ANTIOXIDANT ENZYME LEVELS AS A FUNCTION OF GROWTH-STATE IN CELL-CULTURE

Manganese superoxide dismutase (MnSOD) levels were monitored as a func tion of time in culture to determine whether these levels were altered at logarithmic growth versus when the cells exhibited density limitat ion of growth. For comparison, activities of the antioxidant enzymes c opper, zinc superoxide dismutase (CuZnSOD), catalase, and glutathione peroxidase were also evaluated. Four cell lines were studied, two of w hich exhibited density limitation of growth and two of which did not. Each cell line showed a unique antioxidant enzyme profile. The two cel l lines that showed density limitation of growth also demonstrated ind uction of MnSOD at the time when the cells stopped proliferating in cu lture, whereas the other two cell lines did not show induction of MnSO D. There was no strict correlation between density limitation of growt h and activities of the other antioxidant enzymes. To determine whethe r SOD varied with various phases of the cell cycle, NIH/3T3 cells were synchronized using serum starvation, and then SOD activities were mea sured during quiescence (G(0)) and the phase of DNA synthesis (S-phase ). MnSOD was decreased during S-phase compared with G(0), whereas CuZn SOD was increased during S-phase compared with G(0), demonstrating alt eration of SOD activities with varying phases of the cell cycle. This study suggests the possibility that increased MnSOD may correlate with decreased cell proliferation and suggests significant alterations in SOD activities during the cell cycle.