COBALT CHLORIDE AND DESFERRIOXAMINE ANTAGONIZE THE INHIBITION OF ERYTHROPOIETIN PRODUCTION BY REACTIVE OXYGEN SPECIES

Cobalt chloride and desferrioxamine antagonize the inhibition of eryth ropoietin production by reactive oxygen species, We have recently prop osed a H2O2-generating b-type cytochrome as part of the cellular oxyge n sensor that controls O-2-dependent erythropoietin (Epo) production I n the human hepatocellular carcinoma cell line HepG2. H2O2 could act a s an intracellular signaling molecule because its production in HepG2 cells is strictly dependent on the pericellular PO2. High cellular lev els of H2O2 inhibit hypoxia-induced Epo production while low levels-as under hypoxic conditions-allow full expression of the Epo gene. Since cobalt chloride (CoCl2) and the iron chelator desferrioxamine (DSF) b oth mimic the hypoxic induction of Epo production we studied the influ ence of CoCl2 and DSF on the formation and on the action of reactive O -2-species with respect to Epo production. Both chemicals reduced the H2O2-dependent 123-dihydrorhodamine fluorescence in HepG2 cells. The i nhibition of Epo production by exogenous H2O2 was completely antagoniz ed by DSF. This might indicate that H2O2 exerts its inhibition through a Fenton type reaction. On the other hand, NADPH and pyrogallol which stimulate the production of O-2(-) inhibited Epo production. CoCl2, a ntagonized their effects. From our results we propose different sites of interaction with the putative signaling chain for DSF and CoCl2. Wh ile DSF appears to reduce the action of the H2O2 molecule, CoCl2, migh t act further upstream through the induction of H2O2-scavenger systems or by interfering with its production.