Generation of reactive oxygen species by human mesothelioma cells

Our plain-English summary of Generation of reactive oxygen species by human mesothelioma cells, by K. Kahlos, S. Pitkänen, I. Hassinen, et al (British Journal of Cancer, 1999).

The study

• Authors: K. Kahlos, S. Pitkänen, I. Hassinen, K. Linnainmaa, V.L. Kinnula
• Journal: British Journal of Cancer
• Published: 1999;80(1-2):25-31
• Cited by: 30 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma cells contain elevated levels of manganese superoxide dismutase (MnSOD) and are highly resistant to oxidants compared to non-malignant mesothelial cells. Since the level of cellular free radicals may be important for cell survival, we hypothesized that the increase of MnSOD in the mitochondria of mesothelioma cells may alter the free radical levels of these organelles. First, MnSOD activity was compared to the activities of two constitutive mitochondrial enzymes; MnSOD activity was 20 times higher in the mesothelioma cells than in the mesothelial cells, whereas the activities of citrate synthase and cytochrome c oxidase did not differ significantly in the two cell lines. This indicates that the activity of MnSOD per mitochondrion was increased in the mesothelioma cells. Superoxide production was assayed in the isolated mitochondria of these cells using lucigenin chemiluminescence. Mitochondrial superoxide levels were significantly lower (72%) in the mesothelioma cells compared to the mesothelial cells. Oxidant production in intact cells, assayed by fluorimetry using 2',7'-dichlorodihydrofluorescein as a fluorescent probe, did not differ significantly between these cells. We conclude that mitochondrial superoxide levels are lower in mesothelioma cells compared to nonmalignant mesothelial cells, and that this difference may be explained by higher MnSOD activity in the mitochondria of these cells. Oxidant production was not different in these cells, which may be due to the previously observed increase in H2O2-scavenging mechanisms of mesothelioma cells.

In plain English

This was a laboratory study of cells grown in culture. It did not involve people and did not test asbestos. The authors compared one human malignant mesothelioma cell line (M38K), established from a patient's tumour, with a non-malignant, virus-transformed human pleural mesothelial cell line (Met5A). They measured an antioxidant enzyme, manganese superoxide dismutase (MnSOD), and the cells' production of reactive oxygen species. MnSOD activity was 36.0 units per mg of protein in the mesothelioma cells and 1.8 in the mesothelial cells. Two other mitochondrial enzymes did not differ significantly, which the authors read as more MnSOD per mitochondrion. Isolated mitochondria from the mesothelioma cells showed 72% less superoxide. In whole cells, production of hydrogen peroxide and other peroxides did not differ significantly between the two cell lines. The oxidant menadione raised this signal by 68% in the mesothelioma cells and 59% in the mesothelial cells. The authors concluded that the mesothelioma cells had elevated MnSOD and decreased mitochondrial superoxide, which, if it also occurs in the body, may prolong cell survival. They noted limits of their measuring methods and said effects on survival and drug resistance remain to be investigated.

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) study comparing two cultured human cell lines
• Who was studied: Two human cell lines: M38K, a malignant mesothelioma cell line established from the tumour of an untreated mesothelioma patient and chosen for its high MnSOD activity; and Met5A, SV-40 virus-transformed, immortalized, non-tumorigenic human pleural mesothelial cells. Experiments were repeated three to seven times. No people were studied.
• Exposure: No asbestos exposure was tested in this study. Cells were exposed to the superoxide-producing oxidant menadione (10 µM). Some cells were first pre-treated with aminotriazole (30 mM for 60 min) to inhibit catalase, or with buthionine sulfoximine (0.2 mM for 15 h) to deplete glutathione.
• Main results:
  • MnSOD specific activity was 36.0 ± 3.4 U per mg protein in M38K mesothelioma cells and 1.8 ± 1.0 U per mg protein in Met5A mesothelial cells.
  • Citrate synthase activity did not differ significantly between the cell lines: 45.9 ± 5.3 nmol per min per mg protein in M38K cells and 32.7 ± 10.7 in Met5A cells (P = 0.127).
  • Cytochrome c oxidase activity also did not differ significantly: 3.2 ± 1.0 in M38K cells and 2.4 ± 0.9 nmol per min per mg protein in Met5A cells (P = 0.340).
  • Relative to these mitochondrial marker enzymes, MnSOD activity was sixfold higher in M38K cells than in Met5A cells, which the authors interpreted as enhanced MnSOD activity per mitochondrion.
  • Isolated mitochondria of M38K cells generated significantly less superoxide than those of Met5A cells: 0.1 ± 0.01 vs 0.37 ± 0.03 counts per second per 15 µg of mitochondrial protein (P = 0.00007).
  • Mitochondrial superoxide levels in M38K mesothelioma cells were 72% lower than in Met5A mesothelial cells.
  • In intact cells, oxidant production (fluorescence standardized to cell protein) did not differ significantly between M38K and Met5A cells.
  • Inhibiting catalase increased fluorescence by 213% in M38K cells and 244% in Met5A cells. Glutathione depletion caused no significant change.
  • Menadione (10 µM) increased fluorescence by 68% in M38K cells and 59% in Met5A cells.
  • In menadione-exposed cells, buthionine sulfoximine pre-treatment enhanced fluorescence less than aminotriazole pre-treatment did, and the enhancement was significant only in M38K cells.
• The authors' conclusion: The authors concluded that human mesothelioma cells contain highly elevated MnSOD levels together with decreased superoxide generation in the mitochondria. They said that, if this also occurs in the body, it may prolong cell survival and contribute to the cells' oxidant resistance.
• Limitations the authors state:
  • The lucigenin method is not specific to superoxide and gives only a rough estimate. It measures net superoxide appearance (production minus scavenging), not total generation.
  • The fluorescent probe used in intact cells also detects various peroxides, and its location does not show the exact compartment where the reaction happened.
  • Met5A cells are not primary mesothelial cells, although they are considered representative models.
  • The effects of the lowered free radical generation on cell survival and drug resistance were not studied.

Topics

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

Medical terms in this study, explained in our Lexicon: Reactive Oxygen Species (ROS), Mesothelioma, Superoxide, Mesothelial Cells.

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