A secretomics analysis reveals major differences in the macrophage responses towards different types of carbon nanotubes.

Certain types of carbon nanotubes (CNT) can evoke inflammation, fibrosis and mesothelioma in vivo, raising concerns about their potential health effects. It has been recently postulated that NLRP3 inflammasome activation is important in the CNT-induced toxicity. However, more comprehensive studies of the protein secretion induced by CNT can provide new information about their possible pathogenic mechanisms. Here, we studied protein secretion from human macrophages with a proteomic approach in an unbiased way. Human monocyte-derived macrophages (MDM) were exposed to tangled or rigid, long multi-walled CNT (MWCNT) or crocidolite asbestos for 6 h. The growth media was concentrated and secreted proteins were analyzed using 2D-DIGE and DeCyder software. Subsequently, significantly up- or down-regulated protein spots were in-gel digested and identified with an LC-MS/MS approach. Bioinformatics analysis was performed to reveal the different patterns of protein secretion induced by these materials. The results show that both long rigid MWCNT and asbestos elicited ample and highly similar protein secretion. In contrast, exposure to long tangled MWCNT induced weaker protein secretion with a more distinct profile. Secretion of lysosomal proteins followed the exposure to all materials, suggesting lysosomal damage. However, only long rigid MWCNT was associated with apoptosis. This analysis suggests that the CNT toxicity in human MDM is mediated via vigorous secretion of inflammation-related proteins and apoptosis. This study provides new insights into the mechanisms of toxicity of high aspect ratio nanomaterials and indicates that not all types of CNT are as hazardous as asbestos fibers.