Page 443 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Toxicological Impacts of Nanomaterials 423

Sandhu et al., 2002), DNA-binding agents (Gearheart et al., 2001;
McIntosh et al., 2001; Wang et al., 2002), protein inhibitors (Fischer et al.,
2002), and spectroscopic markers (Gole et al., 2001; Otsuka et al., 2001;
Park et al., 2002; Weizmann et al., 2001). These nanoparticle systems,
however, have not been well evaluated to determine their interactions
with cells beyond the designated functions.
Cationically functionalized mixed monolayer–protected gold clusters
can be used to mediate DNA translocation across the cell membrane in
mammalian cells at levels much higher than polyethyleneimine, a widely
used transfection vector (Sandhu et al., 2002). Nevertheless, the toxic-
ity of the nanoparticles was observed at concentrations only twofold in
excess of that found to have maximal transfection activity (Sandhu et al.,
2002). The cytotoxicity of cationic (quaternary ammonium functionalized)
and anionic (carboxylate-substituted) gold nanoparticles (2 nm core
particles) has been evaluated in red blood cells, Cos-1 cells, and bacte-
rial cultures (Escherichia coli). LC50 levels were determined only with
the cationic gold nanoparticles. Virtually indistinguishable toxicity
profiles have been reported for the two mammalian cells, while a two-
to threefold increase is required as a lethal concentration for the bacte-
rial cultures (Goodman et al., 2004). The small variation in LC50 values
reported suggests that the mechanism of toxicity is similar for all three
cell types, and this implies that the nanoparticles should interact with
the cells in a passive process (Goodman et al., 2004). Thus, toxicity should
not be caused by cellular uptake via endocytosis as the endocytotic path-
way is actively utilized by Cos-1 cells, but not erythrocytes. Additional
experiments using a vesicle-disruption assay have demonstrated that the
specific charge pairing of the nanoparticles and lipid bilayers mediates
membrane interaction and lysis. Thus, the toxicity of the gold nanopar-
ticles seems to be related to their interactions with the cell membrane,
a feature initially mediated by their strong electrostatic attraction to the
negatively charged bilayer and that the core shell is of great importance
in the toxicity properties of the nanoparticles (Goodman et al., 2004).
Water-soluble gold nanoparticles have been functionalized with a Tat
protein-derived peptide sequence, with the ability to reach the nucleus.
The particles were tested in vitro in human fibroblasts by light and
transmission electron microscopy, and the biocompatibility and efficacy
of the functionalization with the translocated peptide allowed particles
to transfer across the cell membrane and locate within the nucleus.
Only a slight decrease in MTT metabolic activity and/or proliferation
was observed following 24-hour exposure at 10 µM (de la Fuente, 2005).
Gold nanoparticles can be used as X-ray contrast agents. There have
been few fundamental improvements in clinical X-ray contrast agents
in more than 25 years, and the chemical platform of tri-iodobenzene has
not changed. In mice intravenously injected with gold nanoparticles