Analyzing the Biological Entity of Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 69

4.2 NANOMATERIAL INTERACTIONS WITH SERUM OR

SERUM-CONTAINING CELL CULTURE MEDIUM

4.2.1 P hysiologiCal C onsiderations
Blood is most likely the route via which nanomaterials are intentionally adminis-
tered, either for therapeutic purposes (e.g., imaging or cancer treatment) in humans
or as part of a toxicological study in animals. In the case of unintentional exposure,
nanomaterials will most likely not directly interact with the blood circuit, leaving
aside of course skin injuries that would allow a direct systemic access. In uninten-
tional exposure scenarios, nanomaterials will first need to pass body barriers such as
lungs or GIT to secondarily interact with the blood. In all scenarios, blood then may
facilitate distribution of nanomaterials throughout the body. When nanoparticles
pass from one body compartment into another, the composition of the corona evolves
(Dell'Orco et al. 2010; Lundqvist et al. 2011), meaning a significant or even major
part of the corona will be exchanged as the nanomaterials encounter a different envi-
ronment. However, a fingerprint of the earlier surroundings is always retained.
Analysis of nanomaterial interaction with blood is not trivial as blood is a highly
complex body fluid. Blood plasma accounts for about 55% of the volume of human
blood and the remaining part is composed of various cells (erythrocytes > leuko-
cytes > thrombocytes). The blood plasma is an aqueous solution containing approxi-
mately 300 different proteins, and if taking into account the rich posttranslational
modifications, it contains more than 3700 protein species as well as other biomole-
cules like amino acids, fatty acids, glucose, other metabolites, hormones, or vitamins
(Anderson and Anderson 2002; Pieper et al. 2003; Klein 2007). Plasma proteins
display a huge dynamic range, which covers approximately 10 orders of magnitude.
A few highly abundant proteins such as albumin, transferrin, or immunoglobulins
account for 50% of the total protein content. The most abundant protein is albu-
min, which has a physiological concentration of 35-50 mg/ml (35-50 × 10 9 pg/ml).
In contrast, there are many low abundant proteins such as interleukin 6, which is
typically present in the concentration of 0-5 pg/ml. In addition to “classical plasma
proteins,” plasma contains many other proteins such as different tissue proteins
(“leakage markers”), foreign proteins (resulting from microorganisms or parasites
occurring during infections), or aberrantly secreted proteins (e.g., tumor markers)
(Anderson and Anderson 2002).
One major obstacle in serum analysis is the high dynamic range. Thus, without any
additional approaches, for example, depleting highly abundant components, it will not
be possible to analyze the full complexity of serum proteins and one will only detect
and characterize the most abundant species interacting with nanoparticles or those
that are highly enriched on the surface. Others, which may be present in tiny amounts
on the surface only, may be “masked” due to high abundance of a few other proteins
and thus they will not be detected although they may be functionally relevant and
important as well. For instance, with a typical 2D approach it is possible to resolve
only 3-4 orders of magnitude but not 10 as naturally occurring in plasma. As albumin
is by far the most abundant serum protein it is not astonishing that it is often the most
abundant component of nanoparticle biomolecule corona (Tenzer et al. 2011).