Toxicological Effects of Metal Oxide Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 169

in either the MN assay or the Ames test. However, two of the SiO 2 nanoparticles
tested (SiO 2 .naked and SiO 2 .phosphate) displayed genotoxic effects when using the
comet assay (Table 8.3). The Comet assay has previously been performed with SiO 2
nanoparticles of different sizes (30 nm, 80 nm, and 400 nm), but failed to reveal
genotoxic effects in 3T3-L1 fibroblasts (Barnes et al. 2008). Using another SiO 2
nanomaterial, Wang et al. reported opposing results. Their study identified geno-
toxicity of SiO 2 nanomaterials in the MN but not the Comet assay (Wang, Wang,
and Sanderson 2007). Recent results from Downs et al. highlighted the mechanisms
of SiO 2 -induced genotoxicity. They found no effect of these particles in in vitro
MN assays, but demonstrated in parallel in vivo studies a secondary, inflammatory
response-dependent genotoxicity of SiO 2 (Downs et al. 2012).
8.2.4 g ene e xPression P rofiles
DNA microarray analyses revealed the gene expression profiles of human keratino-
cyte HaCaT cells that were exposed in the dark to anatase TiO 2 nanoparticles of dif-
ferent (7 nm, 20 nm, and 200 nm) average sizes (Fujita et al. 2009). The data suggest
that TiO 2 nanoparticles, in the absence of illumination, have no significant impact on
ROS-associated oxidative damage. However, these particles seem to affect the cell-
matrix adhesion and thus extracellular matrix remodeling of keratinocytes. In addi-
tion, mouse cDNA microarrays revealed that TiO 2 nanoparticles induced differential
gene expression of hundreds of genes including activation of pathways involved in
cell cycle control, apoptosis, chemokine, and complement cascades. In vivo it was
found that TiO 2 nanoparticles can induce severe lung emphysema, which may be
triggered via activation of placental growth factor and related inflammatory path-
ways (Chen et al. 2006). Studies assessing the toxic effects of P25 TiO 2 and CeO 2
nanoparticles of different sizes (15, 25, 30, and 45 nm) in bronchial epithelial cells
(BEAS-2B) revealed that both particle types induced oxidative stress-related gene
expression whereas inflammation-related genes were only induced by TiO 2 nanopar-
ticles (Park et al. 2008a; Park et al. 2008b). This again suggests that the chemical
composition of the particles decisively influences their inherent toxicity.
8.2.5 i inflammatory r esPonse
For evaluating immunotoxic effects induced by nanomaterials, the production of
inflammatory markers such as the chemokines, interleukin8 (IL-8), TNF-α, or IL-6
are usually measured in cell culture supernatants using the enzyme-linked immu-
nosorbent assay (ELISA). TiO 2 nanoparticles (P25) but not fine TiO 2 particles were
found to trigger Il-8 release in A549 cells indicating a size -dependent effect of
immunotoxicity. Since the P25 TiO 2 nanoparticles remained highly aggregated in
cell culture as well as inside the cells, inflammatory properties of TiO 2 particles
appear to be driven by their specific surface area (Singh et al. 2007). In a compre-
hensive study aimed to determine the importance of surface area and surface reac-
tivity of particles to induce inflammatory responses, Duffin et al. used a variety of
manufactured particles, such as TiO 2 , CB, and metal nanoparticles (Ni and Co), both
for instillation and for treatment of A549 cells. They observed a correlation between