Effects of Hepcidin, Ferritin, and Iron Deprivation on Erythroid Colony Formation in Vitro.

The anemia of chronic disease (ACD) results from a combination of three pathologic processes. In ACD, a modest shortening of red cell survival creates an increased demand for red cell production, which is not met because of an impaired erythropoietic response and defects in reticuloendothelial iron mobilization and utilization. The impaired erythropoietic response, in turn, has two components: a blunted erythropoietin response, and an impaired response of erythroid progenitors to erythropoietin. Recombinant human erythropoietin (rhEPO) can reverse this impaired progenitor response in vitro, and can also correct ACD in patients. These processes have generally been considered effects of the cytokines which mediate the immune and inflammatory response, such as tumor necrosis factor, interleukin-1, and the interferons. It has recently been proposed that hepcidin, a mediator of innate immunity with the iron regulatory properties, is the factor responsible for ACD. If this is the case, then hepcidin should be able to induce the pathophysiologic mechanisms implicated in ACD. We therefore evaluated the effects of hepcidin and associated phenomena on human CFU-E colony formation in vitro. All CFU-E cultures were performed in plasma clots in serum-containing medium with rhEPO 1 U/mL. Hepcidin at concentrations 10 ng/mL -10 μg/mL had no effect on CFU-E colony formation. A number of studies have demonstrated that increased hepcidin message expression and protein production are strongly associated with increases in serum ferritin concentrations, and so the effect of added ferritin on erythroid colony formation was studied. Neither ferritin nor apo-ferritin 10 – 1000 ng/mL had inhibitory effects on CFU-E colony formation. The effect of iron deprivation on erythroid colony formation was evaluated with using desferrioxamine. Desferrioxamine 0.01mM decreased CFU-E colony formation to 60% of control values, while higher concentrations completely ablated colony growth. In summary, hepcidin does not appear to inhibit CFU-E colony formation directly or indirectly through ferritin. It may exert such an effect by decreasing availability of iron for erythropoiesis; however, such a finding would be difficult to reconcile with the observed clinical response of ACD to rhEPO, given that iron availability is typically a limiting factor in the erythropoietic response to rhEPO. The role of hepcidin in the overall pathogenesis of ACD remains to be fully determined.