Biomedical Engineering Reference
In-Depth Information
validated by numerous investigators. The permeation of NPs throughout the
models seems to be an accurate predictive tool for human extrapolation.
9.3 Distribution
After absorption from oral, inhalation, or cutaneous routes, these NPs are
then translocated in the systemic circulation and delivered to different
organs, including the liver, spleen, kidneys, heart, and brain, where they
may be deposited [24]. Many target organs are being studied to measure the
impact of these exposures; however, only a few groups are working on the
kinetic distribution of NPs in these organs.
A study conducted by Kreyling and colleagues [32] indicated that 1 week after
inhalation, only a very small fraction of ultrafine iridium particles (18 and 80
nm in diameter) had access to systemic circulation and extrapulmonary organs.
The chemical composition and physical structure of the NP surface may be an
important determinant in influencing systemic translocation of ultrafine par-
ticles [32]. De Jong and Borm exposed rats aged between 6 to 8 weeks to a single
oral exposure of polystyrene NPs from 10 to 250 nm in diameter at concentra-
tions varying from 77 to 108 μg mL
-1
(25). NPs <100 nm were found mainly in
the blood and liver 24 h postexposure. In addition, De Jong's group found a
lower amount of NPs expressed in percentage of doses in the spleen and kidney
and only trace levels in the lungs, testis, heart, brain, and thymus [25].
These studies demonstrated that NPs, after deposition, are rapidly distrib-
uted across tissue compartments of the lung, and that these NPs may move
between the tissue compartments. The NPs eventually reach the capillary
lumen and may penetrate into circulating cells and constituents (e.g., erythro-
cytes, blood macrophages). Thereby, they may be distributed into other organs
of the body, such as the liver, heart, kidneys, and even the brain [14,25]. Nemmar
and colleagues [33] conducted an interesting human study in which they
used the inhalation of radiolabeled technetium 99 carbon NPs <100 nm in
diameter. The findings showed that radiolabeled technetium 99 carbon was
detected in the blood 1 min after inhalation, reached a maximum after 10-20
min, and remained for >60 min. A gamma camera showed substantial radio-
activity in the liver and other organs.
9.4 Excretion
In a study of rats by Peters and colleagues [24], a single intravenous dose
of a fullerene labeled with technetium 99 m showed a rapid distribution in
