Biomedical Engineering Reference
In-Depth Information
Studies have shown that water-soluble QDs cause slow but long-term inhi-
bition of cell proliferation that are speculated to result from reactive oxygen
species (ROS) role in QD-induced cytotoxicity.
123
Previous studies have shown
that cadmium-based QDs can generate free radicals including ROS.
133,134
that
can cause oxidative stress
135
and mitochondrial damage that can result in loss
of metabolic functions.
136
When the oxidative damages are not repaired, the
cadmium-based QDs induced apoptotic changes in the IMR-32 human neuro-
blastoma cell including loss of mitochondrial membrane potential, mitochon-
drial release of cytochrome C, and activation of caspase-9 and caspase-3.
137
The effect of cadmium-based QDs was investigated on HEK293 cells
against CdCl
2.
The results showed that the cell proliferation was inhibited but
not stopped by 25 µM solution of CdCl
2
but at higher concentrations, 50 µM
or 100 µM, the cell proliferation was completely inhibited.
135
Inductively cou-
pled plasma-mass spectrometry (ICP-MS) showed that the concentrations of
intracellular Cd
2+
ions from the 10 µM CdCl
2
resulted in significantly higher
intracellular concentration of Cd
2+
ion (>20 ng/10
5
cells) than that with 150 nM
CdTe QDs (<10 ng/10
5
cells).
128
In this study, it was shown that both cellu-
lar metabolic activity and proliferation rate suggested that treatment of cells
with 150 nM CdTe QDs caused stronger inhibition effects than that with 10 µM
CdCl
2
. It was also shown that the cadmium-based QDs affected the various gene
expressions from the HEK293 cells.
128
Treatment with different concentrations
of CdTe QDs from 18.75 nM to 300 nM all caused similar induction levels of
the mRNA transcripts.
Investigation of the distribution of QDs in the cell have also been reported to
elucidate the toxicity of the QDs.
128
Optical fluorescence imaging has indicated
that CdTe QDs were located predominantly in the cytoplasmic/perinuclear area
(200-300 nm resolution).
123
It is very important to study and to understand the effect of QDs on live cells,
tissues, or organs in order to support its growing applications in medicine. In
addition, it is equally important to determine the related mechanism of toxic-
ity in order to evaluate the pros and cons for its applications in medical imag-
ing, diagnostics, and therapy. At present, it is still a challenge to compare and
draw unambiguous conclusion from reported studies because these studies have
focused on a wide variety of QDs, cell lines, and analytic methods.
138,139
The
synthesis and purification process, the chemical composition, size, shape, and
the surface modifications of the QDs are factors that can affect its interactions
with the cell membrane that may or may not lead to subsequent uptake into the
cells.
14,140
In addition, different cell types have varying reactions and responses
as well as different threshold to stimuli like the QDs making evaluations of
toxicity much more challenging. The various ways to interpret cytotoxicity
such as cell number, cell growth, apoptosis, cellular morphology or changes in
metabolic activity complicate the interpretation of QD toxicity. Thus, a standard
method for the evaluation of QD toxicity has yet to be written in order to have a
consistent basis for predicting effects in living organisms.
