Distinct Pro-Inflammatory Mechanisms Elicited by Short and Long Amosite Asbestos Fibers in Macrophages

Our plain-English summary of Distinct Pro-Inflammatory Mechanisms Elicited by Short and Long Amosite Asbestos Fibers in Macrophages, by R. Leinardi, J.R. Petriglieri, A. Pochet, et al (International Journal of Molecular Sciences, 2023).

The study

• Authors: R. Leinardi, J.R. Petriglieri, A. Pochet, Y. Yakoub, M. Lelong, A. Lescoat, F. Turci, V. Lecureur, F. Huaux
• Journal: International Journal of Molecular Sciences
• Published: 2023;24(20)
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

While exposure to long amphibolic asbestos fibers (L > 10 µm) results in the development of severe diseases including inflammation, fibrosis, and mesothelioma, the pathogenic activity associated with short fibers (L < 5 µm) is less clear. By exposing murine macrophages to short (SFA) or long (LFA) fibers of amosite asbestos different in size and surface chemistry, we observed that SFA internalization resulted in pyroptotic-related immunogenic cell death (ICD) characterized by the release of the pro-inflammatory damage signal (DAMP) IL-1α after inflammasome activation and gasdermin D (GSDMD)-pore formation. In contrast, macrophage responses to non-internalizable LFA were associated with tumor necrosis factor alpha (TNF-α) release, caspase-3 and -7 activation, and apoptosis. SFA effects exclusively resulted from Toll-like receptor 4 (TLR4), a pattern-recognition receptor (PRR) recognized for its ability to sense particles, while the response to LFA was elicited by a multifactorial ignition system involving the macrophage receptor with collagenous structure (SR-A6 or MARCO), reactive oxygen species (ROS) cascade, and TLR4. Our findings indicate that asbestos fiber size and surface features play major roles in modulating ICD and inflammatory pathways. They also suggest that SFA are biologically reactive in vitro and, therefore, their inflammatory and toxic effects in vivo should not be underestimated.

In plain English

This laboratory study used mouse immune cells (macrophages), not people or live animals. The authors exposed a mouse macrophage cell line, and macrophages from normal mice and mice lacking the protein gasdermin D, to short or long amosite asbestos fibers (12.5 to 100 µg/cm2, up to 24 hours). Short fibers were largely taken inside the cells; long fibers were poorly taken up, mainly touching the cells from outside. Short-fiber exposure killed more cells and prompted more release of the inflammatory signal IL-1α. Cells exposed to long fibers released TNF-α; short fibers did not raise TNF-α above untreated cells. In one test, 39% of short-fiber-exposed cells showed caspase-1 activation, which the authors linked to an inflammatory cell death called pyroptosis, versus 15.8% with long fibers. Apoptosis was seen in 8% of long-fiber cells versus 1.4% of short-fiber cells. Blocking the receptor TLR4 reduced the short-fiber response. The long-fiber response also involved the receptor MARCO and reactive oxygen species. The authors concluded that short fibers are not biologically inert. They noted that lung clearance of short fibers is a limitation of lab-dish tests, to be studied in live animals.

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 on mouse macrophages (cell line and primary cells from mice)
• Who was studied: J774 mouse macrophage cell line, plus primary peritoneal macrophages from wild-type C57BL/6 mice and GSDMD-deficient mice
• Exposure: Short (SFA) and long (LFA) amosite asbestos fibers from the same batch of South African amosite. The short fibers were made by grinding the long ones. The 75th percentile of length was about 1.5 µm (SFA) and 9 µm (LFA). Doses were 12.5, 25, 50 and 100 µg/cm2, mostly for 24 h.
• Main results:
  • In J774 macrophages, SFA caused a larger cytotoxic response than LFA.
  • Macrophages exposed to SFA showed larger dose-dependent IL-1α secretion than those exposed to LFA, especially at 50 and 100 µg/cm2.
  • LFA exposure led to strong dose-dependent TNF-α release by the macrophages. With SFA there was no increase compared with control cells.
  • In imaging, SFA were largely internalized by macrophages, while LFA interacted with cells via external contact.
  • The authors describe LFA as poorly internalized. In the discussion they say a fraction of LFA, possibly small fibers and cleavage fragments, could be engulfed by macrophages.
  • Necrotic cell death was lower with LFA than with SFA (figures given as 30% vs. 13.9%).
  • Caspase-1 activation was seen in 39% of single cells treated with SFA versus 15.8% of cells treated with LFA.
  • Apoptotic cells were 8% after LFA versus 1.4% after SFA.
  • IL-1α secretion after SFA was strongly reduced by TLR4 inhibition. It was not reduced by MARCO inhibition or by the ROS scavengers ascorbic acid or mannitol.
  • TNF-α release after LFA was prevented by TLR4 inhibition and also by MARCO or ROS cascade inhibitors.
  • In GSDMD-deficient peritoneal macrophages, SFA-induced IL-1α secretion was much lower. GSDMD deficiency did not affect TNF-α release after LFA.
• The authors' conclusion: The authors concluded that short amosite fibers are not biologically inert and that the toxicity of short fibers should not be underestimated or disregarded.
• Limitations the authors state:
  • The authors note that the low lung pathogenicity reported for short fibers may be due to clearance from the lungs. They describe this as a common limitation of in vitro work, to be investigated in a future in vivo study.
  • The authors note that their results differ from studies finding long fibers more toxic in epithelial cells. They say the in vitro model chosen plays a major role.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Amosite.

Medical terms in this study, explained in our Lexicon: Amosite, Macrophage, Inflammation, Fibrosis, Mesothelioma, Necrosis, Apoptosis, Reactive Oxygen Species (ROS).

Related studies

• Long and short fiber amosite asbestos alters at a different extent the redox metabolism in human lung epithelial cells — C. Riganti, E. Aldieri, et al. (2003)
• High aspect ratio materials: role of surface chemistry vs. length in the historical "long and short amosite asbestos fibers" — M. Tomatis, F. Turci, et al. (2010)
• Differential release of superoxide anions by macrophages treated with long and short fibre amosite asbestos is a consequence of differential affinity for opsonin — I.M. Hill, P.H. Beswick, et al. (1995)
• Cytogenetic and pathogenic effects of long and short amosite asbestos — K. Donaldson, N. Golyasnya (1995)
• Chemical differences between long and short amosite asbestos: differences in oxidation state and coordination sites of iron, detected by infrared spectroscopy — A. Graham, J. Higinbotham, et al. (1999)
• The mechanism of pleural inflammation by long carbon nanotubes: interaction of long fibres with macrophages stimulates them to amplify pro-inflammatory responses in mesothelial cells — F.A. Murphy, A. Schinwald, et al. (2012)

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