Inorganic arsenic alters the development of dopaminergic neurons but not serotonergic neurons and induces motor neuron development via Sonic hedgehog pathway in zebrafish

Special Issue "Zebrafish: A Model Organism for Human Health and Disease"

In 1996, a special zebrafish (Danio rerio) issue of the journal Development, with a 481-page volume containing 37 papers from four different laboratories, published genetic and phenotypic details of hundreds of different mutants, obtained through mutagenesis screening [...].

Polylactic acid microplastics before and after aging induced neurotoxicity in zebrafish by disrupting the microbiota-gut-brain axis

Polylactic acid (PLA) is a biodegradable alternative to traditional plastics due to its excellent biocompatibility. However, PLA is challenging to fully degrade and can easily become microplastics (MPs) in surface water, a process accompanied by aging. This study found that aged PLA (APLA) MPs exhibited increased surface roughness, decreased surface potential, and more oxygen-containing functional groups compared to PLA. Acute exposure to PLA/APLA in zebrafish larvae resulted in sluggish behavior and inhibited neuronal development. Chronic exposure to PLA/APLA in adult zebrafish led to reduced exploratory behavior, poor memory, increased aggression, and neuron loss. Overall, PLA/APLA induced dose-dependent neurotoxicity, with APLA exhibiting greater toxicity than PLA, potentially due to its higher rate of uptake. Additionally, exposure to PLA/APLA led to thinning of the intestinal wall, shortening of villi, and suppression of intestinal neurotransmitter levels, accompanied by alterations in microbial abundance and gut dysbiosis. Meanwhile, supplementation with bile acid, considered as the key regulator in the gut-brain axis, significantly mitigated the neurotoxicity induced by PLA/APLA. These findings confirm that PLA/APLA MPs indeed elicit neurotoxicity via the gut-brain axis and provide scientific evidence for targeted environmental interventions to minimize the adverse ecological impacts of biodegradable MPs.

Acetyl L-Carnitine Protects Zebrafish Embryos From Verapamil and Inorganic Arsenic-Induced Cardiotoxicity and Developmental Toxicity With No Effect on Supernumerary Motor Neuron Development

Verapamil (a P-glycoprotein inhibitor) and inorganic arsenic cotreatment has been shown to be toxic in chick cardiomyocytes. Previously, we have shown that sodium arsenite at 200 mg/L did not cause developmental toxicity or cardiotoxicity in zebrafish embryos. Here, we investigated the effect of verapamil and sodium arsenite cotreatment on the zebrafish embryos. Embryos at 5 h post-fertilization (hpf) were exposed to sodium arsenite (100-400 mg/L; 0.77-3.08 mM) in the presence or absence of 20 μM verapamil for 67 h. At 72 hpf, all the embryos treated with sodium arsenite or verapamil alone were alive, while only ~23% and ~17% survived in the groups cotreated with 20 μM verapamil and 100 mg/L or 200 mg/L arsenite, respectively. However, 10 μM of verapamil and 200 mg/L sodium arsenite cotreatment resulted in 100% embryo survival. Inductively coupled plasma mass spectrometry analysis showed that in the verapamil and sodium arsenite cotreated group, the internal arsenic concentration was significantly higher than in the group treated with only sodium arsenite, suggesting that verapamil inhibited arsenic efflux. Surprisingly, verapamil, a calcium channel blocker, reduced sodium arsenite-induced apoptosis but caused developmental toxicity and cardiotoxicity in the sodium arsenite cotreated embryos, without affecting arsenite-induced supernumerary motor neuron development. Furthermore, acetyl L-carnitine (ALCAR) completely abolished both developmental toxicity and cardiotoxicity induced by sodium arsenite and verapamil cotreatment. We show for the first time that ALCAR prevents toxicities induced by arsenic and verapamil cotreatment in zebrafish embryos, a vertebrate model for investigating chemical toxicity.

A comprehensive review of arsenic-induced neurotoxicity: Exploring the role of glial cell pathways and mechanisms

The review aims to examine the neurotoxic effects of arsenic, particularly exploring the roles of glial cells-astrocytes, microglia, and oligodendrocytes, amid its widespread environmental contamination and impact on cognitive impairments. It highlights the role of altered neurotrophin and growth factor signaling in disrupting neuronal health and cognitive performance. It elucidates the intricate interactions between oxidative stress, DNA damage, neurotransmitter disruption, and cellular signaling alterations, underscoring the vital importance of the glial cells. These cells are crucial for preserving neural health and responding to environmental toxins, and arsenic disrupts their functions, resulting in decreased antioxidative responses, induction of inflammatory pathways, and subsequent neuronal dysfunction. The brain's cytotoxic impact arises from a complex network of cellular responses, with pathways such as MAPK, transcription factor and autophagy signaling to play critical roles in mediating these dysregulated inflammation and oxidative stress mechanisms. The detailed exploration into specific impacts of arsenic on glial cell morphology, activation, and mitochondrial functions illuminates the cascade of neuroinflammatory and neurodegenerative changes that may be triggered upon arsenic exposure. The review recommends a multidisciplinary research approach by emphasizing the significance of the brain's microenvironment, methylation processes, and the enzyme AS3MT in arsenic neurotoxicity. It calls for converging environmental science, neurobiology, and toxicology to develop targeted interventions for preventing and mitigating arsenic's neurotoxic effects. This in-depth exploration into glial cell dynamics aims to advance public health and neurotoxicology research, striving to devise strategies that reduce the cognitive and neurodegenerative damage caused by arsenic, thereby enhancing global health outcomes.

Multi-faceted potential of sophoridine compound's anti-arrhythmic and antioxidant effects through ROS/CaMKII pathway

Cardiac arrhythmias remain a significant cause of mortality and morbidity, for novel antiarrhythmic therapies. This study states that the first report of sophoridine (SPN), a quinolizidine alkaloid derived from traditional Chinese herbs, shows promise as a potential candidate due to its anti-arrhythmic and antioxidant properties. The study found that cell viability in H9C2 rat cardiomyocytes remained stable even when treated with SPN at a higher dosage of 100 μg/ml. This phenomenon was accompanied by increases in mitochondria-derived reactive oxygen species (ROS) and calcium/calmodulin-dependent protein kinase II (CaMKII) signaling, at 50 and 100 μg/ml. Glucose fluctuations regulate ventricular arrhythmias caused by SPN by activating the ROS/CaMKII pathway. Experimental models using zebrafish provided additional evidence supporting the regulatory effects of SPN on heart rate. In addition, the administration of SPN resulted in substantial deregulation of crucial genes involved in heart development (nppa, nppb, tnnt2a) at the transcriptional level in zebrafish. These findings provide insight into the various pharmacological properties of SPN and this opens up new possibilities for anti-arrhythmic treatment strategies.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

The uses of zebrafish (Danio rerio) as an in vivo model for toxicological studies: A review based on bibliometrics

An in vivo model is necessary for toxicology. This review analyzed the uses of zebrafish (Danio rerio) in toxicology based on bibliometrics. Totally 56,816 publications about zebrafish from 2002 to 2023 were found in Web of Science Core Collection, with Toxicology as the top 6 among all disciplines. Accordingly, the bibliometric map reveals that "toxicity" has become a hot keyword. It further reveals that the most common exposure types include acute, chronic, and combined exposure. The toxicological effects include behavioral, intestinal, cardiovascular, hepatic, endocrine toxicity, neurotoxicity, immunotoxicity, genotoxicity, and reproductive and transgenerational toxicity. The mechanisms include oxidative stress, inflammation, autophagy, and dysbiosis of gut microbiota. The toxicants commonly evaluated by using zebrafish model include nanomaterials, arsenic, metals, bisphenol, and dioxin. Overall, zebrafish provide a unique and well-accepted model to investigate the toxicological effects and mechanisms. We also discussed the possible ways to address some of the limitations of zebrafish model, such as the combination of human organoids to avoid species differences.

Gene expression analyses reveal potential mechanism of inorganic arsenic-induced apoptosis in zebrafish

Our previous study showed that sodium arsenite (200 mg/L) affected the nervous system and induced motor neuron development via the Sonic hedgehog pathway in zebrafish larvae. To gain more insight into the effects of arsenite on other signaling pathways, including apoptosis, we have performed quantitative polymerase chain reaction array-based gene expression analyses. The 96-well array plates contained primers for 84 genes representing 10 signaling pathways that regulate several biological functions, including apoptosis. We exposed eggs at 5 h postfertilization until the 72 h postfertilization larval stage to 200 mg/L sodium arsenite. In the Janus kinase/signal transducers and activators of transcription, nuclear factor κ-light-chain-enhancer of activated B cells, and Wingless/Int-1 signaling pathways, the expression of only one gene in each pathway was significantly altered. The expression of multiple genes was altered in the p53 and oxidative stress pathways. Sodium arsenite induced excessive apoptosis in the larvae. This compelled us to analyze specific genes in the p53 pathway, including cdkn1a, gadd45aa, and gadd45ba. Our data suggest that the p53 pathway is likely responsible for sodium arsenite-induced apoptosis. In addition, sodium arsenite significantly reduced global DNA methylation in the zebrafish larvae, which may indicate that epigenetic factors could be dysregulated after arsenic exposure. Together, these data elucidate potential mechanisms of arsenic toxicity that could improve understanding of arsenic's effects on human health.

Arsenic Impairs Differentiation of Human Induced Pluripotent Stem Cells into Cholinergic Motor Neurons

Arsenic exposure during embryogenesis can lead to improper neurodevelopment and changes in locomotor activity. Additionally, in vitro studies have shown that arsenic inhibits the differentiation of sensory neurons and skeletal muscle. In the current study, human-induced pluripotent stem (iPS) cells were differentiated into motor neurons over 28 days, while being exposed to up to 0.5 μM arsenic. On day 6, neuroepithelial progenitor cells (NEPs) exposed to arsenic had reduced transcript levels of the neural progenitor/stem cell marker nestin (NES) and neuroepithelial progenitor marker SOX1, while levels of these transcripts were increased in motor neuron progenitors (MNPs) at day 12. In day 18 early motor neurons (MNs), choline acetyltransferase (CHAT) expression was reduced two-fold in cells exposed to 0.5 μM arsenic. RNA sequencing demonstrated that the cholinergic synapse pathway was impaired following exposure to 0.5 μM arsenic, and that transcript levels of genes involved in acetylcholine synthesis (CHAT), transport (solute carriers, SLC18A3 and SLC5A7) and degradation (acetylcholinesterase, ACHE) were all downregulated in day 18 early MNs. In day 28 mature motor neurons, arsenic significantly downregulated protein expression of microtubule-associated protein 2 (MAP2) and ChAT by 2.8- and 2.1-fold, respectively, concomitantly with a reduction in neurite length. These results show that exposure to environmentally relevant arsenic concentrations dysregulates the differentiation of human iPS cells into motor neurons and impairs the cholinergic synapse pathway, suggesting that exposure impairs cholinergic function in motor neurons.