Biocompatibility and Carcinogenicity of Carbon Nanotubes as Biomaterials

Our plain-English summary of Biocompatibility and Carcinogenicity of Carbon Nanotubes as Biomaterials, by K. Aoki, N. Saito (Nanomaterials, 2020).

The study

• Authors: K. Aoki, N. Saito
• Journal: Nanomaterials
• Published: 2020;10(2)
• Type of article: Review
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

With the development of nanotechnology in recent years, there have been concerns about the health effects of nanoparticles. Carbon nanotubes (CNTs) are fibrous nanoparticles with a micro-sized length and nano-sized diameter, which exhibit excellent physical properties and are widely studied for their potential application in medicine. However, asbestos has been historically shown to cause pleural malignant mesothelioma and lung cancer by inhalation exposure. Because carbon nanotubes are also fibrous nanotubes, some have raised concerns about its possible carcinogenicity. We have reported that there is no clear evidence of carcinogenicity by local and intravenous administration of multi-walled CNTs to cancer mice models. We firmly believe that CNTs can be a safe, new, and high-performance biomaterials by controlling its type, site of administration, and dosage.

In plain English

This article is a review. The authors summarized published cell and animal tests of carbon nanotubes, fibrous nanoparticles studied as medical materials, amid concern that they might cause cancer like asbestos. In one reviewed study, crocidolite asbestos was seen inside human peritoneal mesothelial cells, while multi-walled nanotubes only attached to the surface. Other reviewed studies reported mesothelioma in the abdominal cavity of p53+/− mice after nanotubes were injected into the abdomen. In rats given nanotubes into the windpipe, 6/38 developed malignant mesothelioma and 14/38 lung tumors, while controls had none. In the authors' earlier work with cancer-prone rasH2 mice, survival 26 weeks after injection under the skin was 100% with nanotubes, versus 60% with a known carcinogen. After intravenous injection, some nanotube-treated mice showed mesothelioma in the lung, but tumor incidence did not differ significantly from the vehicle group. The authors stated their belief that nanotube carcinogenicity is caused by exposure of mesothelial tissue, and that medical use may be feasible if general safety and carcinogenicity tests give good results. They noted that nanotube types and doses vary between reports.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review of published in vitro (cell) and in vivo (animal) biocompatibility and carcinogenicity tests of carbon nanotubes, including the authors' own earlier studies
• Who was studied: Studies of cultured cells (including human bronchial epithelial and mesothelial cells) and laboratory animals (mice and rats); no human subjects
• Exposure: Carbon nanotubes, mainly multi-walled (MWCNTs) and single-walled (SWCNTs), given by various routes. Asbestos is discussed for comparison, and crocidolite was the control in one reviewed cell study.
• Main results:
  • In a reviewed study of human peritoneal mesothelial cells, crocidolite asbestos was seen inside the cells, while MWCNTs were only attached to the cell surface
  • A reviewed study (Takagi et al.) found mesothelioma in the abdominal cavity of p53+/− mice after intraperitoneal MWCNTs. A separate study by the same group reported that higher MWCNT doses increased mortality from mesothelioma in these mice.
  • In a reviewed rat study (Suzui et al.) with intratracheal MWCNTs, 6/38 animals in the MWCNT group had malignant mesothelioma and 14/38 had lung tumors (bronchiolo-alveolar adenomas and carcinomas). No vehicle-control animals had tumors.
  • In the authors' earlier study of rasH2 mice given MWCNTs under the skin, 26-week survival was 100% in the MWCNT group, with one inflammatory pseudotumor in the spleen. Survival was 60% in the group given the carcinogen MNU.
  • In the authors' earlier study of rasH2 mice given MWCNTs intravenously, some mice in the MWCNT group showed mesothelioma in the lung. Tumor incidence did not differ significantly from the vehicle group.
  • In the same intravenous study, 3.2% of mice showed fiber deposition in the pancreas, without tumor formation there
  • Across the reviewed animal studies, CNTs generally caused inflammation when given into the respiratory tract. They were reported as relatively safe when given intravenously, under the skin or into bone.
• The authors' conclusion: The authors stated their belief that CNT carcinogenicity is caused by exposure of mesothelial tissues. They concluded that CNTs need general biological safety tests and carcinogenicity tests according to type and intended use, and that if the results are good, biological applications may be feasible.
• Limitations the authors state:
  • The authors stated that, because there are many types of CNTs, they cannot say in general terms whether CNTs are safe or dangerous
  • The type and dosage of CNTs vary between the reviewed reports
  • The reports on how CNTs move through and are distributed in the body do not agree, and the authors called for further research

Topics

Medical terms in this study, explained in our Lexicon: Malignant Mesothelioma, Lung Cancer.

Related studies

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• Carcinogenicity of fluoro-edenite, silicon carbide fibres and whiskers, and carbon nanotubes — Y. Grosse, D. Loomis, et al. (2014)
• Genotoxicity and carcinogenicity risk of carbon nanotubes — S. Toyokuni (2013)
• Comparative carcinogenicity study of a thick, straight-type and a thin, tangled-type multi-walled carbon nanotube administered by intra-tracheal instillation in the rat — D.M. Saleh, W.T. Alexander, et al. (2020)
• Assessment of the Carcinogenicity of Carbon Nanotubes in the Respiratory System — M. Barbarino, A. Giordano (2021)
• Effect of dispersants of multi-walled carbon nanotubes on cellular uptake and biological responses — H. Haniu, N. Saito, et al. (2011)

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