Antibacterial properties of silver nanoparticles as a root canal irrigant against Enterococcus faecalis biofilm and infected dentinal tubules

A one-step simple synthesis of silver colloid nanoparticles with controllable sizes is presented. In this synthesis, reduction of [Ag(NH(3))(2)](+) complex cation by four saccharides was performed. Four saccharides were used: two monosaccharides (glucose and galactose) and two disaccharides (maltose and lactose). The syntheses performed at various ammonia concentrations (0.005-0.20 mol L(-1)) and pH conditions (11.5-13.0) produced a wide range of particle sizes (25-450 nm) with narrow size distributions, especially at the lowest ammonia concentrations. The average size, size distribution, morphology, and structure of particles were determined by dynamic light scattering (DLS), transmission electron microscopy (TEM), and UV/Visible absorption spectrophotometry. The influence of the saccharide structure (monosacharides versus disaccharides) on the size of silver particles is briefly discussed. The reduction of [Ag(NH(3))(2)](+) by maltose produced silver particles with a narrow size distribution with an average size of 25 nm, which showed high antimicrobial and bactericidal activity against Gram-positive and Gram-negative bacteria, including highly multiresistant strains such as methicillin-resistant Staphylococcus aureus. Antibacterial activity of silver nanoparticles was found to be dependent on the size of silver particles. A very low concentration of silver (as low as 1.69 mug/mL Ag) gave antibacterial performance.

Nanotechnology is a most promising field for generating new applications in medicine. However, only few nanoproducts are currently in use for medical purposes. A most prominent nanoproduct is nanosilver. Nanosilver particles are generally smaller than 100nm and contain 20-15,000 silver atoms. At nanoscale, silver exhibits remarkably unusual physical, chemical and biological properties. Due to its strong antibacterial activity, nanosilver coatings are used on various textiles but as well as coatings on certain implants. Further, nanosilver is used for treatment of wounds and burns or as a contraceptive and marketed as a water disinfectant and room spray. Thus, use of nanosilver is becoming more and more widespread in medicine and related applications and due to increasing exposure toxicological and environmental issues need to be raised. In sharp contrast to the attention paid to new applications of nanosilver, few studies provide only scant insights into the interaction of nanosilver particle with the human body after entering via different portals. Biodistribution, organ accumulation, degradation, possible adverse effects and toxicity are only slowly recognized and this review is focusing on major questions associated with the increased medical use of nanosilver and related nanomaterials.

Cytotoxicity induced by silver nanoparticles (AgNPs) and the role that oxidative stress plays in this process were demonstrated in human hepatoma cells. Toxicity induced by silver (Ag(+)) ions was studied in parallel using AgNO(3) as the Ag(+) ion source. Using cation exchange treatment, we confirmed that the AgNP solution contained a negligible amount of free Ag(+) ions. Metal-responsive metallothionein 1b (MT1b) mRNA expression was not induced in AgNP-treated cells, while it was induced in AgNO(3)-treated cells. These results indicate that AgNP-treated cells have limited exposure to Ag(+) ions, despite the potential release of Ag(+) ions from AgNPs in cell culture. AgNPs agglomerated in the cytoplasm and nuclei of treated cells, and induced intracellular oxidative stress. AgNPs exhibited cytotoxicity with a potency comparable to that of Ag(+) ions in in vitro cytotoxicity assays. However, the toxicity of AgNPs was prevented by use of the antioxidant N-acetylcysteine, and AgNP-induced DNA damage was also prevented by N-acetylcysteine. AgNO(3) treatment induced oxidative stress-related glutathione peroxidase 1 (GPx1) and catalase expression to a greater extent than AgNP exposure, but treatment with AgNO(3) and AgNPs induced comparable superoxide dismutase 1 (SOD1) expression levels. Our findings suggest that AgNP cytotoxicity is primarily the result of oxidative stress and is independent of the toxicity of Ag(+) ions.