Cobalt oxide nanoparticles mediate tau denaturation and cytotoxicity against PC-12 cell line

It has not been well explored how NPs may induce some adverse effects on the biological systems. In this research, the interaction of cobalt oxide NPs (Co3O4 NPs) with tau protein and PC-12 cell line, as nervous system models, was investigated with several approaches including fluorescence spectroscopy, CD spectroscopy, docking study, MTT, LDH, AO/EB dual staining, and flow cytometry assays. Fluorescence investigation displayed that Co3O4 NPs spontaneously mediate the formation of a static complex with tau protein through hydrogen bonds and van der Waals forces. Docking study also revealed that Ser and Gln residues play important roles in the formation of hydrogen bonds between tau and Co3O4 NPs. Far UV-CD measurement determined that Co3O4 NPs changed the unfolded structure of tau protein toward a more folded conformation. Moreover, Co3O4 NPs demonstrated to stimulate the reduction of PC-12 cell viability through membrane leakage, fragmentation of DNA, apoptosis, and necrosis. In conclusion, Co3O4 NPs may trigger marked alterations on the tertiary and secondary structure of tau protein. Also, the dose of Co3O4 NPs is the crucial factor which induces their adverse effects on the cells. Because, all side effects of NPs are not well explored, additional detailed experiments are more needed.