2024 International Academy of Toxicologic Pathology (IATP) Satellite Symposium: New Approach Methodologies (NAMs) for Neurotoxicity Assessment and Regulatory Perspectives

Abstract

The International Academy of Toxicologic Pathology (IATP) Satellite Symposium on "New Approach Methodologies (NAMs) for Neurotoxicity Assessment and Regulatory Perspectives," organized in Spain, addressed the growing need for improved assessment of neurotoxicity. Traditional neurotoxicity assessment using in vivo animal studies are impractical for testing the substantial number of environmental chemicals that currently lack data and in the early detection of neuro-related adverse reactions in drug discovery. The NAMs, including human in vitro assays and small model organisms, have been developed for faster and cost-effective assessment of neurotoxic potential. While NAMs offer improved practicality, utility, and valuable mechanistic insights, their integration into regulatory decision-making requires robust scientific validation and technical characterization. Confidence in and regulatory application of NAMs data can be supported by mapping cellular outcomes to neuropathological findings in mammals, including humans, through the Adverse Outcome Pathway (AOP) framework, and the Integrated Approach to Testing and Assessment (IATA). Case studies presented demonstrated the application of NAMs in chemical and drug safety evaluations, focusing on developmental neurotoxicity (DNT), Parkinson's disease, and drug-induced seizures. In conjunction with in vivo toxicology studies, NAMs represent a significant step toward advancing chemical and drug toxicity assessment via hazard identification and drug screening safety assessments.

Keywords: Parkinson’s disease; adult neurotoxicity; adverse outcome pathway.; developmental neurotoxicity; new approach methodologies; seizure.

Figure 1.

Prevalence of neurodevelopmental disorders in 1990 and 2021, presenting the significant increase over time (adapted from IHME, Global Burden of Disease (2024) https://www.healthdata.org/research-analysis/gbd).

Figure 2.

Gaining confidence in DNT IVB assays: Biological Relevance, robustness and predictivity of positive and negative reference compounds was shown. Images produced with BioRender; the `Predictivity` image taken from Blum et al. 2022.

Figure 3.

Human induced pluripotent stem cell (hiPSC) derived neural cultures: hiPSC can differentiate in 2D and 3D into human induced neural progenitor cells (hiNPC). Using different media and protocols, hiNPC can be further differentiated and matured into spontaneous mixed 2D or 3D cultures including organoids, which add anatomical structures to the 3D BrainSpheres. Alternatively, genetically or pharmacologically-driven iNeurons and iAstrocytes can be produced, which can be utilized as single cultures or can subsequently be placed in certain ratios into defined mixed cultures. Finally, the goal is to add also microglia to the neuroectodermal in vitro systems for including immune cell function into the mixed neural cultures. Images produced with BioRender.

Figure 4.

Examples of Molecular Initiating Events (MIEs) followed by Key Events (KEs) that can be measured by the DNT IVB (yellow and orange box) leading to DNT adverse outcomes such as impaired cognition.

Figure 5.

Workflow of IATA case study for prioritization of compounds for further DNT testing by integrating data from various sources (yellow boxes). These sources produce different types of data (purple) that going through data analysis pipelines (green). The final output data (orange) can then be combined to conclude on the toxicity of compounds and select high priority examples for further testing.

Figure 6.

AOP 3: Inhibition of the mitochondrial complex I, II or III of nigro-striatal neurons leads to parkinsonian motor deficits, as implemented in Delp et al. 2019.

Figure 7.

Tebufenpyrad case study integrating NAMs data, exposure and PBPK modelling to predict a margin of internal exposure (MoIE).