Exposure to chrysotile asbestos causes carbonylation of glucose 6-phosphate dehydrogenase through a reaction with lipid peroxidation products in human lung epithelial cells

Our plain-English summary of Exposure to chrysotile asbestos causes carbonylation of glucose 6-phosphate dehydrogenase through a reaction with lipid peroxidation products in human lung epithelial cells, by Y. Ogasawara, K. Ishii (Toxicology Letters, 2010).

The study

• Authors: Y. Ogasawara, K. Ishii
• Journal: Toxicology Letters
• Published: 2010;195(1):1-8
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Exposure to asbestos is known to lead to a reduction in glucose 6-phosphate dehydrogenase (G6PDH) activity and to cause oxidative damage to cells. In the present study, we exposed the human lung carcinoma cell line A549 to chrysotile. We observed an increase in the production of thiobarbituric acid-reactive substances (TBARS, the breakdown products of lipid peroxide) along with a significant decrease in G6PDH activity. Alternatively, when chrysotile was added directly to the cell extract obtained by removing the cell membrane, no loss of G6PDH activity was observed. To elucidate the mechanism of G6PDH inactivation due to exposure to chrysotile, we focused on the TBARS responsible for protein modification via carbonylation. When malondialdehyde or 4-hydroxy-2-nonenal was added to a membrane-free A549 cell extract, G6PDH activity was reduced markedly. However, when t-butylhydroperoxide was added to the extract, there was no significant decrease in G6PDH activity. Western blot analysis and immunoprecipitation of the carbonylated proteins in the A549 cell lysate that was prepared after exposure to chrysotile demonstrated that G6PDH had been carbonylated. Our findings indicate that the decrease in G6PDH activity that occurs after exposure of the cultured cells to chrysotile results from the carbonylation of G6PDH by TBARS.

Copyright (c) 2010 Elsevier Ireland Ltd. All rights reserved.

In plain English

In this laboratory study, the authors exposed A549 cells, a human lung carcinoma cell line described as lung epithelial type II cells, to UICC chrysotile B asbestos for 5 hours. One comparison also used crocidolite. No people or animals were studied. Activity of G6PDH, an enzyme in an antioxidant pathway, fell significantly after exposure to both fibers, with a clearer effect for chrysotile. Cell viability was unaffected under these experimental conditions. Chrysotile-exposed cells had significantly lower reduced and total glutathione, no build-up of oxidized glutathione, no significant change in the NADPH ratio, and more TBARS, which are breakdown products of lipid peroxides. Chrysotile added directly to cell extracts with the membrane removed did not significantly change G6PDH activity. In those extracts, the aldehydes malondialdehyde and 4-hydroxy-2-nonenal reduced it, while t-butylhydroperoxide caused no statistically significant decrease. Glutathione protected against 4-hydroxy-2-nonenal. Western blotting and immunoprecipitation showed increased carbonylation, a chemical modification, of G6PDH after chrysotile exposure. The authors concluded that the loss of G6PDH activity was mainly due to this carbonylation. They called for studies in normal lung epithelial and pleural mesothelial cells.

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 cell-culture (in vitro) experiment, including tests in a cell-free system made from membrane-free cell extracts
• Who was studied: A549 cells, a human lung carcinoma cell line described as lung epithelial type II cells, obtained from the Health Science Research Resources Bank (Osaka, Japan). Most measurements used n = 4 per group; the immunoprecipitation densitometry used n = 3. No human subjects.
• Exposure: Union Internationale Contre le Cancer (UICC) chrysotile B, and UICC crocidolite for comparison in the enzyme-activity experiment. Fibers were serum-coated and washed with deferoxamine. Cells were exposed for 5 hours at a dose printed as '5 g/cm2'; the micro sign appears lost, so this is likely 5 micrograms per square centimetre. In the cell-free tests, chrysotile was printed as '50 g/ml', and malondialdehyde, 4-hydroxy-2-nonenal and t-butylhydroperoxide were each printed as '500 M'.
• Main results:
  • In A549 cells, G6PDH activity decreased significantly after 5 hours of exposure to both chrysotile and crocidolite, with a clearer effect for chrysotile (figure marked p less than 0.01).
  • Cell viability was not affected by asbestos fibers under the experimental conditions tested.
  • In chrysotile-exposed cells, reduced GSH and total GSH fell significantly, and oxidized glutathione (GSSG) did not accumulate.
  • No significant change in the NADPH ratio was seen after 5 hours of asbestos exposure.
  • Chrysotile exposure for 5 hours produced a significant amount of TBARS in the cells (figure marked p less than 0.01).
  • Chrysotile added directly to membrane-free cell extracts caused no statistically significant change in G6PDH activity.
  • In membrane-free cell extracts, malondialdehyde and 4-hydroxy-2-nonenal reduced G6PDH activity, while t-butylhydroperoxide caused no statistically significant decrease.
  • Glutathione protected G6PDH against inactivation by 4-hydroxy-2-nonenal in the cell-free system.
  • In chrysotile-exposed cells, Western blotting showed a more carbonylated 56 kDa protein that matched G6PDH. Immunoprecipitation showed increased carbonylation of G6PDH (densitometry n = 3, p less than 0.05).
• The authors' conclusion: The authors concluded that the loss of G6PDH activity after chrysotile exposure is mainly due to carbonylation of the enzyme, a lysine-aldehyde adduct, through reaction with lipid peroxidation breakdown products (TBARS).
• Limitations the authors state:
  • The authors stated that future studies should clarify whether G6PDH carbonylation from chrysotile also occurs in normal human lung epithelial and pleural mesothelial cells.
  • The authors stated that the mechanism by which chrysotile generates reactive oxygen species leading to lipid aldehydes remains to be elucidated.

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, Carcinoma.

Related studies

• 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)
• Chrysotile inhibits glutathione-dependent protection against the onset of lipid peroxidation in rat lung microsomes — J.M. Arif, I. Ahmad, et al. (1996)
• Chrysotile Causes Human Bronchial Epithelial Cell Apoptosis in Response to the Fas-Mediated Apoptosis Pathway — M. Zhang, J. Chen, et al. (2017)
• Fibre-induced lipid peroxidation leads to DNA adduct formation in Salmonella typhimurium TA104 and rat lung fibroblasts — P.J. Howden, S.P. Faux (1996)
• 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)
• Lipid peroxidation and disintegration of the cell membrane structure in cultures of rat lung fibroblasts treated with asbestos — H. Iguchi, S. Kojo, et al. (1993)

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