Interactions between nanoparticles and lung surfactant investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry: Interactions between nanoparticles and lung surfactants

Rationale Inhaled nanoparticles may cause adverse effects due to inactivation of lung surfactants. We have studied how three different nanoparticles interact with dipalmitoyl-phosphatidylcholine (DPPC), the main component in lung surfactant. Methods DPPC in solution was mixed with a suspension of nanoparticles, both in organic solvent, and allowed to interact for 40 min under conditions partly resembling the alveolar lining. Nanoparticles were isolated by centrifugation, washed, and re-suspended in ethanol/water 1:1 (v/v). The resulting solution was analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) using dihydroxybenzoic acid as matrix. Results The developed methodology was successfully applied for quantitative detection of phospholipid lung surfactant bound to three different types of nanoparticles. Titanium dioxide nanoparticles had a strong affinity for binding of lipid lung surfactant in contrast to pristine and methylated silica nanoparticles. When the concentration of lipid surfactant was raised in the reaction mixture, the titanium dioxide nanoparticles showed an apparently non-linear binding process. Conclusions This work demonstrates that MALDI-TOFMS can be used for direct determination of the binding of surfactant lipids to nanoparticles and represents an important initial step towards a simple and quantitative in vitro method for assessment of interactions of nanoparticles with lung surfactants.