Studies on biocompatibility and interaction of silver nanoparticles on human mesenchymal stem cells (hMSCs)

Abstract

Silver nanoparticles (Ag-NPs) are extensively used in different areas including clothing or food industry. In particular, silver has been used in a range of medical settings such as coatings of medical devices due to well-known long-lasting antimicrobial properties. Silver ions exert antimicrobial effects after binding to a variety of microbial molecules such as DNA, cell wall components or membrane proteins. Despite the widespread use of nanosilver there is a serious lack of information on the biological effects of nanosilver on human tissue cells.

It was the purpose of this study to analyze the influence of Ag−NPs on biological functions (proliferation, cytokine release and chemotaxis) of human mesenchymal stem cells (hMSCs). Silver nanoparticles were prepared by the polyol process, i.e. by the reduction of silver nitrate with ethylene glycol in the presence of polyvinylpyrrolidone, PVP. Thereby, the silver nanoparticles were colloidally stabilized by the polymer. hMSCs were incubated with or without PVP-functionalized Ag-NPs (diameter about 100 nm, concentrations 50 ng mL⁻¹ −50 μg mL⁻¹) up to 7 days using cell culture conditions. In addition, control experiments with dissolved silver ions (diluted silver acetate) were performed to separate particle and ion effects. Cell viability was determined after calcein-AM/propidium iodine staining. Chemotaxis of hMSC was quantitated after membrane transmigration and subsequent cell staining. Cell proliferation was analyzed using AlamarBlue-assay. Cytokines were determined by ELISA technique and particle agglomeration was analyzed by the Eye Tech-Particle-Analyzer (Ankersmid, Netherlands).

A concentration-dependent activation of hMSCs was observed at nanosilver levels of 2.5 μg mL⁻¹, cytotosic cell reactions occurred at Ag-NPs concentrations above 5 μg mL⁻¹. Cell proliferation and the chemotactic response of hMSC decreased in parallel with increasing nanosilver concentrations. In the presence of Ag−NPs/Ag-ions different effects on cytokine release from hMSCs were observed. At high but non-cytotoxic concentrations of Ag-NPs (2.5 μg mL⁻¹) the release of IL-8 was significantly increased, in contrast, the levels of IL-6 and VEGF were decreased compared to the control. The synthesis of IL-11 was not affected in the presence of silver. The agglomeration of Ag-NPs in different biological media increased after prolonged incubation periods (7 days).

These data clearly show that Ag-NPs exert cytotoxic effects on hMSCs at high concentrations but also induced cell activation (as analyzed by IL-8 release) at sublethal concentrations of Ag−NPs.