The longer the worse: a combined proteomic and targeted study of the long-term versus short-term effects of silver nanoparticles on macrophages†
Despite considerable research effort devoted to the study of the effects of silver nanoparticles on mammalian cells in recent years, data on the potential long term effects of this nanomaterial remain scarce, and centered on epithelial cells. The aim of this study was to explore the effects of silver nanoparticles on macrophages. To this end, RAW 264.7 murine macrophages were exposed to either 1 μg ml−1 silver nanoparticles for 20 days, i.e. a chronic exposure scheme, or to 20 μg ml−1 silver nanoparticles for 24 hours, i.e. an acute exposure scheme. A proteomic study was then conducted to study and compare the cellular responses to both exposure schemes. They proved to be essentially different, and stronger for the chronic exposure scheme. Targeted validation studies showed effects of chronic exposure to silver nanoparticles on detoxifying enzymes such as flavin reductase, which was increased, and on central metabolism enzymes such as triose phosphate isomerase, the activity of which decreased under chronic exposure to silver nanoparticles. Chronic exposure to silver nanoparticles also induced a decrease of reduced glutathione content, a decreased phagocytic activity and reduced macrophage responses to lipopolysaccharide, as exemplified by nitric oxide and interleukin 6 production. Overall, chronic exposure to silver nanoparticles induced stronger effects than acute exposure on macrophages in the metabolic (glutathione level, mitochondrial potential) and functional (phagocytosis, cytokine production) parameters tested.