Imogolite: An Aluminosilicate Nanotube Endowed with Low Cytotoxicity and Genotoxicity

High-Aspect Ratio Nanomaterials (HARN) - typically single-walled (SWCNT) or multi-walled carbon nanotubes (MWCNT) - impair airway barrier function and are toxic to macrophages. Here we assess the biological effects of nanotubes of imogolite (INT), a hydrated alumino-silicate [(OH)3Al2O3SiOH] occurring as single-walled NT, on murine macrophages and human airway epithelial cells. Cell viability was assessed with resazurin. RT-PCR was used to study the expression of Nos2 and Arg1, markers of classical or alternative macrophage activation, respectively, and nitrite concentration in the medium was determined to assess NO production. Epithelial barrier integrity was evaluated from the Trans-Epithelial Electrical Resistance (TEER). Potential genotoxicity of INT was assessed with Comet and Cytokinesis-block Micronucleus Cytome assays. Compared to MWCNT and SWCNT, INT caused much smaller effects on RAW264.7 and MH-S macrophage viability. The incubation of macrophages with INT at doses as high as 120 μg/cm2 for 72h did not alter either Nos2 or Arg1 expression nor increased NO production, while IL6 was induced in RAW264.7 but not in MH-S cells. INT did not show any genotoxic effect in RAW264.7 and A549 except for the decrease of DNA integrity observed in epithelial A549 cells after the treatment with the highest dose (80 μg/cm2). No significant change in permeability was recorded in Calu-3 epithelial cells monolayers exposed to INT, while comparable doses of both SWCNT and MWCNT lowered TEER. Thus, in spite of their fibrous nature, INT appear not markedly toxic for in vitro models of lung-blood barrier cells.