SCR&Tox: Stem Cells for Relevant efficient extended and normalised Toxicology

Abstract

Neurotoxicity is one of the most challenging fields for the development of in vitro testing systems. In the last years, alternative in vitro testing strategies for chemical risk assessment have been designed, according to the current REACH legislation, to reduce the number of animal required for testing. However, to date in vitro assays for neurotoxicity have not been formally validated yet [1]. This is mostly due to the extreme complexity of the nervous system in which many different cell types are organized in a well orchestrated and functional network difficult to reproduce in vitro, but also to the lack of in vitro systems and methods capable to fully cover some of the endpoints of the in vivo tests such as the neurobehavioral and neurocognitive aspects as well as the motor functionality. Nowadays, many cellular models are available for the nervous system, including primary cultures of fetal and adult neurons and glial cells, tumor-derived cell lines, hippocampal brain slices and neural progenitor cells, but all of this models suffer from considerable drawbacks, e.g. non-human origin, limited access or non-physiological transformed cell types [2]. Human pluripotent stem cells (hPSCs) are considered as a powerful tool for drug screening and the development of new in vitro testing strategies. Indeed, these cells can be indefinitely expanded and efficiently differentiated into neuronal derivatives, including different regionalized neuronal subtypes, glial cells and peripheral neurons [3]. In this context, the European project ESNATS has taken the first step toward the design of developmental neurotoxicity tests based on the use of hPSCs, particularly developing battery of tests covering different aspects of neural teratogenicity [4-6]. Many of these hPSCs-based models are very well characterized on the molecular basis, but to date there are few data indicating how they reflect the functionality of the in vivo central nervous system (CNS)/ peripheral nervous system (PNS) and clearly none of these systems can completely resemble the complex physiology of the entire nervous system. Consequently, the main problem in the development of novel test strategies relies on the fact that the mechanisms underlying neurotoxicity are too extensive to be covered with a single model and a small set of endpoints. Therefore, in vitro neurotoxicity tests should include different cellular models and multiple levels of evaluation, ranging from cytotoxicity and cell physiology to neuronal specific cell function endpoints. Moreover, the obtained data, in order to be considered reliable and predictive, should be compared across diverse in vitro models, extrapolated and further aligned to in vivo available data sets, in order to bridge the gap between in vivo and in vitro neurotoxicity.JRC.I.5-Systems Toxicolog