PGE2-regulated wnt signaling and N-acetylcysteine are synergistically hepatoprotective in zebrafish acetaminophen injury. Proc Natl Acad Sci U S A. 2010;107:17315-17320. [PMID: 20855591 DOI: 10.1073/pnas.1008209107]

Myeloid-specific deficiency of group VIA calcium-independent phospholipase A2 preconditions myeloid cells for injury resolution after acetaminophen exposure

Genetic PLA2G6 variants are associated with C-reactive protein in humans. Myeloid-specific PLA2G6-deficient (Pla2g6M-/-) mice show increased hepatic myeloperoxidase and recruitment of granulocytes in response to lipopolysaccharide (LPS). We hypothesized that Pla2g6M-/- mice could be protected from acetaminophen (APAP) hepatotoxicity whereby neutrophils, eosinophils, and alternatively activated macrophages are reportedly protective. Herein, Pla2g6M-/- mice treated with 300 mg/kg APAP for 24 h showed attenuated hepatic necrosis and plasma cytokines, and with elevated levels of Ly6Clo in peripheral blood mononuclear cells and plasma lipoxin A4. Remarkably, bone-marrow-derived macrophages (BMDMs) from untreated Pla2g6M-/- mice exhibited elevated baseline expression of cPLA2α, NOX2, Rac1, Arg-1, phospho-MLKL, and iNOS protein, which was exacerbated by LPS in vitro. APAP administration preconditioned Pla2g6M-/- BMDMs for further activation of enzymes involving in phagocytosis (Rac1 and phospho-MLKL) and eicosanoids (COX2 and A15LOXB). Pla2g6M-/- BMDMs showed an increased release of pro-resolution lipid mediators lipoxin A4, PGE2, and 15d-PGJ2, which was further elevated by LPS in vitro or APAP in vivo. Phagocytic gene signatures (myeloperoxidase and NOX2) were also upregulated in livers of untreated and APAP-treated Pla2g6M-/- mice. APAP protection in Pla2g6M-/- mice was associated with increased proportion of neutrophils (Ly6G), eosinophils (eosinophilic cationic protein), and M2 macrophages (CD206) in/at the portal tract and central vein as determined by immunohistochemistry. Thus, myeloid-specific PLA2G6 deficiency preconditioned macrophages for eicosanoid and phagocytic pathways rendering protection against APAP hepatotoxicity. Our results may be applicable to patients with PLA2G6 mutations, and PLA2G6 inhibition specifically in myeloid cells may represent a new strategy to alleviate APAP poisoning.

SW033291 promotes liver regeneration after acetaminophen-induced liver injury in mice

Acetaminophen (APAP) is a commonly utilized antipyretic and analgesic drug. Overdose of APAP is a primary contributor to drug-induced liver injury and acute liver failure (ALF). SW033291 has been shown to play a role in tissue regeneration in various diseases; however, its potential to facilitate liver regeneration following APAP-induced hepatic injury remains unexamined. Thus, this study focused on exploring the therapeutic impacts and mechanisms of SW033291 on liver damage by establishing models of APAP-induced acute liver injury in mice. The results showed that treatment with SW033291 reduces serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activities, decreases the area of hepatic necrosis, increases glutathione (GSH) levels, and decreases tissue malondialdehyde (MDA) content, as well as the expression levels of tumor necrosis factor-alpha (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) in mice with liver injury. It could also promote hepatocyte proliferation and inhibit apoptosis by increasing tissue prostaglandin E2 (PGE2) levels. In conclusion, SW033291 demonstrates the capacity to ameliorate APAP-induced hepatic injury in mice by fostering liver regeneration, attenuating oxidative stress, and modulating inflammatory responses, thereby presenting itself as a promising candidate for the development of therapeutic interventions targeting acute liver failure.

Examining the liver-pancreas crosstalk reveals a role for the molybdenum cofactor in β-cell regeneration

Regeneration of insulin-producing β-cells is an alternative avenue to manage diabetes, and it is crucial to unravel this process in vivo during physiological responses to the lack of β-cells. Here, we aimed to characterize how hepatocytes can contribute to β-cell regeneration, either directly or indirectly via secreted proteins or metabolites, in a zebrafish model of β-cell loss. Using lineage tracing, we show that hepatocytes do not directly convert into β-cells even under extreme β-cell ablation conditions. A transcriptomic analysis of isolated hepatocytes after β-cell ablation displayed altered lipid- and glucose-related processes. Based on the transcriptomics, we performed a genetic screen that uncovers a potential role of the molybdenum cofactor (Moco) biosynthetic pathway in β-cell regeneration and glucose metabolism in zebrafish. Consistently, molybdenum cofactor synthesis 2 (Mocs2) haploinsufficiency in mice indicated dysregulated glucose metabolism and liver function. Together, our study sheds light on the liver-pancreas crosstalk and suggests that the molybdenum cofactor biosynthesis pathway should be further studied in relation to glucose metabolism and diabetes.

Using different zebrafish models to explore liver regeneration

The liver possesses an impressive capability to regenerate following various injuries. Given its profound implications for the treatment of liver diseases, which afflict millions globally, liver regeneration stands as a pivotal area of digestive organ research. Zebrafish (Danio rerio) has emerged as an ideal model organism in regenerative medicine, attributed to their remarkable ability to regenerate tissues and organs, including the liver. Many fantastic studies have been performed to explore the process of liver regeneration using zebrafish, especially the extreme hepatocyte injury model. Biliary-mediated liver regeneration was first discovered in the zebrafish model and then validated in mammalian models and human patients. Considering the notable expansion of biliary epithelial cells in many end-stage liver diseases, the promotion of biliary-mediated liver regeneration might be another way to treat these refractory liver diseases. To date, a comprehensive review discussing the current advancements in zebrafish liver regeneration models is lacking. Therefore, this review aims to investigate the utility of different zebrafish models in exploring liver regeneration, highlighting the genetic and cellular insights gained and discussing the potential translational impact on human health.

PGE2 synthesis and signaling in the liver physiology and pathophysiology: An update

The liver plays a central role in systemic metabolism and drug degradation. However, it is highly susceptible to damage due to various factors, including metabolic imbalances, excessive alcohol consumption, viral infections, and drug influences. These factors often result in conditions such as fatty liver, hepatitis, and acute or chronic liver injury. Failure to address these injuries could promptly lead to the development of liver cirrhosis and potentially hepatocellular carcinoma (HCC). Prostaglandin E2 (PGE2) is a metabolite of arachidonic acid that belongs to the class of polyunsaturated fatty acids (PUFA) and is synthesized via the cyclooxygenase (COX) pathway. By binding to its G protein coupled receptors (i.e., EP1, EP2, EP3 and EP4), PGE2 has a wide range of physiological and pathophysiology effects, including pain, inflammation, fever, cardiovascular homeostasis, etc. Recently, emerging studies showed that PGE2 plays an indispensable role in liver health and disease. This review focus on the research progress of the role of PGE2 synthase and its receptors in liver physiological and pathophysiological processes and discuss the possibility of developing liver protective drugs targeting the COXs/PGESs/PGE2/EPs axis.

Embryonic dexamethasone exposure exacerbates hepatic steatosis and APAP-mediated liver injury in zebrafish

Dexamethasone (DXMS), a synthetic glucocorticoid, is known for its pharmacological effects on anti-inflammation, stress response enhancement and immune suppression, and has been widely used to treat potential premature delivery and related diseases. However, emerging evidence has shown that prenatal DXMS exposure leads to increased susceptibility to multiple diseases. In the present study, we used zebrafish as a model to study the effects of embryonic DXMS exposure on liver development and disease. We discovered that embryonic DXMS exposure upregulated the levels of total cholesterol and triglycerides in the liver, increased the glycolysis process and ultimately caused hepatic steatosis in zebrafish larvae. Furthermore, DXMS exposure exacerbated hepatic steatosis in a zebrafish model of fatty liver disease. In addition, we showed that embryonic DXMS exposure worsened liver injury induced by paracetamol (N-acetyl-p-aminophenol, APAP), increased the infiltration of macrophages and neutrophils, and promoted the expression of inflammatory factors, leading to impeded liver regeneration. Taken together, our results provide new evidence that embryonic DXMS exposure exacerbates hepatic steatosis by activating glycolytic pathway, aggravates APAP-induced liver damage and impeded regeneration under a persistent inflammation, calling attention to DXMS administration during pregnancy with probable clinical implications for offspring.

Development of a hepatic cryoinjury model to study liver regeneration

The liver is a remarkable organ that can regenerate in response to injury. Depending on the extent of injury, the liver can undergo compensatory hyperplasia or fibrosis. Despite decades of research, the molecular mechanisms underlying these processes are poorly understood. Here, we developed a new model to study liver regeneration based on cryoinjury. To visualise liver regeneration at cellular resolution, we adapted the CUBIC tissue-clearing approach. Hepatic cryoinjury induced a localised necrotic and apoptotic lesion characterised by inflammation and infiltration of innate immune cells. After this initial phase, we observed fibrosis, which resolved as regeneration re-established homeostasis in 30 days. Importantly, this approach enables the comparison of healthy and injured parenchyma within an individual animal, providing unique advantages to previous models. In summary, the hepatic cryoinjury model provides a fast and reproducible method for studying the cellular and molecular pathways underpinning fibrosis and liver regeneration.

Development of a hepatic cryoinjury model to study liver regeneration

The liver is a remarkable organ that can regenerate in response to injury. Depending on the extent of injury, the liver can undergo compensatory hyperplasia or fibrosis. Despite decades of research, the molecular mechanisms underlying these processes are poorly understood. Here, we developed a new model to study liver regeneration based on cryoinjury. To visualise liver regeneration at cellular resolution, we adapted the CUBIC tissue-clearing approach. Hepatic cryoinjury induced a localised necrotic and apoptotic lesion characterised by inflammation and infiltration of innate immune cells. Following this initial phase, we observed fibrosis, which resolved as regeneration re-established homeostasis in 30 days. Importantly, this approach enables the comparison of healthy and injured parenchyma with an individual animal, providing unique advantages to previous models. In summary, the hepatic cryoinjury model provides a fast and reproducible method for studying the cellular and molecular pathways underpinning fibrosis and liver regeneration.

Zebrafish as Versatile Model for Assessing Animal Venoms and Toxins: Current Applications and Future Prospects

Animal venoms and toxins hold promise as sources of novel drug candidates, therapeutic agents, and biomolecules. To fully harness their potential, it is crucial to develop reliable testing methods that provide a comprehensive understanding of their effects and mechanisms of action. However, traditional rodent assays encounter difficulties in mimicking venom-induced effects in human due to the impractical venom dosage levels. The search for reliable testing methods has led to the emergence of zebrafish (Danio rerio) as a versatile model organism for evaluating animal venoms and toxins. Zebrafish possess genetic similarities to humans, rapid development, transparency, and amenability to high-throughput assays, making it ideal for assessing the effects of animal venoms and toxins. This review highlights unique attributes of zebrafish and explores their applications in studying venom- and toxin-induced effects from various species, including snakes, jellyfish, cuttlefish, anemones, spiders, and cone snails. Through zebrafish-based research, intricate physiological responses, developmental alterations, and potential therapeutic interventions induced by venoms are revealed. Novel techniques such as CRISPR/Cas9 gene editing, optogenetics, and high-throughput screening hold great promise for advancing venom research. As zebrafish-based insights converge with findings from other models, the comprehensive understanding of venom-induced effects continues to expand, guiding the development of targeted interventions and promoting both scientific knowledge and practical applications.

Acetaminophen overdose-induced acute liver injury can be alleviated by static magnetic field

Acetaminophen (APAP), the most frequently used mild analgesic and antipyretic drug worldwide, is implicated in causing 46% of all acute liver failures in the USA and between 40% and 70% in Europe. The predominant pharmacological intervention approved for mitigating such overdose is the antioxidant N-acetylcysteine (NAC); however, its efficacy is limited in cases of advanced liver injury or when administered at a late stage. In the current study, we discovered that treatment with a moderate intensity static magnetic field (SMF) notably reduced the mortality rate in mice subjected to high-dose APAP from 40% to 0%, proving effective at both the initial liver injury stage and the subsequent recovery stage. During the early phase of liver injury, SMF markedly reduced APAP-induced oxidative stress, free radicals, and liver damage, resulting in a reduction in multiple oxidative stress markers and an increase in the antioxidant glutathione (GSH). During the later stage of liver recovery, application of vertically downward SMF increased DNA synthesis and hepatocyte proliferation. Moreover, the combination of NAC and SMF significantly mitigated liver damage induced by high-dose APAP and increased liver recovery, even 24 h post overdose, when the effectiveness of NAC alone substantially declines. Overall, this study provides a non-invasive non-pharmaceutical tool that offers dual benefits in the injury and repair stages following APAP overdose. Of note, this tool can work as an alternative to or in combination with NAC to prevent or minimize liver damage induced by APAP, and potentially other toxic overdoses.

SLAM-ITseq identifies that Nrf2 induces liver regeneration through the pentose phosphate pathway

The liver exhibits a remarkable capacity to regenerate following injury. Despite this unique attribute, toxic injury is a leading cause of liver failure. The temporal processes by which the liver senses injury and initiates regeneration remain unclear. Here, we developed a transgenic zebrafish model wherein hepatocyte-specific expression of uracil phosphoribosyltransferase (UPRT) enabled the implementation of SLAM-ITseq to investigate the nascent transcriptome during initiation of liver injury and regeneration. Using this approach, we identified a rapid metabolic transition from the fed to the fasted state that was followed by induction of the nuclear erythroid 2-related factor (Nrf2) antioxidant program. We find that activation of Nrf2 in hepatocytes is required to induce the pentose phosphate pathway (PPP) and improve survival following liver injury. Mechanistically, we demonstrate that inhibition of the PPP disrupts nucleotide biosynthesis to prevent liver regeneration. Together, these studies provide fundamental insights into the mechanism by which early metabolic adaptation to injury facilitates tissue regeneration.

Methods to Study Liver Disease Using Zebrafish Larvae

Liver disease affects millions of people worldwide, and the high morbidity and mortality is attributed in part to the paucity of treatment options. In many cases, liver injury self-resolves due to the remarkable regenerative capacity of the liver, but in cases when regeneration cannot compensate for the injury, inflammation and fibrosis occur, creating a setting for the emergence of liver cancer. Whole animal models are crucial for deciphering the basic biological underpinnings of liver biology and pathology and, importantly, for developing and testing new treatments for liver disease before it progresses to a terminal state. The cellular components and functions of the zebrafish liver are highly similar to mammals, and zebrafish develop many diseases that are observed in humans, including toxicant-induced liver injury, fatty liver, fibrosis, and cancer. Therefore, the widespread use of zebrafish larvae for studying the mechanisms of these pathologies and for developing potential treatments necessitates the optimization of experimental approaches to assess liver disease in this model. Here, we describe protocols using staining methods, imaging, and gene expression analysis to assess liver injury, fibrosis, and preneoplastic changes in the liver of larval zebrafish.

Heme-deficient primitive red blood cells induce HSPC ferroptosis by altering iron homeostasis during zebrafish embryogenesis

The crosstalk between hematopoietic lineages is important for developmental hematopoiesis. However, the role of primitive red blood cells (RBCs) in the formation of definitive hematopoietic stem and progenitor cells (HSPCs) is largely unknown. Primitive RBC deficiencies in mammals always lead to early embryonic lethality, but zebrafish lines with RBC deficiencies can survive to larval stage. By taking advantage of a zebrafish model, we find that the survival of nascent HSPCs is impaired in alas2- or alad-deficient embryos with aberrant heme biosynthesis in RBCs. Heme-deficient primitive RBCs induce ferroptosis of HSPCs through the disruption of iron homeostasis. Mechanistically, heme-deficient primitive RBCs cause blood iron-overload via Slc40a1, and an HSPC iron sensor, Tfr1b, mediates excessive iron absorption. Thus, iron-induced oxidative stress stimulates the lipid peroxidation, which directly leads to HSPC ferroptosis. Anti-ferroptotic treatments efficiently reverse HSPC defects in alas2 or alad mutants. HSPC transplantation assay reveals that the attenuated erythroid reconstitution efficiency may result from the ferroptosis of erythrocyte-biased HSPCs. Together, these results illustrate that heme-deficient primitive RBCs are detrimental to HSPC production and may provide potential implications for iron dysregulation-induced hematological malignancies.

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.

Hepatotoxicity screening and ranking of structurally different pyrrolizidine alkaloids in zebrafish

Pyrrolizidine alkaloids (PAs) are phytotoxins distributed in ∼6000 plant species. PA-contaminated/containing foodstuffs/herbs/supplements pose a potential threat to human health. Various regulatory authorities established different PA margins of exposure assuming an equal hepatotoxic potency of structurally diverse PAs, although they exhibit different toxic potencies. Therefore, understanding hepatotoxic potencies of different PAs would facilitate a more appropriate risk assessment of PA exposure. In this study, a zebrafish model, which mimics physiological processes of absorption, distribution, metabolism, and excretion, was selected to evaluate acute hepatotoxic potency of different PAs (7 PAs and 2 PA N-oxides) and explore possible physiological pathways involved in PA-induced hepatotoxicity. After 6 h oral administration, PAs caused distinct structure-dependent hepatotoxicity with a series of biochemical and histological changes in zebrafish. Based on the measured toxicological endpoints, the relative toxic potency order of different PAs was derived as lasiocarpine ∼ retrorsine > monocrotaline > riddelliine > clivorine > heliotrine > retrorsine N-oxide ∼ riddelliine N-oxide≫>platyphyline. Further, compared to control group, different upregulation/downregulation of mRNA expression in PA-treated groups indicated that inflammation, apoptosis, and steatosis were involved in PA-induced hepatotoxicity in zebrafish. These findings demonstrate that zebrafish model is useful for screening and ranking hepatotoxicity of PAs with diverse structures, which would facilitate the more accurate risk assessment of PA exposure.

Efficient knock-in method enabling lineage tracing in zebrafish

Here, we devised a cloning-free 3' knock-in strategy for zebrafish using PCR amplified dsDNA donors that avoids disrupting the targeted genes. The dsDNA donors carry genetic cassettes coding for fluorescent proteins and Cre recombinase in frame with the endogenous gene but separated from it by self-cleavable peptides. Primers with 5' AmC6 end-protections generated PCR amplicons with increased integration efficiency that were coinjected with preassembled Cas9/gRNA ribonucleoprotein complexes for early integration. We targeted four genetic loci (krt92, nkx6.1, krt4, and id2a) and generated 10 knock-in lines, which function as reporters for the endogenous gene expression. The knocked-in iCre or CreERT2 lines were used for lineage tracing, which suggested that nkx6.1 + cells are multipotent pancreatic progenitors that gradually restrict to the bipotent duct, whereas id2a + cells are multipotent in both liver and pancreas and gradually restrict to ductal cells. In addition, the hepatic id2a + duct show progenitor properties upon extreme hepatocyte loss. Thus, we present an efficient and straightforward knock-in technique with widespread use for cellular labelling and lineage tracing.

Transgenic Zebrafish Expressing Rat Cytochrome P450 2E1 (CYP2E1): Augmentation of Acetaminophen-Induced Toxicity in the Liver and Retina

Metabolic activation is the primary cause of chemical toxicity including hepatotoxicity. Cytochrome P450 2E (CYP2E) is involved in this process for many hepatotoxicants, including acetaminophen (APAP), one of the most common analgesics and antipyretics. Although the zebrafish is now used as a model for toxicology and toxicity tests, the CYP2E homologue in zebrafish has not been identified yet. In this study, we prepared transgenic zebrafish embryos/larvae expressing rat CYP2E1 and enhanced green fluorescent protein (EGFP) using a β-actin promoter. Rat CYP2E1 activity was confirmed by the fluorescence of 7-hydroxycoumarin (7-HC), a metabolite of 7-methoxycoumarin that was specific for CYP2 in transgenic larvae with EGFP fluorescence (EGFP [+]) but not in transgenic larvae without EGFP fluorescence (EGFP [-]). APAP (2.5 mM) caused reduction in the size of the retina in EGFP [+] larvae but not in EGFP [-] larvae, while APAP similarly reduced pigmentation in both larvae. APAP at even 1 mM reduced the liver size in EGFP [+] larvae but not in EGFP [-] larvae. APAP-induced reduction of liver size was inhibited by N-acetylcysteine. These results suggest that rat CYP2E1 is involved in some APAP-induced toxicological endpoints in the retina and liver but not in melanogenesis of the developing zebrafish.

Update on Hepatobiliary Plasticity

The liver field has been debating for decades the contribution of the plasticity of the two epithelial compartments in the liver, hepatocytes and biliary epithelial cells (BECs), to derive each other as a repair mechanism. The hepatobiliary plasticity has been first observed in diseased human livers by the presence of biphenotypic cells expressing hepatocyte and BEC markers within bile ducts and regenerative nodules or budding from strings of proliferative BECs in septa. These observations are not surprising as hepatocytes and BECs derive from a common fetal progenitor, the hepatoblast, and, as such, they are expected to compensate for each other's loss in adults. To investigate the cell origin of regenerated cell compartments and associated molecular mechanisms, numerous murine and zebrafish models with ability to trace cell fates have been extensively developed. This short review summarizes the clinical and preclinical studies illustrating the hepatobiliary plasticity and its potential therapeutic application.

Renal interstitial cells promote nephron regeneration by secreting prostaglandin E2

In organ regeneration, progenitor and stem cells reside in their native microenvironment, which provides dynamic physical and chemical cues essential to their survival, proliferation, and differentiation. However, the types of cells that form the native microenvironment for renal progenitor cells (RPCs) have not been clarified. Here, single-cell sequencing of zebrafish kidney reveals fabp10a as a principal marker of renal interstitial cells (RICs), which can be specifically labeled by GFP under the control of fabp10a promoter in the fabp10a:GFP transgenic zebrafish. During nephron regeneration, the formation of nephrons is supported by RICs that form a network to wrap the RPC aggregates. RICs that are in close contact with RPC aggregates express cyclooxygenase 2 (Cox2) and secrete prostaglandin E2 (PGE2). Inhibiting PGE2 production prevents nephrogenesis by reducing the proliferation of RPCs. PGE2 cooperates with Wnt4a to promote nephron maturation by regulating β-catenin stability of RPC aggregates. Overall, these findings indicate that RICs provide a necessary microenvironment for rapid nephrogenesis during nephron regeneration.

Biliary epithelial cells are facultative liver stem cells during liver regeneration in adult zebrafish

The liver is a highly regenerative organ, yet the presence of a dedicated stem cell population remains controversial. Here, we interrogate a severe hepatocyte injury model in adult zebrafish to define that regeneration involves a stem cell population. After near-total hepatocyte ablation, single-cell transcriptomic and high-resolution imaging analyses throughout the entire regenerative timeline reveal that biliary epithelial cells undergo transcriptional and morphological changes to become hepatocytes. As a population, biliary epithelial cells give rise to both hepatocytes and biliary epithelial cells. Biliary epithelial cells proliferate and dedifferentiate to express hepatoblast transcription factors prior to hepatocyte differentiation. This process is characterized by increased MAPK, PI3K, and mTOR signaling, and chemical inhibition of these pathways impairs biliary epithelial cell proliferation and fate conversion. We conclude that, upon severe hepatocyte ablation in the adult liver, biliary epithelial cells act as facultative liver stem cells in an EGFR-PI3K-mTOR-dependent manner.

Wnt signaling in liver regeneration, disease, and cancer

The liver exhibits the highest recovery rate from acute injuries. However, in chronic liver disease, the long-term loss of hepatocytes often leads to adverse consequences such as fibrosis, cirrhosis, and liver cancer. The Wnt signaling plays a pivotal role in both liver regeneration and tumorigenesis. Therefore, manipulating the Wnt signaling has become an attractive approach to treating liver disease, including cancer. Nonetheless, given the crucial roles of Wnt signaling in physiological processes, blocking Wnt signaling can also cause several adverse effects. Recent studies have identified cancer-specific regulators of Wnt signaling, which would overcome the limitation of Wnt signaling target approaches. In this review, we discussed the role of Wnt signaling in liver regeneration, precancerous lesion, and liver cancer. Furthermore, we summarized the basic and clinical approaches of Wnt signaling blockade and proposed the therapeutic prospects of cancer-specific Wnt signaling blockade for liver cancer treatment.

A critical review on paracetamol removal from different aqueous matrices by Fenton and Fenton-based processes, and their combined methods

Paracetamol (PCT), also known as acetaminophen, is a drug used to treat fever and mild to moderate pain. After consumption by animals and humans, it is excreted through the urine to the sewer systems, wastewater treatment plants, and other aquatic/natural environments. It has been detected in trace amounts in effluents of wastewater plant treatments, sewage sludge, hospital wastewaters, surface waters, and drinking water. PCT can cause genetic code damage, oxidative degradation of lipids, and denaturation of protein in cells, and its toxicity has been well-proven in bacteria, algae, macrophytes, protozoan, and fishes. To avoid its harmful health problems over living beings, powerful Fenton and Fenton-based treatments as pre-eminent advanced oxidation processes (AOPs) have been developed because of the inefficient treatment by conventional treatments. This paper presents a comprehensive and critical review over the application of such Fenton technologies to remove PCT from natural waters, synthetic wastewaters, and real wastewaters. The characteristics and main results obtained using Fenton, photo-Fenton, electro-Fenton, and photoelectro-Fenton are described, making special emphasis in the oxidative action of the generated reactive oxygen species. Hybrid processes based on the coupling with ultrasounds, gamma radiation, photocatalysis, photoelectrocatalysis, zero-valent iron-activated persulfate, adsorption, and microbial fuel cells, are analyzed. Sequential treatments involving the initiation with plasma gliding arc discharge and post-biological process are detailed. Comparative results with other available AOPs are also described and discussed. Finally, 13 aromatic by-products and 9 short-linear aliphatic carboxylic acid detected during the PCT removal by Fenton and Fenton-based processes are reported, with the proposal of three parallel pathways for its initial degradation.

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.

Single-cell transcriptomics reveals conserved cell identities and fibrogenic phenotypes in zebrafish and human liver

The mechanisms underlying liver fibrosis are multifaceted and remain elusive with no approved antifibrotic treatments available. The adult zebrafish has been an underutilized tool to study liver fibrosis. We aimed to characterize the single-cell transcriptome of the adult zebrafish liver to determine its utility as a model for studying liver fibrosis. We used single-cell RNA sequencing (scRNA-seq) of adult zebrafish liver to study the molecular and cellular dynamics at a single-cell level. We performed a comparative analysis to scRNA-seq of human liver with a focus on hepatic stellate cells (HSCs), the driver cells in liver fibrosis. scRNA-seq reveals transcriptionally unique populations of hepatic cell types that comprise the zebrafish liver. Joint clustering with human liver scRNA-seq data demonstrates high conservation of transcriptional profiles and human marker genes in zebrafish. Human and zebrafish HSCs show conservation of transcriptional profiles, and we uncover collectin subfamily member 11 (colec11) as a novel, conserved marker for zebrafish HSCs. To demonstrate the power of scRNA-seq to study liver fibrosis using zebrafish, we performed scRNA-seq on our zebrafish model of a pediatric liver disease with mutation in mannose phosphate isomerase (MPI) and characteristic early liver fibrosis. We found fibrosis signaling pathways and upstream regulators conserved across MPI-depleted zebrafish and human HSCs. CellPhoneDB analysis of zebrafish transcriptome identified neuropilin 1 as a potential driver of liver fibrosis. Conclusion: This study establishes the first scRNA-seq atlas of the adult zebrafish liver, highlights the high degree of similarity to human liver, and strengthens its value as a model to study liver fibrosis.

Lipids in Liver Failure Syndromes: A Focus on Eicosanoids, Specialized Pro-Resolving Lipid Mediators and Lysophospholipids

Lipids are organic compounds insoluble in water with a variety of metabolic and non-metabolic functions. They not only represent an efficient energy substrate but can also act as key inflammatory and anti-inflammatory molecules as part of a network of soluble mediators at the interface of metabolism and the immune system. The role of endogenous bioactive lipid mediators has been demonstrated in several inflammatory diseases (rheumatoid arthritis, inflammatory bowel disease, atherosclerosis, cancer). The liver is unique in providing balanced immunotolerance to the exposure of bacterial components from the gut transiting through the portal vein and the lymphatic system. This balance is abruptly deranged in liver failure syndromes such as acute liver failure and acute-on-chronic liver failure. In these syndromes, researchers have recently focused on bioactive lipid mediators by global metabonomic profiling and uncovered the pivotal role of these mediators in the immune dysfunction observed in liver failure syndromes explaining the high occurrence of sepsis and subsequent organ failure. Among endogenous bioactive lipids, the mechanistic actions of three classes (eicosanoids, pro-resolving lipid mediators and lysophospholipids) in the pathophysiological modulation of liver failure syndromes will be the topic of this narrative review. Furthermore, the therapeutic potential of lipid-immune pathways will be described.

Evaluation of the hepatoprotective effect of curcumin-loaded solid lipid nanoparticles against paracetamol overdose toxicity: Role of inducible nitric oxide synthase

Curcumin (Cur) is a natural compound that exhibited therapeutic effects against various liver injuries however Cur showed poor water solubility and bioavailability. This study aimed to design Cur-loaded solid lipid nanoparticles (SLNs) and to evaluate the hepatoprotective and antioxidant effects in a model of acute hepatotoxicity induced by paracetamol (PCM) overdose compared to the raw Cur and N-acetylcysteine (NAC). SLNs were prepared by emulsion/solvent evaporation method and 3² factorial design was employed. Wistar rats were divided into Control, PCM, PCM + NAC, PCM + raw Cur, and PCM + Cur-SLNs groups and treated orally for 14 days before receiving a single PCM dose. The Cur-loaded SLNs showed high entrapment efficiency % ranging between 69.1 and 92.1%, particle size (PS) between 217 and 506 nm, and zeta potential values between -17.9 and -25.5 mV. The in vivo results revealed that the PCM group exhibited deterioration of liver functions, pathological lesions on the liver tissues, severe oxidative stress, and increases in both the serum and hepatic iNOS levels. Remarkably, the PCM + Cur-SLNs group showed significantly better liver functions and tissue integrity compared to the PCM group. Furthermore, higher reduced glutathione and catalase but lower malondialdehyde and iNOS levels were observed. In conclusion, Cur-loaded SLNs effectively prevented the liver damage induced by PCM overdose through alleviating the oxidative stress and inhibiting the serum and hepatic iNOS expression in an effect comparable to NAC and better than raw Cur.

Identification of NQO2 As a Protein Target in Small Molecule Modulation of Hepatocellular Function

The utility of in vitro human disease models is mainly dependent on the availability and functional maturity of tissue-specific cell types. We have previously screened for and identified small molecules that can enhance hepatocyte function in vitro. Here, we characterize the functional effects of one of the hits, FH1, on primary human hepatocytes in vitro, and also in vivo on primary hepatocytes in a zebrafish model. Furthermore, we conducted an analogue screen to establish the structure-activity relationship of FH1. We performed affinity-purification proteomics that identified NQO2 to be a potential binding target for this small molecule, revealing a possible link between inflammatory signaling and hepatocellular function in zebrafish and human hepatocyte model systems.

Role of prostaglandin E2 in tissue repair and regeneration

Tissue regeneration following injury from disease or medical treatment still represents a challenge in regeneration medicine. Prostaglandin E2 (PGE2), which involves diverse physiological processes via E-type prostanoid (EP) receptor family, favors the regeneration of various organ systems following injury for its capabilities such as activation of endogenous stem cells, immune regulation, and angiogenesis. Understanding how PGE2 modulates tissue regeneration and then exploring how to elevate the regenerative efficiency of PGE2 will provide key insights into the tissue repair and regeneration processes by PGE2. In this review, we summarized the application of PGE2 to guide the regeneration of different tissues, including skin, heart, liver, kidney, intestine, bone, skeletal muscle, and hematopoietic stem cell regeneration. Moreover, we introduced PGE2-based therapeutic strategies to accelerate the recovery of impaired tissue or organs, including 15-hydroxyprostaglandin dehydrogenase (15-PGDH) inhibitors boosting endogenous PGE2 levels and biomaterial scaffolds to control PGE2 release.

Indoleamine 2, 3-dioxygenase 1 aggravates acetaminophen-induced acute liver failure by triggering excess nitroxidative stress and iron accumulation

Acetaminophen (APAP) is the leading cause of acute liver failure (ALF), which is characterized by GSH depletion, oxidative stress and mitochondrial dysfunction. However, the specific mechanism of APAP-induced ALF remains to be clarified. In this study, we demonstrated that indoleamine 2,3-dioxygenase 1 (IDO1) aggravated APAP-induced ALF associated with excess lipid peroxidation, which was reversed by lipid peroxidation inhibitor (ferrostatin-1). Meanwhile, IDO1 deficiency effectively decreased the accumulation of reactive nitrogen species. Additionally, IDO1 deficiency prevented against APAP-induced liver injury through suppressing the activation of macrophages, thereby reduced their iron uptake and export, eventually reduced iron accumulation in hepatocytes through transferrin and transferrin receptor axis. In summary, our study confirmed that APAP-induced IDO1 aggravated ALF by triggering excess oxidative and nitrative stress and iron accumulation in liver. These results offer new insights for the clinical treatment of ALF or iron-dysregulated liver diseases in the future.

Zebrafish disease models in drug discovery: from preclinical modelling to clinical trials

Numerous drug treatments that have recently entered the clinic or clinical trials have their genesis in zebrafish. Zebrafish are well established for their contribution to developmental biology and have now emerged as a powerful preclinical model for human disease, as their disease characteristics, aetiology and progression, and molecular mechanisms are clinically relevant and highly conserved. Zebrafish respond to small molecules and drug treatments at physiologically relevant dose ranges and, when combined with cell-specific or tissue-specific reporters and gene editing technologies, drug activity can be studied at single-cell resolution within the complexity of a whole animal, across tissues and over an extended timescale. These features enable high-throughput and high-content phenotypic drug screening, repurposing of available drugs for personalized and compassionate use, and even the development of new drug classes. Often, drugs and drug leads explored in zebrafish have an inter-organ mechanism of action and would otherwise not be identified through targeted screening approaches. Here, we discuss how zebrafish is an important model for drug discovery, the process of how these discoveries emerge and future opportunities for maximizing zebrafish potential in medical discoveries.

Hydroxysafflor yellows alleviate thrombosis and acetaminophen-induced toxicity in vivo by enhancing blood circulation and poison excretion

BACKGROUND

Hydroxysafflor yellow A (HSYA) from the flower of Carthamus tinctorius (Safflower) has been reported to have various pharmacological effects. However, little is known about the bioactivities of other chemical constituents in Safflower and the relationship between enhancement of blood circulation and hepatoprotection by HSYA.

PURPOSE

The present research was to evaluate the antithrombotic and hepatoprotective activities of HSYA and C, examine their mechanisms of actions, including influence on the excretion velocity of acetaminophen, and the relationship between the antithrombotic, hepatoprotective, and other bioactivities.

METHODS

The hepatoprotective activities were examined by acetaminophen (APAP)-induced zebrafish toxicity and carbon tetrachloride (CCl4)-induced mouse liver injury. The concentrations of APAP in zebrafish and APAP that was excreted to the culture media were quantified by UHPLC-MS. The anti-thrombosis effect of HSYA and C were examined by the phenylhydrazine (PHZ)-induced zebrafish thrombosis.

RESULTS

HSYA and HSYC showed robust protection on APAP-induced toxicity and PHZ-induced thrombosis. The hepatoprotective effects of HSYA and C were more potent than that of the positive control, acetylcysteine (61.7% and 58.0%, respectively, vs. 56.9% at 100 µM) and their antithrombosis effects were more robust than aspirin (95.1% and 86.2% vs. 52.7% at 100 µM). HSYA and C enhanced blood circulation, rescued APAP-treated zebrafish from morphological abnormalities, and mitigated APAP-induced toxicity in liver development in liver-specific RFP-expressing transgenic zebrafish. HSYC attenuated CCl4-induced mouse liver injury and regulated the levels of HIF-1α, iNOS, TNF-α, α-SMA, and NFκB in liver tissues. HSYA was also protective in a dual thrombotic and liver toxicity zebrafish model. By UHPLC-MS, HSYA accelerated the excretion of APAP.

CONCLUSION

HSYA and C are the bioactive constituents of Safflower that are responsible for the herbal drug's traditional use in promoting blood circulation to remove blood stasis. Safflower and its chalcone constituents may protect from damage due to exogenous or disease-induced endogenous toxins by enhancing the excretion velocity of toxins.

Dimethyl fumarate reduces hepatocyte senescence following paracetamol exposure

Liver disease is a major cause of premature death. Oxidative stress in the liver represents a key disease driver. Compounds, such as dimethyl fumarate (DMF), can activate the antioxidant response and are used clinically to treat disease. In this study, we tested the protective properties of DMF before or after paracetamol exposure. Following DMF administration, Nrf2 nuclear translocation was tracked at the single-cell level and target gene transactivation confirmed. Next, the protective properties of DMF were examined following paracetamol exposure. Transcriptomic and biochemical analysis revealed that DMF rescue was underpinned by reduced Nf-kB and TGF-β signaling and cell senescence. Following on from these studies, we employed a Zebrafish model to study paracetamol exposure in vivo. We combined a genetically modified Zebrafish model, expressing green fluorescent protein exclusively in the liver, with automated microscopy. Pre-treatment with DMF, prior to paracetamol exposure, led to reduced liver damage in Zebrafish demonstrating protective properties.

Hepatoprotective effect of forsythiaside a against acetaminophen-induced liver injury in zebrafish: Coupling network pharmacology with biochemical pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Forsythiae Fructus, the dried fruit of Forsythia suspensa (Thunb.) Vahl, is a commonly used traditional Chinese medicine and possesses various pharmacological activities, including anti-inflammation, anti-oxidant and liver protection.

AIM OF THE STUDY

Although acetaminophen (APAP) has been frequently used for its antipyretic and analgesic effects, it leads to liver injury at an overdose or long-term medication. Forsythiaside A (FA), the principal active component of Forsythiae Fructus, exerts prominent antioxidant, anti-inflammatory and hepatoprotective effects. However, the protective property and underlying mechanism of FA against APAP challenge have not yet been elucidated. Therefore, we aimed to explore the hepatoprotective effect and action mechanism of FA against APAP-induced liver injury in zebrafish.

MATERIALS AND METHODS

In this study, liver-specific transgenic zebrafish larvae (lfabp: EGFP) were used to investigate the protective effect of FA against overdose APAP exposure. The liver phenotype, morphological and biochemical assessments were carried out to evaluate the hepatoprotective effect of FA. Network pharmacology and molecular docking study were conducted to analyze the potential targets of FA in the treatment of APAP-induced liver injury. Finally, the mechanism of action was verified by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR).

RESULTS

The liver phenotype, morphological and biochemical assessments indicated that FA could mitigate APAP-triggered liver injury. Network pharmacology and molecular docking analysis indicated that the protective effect of FA might be related to the regulation of targets tumor necrosis factor (TNF), matrix metallopeptidase 9 (MMP9), matrix metallopeptidase 2 (MMP2), and phosphatidylinositol 3-kinase (PI3K). PCR results confirmed that FA could reverse the progressive alterations of genes involving in extracellular matrix remolding and PI3K/AKT-mediated apoptosis signaling pathway.

CONCLUSIONS

Our results indicated that FA could mitigate APAP-induced liver injury through modulating the remolding of extracellular matrix and PI3K/AKT-mediated apoptosis.

Putative anxiolytic-like behavioral effects of acute paracetamol in adult zebrafish

Typically triggered by stress, anxiety disorders are most common and widespread mental illnesses. The zebrafish (Danio rerio) is rapidly becoming an important aquatic model species in stress research and central nervous system (CNS) drug screening. Paracetamol is currently the most prescribed medication for pain and fever, and is among the most used drugs globally. However, its CNS effects, especially on anxiety, in both clinical and animal studies remain poorly understood. Capitalizing on zebrafish as a powerful model system, here we evaluate the effects of paracetamol on anxiety-like behavior in adult fish, and its changes following an acute stress exposure. Overall, we report an anxiolytic-like profile of acute paracetamol treatment, and its alleviation of stress-evoked anxiety, in adult short-fin wild type zebrafish. Collectively, these findings suggest complex neuroactive effects of paracetamol, and reinforce the growing importance of zebrafish models for drug screening, including the search for novel putative anti-stress therapies.

In vivo hepatoprotective activity and the underlying mechanism of chebulinic acid from Terminalia chebula fruit

BACKGROUND

The fruit of Terminalia chebula Retz. is one of the most widely used herbal drug in Traditional medicine prescriptions including those for liver diseases. In the screening of bioactive constituents that have potential hepatoprotective activity, chebulinic acid (CA) which is a major chemical constituent of T. chebula fruit showed potent activity.

PURPOSE

This work was conducted to investigate the hepatoprotective activity and mechanisms of CA.

METHODS

The hepatoprotective effect of CA was examined on hepatotoxic models of cells, zebrafish larvae and mice caused by tert-butyl hydrogen peroxide (t-BHP), acetaminophen (APAP) and CCl4, respectively.

RESULTS

Pretreatment with CA could prevent t-BHP-induced damage in L-02 hepatocytes by blocking the production of ROS, reducing LDH levels and enhancing HO-1 and NQO1 expression via MAPK/Nrf2 signaling pathway. In animal experiments, CA significantly protected mice from CCl4-induced liver injury, as demonstrated by reduced ALT, AST and MDA levels, enhanced SOD activity, improved liver histopathological changes, and the activation of the Nrf2/HO-1 signaling pathway. CA metabolized to chebulic acid isomers with DPPH radical scavenging activity. In a transgenic zebrafish line with liver specific expression of DsRed RFP, CA diminished the hepatotoxicity induced by 10 mM APAP.

CONCLUSION

Experiments in cell and two animal models demonstrated consistent results and comprehensively expounded the hepatoprotective effects of CA.

All routes lead to Rome: multifaceted origin of hepatocytes during liver regeneration

Liver is the largest internal organ that serves as the key site for various metabolic activities and maintenance of homeostasis. Liver diseases are great threats to human health. The capability of liver to regain its mass after partial hepatectomy has widely been applied in treating liver diseases either by removing the damaged part of a diseased liver in a patient or transplanting a part of healthy liver into a patient. Vast efforts have been made to study the biology of liver regeneration in different liver-damage models. Regarding the sources of hepatocytes during liver regeneration, convincing evidences have demonstrated that different liver-damage models mobilized different subtype hepatocytes in contributing to liver regeneration. Under extreme hepatocyte ablation, biliary epithelial cells can undergo dedifferentiation to liver progenitor cells (LPCs) and then LPCs differentiate to produce hepatocytes. Here we will focus on summarizing the progresses made in identifying cell types contributing to producing new hepatocytes during liver regeneration in mice and zebrafish.

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.

Estrogen receptor agonists protect against acetaminophen-induced hepatorenal toxicity in rats

AIMS

Acetaminophen-induced hepatorenal toxicity varies among sexes with controversial results among species. The aim was to compare the impact of sex and ovarian hormones on hepatorenal toxicity and to elucidate protective effects of estrogen and estrogen receptor (ER) agonists.

MAIN METHODS

Under anesthesia, female rats underwent ovariectomy (OVX) or sham-OVX. Starting at postsurgical 40th day, OVX-rats received subcutaneously (each, 1 mg/kg/day) 17β-estradiol (E₂), ERβ-agonist (DPN) or ERα-agonist (PPT) for 10 days, while male and sham-OVX rats received vehicle for 10 days. Then, rats received either acetaminophen (3 g/kg) or saline by orogastric gavage and were decapitated at 24th h. Blood samples were obtained to measure serum ALT, AST, BUN, creatinine levels. Liver and kidney samples were obtained for histopathologic examination and for analyzing levels of luminol- and lucigenin-chemiluminescence, glutathione and myeloperoxidase activity.

KEY FINDINGS

Compared to their control groups, levels of AST, ALT, BUN, creatinine, hepatic and renal myeloperoxidase activity and chemiluminescence levels were increased, and hepatic glutathione level was decreased in acetaminophen-administered male groups, while ALT and hepatic chemiluminescence levels were not elevated in sham-OVX-rats. Both ER-agonists and E₂ reduced BUN, creatinine and reversed all oxidative parameters in renal tissues of OVX-rats. Additionally, ERα-agonist reversed all hepatic injury parameters, while ERβ-agonist elevated hepatic glutathione level.

SIGNIFICANCE

Acetaminophen toxicity in female rats presented with a more preserved hepatic function, while renal toxicity was not influenced by sex or by the lack of ovarian hormones. Pretreatment with estrogen or ER agonists, via their antioxidant actions, provided protective effects on acetaminophen-induced hepatorenal toxicity.

Zebrafish as an integrative vertebrate model to identify miRNA mechanisms regulating toxicity

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Zebrafish are an established vertebrate model for toxicity studies.

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Zebrafish have a fully sequenced genome and the capability to create genetic models.

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Zebrafish have over 80 % homology for genes related to human disease.

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Functions of miRNAs in the zebrafish genome are being characterized.

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Zebrafish are ideal for mechanistic studies on how miRNAs regulate toxicity.

Zebrafish (Danio rerio) are an integrative vertebrate model ideal for toxicity studies. The zebrafish genome is sequenced with detailed characterization of all life stages. With their genetic similarity to humans, zebrafish models are established to study biological processes including development and disease mechanisms for translation to human health. The zebrafish genome, similar to other eukaryotic organisms, contains microRNAs (miRNAs) which function along with other epigenetic mechanisms to regulate gene expression. Studies have now established that exposure to toxins and xenobiotics can change miRNA expression profiles resulting in various physiological and behavioral alterations. In this review, we cover the intersection of miRNA alterations from toxin or xenobiotic exposure with a focus on studies using the zebrafish model system to identify miRNA mechanisms regulating toxicity. Studies to date have addressed exposures to toxins, particulate matter and nanoparticles, various environmental contaminants including pesticides, ethanol, and pharmaceuticals. Current limitations of the completed studies and future directions for this research area are discussed.

Does hepatotoxicity interfere with endocrine activity in zebrafish (Danio rerio)?

Vitellogenin (VTG), a well-established biomarker for the diagnosis of endocrine activity in fish, is used in multiple OECD test guidelines (TG) to identify activities of chemicals on hormonal pathways. However, the synthesis of VTG may not only be modified by typical endocrine-related pathways, but also through non-endocrine-mediated processes. In particular, hepatotoxicity, i.e. toxicant-induced impairment of liver structure and function, might influence VTG as a biomarker, since VTG is synthesized in hepatocytes. An intimate understanding of the interplay between endocrine-related and non-endocrine-related pathways influencing VTG production is crucial for the avoidance of erroneous diagnoses in hazard assessment for regulatory purposes of chemical compounds. In order to investigate whether hepatotoxicity may interfere with hepatic VTG synthesis, adult zebrafish (Danio rerio) were exposed to three well-known hepatotoxicants, acetaminophen, isoniazid and acetylsalicylic acid, according to OECD TG 230. Various hepatotoxicity- and endocrine system-related endpoints were recorded: mRNA expression of selected endocrine- and hepatotoxicity-related marker genes in the liver; VTG levels in head/tail homogenates; and liver histopathology. All three test compounds induced significant, but mild single cell necrosis of hepatocytes and transcriptional changes of hepatotoxicity-related marker genes, thus confirming hepatotoxic effects. A positive correlation between hepatotoxicity and reduced hepatic VTG synthesis was not observed, with the single exception of a weak increase in female zebrafish exposed to APAP. This suggests that - in studies conducted according to OECD TG 229 or 230 - it is unlikely that hepatotoxic chemicals will interfere with the hepatic capacity for VTG synthesis.

New insights into organ-specific oxidative stress mechanisms using a novel biosensor zebrafish

BACKGROUND

Reactive oxygen species (ROS) arise as a result from, and are essential in, numerous cellular processes. ROS, however, are highly reactive and if left unneutralised by endogenous antioxidant systems, can result in extensive cellular damage and/or pathogenesis. In addition, exposure to a wide range of environmental stressors can also result in surplus ROS production leading to oxidative stress (OS) and downstream tissue toxicity.

OBJECTIVES

Our aim was to produce a stable transgenic zebrafish line, unrestricted by tissue-specific gene regulation, which was capable of providing a whole organismal, real-time read-out of tissue-specific OS following exposure to a wide range of OS-inducing environmental contaminants and conditions. This model could, therefore, serve as a sensitive and specific mechanistic in vivo biomarker for all environmental conditions that result in OS.

METHODS

To achieve this aim, we exploited the pivotal role of the electrophile response element (EpRE) as a globally-acting master regulator of the cellular response to OS. To test tissue specificity and quantitative capacity, we selected a range of chemical contaminants known to induce OS in specific organs or tissues, and assessed dose-responsiveness in each using microscopic measures of mCherry fluorescence intensity.

RESULTS

We produced the first stable transgenic zebrafish line Tg (3EpRE:hsp70:mCherry) with high sensitivity for the detection of cellular RedOx imbalances, in vivo in near-real time. We applied this new model to quantify OS after exposure to a range of environmental conditions with high resolution and provided quantification both of compound- and tissue-specific ROS-induced toxicity.

DISCUSSION

Our model has an extremely diverse range of potential applications not only for biomonitoring of toxicants in aqueous environments, but also in biomedicine for identifying ROS-mediated mechanisms involved in the progression of a number of important human diseases, including cancer.

Temperature-dependent toxicity of acetaminophen in Japanese medaka larvae

Because of its analgesic properties, acetaminophen (AAP) is widely used to relieve headache. AAP is generally considered safe for humans, but its effects on aquatic organisms are not well known. Here, we have hypothesis that effects of AAP on aquatic organisms would be environmental temperature dependent, because their physiological function depend on the temperature. To test this hypothesis, we used medaka (Oryzias latipes) as a model, because they can live at a wide range of temperatures (0-40 °C). We exposed medaka larvae to 0 (control), 50, or 150 mg/L of AAP at 15, 25 (optimal temperature), or 30 °C for 4 days. Egg yolk absorption was accelerated with raising temperature at any AAP dose. AAP exposure did not have biologically significant effects on survival ratio and body length of larvae at any tested temperature or dose, but heart rate decreased as the dose of AAP and environmental temperature increased. In addition, as the temperature increased, amount of ATP in individual larvae increased in control group, but decreased in AAP exposed group. Subsequently, exposure to 150 mg/L of AAP at 30 °C decreased the number of red blood cells in the gills; we used 150 mg/L of AAP in subsequent hematological and histological analyses. Hematological analysis showed that rising temperature increased the proportion of morphologically abnormal red blood cells in AAP-exposed larvae, suggesting that AAP induced anemia-like signs in larvae. Histological observation of the kidney, which is a hematopoietic organ in fish, revealed no abnormalities. However, in the liver, which is responsible for drug metabolism, the proportion of vacuoles increased with increasing temperature. Although the exposure concentration we tested was higher than environmentally relevant concentrations, our data indicated that rising temperature enhances the toxicity of AAP to medaka larvae, suggesting an ecological risk of AAP due to global warming.

Effect of 3 Euthanasia Methods on Serum Yield and Serum Cortisol Concentration in Zebrafish (Danio rerio)

Zebrafish are an important model in neuroscience and developmental biology and are also an emerging model in hematology and immunology. Little information is available for zebrafish regarding the physiologic impact of different euthanasia methods and whether a chosen method of euthanasia can impact serum yield. These parameters could impact the choice of euthanasia method for a study. To that end, the current study compared 3 methods of adult zebrafish euthanasia and their effects on 3 distinct criteria; time to loss of opercular movement, volume of serum obtained, and serum cortisol concentration. Blood was collected using a postmortem tail amputation and centrifugation blood collection technique. Time to loss of opercular movement differed significantly among euthanasia methods, with animals undergoing rapid chilling displaying the shortest time (mean Rapid Chilling: 40 s; Benzocaine: 86 s; MS222: 96 s). All methods of euthanasia resulted in a comparable average serum yield (Rapid Chilling = 7.5 μL; Benzocaine = 8.5 μL; MS222 = 7.5 μL per fish). None of the euthanasia methods tested resulted in average cortisol concentrations above the reported physiologic range. Although no significant differences were observed in serum yield or serum cortisol concentration, rapid chilling remains the preferred method for painless, humane euthanasia.

There Is Something Fishy About Liver Cancer: Zebrafish Models of Hepatocellular Carcinoma

The incidence of hepatocellular carcinoma (HCC) and the mortality resulting from HCC are both increasing. Most patients with HCC are diagnosed at advanced stages when curative treatments are impossible. Current drug therapy extends mean overall survival by only a short period of time. Genetic mutations associated with HCC vary widely. Therefore, transgenic and mutant animal models are needed to investigate the molecular effects of specific mutations, classify them as drivers or passengers, and develop targeted treatments. Cirrhosis, however, is the premalignant state common to 90% of HCC patients. Currently, no specific therapies are available to halt or reverse the progression of cirrhosis to HCC. Understanding the genetic drivers of HCC as well as the biochemical, mechanical, hormonal, and metabolic changes associated with cirrhosis could lead to novel treatments and cancer prevention strategies. Although additional therapies recently received Food and Drug Administration approval, significant clinical breakthroughs have not emerged since the introduction of the multikinase inhibitor sorafenib, necessitating alternate research strategies. Zebrafish (Danio rerio) are effective for disease modeling because of their high degree of gene and organ architecture conservation with human beings, ease of transgenesis and mutagenesis, high fecundity, and low housing cost. Here, we review zebrafish models of HCC and identify areas on which to focus future research efforts to maximize the advantages of the zebrafish model system.

Estrogen Activation of G-Protein-Coupled Estrogen Receptor 1 Regulates Phosphoinositide 3-Kinase and mTOR Signaling to Promote Liver Growth in Zebrafish and Proliferation of Human Hepatocytes

BACKGROUND & AIMS

Patients with cirrhosis are at high risk for hepatocellular carcinoma (HCC) and often have increased serum levels of estrogen. It is not clear how estrogen promotes hepatic growth. We investigated the effects of estrogen on hepatocyte proliferation during zebrafish development, liver regeneration, and carcinogenesis. We also studied human hepatocytes and liver tissues.

METHODS

Zebrafish were exposed to selective modifiers of estrogen signaling at larval and adult stages. Liver growth was assessed by gene expression, fluorescent imaging, and histologic analyses. We monitored liver regeneration after hepatocyte ablation and HCC development after administration of chemical carcinogens (dimethylbenzanthrazene). Proliferation of human hepatocytes was measured in a coculture system. We measured levels of G-protein-coupled estrogen receptor (GPER1) in HCC and nontumor liver tissues from 68 patients by immunohistochemistry.

RESULTS

Exposure to 17β-estradiol (E2) increased proliferation of hepatocytes and liver volume and mass in larval and adult zebrafish. Chemical genetic and epistasis experiments showed that GPER1 mediates the effects of E2 via the phosphoinositide 3-kinase-protein kinase B-mechanistic target of rapamycin pathway: gper1-knockout and mtor-knockout zebrafish did not increase liver growth in response to E2. HCC samples from patients had increased levels of GPER1 compared with nontumor tissue samples; estrogen promoted proliferation of human primary hepatocytes. Estrogen accelerated hepatocarcinogenesis specifically in male zebrafish. Chemical inhibition or genetic loss of GPER1 significantly reduced tumor development in the zebrafish.

CONCLUSIONS

In an analysis of zebrafish and human liver cells and tissues, we found GPER1 to be a hepatic estrogen sensor that regulates liver growth during development, regeneration, and tumorigenesis. Inhibitors of GPER1 might be developed for liver cancer prevention or treatment.

TRANSCRIPT PROFILING

The accession number in the Gene Expression Omnibus is GSE92544.

Developing zebrafish disease models for in vivo small molecule screens

The zebrafish is a model organism that allows in vivo studies to be performed at a scale usually restricted to in vitro studies. As such, the zebrafish is well suited to in vivo screens, in which thousands of small molecules are tested for their ability to modify disease phenotypes in zebrafish disease models. Numerous approaches have been developed for modeling human diseases in zebrafish, including mutagenesis, transgenesis, pharmacological approaches, wounding, and exposure to infectious or cancerous agents. We review the various strategies for modeling human diseases in zebrafish and discuss important considerations when developing zebrafish models for use in in vivo small molecule screens.