Toxic response of HIPCO single-walled carbon nanotubes in mice and RAW264.7 macrophage cells

- We identified an innate immune toxic response of SWCNT synthesized by HIPCO method.
- In mice, the number of total cells and the secretion of IL-6 and MCP-1 increased.
- The portion of neutrophils, lymphocytes, and eosinophils increased.
- In RAW264.7 cells, cell viability and ATP production decreased.
- The levels of apoptosis-, autophagy- and ER stress-related proteins increased.
- Autophagosome, the ER dilatation and mitochondrial flocculent densities were observed.

In this study, we identified the toxic response of pristine single-walled carbon nanotubes (P-SWCNTs) synthesized by HIPCO method in mice and RAW264.7 cells, a murine peritoneal macrophage cell line. P-SWCNT contained a large amount of Fe ion (36 wt%). In the lungs of mice 24 h after intratracheal administration, P-SWCNTs increased the secretion of IL-6 and MCP-1, and the number of total cells, the portion of neutrophils, lymphocytes, and eosinophils, also significantly increased at a 100 μg/mL of concentration. In RAW264.7 cells, cell viability and ATP production decreased in a dose-dependent manner at 24 h after exposure, whereas the generations of ROS and NO were enhanced at all concentrations together with the activation of the MAP kinase pathway. Moreover, the levels of both apoptosis- and autophagy-related proteins and ER stress-related proteins clearly increased, and the concentrations of Fe, Cu, and Zn ions, but not of Mn ions, increased in a dose-dependent manner. TEM images also revealed that P-SWCNTs induced the formation of autophagosome-like vacuoles, the dilatation of the ER, the generation of mitochondrial flocculent densities, and the separation of organelle by disappearance of the cell membrane. Taken together, we suggest that P-SWCNTs cause acute inflammatory response in the lungs of mice, and induce autophagy accompanied with apoptosis through mitochondrial dysfunction and ER stress in RAW264.7 cells. Furthermore, further study is required to elucidate how the physicochemical properties of SWCNTs determine the cell death pathway and an immune response.