Effects on human bronchial epithelial cells following low-dose chronic exposure to nanomaterials: A 6-month transformation study.

The most plausible exposure route to manufactured nanomaterials (MNM) remains pulmonary inhalation. Yet, few studies have attempted to assess carcinogenic properties in vitro following long-term exposure of human pulmonary cells to low and occupationally relevant doses. The most advanced in vitro tests for carcinogenicity, the cell transformation assay (CTA), rely mostly on rodent cells and short-term exposure. We hypothesized that long-term exposure of human bronchial epithelial cells with a normal phenotype could be a valuable assay for testing carcinogenicity of nanomaterials. Therefore, this study (performed within the framework of the FP7-NANoREG project) assessed carcinogenic potential of chronic exposure (up to 6months) to low doses of multi-walled carbon nanotubes (MWCNT, NM-400 and NM-401) and TiO2 materials (NM62002 and KC7000). In order to harmonize and standardize the experiments, standard operating protocols of MNM dispersion (NANOGENOTOX) were used by three different NANoREG project partners. All nanomaterials showed low cytotoxicity in short-term tests for the tested doses (0.96 and 1.92μg/cm2). During long-term exposure, however, NM-401 clearly affected cell proliferation. In contrast, no cell transformation was observed for NM-401 by any of the partners. NM-400 and NM62002 formed some colonies after 3months. We conclude that agglomerated NM-401 in low doses affect cell proliferation but do not cause cell transformation in the CTA assay used.