Abstract
BackgroundNanosilver shows great promise for use in industrial, consumer or medical products because of its antimicrobial properties. However, the underlying mechanisms of the effects of silver nanoparticles on human cells are still controversial. Therefore, in the present study the influence of the chloride concentration and different serum content of culture media on the cytotoxic effects of nanosilver was systematically evaluated.ResultsOur results show that nanosilver toxicity was strongly affected by the composition of the culture media. The chloride concentration, as well as the carbon content affected the silver agglomeration and the complex formation. But also the dissolution of nanosilver and the availability of free silver ions (Ag+) were severely affected by the compositions of the culture media. Cells, only exposed to silver particles in suspension and dissolved silver complexes, did not show any effects under all conditions. Nanosilver agglomerates and silver complexes were not very soluble. Thus, cells growing on the bottom of the culture dishes were exposed to sedimented nanosilver agglomerates and precipitated silver complexes. Locally, the concentration of silver on the cell surface was very high, much higher compared the silver concentration in the bulk solution. The cytotoxic effects of nanosilver are therefore a combination of precipitated silver complexes and organic silver compounds rather than free silver ions.ConclusionsSilver coatings are used in health care products due to their bacteriostatic or antibacterial properties. The assessment of the toxicity of a certain compound is mostly done using in vitro assays. Therefore, cytotoxicity studies of nanosilver using human cell cultures have to be undertaken under well controlled and understood cultivations conditions in order to improve the compatibility of different studies. Especially when eukaryotic versus prokaryotic systems are compared for the evaluation of the use of nanosilver as antibacterial coatings for implants in order to prevent bacterial colonization.
Highlights
Nanosilver shows great promise for use in industrial, consumer or medical products because of its antimicrobial properties
The variety of protocols and media compositions is huge and the media vary in sodium chloride concentrations as well as protein content, which is mainly determined by the fetal calf serum (FCS) content, ranging from 0 to 10% or more
Our results show that nanosilver toxicity was strongly affected by the composition of the culture media
Summary
Nanosilver shows great promise for use in industrial, consumer or medical products because of its antimicrobial properties. The underlying mechanisms of the effects of silver nanoparticles on human cells are still controversial. In the present study the influence of the chloride concentration and different serum content of culture media on the cytotoxic effects of nanosilver was systematically evaluated. According to Singh et al [13] nanosilver is internalized by cells and, once internalized, silver ions are released and these may interact with cellular compounds such as nucleic acids, sulfhydryl groups of metabolic enzymes or sulfur-containing cell components [14, 15]. Comprehensive nanomaterial characterization and the precise composition of the environment in which the biological effects were assessed must be known prior to studying the underlying mechanisms of nanosilver toxicity. Independent of agglomeration, uncoated silver nanoparticles dissolve and release silver ions, which are highly reactive and bind strongly to electron donor groups and are thereby transformed into silver complexes with different bioavailability and toxicity [15, 18, 19]
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