A Retrospective Performance Assessment of the Developmental Neurotoxicity Study in Support of OECD Test Guideline 426

Office of Research and Development, National Center for Environmental Assessment, U.S Environmental Protection Agency, Washington, DC 20460-0001, USA.
Environmental Health Perspectives (Impact Factor: 7.98). 02/2009; 117(1):17-25. DOI: 10.1289/ehp.11447
Source: PubMed


We conducted a review of the history and performance of developmental neurotoxicity (DNT) testing in support of the finalization and implementation of Organisation of Economic Co-operation and Development (OECD) DNT test guideline 426 (TG 426).

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In this review we summarize extensive scientific efforts that form the foundation for this testing paradigm, including basic neurotoxicology research, interlaboratory collaborative studies, expert workshops, and validation studies, and we address the relevance, applicability, and use of the DNT study in risk assessment.

The OECD DNT guideline represents the best available science for assessing the potential for DNT in human health risk assessment, and data generated with this protocol are relevant and reliable for the assessment of these end points. The test methods used have been subjected to an extensive history of international validation, peer review, and evaluation, which is contained in the public record. The reproducibility, reliability, and sensitivity of these methods have been demonstrated, using a wide variety of test substances, in accordance with OECD guidance on the validation and international acceptance of new or updated test methods for hazard characterization. Multiple independent, expert scientific peer reviews affirm these conclusions.

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    • "There is no doubt that the developing central nervous system is particularly vulnerable to damage by chemicals (Rice and Barone, 2000) and that evaluation of chemicals for developmental neurotoxicity (DNT) is critical to human health (Grandjean and Landrigan, 2006, 2014). However, only a very small number of chemicals has been tested for DNT in recent decades (Makris et al., 2009; Middaugh et al., 2003), presumably because first, there is no legal obligation for DNT testing and second, the current guidelines for DNT testing involve animal experiments (OECD, 2007) (US EPA 712-C-98-239; US EPA, 1998) that are prohibitively expensive, of poor reproducibility and predictive quality, low in throughput as well as limited with regard to mechanistic insights into the developmental toxicant's mode of action (Smirnova et al., 2014). For these reasons, alternatives to animal-based DNT testing methods such as in vitro screening assays using human culture models allowing for systematic DNT studies in high-throughput and large-scale format are urgently required (NRC, 2007). "
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    ABSTRACT: Human pluripotent embryonal carcinoma (NT2) cells are increasingly considered as a suitable model for in vitro toxicity testing, e.g. developmental toxicity and neurotoxicity (DT/DNT) studies, as they undergo neuronal differentiation upon stimulation with retinoic acid (RA) and permit toxicity testing at different stages of maturation. NT2 cells have recently been reported to show specific changes in dielectric resistance profiles during differentiation which can be observed as early as 24 hours upon RA-stimulation. These observations suggest altered susceptibility to chemicals at an early stage of differentiation. However, chemical susceptibility of early differentiating NT cells has not yet been studied. To address this question, we have established a cell fitness screening assay based on the analysis of intracellular ATP levels and we applied the assay in a large-scale drug screening experiment in NT2 stem cells and early differentiating NT2 cells. Subsequent analysis of ranked fitness phenotypes revealed 19 chemicals with differential toxicity profile in early differentiating NT2 cells. To evaluate whether any of the identified drugs have previously been associated with DT/DNT, we conducted a literature search on the identified molecules and quantified the fraction of chemicals assigned to the FDA (Food and Drug Administration) pregnancy risk categories (PRC) N, A, B, C, D, and X in the hit list and the small molecule library. While the fractions of the categories N and B were decreased (0.81 and 0.35-fold), the classes C, D and X were increased (1.35, 1.47 and 3.27-fold) in the hit list compared to the chemical library. From these data as well as from the literature review, identifying large fractions of chemicals being directly (∼42%) and indirectly associated with DT/DNT (∼32%), we conclude that our method may be beneficial to systematic in vitro-based primary screening for developmental toxicants and neurotoxicants and we propose cell fitness screening in early differentiating NT2 cells as a strategy for evaluating chemical susceptibility at different stages of differentiation to reduce animal testing in the context of the 3Rs.
    Toxicology 10/2015; DOI:10.1016/j.tox.2015.10.007 · 3.62 Impact Factor
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    • "Considering that only 100 or so chemicals have actually been tested using regulatory DNT guidelines (Makris et al. 2009), the challenge facing the field of DNT testing is daunting. An alternative to currently available regulatory test methods that reduces both time and costs while maintaining or improving our understanding of DNT potential is urgently needed. "
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    ABSTRACT: A major problem in developmental neurotoxicity (DNT) risk assessment is the lack of toxicological hazard information for most compounds. Therefore, new approaches are being considered to provide adequate experimental data that allow regulatory decisions. This process requires a matching of regulatory needs on the one hand and the opportunities provided by new test systems and methods on the other hand. Alignment of academically and industrially driven assay development with regulatory needs in the field of DNT is a core mission of the International STakeholder NETwork (ISTNET) in DNT testing. The first meeting of ISTNET was held in Zurich on 23-24 January 2014 in order to explore the concept of adverse outcome pathway (AOP) to practical DNT testing. AOPs were considered promising tools to promote test systems development according to regulatory needs. Moreover, the AOP concept was identified as an important guiding principle to assemble predictive integrated testing strategies (ITSs) for DNT. The recommendations on a road map towards AOP-based DNT testing is considered a stepwise approach, operating initially with incomplete AOPs for compound grouping, and focussing on key events of neurodevelopment. Next steps to be considered in follow-up activities are the use of case studies to further apply the AOP concept in regulatory DNT testing, making use of AOP intersections (common key events) for economic development of screening assays, and addressing the transition from qualitative descriptions to quantitative network modelling.
    Archive für Toxikologie 01/2015; 89(2). DOI:10.1007/s00204-015-1464-2 · 5.98 Impact Factor
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    • "Thus, the use of these tests in regulatory science has been suggested by international, national, and private sectors. However, there have been some controversies on the test methods with respect to the sensitivity and specificity of the neurotoxicity tests, the kinds of endpoints that should be included, the complexity of the test protocol, and the large variability of some endpoints (Kuwagata 2012; Makris et al. 2009). The scientific literature used to derive the acceptable daily intake or tolerable daily intake values is limited. "
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    ABSTRACT: The prevalence of cognitive abnormalities in children has partly been ascribed to environmental chemical exposure. Appropriate animal models and tools for evaluating higher brain function are required to examine this problem. A recently developed behavioral test in which rats learn six unique flavor-location pairs in a test arena was used to evaluate paired-associate learning, a hallmark of the higher cognitive function that is essential to language learning in humans. Pregnant Long-Evans rats were dosed by gavage with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or 2,3,7,8-tetrabromodibenzo-p-dioxin (TBDD) at a dose of 0, 200, or 800 ng/kg (referred as Control, TCDD-200, TCDD-800, TBDD-200, or TBDD-800, hereafter) on gestational day 15, and the offspring was tested during adulthood. Paired-associate learning was found to be impaired in the TCDD-200 and TBDD-200 groups, but not in either group exposed to 800 ng/kg, the observations of which were ensured by non-cued trials. As for the emotional aspect, during habituation, the TCDD-200 and TBDD-200 groups showed significantly longer latencies to enter the test arena from a start box than the Control, TCDD-800, and TBDD-800 groups, suggesting that the TCDD-200 and TBDD-200 groups manifested anxiety-like behavior. Thus, both the chlorinated dioxin and its brominated congener affected higher brain function to a similar extent in a nearly identical manner. Use of the behavioral test that can evaluate paired-associate learning in rats demonstrated that in utero and lactational exposure to not only TCDD but also TBDD perturbed higher brain function in rat offspring in a nonmonotonic manner. Electronic supplementary material The online version of this article (doi:10.1007/s00204-013-1161-y) contains supplementary material, which is available to authorized users.
    Archives of Toxicology 11/2013; 88(3). DOI:10.1007/s00204-013-1161-y · 5.98 Impact Factor
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