Cytotoxicity screening and cytokine profiling of nineteen nanomaterials enables hazard ranking and grouping based on inflammogenic potential

Engineered nanomaterials (ENMs) are being produced for an increasing number of applications. Therefore, it is important to assess and categorize ENMs on the basis of their hazard potential. The immune system is the foremost defence against foreign bodies. Here we performed cytokine profiling of a panel of nineteen representative ENMs procured from the Joint Research Centre (JRC) and commercial sources. Physicochemical characterization was performed using dynamic light scattering. The ENMs were all shown to be endotoxin content free. The human macrophage-differentiated THP.1 cell line was employed for cytotoxicity screening and based on the calculated IC50 values, the multi-walled carbon nanotubes (MWCNTs), ZnO, Ag and SiO2 NMs were found to be the most cytotoxic while single-walled carbon nanotubes (SWCNTs), TiO2, BaSO4 and CeO2 NMs, as well as the nanocellulose materials, were non-cytotoxic (at doses up to 100 mu g/mL). Multiplex profiling of cytokine and chemokine secretion indicated that the TiO2, SiO2, BaSO4, CeO2 and nanocellulose materials induced potent inflammatory responses at sub-cytotoxic doses. Hierarchical clustering of cytokine responses coupled with pathway analysis demonstrated that the panel of ENMs could be segregated into two distinct groups characterized by activation and deactivation, respectively, of PPAR (peroxisome proliferator-activated receptor)/LXR (liver X receptor/retinoid X receptor) nuclear receptor pathways (NRPs). Furthermore, using rosiglitazone, a selective PPAR-gamma agonist, we could show that PPAR-gamma played an important role in the activation of inflammatory responses in cells exposed to TiO2 and SiO2 NMs. These studies show that ENMs of diverse chemical compositions can be grouped according to their inflammatory potential.