Toxicological Effects of Metal Oxide Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 179

the fact that also SiO 2 .FITC particles were fairly well suspended and truly nanosized
during application, this finding highlights the role of AM for clearing the lung from
nanoparticulate matter. The degree of inflammation caused by the SiO 2 particles
displayed a clear rank order of biologic activity (SiO 2 .naked > SiO 2 .amino > SiO 2 .
PEG > SiO 2 .phosphate), which was reflected by the concentration of total protein in
the BALF, the total number of lavageable cells, and by the percentage of neutrophilic
granulocytes (Wiemann and Vennemann, unpublished results from the nanoGEM
study). The obvious similarity between these in vivo findings and the in vitro experi-
ments with AM led us to calculate various correlations between both types of experi-
ments. In fact, we found positive correlation between the amount of bioactive TNFα
released in vitro by AM (NR8383) and the occurrence of PMN or protein in BALF
(Figure 8.1). Similarly, there was a correlation between the in vitro release of LDH
or glucuronidase and the in vivo parameters describing inflammation.
These results are not in contrast to other findings obtained in nanoGEM for the
same types of particles, although most types of SiO 2 NP showed no overt effect on
various cell lines. This is because experiments described earlier were conducted
at lower concentration and in the presence of serum, which lowers toxicity. With
respect to the discrepancies between the results from the instillation and inhalation
studies on SiO 2 NP (see Table 8.5) one should consider that the dose rate during
inhalation is far lower compared to that of the bolus application during instillation.
Binding of SiO 2 NP to lung proteins and/or surfactant components, in situ agglom-
eration, and ongoing clearance by AM most likely counteract the effects of accumu-
lating particles, such that an inhaled lung burden of SiO 2 particles ranging between
343 µg/lung and 836 µg/lung may cause no, or, in the case of SiO 2 .naked and SiO 2 .
amino, minor effects (see Table 8.5).
Considering the previously outlined results, one major conclusion from the nano-
GEM experiments on SiO2 NP is that the comparison between in vitro macrophage
responses and the in vivo response upon intratracheal instillation is a versatile tool

2

30
25
20

1

15
10

5
0

R 2 = 0.9011 R 2 = 0.9466

0

0 2
TNF formation in vitro (fold control)

4 6 0 2

TNF formation in vitro (fold control)

4 6

FIGURE 8.1 In vitro - in vivo correlation of the effects of SiO 2 .naked, SiO 2 .amino, SiO 2 .
PEG, and SiO 2 .phosphate. In vitro results were obtained with AM (NR8383) subjected to
nanoparticle suspended in cell culture medium (45 µg/ml) for 16 h. TNFα was measured indi-
rectly (loss of L-929 cells upon treatment with the macrophage supernatant) and expressed as
fold control values. In vivo results (bronchoalveolar fluid protein, Lowry method) were from
rats treated with 360 µg/lung for 3 days.