Endogenous antioxidant enzymes and glutathione S-transferase in protection of mesothelioma cells against hydrogen peroxide and epirubicin toxicity

Our plain-English summary of Endogenous antioxidant enzymes and glutathione S-transferase in protection of mesothelioma cells against hydrogen peroxide and epirubicin toxicity, by K. Kinnula, K. Linnainmaa, K.O. Raivio, et al (British Journal of Cancer, 1998).

The study

• Authors: K. Kinnula, K. Linnainmaa, K.O. Raivio, V.L. Kinnula
• Journal: British Journal of Cancer
• Published: 1998;77(7):1097-102
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We have previously shown that cultured malignant mesothelioma cells contain elevated manganese superoxide dismutase (MnSOD) mRNA levels and activities compared with non-malignant mesothelial cells. As many cytotoxic drugs generate both superoxide and hydrogen peroxide, we assessed the relative significance of catalase and the glutathione redox cycle, as well as glutathione S-transferase (GST), in protecting these cells against hydrogen peroxide and epirubicin toxicity. Mesothelioma cell lines containing high (M38K cells) and low (M14K cells) MnSOD, and non-malignant MeT-5A mesothelial cells were selected for the study. M38K cells were the most resistant of these three cell types to hydrogen peroxide (0.1-0.5 mM, 4 h) and epirubicin (0.1-0.5 microg ml(-1), 48 h) as judged by lactate dehydrogenase (LDH) release and by high-energy nucleotide (ATP, ADP, AMP) depletion. Total glutathione was higher in M38K cells (63.8 +/- 20.3 nnmol mg(-1) protein) than in M14K (25.2 +/- 8.2 nmol mg[-1]) or MeT-5A cells (23.5 +/- 4.5 nmol mg[-1]). Furthermore, GST specific activity was higher in M38K cells (111.3 +/- 15.8 U mg[-1]) than in M14K cells (77.4 +/- 6.6 U mg[-1]) or in MeT-5A cells (68.8 +/- 7.6 U mg[-1]). Western blotting indicated the presence of GST-pi in all these cells, the reactivity again being highest in M38K cells. Depletion of glutathione by buthionine sulphoximine and inhibition of catalase by aminotriazole enhanced hydrogen peroxide toxicity in all cell types, while only the depletion of glutathione increased epirubicin toxicity. We conclude that simultaneous induction of multiple antioxidant enzymes can occur in human mesothelioma cells. In addition to the high MnSOD activity, hydrogen peroxide scavenging antioxidant enzymes, glutathione and GST can partly explain the high hydrogen peroxide and epirubicin resistance of these cells in vitro.

In plain English

This was a laboratory study of human cells grown in dishes. It did not study people or measure asbestos exposure. The authors compared two mesothelioma cell lines, M38K (high in the enzyme MnSOD) and M14K (low in MnSOD), with non-malignant mesothelial cells called MeT-5A. The cells were exposed to hydrogen peroxide or to the chemotherapy drug epirubicin. Some cells were first treated with aminotriazole, which reduced activity of the enzyme catalase by 82% to 89%, or with buthionine sulphoximine, which depletes glutathione. M38K cells were the most resistant to both agents. They had the highest starting glutathione (63.8 ± 20.3 nmol per mg protein, against 25.2 ± 8.2 in M14K and 23.5 ± 4.5 in MeT-5A) and GST activity (111.3 ± 15.8 against 77.4 ± 6.6 and 68.8 ± 7.6 U per mg protein). Depleting glutathione made epirubicin more damaging in all three cell types. Partly inhibiting catalase did not, but the authors said this does not exclude a role for catalase. The authors concluded that several antioxidant defenses together matter more than any single enzyme and can partly explain these cells' resistance in the laboratory. They cautioned that the inhibitor experiments give indirect evidence.

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 human cell lines
• Who was studied: Two human mesothelioma cell lines, M38K and M14K, which were established from tumours of untreated mesothelioma patients. M38K had the highest and M14K the lowest MnSOD activity of five such lines. They were compared with MeT-5A cells, which are SV-40 immortalized, non-malignant human pleural mesothelial cells.
• Exposure: Hydrogen peroxide (0.1-0.5 mM for 1-4 h) or the chemotherapy drug epirubicin (0.1-0.5 micrograms per ml for 48 h). Some cells were pretreated with 20 mM aminotriazole to inactivate catalase, or with 0.2 or 1 mM buthionine sulphoximine to deplete glutathione. Asbestos was not used as an exposure in this study.
• Main results:
  • M38K mesothelioma cells were the most resistant of the three cell types to hydrogen peroxide, judged by LDH release.
  • In preliminary experiments, 0.1 micrograms per ml epirubicin caused significant nucleotide breakdown in MeT-5A and M14K cells but not in untreated or pretreated M38K cells.
  • Baseline total glutathione was 63.8 ± 20.3 nmol per mg protein (n=3) in M38K cells, 25.2 ± 8.2 (n = 3) in M14K cells and 23.5 ± 4.5 (n = 3) in MeT-5A cells.
  • Total GST activity was 111.3 ± 15.8 U per mg protein in M38K cells, 77.4 ± 6.6 in M14K cells and 68.8 ± 7.6 in MeT-5A cells. The M38K value was significantly higher (P less than 0.05) than both other cell types.
  • Aminotriazole reduced catalase activity by 85% in MeT-5A cells, 82% in M14K cells and 89% in M38K cells (two duplicate experiments).
  • Hydrogen peroxide caused more nucleotide breakdown in MeT-5A and M38K cells pretreated with either aminotriazole or buthionine sulphoximine. In M14K cells, only buthionine sulphoximine pretreatment had this effect. M38K cells were given a higher dose (0.5 mM) than the other cells (0.1 mM).
  • Buthionine sulphoximine (glutathione depletion) increased epirubicin toxicity in all three cell types. Aminotriazole (catalase inhibition) had no effect on epirubicin toxicity in any of them.
  • The authors noted that the lack of an aminotriazole effect on epirubicin toxicity does not exclude the importance of catalase in mesothelioma.
  • Western blotting showed the GST-pi enzyme most prominently in M38K cells.
• The authors' conclusion: The authors concluded that antioxidant enzyme levels in mesothelioma cells can vary. In their view, elevated MnSOD and hydrogen peroxide-scavenging enzymes, together with glutathione and GST, play a more important role than any single antioxidant enzyme in the oxidant and drug resistance of these cells in vitro. They also wrote that these factors can partly explain the cells' resistance to hydrogen peroxide and epirubicin in vitro.
• Limitations the authors state:
  • Results obtained with the inhibitors (aminotriazole and buthionine sulphoximine) are indirect, and these inhibitors could theoretically affect other unknown properties of the cells.
  • Catalase cannot be completely inhibited, so these inhibition experiments underestimate catalase's role.
  • GST-pi is not necessarily the only GST type that may be altered in these cells.

Topics

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

Medical terms in this study, explained in our Lexicon: Glutathione (GSH), Mesothelioma, Superoxide, Mesothelial Cells, Lactate Dehydrogenase (LDH), MeT-5A Cells.

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