Abstract
Thioredoxin reductase 2 (TR2) activity, its gene transcripts, and hydrogen peroxide (H&sub2;O&sub2;) generation were examined in biochemically identified early-senescent P20 and senescent P30 fibroblasts subcultured in media (MEM2-MEM8) containing Se concentrations at 1.25, 2.5, 3.5, 5.0, 6.0, 7.0, and 8.0 µM, respectively. Although TR2 activity was moderately increased in P20 and P30 cells subcultured in routine growth medium (MEM1), there were progressive significant activity increases in the same cells subcultured in MEM2-MEM8. Such increases were proportional to Se concentration and peaked in P30 cells incubated with MEM7 and MEM8. H&sub2;O2 generation underwent progressive increases in MEM1-incubated P20 and P30 cells, peaking in the latter, but was gradually lowered in those incubated with MEM2-MEM8, reaching its lowest values when cells were incubated with MEM7 and MEM8. In parallel, TR2 gene transcripts underwent significant upregulation in P20 cells and higher magnitude upregulation in P30 cells subcultured in MEM2, MEM4, and MEM8 compared to those recorded for P5 pre-senescent cells subcultured in the same media. The computed Km Se values with respect to TR2 activity equaled 3.34 and 4.98 µM for P20 and P30 cells, respectively, with corresponding Vmax activities of 55.9 and 96.2 nmol/min/mg protein. It is concluded that senescent P30 cells utilize more Se and achieve maximal TR2 activity to combat oxidative injury.