Single-walled carbon nanotubes and graphene oxides induce autophagosome accumulation and lysosome impairment in primarily cultured murine peritoneal macrophages

• Two carbon nanomaterials were used to study the cytotoxicity in macrophages.
• Both carbon nanomaterials induced autophagosome accumulation.
• Both carbon nanomaterials blocked autophagy flux.
• Carbon nanomaterials accumulated in lysosomes and caused lysosome destabilization.
• Graphene oxides were more potent than carbon nanotubes in inducing cell responses.

The wide application of carbon nanomaterials in various fields urges in-depth understanding of the toxic effects and underlying mechanisms of these materials on biological systems. Cell autophagy was recently recognized as an important lysosome-based pathway of cell death, and autophagosome accumulation has been found to be associated with the exposure of various nanoparticles, but the underlying mechanisms are still uncertain due to the fact that autophagosome accumulation can result from autophagy induction and/or autophagy blockade. In this study, we first evaluated the toxicity of acid-functionalized single-walled carbon nanotubes and graphene oxides, and found that both carbon nanomaterials induced adverse effects in murine peritoneal macrophages, and GOs were more potent than AF-SWCNTs. Both carbon nanomaterials induced autophagosome accumulation and the conversion of LC3-I to LC3-II. However, degradation of the autophagic substrate p62 protein was also inhibited by both nanomaterials. Further analyses on lysosomes revealed that both carbon nanomaterials accumulated in macrophage lysosomes, leading to lysosome membrane destabilization, which indicates reduced autophagic degradation. The effects of AF-SWCNTs and GOs on cell autophagy revealed by this study may shed light on the potential toxic mechanism and suggest caution on their utilization.