Toxicological Effects of Metal Oxide Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 172

For nanoGEM in vivo experiments based on intratracheal instillation, ZrO 2
nanoparticles had to be suspended in such a way that (a) a coarse agglomeration is
avoided and (b) the suspension does not interfere with the physiologic requirements
of the lung. In the case of acid- or alkaline-stabilized ZrO 2 nanoparticle suspen-
sions, a protein precoating with rat serum (Bihari et al. 2008) followed by a transfer
to bicarbonate buffer was used to prevent agglomeration. This type of coating and
buffering allowed two investigated surface modifications of ZrO 2 nanoparticles. The
bioactivity of ZrO 2 .acryl was tested in vivo and compared to ZrO 2 .TODS, which was
the least active modification in vitro . However, to circumvent agglomeration prior
to intratracheal instillation, ZrO 2 .acryl and ZrO 2 .TODS had to be coated with rat
serum. Unbound proteins were removed and particle fractions were applied to rat
lungs in three doses (0.6, 1.2, and 2.4 mg/lung). Effects were studied in bronchoal-
veolar fluid (BALF) and also histologically after 3 and 21 days. The distribution of
fluorescence labeled ZrO 2 .Acryl and ZrO 2 .TODS was carried out in parallel and
revealed a progressive uptake into AM (nanoGEM, not shown). Effects on BALF
parameters (cell count, increase in PMN) commenced at 0.6-1.2 mg/lung; this dose
range properly reflects the LOAEL observed in vitro if the LOAEL (30 pg/cell) is
multiplied by the macrophage number per lung (2 × 10 7 ). However, slight differ-
ences seen between ZrO 2 .acryl and ZrO 2 .TODS in vitro were largely absent in vivo
(Wiemann and Venneman, unpublished results from nanoGEM). Although further
research, for example, on oxidative damage is needed, it may be speculated that this
may be due to the precoating with proteins. In addition, nanoparticle surfaces could
be further changed upon contact with the lung lining fluid. Based on these results
obtained for modified ZrO 2 -NP it can be stated that the influence of surface modi-
fications is obvious in highly loaded AM in vitro , but may be blunted under in vivo
conditions.
8.4.2 B iologiCal a Ctivity of m etal o xide n anoPartiCles
in r at l ungs after i inhalation
In rat lung inhalation studies, ZnO, TiO 2 , CeO 2 , ZrO 2 , and SiO 2 nanoparticles of
similar size and shape differed largely in their toxicity (Landsiedel et al. 2010). ZnO
and CeO 2 nanoparticles were found to be most toxic whereas SiO 2 and ZrO 2 did not
show any adverse effect at the highest tested aerosol concentration of 10 mg/m 3 ,
which was higher than the general thresholds for fine dusts (Landsiedel et al. 2010).
Based on the level of no adverse effects in inhalation, decreasing effects were found
in the following order: CeO 2 > ZnO > TiO 2 > SiO 2 , ZrO 2 (Landsiedel et al. 2010).
Similar to the results from the in vitro studies mentioned earlier, the chemical com-
position influenced the toxicity and not—or not exclusively—the size or shape of
the material. Moreover, a contribution of solubility to nanomaterial toxicity that has
been found in vitro for ZnO (Buerki-Thurnherr et al. 2013; Xia et al. 2011; Kao et al.
2012) has also been suggested in studies based on intratracheal instillation (Cho et al.
2011) and in rat inhalation studies (Landsiedel et al. 2010). In rat lungs, ZnO induced
a concentration-related inflammation reaction in addition to necrosis, which was
detected in the lung and the nose. At least the observed necrosis could be attributed
to soluble zinc ions released from the ZnO nanoparticles (Landsiedel et al. 2010).