Asbestos fibers and interferon-gamma up-regulate nitric oxide production in rat alveolar macrophages

Our plain-English summary of Asbestos fibers and interferon-gamma up-regulate nitric oxide production in rat alveolar macrophages, by G. Thomas, T. Ando, K. Verma, et al (American Journal of Respiratory Cell and Molecular Biology, 1994).

The study

• Authors: G. Thomas, T. Ando, K. Verma, E. Kagan
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 1994;11(6):707-15
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The present study was undertaken to determine whether asbestos exposure induces the formation of nitric oxide (NO.) radical by rat alveolar macrophages (AM). For this purpose, AM from Sprague-Dawley rats were cultured for 48 h in the presence or absence of either chrysotile (serpentine) or crocidolite (amphibole) asbestos fibers. The effects of asbestos fibers were compared with those of nonfibrogenic carbonyl iron particles. Nitrite (NO2-), the stable oxidation product of NO. in macrophage conditioned medium, was assayed by the Griess reaction. Production of NO2- by AM was significantly increased by both chrysotile (P < 0.01) and crocidolite (P < 0.05) asbestos fibers (10 micrograms/ml). Since interferon-gamma (IFN-gamma) is known to induce NO. synthase within macrophages, and since elevated levels of intrapulmonary IFN-gamma have been noted in asbestos workers, the combined effects of asbestos and IFN-gamma also were studied in the context of NO. formation. Addition of IFN-gamma (250 to 500 IU/ml) synergistically enhanced the formation of NO2- induced by chrysotile and crocidolite. Notably, carbonyl iron had no significant effect on NO. production by AM. NO2- production was significantly attenuated by the NO. synthase inhibitor, NG-monomethyl-L-arginine (0.5 to 1 mg/ml). By contrast, superoxide dismutase (150 U/ml) significantly enhanced asbestos-induced NO2- production by AM (P < 0.001). Since superoxide anion can interact with NO. to generate the toxic hydroxyl radical, and since superoxide dismutase is known to protect against asbestos-induced injury, the induction of NO. radical by asbestos fibers may represent a novel form of asbestos-related injury.

In plain English

This was a laboratory study of lung immune cells (alveolar macrophages) taken from adult male Sprague-Dawley rats and grown in culture. The cells were exposed to chrysotile or crocidolite asbestos fibers, or to nonfibrogenic carbonyl iron particles. The authors then measured nitrite, a breakdown product of nitric oxide. Both chrysotile and crocidolite at 10 micrograms per milliliter significantly increased nitrite compared with unexposed cells. Carbonyl iron did not, even at a higher dose that damaged cells about as much as crocidolite did. Crocidolite's effect rose with time and with dose. Adding the immune signal interferon-gamma to either asbestos type produced more nitrite than the two separate effects combined. A superoxide-removing enzyme (SOD) raised nitrite in all cultures, significantly more with asbestos. A nitric oxide blocker cut nitrite significantly only when interferon-gamma was present. It did not reduce crocidolite's damage to the cells. The authors concluded that nitric oxide production by asbestos fibers may represent a novel mechanism of asbestos-related lung injury.

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) experiment on cultured rat cells
• Who was studied: Alveolar macrophages collected by lung lavage from adult male Sprague-Dawley rats, studied at Georgetown University School of Medicine, Washington, DC; the number of rats is not stated
• Exposure: NIEHS chrysotile and crocidolite asbestos, mostly at 10 micrograms per milliliter (crocidolite also at 2.5 to 10). Carbonyl iron particles at 10, 50 and 100 micrograms per milliliter. Recombinant rat interferon-gamma at 250 or 500 IU/ml, the nitric oxide synthase inhibitor L-NMMA, and superoxide dismutase (150 U/ml).
• Main results:
  • In 48-hour cultures, cells exposed to chrysotile or crocidolite (10 micrograms per milliliter) produced significantly more nitrite than unexposed control cells (P less than 0.01 for chrysotile; P less than 0.05 for crocidolite).
  • Nitrite production in crocidolite-exposed cultures rose progressively over time, with a maximum at 48 hours.
  • Crocidolite at 2.5 to 10 micrograms per milliliter showed a dose-response relationship. All three concentrations gave significantly more nitrite than control cultures.
  • Carbonyl iron at 10 micrograms per milliliter had an effect on nitric oxide production that was not significantly different from control cultures.
  • With interferon-gamma (250 IU/ml), crocidolite-exposed cultures produced 30.09 ± 1.87 nmol nitrite per 500,000 cells. This exceeded the sum for crocidolite alone (4.3 ± 0.9) and interferon-gamma alone (20.28 ± 2.01). A similar synergy was seen with chrysotile (26.1 ± 4.96 with interferon-gamma, versus 2.87 ± 0.66 for chrysotile alone).
  • Carbonyl iron plus interferon-gamma gave no different result from interferon-gamma alone.
  • Superoxide dismutase increased nitrite in all cultures. In cultures containing it, nitrite was significantly higher after crocidolite or chrysotile exposure than in unexposed controls (P less than 0.001).
  • Without interferon-gamma, the inhibitor L-NMMA reduced nitrite, but not to a statistically significant degree. With interferon-gamma (250 IU/ml), it significantly reduced nitrite in both particle-exposed and control cultures (P less than 0.001).
  • Crocidolite significantly increased cell damage, measured as LDH release. L-NMMA did not prevent this damage.
  • Carbonyl iron at 100 micrograms per milliliter damaged cells about as much as crocidolite at 10 micrograms per milliliter, but did not affect nitric oxide production.
  • In a rat aorta relaxation test, medium from chrysotile-exposed cultures caused more vessel relaxation than medium from unexposed cultures. Control medium also showed some relaxing activity. The effect was blocked by methylene blue.
• The authors' conclusion: The authors concluded that crocidolite and chrysotile can increase nitric oxide production by rat alveolar macrophages, an effect potentiated by interferon-gamma. They suggested this may represent a novel mechanism of asbestos-related lung injury.
• Limitations the authors state:
  • A significant fraction of nitric oxide production was not blocked by L-NMMA. The authors suggest some nitrite may have come from sources other than L-arginine.
  • The authors describe the superoxide dismutase findings as only indirect evidence that asbestos increases both nitric oxide and superoxide.
  • L-NMMA itself was somewhat toxic to the cells.

Topics

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

Medical terms in this study, explained in our Lexicon: Alveolar Macrophage, Asbestos Exposure, Chrysotile, Serpentine Group, Crocidolite, Amphibole Group, Macrophage, Superoxide.

Related studies

• Mechanisms of asbestos-induced nitric oxide production by rat alveolar macrophages in inhalation and in vitro models — T.R. Quinlan, K.A. BeruBe, et al. (1998)
• Nitric oxide (NO) synthase activity in the lung and NO synthesis in alveolar macrophages of rats increased on exposure to asbestos — H. Iguchi, S. Kojo, et al. (1996)
• Iron inhibits the nitric oxide synthesis elicited by asbestos in murine macrophages — E. Aldieri, D. Ghigo, et al. (2001)
• Lung mesothelial cell and fibroblast responses to pleural and alveolar macrophage supernatants and to lavage fluids from crocidolite-exposed rats — I.Y. Adamson, H. Prieditis, et al. (1997)
• Production of nitric oxide elevates nitrosothiol formation resulting in decreased glutathione in macrophages exposed to asbestos or asbestos substitutes — T. Nishiike, Y. Nishimura, et al. (2005)
• Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis — K.E. Driscoll, J.K. Maurer, et al. (1995)

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