Antioxidants prevent the RhoA inhibition evoked by crocidolite asbestos in human mesothelial and mesothelioma cells

Our plain-English summary of Antioxidants prevent the RhoA inhibition evoked by crocidolite asbestos in human mesothelial and mesothelioma cells, by E. Aldieri, C. Riganti, F. Silvagno, et al (American Journal of Respiratory Cell and Molecular Biology, 2011).

The study

• Authors: E. Aldieri, C. Riganti, F. Silvagno, S. Orecchia, P.G. Betta, S. Doublier, E. Gazzano, M. Polimeni, A. Bosia, D. Ghigo
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2011;45(3):625-31
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos is a naturally occurring fibrous silicate, whose inhalation is highly related to the risk of developing malignant mesothelioma (MM), and crocidolite is one of its most oncogenic types. The mechanism by which asbestos may cause MM is unclear. We have previously observed that crocidolite in human MM (HMM) cells induces NF-κB activation and stimulates the synthesis of nitric oxide by inhibiting the RhoA signaling pathway. In primary human mesothelial cells (HMCs) and HMM cells exposed to crocidolite asbestos, coincubated or not with antioxidants, we evaluated cytotoxicity and oxidative stress induction (lipid peroxidation) and the effect of asbestos on the RhoA signaling pathway (RhoA GTP binding, Rho kinase activity, RhoA prenylation, hydroxy-3-methylglutharyl-CoA reductase activity). In this paper we show that the reactive oxygen species generated by the incubation of crocidolite with primary HMCs and three HMM cell lines mediate the inhibition of 3-hydroxy-3-methylglutharyl-CoA reductase (HMGCR). The coincubation of HMCs and HMM cells with crocidolite together with antioxidants, such as Tempol, Mn-porphyrin, and the association of superoxide dismutase and catalase, prevented the cytotoxicity and lipoperoxidation caused by crocidolite alone as well as the decrease of HMGCR activity and restored the RhoA/RhoA-dependent kinase activity and the RhoA prenylation. The same effect was observed when the oxidizing agent menadione was administrated to the cells in place of crocidolite. Such a mechanism could at least partly explain the effects exerted by crocidolite fibers in mesothelial cells.

In plain English

This was a laboratory study of human cells grown in culture, not a study of people. The authors exposed two kinds of cells to crocidolite asbestos fibers for 24 hours. The first were normal mesothelial cells from three patients with no history of malignant disease. The second were three malignant mesothelioma cell lines obtained from the pleural effusions of three patients. Some cells also received antioxidants: Tempol, Mn-porphyrin, or superoxide dismutase together with catalase. In both cell types, crocidolite increased cell damage and a marker of oxidative stress. It also lowered the activity of a signaling protein called RhoA and its dependent kinase, reduced RhoA prenylation (a chemical modification), and reduced activity of HMGCR, the enzyme needed for that modification. The antioxidants prevented these changes. Menadione, a chemical used to cause oxidative stress, produced a similar pattern. Normal mesothelial cells were more sensitive to crocidolite than mesothelioma cells. The authors proposed that reactive oxygen species produced by crocidolite block HMGCR and so prevent RhoA prenylation. They stated that the mechanism of this inactivation needs to be investigated.

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
• Who was studied: Primary human mesothelial cells from three patients with no history of malignant disease, and three human malignant mesothelioma cell lines (MM98, OC99, GF99) from the pleural effusions of three patients with histologically confirmed malignant mesothelioma. All came from the biobank of the Hospital of Alessandria, Italy.
• Exposure: UICC crocidolite fibers for 24 hours: 10 (mesothelial cells) or 25 (mesothelioma cells) per square centimetre, with the unit printed as 'mg/cm2'. Some cells were also given antioxidants (Tempol, Mn-porphyrin, superoxide dismutase/catalase). Menadione was used as a comparison oxidizing agent.
• Main results:
  • The authors reported that the crocidolite doses used did not cause significant toxic effects (fewer than 20% cell deaths) after 24 hours, and that normal mesothelial cells were more sensitive to crocidolite than mesothelioma cells.
  • In both normal mesothelial and mesothelioma cells, crocidolite increased LDH release (a marker of cell damage) and 8-isoprostane production (a marker of oxidative stress). These effects were significantly reversed by the antioxidants.
  • Crocidolite markedly lowered the level of GTP-bound RhoA in both cell types.
  • Crocidolite also lowered the activity of the RhoA-dependent kinase (ROCK) in both cell types, and the antioxidants reversed this effect.
  • After crocidolite exposure, the prenylated form of RhoA decreased and the unprenylated form increased in both cell types. Tempol and superoxide dismutase/catalase completely reversed these effects.
  • Crocidolite significantly decreased HMGCR enzyme activity in both cell types. This was completely prevented when antioxidants were present.
  • Menadione, an oxidizing agent used in place of crocidolite, also significantly inhibited GTP-bound RhoA and ROCK activity, and Tempol prevented this.
  • In mesothelioma cells, crocidolite, menadione and simvastatin changed the organization of actin (part of the cell skeleton). The antioxidant Mn-porphyrin reversed this.
• The authors' conclusion: The authors proposed that reactive oxygen species produced by crocidolite prevent RhoA prenylation by blocking HMGCR activity.
• Limitations the authors state:
  • The authors stated that the mechanism by which HMGCR is inactivated still needs to be investigated.
  • The authors stated that this is not the only effect of asbestos, and that the molecular basis of crocidolite toxicity and carcinogenesis is still under investigation.

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Mesothelioma, Silicate, Malignant Mesothelioma, Mesothelial Cells, Oxidative Stress, Reactive Oxygen Species (ROS), Superoxide.

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• Patterns of 8-hydroxydeoxyguanosine formation in DNA and indications of oxidative stress in rat and human pleural mesothelial cells after exposure to crocidolite asbestos — H. Fung, Y.W. Kow, et al. (1997)
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• Iron-related toxicity of single-walled carbon nanotubes and crocidolite fibres in human mesothelial cells investigated by Synchrotron XRF microscopy — F. Cammisuli, S. Giordani, et al. (2018)
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