Transcriptomic analysis revealed that multi-walled carbon nanotubes diameter-dependently induced pyroptosis in THP-1 macrophages

Direct contact with multi-walled carbon nanotubes (MWCNTs) could compromise the viability of macrophages, but the mechanisms remained poorly understood. Previously we investigated the cytotoxicity of MWCNTs with different diameters (XFM4 < XFM22 < XFM34), and showed that MWCNTs induced cytotoxicity in an order of XFM4 > XFM22 > XFM34. In this study, we analyzed the transcriptomic data and found that MWCNTs diameter-dependently (in an order of XFM4 > XFM22 > XFM34) affected gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related with immune responses. Therefore, we speculated that MWCNT-induced cytotoxicity was inflammation-driving pyroptosis. To test this hypothesis, we investigated the changes of morphologies, reactive oxygen species (ROS) and key proteins related with pyroptosis. We found that only XFM4 induced multi-pores of cellular membranes and ROS. Meanwhile, MWCNTs promoted the protein levels of caspase 1, NLRP3, interleukin-18 (IL-18) and IL-1β, and the observed effects were typically more obvious for XFM4 compared with XFM22 or XFM34. Finally, we found that transfection with casp1 or nlrp3 siRNA down-regulated both pro-caspase 1 and NLRP3 proteins and consequently inhibited the cytotoxicity of XFM4. In conclusion, the results from this study suggested that MWCNTs induced pyroptosis in THP-1 macrophages. XFM4 more effectively promoted pyroptosis compared with XFM22 or XFM34, which could provide a basis for rational design of biocompatible MWCNTs.