DEVELOPMENT AND CHARACTERIZATION OF HYDROGEN PEROXIDE-RESISTANT CHINESE-HAMSTER OVARY CELL VARIANTS .1. RELATIONSHIP BETWEEN CATALASE ACTIVITY AND THE INDUCTION STABILITY OF THE OXIDANT-RESISTANT PHENOTYPE

Hydrogen peroxide (H2O2)-resistant sublines of Chinese hamster ovary ( CHO) cells were isolated by in vitro exposure to the oxidant (treatmen t for 1 hr followed by 3 days of growth in peroxide-free medium). Step wise increase in low level H2O2 concentrations produced variants which were progressively more resistant to the growth inhibitory effect eli cited by the oxidant. Removal from H2O2 decreased resistance and the c urve describing this process was biphasic in nature. In addition, the rate of loss of the H2O2-resistant phenotype was more rapid for the to xicity elicited by low concentrations of hydrogen peroxide, compared t o that produced by high concentrations. Changes in total cell proteins were found to parallel the variations in sensitivity to the oxidant, since the protein content constantly increased during the adaptation p rocess and decreases upon removal from H2O2. Catalase activity did not show large variations in resistant sublines with respect to the paren tal cell line, and these changes were at least partially related to di fferences in cell size/amount of total cell proteins of the sublines. In addition, the minor changes observed for catalase activity did not correlate with the degree of resistance to growth inhibition elicited by the oxidant. It may therefore be suggested that the H2O2-resistant phenotype of mammalian cells, initially adapted to low-then gradually increased-concentrations of the oxidant, is the result of a complex ph enomenon which only partially involves over-expression of catalase.