Hydroxyl radicals are formed in the rat lung after asbestos instillation in vivo

Our plain-English summary of Hydroxyl radicals are formed in the rat lung after asbestos instillation in vivo, by R.M. Schapira, A.J. Ghio, R.M. Effros, et al (American Journal of Respiratory Cell and Molecular Biology, 1994).

The study

• Authors: R.M. Schapira, A.J. Ghio, R.M. Effros, J. Morrisey, C.A. Dawson, A.D. Hacker
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 1994;10(5):573-9
• Cited by: 52 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The hydroxyl radical (.OH) has been implicated as a cause of lung injury following asbestos exposure. However, despite in vitro evidence associating asbestos with .OH production, there has been no demonstration of such generation in vivo. We tested the hypothesis that .OH is formed in the lungs of rats exposed to asbestos in vivo by using salicylate as a free radical trap. Asbestos was instilled intratracheally, and control rats were sham-exposed. Six to seven days after exposure, the rats were given salicylate, the lungs were isolated, and salicylate hydroxylation products (2,3- and 2,5-dihydroxybenzoic acid), reflecting .OH production, were measured. There was significantly more 2,3-dihydroxybenzoic acid in asbestos-exposed lungs compared with control lungs (2.32 +/- 0.360 nmol/lung versus 0.292 +/- 0.125, respectively, P < 0.001) and 2,5-dihydroxybenzoic acid (9.69 +/- 1.65 nmol/lung versus 2.63 +/- 0.274, respectively, P < 0.001). To demonstrate that the dihydroxybenzoic acid was actually formed in the lungs, the lungs from asbestos-exposed and control rats were isolated and perfused with either salicylate or 2,3-dihydroxybenzoic acid. In the lungs perfused with salicylate, 2,3- and 2,5-dihydroxybenzoic acids were detectable only in asbestos-exposed lungs. In the isolated lungs perfused with 2,3-dihydroxybenzoic acid, there was no significant difference in 2,3-dihydroxybenzoic acid between asbestos-exposed and control lungs. We conclude that asbestos stimulates .OH production in lungs in vivo.

In plain English

This was an animal experiment in rats. The authors placed a single dose of 6.0 mg of iron-loaded chrysotile asbestos into the windpipes of 11 rats, and 13 control rats received salt water. Six to seven days later the rats were given salicylate. Salicylate reacts with hydroxyl radicals, a highly reactive form of oxygen, to form products called 2,3- and 2,5-DHBA, which the authors measured in the lungs. The asbestos-exposed lungs showed injury and were heavier than control lungs (2.50 versus 1.41 g). They contained more 2,3-DHBA (2.32 versus 0.292 nmol per lung) and more 2,5-DHBA (9.69 versus 2.63 nmol per lung), both p less than 0.001. Blood levels did not differ significantly between the groups. In lungs removed from the body and perfused with salicylate, the products appeared in asbestos-exposed lungs, while 2,3-DHBA was not detectable in control lungs. The authors concluded that instilling iron-loaded chrysotile asbestos into rat lungs was associated with hydroxyl radical production in the lungs. They noted that their method captured only radicals formed while salicylate was present, and that the timing of production remains open.

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 in rats (intratracheal instillation of asbestos versus sham exposure), with additional isolated, perfused lung experiments
• Who was studied: Sprague-Dawley rats weighing 351 to 400 g. In the main experiment, 11 rats were asbestos-exposed and 13 were sham-exposed controls. Further rats were used for the isolated lung experiments: 4 asbestos-exposed and 4 sham-exposed lungs perfused with salicylate, and 3 asbestos-exposed and 5 sham-exposed lungs perfused with 2,3-DHBA. Lungs from 2 normal rats were used to check the homogenization step. The article does not state where or when the experiments were done.
• Exposure: Iron-loaded chrysotile asbestos, given as a single intratracheal instillation of 0.3 cc (6.0 mg). Controls received 0.3 ml of sterile 0.9% saline. Lungs were studied 6 to 7 days later (11 to 15 days later in the 2,3-DHBA uptake experiment).
• Main results:
  • Asbestos-exposed lungs showed injury and weighed significantly more than sham-exposed lungs: 2.50 ± 0.11 g versus 1.41 ± 0.03 g (P < 0.001).
  • Asbestos-exposed lungs (n = 11) contained more 2,3-DHBA than sham-exposed lungs (n = 13): 2.32 ± 0.360 versus 0.292 ± 0.125 nmol/lung (mean ± SEM, P < 0.001).
  • Asbestos-exposed lungs contained more 2,5-DHBA than sham-exposed lungs: 9.69 ± 1.65 versus 2.63 ± 0.274 nmol/lung (P < 0.001).
  • Plasma 2,3-DHBA, 2,5-DHBA and salicylate did not differ significantly between asbestos-exposed (n = 8) and sham-exposed (n = 7) rats.
  • In asbestos-exposed lungs (n = 4) that were removed and perfused with salicylate for 1 h, 2,3-DHBA measured 0.725 ± 0.127 nmol/lung.
  • In sham-exposed lungs treated the same way, 2,3-DHBA was not detectable.
  • Isolated lungs perfused with 2,3-DHBA took it up without a significant difference between asbestos-exposed (n = 3) and control (n = 5) lungs: 0.794 ± 0.115 versus 0.467 ± 0.059 nmol/lung (P > 0.05).
  • Adding asbestos to normal lungs only during homogenization gave 0.062 ± 0.062 nmol/lung of 2,3-DHBA. The authors reported this was within the range of the sham-exposed lungs.
• The authors' conclusion: The authors concluded that instilling iron-loaded chrysotile asbestos into rat lungs is associated with hydroxyl radical production in the living lung. They wrote that this supports the hypothesis that oxygen-based free radicals could mediate lung injury associated with silicates.
• Limitations the authors state:
  • The measured 2,3-DHBA reflects only hydroxyl radicals produced while salicylate was present, not the total produced since exposure.
  • The time course of hydroxyl radical production after asbestos exposure remains an open question.
  • This was an initial study that used iron-loaded asbestos to maximize the chance of detecting the radicals.
  • 2,5-DHBA is a less specific marker, because it can also be made from salicylate by an enzyme system (cytochrome P-450) rather than by hydroxyl radicals.

Topics

Medical terms in this study, explained in our Lexicon: Hydroxyl Radical, Asbestos Exposure.

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