Biomedical Engineering Reference
In-Depth Information
different organs. The researchers measured the biodistribution in different
organs in mice and rabbits. They observed a decrease of the NPs in the organ
tissues only between 1 and 3 h postexposures, except for the liver at 3 h,
where it was higher than at 1 h postexposure. The elimination of the fuller-
ene was mainly via the urinary route [34]. In another comparison, Ogawara
and colleagues [35] administered a single intravenous dose of polystyrene
microsphere (50 and 500 nm in diameter) to rats. The distributions were
independent of the size. The researchers measured the half-life (
t
1/2
) for the
alpha phase and terminal phase at approximately 1 and 53 h, respectively
[35]. The researchers believed that urinary elimination seemed to be the
major elimination route. Singh and colleagues [36] exposed mice to a single
intravenous dose of single-walled carbon nanotubes (1 nm in diameter and
300-1000 nm in length). The distribution was very quick across the organs,
and excretion occurred via the urine pathway. In the same experiment, the
researchers also studied the impact of the exposure route on the elimina-
tion half-life. Depending on the absorption route, the other local mechanism
previously mentioned may also contribute to the elimination. In a study by
Furumoto and colleagues [37], the researchers demonstrated that NPs can
also be excreted via the biliary tract.
9.5 Discussion and Conclusion
The interaction between NPs and the biological system is a huge challenge in
the field of toxicokinetics. The toxicokinetics discipline describes the absorp-
tion, the distribution during the metabolism process, and the excretion of
the xenobiotics (the NPs). At this point, our focus is to apply the approach
that we have in place in case we need to use the same kinetic approaches or
need to develop new tools. However, it is important to point out that comple-
mentary approaches will be required to be able to adequately describe the
experimental observation.
At the beginning of the nanotoxicokinetics observations, we believed that
inhalation was the major exposure route, with negligible contribution from
the skin. However, observations such as those by Ryman-Rasmussen and
colleagues [38] or results from Monteiro-Riviere and colleagues [19] clearly
suggest that skin is surprisingly permeable to nanomaterials with diverse
physicochemical properties and may serve as a portal of entry for localized,
and possibly systemic, exposure of humans to quantum dots and other engi-
neered nanoscale materials [38]. There is a particle size dependency; thus,
in the GIT, NPs with size <100 nm show significantly greater uptake in tis-
sues [13]. For skin absorption, these findings suggest that the toxicology of
these structures must be assessed before widespread public exposure so that
appropriate protective measures can be developed [19]. The status of this
