Characterization of blood protein adsorption on PM2.5 and its implications on cellular uptake and cytotoxicity of PM2.5.

In biological fluids, micro- or nano-size particles are prone to adsorb proteins and form a layer. The ambient air fine particulate matter (PM2.5) is inhaled via the lung, penetrates biological barriers and eventually reaches systemic blood circulation. However, there are very few data available regarding the adsorption of proteins on PM2.5. Here, we compared protein corona formed in plasma after bronchoalveolar lavage fluid (BALF) exposure with those formed in plasma alone. Using purified coronal proteins, we explored their adsorption behaviors on PM2.5 and their influence on biological reactivity of PM2.5. Liquid-chromatography tandem mass-spectrometry (LC-MS/MS) analysis revealed that exposure to BALF significantly changed the blood protein profile on PM2.5. Regardless of the presence of BALF, the protein corona on PM2.5 contained an abundance of serum albumin, hemoglobin (Hb) and fibrinogen (Fg) proteins. Using Fg as a corona surrogate, we found that van der Waals interactions, hydrophobic interactions, π-π stacking and electrostatic attractions contributed to the Fg adsorption and led to the conformational changes of Fg. In addition, Fg decoration decreased cellular internalization of PM2.5 and corresponding subsequent oxidative stress responses in a murine RAW264.7 macrophage. These results support the view that the formation of PM2.5 corona should be considered for toxicity assessment of PM2.5.