Biomedical Engineering Reference
In-Depth Information
mouse leukemic macrophage cell line (RAW 264.7) was treated with nonpurified SWCNT (26%
Fe by weight) or purified SWCNT (0.23% Fe by weight) and the nonpurified SWCNT generated
more hydroxyl radicals than did the purified SWCNT (Kagan et al., 2006). 26 weight% iron-rich
SWCNTs resulted in a significant loss of intracellular low-molecular-weight thiols (GSH) and
the accumulation of lipid hydroperoxides in mouse macrophages. The human alveolar epithelial
cell line (A549) and rat alveolar macrophage cell line (NR8383) were treated with nonpurified
SWCNT and purified (acid treated) SWCNT. The metal contaminants in these CNTs were mainly
cobalt (Co) and nickel (Ni) with the purified SWCNT having a 2.5 weight% metal content versus
the nonpurified SWCNT having an 8 weight% metal content. Both the human alveolar epithelial
cell line and the rat alveolar macrophage cell line had increased intracellular reactive oxygen spe-
cies and decreased mitochondrial membrane potential when treated with the nonpurified SWCNT
(Pulskamp et al., 2007). Death due to the intratracheal instillation of SWCNTs at high doses in mice
has been reported. The deaths were preceded by lethargy, inactivity, and loss of body weight (Lam
et al., 2004). These studies suggest that metal contamination in CNTs (from their synthesis) may
importantly contribute to their pulmonary toxicity.
6.7 PULMONARY TOXICITY OF FUNCTIONALIZED CNTs
Surface functionalization renders the CNTs more interactive with the physiological systems, result-
ing in higher toxicities. In a study, mice were treated with SWCNTs or acid-functionalized SWCNTs
(SWCNT-AF) via oropharyngeal aspiration at a dose of 10 or 40 μg. Acid functionalization reduced
the carbon content by about 20% as well as reduced the content of cobalt (Co), chromium (Cr), iron
(Fe), manganese (Mn), and nickel (Ni) by 24-33%. The SWCNT-AF-treated mice demonstrated
greater pulmonary toxicity than SWCNT-treated mice as measured by an increased number of
pulmonary neutrophils (Tong et al., 2009). Human lung tumor cell lines (H596) were treated with
nonfunctionalized MWCNTs and acid-functionalized MWCNTs (MWCNT-AT). The acid treat-
ment resulted in adding carbonyl, carboxyl, and/or hydroxyl functional groups to the CNT. The
MWCNT-AT-treated H596 cells demonstrated greater cytotoxicity than did the MWCNT-treated
H596 cells as determined by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bro-
mide] assay (Magrez et al., 2006). Human lung epithelial cells (A549) were treated with nonfunc-
tionalized MWCNTs and highly functionalized MWCNTs (hf-MWCNT-NH2). The water-soluble
hf-MWCNT-NH2 caused cytotoxicity in A549 cells at the doses of >100 μg/mL as determined
by the calcein/propidium iodide assay, whereas MWCNT did not cause cytotoxicity in this assay
(Coccini et al., 2010). In another study, A549 cells were treated with nonfunctionalized MWCNT
and hydroxyl-functionalized MWCNT-OH at low concentrations (1-40 μg) for 2, 4, and 24 h, which
attempts to mimic human environmental exposure. MWCNT damaged the A549 cell membranes
at lower concentrations than did the MWCNT-OH, which might be due to differences in aggrega-
tion and water solubilities. Also, MWCNT-OH induced more apoptosis in the A549 cells than did
MWCNTs (Ursini et al., 2012). In 2004, Kam et al. examined endocytosis (intracellular localization)
of SWCNTs and SWCNTs-biotin-streptavidin conjugates within human promyelocytic leukemia
(HL60) cells and human T (Jurkat) cells. They found that unfunctionalized SWCNTs exhibited little
toxicity, but the SWCNTs-biotin-streptavidin complexes caused extensive cell death. The surface
charge plays an important role in the structure-activity relationships that determine the profibro-
genic potential of f-CNTs in the lung. Carboxylated (COOH)-, polyethylene glycol (PEG)-, amine
(NH2)-, sidewall amine (sw-NH2)-, and polyetherimide (PEI)-modified MWCNTs were success-
fully established from raw or as-prepared (AP-) MWCNTs, and comprehensively characterized by
transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), Fourier trans-
form infrared spectroscopy (FTIR), and dynamic light scattering (DLS) to obtain information about
morphology, length, degree of functionalization, hydrodynamic size, and surface charge. Cellular
screening in BEAS-2B and THP-1 cells showed that, compared to AP-MWCNTs, anionic function-
alization (COOH and PEG) decreased the production of profibrogenic cytokines and growth factors
