gms | German Medical Science

Questionnaire: Silver nanoparticles (Ag-NP) are increasingly used in biomedical applications due to their remarkable antimicrobial activity. In biomedicine, Ag-NP are used as coatings or embedded into wound dressings, surgical instruments, and bone substitute biomaterials, such as silver-containing calcium phosphate cements. Ag-NP will be released after resorption of a biomaterial or from coatings and then may come into close contact with blood cells. Despite the widespread use of Ag-NP, there is a serious lack of information on the biological effects of Ag-NP on human blood cells. Therefore, we investigated the biological effects of Ag-NP at non-toxic concentrations on human peripheral blood mononuclear cells (PBMC). PBMC mainly consist of lymphocytes (e.g. T-cells) and monocytes. In this study the uptake of Ag-NP by monocytes and lymphocytes was analyzed, and the influence of nanosilver on cell-biological functions (proliferation, expression of adhesion molecules, cytokine release and generation of reactive oxygen species) was studied.

Methods: PVP-coated Ag-NP (spherical, Ø<75 nm) were synthesized by reduction with glucose. PBMC were isolated by a single step procedure based on a discontinuous double Ficoll-gradient. Freshly isolated cells were cultured at 37 °C for 24 h in the presence or absence of different concentrations of Ag-NP or silver ions to separate the particle and ion effect. Silver treated PBMC were analyzed for the particle uptake by using phase-contrast microscopy, flow cytometry and FIB/SEM. The generation of reactive oxygen species from silver-treated PBMC was measured by the oxidant-sensitive dye DCFH-DA. The cytokine release (IL-1ra, IL-6, IL-8 and TNF-a) of silver-treated PBMC was quantified by ELISA. For analyzing the expression of adhesion molecules different fluorochrome-labeled antibodies were used.

Results and Conclusions: We have shown that the uptake rate of Ag-NP and the cell activation after exposure of silver is a cell type-dependent process. Whereas, agglomerates of Ag-NP were detected within the cytoplasm of monocytes no agglomerated silver was found in T-cells. Obviously, only monocytes which have taken up Ag-NP showed a modulation of different biological function in contrast to lymphocytes. Thereby, a concentration-dependent activation (e.g. an increased expression of the adhesion molecule CD54) and generation of reactive oxygen species of monocytes at sub-toxic Ag-NP concentrations were observed. No modulation of T-cell-proliferation and activation was observed in the presence of Ag-NP. However when dissolved silver ions were used, T-cells were activated as well.

In conclusion our findings demonstrate the cell-type dependent cellular response of leukocytes towards silver and shows that cells which are able to accumulate nanosilver are activated by ROS-driven signal transduction mechanisms. Thereby, silver ions are very likely to act as the reactive silver species, because in the presence of silver ions T-cells were activated as well.