Adult Zebrafish Model for Screening Drug-Induced Kidney Injury

Zebrafish as a model for podocyte research

Podocytes, specialized postmitotic cells, are central players in various kidney-related diseases. Zebrafish have become a valuable model system for studying podocyte biology because they are genetically easy to manipulate, transparent, and their glomerular structure is similar to that of mammals. This review provides an overview of the knowledge of podocyte biology in zebrafish larvae, with particular focus on their essential contribution to understanding the mechanisms that underlie kidney diseases as well as supporting drug development. In addition, special attention is given to advances in live-imaging techniques allowing the observation of dynamic processes, including podocyte motility, podocyte process behavior, and glomerulus maturation. The review further addresses the functional aspects of podocytes in zebrafish larvae. This includes topics such as glomerular filtration, ultrastructural analyses, and evaluation of podocyte response to nephrotoxic insults. Studies presented in this context have provided important insights into the maintenance and resistance of the glomerular filtration barrier in zebrafish larvae and explored the potential transferability of these findings to mammals such as mice, rats, and most importantly, humans. The recent ability to identify potential therapeutic targets represents a promising new way to identify drugs that could effectively treat podocyte-associated glomerulopathies in humans. In summary, this review gives an overview about the importance of zebrafish as a model for podocyte-related disease and targeted drug development. It also highlights the key role of advanced imaging techniques in transparent zebrafish larvae, improving our understanding of glomerular diseases and the significant potential for translation of these findings to humans.

Animal Models of Kidney Disease: Challenges and Perspectives

Kidney disease is highly prevalent and affects approximately 850 million people worldwide. It is also associated with high morbidity and mortality, and current therapies are incurable and often ineffective. Animal models are indispensable for understanding the pathophysiology of various kidney diseases and for preclinically testing novel remedies. In the last two decades, rodents continue to be the most used models for imitating human kidney diseases, largely because of the increasing availability of many unique genetically modified mice. Despite many limitations and pitfalls, animal models play an essential and irreplaceable role in gaining novel insights into the mechanisms, pathologies, and therapeutic targets of kidney disease. In this review, we highlight commonly used animal models of kidney diseases by focusing on experimental AKI, CKD, and diabetic kidney disease. We briefly summarize the pathological characteristics, advantages, and drawbacks of some widely used models. Emerging animal models such as mini pig, salamander, zebrafish, and drosophila, as well as human-derived kidney organoids and kidney-on-a-chip are also discussed. Undoubtedly, careful selection and utilization of appropriate animal models is of vital importance in deciphering the mechanisms underlying nephropathies and evaluating the efficacy of new treatment options. Such studies will provide a solid foundation for future diagnosis, prevention, and treatment of human kidney diseases.

Flight for fish in drug discovery: a review of zebrafish-based screening of molecules

Human disease and biological practices are modelled in zebrafish (Danio rerio) at various phases of drug development as well as toxicity evaluation. The zebrafish is ideal for in vivo pathological research and high-resolution investigation of disease progress. Zebrafish has an advantage over other mammalian models, it is cost-effective, it has external development and embryo transparency, easy to apply genetic manipulations, and open to both forward and reverse genetic techniques. Drug screening in zebrafish is suitable for target identification, illness modelling, high-throughput screening of compounds for inhibition or prevention of disease phenotypes and developing new drugs. Several drugs that have recently entered the clinic or clinical trials have their origins in zebrafish. The sophisticated screening methods used in zebrafish models are expected to play a significant role in advancing drug development programmes. This review highlights the current developments in drug discovery processes, including understanding the action of drugs in the context of disease and screening novel candidates in neurological diseases, cardiovascular diseases, glomerulopathies and cancer. Additionally, it summarizes the current techniques and approaches for the selection of small molecules and current technical limitations on the execution of zebrafish drug screening tests.

Selecting the right therapeutic target for kidney disease

Kidney disease is a complex disease with several different etiologies and underlying associated pathophysiology. This is reflected by the lack of effective treatment therapies in chronic kidney disease (CKD) that stop disease progression. However, novel strategies, recent scientific breakthroughs, and technological advances have revealed new possibilities for finding novel disease drivers in CKD. This review describes some of the latest advances in the field and brings them together in a more holistic framework as applied to identification and validation of disease drivers in CKD. It uses high-resolution ‘patient-centric’ omics data sets, advanced in silico tools (systems biology, connectivity mapping, and machine learning) and ‘state-of-the-art‘ experimental systems (complex 3D systems in vitro, CRISPR gene editing, and various model biological systems in vivo). Application of such a framework is expected to increase the likelihood of successful identification of novel drug candidates based on strong human target validation and a better scientific understanding of underlying mechanisms.

Zebrafish (Danio rerio) as a model organism for screening nephrotoxic chemicals and related mechanisms

Because of essential role in homeostasis of the body fluid and excretion of wastes, kidney damage can lead to severe impacts on health and survival of humans. For most chemicals, nephrotoxic potentials and associated mechanisms are unclear. Hence, fast and sensitive screening measures for nephrotoxic chemicals are required. In this study, the utility of zebrafish (Danio rerio) was evaluated for the investigation of chemical-induced kidney toxicity and associated modes of toxicity, based on the literature review. Zebrafish has a well-understood biology, and many overlapping physiological characteristics with mammals. One such characteristic is its kidneys, of which histology and functions are similar to those of mammals, although unique differences of zebrafish kidneys, such as kidney marrow, should be noted. Moreover, the zebrafish kidney is simpler in structure and easy to observe. For these advantages, zebrafish has been increasingly used as an experimental model for screening nephrotoxicity of chemicals and for understanding related mechanisms. Multiple endpoints of zebrafish model, from functional level, i.e., glomerular filtration, to transcriptional changes of key genes, have been assessed to identify chemical-induced kidney toxicities, and to elucidate underlying mechanisms. The most frequently studied mechanisms of chemical-induced nephrotoxicity in zebrafish include oxidative stress, inflammation, DNA damage, apoptosis, fibrosis, and cell death. To date, several pharmaceuticals, oxidizing agents, natural products, biocides, alcohols, and consumer chemicals have been demonstrated to exert different types of kidney toxicities in zebrafish. The present review shows that zebrafish model can be efficiently employed for quick and reliable assessment of kidney damage potentials of chemicals, and related toxic mechanisms. The toxicological information obtained from this model can be utilized for identification of nephrotoxic chemicals and hence for protection of public health.

A multidimensional metabolomics workflow to image biodistribution and evaluate pharmacodynamics in adult zebrafish

An integrated evaluation of the tissue distribution and pharmacodynamic properties of a therapeutic is essential for successful translation to the clinic. To date, however, cost-effective methods to measure these parameters at the systems level in model organisms are lacking. Here, we introduce a multidimensional workflow to evaluate drug activity that combines mass spectrometry-based imaging, absolute drug quantitation across different biological matrices, in vivo isotope tracing and global metabolome analysis in the adult zebrafish. As a proof of concept, we quantitatively determined the whole-body distribution of the anti-rheumatic agent hydroxychloroquine sulfate (HCQ) and measured the systemic metabolic impacts of drug treatment. We found that HCQ distributed to most organs in the adult zebrafish 24 h after addition of the drug to water, with the highest accumulation of both the drug and its metabolites being in the liver, intestine and kidney. Interestingly, HCQ treatment induced organ-specific alterations in metabolism. In the brain, for example, HCQ uniquely elevated pyruvate carboxylase activity to support increased synthesis of the neuronal metabolite, N-acetylaspartate. Taken together, this work validates a multidimensional metabolomics platform for evaluating the mode of action of a drug and its potential off-target effects in the adult zebrafish. This article has an associated First Person interview with the first author of the paper.

Analysis of the Expression of Neurotrophins and Their Receptors in Adult Zebrafish Kidney

Neurotrophins and their receptors are involved in the development and maintenance of neuronal populations. Different reports have shown that all neurotrophin/receptor pathways can also play a role in several non-neuronal tissues in vertebrates, including the kidney. These signaling pathways are involved in different events to ensure the correct functioning of the kidney, such as growth, differentiation, and regulation of renal tubule transport. Previous studies in some fish species have identified the neurotrophins and receptors in the kidney. In this study, for the first time, we compare the expression profiles (mRNA and protein) of all neurotrophin/receptor pathways in the kidney of the adult zebrafish. We quantify the levels of mRNA by using qPCR and identify the expression pattern of each neurotrophin/receptor pathway by in situ hybridization. Next, we detect the proteins using Western blotting and immunohistochemistry. Our results show that among all neurotrophins analyzed, NT-3/TrkC is the most expressed in the glomerule and tubule and in the hematopoietic cells, similar to what has been reported in the mammalian kidney.

Progress in using zebrafish as a toxicological model for traditional Chinese medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Chinese medicine (TCM) has been applied for more than 2000 years. However, modern basic research on the safety of TCMs is limited. Establishing safety evaluation technology in line with the characteristics of TCM and conducting large-scale basic toxicity research are keys to comprehensively understand the toxicity of TCMs. In recent years, zebrafish has been used as a model organism for toxicity assessment and is increasingly utilized for toxicity research of TCMs. Yet, a comprehensive review in using zebrafish as a toxicological model for TCMs is lacked.

AIM OF THE STUDY

We aim to summarize the progress and limitation in toxicity evaluation of TCMs using zebrafish and put forward the future research ideas.

MATERIALS AND METHODS

The scientific databases, including Springer, Science Direct, Wiley, Pubmed and China Knowledge Resource Integrated (CNKI) were searched using the key words of zebrafish, toxicology, traditional Chinese medicine, acute toxicity, liver injury, cardiotoxicity, kidney toxicity, developmental toxicity, neurotoxicity, gastrointestinal irritation, immunotoxicity, ototoxicity, and osteotoxicity.

RESULTS

Zebrafish assays are low experimental cost and short cycle, easily achieving high-throughput toxicity screening, and exemption from ethical legislation up to 5 dpf. It has been widely used to evaluate the acute toxicity, liver toxicity, cardiotoxicity, nephrotoxicity, developmental toxicity, neurotoxicity, gastrointestinal irritation, immunotoxicity, and ototoxicity caused by TCMs, although some physiological difference limited its application.

CONCLUSIONS

Zebrafish is a powerful model for TCMs toxicity evaluation, but it is not flawless. The toxicity testing criterion and high throughput assays are urgent to be established. This review provides references for future studies.

Exploration of zebrafish larvae as an alternative whole-animal model for nephrotoxicity testing

Due to an increasing demand for testing of new and existing chemicals and legal restrictions for the use of animals, there is a strong need for alternative approaches to assess systemic toxicity. Embryonic and larval zebrafish (Danio rerio) are increasingly recognized as a promising alternative whole-animal model that may be able to overcome limitations of cell-based in vitro assays and bridge the gap between high-throughput in vitro screening and low-throughput in vivo tests in animals. Despite the relatively simple anatomical structure of the zebrafish larval kidney (pronephros) - composed of only two nephrons - the pronephros shares major functions and cell types with mammalian nephrons. Glomerular filtration begins at 48 h post fertilization. The aim of the present study was to investigate if early zebrafish larvae might be a suitable model for nephrotoxicity testing. On day 3 post fertilization, larval zebrafish were treated with selected nephrotoxins (aristolochic acid, cadmium chloride, potassium bromate, ochratoxin A, gentamicin) for 48 h. Histological evaluation of zebrafish larvae exposed to model nephrotoxins revealed tubule injury as evidenced by dilated tubules with loss of the brush border, tubule cell necrosis and disorganization of the tubular epithelium. These changes were most severe after treatment with gentamicin, which also impaired pronephros function as evidenced by reduced clearance of FITC-dextran. Whole-mount in situ hybridization showing loss of cdh17 expression revealed site-specific injury to the proximal tubule segment. Analysis of genes previously identified as novel biomarkers of kidney injury in mammals showed upregulation of the kidney injury marker genes heme oxygenase 1 (hmox1), clusterin (clu), secreted phosphoprotein/osteopontin (spp1), connective tissue growth factor (ctgf) and kim-1 (havcr-1) in response to nephrotoxin treatment, although the response of individual genes varied across compounds. Consistent with the severity of lesions and impaired kidney function, the most prominent gene expression changes occurred in larvae exposed to gentamicin. Overall, our results suggest that larval zebrafish may be a suitable alternative model organism for nephrotoxicity screening, yet further improvements and integration with quantitative in vitro to in vivo extrapolation will be needed to predict human toxicity.

Prolonged podocyte depletion in larval zebrafish resembles mammalian focal and segmental glomerulosclerosis

Focal and segmental glomerulosclerosis (FSGS) is a histological pattern frequently found in patients with nephrotic syndrome that often progress to end-stage kidney disease. The initial step in development of this histologically defined entity is injury and ultimately depletion of podocytes, highly arborized interdigitating cells on the glomerular capillaries with important function for the glomerular filtration barrier. Since there are still no causal therapeutic options, animal models are needed to develop new treatment strategies. Here, we present an FSGS-like model in zebrafish larvae, an eligible vertebrate model for kidney research. In a transgenic zebrafish strain, podocytes were depleted, and the glomerular response was investigated by histological and morphometrical analysis combined with immunofluorescence staining and ultrastructural analysis by transmission electron microscopy. By intravenous injection of fluorescent high-molecular weight dextran, we confirmed leakage of the size selective filtration barrier. Additionally, we observed severe podocyte foot process effacement of remaining podocytes, activation of proximal tubule-like parietal epithelial cells identified by ultrastructural cytomorphology, and expression of proximal tubule markers. These activated cells deposited extracellular matrix on the glomerular tuft which are all hallmarks of FSGS. Our findings indicate that glomerular response to podocyte depletion in larval zebrafish resembles human FSGS in several important characteristics. Therefore, this model will help to investigate the disease development and the effects of potential drugs in a living organism.

Application of zebrafish to safety evaluation in drug discovery

Traditionally, safety evaluation at the early stage of drug discovery research has been done using in silico, in vitro, and in vivo systems in this order because of limitations on the amount of compounds available and the throughput ability of the assay systems. While these in vitro assays are very effective tools for detecting particular tissue-specific toxicity phenotypes, it is difficult to detect toxicity based on complex mechanisms involving multiple organs and tissues. Therefore, the development of novel high throughput in vivo evaluation systems has been expected for a long time. The zebrafish (Danio rerio) is a vertebrate with many attractive characteristics for use in drug discovery, such as a small size, transparency, gene and protein similarity with mammals (80% or more), and ease of genetic modification to establish human disease models. Actually, in recent years, the zebrafish has attracted interest as a novel experimental animal. In this article, the author summarized the features of zebrafish that make it a suitable laboratory animal, and introduced and discussed the applications of zebrafish to preclinical toxicity testing, including evaluations of teratogenicity, hepatotoxicity, and nephrotoxicity based on morphological findings, evaluation of cardiotoxicity using functional endpoints, and assessment of seizure and drug abuse liability.

Translational Toxicology in Zebrafish

A major goal of translational toxicology is to identify adverse chemical effects and determine whether they are conserved or divergent across experimental systems. Translational toxicology encompasses assessment of chemical toxicity across multiple life stages, determination of toxic mode-of-action, computational prediction modeling, and identification of interventions that protect or restore health following toxic chemical exposures. The zebrafish is increasingly used in translational toxicology because it combines the genetic and physiological advantages of mammalian models with the higher-throughput capabilities and genetic manipulability of invertebrate models. Here, we review recent literature demonstrating the power of the zebrafish as a model for addressing all four activities of translational toxicology. Important data gaps and challenges associated with using zebrafish for translational toxicology are also discussed.