Biomedical Engineering Reference
In-Depth Information
NP
ROS
DNA damage
DNA repair
ATM
Nucleus
Sumoylation Ubiquitilation
FIGURE 19.6
Postulated mechanism for the repair of damaged DNA on exposure to NP based on the ioniz-
ing radiation model. NP, nanoparticle; ATM, ataxia telangiectasia mutated. (Reprinted with permission from
Li JJ et al.
Experimental Biology and Medicine
. 2010;235:1025-33.)
is questioned [184]. Nevertheless, a recent study has shown that TiO
2
NPs may be able to switch on
regressive cancer cells.
In vivo
preimplantation of TiO
2
NPs, followed by coculturing of a regres-
sive cancer cell line over the implantation site, was observed to induce tumorigenic characteristics
such as an upregulation of TGF-β and prostaglandin E2 [185]. The long-term exposure to NPs, such
as nanoparticulates in PM10, displayed genome instability under comet assay analysis, altered cell
cycle kinetics in flow cytometry, and induced protein expression of p53 and DNA repair-related
proteins, similar to that observed in irradiated cells. Hence, they postulate that these NPs could
activate signaling pathways similar to ionizing radiation, resulting in carcinogenesis as a conse-
quence of errors in DNA replication. DNA repair in ionizing radiation requires activation of ataxia
telangiectasia-mutated protein, which is a serine-/threonine-specific kinase, and subsequently, the
ubiquitylation-signaling cascade and sumoylation pathway (Figure 19.6).
19.9.4.1 Comet Assay
The comet assay is a widely used
in vitro
assay in fundamental research for DNA damage and
repair, in genotoxicty testing of nanomaterials. This study has been employed to investigate the
genotoxic potential of manufactured NPs that allowed DNA strand breaks or oxidative lesions.
Considering the sensitivity of the assay, it can enable the assessment of its relative potency [186].
19.9.4.2 F
pg
-Modiied Comet Assay
The DNA formamidopyrimidine DNA glycosylase (F
pg
) enzyme is used for detection of oxidative
DNA base damage, in particular, 8-OH guanine. Therefore, F
pg
-modiied comet assay is used after
treating with NPs [163].
19.9.4.3 Ames Test
Ames test (or bacterial reversion mutation test) is an
in vitro
assay used to assess the genotoxic
potential of nanomaterials [187]. The test employs histidine-dependent (auxotrophic) mutant strains
of
Salmonella typhimurium
. The test is usually employed as an adjunct technique because it is dif-
ficult to interpret that data generated in a prokaryotic system to a eukaryotic genotoxicity testing.
Furthermore, results could be ambiguous in some instances when certain nanomaterials are not able
to cross the bacterial wall or in situations where the nanomaterials are bactericidal.
19.9.4.4 Alkaline Single-Cell Microgel Electrophoresis Assay
The alkaline single-cell microgel electrophoresis assay is applied to detect DNA strand breaks and
alkali labile as well as incomplete excision repair sites in single cells. The percentage of DNA in the
