Nanoparticles and human health

The potential toxicity of nanoparticles currently raises many
discussions in public and scientific life. The question whether
nanoparticles are a threat to human health cannot be answered to
complete satisfaction at the current state of knowledge. A
versatile tool to investigate nanotoxicity are fluorescence
microscopy and live-cell imaging as they provide excellent
resolution and direct insight into cellular processes. In this work
fluorescence based methods are used to investigate the influence of
silica nanoparticles on human health, more precisely on the blood
vessel system. At first, the synthesis and characterization of the
following three different types of perylene labeled amorphous SiO 2
nanoparticle species is described: surface-labeled monodisperse
particles, particles with a dye-containing silica core and a
non-fluorescent silica shell and a surface-labeled nanoparticle
network. The labeling of nanoparticles should not induce artificial
cytotoxic effects when they are used for cytotoxicity assessment.
This is achieved either by incorporating the dye into the
nanoparticle’s structure or by covering only a minor surface
fraction by dye molecules. The surface-labeled silica species are
used to investigate nanotoxicity throughout this thesis. Another
prerequisite for reliable dose-dependent nanotoxicity studies is
the knowledge about the number of nanoparticles taken up by an
individual cell. We therefore developed the Nano_In_Cell_3D ImageJ
macro which is able to quantify nanoparticle uptake into cells.
Nano_In_Cell_3D uses the fluorescence image of the cell membrane to
segment the cell into an intracellular space, a transition region
(e-membrane region) and an extracellular space. The number of
present nanoparticles is calculated from the fluorescence intensity
of each region. This custom-made method offers the possibility to
quantify nanoparticles in the individual cellular regions.
Nano_In_Cell_3D was validated by comparing the results to the well
established quenching method. By using Nano_In_Cell_3D we could
show that the cytotoxic impact of nanoparticles onto different cell
lines correlates to their intracellular uptake. Primary human
vascular endothelial cells (HUVEC) take up 310 nm silica
nanoparticles more efficiently and are more sensitive to this
nanoparticle species than cancer cells derived from the cervix
carcinoma (HeLa). Upon nanoparticle contact, cellular viability of
HUVEC is strongly reduced and membrane permeability increases
leading to apoptosis. In contrast, HeLa cells show a considerable
lower effect in both cellular viability and membrane permeability
and do not show apoptosis. In consistence to these findings, HUVEC
take up approximately 20 times more particles than HeLa cells
within 4h. Interestingly nanoparticle uptake is clathrin mediated
in both cell types. HUVEC grow in the blood vessel system under
natural conditions and are therefore exposed to blood flow
conditions. The latter can be simulated using a microfluidic system.
We chose a microfluidic system based on the surface acoustic wave
(SAW) technology which was characterized concerning fluid
evaporation behavior, fluid temperature and flow velocities. Based on
these results the system can be further improved to allow the
assessment of nanotoxicity at blood flow conditions in a next step.
The last part of the thesis focuses on interactions between silica
nanoparticles and giant unilamellar vesicles (GUV)s. The latter
serve as a simple model for the cell membrane. Nanoparticles in
contact with the lipid membrane influence the morphological behavior
of the vesicles during phase transition. In absence of
nanoparticles, vesicles typically show extracellular budding
processes. Nanoparticlesin contact with the cell membrane induce
intravesicular budding of daughter vesicles, similar to endocytosis
observed in living cells. Furthermore exocytosis processes were
observed where daughter vesicles crossed the GUV membrane and were
transferred from the intravesicular to the extravesicular space.
These observations suggest that the fundamental mechanism of
endocytosis can partly be explained by simple physical effects. In
summary, this theses provides an experimental strategy to
investigate the impact of nanoparticles onto human cells using SiO
2 nanoparticles as an example. Starting with the synthesis and
characterization of nanoparticles it tackles the question how to
quantify nanoparticle uptake into cells. Furthermore we could prove
that cytotoxic effects can be correlated to nanoparticle uptake and
were able to show that nanoparticles influence artificial membranes
which is a first step to understand the basic mechanisms of
nano-toxicity. The methodology developed in this thesis is expected
to provide insight into cytotoxicity of a broad variety of different
nanoparticle types.