Citiraj:
Unfortunately, the effect
of this increase in the use of nanoscale silver on human health
and the environment is unclear.
The number of AgNP in vivo toxicological studies is still incredibly
small, so generalized conclusions about the effects of AgNP
exposure via food-relevant routes of exposure remains limited. It
is, for example, still unclear to what extent the biochemical pathways
which facilitate processing of silver ions apply to AgNPs, to
what extent AgNPs pass through the intestinal lining intact or
are dissolved into silver ions in the highly acidic environment of
the stomach, and to what extent AgNPs can pass through natural
biological barriers such as the blood–brain barrier, the placenta
or into breast milk. It is also crucial to note that regardless of one’s
interpretation of the available body of literature, there have been
almost no attempts to study the cumulative effects of chronic
AgNP exposure, and systematic investigations of the relationship
between particle characteristics (size, shape, surface charge, etc.)
and toxicity have yet to be performed.
Citiraj:
In vitro toxicological studies have shown that AgNPs may not be
benign to isolated mammalian cells. Human lung fibroblasts and
glioblastoma cells exposed to AgNPs exhibit reduced ATP content,
increased ROS production, damaged mitochondria, DNA damage
and chromosomal aberrations in a dose-dependent manner compared
to controls, suggesting that AgNPs have the potential to be
cytotoxic, genotoxic, antiproliferative and possibly carcinogenic
[333]. AgNPs at low concentrations in vitro cause changes to the
cell cycle progression of human hepatoma cells, whereas at higher
concentrations AgNPs induced abnormal cellular morphology, cell
shrinkage, and chromosomal damage to a much worse extent than
that caused by similar Ag+ concentrations, indicating that the toxicity
of AgNPs is not only caused by Ag cation release [334]. Exposure
of spermatogonial mouse stem cells to 15 nm AgNPs at low
(10 lg/mL) levels in vitro results in cellular morphological changes
and mitochondrial damage, etc., and thus AgNPs may represent a
threat to male reproductive health under some conditions [335].
AgNPs also exhibit cytotoxicity to rat liver cells mediated through
oxidative stress (e.g., disrupted membrane potentials, ROS formation
etc.) at far lower concentrations than particles composed of
other metals and metal oxides [336]; AgNP size-dependent cytotoxicity
caused by oxidative stress and ROS formation was also
demonstrated for rat alveolar macrophages [337]. While at least
one AgNP-based dermatological ointment has been demonstrated
to be cytotoxic to human fibroblasts and skin/carcinoma cells,
causing concentration-dependent morphological changes, signs of
oxidative stress, lipid oxidation, DNA fragmentation/apoptosis
and, at very high concentrations, necrosis, it has nevertheless been
concluded that AgNPs were safe for skin contact at concentrations
up to 6.25 lg/mL [338]; however this dosage may be expected to be highly AgNP-size dependent, so the absolute usefulness of this
mass-based dosage metric is debatable, particularly since the AgNP
characteristics in this study were not disclosed. Despite these reports
of AgNP cytotoxicity, some other studies have arrived at contrary
conclusions: one group of researchers found that epidermal
cells are unaffected by antimicrobial-relevant concentrations of
AgNPs [223] and several groups have determined that AgNPs contained
in LBL-assembled PNCs or bone-cements cause no observable
toxic effects on human osteoblasts under the tested conditions
[266,272,339].
