Crocidolite asbestos inhibits pentose phosphate oxidative pathway and glucose 6-phosphate dehydrogenase activity in human lung epithelial cells

Our plain-English summary of Crocidolite asbestos inhibits pentose phosphate oxidative pathway and glucose 6-phosphate dehydrogenase activity in human lung epithelial cells, by C. Riganti, E. Aldieri, L. Bergandi, et al (Free Radical Biology & Medicine, 2002).

The study

• Authors: C. Riganti, E. Aldieri, L. Bergandi, I. Fenoglio, C. Costamagna, B. Fubini, A. Bosia, D. Ghigo
• Journal: Free Radical Biology & Medicine
• Published: 2002;32(9):938-49
• Cited by: 55 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The cytotoxicity of asbestos has been related to its ability to increase the production of reactive oxygen species (ROS), via the iron-catalyzed reduction of oxygen and/or the activation of NADPH oxidase. The pentose phosphate pathway (PPP) is generally activated by the cell exposure to oxidant molecules. Contrary to our expectations, asbestos (crocidolite) fibers caused a dose- and time-dependent inhibition of PPP and decreased its activation by an oxidative stress in human lung epithelial cells A549. In parallel, the intracellular activity of the PPP rate-limiting enzyme, glucose 6-phosphate dehydrogenase (G6PD), was significantly diminished by crocidolite exposure. This inhibition was selective, as the activity of other PPP and glycolysis enzymes was not modified, and was not attributable to a decreased expression of G6PD. On the opposite, the incubation with glass fibers MMVF10 did not modify PPP and G6PD activity. PPP and G6PD inhibition did not correlate with the increased nitric oxide (NO) production elicited by crocidolite in A549 cells. Experiments with the purified enzyme suggest that crocidolite inhibits G6PD by directly interacting with the protein. We propose here a new mechanism of asbestos-evoked oxidative stress, wherein fibers increase the intracellular ROS levels also by inhibiting the main antioxidant pathway of the cell.

In plain English

This laboratory study exposed cultured human lung epithelial cells (the A549 line), not people, to UICC crocidolite asbestos at several doses for 1 to 24 hours. Comparisons were untreated cells and cells given glass wool fibers (MMVF10). The authors measured the pentose phosphate pathway, which supplies NADPH for the cell's antioxidant defenses. Crocidolite inhibited this pathway in a dose- and time-dependent way. It also abolished or blunted the pathway's normal increase when cells met oxidant chemicals. Activity of the pathway's key enzyme, G6PD, fell. Other enzymes tested, and the amount of G6PD protein and mRNA, did not change significantly. Inhibition did not track nitric oxide production. Iron-depleted crocidolite inhibited the pathway as much as ordinary crocidolite, although it raised nitrite more. At a dose matching the highest crocidolite dose, for 24 hours, MMVF10 did not significantly change pathway or G6PD activity. Purified G6PD fell to 50% of control activity when mixed with crocidolite. Crocidolite-treated cells released more LDH, a sign of cell damage. The authors proposed that crocidolite may cause oxidative stress partly by inhibiting this main antioxidant pathway, without excluding other mechanisms.

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, with additional cell-free tests on purified enzymes
• Who was studied: Cultured human lung epithelial cells of the A549 line (University of Torino, Italy), incubated for 1 to 24 hours with or without fibers
• Exposure: UICC crocidolite asbestos fibers at three doses (0.25, 2.5 and 25 per square centimetre of dish; the unit symbol is damaged in the text) and iron-depleted crocidolite (treated with desferrioxamine). Glass wool fibers (man-made vitreous fibers MMVF10) were used as controls.
• Main results:
  • In A549 cells, crocidolite caused a dose- and time-dependent inhibition of basal pentose phosphate pathway activity.
  • In crocidolite-treated cells, the rise in pathway activity normally caused by three oxidant chemicals (methylene blue, tert-butyl hydroperoxide, menadione) was abolished or significantly blunted.
  • In crocidolite-treated cells, G6PD activity was significantly diminished. Activity of 6PGD, GAPDH and LDH was not significantly changed.
  • After 24 hours with crocidolite, the amount of G6PD protein (western blot) and G6PD mRNA (RT-PCR) in the cells was not significantly different from controls.
  • Crocidolite increased nitrite (a marker of nitric oxide production) in the culture medium, but nitrite levels did not correlate with pathway inhibition.
  • Iron-depleted (desferrioxamine-treated) crocidolite inhibited the pathway to the same extent as the original crocidolite. It produced significantly more nitrite than both controls and the original crocidolite.
  • MMVF10 glass fibers, at the highest dose and longest time used for crocidolite, did not significantly change pathway activity or G6PD activity compared with controls.
  • In cell-free tests (n = 4), purified G6PD fell to 50% of control activity with crocidolite, a significant decrease. Purified LDH was not appreciably changed (102% of control).
  • Crocidolite-treated cells released significantly more LDH (a sign of cell damage) into the medium, both without and after a further 3-hour exposure to menadione or tert-butyl hydroperoxide.
• The authors' conclusion: The authors proposed that, besides iron-driven radical production and inflammation, crocidolite may cause oxidative stress by inhibiting G6PD and the pentose phosphate pathway, which they describe as the cell's main antioxidant machinery.
• Limitations the authors state:
  • The authors state that their proposed mechanism does not exclude other mechanisms, which may vary with cell type, fiber type and experimental conditions.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Reactive Oxygen Species (ROS), Oxidative Stress, A549 Cells.

Related studies

• Exposure to chrysotile asbestos causes carbonylation of glucose 6-phosphate dehydrogenase through a reaction with lipid peroxidation products in human lung epithelial cells — Y. Ogasawara, K. Ishii (2010)
• 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)
• 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)
• Apoptosis induced by crocidolite asbestos in human lung epithelial cells involves inactivation of Akt and MAPK pathways — A. Baldys, P. Pande, et al. (2007)
• 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)
• Efflux of reduced glutathione after exposure of human lung epithelial cells to crocidolite asbestos — S.A. Golladay, S.H. Park, et al. (1997)

Browse more research in Free Radical Biology & Medicine, or return to medical research.