The MicroSprayer delivers more aerosolized nanoparticles to the cells than the VITROCELL/PARI BOY system, which is important for cytotoxicity testing. On the other hand application with the MicroSprayer might damage cells by generation of shear stress because high flow rates are needed for effective particle deposition. Decreases in cell viability due to impaction of aerosols have been shown by Mühlhopt et al. Selleck SRT1720 (Mülhopt et al., 2007). Although adverse effects on cells cannot be excluded this

study do not provide any indication for cell damage by using the MicroSprayer. Both aerosol generating systems were assessed with respect to cytotoxicity testing. This assessment is an important first step in the toxicological assessment of compounds. Routine cytotoxicity testing, the exposure by addition of the test compounds to the medium above cells seeded in plastic wells (submersed culture), is not physiological for respiratory cells. It may lead to a sub-estimation of their cytotoxicity because a direct contact of the nanoparticles with the plasma membrane is not likely. Therefore, cells cultured in

ALI and exposed to aerosols are recommended for physiologically relevant in vitro testing. This recommendation is supported by data showing the higher induction of the anti-oxidative enzyme HO-1 Selleckchem Cabozantinib in A549 upon exposure to ZnO nanoparticles in ALI than in submersed culture (Lenz et al., 2009). The higher cytotoxicity of aerosolized polystyrene nanoparticles reported in this study also suggests a stronger effect upon aerosol application. It may be suspected

that for nanoparticles with a greater tendency for aggregation, Org 27569 like CNTs, the exposure condition (aerosol or suspension) has a much smaller influence on the cytotoxicity. For cytotoxicity testing, where high concentrations have to be tested to determine safety margins, the use of the MicroSprayer appears indicated because much higher doses than with the VITROCELL/PARI BOY system can be applied and the application itself did not cause adverse effects on cells. These data together with data from other groups (Fiegel et al., 2003, Knebel et al., 2001 and Savi et al., 2008) show that higher aerosol delivery rates can only be obtained by a less physiological application mode. To assess the efficacy of aerosolized nanoparticles at therapeutic doses the VITROCELL/PARI BOY system appears better because it mimics better the low flow velocities in the alveoli. Providing every compartment with one nebulizer could decrease the differences in the deposition rates between the compartments. This work was financed by the Austrian Research Science Grant P22576-B18. The Federal Ministry Transport, Innovation and Technology provided student grants for this work. The authors thank Dr. S. Mautner for help with the manuscript. “
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