Zebrafish: an emerging real-time model system to study Alzheimer's disease and neurospecific drug discovery

Using Single-Cell RNA sequencing with Drosophila, Zebrafish, and mouse models for studying Alzheimer's and Parkinson's disease

Alzheimer's and Parkinson's disease are the most common neurodegenerative diseases, significantly affecting the elderly with no current cure available. With the rapidly aging global population, advancing research on these diseases becomes increasingly critical. Both disorders are often studied using model organisms, which enable researchers to investigate disease phenotypes and their underlying molecular mechanisms. In this review, we critically discuss the strengths and limitations of using Drosophila, zebrafish, and mice as models for Alzheimer's and Parkinson's research. A focus is the application of single-cell RNA sequencing, which has revolutionized the field by providing novel insights into the cellular and transcriptomic landscapes characterizing these diseases. We assess how combining animal disease modeling with high-throughput sequencing and computational approaches has advanced the field of Alzheimer's and Parkinson's disease research. Thereby, we highlight the importance of integrative multidisciplinary approaches to further our understanding of disease mechanisms and thus accelerating the development of successful therapeutic interventions.

Zebrafish as a Suitable Model for Utilizing the Bioactivity of Coumarins and Coumarin-Based Compounds

The aim of this review is to summarize the current knowledge on the use of coumarin-derived compounds in the zebrafish (Danio rerio) model. Coumarins, a class of naturally occurring compounds with diverse biological activities, including compounds such as coumarin, angelicin, and warfarin, have attracted considerable attention in the study of potential therapeutic agents for cancer, central nervous system disorders, and infectious diseases. The capabilities of coumarins as active compounds have led to synthesizing various derivatives with their own properties. While such variety is certainly promising, it is also cumbersome due to the large amount of research needed to find the most optimal compounds. The zebrafish model offers unique advantages for such studies, including high genetic and physiological homology to mammals, optical transparency of the embryos, and rapid developmental processes, facilitating the assessment of compound toxicity and underlying mechanisms of action. This review provides an in-depth analysis of the chemical properties of coumarins, their mechanisms of biological activity, and the results of previous studies evaluating the toxicity and efficacy of these compounds in zebrafish assays. The zebrafish model allows for a holistic assessment of the therapeutic potential of coumarin derivatives, offering valuable insights for advancing drug discovery and development.

Bioactivity of Talisia esculenta extracts: Antioxidant and anti-inflammatory action on RAW 264.7 macrophages and protective potential on the zebrafish exposed to oxidative stress inducers

ETHNOPHARMACOLOGICAL RELEVANCE

Talisia esculenta is a fruit tree commonly found in various regions of Brazil. Its fruit is consumed by the local population, and the leaves are used in infusions within traditional Brazilian medicine. These infusions are employed to alleviate pathological conditions such as rheumatic diseases and hypertension, both of which are strongly linked to oxidative stress and chronic inflammation. The investigation of plant extracts represents a promising field of research, as bioactive compounds abundant in plants exhibit pharmacological effects against a variety of pathological conditions.

AIM OF THE STUDY

To investigate the antioxidant, anti-inflammatory activities, and toxicity of the infusion and hydroethanolic extracts of T. esculenta leaves (IF and HF) and fruit peels (IC and HC).

MATERIALS AND METHODS

Initially, the cytotoxicity and the effects of the extracts on oxidative stress in RAW264.7 macrophages were assessed through exposure to H₂O₂, as well as their impact on NO production in RAW264.7 macrophages exposed to LPS. Additionally, the toxicity and ROS production in zebrafish larvae were evaluated using two oxidative stress inducers: H₂O₂ and CuSO₄ combined with ascorbate.

RESULTS

The MTT assay indicated that the extracts exhibited low cytotoxicity, with HF and IF demonstrating protective effects against H₂O₂ exposure. HC reduced NO production in macrophages by 30%. The zebrafish analysis showed that all four T. esculenta extracts (100 μg/mL) were non-toxic, as they did not affect the survival, heart rate, or body size of the animals. Furthermore, all extracts were capable of reducing ROS levels in zebrafish larvae exposed to the H₂O₂ stressor. Notably, ROS reduction by HF, IF, and HC extracts exceeded 50% compared to the positive control (H₂O₂ alone). T. esculenta extracts also demonstrated a significant ability to reduce ROS levels in zebrafish larvae exposed to CuSO₄, with a 70% reduction observed for leaf extracts and over 30% for fruit peel extracts.

CONCLUSION

This study demonstrated that T. esculenta extracts exhibit significant activity against oxidative damage and contain components with anti-inflammatory properties. Among the extracts, those obtained from leaves were the most effective in providing oxidative protection, supporting the traditional use of leaf infusions.

Tirzepatide mitigates cognitive decline in zebrafish model of type 2 diabetes mellitus induced by high-fat diet

In examining the enduring consequences of diabetes, recent research has focused on the anticipated outcomes of the condition. Specifically, cognitive impairment has been linked to diabetes mellitus dating back to the discovery of insulin. This study delves into the neuroprotective effects of TZP, i.e. tirzepatide a dual GIP and GLP-1 receptor agonist that works by mimicking these two gut hormones, against cognitive impairment associated with type 2 diabetes mellitus (T2DM). T2DM-like zebrafish model of varying age groups was created through a 6-week administration of a high-fat diet (HFD). Parameters such as body weight, body mass index, and blood glucose levels were monitored, and behavioural assessments (T-maze, novel tank diving test, and inhibitory avoidance test) were conducted at the conclusion of the protocol to assess learning and memory. Additionally, lipid profile biochemical parameters (MDA, AChEs, and GSH), molecular markers (IL-1β, IL-10, TNF-α, Bcl-2, Bax, GSK-3β, and AMPK), and histopathological examinations were performed. Treatment with the novel GLP-1 and GIP dual agonist TZP (10 nM/kg, i.p.) significantly ameliorated cognitive impairment, as evidenced by behavioural parameters, and restored antioxidant like GSH (p < 0.05) and catalase (p < 0.05) and anti-inflammatory marker levels, i.e. IL-10 (p < 0.05) compared to the HFD group. TZP also mitigated abnormal glucose (73.2 ± 5.889) and lipid profiles (TG 0.159 ± 0.0075 and TC 0.100 ± 0.0020) in hyperglycaemic zebrafish. This study suggests that the positive effects of TZP on cognition and memory may stem from its neuroprotective capabilities, potentially attributed to its antioxidant, anti-inflammatory, and anti-apoptotic properties, as well as its ability to enhance AMPK levels as GLP-1 agonist has the potential to increase the level of AMPK.

Enhancement of Cognitive Benefits and Anti-Anxiety Effects of Phytolacca americana Fruits in a Zebrafish (Danio rerio) Model of Scopolamine-Induced Memory Impairment

Phytolacca americana fruits exhibit a wide range of biological activities, including antimicrobial, anti-inflammatory, and anticancer properties. This study aims to investigate the phenolic profile of hydroethanolic extracts from both fresh (PEC) and dried (PEU) fruits of P. americana using high-performance liquid chromatography (HPLC) and to evaluate their impact on anxiety-like behavior, memory, oxidative stress, and cholinergic status in zebrafish (Danio rerio, Tübingen strain) treated with scopolamine (SCO, 100 μM). Acute administration of PEC and PEU (0.1, 0.5, and 1 mg/L) was conducted for one hour per day. In silico analyses were performed to evaluate the pharmacokinetic characteristics of the phenolic compounds discerned in the two extracts, using platforms such as SwissAdme, Molinspiration, ProToX-III, AdmetLab 3.0, PKCSM, and PASS. Anxiety-like behavior and memory performance were assessed through specific behavioral assays, including the novel tank test (NTT), light/dark test (LD), novel approach test (NAT), Y-maze, and novel object recognition (NOR). Subsequently, the activity of acetylcholinesterase (AChE) and the extent of oxidative stress in the zebrafish brain were investigated. Our findings suggest that both PEC and PEU possess anxiolytic effects, alleviating SCO-induced anxiety and enhancing cognitive performance in amnesic zebrafish. Furthermore, these extracts demonstrated the ability to mitigate cholinergic deficits by inhibiting AChE activity and supporting antioxidant defense mechanisms through increased activity of antioxidant enzymes and reduced lipid and protein peroxidation. These results highlight the potential use of P. americana fruit extracts in managing anxiety and cognitive impairments related to dementia conditions.

Therapeutic potential of hydrogen-rich water in zebrafish model of Alzheimer's disease: targeting oxidative stress, inflammation, and the gut-brain axis

Alzheimer's disease (AD) is a complex neurodegenerative disorder, with amyloid-beta (Aβ) aggregation playing a key role in its pathogenesis. Aβ-induced oxidative stress leads to neuronal damage, mitochondrial dysfunction, and apoptosis, making antioxidative strategies promising for AD treatment. This study investigates the effects of hydrogen-rich water (HRW) in a zebrafish AD model. Zebrafish were exposed to aluminum chloride to induce AD-like pathology and then treated with HRW using a nanobubble device. Behavioral assays, ELISA, Hematoxylin-eosin (H&E) staining, and reactive oxygen species (ROS) and neutrophil fluorescence labeling were employed to assess HRW's impact. Additionally, 16S rRNA sequencing analyzed HRW's effect on gut microbiota. HRW can significantly improve cognitive impairment and depression-like behavior in zebrafish AD model, reduce Aβ deposition (p < 0.0001), regulate liver Soluble epoxide hydrolase (sEH) levels (p < 0.05), reduce neuroinflammation, and reduce oxidative stress. Furthermore, HRW reduced the number of harmful bacteria linked to AD pathology by restoring the balance of microbiota in the gut. These findings suggest that HRW has potential as a therapeutic strategy for AD by targeting oxidative stress, inflammation, and gut-brain axis modulation.

A Comprehensive Review on Preclinical Alzheimer's Disease Models: Evaluating their Clinical Relevance

Alzheimer's disease (AD) is a neurological disorder that increases with age and must be treated immediately by worldwide healthcare systems. Internal neurofibrillary tau tangles and extracellular amyloid accumulation have been widely recognized as the primary causes of Alzheimer's disease. These degenerative age-related ailments are expected to proliferate exponentially as life expectancy rises. Experimental models of AD are essential for acquiring a deep knowledge of its pathogenesis and determining the viability of novel therapy options. Although there isn't a model that encompasses all the characteristics of real AD, these models are nonetheless highly helpful for the research of various modifications associated with it, even though they are only partially indicative of the disease circumstances being studied. Better knowledge of the advantages and disadvantages of each of the different models, as well as the use of more than one model to evaluate potential medications, would increase the effectiveness of therapy translation from preclinical research to patients. We outline the pathogenic characteristics and limitations of the main experimental models of AD in this review, including transgenic mice, transgenic rats, primates and non-primate models along with in-vitro cell culture models in humans. Additionally, it highlights the possible future of experimental modeling of AD and includes the co-morbid models.

Wnt/β-catenin Signaling in Central Nervous System Regeneration

The Wnt/β-catenin signaling pathway plays a pivotal role in the development, maintenance, and repair of the central nervous system (CNS). This chapter explores the diverse functions of Wnt/β-catenin signaling, from its critical involvement in embryonic CNS development to its reparative and plasticity-inducing roles in response to CNS injury. We discuss how Wnt/β-catenin signaling influences various CNS cell types-astrocytes, microglia, neurons, and oligodendrocytes-each contributing to repair and plasticity after injury. The chapter also addresses the pathway's involvement in CNS disorders such as Alzheimer's and Parkinson's diseases, psychiatric disorders, and traumatic brain injury (TBI), highlighting potential Wnt-based therapeutic approaches. Lastly, zebrafish are presented as a promising model organism for studying CNS regeneration and neurodegenerative diseases, offering insights into future research and therapeutic development.

Assessment of Replicability and Efforts to Refine an Operant Conditioning Procedure for Larval Zebrafish

The zebrafish model is rapidly advancing numerous areas of basic and translational research, including toxicology, drug discovery, molecular genetics, genomic research, developmental biology, and the study of human diseases (reviewed in [...].

Long-Term Neurotoxic Effects and Alzheimer's Disease Risk of Early EHDPP Exposure in Zebrafish: Insights from Molecular Mechanisms to Adult Pathology

2-Ethylhexyl diphenyl phosphate (EHDPP), ubiquitously monitored in environmental media, is highly bioaccumulative and may pose long-term risks, even after short-term exposure. In this investigation, larval zebrafish were exposed to 0.05, 0.5, and 5.0 μg/L EHDPP from 4 to 120 h postfertilization (hpf) to examine the long-term neurotoxicity effects of early exposure. Exposure to 5.0 μg/L EHDPP yielded hyperactive locomotor behavior, which was characterized by increased swimming speed, larger turning angles, and heightened sensitivity to light-dark stimulation. The predicted targets of EHDPP (top 100 potential macromolecules) were primarily associated with brain diseases like Alzheimer's disease (AD). Comparisons of differentially expressed genes (DEGs) from AD patients (GSE48350) and RNA-seq data from EHDPP-exposed zebrafish confirmed consistently abnormal regulatory pathways. EHDPP's interaction with M1 and M5 muscarinic acetylcholine receptors likely disrupted calcium homeostasis, leading to mitochondrial dysfunction and neurotransmitter imbalance as well as abnormal locomotor behavior. Especially, 5.0 μg/L EHDPP exposure during early development (4-120 hpf) triggered early- and midstage AD-like symptoms in adulthood (180 dpf), characterized by cognitive confusion, aggression, blood-brain barrier disruption, and mitochondrial damage in brains. These findings provide deep insights into the long-term neurotoxicity effects and Alzheimer's disease risks of early EHDPP exposure at extremely low dosages.

Brazilian kefir fraction mitigates the Alzheimer-like phenotype in Drosophila melanogaster with β-amyloid overexpression model

Alzheimer's disease (AD) is a progressive neurodegenerative condition and the primary form of dementia among elderly people. The amyloidogenic hypothesis is the main theory that explains this phenomenon and describes the extracellular accumulation of amyloid beta (Aβ) peptides. Model organisms such as Drosophila melanogaster have been utilized to improve the understanding of this disease and its treatment. This study evaluated the effects of peptide and metabolic fractions of Brazilian kefir on a strain of D. melanogaster that expresses human Aβ peptide 1-42 in the eye. The parameters assessed included ommatidial organization, vacuole area, retinal thickness, and Aβ peptide quantification. The present study revealed that the fractions, particularly the peptidic fraction, significantly reduced the vacuole area and increased the retina thickness in treated flies, indicating an improvement in neurodegeneration phenotype. The peptidic fraction was also found to alter Aβ aggregation dynamics, inhibiting Aβ fibril formation, as revealed by dynamic light scattering. This study demonstrated that kefir fractions, particularly the peptidic fraction < 10 kDa, have the potential to regulate Aβ aggregation and alleviate neurodegeneration in a Drosophila melanogaster AD-like model. These findings suggest that kefir fractions could be viable for the bioprospection of novel drug prototypes for AD treatment, providing valuable insights into strategies targeting Aβ aggregation and neurodegeneration in AD.

Zebrafish as a model organism to study sporadic Alzheimer's disease: Behavioural, biochemical and histological validation

Alzheimer's disease (AD) is a global burden to the healthcare system with no viable treatment options till date. Rodents and primates have been extensively used as models for understanding AD pathogenesis and identifying therapeutic targets. However, the focus is now shifting towards developing alternate models. Zebrafish is emerging as a preferred model for neurodegenerative conditions because of its simple nervous system, highly conserved genome and short duration required to model disease condition. The present study is aimed to develop streptozotocin (STZ)-induced model of sporadic AD (sAD) in zebrafish. STZ was administered to adult zebrafish (4-6 mo) at different doses (1 to 50 mg/kg body weight, intracerebroventricularly). Kaplan-Meier survival analysis revealed time and dose dependent mortality in the zebrafish administered with STZ. Based on survival analysis, 1 to 10 mg/kg body weight of STZ was selected for behavioural, molecular and histological studies. STZ administered fish had anxiety and stress-like behaviour in novel tank and light/dark preference tests. STZ-induced cognitive and memory deficits assessed using novel object recognition and spatial alternation tests. Further, expression of markers of amyloidogenic pathway (appa and bace1) were increased in terms of mRNA and protein levels in a time and dose dependent manner following STZ administration. However, expression of non-amyloidogenic pathway mediator (adam10) was reduced at both mRNA and protein level. Histological assessment using hematoxylin and eosin, and Nissl stain revealed loss of neurons in STZ administered fish. The ratio of phosphor-tauser396/total-tau was increased in STZ administered fish. Based on these findings, 5 mg/kg body weight of STZ was found to be most appropriate dose to exhibit sAD phenotype. Mass spectrometric analysis confirmed the presence of amyloid beta oligomers in brains of STZ administered fish. Transmission electron microscopy also showed the presence of higher order insoluble amyloid fibrils with twists. Immunohistochemical analysis revealed amyloid beta deposits in brain of STZ administered fish. Golgi-cox staining indicated decreased number of dendrites, whereas microglia had increased density, span ratio, soma area and lacunarity. The results of the present study demonstrate presence of AD hallmarks and phenotype in zebrafish 7 days post STZ administration (5 mg/kg). The study validates the potential of STZ-induced sAD in zebrafish as a reliable model for studying pathophysiology and rapid screening of therapeutic molecules against sAD.

A novel high signal-to-noise ratio fluorescent probe for real-time mitochondrial viscosity detection and imaging in vitro and in vivo

Mitochondrial viscosity serves as a critical indicator for assessing mitochondrial functionality and offers valuable insights into cellular homeostasis. Continuous, real-time monitoring of mitochondrial viscosity is indispensable for understanding and diagnosing diseases associated with these dynamic changes. In this study, we introduce a novel mitochondrial viscosity-responsive probe named "JL-JC" which is designed by using a molecular strategy, with a classic "D-π-A" molecular structure. Leveraging the distinctive twisted intramolecular charge transfer (TICT) properties of the probe, JL-JC exhibits exceptional sensitivity and a high signal-to-noise ratio, enabling precise detection of viscosity variations within its microenvironment while remaining unaffected by other factors. Upon rapid cellular uptake, JL-JC can efficiently evaluate the mitochondrial viscosity changes under diverse physiological and pathological conditions. Notably, this probe also enables viscosity imaging in zebrafish, offering insights into mitochondrial states in vivo. Our findings present JL-JC as a promising tool and potential diagnostic platform for mitochondria-related diseases.

Using Zebrafish to Study Multiciliated Cell Development and Disease States

Multiciliated cells (MCCs) serve many important functions, including fluid propulsion and chemo- and mechanosensing. Diseases ranging from rare conditions to the recent COVID-19 global health pandemic have been linked to MCC defects. In recent years, the zebrafish has emerged as a model to investigate the biology of MCCs. Here, we review the major events in MCC formation including centriole biogenesis and basal body docking. Then, we discuss studies on the role of MCCs in diseases of the brain, respiratory, kidney and reproductive systems, as well as recent findings about the link between MCCs and SARS-CoV-2. Next, we explore why the zebrafish is a useful model to study MCCs and provide a comprehensive overview of previous studies of genetic components essential for MCC development and motility across three major tissues in the zebrafish: the pronephros, brain ependymal cells and nasal placode. Taken together, here we provide a cohesive summary of MCC research using the zebrafish and its future potential for expanding our understanding of MCC-related disease states.

Standardizing CRISPR-Cas13 knockdown technique to investigate the role of cdh2 gene in pituitary development through growth hormone expression and transcription factors

Introduction

Congenital hypopituitarism (CH) is characterized by the deficiency of pituitary hormones. Among CH patients, 85% lack a molecular diagnosis. Whole Exome Sequencing (WES) identified a homozygous variant (c.865G>A, p.Val289Ile) in the CDH2 gene, responsible for N-Cadherin production, crucial for cell-cell adhesion. Predicted to be likely pathogenic, the variant was found in a patient deficient in GH, TSH, ACTH, and LH/FSH. Its impact on cell adhesion was confirmed in L1 fibroblast cell lines.

Objective

Create a cdh2 knockdown in zebrafish for investigating its role in pituitary development through growth hormone and transcription factors expression.

Methods

Utilized pET28B-RfxCas13d-His plasmid for Cas13 mRNA production via in vitro transcription, guiding Cas13 to cdh2 with three RNAs. Injected the complex into single-cell embryos for analysis up to 96 hpf. Assessed gene expression of cdh2, prop1, pit1, and gh1 using RT-qPCR. Evaluated cdh2 protein expression through the western blot technique.

Results

Knockdown animals displayed developmental delay. The cdh2 expression decreased by 75% within 24 hours, rebounded by 48 hours, and reached wild-type levels by 96 hpf. gh1 expression decreased at 48h but increased by 96 hpf, aligning with WT. No significant differences in prop1 and pit1 expression were observed.

Conclusion

Our findings underscore cdh2's role in pituitary development and hormonal regulation, offering insights for developmental biology research.

Experimental models of Parkinson's disease: Challenges and Opportunities

Parkinson's disease (PD) is a widespread neurodegenerative disorder occurs due to the degradation of dopaminergic neurons present in the substantia nigra pars compacta (SNpc). Millions of people are affected by this devastating disorder globally, and the frequency of the condition increases with the increase in the elderly population. A significant amount of progress has been made in acquiring more knowledge about the etiology and the pathogenesis of PD over the past decades. Animal models have been regarded to be a vital tool for the exploration of complex molecular mechanisms involved in PD. Various animals used as models for disease monitoring include vertebrates (zebrafish, rats, mice, guinea pigs, rabbits and monkeys) and invertebrate models (Drosophila, Caenorhabditis elegans). The animal models most relevant for study of PD are neurotoxin induction-based models (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 6-Hydroxydopamine (6-OHDA) and agricultural pesticides (rotenone, paraquat), pharmacological models (reserpine or haloperidol treated rats), genetic models (α-synuclein, Leucine-rich repeat kinase 2 (LRRK2), DJ-1, PINK-1 and Parkin). Several non-mammalian genetic models such as zebrafish, Drosophila and Caenorhabditis elegance have also gained popularity in recent years due to easy genetic manipulation, presence of genes homologous to human PD, and rapid screening of novel therapeutic molecules. In addition, in vitro models (SH-SY5Y, PC12, Lund human mesencephalic (LUHMES) cells, Human induced pluripotent stem cell (iPSC), Neural organoids, organ-on-chip) are also currently in trend providing edge in investigating molecular mechanisms involved in PD as they are derived from PD patients. In this review, we explain the current situation and merits and demerits of the various animal models.

Anxiolytic and Antidepressant Effects of Tribulus terrestris Ethanolic Extract in Scopolamine-Induced Amnesia in Zebrafish: Supported by Molecular Docking Investigation Targeting Monoamine Oxidase A

Plants of the genus Tribulus have been used in folk medicine for wound healing, alleviating liver, stomach, and rheumatism pains, and as cognitive enhancers, sedatives, antiseptics, tonics, and stimulants. The present work aimed to evaluate whether Tribulus terrestris (Tt) administered for 15 days attenuated cognitive deficits and exhibited anxiolytic and antidepressant profiles in scopolamine-induced amnesia in zebrafish. Animals were randomly divided into six groups (eight animals per group): (1)-(3) Tt treatment groups (1, 3 and 6 mg/L), (4) control, (5) scopolamine (SCOP, 0.7 mg/kg), and (6) galantamine (Gal, 1 mg/L). Exposure to SCOP (100 µM) resulted in anxiety in zebrafish, as assessed by the novel tank diving test (NTT) and novel approach test (NAT). When zebrafish were given SCOP and simultaneously given Tt (1, 3, and 6 mg/L once daily for 10 days), the deficits were averted. Molecular interactions of chemical compounds from the Tt fractions with the monoamine oxidase A (MAO-A) were investigated via molecular docking experiments. Using behavioral experiments, we showed that administration of Tt induces significant anxiolytic-antidepressant-like effects in SCOP-treated zebrafish. Our result indicated that flavonoids of Tt, namely kaempferol, quercetin, luteolin, apigetrin, and epigallocatechin, could act as promising phytopharmaceuticals for improving anxiety-related disorders.

Co-occurrence of azorubine and bisphenol A in beverages increases the risk of developmental toxicity: A study in zebrafish model

The prevalent use of Azorubine (E122) and the unintentional food additive, Bisphenol A (BPA), in ready-to-drink (RTD) beverages raises significant health concerns, especially for children. The combined impact on embryonic development must be explored despite individual safety assessments. Our investigation revealed that the combined exposure of E122 and BPA at beverage concentration significantly induces mortality and morphological deformities, including reduced growth, pericardial edema, and yolk sac edema. The co-exposure triggers oxidative stress, impairing antioxidant enzyme responses and resulting in lipid and cellular damage. Notably, apoptotic cells are observed in the neural tube and notochord of the co-exposed larvae. Critical genes related to the antioxidant response elements (nrf2, ho1, and nqo1), apoptosis activation (bcl2, bax, and p53), and pro/anti-inflammatory cytokines (nfkb, tnfa, il1b, tgfb, il10, and il12) displayed substantial changes, highlighting the molecular mechanisms. Behavior studies indicated hypo-locomotion with reduced thigmotaxis and touch response in co-exposed larvae, distinguishing it from individual exposures. These findings underscore the neurodevelopmental impacts of E122 and BPA at reported beverage concentrations, emphasizing the urgent need for comprehensive safety assessments, particularly for child consumption.

Advancing Alzheimer's Research With Zebrafish Models: Current Insights, Addressing Challenges, and Charting Future Courses

Alzheimer's disease (AD) is a neurological condition that progressively impairs cognitive function and results in memory loss. Despite substantial research efforts, little is known about the specific processes driving AD, and there are few proven therapies. Because of their physiological and genetic resemblance to humans, zebrafish (Danio rerio) have become an important model organism for furthering research on AD. This abstract discusses the difficulties faced, looks at the insights currently garnered from zebrafish models, and suggests future research options. AD knowledge has greatly benefited from the use of zebrafish models. Transgenic zebrafish that express human AD-associated genes, such as tau and amyloid precursor protein (APP), display tau neurofibrillary tangles (NFTs) and amyloid-beta (Aβ) plaques, two of the disease's main clinical characteristics. These models have clarified the roles of oxidative stress, inflammation, and calcium homeostasis in the course of AD and allowed for the purpose of high-throughput screening of potential therapeutic agents. Understanding the growth and deterioration of neurons has been greatly aided by real-time zebrafish imaging. Fully using zebrafish models in AD research requires addressing a number of issues. The dissimilarities in zebrafish anatomy and physiology from humans, the difficulty of developing models that replicate progressive and late-onset AD (LOAD), and the requirement for standardized procedures to evaluate alterations in zebrafish cognition and behavior are a few issues. Furthermore, variations in the genetic makeup of zebrafish strains might affect the results of experiments. Future directions include developing standardized behavioral assays and cognitive tests, working together to create extensive databases of zebrafish genetic and phenotypic data, and using genetic engineering techniques like CRISPR/Cas9 to create more complex zebrafish models. Combining zebrafish models with other model species helps expedite the conversion of research results into therapeutic applications and offers a more thorough knowledge of AD. To sum up, zebrafish models have made a substantial contribution to Alzheimer's research by offering insightful information on the causes of the illness and possible therapies. By tackling present issues and formulating a planned future path, we can improve the use of zebrafish to decipher the mysteries of Alzheimer's and help create successful treatments.

Upgrading Mitochondria-Targeting Peptide-Based Nanocomplexes for Zebrafish In Vivo Compatibility Assays

The lack of effective delivery systems has slowed the development of mitochondrial gene therapy. Delivery systems based on cell-penetrating peptides (CPPs) like the WRAP (tryptophan and arginine-rich peptide) family conjugated with a mitochondrial targeting sequence (MTS) have emerged as adequate carriers to mediate gene expression into the mitochondria. In this work, we performed the PEGylation of WRAP/pDNA nanocomplexes and compared them with previously analyzed nanocomplexes such as (KH)9/pDNA and CpMTP/pDNA. All nanocomplexes exhibited nearly homogeneous sizes between 100 and 350 nm in different environments. The developed complexes were biocompatible and hemocompatible to both human astrocytes and lung smooth muscle cells, ensuring in vivo safety. The nanocomplexes displayed mitochondria targeting ability, as through transfection they preferentially accumulate into the mitochondria of astrocytes and muscle cells to the detriment of cytosol and lysosomes. Moreover, the transfection of these cells with MTS-CPP/pDNA complexes produced significant levels of mitochondrial protein ND1, highlighting their efficient role as gene delivery carriers toward mitochondria. The positive obtained data pave the way for in vivo research. Using confocal microscopy, the cellular internalization capacity of these nanocomplexes in the zebrafish embryo model was assessed. The peptide-based nanocomplexes were easily internalized into zebrafish embryos, do not cause harmful or toxic effects, and do not affect zebrafish's normal development and growth. These promising results indicate that MTS-CPP complexes are stable nanosystems capable of internalizing in vivo models and do not present associated toxicity. This work, even at an early stage, offers good prospects for continued in vivo zebrafish research to evaluate the performance of nanocomplexes for mitochondrial gene therapy.

Speckle statistics as a tool to distinguish collective behaviors of Zebrafish shoals

Zebrafish have become an important model animal for studying the emergence of collective behavior in nature. Here, we show how to properly analyze the polarization statistics to distinguish shoal regimes. In analogy with the statistical properties of optical speckles, we show that exponential and Rayleigh distributions emerge in shoals with many fish with uncorrelated velocity directions. In the opposite limit of just two fish, the polarization distribution peaks at high polarity, with the average value being a decreasing function of the shoal's size, even in the absence of correlations. We also perform a set of experiments unveiling two shoaling regimes. Large shoals behave as small domains with strong intra-domain and weak inter-domain correlations. A strongly correlated regime develops for small shoals. The reported polarization statistical features shall guide future automated neuroscience, pharmacological, toxicological, and embryogenesis-motivated experiments aiming to explore the collective behavior of fish shoals.

Dermal Dive: An Overview of Cutaneous Wounding Techniques in Zebrafish

Cutaneous wounds are common injuries that affect millions of people around the world. In vulnerable populations such as the elderly and those with diabetes, defects in wound healing can lead to the development of chronic open wounds. Although mammalian models are commonly used to study cutaneous wound healing, the challenges of in vivo imaging in mammals have hampered detailed observation of cell coordination and cell signaling during wound healing. The zebrafish is becoming increasingly popular for studying cutaneous wound healing owing to its genetic accessibility, suitability for experimental manipulation, and the ability to perform live, in vivo imaging with cellular or even subcellular resolution. In this paper, we review some of the techniques that have been developed for eliciting cutaneous wounds in the zebrafish, including an economical method we recently developed using a rotary tool that generates consistent and reproducible full-thickness wounds. Combined with the thousands of transgenic lines and experimental assays available in zebrafish, the ability to generate reproducible cutaneous wounds makes it possible to study key cellular and molecular events during wound healing using this powerful experimental model organism.

Alzheimer's Disease: Cellular and Pharmacological Aspects

Alzheimer's disease was described more than 100 years ago and despite the fact that several molecules are being tested for its treatment, which are in phase III trials, the disease continues to progress. The main problem is that these molecules function properly in healthy neurons, while neuronal pathology includes plasma membrane disruption, malfunction of various organelles, and hyperphosphorylation of Tau and amyloid plaques. The main objective of this article is the discussion of a neuronal restoration therapy, where molecules designed for the treatment of Alzheimer's disease would probably be more effective, and the quality of life of people would be better.

Evaluating the inter-species transmission risk of amyloid beta peptide aggregates via ingestion

BACKGROUND

Recent reports suggest that amyloid beta (Aβ) peptides can exhibit prion-like pathogenic properties. Transmission of Aβ peptide and the development of associated pathologies after surgeries with contaminated instruments and intravenous or intracerebral inoculations have now been reported across fish, rodents, primates, and humans. This raises a worrying prospect of Aβ peptides also having other characteristics typical of prions, such as evasion of the digestive process. We asked if such transmission of Aβ aggregates via ingestion was possible.

METHODS

We made use of a transgenic Drosophila melanogaster line expressing human Aβ peptide prone to aggregation. Fly larvae were fed to adult zebrafish under two feeding schemes. The first was a short-term, high-intensity scheme over 48 h to determine transmission and retention in the gut. The second, long-term scheme specifically examined retention and accumulation in the brain. The gut and brain tissues were examined by histology, western blotting, and mass spectrometric analyses.

RESULTS

None of the analyses could detect Aβ aggregates in the guts of zebrafish following ingestion, despite being easily detectable in the feed. Additionally, there was no detectable accumulation of Aβ in the brain tissue or development of associated pathologies after prolonged feeding.

CONCLUSIONS

While human Aβ aggregates do not appear to be readily transmissible by ingestion across species, two prospects remain open. First, this mode of transmission, if occurring, may stay below a detectable threshold and may take much longer to manifest. A second possibility is that the human Aβ peptide is not able to trigger self-propagation or aggregation in other species. Either possibility requires further investigation, taking into account the possibility of such transmission from agricultural species used in the food industry.

Investigating the impact of Psidium guajava leaf hydroalcoholic extract in improving glutamatergic toxicity-induced oxidative stress in Danio rerio larvae

Glutamate is one of the predominant excitatory neurotransmitters released from the central nervous system; however, at high concentrations, this substance may induce excitotoxicity. This phenomenon is involved in numerous neuropathologies. At present, clinically available pharmacotherapeutic agents to counteract glutamatergic excitotoxicity are not completely effective; therefore, research to develop novel compounds is necessary. In this study, the main objective was to determine the pharmacotherapeutic potential of the hydroalcoholic extract of Psidium guajava (PG) in a model of oxidative stress-induced by exposure to glutamate utilizing Danio rerio larvae (zebrafish) as a model. Data showed that treatment with glutamate produced a significant increase in oxidative stress, chromatin damage, apoptosis, and locomotor dysfunction. All these effects were attenuated by pre-treatment with the classical antioxidant N-acetylcysteine (NAC). Treatment with PG inhibited oxidative stress responsible for cellular damage induced by glutamate. However, exposure to PG failed to prevent glutamate-initiated locomotor damage. Our findings suggest that under conditions of oxidative stress, PG can be considered as a promising candidate for treatment of glutamatergic excitotoxicity and consequent neurodegenerative diseases.

Utility of zebrafish-based models in understanding molecular mechanisms of neurotoxicity mediated by the gut-brain axis

The gut microbes perform several beneficial functions which impact the periphery and central nervous systems of the host. Gut microbiota dysbiosis is acknowledged as a major contributor to the development of several neuropsychiatric and neurological disorders including bipolar disorder, depression, anxiety, Parkinson's disease, Alzheimer's disease, attention deficit hyperactivity disorder, and autism spectrum disorder. Thus, elucidation of how the gut microbiota-brain axis plays a role in health and disease conditions is a potential novel approach to prevent and treat brain disorders. The zebrafish (Danio rerio) is an invaluable vertebrate model that possesses conserved brain and intestinal features with those of humans, thus making zebrafish a valued model to investigate the interplay between the gut microbiota and host health. This chapter describes current findings on the utility of zebrafish in understanding molecular mechanisms of neurotoxicity mediated via the gut microbiota-brain axis. Specifically, it highlights the utility of zebrafish as a model organism for understanding how anthropogenic chemicals, pharmaceuticals and bacteria exposure affect animals and human health via the gut-brain axis.

Optogenetic and chemogenetic approaches for modeling neurological disorders in vivo

Animal models of human neurological disorders provide valuable experimental tools which enable us to study various aspects of disorder pathogeneses, ranging from structural abnormalities and disrupted metabolism and signaling to motor and mental deficits, and allow us to test novel therapies in preclinical studies. To be valid, these animal models should recapitulate complex pathological features at the molecular, cellular, tissue, and behavioral levels as closely as possible to those observed in human subjects. Pathological states resembling known human neurological disorders can be induced in animal species by toxins, genetic factors, lesioning, or exposure to extreme conditions. In recent years, novel animal models recapitulating neuropathologies in humans have been introduced. These animal models are based on synthetic biology approaches: opto- and chemogenetics. In this paper, we review recent opto- and chemogenetics-based animal models of human neurological disorders. These models allow for the creation of pathological states by disrupting specific processes at the cellular level. The artificial pathological states mimic a range of human neurological disorders, such as aging-related dementia, Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, epilepsy, and ataxias. Opto- and chemogenetics provide new opportunities unavailable with other animal models of human neurological disorders. These techniques enable researchers to induce neuropathological states varying in severity and ranging from acute to chronic. We also discuss future directions for the development and application of synthetic biology approaches for modeling neurological disorders.

The Effect of a Tribulus-Based Formulation in Alleviating Cholinergic System Impairment and Scopolamine-Induced Memory Loss in Zebrafish (Danio rerio): Insights from Molecular Docking and In Vitro/In Vivo Approaches

Tribulus terrestris L. (Tt) has been recently gaining attention for its pharmacological value, including its neuroprotective activities. In this study, we explore the neuroprotective effects of a Tribulus terrestris extract in a zebrafish (Danio rerio) model of scopolamine (SCOP)-induced memory impairment and brain oxidative stress. SCOP, an anticholinergic drug, was employed to replicate fundamental aspects of Alzheimer's disease (AD) in animal models. The fish were treated with ethanolic leaf extract (ELE) from Tt (1, 3, and 6 mg/L) for 15 days. SCOP (100 µM) was administered 30 min before behavioral tests were conducted. Molecular interactions of the major compounds identified via UPLC-PDA/MS in Tt fractions with the active site of acetylcholinesterase (AChE) were explored via molecular docking analyses. Terrestrosin C, protodioscin, rutin, and saponin C exhibited the most stable binding. The spatial memory performance was assessed using the Y-maze test, and memory recognition was examined using a novel object recognition (NOR) test. Tt extract treatment reversed the altered locomotion patterns that were caused by SCOP administration. Biochemical analyses also verified Tt's role in inhibiting AChE, improving antioxidant enzyme activities, and reducing oxidative stress markers. The present findings pave the way for future application of Tt as a natural alternative to treat cognitive disorders.

Single-cell transcriptomics analysis of zebrafish brain reveals adverse effects of manganese on neurogenesis

Manganese (Mn) is considered as an important environmental risk factor for Parkinson's disease. Excessive exposure to Mn can damage various neural cells and affect the neurogenesis, resulting in neurological dysfunction. However, the specific mechanisms of Mn exposure affecting neurogenesis have not been well understood, including compositional changes and heterogeneity of various neural cells. Zebrafish have been successfully used as a neurotoxicity model due to its homology with mammals in several key regions of the brain, as well as its advantages such as small size. We performed single-cell RNA sequencing of zebrafish brains from normal and Mn-exposed groups. Our results suggested that low levels of Mn exposure activated neurogenesis in the zebrafish brain, including promoting the proliferation of neural progenitor cells and differentiation to newborn neurons and oligodendrocytes, while high levels of Mn exposure inhibited neurogenesis and neural function. Mn could affect neurogenesis through specific molecular pathways. In addition, Mn regulated intercellular communication and affected cellular communication in neural cells through specific signaling pathways. Taken together, our study elucidates the cellular composition of the zebrafish brain and adds to the understanding of the mechanisms involved in Mn-induced neurogenesis damage.

Synthetic azo-dye, Tartrazine induces neurodevelopmental toxicity via mitochondria-mediated apoptosis in zebrafish embryos

Tartrazine (TZ), or E 102 or C Yellow, is a commonly used azo dye in the food and dyeing industries. Its excessive usage beyond permissible levels threatens human health and the aquatic environment. While previous studies have reported adverse effects such as mutagenicity, carcinogenicity, and reproductive toxicity. Our study aimed to comprehensively evaluate the developmental neurotoxicity of TZ exposure via biochemical and behavioral examinations and explored the underlying mechanism via gene expression analyses. TZ at an environmentally relevant concentration (50 mg/L) significantly induces oxidative stress, altered antioxidant (SOD, CAT and GSH) response, triggered cellular damage (MDA and LDH), and induced neuro-biochemical changes (AChE and NO). Gene expression analyses revealed broad disruptions in genes associated with antioxidant defense (sod1, cat, and gstp1), mitochondrial dysfunction (mfn2, opa1, and fis1),evoked inflammatory response (nfkb, tnfa, and il1b), apoptosis activation (bcl2, bax, and p53), and neural development (bdnf, mbp, and syn2a). Behavioral analysis indicated altered thigmotaxis, touch response, and locomotion depending on the concentration of TZ exposure. Remarkably, the observed effective concentrations were consistent with the permitted levels in food products, highlighting the neurodevelopmental effects of TZ at environmentally relevant concentrations. These findings provide valuable insights into the underlying molecular mechanisms, particularly the role of mitochondria-mediated apoptosis, contributing to TZ-induced neurodevelopmental disorders in vivo.

Zebrafish Experimental Animal Models for AD: A Comprehensive Review

AD disease (AD) is a multifaceted and intricate neurodegenerative disorder characterized by intracellular neurofibrillary tangle (NFT) formation and the excessive production and deposition of Aβ senile plaques. While transgenic AD models have been found instrumental in unravelling AD pathogenesis, they involve cost and time constraints during the preclinical phase. Zebrafish, owing to their simplicity, well-defined behavioural patterns, and relevance to neurodegenerative research, have emerged as a promising complementary model. Zebrafish possess glutaminergic and cholinergic pathways implicated in learning and memory, actively contributing to our understanding of neural transmission processes. This review sheds light on the molecular mechanisms by which various neurotoxic agents, including okadaic acid (OKA), cigarette smoke extract, metals, and transgenic zebrafish models with genetic similarities to AD patients, induce cognitive impairments and neuronal degeneration in mammalian systems. These insights may facilitate the identification of effective neurotoxic agents for replicating AD pathogenesis in the zebrafish brain. In this comprehensive review, the pivotal role of zebrafish models in advancing our comprehension of AD is emphasized. These models hold immense potential for shaping future research directions and clinical interventions, ultimately contributing to the development of novel AD therapies.

TMBPF-induced neurotoxicity and oxidative stress in zebrafish larvae: impacts on central nervous system development and dopamine neurons

Bisphenol A (BPA), a common bisphenol molecule, is well known in the environment as an endocrine disruptor. Furthermore, BPs (BPA, BPS, BPF, and BPAF) have been shown in recent years to be neurotoxic to zebrafish. Tetramethyl bisphenol F (TMBPF) has recently been introduced as a substitute for bisphenol A (BPA) in various industries, including plastics and food contact coatings. However, a growing number of studies have demonstrated that the toxicity of some BPA substitutes is similar to or even stronger than BPA, posing potential harm to human health and the environment. In this study, we used zebrafish larvae as a model to investigate the neurodevelopmental effects of TMBPF at different concentrations (0, 0.25, 0.5, 1, 2, 4 and 8 mg/L). Our results showed that exposure to TMBPF at concentrations higher than 4 mg/L for 72 h post-fertilization (hpf) resulted in zebrafish mortality, whereas exposure to 2 mg/L for 144 hpf caused deformities. Furthermore, TMBPF exposure inhibited the development of the central nervous system, motor nerves, and dopamine neurons in zebrafish. Real-time polymerase chain reaction (PCR) analysis revealed that TMBPF exposure significantly down-regulated the expression of oxidative stress-related genes (Cu/Zn-SOD, Mn-SOD, and CAT) and neurodevelopmental genes (mbp, gafp, and syn2a), while up-regulated the expression of dopamine-related genes (th1, th2, and dat). Notably, treatment with the antioxidant N-acetylcysteine (NAC) alleviated TMBPF-induced toxicity. NAC can regulate the expression of genes related to oxidative stress, neurodevelopment and dopamine development, and make the nerve development of zebrafish normal. Overall, our research suggested that TMBPF may disrupt the development of the early central nervous system and dopamine neurons, leading to abnormal motor behavior in zebrafish larvae. These results highlight the potential risks associated with the use of TMBPF in various industries and the importance to evaluate its potential risks to human health and the environment.

The role of cilia during organogenesis in zebrafish

Cilia are hair-like organelles that protrude from the surface of eukaryotic cells and are present on the surface of nearly all human cells. Cilia play a crucial role in signal transduction, organ development and tissue homeostasis. Abnormalities in the structure and function of cilia can lead to a group of human diseases known as ciliopathies. Currently, zebrafish serves as an ideal model for studying ciliary function and ciliopathies due to its relatively conserved structure and function of cilia compared to humans. In this review, we will summarize the different types of cilia that present in embryonic and adult zebrafish, and provide an overview of the advantages of using zebrafish as a vertebrate model for cilia research. We will specifically focus on the roles of cilia during zebrafish organogenesis based on recent studies. Additionally, we will highlight future prospects for ciliary research in zebrafish.

Chitosan nanoparticle toxicity: A comprehensive literature review of in vivo and in vitro assessments for medical applications

Topic definition

This literature review aims to update the current knowledge on toxicity of chitosan nanoparticles, compare the recent findings and identify the gaps with knowledge that is present for the chitosan nanoparticles.

Methods

The publications between 2010 and 2020 were searched in Science Direct, Pubmed.gov, Google Scholar, Research Gate, and ClinicalTrials.gov, according to the inclusion and exclusion criteria. 30 primary research studies were obtained from the literature review to compare the in vitro in vivo toxicity profiles among the chitosan nanoparticles.

Major highlights

Chitosan nanoparticles and other types of nanoparticles show cytotoxic effects on cancer cells while having minimal toxicity on normal cells. This apparent effect poses some considerations for use in incorporating cancer therapeutics into chitosan nanoparticles as an administration form. The concentration, duration of exposure, and pH of the solution can influence nanoparticle cytotoxicity, particularly in zebrafish. Different cell lines exhibit varying degrees of toxicity when exposed to nanoparticles, and of note are liver cells that show toxicity under exposure as indicated by increased alanine transaminase (ALT) levels. Aside from ALT, platelet aggregation can be considered a toxicity induced by chitosan nanoparticles. In addition, zebrafish cells experience the most toxicity, including organ damage, neurobehavioral impairment, and developmental abnormalities, when exposed to nanoparticles. However, nanoparticles may exhibit different toxicity profiles in different organisms, with brain toxicity and liver toxicity being present in zebrafish but not rats. Different organs exhibit varying degrees of toxicity, with the eye and mouth apparently having the lowest toxicity, while the brain, intestine, muscles and lung showing mixed results. Cardiotoxicity induced by chitosan nanoparticles was not observed in zebrafish embryos, and nanoparticles may reduce cardiotoxicity when delivering drug. Toxicity found in an organ may not necessarily mean that it is toxic towards all the cells found in that organ, as muscle toxicity was present when tested in zebrafish but not in C2C12 myoblast cells. Some of the studies conducted may have limitations that need to be reconsidered to account for differing results, with some examples being two experiments done on HeLa cells where one study concluded chitosan nanoparticles were toxic to the cells while the other seems to have no toxicity present. With regards to LD50, one study has stated the concentration of 64.21 mg/ml was found. Finally, smaller nanoparticles generally exhibit higher toxicity in cells compared to larger nanoparticles.

Scope for future work

This literature review did not uncover any published clinical trials with available results. Subsequent research endeavors should prioritize conducting clinical trials involving human volunteers to directly assess toxicity, rather than relying on cell or animal models.

Towards experimental models of delirium utilizing zebrafish

Delirium is an acute neuropsychiatric condition characterized by impaired behavior and cognition. Although the syndrome has been known for millennia, its CNS mechanisms and risk factors remain poorly understood. Experimental animal models, especially rodent-based, are commonly used to probe various pathogenetic aspects of delirium. Complementing rodents, the zebrafish (Danio rerio) emerges as a promising novel model organism to study delirium. Zebrafish demonstrate high genetic and physiological homology to mammals, easy maintenance, robust behaviors in various sensitive behavioral tests, and the potential to screen for pharmacological agents relevant to delirium. Here, we critically discuss recent developments in the field, and emphasize the developing utility of zebrafish models for translational studies of delirium and deliriant drugs. Overall, the zebrafish represents a valuable and promising aquatic model species whose use may help understand delirium etiology, as well as develop novel therapies for this severely debilitating disorder.

Teleosts as behaviour test models for social stress

Stress is an important aspect of our everyday life and exposure to it is an unavoidable occurrence. In humans, this can come in the form of social stress or physical stress from an injury. Studies in animal models have helped researchers to understand the body's adaptive response to stress in human. Notably, the use of behavioural tests in animal models plays a pivotal role in understanding the neural, endocrine and behavioural changes induced by social stress. Under socially stressed conditions, behavioural parameters are often measured physiological and molecular parameters as changes in behaviour are direct responses to stress and are easily assessed by behavioural tests. Throughout the past few decades, the rodent model has been used as a well-established animal model for stress and behavioural changes. Recently, more attention has been drawn towards using fish as an animal model. Common fish models such as zebrafish, medaka, and African cichlids have the advantage of a higher rate of reproduction, easier handling techniques, sociability and most importantly, share evolutionary conserved genetic make-up, neural circuitry, neuropeptide molecular structure and function with mammalian species. In fact, some fish species exhibit a clear diurnal or seasonal rhythmicity in their stress response, similar to humans, as opposed to rodents. Various social stress models have been established in fish including but not limited to chronic social defeat stress, social stress avoidance, and social stress-related decision-making. The huge variety of behavioural patterns in teleost also aids in the study of more behavioural phenotypes than the mammalian species. In this review, we focus on the use of fish models as alternative models to study the effects of stress on different types of behaviours. Finally, fish behavioural tests against the typical mammalian model-based behavioural test are compared and discussed for their viability.

Zebrafish as a model organism - can a fish mimic human?

From pre-historic era, all scientific discoveries have evolved around a concept - THINK BIG but for a change zebrafish as a model organism in research had managed to halt the entire medical community and made us realize that it's time to think small. From a barely imagined being in research few years ago to around 4,000 publications in just last year, zebrafish has definitely come a long way. Through these tiny fish, scientists have managed to find genes that caused human diseases and have also developed various specific models to know more about the pathology behind such diseases. This review will focus on zebrafish as a model organism from the time it was introduced to the most novel targets with particular emphasis on central nervous system (CNS) as it is rapidly evolving branch in zebrafish research these days. This review will try to shed light on the early stages of zebrafish as a model organism and will try to cover the journey of it developing as a successful model organism to map many diseases like diabetes, Alzheimer's and autism describing the rationale for using this specific model and briefly the techniques under each category and finally will summarize the pros and cons of the model with its expected future directions.

Investigation of Kelussia Odoratissima and Angelica Sinensis Similarities in Zebrafish-based In-vivo Bioactivity Assays and Their Chemical Composition

BACKGROUND

Kelussia odoratissima and Angelica sinensis are two medicinal plants commonly used in Iran and China, respectively. They have been used in their indigenous traditional medicine, for various diseases including, blood refining, inflammation, cold, flu, stress, cardiovascular diseases, and nervous disorders. This study was conducted to evaluate the volatile oil composition of K. odoratissima leaves (KVL) and A. sinensis root (AVR); we also examined the biological activity of essential oils (EOs) and hydroalcoholic extracts of both plants using two different transgenic zebrafish (Danio rerio) models: angiogenesis and pancreatic beta cell (pBC) regeneration models.

MATERIALS AND METHODS

Both EOs were isolated by hydrodistillation and analysed by GC and GC/MS. For viability tests, larvae were treated with different concentrations of extracts to determine an appropriate starting concentration. Hydroalcoholic extracts and EOs have been tested in a dose-dependent manner for their biological activity using tissue-specific transgenic zebrafish Tg(fli-1: EGFP) and Tg (ins: GFP-NTR) embryos and larvae. One-way ANOVA was used to compare the mean of pBC area and intersegmental vessels (ISVs) outgrowth between the treatment groups.

RESULTS

Eleven compounds were in common to both oils, comprising 51.3% of KVL and 61.7% of AVR, of which 39.3% in KVL and 37.6% in AVR were phthalide structures. Results revealed that both EOs blocked ISVs formation in the Tg (fli-1: EGFP) embryos increased to 10% of the control value, while both hydroalcoholic extracts did not show any anti-angiogenesis effects in these embryos. In addition, AVR has been shown to significantly induce PBC regeneration following ablation in the Tg (ins: GFP-NTR), but its regenerative activity was lower than that of 5'-N-ethylcarboxamidoadenosine (NECA) as a positive control. Taken together, the anti-angiogenesis activity of both EOs could be attributed to the phthalide structures while for the PBC regenerative activity, other compounds including β-Thujaplicinol, exclusively existing in AVR, might be effective.

CONCLUSION

Although the genera, organs, and origin of these plants are different, their similar chemical composition and biological activities make them valuable resources for further investigation in basic medical and pharmaceutical science.

Betanin mitigates scopolamine-induced cognitive impairment by restoring cholinergic function, boosting brain antioxidative status, and increasing BDNF level in the zebrafish model

Betalains obtained from Beta vulgaris (family Caryophyllales) are regularly consumed as part of the regular diet with medicinal benefits due to antioxidant and anti-inflammatory properties. The objective of this article was to evaluate betanin's neuroprotective properties in a scopolamine-induced zebrafish paradigm. Betanin (BET) (50, 100, and 200 mg/L), and donepezil (10 mg/L) were delivered to zebrafish in a treatment tank once a day for 8 days, while memory impairment was produced by scopolamine (100 µM), which was given 60 min before behavioral assessments. The treatment dosages were determined based on acute toxicity studies. The existence of betacyanin and betaxanthins of BET was tested using liquid chromatography-mass spectrometry (LC-MS). The Y-maze task was used to examine the novelty and spatial memory, while the novel tank diving test was used to assess anxiety-like behavior (NTT). The activities of acetylcholinesterase (AChE) and the oxidative stress sensitivity in zebrafish brains were examined. Also, brain-derived neurotrophic factor (BDNF) level is quantified by an ELISA kit. Scopolamine-induced rises in AChE activity, memory loss, anxiety, and brain oxidant capacity were all reduced by BET. These results suggest that BET (50 and 100 mg/L) has a therapeutic ability to treat brain oxidative stress and cognitive deficits in amnesic zebrafish.

Promnesic, Anxiolytic and Antioxidant Effects of Glaucosciadium cordifolium (Boiss.) Burtt & Davis Essential Oil in a Zebrafish Model of Cognitive Impairment

The purpose of this study was to investigate the effect of Glaucosciadium cordifolium essential oil (GCEO, 25 and 150 µL/L) on anxiety and learning and memory impairment induced by scopolamine (SCOP) in zebrafish. The chemical composition was analyzed by GC-MS, and the results showed that the highest content was limonene followed by α- and β-pinene, p-cymene and α-phellandrene. The dementia model was induced by SCOP (100 µM), whereas GCEO and galantamine (GAL, 1 mg/L) were delivered to the SCOP-induced model. It was found that GCEO significantly improved memory impairment and anxiety-like response induced by SCOP through the Y-maze, novel object recognition (NOR) test, and novel tank diving tests (NTT). Biochemical analyses showed that GCEO reduced SCOP-induced oxidative damage. Additionally, the cholinergic system activity was improved in the SCOP-induced model by decreasing the acetylcholinesterase (AChE) activity following the exposure to GCEO. It was clear that as a mixture, GCEO displays positive action in improving memory impairment through restoring cholinergic dysfunction and brain antioxidant status.

Zebrafish as a Potential Model for Neurodegenerative Diseases: A Focus on Toxic Metals Implications

In the last century, industrial activities increased and caused multiple health problems for humans and animals. At this moment, heavy metals are considered the most harmful substances for their effects on organisms and humans. The impact of these toxic metals, which have no biological role, poses a considerable threat and is associated with several health problems. Heavy metals can interfere with metabolic processes and can sometimes act as pseudo-elements. The zebrafish is an animal model progressively used to expose the toxic effects of diverse compounds and to find treatments for different devastating diseases that human beings are currently facing. This review aims to analyse and discuss the value of zebrafish as animal models used in neurological conditions, such as Alzheimer's disease (AD), and Parkinson's disease (PD), particularly in terms of the benefits of animal models and the limitations that exist.

Developing Novel Experimental Models of m-TORopathic Epilepsy and Related Neuropathologies: Translational Insights from Zebrafish

The mammalian target of rapamycin (mTOR) is an important molecular regulator of cell growth and proliferation. Brain mTOR activity plays a crucial role in synaptic plasticity, cell development, migration and proliferation, as well as memory storage, protein synthesis, autophagy, ion channel expression and axonal regeneration. Aberrant mTOR signaling causes a diverse group of neurological disorders, termed 'mTORopathies'. Typically arising from mutations within the mTOR signaling pathway, these disorders are characterized by cortical malformations and other neuromorphological abnormalities that usually co-occur with severe, often treatment-resistant, epilepsy. Here, we discuss recent advances and current challenges in developing experimental models of mTOR-dependent epilepsy and other related mTORopathies, including using zebrafish models for studying these disorders, as well as outline future directions of research in this field.

Zebrafish: A Model Deciphering the Impact of Flavonoids on Neurodegenerative Disorders

Over the past century, advances in biotechnology, biochemistry, and pharmacognosy have spotlighted flavonoids, polyphenolic secondary metabolites that have the ability to modulate many pathways involved in various biological mechanisms, including those involved in neuronal plasticity, learning, and memory. Moreover, flavonoids are known to impact the biological processes involved in developing neurodegenerative diseases, namely oxidative stress, neuroinflammation, and mitochondrial dysfunction. Thus, several flavonoids could be used as adjuvants to prevent and counteract neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Zebrafish is an interesting model organism that can offer new opportunities to study the beneficial effects of flavonoids on neurodegenerative diseases. Indeed, the high genome homology of 70% to humans, the brain organization largely similar to the human brain as well as the similar neuroanatomical and neurochemical processes, and the high neurogenic activity maintained in the adult brain makes zebrafish a valuable model for the study of human neurodegenerative diseases and deciphering the impact of flavonoids on those disorders.

Animal Inflammation-Based Models of Neuropsychiatric Disorders

Mounting evidence links psychiatric disorders to central and systemic inflammation. Experimental (animal) models of psychiatric disorders are important tools for translational biopsychiatry research and CNS drug discovery. Current experimental models, most typically involving rodents, continue to reveal shared fundamental pathological pathways and biomarkers underlying the pathogenetic link between brain illnesses and neuroinflammation. Recent data also show that various proinflammatory factors can alter brain neurochemistry, modulating the levels of neurohormones and neurotrophins in neurons and microglia. The role of "active" glia in releasing a wide range of proinflammatory cytokines also implicates glial cells in various psychiatric disorders. Here, we discuss recent animal inflammation-related models of psychiatric disorders, focusing on their translational perspectives and the use of some novel promising model organisms (zebrafish), to better understand the evolutionally conservative role of inflammation in neuropsychiatric conditions.

Preclinical Models for Alzheimer's Disease: Past, Present, and Future Approaches

A robust preclinical disease model is a primary requirement to understand the underlying mechanisms, signaling pathways, and drug screening for human diseases. Although various preclinical models are available for several diseases, clinical models for Alzheimer's disease (AD) remain underdeveloped and inaccurate. The pathophysiology of AD mainly includes the presence of amyloid plaques and neurofibrillary tangles (NFT). Furthermore, neuroinflammation and free radical generation also contribute to AD. Currently, there is a wide gap in scientific approaches to preventing AD progression. Most of the available drugs are limited to symptomatic relief and improve deteriorating cognitive functions. To mimic the pathogenesis of human AD, animal models like 3XTg-AD and 5XFAD are the primarily used mice models in AD therapeutics. Animal models for AD include intracerebroventricular-streptozotocin (ICV-STZ), amyloid beta-induced, colchicine-induced, etc., focusing on parameters such as cognitive decline and dementia. Unfortunately, the translational rate of the potential drug candidates in clinical trials is poor due to limitations in imitating human AD pathology in animal models. Therefore, the available preclinical models possess a gap in AD modeling. This paper presents an outline that critically assesses the applicability and limitations of the current approaches in disease modeling for AD. Also, we attempted to provide key suggestions for the best-fit model to evaluate potential therapies, which might improve therapy translation from preclinical studies to patients with AD.

Zebrafish - The Neurobehavioural Model in Trend

Zebrafish (Danio rerio) is currently in vogue as a prevalently used experimental model for studies concerning neurobehavioural disorders and associated fields. Since the 1960s, this model has succeeded in breaking most barriers faced in the hunt for an experimental model. From its appearance to its high parity with human beings genetically, this model renders itself as an advantageous experimental lab animal. Neurobehavioural disorders have always posed an arduous task in terms of their detection as well as in determining their exact etiology. They are still, in most cases, diseases of interest for inventing or discovering novel pharmacological interventions. Thus, the need for a harbinger experimental model for studying neurobehaviours is escalating. Ensuring the same model is used for studying several neuro-studies conserves the results from inter-species variations. For this, we need a model that satisfies all the pre-requisite conditions to be made the final choice of model for neurobehavioural studies. This review recapitulates the progress of zebrafish as an experimental model with its most up-to-the-minute advances in the area. Various tests, assays, and responses employed using zebrafish in screening neuroactive drugs have been tabulated effectively. The tools, techniques, protocols, and apparatuses that bolster zebrafish studies are discussed. The probable research that can be done using zebrafish has also been briefly outlined. The various breeding and maintenance methods employed, along with the information on various strains available and most commonly used, are also elaborated upon, supplementing Zebrafish's use in neuroscience.

Aaptamine - a dual acetyl - and butyrylcholinesterase inhibitor as potential anti-Alzheimer's disease agent

CONTEXT

Alzheimer's disease (AD) is a neurodegenerative disorder that affects millions of people worldwide. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are promising therapeutic targets for AD.

OBJECTIVE

To evaluate the inhibitory effects of aaptamine on two cholinesterases and investigate the in vivo therapeutic effect on AD in a zebrafish model.

MATERIALS AND METHODS

Aaptamine was isolated from the sponge Aaptos suberitoides Brøndsted (Suberitidae). Enzyme inhibition, kinetic analysis, surface plasmon resonance (SPR) and molecular docking assays were used to determine its inhibitory effect on AChE and BuChE in vitro. Zebrafish were divided into six groups: control, model, 8 μM donepezil, 5 , 10  and 20 μM aaptamine. After three days of drug treatment, the behaviour assay was performed.

RESULTS

The IC₅₀ values of aaptamine towards AChE and BuChE were 16.0 and 4.6 μM. And aaptamine directly inhibited the two cholinesterases in the mixed inhibition type, with K_i values of 6.96 ± 0.04 and 6.35 ± 0.02 μM, with K_d values of 87.6 and 10.7 μM. Besides, aaptamine interacts with the crucial anionic sites of AChE and BuChE. In vivo studies indicated that the dyskinesia recovery rates of 5 , 10  and 20 μM aaptamine group were 34.8, 58.8 and 60.0%, respectively, and that of donepezil was 63.7%.

DISCUSSION AND CONCLUSIONS

Aaptamine showed great potential to exert its anti-AD effects by directly inhibiting the activities of AChE and BuChE. Therefore, this study identified a novel medicinal application of aaptamine and provided a new structural scaffold for the development of anti-AD drugs.

Commentary: Zebrafish as a Model for Osteoporosis-An Approach to Accelerating Progress in Drug and Exercise-Based Treatment

Osteoporosis (OP) is a degenerative disease characterized by reduced bone strength and increased fracture risk. As the global population continues to age, the prevalence and economic burden of osteoporosis can be expected to rise substantially, but there remain various gaps in the field of OP care. For instance, there is a lack of anti-fracture drugs with proven long-term efficacy. Likewise, though exercise remains widely recommended in OP prevention and management, data regarding the safety and efficacy for patients after vertebral fracture remain limited. This lack of evidence may be due to the cost and inherent difficulties associated with exercise-based OP research. Thus, the current research landscape highlights the need for novel research strategies that accelerate OP drug discovery and allow for the low-cost study of exercise interventions. Here, we outline an example of one strategy, the use of zebrafish, which has emerged as a potential model for the discovery of anti-osteoporosis therapeutics and study of exercise interventions. The strengths, limitations, and potential applications of zebrafish in OP research will be outlined.

Zebrafish: A Pharmacological Model for Learning and Memory Research

Learning and memory are essential to organism survival and are conserved across various species, especially vertebrates. Cognitive studies involving learning and memory require using appropriate model organisms to translate relevant findings to humans. Zebrafish are becoming increasingly popular as one of the animal models for neurodegenerative diseases due to their low maintenance cost, prolific nature and amenability to genetic manipulation. More importantly, zebrafish exhibit a repertoire of neurobehaviors comparable to humans. In this review, we discuss the forms of learning and memory abilities in zebrafish and the tests used to evaluate the neurobehaviors in this species. In addition, the pharmacological studies that used zebrafish as models to screen for the effects of neuroprotective and neurotoxic compounds on cognitive performance will be summarized here. Lastly, we discuss the challenges and perspectives in establishing zebrafish as a robust model for cognitive research involving learning and memory. Zebrafish are becoming an indispensable model in learning and memory research for screening neuroprotective agents against cognitive impairment.