Induction of heme oxygenase in mammalian cells by mineral fibers: distinctive effect of reactive oxygen species

Our plain-English summary of Induction of heme oxygenase in mammalian cells by mineral fibers: distinctive effect of reactive oxygen species, by K. Suzuki, T.K. Hei (Carcinogenesis, 1996).

The study

• Authors: K. Suzuki, T.K. Hei
• Journal: Carcinogenesis
• Published: 1996;17(4):661-7
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Exponentially growing human-hamster hybrid [AL] cells treated with a 40 micrograms/ml (8 micrograms/cm2) dose of UICC standard reference chrysotile fibers induced heme oxygenase (HO) protein with a maximum expression level at 8 h post-treatment. While the constitutive HO expression was detectable in non-treated AL cells, the protein level was increased approximately 4.5-fold in fiber-treated cells. The induction was dose-dependent at fiber concentration between 2.5 micrograms/ml (0.5 microgram/cm2) and 40 micrograms/ml (8 micrograms/cm2) with the induced HO concentrated mostly in the cytoplasm as shown by immunostaining. Several other types of mineral fibers examined including crocidolites, tremolites, and erionites also induced HO synthesis with varying degree of efficiency. In general, chrysotile and crocidolite were more efficient inducers of HO than tremolite and erionite when compared at fiber doses that resulted in approximately 50% survival (LD50) level. The effects of antioxidant enzymes on HO induction were examined by concurrent treatment of fiber-exposed cultures with SOD and catalase. Although addition of superoxide dismutase (SOD) and catalase inhibited HO induction in a dose-dependent manner, they offered no protection on fiber-mediated clonogenic toxicity in the same population of treated cells. These results suggest that reactive oxygen species (ROS) produced by asbestos fibers play an essential role in the induction of HO and that different mineral fibers, when applied at equitoxic doses, often result in different oxidative stress status as determined by the induction of HO proteins.

In plain English

In this laboratory study of cultured cells, the authors exposed human-hamster hybrid (AL) cells to several mineral fibers: UICC reference chrysotile and crocidolite asbestos, tremolite from Metsovo, Greece, and erionite from Rome, Oregon. They measured heme oxygenase (HO), a protein cells make under oxidative stress. With 40 micrograms per milliliter of chrysotile, HO rose more than 2-fold within 1 hour and peaked at more than 4-fold above background at 8 hours. The surviving fraction of cells able to form colonies fell to about 25% of control at 8 hours. At fiber doses leaving about half the cells able to form colonies, HO rose 3.89-fold for chrysotile, 3.86-fold for crocidolite, 2.75-fold for tremolite and 2.78-fold for erionite. The antioxidant enzymes SOD and catalase each reduced HO induction. In chrysotile-treated cells, SOD at 200 units per milliliter or more suppressed the induction completely, while catalase did not suppress it completely even at 5000 units per milliliter. Neither enzyme improved colony-forming survival after chrysotile or crocidolite exposure. The authors concluded that reactive oxygen species were mediators of HO induction.

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 experiment on cultured cells (in vitro); no human or animal subjects
• Who was studied: Human-hamster hybrid AL cells grown in culture
• Exposure: UICC standard reference chrysotile and crocidolite fibers, erionites from Rome, Oregon, and tremolite fibers from Metsovo, Greece, at graded doses. The main chrysotile dose was 40 micrograms per milliliter (8 micrograms per square centimeter), mostly for 8 hours. Some cultures were also treated with the antioxidant enzymes superoxide dismutase (SOD) or catalase.
• Main results:
  • In AL cells treated with 40 micrograms per milliliter of chrysotile, the surviving fraction fell to about 25% of control after 8 hours and about 15% after 24 hours of treatment, measured by colony formation.
  • In AL cells treated with 40 micrograms per milliliter of chrysotile, HO reached more than 2-fold the background level within 1 hour.
  • In the same cells, HO peaked at more than 4-fold above background at 8 hours after treatment, then stayed about 3-fold above background.
  • With 8-hour chrysotile treatment, HO induction was statistically significant (P less than 0.05) at concentrations above 5.0 micrograms per milliliter (1.0 microgram per square centimeter). The increase was dose-dependent up to 20 micrograms per milliliter.
  • Crocidolite, tremolite and erionite all induced significant amounts of HO compared with untreated control cells.
  • Fiber doses were chosen to give relative surviving fractions of 0.5 and 0.3, matching those of 20 and 40 micrograms per milliliter of chrysotile.
  • At doses giving about 50% survival (LD50), HO was 3.89-fold above background for chrysotile, 3.86-fold for crocidolite, 2.75-fold for tremolite and 2.78-fold for erionite.
  • In chrysotile-treated cells, SOD at 25 units per milliliter significantly reduced HO induction (P less than 0.05).
  • In chrysotile-treated cells, SOD at 200 units per milliliter or higher completely suppressed HO induction.
  • In chrysotile-treated cells, catalase significantly decreased HO induction even at the lowest dose tested, 28.5 units per milliliter.
  • The authors stated that SOD obliterated HO induction by chrysotile fibers, whereas catalase did not suppress fiber-induced HO completely, even at 5000 units per milliliter.
  • In cells treated with equivalent doses of crocidolite, the dose-response inhibition of HO induction by SOD and catalase was similar to that seen with chrysotile.
  • Neither SOD nor catalase was toxic on its own, and neither protected AL cells against the cytotoxic effects of 40 micrograms per milliliter of chrysotile; results were similar with crocidolite.
• The authors' conclusion: The authors concluded that SOD and catalase were working in the culture medium and that reactive oxygen species were mediators of HO induction by the fibers.
• Limitations the authors state:
  • Preliminary tests found that the metal chelator EDTA had no effect on HO induction. The authors said this conclusion might not be decisive, because metal-bound EDTA can still generate reactive oxygen species.
  • The authors noted that the viability measure used here was reproductive integrity (colony formation), which does not necessarily equate with the metabolic viability measures used in other studies, possibly explaining differing findings on antioxidant protection.
  • SOD and catalase are large molecules unlikely to enter cells, so the authors said future experiments with a compound that crosses cell membranes (Tempol) would be needed to separate the effects of reactive oxygen species inside versus outside the cells.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Reactive Oxygen Species (ROS), UICC, Chrysotile, Crocidolite, Tremolite, erionite, Superoxide.

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• Production of reactive oxygen species by man-made vitreous fibres in human polymorphonuclear leukocytes — M. Ruotsalainen, M.R. Hirvonen, et al. (1999)
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