Acute effects of multi-walled carbon nanotubes on primary bronchial epithelial cells from COPD patients

Our plain-English summary of Acute effects of multi-walled carbon nanotubes on primary bronchial epithelial cells from COPD patients, by S. Beyeler, S. Chortarea, B. Rothen-Rutishauser, et al (Nanotoxicology, 2018).

The study

• Authors: S. Beyeler, S. Chortarea, B. Rothen-Rutishauser, A. Petri-Fink, P. Wick, S.A. Tschanz, C. von Garnier, F. Blank
• Journal: Nanotoxicology
• Published: 2018;12(7):699-711
• Cited by: 18 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The risks of occupational exposure during handling of multi-walled carbon nanotubes (MWCNTs) have received limited attention to date, in particular for potentially susceptible individuals with highly prevalent chronic obstructive pulmonary disease (COPD). In this in vitro study, we simulated acute inhalation of MWCNTs employing an air-liquid interface cell exposure (ALICE) system: primary human bronchial epithelial cells from COPD patients and healthy donors (controls), cultured at the air-liquid interface (ALI) were exposed to MWCNTs. To study acute health effects on the respiratory epithelium, two different concentrations (0.16; 0.34 µg/cm2) of MWCNTs were aerosolized onto cell cultures followed by analysis after 24 h. Following MWCNT exposure, epithelial integrity and differentiation remained intact. Electron microscopy analyses identified MWCNTs both extra- and intracellular within vesicles of mucus producing cells. In both COPD and healthy control cultures, MWCNTs neither caused increased release of lactate dehydrogenase (LDH), nor alterations in inflammatory responses, as measured by RNA expression and protein secretion of the cytokines IL-6, IL-8, CXCL10, IL-1β and TGF-β and oxidative stress markers HMOX-1 and SOD-2. No short-term alteration of epithelial cell function, as determined by ciliary beating frequency (CBF), occurred in any of the conditions tested. In conclusion, the present study provided a reliable and realistic in vitro acute-exposure model of the respiratory tract, responsive to positive controls such as Dörentruper Quartz (DQ12) and asbestos. Acute exposure to MWCNTs did not affect epithelial integrity, nor induce increased cell death, apoptosis or inflammatory changes.

In plain English

This was a laboratory study of human airway cells, not of people. The authors grew bronchial lining cells from six healthy donors and four donors with chronic obstructive pulmonary disease (COPD). They sprayed multi-walled carbon nanotubes onto the cells at two deposited doses, 0.16 and 0.34 micrograms per square centimetre, which they chose with reference to a permissible occupational exposure limit. Crocidolite asbestos and a quartz dust (DQ12) served as comparison materials. The asbestos was added in liquid because it blocked the spraying device. After 24 hours, the nanotubes did not increase cell death or disturb the cell layer, in either healthy or COPD cells. They also did not significantly change inflammation or oxidative-stress markers, or the beating of the cells' cilia. Nanotubes were seen both inside and outside cells. Asbestos did not increase cell death or significantly change cytokines, but it increased expression of the oxidative-stress marker HMOX-1. The authors concluded that acute exposure did not alter these measures. They named the 24-hour exposure as a limitation and said long-term repeated-exposure studies are needed.

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: In vitro laboratory experiment: human airway cells grown at an air–liquid interface and exposed to sprayed (aerosolized) nanotubes, with measurements 24 hours later
• Who was studied: Primary human bronchial epithelial cells from six healthy donors and four donors with COPD, obtained from Epithelix (Geneva, Switzerland). No human participants were studied directly.
• Exposure: Multi-walled carbon nanotubes (Cheaptubes Inc.) sprayed onto cells at deposited doses of 0.16 (low) and 0.34 (high) micrograms per square centimetre, selected with reference to the NIOSH permissible exposure limit of 1 mg/m3. Comparison (positive control) materials were crocidolite asbestos, added in culture medium at 30 micrograms per ml, and DQ12 quartz, sprayed at 0.60 micrograms per square centimetre.
• Main results:
  • Neither nanotube dose increased release of LDH, a marker of cell death, in cells from healthy donors or COPD donors (p > 0.9999).
  • Asbestos (30 micrograms per ml) and DQ12 (0.60 micrograms per square centimetre) also did not increase LDH release.
  • After nanotube exposure, the cell layer stayed intact and differentiated, based on qualitative microscopy.
  • Electron microscopy found nanotubes outside cells and inside cells, including within mucus vesicles of mucus-producing cells. In the discussion, the authors described intracellular nanotubes as very rare events.
  • Nanotubes did not change secretion of the cytokines IL-6, IL-8 or CXCL10 in COPD or healthy cell cultures (p > 0.9999). Asbestos-treated cultures also showed no detectable change in cytokine patterns.
  • Neither nanotube dose significantly changed gene expression of IL-6, IL-8, CXCL10, IL-1β, TGF-β or the oxidative-stress markers HMOX-1 and SOD-2, in healthy or COPD cells (p > 0.9999), compared with the dispersant-only control.
  • Asbestos did not significantly change cytokine gene expression. It did increase expression of the oxidative-stress marker HMOX-1 in healthy cells (p = 0.0062) and in COPD cells (p = 0.0017).
  • The quartz control DQ12 significantly increased expression of several markers. These included IL-1β in healthy cells (p = 0.0014) and COPD cells (p less than 0.0001), and TGF-β in both healthy and COPD cells (p less than 0.0001).
  • Neither asbestos nor the nanotubes altered the beating frequency of the cells' cilia, in healthy or COPD cultures.
• The authors' conclusion: The authors concluded that acute exposure of cells from COPD and healthy donors to occupationally relevant nanotube doses did not alter cell viability, epithelial integrity, inflammatory cytokine profiles or oxidative stress markers. They stated that long-term studies with repeated exposure will be needed to assess workplace hazards.
• Limitations the authors state:
  • Cells were exposed only for a single 24-hour period, so only acute effects were studied.
  • The authors suggested the limited effects seen with asbestos may be due to the short-term exposure.
  • Asbestos could not be sprayed like the nanotubes and was instead added in liquid, because it blocked the exposure system.
  • Cytokine results varied between cultures, which the authors attributed to biological differences between donors.
  • Intracellular nanotubes were very rare, and the authors could not exclude that some were located in other parts of the cell.
  • Long-term studies with repeated exposure are needed to assess occupational hazards.

Topics

Medical terms in this study, explained in our Lexicon: COPD, Occupational Exposure, Epithelium, Lactate Dehydrogenase (LDH), Cytokine, Oxidative Stress, Apoptosis.

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