Effects of HO-1 expression as determined by the measurement of anti-oxidant activity and levels of ROS. (a) Total anti-oxidant activity in the cells following transfection with one of four different plasmid constructs expressing HO-1 was determined under hypoxic and normoxic conditions and compared. (b) The levels of ROS were detected under the same experimental conditions as the anti-oxidant activity assay (data presented as the mean±SD, n=4 triplicate, *p<0.01). The anti-oxidant activity and ROS level were calculated as relative values to the non-transfected control. The raw values of non-transfected controls were 1.73±0.04 under hypoxia and 1.96±0.06 under normoxia (anti-oxidant activity/mg total protein) and ~1,210,000±23,000 under hypoxia and ~1,360,000±26,000 under normoxia (fluorescence intensity of ROS/viable cells; data presented as the mean±SD, n=4 triplicate).