Comparing the Toxicological Responses of Pulmonary Air-Liquid Interface Models upon Exposure to Differentially Treated Carbon Fibers

Our plain-English summary of Comparing the Toxicological Responses of Pulmonary Air-Liquid Interface Models upon Exposure to Differentially Treated Carbon Fibers, by A. Friesen, S. Fritsch-Decker, S. Mülhopt, et al (International Journal of Molecular Sciences, 2023).

The study

• Authors: A. Friesen, S. Fritsch-Decker, S. Mülhopt, C. Quarz, J. Mahl, W. Baumann, M. Hauser, M. Wexler, C. Schlager, B. Gutmann, T. Krebs, A.K. Goßmann, F. Weis, M. Hufnagel, D. Stapf, A. Hartwig, C. Weiss
• Journal: International Journal of Molecular Sciences
• Published: 2023;24(3)
• Cited by: 6 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

In recent years, the use of carbon fibers (CFs) in various sectors of industry has been increasing. Despite the similarity of CF degradation products to other toxicologically relevant materials such as asbestos fibers and carbon nanotubes, a detailed toxicological evaluation of this class of material has yet to be performed. In this work, we exposed advanced air-liquid interface cell culture models of the human lung to CF. To simulate different stresses applied to CF throughout their life cycle, they were either mechanically (mCF) or thermo-mechanically pre-treated (tmCF). Different aspects of inhalation toxicity as well as their possible time-dependency were monitored. mCFs were found to induce a moderate inflammatory response, whereas tmCF elicited stronger inflammatory as well as apoptotic effects. Furthermore, thermal treatment changed the surface properties of the CF resulting in a presumed adhesion of the cells to the fiber fragments and subsequent cell loss. Triple-cultures encompassing epithelial, macrophage, and fibroblast cells stood out with an exceptionally high inflammatory response. Only a weak genotoxic effect was detected in the form of DNA strand breaks in mono- and co-cultures, with triple-cultures presenting a possible secondary genotoxicity. This work establishes CF fragments as a potentially harmful material and emphasizes the necessity of further toxicological assessment of existing and upcoming advanced CF-containing materials.

In plain English

This laboratory study tested carbon fibers, not asbestos. Asbestos is mentioned only as a comparable fibrous material. The authors exposed human lung cells, grown at an air–liquid interface, to fragments of one polyacrylonitrile (PAN)-based carbon fiber for 1 hour. The fiber was either milled (mCF) or heated and then milled (tmCF). There were three cell models: bronchial epithelial cells alone; those cells with macrophage-like cells; and a triple-culture that added lung fibroblasts, which was tested with mCF only. Neither fiber sample significantly raised LDH release, a marker of cell damage. tmCF lowered cell counts, which the authors presumed was due to cells sticking to fiber clumps. mCF caused a moderate inflammatory gene response. tmCF caused stronger inflammatory and stress responses, including an 18-fold rise in the IL-6 gene in epithelial cells alone. After mCF, the triple-culture released 4.92 ng/mL of the inflammatory signal IL-8. DNA strand breaks were slight in the simpler models. In the triple-culture, double-stranded DNA fell from about 62% to 44%, which the authors interpreted as possible secondary genotoxicity. They called this first study limited.

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 (in vitro) cell culture experiment using human lung cell models exposed to airborne carbon fiber fragments at an air–liquid interface
• Who was studied: Human cell lines, not people or animals: BEAS-2B bronchial epithelial mono-cultures; BEAS-2B with differentiated THP-1 macrophage-like cells (co-cultures); and triple-cultures that added CCD-33Lu lung fibroblasts in the basolateral compartment. Results are from at least three independent experiments.
• Exposure: One PAN-based carbon fiber (Tenax-J UMS40). It was either mechanically treated in a planetary ball mill (mCF) or thermo-mechanically treated: heated in two furnaces, then milled (tmCF). Cells were exposed for 1 h to average surface doses of 7.00 ± 1.25 µg/cm2 (mCF) or 6.55 ± 1.96 µg/cm2 (tmCF), then post-incubated for 0, 3 or 23 h. Triple-cultures received mCF only, with 23 h post-incubation. WHO-sized fibers made up 20.1 ± 10.4% of deposited mCF objects and 9.4 ± 10.6% of tmCF objects.
• Main results:
  • mCF did not cause significant cytotoxicity in mono- or co-cultures. LDH release ranged from 3 to 9% in clean air controls and CF-exposed cells.
  • tmCF did not significantly change LDH release but reduced cell counts. Exposed cells dropped to 4.5–6.0 × 10^5 cells in mono-cultures and 6.0–7.0 × 10^5 cells in co-cultures, while controls kept growing. The authors presumed this cell loss was due to cells being trapped in fiber agglomerates.
  • In triple-cultures exposed to mCF, the fibroblasts showed a small but significant reduction in cell count, from 2.27 × 10^5 cells in controls to 1.95 × 10^5 cells.
  • mCF: in mono-cultures, IL-6 and IL-8 genes rose 3.2-fold and 2.8-fold immediately after exposure, returning to baseline 23 h later. In co-cultures the rises were 4.6-fold for IL-6 and 2.6-fold for IL-8.
  • tmCF: in mono-cultures, IL-6 and IL-8 gene expression peaked at 1 + 3 h with 18-fold and 7.8-fold rises. The DNA damage marker DDIT3 rose 19-fold in mono-cultures after 1 + 3 h.
  • IL-8 protein release: mCF in co-cultures peaked at 354 pg/mL after 1 + 3 h. tmCF reached a maximum of 773 pg/mL in mono-cultures and 563 pg/mL in co-cultures. Triple-cultures released 4.92 ng/mL after mCF and 19.9 ng/mL after the positive control LPS.
  • DNA strand breaks: mCF and tmCF caused only a slight but significant reduction in double-stranded DNA in mono- and co-cultures. In triple-cultures exposed to mCF, double-stranded DNA fell from about 62% in untreated cells to 44%.
• The authors' conclusion: The authors concluded that neither fiber sample caused cytotoxicity. mCF caused a moderate inflammatory response; tmCF caused more pronounced pro-inflammatory and stress signaling. DNA strand breaks in the triple-culture suggested a possible secondary genotoxicity, possibly driven by inflammation. Based on literature comparison, they placed carbon fiber toxicologically between carbon black and multi-walled carbon nanotubes, depending on the share of fiber-shaped fragments.
• Limitations the authors state:
  • Only one specific carbon fiber was examined, with two types of treatment. The authors call this a first and limited study that needs to be expanded.
  • The single 23 h time point used for triple-cultures was presumably too late to capture gene expression changes.
  • Some co-culture findings after tmCF may be partly an artifact of cell loss from cells adhering to the thermally treated fibers.
  • The deposited dose fluctuated between experiments, so it is reported as a mean with standard deviation.

Topics

Medical terms in this study, explained in our Lexicon: Macrophage, Fibroblast, Genotoxicity.

Related studies

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• Multiwalled carbon nanotube-induced pulmonary inflammatory and fibrotic responses and genomic changes following aspiration exposure in mice: A 1-year postexposure study — B.N. Snyder-Talkington, C. Dong, et al. (2016)
• Role of p53 in the chronic pulmonary immune response to tangled or rod-like multi-walled carbon nanotubes — K.S. Duke, E.A. Thompson, et al. (2018)
• Length-dependent pleural inflammation and parietal pleural responses after deposition of carbon nanotubes in the pulmonary airspaces of mice — F.A. Murphy, C.A. Poland, et al. (2013)
• A review of exposure and toxicological aspects of carbon nanotubes, and as additives to fire retardants in polymers — A. Christou, A.A. Stec, et al. (2016)

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