Induction of Gamma-Glutamyltransferase Activity and Consequent Pro-oxidant Reactions in Human Macrophages Exposed to Crocidolite Asbestos

Our plain-English summary of Induction of Gamma-Glutamyltransferase Activity and Consequent Pro-oxidant Reactions in Human Macrophages Exposed to Crocidolite Asbestos, by A. Corti, J. Bonetti, S. Dominici, et al (Toxicological Sciences, 2020).

The study

• Authors: A. Corti, J. Bonetti, S. Dominici, S. Piaggi, V. Fierabracci, R. Foddis, A. Pompella
• Journal: Toxicological Sciences
• Published: 2020;177(2):476-482
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos is the main causative agent of malignant pleural mesothelioma. The variety known as crocidolite (blue asbestos) owns the highest pathogenic potential, due to the dimensions of its fibers as well as to its content of iron. The latter can in fact react with macrophage-derived hydrogen peroxide in the so called Fenton reaction, giving rise to highly reactive and mutagenic hydroxyl radical. On the other hand, hydroxyl radical can as well originate after thiol-dependent reduction of iron, a process capable of starting its redox cycling. Previous studies showed that glutathione (GSH) is one such thiol, and that cellular gamma-glutamyltransferase (GGT) can efficiently potentiate GSH-dependent iron redox cycling and consequent oxidative stress. As GGT is expressed in macrophages and is released upon their activation, the present study was aimed at verifying the hypothesis that GSH/GGT-dependent redox reactions may participate in the oxidative stress following the activation of macrophages induced by crocidolite asbestos. Experiments in acellular systems confirmed that GGT-mediated metabolism of GSH can potentiate crocidolite-dependent production of superoxide anion, through the production of highly reactive dipeptide thiol cysteinyl-glycine. Cultured THP-1 macrophagic cells, as well as isolated monocytes obtained from healthy donors and differentiated to macrophages in vitro, were investigated as to their expression of GGT and the effects of exposure to crocidolite. The results show that crocidolite asbestos at subtoxic concentrations (50-250 ng/1000 cells) can upregulate GGT expression, which raises the possibility that macrophage-initiated, GSH/GGT-dependent pro-oxidant reactions may participate in the pathogenesis of tissue damage and inflammation consequent to crocidolite intoxication.

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In plain English

This laboratory study used cells and chemical mixtures, not exposed people. The authors tested whether the enzyme gamma-glutamyltransferase (GGT), acting on glutathione (GSH), boosts the iron-driven oxidative reactions of crocidolite asbestos. In cell-free mixtures, crocidolite plus GSH produced some superoxide, a reactive oxygen species. Adding GGT greatly increased this, a GGT blocker abolished the increase, and an iron-binding drug inhibited it. Two types of human macrophage-like cells were then exposed for 48 hours to non-toxic crocidolite doses (0.05 and 0.25 micrograms per 1,000 cells respectively): a leukaemia cell line (THP-1) and macrophages grown from healthy donors' blood monocytes (M0 cells). GGT rose by approximately 40% in both. M0 cells were about 5-fold more resistant to crocidolite toxicity and had higher GSH levels and GSH-related enzyme activities. Blocking GGT did not protect THP-1 cells from crocidolite toxicity. The authors concluded that crocidolite can induce GGT in macrophage-type cells. They said it remains open whether this strengthens cell defenses or contributes to damage and inflammation.

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 in cell-free chemical systems and in cultured human macrophage-like cells
• Who was studied: Two cell models: THP-1 human monocytic leukaemia cells differentiated to macrophages with PMA, and blood monocytes from healthy donors (number not stated) differentiated to macrophages with M-CSF (M0 cells), Pisa, Italy
• Exposure: Crocidolite asbestos at non-cytotoxic concentrations for 48 hours: 0.05 micrograms per 1,000 cells for THP-1 cells and 0.25 micrograms per 1,000 cells for M0 cells
• Main results:
  • In cell-free mixtures, adding GSH to crocidolite produced some stimulation of superoxide production (measured by NBT reduction), and adding GGT greatly enhanced this effect
  • In cell-free mixtures, the specific GGT inhibitor GGsTop abolished the stimulation
  • In cell-free mixtures, the iron chelator deferoxamine inhibited the GGT-induced superoxide production
  • Before exposure, GGT activity was significantly higher in THP-1 cells than in M0 cells
  • After crocidolite exposure, GGT increased by approximately 40% in both THP-1 and M0 cells, seen as both enzyme activity and GGT protein
  • M0 cells were approximately 5-fold more resistant to crocidolite toxicity than THP-1 cells
  • Crocidolite significantly increased total GSH in THP-1 cells but not in M0 cells
  • In THP-1 cells, the GSSG to GSH ratio was 5.0% (plus or minus 0.1) in crocidolite-treated cells versus 3.6% (plus or minus 0.6) in controls, an increase of 38% (p less than 0.05)
  • GSH reductase and GSH peroxidase activities were markedly higher in M0 cells than in THP-1 cells
  • Blocking GGT with GGsTop did not protect THP-1 cells from crocidolite toxicity (data not shown in the article)
• The authors' conclusion: The authors concluded that their results show crocidolite asbestos can induce GGT expression in cells of macrophage lineage
• Limitations the authors state:
  • The authors stated it remains unresolved whether GGT induction strengthens the macrophages' antioxidant defenses or contributes to crocidolite's damaging and pro-inflammatory effects
  • The authors stated that experiments in GGT knock-out animals would be needed to test any role in crocidolite-induced cancer

Topics

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

Medical terms in this study, explained in our Lexicon: Macrophage, Crocidolite, Pleural Mesothelioma, Fenton Reaction, Hydroxyl Radical, Redox Cycling, Glutathione (GSH), Oxidative Stress.

Related studies

• Oxidant-mediated increases in redox factor-1 nuclear protein and activator protein-1 DNA binding in asbestos-treated macrophages — D.M. Flaherty, M.M. Monick, et al. (2002)
• Big and Free Fractions of Gamma-Glutamyltransferase: New Diagnostic Biomarkers for Malignant Mesothelioma? — R. Foddis, M. Franzini, et al. (2022)
• Changes in DNA 8-hydroxyguanine levels, 8-hydroxyguanine repair activity, and hOGG1 and hMTH1 mRNA expression in human lung alveolar epithelial cells induced by crocidolite asbestos — H.N. Kim, Y. Morimoto, et al. (2001)
• Crocidolite asbestos inhibits pentose phosphate oxidative pathway and glucose 6-phosphate dehydrogenase activity in human lung epithelial cells — C. Riganti, E. Aldieri, et al. (2002)
• Asbestos fibers and interferon-gamma up-regulate nitric oxide production in rat alveolar macrophages — G. Thomas, T. Ando, et al. (1994)
• Macrophage phagocytic activity and cell phagocytic capacity following intratracheal instillation of a comixture of asbestos fibers — I. Trosic, M. Matausic-Pisl, et al. (1995)

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