Supplementation with Selenium yeast on the prooxidant-antioxidant activities and anti-tumor effects in breast tumor xenograft-bearing mice

Selenium (Se) is essential for antioxidant activity involved in immune function and anti-carcinogenic action, whereas at higher concentrations, Se may have pro-oxidant properties. The present study was aimed at determining the effects of Se supplementation, as Se yeast, on oxidative stress in non-tumor/tumor tissues, as well as regulation of the apoptotic process, and immune responses in mice-bearing breast tumor xenografts. Female BALB/cByJNarl mice were divided into control (CNL and CNL-con), Se-supplemented control (CNL-HS, given as a single oral dose of 912 ng Se daily), breast tumor-bearing (TB and TB-con), TB-LS (228 ng Se), TB-MS (456 ng Se) and TB-HS (912 ng Se) groups. All mice were treated with/without Se for 14 days. A number of variables were further measured. Compared with the TB groups, tumor bearing mice with Se supplement had increased plasma Se concentrations, reduced erythrocyte Se-dependent glutathione peroxidase (GPx) activity and malondialdehyde (MDA) products and inhibited tumor growth. They have also higher Se concentrations in non-tumor and tumor tissues. Significantly elevated concentrations of MDA and reduced GPx activities, as well as increased anti-apoptotic bcl-2 and tumor suppressor p53 concentrations in tumor tissues were observed as Se accumulated in tumor, whereas lower MDA products were found in various non-tumor tissues than did the corresponding values. Further, there were elevated concentrations of Th1-derived cytokines and decreased Th2-type interleukin (IL)-4 in tumor-bearing mice with the treatment of Se. In conclusion, accumulation of Se in tumors may induce oxidative stress and p53-dependent pro-oxidative apoptosis, thus inhibiting the growth of breast tumor.