We hypothesized that manganese superoxide dismutase (MnSOD), known to be induced in rat mesothelial cells by asbestos fibers, cytokines, and hyperoxia, may also be induced in asbestos-related pleural diseases such as mesothelioma. MnSOD was assessed in healthy human pleural mesothelium ( n ϭ 6), in biopsy samples of human pleural mesothelioma ( n ϭ 7), in transformed nonmalignant human mesothelial cells (Met5A), and in two human mesothelioma cell lines (M14K and M38K) established from the tumor tissue of mesothelioma patients. There was no MnSOD immunoreactivity in five of the six samples of healthy pleural mesothelium, whereas MnSOD immunoreactivity was high in the tumor cells in all the mesothelioma samples. Northern blotting, immunohistochemistry, Western blotting, and specific activity measurements showed lower MnSOD in the nonmalignant Met5A mesothelial cells than in the M14K and M38K mesothelioma cells. In additional experiments the mesothelial and mesothelioma cells were exposed to menadione, which generates superoxide intracellularly, and to epirubicin, a cytotoxic drug commonly used to treat mesothelioma. The M38K mesothelioma cells were most resistant to menadione and epirubicin when assessed by LDH release or by adenine nucleotide (ATP, ADP, and AMP) depletion. These same cells showed not only the highest MnSOD levels, but also the highest mRNA levels and activities of catalase, whereas glutathione peroxidase and glutathione reductase levels did not differ significantly. We conclude that MnSOD expression is low in healthy human pleural mesothelium and high in human malignant mesothelioma. The most resistant mesothelioma cells contained coordinated induction of MnSOD and catalase. Kahlos, K., S. Anttila, T. Asikainen, K. Kinnula, K. O. Raivio, K. Mattson, K. Linnainmaa, and V. L. Kinnula. 1998. Manganese superoxide dismutase in healthy human pleural mesothelium and in malignant pleural mesothelioma. Am. J. Respir. Cell Mol. Biol. 18:570-580.

Summary 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,g ml-', 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-') or MeT-5A cells (23.5 ± 4.5 nmol mg-'). Furthermore, GST specific activity was higher in M38K cells (111.3 ± 15.8 U mg-') than in M14K cells (77.4 ± 6.6 U mg-') or in MeT-5A cells (68.8 ± 7.6 U mg-'). Western blotting indicated the presence of GST-i 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.

M u m c e of 2ymWran (Zy) loaded w i t h various catianr (Ft2+, W+, Znz+, Cuz+) on respiratory burst activation (RBA) of human and rat phagocytcs in vitro w.ll studied using chemilumincsamc (CL). Treatment of unopsonized Zy by either F&+ and Pb2+ cawed pronounced intxawc in RBA, w h m treatment by Cu2+ markedly inhibited RBA. Loading of opumizcd Zy w i t h cithcr Cuz+ or Ft2+ rc~ultcd in CL deaeore. Since cell activation by Zy is Ca2+.dependmt, influence of Zy-preporotiws on Caz+i, content was uamined.Thus we observed some changes in RBA after loading of z y with Fez+, w+, cuz+. occupational Health Helsinki, FinlandWe have previously shown that superoxide radical scavenging antioxidant enzyme manganese superoxide dismutase (MnSOD) can