ENDOGENOUS ANTIOXIDANT ENZYMES AND GLUTATHIONE-S-TRANSFERASE IN PROTECTION OF MESOTHELIOMA CELLS AGAINST HYDROGEN-PEROXIDE AND EPIRUBICIN TOXICITY

We have previously shown that cultured malignant mesothelioma cells co ntain elevated manganese superoxide dismutase (MnSOD) mRNA levels and activities compared with non-malignant mesothelial cells. As many cyto toxic drugs generate both superoxide and hydrogen peroxide, we assesse d the relative significance of catalase and the glutathione redox cycl e, as well as glutathione S-transferase (GST), in protecting these cel ls against hydrogen peroxide and epirubicin toxicity Mesothelioma cell lines containing high (M38K cells) and low (M14K cells) MnSOD, and no n-malignant MeT-5A mesothelial cells were selected for the study. M38K cells were the most resistant of these three cell types to hydrogen p eroxide (0.1-0.5 mM, 4 h) and epirubicin (0.1-0.5 mu g ml(-1), 48 h) a s judged by lactate dehydrogenase (LDH) release and by high-energy nuc leotide (ATP, ADP, AMP) depletion. Total glutathione was higher in M38 K 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-p i in all these cells, the reactivity again being highest in M38K cells . Depletion of glutathione by buthionine sulphoximine and inhibition o f catalase by aminotriazole enhanced hydrogen peroxide toxicity in all cell types, while only the depletion of glutathione increased epirubi cin toxicity. We conclude that simultaneous induction of multiple anti oxidant enzymes can occur in human mesothelioma cells. In addition to the high MnSOD activity, hydrogen peroxide scavenging antioxidant enzy mes, glutathione and GST can partly explain the high hydrogen peroxide and epirubicin resistance of these cells in vitro.