Zebrafish (Danio rerio): A potential model for nephroprotective drug screening

Phenylthiourea-mediated experimental depigmentation reduces seizurogenic response of pentylenetetrazol in zebrafish larva

Zebrafish larvae exposed to chemoconvulsants show behavioral seizures and electrographic abnormalities similar to the other mammalian models, making it a potential tool in epilepsy research. During the embryonic stage, zebrafish remains transparent which enables real-time developmental detection and in-situ gene/protein expression. However, pigmentation during the larval stage restricts transparency. Phenylthiourea (1-phenyl-2-thiourea; PTU) is a commonly used pigmentation blocker that maintains larval transparency. It is widely used along with chemoconvulsants to study in situ expressions in epileptic larvae, however, its effect on seizures largely remains unknown. Therefore, in the present study, the effect of PTU-mediated depigmentation was studied on pentylenetetrazol (PTZ)-induced seizures in zebrafish larvae. After spawning, the fish embryos were subjected to standard depigmentation protocol using 0.13 mM PTU. At 7-days post fertilization seizures were induced using 8 mM PTZ. PTU exposure significantly reduced PTZ-mediated hyperactive responses indicated by decreased distance travelled and swimming velocity of the larvae. Furthermore, PTU-exposed depigmented larvae also showed an increase in the latency to the onset of PTZ-mediated clonic-like seizures. The results concluded that PTU depigmentation protocol reduces the seizurogenic response of PTZ, hence its usage for imaging zebrafish larvae must be carefully monitored to avoid erroneous results.

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.

Inhibition of Mammalian Target of Rapamycin Attenuates Recurrent Seizures Associated Cardiac Damage in a Zebrafish Kindling Model of Chronic Epilepsy

Sudden Unexpected Death in Epilepsy (SUDEP) is primarily linked with the cardiac irregularities that occur due to recurrent seizures. Our previous studies found a role of mTOR pathway activation in seizures-linked cardiac damage in a rat model. In continuation to the earlier work, the present study was devised to explore the role of rapamycin (mTOR inhibitor and clinically used immunosuppressive agent) in a zebrafish kindling model and associated cardiac damage. Adult zebrafish were incubated with increasing concentrations of rapamycin (1, 2 and, 4 μM), followed by pentylenetetrazole (PTZ) exposure to record seizure latency and severity. In another experiment, zebrafish were subjected to a standardized PTZ kindling protocol. The kindled fish were treated daily with rapamycin for up to 25 days, along with PTZ to record seizure severity. At the end, zebrafish heart was excised for carbonylation assay, gene expression, and protein quantification studies. In the acute PTZ convulsion test, treatment with rapamycin showed a significant increase in seizure latency and decreased seizure severity without any change in seizure incidence. Treatment with rapamycin also reduced the severity of seizures in kindled fish. The cardiac expressions of gpx, nppb, kcnh2, scn5a, mapk8, stat3, rps6 and ddit were decreased, whereas the levels of trxr2 and beclin 1 were increased following rapamycin treatment in kindled fish. Furthermore, rapamycin treatment also decreased p-mTOR expression and protein carbonyls level in the fish cardiac tissue. The present study concluded that rapamycin reduces seizures and associated cardiac damage by inhibiting mTOR activation in the zebrafish kindling model.

Zebrafish Embryos and Larvae as Alternative Animal Models for Toxicity Testing

Prerequisite to any biological laboratory assay employing living animals is consideration about its necessity, feasibility, ethics and the potential harm caused during an experiment. The imperative of these thoughts has led to the formulation of the 3R-principle, which today is a pivotal scientific standard of animal experimentation worldwide. The rising amount of laboratory investigations utilizing living animals throughout the last decades, either for regulatory concerns or for basic science, demands the development of alternative methods in accordance with 3R to help reduce experiments in mammals. This demand has resulted in investigation of additional vertebrate species displaying favourable biological properties. One prominent species among these is the zebrafish (Danio rerio), as these small laboratory ray-finned fish are well established in science today and feature outstanding biological characteristics. In this review, we highlight the advantages and general prerequisites of zebrafish embryos and larvae before free-feeding stages for toxicological testing, with a particular focus on cardio-, neuro, hepato- and nephrotoxicity. Furthermore, we discuss toxicokinetics, current advances in utilizing zebrafish for organ toxicity testing and highlight how advanced laboratory methods (such as automation, advanced imaging and genetic techniques) can refine future toxicological studies in this species.

Evaluation of the Antidiabetic and Antihyperlipidemic Activity of Spondias purpurea Seeds in a Diabetic Zebrafish Model

Diabetes mellitus (DM) is a serious chronic degenerative disease characterized by high levels of glucose in the blood. It is associated with an absolute or relative deficiency in the production and/or action of insulin. Some of the complications associated with DM are heart disease, retinopathy, kidney disease, and neuropathy; therefore, new natural alternatives are being sought to control the disease. In this work, we evaluate the antidiabetic effect of Spondias purpurea seed methanol extract (CSM) in vitro and in a glucose-induced diabetic zebrafish model. CSM is capable of lowering blood glucose and cholesterol levels, as well as forming advanced glycation end-products, while not presenting toxic effects at the concentrations evaluated. These data show that CSM has a promising antidiabetic effect and may be useful in reducing some of the pathologies associated with diabetes mellitus.

Development and validation of chemical kindling in adult zebrafish: A simple and improved chronic model for screening of antiepileptic agents

BACKGROUND

Zebrafish has emerged as a potential animal model of acute convulsion for early screening of antiepileptic agents. There is a need for alternative chronic zebrafish models of epilepsy with more correlation to the clinical condition.

NEW METHOD

Adult zebrafish were repeatedly exposed to subeffective concentrations of pentylenetetrazole (PTZ), until appearance to tonic-clonic seizures, considered as kindled. Valproic acid (VPA) exposure was given during kindling and in kindled fish in 2 different groups. The neurotransmitters level and expression of the genes associated with kindling were studied in the fish brain.

RESULTS

There was an increase in seizure severity score at 1.25 mM concentration of PTZ, and 66.66 % of fish achieved kindling after 22 days' exposure. A marked increase in c-fos, crebbpa and crebbpbexpression, and glutamate/GABA level was observed in the brain of kindled fish. VPA inhibited the induction of PTZ-mediated kindling and reduced seizure severity in kindled fish.

COMPARISON WITH EXISTING METHOD

In contrast to an existing adult zebrafish kindling method, the present protocol is of longer duration, with more similarity to clinical epilepsy. Moreover, the induction of kindling involves a simple non-invasive technique without the use of anesthesia. The protocol can be used for evaluation of both antiepileptic and antiepileptogenic agents.

CONCLUSION

Repeated exposure of 1.25 mM PTZ induced kindling in zebrafish, altering the brain neurotransmitter levels and gene expression. Inhibition of kindling induction and decrease in seizures in normal and kindled fish, respectively by VPA validated application of the model for preclinical testing of agents against epilepsy.

The identification of dual protective agents against cisplatin-induced oto- and nephrotoxicity using the zebrafish model

Dose-limiting toxicities for cisplatin administration, including ototoxicity and nephrotoxicity, impact the clinical utility of this effective chemotherapy agent and lead to lifelong complications, particularly in pediatric cancer survivors. Using a two-pronged drug screen employing the zebrafish lateral line as an in vivo readout for ototoxicity and kidney cell-based nephrotoxicity assay, we screened 1280 compounds and identified 22 that were both oto- and nephroprotective. Of these, dopamine and L-mimosine, a plant-based amino acid active in the dopamine pathway, were further investigated. Dopamine and L-mimosine protected the hair cells in the zebrafish otic vesicle from cisplatin-induced damage and preserved zebrafish larval glomerular filtration. Importantly, these compounds did not abrogate the cytotoxic effects of cisplatin on human cancer cells. This study provides insights into the mechanisms underlying cisplatin-induced oto- and nephrotoxicity and compelling preclinical evidence for the potential utility of dopamine and L-mimosine in the safer administration of cisplatin.

Toxicity study on Clinacanthus nutans leaf hexane fraction using Danio rerio embryos

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The C. nutans n-hexane fraction is harmful with the LC₅₀ of 75.49 μg/mL.

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The mortality rate increased as the fraction concentration increased.

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Morphological defects such as less pigmentation, dented tail, oedema malformed yolk sac was detected at the median lethal concentration.

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GC–MS analysis revealed the presence of sterols, fatty acids and some of its derivatives in the n-hexane fraction.

Clinacanthus nutans, an herbal shrub belonging to the Acanthaceae family, is traditionally used as a functional food to treat various ailments in Malaysia and Indonesia. Although the polar fraction of this plant shows non-toxic effect, the toxicity of the non-polar extract is not reported so far. The present study aimed to assess the toxic effect and determine the lethal concentration of this non-polar fraction using zebrafish embryos. The n-hexane fraction was partitioned from the crude extract of C. nutans obtained using 80% methanolic solution. After spawning of the adult male and female zebrafish, the eggs were collected, transferred into a 96-well plate and incubated with the n-hexane fraction at concentrations of 15.63 μg/ml, 31.25 μg/ml, 62.5 μg/ml, 125 μg/ml, 250 μg/ml and 500 μg/ml in 2% DMSO. The survival and sublethal endpoint were assessed, the mortality and hatchability rates were calculated based on microscopic observation, while the heartbeat rate was measured using DanioScope software. The median lethal concentration (LC₅₀) of the C. nutans n-hexane fraction, which was determined using probit analysis, was calculated to be 75.49 μg/mL, which is harmful. Moreover, gas chromatography-mass spectrometry (GC–MS) analysis revealed the presence of palmitic acid, phytol, hexadecanoic acid, 1-monopalmitin, stigmast-5-ene, pentadecanoic acid, heptadecanoic acid, 1-linolenoylglycerol and stigmasterol in the n-hexane fraction.

How Surrogate and Chemical Genetics in Model Organisms Can Suggest Therapies for Human Genetic Diseases

Genetic diseases are both inherited and acquired. Many genetic diseases fall under the paradigm of orphan diseases, a disease found in < 1 in 2000 persons. With rapid and cost-effective genome sequencing becoming the norm, many causal mutations for genetic diseases are being rapidly determined. In this regard, model organisms are playing an important role in validating if specific mutations identified in patients drive the observed phenotype. An emerging challenge for model organism researchers is the application of genetic and chemical genetic platforms to discover drug targets and drugs/drug-like molecules for potential treatment options for patients with genetic disease. This review provides an overview of how model organisms have contributed to our understanding of genetic disease, with a focus on the roles of yeast and zebrafish in gene discovery and the identification of compounds that could potentially treat human genetic diseases.

Ultrafast synthesis of stabilized gold nanoparticles using aqueous fruit extract of Limonia acidissima L. and conjugated epirubicin: targeted drug delivery for treatment of breast cancer

Green synthesis of AuNPs using extract ofLimonia acidissimaL. as a reducing agent. Epirubicin was successfully loaded on folic acid–AuNPs. This formulation revealed better site specific delivery of epirubicin to MCF-7 cells.