Induction of Antioxidant Enzymes and DT-Diaphorase in Human Blood Mononuclear Cells by Light Stress

Human blood mononuclear cells exposed to visible light increase their antioxidant enzyme (superoxide dismutase, catalase, and glutathione peroxidase) and DT-diaphorase activities. The activities of CuZn-superoxide dismutase (3.70 ± 0.25 U/mg protein), catalase (4.60 ± 0.39 U/mg protein), and DT-diaphorase (1.40 ± 0.11 μmol DCPIP/min·mg protein) increased 1.5-fold when mononuclear cells were exposed at 38 W/m2 for 4 h. Se-containing glutathione peroxidase activity (6.76 ± 0.21 mU/mg protein) increased 1.3 times after 3 h of exposure to 38 W/m2. Conversely, Mn-superoxide dismutase (2.20 ± 0.20 U/mg protein), succinate dehydrogenase (0.86 ±0.04 μmol DCPIP/min·mg protein), and cytochrome oxidase (0.54 ± 0.04 min−1 (k′)/mg protein) activities remained constant during this period of exposure. The treatment of cells with cycloheximide prevented the response triggered by light exposure. These results introduce new insight to the adaptive response of human cells to light stress suggesting that: (a) the response observed might be ascribed to synthesis of stress proteins rather than to activation of a preexisting pool, and (b) that DT-diaphorase and CuZn-superoxide dismutase may operate biologically in a concerted fashion resulting in antioxidant activity.