Environmental Engineering Reference
In-Depth Information
chain dysfunction, microsomes, peroxisomes and inflammatory reactions within the cell.
InterferenceofENPswiththeintrinsicsourcesformsthesuperoxideanion(O
2
ﾯǙ).
Superoxide radical can be further converted to either hydrogen peroxide (H
2
O
2
)
orhydroxyl(OH˙)radicals.Ngetal.(
2010
)andLietal.(
2009
) showed that the
presenceofintracellularmetalionscanfacilitateaFenton-likereactionbyinteract-
ing with the superoxide and peroxide radicals. This forms OHǙ radicals that are
extremely toxic to cells.
The following are possible reactions of metal ions with the H
2
O
2
and O
2
ﾯǙ:
X
(a)
+ O
2
−
ₒ X
(a−1)
+ O
2
X
(a−1)
+ H
2
O
2
ₒ X
(a)
+ OHǙ + OH
−
,
Where, X = Fe, Zn, Cr, Cd and other metal ions.
ENPs ultimately cause toxicity by inducing oxidative stress. He et al. (
2011
)
observed that carbon nanotubes can cause mitochondrial damage by inducing pro-
inflammatory and fibrotic signals.
Huangetal.(
2010
) found that metal and metal oxide NPs can induce oxidative
stress through Fenton reactions, when these NPs interact with the extracellular or
intracellularcomponentsofcells.Asharanietal.(
2009
) reported that AgNPs gener-
ate free radicals in the form of Ag
+
ions within the cell. Ag
+
ions are generated after
the AgNPs interact with intracellular H
2
O
2
. Similar reaction mechanisms have been
proposedforothermetalNPslikecobaltandnickel(Asharanietal.
2009
) and fol-
low the pattern:
2Ag + H
2
O
2
+ 2H
+
ₒ 2Ag
+
+ 2H
2
O Eﾰ = 0.17 V
Choi et al. (
2008
) studied the interaction of mitochondrial enzymes with oxi-
dizedAgandfoundthattheygeneratedROS.
Cells normally have inbuilt mechanisms to overcome oxidative stress. However,
excess stress may damage the mitochondria, cause lipid peroxidation, disrupt ion
channels, interrupt Ca
2+
homeostasis, curtail oxidation of sulfhydryls, damage DNA
andcausecelldeath(Fig.
5
).
6.2
Interaction with Proteins
The physico-chemical properties of NPs influence how they interact with proteins.
Kim et al. (
2007
) reported that multireceptor sites on rat brain epithelial cells
(RBEC)facilitatetheinteractionofNPswithapolipoproteinsinwaysthatallowthe
NPstoenterthecells.LynchandDawson(
2008
) suggested that the interaction of
NPswithproteinscouldforma“proteincorona”,whichpromotescellinternaliza-
tion of NPs.
Aggarwaletal.(
2009
) found that NP-protein interactions alter the 3D confirma-
tionofproteins,leadingtoimpairmentofproteinactivity.HalliwellandGutteridge
(
1999
) reported that metal NPs interact with sulfhydryl (-SH) groups present on
proteins.SuchinteractionscouldoxidizeGSH,andinhibitantioxidantpathways.
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