Cigarette smoke augments asbestos-induced alveolar epithelial cell injury: role of free radicals

Our plain-English summary of Cigarette smoke augments asbestos-induced alveolar epithelial cell injury: role of free radicals, by D.W. Kamp, M.J. Greenberger, J.S. Sbalchierro, et al (Free Radical Biology & Medicine, 1998).

The study

• Authors: D.W. Kamp, M.J. Greenberger, J.S. Sbalchierro, S.E. Preusen, S.A. Weitzman
• Journal: Free Radical Biology & Medicine
• Published: 1998;25(6):728-39
• Cited by: 39 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Cigarette smoke augments asbestos-induced bronchogenic carcinoma by mechanisms that are not established. Alveolar epithelial cell (AEC) injury due to oxidant-induced DNA damage and depletion of glutathione (GSH) and adenosine triphosphate (ATP) may be one important mechanism. We previously showed that amosite asbestos-induces hydroxyl radical production and DNA damage to cultured AEC and that phytic acid, an iron chelator, is protective. We hypothesized that whole cigarette smoke extracts (CSE) augment amosite asbestos-induced AEC injury by generating iron-induced free radicals that damage DNA and reduce cellular GSH and ATP levels. Asbestos or CSE each caused dose-dependent toxicity to AEC (WI-26 and rat alveolar type I-like cells) as assessed by 51chromium release. The combination of asbestos (5 microg/cm2) and CSE (0.O1-0.1%) caused synergistic injury whereas higher doses of each agent primarily had an additive toxic effect. Asbestos (5 microg/cm2) augmented CSE-induced (0.01-1.0%) AEC DNA damage over a 4 h exposure period as assessed by an alkaline unwinding, ethidium bromide fluorometric technique. These effects were synergistic in A549 cells and additive in WI-26 cells. Asbestos (5 microg/cm2) and CSE (0.5-1.0%) reduced A549 and WI-26 cell GSH levels as assessed spectrophotometrically and ATP levels as assessed by luciferin/luciferase chemiluminescence but a synergistic interaction was not detected. Phytic acid (500 microM) and catalase (100 microg/ml) each attenuated A549 cell DNA damage and depletion of ATP caused by asbestos and CSE. However, neither agent attenuated WI-26 cell DNA damage nor the reductions in GSH levels in WI-26 and A549 cells exposed to asbestos and CSE. We conclude that CSE enhance asbestos-induced DNA damage in cultured alveolar epithelial cells. These data provide additional support that asbestos and cigarette smoke are genotoxic to relevant target cells in the lung and that iron-induced free radicals may in part cause these effects.

In plain English

This was a laboratory study on cultured cells, not people. The authors exposed alveolar (air-sac) lung cells from two human cell lines (WI-26 and A549) and from rats to amosite asbestos, cigarette smoke extract, or both. Asbestos alone at the main dose tested caused little cell death in WI-26 cells, while smoke extract caused dose-dependent cell death. Together they caused more than the sum of their separate effects (synergy) at 0.01% smoke extract in WI-26 cells and at 0.1% in rat cells. At higher doses the effects mainly added up. For DNA damage, the combination was synergistic in A549 cells at higher smoke doses but additive or less in WI-26 and rat cells. Smoke extract lowered cell glutathione and ATP, and adding asbestos lowered them no further than smoke alone. An iron-binding agent (phytic acid) and the enzyme catalase reduced DNA damage and ATP loss in A549 cells, but did not reduce DNA damage in WI-26 cells. The authors concluded the toxicity is due in part to DNA damage by iron-induced free radicals. They added that the relevance of these laboratory findings requires additional study.

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: In vitro laboratory experiment on cultured lung cells
• Who was studied: Cultured alveolar epithelial cells: WI-26 cells (SV-40 transformed, derived from human embryonal lung, type I-like), A549 cells (human bronchoalveolar carcinoma-derived, with type II cell features), and rat alveolar type II cells from Harlan–Sprague–Dawley rats cultured 7 to 10 days until they resembled type I cells (RAEC). No human subjects.
• Exposure: UICC reference standard amosite asbestos, mainly at 5 micrograms per square centimetre (some experiments used 1 and 2.5, or 25 to 250). Cigarette smoke extract was made from unfiltered Pall Mall cigarettes at 0.01 to 1.0% vol/vol; the authors estimated about 0.1% simulates the concentration in an adult smoker's lung. Exposures lasted 4 h (DNA damage, glutathione) or 18 h (cell death, ATP).
• Main results:
  • In WI-26 cells, smoke extract at 0.01% plus asbestos caused synergistic cell injury (18 h, chromium-51 release), while asbestos alone caused negligible injury.
  • In WI-26 cells, higher smoke extract doses (0.1 and 1.0%) combined with asbestos had an additive, not synergistic, toxic effect.
  • In rat RAEC cells, smoke extract at 0.1% plus asbestos caused synergistic injury.
  • Smoke extract alone caused dose-dependent DNA strand breaks in WI-26 cells after 4 h. In A549 cells it caused minimal DNA damage except at the highest dose.
  • DNA damage from asbestos plus smoke extract was mainly additive in WI-26 cells, and not synergistic in RAEC cells.
  • In A549 cells, higher smoke extract doses (0.5 to 1%) plus asbestos caused synergistic DNA damage after 4 h.
  • In WI-26 and A549 cells, smoke extract reduced glutathione levels in a dose-dependent way. Asbestos caused negligible reductions, and the combination reduced glutathione about as much as smoke extract alone.
  • In WI-26 and A549 cells, smoke extract reduced ATP levels in a dose-dependent way, and the combination reduced ATP about as much as smoke extract alone; no synergy was detected.
  • In A549 cells exposed to 1% smoke extract plus asbestos, phytic acid and catalase each reduced DNA strand breaks and ATP loss but not glutathione loss.
  • In WI-26 cells, phytic acid and catalase did not reduce DNA damage from the combination of asbestos and smoke extract.
• The authors' conclusion: The authors concluded that alveolar epithelial cell toxicity after exposure to cigarette smoke and asbestos is due in part to DNA damage by iron-induced free radicals, and that the effects depend on the cell type exposed.
• Limitations the authors state:
  • The relevance of these in vitro findings requires additional study.
  • Effects were measured over hours, whereas in people the combined effect of smoking and asbestos takes many years to appear.
  • The type of cell death (apoptotic or necrotic) was not examined.
  • The specific smoke component(s) responsible for the effects were not identified.
  • The role of reactive nitrogen species in this model is unclear.

Topics

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

Medical terms in this study, explained in our Lexicon: Bronchogenic Carcinoma, Glutathione (GSH), Amosite, Hydroxyl Radical, A549 Cells.

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• Cigarette smoke and asbestos activate poly-ADP-ribose polymerase in alveolar epithelial cells — D.W. Kamp, M. Srinivasan, et al. (2001)
• P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis — V. Panduri, S. Surapureddi, et al. (2006)
• Asbestos causes DNA strand breaks in cultured pulmonary epithelial cells: role of iron-catalyzed free radicals — D.W. Kamp, V.A. Israbian, et al. (1995)
• Asbestos fibre length-dependent detachment injury to alveolar epithelial cells in vitro: role of a fibronectin-binding receptor — K. Donaldson, B.G. Miller, et al. (1993)
• Cigarette smoke increases amosite asbestos fiber binding to the surface of tracheal epithelial cells — A. Churg, J. Sun, et al. (1998)

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