Biomedical Engineering Reference
In-Depth Information
Of particular interest to nanotoxicologists is the shape of a particle. Asbestos
is a fibrous silicate particle that has a high aspect ratio (1:3). The shape of car-
bon nanotubes is very similar to that of chrysotile asbestos. Although carbon
nanotubes are not made of silicates, both asbestos and carbon nanotubes
are biopersistent and probably cause similar cellular responses (e.g., for the
induction of lung fibrosis).
It has been shown that positively charged nanoparticles are taken up
more rapidly via the clathrin-mediated endocytotic pathway than negatively
charged nanoparticles [30]. This phenomenon is also proved in the
in vivo
study. When cationic quantum dots were injected into the lung, particles were
retained in the lung tissue, while noncationic quantum dots translocated to
the extrapulmonary tissues very quickly [31]. The cell surface is negatively
charged because of the presence of sialic acid residues of glycoproteins on the
plasma membrane, which is the reason why cationic nanoparticles interact
quickly and strongly with cells. The trafficking of positively charged poly-
styrene nanoparticles in rat alveolar epithelial cell monolayers was 20-40
times faster than that of highly negatively charged polystyrene particles [32].
However, the interaction of nanoparticles with red blood cells does not seem
to be influenced by the cell surface charge [33]. It should be noted that silica
and titanium dioxide particles have negative zeta-potential, while zirconium
oxide and cerium oxide particles have positive zeta-potential in pure water.
However, the zeta-potential of all those particles shifts to around -18 mV in
cell culture medium because of adsorption of proteins [13]. As to metal oxide
nanoparticles, solubility was the major factor determining the cytotoxicity of
nanoparticles in both mesothelial cells and fibroblasts [23].
8.5 Implications and Recommendation for
In Vitro
Study
The
in vitro
study is more appropriate for investigating the “toxicity mech-
anism” and is not directly linked with “regulation issues.” However, once
the standard methods are established, the
in vitro
toxicity assay can be used
for screening various nanomaterials. As physicochemical characteristics
and minor components of nanomaterials vary among industrial nanomate-
rial products, rapid, reproducible, and accurate screening methods should
be developed for the beneficial use of nanomaterials. In this context, the
international harmonization research strategy is very important for the
standardization of
in vitro
toxicity assay methods of nanomaterials. One of
the most difficult issues regarding
in vitro
toxicity assay is to disperse test
samples. Especially carbon-based nanomaterials such as carbon nanotubes
and fullerene are difficult substances to disperse in culture medium, and the
toxicity outcome would be completely different between well-dispersed and
agglomerated samples. Biologically inactive and pyrogen-free detergent can
