High levels of catalase and glutathione peroxidase activity dampen H2O2 signaling in human alveolar macrophages

Our plain-English summary of High levels of catalase and glutathione peroxidase activity dampen H2O2 signaling in human alveolar macrophages, by A.B. Carter, L.A. Tephly, S. Venkataraman, et al (American Journal of Respiratory Cell and Molecular Biology, 2004).

The study

• Authors: A.B. Carter, L.A. Tephly, S. Venkataraman, L.W. Oberley, Y. Zhang, G.R. Buettner, D.R. Spitz, G.W. Hunninghake
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2004;31(1):43-53
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Results are presented which support the hypothesis that adequate steady-state levels of hydrogen peroxide (H2O2) are required to overcome the effects of high catalase and glutathione peroxidase (GPx) expression for p38 mitogen-activated protein (MAP) kinase activation and tumor necrosis factor (TNF)-alpha gene expression in human alveolar macrophages stimulated with asbestos. We found significant differences in the types and amounts of reactive oxygen species generated in human blood monocytes compared with human alveolar macrophages. This difference in reactive oxygen species production is related, in part, to the differences in antioxidant enzyme expression and activity. Most importantly, catalase and GPx activities were significantly increased in alveolar macrophages compared with blood monocytes. Asbestos activated the p38 MAP kinase and induced TNF-alpha gene expression only in blood monocytes. Increasing the steady-state levels of H2O2 by using polyethylene glycol superoxide dismutase, an antioxidant that crosses the cell membrane, or aminotriazole, an irreversible inhibitor of catalase, allowed the p38 MAP kinase to be activated in alveolar macrophages. In addition, asbestos-stimulated macrophages cultured with polyethylene glycol superoxide dismutase had a significant increase in gene expression mediated by the TNF-alpha promoter. These results demonstrate that high catalase and GPx activity in human alveolar macrophages limits the effectiveness of H2O2 to act as a mediator of inflammatory gene expression.

In plain English

This was a laboratory study of human immune cells exposed to crocidolite asbestos in culture. The authors took alveolar macrophages (cells washed out of the lungs) and blood monocytes from healthy lifetime nonsmokers aged 18 to 45, and also used a mouse macrophage cell line. They compared reactive oxygen molecules, antioxidant enzymes, activation of a signaling protein called p38 MAP kinase, and production of the inflammatory messenger TNF-alpha. Alveolar macrophages released about nine times more hydrogen peroxide than blood monocytes and had significantly higher activity of catalase and glutathione peroxidase, enzymes that break it down. Crocidolite activated p38 and induced TNF-alpha only in blood monocytes. Raising hydrogen peroxide levels with PEG-SOD or the catalase blocker aminotriazole allowed p38 activation in alveolar macrophages. PEG-SOD also raised TNF-alpha promoter activity almost 12-fold in asbestos-exposed mouse cells. The authors concluded that high catalase and glutathione peroxidase activity in alveolar macrophages limits hydrogen peroxide's ability to drive inflammatory gene activity.

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 experiment comparing human alveolar macrophages and blood monocytes exposed to asbestos, with additional experiments in a mouse macrophage cell line (RAW 264.7)
• Who was studied: Alveolar macrophages (obtained by bronchoalveolar lavage) and blood monocytes (obtained by blood draw) from normal volunteers at the University of Iowa. Volunteers were aged 18 to 45, had no cardiopulmonary or other chronic disease, took no medications except oral contraceptives, and were lifetime nonsmokers. The number of volunteers is not stated. Some monocytes were differentiated in culture for 7 to 10 days. The mouse macrophage cell line RAW 264.7 was also used.
• Exposure: Crocidolite asbestos (NAIMA Fiber Repository) added to cultured cells, mostly at a dose printed as "5 g/cm2" (the unit prefix is lost in the text). Exposure lasted 15 minutes for most signaling and oxidant tests, 6 hours for reporter-gene tests, and 24 hours for TNF-alpha measurement. Blood monocytes were also tested over a range printed as 0.5 to 15 per cm2. Lipopolysaccharide was used as a positive control.
• Main results:
  • Hydrogen peroxide release, in pmol per million cells per minute. Blood monocytes: 3.95 without asbestos and 6.75 with asbestos; this increase approached but did not reach statistical significance (P 0.079). Alveolar macrophages: 35.6 without asbestos and 59.7 with asbestos. Alveolar macrophages released nine times the level of blood monocytes in both conditions.
  • Alveolar macrophages generated about nine times the hydrogen peroxide of blood monocytes, both without and with crocidolite.
  • Catalase activity was significantly greater in alveolar macrophages than in blood monocytes. Crocidolite caused no significant change in catalase activity in either cell type.
  • Total glutathione peroxidase (GPx) activity was significantly greater in alveolar macrophages than in blood monocytes.
  • Crocidolite strongly activated p38 MAP kinase in blood monocytes. It did not activate p38 in differentiated monocytes or in alveolar macrophages.
  • In blood monocytes, adding catalase reduced both baseline and crocidolite-induced p38 activation to below control levels.
  • In alveolar macrophages, pretreatment with PEG-SOD allowed p38 activation with asbestos. Aminotriazole (a catalase inhibitor) also increased p38 activation, more so after 3 hours of pretreatment than after 1 hour.
  • Crocidolite induced significant TNF-alpha production in blood monocytes at every concentration tested, with the largest response at 5 per cm2. TNF-alpha release by asbestos-exposed alveolar macrophages was no different from control.
  • In mouse RAW 264.7 macrophages, asbestos-exposed cells treated with PEG-SOD showed a significant, almost 12-fold increase in gene expression driven by the TNF-alpha promoter.
• The authors' conclusion: The authors concluded that activating p38 MAP kinase and TNF-alpha gene expression in asbestos-exposed alveolar macrophages requires adequate steady-state levels of hydrogen peroxide inside the cell. In their view, the high catalase and GPx activity of these cells works against this.
• Limitations the authors state:
  • The authors did not specifically evaluate the mechanism by which hydrogen peroxide activates p38 MAP kinase.

Topics

Medical terms in this study, explained in our Lexicon: Glutathione (GSH), Alveolar Macrophage, Necrosis, Reactive Oxygen Species (ROS), Superoxide, Macrophage.

Related studies

• Asbestos stimulation triggers differential cytokine release from human monocytes and alveolar macrophages — L.J. Geist, L.S. Powers, et al. (2000)
• Alveolar macrophage kinetics and multinucleated giant cell formation after lung injury — H. Prieditis, I.Y. Adamson (1996)
• Iron and reactive oxygen species in the asbestos-induced tumor necrosis factor-alpha response from alveolar macrophages — P.P. Simeonova, M.I. Luster (1995)
• Effect of kerosene and its soot on the chrysotile-mediated toxicity to the rat alveolar macrophages — J.M. Arif, S.G. Khan, et al. (1997)
• Asbestos-induced lung epithelial permeability: potential role of nonoxidant pathways — M.W. Peterson, J. Kirschbaum (1998)
• 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)

Browse more research in American Journal of Respiratory Cell and Molecular Biology, or return to medical research.