Early life stage transient aristolochic acid exposure induces behavioral hyperactivity but not nephrotoxicity in larval zebrafish

Screening tools to evaluate the neurotoxic potential of botanicals: building a strategy to assess safety

AREAS COVERED

This paper outlines the selection of NAMs, including in vitro assays using primary rat cortical neurons, zebrafish embryos, and Caenorhabditis elegans. These assays aim to assess neurotoxic endpoints such as neuronal activity and behavioral responses. Microelectrode array recordings of rat cortical neurons provide insights into the impact of botanical extracts on neuronal function, while the zebrafish embryos and C. elegans assays evaluate neurobehavioral responses. The paper also provides an account of the selection of botanical case studies based on expert judgment and existing neuroactivity/toxicity information. The proposed battery of assays will be tested with these case studies to evaluate their utility for neurotoxicity screening.

EXPERT OPINION

The complexity of botanicals necessitates the use of multiple NAMs for effective neurotoxicity screening. This paper discusses the evaluation of methodologies to develop a robust framework for evaluating botanical safety, including complex neuronal models and key neurodevelopmental process assays. It aims to establish a comprehensive screening framework.

Therapeutic Efficacy of Selenium Pre-treatment in Mitigating Cadmium-Induced Cardiotoxicity in Zebrafish (Danio rerio)

Cardiovascular diseases are a rampant public health threat. Environmental contaminants, such as Cadmium (Cd), a toxic metal, have been linked to increased risk for cardiovascular diseases. Given that human exposure to Cd is increasing overtime, there is a need to develop new therapies to ameliorate Cd toxicity. Selenium (Se), an essential trace element, has been proposed to rescue the effects of Cd toxicity, with mixed effects. Se's narrow therapeutic window necessitates precise dosing to avoid toxicity. Here, we assessed the effects of various waterborne Cd and Se concentrations and sequences on cardiac function using zebrafish ( Danio rerio ). We showed that Cd induced pericardial edemas and modified heart rates in a concentration-dependent manner. To identify the therapeutic range of Se for Cd-induced cardiotoxicity, zebrafish embryos were treated with 0, 10, 50, 100, 150, or 200 μg/L Se for 1-4 days prior to exposure to Cd at 2.5, and 5 μg/L. We found that a 50 µg/L Se pre-treatment prior to Cd at 2.5 μg/L, but not at 5 μg/L, reduced the prevalence of pericardial edemas and ameliorated Cd-induced bradycardia in zebrafish. Embryos exposed to 10 and 50 μg/L of Se showed typical heart morphology, whereas other Se-exposed and Se-deficient fish presented pericardial edemas. Longer Se pre-treatment durations led to fewer incidences of pericardial edemas. Overall, this study highlights the importance of optimizing Se concentration and pre-treatment periods to harness its protective effects against Cd-induced cardiotoxicity. These findings provide insights into potential therapeutic strategies for reducing Cd-related cardiovascular damage in humans.

Advances of microplastics ingestion on the morphological and behavioral conditions of model zebrafish: A review

Concerns have been conveyed regarding the availability and hazards of microplastics (MPs) in aquatic biota due to their widespread presence in aquatic habitats. Zebrafish (Danio rerio) are widely used as a model organism to study the adverse impacts of MPs due to their several compelling advantages, such as their small size, ease of breeding, inexpensive maintenance, short life cycle, year-round spawning, high fecundity, fewer legal restrictions, and genetic resemblances to humans. Exposure of organisms to MPs produces physical and chemical toxic effects, including abnormal behavior, oxidative stress, neurotoxicity, genotoxicity, immune toxicity, reproductive imbalance, and histopathological effects. But the severity of the effects is size and concentration-dependent. It has been demonstrated that smaller particles could reach the gut and liver, while larger particles are only confined to the gill, the digestive tract of adult zebrafish. This thorough review encapsulates the current body of literature concerning research on MPs in zebrafish and demonstrates an overview of MPs size and concentration effects on the physiological, morphological, and behavioral characteristics of zebrafish. Finding gaps in the literature paves the way for further investigation.

DDT exposure induces tremor-like behavior and neurotoxicity in developmental stages of embryonic zebrafish

Dichlorodiphenyltrichloroethane (DDT) is a broad-spectrum insecticide, widely detected in environments due to its high stability characteristic and long natural half-life period. The adverse impact of DDT exposure on organisms and humans has attracted great concern worldwide. The current study explored the developmental and neurobehavioral toxicity response of DDT in embryonic zebrafish. The embryos were treated with DDT (0, 0.1, 1, 2.5 and 5 µM) during 6 h post fertilization (hpf) to 144 hpf. Our result indicated that DDT exposures increased the embryo hatching rate at 48 and 60 hpf, the larval malformation rate at 120 hpf and mortality rate at 144 hpf. The manifested malformations included uninflated swim bladder, bent spine and tail, deformed liver, and pericardial edema. The 120 hpf larval organs size of the gut and swim bladder was decreased in higher exposed concentration groups. Besides, DDT exposure resulted in hyperactivity for the embryo spontaneous movement at 24 hpf and tremor like movement measured by the free larval activity at 72 hpf, as well as the larval activity at 96 hpf under light-dark transition stimulus. Mechanistic examinations at 120 hpf revealed DDT exposure elevated oxidative stress through MDA formation increase, ATP level decrease as well as antioxidant enzyme genes (sod1 and gpx1a) expression decrease. DDT exposure induced abnormal neurotransmitters expression with DA level increase, 5-HT and NOS level decrease. DDT exposure suppressed the gene expressions involved in axon development (rab33a and nrxn2a) and potassium channel (kcnq2 and kcnq3). Our results suggest that the hyperactivity and tremor like movement in DDT-exposed embryos/larvae may result from oxidative stress involved with neuronal damage.

Green synthesis of chlorella-derived carbon dots and their fluorescence imaging in zebrafish

Recently, carbon dots (CDs) have been shown to exhibit exceptional water solubility, low toxicity, favorable biocompatibility, stable fluorescence properties with a wide and continuous excitation spectrum, and an adjustable emission spectrum. Their remarkable characteristics make them highly promising for applications in the field of bioimaging. Zebrafish is currently extensively studied because of its high genetic homology with humans and the applicability of disease research findings from zebrafish to humans. Therefore, spirulina, a commonly used feed additive in aquaculture, was chosen as the raw material for synthesizing fluorescent CDs using a hydrothermal method. On the one hand, CDs can modulate dopamine receptors in the brain of zebrafish, leading to an increase in dopamine production and subsequently promoting their locomotor activity. On the other hand, CDs have been shown to enhance the intestinal anti-inflammatory capacity of zebrafish. This study aimed to explore the chronic toxicity and genotoxicity of CDs in zebrafish while providing valuable insights for their future application in biological and medical fields.

Neurotoxicity of the Cu(OH)2 Nanopesticide through Perturbing Multiple Neurotransmitter Pathways in Developing Zebrafish

The copper hydroxide [Cu(OH)2] nanopesticide is an emerging agricultural chemical that can negatively impact aquatic organisms. This study evaluated the behavioral changes of zebrafish larvae exposed to the Cu(OH)2 nanopesticide and assessed its potential to induce neurotoxicity. Metabolomic and transcriptomic profiling was also conducted to uncover the molecular mechanisms related to potential neurotoxicity. The Cu(OH)2 nanopesticide at 100 μg/L induced zebrafish hypoactivity, dark avoidance, and response to the light stimulus, suggestive of neurotoxic effects. Altered neurotransmitter-related pathways (serotoninergic, dopaminergic, glutamatergic, GABAergic) and reduction of serotonin (5-HT), dopamine (DA), glutamate (GLU), γ-aminobutyric acid (GABA), and several of their precursors and metabolites were noted following metabolomic and transcriptomic analyses. Differentially expressed genes (DEGs) were associated with the synthesis, transport, receptor binding, and metabolism of 5-HT, DA, GLU, and GABA. Transcripts (or protein levels) related to neurotransmitter receptors for 5-HT, DA, GLU, and GABA and enzymes for the synthesis of GLU and GABA were downregulated. Effects on both the glutamatergic and GABAergic pathways in zebrafish were specific to the nanopesticide and differed from those in fish exposed to copper ions. Taken together, the Cu(OH)2 nanopesticide induced developmental neurotoxicity in zebrafish by inhibiting several neurotransmitter-related pathways. This study presented a model for Cu(OH)2 nanopesticide-induced neurotoxicity in developing zebrafish that can inform ecological risk assessments.

The neurodevelopmental toxicity induced by combined exposure of nanoplastics and penicillin in embryonic zebrafish: The role of aging processes

As ubiquitous contaminants, nanoplastics and antibiotics are frequently co-presence and widely detected in the freshwater environment and biota, posing a high co-exposure risk to aquatic organisms and even humans. More importantly, how the aging process of nanoplastics affects the joint toxic potential of nanoplastics and antibiotics has not been explored. Here, we generated two aged polystyrene nanoplastics (PS) by UV radiation (UV-PS) and ozonation (O3-PS). Non-teratogenic concentrations of pristine PS (80 nm) and antibiotics penicillin (PNC) co-exposure synergistically suppressed the embryo heart beating and behaviors of spontaneous movement, touch response, and larval swimming behavioral response. Pristine PS and aged UV-PS, but not aged O3-PS, showed similar effects on zebrafish embryo/larval neurodevelopment. However, when co-exposure with PNC, both aged PS, but not pristine PS, showed antagonistic effects. In late-stage juvenile social behavior testing, we found that PS decreased the exploration in light/dark preference assay. The synergistic effect of aged PS with PNC was further explored, including cellular apoptosis, ROS formation, and neurotransmitter metabolite regulation. Mechanistically, aged UV-PS but not O3-PS significantly increased the adsorption rate of PNC compared to pristine PS, which may account for the toxicity difference between the two aged PS. In conclusion, our results confirmed that PS served as a carrier for PNC, and the environmental aging process changed their neurobehavioral toxicity pattern in vivo.

Fish to learn: insights into the effects of environmental chemicals on eye development and visual function in zebrafish

Vision is the most essential sense system for the human being. Congenital visual impairment affects millions of people globally. It is increasingly realized that visual system development is an impressionable target of environmental chemicals. However, due to inaccessibility and ethical issues, the use of humans and other placental mammals is constrained, which limits our better understanding of environmental factors on ocular development and visual function in the embryonic stage. Therefore, as complementing laboratory rodents, zebrafish has been the most frequently employed to understand the effects of environmental chemicals on eye development and visual function. One of the major reasons for the increasing use of zebrafish is their polychromatic vision. Zebrafish retinas are morphologically and functionally analogous to those of mammalian, as well as evolutionary conservation among vertebrate eye. This review provides an update on harmful effects from exposure to environmental chemicals, involving metallic elements (ions), metal-derived nanoparticles, microplastics, nanoplastics, persistent organic pollutants, pesticides, and pharmaceutical pollutants on the eye development and visual function in zebrafish embryos. The collected data provide a comprehensive understanding of environmental factors on ocular development and visual function. This report highlights that zebrafish is promising as a model to identify hazardous toxicants toward eye development and is hopeful for developing preventative or postnatal therapies for human congenital visual impairment.

Advances in the Utilization of Zebrafish for Assessing and Understanding the Mechanisms of Nano-/Microparticles Toxicity in Water

A large amount of nano-/microparticles (MNPs) are released into water, not only causing severe water pollution, but also negatively affecting organisms. Therefore, it is crucial to evaluate MNP toxicity and mechanisms in water. There is a significant degree of similarity between the genes, the central nervous system, the liver, the kidney, and the intestines of zebrafish and the human body. It has been shown that zebrafish are exceptionally suitable for evaluating the toxicity and action mechanisms of MNPs in water on reproduction, the central nervous system, and metabolism. Providing ideas and methods for studying MNP toxicity, this article discusses the toxicity and mechanisms of MNPs from zebrafish.

Neurotoxic effects of synthetic phenolic antioxidants on dopaminergic, serotoninergic, and GABAergic signaling in larval zebrafish (Danio rerio)

Synthetic phenolic antioxidants (SPAs) are an environmental concern because they are widely detected in aquatic ecosystems and can pose potential threats to organisms. Studies have reported developmental deficits and behavioral changes in response to SPAs, indicating possible neurotoxic effects. However, their neuroactive potency as well as their mode of action (MoA) remain unclear. As such, this study evaluated the potential neurotoxicity of three SPAs [butylated hydroxytoluene (BHT), 2,4-di-tert-butylphenol (2,4-DTBP), and 4-tert-octylphenol (4-t-OP)] at three concentrations (0.01, 0.1 and 1 μM) to zebrafish larvae. Both 2,4-DTBP and BHT decreased spontaneous tail coiling (STC) at 28 hpf (hours post fertilization) whereas 4-t-OP increased STC. Locomotor activity, based on the velocity and distance of larvae (144 hpf) travelled, was promoted by 2,4-DTBP while it decreased in larvae with exposure to 4-t-OP and BHT. In the light-dark preference assay, exposure to either 2,4-DTBP or BHT resulted in variability in the visiting frequency to the dark zone, and larvae (144 hpf) spent less time in the dark, suggesting anxiety-like behavior. Conversely, zebrafish exposed to 4-t-OP, especially at 1 μM concentration, were hypoactive and spent more time in dark, suggestive of anxiolytic-like responses. RNA-seq was conducted to discern mechanisms underlying behavioral responses. Transcriptomic analysis revealed that gene networks related to neuroactive ligand-receptor interaction as well as neurotransmitter-related pathways were altered by all three SPAs based on gene set and subnetwork enrichment analysis. Modulation of dopaminergic, serotoninergic, and/or GABAergic signaling at the transcript level was noted for each of the three SPAs, but different expression patterns were observed, indicating SPA- and dose-specific responses of the transcriptome. The present study provides novel insight into potential mechanisms associated with neurotoxicity of SPAs congeners.

Characterization of Developmental Neurobehavioral Toxicity in a Zebrafish MPTP-Induced Model: A Novel Mechanism Involving Anemia

Zebrafish represent an economical alternative to rodents for developmental neurotoxicity (DNT) testing. Mechanistic understanding is the key to successfully translating zebrafish findings to humans. In the present study, we used a well-known dopaminergic (DA) neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a model chemical to uncover the molecular pathways for observed DNT effects. To enhance the specificity of potential molecular targets, we restricted our exposure to a concentration that is nonteratogenic yet exhibits high DNT effects and an exposure window sensitive to MPTP. Our DNT assessment based on a battery of motor and social behavioral tests revealed an effective concentration of 1 μM and a sensitive window of 48-96 h postfertilization (hpf) for MPTP-induced hypoactivity. It is worth noting that this hypoactivity persisted into later larval development until 28 dpf. We observed increased cell apoptosis, oxidative stress, and decreased ATP levels in larvae immediately after exposure at 96 hpf. Significant reductions of DA neurons were found in the retina at 72, 96, and 120 hpf. No visible deformity was found in motoneurons at 72, 96, and 120 hpf. Transcriptome analysis uncovered a novel pathway manifested by significant upregulation of genes enriched with erythropoiesis. Sensitive window exposure of MPTP and other DA neurotoxins rotenone and paraquat exhibited a concentration-dependent effect on transcriptional changes of embryonic hemoglobins and anemia. Given that anemia is a significant risk factor for Parkinson's disease and MPTP is known to cause parkinsonism in humans, we concluded that anemia resulting from dysregulation of primitive erythropoiesis during embryonic development might serve as a common mechanism underlying DA neurotoxin-induced DNT effects between zebrafish and humans.