Publications by authors named "Hilda Witters"

42 Publications

An in vitro air-liquid interface inhalation platform for petroleum substances and constituents.

ALTEX 2021 04 20. Epub 2021 Apr 20.

VITO NV (Flemish Institute for Technological Research), Unit HEALTH, Mol, Belgium.

The goal is to optimize and show the validity of an in vitro method for inhalation testing of petroleum substances and its constituents at the air-liquid interface (ALI). The approach is demonstrated in a pilot study with ethylbenzene (EB), a mono-constituent petroleum substance using a human alveolar epithelial cell line model. This included the development and validation of a generation facility to obtain EB vapors and the optimization of an exposure system for a negative control (clean air, CA), positive control (nitrogen dioxide), and EB vapors. The optimal settings for the VITROCELL® 24/48 system were defined. Cytotoxicity, cell viability, inflammation, and oxidative stress were assessed in A549 after exposure to EB vapors. A concentration-dependent significant decrease in mean cell viability was observed after exposure, which was confirmed by a cytotoxicity test. The oxidative stress marker superoxide dismutase 2 was significantly increased, but no concentration-response was observed. A concentration-dependent significant increase in pro-inflammatory markers C-C motif chemokine ligand 2, interleukin (IL)6, and IL8 was observed for EB-exposed A549 cells compared to CA. The data demonstrated consistency between in vivo air concentrations at which adverse respiratory effects were observed and ALI-concentrations affecting cell viability, provided that the actual measured in vitro delivery efficiency of the compound were included. It can be concluded that extrapolating in vitro air concentrations (adjusted for delivery efficiency and absorption characteristics and applied for testing cell viability) to simulate in vivo air concentrations may be a promising method to screen for acute inhalation toxicity.
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http://dx.doi.org/10.14573/altex.2010211DOI Listing
April 2021

Alternative air-liquid interface method for inhalation toxicity testing of a petroleum-derived substance.

MethodsX 2020 8;7:101088. Epub 2020 Oct 8.

VITO NV (Flemish Institute for Technological Research), Unit HEALTH, Mol, Belgium.

-based new approach methodologies (NAMs) provide a pragmatic solution to animal testing of petroleum substances and their constituents. A previous study exposed an in vitro model (A549 cells) at the air-liquid interface (ALI) to assess inhalation toxicity of a single compound, ethylbenzene. Experimental conditions using VITROCELL 24/48 exposure system were optimized to achieve a deposition efficiency that resulted in dose-dependent biological changes. The feasibility of this set-up was evaluated for testing the complex substance gasoline, which, at only high concentrations, can induce mild respiratory irritation in animals and cough in humans.•Results showed that perpendicular ALI exposure flow systems (VITROCELL® 6/4 and 24/48) may not be appropriate for testing gasoline because it was not possible to achieve enough deposition onto the cells and in the culture medium to measure dose and to determine dose-dependent biological changes (more information can be found in 'Supplementary material and/or Additional information' section).•Structural features ( aromatic or saturated hydrocarbon structure) and high hydrophobicity, together with the low concentrations of individual components in gasoline, may have caused the low deposition.•To achieve a higher deposition on the cells, A549 cells were exposed to gasoline at the ALI by passive dosing.The results demonstrate that the presented methodology is a promising NAM for inhalation toxicity testing of (semi-)volatile complex substances with low aqueous solubility.
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http://dx.doi.org/10.1016/j.mex.2020.101088DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7581970PMC
October 2020

Xenopus laevis as a Bioindicator of Endocrine Disruptors in the Region of Central Chile.

Arch Environ Contam Toxicol 2019 Oct 17;77(3):390-408. Epub 2019 Aug 17.

Departamento de Ecología y Biodiversidad, Facultad Ciencias de la Vida, Universidad Andres Bello, República 440, Santiago, Chile.

One of the direct causes of biodiversity loss is environmental pollution resulting from the use of chemicals. Different kinds of chemicals, such as persistent organic pollutants and some heavy metals, can be endocrine disruptors, which act at low doses over a long period of time and have a negative effect on the reproductive and thyroid system in vertebrates worldwide. Research on the effects of endocrine disruptors and the use of bioindicators in neotropical ecosystems where pressure on biodiversity is high is scarce. In Chile, although endocrine disruptors have been detected at different concentrations in the environments of some ecosystems, few studies have been performed on their biological effects in the field. In this work, Xenopus laevis (African clawed frog), an introduced species, is used as a bioindicator for the presence of endocrine disruptors in aquatic systems with different degrees of contamination in a Mediterranean zone in central Chile. For the first time for Chile, alterations are described that can be linked to exposure to endocrine disruptors, such as vitellogenin induction, decreased testosterone in male frogs, and histological changes in gonads. Dioxin-like and oestrogenic activity was detected in sediments at locations where it seem to be related to alterations found in the frogs. In addition, an analysis of land use/cover use revealed that urban soil was the best model to explain the variations in frog health indicators. This study points to the usefulness of an invasive species as a bioindicator for the presence of endocrine-disruptive chemicals.
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http://dx.doi.org/10.1007/s00244-019-00661-6DOI Listing
October 2019

Corrigendum to Recommendation on test readiness criteria for new approach methods in toxicology: exemplified for developmental neurotoxicity.

ALTEX 2019 ;36(3):506

Center for Alternatives to Animal Testing, CAAT-Europe, University of Konstanz, Konstanz, Germany.

In this manuscript, which appeared in ALTEX 35 , 306-352 ( doi:10.14573/altex.1712081 ), the Acknowledgements should read: This work was supported by the Doerenkamp-Zbinden Foundation, EFSA, the BMBF, JPI-NutriCog-Selenius, and it has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 681002 (EU-ToxRisk).
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http://dx.doi.org/10.14573/altex.1904112DOI Listing
January 2019

Adaptation of the Systematic Review Framework to the Assessment of Toxicological Test Methods: Challenges and Lessons Learned with the Zebrafish Embryotoxicity Test.

Toxicol Sci 2018 Jun 13. Epub 2018 Jun 13.

Evidence-Based Toxicology Collaboration at Johns Hopkins Bloomberg School of Public Health (EBTC), Baltimore, MD, USA.

Systematic review methodology is a means of addressing specific questions through structured, consistent, and transparent examinations of the relevant scientific evidence. This methodology has been used to advantage in clinical medicine, and is being adapted for use in other disciplines. While some applications to toxicology have been explored, especially for hazard identification, the present preparatory study is, to our knowledge, the first attempt to adapt it to the assessment of toxicological test methods. As our test case, we chose the zebrafish embryotoxicity test (ZET) for developmental toxicity and its mammalian counterpart, the standard mammalian prenatal development toxicity study, focusing the review on how well the ZET predicts the presence or absence of chemical-induced pre-natal developmental toxicity observed in mammalian studies. An interdisciplinary team prepared a systematic review protocol and adjusted it throughout this piloting phase, where needed. The final protocol was registered and will guide the main study (systematic review), which will execute the protocol to comprehensively answer the review question. The goal of this preparatory study was to translate systematic review methodology to the assessment of toxicological test method performance. Consequently, it focused on the methodological issues encountered, whereas the main study will report substantive findings. These relate to numerous systematic review steps, but primarily to searching and selecting the evidence. Applying the lessons learned to these challenges can improve not only our main study, but may also be helpful to others seeking to use systematic review methodology to compare toxicological test methods. We conclude with a series of recommendations that, if adopted, would help improve the quality of the published literature, and make conducting systematic reviews of toxicological studies faster and easier over time.
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http://dx.doi.org/10.1093/toxsci/kfz128DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6736188PMC
June 2018

Repeatability and Reproducibility of the RTgill-W1 Cell Line Assay for Predicting Fish Acute Toxicity.

Toxicol Sci 2019 06;169(2):353-364

Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Environmental Toxicology, 8600 Dübendorf, Switzerland.

Predicting fish acute toxicity of chemicals in vitro is an attractive alternative method to the conventional approach using juvenile and adult fish. The rainbow trout (Oncorhynchus mykiss) cell line assay with RTgill-W1 cells has been designed for this purpose. It quantifies cell viability using fluorescent measurements for metabolic activity, cell- and lysosomal-membrane integrity on the same set of cells. Results from over 70 organic chemicals attest to the high predictive capacity of this test. We here report on the repeatability (intralaboratory variability) and reproducibility (interlaboratory variability) of the RTgill-W1 cell line assay in a round-robin study focusing on 6 test chemicals involving 6 laboratories from the industrial and academic sector. All participating laboratories were able to establish the assay according to preset quality criteria even though, apart from the lead laboratory, none had previously worked with the RTgill-W1 cell line. Concentration-response modeling, based on either nominal or geometric mean-derived measured concentrations, yielded effect concentrations (EC50) that spanned approximately 4 orders of magnitude over the chemical range, covering all fish acute toxicity categories. Coefficients of variation for intralaboratory and interlaboratory variability for the average of the 3 fluorescent cell viability measurements were 15.5% and 30.8%, respectively, which is comparable to other fish-derived, small-scale bioassays. This study therefore underlines the robustness of the RTgill-W1 cell line assay and its accurate performance when carried out by operators in different laboratory settings.
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http://dx.doi.org/10.1093/toxsci/kfz057DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6542334PMC
June 2019

An AOP-based alternative testing strategy to predict the impact of thyroid hormone disruption on swim bladder inflation in zebrafish.

Aquat Toxicol 2018 Jul 21;200:1-12. Epub 2018 Apr 21.

Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium. Electronic address:

The adverse outcome pathway (AOP) framework can be used to help support the development of alternative testing strategies aimed at predicting adverse outcomes caused by triggering specific toxicity pathways. In this paper, we present a case-study demonstrating the selection of alternative in chemico assays targeting the molecular initiating events of established AOPs, and evaluate use of the resulting data to predict higher level biological endpoints. Based on two AOPs linking inhibition of the deiodinase (DIO) enzymes to impaired posterior swim bladder inflation in fish, we used in chemico enzyme inhibition assays to measure the molecular initiating events for an array of 51 chemicals. Zebrafish embryos were then exposed to 14 compounds with different measured inhibition potentials. Effects on posterior swim bladder inflation, predicted based on the information captured by the AOPs, were evaluated. By linking the two datasets and setting thresholds, we were able to demonstrate that the in chemico dataset can be used to predict biological effects on posterior chamber inflation, with only two outliers out of the 14 tested compounds. Our results show how information organized using the AOP framework can be employed to develop or select alternative assays, and successfully forecast downstream key events along the AOP. In general, such in chemico assays could serve as a first-tier high-throughput system to screen and prioritize chemicals for subsequent acute and chronic fish testing, potentially reducing the need for long-term and costly toxicity tests requiring large numbers of animals.
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http://dx.doi.org/10.1016/j.aquatox.2018.04.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6002951PMC
July 2018

Recommendation on test readiness criteria for new approach methods in toxicology: Exemplified for developmental neurotoxicity.

ALTEX 2018 23;35(3):306-352. Epub 2018 Feb 23.

Center for Alternatives to Animal Testing, CAAT-Europe, University of Konstanz, Konstanz, Germany.

Multiple non-animal-based test methods have never been formally validated. In order to use such new approach methods (NAMs) in a regulatory context, criteria to define their readiness are necessary. The field of developmental neurotoxicity (DNT) testing is used to exemplify the application of readiness criteria. The costs and number of untested chemicals are overwhelming for in vivo DNT testing. Thus, there is a need for inexpensive, high-throughput NAMs, to obtain initial information on potential hazards, and to allow prioritization for further testing. A background on the regulatory and scientific status of DNT testing is provided showing different types of test readiness levels, depending on the intended use of data from NAMs. Readiness criteria, compiled during a stakeholder workshop, uniting scientists from academia, industry and regulatory authorities are presented. An important step beyond the listing of criteria, was the suggestion for a preliminary scoring scheme. On this basis a (semi)-quantitative analysis process was assembled on test readiness of 17 NAMs with respect to various uses (e.g. prioritization/screening, risk assessment). The scoring results suggest that several assays are currently at high readiness levels. Therefore, suggestions are made on how DNT NAMs may be assembled into an integrated approach to testing and assessment (IATA). In parallel, the testing state in these assays was compiled for more than 1000 compounds. Finally, a vision is presented on how further NAM development may be guided by knowledge of signaling pathways necessary for brain development, DNT pathophysiology, and relevant adverse outcome pathways (AOP).
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http://dx.doi.org/10.14573/altex.1712081DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6545888PMC
November 2018

Consensus statement on the need for innovation, transition and implementation of developmental neurotoxicity (DNT) testing for regulatory purposes.

Toxicol Appl Pharmacol 2018 09 12;354:3-6. Epub 2018 Feb 12.

European Commission -DG Joint Research Centre (JRC), Ispra, Italy. Electronic address:

This consensus statement voices the agreement of scientific stakeholders from regulatory agencies, academia and industry that a new framework needs adopting for assessment of chemicals with the potential to disrupt brain development. An increased prevalence of neurodevelopmental disorders in children has been observed that cannot solely be explained by genetics and recently pre- and postnatal exposure to environmental chemicals has been suspected as a causal factor. There is only very limited information on neurodevelopmental toxicity, leaving thousands of chemicals, that are present in the environment, with high uncertainty concerning their developmental neurotoxicity (DNT) potential. Closing this data gap with the current test guideline approach is not feasible, because the in vivo bioassays are far too resource-intensive concerning time, money and number of animals. A variety of in vitro methods are now available, that have the potential to close this data gap by permitting mode-of-action-based DNT testing employing human stem cells-derived neuronal/glial models. In vitro DNT data together with in silico approaches will in the future allow development of predictive models for DNT effects. The ultimate application goals of these new approach methods for DNT testing are their usage for different regulatory purposes.
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http://dx.doi.org/10.1016/j.taap.2018.02.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6097873PMC
September 2018

Phenotypic and biomarker evaluation of zebrafish larvae as an alternative model to predict mammalian hepatotoxicity.

J Appl Toxicol 2016 09 4;36(9):1194-206. Epub 2016 Mar 4.

VITO NV, Applied Bio & Molecular Systems, Boeretang 200, B-2400, Mol, Belgium.

Zebrafish phenotypic assays have shown promise to assess human hepatotoxicity, though scoring of liver morphology remains subjective and difficult to standardize. Liver toxicity in zebrafish larvae at 5 days was assessed using gene expression as the biomarker approach, complementary to phenotypic analysis and analytical data on compound uptake. This approach aimed to contribute to improved hepatotoxicity prediction, with the goal of identifying biomarker(s) as a step towards the development of transgenic models for prioritization. Morphological effects of hepatotoxic compounds (acetaminophen, amiodarone, coumarin, methapyrilene and myclobutanil) and saccharin as the negative control were assessed after exposure in zebrafish larvae. The hepatotoxic compounds induced the expected zebrafish liver degeneration or changes in size, whereas saccharin did not have any phenotypic adverse effect. Analytical methods based on liquid chromatography-mass spectrometry were optimized to measure stability of selected compounds in exposure medium and internal concentration in larvae. All compounds were stable, except amiodarone for which precipitation was observed. There was a wide variation between the levels of compound in the zebrafish larvae with a higher uptake of amiodarone, methapyrilene and myclobutanil. Detection of hepatocyte markers (CP, CYP3A65, GC and TF) was accomplished by in situ hybridization of larvae to coumarin and myclobutanil and confirmed by real-time reverse transcription-quantitative polymerase chain reaction. Experiments showed decreased expression of all markers. Next, other liver-specific biomarkers (i.e. FABP10a and NR1H4) and apoptosis (i.e. CASP-3 A and TP53) or cytochrome P450-related (CYP2K19) and oxidoreductase activity-related (ZGC163022) genes, were screened. Links between basic mechanisms of liver injury and results of biomarker responses are described. Copyright © 2016 John Wiley & Sons, Ltd.
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http://dx.doi.org/10.1002/jat.3288DOI Listing
September 2016

Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part II: Zebrafish.

Aquat Toxicol 2016 Apr 18;173:204-217. Epub 2016 Jan 18.

Zebrafishlab, Veterinary Physiology and Biochemistry, Department of Veterinary Sciences, University of Antwerp, Universiteitsplein 1, 2610 Wilrijk, Belgium. Electronic address:

Disruption of the thyroid hormone (TH) system, an important mode of action, can lead to ecologically relevant adverse outcomes, especially during embryonic development. The present study characterizes the effects of disruption of TH synthesis on swim bladder inflation during zebrafish early-life stages using 2-mercaptobenzothiazole (MBT), a thyroid peroxidase (TPO) inhibitor. Zebrafish were exposed to different MBT concentrations until 120/168h post fertilization (hpf) and 32days post fertilization (dpf), in two sets of experiments, to investigate the effects of TPO inhibition on posterior and anterior swim bladder inflation respectively, as well as whole body thyroid hormone concentrations (triiodothyronine (T3) and its prohormone, thyroxine (T4)). At 120hpf, MBT did not directly impair posterior chamber inflation or size, while anterior chamber inflation and size was impaired at 32dpf. As previously shown in amphibians and mammals, we confirmed that MBT inhibits TPO in fish. Whole-body T4 decreased after MBT exposure at both time points, while T3 levels were unaltered. There was a significant relationship between T4 levels and the anterior chamber surface at 32dpf. The absence of effects on posterior chamber inflation can possibly be explained by maternal transfer of T4 into the eggs. These maternally derived THs are depleted at 32dpf and cannot offset TPO inhibition, resulting in impaired anterior chamber inflation. Therefore, we hypothesize that TPO inhibition only inhibits swim bladder inflation during late development, after depletion of maternally derived T4. In a previous study, we showed that iodothyronine deiodinase (ID) knockdown impaired posterior chamber inflation during early development. Our findings, in parallel with similar effects observed in fathead minnow (see part I, this issue) suggest that thyroid disruption impacts swim bladder inflation, and imply an important distinction among specific subtypes of TH disrupting chemicals. However, the existence of another - yet unknown - mode of action of MBT impacting swim bladder inflation cannot be excluded. These results can be helpful for delineating adverse outcome pathways (AOPs) linking TPO inhibition, ID inhibition and other TH related molecular initiating events, to impaired swim bladder inflation in fish during early life stages. Such AOPs can support the use of in vitro enzyme inhibition assays for predicting reduced survival due to impaired posterior and anterior chamber inflation.
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http://dx.doi.org/10.1016/j.aquatox.2015.12.023DOI Listing
April 2016

OECD validation study to assess intra- and inter-laboratory reproducibility of the zebrafish embryo toxicity test for acute aquatic toxicity testing.

Regul Toxicol Pharmacol 2014 Aug 27;69(3):496-511. Epub 2014 May 27.

European Commission Joint Research Centre, Institute for Health and Consumer Protection, via E. Fermi 2749, 21027 Ispra (VA), Italy. Electronic address:

The OECD validation study of the zebrafish embryo acute toxicity test (ZFET) for acute aquatic toxicity testing evaluated the ZFET reproducibility by testing 20 chemicals at 5 different concentrations in 3 independent runs in at least 3 laboratories. Stock solutions and test concentrations were analytically confirmed for 11 chemicals. Newly fertilised zebrafish eggs (20/concentration and control) were exposed for 96h to chemicals. Four apical endpoints were recorded daily as indicators of acute lethality: coagulation of the embryo, lack of somite formation, non-detachment of the tail bud from the yolk sac and lack of heartbeat. Results (LC50 values for 48/96h exposure) show that the ZFET is a robust method with a good intra- and inter-laboratory reproducibility (CV<30%) for most chemicals and laboratories. The reproducibility was lower (CV>30%) for some very toxic or volatile chemicals, and chemicals tested close to their limit of solubility. The ZFET is now available as OECD Test Guideline 236. Considering the high predictive capacity of the ZFET demonstrated by Belanger et al. (2013) in their retrospective analysis of acute fish toxicity and fish embryo acute toxicity data, the ZFET is ready to be considered for acute fish toxicity for regulatory purposes.
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http://dx.doi.org/10.1016/j.yrtph.2014.05.018DOI Listing
August 2014

Gene expression profiles reveal distinct immunological responses of cobalt and cerium dioxide nanoparticles in two in vitro lung epithelial cell models.

Toxicol Lett 2014 Aug 10;228(3):157-69. Epub 2014 May 10.

Flemish Institute for Technological Research (VITO NV), Environmental Risk and Health Unit, Mol, Belgium. Electronic address:

Fragmentary knowledge exists on cellular signaling responses underlying possible adverse health effects of CoO- and CeO2-nanoparticles (NP)s after inhalation. We aimed to perform a time kinetic study of gene expression profiles induced by these NPs in alveolar A549 and bronchial BEAS-2B epithelial cells, and investigated possible immune system modulation. The kinetics of the cell responses induced by the NPs were different between the lung epithelial models. Both CoO- and CeO2-NP exposure induced mainly downregulation of gene transcription. BEAS-2B cells were found to be more sensitive, as they showed a higher number of differentially expressed transcripts (DET) at a 10-fold lower NP-concentration than A549 cells. Hierarchical clustering of all DET indicated that the transcriptional responses were heterogeneous among the two cell types and two NPs. Between 1% and 14% DET encoding markers involved in immune processes were observed. The transcriptional impact of the metal oxide NPs appeared to be cell-dependent, both at the general and immune response level, whereas each lung epithelial cell model responded differently to the two NP types. Thus, the study provides gene expression markers and immune processes involved in CoO- and CeO2-NP-induced toxicity, and demonstrates the usefulness of comprehensive-omics studies to differentiate between NP responses.
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http://dx.doi.org/10.1016/j.toxlet.2014.05.006DOI Listing
August 2014

A European perspective on alternatives to animal testing for environmental hazard identification and risk assessment.

Regul Toxicol Pharmacol 2013 Dec 23;67(3):506-30. Epub 2013 Oct 23.

UFZ - Helmholtz Centre for Environmental Research, Department of Bioanalytical Ecotoxicology, 04318 Leipzig, Germany. Electronic address:

Tests with vertebrates are an integral part of environmental hazard identification and risk assessment of chemicals, plant protection products, pharmaceuticals, biocides, feed additives and effluents. These tests raise ethical and economic concerns and are considered as inappropriate for assessing all of the substances and effluents that require regulatory testing. Hence, there is a strong demand for replacement, reduction and refinement strategies and methods. However, until now alternative approaches have only rarely been used in regulatory settings. This review provides an overview on current regulations of chemicals and the requirements for animal tests in environmental hazard and risk assessment. It aims to highlight the potential areas for alternative approaches in environmental hazard identification and risk assessment. Perspectives and limitations of alternative approaches to animal tests using vertebrates in environmental toxicology, i.e. mainly fish and amphibians, are discussed. Free access to existing (proprietary) animal test data, availability of validated alternative methods and a practical implementation of conceptual approaches such as the Adverse Outcome Pathways and Integrated Testing Strategies were identified as major requirements towards the successful development and implementation of alternative approaches. Although this article focusses on European regulations, its considerations and conclusions are of global relevance.
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http://dx.doi.org/10.1016/j.yrtph.2013.10.003DOI Listing
December 2013

Assessment of the developmental neurotoxicity of compounds by measuring locomotor activity in zebrafish embryos and larvae.

Neurotoxicol Teratol 2013 May-Jun;37:44-56. Epub 2013 Jan 26.

VITO NV, Flemish Institute for Technological Research, Environmental Risk and Health, Boeretang 200, Mol, Belgium.

The developmental neurotoxic potential of the majority of environmental chemicals and drugs is currently undetermined. Specific in vivo studies provide useful data for hazard assessment but are not amenable to screen thousands of untested compounds. In this study, methods which use zebrafish embryos, eleutheroembryos and larvae as model organisms, were proposed as alternatives for developmental neurotoxicity (DNT) testing. The evaluation of spontaneous tail coilings in zebrafish embryos aged 24-26 hours post fertilization (hpf) and the swimming activity of eleutheroembryos at 120 and larvae at 144 hpf, i.e. parameters for locomotor activity, were investigated as potential endpoints for DNT testing, according to available standard protocols. The overall performance and predictive value of these methods was then examined by testing a training set of 10 compounds, including known developmental neurotoxicants and compounds not considered to be neurotoxic. The classification of the selected compounds as either neurotoxic or non-neurotoxic, based on the effects observed in zebrafish embryos and larvae, was compared to available mammalian data and an overall concordance of 90% was achieved. Furthermore, the specificity of the selected endpoints for DNT was evaluated as well as the potential similarities between zebrafish and mammals with regard to mechanisms of action for the selected compounds. Although further studies, including the screening of a large testing set of compounds are required, we suggest that the proposed methods with zebrafish embryos and larvae might be valuable alternatives for animal testing for the screening and prioritization of compounds for DNT.
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http://dx.doi.org/10.1016/j.ntt.2013.01.003DOI Listing
December 2013

Expert opinion on toxicity profiling--report from a NORMAN expert group meeting.

Integr Environ Assess Manag 2013 Apr 19;9(2):185-91. Epub 2013 Feb 19.

VU University Amsterdam, Institute for Environmental Studies, Amsterdam, The Netherlands.

This article describes the outcome and follow-up discussions of an expert group meeting (Amsterdam, October 9, 2009) on the applicability of toxicity profiling for diagnostic environmental risk assessment. A toxicity profile was defined as a toxicological "fingerprint" of a sample, ranging from a pure compound to a complex mixture, obtained by testing the sample or its extract for its activity toward a battery of biological endpoints. The expert group concluded that toxicity profiling is an effective first tier tool for screening the integrated hazard of complex environmental mixtures with known and unknown toxicologically active constituents. In addition, toxicity profiles can be used for prioritization of sampling locations, for identification of hot spots, and--in combination with effect-directed analysis (EDA) or toxicity identification and evaluation (TIE) approaches--for establishing cause-effect relationships by identifying emerging pollutants responsible for the observed toxic potency. Small volume in vitro bioassays are especially applicable for these purposes, as they are relatively cheap and fast with costs comparable to chemical analyses, and the results are toxicologically more relevant and more suitable for realistic risk assessment. For regulatory acceptance in the European Union, toxicity profiling terminology should keep as close as possible to the European Water Framework Directive (WFD) terminology, and validation, standardization, statistical analyses, and other quality aspects of toxicity profiling should be further elaborated.
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http://dx.doi.org/10.1002/ieam.1395DOI Listing
April 2013

Feasibility study of the zebrafish assay as an alternative method to screen for developmental toxicity and embryotoxicity using a training set of 27 compounds.

Reprod Toxicol 2012 Apr 17;33(2):142-54. Epub 2011 Aug 17.

VITO NV, Flemish Institute for Technological Research, CARDAM, Centre for Advanced R&D on Alternative Methods, Boeretang 200, 2400 Mol, Belgium.

To anticipate to increased testing needs for reproductive toxicity and 3R approaches, we studied zebrafish embryo/larva as an alternative for animal testing for developmental toxicity and embryotoxicity and evaluated a training set of 27 compounds with a standardized protocol. The classification of compounds in the zebrafish embryo/larva assay, based on a prediction model using a TI (teratogenic index) cut-off value of 2, was compared to available animal and human data. When comparing the classification of compounds in the zebrafish embryo/larva assay to available animal classification, a sensitivity of 72% and specificity of 100% were obtained. The predictive values obtained in comparison to a limited set of human data were 50, 60% respectively for teratogens, non-teratogens. Overall, we demonstrated that the zebrafish embryo/larva assay, may be used as screening tool for prioritization of compounds and could contribute to reduction of animal experiments in the field of developmental toxicology.
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http://dx.doi.org/10.1016/j.reprotox.2011.08.003DOI Listing
April 2012

The zebrafish embryo model in toxicology and teratology, September 2–3, 2010, Karlsruhe, Germany.

Reprod Toxicol 2011 May;31(4):585-8

UFZ – Helmholtz Centre for Environmental Research, Department of Bioanalytical Ecotoxicology, Permoserstr. 15, 04318 Leipzig, Germany.

The use of fish embryos is gaining popularity for research in the area of toxicology and teratology. Particularly embryos of the zebrafish offer an array of different applications ranging from regulatory testing to mechanistic research. For this reason a consortium of two research centres and a company with the support of the COST Action EuFishBiomed has organised the Workshop “The zebrafish embryo model in toxicology and teratology”, in Karlsruhe, Germany, 2nd–3rd September 2010. The workshop aimed at bringing together experts from different areas of toxicology using the (zebra)fish embryo and stimulating networking between scientists and representatives from regulatory bodies, research institutions and industry. Recent findings, presented in various platform presentations in the area of regulatory toxicity, high throughput screening, toxicogenomics, as well as environmental and human risk assessment are highlighted in this meeting report. Furthermore, the constraints and possibilities of the model as discussed at the workshop are described. A follow up-meeting was appreciated by the about 120 participants and is planned for 2012.
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http://dx.doi.org/10.1016/j.reprotox.2011.02.010DOI Listing
May 2011

Zebrafish embryos as an alternative to animal experiments--a commentary on the definition of the onset of protected life stages in animal welfare regulations.

Reprod Toxicol 2012 Apr 25;33(2):128-32. Epub 2011 Jun 25.

Karlsruhe Institute of Technology, Institute of Toxicology and Genetics, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany.

Worldwide, the zebrafish has become a popular model for biomedical research and (eco)toxicology. Particularly the use of embryos is receiving increasing attention, since they are considered as replacement method for animal experiments. Zebrafish embryos allow the analysis of multiple endpoints ranging from acute and developmental toxicity determination to complex functional genetic and physiological analysis. Particularly the more complex endpoints require the use of post-hatched eleutheroembryo stages. According to the new EU Directive 2010/63/EU on the protection of animals used for scientific purposes, the earliest life-stages of animals are not defined as protected and, therefore, do not fall into the regulatory frameworks dealing with animal experimentation. Independent feeding is considered as the stage from which free-living larvae are subject to regulations for animal experimentation. However, despite this seemingly clear definition, large variations exist in the interpretation of this criterion by national and regional authorities. Since some assays require the use of post-hatched stages up to 120 h post fertilization, the literature and available data are reviewed in order to evaluate if this stage could still be considered as non-protected according to the regulatory criterion of independent feeding. Based on our analysis and by including criteria such as yolk consumption, feeding and swimming behavior, we conclude that zebrafish larvae can indeed be regarded as independently feeding from 120 h after fertilization. Experiments with zebrafish should thus be subject to regulations for animal experiments from 120 h after fertilization onwards.
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http://dx.doi.org/10.1016/j.reprotox.2011.06.121DOI Listing
April 2012

Functionality and specificity of gene markers for skin sensitization in dendritic cells.

Toxicol Lett 2011 Jun 26;203(2):106-10. Epub 2011 Feb 26.

Flemish Institute for Technological Research (VITO N.V.), Environmental Risk and Health Unit, Toxicology, Belgium.

Transcriptomic analyses revealed a discriminating gene expression profile in human CD34+ progenitor-derived dendritic cells (DC) after exposure to skin sensitizers versus non-sensitizers. Starting from the differential expression in a small set of genes, a preliminary classification model (VITOSENS®) has been developed to identify chemicals as (non-)sensitizing. The objective of the current study is to gain knowledge on the role of the VITOSENS® markers in the DC maturation process, as well as to investigate their activation by a skin sensitizer versus a non-sensitizing danger molecule. To evaluate the functional relevance of VITOSENS® biomarkers in DC maturation, their response induced by the sensitizer dinitrofluorobenzene (DNFB) was pharmacologically counteracted. Flow cytometry analyses revealed that CD86 was down-regulated after COX2 inhibition, whereas expression of HLA-DR was reduced by stimulating CCR2. When exposing DC to DNFB versus lipopolysaccharide S (LPS), expression of most discriminating genes CREM and CCR2 was not altered by LPS as opposed to DNFB. To summarize, the observations in this research indicate that a selection of the VITOSENS® genes may be functionally involved in sensitizer-induced DC activation. By comparing their responsiveness towards a non-sensitizing danger signal and a sensitizer, VITOSENS® gene markers CREM and CCR2 appear to display a specific response.
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http://dx.doi.org/10.1016/j.toxlet.2011.02.015DOI Listing
June 2011

The ReProTect Feasibility Study, a novel comprehensive in vitro approach to detect reproductive toxicants.

Reprod Toxicol 2010 Aug 21;30(1):200-18. Epub 2010 May 21.

Institute of Experimental and Clinical Pharmacology and Toxicology, Department of Toxicology, Tübingen, Germany.

ReProTect is a project within the 6th European Framework Program which has developed alternative methods aimed to reduce or replace animal experimentation in the field of reproductive toxicology. In its final year, a ring trial, named the "Feasibility Study", was conducted, in which 10 blinded chemicals with toxicologically well-documented profiles were analyzed by employing a test battery of 14 in vitro assays. EC(50) (half maximal effective concentration) or equivalent endpoints were determined and the test compounds were ranked relative to chemicals previously assayed in the tests of the battery. This comparative analysis together with a weight of evidence approach allowed a robust prediction of adverse effects on fertility and embryonic development of the 10 test chemicals in vivo. In summary, the vast majority of the predictions made based on the in vitro results turned out to be correct when compared to the whole animal data. The procedure used here, a nearest neighbor analysis coupled with a weight of evidence approach, may guide future activities in the field of alternative toxicity testing.
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http://dx.doi.org/10.1016/j.reprotox.2010.05.012DOI Listing
August 2010

Optimization and prevalidation of the in vitro AR CALUX method to test androgenic and antiandrogenic activity of compounds.

Reprod Toxicol 2010 Aug 10;30(1):18-24. Epub 2010 May 10.

BioDetection Systems BV, Science Park 406, Amsterdam, The Netherlands.

To date there are no validated methods available to test androgenicity or antiandrogenicity in vitro. A problem with testing androgenicity using reporter genes is the possibility by other steroid receptors than androgen receptors to activate the same reporter gene, thereby lowering selectivity. To avoid this we have established a robust and very selective method, the AR CALUX reporter gene assay, to test androgenic and antiandrogenic activity of compounds in vitro. This assay uses a human U2-OS cell line stably transfected with the human androgen receptor and an androgen receptor responsive reporter gene. We optimized protocols to be used in combination with AR CALUX cells and carried out an in house prevalidation. In addition we successfully transferred this assay to another laboratory, leading to comparable test results with a panel of androgen receptor agonists and antagonists. The assay was able to readily rank a range of chemicals on the basis of their EC50 values. The CALUX assay was found to be selective for androgens and seemed not influenced by signaling through other steroid receptors.
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http://dx.doi.org/10.1016/j.reprotox.2010.04.012DOI Listing
August 2010

Optimization and prevalidation of the in vitro ERalpha CALUX method to test estrogenic and antiestrogenic activity of compounds.

Reprod Toxicol 2010 Aug 8;30(1):73-80. Epub 2010 May 8.

BioDetection Systems BV, Science Park 406, Amsterdam, The Netherlands.

Estrogenicity of chemicals has received significant attention and is linked to endocrine-disrupting activities. However, there is a paucity of validated methods to assess estrogenicity in vitro. We have established a robust method to test estrogenic and antiestrogenic activity of compounds in vitro, as an alternative to using animal models such as the uterotrophic assay. To this end we optimized protocols to be used in combination with CALUX reporter gene assays and carried out an in house prevalidation, followed by two rounds of tests to establish transferability. Problems in the initial test with transferability were solved by isolation of a novel cell clone of the ERalpha CALUX line with greatly improved stability and luciferase levels. This cell line proved to be a very suitable and reliable predictor of estrogenicity of chemicals and was able to readily rank a range of chemicals on the basis of their EC50 values.
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http://dx.doi.org/10.1016/j.reprotox.2010.04.007DOI Listing
August 2010

Gene markers in dendritic cells unravel pieces of the skin sensitization puzzle.

Toxicol Lett 2010 Jul 10;196(2):95-103. Epub 2010 Apr 10.

Flemish Institute for Technological Research (VITO N.V.), Environmental Risk and Health Unit, Toxicology, Belgium.

The underlying events of how dendritic cells (DC) are capable of evoking an antigen-specific skin sensitization response are not yet understood. Recently, we revealed a set of genes in human cord blood CD34(+) DC (CD34-DC) that show a discriminating behaviour after skin sensitizing exposure. Based on their differential expression, an in vitro assay was developed to identify chemicals as sensitizing or not. This study was designed to investigate the genes' involvement in the DC response to skin sensitizers and as such gain insights in the sensitization cascade. Functional connection of the marker genes was inquired by constructing a molecular network using Ingenuity software. By real-time RT-qPCR, we established the effective expression of 3 additional gene transcripts in the generated network in CD34-DC, of which CREB1 and TNF-alpha were significantly altered in expression by sensitizing versus non-sensitizing exposure. Next, it was tested whether the discriminating response of CCR2 and COX2 marker genes was translated at the protein level in CD34-DC exposed to 3 sensitizers versus 3 non-sensitizers. Significantly differential protein expression of CCR2 and COX2 was confirmed using flow cytometry. Our results indicate that the marker genes may be functionally relevant in DC mediated skin sensitization.
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http://dx.doi.org/10.1016/j.toxlet.2010.04.003DOI Listing
July 2010

Assessment of chemical skin-sensitizing potency by an in vitro assay based on human dendritic cells.

Toxicol Sci 2010 Jul 7;116(1):122-9. Epub 2010 Apr 7.

Unit Environmental Risk and Health, Toxicology, Flemish Institute for Technological Research (VITO NV), Mol, Belgium.

The skin-sensitizing potential of chemicals is an important concern for public health and thus a significant end point in the hazard identification process. To determine skin-sensitizing capacity, large research efforts focus on the development of assays, which do not require animals. As such, an in vitro test has previously been developed based on the differential expression of CREM and CCR2 transcripts in CD34(+) progenitor-derived dendritic cells (CD34-DC), which allows to classify chemicals as skin (non-)sensitizing. However, skin sensitization is not an all-or-none phenomenon, and up to now, the assessment of relative potency can only be derived using the in vivo local lymph node assay (LLNA). In our study, we analyzed the feasibility to predict the sensitizing potency, i.e., the LLNA EC3 values, of 15 skin sensitizers using in vitro data from the CD34-DC-based assay. Hereto, we extended the in vitro-generated gene expression data set by an additional source of information, the concentration of the compound that causes 20% cell damage (IC20) in CD34-DC. We statistically confirmed that this IC20 is linearly independent from the gene expression changes but that it does correlate with LLNA EC3 values. In a further analysis, we applied a robust linear regression with both IC20 and expression changes of CREM and CCR2 as explanatory variables. For 13 out of 15 compounds, a high linear correlation was established between the in vitro model and the LLNA EC3 values over a range of four orders of magnitude, i.e., from weak to extreme sensitizers.
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http://dx.doi.org/10.1093/toxsci/kfq108DOI Listing
July 2010

Locomotor activity in zebrafish embryos: a new method to assess developmental neurotoxicity.

Neurotoxicol Teratol 2010 Jul-Aug;32(4):460-71. Epub 2010 Mar 6.

VITO, Flemish Institute for Technological Research, Unit of Environmental Risk and Health, Division of Toxicology, Boeretang 200, 2400 Mol, Belgium.

Currently, neurotoxicity testing defined by OECD and FDA is based solely on in vivo experiments, using large numbers of animals, being expensive, time-consuming and unsuitable for screening numerous chemicals. The great demand for thousands of chemicals yet to be evaluated, urges the development of alternative test methods which are cheaper, faster and highly predictive for developmental neurotoxicity. In this study, we developed a new method to assess locomotor activity in early life stage of zebrafish at 24 h post fertilization (hpf), in comparison to locomotor activity of zebrafish larvae at 96 to 192 hpf. We hypothesized that this endpoint at early life stages could be used to predict the developmental neurotoxic potential of chemicals and performed exposure studies with chlorpyrifos to demonstrate this. Furthermore, the case study with chlorpyrifos was used to critically evaluate behavioral data analysis and improve method sensitivity. The approach for data analysis using distribution plots for parameters on locomotor activity, next to mean values allowed to obtain more accurate information from the same set of behavioral data, both for embryos and larvae. Embryos exposed to chlorpyrifos, within the range 0.039 to 10 mg/l, exhibited a significant concentration-dependent increase in the frequency and total duration of their spontaneous tail coilings at 24-26 hpf. Larvae exhibited altered swimming activity, as evidenced by a significant decrease in the total duration of movement and an increase in mean turn angle in the range 0.18 to 0.75 mg/l chlorpyrifos. Methodological evaluation showed that locomotor effects in larvae were most pronounced and reproducible at 96 hpf, compared to older individuals (120, 144, 168 and 192 hpf). These new methods based on locomotor activity at early life stages of zebrafish allowed to classify chlorpyrifos as a developmental neurotoxicant. Further research to judge the validity of these alternative methods is currently performed with an extended set of expected positive or negative chemicals for developmental neurotoxicity.
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http://dx.doi.org/10.1016/j.ntt.2010.03.002DOI Listing
September 2010

MUTZ-3-derived dendritic cells as an in vitro alternative model to CD34+ progenitor-derived dendritic cells for testing of chemical sensitizers.

Toxicol In Vitro 2009 Dec 2;23(8):1477-81. Epub 2009 Sep 2.

Flemish Institute for Technological Research (VITO NV), Environmental Risk and Health, BE-2400 Mol, Belgium.

The cytokine-dependent CD34(+) human acute myeloid leukaemia cell line MUTZ-3 was used to generate immature dendritic-like cells (MUTZ-3 DC) and their validity as an alternative to primary CD34(+) progenitor-derived DC (CD34-DC) for testing chemical-induced sensitization was assessed. Expression levels of the DC maturation markers HLA-DR, CD86, CD83 and CD11c were studied using flow cytometry after 24 and 48 h exposure to the model compound nickel sulphate (100 and 300 microM). No maturation of MUTZ-3 DC was observed, whereas significantly upregulated expression levels of CD83 and CD86 were noticed in CD34-DC after 24h treatment with 300 microM nickel sulphate compared to control cells. Differential expression of the cytokine genes IL1beta, IL6, IL8, CCL2, CCL3, CCL3L1, CCL4 was analyzed using real-time RT-PCR after 6, 10 and 24h of nickel sulphate exposure. In response to 100 microM nickel sulphate MUTZ-3 DC revealed slightly upregulated mRNA levels after 24h, whereas 300 microM induced transcription of CCL3, CCL3L1 and IL8 significantly after 6 or 10h. These cytokine data correspond to the previously observed effects of 100 microM nickel sulphate in CD34-DC. Our findings underline the stimulatory capacity of nickel sulphate in MUTZ-3 DC with regard to cytokine mRNA induction, but not surface marker expression. Compared to CD34-DC, however, the studied endpoint markers seemed to be less inducible, making the MUTZ-3 DC model in its presented form less suitable for in vitro testing of sensitization. Further assessment of MUTZ-3 DC using other differentiation protocols and an extended set of chemicals will be required to reveal whether this cell line may be a valid alternative model system to primary CD34-DC.
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http://dx.doi.org/10.1016/j.tiv.2009.08.022DOI Listing
December 2009

Gene profiles of THP-1 macrophages after in vitro exposure to respiratory (non-)sensitizing chemicals: identification of discriminating genetic markers and pathway analysis.

Toxicol In Vitro 2009 Sep 13;23(6):1151-62. Epub 2009 Jun 13.

Unit Environmental Risk and Health, Flemish Institute for Technological Research (VITO NV), Boeretang 200, 2400 Mol, Belgium.

It is recognized that respiratory sensitization is a hazard of high concern. Despite international regulatory requirements there is no established protocol for the identification of chemical respiratory sensitizers. New tests should be based on mechanistic understanding and should be preferentially restricted to in vitro assays. The major goal of this study was to investigate the genetic response of human THP-1 macrophages after contact with respiratory (non-)sensitizers, and to identify genes that are able to discriminate between both groups. THP-1 macrophages were exposed during different time points to 3 respiratory sensitizers, 2 irritants, and 1 skin sensitizer. Gene expression changes were evaluated using Agilent Whole Human Genome arrays. Fisher Linear Discriminant Analysis was used to obtain a ranking of genes that reflects their potential to discriminate between respiratory (non-)sensitizing chemicals. Among the 20 most discriminating genes which were categorized into molecular and biological Gene Ontology (GO) terms, EIF4E, PDGFRB, SEMA7A, and ZFP36L2 could be associated with respiratory sensitization. When categorizing the top-1000 genes into biological GO terms, 24 genes were associated with immune function. Using a pathway analysis tool, platelet-derived growth factor signaling was observed to be activated in THP-1 macrophages in the context of respiratory sensitization.
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http://dx.doi.org/10.1016/j.tiv.2009.06.007DOI Listing
September 2009

Development of a screening assay to identify teratogenic and embryotoxic chemicals using the zebrafish embryo.

Reprod Toxicol 2009 Nov 15;28(3):308-20. Epub 2009 May 15.

VITO NV, Flemish Institute for Technological Research, Unit of Environmental Risk and Health, Toxicology, Boeretang 200, 2400 Mol, Belgium.

We developed and optimized a screening procedure, in which zebrafish embryos were explored as a model for the evaluation of the specific embryotoxic and teratogenic potential of chemicals. A selection of known positive (retinoic acid, valproic acid, caffeine, lithium chloride) and negative (glucose, saccharin) compounds for developmental toxicity were used to evaluate this method. We exposed embryos and evaluated embryotoxicity and morphological characteristics of the embryos at 24, 48, 72 and 144 h post fertilization. After evaluation of the induced effects, concentration-response curves were created for both embryotoxicity and teratogenic effects. Values for teratogenic indices (TI) were calculated as the ratio LC(50)/EC(50). The results obtained were compared to existing data from studies with laboratory animals and humans. We demonstrated that our classification of the compounds, based on TI values, allows to distinguish teratogens from non-teratogens and supports the application of zebrafish embryos as an alternative method for developmental toxicity studies to predict effects in mammals.
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http://dx.doi.org/10.1016/j.reprotox.2009.05.004DOI Listing
November 2009