Efflux of reduced glutathione after exposure of human lung epithelial cells to crocidolite asbestos

Our plain-English summary of Efflux of reduced glutathione after exposure of human lung epithelial cells to crocidolite asbestos, by S.A. Golladay, S.H. Park, A.E. Aust (Environmental Health Perspectives, 1997).

The study

• Authors: S.A. Golladay, S.H. Park, A.E. Aust
• Journal: Environmental Health Perspectives
• Published: 1997;105 Suppl 5(Suppl 5):1273-7
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

This study investigated glutathione (GSH) homeostasis in human lung epithelial cells (A549) exposed to crocidolite. Exposure of A549 cells to 3 micrograms/cm2 crocidolite resulted in a decrease in intracellular reduced glutathione by 36% without a corresponding increase in GSH disulfide. After a 24-hr exposure to crocidolite, 75% of the intracellular GSH lost was recovered in the extracellular medium, of which 50% was in reduced form. Since the half-life of reduced GSH in culture medium was less than 1 hr, this suggests that reduced GSH was released continuously from the cells after treatment. The release of GSH did not appear to result from nonspecific membrane damage, as there was no concomitant release of lactate dehydrogenase or 14C-adenine from loaded cells after crocidolite treatment for 24 hr. Crocidolite exposure resulted in the formation of S-nitrosothiols but no increase in the level of GSH-protein mixed disulfides or GSH conjugates. Exposure of A549 cells to crocidolite for 24 hr decreased gamma glutamylcysteine synthetase (gamma-GCS) activity by 47% without changes in the activities of GSH reductase, GSH peroxidase, GSH S-transferase, or glucose-6-phosphate dehydrogenase. Treatment of cells with crocidolite pretreated with the iron chelator desferrioxamine B resulted in the same level of intracellular GSH depletion and efflux and the same decrease in gamma-GCS activity as treatment with unmodified crocidolite, which suggests that iron-catalyzed reactions were not responsible for the GSH depletion.

In plain English

This was a laboratory study of human lung epithelial cells (the A549 cell line), not a study of people. The authors exposed the cells to crocidolite asbestos, sometimes using crocidolite from which iron had been partly removed with desferrioxamine B. They then measured glutathione, a protective substance inside cells. At 3 micrograms of crocidolite per square centimeter, reduced glutathione inside the cells fell by 36%, with no matching rise in its oxidized form. After 24 hours, 75% of the lost glutathione was found in the surrounding culture medium, half of it in reduced form. Reduced glutathione had a half-life of less than an hour in that medium, so the authors suggested it was released from the cells continuously. They found no sign of general membrane damage. Activity of the enzyme gamma glutamylcysteine synthetase fell by 47%, while four other glutathione-related enzymes were unchanged. Iron-depleted crocidolite caused the same glutathione loss, which suggested to the authors that iron-driven reactions were not responsible. The authors concluded that the role of this glutathione release in crocidolite's damaging effects remains unclear.

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) experiment on cultured human cells
• Who was studied: A549 human lung epithelial cell line obtained from the American Type Culture Collection, grown in culture; no human subjects
• Exposure: Crocidolite asbestos containing 27% iron by weight, and crocidolite from which iron had been partially removed with desferrioxamine B (DF crocidolite). Doses were 1.5, 3.0 and 6.0 micrograms per square centimeter, mostly for 24 hours.
• Main results:
  • In cells exposed to 3 micrograms per square centimeter of crocidolite, intracellular reduced glutathione decreased by 36% without a corresponding increase in glutathione disulfide (the oxidized form).
  • After 24 hours of exposure, 75% of the glutathione lost from inside the cells was recovered in the extracellular medium.
  • Of the glutathione recovered in the medium, 50% was in reduced form.
  • The half-life of reduced glutathione in the culture medium was less than 1 hour, which the authors said suggests continuous release from the cells.
  • There was no release of lactate dehydrogenase or 14C-adenine from treated cells, so the glutathione release did not appear to result from nonspecific membrane damage.
  • Crocidolite exposure led to formation of S-nitrosothiols but no increase in glutathione-protein mixed disulfides or glutathione conjugates. The S-nitrosothiols accounted for less than 1% of the glutathione depleted.
  • After 24 hours at 3 micrograms per square centimeter, gamma glutamylcysteine synthetase activity fell from 15 plus or minus 1 to 7 plus or minus 1 U/mg protein (a 47% decrease). Glutathione reductase, glutathione peroxidase, glutathione S-transferase and glucose-6-phosphate dehydrogenase activities did not change.
  • Crocidolite with iron partially removed (DF crocidolite) produced the same glutathione depletion, the same efflux and the same enzyme decrease as unmodified crocidolite. The authors said this suggests that iron-catalyzed reactions were not responsible.
• The authors' conclusion: The authors concluded that, in A549 cells, crocidolite exposure caused glutathione efflux, formation of S-nitrosothiols and decreased gamma glutamylcysteine synthetase activity. They concluded that these led to a decrease in intracellular glutathione with no detectable oxidation, and that the role of this efflux in crocidolite's damaging effects in the epithelial cells remains unclear.

Topics

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

Medical terms in this study, explained in our Lexicon: Glutathione (GSH), Crocidolite, A549 Cells, Lactate Dehydrogenase (LDH), Desferrioxamine B.

Related studies

• Role of alphavbeta5 integrin receptor in endocytosis of crocidolite and its effect on intracellular glutathione levels in human lung epithelial (A549) cells — P. Pande, T.A. Mosleh, et al. (2006)
• Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells — S.H. Park, A.E. Aust (1998)
• Apoptosis induced by crocidolite asbestos in human lung epithelial cells involves inactivation of Akt and MAPK pathways — A. Baldys, P. Pande, et al. (2007)
• Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers — A. Puhakka, T. Ollikainen, et al. (2002)
• 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)
• Novel functional view of the crocidolite asbestos-treated A549 human lung epithelial transcriptome reveals an intricate network of pathways with opposing functions — J.M. Hevel, L.C. Olson-Buelow, et al. (2008)

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