Antioxidant defense mechanisms of human mesothelioma and lung adenocarcinoma cells

Our plain-English summary of Antioxidant defense mechanisms of human mesothelioma and lung adenocarcinoma cells, by K. Järvinen, P. Pietarinen-Runtti, K. Linnainmaa, et al (American Journal of Physiology. Lung Cellular and Molecular Physiology, 2000).

The study

• Authors: K. Järvinen, P. Pietarinen-Runtti, K. Linnainmaa, K.O. Raivio, C.M. Krejsa, T. Kavanagh, V.L. Kinnula
• Journal: American Journal of Physiology. Lung Cellular and Molecular Physiology
• Published: 2000;278(4):L696-702
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The development of drug resistance of tumors is multifactorial and still poorly understood. Some cytotoxic drugs generate free radicals, and, therefore, antioxidant enzymes may contribute to drug resistance. We investigated the levels of manganese superoxide dismutase (Mn SOD), its inducibility, and its protective role against tumor necrosis factor-alpha and cytotoxic drugs (cisplatin, epirubicin, methotrexate, and vindesin) in human pleural mesothelioma (M14K) and pulmonary adenocarcinoma (A549) cells. We also studied other major antioxidant mechanisms in relation to oxidant and drug resistance of these cells. A549 cells were more resistant than M14K cells toward both oxidants (hydrogen peroxide and menadione) and all the cytotoxic drugs tested. M14K cells contained higher basal Mn SOD activity than A549 cells (28.3 +/- 3.4 vs. 1.8 +/- 0.3 U/mg protein), and Mn SOD activity was significantly induced by tumor necrosis factor-alpha only in A549 cells (+524%), but the induction did not offer any protection during subsequent oxidant or drug exposure. Mn SOD was not induced significantly in either of these cell lines by any of the cytotoxic drugs (0.007-2 microM, 48 h) tested when assessed by Northern blotting, Western blotting, or specific activity. A549 cells contained higher catalase activity than M14K cells (7.6 +/- 1.3 vs. 3.6 +/- 0.5 nmol O(2). min(-1). mg protein(-1)). They also contained twofold higher levels of glutathione and higher immunoreactivity of the heavy subunit of gamma-glutamylcysteine synthetase than M14K cells. Experiments with inhibitors of gamma-glutamylcysteine synthetase and catalase supported our conclusion that mechanisms associated with glutathione contribute to the drug resistance of these cells.

In plain English

This laboratory study compared two human cancer cell lines grown in culture: M14K pleural mesothelioma cells and A549 lung adenocarcinoma cells. It did not study asbestos exposure. The authors measured antioxidant defenses, mainly the enzyme manganese superoxide dismutase (Mn SOD), along with catalase and glutathione. They exposed the cells to tumor necrosis factor-alpha (TNF-alpha), to oxidants (hydrogen peroxide and menadione) and to the cancer drugs cisplatin, epirubicin, methotrexate and vindesin. A549 cells resisted the oxidants and all the drugs better than M14K cells. M14K cells had much higher starting Mn SOD activity. TNF-alpha raised Mn SOD activity significantly only in A549 cells, and this rise did not protect them against menadione or epirubicin. The drugs did not significantly change Mn SOD activity. A549 cells had higher catalase activity, about twice as much glutathione, and more of a glutathione-making enzyme. The authors concluded that Mn SOD did not explain the cells' resistance and that glutathione-related mechanisms contribute to the drug resistance of these cells.

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 two human cancer cell lines grown in culture
• Who was studied: Two human cell lines: M14K pleural mesothelioma cells and A549 lung adenocarcinoma cells (A549 obtained from the American Type Culture Collection). No patients were studied.
• Exposure: No asbestos exposure was studied. The cells were treated with TNF-alpha (10 ng/ml), with the cytotoxic drugs cisplatin, epirubicin, methotrexate or vindesin for 24 to 48 h, and with the oxidants menadione (5 to 100 µM) or hydrogen peroxide (0.01 to 1 mM). Some cells were also treated with inhibitors of glutathione synthesis (buthionine sulfoximine, BSO) or of catalase (aminotriazole, ATZ).
• Main results:
  • A549 cells were more resistant than M14K cells to both oxidants (hydrogen peroxide and menadione) and to all the cytotoxic drugs tested.
  • The concentration of methotrexate that killed 50% of cells in 48 h was 1 µM for A549 cells and 0.01 µM for M14K cells. For vindesin the figures were 0.07 µM and 0.007 µM, respectively.
  • Cisplatin at 2 µM for 48 h reduced A549 cell viability by 16%. The estimated concentration causing 50% loss of M14K cells was 1.7 µM.
  • Basal Mn SOD activity was higher in M14K cells (28.3 plus or minus 3.4 U/mg protein) than in A549 cells (1.8 plus or minus 0.3 U/mg protein).
  • TNF-alpha significantly increased Mn SOD activity only in A549 cells, by 524%.
  • In A549 cells, the Mn SOD increase caused by TNF-alpha did not protect the cells against menadione or epirubicin.
  • None of the cytotoxic drugs significantly changed Mn SOD activity in either cell line.
  • Catalase activity was 7.6 plus or minus 1.3 nmol oxygen per minute per mg protein in A549 cells and 3.6 plus or minus 0.5 in M14K cells (p less than 0.05; 4 experiments).
  • A549 cells contained twofold higher glutathione levels than M14K cells.
  • The heavy subunit of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in glutathione synthesis, was prominently expressed in A549 cells but not in M14K cells.
  • Total glutathione S-transferase activity was 56 plus or minus 4.8 U/mg protein in A549 cells and 74 plus or minus 6.3 U/mg in M14K cells. The authors judged that this enzyme did not account for the greater resistance of A549 cells.
  • In A549 cells, both the glutathione-synthesis inhibitor (BSO) and the catalase inhibitor (ATZ) increased vulnerability to hydrogen peroxide. ATZ had no effect on epirubicin toxicity. These data were not shown in the article.
• The authors' conclusion: The authors concluded that neither the basal level of Mn SOD nor its inducibility explained the cells' resistance to oxidants or drugs, and that mechanisms associated with glutathione contribute to the drug resistance of these cells.
• Limitations the authors state:
  • The catalase inhibitor ATZ does not completely inhibit catalase, so the role of catalase in malignant cells remains unclear.
  • The results cannot rule out that cytotoxic drugs may induce Mn SOD activity in the body (in vivo).

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Lung Adenocarcinoma, Superoxide, Tumor Necrosis Factor-alpha (TNF-α), Cisplatin, Pleural Mesothelioma, Adenocarcinoma, A549 Cells.

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