There exists critical concern that exposures to drugs and chemicals during early life contributeto the increasing incidence of neurodevelopmental disorders, such as lowered IQ, learningdisabilities, autism and attention deficit and hyperactivity disorder (ADHD). The developing brainis more susceptible to substance-induced injury compared to the adult brain due to the complexdevelopmental processes, the absence of a functional blood/brain-barrier and a diminishedability to detoxify chemicals. Demanding animal tests have been devised, but because of lowfrequencies of hazardous substances and manifestations, as well as complex underlyingmechanisms, limitations of current approaches are enormous. The area is therefore of keyinterest for new approaches, as outlined in the NRC vision document for a toxicology in the 21stcentury and the critical path initiative. The applicants have steering such a paradigm change.As a pilot reproductive toxicity concern, we propose to address the developmental neurotoxicityarea, since this is a stand-alone health issue not adequately covered by current testingstrategies. It represents a key element in the current transition from the two-generation study toan extended one-generation study and profits from an explosion of knowledge from basicscience. In a 6-year process with critical involvement of the applicants, including threeinternational conferences and a workshop co-organized, promising models and prototypic testsubstances have been identified. Extending our recent metabolomics and genomicsapproaches, a systems toxicology approach shall be applied now, in order to identify andvalidate critical pathways of toxicity (PoT). PoT-specific reporter gene models shall then beestablished allowing higher test throughput. We will make use of our rat primary three-dimensional organotypic in vitro model, i.e. aggregating brain cell cultures, which was shown toclosely reproduce the in vivo situation of the CNS and neurotoxic mechanisms. Moreover,neurodevelopment processes have been well characterized, making the model relevant for DNTstudies. Cell cultures will be exposed to DNT reference compounds during development and theexpression levels of cell-specific genes will be quantified by real-time PCR. Furthermore, lowmolecular weight metabolites relevant for neurodevelopment will be quantified by massspectrometry based metabolomics. Results shall give insight into the specific cell types targetedand the neurodevelopmental alterations induced. The creation of reporter gene assays inmurine embryonic stem cells shall make PoT-specific testing with higher throughput possible.This will advance our understanding of DNT and test capabilities.
A 3D-organotypic rat brain cell model will be combined with mass-spectrum-based metabolomics to identify pathways of developmental neurotoxicity. After pathway validation, pathway-specific reporter gene assays are constructed to allow higher throughput testing. Such assays promise to overcome some limitations of current reproductive and neurodevelopmental toxicity testing.
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