Pharmacokinetics in Zebrafish Embryos (ZFE) Following Immersion and Intrayolk Administration: A Fluorescence-Based Analysis.

Zebrafish embryos (ZFE) have increasingly gained in popularity as a model to perform safety screenings of compounds. Although immersion of ZFE is the main route of exposure used, evidence shows that not all small molecules are equally absorbed, possibly resulting in false-negative readouts and incorrect conclusions. In this study, we compared the pharmacokinetics of seven fluorescent compounds with known physicochemical properties that were administered to two-cell stage embryos by immersion or by IY microinjection. Absorption and distribution of the dyes were followed at various timepoints up to 120 hpf by spatiotemporal fluorescence imaging. The concentration (10 µM) and dose (2 mg/kg) used were selected as quantities typically applied in preclinical experiments and zebrafish studies. The data show that in the case of a lipophilic compound (log D: 1.73) the immersion procedure resulted in an intrabody exposure which is similar or higher than that seen after the IY microinjection. In contrast, zero to low intrabody exposure was reached after immersion of the embryos with less lipophilic compounds. In the latter case IY microinjection, a technical procedure that can be easily automated, is highly recommended.

Pre-validation of choriogenin H transgenic medaka eleutheroembryos as a quantitative estrogenic activity test method.

The choriogenin H - EGFP transgenic medaka (Oryzias melastigma) has been used to test estrogenic substances and quantify estrogenic activity into 17ß-estradiol (E2) equivalency (EEQ). The method uses 8 eleutheroembryos in 2 ml solution per well and 3 wells per treatment in 24-well plates at 26 ± 1 °C for 24 ± 2 h, with subsequent measurements of induced GFP signal intensity. EEQ measurements are calculated using a E2 probit regression model with a coefficient of determination (R2) > 0.90. The selectivity was confirmed evaluating 27 known estrogenic and 5 known non-estrogenic compounds. Limit of quantitation (LOQ), recovery rate and bias were calculated to be 1 ng/ml EEQ, 104% and 4% respectively. Robustness analysis revealed exposure temperature is a sensitive parameter that should be kept at 26 ± 1 °C. The repeatability of intra- and inter-laboratories achieved CV < 30% for most tested food and cosmetics samples. The lot-lot stability was confirmed by the stable EEQ qualitative control (QC, 1 ng/mL E2) and calibration curve results. The stability of standard reagents, samples and sample extracts was also investigated. These data demonstrated this method to be an accurate indicator of estrogenic activity for both chemicals and extracts.

Spatiotemporal imaging and pharmacokinetics of fluorescent compounds in zebrafish eleuthero-embryos after different routes of administration.

Zebrafish (Danio rerio) is increasingly used to assess the pharmacological activity and toxicity of compounds. The spatiotemporal distribution of seven fluorescent alkyne compounds was examined during 48 h after immersion (10 µM) or microinjection (2 mg/kg) in the pericardial cavity (PC), intraperitoneally (IP) and yolk sac (IY) of 3 dpf zebrafish eleuthero-embryos. By modelling the fluorescence of whole-body contours present in fluorescence images, the main pharmacokinetic (PK) parameter values of the compounds were determined. It was demonstrated that especially in case of short incubations (1-3 h) immersion can result in limited intrabody exposure to compounds. In this case, PC and IP microinjections represent excellent alternatives. Significantly, IY microinjections did not result in a suitable intrabody distribution of the compounds. Performing a QSPkR (quantitative structure-pharmacokinetic relationship) analysis, LogD was identified as the only molecular descriptor that explains the final uptake of the selected compounds. It was also shown that combined administration of compounds (immersion and microinjection) provides a more stable intrabody exposure, at least in case of a prolonged immersion and compounds with LogD value > 1. These results will help reduce the risk of false negative results and can offer an invaluable input for future translational research and safety assessment applications.

Infection of zebrafish larvae with human norovirus and evaluation of the in vivo efficacy of small-molecule inhibitors.

We have recently established that human norovirus (HuNoV) replicates efficiently in zebrafish larvae after inoculation of a clinical sample into the yolk, providing a simple and robust in vivo system in which to study HuNoV. In this Protocol Extension, we present a detailed description of virus inoculation by microinjection, subsequent daily monitoring and harvesting of larvae, followed by viral RNA quantification. This protocol can be used to study viral replication of genogroup (G)I and GII HuNoVs in vivo within 3-4 d. Additionally, we describe how to evaluate the in vivo antiviral effect and toxicity of small molecules using HuNoV-infected zebrafish larvae, in multi-well plates and without the need for specific formulations. This constitutes a great advantage for drug discovery efforts, as no specific antivirals or vaccines currently exist to treat or prevent norovirus gastroenteritis.

Nephrotoxic Effects in Zebrafish after Prolonged Exposure to Aristolochic Acid.

With the aim to explore the possibility to generate a zebrafish model of renal fibrosis, in this study the fibrogenic renal effect of aristolochic acid I (AAI) after immersion was assessed. This compound is highly nephrotoxic able to elicit renal fibrosis after exposure of rats and humans. Our results reveal that larval zebrafish at 15 days dpf (days post-fertilization) exposed for 8 days to 0.5 µM AAI showed clear signs of AKI (acute kidney injury). The damage resulted in the relative loss of the functional glomerular filtration barrier. Conversely, we did not observe any deposition of collagen, nor could we immunodetect α-SMA, a hallmark of myofibroblasts, in the tubules. In addition, no increase in gene expression of fibrogenesis biomarkers after whole animal RNA extraction was found. As zebrafish have a high capability for tissue regeneration possibly impeding fibrogenic processes, we also used a tert-/- zebrafish line exhibiting telomerase deficiency and impaired tissue homeostasis. AAI-treated tert-/- larvae displayed an increased sensitivity towards 0.5 µM AAI. Importantly, after AAI treatment a mild collagen deposition could be found in the tubules. The outcome implies that sustained AKI induced by nephrotoxic compounds combined with defective tert-/- stem cells can produce a fibrotic response.

A robust human norovirus replication model in zebrafish larvae.

Human noroviruses (HuNoVs) are the most common cause of foodborne illness, with a societal cost of $60 billion and 219,000 deaths/year. The lack of robust small animal models has significantly hindered the understanding of norovirus biology and the development of effective therapeutics. Here we report that HuNoV GI and GII replicate to high titers in zebrafish (Danio rerio) larvae; replication peaks at day 2 post infection and is detectable for at least 6 days. The virus (HuNoV GII.4) could be passaged from larva to larva two consecutive times. HuNoV is detected in cells of the hematopoietic lineage and the intestine, supporting the notion of a dual tropism. Antiviral treatment reduces HuNoV replication by >2 log10, showing that this model is suited for antiviral studies. Zebrafish larvae constitute a simple and robust replication model that will largely facilitate studies of HuNoV biology and the development of antiviral strategies.

Safety Assessment of Compounds after In Vitro Metabolic Conversion Using Zebrafish Eleuthero Embryos.

Zebrafish-based platforms have recently emerged as a useful tool for toxicity testing as they combine the advantages of in vitro and in vivo methodologies. Nevertheless, the capacity to metabolically convert xenobiotics by zebrafish eleuthero embryos is supposedly low. To circumvent this concern, a comprehensive methodology was developed wherein test compounds (i.e., parathion, malathion and chloramphenicol) were first exposed in vitro to rat liver microsomes (RLM) for 1 h at 37 °C. After adding methanol, the mixture was ultrasonicated, placed for 2 h at -20 °C, centrifuged and the supernatant evaporated. The pellet was resuspended in water for the quantification of the metabolic conversion and the detection of the presence of metabolites using ultra high performance liquid chromatography-Ultraviolet-Mass (UHPLC-UV-MS). Next, three days post fertilization (dpf) zebrafish eleuthero embryos were exposed to the metabolic mix diluted in Danieau's medium for 48 h at 28 °C, followed by a stereomicroscopic examination of the adverse effects induced, if any. The novelty of our method relies in the possibility to quantify the rate of the in vitro metabolism of the parent compound and to co-incubate three dpf larvae and the diluted metabolic mix for 48 h without inducing major toxic effects. The results for parathion show an improved predictivity of the toxic potential of the compound.

Bioassay-guided isolation of anti-seizure principles from Semen Pharbitidis using a zebrafish pentylenetetrazol seizure model.

ETHNOPHARMACOLOGICAL RELEVANCE: Semen Pharbitidis, the seeds of Pharbitis nil (Linn.) Choisy (Convolvulaceae) is a well-known traditional Chinese medicinal plant used for treating helminthiasis and epilepsy in China. AIM OF THE STUDY: This study aims to identify the anti-seizure components from Semen Pharbitidis. METHODS: A bioassay-guided isolation of anti-seizure compounds from Semen Pharbitidis was performed using a zebrafish pentylenetetrazol seizure model. The structures of active compounds were elucidated by high resolution mass spectrometry. The fragments of active compounds were tested for anti-seizure activity as well. RESULTS: The bioassay-guided isolation of ethanol extract of Semen Pharbitidis led to a group of resin glucosides, namely pharbitin. One of the fragments of pharbitin, 2-methylbutyric acid, also showed anti-seizure activity. CONCLUSIONS: We provided further experimental scientific evidence to support the traditional use of Semen Pharbitidis for the treatment of epilepsy. Pharbitin was identified to be the main anti-seizure component in Semen Pharbitidis.

Methylated flavonoids as anti-seizure agents: Naringenin 4',7-dimethyl ether attenuates epileptic seizures in zebrafish and mouse models.

Epilepsy is a neurological disease that affects more than 70 million people worldwide and is characterized by the presence of spontaneous unprovoked recurrent seizures. Existing anti-seizure drugs (ASDs) have side effects and fail to control seizures in 30% of patients due to drug resistance. Hence, safer and more efficacious drugs are sorely needed. Flavonoids are polyphenolic structures naturally present in most plants and consumed daily with no adverse effects reported. These structures have shown activity in several seizure and epilepsy animal models through allosteric modulation of GABAA receptors, but also via potent anti-inflammatory action in the brain. As such, dietary flavonoids offer an interesting source for ASD and anti-epileptogenic drug (AED) discovery, but their pharmaceutical potential is often hampered by metabolic instability and low oral bioavailability. It has been argued that their drug-likeness can be improved via methylation of the free hydroxyl groups, thereby dramatically enhancing metabolic stability and membrane transport, facilitating absorption and highly increasing bioavailability. Since no scientific data is available regarding the use of methylated flavonoids in the fight against epilepsy, we studied naringenin (NRG), kaempferol (KFL), and three methylated derivatives, i.e., naringenin 7-O-methyl ether (NRG-M), naringenin 4',7-dimethyl ether (NRG-DM), and kaempferide (4'-O-methyl kaempferol) (KFD) in the zebrafish pentylenetetrazole (PTZ) seizure model. We demonstrate that the methylated flavanones NRG-DM and NRG-M are highly effective against PTZ-induced seizures in larval zebrafish, whereas NRG and the flavonols KFL and KFD possess only a limited activity. Moreover, we show that NRG-DM is active in two standard acute mouse seizure models, i.e., the timed i.v. PTZ seizure model and the 6-Hz psychomotor seizure model. Based on these results, NRG-DM is proposed as a lead compound that is worth further investigation for the treatment of generalized seizures and drug-resistant focal seizures. Our data therefore highlights the potential of methylated flavonoids in the search for new and improved ASDs.

Inhibition of glutamate decarboxylase (GAD) by ethyl ketopentenoate (EKP) induces treatment-resistant epileptic seizures in zebrafish.

Epilepsy is a chronic brain disorder characterized by recurrent seizures due to abnormal, excessive and synchronous neuronal activities in the brain. It affects approximately 65 million people worldwide, one third of which are still estimated to suffer from refractory seizures. Glutamic acid decarboxylase (GAD) that converts glutamate into GABA is a key enzyme in the dynamic regulation of neural network excitability. Importantly, clinical evidence shows that lowered GAD activity is associated with several forms of epilepsy which are often treatment resistant. In the present study, we synthetized and explored the possibility of using ethyl ketopentenoate (EKP), a lipid-permeable GAD-inhibitor, to induce refractory seizures in zebrafish larvae. Our results demonstrate that EKP evoked robust convulsive locomotor activities, excessive epileptiform discharges and upregulated c-fos expression in zebrafish. Moreover, transgenic animals in which neuronal cells express apoaequorin, a Ca2+-sensitive bioluminescent photoprotein, displayed large luminescence signals indicating strong EKP-induced neuronal activation. Molecular docking data indicated that this proconvulsant activity resulted from the direct inhibition of both gad67 and gad65. Limited protective efficacy of tested anti-seizure drugs (ASDs) demonstrated a high level of treatment resistance of EKP-induced seizures. We conclude that the EKP zebrafish model can serve as a high-throughput platform for novel ASDs discovery.

Cystinosis (ctns) zebrafish mutant shows pronephric glomerular and tubular dysfunction.

The human ubiquitous protein cystinosin is responsible for transporting the disulphide amino acid cystine from the lysosomal compartment into the cytosol. In humans, Pathogenic mutations of CTNS lead to defective cystinosin function, intralysosomal cystine accumulation and the development of cystinosis. Kidneys are initially affected with generalized proximal tubular dysfunction (renal Fanconi syndrome), then the disease rapidly affects glomeruli and progresses towards end stage renal failure and multiple organ dysfunction. Animal models of cystinosis are limited, with only a Ctns knockout mouse reported, showing cystine accumulation and late signs of tubular dysfunction but lacking the glomerular phenotype. We established and characterized a mutant zebrafish model with a homozygous nonsense mutation (c.706 C > T; p.Q236X) in exon 8 of ctns. Cystinotic mutant larvae showed cystine accumulation, delayed development, and signs of pronephric glomerular and tubular dysfunction mimicking the early phenotype of human cystinotic patients. Furthermore, cystinotic larvae showed a significantly increased rate of apoptosis that could be ameliorated with cysteamine, the human cystine depleting therapy. Our data demonstrate that, ctns gene is essential for zebrafish pronephric podocyte and proximal tubular function and that the ctns-mutant can be used for studying the disease pathogenic mechanisms and for testing novel therapies for cystinosis.

Cell Imaging Counting as a Novel Ex Vivo Approach for Investigating Drug-Induced Hepatotoxicity in Zebrafish Larvae.

Drug-induced liver injury (DILI) is the most common reason for failures during the drug development process and for safety-related withdrawal of drugs from the pharmaceutical market. Therefore, having tools and techniques that can detect hepatotoxic properties in drug candidates at an early discovery stage is highly desirable. In this study, cell imaging counting was used to measure in a fast, straightforward, and unbiased way the effect of paracetamol and tetracycline, (compounds known to cause hepatotoxicity in humans) on the amount of DsRed-labeled hepatocytes recovered by protease digestion from Tg(fabp10a:DsRed) transgenic zebrafish. The outcome was in general comparable with the results obtained using two reference methods, i.e., visual analysis of liver morphology by fluorescence microscopy and size analysis of fluorescent 2D liver images. In addition, our study shows that administering compounds into the yolk is relevant in the framework of hepatotoxicity testing. Taken together, cell imaging counting provides a novel and rapid tool for screening hepatotoxicants in early stages of drug development. This method is also suitable for testing of other organ-related toxicities subject to the organs and tissues expressing fluorescent proteins in transgenic zebrafish lines.

Use of Zebrafish Larvae as a Multi-Endpoint Platform to Characterize the Toxicity Profile of Silica Nanoparticles.

Nanomaterials are being extensively produced and applied in society. Human and environmental exposures are, therefore, inevitable and so increased attention is being given to nanotoxicity. While silica nanoparticles (NP) are one of the top five nanomaterials found in consumer and biomedical products, their toxicity profile is poorly characterized. In this study, we investigated the toxicity of silica nanoparticles with diameters 20, 50 and 80 nm using an in vivo zebrafish platform that analyzes multiple endpoints related to developmental, cardio-, hepato-, and neurotoxicity. Results show that except for an acceleration in hatching time and alterations in the behavior of zebrafish embryos/larvae, silica NPs did not elicit any developmental defects, nor any cardio- and hepatotoxicity. The behavioral alterations were consistent for both embryonic photomotor and larval locomotor response and were dependent on the concentration and the size of silica NPs. As embryos and larvae exhibited a normal touch response and early hatching did not affect larval locomotor response, the behavior changes observed are most likely the consequence of modified neuroactivity. Overall, our results suggest that silica NPs do not cause any developmental, cardio- or hepatotoxicity, but they pose a potential risk for the neurobehavioral system.

A transgenic Xenopus laevis reporter model to study lymphangiogenesis.

The importance of the blood- and lymph vessels in the transport of essential fluids, gases, macromolecules and cells in vertebrates warrants optimal insight into the regulatory mechanisms underlying their development. Mouse and zebrafish models of lymphatic development are instrumental for gene discovery and gene characterization but are challenging for certain aspects, e.g. no direct accessibility of embryonic stages, or non-straightforward visualization of early lymphatic sprouting, respectively. We previously demonstrated that the Xenopus tadpole is a valuable model to study the processes of lymphatic development. However, a fluorescent Xenopus reporter directly visualizing the lymph vessels was lacking. Here, we created transgenic Tg(Flk1:eGFP) Xenopus laevis reporter lines expressing green fluorescent protein (GFP) in blood- and lymph vessels driven by the Flk1 (VEGFR-2) promoter. We also established a high-resolution fluorescent dye labeling technique selectively and persistently visualizing lymphatic endothelial cells, even in conditions of impaired lymph vessel formation or drainage function upon silencing of lymphangiogenic factors. Next, we applied the model to dynamically document blood and lymphatic sprouting and patterning of the initially avascular tadpole fin. Furthermore, quantifiable models of spontaneous or induced lymphatic sprouting into the tadpole fin were developed for dynamic analysis of loss-of-function and gain-of-function phenotypes using pharmacologic or genetic manipulation. Together with angiography and lymphangiography to assess functionality, Tg(Flk1:eGFP) reporter tadpoles readily allowed detailed lymphatic phenotyping of live tadpoles by fluorescence microscopy. The Tg(Flk1:eGFP) tadpoles represent a versatile model for functional lymph/angiogenomics and drug screening.

Inhibition of tumor angiogenesis and growth by a small-molecule multi-FGF receptor blocker with allosteric properties.

Receptor tyrosine kinases (RTK) are targets for anticancer drug development. To date, only RTK inhibitors that block orthosteric binding of ligands and substrates have been developed. Here, we report the pharmacologic characterization of the chemical SSR128129E (SSR), which inhibits fibroblast growth factor receptor (FGFR) signaling by binding to the extracellular FGFR domain without affecting orthosteric FGF binding. SSR exhibits allosteric properties, including probe dependence, signaling bias, and ceiling effects. Inhibition by SSR is highly conserved throughout the animal kingdom. Oral delivery of SSR inhibits arthritis and tumors that are relatively refractory to anti-vascular endothelial growth factor receptor-2 antibodies. Thus, orally-active extracellularly acting small-molecule modulators of RTKs with allosteric properties can be developed and may offer opportunities to improve anticancer treatment.

Role of synectin in lymphatic development in zebrafish and frogs.

The molecular basis of lymphangiogenesis remains incompletely characterized. Here, we document a novel role for the PDZ domain-containing scaffold protein synectin in lymphangiogenesis using genetic studies in zebrafish and tadpoles. In zebrafish, the thoracic duct arises from parachordal lymphangioblast cells, which in turn derive from secondary lymphangiogenic sprouts from the posterior cardinal vein. Morpholino knockdown of synectin in zebrafish impaired formation of the thoracic duct, due to selective defects in lymphangiogenic but not angiogenic sprouting. Synectin genetically interacted with Vegfr3 and neuropilin-2a in regulating lymphangiogenesis. Silencing of synectin in tadpoles caused lymphatic defects due to an underdevelopment and impaired migration of Prox-1(+) lymphatic endothelial cells. Molecular analysis further revealed that synectin regulated Sox18-induced expression of Prox-1 and vascular endothelial growth factor C-induced migration of lymphatic endothelial cells in vitro. These findings reveal a novel role for synectin in lymphatic development.

Role of delta-like-4/Notch in the formation and wiring of the lymphatic network in zebrafish.

OBJECTIVE: To study whether Notch signaling, which regulates cell fate decisions and vessel morphogenesis, controls lymphatic development. METHODS AND RESULTS: In zebrafish embryos, sprouts from the axial vein have lymphangiogenic potential because they give rise to the first lymphatics. Knockdown of delta-like-4 (Dll4) or its receptors Notch-1b or Notch-6 in zebrafish impaired lymphangiogenesis. Dll4/Notch silencing reduced the number of sprouts producing the string of parchordal lymphangioblasts; instead, sprouts connecting to the intersomitic vessels were formed. At a later phase, Notch silencing impaired navigation of lymphatic intersomitic vessels along their arterial templates. CONCLUSIONS: These studies imply critical roles for Notch signaling in the formation and wiring of the lymphatic network.

Claudin-like protein 24 interacts with the VEGFR-2 and VEGFR-3 pathways and regulates lymphatic vessel development.

The Claudin-like protein of 24 kDa (CLP24) is a hypoxia-regulated transmembrane protein of unknown function. We show here that clp24 knockdown in Danio rerio and Xenopus laevis results in defective lymphatic development. Targeted disruption of Clp24 in mice led to enlarged lymphatic vessels having an abnormal smooth muscle cell coating. We also show that the Clp24(-/-) phenotype was further aggravated in the Vegfr2(+/LacZ) or Vegfr3(+/LacZ) backgrounds and that CLP24 interacts with vascular endothelial growth factor receptor-2 (VEGFR-2) and VEGFR-3 and attenuates the transcription factor CREB phosphorylation via these receptors. Our results indicate that CLP24 is a novel regulator of VEGFR-2 and VEGFR-3 signaling pathways and of normal lymphatic vessel structure.

Liprin (beta)1 is highly expressed in lymphatic vasculature and is important for lymphatic vessel integrity.

The lymphatic vasculature is important for the regulation of tissue fluid homeostasis, immune response, and lipid absorption, and the development of in vitro models should allow for a better understanding of the mechanisms regulating lymphatic vascular growth, repair, and function. Here we report isolation and characterization of lymphatic endothelial cells from human intestine and show that intestinal lymphatic endothelial cells have a related but distinct gene expression profile from human dermal lymphatic endothelial cells. Furthermore, we identify liprin beta1, a member of the family of LAR transmembrane tyrosine phosphatase-interacting proteins, as highly expressed in intestinal lymphatic endothelial cells in vitro and lymphatic vasculature in vivo, and show that it plays an important role in the maintenance of lymphatic vessel integrity in Xenopus tadpoles.

Endothelial cell O-glycan deficiency causes blood/lymphatic misconnections and consequent fatty liver disease in mice.

Mucin-type O-glycans (O-glycans) are highly expressed in vascular ECs. However, it is not known whether they are important for vascular development. To investigate the roles of EC O-glycans, we generated mice lacking T-synthase, a glycosyltransferase encoded by the gene C1galt1 that is critical for the biosynthesis of core 1-derived O-glycans, in ECs and hematopoietic cells (termed here EHC T-syn(-/-) mice). EHC T-syn(-/-) mice exhibited embryonic and neonatal lethality associated with disorganized and blood-filled lymphatic vessels. Bone marrow transplantation and EC C1galt1 transgene rescue demonstrated that lymphangiogenesis specifically requires EC O-glycans, and intestinal lymphatic microvessels in EHC T-syn(-/-) mice expressed a mosaic of blood and lymphatic EC markers. The level of O-glycoprotein podoplanin was significantly reduced in EHC T-syn(-/-) lymphatics, and podoplanin-deficient mice developed blood-filled lymphatics resembling EHC T-syn(-/-) defects. In addition, postnatal inactivation of C1galt1 caused blood/lymphatic vessel misconnections that were similar to the vascular defects in the EHC T-syn(-/-) mice. One consequence of eliminating T-synthase in ECs and hematopoietic cells was that the EHC T-syn(-/-) pups developed fatty liver disease, because of direct chylomicron deposition via misconnected portal vein and intestinal lymphatic systems. Our studies therefore demonstrate that EC O-glycans control the separation of blood and lymphatic vessels during embryonic and postnatal development, in part by regulating podoplanin expression.