Toxicological Effects of Metal Oxide Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 178

(Di Valentin et al. 2009) whereas SiO 2 .amino and SiO 2 .phosphate had no effect
on the expression of Th1 and Th2 cytokines and of eosinophil activation markers
(Marzaioli and Alessandrini, unpublished results).
This study demonstrates that SiO 2 nanoparticles exert an adjuvant effect in an in
vivo model of allergic airway inflammation and that the functionalization of these
particles through PEG does not modulate their adjuvant activity. In contrast, surface
coating of SiO 2 nanoparticles with amino or phosphate groups effectively mitigates
the SiO 2 nanoparticles-induced adjuvant effects in allergic airway inflammation.
8.5 CASE STUDY ON CORRELATIONS OF
in ViVo AND in VitRo DATA
The following section intends to show that it is possible to correlate the gradual
responses from in vitro and in vivo experimentation under certain conditions.
Therefore, experiments with all four surface modifications of identical SiO 2 core NP
(Table 1.2) were carried out on AM (primary cells as well as NR8383 cell line) under
serum-free conditions, as introduced in section 8.3. Furthermore, particles were
used for intratracheal instillation into the rat lung. Interestingly, gradual responses
observed with both approaches were highly similar with respect to the rank order
of inflammatory response or cytotoxicity, provided that the doses used were at or
beyond the threshold for biological effects.
In vitro testing revealed a clear cytotoxic effect of SiO 2 .naked on primary and
cultured AM (release of LDH and glucuronidase) starting at 11.25 µg/ml and being
fully developed upon 45 µg/ml under serum-free conditions. Within the same con-
centration range the effect of SiO 2 .amino on release of LDH or glucuronidase was
less pronounced, followed by SiO 2 .PEG and SiO 2 .phosphate, which had nearly no
effect up to 45 µg/ml. Similarly, we obtained a severe induction of TNFα upon SiO 2 .
naked followed by SiO 2 .amino and SiO 2 .PEG, which was equally noneffective as
was SiO 2 .phosphate. All effects were largely diminished, although not abolished,
when tests were run in the presence of 10% (v/v) fetal calf serum, albumin, or in the
presence of native surfactant preparation (compare section 4.3.4). Under these condi-
tions a precipitation of particles was observed. Together these results suggested that
the cytotoxicity of SiO 2 NP is strongly influenced by their surface chemistry and,
at least in part, seems to be competitively inhibited by the binding of protein to the
particles' surface, as also suggested by others (Panas et al. 2013).
Previous in vivo experiments with amorphous silica carried out by us and others
revealed high inflammatory potential of SiO 2 NP which, however, is transient in
nature (Arts et al. 2007). We, therefore, restricted our in vivo experiments with SiO 2
NP to a short incubation period (3 days after intratracheal instillation) in order to
observe early, albeit fully developed signs of inflammation. The instilled dose was
set 0.36 mg per rat lung as this corresponded to the calculated and also measured
lung burden obtained upon inhalation exposure after a five day exposure to 50 mg/m 3
(see Table 8.5).
We found that, after 3 days, SiO 2 .FITC was nearly exclusively incorporated within
CD68 positive alveolar macrophages. No enrichment of fluorescence such as fluo-
rescent patches or punctuate labeling was found within alveolar septae. Considering