Asbestos-derived reactive oxygen species activate TGF-beta1

Our plain-English summary of Asbestos-derived reactive oxygen species activate TGF-beta1, by D.A. Pociask, P.J. Sime, A.R. Brody (Laboratory Investigation; a Journal of Technical Methods and Pathology, 2004).

The study

• Authors: D.A. Pociask, P.J. Sime, A.R. Brody
• Journal: Laboratory Investigation; a Journal of Technical Methods and Pathology
• Published: 2004;84(8):1013-23
• Cited by: 119 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Transforming growth factor-beta1 (TGF-beta1) is a potent peptide that inhibits epithelial and mesenchymal cell proliferation and stimulates the synthesis of extracellular matrix components. This cytokine is produced in a biologically latent complex bound to a latent-associated peptide (LAP), and it is the disassociation of this complex that regulates TGF-beta activity. A number of mechanisms have been shown to activate TGF-beta1. We show here that reactive oxygen species (ROS), generated by the iron in chrysotile or crocidolite asbestos, mediate the biological activity of TGF-beta1. Recombinant human latent TGF-beta1 was activated in a cell free system in the presence of asbestos and ascorbic acid. Latent TGF-beta1 was overexpressed in both A549 and mink lung epithelial cell lines through an adenovirus vector containing the full-length construct for porcine TGF-beta1. This latent TGF-beta1 was activated in a concentration-dependant fashion by introducing asbestos into the cell cultures. This activation was reduced significantly through the use of superoxide dismutase, catalase or deferoxamine. Amino-acid constituents of the LAP were oxidized as demonstrated by the appearance of carbonyls detected by Western analysis. The oxidized LAP could no longer form a complex with TGF-beta1. Our data support the postulate that ROS derived from asbestos provide a mechanism for activating TGF-beta1 in the alveolar environment by oxidizing amino acids in LAP.

In plain English

This laboratory study used cells and proteins, not people or animals. The authors tested whether reactive oxygen species (reactive forms of oxygen) produced by the iron in chrysotile and crocidolite asbestos can switch on TGF-beta1. TGF-beta1, a signalling protein linked to lung scarring, is normally held inactive by a partner protein called LAP. In a cell-free system, iron released from both fiber types activated the inactive protein; with citrate and ascorbate both present, crocidolite activated more than chrysotile. After oxidation, LAP could no longer hold TGF-beta1 inactive, and it showed chemical signs of oxidation. In human A549 epithelial cells engineered to make inactive TGF-beta1, chrysotile increased active TGF-beta1 in a concentration-dependent way after 3 days. The antioxidant enzymes superoxide dismutase and catalase used together, or the iron-binding drug deferoxamine, significantly reduced this activation. Mink lung cells showed the same pattern. The authors concluded that asbestos can activate TGF-beta1 through iron-induced oxidation. They noted this had not yet been shown in living organisms. They also made no direct dose-response comparison of the two fibers, since chrysotile has more fibers per unit mass.

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) experiments using a cell-free protein system and cultured cell lines
• Who was studied: No people or animals. The experiments used recombinant human latent TGF-beta1, the human A549 epithelial cell line and mink lung epithelial cells. The cell lines were made to produce latent porcine TGF-beta1 through an adenovirus vector.
• Exposure: Chrysotile and crocidolite asbestos supplied by NIEHS. Chrysotile was the fiber used in the cell-culture experiments.
• Main results:
  • In the cell-free system, iron released from both chrysotile and crocidolite produced significant activation of latent TGF-beta1.
  • With citrate plus ascorbate, iron from crocidolite activated more TGF-beta1 than iron from chrysotile (p less than 0.05).
  • LAP added at 100 ng/ml reduced active TGF-beta1 signalling three-fold. This inhibition did not occur when LAP had first been oxidized with iron chloride and ascorbate.
  • Oxidized LAP showed carbonyl groups (a chemical marker of protein oxidation) on Western blot. These were not seen in non-oxidized LAP.
  • In A549 cells producing latent TGF-beta1, chrysotile caused concentration-dependent activation of TGF-beta1 at 3 days.
  • In A549 cells, catalase and superoxide dismutase used together significantly reduced activation. Used separately, they showed little or no protective effect.
  • In A549 cells, the iron chelator deferoxamine significantly reduced chrysotile-induced activation of TGF-beta1 (p less than 0.001).
  • Other agents killed cells as much as or more than asbestos: LPS left 37% of cells viable, water 0%, and asbestos 42% at 3 days. These agents did not activate TGF-beta1 much above background (data not shown).
  • In mink lung cells producing latent TGF-beta1, chrysotile significantly reduced cell growth. Antioxidants and deferoxamine reversed this growth inhibition.
• The authors' conclusion: The authors concluded that latent TGF-beta1 can be activated by chrysotile and crocidolite asbestos through iron-induced oxidation.
• Limitations the authors state:
  • The authors did not make direct dose-response comparisons between chrysotile and crocidolite, because chrysotile has many more fibers per unit mass.
  • The experiments were done in vitro only. The authors state that the mechanism would apply only if the same reactions take place in living organisms.
  • The exact way reactive oxygen species activate latent TGF-beta1 is not known.
  • Other TGF-beta1 activating mechanisms may also have been at work in the cell cultures.

Topics

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

Medical terms in this study, explained in our Lexicon: Reactive Oxygen Species (ROS), Cytokine, Chrysotile, Crocidolite, Superoxide.

Related studies

• Wollastonite fibers in vitro generate reactive oxygen species able to lyse erythrocytes and activate the complement alternate pathway — M. Governa, L. Camilucci, et al. (1998)
• Relationship of fiber surface iron and active oxygen species to expression of procollagen, PDGF-A, and TGF-beta(1) in tracheal explants exposed to amosite asbestos — J. Dai, A. Churg (2001)
• The latent form of TGFbeta(1) is induced by TNFalpha through an ERK specific pathway and is activated by asbestos-derived reactive oxygen species in vitro and in vivo — D.E. Sullivan, M. Ferris, et al. (2008)
• Mobilization of iron from urban particulates leads to generation of reactive oxygen species in vitro and induction of ferritin synthesis in human lung epithelial cells — K.R. Smith, A.E. Aust (1997)
• Beyond foreign-body-induced carcinogenesis: impact of reactive oxygen species derived from inflammatory cells in tumorigenic conversion and tumor progression — F. Okada (2007)
• Mitochondria-derived reactive oxygen species drive GANT61-induced mesothelioma cell apoptosis — C.B. Lim, C.M. Prêle, et al. (2015)

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