ELEVATED FERRITIN PRODUCTION, IRON CONTAINMENT, AND OXIDANT RESISTANCE IN HEMIN-TREATED LEUKEMIA-CELLS

Hemin (ferriprotoporphyrin IX), the oxidized prosthetic group of hemog lobin, is a source of potentially cytotoxic iron, but in chronic low d oses can induce cytoprotection against iron-stimulated oxidative stres s, The latter property of hemin has been examined, using murine L1210 cells and three different oxidant generating systems: (i) glucose/gluc ose oxidase, (ii) near-ultraviolet irradiation, and (iii) dye-mediated photodynamic action, Cells treated with the lipophilic iron donor fer ric-8-hydroxyquinoline, Fe(HQ)(2) (1 mu M, 30 min) were found to be mo re sensitive to oxidative killing than nontreated controls, However, c ells challenged after long-term (20-24 h) exposure to hemin (10 mu M) were substantially more resistant than controls and were sensitized fa r less by Fe(HQ)(2). Immunoblot analyses of 24-h hemin-treated cells i ndicated that the ferritin heavy (H) subunit was elevated 12- to 15-fo ld, whereas the light (L) subunit was essentially unchanged, Experimen ts carried out with Fe-55(HQ)(2) showed that iron uptake capacity of c ells was greatly enhanced after hemin treatment. More specifically, he min-stimulated cells were found to contain similar to 9 times more imm unoprecipitable ferritin iron after incubation with saturating levels (4-5 mu M) of Fe-55(HQ)(2) and similar to 3 times more iron per ferrit in molecule compared with nonstimulated controls. The nonferritin iron content of the latter was estimated to be similar to 40 times greater than that of the former following low-level (0.5 mu M) Fe-55(HQ)(2) t reatment. These results are consistent with the idea that induced ferr itin, enriched in H-chain, sequesters redox active iron rapidly and co piously, thereby enhancing cellular resistance to oxidants. (C) 1997 A cademic Press.