LSC 2013 abstract - Apoptotic, inflammatory and fibrogenic effects of two different types of multi-walled carbon nanotubes in mouse lung

There is increasing concern about the toxicity of inhaled multi walled carbon nanotubes (MW-CNT). Pulmonary macrophages represent the primary cell type involved in the clearance of inhaled particulates and induction of apoptosis in these cells has been considered to contribute to fibrosis development. We have investigated the apoptotic, pro-inflammatory and fibrotic potential of two samples of MW-CNT, characterized by a contrasting average tube length and entanglement/agglomeration. The damaging effects of two MW-CNTs with different properties (average length of respectively 13 and 5 µm and diameter of 40-100 or 30 nm) have been investigated in vivo via pharyngeal aspiration in C57Bl6/J mice and in vitro in RAW 264.7 macrophage-like murine cells. Main endpoints included toxicity, apoptosis, production of reactive oxygen species (ROS) and cytokines, gene expression and Masson9s Trichrome staining. Both nanotubes caused granuloma and apoptosis in the mouse lungs. However, the long sample induced a more pronounced inflammatory and pro-fibrotic response as indicated by increased collagen deposition, mRNA expression of matrix metalloproteinase-8 and serum level of monocyte chemotactic protein-1. Interestingly, apoptosis was merely localized in the granulomatous foci. In vitro , neither of the samples induced apoptosis whereas both nanotube types triggered ROS formation and only the longer sample induced toxicity. Our study reveals that the inflammatory, apoptotic and fibrogenic effects of MW-CNT in mouse lung can vary considerably depending on their composition. The in vitro analysis of macrophage apoptosis appears to be a poor predictor of their pulmonary hazard.