Analyzing the Biological Entity of Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 84

Via oral ingestion humans may be exposed to several types of nanoparticles.
Endogenous particles, being micro- and nano-sized, do occur naturally in food.
Typically they may either be composed of inorganic salts such as calcium and phos-
phate or may contain food compounds such lipid vesicles or protein aggregates.
Exogenous particles may be present in food as some particles are used as food addi-
tives such as TiO 2 or SiO 2 . Such additives are typically microscaled but due to the
large size distribution they always will contain a nanoscaled fraction. In addition
one also needs to consider migration of nanoparticles for instance from food pack-
aging materials. Similar to the formation of endogenous nanoparticles containing
calcium phosphate (naturally occurring), nanoparticles may form in vivo also from
other inorganic species such as ionic silver as shown in a recent study by van der
Zande and coworkers (van der Zande et al. 2012). In this study the authors applied
silver nanoparticles and also ionic silver in a 28d oral study. Dissection was per-
formed either on day 29 or 1 or 8 weeks after last application. Interestingly at day 29
the authors could show the presence of silver containing nanoparticles in the GIT
as well as in several organs (e.g., liver, spleen, and lung) not only in the nanosilver
treated groups but also in the ionic silver treated group using Single Nanoparticle
ICP-MS, although these particles were completely missing in control animals. This
demonstrates that within the GIT, nanoparticles may be formed from various ions
(endogenous or exogenous) when present in food. On the other hand, nanoparticles
that may be present in food could be dissolved in gastric juices and be reformed
again later on inside or outside GIT as several other studies suggest (Peters et al.
2012; Liu et al. 2012).
In recent years there is increasing evidence that human exposure to nano- or mic-
roparticles influences clinical manifestation of certain diseases. For instance Crohn's
disease seems to be influenced by a combination of genetic predisposition and envi-
ronmental factors. It has been hypothesized that microsized particles (100-1000 nm)
might be associated with the development of this disease. Those particles might be
endogenous (e.g., composed of calcium and phosphate) or exogenous (e.g., food addi-
tives like TiO 2 ) in origin. In a study performed by Lomer and colleagues, micro-TiO 2
and aluminosilicate accumulated in human gut associated lymphoid tissue—the tis-
sue that is first affected in Crohn's disease (Lomer, Thompson, and Powell 2007).
A diet low in endogenous and exogenous particles was then found to alleviate the
disease symptoms.
4.4.2 a vailaBle m odels
Of course it is not straightforward to purify original gastric juices from animal
sources in the same way as this might be more or less achievable with lung flu-
ids. But there are different types of simulants available that have already been used
successfully to study nanoparticle behavior and that quite well mimic what might
occur during passage of the nanoparticle through the GIT. The study performed by
Peters and co-workers is a very good example, where such gastric fluid simulants
were successfully used to characterize silica nanoparticle (Peters et al. 2012). In
this study, the authors analyzed different types of food matrices with and without
adding silica nanoparticles. They first dispersed the food matrix with and without