Planarians as an in vivo model for a high-throughput assessment of developmental, neuro- and genotoxicity

Abstract

The use of in vitro methods in toxicity testing often fails to include complex toxicological endpoints and is limited in its ability to link observed alterations to adverse outcomes. Here we demonstrate the added value of planarians within the 3R principle for in vivo toxicity assessments, with a specific focus on developmental toxicity, neurotoxicity and genotoxicity. The freshwater planarian Schmidtea mediterranea is characterized by a high regenerative capacity, which is attributed to a large pool of pluripotent stem cells (neoblasts). Based on planarian behavior, regenerative success and underlying stem cell responses, we investigate complex toxicological outcomes at different levels of biological organization and aim to identify specific adverse outcome pathways. To assess developmental toxicity, we exploit the regenerative capacities of S. mediterranea by artificially amputating the worm and subsequently study its regenerative success after exposure to toxicological compounds. Phenotypic abnormalities, aberrant eye development and reduced tissue outgrowth are combined with a well established set of cellular markers to assess underlying stem cell dynamics. Behavioral abnormalities are used to evaluate neurotoxicity, which we further investigate by scoring the development of the planarian brain and central nervous system. To specify neurotoxicity, specific neuronal populations can be visualized. Additionally, based on specific planarian stem cell responses we developed a high-throughput screening alternative in the field of carcinogenicity testing. Our assay quantifies the number of proliferating stem cells and, based on the resulting patterns, enables the prediction of genotoxicity and the classification of carcinogenic compounds as genotoxic or non-genotoxic. In conclusion, planarians allow for a high-throughput, inexpensive and reliable screening of toxicological compounds, here demonstrated in the field of developmental, neuro- and genotoxicity. Future studies regarding the underlying mechanisms will allow us to identify adverse outcome pathways.