Extracellular superoxide dismutase inhibits inflammation by preventing oxidative fragmentation of hyaluronan

Our plain-English summary of Extracellular superoxide dismutase inhibits inflammation by preventing oxidative fragmentation of hyaluronan, by F. Gao, J.R. Koenitzer, J.M. Tobolewski, et al (The Journal of Biological Chemistry, 2008).

The study

• Authors: F. Gao, J.R. Koenitzer, J.M. Tobolewski, D. Jiang, J. Liang, P.W. Noble, T.D. Oury
• Journal: The Journal of Biological Chemistry
• Published: 2008;283(10):6058-66
• Cited by: 146 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Extracellular superoxide dismutase (EC-SOD) is expressed at high levels in lungs. EC-SOD has a polycationic matrix-binding domain that binds to polyanionic constituents in the matrix. Previous studies indicate that EC-SOD protects the lung in both bleomycin- and asbestos-induced models of pulmonary fibrosis. Although the mechanism of EC-SOD protection is not fully understood, these studies indicate that EC-SOD plays an important role in regulating inflammatory responses to pulmonary injury. Hyaluronan is a polyanionic high molecular mass polysaccharide found in the extracellular matrix that is sensitive to oxidant-mediated fragmentation. Recent studies found that elevated levels of low molecular mass hyaluronan are associated with inflammatory conditions. We hypothesize that EC-SOD may inhibit pulmonary inflammation in part by preventing superoxide-mediated fragmentation of hyaluronan to low molecular mass fragments. We found that EC-SOD directly binds to hyaluronan and significantly inhibits oxidant-induced degradation of this glycosaminoglycan. In vitro human polymorphic neutrophil chemotaxis studies indicate that oxidative fragmentation of hyaluronan results in polymorphic neutrophil chemotaxis and that EC-SOD can completely prevent this response. Intratracheal injection of crocidolite asbestos in mice leads to pulmonary inflammation and injury that is enhanced in EC-SOD knock-out mice. Notably, hyaluronan levels are increased in the bronchoalveolar lavage fluid after asbestos-induced pulmonary injury, and this response is markedly enhanced in EC-SOD knock-out mice. These data indicate that inhibition of oxidative hyaluronan fragmentation probably represents one mechanism by which EC-SOD inhibits inflammation in response to lung injury.

In plain English

This was a laboratory study that combined test-tube experiments with an experiment in mice. The authors asked whether extracellular superoxide dismutase (EC-SOD), an antioxidant enzyme found at high levels in the lung, protects hyaluronan, a material in the tissue around lung cells, from being broken into small fragments by reactive oxygen molecules. In the test tube, EC-SOD bound to hyaluronan. A trimmed form of the enzyme that lacked its matrix-binding region did not bind. Reactive oxygen broke hyaluronan down, and EC-SOD blocked this; 300 units fully prevented it in the authors' system. Fragmented hyaluronan drew human neutrophils (a type of white blood cell) toward it, and EC-SOD stopped this. Normal mice and mice lacking EC-SOD, 5 to 6 per group, received 0.1 mg of crocidolite asbestos or titanium dioxide into the windpipe. After asbestos, the mice lacking EC-SOD had more inflammatory cells and more hyaluronan in lung-wash fluid than normal mice given asbestos, and more hyaluronan in their blood serum. Their lung hyaluronan was also smaller. The authors noted that their sizing method was not quantitative. They concluded that preventing hyaluronan fragmentation is at least one way EC-SOD may limit lung inflammation.

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 on enzyme binding and hyaluronan breakdown, a human neutrophil migration assay, and an animal experiment in mice
• Who was studied: Male normal (wild-type C57BL/6) mice and EC-SOD knock-out mice, 8 to 10 weeks old, 5 to 6 mice per group, at the University of Pittsburgh. Neutrophils were also taken from the blood of human volunteers; the number of volunteers is not given.
• Exposure: A single dose of 0.1 mg of NIEHS crocidolite asbestos, placed into the windpipe (intratracheal instillation). Control mice received 0.1 mg of titanium dioxide. Mice were examined 14 days after treatment. In the test-tube work, reactive oxygen was generated with a copper/hydrogen peroxide system.
• Main results:
  • In the test tube, purified mouse EC-SOD bound directly to hyaluronan.
  • EC-SOD with its matrix-binding domain removed by trypsin did not bind to hyaluronan. The authors took this to mean the domain is responsible for the binding.
  • Reactive oxygen broke down hyaluronan in a dose-related way. EC-SOD inhibited this breakdown in a dose-dependent way, and 300 units fully prevented it in the authors' system. CuZn-SOD, which lacks the matrix-binding domain, needed higher concentrations to give the same protection.
  • Hyaluronan fragmented by reactive oxygen increased migration of human neutrophils compared with samples without reactive oxygen (reported as statistically significant).
  • Adding EC-SOD before reactive oxygen was generated inhibited this neutrophil migration.
  • Asbestos-treated normal mice had more inflammatory cells, mainly neutrophils, in lung-wash (BAL) fluid than titanium dioxide-treated controls. This increase was greater in asbestos-treated EC-SOD knock-out mice. Results were shown in figures only; no numbers were printed in the text.
  • Serum hyaluronan was significantly higher in asbestos-treated EC-SOD knock-out mice than in controls and than in asbestos-treated normal mice.
  • BAL fluid hyaluronan was significantly raised after asbestos in both normal and knock-out mice, and was raised even more in asbestos-treated knock-out mice than in asbestos-treated normal mice.
  • Hyaluronan in lung tissue of knock-out mice had a lower molecular mass than in normal mice given the same treatment. Lung hyaluronan was greater than 250 kDa after titanium dioxide but ranged from above 250 to less than 37 kDa after asbestos.
  • Hyaluronan-making enzymes in lung samples were not increased, and hyaluronidase (hyaluronan-cutting enzyme) activity in serum did not differ between knock-out and normal mice or between asbestos and titanium dioxide groups. The authors took this to mean the extra hyaluronan was not newly made.
• The authors' conclusion: The authors concluded that their results support the hypothesis that EC-SOD helps prevent asbestos-induced lung injury by inhibiting fragmentation of hyaluronan by reactive oxygen. They suggested this is at least one mechanism by which EC-SOD limits inflammation after lung injury.
• Limitations the authors state:
  • The method used to size hyaluronan was not quantitative, so the amount of fragmentation could not be compared directly between normal and knock-out mice.
  • Hyaluronan in BAL fluid could not easily be sized because its concentration was low.

Topics

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

Medical terms in this study, explained in our Lexicon: Superoxide, Inflammation, Pulmonary Fibrosis, Crocidolite, 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)
• 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)
• Oxidative stress alters syndecan-1 distribution in lungs with pulmonary fibrosis — C.R. Kliment, J.M. Englert, et al. (2009)
• Extracellular superoxide dismutase protects against matrix degradation of heparan sulfate in the lung — C.R. Kliment, J.M. Tobolewski, et al. (2008)
• 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)

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