Toxicological Effects of Metal Oxide Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 166

In the nanoGEM project, exposure of cultured cells to ZnO nanoparticles was
shown to adversely affect cell viability to a substantial extent. Cytotoxicity caused
by 32 μg/mL ZnO is in the range of 25% to 95%, depending on the specific cell lines
tested. None of the SiO 2 and ZrO 2 nanoparticles from the nanoGEM project (applied
at concentrations between 0.32 μg/mL and 32 μg/mL) induced an increase in LDH
release in any of the cell lines tested, at least in the presence of serum proteins. By
contrast, ZnO nanoparticles have been shown to almost completely reduce viability
of all cell lines tested in WST-8 assays. Only A549 cells displayed a slightly weaker
reactivity toward ZnO nanoparticles with an inhibition of proliferation of 70% to
80%. SiO 2 .naked nanoparticles were found to affect proliferation of RAW264.7 mac-
rophage-like cells. Conversely, none of the surface-modified SiO 2 particles (SiO 2 .
PEG, SiO 2 .amino, or SiO 2 .phosphate) were found to affect proliferation of this cell
type. When applied at 32 μg/mL, SiO 2 .naked nanoparticles significantly reduced the
total metabolic activity of the macrophage cell culture, and microscopic inspection
confirmed a reduction in cell numbers. Surface modification of the SiO 2 nanopar-
ticles (as shown for the listed nanoGEM materials SiO 2 .PEG, SiO 2 .amino, or SiO 2 .
phosphate) could be demonstrated to clearly influence their cytotoxicity. The find-
ing that fluorescently labeled SiO 2 nanoparticles with unmodified surface (SiO 2 .
FITC) also affected the proliferation of RAW264.7 cells (measured via WST8 assay)
further supported these results. Similarly, when using the WST-8 assay, a cell type
specific effect for ZrO 2 .amino nanoparticles could be observed. After addition of
32 μg/mL of these nanoparticles to a growing culture of RLE-6TN lung epithelium-
like cells, reduced cell proliferation became obvious. Yet, all other tested cell lines
(see Table 8.1) were not affected. Moreover, at concentrations of up to 32 μg/mL no
other types of ZrO 2 nanoparticles (ZrO 2 .acryl, ZrO 2 .PEG, and ZrO 2 .TODS) could
impair the proliferation of the cell lines tested (Ossig and Schnekenburger, unpub-
lished results from nanoGEM).
These data verify that specific surface modifications of nanomaterials can modu-
late their cytotoxic activity and that selected cell types may be uniquely sensitive for
such adverse effects.
8.2.3 g enotoxiCity
For any comprehensive evaluation of genotoxicity and the mutagenic potential of a
substance, information is required on its capability to induce gene mutations, struc-
tural (clastogenicity) and numerical (aneugenicity) chromosome aberrations. Recent
studies demonstrate that nanomaterials do not reveal a new quality of genotoxicity,
but rather display effects well known from other genotoxins, for example, gene muta-
tions, clastogenic or aneugenic effects, either through direct or indirect mechanisms
(Pfuhler et al. 2013; Oesch and Landsiedel 2012). An overview on genotoxicity stud-
ies with engineered nanoparticles is provided by Magdolenova et al. (2013).
Test methods preferred for the application in Regulatory Toxicology are officially
adopted through OECD testing guidelines (TG). The Ames test (OECD TG471
“Bacterial Reverse Mutation Test” Adopted 21 July, 1997) is commonly used to
detect substances, which cause two classes of gene mutations, base pair substitution
and small frame shifts. However, it has been questioned several times whether the