Differential activation of the inflammasome in THP-1 cells exposed to chrysotile asbestos and Libby "six-mix" amphiboles and subsequent activation of BEAS-2B cells

Our plain-English summary of Differential activation of the inflammasome in THP-1 cells exposed to chrysotile asbestos and Libby "six-mix" amphiboles and subsequent activation of BEAS-2B cells, by M. Li, M.E. Gunter, N.K. Fukagawa (Cytokine, 2012).

The study

• Authors: M. Li, M.E. Gunter, N.K. Fukagawa
• Journal: Cytokine
• Published: 2012;60(3):718-30
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Inflammatory responses of THP-1 cells (macrophage cell line) exposed to chrysotile asbestos (Chry) and Libby six-mix (LIB) and the subsequent impact on bronchial epithelial cells were determined. Direct treatment of THP-1 cells with Chry caused cell death, activation of caspase-1 and release of IL-1β, while the addition of caspase-1 inhibitor, Z-YVAD-FMK, reduced IL-1β, suggesting that Chry activated the caspase-1 mediated Nod-like receptor protein 3 (NLRP3) inflammasome; by comparison, LIB had less effects on all of these parameters. Expression of antioxidant enzymes, protein oxidation and nitration, and lipid peroxides in THP-1 cells treated with the two particles suggest that LIB generated more reactive oxygen species (ROS) than the same dose of Chry. Differences in fiber length and surface area suggest a possible role for particulate size in the differential activation of the inflammasome. BEAS-2B cells, representing the bronchial epithelium, treated with supernatants of medium from Chry- or LIB-treated THP-1 cells (conditioned medium) activated the MAPK cascade, increased phosphorylation of ERK and Cot (MAP3K8), increased AP-1 binding activity and induced IL-6 release. To verify that IL-1β from THP-1 cells was responsible for activation of BEAS-2B, conditioned medium with added IL-1Ra, an IL-1β antagonist, was applied to BEAS-2B. Results show that IL-1Ra attenuated effects of conditioned medium, supporting a role of IL-1β, as a secondary mediator, in the transduction of inflammatory signaling from the macrophage to epithelial cells. The effects of LIB-conditioned medium appeared to be less dependent on IL-1β. In conclusion, Chry and LIB induce differential inflammatory responses in THP-1 cells that subsequently lead to differential effects in epithelial cells.

Copyright © 2012 Elsevier Ltd. All rights reserved.

In plain English

This was a laboratory study of human cells grown in dishes, not of people or animals. The authors exposed THP-1 cells (a human monocyte cell line made macrophage-like) and BEAS-2B cells (a human bronchial epithelial cell line) to chrysotile asbestos or Libby "six-mix" amphiboles at 20 or 40 micrograms per milliliter for 24 hours. Glass beads served as a control. They also grew BEAS-2B cells in fiber-free medium collected from exposed THP-1 cells, called conditioned medium. In THP-1 cells, chrysotile significantly reduced survival and raised release of the inflammatory signal IL-1β 4-fold at the lower dose and 6-fold at the higher dose. Libby amphiboles at the higher dose raised it 2.9-fold. A caspase-1 blocker reduced this IL-1β release. Oxidative stress measures suggested Libby amphiboles produced more oxidative stress than chrysotile. Conditioned medium raised IL-6 release from BEAS-2B cells. Adding the IL-1β blocker IL-1Ra lowered the effect of chrysotile-conditioned medium; for Libby, none of the differences reached significance. The authors concluded that the two materials differentially activated the inflammasome, with IL-1β acting as a secondary mediator.

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: human macrophage-like cells were exposed directly to fibers, and their fiber-free culture medium (conditioned medium) was then used to treat bronchial epithelial cells
• Who was studied: Two human cell lines, not people: THP-1 cells (a human monocyte cell line differentiated with PMA into macrophage-like cells) and BEAS-2B cells (a human bronchial epithelial cell line from ATCC); work done at the University of Vermont
• Exposure: Chrysotile asbestos (NIEHS reference sample) and Libby six-mix amphiboles (USGS), with glass beads as a non-toxic control, at 20 and 40 micrograms per milliliter for 24 hours; additional comparisons at matched fiber surface area
• Main results:
  • In THP-1 cells, chrysotile significantly reduced cell survival after 24 hours compared with control; Libby six-mix had less of an effect
  • In THP-1 cells, chrysotile at 40 micrograms per milliliter induced significant cell death (60%) by 24 hours in the LDH assay; lesser degrees with chrysotile at 20 and Libby at 40 and 20
  • No reduction of cell viability was seen in BEAS-2B bronchial epithelial cells exposed directly to the fibers
  • IL-1β secretion by THP-1 cells, compared with control: chrysotile at 20 increased it 4-fold and chrysotile at 40 6-fold; Libby at 40 increased it 2.9-fold (3 independent experiments)
  • NLRP3 protein levels in THP-1 cells were higher with all treatments, but none was statistically significant compared with control
  • The caspase-1 inhibitor ZYF significantly reduced IL-1β release by THP-1 cells exposed to chrysotile or Libby at 40 micrograms per milliliter
  • Libby treatments produced more lipid peroxide in THP-1 conditioned medium than chrysotile treatments; the difference was significant for Libby at 20 versus chrysotile at 20
  • In BEAS-2B cells, direct chrysotile at 40 increased IL-6 4.8-fold over control, while chrysotile-40 conditioned medium increased it 1.5-fold; Libby-conditioned medium increased it less than chrysotile-conditioned medium
  • Adding IL-1Ra to chrysotile-40 conditioned medium suppressed IL-6 release by BEAS-2B cells; Libby treatments showed the same trends, but none of the differences reached significance
  • When chrysotile and Libby doses were matched by total fiber surface area, the authors reported chrysotile still had a much greater effect on IL-1β and IL-6 secretion
• The authors' conclusion: The authors concluded that direct treatment of THP-1 cells with chrysotile and Libby amphiboles activated the inflammasome to different degrees in processing IL-1β. They also concluded that IL-1β in conditioned medium acted as a secondary mediator triggering signaling and IL-6 release in BEAS-2B cells.
• Limitations the authors state:
  • The authors stated that lipid peroxides detected in conditioned medium may be another signal to the epithelial cells, but this should be identified and confirmed in future studies
  • The authors stated that the link between particle size and inflammasome activation needs further study

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Amphibole Group, Macrophage, Reactive Oxygen Species (ROS), Fiber Length, Epithelium.

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