Toxicological Effects of Metal Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 196

to be very suitable to analyze the oxidative stress potential of nanomaterials (see
Chapter 8). Here, we applied this assay to assess the oxidative stress potential of
nanoGEM nanomaterials in NRK-52E cells and figured out that 8 out of 16 nano-
GEM nanoparticles did induce protein carbonyls. The strongest effects within the
silver group were detected for Ag50.PVP. Basically, both 50 nm variants of silver
nanoparticles were positive (Ag50.PVP and Ag50.Citrate) but Ag50.Citrate showed
much less pronounced effects compared to Ag50.PVP. Ag200.PVP was not positive
and did not induce protein carbonyls.
In summary, a more articulated cytotoxic effect was observed for Ag50.EO com-
pared to the surface modified Ag50.Citrate, and severe adverse effects of Ag50.PVP,
which were less pronounced or not measurable during the exposure of the larger
A g 2 0 0 . P V P.
To conclude, the biological activity of the nanoGEM Ag materials was size and
surface dependent.
9.2.2 g enotoxiCity
Genotoxicity of silver nanoparticles has been analyzed in vitro (Kim et al. 2011a;
AshaRani et al. 2009; Ahamed et al. 2008) and in vivo (Kim et al. 2008; Kim
et al. 2011b; Tiwari, Jin, and Behari 2011). Kim and coworkers analyzed cyto- and
genotoxicity of silver nanoparticles in L5178Y and BEAS-2B cells using comet
assay and a gene mutation assay (thymidine kinase) (Kim et al. 2011) and found a
positive result in comet but a negative result in the gene mutation assay. AshaRani
and coworkers used silver nanoparticles (6-20 nm, starch coated) and assessed the
effects in lung fibroblasts (IMR-90) and human glioblastoma cells (U251) for up
to 72 h and found a dose-dependent genotoxicity for nanosilver in both the comet
and the micronucleus assay (AshaRani et al. 2009). In another study, 25 nm poly-
saccharide capped and uncapped silver were analyzed and an increased protein
phosphorylation of p53, Rad51, and H2AX, all of which are related to DNA damage
or repair of DNA double strand breaks, was observed, with stronger effects being
caused by the uncapped silver (Ahamed et al. 2008). These results indicate a posi-
tive genotoxic effect in vitro . In two in vivo rat studies genotoxicity of nanosilver
was assessed after 28 days of oral administration (Kim et al. 2008) or 90 days
of inhalation (Kim et al. 2011) and no genotoxic effect could be detected with in
vivo micronucleus assay in the bone marrow according to the OECD guideline 474.
Other tissues (e.g., lungs) have not been assessed. Another in vivo study was per-
formed by Tiwari et al. with repeated intravenous injection in rats (Tiwari, Jin, and
Behari 2011). Here, genotoxic effects of silver nanoparticles (15-40 nm) via an
alkaline comet assay were detectable. Thus, for nanosilver the genotoxicity in vitro
and in vivo seems to be dependent on many aspects such as specific particle char-
acteristics (size, coating), the assays that have been used, or the addressed tissues or
target cells which were analyzed.
In contrast to nanosilver, most of the gold nanomaterials tested so far do not
seem to induce oxidative stress in human cells and therefore only a few reports on
the potential genotoxicity of these particles can be found in the literature. Li et al.
demonstrated that 20 nm colloidal gold nanoparticles could induce oxidative DNA