Profibrotic Activity of Multiwalled Carbon Nanotubes Upon Prolonged Exposures in Different Human Lung Cell Types

Abstract

Introduction: The expanding use of multiwalled carbon nanotubes (MWCNTs) in various consumer and industrial products has raised concerns regarding the potential health risks following the inhalation of this nanomaterial. Recent studies indicate that MWCNT exposure can cause deleterious lung effects. Pulmonary fibrosis is one of the diseases associated with the inhalation of classical fiber-shaped materials (e.g., asbestos), and recently MWCNTs. Materials and Methods: Herein, the presented work investigated early signs of fibrosis in key human lung cell types implicated directly (fibroblasts) or indirectly (alveolar epithelial cells and macrophages) in the pathogenesis of lung fibrosis, upon acute (24 hours) and prolonged (96 hours) exposure to different concentrations (5-20 μg/mL) of long, rigid Mitsui-7 MWCNTs. These results were compared to those inflicted upon the same cell types following exposure to tangled nanofibers, that is, Nanocyl-7000, and a positive particle control, crystalline quartz (i.e., Min-U-Sil). Results: Mitsui-7 interacted with all cell types tested, in particular, single nanotubes were readily internalized by each cell type. Exposure to Mitsui-7 resulted in a proinflammatory response in macrophages at 24 hours (interleukin-1β release). However, only prolonged Mitsui-7 exposure induced a significant release of profibrotic mediators (transforming growth factor-β, platelet derived-growth factor, and osteopontin) in all tested cell cultures and concentrations, highlighting the importance of prolonged exposure studies in nanosafety assessment. This elevated release of profibrotic markers was not accompanied by an increased collagen production or cell proliferation in fibroblasts in the tested time frame. Conclusion: Overall, prolonged exposure to human-relevant CNT concentrations appears to be a highly suitable approach to predict profibrotic response in vitro.