Assessment of the in vitro developmental toxicity of diethylstilbestrol and estradiol in the zebrafish embryotoxicity test

The present study investigated the developmental toxicity of diethylstilbestrol (DES) in the zebrafish embryotoxicity test (ZET). This was done to investigate whether the ZET would better capture the developmental toxicity of DES than the embryonic stem cells test (EST) that was previously shown to underpredict the DES-induced developmental toxicity as compared to in vivo data, potentially because the EST does not capture late events in the developmental process. The ZET results showed DES-induced growth retardation, cumulative mortality and dysmorphisms (i.e. induction of pericardial edema) in zebrafish embryos while the endogenous ERα agonist 17β-estradiol (E2) showed only growth retardation and cumulative mortality with lower potency compared to DES. Furthermore, the DES-induced pericardial edema formation in zebrafish embryos could be counteracted by co-exposure with ERα antagonist fulvestrant, indicating that the ZET captures the role of ERα in the mode of action underlying the developmental toxicity of DES. Altogether, it is concluded that the ZET differentiates DES from E2 with respect to their developmental toxicity effects, while confirming the role of ERα in mediating the developmental toxicity of DES. Furthermore, comparison to in vivo data revealed that, like the EST, in a quantitative way also the ZET did not capture the relatively high in vivo potency of DES as a developmental toxicant.     

Albendazole causes stage-dependent developmental toxicity and is deactivated by a mammalian metabolization system in a modified zebrafish embryotoxicity test

The zebrafish embryotoxicity test has previously been combined with an external metabolic activation system (MAS) to assess developmental toxicity of metabolites produced by maternal metabolism. Due to toxicity of MAS the exposure was limited to one early and short period. We have modified the method and included additional testing time points with extended exposure durations. Using the anthelmintic drug albendazole as a model substance, we demonstrated stage-dependent toxic effects at three windows of zebrafish embryo development, i.e. 2-3, 12-14 and 24-28h post fertilization, and showed that MAS, by metabolic deactivation, reduced the toxicity of albendazole at all time points. Chemical analysis confirmed that albendazole was efficiently metabolized by MAS to the corresponding sulfoxide and sulfone, which are non-toxic to zebrafish embryos. To conclude, the modified zebrafish embryotoxicity test with MAS can be expanded for assessment of metabolites at different developmental stages.     

Chick embryo neural retina cell culture as a screen for developmental toxicity

An in vitro screen for developmental toxic potential of chemicals using primary cultures of chick embryo neural retina cells is described. The neural retinas of incubation Day 6.5 White Leghorn chick embryos are dissociated into single cells, which are subsequently maintained in a rotating suspension culture. Under normal circumstances, neural retina cells form spheroidal aggregates of a consistent size over the first 24 hr of culture, an event which is dependent on competent cell-cell interactions. Over the remaining 7-day period of culture, cells continue to divide and grow, and differentiation takes place. Each of these developmentally important events--aggregation, growth, and differentiation--is objectively and quantitatively measured as aggregate size and number, aggregate protein content, and glutamine synthetase (a marker of differentiation) activity, respectively. The effects on each developmental endpoint of 22 chemicals, 14 of which have been demonstrated to be developmentally toxic in one or more mammalian species in vivo, and 8 of which are not developmentally toxic, were evaluated. Chemicals were tested up to a concentration of 40 mM, or until marked cytolethality was observed. Of the known developmental toxicants, all but one, 2-methoxyethanol, affected one or more endpoints in the assay. The teratogenic metabolite of 2-methoxyethanol, 2-methoxyacetic acid, was active in the assay. None of the 8 nondevelopmental toxicants had any effect up to a concentration of 40 mM, or at biologically achievable concentrations (e.g., in vivo systemic concentrations at the LD50). Thus, the assay is 95% concordant with in vivo results for this set of chemicals. Quantitative comparisons were made (1) between developmentally toxic ip dosages in rats or mice in vivo and effective concentrations in the chick retina cell culture, and (2) between effective concentrations in chick retina cell culture and rodent whole embryo culture. In the first instance, 71% of the comparisons, and in the second instance, 89% of the comparisons, were within the same order of magnitude (and usually within a factor of two), indicating that the chick retina cell culture is also concordant with developmental toxic potency. Last, it was observed that test agents differentially affect developmental endpoints. Because the assay's endpoints are measured separately and objectively, it may be possible to use the assay to evaluate the effects of test agents on cellular development.(ABSTRACT TRUNCATED AT 400 WORDS)     

The classification of motor neuron defects in the zebrafish embryo toxicity test (ZFET) as an animal alternative approach to assess developmental neurotoxicity

Rodents are widely used to test the developmental neurotoxicity potential of chemical substances. The regulatory test procedures are elaborate and the requirement of numerous animals is ethically disputable. Therefore, non-animal alternatives are highly desirable, but appropriate test systems that meet regulatory demands are not yet available. Hence, we have developed a new developmental neurotoxicity assay based on specific whole-mount immunostainings of primary and secondary motor neurons (using the monoclonal antibodies znp1 and zn8) in zebrafish embryos. By classifying the motor neuron defects, we evaluated the severity of the neurotoxic damage to individual primary and secondary motor neurons caused by chemical exposure and determined the corresponding effect concentration values (EC₅₀). In a proof-of-principle study, we investigated the effects of three model compounds thiocyclam, cartap and disulfiram, which show some neurotoxicity-indicating effects in vertebrates, and the positive controls ethanol and nicotine and the negative controls 3,4-dichloroaniline (3,4-DCA) and triclosan. As a quantitative measure of the neurotoxic potential of the test compounds, we calculated the ratios of the EC₅₀ values for motor neuron defects and the cumulative malformations, as determined in a zebrafish embryo toxicity test (zFET). Based on this index, disulfiram was classified as the most potent and thiocyclam as the least potent developmental neurotoxin. The index also confirmed the control compounds as positive and negative neurotoxicants. Our findings demonstrate that this index can be used to reliably distinguish between neurotoxic and non-neurotoxic chemicals and provide a sound estimate for the neurodevelopmental hazard potential of a chemical. The demonstrated method can be a feasible approach to reduce the number of animals used in developmental neurotoxicity evaluation procedures.     

A category approach to predicting the developmental (neuro) toxicity of organotin compounds: The value of the zebrafish (Danio rerio) embryotoxicity test (ZET)

Zebrafish embryos were exposed to different organotin compounds during very early development (<100 h post fertilization). Morphology, histopathology and swimming activity (in a motor activity test) were the endpoints analyzed. DBTC was, by far, the most embryotoxic compound at all time points and endpoints studied. In fact, we observed a clear concordance between the effects observed in our zebrafish embryo model, and those observed with these compounds in full rodent in vivo studies. All organotin compounds classified as developmental (neuro) toxicants in vivo, were correctly classified in the present assay. Together, our results support the ZET model as a valuable tool for providing biological verification for a grouping and a read-across approach to developmental (neuro) toxicity.     

Acute toxicity assay using mysid as an alternative test organism in the assessment of the aqueous fraction of sediment

Ecotoxicology - The evaluation of sediment quality through biological testing of the aqueous fraction can be applied in dredging situations and is associated with a small number of confounding...     

A near-infrared method for the assay of cineole in eucalyptus oil as an alternative to the official BP method

Thirty different eucalyptus oil samples were scanned on the FOSS NIRSystems 6500 Rapid Content Sampler using a reflectance vessel as sample presentation method. The cineole content of each sample was determined by the BP method and these reference data were used to construct two calibration equations for cineole content in the oils using Vision software. The mean accuracy for the NIR method differed by 1.01% or less, and the mean bias by +/-0.33% or less, compared with the BP method. Calculation of the 95% confidence intervals for the slope and intercept of plots of NIR predicted values against BP method reference values showed that there was no evidence of fixed or relative systematic errors. Tests for short-term and intermediate repeatability were conducted. The standard deviation was 0.83% w/w or less and the coefficient of variation was 1.11% or less. The confidence intervals for both short-term and intermediate repeatability overlapped with that for the BP method, suggesting that there was no evidence for a difference in values obtained by the BP and NIR methods. The range of cineole contents used in the calibrations was extended by incorporating five samples of eucalyptus oil spiked with cineole, and five samples of two essential oils known to have a lower cineole content than eucalyptus oil, to give a range of 52.5 to 99.0% w/w. The mean accuracy decreased to an error of 1.26% or less and the bias to +/-0.50% or less. Again, confidence intervals suggested there was no evidence for fixed or systematic errors in the NIR calibrations. We propose that NIR spectroscopy could be used as an alternative method for the determination of cineole content in eucalyptus oils.     

The Microtox as an alternative assay in the acute toxicity assessment of water pollutants

The toxicity of 15 chemicals was determined with the Microtox Assay System (MAS). Subsequently the sensitivity of the MAS was compared with that of standard aquatic toxicity tests, comprising 20 different species including recommended test species. The MAS yielded fairly replicable results which were comparable with those obtained with the standard tests. As the MAS does not require the culturing of test organisms and takes about 5% of the actual work involved in the standard procedures, it is suggested to use the MAS as a prescreening tool in the hazard assessment of chemicals.     

斑马鱼胚胎评价5种药物的发育毒性与模型验证

目的用斑马鱼胚胎探究环磷酰胺、乙酰水杨酸、盐酸四环素、乙酸地塞米松、阿扎胞苷5种已知对人类胚胎致畸药物的毒性和安全性。方法挑选4 hpf发育正常的受精卵,采用水浴染毒法,将药物添加到人工海水中,每种药物分别设置5个浓度组,另设空白对照组和溶剂对照组,观察给药120 hpf后斑马鱼的死亡情况,统计各实验组斑马鱼胚胎的死亡数、畸形数,并求出120 hpf时斑马鱼胚胎的死亡率、畸形率、半数致死浓度(LC50)、半数致畸浓度(EC50)、致畸指数(TI)。并利用公式:TI=LC50/EC50计算出阳性药物的致畸指数。根据已经测得的LC50,求出各药物的最大非致死浓度(MNLC),分别设置1/10 MNLC、1/3 MNLC,MNLC和LC104个浓度,以沙利度胺为阳性对照,维生素C为阴性对照,人工海水为空白对照,0.5%DMSO为溶剂对照,28.5℃下作用至120 h,每天观察胚胎的发育情况,统计胚胎死亡及畸形状态。结果 5种药物的LC50从大到小依次为:环磷酰胺>阿扎胞苷>盐酸四环素>乙酰水杨酸>乙酸地塞米松。EC50从大到小依次为:环磷酰胺>盐酸四环素>阿扎胞苷>乙酰水杨酸>乙酸地塞米松。环磷酰胺、乙酰水杨酸、盐酸四环素、乙酸地塞米松、阿扎胞苷TI值分别为1.92,1.11,1.05,1.44,2.99。结论斑马鱼胚胎模型可用于初步评价药物的发育毒性和安全性。     

Establishment of an in vitro reporter gene assay for developmental cardiac toxicity.

This study is based on the unique potential of pluripotent embryonic stem (ES) cells to differentiate in vitro into embryoid bodies containing cell lineages representative of most cell types found in the mammalian fetus. However, the use of wild type ES cells as an in vitro assay for embryotoxicological studies is complicated by the simultaneous development of various cellular phenotypes. This prevents a quantitative assessment of drug effects on one specific cell type. Here we report the effects of 15 chemicals on cardiac differentiation as determined by various specific toxicological endpoints such as morphological inspection (contractile activity), quantitative mRNA analysis and cardiac-specific expression of green fluorescent protein (GFP), used as a quantitative reporter. The data from the different endpoints have been subjected to a statistical analysis, and a preliminary prediction model is proposed. The results demonstrate that genetically-engineered ES cells could provide a valuable tool for estimating the developmental cardiotoxic potential of compounds in vitro and form the basis for automated analysis in a high-throughput system.     

Validation of visualized transgenic zebrafish as a high throughput model to assay bradycardia related cardio toxicity risk candidates

Drug‐induced QT prolongation usually leads to torsade de pointes (TdP), thus for drugs in the early phase of development this risk should be evaluated. In the present study, we demonstrated a visualized transgenic zebrafish as an in vivo high‐throughput model to assay the risk of drug‐induced QT prolongation. Zebrafish larvae 48 h post‐fertilization expressing green fluorescent protein in myocardium were incubated with compounds reported to induce QT prolongation or block the human ether‐a‐go‐go‐related gene (hERG) K⁺ current. The compounds sotalol, indapaminde, erythromycin, ofoxacin, levofloxacin, sparfloxacin and roxithromycin were additionally administrated by microinjection into the larvae yolk sac. The ventricle heart rate was recorded using the automatic monitoring system after incubation or microinjection. As a result, 14 out of 16 compounds inducing dog QT prolongation caused bradycardia in zebrafish. A similar result was observed with 21 out of 26 compounds which block hERG current. Among the 30 compounds which induced human QT prolongation, 25 caused bradycardia in this model. Thus, the risk of compounds causing bradycardia in this transgenic zebrafish correlated with that causing QT prolongation and hERG K⁺ current blockage in established models. The tendency that high logP values lead to high risk of QT prolongation in this model was indicated, and non‐sensitivity of this model to antibacterial agents was revealed. These data suggest application of this transgenic zebrafish as a high‐throughput model to screen QT prolongation‐related cardio toxicity of the drug candidates. Copyright © 2012 John Wiley & Sons, Ltd.