title: The carcinogenic effect of various multi-walled carbon nanotubes (MWCNTs) after intraperitoneal injection in rats.
abstract: BACKGROUND
  Biological effects of tailor-made multi-walled carbon nanotubes (MWCNTs) without functionalization were investigated in vivo in a two-year carcinogenicity study. In the past, intraperitoneal carcinogenicity studies in rats using biopersistent granular dusts had always been negative, whereas a number of such studies with different asbestos fibers had shown tumor induction. The aim of this study was to identify possible carcinogenic effects of MWCNTs. We compared induced tumors with asbestos-induced mesotheliomas and evaluated their relevance for humans by immunohistochemical methods.
  
  
  METHODS
  A total of 500 male Wistar rats (50 per group) were treated once by intraperitoneal injection with 10⁹ or 5 × 10⁹ WHO carbon nanotubes of one of four different MWCNTs suspended in artificial lung medium, which was also used as negative control. Amosite asbestos (10⁸ WHO fibers) served as positive control. Morbid rats were sacrificed and necropsy comprising all organs was performed. Histopathological classification of tumors and, additionally, immunohistochemistry were conducted for podoplanin, pan-cytokeratin, and vimentin to compare induced tumors with malignant mesotheliomas occurring in humans.
  
  
  RESULTS
  Treatments induced tumors in all dose groups, but incidences and times to tumor differed between groups. Most tumors were histologically and immunohistochemically classified as malignant mesotheliomas, revealing a predominantly superficial spread on the serosal surface of the abdominal cavity. Furthermore, most tumors showed invasion of peritoneal organs, especially the diaphragm. All tested MWCNT types caused mesotheliomas. We observed highest frequencies and earliest appearances after treatment with the rather straight MWCNT types A and B. In the MWCNT C groups, first appearances of morbid mesothelioma-bearing rats were only slightly later. Later during the two-year study, we found mesotheliomas also in rats treated with MWCNT D - the most curved type of nanotubes. Malignant mesotheliomas induced by intraperitoneal injection of different MWCNTs and of asbestos were histopathologically and immunohistochemically similar, also compared with mesotheliomas in man, suggesting similar pathogenesis.
  
  
  CONCLUSIONS
  We showed a carcinogenic effect for all tested MWCNTs. Besides aspect ratio, curvature seems to be an important parameter influencing the carcinogenicity of MWCNTs.
authors.affiliation: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, 30625, Hannover, Germany. susanne.rittinghausen@item.fraunhofer.de.
authors.forename: Susanne
authors.initials: S
authors.lastname: Rittinghausen
authors.affiliation: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, 30625, Hannover, Germany. anja.hackbarth@item.fraunhofer.de.
authors.forename: Anja
authors.initials: A
authors.lastname: Hackbarth
authors.affiliation: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, 30625, Hannover, Germany. otto.creutzenberg@item.fraunhofer.de.
authors.forename: Otto
authors.initials: O
authors.lastname: Creutzenberg
authors.affiliation: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, 30625, Hannover, Germany. heinrich.ernst@item.fraunhofer.de.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Ernst
authors.affiliation: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, 30625, Hannover, Germany. uwe.heinrich@item.fraunhofer.de.
authors.forename: Uwe
authors.initials: U
authors.lastname: Heinrich
authors.affiliation: Leibniz Institute for Solid State and Materials Research Dresden, PF 270116, 01171, Dresden, Germany. A.Leonhardt@ifw-dresden.de.
authors.forename: Albrecht
authors.initials: A
authors.lastname: Leonhardt
authors.affiliation: Fraunhofer Institute for Toxicology and Experimental Medicine ITEM, Nikolai-Fuchs-Str. 1, 30625, Hannover, Germany. dirk.schaudien@item.fraunhofer.de.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schaudien
mesh_terms: D000008:Abdominal Neoplasms / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D000818:Animals; D015197:Carcinogenicity Tests; D002273:Carcinogens / Q000008:administration & dosage / Q000737:chemistry / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D007150:Immunohistochemistry; D007274:Injections, Intraperitoneal; D008297:Male; D008654:Mesothelioma / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D008855:Microscopy, Electron, Scanning; D037742:Nanotubes, Carbon / Q000737:chemistry / Q000633:toxicity* / Q000648:ultrastructure; D009361:Neoplasm Invasiveness; D009363:Neoplasm Proteins / Q000378:metabolism; D010316:Particle Size; D017208:Rats, Wistar; D012704:Serous Membrane; D016019:Survival Analysis
chemical_list: D002273:Carcinogens; D037742:Nanotubes, Carbon; D009363:Neoplasm Proteins