative swimming distance could be used as a promising biomarker for the aquatic contamination. The optimized method herein showed the potential for utilization as part of a monitoring system and an ideal tool for the risk assessment of drinking water in the military and public safety.

Predictive in silico modeling of emetic potency of liquid cleaning products using an historical in vivo database

The induction of vomiting by activation of mechanisms protecting the body against ingested toxins is not confined to natural products but can occur in response to manmade medicinal and non-medicinal products such as liquid cleaning products where it is a commonly reported adverse effect of accidental ingestion. The present study examined the utility of an historic database (>30 years old) reporting emetic effects of 98 orally administered liquid cleaning formulations studied in vivo (canine model) to objectively identify the main pro-emetic constituents and to derive a predictive model. Data were analysed by categorizing the formulation constituents into 10 main groups followed by using multivariate correlation, partial least squares and recursive partitioning analysis. Using the ED₅₀ we objectively identified high ionic strength, non-ionic surfactants (alcohol ethoxylate) and alkaline pH as the main pro-emetic factors. Additionally, a mathematical model was developed which allows prediction of the ED₅₀ based on formulation. The limitations of the use of historic data and the model are discussed. The results have practical applications in new product formulation and safety but additionally the principles underpinning this in silico study have wider applicability in demonstrating the potential utility of such archival data in current research contributing to animal replacement.