Transcriptional profiling of cytochrome P450 genes in the liver of adult zebrafish, Danio rerio

Assessment of developmental toxicity and the potential mode of action underlying single and binary exposure to estrogenic endocrine disrupting chemicals in zebrafish (Danio rerio)

The current study investigated the effect of single and binary exposure to distinct xenoestrogens, including diethylstilbestrol (DES) and zearalenone (ZEN), on zebrafish embryos subjected to continuous exposure for 4 days starting from 4 h post fertilization. Noteworthy impact on cumulative mortality, hatchability, spinal and tail curvature, pericardial edema, and reduction in blood circulation were observed in DES-treated embryos, with lower incidence and intensity shown for ZEN at the same nominal concentration (3 μM). An interactive effect was seen for the combined exposure to DES and ZEN, in which deformities and circulatory failure mediated by DES were mitigated by co-treatment with low concentrations of ZEN. Similarly, ZEN-induced spinal and tail curvature, pericardial edema, and blood flow reduction declined dramatically following DES co-exposure at low concentrations. A significant counteracting effect has been observed against DES- and ZEN-induced developmental anomalies following co-treatment with an estrogen receptor (ER) antagonist, fulvestrant (FUL). The assessment of the aromatase gene (CYP19A1b) showed that DES strongly upregulated mRNA expression of CYP19A1b with a lower EC50 (1.1 × 10-3 nM) than a natural estrogen, 17β-estradiol (2.5 nM). Similarly, ZEN induced CYP19A1b mRNA expression with an EC50 of 57 nM. Exposure to 10 or 20 μM FUL inhibited the expression of CYP19A1b induced by a single treatment of DES or ZEN. Overall, the competitive action against ER could be the main mechanism underlying the developmental toxicity induced by DES and ZEN.

In vivo and in silico assessments of estrogenic potencies of bisphenol A and its analogs in zebrafish (Danio rerio): Validity of in silico approaches to predict in vivo effects

This study assessed the estrogen-like potencies of bisphenol A (BPA) and its analogs (BPs) using in vivo and in silico approaches in zebrafish. Zebrafish embryos were exposed to 16 BPs, most of which concentration-dependently induced cytochrome P450 19A1b (CYP19A1b) expression. BPs-induced CYP19A1b expression was suppressed by fulvestrant, a nonselective high affinity antagonist for estrogen receptor (Esr) subtypes. For BPs that concentration-dependently induced CYP19A1b expression, we estimated their 50 % effective concentration (EC₅₀) and relative potencies (REPs) with respect to the potency of BPA for inducing CYP19A1b expression. BP C2, Bis-MP, and BPAF showed lower EC₅₀ than BPA, BPE, and BPF, while BPZ and BPB showed moderate EC₅₀. The REP order of the BPs was BP C2 (26) > Bis-MP (24) > BPAF (21) > BPZ (5.8) > BPB (2.7) > BPE (1.5) > BPF (0.63) > 2,4'-BPF (0.22), indicating that some BPs showed greater estrogenic potencies than BPA in our system. We also constructed in silico homology models of ligand binding domains for zebrafish Esr subtypes, including Esr1, Esr2a, and Esr2b. Molecular docking simulations of ligands with the Esr subtypes revealed the interaction energies of some BPs were lower than that of BPA. The interaction energies showed significant positive correlations with their EC₅₀ values for inducing CYP19A1b expression in vivo. This study showed that some BPA analogs have greater estrogenic potencies than BPA and that in silico simulations of interactions between ligands and Esr subtypes may help predict in vivo estrogenic potencies of untested chemicals.

Efficient in vivo and in silico assessments of antiandrogenic potential in zebrafish

This study aimed to establish zebrafish-based in vivo and in silico assay systems to evaluate the antiandrogenic potential of environmental chemicals. Zebrafish embryos were exposed to 17α-methyltestosterone (TES) alone or coexposed to TES and representative antiandrogens including flutamide, p,p'-DDE, vinclozolin, fenitrothion, and linuron. We assessed the transcript expression of the androgen-responsive gene sulfotransferase family 2, cytosolic sulfotransferase 3 (sult2st3). The expression of sult2st3 was significantly induced by TES in the later stages of embryonic development. However, the TES-induced expression of sult2st3 was inhibited by flutamide in a concentration-dependent manner (IC₅₀: 5.7 μM), suggesting that the androgen receptor (AR) plays a role in sult2st3 induction. Similarly, p,p'-DDE, vinclozolin, and linuron repressed the TES-induced expression of sult2st3 (IC_50s: 0.35, 3.9, and 52 μM, respectively). At the highest concentration tested (100 μM), fenitrothion also suppressed sult2st3 expression almost completely. Notably, p,p'-DDE and linuron did not inhibit sult2st3 induction due to higher concentrations of TES; instead, they potentiated TES-induced sult2st3 expression. Fenitrothion and linuron, which had relatively low antiandrogenic potentials in terms of sult2st3 inhibition, induced broader toxicities in zebrafish embryos; thus, the relationship between developmental toxicities and antiandrogenic potency was unclear. Additionally, an in silico docking simulation showed that all five chemicals interact with the zebrafish AR at relatively low interaction energies and with Arg702 as a key amino acid in ligand binding. Our findings suggest that a combination of zebrafish-based in vivo and in silico assessments represents a promising tool to assess the antiandrogenic potentials of environmental chemicals.

Tulp1 deficiency causes early-onset retinal degeneration through affecting ciliogenesis and activating ferroptosis in zebrafish

Mutations in TUB-like protein 1 (TULP1) are associated with severe early-onset retinal degeneration in humans. However, the pathogenesis remains largely unknown. There are two homologous genes of TULP1 in zebrafish, namely tulp1a and tulp1b. Here, we generated the single knockout (tulp1a^-/- and tulp1b^-/-) and double knockout (tulp1-dKO) models in zebrafish. Knockout of tulp1a resulted in the mislocalization of UV cone opsins and the degeneration of UV cones specifically, while knockout of tulp1b resulted in mislocalization of rod opsins and rod-cone degeneration. In the tulp1-dKO zebrafish, mislocalization of opsins was present in all types of photoreceptors, and severe degeneration was observed at a very early age, mimicking the clinical manifestations of TULP1 patients. Photoreceptor cilium length was significantly reduced in the tulp1-dKO retinas. RNA-seq analysis showed that the expression of tektin2 (tekt2), a ciliary and flagellar microtubule structural component, was downregulated in the tulp1-dKO zebrafish. Dual-luciferase reporter assay suggested that Tulp1a and Tulp1b transcriptionally activate the promoter of tekt2. In addition, ferroptosis might be activated in the tulp1-dKO zebrafish, as suggested by the up-regulation of genes related to the ferroptosis pathway, the shrinkage of mitochondria, reduction or disappearance of mitochondria cristae, and the iron and lipid droplet deposition in the retina of tulp1-dKO zebrafish. In conclusion, our study establishes an appropriate zebrafish model for TULP1-associated retinal degeneration and proposes that loss of TULP1 causes defects in cilia structure and opsin trafficking through the downregulation of tekt2, which further increases the death of photoreceptors via ferroptosis. These findings offer insight into the pathogenesis and clinical treatment of early-onset retinal degeneration.

Estrogenic and growth inhibitory responses to organophosphorus flame retardant metabolites in zebrafish embryos

Recent evidence has revealed that organophosphorus flame retardants (OPFRs) elicit a variety of toxic effects, including endocrine disruption. The present study examined estrogenic and growth inhibitory responses to OPFR metabolites in comparison to their parent compounds using zebrafish eleutheroembryos.¹ Exposure to 4-hydroxylphenyl diphenyl phosphate (HO-p-TPHP) but not its parent compound triphenyl phosphate (TPHP) elicited upregulation of a marker gene of estrogenic responses, cytochrome P450 19A1b (CYP19A1b), and this upregulation was reversed by co-exposure to an estrogen receptor antagonist. Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), as well as 3-hydroxylphenyl diphenyl phosphate (HO-m-TPHP) and diphenyl phosphate (DPHP), did not elicit significant changes in the CYP19A1b expression. Reduction in body length was induced by TPHP and to a lesser extent by its hydroxylated metabolites. Altered expression of genes involved in the synthesis and action of thyroid hormones, including iodothyronine deiodinases 1 and 2, thyroid hormone receptor alpha, and transthyretin, were commonly observed for TPHP and its hydroxylated metabolites. Reduction in the body length was also seen in embryos exposed to TDCIPP but not BDCIPP. The transcriptional effect of TDCIPP was largely different from that of TPHP, with decreased expression of growth hormone and prolactin observed only in TDCIPP-exposed embryos. Considering the concentration-response relationships for the growth retardation and gene expression changes, together with existing evidence from other researchers, it is likely that prolactin is in part involved in the growth inhibition caused by TDCIPP. The present study showed similarities and differences in the endocrine disruptive effects of OPFRs and their metabolites.

Combined effects of arsenic and 2,2-dichloroacetamide on different cell populations of zebrafish liver

Arsenic (As) and disinfection by-products are important health risk factors in the water environment. However, their combined effects on different cell populations in the liver are not well known. Here, zebrafish were exposed to 100 μg/L As, 300 μg/L 2,2-dichloroacetamide (DCAcAm), and their combination for 23 days. Then transcriptome profiles of cell populations in zebrafish liver were analyzed by single-cell RNA sequencing (scRNA-seq). A total of 13,563 cells were obtained, which were identified as hepatocytes, hepatic duct cells, endothelial cells and macrophages. Hepatocytes were the main target cell subtype of As and DCAcAm exposures. DCAcAm exposure induced higher toxicity in male hepatocytes, which specifically changed amino acid metabolism, response to hormone and cofactor metabolism. However, As exposure caused higher toxicity in female hepatocytes, which altered lipid metabolism, carbon metabolism, and peroxisome. Combined exposure to As and DCAcAm decreased toxicities in hepatocytes compared to each one alone. Female hepatocytes had higher tolerance to co-exposure of As and DCAcAm than male hepatocytes. Further, combined exposure to As and DCAcAm induced functional changes in macrophages similar to As alone groups, which mainly altered the transfer of sterol and cholesterol. Hepatic duct cells and endothelial cells were not influenced by exposures to As and DCAcAm. This study for the first time highlights the cell-specific combined responses of As and DCAcAm in zebrafish liver, which provide useful information for their health risk assessment in a co-exposure environment.

Transcriptome analysis of developing zebrafish (Danio rerio) embryo following exposure to Gaudichaudione H reveals teratogenicity and cardiovascular defects caused by abnormal iron metabolism

Gaudichaudione H (GH), a caged polyprenylated xanthone from Garcinia plants, showed anti-cancer and anti-inflammatory effects in vitro. However, the in vivo toxicity of this compound has never been reported. The present study was aimed to address the toxic effects of Gaudichaudione H using zebrafish embryos and larvae as an in vivo test model. The zebrafish embryos were treated with GH having different concentrations (0, 0.28, 0.38 and 0.57 μg/mL). The results revealed that GH induces significant embryonic mortality, decreased heartbeat, cardiotoxicity, cardiovascular defects, increased apoptosis and decreased hemoglobinization in zebrafish embryos and larvae. According to transcriptome analysis, 1841 genes were significantly differentially expressed (1185 down-regulated and 656 up-regulated) after GH treatment. The main functions of these genes were related to iron metabolism pathways. The toxicity of GH on zebrafish embryonic development and cardiovascular may due to large amounts of downregulated genes involved in metabolic pathways and DEGs related to 'Iron ion binding' and 'Heme binding' functions.

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

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

Dysregulation of lipid metabolism in PLHC-1 and ZFL cells exposed to tributyltin an all-trans retinoic acid

There is increasing awareness that exposure to endocrine disrupters interferes with lipid homeostasis in vertebrates, including fish. Many of these compounds exert their action by binding to nuclear receptors, such as peroxisome proliferator-activated receptors and retinoid X receptor. This work investigates the use of fish liver cells (PLHC-1 and ZFL cells) for the screening of metabolic and lipid disrupters in the aquatic environment by assessing changes in the cell's lipidome after exposure to the model compounds, tributyltin chloride and all-trans retinoic acid. Lipid extracts, analyzed by FIA-ESI (+/-) Orbitrap, evidenced the intracellular accumulation of triglycerides and diglycerides in both cell models after exposure to 100 and 200 nM tributyltin chloride for 24 h. Exposure to 1 μM all-trans retinoic acid led to a significant accumulation of triglycerides in PLHC-1 cells, while few triglycerides were accumulated in ZFL cells. Retinoic acid (cyp26b1, cyp3a65, lrata) and lipid metabolism (fasn, scd, elovl6) related genes were up-regulated by tributyltin chloride and all-trans retinoic acid, while only all-trans retinoic acid down-regulated the expression of dgat1a. The two cell models show sensitivity and responses to tributyltin chloride and all-trans retinoic acid comparable to those previously reported in mammalian cells. These results support the use of fish liver cells as alternative models for the detection of contaminants that act as lipid disrupters in the aquatic environment.

[Current status of drug safety evaluation using zebrafish]

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

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

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

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.

Developmental circulatory failure caused by metabolites of organophosphorus flame retardants in zebrafish, Danio rerio

Organophosphate triesters are used worldwide as additives in flame retardants and plasticizer as a replacement of polybrominated diphenyl ethers. Increasing evidence on human exposure to and environmental contamination with organophosphorus flame retardants (OPFRs) requires an adequate toxicity assessment for this class of chemicals. While developmental toxicity of several OPFRs has been reported, developmental effects of OPFR metabolites have still to be understood. The present study aimed at characterizing developmental effects of OPFR metabolites using zebrafish embryos (Danio rerio). Triphenyl phosphate (TPHP) and two of its metabolites, 3-hydroxylphenyl diphenyl phosphate and 4-hydroxylphenyl diphenyl phosphate, were most potent for inducing pericardial edema and reduction in blood flow in trunk vessels. Other TPHP metabolites, such as diphenyl phosphate and 4-hydroxylphenyl phenyl phosphate, showed no substantial increase in circulatory failure at concentrations up to 30 μM. Tris (1,3-dichloro-2-propyl) phosphate showed circulatory failure at 30 μM, but its metabolite bis(1,3-dichloro-2-propyl) phosphate did not. Neither tris(2-chloroethyl) phosphate nor its metabolite bis(2-chloroethyl) phosphate, induced circulatory failure. The circulatory failure appeared to be enhanced with the increase in the octanol-water partition coefficients of OPFRs and their metabolites, suggesting that developmental circulatory failure posed by these chemicals could be estimated by their bioaccumulative potential. The present study demonstrated developmental circulatory failure of hydroxylated TPHP metabolites, which was almost equipotent to TPHP. Diester OPFR metabolites showed no major developmental toxicity at the concentrations used in this study. The current results establish the foundation for further understanding the similarities and differences in the toxic mechanisms between OPFRs and their metabolites.

Western Diet-Induced Metabolic Alterations Affect Circulating Markers of Liver Function before the Development of Steatosis

Since nutrition might have a significant impact on liver function, we analyzed the early effect of Western-type diet on hepatic tissue and lipid and drug metabolism in Wistar–Kyoto rats (n = 8); eight rats fed with a standard diet were used as controls. Histological analysis of liver tissue was performed, and plasma biochemical parameters were measured. Plasma concentration of six bile acids was determined by ultra-liquid chromatography-tandem mass spectrometry UHPLC-MS/MS. Hepatic gene expressions of enzymes involved in drug and lipid metabolism were assessed by means of real-time reverse transcription (qRT)-PCR. Liver of rats fed with a Western diet did not show macroscopic histological alterations, but number and diameter of lipid droplets increased, as well as DGAT1, GPAT4, SCD, FASN and SREBP2 expression. Furthermore, Western diet-fed animals showed an increase in the activation of hepatic stellate cells and macrophage number in liver tissue, as well as a significant increase in AST and bilirubin levels (p < 0.01), and in the LDL:HDL cholesterol ratio (p < 0.001). Plasma chenodeoxycholic acid concentration increased significantly, whereas cholic acid decreased (p < 0.05), and cytochrome P450 genes were generally downregulated. Significant changes in hepatic lipid and drug metabolism are early induced by the Western diet, prior to steatosis development. Such changes are associated with a peculiar alteration in circulating bile acids, which could represent an early marker of non-alcoholic fatty liver disease (NAFLD) development.