Tiopronin monolayer-protected silver nanoparticles modulate IL-6 secretion mediated by Toll-like receptor ligands.
OBJECTIVE
Capped silver nanoparticles that can be coupled to a variety of molecules and biomolecules are of great interest owing to their potential applications in biomedicine. However, there are no data about their toxicity or functional effects on a key innate immune response, such as IL-6 secretion, after the engagement of the main group of pathogen-associated molecular patterns receptors, that is, the Toll-like receptors (TLRs).


METHODS
N-(2-mercaptopropionyl)glycine (tiopronin)-capped silver (Ag@tiopronin) nanoparticles of a narrow sized distribution ( approximately 5 nm) were synthesized and characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, Raman, (1)H-NMR and total correlation spectroscopy. Cytotoxicity was determined by lactate deshidrogenase and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium assays in Raw 264.7 macrophages. IL-6 was measured by ELISA.


CONCLUSIONS
Ag@tiopronin nanoparticles have a narrow size distribution ( approximately 5 nm), high solubility and stability in aqueous environment with no cytotoxicity in terms of mitochondrial function or plasma-membrane integrity at concentrations as high as 200 microg/10(6) cells. Ag@tiopronin nanoparticles were not proinflammatory agents, but remarkably they specifically impaired the IL-6 secretion mediated by TLR2, TLR2/6, TLR3 or TLR9 stimulation in co-treatment experiments. However, in pretreatment experiments, nanoparticles enhanced the susceptibility of macrophages to inflammatory stimulation mediated by TLR2/1 and TLR2/6 specific ligands while severely impairing the IL-6 secretion activated by the TLR3 or TLR9 ligands.


CONCLUSIONS
Contrary to what is found for bare silver nanoparticles, Ag@tiopronin nanoparticles are noncytotoxic to macrophages. Ag@tiopronin nanoparticles showed differential effects on TLR signaling of a high degree of specificity, without proinflammatory effects by themselves. These effects have to be borne in mind when using bioconjugates of Ag@tiopronin nanoparticles for future medical applications.
Department of Physical, Chemical & Natural Systems, Pablo de Olavide University, Seville, Spain.
Paula M
PM
Castillo
Juan L
JL
Herrera
Rafael
R
Fernandez-Montesinos
Carlos
C
Caro
Ana P
AP
Zaderenko
Jose A
JA
Mejías
David
D
Pozo
D000818:Animals; D002460:Cell Line; D015850:Interleukin-6 / Q000378:metabolism*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles / Q000737:chemistry / Q000648:ultrastructure; D012834:Silver / Q000737:chemistry / Q000494:pharmacology*; D017550:Spectroscopy, Fourier Transform Infrared; D008625:Tiopronin / Q000494:pharmacology*; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D051196:Toll-Like Receptor 3 / Q000378:metabolism; D051217:Toll-Like Receptor 9 / Q000378:metabolism; D051193:Toll-Like Receptors / Q000378:metabolism*
D015850:Interleukin-6; D051195:Toll-Like Receptor 2; D051196:Toll-Like Receptor 3; D051217:Toll-Like Receptor 9; D051193:Toll-Like Receptors; D012834:Silver; D008625:Tiopronin