title: Is the toxic potential of nanosilver dependent on its size?
abstract: BACKGROUND
  Nanosilver is one of the most commonly used engineered nanomaterials (ENMs). In our study we focused on assessing the size-dependence of the toxicity of nanosilver (Ag ENMs), utilising materials of three sizes (50, 80 and 200 nm) synthesized by the same method, with the same chemical composition, charge and coating.
  
  
  METHODS
  Uptake and localisation (by Transmission Electron Microscopy), cell proliferation (Relative growth activity) and cytotoxic effects (Plating efficiency), inflammatory response (induction of IL-8 and MCP-1 by Enzyme linked immune sorbent assay), DNA damage (strand breaks and oxidised DNA lesions by the Comet assay) were all assessed in human lung carcinoma epithelial cells (A549), and the mutagenic potential of ENMs (Mammalian hprt gene mutation test) was assessed in V79-4 cells as per the OECD protocol. Detailed physico-chemical characterization of the ENMs was performed in water and in biological media as a prerequisite to assessment of their impacts on cells. To study the relationship between the surface area of the ENMs and the number of ENMs with the biological response observed, Ag ENMs concentrations were recalculated from μg/cm2 to ENMs cm2/cm2 and ENMs/cm2.
  
  
  RESULTS
  Studied Ag ENMs are cytotoxic and cytostatic, and induced strand breaks, DNA oxidation, inflammation and gene mutations. Results expressed in mass unit [μg/cm2] suggested that the toxicity of Ag ENMs is size dependent with 50 nm being most toxic. However, re-calculation of Ag ENMs concentrations from mass unit to surface area and number of ENMs per cm2 highlighted that 200 nm Ag ENMs, are the most toxic. Results from hprt gene mutation assay showed that Ag ENMs 200 nm are the most mutagenic irrespective of the concentration unit expressed.
  
  
  CONCLUSIONS
  We found that the toxicity of Ag ENMs is not always size dependent. Strong cytotoxic and genotoxic effects were observed in cells exposed to Ag ENMs 50 nm, but Ag ENMs 200 nm had the most mutagenic potential. Additionally, we showed that expression of concentrations of ENMs in mass units is not representative. Number of ENMs or surface area of ENMs (per cm2) seem more precise units with which to compare the toxicity of different ENMs.
authors.forename: Anna
authors.initials: A
authors.lastname: Huk
authors.forename: Emilia
authors.initials: E
authors.lastname: Izak-Nau
authors.forename: Bogumila
authors.initials: B
authors.lastname: Reidy
authors.forename: Matthew
authors.initials: M
authors.lastname: Boyles
authors.forename: Albert
authors.initials: A
authors.lastname: Duschl
authors.forename: Iseult
authors.initials: I
authors.lastname: Lynch
authors.forename: Maria
authors.initials: M
authors.lastname: Dušinska
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D048430:Cell Shape / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D018932:Chemokine CCL2 / Q000378:metabolism; D006224:Cricetinae; D004249:DNA Damage; D004305:Dose-Response Relationship, Drug; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D016209:Interleukin-8 / Q000378:metabolism; D008168:Lung / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D053768:Metal Nanoparticles / Q000737:chemistry / Q000633:toxicity*; D009154:Mutation; D018384:Oxidative Stress / Q000187:drug effects; D010316:Particle Size; D018570:Risk Assessment; D012834:Silver / Q000737:chemistry / Q000378:metabolism / Q000633:toxicity*; D013499:Surface Properties; D013997:Time Factors
chemical_list: C111835:CCL2 protein, human; C508606:CXCL8 protein, human; D018932:Chemokine CCL2; D018836:Inflammation Mediators; D016209:Interleukin-8; D012834:Silver