Cell type-specific effects of asbestos on intracellular ROS levels, DNA oxidation and G1 cell cycle checkpoint

Our plain-English summary of Cell type-specific effects of asbestos on intracellular ROS levels, DNA oxidation and G1 cell cycle checkpoint, by P.B. Kopnin, I.V. Kravchenko, V.A. Furalyov, et al (Oncogene, 2004).

The study

• Authors: P.B. Kopnin, I.V. Kravchenko, V.A. Furalyov, L.N. Pylev, B.P. Kopnin
• Journal: Oncogene
• Published: 2004;23(54):8834-40
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Exposure to asbestos fibers increases the risk of development of mesotheliomas and lung carcinomas, but not fibrosarcomas. We present data suggesting that resistance of fibroblasts to asbestos-induced carcinogenesis is likely to be connected with their lower ability to generate reactive oxygen species (ROS) in response to asbestos exposure and stricter control of proliferation of cells bearing asbestos/ROS-induced injuries. In fact, chrysotile (Mg6Si4O10(OH)8) asbestos exposure (5-10 microg/cm2) increased intracellular ROS and 8-oxo-guanine contents in rat pleural mesothelial cells, but not in lung fibroblasts. Simultaneously, moderate dosages of chrysotile and other agents increasing ROS levels (hydrogen peroxide, H2O2 and ethyl-methanesulfonate, EMS) inhibited cell cycle progression, in particular G1-to-S transition, in fibroblasts, but not in mesothelial cells. The arrested fibroblasts underwent cell death, while the majority of chrysotile-treated mesothelial cells survived. The differences in cell cycle response to asbestos/ROS-induced injuries correlated with distinct activity of p53-p21Cip1/Waf1 pathway in the two cell types. Chrysotile, H2O2 and EMS caused p53 upregulation in both cell types, but mesothelial cells, unlike fibroblasts, showed no accumulation of p21Cip1/Waf1. Of note, treatment with doxorubicin caused similar p53-dependent p21Cip1/Waf1 upregulation and cell cycle arrest in both cell types. This suggests differential response of fibroblasts and mesothelial cells specifically to asbestos/ROS exposure rather than to all DNA-damaging insults.

In plain English

This laboratory study used cultured cells; no people or whole animals were exposed to asbestos. Researchers in Moscow exposed pleural mesothelial cells (from the chest lining) and lung fibroblasts from Wistar rats to Canadian chrysotile B asbestos. After 4 to 6 hours at 5 to 10 micrograms per square centimetre, a dye that detects reactive oxygen species (ROS) glowed 5 to 10 times brighter in most mesothelial cells. Chrysotile also raised oxidized DNA (8-oxo-guanine) in mesothelial cells, more at higher doses. Neither happened in fibroblasts. Chrysotile cut the share of fibroblasts copying their DNA and sharply increased fibroblast death. Mesothelial cultures were not significantly inhibited; at 5 micrograms per square centimetre they grew more. After 24 hours at moderate doses, chrysotile raised the protein p53 in both cell types. The protein p21, which can halt cell division, rose in fibroblasts but not significantly in mesothelial cells. Longer, higher-dose exposure did bring some p21 rise in mesothelial cells. Doxorubicin, a cancer drug, raised p21 and slowed growth in both cell types. The authors concluded this can provide at least one explanation for why asbestos-exposed humans and animals have a significantly higher risk of mesothelioma than of fibrosarcoma.

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 (in vitro) experiment on cultured cells isolated from rats; no humans or whole animals were exposed to asbestos
• Who was studied: Pleural mesothelial cells (from parietal pleura) and lung fibroblasts isolated from Wistar rats and grown in culture, used at passages 3 to 7; work done at the Blokhin Cancer Research Center, Moscow (dates not stated)
• Exposure: Canadian chrysotile B asbestos (UICC sample), mostly at 1 to 10 micrograms per square centimetre of culture surface, for hours to 5 days. The scanned text prints this as 'mg/cm2', but the figure axes show µg/cm2. For comparison, cells were treated with hydrogen peroxide (75 micromolar), ethyl-methanesulfonate (EMS, 0.5 mg/ml) and doxorubicin (0.5 micrograms/ml), and with the antioxidant N-acetyl-L-cysteine (NAC).
• Main results:
  • In mesothelial cells, chrysotile (5 to 10 micrograms per square centimetre, 4 to 6 h) increased the fluorescence of DCF-DA, a dye marking cellular oxidant production, 5 to 10-fold in most cells. Fluorescence fell in 30 to 40% of cells, which the authors attributed probably to membrane damage and dye leakage rather than to lower ROS.
  • Lung fibroblasts did not show increased ROS-dye fluorescence in response to chrysotile.
  • Mesothelial cells had about twofold higher ROS levels than fibroblasts, both before and after treatment with hydrogen peroxide or EMS.
  • Chrysotile caused a dose-dependent increase in oxidized DNA (8-oxo-guanine) in mesothelial cells, but not in fibroblasts.
  • In fibroblasts, chrysotile (5 to 10 micrograms per square centimetre, 24 h) significantly reduced the proportion of cells in S phase, the stage when DNA is copied. The authors judged that the fibroblasts died mainly by necrosis rather than apoptosis.
  • Chrysotile-treated mesothelial cell cultures showed no significant inhibition of growth. At 5 micrograms per square centimetre, dead cells rose to up to 15% (including 3 to 5% apoptotic cells), but the numbers of dividing and viable cells increased.
  • In synchronized cultures, chrysotile at 2.5 to 10.0 micrograms per square centimetre strongly blocked fibroblasts from moving from G1 into S phase. Mesothelial cells showed no such arrest.
  • After 24 h treatment, chrysotile, hydrogen peroxide, EMS and doxorubicin all increased p53 protein in both cell types.
  • After 24 h at moderate doses, chrysotile, hydrogen peroxide or EMS did not significantly raise p21Cip1/Waf1 in mesothelial cells. In fibroblasts, all treatments raised p21Cip1/Waf1. Doxorubicin raised p21Cip1/Waf1 in mesothelial cells as well.
  • After prolonged treatment with higher chrysotile doses (10 to 20 micrograms per square centimetre, 2 to 3 days), mesothelial cells showed some increase in p21Cip1/Waf1. The data were not shown.
  • Doxorubicin inhibited growth similarly in fibroblasts and mesothelial cells.
• The authors' conclusion: The authors concluded that mesothelial cells, unlike fibroblasts, respond to chrysotile with more ROS and DNA oxidation, and do not stop dividing because p21Cip1/Waf1 is not raised. In their view, this can provide at least one explanation for why the risk of mesothelioma in asbestos-exposed humans and experimental animals is significantly higher than the risk of fibrosarcoma.
• Limitations the authors state:
  • The authors stated that the mechanisms behind the weak p53-p21Cip1/Waf1 response in mesothelial cells remain to be established.
  • The authors noted that fibroblasts may differ from mesothelial cells not only in generating ROS but also in their ability to detoxify it.
  • The authors noted that fibroblast arrest and death were probably caused both by ROS-induced injury and by other asbestos effects, such as mechanical damage.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Carcinoma, Fibroblast, Carcinogenesis, Reactive Oxygen Species (ROS), Asbestos Exposure, Chrysotile, Mesothelial Cells.

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