Diverse Responses of Neurons and Monocytes to Titanium Dioxide Nanoparticle Exposure
Engin, Evren Doruk
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Introduction: The toxicity of titanium dioxide nanoparticles (TiO2NPs) in neurons occurs by glutamate signaling via N-methyl-d-aspartate (NMDA) receptors. Although cellular uptake of TiO2NPs may lead to oxidative stress in macrophages, it is not known whether TiO2NPs have toxic effects on U937 monocytic cell line. Material and Methods: Human neuroblastoma (SH-SY5Y) and U937 human monocytic cell lines were exposed to 25nm and 10nm TiO2NPs, in medium with or without fetal bovine serum (FBS). Mitochondrial metabolic activity was assessed using the MTT-assay before and after treatment with 15 mM N-acetylcysteine (NAC) and 0.1µM or 10µM neopterin. Results: TiO2NPs displayed no toxicity on SH-SY5Y and U937 cells in FBS-free medium. The addition of FBS resulted in a significant reduction in cell viability with both sizes of TiO2NPs on SH-SY5Y and U937 cells. In FBScontaining medium, NAC pretreatment significantly increased cell viability of SH-SY5Y cells in comparison to U937 cells. Both neopterin doses enhanced cell viability of TiO2NPs-exposed SH-SY5Y cells for all concentrations. Only a limited increase in the cell viability was achieved in 10nm TiO2NPs-exposed neurons by pretreatment with neopterin. Whereas, neopterin could not provide a constant amelioration for both 25nm and 10nm sized TiO2NPs-exposed U937 monocytic cells. TiO2NPs displayed size-dependent neuronal toxicity. In FBS-containing medium, both sizes of TiO2NPs caused reduction in cell viability of both cell lines. Conclusion: While toxicity of TiO2NPs emerged via NMDA and AMPA receptors in SH SY5Y cells, U937 cells were most probably activated by AMPA receptors only. Unlike SHSY5Y cells, NADPH oxidase complex inhibition was not effective in TiO2NPs exposed U937 cells.