Toxicological Effects of Metal Oxide Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 171

or with a polyethylene glycol (PEG) (ZrO 2 .PEG) (compare properties in Table 1.2).
All types of ZrO 2 nanoparticles agglomerated under serum-free cell culture condi-
tions. This led to a complete gravitational settling of fine grains, which were vis-
ible by phase contrast microscopy (compare Chapter 7). Particles were quantitatively
ingested by AM, and nearly no nanoparticle remained dispersed in the supernatant.
Consequently, a mean dose in picograms per macrophage could be calculated. The
cytotoxic effects of all ZrO 2 nanoparticles, measured as release of LDH, were largely
similar, and started upon a dose of approximately 30 pg/cell (corresponding to 45
µg/ml), comparable to the lowest observed adverse effect level of TiO 2 NM105, but
nearly an order of magnitude above ZnO NM110. Minor differences were observed
among modifications, with ZrO 2 .acryl being the most bioactive particle: ZrO 2 .
acryl led to a release of TNFα and glucuronidase and extracellular H 2 O 2 formation
(Wiemann and Vennemann, unpublished results from the nanoGEM study).
8.4 EFFECTS OF METAL OXIDE NANOPARTICLES IN ANIMALS
Compared to the in vitro assessment of nanoparticle toxicity, in vivo investigations
are highly expensive and most often require the sacrifice of animals. In vivo studies
are the gold standard of toxicity testing, however, there is only a limited number of
studies available that evaluate the effects of metal oxide nanoparticles in vivo . In vivo
studies generally focus on a single route of exposure and by far the greatest num-
ber of available studies concentrate on the pulmonary exposure of nanomaterials.
Consequently, this chapter will focus on intratracheal instillation and rat lung inha-
lation studies using metal oxide nanoparticles. End points of toxicity for pulmonary
exposure range from oxidative stress, cell proliferation to markers of inflammation
and histopathology of the lung.
8.4.1 B iologiCal a Ctivity of m etal o xide n anoPartiCles
in r at l ungs after i ntratraCheal i instillation
Based on intratracheal instillation studies and literature review, it was concluded
that, in general, “ultrafine particles” are more inflammogenic in the rat lung than
fine, respirable particles made from the same material, which is driven by their
surface area (Donaldson et al. 2008). Recently, Sun et al. found intratracheally
(i.t.) instilled TiO 2 nanoparticles of 5-6 nm to elicit pulmonary inflammation via
induction of inflammatory cytokines (Sun et al. 2012). Likewise, intratracheal
instillation of anatase TiO 2 nanoparticles for 24 h led to pulmonary inflammation
(Saber et al. 2012). Since DNA damage (detected by the comet assay) could not
be observed in this study, the authors suggested that inflammation is not linked to
DNA damage when using TiO 2 nanoparticles. Similar results were observed in a
recent instillation study with 5 nm anatase TiO 2 nanoparticles, which were found
not to be genotoxic as detected by the comet assay (Naya et al. 2012). However, an
early report demonstrated in vivo genotoxicity of TiO 2 nanoparticles. After intra-
tracheal instillation of 18 nm anatase TiO 2 nanoparticles in rats, hypoxanthine
phosphoribosyltransferase (HPRT) mutation frequency was increased in alveolar
type II cells (Driscoll et al. 1997).