New school in liver development: lessons from zebrafish

In toto live imaging of Erk signaling dynamics in developing zebrafish hepatocytes

Regional and tissue-wide regulation of signaling pathways orchestrates cellular proliferation and differentiation during organ development. In this study, we established an imaging platform for longitudinal analysis of liver development in live developing zebrafish. We generated hepatocyte-specific transgenic lines for kinase translocation reporters of extracellular signal-regulated kinase (Erk) and c-Jun N-terminal kinase (Jnk) signaling, and with these we captured signaling dynamics that govern rapid expansion of hepatocytes toward creation of the functioning liver at single-cell resolution. Our findings reveal Erk signaling fluctuations as the liver develops and introduce methodology for investigating cell-type specific signaling dynamics during organ morphogenesis.

Fucoidan JHCF4s from Hizikia fusiformis against ethanol-induced damage in vitro and in vivo

Fucoidan has strong antioxidant and free radical scavenging activities. We successfully isolated the active fucoidan, JHCF4, from edible Hizikia fusiformis. The effects of high-temperature water-extracted (T-JHCF4) and cellulase-assisted extraction (C-JHCF4) of JHCF4 were compared and to demonstrate those potential for treating alcoholic liver disease (ALD). C-JHCF4 contained higher amounts of fucose, arabinose, rhamnose, mannose, and sulfate groups, whereas T-JHCF4 had a higher galactose content. Importantly, C-JHCF4 downregulated the expression of Bax, Caspase 3, and cytochrome C in alcohol-treated LO2 cells and upregulated Bcl-2 expression, indicating its protective effect via an apoptosis-related pathway. In vivo, C-JHCF4 protected alcohol-induced zebrafish from reduced reactive oxygen species production and cell death, further regulating malondialdehyde and glutathione levels. Collectively, T-JHCF4 has advantages in extraction, such as short extraction time and low cost, making it suitable for large-scale industrial production. C-JHCF4 exhibited a stronger hepatoprotective effect than T-JHCF4, indicating its suitability for treating ALD.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-025-01865-4.

A mixture parameterized biologically based dosimetry model to predict body burdens of polycyclic aromatic hydrocarbons in developmental zebrafish toxicity assays

Polycyclic aromatic hydrocarbons (PAHs) are a group of environmental toxicants found ubiquitously as complex mixtures in human-impacted environments. Developmental zebrafish exposures have been used widely to study PAH toxicity, but most studies report nominal exposure concentrations. Nominal exposure concentrations can be unreliable dose metrics due to differences in toxicant bioavailability resulting from disparate exposure methodologies and chemical properties. Toxicokinetic modeling can predict toxicant tissue doses to facilitate comparison between exposures of different chemicals, methodologies, and biological models. We parameterize a biologically based dosimetry model for developmental zebrafish toxicity assays for 9 PAHs. The model was optimized with measurements from media, tissue, and plastic plate walls throughout a static developmental exposure to a mixture of 10 PAHs of high abundance within the Portland Harbor Superfund Site. Plate binding, volatilization, zebrafish permeability, and tissue-media partitioning coefficients vary widely between PAHs. Model predictions accounted for 83% and 54% of 48 hpf body burdens within a factor of 2 resulting from exposures to mixtures and individual PAHs, respectively. Accounting for solubility significantly improves model performance. Competition for active sites in metabolizing enzymes may change biotransformation kinetics between individual PAH and mixture exposures. Area under the curve estimations of concentrations in zebrafish resulted in altered hazard rankings from nominal exposure concentrations. Future work will be oriented to generalizing the model to other PAHs. This PAH dosimetry model improves the interpretability of developmental zebrafish toxicity assays by providing time-resolved body burdens from nominal exposure concentrations.

2024 International Academy of Toxicologic Pathology (IATP) Satellite Symposium: New Approach Methodologies (NAMs) for Neurotoxicity Assessment and Regulatory Perspectives

The International Academy of Toxicologic Pathology (IATP) Satellite Symposium on "New Approach Methodologies (NAMs) for Neurotoxicity Assessment and Regulatory Perspectives," organized in Spain, addressed the growing need for improved assessment of neurotoxicity. Traditional neurotoxicity assessment using in vivo animal studies are impractical for testing the substantial number of environmental chemicals that currently lack data and in the early detection of neuro-related adverse reactions in drug discovery. The NAMs, including human in vitro assays and small model organisms, have been developed for faster and cost-effective assessment of neurotoxic potential. While NAMs offer improved practicality, utility, and valuable mechanistic insights, their integration into regulatory decision-making requires robust scientific validation and technical characterization. Confidence in and regulatory application of NAMs data can be supported by mapping cellular outcomes to neuropathological findings in mammals, including humans, through the Adverse Outcome Pathway (AOP) framework, and the Integrated Approach to Testing and Assessment (IATA). Case studies presented demonstrated the application of NAMs in chemical and drug safety evaluations, focusing on developmental neurotoxicity (DNT), Parkinson's disease, and drug-induced seizures. In conjunction with in vivo toxicology studies, NAMs represent a significant step toward advancing chemical and drug toxicity assessment via hazard identification and drug screening safety assessments.

6-PPD triggered lipid metabolism disorder and inflammatory response in larval zebrafish (Danio rerio) by regulating PPARγ/NF-κB pathway

As a synthetic rubber antioxidant, the environmental monitoring concentrations of N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6-PPD) have exceeded the risk threshold, attracting widespread attention. Although investigations into the harmful effects on zebrafish have commenced, a comprehensive exploration of its toxicological impacts and underlying molecular mechanisms remains to be conducted. By using zebrafish as a model, this study systematically evaluated 6-PPD-induced lipid metabolism disorders and inflammation response following environmental exposure. Bioinformatics analysis revealed that 6-PPD target genes enriched in the hepatitis B pathway, indicating potential hepatic toxicity via inflammatory pathways. Therefore, we hypothesize that 6-PPD could trigger hepatotoxicity through the crosstalk between lipid metabolism and inflammation. Further experiments substantiated this hypothesis by showing lipid accumulation in the liver following 6-PPD exposure, along with elevated triglyceride (TG) and total cholesterol (TC) levels, and imbalanced expression of lipid metabolism-related marker genes. Additionally, 6-PPD exposure induced the accumulation of reactive oxygen species (ROS) and inhibited the differentiation and maturation of immune cells, resulting in immune evasion. Most of these abnormalities were exacerbated in a dose-dependent manner with increasing concentrations of 6-PPD. The addition of the PPARγ pathway agonist puerarin (PUE) or NF-κB pathway inhibitor quinazoline (QNZ) to 6-PPD exposure group mitigated these toxic effects, validating our conjecture that lipid metabolism disorder and inflammatory responses may result from the regulation of the PPARγ/NF-κB pathway.

A Rapid Quantitative Assessment Method for Liver Damage Effects of Compounds Based on Zebrafish Liver Partition Area Ratio

Total liver area is a traditional indicator in evaluating compound liver damage with zebrafish models. However, in some experiments, compounds changed zebrafish liver morphology but total liver area showed no significant difference, indicating it is inaccurate for evaluating compound effects on zebrafish liver damage. Therefore, in this study, transgenic zebrafish Tg(l-fabp:EGFP) labeled with liver cells using green fluorescent protein was used to evaluate compound effects on liver by the liver partition area ratio. The coefficient of variation of the total liver area and the liver partition area ratio of normal zebrafish at different development stages was calculated to determine the precision and dispersion of the liver partition area ratio. Three known hepatotoxic compounds (water extract of psoralea, alcohol, and α-naphthalene isothiocyanate) were used to treat zebrafish, and liver partition area ratio was calculated and verified by liver tissue pathological sections. The Pearson correlation coefficient was used to analyze the correlation between the liver partition area ratio, total liver area, and alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Results showed significant difference in liver partition area ratio between hepatotoxic compound treated group and control group, and it could accurately reflect liver morphology changes. There was a strong correlation between liver partition area ratio and ALT and AST level, whereas that between total liver area and ALT and AST level was low. Therefore, the change in zebrafish liver partition area ratio can be an evaluation indicator for rapid assessment of compound effects on zebrafish liver function damage, more sensitive and accurate than total liver area.

Khdrbs1 drives re-differentiation of bipotential progenitor cells by inhibiting p53 in zebrafish biliary-mediated liver regeneration

After severe liver injury, biliary epithelial cells (BECs) undergo de-differentiation into bipotential progenitor cells (BPPCs), which subsequently re-differentiate into nascent hepatocytes and BECs to accomplish liver regeneration. However, the crucial factors governing the re-differentiation process of BPPCs remain largely unknown. Here, using a zebrafish model of severe liver injury, we observed specific expression of khdrbs1a and khdrbs1b (collectively known as khdrbs1) in BPPCs through single-cell RNA analyses and fluorescence in situ hybridization. Subsequently, to eliminate the genetic compensation, we generated a CRISPR/dead Cas9-mediated system for interfering with khdrbs1 in BECs, which caused defective liver regeneration and impaired re-differentiation of BPPCs. Furthermore, the khdrbs1-/- mutant displayed impaired proliferation and re-differentiation of BPPCs during liver regeneration. Mechanistically, p53 signaling was activated in response to the loss of khdrbs1, and tp53 mutation partially rescued the defective liver regeneration of the khdrbs1-/- mutant. In summary, we conclude that Khdrbs1 promotes the re-differentiation of BPPCs in part by inhibiting p53 activation during biliary-mediated liver regeneration in zebrafish.

Zebrafish as a model for human epithelial pathology

Zebrafish (Danio rerio) have emerged as an influential model for studying human epithelial pathology, particularly because of their genetic similarity to humans and their unique physiological traits. This review explores the structural and functional homology between zebrafish and human epithelial tissues in organs, such as the gastrointestinal system, liver, and kidneys. Zebrafish possess significant cellular and functional homology with mammals, which facilitates the investigation of various diseases, including inflammatory bowel disease, nonalcoholic fatty liver disease, and polycystic kidney disease. The advantages of using zebrafish as a model organism include rapid external development, ease of genetic manipulation, and advanced imaging capabilities, allowing for the real-time observation of disease processes. However, limitations exist, particularly concerning the lack of organs in zebrafish and the potential for incomplete phenocopy of human conditions. Despite these challenges, ongoing research in adult zebrafish promises to enhance our understanding of the disease mechanisms and regenerative processes. By revealing the similarities and differences in epithelial cell function and disease pathways, this review highlights the value of zebrafish as a translational model for advancing our knowledge of human health and developing targeted therapies.

Preparation and Efficacy Evaluation of Antihyperuricemic Peptides from Marine Sources

Marine-derived foods, often called blue foods, are promising sustainable alternatives to conventional food sources owing to their abundant amino acids and high protein content. Current treatments for hyperuricemia, a chronic condition attributed to purine metabolism disorders, are associated with various side effects. Novel peptide xanthine oxidase inhibitors have been discovered in the hydrolyzed products of marine fish and invertebrate proteins, which have demonstrated promising therapeutic potential by reducing uric acid levels in vitro and in vivo. This review explores the potential therapeutic effects of xanthine oxidase inhibitors derived from marine fish and invertebrates, summarizes the methods for extracting bioactive peptides from marine organisms, and emphasizes the impact of different proteases on the structure-activity relationship of bioactive peptides. The hypouricemic effects of these bioactive peptides warrant further verification. There is consensus on the in vitro chemical methods used to verify the xanthine oxidase inhibitory effects of these peptides. Considering several cell and animal model development strategies, this review summarizes several highly recognized modeling methods, proposes strategies to improve the bioavailability of bioactive peptides, and advocates for a diversified evaluation system. Although the screening and evaluation methods for antihyperuricemic peptides have been shown to be feasible across numerous studies, they are not optimal. This review examines the deficiencies in bioavailability, synthesis efficiency, and evaluation mechanisms in terms of their future development and proposes potential solutions to address these issues. This review provides a novel perspective for the exploration and application of marine-derived hypouricemic bioactive peptides.

Aryl hydrocarbon receptor-dependent toxicity by retene requires metabolic competence

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds frequently detected in the environment with widely varying toxicities. Many PAHs activate the aryl hydrocarbon receptor (AHR), inducing the expression of a battery of genes, including xenobiotic metabolizing enzymes like cytochrome P450s (CYPs); however, not all PAHs act via this mechanism. We screened several parent and substituted PAHs in in vitro AHR activation assays to classify their unique activity. Retene (1-methyl-7-isopropylphenanthrene) displays Ahr2-dependent teratogenicity in zebrafish, but did not activate human AHR or zebrafish Ahr2, suggesting a retene metabolite activates Ahr2 in zebrafish to induce developmental toxicity. To investigate the role of metabolism in retene toxicity, studies were performed to determine the functional role of cyp1a, cyp1b1, and the microbiome in retene toxicity, identify the zebrafish window of susceptibility, and measure retene uptake, loss, and metabolite formation in vivo. Cyp1a-null fish were generated using CRISPR-Cas9. Cyp1a-null fish showed increased sensitivity to retene toxicity, whereas Cyp1b1-null fish were less susceptible, and microbiome elimination had no significant effect. Zebrafish required exposure to retene between 24 and 48 hours post fertilization (hpf) to exhibit toxicity. After static exposure, retene concentrations in zebrafish embryos increased until 24 hpf, peaked between 24 and 36 hpf, and decreased rapidly thereafter. We detected retene metabolites at 36 and 48 hpf, indicating metabolic onset preceding toxicity. This study highlights the value of combining molecular and systems biology approaches with mechanistic and predictive toxicology to interrogate the role of biotransformation in AHR-dependent toxicity.

Ecotoxicity and environmental safety assessment of two-dimensional niobium carbides (MXenes)

Two-dimensional (2D) MXenes have gained great interest in water treatment, biomedical, and environmental applications. The antimicrobial activity and cell toxicity of several MXenes including Nb4C3Tx and Nb2CTx have already been explored. However, potential side effects related to Nb-MXene toxicity, especially on aquatic pneuma, have rarely been studied. Using zebrafish embryos, we investigated and compared the potential acute toxicity between two forms of Nb-MXene: the multilayer (ML-Nb4C3Tx, ML-Nb2CTx) and the delaminated (DL-Nb2CTx, and DL-Nb4C3Tx) Nb-MXene. The LC50 of ML-Nb4C3Tx, ML-Nb2CTx, DL-Nb2CTx, and DL-Nb4C3Tx were estimated to be 220, 215, 225, and 128 mg/L, respectively. Although DL-Nb2CTx, and DL-Nb4C3Tx derivatives have similar sizes, DL-Nb4C3Tx not only shows the higher mortality (LC50 = 128 mg/L Vs 225 mg/L), but also the highest teratogenic effect (NOEC = 100 mg/L Vs 200 mg/L). LDH release assay suggested more cell membrane damage and a higher superoxide anion production in DL-Nb4C3Tx than DL-Nb2CTx,. Interestingly, both DL-Nb-MXene nanosheets showed insignificant cardiac, hepatic, or behavioral toxic effects compared to the negative control. Embryos treated with the NOEC of DL-Nb2CTx presented hyperlocomotion, while embryos treated with the NOEC of DL-Nb4C3Tx presented hyperlocomotion, suggesting developmental neurotoxic effect and muscle impairment induced by both DL-Nb-MXene. According to the Fish and Wildlife Service (FSW) Acute Toxicity Rating Scale, all tested Nb-MXene nanosheets were classified as "Practically not toxic". However, DL-Nb4C3Tx should be treated with caution as it might cause a neurotoxic effect on fauna when it ends up in wastewater in high concentrations.

CRISPR/Cas9-Mediated fech Knockout Zebrafish: Unraveling the Pathogenesis of Erythropoietic Protoporphyria and Facilitating Drug Screening

Erythropoietic protoporphyria (EPP1) results in painful photosensitivity and severe liver damage in humans due to the accumulation of fluorescent protoporphyrin IX (PPIX). While zebrafish (Danio rerio) models for porphyria exist, the utility of ferrochelatase (fech) knockout zebrafish, which exhibit EPP, for therapeutic screening and biological studies remains unexplored. This study investigated the use of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated fech-knockout zebrafish larvae as a model of EPP1 for drug screening. CRISPR/Cas9 was employed to generate fech-knockout zebrafish larvae exhibiting morphological defects without lethality prior to 9 days post-fertilization (dpf). To assess the suitability of this model for drug screening, ursodeoxycholic acid (UDCA), a common treatment for cholestatic liver disease, was employed. This treatment significantly reduced PPIX fluorescence and enhanced bile-secretion-related gene expression (abcb11a and abcc2), indicating the release of PPIX. Acridine orange staining and quantitative reverse transcription polymerase chain reaction analysis of the bax/bcl2 ratio revealed apoptosis in fech-/- larvae, and this was reduced by UDCA treatment, indicating suppression of the intrinsic apoptosis pathway. Neutral red and Sudan black staining revealed increased macrophage and neutrophil production, potentially in response to PPIX-induced cell damage. UDCA treatment effectively reduced macrophage and neutrophil production, suggesting its potential to alleviate cell damage and liver injury in EPP1. In conclusion, CRISPR/Cas9-mediated fech-/- zebrafish larvae represent a promising model for screening drugs against EPP1.

Early stress exposure on zebrafish development: effects on survival, malformations and molecular alterations

The effects of stress during early vertebrate development can be especially harmful. Avoiding stressors in fish larvae is essential to ensure the health of adult fish and their reproductive performance and overall production. We examined the consequences of direct exposure to successive acute stressors during early development, including their effects on miR-29a and its targets, survival, hatching and malformation rates, larval behaviour and cartilage and eye development. Our aim was to shed light on the pleiotropic effects of early-induced stress in this vertebrate model species. Our results showed that direct exposure to successive acute stressors during early development significantly upregulated miR-29a and downregulated essential collagen transcripts col2a1a, col6a2 and col11a1a, decreased survival and increased malformation rates (swim bladder, otoliths, cardiac oedema and ocular malformations), promoting higher rates of immobility in larvae. Our results revealed that stress in early stages can induce different eye tissular architecture and cranioencephalic cartilage development alterations. Our research contributes to the understanding of the impact of stressful conditions during the early stages of zebrafish development, serving as a valuable model for vertebrate research. This holds paramount significance in the fields of developmental biology and aquaculture and also highlights miR-29a as a potential molecular marker for assessing novel larval rearing programmes in teleost species.

Distribution and developmental timing of zebrafish liver innervation

Hepatic innervation regulates multiple aspects of liver function, repair and regeneration, and liver denervation is associated with higher rates of metabolic disorders in humans. However, the mechanisms regulating the development of the hepatic nervous system, as well as the role of the hepatic nervous system in liver development and maturation, are still largely unknown. Zebrafish are a widely used model of liver development and regeneration, but hepatic innervation in zebrafish has not yet been described in detail. Here, we examine the extent and developmental timing of hepatic innervation in zebrafish. We demonstrate that innervation is restricted to large bile ducts and blood vessels in both juvenile and adult zebrafish livers, as we find no evidence for direct innervation of hepatocytes. Innervation contacting the periphery of the liver is visible as early as 72 h post-fertilization, while intrahepatic innervation is not established until 21 days post-fertilization. Therefore, zebrafish hepatic innervation resembles that of previously examined fish species, making them an excellent model to investigate both the role of the hepatic nervous system during liver maturation and the mechanisms governing the elaboration of the intrahepatic nerve network between fish and mammals.

Effect of Voltage-Gated K+ Channel Inhibition by 4-aminopyridine in Spinal Cord Injury Recovery in Zebrafish

Spinal cord injury (SCI) affects between 250,000 to 500,000 individuals annually. After the initial injury, a delayed secondary cascade of cellular responses occurs causing progressive degeneration and permanent disability. One part of this secondary process is disturbance of ionic homeostasis. The K+ channel blocker, 4-aminopyridine (4-AP), is used clinically to alleviate symptoms of multiple sclerosis (MS). Several ongoing studies are being conducted to explore additional areas where 4-AP may have an effect, including stroke, traumatic brain injury, and nervous system recovery after SCI. The goal of our study was to determine whether 4-AP affects recovery from SCI in zebrafish (Danio rerio). Using the transgenic line Tg(gfap:EGFP), we created a spinal transection and tracked swim recovery. We found that constant treatment with 10 μM 4-AP increases swimming distance 40%. Live imaging demonstrated that treatment with 4-AP increases radial glial cells bridging at the site of injury in the presence of 4-AP. We conclude that 10 μM 4-AP is pro-regenerative after SCI.

Embryonic Zebrafish as a Model for Investigating the Interaction between Environmental Pollutants and Neurodegenerative Disorders

Environmental pollutants have been linked to neurotoxicity and are proposed to contribute to neurodegenerative disorders. The zebrafish model provides a high-throughput platform for large-scale chemical screening and toxicity assessment and is widely accepted as an important animal model for the investigation of neurodegenerative disorders. Although recent studies explore the roles of environmental pollutants in neurodegenerative disorders in zebrafish models, current knowledge of the mechanisms of environmentally induced neurodegenerative disorders is relatively complex and overlapping. This review primarily discusses utilizing embryonic zebrafish as the model to investigate environmental pollutants-related neurodegenerative disease. We also review current applicable approaches and important biomarkers to unravel the underlying mechanism of environmentally related neurodegenerative disorders. We found embryonic zebrafish to be a powerful tool that provides a platform for evaluating neurotoxicity triggered by environmentally relevant concentrations of neurotoxic compounds. Additionally, using variable approaches to assess neurotoxicity in the embryonic zebrafish allows researchers to have insights into the complex interaction between environmental pollutants and neurodegenerative disorders and, ultimately, an understanding of the underlying mechanisms related to environmental toxicants.

Bifenox induces hepatotoxicity and vascular toxicity in zebrafish embryos via ROS production and alterations in signaling pathways

Existing evidence shows that currently used pesticides pose toxicological risks to exposed wildlife. Chemically, bifenox belongs to diphenyl ethers, a well-known group of herbicides. Its mechanism of action primarily involves inducing lipid peroxidation and blocking protoporphyrinogen oxidases. Toxicity of diphenyl ether herbicides has been elucidated in animal cells; however, in vivo toxicological evaluations of bifenox are required to determine its unexpected effects. This study aimed to determine the negative effects of bifenox, and its effects on higher eukaryotes. We found that early stages of zebrafish embryo exposed to bifenox demonstrated increased mortality and physiological defects, based on the LC50 value. Bifenox severely inhibited blood vessel growth by reducing key elements of complex connectivity; fluorescently tagged transgenic lines (fli1a:EGFP) showed morphological changes. Additionally, transgenic lines that selectively identified hepatocytes (fabp10a:DsRed) showed reduced fluorescence, indicating that bifenox may inhibit liver development. To evaluate the level of oxidative stress, we used 2',7'-dichlorofluorescein diacetate (DCFH-DA) probes in zebrafish embryos to identify the underlying mechanisms causing developmental damage. Our findings demonstrate that exposure to bifenox causes abnormalities in the hepatic and cardiovascular systems during zebrafish embryogenesis. Therefore, this study provides new information for the evaluation of toxicological risks of bifenox in vertebrates.

Effects of nanomolar methylmercury on developing human neural stem cells and zebrafish Embryo

Exposure to mercury and its organic form methylmercury (MeHg), is of great concern for the developing nervous system. Despite available literature on MeHg neurotoxicity, there is still uncertainty about its mechanisms of action and the doses that trigger developmental effects. Our study combines two alternative methodologies, the human neural stem cells (NSC) and the zebrafish (ZF) embryo, to address the neurotoxic effects of early exposure to nanomolar concentrations of MeHg. Our results show linear or nonmonotonic (hormetic) responses depending on studied parameters. In ZF, we observed a hormetic response in locomotion and larval rotation, but a concentration-dependent response for sensory organ size and habituation. We also observed a possible delayed response as MeHg had greater effects on larval activity at 5 days than at 24 h. In NSC cells, some parameters show a clear dose dependence, such as increased apoptosis and differentiation to glial cells or decreased neuronal precursors; while others show a hormetic response: neuronal differentiation or cell proliferation. This study shows that the ZF model was more susceptible than NSC to MeHg neurotoxicity. The combination of different models has improved the understanding of the underlying mechanisms of toxicity and possible compensatory mechanisms at the cellular and organismal level.

Biallelic variants in LARS1 induce steatosis in developing zebrafish liver via enhanced autophagy

BACKGROUND

Biallelic pathogenic variants of LARS1 cause infantile liver failure syndrome type 1 (ILFS1), which is characterized by acute hepatic failure with steatosis in infants. LARS functions as a protein associated with mTORC1 and plays a crucial role in amino acid-triggered mTORC1 activation and regulation of autophagy. A previous study demonstrated that larsb-knockout zebrafish exhibit conditions resembling ILFS. However, a comprehensive analysis of larsb-knockout zebrafish has not yet been performed because of early mortality.

METHODS

We generated a long-term viable zebrafish model carrying a LARS1 variant identified in an ILFS1 patient (larsb-I451F zebrafish) and analyzed the pathogenesis of the affected liver of ILFS1.

RESULTS

Hepatic dysfunction is most prominent in ILFS1 patients during infancy; correspondingly, the larsb-I451F zebrafish manifested hepatic anomalies during developmental stages. The larsb-I451F zebrafish demonstrates augmented lipid accumulation within the liver during autophagy activation. Inhibition of DGAT1, which converts fatty acids to triacylglycerols, improved lipid droplets in the liver of larsb-I451F zebrafish. Notably, treatment with an autophagy inhibitor ameliorated hepatic lipid accumulation in this model.

CONCLUSIONS

Our findings suggested that enhanced autophagy caused by biallelic LARS1 variants contributes to ILFS1-associated hepatic dysfunction. Furthermore, the larsb-I451F zebrafish model, which has a prolonged survival rate compared with the larsb-knockout model, highlights its potential utility as a tool for investigating the pathophysiology of ILFS1-associated liver dysfunction.

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.

Hepatotoxicity and lipid metabolism disorders of 8:2 polyfluoroalkyl phosphate diester in zebrafish: In vivo and in silico evidence

8:2 polyfluoroalkyl phosphate diester (8:2 diPAP) has been shown to accumulate in the liver, but whether it induces hepatotoxicity and lipid metabolism disorders remains largely unknown. In this study, zebrafish embryos were exposed to 8:2 diPAP for 7 d. Hepatocellular hypertrophy and karyolysis were noted after exposure to 0.5 ng/L 8:2 diPAP, suggesting suppressed liver development. Compared to the water control, 8:2 diPAP led to significantly higher triglyceride and total cholesterol levels, but markedly lower levels of low-density lipoprotein, implying disturbed lipid homeostasis. The levels of two peroxisome proliferator activated receptor (PPAR) subtypes (pparα and pparγ) involved in hepatotoxicity and lipid metabolism were significantly upregulated by 8:2 diPAP, consistent with their overexpression as determined by immunohistochemistry. In silico results showed that 8:2 diPAP formed hydrogen bonds with PPARα and PPARγ. Among seven machine learning models, Adaptive Boosting performed the best in predicting the binding affinities of PPARα and PPARγ on the test set. The predicted binding affinity of 8:2 diPAP to PPARα (7.12) was higher than that to PPARγ (6.97) by Adaptive Boosting, which matched well with the experimental results. Our results revealed PPAR - mediated adverse effects of 8:2 diPAP on the liver and lipid metabolism of zebrafish larvae.

New approach methods to assess developmental and adult neurotoxicity for regulatory use: a PARC work package 5 project

In the European regulatory context, rodent in vivo studies are the predominant source of neurotoxicity information. Although they form a cornerstone of neurotoxicological assessments, they are costly and the topic of ethical debate. While the public expects chemicals and products to be safe for the developing and mature nervous systems, considerable numbers of chemicals in commerce have not, or only to a limited extent, been assessed for their potential to cause neurotoxicity. As such, there is a societal push toward the replacement of animal models with in vitro or alternative methods. New approach methods (NAMs) can contribute to the regulatory knowledge base, increase chemical safety, and modernize chemical hazard and risk assessment. Provided they reach an acceptable level of regulatory relevance and reliability, NAMs may be considered as replacements for specific in vivo studies. The European Partnership for the Assessment of Risks from Chemicals (PARC) addresses challenges to the development and implementation of NAMs in chemical risk assessment. In collaboration with regulatory agencies, Project 5.2.1e (Neurotoxicity) aims to develop and evaluate NAMs for developmental neurotoxicity (DNT) and adult neurotoxicity (ANT) and to understand the applicability domain of specific NAMs for the detection of endocrine disruption and epigenetic perturbation. To speed up assay time and reduce costs, we identify early indicators of later-onset effects. Ultimately, we will assemble second-generation developmental neurotoxicity and first-generation adult neurotoxicity test batteries, both of which aim to provide regulatory hazard and risk assessors and industry stakeholders with robust, speedy, lower-cost, and informative next-generation hazard and risk assessment tools.

DNA hypomethylation activates Cdk4/6 and Atr to induce DNA replication and cell cycle arrest to constrain liver outgrowth in zebrafish

Coordinating epigenomic inheritance and cell cycle progression is essential for organogenesis. UHRF1 connects these functions during development by facilitating maintenance of DNA methylation and cell cycle progression. Here, we provide evidence resolving the paradoxical phenotype of uhrf1 mutant zebrafish embryos which have activation of pro-proliferative genes and increased number of hepatocytes in S-phase, but the liver fails to grow. We uncover decreased Cdkn2a/b and persistent Cdk4/6 activation as the mechanism driving uhrf1 mutant hepatocytes into S-phase. This induces replication stress, DNA damage and Atr activation. Palbociclib treatment of uhrf1 mutants prevented aberrant S-phase entry, reduced DNA damage, and rescued most cellular and developmental phenotypes, but it did not rescue DNA hypomethylation, transposon expression or the interferon response. Inhibiting Atr reduced DNA replication and increased liver size in uhrf1 mutants, suggesting that Atr activation leads to dormant origin firing and prevents hepatocyte proliferation. Cdkn2a/b was downregulated pro-proliferative genes were also induced in a Cdk4/6 dependent fashion in the liver of dnmt1 mutants, suggesting DNA hypomethylation as a mechanism of Cdk4/6 activation during development. This shows that the developmental defects caused by DNA hypomethylation are attributed to persistent Cdk4/6 activation, DNA replication stress, dormant origin firing and cell cycle inhibition.

Bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate Enhances foxo1-Mediated Lipophagy to Remodel Lipid Metabolism in Zebrafish Liver

An emerging environmental contaminant, bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH), can bioaccumulate in the liver and affect hepatic lipid metabolism. However, the in-depth mechanism has yet to be comprehensively explored. In this study, we utilized transgenic zebrafish Tg (Apo14: GFP) to image the interference of TBPH on zebrafish liver development and lipid metabolism at the early development stage. Using integrated lipidomic and transcriptomic analyses to profile the lipid remodeling effect, we uncovered the potential effects of TBPH on lipophagy-related signaling pathways in zebrafish larvae. Decreased lipid contents accompanied by enhanced lipophagy were confirmed by the measurements of Oil Red O staining and transmission electron microscopy in liver tissues. Particularly, the regulatory role of the foxo1 factor was validated via its transcriptional inhibitor. Double immunofluorescence staining integrated with biochemical analysis indicated that the enhanced lipophagy and mitochondrial fatty acid oxidation induced by TBPH were reversed by the foxo1 inhibitor. To summarize, our study reveals, for the first time, the essential role of foxo1-mediated lipophagy in TBPH-induced lipid metabolic disorders and hepatoxicity, providing new insights for metabolic disease studies and ecological health risk assessment of TBPH.

Single-cell transcriptome landscape of zebrafish liver reveals hepatocytes and immune cell interactions in understanding nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is becoming the most common chronic liver disease in the world. Immunity is the major contributing factor in NAFLD; however, the interaction of immune cells and hepatocytes in disease progression has not been fully elucidated. As a popular species for studying NAFLD, zebrafish, whose liver is a complex immune system mediated by immune cells and non-immune cells in maintaining immune tolerance and homeostasis. Understanding the cellular composition and immune environment of zebrafish liver is of great significance for its application in NAFLD. Here, we established a liver atlas that consists of 10 cell types using single-cell RNA sequencing (scRNA-seq). By examining the heterogeneity of hepatocytes and analyzing the expression of NAFLD-associated genes in the specific cluster, we provide a potential target cell model to study NAFLD. Additionally, our analysis identified two subtypes of distinct resident macrophages with inflammatory and non-inflammatory functions and characterized the successive stepwise development of T cell subclusters in the liver. Importantly, we uncovered the possible regulation of macrophages and T cells on target cells of fatty liver by analyzing the cellular interaction between hepatocytes and immune cells. Our data provide valuable information for an in-depth study of immune cells targeting hepatocytes to regulate the immune balance in NAFLD.

Embryonic Amoxicillin Exposure Has Limited Impact on Liver Development but Increases Susceptibility to NAFLD in Zebrafish Larvae

Amoxicillin is commonly used in clinical settings to target bacterial infection and is frequently prescribed during pregnancy. Investigations into its developmental toxicity and effects on disease susceptibility are not comprehensive. Our present study examined the effects of embryonic amoxicillin exposure on liver development and function, especially the effects on susceptibility to non-alcoholic fatty liver disease (NAFLD) using zebrafish as an animal model. We discovered that embryonic amoxicillin exposure did not compromise liver development, nor did it induce liver toxicity. However, co-treatment of amoxicillin and clavulanic acid diminished BESP expression, caused bile stasis and induced liver toxicity. Embryonic amoxicillin exposure resulted in elevated expression of lipid synthesis genes and exacerbated hepatic steatosis in a fructose-induced NAFLD model, indicating embryonic amoxicillin exposure increased susceptibility to NAFLD in zebrafish larvae. In summary, this research broadens our understanding of the risks of amoxicillin usage during pregnancy and provides evidence for the impact of embryonic amoxicillin exposure on disease susceptibility in offspring.

Hhex and Prox1a synergistically dictate the hepatoblast to hepatocyte differentiation in zebrafish

The specification of endoderm cells to prospective hepatoblasts is the starting point for hepatogenesis. However, how a prospective hepatoblast gains the hepatic fate remains elusive. Previous studies have shown that loss-of-function of either hhex or prox1a alone causes a small liver phenotype but without abolishing the hepatocyte differentiation, suggesting that absence of either Hhex or Prox1a alone is not sufficient to block the hepatoblast differentiation. Here, via genetic studies of the zebrafish two single (hhex-/- and prox1a-/-) and one double (hhex-/-prox1a-/-) mutants, we show that simultaneous loss-of-function of the hhex and prox1a two genes does not block the endoderm cells to gain the hepatoblast potency but abolishes the hepatic differentiation from the prospective hepatoblast. Consequently, the hhex-/-prox1a-/- double mutant displays a liverless phenotype that cannot be rescued by the injection of bmp2a mRNA. Taken together, we provide strong evidences showing that Hhex teams with Prox1a to act as a master control of the differentiation of the prospective hepatoblasts towards hepatocytes.

Zebrafish ppp1r21 mutant as a model for the study of primary biliary cholangitis

Primary biliary cholangitis (PBC) is an autoimmune cholestatic liver disease that progresses to fibrosis and cirrhosis, resulting from the gradual destruction of intrahepatic bile ducts. Exploring genetic variants associated with PBC is essential to understand the pathogenesis of PBC. Here we identify a zebrafish balloon dog (blg) mutant with intrahepatic bile duct branching defects, exhibiting several key pathological PBC-like features, including immunodominant autoantigen PDC-E2 production, cholangiocyte apoptosis, immune cell infiltration, inflammatory activation, and liver fibrosis. blg encodes the protein phosphatase 1 regulatory subunit 21 (Ppp1r21), which is enriched in the liver and its peripheral tissues and plays a vital role in the early intrahepatic bile duct formation stage. Further studies show an excessive activation of the PI3K/AKT/mTOR pathway in the hepatic tissues in the mutant, while treatment with the pathway inhibitor LY294002 and rapamycin partially rescues intrahepatic bile duct branching defects and alleviates the PBC-like symptoms. These findings implicate the potential role of the Ppp1r21-mediated PI3K/AKT/mTOR pathway in the pathophysiology of PBC.

A zebrafish model for studying the mechanisms of newborn hyperbilirubinemia and bilirubin-induced neurological damage

Unresolved neonatal hyperbilirubinemia may lead to the accumulation of excess bilirubin in the body, and bilirubin in neural tissues may induce toxicity. Bilirubin-induced neurological damage (BIND) can result in acute or chronic bilirubin encephalopathy, causing temporary or lasting neurological dysfunction or severe damage resulting in infant death. Although serum bilirubin levels are used as an indication of severity, known and unknown individual differences affect the severity of the symptoms. The mechanisms of BIND are not yet fully understood. Here, a zebrafish newborn hyperbilirubinemia model is developed and characterized. Direct exposure to excess bilirubin induced dose- and time-dependent toxicity linked to the accumulation of bilirubin in the body and brain. Introduced bilirubin was processed by the liver, which increased the tolerance of larvae. BIND in larvae was demonstrated by morphometric measurements, histopathological analyses and functional tests. The larvae that survived hyperbilirubinemia displayed mild or severe morphologies associated with defects in eye movements, body posture and swimming problems. Interestingly, a plethora of mild to severe clinical symptoms were reproduced in the zebrafish model.

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.

Zebrafish as a model organism - can a fish mimic human?

From pre-historic era, all scientific discoveries have evolved around a concept - THINK BIG but for a change zebrafish as a model organism in research had managed to halt the entire medical community and made us realize that it's time to think small. From a barely imagined being in research few years ago to around 4,000 publications in just last year, zebrafish has definitely come a long way. Through these tiny fish, scientists have managed to find genes that caused human diseases and have also developed various specific models to know more about the pathology behind such diseases. This review will focus on zebrafish as a model organism from the time it was introduced to the most novel targets with particular emphasis on central nervous system (CNS) as it is rapidly evolving branch in zebrafish research these days. This review will try to shed light on the early stages of zebrafish as a model organism and will try to cover the journey of it developing as a successful model organism to map many diseases like diabetes, Alzheimer's and autism describing the rationale for using this specific model and briefly the techniques under each category and finally will summarize the pros and cons of the model with its expected future directions.

Deiodinase inhibition impairs the formation of the three posterior swim bladder tissue layers during early embryonic development in zebrafish

Thyroid hormone system disruption (THSD) negatively affects multiple developmental processes and organs. In fish, inhibition of deiodinases, which are enzymes crucial for (in)activating thyroid hormones (THs), leads to impaired swim bladder inflation. Until now, the underlying mechanism has remained largely unknown. Therefore, the objective of this study was to identify the process during swim bladder development that is impacted by deiodinase inhibition. Zebrafish embryos were exposed to 6 mg/L iopanoic acid (IOP), a model deiodinase inhibitor, during 8 different exposure windows (0-60, 60-120, 24-48, 48-72, 72-96, 96-120, 72-120 and 0-120 h post fertilization (hpf)). Exposure windows were chosen based on the three stages of swim bladder development: budding (24-48 hpf), pre-inflation, i.e., the formation of the swim bladder tissue layers (48-72 hpf), and inflation phase (72-120 hpf). Exposures prior to 72 hpf, during either the budding or pre-inflation phase (or both), impaired swim bladder inflation, while exposure during the inflation phase did not. Based on our results, we hypothesize that DIO inhibition before 72 hpf leads to a local decrease in T3 levels in the developing swim bladder. Gene transcript analysis showed that these TH level alterations disturb both Wnt and hedgehog signaling, known to be essential for swim bladder formation, eventually resulting in impaired development of the swim bladder tissue layers. Improper development of the swim bladder impairs swim bladder inflation, leading to reduced swimming performance. This study demonstrates that deiodinase inhibition impacts processes underlying the formation of the swim bladder and not the inflation process, suggesting that these processes primarily rely on maternal rather than endogenously synthetized THs since TH measurements showed that THs were not endogenously synthetized during the sensitive period.

Rngtt governs biliary-derived liver regeneration initiation by transcriptional regulation of mTORC1 and Dnmt1 in zebrafish

In cases of end-stage liver diseases, the proliferation of existing hepatocytes is compromised, a feature of human chronic liver disease, in which most hepatocytes are dysfunctional. So far, liver transplantation represents the only curative therapeutic solution for advanced liver diseases, and the shortage of donor organs leads to high morbidity and mortality worldwide. The promising treatment is to prompt the biliary epithelial cells (BECs) transdifferentiation. However, the critical factors governing the initiation of BEC-derived liver regeneration are largely unknown. The zebrafish has advantages in large-scale genetic screens to identify the critical factors involved in liver regeneration. Here, we combined N-ethyl-N-nitrosourea screen, positional cloning, transgenic lines, antibody staining, and in situ hybridization methods and identified a liver regeneration defect mutant ( lrd ) using the zebrafish extensive liver injury model. Through positional cloning and genomic sequencing, we mapped the mutation site to rngtt . Loss of rngtt leads to the defects of BEC dedifferentiation, bipotential progenitor cell activation, and cell proliferation in the initiation stage of liver regeneration. The transdifferentiation from BECs to hepatocytes did not occur even at the late stage of liver regeneration. Mechanically, Rngtt transcriptionally regulates the attachment of mRNA cap to mTOR complex 1 (mTORC1) components and dnmt1 to maintain the activation of mTORC1 and DNA methylation in BECs after severe liver injury and prompt BEC to hepatocyte conversion. Furthermore, rptor and dnmt1 mutants displayed the same liver regeneration defects as rngtt mutation. In conclusion, our results suggest Rngtt is a new factor that initiates BEC-derived liver regeneration.

Copper induces liver lipotoxicity disease by up-regulating Nrf2 expression via the activation of MTF-1 and inhibition of SP1/Fyn pathway

Excessive copper (Cu) intake leads to hepatic lipotoxicity disease, which has adverse effects on health, but the underlying mechanism is unclear. We found that Cu increased lipotoxicity by promoting Nrf2 recruitment to the ARE site in the promoters of five lipogenic genes (g6pd, 6pgd, me, icdh and pparγ). We also found that Cu affected the Nrf2 expression via different pathways: metal regulatory transcription factor 1 (MTF-1) mediated the Cu-induced Nrf2 transcriptional activation; Cu also enhanced the expression of Nrf2 by inhibiting the SP1 expression, which was achieved by inhibiting the negative regulator Fyn of Nrf2. These promoted the enrichment of Nrf2 in the nucleus and ultimately affected lipotoxicity. Thus, for the first time, we elucidated that Cu induced liver lipotoxicity disease by up-regulating Nrf2 expression via the MTF-1 activation and the inhibition of SP1/Fyn pathway. Our study elucidates the Cu-associated obesity and NAFLD for fish and possibly humans.

Developmental defects induced by thiabendazole are mediated via apoptosis, oxidative stress and alteration in PI3K/Akt and MAPK pathways in zebrafish

Thiabendazole, a benzimidazole fungicide, is widely used to prevent yield loss in agricultural land by inhibiting plant diseases derived from fungi. As thiabendazole has a stable benzimidazole ring structure, it remains in the environment for an extended period, and its toxic effects on non-target organisms have been reported, indicating the possibility that it could threaten public health. However, little research has been conducted to elucidate the comprehensive mechanisms of its developmental toxicity. Therefore, we used zebrafish, a representative toxicological model that can predict toxicity in aquatic organisms and mammals, to demonstrate the developmental toxicity of thiabendazole. Various morphological malformations were observed, including decreased body length, eye size, and increased heart and yolk sac edema. Apoptosis, reactive oxygen species (ROS) production, and inflammatory response were also triggered by thiabendazole exposure in zebrafish larvae. Furthermore, PI3K/Akt and MAPK signaling pathways important for appropriate organogenesis were significantly changed by thiabendazole. These results led to toxicity in various organs and a reduction in the expression of related genes, including cardiovascular toxicity, neurotoxicity, and hepatic and pancreatic toxicity, which were detected in flk1:eGFP, olig2:dsRED, and L-fabp:dsRed;elastase:GFP transgenic zebrafish models, respectively. Overall, this study partly determined the developmental toxicity of thiabendazole in zebrafish and provided evidence of the environmental hazards of this fungicide.

Piperlongumine treatment impacts heart and liver development and causes developmental delay in zebrafish (Danio rerio) embryos

Piperlongumine (PL) and piperine (PP) are alkaloids presented in long pepper (Piper longum), and they exhibit various biological activities, especially anti-cancer properties. With these regards, they are considered as future medicines with high potential. Even they are exposed to humans such a long time, their potential toxicities in the environment have not been studied. Therefore, their ecological toxicities were assessed using zebrafish embryos. PP showed low mortality and no abnormal phenotype up to 10 µM. However, PL exhibited strong acute toxicity at the concentration of 5-10 µM ranges, and abnormal development were frequently found in the range of 1-2.5 µM with pericardial and yolk sac edemas. In transgenic zebrafish embryos, PL induced an increase in the number of intersegmental vessels and delayed the early-stage development. PL treatment affected heart formation and heart rate. The presence of PL induced the expression of cytokines, inflammatory markers, and inflammasome in the embryos. The PL treatment changed the mRNA levels of the ER stress and apoptosis-related genes. In addition, ROS production was observed during early-stage development of PL-treated zebrafish embryos. These results indicate that developing PL as a medicine would require extremely meticulous strategies to prevent potential toxicity.

A New In Vivo Zebrafish Bioassay Evaluating Liver Steatosis Identifies DDE as a Steatogenic Endocrine Disruptor, Partly through SCD1 Regulation

Non-alcoholic fatty liver disease (NAFLD), which starts with liver steatosis, is a growing worldwide epidemic responsible for chronic liver diseases. Among its risk factors, exposure to environmental contaminants, such as endocrine disrupting compounds (EDC), has been recently emphasized. Given this important public health concern, regulation agencies need novel simple and fast biological tests to evaluate chemical risks. In this context, we developed a new in vivo bioassay called StAZ (Steatogenic Assay on Zebrafish) using an alternative model to animal experimentation, the zebrafish larva, to screen EDCs for their steatogenic properties. Taking advantage of the transparency of zebrafish larvae, we established a method based on fluorescent staining with Nile red to estimate liver lipid content. Following testing of known steatogenic molecules, 10 EDCs suspected to induce metabolic disorders were screened and DDE, the main metabolite of the insecticide DDT, was identified as a potent inducer of steatosis. To confirm this and optimize the assay, we used it in a transgenic zebrafish line expressing a blue fluorescent liver protein reporter. To obtain insight into DDE's effect, the expression of several genes related to steatosis was analyzed; an up-regulation of scd1 expression, probably relying on PXR activation, was found, partly responsible for both membrane remodeling and steatosis.

Hexafluoropropylene oxide trimer acid (HFPO-TA) disturbs embryonic liver and biliary system development in zebrafish

Hexafluoropropylene oxide trimer acid (HFPO-TA), a novel alternative to perfluorooctanoic acid (PFOA), has emerged as a potential environmental pollutant. Here, to investigate the toxic effects of HFPO-TA on liver and biliary system development, zebrafish embryos were exposed to 0, 50, 100, or 200 mg/L HFPO-TA from 6 to 120 h post-fertilization (hpf). Results showed that the 50 % lethal concentration (LC₅₀) of HFPO-TA was 231 mg/L at 120 hpf, lower than that of PFOA. HFPO-TA exposure decreased embryonic hatching, survival, and body length. Furthermore, HFPO-TA exerted higher toxicity at the specification stage than during the differentiation and maturation stages, leading to small-sized livers in Tg(fabp10a: DsRed) transgenic larvae and histopathological changes. Significant decreases in the mRNA expression of genes related to liver formation were observed. Alanine transaminase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), and direct bilirubin (DBIL) levels were significantly increased. HFPO-TA decreased total cholesterol (TCHO) and triglyceride (TG) activities, disturbed lipid metabolism through the peroxisome proliferator-activated receptor (PPAR) pathway, and induced an inflammatory response. Furthermore, HFPO-TA inhibited intrahepatic biliary development in Tg(Tp1:eGFP) transgenic larvae and interfered with transcription of genes associated with biliary duct development. HFPO-TA reduced bile acid synthesis but increased bile acid transport, resulting in disruption of bile acid metabolism. Therefore, HFPO-TA influenced embryonic liver and biliary system morphogenesis, caused liver injury, and may be an unsafe alternative for PFOA.

Contributions towards the hazard evaluation of two widely used cytostatic drugs

Cytostatic drugs are one of the most important therapeutic options for cancer, a disease that is expected to affect 29 million individuals by 2040. After being excreted, cytostatics reach wastewater treatment plants (WWTPs), which are unable to efficiently remove them, and consequently, they will be released into the aquatic environment. Due to the highly toxic properties of cytostatics, it is particularly relevant to evaluate their potential ecological risk. Yet, cytostatics toxicity data is still not available for various species. In this work, the ecotoxicity of two widely consumed cytostatics, cyclophosphamide (CYP-as a model cytostatic) and mycophenolic acid (MPA-as a priority cytostatic), was evaluated on three freshwater species-Raphidocelis subcapitata, Brachionus calyciflorus, and Danio rerio, and the risk quotient (RQ) was assessed. Both drugs significantly affected the yield and growth inhibition of the microalgae, while for rotifers, the least sensitive species, only significant effects were registered for CYP. These drugs also caused significant effects on the mortality and morphological abnormalities on zebrafish. The estimation of the RQ discloses that CYP seems to pose a low risk to aquatic biota while MPA poses a very high risk. Altogether, these results emphasize the need for more complete environmental risk assessments, to properly prioritize and rank cytostatics according to their potentially toxic effects on the environment and aquatic biota.

Progress on the toxicity of quantum dots to model organism-zebrafish

In vivo toxicological studies are currently necessary to analyze the probable dangers of quantum dots (QDs) to the environment and human safety, due to the fast expansion of QDs in a range of applications. Because of its high fecundity, cost-effectiveness, well-defined developmental phases, and optical transparency, zebrafish has long been considered the "gold standard" for biosafety assessment of chemical substances and pollutants. In this review, the advantages of using zebrafish in QD toxicity assessment were explored. Then, the target organ toxicities such as developmental toxicity, immunotoxicity, cardiovascular toxicity, neurotoxicity, and hepatotoxicity were summarized. The hazardous effects of different QDs, including cadmium-containing QDs like CdTe, CdSe, and CdSe/ZnS, as well as cadmium-free QDs like graphene QDs (GQDs), graphene oxide QDs (GOQDs), and others, were emphasized and described in detail, as well as the underlying mechanisms of QDs generating these effects. Furthermore, general physicochemical parameters determining QD-induced toxicity in zebrafish were introduced, such as chemical composition and surface coating/modification. The limitations and special concerns of using zebrafish in QD toxicity studies were also mentioned. Finally, we predicted that the utilization of high-throughput screening assays and omics, such as transcriptome sequencing, proteomics, and metabolomics will be popular topic in nanotoxicology.

Transcriptome analysis reveals hepatotoxicity in zebrafish induced by cyhalofop‑butyl

Cyhalofop‑butyl is a highly effective aryloxyphenoxypropionate herbicide and widely used for weed control in paddy fields. With the increasing residue of cyhalofop‑butyl, it poses a threat to the survival of aquatic organisms. Here, we investigated the effect of cyhalofop‑butyl on zebrafish to explore its potential hepatotoxic mechanism. The results showed that cyhalofop‑butyl induced hepatocyte degeneration, vacuolation and necrosis of larvae after embryonic exposure for 4 days and caused liver atrophy after 5 days. Meanwhile, the activities of enzymes related to liver function were significantly increased by 0.2 mg/L cyhalofop‑butyl and higher, such as alanine transaminase (ALT) and aspartate transaminase (AST). And the contents of triglyceride (TG) involved in lipid metabolism were significantly decreased by 0.4 mg/L cyhalofop-buty. The expression of genes related to liver development was also significantly down-regulated. Furthermore, transcriptome results showed that the pathways involved in metabolism, immune system and endocrine system were significantly impacted, which may be related to hepatoxicity. To sum up, the present study demonstrated the hepatoxicity caused by cyhalofop-buty and its underlying mechanism. The results may provide new insights for the risk of cyhalofop‑butyl to aquatic organisms and new horizons for the pathogenesis of hepatotoxicity.

Comparative Transcriptome Analysis Provides Novel Molecular Events for the Differentiation and Maturation of Hepatocytes during the Liver Development of Zebrafish

The liver plays an essential role in multiple biological functions including metabolism, detoxification, digestion, coagulation, and homeostasis in vertebrates. The specification and differentiation of embryonic hepatoblasts, the proliferation of hepatocytes, and the hepatic tissue architecture are well documented, but molecular events governing the maturation of hepatocytes during liver development remain largely unclear. In this study, we performed a comparative transcriptome analysis of hepatocytes that were sorted by flow cytometry from developing zebrafish embryos at 60, 72, and 96 hpf. We identified 667 up-regulated and 3640 down-regulated genes in hepatocytes between 60 and 72 hpf, 606 up-regulated and 3924 down-regulated genes between 60 and 96 hpf, and 1693 up-regulated genes and 1508 down-regulated genes between 72 and 96 hpf. GO enrichment analysis revealed that key biological processes, cellular components, and molecular functions in hepatocytes between 60 to 72 hpf, such as cell cycle, DNA replication, DNA repair, RNA processing, and transcription regulation, are mainly associated with the proliferation of hepatocytes. In addition to biological processes, cellular components, and molecular functions for cell proliferation, molecular functions for carbohydrate metabolism were enriched in hepatocytes during 72 to 96 hpf. KEGG enrichment analysis identified key signaling pathways, such as cell cycle, RNA degradation, ubiquitin-mediated proteolysis, ErbB and Hedgehog signaling, basal transcription factors, Wnt signaling, and glycan degradation, which are closely associated with cell proliferation or carbohydrate metabolism in hepatocytes between 60 to 72 hpf. Newly enriched signaling pathways in hepatocytes during 72 to 96 hpf include metabolisms of pyrimidine, purine, nicotinate and nicotinamide, caffeine, glycine, serine and threonine, ABC transporters, and p53 signaling that function in metabolisms of lipid, protein and energy, cellular secretion, or detoxification, indicating the functional maturation of hepatocytes between 72 to 96 hpf. These findings provide novel clues for further understanding the functional differentiation and maturation of hepatocytes during liver development.

Inflammation aggravated the hepatotoxicity of triptolide by oxidative stress, lipid metabolism disorder, autophagy, and apoptosis in zebrafish

Triptolide is a major compound isolated from the Tripterygium wilfordii Hook that is mainly used for the treatment of autoimmune disorders and inflammatory diseases. Though triptolide-induced hepatotoxicity has been widely reported, the hepatic effects when the patients are in an inflammatory state are not clear. In this study, we used low-dose Lipopolysaccharides (LPS) to disrupt the inflammation homeostasis in the liver of zebrafish and explored the hepatotoxicity of triptolide under an inflammatory state. Compared with the Triptolide group, LPS-Triptolide cotreatment exacerbate the liver injury with a remarkable decrease of liver size and liver-specific fluorescence intensity, accompanied by significant elevation of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities. Liver cell damages were further demonstrated by histological staining and scanning electron microscopy observation. Lipid metabolism was severely impaired as indicated by delayed yolk sac absorption, accumulated triglycerides in the liver, and dysregulation of the related genes, such as ppar-α, cpt-1, mgst, srebf1/2, and fasn. Oxidative stress could be involved in the molecular mechanism as the Nrf2/keap1 antioxidant pathways were down-regulated when the zebrafish in an inflammatory state. Moreover, the expression of autophagy-related genes such as beclin, atg5, map1lc3b, and atg3 was also dysregulated. Finally, apoptosis was significantly induced in responses to LPS-Triptolide co-treatment. We speculate that triptolide could exacerbate the immune response and impair lipid metabolism, resulting in enhanced sensitivity of the zebrafish liver to triptolide-induced toxic effects through disruption of the antioxidant system and induction of apoptosis.

Potential of the zebrafish (Danio rerio) embryo test to discriminate between chemicals of similar molecular structure-a study with valproic acid and 14 of its analogues

Valproic acid is a frequently used antiepileptic drug and known pediatric hepatotoxic agent. In search of pharmaceuticals with increased effectiveness and reduced toxicity, analogue chemicals came into focus. So far, toxicity and teratogenicity data of drugs and metabolites have usually been collected from mammalian model systems such as mice and rats. However, in an attempt to reduce mammalian testing while maintaining the reliability of toxicity testing of new industrial chemicals and drugs, alternative test methods are being developed. To this end, the potential of the zebrafish (Danio rerio) embryo to discriminate between valproic acid and 14 analogues was investigated by exposing zebrafish embryos for 120 h post fertilization in the extended version of the fish embryo acute toxicity test (FET; OECD TG 236), and analyzing liver histology to evaluate the correlation of liver effects and the molecular structure of each compound. Although histological evaluation of zebrafish liver did not identify steatosis as the prominent adverse effect typical in human and mice, the structure–activity relationship (SAR) derived was comparable not only to human HepG2 cells, but also to available in vivo mouse and rat data. Thus, there is evidence that zebrafish embryos might serve as a tool to bridge the gap between subcellular, cell-based systems and vertebrate models.

Protective effect of curcumin on zebrafish liver under ethanol-induced oxidative stress

Oxidative stress has an important role in determining severe damage to the liver, including steatosis. Curcumin (CUR) is a natural polyphenol compound with antioxidant potential but its mechanism is still unclear. In this study, 2% ethanol (ETH) was used to establish a liver injury model in Tg (fabp10: Ps Red) transgenic zebrafish with the fluorescent liver. Ethanol-treated zebrafish had an increased vacuole rate at 144 h post-fertilization (hpf), thus confirming the effectiveness of the proposed model in inducing liver damage. However, when ethanol was submitted to co-exposure with curcumin, fluorescence area and signal intensity, as well as vacuole rate, were similar to the levels found in the control group. RNA-seq results showed that ethanol and CUR affected the regulation of catalytic activity and phenylalanine metabolism, biosynthesis of amino acids, and arginine and proline metabolism signaling pathways. QRT-PCR analysis also showed that treatment with CUR led to the downregulation of genes involved in the Nrf2-Keap1 signaling pathway and altered the expression pattern of genes related to glutathione metabolism (gsr, gpx1a, gstp1, gsto1, and idh1a). CUR also induced an increase in GSH content and recovered decreased GSH caused by ethanol exposure. The findings discussed herein indicate that CUR can promote glutathione synthesis, which aided in the recovery from ethanol-induced liver damage in zebrafish larvae.

BML-257, a Small Molecule that Protects against Drug-Induced Liver Injury in Zebrafish

The use of many essential drugs is restricted due to their deleterious effects on the liver. Molecules that can prevent or protect the liver from drug-induced liver injury (DILI) would be invaluable in such situations. We used a transgenic line in zebrafish with a hepatocyte-specific expression of bacterial nitroreductase to cause temporally controlled liver damage. A whole organism-based chemical screen using the transgenic line identified BML-257, a potent small molecule AKT inhibitor, that protected the liver against metronidazole-induced liver injury. BML-257 also showed potent prophylactic and pro-regenerative activity in this liver damage model. BML-257 was tested in two independent toxicological models of liver injury caused by acetaminophen and isoniazid and was found to be protective against damage. This suggests that BML-257 has the potential to protect against multiple kinds of DILI.

Three-dimensional (3D) liver cell models - a tool for bridging the gap between animal studies and clinical trials when screening liver accumulation and toxicity of nanobiomaterials

Despite the exciting properties and wide-reaching applications of nanobiomaterials (NBMs) in human health and medicine, their translation from bench to bedside is slow, with a predominant issue being liver accumulation and toxicity following systemic administration. In vitro 2D cell-based assays and in vivo testing are the most popular and widely used methods for assessing liver toxicity at pre-clinical stages; however, these fall short in predicting toxicity for NBMs. Focusing on in vitro and in vivo assessment, the accurate prediction of human-specific hepatotoxicity is still a significant challenge to researchers. This review describes the relationship between NBMs and the liver, and the methods for assessing toxicity, focusing on the limitations they bring in the assessment of NBM hepatotoxicity as one of the reasons defining the poor translation for NBMs. We will then present some of the most recent advances towards the development of more biologically relevant in vitro liver methods based on tissue-mimetic 3D cell models and how these could facilitate the translation of NBMs going forward. Finally, we also discuss the low public acceptance and limited uptake of tissue-mimetic 3D models in pre-clinical assessment, despite the demonstrated technical and ethical advantages associated with them.

Evaluation of Metal-Organic Framework MIL-89 nanoparticles toxicity on embryonic zebrafish development

Metal-Organic Framework MIL-89 nanoparticles garnered remarkable attention for their widespread use in technological applications. However, the impact of these nanomaterials on human and environmental health is still limited, and concerns regarding the potential risk of exposure during manipulation is constantly rising. Therefore, the extensive use of nanomaterials in the medical field necessitates a comprehensive assessment of their safety and interaction with different tissues of the body system. In this study, we evaluated the systemic toxicity of nanoMIL-89 using Zebrafish embryos as a model system to determine the acute developmental effect. Zebrafish embryos were exposed to a range of nanoMIL-89 concentrations (1 - 300 µM) at 4 h post-fertilization (hpf) for up to 120 hpf. The viability and hatching rate were evaluated at 24-72 hpf, whereas the cardiac function was assessed at 72 and 96 hpf, and the neurodevelopment and hepatic steatosis at 120 hpf. Our study shows that nanoMIL-89 exerted no developmental toxicity on zebrafish embryos at low concentrations (1-10 µM). However, the hatching time and heart development were affected at high concentrations of nanoMIL-89 (> 30 µM). Our findings add novel information into the available data about the in vivo toxicity of nanoMIL-89 and demonstrate its innocuity and safe use in biological, environmental, and medical applications.

Transcriptomic analysis in zebrafish larvae identifies iron-dependent mitochondrial dysfunction as a possible key event of NAFLD progression induced by benzo[a]pyrene/ethanol co-exposure

Non-alcoholic fatty liver disease (NAFLD) is a worldwide epidemic for which environmental contaminants are increasingly recognized as important etiological factors. Among them, the combination of benzo[a]pyrene (B[a]P), a potent environmental carcinogen, with ethanol, was shown to induce the transition of steatosis toward steatohepatitis. However, the underlying mechanisms involved remain to be deciphered. In this context, we used high-fat diet fed zebrafish model, in which we previously observed progression of steatosis to a steatohepatitis-like state following a 7-day-co-exposure to 43 mM ethanol and 25 nM B[a]P. Transcriptomic analysis highlighted the potent role of mitochondrial dysfunction, alterations in heme and iron homeostasis, involvement of aryl hydrocarbon receptor (AhR) signaling, and oxidative stress. Most of these mRNA dysregulations were validated by RT-qPCR. Moreover, similar changes were observed using a human in vitro hepatocyte model, HepaRG cells. The mitochondria structural and functional alterations were confirmed by transmission electronic microscopy and Seahorse technology, respectively. Involvement of AhR signaling was evidenced by using in vivo an AhR antagonist, CH223191, and in vitro in AhR-knock-out HepaRG cells. Furthermore, as co-exposure was found to increase the levels of both heme and hemin, we investigated if mitochondrial iron could induce oxidative stress. We found that mitochondrial labile iron content was raised in toxicant-exposed larvae. This increase was prevented by the iron chelator, deferoxamine, which also inhibited liver co-exposure toxicity. Overall, these results suggest that the increase in mitochondrial iron content induced by B[a]P/ethanol co-exposure causes mitochondrial dysfunction that contributes to the pathological progression of NAFLD.