Developmental neurotoxicity guideline study: Issues with methodology, evaluation and regulation*

Abstract

Recently social concerns have been increasing about the effects of environmental factors on children's health, especially on their nervous systems. The U.S. Environmental Protection Agency (EPA) and the Organisation for Economic Co-operation and Development (OECD) have published testing guidelines for developmental neurotoxicity (DNT). Approximately 110 guideline studies have been conducted to date. Importantly, information from these studies has provided data critical for regulatory decisions for a number of chemicals. However, the DNT guidelines do not always satisfy all stakeholders because of some uncertainties in their methodology, evaluation, and regulation. Methodological issues include incomplete harmonization between EPA and OECD guidelines, criticisms of the methodology for learning and memory testing, and unspecified positive control substances. Potential artifacts in morphometric neuropathological measures, criteria for observation measures, uncertainty of postnatal offspring exposure, especially in feeding studies, and extrapolation of data from rats to humans are major evaluation issues. In addition, there is some uncertainty in the use of an additional safety factor for susceptibility of infants and children. Moreover, the DNT guidelines have extensive time and cost requirements, use large numbers of animals, and there is a limited set of laboratories that can conduct the study. This paper reviews some of these issues and summarizes discussions from the symposium 'Developmental neurotoxicity testing: Scientific approaches towards the next generation to protecting the developing nervous system of children' held at the 2011 annual meeting of the Japanese Teratology Society.

Recommended Methods for Brain Processing and Quantitative Analysis in Rodent Developmental Neurotoxicity Studies

“…Accordingly, animal testing for potential DNT is an important element of the registration package presented to regulatory agencies for new chemical entities. The push for evidence-based DNT regulation is decades old (Buelke-Sam and Mactutus 1990;Francis, Kimmel, and Rees 1990;Levine and Butcher 1990;Rees, Francis, and Kimmel 1990;Stanton and Spear 1990;Tyl and Sette 1990), but only recently has the degree of communal experience expanded to the point where intelligent adjustments to regulatory guidelines may be considered (Crofton et al 2004;de Groot, Bos-Kuijpers, et al 2005;Crofton et al 2008;Tyl et al 2008;Makris et al 2009;Raffaele et al 2010;Tsuji and Crofton 2012).…”

OECD/EFSA workshop on developmental neurotoxicity (DNT): The use of non-animal test methods for regulatory purposes

“…Additionally, they can result in methodological and scientific uncertainties. This includes the challenges in extrapolation of findings from rats to humans that result from timing differences in brain development, toxicokinetics, and inherent difficulties in the use of non-homologous functional tests (Tsuji and Crofton, 2012;Dorman et al, 2001;Kaufmann, 2003). For these reasons, DNT has been regarded as an area in need of the development of alternative methods in order to establish a timeand cost-efficient predictive testing strategy.…”

Fingerprinting of neurotoxic compounds using a mouse embryonic stem cell dual luminescence reporter assay

“…Animal tests remain the principal experimental approach. Although the guidelines for testing neurodevelopmental toxicity of compounds (Tsuji and Crofton 2012) rely mainly on in vivo testing, logistic, scientific, and ethical arguments suggest that well-controlled in vitro systems that detect neurodevelopmental toxicity and/or neurotoxicity should be developed (Hartung and Leist 2008; Leist et al 2008). Stem cell-based technologies are particularly promising in this respect and the EU consortium “embryonic stem cell-based novel alternative tests” (ESNATS www.esnats.eu) was dedicated to the development of such in vitro systems.…”