Nitric oxide (NO) synthase activity in the lung and NO synthesis in alveolar macrophages of rats increased on exposure to asbestos

Our plain-English summary of Nitric oxide (NO) synthase activity in the lung and NO synthesis in alveolar macrophages of rats increased on exposure to asbestos, by H. Iguchi, S. Kojo, M. Ikeda (Journal of Applied Toxicology, 1996).

The study

• Authors: H. Iguchi, S. Kojo, M. Ikeda
• Journal: Journal of Applied Toxicology
• Published: 1996;16(4):309-15
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We examined whether the lung of rats induced nitric oxide synthase (NOS) on instillation of Union Internationale Contre le Cancer (UICC) asbestos into the trachea, and whether alveolar macrophages (M phi s) of rats increased synthesis of nitric oxide (NO) on exposure to the asbestos. Instillation of chrysotile asbestos (CH) into rat tracheas increased NOS activity in the lung up to fourfold compared with that of normal control rats. On instillation of amosite asbestos (AM), the activity did not significantly increase. In the culture of alveolar M phi s with CH, NO2-, a stable oxidation product of NO, in the conditioned medium markedly increased while in the culture with AM or crocidolite (CR) asbestos it was comparable to that in the control culture without asbestos. Thus, it was assumed that the lung as well as alveolar M phi s induced NOS on exposure to CH. Viability of M phi s was lower in the culture with CH than in the culture with AM or CR. When alveolar M phi s were cultured in the presence of lipopolysaccharide (LPS), a potent inducer of NOS, NO2- in the medium dramatically increased, indicating a possible induction of NOS, while NO2- was decreased significantly in the presence of both LPS and CH, AM or CR. On the other hand, when M phi s which had previously been stimulated with LPS were cultured in LPS-free medium, NO2- synthesis retained a significantly increased level, irrespective of the presence or absence of asbestos. Thus, the three kinds of asbestos used seemed to interfere with LPS in inducing NOS and to decrease subsequently the synthesis of NO2-, but not to affect the synthesis of NO2- by LPS-induced NOS. Taken altogether, lung or alveolar M phi s of rats induced NOS to increase NO synthesis on exposure to CH.

In plain English

This laboratory study in rats, from Japan, asked whether asbestos makes the lung produce more nitric oxide, a reactive molecule, by switching on the enzyme nitric oxide synthase (NOS). Male Wistar rats had chrysotile or amosite asbestos (UICC reference samples) or plain saline put into the windpipe, four rats per group, and their lungs were examined 48 hours later. Separately, alveolar macrophages (immune cells washed out of rat lungs) were grown in culture with amosite, crocidolite or chrysotile. In lungs given chrysotile, NOS activity was about fourfold that of control rats. With amosite it was slightly, but not significantly, higher. Both fibers increased lung weight. In culture, only chrysotile raised nitrite, a breakdown product of nitric oxide, and it lowered cell survival more than the other fibers. All three fibers reduced the nitrite produced when cells were stimulated with bacterial endotoxin (LPS). The authors concluded that only chrysotile appeared able to induce NOS. They noted that other lung cells might have contributed, and that microscopic tissue examination was not done.

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: asbestos instilled into rat tracheas, combined with laboratory (in vitro) cultures of rat alveolar macrophages
• Who was studied: Male Wistar rats weighing about 300 g, Kyoto University, Japan. In the instillation experiment there were 4 rats per group (saline control, amosite, chrysotile). Alveolar macrophages were collected by lung lavage from rats of the same strain and cultured in more than six wells per condition.
• Exposure: UICC standard reference amosite, crocidolite and Canadian chrysotile, ground and sonicated, with almost all fibers shorter than about 50 micrometres. Cultures used 50, 100 or 200 micrograms per ml of asbestos, with or without E. coli lipopolysaccharide (LPS) at 1.0 micrograms per ml. Rats were instilled with 0.5 ml of saline containing 10 mg per ml of amosite or chrysotile, or with saline alone. Crocidolite was not instilled.
• Main results:
  • In the lungs of chrysotile-instilled rats (n = 4), NOS activity was about fourfold that of saline control rats (n = 4).
  • In the lungs of amosite-instilled rats, NOS activity was slightly, but not significantly, higher than in control rats.
  • Lung wet weight 48 h after instillation was 1.36 ± 0.05 g in control rats, 1.64 ± 0.09 g in amosite-treated rats and 1.99 ± 0.12 g in chrysotile-treated rats. Both increases were significant at P less than 0.01.
  • Chrysotile-instilled lungs showed marked swelling and blotchy brownish lesions to the naked eye. Amosite-instilled lungs showed swelling only. Saline controls showed neither.
  • Adding NOS inhibitors (NMMA or NNA) to the assay cut NOS activity in chrysotile-instilled lungs by about 50% (data not shown).
  • In macrophage cultures, nitrite rose significantly after 24 or 48 h with chrysotile. With amosite or crocidolite at each concentration, nitrite was comparable to control cultures without asbestos.
  • After 24 h at 200 micrograms per ml, macrophage viability with amosite, crocidolite and chrysotile was about 97%, 98% and 74% by trypan blue, and 86%, 84% and 69.1% by MTT test. Control cultures were nearly 100%. The authors stated that chrysotile was more toxic to the cells.
  • LPS alone markedly raised nitrite in macrophage cultures. With LPS plus chrysotile, amosite or crocidolite, nitrite was significantly lower than with LPS alone.
  • Macrophages first stimulated with LPS for 12 h and then cultured without LPS kept significantly raised nitrite whether or not 200 micrograms per ml of asbestos was present.
• The authors' conclusion: The authors concluded that rat lungs and alveolar macrophages induced NOS and increased nitric oxide synthesis on exposure to chrysotile. They stated that only chrysotile, among the asbestos types tested, appeared able to induce NOS in both the animal and the culture experiments.
• Limitations the authors state:
  • The authors could not rule out that lung cells other than alveolar macrophages contributed to the NOS activity measured in instilled lungs.
  • Microscopic (histopathological) examination of the chrysotile-instilled lungs was not done.

Topics

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

Medical terms in this study, explained in our Lexicon: Alveolar Macrophage, UICC, Chrysotile, Amosite, Crocidolite.

Related studies

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• Asbestos fibers and interferon-gamma up-regulate nitric oxide production in rat alveolar macrophages — G. Thomas, T. Ando, et al. (1994)
• Dual role of inducible nitric oxide synthase in acute asbestos-induced lung injury — M. Dörger, A.M. Allmeling, et al. (2002)
• 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)
• Early inflammatory response to asbestos exposure in rat and hamster lungs: role of inducible nitric oxide synthase — M. Dörger, A.M. Allmeling, et al. (2002)
• Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells — S.H. Park, A.E. Aust (1998)

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