Accumulation and metabolism of drugs and CYP probe substrates in zebrafish larvae

Investigation on the mechanism of hepatotoxicity of dictamnine on juvenile zebrafish by integrating metabolomics and transcriptomics

Dictamnine(DIC), as the key pharmacological component of the classical Chinese herbal medicine cortex dictamni, possesses multiple pharmacological activities such as anti-microbial, anti-allergic, anti-cancer, and anti-inflammatory activities, however it is also the main toxicant of cortex dictamni induced hepatic damage, yet the underlying molecular mechanisms causing hepatic damage are still largely unknown. With the purpose of explore possibilities hepatotoxicity of dictamnine in zebrafish and to identify the key regulators and metabolites involved in the biological process, we administered zebrafish to dictamnine at a sub-lethal dose ( Collapse

Key Words

• Dictamnine
• Hepatotoxicity
• Metabolomics
• Transcriptome sequencing
• Zebrafish

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MESH Headings

• Animals
• Zebrafish/genetics
• Chemical and Drug Induced Liver Injury/genetics
• Chemical and Drug Induced Liver Injury/metabolism
• Metabolomics/methods
• Liver/drug effects
• Liver/metabolism
• Liver/pathology
• Transcriptome/drug effects
• Gene Expression Profiling/methods
• Drugs, Chinese Herbal/toxicity
• Apoptosis/drug effects

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Affiliation(s)

Xiaomin Xu Institute of Traditional Chinese Medicine, Heilongjiang University of Chinese Medicine, Harbin 150040, Heilongjiang, China
Fang Lu Institute of Traditional Chinese Medicine, Heilongjiang University of Chinese Medicine, Harbin 150040, Heilongjiang, China
Yu Wang Institute of Traditional Chinese Medicine, Heilongjiang University of Chinese Medicine, Harbin 150040, Heilongjiang, China
Shumin Liu Institute of Traditional Chinese Medicine, Heilongjiang University of Chinese Medicine, Harbin 150040, Heilongjiang, China.

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Diving into drug-screening: zebrafish embryos as an in vivo platform for antimicrobial drug discovery and assessment

The rise of multidrug-resistant bacteria underlines the need for innovative treatments, yet the introduction of new drugs has stagnated despite numerous antimicrobial discoveries. A major hurdle is a poor correlation between promising in vitro data and in vivo efficacy in animal models, which is essential for clinical development. Early in vivo testing is hindered by the expense and complexity of existing animal models. Therefore, there is a pressing need for cost-effective, rapid preclinical models with high translational value. To overcome these challenges, zebrafish embryos have emerged as an attractive model for infectious disease studies, offering advantages such as ethical alignment, rapid development, ease of maintenance, and genetic manipulability. The zebrafish embryo infection model, involving microinjection or immersion of pathogens and potential antibiotic hit compounds, provides a promising solution for early-stage drug screening. It offers a cost-effective and rapid means of assessing the efficacy, toxicity and mechanism of action of compounds in a whole-organism context. This review discusses the experimental design of this model, but also its benefits and challenges. Additionally, it highlights recently identified compounds in the zebrafish embryo infection model and discusses the relevance of the model in predicting the compound's clinical potential.

Ethyl glucuronide and ethyl sulfate in the zebrafish after ethanol exposure

Ethanol exposure during pregnancy is an important problem and is the cause of fetal alcohol syndrome (FAS) and fetal alcohol spectrum disorder (FASD). The etiology of FAS and FASD can be elucidated using animal models. Recently, a novel model, the zebrafish (Danio rerio), has garnered the interest of researchers. This study confirmed the negative influence of ethyl alcohol (0.5 %, 1.5 %, and 2.5 % v/v) on the development of zebrafish embryos. The observed malformations included pericardial and yolk sac edema, increased body curvature, tail edema, and a decreased embryo hatching rate. The differences in body length, body width, and heart rate were statistically significant. Due to the similarities in the quantity and function of ethanol biotransformation enzymes between zebrafish and mammals, this study investigated the nonoxidative metabolites of ethanol - ethyl glucuronide (EtG) and ethyl sulfate (EtS) - in zebrafish following ethanol exposure. This research confirmed that EtG and EtS concentrations can be measured in zebrafish embryos, and the levels of these metabolites appear to be associated with the ethyl alcohol concentration in the medium.

Identification and pretreatment analysis of endogenous degradation products of patulin in zebrafish

Identification and pretreatment analysis of endogenous metabolites of patulin (PAT) in zebrafish were successfully carried out using UHPLC-Q-Orbitrap-HRMS. Three major metabolites, namely hydroascladiol, E-ascladiol, and Z-ascladiol, were identified. They exhibited similar fragmentation pathways to PAT, with the structurally significant ions *b' and *c' generated through the cleavage of the side chains of *b and *c, respectively. These ions were crucial for confirming the modification site and have been confirmed as characteristic fragments for the identification of PAT metabolites. Furthermore, a pretreatment method for analyzing PAT and the three metabolites in zebrafish was proposed, using solid-phase-assisted liquid/liquid extraction (SLLE) and matrix solid-phase dispersion (MSPD) techniques. The initial purification process involved loading the aqueous phase onto a macroporous diatomaceous column, followed by elution with acetonitrile. Following this, neutral alumina powder was added to the organic phase, effectively eliminating interference from hydrophilic and lipid-soluble compounds through the optimization of this step. Due to their structural similarity, the three metabolites were semi-quantitatively analyzed using a PAT standard curve. The results demonstrated a good linear relationship in the concentration range of 0.001-0.02 μg/mL (r2 ≥ 0.999). The limit of detection for PAT and the three metabolites ranged from 0.01 to 0.03 mg/kg.

Zebrafish as a Useful Model System for Human Liver Disease

Liver diseases represent a significant global health challenge, thereby necessitating extensive research to understand their intricate complexities and to develop effective treatments. In this context, zebrafish (Danio rerio) have emerged as a valuable model organism for studying various aspects of liver disease. The zebrafish liver has striking similarities to the human liver in terms of structure, function, and regenerative capacity. Researchers have successfully induced liver damage in zebrafish using chemical toxins, genetic manipulation, and other methods, thereby allowing the study of disease mechanisms and the progression of liver disease. Zebrafish embryos or larvae, with their transparency and rapid development, provide a unique opportunity for high-throughput drug screening and the identification of potential therapeutics. This review highlights how research on zebrafish has provided valuable insights into the pathological mechanisms of human liver disease.

Factors Determining the Susceptibility of Fish to Effects of Human Pharmaceuticals

The increasing levels and frequencies at which active pharmaceutical ingredients (APIs) are being detected in the environment are of significant concern, especially considering the potential adverse effects they may have on nontarget species such as fish. With many pharmaceuticals lacking environmental risk assessments, there is a need to better define and understand the potential risks that APIs and their biotransformation products pose to fish, while still minimizing the use of experimental animals. There are both extrinsic (environment- and drug-related) and intrinsic (fish-related) factors that make fish potentially vulnerable to the effects of human drugs, but which are not necessarily captured in nonfish tests. This critical review explores these factors, particularly focusing on the distinctive physiological processes in fish that underlie drug absorption, distribution, metabolism, excretion and toxicity (ADMET). Focal points include the impact of fish life stage and species on drug absorption (A) via multiple routes; the potential implications of fish's unique blood pH and plasma composition on the distribution (D) of drug molecules throughout the body; how fish's endothermic nature and the varied expression and activity of drug-metabolizing enzymes in their tissues may affect drug metabolism (M); and how their distinctive physiologies may impact the relative contribution of different excretory organs to the excretion (E) of APIs and metabolites. These discussions give insight into where existing data on drug properties, pharmacokinetics and pharmacodynamics from mammalian and clinical studies may or may not help to inform on environmental risks of APIs in fish.

Biotransformation, metabolic response, and toxicity of UV-234 and UV-326 in larval zebrafish (Danio rerio)

Benzotriazole ultraviolet stabilizers (BUVSs) are emerging pollutants that are widely detected in aquatic ecosystems. While structure-dependent effects of BUVSs are reported, the relationship between biotransformation and toxicity outcomes remains unclear. In this study, zebrafish embryos were exposed to two common BUVSs (UV-234 and UV-326) at 1, 10, and 100 µg/L for up to 7 days. Comparison of their uptake and biotransformation revealed that the bioaccumulation capacity of UV-234 was higher than that of UV-326, while UV-326 was more extensively biotransformed with additional conjugation reactions. However, UV-326 showed low metabolism due to inhibited phase II enzymes, which may result in the comparable internal concentrations of both BUVSs in larval zebrafish. Both BUVSs induced oxidative stress while decreased MDA, suggesting the disturbance of lipid metabolism. The subsequent metabolomic profiling revealed that UV-234 and UV-326 exerted different effects on arachidonic acid, lipid, and energy metabolism. However, both BUVSs negatively impacted the cyclic guanosine monophosphate / protein kinase G pathway. This converged metabolic change resulted in comparable toxicity of UV-234 and UV-326, which was confirmed by the induction of downstream apoptosis, neuroinflammation, and abnormal locomotion behavior. These data have important implications for understanding the metabolism, disposition, and toxicology of BUVSs in aquatic organisms.

Sustainable architecting of Co2SnO4/CE-BN-based electrochemical platform for highly selective and ultrasensitive detection of 2-nitroaniline in life samples

A novel binary heterogeneous electrocatalyst, Co2SnO4, decorated on chemically exfoliated boron nitride sheets (CE-BN) with an exceptional capacity to detect electrochemical properties has been prepared by the simple hydrothermal method. The structural, surface morphology and electrochemical characteristics of Co2SnO4/CE-BN were characterized using a range of physicochemical and electrochemical techniques. Various voltammetric approaches were used to observe the analytical behaviour and applications of Co2SnO4/CE-BN/GCE for the determination of 2-nitroaniline (2-NA). The whole experiment is operated in the potential range from 0 to - 1.0 V vs Ag/AgCl (sat. KCl). The impact of operational factors on the peak current of 2-NA was investigated, including the pH, sample concentration, modifier amount and scan speed. With an estimated differential pulse voltammetry detection limit of 0.0371 µM and excellent sensitivity of 1,35 µA µM-1 cm-2, the produced sensor, Co2SnO4/CE-BN/GCE, revealed high electrocatalytic activity (DPV). The system is more practical and sustainable due to its repeatability, stability and reproducibility with respect to the results achieved for detection of 2-NA. The synthesized Co2SnO4/CE-BN-modified sensor may thus be a likely choice for the detection of 2-NA in actual water sample analysis.

Environmentally relevant concentration of caffeine-effect on activity and circadian rhythm in wild perch

We studied the ecological consequences of widespread caffeine contamination by conducting an experiment focused on changes in the behavioral traits of wild perch (Perca fluviatilis) after waterborne exposure to 10 μg L^-1 of caffeine. We monitored fish swimming performance during both light and dark conditions to study the effect of caffeine on fish activity and circadian rhythm, using a novel three-dimensional tracking system that enabled positioning even in complete darkness. All individuals underwent three behavioral trials-before exposure, after 24 h of exposure, and after 5 days of exposure. We did not observe any effect of the given caffeine concentration on fish activity under light or dark conditions. Regardless of caffeine exposure, fish swimming performance was significantly affected by both the light-dark conditions and repeating of behavioral trials. Individuals in both treatments swam significantly more during the light condition and their activity increased with time as follows: before exposure < after 24 h of exposure < after 5 days of exposure. We confirmed that the three-dimensional automated tracking system based on infrared sensors was highly effective for conducting behavioral experiments under completely dark conditions.

Acetaminophen Disrupts the Development of Pharyngeal Arch-Derived Cartilage and Muscle in Zebrafish

Acetaminophen is a common analgesic, but its potential effects on early embryonic development are not well understood. Previous studies using zebrafish (Danio rerio) have described the effects of acetaminophen on liver development and physiology, and a few have described gross physiological and morphological defects. Using a high but non-embryonic lethal dose of acetaminophen, we probed for defects in zebrafish craniofacial cartilage development. Strikingly, acetaminophen treatment caused severe craniofacial cartilage defects, primarily affecting both the presence and morphology of pharyngeal arch-derived cartilages of the viscerocranium. Delaying acetaminophen treatment restored developing cartilages in an order correlated with their corresponding pharyngeal arches, suggesting that acetaminophen may target pharyngeal arch development. Craniofacial cartilages are derived from cranial neural crest cells; however, many neural crest cells were still seen along their expected migration paths, and most remaining cartilage precursors expressed the neural crest markers sox9a and sox10, then eventually col2a1 (type II collagen). Therefore, the defects are not primarily due to an early breakdown of neural crest or cartilage differentiation. Instead, apoptosis is increased around the developing pharyngeal arches prior to chondrogenesis, further suggesting that acetaminophen may target pharyngeal arch development. Many craniofacial muscles, which develop in close proximity to the affected cartilages, were also absent in treated larvae. Taken together, these results suggest that high amounts of acetaminophen can disrupt multiple aspects of craniofacial development in zebrafish.

Combined Metabolomics and Network Toxicology to Explore the Molecular Mechanism of Phytolacca acinose Roxb-Induced Hepatotoxicity in Zebrafish Larvae in Vivo

Phytolacca acinosa Roxb (PAR), a traditional Chinese medicine, has been widely used as a diuretic drug for a long period of time for the treatment edema, swelling, and sores. However, it has been reported that PAR might induce hepatotoxicity, while the mechanisms of its toxic effect are still unclear. In this study, network toxicology and metabolomic technique were applied to explore PAR-induced hepatotoxicity on zebrafish larvae. We evaluated the effect of PAR on the ultrastructure and the function of the liver, predictive targets, and pathways in network toxicology, apoptosis of liver cells by PCR and western blot, and metabolic profile by GC-MS. PAR causes liver injury, abnormal liver function, and apoptosis in zebrafish. The level of arachidonic acid in endogenous metabolites treated with PAR was significantly increased, leading to oxidative stress in vivo. Excessive ROS further activated the p53 signal pathway and caspase family, which were obtained from KEGG enrichment analysis of network toxicology. The gene levels of caspase-3, caspase-8, and caspase-9 were significantly increased by RT-PCR, and the level of Caps3 protein was also significantly up-regulated through western blot. PAR exposure results in the liver function abnormal amino acid metabolism disturbance and motivates hepatocyte apoptosis, furthermore leading to liver injury.

Developmental Toxicity and Biotransformation of Two Anti-Epileptics in Zebrafish Embryos and Early Larvae

The zebrafish (Danio rerio) embryo is gaining interest as a bridging tool between in-vitro and in-vivo developmental toxicity studies. However, cytochrome P450 (CYP)-mediated drug metabolism in this model is still under debate. Therefore, we investigated the potential of zebrafish embryos and larvae to bioactivate two known anti-epileptics, carbamazepine (CBZ) and phenytoin (PHE), to carbamazepine-10,11-epoxide (E-CBZ) and 5-(4-hydroxyphenyl)-5-phenylhydantoin (HPPH), respectively. First, zebrafish were exposed to CBZ, PHE, E-CBZ and HPPH from 5¼- to 120-h post fertilization (hpf) and morphologically evaluated. Second, the formations of E-CBZ and HPPH were assessed in culture medium and in whole-embryo extracts at different time points by targeted LC-MS. Finally, E-CBZ and HPPH formation was also assessed in adult zebrafish liver microsomes and compared with those of human, rat, and rabbit. The present study showed teratogenic effects for CBZ and PHE, but not for E-CBZ and HPPH. No HPPH was detected during organogenesis and E-CBZ was only formed at the end of organogenesis. E-CBZ and HPPH formation was also very low-to-negligible in adult zebrafish compared with the mammalian species. As such, other metabolic pathways than those of mammals are involved in the bioactivation of CBZ and PHE, or, these anti-epileptics are teratogens and do not require bioactivation in the zebrafish.

Cytochrome P450-dependent biotransformation capacities in embryonic, juvenile and adult stages of zebrafish (Danio rerio)-a state-of-the-art review

Given the strong trend to implement zebrafish (Danio rerio) embryos as translational model not only in ecotoxicological, but also toxicological testing strategies, there is an increasing need for a better understanding of their capacity for xenobiotic biotransformation. With respect to the extrapolation of toxicological data from zebrafish embryos to other life stages or even other organisms, qualitative and quantitative differences in biotransformation pathways, above all in cytochrome P450-dependent (CYP) phase I biotransformation, may lead to over- or underestimation of the hazard and risk certain xenobiotic compounds may pose to later developmental stages or other species. This review provides a comprehensive state-of-the-art overview of the scientific knowledge on the development of the CYP1-4 families and corresponding phase I biotransformation and bioactivation capacities in zebrafish. A total of 68 publications dealing with spatiotemporal CYP mRNA expression patterns, activities towards mammalian CYP-probe substrates, bioactivation and detoxification activities, as well as metabolite profiling were analyzed and included in this review. The main results allow for the following conclusions: (1) Extensive work has been done to document mRNA expression of CYP isoforms from earliest embryonic stages of zebrafish, but juvenile and adult zebrafish have been largely neglected so far. (2) There is insufficient understanding of how sex- and developmental stage-related differences in expression levels of certain CYP isoforms may impact biotransformation and bioactivation capacities in the respective sexes and in different developmental stages of zebrafish. (3) Albeit qualitatively often identical, many studies revealed quantitative differences in metabolic activities of zebrafish embryos and later developmental stages. However, the actual relevance of age-related differences on the outcome of toxicological studies still needs to be clarified. (4) With respect to current remaining gaps, there is still an urgent need for further studies systematically assessing metabolic profiles and capacities of CYP isoforms in zebrafish. Given the increasing importance of Adverse Outcome Pathway (AOP) concepts, an improved understanding of CYP capacities appears essential for the interpretation and outcome of (eco)toxicological studies.

Pharmaceutical Assessment Suggests Locomotion Hyperactivity in Zebrafish Triggered by Arecoline Might Be Associated with Multiple Muscarinic Acetylcholine Receptors Activation

Arecoline is one of the nicotinic acid-based alkaloids, which is found in the betel nut. In addition to its function as a muscarinic agonist, arecoline exhibits several adverse effects, such as inducing growth retardation and causing developmental defects in animal embryos, including zebrafish, chicken, and mice. In this study, we aimed to study the potential adverse effects of waterborne arecoline exposure on zebrafish larvae locomotor activity and investigate the possible mechanism of the arecoline effects in zebrafish behavior. The zebrafish behavior analysis, together with molecular docking and the antagonist co-exposure experiment using muscarinic acetylcholine receptor antagonists were conducted. Zebrafish larvae aged 96 h post-fertilization (hpf) were exposed to different concentrations (0.001, 0.01, 0.1, and 1 ppm) of arecoline for 30 min and 24 h, respectively, to find out the effect of arecoline in different time exposures. Locomotor activities were measured and quantified at 120 hpf. The results showed that arecoline caused zebrafish larvae locomotor hyperactivities, even at a very low concentration. For the mechanistic study, we conducted a structure-based molecular docking simulation and antagonist co-exposure experiment to explore the potential interactions between arecoline and eight subtypes, namely, M1a, M2a, M2b, M3a, M3b, M4a, M5a, and M5b, of zebrafish endogenous muscarinic acetylcholine receptors (mAChRs). Arecoline was predicted to show a strong binding affinity to most of the subtypes. We also discovered that the locomotion hyperactivity phenotypes triggered by arecoline could be rescued by co-incubating it with M1 to M4 mAChR antagonists. Taken together, by a pharmacological approach, we demonstrated that arecoline functions as a highly potent hyperactivity-stimulating compound in zebrafish that is mediated by multiple muscarinic acetylcholine receptors.

Mechanism of hepatotoxicity of first-line tyrosine kinase inhibitors: Gefitinib and afatinib

AIMS

Both gefitinib and afatinib are epidermal growth factor tyrosine kinase inhibitors (EGFR-TKI) in the treatment of non-small cell lung cancer (NSCLC). It has been reported that gefitinib and afatinib could cause hepatotoxicity during the clinic treatment, therefore it is critical to investigate their hepatotoxicity systematically. In this study, zebrafish (Danio rerio) were used as model animals to compare the hepatotoxicity and their toxic mechanism.

MAIN METHODS

The zebrafish transgenic line [Tg (fabp10a: dsRed; ela3l:EGFP) was used in this study. After larvae developed at 3 days post fertilization (dpf), they were put into different concentrations of gefitinib and afatinib. At 6 dpf, the viability, liver area, fluorescence intensity, histopathology, apoptosis, transaminase reflecting liver function, the absorption of yolk sac, and the expression of relative genes were observed and analyzed respectively.

KEY FINDINGS

Both gefitinib and afatinib could induce the larvae hepatotoxicity dose-dependently. Based on the liver morphology, histopathology, apoptosis and function assessments, gefitinib showed higher toxicity, causing more serious liver damage. Both gefitinib and afatinib caused abnormal expressions of genes related to endoplasmic reticulum stress (ERS) pathway and apoptosis. For example, jnk, perk, bip, chop, ire1, bid, caspase3 and caspase9 were up-regulated, while xbp1s, grp78, bcl-2/bax, and caspase8 were down-regulated. The hepatotoxicity difference of gefitinib and afatinib might be due to the different expression level of related genes.

[Current status of drug safety evaluation using zebrafish]

In recent years, the success rate of drug development has declined, and along with it, R&D costs have continued to rise. The rate of discontinuation of drug development due to safety reasons remains unchanged from 20 years ago. Therefore, it is important to check the safety of candidate compounds early in drug discovery in order to improve drug discovery efficiency. Under such circumstances, each company is focusing on establishing a low-cost, high-precision, and high-throughput safety screening system. The zebrafish is expected as a new experimental animal that serves as a bridge between in vitro and in vivo, and the progress of research in the last 15 years has been remarkable. At present, zebrafish are becoming a major experimental animal in Japan. At the same time, the gap between ideal and reality began to be seen, and it was time to once again understand the characteristics of zebrafish and think about its usage. This paper summarizes the points to be noted in the screening using zebrafish and introduces the use for actual safety evaluation.

Zebrafish: An emerging model system to study liver diseases and related drug discovery

The zebrafish has emerged as a powerful vertebrate model for studying liver-associated disorders. Liver damage is a crucial problem in the process of drug development and zebrafish have proven to be an important tool for the high-throughput screening of drugs for hepatotoxicity. Although the structure of the zebrafish liver differs to that of mammals, the fundamental physiologic processes, genetic mutations and manifestations of pathogenic responses to environmental insults exhibit much similarity. The larval transparency of the zebrafish is a great advantage for real-time imaging in hepatic studies. The zebrafish has a broad spectrum of cytochrome P450 enzymes, which enable the biotransformation of drugs via similar pathways as mammals, including oxidation, reduction and hydrolysis reactions. In the present review, we appraise the various drugs, chemicals and toxins used to study liver toxicity in zebrafish and their similarities to the rodent models for liver-related studies. Interestingly, the zebrafish has also been effectively used to study the pathophysiology of nonalcoholic and alcoholic fatty liver disease. The genetic models of liver disorders and their easy manipulation provide great opportunity in the area of drug development. The zebrafish has proven to be an influential model for the hepatic system due to its invertebrate-like advantages coupled with its vertebrate biology. The present review highlights the pivotal role of zebrafish in bridging the gap between cell-based and mammalian models.

Cytochrome P450 Expression and Chemical Metabolic Activity before Full Liver Development in Zebrafish

Zebrafish are used widely in biomedical, toxicological, and developmental research, but information on their xenobiotic metabolism is limited. Here, we characterized the expression of 14 xenobiotic cytochrome P450 (CYP) subtypes in whole embryos and larvae of zebrafish (4 to 144 h post-fertilization (hpf)) and the metabolic activities of several representative human CYP substrates. The 14 CYPs showed various changes in expression patterns during development. Many CYP transcripts abruptly increased at about 96 hpf, when the hepatic outgrowth progresses; however, the expression of some cyp1s (1b1, 1c1, 1c2, 1d1) and cyp2r1 peaked at 48 or 72 hpf, before full liver development. Whole-mount in situ hybridization revealed cyp2y3, 2r1, and 3a65 transcripts in larvae at 55 hpf after exposure to rifampicin, phenobarbital, or 2,3,7,8-tetrachlorodibenzo-p-dioxin from 30 hpf onward. Marked conversions of diclofenac to 4′-hydroxydiclofenac and 5-hydroxydiclofenac, and of caffeine to 1,7-dimethylxanthine, were detected as early as 24 or 50 hpf. The rate of metabolism to 4’-hydroxydiclofenac was more marked at 48 and 72 hpf than at 120 hpf, after the liver had become almost fully developed. These findings reveal the expression of various CYPs involved in chemical metabolism in developing zebrafish, even before full liver development.

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.

Stereoselective uptake and metabolism of prothioconazole caused oxidative stress in zebrafish (Danio rerio)

Prothioconazole (PTA) is a novel, broad-spectrum, chiral triazole fungicide that is mainly used to prevent and control the disease of cereal crops. However, the adverse effects of PTA and its major metabolite on nontarget organisms have aroused wide concern. In the present work, the acute toxic of the metabolite prothioconazole-desthio (PTA-desthio), with an LC₅₀ of 1.31 mg L^-1, was 3.5-fold more toxic than the parent compound, indicating that the metabolism of PTA in zebrafish was toxic. The stereoselective uptake and metabolism of PTA and PTA-desthio in zebrafish was firstly investigated using LC-MS/MS. Remarkable enantioselectivity was observed: S-PTA and S-PTA-desthio were preferentially uptake with the uptake rate constants of 8.22 and 8.15 d^-1 at exposure concentration of 0.5 mg L^-1, respectively, and the R-PTA-desthio were preferentially metabolized. PTA-desthio was rapidly formed during the uptake processes. The antioxidant enzyme activities in the zebrafish changed significantly, and these effects were reversible. A metabolic pathway including 13 phase I metabolites and 2 phase II metabolites was firstly proposed. A glucuronic acid conjugate and sulfate conjugate were observed in zebrafish. The results of this work provide information that highlights and can help mitigate the potential toxicity of PTA to the ecological environment and humans health.

Dose addition in chemical mixtures inducing craniofacial malformations in zebrafish (Danio rerio) embryos

A challenge in cumulative risk assessment is to model hazard of mixtures. EFSA proposed to only combine chemicals linked to a defined endpoint, in so-called cumulative assessment groups, and use the dose-addition model as a default to predict combined effects. We investigated the effect of binary mixtures of compounds known to cause craniofacial malformations, by assessing the effect in the head skeleton (M-PQ angle) in 120hpf zebrafish embryos. We combined chemicals with similar mode of action (MOA), i.e. the triazoles cyproconazole, triadimefon and flusilazole; next, reference compounds cyproconazole or triadimefon were combined with dissimilar acting compounds, TCDD, thiram, VPA, prochloraz, fenpropimorph, PFOS, or endosulfan. These mixtures were designed as (near) equipotent combinations of the contributing compounds, in a range of cumulative concentrations. Dose-addition was assessed by evaluation of the overlap of responses of each of the 14 tested binary mixtures with those of the single compounds. All 10 test compounds induced an increase of the M-PQ angle, with varying potency and specificity. Mixture responses as predicted by dose-addition did not deviate from the observed responses, supporting dose-addition as a valid assumption for mixture risk assessment. Importantly, dose-addition was found irrespective of MOA of contributing chemicals.

Hepatotoxicity evaluation of Euphorbia kansui on zebrafish larvae in vivo

BACKGROUND

Euphorbia kansui is effective in treating various diseases, such as ascites and edema, but its liver toxicity is a major obstacle in its wide use in the clinic. However, further investigations have suggested that Euphorbia kansui can cause liver injury.

HYPOTHESIS

The study aims to investigate the effect of Euphorbia kansui exposure on zebrafish, and explain the underlying toxicity mechanisms from a comprehensive perspective.

STUDY DESIGN

The 4dpf zebrafish larvae were exposed to Euphorbia kansui at a sub-lethal concentration.

METHODS

We evaluated the effect of Euphorbia kansui on the ultrastructure and function of the liver, apoptosis of liver cells by PCR and western blot, and metabolic profile by GC-MS based on sub-lethal concentrations.

RESULTS

Our results suggested Euphorbia kansui could lead to liver injury and significant alteration of the metabolomics of the zebrafish larvae in sub-lethal concentration conditions. It could also induce alterations in liver microstructure, hepatic function, gene expression and protein associated with the apoptosis process, as well as endogenous metabolism. KEGG pathway analysis identified some biological processes on the basis of different metabolisms and their associated processes especially for amino acid metabolism.

CONCLUSION

The results bring us closer to an in-depth understanding of the toxic effects of Euphorbia kansui on zebrafish liver, which will be significantly helpful in effectively guiding safer clinical application of this herb in the clinic. Furthermore, our results also showed the zebrafish model is reliable for evaluation of Euphorbia kansui extract hepatotoxicity and as a methodological reference for the evaluation of Traditional Chinese Medicine with underlying liver toxicity.

Review on the use of zebrafish embryos to study the effects of anesthetics during early development

Over the years, the potential toxicity of anesthetics has raised serious concerns about its safe use during pregnancy. As evidence emerged from research in animal models, showing that some anesthetic drugs are potential teratogenic, the determination of the risk of exposures to anesthetic drugs at early life stages became mandatory. However, due to inaccessibility and ethical constrains related to experimental conditions, the use of early life stages in mammalian models is limited. In this regard, some animal and nonanimal models have been suggested to surpass mammalian use in experimentation. Among them, the zebrafish embryo test has been recognized as a promising alternative in toxicology research, as well as an inexpensive and practical test. Substantial information collected from developmental research following compounds exposure, has contributed to the application of zebrafish assays in research, although only a few studies have focused on the use of early life stages of zebrafish to evaluate the developmental effects of anesthetics. Based on the recent advances of science and technology, there is a clear potential for zebrafish early life stages to provide new insights into anesthetics teratogenicity. This review provides an overview of recent anesthesia research using zebrafish embryos, demonstrating its usefulness to the anesthesia field, discussing the recent findings on various aspects related to the effects of anesthetics during early life development and the strengths and limitations of this model system.

The Melding of Drug Screening Platforms for Melanoma

The global incidence of cancer is rising rapidly and continues to be one of the leading causes of death in the world. Melanoma deserves special attention since it represents one of the fastest growing types of cancer, with advanced metastatic forms presenting high mortality rates due to the development of drug resistance. The aim of this review is to evaluate how the screening of drugs and compounds for melanoma has been performed over the last seven decades. Thus, we performed literature searches to identify melanoma drug screening methods commonly used by research groups during this timeframe. In vitro and in vivo tests are essential for the development of new drugs; however, incorporation of in silico analyses increases the possibility of finding more suitable candidates for subsequent tests. In silico techniques, such as molecular docking, represent an important and necessary first step in the screening process. However, these techniques have not been widely used by research groups to date. Our research has shown that the vast majority of research groups still perform in vitro and in vivo tests, with emphasis on the use of in vitro enzymatic tests on melanoma cell lines such as SKMEL and in vivo tests using the B16 mouse model. We believe that the union of these three approaches (in silico, in vitro, and in vivo) is essential for improving the discovery and development of new molecules with potential antimelanoma action. This workflow would provide greater confidence and safety for preclinical trials, which will translate to more successful clinical trials and improve the translatability of new melanoma treatments into clinical practice while minimizing the unnecessary use of laboratory animals under the principles of the 3R's.

Cardiac Rhythm and Molecular Docking Studies of Ion Channel Ligands with Cardiotoxicity in Zebrafish

Safety is one of the most important and critical issues in drug development. Many drugs were abandoned in clinical trials and retracted from the market because of unknown side effects. Cardiotoxicity is one of the most common reasons for drug retraction due to its potential side effects, i.e., inducing either tachycardia, bradycardia or arrhythmia. The zebrafish model could be used to screen drug libraries with potential cardiotoxicity in a high-throughput manner. In addition, the fundamental principles of replacement, reduction, and refinement of laboratory animal usage, 3R, could be achieved by using zebrafish as an alternative to animal models. In this study, we used a simple ImageJ-based method to evaluate and screen 70 ion channel ligands and successfully identify six compounds with strong cardiotoxicity in vivo. Next, we conducted an in silico-based molecular docking simulation to elucidate five identified compounds that might interact with domain III or domain IV of the Danio rerio L-type calcium channel (LTCC), a known pharmaceutically important target for arrhythmia. In conclusion, in this study, we provide a web lab and dry lab combinatorial approach to perform in vivo cardiotoxicity drug screening and in silico mechanistic studies.

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.

New Synthetic Cannabinoids Metabolism and Strategies to Best Identify Optimal Marker Metabolites

Synthetic cannabinoids (SCs) were initially developed as pharmacological tools to probe the endocannabinoid system and as novel pharmacotherapies, but are now highly abused. This is a serious public health and social problem throughout the world and it is highly challenging to identify which SC was consumed by the drug abusers, a necessary step to tie adverse health effects to the new drug's toxicity. Two intrinsic properties complicate SC identification, their often rapid and extensive metabolism, and their generally high potency relative to the natural psychoactive Δ9-tetrahydrocannabinol in cannabis. Additional challenges are the lack of reference standards for the major urinary metabolites needed for forensic verification, and the sometimes differing illicit and licit status and, in some cases, identical metabolites produced by closely related SC pairs, i.e., JWH-018/AM-2201, THJ-018/THJ-2201, and BB-22/MDMB-CHMICA/ADB-CHMICA. We review current SC prevalence, establish the necessity for SC metabolism investigation and contrast the advantages and disadvantages of multiple metabolic approaches. The human hepatocyte incubation model for determining a new SC's metabolism is highly recommended after comparison to human liver microsomes incubation, in silico prediction, rat in vivo, zebrafish, and fungus Cunninghamella elegans models. We evaluate SC metabolic patterns, and devise a practical strategy to select optimal urinary marker metabolites for SCs. New SCs are incubated first with human hepatocytes and major metabolites are then identified by high-resolution mass spectrometry. Although initially difficult to obtain, authentic human urine samples following the specified SC exposure are hydrolyzed and analyzed by high-resolution mass spectrometry to verify identified major metabolites. Since some SCs produce the same major urinary metabolites, documentation of the specific SC consumed may require identification of the SC parent itself in either blood or oral fluid. An encouraging trend is the recent reduction in the number of new SC introduced per year. With global collaboration and communication, we can improve education of the public about the toxicity of new SC and our response to their introduction.

The Toxicity and Metabolism Properties of Herba Epimedii Flavonoids on Laval and Adult Zebrafish

Zebrafish is being increasingly used for metabolism and toxicity assessment. The drugs consumed in zebrafish metabolism studies are far less than those used in rat studies. In our study, zebrafish embryos were exposed to icariin, Baohuoside I (BI), Epimedin A (EA), Epimedin B (EB), Epimedin C (EC), Sagittatoside A (SA), Sagittatoside B (SB), and 2′′-O-rhamnosylicariside II (SC), respectively, to examine the toxicity and metabolic profiles of these flavonoids. The order of toxicity was SC, SB > EC, SA > BI, icariin, EA, EB. After 24 h exposure to SB and SC, the mortality of zebrafish larvae reached 100% and yolk sac swollen was obvious. Both SC and SB caused severe hepatocellular vacuolization and liver cells degeneration in adult zebrafish after 15 consecutive days' treatment. The metabolic profiles of these flavonoids with trace amount were also monitored in larvae. BI was the common metabolite shared by icariin, EA, EB, SA, and SB, via deglycosylation. Both BI and SC remained as the prototype in the medium, suggesting that it is hard for BI and SC to cleave the rhamnose residue. EC was metabolized into SC and BI in zebrafish, inferring that SC might be responsible for the toxicity observed in EC group. The metabolites of icariin, EA, EB, EC, and BI in zebrafish larvae coincided with results from rats and intestinal flora. These data support the use of this system as a surrogate in predicting metabolites and hepatotoxicity risk, especially for TCM compound with trace amount.

From mRNA Expression of Drug Disposition Genes to In Vivo Assessment of CYP-Mediated Biotransformation during Zebrafish Embryonic and Larval Development

The zebrafish (Danio rerio) embryo is currently explored as an alternative for developmental toxicity testing. As maternal metabolism is lacking in this model, knowledge of the disposition of xenobiotics during zebrafish organogenesis is pivotal in order to correctly interpret the outcome of teratogenicity assays. Therefore, the aim of this study was to assess cytochrome P450 (CYP) activity in zebrafish embryos and larvae until 14 d post-fertilization (dpf) by using a non-specific CYP substrate, i.e., benzyloxy-methyl-resorufin (BOMR) and a CYP1-specific substrate, i.e., 7-ethoxyresorufin (ER). Moreover, the constitutive mRNA expression of CYP1A, CYP1B1, CYP1C1, CYP1C2, CYP2K6, CYP3A65, CYP3C1, phase II enzymes uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1) and sulfotransferase 1st1 (SULT1ST1), and an ATP-binding cassette (ABC) drug transporter, i.e., abcb4, was assessed during zebrafish development until 32 dpf by means of quantitative PCR (qPCR). The present study showed that trancripts and/or the activity of these proteins involved in disposition of xenobiotics are generally low to undetectable before 72 h post-fertilization (hpf), which has to be taken into account in teratogenicity testing. Full capacity appears to be reached by the end of organogenesis (i.e., 120 hpf), although CYP1-except CYP1A-and SULT1ST1 were shown to be already mature in early embryonic development.

Zebrafish: Speeding Up the Cancer Drug Discovery Process

Zebrafish (Danio rerio) is an ideal in vivo model to study a wide variety of human cancer types. In this review, we provide a comprehensive overview of zebrafish in the cancer drug discovery process, from (i) approaches to induce malignant tumors, (ii) techniques to monitor cancer progression, and (iii) strategies for compound administration to (iv) a compilation of the 355 existing case studies showing the impact of zebrafish models on cancer drug discovery, which cover a broad scope of scenarios. Finally, based on the current state-of-the-art analysis, this review presents some highlights about future directions using zebrafish in cancer drug discovery and the potential of this model as a prognostic tool in prospective clinical studies. Cancer Res; 78(21); 6048-58. ©2018 AACR.

Zebrafish (Danio rerio): A valuable tool for predicting the metabolism of xenobiotics in humans?

Zebrafish has become a popular model organism in several lines of biological research sharing physiological, morphological and histological similarities with mammals. In fact, many human cytochrome P450 (CYP) enzymes have direct orthologs in zebrafish, suggesting that zebrafish xenobiotic metabolic profiles may be similar to those in mammals. The focus of the review is to analyse the studies that have evaluated the metabolite production in zebrafish over the years, either of the drugs themselves or xenobiotics in general (environmental pollutants, natural products, etc.), bringing a vision of how these works were performed and comparing, where possible, with human metabolism. Early studies that observed metabolic production by zebrafish focused on environmental toxicology, and in recent years the main focus has been on toxicity screening of pharmaceuticals and drug candidates. Nevertheless, there is still a lack of standardization of the model and the knowledge of the extent of similarity with human metabolism. Zebrafish screenings are performed at different life stages, typically being carried out in adult fish through in vivo assays, followed by early larval stages and embryos. Studies comparing metabolism at the different zebrafish life stages are also common. As with any non-human model, the zebrafish presents similarities and differences in relation to the profile of generated metabolites compared to that observed in humans. Although more studies are still needed to assess the degree to which zebrafish metabolism can be compared to human metabolism, the facts presented indicate that the zebrafish is an excellent potential model for assessing xenobiotic metabolism.

Assessment of the Acute Toxicity, Uptake and Biotransformation Potential of Benzotriazoles in Zebrafish ( Danio rerio) Larvae Combining HILIC- with RPLC-HRMS for High-Throughput Identification

The current study reports on the toxicity, uptake, and biotransformation potential of zebrafish (embryos and larvae) exposed to benzotriazoles (BTs). Acute toxicity assays were conducted. Cardiac function abnormalities (pericardial edema and poor blood circulation) were observed from the phenotypic analysis of early life zebrafish embryos after BTs exposure. For the uptake and biotransformation experiment, extracts of whole body larvae were analyzed using liquid chromatography-high-resolution tandem mass spectrometry (UPLC-Q-TOF-HRMS/MS). The utility of hydrophilic interaction liquid chromatography (HILIC) as complementary technique to reversed phase liquid chromatography (RPLC) in the identification process was investigated. Through HILIC analyses, additional biotransformation products (bio-TPs) were detected, because of the enhanced sensitivity and better separation efficiency of isomers. Therefore, reduction of false negative results was accomplished. Both oxidative (hydroxylation) and conjugative (glucuronidation, sulfation) metabolic reactions were observed, while direct sulfation proved the dominant biotransformation pathway. Overall, 26 bio-TPs were identified through suspect and nontarget screening workflows, 22 of them reported for the first time. 4-Methyl-1- H-benzotriazole (4-MeBT) demonstrated the highest toxicity potential and was more extensively biotransformed, compared to 1- H-benzotriazole (BT) and 5-methyl-1- H-benzotriazole (5-MeBT). The extent of biotransformation proved particularly informative in the current study, to explain and better understand the different toxicity potentials of BTs.

Membrane Remodeling as a Key Player of the Hepatotoxicity Induced by Co-Exposure to Benzo[a]pyrene and Ethanol of Obese Zebrafish Larvae

The rise in prevalence of non-alcoholic fatty liver disease (NAFLD) constitutes an important public health concern worldwide. Including obesity, numerous risk factors of NAFLD such as benzo[a]pyrene (B[a]P) and ethanol have been identified as modifying the physicochemical properties of the plasma membrane in vitro thus causing membrane remodeling—changes in membrane fluidity and lipid-raft characteristics. In this study, the possible involvement of membrane remodeling in the in vivo progression of steatosis to a steatohepatitis-like state upon co-exposure to B[a]P and ethanol was tested in obese zebrafish larvae. Larvae bearing steatosis as the result of a high-fat diet were exposed to ethanol and/or B[a]P for seven days at low concentrations coherent with human exposure in order to elicit hepatotoxicity. In this condition, the toxicant co-exposure raised global membrane order with higher lipid-raft clustering in the plasma membrane of liver cells, as evaluated by staining with the fluoroprobe di-4-ANEPPDHQ. Involvement of this membrane’s remodeling was finally explored by using the lipid-raft disruptor pravastatin that counteracted the effects of toxicant co-exposure both on membrane remodeling and toxicity. Overall, it can be concluded that B[a]P/ethanol co-exposure can induce in vivo hepatotoxicity via membrane remodeling which could be considered as a good target mechanism for developing combination therapy to deal with steatohepatitis.

Applicability of the fish embryo acute toxicity (FET) test (OECD 236) in the regulatory context of Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH)

In 2013 the Organisation for Economic Co-operation and Development (OECD) test guideline (236) for fish embryo acute toxicity (FET) was adopted. It determines the acute toxicity of chemicals to embryonic fish. Previous studies show a good correlation of FET with the standard acute fish toxicity (AFT) test; however, the potential of the FET test to predict AFT, which is required by the Registration, Evaluation, Authorisation, and Restriction of Chemicals (REACH) regulation (EC 1907/2006) and the Classification, Labelling and Packaging (CLP) Regulation (EC 1272/2008), has not yet been fully clarified. In 2015 the European Chemicals Agency (ECHA) requested that a consultant perform a scientific analysis of the applicability of FET to predict AFT. The purpose was to compare the toxicity of substances to fish embryos and to adult fish, and to investigate whether certain factors (e.g., physicochemical properties, modes of action, or chemical structures) could be used to define the applicability boundaries of the FET test. Given the limited data availability, the analysis focused on organic substances. The present critical review summarizes the main findings and discusses regulatory application of the FET test under REACH. Given some limitations (e.g., neurotoxic mode of action) and/or remaining uncertainties (e.g., deviation of some narcotic substances), it has been found that the FET test alone is currently not sufficient to meet the essential information on AFT as required by the REACH regulation. However, the test may be used within weight-of-evidence approaches together with other independent, relevant, and reliable sources of information. The present review also discusses further research needs that may overcome the remaining uncertainties and help to increase acceptance of FET as a replacement for AFT in the future. For example, an increase in the availability of data generated according to OECD test guideline 236 may provide evidence of a higher predictive power of the test. Environ Toxicol Chem 2018;37:657-670. © 2017 SETAC.

First profiling of lysine crotonylation of myofilament proteins and ribosomal proteins in zebrafish embryos

Zebrafish embryos are translucent and develop rapidly in individual eggs ex utero; they are widely used as models for embryogenesis and organ development for human diseases and drug discovery. Lysine crotonylation (Kcr) is a type of histone post-translational modifications discovered in 2011. Kcr dynamics are involved in gene expression regulation and acute kidney injury; however, little is known about the effects of Kcr on non-histone proteins. In the present study, we conducted the first proteome-wide profiling of Kcr in zebrafish larvae and identified 557 Kcr sites on 218 proteins, representing the Kcr event in zebrafish. We identified two types of Kcr motifs containing hydrophobic (Leu, Ile, Val) and acidic (Asp and Glu) amino acids near the modified lysine residues. Our results show that both crotonylated proteins and sites of crotonylation were evolutionarily conserved between zebrafish embryos and humans. Specifically, Kcr on ribosomal proteins and myofilament proteins, including myosin, tropomyosin and troponin, were widely enriched. Interestingly, 55 lysine crotonylation sites on myosin were distributed throughout coiled coil regions. Therefore, Kcr may regulate muscle contraction and protein synthesis. Our results provide a foundation for future studies on the effects of lysine crotonylation on aging and heart failure.

First profiling of lysine crotonylation of myofilament proteins and ribosomal proteins in zebrafish embryos

Zebrafish embryos are translucent and develop rapidly in individual eggs ex utero; they are widely used as models for embryogenesis and organ development for human diseases and drug discovery. Lysine crotonylation (Kcr) is a type of histone post-translational modifications discovered in 2011. Kcr dynamics are involved in gene expression regulation and acute kidney injury; however, little is known about the effects of Kcr on non-histone proteins. In the present study, we conducted the first proteome-wide profiling of Kcr in zebrafish larvae and identified 557 Kcr sites on 218 proteins, representing the Kcr event in zebrafish. We identified two types of Kcr motifs containing hydrophobic (Leu, Ile, Val) and acidic (Asp and Glu) amino acids near the modified lysine residues. Our results show that both crotonylated proteins and sites of crotonylation were evolutionarily conserved between zebrafish embryos and humans. Specifically, Kcr on ribosomal proteins and myofilament proteins, including myosin, tropomyosin and troponin, were widely enriched. Interestingly, 55 lysine crotonylation sites on myosin were distributed throughout coiled coil regions. Therefore, Kcr may regulate muscle contraction and protein synthesis. Our results provide a foundation for future studies on the effects of lysine crotonylation on aging and heart failure.

In vitro and in vivo estrogenic activity of BPA, BPF and BPS in zebrafish-specific assays

Bisphenol A (BPA) is a widely used chemical that has been extensively studied as an endocrine-disrupting chemical (EDC). Other bisphenols sharing close structural features with BPA, are increasingly being used as alternatives, increasing the need to assess associated hazards to the endocrine system. In the present study, the estrogenic activity of BPA, bisphenol S (BPS) and bisphenol F (BPF) was assessed by using a combination of zebrafish-specific mechanism-based in vitro and in vivo assays. The three bisphenols were found to efficiently transactivate all zebrafish estrogen receptor (zfER) subtypes in zebrafish hepatic reporter cell lines (ZELH-zfERs). BPA was selective for zfERα while BPS and BPF were slightly more potent on zfERβ subtypes. We further documented the estrogenic effect in vivo by quantifying the expression of brain aromatase using a transgenic cyp19a1b-GFP zebrafish embryo assay. All three bisphenols induced GFP in a concentration-dependent manner. BPS only partially induced brain aromatase at the highest tested concentrations (>30µM) while BPA and BPF strongly induced GFP, in an ER-dependent manner, at 1-10µM. Furthermore, we show that BPF strongly induced vitellogenin synthesis in adult male zebrafish. Overall, this study demonstrates the estrogenic activity of BPA, BPF and BPS in different cell- and tissue-contexts and at different stages of development. Differences between in vitro and in vivo responses are discussed in light of selective ER activation and the fate of the compounds in the models. This study confirms the relevance of combining cellular and whole-organism bioassays in a unique model species for the hazard assessment of candidate EDCs.

Monitoring Toxic Ionic Liquids in Zebrafish (Danio rerio) with Desorption Electrospray Ionization Mass Spectrometry Imaging (DESI-MSI)

Ambient mass spectrometry imaging has become an increasingly powerful technique for the direct analysis of biological tissues in the open environment with minimal sample preparation and fast analysis times. In this study, we introduce desorption electrospray ionization mass spectrometry imaging (DESI-MSI) as a novel, rapid, and sensitive approach to localize the accumulation of a mildly toxic ionic liquid (IL), AMMOENG 130 in zebrafish (Danio rerio). The work demonstrates that DESI-MSI has the potential to rapidly monitor the accumulation of IL pollutants in aquatic organisms. AMMOENG 130 is a quaternary ammonium-based IL reported to be broadly used as a surfactant in commercialized detergents. It is known to exhibit acute toxicity to zebrafish causing extensive damage to gill secondary lamellae and increasing membrane permeability. Zebrafish were exposed to the IL in a static 96-h exposure study in concentrations near the LC₅₀ of 1.25, 2.5, and 5.0 mg/L. DESI-MS analysis of zebrafish gills demonstrated the appearance of a dealkylated AMMOENG 130 metabolite in the lowest concentration of exposure identified by a high resolution hybrid LTQ-Orbitrap mass spectrometer as the trimethylstearylammonium ion, [C₂₁H₄₆N]⁺. With DESI-MSI, the accumulation of AMMOENG 130 and its dealkylated metabolite in zebrafish tissue was found in the nervous and respiratory systems. AMMOENG 130 and the metabolite were capable of penetrating the blood brain barrier of the fish with significant accumulation in the brain. Hence, we report for the first time the simultaneous characterization, distribution, and metabolism of a toxic IL in whole body zebrafish analyzed by DESI-MSI. This ambient mass spectrometry imaging technique shows great promise for the direct analysis of biological tissues to qualitatively monitor foreign, toxic, and persistent compounds in aquatic organisms from the environment. Graphical Abstract ᅟ.

Comparison of the In Vivo Biotransformation of Two Emerging Estrogenic Contaminants, BP2 and BPS, in Zebrafish Embryos and Adults

Zebrafish embryo assays are increasingly used in the toxicological assessment of endocrine disruptors. Among other advantages, these models are 3R-compliant and are fit for screening purposes. Biotransformation processes are well-recognized as a critical factor influencing toxic response, but major gaps of knowledge exist regarding the characterization of functional metabolic capacities expressed in zebrafish. Comparative metabolic studies between embryos and adults are even scarcer. Using ³H-labeled chemicals, we examined the fate of two estrogenic emerging contaminants, benzophenone-2 (BP2) and bisphenol S (BPS), in 4-day embryos and adult zebrafish. BPS and BP2 were exclusively metabolized through phase II pathways, with no major qualitative difference between larvae and adults except the occurrence of a BP2-di-glucuronide in adults. Quantitatively, the biotransformation of both molecules was more extensive in adults. For BPS, glucuronidation was the predominant pathway in adults and larvae. For BP2, glucuronidation was the major pathway in larvae, but sulfation predominated in adults, with ca. 40% conversion of parent BP2 and an extensive release of several conjugates into water. Further larvae/adults quantitative differences were demonstrated for both molecules, with higher residue concentrations measured in larvae. The study contributes novel data regarding the metabolism of BPS and BP2 in a fish model and shows that phase II conjugation pathways are already functional in 4-dpf-old zebrafish. Comparative analysis of BP2 and BPS metabolic profiles in zebrafish larvae and adults further supports the use of zebrafish embryo as a relevant model in which toxicity and estrogenic activity can be assessed, while taking into account the absorption and fate of tested substances.

Bioaccumulation and trophic transfer of pharmaceuticals in food webs from a large freshwater lake

Pharmaceuticals are increasingly detected in environmental matrices, but information on their trophic transfer in aquatic food webs is insufficient. This study investigated the bioaccumulation and trophic transfer of 23 pharmaceuticals in Taihu Lake, China. Pharmaceutical concentrations were analyzed in surface water, sediments and 14 aquatic species, including plankton, invertebrates and fish collected from the lake. The median concentrations of the detected pharmaceuticals ranged from not detected (ND) to 49 ng/L in water, ND to 49 ng/g dry weight (dw) in sediments, and from ND to 130 ng/g dw in biota. Higher concentrations of pharmaceuticals were found in zoobenthos relative to plankton, shrimp and fish muscle. In fish tissues, the observed pharmaceutical contents in the liver and brain were generally higher than those in the gills and muscle. Both bioaccumulation factors (median BAFs: 19-2008 L/kg) and biota-sediment accumulation factors (median BSAFs: 0.0010-0.037) indicated a low bioaccumulation potential for the target pharmaceuticals. For eight of the most frequently detected pharmaceuticals in food webs, the trophic magnification factors (TMFs) were analyzed from two different regions of Taihu Lake. The TMFs for roxithromycin, propranolol, diclofenac, ibuprofen, ofloxacin, norfloxacin, ciprofloxacin and tetracycline in the two food webs ranged from 0.28 to 1.25, suggesting that none of these pharmaceuticals experienced trophic magnification. In addition, the pharmaceutical TMFs did not differ significantly between the two regions in Taihu Lake.

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.

In Vitro Biotransformation of Two Human CYP3A Probe Substrates and Their Inhibition during Early Zebrafish Development

At present, the zebrafish embryo is increasingly used as an alternative animal model to screen for developmental toxicity after exposure to xenobiotics. Since zebrafish embryos depend on their own drug-metabolizing capacity, knowledge of their intrinsic biotransformation is pivotal in order to correctly interpret the outcome of teratogenicity assays. Therefore, the aim of this in vitro study was to assess the activity of cytochrome P450 (CYP)—a group of drug-metabolizing enzymes—in microsomes from whole zebrafish embryos (ZEM) of 5, 24, 48, 72, 96 and 120 h post-fertilization (hpf) by means of a mammalian CYP substrate, i.e., benzyloxy-methyl-resorufin (BOMR). The same CYP activity assays were performed in adult zebrafish liver microsomes (ZLM) to serve as a reference for the embryos. In addition, activity assays with the human CYP3A4-specific Luciferin isopropyl acetal (Luciferin-IPA) as well as inhibition studies with ketoconazole and CYP3cide were carried out to identify CYP activity in ZLM. In the present study, biotransformation of BOMR was detected at 72 and 96 hpf; however, metabolite formation was low compared with ZLM. Furthermore, Luciferin-IPA was not metabolized by the zebrafish. In conclusion, the capacity of intrinsic biotransformation in zebrafish embryos appears to be lacking during a major part of organogenesis.

Pharmaceutical Metabolism in Fish: Using a 3-D Hepatic In Vitro Model to Assess Clearance

At high internal doses, pharmaceuticals have the potential for inducing biological/pharmacological effects in fish. One particular concern for the environment is their potential to bioaccumulate and reach pharmacological levels; the study of these implications for environmental risk assessment has therefore gained increasing attention. To avoid unnecessary testing on animals, in vitro methods for assessment of xenobiotic metabolism could aid in the ecotoxicological evaluation. Here we report the use of a 3-D in vitro liver organoid culture system (spheroids) derived from rainbow trout to measure the metabolism of seven pharmaceuticals using a substrate depletion assay. Of the pharmaceuticals tested, propranolol, diclofenac and phenylbutazone were metabolised by trout liver spheroids; atenolol, metoprolol, diazepam and carbamazepine were not. Substrate depletion kinetics data was used to estimate intrinsic hepatic clearance by this spheroid model, which was similar for diclofenac and approximately 5 fold higher for propranolol when compared to trout liver microsomal fraction (S9) data. These results suggest that liver spheroids could be used as a relevant and metabolically competent in vitro model with which to measure the biotransformation of pharmaceuticals in fish; and propranolol acts as a reproducible positive control.