Rat pleural mesothelial cells show damage after exposure to external but not internal cigarette smoke

Our plain-English summary of Rat pleural mesothelial cells show damage after exposure to external but not internal cigarette smoke, by H.S. Sekhon, B. Keeling, A. Churg (Environmental Health Perspectives, 1993).

The study

• Authors: H.S. Sekhon, B. Keeling, A. Churg
• Journal: Environmental Health Perspectives
• Published: 1993;101(4):326-30
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The combination of cigarette smoke and high-level occupational asbestos exposure produces a synergistic increase in the incidence of lung cancer; however, smoking does not affect the incidence of mesothelioma. Here we present the results of tests of two theories that have been proposed to explain this phenomenon; namely, that pleural mesothelial cells are resistant to cigarette smoke-induced damage and that the pleural connective tissue acts as a barrier that prevents smoke from reaching the mesothelial cells. To test these hypotheses, excised whole rat lung preparations were exposed to either internal (intratracheal) or external (pleural surface) smoke. For comparison, additional excised lung preparations were exposed to solutions of hydrogen peroxide either externally or intratracheally. Mesothelial cells exposed to external smoke showed widespread, dose-dependent uptake of Trypan blue. Mesothelial cells did not take up Trypan blue after exposure to internal smoke. Bronchial epithelial cells exposed to internal smoke did show uptake, but to a lesser degree than externally exposed mesothelial cells. Examination by scanning and transmission electron microscopy showed that internal smoke did not affect mesothelial cell ultrastructure, whereas external smoke produced obvious mesothelial cell damage and mesothelial cell detachment. Catalase and deferoxamine, scavengers of active oxygen species, provided protection against smoke-induced mesothelial cell injury, but inactivated catalase did not. External hydrogen peroxide produced a very similar, dose-dependent pattern of Trypan blue uptake and ultrastructural changes. Intratracheal hydrogen peroxide also damaged mesothelial cells, but the extent of damage was always less than with comparable concentrations of external hydrogen peroxide.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This laboratory experiment used lungs removed from female rats to test whether cigarette smoke damages the cells lining the lung surface (pleural mesothelial cells) and whether the pleura blocks smoke. No asbestos was used. Smoke from a nonfilter cigarette was applied either to the outer lung surface or through the windpipe. Other lungs received hydrogen peroxide. Damage was measured by blue dye uptake and electron microscopy. Smoke inside the lung caused no significant dye uptake by mesothelial cells. Smoke on the outer surface stained 34.1% of the surface after 6 puffs and 47.1% after 15 puffs, compared with 0.4% in air controls, and damaged and detached cells. Catalase pretreatment abolished this dye uptake; boiled catalase did not. Internal hydrogen peroxide damaged mesothelial cells less than external. The authors concluded that mesothelial cells are sensitive to smoke damage through active oxygen species, and that the pleura's barrier effect might help explain the lack of synergism between smoke and asbestos in pleural mesothelioma. They noted the barrier finding applies only to short exposures.

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 laboratory experiment using excised (ex vivo) rat heart-lung preparations
• Who was studied: Female Sprague-Dawley rats weighing 250 g, in treatment groups of three or four animals each, studied in Vancouver, Canada
• Exposure: Whole smoke from a commercial nonfilter cigarette, applied either externally to the pleural surface or internally through the trachea. Doses were 6 puffs over 10 min or 15 puffs over 15 min, compared with air controls. Separate preparations received hydrogen peroxide solutions (0.002%, 0.01%, 0.05%) externally or internally for 10 min. Some smoke-exposed lungs were pretreated with catalase, boiled (inactivated) catalase or deferoxamine. No asbestos was used.
• Main results:
  • Mesothelial cells exposed to internal smoke showed no significant dye uptake compared with air controls. The percentage of pleural surface stained was 0.1 ± 0.1 after 6 puffs and 0.5 ± 0.7 after 15 puffs, compared with 0.4 ± 0.6 in 10-minute air controls.
  • External smoke stained 34.1 ± 16.1% of the pleural surface after 6 puffs and 47.1 ± 15.4% after 15 puffs. Both were significantly greater than the 10-minute air control (p less than 0.01). Damage was more severe with 15 puffs.
  • Under the electron microscope, external smoke caused swelling of structures inside the cells, loss of microvilli, separation of junctions between cells, and lifting or detachment of mesothelial cells.
  • With 6 puffs of external smoke, pretreatment with catalase reduced pleural staining to 1.2 ± 1.4%. Deferoxamine reduced it to 3.6 ± 5.4%, with less complete protection. Boiled catalase did not protect (33.1 ± 10.9%).
  • The airway surface (trachea and mainstem bronchi) exposed to 6 puffs of internal smoke showed 4.9 ± 0.6% staining, compared with 0.5 ± 0.3% in air controls. This was significantly greater than air control (p less than 0.001) and significantly less than the pleura exposed externally to 6 puffs.
  • Hydrogen peroxide produced damage similar to external smoke, which the authors described as dose dependent. External exposure stained 11.4 ± 3.8%, 16.8 ± 7.3% and 21.4 ± 8.5% of the pleural surface at 0.002%, 0.01% and 0.05%. Internal exposure stained 3.5 ± 2.9%, 2.8 ± 2.9% and 9.7 ± 1.7% at the same concentrations. Internal damage was always less than external at the same concentration.
• The authors' conclusion: The authors concluded that rat pleural mesothelial cells are sensitive to smoke-induced damage that appears to be produced by active oxygen species, and that they are more sensitive than bronchial epithelial cells. They also concluded that smoke components do not penetrate the pleura, or penetrate only in relatively small amounts. They suggested that this barrier effect might help explain the lack of synergism between smoke and asbestos exposure in producing pleural mesotheliomas.
• Limitations the authors state:
  • The authors described the system as artificial. When exposures were extended to 30 minutes, air alone caused damage, so only short exposures could be tested.
  • The finding on lack of smoke penetration applies only to short-term exposures. Penetration with long or repeated in vivo exposures cannot be ruled out.
  • The system cannot detect subtle mesothelial damage such as oxidant-induced DNA single strand breaks.
  • Only oxidant damage was examined. Other forms of smoke-related injury, for example from aromatic hydrocarbon carcinogens that may diffuse across the pleura, might also occur.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Asbestos Exposure, Lung Cancer, Mesothelioma, Transmission Electron Microscopy (TEM).

Related studies

• Effects of cigarette smoke and asbestos on airway, vascular and mesothelial cell proliferation — H. Sekhon, J. Wright, et al. (1995)
• 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)
• Scavengers of active oxygen species prevent cigarette smoke-induced asbestos fiber penetration in rat tracheal explants — A. Churg, J. Hobson, et al. (1989)
• Effects of cigarette smoke on epithelial uptake of non-asbestos mineral particles in tracheal organ culture — B. Keeling, J. Hobson, et al. (1993)
• Cigarette smoke increases amosite asbestos fiber binding to the surface of tracheal epithelial cells — A. Churg, J. Sun, et al. (1998)
• Role of oxygen derivatives in the cytotoxicity and DNA damage produced by asbestos on rat pleural mesothelial cells in vitro — H. Dong, A. Buard, et al. (1994)

Browse more research in Environmental Health Perspectives, or return to medical research.