Biomedical Engineering Reference
In-Depth Information
Peyer's patches. The ingestion of ultrafine particles by the GI tract can stimulate phagocytosis at the
GI mucosa and cause antigen-antibody-mediated reactions and inflammatory responses and, from
there onward, systematic transportation to other organs of the body (Hussain et al. 2001).
Nanomaterials present in food may be readily absorbed from the GI tract. Nanomaterial trans-
location takes place through the epithelium of the intestinal wall depending on the physiochemical
properties, for example, size, surface charge, presence/absence of a ligand, lipophilicity/hydrophi-
licity, and physiology of the intestinal tract (Des Rieux et al. 2006). Oral administration of gold
NPs to mice showed that the GI uptake of gold NPs increased with diminishing size (Hillyer and
Albrecht 2001) and smaller particles are absorbed more readily and faster than larger particles
(Szentkuri 1997).
On the other hand, it is also possible that the ingested nanomaterials may not remain in a free
form in the lumen due to transformations such as agglomeration, adsorption, aggregation, or bind-
ing with other food components and, hence, are not readily available for translocation through the
intestinal wall. Currently, only limited information is available on the absorption of nanomaterials
after ingestion (FAO and WHO 2009). The translocation of nanosized particles potentially used as
food components through the GI tract remains to be explored (EFSA 2009).
13.4.2 d
IstrIButIoN
Ingested nanomaterials can enter the capillaries, which will carry nanomaterials through the portal
circulation to the liver, or nanomaterials enter the lymphatic system by way of the thoracic ducts
upon contact with the intestinal submucosal tissue. Data obtained from experiments demonstrated
that the distribution of NPs after oral administration is dependent on particle size. NPs with a
smaller size have a more widespread tissue distribution to organs such as the brain, liver, lungs, and
kidneys, while bigger particles (28 and 58 nm) remain almost solely inside the GI tract (Hillyer and
Albrecht 2001). Studies have been carried out on the ability of NPs to penetrate the placental bar-
rier. Moreover, certain nanomaterials (C
60
fullerene) can pass across the placenta (Tsuchiya et al.
1996). Nevertheless, due to the conflicting results of some
in vitro
(Myllynen et al. 2008) and animal
studies (Tsuchiya et al. 1996), no general conclusions on the penetrating power of NPs across the
placental barrier can be made. No information is available on whether nanomaterials are transferred
into milk (EFSA 2009).
13.4.3 e
xcretIoN
/e
lIMINatIoN
There is very limited information on the excretion of absorbed nanomaterials. In animal studies,
feeding rats with radioactive iridium NPs (192Ir) showed that the ingested NPs were not substan-
tially taken up through the GI tract and were rapidly eliminated via feces within 2-3 days. No major
NP translocations from the GI tract to other organs through the blood were observed (Kreyling
et al. 2002). A positive surface charge was also found to increase both urinary and fecal excretion
(Balogh et al. 2007).
NPs may primarily target respiratory organs; however, on the other hand, other organs, for exam-
ple, the GI tract, also need to be considered, because NPs could get into the GI tract by many ways,
such as indirectly via mucociliary movement, directly via the oral intake of water, cosmetics, food,
drugs, and nanoscale drug-delivery systems (Meng et al. 2007).
13.5
TOXICITY OF NANOMATERIALS ON GI TRACT
13.5.1 t
oxIcIty
of
t
I
o
2
Np
s
Koeneman et al. investigated the possible pathways by which TiO
2
NPs could cross the epithelium
layer by employing both toxicity and mechanistic studies. Microvillar organization was investigated
