title: Synthesis, characterization, and bioactivity of carboxylic acid-functionalized titanium dioxide nanobelts.
abstract: BACKGROUND
  Surface modification strategies to reduce engineered nanomaterial (ENM) bioactivity have been used successfully in carbon nanotubes. This study examined the toxicity and inflammatory potential for two surface modifications (humic acid and carboxylation) on titanium nanobelts (TNB).
  
  
  METHODS
  The in vitro exposure models include C57BL/6 alveolar macrophages (AM) and transformed human THP-1 cells exposed to TNB for 24 hrs in culture. Cell death and NLRP3 inflammasome activation (IL-1β release) were monitored. Short term (4 and 24 hr) in vivo studies in C57BL/6, BALB/c and IL-1R null mice evaluated inflammation and cytokine release, and cytokine release from ex vivo cultured AM.
  
  
  RESULTS
  Both in vitro cell models suggest that the humic acid modification does not significantly affect TNB bioactivity, while carboxylation reduced both toxicity and NLRP3 inflammasome activation. In addition, short term in vivo exposures in both C57BL/6 and IL-1R null mouse strains demonstrated decreased markers of inflammation, supporting the in vitro finding that carboxylation is effective in reducing bioactivity. TNB instillations in IL-1R null mice demonstrated the critical role of IL-1β in initiation of TNB-induced lung inflammation. Neutrophils were completely absent in the lungs of IL-1R null mice instilled with TNB for 24 hrs. However, the cytokine content of the IL-1R null mice lung lavage samples indicated that other inflammatory agents, IL-6 and TNF-α were constitutively elevated indicating a potential compensatory inflammatory mechanism in the absence of IL-1 receptors.
  
  
  CONCLUSIONS
  Taken together, the data suggests that carboxylation, but not humic acid modification of TNB reduces, but does not totally eliminate bioactivity of TNB, which is consistent with previous studies of other long aspect ratio nanomaterials such as carbon nanotubes.
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Hamilton
authors.forename: Nianqiang
authors.initials: N
authors.lastname: Wu
authors.forename: Chengcheng
authors.initials: C
authors.lastname: Xiang
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.forename: Feng
authors.initials: F
authors.lastname: Yang
authors.forename: Michael
authors.initials: M
authors.lastname: Wolfarth
authors.forename: Dale W
authors.initials: DW
authors.lastname: Porter
authors.affiliation: Center for Environmental Health Sciences, Department of Biomedical and Pharmaceutical Sciences, University of Montana, Missoula, 59812, MT, USA. andrij.holian@umontana.edu.
authors.forename: Andrij
authors.initials: A
authors.lastname: Holian
mesh_terms: D000818:Animals; D002264:Carboxylic Acids / Q000138:chemical synthesis* / Q000633:toxicity*; D002352:Carrier Proteins / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006801:Humans; D058847:Inflammasomes / Q000187:drug effects / Q000378:metabolism; D007249:Inflammation / Q000139:chemically induced / Q000276:immunology / Q000378:metabolism; D018836:Inflammation Mediators / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D016676:Macrophages, Alveolar / Q000187:drug effects / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D053758:Nanoparticles / Q000737:chemistry* / Q000633:toxicity*; D017472:Receptors, Interleukin-1 / Q000172:deficiency / Q000235:genetics; D013499:Surface Properties; D013997:Time Factors; D014025:Titanium / Q000737:chemistry* / Q000633:toxicity*
chemical_list: D002264:Carboxylic Acids; D002352:Carrier Proteins; C508585:IL1B protein, human; C587672:IL1B protein, mouse; D058847:Inflammasomes; D018836:Inflammation Mediators; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C453881:NLRP3 protein, human; C492716:Nlrp3 protein, mouse; D017472:Receptors, Interleukin-1; C009495:titanium dioxide; D014025:Titanium