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

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          Abstract

          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.

          Highlights

          • An increased prevalence of neurodevelopmental disorders in children is observed.

          • There is very limited information on neurodevelopmental toxicity (DNT) induced by environmental chemicals.

          • A new framework is required for assessment of chemicals with the potential to disrupt brain development.

          • In vitro DNT data together with in silico approaches should be used for regulatory purposes.

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          Most cited references32

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          ToxCast Chemical Landscape: Paving the Road to 21st Century Toxicology

          The U.S. Environmental Protection Agency's (EPA) ToxCast program is testing a large library of Agency-relevant chemicals using in vitro high-throughput screening (HTS) approaches to support the development of improved toxicity prediction models. Launched in 2007, Phase I of the program screened 310 chemicals, mostly pesticides, across hundreds of ToxCast assay end points. In Phase II, the ToxCast library was expanded to 1878 chemicals, culminating in the public release of screening data at the end of 2013. Subsequent expansion in Phase III has resulted in more than 3800 chemicals actively undergoing ToxCast screening, 96% of which are also being screened in the multi-Agency Tox21 project. The chemical library unpinning these efforts plays a central role in defining the scope and potential application of ToxCast HTS results. The history of the phased construction of EPA's ToxCast library is reviewed, followed by a survey of the library contents from several different vantage points. CAS Registry Numbers are used to assess ToxCast library coverage of important toxicity, regulatory, and exposure inventories. Structure-based representations of ToxCast chemicals are then used to compute physicochemical properties, substructural features, and structural alerts for toxicity and biotransformation. Cheminformatics approaches using these varied representations are applied to defining the boundaries of HTS testability, evaluating chemical diversity, and comparing the ToxCast library to potential target application inventories, such as used in EPA's Endocrine Disruption Screening Program (EDSP). Through several examples, the ToxCast chemical library is demonstrated to provide comprehensive coverage of the knowledge domains and target inventories of potential interest to EPA. Furthermore, the varied representations and approaches presented here define local chemistry domains potentially worthy of further investigation (e.g., not currently covered in the testing library or defined by toxicity "alerts") to strategically support data mining and predictive toxicology modeling moving forward.
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            The Tox21 robotic platform for the assessment of environmental chemicals--from vision to reality.

            Since its establishment in 2008, the US Tox21 inter-agency collaboration has made great progress in developing and evaluating cellular models for the evaluation of environmental chemicals as a proof of principle. Currently, the program has entered its production phase (Tox21 Phase II) focusing initially on the areas of modulation of nuclear receptors and stress response pathways. During Tox21 Phase II, the set of chemicals to be tested has been expanded to nearly 10,000 (10K) compounds and a fully automated screening platform has been implemented. The Tox21 robotic system combined with informatics efforts is capable of screening and profiling the collection of 10K environmental chemicals in triplicate in a week. In this article, we describe the Tox21 screening process, compound library preparation, data processing, and robotic system validation. Published by Elsevier Ltd.
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              Potential developmental neurotoxicity of pesticides used in Europe

              Pesticides used in agriculture are designed to protect crops against unwanted species, such as weeds, insects, and fungus. Many compounds target the nervous system of insect pests. Because of the similarity in brain biochemistry, such pesticides may also be neurotoxic to humans. Concerns have been raised that the developing brain may be particularly vulnerable to adverse effects of neurotoxic pesticides. Current requirements for safety testing do not include developmental neurotoxicity. We therefore undertook a systematic evaluation of published evidence on neurotoxicity of pesticides in current use, with specific emphasis on risks during early development. Epidemiologic studies show associations with neurodevelopmental deficits, but mainly deal with mixed exposures to pesticides. Laboratory experimental studies using model compounds suggest that many pesticides currently used in Europe – including organophosphates, carbamates, pyrethroids, ethylenebisdithiocarbamates, and chlorophenoxy herbicides – can cause neurodevelopmental toxicity. Adverse effects on brain development can be severe and irreversible. Prevention should therefore be a public health priority. The occurrence of residues in food and other types of human exposures should be prevented with regard to the pesticide groups that are known to be neurotoxic. For other substances, given their widespread use and the unique vulnerability of the developing brain, the general lack of data on developmental neurotoxicity calls for investment in targeted research. While awaiting more definite evidence, existing uncertainties should be considered in light of the need for precautionary action to protect brain development.
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                Author and article information

                Contributors
                Journal
                Toxicol Appl Pharmacol
                Toxicol. Appl. Pharmacol
                Toxicology and Applied Pharmacology
                Academic Press
                0041-008X
                1096-0333
                01 September 2018
                01 September 2018
                : 354
                : 3-6
                Affiliations
                [a ]IUF – Leibniz Research Institute for Environmental Medicine, Duesseldorf, Germany
                [b ]University of Southern Denmark, Harvard T.H. Chan School of Public Health, USA
                [c ]Neurotoxicologist, Durham, NC, USA
                [d ]Albert Einstein College of Medicine Bronx, New York, USA
                [e ]Bloomberg School of Public Health, Founding Director (Emeritus) of Center for Alternatives to Animal Testing (CAAT), Johns Hopkins University, Baltimore, USA
                [f ]Finnish Centre for Alternative Methods (FICAM), University of Tampere, Tampere, Finland
                [g ]National Institute for Public Health and the Environment, RIVM Center for Health Protection, Bilthoven, Netherlands
                [h ]Centre for Alternatives to Animal Testing (CAAT), Johns Hopkins University, Baltimore, USA
                [i ]The Danish Environmental Protection Agency (EPA), Copenhagen, Denmark
                [j ]Department of Molecular Biosciences, School of Veterinary Medicine, University of California Davis, Davis, USA
                [k ]CAAT – Centre for Alternatives to Animal Testing, University of Konstanz, Konstanz, Germany
                [l ]Neurotoxicologist, Durham, USA
                [m ]Austrian National Coordinator of Testing Methods, Austria
                [n ]RIVM Center for Health Protection, Bilthoven and Institute for Risk Assessment Sciences, Utrecht University, Utrecht, Netherlands
                [o ]Organisation for Economic Co-operation and Development (OECD), Paris, France
                [p ]Bayer, Wuppertal, Germany
                [q ]Federal Institute for Risk Assessment (BfR), Berlin, Germany
                [r ]European Food Safety Authority (EFSA), Parma, Italy
                [s ]Department of Physiology, University of Lausanne and SCAHT, Switzerland
                [t ]SCAHT – Swiss Centre for Applied Human Toxicology, University of Basel, Basel, Switzerland
                [u ]VITO, Flemish Institute for Technological Research, Unit Environmental Risk and Health, Belgium
                [v ]European Commission –DG Joint Research Centre (JRC), Ispra, Italy
                [w ]Global Food Ethics, Johns Hopkins University, Baltimore, USA
                Author notes
                [* ]Corresponding author at: Directorate F – Health, Consumers and Reference Materials, Unit F3: Chemicals Safety and Alternative Methods, via E. Fermi, 2749,  I-21027 Ispra (VA), Italy. anna.price@ 123456ec.europa.eu
                Article
                S0041-008X(18)30043-7
                10.1016/j.taap.2018.02.004
                6097873
                29447839
                8a9362fe-6fee-469f-a443-951fe38d9aa8
                © 2018 The Authors

                This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

                History
                : 2 February 2018
                : 9 February 2018
                : 10 February 2018
                Categories
                Article

                developmental neurotoxicity,in vitro testing,regulatory purposes

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