title: Evaluation of silver nanoparticle toxicity in skin in vivo and keratinocytes in vitro.
abstract: BACKGROUND
  Products using the antimicrobial properties of silver nanoparticles (Ag-nps) may be found in health and consumer products that routinely contact skin.
  
  
  OBJECTIVE
  This study was designed to assess the potential cytotoxicity of Ag-nps in human epidermal keratinocytes (HEKs) and their inflammatory and penetrating potential into porcine skin in vivo.
  
  
  METHODS
  We used eight different Ag-nps in this study [unwashed/uncoated (20, 50, and 80 nm particle diameter), washed/uncoated (20, 50, and 80 nm), and carbon-coated (25 and 35 nm)]. Skin was dosed topically for 14 consecutive days. HEK viability was assessed by MTT, alamarBlue (aB), and CellTiter 96 AQueous One (96AQ). Release of the proinflammatory mediators interleukin (IL)-1beta, IL-6, IL-8, IL-10, and tumor necrosis factor-alpha (TNF-alpha) were measured.
  
  
  RESULTS
  The effect of the unwashed Ag-nps on HEK viability after a 24-hr exposure indicated a significant dose-dependent decrease (p < 0.05) at 0.34 microg/mL with aB and 96AQ and at 1.7 microg/mL with MTT. However, both the washed Ag-nps and carbon-coated Ag-nps showed no significant decrease in viability at any concentration assessed by any of the three assays. For each of the unwashed Ag-nps, we noted a significant increase (p < 0.05) in IL-1beta, IL-6, IL-8, and TNF-alpha concentrations. We observed localization of all Ag-nps in cytoplasmic vacuoles of HEKs. Macroscopic observations showed no gross irritation in porcine skin, whereas microscopic and ultrastructural observations showed areas of focal inflammation and localization of Ag-nps on the surface and in the upper stratum corneum layers of the skin.
  
  
  CONCLUSIONS
  This study provides a better understanding Ag-nps safety in vitro as well as in vivo and a basis for occupational and risk assessment. Ag-nps are nontoxic when dosed in washed Ag-nps solutions or carbon coated.
authors.affiliation: Center for Chemical Toxicology Research and Pharmacokinetics, North Carolina State University, Raleigh, North Carolina, USA.
authors.forename: Meghan E
authors.initials: ME
authors.lastname: Samberg
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Oldenburg
authors.forename: Nancy A
authors.initials: NA
authors.lastname: Monteiro-Riviere
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005069:Evaluation Studies as Topic; D006801:Humans; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D007378:Interleukins / Q000378:metabolism; D015603:Keratinocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D053768:Metal Nanoparticles / Q000008:administration & dosage / Q000633:toxicity*; D010316:Particle Size; D012834:Silver / Q000008:administration & dosage / Q000633:toxicity*; D012867:Skin / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D013552:Swine; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D007378:Interleukins; D014409:Tumor Necrosis Factor-alpha; D012834:Silver