Biopersistence and potential adverse health impacts of fibrous nanomaterials: what have we learned from asbestos?

Our plain-English summary of Biopersistence and potential adverse health impacts of fibrous nanomaterials: what have we learned from asbestos?, by V.C. Sanchez, J.R. Pietruska, N.R. Miselis, et al (Wiley Interdisciplinary Reviews. Nanomedicine and Nanobiotechnology, 2009).

The study

• Authors: V.C. Sanchez, J.R. Pietruska, N.R. Miselis, R.H. Hurt, A.B. Kane
• Journal: Wiley Interdisciplinary Reviews. Nanomedicine and Nanobiotechnology
• Published: 2009;1(5):511-29
• Type of article: Review
• Cited by: 123 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Human diseases associated with exposure to asbestos fibers include pleural fibrosis and plaques, pulmonary fibrosis (asbestosis), lung cancer, and diffuse malignant mesothelioma. The critical determinants of fiber bioactivity and toxicity include not only fiber dimensions, but also shape, surface reactivity, crystallinity, chemical composition, and presence of transition metals. Depending on their size and dimensions, inhaled fibers can penetrate the respiratory tract to the distal airways and into the alveolar spaces. Fibers can be cleared by several mechanisms, including the mucociliary escalator, engulfment, and removal by macrophages, or through splitting and chemical modification. Biopersistence of long asbestos fibers can lead to inflammation, granuloma formation, fibrosis, and cancer. Exposure to synthetic carbon nanomaterials, including carbon nanofibers and carbon nanotubes (CNTs), is considered a potential health hazard because of their physical similarities with asbestos fibers. Respiratory exposure to CNTs can produce an inflammatory response, diffuse interstitial fibrosis, and formation of fibrotic granulomas similar to that observed in asbestos-exposed animals and humans. Given the known cytotoxic and carcinogenic properties of asbestos fibers, toxicity of fibrous nanomaterials is a topic of intense study. The mechanisms of nanomaterial toxicity remain to be fully elucidated, but recent evidence suggests points of similarity with asbestos fibers, including a role for generation of reactive oxygen species, oxidative stress, and genotoxicity. Considering the rapid increase in production and use of fibrous nanomaterials, it is imperative to gain a thorough understanding of their biologic activity to avoid the human health catastrophe that has resulted from widespread use of asbestos fibers.

Copyright (c) 2009 John Wiley & Sons, Inc.

In plain English

This article was a review, not a new study. The authors compared asbestos fibers (chrysotile, and the amphiboles actinolite, amosite, anthophyllite, crocidolite and tremolite) with synthetic carbon nanofibers and nanotubes. They described chrysotile as cleared from the lung more effectively than amphiboles. They also described a laboratory test in which single-walled nanotubes persisted for two months in a pH 4.5 fluid imitating the acidic compartments inside macrophages, the lung's scavenger cells. They reported that cell-culture studies of nanotube toxicity were sometimes conflicting and inconclusive. They described animal data showing nanotubes could potentially produce lung injury, inflammation and fibrosis, and granulomas in mice given nanotubes through the windpipe. They also reported that peritoneal tumors formed in mice lacking one copy of the p53 gene after multi-walled nanotubes were injected into the abdominal cavity. They noted that no human 'nanodiseases' had yet been identified. They linked conflicting results partly to variation between nanomaterial samples. The authors concluded it was unclear whether these materials would be equally, more, or less hazardous than asbestos, and proposed using asbestos knowledge to guide their design.

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 article (Advanced Review) of published research comparing asbestos fibers with fibrous carbon nanomaterials
• Who was studied: No new subjects; the review covered published cell-culture, animal and human research on asbestos fibers and on carbon nanofibers (CNFs) and carbon nanotubes (CNTs)
• Exposure: Asbestos fibers: chrysotile (serpentine) and the amphiboles actinolite, amosite, anthophyllite, crocidolite and tremolite. Synthetic carbon nanofibers and single-walled and multi-walled carbon nanotubes, including their residual metal catalysts such as iron and nickel
• Main results:
  • The review described chrysotile asbestos as more effectively cleared than amphiboles, in part because its brucite layer dissolves in the acidic interior of macrophages
  • Citing earlier work, the review reported that single-walled carbon nanotubes persisted for two months in an in vitro flow-through test using a fluid that simulates the acidic phagolysosome of macrophages, at pH 4.5
  • Citing earlier work, the review stated that soluble iron and nickel could be released even from vendor-purified carbon nanotube samples
  • The review described cell-culture (in vitro) studies of fibrous nanomaterial toxicity as sometimes conflicting and inconclusive
  • The review stated that animal (in vivo) data showed the potential for carbon nanotubes to produce acute lung injury, inflammation and fibrosis
  • Citing earlier work, the review reported that mice given carbon nanotubes by intratracheal instillation developed granulomas in the bronchioles
  • Citing earlier work, the review reported that peritoneal tumors formed in p53 heterozygous mice after injection of multi-walled carbon nanotubes
  • The cited study (reference 142) applied the multi-walled carbon nanotubes intraperitoneally (into the abdominal cavity) of p53+/- mice
  • Citing earlier sources, the review stated that pleural plaques occur in approximately 50% of individuals with heavy and prolonged asbestos exposure
  • The review stated that no human 'nanodiseases' had yet been identified
• The authors' conclusion: The authors concluded that it was unclear whether high aspect ratio nanoparticles would be equally, more, or less hazardous than asbestos fibers. They proposed using current understanding of asbestos to guide the design and post-processing of carbon nanomaterials.
• Limitations the authors state:
  • The authors attributed conflicting results in the studies they reviewed to variation among nanomaterial samples
  • The authors noted that nanomaterials can interfere with the dyes used in common cell-viability tests, which can make toxicity appear where there is none
  • The authors noted that animal studies were complicated by the tendency of carbon nanomaterials to clump, which made it hard to deliver them the same way as asbestos

Topics

Medical terms in this study, explained in our Lexicon: biopersistence, Fibrosis, Pulmonary Fibrosis, Lung Cancer, Mesothelioma, Fiber Dimensions, Surface Reactivity, Mucociliary Clearance.

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