Nanoparticles attenuate P-glycoprotein/MDR1 function in A549 human alveolar epithelial cells.

P-glycoprotein/MDR1 (P-gp) is a well-characterised membrane transporter relevant in drug disposition and multi-drug resistance. In this study, we aimed to investigate how far nanoparticulates impair the function of the P-gp transport system and which particle properties govern these interactions. Expression and function of P-gp was confirmed in A549 cell monolayers. Rhodamine 123 (Rh123) release studies were carried out in the presence of known inhibitors of P-gp function (i.e., cyclosporine A and verapamil), under ATP depletion (NaN(3)/DOG) and after acute exposure to nanoparticles (NPs) with different surface modifications, ζ-potentials and sizes (plain, carboxylated, and amine- and sulphate-modified). The cytotoxic potential of NPs on A549 monolayers was evaluated by MTT assay. The effects on P-gp protein level, after incubation with NPs, were investigated by Western blot analysis of A549 cell lysate and supernatant. Cellular retention of Rh123 was significantly (P<0.05) increased in the presence of carboxylated (100 nm), amine- and sulphate-modified NPs. A slight, but not significant, decrease in Rh123 release was also observed for plain latex and carboxylated (500 nm) NPs. The MTT assay demonstrated that most NPs caused only marginal levels of cytotoxicity (78-88% cell viability); the positively charged amine-NPs, however, were considerably more cytotoxic. Western blot showed that NPs did not cause any cell membrane disruption. Our findings suggest that nanomaterials can attenuate membrane transporter function depending on their size and surface properties and hence might influence the disposition of xenobiotics as well as endogenous substrates.