Human Asthmatic Bronchial Cells Are More Susceptible to Subchronic Repeated Exposures of Aerosolized Carbon Nanotubes At Occupationally Relevant Doses Than Healthy Cells

Although acute pulmonary toxicity of carbon nanotubes (CNTs) has been extensively investigated, the knowledge of potential health effects following chronic occupational exposure.is currently limited and based only upon in vivo approaches. Our aim was to realistically mimic subchronic inhalation of multiwalled CNTs (MWCNTs) in vitro, using the air liquid interface cell exposure (ALICE) system for aerosol exposures on reconstituted human bronchial tissue from healthy and asthmatic donors. The reliability and sensitivity of the system were validated using crystalline quartz (DQ12), which elicited an increased (pro-)inflammatory response, as reported in vivo. At the administrated MWCNT doses relevant to human occupational lifetime exposure (10 mu g/cm(2) for 5 weeks of repeated exposures/5 days per week) elevated cilia beating frequency (in both epithelial cultures), and mucociliary clearance (in asthmatic cells only) occurred, whereas no cytotoxic reactions or morphological changes were observed. However, chronic MWCNT exposure did induce an evident (pro-)inflammatory and oxidative stress response in both healthy and asthmatic cells. The latter revealed stronger and more durable long-term effects compared to healthy cells, indicating that individuals with asthma may be more susceptible to adverse effects from chronic MWCNT exposure. Our results highlight the power of occupationally relevant subchronic exposures on human in vitro models in nanosafety hazard assessment.