Analyzing the Biological Entity of Nanomaterials - Safety of Nanomaterials along Their Lifecycle - page 78

are generally exploited to obtain meaningful quantities of BAL fluid from which
then the native surfactant can be laboriously isolated and purified. Performing BAL
means that a volume of saline buffer is instilled into the lungs and aspirated again
afterwards. Consequently, the thin surface film is disrupted and diluted when the
inner lung surfaces are lavaged, which not only causes dilution of the retrieved
material but also leads to formation of vesicular structures, and might alter its bio-
chemical composition, too. In addition, tissue damage may occur during the lavage
leading to leakage of tissue or serum proteins that are typically not found at all or
only at much lower concentrations in the lung lining fluid in vivo . Due to the dilution
of the lung lining fluid during lavage, it is impossible to assess the original volume
of the lung lining fluid and the original protein and lipid concentration taking also
into account that not all components might be recovered quantitatively. Therefore,
the material obtained from BAL, although derived from a biological source, should
be considered as a semiartificial system.
Due to the dilution occurring during the lavage, PS—a most important biological
matrix for nanomaterial-lung interactions—is only present in very low concentra-
tions in BAL fluid, making it necessary to isolate and concentrate PS to obtain useful
amounts and concentrations for studying bio-nano interaction with nanomaterials.
During the last 30-40 years, extensive research has been carried out in this field
to develop and improve treatment of acute respiratory distress syndrome (ARDS)
(Halliday 2008). PS has been purified and analyzed in the past from various spe-
cies and different isolation methodologies have been published, and even commer-
cial clinical surfactants are available. BAL fluid can be further purified from blood
contaminations (especially necessary when working with material from slaughter
processes) and concentrated using ultracentrifugation and density-gradient centrifu-
gation (Griese 1999). Native surfactant that has been purified and concentrated in
such a manner from BAL is the most complete model of PS that can be isolated
from the lungs, and contains physiological proportions of surfactant lipids, as well as
SP-A, -B, and -C (Bernhard et al. 2000). For this reason, purified native surfactant
has been regularly used as reference substance (Bernhard et al. 2000; Blanco et al.
2012). However, as native surfactant causes immunogenicity issues when applied to
treat acute respiratory distress syndrome (ARDS) (mostly due to residual proteins
resulting from inefficient purification and species incompatibilities), organic extrac-
tions of BAL fluid were performed to obtain semicomplex lipophilic extract surfac-
tants, which represent the majority of available clinical surfactants on the market
today. These products contain the lipophilic fraction of PS, that is, the surfactant
lipids plus the hydrophobic surfactant proteins B and C but lack the hydrophilic
surfactant proteins A and D. This material is biophysically active and functional
on the one hand, but with defined composition on the other hand. Therefore, they
are successfully used and are the products of first choice for surfactant replacement
therapy in clinical treatment of ARDS. There are several such clinical surfactants on
the market, which are standardized and quality controlled in terms of their produc-
tion process (e.g., Alveofact ® , Curosurf ® , Survanta ® , or Infasurf ® ). Due to their good
accessibility, clinical surfactants have often been used in recent studies as surfactant
models to investigate bio-nano interactions of nanomaterials in the lungs. However,
one should be aware of the fact that these products are organic extracts, which means