title: Silica nanoparticle uptake induces survival mechanism in A549 cells by the activation of autophagy but not apoptosis.
abstract: We report here an in vitro evaluation of silica nanoparticle uptake by lung epithelial cells (A549), the cytotoxic effect of the particles and we propose autophagy as possible survival strategy. The effect of surface charge, serum proteins and the influence of inhibitors on the uptake of 20 nm monodispersed nanoparticles with various functional groups are discussed. Uptake rate of the particles with various functional groups is demonstrated to be similar in the presence of serum proteins, while the uptake rate ranking is COOH>NH2>OH under serum free conditions. Our results suggest an actin-dependent, macropinocytotic uptake process that was also confirmed by scanning and transmission electron microscopy. In spite of the intensive active uptake, significant cytotoxic effect is detected only at relatively high concentrations (above 250 μg/mL). Blebbing of the cell surface is observed already at 5h of exposure and is shown to be related to autophagy rather than apoptotic cell death. The A549 cells display elevated levels of autophagosomes, however they do not express typical apoptosis markers such as increased amount of active caspase-3 and release of mitochondrial cytochrome C. Based on these results, we propose here an autophagic activity and cross-talk between autophagic and apoptotic pathways as a mechanism allowing the survival of A549 cells under exposure to silica nanoparticles.
authors.affiliation: Nanobiosciences Unit, Institute of Health and Consumer Protection, Joint Research Centre, Via Fermi 2749, 21027 Ispra, Italy.
authors.forename: Jakub Stanislaw
authors.initials: JS
authors.lastname: Nowak
authors.forename: Dora
authors.initials: D
authors.lastname: Mehn
authors.forename: Paola
authors.initials: P
authors.lastname: Nativo
authors.forename: César Pascual
authors.initials: CP
authors.lastname: García
authors.forename: Sabrina
authors.initials: S
authors.lastname: Gioria
authors.forename: Isaac
authors.initials: I
authors.lastname: Ojea-Jiménez
authors.forename: Douglas
authors.initials: D
authors.lastname: Gilliland
authors.forename: François
authors.initials: F
authors.lastname: Rossi
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D001343:Autophagy / Q000187:drug effects*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D006801:Humans; D053758:Nanoparticles / Q000633:toxicity*; D012822:Silicon Dioxide / Q000493:pharmacokinetics / Q000633:toxicity*
chemical_list: D012822:Silicon Dioxide
keywords: A549; Autophagy; Cytotoxicity; Nanoparticle; Silica