g., body fluids) onto their surface. The adsorption process is influenced by surface energy, surface charge and the affinity to specific biomolecules. Hydrophilic silica can effectively adsorb high-molecular proteins of synthetic and natural origin. Dutta and co-workers showed that the protein adsorption profiles for 50–1000-nm amorphous silica particles were comparable ( Dutta et al., 2007). Silica particles may also adsorb bronchoalveolar lining fluid components, including

lung surfactant and proteins, such as the surfactant protein D (SP-D) ( Hamilton et al., 2008). Hence, before inhaled silica particles come into contact with alveolar macrophages, lung surfactant composed of phospholipids and surfactant Gemcitabine clinical trial proteins (SP) could potentially coat the outer surface of the silica particles modifying the surface chemistry and ultimately influence the toxicity ( Hamilton et al., 2008). A high specific surface area may promote the adsorption of

Epacadostat cost peptides and proteins contained in the alveolar lining fluid. Though agglomerated and aggregated particles in the μm range might theoretically be broken down to the size of the primary nanoparticle within the body, research results show the robustness of aggregates and agglomerates to disaggregation, even in the context of high-energy processing (Maier et al., 2006). The denaturation of cell membrane proteins by proton-donating silanol groups is the major underlying mechanism for membrane damage. Pandurangi et al. (1990) found a strong correlation between surface silanol groups (Si O H) and the haemolytic activity of amorphous silica and suggested that the surface hydrogen of silica bonds to protein components of the membrane and subsequently abstracts these proteins from the membrane. The haemolytic activity is highly specific for silanol and seems to depend only on the concentration Protein kinase N1 of negatively charged silanol groups that are accessible by the cell membranes of erythrocytes (Slowing et al., 2009). A strong distortion of the membrane

after interaction with silica particles can lead to loss of membrane flexibility and resiliency as well as the release of haemoglobin (haemolysis). The agglutination of erythrocytes can be enhanced due to interaction with aggregates of SAS particles which prevent the electrostatic repulsive interaction of negatively charged cells due to the strong interaction of SAS particles with proteins integrated into the cell membranes (Chuiko, 2003). In contrast, the haemolytic potential of hydrophobic silica particles with a siloxane surface structure is low. Translocation of particles into cells is dependent on interactions with the cell membrane, i.e., processes of endocytosis (mainly pinocytosis and phagocytosis or receptor-mediated endocytosis).