In an attempt to understand the change of superoxide dismutase (SOD) in tumor cells by hypoxia and hypoxia-normoxia exposure, the present study performed an in vitro investigation using rat glioma cell line in culture. Hypoxia was induced by an incubation with nitrogen gas for 15 h followed the normoxia exposure with air for 30 min. Activity of SOD in cytosolic and particulate of cells was determined by the reduction of nitroblue tetrazolium. Changes of mRNA for Cu,Zn-SOD or Mn-SOD were also characterized using Northern blotting analysis. Hypoxic stress decreased the activity of SOD, both Cu,Zn-SOD and Mn-SOD, in glioma cells. Expression of mRNA for SOD was elevated by hypoxic stress and the increase of mRNA level for Cu,Zn-SOD was more marked than that for Mn-SOD. In response to hypoxia-normoxia exposure, an increase of activity with a lower mRNA level for Mn-SOD was observed in glioma cells. However, changes of Cu,Zn-SOD both the activity and the level of mRNA were not found in glioma cells by hypoxia-normoxia. The obtained results suggest that the SOD in glioma cells can be activated to compensate the damage from free radicals during hypoxic stress.
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