Analyzing the Biological Entity of Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 80

are not yet investigated in detail, a massive disturbance of the PS system due to
nanomaterial interaction might potentially lead to ARDS-like modalities, affecting
the integrity of the respiratory tract. Such effects cannot be detected when in vitro
cell cultures are the only models used, and underline the necessity to apply differ-
ent, independent methods to assess the toxicity profile of nanomaterials in biologi-
cal fluids. For biophysical studies of this kind, semicomplex or artificial surfactant
models are sufficient, although it is not possible to exclude additional effects that
might occur from other surfactant components, which for instance are not contained
in lipophilic extract surfactants, but that are present in vivo .
Surprisingly, in most of the biophysical investigations on nanomaterial-PS inter-
actions published so far, the aspect of biomolecule adsorption was not at all studied,
although this issue is most probably the reason for the observed adverse effects on the
biophysical functionality of PS. Binding of lung proteins and lipids has been so far
mainly studied to investigate the effect of biomolecule adsorption to nanomaterials
and the subsequent cellular effects. The characterization of nanomaterials regarding
their toxic potential within the lungs is a very complex and complicated task. The
epithelium of the lungs forms a large surface with an air interface. Inhaled nanoma-
terials are normally airborne and are wetted by the lung lining fluid after deposition.
To transfer this situation to in vitro test systems that can be later used to characterize
and study nanomaterials under physiological conditions is an immense technologi-
cal challenge. In addition, controlling the applied dose and exposure time requires
a close “dialog between aerosol science and biology” (Paur et al. 2011). However,
after deposition and submersion of nanomaterials in the lung lining fluid, the situa-
tion can be considered as a submersed condition. Therefore, most studies published
on adsorption of surfactant components to nanomaterials incubate the respective
material in the biological fluid, isolating it and finally analyzing the adsorbed mol-
ecules. The latter step was performed with respect to either the adsorbed protein
species (mostly by gel electrophoresis, western blotting, and mass spectrometry) or
the adsorbed surfactant lipids (often performed by thin layer chromatography and
LC-MS) (Salvador-Morales et al. 2007; Kendall 2007; Schleh et al. 2011; Schulze,
Rothen-Rutishauser, and Kreyling 2011). In this respect, Gasser et al. were able to
demonstrate that the binding pattern of surfactant PLs from Curosurf ® was different
for functionalized MWCNTs compared to uncoated ones, indicating that the surface
chemistry of a nanomaterial dictates the identity of adsorbed biomolecule (Gasser
et al. 2010). Furthermore, when the MWCNTs were precoated with PS before incu-
bation in serum, protein adsorption profiles that differed from MWCNTs without
precoating were obtained. These results indicate that nanomaterials, which enter
the body via the lungs, might experience a certain “pre-conditioning” that signifi-
cantly influences later secondary adsorption processes (e.g., formation of a second-
ary corona, Figure 4.1). In a subsequent study, PS-coated MWCNTs were found to
be internalized to a higher degree in monocyte derived macrophages (MDM) com-
pared to non-coated MWCNTs, indicating that adsorbed PS components can affect
the cellular uptake of nanomaterials. Moreover, the group could show that precoat-
ing of MWCNTs with PS affected their ability to cause oxidative stress, cytokine/
chemokine release, and apoptosis in MDM (Gasser et al. 2012). In another study by
Kapralov et al. (2012) single-walled CNTs (SWCNTs) were instilled in mice and