Biomedical Engineering Reference
In-Depth Information
form. Microscopic and energy-dispersive spectroscopy analyses of colon mucosa indicated the pres-
ence of carbon, ceramic filosilicates, gypsum, sulfur, calcium, silicon, stainless steel, silver, and
zirconium (Gatti 2004). The size of the debris varied from 50 nm to 100 μm; the smaller the par-
ticle, the further it is able to penetrate. The particles were found at the interface between healthy and
cancerous tissues. On the basis of these findings, it was suggested that the GI barrier is not efficient
for particles smaller than 20 μm (Ballestri et al. 2001).
Crohn's disease affects people primarily in developed countries, and occurs in both the native
population and in immigrants from underdeveloped countries. It affects 1 in 1000 people (Lomer
et al. 2002). Crohn's disease is believed to be caused by a genetic predisposition together with
environmental factors (Lomer et al. 2002). It was recently suggested that there is an associa-
tion between high levels of dietary NPs (100 nm-1 μm) and Crohn's disease (Lomer et al. 2002).
Exogenous NPs were found in macrophages accumulated in the lymphoid tissue of the human gut,
the lymphoid aggregates being the earliest sign of lesions in Crohn's disease (Lomer et al. 2002).
Microscopy studies showed that macrophages located in lymphoid tissue uptake NPs of spherical
anatase (TiO
2
) with sizes ranging between 100 and 200 nm from food additives, 100 and 400 nm
aluminosilicates typical of natural clay, and 100 and 700 nm environmental silicates with various
morphologies (Powell et al. 1996). A diet low in exogenous particles seems to alleviate the symp-
toms of Crohn's disease (Lomer et al. 2002). This analysis is still controversial, with some propos-
ing that an abnormal response to dietary NPs may be the cause of this disease and not an excess
intake (Lomer et al. 2004). More precisely, some members of the population may have a genetic
predisposition where they are more affected by the intake of NPs and, therefore, develop Crohn's
disease (Oberdörster 2004).
Some evidence suggests that dietary NPs may exacerbate inflammation in Crohn's disease
(Lomer et al. 2004). These studies measured the intake of dietary particles, but did not analyze the
levels of indoor and outdoor NP pollution at the subjects' residences. As was described previously,
significant quantities of NPs are cleared by the mucociliary escalator and subsequently swallowed,
ultimately reaching the GI tract.
13.2.5 t
reatMeNt
The diseases associated with the GI uptake of NPs (such as Crohn's disease and ulcerative colitis)
have no cure and often require surgical intervention. Treatments aim to keep the disease in remis-
sion and consist of anti-inflammatory drugs along with specially formulated liquid meals (Lomer
et al. 2002). If dietary NPs are conclusively shown to cause these chronic diseases, their use in foods
should be avoided or strictly regulated.
13.3 UPTAKE OF NPs THROUGH GI BARRIER
The GI barriers consist of cellular (epithelium) and acellular parts (dead cells, mucus). Permeation
through the GI barrier has been shown for micro- and NPs. NP absorption is estimated to be about
15-250 times higher than that of microparticles (Desai et al. 1996).
13.3.1 a
cellular
l
ayers
of
the
o
rogastroINtestINal
t
ract
Mucus represents an efficient acellular barrier for the entire GI tract, composed of the oral cavity,
esophagus, stomach, and the intestine. The composition of mucus is primarily based on mucin pro-
teins (highly glycosylated extracellular proteins with characteristic gel-forming properties), antisep-
tic proteins such as lysozyme, and other proteins, that is, lactoferrin, inorganic salts, and water. The
major functions of mucus are the protection and lubrication of the underlying tissue.
Saliva, which is produced by the salivary glands, is mainly composed of water (up to 99.5%),
proteins, inorganic salts, and mucins. The so-called mucus layer, constituting the acellular barrier
