Detecting cryptic epitopes created by nanoparticles.

As potential applications of nanotechnology and nanoparticles increase, so too does the likelihood of human exposure to nanoparticles. Because of their small size, nanoparticles are easily taken up into cells (by receptor-mediated endocytosis), whereupon they have essentially free access to all cellular compartments. Similarly to macroscopic biomaterial surfaces (that is, implants), nanoparticles become coated with a layer of adsorbed proteins immediately upon contact with physiological solutions (unless special efforts are taken to prevent this). The process of adsorption often results in conformational changes of the adsorbed protein, which may be affected by the larger curvature of nanoparticles compared with implant surfaces. Protein adsorption may result in the exposure at the surface of amino acid residues that are normally buried in the core of the native protein, which are recognized by the cells as "cryptic epitopes." These cryptic epitopes may trigger inappropriate cellular signaling events (as opposed to being rejected by the cells as foreign bodies). However, identification of such surface-exposed epitopes is nontrivial, and the molecular nature of the adsorbed proteins should be investigated using biological and physical science methods in parallel with systems biology studies of the induced alterations in cell signaling.