Extracellular superoxide dismutase protects against matrix degradation of heparan sulfate in the lung

Our plain-English summary of Extracellular superoxide dismutase protects against matrix degradation of heparan sulfate in the lung, by C.R. Kliment, J.M. Tobolewski, M.L. Manni, et al (Antioxidants & Redox Signaling, 2008).

The study

• Authors: C.R. Kliment, J.M. Tobolewski, M.L. Manni, R.J. Tan, J. Enghild, T.D. Oury
• Journal: Antioxidants & Redox Signaling
• Published: 2008;10(2):261-8
• Cited by: 83 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestosis is a form of interstitial lung disease caused by the inhalation of asbestos fibers, leading to inflammation and pulmonary fibrosis. Inflammation and oxidant/antioxidant imbalances are known to contribute to the disease pathogenesis. Extracellular superoxide dismutase (EC-SOD) is an antioxidant enzyme that has been shown to protect the lung from oxidant-mediated damage, inflammation, and interstitial fibrosis. Extracellular matrix (ECM) components, such as collagen and glycosaminoglycans, are known to be sensitive to oxidative fragmentation. Heparan sulfate, a glycosaminoglycan, is highly abundant in the ECM and tightly binds EC-SOD. We investigated the protective role of EC-SOD by evaluating the interaction of EC-SOD with heparan sulfate in the presence of reactive oxygen species (ROS). We found that ROS-induced heparin and heparan sulfate fragments induced neutrophil chemotaxis across a modified Boyden chamber, which was inhibited by the presence of EC-SOD by scavenging oxygen radicals. Chemotaxis in response to oxidatively fragmented heparin was mediated by Toll-like receptor-4. In vivo, bronchoalveolar lavage fluid from EC-SOD knockout mice at 1, 14, and 28 days after asbestos exposure showed increased heparan sulfate shedding from the lung parenchyma. We demonstrate that one mechanism through which EC-SOD inhibits lung inflammation and fibrosis in asbestosis is by protecting heparin/heparan sulfate from oxidative fragmentation.

In plain English

This laboratory study examined extracellular superoxide dismutase (EC-SOD), an antioxidant enzyme in the lung, and heparan sulfate, a component of the tissue framework that binds it. In test-tube experiments, the authors broke down heparin and heparan sulfate with reactive oxygen species made from copper sulfate and hydrogen peroxide. They then measured whether human neutrophils (white blood cells from volunteers) moved toward the fragments. Fragmented heparin and heparan sulfate drew neutrophils, while intact heparin and the reactive oxygen species alone did not, and adding EC-SOD inhibited this movement. An antibody blocking Toll-like receptor 4 prevented movement toward heparin fragments. In mice, crocidolite asbestos was injected into the lungs of normal mice and of mice lacking EC-SOD. Lung washing fluid from asbestos-treated normal mice showed an increase in shed heparan sulfate at 1, 14 and 28 days, and mice lacking EC-SOD showed a larger increase. The authors measured blot band density and reported significant increases in mice lacking EC-SOD. The authors concluded that EC-SOD can protect heparin and heparan sulfate from oxidant-mediated breakdown and inhibit associated inflammatory responses.

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 study: test-tube (in vitro) experiments with human neutrophils, plus an animal experiment in mice
• Who was studied: Neutrophils isolated from blood drawn from human volunteers (University of Pittsburgh); 8- to 10-week-old male C57BL/6 wild-type mice and EC-SOD knockout mice. A symbol next to the group size was lost in scanning, so the exact number of mice per time point and genotype cannot be read with certainty.
• Exposure: In mice: crocidolite asbestos, or titanium dioxide as an inert control particle, at 0.1 mg in sterile saline, injected into the lungs through the windpipe; lung washing fluid was collected 1, 14 and 28 days later. In vitro: heparin and heparan sulfate exposed to reactive oxygen species generated by a copper sulfate and hydrogen peroxide system, with or without EC-SOD.
• Main results:
  • In the test system, superoxide was significantly higher in reactions containing both hydrogen peroxide and copper sulfate (heparin system).
  • Heparin fragmented by reactive oxygen species increased neutrophil movement across the membrane compared with heparin without reactive oxygen species.
  • EC-SOD inhibited neutrophil movement toward fragmented heparin at 50 U (data not shown) and 100 U per lower well.
  • Unfragmented heparin without reactive oxygen species did not stimulate neutrophil movement.
  • Similar results were seen with heparan sulfate fragmented by reactive oxygen species. Reactive oxygen species without heparin or heparan sulfate produced no neutrophil movement.
  • An antibody against Toll-like receptor 4 prevented neutrophil movement induced by heparin fragments.
  • Lung washing fluid from asbestos-treated wild-type mice showed an increase in shed heparan sulfate at 1, 14 and 28 days after exposure (Western blot).
  • In EC-SOD knockout mice, asbestos led to a larger increase in heparan sulfate shedding: at 1 day (HS2), 14 days (HS1 and 2) and 28 days (HS1 and 3). The authors predicted, from molecular size, that these heparan sulfate species are syndecans.
  • The Western blot bands were quantified by densitometry, normalized to protein loading, and tested statistically. The authors reported significant increases in three heparan sulfate species (HS1, HS2 and HS3) in EC-SOD knockout mice compared with wild-type mice. The measured values are not printed in the text.
• The authors' conclusion: The authors concluded that EC-SOD can protect heparin and heparan sulfate from oxidant-mediated degradation and inhibit associated inflammatory responses.
• Limitations the authors state:
  • The authors stated that more work is needed to determine the direct interactions between EC-SOD and heparan sulfate in living animals.

Topics

Medical terms in this study, explained in our Lexicon: Superoxide, Interstitial Lung Disease, Inflammation, Pulmonary Fibrosis, Interstitial Fibrosis, Collagen, Reactive Oxygen Species (ROS), Bronchoalveolar Lavage (BAL).

Related studies

• Inflammatory cells as a source of airspace extracellular superoxide dismutase after pulmonary injury — R.J. Tan, J.S. Lee, et al. (2006)
• Extracellular superoxide dismutase inhibits inflammation by preventing oxidative fragmentation of hyaluronan — F. Gao, J.R. Koenitzer, et al. (2008)
• Leukocyte-derived extracellular superoxide dismutase does not contribute to airspace EC-SOD after interstitial pulmonary injury — M.L. Manni, M.W. Epperly, et al. (2012)
• Extracellular superoxide dismutase in pulmonary fibrosis — F. Gao, V.L. Kinnula, et al. (2008)
• Increased sensitivity to asbestos-induced lung injury in mice lacking extracellular superoxide dismutase — C.L. Fattman, R.J. Tan, et al. (2006)
• Syndecan-1 alters heparan sulfate composition and signaling pathways in malignant mesothelioma — G. Heidari-Hamedani, R.R. Vivès, et al. (2015)

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