DIETARY SE AND TUMOR GLUTATHIONE-PEROXIDASE AND SUPEROXIDE-DISMUTASE ACTIVITIES

The purpose of this study was to examine tumor activity of the radical scavenging enzymes selenium dependent glutathione peroxidase (SeGSHPx), cupro,zinc-superoxide dismutase (CuZnSOD), and manganese dependent SOD (MnSOD) from rats fed varying amounts of selenium and to compare the effects due to diet with those due to the development of the tumor. Enzyme activities were measured in mammary tumors from DMBA-treated rats fed 0.035, 0.1, 1.0, and 2.0 mg Se/kg diet for 25 weeks (n = 58, 33, 24, and 14 tumors from 8, 8, 7, and 8 tumor-bearing rats, respectively). Increasing dietary Se had no effect on tumor SeGSHPx, non-SeGSHPx, and MnSOD activities. In contrast, tumor CuZnSOD and total SOD activities decreased with increasing dietary Se. Tumor size had a significant effect on MnSOD, SeGSHPx, non-SeGSHPx, and total GSHPx activities with increasing activity observed with increasing tumor weight. Malignant tumors were unique in two ways with respect to the activity of antioxidative protective enzymes. Tumor SeGSHPx activity was unresponsive to dietary Se while CuZnSOD and total SOD activities were significantly reduced with increasing dietary Se compared to erythrocytes, liver, and spleen from the same animals. Thus, the overall effect of high dietary Se was to decrease the ratio of total SOD to total GSHPx activity (P < 0.003). Tumor size had no effect on the ratio. This ratio of total SOD/GSHPx activity was several-fold higher in tumors than in other tissues from the same animals.