title: Promotion of lung adenocarcinoma following inhalation exposure to multi-walled carbon nanotubes.
abstract: BACKGROUND
  Engineered carbon nanotubes are currently used in many consumer and industrial products such as paints, sunscreens, cosmetics, toiletries, electronic processes and industrial lubricants. Carbon nanotubes are among the more widely used nanoparticles and come in two major commercial forms, single-walled carbon nanotubes (SWCNT) and the more rigid, multi-walled carbon nanotubes (MWCNT). The low density and small size of these particles makes respiratory exposures likely. Many of the potential health hazards have not been investigated, including their potential for carcinogenicity. We, therefore, utilized a two stage initiation/promotion protocol to determine whether inhaled MWCNT act as a complete carcinogen and/or promote the growth of cells with existing DNA damage. Six week old, male, B6C3F1 mice received a single intraperitoneal (ip) injection of either the initiator methylcholanthrene(MCA, 10 μg/g BW, i.p.), or vehicle (corn oil). One week after i.p. injections, mice were exposed by inhalation to MWCNT (5 mg/m³, 5 hours/day, 5 days/week) or filtered air (controls) for a total of 15 days. At 17 months post-exposure, mice were euthanized and examined for lung tumor formation.
  
  
  RESULTS
  Twenty-three percent of the filtered air controls, 26.5% of the MWCNT-exposed, and 51.9% of the MCA-exposed mice, had lung bronchiolo-alveolar adenomas and lung adenocarcinomas. The average number of tumors per mouse was 0.25, 0.81 and 0.38 respectively. By contrast, 90.5% of the mice which received MCA followed by MWCNT had bronchiolo-alveolar adenomas and adenocarcinomas with an average of 2.9 tumors per mouse 17 months after exposure. Indeed, 62% of the mice exposed to MCA followed by MWCNT had bronchiolo-alveolar adenocarcinomas compared to 13% of the mice that received filtered air, 22% of the MCA-exposed, or 14% of the MWCNT-exposed. Mice with early morbidity resulting in euthanasia had the highest rate of metastatic disease. Three mice exposed to both MCA and MWCNT that were euthanized early had lung adenocarcinoma with evidence of metastasis (5.5%). Five mice (9%) exposed to MCA and MWCNT and 1 (1.6%) exposed to MCA developed serosal tumors morphologically consistent with sarcomatous mesotheliomas, whereas mice administered MWCNT or air alone did not develop similar neoplasms.
  
  
  CONCLUSIONS
  These data demonstrate that some MWCNT exposures promote the growth and neoplastic progression of initiated lung cells in B6C3F1 mice. In this study, the mouse MWCNT lung burden of 31.2 μg/mouse approximates feasible human occupational exposures. Therefore, the results of this study indicate that caution should be used to limit human exposures to MWCNT.
authors.affiliation: National Institute for Occupational Safety and Health, 1095 Willowdale Road, Mailstop L-3014, Morgantown, WV 26505, USA. lqs1@cdc.gov.
authors.forename: Linda M
authors.initials: LM
authors.lastname: Sargent
authors.forename: Dale W
authors.initials: DW
authors.lastname: Porter
authors.forename: Lauren M
authors.initials: LM
authors.lastname: Staska
authors.forename: Ann F
authors.initials: AF
authors.lastname: Hubbs
authors.forename: David T
authors.initials: DT
authors.lastname: Lowry
authors.forename: Lori
authors.initials: L
authors.lastname: Battelli
authors.forename: Katelyn J
authors.initials: KJ
authors.lastname: Siegrist
authors.forename: Michael L
authors.initials: ML
authors.lastname: Kashon
authors.forename: Robert R
authors.initials: RR
authors.lastname: Mercer
authors.forename: Alison K
authors.initials: AK
authors.lastname: Bauer
authors.forename: Bean T
authors.initials: BT
authors.lastname: Chen
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Salisbury
authors.forename: David
authors.initials: D
authors.lastname: Frazer
authors.forename: Walter
authors.initials: W
authors.lastname: McKinney
authors.forename: Michael
authors.initials: M
authors.lastname: Andrew
authors.forename: Shuji
authors.initials: S
authors.lastname: Tsuruoka
authors.forename: Morinobu
authors.initials: M
authors.lastname: Endo
authors.forename: Kara L
authors.initials: KL
authors.lastname: Fluharty
authors.forename: Vince
authors.initials: V
authors.lastname: Castranova
authors.forename: Steven H
authors.initials: SH
authors.lastname: Reynolds
mesh_terms: D000230:Adenocarcinoma / Q000139:chemically induced* / Q000473:pathology; D000077192:Adenocarcinoma of Lung; D000236:Adenoma / Q000139:chemically induced / Q000473:pathology; D000818:Animals; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D005455:Fluorescent Antibody Technique; D006965:Hyperplasia / Q000139:chemically induced / Q000473:pathology; D019570:Inhalation Exposure; D008168:Lung / Q000473:pathology; D008175:Lung Neoplasms / Q000139:chemically induced* / Q000473:pathology; D008654:Mesothelioma / Q000139:chemically induced / Q000473:pathology; D051379:Mice; D008815:Mice, Inbred Strains; D008859:Microscopy, Polarization; D037742:Nanotubes, Carbon / Q000633:toxicity*; D020556:Neutrophil Infiltration / Q000187:drug effects; D016019:Survival Analysis
chemical_list: D037742:Nanotubes, Carbon