PEGylation of ORMOSIL nanoparticles differently modulates the in vitro toxicity toward human lung cells

ORganically MOdified SILica (ORMOSIL) nanoparticles (NPs) appear promising carriers for the delivery of drugs to target tissues and cells but some concerns on possible cytotoxic effects still exist. We therefore studied the in vitro responses to ORMOSIL NPs in different types of human lung cells (i.e. CCD-34Lu normal fibroblasts, carcinoma alveolar type II A549 cells, NCI-H2347 adenocarcinoma cells) to determine the effects of polyethylene glycol (PEG) coating on NP cytotoxicity. Our results show that non-PEG NPs caused a concentration-dependent decrease of viability of all types of cells. On the contrary, PEG-coated NPs increased plasma membrane permeability and induced cell death only in carcinoma alveolar type II A549 cells, while did not produce deleterious effects on CCD-34Lu and NCI-H2347 cells. PEG-coated NPs promoted the formation of reactive oxygen species (ROS) in A549 and CCD-34Lu cells; nevertheless, the decrease of ROS levels in the presence of superoxide dismutase and catalase did not protect A549 cells from death, suggesting that the oxidative stress was not the main determinant of cytotoxicity. Analysis of gene expression in A549 cells exposed to PEG-coated NPs showed alterations in genes involved in inflammation, signal transduction and cell death, while the transcriptional response was not significantly affected in CCD-34Lu fibroblasts. Our transmission electron microscopy analysis evidenced a unique intracellular localization of PEG NPs in the lamellar bodies of A549 cells, which could be the most relevant factor leading to cytotoxicity by reducing the production of surfactant proteins and by interfering with the pulmonary surfactant system. Gene expression signature was defined in A549 and CCD-34Lu controls and treated cells, incubated with PEGylated ORMOSIL nanoparticles. Three replicates for each single sample were performed for both untreated and NP-treated A549 and CCD-34Lu cells at the end of each incubation time (24 h; 24+24h). The level of each transcript was represented as Log2.