Developmental Neurotoxicity Health Effects Innovation Research Program

National Institute Of Environmental Health Sciences

Investigators

Linked publications, trials & patents

Abstract

Value Proposition and Summary Given the large number of chemicals in use that need to be evaluated for potential DNT hazard, a decades long effort by the international regulatory and scientific communities has focused on developing an improved method for developmental neurotoxicity testing. An integrated framework has been developed by experts in the DNT field. This framework is designed to integrate all existing data, including in silico, in vitro, and in vivo data for use in chemical regulatory assessments and provide data elucidating mechanisms leading to adverse neurodevelopmental outcomes following chemical exposure. The current work of the DNT HEI is focused on implementing and refining this new framework for evaluating DNT potential of environmental chemicals. Study 1. The DNT HEI implemented a screening battery that models key neurodevelopmental processes. Selected assays include proliferation and apoptosis of human neural progenitor cells (hNPC), migration of human neural crest cells (NCC), neurite outgrowth in human induced pluripotent stem cells (iPSCs), synaptogenesis and network formation/maturation in multi electrode array (MEA) using rat primary cortical neurons, zebrafish behavior during early development (total distanced and larval movement pattern), and 3D neurosphere assay using hNPCs (proliferation, apoptosis, migration and differentiation) to allow for interaction of multiple brain cell types. A first phase (Phase 1) and a second phase (Phase 2) library of stakeholder nominated chemicals was procured and distributed to contract laboratories and collaborators to run in the screening battery. The chemical libraries are composed of a diverse set of chemicals representing the following classes: botanicals, cannabinoids, insecticides, fungicides, herbicides, industrial chemicals, therapeutic drugs, flame retardants, insecticides, positive DNT controls and negative DNT controls. Data from the screening of the Phase 1 and Phase 2 libraries will provide weight of evidence evaluation of DNT potential and will serve to prioritize compounds for further study (e.g., using short-term in vivo behavioral, in vivo neuroimaging, and mechanistic studies). Additional behavior assays using Drosophila and Planarian were recently included in the Phase 1 screen and testing in these assays are still ongoing. Study 2. The DNT HEI is currently developing and refining high throughput assessment of rodent behavior using automated home cage monitoring. These methods will improve the ability to track subtle behavioral perturbations, reduce experimenter variability, and potentially link the behavioral perturbations to alterations in neural networks using in vivo imaging. The goal of these studies is to link behavioral changes from neurotoxicants to mechanisms modeled in the screening battery. IVIVE and in silico approaches are being used to contextualize in vitro and in vivo findings with human exposure to provide relevant and translatable information to protect human health. The DNT HEI is also currently developing assays to assess microglia and astrocyte functional changes contributing to chemical-induced DNT. Study 3. The DNT HEI has developed an integrated approaches to testing and assessment (IATA)case study on the use of the screening battery to prioritize a class of compounds for further testing. The case study was endorsed and published by the OECD in September 2022 (https://one.oecd.org/document/env/cbc/mono(2022)26/en/pdf). The IATA case study is also included as an appendix in the guidance document (GD) titled Initial Recommendations on Evaluation of Data from the Developmental Neurotoxicity (DNT) In Vitro Testing Battery. The GD was published by OECD in June 2023 (https://one.oecd.org/document/ENV/CBC/MONO(2023)13/en/pdf) and includes descriptions of the assays, the relevance of the data to DNT and assist in the determination of the degree of certainty to support the use of this data for regulatory hazard assessment. Study 2. The DNT HEI is currently developing and refining high throughput assessment of rodent behavior using automated homecage monitoring. These methods will improve the ability to track subtle behavioral perturbations, reduce experimenter variability, and potentially link the behavioral perturbations to alterations in neural networks using in vivo imaging. The goal of these studies is to link behavioral changes from neurotoxicants to mechanisms modeled in the screening battery. IVIVE and in silico approaches are being used to contextualize in vitro and in vivo findings with human exposure to provide relevant and translatable information to protect human health. Study 3. The DNT HEI has developed an integrated approaches to testing and assessment (IATA) case study on the use of the screening battery to prioritize a class of compounds for further testing. The case study will be included in an OECD guidance document that will provide information on the application and interpretation of the testing battery in a regulatory context. The IATA case study has been discussed in several OECD meetings and was presented at ICCVAMs public forum 2022.