Helical Carbon Nanotubes Alter F-Actin and ARP2 Distribution in Macrophages and Inhibit Pseudomonas aeruginosa Phagocytosis in an Intracellular Accumulation-Dependent Manner

The similarity of carbon nanotubes (CNTs) to the shape and size of asbestos fibers has raised concern over their potential pulmonary toxicity in occupational and environmental settings. Studies have demonstrated pulmonary toxicity associated with exposure to CNTs, including modulation of the pulmonary immune system and impaired phagocytosis. However, mechanisms underlying this inhibition have not been fully elucidated. In this study, intracellular accumulation of helical CNTs (HCNTs) and inhibition of Pseudomonas aeruginosa internalization were measured in RAW 264.7 and alveolar macrophages. Distribution and co-localization of F-actin and actin-related-protein 2 (Arp2) - key proteins in the formation of phagosomes —by HCNTs, were examined using fluorescent microscopy, and inhibition of F-actin polymerization was quantified. Our results indicated that inhibition of P. aeruginosa internalization by RAW 264.7 and alveolar macrophages was directly related to the amount of intracellular accumulation of HCNTs. Additionally; HCNTs inhibited F-actin polymerization in vitro, and disrupted normal F-actin and Arp2 distribution in RAW 264.7 macrophages. Disruption of F-actin polymerization, and F-actin and Arp2 distribution, may explain how HCNTs interfere with the phagocytosis of pathogens by macrophages. This information can also contribute to evaluating the health risk of individuals exposed to potentially high levels of CNTs.