Smoking inhibits asbestos clearance

Our plain-English summary of Smoking inhibits asbestos clearance, by D. McFadden, J.L. Wright, B. Wiggs, et al (The American Review of Respiratory Disease, 1986).

The study

• Authors: D. McFadden, J.L. Wright, B. Wiggs, A. Churg
• Journal: The American Review of Respiratory Disease
• Published: 1986;133(3):372-4
• Cited by: 54 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000422).

Abstract

To determine whether smoking affects the clearance of asbestos fibers, guinea pigs were given amosite asbestos by intratracheal instillation and divided into 3 groups: (1) nonsmokers, (2) animals exposed to smoke only after asbestos instillation, and (3) animals exposed to smoke both before and after asbestos instillation. Asbestos fiber concentrations and sizes were measured at 1 wk and 1 month after exposure. Between 1 wk and 1 month the asbestos burden in nonsmokers decreased on average 6-fold, whereas both smoking groups failed to show a significant decrease. Over this time period, the mean length of retained fibers increased in the nonsmokers but decreased in both smoking groups. This phenomenon was seen in tissue samples and lavage samples, although lavaged fibers were consistently shorter than tissue fibers. We conclude that in this model, cigarette smoking impedes asbestos clearance, largely by increasing retention of short fibers. This increased pulmonary fiber burden may be important in the increased disease rate seen in asbestos workers who smoke.

In plain English

This was an animal experiment. Thirty female guinea pigs were given 1 mg of UICC amosite asbestos directly into the windpipe (intratracheal instillation). Ten were never exposed to cigarette smoke. Ten were exposed starting the day after the asbestos, and ten starting 2 weeks before it. The smoking animals breathed the smoke of 10 nonfilter cigarettes, 5 days a week. Half of each group was killed at 1 week and half at 1 month, and the amosite fibers in their lungs were counted and measured. Between 1 week and 1 month, the fiber burden in the nonsmoking animals fell on average 6-fold, while neither smoking group showed a significant decrease. Average fiber length in lung tissue rose in nonsmokers but fell in both smoking groups. The authors concluded that, in this model, smoking impedes asbestos clearance, largely by increasing retention of short fibers. They cautioned that the instillation method is unphysiologic, that an inhalation model might give different results, and that relevance to humans should be interpreted with caution.

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 (guinea pigs given asbestos by intratracheal instillation, with and without cigarette smoke exposure)
• Who was studied: 30 female Hartley strain guinea pigs (mean weight 400 g) at the University of British Columbia, Vancouver. There were 10 per group: nonsmokers, smoked starting the day after asbestos (post-smoked), and smoked starting 2 weeks before asbestos and throughout (presmoked). Half of each group was killed at 1 week and half at 1 month. Dates of the experiment are not given.
• Exposure: 1 mg UICC amosite asbestos in 0.5 ml saline by intratracheal instillation. Smoking groups also received head-only exposure to the whole smoke of 10 nonfilter standard cigarettes (200 puffs total, 20 ml smoke per puff) 5 days per week.
• Main results:
  • From 1 week to 1 month, the asbestos burden in nonsmoking animals decreased on average 6-fold (p less than 0.01). Neither smoking group showed a significant decrease.
  • At 1 week the presmoked animals had a lower fiber burden than the post-smoked group. At 1 month the presmoked animals still had lower concentrations than the post-smoked animals (p less than 0.01).
  • Mean tissue fiber length (geometric mean, microns) changed from 1 week to 1 month as follows: nonsmokers rose from 5.6 to 6.3; post-smoked animals fell from 5.8 to 5.1; presmoked animals fell from 5.9 to 4.6.
  • At 1 month, mean tissue fiber aspect ratio (length to width) was 21 in nonsmokers, 18 in post-smoked animals and 14 in presmoked animals. Each comparison was significant (p less than 0.01). Fiber widths did not differ significantly at 1 month.
  • Fibers recovered by lung lavage were shorter, thinner and of lower aspect ratio than tissue fibers. Mean lavage fiber length increased in nonsmokers; in smoking animals it either did not increase or decreased.
  • Fiber counts by length (mean concentrations x 10^6 per gram dry lung, from 1 week to 1 month):
• Post-smoked animals: fibers shorter than 10 microns went from 75 to 66; fibers longer than 10 microns went from 25 to 12.
• Nonsmokers: shorter fibers went from 74 to 13; longer fibers went from 21 to 3.
  At 1 month the smoking animals retained 4 times as many long fibers as nonsmokers.
• The authors' conclusion: The authors concluded that, in this model, cigarette smoking impedes asbestos clearance, largely by increasing retention of short fibers. They suggested this increased lung fiber burden may be important in the higher disease rate seen in asbestos workers who smoke.
• Limitations the authors state:
  • The intratracheal instillation model is unphysiologic: doses are high and fibers are distributed unevenly in the lung.
  • Different results might be obtained with an inhalation model, or with different amounts of asbestos or smoking.
  • The authors' comments on relevance to humans are meant to be interpreted with caution.
  • Because smoking animals retained more of both long and short fibers, the study cannot determine which fiber length accounts for higher disease rates in smoking asbestos workers.

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Fiber Burden.

Related studies

• 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)
• Rapid short-term clearance of chrysotile compared with amosite asbestos in the guinea pig — A. Churg, J.L. Wright, et al. (1989)
• Deposition and clearance of chrysotile asbestos — A. Churg (1994)
• 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)
• Cigarette smoke makes airway and early parenchymal asbestos-induced lung disease worse in the guinea pig — V. Tron, J.L. Wright, et al. (1987)
• Types, numbers, sizes, and distribution of mineral particles in the lungs of urban male cigarette smokers — A. Churg, B. Wiggs (1987)

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