Discovering novel neuroactive drugs through high-throughput behavior-based chemical screening in the zebrafish

Effects of embryonic exposure to polychlorinated biphenyls (PCBs) on anxiety-related behaviors in larval zebrafish

The zebrafish (Danio rerio) is an excellent model system for assessing the effects of toxicant exposure on behavior and neurodevelopment. In the present study, we examined the effects of sub-chronic embryonic exposure to polychlorinated biphenyls (PCBs), a ubiquitous anthropogenic pollutant, on anxiety-related behaviors. We found that exposure to the PCB mixture, Aroclor (A) 1254, from 2 to 26h post-fertilization (hpf) induced two statistically significant behavioral defects in larvae at 7 days post-fertilization (dpf). First, during 135min of free swimming, larvae that had been exposed to 2ppm, 5ppm or 10ppm A1254 exhibited enhanced thigmotaxis (edge preference) relative to control larvae. Second, during the immediately ensuing 15-min visual startle assay, the 5ppm and 10ppm PCB-exposed larvae reacted differently to a visual threat, a red 'bouncing' disk, relative to control larvae. These results are consistent with the anxiogenic and attention-disrupting effects of PCB exposure documented in children, monkeys and rodents and merit further investigation.

Effects of embryonic exposure to polychlorinated biphenyls (PCBs) on larval zebrafish behavior

Developmental disorders such as anxiety, autism, and attention deficit hyperactivity disorders have been linked to exposure to polychlorinated biphenyls (PCBs), a ubiquitous anthropogenic pollutant. The zebrafish is widely recognized as an excellent model system for assessing the effects of toxicant exposure on behavior and neurodevelopment. In the present study, we examined the effect of sub-chronic embryonic exposure to the PCB mixture, Aroclor (A) 1254 on anxiety-related behaviors in zebrafish larvae at 7 days post-fertilization (dpf). We found that exposure to low concentrations of A1254, from 2 to 26 h post-fertilization (hpf) induced specific behavioral defects in two assays. In one assay with intermittent presentations of a moving visual stimulus, 5 ppm and 10 ppm PCB-exposed larvae displayed decreased avoidance behavior but no significant differences in thigmotaxis or freezing relative to controls. In the other assay with intermittent presentations of a moving visual stimulus and a stationary visual stimulus, 5 ppm and 10 ppm PCB-exposed larvae had elevated baseline levels of thigmotaxis but no significant differences in avoidance behavior relative to controls. The 5 ppm larvae also displayed higher terminal levels of freezing relative to controls. Collectively, our results show that exposure to ecologically valid PCB concentrations during embryonic development can induce functional deficits and alter behavioral responses to a visual threat.

A high-throughput method for predicting drug effects on gut transit time using larval zebrafish

INTRODUCTION

Zebrafish are an attractive vertebrate model due to their small size, transparency through organogenesis, and high fecundity. The zebrafish gastrointestinal (GI) tract is similar to the mammalian GI tract in gene expression, nervous system control, and response to chemical challenges. GI intolerance is a common preclinical finding and can be a serious clinical safety concern. Mammalian GI liability tests are conducted at the expense of time, test article, and labor. We developed a high-throughput method to predict mammalian GI safety issues using larval zebrafish.

METHODS

Fluorescent food is fed to larval zebrafish (7 days post fertilization). After feeding, larvae are placed individually into wells of a 96-well plate and dosed with test compounds. Fluorescence is measured from the bottom of the wells repeatedly over the course of 24h and thus fecal accumulation is tracked over time. The area under the curve is compared between treated and vehicle-treated groups.

RESULTS

Drugs with established clinical GI effects significantly impacted zebrafish GI transit time as measured by this method; tegaserod and metoclopramide accelerated transit time, while atropine and amitriptyline slowed transit time. This method is sensitive enough to reflect dose-level associated effects as demonstrated using atropine. Using a suite of 24 compounds with known (positive or negative) mammalian GI effects, we characterized this method as having a high positive predictive value.

DISCUSSION

Here we present an efficient assay for predicting mammalian GI transit liabilities using larval zebrafish. With this assay, an investigator can evaluate dozens of compounds in a single day using very little amount of each test article. As such, safe drug candidates can be prioritized for mammalian testing, which expedites the discovery process and provides 3 Rs impact.

AMP/GMP Analogs as Affinity ESIPT Probes for Highly Selective Sensing of Alkaline Phosphatase Activity in Living Systems

Current probes for alkaline phosphatase (ALP) detection had been developed mainly by adding a phosphate group to a dye, which would lead to indistinct performance when implemented in a living system as several phosphatases exist together. In this study, the nucleotides adenosine monophosphate (AMP) and guanosine monophosphate (GMP) were introduced into 2'-(2'-hydroxyphenyl)-benzothiazole-based probes, and highly fluorescent turn-on probes with good selectivity towards ALP over several phosphatases, as well as high affinity and low toxicity were obtained. In the presence of L-phenylalanine, an ALP inhibitor, a strong decrease in fluorescence recovery was observed. These probes allowed for real-time imaging of endogenous ALP activity in living cells as well as in a zebrafish model.

Methods for studying the zebrafish brain: past, present and future

The zebrafish (Danio rerio) is one of the most promising new model organisms. The increasing popularity of this amazing small vertebrate is evident from the exponentially growing numbers of research articles, funded projects and new discoveries associated with the use of zebrafish for studying development, brain function, human diseases and screening for new drugs. Thanks to the development of novel technologies, the range of zebrafish research is constantly expanding with new tools synergistically enhancing traditional techniques. In this review we will highlight the past and present techniques which have made, and continue to make, zebrafish an attractive model organism for various fields of biology, with a specific focus on neuroscience.

Paeonolum protects against MPP(+)-induced neurotoxicity in zebrafish and PC12 cells

Background

Parkinson’s disease (PD) is the second most common neurodegenerative disease, affecting 2% of the population aged over 65 years old. Mitochondrial defects and oxidative stress actively participate in degeneration of dopaminergic (DA) neurons in PD. Paeonolum, a main component isolated from Moutan cortex, has potent antioxidant ability. Here, we have examined the effects of paeonolum against MPP⁺-induced neurotoxicity in zebrafish and PC12 cells.

Methods

The overall viability and neurodegeneration of DA neurons was assessed in ETvmat2:green fluorescent protein (GFP) transgenic zebrafish, in which most monoaminergic neurons are labeled by GFP. Damage to PC12 cells was measured using a cell viability assay and assessment of nuclear morphology. Intracellular reactive oxygen species (ROS) and the level of total GSH were assessed. The mitochondrial cell death pathway including mitochondrial membrane potential, cytochrome C release and caspase-3 activity were also examined in PC12 cells.

Results

Paeonolum protected against MPP⁺-induced DA neurodegeneration and locomotor dysfunction in zebrafish in a concentration-dependent manner. Similar neuroprotection was replicated in the PC12 cellular model of MPP⁺ toxicity. Paeonolum attenuated MPP⁺-induced intracellular ROS accumulation and restored the level of total GSH in PC12 cells. Furthermore, paeonolum significantly inhibited the mitochondrial cell death pathway induced by MPP⁺.

Conclusions

Collectively, the present study demonstrates that paeonolum protects zebrafish and PC12 cells against MPP⁺-induced neurotoxicity.

Benzodiazepines alter nucleotide and nucleoside hydrolysis in zebrafish (Danio rerio) brain

Anxiety is characterized by unpleasant bodily sensations, such as pounding heart and intense fear. The therapy involves the administration of benzodiazepine drugs. Purinergic signaling participates in the induction of several behavioral patterns and their actions are inactivated by ectonucleotidases and adenosine deaminase (ADA). Since there is evidence about the involvement of purinergic system in the actions mediated by benzodiazepines, we evaluated the effects in vitro and in vivo of administration of diazepam and midazolam on nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, and ADA activities in zebrafish brain, followed by the analysis of gene expression pattern of these enzymes and adenosine receptors (A1, A2a1, A2a2, A2b). The in vitro studies demonstrated that diazepam decreased ATP (66 % for 500 µM) and ADP hydrolysis (40-54 % for 10-500 µM, respectively). Midazolam decreased ATP (16-71 % for 10-500 µM, respectively) and ADP (48-73.5 % for 250-500 µM, respectively) hydrolysis as well as the ecto-ADA activity (26-27.5 % for 10-500 µM, respectively). AMP hydrolysis was decreased in animals treated with of 0.5 and 1 mg/L midazolam (32 and 36 %, respectively). Diazepam and midazolam decreased the ecto-ADA activity at 1.25 mg/L and 1 mg/L (31 and 33 %, respectively), but only 0.1 mg/L midazolam induced an increase (40 %) in cytosolic ADA. The gene expression analysis demonstrated changes on ecto-5'-nucleotidase, A1, A2a1, A2a2, and A2b mRNA transcript levels after acute treatment with benzodiazepines. These findings demonstrated that benzodiazepine exposure induces a modulation of extracellular nucleotide and nucleoside metabolism, suggesting the purinergic signaling may be, at least in part, related to benzodiazepine effects.

Developing highER-throughput zebrafish screens for in-vivo CNS drug discovery

The high prevalence of brain disorders and the lack of their efficient treatments necessitate improved in-vivo pre-clinical models and tests. The zebrafish (Danio rerio), a vertebrate species with high genetic and physiological homology to humans, is an excellent organism for innovative central nervous system (CNS) drug discovery and small molecule screening. Here, we outline new strategies for developing higher-throughput zebrafish screens to test neuroactive drugs and predict their pharmacological mechanisms. With the growing application of automated 3D phenotyping, machine learning algorithms, movement pattern- and behavior recognition, and multi-animal video-tracking, zebrafish screens are expected to markedly improve CNS drug discovery.

Aquatic toxicology of fluoxetine: understanding the knowns and the unknowns

Fluoxetine is one of the most prescribed psychotropic medications, and is an agent of increasing interest for environmental toxicology. Fish and other aquatic organisms are excellent models to study neuroactive small molecules like fluoxetine. However, prone to variance due to experimental factors, data obtained in these models need to be interpreted with caution, using proper experimental protocols, study designs, validated endpoints as well as well-established models and tests. Choosing the treatment protocol and dose range for fluoxetine and other serotonergic drugs is critical for obtaining valid test results and correct data interpretation. Here we discuss the value of aquatic models to study fluoxetine effects, based on prior high-quality research, and outline the directions of future translational studies in the field. We review fluoxetine-evoked phenotypes in acute vs. chronic protocols, discussing them in the contact of complex role of serotonin in behavioral regulation. We conclude that zebrafish and other aquatic models represent a useful in-vivo tool for fluoxetine pharmacology and (eco)toxicology research.

Toxins and drug discovery

Components from venoms have stimulated many drug discovery projects, with some notable successes. These are briefly reviewed, from captopril to ziconotide. However, there have been many more disappointments on the road from toxin discovery to approval of a new medicine. Drug discovery and development is an inherently risky business, and the main causes of failure during development programmes are outlined in order to highlight steps that might be taken to increase the chances of success with toxin-based drug discovery. These include having a clear focus on unmet therapeutic needs, concentrating on targets that are well-validated in terms of their relevance to the disease in question, making use of phenotypic screening rather than molecular-based assays, and working with development partners with the resources required for the long and expensive development process.