Effects of cigarette smoke on tissue uptake and retention of iron oxide in the guinea pig

Our plain-English summary of Effects of cigarette smoke on tissue uptake and retention of iron oxide in the guinea pig, by B. Gilks, J. Wright, A. Churg (The American Review of Respiratory Disease, 1988).

The study

• Authors: B. Gilks, J. Wright, A. Churg
• Journal: The American Review of Respiratory Disease
• Published: 1988;137(6):1382-4
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We have previously shown that cigarette smoke increases retention and tissue penetration of asbestos, a pathogenic dust. To determine whether these same phenomena occur with an inert dust, we administered iron oxide particles to guinea pigs by intratracheal instillation. Half of the animals were exposed to cigarette smoke. Animals were killed at 1 day, 1 wk, and 1 month. Numbers of particles in airway epithelia and walls were counted in histologic sections of one lung, and the other lung was analyzed chemically for iron content. In both smoke-exposed and nonexposed groups, the chemically determined concentration of iron in the lung tissue decreased between 1 day and 1 month; however, the concentration of iron was significantly greater in the smoke-exposed group at 1 day and 1 wk. By 1 month, there was no significant difference between the 2 groups. The number of particles in the epithelia of respiratory bronchioles also decreased in both smoke-exposed and nonexposed groups between 1 day and 1 month, but the smoke-exposed group had significantly more intraepithelial particles at 1 day and 1 wk than did the nonexposed group. The number of particles in the walls of respiratory bronchioles increased between 1 day and 1 month in both smoke-exposed and nonexposed groups; the difference between these groups was significant only at 1 wk, when airway walls of the smoke-exposed animals contained more particles.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This was an animal experiment in guinea pigs. No asbestos was given. The authors had earlier reported that cigarette smoke increased asbestos retention in guinea pigs. Here they tested iron oxide, a relatively inert dust. Thirty female guinea pigs had 25 mg of iron oxide placed into the windpipe. Half were also exposed to smoke from 10 cigarettes a day, 5 days a week. Animals were killed at 1 day, 1 week and 1 month. Lung iron was significantly higher in smoke-exposed animals at 1 day and 1 week but not at 1 month, and it fell over time in both groups. In the respiratory bronchioles, smoke-exposed animals had significantly more particles in the airway lining at 1 day and 1 week, and in the airway walls at 1 week. In the membranous bronchioles, there were no differences between smoke-exposed and nonexposed animals at any time point. The authors concluded that smoke increased early retention and tissue penetration of iron oxide but did not significantly slow its clearance from tissue. They noted that dust placed in the windpipe might behave differently from inhaled dust.

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. Iron oxide (not asbestos) was placed directly into the windpipe (intratracheal instillation) of guinea pigs, half of which were also exposed to cigarette smoke. The study follows the authors' earlier asbestos work in the same model.
• Who was studied: 30 female Hartley strain guinea pigs weighing 400 g, divided into two groups (smoke-exposed and not exposed). Animals were killed at 1 day, 1 week and 1 month after instillation, 5 from each group at each time.
• Exposure: All animals received 25 mg iron oxide (particles about 0.1 micrometre geometric mean diameter). Half were exposed to whole smoke of 10 nonfilter-type cigarettes a day (200 puffs total), 5 days a week, starting 2 weeks before the iron oxide and continuing to the end of the experiment.
• Main results:
  • The chemically measured iron concentration in lung tissue was significantly greater in the smoke-exposed groups than in the non-smoke-exposed groups at 1 day and 1 week (p less than 0.05 for each comparison).
  • At 1 month there was no significant difference in lung iron between the groups. The amount of iron decreased from 1 day to 1 month in both smoke-exposed and nonexposed groups.
  • In total, 1746 respiratory bronchioles and 793 membranous bronchioles were analyzed.
  • In respiratory bronchioles, smoke-exposed animals had significantly more particles within the airway epithelium than nonexposed animals at 1 day (p less than 0.01) and 1 week (p less than 0.001). They also had significantly more particles in the airway walls at 1 week (p less than 0.005).
  • There were no differences between smoke-exposed and nonexposed animals in respiratory bronchioles at 1 month, or in membranous bronchioles at any time point.
  • Within the membranous bronchioles, iron levels did change over time. In smokers, the epithelial volume fraction of iron dropped from 1 day to 1 month, and in nonsmokers it dropped between 1 week and 1 month. In both groups, the volume fraction of iron in the airway walls increased from 1 day to 1 month (each comparison p less than 0.01).
  • In both groups, the volume fraction of iron in respiratory bronchiole walls increased from 1 day to 1 week to 1 month (each comparison p less than 0.001). The exception was smokers between 1 week and 1 month, where the change was not significant.
• The authors' conclusion: The authors concluded that cigarette smoke increased whole-lung retention of iron oxide and its penetration into the walls of respiratory bronchioles. In their view, this penetration appeared to occur by transport of particles through the epithelium, and smoke did not significantly decrease clearance of iron oxide once it reached the interstitium.
• Limitations the authors state:
  • The model placed dust directly into the windpipe, and results might differ from those found with inhaled dust.
  • Individual particles were too small to see by light microscopy, so the structures counted were actually clumps of particles.
  • Iron oxide particles could not be reliably assessed in more flattened epithelium with this technique, so respiratory bronchioles were followed only as far as the low cuboidal epithelium.

Related studies

• Effects of cigarette smoke exposure on retention of asbestos fibers in various morphologic compartments of the guinea pig lung — A. Churg, V. Tron, et al. (1987)
• Effects of cigarette smoke dose and time after smoke exposure on uptake of asbestos fibers by rat tracheal epithelial cells — A. Churg, J. Hobson, et al. (1990)
• Cigarette smoke makes airway and early parenchymal asbestos-induced lung disease worse in the guinea pig — V. Tron, J.L. Wright, et al. (1987)
• Effects of cigarette smoke on the clearance of short asbestos fibres from the lung and a comparison with the clearance of long asbestos fibres — A. Churg, J.L. Wright, et al. (1992)
• Effects of cigarette smoke on epithelial uptake of non-asbestos mineral particles in tracheal organ culture — B. Keeling, J. Hobson, et al. (1993)
• Effects of cigarette smoke and asbestos on airway, vascular and mesothelial cell proliferation — H. Sekhon, J. Wright, et al. (1995)

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