Non-functionalized multi-walled carbon nanotubes alter the paracellular permeability of human airway epithelial cells

Little information is available upon the effects of carbon nanotubes (CNT) on the airway barrier. Here we study the barrier function of Calu-3 human airway epithelial cells, grown on permeable filters, after the exposure to commercial single-walled or multi-walled CNT, produced through chemical vapour deposition. To assess changes in the paracellular permeability of CNT-treated Calu-3 monolayers, we have measured the trans-epithelial electrical resistance (TEER) and the permeability to mannitol. Multi-walled CNT caused a large decrease in TEER and an increase in mannitol permeability but no substantial alteration in monolayer viability. Single-walled CNT produced much smaller changes of TEER while CNT, synthesized through the arc discharge method, and Carbon Black nanoparticles had no effect. If commercial multi-walled CNT were added during the formation of the tight monolayer, no further increase in trans-epithelial resistance was observed. Moreover, the same nanomaterials, but neither single-walled counterparts nor Carbon Black, prevented the TEER recovery observed after the discontinuation of interleukin-4, a Th2 cytokine that causes a reversible barrier dysfunction in airway epithelia. These findings suggest that commercial multi-walled CNT interfere with the formation and the maintenance of tight junctional complexes in airway epithelial cells.