Uptake and Effects of Carbon Nanotubes - Safety of Nanomaterials along Their Lifecycle - page 223

Carbon nanotubes

Environmental
susceptibility factors

Genetic
susceptibility factors

Inhalation and lung
deposition

*Bacterial or viral infection
*Pre-existing disease
(e.g., asthma)
*Other pollutant exposures
(e.g., smoking, ozone, etc)

*Loss of tumor suppressor genes
*Gain of pro-brogenic genes
*Epigenetic alterations

Neutrophilic
inflammation

CNT clearance

CNT persistence

Resolution & repair Fibroproliferative

disease

FIGURE 10.6 Environmental or genetic susceptibility factors (within circles) that are pro-
posed or have been shown to increase inflammation and fibroproliferative lung disease in
mice after exposure to CNTs.

CNTs will cause or exacerbate asthma in humans. However, the evidence in rodents
suggests that CNTs would be a hazard to individuals with asthma.
The effects of CNTs in the lung could also be exacerbated by pre-existing bac-
terial or viral infection. For example, bacterial lipopolysaccharide (LPS), a potent
proinflammatory agent, has been implicated in a number of occupational and
environmental lung diseases in humans, including bronchitis, COPD, and asthma.
SWCNTs or MWCNTs exacerbated LPS-induced lung inflammation, pulmonary
vascular permeability, and production of proinflammatory cytokines in the lungs of
mice (Inoue et al. 2008). LPS pre-exposure also enhanced MWCNT-induced pul-
monary fibrosis in rats and synergistically enhanced MWCNT-induced production
of PDGF by rat alveolar macrophages and lung epithelial cells (Cesta et al. 2010).
These studies provide evidence that LPS-induced lung inflammation is a susceptibil-
ity factor that increases the severity of fibroproliferative lung disease caused by CNT
exposure.

10.5 CONCLUSIONS AND SUMMARY
CNTs offer innovative structural platforms for a wide variety of novel applications
in engineering, electronics, and medicine. However, careful consideration should be
given to the potential human health risks that CNTs pose in occupational, consumer,
or environmental exposure scenarios. Predictions that CNTs will have the potential
to cause fibrosis and/or cancer in humans are based on physical similarities to toxic
fibers and growing evidence that CNTs cause fibrosis and perhaps cancer in rodents.
As with other engineered nanomaterials, the nanoscale of CNTs makes it difficult
to predict how these structures will interact with intracellular structures such as
DNA, cell membranes, and cytoskeletal proteins. Also, CNTs contain residual met-
als (e.g., nickel, cobalt, iron) introduced from the manufacturing process and many