Environmental Engineering Reference
In-Depth Information
cells, such as macrophages, to produce and deliver oxidants to cells, thus causing genotoxicity from inflammation [51]. The
direct interaction of nanoparticles and the DNA molecule or DNA-related proteins can lead to physical damage to the genetic
material. Nanoparticles can also cause DNA damage by interacting with other cellular proteins such as those involved in the
cell division process. Thus, nanoparticles can induce various cellular responses that can lead to genotoxicity, such as oxidative
stress, inflammation, and aberrant signaling responses [52].
31.5
In VItro
and
In VIVo
toxicity assays
The toxicity of nanoparticles can be assessed by a number of
in vitro
and
in vivo
studies. The reduction of tetrazolium salts such
as mTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) and xTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-
2
H
-tetrazolium-5-carboxanilide) can be used to estimate cell viability and proliferation. However, tetrazolium salts get reduced
by superoxides and produce absorbant formazan end products. For example, nano-Tio
2
induces superoxide formation in differ-
ent mammalian cells and the use of mTT/xTT to measure viability or proliferation in such cytological investigations can lead
to false positive results. Therefore, mTT and xTT assays may inaccurately predict cell toxicity or overestimate cell viability,
respectively [53].
In vivo
studies are necessary to elucidate mechanisms, pathways, and entry routes of nanoparticles in a complex multi-
cellular organism. This is required not only for nanomaterials used in industrial processes, where human exposure could
occur via the environment, but also for nanomaterial use where human exposure is part of the design, for example, nano-
medicines. For nanoparticles produced on an industrial scale, the extent to which factory workers, specific population sub-
groups, or the public in general are exposed needs to be established. it has been demonstrated that nanoparticles gain access
to the body mainly via the airways, the skin, or by ingestion. They are also able to translocate to secondary organs; however,
this has only been demonstrated in small quantities. For example, observations on the toxic effects of nanoparticles can be
carried out using zebrafish as a model due to its fast embryonic development and transparent body structure. The other
advantages of using zebrafish as an organism for studying the potential toxic effects of nanoparticles are that it has a high
degree of homology and similar physiological reactions as in mammals. This allows for real-time, noninvasive visualization
of the uptake and translocation of nanoparticles, and their effects on organogenesis and morphological development [54].
cell culture-based assays are used as a prescreening tool to understand the biological effects of nanoparticles. However,
along with the
in vitro
assays, it is necessary to confirm the
in vivo
biological activities of nanoparticles in animal models to
study the suitability of their application [55].
Apart from
in vivo
and
in vitro
studies, the use of genomic tools such as gene expression profiling is being considered
as a potentially rapid and cost-effective approach for identifying and assessing prospective hazard, characterizing chemical
(or particle) mode of action, and assessing human relevance in support of human health risk assessment. once it is proved
that mRNA/protein expression profiles can effectively predict the modes of action and biological outcomes of exposure at
relevant doses, gene expression data will be more reliable for use in risk assessment studies. gene expression profiling can
be extremely useful in identifying effects at low doses and be used to distinguish between doses that elicit an adaptive
response and those that result in adverse toxic effects. So far, the application of gene expression profiling in regulatory
toxicology has focused more on the qualitative identification of the chemical modes of action and transcription biomarkers
that can predict specific toxicities than on the quantitative determination of threshold values, such as benchmark doses
[56]. The advantages of using toxicogenomic profiling is that it can be used as a screening tool to prioritize the specific
assays that should be conducted from the standard battery of tests, and this will minimize the use of animals, and be more
cost-effective and time-saving [57]. The other benefits are that the global analyses of transcriptional changes provide a
wealth of information that will be useful in identifying the probable modes of action and to query their relevance to human
adverse health outcomes [58].
proteomics involves the study of the complete profile of proteins in a given cell, tissue, or biological system at a given time.
it uses a set of high-throughput methodologies with a wide dynamic range that enables the discovery of novel biomarkers. The
application of proteomic tools such as two-dimensional electrophoresis and mass spectrometry methods could also help address
the growing environmental threat posed by nanoparticles and provide useful information while increasing knowledge about
nano-bio interactions. However, the limitations and challenges of this approach are the shortage of genome sequence data
necessary for protein identification and the growing requirement for more stringent study designs [59].
However, before the full-fledged applicability of toxigenomic and proteomic approaches in human health risk assessment, it
is essential to know whether gene expression profiling and other such genomic and proteomic tools can identify hazards, assess
risk of exposure via quantitative dose-response analysis, and identify adverse effects associated with specific modes of action
of nano-bio interactions [60].
