Asbestos and multi-walled carbon nanotubes generate distinct oxidative responses in inflammatory cells

Our plain-English summary of Asbestos and multi-walled carbon nanotubes generate distinct oxidative responses in inflammatory cells, by S. Funahashi, Y. Okazaki, D. Ito, et al (Journal of Clinical Biochemistry and Nutrition, 2015).

The study

• Authors: S. Funahashi, Y. Okazaki, D. Ito, A. Asakawa, H. Nagai, M. Tajima, S. Toyokuni
• Journal: Journal of Clinical Biochemistry and Nutrition
• Published: 2015;56(2):111-7
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos exposure is considered a social burden by causing mesothelioma. Despite the use of synthetic materials, multi-walled carbon nanotubes (MWCNTs) are similar in dimension to asbestos and produce mesothelioma in animals. The role of inflammatory cells in mesothelial carcinogenesis remains unclear. Here, we evaluated the differences in inflammatory cell responses following exposure to these fibrous materials using a luminometer and L-012 (8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H) dione) to detect reactive oxygen species (ROS). Rat peripheral blood or RAW264.7 cells were used to assess the effects on neutrophils and macrophages, respectively. Crocidolite and amosite induced significant ROS generation by neutrophils with a peak at 10 min, whereas that of chrysotile was ~25% of the crocidolite/amosite response. MWCNTs with different diameters (~15, 50, 115 and 145 nm) and different carcinogenicity did not induce significant ROS in peripheral blood. However, the MWCNTs induced a comparable amount of ROS in RAW264.7 cells to that following asbestos treatment. The peaks for MWCNTs (0.5-1.5 h) were observed earlier than those for asbestos (1-5 h). Apocynin and superoxide dismutase significantly inhibited ROS generation for each fiber, suggesting an involvement of NADPH oxidase and superoxide. Thus, asbestos and MWCNTs induce different oxidative responses in inflammatory cells, indicating the importance of mesothelial cell evaluation for carcinogenesis.

In plain English

This laboratory study compared how inflammatory cells react to crocidolite, amosite and chrysotile asbestos and to four multi-walled carbon nanotubes (MWCNTs) of different diameters. The authors measured reactive oxygen species (ROS). They tested neutrophils in whole blood from rats (three per group) and macrophages in a mouse cell line, RAW264.7. In blood, all three asbestos types raised ROS in a dose-dependent way, peaking at about 10 minutes. Amosite gave the most, then crocidolite, with chrysotile about 25% of their level. No nanotube raised ROS significantly in blood. In macrophages, both asbestos and nanotubes raised ROS, but nanotube peaks came earlier (0.5 to 1.5 hours) than asbestos peaks (2 to over 5 hours). Only chrysotile caused massive breakdown of red blood cells (75% after 4 hours). Macrophages gathered around asbestos fibers but stayed dispersed with nanotubes. In the authors' earlier rat studies, CNT-50 was potently carcinogenic, CNT-145 less so and CNT-tngl not carcinogenic; CNT-115's carcinogenicity was not determined. Here, macrophage responses were basically the same among the nanotubes used. The authors therefore concluded that mesothelial cell injury is a more important indicator of fiber-induced mesothelial cancer than these responses.

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: Laboratory (ex vivo and cell culture) experiment comparing ROS generation by inflammatory cells exposed to asbestos and to MWCNTs
• Who was studied: Neutrophils in whole blood taken from 15-week-old male Sprague-Dawley rats (n = 3 per group), and the mouse macrophage cell line RAW264.7, in Japan
• Exposure: UICC crocidolite, amosite and chrysotile asbestos, and four MWCNTs (CNT-50, CNT-115, CNT-145 and the tangled, about 15 nm CNT-tngl). In blood the doses were 1.0, 2.0 or 4.0 mg/ml. In macrophage cultures the dose was 5 μg/cm2.
• Main results:
  • In rat blood (neutrophils), all asbestos types significantly increased ROS in a dose-dependent manner, with a peak at about 10 minutes.
  • In rat blood, amosite induced the highest ROS, followed by crocidolite and then chrysotile. Chrysotile was about 25% of the crocidolite/amosite level.
  • In rat blood, MWCNTs of all diameters did not induce significant ROS generation under the same conditions.
  • In neutrophils, SOD1, catalase (crocidolite only), sodium azide and apocynin significantly inhibited ROS induced by crocidolite and amosite.
  • In macrophages (RAW264.7), ROS peak times for asbestos were 3 h for crocidolite, 2 h for amosite and more than 5 h for chrysotile.
  • MWCNTs also induced ROS in macrophages, with earlier peaks: 1.5 h for CNT-50 and CNT-115, 0.5 h for CNT-145 and 1 h for CNT-tngl.
  • In macrophages, SOD1 and apocynin consistently inhibited ROS generation; catalase did not.
  • In macrophages, DFO (an iron chelator) promoted ROS generation only with chrysotile.
  • Only chrysotile caused massive hemolysis (breakdown of red blood cells): 75% after a 4-hour incubation.
  • In time-lapse microscopy, macrophages moved toward asbestos fibers and isolated them in groups of cells, but remained dispersed with MWCNTs.
  • In the authors' earlier rat experiments, CNT-50 was potently carcinogenic, CNT-145 less so and CNT-tngl not carcinogenic. Carcinogenicity was not determined for CNT-115. In this study, neutrophil responses were subtle and macrophage responses were basically the same among the MWCNTs used.
• The authors' conclusion: The authors concluded that asbestos and MWCNTs generate distinct responses in inflammatory cells. They judged mesothelial cell injury to be a more important indicator of fiber-induced mesothelial carcinogenesis than neutrophil and macrophage responses.
• Limitations the authors state:
  • Inhibitor experiments in neutrophils were not performed for chrysotile because its ROS generation was relatively low.

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Mesothelioma, Carcinogenesis, Reactive Oxygen Species (ROS), Macrophage, Crocidolite, Amosite, Chrysotile.

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