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Engineered amorphous silica nanoparticles (nanosilica) are one of the most abundant nanomaterials and are widely used in industry. Furthermore, novel nanosilica materials are promising theranostic tools for biomedicine. However, hazardous effects of nanosilica especially after inhalation into the lung have been documented. Therefore, the safe development of nanosilica materials urgently requires predictive assays to monitor toxicity. Here, we further investigate the impact of the protein corona on the biological activity of two different types of nanosilica (colloidal and pyrogenic) in lung cells. As previously described, adsorption of serum proteins to the nanosilica surface suppresses cytotoxicity in macrophages and lung epithelial cells. As the increase of pro-inflammatory mediators is a hallmark of inflammation in the lung upon nanosilica exposure, we studied the potential coupling of the cytotoxic and pro-inflammatory response in A549 human lung epithelial cells and RAW264.7 mouse macrophages. Indeed, cytotoxicity precedes the onset of pro-inflammatory gene expression and cytokine release as exemplified for IL-8 in A549 cells and TNF-alpha in RAW264.7 macrophages after exposure to 0-100 µg/mL nanosilica in medium without serum. Formation of a protein corona not only inhibited cellular toxicity, but also the pro-inflammatory response. Of note, uptake of nanosilica into cells was negligible in the absence, but enhanced in the presence of a protein corona. Hence, the prevailing explanation that the protein corona simply interferes with cellular uptake thus preventing adverse effects needs to be revisited. In conclusion, for the reliable prediction of adverse effects of nanosilica in the lung, in vitro assays should be performed in media not complemented with complete serum. However, in case of different exposure routes, e.g., injection into the blood stream as intended for biomedicine, the protein corona prevents acute toxic actions of nanosilica.

Manufactured nanomaterials (MNMs) selected from a library of over 120 different MNMs with varied compositions, sizes, and surface coatings were tested by four different laboratories for toxicity by high-throughput/-content (HT/C) techniques. The selected particles comprise 14 MNMs composed of CeO2, Ag, TiO2, ZnO and SiO2 with different coatings and surface characteristics at varying concentrations. The MNMs were tested in different mammalian cell lines at concentrations between 0.5 and 250 µg/mL to link physical–chemical properties to multiple adverse effects. The cell lines are derived from relevant organs such as liver, lung, colon and the immune system. Endpoints such as viable cell count, cell membrane permeability, apoptotic cell death, mitochondrial membrane potential, lysosomal acidification and steatosis have been studied. Soluble MNMs, Ag and ZnO, were toxic in all cell types. TiO2 and SiO2 MNMs also triggered toxicity in some, but not all, cell types and the cell type-specific effects were influenced by the specific coating and surface modification. CeO2 MNMs were nearly ineffective in our test systems. Differentiated liver cells appear to be most sensitive to MNMs, Whereas most of the investigated MNMs showed no acute toxicity, it became clear that some show adverse effects dependent on the assay and cell line. Hence, it is advised that future nanosafety studies utilise a multi-parametric approach such as HT/C screening to avoid missing signs of toxicity. Furthermore, some of the cell type-specific effects should be followed up in more detail and might also provide an incentive to address potential adverse effects in vivo in the relevant organ.

Although the technological and economic benefits of engineered nanomaterials are obvious, concerns have been raised about adverse effects if such material is inhaled, ingested, applied to the skin or even released into the environment. Here we studied the cytotoxic effects of the most abundant nanomaterial, silica nanoparticles (SiO2-NPs), in murine RAW264.7 macrophages. SiO2-NPs dose-dependently induce membrane leakage and cell death without obvious involvement of reactive oxygen species. Interestingly, at low concentrations SiO2-NPs trigger autophagy, evidenced by morphological and biochemical hallmarks such as autophagolysosomes or increased levels of LC3-II, which serves to protect cells from cytotoxicity. Hence SiO2-NPs initiate an adaptive stress response which dependent on dose serve to balance survival and death and ultimately dictates the cellular fate.

Engineered amorphous silica nanoparticles (nanosilica) are widely used in industry yet can induce adverse effects, which might be classified according to the oxidative stress model. However, the underlying mechanisms as well as the potential interactions of the three postulated different tiers of toxicity—i.e. oxidative-, pro-inflammatory- and cytotoxic-stress response—are poorly understood. As macrophages are primary targets of nanoparticles, we used several macrophage models, primarily murine RAW264.7 macrophages, and monitored pro-inflammatory and anti-oxidative reactions as well as cytotoxicity in response to nanosilica at max. 50 µg/mL. Special attention was given to the activation of mitogen-activated protein kinases (MAPKs) as potential regulators of the cellular stress response. Indeed, according to the oxidative stress model, also nanosilica elicits an, albeit modest, anti-oxidative response as well as pronounced pro-inflammatory reactions and cytotoxicity in macrophages. Interestingly however, these three tiers of toxicity seem to operate separately of each other for nanosilica. Specifically, impeding the anti-oxidative response by scavenging of reactive oxygen species does not prevent the pro-inflammatory and cytotoxic response. Furthermore, blocking the pro-inflammatory response by inhibition of MAPKs does not impair cell death. As hazard assessment has been guided by the prevailing assumption of a dose-dependent coupling of sequential tiers of toxicity, identification of critical physico-chemical parameters to assist the safe-by-design concept should be enabled by simply monitoring one of the toxicity read-outs. Our results indicate a more complex scenario in the case of nanosilica, which triggers independent pleiotropic effects possibly also related to different material properties and primary cellular targets.

Background Acute exposure to elevated levels of environmental particulate matter (PM) is associated with increasing morbidity and mortality rates. These adverse health effects, e.g. culminating in respiratory and cardiovascular diseases, have been demonstrated by a multitude of epidemiological studies. However, the underlying mechanisms relevant for toxicity are not completely understood. Especially the role of particle-induced reactive oxygen species (ROS), oxidative stress and inflammatory responses is of particular interest. In this in vitro study we examined the influence of particle-generated ROS on signalling pathways leading to activation of the arachidonic acid (AA) cascade. Incinerator fly ash particles (MAF02) were used as a model for real-life combustion-derived particulate matter. As macrophages, besides epithelial cells, are the major targets of particle actions in the lung murine RAW264.7 macrophages and primary human macrophages were investigated. Results The interaction of fly ash particles with macrophages induced both the generation of ROS and as part of the cellular inflammatory responses a dose- and time-dependent increase of free AA, prostaglandin E2/thromboxane B2 (PGE2/TXB2), and 8-isoprostane, a non-enzymatically formed oxidation product of AA. Additionally, increased phosphorylation of the mitogen-activated protein kinases (MAPK) JNK1/2, p38 and ERK1/2 was observed, the latter of which was shown to be involved in MAF02-generated AA mobilization and phosphorylation of the cytosolic phospolipase A2. Using specific inhibitors for the different phospolipase A2 isoforms the MAF02-induced AA liberation was shown to be dependent on the cytosolic phospholipase A2, but not on the secretory and calcium-independent phospholipase A2. The initiation of the AA pathway due to MAF02 particle exposure was demonstrated to depend on the formation of ROS since the presence of the antioxidant N-acetyl-cysteine (NAC) prevented the MAF02-mediated enhancement of free AA, the subsequent conversion to PGE2/TXB2 via the induction of COX-2 and the ERK1/2 and JNK1/2 phosphorylation. Finally we showed that the particle-induced formation of ROS, liberation of AA and PGE2/TXB2 together with the phosphorylation of ERK1/2 and JNK1/2 proteins was decreased after pre-treatment of macrophages with the metal chelator deferoxamine mesylate (DFO). Conclusions These results indicate that one of the primary mechanism initiating inflammatory processes by incinerator fly ash particles seems to be the metal-mediated generation of ROS, which triggers via the MAPK cascade the activation of AA signalling pathway.