Asbestos causes apoptosis in alveolar epithelial cells: role of iron-induced free radicals

Our plain-English summary of Asbestos causes apoptosis in alveolar epithelial cells: role of iron-induced free radicals, by A. Aljandali, H. Pollack, A. Yeldandi, et al (The Journal of Laboratory and Clinical Medicine, 2001).

The study

• Authors: A. Aljandali, H. Pollack, A. Yeldandi, Y. Li, S.A. Weitzman, D.W. Kamp
• Journal: The Journal of Laboratory and Clinical Medicine
• Published: 2001;137(5):330-9
• Cited by: 64 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos causes asbestosis and malignancies by mechanisms that are not fully understood. Alveolar epithelial cell (AEC) injury by iron-induced reactive oxygen species (ROS) is one important mechanism. To determine whether asbestos causes apoptosis in AECs, we exposed WI-26 (human type I-like cells), A549 (human type II-like cells), and rat alveolar type II cells to amosite asbestos and assessed apoptosis by terminal deoxynucleotidyl transferase-mediated deoxyuridine-5'-triphosphate-biotin nick end labeling (TUNEL) staining, nuclear morphology, annexin V staining, DNA nucleosome formation, and caspase 3 activation. In contrast to control medium and TiO2, amosite asbestos and H2O2 each caused AEC apoptosis. A role for iron-catalyzed ROS was suggested by the finding that asbestos-induced AEC apoptosis and caspase 3 activation were each attenuated by either an iron chelator (phytic acid and deferoxamine) or a.OH scavenger (dimethyl-thiourea, salicylate, and sodium benzoate) but not by iron-loaded phytic acid. To determine whether asbestos causes apoptosis in vivo, rats received a single intratracheal instillation of amosite (5 mg) or normal saline solution, and apoptosis in epithelial cells in the bronchoalveolar duct regions was assessed by TUNEL staining. One week after exposure, amosite asbestos caused a 3-fold increase in the percentage of apoptotic cells in the bronchoalveolar duct regions as compared with control (control, 2.1% +/- 0.35%; asbestos, 7.61% +/- 0.15%; n = 3). However, by 4 weeks the number of apoptotic cells was similar to control. We conclude that asbestos-induced pulmonary toxicity may partly be caused by apoptosis in the lung epithelium that is mediated by iron-catalyzed ROS and caspase 3 activation.

In plain English

This laboratory study tested whether amosite asbestos causes apoptosis (programmed cell death) in cells lining the lung's air sacs. The authors exposed two human cell lines (WI-26 and A549) and rat type II cells to amosite, and gave rats a single 5 mg dose of amosite into the windpipe. Amosite caused a 2.5- to 3-fold increase in apoptosis in all three cell types compared with controls; titanium dioxide, a comparison dust, did not. In A549 cells, amosite raised the activity of caspase 3, a cell-death enzyme, 15-fold. Iron-binding agents or free-radical scavengers reduced apoptosis by 35% to 50%, while iron-loaded phytic acid did not protect. In rats, 7.6% of bronchoalveolar duct cells were apoptotic one week after amosite, versus 2.1% in controls (3 rats per group). At four weeks the figures were 3.1% versus 2.0%, which the authors described as approaching control levels. The authors concluded that asbestos lung toxicity may partly be caused by apoptosis in the lung lining, driven by iron-catalyzed free radicals and caspase 3 activation.

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: Laboratory study: cell culture experiments plus an animal experiment (rats given a single intratracheal instillation)
• Who was studied: Cultured WI-26 cells (SV-40 transformed cells from human embryonal lung, type I-like), A549 cells (human bronchoalveolar carcinoma-derived, with type II features), and type II cells isolated from adult Harlan Sprague-Dawley rats. Also adult Harlan Sprague-Dawley rats (200 to 250 g), 3 per group at each time point (1 and 4 weeks). Northwestern University Medical School and Veterans Administration Chicago Health Care System; study dates not stated.
• Exposure: Amosite asbestos (UICC reference standard). In cell experiments, doses ranged from 2 to 100 µg/cm2, mostly for 24 hours. Hydrogen peroxide served as a comparison agent and titanium dioxide as a negative-control dust. Rats received a single intratracheal instillation of 5 mg amosite in 0.5 mL PBS, or PBS alone.
• Main results:
  • Measured by nuclear appearance, amosite caused a 2.5- to 3-fold increase in apoptosis in A549, WI-26 and rat type II cells compared with controls.
  • Hydrogen peroxide, but not titanium dioxide, also induced apoptotic changes in the cells.
  • In a single experiment using annexin V staining (amosite 25 µg/cm2 for 72 hours), A549 cells showed early apoptosis in 0.7% of controls versus 7.3% with amosite, and late apoptosis in 7.8% of controls versus 24.7% with amosite.
  • In A549 cells, amosite (25 µg/cm2) increased caspase 3 activity 15-fold and hydrogen peroxide (250 µmol/L) 10-fold. Caspase 3 inhibitors reduced amosite-induced apoptosis by 30% to 50%.
  • Iron chelators (phytic acid or deferoxamine) and hydroxyl radical scavengers (dimethylthiourea, salicylate or sodium benzoate) each reduced apoptosis caused by amosite and by hydrogen peroxide by 35% to 50% in A549 cells.
  • Phytic acid loaded with iron (FeCl3) did not protect against amosite-induced apoptosis.
  • In rats one week after instillation, TUNEL-positive cells in the bronchoalveolar duct region were 2.1% plus or minus 0.35% in controls versus 7.6% plus or minus 0.15% with asbestos (3 rats per group).
  • At 4 weeks, rat values were 2.0% plus or minus 0.17% in controls versus 3.1% plus or minus 0.15% with amosite, which the authors described as approaching control levels.
• The authors' conclusion: The authors concluded that asbestos-induced lung toxicity may partly be caused by apoptosis in the lung epithelium, mediated by iron-catalyzed reactive oxygen species and caspase 3 activation.
• Limitations the authors state:
  • The authors could not detect DNA fragmentation (laddering) in the cells, for reasons they said remain unclear; they suggested the assay may not have been sensitive enough.

Topics

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

Medical terms in this study, explained in our Lexicon: Apoptosis, Reactive Oxygen Species (ROS), Amosite, Epithelium.

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