Leukocyte-derived extracellular superoxide dismutase does not contribute to airspace EC-SOD after interstitial pulmonary injury

Our plain-English summary of Leukocyte-derived extracellular superoxide dismutase does not contribute to airspace EC-SOD after interstitial pulmonary injury, by M.L. Manni, M.W. Epperly, W. Han, et al (American Journal of Physiology. Lung Cellular and Molecular Physiology, 2012).

The study

• Authors: M.L. Manni, M.W. Epperly, W. Han, T.S. Blackwell, S.R. Duncan, J.D. Piganelli, T.D. Oury
• Journal: American Journal of Physiology. Lung Cellular and Molecular Physiology
• Published: 2012;302(1):L160-6
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The antioxidant enzyme extracellular superoxide dismutase (EC-SOD) is abundant in the lung and is known to limit inflammation and fibrosis following numerous pulmonary insults. Previous studies have reported a loss of full-length EC-SOD from the pulmonary parenchyma with accumulation of proteolyzed EC-SOD in the airspace after an interstitial lung injury. However, following airspace only inflammation, EC-SOD accumulates in the airspace without a loss from the interstitium, suggesting this antioxidant may be released from an extrapulmonary source. Because leukocytes are known to express EC-SOD and are prevalent in the bronchoalveolar lavage fluid (BALF) after injury, it was hypothesized that these cells may transport and release EC-SOD into airspaces. To test this hypothesis, C57BL/6 wild-type and EC-SOD knockout mice were irradiated and transplanted with bone marrow from either wild-type mice or EC-SOD knockout mice. Bone marrow chimeric mice were then intratracheally treated with asbestos and killed 3 and 7 days later. At both 3 and 7 days following asbestos injury, mice without pulmonary EC-SOD expression but with EC-SOD in infiltrating and resident leukocytes did not have detectable levels of EC-SOD in the airspaces. In addition, leukocyte-derived EC-SOD did not significantly lessen inflammation or early stage fibrosis that resulted from asbestos injury in the lungs. Although it is not influential in the asbestos-induced interstitial lung injury model, EC-SOD is still known to be present in leukocytes and may play an influential role in attenuating pneumonias and other inflammatory diseases.

In plain English

This was a laboratory experiment in mice testing where the antioxidant enzyme extracellular superoxide dismutase (EC-SOD) found in the airspaces after lung injury comes from. C57BL/6 wild-type (WT) and EC-SOD knockout (KO) mice were irradiated and given bone marrow from WT or KO donors, producing four chimeric groups (WT/WT, WT/KO, KO/WT, KO/KO). Resident alveolar macrophages were depleted with intratracheal liposomal clodronate, and mice were then treated intratracheally with crocidolite asbestos and killed 3 or 7 days later. Western blotting of bronchoalveolar lavage fluid showed EC-SOD accumulating in WT/KO mice (lung EC-SOD, leukocytes without it) at both time points, but no EC-SOD in KO/WT mice (leukocyte EC-SOD only). Total and differential white cell counts in lavage fluid, and blinded fibrosis scoring at 7 days, showed no significant differences between the chimeric groups. The authors concluded that leukocytes do not release detectable EC-SOD into airspaces after asbestos-induced interstitial injury and that leukocyte-derived EC-SOD did not lessen inflammation or early fibrosis.

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: Animal experiment using bone marrow chimeric mice (irradiation and bone marrow transplantation, then intratracheal asbestos)
• Who was studied: Male 7-week-old C57BL/6 wild-type (Thy 1.1 and Thy 1.2) and EC-SOD null mice used as bone marrow donors and recipients, giving four chimeric groups (n = 8-12 mice per chimeric group for chimerism verification; for lavage cell counts, 5-6 mice per group at 3 days and 3-5 mice per group at 7 days); work approved at the University of Pittsburgh
• Exposure: A single intratracheal dose of crocidolite asbestos (reported as 0.14 mg, 0.1 mg per 50 microlitres in 0.9% saline), four weeks after intratracheal liposomal clodronate; nontransplanted wild-type controls received asbestos or titanium dioxide as an inert particulate control
• Main results:
  • EC-SOD was detected in the lavage fluid of WT/KO mice (lung EC-SOD present, leukocytes EC-SOD-deficient) at 3 and 7 days after asbestos, but was absent from the lavage fluid of KO/WT mice (leukocyte EC-SOD only)
  • Immunostaining 7 days after asbestos showed EC-SOD in the lung parenchyma of WT/WT and WT/KO mice; in KO/WT mice EC-SOD was only in resident alveolar macrophages and infiltrating inflammatory cells; KO/KO lungs showed none
  • Total and differential leukocyte counts in lavage fluid of the chimeric mice showed no effect of leukocyte-derived EC-SOD at 3 or 7 days
  • Blinded histological fibrosis scoring at 7 days found fibrotic areas in all mice but no significant differences between the chimeric groups; only a trend between WT/WT and KO/KO
  • Nontransplanted wild-type mice given asbestos had significantly more inflammatory cells, predominantly neutrophils, in lavage fluid than control-treated wild-type mice at 3 and 7 days
  • Nontransplanted wild-type mice had higher lavage EC-SOD levels than the bone marrow chimeric mice at 3 and 7 days after asbestos
  • Clodronate pretreatment did not change EC-SOD levels in the lavage fluid of chimeric mice
  • Chimerism, as mean percentage of donor cells among total T lymphocytes: WT/WT 74.62 plus or minus 6.91; WT/KO 80.33 plus or minus 3.28; KO/WT 58.87 plus or minus 6.93; KO/KO 99.08 plus or minus 0.60
• The authors' conclusion: The authors concluded that leukocytes do not release detectable EC-SOD into the airspaces after asbestos-induced interstitial lung injury and that leukocyte-derived EC-SOD did not appear to protect against inflammation or early fibrosis in this model
• Limitations the authors state:
  • Leukocytes might release EC-SOD at levels below the detection of the assays used
  • Absolute levels of EC-SOD in the lungs of the mice were not directly measured (the authors suggested radiation treatment might explain why wild-type mice had more lavage EC-SOD than WT/WT chimeric mice)
  • The 7-day time point is only the beginning of fibrosis, which may explain why only a trend, not a significant difference, was seen between WT/WT and KO/KO mice
  • The findings are specific to this interstitial injury model; the authors noted leukocyte-derived EC-SOD may still matter in pulmonary infection

Topics

Medical terms in this study, explained in our Lexicon: Superoxide, Interstitial, Inflammation, Fibrosis, Parenchyma, 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)
• Increased sensitivity to asbestos-induced lung injury in mice lacking extracellular superoxide dismutase — C.L. Fattman, R.J. Tan, et al. (2006)
• Extracellular superoxide dismutase inhibits inflammation by preventing oxidative fragmentation of hyaluronan — F. Gao, J.R. Koenitzer, et al. (2008)
• 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)
• Mitochondrial biogenesis in the pulmonary vasculature during inhalational lung injury and fibrosis — M.S. Carraway, H.B. Suliman, et al. (2008)

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