In vitro cellular models for neurotoxicity studies: neurons derived from P19 cells

Humans are exposed to a variety of chemicals including environmental pollutants, cosmetics, food preservatives and drugs. Some of these substances might be harmful to the human body. Traditional toxicological and behavioural investigations performed in animal models are not suitable for the screening of a large number of compounds for potential toxic effects. There is a need for simple and robust in vitro cellular models that allow high-throughput toxicity testing of chemicals, as well as investigation of specific mechanisms of cytotoxicity. The overall aim of the thesis has been to evaluate neuronally differentiated mouse embryonal carcinoma P19 cells (P19 neurons) as a model for such testing. The model has been compared to other cellular models used for neurotoxicity assessment: retinoic acid-differentiated human neuroblastoma SH-SY5Y cells and nerve growth factor-treated rat pheochromocytoma PC12 cells. The chemicals assessed in the studies included the neurotoxicants methylmercury, okadaic acid and acrylamide, the drug of abuse MDMA (“ecstasy”) and a group of piperazine derivatives known as “party pills”. Effects of the chemicals on cell survival, neurite outgrowth and mitochondrial function have been assessed. In Paper I, we describe a fluorescence-based microplate method to detect chemical-induced effects on neurite outgrowth in P19 neurons immunostained against the neuron-specific cytoskeletal protein βIII-tubulin. In Paper II, we show that P19 neurons are more sensitive than differentiated SH-SY5Y and PC12 cells for detection of cytotoxic effects of methylmercury, okadaic acid and acrylamide. Additionally, in P19 neurons and differentiated SH-SY5Y cells, we could demonstrate that toxicity of methylmercury was attenuated by the antioxidant glutathione. In Paper III, we show a timeand temperature-dependent toxicity produced by MDMA in P19 neurons. The mechanisms of MDMA toxicity did not involve inhibition of the serotonin re-uptake transporter or monoamine oxidase, stimulation of 5-HT2A receptors, oxidative stress or loss of mitochondrial membrane potential. In Paper IV, the piperazine derivatives are evaluated for cytotoxicity in P19 neurons and differentiated SH-SY5Y cells. The most toxic compound in both cell models was TFMPP. In P19 neurons, the mechanism of action of TFMPP included loss of mitochondrial membrane potential. In conclusion, P19 neurons are a robust cellular model that may be useful in conjunction with other models for the assessment of chemical-induced neurotoxicity.