Environmental Risks of Nanomaterials - Nanotechnologies for Water Environment Applications - page 607

(statistically derived dose of a chemical/physical agent expected to kill 50% of
organisms in a given population) of substances in animal and in vitro cellular toxicology
are used for characterization of NM biological effects. More specific information
concerning NMs risks and bioavailability can be gleaned from the development of NMs
for biotechnology (Henry, 2003).
In vitro studies are an essential element in toxicity assessment of NMs. In vitro
assays allow specific biological and mechanistic pathways to be isolated and tested
under controlled conditions in ways that are not feasible by using in vivo studies,
including different time-length exposures. The use of in vitro methods for nanotoxicity
is rapidly growing, as reflected by their evolution from systems principally for study of
toxicity mechanisms to high-throughput systems for rapid and cost-effective screening
of toxicity of NMs. These in vitro studies may reveal a link of the mechanism of injury
to the pathophysiological outcome in the target organ (Nel et al., 2006).
For example, ROS generation may result in protein, DNA and membrane injury.
Oxidative stress may result in phase II enzyme induction, inflammation, and
mitochondrial perturbation. Inflammation may result in tissue infiltration with
inflammatory cells, fibrosis, granulomas, atherogenesis, and acute phase protein
expression. Moreover, in vitro assessment of nanotoxicity are being advanced by
understanding particle physicochemical properties in cell culture media as they relate to
dosimetry and dose-response assessment, by introducing the concept of cellular dose in
vitro , and by integrating aspects of material science, solution chemistry, and reaction
kinetics that may affect the cellular dose (Teeguarden et al., 2007). It is important to
develop appropriate dose metrics for NMs to reflect their unique quantum size
characteristics and behaviors. Dose for NMs in vitro can be defined at various levels to
account for the consideration of the target site and mode of action, reflecting the dose at
the nonspecific level, apparent exposure at a more specific level, or cellular dose at the
most specific level. Cellular dose is a function of many factors as they affect transport of
NMs into the cells. While equal mass concentrations imply equal doses for different
materials, the corresponding NP numbers or surface areas could differ by orders of
magnitude. Simple surrogates of dose may therefore cause misleading of response and
uptake data for NMs in vitro . Incorporating particokinetics and principles of dosimetry
would probably significantly improve the methods for nanotoxicity assessment.
Initial screening of the uptake potential of NPs in cells has been investigated by
using flow cytometric light scatter and confocal laser scanning microscopy. For example,
uptake potential of NMs (TiO 2 , Ag, Fe 3 O 4 ) to Chinese hamster ovary cells was evaluated
by using flow cytometric light scatter and confocal laser scanning microscopy (Suzuki et
al., 2007). Results shows TiO 2 NPs can easily move to the cytoplasm of the cultured
mammalian cells, not to the nucleus, and the NPs are taken up in the cells dose-, time-,
surface-, and size-dependently.