INDUCTION OF GRANULOCYTIC MATURATION IN HL-60 HUMAN LEUKEMIA-CELLS BYFREE-RADICALS - A HYPOTHESIS OF CELL-DIFFERENTIATION INVOLVING HYDROXYL RADICALS

Tumor cells usually contain lower superoxide dismutase (SOD) activity than differentiating cells, suggesting the involvement of oxygen free radicals in cell maturation. The effects of a system known to produce the OH. radicals were tested on HL-60 cells cultured under optimum con ditions for 96 hr. Hydroxyl radicals were generated by a Fenton reacti on, involving an ADP-Fe2+ (or ATP-Fe2+) complex and H2O2. Changes indu ced by OH. were compared to the effects of DMSO-induced differentiatio n of HL-60 cells. Cell numbers, viability, thymidine incorporation, TP A-induced NBT reduction and propidium iodide staining in flow cytometr y were determined. The OH. generating system inhibited the growth and thymidine incorporation of leukemic cells in a manner dependent on the dose of added H2O2 (from 0.005 to 0.05 mM). In addition, an increasin g proportion of the treated cells displayed signs of cell differentiat ion. In DMSO-treated cells, SOD and catalase activities increased afte r 6 days of culturing. The results show that a portion of the OH. free radicals derived from H2O2, produced by the action of SOD, may be a n ecessary prerequisite for differentiation, whereas an overproduction o f OH. causes cell lethality or aging. We suggest that OH. free radical s may have a more complex role in cell physiology than simply causing oxidative damage.